WO2009051278A2

WO2009051278A2 - Extruder and process for preparing a mixture of polymer and diluent

Info

Publication number: WO2009051278A2
Application number: PCT/JP2008/069382
Authority: WO
Inventors: Tetsuro Nogata; Soichiro Yamaguchi; Norimitsu Kaimai; Kotaro Takita
Original assignee: Tonen Chemical Corporation
Priority date: 2007-10-19
Filing date: 2008-10-20
Publication date: 2009-04-23
Also published as: WO2009051278A3; JP5017455B2; JP2011500368A

Abstract

This invention relates to an extruder, system, and extrusion process for producing a mixture of polymer and diluent. The extruder and extruder process can be used to produce mixtures of polymer and diluent that are useful for making microporous film such as battery separator film.

Description

EXTRUDER, SYSTEM, AND PROCESS FOR PREPARING A MIXTURE OF POLYMER AND DILUENT

FIELD OF THE INVENTION

[0001] This disclosure relates generally to an extruder, system, and process for producing a mixture of polymer and diluent. The extruder, system, and process can be used to produce mixtures of polymer and diluent that are useful for making microporous film such as battery separator film. BACKGROUND OF THE INVENTION

[0002] Polymeric materials are useful for the fabrication of a variety of films, sheets and molded or shaped articles. As is well-known to those skilled in the art, plastication refers to the softening of a polymeric material to such an extent that it flows freely and will assume any shape. In the case of a polymeric material that is crystalline, plastication is synonymous with melting. In the case of a polymeric material that is amorphous, plastication occurs at or about the glass transition temperature (T_g) thereof. [0003] In the processing of polymeric resins and other materials, extruders are commonly employed for the plastication, mixing and pumping of such materials. In their simplest form, extruders include a frame designed to be bolted to a concrete floor, a barrel mounted to the frame, and, in the case of a twin screw extruder, two interconnecting bores extending longitudinally from one end of the barrel to the other. A twin screw extruder also includes two intermeshing screws located within the two interconnecting bores and drive means for turning the screws in the same (co-rotating) or opposite (counter-rotating) direction.

[0004] An extruder screw is shaped generally in the form of an elongated cylinder, and has one or more raised ridges helically disposed thereabout, each of which is a commonly referred to as a flight. A flight may have forward, reverse or neutral pitch, with the degree of pitch varied to accommodate a particular application. The surface of the screw above which the flight is raised is commonly referred to as the root of the screw. When the screw is viewed in cross section, the course of a particular flight, between one point of intersection with a line parallel to the screw axis and the next closest point of intersection of the flight with such line, typically defines a 360° circle. The tip of a flight, which extends toward the perimeter of such circular-shaped cross section, defines a lobe above the root of the screw. The space bounded by the root of the screw and the side walls of any two flights is a channel of the screw. The screw rotates on its longitudinal axis within a barrel or sleeve, which may be generally described as the bore of an annular cylinder. [0005] The screw typically has an initial, feed section which begins the process of conveying solid polymeric material forward within the barrel of the extruder. Polymeric material may be fed into the extruder by means of a hopper which empties into the barrel, or may be metered into the barrel of the extruder (also called a cylinder or bore) through a feed chute or a side feeder. The direction of travel of the polymeric material in the barrel as it is transported away from the feed port by the screw is known as the downstream direction. In the case of the extrusion of polymer melts, the feed or inlet section of the screw is typically followed, with or without other intervening sections, by a melting section in which partial or complete plastication of the polymeric material occurs. [0006] The melting section of the screw is typically followed, with or without other intervening sections, by a metering section which functions to pump the material, as extrudate, out through the downstream end of the extruder, which typically contains a die or some other form of restricted orifice. The sections of the extruder and screw through which the polymeric material travels before it reaches the die are considered to be upstream from the die. [0007] With respect to a twin screw extruder, two screws are said to be intermeshing if a flight of one screw is disposed within a channel of the other screw. In such a configuration, the distance between the axes of each screw is less than the sum of the respective radii of the two screws, when each radius is measured from the axis to the top of the tallest or highest flight of the screw. When, on a pair of screws, a flight has a shape and size such that its fit into a channel in which it is intermeshed is close enough that essentially no extrudable material passes through the space between the flight and channel, the screws are said to be conjugated. Otherwise, the screws are said to be non-conjugated, and the degree of intermeshing in the case of non-conjugation can be varied to an essentially unlimited extent. [0008] Co-rotating screws, even when conjugated, allow for extensive movement of polymeric material laterally from one screw to the other. Mixing is benefited by this movement and it is further enhanced when the screws are not conjugated. The shape of the flights on non-conjugated screws may be arranged to create the passage of polymeric material from one channel into two channels on another screw. Or, when screws are conjugated, or essentially conjugated, certain flights can be designed in a shape such that they wipe each other in the zone of intermeshing but do not wipe the wall of the barrel. [0009] In contrast to the processing polymeric resins in the form of melts, the production of polymer-diluent mixtures such as those used to make microporous polymeric membranes present unique requirements in the extruder and process design. This is due in large part by the need to introduce a large amount of a solvent or diluent for the polymeric material so that a polymeric solution is prepared for subsequent extrusion. Microporous membranes are useful as separators for primary batteries and secondary batteries such as lithium ion secondary batteries, lithium-polymer secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, nickel-zinc secondary batteries, silver-zinc secondary batteries, etc. When the microporous membrane is used as a battery separator, particularly as a lithium ion battery separator, the membrane's performance significantly affects the properties, productivity and safety of the battery. Accordingly, the microporous membrane should have suitably well-balanced permeability, mechanical properties, dimensional stability, shutdown properties, meltdown properties, etc. The term "well-balanced" means that the optimization of one of these characteristics does not result in a significant degradation in another. [0010] As is known, it is desirable for the batteries to have a relatively low shutdown temperature and a relatively high meltdown temperature for improved battery safety, particularly for batteries exposed to high temperatures under operating conditions. Consistent dimensional properties, such as film thickness, are essential to high performing films. A separator with high mechanical strength is desirable for improved battery assembly and fabrication, and for improved durability. The optimization of material compositions, casting and stretching conditions, heat treatment conditions, etc. have been proposed to improve the properties of microporous polyolefin membranes. [0011] In general, microporous polyolefin membranes consisting essentially of polyethylene (i.e., they contain polyethylene only with no significant presence of other species) have relatively low meltdown temperatures. Accordingly, proposals have been made to provide microporous polyolefin membranes made from mixed resins of polyethylene and polypropylene, and multi-layer, microporous polyolefin membranes - A - having polyethylene layers and polypropylene layers in order to increase meltdown temperature. The use of these mixed resins and the production of multilayer films having layers of differing polyolefins can make the production of films having consistent dimensional properties, such as film thickness, all the more difficult. [0012] U.S. Patent No. 5,573,332 proposes a screw element for a screw-type extrusion machine. The screw elements are helical and have varying pitch directions. Lengthwise mixing is obtained by the screwing in opposite directions, whereas crosswise mixing is attained by the elongated wedge of the flank arc. This crosswise flow is a typical continuous shear flow, which is primarily a dispersive mixing operation. Dividing the flow into various partial flows, recirculation and offset combination do not take place.

[0013] U.S. Patent No. 6,062,719 proposes a co-rotating multiple-screw extruder comprising first and second intermeshing screws of more than one flight. The first screw comprises first and second segments paired with first and second segments of the second screw, respectively. On the first segment of the first screw, the height of the first flight is less than the height of the second flight and on the second segment of the second screw, the height of the first flight is less than the height of the second flight and screws for use in such extruder.

[0014] U.S. Publication No. 2005/0013192 discloses a kneading disk having a plurality of disk elements having flight tips arranged at a helix angle E in a direction supporting main streams of a resin. The flight tips of every two adjoining disks have a clearance formed therebetween. The resin is kneaded by undergoing dispersion and distribution without having any excessive temperature elevation in approximately three kinds of streams, i.e. its main streams flowing along the flight tips, its back streams through the clearances and its tip riding streams flowing over the flight tips. The reference discloses a continuous or "rotor"-type screw segment in the "dispersion" region of the extruder for improved melt-shearing in that region. When distribution or "stirring" in needed, a discontinuous or "disk-type" segment having disk elements arranged along a screw axis and flight tips arranged discontinuously and helically in parallel to the screw axis is employed. Polymer flowing counter-currently in the regions between the flight tips (see, e.g., FIG. 7) increases polymer residence time to increase mixing uniformity. With conventional screw segments, the L/D value is small and multiple segments are needed to get good dispersion. This however leads to a problem since, at the interface between two segments in registry, what is effectively produced is a lobe that is twice as long as the interior lobes. This abruptly changes the "pitch" of the flight of lobes. Moreover, the total number of lobes is reduced by the number of segment interfaces. All of these effects serve to reduce the amount of beneficial countercurrent polymer flow. [0015] JP2008-018687A discloses a process and equipment for mixing polymeric resins where a first extruder (a twin screw extruder) is followed by a second extruder (a single screw extruder) and filtration of the polymer melt is carried out after each extruder to remove un-melted polymeric resin which. A gear pump is disposed between twin extruder and filter. A static mixer can be used optionally at the inlet of die to prevent temperature variations in the melt.

[0016] JP 2003-053821 discloses a wet process for manufacturing a microporous film where a polyolefm solution is extruded through a twin-screw extruder and each screw contains at least one of (a) a normal screw-notch screw element, (b) a reverse screw-notch screw element, and (c) a collar. This arrangement is said to benefit the mixing of different kinds and molecular weight polymers.

[0017] JP7-216118A discloses a battery separator formed from a porous film comprising polyethylene and polypropylene as indispensable components and having at least two microporous layers each with different polyethylene content. The polyethylene content is 0 to 20% by weight in one microporous layer, 21 to 60% by weight in the other microporous layer, and 2 to 40% by weight in the overall film. The battery separator has relatively high shutdown-starting temperature and mechanical strength. Since this is a "dry" process, the resins are combined as a polymer melt and then extruded. [0018] WO 2005/113657 discloses a microporous polyolefin membrane having conventional shutdown properties, meltdown properties, dimensional stability and high-temperature strength. The membrane is made using a polyolefin composition comprising (a) composition comprising lower molecular weight polyethylene and higher molecular weight polyethylene, and (b) polypropylene. This microporous polyolefin membrane is produced by a so-called "wet process", i.e., from a mixture of polymer and diluent. It is believed that improved mixing of the polymer and diluent will lead to improved microporous membrane yield from the process and improved properties of the microporous membrane. [0019] As those skilled in the art will plainly recognize, extruder screw design requirements for extruding polymer melts differ greatly from those relating to polymer-diluent mixtures. While much work has been conducted with respect to polymer melts, this work largely fails to translate to the field of polymer-diluent mixture extrusion. Since polymer-diluent mixtures behave differently from polymer melts, those skilled in the art recognize that there is no expectation that a combination of extruder screw segments used for extruding a polymer melt will yield satisfactory performance when extruding a polymer-diluent mixture. As may be appreciated, a counter current flow of the solvent or diluent phase in the extruder can be (and generally is) undesirable. As such, it is desirable to have no significant amount of diluent (preferably none) in the inlet stage of an extruder, since even a small amount of diluent would interfere with polymer blending as a result of the much lower viscosity of the diluent compared to the polymer.

[0020] Despite these advances in the art, there remains a need for improved extrusion systems capable of producing high quality microporous polyolefin membranes and other films or sheets from polymer-diluent mixtures. SUMMARY OF THE INVENTION

[0021] In one aspect, provided is an extruder for preparing a mixture of polymer and diluent. The extruder includes an elongated housing having an inlet end, an outlet end and at least one intersecting bores disposed within the housing, at least one elongated extruder shaft having an axis of rotation, the at least one elongated extruder shaft disposed within the at least one intersecting bore, and a plurality of extruder screw segments positioned along the at least one elongated extruder shaft in a fixed angular relationship therewith, the plurality of extruder screw segments selected to form multiple extruder stages, the multiple extruder stages comprising an inlet stage and a dispersion stage, the plurality of extruder screw segments forming the dispersion stage including at least one first kneading segment comprising a plurality of kneading disks having at least one flight tip, wherein each adjacent flight tip is progressively offset by an angle θ, wherein 0° < θ < 90°. [0022] In another aspect, provided is an extruder for preparing a mixture of polymer and diluent. The extruder includes an elongated housing having an inlet end, an outlet end an extruder shaft length L and a pair of intersecting bores disposed within the housing, a pair of elongated extruder shafts each having an axis of rotation, the pair of elongated extrader shafts disposed within the pair of intersecting bores and drivable in at least one direction of rotation, a plurality of extruder screw segments positioned along the pair of elongated extruder shafts in a fixed angular relationship therewith, the plurality of extruder screw segments selected to form multiple extruder stages, the multiple extruder stages comprising an inlet stage having a length Li of about 3% L < Li < about 30% L, a dispersion stage Ld having a length of about 10% L < Ld < about 35% L, a first mixing stage having a length LmI of about 5% L < LmI < about 45% L, a second mixing stage having a length Lm2 of about 0% L < Lm2 < about 50% L, and an outlet stage having a length Lo of about 0% L < Lo < about 40% L, a material inlet adjacent the inlet end of the elongated barrel, and a first fluid inlet located within the dispersion stage for introducing a at least a portion of the diluent.

[0023] In yet another aspect, provided is a process for extruding a mixture of polymer and diluent. The process includes the steps of blending a polymer at a rate of P grams per second in an inlet stage of an extruder and conducting the blended polymer to a dispersion stage of the extruder. All or a portion of the diluent is introduced to the blended polymer in the dispersion stage at a rate of Sl (measured, e.g., in grams per second), the diluent having a lower viscosity than the polymer. The diluent is then dispersed in the polymer and conducted to a first mixing stage. A second portion of the diluent can be introduced in the blended polymer in the extruder's mixing stage, if desired. The second portion can be introduced through a second fluid inlet at a rate of S2 grams per second for dispersing the second diluent portion in the combined polymer-diluent mixture. The location of the second fluid inlet is not critical. For example, the second portion of the diluent can be introduced from the second mixing stage. A third portion of the diluent can be added, e.g., to the mixing stage, if desired. When a third diluent portion is added, it can be introduced in to the combined polymer-diluent mixture at a rate of Sa grams per second, where the rate of introduction of the second diluent portion is Sb grams per second, and wherein (Sa + Sb) is equal to S2. In the first mixing stage, diluent and the polymer are blended in order to produce a third-stage product, the third stage product comprising (i) the polymer-diluent mixture in a first phase, (ii) a portion of the diluent in a second phase separate from the first phase, and (iii) a portion of the polymer in a third phase separate from the first and second phases. In one form, the mixing energy in the first mixing stage is greater than the mixing energy in either the inlet stage or dispersion stage. [0024] In still another aspect, the invention provides a system for producing an extrudate comprising combined polymer and diluent. Embodiments of the system include a first extrusion means and a second extrusion means located downstream of and in fluid communication with the first extrusion means. A pumping means located downstream of the second extrusion means and in fluid communication with the second extrusion means, optionally the first pumping means is a gear pump. Embodiments of the system also include a separation means for removing at least a portion of any uncombined polymer from the second extrusion means' effluent. The separation means is generally located downstream of the second extrusion means and is in fluid communication with the second extrusion means. A mixing means is located downstream of the separation means and in fluid communication with the separation means. The system also includes at least one die located downstream of the mixing means and in fluid communication with the mixing means. The system may option ally also include a second pumping means located between the first extrusion means and the second extrusion means. One advantageous second pumping means is a gear pump.

[0025] In an exemplary form disclosed herein, the number of kneading disks of the at least one first kneading segment of the dispersion stage is greater than 10 and the extruder screw segments forming the dispersion stage have a total length greater than about 4D, where D is the diameter of the extruder screw segment.

[0026] In another exemplary form disclosed herein, the number of kneading disks is greater than 10 and is selected to achieve an offset angle between a flight tip of a last kneading disk of said at least one first kneading segment and a flight tip of a first kneading disk of an adjacent kneading segment equal to about 0°.

[0027] In a further exemplary form disclosed herein, the number of kneading disks and the angle θ of the at least one first kneading segment are selected to enable an adjacent kneading segment to be positioned to achieve an offset angle between a flight tip of a last kneading disk of the at least one first kneading segment and a flight tip of a first kneading disk of the adjacent kneading segment substantially equivalent to the angle θ. [0028] In a yet further exemplary form disclosed herein, the number of kneading disks is selected to achieve an offset angle between a flight tip of a last kneading disk of said at least one first kneading segment and a flight tip of a first kneading disk of an adjacent kneading segment equal to about 0°. [0029] In a yet further exemplary form disclosed herein, the elongated extruder shafts are co-rotating or counter-rotating.

[0030] In a still yet further exemplary form disclosed herein, the process further includes the steps of extruding the polymer-diluent mixture (e.g., a polyolefm solution) through an extrusion die, the extrusion die comprising a slotted die outlet through which a stream of the polymer solution is extruded; and cooling the extrudate to form a cooled extrudate.

[0031] In still another form, the invention relates to a process of producing a polymeric extrudate. Embodiments of the process include combining polymer and diluent in a first extruder and removing an effluent comprising the combined polymer and diluent therefrom the first extruder. The effluent from the first extruder is conducted to a second extruder whose effluent is conducted to a first pumping means. The effluent of the first pumping means is separated into a retentate and a filtrate. The filtrate is mixed with polymer and diluent to provide a mixed filtrate and the mixed filtrate is extruded through at least one die. [0032] Optionally, additional pumping means can be located in series downstream of the first extrusion means and upstream of the second extrusion means and in fluid communication with the first and second extrusion means. The first extrusion means can be a twin-screw extruder, for example. The second extruder means be a single screw extruder, for example. The first and second pumping means can each be one or more gear pumps, for example. The separation means can be a filter, for example. The mixing means can be a static mixer, for example.

[0033] These and other advantages, features and attributes of the disclosed extruder and process and its advantageous applications and/or uses will be apparent from the detailed description that follows, particularly when read in conjunction with the figures appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS [0034] FIG. 1 is a diagrammatic illustration of a lateral longitudinal view of a twin screw extruder, in accordance herewith;

[0035] FIG. 2 is a cross-section through the extruder on the line 2-2 of FIG. 1 with the illustration of two kneading segments, in accordance herewith; [0036] FIG. 3 is a schematic of a screw segment configuration for preparing a polymer solution, in accordance herewith;

[0037] FIG. 4 A shows a kneading segment of an extruder screw, in accordance herewith; and

[0038] FIG. 4B shows an end view of the kneading segment of FIG. 4A, in accordance herewith;

[0039] FIG. 5 is a schematic of another screw segment configuration for preparing a polymer solution, in accordance herewith;

[0040] FIG. 6 is a schematic of still another screw segment configuration for preparing a polymer solution, in accordance herewith; [0041] FIG. 7 is a schematic of yet still another screw segment configuration for preparing a polymer solution, in accordance herewith;

[0042] FIG. 8 is a schematic of a further screw segment configuration for preparing a polymer solution, in accordance herewith; and

[0043] FIG. 9 is a schematic of a still further screw segment configuration for preparing a polymer solution, in accordance herewith.

DETAILED DESCRIPTION OF THE INVENTION

[0044] In one form, the invention relates to a system for producing an extrudate from a mixture comprising polymer and diluent. In this form a twin screw extruder is disposed as first extruder for combining the polymer and diluent. A single screw extruder is located downstream of the twin-screw extruder to receive the combined polymer and diluent therefrom. The first extruder is generally a twin-screw extruder because it has been observed that twin screw extruders more completely mix the polymer and diluent than do single screw extruders. The second extruder (the single screw extruder) is located downstream of the first extruder (the twin screw extruder) because it has been observed that single screw extruders have less variation in extrudate mass flow rate and pressure compared to twin screw extruders extruding polyolefin-diluent mixtures, and thus provide a more constant flow of polymer-diluent mixture to the die for more uniform extrudate production. In an embodiment, separation means, e.g., a one or more filters, can be located downstream of the first and/or second extruders to separate and remove at least a portion of, e.g., polymerization catalyst fines, uncombined polymer and metallic particles abraded from the process equipment. Pumping means such as one or more gear pumps can be used to overcome pressure drops introduced into the system by the filter(s). It has been observed that locating a combination of pumping means (a gear pump in this case) and separation means (a filter in this case) downstream of the second extruder and upstream of the die can result in phase separation of the combined diluent and polymer. Mixing means (a static mixer in this case) is used to recombine the polymer and diluent into a single phase before introducing the extrudate into the die.

[0045] The invention is based in part on the discovery that when extruding polymer and diluent (fluid) to produce a mixture of polymer and diluent, it is desirable for the mixing screw or screws in the inlet stage of the extruder (e.g., the first extruder) to comprise (or consist of) one or more screw segments of the "rotor" type, i.e., having continuous flights for the "distribution" or "stirring" of the polymer as defined in U.S. Publication No. 2005/0013192. It is also desirable for the inlet stage to be followed by a dispersion stage, where the mixing screw or screws in the dispersion stage of the extruder comprise (or consist of) the "disk" type for the "dispersion" and shearing of the polymer, diluent, and polymeric solution. It has also been discovered that it can be advantageous to introduce the diluent at least two locations along the extruder for improved mixing of the polymer and diluent Definitions

[0046] By "forward flight screw segment" is meant a continuous conveying element having a flight angle sufficient to cause flow in a direction from the inlet end to the outlet end of the extruder. Suitable forward flight screw segments may be obtained from Japan Steel Works of Tokyo, Japan, and may include segments such as H259, H261, H262 and H265, all of which are compatible with, e.g., shaft TEX 65.

[0047] By "forward screw segment" is meant a screw element with a flight pitch designed to convey material forward to the screw segment ahead of it. • [0048] By "gear kneading segment" is mean a screw segment having a plurality of gear-like kneading disks. Suitable gear kneading segments may be obtained from Japan Steel Works of Tokyo, Japan, and may include neutral gear kneading segments such as H726 and H727.

[0049] By "kneading segment" is meant a screw segment that may be continuous or discontinuous. Examples of discontinuous kneading segments include single and dual flight kneading segments having a plurality of lobed kneading disks and gear kneading segments having a plurality of gear-like kneading disks. The length or thickness of the kneading disks typically range between a few to a several millimeters, for example from 2 mm to 100 mm, depending on the required dispersion rate of mixing. A continuous kneading segment may have the shape of a continuous conveying element with a flight angle of 90° so as to cause no flow in either direction.

[0050] By "reverse screw segment" is meant a screw element with a pitch designed to convey material back to the screw segment preceding it, creating a filled barrel section. [0051] By "screw configuration" is meant the general profile of the screw resulting from the change of its geometric characteristics and/or the organization of successive screw segments, insuring different functions are performed along its length.

[0052] By "segment" or "screw segment" is meant an extrusion screw element, positioned along a keyed or splined shaft, which conveys, shears, pressurizes, heats and/or transforms materials into a continuous solution or mass. Such elements may be of the conveying type or non-conveying or kneading type. [0053] By "single flight" or "dual flight kneading segment" is meant a kneading segment having a plurality of lobed kneading disks. Suitable single flight or dual flight kneading segments may be obtained from Japan Steel Works of Tokyo, Japan, and may include forward kneading segments such as H266 and H267, reverse kneading segments, such as H299, or neutral kneading segments, such as H294 and H306. [0054] By "twin screw extruder" is meant a machine having two parallel screw shafts running side by side in a double-bored barrel for the mixing and processing of products, such as polymer solutions.

[0055] Reference is now made to FIGS. 1-9, wherein like numerals are used to designate like parts throughout. [0056] Referring now to FIG. 1, a twin screw extruder 10 is shown. Twin screw extruder 10 may be obtained from Japan Steel Works of Tokyo, Japan, and may be a Model TEX 54, TEX 65, or the like, for commercial use, or may be a TEX30, TEX44, or the like, for small-scale and laboratory use. Other polyolefin extruders may be employed, as those skilled in the art will readily understand. Twin screw extruder 10 includes a drive motor 12, a gear mechanism 14 joined thereto on the input side and a housing 16 having an inlet end 18 and an outlet end 20. As shown in FIG. 2 housing 16 includes a pair of intersecting bores 22 disposed within housing 16. Referring again to FIG. 1, provided on housing 16 is an inlet hopper 24 for the supply of thermoplastic material to be processed. The aforementioned components of the extruder 10 are supported by a plurality of props 26 positioned on a foundation 28 and joined thereto. Above the inlet hopper 24 may be positioned metering devices (not shown) for the metered addition of plastic pellets or other materials to the inlet hopper 24. At the end of the housing 16, which is downstream of the inlet end 18 and adjacent the outlet end 20 is a discharge opening 30 for the discharge of the material processed in the extruder 10. At least one diluent (e.g., a solvent) may be introduced into the extruder at one or more locations. For example, the diluent can be introduced at a first injection tube 32 in the dispersion stage, or at that location and at a second injection tube 33 located in a second mixing stage.

[0057] Referring again to FIG. 2, intersecting bores 22 of housing 16 are parallel to each other. A pair of elongated extruder shafts 34, each having an axis of rotation, are disposed within the pair of intersecting bores 22 and drivable in at least one direction of rotation by being joined to the power take-off side of gear mechanism 14, gear mechanism 14 driven by drive motor 12. In one form, to enable the keying of a plurality of screw segments to the pair of elongated extruder shafts 34, the pair of elongated extruder shafts 34 may be provided with a square, pentagonal, hexagonal or octagonal cross section or a cross section defined by a perimeter formed by a plurality of scallops (forming, e.g., a spline-like perimeter). [0058] As will be described in more detail below, a variety of screw segments are provided in a non-rotatable, fixed angular relationship on the elongated extruder shafts 34, such as intermeshing screws segments and kneading disks, which are selected in dependence on their function and disposed successively in the along the pair of elongated extruder shafts 34. [0059] Referring now to FIG. 3, a plurality of extruder screw segments are shown, the plurality of extruder screw segments selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 100, a dispersion stage 200, a first mixing stage 300, a second mixing stage 400, and an outlet stage 500. These stages are also shown with respect to extruder 10 in FIG.1. Each stage will now be described with reference to FIG. 3. [0060] A plurality of extruder screw segments is provided to form inlet stage 100. As shown in FIG. 1, inlet stage 100 initiates near first end 18, terminates at dispersion stage 200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 3, in one form, inlet stage 100 includes a first forward full flight screw segment 102, a pair of second forward full flight screw segments 104, and six third forward full flight screw segments 106. In one form, first forward full flight screw segment 102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder screw diameter "D"). Second forward full flight screw segment 104 has a length of 1.00 D₅ for a total length of 2.00 D for the pair. Third forward full flight screw segment 106 also has a length of 0.75 D, for a total length of 4.50 D. In one form, third forward full flight screw segment 106 has a shorter pitch than the pair of second forward full flight screw segments 104. In one form, inlet stage 100 has a length Li of about 10% L < Li < about 30% L, where L is the total length of extruder shaft 34.

[0061] Referring still to FIG. 3, a plurality of extruder screw segments is provided to form dispersion stage 200. As shown in FIG. 1, dispersion stage 200 follows inlet stage 100, terminates at first mixing stage 300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 100. As shown in FIG. 3, in one form, dispersion stage 200 includes a pre-kneading segment 202, three first kneading segments 204, and twelve second kneading segments 206. In one form, the ability of pre-kneading segment 202 to the move material forward is less than that of third forward full flight screw segment 106 and second kneading segment 206. In one form, pre-kneading segment 202 has a length of 1.00 D. First kneading segment 204 has a length of 1.50 D, for a total length of 4.50 D for the three first kneading segments 204. Second kneading segment 206 has a length of 0.50 D, for a total length of 6.00 D for the twelve second kneading segments 206. In one form, dispersion stage 200 has a length Ld of about 15% L < Ld < about 35% L, where L is the total length of extruder shaft 34.

[0062] As shown in FIG. 4A, in one form, first kneading segment 204 includes a plurality of kneading disks 208. As may be seen by reference to FIG. 4B₅ each adjacent flight tip of kneading disks 208 is progressively offset by an angle θ, wherein 0° < θ < 90° or angle θ may equal about 45°. In another form, the number of kneading disks is greater than 10 and is selected to achieve an offset angle between a flight tip of a last kneading disk 208 of the at least one first kneading segment and a flight tip of a first kneading disk of an adjacent kneading segment equal to about 0°. In yet another form, the number of kneading disks 208 and angle θ are selected to enable an adjacent kneading segment 204 to be positioned to achieve an offset angle between a flight tip of a last kneading disk 208 of the at least one first kneading segment 204 and a flight tip of a first kneading disk of an adjacent kneading segment substantially equivalent to the angle θ. [0063] In one form, the pair of elongated extruder shafts 34 has a hexagonal cross section and the offset angle θ is defined as 40° < θ < 50°. In another form, angle θ is equal to about 45°. In yet another form, the number of kneading disks 208 of first kneading segment 204 is greater than 15. In still yet another form, the number of kneading disks 208 of first kneading segment 204 is 17 and the offset angle between a flight tip of a last dual flight kneading disk 208 of the at least one first kneading segment and a flight tip of a first kneading disk 208 of an adjacent kneading segment equal to about 0°. As may be appreciated, the greater the number of kneading disks 208 of the first kneading segment 204, the more efficient the dispersion. Also the thinner the disk thickness is, the more efficient the dispersion. [0064] Traditionally, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first kneading segment 204 is a 45/17/0.09D/1.5D forward kneading segment, while second kneading segments 206 is a 45/5/0. lOD/0.5OD forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flight tips, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°.

[0065] It is interesting to note that, in the case of a dispersion stage disclosed herein, designed for preparing a mixture of polymer and diluent, the discontinuous kneading segments described above provide dispersion utility, rather than distribution and stirring utility. This is contrary to their utility when employed in a system designed to prepare a melt-blended polymer, wherein a continuous flight kneading segment would be utilized for dispersion and a discontinuous lαieading segment utilized for distribution and stirring. Importantly, the discontinuous lαieading segments described above permit reverse polymer or polymer-diluent mixture flow, but do not permit the reverse flow of the solvent or diluent introduced within the dispersion stage. [0066] Referring again to FIG. 3, a plurality of extruder screw segments is provided to form first mixing stage 300. As shown in FIG. 1, first mixing stage 300 follows dispersion stage 200 and terminates at second mixing stage 400. As shown in FIG. 3, in one form, first mixing stage 300 includes a plurality of gear lαieading segments 302. In another form, first mixing stage 300 includes seven gear kneading segments 302, each having a length of 1.50 D, for a total length of 10.50 D. In one form, first mixing stage 300 has a length LmI of about 15% L < LmI < about 35% L, where L is the total length of extruder shaft 34.

[0067] In one form, each gear kneading segment 302 includes a plurality of multi-tooth disks, each niulti -tooth disks including 12 gear teeth. In another form, each gear kneading segment 302 includes a five multi-tooth disks.

[0068] Referring still to FIG. 3, a plurality of extruder screw segments is provided to form second mixing stage 400. As shown in FIG. 1, second mixing stage 400 follows first mixing stage 300, terminates at outlet stage 500 and is positioned so as to receive a liquid diluent from second fluid inlet 33 for mixing with the polymer solution formed within dispersion stage 200 and first mixing stage 300. As shown in FIG. 3, in one form, second mixing stage 400 includes a plurality of pre-kneading segments 402. In one form, four pre-kneading segments 402 are employed, each have a length of 1.00 D, for a total length of 4.00 D. Second mixing stage 400 also includes a plurality of gear lαieading segments 404 and a plurality of neutral kneading segments 406. In one form, second mixing stage 400 includes three gear kneading segments 404, each having a length of 1.50 D, for a total length of 4.50 D. Second mixing stage 400 also includes, in one form, two neutral lαieading segments 406, each having a length of 0.50 D, for a total length of 1.00 D. In one form, second mixing stage 400 has a length Lm2 of about 0% L < Lni2 < about 30% L, where L is the total length of extruder shaft 34. [0069] In one form, each gear kneading segment 404 includes a plurality of multi-tooth disks, each multi-tooth disks including 12 gear teeth. In another form, each gear lαieading segment 404 includes six multi-tooth disks. In one form, each neutral lαieading segment 406 includes a plurality of dual flight kneading disks. As is conventional, each dual flight kneading disk is progressively offset by a 90° angle.

[0070] Referring again to FIG. 3, a plurality of extruder screw segments is provided to form outlet stage 500. As shown in FIG. 1, outlet stage 500 follows second mixing stage 400, terminates at outlet end 20 and is positioned so as to permit venting from at least one vent 36. Optionally, recycled fluff may be introduced at fluff feed inlet 38. As shown in FIG. 3, in one form, outlet stage 500 includes a pair of first forward full flight screw segment 502, and a second forward full flight screw segments 504. In one form, each first forward full flight screw segment 502 has a length of 1.5 D, for a total length of 3.00 D. Second forward full flight screw segment 504 has a length of 1.00 D.

[0071] In one form, when recycled fluff in introduced, outlet stage 500 further includes a second kneading stage 520. Second kneading stage 520 may include a pair of forward kneading segments 506, each have a length of 1.00 D, for a total length of 2.00 D, and a neutral kneading stage 508, having a length of 1.00 D. Second kneading stage 520 also includes a back kneading segment 510 having a length of 0.50 D. Back kneading segment 508 includes a plurality of kneading disks, each adjacent flight tip of the plurality of kneading disks progressively offset by an angle θ, wherein 0° < θ < -90° or angle θ may equal about -45°. In the event no recycled fluff is employed, a plurality of forward full flight screw segments (not shown) may be substituted for second kneading stage 520, wherein the plurality of forward full flight screw segments has a total length of 3.50 D.

[0072] As shown in FIG. 3, following second kneading stage 520, or following a plurality of forward full flight screw segments (not shown), outlet stage 500, includes a pair of third forward full flight screw segment 512, and a fourth forward full flight screw segments 514. In one form, each third forward full flight screw segment 512 is the same as first forward full flight screw segment 502 and has a length of 1.5 D, for a total length of 3.00 D. Likewise, fourth forward full flight screw segments 514 may be the same as second forward full flight screw segment 504, having a length of 1.00 D. Finally, outlet stage 500 may terminate in a plurality of fifth forward full flight screw segments 516, each fifth forward full flight screw segment having a length of 0.75 D, for a total length of 2.25 D. In one form, outlet stage 500 has a length Lo of about 0% L < Lo < about 40% L, where L is the total length of extruder shaft 34. [0073] In another form, a plurality of extruder screw segments is shown in FIG. 5. The plurality of extruder screw segments shown are selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 1100, a dispersion stage 1200, a mixing stage 1300, and an outlet stage 1400. Each stage will now be described with reference to FIG. 5.

[0074] A plurality of extruder screw segments is provided to form inlet stage 1100. Referring generally to FIG. 1, inlet stage 1100 initiates near first end 18, terminates at dispersion stage 1200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 5, in one form, inlet stage 1100 includes a first forward full flight screw segment 1102, a second forward full flight screw segments 1104, and six third forward full flight screw segments 1106. In one form, first forward full flight screw segment 1102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder shaft diameter "D"). Second forward full flight screw segment 1104 has a length of 1.00 D. Third forward full flight screw segment 1106 has a length of 0.75 D, for a total length of 4.50 D. In one form, third forward full flight screw segment 106 has a shorter pitch than the pair of second forward full flight screw segments 104. In one form, inlet stage 1100 has a length Li of about 10% L < Li < about 30% L, where L is the total length of extruder shaft 34. [0075] Referring still to FIG. 5, a plurality of extruder screw segments is provided to form dispersion stage 1200. As shown generally in FIG. 1, dispersion stage 1200 follows inlet stage 1100, terminates at first mixing stage 1300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 1100. As shown in FIG. 5, in one form, dispersion stage 1200 includes a pair of pre-kneading segments 1202, eleven first forward kneading segments 1204, and two second neutral kneading segments 1206. In one form, the ability of pre-kneading segment 1202 to the move material forward is lower than that of third forward full flight screw segment 1106 and first kneading segment 1204. In one form, pre-kneading segment 1202 has a length of 0.75 D, for a total length of 1.5 D. First forward kneading segment 1204 has a length of 0.50 D, for a total length of 5.50 D for the eleven first forward kneading segments 1204. Second neutral kneading segment 1206 has a length of 0.50 D, for a total length of 1.00 D for the two second neutral kneading segments 1206. In one form, dispersion stage 1200 has a length Ld of about 15% L < Ld < about 20% L, where L is the total length of extruder shaft 34.

[0076] As indicated above, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first forward kneading segment 1204 is a 45/5/0. lOD/0.50D forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flights, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°. [0077] Referring still to FIG. 5, a plurality of extruder screw segments is provided to form mixing stage 1300. Mixing stage 1300 follows dispersion stage 1200, terminates at outlet stage 1400 and is positioned so as to receive a liquid diluent from second fluid inlet (when a second fluid inlet is used) for mixing with the polymer solution formed within dispersion stage 1200. As shown in FIG. 5, in one form, first mixing stage 1300 includes a full flight screw segment 1302, having a length of 0.75, a pair of neutral kneading segments 1304 having a length of 0.50 D, for a total length of 1.00 D, and a back kneading segment 1306 having a length of 0.50 D. Following the back kneading segment 1306 is a plurality of gear kneading segments 1308. Following back kneading segment 1306 are seven gear kneading segments 1308, each having a length of 1.50 D, for a total length of 10.50 D. In one form, each gear kneading segment 1308 includes a plurality of multi -tooth disks, each multi-tooth disks including 12 gear teeth. In another form, each gear kneading segment 1308 includes a five multi -tooth disks. Following gear kneading segments 1308 is a plurality of forward kneading segments 1310. In one form, eight kneading segments 1310 are employed, each have a length of 0.5 D, for a total length of 4.00 D. In one form, mixing stage 1300 has a length Lm of about 30% L < Lm < about 45% L, where L is the total length of the extruder shaft.

[0078] As shown in FIG. 5, a plurality of extruder screw segments is provided to form outlet stage 1400. Outlet stage 1400 follows mixing stage 1300, terminates at outlet end 20 (see FIG. 1) and is positioned so as to permit venting from at least one vent 36. As shown in FIG. 5, in one form, outlet stage 1400 includes five first forward full flight screw segment 1402, a second forward full flight screw segments 1404, and a pair of third forward full flight screw segment 1406. In one form, each first forward full flight screw segment 1402 has a length of 1.5 D, for a total length of 7.50 D. Second forward full flight screw segment 1404 has a length of 1.00 D. Each third forward full flight screw segment has a length of 0.50 D, for a total length of 1.50 D. In one form, outlet stage 1400 has a length Lo of about 0% L < Lo < about 30% L, where L is the total length of extruder shaft 34.

[0079] In yet another form, a plurality of extruder screw segments is shown in FIG. 6. The plurality of extruder screw segments shown are selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 2100, a dispersion stage 2200, a first mixing stage 2300, a second mixing stage 2400, and an outlet stage 2500. Each stage will now be described with reference to FIG. 6.

[0080] A plurality of extruder screw segments is provided to form inlet stage 2100. Referring generally also to FIG. 1, inlet stage 2100 initiates near first end 18, terminates at dispersion stage 2200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 6, in one form, inlet stage 2100 includes a first forward full flight screw segment 2102, and four second forward full flight screw segments 2104. In one form, first forward full flight screw segment 2102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder screw diameter "D"). The second forward full flight screw segments 2104 each have a length of 0.75 D, for a total length of 3.00 D. In one form, inlet stage 2100 has a length Li of about 5% L < Li < about 30% L, where L is the total length of extruder shaft 34.

[0081] Referring still to FIG. 6, a plurality of extruder screw segments is provided to form dispersion stage 2200. Dispersion stage 2200 follows inlet stage 2100, terminates at first mixing stage 2300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 2100. As shown in FIG. 6, in one form, dispersion stage 2200 includes a collar segment 2202, eleven first forward kneading segments 2204, a gear kneading segment 2206 and two second neutral kneading segments 2208. In one form, collar segment 2202 has a length of 0.75 D. First forward kneading segment 2204 has a length of 0.50 D, for a total length of 5.50 D for the eleven first forward kneading segments 2204. Gear kneading segment 2206 has a length of 1.50 D. Second neutral kneading segment 2206 has a length of 0.50 D, for a total length of 1.00 D for the two second neutral kneading segments 2206. In one form, dispersion stage 2200 has a length Ld of about 10% L < Ld < about 35% L, where L is the total length of extruder shaft 34.

[0082] As indicated above, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first forward kneading segment 2204 is a 45/5/0.10D/0.50D forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flights, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°. [0083] Referring still to FIG. 6, a plurality of extruder screw segments is provided to form first mixing stage 2300. First mixing stage 2300 follows dispersion stage 2200, terminates at second mixing stage 2400 and is positioned so as to receive a liquid diluent from a second fluid inlet (when a second fluid inlet is used) for mixing with the polymer solution formed within dispersion stage 2200. As shown in FIG. 6, in one form, first mixing stage 2300 includes a full flight screw segment 2302, having a length of 0.75 D₅ a forward kneading segment 2304 having a length of 0.50 D, and a plurality of gear kneading segments 2306. In another form, first mixing stage 2300 includes six gear kneading segments 2306, each having a length of 1.50 D, for a total length of 9.00 D. In one form, first mixing stage 2300 has a length LmI of about 15% L < LmI < about 35% L, where L is the total length of extruder shaft. In one form, each gear kneading segment 2306 includes a plurality of multi-tooth disks, each multi-tooth disks including 12 gear teeth. In another form, each gear kneading segment 2306 includes a five multi-tooth disks. [0084] Referring still to FIG. 6, a plurality of extruder screw segments is provided to form second mixing stage 2400. Second mixing stage 2400 follows first mixing stage 2300, terminates at outlet stage 2500. As shown in FIG. 6, in one form, second mixing stage 2400 includes a plurality of neutral gear kneading segments 2402. In one form, seven neutral gear kneading segments 2402 are employed, each have a length of 1.5 D, for a total length of 10.50 D. Following the plurality of neutral gear kneading segments 2402 are three neutral kneading segments 2404, each having a length of 0.50 D, for a total length of 1.50 D. Following the neutral kneading segments 2404 is a back kneading segment 2406, having a length of 0.50 D. In one form, second mixing stage 2400 has a length Lm2 of about 0% L< Lm2 < about 35% L, where L is the total length of the extruder shaft. [0085] As shown in FIG. 6, a plurality of extruder screw segments is provided to form outlet stage 2500. As shown generally in FIG. 1 , outlet stage 2500 follows second mixing stage 2400, terminates at outlet end 20 and is positioned so as to permit venting from at least one vent 36. As shown in FIG. 6, in one form, outlet stage 2500 includes three first forward full flight screw segment 2502, a second forward full flight screw segment 2504 and a third forward full flight screw segment 2506. In one form, each first forward full flight screw segment 2502 has a length of 1.5 D, for a total length of 4.50 D. Second forward full flight screw segment 2504 has a length of 1.00 D and third forward full flight screw segment 2506 has a length of 0.75 D. In one form, outlet stage 2500 has a length Lo of about 0% L < Lo < about 20% L, where L is the total length of extruder shaft. [0086] In still yet another form, a plurality of extruder screw segments are shown in FIG. 7. The plurality of extruder screw segments shown are selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 3100, a dispersion stage 3200, a first mixing stage 3300, a second mixing stage 3400, and an outlet stage 3500. Each stage will now be described with reference to FIG. 7. [0087] A plurality of extruder screw segments is provided to form inlet stage 3100. Referring generally also to FIG. 1, inlet stage 3100 initiates near first end 18, terminates at dispersion stage 3200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 7, in one form, inlet stage 3100 includes a first forward full flight screw segment 3102, and three second forward full flight screw segments 3104. In one form, first forward full flight screw segment 3102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder screw diameter "D"). The second forward full flight screw segments 3104 each have a length of 0.75 D, for a total length of 2.25 D. In one form, inlet stage 3100 has a length Li of about 3% L < Li < about 25% L, where L is the total length of extruder shaft.

[0088] Referring still to FIG. 7, a plurality of extruder screw segments is provided to form dispersion stage 3200. Dispersion stage 3200 follows inlet stage 3100, terminates at first mixing stage 3300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 3100. As shown in FIG. 7, in one form, dispersion stage 3200 includes three gear kneading segments 3202, six first forward kneading segments 3204, and one neutral gear kneading segment 3206. In one form, each gear kneading segment 3202 has a length of 1.50 D, for a total length of 4.50 D. Each first forward kneading segment 3204 has a length of 0.50 D, for a total length of 3.00 D for the six first forward kneading segments 3204. Neutral gear kneading segment 3206 has a length of 1.50 D. In one form, dispersion stage 3200 has a length Ld of about 15% L < Ld < about 30% L, where L is the total length of extruder shaft.

[0089] As indicated above, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first forward kneading segment 3204 is a 45/5/0. lOD/0.50D forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flights, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°. [0090] Referring still to FIG. 7, a plurality of extruder screw segments is provided to form first mixing stage 3300. First mixing stage 3300 follows dispersion stage 3200, terminates at second mixing stage 3400 and is positioned so as to receive a liquid diluent from second fluid inlet 33 (when a second fluid inlet is used) for mixing with the polymer solution formed within dispersion stage 3200. As shown in FIG. 7, in one form, first mixing stage 3300 includes a full flight screw segment 3302, having a length of 0.75 D, a neutral gear kneading segment 3304, a plurality of forward gear kneading segments 3306 and a plurality of neutral gear kneading segments 3308. In another form, first mixing stage 3300 includes four forward gear kneading segments 3306, each having a length of 1.50 D, for a total length of 6.00 D and five neutral gear kneading segments 3308, each having a length of 1.50 D, for a total length of 7.50 D. In one form, first mixing stage 3300 has a length LmI of about 25% L < LmI < about 45% L, where L is the total length of extruder shaft.

[0091] Referring still to FIG. 7, a plurality of extruder screw segments is provided to form second mixing stage 3400. Second mixing stage 3400 follows first mixing stage 3300, terminates at outlet stage 3500. As shown in FIG. 7, in one form, second mixing stage 3400 includes eleven neutral kneading segments 3402, each having a length of 0.50 D, for a total length of 5.50 D. Following the neutral kneading segments 3402 are five back kneading segments 3404, each having a length of 0.50 D, for a total length of 2.50 D. In one form, second mixing stage 3400 has a length Lm2 of about 0% L < Lm2 < about 25% L, where L is the total length of the extruder shaft.

[0092] As shown in FIG. 7, a plurality of extruder screw segments is provided to form outlet stage 3500. As shown generally in FIG. 1, outlet stage 3500 follows second mixing stage 3400, terminates at outlet end 20 and is positioned so as to permit venting from at least one vent 36. As shown in FIG. 7, in one form, outlet stage 3500 includes three first forward full flight screw segment 3502, a second forward full flight screw segments 3504 and a third forward full flight screw segment 3506. In one form, each first forward full flight screw segment 3502 has a length of 1.5 D, for a total length of 4.50 D. Second forward full flight screw segment 3504 has a length of 1.00 D and third forward full flight screw segment 3506 has a length of 0.75 D. In one form, outlet stage 3500 has a length Lo of about 0% L < Lo < about 20% L, where L is the total length of extruder shaft 34. [0093] In a further form, a plurality of extruder screw segments is shown in FIG. 8. The plurality of extruder screw segments shown are selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 4100, a dispersion stage 4200, a first mixing stage 4300, a second mixing stage 440O₅ and an outlet stage 4500. Each stage will now be described with reference to FIG. 8. [0094] A plurality of extruder screw segments is provided to form inlet stage 4100. Referring generally also to FIG. 1, inlet stage 4100 initiates near first end 18, terminates at dispersion stage 4200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 8, in one form, inlet stage 4100 includes a first forward full flight screw segment 4102, and four second forward full flight screw segments 4104. In one form, first forward full flight screw segment 4102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder screw diameter "D"). The second forward full flight screw segments 4104 each have a length of 0.75 D, for a total length of 3.00 D. In one form, inlet stage 4100 has a length Li of about 5% L < Li < about 30% L, where L is the total length of extruder shaft. [0095] Referring still to FIG. 8, a plurality of extruder screw segments is provided to form dispersion stage 4200. Dispersion stage 4200 follows inlet stage 4100, terminates at first mixing stage 4300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 4100. As shown in FIG. 8, in one form, dispersion stage 4200 includes a collar segment 4202 and twelve first forward kneading segments 4204. In one form, collar segment 4202 has a length of 0.75 D. Each first forward kneading segment 4204 has a length of 0.50 D, for a total length of 6.00 D for the twelve first forward kneading segments 4204. In one form, dispersion stage 4200 has a length Ld of about 10% L < Ld < about 35% L, where L is the total length of extruder shaft 34.

[0096] As indicated above, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first forward kneading segment 4204 is a 45/5/0.10D/0.50D forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flights, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°. [0097] Referring still to FIG. 8, a plurality of extruder screw segments is provided to form first mixing stage 4300. First mixing stage 4300 follows dispersion stage 4200 and terminates at second mixing stage 4400. As shown in FIG. 8, in one form, first mixing stage 4300 a plurality of forward gear kneading segments 4302. In another form, first mixing stage 4300 includes four forward gear kneading segments 4302, each having a length of 1.50 D, for a total length of 6.00 D. In one form, first mixing stage 4300 has a length LmI of about 5% < LmI < about 35% L, where L is the total length of extruder shaft.

[0098] Referring still to FIG. 8, a plurality of extruder screw segments is provided to form second mixing stage 4400. Second mixing stage 4400 follows first mixing stage 4300, terminates at outlet stage 4500 and is positioned so as to receive a liquid diluent from second fluid inlet 33 (when a second fluid inlet is used) for mixing with the polymer solution. As shown in FIG. 8, in one form, second mixing stage 4400 includes a full flight screw segment 4402, a neutral gear kneading segment 4404, having a length of 1.50 D, three forward gear kneading segments 4406, each having a length of 1.50 D, for a total length of 4.50 D, six neutral gear kneading segments 4408, each having a length of 1.50 D, for a total length of 9.00 D and seven neutral kneading segments 4410, each having a length of 0.50 D, for a total length of 3.50 D. In one form, second mixing stage 4400 has a length Lm2 of about 0% L < Lm2 < about 50% L, where L is the total length of the extruder shaft.

[0099] As shown in FIG. 8, a plurality of extruder screw segments is provided to form outlet stage 4500. As shown generally in FIG. 1, outlet stage 4500 follows second mixing stage 4400, terminates at outlet end 20 and is positioned so as to permit venting from at least one vent 36. As shown in FIG. 8, in one form, outlet stage 4500 includes three first forward full flight screw segment 4502, a second forward full flight screw segment 4504 and a third forward full flight screw segment 4506. In one form, each first forward full flight screw segment 4502 has a length of 1.5 D, for a total length of 4.50 D. Second forward full flight screw segment 4504 has a length of 1.00 D and third forward full flight screw segment 4506 has a length of 0.75 D. In one form, outlet stage 4500 has a length Lo of about 0% L < Lo < about 20% L, where L is the total length of extruder shaft. [00100] In a further form, a plurality of extruder screw segments is shown in FIG. 9. The plurality of extruder screw segments shown are selected to form multiple extruder stages. In one form, the multiple extruder stages include an inlet stage 5100, a dispersion stage 5200, a first mixing stage 5300, a second mixing stage 5400, and an outlet stage 5500. Each stage will now be described with reference to FIG. 9.

[00101] A plurality of extruder screw segments is provided to form inlet stage 5100. Referring generally also to FIG. 1, inlet stage 5100 initiates near first end 18, terminates at dispersion stage 5200 and is positioned so as to receive thermoplastic material from inlet 24 for processing. As shown in FIG. 9, in one form, inlet stage 5100 includes a first forward full flight screw segment 5102, and four second forward full flight screw segments 5104. In one form, first forward full flight screw segment 5102 has a length of 40.5mm. (When used in a 54 mm extruder, 0.75 X extruder screw diameter "D"). The second forward full flight screw segments 5104 each have a length of 0.75 D, for a total length of 2.25 D. In one form, inlet stage 5100 has a length Li of about 5% L < Li < about 30% L, where L is the total length of extruder shaft.

[00102] Referring still to FIG. 9, a plurality of extruder screw segments is provided to form dispersion stage 5200. Dispersion stage 5200 follows inlet stage 5100, terminates at first mixing stage 5300 and is positioned so as to receive a liquid diluent from first fluid inlet 32 for mixing with the thermoplastic material introduced at inlet stage 5100. As shown in FIG. 9, in one form, dispersion stage 5200 includes a collar segment 5202 and twelve first forward kneading segments 5204. In one form, collar segment 5202 has a length of 0.75 D. Each first forward kneading segment 5204 has a length of 0.50 D, for a total length of 6.00 D for the twelve first forward kneading segments 5204. In one form, dispersion stage 5200 has a length Ld of about 10% L < d < about 35% L, where L is the total length of extruder shaft.

[00103] As indicated above, kneading segments are identified by offset angle/number of disks/disk length/segment length. As such, in one form, first forward kneading segment 5204 is a 45/5/0. lOD/0.5OD forward kneading segment. As may be appreciated, these kneading disks are relatively narrow, allowing the polymer solution to flow around the flights, resulting in the stream splitting and recombining numerous times. With an offset angle of 40° < θ < 50°, more forward conveying ability and less reverse conveying ability exists than for an offset angle θ of 60°.

[00104] Referring still to FIG. 9, a plurality of extruder screw segments is provided to form first mixing stage 5300. First mixing stage 5300 follows dispersion stage 5200 and terminates at second mixing stage 5400. As shown in FIG. 9, in one form, first mixing stage 5300 a plurality of forward gear kneading segments 5302. In another form, first mixing stage 5300 includes six forward gear kneading segments 5302, each having a length of 1.50 D, for a total length of 9.00 D. In one form, first mixing stage 5300 has a length Lmlof about 10% L < LmI < about 35% L, where L is the total length of extruder shaft.

[00105] Referring still to FIG. 9, a plurality of extruder screw segments is provided to form second mixing stage 5400. Second mixing stage 5400 follows first mixing stage 5300, terminates at outlet stage 5500 and is positioned so as to receive a liquid diluent from a second fluid inlet 33 (when a second fluid inlet is used) for mixing with the polymer solution. As shown in FIG. 9, in one form, second mixing stage 5400 includes a full flight screw segment 5402, a neutral gear kneading segment 5404, having a length of 1.50 D, a forward gear kneading segment 5406, having a length of 1.50 D and six neutral gear kneading segments 5408, each having a length of 1.50 D, for a total length of 9.00 D. In one form, second mixing stage 5400 has a length Lm2 of about 0% L < Lm2 < about 35% L, where L is the total length of the extruder shaft.

[00106] As shown in FIG. 9, a plurality of extruder screw segments is provided to form outlet stage 5500. As shown generally in FIG. 1, outlet stage 5500 follows second mixing stage 5400, terminates at outlet end 20 and is positioned so as to permit venting from at least one vent 36. As shown in FIG. 9, in one form, outlet stage 5500 includes seven neutral kneading segments 5502, each having a length of 0.50 D, for a total length of 3.50 D, three first forward full flight screw segment 5504, a second forward full flight screw segments 5506 and a third forward full flight screw segment 5508. In one form, each first forward full flight screw segment 5504 has a length of 1.5 D, for a total length of 4.50 D. Second forward full flight screw segment 5506 has a length of 1.00 D and third forward full flight screw segment 5508 has a length of 0.75 D. In one form, outlet stage 5500 has a length Lo of about 0% L < Lo < about 30% L, where L is the total length of extruder shaft 34.

[00107] In another form, provided is a process for extruding a mixture of polymer and diluent. The process includes the steps of blending a polymer at a rate of P (measured, e.g., as grams per second) in an inlet stage 100 of an extruder (e.g., a twin-screw extruder) and conducting the blended polymer to a dispersion stage 200 of the extruder. At least one diluent is introduced to the blended polymer in the dispersion stage 200 at a rate of Sl (measured e.g., as grams per second), with the diluent having a lower viscosity than the polymer. The diluent is then dispersed in the polymer and conducted to a first mixing stage 300. In one form, diluent is introduced into to the blended polymer at a rate of S2 at locations downstream of the dispersion stage, e.g., the first mixing stage 300 and/or a second mixing stage 400. In the first mixing stage 300, diluent and the polymer is blended in order to produce a third-stage product, the third stage product comprising (i) the polymer-diluent mixture in a first phase, (ii) a portion of the diluent in a second phase separate from the first phase, and (iii) a portion of the polymer in a third phase separate from the first and second phases. In one form, the mixing energy in the first mixing stage 300 is greater than the mixing energy in the inlet stage 100 and/or the dispersion stage 200. [00108] In one form, the first phase is produced at a rate of R (measured, e.g., in grams per second), with R being about 0.9 x (P + S) or greater, wherein S is equal to Sl +S2, the second phase is produced at a rate that does not exceed 0.05 x Sl, and the third phase is produced at a rate that does not exceed 0.05 x P. In another form, rate of countercurrent diluent flow from the dispersion stage to the inlet stage 100 does not exceed 0.1 x Sl. The relative amounts of S, Sl and S2 are selected to prevent deterioration of the polymer in the extruder, and to prevent countercurrent flow (downstream to upstream) of the diluent. In one form, the value of S1/S2 is in the range of from about 51 wt. %/49 wt. % to about 99 wt. %/l wt%, preferably from about 55 wt. %/45 wt. % to about 95wt. %/5 wt. %, more preferably from about 60 wt. %/40 wt. % to about 90 wt. %/10 wt. %, based on the total weight of S1+S2. In one form, diluent Sl is injected to the extruder from a first fluid inlet in the dispersion stage, the position of the first fluid inlet is positioned at within a length of about 50% of Ld from the beginning of the dispersion stage, preferably within a length of about 30% of Ld. In one form, diluent S2 is injected to the extruder from a second fluid inlet in the mixing stage, the position of the second fluid inlet is positioned at the first mixing stage and /or the second mixing stage, preferably at the second mixing stage. When the diluent is injected at two mixing-stage locations, the diluent can be introduced in the first mixing stage and the second mixing stage respectively. Higher yield and a more stable output mass flow rate from the extruder is by regulating the relative values of S, S 1 and S2, and properly selecting the positions of injection for diluent as described herein. In one form, the extruder produces the polymer-diluent mixture at a rate > 1 Kg/hr, e.g., > 20 Kg/hr or > 50 Kg/hr or > 100 Kg/hr, such as in the range of about 1 Kg/hr to 100 Kg/hr, or 20 Kg/hr to 75 Kg/hr.

[00109] In another form, a major portion of the polymer is a first polyethylene, having a molecular weight in the range of from 1.0x10⁴ to 9 x 10⁵ and a second polyethylene, having a molecular weight in the range of from 9.0 x 10⁵ to 5.0 x 10⁶. In yet another form, the polymer further comprises polypropylene having a molecular weight in the range of from 3.0 x 10⁵ to 3.0 x 10⁶. In one form, the first polyethylene is present in the polymer in an amount in the range of from 0 to 100%, the second polyethylene is present in the polymer in an amount in the range of from 0 to 100%, and the polypropylene is in the polymer in an amount in the range of from 0 to 70%. In another form, the diluent is liquid paraffin, P is from 3 to 20, and S is from 5 to 50.

[00110] In one form the mixing energy in the inlet stage 100 and dispersion stage 200 is lower than the first mixing stage 300. The process conditions in the inlet stage 100 are characterized by a temperature set to 15O⁰C, P=IO, a pressure less than 5 kg/cm , and a residence time of about 18 seconds, and the dispersion stage 200 is characterized by a temperature of 200⁰C, S=23, a pressure of less than 5 kg/cm², and a residence time of about 14 seconds. In another form, the mixing energy is obtained from at least one segmented mixing screw extending continuously in the direction of polymer flow through the inlet stage 100 and the dispersion stage 200.

[00111] The extruder, system, and process forms disclosed herein find utility in the extrusion and production of microporous films and sheets. Monolayer and multi-layer microporous films and sheets are within the scope of the invention. These films and sheets find particular utility in the critical field of battery separators. The multi-layer films and sheets described hereinbelow can either be produced using a coextrusion die or be produced using a monolayer die to produce a monolayer film or sheet, with additional layers laminated thereto in a conventional manner. [00112] In one form, the multi-layer, microporous polyolefin membrane comprises two layers. The first layer (e.g., the skin, top or upper layer of the membrane) comprises a first microporous layer material, and the second layer (e.g., the bottom or lower or core layer of the membrane) comprises a second microporous layer material. For example, the membrane can have a planar top layer when viewed from above on an axis approximately perpendicular to the transverse and longitudinal (machine) directions of the membrane, with the bottom planar layer hidden from view by the top layer.

[00113] In another form, the multi-layer, microporous polyolefin membrane comprises three or more layers, wherein the outer layers (also called the "surface" or "skin" layers) comprise the first microporous layer material and at least one core or intermediate layer comprises the second microporous layer material. In a related form, where the multi-layer, microporous polyolefin membrane comprises two layers, the first layer consists essentially of the first microporous layer material and the second layer consists essentially of the second microporous layer material. In a related form where the multi-layer, microporous polyolefin membrane comprises three or more layers, the outer layers consist essentially of the first microporous layer material and at least one intermediate layer consists essentially of (or consists of) the second microporous layer material. In an embodiment, the microporous membranes produced by the process have a thickness of form about 3 to about 200μm, or from about 5 to about 50μm, or from about 7 to about 35μm. The microporous membranes produced in the process of the present invention can be used as battery separators for primary and secondary batteries, particularly such as lithium ion secondary batteries, lithium-polymer secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, nickel-zinc secondary batteries, silver-zinc secondary batteries, particularly for lithium ion secondary batteries.

[00114] Starting materials having utility in the production of the afore-mentioned films and sheets will now be described. As will be appreciated by those skilled in the art, the selection of a starting material is not critical. Polymers and mixtures of polymers such as polyolefm and mixtures of polyolefin can be used. The polymers, process, and process conditions described in WO2008/016174, US2008/0057388, and US2008/0057389, which are incorporated by reference herein in their entirety, are suitable for the invention. In one form, the first and second microporous layer materials contain polyethylene. In one form, the first microporous layer material contains a first polyethylene ("PE-I") having an Mw value of less than about 1 x 10⁶ or a second polyethylene ("UHMWPE-I") having an Mw value of at least about 1 x 10⁶. In one form, the first microporous layer material can contain a first polypropylene ("PP-I"). In one form, the first microporous layer material comprises one of (i) polyolefm such as polyethylene and/or polypropylene, (ii) an ultra high molecular weight polyethylene (UHMWPE), (iii) PE-I and PP-I, or (iv) PE-I, UHMWPE-I, and PP-I.

[00115] In one form of the above (ii) and (iv), UHMWPE-I can preferably have an Mw in the range of from about 1 x 10⁶ to about 15 x 10⁶ or from about 1 x 10⁶ to about 5 x 10⁶ or from about 1 x 10⁶ to about 3 x 10⁶,and preferably contain greater than about 1 wt.%, or about 15 wt.% to 40 wt.%, on the basis of total amount of PE-I and UHMWPE-I in order to obtain a microporous layer having a hybrid structure defined in the later section, and can be at least one of homopolymer or copolymer. In one form of the above (iii) and (iv), PP-I can be at least one of a homopolymer or copolymer, or can preferably contain no more than about 25 wt. %, on the basis of total amount of the first layer microporous material. In one form, the Mw of polyolefin in the first microporous layer material can have about 1 x 10⁶ or less, or in the range of from about 1 x 10⁵ to about 1 x 10⁶ or from about 2 x 10⁵ to about 1 x 10⁶ in order to obtain a microporous layer having a hybrid structure defined in the later section. In one form, PE-I can preferably have an Mw ranging from about 1 x 10⁴ to about 9 x 10⁵, or from about 2 x 10⁵ to about 8 x 10⁵, and can be one or more of a high-density polyethylene, a medium-density polyethylene, a branched low-density polyethylene, or a linear low-density polyethylene, and can be at least one of a homopolymer or copolymer. [00116] In one form, the first microporous layer material (the first layer of the two-layer, microporous polyolefin membrane and the first and third layers of a three-layer microporous polyolefin membrane) has a hybrid structure, which is characterized by a pore size distribution exhibiting relatively dense domains having a main peak in a range of 0.01 μm to 0.08 μm and relatively coarse domains exhibiting at least one sub-peak in a range of more than 0.08 μm to 1.5 μm or less in the pore size distribution curve. The ratio of the pore volume of the dense domains (calculated from the main peak) to the pore volume of the coarse domains (calculated from the sub-peak) is not critical, and can range, e.g., from about 0.5 to about 49. [00117] In one form, the second microporous layer material comprises the same materials used to produce the first microporous layer material, optionally in different relative amounts, e.g., polyethylene and/or polypropylene. For example, the second microporous layer material can comprise one of: (i) a fourth polyethylene having an Mw of at least about 1 x 10⁶, (UHMWPE-2), (ii) a third polyethylene having an Mw that is less than 1 x 10 and UHMWPE-2 and the fourth polyethylene(the fourth polyethylene is present, e.g., in an amount of at least about 8% by mass based on the combined mass of the third and fourth polyethylene); (iii) UHMWPE-2 and PP-2, or (iv) PE-2, UHMWPE-2, and PP -2. In one form of the above (ii), (iii) and (iv), UHMWPE-2 can contain at least about 8 wt. %, or at least about 20 wt.%, or at least about 25 wt.%, based on the total amount of UHMWPE-2, PE-2 and PP-2 in order to produce a relatively strong multi-layer, microporous polyolefin membrane. In one form of the above (iii) and (iv), PP-2 can be at least one of a homopolymer or copolymer, and can contain 50 wt. % or less, 35 wt.% or less, 25 wt.% or less, or in the range of from about 2% to about 50%, of from about 2% to about 15%, or from about 3% to about 10%, based on the total amount of the second microporous layer material. In one form, preferable PE-2 can be the same as PE-I, but can be selected independently. In one form, preferable UHMWPE-2 can be the same as UHMWPE-I, but can be selected independently.

[00118] In addition to the first, second, third, and fourth polyethylenes and the first and second polypropylenes, each of the first and second layer materials can optionally contain one or more additional polyolefms, identified as the seventh polyolefin, which can be, e.g., one or more of polybutene-1, polypentene-1, poly-4-methylpentene-l, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene and an ethylene α-olefm copolymer (except for an ethylene-propylene copolymer) and can have an Mw in the range of about 1 x 10⁴ to about 4 x 10⁶. In addition to or besides the seventh polyolefin, the first and second microporous layer materials can further comprise a polyethylene wax, e.g., one having an Mw in the range of about 1 x 10³ to about 1 x 10⁴. [00119] In one form, a process for producing a two-layer microporous membrane is provided. In another form, the microporous polyolefin membrane has at least three layers. For the sake of brevity, the production of the microporous membrane will be mainly described in terms of two-layer and three-layer membrane. [00120] In one form, a three-layer microporous polyolefin membrane comprises first and third microporous layers constituting the outer layers of the microporous polyolefin membrane and a second (core) layer situated between (and optionally in planar contact with) the first and third layers. In another form, the first and third layers are produced from a first mixture of polymer and diluent and the second (core) layer is produced from a second mixture of polymer and diluent. [00121] In one form, a method for producing the multi-layer, microporous polyolefin membrane is provided. The method comprises the steps of (1) combining (e.g., by blending) a first polymer or mixture of polymers (e.g., a polyolefin composition) and at least one diluent (which can be a solvent for the polymer) to prepare a first mixture in an extruder of the type disclosed herein, (2) combining a second polymer or mixture of polymers (e.g., a second polyolefin composition) and at least one second diluent (which can be a solvent for the second polymer and is generally compatible with the first diluent) to prepare a mixture in an extruder of the type disclosed herein, (3) producing a multi -layer extrudate by, e.g., extruding the first mixture through a first die and the second mixture through a second die and then laminating the extruded mixtures; or coextruding the first and second mixtures through a coextrusion die, (4) optionally cooling the multi-layer extrudate to form a multi-layer, gel-like sheet (cooled extrudate), (5) removing at least a portion of the first and second diluents from the extrudate or cooled extrudate to produce the multi-layer, microporous membrane. Optionally, the membrane can be subjected to the following optional steps: (6) a step for drying the membrane, a step for stretching the membrane or dried membrane (7), and/or an optional hot solvent treatment step (8) conducted between steps (4) and (5). After step (6), an optional step (9) of stretching a multi-layer, microporous membrane, an optional heat treatment step (10), an optional cross-lmking step with ionizing radiations (11), and an optional hydrophilic treatment step (12), etc., can be conducted. Such membranes and membrane production processes are described in PCT Publication WO2008/016174, US2008/0057388, and US2008/0057389. [00122] In one form, the first and second polymers are each produced from a polyolefin composition comprising polyolefin resins as described above that can be combined, e.g., by dry mixing or blending with the first and second diluents respectively to produce the first and second mixtures. Optionally, the first and second mixtures can contain various additives such as one or more antioxidant, fine silicate powder (pore-forming material), etc., provided these are used in a concentration range that does not significantly degrade the desired properties of the multi-layer, microporous polyolefin membrane.

[00123] The first and second diluents (which can be the same diluent) are preferably a solvent for the first and/or second polymer and are liquid at room temperature. While not wishing to be bound by any theory or model, it is believed that the use of a liquid solvent to form the first and second mixtures makes it possible to conduct stretching of the gel-like sheet at a relatively high stretching magnification. In one form, the first diluent can be at least one of aliphatic, alicyclic or aromatic hydrocarbons such as nonane, decane, decalin, p-xylene, undecane, dodecane, liquid paraffin, etc.; mineral oil distillates having boiling points comparable to those of the above hydrocarbons; and phthalates liquid at room temperature, such as dibutyl phthalate, dioctyl phthalate, etc. In one form where it is desired to obtain a multi-layer, extrudate having a stable liquid diluent content, non- volatile liquid solvents such as liquid paraffin can be used as the diluent, either alone or in combination with other solvents. Optionally, a diluent which is miscible with polyethylene in a blended state but solid at room temperature can be used, either alone or in combination with a liquid diluent. Such solid diluent can include, e.g., stearyl alcohol, ceryl alcohol, paraffin waxes, etc.

[00124] The first and second diluents' viscosity is not a critical parameter. For example, the diluents' viscosity can range from about 30 cSt to about 500 cSt, or from about 30 cSt to about 200 cSt, at 25°C. Although it is not a critical parameter, when the viscosity at 25°C is less than about 30 cSt, it can be more difficult to prevent foaming the mixture, which can lead to difficulty in blending. On the other hand, when the viscosity is greater than about 500 cSt, it can be more difficult to remove the diluent from the multi-layer microporous polyolefin membrane. [00125] In one form, the resins, etc., used to produce to the first polyolefin composition are blended in, e.g., a double screw extruder or mixer. For example, a conventional extruder (or mixer or mixer-extruder) such as a double-screw extruder can be used to combine the resins, etc., to form the first and second polymers or mixtures of polymers. The diluent can be added to the polymer (or alternatively to the resins used to produce the polymer or mixture of polymers) at specified points in the process as described in connection with the extruder. For example, in one form where a polyolefin composition and the diluent are combined, a portion of the diluent can be added to the polyolefin composition (or its components) at any of (i) before the start of mixing, (ii) during polymer-diluent mixing, or (iii) after mixing, e.g., by supplying the diluent to the blended or partially blended polyolefin composition in a second extruder or extruder zone located downstream of the extruder zone used to blend the polyolefin composition. [00126] When an extruder of the type disclosed herein is employed, the screw can be characterized by a ratio L/D of the screw length L to the screw diameter D in the double-screw extruder, which can range, for example, from about 20 to about 200 or from about 25 to about 100. Although this parameter is not critical, when L/D is less than about 20, blending can be more difficult, and when L/D is more than about 100, faster extruder speeds might be needed to prevent excessive residence time of the polymer-diluent mixture in the double-screw extruder, which can lead to undesirable molecular weight degradation. Although it is not a critical parameter, the cylinder (or bore) of the double-screw extruder can have an inner diameter of in the range of about 30 mm to about 100 mm, for example.

[00127] The amount of the first polymer composition in the first mixture is not critical. In one form, the amount of first polymer in the first mixture is > 1 wt. %, e.g., in the range of from about 1 wt.% to about 75 wt.%, based on the weight of the mixture, for example from about 20 wt.% to about 40 wt.%.

[00128] The second mixture can be prepared by the same methods used to prepare the first mixture. For example, the second mixture can be prepared by blending a second polymer with a second diluent. [00129] The amount of the second polymer composition in the second mixture is not critical. In one form, the amount of second polymer in the second mixture is > 1 wt. %, e.g., in the range of from about 1 wt.% to about 75 wt.%, based on the weight of the mixture, for example from about 20 wt.% to about 40 wt.%.

[00130] In an embodiment, two extruders are used in series, with a twin screw extruder located upstream of a single screw extruder. A filter can be located downstream of each extruder to remove, e.g., particulates such as catalyst fines, unmixed polymer, metal particles, and the like. Metal particles (such as those abraded from internal extruder surface in close contact) are particularly problematic for battery separator film because they can cause short-circuits in the film. Fine filters, e.g., those having a pore size < lOOμm, or < 40μm, or < 20μm, such as in the range of 20μm to 50μm can be used to remove such particles. It has been observed that the introduction of such a filter, especially downstream of the second extruder, can lead to phase separation of the polymer-diluent mixture. When pumping means such as a gear pump is used to overcome the filter's pressure drop, this problem can worsen. In these cases, it has been discovered that such phase separation can be cured by inserting mixing means such as a static mixer upstream of the die. Using mixing means upstream of the die improves temperature uniformity in the polymer-diluent mixture and lessens the amount of polymer-diluent phase separation. It is also believed that the use of such mixing means leads to a more uniform concentration of polymer and diluent in the polymer-diluent mixture. Increased uniformity is believed to lessen the amount of polymer-diluent phase separation. While not wishing to be bound by any theory or model, it is believed that the onset of polymer-diluent phase separation is very sensitive to the temperature of the polymer-diluent mixture and the amount of polymer in the mixture. Fluctuations in polymer concentration that occur (e.g., when a portion of the polymer is separated from the mixture by the fine mesh of the filter) can result in polymer-diluent phase separation generating an undesirable diluent-rich phase which when extruded through the die produces an extrudate having undesirable thickness uniformity and/or compositional non-homogeneity .

[00131] In an embodiment, process conditions such as polymer and diluent type and amounts, processing temperatures and flow rates, die section, etc. are selected from among those disclosed in PCT Publications WO2008/016174, US2008/0057388, and US2008/0057389. [00132] A monolayer extrusion die may be used to form an extrudate that can be laminated. In one form, extrusion dies, which can be adjacent or connected, are used to form the extrudates. The first and second sheet dies are connected to first and second extruders, respectively, where the first extruder contains the first mixture and the second extruder contains the second mixture. While not critical, lamination is generally easier to accomplish when the extruded first and second mixture are still at approximately the extrusion temperature. In one form lamination of the extrudate is conducted before cooling. In another form, lamination is conducted after cooling. In yet another form, lamination is conducted after at least a portion of the first and second diluents have been removed, i.e., in this form the membrane is laminated not the extrudate. In yet another form, coextrusion is used to produce a multi-layer extrudate without lamination. [00133] For example, in one form, first, second, and third dies are connected to first, second and third extruders of the type disclosed herein, where the first and third dies contain the first mixture, and the second die contains the second mixture. In this form, a laminated extrudate is formed constituting outer layers comprising the extruded first mixture and one intermediate comprising the extruded second mixture. [00134] In yet another form, the first, second, and third dies are connected to first, second, and third extruders of the type disclosed herein, where the second die contains the first mixture, and the first and third dies contain the second mixture. In this form, a laminated extrudate is formed constituting outer layers comprising the extruded second mixture and one intermediate comprising extruded first mixture.

[00135] The die gaps are generally not critical. For example, extrusion dies can have a die gap of about 0.1 mm to about 5 mm. Die temperature and extruding speed are also non-critical parameters. For example, the dies can be heated to a die temperature ranging from about 140°C to about 25O⁰C during extrusion. The extruding speed can range, for example, from about 0.2 m/minute to about 15 m/minute. The thickness of the layers of the layered extrudate can be independently selected. For example, the resultant sheet can have relatively thick skin or surface layers compared to the thickness of an intermediate layer of the layered extrudate. [00136] A cooled extrudate, e.g., a multi-layer, gel-like sheet can be obtained by cooling, for example. Cooling rate and cooling temperature are not particularly critical. For example, the multi-layer, gel-like sheet can be cooled at a cooling rate of at least about 50°C/minute until the temperature of the multi-layer, gel-like sheet (the cooling temperature) is approximately equal to the multi-layer, gel-like sheet's gelatin temperature (or lower). In one form, the extrudate is cooled to a temperature of about 25°C or lower in order to form the multi-layer gel-like sheet. [00137] In one form, the first and second diluents are removed (or displaced) from the multi-layer gel-like sheet in order to form a diluent-removed gel-like sheet. A displacing (or "washing") solvent can be used to remove (wash away, or displace) the first and second diluents. The choice of washing solvent is not critical provided it is capable of dissolving or displacing at least a portion of the first and/or second diluent. Suitable washing solvents include, for instance, one or more of volatile solvents such as saturated hydrocarbons such as pentane, hexane, heptane, etc.; chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride, etc.; ethers such as diethyl ether, dioxane, etc.; ketones such as methyl ethyl ketone, etc.; linear fluorocarbons such as trifluoroethane, C₆Fi₄, C₇F]₆, etc.; cyclic hydrofluorocarbons such as C₅H₃F₇, etc.; hydrofluoroethers such as C₄F₉OCH₃, C₄F₉OC₂H₅, etc.; and perfluoroethers such as C₄F₉OCF₃, C₄F₉O C₂H₅, etc. [00138] The diluent-removal method is not critical, and any method capable of removing a significant amount of diluent can be used, including conventional solvent-removal methods. For example, the multi-layer, gel-like sheet can be washed by immersing the sheet in the washing solvent and/or showering the sheet with the washing solvent. The amount of washing solvent used is not critical, and will generally depend on the method selected for diluent removal. In one form, the diluent is removed from the gel-like sheet (e.g., by washing) until the amount of the remaining diluent in the multi-layer gel-like sheet becomes less than 1 wt.%, based on the weight of the gel-like sheet. [00139] In one form, the diluent-removed multi-layer, gel-like sheet obtained by removing the diluents is dried in order to remove the washing solvent. Any method capable of removing the washing solvent can be used, including conventional methods such as heat-drying, wind-drying (moving air), etc. The temperature of the gel-like sheet during drying (i.e., drying temperature) is not critical. For example, the drying temperature can be equal to or lower than the crystal dispersion temperature Ted. Ted is the lower of the crystal dispersion temperature Tcdi of the polyethylene in the first resin and the crystal dispersion temperature Tcd₂ of the polyethylene in the second resin. For example, the drying temperature can be at least 5°C below the crystal dispersion temperature Ted. The crystal dispersion temperature of the polyethylene in the first and second resins can be determined by measuring the temperature characteristics of the kinetic viscoelasticity of the polyethylene according to ASTM D 4065. In one form, the polyethylene in at least one of the first or second resins has a crystal dispersion temperature in the range of about 9O⁰C to about 100°C.

[00140] Although it is not critical, drying can be conducted until the amount of remaining washing solvent is about 5 wt. % or less on a dry basis, i.e., based on the weight of the dry multi-layer, microporous polyolefin membrane. In another form, drying is conducted until the amount of remaining washing solvent is about 3 wt. % or less on a dry basis.

[00141] Prior to the step for removing the diluent, the multi-layer, gel-like sheet can be stretched in order to obtain a stretched, multi-layer, gel-like sheet. [00142] Neither the choice of stretching method nor the degree of stretching magnification is particularly critical. In one form, the stretching can be accomplished by one or more of tenter-stretching, roller-stretching, or inflation stretching (e.g., with air). Although the choice is not critical, the stretching can be conducted monoaxially (i.e., in either the machine or transverse direction) or biaxially (both the machine and transverse direction). In the case of biaxial stretching (also called biaxial orientation), the stretching can be simultaneous biaxial stretching, sequential stretching along one planar axis and then the other (e.g., first in the transverse direction and then in the machine direction), or multi-stage stretching (for instance, a combination of the simultaneous biaxial stretching and the sequential stretching). [00143] The stretching magnification is not critical. In a form where monoaxial stretching is used, the linear stretching magnification can be, e.g., about 2 fold or more, or about 3 to about 30 fold. In a form where biaxial stretching is used, the linear stretching magnification can be, e.g., about 3 fold or more in any lateral direction. In another form, the linear magnification resulting from stretching is at least about 9 fold, or at least about 16 fold, or at least about 25 fold in area magnification. [00144] The temperature of the multi-layer, gel-like sheet during stretching (namely the stretching temperature) is not critical. In one form, the temperature of the gel-like sheet during stretching can be about (Tm + 10⁰C) or lower, or optionally in a range that is higher than Ted but lower than Tm, wherein Tm is the lesser of the melting point Tm₁ of the polyethylene in the first resin and the melting point Tm₂ of the polyethylene in the second resin.

[00145] The stretching when used generally makes it easier to produce a relatively high-mechanical strength multi-layer, microporous polyolefm membrane with a relatively large pore size. Such multi-layer, microporous membranes are believed to be particularly suitable for use as battery separators.

[00146] Optionally, stretching can be conducted in the presence of a temperature gradient in a thickness direction (i.e., a direction approximately perpendicular to the planar surface of the multi-layer, microporous polyolefm membrane) as described in JP 3,347,854

B2. In this case, it can be easier to produce a multi-layer, microporous polyolefϊn membrane with improved mechanical strength.

[00147] Although it is not required, the multi-layer, gel-like sheet can be treated with a hot solvent. When used, it is believed that the hot solvent treatment provides the fibrils (such as those formed by stretching the multi-layer gel-like sheet) with a relatively thick leaf-vein-like structure. The.details of this method are described in WO 2000/20493.

[00148] In one form, the dried multi-layer, microporous membrane can be stretched, at least monoaxially. The stretching method selected is not critical, and conventional stretching methods can be used such as by a tenter method, etc. When the multi-layer gel-like sheet has been stretched as described above the stretching of the dry multi-layer, microporous polyolefin membrane can be called dry-stretching, re-stretching, or dry-orientation.

[00149] The temperature of the dry multi-layer, microporous membrane during stretching (the "dry stretching temperature") is not critical. In one form, the dry stretching temperature is approximately equal to the melting point Tm or lower, for example in the range of from about the crystal dispersion temperature Ted to the about the melting point Tm. In one form, the dry stretching temperature ranges from about 9O⁰C to about 135°C or from about 95°C to about 130⁰C.

[00150] When dry-stretching is used, the stretching magnification is not critical. For example, the stretching magnification of the multi-layer, microporous membrane can range from about 1.1 fold to about 2.5 or about 1.1 to about 2.0 fold in at least one lateral

(planar) direction. [00151] In one form, the dried multi-layer, microporous membrane can be heat-treated. In one form, the heat treatment comprises heat-setting and/or annealing. When heat-setting is used, it can be conducted using conventional methods such as tenter methods and/or roller methods. Although it is not critical, the temperature of the dried multi-layer, microporous polyolefϊn membrane during heat-setting (i.e., the "heat-setting temperature") can range from the Ted to about the Tm.

[00152] Annealing differs from heat-setting in that it is a heat treatment with no load applied to the multi-layer, microporous polyolefin membrane. The choice of annealing method is not critical, and it can be conducted, for example, by using a heating chamber with a belt conveyer or an air-fioating-type heating chamber. Alternatively, the annealing can be conducted after the heat-setting with the tenter clips slackened. The temperature of the multi-layer, microporous polyolefin membrane during annealing can range from about the melting point Tm or lower, from about 6O⁰C to (Tm - 1O⁰C), or in a range of from about 60°C to (Tm - 5⁰C). [00153] In one form, the multi-layer, microporous polyolefin membrane can be cross-linked (e.g., by ionizing radiation rays such as a-rays, (3-rays, 7-rays, electron beams, etc.) or can be subjected to a hydrophilic treatment (i.e., a treatment which makes the multi-layer, microporous polyolefin membrane more hydrophilic (e.g., a monomer-grafting treatment, a surfactant treatment, a corona-discharging treatment, etc.))). [00154] While the extrusion has been described in terms of producing two and three-layer extrudates, the extrusion step is not limited thereto. For example, a plurality of dies and/or die assemblies can be used to produce multi-layer extrudates having four or more layers using the principles of the extrusion dies and methods disclosed herein. [00155] All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent and for all jurisdictions in which such incorporation is permitted. [00156] While the illustrative forms disclosed herein have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside herein, including all features which would be treated as equivalents thereof by those skilled in the art to which this disclosure pertains.

[00157] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. Examples

[00158] Aspects of forms of the invention are described in the following examples.

The invention is not limited to the exemplified forms.

Example 1

[00159] Polyolefm resins are dry-blended as follows: (i) 99.625 parts by mass of a polyolefm (PO) composition comprising 20% by mass of ultra-high-molecular- weight polyethylene (UHMWPE) having a weight-average molecular weight (Mw) of 1.9 x 10⁶ and a molecular weight distribution ("MWD" defined as Mw/Mn) of 5.09, (ii) 80% by mass of high-density polyethylene (HDPE) having Mw of 7.5 x 10⁵ and an MWD of 11.85; and (iii) 0.375 parts by mass of tetralds[methylene-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate] methane as an antioxidant.

[00160] 30 parts by mass of liquid paraffin solvent having a viscosity of 50 cSt at 4O⁰C is introduced to the extruder. 70 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the first fluid inlet 32 in the dispersion stage and 30 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the second fluid inlet 33 in the second mixing stage. The temperature of each stage in the extruder is all in the range 150°C to 200°C. [00161] Mw, Mn, and MWD of the polyethylenes are determined using a High Temperature Size Exclusion Chromatograph, or "SEC", (GPC PL 220, Polymer Laboratories), equipped with a differential refractive index detector (DRI). Three PLgel Mixed-B columns (available from Polymer Laboratories) are used. The nominal flow rate is 0.5 cmVmin, and the nominal injection volume was 300 μL. Transfer lines, columns, and the DRI detector were contained in an oven maintained at 145°C. The measurement is made in accordance with the procedure disclosed in "Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)".

[00162] The GPC solvent used is filtered Aldrich reagent grade 1,2,4-Trichlorobenzene (TCB) containing approximately 1000 ppm of butylated hydroxy toluene (BHT). The TCB was degassed with an online degasser prior to introduction into the SEC. Polymer solutions were prepared by placing dry polymer in a glass container, adding the desired amount of above TCB solvent, then heating the mixture at 160°C with continuous agitation for about 2 hours. The concentration of UHMWPE solution was 0.25 to 0.75mg/ml. Sample solution will be filtered off-line before injecting to GPC with 2μm filter using a model SP260 Sample Prep Station (available from Polymer Laboratories). [00163] The separation efficiency of the column set is calibrated with a calibration curve generated using a seventeen individual polystyrene standards ranging in Mp from about 580 to about 10,000,000, which is used to generate the calibration curve. The polystyrene standards are obtained from Polymer Laboratories (Amherst, MA). A calibration curve (logMp vs. retention volume) is generated by recording the retention volume at the peak in the DRI signal for each PS standard, and fitting this data set to a 2nd-order polynomial. Samples are analyzed using IGOR Pro, available from Wave Metrics, Inc. [00164] The composition is extruded by placing 30 parts by mass of the polyethylene composition into the inlet hopper 24 of a co-rotating, double-screw extruder having a screw configuration as shown in Fig.3 to make a polyethylene solution. The extruder is a Model TEX 54 double-screw extruder obtained from Japan Steel Works of Tokyo, Japan. Example 2 [00165] A polyethylene solution is produced in the same manner as in Example 1, except that an extruder in Fig. 9 was used, 55 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the first fluid inlet in the dispersion stage, and 45 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the second fluid inlet in the second mixing stage. Example 3

[00166] A polyethylene solution is produced in the same manner as in Example 1, except that 90 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the first fluid inlet in the dispersion stage, and 10 weight % of the liquid paraffin based on the total amounts of the liquid paraffin is introduced into at the second fluid inlet in the second mixing stage. Comparative Example 1 [00167] A polyethylene solution is produced in the same manner as in Example 1, except that all of the liquid paraffin is introduced into at the first fluid inlet in the dispersion stage.

PROPERTIES

[00168] The properties of the polyethylene solution of Examples 1-3 and Comparative Example 1 are measured by the following methods. The results are shown in Tables 1.

(1) Output rate of the polyethylene solution (kg/h)

[00169] The output rate of the polyethylene solution is amount of the polyethylene solution per an hour extruded from a twin screw extruder. The weight of the polyethylene solution extruded per 36 seconds is measured five times and averaged. The weighing machine is an electronic balance made by Sartorius Corporation.

(2) Melt Index fg/lOmin)

[00170] In accordance with ASTM D1238, the melt index of the polyethylene solution is measured. The melt index may become to be higher value when the polymer and the solvent are not mixed homogeneously or the polymer deteriorates due to shear stress in a twin screw extruder.

* Mixing started with 50kg/h of total input rate of the polymer and the solvent. However, mixing was halted as a result because high pressure and high temperature over 250C in the extruder.

[00171] Table 1 shows that the inventive examples allow for high extrusion rates while providing a polyethylene solution with stable Melt Index and uniform appearance. On the other hand, the polyethylene solution of the Comparative Example can not be extruded well, even though output rate of the polyethylene solution is less than that of Examples 1, 2, and 3.

[00172] It is very difficult to uniformly mix and extrude compositions comprising a small amount of polymer dispersed in a large amount of liquid. Generally, more uniform mixing requires a lower output rate. The invention is based in part on the discovery that the extruder as described above exemplified in the Examples 1 through 3 can provide desirably uniform mixing at a desirably high output rate where the diluent is provided partially in the dispersion phase and partially in the mixing stage of the extruder. [00173] Using such an extruder capable of providing the diluent in this manner can give better membrane properties, more stable manufacturing operation, and higher productivity. [00174] The invention as disclosed is further illustrated but not limited by the following embodiments.

1. An extruder for combining polymer and diluent, the extruder comprising:

(a) an elongated housing having an inlet end, an outlet end and at least one bore disposed within said housing; (b) at least one elongated extruder shaft having an axis of rotation, said at least one elongated extruder shaft disposed within said at least one bore; and

(c) a plurality of extruder screw segments positioned along said at least one elongated extruder shaft in a fixed angular relationship therewith, said plurality of extruder screw segments selected to form multiple extruder stages, said multiple extruder stages comprising an inlet stage, and a dispersion stage, said plurality of extruder screw segments forming said dispersion stage including at least one first kneading segment comprising a plurality of kneading disks having at least one flight tip, wherein each adjacent flight tip is progressively offset by an angle θ, wherein 0° < θ < 90°.

2. The extruder of embodiment 1, wherein the number of kneading disks is greater than 10 and is selected to achieve an offset angle between a last kneading disk of said at least one first kneading segment and a first kneading disk of an adjacent kneading segment equal to about 0°.

3. The extruder of embodiment 1 or 2, wherein said multiple extruder stages further comprise a first mixing stage, a second mixing stage, and an outlet stage. 4. The extruder of any of embodiments 1-3, wherein said at least one elongated extruder shaft has a square, pentagonal, hexagonal or octagonal cross section or a cross section defined by a perimeter formed by a plurality of scallops.

5. The extruder of any of embodiments 1-4, wherein 40° < θ < 50°.

6. The extruder of any of embodiments 1-5, wherein the number of kneading disks of said at least one first kneading segment is greater than 15.

7. The extruder of any of embodiments 1-6, wherein said dispersion stage further comprises at least one second kneading segment, said at least one second kneading segment comprising five kneading disks, wherein each adjacent flight tip is progressively offset by an angle θ in the range of 40° to 50°.

8. The extruder of any of embodiments 1-7, wherein said dispersion stage further comprises at least one second lcneading segment, said at least one second lcneading segment comprising five lcneading disks, wherein each adjacent flight tip is progressively offset by an angle θ equal to about 45°.

9. A twin screw extruder for combining polymer and diluent, the extruder comprising: (a) an elongated housing having an inlet end, an outlet end an extruder shaft length L and a pair of intersecting bores disposed within said housing; (b) a pair of elongated extruder shafts each having an axis of rotation, said pair of elongated extruder shafts disposed within said pair of intersecting bores and drivable in at least one direction of rotation,

(c) a plurality of extruder screw segments positioned along said pair of elongated extruder shafts in a fixed angular relationship therewith, said plurality of extruder screw segments selected to form multiple extruder stages, said multiple extruder stages comprising an inlet stage having a length Li of about 3% L < Li < about 30% L, a dispersion stage having a length Ld of about 10% L < Ld < about 35% L, a first mixing stage having a length LmI of about 5% L < LmI < about 45% L, a second mixing stage having a length Lm2 of about 0% L < Lm2 < about 50% L, and an outlet stage having a length Lo of about 0% L < Lo < about 40% L;

(d) a material inlet adjacent said inlet end of said elongated barrel; and

(e) a first fluid inlet located within said dispersion stage for introducing a solvent.

10. The twin screw extruder of embodiment 9, wherein said plurality of extruder screw segments forming said dispersion stage includes at least one first lcneading segment comprising a plurality of lcneading disks having at least one flight tip, wherein each adjacent flight tip is progressively offset by an angle θ, wherein 0° < θ < 90°.

11. The twin screw extruder of embodiment 9 or 10, wherein the number of lcneading disks of the at least one first lcneading segment is greater than 10 and is selected to achieve an offset angle between a last lcneading disk of said at least one first lcneading segment and a first lcneading disk of an adjacent lcneading segment equal to about 0°. 12. The twin screw extruder of any of embodiments 9-11, wherein the number of kneading disks and said angle θ of the at least one first kneading segment are selected to enable an adjacent kneading segment to be positioned to achieve an offset angle between a last kneading disk of said at least one first kneading segment and a first kneading disk of said adjacent kneading segment substantially equivalent to said angle θ.

13. The extruder of any of embodiments 9-12, further comprising a second fluid inlet located within said second mixing stage for introducing a diluent portion.

14. The extruder of embodiment 13, further comprising a third fluid inlet located within said second mixing stage. 15. The extruder of claim 14, wherein the third fluid inlet is located downstream of the second fluid inlet.

16. The twin screw extruder of embodiment 11-15, wherein axes of rotation are substantially parallel, wherein said elongated extruder shafts are co-rotating or counter-rotating. 17. A process for extruding a mixture of polymer and diluent comprising:

(a) blending the polymer at a rate P in an inlet stage and conducting the blended polymer to a dispersion stage of the extruder;

(b) adding the at least a portion of the diluent to the blended polymer in the dispersion stage at a rate Sl, the diluent having a lower viscosity than the polymer, dispersing the diluent in the polymer, and conducting the dispersed diluent to a first mixing stage; and

(c) blending the dispersed diluent and the blended polymer in the first mixing stage to produce a third stage product, the third stage product comprising (i) the mixture in a first phase, (ii) a portion of the diluent in a second phase separate from the first phase, and (iii) a portion of the polymer in a third phase separate from the first and second phases; wherein the mixing energy in the first mixing stage is greater than the mixing energy in either the inlet stage or the dispersion stage.

18. The process of embodiment 17, wherein the first phase is produced at a rate of R₃ with R being about 0.9 x (P + Sl) or greater.

19. The process of embodiment 17 or 18, further comprising adding at least a second portion of the diluent to the blended polymer in the first mixing stage and/or a second mixing stage at a rate of S2, and dispersing the second portion of the diluent in the polymer; the weight ratio of S1/S2 being in the range of from 51 wt. %/49 wt. % to 99 wt. %/l wt. %.

20. The process of any of embodiments 17-19, wherein the second phase is produced at a rate that does not exceed 0.05 x S 1.

21. The process of any of embodiments 17-20, wherein the third phase is produced at a rate that does not exceed 0.05 x P.

22. The process of any of embodiments 17-21, wherein the rate of countercurrent diluent flow from the second region to the first region does not exceed 0.1 x Sl. 23. The process of any of embodiments 17-22, further comprising the steps of:

(e) extruding the mixture through an extrusion die, the extrusion die comprising a slotted die outlet through which a stream of the polymer solution is extruded; and

(f) cooling the extrudate to form a cooled extrudate.

24. The process of any of embodiments 17-23, further comprising the steps of: (g) removing the diluent from the cooled extrudate to form a diluent-removed cooled extrudate;

(h) drying the diluent-removed cooled extrudate to form the microporous membrane; and

(i) stretching the cooled extrudate and/or the microporous membrane. 25. The process of any of embodiments 17-24, wherein the extruder is a twin screw extruder comprising:

(a) an elongated housing having an inlet end, an outlet end an extruder shaft length L and a pair of intersecting bores disposed within said housing;

(b) a pair of elongated extruder shafts each having an axis of rotation, said pair of elongated extruder shafts disposed within said pair of intersecting bores and drivable in at least one direction of rotation,

(c) a plurality of extruder screw segments positioned along said pair of elongated extruder shafts in a fixed angular relationship therewith, said plurality of extruder screw segments selected to form multiple extruder stages, said multiple extruder stages comprising an inlet stage having a length Li of about 3% L < Li ≤ about 30% L, a dispersion stage having a length Ld of about 10% L < Ld < about 35% L, a first mixing stage having a length LmI of about 5% L < LmI < about 45% L, a second mixing stage having a length Lm2 of about 0% L < Lm2 < about 50% L, and an outlet stage having a length Lo of about 0% L < Lo < about 40% L;

(d) a material inlet adjacent said inlet end of said elongated barrel;

(e) a first fluid inlet located within said dispersion stage for introducing the first diluent portion, the first fluid inlet being located within a length of about 50% Ld from the beginning of the inlet of the dispersion stage; and

(f) a second fluid inlet located within said second mixing stage for introducing a second portion of diluent.

26. The product of any of embodiments 17-25. 27. A battery separator film for a lithium ion battery produced by the process of any of embodiments 17-26.

Claims

1. A system for producing an extrudate comprising combined polymer and diluent, comprising: a first extrusion means, a second extrusion means located downstream of and in fluid communication with the first extrusion means, a pumping means located downstream of the second extrusion means and in fluid communication with the second extrusion means, a separation means for removing at least a portion of any uncombined polymer from the second extrusion means' effluent, the separation means being located downstream of the second extrusion means and in fluid communication with the second extrusion means, a mixing means located downstream of the separation means and in fluid communication with the separation means, and at least one die located downstream of the mixing means and in fluid communication with the mixing means.

2. The system of claim 1, wherein the second extrusion means is a second extruder, comprising

(a) an elongated housing having an inlet end, an outlet end and at least one bore disposed within said housing;

(b) at least one elongated extruder shaft having an axis of rotation, said at least one elongated extruder shaft disposed within said at least one bore; and

3. The system of claim 2, wherein the number of kneading disks of the second extruder is greater than 10 and is selected to achieve an offset angle between a last kneading disk of said at least one first kneading segment and a first kneading disk of an adjacent kneading segment equal to about 0°.

4. The system of claims 2 or 3, wherein said multiple extruder stages of the second extruder further comprise a first mixing stage, a second mixing stage, and an outlet stage.

5. The system of claims 2-4, wherein said at least one elongated extruder shaft of the second extruder has a square, pentagonal, hexagonal or octagonal cross-section or a cross-section defined by a perimeter formed by a plurality of scallops.

6. The system of claims 2-5, wherein the first extrusion means is a first extruder, the extruder comprising: (a) an elongated housing having an inlet end, an outlet end an extruder shaft length L and a pair of intersecting bores disposed within said housing;

(b) a pair of elongated extruder shafts each having an axis of rotation, said pair of elongated extruder shafts disposed within said pair of intersecting bores and drivable in at least one direction of rotation, (c) a plurality of extruder screw segments positioned along said pair of elongated extruder shafts in a fixed angular relationship therewith, said plurality of extruder screw segments selected to form multiple extruder stages, said multiple extruder stages comprising an inlet stage having a length Li of about 3% L < Li < about 30% L, a dispersion stage having a length Ld of about 10% L < Ld < about 35% L, a first mixing stage having a length LmI of about 5% L < LmI < about 45% L, a second mixing stage having a length Lm2 of about 0% L < Lm2 < about 50% L, and an outlet stage having a length Lo of about 0% L < Lo < about 40% L;

(d) a material inlet adjacent said inlet end of said elongated barrel; and

(e) a first fluid inlet located within said dispersion stage for introducing a diluent portion.

7. The system of claim 6, wherein in the first extruder said plurality of extruder screw segments forming said dispersion stage includes at least one first kneading segment comprising a plurality of kneading disks having at least one flight tip, wherein each adjacent flight tip is progressively offset by an angle θ, wherein 0° < θ < 90°.

8. The system of claims 6 or 7, wherein in the first extruder the number of kneading disks of the at least one first kneading segment is greater than 10 and is selected to achieve an offset angle between a last kneading disk of said at least one first kneading segment and a first kneading disk of an adjacent kneading segment equal to about 0°.

9. The system of any of any of claims 6-8, wherein in the first extruder the number of kneading disks and said angle θ of the at least one first kneading segment are selected to enable an adjacent kneading segment to be positioned to achieve an offset angle between a last kneading disk of said at least one first kneading segment and a first kneading disk of said adjacent kneading segment substantially equivalent to said angle θ.

10. The system of any of claims 6-9, wherein the first extruder further comprises a second fluid inlet located within said second mixing stage for introducing a diluent, and wherein in the first extruder (i) the axes of rotation are substantially parallel, and (ii) said elongated extruder shafts are co-rotating or counter-rotating.

11. The system of any of claims 1-10 further including a second pumping means between the first and second extrusion means.

12. A process of producing a polymeric extrudate, comprising: (a) combining polymer and diluent in a first extruder and removing an effluent comprising combined polymer and diluent therefrom,

(b) conducting the effluent of the first extruder to a second extruder,

(c) conducting the effluent of the second extruder to a first pumping means,

(d) separating the effluent of the first pumping means into a retentate and a filtrate, and

(e) mixing the polymer and diluent in the filtrate to provide a mixed filtrate, and

(f) extruding the mixed filtrate through at least one die.

13. The process of claim 12 wherein the retentate is conducted away from the process.

14. The process of any of claims 12-13, wherein the first extruder is twin screw extruder and second extruder is single screw extruder.

15. The process of any of claims 12-14, further comprising filtering the first pumping means' effluent, conducting effluent of the first gear pump to the second extruder and conducting the filtrate away from the process.

16. The process of any of claims 12-15, wherein the extrudate is produced at a rate > 20 kg per hour.

17. The process of any of claims 12-16, wherein the combined polymer and .diluent in the first extruder and second extruder is exposed to a temperature in the range of 150°C to 250⁰C.

18. The process of any of claims 12-17, wherein the polymer is one or more polyolefin.

19. The process of claim 18, wherein the diluent comprises liquid paraffin, and wherein the amount of liquid paraffin in the combined polymer and diluent in the first extruder is in the range of 40 wt. % to 90 wt % based on the weight of polyolefin and liquid paraffin.

20. The process of any of claims 12-19, further comprising: conducting the effluent of the first extruder to a second pumping means; and conducting the effluent of the second pumping means to the second extruder.

21. The process of any of claims 12-20, wherein the first pumping means is a gear pump.

22. The process of any of claims 12-21, wherein the second pumping means is a gear pump.

23. A microporous film produced by the process of any of claims 12-21.

24. A battery separator film for a lithium ion battery produced by the process of any of claims 12-21.

25. An extruder for combining polymer and diluent, the extruder comprising:

^' (b) at least one elongated extruder shaft having an axis of rotation, said at least one elongated extruder shaft disposed within said at least one bore; and