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...
Reexamination Certificate
2000-03-14
2002-05-21
Michl, Paul R. (Department: 1714)
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...
C524S315000, C524S377000, C524S442000
Reexamination Certificate
active
06391956
ABSTRACT:
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP99/00757 which has an International filing date of Feb. 22, 1999, which designated the United States of America.
TECHNICAL FIELD
The present invention relates to a polyoxymethylene resin composition and the molded product thereof, which exhibits excellent resistance to friction and wearing, high stiffness, high repeated impact strength, and small molding strain, and is excellent in gear precision.
BACKGROUND ART
A polyoxymethylene resin has been widely used as an engineering resin having well-balanced mechanical properties and excellent moldability in fields such as automobile parts, electrical and electronic products, etc. In the field of electrical and electronic products, downsizing and lightening of products have been recently proceeding. As a result, the polyoxymethylene resin is required, not only for further improvement in stiffness and resistance to friction and wearing, but also for improvement in impact strength, molding strain and gear precision.
For the purpose of improving stiffness and resistance to friction and wearing, techniques of incorporating an inorganic filler, a lubricant and the like with a polyoxymethylene resin have been proposed. Japanese Patent Publication Unexamined No. 1-263145 (corresponding to U.S. Pat. No. 5,106,896) discloses a technique of adding inorganic powder having a mean particle diameter of 100 &mgr;m or less and an ester of mono- or poly-valent alcohol and fatty acid to a polyacetal resin. Japanese Patent Publication Unexamined No. 3-111446 (corresponding to U.S. Pat. No. 5,173,532) discloses a resin composition obtainable by incorporating with a polyacetal resin a graft copolymer wherein an olefin polymer and a vinyl or ether polymer are chemically bonded in a branch or cross-linking structure, a lubricant, and inorganic powder having a mean particle diameter of 100 &mgr;m or less. These prior art documents do not exemplify, as the inorganic filler, wollastonite which is one of the components of the present invention; therefore, they are totally insufficient in improvement of stiffness and resistance to friction and wearing. Japanese Patent Publication Unexamined No. 5-51514 discloses a technique of adding spindle-shaped calcium carbonate and an ester of mono- or poly-valent alcohol and fatty acid to a polyacetal resin, but this is also insufficient in improving stiffness and resistance to friction and wearing. Japanese Patent Publication Unexamined No. 7-157630 discloses a composition comprising a graft or block copolymer obtained from olefin polymers and at least one of vinyl polymers, fatty ester, inorganic powder having a mean particle diameter of 30 &mgr;m or less and potassium titanate whisker, and a polyacetal resin. The composition disclosed therein is sufficient in improving stiffness, but is still insufficient in improving resistance to friction and wearing. Further, it has a drawback that molding strain (warpage of a molded product) is large.
On the other hand, techniques using wollastonite for a polyoxymethylene resin are described in Japanese Patent Publication Unexamined No. 49-21451 (corresponding to U.S. Pat. No. 3,775,363) which discloses an intimate mixture comprising 98 to 25 parts by weight of a polyoxymethylene resin and 2 to 75 parts by weight of needle-like calcium metasilicate without using a coupling agent. This composition is improved in processability, thermal stability and dimensional accuracy compared with the case using a glass fiber. Japanese Patent Publication Unexamined No. 61-120848 (corresponding to U.S. Pat. No. 4,645,785) discloses a composition having high resistance to wearing comprising 40 to 94.7 parts by weight of a polyoxymethylene, 5 to 50 parts by weight of wollastonite, 0.2 to 5 parts by weight of N-hydroxymethylmelamine, 0.1 to 5 parts by weight of silicone oil having a polymerization degree of 10 to 5,000, 0.1 to 10 parts by weight of polyethylene or a copolymer of ethylene and &agr;-olefin having a molecular weight of 100,000 to 1,000,000. It is observed that this composition is improved in resistance to friction and wearing with metals, but the resistance to friction and wearing with a polyoxymethylene resin or the same composition, which is to be necessary for practical use, is considerably insufficient. Japanese Patent Publication Unexamined No. 64-43555 (corresponding to U.S. Pat. No. 4,987,176) discloses a composition containing polyoxymethylene polymers, wollastonite having a mean thickness of 5 &mgr;m or less and a mean length/thickness ratio of 5 or more, and if necessary additives, and a production method thereof. Further, this prior art specifically discloses, as additives, melamines such as N-hydroxymethylmelamine, silicone oil having a polymerization degree n of 10 to 5,000 and a polyethylene and/or a copolymer of ethylene and &agr;-olefin having a molecular weight of 100,000 to 1,000,000, and this prior art further discloses as more preferable additives, stabilizers, nucleating agents, antistatic agents, light stabilizers, flame-retardants, lubricants, plasticizers, pigments, dyes, thermal stabilizers, and mold release agents. However, this prior art does not teach specific examples of lubricants. The composition disclosed in this prior art purposes improving mechanical strength.
DESCRIPTION OF THE INVENTION
The present inventors have made studies about adding various inorganic fillers, lubricants and other resin components to a polyoxymethylene resin. As a result, they accomplished the present invention by finding a composition which comprises (A) a polyoxymethylene resin, (B) wollastonite, (C) at least one member selected from the group consisting of an ester of (i) an alcohol and a fatty acid, (ii) an ester of an alcohol and a dicarboxylic acid, and (iii) a compound of a polyoxyalkylene glycol, and (D) a polyolefin resin, whereby said composition exhibits excellent resistance to friction and wearing, high stiffness, high repeated impact strength, and small molding strain, and is excellent in gear precision.
Accordingly, the present invention relates to a polyoxymethylene resin composition comprising:
(A) 50 to 99 parts by weight of a polyoxymethylene resin;
(B) 1 to 50 parts by weight of a wollastonite having a volume-average particle diameter of 0.5 to 40 &mgr;m;
(C) 0.1 to 10 parts by weight of at least one member selected from the group consisting of (i) an ester of an alcohol and a fatty acid, (ii) an ester of an alcohol and a dicarboxylic acid, and (iii) a compound of a polyoxyalkylene glycol based on 100 parts by weight of the total amount of Component (A) and Component (B); and
(D) 0.1 to 10 parts by weight of a polyolefin resin based on 100 parts by weight of the total amount of Component (A) and Component (B).
Further, the present invention relates to a molded product prepared by molding the above composition, particularly working parts such as a gear, a cam, a slider, a lever, an arm, a clutch, a joint, an axis, a bearing, a key-stem and a key-top, outsert resinous parts for a chassis, a chassis, a tray and a side plate, which are used for office automation apparatuses represented by a printer and a copying machine; for video apparatuses represented by a video tape recorder (VTR) and a video movie (a video camera); for apparatuses for music, image, or information represented by a cassette player, a laser disc (LD), a mini disc (MD), a compact disc (CD) [including CD-ROM (read only memory), CD-R (recordable) and CD-RW (rewritable)], a digital video disc (DVD) [including DVD-ROM, DVD-R, DVD-RAM (random access memory) and DVD-Audio], a navigation system and a mobile personal computer; for telecommunication apparatuses represented by a cellular phone and a facsimile machine; for an interior or exterior working part for an automobile; and for industrial miscellaneous goods represented by a disposable camera, a toy, a fastener, a conveyor, a buckle, and an apparatus for house-building.
BEST MODE FOR CARRYING OUT THE INVENTION
The polyoxymethyl
Horio Mitsuhiro
Yoshinaga Yuuji
Asahi Kasei Kabushiki Kaisha
Michl Paul R.
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