Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Including surface treatment of porous body
Reexamination Certificate
2001-10-15
2003-05-27
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Including surface treatment of porous body
C264S17800F, C264S184000, C264S210700, C264S210800, C264S211150, C264S211160, C264S211170, C264S233000, C264S235600
Reexamination Certificate
active
06569366
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing meta-type wholly aromatic polyamide filaments comprising, as principal repeating units, metaphenylenediamineisophthalamide units and having good mechanical properties and heat resistance, with high productivity, and wholly aromatic polyamide filaments produced by the process.
BACKGROUND ART
It is well known that wholly aromatic polyamides produced by poly-condensing aromatic diamines with aromatic dicarboxylic acid dichloride exhibit excellent heat resistance and flame-retardance. Also, it is known that the above-mentioned wholly aromatic polyamides are soluble in amide compound solvents and that from the solution of the polymer dissolved in the solvent, filaments can be produced by a dry-spinning, a wet-spinning or a semidry-semiwet-spinning method.
Among the above-mentioned wholly aromatic polyamides, meta-type wholly aromatic polyamides, which will be referred to as meta-aramids hereinafter and a representative of which is polymetaphenyleneisophthalamide, are used for producing filaments which are useful as heat-resistant, flame-retardant filaments. It is known that the above-mentioned heat resistant, flame retardant meta-aramid filaments are industrially produced by the methods (a) and (b) indicated below.
(a) A method in which a solution of polymetaphenyleneisophthalamide is prepared by subjecting metaphenylenediamine and isophthalic acid chloride to a low-temperature solution polymerization procedure in N,N-dimethylacetamide; hydrochloric acid contained, as a by-product, in the resultant polymer solution is neutralized with calcium hydroxide; the polymer solution containing the produced calcium chloride is subjected to a dry-spinning procedure to produce polymetaphenylenediamine isophthalamide filaments. (Japanese Examined Patent Publication No. 35-14,399, U.S. Pat. No. 3,360,595)
(b) A method in which a polymerization reaction system prepared by poly-condensing a meta-phenylenediamine salt and isophthalic acid chloride is brought into contact with and mixed with an aqueous liquid system comprising an organic solvent (for example, tetrahydrofuran) which is not a good solvent for the target polyamide, an inorganic acid-acceptor and a water-soluble neutral salt, to produce particles of polymetaphenyleneisophthalamide; the polymer particles are separated from the mixture system (Japanese Examined Patent Publication No. 47-10,863); the separated polymer particles are dissolved in an amide compound solvent; and the resultant polymer solution is subjected to a wet-spinning procedure in an aqueous coagulation bath containing an inorganic salt (Japanese Examined Patent Publication No. 48-17,551)
Beside the above-mentioned methods (a) and (b), the following methods (c) to (f) have been proposed as methods of producing meta-aramid filaments.
(c) A method in which a solution of a meta-aramid prepared by dissolving a meta-aramid produced by a solution polymerization method in an amide compound solvent and not containing inorganic salts or containing a small amount (2 to 3%) of lithium chloride, is subjected to a wet-shaping procedure to produce shaped articles, for example, filaments. (Japanese Examined Patent Publication No. 50-52,167)
(d) A method in which a meta-aramid solution produced by a solution polymerization in an amide compound solvent is neutralized with calcium hydroxide or calcium oxide; the resultant meta-aramid polymer solution containing calcium chloride and water is extruded into a gas atmosphere through orifices; the extruded filamentary polymer solution streams are passed through a gas atmosphere and introduced into an aqueous coagulation bath to coagulate the polymer solution streams into solid filament form; the coagulated filamentary products are passed through an aqueous solution of an inorganic salt, for example, calcium chloride, to produce meta-aramid filaments. (Japanese Unexamined Patent Publication No. 56-31,009)
(e) A method in which a meta-aramid solution produced by a solution polymerization in an amide compound solvent is neutralized with calcium hydroxide or calcium oxide; the resultant meta-aramid polymer solution containing calcium chloride and water is subjected to a wet spinning procedure, through spinning orifices, in an aqueous coagulation bath containing calcium chloride in a high concentration, to form filaments. (Japanese Unexamined Patent Publications No. 8-074,121 and No. 10-88,421)
(f) A method in which a solution of a meta-aramid containing an inorganic salt is extruded in the form of filamentary streams into a spinning chimney having a high temperature; immediately after the resultant meta-aramid filaments are withdrawn from spinning chimney, the filaments are cooled with a low temperature aqueous solution to cause the filaments to be swollen with water; the water-swollen meta-aramide filaments are drawn in an aqueous drawing bath containing a salt capable of plasticizing the filaments, to thereby produce easy-dyeable porous filaments having a plurality of very fine pores and exhibiting a bulk density of 1.3 or less. (Japanese Examined Patent Publication No. 52-43,930)
The above-mentioned method (a) is advantageous in that a polymer solution (a material solution for a spinning procedure) for a spinning procedure can be prepared without isolating the polymer from the polymerization system, but disadvantageous in that, because a dry-spinning procedure using an amide compound solvent having a high boiling temperature is employed, a necessary production cost is high and the stability of the spinning procedure is significantly decreased with an increase in the number of the spinning orifices per spinneret. Also, when the polymer solution is wet-spun in an aqueous coagulation bath, only filaments which are opaque and have a low mechanical strength may be obtained. Thus, there are many difficulties in the method in which the meta-aramid polymer solution obtained by the solution polymerization is subjected to a wet-spinning procedure using a aqueous coagulation bath, and therefore, this wet-spinning method has not yet been utilized in industry.
On the other hand, in the methods (b) and (c), although the problems occurring in the method (a) can be avoided, the resultant filaments are unsatisfactory in the structural density of the filaments.
Also, in the method (d), in the spinning procedure in which the polymer solution is extruded through a spinneret into the air, the stability of the spinning procedure is significantly decreased with an increase in the number of the orifices per spinneret, and thus this method has low productivity and efficiency.
Further, in the method (e), there is a problem such that although the resultant filaments exhibit good properties, it is difficult to carry out the method (e) at a high spinning rate, and thus the productivity of the method (e) is low.
The method (f) is utilized to produce porous filaments having a bulk density significantly less than 1.3. However, the method (f) is a variation of the dry-spinning method and thus has the same problems as those of the dry-spinning method.
Meta-aramid filaments can be used for electronic materials in which the excellent heat resistance and insulation property of the filaments are utilized. In this case, to employ the filaments for the electronic materials, the contamination of ionic substances in the filaments must be as low as possible, and if possible, the filaments preferably contain no inorganic ionic substances. However, in the conventional production processes, it is unavoidable that, in the filament-forming procedures, the polymer solution and the coagulation bath contains salts, for example, calcium chloride or lithium chloride which have high affinities to the polymer dope and is easily soluble in the polymer dope, in a high concentration. Therefore, there is a problem such that contamination of the resultant filaments with a large amount of salts cannot be prevented. To remove the salts from the filaments, a large scale of water-washing procedure must be applied to the filaments, and
Nakamura Tsutomu
Sadanobu Jiro
Toyohara Kiyotsuna
Teijin Limited
Tentoni Leo B.
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