JP2000160017A - Silicon rubber sponge composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber sponge composition having a high expandability and a uniform, fine cell structure, wherein its skin layer is smooth and exerts no adhesion. SOLUTION: This composition essentially comprises (A) 100 pts.wt. organopolysiloxane of the formula: R1aSiO(4-a)/2 (wherein R1 is a monovalent hydrocarbon group where at least 0.001 mol% but less than 1.0 mol% is an alkenyl group; and (a) is 1.98-2.02), (B) from 0.1 to 20 pts.wt. organopolysiloxane of the formula: R2aSiO(4-a)/2 (wherein R2 is a monovalent hydrocarbon group where from 1.0 to 20 mol% is an alkenyl group; and (A) is 1.98-2.02), (C) from 5 to 200 pts.wt. reinforcing filling silica, (D) from 0.01 to 50 pts.wt. foaming agent selected from organic azo compounds and (E) from 0.1 to 10 pts.wt. halogen atom-free organic peroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a sponge roll,
The present invention relates to a silicone rubber sponge composition used for architectural gaskets, heat insulating sheets, packings, etc., and more specifically, has excellent foamability, has a uniform and fine cell structure, and has a surface of a skin layer. The present invention relates to a silicone rubber sponge composition that can be formed into a smooth silicone rubber sponge.

[0002]

2. Description of the Related Art Conventionally, silicone rubber sponges have physical properties unique to silicone rubber, and are excellent in heat resistance, cold resistance, electrical insulation, flame retardancy, compression set and the like. Has properties. This silicone rubber sponge basically foams and cures a thermosetting silicone rubber sponge composition by heating,
A method of forming a sponge is used, in which case,
It is important that the skin layer has excellent foaming properties, has a uniform and fine cell structure, the surface of the skin layer is smooth, has no tackiness, and does not impair the physical properties unique to silicone rubber. From such a viewpoint, azobisisobutyronitrile (AIBN) has conventionally been used as a foaming agent, and 2,4-dichlorobenzoyl peroxide has been used as a curing agent. Particularly, this 2,4-dichlorobenzoyl peroxide has been used. However, when decomposed, a chlorine compound is produced as a by-product, and a long-time heat treatment is required to remove the by-product, resulting in a problem that the molding time is prolonged. In addition, it is difficult to use such a peroxide by-produced by a chlorine compound in the future due to environmental problems.

[0003] From such a viewpoint, there has been proposed a method of forming a silicone rubber sponge by applying addition vulcanization using a platinum-based catalyst instead of peroxide.
In addition vulcanization, it is very difficult to control the process from the addition of the catalyst to the molding of the sponge, and there is a drawback that it is greatly affected by temperature and humidity. Japanese Patent Application Laid-Open No. 5-43802 proposes a method using a peroxide having no halogen, but has a disadvantage that the decomposition temperature is high, so that the vulcanization rate is slow and the productivity is poor.

Further, Japanese Patent Application Laid-Open No. Hei 10-120817 proposes a method using a non-chlorine-based acyl peroxide as a curing agent. According to this method, a chlorine compound is not produced as a by-product. Silicone rubber compounds have insufficient sponge cell uniformity and insufficient surface non-adhesion of the skin layer.

[0005] The problem of the silicone rubber sponge in a vulcanization system other than 2,4-dichlorobenzoyl peroxide is that the timing (balance) of the most important crosslinking reaction and foaming reaction in sponge molding is large. This is caused by deviation.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned problems. Even when an organic peroxide having no halogen is used, the cell structure is excellent in foaming property, uniform and fine without reducing workability. It is an object of the present invention to provide a silicone rubber sponge composition having a silicone rubber sponge having a smooth skin layer and no tackiness.

[0007]

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 when an organic peroxide having no halogen atom is used, a delay is longer than a foaming reaction. In order to promote the cross-linking reaction,
(A) Average composition formula (1) R ¹ _a SiO _{(4-a) / 2} (1) (wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group, of which 0.001 mol% At least 1.0 mol% is an alkenyl group, and a is a positive number from 1.98 to 2.02).
(B) Average composition formula (2) R ² _a SiO _{(4-a) / 2} (2) (wherein, R ² is an unsubstituted or substituted monovalent hydrocarbon group, of which 1.0 to 20 Mol% is an alkenyl group. A is a positive number from 1.98 to 2.02.) By adding an appropriate amount of an organopolysiloxane represented by It has been found that a silicone rubber sponge composition having excellent, uniform and fine cells, a smooth skin layer and a tack-free silicone rubber sponge can be obtained.

Accordingly, the present invention provides: (A) 100 parts by weight of the organopolysiloxane of the above average composition formula (1); (B) 0.1 to 20 parts by weight of the organopolysiloxane of the above average composition formula (2); C) silica for reinforcing filling 5 to 200 parts by weight, (D) a blowing agent selected from organic azo compounds 0.01 to 50 parts by weight, (E) an organic peroxide having no halogen atom 0.1 to 10 parts by weight. A silicone rubber sponge composition characterized in that the essential component is a silicone rubber sponge composition.

That is, the present inventors have already disclosed in JP-A-10-1
No. 822972, (A), (C), (D),
A silicone rubber sponge composition comprising the component (E) has been proposed to improve foamability, cell uniformity, surface tackiness, etc., but the present invention further uses the component (B) in combination. Thus, these characteristics are remarkably improved.

Hereinafter, the present invention will be described in more detail.

The organopolysiloxane of the component (A) constituting the silicone rubber sponge composition of the present invention has the following average composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) ¹ is an unsubstituted or substituted monovalent hydrocarbon group, of which 0.001 mol% or more and less than 1.0 mol% is an alkenyl group, and a is a positive number from 1.98 to 2.02. ).

In this case, R ¹ represents an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group,
Alkenyl groups such as butenyl group and hexenyl group, aryl groups such as phenyl group and tolyl group, aralkyl groups such as benzyl group and β-phenylpropyl group, or part or all of the hydrogen atoms bonded to carbon atoms of these groups Is selected from a chloromethyl group substituted with a halogen atom, a cyano group, etc., a trifluoropropyl group, a cyanoethyl group,
The same or different, preferably unsubstituted or substituted monovalent hydrocarbon groups having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. A is a positive number from 1.98 to 2.02, and the organopolysiloxane has a trimethylsilyl group, a dimethylvinylsilyl group, a methyldivinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like at a molecular chain end. It can be blocked. In the present invention, the organopolysiloxane must have at least two alkenyl groups in the molecule, and R
^It is preferable that 0.001 mol% or more and less than 1.0 mol%, more preferably 0.01 to 0.5 mol% of 1 is an alkenyl group, especially a vinyl group. The viscosity is 25
At 100 ° C. or more, preferably 100,00 ° C.
0 to 10,000,000 cS. The degree of polymerization is 100
As mentioned above, it is preferably from 3,000 to 100,000, particularly preferably from 3,000 to 10,000.

When the organopolysiloxane of the component (B) uses an organic peroxide having no halogen atom, it promotes a cross-linking reaction, which is slower than a foaming reaction, and is excellent in foamability and uniform. It is an essential component for producing a silicone rubber sponge having a fine cell structure and a smooth skin layer and having no tackiness, and has the following average composition formula (2) R ² _a SiO _{(4-a) / 2} (2) ( In the formula, R ² is an unsubstituted or substituted monovalent hydrocarbon group, of which 1.0 to 20 mol% is an alkenyl group, and a is a positive number of 1.98 to 2.02.) It is shown by.

In this case, R ² is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group; a cycloalkyl group such as a cyclohexyl group; a vinyl group;
Alkenyl groups such as butenyl group and hexenyl group, aryl groups such as phenyl group and tolyl group, aralkyl groups such as benzyl group and β-phenylpropyl group, or part or all of the hydrogen atoms bonded to carbon atoms of these groups Is selected from a chloromethyl group substituted with a halogen atom, a cyano group, etc., a trifluoropropyl group, a cyanoethyl group,
The same or different, preferably unsubstituted or substituted monovalent hydrocarbon groups having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. A is a positive number of 1.98 to 2.02, and the organopolysiloxane has a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a methyldivinylsilyl group, a trivinylsilyl group, or the like at a molecular chain end. Blocked ones are preferred. In the present invention, the organopolysiloxane is one to two of R ² .
It is preferred that 0 mol%, more preferably 1 to 10 mol%, is an alkenyl group, especially a vinyl group. The viscosity at 25 ° C. is preferably 10 cS or more, and particularly preferably 100 to 10,000,000 cS. The polymerization degree is preferably from 10 to 100,000, particularly preferably from 100 to 1
000 is preferred.

As the above-mentioned organopolysiloxane, those represented by the following formula can be exemplified.

[0016]

Embedded image [A: alkenyl group, preferably vinyl group R ³ : R ² excluding alkenyl group, preferably methyl group,
Phenyl group R ⁴ : Same as R ² , preferably methyl group, vinyl group R ⁵ : Same as R ² or hydroxyl group, preferably vinyl group, methyl group, hydroxyl group, p and q are integers of 0 or more and 10 ≦ p + q
≦ 100,000, but p and q are selected so as to contain 1 to 20 mol% of alkenyl groups. ]

The amount of the component (B) is 0.1 to 100 parts by weight of the organopolysiloxane of the component (A).
If the amount is less than 20 parts by weight, a sufficient effect is not exhibited,
If it is too large, the crosslink density becomes too high, so that a sufficient expansion ratio cannot be obtained, and the heat resistance also deteriorates. Preferably it is 0.3 to 10 parts by weight.

Next, the reinforcing silica as the component (C) is used for obtaining a silicone rubber having excellent mechanical strength. For this purpose, the specific surface area is at least 50 m ² / g,
Preferably it is 100-400 m < ² > / g. When the specific surface area is less than 50 m ² / g, the mechanical strength of the molded product is reduced.
Examples of such reinforcing silica include dry silica (fumed silica), precipitated silica, and hydrophobic silica whose surface is surface-treated with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. This reinforcing silica may be used in combination of two or more kinds such as a combination of dry silica and precipitated silica. Preferred are fumed silica and surface-treated silica.

The amount of the reinforcing silica added is as follows:
With respect to 100 parts by weight of the organopolysiloxane of the component (A), if the amount is too small, a sufficient reinforcing effect is not exhibited, and if the amount is too large, the processability deteriorates remarkably, and the strength of the obtained silicone rubber also decreases. It is 5 to 200 parts by weight, preferably 30 to 100 parts by weight.

As the foaming agent selected from the organic azo compounds as the component (D), azobisisobutyronitrile, 2,2
2'-azobis-2-methylbutyronitrile, 2,2 '
-Azo-2,4-dimethylvaleronitrile, 1,1'-
Organic azo compounds such as azobis (1-acetoxy-1-phenylethane) and azodicarbonamide are exemplified.
The amount of the foaming agent is 0.01 to 50 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the organopolysiloxane (A). If the amount is too small, the foaming is insufficient. If the amount is too large, the sponge cells become large and non-uniform.

The organic peroxide having no halogen atom as the component (E) is a low-temperature decomposable organic peroxide such as benzoyl peroxide, paramethylbenzoyl peroxide, orthomethylbenzoyl peroxide, and 2,4-dimethylbenzoyl peroxide. Peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-
Organic peroxides that do not contain halogen atoms such as high-temperature decomposable organic peroxides such as butylperoxybenzoate, dicumyl peroxide and cumyl-t-butyl peroxide are used, and especially for normal pressure hot air vulcanization. , Benzoyl peroxide, paramethylbenzoyl peroxide, orthomethylbenzoyl peroxide, 2,4-
Examples thereof include dimethylbenzoyl peroxide, and an acyl organic peroxide represented by the following formula (3) is preferable.

[0022]

Embedded image (In the formula, R is a hydrogen atom or an unsubstituted monovalent hydrocarbon group, and a lower alkyl group, particularly a methyl group, is more preferable.
Is an integer of 1 to 3. )

Of these, paramethylbenzoyl peroxide and orthomethylbenzoyl peroxide are particularly preferred.

These organic peroxides may be used alone or in combination of two or more. When two or more kinds are used in combination, a low-temperature decomposable organic peroxide (particularly a non-chlorinated acyl-based organic peroxide) and a high-temperature decomposable organic peroxide (particularly a non-acyl-based organic peroxide) are preferably used. : 9 to 9: 1, more preferably 2: 8 to 8: 2. In this case, as the high-temperature decomposition type organic peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-
Di-t-butylperoxyhexane is preferred.

The amount of the organic peroxide to be added is 0.1 to 100 parts by weight of the organopolysiloxane (A).
It is 1 to 10 parts by weight, preferably 0.3 to 5 parts by weight.
If the amount is too small, the crosslinking is insufficient, and even if the amount is too large, a further increase in the crosslinking speed cannot be expected.

The silicone rubber sponge composition of the present invention is obtained by uniformly mixing the above components (A), (B) and (C) using a rubber kneader such as a two-roll mill, a Banbury mixer or a dough mixer (kneader). The composition can be obtained by blending the components (D) and (E) after performing a heat treatment as necessary to obtain a base compound.

In this case, the silicone rubber-based compound contains the above-mentioned organopolysiloxane and reinforcing silica as main components and, if necessary, non-reinforcing silica such as ground quartz, diatomaceous earth, acetylene black, furnace black, channel black and the like. Fillers such as carbon black, calcium carbonate, and ferrite, coloring agents, heat resistance improvers, fire resistance improvers, flame retardant improvers, acid acceptors, thermal conductivity improvers, and other various additives and release agents, Alternatively, as a filler dispersant, an organosilicon compound such as various alkoxysilanes, diphenylsilanediol, carbon functional silane, silanol group-containing low molecular siloxane,
An additive usually called a wetter may be blended. In particular, the organopolysiloxane represented by the following formula
It is preferable to add 0.1 to 20 parts by weight to 100 parts by weight of the components.

[0028]

Embedded image (N is an integer of 0 to 100, preferably 0 to 20.)

The silicone rubber sponge composition of the present invention comprises a foaming agent,
The silicone rubber sponge can be obtained by blending an organic peroxide, and the silicone rubber sponge composition thus obtained is easily foamed and cured by heating. The curing and foaming method may be a method of decomposing a foaming agent and applying sufficient heat to the silicone rubber, and the molding method is also particularly limited, such as continuous vulcanization by extrusion molding, tube foaming, pressing, and mold foaming by injection. Although not intended, the present invention preferably employs normal pressure hot air vulcanization. In this case, the heating temperature is preferably 100 to 500 ° C., particularly preferably 150 to 400 ° C., and the heating time is preferably several seconds to 1 hour, particularly preferably 10 seconds to 30 minutes. Also, if necessary, at 150 to 250 ° C., 1 to 10
Secondary vulcanization may be performed for about an hour.

[0030]

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.

[Example 1] Dimethylsiloxane unit 9
9.850 mol%, methylvinylsiloxane unit 0.1
25 mol%, dimethylvinylsiloxane unit 0.025
100% by weight of an organopolysiloxane [I] having an average degree of polymerization of about 8,000, 90.000% by mole of a dimethylsiloxane unit, 9.975% by mole of a methylvinylsiloxane unit, and 0.9% by mole of a dimethylvinylsiloxane unit. 025 mol%, with an average degree of polymerization of about 8,000
5 parts by weight of organopolysiloxane [II], 0 parts by weight, 45 parts by weight of fumed silica having a specific surface area of 200 m ² / g [Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.)], and having silanol groups at both terminals as a dispersant Then, 10 parts by weight of dimethylpolysiloxane having an average degree of polymerization of 13 and a viscosity of 15 cS at 25 ° C. is kneaded with a kneader,
Heat treatment was performed at 0 ° C. for 3 hours to prepare Compound 1.

2 parts by weight of azobisisobutyronitrile as a foaming agent and 0.5 parts by weight of paramethylbenzoyl peroxide and 1.0 part by weight of dicumyl peroxide are used as crosslinking agents with respect to 100 parts by weight of Compound 1 described above. Is mixed with two rolls to form a 2 mm thick sheet.
Heat treatment was performed at 50 ° C. for 10 minutes.

The obtained silicone rubber sponge has an expansion ratio of 350% and a sponge hardness (Asker C) of 32.
The diameter of the sponge cell was uniform at about 200 μm, and the surface was smooth.

Example 2 Dimethylsiloxane Unit 9
9.850 mol%, methylvinylsiloxane unit 0.1
25 mol%, dimethylvinylsiloxane unit 0.025
100 parts by weight of an organopolysiloxane [I] having an average degree of polymerization of about 8,000, 88.000 mol% of dimethylsiloxane units, 10.000 mol% of methylvinylsiloxane units, and 2 mol of trimethylvinylsiloxane units. %, An organopolysiloxane [III] having an average degree of polymerization of about 100, 3 parts by weight, a fumed silica having a specific surface area of 200 m ² / g [Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.)] 45 parts by weight, It has a silanol group at both terminals as a dispersant, an average degree of polymerization of 13,
10 parts by weight of dimethylpolysiloxane having a viscosity of 15 cS at 25 ° C. was kneaded in a kneader and heat-treated at 180 ° C. for 3 hours to prepare Compound 2.

With respect to 100 parts by weight of Compound 2, 2 parts by weight of azobisisobutyronitrile as a foaming agent, 0.5 parts by weight of paramethylbenzoyl peroxide and 1.0 part by weight of dicumyl peroxide as crosslinking agents Is mixed with two rolls to form a 2 mm thick sheet.
Heat treatment was performed at 50 ° C. for 10 minutes.

The obtained silicone rubber sponge has an expansion ratio of 350% and a sponge hardness (Asker C) of 30,
The diameter of the sponge cell was uniform at about 300 μm, and the surface was smooth.

Example 3 A silicone rubber sponge obtained according to Example 1 had an expansion ratio of 380 except that the amount of the organopolysiloxane [II] compounded in Example 1 was changed to 3 parts by weight. %, Sponge hardness (Asker C)
Was 27, the diameter of the sponge cell was about 550 μm, and the surface was smooth.

Example 4 2 parts by weight of azobisisobutyronitrile as a foaming agent and 0.5 parts by weight of benzoyl peroxide as a crosslinking agent were added to 100 parts by weight of the base compound 1 obtained in Example 1. And 1.0 part by weight of dicumyl peroxide were mixed with a two-roll mill to prepare a sheet having a thickness of 2 mm and heat-treated at 250 ° C. for 10 minutes.

The obtained silicone rubber sponge had an expansion ratio of 330% and a sponge hardness (Asker C) of 32.
The diameter of the sponge cell was uniform at about 200 μm, and the surface was smooth.

Example 5 Dimethylsiloxane Unit 9
9.850 mol%, methylvinylsiloxane unit 0.1
25 mol%, dimethylvinylsiloxane unit 0.025
100% by weight of an organopolysiloxane [I] having an average degree of polymerization of about 8,000, 97.000% by mole of dimethylsiloxane unit, 2.975% by mole of methylvinylsiloxane unit and 0.1% by mole of dimethylvinylsiloxane unit. 025 mol%, with an average degree of polymerization of about 8,000
5 parts by weight of the organopolysiloxane [III] which is 0,
Fumed silica having a specific surface area of 200 m ² / g [Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.)] 45 parts by weight, a silanol group at both terminals as a dispersant, an average degree of polymerization of 13, and a viscosity at 25 ° C. of 15 cS 10 parts by weight of dimethylpolysiloxane, which is
Heat treatment was performed at 0 ° C. for 3 hours to prepare Compound 3.

2 parts by weight of azobisisobutyronitrile as a foaming agent, 0.5 parts by weight of paramethylbenzoyl peroxide and 1.0 part by weight of dicumyl peroxide are used as crosslinking agents with respect to 100 parts by weight of the above compound 3. Is mixed with two rolls to form a 2 mm thick sheet.
Heat treatment was performed at 50 ° C. for 10 minutes.

The obtained silicone rubber sponge had an expansion ratio of 370% and a sponge hardness (Asker C) of 32.
The diameter of the sponge cell was uniform at about 500 μm, and the surface was smooth.

Comparative Example 1 Dimethylsiloxane Unit 9
9.850 mol%, methylvinylsiloxane unit 0.1
25 mol%, dimethylvinylsiloxane unit 0.025
% Of an organopolysiloxane [I] having an average degree of polymerization of about 8,000 and a specific surface area of 2
00m ² / g and a fumed silica [Aerosil 20
0 (manufactured by Nippon Aerosil Co., Ltd.)] 45 parts by weight, having a silanol group at both terminals as a dispersant, and having an average degree of polymerization of 13, 25
10 parts by weight of dimethylpolysiloxane having a viscosity at 15 ° C of 15 cS was kneaded with a kneader and heat-treated at 180 ° C for 3 hours to prepare Compound 4.

2 parts by weight of azobisisobutyronitrile as a foaming agent and 0.5 parts by weight of paramethylbenzoyl peroxide and 1.0 part by weight of dicumyl peroxide as crosslinking agents, based on 100 parts by weight of the above compound 4, Is mixed with two rolls to form a 2 mm thick sheet.
Heat treatment was performed at 50 ° C. for 10 minutes.

The obtained silicone rubber sponge had an expansion ratio of 300% and a sponge hardness (Asker C) of 33.
The diameter of the sponge cell was about 700 μm or more, and the cell was large and uneven at the surface, and large bubbles were generated in a part of the skin layer.

Comparative Example 2 Dimethylsiloxane Unit 9
9.850 mol%, methylvinylsiloxane unit 0.1
25 mol%, dimethylvinylsiloxane unit 0.025
100 parts by weight of an organopolysiloxane [I] having an average degree of polymerization of about 8,000, 99.500% by mole of dimethylsiloxane units, 0.475% by mole of methylvinylsiloxane units, and 0.1% by weight of dimethylvinylsiloxane units. 025 mol%, with an average degree of polymerization of about 8,000
5 parts by weight of organopolysiloxane [IV] of 0, 45 parts by weight of fumed silica having a specific surface area of 200 m ² / g [Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.)], and having silanol groups at both terminals as a dispersant Then, 10 parts by weight of dimethylpolysiloxane having an average degree of polymerization of 13 and a viscosity of 15 cS at 25 ° C. is kneaded with a kneader,
Heat treatment was performed at 0 ° C. for 3 hours to prepare Compound 5.

2 parts by weight of azobisisobutyronitrile as a foaming agent, and 0.5 parts by weight of paramethylbenzoyl peroxide and 1.0 part by weight of dicumyl peroxide as crosslinking agents, based on 100 parts by weight of the above compound 5, Is mixed with two rolls to form a 2 mm thick sheet.
Heat treatment was performed at 50 ° C. for 10 minutes.

The obtained silicone rubber sponge had an expansion ratio of 340% and a sponge hardness (Asker C) of 30,
The diameter of the sponge cell was about 700 μm or more, and the cell was large and uneven at the surface, and large bubbles were generated in a part of the skin layer.

[0049]

According to the present invention, even if an organic peroxide having no halogen is used, workability is not reduced.
A silicone rubber sponge composition having excellent foaming properties, a uniform and fine cell structure, a smooth skin layer and no tackiness can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Teruoka Sato 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture F-term in the Silicon Electronics Research Laboratory, Shin-Etsu Chemical Co., Ltd. 4F074 AA90 AC32 AG01 BA14 BB03 BB12 CA22 CA23 CA26 CC04X DA02 DA03 DA32 DA39 4J002 CP031 CP131 CP132 DJ016 EK038 EK048 EQ017 FD010 FD016 FD327 GL00 GM00

Claims (5)

[Claims] (A) Average composition formula (1) R ¹ _a SiO _{(4-a) / 2} (1) (wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group, and 100% by weight of an organopolysiloxane represented by the following formula: (B) an average composition of (B) an alkenyl group in an amount of from 0.001 mol% to less than 1.0 mol%, and a is a positive number from 1.98 to 2.02. Formula (2) R ² _a SiO _{(4-a) / 2} (2) (wherein, R ² is an unsubstituted or substituted monovalent hydrocarbon group, of which 1.0 to 20 mol% is an alkenyl group. A is a positive number from 1.98 to 2.02.) 0.1 to 20 parts by weight of an organopolysiloxane represented by the following formula: (C) silica for reinforcing filling 5 to 200 parts by weight, (D) Blowing agent selected from organic azo compounds 0.01 to 50 parts by weight, (E) halogen-free organic peroxide 0.1 to 10 parts by weight A silicone rubber sponge composition comprising: 2. The organic peroxide is represented by the following formula (3): (Wherein R is a hydrogen atom or an unsubstituted monovalent hydrocarbon group, m
Is an integer of 1 to 3. The silicone rubber sponge composition according to claim 1, which is an organic peroxide represented by the following formula: 3. The silicone rubber sponge composition according to claim 2, wherein the organic peroxide is selected from benzoyl peroxide, paramethylbenzoyl peroxide and orthomethylbenzoyl peroxide. 4. An organic peroxide comprising at least one organic peroxide represented by the formula (3) and dicumyl peroxide:
4. The method according to claim 1, wherein at least one organic peroxide selected from 2,5-dimethyl-2,5-di-t-butylperoxyhexane is used in combination. Silicone rubber sponge composition. 5. The silicone rubber sponge composition according to claim 1, wherein the foaming agent is azobisisobutyronitrile.