Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-09-20
2001-05-08
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S394000, C428S359000
Reexamination Certificate
active
06228489
ABSTRACT:
This invention relates to fibrillated acrylic fibers, and in particular to fibers which are oxidizable to form oxidized acrylic fibers.
Polyacrylonitrile fibers have been converted commercially to carbon fibers for a number of years. A known process is described in U.S. Pat. No. 3,533,743, in which the acrylonitrile fiber is oxidized prior to carbonization and graphitization. The acrylonitrile fiber is typically placed under tension during the oxidation phase of the process so that essentially carbon fiber is made from continuous filament acrylonitrile fiber. Continuous filament carbon fiber is used as reinforcement in composite materials for the manufacture of high-strength/low-weight composites, used for example in fishing rods, tennis racquets and racing car body parts. Where the carbon fibers are used in short lengths for discontinuous fiber reinforcement, these are obtained by chopping the continuous filament into short lengths.
Fibrillated acrylic fibers are disclosed, for example, in EP-A-0,265,762.
The present invention provides fibrillated acrylic fibers which are suitable for oxidation in the form of staple fibers, and which are copolymers of acrylonitrile and an unsaturated carboxylic acid.
Such fibers are particularly suitable for oxidation to form fibrillated oxidized acrylic fibers. Preferably the fibers are copolymers of acrylonitrile and itaconic acid or methacrylic acid. Preferably the fiber contains 0.5-2% itaconic acid groups. The copolymer fiber may comprise a further monomer such as methylacrylate, methylmethacrylate or vinylacetate, or any combination thereof. Typically the copolymer contains 3-8% of the further monomer. The staple fibers have a length of about 4-8 mm and are fibrillated to a Canadian Freeness value of less than 700 and more typically 350-500.
The fiber has a decitex value of between 0.6 and 6.0 decitex, preferably about 1.2-1.7 decitex.
Also according to the invention there is provided a method of manufacture of oxidizable acrylic fiber in which a staple acrylic fiber is made by copolymerization of acrylonitrile and an unsaturated carboxylic acid, and is fibrillated in the gel state prior to drying.
The staple fiber is cut to a length in the range of 4-8 mm, preferably 6 mm.
Further monomers such as methyl acrylate, methyl methacrylate or vinyl acetate may be added to the copolymerization.
Preferably the acrylic fiber comprises 0.5-2% itaconic acid, 3-8% methyl acrylate, and 90-96.5% of acrylonitrile.
The itaconic acid or methacrylic acid may be added in the form of free acid or as a sodium or amine salt.
REFERENCES:
patent: 3867499 (1975-02-01), Morgan
patent: 4789509 (1988-12-01), Iked et al.
patent: 5508109 (1996-04-01), Patil et al.
Fagge John
Holzinger Ulrich
Acordis UK Limited
Edwards N.
Howson & Howson
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