Silicone rubber sheet and method for manufacturing the same

Abstract

This invention provides a silicone rubber sheet in which one side of the sheet in the thickness direction has low friction without undergoing a surface treatment process. [Solution] The present invention relates to a method for producing a silicone rubber sheet and a silicone rubber sheet, comprising at least a mixing step of mixing an organopolysiloxane, a curing agent for organopolysiloxane, and an alkyl silicate; a first curing step of curing the mixture obtained in the mixing step; and a second curing step of curing the alkyl silicate.

Description

Technical Field

[0001] The present invention relates to a silicone rubber sheet and a method for producing the same.

Background Art

[0002] Silicone rubber has excellent heat resistance, cold resistance, gas permeability, etc. compared to natural rubber, and is widely used in various fields such as not only the industrial field but also the food field. On the other hand, the surface of rubber containing silicone rubber usually exhibits a high coefficient of friction. By further reducing the coefficient of friction of silicone rubber, it is also possible to expand its applications.

[0003] So far, various methods for reducing the coefficient of friction of the silicone rubber surface have been proposed. For example, there is a method of applying lubricating powder or oil to the surface of silicone rubber to reduce the coefficient of friction (see Patent Document 1). There is also a method of coating the surface of silicone rubber with a low-friction resin to reduce the coefficient of friction (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above-mentioned conventionally known methods, after obtaining the silicone rubber, special surface treatment such as applying powder or oil to its surface or coating another layer on its surface is required. Therefore, many steps and associated costs are required for the treatment to reduce the coefficient of friction of the silicone rubber. <000​Therefore, the present invention aims to provide a silicone rubber sheet and a method for manufacturing the same, in which one side of the sheet in the thickness direction has a lower coefficient of friction than the opposite side, without undergoing a surface treatment process. [Means for solving the problem]

[0007] (1) A method for manufacturing a silicone rubber sheet according to one embodiment for achieving the above objective is: At a minimum, a mixing step of mixing an organopolysiloxane, a curing agent for the organopolysiloxane, and an alkyl silicate, A first curing step in which the mixture obtained in the mixing step is cured, The method includes a second curing step of curing the alkyl silicate. (2) In a method for manufacturing a silicone rubber sheet according to another embodiment, the curing agent may preferably contain an organic peroxide. (3) In a method for producing a silicone rubber sheet according to another embodiment, the curing agent may preferably include a first catalyst for promoting the polymerization of the organopolysiloxane. (4) In a method for manufacturing a silicone rubber sheet according to another embodiment, preferably the first catalyst may be a platinum-based catalyst. (5) In a method for manufacturing a silicone rubber sheet according to another embodiment, the mixture may be formed into a sheet before the second curing step. (6) In another embodiment of the method for producing a silicone rubber sheet, preferably the alkyl silicate may be a methyl silicate oligomer. (7) In another embodiment of the method for producing a silicone rubber sheet, the mixture may preferably include a second catalyst for promoting the polymerization of the alkyl silicate. (8) In a method for manufacturing a silicone rubber sheet according to another embodiment, preferably the second catalyst may be a titanium-based catalyst. (9) A silicone rubber sheet according to one embodiment for achieving the above objective has a static friction coefficient measured according to JIS K7125 on one side of the thickness direction, which is 40% to 70% of the static friction coefficient measured on the opposite side of the said side. (10) A silicone rubber sheet according to one embodiment for achieving the above objective has a dynamic friction coefficient measured according to JIS K7125 on one side of the thickness direction, which is 40% to 70% of the value of the dynamic friction coefficient measured on the opposite side of the said side. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a silicone rubber sheet in which one side in the thickness direction of the sheet has a lower coefficient of friction than the opposite side, without undergoing a surface treatment process. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the main process flow of a silicone rubber sheet according to one embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Note that the embodiments described below are not intended to limit the inventions claimed in the patent claims. Furthermore, not all of the elements and combinations described in the embodiments are necessarily essential to the solution of the present invention. 1. Method for manufacturing a silicone rubber sheet

[0011] The method for producing a silicone rubber sheet according to this embodiment includes at least a mixing step (S110) of mixing an organopolysiloxane, a curing agent for the organopolysiloxane, and an alkyl silicate; a first curing step (S120) of curing the mixture obtained in the mixing step; and a second curing step (S130) of curing the alkyl silicate. The materials mixed in the mixing step may include materials other than the organopolysiloxane, the curing agent for the organopolysiloxane, and the alkyl silicate. (1) Mixing step (S110)

[0012] In the mixing step (S110), the materials described in detail below are mixed. The method of mixing each material is not particularly limited and can be appropriately selected depending on the properties of the organopolysiloxane, which is the main raw material of the silicone rubber, before curing and the curing mechanism. The method of crosslinking and curing the organopolysiloxane, which is the main raw material (also called the main material) of the silicone rubber sheet according to this embodiment, may be, for example, an addition reaction curing method in which the organopolysiloxane is cured by an addition reaction, or a peroxide curing method in which the organopolysiloxane is cured by a peroxide (especially an organic peroxide), or a method utilizing other curing mechanisms. As an example of the addition reaction curing method, a liquid first curable composition obtained by mixing organopolysiloxane and a curing catalyst and a liquid second curable composition obtained by mixing organopolysiloxane and a crosslinking agent (especially hydrogenated organopolysiloxane) can be obtained by heating at room temperature (20-25°C) or higher than room temperature. Furthermore, as a peroxide-curing method, for example, one can mention a method in which a millable-type organopolysiloxane and an organic peroxide as a curing agent are mixed under heating. (1-1) Organopolysiloxane

[0013] Organopolysiloxane, the main raw material for silicone rubber, is a polymer of organopolysiloxane represented by the following chemical formula (I). Note that formula (I) is also referred to as chemical formula (I).

[0014] [Chemical formula] (R in formula (I) 1 is a hydrocarbon group having 1 to 10 carbon atoms. n in formula (I) is, for example, 1.98 to 2.02.)

[0015] R in formula (I) 1 is a hydrocarbon group having 1 to 10, preferably 1 to 8 carbon atoms. Examples of the hydrocarbon group include an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, etc. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, etc. Examples of the cycloalkyl group include a cyclohexyl group, etc. Examples of the alkenyl group include a vinyl group, an aryl group, a butenyl group, a hexenyl group, etc. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, etc. Further, R 1 may be a group in which some or all of the hydrogen atoms of the hydrocarbon group are substituted with a halogen atom such as a halogenated alkyl group (3-chloropropyl group, 3,3,3-trifluoropropyl group, etc.) or a group substituted with a cyano group or the like. n in formula (I) is preferably 1.98 to 2.02.

[0016] The organopolysiloxane cured by an addition reaction curing type preferably has an average of 2 or more alkenyl groups in one molecule. Among the alkenyl groups, it is preferable to use a vinyl group. Further, in this component, it is preferable to use a methyl group as an example of an organic group other than the alkenyl group bonded to the silicon atom. Examples of the molecular structure of this component include linear, linearly branched with a part, branched, network, dendritic.

[0017] Examples of organopolysiloxanes that cure by addition reaction include polydimethylsiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, and (CH3)3SiO 1 / 2 The siloxane units shown are (CH3)2(CH2=CH)SiO 1 / 2 Siloxane units and SiO shown 4 / 2 Organopolysiloxanes consisting of siloxane units represented by , organopolysiloxanes in which at least a portion of the methyl groups of these organopolysiloxanes are substituted with substituents selected from alkyl groups (ethyl group, propyl group, etc.), aryl groups (phenyl group, tolyl group, etc.), and halogenated alkyl groups (3,3,3-trifluoropropyl group, etc.), organopolysiloxanes in which at least a portion of the vinyl groups of these organopolysiloxanes are substituted with alkenyl groups (allyl group, propenyl group, etc.), and mixtures of two or more of these organopolysiloxanes can be used.

[0018] The organopolysiloxane cured by the peroxide curing method is not particularly limited, but preferably has at least two alkenyl groups in one molecule. Examples include polydimethylsiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylpolysiloxane with methylphenylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylphenylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, methyl(3,3,3-trifluoropropyl)polysiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with silanol groups sealed at both ends of the molecular chain, and dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer with silanol groups sealed at both ends of the molecular chain. These can be used individually or in combination of two or more types. (1-2) Organopolysiloxane hardener

[0019] In the case of addition reaction curing, hydrogenated organopolysiloxane can preferably be used as the curing agent for organopolysiloxane. Hydrogenated organopolysiloxane has an average of two or more silicon-bonded hydrogen atoms in one molecule. Examples of organic groups that bond to silicon in this component include alkyl groups (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, etc.), aryl groups (phenyl group, tolyl group, xylyl group, etc.), and halogenated alkyl groups (3-chloropropyl group, 3,3,3-trifluoropropyl group, etc.). Among the above, the use of a methyl group is preferred. Examples of molecular structures of this component include linear, partially branched linear, branched, reticular, and dendritic structures.

[0020] As hydrogenated organopolysiloxanes, polydimethylsiloxane with dimethylhydrogensiloxy groups sealed at both ends of the molecular chain, polymethylhydrogensiloxane with trimethylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylhydrogensiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, cyclic polymethylhydrogensiloxane, organopolysiloxanes consisting of siloxane units represented by (CH3)2HSiO1 / 2 and siloxane units represented by SiO4 / 2, organopolysiloxanes in which at least a portion of the methyl groups of these organopolysiloxanes are substituted with alkyl groups (ethyl group, propyl group, etc.), aryl groups (phenyl group, tolyl group, etc.), halogenated alkyl groups (3,3,3-trifluoropropyl group, etc.), and mixtures of two or more of these organopolysiloxanes can be used. Among these, it is preferable to use a mixture of an organopolysiloxane having silicon-bonded hydrogen atoms only at both ends of the molecular chain and an organopolysiloxane having silicon-bonded side chains, as this improves the mechanical properties (especially elongation) of the resulting cured product.

[0021] In the case of addition reaction curing, the amount of hydrogenated organopolysiloxane blended is such that the molar ratio of silicon-bonded hydrogen atoms in this component to the alkenyl groups in the organopolysiloxane (component 1-1) is in the range of 0.01 to 20, preferably in the range of 0.1 to 10, and more preferably in the range of 0.1 to 5.

[0022] The curing agent described above may preferably further contain a first catalyst to promote the polymerization of organopolysiloxane. In particular, in the case of addition reaction curing, the curing agent may contain a platinum-based catalyst for the hydrosilylation reaction. Examples of platinum-based catalysts for the hydrosilylation reaction include platinum powder, platinum black, chlorplatinic acid, alcohol-modified chlorplatinic acid, complexes of platinum and diketones, complexes of chlorplatinic acid and olefins, complexes of chlorplatinic acid and alkenylsiloxanes, and these supported on a carrier (alumina, silica, carbon black, etc.). Among these, a complex of chlorplatinic acid and alkenylsiloxane is preferred due to its high catalytic activity. Furthermore, a complex of chlorplatinic acid and divinyltetramethyldisiloxane is even more preferred. The amount of this component is preferably in the range of 1 to 1,000 parts by mass, and more preferably in the range of 1 to 100 parts by mass, as platinum metal atoms, per 1,000,000 parts by mass of organopolysiloxane, which is component (1-1).

[0023] In the case of peroxide-cured types, organic peroxides can preferably be used as curing agents for organopolysiloxane. Examples of organic peroxides include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis(2,5-t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, and 1,6-hexanediol-bis-t-butyl peroxycarbonate. The amount of organic peroxide added is usually 0.1 to 5 parts by mass, and particularly preferably 0.5 to 3 parts by mass, per 100 parts by mass of the organopolysiloxane, which is component (1-1). (1-3) Alkyl silicate

[0024] Examples of alkyl silicates include methyl silicate, ethyl silicate, propyl silicate, butyl silicate, pentyl silicate, hexyl silicate, heptyl silicate, or octyl silicate. Among these, methyl silicate is preferred. Preferably, a methyl silicate oligomer can be used as the methyl silicate. For example, MKC® silicate manufactured by Mitsubishi Chemical Corporation can be used as the methyl silicate oligomer. The amount of alkyl silicate added may be 5 to 12 parts by mass, and particularly preferably 7 to 10 parts by mass, per 100 parts by mass of organopolysiloxane, which is component (1-1). (1-4) Catalyst for alkyl silicates (second catalyst)

[0025] To further cure the alkyl silicate, a second catalyst may be added to promote the condensation reaction between the alkyl silicates. Examples of the second catalyst include metal catalysts such as tin-based catalysts, titanium-based catalysts, cerium-based catalysts, zirconium-based catalysts, molybdenum-based catalysts, manganese-based catalysts, copper-based catalysts, and aluminum-based catalysts. Preferably, a titanium-based catalyst can be used as the second catalyst. Examples of titanium-based catalysts include titanium diisopropoxybis(ethylacetoacetate), titanium tetra-n-butoxide, titanium tetra-2-ethylhexoxide, and titanium tetraacetylacetonate. The amount of the second catalyst added may be 0.5 to 5 parts by mass, preferably 1 to 3 parts by mass, per 100 parts by mass of alkyl silicate. (1-4) Other ingredients

[0026] To improve the mechanical strength of the silicone rubber sheet, fillers may be added in addition to the above components. The fillers are known compounds used in the formulation of silicone rubber, and examples include fumed silica, precipitated silica, calcined silica, pulverized quartz, and powders obtained by surface-treating these silica powders with organosilicon compounds (organoalkoxysilanes, organohalosilanes, organosilazanes, etc.).

[0027] In the production of silicone rubber sheets by addition reaction curing or peroxide curing, the addition of the above-mentioned filler is optional. To improve the mechanical strength of the cured silicone rubber sheet, the amount of filler is preferably in the range of 1 to 1000 parts by mass, and more preferably in the range of 1 to 400 parts by mass, per 100 parts by mass of organosiloxane, which is component (1-1). Furthermore, the curable silicone rubber composition produced by addition reaction curing or peroxide curing may also contain other optional components, such as inorganic fillers and organic fillers such as fumed titanium oxide, diatomaceous earth, iron oxide, aluminum oxide, aluminosilicate, calcium carbonate, zinc oxide, and aluminum hydroxide. The above-mentioned curable silicone rubber composition may also contain fillers whose surfaces have been treated with the above-mentioned organosilicon compounds. The amount of filler can be selected depending on the purpose and type of filler, but it is preferably in the range of 1 to 90 parts by volume, and more preferably in the range of 5 to 60 parts by volume, per 100 parts by volume of organosiloxane, which is component (1-1). (2) First curing step (S120)

[0028] The first curing step (S120) is a step in which the organopolysiloxane in the mixture obtained in the mixing step (S110) is crosslinked and cured. This mixture contains the organopolysiloxane and a curing agent for the organopolysiloxane. The curing agent is broadly interpreted to include any of the following, depending on the curing method of the organopolysiloxane: a crosslinking agent, a crosslinking agent + first catalyst, or a peroxide. As a result of this step, the organopolysiloxane is crosslinked and cured.

[0029] Sheet forming is preferably performed before the second curing step, as described below. "Before the second curing step" is broadly interpreted to include simultaneous with or immediately after the first curing step. The forming method is not particularly limited, but examples include die forming, injection molding, extrusion molding, and calendering after extrusion. The forming method should be appropriately selected in accordance with the curing mechanism of the organopolysiloxane, as described below.

[0030] In the case of addition reaction curing, organopolysiloxane can be cured under heating in the presence of a platinum-based first catalyst and a crosslinking agent, such as hydrogenated organopolysiloxane, as curing agents. In this case, a liquid type organopolysiloxane may be used. In the case of a two-component mixture type, preferably, agent A containing organopolysiloxane and a crosslinking agent and agent B containing organopolysiloxane and a first catalyst are mixed, and then the organopolysiloxane is cured under heating. The heating temperature in the case of addition reaction curing is preferably 100 to 150°C, more preferably 110 to 140°C.

[0031] In the case of peroxide curing, preferably, a mixture containing organopolysiloxane and a peroxide as a curing agent is heated to a temperature above the decomposition temperature of the peroxide. The organopolysiloxane hardens due to the action of radicals generated by the thermal decomposition of the peroxide. The heating temperature in the case of peroxide curing is preferably 100 to 180°C, more preferably 110 to 170°C. In both addition reaction curing and peroxide curing, the curing of the organopolysiloxane is complete or nearly complete, but the alkyl silicate is not yet fully cured. (3) Second curing step (S130)

[0032] The second curing step is a step to cure the alkyl silicate. The curing of the alkyl silicate is preferably a moisture-curing type, where the alkyl silicates condense together due to the action of moisture. The second curing step is preferably carried out in the presence of a second catalyst. Preferred second catalysts include tin-based catalysts and titanium-based catalysts. The second curing step does not require heating and can proceed even at room temperature (20-25°C). In the second curing step, only one side of the silicone rubber sheet in the thickness direction is exposed to air (gas phase). This promotes the curing of the alkyl silicate on that side, resulting in lower static and dynamic friction coefficients on that side compared to the opposite side. 2. Silicone rubber sheet

[0033] In one embodiment obtained by the above manufacturing method, the static friction coefficient on one side of the thickness direction is smaller than the static friction coefficient on the opposite side. This value is 40% to 70% of the value on the other side, preferably 55% to 70%.

[0034] Furthermore, in one embodiment of the silicone rubber sheet, the coefficient of dynamic friction on one side of the sheet in the thickness direction is smaller than the coefficient of dynamic friction on the opposite side of that side. This value is 40% to 70%, preferably 55% to 70%, of the value on that side. Therefore, when one side exhibiting a small coefficient of kinetic friction comes into contact with an object, the resistance received from the contact surface is smaller when the silicone rubber sheet moves along the contact surface compared to when the opposite side of that side comes into contact with the object.

[0035] Thus, the silicone rubber sheet according to one embodiment has different frictional properties. Its smoothness on one side could be used for applications such as artificial leather. [Examples]

[0036] Next, embodiments of the present invention will be described in comparison with comparative examples. However, the present invention is not limited to the following embodiments.

[0037] 1. Evaluation of the coefficient of friction The static and dynamic friction coefficients were measured on both sides of the silicone rubber sheet being evaluated, in the thickness direction. The measurements were performed in accordance with JIS K7125-1999. Measurements were taken three times at three different locations on each surface of the sheet being evaluated. The specific measurement conditions are as follows:

[0038] Friction coefficient measuring device: Manufactured by Shinto Kagaku Co., Ltd. (Model number: HEIDON14FW) Vertical load: 100g Sliding speed: 100m / min Indenter: φ10 steel ball and φ16.7 B ball

[0039] 2. Method for producing samples <Examples> Using a vacuum degassing and stirring device manufactured by Mikista Industries Co., Ltd., 100 parts by mass of silicone compound (product code: KE-541-U(A)) manufactured by Shin-Etsu Chemical Co., Ltd. (including 60 parts by mass of organopolysiloxane and its curing catalyst), 5 parts by mass of methyl silicate (product name: MS51) manufactured by Mitsubishi Chemical Corporation, and 0.1 parts by mass of titanium ethyl acetacetate (product code: TC-750), a titanium-based catalyst manufactured by Matsumoto Fine Chemical Co., Ltd. were mixed. Here, 1 part by mass corresponds to 1 g. The specific mixing method was as follows: Each material was placed on top of the twin-screw mixing rolls of the above device, mixed, and dispensed in portions. The material required to form a sheet was cut out by dispensing in portions. Forming was performed by hot pressing using a mold. The conditions for hot pressing were a temperature of 120°C and a holding time of 5 minutes. As a result, a silicone rubber sheet with a thickness of 2 mm, a width of 150 mm, and a length of 210 mm was obtained. Next, the obtained silicone rubber sheet was left to stand for two days in an atmosphere with a temperature of 23°C and a relative humidity of 50%.

[0040] <Comparative Example> The materials used in the examples were modified by removing methyl silicate and titanium ethyl acetate. The materials were then added, mixed, dispensed, molded, and allowed to stand under constant humidity conditions using the same apparatus and conditions as in the examples.

[0041] Table 1 shows the materials and their ratios (parts by mass) of the silicone rubber sheets produced under the conditions of the Examples and Comparative Examples. Table 2 shows the static and dynamic friction coefficients of one side of the measured surface of each silicone rubber sheet obtained using a φ10 mm steel ball as an indenter. Table 3 shows the static and dynamic friction coefficients of the same surface as in Table 2 when a φ16.7 mm marble was used as an indenter. Here, the "ratio of average values" in Tables 2 and 3 is the value obtained by dividing the average value of the friction coefficient by the average value of the friction coefficient of the Comparative Example (rounded to two decimal places). The measured surface refers to both sides of the silicone rubber sheet in the thickness direction. The surfaces on both sides of the thickness direction of the silicone rubber obtained under the conditions of the Comparative Example had almost the same static and dynamic friction coefficients. Furthermore, the static and dynamic friction coefficients of the surface opposite to the one side in the thickness direction of the silicone rubber obtained under the conditions of the Examples had almost the same static and dynamic friction coefficients as the surfaces on both sides of the thickness direction of the silicone rubber obtained under the conditions of the Comparative Example.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] As shown in Tables 2 and 3, the static and dynamic friction coefficients of one side of the silicone rubber sheet obtained in the examples were 30-40% lower than those of the opposite side. Furthermore, both sides of the silicone rubber sheet obtained in the comparative example had the same static and dynamic friction coefficients as the opposite side of the silicone rubber sheet obtained in the examples. In other words, it was found that only one side of the silicone rubber sheet prepared with added methyl silicate had an extremely low friction coefficient. From these results, it is considered that adding methyl silicate to the silicone rubber sheet material can reduce the friction coefficient of the silicone rubber sheet without surface treatment. [Industrial applicability]

[0046] The present invention can be used, for example, in artificial leather and the like.

Claims

1. At a minimum, a mixing step of mixing an organopolysiloxane, a curing agent for the organopolysiloxane, and an alkyl silicate, A first curing step in which the mixture obtained in the mixing step is cured, A method for producing a silicone rubber sheet, comprising a second curing step of curing the alkyl silicate.

2. The method for producing a silicone rubber sheet according to claim 1, characterized in that the curing agent contains an organic peroxide.

3. The method for producing a silicone rubber sheet according to claim 1, characterized in that the curing agent includes a first catalyst for promoting the polymerization of the organopolysiloxane.

4. The method for producing a silicone rubber sheet according to claim 3, characterized in that the first catalyst is a platinum-based catalyst.

5. The method for producing a silicone rubber sheet according to claim 1, characterized in that the mixture is formed into a sheet before the second curing step.

6. A method for producing a silicone rubber sheet according to any one of claims 1 to 5, characterized in that the alkyl silicate is a methyl silicate oligomer.

7. A method for producing a silicone rubber sheet according to any one of claims 1 to 5, characterized in that the mixture includes a second catalyst for promoting the polymerization of the alkyl silicate.

8. The method for producing a silicone rubber sheet according to claim 7, characterized in that the second catalyst is a titanium-based catalyst.

9. It is a silicone rubber sheet, A silicone rubber sheet characterized in that the static friction coefficient measured on one side in the thickness direction according to JIS K7125 is 40% to 70% of the static friction coefficient measured on the opposite side.

10. It is a silicone rubber sheet, A silicone rubber sheet characterized in that the coefficient of dynamic friction measured on one side in the thickness direction according to JIS K7125 is 40% to 70% of the coefficient of dynamic friction measured on the opposite side.

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