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
2001-12-21
2004-06-15
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...
C525S09200D, C525S09200D, C525S09200D, C525S100000, C525S328200
Reexamination Certificate
active
06750287
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polyoxymethylene resin composition, and a molding obtained from the composition. The molding comprising the polyoxymethylene resin composition of the present invention have both the excellent frictional wear characteristics and the very high vibration damping properties, and, hence, is suitably usable as materials of vibration-proof sliding components in the fields of precision machines, OA appliances and automobiles.
Hitherto, polyoxymethylene resins have been widely used for various mechanical working components, OA appliances, etc. as engineering resins having excellent mechanical characteristics and heat resistance characteristics. This is especially found in the moldings comprising polyoxymethylene resins, which have excellent frictional wear characteristics, and have been suitably used as gear materials of printers, etc. However, with recent enhancements in precision and function of apparatuses, the reduction in vibration and noise generated by the apparatuses is an important task, and a higher vibration damping ability is now required for material resins.
In general, as vibration dampers, rubbers or thermoplastic elastomers, or resins or rubbers sandwiched between metal sheets have been used. However, the rubbers or thermoplastic elastomers have insufficient heat resistance under high temperature conditions caused by the generation of heat, and furthermore they have frictional wear problems when used against metals and resins, and chemical resistance problems when contacted with chemicals such as ink. On the other hand, resins or rubbers sandwiched between metal sheets have a problem in molding processability.
JP-A-8-165405 discloses a polymer composition obtained by polymerizing formaldehyde in the presence of a block copolymer of a specific vinyl aromatic compound, and JP-A-10-60224 discloses a mixture of a polyoxymethylene polymer and a styrene resin having a functional group. However, both of these techniques aim at improving the impact resistance, and they do not suggest the present invention.
SUMMARY OF THE INVENTION
The present invention provides a polyoxymethylene resin composition to which a very high vibration damping ability is imparted without damaging the excellent frictional wear characteristics of the polyoxymethylene resin, and further provides moldings comprising the resin composition, particularly, mechanical working components such as gears, cams, sliders, levers, arms, clutches, joints, shafts, bearings, key stems, key tops, shutters, reels, etc.
The inventors have conducted intensive research in an attempt to provide a polyoxymethylene resin composition which can solve the above problems without sacrificing the characteristics inherent to the polyoxymethylene resins to the extent possible and which have excellent vibration damping properties. As a result, it has been found that a molding comprising a polyoxymethylene resin composition containing a polyoxymethylene polymer and a specific thermoplastic elastomer has both the superior frictional wear characteristics and a high vibration damping ability. Thus, the present invention has been accomplished.
That is, the present invention relates to a polyoxymethylene resin composition containing (I) 100 parts by weight of a polyoxymethylene polymer and (II) 1-200 parts by weight of a thermoplastic elastomer having a main dispersion peak temperature of −30° C. to +50° C. in a tan &dgr; curve obtained by the measurement of viscoelasticity and having a number average molecular weight of 10,000-500,000.
The polyoxymethylene resin composition of the present invention may further contain (III) 0.1-30 parts by weight of a lubricant and/or (IV) 1-100 parts by weight of a polyolefinic resin based on 100 parts by weight of the polyoxymethylene polymer.
Furthermore, the present invention relates to a molding having a high vibration damping ability that is obtained by molding the above resin composition, particularly, a mechanical working component such as a gear, cam, slider, lever, arm, clutch, joint, shaft, bearing, key stem, key top, shutter, reel, or the like.
DETAILED DESCRIPTION OF THE INVENTION
The polyoxymethylene resin (I) used in the present invention includes homopolymers which are obtained by polymerizing formaldehyde or cyclic oligomers of formaldehyde such as trioxane as its trimer, tetraoxane as its tetramer, etc. and terminated with ether or ester groups at both ends of the polymer; oxymethylene copolymers which contain oxyalkylene units of 2-8 carbon atoms in an amount of 0.1-20 mole % based on the oxymethylene and which are obtained by copolymerizing formaldehyde, trioxane as its trimer or tetraoxane as its tetramer with ethylene oxide, propylene oxide, 1,3-dioxolane, formal of glycol, formal of diglycol, etc.; those which have branches of molecular chains; oxymethylene block polymers containing not less than 50% by weight of segments consisting of oxymethylene units and not more than 50% by weight of different segments; etc.
The above polyoxymethylene polymer preferably has a number average molecular weight of 10,000-500,000.
There are various methods for adjusting the molecular weight of the polyoxymethylene polymer. For example, water, an alcohol (e.g., methanol), an acid (e.g., formic acid), etc. can be chain transferred, or a polymer having at least one of hydroxyl group, carboxyl group, amino group, ester group, and alkoxy group can be chain transferred. Furthermore, if necessary, a formal such as methylal may be added simultaneously. In the present invention, it is preferred to use a polyoxymethylene block copolymer obtained by chain transferring a polymer having a number average molecular weight of not less than 400 and having at least one of hydroxyl group, carboxyl group, amino group, ester group, and alkoxy group.
Furthermore, as preferred polyoxymethylene polymers, mention may be made of polyoxymethylene copolymers (i-1) having oxymethylene groups as main recurring units and containing an oxyalkylene group of 2 or more carbon atoms in an amount of 0.1-5 mole %, more preferably 0.2-3 mole % based on the total oxymethylene groups.
Above all, especially preferred are polyoxymethylene block copolymers (i-2) represented by the following formula (1) which have a number average molecular weight of 10,000-500,000 and comprise a polyacetal segment and a hydrogenated polybutadiene segment hydroxyalkylated at both ends having a number average molecular weight of 500-10,000:
[where A is a polyacetal copolymer residue and comprises 95-99.9 mole % of oxymethylene units and 0.1-5 mole % of oxyalkylene units represented by the following formula (2):
(where R
2
is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and j is an integer selected from 2 to 6), the terminal group being represented by the following formula (3):
(where R
2
and j have the same meanings as defined above), B is a hydrogenated polybutadiene having an iodine value of 20 g-I
2
/100 g or less and containing 2-98 mole % of 1,2-bonds and 2-98 mole % of 1,4-bonds, said 1,2-bonds and 1,4-bonds being present in the polymer chain either in random or in blocks, R
1
is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and k is an integer selected from 2 to 6 where two ks are the same or different from each other].
The above polyoxymethylene copolymer (i-1) and (i-2) can each be naturally used alone or in an optional combination, the weight ratio of (i-1)/(i-2) is preferably in the range of 0/100-95/5.
The polymerization process of the polyoxymethylene polymer has no special limitation, and an example is bulk polymerization, which may be a batch process or a continuous process. According to this bulk polymerization, generally, monomers in a molten state are used and solid bulky polymers are obtained as the polymerization progresses.
Polymerization catalysts are
Doki Makoto
Nakamura Hideki
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Mullis Jeffrey
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