Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-12-12
1999-09-07
Hoke, Veronica P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
523204, 523210, 524400, C08K 504
Patent
active
059488441
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polyacetal resin composition. More particularly, the present invention is concerned with a polyacetal resin composition comprising a terminal-stabilized polyacetal resin, and at least one aliphatic carboxylic acid metal salt added to the terminal-stabilized polyacetal resin, the at least one aliphatic carboxylic acid metal salt having occluded therein a specific amount of at least one metal compound selected from the group consisting of a metal hydroxide and a metal chloride, wherein the aliphatic carboxylic acid metal salt does not have attached to a surface thereof at least one metal compound selected from the group consisting of a metal hydroxide and a metal chloride, or has on a surface thereof a very limited specific amount of the metal compound. The polyacetal resin composition of the present invention has not only excellent thermal aging resistance, but also excellent aging discoloration resistance and excellent anti-mold deposit properties. The polyacetal resin composition of the present invention can be extremely advantageously used for various applications, especially, production of mechanical parts which will be used under high temperature conditions for a prolonged period of time (for example, mechanical parts employed in association with automobile engines).
BACKGROUND ART
Polyacetal resins not only have an excellent balance of mechanical strength, chemical resistance and sliding properties, but can also be easily processed. By virtue of these advantages, polyacetal resins are widely used, as engineering plastic materials, for a wide variety of applications including mechanical parts, such as mechanical parts for electric and electronic equipment as well as automobiles.
When a polyacetal resin is used in the above-mentioned fields, it is necessary that the polyacetal resin have good thermal aging resistance and aging discoloration resistance. Further, from the viewpoint of improving molding productivity, it is important that the polyacetal resin have good anti-mold deposit properties.
Conventionally, as a method for improving the thermal aging resistance of a polyacetal resin, it is generally known to add an aliphatic carboxylic Japanese Patent Application Publication Specification No. 55-22508 (corresponding to U.S. Pat. No. 3,743,614) and Examined Japanese Patent Application Publication Specification No. 60-56748 (corresponding to GB Patent Application Publication No. 1425771)!.
However, when a conventionally known aliphatic carboxylic acid metal salt is added to a polyacetal resin, although the thermal aging resistance of the polyacetal resin can be improved to some degree, the aging discoloration resistance and anti-mold deposit properties of the polyacetal resin become low. The poor aging discoloration resistance causes a molded product to have a poor appearance. The poor anti-mold deposit properties of the polyacetal resin lead to a lowering of the molding productivity, because a set of mold halves used for molding such a polyacetal resin needs to be frequently dismantled and cleaned. It has been strongly desired in the art to solve these problems.
SUMMARY OF THE INVENTION
The present inventors have made extensive and intensive studies with a view toward solving the above-mentioned problems of the prior art. As a result, it has unexpectedly been found that when a specific aliphatic carboxylic acid metal salt is added to a terminal-stabilized polyacetal resin, wherein the aliphatic carboxylic acid metal salt has occluded therein a metal compound selected from the group consisting of a metal hydroxide and a metal chloride, and occasionally has attached to a surface thereof a metal compound selected from the group consisting of a metal hydroxide and a metal chloride, and wherein the occluded metal compound and the surface-attached metal compound are, respectively, present in an amount of from 1 to 300 ppm by weight and in an amount of from 0 to 20 ppm by weight, each based on the total weight of the aliphatic carboxylic acid metal sa
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Hata Tadashige
Oka Mikio
Asahi Kasei Kogyo Kabushiki Kaisha
Hoke Veronica P.
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