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
2000-10-25
2003-01-14
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S398000, C525S400000, C525S401000, C524S736000, C524S741000, C524S877000, C528S230000, C528S250000, C528S270000
Reexamination Certificate
active
06506838
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to modified oxymethylene polymers capable of giving moldings with a good repeated impact resistance at the welded parts and a well controlled waxy smell. Furthermore, the present invention relates to modified oxymethylene polymer compositions capable of giving moldings with improved sliding characteristic at the welded parts.
Polyoxymethylene gives moldings with distinguished mechanical strength, fatigue resistance, electrical characteristics, etc. and thus are widely applied to gears, bearings, other mechanical or electrical parts, etc. as an engineering resin. Furthermore, polyoxymethylene moldings are distinguished by their self lubrication properties and thus have many uses utilizing the self lubrication properties.
However, the self lubrication of the polyoxymethylene moldings themselves and sliding characteristics of moldings of polyoxymethylene compositions consisting only of polyoxymethylene and various lubricants are not always satisfactory for recent multifunctional and diversified uses of polyoxymethylene moldings, so that the sliding characteristics of polyoxymethylene moldings need to be improved. Almost all the moldings have welded parts, and it has been keenly desired to stably obtain moldings with distinguished impact resistance and sliding characteristics even at the welded parts.
Well known methods for improving the sliding characteristics of polyoxymethylene moldings include, for example, (1) a method for adding a solid lubricant such as molybdenum disulfide, etc. to polyoxymethylene, (2) a method for adding powder or fibers of polyethylene, polytetrafluoroethylene, etc. to polyoxymethylene, and (3) a method for adding a liquid or solid lubricant such as petroleum-based lubricating oil, synthetic lubricating oil, etc. to polyoxymethylene.
Above all, addition of liquid ethylene. &agr;-olefin copolymer as a lubricant to polyoxymethylene, as disclosed in Japanese Patent No. 2,909,228 is very useful for improving the sliding characteristics of polyoxymethylene moldings, but the liquid ethylene-a-olefin copolymer is essentially less compatible with polyoxymethylene and its good sliding characteristics of the moldings cannot be maintained for a long time. That is, the good sliding characteristics of moldings can be maintained while the lubricant can bleed out onto the surfaces of moldings at the sliding interfaces, but the sliding characteristics of the moldings are largely lowered when the lubricant dissipates from the sliding interfaces of moldings. Furthermore, peeling sometimes occurs on the surface of injection moldings by phase separation due to poor compatibility of the lubricant with polyoxymethylene.
Other methods for improving the sliding characteristics than the above-mentioned are also disclosed in U.S. Pat. No. 4,377,667, JP-A-2-24307, JP-A-3-31742, JP-A-4-323248, JP-A-5-9363, etc., where modified oxymethylene polymers blocked at one end of polyoxymethylene by an alkylene oxide as an adduct residue to alcohol and/or carboxylic acid, are proposed.
However, the modified oxymethylene polymers disclosed in these references fail to give satisfactory repeated impact resistance at the welded parts of moldings, requiring further improvement. The moldings of modified oxymethylene polymers sometimes give off a waxy smell, giving a highly unpleasant feeling.
Said JP-A-5-9363 further discloses a resin composition comprising the modified oxymethylene polymer and an olefin compound, where the sliding characteristics are improved at the unwelded parts of moldings, but the repeated impact resistance is not satisfactory at the welded parts of the molding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide modified oxymethylene polymers capable of giving moldings with a good improved repeated impact resistance at the welded parts and a controlled waxy smell at the same time, and also to polymer compositions capable of giving moldings with improved sliding characteristics at the welded parts.
As a result of extensive studies, the present inventors have found that modified oxymethylene polymers capable of giving moldings with a distinguished repeated impact resistance at welded parts and a controlled waxy smell at the same time by using modified oxymethylene polymers with a specific molecular weight distribution. Moreover, the present inventors have found that said modified oxymethylene polymers can be obtained by making a hindered phenol-based antioxidant present during the polymerization of specific modified oxymethylene polymers.
Furthermore, the present inventors have found that polymer compositions comprising said modified oxymethylene polymers and a specific olefinic polymer can give moldings with distinguished sliding characteristics at the welded parts and particularly a distinguished repeated impact resistance at the welded parts.
That is, the present invention involves the following aspects [1]-[8]:
[1] Modified oxymethylene polymers, which comprise a linear polymer of oxymethylene repeat units, blocked at one end by at least one terminal group selected from the group consisting of an alkylene oxide as an adduct to an alcohol residue, represented by the following general formula (1):
and an alkylene oxide as an adduct to a carboxylic acid residue, represented by the following formula (2):
where in the general formula (1) and (2) R
1
and R
1
, are independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group; R
2
is selected from the group consisting of an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group; m is an integer selected from 2-6 and n is an integer selected from 1-1,000, (a) the linear polymer excluding the terminal group having a number average molecular weight of 10,000-500,000 and (b) the modified oxymethylene polymers having a molecular weight distribution (Mw/Mn) of not more than 2.5.
[2] Modified oxymethylene polymers according to said [1], wherein the modified oxymethylene polymers have a molecular weight distribution of not more than 2.2.
[3] A process for producing modified oxymethylene polymers according to said [1], which comprises anionically polymerizing formaldehyde with at least one compound selected from the group consisting of an alkylene oxide as an adduct to alcohol and an alkylene oxide as an adduct to carboxylic acid as a chain transfer agent (both of which will be hereinafter referred to merely as “alkylene oxide adduct”), wherein 0.001-1 part by weight of a hindered phenol-based antioxidant on the basis of 100 parts by weight of the alkylene oxide adduct is added to the alkylene oxide adduct in advance, and then the formaldehyde and the alkylene oxide adduct are subjected to anionic polymerization.
[4] A process according to said [3], wherein the hindered phenol-based antioxidant has no ester bond and a molecular weight of not more than 400.
[5] Modified oxymethylene polymer compositions, which comprise 100 parts by weight of modified oxymethylene polymers according to said [1] or [2] and 0.3-15 parts by weight of an olefinic polymer of structural units represented by the following general formula (3):
where R
3
and R
3
′ are independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group and an ether group, and k is an integer selected from 10-500.
[6] Modified oxymethylene polymer compositions according to said [5], wherein the olefinic polymer is an ethylene.&agr;-olefin random copolymer comprising 20-80 mol % of ethylene units, 20-80 mol % of propylene units and 0-10 mol % of other a-olefin units than the propylene units, and the olefinic polymer has a molecular weight distribution (Mw/Mn) of not more than 2.
[7] Modified oxymethylene polymer compositions, which comprise 5-95 wt % of modif
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Short Patricia A.
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