Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-01-04
2002-05-14
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S222000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06388013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polyolefin fibers which contain a small amount of a hydrocarbon resin and to a process for the production thereof Polyolefin fibers, most notably polypropylene fibers, produced in accordance with the invention have improved tenacity and exhibit other improved characteristics.
2. Description of the Prior Art
It is known to incorporate small amounts of additives in polymer compositions used to produce fibers to improve processing and, in some instances, fiber characteristics. The additives can include other polymers. This approach has been widely utilized with polyesters, polyamides and polyolefins, including polypropylene.
The addition of a small amount of additive polymer capable of forming an anisotropic melt with a fiber-forming polymer in the temperature range at which fibers are spun is disclosed in U.S. Pat. Nos. 4,442,057 and 4,442,266. The additive polymers are liquid crystal polymers such as copoly chloro 1,4 phenylene ethylene dioxy 4,4′ dibenzoate/terephthalate and copolymers of 6-oxy-2 naphthoyl and p-oxybenzoyl moieties. Fiber-forming polymers to which the additive polymers can be added include polyesters, polyamides and polypropylene.
U.S. Pat. No. 4,518,744 discloses an improved melt spinning process and fibers obtained by the addition of 0.1 to 10 weight percent of a polymer which is immiscible in a melt of common fiber-forming polymers such as polyester, copolyesters, polyamides, copolyamides and polyolefins. While the immiscible polymers can be from the same chemical family as the fiber-forming polymer, the immiscible polymer must have an extensional viscosity such that molten spheres of the additive polymer deform into microfibrils along the spinning threadline.
Imidated polyalkyl methacrylate is added to polyethylene terephthalate at a 0.1 to 5 weight percent level in U.S. Pat. No. 5,565,522 to improve spinning and reduce thread break.
Aromatic resins of pure or mixed aromatic monomer feed streams and which may be partially hydrogenated are known and used for various non-fiber applications. For example, resins made from pure aromatic feed streams are recommended as flow modifiers for use in paint, caulking, coating and adhesive applications. Selectively partially hydrogenated resins polymerized from mixed aromatic feed streams are used as tackifiers for polyolefin, ethylene-vinyl acetate and styrenic block copolymers. Selectively partially hydrogenated resins obtained from styrenic monomers are used for polymer-based adhesives, caulk, sealants and coatings. Certain of these aromatic hydrocarbon resins are also disclosed for use with polyolefin resin films. At 8 to 15 weight percent levels, they are reported to increase stiffness, reduce MVTR, improve opticals and decrease elasticity of polypropylene films. While numerous applications have been suggested for these aromatic resins, nowhere is it suggested that the resins can be used for polyolefin fiber production or that any advantages may result therefrom.
SUMMARY OF THE INVENTION
The present invention provides polyolefin fibers with improved tenacity obtained by the addition of a small amount of aromatic hydrocarbon resin to the polyolefin. More specifically, the invention relates to improved polypropylene fibers extruded and drawn from a blend comprising polypropylene and 1 to 10 weight percent aromatic hydrocarbon resin derived from a fully or partially hydrogenated oligomeric mixture of compounds which exhibit higher tenacity at equivalent elongations and/or higher elongations at equivalent tenacity than that of fibers produced from conventional homopolymer polypropylene of the same melt flow. Fibers made using the above composition have the ability to process at higher speeds and in finer deniers.
More specifically, the fibers of the invention are comprised of from 90 to 99 weight percent polypropylene and 1 to 10 weight percent aromatic hydrocarbon resin selected from the group consisting of selectively hydrogenated resins of polymerized styrenic-based polymers, resins obtained from polymerized mixed aromatic monomer/feed streams and resins obtained by polymerizing pure monomer feed streams. In a highly useful embodiment of the invention, the aromatic hydrocarbon additive resin has a weight average molecular weight from about 300 to 8000 and molecular weight distribution from about 1.2 to 5.0. It is even more preferred if the aromatic hydrocarbon has a ring and ball softening point from about 75° C. to about 140° C. and is present in an amount from about 2.5 to 7.5 weight percent of the total weight of the fiber-forming composition. Preferably the polypropylene is a propylene homopolymer having an isotacticity of 92 percent or higher. In an alternative preferred embodiment, the polypropylene is a blend of 70 percent of less ethylene-alkyl acrylate copolymer, preferably ethylene-methyl acrylate copolymer. Fine denier fibers or the invention obtained using the above-described improved fiber-forming compositions and having an improved balance of properties including tenacity, modulus and elongation at break have a denier per filament of 6 or less and melt flow rate of 14 to 40 g/10 min. Improved medium denier fibers of the invention will have a denier per filament between 6 and about 30 and are produced from using fiber-forming compositions having melt flow rates of 9 to 25 g/10 min.
DETAILED DESCRIPTION
The invention relates to polyolefin fibers and fiber-spinning process. More particularly, the invention relates to polypropylene (PP) fibers and process for their preparation.
PP resins utilized for the formation of fibers include homopolymers and copolymers of polypropylene as well as blends of these homopolymers and copolymers with minor amounts of other resins. Propylene polymers and polymer blends having have melt flow rates (MFRs) less than about 45 g/10 min and, more preferably, from about 15 to 40 g/10 min. determined in accordance with ASTM D 1248 are useful for melt-spinning of fine denier fibers, such as 6 denier per filament or less, by conventional processes for textile, apparel and industrial high tenacity fiber applications. PP polymers and blends with MFRs from 25 to 35 g/10 min are most useful for the formation of such fine denier fibers. PP polymers or blends suitable for making coarser fibers such as those needed for carpets in a bulk continuous fiber (BCF) process or for medium denier industrial fibers, will have MFRs in the range of 9 to 25 g/10 min, more preferably, from about 12 to 22 g/10 min. Such fibers have a denier per filament ranging between 6 dpf and 30 dpf.
Conventional processes of fiber formation from a melt involve extrusion of the polymer in the melt state from a spinnerette followed by drawing in a one step operation or in a second step. Utilizing lower MFR polymers for fine denier fiber formation significantly increases stresses on the spinline which causes melt fracture at nominal spinning speeds and, therefore, is not commercially feasible. On the other hand, using higher MFR polymers for coarse denier spinning results in excessive fiber breakage due to the material not having sufficient melt strength to sustain it in the melt for the comparatively longer time than required for finer fibers. One of the objectives of this invention is to provide a polymer that would have the melt strength for processing in coarser denier fibers as well as the ability to process fine deniers at conventional process speeds.
PP has been conventionally used to produce high tenacity fibers using a high tenacity fiber process which involves an additional hot air drawing zone. An example of this process would be the AUSTROFIL SML system designed for high tenacity fiber applications. Fibers having tenacities of between 5.5 to 7.0 gm/den and breaking elongations of 25 to 35% are commercially feasible using conventional PP homopolymers or copolymers through such a process. To achieve higher tenacities, it is necessary to draw the fibers to a greater extent; however, the breaking elongation of highly drawn fibe
Bridges Michael
Saraf Anil W.
Baracka Gerald A.
Equistar Chemicals LP
Heidrich William A.
Nutter Nathan M.
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