JPH07258548A - Conductive silicone rubber composition - Google Patents

Abstract

PURPOSE:To obtain a conductive silicone rubber compsn. with a stable resistivity in a semiconductive region by compounding a specific polyorganosiloxane mixture, a conductive carbon black, a cross-linking aid, and a curative. CONSTITUTION:This compsn. comprises 100 pts.wt. polyorganosiloxane mixture comprising 5-95wt.% polyorganosiloxane of formula I: R<1>nSiO(4-n)/2 (wherein R<1> is an optionally substd. monovalent hydrocarbon group provided 97mol% or lower of all the R<1>s are methyl; and n is 1.95-2.05) and 95-5wt.% polyorganosiloxane of formula II: R<2>mSiO(4-m)/2 (wherein R<2> is an optionally substd. monovalent hydrocarbon group provided the amt. of methyl groups in the compd. of formula II is at least 3mol% higher than that in the compd. of formula I: and m is 1.95-2.05). 3-150 pts.wt. conductive carbon black, 0.01-10 pts.wt. cross-linking aid, and a necessary amt. of a curative.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a semiconductive region (10 ³ to 10 ^10).
The present invention relates to a silicone rubber composition which gives a rubber product having a stable electric resistivity at about Ω · cm.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION AND PROBLEMS OF THE INVENTION Silicone rubber compositions which are cured into silicone rubber have been well known, and have excellent properties such as weather resistance, heat resistance, cold resistance and electric insulation. It is widely used as a potting material for electric and electronic parts, a coating material, and a molding material for molding. In addition, a conductive material such as conductive carbon black, graphite, and metal powder is blended with the silicone rubber composition, which is originally an insulating material, to have an electric resistance of 10 ^-1.
It has been put to practical use as a conductive silicone rubber in the range of ~ 10 ^-2 Ω · cm. However, when a conductive carbon black is blended with silicone rubber and an attempt is made to obtain a conductive silicone rubber molded product in the semi-conductive region of about 10 ³ to 10 ¹⁰ Ω · cm, the electrical resistance The variation in the rate was extremely large, and it was difficult to stabilize the electrical resistivity. It is considered that this is because strain is generated inside the rubber during molding, and the uniform carbon chain changes due to the strain, and the carbon chains become dense and dense. As a way to solve this problem,
A method of preparing conductive silicone rubber powder in advance and blending it with an insulating silicone rubber composition (JP-A-61-10).
No. 8661, JP-A-63-156858, JP-A-63-251464), and a conductive silicone rubber composition containing carbon black in advance and an insulating silicone rubber composition containing no carbon black. A method of producing, mixing and macro-dispersing them (Japanese Patent Application Laid-Open No. Hei 3
No. 190964) is proposed. However, in the former method of blending conductive silicone rubber powder, it is extremely difficult to obtain a uniform and stable conductive silicone rubber fine powder, and since the compound contains rubber powder, roll processability and sheeting property are improved. However, there is a problem that the extrudability is difficult. Furthermore, in the case of a molded product obtained by such a method, when this is used for a rubber roll of a copying machine or the like, when polishing the surface, conductive rubber powder is scraped off and crater-like projections (holes) are formed on the surface. There is also a problem that it occurs and it takes a long time for polishing, and further, there is a problem that durability is deteriorated due to poor wear resistance when used as a rubber roll. On the other hand, the latter method of mixing a silicone rubber composition containing carbon black and a silicone rubber composition not containing carbon black is that both are macro-dispersed to form a sea-island structure to obtain a stable conductive silicone rubber. However, the dispersibility varies depending on the kneading conditions when the compound is produced or when it is processed into a molded product, and there is a drawback that the conductivity of the obtained silicone rubber varies. In addition, the molded product obtained by this method has weak mechanical strength, and due to mixing of silicone rubber compositions that are originally incompatible with each other, a layer peeling phenomenon occurs, and when used in a roll such as a copying machine, the conductivity is low. Similar to the method of blending the silicone rubber powder, craters were generated during polishing and the durability was lowered, and it was not usable in actual use.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a molded product, the electrical resistivity in the semiconductive region is extremely stable, has reproducibility, and has moldability such as polishing property. It is an object of the present invention to provide a silicone rubber composition having excellent durability without lowering mechanical strength.

[0004]

The present inventor has conducted extensive studies to achieve the above-mentioned object, and as a result, two kinds of polyorganosiloxanes having different methyl group contents were used, and conductive carbon black,
The inventors have found that a composition containing a crosslinking aid and a curing agent is effective, and completed the present invention. That is, the present invention provides a polyorganosiloxane mixture containing (A) the following components (a) and (b) in a proportion of 5 to 95% by weight: 95 to 5% by weight.
100 parts by weight (a) Polyorganosiloxane represented by the average composition formula (1) R ¹ _n SiO _{(4-n) / 2} (1) (wherein R ¹ is unsubstituted or substituted monovalent carbon A hydrogen group is shown, but the methyl group in R ¹ is 97 mol% or less, and n is 1.95.
It is a positive number from ~ 2.05. ) (B) Polyorganosiloxane represented by the average composition formula (2) R ² _m SiO _{(4-m) / 2} (2) (wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group) The amount of methyl groups in R ² is at least 3 mol% or more than the amount of methyl groups in the above formula (1), and m is a positive number from 1.95 to 2.05.) (B) Conductive carbon black 3 To 150 parts by weight (C) crosslinking aid 0.01 to 10 parts by weight (D) curing agent A necessary amount of curing is contained in the conductive silicone rubber composition.

The present invention will be described in detail below. The component (A) of the present invention is a polyorganosiloxane mixture of the following components (a) and (b). The component (a) is a polyorganosiloxane represented by the average composition formula (1). R ¹ _n SiO _{(4-n) / 2} (1) In the formula, R ¹ represents an unsubstituted or substituted monovalent hydrocarbon group,
It preferably has 1 to 10 carbon atoms. Specifically, a methyl group, an ethyl group, an alkyl group such as a propyl group, a cyclopentyl group, a cycloalkyl group such as a cyclohexyl group,
Alkenyl group such as vinyl group, allyl group, cycloalkenyl group, aryl group such as phenyl group, tolyl group, or hydrogen atom of these groups is partially fluorine atom, chlorine atom, chloromethyl group, γ-trifluoropropyl Group, a perfluoroalkyl group, a halogenated hydrocarbon group substituted with an organic group such as a cyano group, and a cyanated hydrocarbon group are exemplified, but the methyl group in R ¹ is 97 mol% or less. It is necessary, and is preferably 95 mol% or less. Also, n is
It is a positive number between 1.95 and 2.05. Component (b) is the average composition formula (2)
It is a polyorganosiloxane represented by. R ² _m SiO _{(4-m) / 2} (2) In the formula, R ² represents an unsubstituted or substituted monovalent hydrocarbon group,
Examples of the preferable group are the same as those of R ¹ described above, but the amount of the methyl group in R ² needs to be at least 3 mol% or more than the amount of the methyl group of the above formula (1). Further, m is a positive number from 1.95 to 2.05. Here, when the difference in the amount of methyl groups of R ¹ and R ² in the polyorganosiloxane represented by the above average composition formulas (1) and (2) is less than 3 mol%,
The stable electric resistivity which is the intended purpose of the present invention cannot be obtained. Preferably, the difference in the amount of methyl groups between R ¹ and R ² is 5 mol% or more. Here, the ratio of component (a) and component (b) is
It is necessary to be in the range of 5 to 95% by weight: 95 to 5% by weight. If it is out of this range, variations in electrical resistivity will occur during molding. The average degree of polyorganosiloxane polymerization of each of the components (a) and (b) is preferably 2000 or more. This is because if the average degree of polymerization is less than 2000, the mechanical strength after molding or curing may decrease.

As the conductive carbon black as the component (B), those commonly used in conductive rubber compositions can be used. For example, acetylene black, conductive furnace black (CF), super conductive furnace black (SCF). ), Extra conductive furnace black (XCF), conductive channel black (CC), furnace black heat-treated at a high temperature of about 1500 ° C., channel black, and the like. Specifically, as acetylene black, electrified acetylene black (manufactured by Denki Kagaku), Shawnigan acetylene black (manufactured by Shawnigan Chemical), etc., as conductive channel black, Continex CF (manufactured by Continental Carbon),
Vulcan C (manufactured by Cabot) and others are Continex SC as super conductive furnace black.
F (Continental Carbon Co., Ltd.), Vulcan SC (Cabot Co.), etc., as Extra Conductive Furnace Black, Asahi HS-500 (Asahi Carbon Co., Ltd.), Vulcan XC-72 (Cabot Co., Ltd.), etc. Conductive Channel Black As a Courlux L
(Manufactured by Degussa) and the like, and Ketjen Black EC and Ketjen Black EC-600 JD (manufactured by Ketjen Black International), which are types of furnace black, can also be used. The conductive carbon black may be used alone or in combination of two or more, and the compounding amount thereof is 3 to 150 parts by weight, more preferably 5 parts by weight, relative to 100 parts by weight of the organopolysiloxane mixture (A). It is desirable to use up to 100 parts by weight. If the amount added is less than 3 parts by weight, the desired conductivity cannot be obtained.
If the amount is more than 150 parts by weight, further effects cannot be obtained, and the silicone rubber composition may become hard and the moldability may be deteriorated, or the mechanical strength after curing may be decreased.

The cross-linking aid as the component (C) is roughly classified into polyorganosiloxane type and organic compound type. As the polyorganosiloxane-based crosslinking aid, for example, the following average composition formula
An example is the polyorganosiloxane represented by (3). R ³ _e SiO _{(4-e) / 2} (3) In the formula, R ³ represents an unsubstituted or substituted monovalent hydrocarbon group,
The amount of vinyl group in R ³ is 1 mol% or more, preferably 2 mol%
That is all. As the monovalent hydrocarbon group other than the vinyl group,
Specifically, an alkyl group such as a methyl group, an ethyl group and a propyl group, a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, an alkenyl group such as a vinyl group and an allyl group, a cycloalkenyl group, an aryl such as a phenyl group and a tolyl group. Groups or halogenated hydrocarbon groups in which the hydrogen atoms of these groups are partially substituted with organic groups such as fluorine atom, chlorine atom, chloromethyl group, γ-trifluoropropyl group, perfluoroalkyl group and cyano group , Cyanated hydrocarbon groups and the like. Also, e is a positive number 0 <e <3.05. Usually, a polymerization degree of 10,000 or less can be used, but it is preferably 1,000 or less, more preferably 500 or less. If the degree of polymerization exceeds 10,000, the effect as a crosslinking aid may not be obtained. Examples of the organic compound-based crosslinking aid include ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and 1,4.
-Butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, 1.4-butanediol diacrylate, 1,6-hexanediol diacrylate, 2,2
-Bis (4-methacryloyldiethoxyphenyl) propane, trimethylolpropane trimethacrylate,
Trimethylolpropane triacrylate, pentaerythritol triacrylate, divinylbenzene, N, N
-Methylenebisacrylamide, p-quinonedioxime, p, p-dibenzoylquinonedioxime, triazinedithiol, triallyl cyanurate, triallyl isocyanurate, bismaleimide and the like. The amount of these crosslinking aids added is 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polyorganosiloxane mixture as the component (A). If it is less than 0.01 parts by weight, the desired effect cannot be obtained, and if it exceeds 10 parts by weight, further effects cannot be obtained, and the mechanical strength of the cured product may be reduced.

(D) As the curing agent, as long as it can be vulcanized and cured by using an organic peroxide vulcanization reaction, addition reaction, etc. used for vulcanization of conductive silicone rubber, its curing mechanism There is no limitation to the above, and various conventionally known curing agents can be used. For example, di-t-butyl peroxide,
In addition to alkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and aralkyl peroxides such as dicumyl peroxide, one molecule is used as an addition reaction curing agent. An organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms and a platinum catalyst can be used. The amount of the curing agent added may be the same as the amount used for ordinary conductive silicone rubber.

In the silicone rubber composition of the present invention, if necessary, a filler such as dry or wet silica, coal powder, diatomaceous earth and calcium carbonate, cerium oxide, cerium hydroxide, cerium octoate and other cerium compounds. , Iron sesquioxide, iron oxides such as iron octoate, heat resistance improvers such as titanium dioxide, azo compounds, ferrosoferric oxide,
A flame retardant aid such as a platinum compound, an alkoxysilane or the like may be added, and a foaming agent such as AIBN, ADCA or DPT may be added to form a sponge composition. The silicone rubber composition of the present invention can be kneaded by using a usual rubber compounding device such as a kneader, two rolls, Banbury mixer. Examples of the kneading method include a method in which the component (a) and the component (b) are mixed with the polyorganosiloxane in advance, and then carbon black and a crosslinking aid are mixed, but the mixing order is not particularly limited. is not. Further, the conductive silicone rubber composition of the present invention can be molded and processed by a usual method such as pressure molding, extrusion molding, injection molding, calender molding or the like to be a product.

[0010]

EFFECTS OF THE INVENTION According to the present invention, the electric resistivity in the semiconductive region of a molded product is not affected by the molding conditions and is stable with little variation, and at the same time, the molding processability, the vulcanization property, and the rubber elasticity. In addition, the silicone rubber composition and the cured product of the present invention can be used as, for example, a charging roll, a transfer roll, a developing roll, and a paper feed in a dry copying machine. Office equipment field such as rolls, fixing rolls, pressure rolls, static elimination rolls, cleaning rolls, rubber roll materials such as oil coating rolls, rubber members such as cleaning belts, fixing belts, etc. Etc. have a wide range of fields.

[0011]

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, all parts are parts by weight. Example 1 (A) (a) 40 parts of methyl-phenylvinylpolysiloxane having a degree of polymerization of about 7000, consisting of 89.8 mol% dimethylsiloxane units, 10 mol% diphenylsiloxane units and 0.2 mol% methylvinylsiloxane units (b) Consists of 99.8 mol% of dimethyl siloxane units and 0.2 mol% of methyl vinyl siloxane units, the degree of polymerization of which is blocked by vinyl dimethyl silyl groups at about 7,000 methyl vinyl polysiloxane 60 parts (B) As conductive carbon black, Denka Black Granular (manufactured by Denki Kagaku Kogyo Co., Ltd.) 15 parts (C) 90 mol% dimethylsiloxane unit as a crosslinking aid
And methyl vinyl siloxane unit 10 mol%,
2 parts of methylvinylpolysiloxane having a degree of polymerization of about 10 and having a terminal blocked with a vinyldimethylsilyl group. The above components were blended and kneaded using a kneader to obtain a silicone rubber composition A.

Example 2 (A) (a) Dimethylsiloxane unit 64.8 mol%, methyl-
Consists of 35 mol% of γ-trifluoropropyl siloxane unit and 0.2 mol% of methyl vinyl siloxane unit, the degree of polymerization of which is blocked by vinyldimethylsilyl group at the end.
5000 parts of methylfluorovinylpolysiloxane (b) dimethylsiloxane unit 84.8 mol%, methyl-γ-
Consisting of 15.0 mol% of trifluoropropylsiloxane units and 0.2 mol% of methylvinylsiloxane units, the degree of polymerization was about 6000 with a trimethylsilyl group at the end. Methylfluorovinylpolysiloxane 50 parts (B) As conductive carbon black, Ketjen Black EC (Ketjen Black International)
5 parts (C) Trimethylolpropane trimethacrylate as a cross-linking aid 1 part The above components were compounded and kneaded using a kneader to obtain a silicone rubber composition B.

Example 3 (A) (a) Dimethylsiloxane unit 91.7 mol%, methyl-
It consists of 8 mol% of γ-trifluoropropyl siloxane unit and 0.3 mol% of methyl vinyl siloxane unit, and the degree of polymerization of which terminal is blocked by vinyl dimethyl silyl group is about
7,000 methylfluorovinylpolysiloxane 60 parts (b) Methylvinylpolysiloxane having a degree of polymerization of about 7,000, which is composed of 99.7 mol% of dimethylsiloxane units and 0.3 mol% of methylvinylsiloxane units and is blocked at the end by vinyldimethylsilyl groups. Part (B) As conductive silicone rubber, Diablack # 30
30B (manufactured by Mitsubishi Kasei Co.) 20 parts (C) Tetramethyltetravinylcyclosiloxane 1 part as a crosslinking aid 1 part The above components were blended and kneaded using a kneader to obtain a silicone rubber composition C.

Comparative Example 1 Methyl vinyl having a polymerization degree of about 10 which was composed of 90 mol% of dimethyl siloxane units and 10 mol% of methyl vinyl siloxane units, which are cross-linking aids, and whose ends were blocked with vinyl dimethyl silyl groups. A silicone rubber composition D was obtained by blending and kneading each component using a kneader with the same formulation as in Example 1 except that polysiloxane was not added.

Comparative Example 2 (A) (a) A polymerization degree of about 95.8 mol% dimethylsiloxane units, 4 mol% diphenylsiloxane units and 0.2 mol% methylvinylsiloxane units, the degree of polymerization of which was blocked by vinyldimethylsilyl groups at the ends. 8,000 methylphenylvinylpolysiloxane 50 parts (b) dimethylsiloxane unit 97.8 mol%, diphenylsiloxane unit 2 mol% and methylvinylsiloxane unit
50 parts of methylphenylvinylpolysiloxane with a degree of polymerization of about 8000, which was composed of 0.2 mol% and was blocked with vinyldimethylsilyl groups at the ends (B) 15 parts of Denka Black granular (manufactured by Denki Kagaku Kogyo) as conductive carbon black (C) Tetramethyltetravinylcyclosiloxane as a crosslinking aid 1 part The above components were blended and kneaded using a kneader to obtain a silicone rubber composition E.

Comparative Example 3 (A) A dimethylsiloxane unit of 89.8 mol%, a methylvinylsiloxane unit of 0.2 mol% and a methylphenylsiloxane unit of 10 mol%, the end of which was blocked with a vinyldimethylsilyl group, and the degree of polymerization was about 8000. Methylphenylvinylpolysiloxane 100 parts (B) Ketjen Black EC (manufactured by Ketjen Black International) 8 parts These were kneaded with a kneader to obtain a silicone rubber composition F-1. Further, (A) 100 parts of methylphenylvinylpolysiloxane having a polymerization degree of about 8000, which is composed of 99.8 mol% of dimethylsiloxane units and 0.2 mol% of methylvinylsiloxane units, and the end of which is blocked by vinyldimethylsilyl groups. Specific surface area 200 m ² / g (Product name Aerosil 200; manufactured by Nippon Aerosil Co., Ltd.)] 15 parts ・ 3 parts of dimethylpolysiloxane oil having an average degree of polymerization of 20 and having a terminal blocked with a hydroxyl group, kneaded with a kneader Further, the mixture was kneaded at 150 ° C. for 2 hours to obtain a silicone rubber composition F-2. next,
Silicone rubber composition F was obtained by mixing 100 parts of each of the above compositions F-1 and F-2 using two rolls.

Comparative Example 4 (A) A dimethylsiloxane unit of 99.6 mol% and a methylvinylsiloxane unit of 0.4 mol%, the degree of polymerization of which was blocked by a vinyldimethylsilyl group at a degree of about 100 Methylvinylpolysiloxane 100 parts (B) Denka black granular (manufactured by Denki Kagaku Kogyo Co., Ltd.) as conductive carbon black 25 parts-Methylhydrogenpolysiloxane with a degree of polymerization of about 20 (content of hydrogen atoms bonded to silicon atoms 2%) 0.6 parts-3% of chloroplatinic acid Isopropyl alcohol solution 0.5
Parts After kneading these with a three-roll mill, 1500 parts of ion-exchanged water and 5 parts of a surfactant [ethylene oxide adduct of trimethylnotinol (manufactured by Union Carbide Co.)] were added to a colloid mill, and 1300 rpm Milling was carried out under the conditions of a gap of 0.1 mm to obtain an aqueous dispersion of the conductive silicone rubber composition. After leaving this aqueous dispersion at room temperature for 2 hours, use a spray dryer to set the inlet temperature and the outlet temperature at 120
It was sprayed in a dryer at ℃ to complete the sulfurization to obtain a conductive silicone rubber powder. Next, dimethyl siloxane unit 99.8 mol%, methyl vinyl siloxane unit 0.2 mol%
100 parts of methyl vinyl polysiloxane having a degree of polymerization of about 7,000 and having a terminal blocked with a vinyldimethylsilyl group, and 100 parts of the above conductive silicone rubber powder were mixed with a two-roll to form a silicone rubber composition. Got G.

Next, with respect to 100 parts of each of the silicone rubber compositions A to G prepared as described above, 2,5-dimethyl-2,5-bis (t-butylperm) was used as a cross-linking agent in a double roll. 1 part of (oxy) hexane was blended, vulcanized at 170 ° C for 10 minutes, and then vulcanized at 200 ° C for 4 hours to obtain a thickness of 1 mm and 2
A sheet of mm was formed and the physical properties were measured according to JIS K 6301. Further, Hiresta IP (manufactured by Mitsubishi Petrochemical Co., Ltd.) was used to measure the volume resistivity at 5 locations in the sheet. Also, JI
The abrasion resistance was evaluated by the Taber abrasion test specified in SK 6902. The results are shown in Table 1.

[0019]

[Table 1]

Example 4 (A) (a) A vinyl polysiloxane having 95.6 mol% of dimethylsiloxane units, 4 mol% of diphenylsiloxane units and 0.4 mol% of methylvinylsiloxane units and having a terminal blocked with a vinyldimethylsilyl group. Part (b) Siloxane consisting of 99.6 mol% of dimethylsiloxane units and 0.3 mol% of methylvinylsiloxane units, with the ends blocked with vinyldimethylsilyl groups 60 parts (B) As conductive carbon black, Denka black granular (electrochemical (Manufactured by Kogyo Co., Ltd.) 17 parts (C) Methylphenylsiloxane unit 20 as a crosslinking aid
Mol% and methylvinylsiloxane unit 10 mol%, methylphenylvinylpolysiloxane having a terminal blocked with a vinyldimethylsilyl group 3 parts The above components were blended and kneaded using a kneader to obtain a silicone rubber composition H. It was

Example 5 (A) (a) Dimethylsiloxane unit 50 mol%, methyl-γ
40 parts of methylfluorovinylpolysiloxane with a degree of polymerization of about 4000, which is composed of 49.7 mol% of trifluoropropyl units and 0.3 mol% of methylvinylsiloxane units, and is blocked with vinyldimethylsilyl groups at the terminals (b) 80 mol% of dimethylsiloxane units. , Diphenylsiloxane units 19.6 mol% and methylvinylsiloxane units
Diphenyl black # 3 as a conductive carbon black 70 parts by weight of about 6000 methylphenylvinylpolysiloxane (0.4 mol%, blocked with vinyl dimethylsilyl groups at the end) (B)
030 B (manufactured by Mitsubishi Kasei Co., Ltd.) 20 parts (C) Methyl vinyl polysiloxane similar to that of Example 1 as a cross-linking aid 1 part The above components were blended and kneaded using a kneader to obtain a silicone rubber composition I. .

Comparative Example 5 (A) 100 parts of methylvinylpolysiloxane having a degree of polymerization of about 7,000, which was composed of 99.7 mol% of dimethylsiloxane units and 0.3 mol% of methylvinylsiloxane units and was terminated with vinyldimethylsilyl groups at the end (B) ) Denka black granules (manufactured by Denki Kagaku Kogyo) as conductive carbon black 15 parts The above components were blended and kneaded using a kneader to obtain a silicone rubber composition J.

Next, with respect to 100 parts of each of the silicone rubber compositions H to J prepared as described above, 2 rolls of 2 parts of methylhydrogenpolysiloxane having both ends of the molecular chain blocked with trimethylsilyl group were used as a catalyst. 1 part of isopropyl alcohol solution containing 1% by weight of chloroplatinic acid and 0.1 part of isopropyl alcohol solution containing 30% by weight of benzotriazole as an addition reaction retarder were added and mixed at 170 ° C.
The sheet was press-vulcanized for 10 minutes and then subjected to atto vulcanization at 200 ° C. for 1 hour to form a sheet having a thickness of 1 mm or 2 mm, and the same evaluation as in Example 1 was performed. The results are shown in Table 2.

[0024]

[Table 2]

From the results shown in Tables 1 and 2, it can be seen that the silicone rubber composition of the present invention has a stable electric resistivity after molding and less decrease in mechanical strength as compared with the conventional materials.

Example 6 (A) (a) A polymerization degree of about 89.8 mol% of dimethylsiloxane units, 10 mol% of diphenylsiloxane units and 0.2 mol% of methylvinylsiloxane units, the degree of polymerization of which was terminated by vinyldimethylsilyl groups. 40 parts of 8,000 methylphenylpolysiloxane (b) 50 parts of methylvinylpolysiloxane of 98,000 mol% dimethylsiloxane units and 0.2 mol% of methylvinylsiloxane units, the ends of which are blocked by vinyldimethylsilyl groups and the degree of polymerization is about 8000. (B) Denka black granular (manufactured by Denki Kagaku Kogyo Co., Ltd.) as conductive carbon black 15 parts (C) Dimethylsiloxane unit 90 mol% as a crosslinking aid
And methyl vinyl siloxane unit 10 mol%,
Degree of polymerization blocked at the end with vinyldimethylsilyl groups Approximately 8000 methyl vinyl polysiloxane 2 parts The above components were blended and kneaded using a kneader to obtain a silicone rubber composition K. Example 7 (C) A silicone rubber composition L was obtained in the same manner as in Example 6 except that a crosslinking agent having a degree of polymerization of about 800 was used. Example 8 (C) A silicone rubber composition M was obtained in the same manner as in Example 6 except that a crosslinking assistant having a polymerization degree of about 100 was used. Comparative Example 6 To 100 parts of the same methylvinylpolysiloxane as in Comparative Example 4, 50 parts of the same conductive silicone rubber powder and 10 parts of Denka black granules were mixed by a two-roll mill to obtain a silicone rubber composition N. It was Using the silicone rubber compositions K to N prepared as described above, a sheet was molded in the same manner as in the case of the silicone rubber compositions A to G, and the same test was conducted. The results are shown in Table 3.

[0027]

[Table 3]

Claims (1)

[Claims] 1. A polyorganosiloxane mixture containing (A) the following components (a) and (b) in a proportion of 5 to 95% by weight: 95 to 5% by weight: 100 parts by weight (a) Average composition formula (1) ) polyorganosiloxane R ¹ _n SiO represented by _{(4-n) / 2 ......} (1) ( in the formula, R ¹ shows a substituted or unsubstituted monovalent hydrocarbon group, methyl of R ¹ The amount of the group is 97 mol% or less, and n is 1.95.
It is a positive number from ~ 2.05. ) (B) Polyorganosiloxane represented by the average composition formula (2) R ² _m SiO _{(4-m) / 2} (2) (wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group) The amount of methyl groups in R ² is at least 3 mol% or more than the amount of methyl groups in the above formula (1), and m is a positive number from 1.95 to 2.05.) (B) Conductive carbon black 3 To 150 parts by weight (C) crosslinking aid 0.01 to 10 parts by weight (D) curing agent A necessary amount of curing, a conductive silicone rubber composition.