Thermally conductive silicone composite sheet

Abstract

Provided is a thermally conductive silicone composite sheet in which a high-hardness thermally conductive silicone layer and a low-hardness thermally conductive silicone layer are laminated so as to be in a favorable state of adhesion.　The thermally conductive silicone composite sheet comprises a support layer (X), a high-hardness thermally conductive silicone rubber layer (Y), and a low-hardness thermally conductive silicone rubber layer (Z) laminated in this order. The support layer (X) is obtained by filling a mesh-like reinforcing material with a cured product of a thermally conductive composition. The high-hardness thermally conductive silicone rubber layer (Y) and the low-hardness thermally conductive silicone rubber layer (Z) are both a cured product of an addition-curable silicone rubber composition.

Description

Thermally conductive silicone composite sheet

[0001] The present invention relates to a thermally conductive silicone composite sheet.

[0002] A thermally conductive silicone composite sheet, consisting of a high-hardness thermally conductive silicone rubber layer (high-hardness layer) and a low-hardness thermally conductive silicone rubber layer (low-hardness layer), is used as a material for heat dissipation in electronic components and other devices. While the high-hardness layer is easy to handle, it suffers from the problem of high stress when fixed between the heat-generating component and the cooling component. On the other hand, the low-hardness layer does not apply high stress to the heat-generating component and has good adhesion, resulting in low contact thermal resistance. However, due to its low hardness, it is difficult to handle and easily deforms. Laminating these layers results in a composite sheet that is easy to handle and does not apply stress to the heat-generating component. Furthermore, it is known that reinforcing the high-hardness layer with glass cloth or the like can further improve handleability and strength (Patent Document 1). However, because the high-hardness layer is formed using a peroxide vulcanization system and the low-hardness layer is formed using an addition vulcanization system, the two layers have poor compatibility. Therefore, a large amount of primer treatment is required to improve the adhesion between the two. Even if the adhesion between the two is improved, reliability is compromised, such as oil bleeding from the low-hardness layer. One solution to this problem is to apply an uncured low-hardness layer onto an uncured high-hardness layer and simultaneously cure both layers. A method is also known in which sufficient adhesion between the two layers is achieved without primer treatment (Patent Document 2). However, forming a high-hardness layer requires a release-treated resin film as the substrate. A peeling process for this substrate is required after molding, and the use of fluorine-based release agents with excellent release properties is being restricted due to recent environmental regulations. Furthermore, because the surface of the substrate is mirror-finished, tack remains in the high-hardness layer after curing. This results in a thermally conductive silicone composite sheet with tack in both the high-hardness and low-hardness layers, which may reduce workability during alignment and other operations during use.

[0003] On the other hand, there is a method for obtaining a thermally conductive silicone composite sheet in which a mesh-like reinforcing material filled with a thermally conductive material is interposed between the high-hardness layer and the low-hardness layer, and the anchoring effect of this interposition improves adhesion (Patent Document 3). However, increasing the amount of thermally conductive filler in the low-hardness layer reduces the flexibility of the low-hardness layer, making it difficult to obtain good adhesion between the low-hardness layer and the high-hardness layer. Furthermore, since the low-hardness layer is thin, with a thickness of 0.015 to 0.2 mm, the compressive stress is high, making it difficult to use under high compression.

[0004] Japanese Patent Application Laid-Open No. 06-155517 Japanese Patent Application Laid-Open No. 2021-089908 Japanese Patent Application Laid-Open No. 2014-193598

[0005] The present invention has been made to solve the above problems, and aims to provide a thermally conductive silicone composite sheet in which a high-hardness thermally conductive silicone rubber layer and a low-hardness thermally conductive silicone rubber layer are laminated in a state of good adhesion. Another aim is to suppress oil bleeding from the composite sheet. A further aim is to eliminate the need for a resin film that is required when molding a silicone sheet.

[0006] The present inventors conducted extensive research to solve the above problems and discovered that the following thermally conductive silicone composite sheet could achieve the above object, leading to the completion of the present invention. That is, the present invention provides the following thermally conductive silicone composite sheet.

[0007] [1] A thermally conductive silicone composite sheet comprising a support layer (X), a high-hardness thermally conductive silicone rubber layer (Y), and a low-hardness thermally conductive silicone rubber layer (Z) laminated in this order, wherein the support layer (X) comprises a mesh-like reinforcing material sealed with a cured product of a thermally conductive composition, and the high-hardness thermally conductive silicone rubber layer (Y) and the low-hardness thermally conductive silicone rubber layer (Z) are each cured products of an addition-cure silicone rubber composition, and the high-hardness thermally conductive silicone rubber layer (Y) has a hardness of 50 to 97 as measured by a Shore A hardness scale according to the method specified in JIS K6253-1:2012, and the low-hardness thermally conductive silicone rubber layer (Z) has a hardness of 2 to 30 as measured by an Asker C hardness scale according to the method specified in JIS K7312:1996. [2] The thermally conductive silicone composite sheet according to [1], wherein the mesh-like reinforcing material is glass cloth. [3] The thermally conductive silicone composite sheet according to [1] or [2], wherein the high-hardness thermally conductive silicone rubber layer (Y) is a cured product of an addition-curable silicone rubber composition comprising the following (A1) to (D1): (A1) 100 parts by mass of an organopolysiloxane having two or more alkenyl groups per molecule and an average degree of polymerization of 100 to 20,000; (B1) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, in an amount such that the ratio of the number of moles of hydrosilyl groups in component (B1) to the number of moles of alkenyl groups in component (A1) is 1.0 to 3.5; (C1) a platinum group metal catalyst, in terms of the mass of platinum group metal, of 0.1 to 1,000 ppm; and (D1) a thermally conductive filler, in an amount such that 300 to 4,000 parts by mass of a metal stearate compound represented by the following formula (2) is added to the addition-curable silicone rubber composition. (In the formula, R 5are independently alkyl groups having 1 to 6 carbon atoms, and c is a number from 4 to 100. The thermally conductive silicone composite sheet according to [3], containing a dimethylpolysiloxane in which one molecular chain end is capped with a trialkoxy group, represented by the formula (I). [5] The thermally conductive silicone composite sheet according to any of [1] to [4], in which the thermally conductive composition constituting the (X) layer is the same as the thermally conductive silicone rubber composition constituting the high hardness thermally conductive silicone rubber layer (Y). [6] The thermally conductive silicone composite sheet according to any of [1] to [5], in which the low hardness thermally conductive silicone rubber layer (Z) is a cured product of an addition-cure silicone rubber composition containing the following (A2) to (E2): (A2) Organopolysiloxane having two or more alkenyl groups per molecule and an average degree of polymerization of 100 to 2,000: 100 parts by mass. (B2) Organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the ratio of the number of moles of hydrosilyl groups in component (B2) to the number of moles of alkenyl groups in component (A2) is 0.5 to 1.5. (C2) Platinum group metal catalyst: 0.1 to 1,000 ppm in terms of the mass of platinum group metal. (D2) Thermally conductive filler: 500 to 4,000 parts by mass. (E2) Dimethylpolysiloxane having one molecular chain end blocked with a trialkoxy group, represented by the following formula (2), as a surface treatment agent: 10 to 300 parts by mass. (In the formula, R 5 are independently an alkyl group having 1 to 6 carbon atoms, and c is a number from 4 to 100.) [7] The thermally conductive silicone composite sheet according to any one of [1] to [6], wherein the thickness of the high-hardness thermally conductive silicone rubber layer (Y) is 0.15 to 0.5 mm, and the thickness of the entire thermally conductive silicone composite sheet is 0.3 to 10 mm. [8] The thermally conductive silicone composite sheet according to any one of [1] to [6], wherein the thickness of the support layer (X) is 0.03 to 0.10 mm.

[0008] The thermally conductive silicone composite sheet of the present invention can be produced simply and stably by laminating a high-hardness thermally conductive silicone rubber layer and a low-hardness thermally conductive silicone rubber layer of the thermally conductive silicone composite sheet in a state of good adhesion. Furthermore, because the high-hardness thermally conductive silicone rubber layer is applied to a support layer sealed with a thermally conductive composition, a release-treated resin film serving as the base is not required, eliminating the need for the user to peel off the base. Furthermore, the tackiness of the high-hardness thermally conductive silicone rubber layer can be reduced by curing it by addition curing, allowing the coated surface to be stored without covering it with a release-treated resin film before laminating the low-hardness thermally conductive silicone layer. Furthermore, if oil bleeding occurs from the low-hardness thermally conductive silicone rubber layer after adhesion, the support layer with a network structure can contain it, resulting in superior oil-bleed resistance compared to conventional thermally conductive silicone composite sheets. Therefore, the thermally conductive silicone composition of the present invention is useful as a heat-dissipating material for electric vehicles, mobile devices, and wearable devices, which require lightweight construction.

[0009] The present invention will be described in more detail below.

[0010] <Thermal Conductive Silicone Composite Sheet> The present invention provides a thermally conductive silicone composite sheet having a high-hardness thermally conductive silicone rubber layer (Y) laminated on a support layer (X) comprising a mesh-like reinforcing material sealed with a cured product of a thermally conductive composition, and a low-hardness thermally conductive silicone rubber layer (Z) laminated on the high-hardness thermally conductive silicone rubber layer (Y), wherein the hardness of the high-hardness silicone rubber layer (Y) is greater than the hardness of the low-hardness silicone rubber layer (Z).

[0011] The thermally conductive silicone composite sheet has a support layer (X), a high-hardness thermally conductive silicone rubber layer (Y), and a low-hardness thermally conductive silicone rubber layer (Z). The support layer (X) is formed by sealing a mesh-like reinforcing material with a cured product of a thermally conductive composition. The high-hardness thermally conductive silicone rubber layer (Y) and the low-hardness thermally conductive silicone rubber layer (Z) are each cured products of an addition-curing silicone rubber composition. By using an addition-curing silicone rubber composition for both the silicone rubber layer (Y) and the silicone rubber layer (Z), adhesion between these two layers is possible without applying a primer layer. A primer treatment may be applied if necessary. These will be described in more detail below.

[0012] <Support Layer (X)> The support layer (X) is a mesh-like reinforcing material that has been sealed with a cured product of a thermally conductive material composition (thermally conductive material), and in the thermally conductive silicone composite sheet of the present invention, it imparts good workability by being tack-free, and also serves as a mechanism for suppressing oil bleeding.

[0013] <Mesh-like Reinforcement Material> Examples of the mesh-like reinforcing material used here include inorganic fiber cloths such as glass cloth, ceramic cloth, and quartz cloth, as well as organic fiber cloths such as nylon and polyester. However, considering heat resistance and other factors, inorganic fiber cloths are preferred, and glass cloth is more preferred. There are no particular restrictions on the mesh size or weaving method of the cloth, but it is preferable to use yarns with a count of 5 Tex or higher and a density of 25 threads / 25 mm or higher. The use of such a mesh-like reinforcing material provides sufficient reinforcing effects. The thickness of the mesh-like reinforcing material is preferably 0.02 to 0.0.09 mm, more preferably 0.04 to 0.08 mm. If the thickness of the mesh-like reinforcing material is less than 0.02 mm, the strength of the laminated sheet may be significantly reduced. On the other hand, if it exceeds 0.09 mm, it may be difficult to obtain the desired thermal conductivity.

[0014] <Sealing Material> The sealing material is not particularly limited as long as it is a thermally conductive material, but is preferably a thermally conductive silicone rubber material (thermally conductive silicone rubber composition), and furthermore, in consideration of cost and adhesion, it is more preferably the same as the material used in the high-hardness thermally conductive silicone rubber layer (Y) described below.

[0015] Furthermore, when the surface roughness Rz of the support layer (X) measured with a surface texture measuring instrument SV-C3200 (manufactured by Daiichi Scientific Co., Ltd.) is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, the effects of improving workability and suppressing oil bleeding due to the above-mentioned tack-free property become favorable.

[0016] <High-Hardness Thermally Conductive Silicone Rubber Layer (Y)> In the thermally conductive silicone composite sheet of the present invention, the high-hardness thermally conductive silicone rubber layer (Y) supports the low-hardness layer and serves as its reinforcing layer. This silicone rubber layer (Y) is preferably made of a cured product of an addition-curable thermally conductive silicone composition containing the following components (A1) to (D1). Each component is described below.

[0017] [(A1) Organopolysiloxane] The organopolysiloxane of component (A1) is an organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 100 to 20,000. This organopolysiloxane is preferably a linear organopolysiloxane whose main chain comprises repeating diorganosiloxane units, but it may also contain a branched structure as part of its molecular structure, or it may be cyclic. Linear diorganopolysiloxanes are preferred from the standpoint of physical properties such as the mechanical strength of the cured product.

[0018] Examples of functional groups other than alkenyl groups bonded to silicon atoms include monovalent hydrocarbon groups, preferably monovalent hydrocarbon groups having 1 to 10 carbon atoms, and particularly preferably monovalent hydrocarbon groups having 1 to 6 carbon atoms. Examples of such monovalent hydrocarbon groups 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; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Of these, preferred are alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, and propyl, and phenyl groups. These groups may also be used in which some of the hydrogen atoms bonded to carbon atoms are substituted with halogen atoms. Furthermore, it is not essential that all functional groups other than the alkenyl group bonded to the silicon atom are the same.

[0019] Examples of alkenyl groups include those having 2 to 8 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl. Of these, vinyl and allyl groups are preferred, with vinyl being particularly preferred. Component (A1) may have two or more silicon-bonded alkenyl groups per molecule, preferably 2 to 20, and more preferably 2 to 10 alkenyl groups.

[0020] The organopolysiloxane of component (A1) may be used alone or in combination with multiple types. The organopolysiloxane of component (A1) is preferably linear, but may have some branching as long as the rubber strength of the thermally conductive, high-hardness layer is not impaired. It may also be a mixture of two or more organopolysiloxanes with different molecular structures or degrees of polymerization. Furthermore, the organopolysiloxane preferably has an average degree of polymerization of 100 to 20,000, particularly 1,000 to 10,000. The average degree of polymerization is the number-average degree of polymerization calculated in terms of polystyrene by gel permeation chromatography (GPC). [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractive index detector (RI) Column: TSK Guard column Super H-L TSKgel Super H4000 (6.0 mm I.D. × 15 cm × 1) TSKgel Super H3000 (6.0 mm I.D. × 15 cm × 1) TSKgel Super H2000 (6.0 mm I.D. × 15 cm × 2) (all manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 20 μL (THF solution with a concentration of 0.5% by mass)

[0021] In addition-curable thermally conductive silicone compositions containing the above components (A1) to (D1), the proportion of component (A1) relative to the entire composition is preferably 5 to 50 mass%, more preferably 7 to 45 mass%, and even more preferably 10 to 40 mass%.

[0022] [(B1) Organohydrogenpolysiloxane] Component (B1) is an organohydrogenpolysiloxane having two or more, preferably 2 to 100, hydrogen atoms directly bonded to silicon atoms (hydrosilyl groups) per molecule, and functions as a crosslinker for component (A1). Specifically, the hydrosilyl groups in component (B1) and the alkenyl groups in component (A) undergo a hydrosilylation reaction in the presence of platinum group catalyst (C1), described below, to form a three-dimensional network structure with a crosslinked structure. Furthermore, if the number of hydrosilyl groups is one or less, the composition may not cure. The organohydrogenpolysiloxane may be represented, for example, by the following formula (1):

[0023] In formula (1), R are each independently a hydrogen atom or a monovalent hydrocarbon group free of aliphatic unsaturated bonds, provided that two or more of R are hydrogen atoms, and x is a number of 1 or greater, preferably a number from 2 to 100, and more preferably a number from 3 to 50. In formula (1), the hydrogen atom directly bonded to the silicon atom may be located in either a side chain or at the terminal, but preferably two or more of R in the side chain are hydrogen atoms.

[0024] In formula (1), the monovalent hydrocarbon group without an aliphatic unsaturated bond, represented by R, is preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, and particularly preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms. Examples of the monovalent hydrocarbon group without an aliphatic unsaturated bond 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; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Of these, alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, and propyl, and phenyl are preferred. In addition, some of the hydrogen atoms bonded to carbon atoms in these groups may be substituted with halogen atoms. In addition, all Rs are not necessarily the same.

[0025] The amount of component (B1) is such that the ratio of the number of hydrosilyl groups in component (B1) to the number of alkenyl groups in component (A1) is 1.0 or greater, preferably 1.1 or greater, and more preferably 1.2 or greater. While there is no particular upper limit, it is 3.5 or less, preferably 2.5 or less. When the amount of component (B1) is within this range, good adhesion to the low-hardness, thermally conductive silicone rubber layer (Z), described below, can be obtained. The organohydrogenpolysiloxane of component (B1) may be used alone, or multiple types may be used in combination.

[0026] [(C1) Platinum Group Metal Catalyst] Component (C1) is an addition reaction catalyst that promotes the addition reaction between the alkenyl group in component (A1) and the hydrosilyl group in component (B1). As this catalyst, any of the well-known platinum group metal catalysts used in hydrosilylation reactions may be used. For example, platinum group metals such as platinum (including platinum black), rhodium, and palladium; platinum chlorides such as HPtCl.nH2O, HPtCl.nH2O, NaHPtCl.nH2O, KaHPtCl.nH2O, NaPtCl.nH2O, KPtCl.nH2O, PtCl.nH2O, PtCl.nH2O, PtCl, and NaHPtCl.nH2O (wherein n is a number from 0 to 6, preferably 0 or 6); chloroplatinic acid and chloroplatinic acid salts; alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972); salts; Examples of such a catalyst include a complex of chloroplatinic acid and an olefin (see U.S. Pat. Nos. 3,159,601, 3,159,662, and 3,775,452), platinum black, a platinum group metal such as palladium supported on a support such as alumina, silica, or carbon, a rhodium-olefin complex, chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst), and a complex of platinum chloride, chloroplatinic acid, or a chloroplatinate salt with a vinyl group-containing siloxane, particularly a vinyl group-containing cyclic siloxane. One type of platinum group metal catalyst may be used alone, or two or more types may be used in combination.

[0027] The amount of component (C1) may be a so-called catalytic amount (i.e., an amount effective to promote the addition reaction) of 0.1 to 1,000 ppm, preferably 1 to 500 ppm, calculated as the mass of platinum group metal element relative to component (A1).

[0028] [(D1) Thermally Conductive Filler] The (D1) thermally conductive filler may be any known filler contained in a thermally conductive composition, but is preferably one or more selected from the group consisting of metals, metal oxides, and metal nitrides. Known thermally conductive fillers may be used, including non-magnetic metals such as copper and aluminum; metal oxides such as alumina, silica, magnesia, red iron oxide, beryllia, titania, and zirconia; metal nitrides such as aluminum nitride, silicon nitride, and boron nitride; artificial diamond; and silicon carbide. The thermally conductive filler has an average particle size of 0.1 to 70 μm, preferably 0.5 to 60 μm, and more preferably 1 to 50 μm. The thermally conductive filler may be used alone or in combination with multiple types. Furthermore, two or more types of particles with different average particle sizes may be used. In the present invention, the average particle size is a volume average particle size, and is a value measured using a Microtrac particle size distribution measuring device MT3300EX (Nikkiso Co., Ltd.).

[0029] The amount of the thermally conductive filler is 300 to 4,000 parts by mass, preferably 500 to 3,500 parts by mass, per 100 parts by mass of component (A1). If the amount of the thermally conductive filler exceeds 4,000 parts by mass per 100 parts by mass of component (A1), adhesion to the low-hardness, thermally conductive silicone rubber layer (Z), described below, may be reduced. If the amount of the thermally conductive filler is less than 300 parts by mass per 100 parts by mass of component (A1), the desired thermal conductivity may not be achieved.

[0030] The high-hardness, heat-conductive silicone rubber composition of the present invention may contain a surface treatment agent such as a silane coupling agent that improves compatibility between the component (D1) and the component (A1).

[0031] [Surface Treatment Agent (E1)] In the high-hardness thermally conductive silicone rubber layer (Y), it is preferable to add, to the addition-curable thermally conductive silicone composition, a surface treatment agent that improves compatibility between the component (D1) and the component (A1). The surface treatment agent is (E1), a dimethylpolysiloxane in which one molecular chain terminal is capped with a trialkoxy group, as shown in formula (2) below: (In the formula, R 5are independently alkyl groups having 1 to 6 carbon atoms, and c is a number from 4 to 100.

[0032] When component (E1) is incorporated into an addition-curable thermally conductive silicone composition, the amount is preferably 10 to 300 parts by weight, more preferably 20 to 150 parts by weight, per 100 parts by weight of component (A1). If the proportion of this component exceeds 300 parts by weight per 100 parts by weight of component (A1), oil separation may be more likely to occur, potentially reducing adhesion between layer (Y) and layer (Z). Furthermore, if the proportion of this component is less than 10 parts by weight per 100 parts by weight of component (A1), the wettability of the organopolysiloxane (A1) with the thermally conductive filler (D1) may be reduced, potentially reducing the moldability of the composition. The surface treatment agent for component (E1) may be used alone, or multiple types may be used in combination.

[0033] If necessary, optional components such as pigments, internal release agents, and plasticizers may also be added to the addition-curable thermally conductive silicone composition.

[0034] <Low-hardness thermally conductive silicone rubber layer (Z)> The low-hardness thermally conductive silicone rubber layer (Z) in the thermally conductive silicone composite sheet of the present invention provides stress relaxation properties, accommodates tolerances, and reduces contact thermal resistance. This silicone rubber layer (Z) is made of a cured product of an addition-cure thermally conductive silicone composition containing the following components (A2) to (D2). Each component is described below.

[0035] [(A2) Organopolysiloxane] The organopolysiloxane of component (A2) is an organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 100 to 2,000. The organopolysiloxane is preferably linear, but may have some branching as long as the rubber strength of the thermally conductive low-hardness layer is not impaired. It may also be a mixture of two or more organopolysiloxanes with different molecular structures or degrees of polymerization. From the viewpoint of physical properties such as the mechanical strength of the cured product, linear diorganopolysiloxanes are preferred.

[0036] Examples of functional groups other than alkenyl groups bonded to silicon atoms include the same functional groups as those exemplified for component (A1) above. Component (A2) in the low hardness, thermally conductive silicone rubber layer (Z) may have two or more alkenyl groups bonded to silicon atoms per molecule, preferably 2 to 20, and more preferably 2 to 10 alkenyl groups.

[0037] The organopolysiloxane of component (A2) may be used alone or in combination of two or more. The average degree of polymerization of component (A2) in the low-hardness, thermally conductive silicone rubber layer (Z) is preferably 100 to 2,000, more preferably 200 to 1,000. The average degree of polymerization is the number-average degree of polymerization calculated in terms of polystyrene by gel permeation chromatography (GPC). [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractive index detector (RI) Column: TSK Guard column Super H-L TSKgel Super H4000 (6.0 mm I.D. × 15 cm × 1) TSKgel Super H3000 (6.0 mm I.D. × 15 cm × 1) TSKgel Super H2000 (6.0 mm I.D. × 15 cm × 2) (all manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 20 μL (THF solution with a concentration of 0.5% by mass)

[0038] In addition-curable thermally conductive silicone compositions containing the above components (A2) to (D2), the proportion of component (A2) relative to the total composition is preferably 5 to 45 mass%, more preferably 7 to 40 mass%, and even more preferably 10 to 40 mass%.

[0039] [(B2) Organohydrogenpolysiloxane] Component (B2) is an organohydrogenpolysiloxane containing two or more, preferably 2 to 100, hydrogen atoms directly bonded to silicon atoms (hydrosilyl groups) per molecule, and functions as a crosslinker for component (A2). Specific examples include the same as those for component (B1). The amount of component (B2) is such that the ratio of the number of hydrosilyl groups in component (B2) to the number of alkenyl groups in component (A2) is 1.5 or less, preferably 1.3 or less, and more preferably 1.1 or less. There is no particular lower limit, but it is 0.5 or more, preferably 0.6 or more. When the amount of component (B2) is within this range, it is easy to achieve low hardness for the (Z) layer and also ensure adhesion to the (Y) layer. The organohydrogenpolysiloxane of component (B2) may be used alone or in combination of two or more different types.

[0040] [(C2) Platinum Group Metal Catalyst] Component (C2) is an addition reaction catalyst that promotes the addition reaction between the alkenyl groups of component (A2) and the hydrosilyl groups of component (B2). Well-known platinum group metal catalysts used in hydrosilylation reactions may be used as this catalyst. Specific examples include the same catalysts as those used for component (C1). This platinum group metal catalyst may be used alone or in combination with multiple catalysts. The amount of component (C2) may be a so-called catalytic amount (i.e., an amount effective to promote the addition reaction). The amount of platinum group metal element relative to component (A2) is 0.1 to 1,000 ppm, preferably 1 to 500 ppm, by mass.

[0041] [(D2) Thermally Conductive Filler] The thermally conductive filler (D2) may be any known filler commonly found in thermally conductive compositions, but is preferably at least one selected from the group consisting of metals, metal oxides, and metal nitrides. Specific examples include the same fillers as those used in the aforementioned component (D1). The blending amount of component (D2) is 500 to 4,000 parts by mass, preferably 700 to 3,000 parts by mass, per 100 parts by mass of component (A2). If the blending amount of the thermally conductive filler exceeds 4,000 parts by mass per 100 parts by mass of component (A2), not only will a silicone rubber layer with the desired hardness not be obtained, but adhesion to the high-hardness thermally conductive silicone rubber layer (Y) may also be reduced. If the blending amount is less than 500 parts by mass per 100 parts by mass of component (A2), the desired thermal conductivity may not be achieved.

[0042] [Surface Treatment Agent (E2)] As a surface treatment agent to improve compatibility between component (D2) and component (A2), (E2) dimethylpolysiloxane having one molecular chain end blocked with a trialkoxy group, represented by the following formula (2), is added to the addition-curable thermally conductive silicone composition. This surface treatment agent also contributes to reducing the hardness of the low-hardness thermally conductive silicone rubber layer (Z). (In the formula, R 5 are independently alkyl groups having 1 to 6 carbon atoms, and c is a number from 4 to 100.

[0043] When component (E2) is incorporated into an addition-curable thermally conductive silicone composition, the amount is 10 to 300 parts by weight, preferably 20 to 150 parts by weight, per 100 parts by weight of component (A2). If the proportion of this component exceeds 300 parts by weight per 100 parts by weight of component (A2), oil separation may be more likely to occur, potentially reducing adhesion between layer (Y) and layer (Z). If the proportion of this component is less than 10 parts by weight per 100 parts by weight of component (A2), the wettability of the organopolysiloxane (A2) with the thermally conductive filler (D2) may decrease, reducing the moldability of the composition and making it difficult to achieve a low hardness. The surface treatment agent for component (E2) may be used alone or in combination with multiple types.

[0044] If necessary, the addition-curable thermally conductive silicone composition may further contain optional components such as pigments, internal release agents, and plasticizers.

[0045] <Manufacturing Method> <Step 1> Step (1) is a step of applying a thermally conductive material to a mesh-like reinforcement material and molding a sealed support layer (X). By applying and curing this sealing material to the mesh-like reinforcement material, a resin film for sheet production is not required when laminating the high-hardness thermally conductive silicone rubber layer (Y) in the next step. The sealing method is a known method, but it involves diluting the thermally conductive material with a solvent to prepare a sealing solution, which is then applied to the mesh-like reinforcement material. The solution is then applied continuously to the mesh-like reinforcement material using a coating device such as a knife coater or kiss coater equipped with a drying oven, a heating oven, and a winding device, after which the solvent is dried and the material is heated and cured, preferably at about 80 to 120°C, more preferably about 100 to 150°C, to obtain a sealed mesh-like reinforcement material.

[0046] <Step 2> Step (2) is a step of laminating a high-hardness thermally conductive silicone composition on the support layer (X) prepared in step (1) and curing the composition to obtain a high-hardness thermally conductive silicone rubber layer (Y). The method for applying the high-hardness thermally conductive silicone composition to the support layer (X) is not particularly limited. For example, by using a comma coater, the high-hardness thermally conductive silicone rubber layer (Y) can be continuously laminated on the support layer (X) in one step. If necessary, the high-hardness thermally conductive silicone composition may be diluted with a solvent (e.g., xylene, toluene, etc.), and the solvent may be evaporated after application. In the present invention, it is preferable to complete the curing reaction of the high-hardness thermally conductive silicone rubber layer (Y) before laminating the low-hardness thermally conductive silicone rubber layer (Z) described below. The tackiness of the surface of the (Y) layer is reduced by curing, eliminating the need for protection with a release-treated resin film or the like. The curing conditions are 100°C to 170°C, 5 to 30 minutes, preferably 120°C to 150°C, and 10 to 20 minutes. Furthermore, the tack strength of the surface of the (Y) layer after curing is preferably 30 gf or less, more preferably 20 gf or less, and even more preferably 10 gf or less. If the tack strength is within this range, even if the high-hardness thermally conductive silicone rubber layer molded into a sheet is wound up into a roll, sticking of the sheet (blocking) can be suppressed. The hardness of the resulting sheet can be measured using a Shore A hardness tester according to the method described in JIS K6253-1:2012.

[0047] <Step 3> Step (3) is a step of laminating a low-hardness thermally conductive silicone composition on the high-hardness thermally conductive silicone rubber layer (Y) and curing the composition to adhere the (Y) and low-hardness thermally conductive silicone rubber layer (Z) together to obtain a thermally conductive silicone composite sheet. The hardness of the resulting sheet can be measured using an Asker C hardness tester according to the method described in JIS K7312:1996. The method for laminating a low-hardness thermally conductive silicone composition on the (Y) layer and curing it to form the (Z) layer is not particularly limited, but examples include coating and press molding. The curing conditions are 100°C to 150°C for 5 to 30 minutes, preferably 110°C to 130°C for 10 to 20 minutes. The hardness of the low-hardness thermally conductive silicone layer after curing is preferably 2 to 30 on Asker C, and more preferably 20 or less on Asker C. If the hardness of the low-hardness thermally conductive silicone layer is within this range, the stress applied to the heat-generating member can be reduced due to good compression characteristics.

[0048] <Thermal Conductive Silicone Composite Sheet> In the present invention, the thickness of the high-hardness thermally conductive silicone rubber layer (Y) can be 0.15 mm or more and 0.5 mm or less, the hardness of the low-hardness thermally conductive silicone rubber layer (Z) after curing can be 30 or less on Asker C, and the thickness of the thermally conductive silicone composite sheet can be 0.3 mm or more and 10 mm or less. Furthermore, in the present invention, the hardness of the high-hardness thermally conductive silicone rubber layer (Y) in the thermally conductive silicone composite sheet can be 50 or more and 97 or less on Shore A, and the thickness can be 0.15 mm or more and 0.5 mm or less. The thermally conductive silicone composite sheet of the present invention does not require the resin film required when producing a conventional silicone sheet during its production, and blocking can be suppressed even when the high-hardness thermally conductive silicone rubber layer (Y) is stored. Furthermore, the low-hardness thermally conductive silicone rubber layer (Z) can be laminated in a state of good adhesion, and the resulting thermally conductive silicone composite sheet exhibits excellent workability and compression characteristics.

[0049] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0050] <Preparation of Compositions 1-A to 1-D and Compositions 2-A to 2-C> Compositions 1-A to 1-D and Compositions 2-A to 2-C were prepared by mixing the components according to the formulations shown in Tables 1 and 2. Compositions 1-A, 1-B, 1-C, and 1-D were kneaded using a kneader. Compositions 2-A, 2-B, and 2-C were kneaded using a planetary mixer.

[0051] [Component (a)] Component (a-1): A dimethylpolysiloxane having an average degree of polymerization of 8,000 and both ends blocked with dimethylvinyl groups, as shown in the following formula (3). Component (a-2): A dimethylpolysiloxane having an average degree of polymerization of 400 and both ends blocked with dimethylvinyl groups, as shown in the following formula (3). (p is a number that satisfies the above average degree of polymerization)

[0052] [Component (b)] Component (b-1): an organohydrogenpolysiloxane in which q = 20 and r = 9 in the following formula (4); Component (b-2): an organohydrogenpolysiloxane in which q = 27 and r = 3 in the following formula (4).

[0053] [Component (c)] 5% chloroplatinic acid 2-ethylhexanol solution

[0054] [Component (d)] Component (d-1): Aluminum hydroxide with an average particle size of 2 μm Component (d-2): Aluminum hydroxide with an average particle size of 8 μm Component (d-3): Aluminum hydroxide with an average particle size of 50 μm Component (d-4): Aluminum oxide with an average particle size of 1 μm Component (d-5): Aluminum oxide with an average particle size of 10 μm Component (d-6): Aluminum oxide with an average particle size of 45 μm Component (d-7): Aluminum oxide with an average particle size of 70 μm

[0055] [Component (e)] A dimethylpolysiloxane represented by formula (5) in which one end is blocked with a trimethoxysilyl group.

[0056] [Component (f)] Addition reaction inhibitor: 2-ethynyl-2-undecanol

[0057] [Component (g)] Internal release agent: dimethyldiphenyl silicone oil ("KF-54" manufactured by Shin-Etsu Chemical Co., Ltd.)

[0058] [Component (h)] Plasticizer: dimethyl silicone oil ("KF-96-100cs" manufactured by Shin-Etsu Chemical Co., Ltd.)

[0059] <Evaluation of High Hardness Thermally Conductive Silicone Rubber Layer (Y)> [Production Method] The obtained compositions 1-A to 1-D were molded into sheets with a thickness of 6 mm and cured to obtain sheet-like cured products (hereinafter referred to as sheets). [Thermal Conductivity] Using two of the obtained sheets, the thermal conductivity (W / m·K) of the sheets was measured using a thermal conductivity meter (TPA-501, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). [Tackiness] The tackiness of the obtained sheets was measured using a solder paste tackiness tester. [Hardness] The hardness of the obtained sheets was measured using a Shore A hardness tester according to the method described in JIS K6253-1:2012.

[0060]

[0061] <Evaluation of Low Hardness Thermally Conductive Silicone Rubber Layer (Z)> [Production Method] The obtained compositions 2-A to 2-C were molded into sheets with a thickness of 6 mm and cured to obtain sheet-shaped cured products (hereinafter referred to as sheets). [Thermal Conductivity] Using two of the obtained sheets, the thermal conductivity (W / m K) of the sheets was measured with a thermal conductivity meter (TPA-501, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). [Hardness] The hardness of the obtained sheets was measured with an Asker C hardness tester according to the method described in JIS K7312:1996.

[0062]

[0063] <Preparation of Composite Sheet> [Mesh Reinforcement] As the mesh reinforcement for preparing the support layer (X), a glass cloth (thickness 30 μm) using 5 Tex glass fibers and 50 fibers / 25 mm in the warp and weft directions was used.

[0064] Example 1 A glass cloth sealing solution was obtained by adding 80% by mass of xylene to composition 1-A. The sealing solution was placed in a container large enough to accommodate a glass cloth, and the glass cloth was then placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up to remove excess sealing solution adhering to the glass cloth. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to composition 1-A. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-A on a support layer (X). Next, composition 2-A was applied to the surface of the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-A, thereby obtaining a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-A were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 0.8 mm, total thickness: 1.0 mm

[0065] Example 2: A glass cloth sealing solution was obtained by adding 60% by mass of xylene to composition 1-B. The sealing solution was placed in a container large enough to accommodate a glass cloth, and the glass cloth was then placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. Once the glass cloth was sufficiently impregnated with the sealing solution, the glass cloth was continuously pulled up, and excess sealing solution adhering to the glass cloth was removed. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to composition 1-B. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and a laminate was obtained having a silicone rubber layer (Y) which was a cured product of composition 1-B on a support layer (X). Subsequently, composition 2-B was applied to the surface of the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-B, resulting in a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-B were laminated in this order. X: 0.05 mm, Y: 0.10 mm, Z: 0.35 mm, total thickness: 0.5 mm

[0066] Example 3: A glass cloth sealing solution was obtained by adding 80% by mass of xylene to composition 1-A. The sealing solution was placed in a container large enough to accommodate a glass cloth, and then the glass cloth was placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up to remove excess sealing solution adhering to the glass cloth. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to composition 1-A. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-A on a support layer (X). Next, composition 2-A was applied to the surface of the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-A, thereby obtaining a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-A were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 1.8 mm, total thickness: 2.0 mm

[0067] Example 4: A glass cloth sealing solution was obtained by adding 60% by mass of xylene to composition 1-C. The sealing solution was placed in a container large enough to accommodate a glass cloth, and then the glass cloth was placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up to remove excess sealing solution adhering to the glass cloth. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 30% by mass of xylene to composition 1-C. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-C on a support layer (X). Subsequently, composition 2-A was applied to the surface of the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-A, thereby obtaining a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-A were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 0.8 mm, total thickness: 1.0 mm

[0068] Example 5: A glass cloth sealing solution was obtained by adding 60% by mass of xylene to composition 1-C. The sealing solution was placed in a container large enough to accommodate a glass cloth, and then the glass cloth was placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up to remove excess sealing solution adhering to the glass cloth. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 30% by mass of xylene to composition 1-C. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-C on a support layer (X). Subsequently, composition 2-B was applied to the surface of the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-B, thereby obtaining a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-B were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 1.3 mm, total thickness: 1.5 mm

[0069] Example 6: A glass cloth sealing solution was obtained by adding 60% by mass of xylene to composition 1-B. The sealing solution was placed in a container large enough to accommodate a glass cloth, and then the glass cloth was placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up, and excess sealing solution adhering to the glass cloth was removed. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to composition 1-B. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were set to 80°C, 80°C, 150°C, and 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) formed from the cured product of Composition 1-B on a support layer (X). A 1% by mass toluene solution of dimethylpolysiloxane (38 dimethylsiloxane units) capped at both ends with trimethylsiloxy was prepared as a primer. The primer was applied to the surface of the silicone rubber layer (Y) of the laminate using a gravure coater and dried at 80°C to obtain a dimethylpolysiloxane-treated silicone rubber layer (Y'). Composition 2-B was then applied to the surface of the silicone rubber layer (Y'), and the laminate was press-molded at 120°C for 10 minutes to cure Composition 2-B, resulting in a thermally conductive silicone composite sheet laminated in this order: support layer (X), silicone rubber layer (Y), silicone rubber layer (Y'), and silicone rubber layer (Z) formed from the cured product of Composition 2-B. X: 0.05 mm, Y+Y': 0.15 mm (same as in Table 3), Z: 0.8 mm, total thickness: 1.0 mm

[0070] Comparative Example 1 A coating liquid was prepared by adding a 20% by mass xylene solution to Composition 1-A. The coating liquid was applied to one side of a 50 μm-thick fluorine-treated PET film (FL-1-01 (Takaline Corporation)) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 60°C / 60°C / 60°C / 60°C, and heating was carried out for a total of 15 minutes to obtain a laminate having an uncured silicone rubber layer of Composition 1-A on the substrate. Glass cloth was laminated to this uncured silicone rubber layer at a pressure of 0.1 MPa and immersed in the coating liquid, thereby impregnating the glass cloth with the coating liquid. Thereafter, a fluorine-treated PET film (FL-1-01 (Takaline Corporation)) was further laminated to the coated surface. Next, Composition 2-A was applied to the surface of the laminated fluorine-treated PET film and press-molded at 120°C for 10 minutes to cure Composition 2-A, yielding a thermally conductive silicone composite sheet with dimensions X: 0.05 mm, Y: 0.15 mm, Z: 0.8 mm, and a total thickness of 1.0 mm.

[0071] Comparative Example 2: Composition 1-B' was prepared by adding 1.5 parts of Perhexa 25B (manufactured by NOF Corp.) as a vulcanizing agent, omitting the components (B), (C), and (F) from Composition 1-B. 60% by mass of xylene was added to Composition 1-B' to obtain a glass cloth sealing solution. The sealing solution was placed in a container large enough to accommodate a glass cloth, and the glass cloth was then placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After impregnating the glass cloth with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up and any excess sealing solution adhering to the glass cloth was removed. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 150°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to Composition 1-B'. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-B' on the support layer (X). Next, composition 2-B was applied to the surface of the silicone rubber layer (Y), and the mixture was press-molded at 120°C / 10 min to cure composition 2-B, thereby obtaining a thermally conductive silicone composite sheet in which the support layer (X), silicone rubber layer (Y), and silicone rubber layer (Z) which was a cured product of composition 2-B were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 0.8 mm, total thickness: 1.0 mm

[0072] (Comparative Example 3) A glass cloth sealing solution was obtained by adding 80% by mass of xylene to composition 1-A. The sealing solution was placed in a container large enough to accommodate a glass cloth, and then the glass cloth was placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up and excess sealing solution adhering to the glass cloth was removed. The glass cloth was then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a support layer (X) with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to composition 1-A. The coating solution was applied to one side of the support layer (X) using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-A on a support layer (X). Next, composition 2-A was applied to the other side of the support layer (X) which did not have the silicone rubber layer (Y) of the laminate, and the laminate was press-molded under conditions of 120°C / 10 min to cure composition 2-A, thereby obtaining a thermally conductive silicone composite sheet in which the silicone rubber layer (Y), support layer (X), and silicone rubber layer (Z) which was a cured product of composition 2-A were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 0.15 mm, total thickness: 0.35 mm

[0073] (Comparative Example 4) A glass cloth sealing solution was obtained by adding 80% by mass of xylene to Composition 1-A. The sealing solution was placed in a container large enough to accommodate a glass cloth, and the glass cloth was then placed in the container and immersed in the sealing solution, thereby impregnating the glass cloth with the sealing solution. After the glass cloth was impregnated with the sealing solution at room temperature for 5 minutes, the glass cloth was continuously pulled up to remove excess sealing solution adhering to the glass cloth, and then placed in an oven, dried at 80°C for 10 minutes, and cured at 120°C for 10 minutes to obtain a sealed glass cloth with a thickness of 0.05 mm. Next, a coating solution was prepared by adding 20% ​​by mass of xylene to Composition 1-A. The coating solution was applied to one side of the sealed glass cloth using a comma coater at a coating speed of 0.5 m / min. The oven temperatures were 80°C / 80°C / 150°C / 150°C, and heating was carried out for a total of 15 minutes to obtain a laminate having a silicone rubber layer (Y) which was a cured product of composition 1-A on a sealed glass cloth. Next, composition 2-C was applied to the other side of the sealed glass cloth layer of the laminate, which did not have the silicone rubber layer (Y), and press-molded under conditions of 120°C / 10 min to cure composition 2-C, thereby obtaining a thermally conductive silicone composite sheet in which the silicone rubber layer (Y), the sealed glass cloth layer, and the silicone rubber layer (Z) which was a cured product of composition 2-C were laminated in this order. X: 0.05 mm, Y: 0.15 mm, Z: 1.8 mm, total thickness: 2.0 mm

[0074] <Evaluation of Composite Sheet> [Adhesion between High Hardness Thermally Conductive Silicone Rubber Layer (Y) and Low Hardness Thermally Conductive Silicone Rubber Layer (Z)] In the obtained thermally conductive silicone composite sheet, the low hardness thermally conductive silicone rubber layer was peeled off from the high hardness thermally conductive silicone rubber layer, and if there was any adhesive residue, this was deemed to be "cohesive failure," and if there was separation without any adhesive residue, this was deemed to be "interfacial peeling."

[0075] [Compression Stress] The resulting thermally conductive silicone composite sheet was compressed by 50% at a compression rate of 0.5 mm / min using an autograph (manufactured by Shimadzu Corporation), and the maximum stress was measured.

[0076] [Oil Bleeding] The obtained thermally conductive silicone composite sheet was cut into a disk with a diameter of 13 mm, placed on a frosted glass, compressed to 50% using a compression jig, and then aged in this compressed state for 100 hours at 100°C. After aging, the compression was released and the width (mm) of oil that had bled from the thermally conductive silicone composite sheet onto the frosted glass was measured.

[0077] [Number of Uses of Release PET Film] The number of uses of release PET film before molding the thermally conductive silicone composite sheet is recorded.

[0078] The results of Examples 1 to 6 are shown in Table 3, and the results of Comparative Examples 1 to 4 are shown in Table 4.

[0079]

[0080]

[0081] As can be seen from Tables 3 and 4, Examples 1 to 5 provide thermally conductive silicone composite sheets that exhibit good adhesion and compression properties without the use of a release PET film, and also exhibit excellent oil-bleeding reliability. On the other hand, in Comparative Example 1, release PET films were used twice when molding the high-hardness thermally conductive silicone rubber layer, which increased costs and required the user to perform an additional peeling process. In Comparative Example 2, the high-hardness thermally conductive silicone rubber layer was prepared using a peroxide vulcanization system, which prevented good adhesion with the low-hardness thermally conductive silicone rubber layer and significantly increased oil-bleeding. In Comparative Examples 3 and 4, composite sheets were molded using an intermediate layer of a mesh-like reinforcing material sealed with a thermally conductive material. In Comparative Example 3, even though good adhesion was achieved between the high-hardness thermally conductive silicone rubber layer and the low-hardness thermally conductive silicone rubber layer, the low-hardness thermally conductive silicone rubber layer was thin, resulting in high compressive stress when compressed highly. Furthermore, in Comparative Example 4, there was a problem in that, when the thermal conductivity of the low-hardness silicone rubber layer was increased, interfacial peeling occurred.

Claims

1. A thermally conductive silicone composite sheet having a support layer (X), a high hardness thermally conductive silicone rubber layer (Y), and a low hardness thermally conductive silicone rubber layer (Z) laminated in this order, wherein the support layer (X) is formed by sealing a mesh-like reinforcing material with a cured product of a thermally conductive composition, and the high hardness thermally conductive silicone rubber layer (Y) and the low hardness thermally conductive silicone rubber layer (Z) are each cured products of an addition-curing type silicone rubber composition, and the high hardness thermally conductive silicone rubber layer (Y) has a hardness of 50 to 97 as measured by a Shore A hardness scale according to the method described in JIS K6253-1:2012, and the low hardness thermally conductive silicone rubber layer (Z) has a hardness of 2 to 30 as measured by an Asker C hardness scale according to the method described in JIS K7312:1996.

2. The thermally conductive silicone composite sheet according to claim 1, wherein the mesh-like reinforcing material is glass cloth.

3. The thermally conductive silicone composite sheet according to claim 1, wherein the high hardness thermally conductive silicone rubber layer (Y) is a cured product of an addition curing type silicone rubber composition containing the following (A1) to (D1): (A1) 100 parts by mass of an organopolysiloxane having two or more alkenyl groups per molecule and an average degree of polymerization of 100 to 20,000 (B1) 100 parts by mass of an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, such that the ratio of the number of moles of hydrosilyl groups in component (B1) to the number of moles of alkenyl groups in component (A1) is 1.0 to 3.5 (C1) Platinum group metal catalyst: 0.1 to 1,000 ppm calculated as the mass of platinum group metal (D1) Thermally conductive filler: 300 to 4,000 parts by mass 4. An addition curing type silicone rubber composition is provided with (E1) a surface treatment agent represented by the following formula (2): (In the formula, R 5 are independently an alkyl group having 1 to 6 carbon atoms, and c is a number from 4 to 100.

5. The thermally conductive silicone composite sheet according to claim 1, wherein the thermally conductive composition constituting the (X) layer is the same as the thermally conductive silicone rubber composition constituting the high hardness thermally conductive silicone rubber layer (Y).

6. The thermally conductive silicone composite sheet according to claim 1, wherein the low-hardness thermally conductive silicone rubber layer (Z) is a cured product of an addition-curing type silicone rubber composition containing the following (A2) to (E2): (A2) an organopolysiloxane having two or more alkenyl groups per molecule and an average degree of polymerization of 100 to 2,000: 100 parts by mass; (B2) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the ratio of the number of moles of hydrosilyl groups in component (B2) to the number of moles of alkenyl groups in component (A2) is 0.5 to 1.5; (C2) a platinum group metal catalyst: 0.1 to 1,000 ppm in terms of the mass of platinum group metal; (D2) a thermally conductive filler: 500 to 4,000 parts by mass; (E2) a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxy group, as represented by the following formula (2), as a surface treatment agent: 10 to 300 parts by mass: (In the formula, R 5 are independently an alkyl group having 1 to 6 carbon atoms, and c is a number from 4 to 100.

7. The thermally conductive silicone composite sheet according to claim 1, wherein the thickness of the high-hardness thermally conductive silicone rubber layer (Y) is 0.15 to 0.5 mm, and the overall thickness of the thermally conductive silicone composite sheet is 0.3 to 10 mm.

8. The thermally conductive silicone composite sheet according to claim 1, wherein the thickness of the support layer (X) is 0.03 to 0.10 mm.

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