JP2000044804A - Electrically insulating silicone rubber composition and silicone rubber insulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicone rubber composition capable of giving a silicone rubber product excellent in electric insulation, esp. excellent in high voltage electrical characteristics such as tracking resistance and arc resistance, and excellent in mechanical property as well in a good workability. SOLUTION: This silicone rubber composition includes (A) polyorganosiloxane having two or more alkenyl groups combined with silicon atom in a molecule, (B) polyorganohydrogensiloxane having three or more hydrogen atoms combined with silicon atom, (C) a platinum group metal atom-including compound, (D) ground granulated hydrophobic silica having a specific BET specific surface area and apparent density and (E) aluminium hydroxide having <=10 μm average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to compositions that cure to form silicone rubber, and more particularly, to the essential electrical insulating rubber used for high voltage insulation, such as polymeric insulators. The present invention relates to a silicone rubber composition suitable for obtaining a high-strength silicone rubber having excellent tracking resistance, arc resistance and water repellency. The present invention also relates to a silicone rubber insulator obtained by curing such a silicone rubber composition.

[0002]

2. Description of the Related Art In general, insulators used for distribution lines and high-voltage transmission lines are required to have durability, weather resistance and high insulation resistance. Therefore, ceramic insulators have been mainly used. However, in environments that are susceptible to pollution, such as coastal areas and industrial areas, fine particles, salts, fog, etc. adhere to the surface of the insulator, causing leakage current and dry land discharge, which leads to flashover. Happens. For this reason, a grease-like material containing silicone oil as a main component is applied to the surface of the insulator to wrap up the fine particles and salts on the insulator surface and make the surface water-repellent to prevent the occurrence of leakage current. However, it is necessary to repeat complicated application work every time the applied grease is effective.

Various solutions have been proposed in order to improve the disadvantages of these ceramic insulators.
For example, U.S. Pat. No. 3,116,986 discloses a weather-resistant insulator comprising a member made of a curable resin and a polyorganosiloxane rubber containing a platinum compound. Also, JP-A-59-198604 discloses that
By applying a room-temperature-curable polyorganosiloxane composition to the outer surface of a ceramic insulator, to maintain the high-performance electrical performance of the insulator even in the presence of outdoor stresses such as moisture, air pollution, and ultraviolet rays. Is disclosed. Further, Japanese Patent Publication No. 53-35982 discloses a mixture of a raw rubber-like high molecular weight polydiorganosiloxane, which becomes a silicone rubber by heat curing, and aluminum oxide hydrate at a temperature higher than 100 ° C.
It is disclosed that a silicone rubber composition having improved electrical insulation can be obtained by heating for 0 minutes or more.

Japanese Patent Application Laid-Open No. Hei 4-209655 discloses that silica powder, aluminum hydroxide and diorganosilanediol or α, ω-dihydroxydiorganosiloxane oligomer are mixed with the same high molecular weight polydiorganosiloxane as described above. Discloses that a silicone rubber having electrical properties suitable for an insulator can be obtained. Japanese Patent Application Laid-Open No. 8-41347 discloses that the silicone rubber composition cured by an addition reaction is mixed with silica fine powder, aluminum hydroxide and polydimethylsiloxane to improve the electrical insulation of the obtained silicone rubber. Is disclosed.

Although these methods can improve electrical insulation at a high voltage as compared with conventional silicone rubber, they are still not sufficiently satisfactory. In addition, the filling of the silicone rubber has a problem that the mechanical strength of the silicone rubber decreases and the water resistance decreases.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the above-mentioned techniques, and to obtain an electric insulating property at high voltage such as an electric resistance, especially a tracking resistance and an arc resistance, by curing. An object of the present invention is to provide a silicone rubber composition having excellent workability and a silicone rubber excellent in mechanical properties, and a silicone rubber insulator obtained by curing the same.

[0007]

Means for Solving the Problems The present inventors have made intensive studies in order to achieve the above object, and as a result, a specific hydrophobic silica fine powder was added to a polyorganosiloxane composition cured by an addition reaction. The present inventors have found that the object can be achieved by blending with aluminum, and have completed the present invention.

That is, the electrically insulating silicone rubber composition of the present invention comprises: (A) a polyorganosiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule; and (B) a hydrogen atom bonded to a silicon atom. (C) a compound containing a platinum group metal atom; (D) a surface treated with an organosilicon compound, a BET specific surface area of 100 to 300 m ² / g, and a bulk density of Is 100 to 200
g / l of hydrophobic silica fine powder; and (E) aluminum hydroxide having an average particle size of 10 μm or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The alkenyl group-containing polyorganosiloxane of the component (A) used in the present invention is a component serving as a base polymer in the electrically insulating silicone rubber composition of the present invention. The component (A) has two or more alkenyl groups bonded to a silicon atom in one molecule, and can form a network structure by an addition reaction. The siloxane skeleton of the alkenyl group-containing polyorganosiloxane may be linear or branched.

Has a high average molecular weight in a range showing a liquid state,
Therefore, in order to easily obtain the alkenyl group-containing polyorganosiloxane (A) having high electrical insulation properties with good control, the component (A) preferably has a linear siloxane skeleton. As the component (A) having such a linear siloxane skeleton, general formulas (Ia to Ic):

Embedded image (Wherein, R ¹ represents an alkenyl group; R ² represents an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic carbon-carbon unsaturated bond; and m represents R in the molecule. is a number which a number of ¹ to 2 or more; n is a number which renders the 3,000~100,000cP a viscosity at 25 ° C. component (a))
The polydiorganosiloxane shown by these is illustrated. In the present specification, the molecular structural formula of a polyorganosiloxane having two or more kinds of intermediate siloxane units simply indicates the type and amount of the siloxane unit, and does not mean a block copolymer.

R ¹ may be present in either the terminal group or the intermediate unit of the molecular chain of the component (A), or may be present in both of them. In order to impart properties, it is preferable that the compound is present at least at both ends as in the general formula (Ia) or (Ic).

On the other hand, in order to improve the mechanical properties of the cured composition and to use it for molding insulators having a complicated shape, a branched polyorganosiloxane is mixed with the above-mentioned linear polydiorganosiloxane. It is preferable to use them.
Mechanical strength of the cured product, in order to particularly improve the tear strength and elastic modulus, (A) in component, R ₃ SiO _1/2 units and SiO ₂ units and also R ² SiO units and optionally / or RSiO _3/2 units (wherein, R are each identical represents an R ¹ or R ² be different or) a, of the R attached to the silicon atom, at least two per molecule, preferably Is a mixture of 2 to 50% by weight of a branched polyorganosiloxane in which three or more are R ¹ , and a mixture comprising a linear polydiorganosiloxane in which both ends are blocked with R ¹ groups. More preferred.

The alkenyl group R ¹ is exemplified by vinyl, allyl, 1-butenyl and 1-hexenyl, and is preferably a vinyl group because it is easy to synthesize and has a suitable addition rate and storage stability. .

The other organic group R ² bonded to the silicon atom of the component (A), ie, an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic carbon-carbon unsaturated bond, includes methyl, ethyl, Propyl, butyl, pentyl, hexyl,
Alkyl groups such as octyl, decyl and dodecyl; cycloalkyl groups such as cyclohexyl; aralkyl groups such as 2-phenylethyl and 2-phenylpropyl; aryl groups such as phenyl, tolyl and xylyl; chloromethyl, chlorophenyl, 3,3 and 3-trifluoropropyl, (2-perfluorobutyl) ethyl, (2-perfluorooctyl) ethyl, general formula:

Embedded image (Wherein R ³ represents a perfluoroalkyl group such as perfluoropropyl; a is an integer of 1 to 6), and a monovalent substituted hydrocarbon group such as a perfluoropolyoxypropylene-substituted propyl group is exemplified. You. Of these, a methyl group is most preferred because it is easy to synthesize and has an excellent balance of properties such as mechanical properties and fluidity before curing. When the cured product is required to have oil resistance, it preferably has a fluoro-substituted alkyl group and / or a perfluoropolyoxypropylene-substituted propyl group in addition to the methyl group.

The viscosity of the component (A) at 25 ° C. is such that the uncured composition has excellent fluidity and good workability, and has excellent mechanical strength and electrical insulation after curing.
The range of 3,000 to 100,000 cP is preferred,
000-50,000 cP is more preferred. The range of the average molecular weight showing the preferable viscosity corresponds to 3.5 × 10 ^{4 to} 1.5 × 10 ^{5 in} the case of α, ω-divinylpoly (dimethylsiloxane) which is most typical as the component (A).

The polyorganohydrogensiloxane of the component (B) used in the present invention is prepared by subjecting the hydrosilyl group contained in the molecule to an addition reaction to the alkenyl group of the component (A). It functions as a cross-linking agent, and has at least three hydrogen atoms bonded to silicon atoms in order to reticulate the cured product.

As the organic group bonded to the silicon atom of the siloxane unit, those similar to R ² in the above-mentioned component (A) are exemplified, and among them, a methyl group is most preferable in view of easy synthesis.

The siloxane skeleton in the component (B) may be linear, branched or cyclic. Moreover, you may use these mixtures.

The degree of polymerization of component (B) is not particularly limited, but it is difficult to synthesize a polyorganohydrogensiloxane in which two or more hydrogen atoms are bonded to the same silicon atom. Is preferred. The viscosity of the component (B) at 25 ° C. is preferably in the range of 5 to 10,000 cP for easy handling.

The following are specific examples of the component (B). a. (CH ₃₎ include ₂ HSiO _1/2 units and SiO ₂ units,
Branched polyorganohydrogensiloxane containing optionally further _{(CH 3) 3 SiO 1/} 2 units; b. The following formula:

Embedded image (Wherein p is an integer of 3 to 100; q is 0 to 100)
A linear polyorganohydrogensiloxane represented by the formula: and c. The following formula:

Embedded image (Wherein p is an integer of 1 to 100; q is 0 to 100)
A linear polyorganohydrogensiloxane represented by the formula:

The amount of the component (B) is such that the silicone rubber is completely cured, has excellent mold release properties of the molded silicone rubber, does not generate foaming, has excellent mechanical properties and a smooth surface. Is obtained, the amount is preferably 0.5 to 5 hydrogen atoms bonded to a silicon atom in the component (B) with respect to one alkenyl group in the component (A).
More preferred is an amount of three.

The platinum group metal atom-containing compound of component (C) used in the present invention is a homogeneous compound for accelerating the addition reaction between the alkenyl group in component (A) and the hydrosilyl group in component (B). It is a system catalyst.

Examples of the compound containing a platinum group metal atom include platinum compounds such as chloroplatinic acid, platinum complexes obtained by heating chloroplatinic acid and alcohol, platinum-olefin complexes, platinum-vinylsiloxane complexes, and platinum-phosphine complexes. A palladium complex such as a palladium-phosphine complex; a rhodium complex such as a rhodium-phosphine complex or a rhodium-sulfide complex; this house,
Platinum complexes and platinum-vinylsiloxane complexes obtained from chloroplatinic acid and alcohol are particularly preferred from the viewpoint of good solubility in the components (A) and (B) and good catalytic activity.

The amount of component (C) is from 1 to 200 ppm, preferably from 2 to 50 ppm, in terms of platinum group metal atom per unit amount of component (A), since an appropriate curing rate can be obtained.

The hydrophobic silica fine powder of the component (D) used in the present invention imparts excellent mechanical strength to the silicone rubber obtained by curing without impairing the workability of the composition of the present invention. It is a characteristic component in the composition of the present invention. The component (D) is obtained by hydrophobizing the surface of fine silica powder with an organosilicon compound. As the silica fine powder, fumed silica is preferably used. Examples of the organosilicon compound used for the surface treatment include dimethyldichlorosilane, trimethylchlorosilane, and hexamethyldisilazane.The fluidity of the composition is excellent in the uncured stage, and the storage stability is excellent. Methyldisilazane is particularly preferred. In the treatment, the organosilicon compound used for the treatment is adsorbed on the surface of the silica fine powder at room temperature or high temperature by a gas phase or a liquid phase using an inert solvent such as n-hexane, and the silica is heat-treated. It can be carried out by organosilylating silanol groups on the surface of the fine powder. The silica fine powder having been subjected to such a surface treatment may be used after being pulverized by a pulverizing means such as a jet mill or a ball mill, if necessary.

The BET specific surface area of the component (D) used in the present invention thus obtained is 100 to 300 m ² / g.
And preferably from 120 to 220 m ² / g. If the specific surface area is less than 100 m ² / g, sufficient mechanical strength for the cured product,
In particular, when the tear strength cannot be imparted, and if it exceeds 300 m ² / g, the apparent viscosity of the composition before curing becomes extremely high, and workability is impaired.

The bulk density of the component (D) is from 100 to
It is 200 g / l, preferably 120-200 g / l. When the bulk density is less than 100 g / l, the apparent viscosity of the composition before curing becomes extremely high, and the tear strength of the cured product is not sufficient. On the other hand, even if the bulk density exceeds 200 g / l, there is no effect of further reducing the apparent viscosity of the composition before curing,
The cured product has low tear strength. The hydrophobic silica fine powder having such a bulk density can be obtained by physically aggregating silica fine powder which has been hydrophobized by an organosilicon compound.

The compounding amount of the component (D) having such properties gives excellent workability and excellent mechanical strength after curing, and gives a silicone rubber having particularly excellent arc resistance and tracking resistance. Component (A)
5 to 100 parts by weight, preferably 15 to 8 parts by weight, per part by weight
0 parts by weight is more preferred.

The aluminum hydroxide component (E) used in the present invention is a component that imparts excellent electrical insulation properties, particularly arc resistance, to the silicone rubber obtained by curing the composition. The component (E) includes those represented by the molecular formula Al (OH) ₃ or AlO (OH), and also includes aluminum oxide hydrate (Al ₂ O ₃ .3H ₂ O). Gibbs stone, diaspore and the like are applicable, and one kind or a mixture thereof may be used. As the component (E), those produced by the Bayer method are preferable, and impurities N
More preferably, the content of aO is 0.2% or less.
The average particle size is 10 μm or less, and is 0.1 to 5 μm, because it is easy to mix and gives silicone rubber a smooth surface and excellent tracking resistance and arc resistance.
Is preferred. The aluminum hydroxide may be used as it is, or may be one whose surface is hydrophobized with hexamethyldisilazane, polydimethylsiloxane oil, stearic acid, or the like.

The compounding amount of the component (E) is such that the silicone rubber composition is excellent in processability, the physical properties of the silicone rubber obtained by curing are sufficient, and excellent tracking properties and arc resistance are obtained. For this reason, the amount is preferably from 10 to 300 parts by weight, more preferably from 30 to 200 parts by weight, based on 100 parts by weight of the base polymer in the component (A).

The silicone rubber composition of the present invention comprises (A)
(B) based on 100 parts by weight of the polyorganosiloxane
Polyorganohydrogensiloxane, an amount such that the number of hydrogen atoms bonded to silicon atoms is 0.5 to 5 with respect to one alkenyl group in component (A); Group atom-containing compound, 1 to 200 ppm by weight in terms of platinum group metal atom per unit amount of (A); (D)
Preferably, it contains 5 to 100 parts by weight of hydrophobic silica fine powder; and 10 to 300 parts by weight of (E) aluminum hydroxide.

In order to impart the required physical properties to the silicone rubber composition of the present invention, other fillers can be further compounded within a range that does not impair the features of the present invention. As the filler, fumed silica not included in the range of the component (D), and reinforcing fillers such as calcined silica and precipitated silica; and ground quartz, fused quartz, diatomaceous earth, titanium oxide, magnesium oxide, Non-reinforcing fillers such as zinc oxide, iron oxide, cerium oxide, vanadium oxide, chromium oxide, mica, talc are exemplified.

The composition of the present invention may further comprise, if necessary, a pigment such as red iron oxide; a dye; a heat-resistance improver such as a rare earth oxide, a rare earth hydroxide, cerium silanolate, a fatty acid cerium salt, or ferrite. A flame retardant: an internal mold release agent; a thermal conductivity improver; an epoxy group-containing alkoxysilane, a vinyl group-containing alkoxysilane, a (meth) acryloxy group-containing alkoxysilane, and a carbon functional group contained in the above-mentioned alkoxysilane. A cyclic siloxane oligomer having at least one kind in a side chain and having a Si—H bond, an adhesion imparting agent such as an isocyanuric ring-containing alkoxysilane; a thixotropic agent; a mechanical strength such as a vinyl group-containing silicone resin Enhancer; 3-methyl-1
A curing retarder such as -butyn-3-ol may be blended.

The composition of the present invention comprises the components (A) to (E),
Further, other components to be blended as required can be uniformly kneaded by a mixing means such as a universal kneader, a kneader mixer, a twin-screw continuous mixing extruder, or the like. For stable long-term storage, the components (B) and (C) are separately stored in two containers so that the components (B) and (C) are in separate containers, and mixed immediately before use. Alternatively, the composition may be defoamed under reduced pressure for use, or the composition containing the curing retarder may be stored in a single container.

The silicone rubber composition of the present invention usually comprises
By heating at a temperature of 80 to 200 ° C. for 3 minutes to 4 hours, the composition can be cured to obtain a rubber-like molded product. The method for molding the silicone rubber composition of the present invention can be freely selected according to the apparent viscosity of the composition, and any of casting, compression molding, injection molding, transfer molding and the like may be used.

[0036]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. In these examples, parts indicate parts by weight, and viscosity indicates a viscosity at 25 ° C. The present invention is not limited by these examples.

The silicone rubber tracking test was performed according to I
It carried out according to the standard of the inclined flat plate method in EC-587. That is, a 120 mm × 50 mm × 6 mm sheet was used as a sample, the sample was tilted at 45 °, and the distance between electrodes was 50 mm.
between 0.1 mm and 0.1% of NH ₄ Cl as a contaminant solution.
An aqueous solution in which 0.02% of ton X-100 (trade name of Rohm & Haas, polyoxyethylene octylphenol ether) is dissolved is allowed to flow from the upper electrode to the lower electrode, and charging is performed at 3.5 kV for 6 hours. Was. After the test was completed, the weight loss of the sample and the area of the discharge trace were measured.

Example 1 Polydimethylsiloxane 100 having a viscosity of 10,000 cP and having a molecular chain terminal blocked with a vinyldimethylsilyl group
Part, surface treated with hexamethyldisilazane, BET
40 parts by weight of fumed silica having a specific surface area of 130 m ² / g and a bulk density of 130 g / l, and 100 parts by weight of aluminum hydroxide having an average particle size of about 0.5 μm are charged into a kneader mixer, and stirred at room temperature until uniform. Thus, a base compound was prepared. To 100 parts of this base compound, 2 parts of linear polymethyl hydrogen siloxane having a molecular end blocked by a trimethylsilyl group, comprising 67 mol% of dimethyl siloxane units and 33 mol% of methyl hydrogen siloxane units and having a viscosity of 80 cP. , And a platinum complex obtained by heating chloroplatinic acid and octyl alcohol were added as platinum atoms in an amount of 10 ppm per unit amount of polydimethylsiloxane, and uniformly mixed at room temperature to obtain a silicone rubber composition. The results of measuring the apparent viscosity with a rotational viscometer are as shown in Table 1.

The silicone rubber composition was cast to give 15
By heating at 0 ° C. for 10 minutes, two types of silicone rubber sheets to be subjected to the test were produced.

The mechanical properties of the silicone rubber thus obtained were measured using a sheet having a thickness of 2 mm according to JIS K6.
301 and JIS C2321. Further, a tracking test was performed by the method described above. The results were as shown in Table 1.

Examples 2 to 4, Comparative Examples 1 and 2 Instead of the hexamethyldisilazane-treated fumed silica used in Example 1, hexamethyldisilazane-treated fume having a BET specific surface area and a bulk density shown in Table 1 A silicone rubber composition was prepared and the apparent viscosity was measured in the same manner as in Example 1 except that porous silica was used. Further, a silicone rubber was obtained from the silicone rubber composition, and its physical properties were measured and a tracking test was performed. The results were as shown in Table 1.

Example 5, Comparative Example 3 In place of the aluminum hydroxide used in Example 1, Table 1
A silicone rubber composition was prepared and the apparent viscosity was measured in the same manner as in Example 1 except that aluminum hydroxide having an average particle size shown in Table 1 was used. Further, a silicone rubber was obtained from the silicone rubber composition, and its physical properties were measured and a tracking test was performed. The results were as shown in Table 1.

[0043]

[Table 1]

As is clear from Table 1, the silicone rubber composition obtained by the method of the present invention has a low apparent viscosity and excellent workability in an uncured state, and is obtained by curing the silicone rubber composition. The rubber had high tensile strength and tear strength and excellent tracking resistance. In contrast, the compositions of Comparative Examples 1 and 2 not only have extremely high viscosity and poor workability, but also have poor mechanical properties as a whole,
The weight loss by the tracking test is also large. Further, the silicone rubber obtained from the composition of Comparative Example 3 was extremely poor in tracking resistance.

[0045]

Industrial Applicability According to the present invention, excellent workability, hardened mechanical strength, particularly excellent tear strength, suitable for manufacturing insulators, and electrical insulation, particularly tracking resistance and arc resistance. A silicone rubber composition that becomes an excellent silicone rubber is obtained. The silicone rubber obtained by curing the composition of the present invention is useful for electrical insulators such as insulators by making use of the above various properties.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 3/46 H01B 3/46 D

Claims (5)

[Claims] 1. A polyorganosiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule; and (B) a polyorganohydro having three or more hydrogen atoms bonded to a silicon atom in one molecule. (C) a compound containing a platinum group metal atom; (D) a surface treated with an organosilicon compound, a BET specific surface area of 100 to 300 m ² / g, and a bulk density of 100 to 200.
(E) aluminum hydroxide having an average particle diameter of 10 μm or less. 2. The composition according to claim 1, wherein (D) is a hydrophobic silica fine powder that has been hydrophobized with hexamethyldisilazane. 3. The viscosity of (A) at 25 ° C. is 3,0
3. The composition according to claim 1, wherein the composition is from 100 to 100,000 cP. (A) 100 parts by weight of a polyorganosiloxane having two or more silicon-bonded alkenyl groups in one molecule; and (B) three or more silicon-bonded hydrogen atoms in one molecule. Polyorganohydrogensiloxane,
(A) an amount such that the number of hydrogen atoms bonded to silicon atoms per one alkenyl group in the component is 0.5 to 5; (C) a compound containing a platinum group metal atom, a unit of (A) (D) the surface is treated with an organosilicon compound, the BET specific surface area is 100 to 300 m ² / g, and the bulk density is 100 to 200
g / l of hydrophobic silica fine powder in an amount of 5 to 100 parts by weight; and (E) aluminum hydroxide 1 having an average particle size of 10 μm or less.
The composition according to any one of claims 1 to 3, comprising 0 to 300 parts by weight. 5. A silicone rubber insulator obtained by curing the composition according to claim 1. Description: