Thermally conductive silicone compositions and methods for making same

Abstract

Provided is a thermally conductive silicone composition for forming a cured product, which exhibits high heat dissipation performance, does not produce voids, and has excellent processability. The thermally conductive silicone composition includes: an organopolysiloxane (A) containing an alkenyl group; a linear organopolysiloxane (B) having two or more hydrosilyl groups in one molecule; a hydrogenated cyclic siloxane (C) having only repeating units of-SiRHO-and having a degree of polymerization of 4 to 8; an addition reaction catalyst (D); and a thermally conductive filler (E). In the composition, the content of the component (C) is 0.5 to 1.8 parts by mass or less and the content of the component (E) is 500 to 3,000 parts by mass or less with respect to 100 parts by mass of the total amount of the components (A) and (B).

Description

Technical Field

[0001] The present invention relates to a thermally conductive silicone composition comprising a thermally conductive filler and a predetermined hydrogenated cyclic siloxane, a method for preparing the composition, and a method for preparing a cured product using the composition. Background Art

[0002] Silicone thermally conductive components (such as gap fillers) are used as thermally conductive materials to fill the gap between a heat generating element and a heat dissipating element. Such components are used to transfer heat from a heat generating element (such as an electric vehicle battery or an electronic device semiconductor) to a heat dissipating component (such as a radiator).

[0003] In order to transfer heat from the heating element to the heat sink, this gap filler needs to always be in contact with the two bodies at the corresponding interface. When used as a heat sink for a battery, the gap filler in an uncured state is usually applied to the surface of a cooling body or a heating body (such as a battery cell or a battery pack) and then compressed between the two bodies. Therefore, the gap filler fills the gap between the two bodies and then undergoes curing and adheres to the two bodies with a firm contact interface, thereby playing a role in transferring heat.

[0004] Typically, such gap fillers are used in heat dissipation of batteries that can generate heat within a temperature increase of approximately 50° C. However, in recent years, gap fillers have also been used for heat dissipation of components such as on-board electrical modules, electronic control units (ECUs) such as inverters, or the like that reach high temperatures of, for example, 180° C. or higher.

[0005] In this case, assuming that the higher heat generation is caused by the higher current, a more effective countermeasure for dissipating the generated heat is required. That is, a higher heat dissipation performance (e.g., 5 W / m·K or more) than that of ordinary heat dissipation materials used for batteries is required. In addition, thermal conductivity must be reliably maintained at high temperatures, and any changes in temperature-dependent physical properties are also expected to be small, and the adhesion of the gap filler at the interface to the heat-generating body and the heat-dissipating body (such as a radiator) is sufficiently high.

[0006] Several silicone products have been developed that exhibit excellent properties even at high temperatures.

[0007] For example, PTL 1 discloses a thermally conductive silicone adhesive composition that provides a cured product with good adhesion and minimal hardness change after aging at 150°C. This composition can be obtained by blending a hydrogenated cyclic siloxane containing oxygen-containing functional groups, such as epoxy groups. However, there is no description of adhesion after aging, and further improvement in thermal conductivity is desired.

[0008] Patent Document 2 discloses a thermally conductive silicone heat dissipation material with improved heat resistance. This material is obtained by surface-treating a thermally conductive inorganic filler having a large specific surface area and a small average particle size with a low molecular weight silane coupling agent. The material is described as having an Asker C hardness of -15 to 0 relative to the initial hardness after aging at 220°C in air for 100 hours, and an Asker C hardness of -20 to +20 relative to the initial hardness after continuous aging at 220°C in air for 500 hours. However, there is no description of adhesiveness, and further improvement of thermal conductivity is desired.

[0009] Reference List

[0010] Patent Literature

[0011] PTL 1: Japanese Patent Application Publication No. 2021-113289

[0012] PTL 2: Japanese Patent No. 6988023 (corresponding to WO 2022 / 049902) Summary of the Invention

[0013] Technical issues

[0014] In order to achieve high heat dissipation, a high degree of thermal conductive filler filling is required. Therefore, the proportion of alkenyl group-containing organopolysiloxane and hydrosilyl group-containing organopolysiloxane as polymer components becomes low.

[0015] As a result, the initial crosslink density achieved through the hydrosilylation reaction tends to decrease. Consequently, the hardness of the composition is low in the initial stages of the reaction, but rapidly increases during exposure to high temperatures. Consequently, voids form between the composition and the substrate. The presence of voids reduces adhesion to the substrate, leading to impaired heat dissipation.

[0016] In particular, in recent hybrid vehicles, electric vehicles, fuel cell vehicles, etc., power control units, reactors and similar components are used and reach high temperatures during use. When heat dissipation materials are used in such components, the above-mentioned problems become more pronounced.

[0017] Furthermore, increasing the amount of hydrosilyl-containing siloxane blended to relatively improve crosslink density increases the amount of polymer blended. Consequently, the amount of thermally conductive filler blended decreases, potentially leading to insufficient thermal conductivity.

[0018] When using siloxanes with a high hydrosilyl content per unit weight, some hydrosilyl-containing siloxanes have a higher curing rate, resulting in a shorter pot life (working time). Therefore, the time from application to compression of the thermally conductive silicone composition must be reduced, and to do so, the application work needs to be performed in a short period of time, causing a problem of deterioration in workability.

[0019] Under such circumstances, there is a demand for developing a thermally conductive silicone composition that exhibits high heat dissipation performance, undergoes little change in physical properties even after exposure to a high temperature of 190° C., and is balanced in being excellent in both adhesion and workability.

[0020] An object of the present invention is to provide a thermally conductive silicone composition for producing a cured product having the following properties: the cured product exhibits high heat dissipation performance (e.g., 5.0 W / m·K or greater), does not generate voids because physical properties (e.g., adhesion and hardness) hardly change when exposed to high temperatures, and has excellent workability.

[0021] Solution to the problem

[0022] The present inventors have found that the problems of the present invention can be solved by blending a thermally conductive filler having only -SiRHO- repeating units and a polymerization degree of 4 or more and 8 or less and a hydrogenated cyclic siloxane in a silicone composition containing an organopolysiloxane, thereby completing the present invention.

[0023] When the above-mentioned hydrogenated cyclic siloxane is blended into a thermally conductive silicone composition, even with a small blending amount, the crosslinking density can be enhanced, making it possible to obtain a composition having a relatively slow curing rate at room temperature (e.g., 10°C or higher and 30°C or lower). As a result, the composition has the following characteristics: the crosslinking reaction (also called the curing reaction) is completed within a predetermined time after the start of the curing reaction, and even when exposed to high temperatures after the reaction, the hardness of the cured product hardly changes, and voids are unlikely to occur after high-temperature exposure.

[0024] Since the above-mentioned effects can be obtained by blending a small amount of hydrogenated cyclic siloxane, a relatively large amount of thermally conductive filler can be blended to obtain a cured product having high thermal conductivity.

[0025] Furthermore, a sufficient pot life (workable time), in other words, the amount of time until the crosslinking reaction is complete, can be ensured for applying the composition as a gap filler to a substrate such as a reactor or a heat sink.

[0026] The thermally conductive silicone composition according to the present invention is a thermally conductive silicone composition comprising:

[0027] Component (A) which is an alkenyl group-containing organopolysiloxane;

[0028] Component (B) which is a linear organopolysiloxane having two or more hydrosilyl groups in one molecule;

[0029] Component (C), which is a hydrogenated cyclic siloxane represented by the following general formula (1)

[0030] [Chemical Formula 1]

[0031]

[0032] (wherein n is an integer of 4 or more and 8 or less, and R is a monovalent hydrocarbon group having 1 to 6 carbon atoms);

[0033] component (D), which is an addition reaction catalyst; and

[0034] Component (E), which is a thermally conductive filler. In the thermally conductive silicone composition, relative to 100 parts by mass of the total amount of the component (A) and the component (B),

[0035] The content of component (C) is 0.5 parts by mass or more and 1.8 parts by mass or less; and

[0036] The content of component (E) is 500 parts by mass or more and 3,000 parts by mass or less.

[0037] The thermally conductive silicone composition of the present invention (hereinafter, simply referred to as the composition) may preferably be a composition for forming a cured product, which is used as a thermally conductive member disposed on a surface of a substrate such as a heat-generating body or a heat-dissipating body, specifically, a reactor surface, a battery cell surface, or a battery pack surface. Examples of the form of the thermally conductive member include a gap filler.

[0038] The above-mentioned thermally conductive silicone composition according to one aspect of the present invention is characterized in that the composition comprises the above-mentioned component (C).

[0039] In the thermally conductive silicone composition, component (A) (alkenyl-containing organopolysiloxane), component (B) (straight-chain organopolysiloxane having two or more hydrosilyl groups in one molecule), and component (C) (hydrogenated cyclic siloxane represented by the above-mentioned general formula (1)) are cured by a crosslinking reaction in the presence of component (D) (addition reaction catalyst). In this article, within the above-mentioned mixing amount range, as a hydrosilyl-containing siloxane, the thermally conductive silicone composition contains not only component (B) but also component (C). Therefore, this composition makes it possible to increase the crosslinking density of the cured product obtained by curing the composition, and at the same time, increase the curing rate to a range in which a sufficient pot life can be ensured. Therefore, the composition has such characteristics that even after exposure to high temperatures (e.g., about 190°C), the hardness of the cured product hardly changes, and voids are unlikely to occur between the substrate and the cured product, allowing the cured product to maintain good thermal conductivity.

[0040] Furthermore, component (C) can sufficiently enhance the crosslinking density even in a smaller amount. Therefore, the relative mixing amount of the thermally conductive filler as component (E) does not need to be reduced, so that a cured product having good thermal conductivity can be obtained.

[0041] Furthermore, the component (C) has a large content of -SiH groups per unit weight, making it possible to obtain good adhesion of the cured product to the substrate even if the component (C) is mixed in a small amount.

[0042] Advantageous Effects of the Invention

[0043] As described above, the thermally conductive silicone composition according to the present invention can ensure a sufficient pot life. After high-temperature exposure, the cured product of the thermally conductive silicone composition shows minimal change in hardness, and no gaps are likely to form between the substrate and the cured product, allowing the cured product to exhibit excellent thermal conductivity. Consequently, a cured product can be obtained that maintains high thermal conductivity even after high-temperature exposure. This cured product is particularly suitable as a gap filler between heat sinks and batteries, reactors, and the like, for example, mounted on vehicle bodies. DETAILED DESCRIPTION

[0044] Hereinafter, a thermally conductive silicone composition, a method for producing the composition, and a method for producing a cured product using the composition according to the present invention will be described in detail.

[0045] The thermally conductive silicone composition according to the present invention is a thermally conductive silicone composition comprising:

[0046] Component (A) which is an alkenyl group-containing organopolysiloxane;

[0047] Component (B) which is a linear organopolysiloxane having two or more hydrosilyl groups in one molecule;

[0048] Component (C), which is a hydrogenated cyclic siloxane represented by the following general formula (1)

[0049] [Chemical Formula 1]

[0050]

[0051] (wherein n is an integer of 4 or more and 8 or less, and R is a monovalent hydrocarbon group having 1 to 6 carbon atoms);

[0052] component (D), which is an addition reaction catalyst; and

[0053] Component (E), which is a thermally conductive filler. In the thermally conductive silicone composition, relative to 100 parts by mass of the total amount of the component (A) and the component (B),

[0054] The content of component (C) is 0.5 parts by mass or more and 1.8 parts by mass or less; and

[0055] The content of component (E) is 500 parts by mass or more and 3,000 parts by mass or less.

[0056] The thermally conductive silicone composition of the present invention is preferably a composition for forming a cured product for use as a thermally conductive member. Examples of thermally conductive members include gap fillers applied to heating elements such as automotive batteries or reactors, films covering heating elements, and housings for packaging heating elements.

[0057] The thermally conductive silicone composition of the present invention, which is in a liquid state before being cured, is applied to a substrate, and then cured to provide a cured product serving as a thermally conductive member.

[0058] Component (A):

[0059] Component (A), which is the main component of the composition, is an organopolysiloxane having alkenyl groups bonded to silicon atoms.

[0060] The viscosity and polymerization degree of component (A) are not particularly limited and may be selected according to the desired mixing viscosity of the composition, etc., and the viscosity at 25° C. may be, for example, 10 mPa·s or more and 10,000 mPa·s or less.

[0061] As the organopolysiloxane, one type thereof may be used alone, or two or more types thereof may be used in appropriate combination. The organopolysiloxane is a main component of the composition and has an average of at least two alkenyl groups bonded to silicon atoms in one molecule, preferably 2 to 50 alkenyl groups, and more preferably 2 to 20 alkenyl groups.

[0062] The molecular structure of component (A) is not particularly limited and can be, for example, a linear structure, a partially branched linear structure, a branched structure, a cyclic structure or a branched cyclic structure. Wherein, component (A) is preferably a substantially straight-chain organopolysiloxane. Specifically, component (A) can be a linear diorganopolysiloxane, wherein the molecular chain is mainly composed of diorganosiloxane repeating units, and the two ends of the molecular chain are closed by triorganosiloxy groups. Some or all of the molecular chain ends or some side chains can be silanol groups.

[0063] The position of the alkenyl group bonded to the silicon atom in component (A) is not particularly limited, and component (A) may be an organopolysiloxane having alkenyl groups bonded to silicon atoms at both molecular chain terminals.

[0064] An organopolysiloxane having one alkenyl group at each end of the molecular chain has advantages in that the content of the alkenyl group serving as a reaction point for a cross-linking reaction is small and the flexibility of a cured product obtained after curing is enhanced.

[0065] In addition to having alkenyl groups at both terminals, an organopolysiloxane having alkenyl groups in a side chain of a molecular chain can enhance the crosslinking density and hardness of a cured product.

[0066] The number of alkenyl groups in one molecule of component (A) can be appropriately determined depending on the desired hardness of the cured product, the molecular weight of component (A), etc. The number of alkynyl groups in one molecule may be two or more, more preferably two or more and five or less, and most preferably two (with one alkynyl group at each end of the molecular chain).

[0067] The alkenyl group may be bonded to the silicon atom at a molecular chain terminal, bonded to the silicon atom at a non-terminal molecular chain site (in the middle of the molecular chain), or bonded to both.

[0068] Component (A) may be a polymer composed of a single type of siloxane unit or a copolymer composed of two or more types of siloxane units.

[0069] The viscosity of component (A) at 25° C. is 10 mPa·s or more and 10,000 mPa·s or less, preferably 50 mPa·s or more and 1,000 mPa·s or less, and more preferably 100 mPa·s or more and 500 mPa·s or less.

[0070] In order to adjust the viscosity of a composition obtained by mixing liquid compositions before curing (mixed viscosity), two or more types of organopolysiloxanes having alkenyl groups and having different viscosities may also be used in combination.

[0071] Specifically, component (A) is represented by the following general formula (1) as an average composition formula:

[0072] R 1 a SiO (4-a) / 2 …(1)

[0073] (In formula (1), R 1 are the same as or different from each other and are each an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, a is 1.7 to 2.1, preferably 1.8 to 2.5, and more preferably 1.95 to 2.05).

[0074] In one embodiment, the above R 1 The at least two or more monovalent hydrocarbon groups represented by are selected from alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, isobutenyl, hexenyl and cyclohexenyl. Groups other than these groups are substituted or unsubstituted monovalent hydrocarbon groups having 1 to 18 carbon atoms. Specifically, the above R 1 Selected from the group consisting of alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, 2-ethylhexyl, heptyl, octyl, nonyl, decyl and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, biphenyl and naphthyl; aralkyl groups such as benzyl, phenethyl, phenylpropyl and methylbenzyl; and halogen-substituted or cyano-substituted alkyl groups, wherein some or all of the hydrogen atoms in the above hydrocarbon groups have been substituted by halogen atoms, cyano groups, etc., such as chloromethyl, 2-bromoethyl, 3,3,3-trifluoropropyl, 3-chloropropyl and cyanoethyl.

[0075] As the desired two or more alkenyl groups, it is preferred to select R 1 Examples of R include vinyl, allyl, propenyl, isopropenyl, 2-methyl-1-propenyl, 2-methylallyl and 2-butenyl. Vinyl is particularly preferred. 1 Preferred embodiments of include methyl and phenyl, wherein methyl is particularly preferred. In addition, considering the physical properties and economic efficiency of the cured product, it is preferred that 70 mol% or more of R 1 is methyl, and usually, preferably 80 mol% or more of R 1 It's methyl.

[0076] Specific examples of the molecular structure of the component (A) include dimethylpolysiloxane having two molecular chain ends capped with dimethylvinylsiloxy groups, a dimethylsiloxane-methylphenylsiloxane copolymer having two molecular chain ends capped with dimethylvinylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane copolymer having two molecular chain ends capped with dimethylvinylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer having two molecular chain ends capped with dimethylvinylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane copolymer having two molecular chain ends capped with trimethylsiloxy groups, and a dimethylsiloxane-methylvinylsiloxane copolymer having two molecular chain ends capped with trimethylsiloxy groups, represented by the formula (CH3)2ViSiO 1 / 2 Siloxane units represented by the formula (CH3)3SiO 1 / 2 The siloxane unit represented by the formula: SiO 4 / 2 Organopolysiloxanes composed of siloxane units represented by (wherein Vi represents a vinyl group), organopolysiloxanes in which some or all of the methyl groups in the above organopolysiloxanes are substituted with alkyl groups such as ethyl or propyl groups, aryl groups such as phenyl or tolyl groups, and halogenated alkyl groups such as 3,3,3-trifluoropropyl groups, and mixtures of two or more of these organopolysiloxanes. From the viewpoint of enhancing the elongation of the cured product at break due to increased molecular chain length, linear diorganopolysiloxanes having one vinyl group at each molecular chain end are preferred.

[0077] These diorganopolysiloxanes may be commercially available or prepared by methods known to those skilled in the art.

[0078] The content of the organopolysiloxane of component (A) is preferably 20 parts by mass or more and less than 90 parts by mass, and more preferably 40 parts by mass or more and 80 parts by mass or less, relative to 100 parts by mass of the total amount of components (A) and (B) in the thermally conductive silicone composition of the present invention. When the content falls within the above range, the viscosity of the entire composition can fall within an appropriate range, and the composition can have appropriate fluidity while maintaining high thermal conductivity of the resulting cured product.

[0079] Component (B):

[0080] Component (B) is a linear organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms.

[0081] Component (B) may have a viscosity and a degree of polymerization, which are not limited to specific values ​​and may be selected according to the desired mixed viscosity of the composition. For example, component (B) may have a viscosity of 10 mPa·s or more and 10,000 mPa·s or less at 25°C.

[0082] Component (B) is an organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms in one molecule, and serves as a crosslinking agent for curing the composition of the present invention.

[0083] The number of hydrogen atoms bonded to silicon atoms is not particularly limited as long as it is two or more, and may be two or more and four or less. Particularly preferably, the linear component (B) may have a hydrogen atom bonded to a silicon atom at each of both ends of the molecular chain, and may have two hydrogen atoms bonded to one silicon atom in the molecule.

[0084] Component (B) can be any organopolysiloxane as long as it contains two or more hydrogen atoms (hydrogen silyl groups) bonded to one or more silicon atoms in one molecule. Examples that can be used include methyl hydrogen polysiloxane, dimethylsiloxane-methyl hydrogen siloxane copolymer, methylphenylsiloxane-methyl hydrogen siloxane copolymer, cyclic methyl hydrogen polysiloxane, and polysiloxanes composed of dimethyl hydrogen siloxy units and SiO 4 / 2 As component (B), one type thereof may be used alone, or two or more types thereof may be used in appropriate combination.

[0085] The molecular structure of component (B) is not particularly limited and may be, for example, a linear, branched, cyclic or three-dimensional network structure. Specifically, a structure represented by the following average composition formula (2) may be used:

[0086] R 3 p H q SiO (4-p-q) / 2 (2)

[0087] (In this formula, R 3 is an unsubstituted or substituted monovalent hydrocarbon group excluding an aliphatic unsaturated hydrocarbon group, p is 0 to 3.0, preferably 0.7 to 2.1, q is 0.0001 to 3.0, preferably 0.001 to 1.0, and p+q is a positive number satisfying 0.5 to 3.0, preferably 0.8 to 3.0).

[0088] R in formula (2) 3 Examples of include unsubstituted or halogen-substituted monovalent hydrocarbon groups, etc., which have 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, excluding aliphatic unsaturated hydrocarbon groups. Specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, tert-butyl, and cyclohexyl; aryl groups such as phenyl, tolyl, and xylyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups such as 3-chloropropyl and 3,3,3-trifluoropropyl groups. Among them, methyl, ethyl, propyl, phenyl, and 3,3,3-trifluoropropyl are preferred, and methyl is particularly preferred.

[0089] Specific examples of component (B) include dimethylsiloxane with two molecular chain ends blocked by dimethylhydrogensiloxy groups, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, dimethylsiloxane-methylhydrogensiloxane copolymer with two molecular chain ends blocked by dimethylhydrogensiloxy groups, methylhydrogenpolysiloxane with two molecular chain ends blocked by dimethylhydrogensiloxy groups, methylhydrogenpolysiloxane with two molecular chain ends blocked by trimethylsiloxy groups, and dimethylhydrogensiloxane-methylhydrogensiloxane copolymer with two molecular chain ends blocked by dimethylhydrogensiloxy groups. chain end dimethylpolysiloxane, dimethylsiloxane-diphenylsiloxane copolymer with two molecular chain ends blocked by dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer with two molecular chain ends blocked by trimethylsiloxy groups, dimethylsiloxane-diphenylsiloxane-methylhydrogensiloxane copolymer with two molecular chain ends blocked by trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer with two molecular chain ends blocked by dimethylhydrogensiloxy groups, H(CH3)2SiO 1 / 2 Copolymers of units and SiO2 units, H(CH3)2SiO 1 / 2 Copolymer of units, (CH3)3SiO 1 / 2 units and SiO2 units, as well as mixtures of two or more of these organopolysiloxanes.

[0090] In the above composition, the content of component (B) is preferably within a range where the ratio of the number of hydrosilyl groups in component (B) to the number of alkenyl groups in component (A) falls within a range of 1 / 5 to 7, more preferably within a range of 1 / 3 to 2, and even more preferably within a range of 2 / 5 to 1. When the content of component (B) falls within the above range, the composition is sufficiently cured and the hardness of the entire composition becomes a more preferred range, making it less likely that cracks will occur when the cured product of the composition is used as a gap filler. In addition to these, there is an advantage that the composition does not sag and can maintain its retention ability in the vertical direction even when the substrate is arranged in a vertical orientation (standing upright).

[0091] The number of hydrosilyl groups in one molecule can be appropriately determined depending on the desired hardness of the cured product of the composition, the molecular weight of component (A), etc. The number of hydrosilyl groups in one molecule may be 2 or more, and from the viewpoint of workability, it is more preferably 2 or more and 5 or less, and even more preferably 2 or more and 3 or less. A linear organopolysiloxane having a hydrosilyl group at each end of the molecular chain used as component (B) is most excellent in workability and processability during application of the unvulcanized composition.

[0092] The hydrosilyl groups in component (B) may be present at the molecular chain terminals, in the side chains, or both. A mixture of an organopolysiloxane having only one hydrosilyl group at each molecular chain terminal and an organopolysiloxane having only hydrosilyl groups in the side chains of the molecular chain is preferably used.

[0093] Component (B) can be an organopolysiloxane having hydrogen atoms bonded to silicon atoms only at both molecular chain ends. Organopolysiloxanes having hydrosilyl groups at each of the two molecular chain ends have a low hydrosilyl content per unit weight and can adjust the curing reaction rate to ensure a sufficient pot life. Furthermore, this has the advantage of increasing the flexibility of the cured product obtained after curing and further enhancing adhesion to substrates.

[0094] Organopolysiloxanes having SiH groups only at the molecular chain ends have the following advantages: they are highly reactive due to low steric hindrance, and they contribute to network formation through crosslinking reactions, thereby enhancing the strength of the cured product. To impart flexibility to the cured product after curing, organopolysiloxanes having SiH groups only at the molecular chain ends are preferably used.

[0095] From the viewpoint of improving adhesion and heat resistance, component (B) is most preferably a dimethylpolysiloxane having a dimethylhydrogensiloxy group at each end of the molecular chain.

[0096] Component (B) may comprise an organohydrogenpolysiloxane having trimethylsiloxy groups at each molecular chain end and containing at least one aromatic group within the molecule. For economic reasons, the aromatic group is more preferably a phenyl group. Aromatic-group-containing organohydrogenpolysiloxanes and aromatic-group-free organohydrogenpolysiloxanes may be used in combination.

[0097] The viscosity of component (B) at 25° C. is 10 mPa·s or more and 10,000 mPa·s or less, preferably 20 mPa·s or more and 5,000 mPa·s or less, and more preferably 30 mPa·s or more and 2,000 mPa·s or less.

[0098] To adjust the viscosity of the final composition, two or more types of organopolysiloxanes having two or more hydrosilyl groups and having different viscosities may be used. The mixed viscosity of the composition may be 10 to 1,000 Pa·s, more preferably 20 to 500 Pa·s, and even more preferably 30 to 250 Pa·s.

[0099] The content of the organopolysiloxane of component (B) is preferably 10 parts by mass or more and 80 parts by mass or less, and more preferably 20 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the total amount of components (A) and (B) in the composition of the present invention. When the content falls within the above range, the hardness of the cured product of the composition can fall within an appropriate range. In addition, the cured product of the composition can exhibit flexibility and robustness.

[0100] Component (C):

[0101] Component (C) is a hydrogenated cyclic siloxane represented by the following general formula (1).

[0102] [Chemical Formula 1]

[0103]

[0104] In the general formula (1), n ​​is an integer of 4 to 8, and R is a monovalent hydrocarbon group having 1 to 6 carbon atoms. One hydrocarbon group and one hydrogen atom are bonded to each silicon atom in component (C). Even when blended in a small amount, a hydrogenated cyclic siloxane in which n is 4 to 8 can enhance the crosslinking density and, at the same time, can increase the curing reaction rate to a range that can ensure a sufficient pot life due to the steric hindrance caused by the cyclic structure.

[0105] If n is 3 or less, the amount of the compound in the thermally conductive silicone composition may vary due to low molecular weight and high volatility. In addition, if n is 9 or more, a ring-opening reaction is likely to occur, and the ring structure itself is likely to become unstable.

[0106] When the thermally conductive silicone composition of the present invention is cured on a substrate at room temperature (e.g., 10°C to 30°C), and the cured product is then exposed to a high temperature (e.g., 190°C), the component (C) contained in the composition can reduce the change in Shore 00 hardness (e.g., to a rate of change of 10% or less) compared to the change in Shore 00 hardness immediately after curing at room temperature. Furthermore, the relatively low thermal expansion can reduce the occurrence of voids between the cured product and the substrate.

[0107] Compared to the case of using a linear low-molecular-weight siloxane having only hydrosilyl groups at both ends of the molecular chain, the use of the above-mentioned component (C) allows the curing reaction to proceed sufficiently and be completed in about 24 hours. After the curing reaction is completed, the cured product shows little change in hardness even when exposed to high temperatures and is less likely to develop voids.

[0108] Furthermore, component (C) is effective even when added in a small amount. Therefore, the thermally conductive filler can be blended in a relatively large amount.

[0109] When using a linear siloxane having a large number of hydrosilyl groups in the molecule, where the hydrosilyl groups are bonded at both ends of the molecular chain and in the side chains, there is a problem in that the curing reaction proceeds too quickly and begins to cure before the application to the substrate is completed. Compared to this case, when using the above-mentioned component (C), the reaction rate is reduced, making it possible to ensure a pot life of approximately 30 minutes. After application to a substrate, etc., at room temperature (e.g., approximately 23°C) for 1 hour.

[0110] In addition, the cyclic form of the hydrogenated siloxane component (C) used in the present invention has a smaller thermal expansion coefficient than the linear form of the hydrogenated siloxane, which occurs when a network is formed by a crosslinking reaction. In this regard, the occurrence of voids can also be reduced.

[0111] The term "pot life at room temperature" as used herein refers to the period during which a thermally conductive silicone composition can be used, particularly under an environment of a temperature of 23°C ± 5°C and a humidity of 50% RH ± 5% RH. If the uncured thermally conductive silicone composition filled in a container is a two-component type, the term "pot life" is defined as the period from the mixing of the first liquid and the second liquid until the viscosity of the composition reaches twice the viscosity of the composition initially filled in the container. Note that the viscosities described herein are values ​​measured at 23°C and, unless otherwise specified, are values ​​measured using a rotational viscometer (according to JIS K7117-2) at a shear rate of 10 / s.

[0112] As the component (C) of the present invention, any one component in which n is 4, 5, 6, 7 or 8 may be blended, or two or more types of components in which n is 4 or more and 8 or less may be mixed and blended.

[0113] The three components with n=5, 6, and 7 may be mixed and blended separately, or the four components with n=4, 5, 6, and 7 may be mixed and blended separately. In particular, when multiple types of components (C) are used, the components (C) with n=5 and n=6 are preferably used in larger amounts.

[0114] For example, relative to 100 parts by mass of the total amount of component (C), 0 parts by mass or more and less than 10 parts by mass of the component (C) wherein n=4, 10 parts by mass or more and less than 70 parts by mass of the component (C) wherein n=5, 10 parts by mass or more and less than 70 parts by mass of the component (C) wherein n=6, 0 parts by mass or more and less than 30 parts by mass of the component (C) wherein n=7, and 0 parts by mass or more and less than 10 parts by mass of the component (C) wherein n=8 may be included.

[0115] As component (C) of the present invention, particularly preferred are 1,3,5,7,9-pentamethylcyclopentasiloxane (HD5) and 1,3,5,7,9,11-hexamethylcyclohexasiloxane (HD6).

[0116] The mixing amount of component (C) can be appropriately determined according to required cross-linking density and cure rate. However, the mixing amount is preferably in the range of more than 0.5 mass parts and less than 1.8 mass parts relative to the total amount of 100 mass parts of components (A) and component (B). The mixing amount is more preferably more than 0.6 mass parts and less than 1.5 mass parts, and even more preferably more than 0.7 mass parts and less than 1.3 mass parts. Within the above range, even after high temperature exposure, the hardness of the cured product is almost unchanged, and the good adhesion between substrate and the cured product can be obtained. Thus, it is possible to form a cured product with excellent thermal conductivity (for example, thermal conductivity is more than 5.0W / m·K).

[0117] If the blending amount of component (C) is less than 0.5 parts by mass, the curing reaction does not proceed sufficiently when the composition is applied to a substrate. Subsequently, when the composition is exposed to high temperatures, the uncured portions, where the functional groups have not been cross-linked, are cured, causing a rapid increase in the hardness of the cured product and, consequently, the formation of voids. Consequently, thermal conductivity decreases.

[0118] If the blending amount of component (C) exceeds 1.8 parts by mass, the content of component (E), ie, the thermally conductive filler, is relatively reduced, resulting in a decrease in the thermal conductivity of the cured product.

[0119] In the thermally conductive silicone composition of the present invention, the mass ratio of component (A) to component (B) (mass of component (A) : mass of component (B)) falls within the range of 80:20 to 50:50. In addition, the total amount of HD5 and HD6 as component (C) is most preferably 0.5 parts by mass or more and 1.5 parts by mass or less relative to 100 parts by mass of the total amount of component (A) and component (B).

[0120] When the mass ratio falls within the above range and the total amount of HD5 and HD6 falls within the above range, the hardness of the cured product of the composition is within an appropriate range, and when the cured product is used as a gap filler, its vibration absorbency is also favorable.

[0121] Component (D):

[0122] The addition reaction catalyst of component (D) is a catalyst that promotes the addition curing reaction between the alkenyl group bonded to the silicon atom in the above-mentioned component (A) and the hydrogen atom bonded to the silicon atom in the above-mentioned component (B), and is a catalyst known to those skilled in the art. Examples of component (D) include platinum group metals such as platinum, rhodium, palladium, osmium, iridium and ruthenium, and catalysts in which any of the above metals is supported by a particulate support material (e.g., activated carbon, aluminum oxide and silicon oxide).

[0123] In addition, specific examples of component (D) include molybdenum halides, molybdenum-olefin complexes, molybdenum-alcohol complexes, molybdenum-alcoholate complexes, molybdenum-vinylsiloxane complexes, dicyclopentadiene-molybdenum dichloride, cyclooctadiene-molybdenum dichloride, and cyclopentadiene-molybdenum dichloride.

[0124] In addition, from an economic point of view, metal compound catalysts other than the above-mentioned platinum group metals can be used as component (D). Examples of iron catalysts for hydrosilylation include iron-carbonyl complex catalysts, iron catalysts having a cyclopentadienyl group as a ligand, iron catalysts having a terpyridine ligand or a combination of a terpyridine ligand and a bistrimethylsilylmethyl group, iron catalysts having a bisiminopyridine ligand, iron catalysts having a bisiminoquinoline ligand, iron catalysts having an aryl group as a ligand, iron catalysts having a cyclic or acyclic olefin group with an unsaturated group, and iron catalysts having a cyclic or acyclic olefin group with an unsaturated group. Other examples of catalysts for hydrosilylation include cobalt catalysts, vanadium catalysts, ruthenium catalysts, iridium catalysts, samarium catalysts, nickel catalysts, and manganese catalysts.

[0125] The blending amount of component (D) is preferably within the range of 0.5 ppm to 1,000 ppm, more preferably 1 ppm to 500 ppm, and even more preferably 1 ppm to 100 ppm, relative to the total mass of the thermally conductive silicone composition, in terms of the concentration of the catalyst metal element, although an effective amount is used depending on the desired curing temperature and curing time for the application. If the blending amount is less than 0.5 ppm, the addition reaction becomes significantly slow. If the blending amount exceeds 1,000 ppm, it is not economically preferable due to increased costs.

[0126] Component (E):

[0127] The thermally conductive filler of component (E) is a filler material component that improves the thermal conductivity of the thermally conductive silicone composition. The thermally conductive filler used in the present invention is at least one or more selected from the group consisting of metals, metal oxides, metal hydroxides, metal nitrides, and metal carbides. There is no particular limitation on the specific surface area and particle size of the thermally conductive filler, and they can be appropriately determined according to the desired performance of the thermally conductive silicone composition. For example, the BET specific surface area can be 30 m 2 / g or less, and the average particle size can be 1 to 100 μm. On the surface of the thermally conductive filler, OH groups can be generated due to reaction with atmospheric water. The surface OH groups are uniformly dispersed in the thermally conductive silicone composition through interaction with component (C), and the thermally conductive filler hardly precipitates even when stored for a long time. This is presumably due to hydrogen bonds formed between the OH groups on the surface of the thermally conductive filler and the silanol groups of component (C), and due to the fact that all components (A), (B) and (C) have a siloxane skeleton and are highly compatible with each other.

[0128] The thermally conductive filler may be added in an amount required to increase the thermal conductivity of the cured product (e.g., 5.0 W / m·K or more), and, for example, the content of component (E) may be preferably 300 parts by mass or more and 2,500 parts by mass or less, more preferably 400 parts by mass or more and 2,000 parts by mass or less, and even more preferably 500 parts by mass or more and 1,800 parts by mass or less, relative to 100 parts by mass of the total amount of components (A) and (B).

[0129] When the content of component (E) falls within the above range, the thermally conductive silicone composition as a whole has sufficient thermal conductivity, is easy to mix when blended, and maintains flexibility even after curing. In addition, because component (E) included in such an amount does not excessively increase the specific gravity, the resulting composition is more suitable for use as a thermally conductive silicone composition for forming a cured product having high thermal conductivity and reduced weight. If the content of component (E) is too small, it becomes difficult to sufficiently increase the thermal conductivity of the cured product obtained from the thermally conductive silicone composition, while if the content of component (E) is too large, the resulting silicone composition becomes highly viscous and there is a possibility that it becomes difficult to evenly apply the thermally conductive silicone composition, leading to problems such as an increase in the thermal resistance value of the cured product of the composition and a decrease in the flexibility of the cured product.

[0130] For example, the shape of the thermally conductive filler may be spherical, amorphous, fine powder, fibrous, flaky, etc. In order to blend the thermally conductive filler in an amount required to enhance the thermal conductivity of the cured product of the composition, the thermally conductive filler preferably has a spherical shape, and its average particle size may be 1 to 100 μm. In this context, the spherical shape may be not only a true spherical shape but also a round shape.

[0131] The BET specific surface area of ​​the thermally conductive filler is not particularly limited and may be, for example, 0.01 m 2 / g and above and 500m 2 / g or less, preferably 0.03m 2 / g or above and 50m 2 / g or less, even more preferably 0.05m 2 / g or more and 10m 2 / g or less.

[0132] The thermally conductive filler preferably has a thermal conductivity of 10 W / m·K or higher. If the thermal conductivity is less than 10 W / m·K, the thermal conductivity of the thermally conductive silicone composition itself may be reduced. In particular, if the cured product requires electrical insulation, it is conceivable to select a non-conductive thermally conductive filler.

[0133] Component (E) may preferably be a metal oxide, metal hydroxide, nitride, or a mixture thereof, and in some cases may be an amphoteric hydroxide or amphoteric oxide. Specifically, one or more selected from aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, zinc oxide, aluminum nitride, and boron nitride are preferably used. Component (E) preferably contains at least one selected from aluminum hydroxide and aluminum oxide.

[0134] It should be noted that alumina is an insulating material, has relatively good compatibility with components (A) and (B), can be industrially selected from a variety of particle sizes, is a readily available resource, and is relatively inexpensive, and is therefore suitable as a thermally conductive filler.

[0135] When spherical alumina is used as component (E), alumina obtained by high-temperature thermal spraying or hydrothermal treatment of alumina hydrate can be used.

[0136] The average particle size of component (E) may be in the range of 1 μm or more and 100 μm or less, more preferably 2 μm or more and 80 μm or less, and even more preferably 2 μm or more and 70 μm or less. If the average particle size is too small, the fluidity of the thermally conductive silicone composition decreases. If the average particle size is too large, the dispersion characteristics are impaired, and there is a possibility that problems such as scratches of the coating equipment may occur due to the filler being caught by the sliding part of the coating equipment. In the present invention, the average particle size of component (E) is defined as D50 (or median diameter), which is the 50% particle size in the volume-based cumulative particle size distribution measured by a laser diffraction particle size measuring device.

[0137] As component (E), a spherical thermally conductive filler can be used, or a thermally conductive filler other than a spherical filler, such as an amorphous, powdered, fibrous, or plate-shaped filler, can be used in combination. When at least two or more types of thermally conductive fillers having different shapes are used in combination, the composition during application can be filled with the filler in a state of almost full packing, so that the thermal conductivity is further increased. When a spherical thermally conductive filler is used in combination with a thermally conductive filler other than a spherical filler, the proportion of the spherical thermally conductive filler relative to 100% by mass of the total component (E) is 30% by mass or more, the thermal conductivity can be further increased.

[0138] In the thermally conductive silicone composition according to the present invention, fillers other than component (E) may be further added. Examples of fillers other than component (E) may include fillers having non-thermal conductivity, such as fumed silica, crystalline silica, precipitated silica, hollow fillers, silsesquioxane, magnesium carbonate, calcium carbonate, zinc carbonate, layered mica, carbon black, diatomaceous earth, glass fiber, silicone rubber powder, and silicone resin powder, as well as fillers having 500 m 2 A thermally conductive filler having a BET specific surface area of ​​1 / g or more.

[0139] When the mixture has more than 500m 2 / g of BET specific surface area of ​​the filler, the viscosity of the thermally conductive silicone composition increases, the adhesion of the thermally conductive silicone composition to the substrate is impaired after curing, and the flexibility tends to decrease. Therefore, the heat dissipation performance can be reduced. When the composition is densely filled with a large volume of filler, the movement of the silicone rubber molecules in the composition is hindered and the resilience is impaired. Relative to 100 parts by mass of the total amount of components (A) and (B), the thermally conductive silicone composition according to the present invention having 500m 2 The content of the filler having a BET specific surface area of ​​1000 Å / g or more needs to be 3 parts by mass or less.

[0140] In the present invention, the BET specific surface area of ​​component (E) is a value obtained by measuring the amount of gas physically adsorbed to the surface of particles in a low temperature state and calculating the specific surface area.

[0141] In the thermally conductive silicone composition of the present invention, as an additional optional component in addition to the above-mentioned components (A) to (E), the conventional known additives used in silicone rubber or gel can be used, as long as the purpose of the present invention is not damaged. The embodiment of this additive includes a cross-linking agent, an organosilicon compound or an organosiloxane (also referred to as a silane coupling agent) for producing silanol by hydrolysis, a condensation catalyst, an adhesion promoter, a pigment, a dye, a curing inhibitor, a heat resistance imparting agent, a flame retardant, an antistatic agent, an electrical conductivity imparting agent, an airtightness improver, a radiation shielding agent, an electromagnetic wave shielding agent, a preservative, a stabilizer, an organic solvent, a plasticizer, a fungicide, an organopolysiloxane comprising a hydrogen atom or an alkenyl group bonded to a silicon atom in a molecule and not comprising other functional groups, and a non-functional organopolysiloxane comprising neither a hydrogen atom bonded to a silicon atom nor a alkenyl group bonded to a silicon atom. As these optional components, one of these types can be used alone, or two or more types can be suitably used in combination.

[0142] Crosslinking agent:

[0143] In the thermally conductive silicone composition of the present invention, since component (C) serves as a crosslinking agent, although an optional crosslinking agent may be blended separately, another crosslinking agent may not be blended separately. As a crosslinking agent, organohydrogen polysiloxanes other than those used as components (B) and (C) can be used. The crosslinking agent forms a cured product by an addition reaction with an alkenyl group and may have a hydrogen atom (hydrosilyl group) bonded to at least one or more silicon atoms in a side chain in the molecule. The crosslinking agent preferably has three or more hydrosilyl groups in one molecule and at least one hydrosilyl group in a side chain in the molecule.

[0144] The crosslinking agent that can be used in the present invention is more preferably an organohydrogen polysiloxane with more than 5 hydrosilyl groups, and may have more than 10 to less than 15 hydrosilyl groups. The organohydrogen polysiloxane as a crosslinking agent has at least two hydrosilyl groups in its side chain. The number of hydrosilyl groups on the molecular chain end can be more than zero and less than two, and from an economic point of view, preferably two. The molecular structure of the organohydrogen polysiloxane can be any one of a straight chain, a cyclic, a branched chain, and a three-dimensional network structure. The position of the silicon atom to which the hydrogen atom is bonded is not particularly limited, and may be at the molecular chain end, a non-terminal molecular chain site (in the middle of the molecular chain), or in a side chain. Other conditions in the organohydrogen polysiloxane used as a crosslinking agent, the type of organic group other than the hydrosilyl group, the bonding position, the degree of polymerization, the structure, etc. are not particularly limited. Two or more types of organohydrogen polysiloxanes can be used.

[0145] A crosslinking agent does not necessarily need to be blended. When a crosslinking agent is blended, the blending amount thereof may be 0 parts by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 6 parts by mass or less, and even more preferably 1 part by mass or more and 4 parts by mass or less, relative to 100 parts by mass of the total amount of component (A) and component (B).

[0146] Silane coupling agent:

[0147] Examples of the silane coupling agent include organosilicon compounds and organosiloxanes having an organic group and an alkoxy group bonded to a silicon atom in one molecule, and the organic group includes an epoxy group, an alkyl group, an aryl group, a vinyl group, a styryl group, a methacryloyl group, an acryl group, an amino group, an isocyanurate group, a urea group, a mercapto group, an isocyanate group, and an acid anhydride. The embodiment of the silane coupling agent is silane compound such as octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, p-phenylenediaminetrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureapropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-isocyanatopropyltriethoxysilane and 3-trimethoxysilylpropyl succinic anhydride. The silane compound can be a compound without a hydrosilyl group. One type thereof can be used alone, or two or more types thereof can be suitably used in combination. When the surface of the thermally conductive filler is treated with a silane coupling agent, the affinity with the silicone polymer can be improved, the viscosity of the composition can be reduced, and the filling performance of the thermally conductive filler can be improved. Therefore, when a larger amount of filler is added, the thermal conductivity can be improved.

[0148] The silanol generated by hydrolysis can react and bond with condensable groups (e.g., hydroxyl groups, alkoxy groups, acid groups, etc.) present on the surface of a metal substrate or an organic resin substrate. The silanol and condensable groups react and bond with each other under the catalytic action of a condensation catalyst described later, thereby improving the adhesion of the cured product to various substrates.

[0149] The amount of silane coupling agent to be blended relative to the thermally conductive filler is determined by an effective amount based on the desired curing temperature or curing time for the intended application. The optimal amount is generally 0.5 wt% or more and 2 wt% or less relative to the thermally conductive filler. The required amount can be calculated using the following formula. The silane coupling agent can be added in an amount one to three times the required amount.

[0150] The required amount of silane coupling agent (g) = the mass of thermal conductive filler (g) × the specific surface area of ​​thermal conductive filler (m 2 / g) / Specific minimum coverage area of ​​silane coupling agent (m 2 / g)

[0151] Condensation catalyst:

[0152] As needed, a condensation catalyst can be used together with the above-mentioned silane coupling agent. As a condensation catalyst, a compound of a metal selected from magnesium, aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc, zirconium, tungsten and bismuth can be used. Preferred embodiments of the condensation catalyst include metal compounds, such as organic acid salts, alkoxides and chelate compounds of trivalent aluminum, trivalent iron, trivalent cobalt, divalent zinc, tetravalent zirconium and trivalent bismuth. Specific embodiments include organic acids such as octanoic acid, lauric acid and stearic acid, alkoxides such as propoxides and butoxides, and polydentate ligand chelate compounds such as catechol, crown ethers, polycarboxylic acids, hydroxy acids, diketones and keto acids. Here, various types of ligands can be bound to a metal. In particular, it is preferred that stable curable zirconium, aluminum or iron compounds are easily obtained even when the chemical composition and use conditions are slightly different. In addition, more desirable embodiments of the compound include butoxides of zirconium and trivalent chelate compounds of aluminum or iron containing polydentate ligands, such as malonates, acetoacetates, acetylacetone or their substituted derivatives. In the case of trivalent aluminum or iron metal compounds, organic acids having 5 to 20 carbon atoms, such as octyl acid, can be preferably used.The multidentate ligand and the organic acid can be combined with one metal, and the resulting structure can also be adopted.

[0153] Examples of the above-mentioned substituted derivatives include those in which hydrogen atoms contained in the above-mentioned compounds are substituted by alkyl groups such as methyl or ethyl, alkenyl groups such as vinyl or allyl, aryl groups such as phenyl, halogen atoms such as chlorine or fluorine atoms, hydroxyl groups, fluoroalkyl groups, ester group-containing groups, ether group-containing groups, ketone group-containing groups, amino group-containing groups, amide group-containing groups, carboxylic acid group-containing groups, nitrile group-containing groups, epoxy group-containing groups, etc. Specific examples thereof include 2,2,6,6-tetramethyl-3,5-heptanedione and hexafluoropentanedione.

[0154] Adhesion aids:

[0155] The adhesion promoter is preferably an organosilicon compound or organosiloxane having an organic functional group. Here, the organic functional group is preferably an alkoxy group bonded to a silicon atom (silicon atom-bonded alkoxy group). Examples of silicon atom-bonded alkoxy groups include methoxy, ethoxy, and propoxy. As silyl groups containing silicon atom-bonded alkoxy groups, alkyldialkoxysilyl groups such as methyldimethoxysilyl, ethyldimethoxysilyl, methyldiethoxysilyl, and ethyldiethoxysilyl can be listed. In this case, the alkoxy group can be bonded to the silicon atom via other groups such as an alkylene group.

[0156] Examples of organic groups contained in the adhesion promoter include, in addition to alkoxy groups, alkenyl groups such as vinyl groups, (meth)acryloyl groups, acryloyl groups, hydrosilyl groups, isocyanate groups, epoxy groups, alkyl groups, and aryl groups. Furthermore, organosilicon compounds or organosiloxanes having at least one organic group such as epoxy group, alkyl group, or aryl group and at least two silicon-bonded alkoxy groups in one molecule are more preferred.

[0157] In the case of containing an epoxy group as another organic group, the epoxy group may be a linear or branched alkyl group having 1 to 20 carbon atoms or an epoxy group having an aromatic ring, and the adhesive may contain two to three epoxy groups in one molecule. Examples of the group containing an epoxy group include glycidyloxyalkyl groups such as glycidyloxypropyl groups, and cyclohexylalkyl groups containing an epoxy group such as 2,3-epoxycyclohexylethyl and 3,4-epoxycyclohexylethyl groups.

[0158] Specific examples of the adhesion promoter include tetraethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, oligomers of 3-glycidoxypropyltrimethoxysilane, oligomers of 3-glycidoxypropyltriethoxysilane, methacryloxysilanes such as 3-methacryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, and furandiones such as dihydro-3-(3-(triethoxysilyl)propyl)-2,5-furandione.

[0159] pigment:

[0160] Examples of pigments include titanium oxide, aluminum silicate, iron oxide, zinc oxide, calcium carbonate, carbon black, rare earth oxides, chromium oxide, cobalt pigments, ultramarine blue, cerium silanol, aluminum oxide, aluminum hydroxide, titanium yellow, barium sulfate, precipitated barium sulfate, and mixtures thereof.

[0161] The pigment blending amount is preferably within the range of 0.001% to 5% relative to the total mass of the thermally conductive silicone composition, although an effective amount is used depending on the desired curing temperature and curing time for the intended application. The pigment amount is preferably within the range of 0.01% to 2%, and more preferably within the range of 0.05% to 1%. If the amount is less than 0.001%, the resulting composition will not be sufficiently colored, making it difficult to visually distinguish between the first and second liquids. On the other hand, if the amount exceeds 5%, costs will increase, which is not economically preferable.

[0162] Cure Inhibitors:

[0163] The curing inhibitor has the ability to regulate the curing rate of the addition reaction, and any curing inhibitor conventionally known in the art can be used as a compound having a curing inhibitory effect. Examples thereof include acetylene compounds, hydrazines, triazoles, phosphines, and thiols. Specific examples of such compounds include phosphorus-containing compounds such as triphenylphosphine, nitrogen-containing compounds such as tributylamine, tetramethylethylenediamine, and benzotriazole, sulfur-containing compounds, acetylene compounds, compounds containing two or more alkenyl groups, hydroperoxides, maleic acid derivatives, silanes, silicone compounds having amino groups, and the like.

[0164] The amount of the curing inhibitor blended is preferably in the range of 0.1 to 15 parts by mass relative to 100 parts by mass of the total amount of component (A) and component (B), although an effective amount is used depending on the curing temperature and the curing time required for the application. The amount is preferably in the range of 0.2 to 10 parts by mass, more preferably in the range of 0.5 to 5 parts by mass. If the amount is less than 0.1 parts by mass, the addition reaction is significantly accelerated, and the curing reaction proceeds during coating, which may deteriorate workability. On the other hand, if the amount exceeds 10 parts by mass, the addition reaction is slowed, and pumping may occur.

[0165] Specific examples of cure inhibitors include various "ene-yne" systems, such as 3-methyl-3-pentene-1-yne and 3,5-dimethyl-3-hexene-1-yne; acetylenic alcohols such as 3,5-dimethyl-1-hexan-3-ol, 1-ethynyl-1-cyclohexanol and 2-phenyl-3-butyn-2-ol; well-known maleates and fumarates, such as dialkyl maleates, dienyl maleates, dialkoxyalkyl maleates, dialkyl fumarates, dienyl fumarates and dialkoxyalkyl fumarates; and those containing cyclovinylsiloxanes.

[0166] In particular, when the thermally conductive silicone composition according to the present invention is used to form a gap filler, the composition is cured at room temperature. In this case, a silicone compound having a low viscosity (e.g., a viscosity of 100 mPa·s or less) and three or more vinyl groups is preferably used as a curing inhibitor.

[0167] Heat resistance imparting agent:

[0168] Examples of the heat resistance-imparting agent include cerium hydroxide, cerium oxide, iron oxide, fumed titanium dioxide, and mixtures thereof.

[0169] Airtightness improver:

[0170] As the airtightness improving agent, any agent can be used as long as it has the effect of reducing the air permeability of the cured product, and any organic or inorganic substance can be used. Specific examples thereof include polyurethane, polyvinyl alcohol, polyisobutylene, isobutylene-isoprene copolymer, plate-like talc, mica, glass flakes, boehmite, various metal foils and metal oxide powders, and mixtures thereof.

[0171] The thermally conductive silicone composition according to the present invention may not contain an organosilicon compound having one or more alkenyl groups and one or more alkoxy groups bonded to a silicon atom in one molecule. When the composition contains a compound having an alkenyl group and an alkoxy group bonded to a silicon atom in one molecule, when the compound is cured and used as a gap filler, the compound acts as a component for bonding the substrate to the gap filler. The composition of the present invention that does not contain such a component can further reduce deformation, damage, etc. of the battery, etc. when the cured product is exposed to high temperature and peeled off from the substrate.

[0172] The thermally conductive silicone composition of the present invention may include any one or more selected from the group consisting of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7), and hexadecamethylcyclooctasiloxane (D8).

[0173] The total content of (D4), (D5), (D6), (D7) and (D8) may be less than 0.1 parts by mass (ie, less than 1,000 ppm) relative to 100 parts by mass of the total amount of components (A) and (B).

[0174] When the total content of (D4) to (D8) contained in the thermally conductive silicone composition falls within the above range, the flash point of the entire composition can be increased, and the safety during storage can be improved. In addition, the cured product obtained by curing the composition can be provided in such a manner that the cured product is less likely to cause contact failure with electronic components, etc.

[0175] A thermally conductive silicone composition containing (D4) to (D8) in an amount of less than 0.1 part by mass of the total content of (D4) to (D8) relative to 100 parts by mass of the total amount of the components (A) and (B) can be prepared by using component (A) in which the total content xA of (D4) to (D8) is less than 0.1 part by mass, component (B) in which the total content xB of (D4) to (D8) is less than 0.1 part by mass; and component (C) in which the total content xC of (D4) to (D8) is less than 0.1 part by mass, so that the total content xA+xB+xC is less than 0.1 part by mass.

[0176] The content of each of (D4) to (D8) is measured by gas chromatography. The measurement conditions of the gas chromatography can be appropriately selected according to a conventionally known method.

[0177] The use of components (A), (B), and (C) in which the total content of (D4) to (D8) is low can result in the total content of (D4) to (D8) in the thermally conductive silicone composition falling within the above range. As a method for reducing the content of (D4) to (D8) in components (A) to (C), methods of subjecting the components to a heat treatment under reduced pressure are well known. For example, it is preferred that a reduced pressure heat treatment be performed at 180°C and 20 mmHg for approximately 8 hours during the production of the raw materials for components (A) to (C).

[0178] The cured product obtained by curing the thermally conductive silicone composition according to the present invention may have:

[0179] A hardness change rate of 10% or less according to the hardness change rate evaluation method described below; and

[0180] According to the thermal conductivity measurement method described below, the thermal conductivity is 5.0 W / m·K or higher.

[0181] Hardness change rate evaluation method:

[0182] The cured product obtained by curing the composition at 23° C. for 24 hours was measured for Shore 00 hardness using a Shore 00 durometer according to ASTM D 2240. This value was defined as the initial Shore 00 hardness.

[0183] The cured product obtained by curing the composition at 23° C. for 24 hours was exposed to 190° C. for 500 hours and then cooled to 23° C., and the Shore 00 hardness of the obtained cured product was measured using a Shore 00 hardness meter according to ASTM D 2240. This value is defined as the Shore 00 hardness after high temperature exposure.

[0184] Calculate the ratio of the change in Shore OO hardness after high temperature exposure relative to the initial Shore OO hardness.

[0185] Thermal conductivity measurement method:

[0186] The thermally conductive silicone composition was press-molded into a columnar shape having a diameter of 30 mm and a height of 6 mm, and then cured at 23° C. for 24 hours to produce a columnar cured product. The thermal conductivity of the cured product was measured by a hot plate method according to ISO 22007-2.

[0187] The term "hardness" described herein refers to resistance to permanent indentation when measured under specified conditions. For example, Shore OO hardness, also known as hardness ShOO or Shore scale OO hardness, is determined using a Shore OO durometer according to ASTM D 2240.

[0188] The thermally conductive silicone composition according to the present invention is an addition-curable composition and can be a one-component composition or a two-component composition. When the composition is appropriately designed to be cured by heat, the one-component composition can have improved storage properties.

[0189] In the case of a two-component composition containing a first liquid and a second liquid as a solid, it becomes possible to further enhance storage stability without these designs, and it is easy to obtain a composition that cures at room temperature (e.g., 23° C.). In this case, the thermally conductive silicone composition according to the present invention can be dispensed into the first liquid and the second liquid, for example, as follows.

[0190] For example, the first liquid does not contain component (B) and contains component (D), and the second liquid contains components (B) and (C) and does not contain component (D). Components (A) and (E) and any optionally blended components may be blended in the first liquid, the second liquid, or both.

[0191] When component (D) and components (B) and (C) are respectively contained in separate liquids, the thermally conductive silicone composition according to the present invention can be prepared as a multi-component composition in which the respective components of the composition are distributed in three or more separate liquids.

[0192] Therefore, the method for producing the two-component thermally conductive silicone composition of the present invention comprises:

[0193] a first step of mixing component (A) (i.e., alkenyl group-containing organopolysiloxane), component (D) (i.e., addition reaction catalyst), and component (E) (i.e., thermally conductive filler) to obtain a first liquid; and

[0194] In the second step, component (A) (i.e., an organopolysiloxane containing an alkenyl group), component (B) (i.e., a linear organopolysiloxane having two or more hydrosilyl groups in one molecule), component (C) (i.e., a hydrogenated cyclic siloxane), and component (E) (i.e., a thermally conductive filler) are mixed to obtain a second liquid.

[0195] The amount of each component to be dispensed into the first and second liquids is not particularly limited, as long as component (D) is dispensed into the first liquid and components (B) and (C) are dispensed into the second liquid. For example, when the first and second liquids are mixed in equal amounts, the amount of each component to be dispensed is set to the following relative to 100 parts by mass of component (A) to be dispensed into the first liquid. It should be noted that the ratio of the first liquid to the second liquid can be freely set according to the application.

[0196] First liquid:

[0197] Component (A): 100 parts by mass

[0198] Component (D): 15 ppm or more and 30,000 ppm or less

[0199] Component (E): 500 parts by mass or more and 3,000 parts by mass or less

[0200] Optional components:

[0201] Silane coupling agent: 0% to 2% by weight relative to the thermally conductive filler

[0202] Condensation catalyst: 0 parts by mass or more and 20 parts by mass or less

[0203] Curing inhibitor: 0 parts by mass or more and 20 parts by mass or less

[0204] Pigment: 0 parts by mass or more and 20 parts by mass or less

[0205] Second liquid:

[0206] Component (A): 0 parts by mass or more and 80 parts by mass or less

[0207] Component (B): 20 parts by mass or more and 100 parts by mass or less

[0208] Component (C): 0.5 parts by mass or more and 1.8 parts by mass or less

[0209] Component (E): 500 parts by mass or more and 3,000 parts by mass or less

[0210] Optional components:

[0211] Cross-linking agent: 0 parts by mass or more and 10 parts by mass or less

[0212] Silane coupling agent: 0wt% to 2wt% relative to thermal conductive filler

[0213] Pigment: 0 parts by mass or more and 20 parts by mass or less

[0214] The pigment may be contained in the first liquid or the second liquid, or both.

[0215] The present invention also provides a method for manufacturing a gap filler, comprising:

[0216] Mixing step: mixing the first liquid and the second liquid to obtain a thermally conductive silicone composition;

[0217] a filling step of filling the gap between the heat dissipating body and the heating body with the thermally conductive silicone composition obtained in the mixing step; and

[0218] A curing step of curing the uncured thermally conductive silicone composition filled in the filling step.

[0219] In the filling step, the uncured thermally conductive silicone composition is filled into the gap between the heat generating element and the heat dissipating element (e.g., the gap between the heat sink and the reactor or the gap between the heat sink and the housing containing the reactor) to be applied to the substrate (which is the surface of the heat generating element or the heat dissipating element). When the filling step is performed at, for example, 0°C or higher and 60°C or lower, a non-flowable cured product is formed within about 120 minutes after the filling (curing step).

[0220] The temperature during the filling step is not particularly limited and may be, for example, room temperature, which is 0° C. or higher and 30° C. or lower. To reduce any thermal damage to the substrate, etc., the temperature may be 10° C. or higher and 30° C. or lower. In particular, when the substrate is made of polycarbonate or PET, which has poor heat resistance, it is preferable not to heat the substrate.

[0221] The curing step can be performed without heating and at room temperature (e.g., a temperature of 10°C or higher and 30°C or lower). If the composition is a heat-curable composition, the composition can be first applied to a substrate or the like and then heated. Heating the composition for curing can be performed by utilizing heat radiated from a heat sink. The temperature during heat curing can be, for example, 40°C or higher and 180°C or lower, and preferably 50°C or higher and 150°C or lower.

[0222] The substrate coated with the thermally conductive silicone composition is not particularly limited, and examples thereof include ceramics, resins, glass, and metals such as aluminum, magnesium, iron, nickel, titanium, stainless steel, copper, lead, zinc, molybdenum, and silicon, and materials obtained by coating any of these metals with enamel.

[0223] Preferred examples of ceramic substrates to which the cured thermally conductive silicone composition of the present invention is bonded include those made of oxides, carbides, and nitrides, such as aluminum oxide, aluminum nitride, aluminum oxide zirconia, zirconium oxide, zinc oxide, barium titanate, lead zirconate titanate, beryllium oxide, silicon nitride, and silicon carbide.

[0224] Preferred examples of the resin substrate to which the cured thermally conductive silicone composition is bonded include resin substrates made of polyester, epoxy resin, polyamide, polyimide, ester resin, polyacrylamide, acrylonitrile-butadiene-styrene (ABS) resin, styrene resin, polypropylene, polyacetal, acrylic resin, polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyetheretherketone (PEEK), polymethyl methacrylate (PMMA), and silicone resin.

[0225] In the case where the cured product obtained by curing the thermally conductive silicone composition of the present invention is a gap filler for a battery cell, the battery cell housing (which is the substrate to be bonded) may have an iron surface at least partially coated with a cationic electrodeposition coating on the substrate surface, and the heat sink may have an aluminum surface.

[0226] The thermally conductive silicone composition may be applied to the heat sink first, and then the heat sink may be arranged so that the composition and the heat sink are sandwiched, or the thermally conductive silicone composition may be applied to the heat sink first, and then the heat sink may be arranged so that the composition and the heat sink are sandwiched. Alternatively, the thermally conductive silicone composition may be injected into the gap between the heat sink and the heat sink.

[0227] When the cured product of the thermally conductive silicone composition of the present invention is used as a gap filler, heat generated by a heat generating body can be diffused to a heat dissipating body such as a radiator through the gap filler having good heat dissipation performance, making it possible to manufacture a power control unit having excellent heat dissipation performance.

[0228] The present invention also provides a method for reducing the occurrence of voids in an adhered portion between a cured article and a substrate after the cured article has been exposed to a high temperature of 190° C. or higher, wherein the cured product is obtained by applying a thermally conductive silicone composition to the substrate and curing the applied composition, and is obtained by blending a hydrogenated cyclic siloxane as component (C) into the thermally conductive silicone composition, wherein the thermally conductive silicone composition comprises an organopolysiloxane containing an alkenyl group as component (A), a linear organopolysiloxane having two or more hydrosilyl groups in one molecule as component (B), an addition reaction catalyst as component (D), and a thermally conductive filler as component (E), and the hydrogenated cyclic siloxane as component (C) comprises at least one selected from 1,3,5,7,9-pentamethylcyclopentasiloxane (HD5) and 1,3,5,7,9,11-hexamethylcyclohexasiloxane (HD6).

[0229] [Example]

[0230] The present invention will be described in detail based on examples, but the present invention is not limited to the following examples. Table 1 shows the mixing ratios and evaluation results of the components in Examples and Comparative Examples. The numerical values ​​of the mixing ratios shown in Table 1 are shown in "parts by mass". The hydrogen content shown in Table 1 is the hydrogen content (mass %) in the first liquid or the second liquid relative to 100 parts by mass of the total amount of component (A) and component (B).

[0231] Work ability assessment:

[0232] The first and second liquids described in each Example and Comparative Example were weighed at a 1:1 ratio, thoroughly mixed using a stirrer, and then degassed using a vacuum pump to prepare a thermally conductive silicone composition. The viscosity of each thermally conductive silicone composition was measured using a rotational viscometer (JIS K7117-2) at 23°C and a shear rate of 1 / s or 10 / s.

[0233] When the viscosity at a shear rate of 1 / s was less than 1,000 Pas and the viscosity at a shear rate of 10 / s was less than 200 Pas, the processability was evaluated as good.

[0234] Thermal conductivity evaluation:

[0235] The first and second liquids described in each example and comparative example were weighed at a ratio of 1:1, thoroughly mixed using a stirrer, and then degassed using a vacuum pump. The resulting thermally conductive silicone composition was press-molded into a columnar shape with a diameter of 30 mm and a height of 6 mm, and then cured at 23°C for 24 hours to produce a columnar cured product. The thermal conductivity of the cured product was measured using a measuring device (TPS-500 manufactured by Kyoto Electron Manufacturing Co., Ltd.) based on the hot plate method of ISO 22007-2. A sensor was placed between the two columnar cured products produced as described above, and the thermal conductivity was measured using the measuring device.

[0236] The thermal conductivity is preferably 5.0 W / m·K or higher.

[0237] Hardness change rate assessment:

[0238] The first liquid and the second liquid shown in each embodiment and comparative example were weighed at a ratio of 1:1, thoroughly mixed by a stirrer, and then degassed by a vacuum pump. The resulting thermally conductive silicone composition was press-molded into a columnar shape with a diameter of 30 mm and a height of 6 mm, and then cured at 23°C for 24 hours to prepare a columnar cured product. The Shore OO hardness of the cured product was measured using a Shore OO hardness tester (Model GS754, manufactured by TECLOCK Co., Ltd.) according to ASTM D2240 by sandwiching a sensor between the two columnar cured products prepared as described above. The value obtained is defined as "Shore OO hardness (initial)".

[0239] After curing at 23°C for 24 hours in the same manner as above, the cured product was exposed to 190°C for 500 hours, and the Shore 00 hardness of the cured product was measured under the above conditions. The obtained value was defined as "Shore 00 hardness (after high temperature exposure)".

[0240] When the hardness change rate of "Shore OO Hardness (after high-temperature exposure)" based on "Shore OO Hardness (initial)" is 10% or less, the hardness change after high-temperature exposure is evaluated to be small.

[0241] Measurement method of shear bond stress:

[0242] The first and second liquids described in each Example and Comparative Example were weighed in a 1:1 ratio, thoroughly mixed with a stirrer, and then degassed using a vacuum pump. After preparing an aluminum plate approximately 60 cm long, 25 cm wide, and 2 mm thick as a substrate, the resulting thermally conductive silicone composition was applied to the first substrate over an area approximately 25 mm long and 25 mm wide, with a thickness of approximately 1 mm. The applied product was sandwiched between the first and second substrates and cured at 23°C for 24 hours. The resulting product was used as a test piece before high-temperature exposure.

[0243] The sample before high-temperature exposure was exposed at 190° C. for 500 hours to obtain a sample after high-temperature exposure.

[0244] The shear bond strength before and after high-temperature exposure was evaluated by measuring the shear tensile strength of each specimen according to JIS K 6850. The measurement was performed using an AUTOGRAPH manufactured by Shimadzu Corporation at 23°C. The first and second substrates were then pulled in the shear direction at a speed of 50 mm / min, and the stress at the separation of the two substrates was measured and defined as the shear bond strength.

[0245] The shear adhesion strength before high temperature exposure is preferably 0.1 MPa or more because the cured product needs to be closely adhered to the substrate before exposure to high temperature. The shear adhesion strength after high temperature exposure is also preferably 0.1 MPa or more.

[0246] Assessment of void occurrence:

[0247] The first and second liquids described in each example and comparative example were weighed in a 1:1 ratio, thoroughly mixed with a stirrer, and then degassed using a vacuum pump. After preparing two glass plates measuring approximately 60 cm long, 60 cm wide, and 2 mm thick as substrates, the resulting thermally conductive silicone composition was applied to a glass substrate approximately 25 mm long, 25 mm wide, and approximately 2 mm thick. The applied product was sandwiched between this substrate and another substrate and cured at 23°C for 24 hours.

[0248] In order to evaluate the occurrence of voids, the above test piece was exposed to 190°C for 500 hours, and the presence or absence of voids in the cured product after high temperature exposure was examined. If voids, cracks, etc. were present by visual inspection, it was determined that voids were present (Y), and if not, it was determined that voids were not present (N).

[0249] Appearance evaluation method:

[0250] The first and second liquids described in each example and comparative example were weighed in a 1:1 ratio, thoroughly mixed with a stirrer, and then degassed using a vacuum pump. After preparing two glass plates measuring approximately 60 cm long, 60 cm wide, and 2 mm thick as substrates, the resulting thermally conductive silicone composition was applied to one glass substrate measuring approximately 25 mm long, 25 mm wide, and approximately 2 mm thick. The applied product was sandwiched between this substrate and another substrate and cured at 23°C for 24 hours.

[0251] The appearance evaluation was performed by exposing the above-mentioned specimens at 190° C. for 500 hours and inspecting any changes in the appearance of the cured product after the high-temperature exposure. If yellowing was present by visual inspection (no yellow discoloration was observed before the high-temperature exposure), it was determined that yellowing was present (Y), and if not, it was determined that yellowing was not present (N).

[0252] Applicable period evaluation method:

[0253] The first and second liquids described in each Example and Comparative Example were weighed in a 1:1 ratio, thoroughly mixed with a stirrer, and then degassed using a vacuum pump. The viscosity of the resulting thermally conductive silicone composition at 25°C was measured in accordance with JIS K 7117-2. Specifically, the uncured thermally conductive silicone composition was placed between parallel plates with a diameter of 25 mm, and the viscosity was measured using a Physica MR 301 manufactured by Anton Paar GmbH at a shear rate of 10 (1 / s) and a gap of 0.5 mm. The pot life was defined as the time it took for the viscosity to reach twice the initial viscosity.

[0254] A method for estimating the amount of low molecular weight cyclic siloxane to be used:

[0255] The first liquid and the second liquid shown in each embodiment and comparative example are weighed at a ratio of 1: 1, thoroughly mixed by a stirrer, and then degassed by a vacuum pump. The resulting thermally conductive silicone composition is press-molded into a plate with a height of 100 mm × 100 mm × 6 mm and cured at 23 ° C for 24 hours to produce a cured product. Then, 0.3 g of the cured product is weighed, placed in 10 ml of acetone in a sample vial, and sealed for extraction for 12 hours. The extracted solution is subjected to gas chromatography to measure low molecular weight cyclic compounds (octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecylcycloheptasiloxane (D7), and hexadecylcyclooctasiloxane (D8)).

[0256] Method for preparing a cured product of a thermally conductive silicone composition:

[0257] Example 1

[0258] The first liquid and the second liquid shown in each Example and Comparative Example were prepared according to the following procedure and according to the chemical compositions shown in the following table. The unit of the blending ratio of each component shown in the table is "parts by mass".

[0259] The first liquid of each of Examples 1 to 4 and Comparative Examples 1 to 2:

[0260] The alkenyl group-containing diorganopolysiloxane as component (A) and the platinum-divinyltetramethyldisiloxane complex (addition reaction catalyst) as component (D) were weighed separately and mixed together to form a mixture, which was kneaded at room temperature for 30 minutes using a planetary mixer.

[0261] Component (A) is a linear dimethylpolysiloxane having only one alkenyl group at each terminal and having a viscosity of 120 mPa·s.

[0262] Thereafter, as component (E), half the amount of a thermally conductive filler (comprising a mixture of spherical alumina having an average particle size of 80 μm, spherical alumina having an average particle size of 5 μm, and amorphous alumina having an average particle size of 0.4 μm mixed in a ratio of 7:2:1) was added thereto and kneaded at room temperature for 15 minutes using a planetary mixer.

[0263] The remaining half of the thermally conductive filler was added thereto and kneaded using a planetary mixer at room temperature for 15 minutes to prepare a first liquid.

[0264] The second liquid of each of Examples 1 to 4 and Comparative Examples 1 to 2:

[0265] A mixture of the same alkenyl-containing diorganopolysiloxane as the first liquid (component (A)), a linear dimethylpolysiloxane having one hydrogen atom at each terminal (two hydrogen atoms total) and a viscosity of 70 mPa·s (component (B)), and 2,4,6,8,10-pentamethylcyclopentasiloxane (HD5) and 2,4,6,8,10,12-hexamethylcyclohexasiloxane (HD6) (component (C))) was weighed and kneaded at room temperature for 30 minutes using a planetary mixer. The mixture of component (C) contained a total of 90 wt% of HD5 and HD6 in a weight ratio of 6:4. The hydrogen content of component (C) was 1.6 wt%.

[0266] Thereafter, the same thermally conductive filler as in the first liquid was added as component (E), and the mixture was kneaded using a planetary mixer at room temperature for 15 minutes to prepare a second liquid.

[0267] 2,4,6,8,10-Pentamethylcyclopentasiloxane (CAS 6166-86-5) was obtained from Sigma-Aldrich Corp. 2,4,6,8,10,12-Hexamethylcyclohexasiloxane (CAS 6166-87-6) was prepared by a method described in the literature (N. Omura and J.P. Kennedy, Macromolecules, 30, 3204 (1997)). The compound was obtained by fractional distillation and its purity was determined by gas chromatography (GC).

[0268] Comparative Examples 3 to 4:

[0269] A first liquid and a second liquid were prepared in the same manner as in Example 1, except that a linear low-molecular-weight polymer having SiH groups only at its terminals was added in amounts of 1.5 parts by weight and 7.7 parts by weight, respectively, instead of component (C).

[0270] As a linear low molecular weight polymer having only one SiH group at each end, dimethylpolysiloxane having a molecular weight of 650 and a hydrogen content of 0.31 wt % was used.

[0271] Comparative Examples 5 to 6:

[0272] The first liquid and the second liquid were prepared in the same manner as in Example 1 except that 1.5 parts by mass and 13 parts by mass of a linear dimethylpolysiloxane having a molecular weight of 6800 and containing a low concentration of SiH groups only on the side chains were added instead of component (C).

[0273] As the linear dimethylpolysiloxane containing SiH groups only at a low concentration in the side chains, dimethylpolysiloxane whose terminals were blocked with trimethylsilyl groups having a hydrogen content of 0.19 wt % was used.

[0274] Comparative Example 7:

[0275] The first liquid and the second liquid were prepared in the same manner as in Example 1, except that, instead of component (C), a linear siloxane containing a moderate concentration of SiH groups only in the side chains was added in an amount of 1.5 parts by mass.

[0276] As the linear siloxane containing SiH groups only in a moderate concentration in the side chains, dimethylpolysiloxane (crosslinker V90 manufactured by Wacker Chemie AG) whose terminals were capped with linear trimethylsilyl groups having a hydrogen content of 1.15 wt % was used.

[0277] Comparative Example 8:

[0278] The first liquid and the second liquid were prepared in the same manner as in Example 1, except that, instead of component (C), a linear siloxane containing a high concentration of SiH groups only in the side chains was added in an amount of 1.5 parts by mass.

[0279] As the linear siloxane containing a high concentration of SiH groups only in the side chains, dimethylpolysiloxane (crosslinker V24 manufactured by Wacker Chemie AG) whose terminals were blocked with linear trimethylsilyl groups having a hydrogen content of 1.63 wt % was used.

[0280] Comparative Example 9:

[0281] The first liquid and the second liquid were prepared in the same manner as in Example 1, except that, instead of the component (C), 10 parts by mass of cerium oxide was added as a known heat resistance improver.

[0282] The evaluation results are shown in Table 1.

[0283] In Examples 1 to 4, a methyl-substituted hydrogenated cyclic siloxane as component (C) was blended in an amount of 1.0 to 3.0 parts by weight (the blending amount of component (C) was 0.5 to 1.5 parts by mass relative to 100 parts by mass of the total amount of components (A) and (B) contained in the entire thermally conductive silicone composition. In Table 1, the blending amounts are described as those relative to 100 parts by mass of the total amount of components (A) and (B) in the second liquid). Heat resistance was favorable, with the hardness change rate from the initial hardness after high-temperature exposure being 10% or less, and no voids or yellowing occurring after high-temperature exposure. In addition, the shear adhesion stress in all Examples 1 to 4 was not less than 0.1 MPa before and after high-temperature exposure, which was a favorable result. A pot life of 60 minutes or more was ensured, and workability was good.

[0284] In Comparative Example 1, the hydrogenated cyclic siloxane of the component (C) was blended in an amount of 0.8 parts by mass (0.4 parts by mass relative to 100 parts by mass of the total amount of components (A) and (B) contained in the entire thermally conductive silicone composition), but the hardness change rate after high-temperature exposure was large, and it could not be said that the heat resistance was sufficient.

[0285] In Comparative Example 2, the hydrogenated cyclic siloxane of component (C) was blended in an amount of 4.0 parts by mass (2.0 parts by mass relative to 100 parts by mass of the total amount of components (A) and (B) contained in the entire thermally conductive silicone composition), but since the relative content of the filler was reduced, the thermal conductivity was insufficient.

[0286] In Comparative Example 3, a low-molecular-weight polymer having only one SiH group at each terminal was added in equal parts by mass in place of component (C) in Example 2. Due to insufficient relative hydrogen content, the initial hardness was low, but the hardness increased after high-temperature exposure. Consequently, the hardness varied significantly, voids were observed, and heat resistance was insufficient.

[0287] In Comparative Example 4, a low-molecular-weight polymer containing only one SiH group at each terminal was added in an amount equivalent to the hydrogen content, replacing component (C) of Example 2. Since the amount of the low-molecular-weight polymer containing only SiH groups at the terminals increased, the amount of thermally conductive filler was relatively reduced, resulting in insufficient thermal conductivity. Furthermore, the hardness still varied significantly, and heat resistance was insufficient.

[0288] In Comparative Example 5, a linear siloxane containing only a low concentration of SiH groups in its side chains was added in equal parts by mass in place of component (C) in Example 2. Due to the insufficient relative hydrogen content, the initial hardness was low, but the hardness after high-temperature exposure was high. Consequently, the hardness after high-temperature exposure varied significantly, yellowing was observed, and heat resistance was insufficient.

[0289] In Comparative Example 6, a linear siloxane containing only a low concentration of SiH groups in the side chains was added in an amount equivalent to the hydrogen content, replacing component (C) of Example 2. Consequently, the pot life was short, and curing of the composition occurred during the mixing of the first and second liquids, making it impossible to prepare a sample. In practice, the time required for application to a heating element or heat sink was limited, resulting in poor processability, which is undesirable.

[0290] In Comparative Example 7, a linear siloxane containing only a moderate concentration of SiH groups in its side chains was added in equal parts by mass in place of component (C) in Example 2. The pot life was short, and the composition solidified during the mixing of the first and second liquids, making it impossible to prepare a sample. In practice, the time required for application to a heating element or heat sink was limited, resulting in poor processability, which is undesirable.

[0291] In Comparative Example 8, a linear siloxane containing a high concentration of SiH groups only in its side chains was added in equal parts by mass in place of component (C) in Example 2. The pot life was short, and the composition solidified during the mixing of the first and second liquids, making it impossible to prepare a sample. In practice, the time required for application to a heating element or heat sink was limited, resulting in poor processability, which is undesirable.

[0292] In Comparative Example 9, cerium oxide was added to improve heat resistance. However, the hardness change rate after high-temperature exposure was large and the formation of voids was observed. Therefore, the expected effect was not achieved.

[0293] Table 1

[0294]

[0295]

Claims

1. A thermally conductive silicone composition comprising: Component (A) is an organopolysiloxane containing an alkenyl group; Component (B) is a linear organopolysiloxane having two or more hydrosilyl groups in one molecule; Component (C) is a hydrogenated cyclic siloxane represented by the following general formula (1): [Chemical Formula 1] (wherein n is an integer of 4 or more and 8 or less, and R is a monovalent hydrocarbon group having 1 to 6 carbon atoms); Component (D) is an addition reaction catalyst; as well as Component (E) is a thermally conductive filler, wherein Relative to 100 parts by mass of the total amount of the component (A) and the component (B), The content of component (C) is 0.5 parts by mass or more and 1.8 parts by mass or less, and the content of component (E) is 500 parts by mass or more and 3,000 parts by mass or less.

2. The thermally conductive silicone composition according to claim 1, wherein Component (C) includes 1,3,5,7,9-pentamethylcyclopentasiloxane (HD5) and 1,3,5,7,9,11-hexamethylcyclohexasiloxane (HD6).

3. The thermally conductive silicone composition according to claim 2, wherein: The mass ratio of the component (A) to the component (B) (mass of component (A):mass of component (B)) falls within the range of 80:20 to 50:50; and The total amount of HD5 and HD6 is 0.5 parts by mass or more and 1.5 parts by mass or less relative to 100 parts by mass of the total amount of the component (A) and the component (B).

4. The thermally conductive silicone composition according to claim 1 or 2, wherein The total content of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7) and hexadecamethylcyclooctasiloxane (D8) is less than 0.1 parts by mass relative to 100 parts by mass of the total amount of components (A) and (B).

5. The thermally conductive silicone composition according to claim 1 or 2, wherein: The cured product obtained by curing the thermally conductive silicone composition has: A hardness change rate of 10% or less according to the hardness change rate evaluation method described below; and Thermal conductivity above 5.0 W / m·K according to the thermal conductivity measurement method described below: Hardness change rate evaluation method The Shore OO hardness of the cured product obtained by curing at 23° C. for 24 hours was measured using a Shore OO durometer according to ASTM D 2240, and the obtained value was defined as the initial Shore OO hardness, The cured product obtained by curing at 23° C. for 24 hours was exposed to 190° C. for 500 hours and then cooled to 23° C., and the Shore 00 hardness of the obtained cured product was measured using a Shore 00 durometer according to ASTM D 2240, and the obtained value was defined as the Shore 00 hardness after high temperature exposure, and Calculate the change rate of Shore OO hardness after high temperature exposure relative to the initial Shore OO hardness; as well as Thermal conductivity measurement method The thermally conductive silicone composition was press-molded into a columnar shape having a diameter of 30 mm and a height of 6 mm, and then cured at 23° C. for 24 hours to prepare a columnar cured product. The thermal conductivity of the cured product was measured by a hot plate method according to ISO 22007-2.

6. A thermally conductive silicone composition comprising an alkenyl group-containing organopolysiloxane as component (A), a linear organopolysiloxane having two or more hydrosilyl groups in one molecule as component (B), an addition reaction catalyst as component (D), and a thermally conductive filler as component (E), the composition further comprising a hydrogenated cyclic siloxane as component (C), thereby reducing the occurrence of voids in an adhered portion between a cured product and a substrate after the cured product is exposed to a high temperature of 190° C. or higher, wherein: A cured product is obtained by applying the thermally conductive silicone composition to a substrate and curing the applied composition.

7. A method for producing a two-component thermally conductive silicone composition, comprising: In a first step, an alkenyl group-containing organopolysiloxane as component (A), an addition reaction catalyst as component (D), and a thermally conductive filler are mixed to obtain a first liquid as component (E); as well as In the second step, the alkenyl group-containing organopolysiloxane as component (A), the linear organopolysiloxane having two or more hydrosilyl groups in one molecule as component (B), the hydrogenated cyclic siloxane as component (C), and the thermally conductive filler as component (E) are mixed to obtain a second liquid.

8. A method for reducing the generation of voids in an adhered portion between a cured product and a substrate after the cured product has been exposed to a high temperature of 190° C. or higher, wherein the cured product is obtained by applying a thermally conductive silicone composition to the substrate and curing the applied composition, and the thermally conductive silicone composition is obtained by blending a hydrogenated cyclic siloxane as component (C) into the thermally conductive silicone composition, the thermally conductive silicone composition comprising an alkenyl group-containing organopolysiloxane as component (A), a linear organopolysiloxane having two or more hydrosilyl groups in one molecule as component (B), an addition reaction catalyst as component (D), and a thermally conductive filler as component (E), the hydrogenated cyclic siloxane comprising at least one selected from 1,3,5,7,9-pentamethylcyclopentasiloxane (HD5) and 1,3,5,7,9,11-hexamethylcyclohexasiloxane (HD6).

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