Vulcanized, ethylene/alpha-olefin copolymer rubber composition.

0001The present invention relates to a vulcanized, ethylene/α-olefin copolymer rubber composition, more particularly, a vulcanized, ethylene/α-olefin copolymer rubber composition having a high hardness.

0002The vulcanized, ethylene/α-olefin copolymer rubber composition is excellent in weather resistance and thermal resistance as compared with natural rubbers and general-purpose rubbers such as styrene/butadiene rubber, butadiene rubber, isoprene rubber and the like. Therefore, it is widely used for automobile parts, industrial parts, electric parts and the like to make the most of its characteristics.

0003For some of the above-mentioned uses, the vulcan­ized, ethylene/α-olefin copolymer rubber composition is practically required to have a high hardness. In order to impart a high hardness to a rubber, heretofore, there have been carried out the addition of a large amount of carbon black in combination with a small amount of process oil, the addition of a reactive alkylphenol resin, the addition of a polyolefin and the like.

0004The present inventors have investigated a vulcanized, ethylene/α-olefin copolymer rubber com­position having a high hardness and, as a result, found a novel vulcanized, ethylene/α-olefin copolymer rubber composition obtained by vulcanizing an unvulcanized rubber composition consisting essentially of an ethylene/α-­olefin copolymer rubber; an ethylene/α-olefin copolymer rubber containing an α,β-unsaturated carboxylic acid and/or a derivative thereof; and a polyamide resin.

0005That is to say, the present invention relates to a vulcanized, ethylene/α-olefin copolymer rubber composition obtained by vulcanizing an unvulcanized rubber composition comprising 100 parts by weight of a rubber composition consisting of 0-99% by weight of an ethylene/α-olefin copolymer rubber and 100-1% by weight of an ethylene/α-olefin copolymer rubber containing an α,β-unsaturated carboxylic acid and/or a derivative thereof; and 5-100 parts by weight of a polyamide resin.

0006An object of the present invention is to provide a novel vulcanized, ethylene/α-olefin copolymer rubber composition having a high hardness.

0007Other objects and advantages of the present invention will become apparent from the following description.

0008In the present invention, the ethylene/α-­olefin copolymer rubber (hereinafter referred to as EOR) is at least one selected from ethylene/α-olefin copolymers and ethylene/α-olefin/non-conjugated diene copolymers.

0009The α-olefin is preferably one having 3-10 carbon atoms and, specifically, includes propylene, 1-butene, 1-pentene, 1-hexene and the like.

0010The non-conjugated diene includes dicylco­pentadiene, ethylidenenorbornene, 1,4-hexadiene, methyltetrahydroindene, methylnorbornene and the like.

0011The α,β-unsaturated carboxylic acid includes maleic acid, fumaric acid, itaconic acid, citraconic acid, nadic acid and the like. The derivative thereof includes maleic anhydride, citraconic anhydride, nadic anhydride and the like.

0012The ethylene/α-olefin copolymer rubber containing and α,β-unsaturated carboxylic acid and/or a derivative thereof (hereinafter referred to as the modified EOR) is produced according to the known process such as, for example, the graft copolymerization process stated in Japanese Patent Application Kokoku No. 58-53005 or Japanese Patent Application Kokoku No. 58-445.

0013Also, the modified EOR may contain an alkenyl aromatic monomer such as styrene, methylstyrene or the like together with the α,β-unsaturated carboxylic acid and/or the derivative thereof each of which is produced according to the process stated in Japanese Patent Application Kokai No. 62-112614 or Japanese Patent Application Kokai No. 64-45413.

0014The content of the α,β-unsaturated carboxylic acid and/or the derivative thereof in the modified EOR is preferably in a range of 0.1-10% by weight, more preferably in a range of 0.3-7% by weight, most preferably in a range of 0.5-4% by weight, based on the modified EOR. When the content is smaller than 0.1% by weight, the enhancement of hardness is smaller. When, in contrast, the content is larger than 10% by weight, workability, the properties of the vulcanized rubber and the like are deteriorated.

0015The polyamide resin is not particularly restricted and includes poly-ε-capramide (6-nylon), poly-Ω-undecaneamide (11-nylon), polyhexamethylene adipamide (6,6-nylon), polyhexamethylene sebacamide (6,10-nylon). The polyamide resin can be used irre­spective of its molecular weight and whether or not it has amine groups.

0016The rubber composition comprising the EOR, the modified EOR and the polyamide resin is referred to as the unvulcanized rubber composition.

0017The content of the polyamide resin in the unvul­canized rubber composition is in a range of 5-100 parts by weight, preferably 10-80 parts by weight based on 100 parts by weight of the rubber compound consisting of 0-99% by weight, preferably 0-90% by weight of the EOR and 100-1% by weight, preferably 100-10% by weight of the modified EOR.

0018To the unvulcanized rubber composition, further, may be added an additive such as a reinforcing agent, a filler, a softening agent, a plasticizer, a processing aid, a vulcanization accelerator, a vulcanization agent or the like, which are known in the rubber industry.

0019The unvulcanized rubber composition can be processed according to the conventional process in the rubber industry and can be vulcanized according to the conventional vulcanization process in the rubber industry. Thereby, there can be obtained the vulcanized, ethylene/α-olefin copolymer rubber composition of the present invention.

0020The vulcanized, ethylene/α-olefin copolymer rubber composition of the present invention can be used for automobile parts or industrial rubber parts.

0021The present invention will be explained more specifically below referring to Examples and Comparative Examples. The present invention, however, should not be construed to be restricted by the Examples.

EXAMPLES 1-7 and COMPARATIVE EXAMPLES 1-4

0022A mixture prepared according to the formulation shown in column A of Table 1 was kneaded at a velosity of 60 rpm for 5 min at 250°C in a Brabender Plastograph having a kneading volume of 350 ml. After cooling, carbon black, process oil and stearic acid were added to the above mixture according to the formulation shown in column B of Table 1 and kneaded at a velosity of 60 rpm for 4 min in the Brabender Plastograph kept at a temperature of 100°C. To the resulting mixture, further, were added a vulcanization agent, a vulcanization accelerator and a vulcanization aid and the like, using a 6-in roll according to the formulation shown in column C of Table 1 and kneaded. The resulting unvulcanized rubber composition was vulcanized by heating for 10 min at a temperature of 170°C using a vulcanizing press to obtain a sheet of the vulcanized rubber composition having a thickness of 2 mm. Physical properties of the vulcanized rubber composition were measured according to JIS K6301. Results are collec­tively shown in Table 1. <tables id="tabl0001" num="0001"><img file="EP0346837A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0346837A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0346837A2_D0003.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0346837A2_D0004.tif" /></tables>