JP3119261B2 - Silicone rubber composition for high voltage electrical insulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber for a high-voltage electrical insulator, which is provided with a silicone rubber which becomes an excellent high-voltage electrical insulator when cured by heating, and which can be suitably used as an insulator for a transmission line, a so-called polymer insulator. Composition.

[0002]

2. Description of the Related Art High-voltage electrical insulators used for insulators used in power transmission lines are generally made of porcelain or glass. However, in environments that are susceptible to pollution, such as coastal areas and industrial areas, the passage of fine particles, salts, fog, etc., on the surface of the high-voltage electrical insulator can cause leakage currents or dry over, which can lead to flashover. There is a problem that band discharge or the like occurs.

[0003] Various solutions have been proposed to improve the disadvantages of these porcelain or glass insulators. For example, U.S. Pat. No. 3,116,986 proposes a weather-resistant high-voltage electrical insulator comprising a member made of a curable resin and a platinum catalyst-containing organopolysiloxane elastomer. Japanese Unexamined Patent Publication (Kokai) No. 59-198604 discloses that a one-part, room-temperature-curable organopolysiloxane composition is applied to the outer surface of a glass product or a high-voltage electrical insulator made of porcelain to obtain moisture and air pollution. There has been proposed a technique for maintaining the high performance of the electric insulator even in the presence of an outdoor stress such as ultraviolet rays.

Further, Japanese Patent Publication No. 53-35982, US Pat. No. 3,965,065 and Japanese Patent Application Laid-Open No. Hei 4-2096 are disclosed.
No. 55 discloses a silicone rubber composition having improved electrical insulation by heating a mixture of an organopolysiloxane and an aluminum hydrate which becomes a silicone rubber by heat curing at a temperature higher than 100 ° C. for 30 minutes or more. Is proposed to be obtained.

[0005] However, none of the above silicone rubber compositions has satisfactory high-voltage electrical insulation performance under severe conditions. In addition, a silicone rubber composition containing aluminum hydrate increases the water absorption of the silicone rubber due to the hygroscopicity of the aluminum hydrate added in large amounts, and the electrical properties in a wet state are significantly reduced. A new problem has arisen.
Further, there is a problem that the corona resistance required as a high-voltage electrical insulator is reduced due to moisture absorption. It is difficult to solve this problem simply by treating the surface of the aluminum hydrate with a treating agent. Therefore, a solution to these problems has been desired.

The present invention has been made in view of the above circumstances, and provides weather resistance, stain resistance, voltage resistance, tracking resistance, and arc resistance under severe air pollution or climatic conditions, especially under high humidity conditions. It is an object of the present invention to provide a silicone rubber composition for a high-voltage electrical insulator, which can provide a silicone rubber excellent in high-voltage electrical insulation performance such as erosion.

[0007]

Means for Solving the Problems and Embodiments of the Invention In order to achieve the above-mentioned object, the present invention has made intensive studies, and as a result, has found that an organopolysiloxane represented by the following average composition formula (1), a silica fine powder and In a silicone rubber composition containing an organic peroxide, at least two types of aluminum hydroxides having different average particle diameters surface-treated with a silicon-containing compound, particularly an average surface-treated with a silicon-containing compound having a vinyl group. When an aluminum hydroxide having a particle diameter of 5 to 20 μm and an aluminum hydroxide having an average particle diameter of 0.1 to 2.5 μm surface-treated with a silicon-containing compound having a vinyl group are combined and mixed, It is difficult to solve the problem by simply treating the aluminum hydroxide surface with a treating agent without absorbing the hydroxide. It can satisfactorily solve difficult corona resistance problems, and has weather resistance, stain resistance, and voltage resistance even under prolonged exposure to severe air pollution or climate, especially high humidity conditions. The present inventors have found that it is possible to obtain a silicone rubber composition that gives a cured product having excellent high-voltage electrical insulation performance such as tracking resistance, arc resistance, and erosion resistance, and has accomplished the present invention.

Accordingly, the present invention provides: (A) 100 parts by weight of an organopolysiloxane represented by the following average composition formula (1): R ¹ _n SiO _{(4-n) / 2} (1) (where R ¹ is The same or different unsubstituted or substituted monovalent hydrocarbon groups, and n is a positive number of 1.98 to 2.02.) (B) 1 to 100 parts by weight of silica fine powder (C) vinyl group Aluminum hydroxide having an average particle diameter of 5 to 20 μm which has been surface-treated with a silicon-containing compound having the same, and aluminum hydroxide having an average particle diameter of 0.1 to 2.5 μm which has been surface-treated with a silicon-containing compound having a vinyl group. Combination with hydroxide 50 to 300 parts by weight (D) Provided is a silicone rubber composition for high-voltage electrical insulator, characterized by containing 0.01 to 10 parts by weight of an organic peroxide. I do.

Hereinafter, the present invention will be described in more detail. The organopolysiloxane as the first essential component of the silicone rubber composition for a high-voltage electrical insulator of the present invention is represented by the following average composition formula (1). . R ¹ _n SiO _{(4-n) / 2} (1) (wherein R ¹ is the same or different unsubstituted or substituted 1
And n is a positive number from 1.98 to 2.02. )

Here, in the above formula, R ¹ is a monovalent hydrocarbon group bonded to the same or different unsubstituted or substituted silicon atom, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms. For example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t
tert-butyl group, hexyl group, alkyl group such as octyl group, cycloalkyl group such as cyclohexyl group, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, alkenyl group such as hexenyl group, phenyl group,
Unsubstituted monovalent hydrocarbon groups such as an aryl group such as a tolyl group, aralkyl groups such as a benzyl group, a phenylethyl group and a phenylpropyl group, and a part or all of the hydrogen atoms bonded to the carbon atoms of these groups Can be selected from a halogen-substituted alkyl group such as a chloromethyl group, a bromoethyl group, a trifluoropropyl group, a cyanoethyl group and the like, and a substituted monovalent hydrocarbon group such as a cyano-substituted alkyl group, which is substituted with a halogen atom, a cyano group and the like. Also, n is 1.98
It is a positive number of ~ 2.02.

[0011] Of all R ¹ groups in the molecule, 0.001 to 5
Preferably, mol%, especially 0.01 to 1 mol%, is an alkenyl group, and the remaining R ¹ is preferably a methyl group or a phenyl group. In this case, 95 mol% or more of all R ¹ groups, especially It is preferable that 99 mol% or more is a methyl group.

The molecular structure of the organopolysiloxane of the above formula (1) is not particularly limited, but the molecular chain ends thereof are particularly preferably trimethylsilyl, dimethylvinylsilyl, divinylmethylsilyl, trivinylsilyl and the like. Those blocked with an organosilyl group or the like are preferred. Further, it is preferable that the main chain is a linear diorganopolysiloxane whose molecular main chain is basically formed by repeating diorganosiloxane units, but a branched siloxane unit such as a monoorganosiloxane unit or a SiO ₂ unit is contained in the molecule. It may contain a small amount, or may be one or a mixture of two or more kinds having different molecular structures.

The above-mentioned organopolysiloxane has an average degree of polymerization (or the number of silicon atoms in the molecule) of 100 to 100,
000, especially 4,000 to 20,000, and a viscosity at 25 ° C. of 100 cs (centistokes) or more, particularly 100,000 to 10,000.
Preferably, it is 0000 cs.

Next, the silica fine powder of the component (B) constituting the silicone rubber composition is essential for obtaining a silicone rubber having excellent mechanical strength. The specific surface area (BET method) is 50 m ² / g
Above, usually 50 to 500 m ² / g, especially 100 to 300
It is preferably m ² / g. The specific surface area is 50 m ² / g
If less than the above, the mechanical strength of the cured product may decrease.

As such reinforcing silica, for example, fumed silica, precipitated silica and their surfaces are treated with organochlorosilane, organoalkoxysilane, organosilazane, diorganocyclopolysiloxane, 1,3-
Hydrophobic silica treated with disiloxane diol and the like;

The amount of the silica fine powder to be added is preferably 1 to 100 parts, especially 30 to 50 parts, and more preferably 1 part, per 100 parts (parts by weight, hereinafter the same) of the organopolysiloxane (A). If it is less than 100 parts, the reinforcing effect may not be obtained due to too small an amount, and if it exceeds 100 parts, the processability is poor and the mechanical strength of the obtained silicone rubber may be reduced.

In the present invention, as the component (C), at least two kinds of aluminum hydroxides having different average particle diameters and surface-treated with a silicon-containing compound are blended. This aluminum hydroxide is basically represented by the following composition formula. Al ₂ O ₃ .3H ₂ O or Al (OH) ₃

In the present invention, by blending at least two kinds of the above-mentioned surface-treated aluminum hydroxides having different average particle diameters as the component (C), particularly, the corona resistance is improved, and the resistance of the silicone rubber is improved. The component (C) is essential in the composition of the present invention because it can improve the arcing property and the tracking resistance.

Here, the surface treatment of the aluminum hydroxide with the silicon-containing compound is a treatment necessary for imparting hydrophobicity to the aluminum hydroxide, and the surface treatment method is not particularly limited. Can be done with

In this case, the silicon-containing surface treating agent includes, for example, a silane coupling agent with an organoalkoxysilane such as vinyl trialkoxysilane, and a hexamer such as tetramethyldivinyldisilazane, tetravinyldimethyldisilazane and hexavinyldisilazane. A surface treating agent having a vinyl group on the surface of an aluminum hydroxide, such as a silazane-based coupling agent such as octaorganotrisilazane such as organodisilazane and hexamethyldivinyltrisilazane, is preferably used. The presence of a vinyl group on the surface of the aluminum hydroxide not only improves the corona resistance but also improves the properties required for the polymer insulator, such as power arc resistance, water resistance, and electrical properties. The preferred vinyl group amount is 1.0 × 10 ⁻⁶ mol or more per 1 g of aluminum hydroxide, and is usually 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² mol,
More preferably, it is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ mol.

As the component (C), aluminum hydroxide A having an average particle diameter of 5 to 20 μm, particularly 8 to 15 μm, which is surface-treated with a silicon-containing compound, and average particles which are surface-treated with a silicon-containing compound, Diameter 0.1-2.5
It is preferable to mix and combine with aluminum hydroxide B of μm, especially 0.5 to 1.5 μm. If the average particle size of the aluminum hydroxide A exceeds 20 μm, the mechanical strength of the cured silicone rubber may be significantly reduced, and if it is less than 5 μm, the resistance of the cured product due to the combined use of aluminum hydroxides having different particle sizes may be reduced. Corona characteristics may not be sufficiently exhibited. Further, when the average particle size of the aluminum hydroxide B exceeds 2.5 μm, the corona resistance may be insufficient due to the difference in the particle size.
If the thickness is less than 0.1 μm, the workability is poor and the cured product may not have the required mechanical strength. The average particle diameter can be determined as a weight average value (median diameter) or the like by a particle size distribution analyzer using an analysis means such as a laser light diffraction method.

Further, the blending ratio (blending ratio) of aluminum hydroxide A and aluminum hydroxide B is A: B = 80: 20 to 20:80, especially 60:40 by weight.
It is desirable to be in the range of ４０40: 60. When the blend ratio of the aluminum hydroxide A exceeds 80% by weight,
In some cases, the mechanical strength of the silicone rubber is reduced, and when the blend ratio of the aluminum hydroxide B exceeds 80% by weight, the corona resistance may be reduced.

The total amount of component (C) is 50 to 300 parts per 100 parts of organopolysiloxane of component (A).
Parts, particularly preferably in the range of 100 to 200 parts. If the compounding amount is less than 50 parts, the composition after curing may not be able to obtain the required arc resistance and tracking resistance, and if it exceeds 300 parts, it becomes difficult to add the composition to the composition, and the processability also deteriorates. There are cases.

As the organic peroxide as the component (D), conventionally known organic peroxides can be used. For example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methyl Benzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, di-t-butyl peroxide, t-butyl perbenzoate, 1,1 -Screw (t-
(Butylperoxy) 3,3,5-trimethylcyclohexane, 1,6-bis (t-butylperoxycarboxy) hexane and the like.

The amount of the organic peroxide is 0.01 to 10 parts per 100 parts of the organopolysiloxane of the component (A).
Parts, or 0.01 in the silicone rubber composition.
The content is preferably set to 〜3% by weight.

The silicone rubber composition according to the present invention includes:
In addition to the above-mentioned essential components, a filler such as crushed quartz, diatomaceous earth, or calcium carbonate as an extender may be added as an optional component as needed, as long as the effects of the present invention are not impaired.

The composition of the present invention may further comprise a flame retardant, a fire resistance improver, a sensitizer, a colorant, a heat resistance improver, if necessary.
Various additives such as a reducing agent, a reaction controlling agent, a release agent or a dispersant for a filler can be added. In addition, it is preferable that the amount of various alkoxysilanes, carbon functional silanes, low molecular weight siloxanes containing silanol groups, and the like used as the filler dispersant be minimized so as not to impair the effects of the present invention.

In the silicone rubber composition according to the present invention, the above-mentioned components are uniformly mixed using a rubber kneading machine such as a two-roll mill, a Banbury mixer or a dough mixer (kneader) and, if necessary, heat-treated. Can be obtained. In this case, for example, the organopolysiloxane of the component (A), the silica fine powder of the component (B) and the like may be mixed in advance to prepare a base compound, and any components may be mixed therewith.

The silicone rubber composition thus obtained can be molded into the required silicone rubber by various molding methods such as casting, die pressing and extrusion. The curing conditions can be adjusted as appropriate. For example, in the case of press molding, 120 to 22
It is preferable to set the temperature to about 5 minutes to 1 hour at 0 ° C.

[0030]

Industrial Applicability The silicone rubber composition for a high-voltage electrical insulator of the present invention has a weather resistance and a high durability even under long-term exposure to severe air pollution or climatic conditions, especially high humidity conditions. A cured product excellent in high-voltage electrical insulation performance such as stain resistance, withstand voltage, tracking resistance, arc resistance, and erosion property is provided.

[0031]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. All parts in each example are parts by weight.

[Example 1] Dimethylsiloxane unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units and 100 parts of rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 were added to a dimethylpolysiloxane having terminal silanol group dimethylpolysiloxane (average degree of polymerization: 1) as a dispersant.
0) 5 parts, 10 parts of fumed silica (manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, aluminum hydroxide having an average particle diameter of 8 μm and having a surface treated with vinylsilane (Showa Denko KK ), Heidilight H32
(STV) 110 parts, 70 parts of aluminum hydroxide having an average particle size of 1 μm and having a surface treated with vinyl silane (Hijilite H42STV, manufactured by Showa Denko KK), and compounded with a pressure kneader to form a compound ( 1) was prepared.

This compound (1) contains 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain 2 mm and 1 mm silicone rubber sheets.

Example 2 Dimethylsiloxane Unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units and 100 parts of rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 were added to a dimethylpolysiloxane having terminal silanol group dimethylpolysiloxane (average degree of polymerization: 1) as a dispersant.
0) 5 parts, 10 parts of fumed silica (manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, aluminum hydroxide having an average particle diameter of 8 μm and having a surface treated with vinylsilane (Showa Denko KK ), Heidilight H32
90 parts of STV), 90 parts of aluminum hydroxide having an average particle diameter of 1 μm and having a surface treated with vinylsilane (Hijilite H42STV, manufactured by Showa Denko KK), and compounded with a pressure kneader to obtain a compound ( 2) was prepared.

This compound (2) was added with 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain a silicone rubber sheet.

Example 3 Dimethylsiloxane Unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units and 100 parts of rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 were added to a dimethylpolysiloxane having terminal silanol group dimethylpolysiloxane (average degree of polymerization: 1) as a dispersant.
0) 5 parts, 10 parts of fumed silica (manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, aluminum hydroxide having an average particle diameter of 8 μm and having a surface treated with vinylsilane (Showa Denko KK ), Heidilight H32
(STV) 70 parts, an average particle diameter of 1 μm, and 110 parts of aluminum hydroxide (Hysilite H42STV, manufactured by Showa Denko KK) having a surface treated with vinylsilane, and compounded with a pressure kneader to obtain a compound ( 3) was prepared.

This compound (3) was added with 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain a silicone rubber sheet.

Comparative Example 1 Dimethylsiloxane Unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units and 100 parts of rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 were added to a dimethylpolysiloxane having terminal silanol group dimethylpolysiloxane (average degree of polymerization: 1) as a dispersant.
0) 5 parts, 10 parts of fumed silica having a specific surface area of 200 m ² / g (manufactured by Nippon Aerosil Co., Ltd.), and aluminum hydroxide having an average particle diameter of 8 μm (Showa Denko KK)
110 parts of Heidilite H32M) having an average particle size of 1
70 μm of aluminum hydroxide (Hijilite H42M, manufactured by Showa Denko KK) having a particle size of 70 μm was added, and the mixture was mixed with a pressure kneader to prepare Compound (4).

This compound (4) was added with 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain a silicone rubber sheet.

Comparative Example 2 Dimethylsiloxane Unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units, and 100 parts of a rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 are used as a dispersant as a dispersing agent.
5 parts, 10 parts of fumed silica having a specific surface area of 200 m ² / g (manufactured by Nippon Aerosil Co., Ltd.), and an average particle diameter of 8
180 parts of aluminum hydroxide (Higilite H32M, manufactured by Showa Denko KK) having a particle size of 180 μm was added thereto, and heat-treated at 150 ° C. for 3 hours to prepare Compound (5).

This compound (5) was added with 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain a silicone rubber sheet.

Comparative Example 3 Dimethylsiloxane Unit 9
9.825 mol%, methyl vinyl siloxane unit 0.1
5 mol%, 0.025 mol% of dimethylvinylsiloxy units and 100 parts of rubbery organopolysiloxane A having an average degree of polymerization of about 8,000 were added to a dimethylpolysiloxane having terminal silanol group dimethylpolysiloxane (average degree of polymerization: 1) as a dispersant.
0) 5 parts, 10 parts of fumed silica (manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, aluminum hydroxide having an average particle diameter of 1 μm and having a surface treated with vinylsilane (Showa Denko KK ) Made, Heidilight H42
(STV) 180 parts and methyltrimethoxysilane 5 parts were added and heat-treated at 150 ° C. for 3 hours to prepare a compound (6).

This compound (6) was added with 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane /
The above organopolysiloxane A / specific surface area is 200 m ²
/ G fumed silica (Nippon Aerosil Co., Ltd.)
Was added, and the mixture was uniformly dispersed with two rolls, followed by press curing at 165 ° C. for 10 minutes to obtain a silicone rubber sheet.

The silicone rubber sheets obtained in the above Examples and Comparative Examples were evaluated by the following methods. Table 1 shows the results. Rubber Properties: Rubber properties (hardness, tensile strength, elongation) were measured according to JIS K6301. Weight change: 80 mm x 8 from a 2 mm thick sheet
After cutting a test piece of 0 mm and measuring the initial weight, the weight after immersing in deionized water at 25 ° C. for 100 hours was measured,
The change in weight was determined. Volume resistivity, dielectric constant, dielectric loss, dielectric breakdown voltage: thickness 1
mm sheet, the initial volume resistivity, dielectric constant, dielectric loss, and dielectric breakdown voltage were measured according to JIS K6911. Then, the sheet was placed in deionized water at 25 ° C. for 10 minutes.
The volume resistivity, dielectric constant, dielectric loss, and dielectric breakdown voltage after immersion for 0 hours were measured in the same manner.

Further, the same sheet was immersed in a 1N aqueous solution of nitric acid at 25 ° C. for 96 hours and then was immersed in deionized water for 24 hours, and the weight change with respect to the initial weight and the rubber physical properties were measured in the same manner as described above. .

From the results shown in Table 1, the silicone rubber compositions of the present invention (Examples 1 to 3) have low hygroscopicity and have excellent properties as a high-voltage electrical insulator even when exposed to high humidity conditions. It was confirmed to give silicone rubber.

[0047]

[Table 1]

Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01B 3/00 H01B 3/00 A 3/46 3/46 D (72) Inventor Shuichi Henchi 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Technology Laboratory (72) Inventor Takeo Yoshida 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Technology Laboratory (56) References JP JP-A-9-40871 (JP, A) JP-A-4-209655 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 83/07 H01B 3/00 H01B 3/46

Claims (3)

(57) [Claims] (A) The following average composition formula (1): R ¹ _n SiO _{(4-n) / 2} (1) (wherein R ¹ is the same or different, unsubstituted or substituted monovalent hydrocarbon) 100 parts by weight of an organopolysiloxane represented by the following formula (B): 1 to 100 parts by weight of silica fine powder; and (C) a silicon-containing compound having a vinyl group. An aluminum hydroxide having an average particle size of 5 to 20 μm and a surface treatment with a silicon-containing compound having a vinyl group and an aluminum hydroxide having an average particle size of 0.1 to 2.5 μm. 50 to 300 parts by weight of (D) an organic peroxide, comprising from 0.01 to 10 parts by weight of a silicone rubber composition for a high-voltage electrical insulator. 2. The mixing ratio of an aluminum hydroxide having an average particle diameter of 5 to 20 μm and an aluminum hydroxide having an average particle diameter of 0.1 to 2.5 μm is 80:20 by weight.
The silicone rubber composition according to claim 1, wherein the ratio is 20:80. 3. The silicone rubber composition according to claim 1, which does not contain a platinum catalyst.