Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-06-21
2003-05-27
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S480000, C528S488000, C528S489000, C528S499000, C528S50200C, C528S50200C, C528S50200C, C528S503000, C264S184000, C264S210400, C264S210500, C264S210800, C264S211150, C264S211160, C264S233000
Reexamination Certificate
active
06569987
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing meta aramid filaments having improved quality and an enhanced productivity.
BACKGROUND ART
A meta aramid has a molecular skeleton consisting essentially of aromatic cyclic structures and thus has exhibit excellent heat resistance and flame resistance. Therefore, the meta aramid is employed for the uses of filaments, films and sheets My for which high heat resistance and flame resistance important.
Filaments of above-mentioned meta aramid (which may be referred to as meta-type armide hereinafter), for example, poly-meta-phenyleneisophthalamide filaments, are generally produced by one of the following two industrial methods.
Namely, in the first method, a poly-meta-phenyleneisophthalamide solution is produced by low temperature solution polymerization of meta-phenylenediamine with isophthalic acid chloride in N,N-dimethylacetamide; hydrochloric acid dissolved, as a by-product, in the above-mentioned solution is neutralized with calcium hydroxide; and the polymer solution comprising calcium chloride produced by the above-mentioned neutralization and dissolved in the solution is directly subjected to a dry-spinning procedure, as disclosed in Japanese Examined Patent Publication No. 35-14,399 and U.S. Pat. No. 3,360,595. In this method, the content of calcium chloride contained in the polymer solution is about 45% by weight, based on the weight of the polyamide.
In the second method, meta-phenylenediamine is reacted with isophthalic acid chloride in an organic solvent, for example, tetrahydrofuran, which is not a good solvent for a meta-type aramid produced from the reaction; the reaction system is brought into contact with an aqueous solution system containing an inorganic acid-acceptor and water-soluble neutral salt, to cause the reaction to be completed; the resultant poly-meta-phenyleneisophthalamide produced in a powder form is isolated (as shown in Japanese Examined Patent Publication No. 47-10,863); the polymer powder is dissolved in an amide-type solvent; and the resultant solution is subjected to a wet-spinning procedure using an inorganic salt-containing aqueous coagulation bath, as shown in Japanese Examined Patent Publication No. 48-17,551.
The first method is advantageous in that the polymer solution can be used as a spinning solution without isolating the polymer, but is disadvantageous in that the spinning procedure is carried out in a dry-spinning method using an amide-type solvent having a high boiling temperature, and thus the energy cost for the spinning procedure is high, and when the number of spinning holes per spinneret is increased, the stability of the spinning procedure is significantly decreased. When the polymer solution is subjected to a wet-spinning procedure using an aqueous coagulation liquid, to solve the above-mentioned problems, almost all of the resultant filaments are devitrificated fibers having a low mechanical strength. Therefore, this wet-spinning method has not yet industrially utilized.
The second method is advantageous in that the problems of the first method do not occur, but is disadvantageous in that the solvent for the polymerization system is different from the solvent for the spinning system, a procedure for re-dissolving the polymer which has been isolated from the polymerization system is necessary and, to obtain a stable solution of the re-dissolved polymer, specific care and an accurate control for the re-dissolving procedure are necessary, as disclosed in Japanese Examined Patent Publication No. 48-4,661.
To solve the above-mentioned problems, currently various attempts have been made to obtain meta-type aramid filaments having a high mechanical strength without loss of clarity of the filaments by wet-spinning a meta-type aramid polymer solution prepared by a solution polymerization.
For example, Japanese Unexamined Patent Publication No. 10-88,421 and No. 10-53,920 provide a process in which a meta aramid solution containing a salt, at a concentration of 3% by weight or more, is used as a spinning solution; the spinning solution is wet-spun in an aqueous coagulation bath containing a solvent and a salt each in a specific range of concentration, at a specific range of temperature; the spun filaments are treated in a condition-controlling liquid having specific ranges of solvent concentration and salt concentration at a specific temperate range; and the condition-controlled filaments are drawn in an aqueous drawing bath having specific ranges of solvent concentration and a specific salt concentration at a specific temperature range. It is sure that the above-mentioned process enables filaments having excellent mechanical properties to be obtained with a reduced generation of voids. However, this process has a problem that the productivity of the filaments is lower than that of the process in which a spinning solution containing substantially no inorganic salt is used.
As another process, Japanese Unexamined Patent Publications No. 8-74,121 and No. 8-74,122 disclose a process in which an aromatic diamine is reacted with an aromatic dicarboxylic acid chloride in an amide-type solvent; the resultant meta aramid solution containing hydrochloric acid produced as a by-product is neutralized with calcium hydroxide, calcium oxide or calcium carbonate; the resultant neutralized solution containing an inorganic salt in a high concentration is mixed with specific amounts of an amide-type solvent and water; and the resultant liquid containing the polymer and water each in a specific range of content is employed as a spinning solution for a wet spinning procedure. When the above-mentioned process is carried out by using an aqueous coagulating liquid, the coagulating agent is prevented from penetrating into the coagulated filaments, and thus filaments having a low void content and a high transparency can be produced with a high stability. The filaments have a high drawability and thus drawn filaments having excellent mechanical properties can be obtained. This process, however, has such a problem that when the number of extruding holes of the spinneret is large, for example, 1,000 or 30,000 per spinneret, the wet-spinning with a high stability is difficult, and thus the production of aramid filaments having excellent quality with a high productivity cannot be carried out.
On another hand, as processes for wet-spinning a spinning solution having a low content of the inorganic salts, various processes in which hydrogen chloride produced by the polymerization procedure is neutralized with a specific neutralizing agent which causes a salt produced by the neutralization reaction to be insoluble in the solvent for the polymerization. However, when ammonia gas is used as shown in Japanese Unexamined Patent Publication No. 35-14,399 and Japanese Unexamined Patent Publication No. 49-129,096, it is difficult to completely remove the resultant insoluble ammonium chloride salt from the neutralized intermediate product, and thus, a problem that not only the spinning nozzles are readily soiled, but also that the stability of the wet-spinning procedure is insufficient, occurs. In the processes using a solid neutralizing agent in the form of granules, for example, sodium carbonate or sodium hydroxide, since the neutralization is carried out in the manner of a solid/liquid reaction, and the resultant neutralized salt is insoluble in the solvent and thus deposited on the surfaces of the neutralizing agent granules, the neutralization cannot be completely effected.
Also, in the neutralization procedure using hydrogen solidum carbonate in the state of a solid, as a neutralizing agent, carbon dioxide gas is generated during the neutralization reaction to remove the resultant neutralized salt from the surfaces of the solid neutralizing agent granules and to improve the efficiency of the neutralization procedure. However, the neutralization is imperfectly effected, and the generated gas causes bubbles in the resultant polymer solution and the spinnability of the polymer solution is reduced.
D
Iwasaki Hirozumi
Ohba Akihiro
Takiue Kotaro
Yoshitomi Takashi
Hampton-Hightower P.
Sughrue & Mion, PLLC
Teijin Limited
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