Rubber compositions

The present invention provides a rubber composition which comprises 100 parts by weight of ethylene.multidot..alpha.-olefin.multidot.non-conjugated diene copolymer rubber, 5-40 parts by weight of solid diene rubber and 4-15 parts by weight of sulfur, the butadiene content of said solid diene rubber being 50% by weight or more, the butadiene portions of said solid diene rubber having 40% or more of 1,2 bonds based on all the bonds of said portion, and the ratio of weight-average molecular weight to number-average molecular weight being 2 or less. The rubber composition is a vulcanized rubber excellent in properties such as hardness and strength.

This invention relates to a rubber composition high in hardness. 
More specifically, this invention relates to a rubber composition 
comprising ethylene .alpha.-olefin.multidot.non-conjugated diene copolymer 
rubber (abbreviated to "ethylene.multidot..alpha.-olefin rubber" 
hereinafter), which is high in hardness and has excellent heat resistance 
and weather resistance. 
A rubber composition high in hardness, which comprises an 
ethylene.multidot..alpha.-olefin rubber, a liquid diene rubber such as 
liquid polybutadiene rubber and a large amount of sulfur, is disclosed by 
the present inventors in U.S. Pat. No. 4,708,992 and Japanese Patent 
Publications (Kokai) Nos. 60-262842 and 62-135552. 
The rubber composition, however, has a problem on handling of the liquid 
diene rubber upon weighing and mixing processes because of viscousness of 
the liquid diene rubber used. 
U.S. Pat. No. 4,137,350 discloses a rubber composition high in hardness in 
which a solid diene rubber is used in place of a liquid diene. 
This patent mentions that the solid diene rubber includes polyisoprene 
rubber, polybutadiene rubber, polychloroprene rubber, 
butadiene.multidot.styrene copolymer rubber, 
butadiene.multidot.acrylonitrile copolymer rubber, but does not refer to 
such specific diene rubbers as are used in the present invention. 
As a result of the present inventors' intensive research conducted to find 
out a specific solid diene rubber which provides a rubber composition with 
high hardness and high strength without use of the above-mentioned liquid 
diene rubber, the present invention is completed. 
The present invention relates to a rubber composition which comprises 100 
parts by weight of ethylene.multidot..alpha.-olefin rubber, 5-40 parts by 
weight of solid diene rubber and 4-15 parts by weight of sulfur, the 
butadiene content of said solid diene rubber being 50% by weight or more, 
the butadiene portions of said solid diene rubber having 40% or more of 
1,2 bonds based on all the bonds thereof, and the ratio of weight-average 
molecular weight to number-average molecular weight (abbreviated to "Q 
value" hereinafter) being 2 or less. 
The present rubber composition has excellent properties, that it is, high 
hardness and strength relative to other vulcanized rubbers. 
In the present invention, the ethylene.multidot..alpha.-olefin rubber is a 
copolymer which comprises ethylene, at least one .alpha.-olefin and at 
least one non-conjugated diene. The .alpha.-olefin includes propylene, 
1-butene, 1-pentene and 1-hexene. The non-conjugated diene includes 
dicyclopentadiene, ethylidenenorbornene, 1,4-hexadiene, 
methyltetrahydroindene and methylnorbornene. 
The solid diene rubber used in the present invention is are in which its 
butadiene content is 50% by weight or more, preferably 60% by weight or 
more, its butadiene portions have 40% or more, preferably 50% or more of 
1,2 bonds based on the total bonds of said portion, and Q value being 2 or 
less. 
Preferable examples of the solid diene rubber are polybutadiene rubber and 
styrene.multidot.butadiene rubber. 
The solid diene rubber may be produced by any polymerization process, but 
is commonly produced by anion polymerization. The solid diene rubber may 
be one which is produced by terminal coupling reaction by use of silicon 
chloride, tin chloride and the like. 
If the solid diene rubber has a butadiene content of less than 50 % by 
weight, it becomes hard at room temperature, its roll processability 
degrades, and hardness of the final vulcanized rubber composition changes 
greatly depending upon temperature. 
If the butadiene portion of the solid diene rubber has less than 40% of 
1,2-bonds based on the total bonds of the portion, strength of the final 
vulcanized rubber composition becomes insufficient. 
If Q value of the solid diene rubber is more than 2, hardness of the final 
vulcanized rubber composition is insufficient. 
In the present invention, Q value is obtained from a molecular weight 
distribution which is obtained by a liquid chromatography at 40 .degree. 
C. with tetrahydrofuran (THF). 
Amount of the solid diene rubber added is 5-40 parts by weight, preferably 
10-30 parts by weight, most preferably 13-27 parts by weight based on 100 
parts by weight of the ethylene.multidot..alpha.-olefin rubber. 
If the amount of the solid diene rubber added is less than 5 parts by 
weight, hardness is not sufficiently increased. If the amount is more than 
40 parts by weight, tensile strength is lowered and compression permanent 
set and the like are deteriorated. 
Amount of the sulfur added is 4-15 parts by weight, preferably 5-10 parts 
by weight, most preferably 5-8 parts by weight based on 100 parts by 
weight of the ethylene.multidot..alpha.-olefin rubber. 
If the amount of the sulfur added is less than 4 parts by weight 
sufficiently, high hardness is not obtained. If the amount is more than 15 
parts by weight, the degree of crosslinking markedly increases and 
sufficiently high hardness can be obtained while the breaking extension of 
vulcanized rubbers decreases. Moreover bloom of sulfur occurs at 
unvulcanized condition. 
As mentioned above, the rubber composition of the present invention 
comprises an ethylene.multidot..alpha.-olefin rubber, a solid diene rubber 
and sulfur. If desired, various secondary materials may be added to the 
composition known as compounding ingredients for rubbers such as 
reinforcing agents, fillers, softeners, processing aids, antifoaming 
agents, zinc oxide, stearic acid, vulcanization accelerators, etc. 
The rubber composition of the present invention may be vulcanized by any 
method, such as press vulcanization, steam vulcanization, injection 
modling, hot air vulcanization, UHF vulcanization, LCM vulcanization, PCM 
vulcanization, etc. 
Because of the superior performances of the present rubber composition, it 
has a wide range of uses, such as for automobile parts, industrial parts, 
construction materials. Uses for automobile parts include packings, hoses, 
channel rubber, glass run rubber, weatherstrips, hard solid rubber 
portions in composites of a soft rubber and a hard solid rubber, solid 
rubber portions in composites of a solid rubber and sponge rubber which 
are applied to door seals and trunk seals, etc. Uses for industrial parts 
include rubber rolls, sealing materials, packing, etc. Uses for 
construction materials include setting blocks, rubber tiles, gaskets, etc.