Thermally conductive silicone composition and sheet-like cured product

Abstract

The present invention pertains to a thermally conductive silicone composition containing components (A) to (D). (A) An organopolysiloxane which has alkenyl groups bound to silicon atoms on a side chain of the molecule and in which the number of the alkenyl groups per molecule is 2-8. (B) An organohydrogen polysiloxane in which both terminals are blocked with hydrosilyl groups. (C) A thermally conductive filler containing the following components (C-1) to (C-3): (C-1) an aluminum oxide having an average particle size of 0.5-5 µm; (C-2) a spherical aluminum oxide which has an average particle size of 7-25 µm, and which is contained in an amount such that the mass ratio of (C-2) with respect to (C-1) is 0.7-3.0; and (C-3) a magnesium oxide having an average particle size of 40-90 µm. (D) A platinum group metal-based curing catalyst. Accordingly, the present invention provides a thermally conductive silicone sheet that has high restorability even when having a low hardness, and that has a high thermal conductivity suitable for a heat dissipating member of a product in which vibration is generated.

Description

Thermally conductive silicone composition and sheet-shaped cured product

[0001] The present invention relates to a thermally conductive silicone composition and a sheet-like cured product of said composition.

[0002] In electronic devices, heat dissipation components (cooling components) such as heat sinks are installed to cool the heat generated by heat-generating components such as semiconductor elements. To efficiently transfer heat to these heat dissipation components, a heat dissipation material is sandwiched between the heat-generating component and the heat dissipation component. There are various types of heat dissipation materials, such as thermally conductive sheets, thermally conductive grease, and curing thermally conductive grease, and different types are used depending on the application.

[0003] Thermally conductive sheets are usually easier to use than thermally conductive grease when assembling heat dissipation devices, but thermally conductive sheets have difficulty conforming to the minute irregularities on the surfaces of electronic components and heat sinks.

[0004] Therefore, in order to improve adhesion to the heat sink, it is necessary to use a thermally conductive sheet with a low hardness of 15 or less on the Asker C hardness scale.

[0005] Low-hardness thermally conductive sheets achieve high adhesion to heat dissipation components and are effective for lowering thermal resistance and for uneven structures such as concaves and convexes.

[0006] However, low-hardness thermal conductive sheets have poor recovery properties, so once they are deformed they do not return to their original shape, making subsequent cutting or other shaping difficult, and they have the drawback of being difficult to handle when applied and poorly reworkable.

[0007] On the other hand, in order to improve the handling and reworkability, the hardness of the thermal conductive sheet must be increased, and low hardness is incompatible with handling and reworkability.

[0008] Therefore, Patent Document 1 discloses a heat dissipation sheet that overcomes the above problems by specifying the average polymerization ratio of an organopolysiloxane and an organohydrogenpolysiloxane having 2 to 9 silicon-bonded alkenyl groups in the side chains, thereby achieving low hardness and excellent reworkability.

[0009] In recent years, electronic control has become more prevalent in fields such as automobiles and unmanned aerial vehicles (UAVs) such as drones, resulting in an increasing number of locations requiring heat dissipation measures. The heat dissipation sheets used there are required to have low hardness, reworkability, and high resilience to vibration. However, the heat dissipation sheet disclosed in Patent Document 1, when attempting to produce a sheet with a low hardness of 15 or less on the Asker C scale while maintaining thermal conductivity of 2 W / mK or more, exhibits poor resilience. As a result, it does not have sufficient performance for use as a heat dissipation component in products that generate vibration.

[0010] JP 2016-030774 A

[0011] An object of the present invention is to provide a thermally conductive silicone sheet that has high resilience despite its low hardness and high thermal conductivity, making it suitable for use as a heat dissipation component in products that generate vibration.

[0012] In order to achieve the above object, the present invention provides a thermally conductive silicone composition comprising the following components (A) to (D): (A) 100 parts by mass of an organopolysiloxane having silicon-bonded alkenyl groups in its molecular side chains, with 2 to 8 alkenyl groups per molecule, (B) an organohydrogenpolysiloxane capped at both ends with hydrosilyl groups, in an amount such that the number of moles of hydrosilyl groups in component (B) is 0.1 to 1.5 moles per 1.0 mole of alkenyl groups in component (A), (C) 1,600 to 4,100 parts by mass of a thermally conductive filler comprising the following components (C-1) to (C-3), (C-1) 270 to 1,610 parts by mass of aluminum oxide having an average particle size of 0.5 to 5 μm, (C-2) spherical aluminum oxide having an average particle size of 7 to 25 μm: 430 to 2,010 parts by mass, provided that the mass ratio of (C-2) to (C-1) is 0.7 to 3.0, (C-3) magnesium oxide having an average particle size of 40 to 90 μm: 530 to 1,350 parts by mass, and (D) a platinum group metal-based curing catalyst: 0.01 to 1,000 ppm, calculated as platinum group metal atoms, by mass relative to component (A).

[0013] The thermally conductive silicone composition of the present invention makes it possible to produce a thermally conductive sheet that has low hardness, high recovery, and high thermal conductivity.

[0014] The thermally conductive silicone composition preferably further comprises 10 to 100 parts by mass of (E) a surface treatment agent, and component (E) is preferably at least one selected from (E-1) an alkoxysilane and (E-2) a dimethylpolysiloxane having one end capped with a trialkoxysilyl group.

[0015] By further including the component (E), the component (C) is uniformly dispersed in the matrix of the component (A).

[0016] The present invention also provides a sheet-like cured product of the thermally conductive silicone composition of the present invention, characterized in that the hardness is 20 or less on the Asker C hardness scale.

[0017] Because the cured sheet product of the thermally conductive silicone composition of the present invention has low hardness, it can deform to fit the shape of the heat-dissipating object, exhibiting good heat-dissipating properties without applying stress to the heat-dissipating object. Furthermore, the cured sheet product of the present invention has excellent handleability and reworkability, and has high recovery, making it useful as a heat-dissipating component for products that generate vibration.

[0018] As described above, the thermally conductive silicone composition of the present invention makes it possible to produce a highly thermally conductive silicone sheet that has high recovery despite low hardness and is suitable as a heat dissipation component for products that generate vibration.

[0019] Because the cured sheet product of the thermally conductive silicone composition of the present invention has low hardness, it can deform to fit the shape of the heat-dissipating object, exhibiting good heat-dissipating properties without applying stress to the heat-dissipating object. Furthermore, the cured sheet product of the present invention has excellent handleability and reworkability, and has high recovery, making it useful as a heat-dissipating component for products that generate vibration.

[0020] As mentioned above, there has been a need for the development of a thermally conductive silicone sheet that has high resilience despite its low hardness and high thermal conductivity, making it suitable for use as a heat dissipation component in products that generate vibration.

[0021] As a result of extensive research into the above-mentioned problems, the present inventors discovered that, if a thermally conductive silicone composition containing the following components (A) to (D) is used, by controlling the particle size of the thermally conductive material, it is possible to produce a thermally conductive silicone sheet that has high resilience despite low hardness, and is suitable as a heat dissipation component for products that generate vibration, and thus completed the present invention.

[0022] That is, the present invention provides a thermally conductive silicone composition comprising the following components (A) to (D): (A) 100 parts by mass of an organopolysiloxane having silicon-bonded alkenyl groups in its molecular side chains, with 2 to 8 alkenyl groups per molecule, (B) an organohydrogenpolysiloxane capped at both ends with hydrosilyl groups, in an amount such that the number of moles of hydrosilyl groups in component (B) is 0.1 to 1.5 moles per 1.0 mole of alkenyl groups in component (A), (C) 1,600 to 4,100 parts by mass of a thermally conductive filler comprising the following components (C-1) to (C-3), (C-1) 270 to 1,610 parts by mass of aluminum oxide having an average particle size of 0.5 to 5 μm, (C-2) spherical aluminum oxide having an average particle size of 7 to 25 μm: 430 to 2,010 parts by mass, provided that the mass ratio of (C-2) to (C-1) is 0.7 to 3.0, (C-3) magnesium oxide having an average particle size of 40 to 90 μm: 530 to 1,350 parts by mass, and (D) a platinum group metal-based curing catalyst: 0.01 to 1,000 ppm, calculated as platinum group metal atoms, by mass relative to component (A).

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

[0024] [Thermal Conductive Silicone Composition] The thermally conductive silicone composition of the present invention is a composition containing (A) an organopolysiloxane, (B) an organohydrogenpolysiloxane, (C) a thermally conductive filler, and (D) a platinum group metal curing catalyst. Each of these components is described in detail below.

[0025] [(A) Organopolysiloxane] The alkenyl-group-containing organopolysiloxane of component (A) is an organopolysiloxane that must have alkenyl groups bonded to silicon atoms in the molecular side chains, and has 2 to 8 alkenyl groups per molecule. Fewer than two alkenyl groups may prevent the thermally conductive silicone composition of the present invention from curing, while more than eight alkenyl groups may result in a cured product that is too hard, which is undesirable. The main chain of this organopolysiloxane may be, for example, essentially a straight-chain structure composed of repeating diorganosiloxane units, with both molecular chain ends capped with triorganosiloxy groups. The molecular structure may also contain a branched structure or may be cyclic. Among these, straight-chain diorganopolysiloxanes are preferred from the standpoint of physical properties such as the mechanical strength of the cured product. The alkenyl group-containing organopolysiloxane of component (A) has alkenyl groups on its side chains, which allows the alkenylsiloxane and hydrosiloxane to react to form a uniform network structure, thereby achieving recovery. A non-uniform network structure or a crosslinked structure that is not a network structure reduces recovery.

[0026] The average degree of polymerization of component (A) is preferably 10 to 10,000, and particularly preferably 50 to 2,000. If the average degree of polymerization is 10 or more, the sheet will not be too hard and will not lose compressibility. If the average degree of polymerization is 10,000 or less, the sheet will have high strength and good recovery.

[0027] In the present invention, the average degree of polymerization can be determined as a number average degree of polymerization or number average molecular weight converted into polystyrene by GPC (gel permeation chromatography) analysis using THF (tetrahydrofuran) as a developing solvent.

[0028] The component (A) is preferably an organopolysiloxane represented by the following formula (1). (In the formula, R is independently a group selected from an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms; X is an alkenyl group having 2 to 8 carbon atoms; n is an integer of 0 or more; and m is an integer of 2 to 8.)

[0029] In the above formula (1), R is a group selected from an alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Of these, methyl, ethyl, and phenyl groups are preferred.

[0030] In the above formula (1), X is an alkenyl group having 2 to 8 carbon atoms, preferably 2 to 5. Examples include a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a hexenyl group, and a cyclohexenyl group. Of these, a vinyl group and an allyl group are preferred, and a vinyl group is particularly preferred.

[0031] In the above formula (1), m is an integer of 2 to 8, preferably 2 to 6. n is an integer of 0 or greater, preferably an integer of 5 to 9,000, and m and n are preferably integers that satisfy 10≦m+n≦10,000, more preferably integers that satisfy 50≦m+n≦2,000, even more preferably integers that satisfy 100≦m+n≦500, and further preferably integers that satisfy 0<m / (m+n)≦0.05.

[0032] [(B) Organohydrogenpolysiloxane] The organohydrogenpolysiloxane of component (B) is one that is end-blocked at both ends with hydrosilyl groups (Si—H groups), preferably one in which both ends are end-blocked with hydrosilyl groups and there are 2 to 4 hydrosilyl groups per molecule. If there are 2 or more hydrosilyl groups, the thermally conductive silicone composition of the present invention will cure reliably.

[0033] The average degree of polymerization of component (B) is preferably 2 to 300, and particularly preferably 10 to 150. If the average degree of polymerization is 2 or more, the sheet will not be too hard and the compressibility will not decrease. If the average degree of polymerization is 300 or less, the sheet will have high strength and good recovery.

[0034] The component (B) is preferably an organohydrogenpolysiloxane represented by the following formula (2). (In the formula, R is independently a group selected from an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms; p is an integer of 0 or more; and q is an integer of 0 to 2.)

[0035] In the above formula (2), R is a group selected from an alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Of these, methyl, ethyl, and phenyl groups are preferred.

[0036] In the above formula (2), p is preferably an integer of 0 or more, particularly 2 to 100, and q is preferably an integer of 0 or more and less than 2, particularly 0 to 1. Furthermore, p and q are integers that satisfy 0≦p+q≦101, and are preferably integers that satisfy 2≦p+q≦80, more preferably integers that satisfy 2≦p+q≦50, and even more preferably integers that satisfy 2≦p+q≦30.

[0037] These values ​​indicate the values ​​for the average structural formula of component (B), and are not limited to the individual molecular levels.

[0038] The amount of component (B) to be added is such that the ratio of the number of moles of hydrosilyl groups in component (B) per 1.0 mole of alkenyl groups in component (A) (i.e., Si-H / Si-Vi) is 0.1 to 1.5 moles, and preferably 0.3 to 1.0 moles. If the amount of hydrosilyl groups in component (B) is less than 0.1 mole or more than 1.5 moles per mole of alkenyl groups in component (A), it will be impossible to obtain a sheet-like cured product with the desired low hardness.

[0039] [(C) Thermally Conductive Filler] With regard to the thermally conductive filler, which is component (C), from the standpoint of the flowability of the composition and the thermal conductivity and recovery properties of the molded product, the thermally conductive silicone composition of the present invention contains predetermined amounts of two types of thermally conductive fillers: aluminum oxide and magnesium oxide.

[0040] More specifically, the present invention is characterized by the combined use of, as the thermally conductive filler, (C-1) aluminum oxide having an average particle size of 0.5 to 5 μm, (C-2) spherical aluminum oxide having an average particle size of 7 to 25 μm, and (C-3) magnesium oxide having an average particle size of 40 to 90 μm.

[0041] Each of these will be explained in detail below.

[0042] In the present invention, the average particle diameter is a value determined as a cumulative volume average diameter D50 (median diameter) in particle size distribution measurement by laser light diffraction. Specifically, it is a value of the cumulative 50% particle diameter (D50) on a volume basis measured using a particle size distribution measuring device MT3000II manufactured by Microtrac-Bell Co., Ltd.

[0043] <Component (C-1): Aluminum Oxide> Aluminum oxide has various crystal phases, such as α, β, θ, and γ, depending on the sintering temperature. α-aluminum oxide, which has the highest sintering temperature, is chemically stable, and is therefore preferred.

[0044] In addition, although aluminum oxide generally does not exist in a single crystalline phase, it is preferable that the proportion of the α phase is as high as possible, and the α phase ratio is 90% or more, preferably 95% or more.

[0045] Aluminum oxide can be in granular form, such as spherical or crushed, depending on the manufacturing method. Crushed aluminum oxide generally has a high rate of alpha conversion, so crushed aluminum oxide is preferred, but depending on the amount of thermally conductive filler used, partial use of spherical aluminum oxide can improve the fillability into silicone and thermal conductivity. There are no particular restrictions on the granular form of aluminum oxide for component (C-1).

[0046] The average particle size of component (C-1) is 0.5 to 5 μm, preferably 0.5 to 3 μm, and more preferably 1 to 2 μm. Aluminum oxide with such particle sizes can ensure heat transfer paths and significantly improve the thermal conductivity of the silicone resin cured product. If the average particle size of component (C-1) is less than 0.5 μm, the close-packing properties of the composition decrease, the viscosity increases, and molding becomes difficult. If crushed alumina with a particle size exceeding 5 μm is used, the surface of the cured product becomes uneven, reducing adhesion and increasing thermal resistance.

[0047] <Component (C-2): Spherical Aluminum Oxide> The aluminum oxide used in component (C-2) is spherical aluminum oxide, and preferably has a gelatinization rate of 90% or more, and more preferably 95% or more. In the case of crushed aluminum oxide, thermal conductivity is excellent, but recovery is reduced.

[0048] The average particle size of component (C-2) is 7 μm to 25 μm, preferably 7 to 20 μm, and more preferably 7 to 15 μm. Spherical aluminum oxide with such a particle size has a small specific surface area, which allows for good filling into silicone and facilitates the preparation of compositions. Furthermore, spherical aluminum oxide with such a particle size can ensure a heat transfer path while simultaneously reducing the number of filler / resin interfaces, significantly improving the thermal conductivity and recovery of the silicone resin cured product. If the average particle size of component (C-2) is less than 7 μm or more than 25 μm, thermal conductivity will decrease.

[0049] <Component (C-3): Magnesium Oxide> Magnesium oxide is preferred as a thermally conductive filler due to its high thermal conductivity and insulating properties. However, because moisture resistance is an issue, magnesium oxide with improved moisture resistance is preferred. While there are no particular limitations as long as it is a substance generally considered to be magnesium oxide, low-activity, high-purity magnesium oxide that has been fired at high temperatures (1,800 to 2,000°C) or magnesium oxide whose surface is coated with a polymer such as a resin or an inorganic substance such as aluminum oxide that has excellent moisture resistance is preferred. Magnesium oxide with excellent moisture resistance prevents the composition from exhibiting strong basicity, thereby suppressing decomposition of the silicone in the composition and preventing softening of the cured silicone.

[0050] The average particle size of component (C-3) is 40 to 90 μm, preferably 40 to 80 μm, and more preferably 40 to 70 μm. Magnesium oxide with such a particle size ensures a heat transfer path without impairing recovery, and significantly improves the recovery and thermal conductivity of the silicone cured product. If the average particle size of component (C-3) is less than 40 μm, the viscosity tends to increase and the thermal conductivity tends to decrease. If it exceeds 90 μm, the kneading and molding equipment will wear out.

[0051] <Amount of Thermally Conductive Filler> The amount of the component (C) including the components (C-1) to (C-3) is 1,600 to 4,100 parts by mass, preferably 1,700 to 3,900 parts by mass, and more preferably 1,800 to 3,800 parts by mass, per 100 parts by mass of the component (A).

[0052] If the amount of component (C) is too large, the desired recovery properties cannot be obtained, whereas if the amount is too small, the desired thermal conductivity cannot be obtained.

[0053] Furthermore, the amount of the (C-1) component is 270 to 1,610 parts by mass, preferably 500 to 1,400 parts by mass, per 100 parts by mass of the (A) component, the amount of the (C-2) component is 430 to 2,010 parts by mass, preferably 500 to 1,800 parts by mass, per 100 parts by mass of the (A) component, and the amount of the (C-3) component is 530 to 1,350 parts by mass, preferably 600 to 1,200 parts by mass, per 100 parts by mass of the (A) component.

[0054] However, in order to obtain high recovery, the mass ratio of the component (C-2) to the component (C-1) is set to 0.7 to 3.0.

[0055] Such blending amounts and blending ratios allow the silicone resin cured product to have both high thermal conductivity and high recovery.

[0056] [(D) Platinum Group Metal-Based Curing Catalyst] Component (D) is a platinum group metal-based catalyst that accelerates the curing of the thermally conductive silicone composition, and examples thereof include chloroplatinic acid, an alcohol solution of chloroplatinic acid, an olefin complex of platinum, an alkenylsiloxane complex of platinum, and a carbonyl complex of platinum.

[0057] In the thermally conductive silicone composition of the present invention, the amount of platinum catalyst blended is not particularly limited and may be any amount effective as a catalyst, but is typically an amount that results in the platinum metal in component (D) being 0.01 to 1,000 ppm, and preferably 0.1 to 500 ppm, calculated by mass, relative to component (A). If the blending amount of component (D) is too small, the resulting thermally conductive silicone rubber composition may not cure sufficiently, while using a large amount does not improve the cure rate of the resulting silicone rubber composition, which is economically disadvantageous.

[0058] [Surface Treatment Agent (E)] The thermally conductive silicone composition of the present invention can be blended with a surface treatment agent (E). Component (E) hydrophobizes component (C) during composition preparation, improving wettability with component (A) and enabling component (C) to be uniformly dispersed within the matrix formed by component (A). It is particularly preferred that component (E) be at least one selected from components (E-1) and (E-2) shown below.

[0059] The component (E-1) is, for example, an alkoxysilane compound represented by the following formula (3): ３ ｂ R ４ ｃ Si(OR ５ ) ４－ｂ－ｃ (3) (wherein, R ３ are each independently an alkyl group having 6 to 15 carbon atoms, and R ４ are independently selected from alkyl groups having 1 to 5 carbon atoms, aryl groups having 6 to 12 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms; R ５ are each independently an alkyl group having 1 to 6 carbon atoms, b is an integer of 1 to 3, and c is an integer of 0 to 2, provided that b+c is an integer of 1 to 3.

[0060] In the above formula (3), R ３ Examples of the alkyl group represented by R include a hexyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, and a tetradecyl group. ３ When the alkyl group represented by the formula (I) has 6 to 15 carbon atoms, the wettability of component (A) is improved sufficiently, the composition is easy to handle, and the low-temperature properties of the composition are excellent.

[0061] R ４Examples of alkyl groups having 1 to 5 carbon atoms represented by the formula (I) include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and neopentyl groups. Examples of aryl groups having 6 to 12 carbon atoms include phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups. Examples of aralkyl groups having 7 to 12 carbon atoms include benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups. Of these, preferred are alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, and propyl groups, and phenyl groups. R ４ Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group.

[0062] Component (E-2) is a dimethylpolysiloxane represented by the following formula (4) in which one molecular chain end is blocked with a trialkoxysilyl group. (In the formula, R ６ are each independently an alkyl group having 1 to 6 carbon atoms, and specifically, ５ Examples of the alkyl group include the same alkyl groups as those exemplified in the above. d is an integer of 5 to 100, preferably 5 to 70, and particularly preferably 10 to 50.

[0063] The surface treatment agent (E) may be either the component (E-1) or the component (E-2), or both may be blended in combination.

[0064] When component (E) is blended, the blending amount is preferably 10 to 100 parts by mass, and particularly preferably 20 to 80 parts by mass, per 100 parts by mass of component (A). When the proportion of component (E) is 10 parts by mass or more, the wettability of component (C) can be sufficiently improved, and when it is 100 parts by mass or less, oil separation can be sufficiently suppressed.

[0065] [Other Components] The thermally conductive silicone composition of the present invention may further contain other components, such as a heat resistance improver such as iron oxide, a viscosity modifier such as silica or a plasticizer, a colorant, or a mold release agent.

[0066] [Preparation of Thermally Conductive Silicone Composition] The thermally conductive silicone composition of the present invention can be prepared by mixing the above components (A) to (D) and any other optional components in a mixing device such as a planetary mixer.

[0067] [Sheet-Like Cured Product] The sheet-like cured product of the present invention is a sheet-like cured product of the thermally conductive silicone composition of the present invention, characterized by having a hardness of 20 or less on the Asker C hardness scale.

[0068] The sheet-like cured product of the present invention has low hardness, so it can deform to fit the shape of the heat-dissipating object, and has excellent thermal conductivity, so it exhibits good heat-dissipating properties without applying stress to the heat-dissipating object.Furthermore, it is easy to handle and rework, and has high recovery properties, making it useful as a heat-dissipating component for products that generate vibration.

[0069] The sheet-shaped cured product of the present invention can be produced by forming the thermally conductive silicone composition of the present invention into a sheet and curing it.

[0070] <Curing Conditions> The curing conditions for molding the composition may be the same as those for known addition reaction curing silicone rubber compositions. For example, although the composition will cure sufficiently at room temperature, heat curing is preferred. Heating conditions are preferably at 100 to 180°C, particularly 110 to 150°C, for 5 to 30 minutes, particularly 10 to 20 minutes. For example, addition curing can be achieved at 120°C for 10 minutes. Furthermore, secondary curing (post-curing) at 100 to 200°C, particularly 130 to 170°C, for 1 to 10 hours, particularly 3 to 7 hours, is preferred.

[0071] <Hardness of Sheet-Like Cured Product> The hardness of the sheet-like cured product of the present invention, measured at 25°C using an Asker C hardness tester as specified in JIS K 7312:1996, is 20 or less, preferably 15 or less. The sheet-like cured product of the present invention can exhibit excellent recovery even with such a low hardness. Specifically, because the sheet-like cured product has high recovery even with a hardness of 20 or less, the contact thermal resistance can be kept low and sufficient heat dissipation properties can be exhibited.

[0072] In order to achieve the above-mentioned hardness of the sheet-shaped cured product, the component (B) is blended in the composition in an appropriate amount as described above.

[0073] <Thermal Conductivity of Sheet-Like Cured Product> The thermal conductivity of a sheet-like cured product obtained from the composition of the present invention, i.e., the sheet-like cured product of the present invention, measured by the hot disc method at 25°C, is preferably 2.0 W / m K or more, and particularly preferably 2.5 W / m K or more. A thermal conductivity of 2.0 W / m K or more can be used for heat-generating bodies with a large amount of heat.

[0074] By blending the heat-conductive filler in the composition of the present invention in the amount described above, the thermal conductivity of the sheet-shaped cured product can be adjusted to the above value.

[0075] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0076] [Preparation of Thermally Conductive Silicone Composition] The materials used in the examples and comparative examples are as follows.

[0077] Component (A): Alkenyl polysiloxane Component (A-1): Vinyl polysiloxane A polysiloxane having two side chain vinyl groups per molecule, as represented by the following formula:

[0078] Component (A-2): Vinylpolysiloxane A polysiloxane having nine side chain vinyl groups per molecule, as represented by the following formula:

[0079] Component (B): Hydrogenpolysiloxane (B-1) A methylhydrogenpolysiloxane represented by the following formula, both ends of which are blocked with dimethylhydroxysilyl groups.

[0080] (B-2) Methylhydrogenpolysiloxanes having hydrosilyl groups on side chains and blocked with trimethylsilyl groups, as represented by the following formula:

[0081] Component (C): Thermally conductive filler (C-1) Crushed aluminum oxide with an average particle size of 1 μm (C-2) Spherical aluminum oxide with an average particle size of 10 μm (C-3) Magnesium oxide with an average particle size of 60 μm (C-4) Crushed aluminum oxide with an average particle size of 20 μm

[0082] Component (D): Platinum group metal catalyst 5% by mass chloroplatinic acid-2-ethylhexanol solution

[0083] Component (E): Surface Treatment Agent (E-1) Trimethoxysilane C having a decyl group, represented by the following formula: 10 H 21 Si(OCH3)3

[0084] (E-2) Dimethylpolysiloxane having an average degree of polymerization of 30 and one end blocked with a trimethoxysilyl group, as represented by the following formula:

[0085] Component (F): Addition reaction inhibitor 2-ethynyl-2-undecanol Internal release agent: methylphenyl silicone oil (trade name: KF-54, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0086] <Method of Preparing Compositions> The above components (A), (C), and (E) were added in the respective amounts shown in Tables 1 and 2 for Examples 1 to 8 and Comparative Examples 1 to 7, and kneaded for 60 minutes using a planetary mixer. To this were added components (D) and (F) in the respective amounts shown in Tables 1 and 2 for Examples 1 to 8 and Comparative Examples 1 to 7, and an effective amount of an internal release agent to promote release from the separator was further added, and the mixture was kneaded for an additional 30 minutes. To this were added component (B) in the respective amount shown in Tables 1 and 2 for Examples 1 to 8 and Comparative Examples 1 to 7, and the mixture was kneaded for 30 minutes to obtain the respective compositions.

[0087] [Thermal conductive silicone molded product] <Molding method> Each of the obtained compositions was poured into a mold measuring 200 mm x 300 mm x 3 mm thick and molded into a sheet using a press molding machine at 110°C for 10 minutes. The molded product was then post-cured by heating in a heating furnace at 150°C for 5 hours. In this way, each of the sheet-shaped cured products of Examples 1-8 and Comparative Examples 1-7 was obtained.

[0088] The cured products thus obtained were evaluated according to the following procedures: [Evaluation Method] <Hardness> Four sheets of each cured product obtained were stacked and measured for hardness using an Asker C hardness tester.

[0089] <Thermal Conductivity> The thermal conductivity of each of the obtained sheet-like cured products was measured using a thermal conductivity meter (TPA-501, product name, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0090] <Recovery Rate> A 20 mm square test piece was cut out from the obtained sheet-like molded product, compressed by 50% (to 1.5 mm) in the thickness direction, and aged in the compressed state for 24 hours at 25° C. Thereafter, the test piece was released from compression, and the thickness of the test piece after 2 hours was measured.

[0091]

[0092] [Evaluation results]

[0093] The compositions of Examples 1 to 8 each comprised a polysiloxane (A-1) having two vinyl groups in the side chain, a hydrogenpolysiloxane (B-1) having hydrosilyl groups only at both ends, and components (C-1) to (C-3), in which the molar number of hydrosilyl groups in component (B-1) relative to the molar number of alkenyl groups in component (A) was within the range of 0.1 to 1.5 moles, and the ratio of component (C-2) / component (C-1) was within the range of 0.7 to 3.0. As shown in Table 1, the sheet-like cured products obtained from each of these compositions had a hardness of 20 or less, yet excellent resilience and thermal conductivity. On the other hand, in Comparative Example 1, which used polysiloxane (A-2) having nine vinyl groups in the side chain, the resilience of the sheet-like cured product was reduced.

[0094] In Comparative Example 2, which used methylhydrogenpolysiloxane (B-2) having hydrosilyl groups only on the molecular side chains, the recovery of the sheet-like cured product was lower than in Example 1-8.

[0095] In Comparative Example 3, in which crushed aluminum oxide (C-4) was used instead of spherical aluminum oxide having an average particle size of 7 to 25 μm, the restorability of the sheet-like cured product was also reduced compared to Examples 1-8.

[0096] In Comparative Example 4, where the ratio of (C-2) / (C-1) exceeded the upper limit of 3.0, the restorability of the sheet-like cured product was lower than that of Example 1.

[0097] In Comparative Example 5, in which the total amount of component (C) was less than 1,600 parts by mass, the thermal conductivity of the sheet-like cured product was lower than that of Example 7.

[0098] In Comparative Example 6, in which the total amount of component (C) exceeded 4,100 parts by mass, the recovery property of the sheet-like cured product was lower than that of Example 8.

[0099] In Comparative Example 7, in which the amount of component (C-3) exceeded 1,350 parts by mass, the recovery property of the sheet-like cured product was lower than that of Example 8.

[0100] These results demonstrate that the thermally conductive silicone composition of the present invention can produce a sheet-like cured product that exhibits high recovery and high thermal conductivity despite its low hardness.

[0101] The present invention is not limited to the above-described embodiments. The above-described embodiments 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 exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A thermally conductive silicone composition comprising the following components (A) to (D): (A) an organopolysiloxane having alkenyl groups bonded to silicon atoms in its molecular side chains, with 2 to 8 alkenyl groups per molecule: 100 parts by mass, (B) an organohydrogenpolysiloxane capped at both ends with hydrosilyl groups: in an amount such that the number of moles of hydrosilyl groups in component (B) is 0.1 to 1.5 moles per 1.0 mole of alkenyl groups in component (A), (C) a thermally conductive filler comprising the following components (C-1) to (C-3): 1,600 to 4,100 parts by mass, (C-1) aluminum oxide having an average particle size of 0.5 to 5 μm: 270 to 1,610 parts by mass, (C-2) spherical aluminum oxide having an average particle size of 7 to 25 μm: 430 to 2,010 parts by mass, provided that the mass ratio of (C-2) to (C-1) is 0.7 to 3.0; (C-3) magnesium oxide having an average particle size of 40 to 90 μm: 530 to 1,350 parts by mass; and (D) a platinum group metal-based curing catalyst: 0.01 to 1,000 ppm in terms of the mass of platinum group metal atoms relative to the component (A).

2. The thermally conductive silicone composition according to claim 1, further comprising: (E) 10 to 100 parts by mass of a surface treatment agent, and said component (E) is at least one member selected from the group consisting of (E-1) alkoxysilanes and (E-2) dimethylpolysiloxanes one end of which is blocked with a trialkoxysilyl group.

3. A sheet-like cured product of the thermally conductive silicone composition according to claim 1 or 2, characterized in that the hardness of the cured product is 20 or less on the Asker C hardness scale.

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