CA2242470A1 - Fibers flash-spun from blends of polyolefin polymers - Google Patents
Fibers flash-spun from blends of polyolefin polymers Download PDFInfo
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- CA2242470A1 CA2242470A1 CA002242470A CA2242470A CA2242470A1 CA 2242470 A1 CA2242470 A1 CA 2242470A1 CA 002242470 A CA002242470 A CA 002242470A CA 2242470 A CA2242470 A CA 2242470A CA 2242470 A1 CA2242470 A1 CA 2242470A1
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- polyethylene
- polypropylene
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/11—Flash-spinning
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/28—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from copolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F6/32—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from copolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising halogenated hydrocarbons as the major constituent
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/44—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds
- D01F6/46—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds of polyolefins
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/44—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds
- D01F6/52—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds of polymers of unsaturated carboxylic acids or unsaturated esters
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/88—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds
- D01F6/90—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds of polyamides
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/88—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds
- D01F6/92—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds of polyesters
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
Abstract
A plexifilamentary strand of film-fibrils having a tensile strength of at least 1 gpd and a surface area, measured by the BET nitrogen adsorption method, greater than 2 m2/g. The film-fibrils are comprised of at least 20 % by weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5 % by weight of each of the filmfibrils. A process for the production of such a strand is also provided that includes the steps of forming a spin solution of polyethylene and polypropylene polymers in a solvent and spinning the spin solution at a pressure that is greater than the autogenous pressure of the spin solution into a region of substantially lower pressure and at a temperature at least 50 ~C higher than the atmospheric boiling point of the solvent.
Description
FIBERS FLASH-SPUN FROM
BLENDS OF POLYOLEFIN POLYMERS
BACKGROUND OF THE INVENTION
S This invention relates to fibers that are flash-sp~n from blends of polvmers that include two or more polyolefin polymers. More particularly~ the invention relates to flash-spun plexifilamentary fibers comprised of ;3 polvmer blend that inc]udes sis~nifican~
poiyethylene and polypropylene components.
The art of flash-spinning strands of plexifilamentary film-fibriis from 10 pok~mer in a solution or a dispersion is known in the art. The term "plexifilamentary"
means a three-dimensional integral network of a multitude of thin. ribbon-like. film-fibril elemerlts of random len_th and with a mean film thickness of less than about ~ microns and with a median fibril width of less than about 25 microns In plexifilamentarvstl~ctures~ the film-fibril elements are generallv coextensivel~l aligned with the ion itudinal axis of the struc~ure and they intermittentlv unite and separate atirre~ulal intervals in various places tllroughout the length, width and thickness of the s~ructure to forrn a continuous three-dimensional network.
U.S. Patent 3,Z7,784 to Blades et al. ~assigned to E. I. du Pont de ?~emours ,~~ Company ("DuPont")) describes a process wherein a polymer in solution is for~varded ~0 continuously to a spin orifice at a temperature above the boiling point of the solvent. and at autogenous pressure or greater, and is flash-spun into a zone of lower temperalure and substantially lower pressu}e to generate a strand of plexifilamentary material. U.S.
Patent 3.'~7~794 to Anderson et al. (assigned to ~UPollt) teaches that ple:~ifilamentary film-fibrils are best obtained from solulion when fiber-forming polymel is dissolved in a ~5 solvenl at a temperature and at a pressure above the pressure at which two liquid phases form, which pressure is ~enerally known as the cloud point pressure at the giventemperature. This solution is passed to a pressure let-down chamber, where the pressure decreases below the cloud point pressure for the solution thereby causing phase separation. The resulting two phase dispersion of a solvent-rich phase in a polymer-ricl 30 phase is discharged throu~h a spinneret orifice to form the plexifilamentary strand.
U.S. Patent 3.484,899 to Smith (assigned to DuPont~ discloses an apparatus with a horizontally oriented spin orifice through which a plexifilamentary strand can be flash-spun. The polymer strand is conventionally directed against a rotating lobed deflector baffle to spread the strand into a more planar web structure that the baffle 3:~ allernatelv directs to the left and right as the ~ eb descends to a moving collection belt.
The fibrous sheet formed on the belt has ple~ifilamentary fiim-fibril networks oriented in an ovcrlapping multi-directional configuration.
W O 97125461 PCT~US97/00161 European Patent Publication 645480 filed by 17ni~ika Ltd. discloses a plexifilamentarv fiber structure that is flash-spun from a solut~on of polyolefin and polyester polymers dissolved in methylene chloride. The polyolefins disclosed include polyethylene and polypropylene polymers and copolymers. The polyesters disclosedS include polyethvlene terephthalate and polybutylene terephthalate. The Unitika patent discloses that the mixing ratio (by weight) of the polyolefin to the polyester is from 5/95 to 95/5.
British Patent Specification 970,070 (assigned to I)uPont) discloses nonwoven sheets made from fibers that were flash-spun from a blend of polyethylene and l 0 a minor amount of another polymer such as polyamide, polyvinyl chloride, polystyrene, or polyurethane. The patent suggests that a "blends of linear polyethylene and minor amounts of branched polyethylene, polypropylene, polybutylene, polyisobutylene, polybutadiene. polyvinyl chloride, or cellulose acetate" might be advantageous.
However, the patent does not appear to disclose the actual flash-spinning of polyethylene 15 and polypropylene blends.
Manv improvements to the basic flash-spinning process have been reported or patented over the years. An alternative process for flash-spinning a plexifilamentary strand accordin~ to which a mechanically generated dispersion of melt-spinnable polymer, carbon dioxide and water under high pressure is flashed through a spin orifice 20 into a zone of substantially lower temperature and pressure to form a plexifilamentary strand is disclosed in U.S. Patent 5,192,468 to Coates et al. (assigned to DuPont). Flash-spirming of polyethylene to produce non-woven sheets is practiced commercially and is the subject of numerous patents, including U.S. Patent 3,851,023 to Brethauer et al (assigned to DuPont).
' 5 The commercial application for flash-spinning has been primarily directed to the manufacture of sheets of bonded polyethylene plexifilaments. Polyethylene is an ideal polymer for flash-spinning. It can be flash-spun into a strong well fibrillated plexifilarnent over a wide range of processing conditions. However. its melting point is relatively low (~140~ C), and therefore it is not suitable for applications where end use 30 temperatures are 140~ C or higher. One such application is steam sterilizable sterile packing, and CSR (i.e.. central storage room) ~vraps used in the hospitals for steam sterilization. Polypropylene, on the other hand, has a higher melting point ( 165~ C) that is above the temperatures used during steam sterilization. However, polypropylene is more difficult to flash-spin than polyethylene and as-spun fibers are not as strong. In 35 addition, polypropylene requires substantially higher Spill temperatures than polyethylene.
W O 97/2~461 PCTrUS97/00161 There is a need for a flash-spun product that enJoys the streneth and ease of processin~ associated with polyethylene, but that can withstand higher end use temperatures.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a ple~ifilamentary strand having a tensile strengtll of at least I gpd and a surface area, measured by the BET
nitrogen adsorption method. greater than 2 m2/g comprising a three dimensional integral plexus of semicrystalline, polymeric, fibrous elements, the elements being co-extensively aligned with the network axis and having the stmctural conf;guration of oriented film-fibrils. The film-fibrils have a mean film thichless of less than 4 microns, a median fibril width of less than 25 microns, and are comprised of at least 20% by weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the fiim-fibrils. Preferably, the film-fibrils are comprised of at least 75% by weight of polyethylene and polypropylene, and more preferably ar~ comprised of at least 90% by weight of polyethylene and polypropylene wherein the polyethylene and polypropylene each comprise at least 35% by weight of each of the film-fibrils.
The invention is also directed to a procçss for the production of flash-spun plexifilamentary film-fibril strands of a polymer that is comprised of at least 75% b~
weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the film-fibrils. The process includes the steps of forming a spin solution of polyethylene and polypropyiene polymers in a solvent and spinning the spin solution at a pressure that is greater than the autogenous pressure of ~5 the spin solution into a region of substantially lower pressure and at a temperature at least 50~ C higher than the atmospheric boiling point of the solvent. The solvent in the spin solution has an atmospheric boiling point between 0~ C and 100" C, and is comprised of at least 50% of solvents selected from the group consisting of hydrocarbons, chlorinated hydrocarbons, hydrochlorofluorocarbons and alcohols.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the presently preferred embodiments of the invention and, together with the description, serve to explain the principles of the invention.Figure I is a plot of the cloud point data for 9% by weight polypropylene solution in a solvent comprised of methylene chloride and HFC-43 1 0mee at 3 different solvent ratios.
W O 97/25461 PCT~US97/00161 Figure 2 is a plot of the cloud point data ~or a 12% by weight poivethyiene solution in a solvent comprised of methylene chloride and HFC-43 1 0mee at 5 different solvent ratios.
Figure 3 is a plot of the cloud point data for I ') a 20% by weight polyethylenesolution in a solvent comprised of 60/40 n-pentane/8~.5% pure cyclopentane. and 2) a 12% by weight polypropylene solution in a solvent comprised of 60140 n-pentane/82.5~~O
pure cyclopentane.
DETAILED DESCRIPTION
Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated below.
The flash-spun plexifilamentary fibers of the invention are comprised of blends of thermoplastic polymers with significant polyethylene and polypropylenecomponents. These fibers may be spun using the apparatus and the solution flash-I 5 spinning process disclosed and fully described in U.S. Patent 5,147,5~6 to ~hin et al.
Alternatively, the plexifilamentary fibers of the invention can be flash-spun bv the dispersion flash-spinning process disclosed in U.S. Patent 5,192,468 to Coates et al., according to which a plexifilamentary fiber is spun from a mechanically generated dispersion of polymer in water ~nd carbon dioxide. It is anticipated that in commercial applications, the plexifil~mentary sheets of the invention would most likely be produced using the solution flash-spinning apparatus disclosed in U.S. Patent 3,851,023 to Brethauer et al.
The process for flash-spinning plexifilaments from polyolefin polymer blends in a solvent operates under conditions of elevated temperature and pressure. The '5 polymeric starting material is normally not soluble in the selected solvent under normal temperature and pressure conditions but forrns a solution at certain elevated temperatures and pressures. In the flash-spinning process for making plexifilaments, pressure is decreased below the cloud point to cause phase separation, just before the solution is passed through a spirmeret. When the solution pressure is lowered below the cloud point pressure, the solution phase separates into a polymer-rich phase and a solvent-rich phase.
Upon passing through the spinneret at very high speed into a zone of substantially lower pressure, the solvent flashes off quickly such that the polymer material present in the polymer-rich phase freezes in an elongated plexifilamentary form.
The morphology of plexifilamentary strands obtained by the solution flash-3 5 spinning of a polymer is greatly influenced by the level of pressure used for spinning.
When the spin pressure is much greater than the cloud point pressure of the spin mixture, coarse plexifilamentary "yarn-like" strands are usually obtained. As the spin pressure is gradually decreased, the average distance between the tie points generally becomes shorter ~vllile the fibrils of the strands become progressively fil~er. Whell the spin pressure approaches the cloud point pressure of the spin mixture, very fine fibrils are normally obtained, and the distance between the tie points becomes very short. As the spin pressure is further reduced to below the cloud point pressure, the distance between 5 the tie points becomes longer. Well fibrillated plexifilaments, which are most suitable for sheet formation, are usually obtained when spin pressures slightly below the cloud point pressure are used. The use of pressures which are too much lower than the cloud point pressure of the spin mixture generally leads to a relatively coarse plexifilamentary structure. The effect of spin pressure on fiber molphology also depends on the types OI~
10 poJymers and solvents being spun and the concentration of the polymer in the solvent. At higher concentrations of polvmer in the solvent. foams may be obtained rather than plexifilaments, even at spinning pressures slightly below the cloud point pressure of the solution. In some cases. well fibrillated plexifilaments can be obtained even at spin pressures slightly higher than the cloud point pressure of the spin mixture and at polymer 15 concentrations above ~0% of the spin solution. Therefore, the effect of spin pressure discussed herein is intended merely as a guide in selecting the spinning conditions and not as a general rule.
The polyethylene that has been flash-spun with polypropylene to produce the blended polyolefin polymer plexifilaments of the invention is high density polyethylene.
20 However, it is anticipated that other types of polyethylene, including low density polyethylene and linear Jow density polyethylene, could be used in making the polyolefin blend plexifilaments of the invention. The polypropylene that has been flash~spun with polyethylene to produce the blended polyolefin plexifilaments of the invention is isotactic polypropylene and syndiotactic polypropylene.
'5 While the temperature and pressure conditions that can be withstood by solution flash-spinnine equipment are quite broad, it is generally prei'erred not to operate under extreme temperature and pressure conditions. The preferred temperature range for solution flash-spinning the blends of polyethylene and polypropylene is about 150~ to 250~ C while the preferred pressure range for flash-spinning such blends is in the range 30 of autogenous pressure to 50 MPa, and more preferably in the range of autogenous pressure to 25 MPa. Therefore, if plexifilaments are to be flash-spun from blends of polyethylene and polypropylene from a solution, the solvent should dissolve the polymers at pressures and temperatures within the preferred ranges.
Unfortunately, it has proved to be very difficult to flash-spin polypropylene ~5 plexifilarnentary fibers from many common solvents, including room temperature boiling hydrocarbon solvents and strong solvents such as methylene chloride, dichloroethane and cyclopentane. We have now found that polypropyJene plcxilllall~cll~ can bc llash-spLIll il the polypropylene is blended ~vith polyethylene in sufficient quantities and/or the strong W O 97/25461 PCTfUS97/00161 solvents are blended with weaker solvents. Interestingly, we have found that many blends of polyethylene and polypropylene cannot be flash-spun from many of the important flash-spinning solvents. For example, attempts to flash-spin a blend of 75%
polypropylene and 25% polyethylene from methylene chloride blended ~A~ith a weaker solvent were unsuccessful.
Polyethylene and polypropylene do not form a compatible polymer blend within the range of useful blend ratios (e.g. from 5/95 to 95/5). Consequently, solutions of polyethylene and polypropylene become cloudy when they are dissolved together in a common solvent. For example, polyethylene solutions in 80/2() methylene 10 chloride/HFC-43 1 Omee form a clear, single phase solution as long as pressure applied to the solution at any given temperature is higher than the cloud point pressure of the solution. Likewise, polypropylene solutions in 80/20 methylene chloride/HFC-43 1 Omee form a clear~ sin_le phase solution as long as pressure applied to the solution is higher than the cloud point pressure. However, if both polyethylene and polypropylene are 1~ added to the same common solvent, the solution will not be a clear, single phase solution regardless of the temperature and pressure applied (within a reasonable range). Instead, the solutions will become cloudy since polyethylene is not compatible with polypropylene.
Therefore, there is no cloud point pressure for solutions of polyethylene and ~0 polypropylene blends in a common solvent. Such blends always exist as a dispersion in a phase-separated state. Consequently, when blends of polyethylene and polypropylene are flash-spun using a common solvent, cloud point pressure of individual componentspresent in the "solution" is used. In the case of polyethylene and polypropyiene blends.
polyethylene always gives higher cloud point pressures than polypropyiene. Thus, the ~5 blends are mixed at a pressure higher than the cloud point pressure of polyethylene~ and optimum spin pressures are deter~nined empirically. However, it has been found that optimum spin conditions for the blends are usually closer to the polyethylene spin conditions than to the polypropylene spin conditions.
Good solvents for solution flash-spinning polyethylene and polypropylene 30 polymer blends are generally similar to those used for flash-spinning polyethylene.
However, it is more difficult to select a proper flash-spinning agent for the blends, because the spin agent to be used has to satisfy both of the components present in the blends. Mixed solvent systems have been found to be particularly suited for flash-spinning polyethyleneipolypropylene polymer blends, because solvent power can be3~ adjusted to satisfy both blend components by ch~ngin~ the solvent ratio. Solvents that may be used for flash-spinning blends of polyethylene and polypropylene include mixtures containing as a majcr component hydrocarbons, chlorillated hydrocarbolls, hydrochlorofluorocarbons or certain types of alcohols. Preferred solvents for solution flash-spinning blends of polyethylene and poiypropylene mclude mixed s'olvent sy'stems based on methylene chloride, dichloroethylene, cyclopentane, pentane, HCFC-141b, and bromochloromethane. Co-solvents that can be used in conjunction with these main solvents to improve electrostatic charging and/or to reduce solvent power include hydrofluorocarbons such as HFC-431 Omee, hydrofluoroethers such as methyl(perfluorobutyl)ether, and perfluorinated compounds such as perfluoropentane and perfluoro-N-methylmorpholine.
The apparatus and procedure for determining the cloud point pressures of a polymer/solvent combination are those described in the above cited U.S. patent 5,147,586 10 to Shin et al.
Figure 1 is a plot of the cloud point data for a 9% by weight polypropylene solution in a solvent comprised of methylene chloride and HFC-431 Omee at 3 different solvent ratios (60/40, curve l; 70/30, cwe 2; and 80/20, cwe 3).
Figure 2 is a plot of the cloud point data for a 12% by weight polyethylene 15 solution in a solvent comprised of methylene chloride and HFC-431 Omee at S different solvent ratios (75/25, cwe 4; 80/20, curve 5; 85/15, curve 6; 90/lO, cwe 7; and 100/0,~
cwe 8).
Figure 3 is a plot of the cloud point data for (1) a 20% by weight polyethylene solution in a solvent comprised of 60/40 n-pentane/82.5% pure 20 cyclopentane, cwe 9; and (2) a 12% by weight polypropylene solution in a solvent comprised of 60/40 n-pentane/82.5% pure cyclopentane, cwe 10.
This invention will now illustrated by the following non-limiting examples which are intended to illustrate the invention and not to limit the invention in any manner.
EXAMPLES
Test Methods In the description above and in the non-limiting examples that follow, the 30 following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials, and TAPPI refers to the Technical Association of the Pulp and Paper Industry.
The denier of the strand is determined from the weight of a 15 cm sample length of strand.
Tenacity, elongation and tou~hness of the flash-spun strand are determined i~ith an Instron tensile-testing machine. The strands are conditioned and tested at 70~F
and 65% relative hurnidity. The strands are then twisted to 10 tu~ns per inch and mounted in the jaws of the Instron Tester. A two-inch gauge length was used with an A~NDED SHEET
W O 97/25461 PCT~US97/00161 initial elongation rate of 4 inches per minute. The tenaci~y at break is recorded in grams per denier (gpd). The elongation at break is recorded as a percentage of the two-inch gauge length of the sample. Tol~hness is a measure of the work required to break the sample divided by the denier of the sample and is recorded in gpd. Modulus corresponds to the slope of the stress/strain curve and is expressed in units of gpd.
Fiber qualitv is evaluated using a subjective scale of 0 to 3, with a 3 being the highest quality rating. Under the evaluation procedure, a 10 inch length of a plexifilamentary strand is removed from a fiber batt. The web is spread and mounted on a dark substrate. The fiber quality rating is an average of three subJective ratings, one for fineness of the fiber (finer fibers receive higher ratings), one for the continuity of the fiber strand (continuous plexifilamentary strands receive a higher rating), and the other for the frequency of the ties (more networked ple~ifil~ nt~ry strands receive a higher rating).
Fiber fineness is measured using a technique similar to that disclosed in U.S.
] 5 Patent 5,371,810 to A. Ganesh Vaidyanathan dated 6 December 1994, and which is hereby incorporated by reference. This technique quantitatively analyzes fibril size in webs of fiber. The webs are opened up by hand and imaged using a microscopic lens.
The image is then digitized and computer analyzed to determine the mean fibril width and standard deviation. However, some smaller fibrils may be so tightly bunched together and have such short fibril length, that the fibrils appear as part of a large fibril and are counted as such. Tight fibril bllnçhing and short fibril length (distance from tie point to tie point) can effectively prevent analysis of the fineness of individual fibrils in the bunched fibrils. Thus, the term "apparent fibril size" is used to describe or characterize fibers of plexifilamentary strands.
The surface area of the plexifilamentary t;lm-fibril strand product is another measure of the degree and fineness of fibrillation of the flash-spun product. Surface area is measured by the BET nitrogen absorption method of S. Brunauer~ P. H. Emrnett and E.
Teller, J. Am. Chem. Soc., V. 60 p 309-319 (1938) and is reported as m2/g.
Test Apparatus for Examples I - 7 The apparatus used in the examples I - 7 is the spinning apparatus described in IJ.S. Patent 5,147,5~6. The apparatus consists of two high pressure cylindrical chambers. each e~uipped with a piston which is adapted to apply pressure to the contents of the chamber. The cylinders have an inside diameter of 1.0 incl-l (2.54 cm) and each has an internal capacity of 50 cubic centimeters. The cylinders are connected to each other at one end through a 3~32 inch (0.23 cm) diameter channel and a mixing chamber containing a series of fine mesh screens that act as a static mixer. Mixing is accomplished by forcing the contents of the vessel back and forth between the two W O 97n~461 PCT/US97100161 cylinders through the static mixer. A spirmeret assembly with a c~uick-acting means for opening the orifice is attached to the channel through a tee. The spinneret assembly consists of a lead hole of 0.25 inch (0.63 cm) diameter and about 2.0 inch (5.08 cm) length, and a spinneret orifice with both a length and a diameter shown in the table below. Orifice measurements are expressed in mils [Imil = 0.025~ mm]. In Example 4, a cylindrical turmel was located at the exit of the spin orifice. Tl1e diameter of the tunnel was 200 mils and the length was 100 mils. The tunnel was used in order to obtain a more columnar jet of flash-spun material. The pistons are driven by high pressure water supplied by a hydraulic system.
In the tests reported in Exarnples l - 7, the apparatus described above was charged with pellets of a polyethylene and polypropylene polymer and a solvent. The polyethylene was high density polyethylene (HDPE) with a melt index of 0.7S, a density of 0.957, a number average molecular weight of 21,000 and a wei~ht average molecular weight of 121,000. The polypropylene was isotactic polypropylene with a melt index of 15 0.9 and a number average molecular weight of 9~,000 and a weight average molecular weight of ~3 l ,000. High pressure water was used to drive the pistons to generate a mixing pressure of between l 500 and 3000 psi ( 10,340 - 10,68() kPa). The polymer and solvent were ne~ct heated to mixing temperature and held at that temperature for about an hour during which time the pistons were used to alternately establish a differential 20 pressure of about 50 psi (345 kPa) or higher between the two cylinders so as to repeatedly force the polymer and solvent through the mixing charmel from one cylinder to the other to provide mixing and effect forrnation of a spin mixture. The spin mixture temperature was then raised to the final spin temperature, and held there for about 15 minutes to equilibrate the temperature. during which time mixing was continued. In order tosimulate a pressure letdown chamber, the pressure of the spin mixture was reduced to a desired spinning pressure just prior to spinning. This was accomplished by opening a valve between the spin cell and a much larger tank of high pressure ~ater ("the accumulator") held at the desired spinning pressure. The spinneret orifice is opened about one to five seconds after the opening of the valve between the spin cell and the 30 accumulator. This period roughly corresponds to the residence ~ime in the letdown chamber of a commercial spinning apparatus. The resultant flash-spun product is collected in a stainless steel open mesh screen basket. Tl~e pressure recorded just before the spinneret using a computer during spinning is entered as the spin pressure.
The experimental conditions and the results for Examples I - 7 are given below in the Tables 1. All the test data not originally obtained in the SI system of units has been converted to the SI units.
Table I
POLYI~IER OLVENT MIX111G SPI~NING Prope~esQ10 Pl O~iflce E~ P/P Wt S1/S2 Press (tunnel) Press Mod Ten E ~ET
No Name % % 1 2 Wt% ~C Min MPa mils MPa ~C Den gpd gpd % SA Type PP 50 12 CH2CI2 HFC-43-1ûmee ao/20 210 40 20 7 3~X30 12.6 210 172 6.6 3.6 60 17 plex 2PP 25 12 CH2C12 HFC-43-10mee ~0/20 210 40 20.7 30X30 10.1 210 200 51 34 63 23 plex w so le n-Pen~ne NONE 100/0 190 40 20.7 30X30 15.5 194 285 2.4 17 72 13 plex 4PP 50 18 n-Penbne NONE 100/0 200 30 20.7 (2ûOx100) 12.6 19a Z50 3.5 1.4 60 nm plex SPP 50 18 n-Pen~ne NONE 1001û 200 30 20.7 30X30 14.8 201 ~76 2.1 11 72 nm plex 6PP 60 18 n Penlane NONE 10010 220 30 24.1 30X30 15.9 21a 301 1.1 0 J 69 nm plex HDPE 50 82~~ Pure 7PP 50 18 n-Penl2ne Cyclopentane 60/40 200 60 17.2 30X30 11.4 200 293 2.8 2.5 83 16 plex foomote: nm = not n~easured Test Apparatus for Examples 8 - 11 In Examples 8 - 11, plexifilaments were spun from a spin mixture that comprised a polymer blends dispersed in a solvent system. The spin mixture, was generated in a continuous rotary mixer, as described in U.S. Patent Application Serial No. 60/005,875. The mixer operated at temperatures up to 300~C and at pressures up to 41,000 kPa. The mixer had a polymer inlet through wllicl1 a polymer melt blend was continuously introduced into the mixer. The mixer also had a CO7 inlet through which supercritical CO2 was continuously introduced into the polymer stream entering the mixer before the polymer entered the mixingchamber of the mixer. The mixer had a mixing chamber wilere polymer and CO2 were thoroughly sheared and mixed by a combination of rotating and fixed cuttingblades. The mixer further included an injection port through which water was introduced into the mixing chamber at a point downstream of where the polymer and C~2 were initially mixed in the mixing charnber. At least one additional setof rotating and fixed cutting blades in the mixing chamber further mixed the polymer, C~2 and water before the mixture was continuously discharged from the mixer's mixing chamber. The volume of the mixer's mixing charnber between the point where the polymer first contacts C~2 plasticizing agent and the mixer outlet was 4~5 cm3.
The mixer was operated at a rotational rate of approximately 1200 rpm with power of between 7 and 10 kW. Polymer was injected into the mixer by a polymer screw extruder and gear pump. Supercritical C02, plasticizing agent ]O
from a pressurized stora e tank and distilled water frorn a closed storage tank were both injected into the mixer by double acting piston pumps. .~ dispersion of polymer. supercritical CO~ and water was generated in the mixer's mixing chamber. The spin mixture was discharged from the mixer and passed through a heated transfer line to a round spin orifice from which the mixture was flash-spun into a zone m~int:~ined at atmospheric pressure and room temperature. The residence time of the polymer in the mixer's mixing chamber was generally between 7 and 20 seconds. Unless stated otherwise, the spinning temperature was approximately 240~ C and the spinning pressure was approximately 28,900 l 0 kPa. The spin products were collected on a moving belt from which samples were removed for e~t~min~tion and testing.
The following polymers were flash-spun in examples 8 - I l. The percentages stated in the examples are by weight unless otherwise indicated.
Each ingredient has been assigned a code by which it is referred to in examples 8 -1~ 11.
The polyethylene used in the following Examples was ALATHON~' H6018~ a hi~h density polyethylene that was obtained from Occidental Chemical Corporation of Houston, Texas and its successor in interest Lyondell Petrochemical Company of Houston, Texas. ALATHON(~) is currently a registered tr~m~rk of Lyondell Petrochemical Company. ALATHONOE' H6018 has a melt flow rate of 1 ~ g/10 min by standard techniques at a te~ cldlllre of190~C with a 2.16 Kg weight, and has a melting point of 130- 135CC. ("PE") The poiypropylene used in the following Examples was Valtec HH444 obtained from Himont Corporation of Wilmington, Delaware. Valtec HH444 has a melt flow rate of 70g/10 min by standard techniques at a temperatureof 190~C with a 2.16 kg weight, and has a melting point of 170~C. ~"PP") One 4GT polyester used in the following examples was CRASTIN(~) 6131 obtained from DuPont of Wilmington, Delaware. CRASTIN~3) is a registered trademark of DuPont. CRASTIN(~) 6131 was formerly sold under the ~0 name RYNITE(g 6131. CRASTIN~ 6131 is a non-reinforced low molecular weight 4GT polyester. CRASTIN(~) 6131 has a melt flow rate of 42g/10 min by standard techniques at a te~y.,ldl~re of 250~C with a 2.16 k~ weight, and has a melting point of 225~C. ("4GT-6131") Another 4GT polyester used in the following examples was ~5 CRASTIN(~) 6130 obtained from DuPont of Wilmington, Delaware. CRASTIN
6130 is a non-reinforced 4GT polyester with a higher molecular weight than CRASTIN~) 6131. CRASTIN';~) 6130 has a melt flow rate of' 12.~ ~/10 min by WO 97/25461 PCT~US97/0016 standard techniques at a temperature of 250~C witll a 2.16 k_ weight~ and has a melting point of 225~C. ~"4GT-6130") The polyester elastomer used in the following examples was HYTREL(~' 6133, ~ melt spinnable block copolymer obtained from E. I. du Pont S de Nemours and Co. of Wilmington, DeJaware HYTREL(~ is a registered trademark of DuPont. HYTREL(~) has a melt flow rate of 5.0 g/l 0 min by standard techniques at a temperature of l 90~C with a 2.16 kg .weigllt, and it has a melting point in the range of 170-190~C. ("PEL") The partially neutralized ethylene vinyl alcohol copolymer used in the following examples was SELAR~) OH BX240 obtained from E. I. du Pont de Nemours and Co. of Wilmington, Delaware. SELAR(~) is a registered trademark of DuPont. SELAR~) OH BX240 is a melt-blended, pelletized polymer consisting of 90% SELAR~ OH 4416 and 10% FUSABONDTM E M B-259D, both polymers being obtained from DuPont of Wilmington, Delaware. SELAR(~) OH 4416 is an I j ethylene vinyl alcohol copolymer having 44 mole % ethylene units, a melt flow rate of 16.0 g/10 min by standard techniques at a temperature of 210~C with a 2.16 lcg weight. and a melting point of 168~C. FUSABON DT~ E M B-259D is a polyethylene grafted with 0.2-0.3% maleic anhydride, having a melt flow rate of ~0-25 gllO min by standard techniques at a temperature of 190~C with a 2.16 kg weight, and a melting point of 120-122~C. FUSABONDTM is a trademark of DuPont. ("EVOH") The nylon 6 used in the following examples was CAPRON(~ 8202C
obtained from Allied-Signal Inc. of Morristown, New Jersey. (~APRON(~) is a registered tr~ m~rk of Allied-Signal Inc. CAPRON~) 8202Cis a low viscosity, 2 ~ higi1 crystallinity nylon 6 commonly used for injection molding. CAPRON~) 8202C has a specific gravity of 1.13 g/cc and a melting point of 215~ C. ("Nylon") Ameltedblendof30%4GT-6131, 15%4GT-6130, 13% PEL? 19~/'o PE. 19% PP, 1% EVOH, and 3% Nylon was injected into a continuous mixer and was mixed with CO2 and water as described above. The polymer/CO2 ratio in the mixer was 2.86 and the polymerlwater ratio in the mixer was 1.25. The mixture was subsequently flash-spun from a 0.889 mm spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of ~5 ~.2 gpd, an elongation of 61.5%, a toughness of 0.8 gpd, and a fiber quality rating of 2.25.
WO 9712~461 PCT/US97/00161 A melted blend of 18% 4GT-6131, 45% 4GT-6130. 12% PEL, 16%
PE, 8% PP, and 1~~ EVOH was injected into a continuous mixer and was mixed with CO2 and water as described above. The polymer/CO~ ratio in the mixer was 1.25 and the polymer/water ratio in the mixer was 2.86. The mixture was subsequently flash-spun from a 0.889 mm spinning orifice for approximately 1 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 2.9gpd, an elongation of 37%, a toughness of 0.6 gpd, and a fiber qua]ity rating of2.5.
EXAMPI,E 10 A melted blend of 51% 4GT-6 13 1, 16% 4GT-6 13 (), 10% PEL, 12%
PE, 10% PP, and 1% EVOH was injected into a continuous mixer and was mixed with C~2 and water as described above. The polymerlCO2 ratio in the mixer was 1.25 and the polymeriwater ratio in the mixer was 2.86. The mixture was subsequently flash-spun from a 0.787 mm spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 2.8gpd, an elongation of 62%, a toughness of 1.0 gpd, and a fiber quality rating of2.2.
A melted blend of 82% PE, 9% PP, 4% PEL, and 5% EVOH was injected into a continuous mixer and was mixed with C~2 and water as described above. The polymerlCO~ ratio in the mixer was 1.25 and the polymer/water ratio ~5 in the mixer was 2.86. The mixture was subsequently flash-spun from a 35 mil (0.889 mm) spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 0.8 gpd, an elongation of 86%, a toughness of 0.4 gpd~ and a fiber quality rating of 2.5.
It will be apparent to those skilled in the art that modifications and variations can be made the flash-spinning apparatus and process of this invention. The invention in its broader aspects is, therefore. not limited to the specific details or the illustrative examples described above. Thus, it is intçnded that all matter contained in the foregoing description, drawings and examples shall be interpreted as illustrative and not in a 3~ limiting sense.
BLENDS OF POLYOLEFIN POLYMERS
BACKGROUND OF THE INVENTION
S This invention relates to fibers that are flash-sp~n from blends of polvmers that include two or more polyolefin polymers. More particularly~ the invention relates to flash-spun plexifilamentary fibers comprised of ;3 polvmer blend that inc]udes sis~nifican~
poiyethylene and polypropylene components.
The art of flash-spinning strands of plexifilamentary film-fibriis from 10 pok~mer in a solution or a dispersion is known in the art. The term "plexifilamentary"
means a three-dimensional integral network of a multitude of thin. ribbon-like. film-fibril elemerlts of random len_th and with a mean film thickness of less than about ~ microns and with a median fibril width of less than about 25 microns In plexifilamentarvstl~ctures~ the film-fibril elements are generallv coextensivel~l aligned with the ion itudinal axis of the struc~ure and they intermittentlv unite and separate atirre~ulal intervals in various places tllroughout the length, width and thickness of the s~ructure to forrn a continuous three-dimensional network.
U.S. Patent 3,Z7,784 to Blades et al. ~assigned to E. I. du Pont de ?~emours ,~~ Company ("DuPont")) describes a process wherein a polymer in solution is for~varded ~0 continuously to a spin orifice at a temperature above the boiling point of the solvent. and at autogenous pressure or greater, and is flash-spun into a zone of lower temperalure and substantially lower pressu}e to generate a strand of plexifilamentary material. U.S.
Patent 3.'~7~794 to Anderson et al. (assigned to ~UPollt) teaches that ple:~ifilamentary film-fibrils are best obtained from solulion when fiber-forming polymel is dissolved in a ~5 solvenl at a temperature and at a pressure above the pressure at which two liquid phases form, which pressure is ~enerally known as the cloud point pressure at the giventemperature. This solution is passed to a pressure let-down chamber, where the pressure decreases below the cloud point pressure for the solution thereby causing phase separation. The resulting two phase dispersion of a solvent-rich phase in a polymer-ricl 30 phase is discharged throu~h a spinneret orifice to form the plexifilamentary strand.
U.S. Patent 3.484,899 to Smith (assigned to DuPont~ discloses an apparatus with a horizontally oriented spin orifice through which a plexifilamentary strand can be flash-spun. The polymer strand is conventionally directed against a rotating lobed deflector baffle to spread the strand into a more planar web structure that the baffle 3:~ allernatelv directs to the left and right as the ~ eb descends to a moving collection belt.
The fibrous sheet formed on the belt has ple~ifilamentary fiim-fibril networks oriented in an ovcrlapping multi-directional configuration.
W O 97125461 PCT~US97/00161 European Patent Publication 645480 filed by 17ni~ika Ltd. discloses a plexifilamentarv fiber structure that is flash-spun from a solut~on of polyolefin and polyester polymers dissolved in methylene chloride. The polyolefins disclosed include polyethylene and polypropylene polymers and copolymers. The polyesters disclosedS include polyethvlene terephthalate and polybutylene terephthalate. The Unitika patent discloses that the mixing ratio (by weight) of the polyolefin to the polyester is from 5/95 to 95/5.
British Patent Specification 970,070 (assigned to I)uPont) discloses nonwoven sheets made from fibers that were flash-spun from a blend of polyethylene and l 0 a minor amount of another polymer such as polyamide, polyvinyl chloride, polystyrene, or polyurethane. The patent suggests that a "blends of linear polyethylene and minor amounts of branched polyethylene, polypropylene, polybutylene, polyisobutylene, polybutadiene. polyvinyl chloride, or cellulose acetate" might be advantageous.
However, the patent does not appear to disclose the actual flash-spinning of polyethylene 15 and polypropylene blends.
Manv improvements to the basic flash-spinning process have been reported or patented over the years. An alternative process for flash-spinning a plexifilamentary strand accordin~ to which a mechanically generated dispersion of melt-spinnable polymer, carbon dioxide and water under high pressure is flashed through a spin orifice 20 into a zone of substantially lower temperature and pressure to form a plexifilamentary strand is disclosed in U.S. Patent 5,192,468 to Coates et al. (assigned to DuPont). Flash-spirming of polyethylene to produce non-woven sheets is practiced commercially and is the subject of numerous patents, including U.S. Patent 3,851,023 to Brethauer et al (assigned to DuPont).
' 5 The commercial application for flash-spinning has been primarily directed to the manufacture of sheets of bonded polyethylene plexifilaments. Polyethylene is an ideal polymer for flash-spinning. It can be flash-spun into a strong well fibrillated plexifilarnent over a wide range of processing conditions. However. its melting point is relatively low (~140~ C), and therefore it is not suitable for applications where end use 30 temperatures are 140~ C or higher. One such application is steam sterilizable sterile packing, and CSR (i.e.. central storage room) ~vraps used in the hospitals for steam sterilization. Polypropylene, on the other hand, has a higher melting point ( 165~ C) that is above the temperatures used during steam sterilization. However, polypropylene is more difficult to flash-spin than polyethylene and as-spun fibers are not as strong. In 35 addition, polypropylene requires substantially higher Spill temperatures than polyethylene.
W O 97/2~461 PCTrUS97/00161 There is a need for a flash-spun product that enJoys the streneth and ease of processin~ associated with polyethylene, but that can withstand higher end use temperatures.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a ple~ifilamentary strand having a tensile strengtll of at least I gpd and a surface area, measured by the BET
nitrogen adsorption method. greater than 2 m2/g comprising a three dimensional integral plexus of semicrystalline, polymeric, fibrous elements, the elements being co-extensively aligned with the network axis and having the stmctural conf;guration of oriented film-fibrils. The film-fibrils have a mean film thichless of less than 4 microns, a median fibril width of less than 25 microns, and are comprised of at least 20% by weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the fiim-fibrils. Preferably, the film-fibrils are comprised of at least 75% by weight of polyethylene and polypropylene, and more preferably ar~ comprised of at least 90% by weight of polyethylene and polypropylene wherein the polyethylene and polypropylene each comprise at least 35% by weight of each of the film-fibrils.
The invention is also directed to a procçss for the production of flash-spun plexifilamentary film-fibril strands of a polymer that is comprised of at least 75% b~
weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the film-fibrils. The process includes the steps of forming a spin solution of polyethylene and polypropyiene polymers in a solvent and spinning the spin solution at a pressure that is greater than the autogenous pressure of ~5 the spin solution into a region of substantially lower pressure and at a temperature at least 50~ C higher than the atmospheric boiling point of the solvent. The solvent in the spin solution has an atmospheric boiling point between 0~ C and 100" C, and is comprised of at least 50% of solvents selected from the group consisting of hydrocarbons, chlorinated hydrocarbons, hydrochlorofluorocarbons and alcohols.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the presently preferred embodiments of the invention and, together with the description, serve to explain the principles of the invention.Figure I is a plot of the cloud point data for 9% by weight polypropylene solution in a solvent comprised of methylene chloride and HFC-43 1 0mee at 3 different solvent ratios.
W O 97/25461 PCT~US97/00161 Figure 2 is a plot of the cloud point data ~or a 12% by weight poivethyiene solution in a solvent comprised of methylene chloride and HFC-43 1 0mee at 5 different solvent ratios.
Figure 3 is a plot of the cloud point data for I ') a 20% by weight polyethylenesolution in a solvent comprised of 60/40 n-pentane/8~.5% pure cyclopentane. and 2) a 12% by weight polypropylene solution in a solvent comprised of 60140 n-pentane/82.5~~O
pure cyclopentane.
DETAILED DESCRIPTION
Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated below.
The flash-spun plexifilamentary fibers of the invention are comprised of blends of thermoplastic polymers with significant polyethylene and polypropylenecomponents. These fibers may be spun using the apparatus and the solution flash-I 5 spinning process disclosed and fully described in U.S. Patent 5,147,5~6 to ~hin et al.
Alternatively, the plexifilamentary fibers of the invention can be flash-spun bv the dispersion flash-spinning process disclosed in U.S. Patent 5,192,468 to Coates et al., according to which a plexifilamentary fiber is spun from a mechanically generated dispersion of polymer in water ~nd carbon dioxide. It is anticipated that in commercial applications, the plexifil~mentary sheets of the invention would most likely be produced using the solution flash-spinning apparatus disclosed in U.S. Patent 3,851,023 to Brethauer et al.
The process for flash-spinning plexifilaments from polyolefin polymer blends in a solvent operates under conditions of elevated temperature and pressure. The '5 polymeric starting material is normally not soluble in the selected solvent under normal temperature and pressure conditions but forrns a solution at certain elevated temperatures and pressures. In the flash-spinning process for making plexifilaments, pressure is decreased below the cloud point to cause phase separation, just before the solution is passed through a spirmeret. When the solution pressure is lowered below the cloud point pressure, the solution phase separates into a polymer-rich phase and a solvent-rich phase.
Upon passing through the spinneret at very high speed into a zone of substantially lower pressure, the solvent flashes off quickly such that the polymer material present in the polymer-rich phase freezes in an elongated plexifilamentary form.
The morphology of plexifilamentary strands obtained by the solution flash-3 5 spinning of a polymer is greatly influenced by the level of pressure used for spinning.
When the spin pressure is much greater than the cloud point pressure of the spin mixture, coarse plexifilamentary "yarn-like" strands are usually obtained. As the spin pressure is gradually decreased, the average distance between the tie points generally becomes shorter ~vllile the fibrils of the strands become progressively fil~er. Whell the spin pressure approaches the cloud point pressure of the spin mixture, very fine fibrils are normally obtained, and the distance between the tie points becomes very short. As the spin pressure is further reduced to below the cloud point pressure, the distance between 5 the tie points becomes longer. Well fibrillated plexifilaments, which are most suitable for sheet formation, are usually obtained when spin pressures slightly below the cloud point pressure are used. The use of pressures which are too much lower than the cloud point pressure of the spin mixture generally leads to a relatively coarse plexifilamentary structure. The effect of spin pressure on fiber molphology also depends on the types OI~
10 poJymers and solvents being spun and the concentration of the polymer in the solvent. At higher concentrations of polvmer in the solvent. foams may be obtained rather than plexifilaments, even at spinning pressures slightly below the cloud point pressure of the solution. In some cases. well fibrillated plexifilaments can be obtained even at spin pressures slightly higher than the cloud point pressure of the spin mixture and at polymer 15 concentrations above ~0% of the spin solution. Therefore, the effect of spin pressure discussed herein is intended merely as a guide in selecting the spinning conditions and not as a general rule.
The polyethylene that has been flash-spun with polypropylene to produce the blended polyolefin polymer plexifilaments of the invention is high density polyethylene.
20 However, it is anticipated that other types of polyethylene, including low density polyethylene and linear Jow density polyethylene, could be used in making the polyolefin blend plexifilaments of the invention. The polypropylene that has been flash~spun with polyethylene to produce the blended polyolefin plexifilaments of the invention is isotactic polypropylene and syndiotactic polypropylene.
'5 While the temperature and pressure conditions that can be withstood by solution flash-spinnine equipment are quite broad, it is generally prei'erred not to operate under extreme temperature and pressure conditions. The preferred temperature range for solution flash-spinning the blends of polyethylene and polypropylene is about 150~ to 250~ C while the preferred pressure range for flash-spinning such blends is in the range 30 of autogenous pressure to 50 MPa, and more preferably in the range of autogenous pressure to 25 MPa. Therefore, if plexifilaments are to be flash-spun from blends of polyethylene and polypropylene from a solution, the solvent should dissolve the polymers at pressures and temperatures within the preferred ranges.
Unfortunately, it has proved to be very difficult to flash-spin polypropylene ~5 plexifilarnentary fibers from many common solvents, including room temperature boiling hydrocarbon solvents and strong solvents such as methylene chloride, dichloroethane and cyclopentane. We have now found that polypropyJene plcxilllall~cll~ can bc llash-spLIll il the polypropylene is blended ~vith polyethylene in sufficient quantities and/or the strong W O 97/25461 PCTfUS97/00161 solvents are blended with weaker solvents. Interestingly, we have found that many blends of polyethylene and polypropylene cannot be flash-spun from many of the important flash-spinning solvents. For example, attempts to flash-spin a blend of 75%
polypropylene and 25% polyethylene from methylene chloride blended ~A~ith a weaker solvent were unsuccessful.
Polyethylene and polypropylene do not form a compatible polymer blend within the range of useful blend ratios (e.g. from 5/95 to 95/5). Consequently, solutions of polyethylene and polypropylene become cloudy when they are dissolved together in a common solvent. For example, polyethylene solutions in 80/2() methylene 10 chloride/HFC-43 1 Omee form a clear, single phase solution as long as pressure applied to the solution at any given temperature is higher than the cloud point pressure of the solution. Likewise, polypropylene solutions in 80/20 methylene chloride/HFC-43 1 Omee form a clear~ sin_le phase solution as long as pressure applied to the solution is higher than the cloud point pressure. However, if both polyethylene and polypropylene are 1~ added to the same common solvent, the solution will not be a clear, single phase solution regardless of the temperature and pressure applied (within a reasonable range). Instead, the solutions will become cloudy since polyethylene is not compatible with polypropylene.
Therefore, there is no cloud point pressure for solutions of polyethylene and ~0 polypropylene blends in a common solvent. Such blends always exist as a dispersion in a phase-separated state. Consequently, when blends of polyethylene and polypropylene are flash-spun using a common solvent, cloud point pressure of individual componentspresent in the "solution" is used. In the case of polyethylene and polypropyiene blends.
polyethylene always gives higher cloud point pressures than polypropyiene. Thus, the ~5 blends are mixed at a pressure higher than the cloud point pressure of polyethylene~ and optimum spin pressures are deter~nined empirically. However, it has been found that optimum spin conditions for the blends are usually closer to the polyethylene spin conditions than to the polypropylene spin conditions.
Good solvents for solution flash-spinning polyethylene and polypropylene 30 polymer blends are generally similar to those used for flash-spinning polyethylene.
However, it is more difficult to select a proper flash-spinning agent for the blends, because the spin agent to be used has to satisfy both of the components present in the blends. Mixed solvent systems have been found to be particularly suited for flash-spinning polyethyleneipolypropylene polymer blends, because solvent power can be3~ adjusted to satisfy both blend components by ch~ngin~ the solvent ratio. Solvents that may be used for flash-spinning blends of polyethylene and polypropylene include mixtures containing as a majcr component hydrocarbons, chlorillated hydrocarbolls, hydrochlorofluorocarbons or certain types of alcohols. Preferred solvents for solution flash-spinning blends of polyethylene and poiypropylene mclude mixed s'olvent sy'stems based on methylene chloride, dichloroethylene, cyclopentane, pentane, HCFC-141b, and bromochloromethane. Co-solvents that can be used in conjunction with these main solvents to improve electrostatic charging and/or to reduce solvent power include hydrofluorocarbons such as HFC-431 Omee, hydrofluoroethers such as methyl(perfluorobutyl)ether, and perfluorinated compounds such as perfluoropentane and perfluoro-N-methylmorpholine.
The apparatus and procedure for determining the cloud point pressures of a polymer/solvent combination are those described in the above cited U.S. patent 5,147,586 10 to Shin et al.
Figure 1 is a plot of the cloud point data for a 9% by weight polypropylene solution in a solvent comprised of methylene chloride and HFC-431 Omee at 3 different solvent ratios (60/40, curve l; 70/30, cwe 2; and 80/20, cwe 3).
Figure 2 is a plot of the cloud point data for a 12% by weight polyethylene 15 solution in a solvent comprised of methylene chloride and HFC-431 Omee at S different solvent ratios (75/25, cwe 4; 80/20, curve 5; 85/15, curve 6; 90/lO, cwe 7; and 100/0,~
cwe 8).
Figure 3 is a plot of the cloud point data for (1) a 20% by weight polyethylene solution in a solvent comprised of 60/40 n-pentane/82.5% pure 20 cyclopentane, cwe 9; and (2) a 12% by weight polypropylene solution in a solvent comprised of 60/40 n-pentane/82.5% pure cyclopentane, cwe 10.
This invention will now illustrated by the following non-limiting examples which are intended to illustrate the invention and not to limit the invention in any manner.
EXAMPLES
Test Methods In the description above and in the non-limiting examples that follow, the 30 following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials, and TAPPI refers to the Technical Association of the Pulp and Paper Industry.
The denier of the strand is determined from the weight of a 15 cm sample length of strand.
Tenacity, elongation and tou~hness of the flash-spun strand are determined i~ith an Instron tensile-testing machine. The strands are conditioned and tested at 70~F
and 65% relative hurnidity. The strands are then twisted to 10 tu~ns per inch and mounted in the jaws of the Instron Tester. A two-inch gauge length was used with an A~NDED SHEET
W O 97/25461 PCT~US97/00161 initial elongation rate of 4 inches per minute. The tenaci~y at break is recorded in grams per denier (gpd). The elongation at break is recorded as a percentage of the two-inch gauge length of the sample. Tol~hness is a measure of the work required to break the sample divided by the denier of the sample and is recorded in gpd. Modulus corresponds to the slope of the stress/strain curve and is expressed in units of gpd.
Fiber qualitv is evaluated using a subjective scale of 0 to 3, with a 3 being the highest quality rating. Under the evaluation procedure, a 10 inch length of a plexifilamentary strand is removed from a fiber batt. The web is spread and mounted on a dark substrate. The fiber quality rating is an average of three subJective ratings, one for fineness of the fiber (finer fibers receive higher ratings), one for the continuity of the fiber strand (continuous plexifilamentary strands receive a higher rating), and the other for the frequency of the ties (more networked ple~ifil~ nt~ry strands receive a higher rating).
Fiber fineness is measured using a technique similar to that disclosed in U.S.
] 5 Patent 5,371,810 to A. Ganesh Vaidyanathan dated 6 December 1994, and which is hereby incorporated by reference. This technique quantitatively analyzes fibril size in webs of fiber. The webs are opened up by hand and imaged using a microscopic lens.
The image is then digitized and computer analyzed to determine the mean fibril width and standard deviation. However, some smaller fibrils may be so tightly bunched together and have such short fibril length, that the fibrils appear as part of a large fibril and are counted as such. Tight fibril bllnçhing and short fibril length (distance from tie point to tie point) can effectively prevent analysis of the fineness of individual fibrils in the bunched fibrils. Thus, the term "apparent fibril size" is used to describe or characterize fibers of plexifilamentary strands.
The surface area of the plexifilamentary t;lm-fibril strand product is another measure of the degree and fineness of fibrillation of the flash-spun product. Surface area is measured by the BET nitrogen absorption method of S. Brunauer~ P. H. Emrnett and E.
Teller, J. Am. Chem. Soc., V. 60 p 309-319 (1938) and is reported as m2/g.
Test Apparatus for Examples I - 7 The apparatus used in the examples I - 7 is the spinning apparatus described in IJ.S. Patent 5,147,5~6. The apparatus consists of two high pressure cylindrical chambers. each e~uipped with a piston which is adapted to apply pressure to the contents of the chamber. The cylinders have an inside diameter of 1.0 incl-l (2.54 cm) and each has an internal capacity of 50 cubic centimeters. The cylinders are connected to each other at one end through a 3~32 inch (0.23 cm) diameter channel and a mixing chamber containing a series of fine mesh screens that act as a static mixer. Mixing is accomplished by forcing the contents of the vessel back and forth between the two W O 97n~461 PCT/US97100161 cylinders through the static mixer. A spirmeret assembly with a c~uick-acting means for opening the orifice is attached to the channel through a tee. The spinneret assembly consists of a lead hole of 0.25 inch (0.63 cm) diameter and about 2.0 inch (5.08 cm) length, and a spinneret orifice with both a length and a diameter shown in the table below. Orifice measurements are expressed in mils [Imil = 0.025~ mm]. In Example 4, a cylindrical turmel was located at the exit of the spin orifice. Tl1e diameter of the tunnel was 200 mils and the length was 100 mils. The tunnel was used in order to obtain a more columnar jet of flash-spun material. The pistons are driven by high pressure water supplied by a hydraulic system.
In the tests reported in Exarnples l - 7, the apparatus described above was charged with pellets of a polyethylene and polypropylene polymer and a solvent. The polyethylene was high density polyethylene (HDPE) with a melt index of 0.7S, a density of 0.957, a number average molecular weight of 21,000 and a wei~ht average molecular weight of 121,000. The polypropylene was isotactic polypropylene with a melt index of 15 0.9 and a number average molecular weight of 9~,000 and a weight average molecular weight of ~3 l ,000. High pressure water was used to drive the pistons to generate a mixing pressure of between l 500 and 3000 psi ( 10,340 - 10,68() kPa). The polymer and solvent were ne~ct heated to mixing temperature and held at that temperature for about an hour during which time the pistons were used to alternately establish a differential 20 pressure of about 50 psi (345 kPa) or higher between the two cylinders so as to repeatedly force the polymer and solvent through the mixing charmel from one cylinder to the other to provide mixing and effect forrnation of a spin mixture. The spin mixture temperature was then raised to the final spin temperature, and held there for about 15 minutes to equilibrate the temperature. during which time mixing was continued. In order tosimulate a pressure letdown chamber, the pressure of the spin mixture was reduced to a desired spinning pressure just prior to spinning. This was accomplished by opening a valve between the spin cell and a much larger tank of high pressure ~ater ("the accumulator") held at the desired spinning pressure. The spinneret orifice is opened about one to five seconds after the opening of the valve between the spin cell and the 30 accumulator. This period roughly corresponds to the residence ~ime in the letdown chamber of a commercial spinning apparatus. The resultant flash-spun product is collected in a stainless steel open mesh screen basket. Tl~e pressure recorded just before the spinneret using a computer during spinning is entered as the spin pressure.
The experimental conditions and the results for Examples I - 7 are given below in the Tables 1. All the test data not originally obtained in the SI system of units has been converted to the SI units.
Table I
POLYI~IER OLVENT MIX111G SPI~NING Prope~esQ10 Pl O~iflce E~ P/P Wt S1/S2 Press (tunnel) Press Mod Ten E ~ET
No Name % % 1 2 Wt% ~C Min MPa mils MPa ~C Den gpd gpd % SA Type PP 50 12 CH2CI2 HFC-43-1ûmee ao/20 210 40 20 7 3~X30 12.6 210 172 6.6 3.6 60 17 plex 2PP 25 12 CH2C12 HFC-43-10mee ~0/20 210 40 20.7 30X30 10.1 210 200 51 34 63 23 plex w so le n-Pen~ne NONE 100/0 190 40 20.7 30X30 15.5 194 285 2.4 17 72 13 plex 4PP 50 18 n-Penbne NONE 100/0 200 30 20.7 (2ûOx100) 12.6 19a Z50 3.5 1.4 60 nm plex SPP 50 18 n-Pen~ne NONE 1001û 200 30 20.7 30X30 14.8 201 ~76 2.1 11 72 nm plex 6PP 60 18 n Penlane NONE 10010 220 30 24.1 30X30 15.9 21a 301 1.1 0 J 69 nm plex HDPE 50 82~~ Pure 7PP 50 18 n-Penl2ne Cyclopentane 60/40 200 60 17.2 30X30 11.4 200 293 2.8 2.5 83 16 plex foomote: nm = not n~easured Test Apparatus for Examples 8 - 11 In Examples 8 - 11, plexifilaments were spun from a spin mixture that comprised a polymer blends dispersed in a solvent system. The spin mixture, was generated in a continuous rotary mixer, as described in U.S. Patent Application Serial No. 60/005,875. The mixer operated at temperatures up to 300~C and at pressures up to 41,000 kPa. The mixer had a polymer inlet through wllicl1 a polymer melt blend was continuously introduced into the mixer. The mixer also had a CO7 inlet through which supercritical CO2 was continuously introduced into the polymer stream entering the mixer before the polymer entered the mixingchamber of the mixer. The mixer had a mixing chamber wilere polymer and CO2 were thoroughly sheared and mixed by a combination of rotating and fixed cuttingblades. The mixer further included an injection port through which water was introduced into the mixing chamber at a point downstream of where the polymer and C~2 were initially mixed in the mixing charnber. At least one additional setof rotating and fixed cutting blades in the mixing chamber further mixed the polymer, C~2 and water before the mixture was continuously discharged from the mixer's mixing chamber. The volume of the mixer's mixing charnber between the point where the polymer first contacts C~2 plasticizing agent and the mixer outlet was 4~5 cm3.
The mixer was operated at a rotational rate of approximately 1200 rpm with power of between 7 and 10 kW. Polymer was injected into the mixer by a polymer screw extruder and gear pump. Supercritical C02, plasticizing agent ]O
from a pressurized stora e tank and distilled water frorn a closed storage tank were both injected into the mixer by double acting piston pumps. .~ dispersion of polymer. supercritical CO~ and water was generated in the mixer's mixing chamber. The spin mixture was discharged from the mixer and passed through a heated transfer line to a round spin orifice from which the mixture was flash-spun into a zone m~int:~ined at atmospheric pressure and room temperature. The residence time of the polymer in the mixer's mixing chamber was generally between 7 and 20 seconds. Unless stated otherwise, the spinning temperature was approximately 240~ C and the spinning pressure was approximately 28,900 l 0 kPa. The spin products were collected on a moving belt from which samples were removed for e~t~min~tion and testing.
The following polymers were flash-spun in examples 8 - I l. The percentages stated in the examples are by weight unless otherwise indicated.
Each ingredient has been assigned a code by which it is referred to in examples 8 -1~ 11.
The polyethylene used in the following Examples was ALATHON~' H6018~ a hi~h density polyethylene that was obtained from Occidental Chemical Corporation of Houston, Texas and its successor in interest Lyondell Petrochemical Company of Houston, Texas. ALATHON(~) is currently a registered tr~m~rk of Lyondell Petrochemical Company. ALATHONOE' H6018 has a melt flow rate of 1 ~ g/10 min by standard techniques at a te~ cldlllre of190~C with a 2.16 Kg weight, and has a melting point of 130- 135CC. ("PE") The poiypropylene used in the following Examples was Valtec HH444 obtained from Himont Corporation of Wilmington, Delaware. Valtec HH444 has a melt flow rate of 70g/10 min by standard techniques at a temperatureof 190~C with a 2.16 kg weight, and has a melting point of 170~C. ~"PP") One 4GT polyester used in the following examples was CRASTIN(~) 6131 obtained from DuPont of Wilmington, Delaware. CRASTIN~3) is a registered trademark of DuPont. CRASTIN(~) 6131 was formerly sold under the ~0 name RYNITE(g 6131. CRASTIN~ 6131 is a non-reinforced low molecular weight 4GT polyester. CRASTIN(~) 6131 has a melt flow rate of 42g/10 min by standard techniques at a te~y.,ldl~re of 250~C with a 2.16 k~ weight, and has a melting point of 225~C. ("4GT-6131") Another 4GT polyester used in the following examples was ~5 CRASTIN(~) 6130 obtained from DuPont of Wilmington, Delaware. CRASTIN
6130 is a non-reinforced 4GT polyester with a higher molecular weight than CRASTIN~) 6131. CRASTIN';~) 6130 has a melt flow rate of' 12.~ ~/10 min by WO 97/25461 PCT~US97/0016 standard techniques at a temperature of 250~C witll a 2.16 k_ weight~ and has a melting point of 225~C. ~"4GT-6130") The polyester elastomer used in the following examples was HYTREL(~' 6133, ~ melt spinnable block copolymer obtained from E. I. du Pont S de Nemours and Co. of Wilmington, DeJaware HYTREL(~ is a registered trademark of DuPont. HYTREL(~) has a melt flow rate of 5.0 g/l 0 min by standard techniques at a temperature of l 90~C with a 2.16 kg .weigllt, and it has a melting point in the range of 170-190~C. ("PEL") The partially neutralized ethylene vinyl alcohol copolymer used in the following examples was SELAR~) OH BX240 obtained from E. I. du Pont de Nemours and Co. of Wilmington, Delaware. SELAR(~) is a registered trademark of DuPont. SELAR~) OH BX240 is a melt-blended, pelletized polymer consisting of 90% SELAR~ OH 4416 and 10% FUSABONDTM E M B-259D, both polymers being obtained from DuPont of Wilmington, Delaware. SELAR(~) OH 4416 is an I j ethylene vinyl alcohol copolymer having 44 mole % ethylene units, a melt flow rate of 16.0 g/10 min by standard techniques at a temperature of 210~C with a 2.16 lcg weight. and a melting point of 168~C. FUSABON DT~ E M B-259D is a polyethylene grafted with 0.2-0.3% maleic anhydride, having a melt flow rate of ~0-25 gllO min by standard techniques at a temperature of 190~C with a 2.16 kg weight, and a melting point of 120-122~C. FUSABONDTM is a trademark of DuPont. ("EVOH") The nylon 6 used in the following examples was CAPRON(~ 8202C
obtained from Allied-Signal Inc. of Morristown, New Jersey. (~APRON(~) is a registered tr~ m~rk of Allied-Signal Inc. CAPRON~) 8202Cis a low viscosity, 2 ~ higi1 crystallinity nylon 6 commonly used for injection molding. CAPRON~) 8202C has a specific gravity of 1.13 g/cc and a melting point of 215~ C. ("Nylon") Ameltedblendof30%4GT-6131, 15%4GT-6130, 13% PEL? 19~/'o PE. 19% PP, 1% EVOH, and 3% Nylon was injected into a continuous mixer and was mixed with CO2 and water as described above. The polymer/CO2 ratio in the mixer was 2.86 and the polymerlwater ratio in the mixer was 1.25. The mixture was subsequently flash-spun from a 0.889 mm spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of ~5 ~.2 gpd, an elongation of 61.5%, a toughness of 0.8 gpd, and a fiber quality rating of 2.25.
WO 9712~461 PCT/US97/00161 A melted blend of 18% 4GT-6131, 45% 4GT-6130. 12% PEL, 16%
PE, 8% PP, and 1~~ EVOH was injected into a continuous mixer and was mixed with CO2 and water as described above. The polymer/CO~ ratio in the mixer was 1.25 and the polymer/water ratio in the mixer was 2.86. The mixture was subsequently flash-spun from a 0.889 mm spinning orifice for approximately 1 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 2.9gpd, an elongation of 37%, a toughness of 0.6 gpd, and a fiber qua]ity rating of2.5.
EXAMPI,E 10 A melted blend of 51% 4GT-6 13 1, 16% 4GT-6 13 (), 10% PEL, 12%
PE, 10% PP, and 1% EVOH was injected into a continuous mixer and was mixed with C~2 and water as described above. The polymerlCO2 ratio in the mixer was 1.25 and the polymeriwater ratio in the mixer was 2.86. The mixture was subsequently flash-spun from a 0.787 mm spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 2.8gpd, an elongation of 62%, a toughness of 1.0 gpd, and a fiber quality rating of2.2.
A melted blend of 82% PE, 9% PP, 4% PEL, and 5% EVOH was injected into a continuous mixer and was mixed with C~2 and water as described above. The polymerlCO~ ratio in the mixer was 1.25 and the polymer/water ratio ~5 in the mixer was 2.86. The mixture was subsequently flash-spun from a 35 mil (0.889 mm) spinning orifice for approximately 15 minutes. A plexifilamentary fiber strand was obtained that had a tenacity of 0.8 gpd, an elongation of 86%, a toughness of 0.4 gpd~ and a fiber quality rating of 2.5.
It will be apparent to those skilled in the art that modifications and variations can be made the flash-spinning apparatus and process of this invention. The invention in its broader aspects is, therefore. not limited to the specific details or the illustrative examples described above. Thus, it is intçnded that all matter contained in the foregoing description, drawings and examples shall be interpreted as illustrative and not in a 3~ limiting sense.
Claims
WE CLAIM:
7. A process for the production of flash-spun plexifilamentary film-fibril strands of a polymer that is comprised of at least 75% by weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the film-fibrils; which comprises the steps of:
forming a spin solution of said polyethylene and polypropylene polymers in a solvent, said solvent having an atmospheric boiling point between 0° C and 100° C, and being comprised of at least 50% of solvents selected from the group consisting of hydrocarbons, chlorinated hydrocarbons, hydrochlorofluorocarbons and alcohols; and spinning said spin solution at a pressure that is greater than the autogenous pressure of the spin solution into a region of substantially lower pressure and at a temperature at least 50° C higher than the atmospheric boiling point of the solvent.
8. The process of claim 7 wherein the polymer is comprised of at least 40%
by weight polypropylene.
9. The process of claim 8 wherein the solvent is comprised of at least 80%
by weight hydrocarbon solvent with a boiling point less than 50°C.
10. The process of claim 8 wherein the solvent comprises a blend of solvents in which at least 30% by weight of the solvent blend is selected from the group of methylene chloride, dichloroethylene and cyclopentane.
11. The process of claim 7 wherein the solvent has a boiling point between 10°C and 90°C.
12. The process of claim 11 wherein the solvent comprises a blend of solvents each of which have a boiling point between 10°C and 90°C."
7. A process for the production of flash-spun plexifilamentary film-fibril strands of a polymer that is comprised of at least 75% by weight of polyethylene and polypropylene, wherein the polyethylene and polypropylene each comprise at least 5% by weight of each of the film-fibrils; which comprises the steps of:
forming a spin solution of said polyethylene and polypropylene polymers in a solvent, said solvent having an atmospheric boiling point between 0° C and 100° C, and being comprised of at least 50% of solvents selected from the group consisting of hydrocarbons, chlorinated hydrocarbons, hydrochlorofluorocarbons and alcohols; and spinning said spin solution at a pressure that is greater than the autogenous pressure of the spin solution into a region of substantially lower pressure and at a temperature at least 50° C higher than the atmospheric boiling point of the solvent.
8. The process of claim 7 wherein the polymer is comprised of at least 40%
by weight polypropylene.
9. The process of claim 8 wherein the solvent is comprised of at least 80%
by weight hydrocarbon solvent with a boiling point less than 50°C.
10. The process of claim 8 wherein the solvent comprises a blend of solvents in which at least 30% by weight of the solvent blend is selected from the group of methylene chloride, dichloroethylene and cyclopentane.
11. The process of claim 7 wherein the solvent has a boiling point between 10°C and 90°C.
12. The process of claim 11 wherein the solvent comprises a blend of solvents each of which have a boiling point between 10°C and 90°C."
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US973996P | 1996-01-11 | 1996-01-11 | |
| US60/009,739 | 1996-01-11 |
Publications (1)
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|---|---|
| CA2242470A1 true CA2242470A1 (en) | 1997-07-17 |
Family
ID=21739430
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| CA002242468A Abandoned CA2242468A1 (en) | 1996-01-11 | 1997-01-09 | Fibers flash-spun from partially fluorinated polymers |
| CA002242469A Abandoned CA2242469A1 (en) | 1996-01-11 | 1997-01-09 | Plexifilamentary strand of blended polymers |
| CA002242470A Abandoned CA2242470A1 (en) | 1996-01-11 | 1997-01-09 | Fibers flash-spun from blends of polyolefin polymers |
Family Applications Before (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002242468A Abandoned CA2242468A1 (en) | 1996-01-11 | 1997-01-09 | Fibers flash-spun from partially fluorinated polymers |
| CA002242469A Abandoned CA2242469A1 (en) | 1996-01-11 | 1997-01-09 | Plexifilamentary strand of blended polymers |
Country Status (8)
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| US (1) | US6004672A (en) |
| EP (3) | EP0877835B1 (en) |
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| KR (3) | KR19990077168A (en) |
| CA (3) | CA2242468A1 (en) |
| DE (3) | DE69704343T2 (en) |
| ES (3) | ES2156355T3 (en) |
| WO (3) | WO1997025459A1 (en) |
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| FR2759090B1 (en) * | 1997-02-04 | 1999-03-05 | Atochem Elf Sa | CLEANING OR DRYING COMPOSITIONS BASED ON 1,1,1,2,3,4,4,5,5,5-DECAFLUOROPENTANE |
| US5985196A (en) * | 1998-01-20 | 1999-11-16 | E. I. Du Pont De Nemours And Company | Flash spinning process and flash spinning solution |
| US6153134A (en) * | 1998-12-15 | 2000-11-28 | E. I. Du Pont De Nemours And Company | Flash spinning process |
| US7179413B1 (en) * | 1999-08-20 | 2007-02-20 | E. I. Du Pont De Nemours And Company | Flash-spinning process and solution |
| CN1221688C (en) * | 1999-10-18 | 2005-10-05 | 纳幕尔杜邦公司 | Flash-spun sheet material |
| US6458304B1 (en) | 2000-03-22 | 2002-10-01 | E. I. Du Pont De Nemours And Company | Flash spinning process and solutions of polyester |
| GB0030182D0 (en) * | 2000-12-11 | 2001-01-24 | Univ Brunel | Material processing |
| US7435369B2 (en) | 2001-06-06 | 2008-10-14 | Bpb Plc | Method for targeted delivery of additives to varying layers in gypsum panels |
| US6524679B2 (en) | 2001-06-06 | 2003-02-25 | Bpb, Plc | Glass reinforced gypsum board |
| US20050029695A1 (en) * | 2002-09-25 | 2005-02-10 | Weinberg Mark Gary | Surface-modified plexifilamentary structures, and compositions therefor |
| EP1656474B1 (en) | 2003-04-03 | 2010-08-04 | E.I. Du Pont De Nemours And Company | Rotary process for forming uniform material |
| JP2007514799A (en) | 2003-10-21 | 2007-06-07 | イー・アイ・デュポン・ドウ・ヌムール・アンド・カンパニー | Oriented polyester films, tapes, fibers, and nonwovens modified with ethylene copolymers |
| BRPI0508734A (en) * | 2004-04-01 | 2007-08-14 | Du Pont | membrane, composite sheet, processes and process for forming a material |
| US20070202764A1 (en) * | 2005-04-01 | 2007-08-30 | Marin Robert A | Rotary process for forming uniform material |
| EP2338935B1 (en) | 2008-10-16 | 2012-12-12 | Asahi Glass Company, Limited | Fluorine-containing copolymer composition and process for production thereof |
| WO2011002041A1 (en) | 2009-07-01 | 2011-01-06 | 旭硝子株式会社 | Fluorine-containing copolymer composition and method for producing same |
| KR20130058658A (en) | 2010-04-16 | 2013-06-04 | 아사히 가라스 가부시키가이샤 | Fluorine-containing copolymer composition and production method for same |
| WO2012088235A2 (en) | 2010-12-21 | 2012-06-28 | Dow Global Technologies Llc | Olefin-based polymers and dispersion polymerizations |
| US10920028B2 (en) * | 2014-06-18 | 2021-02-16 | Dupont Safety & Construction, Inc. | Plexifilamentary sheets |
| US11261543B2 (en) * | 2015-06-11 | 2022-03-01 | Dupont Safety & Construction, Inc. | Flash spinning process |
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| FR1106307A (en) * | 1953-05-11 | 1955-12-16 | Thomson Houston Comp Francaise | Process for manufacturing chlorotrifluoroethylene into fibers |
| BE625998A (en) * | 1960-11-08 | 1900-01-01 | ||
| US3227664A (en) * | 1961-12-07 | 1966-01-04 | Du Pont | Ultramicrocellular structures of crystalline organic polymer |
| US3081519A (en) * | 1962-01-31 | 1963-03-19 | Fibrillated strand | |
| NL300881A (en) * | 1962-11-23 | |||
| US3484899A (en) * | 1967-04-06 | 1969-12-23 | Du Pont | Spinneret pack for flash extrusion |
| US3851023A (en) * | 1972-11-02 | 1974-11-26 | Du Pont | Process for forming a web |
| IT995549B (en) * | 1973-10-02 | 1975-11-20 | Anic Spa | PROCEDURE FOR THE PRODUCTION OF FIBROUS STRUCTURES |
| US4127623A (en) * | 1974-08-03 | 1978-11-28 | Sumitomo Chemical Company, Limited | Process for producing polyolefin short fibers |
| DE3308626C2 (en) * | 1983-03-11 | 1986-02-20 | Dynamit Nobel Ag, 5210 Troisdorf | Process for the production of fibrids from thermoplastics |
| CA2029550C (en) * | 1989-11-22 | 2001-07-31 | Don Mayo Coates | Process for flash spinning polyolefins |
| US5147586A (en) * | 1991-02-22 | 1992-09-15 | E. I. Du Pont De Nemours And Company | Flash-spinning polymeric plexifilaments |
| US5328946A (en) * | 1991-08-29 | 1994-07-12 | E. I. Du Pont De Nemours And Company | Solvents for tetrafluoroethylene polymers |
| US5371810A (en) * | 1991-09-27 | 1994-12-06 | E. I. Du Pont De Nemours And Company | Method of determining the interior points of an object in a background |
| US5290846A (en) * | 1992-08-28 | 1994-03-01 | E. I. Du Pont De Nemours And Company | Solvents for fluorinated polymers |
| US5364929A (en) * | 1993-01-13 | 1994-11-15 | E. I. Du Pont De Nemours And Company | Dissolution of tetrafluoroethylene polymers at superautogenous pressure |
| JPH06257011A (en) * | 1993-03-04 | 1994-09-13 | Unitika Ltd | Polyolefinic grid fiber |
| US5786284A (en) * | 1993-04-08 | 1998-07-28 | Unitika, Ltd. | Filament having plexifilamentary structure, nonwoven fabric comprising said filament and their production |
| JP3317703B2 (en) * | 1993-04-08 | 2002-08-26 | ユニチカ株式会社 | Fiber having network structure and method for producing the same |
| JPH08113890A (en) * | 1994-10-12 | 1996-05-07 | Unitika Ltd | Antistatic wet nonwoven fabric and its production |
| JPH08113819A (en) * | 1994-10-12 | 1996-05-07 | Unitika Ltd | Netlike structure-having antistatic fiber and its production |
| JPH08113858A (en) * | 1994-10-12 | 1996-05-07 | Unitika Ltd | Nonwoven fabric comprising antistatic network structure fiber and its production |
| JPH08113859A (en) * | 1994-10-12 | 1996-05-07 | Unitika Ltd | Nonwoven fabric comprising antistatic network structure fiber and its production |
| US5816700A (en) * | 1995-10-26 | 1998-10-06 | E. I. Du Pont De Nemours And Company | Process and apparatus for mechanically mixing polymers and lower viscosity fluids |
-
1997
- 1997-01-09 KR KR1019980705306A patent/KR19990077168A/en not_active Application Discontinuation
- 1997-01-09 JP JP52532897A patent/JP3839489B2/en not_active Expired - Fee Related
- 1997-01-09 CA CA002242468A patent/CA2242468A1/en not_active Abandoned
- 1997-01-09 EP EP97902841A patent/EP0877835B1/en not_active Expired - Lifetime
- 1997-01-09 US US09/101,088 patent/US6004672A/en not_active Expired - Lifetime
- 1997-01-09 ES ES97901926T patent/ES2156355T3/en not_active Expired - Lifetime
- 1997-01-09 EP EP97901926A patent/EP0877834B1/en not_active Expired - Lifetime
- 1997-01-09 DE DE69704343T patent/DE69704343T2/en not_active Expired - Lifetime
- 1997-01-09 WO PCT/US1997/000157 patent/WO1997025459A1/en not_active Application Discontinuation
- 1997-01-09 DE DE69702115T patent/DE69702115T2/en not_active Expired - Fee Related
- 1997-01-09 KR KR1019980705307A patent/KR19990077169A/en not_active Application Discontinuation
- 1997-01-09 KR KR1019980705305A patent/KR19990077167A/en not_active Application Discontinuation
- 1997-01-09 WO PCT/US1997/000160 patent/WO1997025460A1/en not_active Application Discontinuation
- 1997-01-09 EP EP97905560A patent/EP0876520B1/en not_active Expired - Lifetime
- 1997-01-09 ES ES97905560T patent/ES2146982T3/en not_active Expired - Lifetime
- 1997-01-09 CA CA002242469A patent/CA2242469A1/en not_active Abandoned
- 1997-01-09 JP JP52532797A patent/JP3953107B2/en not_active Expired - Fee Related
- 1997-01-09 ES ES97902841T patent/ES2148928T3/en not_active Expired - Lifetime
- 1997-01-09 JP JP9525329A patent/JP2000503078A/en not_active Ceased
- 1997-01-09 DE DE69701673T patent/DE69701673T2/en not_active Expired - Fee Related
- 1997-01-09 WO PCT/US1997/000161 patent/WO1997025461A1/en not_active Application Discontinuation
- 1997-01-09 CA CA002242470A patent/CA2242470A1/en not_active Abandoned
Also Published As
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| ES2148928T3 (en) | 2000-10-16 |
| WO1997025460A1 (en) | 1997-07-17 |
| US6004672A (en) | 1999-12-21 |
| DE69702115D1 (en) | 2000-06-29 |
| DE69701673T2 (en) | 2000-11-30 |
| EP0877835A1 (en) | 1998-11-18 |
| EP0876520A1 (en) | 1998-11-11 |
| EP0877834B1 (en) | 2001-03-21 |
| JP2000503731A (en) | 2000-03-28 |
| EP0877835B1 (en) | 2000-05-24 |
| DE69704343D1 (en) | 2001-04-26 |
| JP2000503078A (en) | 2000-03-14 |
| DE69701673D1 (en) | 2000-05-18 |
| JP2000505154A (en) | 2000-04-25 |
| KR19990077167A (en) | 1999-10-25 |
| JP3839489B2 (en) | 2006-11-01 |
| WO1997025461A1 (en) | 1997-07-17 |
| JP3953107B2 (en) | 2007-08-08 |
| KR19990077169A (en) | 1999-10-25 |
| EP0876520B1 (en) | 2000-04-12 |
| ES2156355T3 (en) | 2001-06-16 |
| DE69702115T2 (en) | 2001-02-01 |
| WO1997025459A1 (en) | 1997-07-17 |
| CA2242468A1 (en) | 1997-07-17 |
| CA2242469A1 (en) | 1997-07-17 |
| ES2146982T3 (en) | 2000-08-16 |
| KR19990077168A (en) | 1999-10-25 |
| DE69704343T2 (en) | 2001-10-31 |
| EP0877834A1 (en) | 1998-11-18 |
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