Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-03-07
2003-07-15
Edwards, N. (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S394000, C428S395000
Reexamination Certificate
active
06592987
ABSTRACT:
DESCRIPTION
TECHNICAL FIELD OF THE INVENTION
The present invention relates to wholly aromatic synthetic fibers spun from a liquid-crystalline polymer solution, such as polyparaphenylene terephthalamide fibers having a low ion content, a high Young's modulus, good dimensional stability, excellent heat resistance and insulating properties; process for preparing the same and use of said fibers.
BACKGROUND OF THE INVENTION
Wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions have been heretofore used as industrial fibers or fibers for special-purpose clothing because of their excellent heat resistance and high Young's modulus. Polyparaphenylene terephthalamide (PPTA) fibers and polyparaphenylene benzobisoxazole (PBO) fibers, for example, are known as the representative of such wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions.
According to known preparation process of PPTA and PBO fibers, the polymers are converted to liquid-crystalline state with strong acid which is used as a solvent for dissolving the polymers to make spinning solutions, and then subjected to shearing force exerted by a spinneret to be shaped into fibers of high crystalline orientation. Immediately after the spinning, the as-spun fibers are washed with water and treated with alkali to neutralize conc. Sulfuric acid or phosphoric acid which is used as the solvent, dried and heat-treated at temperatures not lower than 150° C., and thereafter wound up as filaments (cf. U.S. Pat. Nos. 3,767,756 and 5,296,185).
U.S. Pat. No. 3,869,430 (Japanese Patent Publication No. 14567/1984) also disclosed a preparation method of filaments, in which as-spun fibers spun from a liquid-crystalline polymer solution is given a neutralizing treatment with an alkali, and then washed with water. The crystal size of the polyamide fibers before a heat treatment which are obtained according to the same patent exceeds 50 Å, when calculated based on the X-ray diffraction method specifically described therein.
The fibers so obtained contain, as incorporated therein, the salt or salts formed by the neutralization and normally the salt content of the fibers ranges 0.5 to 3 wt %. For example, when sulfuric acid is used as the solvent and sodium hydroxide is used for the neutralization, the ions constituting the salt are mainly Na
+
and SO
4
2−
, their mol ratio being approximately 2:1.
This salt is apt to be ionized in the presence of water when the fibers are used under highly humid conditions, to deteriorate insulation property of the fibers. This causes a problem when the fibers are put to uses where electrical insulation property is required.
On the other hand, it is known that paper, rope, cord or textile produced from PPTA or PBO fibers exhibit excellent characteristics such as good dimensional stability, processability, high Young's modulus and low shrinkage under high temperature treatments attributable to their polymeric structures, as insulating and low-dielectric materials when used as electronic insulation materials. However, when used in applications requiring high insulation property, for example, a material for electric circuit substrate, there is the possibility that the ionic substance induces migration as above, which has incurred restrictions on development of their further usage.
The purpose of the present invention is to solve the aforesaid problems in prior art and to provide wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions, which, while maintaining the high heat resistance and high Young's modulus inherent in wholly aromatic synthetic fibers such as PPTA and PBO fibers, also have a low ionic substance content and, in particular, are useful as electrical and electronic parts, a process for their preparation and uses thereof.
DISCLOSURE OF THE INVENTION
It is an object of this invention to provide wholly aromatic synthetic fibers spun from liquid-crystalline polymer solution, process for their preparation and use thereof, which are characterized by the features as summarized below:
(1) wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions characterized by having a crystal size (110 plane) of 50Å or less and an ionic substance content of 1.0 wt % or less;
(2) wholly aromatic synthetic fiber according to (1) above, wherein said wholly aromatic synthetic fiber spun from a liquid-crystalline polymer solution is polyparaphenylene terephthalamide fiber;
(3) wholly aromatic synthetic fiber according to (1), wherein said wholly aromatic synthetic fiber spun from a liquid-crystalline polymer solution is polyparaphenylene benzobisoxazole fiber;
(4) wholly aromatic synthetic fiber according to any one of (1) to (3), whose moisture content ranges 15-300 wt %;
(5) Wholly aromatic synthetic fibers wherein the ionic substance content of the fibers described in any one of (1) to (4) is reduced to 0.2 wt % or less by a deionization treatment;
(6) wholly aromatic synthetic fiber having a crystal size larger than 50 Å, which is obtained by heat treating the fiber of (5) above;
(7) A process for manufacturing polyparaphenylene terephthalamide fibers, which is characterized by spinning and neutralizing a sulfuric acid solution of polyparaphenylene terephthalamide, adjusting the moisture content of the resulting fibers to 15 to 300 wt %., and thereafter subjecting the same to a deionizing treatment, without an intervening heat treatment.
(8) A process for manufacturing polyparaphenylene terephthalamide fibers, characterized by heat-treating the polyparaphenylene terephthalamide fibers obtained through the manufacturing process of (7) above at 150 to 500° C.
(9) A process for manufacturing polyparaphenylene benzobisoxazole fibers, which is characterized by spinning and neutralizing a phosphoric acid solution of polyparaphenylene benzobisoxazole, adjusting the moisture content of the resulting fibers to 15 to 300 wt %., and thereafter subjecting the same to a deionizing treatment, without an intervening heat treatment.
(10) A process for manufacturing polyparaphenylene benzobisoxazole fibers, characterized by heat-treating the polyparaphenylene benzobisoxazole fibers obtained through the manufacturing process of (9) above at 150 to 700° C.
(11) Insulating and low dielectric materials characterized by comprising the wholly aromatic synthetic fibers which are described in (5).
(12) Cord characterized by comprising the wholly aromatic synthetic fibers which are described in (5).
(13) Fabric characterized by comprising the wholly aromatic synthetic fibers which are described in (5).
(14) A sheet-form structure for an electric circuit substrate characterized by comprising wholly aromatic synthetic fibers which are described in (5).
Hereinafter the invention is described in further details.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions which have a crystal size (110 plane) of 50 Å or less and an ionic substance content of 1.0 wt % or less.
The term “wholly aromatic synthetic fibers spun from liquid-crystalline polymer solutions” used herein means synthetic fibers obtained by spinning a liquid-crystalline solution of a wholly aromatic polymer or copolymer such as a wholly aromatic polyamide. The kind of wholly aromatic polymer or copolymer is subject to no critical limitation, so long as its liquid-crystalline solution is spinnable into fibers. According to the present invention, PPTA fibers and PBO fibers are preferred as the wholly aromatic fibers obtained by spinning a liquid-crystalline solution, in particular, the former of the two, i.e., PPTA fibers are the most desirable. Accordingly, hereinafter the invention is explained referring mainly to PPTA fibers, but it should be understood that the invention is in no sense limited to PPTA fibers only, but is similarly applicable to any other wholly aromatic synthetic fibers obtained by spinning liquid-crystalline solutions of wholly aromatic po
Sakamoto Shiro
Suzuki Hiroyuki
E. I. du Pont de Namours and Company
Edwards N.
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