Thermally conductive sheet

Abstract

To provide a sheet which can be continuously manufactured by coating molding and wound into a roll, and has high thermal conductivity and fine uniformity in in-plane electric-insulation strength.SOLUTION: This thermally conductive sheet comprises: a glass cloth having pores filled with a thermally conductive resin composition; and a layer of a cured product of a thermally conductive silicone composition layered on one or both of the surfaces of the glass cloth. The thermally conductive silicone composition contains silicone components and a thermally conductive filler (C). The amount of the thermally conductive filler is 700 to 1,100 pts.mass with respect to a total of 100 pts.mass of the silicone components. The thermally conductive filler (C) has an average particle size of less than 15 μm. The amount of particles having a primary particle size of 45 μm or more is 0 to 3 mass%, and the amount of particles having a primary particle size of 75 μm or more is 0 to 0.01 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet, and more particularly to a thermally conductive sheet used as a heat transfer material that can be interposed between a heat-generating electronic component and a heat dissipation member such as a heat sink. [Background technology]

[0002] When attaching heat-generating electronic components such as CPUs and power modules to heat dissipation members such as heat sinks, it is common to place a thermally conductive sheet between them, which has insulating and thermally conductive properties.

[0003] Therefore, to provide thermal conductivity while being resistant to tearing, thermally conductive sheets have been developed in which a thermally conductive resin is laminated onto glass cloth. For example, Patent Document 1 below describes a thermally conductive sheet in which a silicone rubber containing boron nitride powder and spherical silica powder as thermally conductive fillers is laminated onto glass cloth. To manufacture this sheet, a sheet of an appropriate size must be prepared and pressed using a press molding machine or the like. This requires batch production, and the finished thermally conductive sheet cannot be rolled up. This is extremely inefficient in terms of productivity and yield, and the limited size of the raw sheet also limits the packaging size.

[0004] An alternative continuous molding method is coating molding. For example, thermally conductive sheets can be continuously produced by sealing glass cloth with thermally conductive silicone resin and then coating it with a thermally conductive silicone rubber layer. Coating molding is highly efficient because the completed sheet can be continuously wound up. Furthermore, while the width of the sheet is limited by the coating equipment, there is no limit to the length in the longitudinal direction, which allows for much greater freedom in sheet size compared to press molding. However, coating molding has poorer surface accuracy than press molding, resulting in higher contact thermal resistance. Furthermore, because no pressure is applied, it is difficult to increase the density of the thermally conductive silicone rubber layer. For these reasons, it was not suitable as a method for producing sheets with high thermal conductivity.

[0005] In order to solve the above problems, Patent Document 2 below describes the use of a thermally conductive composition highly filled with spherical alumina with few coarse particles for coating molding (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-199880 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-233104 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when spherical alumina is highly filled as described in Patent Document 2, the thermal conductivity of the sheet increases, but the fluidity of the thermally conductive composition decreases, resulting in uneven distribution of voids in the sheet, which causes a problem of in-plane variation in the insulating properties.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a sheet that can be continuously produced by coating molding and wound into a roll, and that has high thermal conductivity and good uniformity of in-plane insulation strength. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have discovered that in a thermally conductive sheet having a cured layer of a thermally conductive silicone composition on one or both sides of a glass cloth that has been sealed with the thermally conductive silicone composition, a thermally conductive silicone composition having the following configuration can be used to produce a thermally conductive sheet with high thermal conductivity by continuous molding, thereby achieving the above-mentioned object, and have arrived at the present invention.

[0010] That is, the present invention is [1] Provided is a thermally conductive sheet comprising glass cloth sealed with a thermally conductive resin composition and a cured layer of a thermally conductive silicone composition laminated on one or both sides of the glass cloth, wherein the thermally conductive silicone composition comprises a silicone component and a thermally conductive filler (C), the amount of the thermally conductive filler is 700 to 1,100 parts by mass per 100 parts by mass of the total of the silicone components, and the thermally conductive filler (C) has an average particle size of less than 15 μm, and the amount of particles having a primary particle size of 45 μm or more is 0 to 3% by mass, and the amount of particles having a primary particle size of 75 μm or more is 0 to 0.01% by mass.

[0011] Furthermore, the present invention provides the above thermally conductive sheet, which further has at least one of the configurations described in the following [2] to

[18] . [2] The thermally conductive sheet, wherein the thermally conductive silicone composition contains 26% by mass to 75% by mass of (E) a dimethylpolysiloxane represented by the following formula (3), based on the total mass of the silicone components: [ka] (wherein r is an integer of 5 to 500). [3] The thermally conductive sheet, wherein the thermally conductive silicone composition is a peroxide-curable composition, and the silicone component further comprises the component (E) described in [2], and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, and (D) an alkoxysilane having at least one alkyl group having 6 to 15 carbon atoms per molecule and having at least one hydrolyzable group, and a linear organopolysiloxane having a trialkoxy group at one terminal and no alkenyl group, and wherein the amount of the thermally conductive filler (C) is 700 to 1,100 parts by mass per 100 parts by mass of the total of the components (A), (D), and (E). [4] The thermally conductive sheet as described above, wherein the thermally conductive silicone composition is a peroxide-curable composition and contains the following components (A) to (E): (A) Organopolysiloxane having at least two alkenyl groups bonded to silicon atoms per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B) Organic peroxide: effective amount (C) the average particle size is less than 15 μm; The amount of particles with a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by mass per 100 parts by mass of the component (A). (D1) Formula (1): R 1 a R 2 b Si(OR 3 ) 4-a-b (1) (In the formula, R 1 are each independently an alkyl group having 6 to 15 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3. and an alkoxysilane represented by (D2) Formula (2): [ka] (In the formula, R 3 is as above, and c is an integer between 5 and 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) [ka] (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the following formula: an amount that is 26% by mass to 75% by mass based on the total mass of the components (A), (D), and (E). [5] The thermally conductive sheet, wherein the thermally conductive silicone composition is an addition reaction curable composition, and the silicone component further comprises component (E) of [2] and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and (D) an alkoxysilane having at least one C alkyl group and at least one hydrolyzable group per molecule, and a linear organopolysiloxane having a trialkoxy group at one terminal and no alkenyl group, and wherein the amount of the thermally conductive filler (C) is 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (B'), (D), and (E). [6] The thermally conductive sheet, wherein the thermally conductive silicone composition is an addition reaction curable composition and contains the following components (A), (B'), (C) to (E), and (b): (A) Organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms (hereinafter referred to as hydrosilyl groups) per molecule: an amount such that the ratio of the number of hydrosilyl groups in component (B') to the number of alkenyl groups in component (A) is 0.1 to 5.0 (b) Addition reaction catalyst: catalytic amount (C) the average particle size is less than 15 μm; The amount of particles with a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (B'), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by mass per 100 parts by mass of the component (A). (D1) Formula (1): R 1 a R 2 b Si(OR 3 ) 4-a-b (1) (In the formula, R 1 are each independently an alkyl group having 6 to 15 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3. and an alkoxysilane represented by (D2) Formula (2): [ka] (In the formula, R 3 is as above, and c is an integer between 5 and 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) [ka] (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the following formula: an amount that is 26% by mass to 75% by mass based on the total mass of the components (A), (B'), (D), and (E). [7] The component (C) is (C1) Alumina having an average particle size of 0.1 μm or more and less than 5 μm, a content of particles having a primary particle size of 45 μm or more of 0 to 3 mass%, and a content of particles having a primary particle size of 75 μm or more of 0 to 0.01 mass%: 20 to 50 mass%, and (C2) Alumina having an average particle size of 5 μm or more and less than 15 μm, a content of particles with a primary particle size of 45 μm or more of 0 to 3 mass%, and a content of particles with a primary particle size of 75 μm or more of 0 to 0.01 mass%: 50 to 80 mass% The thermally conductive sheet comprises: [8] The thermally conductive sheet, wherein the component (A) comprises (A1) an organopolysiloxane that has at least two silicon-bonded alkenyl groups in each molecule and is in a rubber-like state at 25°C, and optionally (A2) an organopolysiloxane that has at least two silicon-bonded alkenyl groups in each molecule and is liquid at 25°C. [9] The thermally conductive sheet as described above, wherein the component (A) comprises: (A1) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is in a rubber-like state at 25°C; and (A2) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is liquid at 25°C; and the ratio of the amounts of the components (A1) and (A2) satisfies (A2) / (A1)≦1.0.

[10] The thermally conductive sheet as described above, wherein the cured product of the thermally conductive silicone composition has a hardness of 80 to 96 as measured with a Type A durometer according to the method described in JIS K6249:2003.

[11] The thermally conductive sheet, wherein the glass cloth has a thickness of 60 μm or less.

[12] A thermally conductive sheet in which a cured product layer of the thermally conductive silicone composition is laminated on both sides of the glass cloth, and the thermally conductive sheet has a thickness of 130 to 900 μm.

[13] A thermally conductive sheet in which a cured layer of the thermally conductive silicone composition is laminated on one side of the glass cloth, wherein the thickness of the cured layer after curing is 50 μm or more and 400 μm or less.

[14] The thermally conductive sheet, wherein the thermally conductive resin composition that seals the glass cloth has the same composition as the thermally conductive silicone composition according to any one of claims [1] to [9].

[15] The thermally conductive sheet as described above, wherein a cured product of the thermally conductive silicone composition has a thermal conductivity of 2.0 W / m·K or more as measured by the method described in ISO 22007-2:2008.

[16] When the total thickness of the thermal conductive sheet is 0.2 mm, the thermal resistance is 1.8 cm as measured by the method described in ASTM D5470:2006. 2 The thermal conductive sheet has a thermal conductivity of 1.0 K / W or less.

[17] The thermally conductive sheet, wherein the breakdown voltage of the thermally conductive sheet when the total thickness is 0.2 mm is 6 kV or more as measured by the normal condition test method described in JIS K6249:2003.

[18] The thermal conductive sheet, when the total thickness is 0.2 mm, does not undergo dielectric breakdown when a DC voltage of 3 kV is applied to both sides of the insulating heat dissipation sheet for 10 seconds using electrodes of 200 mm x 300 mm. [Effects of the Invention]

[0012] The thermally conductive sheet of the present invention can be produced by continuous molding, using a thermally conductive silicone composition that has high thermal conductivity. Therefore, the sheet can be produced continuously by coating molding and wound into a roll, and provides a sheet that has high thermal conductivity and good uniformity of in-plane insulating strength. DETAILED DESCRIPTION OF THE INVENTION

[0013] The thermally conductive sheet of the present invention has a cured layer of a thermally conductive silicone composition (sometimes referred to as a thermally conductive cured layer) on one or both sides of a glass cloth sealed with a thermally conductive resin composition. That is, the present invention is a thermally conductive sheet having a glass cloth sealed with a thermally conductive resin composition and a cured layer of the thermally conductive silicone composition laminated on one or both sides of the glass cloth. In the thermally conductive sheet of the present invention, the thermally conductive silicone composition comprises a silicone component and a thermally conductive filler (C). The thermally conductive filler (C) has an average particle size of less than 15 μm, and the amount of particles with a primary particle size of 45 μm or more is 0 to 3 mass % and the amount of particles with a primary particle size of 75 μm or more is 0 to 0.01 mass %.

[0014] The silicone component is an organosilicon compound contained in the thermally conductive silicone composition, and examples thereof include linear, branched, or cyclic alkenyl group-containing organopolysiloxanes, linear, branched, or cyclic organohydrogensiloxanes, alkenyl group-free hydrolyzable group-containing organopolysiloxanes, hydrolyzable group-containing organosilanes, and alkenyl group-free dimethylpolysiloxanes. The present invention is characterized by including 700 to 1,100 parts by mass of the specific thermally conductive filler (C) per 100 parts by mass of the silicone components. The amount of component (C) is preferably 700 to 1,050 parts by mass per 100 parts by mass of the silicone components. If the amount of the thermally conductive filler is less than the above lower limit, sufficient thermal conductivity cannot be obtained, which may result in increased thermal resistance. Furthermore, if the content exceeds the above upper limit, the fluidity of the thermally conductive silicone composition will decrease, and when the composition is coated to obtain a thermally conductive sheet, voids will be unevenly distributed within the sheet surface, reducing the uniformity of the in-plane insulating strength.

[0015] Preferably, in the thermally conductive sheet of the present invention, the thermally conductive silicone composition contains 26 to 75 mass % of (E) dimethylpolysiloxane represented by the following formula (3), relative to the total mass of the silicone component. [ka] (wherein r is an integer of 5 to 500) The amount of dimethylpolysiloxane (E) is preferably 30% to 75% by mass, and more preferably 35% to 60% by mass, based on the total mass of the silicone components. The dimethylpolysiloxane functions as a plasticizer. By including the dimethylpolysiloxane in this range, the fluidity of the thermally conductive silicone composition is improved and uneven distribution of voids in the cured product sheet is suppressed.

[0016] In the thermally conductive sheet of the present invention, the thermally conductive silicone composition is preferably a peroxide-curable or addition reaction-curable composition.

[0017] In one embodiment of the present invention, the thermally conductive silicone composition is a peroxide-curable composition, and the silicone component preferably further comprises component (E) above and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, (D) an alkoxysilane having at least one alkyl group having 6 to 15 carbon atoms per molecule and at least one hydrolyzable group, and a linear organopolysiloxane having a trialkoxy group at one end and no alkenyl group. In this embodiment, the amount of the thermally conductive filler (C) is 700 to 1,100 parts by mass, preferably 700 to 1,050 parts by mass, per 100 parts by mass of the total of components (A), (D), and (E).

[0018] More preferably, one aspect of the present invention provides a thermally conductive sheet in which the thermally conductive silicone composition is a peroxide-curable composition and contains the following components (A) to (E): (A) Organopolysiloxane having at least two alkenyl groups bonded to silicon atoms per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B) Organic peroxide: effective amount (C) the average particle size is less than 15 μm; The amount of particles with a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by mass per 100 parts by mass of the component (A). (D1) Formula (1): R 1 a R 2 b Si(OR 3 ) 4-a-b (1) (In the formula, R 1are each independently an alkyl group having 6 to 15 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3; and (D2) Formula (2): [ka] (In the formula, R 3 is the same as above, and c is an integer of 5 to 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) [ka] (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the following formula: an amount that is 26% by mass to 75% by mass relative to the total mass of the components (A), (D), and (E).

[0019] In another embodiment of the present invention, the thermally conductive silicone composition is an addition reaction curable composition, and the silicone component preferably further comprises component (E) above and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and (D) an alkoxysilane having at least one C6-C15 alkyl group and at least one hydrolyzable group per molecule, and a linear organopolysiloxane having a trialkoxy group at one end and no alkenyl group. In this embodiment, the amount of thermally conductive filler (C) is 700 to 1,100 parts by mass, preferably 700 to 1,050 parts by mass, per 100 parts by mass of the total of components (A), (B'), (D), and (E) above.

[0020] Another aspect of the present invention provides a thermally conductive sheet, more preferably wherein the thermally conductive silicone composition is an addition reaction curable composition, and comprises the following components (A), (B'), (C) to (E), and component (b): (A) Organopolysiloxane having at least two alkenyl groups bonded to silicon atoms per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms (hereinafter referred to as hydrosilyl groups) per molecule: an amount such that the ratio of the number of hydrosilyl groups in component (B') to the number of alkenyl groups in component (A) is 0.1 to 5.0 (b) Addition reaction catalyst: catalytic amount (C) the average particle size is less than 15 μm; The amount of particles with a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (B'), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by mass per 100 parts by mass of the component (A). (D1) Formula (1): R 1 a R 2 b Si(OR 3 ) 4-a-b (1) (In the formula, R 1 are each independently an alkyl group having 6 to 15 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3; and (D2) Formula (2): [ka] (In the formula, R 3 is the same as above, and c is an integer of 5 to 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) [ka] (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the following formula: an amount that is 26% by mass to 75% by mass relative to the total mass of the components (A), (B'), (D), and (E).

[0021] Each component will be described in detail below.

[0022] [(A) Organopolysiloxane having an alkenyl group] Component (A) of the present invention is an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, and serves as the base component of the thermally conductive silicone composition. This organopolysiloxane can be cured by a hydrosilylation reaction using an organohydrogenpolysiloxane as a crosslinking agent or by a radical reaction with a peroxide. The organopolysiloxane preferably has two or more, preferably 2 to 20, and more preferably 3 to 15, alkenyl groups per molecule. When curing is carried out by an addition reaction, if the content of silicon-bonded alkenyl groups is below the above range, the resulting composition will not cure sufficiently. The alkenyl group preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms. Examples of alkenyl groups include vinyl, allyl, butenyl, pentenyl, and hexenyl. Of these, vinyl is preferred as the alkenyl group. The alkenyl groups may be bonded to either silicon atoms at the molecular chain terminals or silicon atoms other than the molecular chain terminals, and it is preferred that at least one alkenyl group be bonded to a silicon atom at a molecular chain terminal.

[0023] In the (A) organopolysiloxane, examples of substituents other than alkenyl groups include alkyl groups having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, aryl groups having 6 to 12 carbon atoms, preferably 6 to 8 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms, preferably 7 to 10 carbon atoms. Examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, octadecyl, cyclopentyl, and cyclohexyl groups. Examples of aryl groups include phenyl, tolyl, xylyl, and naphthyl groups. Examples of aralkyl groups include benzyl, phenethyl, and 3-phenylpropyl groups.

[0024] The state of component (A) may be liquid or rubber-like at 25°C and can be appropriately selected depending on the desired physical properties. The degree of polymerization of component (A) is preferably 20 to 12,000, more preferably 50 to 10,000. In the present invention, the degree of polymerization refers to the value determined from the weight average molecular weight measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0025] When the thermally conductive silicone composition of the present invention is an addition reaction cure type, examples of component (A) include a dimethylsiloxane-methylvinylsiloxane copolymer terminated at both molecular chain terminals with trimethylsiloxy groups, a methylvinylpolysiloxane terminated at both molecular chain terminals with trimethylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer terminated at both molecular chain terminals with trimethylsiloxy groups, a dimethylpolysiloxane terminated at both molecular chain terminals with dimethylvinylsiloxy groups, a methylvinylpolysiloxane terminated at both molecular chain terminals with dimethylvinylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane copolymer terminated at both molecular chain terminals with dimethylvinylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer terminated at both molecular chain terminals with dimethylvinylsiloxy groups, and a dimethylpolysiloxane terminated at both molecular chain terminals with trivinylsiloxy groups.

[0026] When the thermally conductive silicone composition of the present invention is a peroxide-curable type, examples of component (A) include dimethylpolysiloxanes terminally blocked with dimethylvinylsiloxy groups, dimethylpolysiloxanes terminally blocked with methylphenylvinylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers terminally blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally blocked with trimethylsiloxy groups, methyl(3,3,3-trifluoropropyl)polysiloxanes terminally blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally blocked with silanol groups, and dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers terminally blocked with silanol groups.

[0027] The component (A) of the present invention may be a single compound or a combination of two or more compounds. Preferably, the component (A) comprises (A1) an organopolysiloxane that is a rubber at 25°C and has at least two silicon-bonded alkenyl groups per molecule. More preferably, the component (A) of the present invention comprises the component (A1) and, optionally, (A2) an organopolysiloxane that is liquid at 25°C and has at least two silicon-bonded alkenyl groups per molecule. More preferably, the component (A) comprises both the component (A1) and the component (A2).

[0028] [(A1) Raw rubber-like organopolysiloxane] Component (A1) is an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is rubber-like at 25°C. The number of alkenyl groups and the substituents other than alkenyl groups are as described above for component (A). In the present invention, the organopolysiloxane that is rubber-like at 25°C is preferably an organopolysiloxane having a degree of polymerization of 2,500 to 10,000, and more preferably an organopolysiloxane having a degree of polymerization of 5,000 to 9,000.

[0029] [(A2) Liquid organopolysiloxane] The component (A2) of the present invention is a liquid organopolysiloxane having two or more alkenyl groups per molecule, and the number of alkenyl groups and the substituents other than alkenyl groups are as described above for component (A). In the present invention, the liquid organopolysiloxane is preferably an organopolysiloxane having a degree of polymerization of 100 to less than 2,500, and more preferably an organopolysiloxane having a degree of polymerization of 200 to 2,000.

[0030] The ratio (mass ratio) of the blend amounts of the components (A1) and (A2), (A2) / (A1), is preferably 1.0 or less, and more preferably 0.7 or less.

[0031] More preferably, component (A) comprises (A1) a rubber-like organopolysiloxane having two or more alkenyl groups per molecule and a degree of polymerization of 2500 to 10000, and (A2) a liquid organopolysiloxane having two or more alkenyl groups per molecule and a degree of polymerization of 100 to less than 2500, and the ratio of the amounts of components (A1) and (A2) satisfies (A2) / (A1) ≦ 1.0, more preferably (A2) / (A1) ≦ 0.7. There is no particular lower limit, but it is preferably 0.05 or more, more preferably 0.1 or more.

[0032] [Hardening agent] The thermally conductive silicone composition of the present invention preferably contains a curing agent that reacts with component (A) to produce a cured product from the thermally conductive silicone composition through a curing reaction, thereby forming a thermally conductive cured layer.

[0033] When the thermally conductive silicone composition of the present invention is an addition reaction cure type, the curing agent is (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule and (b) an addition reaction catalyst such as a platinum-based catalyst. The organohydrogenpolysiloxane (B') is preferably one represented by the following average structural formula (5), but is not limited thereto. [ka] (In the formula, R 6 are each independently an unsubstituted or substituted monovalent hydrocarbon group that does not contain a hydrogen atom or an aliphatic unsaturated bond, and R 6 At least two, preferably 2 to 10 of the above are hydrogen atoms, and e is an integer of 1 or more, preferably an integer of 10 to 200.

[0034] In formula (5), R 6 Examples of the unsubstituted or substituted monovalent hydrocarbon group that does not contain an aliphatic unsaturated bond other than a hydrogen atom include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups. 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. Representative examples include monovalent hydrocarbon groups having 1 to 10 carbon atoms, particularly 1 to 6 carbon atoms. Preferred examples include 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, R 6 does not necessarily mean that all are the same.

[0035] The amount of organohydrogenpolysiloxane (B') in the thermally conductive silicone composition is such that the ratio of the number of Si-H groups in the organohydrogenpolysiloxane to the number of alkenyl groups in component (A) is 0.1 to 5.0, preferably 0.3 to 2.0. If the amount of organohydrogenpolysiloxane is less than the above-mentioned lower limit, the silicone composition may not cure, or the strength of the resulting cured product may be insufficient and the molded product may not retain its shape and may become difficult to handle. If the amount of organohydrogenpolysiloxane exceeds the above-mentioned upper limit, the resulting cured product may lose flexibility and become brittle.

[0036] The platinum catalyst may be any catalyst conventionally known as an addition reaction catalyst, such as platinum (including platinum black), rhodium, palladium, or other platinum group metals; platinum chlorides such as HPtCl·nH2O, HPtCl·nH2O, NaHPtCl·nH2O, KaHPtCl·nH2O, NaPtCl·nH2O, KPtCl·nH2O, PtCl·nH2O, PtCl·nH2O, PtCl2, and NaHPtCl·nH2O (wherein n is an integer of 0 to 6, preferably 0 or 6); chloroplatinic acid and chloroplatinic acid salts; and alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972). Examples of suitable platinum catalysts include complexes of chloroplatinic acid and olefins (see U.S. Pat. Nos. 3,159,601, 3,159,662, and 3,775,452), platinum black, platinum group metals such as palladium supported on supports such as alumina, silica, and carbon, rhodium-olefin complexes, chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst), complexes of platinum chloride, chloroplatinic acid, or chloroplatinate salts with vinyl group-containing siloxanes, particularly vinyl group-containing cyclic siloxanes. The amount of platinum catalyst may be an amount sufficient to promote the addition reaction, for example, 0.1 to 2,000 ppm, preferably 50 to 1,000 ppm, of platinum metal element by mass relative to the amount of organopolysiloxane (A).

[0037] When the thermally conductive silicone composition of the present invention is a peroxide-curable composition, the curing agent is (B) an organic peroxide. These organic peroxides can be used alone or in combination. Examples include benzoyl peroxide, monochlorobenzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, o-methylbenzoyl peroxide, p-methylbenzoyl peroxide, di(tert-butyl)perbenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and di(tert-butyl)peroxide. The amount of organic peroxide added may be an amount effective to promote the curing reaction, and is, for example, 1 to 70 parts by weight, preferably 5 to 50 parts by weight, per 100 parts by weight of component (A).

[0038] [(C) Thermally conductive filler] Component (C) of the present invention is a thermally conductive filler having an average particle size of less than 15 μm, with 0 to 3 mass% of particles having a primary particle size of 45 μm or more, and 0 to 0.01 mass% of particles having a primary particle size of 75 μm or more.

[0039] Component (C) may be any commonly used material, such as 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, metal hydroxides such as magnesium hydroxide, artificial diamond, and silicon carbide. Among these, alumina is preferred when thermal conductivity, electrical insulation, and cost are taken into consideration comprehensively.

[0040] The average particle size of component (C) is less than 15 μm, preferably less than 10 μm. Furthermore, the amount of particles with a particle size of 45 μm or greater is 0-3 mass%, preferably 0-2.5 mass%, and the amount of particles with a particle size of 75 μm or greater is 0-0.01 mass%, preferably 0 mass%. If any of the average particle size, the amount of particles with a particle size of 45 μm or greater, or the amount of particles with a particle size of 75 μm or greater exceeds the upper limit, when the thermally conductive silicone composition is coated to obtain a thermally conductive sheet, the filler may protrude from the coating surface, impairing the smoothness of the sheet surface. This leads to an increase in contact thermal resistance when mounted, which is disadvantageous in terms of thermal conductivity.

[0041] The component (C) can be used alone or in combination of two or more types, but it is preferable to use aluminas shown in the following (C1) and (C2) in combination. (C1) Alumina having an average particle size of 0.1 μm or more and less than 5 μm, preferably 0.5 μm or more and less than 2 μm, with the amount of particles having a primary particle size of 45 μm or more being 0 to 3 mass % and the amount of particles having a primary particle size of 75 μm or more being 0 to 0.01 mass %, and (C2) Alumina having an average particle size of 5 μm or more and less than 15 μm, preferably 5 μm or more and less than 10 μm, with the amount of particles having a primary particle size of 45 μm or more being 0 to 3 mass % and the amount of particles having a primary particle size of 75 μm or more being 0 to 0.01 mass %. More preferably, component (C) comprises alumina (C1) and alumina (C2), and the amount of component (C1) in component (C) is 20 to 50 mass%, preferably 20 to 40 mass%, and the amount of component (C2) is 50 to 80 mass%, preferably 60 to 80 mass%.

[0042] In order to smooth the surface of the thermally conductive sheet, the thermally conductive filler (C) is preferably spherical. In particular, when a relatively large filler having an average particle size of 5 μm or more and less than 15 μm, such as the above-mentioned component (C2), is spherical, the surface of the thermally conductive sheet can be made even smoother.

[0043] In the present invention, the average particle size is the value of the cumulative 50% particle size (D50) on a volume basis measured by a particle size distribution measuring device MT3000II manufactured by Microtrack Bell.

[0044] The amount of particles with a primary particle size of 45 μm or more and the amount of particles with a primary particle size of 75 μm or more in component (C) are determined as follows. 10 g of filler is collected and placed in an arbitrary amount of water for ultrasonic dispersion. A sieve with a mesh size of 45 μm and a sieve with a mesh size of 75 μm are placed on top of each other in a sieve shaker, and the thermally conductive filler dispersed in the water is placed in the shaker. The filler remaining on each sieve is dried and weighed.

[0045] As mentioned above, the amount of component (C) is 700 to 1,100 parts by mass, preferably 700 to 1,050 parts by mass, per 100 parts by mass of the total amount of silicone components. If the amount is less than the lower limit, sufficient thermal conductivity cannot be obtained, which can lead to increased thermal resistance. If the amount is greater than the upper limit, the fluidity of the thermally conductive silicone composition decreases, resulting in uneven distribution of voids within the sheet surface when the composition is coated to obtain a thermally conductive sheet, reducing the uniformity of the in-plane insulating strength. When the silicone composition of the present invention is an addition reaction curing type, the amount of the silicone component refers to the total amount of components (A), (B'), (D), and (E) below. When the silicone composition of the present invention is a peroxide curing type, the amount of the silicone component refers to the total amount of components (A), (D), and (E) below.

[0046] The reason for specifying the amount of component (C) based on the total amount of silicone components is that the amount of thermally conductive filler relative to the total amount of silicone components has a significant effect on the thermal conductivity of the thermally conductive silicone composition. Because the thermal conductivity of a composite material of resin and thermally conductive filler increases in proportion to the amount of filler relative to the total amount of resin, it is appropriate to base the amount of component (C) on the total amount of silicone components.

[0047] [(D) Organosilicon compounds] Component (D) of the present invention is one or more organosilicon compounds selected from alkoxysilanes having at least one alkyl group of 6 to 15 carbon atoms and at least one hydrolyzable group per molecule, and linear organopolysiloxanes having a trialkoxy group at one end and no alkenyl group. Component (D) is added to improve the wettability of the thermally conductive filler (C), facilitating the loading of the filler into the silicone component and thereby increasing the loading amount of the filler.

[0048] Preferably, the component (D) of the present invention is one or more organosilicon compounds selected from the alkoxysilanes shown below as (D1) and the linear organopolysiloxanes shown below as (D2). (D1) Formula (1): R 1 a R 2 b Si(OR 3 ) 4-a-b (1) (In the formula, R 1 are each independently an alkyl group having 6 to 15 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3. Alkoxysilane represented by (D2) Formula (2): [ka] (In the formula, R 3 is as described above, and c is an integer from 5 to 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by

[0049] [(D1) Alkoxysilane] In the above formula (1), R 1Examples of the alkyl group having 6 to 15 carbon atoms represented by the formula (R) include a hexyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, and a tetradecyl group. 1 When the alkyl group represented by the formula (I) has 6 to 15 carbon atoms, the wettability of the thermally conductive filler (C) is sufficiently improved, making it easier to fill the thermally conductive silicone composition with the filler, and also imparting good low-temperature properties to the composition.

[0050] R 2 Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms represented by the formula (R) include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups. 2 Preferably, the alkyl group has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and particularly includes alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, and propyl groups, and phenyl groups.

[0051] In the above formula (1), a is an integer of 1 to 3, and b is an integer of 0 to 2, provided that a+b is 1 to 3. Organosilanes in which a is 1 and b is 2 are preferred.

[0052] R 3 Examples of the alkyl group represented by the formula (I) include alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, and hexyl.

[0053] [(D2) Dimethylpolysiloxane] Component (D2) is a dimethylpolysiloxane having one end blocked with a trialkoxy group, as represented by the following formula (2). [ka] (In the formula, R 3 is as described above, and c is an integer from 5 to 100. R 3 The alkyl group represented by the formula (1) is 3 Examples of the alkyl group include those defined for the alkyl group represented by the formula:

[0054] c is an integer of 5 to 100, preferably 10 to 60.

[0055] The amount of component (D) is preferably 1 to 100 parts by mass, more preferably 10 to 60 parts by mass, per 100 parts by mass of component (A). If the amount is less than the lower limit, it may be difficult to fill the silicone component with the thermally conductive filler (C). If the amount is more than the upper limit, the strength of the resulting cured product may be insufficient.

[0056] [(E) Plasticizer] The component (E) of the present invention is a plasticizer represented by the following formula (3): [ka] In the formula, r is an integer of 5 to 500, preferably an integer of 10 to 450, and more preferably an integer of 20 to 400.

[0057] The present invention preferably contains 26 to 75% by mass of (E) dimethylpolysiloxane, based on the total mass of the silicone components. This is preferably 28 to 60% by mass, and more preferably 30 to 50% by mass. The total mass of the silicone components refers to the combined total of the above (A), (B'), and the following (D) and (E) components when the silicone composition of the present invention is an addition reaction curing type, and refers to the combined total of the above (A), (D), and (E) components when the silicone composition of the present invention is a peroxide curing type. More preferably, the amount of component (E) is 1 to 200 parts by mass, preferably 10 to 200 parts by mass, and more preferably 50 to 150 parts by mass per 100 parts by mass of component (A). If the amount is less than the lower limit, the sheet may have too high hardness, and the resulting cured product may have too high hardness, which may reduce adhesion to the adherend and increase heat resistance. If the amount of component (E) exceeds the upper limit, the resulting cured product may have insufficient strength.

[0058] [Thermal conductive silicone composition] The thermally conductive silicone composition of the present invention preferably has a thermal conductivity of 2.0 W / mK or higher when cured, as measured by the method described in ISO 22007-2:2008. Furthermore, the hardness of the cured product, as measured by a Type A durometer according to the method described in JIS K6249:2003, is preferably 80 to 96, more preferably 82 to 94. If the hardness is too low, the surface of the cured product layer may be easily scratched during handling, or the surfaces of the cured product layer may fuse together when wound into a roll during continuous molding. Furthermore, when the thermally conductive sheet of the present invention is secured between the heat-generating and cooling parts of an electronic device by screwing, if the hardness is too low, the sheet may deform due to the pressure applied by the screwing, making it difficult to secure a space between the heat-generating and cooling parts, thereby making it difficult to maintain insulation. On the other hand, if the hardness is too high, the sheet may become inflexible and may crack when bent.

[0059] [Method for preparing thermally conductive silicone composition] The thermally conductive silicone composition of the present invention can be prepared, for example, as follows. Components (A), (C), (D), and (E) are kneaded using a mixer such as a kneader, Banbury mixer, planetary mixer, or Shinagawa mixer, while heating to a temperature of 100°C or higher as needed. During this kneading process, if desired, reinforcing silica such as fumed silica or precipitated silica; silicone oil, silicone wetter, etc.; flame retardants such as platinum, titanium oxide, and benzotriazole may be added within limits that do not impair thermal conductivity. The homogeneous mixture obtained in the kneading process is cooled to room temperature and filtered through a strainer or the like. The required amount of curing agent is then added to the mixture using a two-roll mill, Shinagawa mixer, or the like, and the mixture is kneaded again. During this second kneading process, if desired, an acetylene compound-based addition reaction inhibitor such as 1-ethynyl-1-cyclohexanol, a colorant such as an organic pigment or inorganic pigment, a heat resistance improver such as iron oxide or cerium oxide, and an internal mold release agent may be added. The thermally conductive silicone composition thus obtained can be used directly in the next step as a coating material, but if necessary, a solvent such as toluene can also be added.

[0060] [Thermal conductive sheet] The thermally conductive sheet of the present invention has a layer of the cured product of the thermally conductive silicone composition on one or both sides of a glass cloth sealed with a thermally conductive resin composition, and preferably has a thermally conductive cured layer on both sides.

[0061] The glass cloth may be a commercially available one, for example, a glass cloth having a weight of 30 g / m 2 The glass cloth has a thickness of preferably 60 μm or less, more preferably 30 to 50 μm, and even more preferably 30 to 45 μm. Since the thermal conductivity of glass cloth is relatively low, a thinner glass cloth is preferable when high thermal conductivity is desired. However, if the glass cloth is too thin, the strength decreases.

[0062] The thermally conductive resin composition for sealing the glass cloth preferably has a thermal conductivity of 1.2 W / mK or higher. Examples of such thermally conductive resin compositions include those obtained by adding a thermally conductive filler to a thermosetting silicone resin. Examples include thermally conductive compositions containing the components (A) to (E) described above, which are contained in the thermally conductive silicone composition for the thermally conductive cured layer. The thermally conductive composition may be an addition reaction curable or peroxide curable thermally conductive composition having the components (A) to (E) in the blending ratios of the thermally conductive silicone composition described above. Among these, it is preferable to seal the glass cloth with a thermally conductive resin composition having the same composition as the thermally conductive silicone composition for the cured product layer. Using the same thermally conductive resin composition for sealing as the thermally conductive cured product layer ensures excellent adhesion between the sealed glass cloth and the thermally conductive cured layer.

[0063] Preferably, the thickness of the sheet obtained by sealing the glass cloth (referred to as a sealed glass cloth sheet) is 100 μm or less, more preferably 90 μm or less, and even more preferably 85 μm or less. When attempting to produce a thermally conductive sheet with a predetermined thickness, if the thickness of the sealed glass cloth sheet is too thick, the thickness of the thermally conductive hardened layer will be thin, which will reduce the thermal conductivity of the thermally conductive sheet. Furthermore, from the viewpoint of ensuring electrical insulation, the thickness of the thermally conductive sheet is preferably 180 μm or more. For example, when the thickness of the thermally conductive sheet is 180 μm, if the thickness of the sealed glass cloth sheet is more than 80 μm, the thickness of the thermally conductive hardened layer on both sides will each be less than 50 μm. In this case, the thermally conductive filler contained in the thermally conductive hardened layer will protrude to the surface, impairing the surface smoothness and resulting in reduced thermal conductivity.

[0064] The thermally conductive sheet of the present invention can be obtained by applying and curing the thermally conductive silicone composition to one or both sides of the sealed glass cloth sheet to form a cured layer, as described below. The application is preferably carried out so that the thickness of the cured layer after curing is 50 μm to 400 μm, more preferably 60 μm to 350 μm. As described above, if the thickness of the cured layer is too thin, the thermally conductive filler contained therein will protrude, impairing the smoothness of the surface of the thermally conductive cured layer. The resulting thermally conductive sheet preferably has an overall thickness of 180 to 900 μm, more preferably 200 to 800 μm, when the thermally conductive cured layer is present on both sides of the sealed glass cloth, and 130 to 500 μm, more preferably 150 to 450 μm, when the thermally conductive cured layer is present on one side.

[0065] When the thermally conductive silicone composition obtained in this manner is used as a sealing material, the composition is continuously applied to glass cloth using a conventional coating device such as a comma coater, knife coater, or kiss coater equipped with a drying oven, heating oven, and take-up device, and the solvent is then dried and evaporated, and the composition is heated to 80 to 200°C, preferably 100 to 150°C in the case of curing by addition reaction, or to 100 to 200°C, preferably 110 to 180°C in the case of curing by peroxide, to obtain a sealed glass cloth.

[0066] The thermally conductive sheet of the present invention is continuously produced by coating one or both sides of a sealed glass cloth sheet with the thermally conductive silicone composition to form a thermally conductive cured layer. For example, the thermally conductive silicone composition obtained above is continuously applied to one side (referred to as the front side) of the sealed glass cloth using a conventional coating device such as a comma coater, knife coater, or kiss coater equipped with a drying oven, a heating oven, and a winding device. The solvent is then dried and evaporated, and the resulting thermally conductive cured layer is formed by heating to 80 to 200°C, preferably 100 to 150°C, in the case of addition reaction curing, or to 100 to 200°C, preferably 110 to 180°C, in the case of peroxide curing. When coating both sides, a thermally conductive cured layer is formed on the other side (referred to as the back side) of the glass cloth in the same manner as on the front side to obtain the thermally conductive sheet. Coating on the front side and back side may be performed simultaneously. The completed thermally conductive sheet is continuously wound into a roll. The conductive silicone compositions on the front and back surfaces may be the same or different.

[0067] The thermally conductive sheet thus obtained preferably has a thermal resistance of 1.8 cm when measured in accordance with ASTM D5470:2006 when the total thickness is 0.2 mm. 2 1.5 kV / W or less. Preferably, the breakdown voltage when the total thickness is 0.2 mm is 6 kV or more when measured in accordance with JIS K6249:2003. The thermal resistance and breakdown voltage are approximately proportional to the thickness of the thermally conductive sheet.

[0068] Furthermore, the thermally conductive sheet obtained in this way has good uniformity of insulating properties within the surface, so when a DC voltage of 3 kV is applied to both sides of an insulating heat dissipation sheet for 10 seconds using 200 mm x 300 mm electrodes for a sheet with a total thickness of 0.2 mm, no dielectric breakdown occurs.

[0069] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0070] The materials used in the examples and comparative examples are as follows. (A) Component: (A-1) Dimethylpolysiloxane with an average degree of polymerization of 8,000, both ends of which are capped with dimethylvinyl groups (raw rubber at 25°C) (A-2) Dimethylpolysiloxane with an average degree of polymerization of 3,000, both ends of which are capped with dimethylvinyl groups (liquid at 25°C)

[0071] (B) Component: 2-methylbenzoyl peroxide

[0072] (C) Ingredients: (C-1) Irregular alumina having an average particle size of 1 μm, a content of particles with a primary particle size of 45 μm or more of 3 mass% or less, and a content of particles with a primary particle size of 75 μm or more of 0% (C-2) Spherical alumina having an average particle size of 10 μm, a content of particles having a primary particle size of 45 μm or more of 3 mass% or less, and a content of particles having a primary particle size of 75 μm or more of 0 mass% (C-3) (For comparison) Spherical alumina having an average particle size of 10 μm, a content of particles with a primary particle size of 45 μm or more of 10 mass %, and a content of particles with a primary particle size of 75 μm or more of 3 mass % (C-4) (For comparison) Irregular alumina having an average particle size of 20 μm, a primary particle size of 45 μm or more of 3% or less, and a primary particle size of 75 μm or more of 0%. (C-5) Crushed zinc oxide having an average particle size of 1 μm, a content of particles with a primary particle size of 45 μm or more of 3% or less, and a content of particles with a primary particle size of 75 μm or more of 0%

[0073] Component (D): A dimethylpolysiloxane having the following formula (4), an average degree of polymerization of 30, and one end capped with a trimethoxysilyl group: [ka]

[0074] Component (E): Dimethylpolysiloxane having the following formula (5): [ka]

[0075] Glass cloth: 40 μm thick and 26 g / m 2 Glass cloth

[0076] Examples 1 to 4 and Comparative Examples 1 to 5 [Preparation of Thermally Conductive Silicone Composition] The components shown in Table 1 (parts by mass) were added to a Banbury mixer and kneaded for 20 minutes to prepare thermally conductive silicone compositions (A) to (F). The thermal conductivity and hardness of the cured products of the resulting thermally conductive silicone compositions were measured using the following methods. The results are shown in Table 1.

[0077] thermal conductivity The resulting silicone composition was press-molded into a 6 mm thick sheet using a 60 × 60 × 6 mm mold at 160°C for 10 minutes, adjusting the pressure so that the cured thickness would be 6 mm. The thermal conductivity of the sheet was measured using a thermal conductivity meter (TPS-2500S, product name, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) with a probe sandwiched between two sheets in accordance with ISO22007-2:2008.

[0078] hardness The resulting silicone composition was press-molded at 160°C for 10 minutes using a 60mm x 60mm, 6mm thick mold, with the pressure adjusted so that the thickness after curing would be 6mm, and cured into a 6mm thick sheet. Two of these sheets were stacked together and used as a test piece to measure the hardness using a Durometer A hardness tester.

[0079] [Manufacturing of thermally conductive sheets] Glass cloth sealing The thermally conductive silicone composition obtained above was used as a sealing composition, to which 20% by mass of toluene was added and kneaded using a planetary mixer to prepare a coating material. This coating material was applied to one side of a glass cloth using a comma coater to seal the glass cloth. The comma coater used was 1,300 mm wide and had an effective oven length of 15 m. The 15 m oven was divided into three zones, each 5 m long, with temperature adjustment possible for each zone. The temperatures were 80°C, 150°C, and 180°C from the side closest to the comma section. The coating speed was 2 m / min. The coating material was continuously applied to the glass cloth and then wound up to obtain a sealed glass cloth. The sealed glass cloth had a thickness of 80 μm.

[0080] Coating on sealed glass cloth To the thermally conductive silicone composition obtained above, 20% by mass of toluene was added, and the mixture was kneaded using a planetary mixer to obtain a coating material. This coating material was then applied to one side (front side) of the sealed glass cloth obtained above using a comma coater so that the thickness after curing was 60 μm, and the glass cloth was then wound up. Next, the other side (back side) was similarly coated and wound up, yielding a thermally conductive sheet with a total thickness of 200 μm. The comma coater and coating conditions used were the same as those used for the sealing process. In Comparative Example 4, coating onto the sealed glass cloth was carried out as follows. The oven temperatures were set to 60°C, 80°C, and 80°C from the side closest to the comma, and the coating speed was set to 2 m / min. The oven temperature was lowered to a temperature that would volatilize the toluene but would not cause decomposition of the (B) peroxide, thereby obtaining an unvulcanized product. This unvulcanized product was cut to an appropriate size and press-molded using a press molding machine at 170°C for 10 minutes, adjusting the pressure so that the thickness after curing would be 200 μm, to obtain a thermally conductive sheet.

[0081] The thermal resistance of the resulting thermally conductive sheet was measured according to ASTM D5470:2006. The breakdown voltage was also measured according to JIS K6249:2003. Additionally, a voltage resistance test was conducted on the entire surface of the sheet to evaluate the uniformity of the in-plane insulation strength. Specifically, a 3 kV DC voltage was applied to both sides of the insulating heat dissipation sheet for 10 seconds using 200 mm × 300 mm electrodes, and the number of short-circuited sheets out of 30 sheets was counted. The results are shown in Table 2.

[0082] [Table 1]

[0083] [Table 2]

[0084] The thermally conductive sheet of the present invention is continuously produced by coating molding and wound into a roll. As is clear from Table 2, when the total thickness is 0.2 mm, the thermal conductivity is 1.8 cm. 2 It has a low thermal resistance of less than 1000kJ / W and a high breakdown voltage of more than 6kV. In addition, the uniformity of the insulating properties within the surface is so good that no breakdown occurs when a 3kV DC voltage is applied to both sides of an insulating heat dissipation sheet for 10 seconds using 200mm x 300mm electrodes on a sheet with a total thickness of 0.2mm.

[0085] On the other hand, the sheet of Comparative Example 1 had a lower amount of thermally conductive filler (C) than the range of the present invention, resulting in high thermal resistance. In the sheet of Comparative Example 2, in which the amount of particles with a primary particle diameter of 45 μm or more and the amount of particles with a primary particle diameter of 75 μm or more were higher than the range of the present invention, these large particles protruded from the surface of the sheet, impairing the surface smoothness and increasing the thermal resistance. The sheet of Comparative Example 3, in which the average particle diameter was larger than the range of the present invention, also impaired the smoothness of the sheet surface and increased the thermal resistance. Furthermore, in Comparative Examples 2 and 3, non-uniformity in the in-plane insulating properties occurred, resulting in short circuits in the withstand voltage test. The only difference between the sheet of Comparative Example 4 and Comparative Example 3 is that it was press-molded instead of coated. By using press molding, a sheet with low thermal resistance and good uniformity of in-plane insulating properties was obtained, but press molding makes it impossible to continuously produce a sheet and wind it into a roll. In Comparative Example 5, the amount of thermally conductive filler (C) added was greater than the range specified in the present invention, resulting in a decrease in the fluidity of the thermally conductive silicone composition and uneven distribution of voids within the sheet, which caused variations in the in-plane insulating properties and resulted in short circuits during the voltage resistance test. [Industrial Applicability]

[0086] As described above, the thermally conductive sheet of the present invention can be produced by continuous molding, using a thermally conductive silicone composition that has high thermal conductivity. Therefore, it can be produced continuously by coating molding and wound into a roll, and is useful for providing a thermally conductive sheet that has high thermal conductivity and good uniformity of in-plane insulation strength.

Claims

1. A thermally conductive sheet comprising glass cloth sealed with a thermally conductive resin composition and a cured product layer of a thermally conductive silicone composition laminated on one or both sides of the glass cloth, wherein the thermally conductive silicone composition comprises a silicone component and a thermally conductive filler (C), the amount of the thermally conductive filler is 700 to 1,100 parts by mass per 100 parts by mass of the total of the silicone components, and the thermally conductive filler (C) has an average particle size of less than 15 μm, and the amount of particles having a primary particle size of 45 μm or more is 0 to 3 mass % and the amount of particles having a primary particle size of 75 μm or more is 0 to 0.01 mass %.

2. 2. The thermally conductive sheet according to claim 1, wherein the thermally conductive silicone composition contains 26% by mass to 75% by mass of (E) a dimethylpolysiloxane represented by the following formula (3), relative to the total mass of the silicone components: 【Chemistry 1】 (wherein r is an integer from 5 to 500).

3. 3. The thermally conductive sheet according to claim 2, wherein the thermally conductive silicone composition is a peroxide-curable composition, and the silicone component further comprises component (E) according to claim 2, and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, (D) an alkoxysilane having at least one alkyl group having 6 to 15 carbon atoms per molecule and having at least one hydrolyzable group, and a linear organopolysiloxane having a trialkoxy group at one end and no alkenyl group, and wherein the amount of the thermally conductive filler (C) is 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (D), and (E).

4. 2. The thermally conductive sheet according to claim 1, wherein the thermally conductive silicone composition is a peroxide-curable composition and contains the following components (A) to (E): (A) Organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B) Organic peroxide: effective amount (C) the average particle size is less than 15 μm; The amount of particles having a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by weight per 100 parts by weight of the component (A). (D1) The following formula (1): R １ ａ R ２ ｂ Si(OR ３ ) ４－ａ－ｂ (1) (In the formula, R １ are each independently an alkyl group having 6 to 15 carbon atoms, and R ２ are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R ３ are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3. and an alkoxysilane represented by (D2) The following formula (2): 【Chemistry 2】 (In the formula, R ３ is as defined above, and c is an integer from 5 to 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) 【Transformation 3】 (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the formula: an amount that is 26% by mass to 75% by mass based on the total mass of components (A), (D), and (E).

5. 3. The thermally conductive sheet according to claim 2, wherein the thermally conductive silicone composition is an addition reaction curable composition, and the silicone component further comprises component (E) according to claim 2, and one or more organosilicon compounds selected from (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and (D) an alkoxysilane having at least one C alkyl group and at least one hydrolyzable group per molecule, and a linear organopolysiloxane having a trialkoxy group at one end and no alkenyl group, and wherein the amount of the thermally conductive filler (C) is 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (B), (D), and (E).

6. 2. The thermally conductive sheet according to claim 1, wherein the thermally conductive silicone composition is an addition reaction curable composition and comprises the following components (A), (B'), (C) to (E), and (b): (A) Organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and a degree of polymerization of 20 to 12,000: 100 parts by mass (B') an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms (hereinafter referred to as hydrosilyl groups) per molecule: an amount such that the ratio of the number of hydrosilyl groups in component (B') to the number of alkenyl groups in component (A) is 0.1 to 5.0 (b) Addition reaction catalyst: catalytic amount (C) the average particle size is less than 15 μm; The amount of particles having a primary particle diameter of 45 μm or more is 0 to 3 mass %, and A thermally conductive filler having a primary particle size of 75 μm or more of 0 to 0.01 mass %: 700 to 1,100 parts by mass per 100 parts by mass of the total of components (A), (B'), (D), and (E) (D) One or more organosilicon compounds selected from the following (D1) and (D2): 1 to 100 parts by weight per 100 parts by weight of the component (A). (D1) The following formula (1): R １ ａ R ２ ｂ Si(OR ３ ) ４－ａ－ｂ (1) (In the formula, R １ are each independently an alkyl group having 6 to 15 carbon atoms, and R ２ are each independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R ３ are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, and b is an integer of 0 to 2, with the proviso that a+b is 1 to 3. and an alkoxysilane represented by (D2) The following formula (2): 【Chemistry 4】 (In the formula, R ３ is as defined above, and c is an integer from 5 to 100. Dimethylpolysiloxane having one end capped with a trialkoxy group, represented by (E) The following formula (3) 【Transformation 5】 (wherein r is an integer of 5 to 500) A plasticizer that is a dimethylpolysiloxane represented by the formula: an amount that is 26% by mass to 75% by mass based on the total mass of components (A), (B'), (D), and (E).

7. The component (C) is (C1) Alumina having an average particle size of 0.1 μm or more and less than 5 μm, a content of particles having a primary particle size of 45 μm or more of 0 to 3 mass%, and a content of particles having a primary particle size of 75 μm or more of 0 to 0.01 mass%: 20 to 50 mass%, and (C2) Alumina having an average particle size of 5 μm or more and less than 15 μm, a content of particles having a primary particle size of 45 μm or more of 0 to 3 mass%, and a content of particles having a primary particle size of 75 μm or more of 0 to 0.01 mass%: 50 to 80 mass% The thermally conductive sheet according to any one of claims 1 to 6, comprising:

8. 7. The thermally conductive sheet according to claim 1, wherein component (A) comprises (A1) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is in a rubber-like state at 25°C, and optionally (A2) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is liquid at 25°C.

9. 7. The thermally conductive sheet according to claim 1, wherein the component (A) comprises: (A1) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is in a rubber-like state at 25°C; and (A2) an organopolysiloxane that has at least two silicon-bonded alkenyl groups per molecule and is liquid at 25°C; and the ratio of the amounts of the components (A1) and (A2) satisfies (A2) / (A1)≦1.

0.

10. 3. The thermally conductive sheet according to claim 1, wherein the cured product of the thermally conductive silicone composition has a hardness of 80 to 96 as measured with a Type A durometer according to the method described in JIS K6249:2003.

11. 3. The thermally conductive sheet according to claim 1, wherein the glass cloth has a thickness of 60 [mu]m or less.

12. 3. The thermally conductive sheet according to claim 1, wherein a cured product layer of the thermally conductive silicone composition is laminated on both sides of the glass cloth, and the thickness of the thermally conductive sheet is 180 to 900 μm.

13. 3. The thermally conductive sheet according to claim 1 or 2, wherein a cured layer of the thermally conductive silicone composition is laminated on one side of the glass cloth, and the thickness of the cured layer after curing is 50 μm or more and 400 μm or less.

14. 3. The thermally conductive sheet according to claim 1, wherein the thermally conductive resin composition that seals the glass cloth has the same composition as the thermally conductive silicone composition.

15. 3. The thermally conductive sheet according to claim 1, wherein the cured product of the thermally conductive silicone composition has a thermal conductivity of 2.0 W / m·K or more as measured by the method described in ISO 22007-2:2008.

16. The thermal resistance of the thermally conductive sheet when the total thickness is 0.2 mm is 1.8 cm as measured by the method described in ASTM D5470:2006. ２ 3. The thermally conductive sheet according to claim 1, wherein the thermal conductivity is 0.05 K / W or less.

17. 3. The thermal conductive sheet according to claim 1, wherein the breakdown voltage of the thermal conductive sheet when the total thickness is 0.2 mm is 6 kV or more as measured by the normal state test method described in JIS K6249:2003.

18. 3. A thermally conductive sheet according to claim 1 or 2, wherein when a direct current voltage of 3 kV is applied to both sides of an insulating heat dissipation sheet for 10 seconds using 200 mm x 300 mm electrodes for a thermally conductive sheet having a total thickness of 0.2 mm, no dielectric breakdown occurs.

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