JP5322689B2 - Silicone rubber composition for high voltage electrical insulation - Google Patents

Description

  The present invention relates to a silicone rubber composition for high voltage electrical insulators that provides a silicone rubber that becomes a high voltage electrical insulator excellent by curing.

  High voltage electrical insulators used for insulators used for power transmission lines and the like are generally made of porcelain or glass. However, these insulators lack impact resistance, are easily damaged, and are heavy, so they must be handled with care and have difficulty in workability. In an environment subject to contamination, there are problems that fine currents, salts, fog, etc. pass through the surface of the high-voltage electrical insulator, resulting in leakage current and dry discharge that leads to flashover.

  Various solutions have been proposed to improve the disadvantages of these porcelain or glass insulators. For example, US Pat. No. 3,511,698 (Patent Document 1) proposes a weather-resistant high-voltage electrical insulator comprising a member made of a curable resin and a platinum catalyst-containing organopolysiloxane elastomer. JP-A-59-198604 (Patent Document 2) discloses that a one-part room temperature-curable organopolysiloxane composition is applied to the outer surface of an electrical insulator made of glass or porcelain, so that moisture and There has been proposed a technique for maintaining the high performance of the electric insulator even in the presence of outdoor stress such as air pollution and ultraviolet rays.

  Further, JP-A-53-35982 (Patent Document 3) discloses that a mixture of organopolysiloxane and aluminum hydroxide, which becomes silicone rubber by heat curing, is heated at a temperature higher than 100 ° C. for 30 minutes or more. A silicone composition with improved insulation can be obtained, and Japanese Patent Application Laid-Open No. 7-57574 (Patent Document 4) discloses contact angle recovery characteristics over time by mixing methylalkylsiloxane oil with silicone rubber. It has been proposed that it is effective in preventing flashover.

  However, none of these conventional techniques is satisfactory enough for the high-voltage electrical characteristics of the silicone rubber materials used, and a large amount of aluminum hydroxide is used to improve the electrical insulation performance. Although it must be used, aluminum hydroxide is highly hydrophilic and reduces the electrical properties in a high humidity environment. In order to solve this problem, in Japanese Patent Laid-Open No. 8-259820 (Patent Document 5), surface treatment of aluminum hydroxide is performed, and in Japanese Patent Laid-Open No. 11-152408 (Patent Document 6), the amount of alkenyl groups on the surface Is disclosed. Japanese Patent Application Laid-Open No. 11-12470 (Patent Document 7) describes a method of adding an organopolysiloxane resin to an addition-curable silicone rubber composition.

  However, even in these compositions, in high voltage applications or use in areas where contamination is severe, corona occurs and silicone rubber often deteriorates.

US Pat. No. 3,511,698 JP 59-198604 A JP 53-35982 A JP 7-57574 A JP-A-8-259820 Japanese Patent Laid-Open No. 11-152408 Japanese Patent Laid-Open No. 11-12470

  This invention is made | formed in view of the said situation, and it aims at providing the silicone rubber composition for high voltage electrical insulators which do not lose the rubber | gum intensity | strength of a silicone rubber even if highly filled with aluminum hydroxide.

  As a result of intensive studies in order to achieve the above object, the present inventors have (A) an organic peroxide curable or addition reaction curable organopolysiloxane composition, (B) a silicone resin, and (C). When a silicone rubber composition containing a specific amount of aluminum hydroxide having an average particle size of 20 μm or less is used as a high-voltage electrical insulator, it has excellent corona resistance, long-time high-voltage applications, It has been found that it can be used even in a terrible area, and the present invention has been made.

That is, the present invention provides the following silicone rubber composition for high voltage electrical insulators.
[Claim 1]
(A) (A) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, but 0.001 to 10 mol% of R is an aliphatic unsaturated hydrocarbon group, and 90 mol% or more is a methyl group. A is a positive number from 1.9 to 2.4.)
An organopolysiloxane having an average of 2 or more alkenyl groups in one molecule represented by:
100 parts by mass,
(B) Organic peroxide: Amount of catalyst
Organic consisting peroxide curable O organopolysiloxane composition:
100 parts by mass,
(B) Silicone resin: 3 to 80 parts by mass,
(C) Aluminum hydroxide having an average particle size of 20 μm or less: 30 to 400 parts by mass A silicone rubber composition for high-voltage electrical insulators, characterized by comprising:
[Claim 2 ]
(A) (C) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, but 0.001 to 10 mol% of R is an aliphatic unsaturated hydrocarbon group, and 90 mol% or more is a methyl group. A is a positive number from 1.9 to 2.4.)
An organopolysiloxane having an average of 2 or more alkenyl groups in one molecule represented by:
100 parts by mass,
(D) Organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to silicon atoms in one molecule: 0.1 to 30 parts by mass
(E) Addition reaction catalyst: catalyst amount
Consisting addition-curable organopolysiloxane composition:
100 parts by mass,
(B) Silicone resin: 3 to 80 parts by mass,
(C) Aluminum hydroxide having an average particle size of 20 μm or less: 30 to 400 parts by mass A silicone rubber composition for high-voltage electrical insulators, characterized by comprising:
[Claim 3 ]
The silicone resin as component (B) is composed mainly of R ² ₃ SiO _1/2 units (wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group) and SiO ₂ units, and R ² ₃ SiO _{1 /} The molar ratio [R ² ₃ SiO _1/2 / SiO ₂ ] of ₂ units to SiO ₂ units is 0.5 to 1.5, and the alkenyl group content is 1 × 10 ^{−5 to} 5 × 10 ⁻³ mol. The silicone rubber composition for high voltage electrical insulators according to claim 1 or 2, wherein the composition is / g.
[Claim 4 ]
(C) component of the aluminum hydroxide, or those pre-treated hydrophobic surface (A), according to claim 1 to 3, characterized in that those that are treated hydrophobic surface upon blending with component (B) The silicone rubber composition for high voltage electrical insulators according to any one of the above.
[Claim 5 ]
5. The silicone rubber composition for high voltage electrical insulators according to claim 4 , wherein the aluminum hydroxide as the component (C) has been subjected to surface hydrophobization treatment with silazanes and / or silanes.
[Claim 6 ]
The component (C), aluminum hydroxide, is a mixture of two types of those having an average particle diameter of less than 5 μm and those having an average particle size of 5 μm or more in a mass ratio of 90/10 to 10/90. The silicone rubber composition for high voltage electrical insulators according to any one of claims 1 to 5 .

  The silicone rubber composition for high voltage electrical insulators of the present invention does not lose the rubber strength of silicone rubber even when highly filled with aluminum hydroxide, has excellent corona resistance, is used for high voltage for a long time, and is severely contaminated. Provides high voltage electrical insulation that can also be used in the region.

In the Example of this invention, it is the schematic of the apparatus which performs a corona discharge test.

  Hereinafter, the present invention will be described in more detail. The component (A) of the silicone rubber composition for high voltage electrical insulators of the present invention is an organic peroxide curable or addition reaction curable organopolysiloxane composition. .

As the organic peroxide curable silicone rubber composition of the present invention,
(A) The following average composition formula (I)
R _a Si O _{(4-a) / 2} (I)
(In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, but 0.001 to 10 mol% of R is an aliphatic unsaturated hydrocarbon group, and 90 mol% or more is a methyl group. A is a positive number from 1.9 to 2.4.)
An organopolysiloxane having an average of at least two alkenyl groups in one molecule represented by
(B) A silicone rubber composition comprising an organic peroxide is preferably used.

(A) component is the following average composition formula (I)
R _a Si O _{(4-a) / 2} (I)
An organopolysiloxane having an average of at least two alkenyl groups in one molecule.

Here, R in the formula (I) is preferably an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, specifically methyl, ethyl, propyl, Aliphatic saturated hydrocarbon groups such as alkyl groups such as isopropyl, butyl, isobutyl, tert-butyl, hexyl and cyclohexyl, aliphatic unsaturated hydrocarbon groups such as alkenyl groups such as vinyl, allyl, propenyl and butenyl, phenyl and xylyl Selected from aromatic hydrocarbon groups such as aryl groups, halogen substituted groups such as 3,3,3-trifluoropropyl, and cyano group substituted hydrocarbon groups, and each substituent may be different or the same. However, it is necessary that at least two aliphatic unsaturated hydrocarbon groups are contained in the molecule. In this case, 0.001 to 10 mol%, particularly 0.01 to 5 mol%, more preferably 0.01 to 2 mol% of the total R is an aliphatic unsaturated hydrocarbon group, 90 mol% or more, especially It is preferable that all R groups except 95-99 mol% and an alkenyl group are methyl groups. The aliphatic unsaturated hydrocarbon group may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom in the middle of the molecular chain, or both. Bonding to a silicon atom at the chain end is preferred.
R in the above formula (I) may be basically any of the above, but the aliphatic unsaturated hydrocarbon group is preferably a vinyl group, and the other substituents are a methyl group, phenyl Introduction of groups is desirable.

a is a positive number in the range of 1.9 to 2.4, preferably 1.98 to 2.02, more preferably 1.99 to 2.01, and the organopolysiloxane may be linear. RSiO _3/2 units or branched structures containing SiO _4/2 units may be used, but usually the main chain is composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ), and both molecular chains are A linear diorganopolysiloxane having a terminal end blocked with a triorganosiloxy group (R ₃ SiO _1/2 ) is desirable.

  This organopolysiloxane is produced by a known method. As this production method, an organocyclopolysiloxane and hexaorganodisiloxane can be obtained by carrying out an equilibration reaction in the presence of an alkali or an acid catalyst.

  The degree of polymerization of the organopolysiloxane is 100 to 20,000, preferably 200 to 15,000, particularly preferably 300 to 10,000. This degree of polymerization can be measured as a weight average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis (hereinafter the same).

  The component (b) organic peroxide is used as a catalyst for accelerating the crosslinking reaction of the component (b), and may be a conventionally known one. For example, benzoyl peroxide, 2, 4 -Dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, di Examples include -t-butyl peroxide, t-butyl perbenzoate, 1,1-bis (t-butylperoxycarboxy) hexane, and the like, but are not particularly limited thereto.

  In addition, although the addition amount of (B) component should just be selected suitably according to a cure rate, it is 0.1-10 mass parts normally with respect to 100 mass parts of (I) component, Preferably it is 0.2-2 mass. A range of parts may be used. (B) If the amount of component added is too small, crosslinking may be insufficient and the rubber properties such as strength and elongation may be inferior, and if too large, problems such as scorch may occur.

On the other hand, as an addition reaction curable silicone rubber composition,
(C) an alkenyl group-containing organopolysiloxane represented by the above formula (I),
(D) an organohydrogenpolysiloxane having at least 2, preferably 3 or more, hydrogen atoms directly bonded to silicon atoms in one molecule;
(E) A silicone rubber composition comprising an addition reaction catalyst is preferred, which is cured at room temperature or when heated to form a rubbery elastic body.

  Examples of the alkenyl group-containing organopolysiloxane (C) can be the same as the organopolysiloxane of the component (A) described above.

The organohydrogenpolysiloxane of component (d) is an organohydrogenpolysiloxane having at least 2, preferably 3 or more hydrogen atoms (Si-H groups) directly bonded to silicon atoms in one molecule. Average composition formula (II)
R ¹ _b H _c SiO _{(4-bc) / 2} (II)
Wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, b is 0.7 to 2.1, c is 0.001 to 1.0, and b + c Is a positive number satisfying 0.8 to 3.0.)
It is preferably an organohydrogenpolysiloxane that is liquid at room temperature.

Here, R ¹ in formula (II) is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, which may be the same or different, It is preferable that it does not contain a group unsaturated bond. Specific examples of R ¹ include alkyl groups such as methyl, ethyl and propyl groups, cycloalkyl groups such as cyclohexyl groups, aryl groups such as phenyl and tolyl groups, benzyl groups, 2-phenylethyl groups, 2 -Aralkyl groups such as a phenylpropyl group, and groups in which part or all of the hydrogen atoms of these groups are substituted with halogen atoms, for example, 3,3,3-trifluoropropyl groups, and the like.
Further, b is 0.7 to 2.1, preferably 0.8 to 2.0, c is 0.001 to 1.0, preferably 0.01 to 1.0, and b + c is 0.8 to It is a positive number satisfying 3.0, preferably 0.9 to 2.7.

  The organohydrogenpolysiloxane has at least 2 (usually 2 to 300) Si-H groups in one molecule, preferably 3 or more (for example, about 3 to 200), more preferably 4 or more (for example 4). This may be at the end of the molecular chain, in the middle of the molecular chain, or in both. Moreover, as this organohydrogenpolysiloxane, the number of silicon atoms in the molecule (or polymerization degree) is usually 2 to 300, preferably 3 to 200, more preferably about 4 to 100. Further, the viscosity at 25 ° C. is preferably 0.5 to 1,000 mPa · s, preferably 1 to 500 mPa · s, and particularly preferably 5 to 300 mPa · s. This viscosity can be measured with a rotational viscometer (hereinafter the same).

(D) Component 1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogen Siloxane / dimethylsiloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, trimethylsiloxy group-capped methylhydrogenpolysiloxane, both ends trimethylsiloxy group-capped dimethylsiloxane methyl Hydrogensiloxane copolymer, dimethylhydrogensiloxy group-capped methylhydrogenpolysiloxane at both ends, dimethylhydrogensiloxy group-capped dimethylpolysiloxane at both ends Both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, Both ends trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane copolymer, Both ends trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / Dimethylsiloxane copolymer, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units, (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) Copolymers composed of SiO _3/2 units and those obtained by substituting a part or all of the methyl groups with other alkyl groups or phenyl groups in these exemplified compounds.

  The compounding amount of the organohydrogenpolysiloxane (d) is preferably 0.1 to 30 parts by mass, particularly preferably 0.3 to 10 parts by mass with respect to 100 parts by mass of the organopolysiloxane (C). In addition, the organohydrogenpolysiloxane (d) has a molar ratio of Si—H groups in the component (d) to the sum of the alkenyl groups in the component (c) and the component (B) usually from 0.5 to 5, preferably Can be blended so as to be about 0.8 to 3, more preferably about 1 to 2.5. (D) If the amount of component is too small, crosslinking may be inadequate and rubber properties such as strength and elongation may be inferior. If it is too large, there are too many crosslinking points (crosslinking density is too high), and rubber is similarly used. The physical properties may be inferior.

  (E) Component addition reaction catalysts include platinum black, platinous chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, platinum bisacetoacetate, A palladium catalyst, a rhodium catalyst, etc. are mentioned. The addition amount of the addition reaction catalyst can be a catalyst amount, and is usually 0.5 to 1,000 ppm in terms of the amount of platinum metal with respect to the total mass of the components (c) and (d), It is used in the range of 1 to 500 ppm.

The silicone resin as the component (B) is essential for improving the corona resistance. It is not an oil having a straight chain structure or a raw rubber-like structure, but may be any structure as long as it has a branched structure, particularly a three-dimensional network structure. Preferably, R ² ₃ SiO _1/2 units (R ² is unsubstituted) Or a substituted monovalent hydrocarbon group) and a SiO ₂ unit as a main component, and the molar ratio [R ² ₃ SiO _1/2 / SiO ₂ ] of R ² ₃ SiO _1/2 unit to SiO ₂ unit is 0.5. To 1.5, preferably 0.5 to 1.3. If the molar ratio [R ² ₃ SiO _1/2 / SiO ₂ ] is smaller than 0.5, the corona resistance may be lowered. If the molar ratio is larger than 1.5, not only the compression set is increased, but also the phase There is also a possibility that the solubility is lowered and the blending becomes difficult.

Here, R ² can be exemplified by the same groups as those exemplified above for the unsubstituted or substituted monovalent hydrocarbon group of R, among which alkyl groups such as methyl, ethyl and propyl groups, phenyl groups and the like. Of the aryl group and 3,3,3-trifluoropropyl group.

The silicone resin of the present invention preferably contains an alkenyl group bonded to a silicon atom, and the alkenyl group content is 0.00001 (ie, 1 × 10 ⁻⁵ ) to 0.005 mol / g in the silicone resin. Preferably, it is 0.00005 (5 × 10 ⁻⁵ ) to 0.002 mol / g, more preferably 0.0001 (1 × 10 ⁻⁴ ) to 0.001 mol / g. When the alkenyl group content is less than 0.00001 mol / g, the corona resistance may be insufficient. When the alkenyl group content exceeds 0.005 mol / g, the compression set may be deteriorated. There is.

In addition, the silicone resin of the present invention may contain R ² ₂ SiO _2/2 units or R ² SiO _3/2 units (where R ² is as described above) as a total amount of these as necessary. 50 mass% or less (0-50 mass%) with respect to mass (silicone resin), preferably 40 mass% or less (0-40 mass%), more preferably 30 mass% or less (0-30 mass%). May be included.

  The silicone resin can be usually produced by hydrolyzing an appropriate chlorosilane or alkoxysilane by a method well known in the art.

The compounding quantity of these silicone resins (B) is 3-80 mass parts with respect to 100 mass parts of (A) component, Especially 5-40 mass parts is preferable. If it is less than 3 parts by mass, sufficient acid resistance cannot be obtained, and if it exceeds 80 parts by mass, the compression set becomes large.
In addition, in the case of an addition reaction curable organopolysiloxane composition, the Si-H group in the component (c) is 0.5 to 5 mol per mol of the total amount of alkenyl groups in the component (c) and the component (B). In particular, the ratio is preferably about 0.8 to 3 mol, more preferably about 1 to 2.5 mol.

Aluminum hydroxide having an average particle diameter of 20 μm or less as the component (C) is essential for improving electrical insulation performance such as arc resistance and tracking resistance of the silicone rubber. Here, as the aluminum hydroxide, the following formula Al ₂ O ₃ .3H ₂ O
And having an average particle diameter of 20 μm or less, usually 0.1 to 20 μm, preferably 0.5 to 15 μm, and a BET specific surface area of 1.0 to 10 m ² / g is preferably used. If the average particle diameter of aluminum hydroxide is larger than 20 μm, the rubber physical properties are deteriorated and the corona resistance is inferior. The average particle size can be used a particle size distribution measuring apparatus by laser diffraction method or the like is determined as a cumulative weight average value D ₅₀ (or median diameter).

  In the present invention, two types of aluminum hydroxide having an average particle size of less than 5 μm (usually 0.1 μm or more and less than 5 μm) and 5 μm or more (usually 5 to 20 μm) are used in a mass ratio of 90. It is preferable to use a mixture in the range of / 10 to 10/90, particularly 80/20 to 20/80, from the viewpoint of maintaining and improving both the rubber properties and the corona resistance. If the average particle size is less than 5 μm, the rubber properties may be inferior. If the average particle size is too small, the corona resistance and tracking resistance may be inferior.

  These aluminum hydroxides can be used as they are, but the surface is preferably hydrophobized. Examples of the surface treatment agent include silazanes such as alkylsilazane and vinylsilazane, and silanes such as alkylalkoxysilane, vinylalkoxysilane and chlorosilane. For example, hexamethyldisilazane, diphenyltetramethyldisilazane, divinyltetramethyldisilane. Silazanes such as silazane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, divinyldimethoxysilane, vinylmethyldimethoxysilane, vinyltris (methoxyethoxy) silane Alkoxysilanes such as, methyltrichlorosilane, phenyltrichlorosilane, vinyltrichlorosilane and other chlorosilanes, or partial hydrolysates thereof, Even when used in combination with two or more siloxane oligomers having a degree of polymerization of 50 or less having a functional group such as Si-OH functional group or Si-OR (R is a monovalent hydrocarbon group) at the chain end Good.

As the surface treatment method, a powder previously treated in a powder state may be blended with the components (A) and (B), or a part or the whole amount of the components (A) and / or (B) and water. Surface treatment may be performed while mixing aluminum oxide and a surface treatment agent. The surface treatment degree of these surface-treated aluminum hydroxides is 0.01 to 2% by mass, preferably 0.02 to 1% by mass in terms of carbon amount with respect to aluminum hydroxide. It is preferable from the aspect of improving. The amount of carbon can be obtained by a carbon analyzer or the like based on the principle of measuring the amount of CO ₂ generated by oxidative combustion.

  Moreover, the compounding quantity of aluminum hydroxide (C) is 30-400 mass parts with respect to 100 mass parts of (A) component, Preferably it is 50-300 mass parts, and when there are less than 30 mass parts, tracking resistance etc. are enough. However, when the amount is more than 400 parts by mass, blending is difficult and workability is problematic, and the cured product is hard and brittle.

  In the silicone rubber composition of the present invention, in addition to the above-described components (A) to (C), the fluidity is adjusted and the mechanical strength of the molded product is improved. A filler may be added. Such fillers include precipitated silica, fumed silica, calcined silica, reinforcing fillers such as fumed titanium oxide, ground quartz, diatomaceous earth, asbestos, aminosilicic acid, iron oxide, zinc oxide, calcium carbonate. Such non-reinforcing fillers are exemplified, and the non-reinforcing fillers may be subjected to surface treatment with an organosilicon compound such as hexamethylsilazane, trimethylchlorosilane, or polymethylsiloxane as it is. Moreover, you may mix | blend a pigment, a heat resistant agent, a flame retardant, a plasticizer, etc. as needed.

The silicone rubber composition of the present invention can be prepared by mixing each of the above components according to a conventional method.
The silicone rubber composition thus obtained can be used as a high voltage electrical insulator. In this case, compression molding (compression molding), extrusion molding, injection molding, transfer molding, injection molding can be used as a molding method. Any conventionally known method may be selected depending on the viscosity of the material, the size of the mold, and the like.
In addition, the curing conditions of the silicone rubber composition can employ a wide temperature range from room temperature (25 ° C. ± 10 ° C.) to about 250 ° C., but in the case of an organic peroxide curable type, Under a temperature condition equal to or higher than the decomposition temperature, for example, 120 to 220 ° C., preferably about 150 to 200 ° C., and in the case of addition reaction curing type, preferably 60 to 200 ° C., more preferably about 80 to 180 ° C. is there. The curing time (primary curing) varies depending on the temperature, but can be in the range of 10 seconds to several hours (for example, 1 to 4 hours), and can be molded in a shorter time as the temperature increases. The cured product formed (primary curing) under such conditions is further post-cured (secondary) under conditions of 170 to 220 ° C., particularly about 180 to 200 ° C. for 1 to 6 hours, particularly about 2 to 4 hours. Curing) is optional.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In addition, the average particle diameter of aluminum hydroxide means the cumulative weight average diameter D ₅₀ measured using a particle size distribution measuring apparatus by a laser diffraction method, and the amount of carbon on the surface is measured by a carbon analyzer.

[Example 1]
60 parts by mass of dimethylpolysiloxane (1) having an average degree of polymerization of 500 blocked at both ends with dimethylvinylsiloxy groups, (CH ₃ ) ₃ SiO _1/2 units, CH ₂ = CH (CH ₃ ) ₂ SiO _{1 / 2} units and a silicone resin composed of SiO ₂ units [[(CH ₃ ) ₃ SiO _1/2 units + CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 units] / SiO ₂ units = 0.95 (molar ratio) , Vinyl group content = 0.00045 mol / g, weight average molecular weight 2,200] 18 parts by mass, fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil Co., Ltd., Aerosil 200) 22 parts by mass Then, 5 parts by mass of hexamethyldisilazane and 2.0 parts by mass of water were mixed at room temperature for 30 minutes, heated to 150 ° C., stirred for 3 hours and cooled. Further, 70 parts by mass of aluminum hydroxide (carbon content 0.9% by mass) surface-treated with hexamethyldisilazane having an average particle diameter of 8 μm and surface treatment with methyltrimethoxysilane having an average particle diameter of 1 μm. 100 parts by mass of the aluminum hydroxide (carbon content 0.2% by mass) was blended and passed once through three rolls to obtain a silicone rubber base.

  After adding 60 parts by mass of the dimethylpolysiloxane (1) to 270 parts by mass of this silicone rubber base and stirring for 30 minutes, methyl hydrogen poly having Si—H groups at both ends and side chains as a crosslinking agent. 4.6 parts by mass of siloxane (2) (degree of polymerization 25, Si—H amount 0.0048 mol / g) [Si—H / alkenyl group = 1.5 (molar ratio)], ethynylcyclohexanol 0 as a reaction control agent .05 parts by mass was added and stirring was continued for 15 minutes to obtain a silicone rubber composition. This silicone rubber composition is mixed with 0.1 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), and rubber sheets having a thickness of 2 mm and 6 mm are produced by press curing at 120 ° C./10 minutes, and then 200 ° C. in an oven. X Post-cure for 4 hours was performed.

The obtained cured product was measured for hardness, tensile strength and elongation at break based on JIS K6249 from a 2 mm sheet, and IEC. publ. Based on the 587 method, a tracking test was performed with 4.5 kV applied. The results are shown in Table 1.
Further, with respect to this 2 mm sheet, a pinhole having a diameter of about 0.5 mm is formed at the center, electrodes are arranged at a distance of conducting at 10 kV with the apparatus shown in FIG. 1, and a corona discharge test is performed for 200 hours. Similarly, hardness, tensile strength, and elongation at break were measured. The results are shown in Table 1.

[Example 2]
A rubber having a dimethylvinylsiloxy group blocked at both ends and having an average degree of polymerization of about 8,000, comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units. Organopolysiloxane (3) in 100 parts by mass, 5 parts by mass of silanol group-blocked dimethylpolysiloxane (average polymerization degree 10) as a dispersant, 5 parts by mass of ethyltrialkoxysilane, and BET specific surface area of 200 m ² / g 10 parts by mass of a fumed silica (manufactured by Nippon Aerosil Co., Ltd., Aerosil 200), 90 parts by mass of aluminum hydroxide (manufactured by Showa Denko KK, Heidilite H32M) having an average particle diameter of 8 μm, and an average particle diameter of 1 μm Aluminum hydroxide (manufactured by Showa Denko KK, Hygielite H42M) A silicone resin [[(CH ₃ ) comprising an amount part, (CH ₃ ) ₃ SiO _1/2 unit, CH ₂ ═CH (CH ₃ ) ₂ SiO _1/2 unit, SiO ₂ unit and (CH ₃ ) ₂ SiO unit] ₃ SiO _1/2 unit + CH ₂ ═CH (CH ₃ ) ₂ SiO _1/2 unit] / SiO ₂ unit = 0.72 (molar ratio), (CH ₃ ) ₂ SiO unit content 15 mass%, vinyl group contained Amount = 0.00015 mol / g, weight average molecular weight 8,100] 30 parts by mass were added and blended in a pressure kneader to prepare a rubber compound.

To this rubber compound, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, the above organopolysiloxane (3), and fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil ( 1.0 mass part of 40 mass%: 40 mass%: 20 mass% mixed paste of Aerosil 200) manufactured by Co., Ltd. was added and dispersed uniformly with two rolls, then pressed at 165 ° C. for 10 minutes. Curing was performed to obtain silicone rubber sheets having a thickness of 2 mm and 6 mm, and further post-curing was performed in an oven at 200 ° C. for 4 hours.

This cured product was measured from the 2 mm sheet according to JIS K6249 for hardness, tensile strength and elongation at break, and from the 6 mm sheet, IEC. publ. Based on the 587 method, a tracking test was performed with 4.5 kV applied. The results are shown in Table 1.
Further, with respect to this 2 mm sheet, a pinhole having a diameter of about 0.5 mm is formed at the center, electrodes are arranged at a distance of conducting at 10 kV with the apparatus shown in FIG. 1, and a corona discharge test is performed for 200 hours. Similarly, hardness, tensile strength, and elongation at break were measured. The results are shown in Table 1.

[Example 3]
Both-end dimethylvinylsiloxy having 99.825 mol% of the dimethylsiloxane unit of Example 2, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000 Fumed silica with 100 parts by weight of the blocked rubbery organopolysiloxane (3), 5 parts by weight of silanol group blocked dimethylpolysiloxane (average polymerization degree 10) as a dispersant, and a BET specific surface area of 300 m ² / g. (Aerosil 300 manufactured by Nippon Aerosil Co., Ltd.) 10 parts by mass, 40 parts by mass of aluminum hydroxide (carbon content 0.4% by mass) having an average particle diameter of 3 μm and surface-treated with methyltriethoxysilane, vinyltrimethoxy Average particle size of 1 treated with silane and methyltriethoxysilane Aluminum hydroxide (carbon content of 0.5 wt%, a vinyl content of 0.0001 mol / g) of μm 40 parts by mass and mixed for 30 minutes at a pressure kneader.
Furthermore, a silicone resin [[(CH ₃ ) ₃ SiO _1/2 unit + CH comprising (CH ₃ ) ₃ SiO _1/2 units, CH ₂ ═CH (CH ₃ ) ₂ SiO _1/2 units and SiO ₂ units] ₂ = CH (CH ₃ ) ₂ SiO _1/2 unit] / SiO ₂ unit = 1.10 (molar ratio), vinyl group content = 0.00077 mol / g, weight average molecular weight 1,500] 28 parts by mass are added The mixing was continued for another 30 minutes.

To this rubber compound, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, the above organopolysiloxane (3), and fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil ( 1.5 mass parts of 40 mass%: 40 mass%: 20 mass% mixed paste of Aerosil 200) manufactured by Co., Ltd. was added and dispersed uniformly with two rolls, then pressed at 165 ° C. for 10 minutes. Curing was performed to obtain silicone rubber sheets having a thickness of 2 mm and 6 mm, and further post-curing was performed in an oven at 200 ° C. for 4 hours.

This cured product was measured from the 2 mm sheet according to JIS K6249 for hardness, tensile strength and elongation at break, and from the 6 mm sheet, IEC. publ. Based on the 587 method, a tracking test was performed with 4.5 kV applied. The results are shown in Table 1.
Further, with respect to this 2 mm sheet, a pinhole having a diameter of about 0.5 mm is formed at the center, electrodes are arranged at a distance of conducting at 10 kV with the apparatus shown in FIG. 1, and a corona discharge test is performed for 200 hours. Similarly, hardness, tensile strength, and elongation at break were measured. The results are shown in Table 1.

[Comparative Example 1-1]
60 parts by mass of dimethylpolysiloxane (1) having an average degree of polymerization of 500 blocked at both ends with dimethylvinylsiloxy groups in Example 1, having vinyl groups at both ends and side chains, and an average degree of polymerization of 450 18 parts by mass of a certain dimethylpolysiloxane (4) [vinyl group content 0.00038 mol / g], 22 parts by mass of fumed silica (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 200 m ² / g, After mixing 5 parts by mass of hexamethyldisilazane and 2.0 parts by mass of water at room temperature for 30 minutes, the temperature was raised to 150 ° C., and stirring was continued for 3 hours to cool. Further, 70 parts by mass of aluminum hydroxide (carbon content 0.9% by mass) surface-treated with hexamethyldisilazane having an average particle diameter of 8 μm and surface treatment with methyltrimethoxysilane having an average particle diameter of 1 μm. 100 parts by mass of the aluminum hydroxide (carbon content 0.2% by mass) was blended and passed once through three rolls to obtain a silicone rubber base.
After adding 60 parts by mass of the dimethylpolysiloxane (1) to 270 parts by mass of this silicone rubber base and continuing stirring for 30 minutes, methylhydrogen poly having Si—H groups at both ends and side chains as a crosslinking agent. 4.2 parts by mass of siloxane (2) (degree of polymerization 25, Si—H amount 0.0048 mol / g) [Si—H / alkenyl group = 1.5 (molar ratio)], and ethynylcyclohexanol 0 as a reaction control agent .05 parts by mass was added and stirring was continued for 15 minutes to obtain a silicone rubber composition. This silicone rubber composition is mixed with 0.1 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), and rubber sheets having a thickness of 2 mm and 6 mm are produced by press curing at 120 ° C./10 minutes, and then 200 ° C. in an oven. Post cure was performed at 4 ° C. for 4 hours. For this cured product, various physical properties were measured before and after the corona discharge test in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1-2]
60 parts by mass of dimethylpolysiloxane (1) having an average degree of polymerization of 500 blocked at both ends with dimethylvinylsiloxy groups, (CH ₃ ) ₃ SiO _1/2 units, CH ₂ = CH (CH ₃ ) ₂ SiO _{1 / 2} units and a silicone resin composed of SiO ₂ units [[(CH ₃ ) ₃ SiO _1/2 units + CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 units] / SiO ₂ units = 0.95 (molar ratio) , Vinyl group content = 0.00045 mol / g, weight average molecular weight 2,200] 18 parts by mass, fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil Co., Ltd., Aerosil 200) 22 parts by mass Then, 5 parts by mass of hexamethyldisilazane and 2.0 parts by mass of water were mixed at room temperature for 30 minutes, then heated to 150 ° C., stirred for 3 hours, and cooled to obtain a silicone rubber base.
After adding 60 parts by mass of the dimethylpolysiloxane (1) to 100 parts by mass of this silicone rubber base and continuing stirring for 30 minutes, methylhydrogen poly having Si—H groups at both ends and side chains as a crosslinking agent. 4.6 parts by mass of siloxane (2) (degree of polymerization 25, Si—H amount 0.0048 mol / g) [Si—H / alkenyl group = 1.5 (molar ratio)], ethynylcyclohexanol 0 as a reaction control agent .05 parts by mass was added and stirring was continued for 15 minutes to obtain a silicone rubber composition. This silicone rubber composition is mixed with 0.1 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), and rubber sheets having a thickness of 2 mm and 6 mm are produced by press curing at 120 ° C./10 minutes, and then 200 ° C. in an oven. Post cure was performed at 4 ° C. for 4 hours. For this cured product, various physical properties were measured before and after the corona discharge test in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
Both-end dimethylvinylsiloxy having 99.825 mol% of the dimethylsiloxane unit of Example 2, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000 100 parts by mass of the base-capped rubbery organopolysiloxane (3), 5 parts by mass of silanol group-capped dimethylpolysiloxane (average polymerization degree 10) as a dispersant, 5 parts by mass of ethyltrialkoxysilane, and a BET specific surface area of 200 m 10 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) that is ² / g, 90 parts by mass of aluminum hydroxide (Hidelite H32M, manufactured by Showa Denko KK) having an average particle diameter of 8 μm, average Aluminum hydroxide having a particle diameter of 1 μm (manufactured by Showa Denko KK, Hijilite H42 M) Dimethyl dimethylsiloxane having 70 parts by mass, 99.225 mol% of dimethylsiloxane units, 0.75 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000. 30 parts by mass of a vinylsiloxy-blocked rubber-like organopolysiloxane (5) was added and blended with a pressure kneader to prepare a rubber compound.

To this rubber compound, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, the above organopolysiloxane (3), and fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil ( 1.0 mass part of 40 mass%: 40 mass%: 20 mass% mixed paste of Aerosil 200) manufactured by Co., Ltd. was added and dispersed uniformly with two rolls, then pressed at 165 ° C. for 10 minutes. Curing was performed to obtain silicone rubber sheets having a thickness of 2 mm and 6 mm, and further post-curing was performed in an oven at 200 ° C. for 4 hours. For this cured product, various physical properties were measured before and after the corona discharge test in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
Both-end dimethylvinylsiloxy having 99.825 mol% of the dimethylsiloxane unit of Example 2, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000 Fumed silica with 100 parts by weight of the blocked rubbery organopolysiloxane (3), 5 parts by weight of silanol group blocked dimethylpolysiloxane (average polymerization degree 10) as a dispersant, and a BET specific surface area of 300 m ² / g. (Aerosil 300 manufactured by Nippon Aerosil Co., Ltd.) 10 parts by mass, 40 parts by mass of aluminum hydroxide (carbon content 0.4% by mass) having an average particle diameter of 3 μm and surface-treated with methyltriethoxysilane, vinyltrimethoxy Average particle size of 1 treated with silane and methyltriethoxysilane μm of aluminum hydroxide (carbon content of 0.5 wt%, a vinyl content of 0.0001 mol / g) was added 40 parts by weight, and mixed for 30 minutes at a pressure kneader.

  Further, dimethylvinylsiloxy at both ends having 95,475 mol% of dimethylsiloxane units, 4.5 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000. 28 parts by mass of base-blocked rubbery organopolysiloxane (6) was added, and mixing was further continued for 30 minutes to prepare a rubber compound.

To this rubber compound, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, the above organopolysiloxane (3), and fumed silica having a BET specific surface area of 200 m ² / g (Nippon Aerosil ( 1.5 mass parts of 40 mass%: 40 mass%: 20 mass% mixed paste of Aerosil 200) manufactured by Co., Ltd. was added and dispersed uniformly with two rolls, then pressed at 165 ° C. for 10 minutes. Curing was performed to obtain silicone rubber sheets having a thickness of 2 mm and 6 mm, and further post-curing was performed in an oven at 200 ° C. for 4 hours. For this cured product, various physical properties were measured before and after the corona discharge test in the same manner as in Example 1. The results are shown in Table 1.

1 electrode 2 electrode 3 rubber sheet 4 gear oven

Claims (6)

(A) (A) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, but 0.001 to 10 mol% of R is an aliphatic unsaturated hydrocarbon group, and 90 mol% or more is a methyl group. A is a positive number from 1.9 to 2.4.)
An organopolysiloxane having an average of 2 or more alkenyl groups in one molecule represented by:
100 parts by mass,
(B) Organic peroxide: Amount of catalyst
Organic consisting peroxide curable O organopolysiloxane composition:
100 parts by mass,
(B) Silicone resin: 3 to 80 parts by mass,
(C) Aluminum hydroxide having an average particle size of 20 μm or less: 30 to 400 parts by mass A silicone rubber composition for high-voltage electrical insulators, characterized by comprising: (A) (C) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, but 0.001 to 10 mol% of R is an aliphatic unsaturated hydrocarbon group, and 90 mol% or more is a methyl group. A is a positive number from 1.9 to 2.4.)
An organopolysiloxane having an average of 2 or more alkenyl groups in one molecule represented by:
100 parts by mass,
(D) Organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to silicon atoms in one molecule: 0.1 to 30 parts by mass
(E) Addition reaction catalyst: catalyst amount
Consisting addition-curable organopolysiloxane composition:
100 parts by mass,
(B) Silicone resin: 3 to 80 parts by mass,
(C) Aluminum hydroxide having an average particle size of 20 μm or less: 30 to 400 parts by mass A silicone rubber composition for high-voltage electrical insulators, characterized by comprising: The silicone resin as component (B) is composed mainly of R ² ₃ SiO _1/2 units (wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group) and SiO ₂ units, and R ² ₃ SiO _{1 /} The molar ratio [R ² ₃ SiO _1/2 / SiO ₂ ] of ₂ units to SiO ₂ units is 0.5 to 1.5, and the alkenyl group content is 1 × 10 ^{−5 to} 5 × 10 ⁻³ mol. The silicone rubber composition for high voltage electrical insulators according to claim 1 or 2, wherein the composition is / g. (C) component of the aluminum hydroxide, or those pre-treated hydrophobic surface (A), according to claim 1 to 3, characterized in that those that are treated hydrophobic surface upon blending with component (B) The silicone rubber composition for high voltage electrical insulators according to any one of the above. 5. The silicone rubber composition for high voltage electrical insulators according to claim 4 , wherein the aluminum hydroxide as the component (C) has been subjected to surface hydrophobization treatment with silazanes and / or silanes. The component (C), aluminum hydroxide, is a mixture of two types of those having an average particle diameter of less than 5 μm and those having an average particle size of 5 μm or more in a mass ratio of 90/10 to 10/90. The silicone rubber composition for high voltage electrical insulators according to any one of claims 1 to 5 .