Thermally conductive silicone rubber sheet

Abstract

To provide a thermally conductive silicone rubber sheet having a high filling rate of a thermally conductive filler, high thermal conductivity, low hardness, no restriction on the structure of the obtained sheet, and low heat transfer loss. [Solution] A thermally conductive silicone rubber sheet made from a cured product of a thermally conductive silicone rubber composition having an inorganic filler content of 50% by volume or more and 90% by volume or less, the thermally conductive silicone rubber sheet having a hardness of 60 or less as measured at 25°C using an Asker C hardness tester and a thickness variation of 200 μm or less.

Description

[Technical Field]

[0001] The present invention relates to a heat-conductive silicone rubber sheet that is effective in countering heat from various heat-generating components. [Background technology]

[0002] Thermosetting silicone rubber has excellent heat resistance and electrical insulation properties and is used in a variety of applications. In particular, thermally conductive silicone rubber sheets used to counter heat generation in electronic devices and other devices are required to have higher thermal conductivity due to the increasing integration of such devices. In addition, to reduce heat transfer loss, low hardness is also required to ensure good adhesion to heat-generating components (Patent Document 1).

[0003] One way to achieve high thermal conductivity is to increase the amount of thermally conductive filler in the thermally conductive silicone rubber composition, but this also increases the viscosity of the composition.Methods of heat-curing a highly viscous composition to form a sheet include compression molding using a mold and coating a composition diluted with a solvent.

[0004] Among these, the production of sheets by compression molding using a mold is a method that is often used industrially because it can be produced using simple equipment.

[0005] However, in the case of compression molding, if too little material is supplied to the mold, a molding defect known as a short mold may occur.Furthermore, if too much material is supplied to the mold, flash may protrude from the mold, resulting in a decrease in material yield and an increased likelihood of variations in sheet thickness.

[0006] If the thickness of the thermally conductive sheet varies greatly, tiny gaps form between the heat-generating component and the sheet, creating a layer of air there, making it difficult for heat to be transferred to the heat-dissipating component. One solution to this problem is to devise a shape for the heat-dissipating component (Patent Document 2), but this is not a sufficient solution as it limits the structure of the heat-dissipating component. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-030774 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-129954 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a thermally conductive silicone rubber sheet that has high thermal conductivity, has low hardness despite a high filling rate of a thermally conductive filler, is not limited in structure of the sheet obtained, and has low heat transfer loss. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by the following thermally conductive silicone rubber sheet, which has a high filling rate of thermally conductive filler, a low hardness, and thickness variation below a certain level, and thus completed the present invention. Specifically, the following thermally conductive silicone rubber sheet is used. [1] A thermally conductive silicone rubber sheet made of a cured product of a thermally conductive silicone rubber composition having an inorganic filler content of 50% by volume or more and 90% by volume or less, The hardness measured at 25°C using an Asker C hardness tester is 60 or less, A thermally conductive silicone rubber sheet with a thickness variation of 200 μm or less. [2] [1] The thermally conductive silicone rubber sheet according to [1], wherein the thermal conductivity of the thermally conductive silicone rubber sheet measured by the hot disc method is 2.0 W / m·K or more. [3] The thermally conductive silicone rubber sheet according to [1] or [2], wherein the thermally conductive silicone rubber composition is an addition-curing type silicone rubber composition. [Effects of the Invention]

[0010] The thermally conductive silicone rubber sheet of the present invention can be molded into any desired thickness, shape, and other configurations, so there are no limitations on the sheet structure and there is little variation in thickness, resulting in excellent adhesion to heat-generating components. Furthermore, because the thermally conductive silicone rubber sheet adheres tightly to the heat-generating component without any gaps, heat resistance does not increase and heat can be dissipated efficiently. DETAILED DESCRIPTION OF THE INVENTION

[0011] The thermally conductive silicone rubber sheet of the present invention is a thermally conductive silicone rubber sheet made from a cured product of a thermally conductive silicone rubber composition having an inorganic filler content of 50% by volume or more and 90% by volume or less, characterized in that it has a hardness of 60 or less as measured at 25°C using an Asker C hardness tester, and a thickness variation of 200 μm or less. This is described in detail below.

[0012] [Thermal conductive silicone rubber sheet] The thermally conductive silicone rubber sheet of the present invention is characterized in that the hardness, as measured at 25°C using an Asker C hardness tester according to the method described in JIS K7312:1996, Appendix 2, is 60 or less, and preferably 2 to 40. Furthermore, because the sheet of the present invention has a low hardness, it has excellent adhesion to heat-generating components and can reduce contact thermal resistance.

[0013] The thermally conductive silicone rubber sheet of the present invention has a thickness variation of 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less. By suppressing thickness variation, it is possible to reduce the gap between the component and the sheet and thereby reduce the contact thermal resistance. In the present invention, thickness variation is determined by the following method.

[0014] [Method for measuring thickness variation] Prepare a thermally conductive silicone rubber sheet measuring 300mm x 400mm, and measure the thickness at nine points with a dial gauge, each at least 80mm apart. The difference between the maximum and minimum values ​​of these nine measurements is taken as the thickness variation (μm).

[0015] The thermally conductive silicone rubber sheet of the present invention preferably has a thermal conductivity of 2.0 W / m·K or more, and more preferably 4 to 20 W / m·K, as measured by the hot disc method.

[0016] [Thermal conductive silicone rubber composition] The thermally conductive silicone rubber composition that is the raw material for the thermally conductive silicone rubber sheet of the present invention is characterized by an inorganic filler content of 50% by volume or more and 90% by volume or less. This range is required to impart high thermal conductivity to the rubber sheet. The inorganic filler content is preferably 55 to 87% by volume, and more preferably 60 to 86% by volume.

[0017] It goes without saying that inorganic fillers with excellent thermal conductivity are preferred, but a small amount of inorganic fillers with poor thermal conductivity may also be used in combination. By filling the thermally conductive silicone rubber sheet with a high content of inorganic filler having excellent thermal conductivity, the thermal conductivity of the sheet can be increased.

[0018] Examples of inorganic fillers with excellent thermal conductivity include carbon or metal elements, metal oxides, metal hydroxides, and metal nitrides.

[0019] Specific examples include carbon such as graphite, diamond, and carbon nanotubes, elemental metals such as aluminum and copper, metal oxides such as zinc oxide, magnesium oxide, aluminum oxide, silicon dioxide, cerium oxide, and iron oxide, metal hydroxides such as aluminum hydroxide and cerium hydroxide, and metal nitrides such as aluminum nitride and boron nitride. Of these, aluminum oxide, magnesium oxide, and aluminum hydroxide are preferred. The inorganic fillers having excellent thermal conductivity can be used alone or in appropriate combination of two or more kinds, and a combination of large particle components and small particle components is preferred.

[0020] If the average particle size of the large particle component is 5 μm or more, the viscosity of the resulting composition will not be too high and the processability will not be reduced.If the average particle size of the large particle component is 150 μm or less, the resulting composition will not be non-uniform and there will be no risk of oil bleeding, so the range of 5 to 150 μm, preferably 10 to 100 μm, is preferred.

[0021] Furthermore, if the average particle size of the small particle component is 0.01 μm or more, the viscosity of the resulting composition will not be too high and the processability will not be impaired. On the other hand, if it is less than 5 μm, the resulting composition will not be non-uniform, so it is best to keep it in the range of 0.01 μm or more and less than 5 μm, preferably 0.1 to 3 μm.

[0022] The ratio of the large particle component to the small particle component is not particularly limited, but is preferably in the range of 9:1 to 1:9 (mass ratio).The shapes of the large particle component and the small particle component are not particularly limited and may be spherical, irregular, acicular, etc. In the present invention, the average particle size is determined as the cumulative 50% particle size (D50) on a volume basis in particle size distribution measurement by laser light diffraction method.

[0023] Components other than the inorganic filler include a silicone polymer component that exhibits rubber elasticity through crosslinking. Silicone polymer components can be classified into several types depending on the curing method, such as addition-curable silicone, condensation-curable silicone, peroxide-curable silicone, and ultraviolet-curable silicone. When producing a sheet by compression molding using a mold, addition-curable silicone is preferred.

[0024] The addition-curable silicone composition includes an addition-curable silicone composition containing the following (A), (B), and (D) as essential components: (A) Organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule (B) Organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule (D) Addition reaction catalyst By blending the inorganic filler into this addition-curable silicone composition, it is possible to obtain a silicone rubber composition with superior thermal conductivity.

[0025] (A) Organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule The alkenyl-containing organopolysiloxane of component (A) has two or more alkenyl groups bonded to silicon atoms per molecule, and the main chain generally consists essentially of repeating diorganosiloxane units, although this may also include a branched structure as part of the molecular structure, or may be cyclic. From the perspective of the mechanical strength and other physical properties of the thermally conductive silicone rubber sheet of the present invention, the organopolysiloxane of component (A) is preferably a linear diorganopolysiloxane.

[0026] Groups other than alkenyl groups bonded to silicon atoms include unsubstituted or substituted monovalent hydrocarbon groups, such as alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl. aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl, as well as groups in which some or all of the hydrogen atoms bonded to carbon atoms of these groups have been substituted with halogen atoms such as fluorine, chlorine, or bromine, or with cyano groups, such as chloromethyl, 2-bromoethyl, 3-chloropropyl, 3,3,3-trifluoropropyl, chlorophenyl, fluorophenyl, cyanoethyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl. Of these, the groups other than alkenyl groups bonded to silicon atoms in the organopolysiloxane of component (A) preferably contain 1 to 10 carbon atoms, and more preferably 1 to 6 carbon atoms, and are preferably unsubstituted or substituted alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, propyl, chloromethyl, bromoethyl, 3,3,3-trifluoropropyl, and cyanoethyl, and unsubstituted or substituted phenyl groups, such as phenyl, chlorophenyl, and fluorophenyl. Furthermore, all of the groups bonded to the silicon atom other than the alkenyl group may be the same.

[0027] Examples of alkenyl groups include those having 2 to 8 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups, with lower alkenyl groups such as vinyl and allyl being preferred, and vinyl being particularly preferred.The organopolysiloxane of component (A) has two or more alkenyl groups per molecule, and in order to improve the flexibility of the thermally conductive silicone rubber sheet of the present invention, it is preferred that the alkenyl groups be bonded only to silicon atoms at the ends of the molecular chain.

[0028] The kinematic viscosity of this organopolysiloxane at 25°C is preferably 10 to 100,000 mm 2 / s, and more preferably 300 to 50,000 mm 2 / s. If the kinematic viscosity is too low, the storage stability of the resulting composition may be poor, and if it is too high, the extensibility of the resulting composition may be poor. The kinematic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer according to JIS Z8803:2011.

[0029] The organopolysiloxane of component (A) may be used alone or in combination of two or more different viscosities. The amount of component (A) in the composition is preferably 0.5 to 10 mass %, more preferably 1 to 5 mass %.

[0030] (B) Organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule The organohydrogenpolysiloxane of component (B) is an organohydrogenpolysiloxane having two or more, preferably 2 to 100, hydrogen atoms directly bonded to silicon atoms (Si-H groups) per molecule, and functions as a crosslinker for component (A). Specifically, the Si-H groups in component (B) and the alkenyl groups in component (A) undergo addition via a hydrosilylation reaction promoted by the addition reaction catalyst (D), described below, to provide a three-dimensional network structure with a crosslinked structure in the resulting cured product. Note that if the organohydrogenpolysiloxane of component (B) has one or fewer Si-H groups, it may not cure. The average structural formula of organohydrogenpolysiloxane is expressed as follows: [ka] In formula (3), R is independently an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic unsaturated bonds or a hydrogen atom, provided that at least two Rs are hydrogen atoms, and n is a number of 1 or greater.

[0031] In formula (3), examples of the unsubstituted or substituted monovalent hydrocarbon group R containing no aliphatic unsaturated bonds other than hydrogen include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl. Examples of such groups include aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl, and groups in which some or all of the hydrogen atoms bonded to carbon atoms of these groups have been substituted with halogen atoms such as fluorine, chlorine, and bromine, or with cyano groups, such as chloromethyl, 2-bromoethyl, 3-chloropropyl, 3,3,3-trifluoropropyl, chlorophenyl, fluorophenyl, cyanoethyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl. Among these, the unsubstituted or substituted monovalent hydrocarbon group for R that does not contain an aliphatic unsaturated bond preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and are preferably unsubstituted or substituted alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, propyl, chloromethyl, bromoethyl, 3,3,3-trifluoropropyl, and cyanoethyl, and unsubstituted or substituted phenyl groups, such as phenyl, chlorophenyl, and fluorophenyl. In addition, all of the R's may be the same.

[0032] In formula (3), n is a number of 1 or more, and preferably 1-200.

[0033] The amount of component (B) added is such that the number of Si-H groups derived from component (B) per alkenyl group derived from component (A) is 0.2 to 2.0, preferably 0.3 to 1.5, and more preferably 0.5 to 1.0. If the number of Si-H groups in component (B) per alkenyl group derived from component (A) is less than 0.2, the composition may not cure, or the strength of the cured product may be insufficient to maintain its shape as a sheet and make it difficult to handle. If the number of Si-H groups in component (B) is more than 2.0 per alkenyl group derived from component (A), the cured product will lose flexibility and its thermal resistance will increase significantly.

[0034] (D) Addition reaction catalyst The (D) addition reaction catalyst is a catalyst for promoting the addition reaction between the alkenyl group derived from component (A) and the Si-H group derived from component (B), and examples thereof include catalysts well known for use in hydrosilylation reactions. Specific examples include platinum group metals such as platinum (including platinum black), rhodium, and palladium; platinum chlorides, chloroplatinic acid, and chloroplatinic acid salts such as HPtCl.sub.4·nH.sub.2O, HPtCl.sub.6·nH.sub.2O, NaHPtCl.sub.6·nH.sub.2O, KaHPtCl.sub.6·nH.sub.2O, NaPtCl.sub.6·nH.sub.2O, KPtCl.sub.4·nH.sub.2O, PtCl.sub.4·nH.sub.2O, PtCl.sub.2, and NaHPtCl.sub.4·nH.sub.2O (wherein n is an integer of 0 to 6, preferably 0 or 6); alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972); complexes of chloroplatinic acid and olefins (see U.S. Pat. Nos. 3,159,601, 3,159,662, and 3,775,452); platinum black, palladium, or other platinum group metals supported on a carrier such as aluminum oxide, silica, or carbon; rhodium-olefin complexes; chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst); and complexes of platinum chloride, chloroplatinic acid, or chloroplatinate salts with vinyl group-containing siloxanes, particularly vinyl group-containing cyclic siloxanes. The amount of component (D) used may be a so-called catalytic amount, and is usually about 0.1 to 1,000 ppm in terms of the mass of platinum group metal element relative to component (A).

[0035] The thermally conductive silicone rubber composition may contain optional components such as a surface treatment agent, an addition reaction inhibitor, a plasticizer, a pigment, a heat resistance imparting agent, and an internal release agent.

[0036] Examples of surface treatment agents include organosilicon compounds such as alkoxysilanes, alkylsilazanes, and silane coupling agents, and organopolysiloxanes having alkoxysilyl groups. Among these, linear dimethylpolysiloxanes end-blocked with trimethoxysilyl groups are preferred.

[0037] The addition reaction inhibitor is not particularly limited as long as it is one that is generally used in addition-curable silicone compositions, but specific examples include acetylene compounds such as 1-ethynyl-1-cyclohexanol, 3-butyn-1-ol, and 3-methyl-1-tridecyn-3-ol, various nitrogen compounds, organic phosphorus compounds, oxime compounds, and organic chloro compounds.

[0038] The plasticizer may be an organopolysiloxane having no reactive functional groups, which is preferably liquid at 25° C. A specific example is linear dimethylpolysiloxane.

[0039] Examples of coloring pigments include inorganic pigments such as carbon black, red iron oxide, silica, and titanium oxide.

[0040] Examples of heat resistance imparting agents include cerium oxide, cerium hydroxide, iron oxide (for example, yellow iron oxide), titanium oxide (for example, titanium oxide doped with a metal oxide), and carbon. The compounds exemplified as the pigment and heat resistance imparting agent are also used as the thermally conductive inorganic filler. However, when blended as a pigment or heat resistance imparting agent, the amount is much less than the amount blended for the purpose of imparting thermal conductivity, and therefore they are not included in the blending amount of the inorganic filler.

[0041] [Method of producing the composition] The thermally conductive silicone rubber composition, which is the raw material for the thermally conductive silicone rubber sheet of the present invention, is produced by uniformly mixing the above-mentioned components. The mixing method may be any conventionally known method, and examples of mixing equipment include a planetary mixer. All of the components may be mixed at once, or one or more components may be mixed in several stages.

[0042] [Method for manufacturing thermally conductive silicone rubber sheets] The thermally conductive silicone rubber sheet can be produced by adjusting the thermally conductive silicone rubber composition to a desired thickness by a known method and then curing the composition. (Thickness adjustment process) Methods for adjusting the thickness of the thermally conductive silicone rubber sheet include, for example, sandwiching the thermally conductive silicone rubber composition between two resin films and then treating it with a roll press, or treating it by compression molding with a mold, molding with a vacuum press, injection molding, etc. The conditions for each treatment are optimized as appropriate depending on the plasticity of the silicone rubber composition used, the rolling ratio of the material, etc. (hardening process) The curing conditions for the thermally conductive silicone composition can be selected from known methods depending on the curing method for the silicone polymer component. In the case of an addition reaction curable silicone composition, the curing time is, for example, 100 to 150°C for 1 to 20 minutes, and preferably 120°C for 10 minutes. Following the thickness adjustment step, the curing is preferably carried out by sandwiching the thermally conductive silicone rubber composition between two resin films and curing the composition while pressing at 100 to 150°C for 1 to 20 minutes. This method allows the thermally conductive silicone rubber sheet of the present invention to be obtained. The resin film to be used is one that can withstand heat treatment after lamination and has a heat distortion temperature of 100° C. or higher, such as a film made of PET, PBT, or polycarbonate.

[0043] [Thermal conductivity of thermally conductive silicone rubber sheet] The thermal conductivity of the thermally conductive silicone rubber sheet of the present invention, measured at 25°C by the hot disc method, is preferably 2.0 W / m·K or higher, and more preferably 2.5 W / m·K or higher. If the thermal conductivity is less than 2.0 W / m·K, it will be difficult to apply the sheet to a heat-generating element with a large calorific value. There is no particular upper limit to the thermal conductivity of the sheet, but it is preferably 40 W / m·K or lower, which is the thermal conductivity of magnesium oxide, the highest among the compositions. The thermal conductivity values ​​of the thermally conductive silicone rubber sheets are values ​​measured when the thermally conductive silicone rubber composition is cured at 120° C. for 10 minutes. [Example]

[0044] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited thereto. In the following, the kinematic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer according to JIS Z8803:2011, and the average particle size is a volume-based cumulative 50% particle size (D50) value measured using a particle size distribution analyzer MT3000II manufactured by Microtrack Bell.

[0045] [Preparation of Composition] Components (A) to (G) used in the following examples and comparative examples are shown below. (A) Component: An organopolysiloxane represented by the following formula (1): [ka] (wherein f is a number that gives the following kinematic viscosity) (A-1) Kinematic viscosity: 600mm 2 / s (A-2) Kinematic viscosity: 30,000mm 2 / s

[0046] (B) Ingredients: Organohydrogenpolysiloxane represented by the following formula (2): [ka]

[0047] (C) Ingredients: Spherical alumina, amorphous alumina, and aluminum nitride with the following average particle sizes: (C-1) Granular aluminum nitride with an average particle size of 1.0 μm (C-2) Irregular alumina with an average particle size of 2.3 μm (C-3) Spherical alumina with an average particle size of 10 μm (C-4) Spherical alumina with an average particle size of 45 μm (C-5) Spherical alumina with an average particle size of 70 μm (C-6) Irregular shaped aluminum nitride with an average particle size of 30 μm (C-7) Irregular shaped aluminum nitride with an average particle size of 80 μm

[0048] (D) Ingredients: 5% by mass solution of chloroplatinic acid in 2-ethylhexanol

[0049] (E) Ingredients: 3-Methyl-1-tridecyn-3-ol as an addition reaction inhibitor

[0050] (F) Ingredients: Dimethylpolysiloxane represented by the following formula (4), having an average degree of polymerization of 30 and one end blocked with a trimethoxysilyl group: [ka]

[0051] (G) Component As a plasticizer, dimethylpolysiloxane represented by the following formula (5) [ka]

[0052] Components (A), (C), (F), and (G) were added in the amounts shown in Table 1 below, items 1 to 3, and kneaded for 60 minutes using a planetary mixer. Component (D) was then added in the amount shown in Table 1 below, followed by the addition of methylphenyl silicone oil (trade name: KF-54, manufactured by Shin-Etsu Chemical Co., Ltd.) as an internal release agent to promote release from the separator, and the mixture was kneaded for 30 minutes. To this was further added the components (B) and (E) in the amounts shown in Table 1, and the mixture was kneaded for 30 minutes to obtain a composition.

[0053] [Forming method] A 50 μm thick PET film was placed on the lower mold, and a 2 mm thick, 330 mm x 440 mm medium mold was placed on top of the PET film. The composition obtained in the specified amount shown in Table 1 was poured into the medium mold, and a 50 μm thick PET film was placed on top of the composition. The thickness of the composition was then adjusted to 2.5 to 3.0 mm using a roll press. An upper mold was then placed on the PET film and subjected to press molding. Molding was performed using a press molding machine at a pressure of 5 x 10 6 The test was carried out under the conditions of 1 Pa, 120° C., and 10 minutes (Examples 1 to 3, Comparative Examples 1 and 2). On the other hand, sheet molding was carried out using the above steps, excluding the step of adjusting the thickness of the composition by roll pressing (Comparative Examples 3 to 5). The edges of the formed sheet were cut evenly to a size of 300 mm x 400 mm.

[0054] [Evaluation method] Thickness and thickness variation of cured product For the cured products (300 mm × 400 mm thermally conductive silicone rubber sheets) obtained in Examples 1 to 3 and Comparative Examples 1 to 5, the thickness was measured using a dial gauge at nine points that were at least 80 mm apart. The sheet thickness was calculated by subtracting the thickness of the two PET films (100 μm) from the total thickness including the PET film and the sheet. The average value of the nine measurements obtained by this method was taken as the sheet thickness. The difference between the maximum and minimum measured thickness values ​​was taken as the thickness variation (μm). The results are shown in Table 2.

[0055] Hardness of cured product: The compositions used in Examples 1 to 3 and Comparative Examples 1 to 5 were cured under the above conditions using a press molding machine to form six 2 mm thick sheets, which were then measured for hardness at 25° C. using an Asker C hardness tester. The results are shown in Table 2.

[0056] Thermal conductivity of cured product: The compositions used in Examples 1 to 3 and Comparative Examples 1 to 5 were cured under the above conditions using a press molding machine to form six 2 mm thick sheets, and the thermal conductivity of the sheets was measured using a thermal conductivity meter (product name: TPS-2500S, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) The results are shown in Table 2.

[0057] Compression heat resistance of cured product: The compositions used in Examples 1 to 3 and Comparative Examples 1 to 5 were cured under the above conditions using a press molding machine to form 2 mm thick sheets, and the heat resistance at 10% compression was measured. The measurement was carried out in accordance with ASTM D 5470. The results are shown in Table 2.

[0058] [Table 1]

[0059] [Table 2]

[0060] In Examples 1 to 3, cured products with little variation in thickness were obtained. Because adhesion to the adherend was good, the thermal resistance during compression was also low. In Comparative Examples 3 to 5, the cured products had large variation in thickness, resulting in poor adhesion to the adherend. Each Comparative Example had increased thermal resistance compared to the corresponding Example.

Claims

1. A thermally conductive silicone rubber sheet made of a cured product of a thermally conductive silicone rubber composition having an inorganic filler content of 60% by volume or more and 90% by volume or less, The thermally conductive silicone rubber composition comprises the following (A), (B), and (D): (A) Organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule (B) Organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule (D) Addition reaction catalyst an addition-curable silicone composition comprising the following as an essential component, and the amount of component (B) added is such that the number of Si—H groups derived from component (B) is 0.5 to 1.0 per alkenyl group derived from component (A); The hardness measured at 25°C using an Asker C hardness tester is 60 or less, A thermally conductive silicone rubber sheet having a thickness variation of 150 μm or less in a 300 x 400 mm sheet.

2. 2. The thermally conductive silicone rubber sheet according to claim 1, wherein the thermal conductivity of the thermally conductive silicone rubber sheet measured by the hot disk method is 2.0 W / m·K or more.

3. 2. The thermally conductive silicone rubber sheet according to claim 1, wherein the thermally conductive silicone rubber composition is an addition-curing type silicone rubber composition.

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