Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-06-29
2003-08-05
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S064000, C525S069000, C525S100000, C525S106000
Reexamination Certificate
active
06602953
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyoxymethylene resin composition showing distinguished slidability (low coefficient of friction and low wear rate) without deteriorating the heat stability of the polyoxymethylene resin composition, when molded, and also showing a considerable improvement in thin-molding peeling insusceptibility, while preventing deterioration of slidability due to contact with a solvent, for example, for dry cleaning, etc. Moldings of the present polyoxymethylene resin composition are suitable for sliding components in precision devices, household electrical appliances, OA appliances, automobiles, industrial materials, sundry goods, etc.
BACKGROUND ART
Polyoxymethylene resins have been widely used not only in various mechanical working components, but also in OA appliances, etc. as an engineering resin showing balanced mechanical properties and a distinguished wear resistance, but just the mere distinguished resistance derived from the polyoxymethylene resin composition per se has not been found to be satisfactory for sliding materials. Thus, the sliding components molded from polyoxymethylene resin compositions have been so far used by greasing the sliding portions. The greasing step requires an additional working time and thus greaseless polyoxymethylene resin compositions have been so far keenly desired and several improvements have been proposed.
One of the improvement technologies is to add a silicone compound to a polyacetal resin. For example, JP-A-60-42449 discloses a composition having both friction wear resistance and antistatic effect endowed by adding to the polyacetal resin a dimethylpolysiloxane, some of whose side-chain methyl groups are modified into polyoxyalkylene-substituted alkyl groups; U.S. Pat. Nos. 4,874,807 and 4,879,331 disclose compositions prepared by adding a silicone oil having a specific viscosity to the polyacetal resin; JP-A-4-224856 discloses a composition comprising a polyacetal resin, a polyethylene wax and a silicone oil; JP-A-6-49322 discloses a composition comprising an oxymethylene block copolymer having a specific structure and polyorganosiloxane having a specific molecular weight; and JP-A-5-9362 discloses a composition comprising an oxymethylene block polymer having a specific structure and a silicone compound such as dimethylpolysiloxane or dimethylsiloxane, whose methyl groups are modified by hydrogen, an alkyl group, an aryl group, an ether group, etc.
Furthermore, combinations of a polyoxymethylene resin with an inorganic filler, a lubricant, etc. have been so far studied to improve the rigidity and friction wear resistance. For example, U.S. Pat. No. 4,645,785 discloses a composition comprising polyoxymethylene resin, wollastonite, N-hydroxymethylmelamine, silicone oil having a polycondensation degree of 10-5,000 and polyethylene having a molecular weight of 100,000-1,000,000 or a copolymer of ethylene and &agr;-olefin, but the composition is not satisfactory with respect to the coefficient of friction and wear rate.
Still furthermore, the composition comprising polyoxymethylene resin and a silicone compound and the composition comprising polyoxymethylene resin, an inorganic filler and a silicone compound have a poor compatibility of the polyoxymethylene resin with the silicone compound, resulting in such a disadvantage as peeling occurrence in the gate region during the injection molding. Such a considerable peeling phenomenon appears particularly in the case of moldings having a thickness of 2 mm or less.
As a technology of improving the peeling insusceptibility of moldings made from a composition comprising a polyoxymethylene resin and a silicone compound, JP-A-11-279421 discloses a composition comprising a thermoplastic resin including a polyoxymethylene resin, a compatibilizing agent and a silicone gum or silicone rubber, but the composition has such a disadvantage as considerable deterioration in the heat stability of the polyoxymethylene resin due to use of an acid-modified compatibilizing agent, and no improvement effect on the molding peeling insusceptibility has been observed at all in the case of thin moldings.
As a technology of combining a polyoxymethylene resin with a silicone compound-grafted polyolefinic resin polymer, JP-A-4-146949 discloses a combination of a polyacetal resin with an organosiloxane-modified ethylene-ethyl acrylate copolymer. The technology is directed to an improvement in the impact resistance of an ethylene-ethyl acrylate resin by high level cross-linking of the resin with an organosiloxane to provide a rubber. As to the lubricating properties, it only discloses the lubricating properties proper to the polyacetal resin per se.
Still furthermore, the composition comprising a polyoxymethylene resin and a silicone compound has such a disadvantage that the slidability will be considerably deteriorated, when brought into contact with a solvent for dry cleaning, etc., because the silicone is washed away from the surface, and thus improvements of such a disadvantage have been desired in applications to fasteners, buckles, clips, etc., but no specific improvement technologies have been disclosed yet.
DISCLOSURE OF THE INVENTION
As a result of extensive studies on the aforementioned problems, the present inventors have found that a polyoxymethylene resin composition comprising polyoxymethylene resin (A), a specific amount, based on (A), of a silicone compound-grafted polyolefinic resin (B1) and a silicone compound (B2) shows a distinguished slidability (low coefficient of friction and low wear rate) as moldings without deteriorating the heat stability of the polyoxymethylene resin and also shows considerable improvement in the peeling insusceptibility when made into thin moldings, while preventing deterioration of slidability due to contact with a solvent for dry cleaning, etc. and have accomplished the present invention.
That is, the present invention relates to inventions of the following [1] to [17].
[1] A polyoxymethylene resin composition, which comprises a polyoxymethylene resin (A), a silicone compound-grafted polyolefinic resin (B1) and a silicone compound (B2), the amount of the silicone compound-grafted polyolefinic resin (B1) being 0.05 to 10 parts by weight on the basis of 100 parts by weight of the polyoxymethylene resin (A), and the ratio of (B1)/(B2) by weight being 99/1 to 70/30.
[2] A polyoxymethylene resin composition, which comprises a polyoxymethylene resin (A) and a polyolefinic resin composition (B) comprising a silicone compound-grafted polyolefinic resin (B1), obtained by a grafting reaction of a polyolefinic resin with a silicone compound in a graft ratio of the silicone compound to the polyolefinic resin of 95 to 30% by weight, and a silicone compound (B2), the amount of the silicone compound-grafted polyolefinic resin (B1) being 0.05 to 10 parts by weight on the basis of 100 parts by weight of the polyoxymethylene resin (A), and the ratio of (B1)/(B2) by weight being 99/1 to 70/30.
[3] The polyoxymethylene resin composition according to [2], which comprises a polyoxymethylene resin (A), a polyolefinic resin composition (B) comprising a silicone compound-grafted polyolefinic resin (B1), obtained by a grafting reaction of a polyolefinic resin with a silicone compound in a graft ratio of the silicone compound to the polyolefinic resin of 95 to 30% by weight, and a silicone compound (B2), and a silicone compound (B3), the ratio of (B1)/[total of (B2) and (B3)] by weight being 99/1 to 70/30.
[4] The polyoxymethylene resin composition according to any one of [1] to [3], wherein 0.05 to 5 parts by weight of a lubricant (C) and/or 0.5 to 100 parts by weight of an inorganic filler (D) are further contained on the basis of 100 parts by weight of the polyoxymethylene resin (A).
[5] The polyoxymethylene resin composition according to [2], wherein in the grafting reaction of the polyolefinic resin with the silicone compound the ratio
Horio Mitsuhiro
Yoshinaga Yuuji
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Mullis Jeffrey
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