Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reissue Patent
2000-03-29
2002-01-22
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S331700, C525S331800, C525S348000, C525S349000, C525S350000, C525S387000
Reissue Patent
active
RE037527
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a heat-resistant rubber composition comprising an ethylene-&agr;-olefin-nonconjugated polyene copolymer rubber. More particularly, the invention relates to a vulcanizable heat-resistant rubber composition having high crosslinking efficiency given by an organic peroxide and capable of providing a vulcanized rubber molded product showing not only excellent mechanical and electrical properties but also prominently high thermal aging resistance, specifically a vulcanizable heat-resistant rubber composition having extremely good fluidity (molding processability).
BACKGROUND ART
Crosslinking of ethylene-&agr;-olefin copolymer rubbers is carried out using not sulfur, but organic peroxides, because the copolymers have no double bond in their main chains. The rubbers have been used for automotive parts, industrial packing, electrical wires and electrical wire connecting parts, but these parts are desired to be produced at a low cost. For reducing the production cost, it is included to decrease an amount of an organic peroxide crosslinking agent. In these methods, however, the crosslinking is insufficiently performed, resulting in problems of low modulus and poor resistance to permanent set.
On the other hand, since ethylene-&agr;-olefin-nonconjugated diene copolymer rubbers prepared by copolymerizing ethylene, &agr;-olefins and nonconjugated polyenes have higher crosslinking efficiency given by an organic peroxides than ethylene-&agr;-olefin copolymer rubbers, the amount of the organic peroxide can be decreased. However, with respect to the ethylene-&agr;-olefin-nonconjugated diene copolymer rubber using 1,4-hexadiene, dicyclopentadiene or 5-ethylidene-2-norbornene as the nonconjugated diene, crosslinking is still insufficiently performed, and the thermal aging resistance is low because a large number of double bonds remain after the crosslinking reaction.
By the way, ethylene-propylene copolymer rubbers or ethylene-propylene-diene copolymer rubbers formed by a diene such as ethylidene norbornene, cyclopentadiene or 1,4-hexadiene have excellent mechanical and electrical properties. Moreover, they shows high thermal aging resistance and weathering resistance because they have no double bond in their main chains. Therefore, these rubbers have been widely used for automotive parts, industrial rubber parts, electrical parts and civil engineering and building materials, as described above. In the fields of automotive parts and electrical parts and the like, however, the ethylene-propylene copolymer rubbers and the ethylene-propylene-diene copolymer rubbers have been recently desired to have much higher thermal aging resistance and fluidity (molding processability).
In order to improve a fluidity of the ethylene-propylene copolymer rubbers, a method of adding oils as plasticizers to the copolymer rubbers is generally utilized. In the ethylene-propylene copolymer rubbers prepared utilizing this method, however, there reside problems that the thermal aging resistance of the molded product is lowered and an oil transfer phenomenon (i.e., bleeding) takes place to markedly reduce commercial values.
Further, a method of adding plastics such as polyethylene to the ethylene-propylene copolymer rubbers is also utilized to improve the fluidity. In the ethylene-propylene copolymer rubbers prepared utilizing this method, however, there generally reside problems of low heat resistance and poor elastomeric properties.
Furthermore, an ethylene copolymer rubber composition which is imparted with good processability (fluidity) by blending an ethylene-&agr;-olefin-polyene copolymer rubber having a different molecular weight is proposed in Japanese Patent Publication No. 14497/1984. However, this rubber composition does not show such high thermal aging resistance as desired.
On the other hand, some examples of conventional methods to improve the thermal aging resistance are described below.
(1) An anti-aging agent is added to the ethylene-propylene copolymer rubber or the ethylene-propylene-diene copolymer rubber.
(2) Since a breakage of a polymer main chain, as the heat deterioration reaction, easily takes place, an ethylene-propylene copolymer rubber which is softened after the heat deterioration and an ethylene-propylene-polyene copolymer rubber which is cured after the heat deterioration are blended.
(3) The diene content in the ethylene-propylene-polyene copolymer rubber is decreased.
A large number of combinations of these methods are also proposed.
For example, Japanese Patent Laid-Open Publication No. 23433/1985 proposes a rubber composition for sulfur vulcanization which is prepared by blending 100 parts by weight of an ethylene-&agr;-olefin-diene copolymer rubber having an iodine value of 5 to 12, 1 to 10 parts by weight of a phenol compound and 1 to 4 parts by weight of an imidazole compound.
The compositions proposed in the publication are improved in the thermal aging resistance, but the level thereof is not satisfactory in the uses for automotive parts and electrical parts, so that the thermal aging resistance should be much more improved.
In Japanese Patent Laid-Open Publication No. 108240/1989, a heat-resistant rubber composition comprising an ethylene-&agr;-olefin copolymer rubber, polyorganosiloxane and a silica type filler treated with a silane compound is disclosed as a heat-resistant rubber composition of high thermal aging resistance. The rubber composition disclosed in the publications are obviously improved in the thermal aging resistance, but the level thereof is not satisfactory in the uses for automotive parts and electrical parts, so that the thermal aging resistance should be much more improved. Moreover, these compositions do not show such high fluidity (molding processability) as desired.
Accordingly, development of a vulcanizable heat-resistant rubber composition having high crosslinking efficiency and capable of providing a vulcanized rubber molded product of high thermal aging resistance has been desired.
Further, development of a vulcanizable heat-resistant rubber composition capable of providing a vulcanized rubber molded product of prominently high thermal aging resistance without losing excellent mechanical and electrical properties inherent in the ethylene-propylene copolymer rubber or the ethylene-propylene-diene copolymer rubber has been also desired.
Furthermore, development of a vulcanizable heat-resistant rubber composition showing high fluidity (molding processability) and capable of providing a vulcanized rubber molded product of prominently high thermal aging resistance without losing excellent mechanical and electrical properties inherent in the ethylene-propylene copolymer rubber or the ethylene-propylene-diene copolymer rubber has been also desired.
The present invention is intended to solve such problems associated with the prior art as described above, and it is an object of the invention to provide a heat-resistant rubber composition being vulcanizable and having high crosslinking efficiency and capable of providing a vulcanized rubber molded product of high thermal aging resistance.
It is another object of the invention to provide a heat-resistant rubber composition being vulcanizable and capable of forming a vulcanized rubber molded product showing not only excellent mechanical and electrical properties but also prominently high thermal aging resistance.
It is a further object of the invention to provide a heat-resistant rubber composition being vulcanizable and having extremely good fluidity and capable of forming a vulcanized rubber molded product showing not only excellent mechanical and electrical properties but also prominently high thermal aging resistance.
DISCLOSURE OF THE INVENTION
A heat-resistant rubber composition according to the invention is a vulcanizable composition comprising:
an ethylene-&agr;-olefin-nonconjugated polyene copolymer rubber (A) composed of ethylene, an &agr;-olefin of 3 to 20 carbon atoms and a nonconjugated polyene, and
an organic peroxide (B); and having vulcanizable prope
Hakuta Takashi
Hosoya Mikio
Kawasaki Masaaki
Tojo Tetsuo
Lipman Bernard
Mitsu Chemicals
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