JP3409507B2 - 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 composition for a high-voltage electrical insulator, which gives a silicone rubber which becomes an excellent high-voltage electrical insulator when cured by heating.

[0002]

2. Description of the Related Art High voltage electrical insulators used in insulators used in power transmission lines and the like are generally made of porcelain or glass. However, in an environment susceptible to pollution such as coastal areas and industrial areas, particles, salts, fog, etc. may pass through the surface of the high-voltage electrical insulator, resulting in leakage current or flashover. There was a problem that dry band discharge or the like occurs.

Therefore, various solutions have been proposed in order to improve the drawbacks of these porcelain or glass insulators. For example, in US Pat. No. 3,511,698,
A weather-resistant high-voltage electrical insulator composed of a member made of a curable resin and a platinum catalyst-containing organopolysiloxane elastomer has been proposed. Also, US Pat.
Japanese Patent Application Laid-Open No. 59-198604, which corresponds to Japanese Patent Publication No. 5-58604, discloses a method of applying a one-component room-temperature-curable organopolysiloxane composition to the outer surface of a glass product or a porcelain electric insulator to obtain moisture, Techniques have been proposed for maintaining the high-performance electrical performance of the electrical insulator even in the presence of outdoor stress such as air pollution and ultraviolet rays.

Further, JP-A-53-35982 corresponding to US Pat. No. 3965065 and JP-A-4-20965 corresponding to US Pat. No. 5,369,161.
Japanese Patent Publication No. 5 discloses a silicone rubber composition in which electrical insulation is improved by heating a mixture of an organopolysiloxane that becomes a silicone rubber by heat curing and an aluminum hydrate at a temperature higher than 100 ° C. for 30 minutes or more. It is proposed that the product be obtained.

However, in the above-mentioned conventional techniques, the high-voltage electrical insulation performance of the used silicone rubber materials is not yet sufficiently satisfactory, and therefore the conventional silicone rubber composition has improved electrical insulation performance. In order to do so, a large amount of aluminum hydroxide must be used, but this has the disadvantage that the mechanical strength of the rubber is weakened.

The present invention has been made in view of the above circumstances.
Silicone for high-voltage electrical insulators that provides silicone rubber with excellent high-voltage electrical insulation properties such as weather resistance, tracking resistance, arc resistance, and erogen resistance even under conditions that are exposed to severe air pollution or climate after heat curing An object is to provide a rubber composition.

[0007]

Means for Solving the Problems and Modes for Carrying Out the Invention As a result of extensive studies conducted by the inventor of the present invention, an addition-curable silicone rubber composition and a silicone rubber composition containing fine silica powder have been obtained. Compounded with a specific amount of an aluminum hydroxide and a metal oxide containing at least one cobalt, and a silicone rubber is obtained by the synergistic effect of the aluminum hydroxide and the metal oxide containing cobalt. Tracking resistance, erosion resistance, arc resistance, and other characteristics have been significantly improved, and it is possible to reduce the filling amount of aluminum hydroxide to obtain practical tracking resistance as a high-voltage insulator. Yes, it can contribute to the weight reduction of silicone rubber insulators and the improvement of mechanical properties. Therefore, weather resistance, tracking resistance, arc resistance, and erotic resistance. And found that high-voltage electrical insulating-body silicone rubber composition which gives excellent silicone rubber to a high voltage electrical insulating properties of Zhen and the like is obtained, leading to completion of the present invention.

Accordingly, the present invention provides: (1) 100 parts by weight of an addition-curable silicone rubber composition (parts by weight; the same applies hereinafter) (2) Fine silica powder 1-100 parts (3) Aluminum hydroxide 30-300 parts (4) A silicone rubber composition for a high-voltage electrical insulator, characterized by containing 0.1 to 20 parts of a metal oxide containing at least one cobalt.

The present invention will be described in more detail below. The first component of the silicone rubber composition for high-voltage electrical insulators of the present invention is an addition-curable silicone rubber composition.

The addition-curable silicone composition includes (a) the following average compositional formula (1) R ¹ _a SiO 2 _{(4-a) / 2} (1) (wherein R ¹ is substituted or It is an unsubstituted monovalent hydrocarbon group, but 0.01 to 20 mol% of R ¹ is an alkenyl group. A is a positive number of 1.9 to 2.4. Organopolysiloxane having at least two alkenyl groups in
100 parts by weight (b) The following average composition formula (2) R ² _b H _c SiO ² _{(4-bc) / 2} (2) (wherein R ² is a substituted or unsubstituted C 1 to C 10 group) Is a monovalent hydrocarbon group, and b is 0.7 to 2.1, c
Is 0.002 to 1 and b + c is a positive number satisfying 0.8 to 3. ) Organohydrogenpolysiloxane which has at least two hydrogen atoms bonded to silicon atoms and is liquid at room temperature 0.1 to 100 parts by weight (c) Addition reaction catalyst Silicone rubber composition containing a catalytic amount as a main component Is preferably used.

In the alkenyl group-containing organopolysiloxane of the above formula (1), R ¹ preferably has 1 carbon atom.
To 12, more preferably a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, specifically, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group. Group, hexyl group, cyclohexyl group, alkyl group such as octyl group, vinyl group, allyl group, alkenyl group such as propenyl group, isopropenyl group, butenyl group, aryl group such as phenyl group, tolyl group, xylyl group, benzyl group And the like, and haloalkyl groups such as chloromethyl group, chloromethyl group, 2-bromoethyl group, 3,3,3-trifluoropropyl group, 3-chloropropyl group and cyanoethyl group, and cyano group-substituted hydrocarbon groups. Each substituent may be different or the same, but it is preferable that 0.01 to 20 mol%, more preferably 0.1 to 10 mol% of R ¹ is an alkenyl group, It is also necessary that the molecule has at least two alkenyl groups on average. Furthermore, R
^{Although 1} may be any of the above, it is preferable to introduce a vinyl group as the alkenyl group and a methyl group or a phenyl group as the other substituent. Further, a is a positive number in the range of 1.9 to 2.4, preferably 1.95 to 2.2.

The organopolysiloxane of the above formula (1) has a linear molecular structure, or R ¹ Si.
_{Monoorganosiloxane} unit represented by O _3/2 or SiO
Including _4/2 units may be branched, but usually the main chain consists of repeating diorganosiloxane units basically R ¹ ₂ SiO _2/2, the molecular chain terminals R ¹ ₃ SiO _1/2
Is generally a linear diorganopolysiloxane blocked with triorganosiloxy units. The alkenyl group in the molecule may be bonded to either the terminal of the molecular chain or the silicon atom in the middle of the molecular chain, or may be bonded to both of them, but the curability, the physical properties of the cured product, etc. From the viewpoint of the above, it is preferable to have an alkenyl group bonded to at least a silicon atom at the end of the molecular chain.

The alkenyl group-containing organopolysiloxane has a viscosity of 100 to 1,000,000 at 25 ° C.
cps, especially 500 to 500,000 cps is desirable.

The above alkenyl group-containing organopolysiloxane can be produced by a known method. Specifically, the equilibrium reaction of the organocyclopolysiloxane and the hexaorganodisiloxane is carried out in the presence of an alkali or acid catalyst. Can be obtained by

In the organohydrogenpolysiloxane of the above formula (2), R ² is the same as R ¹ , but preferably has no aliphatic unsaturated bond. b is 0.7-2.1, preferably 1-2, c is 0.002-1, preferably 0.01-0.5, and b + c is 0.8-3, preferably 1.5-. It is a positive number that satisfies 2.6, and more preferably 1.8 to 2.2.

This organohydrogenpolysiloxane acts as a cross-linking agent for the above-mentioned component (a) in the presence of an addition reaction catalyst, and at least two in the molecule,
It preferably has 3 or more hydrogen atoms bonded to silicon atoms (that is, SiH groups). This SiH group may be located at the end of the molecular chain or in the middle of the molecular chain, or at both positions. It may be one that does.

Examples of such an organohydrogenpolysiloxane include trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends, dimethylsiloxy group-blocked dimethylsiloxane / methylhydrogenpolysiloxane copolymer at both ends, and dimethylhydrogensiloxy at both ends. Group-terminated dimethylpolysiloxane, dimethylhydrogensiloxy group-terminated dimethylpolysiloxane, dimethylhydrogensiloxy group-terminated dimethylsiloxane / methylhydrogensiloxane copolymer, trimethylsiloxy group-terminated methylhydrogensiloxane / diphenylsiloxane -Dimethylsiloxane copolymer, copolymer composed of (CH ₃ ) ₂ HSiO _1/2 unit and SiO _4/2 unit, (CH ₃ ) ₂ HS
Examples thereof include a copolymer composed of io _1/2 unit, SiO _4/2 unit and (C ₆ H ₅ ) SiO _3/2 unit.

The organohydrogenpolysiloxane of the above formula (2) may have a linear, cyclic or branched molecular structure, but it must be liquid at room temperature and its viscosity is 25. Usually 1 to 10000c at ℃
ps, preferably 3 to 5000 cps, especially 5 to 100
It is desirable that the organohydrogenpolysiloxane has a number of silicon atoms in the molecule of usually 3 to 400, preferably 4 to 200.

The above organohydrogenpolysiloxane can be manufactured by a known method.

The amount of the above-mentioned organohydrogenpolysiloxane is usually 0.1 to 100 parts, preferably 0.3 to 50 parts, particularly preferably 100 to 100 parts of the first component (component (a)). It is in the range of 0.5 to 30 parts.

In this organohydrogenpolysiloxane, the hydrogen atom (SiH group) bonded to the silicon atom in the molecule is 0.8 to 0.8 in molar ratio with respect to the alkenyl group in the organopolysiloxane of component (a). It may also be blended in an amount of 10, preferably 1 to 5 mol / mol.

As the addition reaction catalyst, platinum black, second chloride
Platinum, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, a platinum-based catalyst such as platinum bisacetoacetate, a palladium-based catalyst, a rhodium-based catalyst and the like. The addition amount of this addition reaction catalyst is a catalytic amount, and is usually 0.1 to 500 ppm as platinum, palladium or rhodium metal relative to the first component, especially 1
~ 100 ppm.

In addition to the above-mentioned main components, the addition-curable silicone rubber composition contains, as optional components, metal oxides other than transition metals such as calcium oxide and magnesium oxide, and aluminum such as alkaline earth metals such as magnesium hydroxide. Metal hydroxides other than, addition reaction control agents such as acetylene compounds such as ethynylcyclohexanol can be added within the range that does not impair the effects of the present invention, silica fine powder, aluminum hydroxide, transition element containing Does not contain metal oxides.

Next, as the second component of silica fine powder,
The type is not particularly limited, and those used in conventional silicone rubber compositions can be used. Such fine silica powder, for example, specific surface area by BET method of 50 m ² / g or more, particularly precipitated silica of 50 to 400 m ² / g, fumed silica, and fired silica, average particle diameter of 50μm or less, particularly 0 Pulverized quartz of 1 to 20 μm, diatomaceous earth, etc. are preferably used.

Although these silica fine powders may be used as they are, they may be surface-treated with an organic silicon compound such as hexamethyldisilazane, trimethylchlorosilane and polymethylsiloxane and used as hydrophobic silica fine powders.

The compounding amount of the above silica fine powder is as follows:
It is in the range of 1 to 100 parts, preferably 2 to 50 parts with respect to 00 parts, and if it is less than 1 part, the mechanical strength becomes weak,
If it exceeds 100 parts, it becomes difficult to highly fill the third component, aluminum hydroxide.

In the present invention, aluminum hydroxide is used as the third component. By blending this component, the electrical insulation performance such as arc resistance and tracking resistance of the silicone rubber can be improved, It is essential in the composition of the present invention.

Here, as the aluminum hydroxide,
A compound represented by the following formula (3) Al ₂ O ₃ .3H ₂ O (3) and having an average particle diameter of 10 μm or less, usually 0.
Those having a BET specific surface area of 1 to 10 μm, particularly 0.5 to 9 μm and a BET specific surface area of 0.5 to 10 m ² / g are preferably used.

The aluminum hydroxide may be surface-treated, for example, using a silane-based or titanate-based coupling agent, dimethylpolysiloxane oil, dimethylhydrogenpolysiloxane oil, or the like. preferable.

Specific examples of silane coupling agents include hexamethyldisilazane, divinyltetramethyldisilazane, diphenyltetramethyldisilazane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylethoxysilane, vinyltris (methoxyethoxy). Silane, trimethylchlorosilane, trimethylaminosilane, glycidoxypropyltrimethoxysilane,
Examples include glycidoxypropylmethyldiethoxysilane, (epoxycyclohexyl) ethyltrimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, dimethyldimethoxysilane, divinyldimethoxysilane and chloropropyltrimethoxysilane. .

As titanate coupling agents, tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetrastearyl titanate, triethanolamine titanate,
Titanium acetyl acetate, titanium ethyl acetoacetate, titanium lactate, octylene glycol titanate, isopropyl tristearoyl titanate, isopropyl tris (dodecylbenzenesulfonyl) titanate, isopropyl tris (dioctyl pyrophosphate) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, Examples thereof include bis (dioctylpyrophosphate) ethylene titanate.

Further, the dimethylpolysiloxane oil has a cyclic or linear viscosity at 25 ° C. of 0.65.
A material of -100 centistokes is preferably used.

The methylhydrogenpolysiloxane may have a linear, branched, cyclic or network molecular structure, but the linear one represented by the following general formula (4) is preferably used. To be done.

[0034]

[Chemical 1]

In the above formula, r is an integer of 0 to 50, preferably 0 to 25, and s is 1 to 50, preferably 2 to
It is an integer of 25. If r exceeds 50, the viscosity may be high and it may be difficult to process, and if s exceeds 50, the viscosity may be high and the surface may be difficult to wet.

In the present invention, among the above-mentioned surface treatment agents, organosilazanes, particularly hexaorganodisilazanes such as hexamethyldisilazane are more preferably used.

The surface treating agent is preferably used in an amount of 1 to 50 parts, particularly 5 to 30 parts, relative to 100 parts of aluminum hydroxide, and if the amount is less than 1 part, the effect as a treating agent is not obtained. In some cases, if the amount exceeds 50 parts, the process may be wasteful and the cost may be disadvantageous.

The surface treatment of aluminum hydroxide can be carried out by a generally known technique. For example, the aluminum hydroxide may be directly treated in advance or may be treated while being kneaded with other components. In particular, it is preferable to directly process in advance. Specifically, aluminum hydroxide and a treating agent are put in a mechanical kneading apparatus closed at atmospheric pressure or in a fluidized bed, and if necessary, the mixture is kneaded at room temperature or heat treatment in the presence of an inert gas, and kneaded. It can be adjusted by post-drying. Depending on the case, a catalyst may be used in accordance with each treating agent to accelerate the treatment.

The content of the third component, aluminum hydroxide, is in the range of 30 to 300 parts, preferably 50 to 250 parts, relative to 100 parts of the first component. If the amount exceeds 300 parts, it will be difficult to fill the composition and the workability will deteriorate.

In the present invention, at least 1 is used as the fourth component.
Using a metal oxide containing cobalt of a kind, tracking resistance of the silicone rubber, erogen resistance by a synergistic effect with the aluminum hydroxide of the third component by blending the metal oxide in a specific amount, The arc resistance and the like can be further improved. In this case, Co ₂ O ₃ and Co ₃ O ₄ are preferably used as the metal oxide containing cobalt. A metal oxide containing a transition metal element other than cobalt may be used in combination with the metal oxide containing cobalt.

Here, the transition metal elements are the first transition element group from Sc at number 21 to Zn at number 0 and the second transition element group from Y at number 39 to Cd at number 48 in the Mendeleev's periodic table. , A third transition element group from Hf of No. 72 to Hg of No. 80, further lanthanoid elements from La of No. 57 to Lu of No. 71 as an internal transition element, Ac of No. 89.
Actinoid elements from Lr to No. 103 are also included. Among these transition metal elements, iron and cerium are preferable.

In the present invention, as the metal oxide containing a transition metal element other than cobalt, a metal oxide containing a metal selected from the above transition elements alone or in combination of two or more, or a transition element is used. It is possible to use a mixture of metal oxides containing at least one, Mo
_{O 3, Ce 2 O 3,} FeO · Fe 2 O 3, Fe 2 O 3, Ti
O ₂ , V ₂ O ₅ , NiO ₃ , ZrO ₂ , Cr ₂ O ₃ , CrO ₃ ,
PdO ₂ , MnO ₂ , ZnO, RuO ₂ , Ni ₃ O ₄ , Nb ₂
O ₅ , La ₂ O ₃ , WO _{2 and the} like are exemplified, but it is preferable to use a metal oxide containing cobalt in combination with a metal oxide containing iron.

The metal oxide containing cobalt and the metal oxide containing a transition metal element other than cobalt preferably have an average particle size of 100 μm or less, particularly 70 μm or less. When the average particle size exceeds 100 μm, dispersibility is obtained. May deteriorate, and uniform blending may become difficult.

The amount of the metal oxide containing cobalt as the fourth component is 0.1 to 20 parts, preferably 0.3 to 17 parts, and 0.1 part to 100 parts of the first component. If it does not meet the requirements, the expected improvement in tracking resistance cannot be obtained, and 2
If it exceeds 0 parts, the obtained rubber strength becomes insufficient, aluminum hydroxide cannot be highly filled, and the tracking property cannot be further improved. When a metal oxide containing a transition metal element other than cobalt is used in combination, the total amount of cobalt and the metal oxide containing a transition metal element other than cobalt is the above blending amount.

If necessary, various additives such as metal oxides, metal carbonates and carbons not containing the above transition metal elements can be added to the silicone rubber composition of the present invention depending on the purpose. Further, a pigment, a heat-resistant agent, a flame retardant, a plasticizer, an antioxidant and the like may be added as long as the desired characteristics are not impaired. In addition, the addition amount of these optional components can be a normal amount within a range that does not impair the effects of the present invention.

The silicone rubber composition of the present invention can be obtained by only uniformly mixing the above-mentioned first to fourth components and optional components at room temperature, but if necessary, the above-mentioned (in the first component) B), essential components other than (c) component, optional components 100-200 with a planetary mixer or kneader
Heat treatment in the range of ℃ for 2 to 4 hours, then (b), (c)
The components may be mixed and cured and molded. The molding method can be freely selected according to the viscosity of the mixture, and injection molding,
Any method such as compression molding, injection molding, extrusion molding or transfer molding may be adopted. The curing conditions are
Usually, it can be heated at 80 to 200 ° C. for 3 minutes to 3 hours.

[0047]

EFFECTS OF THE INVENTION The silicone rubber composition for a high voltage electrical insulator of the present invention has high voltage electrical characteristics such as tracking resistance, erosion resistance and arc resistance even under conditions exposed to severe weather and pollution. It gives a silicone rubber which is not only excellent, but also excellent in weather resistance and water repellency, and this silicone rubber is useful as a high-voltage electrical insulator such as a high-voltage insulator.

The present invention will be specifically described below with reference to Examples, Reference Examples and Comparative Examples, but the present invention is not limited to the following Examples. All parts in each example are parts by weight.

[Examples 1 and 2, Reference Examples 1 to 3] As shown in Table 1, as the component (a) in the first component, both ends were capped with dimethylvinylsiloxy groups, respectively 25
Dimethylpolysiloxane (organopolysiloxane a) having a viscosity of 5000 cp at ℃, wet silica as a second component of silica fine powder (Nipsil LP, manufactured by Nippon Silica Industry Co., Ltd.,
Aluminum oxide having a BET specific surface area of 180 m ² / g), an average particle diameter of 8 μm as the third component and a BET specific surface area of 2 cm ² / g, and each transition metal oxide shown in Table 1 having an average particle diameter of 100 μm or less as the fourth component. The respective substances were blended in the amounts shown in Table 1, stirred and mixed at 150 ° C. for 2 hours in a planetary mixer, and then cooled to room temperature. Further, dimethylhydrogenpolysiloxane represented by the following formula (5) as the component (b) in the remaining first component, a 1% 2-ethylhexanol solution of chloroplatinic acid as the component (c), and further as a reaction control agent. Ethynylcyclohexanol was added in an amount shown in Table 1 and uniformly mixed to obtain a silicone rubber composition. This silicone rubber composition was heated and cured at 120 ° C. for 10 minutes, and each was 128 mm × 44 mm × 6 mm
A (thickness) silicone rubber sheet was obtained.

[0050]

[Chemical 2]

Reference Example 4 As shown in Table 1, as the component (a) in the first component, dimethylpolysiloxane (organopolysiloxane) having a viscosity of 30,000 cps at 25 ° C. and having both ends blocked with trivinylsiloxy groups. b) The second, third and fourth components were heated and mixed in the same manner as in Example 1 except that 100 parts were used, and 0.6 part of dicumyl peroxide was further added as an organic peroxide, and the mixture was homogenized at room temperature. Until mixed to obtain a silicone rubber composition. This silicone rubber composition is treated at 165 ° C.
After heat-curing for 10 minutes, further secondary cure at 200 ° C for 4 hours, each 128 mm × 44 mm × 6 mm
A (thickness) silicone rubber sheet was obtained.

[Comparative Examples 1 to 3] Using the components shown in Table 1, the same as in Example 1
A rubber sheet was obtained. Next, the above examples, reference examples and
Regarding the silicone rubber sheet obtained in Comparative Example,
The tracking test was conducted by the method. The results are shown in Table 1.Tracking test method: Performed according to the standard of ASTM D-2303-64T
It was That is, when the load voltage is 4 kV and the distance between the electrodes is 50 mm
Dye liquor (0.1% NH_FourCl and 0.02% nonionic surface activity
Aqueous agent solution) at the rate of 0.6 ml / min
The time it takes for the track to be generated and conductive after dripping from
And the resulting erosion loss weight (% by weight) is measured
did.Erosion loss weight: During the above test, part of the rubber sheet is not exposed to heat or arc.
Deteriorated and eroded. This erosion amount was calculated by the following formula.
Erosion amount = (weight lost due to erosion / total sheet before test
Body weight) x 100

From the results shown in Table 1, the silicone rubber composition of the present invention is excellent in tracking resistance and erosion resistance, and in particular, the tracking resistance is greatly improved by the synergistic effect of aluminum hydroxide and cobalt oxide. It was confirmed. Further, the silicone rubber composition of the present invention, in order to obtain practical tracking resistance as a high-pressure insulator, it is possible to reduce the filling amount of conventional aluminum hydroxide, and to reduce the weight of the silicone rubber insulator, It was confirmed that it can contribute to the improvement of mechanical properties.

[0054]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-52-32950 (JP, A) JP-A-4-209655 (JP, A) JP-B-50-15318 (JP, B1) (58) Field (Int.Cl. ⁷ , DB name) C08L 83/05 C08L 83/07 H01B 3/46

Claims (5)

(57) [Claims] 1. (1) Addition-curable silicone rubber composition 100 parts by weight (2) Fine silica powder 1-100 parts by weight (3) Aluminum hydroxide 30-300 parts by weight (4) At least one cobalt A silicone rubber composition for a high-voltage electrical insulator, comprising 0.1 to 20 parts by weight of a metal oxide containing 2. The silicone rubber composition for a high voltage electrical insulator according to claim 1, wherein a metal oxide containing cobalt and a metal oxide containing iron are used in combination. 3. A metal oxide containing iron is FeO.Fe ₂ O ₃
The silicone rubber composition for a high voltage electrical insulator according to claim 2. 4. The silicone rubber composition for a high voltage electrical insulator according to claim 1, 2 or 3, wherein the component (4) metal oxide containing cobalt is Co ₂ O ₃ and / or Co ₃ O ₄ . 5. The addition-curable silicone rubber composition has the following average composition formula (1) R ¹ _a SiO 2 _{(4-a) / 2} (1) (wherein R ¹ is substituted Or, it is an unsubstituted monovalent hydrocarbon group, but 0.01 to 20 mol% of R ¹ is an alkenyl group, and a is a positive number of 1.9 to 2.4). Organopolysiloxane having at least two alkenyl groups therein
100 parts by weight (b) The following average composition formula (2) R ² _b H _c SiO ² _{(4-bc) / 2} (2) (wherein R ² is a substituted or unsubstituted C 1 to C 10 group) Is a monovalent hydrocarbon group, and b is 0.7 to 2.1, c
Is 0.002 to 1 and b + c is a positive number satisfying 0.8 to 3. ) Organohydrogenpolysiloxane which is liquid at room temperature and has at least two hydrogen atoms bonded to silicon atoms, 0.1 to 100 parts by weight (c) addition reaction catalyst, which has a catalytic amount as a main component. Item 5. A silicone rubber composition for high-voltage electrical insulators according to any one of items 1 to 4.