| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 11.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 28.11.00 |
| PATENT TITLE |
Flash spinning process |
| PATENT ABSTRACT | A spinning process using azeotropic compounds as spin agents having essentially zero ozone depletion potential and that are either non-flammable or of very low flammability. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 15.12.98 |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polyolefin which comprises flash-spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) 5 to 30 wgt. % synthetic fiber-forming polyolefin, and (b) a spin agent selected from the group consisting of an azeotropic mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and an azeotropic mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene. 2. The process of claim 1, wherein the synthetic fiber-forming polyolefin is selected from the group consisting of polypropylene and polymethylpentene. 3. The process of claim 2, wherein the polypropylene is present in an amount of 6 to 15 wgt. %. 4. The process of claim 2, wherein the polymethylpentene is present in an amount of 8 to 20 wgt. %. 5. A process for the preparation of microcellular foam fibers from a synthetic fiber-forming polyolefin which comprises flash-spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) at least 40 wgt. % synthetic fiber-forming polyolefin, and (b) a spin agent selected from the group consisting of a mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene. 6. The process of claim 5, wherein the synthetic fiber-forming polyolefin is selected from the group consisting of polypropylene, polymethylpentene, partially fluorinated copolymers of ethylene and tetrafluoroethylene and partially fluorinated copolymers of ethylene and chlorotrifluoroethylene. 7. The process of claim 6, wherein the synthetic fiber-forming polyolefin is present at between about 40 and 60 wgt. %. 8. The process of claim 5, wherein the spin fluid comprises nucleating agents selected from the group consisting of fumed silica and kaolin. 9. The process of claim 5, wherein the spin fluid comprises low boiling inflating agents selected from the group consisting of hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, perfluorocarbons, butane, isopentane, carbon dioxide and nitrogen. 10. A process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polyolefin which comprises flash-spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) 10 to 40 wgt. % of a synthetic fiber-forming polyolefin selected from the group consisting of a partially fluorinated copolymer of ethylene and tetrafluoroethylene and a partially fluorinated copolymer of ethylene and chlorotrifluoroethylene and (b) a spin agent selected from the group consisting of a mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to flash-spinning of polymeric, plexifilamentary, film-fibril strands in which the spinning process utilizes compounds having essentially zero ozone depletion potential and in which the spinning process is carried out utilizing compounds that are either non-flammable or of very low flammability. BACKGROUND OF THE INVENTION Commercial spunbonded products made from polyethylene plexifilamentary film-fibril strands have typically been produced by flash-spinning from trichlorofluoromethane; however, trichlorofluoromethane is an atmospheric ozone depletion chemical, and therefore, alternatives have been under investigation. U.S. Pat. No. 5,032,326 to Shin discloses one alternative spin fluid, namely, methylene chloride and a co-spin agent halocarbon having a boiling point between -50.degree. C. and 0.degree. C. As pointed out in Kato et al. U.S. Pat. No. 5,286,422, the Shin methylene chloride-based process is not entirely satisfactory, and the '422 patent discloses an alternative, specifically, a spin fluid of bromochloromethane or 1,2-dichloroethylene and a co-spin agent of, e.g., carbon dioxide, dodecafluoropentane, etc. Published Japanese Application J05263310-A (published Oct. 12, 1993) discloses that three-dimensional fiber favorable for manufacturing flash-spun non-woven sheet may be made from polymer dissolved in mixtures of spin agents where the major component of the spin agent mixture is selected from the group consisting of methylene chloride, dichloroethylene, and bromochloromethane, and the minor component of the spin agent mixture is selected from the group consisting of dodecafluoropentane, decafluoropentane, and tetradecafluorohexane. However, it is known, for example, that methylene chloride is an animal carcinogen and dichloroethylene is somewhat flammable. U.S. Pat. No. 5,023,025 to Shin discloses a process for flash-spinning plexifilamentary film-fibril strands of fiber-forming polyolefin from a group of halocarbon liquids that present a greatly reduced ozone depletion hazard. The patent discloses 1,1-dichloro-2,2,2trifluoroethane (HCFC-123) as a preferred halocarbon (halogenated hydrocarbon). HCFC-123 is a very good spin agent for polypropylene but not for polyethylene, and in the latter case a very high spinning pressure would be required. As such, for use with polyethylene, a co-spin agent has to be employed that is capable of dissolving polyethylene at relatively low pressures (i.e., a strong solvent). The '025 patent also discloses dichlorodifluoroethane (HCFC-132b and its isomers) and dichlorofluoroethane (HCFC-141b and its isomers), all of which have significant disadvantages. For example, HCFC-132b is a good spin agent, but toxic. HCFC-141b is also a good spin agent, but somewhat flammable, and moreover exhibits a relatively high ozone depletion potential. However, regardless of any of their apparent advantages, the aforementioned spin agents all exhibit some amount of ozone depletion potential. Flashspun products have typically been made from polyethylene. However, it is known that both polypropylene and polymethylpentene have higher melting points than does polyethylene and as such provide a flashspun product usable at higher temperatures when compared to product made from polyethylene. Moreover, certain solvents may dissolve polypropylene or polymethylpentene, but not polyethylene, therefore motivation exists to find solvents that are particularly suited to polypropylene and polymethylpentene and yet satisfy the need for non-flammability and zero or extremely low ozone depletion potential. SUMMARY OF THE INVENTION The present invention is a process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polyolefin which comprises flash-spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) 5 to 30 wgt. % synthetic fiber-forming polyolefin, and (b) a spin agent selected from the group consisting of a mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene. This invention is also a spin fluid comprising (a) 5 to 30 wgt. % synthetic fiber-forming polyolefin, and (b) a spin agent selected from the group consisting of a mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2dichloroethylene. This invention is also directed to a process for the preparation of microcellular foam fibers from synthetic fiber-forming polyolefin which comprises flash-spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) at least 40 wgt. % synthetic fiber-forming polyolefin, and (b) a spin agent selected from the group consisting of a mixture of about 46 wgt. % decafluoropentane, about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane; and a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, together with the description, serve to explain the principles of the invention. FIG. 1 is a plot of the cloud point data for a solution of polypropylene at various weight percentages in a spin agent of VERTREL.RTM. MCA PLUS. FIG. 2 is a plot of the cloud point data for a solution of polypropylene at various weight percentages in a spin agent of HFE-71DE. FIG. 3 is a plot of the cloud point data for a solution of polymethylpentene at various weight percentages in a spin agent of VERTREL.RTM. MCA PLUS. FIG. 4 is a plot of the cloud point data for a solution of polymethylpentene at various weight percentages in a spin agent of HFE-71DE. FIG. 5 is a plot of the cloud point data for a solution of TEFZEL at 20% by weight in a spin agent of HFE-71DE. FIG. 6 is a plot of the cloud point data for a solution of HALAR at 20% by weight in a spin agent of HFE-71DE. DETAILED DESCRIPTION OF THE INVENTION The term "synthetic fiber-forming polyolefin" is intended to encompass certain polymers typically used in the flash-spinning art, e.g., polypropylene, and polymethylpentene. A preferred synthetic fiber-forming polyolefin is isotactic polypropylene. The term "polypropylene" is intended to embrace not only homopolymers of propylene but also copolymers where at least 85% of the recurring units are propylene units. The term "polymethylpentene" is intended to embrace not only homopolymers of polymethylpentene but also copolymers where at least 85% of the recurring units are methylpentene units. The preferred process for making plexifilamentary materials employs a spin fluid in which the synthetic fiber-forming polyolefin concentration is in the range of 6 to 18 wgt. % of the spin fluid. The term spin fluid as used herein means the solution comprising the fiber-forming polyolefin and the spin agent. Unless noted otherwise the term wgt. % as used herein refers to the percentage by weight based on the total weight of the spin fluid. Also, for the subject invention, the folloowing may be used as fiber-forming materials: TEFZEL.RTM., a fluoropolymer obtained from DuPont, which is a copolymer of ethylene and tetrafluoroethylene and HALAR.RTM., a fluoropolymer resin obtained from Ausimont, which is a copolymer of ethylene and chlorotrifluoroethylene. The copolymers can be present in an amount of 10 to 40 wgt. %. A spin agent of the subject invention is VERTREL.RTM. MCA PLUS, an azeotrope consisting of a mixture of about 46 wgt. % 2,3-dihydrodecafluoropentane (HFC-4310mee), about 40 wgt. % trans-1,2 dichloroethylene and about 14 wgt. % cyclopentane, (hereafter MCA), available from E.I. du Pont de Nemours and Company, Wilmington, Del. (DuPont). Another spin agent of the subject invention is HFE-71DE, an azeotrope consisting of a mixture of about 50 wgt. % perfluorobutyl methyl ether and about 50 wgt. % trans-1,2-dichloroethylene, (hereafter 71DE) available from Minnesota Mining and Manufacturing Company, St. Paul, Minn. (3M). MCA has extremely low flammability, that is, MCA has no flash point, but does have upper and lower flammability limits (3-10 volume percent in air). On the other hand, 71DE is non-flammable, that is, 71DE has neither a flash point nor flammability limits. It is desirable that the spin agents should be non-flammable or have very low flammability. It should be noted that these azeotropes may contain some portion of cis-1,2-dichloroethylene. The spin agents of this invention will not change in composition when they are spilled because they are azeotropes. Non-azeotropic spin agents based on trans-1,2 dichloroethylene may become flammable under certain conditions. For example, if a non-azeotropic spin agent were spilled, the volatile components would evaporate and leave the non-volatile component in a concentrated form and if it were flammable, it would provide a risk of fire. In such situations, special solvent handling systems would be required to avoid a potential safety hazard. The term azeotrope as used herein is meant to include azeotrope-like materials that may have a composition that is slightly different from the pure azeotropic composition. The term "cloud-point pressure" as used herein, means the pressure at which a single phase liquid solution starts to phase separate into a polymer-rich/spin liquid-rich two-phase liquid/liquid dispersion. However, at temperatures above the critical point, there cannot be any liquid phase present and therefore a single phase supercritical solution phase separates into a polymer-rich/spin fluid-rich, two-phase gaseous dispersion. In order to spread the web formed when polymers are flash spun in the commercial operations, the flash spun material is projected against a rotating baffle: see, for example, Brethauer et al. U.S. Pat. No. 3,851,023, and then subjected to an electrostatic charge. The baffle causes the product to change directions and start to spread, and the electrostatic charge causes the product (web) to further spread. In order to achieve a satisfactory commercial product in a commercially acceptable time, it is necessary that the web achieve a significant degree of spread, and this can be achieved only if sufficient electrostatic charge remains on the web for the desired time. The charge will dissipate too rapidly if the atmosphere surrounding the web has too low a dielectric strength. A major component of the atmosphere surrounding the web is the vaporized spin agents that, prior to flash spinning, dissolved the polymer which was flash spun. As disclosed in U.S. Pat. No. 5,672,307, primary spin agents such as methylene chloride or 1,2-dichloroethylene, with co-spin agents as listed therein, have a dielectric strength, when vaporized, sufficient to maintain an effective electric charge on the web to insure a satisfactory product. These mixtures have a dielectric strength as measured by ASTM D-2477 of greater than about 40 kilovolts per centimeter (KV/cm). The spin agents of the subject invention, however, have a much higher dielectric strength than methylene chloride and approaches that of trichlorofluoromethane (Freon 11). Some typical values are as follows: ______________________________________ Compound Dielectric Strength (KV/cm) ______________________________________ Methylene Chloride .about.45 Dichloroethylene .about.105 HCFC-122 .about.120 Freon 11 .about.120 Decafluoropentane .about.120 Cyclopentane .about.50 Perfluorobutyl methyl >100 ether ______________________________________ Dielectric strengths for the constituents of the inventive azeotropes are presented above and it would be expected that the dielectric strength of the azeotropes would be greater than that of methylene chloride, as an example. Higher dielectric strength is desirable because it favors higher production rates in that the plexifilamentary material "pins" better to the fast-moving, electrically-charged belt due to electrostatic attraction. The spin fluid may further contain additives such as nucleating agents, stabilizers and the like. Microcellular foams can be obtained by flash-spinning and are usually prepared at relatively high polymer concentrations in the spinning solution i.e., at least 40 wgt. % synthetic fiber-forming polyolefin. Polypropylene, and polymethylpentene are the synthetic fiber-forming polyolefins that can be used. However, as noted above for the plexifilamentary fibers, TEFZEL.RTM. and HALAR.RTM. can also be used to obtain microcellular foams. In the case of foams the copolymers would be used at the same wgt. % as polypropylene, and polymethylpentene, i.e., at least 40 wgt. %. Also, relatively low spinning temperatures and pressures that are above the cloud point pressure are used. Microcellular foam fibers may be obtained rather than plexifilaments, even at spinning pressures slightly below the cloud point pressure of the solution. Spin agents used are the same as those noted above for plexifilamentary, film-fibril materials. Nucleating agents, such as fumed silica and kaolin, are usually added to the spin mix to facilitate spin agent flashing and to obtain uniform small size cells. Microcellular foams can be obtained in a collapsed form or in a fully or partially inflated form. For many polymer/solvent systems, microcellular foams tend to collapse after exiting the spinning orifice as the solvent vapor condenses inside the cells and/or diffuses out of the cells. To obtain low density inflated foams, inflating agents are usually added to the spin liquid. Suitable inflating agents that can be used include low boiling temperature partially halogenated hydrocarbons, such as, hydrochlorofluorocarbons and hydrofluorocarbons; or fully halogenated hydrocarbons, such as chlorofluorocarbons and perfluorocarbons; hydrofluoroethers; inert gases such as carbon dioxide and nitrogen; low boiling temperature hydrocarbon solvents such as butane and isopentane; and other low boiling temperature organic solvents and gases. Microcellular foam fibers are normally spun from a round cross section spin orifice. However, annular dies similar to the ones used for blown films can be used to make microcellular foam sheets. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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