JP2000053918A - Silicone rubber composition for wire-coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber composition for wire coating that can give a cured product having stabilized high-voltage endurance characteristics and can increase the yield in electric wire production and can stabilize the quality as electric wires and is useful for covering a variety of electric wires. SOLUTION: The objective silicone rubber composition is prepared by formulating (A) 100 pts.wt. of an organosiloxane green rubber that is represented by the formula: RaSiO(4-a)/2 (R is a substituted or unsubstituted monovalent hydrocarbon group; (a) is 1.8-2.3) and has at least two of alkenyl groups bonding to silicon atom, (B) 10-100 pts.wt. of a reinforcing filler, and (C) 0.1-5 pts.wt. of a methyl group-substituted benzoyl peroxide having a maximum particle size of <= 50μm as essential components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric conductor (tin-plated copper wire, copper wire, etc.) which provides a cured product having excellent withstand voltage characteristics.
The present invention relates to a silicone rubber composition for covering electric wires useful for covering an electric wire comprising:

[0002]

2. Description of the Related Art
Silicone rubber is used as an electric wire covering material because of its excellent heat resistance, weather resistance, electrical insulation and the like. However, in electric wires coated with silicone rubber, a decrease in withstand voltage has been locally confirmed, and in extreme cases, a phenomenon called spark-out frequently occurs. However, the problem that the quality as an electric wire is unstable tends to occur, and improvement of these problems has been desired.

The present invention has been made in view of the above circumstances, and provides a cured product having high withstand voltage characteristics stably maintained.
An object of the present invention is to provide a silicone rubber composition for electric wire coating that can perform electric wire coating with high quality and high yield.

[0004]

Means for Solving the Problems and Embodiments of the Invention As a result of intensive studies to achieve the above object, the present inventor has found that
An organosiloxane rubber having the following average composition formula (1) and having at least two silicon-bonded alkenyl groups per molecule, a reinforcing filler, and a methyl-substituted benzoyl par having a maximum particle size of 50 microns or less. It has been found that, by mixing an oxide as an essential component in a specific ratio, it is possible to obtain a silicone rubber composition for covering electric wires, which gives a cured product having stable and high withstand voltage characteristics.

That is, when the present inventor observed a portion where a problem such as a decrease in the withstand voltage of the above-described coated electric wire occurred by SEM, a relatively large void was found, and the void was formed by a vulcanizing agent. It was confirmed that a crystal having a large particle diameter contained in a methyl group-substituted benzoyl peroxide used as a part decomposed and remained as a pinhole.

Accordingly, the present inventors have further studied based on these results. As a result, the silicone rubber composition containing the organopolysiloxane raw rubber and the reinforcing filler is added to a methyl group-substituted vulcanizing agent. By using benzoyl peroxide having a maximum particle size of 50 microns or less, the above-mentioned problem can be overcome, and a cured product having stable and high withstand voltage characteristics can be obtained. The yield during the production of
The inventors have found that the quality of the electric wire can be stabilized, and have accomplished the present invention.

Accordingly, the present invention provides: (A) the following average composition formula (1): R _a SiO _{(4-a) / 2} (1) (wherein R is a substituted or unsubstituted monovalent hydrocarbon group, a Is a number from 1.8 to 2.3.) 100 parts by weight of an organosiloxane rubber having at least two silicon-bonded alkenyl groups in one molecule (B) Reinforcing filler 10 to 100 Part by weight (C) A silicone rubber composition for covering electric wires, characterized by comprising, as an essential component, 0.1 to 5 parts by weight of a methyl group-substituted benzoyl peroxide having a maximum particle size of 50 microns or less.

Hereinafter, the present invention will be described in more detail. The organopolysiloxane raw rubber of the component (A), which is the main material of the silicone rubber composition for covering electric wires of the present invention, is represented by the following average composition formula (1). , At least 2 per molecule
Having two silicon-bonded alkenyl groups.

R _a SiO _{(4-a) / 2} (1) (wherein, R is a substituted or unsubstituted monovalent hydrocarbon group, and a is a number from 1.8 to 2.3.)

In the above formula (1), R is a substituted or unsubstituted monovalent hydrocarbon group, preferably having 1 to 12 carbon atoms, especially 1 to 8 carbon atoms, such as methyl, ethyl, propyl, Alkyl groups such as butyl group, hexyl group and octyl group; alkenyl groups such as vinyl group, allyl group and hexenyl group; unsubstituted monovalent hydrocarbon groups such as aryl group such as phenyl group, and carbon atoms of these groups Wherein some or all of the hydrogen atoms bonded to are substituted with halogen atoms, etc.
Examples include a substituted monovalent hydrocarbon group such as a 3,3-trifluoropropyl group. Component (A) comprises at least two alkenyl groups, particularly vinyl groups, bonded to a silicon atom,
Preferably it is 0.001 to 5 mol%, especially 0.01 to 0.
It is preferable to contain 5 mol%. R is preferably a methyl group, a phenyl group or a trifluoropropyl group, and particularly preferably a methyl group. 80 mol% of methyl groups
As described above, the content is particularly preferably 95 mol% or more. Further, the molecular chain terminals of the component (A) are trimethylsiloxy, dimethylvinylsiloxy, methyldivinylsiloxy,
It is preferably blocked with a triorganosiloxy group such as a trivinylsiloxy group, and particularly preferably blocked with a vinyl group-containing group. a is a number from 1.8 to 2.3.

The molecular structure of the organopolysiloxane raw rubber is linear, but may have a slightly branched siloxane skeleton. The average degree of polymerization can be within the range referred to as organopolysiloxane raw rubber in the art, but is usually from 3,000 to
It is desirable to be in the range of 12,000, especially 5,000 to 10,000. If the average degree of polymerization is less than 3,000, good mechanical strength may not be obtained.
If it exceeds 0, it may be difficult to add a reinforcing filler.

The reinforcing filler (B) used in the present invention is a component necessary for improving the mechanical strength of the silicone rubber. As the reinforcing filler, conventionally used wet silica, fumed silica and the like can be used, and non-reinforcing silica such as crushed quartz and diatomaceous earth can be used in combination as the filler. In the present invention, the following in particular an average particle size of 50 microns Among these, a specific surface area of 100 m ² / g or more, particularly 100 to 400 m ² / g of fumed silica is preferred.

These reinforcing fillers may be used as they are, or may be those surface-treated with organopolysiloxane, organopolysilazane, chlorosilane, alkoxylane or the like.

The amount of the reinforcing filler (B) added is
(A) 10 to 100 parts by weight with respect to 100 parts by weight of the component;
Preferably it is 40 to 70 parts by weight. If the amount is less than 10 parts by weight, the reinforcing effect is insufficient and sufficient mechanical properties cannot be obtained. If the amount is more than 100 parts by weight, the extrudability deteriorates, and a large amount of reinforcing filler is actually added. Work is impossible.

The methyl group-substituted benzoyl peroxide of the component (C) used in the present invention is a catalyst usually used as a vulcanizing agent for accelerating the heat curing of the silicone rubber composition.

The methyl-substituted benzoyl peroxide includes, for example, monomethylbenzoyl peroxide, dimethylbenzoyl peroxide, trimethylbenzoyl peroxide and the like.
Methylbenzoyl peroxide, m-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,3-dimethylbenzoyl peroxide, 2,
Examples thereof include 4-dimethylbenzoyl peroxide, 2,6-dimethylbenzoyl peroxide, 2,3,4-trimethylbenzoyl peroxide, and 2,4,6-trimethylbenzoyl peroxide. Of these, p-methylbenzoyl peroxide and o-methylbenzoyl peroxide are preferred, and p-methylbenzoyl peroxide is particularly preferred in terms of price and performance.

In the present invention, defining the maximum particle size of these methyl-substituted benzoyl peroxides stabilizes the withstand voltage characteristics, improves the yield in the production of electric wires, and stabilizes the quality as electric wires. Indispensable for planning. The maximum particle size of the methyl-substituted benzoyl peroxide is set to 50 microns or less, and in order to further stabilize the quality, it is preferably 30 microns or less, particularly preferably 15 microns or less. If the maximum particle size exceeds 50 microns, this portion will remain as pinholes after vulcanization, leading to a decrease in withstand voltage. The method for measuring the maximum particle size is as described later.

A methyl-substituted benzoyl peroxide having a maximum particle size of 50 microns or less can be obtained by pulverizing or classifying a commercially available product.

The amount of addition of the methyl-substituted benzoyl peroxide of the component (C) is in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the component (A). If the addition amount is less than 0.1 part by weight, curing is not sufficiently performed, and if it exceeds 5 parts by weight, heat resistance and electrical properties are deteriorated.

The silicone rubber composition for covering electric wires of the present invention can be easily produced by uniformly mixing the above-mentioned components (A) to (C).
Diorganopolysiloxanes such as α, ω-dimethylsiloxanediol having a hydroxyl group at the terminal and having a degree of polymerization of 100 or less; hexaorganodisilazanes such as diphenylsilanediol and hexamethyldisilazane; and organoalkoxysilanes such as vinyltrialkoxysilane. It is preferable to add at least one kind of additive, usually called a wetter, composed of a low molecular weight organosilicon compound. In this case, it is preferable to add 0.1 to 20 parts by weight, especially 0.5 to 10 parts by weight, based on 100 parts by weight of the organopolysiloxane raw rubber as the component (A).

Further, a non-reinforcing inorganic filler or a coloring agent may be added, and further, a known heat-resistance improving agent, a flame-retardant-imparting agent, a fire-resistance-imparting agent, etc. conventionally added to a silicone rubber composition. Can be added to improve the performance.
Further, in addition to the above components (A) to (C), a known metal salt of a fatty acid such as zinc oxide or zinc stearate, which is a known core wire adhesion preventive agent, may be used in combination as long as the withstand voltage characteristics are not impaired. .

The silicone rubber composition for coating electric wires of the present invention can be used for coating various electric wires such as tin-plated copper wires and copper wires. An ordinary method can be adopted as a method of coating the electric wire.

[0023]

EXAMPLES The present invention will be described below in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. The parts in the following examples are parts by weight.

In each example, the methyl-substituted benzoyl peroxide as the component (C) was used after being pasted with 50% dimethyl silicone oil, and the particle size was measured by the following method. Particle size measurement method: Using a grind gauge (manufactured by Toyo Seiki Seisaku-sho, Ltd.), place the paste at a position of 100 μm on a 0-100 μm grind gauge, and use the attached holding fixture so that the paste does not remain on the edge of the grind gauge. The sample was pulled toward 0 micron while being strongly pressed. At this time, the position of the line on the sample was measured for the particle size from the scale of a grind gauge.

[Example 1] Dimethylsiloxane unit 9
9.85 mol% and 0.15 methylvinylsiloxane unit
100 parts by weight of a methylvinylpolysiloxane raw rubber having a degree of polymerization of about 7,000 and having a specific surface area of 200 m ² /
g of fumed silica (40 parts) and 8 parts of dimethylpolysiloxane having an average degree of polymerization of about 10 in which both ends of the molecular chain are blocked by silanol groups are uniformly mixed in a kneader, and heat-treated at 170 ° C. for 2 hours to obtain a base compound. (1) was obtained.

Further, the mixture was cooled to room temperature, and 0.7 parts of p-methylbenzoyl peroxide having a maximum particle size of 15 μm was mixed with 100 parts of the base compound (1) using two rolls. (I) was prepared.

Example 2 0.7 parts of m-methylbenzoyl peroxide having a maximum particle size of 10 microns was mixed with 100 parts of the base compound (1) prepared in Example 1 using two rolls, A rubber composition (II) was prepared.

Example 3 0.7 parts of o-methylbenzoyl peroxide having a maximum particle size of 40 microns was mixed with 100 parts of the base compound (1) prepared in Example 1 using a two-roll mill, and silicone was mixed. Rubber composition (III)
Was prepared.

[Comparative Example 1] With 100 parts of the base compound (1) prepared in Example 1 using two rolls, 0.7 part of p-methylbenzoyl peroxide having a maximum particle size of 80 μm was mixed, and silicone was mixed. A rubber composition (IV) was prepared.

Comparative Example 2 0.7 parts of o-methylbenzoyl peroxide having a maximum particle size of 90 microns was mixed with 100 parts of the base compound (1) prepared in Example 1 using a two-roll mill, and silicone was mixed. A rubber composition (V) was prepared.

The silicone rubber compositions obtained in the above Examples and Comparative Examples were introduced into an extruder and had an outer diameter of 4 mm and an inner diameter of 2 mm.
mm tube was extruded, and then passed through a 400 ° C. hot air vulcanizing furnace for 20 seconds to prepare a sample for withstand voltage measurement. The DC withstand voltage of the silicone rubber tube thus obtained was measured by the following test method. Table 1 shows the results. Withstand voltage test method: The following method according to the use conditions was adopted. 1 molded tube (outer diameter 4 mm, inner diameter 2 mm)
The tube was immersed in water, and when the DC voltage was gradually increased in the core wire, the voltage at the moment when discharge occurred was measured.

[0032]

[Table 1]

[0033]

The silicone rubber composition for covering electric wires of the present invention gives a cured product having stable and high withstand voltage characteristics.
It can improve the yield during the production of electric wires and stabilize the quality as electric wires, and is useful for covering various electric wires.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Teruoka Sato 1-10 Hitomi, Matsuida-machi, Usui-gun, Gunma Prefecture F-term in the Silicon Electronics Research Laboratory, Shin-Etsu Chemical Co., Ltd. 4J002 CP062 CP131 DJ016 EK047 FD016 FD147 GQ01 4J038 DL031 DL052 DL071 GA01 GA03 HA446 HA556 JA66 KA03 KA07 KA08 KA14 KA20 MA14 NA17 PB09

Claims (4)

[Claims] (A) The following average composition formula (1) R _a SiO _{(4-a) / 2} (1) (wherein, R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.8 100 parts by weight of an organosiloxane rubber having at least two silicon-bonded alkenyl groups in one molecule (B) Reinforcing filler 10 to 100 parts by weight (C A silicone rubber composition for covering electric wires, characterized by comprising, as an essential component, 0.1 to 5 parts by weight of a methyl-substituted benzoyl peroxide having a maximum particle size of 50 microns or less. 2. The reinforcing filler of component (B) has a specific surface area of 1
00~400m ² / g is a fumed silica of claim 1 wire coating silicone rubber composition. 3. The silicone rubber composition for covering electric wires according to claim 1, wherein the methyl-substituted benzoyl peroxide of the component (C) is p-methylbenzoyl peroxide. 4. A polymerization degree of 10 having a hydroxyl group at a terminal.
0 or less of at least one selected from diorganopolysiloxane, diphenylsilanediol, hexaorganodisilazane, and organoalkoxysilane as component (A) 1
The silicone rubber composition for covering electric wires according to any one of claims 1 to 3, wherein 0.1 to 20 parts by weight is blended with respect to 00 parts by weight.