Thermosoftening thermally conductive composition

Abstract

To provide a thermosoftening thermally conductive composition excellent in pump-out resistance, heat resistance, and flame retardancy.SOLUTION: The thermosoftening thermally conductive composition contains the following components (A), (B) and (C): (A) a phenyl-modified silicone resin which contains an R1SiO3 / 2 unit (where R1 is a group selected from C1-10 alkyl groups or a phenyl group) and an R22SiO2 / 2 unit (where R2 is a group selected from C1-10 alkyl groups, C2-10 alkenyl groups, or a phenyl group) and has a phenyl modification rate of 30-60 mol%; (B) a linear aryl-modified organopolysiloxane which has one or more C6-10 aryl groups in one molecule and has an aryl modification rate of 20-60 mol%; and (C) a thermally conductive filler which has a thermal conductivity of 10 W / (m K) or more and an average particle diameter of 0.3-20 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-softenable thermally conductive composition. [Background technology]

[0002] In recent years, a number of heat-softening materials have been disclosed as thermally conductive materials that have the advantages of both thermally conductive sheets and thermally conductive greases. These materials are non-fluid at room temperature but soften or melt when heated to become fluid. However, thermosoftening materials that use organic substances as base oils (Patent Documents 1 to 4) have poor heat resistance, and there is concern that they will deteriorate due to high temperatures when used in automobiles and the like. To improve heat resistance, many silicone-based heat-softening materials have been disclosed (e.g., Patent Documents 5 and 6), including, for example, sheet-formed products and paste-like thermally conductive materials (which utilize a curing reaction). However, when a thermally conductive material is quickly placed over a wide area, there is a problem that air bubbles may be trapped between the contact surfaces of the sheet molding. Furthermore, when using thermally conductive materials in electronic components, the fastest and most efficient method is to apply them by screen printing, etc. However, when a sheet-formed product is screen-printed, the curing reaction begins on the surface of the sheet during the drying process after application, which can leave solvent inside the sheet. Therefore, a paste-like heat-softenable composition suitable for application by screen printing, etc. has been disclosed (Patent Document 7). However, because this composition uses a modified silicone wax, it has the drawback of being inferior in fluidity, flame retardancy, and heat resistance to unmodified silicone, and its pump-out resistance at high temperatures is insufficient. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-106283 [Patent Document 2] International Publication No. 2016 / 185936 [Patent Document 3] International Publication No. 2015 / 035575 [Patent Document 4] Patent Publication No. 2021-80316 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-76678 [Patent Document 6] Patent Publication No. 2021-147591 [Patent Document 7] Japanese Patent Application Laid-Open No. 2017-061613 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, an object of the present invention is to provide a heat-softenable thermally conductive composition that is used as a thermally conductive material to be interposed at the thermal boundary between a heat-generating electronic component and a heat-dissipating component such as a heat sink or metal housing for cooling the electronic component, that is in a paste form with excellent fluidity and can be applied by screen printing or the like, that reduces in viscosity, softens, or melts at temperatures within the operating temperature range of the electronic component, so that the thermally conductive material (coating) adheres closely to the thermal boundary, and that has better pump-out resistance than conventional products. [Means for solving the problem]

[0005] As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that a heat-softenable thermally conductive composition capable of reducing thermal resistance can be obtained by blending a heat-softenable phenyl-modified silicone resin with a linear aryl-modified organopolysiloxane and a thermally conductive filler, thereby completing the present invention. Furthermore, a heat-softening thermally conductive composition containing a specific amount of isoparaffin with a boiling point of 80 to 360°C, which can dissolve or disperse the following components (A) and (B), is in a paste form when applied, allowing for easy and rapid screen printing, thereby enabling efficient operation. Furthermore, the present inventors discovered that the composition becomes a thermally conductive coating that is in a non-fluid state at room temperature by volatilizing the contained solvent, thereby improving pump-out resistance and reliability compared to general thermal greases, leading to the completion of the present invention.

[0006] That is, an object of the present invention is to provide a heat-softenable thermally conductive composition containing the following components (A) to (C), and a paste-like heat-softenable thermally conductive composition obtained by dissolving the heat-softenable thermally conductive composition in the following component (D): Here, thermal softening refers to the ability to soften, reduce viscosity, or melt due to heat (at 40°C or higher), and a coating that is thermally softened, reduced viscosity, or melted and fluidizes on the surface can be considered to have "thermosoftening."

[0007] [1] A heat-softenable, thermally conductive composition comprising the following components (A), (B), and (C): (A)R 1 SiO 3 / 2 Units (wherein R 1 is a group selected from an alkyl group having 1 to 10 carbon atoms or a phenyl group), and R 2 2SiO 2 / 2 Units (wherein R 2 is a group selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or a phenyl group), and the phenyl modification rate is 30 to 60 mol %: 100 parts by mass (B) a linear aryl-modified organopolysiloxane having one or more aryl groups having 6 to 10 carbon atoms per molecule and an aryl modification rate of 20 to 60 mol %: 20 to 40 parts by mass (C) Thermally conductive filler having a thermal conductivity of 10 W / (m·K) or more and an average particle size of 0.3 to 20 μm: 800 to 1,300 parts by mass [2] The heat-softenable thermally conductive composition according to [1], further comprising, as component (D), 10 to 300 parts by mass of an isoparaffinic solvent having a boiling point of 80 to 360°C per 100 parts by mass of component (A). [3] The heat-softenable thermally conductive composition according to [1], further comprising a surface treatment agent as component (E) in an amount of 5 to 40 parts by mass per 100 parts by mass of component (A). [4] A cured product of the heat-softenable thermally conductive composition according to any one of [1] to [3]. [Effects of the Invention]

[0008] The heat-softenable thermally conductive composition of the present invention has superior pump-out resistance, heat resistance, and flame retardancy compared to conventional products, and is useful as a heat-dissipating material. Furthermore, the heat-softenable thermally conductive composition of the present invention is disposed between a heat-generating electronic component and a heat-dissipating component, has no fluidity at room temperature, and becomes less viscous, softens, or melts due to heat generated during operation of the electronic component, thereby substantially filling the boundary between the electronic component and the heat-dissipating component. Furthermore, the heat-softenable thermally conductive composition of the present invention can be made into a paste-like material with excellent fluidity, allowing it to be easily applied by screen printing or the like. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] (A) Phenyl-modified silicone resin Component (A) is a heat-softening phenyl-modified silicone resin that forms the matrix of the composition (heat dissipation member) of the present invention. Component (A) is a silicone resin that is substantially non-fluid at room temperature, but that heat-softens, reduces viscosity, or melts and becomes fluid when the heat-generating electronic component generates heat, specifically in the temperature range of 40 to 80°C. Component (A) heat-softens the composition (heat dissipation member) of the present invention and also serves as a binder that imparts processability and workability to the filler that imparts thermal conductivity. In the present invention, "room temperature" refers to a range of 10 to 30°C. Here, the temperature at which the silicone resin softens, reduces viscosity, or melts is the temperature required for the heat dissipation component, and the melting point of the silicone resin itself is preferably 40 to 80°C, and particularly preferably 50 to 70°C. If the melting point of the silicone resin itself is less than 40°C, the surface layer may become tacky when the composition is applied, making it difficult to handle. If the melting point of the silicone resin itself is higher than 80°C, the temperature during thermocompression bonding must be high, which may make the mounting process difficult.

[0011] Component (A) is R 1 SiO 3 / 2 unit (hereinafter referred to as T unit), and R 2 2SiO 2 / 2 In addition to these T units and D units, R 2 3SiO 1 / 2 It may also have a small amount of units (hereinafter referred to as M units). R 1 is a group selected from an alkyl group having 1 to 10 carbon atoms and a phenyl group. 1 Specific examples of R include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl, and phenyl groups. 1 is preferably a methyl group or a phenyl group. R 2 is the above R 1 In addition to the alkyl groups and phenyl groups, R is a group selected from alkenyl groups having 2 to 10 carbon atoms. 2 A specific example of this is R 1 In addition to the above, specific examples include alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexynyl, and octenyl. Among these, from the viewpoint of flame retardancy, R 2 is preferably a methyl group, a phenyl group, a vinyl group, or an allyl group.

[0012] The silicone resin of component (A) will now be described in more detail. The silicone resin of component (A) must contain T units and D units in order to be non-fluid at room temperature. A typical example of such a silicone resin is a silicone resin composed of a combination of T units, D units, and a small amount of M units. Introducing T units increases toughness and reduces brittleness when solid at room temperature, preventing breakage during handling. Introducing D units also improves toughness at room temperature. M units form terminals. In silicone resins consisting of a combination of M units, T units, and D units, the ratio of T units to D units is preferably 10:90 to 90:10, and more preferably 20:80 to 80:20. The ratio of M units to the total of T units and D units is preferably 0.2:100 to 4:100.

[0013] The phenyl modification rate of the silicone resin of component (A) is 30 to 60 mol%, preferably 40 to 60 mol%, and particularly preferably 50 to 60. If the phenyl modification rate is less than 30 mol%, the adhesiveness of the resin may be weakened, and pump-out resistance may decrease. If the phenyl modification rate exceeds 60 mol%, the compatibilizer component (B) may not dissolve even when added, resulting in separation. The phenyl modification rate is the ratio of units containing phenyl groups among M units, D units, and T units, expressed as a molar percentage.

[0014] Specific examples of component (A) include silicone resins having a specific composition of difunctional structural units (D units) and trifunctional structural units (T units) as shown below. Note that the bonding order of the siloxane units listed below may be either block or random. D m Tφ p D Vi n (where D is a dimethylsiloxy unit (i.e., (CH3)2SiO 2 / 2), Tφ is a phenylsiloxy unit (i.e., (C6H5)SiO 3 / 2 ), D Vi is a methylvinylsiloxy unit (i.e., (CH3)(CH2=CH)SiO 2 / 2 ), where p / (m+p+n) (molar ratio) is 0.3 to 0.6, and n / (m+n) (molar ratio) is 0.7 to 1.0.

[0015] Specific examples of component (A) include silicone resins having a specific composition of monofunctional structural units (M units), difunctional structural units (D units), and trifunctional structural units (T units), as shown below. M L D m Tφ p D Vi n (where M is a trimethylsiloxy unit (i.e., (CH3)3SiO 1 / 2 ), and D, Tφ and D Vi are as described above, and p / (m+p+n+L) (molar ratio) = 0.3 to 0.6, n / (m+n) (molar ratio) = 0.7 to 1.0, L / (m+n) (molar ratio) = 0.001 to 0.1.

[0016] How to measure the ratio of M-units, D-units and T-units In the present invention, the monofunctional R 1 3SiO 1 / 2 Unit (M unit), bifunctional R 2 SiO 2 / 2 Units (D units) and trifunctional R 1 SiO 3 / 2 The ratio of units (T units) is 29 This is a value obtained from Si-NMR. 29 The method for preparing a Si-NMR sample is not particularly limited, but for example, a sample can be prepared by dissolving 1 part by mass of organopolysiloxane resin in 3 parts by mass of deuterated chloroform. The average degree of polymerization of the silicone resin, i.e., the total amount of M units, D units, T units, and Q units, is preferably 30 to 300, more preferably 50 to 150. In the present invention, the average degree of polymerization is a value determined as a polystyrene-equivalent number-average degree of polymerization (number-average molecular weight) in GPC (gel permeation chromatography) analysis using toluene as a developing solvent.

[0017] The component (A) may be used alone or in combination of two or more types. The content of component (A) in the composition of the present invention is preferably 6.9 to 9.1 mass %, and more preferably 7.2 to 8.6 mass %.

[0018] (B) Linear aryl-modified organopolysiloxane Component (B) is a linear aryl-modified organopolysiloxane. The heat-softenable thermally conductive composition of the present invention can be made into a paste-like form with excellent fluidity, allowing it to be easily applied by screen printing or other methods. After applying the heat-softenable thermally conductive composition of the present invention to a heat-generating electronic component and / or a heat-dissipating component by screen printing or other methods, if the composition contains the component (D) described below, the isoparaffin in component (D) can be air-dried or heated to volatilize it, rendering the composition non-fluid at room temperature. Subsequently, the composition becomes less viscous, softens, or melts due to heat generated during operation of the electronic component, thereby fluidizing at least the surface of the coating. Here, component (B) is a necessary component for dissolving component (A), the base polymer, in component (D), and also has the effect of increasing the fluidity of the coating surface when it fluidizes due to heat generation.

[0019] Component (B) is a linear organopolysiloxane having one or more aryl groups having 6 to 10 carbon atoms per molecule, and the aryl modification rate is 20 to 60 mol %, preferably 30 to 50 mol %, in order to ensure compatibility with component (A). If the aryl modification rate is less than 20 mol% or more than 60 mol%, the function as a compatibilizer will be reduced, and component (A) may not dissolve and may separate. The aryl modification rate is the ratio of units containing aryl groups or aralkyl groups to all siloxane units, expressed as a molar percentage.

[0020] Specific examples of the component (B) include those represented by the following formula (1). [Chemical formula]

[0021] In formula (1), R 3 is an aryl group having 6 to 10 carbon atoms or an aralkyl group having 7 to 10 carbon atoms. Specific examples include aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group, etc., and aralkyl groups such as benzyl group. Among them, R 3 is preferably a phenyl group. In formula (1), R 4 is a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms. For example, alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, etc., cycloalkyl groups such as cyclopentyl group, cyclohexyl group, cycloheptyl group, etc., and alkenyl groups such as vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, octenyl group, etc. Among them, R 4 is preferably a methyl group or a vinyl group. The bonds of the siloxane units enclosed by a and b may be block or random. In formula (1), the ratio of each siloxane unit is preferably in the range of 0.1 < a < 0.7, 0.3 < b < 0.9, and a + b = 1.

[0022] The component (B) may be used alone or in combination of two or more.

[0023] The kinematic viscosity of the organopolysiloxane of the component (B) at 25°C is preferably 200 to 5,000 mm 2 / s at 25°C, particularly preferably 300 to 4,000 mm 2 / s. 2 If it is lower than / s, oil bleeding will occur easily, and 2 If the kinematic viscosity is greater than 1 / s, the viscosity may become low and the fluidity may be poor when softened or melted. The kinematic viscosity of organopolysiloxane is the value measured at 25°C using an Ostwald viscometer.

[0024] Specific examples of component (B) include organopolysiloxanes with the following structures: [ka]

[0025] The blending amount of component (B) is in the range of 20 to 40 parts by mass, and preferably in the range of 25 to 35 parts by mass, per 100 parts by mass of component (A). If the blending amount is less than 20 parts by mass, the function of the compatibilizer will be weakened and the viscosity will be reduced and the fluidity after softening or melting will be poor. If the blending amount is more than 40 parts by mass, the composition will not become non-fluid at room temperature, and the pump-out resistance may be reduced.

[0026] (C) Thermally conductive filler The thermally conductive filler of component (C) must have a thermal conductivity of 10 W / (m K) or more. If the thermal conductivity is less than 10 W / (m K), the thermal conductivity of the heat-softenable thermally conductive composition itself will be low. The upper limit of thermal conductivity varies depending on the material used for the thermally conductive filler, but there is no specific upper limit. Examples of thermally conductive fillers having a thermal conductivity of 10 W / (m·K) or more include powders and granules such as aluminum powder, copper powder, silver powder, nickel powder, gold powder, alumina powder, zinc oxide powder, magnesium oxide powder, aluminum nitride powder, boron nitride powder, silicon nitride powder, diamond powder, and carbon powder, and these may be used alone or in combination of two or more.

[0027] When a powder or granule is used as the thermally conductive filler, its shape may be irregular, spherical, or any other shape, but the average particle size is 0.3 to 20 μm, preferably 1 to 15 μm. If the average particle size is less than 0.3 μm, the compoundability of the composition decreases and extensibility becomes poor, while if it exceeds 20 μm, it may be difficult to reduce the thickness after thermocompression bonding. The average particle size is determined by measuring the cumulative volume average diameter D 50 Specifically, the cumulative 50% particle diameter (D) on a volume basis measured using a particle size distribution analyzer MT3000II manufactured by Microtrac Bell Co., Ltd. 50 ) (the same applies below). The amount of the thermally conductive filler blended is in the range of 800 to 1,300 parts by mass, and preferably in the range of 900 to 1,200 parts by mass, per 100 parts by mass of component (A). If the blending amount is less than 800 parts by mass, the required thermal conductivity cannot be obtained, and if it exceeds 1,300 parts by mass, the blendability of the composition decreases and extensibility may become poor.

[0028] (D) Isoparaffinic solvents The heat-softenable thermally conductive composition of the present invention preferably further contains, as component (D), an isoparaffinic solvent capable of dissolving or dispersing components (A) and (B). Other volatile solvents can also dissolve the composition, but due to safety and health considerations, their use during packaging is difficult. On the other hand, isoparaffinic solvents pose no safety or health concerns and offer excellent workability during printing.

[0029] In the present invention, the term "isoparaffinic solvent" refers to a solvent containing 80 mass percent or more of isoparaffin, which is an aliphatic hydrocarbon having 10 or more carbon atoms. The boiling point of component (D) is preferably 80 to 360°C, more preferably 150 to 350°C. If the boiling point is less than 80°C, the component volatilizes too quickly, which can cause problems due to an increase in viscosity during printing. If the boiling point is greater than 360°C, the component is more likely to remain in the heat-softenable thermally conductive composition of the present invention, which can result in reduced thermal properties.

[0030] In addition, in the present invention, "dissolved or dispersible" means that when component (A) and component (B) are placed in the isoparaffinic solvent, they are uniformly mixed together or uniformly suspended as fine particles.

[0031] When component (D) is added, the amount is preferably in the range of 10 to 300 parts by mass, more preferably 50 to 200 parts by mass, per 100 parts by mass of component (A). If the amount of component (D) added is less than 10 parts by mass per 100 parts by mass of component (A), the viscosity of the heat-softenable thermally conductive composition of the present invention at room temperature cannot be sufficiently reduced, which may result in poor printability, whereas if the amount is more than 300 parts by mass, the filler will settle quickly, which may result in poor storage stability of the heat-softenable thermally conductive composition.

[0032] The component (D) may be used alone or in combination of two or more types.

[0033] (E) Surface treatment agent The heat-softenable thermally conductive composition of the present invention can be blended with a surface treatment agent of component (E). Component (E) hydrophobizes component (C) during the preparation of the composition, improving the wettability of component (A) with component (B), and enabling component (C) to be uniformly dispersed in the matrix formed by components (A) and (B). Component (E) is preferably at least one selected from the following components (E-1) and (E-2).

[0034] The component (E-1) is an alkoxysilane compound represented by the following formula (3). [ka] (In formula (3), R 5 are independently alkyl groups having 6 to 15 carbon atoms, and R 6 are independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms; R 7are independently an alkyl group having 1 to 6 carbon atoms, b is a number from 1 to 3, and c is a number from 0 to 2, with the proviso that b+c is a number from 1 to 3.

[0035] In the above formula (3), R 5 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. 5 When the number of carbon atoms in the alkyl group represented by the formula (I) is in the range of 6 to 15, the wettability of the component (A) is improved sufficiently, the handling property is good, and the low-temperature properties of the composition are good.

[0036] In the above formula (3), R 6 Examples 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 6 Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group.

[0037] In the above formula (3), R 7 Examples of the alkyl group having 1 to 6 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, and a hexyl group.

[0038] Component (E-2) is a dimethylpolysiloxane represented by the following formula (4) in which one molecular chain end is blocked with a trialkoxysilyl group. [ka] (In formula (4), R 8 are independently alkyl groups having 1 to 6 carbon atoms, and specifically, 7 Examples of the alkyl group include the same alkyl groups as those exemplified in the above. d is a number from 5 to 100, preferably from 5 to 70, and particularly preferably from 10 to 50.

[0039] The surface treatment agent of component (E) may be either component (E-1) or component (E-2), or both may be blended in combination. When component (E) is blended, the blending amount is preferably 5 to 40 parts by mass, and particularly preferably 10 to 30 parts by mass, per 100 parts by mass of component (A). Blending of this component in an amount greater than 40 parts by mass may induce oil separation.

[0040] Other additives The heat-softenable thermally conductive composition of the present invention may further contain additives or fillers as optional components, provided that the purpose of the present invention is not impaired. Specifically, the following may be added: a release agent such as silicone oil or a fluorine-modified silicone surfactant; a colorant such as carbon black, titanium dioxide, or red iron oxide; a flame retardant such as a platinum catalyst, iron oxide, titanium oxide, or cerium oxide, or a metal hydroxide; and a process oil, reactive titanate catalyst, or reactive aluminum catalyst as a processability improver. Furthermore, finely powdered silica such as precipitated silica or pyrogenic silica, a thixotropy improver, or the like may be optionally added as an anti-settling agent for the thermally conductive filler.

[0041] Manufacturing method The heat-softenable thermally conductive composition used in the heat dissipation member of the present invention can be easily produced by blending and kneading the above-mentioned components (A), (B), and (C), as well as other components (component (D) and / or (E)) as needed, using a rubber kneader such as a kneader, gate mixer, or planetary mixer. Heating may be performed as needed.

[0042] Characteristics after thermocompression bonding When the resulting heat-softenable thermally conductive composition after drying is heated and compressed at 50° C. for 30 minutes under a pressure of 0.7 kPa, it can be compressed to a thickness of 60 μm or less. The heat resistance of the obtained heat-softening thermally conductive composition after drying is 20 to 60 μm thick and 10 mm thick. 2 ·K / W or less is preferable, and 7mm 2 The effective thermal resistance was calculated using the following formula from the thermal conductivity determined by the laser flash method and the thickness of the sample.

number

[0043] The heat-softenable thermally conductive composition of the present invention can be applied to a heat-generating electronic component and / or a heat-dissipating component by screen printing or the like, and then air-dried or heated. If an isoparaffinic solvent (D) is added, the component (D) can be volatilized to form a thermally conductive coating that is non-fluid at room temperature. Furthermore, the present invention can provide a heat dissipation structure including a heat-generating electronic component that generates heat when in operation and reaches a temperature higher than room temperature, a heat-dissipating component, and a heat-conductive coating formed from a heat-softenable heat-conductive composition interposed between these two components. The heat-softenable heat-conductive composition is non-fluid at room temperature before the electronic component is in operation, but becomes less viscous, softens, or melts due to heat generated when the electronic component is in operation, causing at least the surface of the coating to become fluid, thereby filling the space between the electronic component and the heat-dissipating component with substantially no voids. [Example]

[0044] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0045] The components (A) to (E) constituting the heat-softenable thermally conductive materials used in the following examples and comparative examples are as follows. In the following, M represents a trimethylsiloxy unit (i.e., (CH3)3SiO 1 / 2 ), D is a dimethylsiloxy unit (i.e., (CH3)2SiO2 / 2 ), Dφ is a diphenylsiloxy unit (i.e., (C6H5)2SiO 2 / 2 ), D Vi is a methylvinylsiloxy unit (i.e., (CH3)(CH2=CH)SiO 2 / 2 ), Tφ is a phenylsiloxy unit (i.e., (C6H5)SiO 3 / 2 )

[0046] (A) Component: Phenyl-modified silicone resin (A-1) Silicone resin (average degree of polymerization: 100) represented by the following formula and having a phenyl modification rate of 55 mol% D 25 Tφ 55 D Vi 20 (A-2) Silicone resin (average polymerization degree: 100) represented by the following formula and having a phenyl modification rate of 73 mol% (for comparison) M 15 D 12 (Dφ) 22 Tφ 51 (A-3) Silicone resin (average degree of polymerization: 100) represented by the following formula and having a phenyl modification rate of 20 mol% (for comparison) D 80 Tφ 20

[0047] Component (B): Linear aryl-modified organopolysiloxane (B-1) An organopolysiloxane having an aryl modification rate of 26.7 mol%, represented by the following formula (5): [ka] (B-2) Organopolysiloxane (for comparison) having an aryl modification rate of 5.6 mol% represented by the following formula (6): [ka] (B-3) Organopolysiloxane (for comparison) having an aryl modification rate of 100 mol% represented by the following formula (7): [ka]

[0048] (C) Component: Thermally conductive filler (C-1) Zinc oxide powder: average particle size 1.0 μm (thermal conductivity: 54 W / (m·K)) (C-2) Alumina powder: average particle size 0.3 μm (thermal conductivity: 27 W / (m·K)) (C-3) Aluminum powder: average particle size 2 μm (thermal conductivity: 236 W / (m·K)) (C-4) Aluminum powder: average particle size 10 μm (thermal conductivity: 236 W / (m·K)) (C-5) Aluminum powder: average particle size 30 μm (thermal conductivity: 236 W / (m·K)) (for comparison)

[0049] Component (D): Isoparaffinic solvent (D-1) IP Solvent 1620 (Idemitsu Kosan Co., Ltd., boiling point: 170-200°C)

[0050] (E) Component: Surface treatment agent (E-1) Silane represented by the following formula C 10 H 21 Si(OCH3)3

[0051] The above components (A), (B), (C), (D), and (E) were charged into a planetary mixer in the amounts shown in Tables 1 and 2 below and mixed for 60 minutes to produce paste-like thermosoftenable thermally conductive compositions for Examples 1 to 6 and Comparative Examples 1 to 7. The paste-like thermosoftenable thermally conductive compositions were then dried to a fixed volume and thickness, volatilizing the solvent in the composition and obtaining thermosoftenable thermally conductive compositions. The properties of the resulting thermosoftenable thermally conductive compositions are also shown in Tables 1 and 2.

[0052] [Evaluation method] Tests relating to the present invention were carried out as follows. [Pump-out resistance] 0.3 g of a paste-like heat-softening thermally conductive composition was applied to an aluminum plate and the solvent in the composition was evaporated in an oven at 120°C for 30 minutes. Then, before cooling, a 0.5 mm spacer was placed between the plate and a glass slide, sandwiching the heat-softening thermally conductive composition. The test specimen was placed vertically above the ground and placed in an Espec Corporation thermal shock tester (model number: TSE-11-A) set to alternate between 0°C and 125°C (30 minutes each), and a 500-cycle test was performed. After 500 cycles, the amount of displacement of the heat-softening thermally conductive composition from its original position was measured. [Thickness and thermal resistance after thermocompression bonding] A paste-like heat-softening thermally conductive composition was applied to a PET light-release separator film, and the solvent in the composition was evaporated in an oven at 120°C for 10 minutes to produce a 200 μm-thick heat-softening thermally conductive composition (hereinafter referred to as a sheet). The sheet was attached to an aluminum plate, the separator film was peeled off, and then another aluminum plate was attached on top of the sheet that had been on the peeled film side. Next, the two aluminum plates were heated at 50°C for 30 minutes while applying a pressure of 0.7 kPa using clips or the like. The thickness of the two aluminum plates was then measured, and the actual thickness of the sheet was determined by subtracting the thickness of the aluminum plate, whose thickness was previously known. A micrometer (Mitutoyo Corporation, Model: M802-25VA) was used to measure the thickness. The thermal resistance of the sheet was also measured using a laser flash measuring instrument (NETZSCH, LFA467 HyperFlash).

[0053] <Examples 1 to 6> Using compositions (a) to (f), sheet-shaped heat-softenable thermally conductive compositions were obtained by the method described above. <Comparative Example 1> Composition (g) was applied to an aluminum plate or a separator film, and after drying, a heat-softenable thermally conductive composition was obtained. In the pump-out resistance test, the deviation was large and the pump-out resistance was poor. <Comparative Example 2> Composition (h) was applied to an aluminum plate or a separator film, and after drying, a heat-softenable thermally conductive composition was obtained. In the pump-out resistance test, the deviation was large and the pump-out resistance was poor. <Comparative Example 3> Composition (i) was applied to an aluminum plate or separator film, and after drying, a heat-softenable thermally conductive composition was obtained. Even when heated and pressed, the thickness did not decrease and the thermal resistance was high. <Comparative Example 4> Composition (j) was applied to an aluminum plate or separator film, and after drying, a heat-softenable thermally conductive composition was obtained. Even when heated and pressed, the thickness did not decrease and the thermal resistance was high. <Comparative Example 5> The oil in composition (k) separated during blending and did not become grease-like, so its physical properties could not be evaluated. <Comparative Example 6> Composition (l) could not be evaluated for its physical properties because the oil separated during blending and it did not become a grease-like substance. <Comparative Example 7> The oil in composition (m) separated during blending and the composition did not become grease-like, so its physical properties could not be evaluated.

[0054] [Table 1]

[0055] [Table 2]

Claims

1. A heat-softenable, thermally conductive composition comprising the following components (A), (B), and (C): (A)R 1 SiO 3 / 2 Units (wherein R 1 is a group selected from an alkyl group having 1 to 10 carbon atoms or a phenyl group), and R 2 2 SiO 2 / 2 Units (wherein R 2 is a group selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or a phenyl group), and the phenyl modification rate is 30 to 60 mol %: 100 parts by mass (B) a linear aryl-modified organopolysiloxane having one or more aryl groups having 6 to 10 carbon atoms per molecule and an aryl modification rate of 20 to 60 mol %: 20 to 40 parts by mass (C) a thermally conductive filler having a thermal conductivity of 10 W / (m·K) or more and an average particle size of 0.3 to 20 μm: 800 to 1,300 parts by mass

2. 2. The heat-softenable thermally conductive composition according to claim 1, further comprising, as component (D), 10 to 300 parts by mass of an isoparaffinic solvent having a boiling point of 80 to 360°C per 100 parts by mass of component (A).

3. The heat-softenable thermally conductive composition according to claim 1, further comprising a surface treatment agent as component (E) in an amount of 5 to 40 parts by mass per 100 parts by mass of component (A).

4. A cured product of the heat-softenable thermally conductive composition according to any one of claims 1 to 3.

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