An ethylene-.alpha.-olefin vulcanized rubber composition with excellent weather resistance and high transparency which is formed by vulcanizing with an organic peroxide an unvulcanized rubber composition comprising an ethylene-.alpha.-olefin rubber containing no metal oxide nor metal carbonate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an ethylene-.alpha.-olefin vulcanized rubber 
composition having a high strength and further an excellent thermal 
resistance, excellent weather resistance, and high transparency. 
Uses of rubber compositions which require a high strength, thermal 
resistance and weather resistance and further a high transparency include 
automotive parts, industrial goods, electrical parts, etc. Rubber 
compositions having such properties can be used, for example, as materials 
for tubes, hoses, sheets, rolls, and the see-through part of masks and the 
like. Further, they can be used to form composite materials by combining 
them with glass or transparent resins such as polymethyl methacrylate and 
polycarbonate. 
2. Description of the Prior Art 
It is known that rubber composition with some transparency, called 
"semi-translucent rubber", can be obtained by adding to 
ethylene-.alpha.-olefin rubber silica and/or magnesium carbonate as a 
reinforcing filler. However, they have defects of a low total light 
transmittance and a high haze value. 
The present inventors have already obtained vulcanized rubber compositions 
which give a high total light transmittance and a low haze value by 
vulcanizing with an organic peroxide an unvulcanized rubber composition 
characterized by being formed by adding to an ethylene-.alpha.-olefin 
rubber 10 to 70 parts by weight of anhydrous silica with an average 
particle diameter of its primary particles of 20 nm or less relative to 
100 parts by weight of said rubber without addition of metal oxides or 
metal carbonates thereto (see Japanese Patent Application No. 183,753/85). 
However, these rubber compositions are still of low strength and 
unsatisfactory in thermal resistance, weather resistance, etc. because 
they contain no metal oxide nor metal carbonate added thereto. 
Accordingly, improvement thereof has been eagerly awaited. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide, obviating the disadvantages of 
prior arts mentioned above, an ethylene-.alpha.-olefin vulcanized rubber 
composition which has a high strength, excellent thermal resistance and 
weather resistance, and further a high total light transmittance and a low 
haze value. 
The present inventors have made extensive studies to develop such a 
vulcanized rubber composition and resultantly attained this invention. 
Thus, this invention relates to an ethylene-.alpha.-olefin vulcanized 
rubber composition with excellent weather resistance and high transparency 
which is obtained by vulcanizing with an organic peroxide an unvulcanized 
rubber composition comprising an ethylene-.alpha.-olefin rubber containing 
no metal oxide nor metal carbonate added thereto and containing 
(1) 10 to 70 parts by weight of anhydrous silica with an average particle 
diameter of its primary particles of 20 nm or less, 0.01 to 2 parts by 
weight of at least one compound selected from those represented by the 
general formulas (I), (II) and (III) shown below, and 0 to 2 parts by 
weight of at least one compound selected from those represented by the 
general formulas (V) and (VI) shown below, each relative to 100 parts by 
weight of said rubber, or 
(2) 10 to 70 parts by weight of anhydrous silica with an average particle 
diameter of its primary particles of 20 nm or less, 0.01 to 2 parts by 
weight of at least one compound selected from those represented by the 
general formulas (I), (II) and (III) shown below, 0.01 to 2 parts by 
weight of a compound represented by the general formula (IV) shown below, 
and 0 to 2 parts by weight of at least one compound selected from those 
represented by the general formulas (V) and (VI) shown below, each 
relative to 100 parts by weight of said rubber: 
General formula (I) 
##STR1## 
wherein R.sub.0 denotes hydrogen or an alkyl group of 1 to 3 carbon atoms, 
and R.sub.1 denotes an alkyl group of 1 to 3 carbon atoms; 
General formula (II) 
##STR2## 
wherein R.sub.2 denotes an alkyl group of 6 to 10 carbon atoms, R.sub.3 
denotes an alkyl group of 1 to 3 carbon atoms, and n denotes a real number 
from 1 to 5; 
General formula (III) 
##STR3## 
wherein R.sub.4 denotes an alkyl group of 1 to 3 carbon atoms, and l 
denotes a real number from 1 to 5; 
General formula (IV) 
##STR4## 
wherein R.sub.5 denotes hydrogen or an alkyl group of 1 to 8 carbon atoms, 
and X denotes hydrogen or chlorine; 
General formula (V) 
##STR5## 
wherein R.sub.6 denotes an alkyl group of 1 to 9 carbon atoms; 
General formula (VI) 
##STR6## 
wherein R.sub.7 denotes an alkyl group of 1 to 6 carbon atoms, Y denotes 
C, S, C--C or O--C--C--O, a denotes a number of 1, 2 or 4, m denotes an 
integer from 1 to 6 and m' denotes an integer from 1 to 16. 
DETAILED DESCRIPTION OF THE INVENTION 
The reason why the silica used for a reinforcing filler is restricted to 
anhydrous silica in this invention is that hydrous silica gives an 
insufficient transparency in view of total light transmittance and haze 
value, and such fillers as magnesium carbonate, clay, talc, and titanium 
white give a very poor transparency. 
The reason why the average particle diameter of the primary particles of 
anhydrous silica is restricted to 20 nm or less in this invention is that 
a sufficient transparency cannot be obtained at larger particle diameter 
than specified above. 
Further, the reason why the amount of anhydrous silica added is restricted 
to 10 to 70 parts by weight relative to 100 parts by weight of 
ethylene-.alpha.-olefin rubber is that outside the above-mentioned range 
the resulting rubber composition is poor in processability and physical 
properties and hence of no practical use and that above the said range the 
transparency also becomes poor. 
The amount of anhydrous silica to be added is preferably 20 to 60 parts by 
weight. 
Ethylene-.alpha.-olefin rubber compositions usually contain metal oxides 
such as zinc oxide and/or metal carbonates such as zinc carbonate added 
thereto for the purpose of increasing the cure rate and improving the 
thermal and weather resistance. However, they are not added in this 
invention because the addition of these metal oxides and/or metal 
carbonates causes marked decrease of total light transmittance, increase 
of haze value, and resultantly severe deterioration of transparency. 
In this invention, stabilizers represented by the above-mentioned general 
formulas (I) to (VI) are used together with above-mentioned anhydrous 
silica. Among these stabilizers of various kinds, at least one compound 
selected from those represented by the general formulas (I), (II) and 
(III), or said at least one compound and a compound represented by the 
general formula (IV), are indispensable components. The amount thereof to 
be added is, for both cases, 0.01 to 2 parts by weight, preferably 0.05 to 
1 part by weight, most preferably 0.1 to 0.5 part by weight, relative to 
100 parts by weight of ethylene-.alpha.-olefin rubber. When the compound 
amount is less than the above-mentioned range, a satisfactory thermal 
resistance and weather resistance cannot be obtained. Use of an amount 
exceeding the range is unnecessary and uneconomical. 
In the compound represented by the general formula (II) or (III), its 
molecular terminal may be in the form of other protective groups which can 
replace a hydrogen atom. Also, it may be the salt of said amine. These are 
treated as equivalent with regard to their effect. 
The compounds represented by the general formulas (V) and (VI) are not 
indispensable components and are not necessarily needed. However, the 
addition of at least one compound selected from these is effective from 
the viewpoint of further enhancing the effect of stabilizers. They are 
used, in general, in an amount of 2 parts by weight or less, preferably in 
the range from 0.05 to 1 part by weight, most preferably 0.1 to 0.5 part 
by weight, relative to 100 parts by weight of ethylene-.alpha.-olefin 
rubber. 
As the example of the compounds represented by the general formula (I) to 
(VI) used in this invention, there may be mentioned the followings. 
General formula (I): 
Bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate 
Bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate 
General formula (II): 
Poly{[6-(1,1,3,3-tetramethyl 
butyl)amino-1,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-pyperidyl)imino 
]-hexamethylene[(2,2,6,6-tetramethyl-4-pyperidyl)imino]} 
General formula (III): 
Poly{(6-morpholino-S-triazine-2,4-diyl) 
[2,2,6,6-tetramethyl-4-pyperidyl)imino]-hexamethylene[(2,2,6,6-tetramethyl 
]-4-pyperidyl)imino]} 
General formula (IV): 
2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 
2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole, 
2-(2'-hydroxy-5'-amylphenyl)benzotriazole, 
2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, 
2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 
2-(2'-hydroxy-3'-5'-di-t-amylphenyl)benzotriazol, 
2-(2'-hydroxy-3'-5'-di-methylphenyl)benzotriazole, 
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 
2-(2'-hydroxy-3'-5'-di-t-butylphenyl)-5-chlorobenzotriazole, 
2-(2'-hydroxy-3',5'-dimethylphenyl)-5-chlorobenzotriazole. 
General formula (V): 
N,N'-Bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine. 
General formula (VI): 
Pentaerythritol-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)]propionate, 
triethyleneglycol-bis[3-(3'-t-butyl-5'-methyl-4'-hydroxyphenyl)]propionate 
, 1,6-hexanediol-bis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)]propionate, 
2,2-thio-diethylene-bis[3-(3',5'-di-t-butyl-4-hydroxyphenyl)]propionate, 
2,2-thio-diethylene-bis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)]propionate, 
octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate. 
These compounds, represented by the general formulas (I) to (VI), are all 
already known as a stabilizer for polyolefin type plastics (see, for 
example, Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 
27,624/72, Japanese Patent Application Kokai (Laid-Open) Nos. 62,835/81 
and 5,349/76, etc.), but are utterly unknown as a stabilizer for 
vulcanized rubber compositions. 
In consideration of the fact that vulcanized rubber composition differ from 
ordinary polyolefin type resisns not only in polymer species but also 
markedly in composition and process steps in respect of the former's 
having been incorporated with many kinds of additives including 
reinforcing agents, vulcanizing agents, and vulcanization accelerators and 
further having been subjected to a vulcanization step, it is quite 
surprising that, as disclosed by this invention, these compounds do 
exhibit an excellent effect on a specific rubber composition, namely 
ethylene-.alpha.-olefin rubber containing anhydrous silica. 
The above-mentioned unvulcanized rubber composition of 
ethylene-.alpha.-olefin rubber incorporated with anhydrous silica and 
stabilizers is then subjected to vulcanization. In this invention, since 
vulcanization with sulfur or the like compounds does not give a vulcanized 
rubber composition of high transparency, vulcanization is conducted with 
an organic peroxide. 
The organic peroxide to be used for the above purpose is not specifically 
limited, and may be one or more kinds of organic peroxides including 
diacyl peroxides, dialkyl peroxides, peroxyesters, and perketals. As 
specific examples thereof, mention may be made of benzoyl peroxide, 
1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 
di-t-butylperoxydiisopropylbenzene, dicumylperoxide and 
2,5-dimethyl-2,5-di(t-butylperoxy)hexane. These peroxides are added in an 
amount of 1 to 5 parts by weight relative to 100 parts by weight of the 
rubber component. 
As occasion demands, ethylene dimethacrylate, trimethylpropane 
trimethacrylate, triallyl isocyanurate, and like compounds may be added as 
a co-crosslinking agent for organic peroxide vulcanization. 
The method of vulcanization itself to be used for the above-mentioned 
organic peroxide vulcanization in this invention is not specifically 
limited and may be any conventional method known to the art. However, 
vulcanization is usually conducted at 140.degree. to 200.degree. C. for 2 
to 60 minutes. 
The "ethylene-.alpha.-olefin rubber" referred to in this invention means a 
copolymer of ethylene and one or more kinds of .alpha.-olefins and a 
copolymer of ethylene, one or more kinds of .alpha.-olefins, and one or 
more kinds of unconjugated dienes. Examples of .alpha.-olefins include 
propylene, 1-butene, 1-pentene, and 1-hexene. Examples of unconjugated 
dienes include dicyclopentadiene, ethylidenenorbornene, 1,4-hexadiene, 
methyltetrahydroindene, and methylnorbornene. 
In this invention, softeners, plasticizers, processing aids, stearic acid, 
etc. known to the rubber industry may be added to the composition as 
occasion demands. 
This invention will be described in detail below with reference to 
Examples. However, it is not limited to these Examples.