JPH11130896A - Production of silicone rubber sponge and silicone rubber sponge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process for carbon black-containing silicone rubber sponge that has excellent storage stability, well hardens with hot-air vulcanization or UHF vulcanization and gives silicone rubber sponge of high permanent compression set, a low specific gravity and fine cells with an average cell diameter of <=20 μm with high flame retardancy. SOLUTION: This silicone rubber composition comprises (A) 100 pts.wt. of a carbon black-containing addition reaction-curing type silicone rubber composition that gives 50% curing rate in one minute at 110-140 deg.C and (B) 0.1-50 pts.wt. of 1,1'-azo-bis(1-acetoxy-1-phenylethane) as a foaming agent. This rubber composition is vulcanized with hot air or UHF-vulcanized at 170-350 deg.C to give the objective silicone rubber sponge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicone rubber sponge containing carbon black and a silicone rubber sponge obtained by the method. The silicone rubber sponge obtained by the present invention has excellent storage stability and hot air. The silicone rubber sponge, which has been cured well by vulcanization or UHF vulcanization, has excellent compression set, low specific gravity, and an average cell system.
Since it has a fine cell of 200 μm or less and exhibits high flame retardancy at the same time, it is useful for conductive silicone rubber rolls for office machines and flame retardant sponge gaskets.

[0002]

BACKGROUND OF THE INVENTION Silicone rubber sponges containing carbon black are used as conductive silicone rubber sponges in conductive silicone rubber rolls for office machines and the like. However, in recent years, it has been desired to increase the resolution of a copying machine, a printer, and the like. As a result, toner particles have become smaller, and there has been a strong demand for finer cells in conductive silicone rubber sponges containing carbon. On the other hand, flame-retardant silicone rubber sponges are used as architectural gaskets and heat insulators, but those with a high blend of various fillers are used to increase flame retardancy in response to demands for improved flame retardancy. For this reason, the compression set characteristic deteriorates, and the basic characteristics as a sealing material decrease. In addition, there is also a problem that the specific gravity is high due to the high content of the filler, making it difficult to work. Conventionally, as a method for obtaining a silicone rubber sponge containing no carbon black, azobisisobutyronitrile as a foaming agent in the silicone rubber composition, an acyl peroxide such as benzoyl peroxide as a curing agent and dicumyl peroxide as a curing agent. It has been general to foam and harden by hot air vulcanization using an alkyl peroxide at the same time. However, in the case of silicone rubber containing carbon black, vulcanization is not performed with an acyl peroxide, so that a sponge having a fine cell structure could not be obtained. For this reason, JP-A-57-91250
JP-A-5-43802, JP-A-5-157908, JP-A-7-922841, JP-A-7-292146, JP-A-7-316330, and other organic peroxides. Products and foaming agents other than azobisisobutyronitrile have been proposed.
It was difficult to obtain a sponge having fine cells of m or less. Furthermore, in the hot air vulcanization, when an organic peroxide was used, vulcanization was inhibited by carbon black, and it was difficult to obtain a sponge rich in rubber elasticity with excellent compression set. For this reason, a molding method by die molding is also conceivable, but it requires a lot of time in the molding step as compared with hot air vulcanization and is industrially disadvantageous. It is known that a silicone rubber containing carbon black can be cured by an addition curing agent. Although it is possible to obtain a certain degree of fine cell sponge by blending azobisisobutyronitrile as a foaming agent here, the decomposition product of azobisisobutyronitrile is a platinum catalyst used as a catalyst for the addition curing agent. Because of the action of poisoning, the curing speed is slower than the foaming speed, and the balance between curing and foaming is lost, so that there is a limit to miniaturization of cells. In addition, in order to obtain a fine cell sponge, a large amount of a platinum catalyst must be blended. For this reason, there was a problem that the life (storage time) became very short and a part of the resin hardened before molding. As a method for obtaining a sponge from a silicone rubber composition containing carbon black utilizing an addition reaction, JP-A-7-247436, JP-A-8-253616
Publications have been proposed. However, azobisisobutyronitrile, azodicarbonamide, and dinitrosopentamethylenetetramine are used as the blowing agent, and azobisisobutyronitrile has a problem of poisoning the platinum catalyst. In this case, the compression set is inferior. On the other hand, a method using 1,1′-azo-bis (1-acetoxy-1-phenyl-ethane) as a foaming agent has been proposed in Japanese Patent Application Laid-Open No. 8-134250, but the average cell system is 200 μm. The following method for obtaining a sponge having fine cells is not described. As a method for obtaining a silicone rubber sponge by UHF vulcanization, a method in which ferrite powder is blended has been proposed. However, a large amount of ferrite powder needs to be blended. It was difficult to obtain a cell sponge. It is known to carry out UHF vulcanization by blending carbon black. However, when azobisisobutyronitrile is used as a blowing agent, there is a problem of the above-mentioned life.

[0003]

As described above, a silicone rubber sponge having fine cells having an average cell system of 200 μm or less can be easily produced from a silicone rubber composition containing carbon black simply by molding with hot air vulcanization or UHF vulcanization. A silicone rubber sponge which is difficult to obtain, has excellent compression set, has a low specific gravity, and exhibits high flame retardancy has not been obtained. In addition, it was difficult to obtain a sufficient life when trying to obtain a fine cell sponge to some extent. The present invention has been made to address such problems of the prior art, and has excellent storage stability and hot air vulcanization or UH
The silicone rubber sponge, which has been cured well by F vulcanization, has excellent compression set, low specific gravity, and has fine cells with an average cell system of 200 μm or less, and has high flame retardancy. An object of the present invention is to provide a method for producing a silicone rubber sponge containing black and a silicone rubber sponge obtained by the method.

[0004]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have excellent storage stability and can be cured well by hot air vulcanization or UHF vulcanization.
The obtained silicone rubber sponge is excellent in compression set, has a low specific gravity, and further has an average cell system having fine cells of 200 μm or less, and at the same time, has found a silicone rubber composition for sponge which exhibits high flame retardancy, The present invention has been completed. That is, the present invention relates to (B) foaming with respect to 100 parts by weight of an addition-curable silicone rubber composition containing carbon black, which has a temperature of 110 to 140 ° C. at which a curing rate of 50% can be obtained in one minute. Vulcanized silicone rubber composition for sponge containing 0.1 to 50 parts by weight of 1,1'-azo-bis (1-acetoxy-1-phenyl-ethane) as an agent at 170 to 350 ° C. Or a method for producing a silicone rubber sponge characterized by vulcanizing with UHF, a silicone rubber sponge having an average cell system of 200 μm or less, and a conductive sponge roll comprising the sponge. It is a sponge gasket.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, (A) the temperature at which a curing rate of 50% per minute is
The addition-curable silicone rubber composition containing carbon black at ~ 140 ° C comprises (a) an organopolysiloxane, (b) carbon black, and (c) an addition reaction curing agent as a curing agent. In addition, a reinforcing silica filler and various additives are blended and uniformly dispersed. The temperature to obtain 50% cure rate in one minute is 110 ~ 14
Must be 0 ° C. The curing rate referred to here is the torque when cured with a curast meter or rheometer at a specific temperature, and the torque when completely cured is 100%.
As a ratio to this. Complete curing refers to a state in which the torque reaches a certain value at a specific temperature (see FIGS. 1 to 1).
5). That is, when the temperature at which a 50% cure rate is obtained in one minute is 110 to 140 ° C., the balance between curing and foaming is good, and the foaming agent such as azobisisobutyronitrile is blended as the foaming agent. Since the decomposition product does not have the poisoning effect of the addition curing agent on the platinum catalyst, a silicone rubber sponge having an average cell system of 200 μm or less can be obtained. 50% in one minute
If the temperature at which the cure rate is lower than 110 ° C, the curing rate will be faster for foaming, the sponge cells will be larger, and if the temperature at which 50% cure rate per minute is higher than 140 ° C, The curing rate is too slow for foaming, and a sufficient foaming ratio cannot be obtained.

[0006] Among the various components used in such a silicone rubber composition, (a) organopolysiloxane is 1
It is necessary to have an alkenyl group bonded to at least two silicon atoms in the molecule. Organic groups other than alkenyl groups are monovalent substituted or unsubstituted hydrocarbon groups, such as alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group, dodecyl group, and phenyl group. Unsubstituted hydrocarbon groups such as an aryl group and an aralkyl group such as a β-phenylpropyl group; and substituted hydrocarbon groups such as a chloromethyl group and a 3,3,3-trifluoropropyl group. In general, a methyl group is frequently used because of ease of synthesis and the like. The average degree of polymerization of (a) organopolysiloxane is 3,000 to 30,000, and the degree of polymerization is
If it is less than 3,000, the mechanical strength of the silicone rubber sponge will decrease, and if the polymerization degree exceeds 30,000, it will be difficult to mix the filler and the workability will decrease. This polymer is desirably substantially linear, but may be partially branched as long as it can be used.

(B) As carbon black, commercially available carbon black may be used. For example, acetylene black, conductive furnace black (CF), superconductive furnace black (SCF), extra conductive furnace black (XCF), conductive channel black (CC), furnace black or channel black heat-treated at a high temperature of about 1500 ° C. Can be mentioned. Specific examples of acetylene black include electrified acetylene black (manufactured by Denki Kagaku) and Shaunigan acetylene black (manufactured by Shaunigan Chemical Co., Ltd.). Specific examples of the conductive furnace black include Continex CF (Continental Carbon Stocks). And Vulcan C (Cabot Co., Ltd.) are examples of Superconductive Furnace Black.
(Continental Carbon Co., Ltd.), Vulcan C
(Manufactured by Cabot Co., Ltd.), and as specific examples of the superconductive furnace black, Continex SCF (manufactured by Continental Carbon Co., Ltd.) and Vulcan SC (manufactured by Cabot Co., Ltd.) are provided. H
S-500 (made by Asahi Carbon Co., Ltd.), Vulcan XC-72
(Manufactured by Cabot Corporation) and the like, and examples of the conductive channel black include Colux L (manufactured by Degussa Co., Ltd.), and Ketchen Black EC and Ketchen Black EC-600 JD (a kind of furnace black). Ketjen Black International Co., Ltd.) can also be used. (b) The addition amount of the conductive carbon black is preferably 1 to 100 parts by weight based on 100 parts by weight of the polyorganosiloxane,
In particular, it is preferably 10 to 70 parts by weight. In order to obtain high flame retardancy, the addition amount is preferably 22 parts by weight or more, and also in the case of performing UHF vulcanization, the addition amount is preferably 20 parts by weight or more. (b) If the added amount of the conductive carbon black is less than 1 part by weight, the desired conductivity and flame retardancy may not be obtained, and if it exceeds 100 parts by weight, the mechanical strength of the cured product may be poor. is there.

[0008] Reinforcing silica filler to be added as required is a substance necessary for improving the processability, mechanical strength and the like of silicone rubber, and has been generally used in the past. Examples thereof include wet silica, fumed silica, silica aerogel, and calcined silica, and non-reinforcing silica such as crushed quartz and diatomaceous earth may be used in combination. These fillers may be used as they are, or may be surface-treated with organosiloxane, polyorganosiloxane, hexaorganodisilazane, or the like. The amount of the reinforcing silica filler is generally in the range of 1 to 100 parts by weight based on 100 parts by weight of the organopolysiloxane (a).
It is not particularly limited to this.

(C) The addition reaction curing agent comprises (c ₁ ) a curing catalyst, (c ₂ ) a cross-linking agent, and (c ₃ ) a retarder, and (c ₁ ) a curing catalyst includes chloroplatinic acid. Platinum catalysts such as platinum olefin complex, platinum vinyl siloxane complex, platinum black, platinum triphenylphosphine complex and the like are used. (C ₂ ) As a crosslinking agent, a hydrogen atom bonded to a silicon atom is contained in one molecule. Polyorganosiloxanes having an average number of at least more than 2 are used. (c ₁ ) The amount of the curing catalyst is (a) an organopolysiloxane and (b) carbon black,
Silicone rubber compound containing carbon black consisting of reinforcing silica filler compounded if necessary 100
On the other hand, an amount in the range of 1 to 1000 ppm in terms of platinum element amount is preferable. The compounding amount of the curing catalyst is 1 ppm as platinum element amount.
If it is less than 10, curing will not proceed sufficiently, and even if it exceeds 1000 ppm, no particular improvement in curing speed can be expected. Also, (c ₂ )
The amount of the crosslinking agent to be added is such that one alkenyl group in the component (a) has a hydrogen atom bonded to a silicon atom in the crosslinking agent of 0.1 to 0.1.
A quantity such as 10 is preferred, more preferably,
The amount is 0.5 to 5.0. The amount of hydrogen atoms is 0.
If the number is less than 1, the curing of the composition does not proceed sufficiently, the hardness after curing is low, and the amount of hydrogen atoms is low.
If it exceeds 4.0, the physical properties and heat resistance of the composition after curing are reduced. (c ₃ ) a retarder has an action of suppressing an addition curing reaction, for example, acetylene-based compounds such as acetylenic alcohols, nitrogen-containing compounds such as benzotriazole, maleic acid esters, maleic amides, maleic imides and the like Examples include unsaturated acid derivatives, azodicarboxylic acid esters, acrylonitrile compounds, and organic peroxides.

As other methods for suppressing the addition curing reaction, there have been proposed a method of sealing the curing catalyst in a thermoplastic resin or a silicone resin, and a method of supporting the curing catalyst on a porous filler. Any conventionally known addition reaction curing agent may be used.

The component (B) 1,1'-azo-bis (1-acetoxy-1-phenyl-ethane) is a foaming agent for obtaining a silicone rubber sponge. By adding to the addition-curable silicone rubber composition blended with carbon black, the curing rate of which is 110-140 ° C, it cures well in hot air vulcanization and UHF vulcanization, and is compressed permanently. Excellent strain, low specific gravity,
Furthermore, the average cell system has fine cells of 200 μm or less,
At the same time, it is possible to obtain a silicone rubber sponge exhibiting high flame retardancy. As described above, when azobisisobutyronitrile is used as the foaming agent, the decomposition product has the effect of poisoning the platinum catalyst used as the catalyst for the addition curing agent. There is a problem, and when other foaming agents are used, there are also problems in cell miniaturization and compression set, but 1,1'-azo-bis (1
-Acetoxy-1-phenyl-ethane) solves these problems. (B) The amount of the component is
(A) 0.1 to 50 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of the addition-curable silicone rubber composition of the component. If the amount of the component (B) is less than 1 part by weight, a sufficient expansion ratio cannot be obtained, and if the amount exceeds 50 parts by weight, the fineness of the cell is lost.

In addition to the above components, a semi-reinforcing or non-reinforcing filler can be added as long as the effect of the present invention is not impaired. Examples of the semi-reinforcing or non-reinforcing filler include metal carbonate, clay, talc, mica, titanium oxide and the like. Further, a heat-resistant additive, a flame retardant, an antioxidant, a processing aid, a conductivity-imparting agent other than carbon black, which are conventionally used in the silicone rubber composition, can also be blended.

The silicone rubber composition for sponge obtained as described above can be favorably foamed and cured by hot air vulcanization or UHF vulcanization. What is characteristic here is that the use of 1,1'-azo-bis (1-acetoxy-1-phenyl-ethane) as a foaming agent significantly improves the life (storage stability) after blending the curing agent. It is a point which becomes excellent. Hot air vulcanization and UHF vulcanization can be performed by a conventionally known method, and extrusion molding and the like are generally used. The foaming temperature of the hot air vulcanization is in the range of 170 to 350 ° C, preferably 190 to 300 ° C.
° C. If the temperature is lower than 170 ° C., the curing does not completely proceed, and if the temperature is higher than 350 ° C., the cells become coarse. The UHF vulcanization method usually uses radio waves around 2450 MHz and 915 MHz, absorbs this microwave and generates heat,
It foams and hardens, and when using UHF vulcanization, it is preferable to use hot air vulcanization in combination.

[0014]

According to the present invention, a silicone rubber composition containing carbon black is simply subjected to hot air vulcanization or UH
By F vulcanization, it cures and foams well, and has excellent storage stability. The obtained silicone rubber sponge has excellent compression set, low specific gravity, and average cell system.
It has fine cells of 200 μm or less and shows high flame retardancy. The obtained silicone rubber sponge is used for developing rolls, transfer rolls, cleaning rolls, pressure rolls, etc. of OA equipment such as gaskets, rolls, conductive rolls, and PPCs.
It is very useful as a paper feed roll, a heat insulating material, a cushion material, and the like.

[0015]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
In addition, the part in an Example represents a weight part. Example 1 100 parts of an organopolysiloxane having an average degree of polymerization of about 6000 and comprising 99.73 mol% of dimethylsiloxane units and 0.25 mol% of methylvinylsiloxane units, both ends of which are blocked with dimethylvinylsilyl groups, and dimethyldichlorosilane as a filler. 23 parts of fumed silica Aerosil R-972 (manufactured by Nippon Aerosil), 30 parts of acetylene black (manufactured by Denki Kagaku Kogyo), and 4 parts of dimethylsiloxane having a degree of polymerization of about 10 and both ends of which are blocked with hydroxyl groups. The base compound was prepared by mixing with an open kneader.
For 100 parts of this base compound, 1 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane (30 ppm based on the total weight of platinum) as a curing catalyst, and dimethylsiloxane / capped with trimethylsiloxy groups at both ends as a crosslinking agent. 1.0 part of methyl hydrogen siloxane copolymer (silicon-bonded hydrogen atom content is 0.8%)
0.01 part of 1-ethynyl-1-cyclohexanol as a curing inhibitor was mixed with a two-roll mill until uniform, to obtain an addition reaction type silicone rubber composition. The temperature for obtaining a cure rate of the base compound of 50% was investigated with a curast meter (JSR curast meter III). next,
1,1′-azo-bis (1-acetoxy-1-phenyl-ethane) 4 is added to 100 parts of this addition-reaction type silicone rubber composition.
Parts were blended and mixed with two rolls. The above silicone rubber compound is supplied to an extruder, and is extruded at 6 / min.
m, continuous extrusion was performed to obtain a tube-shaped silicone rubber compound having an outer diameter of about 40 mm and an inner diameter of about 20 mm. This was cut into a length of 50 cm and left in a dryer at 200 ° C. for 15 minutes to obtain a silicone rubber sponge. About the obtained silicone rubber sponge, specific gravity, surface condition, compression set (50% compression, 180 ° C., 22 hours) were measured, and a cell photograph was taken with an optical microscope to measure the cell diameter. A silicone rubber sponge was obtained in the same manner 24 hours after the preparation of the compound. Also for this silicone rubber sponge, specific gravity and compression set (50% compression,
(180 ° C, 22 hours) was measured, and the life was confirmed.

Example 2 1 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a curing catalyst (30 ppm based on the total weight of platinum) with respect to 100 parts of the base compound of Example 1,
As a cross-linking agent, 1.0 part of a dimethylsiloxane / methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (silicon-bonded hydrogen atom content: 0.8%) was added, and 1-ethynyl-1-cyclohexanol 0.005 as a curing inhibitor. The parts were mixed with a two-roll mill until uniform, to obtain an addition reaction type silicone rubber composition. The temperature for obtaining a degree of cure of the base compound of 50% was examined with a curast meter (JSR Curast Meter III).
Next, 100 parts of the addition reaction type silicone rubber composition
4 parts of 1'-azo-bis (1-acetoxy-1-phenyl-ethane) was blended and further mixed with two rolls. A silicone rubber sponge was obtained and tested in the same manner as in Example 1. In addition, the life was confirmed.

Example 3 To 100 parts of the base compound of Example 1, 0.4 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a curing catalyst (12 parts by weight of platinum as a total weight)
m), as a crosslinking agent, 1.0 part of a dimethylsiloxane / methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (silicon-bonded hydrogen atom content: 0.8%), and 0.04 part of diallyl maleate as a curing inhibitor Mixing was performed with two rolls until the mixture became uniform to obtain an addition reaction type silicone rubber composition. Curative meter (JSR)
Investigated with Curast Meter III). Next, 4 parts of 1,1′-azo-bis (1-acetoxy-1-phenyl-ethane) was mixed with 100 parts of the addition-reaction-type silicone rubber composition, and further mixed with a two-roll mill. A silicone rubber sponge was obtained and tested in the same manner as in Example 1. In addition, the life was confirmed.

Comparative Example 1 1.2 parts of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane was used as a curing catalyst with respect to 100 parts of the base compound of Example 1 (36 pp to the total weight of platinum).
m), as a crosslinking agent, 1.0 part of a dimethylsiloxane / methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (silicon-bonded hydrogen atom content: 0.8%), and 2,5-dimethyl- as a curing inhibitor 0.08 parts of 2,5-di (tert-butylperoxy) hexane was mixed with a two-roll mill until uniform, to obtain an addition reaction type silicone rubber composition. Base compound curing degree 50
% Was measured with a curastometer (JSR Curastometer III).

Next, 4 parts of 1,1'-azo-bis (1-acetoxy-1-phenyl-ethane) was blended with 100 parts of the addition-reaction-type silicone rubber composition, and further mixed with two rolls. . A silicone rubber sponge was obtained and tested in the same manner as in Example 1. In addition, the life was confirmed.

Comparative Example 2 1.5 parts of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane was used as a curing catalyst with respect to 100 parts of the base compound of Example 1 (45 parts by weight of platinum based on the total weight of platinum).
m), as a crosslinking agent, 1.0 part of a dimethylsiloxane / methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (silicon-bonded hydrogen atom content: 0.8%), 1.3 parts of triallylisocyanurate as a curing inhibitor Was mixed with two rolls until uniform, to obtain an addition reaction type silicone rubber composition. The temperature for obtaining a degree of cure of the base compound of 50% was examined with a curast meter (JSR Curast Meter III). Next, 4 parts of 1,1′-azo-bis (1-acetoxy-1-phenyl-ethane) was mixed with 100 parts of the addition-reaction-type silicone rubber composition, and further mixed with a two-roll mill. A silicone rubber sponge was obtained and tested in the same manner as in Example 1. In addition, the life was confirmed.

Comparative Example 3 1 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a curing catalyst (30 ppm based on the total weight of platinum) with respect to 100 parts of the base compound of Example 1,
As a cross-linking agent, 1.0 part of a dimethylsiloxane / methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both terminals (silicon-bonded hydrogen atom content: 0.8%) was added, and 1-ethynyl-1-cyclohexanol 0.001 as a curing inhibitor. The parts were mixed with a two-roll mill until uniform, to obtain an addition reaction type silicone rubber composition. The temperature for obtaining a degree of cure of the base compound of 50% was examined with a curast meter (JSR Curast Meter III).
Next, 100 parts of the addition reaction type silicone rubber composition
4 parts of 1'-azo-bis (1-acetoxy-1-phenyl-ethane) was blended and further mixed with two rolls. A silicone rubber sponge was obtained and tested in the same manner as in Example 1. In addition, the life was confirmed. These results are summarized in Table 1.

[0022]

[Table 1]

Example 4 As a filler, 100 parts of an organopolysiloxane having an average degree of polymerization of about 7000 and comprising 99.73 mol% of dimethylsiloxane units and 0.25 mol% of methylvinylsiloxane units, both ends of which are blocked with dimethylvinylsilyl groups. 35 parts of fumed silica Aerosil R-972 (manufactured by Nippon Aerosil) surface-treated with dimethyldichlorosilane, 30 parts of acetylene black (manufactured by Denki Kagaku Kogyo), and dimethylsiloxane having a degree of polymerization of about 10 in which both molecular terminals are blocked with hydroxyl groups. Six parts were mixed with an open kneader to prepare a base compound. For 100 parts of this base compound, 1 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane (30 ppm based on the total weight of platinum) as a curing catalyst, and dimethylsiloxane / capped with trimethylsiloxy groups at both ends as a crosslinking agent. 1.0 part of a methylhydrogensiloxane copolymer (silicon-bonded hydrogen atom content: 0.8%) was added, and 1-ethynyl-1-cyclohexanol was used as a curing inhibitor.
0.01 part was mixed with a two-roll mill until uniform, to obtain an addition reaction type silicone rubber composition. The temperature for obtaining a degree of cure of the base compound of 50% was examined with a curast meter (JSR Curast Meter III). Next, 4 parts of 1,1′-azo-bis (1-acetoxy-1-phenyl-ethane) was mixed with 100 parts of the addition-reaction-type silicone rubber composition, and further mixed with a two-roll mill. The above silicone rubber compound is cut into approximately 50 × 50 × 5 mm,
UHF cured at 2450 MHz for 2 minutes. About the obtained silicone rubber sponge, specific gravity, surface condition, compression set (50% compression, 180 ° C., 22 hours) were measured, and a cell photograph was taken with an optical microscope to measure the cell diameter. Further, in order to examine the flame retardancy, the oxygen index (test specimen supporting method: A-1) was measured according to JIS K7201 of sponge.

Comparative Example 4 50 parts of ferrite powder and 1 part of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a flame retardant (100 parts of the base compound of Example 4 with respect to the total weight of platinum) 30 ppm) in an open kneader to obtain a flame-retardant silicone rubber composition. Next, 1 part of paramethylbenzoyl peroxide, 1 part of dicumyl peroxide as a vulcanizing agent, and 2 parts of azobisisobutyronitrile as a foaming agent were mixed with two rolls. The specific gravity, surface condition, and compression set (50% compression, 180 ° C., 22 hours) of the silicone rubber sponge obtained in the same manner as in Example 4 were measured, and a cell photograph was taken with an optical microscope. The diameter was measured.

In order to check the flame retardancy, the sponge JIS
Oxygen index according to K 7201 (test specimen support method: A-1)
Was measured. Table 2 shows the results.

[0026]

[Table 2]

Comparative Example 5 The addition reaction type silicone rubber composition of Example 1 was added to 100 parts
AIBN (azobisisobutyronitrile) 2 parts was blended in place of 1,1'-azo-bis (1-acetoxy-1-phenyl-ethane), and continuous extrusion was carried out in the same manner. Poisoned and did not cure. Comparative Example 6 3 parts of a platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a curing catalyst (90 parts by weight based on the total weight of platinum)
ppm) was used, and continuous extrusion was performed in the same manner as in Comparative Example 5 to obtain a silicone rubber sponge. The specific gravity was 0.50 and the surface condition was good, but the compression set was very bad at 89%. The average cell diameter is
It was 320 μm. After 24 hours, the top compound was observed, and it was found that it had completely cured and had become a rubber.

[Brief description of the drawings]

FIG. 1 In an addition-curable silicone rubber composition,
4 is a graph schematically showing a relationship between a curing time and a curing rate when a temperature at which a 50% curing rate in one minute is obtained is 120 ° C.

FIG. 2 In an addition-curable silicone rubber composition,
4 is a graph schematically showing a relationship between a curing time and a curing rate when a temperature at which a 50% curing rate in one minute is obtained is 140 ° C.

FIG. 3 In an addition-curable silicone rubber composition,
4 is a graph schematically showing a relationship between a curing time and a curing rate when a temperature at which a 50% curing rate in one minute is obtained is 110 ° C.

FIG. 4 shows an addition-curable silicone rubber composition.
4 is a graph schematically showing the relationship between the curing time and the curing rate when the temperature at which a 50% curing rate in one minute is obtained is 150 ° C.

FIG. 5 In an addition-curable silicone rubber composition,
4 is a graph schematically showing the relationship between the curing time and the curing rate when the temperature at which a 50% curing rate in one minute is obtained is 90 ° C.

Claims (5)

[Claims] (A) The temperature at which a curing rate of 50% is obtained in one minute is
With respect to 100 parts by weight of an addition-curable silicone rubber composition containing carbon black at 110 to 140 ° C., (B)
1,1'-azo-bis (1-acetoxy-1-
A method for producing a silicone rubber sponge, which comprises subjecting a silicone rubber composition for a sponge, containing 0.1 to 50 parts by weight of phenyl-ethane), to hot air vulcanization at a temperature of 170 to 350 ° C. (2) The temperature at which a curing rate of 50% can be obtained in one minute.
With respect to 100 parts by weight of an addition-curable silicone rubber composition containing carbon black at 110 to 140 ° C., (B)
1,1'-azo-bis (1-acetoxy-1-
(Phenyl-ethane) is blended in an amount of 0.1 to 50 parts by weight, and a silicone rubber composition for a sponge is vulcanized by UHF. 3. A silicone rubber sponge having an average cell system of 200 μm or less, produced by the method according to claim 1. 4. A conductive roll using a silicone rubber sponge produced by the method according to claim 1. 5. A flame-retardant sponge gasket using a silicone rubber sponge produced by the method according to claim 1.