JPH10195297A - Insulating silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the silicone rubber composition capable of giving an excellent black color to molded products without deteriorating their electric insulation properties. SOLUTION: This insulating silicone rubber composition comprises (A) 100 pts.wt. of an organopolysiloxane expressed by the average composition formula: Ra SiO(4-a)/2 [R groups are each the same or different non-substituted or substituted monovalent hydrocarbon group; (a) is a positive number of 1.95-2.051, (B) 10-100 pts.wt. of silica having a specific surface area of >=50m<2> /g, (C) 0.5-5 pts.wt. of a curing agent, and (D) 0.5-10 pts.wt. of carbon black having a conductivity index of <=40. The conductive index is expressed by the equation: conductive index = (specific surface area × DBP oil-absorbing amount)<1/2> (1 + volatile content), wherein the specific surface area (m<2> /g) is a surface area per unit weight of carbon black; DBP oil-absorbing amount (ml/100g) is the volume (ml) of DBP (dibutyl phthalate) contained in 100g of the carbon black; the volatile content (wt.%) is an evaporated reduced amount, when heated at 950 deg.C for 7min.

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 which gives a silicone rubber having a black color and excellent insulating properties.

[0002]

2. Description of the Related Art Silicone rubber is excellent in heat resistance, weather resistance, durability, releasability, and electrical characteristics. It is used in various fields such as OA equipment parts and building materials. Among them, as a method of giving black color to the silicone rubber composition and the silicone rubber obtained from the composition, a method of adding carbon black, black red iron or the like to the silicone rubber composition is generally used. Carbon black has advantages such as being lighter and cheaper than metal.

[0003]

However, when a large amount of carbon black is blended, there is a drawback that the resistance value is lowered and the electric insulation is deteriorated, so that there has been a problem in use in various electric and electronic parts. The inventors have conducted various studies to solve this problem and completed the present invention.

[0004]

Means for Solving the Problems The present invention relates to (A) an average composition formula R _a SiO _{(4-a) / 2} (where R is the same or different unsubstituted or substituted monovalent hydrocarbon group, a Is a positive number of 1.95 to 2.05) 100 parts by weight of an organopolysiloxane represented by the following formula (B): 10 to 100 parts by weight of silica having a specific surface area of 50 m ² / g or more (C) 0.5 to 5 parts by weight of a curing agent ( D) An insulating silicone rubber composition comprising 0.5 to 10 parts by weight of carbon black having a conductivity index represented by the following formula (Equation 1) of 40 or less.

(Equation 1) However, each element in the formula is specific surface area (m ² / g): surface area per unit weight of carbon black. DBP oil absorption (ml / 100 g): the number of ml of DBP (dibutyl phthalate) contained per 100 g of carbon black. Volatile content (% by weight): Loss of volatilization when carbon black is heated at 950 ° C for 7 minutes.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, the organopolysiloxane (A) has an average compositional formula of R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group, and a is a positive or negative number of 1.95 to 2.05). It is a number.) Here, R is a substituted or unsubstituted monovalent hydrocarbon group, of which 0.001 to 0.5 mol%,
Preferably, 0.01 to 0.3 mol% must be alkenyl groups such as vinyl groups and allyl groups. When the content of the alkenyl group in (A) is less than 0.001 mol%, the curability of the organopolysiloxane becomes insufficient, and when it exceeds 0.5 mol%, the properties of the rubber obtained from the composition deteriorate. Examples of usable R groups other than the alkenyl group include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group, decyl group and dodecyl group; phenyl group, An aryl group such as a tolyl group; an aralkyl group such as a β-phenylethyl group; and a group in which part or all of the hydrogen atoms bonded to the carbon atoms of these hydrocarbon groups are substituted with a halogen atom or a cyano group (for example, 3 , 3,3-trifluoropropyl group and cyanoethyl group).
In (A), R other than the alkenyl group is most preferably a methyl group, but when cold resistance and transparency are required, it is preferable to include at most 20 mol% of the phenyl group in R. Further, when oil resistance and gasoline resistance are required, it is preferable that R contains a cyanoethyl group or a 3,3,3-trifluoropropyl group. In the composition formula (A), a is a number from 1.95 to 2.05, and is basically a linear organopolysiloxane.

In the present invention, the organopolysiloxane preferably has a degree of polymerization of 3,000 or more in order to impart sufficient mechanical strength to the silicone rubber (hereinafter simply referred to as silicone rubber) obtained from the silicone rubber composition of the present invention. Particularly preferably, it is from 5,000 to 10,000. Although the organopolysiloxane used in the present invention is substantially composed of diorganopolysiloxane units, triorganosiloxane units, monoorganosiloxane units, and Si
It may contain a small amount of O ₂ unit, and the molecular chain terminal may be blocked with a hydroxyl group or a triorganosiloxane unit.

[0007] The silica (B) in the present invention is added to impart an appropriate hardness to the silicone rubber and to improve the mechanical strength such as the tensile strength thereof.
The silica is preferably 50 m ² / g or more, particularly 100 to 400 m ² / g. As such silica, specifically, fumed silica, precipitated silica or the like is used alone or in combination of two or more thereof. These silicas also
The surface may be treated with a chain organopolysiloxane, cyclic organopolysiloxane, hexamethyldisilazane, dichlorodimethylsilane, or the like. The silica in the present invention is blended in an amount of 10 to 100 parts by weight, particularly preferably 10 to 50 parts by weight, per 100 parts by weight of the organopolysiloxane (A). If the amount is less than 10 parts by weight or more than 100 parts by weight, the processability of the silicone rubber deteriorates and the silicone rubber does not have sufficient mechanical strength.

As the curing agent in the present invention, a conventionally known curing agent depending on the mechanism of the crosslinking reaction of the silicone rubber composition can be used. When the molecular chain terminals of the organopolysiloxane (A) are blocked with non-hydrolyzable groups and the crosslinking reaction is performed between hydrocarbon groups, an organic peroxide such as benzoyl is used as a curing agent. Peroxide, 2,4-dichlorobenzoyl peroxide,
p-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-
T-butylperoxy) hexane, di-t-butyl peroxide, t-butyl perbenzoate and the like are preferably used. The amount of the organic peroxide to be added is preferably 0.1 to 10 parts by weight, particularly preferably 0.2 to 5 parts by weight, per 100 parts by weight of the organopolysiloxane A.

When the organopolysiloxane (A) in the present invention has an alkenyl group directly bonded to a silicon atom, an organohydrogenpolysiloxane containing at least two hydrogen atoms directly bonded to a silicon atom in one molecule is used. It can be used as a curing agent and cured by causing crosslinking by these addition reactions. The organohydrogenpolysiloxane used here may be linear, branched, or cyclic, but preferably has a degree of polymerization of 300 or less, and the terminal is blocked with a dimethylhydrogensilyl group. Diorganopolysiloxane, copolymer of dimethylsiloxane unit with methylhydrogensiloxane unit and terminal trimethylsiloxy unit, dimethylhydrogensiloxane [H (CH ₃ ) ₂ SiO
_0.5 ] low viscosity fluid consisting of units and SiO ₂ units, 1,3,3
5,7-tetrahydrodiene-1,3,5,7-tetramethylcyclotetrasiloxane, 1-propyl-3,
5,7-trihydrodiene-1,3,5,7-tetramethylcyclotetrasiloxane, 1,5-dihydrodiene-3,7-dihexyl-1,3,5,7-tetramethylcyclotetrasiloxane and the like Is exemplified.

The amount of the organohydrogenpolysiloxane used as a curing agent in the present invention is such that hydrogen atoms directly bonded to silicon atoms are 50 to 500 mol% based on the alkenyl groups of the organopolysiloxane (A). It is desirable to use in proportion. It is preferable to use a known platinum-based catalyst for this addition reaction. Specifically, a platinum atom alone, a platinum complex, chloroplatinic acid, an alcohol compound of chloroplatinic acid, an aldehyde compound of chloroplatinic acid, Platinic acid ether compounds and complexes of chloroplatinic acid with various olefins are exemplified. The amount of the platinum-based catalyst to be added is preferably in the range of 1 to 2,000 ppm as platinum atoms with respect to the organopolysiloxane (A). To the silicone rubber composition of the present invention, in addition to the above-mentioned essential components, a filler such as crushed quartz or calcium carbonate may be added as an optional component within a range not to impair the effects of the present invention.

[0011] In the silicone rubber composition of the present invention,
By adding 0.5 to 10 parts by weight of carbon black (D) having a conductivity index of 40 or less as a black additive, a silicone rubber composition which gives a silicone rubber having excellent blackness and excellent insulation properties can be obtained. In general, to evaluate the electrical conductivity of carbon black, a conductivity index given by the following equation (Equation 1) is used.

(Equation 1) However, the specific surface area (m ² / g) is the surface area per unit weight of carbon black, and the DBP oil absorption (ml / 100 g) is the number of ml of DBP (dibutyl phthalate) contained per 100 g of carbon black, which is Indicates the state of the black structure. The volatile content (% by weight) is a loss of volatilization when the carbon black is heated at 950 ° C. for 7 minutes, which is mainly CO, CO ₂ , H ₂ O, etc. bonded to the carbon black surface.

In general, when carbon black forms a conductive network in a polymer, it is considered that electrons flow from a crosslinked portion of the carbon black through the crosslinked portion. Therefore, carbon black having a developed crosslinked structure has high electric conductivity. The specific surface area and the amount of DBP oil absorption indicate the state of development of the crosslinked structure. In addition, oxygen compounds chemically adsorbed on the surface of the carbon black during the production process are volatile components, which act as an insulator and lower the conductivity.

In the present invention, it is necessary that the conductivity index of carbon black be 40 or less.
The insulating properties of the silicone rubber obtained from the silicone rubber composition of the present invention become insufficient. The method of producing carbon black satisfying this condition is not particularly limited, and carbon black satisfying this condition may be selected from channel black, furnace black, acetylene black, lamp black, thermal black, and the like. In the present invention, when this carbon black is blended with the polyorganosiloxane composition, a kneader such as a kneader, a Banbury mixer, or an open roll, which is usually used, can be used. The blending amount of carbon black is arbitrarily selected depending on the degree of blackness desired in each use of the silicone rubber, and is not particularly limited, but is based on 100 parts by weight of the polyorganosiloxane (A).
It is used in the range of 0.5 to 10 parts by weight, preferably 0.5 to 5 parts by weight. If it is less than 0.5 parts by weight, the blackness becomes weak,
On the other hand, if it exceeds 10 parts by weight, the electrical insulation will be reduced. The term "electrical insulation" as used herein means that the characteristics of a blackened material obtained by adding carbon black in a volume resistivity or a dielectric breakdown test hardly decrease compared to those containing no carbon black. The volume resistivity is 1 × 10 ¹⁰ Ω · cm or more, preferably 1 × 10 ¹³ Ω · cm or more,
Particularly preferably, it is 1 × 10 ¹⁵ Ω · cm or more, and the dielectric breakdown voltage by AC is 28 kV or more.

The insulating silicone rubber composition of the present invention can be obtained by kneading the components (A) to (D) with a roll, kneader, dough mixer or the like.
After kneading the components (B) and (D), it is preferable to add the component (C). Since the insulating silicone rubber composition thus produced contains the carbon black (D), it can give excellent black color without lowering its electrical insulation. The silicone rubber composition of the present invention is suitable for any use where black is required, and is preferably used for compression molded products, for example, rubber contacts in electronic desk calculators and push phones, extruded materials such as electric wires, and other transfer molded products and injection molded products. Suitable for use.

[0015]

The following examples are given, but the present invention is not limited to these examples. (Examples 1 to 3) (CH ₃ ) as an organopolysiloxane
_It consists of 99.85 mol% of ₂ SiO units and 0.15 mol% of (CH ₃ ) (CH ₂ = CH) SiO units, and the molecular chain ends are blocked with _0.5 units of (CH ₂ = CH) (CH ₃ ) ₂ SiO. About 7,000 methylvinylpolysiloxane raw rubber was used. In a kneader, 100 parts by weight of the above-mentioned methylvinylpolysiloxane raw rubber, 40 parts by weight of fumed silica having a specific surface area of 200 m ² / g, and 10 parts by weight of a dimethylpolysiloxane having a hydroxyl group at a molecular chain terminal (degree of polymerization 10) as a dispersing agent. And uniformly heat-treated at 150 ° C. for 2 hours to obtain a base compound (1). Next, carbon blacks a to c having the characteristics shown in Table 2 were uniformly kneaded into 100 parts by weight of the base compound using an open roll. Next, 2,5-dimethyl-2,
1.5 parts by weight of 5-di-t-butylperoxyhexane were kneaded and press-molded at 170 ° C., and then a rubber molded product was obtained by post-curing at 200 ° C. for 2 hours. Next, a molded rubber sheet having a thickness of 1 mm was prepared and the volume resistivity and dielectric breakdown were measured using the molded rubber sheet in order to evaluate the electrical insulation of the molded product. The measurement results are shown in Table 1.

(Comparative Examples 1-2, Reference Example 1) As a comparative example, carbon black having characteristics such as d and e in Table 2 was kneaded and mixed with a base compound in the same manner as in the Example, and formed into a sheet. Was prepared, and as a reference example, a molded sheet was prepared without adding carbon black. These were evaluated for insulation by the same method as described above, and the measurement results are shown in Table 1. Table 2 shows the physical property values of the carbon blacks used and the conductivity index calculated from these.

[0017]

[Table 1]

[Table 2]

[0018]

The silicone rubber composition of the present invention can give an excellent black color to those molded products without lowering the electrical insulation.

Claims (1)

[Claims] (A) an average composition formula R _a SiO _{(4-a) / 2} (where R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05) 100 parts by weight of an organopolysiloxane represented by the following formula) (B) 10 to 100 parts by weight of silica having a specific surface area of 50 m ² / g or more (C) 0.5 to 5 parts by weight of a curing agent (D) An insulating silicone rubber composition comprising 0.5 to 10 parts by weight of carbon black having a conductivity index of 40 or less. (Equation 1) However, each element in the formula is specific surface area (m ² / g): surface area per unit weight of carbon black. DBP oil absorption (ml / 100 g): the number of ml of DBP (dibutyl phthalate) contained per 100 g of carbon black. Volatile content (% by weight): Loss of volatilization when carbon black is heated at 950 ° C for 7 minutes.