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POLYMERIC STRUCTURES COMPRISING A
FIELD OF THE INVENTION
The present invention relates to polymer melt compositions, especially polymer melt compositions that can be processed into polymeric structures, especially polymeric structures in the form of fibers.
BACKGROUND OF THE INVENTION
Polymeric structures and polymer melt compositions from which the polymeric structures are obtained are generally known in the art. Particularly, hydroxyl polymer-containing polymeric structures such as starch filaments and/or fibers are generally known in the art. However, starch filaments and/or fibers made by prior art polymer melt compositions and/or polymer processing tend to have a sticky, viscid feeling and are water swellable and/or soluble. Both of these properties of prior art starch filaments and/or fibers negatively impact the use of such filaments and/or fibers in consumer products, especially in products such as fibrous structures and/or sanitary tissue products made from such fibrous structures.
Accordingly, there exists a need to identify polymer melt compositions and/orpolymeric structures obtained from such polymer melt compositions that overcome the disadvantages of the prior art polymer melt compositions and/or polymeric structures obtained therefrom.
SUMMARY OF THE INVENTION
The present invention fulfills the needs described above by providing a polymer melt composition and polymeric struc- 35 tures obtained therefrom that do not suffer from the disadvantages present in the prior art polymer melt compositions and polymeric structures obtained therefrom.
In one aspect of the present invention, a polymer melt composition comprising an aqueous mixture comprising a 40 hydroxyl polymer; a hydrophile/lipophile system comprising a hydrophile component and a lipophile component; and a crosslinking system comprising a crosslinking agent; wherein the hydrophile component facilitates dispersibility of the lipophile component in the aqueous mixture is pro- 45 vided. In other words, the hydrophile component allows the lipophile component to be distributed uniformly or substantially uniformly throughout the aqueous mixture.
In another aspect of the present invention, a polymeric structure derived from a polymer melt composition according to the present invention is provided.
In yet another aspect of the present invention, a fibrous structure comprising one or more polymeric structures according to the present invention is provided. 55
In still another aspect of the present invention, a single- or multi-ply sanitary tissue product comprising a fibrous structure according to the present invention is provided. Preferably, the tissue product exhibits a wet yield stress of from about 1000 to about 6000 Pa at a strain of at least about 1 to 60 about 10 as measured by the Wet Yield Stress Test Method described herein and/or exhibits a wet bulk of at least about 40% and/or at least about 50% of the dry bulk as measured by the Wet Bulk Test Method described herein.
In even another aspect of the present invention, a method 65 for making a polymer melt composition according to the present invention is provided.
In even yet another aspect of the present invention, a method for making a polymeric structure according to the present invention is provided.
In even still yet another aspect of the present invention, a polymeric structure in fiber form produced according to a method of the present invention is provided.
Accordingly, the present invention provides a polymer melt composition, a polymeric structure derived from the polymer melt composition, fibrous structures comprising the polymeric structures, sanitary tissue products comprising the fibrous structures and methods for making the polymer melt composition and the polymeric structure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic side view of a barrel of a twin screw extruder suitable for use in the present invention.
FIG. IB is a schematic side view of a screw and mixing element configuration suitable for use in the barrel of FIG. 1A.
FIG. 2 is a schematic side view of a process for synthesizing a polymeric structure in accordance with the present invention.
FIG. 3 is a schematic partial side view of the process of the present invention, showing an attenuation zone.
FIG. 4 is a schematic plan view taken along lines 4-4 of FIG. 3 and showing one possible arrangement of a plurality of extrusion nozzles arranged to provide polymeric structures of the present invention.
FIG. 5 is a view similar to that of FIG. 4 and showing one possible arrangement of orifices for providing a boundary air around the attenuation zone.
DETAILED DESCRIPTION OF THE INVENTION
Methods of the Present Invention
The methods of the present invention relate to producing polymeric structures from a polymer melt composition comprising a hydroxyl polymer and a hydrophile/lipophile system.
A. Polymer Melt Composition
"Polymer melt composition" as used herein means a composition that comprises a melt processed hydroxyl polymer. "Melt processed hydroxyl polymer" as used herein means any polymer that contains greater than 10% and/or greater than 20% and/or greater than 25% by weight hydroxyl groups and that has been melt processed, with or without the aid of an external plasticizer. More generally, melt processed hydroxyl polymers include polymers, which by the influence of elevated temperatures, pressure and/or external plasticizers may be softened to such a degree that they can be brought into a flowable state, and in this condition may be shaped as desired.
The polymer melt composition may be a composite containing a blend of polymers, wherein at least one is a melt processed hydroxyl polymer according to the present invention, and/or fillers both inorganic and organic, and/or fibers and/or foaming agents.
The polymer melt composition may already be formed or a melt processing step may need to be performed to convert a raw material hydroxyl polymer into a melt processed hydroxyl polymer, thus producing the polymer melt composition. Any suitable melt processing step known in the art may be used to convert the raw material hydroxyl polymer into the melt processed hydroxyl polymer. "Melt processing" as used
herein means any operation and/or process by which a polymer is softened to such a degree that it can be brought into a flowable state.
The polymer melt composition may have a shear viscosity, as measured according to the Shear Viscosity of a Polymer 5 Melt Composition Measurement Test Method described herein, of from about 1 Pascal-Seconds to about 300 Pascal-Seconds, preferably from about 2 Pascal-Seconds to about 200 Pascal-Seconds, and more preferably from about 3 Pascal-Seconds to about 150 Pascal-Seconds, as measured at 10 a shear rate of 3,000 sec-1 and at the processing temperature (23° C. to 100° C), depending upon the polymer processing process used to form the polymeric structures from the polymer melt composition.
In one embodiment, the normalized shear viscosity of the 15 polymer melt composition of the present invention must not increase more than 1.3 times the initial shear viscosity value after 70 minutes and/or 2 times the initial shear viscosity value after 130 minutes when measured at a shear rate of 3,000 sec-1 according to the Shear Viscosity Change Test 20 Method described herein.
The polymer melt composition may have a temperature of from about 23° C. to about 100° C. and/or from about 65° C. to about 95° C. and/or from about 70° C. to about 90° C. when 25 making fibers from the polymer melt composition. The polymer melt composition temperature is generally higher when making film and/or foam polymeric structures, as described below.
The pH of the polymer melt composition may be from 30 about 2.5 to about 9 and/or from about 3 to about 8.5 and/or from about 3.2 to about 8 and/or from about 3.2 to about 7.5.
In one embodiment, a polymer melt composition of the present invention may comprise from about 30% and/or 40% and/or 45% and/or 50% to about 75% and/or 80% and/or 85% 35 and/or 90% and/or 95% and/or 99.5% by weight of the polymer melt composition of a hydroxyl polymer. The hydroxyl polymer may have a weight average molecular weight greater than about 100,000 g/mol prior to crosslinking.
A crosslinking system may be present in the polymer melt 40 composition and/or may be added to the polymer melt composition before polymer processing of the polymer melt composition.
The polymer melt composition may comprise a) from about 30% and/or 40% and/or 45% and/or 50% to about 75% 45 and/or 80% and/or 85% by weight of the polymer melt composition of a hydroxyl polymer; b) a crosslinking system comprising from about 0.1% to about 10% by weight of the polymer melt composition of a crosslinking agent; and c) from about 10% and/or 15% and/or 20% to about 50% and/or 50 55% and/or 60% and/or 70% by weight of the polymer melt composition of external plasticizer e.g., water.
The crosslinking system of the present invention may further comprise, in addition to the crosslinking agent, a 55 crosslinking facilitator.
"Crosslinking facilitator" as used herein means any material that is capable of activating a crosslinking agent thereby transforming the crosslinking agent from its unactivated state to its activated state. In other words, when a crosslinking 60 agent is in its unactivated state, the hydroxyl polymer present in the polymer melt composition does not undergo unacceptable crosslinking as determined according to the Shear Viscosity Change Test Method described herein.
When a crosslinking agent in accordance with the present 65 invention is in its activated state, the hydroxyl polymer present in the polymeric structure may, and preferably does,
undergo acceptable crosslinking via the crosslinking agent as determined according to the Initial Total Wet Tensile Test Method described herein.
Upon crosslinking the hydroxyl polymer, the crosslinking agent becomes an integral part of the polymeric structure as a result of crosslinking the hydroxyl polymer as shown in the following schematic representation:
The crosslinking facilitator may include derivatives of the material that may exist after the transformation/activation of the crosslinking agent. For example, a crosslinking facilitator salt being chemically changed to its acid form and vice versa.
Nonlimiting examples of suitable crosslinking facilitators include acids having a pKa of between 2 and 6 or salts thereof. The crosslinking facilitators may be Bronsted Acids and/or salts thereof, preferably ammonium salts thereof.
In addition, metal salts, such as magnesium and zinc salts, can be used alone or in combination with Bronsted Acids and/or salts thereof, as crosslinking facilitators.
Nonlimiting examples of suitable crosslinking facilitators include acetic acid, benzoic acid, citric acid, formic acid, glycolic acid, lactic acid, maleic acid, phthalic acid, phosphoric acid, succinic acid and mixtures thereof and/or their salts, preferably their ammonium salts, such as ammonium glycolate, ammonium citrate and ammonium sulfate.
Synthesis of Polymer Melt Composition
A polymer melt composition of the present invention may be prepared using a screw extruder, such as a vented twin screw extruder.
A barrel 10 of an APV Baker (Peterborough, England) twin screw extruder is schematically illustrated in FIG. 1A. The barrel 10 is separated into eight zones, identified as zones 1-8. The barrel 10 encloses the extrusion screw and mixing elements, schematically shown in FIG. IB, and serves as a containment vessel during the extrusion process. A solid feed port 12 is disposed in zone 1 and a liquid feed port 14 is disposed in zone 1. A vent 16 is included in zone 7 for cooling and decreasing the liquid, such as water, content of the mixture prior to exiting the extruder. An optional vent stuffer, commercially available from APV Baker, can be employed to prevent the polymer melt composition from exiting through the vent 16. The flow of the polymer melt composition through the barrel 10 is from zone 1 exiting the barrel 10 at zone 8.
A screw and mixing element configuration for the twin screw extruder is schematically illustrated in FIG. IB. The twin screw extruder comprises a plurality of twin lead screws (TLS) (designated A and B) and single lead screws (SLS) (designated C and D) installed in series. Screw elements (A-D) are characterized by the number of continuous leads and the pitch of these leads.
A lead is a flight (at a given helix angle) that wraps the core of the screw element. The number of leads indicates the number of flights wrapping the core at any given location along the length of the screw. Increasing the number of leads reduces the volumetric capacity of the screw and increases the pressure generating capability of the screw.
The pitch of the screw is the distance needed for a flight to complete one revolution of the core. It is expressed as the number of screw element diameters per one complete revolution of a flight. Decreasing the pitch of the screw increases the pressure generated by the screw and decreases the volumetric capacity of the screw.
The length of a screw element is reported as the ratio of length of the element divided by the diameter of the element.
This example uses TLS and SLS. Screw element A is a TLS with a 1.0 pitch and a 1.5 length ratio. Screw element B is a TLS with a 1.0 pitch and a 1.0 L/D ratio. Screw element C is a SLS with a lM pitch and a 1.0 length ratio. Screw element D is a SLS and a lM pitch and a lh length ratio.
Bilobal paddles, E, serving as mixing elements, are also included in series with the SLS and TLS screw elements in order to enhance mixing. Various configurations of bilobal paddles and reversing elements F, single and twin lead screws threaded in the opposite direction, are used in order to control flow and corresponding mixing time.
In zone 1, the hydroxyl polymer is fed into the solid feed port at a rate of 230 grams/minute using a K-Tron (Pitman, N.J.) loss-in-weight feeder. This hydroxyl polymer is combined inside the extruder (zone 1) with water, an external plasticizer, added at the liquid feed at a rate of 146 grams/ minute using a Milton Roy (Ivyland, Pa.) diaphragm pump (1.9 gallon per hour pump head) to form a hydroxyl polymer/ water slurry. This slurry is then conveyed down the barrel of the extruder and cooked. Table 1 describes the temperature, pressure, and corresponding function of each zone of the extruder.
After the slurry exits the extruder, part of the melt processed hydroxyl polymer is dumped and another part (100 g) is fed into a Zenith®, type PEP II (Sanford N.C.) and pumped into a SMX style static mixer (Koch-Glitsch, Woodridge, 111.). The static mixer is used to combine additives such as crosslinking agent, crosslinking facilitator, hydrophile/lipophile system of the present invention, wetting surfactant, external plasticizer, such as water, with the melt processed hydroxyl polymer. The additives are pumped into the static mixer via PREP 100 HPLC pumps (Chrom Tech, Apple Valley MN). These pumps provide high pressure, low volume addition capability. The polymer melt composition of the present invention is ready to be processed by a polymer processing operation.
B. Polymer Processing
"Polymer processing" as used herein means any operation and/or process by which a polymeric structure comprising a processed hydroxyl polymer is formed from a polymer melt composition. Nonlimiting examples of polymer processing operations include extrusion, molding and/or fiber spinning.
Extrusion and molding (either casting or blown), typically produce films, sheets and various profile extrusions. Molding may include injection molding, blown molding and/or compression molding. Fiber spinning may include spun bonding, melt blowing, continuous filament producing and/ortow fiber producing.
A "processed hydroxyl polymer" as used herein means any hydroxyl polymer that has undergone a melt processing operation and a subsequent polymer processing operation.
C. Polymeric Structure
The polymer melt composition can be subjected to one or more polymer processing operations such that the polymer melt composition is processed into a polymeric structure comprising the hydroxyl polymer and a crosslinking system according to the present invention.
"Polymeric structure" as used herein means any physical structure formed as a result of processing a polymer melt composition in accordance with the present invention. Nonlimiting examples of polymeric structures in accordance with the present invention include fibers, films and/or foams.
The crosslinking system via the crosslinking agent crosslinks hydroxyl polymers together to produce the polymeric structure of the present invention, with or without being subjected to a curing step. In other words, the crosslinking system in accordance with the present invention acceptably crosslinks, as determined by the Initial Total Wet Tensile Test Method described herein, the hydroxyl polymers of a processed polymer melt composition together via the crosslinking agent to form an integral polymeric structure. The crosslinking agent is a "building block" for the polymeric structure. Without the crosslinking agent, no polymeric structure in accordance with the present invention could be formed.
Polymeric structures of the present invention do not include coatings and/or other surface treatments that are applied to a pre-existing form, such as a coating on a fiber, film or foam.
In one embodiment, the polymeric structure produced via a polymer processing operation may be cured at a curing temperature of from about 110° C. to about 200° C. and/or from about 120° C. to about 195° C. and/or from about 130° C. to about 185° C. for a time period of from about 0.01 and/or 1 and/or 5 and/or 15 seconds to about 60 minutes and/or from about 20 seconds to about 45 minutes and/or from about 30 seconds to about 30 minutes. Alternative curing methods may include radiation methods such as UV, e-beam, IR and other temperature-raising methods.
Further, the polymeric structure may also be cured at room temperature for days, either after curing at above room temperature or instead of curing at above room temperature.
The polymeric structure may exhibit an initial total wet tensile, as measured by the Initial Total Wet Tensile Test Method described herein, of at least about 1.18 g/cm (3 g/in) and/or at least about 1.57 g/cm (4 g/in) and/or at least about 1.97 g/cm (5 g/in) to about 23.62 g/cm (60 g/in) and/or to about 21.65 g/cm (55 g/in) and/or to about 19.69 g/cm (50 g/in).
In one embodiment, the polymeric structure exhibits a contact angle of less than 40° after 1 second as measured by the Contact Angle Test Method described herein.
The polymeric structures of the present invention may include melt spun fibers and/or spunbond fibers, staple fibers, hollow fibers, shaped fibers, such as multi-lobal fibers and multicomponent fibers, especially bicomponent fibers. The multicomponent fibers, especially bicomponent fibers, may be in a side-by-side, sheath-core, segmented pie, ribbon,
islands-in-the-sea configuration, or any combination thereof. The sheath may be continuous or non-continuous around the core. The ratio of the weight of the sheath to the core can be from about 5:95 to about 95:5. The fibers of the present invention may have different geometries that include round, 5 elliptical, star shaped, rectangular, and other various eccentricities.
The fibers of the present invention may have a fiber diameter of less than about 50 microns and/or less than about 20 microns and/or less than about 10 microns and/or less than 10 about 8 microns and/or less than about 6 microns and/or less than about 4 microns as measured by the Fiber Diameter Test Method described herein.
In another embodiment, the polymeric structures of the present invention may include a multiconstituent polymeric 15 structure, such as a multicomponent fiber, comprising a hydroxyl polymer of the present invention along with a thermoplastic, water-insoluble polymer. A multicomponent fiber, as used herein, means a fiber having more than one separate part in spatial relationship to one another. Multicomponent 20 fibers include bicomponent fibers, which is defined as a fiber having two separate parts in a spatial relationship to one another. The different components of multicomponent fibers can be arranged in substantially distinct regions across the cross-section of the fiber and extend continuously along the 25 length of the fiber.
A nonlimiting example of such a multicomponent fiber, specifically a bicomponent fiber, is a bicomponent fiber in which the hydroxyl polymer of the present invention represents the core of the fiber and the thermoplastic, water-in- 30 soluble polymer represents the sheath, which surrounds or substantially surrounds the core of the fiber. The polymer melt composition from which such a polymeric structure is derived preferably includes the hydroxyl polymer and the thermoplastic, water-insoluble polymer. 35
In another multicomponent, especially bicomponent fiber embodiment, the sheath may comprise a hydroxyl polymer and a crosslinking system having a crosslinking agent, and the core may comprise a hydroxyl polymer and a crosslinking system having a crosslinking agent. With respect to the sheath 40 and core, the hydroxyl polymer may be the same or different and the crosslinking agent may be the same or different. Further, the level of hydroxyl polymer may be the same or different and the level of crosslinking agent may be the same or different. 45
One or more polymeric structures of the present invention may be incorporated into a multi-polymeric structure product, such as a fibrous structure and/or web, if the polymeric structures are in the form of fibers. Such a multi-polymeric structure product may ultimately be incorporated into a com- 50 mercial product, such as a single- or multi-ply sanitary tissue product, such as facial tissue, bath tissue, paper towels and/or wipes, feminine care products, diapers, writing papers, cores, such as tissue cores, and other types of paper products.
Synthesis of Polymeric Structure
Nonlimiting examples of processes for preparing polymeric structures in accordance with the present invention follow. 60
i) Fiber Formation
A polymer melt composition is prepared according to the Synthesis of a Polymer Melt Composition described above. As shown in FIG. 2, the polymer melt composition may be 65 processed into a polymeric structure. The polymer melt composition present in an extruder 102 is pumped to a die 104
using pump 103, such as a Zenith®, type PEP II, having a capacity of 0.6 cubic centimeters per revolution (cc/rev), manufactured by Parker Hannifin Corporation, Zenith Pumps division, of Sanford, N.C., USA. The hydroxyl polymer's, such as starch, flow to die 104 is controlled by adjusting the number of revolutions per minute (rpm) of the pump 103. Pipes connecting the extruder 102, the pump 103, the die 104, and optionally a mixer 116 are electrically heated and thermostatically controlled to 65° C.
The die 104 has several rows of circular extrusion nozzles 200 spaced from one another at a pitch P (FIG. 3) of about 1.524 millimeters (about 0.060 inches). The nozzles 200 have individual inner diameters D2 of about 0.305 millimeters (about 0.012 inches) and individual outside diameters (Dl) of about 0.813 millimeters (about 0.032 inches). Each individual nozzle 200 is encircled by an annular and divergently flared orifice 250 formed in a plate 260 (FIGS. 3 and 4) having a thickness of about 1.9 millimeters (about 0.075 inches). A pattern of a plurality of the divergently flared orifices 250 in the plate 260 correspond to a pattern of extrusion nozzles 200. The orifices 250 have a larger diameter D4 (FIGS. 3 and 4) of about 1.372 millimeters (about 0.054 inches) and a smaller diameter D3 of 1.17 millimeters (about 0.046 inches) for attenuation air. The plate 260 was fixed so that the embryonic fibers 110 being extruded through the nozzles 200 are surrounded and attenuated by generally cylindrical, humidified air streams supplied through the orifices 250. The nozzles can extend to a distance from about 1.5 mm to about 4 mm, and more specifically from about 2 mm to about 3 mm, beyond a surface 261 of the plate 260 (FIG. 3). As shown in FIG. 5, a plurality of boundary-air orifices 300, is formed by plugging nozzles of two outside rows on each side of the plurality of nozzles, as viewed in plane, so that each of the boundarylayer orifice comprised a annular aperture 250 described herein above. Additionally, every other row and every other column of the remaining capillary nozzles are blocked, increasing the spacing between active capillary nozzles
As shown in FIG. 2, attenuation air can be provided by heating compressed air from a source 106 by an electricalresistance heater 108, for example, a heater manufactured by Chromalox, Division of Emerson Electric, of Pittsburgh, Pa., USA. An appropriate quantity of steam 105 at an absolute pressure of from about 240 to about 420 kiloPascals (kPa), controlled by a globe valve (not shown), is added to saturate or nearly saturate the heated air at the conditions in the electrically heated, thermostatically controlled delivery pipe 115. Condensate is removed in an electrically heated, thermostatically controlled, separator 107. The attenuating air has an absolute pressure from about 130 kPa to about 310 kPa, measured in the pipe 115. The polymeric structure fibers 110 being extruded have a moisture content of from about 20% and/or 25% to about 50% and/or 55% by weight. The polymer structure fibers 110 are dried by a drying air stream 109 having a temperature from about 149° C. (about 300° F.) to about 315° C. (about 600° F.) by an electrical resistance heater (not shown) supplied through drying nozzles 112 and discharged at an angle generally perpendicular relative to the general orientation of the embryonic fibers being extruded. The polymeric structure fibers are dried from about 45% moisture content to about 15% moisture content (i.e., from a consistency of about 55% to a consistency of about 85%) and are collected on a collection device 111, such as, for example, a movable foraminous belt.