JP2006077099A - Silicone rubber sponge having high continuous cell rate, method for producing the same and fixing roll by using the silicone rubber sponge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicone sponge having a high continuous cell rate, capable of being produced by a normal temperature hot air vulcanization without considering the regulation of the cross-linking speed of the rubber and a delicate balance of a foaming gas rate, excellent in productivity, capable of forming a uniform and fine cell structure and having less toxicity. <P>SOLUTION: This silicone rubber sponge composition having the high continuous cell rate contains (A) 100 pts. mass organopolysiloxane expressed by the following averaged compositional formula (I): R<SP>1</SP><SB>a</SB>SiO<SB>4-(a/2)</SB>[wherein, R<SP>1</SP>s are each the same or different kind un-substituted or substituted monovalent hydrocarbon group; and (a) is 1.95-2.04 positive number] , (B) 0.5-50 pt. mass blowing agent generating gas at ≥90°C temperature zone and (C) an effective amount for curing the component (A) of a non-acyl-based organic peroxide having ≥150°C half-life temperature at 1 min. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 rubber sponge used for paper rolls, toner transport rolls, cleaning rolls, and the like.

  Silicone sponge has physical properties peculiar to silicone rubber, and has excellent properties such as heat resistance, cold resistance, electrical insulation, flame retardancy, and compression set. This silicone rubber sponge is basically a combination of a thermosetting silicone rubber composition, a curing agent, and a foaming agent, and is foamed and cured by heating to form a sponge. It is important to have a uniform and fine cell structure and not to impair the physical properties unique 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 with a uniform and fine cell structure by molding in such atmospheric pressure hot air, the gas generated when the foaming agent decomposes must be pressed in the form of fine bubbles inside the rubber, so it is normal Before the foaming agent decomposes, the rubber composition must already be thickened and cured in order to suppress the foaming pressure.

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

As described above, since a normal sponge composition is prepared by a method in which the foaming pressure is suppressed by crosslinking, the sponge cell is usually a closed cell, and the open cell rate is usually 10% or less and air is trapped in the sponge cell. ing. In this way, when a sponge molded product in which the sponge cells are independent bubbles is heated, the trapped air is thermally expanded according to Boyle's law, and the sponge that fills the closed space like a gasket material has an air spring component. 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, and conversely, when the sponge roll is cold, the heater roll and backup roll The setting interval becomes wide, and the roll rattles and becomes a source of abnormal noise. Especially for the fixing sponge roll application, from the viewpoint of power saving, the number of models in which the fixing sponge roll is colder than the normal fixing temperature is increasing in the standby state. A high sponge was desired.
Patent Document 1 discloses 1,6-bis (t-butylperoxycarboxy) hexane (peroxyester system, 163 ° C.) and a foaming system in which a non-acyl organic peroxide bridge and an organic azo compound are used in combination. A sponge using AIBN (azoisobutyronitrile) as a blowing agent has been proposed, but in this patent, an ordinary organic material such as an acyl-based organic peroxide is used to apply an atmospheric pressure hot air to a conductive material that cannot be used due to cross-linking inhibition by carbon. This is a technology to obtain a good sponge by using an organic peroxide with excellent surface curability that enables sulfurization. The sponge cell is a closed cell, and it is not a technology that raises the sponge foam rate. There is no description of the foam rate.
Patent Document 2 describes a silicone rubber sponge composition that is foamed with crystal water of an inorganic salt having crystal water, but does not describe an open-cell sponge.

JP-A-5-43802 JP-A-5-156061

The present invention has been made to overcome the above-mentioned problems, and it is possible to produce a sponge by HAV without considering the delicate balance between the rubber crosslinking rate and the foaming gas rate, and it is excellent in productivity, uniform and fine cells. An object of the present invention is to easily provide a silicone foam composition having a high open-cell ratio and a low toxicity by using a sodium hydrogen carbonate-based foaming agent, which has a structure and can be sponge-molded regardless of the foaming agent.

As a result of earnest research, the present inventors have achieved the above object as a means
(A) The following average composition formula (I):
R ¹ _a SiO _{4-a / 2} (I)
(R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.95 to 2.04.)
An organopolysiloxane having at least two alkenyl groups in one molecule: 100 parts by mass
(B) a blowing agent that generates gas in a temperature range of 90 ° C. or higher: 0.5 to 50 parts by mass; and
(C) Non-acyl organic peroxide having a half-life temperature of 150 ° C. or more for 1 minute: (A) Open cell ratio obtained by foaming and curing a sponge composition containing an effective amount capable of curing the component 15 Provided is a silicone rubber sponge having a high reaming rate of at least%.

  In addition, the present invention provides a method for producing a high open-cell silicone rubber sponge having a open cell rate of 15% or more, including foaming and curing the sponge composition by atmospheric pressure hot air vulcanization (HAV).

  Furthermore, the present invention provides a fixing roll comprising at least one layer composed of the high open-cell silicone rubber sponge, and an electrophotographic image forming apparatus provided with the fixing roll. As such a fixing roll, for example, a continuous foam sponge is bonded to a single layer of a fixing roll or a surface release material such as a PFA tube, or a two or more layers fixing roll, or a solid rubber, a sponge rubber layer, and a toner separating layer. Examples thereof include a fixing roll for use in toner fusing and fixing having a multilayer structure fixing roll structure in which shape layers are combined.

  The sponge composition of the present invention has a high open cell ratio, which is impossible in the past by performing atmospheric pressure hot-air vulcanization using a non-acyl organic peroxide having a half-life temperature of 150 ° C. or more for 1 minute, that is, continuous reaming. Silicone sponges with a foam rate of 15% or more, 20% or more if necessary, and 30 to 100% can be obtained. Further, when used as a component (B) in a sodium hydrogencarbonate-based foaming agent, a sponge having a higher open cell ratio can be obtained. Further, by using an organic foaming agent capable of crosslinking and thickening the component (A) by thermal decomposition as a nucleating agent, it is possible to make the open-cell sponge cell fine and uniform. Other effects will be described in the following description.

Hereinafter, the present invention will be described in detail.
-Component (A)-
Component (A) is an organopolysiloxane having the following average composition formula (I)
R ¹ _a SiO _{4-a / 2} (I)
(R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.95 to 2.04.)
It is organopolysiloxane represented by these.

In the average composition formula (I), R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group or a dodecyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group, or a butenyl group. An alkenyl group such as a hexenyl group, an aryl group such as a phenyl group or a tolyl group, an aralkyl group such as a β-phenylpropyl group, or a part or all of the hydrogen atoms bonded to the carbon atoms of these groups is a halogen atom, cyano A chloromethyl group, a trifluoropropyl group, a cyanoethyl group, or the like substituted with a group or the like is selected, preferably the same or different, preferably 1 to 12 carbon atoms, more preferably an unsubstituted or substituted group having 1 to 8 carbon atoms. A monovalent hydrocarbon group is mentioned. Specifically, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and a methyl group is particularly preferably 80 mol% or more, and more preferably 95 mol% or more. Moreover, a is a positive number of 1.95 to 2.04, and this organopolysiloxane is substantially linear, but may be branched as long as the rubber elasticity of the cured silicone rubber sponge is not impaired. The organopolysiloxane may have a molecular chain end blocked with a trimethylsilyl group, a dimethylvinyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like. In the present invention, the organopolysiloxane is included in the molecule. It is necessary to have at least two alkenyl groups. Specifically, it is preferable that 0.001 to 5 mol%, particularly 0.01 to 0.5 mol%, of R ¹ is an alkenyl group, particularly a vinyl group.

This type of organopolysiloxane can be produced by hydrolytic condensation of one or more selected organohalosilanes, or cyclic polysiloxanes (such as siloxane trimers or tetramers) can be made alkaline or acidic. It can be obtained by ring-opening polymerization using the above catalyst. This is basically a linear diorganopolysiloxane, but may be partially branched. Further, it may be a mixture of two or more different molecular structures. The organopolysiloxane preferably has a viscosity at 25 ° C. of 100 mm ² / s or more. More preferably, it is 100,000-10,000,000 mm < ² > / s. The degree of polymerization is preferably 100 or more, particularly preferably 3,000 or more, and the upper limit thereof is preferably 100,000, more preferably 10,000.

-(B) component-
In the present invention, as the component (B), a blowing agent that generates gas in a temperature range of 90 ° C. or higher, preferably 100 to 180 ° C. is used. Although it will not specifically limit if it can be made to gas by thermal decomposition (or evaporation), A well-known organic foaming agent and an inorganic foaming agent can be used as a foaming agent for rubbers incompatible with silicone.

  Examples of the organic blowing agent include nitroso compounds such as N, N′-dimethyl-N, N′-dinitrosoterephthalamide and N, N′-dinitrosopentamethylenetetramine; azodicarbonamide, azobisisobutyronitrile Azocyclohexylnitrile, azodiaminobenzene, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobiz-2,4-dimethylvaleronitrile, 1,1'-azobis (1-acetoxy- 1-phenylethane), azodicarbonamide, barium azodicarboxylate, and other organic azo compounds; benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, P, P'-oxybis (benzenesulfonylhydrazide), diphenylsulfone-3,3'-di Sulfonyl hydrazide, 4,4'-oxybis (benzenesulfonyl hydrazide), para-toluenesulfonyl hydrazide Sulfonyl hydrazide compounds such as; calcium azide, 4,4-diphenyl-sulfonyl azide, etc. p- toluenesulfonyl Le azide such azides and the like. Among them, for example, azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobiz-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) An azo organic foaming agent having no sulfur compound, phosphates, strong amines or the like that inhibits the curing of silicone rubber in the molecule, such as -2-methylpropionamide] is preferable.

  Specific examples of the inorganic foaming agent include sodium bicarbonate (sodium bicarbonate), sodium carbonate, ammonium bicarbonate, ammonium carbonate, and ammonium nitrite. Sodium bicarbonate is preferable. These preferably have no water of crystallization. Unlike other foaming agents such as ammonium carbonate, ammonium nitrite, and azide compound, sodium bicarbonate does not generate strong acids and alkalis due to decomposition, is odorless, and is organically crosslinked with silicone or platinum. Since it does not cause cross-linking inhibition of addition cross-linking using a catalyst, there is an advantage that it can be added in a large amount to obtain a sponge, and there is no toxicity, and it is particularly preferably used in the present invention.

A sodium hydrogen carbonate-based foaming agent containing sodium bicarbonate as a main component can obtain a sponge having a particularly high open cell ratio as compared with other foaming agents. It is known that the decomposition behavior of sodium bicarbonate gradually decomposes from around 120 ° C., mainly decomposes at 150 ° C. and has a wide gas generation temperature range. For this reason, when a sodium hydrogen carbonate-based foaming agent is HAV cured and foamed using a high-temperature decomposition type organic peroxide, foaming occurs before and after the cross-linking temperature range, so-called outgassing occurs and the open cell rate is high. It is thought to become a sponge. The combination of the dialkyl-based organic peroxide and sodium bicarbonate blowing agent it is possible to Ren'awaritsu obtain a sponge than 50%. A sodium hydrogen carbonate-based blowing agent is not particularly specified as long as the main agent of the blowing agent is sodium hydrogen carbonate, and the particle size, product purity, silicone-based hydrophobizing treatment to sodium hydrogen carbonate, etc. are optional, but desirable Preferably have a purity of 50 to 100% and an average particle size of 50 μm or less. Further, the nucleation treatment of the sponge to the foaming agent, the addition of a nucleating agent, the addition of a small amount of acid as a decomposition accelerator, and the addition of a small amount of other inorganic foaming agents are optional.

The amount of the foaming agent (B) added is usually 0.5 to 50 parts by weight, preferably 1.0 to 20 parts by weight, based on 100 parts by weight of the organopolysiloxane (A). If the amount is less than 0.5 parts by mass, the generated gas is insufficient and it is difficult to form a sponge, and the open cell rate does not increase. If the amount exceeds 50 parts by mass, it may be difficult to physically add, and the amount of generated gas will increase during sponge molding. For this reason, the cells become uneven or the sponge breaks from the inside.
-(C) component-
The organic peroxide vulcanizing agent of component (C) of the present invention is used to cure component (A), and uses a non-acyl organic peroxide having a 1 minute half-life temperature of 150 ° C or higher. To do. Specifically, organic peroxides such as peroxyesters, peroxyketals, dialkyl peroxides, hydroperoxides, etc., which inhibit the crosslinking of the rubber surface due to oxygen inhibition (hard to harden) during atmospheric pressure hot air vulcanization (HAV). desirable.

  When an ordinary closed-cell sponge is vulcanized by HAV, the organic peroxide used is a diacyl peroxide (2,4-dichlorobenzoyl peroxide, which has little cross-linking inhibition by oxygen) because the foamed gas needs to be confined to rubber. p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, etc.), 1,6-bis (t-butylperoxycarboxy) hexane, which is a peroxy ester-based organic peroxide that is specifically resistant to oxygen inhibition, or It is necessary to select addition crosslinking without oxygen crosslinking inhibition. Therefore, in general, atmospheric pressure hot air vulcanization does not crosslink the rubber surface due to oxygen inhibition (it does not become a foam). Dialkyl peroxides are not used alone in normal pressure hot air vulcanization, and when used alone. The sponge cell is not uniform and has a high expansion ratio.

  In the present invention, it is preferable to select an organic peroxide that decomposes at a temperature higher than the decomposition temperature of the foaming agent of the component (B) because the sponge open-cell ratio increases. For example, when using a sodium hydrogen carbonate-based foaming agent, it is set to be approximately the same or slower than the main decomposition temperature of 150 ° C, and the surface layer (skin layer) of silicone rubber does not crosslink so much. Carbon dioxide gas generated by the decomposition of the sodium hydride-based foaming agent has a role of making it easy to break through the sponge cell and out of the sponge.

  Specific examples of the organic peroxide are listed below, and the 1-minute half-life temperature of each compound is shown in parentheses. t-hexylperoxyisopropyl monocarbonate (peroxyester, 155 ° C), 2,5-dimethyl-2,5-di-t-butylperoxyhexane (dialkyl, 180 ° C), 2,5-dimethyl- 2,5-di-t-butylperoxyhexyne (dialkyl type, 194 ° C), di-t-butyl peroxide (dialkyl type, 186 ° C), dicumyl peroxide (dialkyl type, 175 ° C), cumyl-t -Butyl peroxide (dialkyl type, 173 ° C), p-menthane hydroperoxide (hydroperoxide type, 200 ° C), etc. are preferably used. Oxide systems are preferably used in view of the stability of organic peroxides. These organic peroxides can be used alone or as a mixture of two or more.

  Since the above-mentioned cross-linking system does not form open bubbles unless there is a passage for the foaming gas, atmospheric pressure hot air vulcanization is suitable instead of compression molding. Atmospheric pressure hot air vulcanization includes a powder curing method in which the bead component is glass beads.

  The compounding amount of the component (C) may be an effective amount. Specifically, it is usually 0.01 to 50 parts by mass, preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). If the amount is too large, the curing rate is not improved, and it takes a long time to remove unreacted substances and decomposition residues.

  Further, an addition reaction type curing agent, that is, a curing agent composed of a combination of a hydrosilylation reaction catalyst (addition reaction catalyst) and an organohydrogensiloxane acting as a crosslinking agent (hereinafter referred to as “addition curing agent”) is used as the curing agent. It is preferable to use a crosslinking reaction by addition reaction together. At that time, as described above, if addition crosslinking is not started after curing of the organic peroxide, the passage of the foaming gas will be blocked. Therefore, in the case of using addition crosslinking together, auxiliary for completely crosslinking component (A) A typical addition crosslinking system. Specifically, as the addition curing agent, an addition curing agent having a crosslinking initiation temperature of 160 ° C. or higher, preferably 170 to 190 ° C. is used in combination. The crosslinking initiation temperature of 160 ° C. or higher can be confirmed by the fact that thickening is not detected immediately after measurement with a torque meter set to 160 ° C. by mixing the component (A) and the addition curing agent.

  When a crosslinking reaction by addition reaction is used, the organopolysiloxane used for component (A) is an organopolysiloxane in which at least one of the organic groups bonded to the silicon atom in one molecule is a vinyl group. . The addition reaction catalyst may be any conventionally known catalyst. Specifically, a platinum group metal simple substance and a compound thereof can be used. For example, particulate platinum metal adsorbed on a support such as silica, alumina or silica gel, platinous chloride, chloroplatinic acid, chloroplatinic acid hexahydrate complex with olefin or divinyldimethylpolysiloxane, chloroplatinic acid Examples include an alcohol solution of hexahydrate, a palladium catalyst, and a rhodium catalyst. The addition amount of these catalysts is a catalyst amount, and is usually used in the range of 1 to 1,000 ppm in terms of the amount of platinum-based metal, and preferably in the range of 10 to 100 ppm. If it is less than 1 ppm, the crosslinking reaction is not sufficiently accelerated and curing is insufficient. On the other hand, addition of more than 1,000 ppm has little influence on reactivity and is uneconomical. As the crosslinking agent for addition reaction, an organohydrogenpolysiloxane having two or more SiH groups in one molecule is used, and this organohydrogenpolysiloxane is any of linear, cyclic, and branched. Well-known organohydrogenpolysiloxane can be used as a curing agent for the addition reaction curable silicone rubber composition. Usually, the following average composition formula (II):

R ² _x H _y SiO _{(4-xy) / 2} (II)
Wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group, and x and y are 1 ≦ x ≦ 2.2 and 0.002 ≦ y ≦ 1, respectively, and 1.002 ≦ x + y ≦ 3 It is a positive number to satisfy.) The monovalent hydrocarbon radical unsubstituted or substituted as represented by R2 in Formula (II), as well as the R ^1, 1 to 12 carbon atoms, are preferred particularly 1 to 8, for R ¹ What was illustrated can be mentioned. The molecule has 2 or more, preferably 3 or more SiH groups in one molecule, which may be at the molecular chain terminal or non-terminal. The organohydrogenpolysiloxane preferably has a viscosity at 25 ° C. of 300 mm ² / s or less.

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

  The compounding amount of the organohydrogenpolysiloxane is 0.01 to 10 parts by mass with respect to 100 parts by mass of the organopolysiloxane as the component (A). Preferably, the ratio of the hydrogen atom bonded to the silicon atom to one alkenyl group in component (A) is in the range of 0.5 to 10, preferably in the range of 1 to 4. . If the amount is too small, the effect of enhancing the crosslinking cannot be obtained sufficiently, and the mechanical strength is not improved. However, if the amount is too large, the physical properties after curing are lowered, and particularly heat resistance and compression set may be significantly deteriorated. Furthermore, it is preferable to add a known platinum catalyst inhibitor such as a polymethylvinylsiloxane cyclic compound, an acetylene group-containing alcohol and a peroxide to the silicone rubber composition to adjust the crosslinking initiation temperature.

-(D) component-
In the present invention, as necessary, the component (D) is composed of “99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxane units, and the degree of polymerization is 100 parts by weight of an average 8,000 organopolysiloxane (hereinafter referred to as standard organopolysiloxane), 40 parts by weight of wet silica having a BET specific surface area of 195 m ² / g, having silanol groups at both ends, and a viscosity of 29 mm ² / s A compound prepared by adding 0.7 to 10.0 parts by mass to 100 parts by mass of a base rubber compound prepared by blending 4 parts of dimethylpolysiloxane (23 ° C.) with a kneader and then heat-treating at 180 ° C. for 2 hours is heated at 150 ° C. Mooney viscosity ML (1 + 4) measured while decomposing is 5% or more than the Mooney viscosity measured at the same temperature with the base rubber compound alone. In particular, it is preferable to add an organic foaming agent exhibiting a high value of 10 to 300% to the composition of the present invention, and by including the organic foaming agent as the component (D), the composition of the present invention The average sponge cell diameter obtained by foaming can be 2 mm or less.

  In the above, the standard organopolysiloxane can be easily produced by those skilled in the art by hydrolytic condensation of the raw material silane compound mixture according to the molecular composition or by the equilibration reaction of the raw material oligosiloxane mixture according to the molecular composition. Can do.

  The organic foaming agent of component (D) has the property that the composition of the present invention can be thickened or cured by thermal decomposition, and when used in combination with such an organic foaming agent, the sponge cells are denser and more uniform. It becomes. Specifically, the organic foaming agent having this characteristic not only generates gas by decomposition of the foaming agent, but also crosslinks the methyl group and alkenyl group present in the molecule of the organopolysiloxane (A) by radical reaction. Polymer viscosity can be increased. Therefore, by using together the organic foaming agent exhibiting such an increase in viscosity, before the decomposition of the sodium hydrogen carbonate-based foaming agent, the “(A) component thickening due to the decomposition of the organic foaming agent in the rubber at the time of sponge molding, and In some cases, “curing” and “gas generation due to decomposition of the organic foaming agent” occur almost simultaneously, so that the foam cell is uniform and fine by acting as a nucleating action of the sponge.

  By the way, in general, azo compounds, which are a kind of organic foaming agent, are widely used as radical polymerization agents for vinyl compounds, but they do not function as such polymerization agents for alkenyl groups in the organopolysiloxane molecules. However, there are few foaming agents that generate strong radicals that increase the viscosity or cause the increase in viscosity at the same time as the decomposition of the foaming agent, with the addition amount used in ordinary foaming agents. Azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobiz-2, 4-dimethylvaleronitrile, 1,1 Even with '-azobis (1-acetoxy-1-phenylethane), etc., no increase in viscosity can be observed due to decomposition. These cannot be used as the component (D) of the present invention.

  The organic foaming agent (D) is more preferably a product that decomposes at 150 ° C. or lower because the sodium hydrogen carbonate foaming agent (B) is endothermicly decomposed at around 150 ° C. to generate carbon dioxide.

  Specifically, the organic foaming agent of component (D) has a Mooney viscosity ML (1 + 4) measured while thermally decomposing a compound to which the foaming agent is added at 150 ° C., and the base rubber compound alone. An azo organic foaming agent that exhibits a high value in the range of 10 to 300%, more preferably 20 to 200%, of the Mooney viscosity measured at the same temperature is preferable. Further, the organic blowing agent is preferably an azo organic blowing agent having a decomposition point of 150 ° C. or lower. By using such an organic foaming agent, when the composition used in the present invention is foamed by atmospheric pressure hot air vulcanization, the average sponge cell diameter of the resulting sponge can be 2 mm or less. Examples of the azo organic foaming agent having such characteristics include 1,1′-azobis (cyclohexane-1-methylcarboxylate), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2 '-Azobis [N- (2-propenyl) -2-methylpropionamide] and the like can be mentioned, and these can be used singly or in combination of two or more.

  Component (D) is added in an amount of 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass, per 100 parts by mass of component (A), polyorganosiloxane. It is desirable that the polyorganosiloxane of component (A) has an addition amount that causes a thickening phenomenon but does not completely cure. If the amount of component (D) added is less than 0.1 parts by mass, the viscosity will not increase very much and there will be no effect on the refinement and homogenization of the sponge cell, and if it exceeds 20 parts by mass, the thickening will proceed too much and foaming pressure will be suppressed. It is difficult to become a continuous foam sponge. In addition, a larger amount of decomposition residue after decomposition of component (D) remains, and if the decomposition residue is not decomposed or volatilized into a low molecular weight hydrocarbon compound or the like by performing heat treatment for a long time at high temperature, bleeds are generated on the sponge surface. And problems such as precipitation of crystals occur. For the above reason, the more preferable range of the amount of the component (B) is 0.2-10.0 parts by mass, and more preferably 0.2-5.0 parts by mass.

-Other ingredients-
It is desirable that reinforcing silica fine powder is added to the silicone sponge composition used in the present invention. The reinforcing silica fine powder is necessary for obtaining a silicone rubber sponge having excellent mechanical strength. For this purpose, the specific surface area is 50 m ² / g or more, preferably 100 to 400 m ² / g. Examples of the silica fine powder 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. These silicas may be used alone or in combination of two or more. The addition amount of the silica fine powder is desirably 5 to 100 parts by weight, preferably 10 to 90 parts by weight, particularly preferably 30 to 80 parts by weight per 100 parts by weight of the organopolysiloxane of the component (A). . If the amount is less than 5 parts by mass with respect to 100 parts by mass, a sufficient reinforcing effect cannot be obtained. If the amount is more than 100 parts by mass, the workability may be deteriorated and the physical properties of the resulting silicone rubber may be deteriorated.

Moreover, this invention can also be set as a conductive sponge by adding a conductive substance.
The type and blending amount of the conductive material are not limited, but conductive carbon black, conductive metal oxide particles such as conductive zinc oxide, conductive titanium oxide, etc. can be used, and the conductive material can be used alone. Two or more types may be used in combination. In that case, since carbon becomes a cross-linking inhibitor for organic peroxides, it is desirable to increase the amount of organic peroxides or to use the aforementioned high-temperature addition curing agent in combination.

  As the 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 black (XCF). ), Conductive channel black (CC), furnace black heat-treated at a high temperature of about 1500 to 3000 ° C., channel black, and the like. Specific commercial product names include Denka Black (manufactured by Electrochemical Co., Ltd.) and Shaunigan acetylene black (manufactured by Shaunigan Chemical Co., Ltd.) as acetylene black, and Continex CF (Continental Carbon) as conductive furnace black. ), Vulcan C (Cabot), etc., SuperConductive Furnace Black, Connex SCF (Continental Carbon), Pulcan SC (Cabot), etc., Extra Conductive Furnace Black, Asahi HS-500 (Asahi Carbon Co., Ltd.), Pulkan XC-72 (Cabot Co., Ltd.), etc., as a conductive channel black, Kourax L (Degussa Co., Ltd.) etc. are exemplified, and Ketjen Black EC, which is a kind of furnace black, and Ketjen Black EC-600JD Rack International Co., Ltd.) can also be used. In furnace black, the amount of impurities, particularly sulfur and sulfur compounds, is 6000 ppm or less, more preferably 3000 ppm or less in terms of the concentration of elemental sulfur. Among these, acetylene black has a low impurity content and has a developed secondary structure structure, so that it has excellent conductivity and is particularly preferably used in the present invention. Further, Ketjen Black EC, Ketjen Black EC-600JD, etc., which exhibit excellent conductivity even at a low filling amount due to their exceptionally large specific surface area, can be preferably used.

  The amount of the conductive carbon black added is preferably 1 to 100 parts by weight, particularly 5 to 50 parts by weight, based on 100 parts by weight of the rubber component (A) described above. If the amount added is less than 1 part by mass, the desired conductivity may not be obtained. If the amount added exceeds 100 parts by mass, physical mixing may be difficult or the mechanical strength may be reduced. Rubber elasticity may not be obtained.

  Examples of the conductive metal oxide fine particles include conductive zinc white, titanium oxide, and tin antimony fine particles. Specifically, as the conductive zinc oxide, zinc oxide 23-K (product of Hakusui Tech Co., Ltd.) Name) and conductive zincated FX (trade name) manufactured by Honjo Chemical Co., Ltd., and white conductive titanium oxide include, for example, ET-500W (trade name, manufactured by Ishihara Sangyo Co., Ltd.). By adding 1 to 300 parts by mass of these fine particles alone or in combination with carbon, the desired electrical resistance can be obtained.

  In the silicone sponge composition of the present invention, if necessary, pulverized quartz, zinc oxide, alumina, aluminum oxide or diatomaceous earth as non-reinforcing silica as a thermal conductivity imparting material, filler such as calcium carbonate, colorant Dispersion of additives such as heat resistance improver, flame retardant improver, acid acceptor, heat conduction improver, mold release agent, alkoxysilane, diphenylsilanediol, carbon functional silane, silanol-blocked low molecular weight siloxane An agent or the like may be added.

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, a kneader, a Banbury mixer, etc. If necessary, heat treatment (kneading under heating) may be performed. Specific examples include a method of adding (B), (C), and (D) after kneading and heat-treating component (A), reinforcing silica, and other additives, and then cooling.
Although the said heat processing temperature and time are not specifically limited, 100-250 degreeC and heat processing for 30 minutes-5 hours are performed.

  In the method of curing and foaming the rubber composition of the present invention, atmospheric pressure hot-air vulcanization is desirable because it is necessary to increase the open cell ratio of the sponge cell with carbon dioxide gas. Continuous vulcanization by a heating furnace using extrusion molding, batch type Hot air crosslinking by a dryer is preferably employed. However, this is not the case when sufficient space is secured inside the mold bridge. In general, a high open-cell sponge can be obtained by curing by foaming and curing at 80 to 400 ° C., particularly 100 to 300 ° C. for about 5 seconds to 1 hour under normal pressure hot air. Moreover, you may post-cure at 100-230 degreeC for about 10 minutes-10 hours.

According to the present invention, the high open-cell silicone rubber sponge having a open cell rate of 15% or more obtained by foaming and curing the sponge composition by atmospheric pressure hot-air vulcanization has at least a layer made of the sponge. It is useful for the production of a fixing roll characterized by having one layer. As such a fixing roll, a fixing roll having a single layer made of open-cell sponge , and a two or more layers fixing roll in which two or more layers made of the sponge are bonded to a surface release material such as a PFA tube. And a fixing roll for toner fusing and fixing having a multi-layered fixing roll structure in which a solid rubber, a sponge rubber layer and a toner release layer are combined.

  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. The Mooney viscosity characteristics of the component (D) are summarized in Table 5.

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

  For 100 parts of the obtained base rubber compound, 4.0 parts of sodium bicarbonate (reagent grade purity 99% or more, particle size 40 μm) as a blowing agent and 2,5-dimethyl-2,5-di-t-butylperoxyhexane 0.6 parts were added and mixed in a two-roll mill to prepare a 9 mm thick rubber compound sheet. Next, this 9 mm thick sheet was vulcanized with hot air at 230 ° C. for 30 minutes under normal pressure to obtain a silicone 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, sponge cell state, average cell diameter of the sponge, and open cell ratio were examined as follows. The evaluation results are shown in Tables 1 to 4.

-Sponge hardness: Asker C hardness according to JIS S 6050.
-Cell state: visually observed.
-Average cell diameter: The average value of the cell diameters on the sponge cut surface.
-Method for measuring the open cell ratio 1) Measure the specific gravity and weight of the sponge sample. 2) The sponge is submerged in water in a container placed in a vacuum container, and in that state, the inside of the vacuum container is depressurized to 10 mmHg or less. 3) After returning the inside of the vacuum vessel to normal pressure, leave it for 5 minutes to allow the sponge to absorb water. 4) Weigh the sponge with water absorbed. Next, a continuous bubble rate is calculated | required according to the following calculation.

[(Weight of sponge sample after water absorption under reduced pressure−weight of initial sponge sample) / specific gravity of water (1.00)]
/ [(1- (sponge specific gravity / unfoamed rubber material specific gravity)) x (sponge sample weight / sponge specific gravity)] x 100 (%)

(Example 2)
A sponge was molded in the same manner as in Example 1 except that 1.0 part of 1,1′-azobis (cyclohexane-1-methylcarboxylate), an organic foaming agent, was added as a cell refining and nucleating agent.

Example 3
A sponge was molded in the same manner as in Example 2, except that the organic foaming agent 1,1′-azobis (cyclohexane-1-methylcarboxylate) was changed to 2.0 parts.

(Example 4)
A sponge was molded in the same manner as in Example 2 except that 4.0 parts of azobisisobutyronitrile was used instead of sodium hydrogen carbonate as a foaming agent.

Example 5
Instead of the blowing agent sodium hydrogen carbonate, 4.0 parts of azobisisobutyronitrile was used, and the organic peroxide curing agent was changed from 2,5-dimethyl-2,5-di-t-butylperoxyhexane to dicumylper A sponge was molded in the same manner as in Example 2 except that the oxide was used.

Example 6
A sponge was molded in the same manner as in Example 2 except that the amount of sodium hydrogen carbonate as a foaming agent was reduced to 2.0 parts.

Example 7
A sponge was molded in the same manner as in Example 2 except that the amount of sodium hydrogen carbonate as a foaming agent was increased to 8.0 parts.

(Example 8)
The same procedure as in Example 2 except that 0.6 parts of dicumyl peroxide was used instead of 0.6 parts of 2,5-dimethyl-2,5-di-t-butylperoxyhexane, which is an organic peroxide as a curing agent. A sponge was formed.

Example 9
Example 2 except that 0.6 part of t-hexylperoxyisopropyl monocarbonate was used instead of 0.6 part of 2,5-dimethyl-2,5-di-t-butylperoxyhexane, which is an organic peroxide of the curing agent. In the same manner, a sponge was molded.

Example 10
Organic foaming agent 1,1'-azobis (cyclohexane-1-methylcarboxylate) added as cell refining and nucleating agent is replaced with another organic foaming agent 2,2'-azobis [N- (2-propenyl)- A sponge was molded in the same manner as in Example 2 except that the compound was changed to 2-methylpropionamide.

Example 11
A sponge was obtained in the same manner as in Example 2 except that 1,1′-azobis (cyclohexane-1-methylcarboxylate) used in Example 2 was changed to an organic blowing agent azobisisobutyronitrile. Molded.

Example 12
Change the organic blowing agent from 1,1'-azobis (cyclohexane-1-methylcarboxylate) used in Example 2 to another organic blowing agent 1,1'-azobis (1-acetoxy-1-phenylethane) A sponge was molded in the same manner as in Example 2 except that.

Example 13
C-25A (platinum catalyst) / C-25B (organohydrogensiloxane crosslinking agent) / acetylene group-containing alcohol, which is an addition crosslinking system in which the crosslinking initiation temperature is controlled at about 170 ° C. in order to use addition crosslinking as a curing agent (Each 0.3 parts / 2.0 parts / 0.7 parts) (in addition, C-25A / C-25B manufactured by Shin-Etsu Chemical Co., Ltd.) was added to form a crosslinking system in which addition crosslinking was used in combination. A sponge was molded in the same manner as in Example 2 except for the above.

Example 14
A rubber compound sheet having a thickness of 9 mm was prepared in the same manner as in Example 2, and this sheet was then subjected to PCM (powder curing method) at 230 ° C./30 minutes to obtain a silicone rubber sponge.

(Comparative Example 1)
For 100 parts of base rubber compound, 4.0 parts of sodium hydrogen carbonate as a foaming agent (reagent grade purity 99%, particle size 40 μm) and p-methylbenzoylpar as a diacyl organic peroxide as a curing agent for organic peroxides A sponge was molded in the same manner as in Example 1 except that 0.6 part of oxide was added.

(Comparative Example 2)
A sponge was molded in the same manner as in Comparative Example 1 except that 1.0 part of 1,1′-azobis (cyclohexane-1-methylcarboxylate) was additionally added as an organic foaming agent.

(Comparative Example 3)
In addition to 0.6 part of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as a curing agent for organic peroxide, 0.2 part of p-methylbenzoyl peroxide, which is a diacyl organic peroxide, was added. A sponge was molded in the same manner as in Example 2 except that a dialkyl / diacyl combined crosslinking system was used.

(Comparative Example 4)
C-25A (platinum catalyst) / C-25B (organohydrogensiloxane crosslinking agent) / acetylene which is an addition crosslinking system in which the crosslinking initiation temperature is controlled at about 120 ° C. from 0.6 part of p-methylbenzoyl peroxide. A sponge was molded in the same manner as in Comparative Example 1 except that the alcohol was changed to a group-containing alcohol (0.5 parts / 2.0 parts / 0.1 parts, respectively).

(Comparative Example 5)
A sponge was molded in the same manner as in Comparative Example 4 except that 1.0 part of 1,1′-azobis (cyclohexane-1-methylcarboxylate) was additionally added as an organic foaming agent.

(Comparative Example 6)
Addition of 0.6 part of organic peroxide 2,5-dimethyl-2,5-di-t-butylperoxyhexane and combined use of organic peroxide crosslinking and addition crosslinking having a crosslinking initiation temperature of about 120 ° C. A sponge was molded in the same manner as in Comparative Example 5 except that.

(Comparative Example 7)
An addition crosslinking system in which the curing agent is controlled to have a crosslinking initiation temperature of about 160 ° C. instead of 0.6 part of 2,5-dimethyl-2,5-di-t-butylperoxyhexane, which is an organic peroxide. C-25A (platinum catalyst) / C-25B (organohydrogensiloxane crosslinking agent) / acetylene group-containing alcohol (0.5 parts / 2.0 parts / 0.7 parts respectively) A sponge was molded in the same manner as in Example 2 except that the system was used.

(Comparative Example 8)
100 parts of base rubber compound, except for adding 1.0 part of organic foaming agent azobisisobutyronitrile as foaming agent and 0.6 part of organic peroxide p-methylbenzoyl peroxide and 0.6 part of dicumyl peroxide as curing agent Was a sponge as in Example 1.

(Comparative Example 9)
A sponge was molded in the same manner as in Comparative Example 7, except that 4.0 parts of sodium hydrogen carbonate was added as a foaming agent, and the organic foaming agent azobisisobutyronitrile was used in combination.

(Comparative Example 10)
100 parts of base rubber compound, 2.0 parts of sodium hydrogen carbonate as foaming agent and 1.0 part of organic foaming agent 1,1'-azobis (1-acetoxy-1-phenylethane) From C-25A (platinum catalyst) / C-25B (organohydrogensiloxane crosslinking agent) / acetylene group-containing alcohol (each 0.5 parts / 2.0 parts / 0.1 part) A sponge was molded by the same molding method as in Comparative Example 1 using only the addition crosslinking system.

(Comparative Example 11)
100 parts of base rubber compound, 1.0 part of organic foaming agent azobisisobutyronitrile as foaming agent, 1,6-bis (t-butylperoxycarboxy) hexane (peroxyester type) as organic peroxide as curing agent , 163 ° C.) A sponge was molded in the same manner as in Example 1 except that 0.6 part was added.

  The sponges obtained in Example 2 to Comparative Example 11 were evaluated in the same manner as in the Examples. The results are shown in Tables 1-4.

[Note 1 to Tables 1 to 4]
* 1: Solid state with almost no foam (some millimeters are in some bubbles)
* 2: Gas accumulation (huge cavities) or cracks inside, and the appearance of the sponge is uneven * 3: Foam gas outside the sponge is removed, and the sponge cells are not uniform. The sponge center is an independent foam.

[Note 2 to Tables 1 to 4]
・ NaHCO ₃ blowing agent: sodium bicarbonate (average particle size 20μm) (gas generation temperature: about 150 ° C)
Organic foaming agent A): 1,1′-azobis (cyclohexane-1-methylcarboxylate) (see Table 5)
Organic blowing agent B): 2,2'-azobis [N- (2-propenyl) -2-methylpropionamide] (see Table 5)
・ Organic foaming agent C): Azobisisobutyronitrile (gas generation temperature: approx. 106 ° C)
・ Organic foaming agent D): 1,1'-azobis (1-acetoxy-1-phenylethane) (gas generation temperature: approx. 107 ° C)
PO curing agent A: 2,5-dimethyl-2,5-di-t-butylperoxyhexane (dialkyl, 1 minute half-life temperature: 180 ° C.)
PO curing agent B: Dicumyl peroxide (dialkyl type, 1 minute half-life temperature: 175 ° C.)
PO curing agent C: t-hexyl peroxyisopropyl monocarbonate (peroxyester, 1 minute half-life temperature: 155 ° C.)
PO curing agent D: p-methylbenzoyl peroxide (diacyl, 1 minute half-life temperature: 128 ° C.)
PO curing agent E: 1,6-bis (t-butylperoxycarboxy) hexane (peroxyester, 1 minute half-life temperature: 163 ° C.)
Addition curing agent A: Addition curing agent with a crosslinking initiation temperature set at about 170 ° C. (C-25A / C-25B = 0.3 parts / 2.0 parts of a blend containing 0.7 parts of acetylene group-containing alcohol)
Addition curing agent B: Addition curing agent with a crosslinking initiation temperature set at about 120 ° C (C-25A / B = 0.5 / 2.0)
(C-25A / C-25B = 0.5 parts / 2.0 parts of the compound with 0.1 part of acetylene group-containing alcohol added)
・ C-25A: Platinum catalyst ・ C-25B: Organohydrogensiloxane crosslinking agent

-Thickening test of component (D)-
The increase characteristic of Mooney viscosity (ML1 + 4) of the organic foaming agent of component (D) described in Examples and Comparative Examples was measured as follows.
Composed of 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxane units, 100 parts of organopolysiloxane having an average degree of polymerization of 8,000, BET specific surface area of 195 m 40 parts of ² / g wet silica (trade name: Nippon Sil LP (manufactured by Nippon Silica Co., Ltd.)), 4 parts of dimethylpolysiloxane having silanol groups at both ends and having a viscosity of 29 cs (23 ° C.) were blended in a kneader. Thereafter, heat treatment was performed at 180 ° C. for 2 hours to prepare a base rubber compound.

Each compound was prepared by adding each organic foaming agent shown in Table 5 to the base rubber compound in the number of parts shown in Table 5 (based on 100 parts of the polyorganosiloxane).
The viscosity of each compound and base rubber compound thus prepared at 40 ° C. in an unfoamed state was measured. Further, the Mooney viscosity ML (1 + 4) of the base rubber compound at 150 ° C. was defined as 100, and the relative value of the Mooney viscosity ML (1 + 4) of each compound at the same temperature was determined.
These results are shown in Table 5. In this table, BC means base rubber compound.

[Remarks]
(Condition) ・ Used equipment is TOYOSEIKI RLM-1
Foaming agent A) 1,1'-azobis (cyclohexane-1-methylcarboxylate)
Foaming agent B) 2,2'-azobis [N- (2-propenyl) -2-methylpropionamide]
Foaming agent C) Azobisisobutylnitrile
Foaming agent D) 1,1'-azobis (1-acetoxy-1-phenylethane)

  The high open-cell silicone rubber sponge composition of the present invention includes construction gaskets, various sponge sheets, sponges for water absorption, heat insulating sheets, industrial rolls, copying machines, facsimiles, printers, and other electrophotographic image forming apparatuses. Used for sponge rolls for office machines, especially toner fusing and fixing rolls, paper feed rolls, toner transport rolls and cleaning rolls

Claims (11)

(A) The following average composition formula (I):
R ¹ _a SiO _{4-a / 2} (I)
(R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.95 to 2.04.)
An organopolysiloxane having at least two alkenyl groups in one molecule represented by: 100 parts by mass
(B) a blowing agent that generates gas in a temperature range of 90 ° C. or higher: 0.5 to 50 parts by mass; and
(C) Non-acyl organic peroxide having a half-life temperature of 150 ° C. or more for 1 minute: (A) Open cell ratio obtained by foaming and curing a sponge composition containing an effective amount capable of curing the component 15 High ream rate silicone rubber sponge that is more than 50%.   2. The high open-cell rate silicone rubber sponge according to claim 1, wherein the component (B) is sodium hydrogen carbonate. The high open cell silicone rubber according to claim 1 or 2, wherein the component (B) is an organic azo foaming agent and the non-acyl organic peroxide of component (C) has a one-minute half-life temperature of 170 ° C or higher. sponge.   The highly open-cell foam according to any one of claims 1 to 3, wherein the non-acyl organic peroxide of component (C) is a dialkyl peroxide organic peroxide having a half-life temperature of 170 ° C or higher for 1 minute. Rate silicone sponge. Furthermore, as component (D)
100 parts by mass of an organopolysiloxane consisting of 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of 8,000, BET specific surface area Base composed of 40 parts by weight of 195m ² / g wet silica, 4 parts of dimethylpolysiloxane having silanol groups at both ends and a viscosity of 29mm ² / s (23 ° C) in a kneader, followed by heat treatment at 180 ° C for 2 hours Mooney viscosity ML (1 + 4) measured while thermally decomposing a compound prepared by adding 0.7 to 10.0 parts by mass to a rubber compound at 150 ° C. is higher than the Mooney viscosity measured at the same temperature with the base rubber compound alone. The organic foaming agent which shows a value higher by 5% or more is contained in an amount of 0.1 to 20 parts by mass per 100 parts by mass of the component (A). High communicating Awaritsu silicone rubber sponge according.   The organic foaming agent of component (D) is an azo organic foaming agent having a decomposition point of 150 ° C. or less, and Mooney viscosity ML (measured while thermally decomposing the compound to which the foaming agent is added at 150 ° C. 1 + 4) is an azo organic foaming agent having a value in the range of 10-300% higher than the Mooney viscosity measured at the same temperature with the base rubber compound alone, and the composition is subjected to atmospheric pressure hot-air vulcanization. 6. The high open-cell silicone rubber sponge according to claim 5, wherein an average sponge cell diameter when foamed is 2 mm or less.   The organic foaming agent of the component (D) is 1,1′-azobis (cyclohexane-1-methylcarboxylate), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis [N -(2-propenyl) -2-methylpropionamide], or a combination of two or more thereof.   8. The high open-cell silicone rubber sponge according to claim 1, further comprising, as component (E), an addition curing agent having a crosslinking initiation temperature set to a temperature of 160 ° C. or higher.   A method for producing a high open-cell rate silicone rubber sponge having a open cell rate of 15% or more, comprising foaming and curing the sponge composition according to any one of claims 1 to 8 by atmospheric pressure hot-air crosslinking.   A fixing roll comprising at least one layer made of a silicone foam sponge having a high open-cell ratio according to any one of claims 1 to 8.   An electrophotographic image forming apparatus comprising the fixing roll according to claim 9.