WO2025187619A1 - Thermally conductive silicone composition - Google Patents

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

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

Many electronic components generate heat during use, and heat must be removed to ensure they function properly. In particular, integrated circuit elements such as CPUs and GPUs used in personal computers and smartphones are generating increasing amounts of heat due to faster operating frequencies and smaller packages, making heat countermeasures and design important issues. Furthermore, with the advancement of electrification in automobiles in recent years, the use of many electronic components means that electronic components are sometimes used in harsher conditions, such as high-temperature, high-humidity environments.

There are many methods for removing this heat. For electronic components that generate a particularly large amount of heat, a method has been disclosed in which heat is released 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 (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 that is silicone-based and contains zinc oxide, aluminum, or alumina powder.

In order to create a silicone-based thermally conductive material with high thermal conductivity, it is necessary to highly fill it with thermally conductive filler. However, simply attempting to fill it highly will significantly reduce the fluidity of the thermoelectrically conductive material, making it difficult to work with, for example, in terms of application (dispensability, screen printing), and will also cause problems such as an 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) and disperse it into the silicone base polymer, thereby maintaining the fluidity of the thermally conductive material.

In recent years, the automotive industry has been moving toward electrification, and even in cold-weather vehicles, it is expected that integrated circuit devices such as CPUs and GPUs, as well as electronic components that generate a lot 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 greater cold resistance for use 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 causes the silicone components to crystallize, increasing the material's hardness and reducing molecular flexibility, resulting in poor cold resistance. Furthermore, typical silicone materials exhibit a thermal expansion trend that deviates from a constant rate of increase around -40°C, generating stress at the interface of the heat-dissipating material, especially when the temperature is repeatedly changed between low and high temperatures. This causes the interface to deteriorate when the temperature is repeatedly changed between low and high temperatures, resulting in reduced heat dissipation performance.

JP 2016-053140 A

Therefore, the object of the present invention is to provide a thermally conductive silicone composition that cures into a stable product even in low-temperature environments. In particular, the object is 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, and that can relieve stress on the substrate.

As a result of extensive research conducted by the present inventors in order to achieve the above-mentioned object, they discovered that the silicone composition described below exhibits a constant 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, thereby completing the present invention.
That is, the present invention provides the following thermally conductive silicone composition.

[1]
A thermally conductive silicone composition comprising the following components (A), (B), (C), (D), (E), (F), (G), and (H):
(A) Organopolysiloxanes having per molecule a silicon atom to which at least two aliphatic unsaturated hydrocarbon groups are bonded, and one or more silicon atoms in the molecular chain having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 ^{mm 2} /s. (B) Organopolysiloxanes having per molecule a silicon atom to which one aliphatic unsaturated hydrocarbon group is bonded, and one or more silicon atoms in the molecular chain having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 mm ^{2 /s.} (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); (D) an organosilane represented by the following general formula (1): R ¹ _a Si(OR 2 ) 4- _a (1): 0.01 to 100 parts by mass per 100 parts by mass of the total of components ( ^A ) and (B):
(In formula (1), ^R1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and ^R1 's may be the same or different. ^R2 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, and R2 ^'s may be the same or different. a is a number from 1 to 3.)
(E) Platinum group metal catalyst: 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 amount of components (G) and (H) is 300 to 3,000 parts by mass per 100 parts by mass of the total amount 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 the component (F) is a reaction inhibitor selected from an acetylene compound, a nitrogen compound, an organic phosphorus compound, an oxime compound, and an organic chloro compound.

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

By using the thermally conductive silicone composition of the present invention, it is possible to obtain a cured product in which the expansion at around -40°C does not deviate from a constant rate of increase, but rather shows a constant change, and in which thickness does not change 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 placing stress on the substrate.

1 is a graph (vertical axis: displacement, horizontal axis: temperature) showing an example of the TMA measurement results of a cold-resistant composition. 1 is a graph (vertical axis: displacement, horizontal axis: temperature) showing an example of the TMA measurement results of a composition that does not have cold resistance.

The present invention is described in further detail below.

Component (A) Component (A) is an organopolysiloxane having, per molecule, at least two silicon atoms bonded to aliphatic unsaturated hydrocarbon groups, one or more silicon atoms bearing an aromatic hydrocarbon group in the molecular chain, and a kinematic viscosity at 25°C of 50 to 100,000 ^mm2 /s. The number of silicon atoms bonded to aliphatic unsaturated hydrocarbon groups in the organopolysiloxane is two or more, preferably 2 to 100, and more preferably 2 to 50. If there are fewer than two, the ratio between the number of unsaturated hydrocarbon groups and the hydrogen atoms bonded to silicon atoms will be disrupted, and sufficient curability and cold resistance may not be achieved. The organopolysiloxane has one or more silicon atoms bearing an aromatic hydrocarbon group in the 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%, based on the total number of non-terminal silicon atoms (100%) 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.

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 aliphatic unsaturated hydrocarbon groups 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 either a silicon atom at the end of the molecular chain, a silicon atom in the middle of the molecular chain, or both.

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. Methyl groups and phenyl groups are particularly preferred.

The organopolysiloxane has a kinematic viscosity of 50 to 100,000 ^{mm 2} /s, preferably 100 to 30,000 ^{mm 2} /s, at 25° C. If the kinematic viscosity is less than 50 mm ² /s, the physical properties of the silicone composition will be impaired, and if it exceeds 100,000 mm ² /s, the extensibility of the silicone composition will be poor.

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

The molecular structure of the organosiloxane is not particularly limited as long as it has the above properties. Examples of the molecular structure include a linear structure, a branched structure, and a linear structure having a partially branched or cyclic structure. Those having such a molecular structure are particularly preferred, with the main chain consisting of repeating diorganosiloxane units and a linear structure in which both ends of the molecular chain are capped with triorganosiloxy groups. Organopolysiloxanes having such a linear structure may also have a partially branched or cyclic structure.

The organopolysiloxane of component (A) may use either a single compound, or a combination of two or more different compounds.
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 %.

Component (B) Component (B) is an organopolysiloxane having one silicon atom bonded to an aliphatic unsaturated hydrocarbon group per molecule, one or more silicon atoms bearing an aromatic hydrocarbon group in the molecular chain, and a kinematic viscosity at 25°C of 50 to 100,000 ^mm2 /s. In this organopolysiloxane, there is one silicon atom bonded to an aliphatic unsaturated hydrocarbon group. The organopolysiloxane also has one or more silicon atoms bearing an aromatic hydrocarbon group in the 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%, 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 achieved.

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 aliphatic unsaturated hydrocarbon groups 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 the end of the molecular chain, a silicon atom in the middle of the molecular chain, or both.

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.

The organopolysiloxane has a kinematic viscosity of 50 to 100,000 ^{mm 2} /s, preferably 100 to 30,000 ^{mm 2} /s, at 25° C. If the kinematic viscosity is less than 50 mm ² /s, the physical properties of the silicone composition will be impaired, and if it exceeds 100,000 mm ² /s, the extensibility of the silicone composition will be poor.

The molecular structure of the organosiloxane is not particularly limited as long as it has the above properties. Examples of the molecular structure include a linear structure, a branched structure, and a linear structure having a partially branched or cyclic structure. Those having such a molecular structure are particularly preferred, with the main chain consisting of repeating diorganosiloxane units and a linear structure in which both ends of the molecular chain are capped with triorganosiloxy groups. Organopolysiloxanes having such a linear structure may also have a partially branched or cyclic structure.

The organopolysiloxane of component (B) may use either a single compound, or a combination of two or more different compounds.
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).

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.

The molecular structure of the organohydrogenpolysiloxane is not particularly limited as long as it has the above properties. Examples of the molecular structure include a linear structure, a branched structure, a cyclic structure, and a linear structure having a partially branched or cyclic structure. A linear or cyclic structure is preferred as the molecular structure.

The organohydrogenpolysiloxane preferably has a kinematic viscosity at 25° C. of 1 to 1,000 ^{mm 2} /s, and more preferably 10 to 300 mm ² /s. If the kinematic viscosity is 1 mm ² /s or higher, there is no risk of the physical properties of the silicone composition being reduced, and if it is 1,000 mm ² /s or lower, there is no risk of the silicone composition having poor extensibility.

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. In particular, an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, is preferred. Examples of organic groups 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, the methyl group and 3-glycidoxypropyl group are preferred.

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

The amount of organohydrogenpolysiloxane of component (C) to be blended is an amount 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 lower limit of 0.4, the addition reaction may not proceed sufficiently, resulting in insufficient crosslinking and poor curing, whereas if the amount exceeds the upper limit of 5, the crosslinked structure may become non-uniform and the shelf life of the composition may be significantly reduced.

Component (D) The component (D) is an organosilane represented by the following general formula (1).
R ¹ _a Si(OR ² ) _4-a (1)
(In formula (1), ^R1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and ^R1 's may be the same or different. ^R2 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, and R2 ^'s may be the same or different. a is a number from 1 to 3.)

Component (D) is used as a wetter (dispersant). Components (A) and (B) have poor wettability with fillers, and sufficient loading cannot be achieved without adding a wetter before mixing. Adding the organosilane of formula (1) above has the effect of significantly increasing the loading of the fillers of components (G) and (H), described below.

In the above formula (1), R ¹ is a monovalent hydrocarbon group having 1 to 20 carbon atoms, and is preferably an alkyl group.
In the above formula (1), ^R2 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 is preferably 1.

Specific examples of organosilanes represented by the above general formula (1) include the following:
C _n H _2n+1 SiX ₃ (1-1)
C _n H _2n+1 Si(CH ₃ )X ₂ (1-2)
C _n H _2n+1 Si(CH ₃ ) ₂ X (1-3)
In the formulas (1-1), (1-2) and (1-3), X is a methoxy group (CH ₃ O) or an ethoxy group (C ₂ H ₅ O), and n is a number from 1 to 20.

The amount of organosilane (component (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 parts 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.

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.

The amount of component (E) blended should be an effective amount as a catalyst, i.e., an 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, by mass, converted into platinum group metal atoms in the composition. If the amount of catalyst is less than the lower limit above, the catalytic effect may not be achieved. Furthermore, exceeding the upper limit above does not increase the catalytic effect, and is therefore uneconomical and undesirable.

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.

The amount of component (F) blended is 0.05 to 5 parts by mass, 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 shelf life and pot life may not be achieved, and if it is more than 5 parts by mass, the curability of the silicone composition may be reduced.

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

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.

In terms 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.

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, which will reduce the thermal resistance of the thermal grease and reduce 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. Component (G) may be of any shape, including amorphous and spherical.

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

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.

In terms 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.

The average particle size of component (H) is in the range of more than 3 μm to 150 μm, preferably more than 3 μm to 100 μm, and more preferably more than 3 μm to 80 μm. 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 be high, 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. Component (H) may be of any shape, including amorphous and spherical.

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).

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.

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.

[Manufacturing 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.).

The thermally conductive silicone composition of the present invention may also be mixed while being heated. While 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.

[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 could result in poor workability. If the viscosity is below the upper limit of the above range, there is little risk of poor extensibility and poor workability.

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

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, as measured by creating a No. 2 dumbbell shape as specified in JIS K6251, is preferably 50% or more, more preferably 65% or more, and even more preferably 80% or more. If the elongation at break is above the above lower limit, peeling is less likely to occur during high-temperature storage, and there is little risk of deterioration in thermal resistance.

Furthermore, the thermally conductive silicone composition of the present invention preferably contains no voids after, for example, sandwiching it between glass plates, applying pressure at room temperature for 15 minutes, heating at 150°C for 60 minutes, cooling it to room temperature, and then heating 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 above conditions.

The present invention will be explained in detail below with 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 vinyl groups, and Ph represents phenyl groups.

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

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

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

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

(C) Component C-1:
An organohydrogenpolysiloxane (Si—H group amount: 0.0010 mol/g) represented by the following formula (C-1) and having a kinematic viscosity of 33 mm ² /s at 25° C.

C-2:
An organohydrogenpolysiloxane (Si—H group amount: 0.0014 mol/g) represented by the following formula (C-2) and having a kinematic viscosity of 36 mm ² /s at 25° C.

(D) Component D-1:
An organosilane represented by the following formula (D-1):

(E) Component E-1:
A solution (platinum atom content: 1 mass % as platinum atoms) of a platinum-divinyltetramethyldisiloxane complex dissolved in dimethylpolysiloxane having a kinematic viscosity of 600 mm ² /s at 25°C and both ends capped with dimethylvinylsilyl groups.

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

(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)

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

[Examples 1 to 8]
Preparation of Silicone Composition Silicone compositions were prepared by blending the components (A) to (H) in the amounts shown in Tables 1 and 2 using the method described below. Note that SiH/SiVi (number ratio) is 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 for 1 hour at 70°C. After cooling to 40°C or below, components (F), (E), and (C) were added and mixed until uniform, to prepare each silicone composition.

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

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

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

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

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

[Thermal conductivity]
Each silicone composition was wrapped in plastic wrap in its 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.

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.

[Cold resistance]
Cured products of each silicone composition were prepared (for example, 2 mm thick samples cut to an appropriate size were prepared), and TMA (thermomechanical analysis) was performed at temperatures from -80°C to 0°C using a NETZSCH TMA4000SE. For cold-resistant materials, 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, for materials that are not cold-resistant, contact occurs between the main polymers upon cooling, microcrystals are formed, and the apparent crosslink density increases. This results in a sudden increase in the value when the temperature rises (in this case, compositions in which this phenomenon can be confirmed are considered to be non-cold-resistant). 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.

The results in Table 1 clearly show 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 low-temperature operating environments.

On the other hand, the thermally conductive silicone compositions of Comparative Examples 1 to 4 in Table 2 lacked cold resistance at temperatures around -40°C. This means that reliability is reduced when operating in low-temperature environments when mounted in electronic component packages or power modules.

As a result, when the thermally conductive silicone composition of the present invention is used in low-temperature environments, it is possible to expect improved cold resistance as it suppresses rapid expansion that occurs with temperature increases. Because of these properties, it is particularly suitable for use as a thermal grease for electronic component packages and power modules that operate in low-temperature environments.

Claims (5)

A thermally conductive silicone composition comprising the following components (A), (B), (C), (D), (E), (F), (G), and (H):
(A) Organopolysiloxanes having per molecule a silicon atom to which at least two aliphatic unsaturated hydrocarbon groups are bonded, and one or more silicon atoms in the molecular chain having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 ^{mm 2} /s. (B) Organopolysiloxanes having per molecule a silicon atom to which one aliphatic unsaturated hydrocarbon group is bonded, and one or more silicon atoms in the molecular chain having an aromatic hydrocarbon group, and having a kinematic viscosity at 25°C of 50 to 100,000 mm ^{2 /s.} (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); (D) an organosilane represented by the following general formula (1): R ¹ _a Si(OR ² ) 4- _a (1): 0.01 to 100 parts by mass per 100 parts by mass of the total of components (A) and (B):
(In formula (1), ^R1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and ^R1 's may be the same or different. ^R2 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, and R2 ^'s may be the same or different. a is a number from 1 to 3.)
(E) Platinum group metal catalyst: 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); The composition according to claim 1, wherein component (G) is zinc oxide powder. The composition according to claim 1, wherein component (H) is aluminum powder. The composition according to claim 1, wherein component (F) is a reaction inhibitor selected from acetylene compounds, nitrogen compounds, organic phosphorus compounds, oxime compounds, and organic chloro compounds. A cured product of the composition described in any one of claims 1 to 4.