Thermally conductive silicone composition

Abstract

Provided is a thermally conductive silicone composition that becomes a cured product having stability even in a low-temperature environment. The thermally conductive silicone composition comprises: (A) an organopolysiloxane having, in each molecule, a silicon atom to which two or more aliphatic unsaturated hydrocarbon groups are bonded; (B) an organopolysiloxane having, in each molecule, a silicon atom to which one aliphatic unsaturated hydrocarbon group is bonded; (C) an organohydrogen polysiloxane having two or more SiH groups in each molecule; (D) an organosilane represented by general formula (1) of R1 aSi(OR2)4-a (in formula (1), R1 is a monovalent hydrocarbon group, R2 is an alkyl group or a cycloalkyl group, and a is a number from 1 to 3); (E) a platinum group metal catalyst; (F) a reaction control agent; (G) an inorganic filler having an average particle diameter of 3 μm or less; and (H) an inorganic filler having an average particle diameter of from greater than 3 μm to 150 μm or less.

Description

Thermally conductive silicone composition

[0001] The present invention relates to a thermally conductive silicone composition, particularly an addition-curable silicone composition that gives a cured product with excellent cold resistance, specifically a thermally conductive silicone composition that gives a cured product with better cold resistance when used in low-temperature environments than the cured product of a typical thermally conductive silicone composition.

[0002] Many electronic components generate heat during use, and heat removal is necessary for them to function properly. In particular, integrated circuit elements such as CPUs and GPUs used in personal computers and smartphones are experiencing increasing heat generation due to faster operating frequencies and smaller packages, making heat countermeasures and design important issues. Furthermore, with the recent evolution of electrified automobiles, the use of many electronic components means that electronic components are sometimes used in harsher conditions, such as high-temperature, high-humidity environments.

[0003] There are many methods for removing this heat. For electronic components that generate a large amount of heat, a method for dissipating heat by placing a thermally conductive material such as thermally conductive grease or a thermally conductive sheet between the electronic component and a member such as a heat sink has been disclosed (Patent Document 1). Thermally conductive grease is particularly suitable because it is amorphous and exhibits high thermal conductivity by adhering to the substrate after curing. Another known example of such a thermally conductive material is a heat-dissipating adhesive based on silicone and containing zinc oxide, aluminum, or alumina powder.

[0004] To create a silicone-based thermally conductive material with high thermal conductivity, it is necessary to highly fill the thermally conductive filler. However, simply attempting to fill the thermally conductive material with a high filler content significantly reduces the fluidity of the thermoelectrically conductive material, resulting in poor workability (dispensability, screen printing), and even the inability to conform to the fine irregularities on the surfaces of electronic components and heat sinks. To solve this problem, a known method is to surface-treat the thermally conductive filler with a wetter (dispersant) to disperse it into the silicone base polymer, thereby maintaining the fluidity of the thermally conductive material.

[0005] In recent years, the automotive industry has seen an increase in electrification, and even in cold-weather vehicles, it is expected that integrated circuit elements such as CPUs and GPUs, or electronic components that generate a large amount of heat, will be used in extremely low-temperature environments. The aerospace industry also requires material stability in low-temperature environments. Therefore, there is a demand for silicone compositions that produce cured products with even higher cold resistance when used in low-temperature environments than the cured products of typical thermally conductive silicone compositions. Typical silicone materials have a brittle point around −40°C, which tends to crystallize the silicone component, increasing material hardness and reducing molecular flexibility, resulting in poor cold resistance. Furthermore, typical silicone materials exhibit a thermal expansion tendency that deviates from a constant rate of increase around −40°C, generating stress at the interface of the heat-dissipating material, particularly when exposed to repeated low and high temperatures. This leads to deterioration of the interface condition and reduced heat dissipation performance when exposed to repeated low and high temperatures.

[0006] JP 2016-053140 A

[0007] Therefore, an object of the present invention is to provide a thermally conductive silicone composition that cures to a stable product even in low-temperature environments, and in particular, to provide a thermally conductive silicone composition that exhibits a constant rate of thermal expansion change at temperatures around -40°C without showing any tendency to deviate from a constant rate of increase, thereby reducing stress on the substrate.

[0008] As a result of extensive research conducted by the present inventors to achieve the above object, they discovered that the silicone composition described below exhibits a consistent rate of expansion at around -40°C without any tendency to deviate from a constant rate of increase, and that it does not experience changes in thickness in the low temperature range compared to conventional thermally conductive silicone compositions, and they have completed the present invention. That is, the present invention provides the following thermally conductive silicone composition.

[0009] [1] A thermally conductive silicone composition containing the following components (A), (B), (C), (D), (E), (F), (G), and (H): (A) a silicone rubber having, per molecule, at least two silicon atoms bonded to aliphatic unsaturated hydrocarbon groups, and containing, in the molecular chain, at least one silicon atom bearing an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 mm 2 (B) an organopolysiloxane having, per molecule, a silicon atom to which one aliphatic unsaturated hydrocarbon group is bonded, and containing, in the molecular chain, one or more silicon atoms having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 mm 2 (C) an organohydrogenpolysiloxane having two or more silicon-bonded hydrogen atoms (SiH groups) per molecule: an amount such that the number of SiH groups in component (C) is 0.4 to 5 relative to the total number of aliphatic unsaturated hydrocarbon groups in components (A) and (B); and (D) an organosilane represented by the following general formula (1): 0.01 to 100 parts by mass per 100 parts by mass of the total of components (A) and (B): R 1 a Si(OR 2 ) 4-a (1) (In formula (1), R 1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and R 1 may be the same or different. 2 is an alkyl group having 1 to 20 carbon atoms which may have a substituent or a cycloalkyl group having 3 to 20 carbon atoms which may have a substituent, R 2may be the same or different. a is a number from 1 to 3.) (E) platinum group metal catalyst: an effective amount; (F) reaction inhibitor: 0.05 to 5.0 parts by mass per 100 parts by mass of the total of components (A) and (B); (G) inorganic filler having an average particle size of 3 μm or less; (H) inorganic filler having an average particle size of more than 3 μm and 150 μm or less: the total of components (G) and (H) is 300 to 3,000 parts by mass per 100 parts by mass of the total of components (A) and (B). [2] The composition according to [1], wherein component (G) is zinc oxide powder. [3] The composition according to [1] or [2], wherein component (H) is aluminum powder. [4] The composition according to any one of [1] to [3], wherein component (F) is a reaction inhibitor selected from acetylene compounds, nitrogen compounds, organic phosphorus compounds, oxime compounds, and organic chloro compounds. [5] A cured product of the composition according to any one of [1] to [4].

[0010] By using the thermally conductive silicone composition of the present invention, it is possible to obtain a cured product in which expansion at around -40°C shows a constant change without showing any tendency to deviate from a constant rate of increase, and which does not experience any change in thickness in the low temperature range compared to conventional thermally conductive silicone compositions. By using this silicone composition, heat generated by electrical and electronic components in extremely low temperature environments can be released without putting stress on the substrate.

[0011] 1 is a graph (vertical axis: displacement, horizontal axis: temperature) showing an example of the TMA measurement results of a composition having cold resistance. 2 is a graph (vertical axis: displacement, horizontal axis: temperature) showing an example of the TMA measurement results of a composition not having cold resistance.

[0012] The present invention will be described in further detail below.

[0013] Component (A) Component (A) is a silicone oil having, in one molecule, at least two silicon atoms bonded to aliphatic unsaturated hydrocarbon groups, and one or more silicon atoms having an aromatic hydrocarbon group in the molecular chain, and having a kinematic viscosity at 25°C of 50 to 100,000 mm 2The organopolysiloxane is an organopolysiloxane having a structure in which the aliphatic unsaturated hydrocarbon group is bonded to at least two silicon atoms, preferably 2 to 100, and more preferably 2 to 50. If the number of silicon atoms is less than two, the ratio between the amount of unsaturated hydrocarbon groups and the hydrogen atoms bonded to silicon atoms will be disrupted, resulting in insufficient curability and cold resistance. The organopolysiloxane has one or more silicon atoms bearing an aromatic hydrocarbon group in its molecular chain. Furthermore, the proportion of aromatic hydrocarbon groups in side chains in the molecular chain of the organopolysiloxane is preferably 1 to 20%, more preferably 2 to 10%, and particularly preferably 3 to 7%, relative to the total number of silicon atoms (100%) at non-terminal positions in the molecular chain. If the molecular chain contains fewer than one silicon atom bearing an aromatic hydrocarbon group, sufficient cold resistance may not be obtained.

[0014] The aliphatic unsaturated hydrocarbon group is preferably a monovalent hydrocarbon group having an aliphatic unsaturated bond and having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and is more preferably an alkenyl group. Examples of the aliphatic unsaturated hydrocarbon group include alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl. Of these, vinyl groups are particularly preferred. The aliphatic unsaturated hydrocarbon group may be bonded to a silicon atom at either the terminal of the molecular chain or a silicon atom in the middle of the molecular chain, or may be bonded to both.

[0015] The organic group other than aliphatic unsaturated hydrocarbons bonded to the silicon atoms of the organopolysiloxane is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms, and containing at least one aromatic hydrocarbon group. Examples of organic groups other than aliphatic unsaturated hydrocarbons include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aromatic hydrocarbon groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as fluorine, bromine, or chlorine, or with cyano groups, such as chloromethyl, chloropropyl, bromoethyl, trifluoropropyl, and cyanoethyl. Particularly preferred are methyl and phenyl groups.

[0016] The organopolysiloxane has a kinematic viscosity at 25°C of 50 to 100,000 mm 2 / s, preferably 100 to 30,000 mm 2 / s. The kinematic viscosity is 50 mm 2 If the viscosity is less than 100,000 mm / s, the physical properties of the silicone composition will be reduced, and 2 If the viscosity exceeds 1 / s, the silicone composition will have poor extensibility.

[0017] In the present invention, the kinematic viscosity is a value measured at 25° C. using an Ubbelohde-type Ostwald viscometer (the same applies hereinafter).

[0018] The molecular structure of the organosiloxane is not particularly limited as long as it has the above properties, and examples of the molecular structure include a linear structure, a branched structure, and a linear structure having a partially branched or cyclic structure. As for those having such a molecular structure, particularly preferred are those having a linear structure in which the main chain is composed of repeating diorganosiloxane units and both molecular chain terminals are blocked with triorganosiloxy groups. The linear organopolysiloxane may also have a partially branched or cyclic structure.

[0019] The organopolysiloxane of component (A) can be used alone or in combination of two or more. The content of component (A) in the entire composition of the present invention is preferably 0.5 to 7.0 mass%, and more preferably 0.9 to 6.8 mass%.

[0020] Component (B) Component (B) is a silicone oil having one silicon atom bonded to one aliphatic unsaturated hydrocarbon group per molecule, one or more silicon atoms having an aromatic hydrocarbon group in the molecular chain, and a kinematic viscosity at 25°C of 50 to 100,000 mm 2 The organopolysiloxane is an organopolysiloxane having a structure in which: ##STR1## In the organopolysiloxane, there is one silicon atom bonded to an aliphatic unsaturated hydrocarbon group. The molecular chain of the organopolysiloxane contains one or more silicon atoms bearing an aromatic hydrocarbon group. The proportion of aromatic hydrocarbon groups in side chains in the molecular chain of the organopolysiloxane is preferably 1 to 20%, more preferably 2 to 10%, and particularly preferably 3 to 7%, based on the total number of silicon atoms (100%) at non-terminal positions in the molecular chain. If there is less than one silicon atom bearing an aromatic hydrocarbon group in the molecular chain, sufficient cold resistance may not be obtained.

[0021] The aliphatic unsaturated hydrocarbon group is preferably a monovalent hydrocarbon group having an aliphatic unsaturated bond and having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and is more preferably an alkenyl group. Examples of the aliphatic unsaturated hydrocarbon group include alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl. Of these, vinyl groups are particularly preferred. The aliphatic unsaturated hydrocarbon group may be bonded to a silicon atom at either the terminal of the molecular chain or a silicon atom in the middle of the molecular chain, or may be bonded to both.

[0022] The organic group other than aliphatic hydrocarbons bonded to the silicon atoms of the organopolysiloxane is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms, and containing at least one aromatic hydrocarbon group. Examples of organic groups other than aliphatic hydrocarbons include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aromatic hydrocarbon groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as fluorine, bromine, or chlorine, or with cyano groups, such as chloromethyl, chloropropyl, bromoethyl, trifluoropropyl, and cyanoethyl. Methyl and phenyl groups are particularly preferred.

[0023] The organopolysiloxane has a kinematic viscosity at 25°C of 50 to 100,000 mm 2 / s, preferably 100 to 30,000 mm 2 / s. The kinematic viscosity is 50 mm 2 If the viscosity is less than 100,000 mm / s, the physical properties of the silicone composition will be reduced, and 2 If the viscosity exceeds 1 / s, the silicone composition will have poor extensibility.

[0024] The molecular structure of the organosiloxane is not particularly limited as long as it has the above properties, and examples of the molecular structure include a linear structure, a branched structure, and a linear structure having a partially branched or cyclic structure. As for those having such a molecular structure, particularly preferred are those having a linear structure in which the main chain is composed of repeating diorganosiloxane units and both molecular chain terminals are blocked with triorganosiloxy groups. The linear organopolysiloxane may also have a partially branched or cyclic structure.

[0025] The organopolysiloxane of component (B) can be used alone or in combination of two or more. The blend amount of component (B) is preferably 40 to 900 parts by mass, and more preferably 60 to 250 parts by mass, per 100 parts by mass of component (A).

[0026] Component (C) is an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms (SiH groups) per molecule, particularly preferably 2 to 100, and even more preferably 2 to 50. Any organohydrogenpolysiloxane may be used as long as the SiH groups in the molecule can undergo an addition reaction with the aliphatic unsaturated hydrocarbon groups in components (A) and (B) described above in the presence of a platinum group metal catalyst, component (E) described below, to form a crosslinked structure.

[0027] The molecular structure of the organohydrogenpolysiloxane is not particularly limited as long as it has the above properties, and examples of the molecular structure include a linear structure, a branched structure, a cyclic structure, a linear structure having a partially branched or cyclic structure, etc. The molecular structure is preferably a linear structure or a cyclic structure.

[0028] The organohydrogenpolysiloxane preferably has a kinematic viscosity at 25°C of 1 to 1,000 mm 2 / s, more preferably 10 to 300 mm 2 / s. The kinematic viscosity is 1 mm 2 / s or more, there is no risk of the physical properties of the silicone composition being reduced, and 2 / s or less, there is no risk of the silicone composition having poor extensibility.

[0029] The organic group bonded to the silicon atom of the organohydrogenpolysiloxane may be an unsubstituted or substituted monovalent hydrocarbon group other than an aliphatic unsaturated hydrocarbon group. Particularly preferred are unsubstituted or substituted monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. Examples of the organic group include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and dodecyl; aryl groups such as phenyl; aralkyl groups such as 2-phenylethyl and 2-phenylpropyl; and groups in which some or all of the hydrogen atoms have been substituted with halogen atoms such as fluorine, bromine, and chlorine, cyano groups, and epoxy ring-containing organic groups (glycidyl or glycidyloxy-substituted alkyl groups), such as chloromethyl, chloropropyl, cyanoethyl, 2-glycidoxyethyl, 3-glycidoxypropyl, and 4-glycidoxybutyl. Among these, methyl and 3-glycidoxypropyl groups are preferred.

[0030] The organohydrogenpolysiloxane of component (C) may be used either alone or in combination of two or more different compounds.

[0031] The amount of organohydrogenpolysiloxane in component (C) is such that the ratio of the number of SiH groups in component (C) to the total number of aliphatic unsaturated hydrocarbon groups in components (A) and (B) is 0.4 to 5, preferably 0.7 to 4.5, and more preferably 0.9 to 4. If the amount of component (C) is less than the above-mentioned lower limit of 0.4, the addition reaction may not proceed sufficiently, resulting in insufficient crosslinking and poor curing. On the other hand, if the amount exceeds the above-mentioned upper limit of 5, the crosslinked structure may become non-uniform and the shelf life of the composition may be significantly reduced.

[0032] Component (D) Component (D) is an organosilane represented by the following general formula (1): 1 a Si(OR 2 ) 4-a (1) (In formula (1), R 1is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and R 1 may be the same or different. 2 is an alkyl group having 1 to 20 carbon atoms which may have a substituent or a cycloalkyl group having 3 to 20 carbon atoms which may have a substituent, R 2 may be the same or different, and a is a number from 1 to 3.

[0033] Component (D) is used as a wetter (dispersant), and components (A) and (B) have poor wettability with fillers, so sufficient loading cannot be achieved unless a wetter is added before mixing. Addition of the organosilane of formula (1) has the effect of significantly increasing the loading of fillers of components (G) and (H), which will be described later.

[0034] Here, in the above formula (1), R 1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably an alkyl group. 2 is an alkyl group having 1 to 20 carbon atoms which may have a substituent or a cycloalkyl group having 3 to 20 carbon atoms which may have a substituent, an alkyl group having 1 to 6 carbon atoms is preferred, and a methyl group or an ethyl group is particularly preferred. In the above formula (1), a is 1, 2 or 3, and preferably 1.

[0035] Specific examples of organosilanes represented by the general formula (1) include the following: n H 2n+1 SiX3 (1-1) C n H 2n+1 Si(CH3)X2 (1-2) C n H 2n+1 Si(CH3)2X (1-3) In the formulas (1-1), (1-2) and (1-3), X is a methoxy group (CH3O) or an ethoxy group (C2H5O), and n is a number from 1 to 20.

[0036] The amount of organosilane (D) blended is in the range of 0.01 to 100 parts by mass, preferably 0.1 to 70 parts by mass, and more preferably 1 to 30 parts by mass, per 100 parts by mass of the total of components (A) and (B). Less than 0.01 part by mass results in poor wettability and may increase the modulus of elasticity when exposed to high temperatures. Blending more than 100 parts by mass does not increase the effect and is uneconomical, and may cause voids to form at high temperatures.

[0037] Component (E) Component (E) is a platinum group metal catalyst that promotes the addition reaction between the above-mentioned components (A) and (B) and component (C). Conventional platinum group metal catalysts used in addition reactions can be used. Examples of platinum group metal catalysts include platinum-based, palladium-based, and rhodium-based catalysts, with platinum or platinum compounds being preferred, as they are relatively readily available. Examples of platinum or platinum compounds include platinum itself, platinum black, chloroplatinic acid, platinum-olefin complexes, platinum-alcohol complexes, and platinum coordination compounds. Platinum group metal catalysts may be used alone or in combination of two or more.

[0038] The amount of component (E) blended should be an effective amount as a catalyst, i.e., an effective amount necessary to promote the addition reaction and cure the thermally conductive silicone composition of the present invention. This effective amount is preferably 0.1 to 500 ppm, more preferably 1 to 200 ppm, and even more preferably 10 to 100 ppm, calculated as platinum group metal atoms by mass in the composition. If the amount of catalyst is less than the lower limit, the catalytic effect may not be obtained. On the other hand, exceeding the upper limit does not increase the catalytic effect and is uneconomical, so is not preferred.

[0039] Component (F) Component (F) is a reaction inhibitor that suppresses the progress of the hydrosilylation reaction at room temperature, thereby extending shelf life and pot life. This reaction inhibitor can be any of the conventional reaction inhibitors used in addition-curable silicone compositions. Examples of reaction inhibitors include acetylene compounds such as acetylene alcohols (e.g., ethynylmethyldecylcarbinol, 1-ethynyl-1-cyclohexanol, 3,5-dimethyl-1-hexyn-3-ol), nitrogen compounds such as tributylamine, tetramethylethylenediamine, and benzotriazole, organophosphorus compounds such as triphenylphosphine, oxime compounds, and organochloro compounds.

[0040] The amount of component (F) blended is 0.05 to 5 parts by mass, and preferably 0.1 to 2 parts by mass, per 100 parts by mass of the total of components (A) and (B). If the amount of reaction inhibitor is less than 0.05 parts by mass, the desired sufficient shelf life and pot life may not be achieved, while if it is more than 5 parts by mass, the curability of the silicone composition may be reduced.

[0041] The reaction inhibitor may be diluted with a conventional organo(poly)siloxane, toluene, or the like to improve dispersibility in the silicone composition.

[0042] Component (G) Component (G) is an inorganic filler with an average particle size of 3 μm or less, and is preferably at least one inorganic filler selected from the group consisting of metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and carbon allotropes. Component (G) preferably has a thermal conductivity of 10 W / mK or more. This is because if the thermal conductivity of the inorganic filler is 10 W / mK or more, the thermal conductivity of the thermally conductive silicone composition itself will be high. Examples of such inorganic fillers include aluminum powder, copper powder, iron powder, nickel powder, gold powder, metal silicon powder, aluminum nitride powder, boron nitride powder, alumina powder, diamond powder, carbon powder, indium powder, gallium powder, and zinc oxide powder. Any inorganic filler with a thermal conductivity of 10 W / mK or more may be used, and one or a combination of two or more types may be used.

[0043] From the viewpoints of thermal conductivity and availability, component (G) is preferably aluminum powder, alumina powder, or zinc oxide powder, more preferably aluminum powder and / or zinc oxide powder, and even more preferably zinc oxide powder.

[0044] The average particle size of component (G) is 3 μm or less, preferably in the range of 0.1 to 3 μm. If the average particle size is 0.1 μm or more, the resulting composition will be grease-like and have good extensibility, while if it is 3 μm or less, the ratio with component (H) will result in close packing, reducing the thermal resistance of the thermal grease and reducing the risk of a decrease in thermal performance. In the present invention, the average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer, such as the Microtrac MT3300EX manufactured by Nikkiso Co., Ltd., and is the volume-average diameter based on volume. The shape of component (G) may be any shape, including amorphous and spherical.

[0045] The amount of component (G) filled is preferably in the range of 30 to 700 parts by mass, more preferably in the range of 40 to 600 parts by mass, and particularly more preferably in the range of 50 to 500 parts by mass, per 100 parts by mass of the total of components (A) and (B).

[0046] Component (H) Component (H) is an inorganic filler with an average particle size of more than 3 μm and less than 150 μm, and is at least one thermally conductive filler selected from the group consisting of metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and carbon allotropes. It is preferable to use component (H) with a thermal conductivity of 10 W / mK or higher. This is because if the thermal conductivity of the inorganic filler is 10 W / mK or higher, the thermal conductivity of the thermally conductive silicone composition itself will be high. Examples of such inorganic fillers include aluminum powder, copper powder, iron powder, nickel powder, gold powder, metal silicon powder, aluminum nitride powder, boron nitride powder, alumina powder, diamond powder, carbon powder, indium powder, gallium powder, and zinc oxide powder. Any inorganic filler with a thermal conductivity of 10 W / mK or higher may be used, and one or a combination of two or more types may be used.

[0047] From the viewpoint of thermal conductivity and availability, component (H) is preferably aluminum powder, alumina powder, or zinc oxide powder, more preferably aluminum powder and / or zinc oxide powder, and even more preferably aluminum powder.

[0048] The average particle size of component (H) is in the range of more than 3 μm to 150 μm or less, preferably more than 3 μm to 100 μm or less, and more preferably more than 3 μm to 80 μm or less. If the average particle size is more than 3 μm, the resulting silicone composition will be grease-like and have good extensibility, while if it is 150 μm or less, the thermal resistance of the heat-dissipating grease will increase, reducing the risk of a decrease in thermal performance. In the present invention, the average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer, such as the Microtrac MT3300EX manufactured by Nikkiso Co., Ltd., and is the volume-average diameter based on volume. The shape of component (H) may be any shape, including amorphous and spherical.

[0049] The amount of component (H) filled is preferably in the range of 270 to 2,300 parts by mass, more preferably 360 to 900 parts by mass, and particularly preferably 500 to 2,500 parts by mass, per 100 parts by mass of the total of components (A) and (B).

[0050] The total amount of components (G) and (H) filled is preferably in the range of 300 to 3,000 parts by mass, more preferably 400 to 2,800 parts by mass, and particularly preferably 500 to 2,500 parts by mass, per 100 parts by mass of the total of components (A) and (B). If the amount is less than the lower limit of 300 parts by mass, the thermal conductivity of the composition will be low, while if it exceeds the upper limit of 3,000 parts by mass, the viscosity of the composition will increase, resulting in poor extensibility.

[0051] Other Components In addition to the components (A) to (H) described above, the thermally conductive silicone composition of the present invention may further contain one or more thermally conductive inorganic fillers other than components (G) and (H). Furthermore, for the purpose of improving the filling ability of the thermally conductive inorganic filler or imparting adhesive properties to the composition, hydrolyzable organopolysiloxanes, various modified silicones, hydrolyzable organosilanes, etc. may be blended. Furthermore, a solvent may be blended to adjust the viscosity of the composition. Furthermore, to prevent deterioration of the silicone composition, a conventionally known antioxidant, such as 2,6-di-tert-butyl-4-methylphenol, may be added as needed. Furthermore, dyes, pigments, flame retardants, anti-settling agents, thixotropy improvers, etc. may be blended as needed.

[0052] [Production Method] There are no particular limitations on the method for producing the thermally conductive silicone composition of the present invention, but examples include methods in which components (A) through (H), and, if necessary, other components, are mixed in a mixer such as a Trimix, Twinmix, or Planetary Mixer (all of which are registered trademarks of mixers manufactured by Inoue Seisakusho Co., Ltd.), an Ultra Mixer (a registered trademark of mixers manufactured by Mizuho Kogyo Co., Ltd.), or a Hivis Dispermix (a registered trademark of mixers manufactured by Tokushu Kika Kogyo Co., Ltd.).

[0053] The thermally conductive silicone composition of the present invention may be mixed while being heated, and although there are no particular restrictions on the heating conditions, the temperature is typically 25 to 220°C, preferably 40 to 200°C, and more preferably 50 to 200°C, and the heating time is typically 3 minutes to 24 hours, preferably 5 minutes to 12 hours, and more preferably 10 minutes to 6 hours. Degassing may also be performed during heating.

[0054] [Characteristics of the Thermally Conductive Silicone Composition] The thermally conductive silicone composition of the present invention obtained in this manner should have a viscosity measured at 25°C in the range of 100 to 1,000 Pa·s, preferably 150 to 800 Pa·s, and more preferably 200 to 600 Pa·s. If the viscosity is at or above the lower limit of the above range, there is little risk of the thermally conductive filler settling over time during storage, which would result in poor workability. If the viscosity is at or below the upper limit of the above range, there is little risk of poor extensibility and poor workability.

[0055] The thermally conductive silicone composition of the present invention has a thermal conductivity of 0.5 to 10 W / mK.

[0056] The thermally conductive silicone composition of the present invention is, for example, heat-cured at 125°C for 90 minutes to produce a 2 mm thick sheet, and then the elongation at break after curing is measured using a No. 2 dumbbell shape as specified in JIS K 6251. If the elongation at break is at or above the above lower limit, peeling is unlikely to occur during high-temperature storage, and there is little risk of deterioration in thermal resistance.

[0057] Furthermore, the thermally conductive silicone composition of the present invention is preferably one that does not contain voids after, for example, being sandwiched between glass plates, pressed at room temperature for 15 minutes, heated at 150°C for 60 minutes, cooled to room temperature, and then heated at 260°C for 5 minutes, which is repeated five times. Such a thermally conductive silicone composition can maintain its heat dissipation performance even under the conditions described above.

[0058] The present invention will be specifically described below with reference to examples (synthesis examples, formulation examples) and comparative examples, but the present invention is not limited to the following examples. In the following examples, the kinematic viscosity is the value measured at 25°C using an Ubbelohde-type Ostwald viscometer. The average particle size is the median diameter D50 measured using a laser diffraction / scattering particle size analyzer (LA-750: manufactured by Horiba, Ltd.). "Parts" means "parts by mass," Vi represents a vinyl group, and Ph represents a phenyl group.

[0059] Component (A) A-1: ​​A copolymer of the following formula (A-1), both ends of which are capped with dimethylvinyl groups (vinyl group amount: 0.0071 mol / 100 g), having a kinematic viscosity of 5000 mm at 25°C. 2 / s diphenyl dimethyl polysiloxane (Wherein, a = 18.7, b = 320, and a / (a + b) = 0.055.)

[0060] A-2: A copolymer of the following formula (A-2), both ends of which are capped with dimethylvinyl groups (vinyl group amount: 0.0130 mol / 100 g), having a kinematic viscosity of 1000 mm at 25°C.2 / s diphenyl dimethyl polysiloxane (Wherein, a = 6.7, b = 216.3, and a / (a + b) = 0.030.)

[0061] A-3: A copolymer represented by the following formula (A-3), both ends of which are capped with dimethylvinyl groups (vinyl group amount: 0.0037 mol / 100 g), having a kinematic viscosity of 20,000 mm at 25°C. 2 / s diphenyl dimethyl polysiloxane (Wherein, a = 31 + b = 1000, and a / (a + b) = 0.030.)

[0062] Component (B) B-1: Represented by the following formula (B-1), one end of which is blocked with a dimethylvinylsilyl group (vinyl group amount 0.0047 mol / 100 g) and the other end of which is blocked with a trimethylsilyl group, and has a kinematic viscosity of 700 mm at 25°C. 2 / s diphenyl dimethyl polysiloxane (In the formula, X+Y=2.0, c=7.5, d=141.6, c / (c+d)=0.050, and Ph represents a phenyl group.)

[0063] Component (C) C-1: A component having a kinematic viscosity at 25°C of 33 mmHg as shown in the following formula (C-1): 2 / s organohydrogenpolysiloxane (Si—H group amount 0.0010 mol / g)

[0064] C-2: A kinematic viscosity at 25°C represented by the following formula (C-2) of 36 mm 2 / s organohydrogenpolysiloxane (Si-H group amount 0.0014 mol / g)

[0065] Component (D) D-1: Organosilane represented by the following formula (D-1):

[0066] Component (E) E-1: A platinum-divinyltetramethyldisiloxane complex having a kinematic viscosity of 600 mm at 25°C, in which both ends are capped with dimethylvinylsilyl groups. 2 / s solution (platinum atom content: 1 mass % as platinum atom)

[0067] Component (F) F-1: 1-ethynyl-1-cyclohexanol represented by the following formula (F-1):

[0068] (G) Component G-1: Zinc oxide powder with an average particle size of 0.3 μm (thermal conductivity of zinc oxide is 25 W / mK)

[0069] Component (H) H-1: Aluminum powder with an average particle size of 10 μm (thermal conductivity of aluminum is 236 W / mK)

[0070] Examples 1 to 8 Preparation of Silicone Compositions Silicone compositions were prepared by blending the components (A) to (H) in the amounts shown in Tables 1 and 2 below using the method described below. The SiH / SiVi (number ratio) refers to the ratio of the total number of SiH groups in component (C) to the total number of aliphatic unsaturated hydrocarbon groups in components (A) and (B). Components (A), (B), (D), (G), and (H) were placed in a 5-liter planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.) and mixed at 70°C for 1 hour. After cooling to 40°C or below, components (F), (E), and (C) were added and mixed until uniform, preparing each silicone composition.

[0071] Comparative Example 1 A silicone composition was prepared in the same manner as in Example 1, except that in Example 1, dimethylpolysiloxane (a-1) in which a = 0 and b = 450.4 in formula (A-1) was used instead of component (A-1), and dimethylpolysiloxane (b-1) in which c = 0 and d = 216.2 in formula (B-1) was used instead of component (B-1).

[0072] Comparative Example 2 A silicone composition was prepared in the same manner as in Example 4, except that, as in Comparative Example 1, dimethylpolysiloxane was used.

[0073] Comparative Example 3 A silicone composition was prepared in the same manner as in Example 7, except that, as in Comparative Example 1, dimethylpolysiloxane was used.

[0074] Comparative Example 4 A silicone composition was prepared in the same manner as in Example 8, except that, as in Comparative Example 1, dimethylpolysiloxane was used.

[0075] [Viscosity] The absolute viscosity of each silicone composition was measured at 25°C using a Malcom viscometer (Type PC-1TL).

[0076] [Thermal Conductivity] Each silicone composition was wrapped in plastic wrap in an uncured state, and the thermal conductivity of each composition was measured at 25°C using a thermal property measuring device (in this example, a TPS-2500S manufactured by Kyoto Electronics Manufacturing Co., Ltd.) that utilizes the hot disk method.

[0077] Preparation of Cured Products Each silicone composition was heated at 125°C for 90 minutes to prepare a cured product having a thickness of 2 mm.

[0078] [Cold Resistance] A cured product of each silicone composition was prepared (for example, a 2 mm thick sample cut to an appropriate size was prepared), and TMA (thermomechanical analysis) was performed at temperatures from -80°C to 0°C using a TMA4000SE manufactured by NETZSCH. In the case of a cold-resistant material, the TMA increases at a constant rate, that is, microcrystals are not formed in the low temperature range, the apparent crosslink density does not increase, and no sudden increase in the value is observed. This is considered to be cold-resistant. On the other hand, in a material that does not have cold resistance, contact occurs between the main polymers upon cooling, microcrystals are formed, and the apparent crosslink density increases. As a result, a sudden increase in the value is observed when the temperature rises (in this case, a composition in which this phenomenon can be confirmed is considered to have no cold resistance). An example of this determination is shown below. Since the CTE values ​​are measured on the order of several μm, the absolute values ​​vary for each measurement and depending on the composition of the sample. Therefore, the absolute values ​​are not discussed, and cold resistance was determined based on whether the tendency of change shown in FIGS. 1 and 2 was observed from −80 to 0° C.

[0079]

[0080]

[0081] The results in Table 1 clearly demonstrate that the thermally conductive silicone compositions of Examples 1 to 8 are cold resistant. In other words, when mounted in electronic component packages or power modules, they offer higher reliability than conventional products in operating environments at low temperatures.

[0082] On the other hand, the thermally conductive silicone compositions of Comparative Examples 1 to 4 in Table 2 lacked cold resistance at around -40°C. In other words, reliability decreased when electronic component packages or power modules were mounted in low-temperature environments.

[0083] Therefore, when the thermally conductive silicone composition of the present invention is used in low-temperature environments, it is possible to expect improved cold resistance because rapid expansion that accompanies temperature increases is suppressed. These properties make it particularly suitable for use as a thermal grease for electronic component packages and power modules that operate in low-temperature environments.

Claims

1. A thermally conductive silicone composition containing the following components (A), (B), (C), (D), (E), (F), (G), and (H): (A) a silicone having, per molecule, at least two silicon atoms bonded to aliphatic unsaturated hydrocarbon groups, and one or more silicon atoms bearing an aromatic hydrocarbon group in the molecular chain, and having a kinematic viscosity at 25°C of 50 to 100,000 mm 2 (B) an organopolysiloxane having, per molecule, a silicon atom to which one aliphatic unsaturated hydrocarbon group is bonded, and containing, in the molecular chain, one or more silicon atoms having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 mm 2 (C) an organohydrogenpolysiloxane having two or more silicon-bonded hydrogen atoms (SiH groups) per molecule: an amount such that the number of SiH groups in component (C) is 0.4 to 5 relative to the total number of aliphatic unsaturated hydrocarbon groups in components (A) and (B); and (D) an organosilane represented by the following general formula (1): 0.01 to 100 parts by mass per 100 parts by mass of the total of components (A) and (B): R 1 a Si(OR 2 ) 4-a (1) (In formula (1), R 1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and R 1 may be the same or different. 2 is an alkyl group having 1 to 20 carbon atoms which may have a substituent or a cycloalkyl group having 3 to 20 carbon atoms which may have a substituent, R 2 may be the same or different. a is a number from 1 to 3.) (E) Platinum group metal catalyst: an effective amount (F) Reaction inhibitor: 0.05 to 5.0 parts by mass per 100 parts by mass of the total of components (A) and (B) (G) Inorganic filler having an average particle size of 3 μm or less (H) Inorganic filler having an average particle size of more than 3 μm to 150 μm or less: the total of components (G) and (H) is 300 to 3,000 parts by mass per 100 parts by mass of the total of components (A) and (B) 2. The composition according to claim 1, wherein component (G) is zinc oxide powder.

3. The composition according to claim 1, wherein component (H) is aluminum powder.

4. The composition according to claim 1, wherein component (F) is a reaction inhibitor selected from the group consisting of acetylene compounds, nitrogen compounds, organic phosphorus compounds, oxime compounds and organic chloro compounds.

5. A cured product of the composition according to any one of claims 1 to 4.