Thermally conductive millable silicone rubber composition and thermally conductive sheet

Abstract

The present invention provides a thermally conductive millable silicone rubber composition comprising: (A)(A-1) a raw-rubber organopolysiloxane that has an alkenyl group at only both ends of a molecular chain, (A-2) a raw-rubber organopolysiloxane that has an alkenyl group at both ends of a molecular chain and in a side chain, and (A-3) a liquid organopolysiloxane that has two or more alkenyl groups per molecule; (B)(B-1) an organohydrogen polysiloxane that has 2-5 hydrosilyl groups per molecule and only in a side chain of the molecule and (B-2) an organohydrogen polysiloxane that has two or more hydrosilyl groups per molecule, two of which are at ends of a molecular chain; (C) a thermally conductive filler; (E) an addition reaction catalyst; and (F) an addition reaction control agent. The present invention provides a thermally conductive millable silicone rubber composition that provides a heat dissipation sheet which has a low contact thermal resistance and which is excellent in long-term stability.

Description

Thermally conductive millable silicone rubber composition and thermally conductive sheet

[0001] The present invention relates to a heat-conductive millable silicone rubber composition and a heat-conductive sheet.

[0002] Heat-generating components and integrated circuit devices used in various electronic devices can generate heat, which can degrade their performance and shorten their lifespan. The placement of components within an electronic device is important for smooth heat dissipation. In addition, heat-generating components and the entire device are forced to cool with cooling fins, and heat generated by integrated circuit devices is dissipated outside the device via a heat dissipation sheet.

[0003] However, in recent years, highly portable electronic devices, such as smartphones and tablet devices, have become increasingly highly integrated, resulting in increased heat generation from the heat-generating components and integrated circuit elements within the devices. As a result, conventional cooling methods may not be sufficient to cool or dissipate heat from these components and elements. In particular, these electronic devices require cooling methods other than forced air cooling to maintain portability. Furthermore, because the printed circuit boards on which the elements are formed use materials with poor thermal conductivity, conventional heat dissipation sheets are unable to adequately dissipate the heat generated by the elements to the board. Therefore, a method has been adopted in which a heat sink, such as a natural-cooling or forced-cooling type heat sink or heat pipe, is installed near the element, and the heat generated by the element is transferred to the heat sink via a heat dissipation medium and dissipated.

[0004] This type of heat dissipation medium uses a heat dissipation sheet approximately 0.2 to 10.0 mm thick to improve thermal conduction between the device and the heat sink. A well-known heat dissipation sheet is one made of a highly filled, high-hardness silicone rubber layer reinforced with a fabric-like reinforcing material such as glass cloth (see Patent Document 1). This type of heat dissipation sheet is highly useful because the rubber layer has a high hardness, allowing it to not only conduct heat but also ensure insulation. However, to prevent a decrease in insulation due to thickness changes caused by pressure during mounting, the insulating heat dissipation sheet must be hard, which creates problems such as poor adhesion to electronic components and heat sinks, resulting in high contact thermal resistance.

[0005] To reduce contact thermal resistance, a heat dissipation sheet has also been proposed in which a low-hardness heat-conductive silicone rubber layer is laminated onto a high-hardness heat-conductive silicone rubber sheet reinforced with the aforementioned reinforcing material (Patent Document 2). However, in the case of this composite heat dissipation sheet, the low-hardness layer is compressed and deformed by pressure, which can lead to thinning or cracking or breaking of the low-hardness layer, resulting in a decrease in insulation.

[0006] Additionally, in order to achieve both excellent strength and high thermal conductivity, a thermally conductive silicone composite sheet has been proposed in which a cured thermally conductive silicone is laminated on both sides of a metal foil (Patent Documents 3 and 4).

[0007] JP 2015-233104 A JP 2014-193598 A JP 2013-095023 A JP 2017-092322 A

[0008] As described above, high-hardness heat-dissipating sheets have excellent heat dissipation properties and insulation reliability due to their strength, but they have the problem of not being able to achieve efficient heat conduction due to high contact thermal resistance. Furthermore, low-hardness / high-hardness composite sheets tend to become thin under high pressure, making it difficult to ensure insulation. Furthermore, when attempting to apply a method of laminating a thin metal film such as metal foil to a silicone rubber sheet, problems arise, such as increased contact thermal resistance, concerns about poor insulation, and increased manufacturing costs. The present invention has been made to solve the above problems, and its object is to provide a thermally conductive millable-type silicone rubber composition that provides a heat-dissipating sheet with excellent thermal conductivity, strength, and insulation properties, moderate hardness, low contact thermal resistance, and excellent long-term stability.

[0009] In order to solve the above problems, the present invention provides: (A) an organopolysiloxane comprising the following components (A-1) to (A-3): (A-1) a rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals; (A-2) a rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains; (A-3) an organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups per molecule; 100 parts by mass of a linear organopolysiloxane having alkenyl groups, (B) an organohydrogenpolysiloxane comprising the following components (B-1) and (B-2): (B-1) an organohydrogenpolysiloxane that has hydrosilyl groups only at side chains on the molecular chain and has 2 to 5 hydrosilyl groups per molecule. (B-2) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-3) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-4) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-5) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-6) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-7) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-8) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-9) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-1) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-10) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain;

[0010] The thermally conductive millable silicone rubber composition of the present invention can provide a heat dissipation sheet that has excellent thermal conductivity, strength, and insulation properties, moderate hardness, low contact thermal resistance, and excellent long-term stability.

[0011] In this case, it is preferable that the proportion of particles having a particle size of 45 μm or more contained in the component (C) be 5% by mass or less.

[0012] When such a thermally conductive millable silicone rubber composition is used to coat a thermally conductive sheet, the thermally conductive filler (filling material) does not protrude from the coating surface, impairing the smoothness of the sheet surface, and contact thermal resistance does not increase.

[0013] The composition preferably further contains 5 to 100 parts by mass of a polysiloxane modified with a trialkoxysilyl group at one end, represented by the following formula (1), as a wetter component (D). (In the formula, R １ is an alkyl group having 1 to 6 carbon atoms, and n is an integer from 5 to 100.

[0014] By incorporating such a component (D), the component (C) is subjected to a hydrophobic treatment during the preparation of the composition, thereby improving the wettability with the component (A), and enabling the component (C) to be uniformly dispersed in a matrix consisting of the component (A).

[0015] The present invention also provides a thermally conductive sheet comprising a cured product of the above-mentioned thermally conductive millable silicone rubber composition and a reticulated reinforcing material.

[0016] Such a thermally conductive sheet has excellent thermal conductivity, strength, and insulating properties, has a suitable hardness, has low contact thermal resistance, and is also excellent in long-term stability.

[0017] In this case, it is preferable that the mesh-like reinforcing material is sealed.

[0018] Such a thermally conductive sheet can improve the contact at the interface between the reinforcing material and the cured product of the thermally conductive millable silicone rubber composition, thereby further reducing the contact thermal resistance.

[0019] As described above, the thermally conductive millable silicone rubber composition of the present invention can be used as a thermally conductive sheet suitable for heat dissipation in electronic devices, etc. Furthermore, a thermally conductive sheet containing a cured product of the millable silicone rubber composition and a mesh-like reinforcing material can be formed into a sheet with low thermal resistance due to good contact without sacrificing insulation. Furthermore, by controlling the particle size of the thermally conductive material, continuous coating molding can be performed, resulting in low-cost, simple manufacturing processes and stable product characteristics over the long term.

[0020] As mentioned above, there has been a demand for the development of a thermally conductive sheet that not only has excellent heat dissipation properties and insulation reliability, but also has low contact thermal resistance.

[0021] As a result of extensive research into the above-mentioned problems, the present inventors discovered that the above-mentioned problems could be solved by a thermally conductive millable-type silicone rubber composition characterized by containing the following components (A), (B), (C), (E), and (F), and a thermally conductive sheet using said composition, and thus completed the present invention.

[0022] That is, the present invention provides: (A) an organopolysiloxane comprising the following components (A-1) to (A-3): (A-1) a rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals; (A-2) a rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains; (A-3) an organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups per molecule; 100 parts by mass of a linear organopolysiloxane having alkenyl groups, (B) an organohydrogenpolysiloxane comprising the following components (B-1) and (B-2): (B-1) an organohydrogenpolysiloxane that has hydrosilyl groups only at side chains on the molecular chain and has 2 to 5 hydrosilyl groups per molecule. (B-2) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-3) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-4) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-5) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-6) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-7) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-8) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-9) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-10) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain; (B-11) an organohydrogenpolysiloxane containing two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain;

[0023] The present invention will be described in detail below, but the present invention is not limited thereto.

[0024] [Thermal conductive millable silicone rubber composition] The thermal conductive millable silicone rubber composition of the present invention (hereinafter also referred to as "thermal conductive silicone rubber composition") contains (A) an organopolysiloxane having alkenyl groups, (B) an organohydrogenpolysiloxane, (C) a thermally conductive filler, (E) an addition reaction catalyst, and (F) an addition reaction inhibitor. Furthermore, additives such as (D) a wetter may also be included as needed. The components contained in the composition of the present invention will be described below.

[0025] [(A) Organopolysiloxane Having Alkenyl Groups] Component (A), a linear organopolysiloxane having alkenyl groups, is the main component of the composition of the present invention. Component (A) is characterized by containing the following three types of organopolysiloxanes (A-1) to (A-3): (A-1) a crude rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals, (A-2) a crude rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains, and (A-3) an organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups per molecule.

[0026] The structure of these three types of organopolysiloxanes having alkenyl groups is a linear diorganopolysiloxane whose main chain is made up of repeating diorganosiloxane units.

[0027] The alkenyl group contained in these three types of organopolysiloxanes is preferably an alkenyl group having 2 to 8 carbon atoms, such as a vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, etc. Of these, vinyl group and allyl group are preferred, with vinyl group being particularly preferred.

[0028] Furthermore, the functional groups other than alkenyl groups bonded to silicon atoms in these three types of organopolysiloxanes are preferably monovalent hydrocarbon groups selected from alkyl groups having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, and octyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, and phenylpropyl. Furthermore, the functional groups other than alkenyl groups bonded to silicon atoms do not necessarily have to be the same.

[0029] Specific examples of organopolysiloxanes having alkenyl groups include dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methylvinylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, methylvinylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, and dimethyl Examples of organosiloxane copolymers include siloxane-methylvinylsiloxane copolymers, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with divinylmethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with divinylmethylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with trivinylsiloxy groups, and organosiloxane copolymers comprising dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with trivinylsiloxy groups.

[0030] (A-1) Raw rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals Component (A-1) is a raw rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals. In the present invention, "raw rubber-like" means either a highly viscous liquid having a viscosity of 200,000 mPa s or more at room temperature (25°C), or a non-liquid (paste or solid) with no self-flowing properties. Note that the viscosity in the present invention refers to a value measured using a rotational viscometer according to the method described in JIS Z8803:2011.

[0031] The degree of polymerization of component (A-1) is preferably 2,000 to 20,000, and more preferably 3,000 to 15,000. In the present invention, the degree of polymerization generally refers to a value calculated from the weight-average degree of polymerization in terms of polystyrene measured by gel permeation chromatography (GPC) analysis using toluene as the developing solvent. [Measurement conditions] Developing solvent: toluene Flow rate: 1 mL / min Detector: differential refractive index detector (RI) Column: KF-805L x 2 (Shodex) Column temperature: 25°C Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

[0032] (A-2) Raw rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains Component (A-2) is a raw rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains. The degree of polymerization of component (A-2) is preferably 2,000 to 20,000, and more preferably 3,000 to 15,000. The number of side chain alkenyl groups per molecule is preferably 1 to 200, and more preferably 2 to 100.

[0033] (A-3) Organopolysiloxane Having Two or More Alkenyl Groups Per Molecule and Being Liquid at 25°C Component (A-3) is an organopolysiloxane having two or more alkenyl groups per molecule and being liquid at 25°C. In the present invention, "liquid" refers to having self-flowing properties at 25°C. The degree of polymerization of component (A-3) is preferably 100 to 2,000, more preferably 500 to 1,500. The number of alkenyl groups per molecule is characterized by being two or more, preferably 2 to 10, and more preferably 2 to 5. The alkenyl groups may be located at either the terminal or side chain of the molecular chain, but it is preferable for alkenyl groups to be located only at the terminals of the molecular chain. Furthermore, the structure of component (A-3) is linear, with the main chain consisting of repeating diorganosiloxane units. Component (A-3) is characterized by being liquid at 25°C. Its viscosity is preferably 500 to 200,000 mPa·s, and more preferably 10,000 to 150,000 mPa·s. The blend ratios of (A-1) to (A-3) are preferably 20 to 45 mass% for component (A-1), 20 to 45 mass% for component (A-2), and 10 to 40 mass% for component (A-3), when the total amount of component (A) is taken as 100 mass%.

[0034] [(B) Organohydrogenpolysiloxane] The organohydrogenpolysiloxane of component (B) reacts with component (A) and acts as a crosslinking agent. Component (B) is characterized by the use of two types of organohydrogenpolysiloxanes: (B-1) an organohydrogenpolysiloxane having hydrosilyl groups only in side chains on the molecular chain and having 2 to 5 hydrosilyl groups per molecule, and (B-2) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain.

[0035] The functional groups other than hydrosilyl groups in the organohydrogenpolysiloxane of component (B) are preferably monovalent hydrocarbon groups selected from alkyl groups having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, and phenylpropyl. Among these, alkyl groups and aryl groups are preferred, and methyl and phenyl groups are even more preferred from the standpoint of flame retardancy. Furthermore, the functional groups other than the hydrogen atoms (hydrosilyl groups) bonded to silicon atoms do not necessarily have to be the same.

[0036] (B-1) Organohydrogenpolysiloxane having hydrosilyl groups only on side chains of the molecular chain and having 2 to 5 hydrosilyl groups per molecule Component (B-1) is an organohydrogenpolysiloxane having hydrosilyl groups only on side chains of the molecular chain and having 2 to 5, preferably 2 to 4, hydrosilyl groups per molecule. In the present invention, "having hydrosilyl groups on side chains of the molecular chain" means that the D units or T units constituting the polysiloxane main chain have Si-H bonds, or that the polysiloxane side chains have Si-H bonds.

[0037] The structure of component (B-1) may be either linear or branched, but linear is preferred. The degree of polymerization of component (B-1) is preferably 4 to 350, and more preferably 10 to 200.

[0038] A specific example of the component (B-1) is the organohydrogenpolysiloxane (o=27, p=2) shown by the following formula:

[0039] (B-2) Organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, two of which are at the molecular chain terminals. Component (B-2) is an organohydrogenpolysiloxane having two or more, preferably 2 to 50, and more preferably 2 to 20, hydrosilyl groups per molecule, two of which are at the molecular chain terminals. The hydrosilyl groups may be at the terminals of the main chain (the longest polysiloxane chain) or the side chains. Thus, in the present invention, the term "terminals of the polysiloxane molecular chain" refers to both the terminals of the polysiloxane main chain and the terminals of the polysiloxane side chains, and when simply referred to as "both terminals," it refers to the two terminals of the polysiloxane main chain.

[0040] The structure of component (B-2) may be either linear or branched, but linear is preferred. The degree of polymerization of component (B-2) is preferably 4 to 200, and more preferably 10 to 100.

[0041] A specific example of the component (B-2) is the organohydrogenpolysiloxane (q=65, r=1) shown in the following formula:

[0042] The content of the organohydrogenpolysiloxane in component (B) is such that the total number of hydrosilyl groups in component (B) is 0.5 to 4.0 moles, preferably 0.6 to 3.0 moles, per mole of the total number of alkenyl groups in component (A). If the content of this component is less than 0.5 moles, the resulting thermally conductive silicone rubber may be tacky, potentially causing blocking when wound. Furthermore, the increased thickness change rate upon compression may result in a decrease in insulating properties. On the other hand, if the content of this component is greater than 4.0 moles but less than 6.0 moles, the resulting thermally conductive silicone rubber composition may have a shorter pot life and may harden before the curing step. Furthermore, the resulting cured product may be too hard, preventing sufficient reduction in contact resistance. Furthermore, if the content of this component is greater than 6.0 moles, the component that does not contribute to the crosslinking reaction acts as a plasticizer, softening the cured product and increasing the thickness change rate, resulting in a decrease in insulating properties. The blending ratio of (B-1) and (B-2) is preferably such that, when the total amount of component (B) is 100% by mass, component (B-1) accounts for 30 to 95% by mass and component (B-2) accounts for 5 to 70% by mass.

[0043] As described above, by using three types of component (A) and two types of component (B) in combination in the present invention, it is possible to precisely control the crosslinked structure (chain extension, crosslinking density) of the polysiloxane while maintaining good handleability of the raw rubber-like organopolysiloxane in component (A).

[0044] [(C) Thermally conductive filler] Component (C) is a thermally conductive filler that imparts thermal conductivity to the thermally conductive silicone rubber composition. Suitable examples of thermally conductive fillers include inorganic powders such as aluminum oxide, zinc oxide, silicon oxide, silicon carbide, aluminum nitride, and boron nitride. Component (C) can be used alone or in combination of two or more.

[0045] The amount of component (C) must be 150 to 2,400 parts by mass, preferably 200 to 2,300 parts by mass, per 100 parts by mass of component (A). If the amount is less than 150 parts by mass, the thermal conductivity is likely to be insufficient, while if the amount is more than 2,400 parts by mass, it may be difficult to uniformly incorporate component (C) into the composition and moldability may be impaired.

[0046] While there are no particular restrictions on the particle size distribution of component (C), it is preferable that the proportion of particles with a particle size of 45 μm or more contained therein be 5% by mass or less, and even more preferably 2% by mass or less. If the proportion of particles with a particle size of 45 μm or more is 5% by mass or less, when a thermally conductive sheet is obtained by coating the thermally conductive millable-type silicone rubber composition, there is no risk of the thermally conductive filler (filling material) protruding from the coating surface, impairing the smoothness of the sheet surface, and there is no risk of an increase in contact thermal resistance.

[0047] In component (C), a filler having multiple particle size distributions may be used as long as the proportion of particles with a particle size of 45 μm or more is 5% by mass or less. For example, a filler having peaks at 1 μm and 10 μm on a particle size distribution curve may be used, or a filler having an average particle size of 5 μm and a filler having an average particle size of 20 μm may be used in combination.

[0048] The average particle size of component (C) is preferably 0.1 to 30 μm, and more preferably 0.1 to 10 μm. If the average particle size is 30 μm or less, when a thermally conductive sheet is obtained by coating the thermally conductive silicone rubber composition, there is no risk of the thermally conductive filler protruding from the coating surface, impairing the smoothness of the sheet surface, or increasing contact thermal resistance. Thermally conductive fillers with an average particle size of 0.1 μm or more are easily available.

[0049] The average particle size is usually determined by measuring the cumulative volume average diameter D ５０ Specifically, it can be determined as the cumulative 50% particle diameter (D) on a volume basis measured by a particle size distribution measuring device MT3000II manufactured by Microtrac Bell Co., Ltd. ５０The proportion of particles having a specific particle size (for example, a particle size of 45 μm) or more can be determined from the particle size distribution measurement.

[0050] [(D) Wetter] The thermally conductive silicone rubber composition of the present invention preferably contains a wetter (D). Component (D) hydrophobizes component (C) during composition preparation, improving wettability with component (A) and allowing component (C) to be uniformly dispersed in the matrix of component (A). Component (D) is particularly preferably a polysiloxane modified with a trialkoxysilyl group at one end, as represented by the following formula (1):

[0051] In the above formula (1), R １ is an alkyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms. n is an integer of 5 to 100, preferably 10 to 50.

[0052] When component (D) is blended, the blending amount is preferably 5 to 100 parts by mass, and more preferably 10 to 60 parts by mass, per 100 parts by mass of component (A). If the proportion of this component is within this range, there is no risk of inducing oil separation.

[0053] [(E) Addition Reaction Catalyst] The addition reaction catalyst for component (E) promotes the addition reaction between the silicon-bonded alkenyl group in component (A) and the hydrosilyl group in component (B). This addition reaction catalyst is a platinum group metal or a platinum group metal compound. Examples include platinum group metals such as platinum, palladium, and rhodium; chloroplatinic acid; alcohol-modified chloroplatinic acid; coordination compounds of chloroplatinic acid with olefins, vinylsiloxanes, or acetylene compounds; and platinum group metal compounds such as tetrakis(triphenylphosphine)palladium and chlorotris(triphenylphosphine)rhodium. Of these, platinum group metal compounds are preferred. The content of component (E) in this composition is 0.01 to 1,000 ppm, preferably 0.1 to 500 ppm, of platinum group metal atomic mass relative to component (A). If the content of this component is too low, the resulting thermally conductive silicone rubber composition may not cure sufficiently, whereas using a large amount will not improve the cure rate of the resulting silicone rubber composition, which may be economically disadvantageous.

[0054] [(F) Addition Reaction Retardant] The addition reaction retardant is not particularly limited as long as it is a compound that has a curing reaction inhibitory effect against the addition reaction catalyst of component (E), and conventionally known addition reaction retarders can be used. Specific examples include phosphorus-containing compounds such as triphenylphosphine; nitrogen-containing compounds such as tributylamine, tetramethylethylenediamine, and benzotriazole; sulfur-containing compounds; acetylene-based compounds such as 1-ethynyl-1-cyclohexanol, 3-butyn-1-ol, 2-methyl-3-butyn-2-ol, and 3-methyl-1-tridecyn-3-ol; vinyl-containing siloxanes such as 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; hydroperoxy compounds; and maleic acid derivatives. The amount of addition reaction inhibitor blended is preferably adjusted to an optimal amount for each addition reaction inhibitor used, since the degree of curing reaction inhibition effect of the addition reaction inhibitor varies depending on its chemical structure. Blending an optimal amount of reaction inhibitor results in a composition with excellent long-term storage stability and curability at room temperature. Thus, the blending amount of component (F) is not particularly limited, but it can be blended in an amount that is 50 to 150 times the amount of platinum group metal atoms contained in the addition reaction catalyst of component (E). For example, when an acetylene compound such as 3-methyl-1-tridecyn-3-ol is used as component (F), it is preferable to blend an amount within the above range.

[0055] [Other Components] The thermally conductive silicone rubber composition of the present invention may further contain other components as needed, such as a heat resistance improver such as iron oxide, a viscosity modifier such as silica, a colorant, and a mold release agent.

[0056] [Cured Product of Thermally Conductive Silicone Rubber Composition and Its Hardness] The thermally conductive silicone rubber composition can be cured under known conditions. The curing conditions are not particularly limited, but are, for example, at 80 to 150°C for approximately 30 seconds to 1 hour. The hardness of the cured product of the thermally conductive silicone rubber composition is 40 to 70, more preferably 50 to 60, in Durometer A hardness measured according to the method described in JIS K 6253:2012. If the hardness is 40 or higher, the cured product is less likely to deform (become thinner) under pressure, making it easier to maintain its insulating properties. If the hardness is 70 or lower, the contact thermal resistance is sufficiently low, and sufficient heat dissipation properties can be exhibited.

[0057] [Thermal conductive sheet] The thermal conductive sheet of the present invention comprises a cured product of the thermal conductive millable silicone rubber composition and a network reinforcing material. Because such a thermal conductive sheet comprises a cured product obtained by curing the thermal conductive millable silicone rubber composition of the present invention and a network reinforcing material, it has excellent thermal conductivity, strength, and insulation properties, moderate hardness, low contact thermal resistance, and excellent long-term stability.

[0058] [Mesh-like Reinforcing Material] The mesh-like reinforcing material used to reinforce the present thermally conductive sheet is not particularly limited, but examples include inorganic fiber cloths such as glass cloth and ceramic cloth, organic fiber cloths such as nylon and polyester, and composites thereof. To improve the interface between the reinforcing material and the cured product of the thermally conductive silicone rubber composition and reduce contact thermal resistance, it is preferable to seal the reinforcing material. By sealing, the openings of the mesh-like reinforcing material are filled, increasing the adhesive strength with the cured product of the thermally conductive silicone rubber composition, and also fixing the mesh of the reinforcing material, thereby making the shape more stable. The sealing material is not particularly limited, and examples include addition reaction curing and peroxide curing materials. Among these, a thermally conductive silicone rubber material is most suitable. The thermally conductive silicone rubber material may be the above-mentioned millable silicone rubber composition, regardless of the curing type, or other materials. It is particularly preferred that the thermally conductive millable silicone rubber composition that gives the cured product that constitutes the thermally conductive sheet is the same as the sealing material, as this will result in superior thermal conductivity, strength, and insulation, moderate hardness, low contact thermal resistance, and improved productivity.

[0059] The thickness of the reinforcing material is, for example, 20 to 100 μm, and more preferably 30 to 80 μm. If the thickness of the reinforcing material is 20 μm or more, the strength of the thermally conductive sheet is sufficient. On the other hand, if the thickness is 100 μm or less, the thermal conductivity is sufficient.

[0060] [Contact Thermal Resistance] The contact thermal resistance of the thermally conductive sheet of the present invention to an adherend is 40 mm when measured under conditions of 50°C / 700 kPa in accordance with ASTM D5470. ２ K / W or less is preferable, and more preferably 5 to 35 mm ２ K / W. The contact thermal resistance is 40 mm ２ If the thermal resistance is less than 100 K / W, the adhesion between the adherend and the thermal conductive sheet is sufficient, resulting in good thermal conduction efficiency. The contact thermal resistance of the thermal conductive sheet to the adherend can be determined by the method described in the examples below.

[0061] [Thickness Change Rate of Thermally Conductive Sheet] A thermally conductive sheet becomes thinner as pressure is applied, and its insulating performance deteriorates. In other words, the smaller the thickness change rate of the thermally conductive sheet, the better from the viewpoint of maintaining its insulating properties. In the thermally conductive sheet of the present invention, the thickness change rate 20 minutes after compressing the thermally conductive sheet under a pressure of 700 kPa is 20% or less of the initial thickness, and more preferably 10% or less. If the thickness change rate is 20% or less, the thickness change rate is small under high-pressure mounting, making it easier to maintain the insulating properties.

[0062] [Production of Thermally Conductive Sheet] The method for producing the thermally conductive sheet of the present invention is not particularly limited, but a pressing method, a coating method, or the like can be applied, and generally the coating method is effective.

[0063] The production of a thermally conductive sheet by the coating method involves, for example, the following steps (1) to (3). (1) Coating composition preparation step: In addition to the components (A) to (F) and a solvent, additives, etc. are added and mixed as needed. The resulting mixture is treated as needed, stirred, and mixed to prepare a coating composition. (2) Filling step: If necessary, the coating composition obtained from the above step is applied to a reinforcing material, and if necessary, heated to obtain a filled reinforcing material. (3) Coating step: This is a step in which a thermally conductive silicone rubber composition is applied to the filled reinforcing material, and then heated to laminate (coat) the cured product of the composition.

[0064] <Preparation of Coating Composition> First, the alkenyl group-containing organopolysiloxane (A), the thermally conductive filler (C), and the wetter (D) are kneaded using a mixer such as a kneader, Banbury mixer, planetary mixer, or Shinagawa mixer, while heating to a temperature of approximately 100°C or higher as necessary. During this kneading process, reinforcing silica such as fumed silica or precipitated silica, flame retardants such as platinum, titanium oxide, or benzotriazole may be added and mixed, if desired. The homogeneous mixture obtained in the kneading process is cooled to room temperature and then filtered through a strainer or the like. Next, using a two-roll mill, Shinagawa mixer, or the like, colorants such as organic pigments or inorganic pigments, heat resistance improvers such as iron oxide or cerium oxide, internal release agents, catalysts, etc. may be added and mixed into the mixture as desired. To the composition obtained in this second kneading step, a curing agent, an acetylene compound-based addition reaction inhibitor (component (F)) such as 1-ethynyl-1-cyclohexanol, a catalyst (component (E)), etc. are added to prepare a coating composition, and a solvent such as toluene is further added and mixed with a stirrer such as a planetary mixer or kneader, and finally a crosslinking agent (component (B)) is added and further mixed to prepare a coating composition.

[0065] <Sealing of reinforcing material> The coating composition obtained by the above process is applied to the reinforcing material to seal it. After the coating composition is applied continuously to the reinforcing 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, the solvent and the like are dried and evaporated, and the coating is heated to 80 to 200°C, preferably about 100 to 150°C in the case of an addition reaction curing type, or to 100 to 200°C, preferably about 110 to 180°C in the case of a peroxide curing type, to obtain a sealed reinforcing material.

[0066] <Coating> A coating composition that will become a cured product of the thermally conductive silicone rubber composition is applied to one or both sides of the filled reinforcing material obtained by the above process. After the coating composition is applied to one side of the filled reinforcing material in succession using a coating device such as a knife coater or kiss coater equipped with a drying oven, a heating oven, and a winding device, the solvent and the like are dried and evaporated, and the material is heated to 80 to 200°C, preferably 100 to 150°C, and laminated.

[0067] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The average degree of polymerization, viscosity, particle size and average particle size were measured by the methods described above.

[0068] The materials used in the examples and comparative examples are as follows.

[0069] [Component (A): Vinyl Polysiloxane] (A-1) An organopolysiloxane raw rubber having an average degree of polymerization of 8,000 and containing 7,998 dimethylsiloxane units and 2 dimethylvinylsiloxane units per molecule. (A-2) An organopolysiloxane raw rubber having an average degree of polymerization of 8,000 and containing 7,960 dimethylsiloxane units, 38 methylvinylsiloxane units, and 2 dimethylvinylsiloxane units per molecule. (A-3) An organopolysiloxane having an average degree of polymerization of 1,130 and containing 1,128 dimethylsiloxane units and 2 dimethylvinylsiloxane units per molecule, which is liquid at 25°C and has a viscosity of 105,000 mPa s.

[0070] [Component (B): Hydrogenpolysiloxane] The following (B-1) and (B-2) were mixed in a ratio of 3:1. (B-1) A methylhydrogenpolysiloxane represented by the following formula: An organohydrogenpolysiloxane (o=27, p=2) represented by the following formula, which serves as a crosslinking agent: (B-2) Methylhydrogenpolysiloxane represented by the following structural formula: Organohydrogenpolysiloxane represented by the following formula (q=65, r=1) as a crosslinking agent:

[0071] [Component (C): Thermally conductive filler] (C-1) Irregular aluminum oxide having an average particle size of 1 μm and containing 0.8% by mass of particles having a particle size of 45 μm or more. (C-2) Spherical aluminum oxide having an average particle size of 1 μm and containing 0.6% by mass of particles having a particle size of 45 μm or more. (C-3) Spherical aluminum oxide having an average particle size of 10 μm and containing 1.2% by mass of particles having a particle size of 45 μm or more. (C-4) Boron nitride having an average particle size of 5 μm and containing 0.9% by mass of particles having a particle size of 45 μm or more. (C-5) Aluminum nitride having an average particle size of 1 μm and containing 1.1% by mass of particles having a particle size of 45 μm or more. (C-6) Spherical aluminum oxide having an average particle size of 10 μm and containing 8.3% by mass of particles having a particle size of 45 μm or more.

[0072] [Component (D): Wetter] A dimethylpolysiloxane having an average degree of polymerization of 30 and terminated at one end with a trimethoxysilyl group, represented by the following formula:

[0073] [Component (E): Platinum group metal catalyst] 5% by mass solution of chloroplatinic acid in 2-ethylhexanol

[0074] [Component (F): Addition reaction inhibitor] 3-methyl-1-tridecyn-3-ol

[0075] [Component (G): Peroxide Curing Agent (for Comparative Example)] Bis(4-methylbenzoyl) peroxide

[0076] Mesh-like reinforcing material: glass cloth (thickness: 55 μm) equivalent to IPC spec 1080.

[0077] [Examples 1 to 5 and Comparative Examples 1 to 5] The thermally conductive sheets of Examples 1 to 5 and Comparative Examples 1 to 5 were produced as follows.

[0078] [Preparation of Thermally Conductive Silicone Rubber Compositions] (Preparation Example 1) The components in the amounts (parts by mass) shown in Tables 1 and 2 were charged into a Banbury mixer and kneaded for 20 minutes to prepare thermally conductive silicone rubber compositions (A) to (D) and (F) to (J).

[0079] [Production of Thermally Conductive Sheet] (Production Example 1) Sealing of Glass Cloth The thermally conductive silicone rubber composition obtained in (Preparation Example 1) 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 glass cloth was then dried at 80°C for 10 minutes and further cured at 170°C for 15 minutes. The thickness of the sealed glass cloth was 80 μm.

[0080] (Production Example 2) Coating on sealed glass cloth (thermal conductive sheet with a total thickness of 0.2 mm) 20% by mass of toluene was added to the thermally conductive silicone rubber composition obtained in (Preparation Example 1) above, and the resulting coating material was kneaded using a planetary mixer. The coating material was applied to one side (front side) of the sealed glass cloth obtained above using a comma coater so that the thickness after curing was 0.06 mm, cured, and wound up. Next, the other side (back side) was similarly coated, cured, and wound up to obtain a thermally conductive sheet with a total thickness of 0.2 mm. The comma coater and coating and curing conditions used were the same as those in the sealing (Production Example 1) above.

[0081] (Production Example 3) Coating on sealed glass cloth (thermal conductive sheet with a total thickness of 0.3 mm) 20% by mass of toluene was added to the thermally conductive silicone rubber composition obtained in (Preparation Example 1) above, and the resulting coating material was kneaded using a planetary mixer. The coating material was applied to one side (front side) of the sealed glass cloth obtained above using a comma coater so that the thickness after curing was 0.11 mm, cured, and wound up. Next, the other side (back side) was similarly coated, cured, and wound up to obtain a thermally conductive sheet with a total thickness of 0.3 mm. The comma coater and coating and curing conditions used were the same as those in the sealing (Production Example 1) above.

[0082] (Production Example 4) Coating on sealed glass cloth (thermal conductive sheet with a total thickness of 0.45 mm) 20% by mass of toluene was added to the thermally conductive silicone rubber composition obtained in (Preparation Example 1) above, and the resulting coating material was kneaded using a planetary mixer. This coating material was applied to one side (front side) of the sealed glass cloth obtained above using a comma coater so that the thickness after curing was 0.185 mm, cured, and wound up. The other side (back side) was then similarly coated, cured, and wound up to obtain a thermally conductive sheet with a total thickness of 0.45 mm. The comma coater and coating and curing conditions used were the same as those used in the sealing (Production Example 1) above.

[0083] [Methods for Evaluating Various Properties] The various properties of the thermally conductive sheet were measured by the following methods. The measurement results are shown in Tables 1 and 2.

[0084] [General Properties] <Initial Thickness> Measured using a Digimatic Thickness Gauge manufactured by Mitutoyo Corporation.

[0085] <Thermal Resistance and Contact Thermal Resistance / Thickness Under Pressure> The thermal resistance of the thermally conductive sheet was measured in accordance with ASTM D 5470 using the following procedure. Thermally conductive sheets with thicknesses of 0.2 mm, 0.3 mm, and 0.45 mm were prepared and pressed at 50°C / 700 kPa to measure the thermal resistance of the thermally conductive sheet of each thickness. Furthermore, the contact thermal resistance was calculated from the intercept of a graph plotting the thickness (mm) of the thermally conductive sheet under pressure (700 kPa or less) on the horizontal axis and the thermal resistance on the vertical axis.

[0086] <Thickness Change Rate> The thickness of the thermally conductive sheet under pressure was measured in the same manner as in the measurement of the thermal resistance. The thickness change rate was calculated using the following formula.

[0087] <Hardness of Cured Product of Thermally Conductive Silicone Rubber Composition> Samples for hardness measurement were separately prepared using each cured product, and the hardness was measured using a Type A durometer in accordance with JIS K 6253:2012 (measurement temperature: 25°C).

[0088] Hereinafter, the thermally conductive silicone rubber composition obtained in (Preparation Example 1) was used as a sealing composition to seal glass cloth in (Production Example 1), and the sealed glass cloth was then coated in accordance with (Production Examples 2) to (Production Examples 4), thereby producing thermally conductive sheets in Examples 1 to 5 and Comparative Examples 1 to 5. Example 1 After sealing the glass cloth with composition (A), the sealed glass cloth was coated with composition (A) to obtain a thermally conductive sheet.

[0089] Example 2 A glass cloth was sealed with the composition (a), and then the sealed glass cloth was coated with the composition (a) to obtain a thermally conductive sheet.

[0090] Example 3 A glass cloth was sealed with the composition (c), and then the sealed glass cloth was coated with the composition (c) to obtain a thermally conductive sheet.

[0091] Example 4 A glass cloth was sealed with the composition (d), and then the sealed glass cloth was coated with the composition (d) to obtain a thermally conductive sheet.

[0092] Example 5 After sealing a glass cloth with composition (f), the sealed glass cloth was coated with composition (a) to obtain a thermally conductive sheet.

[0093] Comparative Example 1 A glass cloth was sealed with the composition (f), and then the sealed glass cloth was coated with the composition (f) to obtain a thermally conductive sheet.

[0094] <Comparative Example 2> A thermally conductive sheet was obtained by sealing a glass cloth with composition (G), and then coating the sealed glass cloth with composition (G). The hardness of the obtained sheet was very low and the adhesion was strong, so accurate measurements of the thermal resistance and thickness were not possible.

[0095] <Comparative Example 3> A glass cloth was sealed with composition (H), and then the glass cloth sealed with composition (H) was coated to obtain a thermally conductive sheet. However, filler aggregates were observed on the surface of the sheet, and accurate measurements of the thermal resistance and thickness were not possible.

[0096] Comparative Example 4 The amount of the thermally conductive filler blended in the composition (I) was too large, and a uniform composition could not be obtained.

[0097] Comparative Example 5: A thermally conductive sheet was obtained by sealing a glass cloth with composition (K) and then coating the sealed glass cloth with composition (K). The thickness of the obtained sheet changed significantly under pressure, and there was concern about a decrease in insulating properties.

[0098]

[0099]

[0100] The thermally conductive sheets of Examples 1 to 5 use the thermally conductive millable silicone rubber composition of the present invention, and as shown in Table 1, they have low contact thermal resistance, excellent thermal conductivity, and moderate hardness. In addition, the thermally conductive sheet is composed of a highly flexible mesh-like reinforcing material, resulting in excellent strength. Since the thickness change under pressure is minimal, the deterioration of insulating properties is minimal (i.e., excellent insulating properties). Furthermore, the thermally conductive millable silicone rubber composition of the present invention contains an effective amount of (F) an addition reaction inhibitor, resulting in excellent long-term stability. Furthermore, because the present invention does not involve lamination of a thin metal film such as a metal foil, there are no problems such as increased contact thermal resistance, poor insulation, or increased manufacturing costs. Furthermore, by appropriately adjusting the particle size of the (C) thermally conductive filler, continuous coating molding can be performed, resulting in low-cost, simple manufacturing processes and stable product characteristics over the long term.

[0101] From the above results, it can be seen that the products of the present invention all have low contact thermal resistance, excellent flexibility, little deterioration in insulating properties under pressure, and can be manufactured at low cost using a simple manufacturing process, whereas the comparative examples that do not meet the requirements of the present invention have problems such as high contact thermal resistance and insufficient material strength. That is, in Comparative Example 1, in which a thermally conductive sheet was obtained by sealing and coating glass cloth using a peroxide-curing composition (F), the contact thermal resistance was too high. In Comparative Example 2, in which the glass cloth was sealed and coated using a composition (G) that did not contain the (A-2) component, and in Comparative Example 3, in which the glass cloth was sealed and coated using a composition (H) that contained too much of the (C) component, a thermally conductive sheet was obtained, but accurate measurements of the contact thermal resistance and thickness were not possible. In Comparative Example 5, in which the glass cloth was sealed and coated using a composition (J) that contained a significantly excessive amount of the (B) component, the (B) component, which does not contribute to the crosslinking reaction, acted like a plasticizer, so the resulting thermally conductive sheet changed in thickness significantly under pressure, raising concerns about a decrease in insulating properties.

[0102] This specification encompasses the following aspects. [1]: (A) an organopolysiloxane comprising the following components (A-1) to (A-3): (A-1) a rubber-like organopolysiloxane having alkenyl groups only at both molecular chain terminals, (A-2) a rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains, (A-3) an organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups per molecule: 100 parts by mass (B) an organohydrogenpolysiloxane comprising the following components (B-1) and (B-2): (B-1) an organohydrogenpolysiloxane that has hydrosilyl groups only at side chains of the molecular chain and has 2 to 5 hydrosilyl groups per molecule. (B-2) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, two of which are at the ends of the molecular chain: an organohydrogenpolysiloxane containing the organohydrogenpolysiloxane in an amount such that the total amount of hydrosilyl groups in component (B) is 0.5 to 4.0 moles per mole of the total amount of alkenyl groups in component (A); (C) a thermally conductive filler: 150 to 2,400 parts by mass; (E) an addition reaction catalyst: an amount equivalent to 0.01 to 1,000 ppm, calculated as the atomic mass of a platinum group metal; and (F) an addition reaction inhibitor: an effective amount. [2]: The thermally conductive millable-type silicone rubber composition according to [1], characterized in that the proportion of particles having a particle size of 45 μm or more contained in component (C) is 5 mass% or less. [3]: (D) a polysiloxane modified with a trialkoxysilyl group at one end, as a wetter component, represented by the following formula (1): 5 to 100 parts by mass (In the formula, R １ is an alkyl group having 1 to 6 carbon atoms, and n is an integer from 5 to 100.) [4]: ​​A thermally conductive sheet comprising a cured product of the thermally conductive millable silicone rubber composition according to any one of [1] to [3] and a mesh-like reinforcing material. [5]: A thermally conductive sheet according to [4], wherein the mesh-like reinforcing material is sealed.

[0103] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. (A) an organopolysiloxane containing the following components (A-1) to (A-3); (A-1) Raw rubber-like organopolysiloxane having alkenyl groups only at both ends of the molecular chain (A-2) A raw rubber-like organopolysiloxane having alkenyl groups at both molecular chain terminals and in side chains. (A-3) Organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups per molecule Linear organopolysiloxane having an alkenyl group, comprising: 100 parts by mass (B) an organohydrogenpolysiloxane containing the following components (B-1) and (B-2); (B-1) Organohydrogenpolysiloxanes having hydrosilyl groups only in side chains of the molecular chain and having 2 to 5 hydrosilyl groups per molecule (B-2) Organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule, two of which are at the ends of the molecular chain. an organohydrogenpolysiloxane containing the above compound in an amount such that the total amount of hydrosilyl groups in component (B) is 0.5 to 4.0 moles per mole of the total amount of alkenyl groups in component (A); (C) Thermally conductive filler: 150 to 2,400 parts by mass (E) Addition reaction catalyst: an amount equivalent to 0.01 to 1,000 ppm by mass of platinum group metal atom (F) Addition reaction inhibitor: effective amount A thermally conductive millable type silicone rubber composition comprising:

2. 2. The thermally conductive millable silicone rubber composition according to claim 1, wherein the proportion of particles having a particle size of 45 μm or more contained in component (C) is 5 mass % or less.

3. Furthermore, (D) a polysiloxane modified with a trialkoxysilyl group at one end as a wetter component, represented by the following formula (1): 5 to 100 parts by mass 【Chemistry 1】 (In the formula, R １ is an alkyl group having 1 to 6 carbon atoms, and n is an integer from 5 to 100.

2. The thermally conductive millable silicone rubber composition according to claim 1, comprising:

4. Further, (D) a polysiloxane modified with a trialkoxysilyl group at one end as a wetter component, represented by the following formula (1): 5 to 100 parts by mass 【Chemistry 2】 (In the formula, R 1 is an alkyl group having 1 to 6 carbon atoms, and n is an integer of 5 to 100.) 3. The thermally conductive millable silicone rubber composition according to claim 2, further comprising:

5. A thermally conductive sheet comprising a cured product of the thermally conductive millable silicone rubber composition according to any one of claims 1 to 4 and a reticulated reinforcing material.

6. 6. The thermally conductive sheet according to claim 5, wherein the mesh-like reinforcing material is filled with pores.

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