Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-06-09
2001-05-08
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S222000
Reexamination Certificate
active
06228966
ABSTRACT:
This invention concerns fibers of homopolymers or copolymers comprising repeating acrylonitrile and/or methacrylonitrile units (called PAN fibers hereinafter) with high modulus and high strength, as well as a process specially adapted for producing them, and their use, especially as reinforcing materials or for production of filters, ropes or friction coatings.
High-strength PAN fibers per se are known. For instance, Dobrecov et al. described high-strength PAN fibers with high modulus, derived from high-molecular-weight types of PANs (e. g., molecular weights of 3·10
6
) in Sowjet. Beiträge zur Faserforschung und Textiltechnik [Soviet Contributions to Fiber Research and Textile Technology], Vol. 9, pages 407-411 (1972).
Fibers with strengths of more than 8.83 cN/dtex and processes for preparing them are known from European Patent Applications 0,165,372 and 0,255,109. High-molecular-weight types of PANs are also used to produce them. According to EP-A 0 255 109, PAN types with a molecular weight greater than 500,000 (weight average) are used, while according to EP-A 0165 372, PAN types with a limiting viscosity greater than 2.5 are used. That corresponds to a molecular weight of more than 210,000 (weight average).
In the documents mentioned above, PAN types with unusually high molecular weight are used without exception. The usual values of the molecular weight of PAN fibers is about 80,000 to 180,000 (cf. the comments of Falkai et al. in “Synthesefasern” [Synthetic Fibers], page 200, Verlag Chemie (1981), or of Masson et al. in “Fiber Producer”, June 1984, pages 34-37).
Use of the high-molecular-weight PAN types reported in those documents entails problems in producing those fibers. Because of the lower solubility of the high-molecular-weight PAN types, the concentration of the spinning dope must be reduced to produce the spinning dope. For instance, in processing PAN types of lower molecular weight it is possible to work with concentrations of 19 to 21%. In the documents above, though, the work is done with reduced concentrations of not more than 10-15%. That means a substantial productivity loss of 25-70% for a production plant. According to EP-A 0 165 372, the processing is done with a concentration of 6-12% in the spinning dope (Examples 5-7). That means a productivity loss of 45-70%.
Furthermore, the residence time for dissolving the PAN in the solvent becomes considerably longer as the molecular weight of the polymer increases. New installations must be built for dissolving in order to retain effectiveness in the dissolution process. Usually additional measures must be taken in order to be able to work at higher concentrations of the spinning dope. In EP-A 0 255 109 an attempt is made to reduce the viscosity by adding 1-10% water to the spinning solution so as to be able to work with higher concentration. But that is linked with danger of corrosion in the plant and that measure allows only limited reduction of the viscosity.
High-strength PAN fibers produced with PAN types having the usual molecular weights are already known. For instance, GB-A 1,193,170 describes PAN fibers which exhibit strengths up to 17.5 g/denier. To be sure, the elongation to break of the fibers described, more than 15%, is too high for many uses.
High-strength PAN fibers with high modulus are known from EP-A 0 044 534. They are also produced with PAN types with the usual molecular weight. Fibers are described with strengths up to 81 cN/tex or with initial moduli up to 1989 cN/tex. PAN fibers with strengths greater than 100 cN/tex and, at the same time, initial moduli greater than 15 N/tex (based on 100% elongation) are not described in this document.
PAN fibers with strength up to 100 cN/tex and with initial modulus up a maximum of 21.5 N/tex are known from EP-A 0 645 479. PAN fibers with strengths greater than 100 cN/tex and, at the same time, initial moduli greater than 15 N/tex (based on 100% elongation) are not described in this document.
PAN fibers are popular reinforcing materials in aggressive environments because of their high resistance, especially to highly alkaline environments or to UV radiation. High strengths and high initial moduli at low elongations to break are particularly desired for industrial applications. There is a need for PAN fibers with such a property profile, and especially for PAN fibers that can be obtained from processes with high productivity.
The subject of this invention is fibers of homopolymers or copolymers comprising at least 70% by weight repeating acrylonitrile and/or methacrylonitrile units, characterized in that the fibers have a strength of more than 100 cN/tex and an initial modulus greater than 15 N/tex, based on 100% elongation.
Precipitation or solution polymers produced by the usual processes can be used as polymer raw materials. Both homopolymers and copolymers of acrylonitrile are used, depending on the requirements for the application. Care should be taken for the highest possible purity in the monomers used. Particularly suitable comonomers include all the unsaturated compounds that can be copolymerized with acrylonitrile, especially unsaturated carboxylic acids such as acrylic acid, methacrylic acid or itaconic acid; unsaturated sulfonic acids such as allyl, methallyl, or styrene sulfonic acid; unsaturated carboxamides such as acrylamide or methacrylamide; esters of unsaturated carboxylic acids, such as the methyl, ethyl, propyl, butyl, or octyl ester of acrylic acid or methacrylic acid, or polyfunctional hydroxyethyl or aminoethyl esters of acrylic acid or methacrylic acid, or their derivatives; esters of carboxylic acids with unsaturated alcohols or ethers based on unsaturated alcohols, such as vinyl esters and ethers, for instance, vinyl acetate, vinyl stearate, vinyl butyrate, vinyl bromoacetate, vinyl dichloracetate, or vinyl trichloracetate; unsaturated aldehydes or ketones, such as acrolein or crotonaldehyde; acid halides of unsaturated carboxylic acids, such as acrylic acid chloride or methacrylic acid chloride; or other monomers which can be copolymerized with acrylonitrile, such as styrene, butadiene, propylene or vinyl halides, such as vinyl chloride, vinylidene dichloride, or vinyl bromide.
Preferred monomers which can be used for copolymerization are acrylic acid or methacrylic acid esters of C
1
-C
22
alcohols, such as methyl acrylate, methyl methacrylate, butyl methacrylate, octyl methacrylate, ethyl acrylate, isobutyl acrylate, (meth)acrylic acid esters of perfluorinated C
1
-C
22
alcohols; vinyl-aromatics with up to 20 carbon atoms, e.g., styrene or vinyl toluene; esters of maleic acid and of fumaric acid with C
1
-C
22
alcohols; vinyl chloride, vinyl acetate, ethylene, and butadiene. Methyl acrylate is preferred.
Other functional monomers which can copolymerize with acrylonitrile or methacrylonitrile can also be used. The functional monomers can contain hydroxy, silane, or epoxy groups. Examples of those are vinyl trimethoxysilane, vinyl tributoxysilane, methacryloxypropyltrimethoxysilane, vinyl-tris-(methoxyethoxy)silane, vinyl triacetoxysilane, hydroxyethyl methacrylate, hydroxybutyl methacrylate, glycidyl acrylate, glycidyl methacrylate, or 2-hydroxyethyl acrylate.
Other suitable acrylonitrile polymers are SAN, ABS and NBR copolymers, in which the acrylonitrile proportion should have the weight percentage specified previously.
It is preferable for the polymers used to contain at least 90% by weight and especially preferably at least 99% by weight acrylonitrile units.
Very specially, polyacrylonitrile homopolymers or copolymers with molecular weights (weight-average) of 80,000 to 210,000, preferably 175,000 to 210,000 are used.
The strengths of the fibers according to the invention are more than 100 cN/tex, preferably 101 to 150 cN/tex.
The initial moduli, based on 100% elongation, of the fibers according to the invention are more than 15 N/tex, preferably 22 to 35 N/tex, and very specially preferably 22-30 N/tex.
The tensile strength at break of the fibers according to the invention is more than 85 cN
Acordis Kehlheim GmbH
Frommer & Lawrence & Haug LLP
Michl Paul R.
LandOfFree
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