JP2007302827A - High-open cell-content silicone rubber sponge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-open cell-content silicone rubber sponge having uniform and fine cell structure, producible in high productivity by ordinary-pressure hot air vulcanization(HAV) without the need of considering the delicate balance regarding rubber crosslinking rate control and foam gas generation rate. <P>SOLUTION: The high-open cell-content silicone rubber sponge 20% or higher in open cell content is obtained by expanding and curing a silicone rubber composition comprising (A) 100 pts.mass of a base material that is obtained by blending reinforcing silica with an organopolysiloxane of the average composition formula(I):R<SP>1</SP><SB>a</SB>SiO<SB>(4-a)/2</SB>[ wherein, R<SP>1</SP>is a (substituted) monovalent hydrocarbon group; and (a) is a positive number of 1.95-2.04 ] having in one molecule at least two alkenyl groups bound to a silicon atom, (B) 0.5-50 pts.mass of an organic foaming agent, (C) an effective amount of a curing agent and (D) 0.1-20 pts.mass of wet silica. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a construction gasket, various sponge sheets, a sponge for water absorption, a heat insulating sheet, an industrial roll, a copier, a facsimile machine, an image forming apparatus such as a printer, and a sponge roll for office machines, particularly a toner fusing fixing roll, The present invention relates to a high open-cell silicone rubber sponge used for paper rolls, toner transport rolls, cleaning rolls, and the like.

  Silicone rubber sponge has physical characteristics peculiar to silicone rubber, and is excellent in heat resistance, cold resistance, electrical insulation, flame resistance, compression set resistance, and the like. The silicone rubber sponge can be basically formed by combining a thermosetting silicone rubber composition, a curing agent, and a foaming agent, and foaming and curing by heating. In that case, it is important to obtain a sponge that has excellent foamability, has a uniform and fine cell structure, and does not impair the physical properties peculiar to silicone rubber.

  Further, as a processing and molding method, curing and foaming are often performed in normal-pressure hot air that enables continuous molding. In order to make a sponge having a uniform and fine cell structure by molding in normal pressure hot air, the gas generated when the foaming agent decomposes must be pressed into the rubber in the form of fine bubbles. Therefore, normally, before the foaming agent is decomposed, the rubber composition needs to be thickened and cured so as to overcome the foaming pressure and hold the bubbles inside.

Therefore, the following order is common as the reaction order that occurs in the rubber when the sponge is molded.
1) Viscosity (curing) of the base polymer organopolysiloxane with a curing agent, and rubber surface curing.
2) Gas generation due to decomposition of foaming agent, sponge cell formation.
3) Complete curing of the base polymer, organopolysiloxane.
In practice, the reaction may be controlled by adjusting the amount of addition crosslinking reaction catalyst so that the reactions occur in the above order, or the decomposition temperature of the organic peroxide may be selected to be the same as or lower than the decomposition temperature of the blowing agent. The reaction sequence as described above is set.

  Thus, since a normal sponge is created by a method in which the foaming pressure is suppressed by cross-linking, the sponge cell is usually a closed cell, the open cell rate is 10% or less, and air is trapped in it. It is in a state. When a sponge molded product in which the sponge cell is an independent foam is heated, the trapped air is thermally expanded by the Boyle Charles' law. As a result, a sponge that fills a closed space such as a gasket material has a strong air spring component and high sponge hardness. In the case of a roll material such as a fixing sponge roll, the sponge diameter increases due to thermal expansion, and the fixing pressure changes. On the contrary, when the sponge roll is cooled, the set interval between the heater roll and the backup roll becomes wide, and the roll rattles and becomes a source of abnormal noise. Especially in recent office machines equipped with a fixing sponge roll, there are an increasing number of models in which the fixing sponge roll is colder than the normal fixing temperature in the standby state from the viewpoint of power saving. Therefore, there is a demand for a sponge having a high open cell ratio in which the sponge cell diameter tends to be constant regardless of the heating temperature.

  In Patent Document 1, 1,6-bis (t-butylperoxycarboxy) hexane (peroxyester system, decomposition temperature: as a foaming system in which a non-acyl organic peroxide bridge and an organic azo compound are used in combination. 163 ° C.) and a sponge using AIBN (azoisobutyronitrile) as a blowing agent has been proposed. Since carbon inhibits crosslinking by an organic peroxide, the conductive silicone rubber composition containing carbon cannot normally be vulcanized at normal pressure by an acyl organic peroxide. Patent Document 1 discloses a technique for obtaining a good sponge by using an organic peroxide that can vulcanize a conductive silicone rubber composition containing carbon at normal pressure and has excellent surface curability. However, the cell of the sponge obtained is a closed cell, and is not a technique for increasing the sponge cell rate, and there is no description of the cell rate.

Patent Document 2 describes a silicone rubber sponge composition that is foamed with crystal water of an inorganic salt, but does not describe open-cell sponge.
JP-A-5-43802 JP-A-5-156061

  The present invention has been made to overcome the above problems, and is manufactured by atmospheric pressure hot air vulcanization (HAV) without considering the delicate balance of the rubber crosslinking rate control and foaming gas generation rate. An object of the present invention is to provide a high-open-cell silicone sponge having excellent productivity and a uniform and fine cell structure.

As a means for achieving the above object, the present invention provides:
(A) The following average composition formula (I):
R ¹ _a SiO _{(4-a) / 2} (I)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.04.)
A base material obtained by mixing an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule and reinforcing silica, followed by heat treatment: 100 parts by mass
(B) Organic foaming agent: 0.5 to 50 parts by mass,
(C) Curing agent: effective amount, and
(D) Wet silica: A high open-cell silicone rubber sponge having a open-cell rate of 20% or more obtained by foaming and curing a silicone rubber composition containing 0.1 to 20 parts by mass is provided.

  According to the present invention, a silicone with a high open-cell ratio is obtained by blending wet silica in a silicone rubber base (component (A)) after heat treatment and performing atmospheric pressure hot-air vulcanization using a curing agent and an organic foaming agent. A rubber sponge can be obtained.

  Hereinafter, the present invention will be described in detail.

-Component (A)-
The component (A) is obtained by heat-treating an organopolysiloxane represented by the above average composition formula (I) and having at least two alkenyl groups bonded to silicon atoms in one molecule and reinforcing silica. Base material (hereinafter, also referred to as “silicone rubber base material of component (A)”). Component (A) may be used alone or in combination of two or more.

In the average compositional formula (I) of organopolysiloxane , R ¹ is, for example, the same or different unsubstituted or substituted, preferably monovalent carbon having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. A hydrogen group is mentioned. Specific examples of R ¹ include alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, and a dodecyl group; a cycloalkyl group such as a cyclohexyl group; a vinyl group, an allyl group, a butenyl group, and a hexenyl group. An aryl group such as a phenyl group and a tolyl group; an aralkyl group such as a β-phenylpropyl group; or a part or all of hydrogen atoms bonded to carbon atoms of these hydrocarbon groups as a halogen atom, a cyano group, etc. And a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like substituted with. Among these, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable. In particular, the ratio of the methyl group to the total R ¹ is preferably 80 to 99.999 mol%, and 95 to 99.99 mol % Is more preferable.

  In the average composition formula (I), a is a positive number of 1.95 to 2.04. This organopolysiloxane is substantially linear, specifically a linear diorganopolysiloxane whose main chain is mainly composed of diorganosiloxane units, but the rubber elasticity of the cured silicone rubber sponge. Branches may be made within a range not to be damaged.

  The organopolysiloxane may have a molecular chain end blocked with a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like.

This organopolysiloxane has at least two alkenyl groups bonded to silicon atoms in one molecule, and specifically, 0.001 to 5 mol%, particularly 0.01 to 0.5 mol, of R ^1. % Is preferably an alkenyl group, especially a vinyl group.

  This organopolysiloxane is usually obtained by hydrolytic condensation of one or more of the corresponding organohalosilanes according to the ratio of siloxane units contained in the structure, or by cyclic organopolysiloxane (organosiloxane). And the like, and the like can be obtained by ring-opening polymerization using an alkaline or acidic catalyst.

The average degree of polymerization of the organopolysiloxane is a mass average degree of polymerization, preferably 200 to 20,000, more preferably 2,000 to 10,000, and still more preferably 3,000 to 8,000. is there. When the average degree of polymerization is within this range, the silicone rubber base material of component (A) can be easily blended with the composition of the present invention, and the viscosity of the composition after blending can be easily maintained at an appropriate height. It is easy to obtain a sufficient rubber feeling in the cured product. The average degree of polymerization was determined by measuring the number average molecular weight by GPC (gel permeation chromatography) using polystyrene as a molecular weight marker.
Number average degree of polymerization = number average molecular weight / (A) The molecular weight of the repeating unit of the component (A) can be calculated and obtained. When a plurality of types of repeating units are contained in the component (A), the “molecular weight of the repeating unit of the component (A)” in the above formula is the number average molecular weight of these types of repeating units.

  This organopolysiloxane may be used alone or in combination of two or more different in molecular structure, average polymerization degree and the like.

Reinforcing silica Reinforcing silica is used to obtain a silicone rubber sponge with excellent mechanical strength. For this purpose, the specific surface area of the reinforcing silica is preferably 50 m ² / g or more, more preferably 100 to 400 m ² / g. Examples of the reinforcing silica include fumed silica (dry silica) and precipitated silica (wet silica), and fumed silica (dry silica) is preferable. Further, these surfaces may be hydrophobized with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. The reinforcing silica may be used alone or in combination of two or more. The amount of reinforcing silica added is preferably 5 to 100 parts by mass, more preferably 10 to 90 parts by mass, and particularly preferably 30 to 80 parts by mass per 100 parts by mass of the organopolysiloxane. When the addition amount is within this range, the reinforcing effect by the reinforcing silica tends to be sufficient, and the processability of the resulting composition and the physical properties of the resulting silicone rubber sponge tend to be good.

  In order to disperse the reinforcing silica in the organopolysiloxane, it is preferable to add a dispersing agent such as trimethylsilanol, diphenylsilanediol, hexamethylsilazane, polydimethylsiloxane having a hydroxyl group at the molecular chain terminal. The amount of the dispersing agent is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass per 100 parts by mass of the reinforcing silica.

  The organopolysiloxane, the reinforcing silica, preferably the dispersant is mixed by a method using a conventionally known roll mill or kneader, and then the resulting mixture is heat treated by a method using a conventionally known kneader or dryer. Thus, the silicone rubber base material of component (A) is obtained. The heat treatment is performed for the purpose of removing volatile components or for promoting the reaction between the reinforcing silica and the dispersant. The heat treatment is performed, for example, by heating the mixture at a temperature in the range of 100 ° C. to 250 ° C., preferably 150 to 220 ° C. for 1 to 6 hours.

-(B) component-
Examples of the organic foaming agent of component (B) include nitroso compounds such as N, N′-dimethyl-N, N′-dinitrosoterephthalamide and N, N′-dinitrosopentamethylenetetramine; dimethyl 1,1 ′ -Azobis (1-cyclohexanecarboxylate), azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis -2,4-dimethylvaleronitrile, 1,1'-azobis (1-acetoxy-1-phenylethane), azodicarbonamide, barium azodicarboxylate, 1,1'-azobis (cyclohexane-1-methylcarboxylate) ), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis [N- (2-propenyl) -2-methylpropionamide] and the like; Zensulfonyl hydrazide, toluenesulfonyl hydrazide, p, p'-oxybis (benzenesulfonyl hydrazide), diphenylsulfone-3,3'-disulfonyl hydrazide, 4,4'-oxybis (benzenesulfonyl hydrazide), p-toluenesulfonyl hydrazine, etc. And azide compounds such as calcium azide, 4,4-diphenyldisulfonyl azide, and p-toluenesulfuronyl azide. Among them, organic azo compounds having no sulfur compounds, phosphates, strong amines, etc. that inhibit the curing of silicone rubber in the molecule, such as dimethyl 1,1′-azobis (1-cyclohexanecarboxylate), azobisiso Butyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobis (1-acetoxy-1-phenylethane), 1,1'-azobis (cyclohexane-1-methylcarboxylate), 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis [N- (2-propenyl) -2-methylpropion Amide] and the like are preferable. (B) A component may be used individually by 1 type, or may be used in combination of 2 or more type.

  The amount of the foaming agent added as the component (B) is usually 0.5 to 50 parts by mass, preferably 1.0 to 20 parts by mass with respect to 100 parts by mass of the silicone rubber base material as the component (A). If the amount added is less than 0.5 parts by mass, the amount of generated gas tends to be insufficient, so that the resulting cured product is unlikely to be in a sponge state, and the open cell rate is difficult to increase. When the added amount exceeds 50 parts by mass, it may be physically difficult to mix the component (B) with other components, and the amount of gas generated at the time of sponge molding increases, so the cells are not uniform. Or the resulting sponge may crack from the inside.

-(C) component-
The curing agent of component (C) is not particularly limited as long as it can cure the rubber composition of the present invention. Preferred examples thereof include (i) organohydrogenpolysiloxane known as a curing agent for rubber. And a combination of hydrosilylation catalyst, (ii) organic peroxide, and (i) and (ii).

(I) Combination of organohydrogenpolysiloxane and hydrosilylation catalyst / hydrosilylation catalyst The curing agent (i) is a curing agent utilizing crosslinking by addition reaction. The hydrosilylation catalyst used in this addition reaction includes an aliphatic unsaturated group (alkenyl group, diene group, etc.) in component (A) and a silicon atom-bonded hydrogen atom of organohydrogenpolysiloxane in curing agent (i). (Ie SiH group) is a catalyst for addition reaction. A hydrosilylation catalyst may be used individually by 1 type, or may be used in combination of 2 or more type.

  Examples of the hydrosilylation catalyst include a platinum group metal catalyst such as a platinum group metal simple substance or a compound thereof. As the platinum group metal catalyst, conventionally known catalysts can be used as the catalyst for the addition reaction curable silicone rubber composition. Specific examples thereof include particulate platinum metal adsorbed on a support such as silica, alumina or silica gel, platinous chloride, chloroplatinic acid, chloroplatinic acid hexahydrate alcohol solution, palladium catalyst, rhodium catalyst, etc. However, those containing platinum as the platinum group metal are preferable.

  The addition amount of the hydrosilylation catalyst may be an effective amount that can promote the above addition reaction, and is usually 1 ppm (mass basis, hereinafter the same) to 1 mass in terms of the component (A) in terms of the platinum group metal amount. %, Preferably 10 to 500 ppm. If the addition amount is within this range, the addition reaction is likely to be sufficiently promoted, the curing and foaming are likely to be sufficient, and the rate of the addition reaction is easily improved as the addition amount increases. It tends to be economically advantageous.

  In addition to the above catalyst, an addition crosslinking controller may be used for the purpose of adjusting the curing rate. Specific examples thereof include ethynylcyclohexanol and tetracyclomethylvinylpolysiloxane.

Organohydrogen polysiloxane The organohydrogen polysiloxane may be either linear or cyclic as long as it contains 2 or more, preferably 3 or more SiH groups in one molecule, and is branched. It may be. Organohydrogenpolysiloxanes may be used singly or in combination of two or more. As such an organohydrogenpolysiloxane, a known organohydrogenpolysiloxane can be used as a crosslinking agent for an addition reaction curable silicone rubber composition. For example, the following average composition formula (V):
R ⁶ _p H _q SiO _{(4-pq) / 2} (V)
Wherein R ⁶ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and p and q are 0 ≦ p <3, 0 <q ≦ 3, and 0 <p + q ≦ 3, preferably It is a positive number satisfying 1 ≦ p ≦ 2.2, 0.002 ≦ q ≦ 1, and 1.002 ≦ p + q ≦ 3.)
An organohydrogenpolysiloxane represented by the formula can be used.

In the above average composition formula (V), R ⁶ is the same or different unsubstituted or substituted, preferably a monovalent hydrocarbon group having 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, It is preferable not to contain a group unsaturated bond. Specific examples of R ⁶ include alkyl groups such as methyl group, ethyl group, and propyl group; cycloalkyl groups such as cyclohexyl group; alkenyl groups such as vinyl group, allyl group, butenyl group, hexenyl group; phenyl group, tolyl group Aryl groups such as benzyl groups, 2-phenylethyl groups, 2-phenylpropyl groups, and the like; and groups in which some or all of the hydrogen atoms of these hydrocarbon groups are substituted with halogen atoms such as fluorine atoms For example, a 3,3,3-trifluoropropyl group etc. are mentioned.

When the organohydrogenpolysiloxane is linear, the SiH group may be present only at one or both of the molecular chain terminal and the non-molecular chain terminal. It is preferable that the viscosity at 25 ° C. of the organohydrogenpolysiloxane is 0.5~10,000mm ² / s, particularly preferably 1 to 300 mm ² / s.

  Specific examples of such organohydrogenpolysiloxanes include compounds having the following structural formula.

（式中、ｋは２〜１０の整数、ｓ及びｔは０〜１０の整数である。）

(In the formula, k is an integer of 2 to 10, and s and t are integers of 0 to 10.)

  The amount of the organohydrogenpolysiloxane is preferably the number of SiH groups in the organohydrogenpolysiloxane per one aliphatic unsaturated bond (alkenyl group, diene group, etc.) in the component (A). The amount is 0.5 to 10, more preferably 0.7 to 5. When the blending amount is within this range, crosslinking is likely to be sufficient, and after curing, mechanical strength is likely to be sufficient, and other physical characteristics, particularly heat resistance and compression set resistance, are easily maintained. Such a compounding amount is, for example, preferably by adding 0.1 to 40 parts by mass, more preferably 0.2 to 10 parts by mass of the organohydrogenpolysiloxane with respect to 100 parts by mass of the component (A). realizable.

(Ii) Organic peroxide The organic peroxide is a vulcanizing agent used for curing the component (A). An organic peroxide may be used individually by 1 type, or may be used in combination of 2 or more type. Examples of the organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, and 2,5-dimethyl. -Bis (2,5-t-butylperoxy) hexane, di-t-butylperoxide, t-butylperbenzoate, 1,6-hexanediol-bis-t-butylperoxycarbonate and the like.

  The addition amount of the organic peroxide may be an effective amount as a vulcanizing agent. Specifically, it is preferably 0.1 to 15 parts by mass, particularly preferably 0.2 to 100 parts by mass with respect to 100 parts by mass of the component (A). 10 parts by mass. If the addition amount is within this range, the curing rate tends to improve as the addition amount increases, so that it tends to be economically advantageous, and the uncured product and decomposition residue are shortened from the resulting cured product. Easy to remove in time.

-(D) component-
Component (D), wet silica, is used to obtain a silicone foam sponge with a high ream rate. For this purpose, the specific surface area of precipitated silica of the component (D) is preferably 50 m ² / g or more, more preferably 100 to 400 m ² / g. As the component (D), for example, NIPSIL (registered trademark) -LP (trade name, manufactured by Tosoh Silica Corporation), Toxeal (registered trademark) USA (trade name, manufactured by Tokuyama Corporation), Zeosil (registered trademark) 132 ( Product name, manufactured by Rhodia Japan). These surfaces may be hydrophobized with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, etc., but untreated wet silica that has not been hydrophobized is preferred. Component (D) may be used alone or in combination of two or more.

  (D) The addition amount of a component is 0.1-20 mass parts per 100 mass parts of (A) component, Preferably it is 1-10 mass parts, Most preferably, it is 1-5 mass parts. When the added amount is less than 0.1 parts by mass, it is difficult to obtain a silicone rubber sponge having a sufficient open cell ratio. When the added amount is more than 20 parts by mass, the processability of the resulting composition is likely to deteriorate, and the physical properties of the resulting silicone rubber may be deteriorated.

-Other ingredients-
The silicone rubber sponge of the present invention can be made into a conductive sponge by adding a conductive substance. The type and amount of the conductive material are not limited, but as the conductive material, conductive carbon black, conductive metal oxide fine particles such as conductive zinc white, conductive titanium oxide, and the like can be preferably used. Conductive substances may be used alone or in combination of two or more. Since carbon is an inhibitor of cross-linking by organic peroxide, when adding conductive carbon black to silicone rubber composition containing organic peroxide, increase the amount of organic peroxide or the above-mentioned high temperature type addition It is desirable to use a combination of a curing agent, that is, an organohydrogenpolysiloxane and a hydrosilylation catalyst, together with the organic peroxide.

  As the conductive carbon black, those commonly used in conductive rubber compositions can be used, for example, acetylene black, conductive furnace black (CF), super conductive furnace black (SCF), extra conductive furnace. Examples thereof include black (XCF), conductive channel black (CC), and furnace black or channel black heat-treated at a high temperature of about 1500 to 3000 ° C. Specific examples of acetylene black include Denka Black (trade name, manufactured by Denki Kagaku Kogyo Co., Ltd.), Shaunigan Acetylene Black (trade name, manufactured by Shaunigan Chemical Co., Ltd.), and the like. Specific examples of conductive furnace black include CONTINEX CF (trade name, manufactured by Continental Carbon), Vulcan C (trade name, manufactured by Cabot), and the like. Specific examples of super conductive furnace black include CONTINEX SCF (trade name, manufactured by Continental Carbon Corporation), Pulcan SC (trade name, manufactured by Cabot Corporation), and the like. Specific examples of extra conductive furnace black include Asahi HS-500 (trade name, manufactured by Asahi Carbon Co., Ltd.), Vulcan XC-72 (trade name, manufactured by Cabot Corp.), and the like. Specific examples of the conductive channel black include KOLAX L (trade name, manufactured by Degussa). Further, Ketjen Black (registered trademark) EC and Ketjen Black EC-600JD (both trade names, manufactured by Ketjen Black International Co., Ltd.), which are a kind of furnace black, can also be used. In furnace black, the amount of impurities, particularly the amount of sulfur and sulfur compounds, is preferably 6000 ppm or less, more preferably 3000 ppm or less in terms of mass in terms of elemental sulfur. Of these, acetylene black has a low impurity content and has a developed secondary structure structure, which is excellent in conductivity, and is particularly preferably used in the present invention. In addition, since Ketjen Black EC, Ketjen Black EC-600JD, etc. exhibiting excellent conductivity even at a low filling amount can be preferably used since it has a large specific surface area.

  The amount of the conductive carbon black added is preferably 1 to 100 parts by mass, particularly preferably 5 to 50 parts by mass with respect to 100 parts by mass of the silicone rubber base material of the component (A) described above. When the addition amount is within this range, desired conductivity can be easily obtained, physical mixing with the resulting composition is facilitated, and a cured product having sufficient mechanical strength and desired rubber elasticity can be obtained. Cheap.

  Examples of the conductive metal oxide fine particles include conductive zinc white (conductive zinc oxide), titanium oxide (for example, white conductive titanium oxide), and tin antimony oxide fine particles. Specific examples of the conductive zinc oxide include zinc oxide 23-K (trade name) manufactured by Hakusui Tech Co., Ltd. and conductive zinc white FX (trade name) manufactured by Honjo Chemical Co., Ltd. Examples of white conductive titanium oxide include ET-500W (trade name, manufactured by Ishihara Sangyo Co., Ltd.). The conductive metal oxide fine particles may be used alone or in combination of two or more. Further, conductive metal oxide fine particles may be used in combination with conductive carbon black. The amount of the conductive metal oxide fine particles added is preferably 1 to 300 parts by mass, more preferably 1 to 100 parts by mass with respect to 100 parts by mass of the silicone rubber base material of the component (A) described above. . When the added amount is within this range, desired conductivity is easily obtained.

  If necessary, the silicone rubber composition of the present invention may further include pulverized quartz, zinc oxide, alumina, aluminum oxide as a thermal conductivity imparting agent, and diatomaceous earth as non-reinforcing silica. Additives such as fillers, coloring agents, heat resistance improvers, flame retardant improvers, acid acceptors, thermal conductivity improvers, mold release agents, alkoxysilanes, diphenylsilanediols, carbon functional silanes, silanols at both ends A dispersant such as a blocked low-molecular siloxane may be added.

-Manufacturing method-
Although the manufacturing method of the rubber composition of this invention is not specifically limited, It can obtain by knead | mixing the predetermined amount of the component mentioned above with a 2 roll mill, a kneader, a Banbury mixer, etc. If necessary, heat treatment (kneading under heating) may be performed. Specifically, component (A) and other components are kneaded and heat-treated to obtain a base rubber compound (silicone rubber substrate of component (A)), and then cooled to the base rubber compound (B), (C) And a method of adding the component (D). Although the temperature and time of the heat treatment are not particularly limited, for example, the heat treatment is performed at 100 to 250 ° C., preferably 150 to 200 ° C. for 30 minutes to 5 hours.

-Foam curing method-
In order to increase the open cell ratio of the sponge cell, the method of curing and foaming the rubber composition of the present invention is preferably atmospheric pressure hot air vulcanization, continuous vulcanization by a heating furnace using extrusion molding, hot air crosslinking by a batch dryer. Etc. are preferably employed. If a sufficient space is secured inside the mold, mold vulcanization can also be suitably used. In general, a high open-cell sponge can be obtained by foaming and curing at 80 to 400 ° C., particularly 100 to 300 ° C. for about 5 seconds to 1 hour by normal pressure hot air vulcanization. Moreover, you may post-cure about 10 minutes-10 hours at 100-230 degreeC, Preferably 150-230 degreeC.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In addition, a part shows a mass part by the following example, and a viscosity shows the value measured with the rotational viscometer.

[Example 1]
100 parts of an organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000,
40 parts dry silica Arosil 200 (trade name, manufactured by Nippon Aerosil Co., Ltd.) with a BET surface area of 200 m ² / g,
5 parts of dimethylpolysiloxane having silanol groups at both ends and having a viscosity of 29 mm ² / s (23 ° C.) are put into a kneader and kneaded under heat treatment at 180 ° C. for 2 hours to form a base rubber. A compound was prepared.

For 100 parts of the resulting base rubber compound,
Organic foaming agent dimethyl 1,1′-azobis (1-cyclohexanecarboxylate) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VE-073) 1.5 parts,
Hardener 2,5-dimethyl-2,5-di-t-butylperoxyhexane (manufactured by NOF Corporation) 0.8 part,
Wet silica NIPSIL (registered trademark) -LP (trade name, manufactured by Tosoh Silica Co., Ltd.) (3 parts) was added and mixed with a two-roll mill to obtain a silicone rubber composition. The obtained composition was molded to produce a 9 mm thick sheet.

  This 9 mm thick sheet was vulcanized at 230 ° C. with a hot air dryer under normal pressure for 30 minutes under normal pressure to obtain a silicone rubber sponge. Thereafter, secondary vulcanization at 200 ° C. for 4 hours was performed. After removing the skin layer from the obtained sponge, the sponge hardness, expansion ratio, average cell diameter, and open cell ratio were examined as the sponge characteristics as follows. The results are shown in Table 1.

Sponge hardness: Measured with an Asker C-type rubber hardness meter in accordance with JIS S 6050.
-Foaming ratio: volume after foaming / volume before foaming x 100 (%)
Average cell diameter (μm): Average cell diameter at the sponge cut surface.
-Open cell rate: measured as follows.
1) Measure the specific gravity of the silicone rubber composition that is the raw material of the sponge, that is, the unfoamed rubber material.
2) Measure the specific gravity and weight of the sponge.
3) The sponge is submerged in the water in the container placed in a vacuum container, and the inside of the vacuum container is depressurized to 10 mmHg or less.
4) After returning the inside of the vacuum vessel to normal pressure, leave it for 5 minutes to allow the sponge to absorb water.
5) Weigh the sponge with water absorbed. Next, a continuous bubble rate is calculated | required according to the following calculation.
[(Weight of sponge after water absorption under reduced pressure−initial weight of sponge) / specific gravity of water (1.00)]
/ [(1- (Sponge specific gravity / unfoamed rubber material specific gravity)) x (Sponge weight / sponge specific gravity)] x 100 (%)

(Example 2)
A silicone rubber sponge was molded in the same manner as in Example 1 except that the wet silica was changed to Zeosil (registered trademark) 132 (trade name, manufactured by Rhodia Japan Co., Ltd.), and the sponge characteristics were examined. The results are shown in Table 1.

Example 3
A silicone rubber sponge was molded in the same manner as in Example 1 except that the wet silica was changed to Toxeal (registered trademark) USA (trade name, manufactured by Tokuyama Corporation), and the above-mentioned sponge characteristics were examined. The results are shown in Table 1.

(Example 4)
Example except that 1.0 part of dicumyl peroxide was used instead of 0.8 part of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as a curing agent (organic peroxide) A silicone rubber sponge was molded in the same manner as in 1, and the above-mentioned sponge characteristics were examined. The results are shown in Table 1.

(Comparative Example 1)
Silicone in the same manner as in Example 1 except that 3 parts of dry silica Arosil 200 (trade name, manufactured by Nippon Aerosil Co., Ltd.) was used instead of 3 parts of wet silica NIPSIL-LP (trade name, manufactured by Tosoh Silica Co., Ltd.). A rubber sponge was molded and the above sponge characteristics were examined. The results are shown in Table 1.

(Comparative Example 2)
A silicone rubber sponge was molded in the same manner as in Example 1 except that wet silica NIPSIL-LP (trade name, manufactured by Tosoh Silica Co., Ltd.) was not added, and the sponge characteristics were examined. The results are shown in Table 1.

Claims (2)

(A) The following average composition formula (I):
R ¹ _a SiO _{(4-a) / 2} (I)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.04.)
A base material obtained by mixing an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule and reinforcing silica, followed by heat treatment: 100 parts by mass
(B) Organic foaming agent: 0.5 to 50 parts by mass,
(C) Curing agent: effective amount, and
(D) Wet silica: A high-open-cell silicone rubber sponge having a open-cell rate of 20% or more obtained by foaming and curing a silicone rubber composition containing 0.1 to 20 parts by mass. 2. The high open-cell silicone rubber sponge according to claim 1, wherein the component (B) is dimethyl 1,1′-azobis (1-cyclohexanecarboxylate).