JPH06157830A - Rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition which gives a molding improved in sliding properties, abrasion resistance, weatherability, ozone resistance, heat resistance, etc., by incorporating a specified amount of a specified acrylic- modified polyorganosiloxane into a synthetic rubber and/or a natural rubber. CONSTITUTION:A polyorganosiloxane (A) of formula I (wherein R<1>, R<2> and R<3> are each a 1-20C hydrocarbon or halogenated hydrocarbon group; Y is a group capable of free-radical reaction, or an organic group having an SH group; Z<1> and Z<2> are each H, lower alkyl, etc.; (m) is a positive integer of 10,000 or smaller, and (n) is 1 or greater) is copolymerized with component (B) comprising a (meth)acrylic ester of formula II (wherein R<7> is H or methyl; and R<8> is alkyl, alkoxy-substituted alkyl, cycloalkyl or aryl) or a mixture of at least 70wt.% of this ester and at most 30wt.% copolymerizable monomer at a weight ratio of component A to component B of (5:95) to (95:5). At least 0.1 pt.wt. acrylic- modified polyorganisiloxane obtained is incorporated into 100 pts.wt. synthetic rubber and/or natural rubber.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is characterized by containing a synthetic rubber or natural rubber composition, particularly a specific acrylic-modified polyorganosiloxane, and has slidability, abrasion resistance, weather resistance and ozone resistance. The present invention relates to a rubber composition that gives a rubber having excellent heat resistance.

[0002]

2. Description of the Related Art Rubber generally has so-called rubber elasticity and is excellent in extensibility, resilience, impact resilience, tear strength, bendability, etc., but it also has tackiness depending on the degree of vulcanization, and therefore is It has the disadvantage of poor mobility and wear resistance. Further, a rubber containing a large number of carbon-carbon double bonds in its main chain portion has the drawback of being inferior in weather resistance, ozone resistance and heat resistance. For example, ethylene-propylene rubbers that do not contain a double bond in the main chain have excellent weather resistance, ozone resistance, heat resistance, and workability, so they have been used for glass runs and window frames. Since it is inferior in properties, flocking may be applied to glass sliding parts (Japanese Patent Laid-Open No. 2-2042
It is necessary to form a urethane slipping layer (see Japanese Patent Application Laid-Open No. 3-163129), which results in a long process and poor productivity. Furthermore, rubber containing many double bonds, such as styrene-butadiene rubber, has excellent cold resistance and workability, but it does not have good slidability, abrasion resistance, weather resistance, ozone resistance, and heat resistance, and acrylonitrile- Butadiene rubber has excellent oil resistance, but it has poor slidability, wear resistance, weather resistance, ozone resistance, heat resistance, etc. There is a problem to be improved in terms of ozone resistance and heat resistance.

[0003]

In view of the above-mentioned circumstances, the present invention provides slidability, wear resistance, weather resistance, ozone resistance,
It was made in an effort to provide a rubber composition having excellent heat resistance.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the object can be achieved by blending a specific acrylic modified polyorganosiloxane, and arrived at the present invention. did.

That is, the present invention has solved the above-mentioned problems, which is (1) synthetic rubber and / or natural rubber.
(2) General formula 1 for 100 parts by weight

[Chemical 2] [Wherein R ¹ , R ² and R ³ independently represent a hydrocarbon group having 1 to 20 carbon atoms or a halogenated hydrocarbon group, Y represents a radical reactive group or an organic group having a —SH group, Z ¹ and Z ²
Are independently a hydrogen atom, a lower alkyl group or the formula --SiR ⁴
R ⁵ R ⁶ (R ⁴ , R ⁵ and R ⁶ independently represent a hydrocarbon group having 1 to 20 carbon atoms, a halogenated hydrocarbon group, a radical reactive group or an organic group having a —SH group). Group, m is a positive integer of 10,000 or less, n is an integer of 1 or more, and the siloxane chain may have a branch. ]
And a polyorganosiloxane represented by the formula 2 CH ₂ ═C (R ⁷ ) COOR ⁸ (wherein R ⁷ represents a hydrogen atom or a methyl group, R ⁸ represents an alkyl group, an alkoxy-substituted alkyl group, a cycloalkyl group or (Meth) acrylic acid ester represented by the formula (7) or a mixture of 70% by weight or more of this (meth) acrylic acid ester and 30% by weight or less of a copolymerizable monomer is used in a weight ratio of 5:95 to. A rubber composition comprising at least 0.1 part by weight of an acrylic-modified polyorganosiloxane formed by graft copolymerization in a ratio of 95: 5.
Is the gist.

The present invention will be described in detail below. The component (1) constituting the composition of the present invention is a synthetic rubber and / or a natural rubber. As the synthetic rubber, various conventionally known rubbers such as styrene-butadiene rubber, acrylonitrile-butadiene rubber and hydrogen are used. Acrylonitrile-butadiene rubber, butadiene rubber, isoprene rubber, chloroprene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, acrylic rubber, ethylene-acrylic ester rubber, ethylene-vinyl acetate rubber, urethane rubber, polysulfide rubber, chlorosulfone Examples thereof include chlorinated polyethylene rubber, chlorinated polyethylene rubber, fluororubber and epichlorohydrin rubber. Two or more kinds of these synthetic rubbers or natural rubbers can be used in combination, if necessary.

In the production of the acrylic modified polyorganosiloxane used in the present invention, the polyorganosiloxane represented by the general formula 1 is used as a raw material. R ¹ , R ² , and R ³ in the general formula 1 are independently an alkyl group such as a methyl group, an ethyl group, a propyl group, and a butyl group, a phenyl group, a tolyl group,
A monovalent hydrocarbon group having 1 to 20 carbon atoms exemplified by an aryl group such as a xylyl group and a naphthyl group, or a group in which at least one hydrogen atom bonded to a carbon atom of these groups is substituted with a halogen atom, Represent Y is vinyl group, allyl group, γ-
It represents a radical-reactive group exemplified by a (meth) acryloxypropyl group or an -SH group-containing organic group exemplified by a γ-mercaptopropyl group. Z ¹ and Z ² are independently a hydrogen atom, a lower alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group, or a formula —SiR ⁴ R ⁵ R ⁶ (R ⁴ , R
⁵ and R ⁶ are independently C 1-20 exemplified by R ^{1 to} R ^3.
And a monovalent halogenated hydrocarbon group having 1 to 20 carbon atoms, or a radical-reactive group exemplified by Y or an organic group having a —SH group. ) Represents a triorganosilyl group. m represents a positive integer of 10,000 or less, and n represents an integer of 1 or more. Each R ^{1 to} R ⁶ and Y may be the same or different in one molecule.

Such polyorganosiloxane can be produced by a known method. For example, a chain or cyclic low molecular weight polyorganosiloxane having the above group or an alkoxysilane can be used in combination with the means of hydrolysis, polymerization and equilibration. Hydrolysis, polymerization and equilibration can be carried out by a known technique even in a state of being emulsified and dispersed in water. m and n are as described above, but in the range of 500 <m <8,000 and 1 <n <500 in view of the characteristics of the polyorganosiloxane or the graft copolymer of the polyorganosiloxane and the (meth) acrylic acid ester monomer. It is preferable that it be adjusted by a known method such as blending raw materials. Note that the siloxane chain may have some branching.

Another (meth) acrylic acid ester represented by the general formula 2 which is another raw material is methyl (meth)
Acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth)
Alkyl (meth) acrylates such as acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, methoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, etc. Cycloalkyl (meth) such as alkoxyalkyl (meth) acrylate and cyclohexyl (meth) acrylate
Aryl (meth) acrylates such as acrylates and phenyl (meth) acrylates are exemplified, and only one of them or a combination of two or more thereof can be used.

This (meth) acrylic acid ester can be used as a mixture with one or more kinds of other monomers copolymerizable therewith. However, in view of characteristics, it is preferable that the (meth) acrylic acid ester is 70% by weight or more and the other monomer copolymerizable therewith is 30% by weight or less. Other copolymerizable monomers include polyfunctional or monofunctional ethylenically unsaturated monomers.

As the polyfunctional ethylenically unsaturated monomer,
Alkylol of unsaturated amides and unsaturated amides such as (meth) acrylamide, diacetone (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide or Unsaturated monomer containing oxirane group such as alkoxyalkylated product, glycidyl (meth) acrylate, glycidyl allyl ether, and unsaturated monomer containing hydroxyl group such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate Body, (meth) acrylic acid, maleic anhydride, crotonic acid, itaconic acid and other carboxyl group-containing unsaturated monomers,
Amino group-containing unsaturated monomers such as N-dimethylaminoethyl (meth) acrylate and N-diethylaminoethyl (meth) acrylate, Polyalkylene oxide group-containing unsaturation such as ethylene oxide and propylene oxide adducts of (meth) acrylic acid Complete ester of (meth) acrylic acid with polyhydric alcohol such as monomer, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and further allyl (meth) acrylate ,
Examples include divinylbenzene and the like.

On the other hand, as the monofunctional ethylenically unsaturated monomer, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, vinyl chloride, vinylidene chloride,
Examples include vinyl acetate and vinyl propionate.

Using the above polyorganosiloxane and a mixture of a (meth) acrylic acid ester or a (meth) acrylic acid ester and another monomer copolymerizable therewith, an acrylic modified polyorgano by graft copolymerization. In the production of siloxane, the weight ratio of the total amount of monomers such as polyorganosiloxane: (meth) acrylic acid ester is 5:95 to 95: 5. If the amount of polyorganosiloxane is too large, the compatibility with rubber deteriorates and the appearance is impaired. If the amount of polyorganosiloxane is too small, the slidability, abrasion resistance, weather resistance, ozone resistance, and heat resistance improvement effects are insufficient.

Graft copolymerization can be carried out by a known technique. For example, when a polyorganosiloxane and a (meth) acrylic acid ester or a mixture thereof with another monomer is emulsified and dispersed in water and polymerized in the presence of a radical polymerization initiator, graft copolymerization occurs. The emulsifier and radical polymerization initiator used in this method may be those known for emulsion polymerization. After the completion of the polymerization, an acryl-modified polyorganosiloxane as a graft copolymer is obtained by salting out, filtering, washing with water and drying. In this emulsion graft copolymerization method, if the polyorganosiloxane is produced in a state of being emulsified and dispersed in water as described above, the obtained polyorganosiloxane emulsion can be directly used as a graft copolymerization raw material. .

The amount of the acrylic modified polyorganosiloxane blended is 100 parts by weight of synthetic rubber and / or natural rubber.
0.1 parts by weight or more, preferably 0.5 to 50 parts by weight,
It is more preferably 0.5 to 40 parts by weight. If this amount is less than 0.1 part by weight, the molded product obtained from the composition has little effect of improving slidability, wear resistance, weather resistance, ozone resistance, and heat resistance,
The effect of the present invention is not sufficiently exhibited. If the amount exceeds 50 parts by weight, the improvement in the effect tends to be difficult to recognize for the amount.

The composition of the present invention (1) can be vulcanized by adding and mixing a vulcanizing agent, a vulcanization accelerator, and other vulcanization aids which are usually used depending on the type of the component. Becomes Further, if desired, various additives such as a filler, an antioxidant, a plasticizer, a process oil, a colorant, and a foaming agent added in a usual rubber compounding may be added within a range not impairing the object of the present invention. it can.

The method for preparing the composition of the present invention is not particularly limited, and a conventionally known method such as the above (1),
(2) Component and various additive components (excluding vulcanizing agent, vulcanization accelerator, vulcanization aid) are used in predetermined proportions, and the compounding components are kneaded with a mixing roll, a pressure kneader, a Banbury mixer, etc. The blend can be prepared by uniformly kneading using a machine.

Further, a vulcanizing agent, a vulcanization accelerator, and a vulcanization aid are uniformly mixed in the compound thus obtained by using the above kneader, and then a conventional extruder, injection molding machine, It can be appropriately molded and vulcanized into a desired shape using a pressure molding machine or the like. Molding and vulcanizing conditions are the same as those for the composition formulated without blending the component (2), and there is no particular problem.

[0019]

EXAMPLES The present invention will be specifically described based on examples.
All parts in the examples are parts by weight, and% is% by weight. (Production of polyorganosiloxane emulsion) 1500 parts of octamethylcyclotetrasiloxane, 1.2 parts of methacryloxypropylmethylsiloxane and 1500 parts of pure water are mixed, and 15 parts of sodium lauryl sulfate and 10 parts of dodecylbenzenesulfonic acid are added thereto. The mixture was stirred with a homomixer to emulsify, and then passed through a homogenizer having a pressure of 3000 psi twice to form a stable emulsion. Then, this
After heating at 70 ℃ for 12 hours, cooling to 25 ℃ and aging for 24 hours, the pH of this emulsion is adjusted with sodium carbonate.
Is adjusted to 7 and nitrogen gas is blown for 4 hours, and then steam distillation is performed to distill off the volatile siloxane, and then pure water is added to adjust the nonvolatile content to 45%, and 0.03 mol% of the methacrylic group is added. An emulsion of the polyorganosiloxane contained therein (hereinafter abbreviated as E-1) was obtained.

Further, as shown in Table 1, polyorganosiloxane emulsions E-2 to E were prepared in the same manner as in E-1, except that the kind, amount and aging conditions of siloxane were changed.
-4 was obtained.

[0021]

[Table 1]

(Production of Acrylic Modified Polyorganosiloxane) 1110 parts (polyorganosiloxane content 500) of the polyorganosiloxane emulsion E-1 obtained above was placed in a reaction vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet. Part) and pure water 1053 parts, and the inside of the vessel was adjusted to 10 ° C. under a nitrogen gas stream, then t-butyl hydroperoxide 1.0 part, L-ascorbic acid 0.5 part, ferrous sulfate heptahydrate 0.002 Then, while maintaining the temperature inside the vessel at 30 ° C, a mixture of 210 parts of methyl methacrylate and 4.5 parts of 2-hydroxyethyl methacrylate was added dropwise over 3 hours, and after completion of the addition, stirring was continued for 1 hour to complete the reaction. Let The obtained copolymer emulsion (hereinafter referred to as P-
(Abbreviated as 1) had a solid content concentration of 30%. Then, 1000 parts of this emulsion was charged into a container equipped with a stirrer and heated to 60 ° C., and a solution of 92 parts of sodium sulfate dissolved in 563 parts of pure water was added thereto to precipitate an acrylic modified polyorganosiloxane, which was then filtered and washed with water. Repeatedly and dried at 60 ° C to obtain acrylic modified polyorganosiloxane (hereinafter referred to as G-
1).

Similarly, emulsions P-2 to P-6 were obtained by copolymerizing the polyorganosiloxane emulsion shown in Table 2 and the type and amount of the (meth) acrylic monomer. Then, this emulsion is similarly deposited, filtered, and
It was washed with water and dried to obtain acrylic modified polyorganosiloxanes G-2 to G-6.

[0024]

[Table 2]

Example 1 To 100 parts of ethylene-propylene rubber (EPT # 3045, manufactured by Mitsui Petrochemical Co., Ltd.), 1 part of stearic acid and an antioxidant (Irganox # 1010, manufactured by Ciba Geigy, product) Name) 1 part, zinc oxide 5 parts, HAF
60 parts carbon, 20 parts paraffinic process oil,
After mixing 2 parts of acrylic modified polyorganosiloxane G-1 and thoroughly kneading with a pressure kneader, 1.5 parts of a vulcanization accelerator (NOXCELLER TS, Ouchi Shinko Co., Ltd., trade name) was added on an 8-inch roll. Sulfurization accelerator (Axel M, manufactured by Kawaguchi Chemical Co., Ltd.,
0.5 part of sulfur and 1.5 parts of sulfur were uniformly kneaded to prepare a roll sheet molding, and then pressure vulcanization was performed at 160 ° C. for 30 minutes to prepare a 2 mm thick vulcanized sheet. For this vulcanized sheet, the vulcanized physical properties were measured according to the measuring method of JIS K-6301, and the surface condition was evaluated visually and by touch, and then the surface of this sheet was further sandpaper AA-
After polishing with 180, a static / dynamic friction coefficient was measured using a friction tester Haydon 14 (trade name, manufactured by Shinto Kagaku Co., Ltd.) under the conditions of a 10φ SUS steel ball, a load of 50 g, and a pulling speed of 100 mm / min.
The results are shown in Table 3.

Examples 2 to 5 Vulcanized sheets were prepared in the same manner as in Example 1 except that various acrylic-modified polyorganosiloxanes shown in Table 3 were blended according to the blending amounts shown in the same table, and their vulcanized physical properties, The static and dynamic friction coefficients were evaluated in the same manner, and the results are shown in Table 3.

Comparative Example 1 A vulcanized sheet was prepared in the same manner as in Example 1 except that the acrylic modified polyorganosiloxane was not added, and its vulcanized physical properties and static / dynamic friction coefficient were also evaluated in the same manner. The results are shown in Table 3.

[0028]

[Table 3]

Example 6 Acrylonitrile-butadiene rubber (Nipol DN-2
01, 100 parts by Nippon Zeon Co., Ltd.), 1 part of stearic acid, 5 parts of zinc oxide, 65 parts of SRF carbon black, 15 parts of DOP, 40 parts of acrylic modified polyorganosiloxane G-1. After blending and thoroughly kneading with a pressure kneader, this is uniformly kneaded on an 8-inch roll with 3 parts of a vulcanization accelerator (Nocceller TT, Ouchi Shinko Co., Ltd., trade name) and 0.3 part of sulfur to form a roll sheet. Create a thing, then 1
It was pressure-vulcanized at 55 ° C. for 30 minutes to prepare a vulcanized sheet having a thickness of 2 mm. For this vulcanized sheet, the vulcanized physical properties were measured according to the measuring method of JIS K-6301, and the surface condition was evaluated visually and by touch, and then the surface of this sheet was further rubbed with sandpaper AA-180 and then rubbed. Using a testing machine Haydon 14 (manufactured by Shinto Kagaku Co., Ltd., trade name), the static / dynamic friction coefficient was measured under the conditions of 10φSUS steel ball, load of 50 g, and pulling speed of 100 mm / min. The physical properties after leaving it in the atmosphere for 70 hours were measured and evaluated. Furthermore, the weather resistance was measured using a light resistance tester FAL-5HB (trade name, manufactured by Suga Test Instruments Co., Ltd.), and after being irradiated with ultraviolet rays at 83 ° C. for 400 hours, the ozone resistance was 20% extension and 50 ppm at 40 ° C. The state of crack generation on the surface of each sheet after standing for 72 hours in an atmosphere of ozone concentration was visually evaluated in three levels. ◯: Few cracks were generated, Δ: Many cracks were generated, X: There were numerous cracks, and the results are shown in Table 4.

Examples 7 to 9 Vulcanized sheets were prepared in the same manner as in Example 6 except that various acrylic modified polyorganosiloxanes shown in Table 4 were blended according to the blending amounts shown in the same table, and their vulcanized physical properties were obtained. The static and dynamic friction coefficients, heat resistance, weather resistance and ozone resistance were evaluated in the same manner, and the results are shown in Table 4.

Example 10 Acrylic-modified polyorganosiloxane emulsion P-
285 parts of 1 and a commercial NBR emulsion (Nipol 156
2. Made by Nippon Zeon Co., Ltd.)
Charge 15 parts into a container equipped with a stirrer and heat to 60 ° C, add a solution of 92 parts of sodium sulfate in 563 parts of pure water to precipitate the polymer, repeat filtration and washing with water, and then
By drying at ° C, an eutectoid rubber product of acrylic modified polyorganosiloxane and acrylonitrile-butadiene rubber (hereinafter abbreviated as K-1) was obtained. About 140 parts of eutectoid rubber K-1 was compounded in the same manner as in Example 6, and a vulcanized sheet was prepared in the same manner, and its vulcanized physical properties, static / dynamic friction coefficient, heat resistance, weather resistance, and ozone resistance were evaluated. Also evaluated in the same manner and the results are shown in Table 4.
It was shown to.

Comparative Example 2 A vulcanized sheet was prepared in the same manner as in Example 6 except that the acrylic modified polyorganosiloxane was not blended, and its vulcanized physical properties, static / dynamic friction coefficient, heat resistance, weather resistance and ozone resistance. The sex was evaluated in the same manner, and the results are shown in Table 4.

[0033]

[Table 4]

Example 11 To 100 parts of styrene-butadiene rubber (JSR1500, manufactured by Japan Synthetic Rubber Co., Ltd.), 1.5 parts of stearic acid was added.
Parts, 5 parts zinc oxide, 50 parts HAF carbon black,
After mixing 10 parts of acrylic modified polyorganosiloxane G-1 and thoroughly kneading with a pressure kneader, 0.4 part of a vulcanization accelerator (Nocceller D, manufactured by Ouchi Shinko Co., Ltd.) was added on an 8-inch roll. Uniformly knead with 1.5 parts of a sulfur accelerator (Nocceller DM, trade name of Ouchi Shinko Co., Ltd.) and 2 parts of sulfur to prepare a roll sheet molding, and then vulcanize it under pressure at 150 ° C. for 20 minutes to obtain a 2 mm thick A vulcanized sheet was created. For this vulcanized sheet, the vulcanized physical properties were measured according to the measuring method of JIS K-6301, and the surface condition was evaluated visually and by touch, and then the vulcanized sheet was left for 20 hours in an atmosphere of 120 ° C for heat resistance. After that, the physical properties were measured and evaluated. Further, the weather resistance was measured by using a light resistance tester FAL-5HB (trade name, manufactured by Suga Test Instruments Co., Ltd.), and after being irradiated with ultraviolet rays at 83 ° C. for 400 hours, ozone resistance was 20% extension and 50 ppm at 40 ° C. The state of crack generation on the surface of each sheet after standing for 72 hours in an atmosphere of ozone concentration was visually evaluated in three levels. ◯: Few cracks were generated, Δ: Many cracks were generated, X: Cracks were numerous, and the results were as shown in Table 5.

Examples 12 to 13 Vulcanized sheets were prepared in the same manner as in Example 11 except that various acrylic modified polyorganosiloxanes shown in Table 5 were blended according to the blending amounts shown in the same table, and their vulcanized physical properties were obtained. ,
Heat resistance, weather resistance and ozone resistance were evaluated in the same manner, and the results are shown in Table 5.

Comparative Example 3 A vulcanized sheet was prepared in the same manner as in Example 11 except that the acrylic modified polyorganosiloxane was not blended, and the vulcanized physical properties, heat resistance, weather resistance, and ozone resistance were also the same. The results are shown in Table 5.

[0037]

[Table 5]

[0038]

According to the present invention, the sliding property, the wear resistance, the weather resistance, the ozone resistance and the heat resistance are extremely excellent, and the bleeding is also extremely small, so that the appearance and the workability are not bad and the other members are not contaminated. Provided is a rubber composition from which a molded article is obtained.

Claims (1)

[Claims] (1) 100 parts by weight of synthetic rubber and / or natural rubber (2) General formula 1 [Wherein R ¹ , R ² and R ³ independently represent a hydrocarbon group having 1 to 20 carbon atoms or a halogenated hydrocarbon group, Y represents a radical reactive group or an organic group having a —SH group, Z ¹ and Z ²
Are independently a hydrogen atom, a lower alkyl group or the formula --SiR ⁴
R ⁵ R ⁶ (R ⁴ , R ⁵ and R ⁶ independently represent a hydrocarbon group having 1 to 20 carbon atoms, a halogenated hydrocarbon group, a radical reactive group or an organic group having a —SH group). Group, m is a positive integer of 10,000 or less, n is an integer of 1 or more, and the siloxane chain may have a branch. ]
And a polyorganosiloxane represented by the formula 2 CH ₂ ═C (R ⁷ ) COOR ⁸ (wherein R ⁷ represents a hydrogen atom or a methyl group, R ⁸ represents an alkyl group, an alkoxy-substituted alkyl group, a cycloalkyl group or (Meth) acrylic acid ester represented by the formula (7) or a mixture of 70% by weight or more of this (meth) acrylic acid ester and 30% by weight or less of a copolymerizable monomer is used in a weight ratio of 5:95 to. A rubber composition comprising at least 0.1 part by weight of an acrylic-modified polyorganosiloxane obtained by graft copolymerization at a ratio of 95: 5.