JP2021113290A - Heat-conductive silicone potting composition, and cured product of the same - Google Patents

Abstract

To provide a heat conductive silicone potting composition having high fluidity in spite of containing a heat-conductive filler in plenty, capable of flowing into a fine space, having required heat conductivity after cure, and giving a cured product having a low density.SOLUTION: A heat-conductive silicone potting composition includes: (A) organopolysiloxane having an alkenyl group, and no organoxysilyl group; (B) organopolysiloxane blocked with an alkoxy group at one end terminal; (C) an alumina powder having an average particle size of 0.1-50 μm; (D) a magnesium oxide powder having an average particle size of 1-150 μm; (E) organohydrogensiloxane; and (F) a hydrosilylation reaction catalyst.SELECTED DRAWING: None

Description

The present invention relates to a thermally conductive silicone potting composition and a cured product thereof.

Due to growing awareness of global warming, the automobile industry is developing environmentally friendly vehicles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles with the aim of reducing greenhouse gases, and improving their fuel efficiency. For the purpose, the inverter mounted on the vehicle has been improved in performance and miniaturized.
Along with this, parts such as ICs and reactors in the inverter have also been miniaturized, and the amount of heat generated has also increased. For such parts that generate heat, conventionally, heat conductivity such as a heat conductive silicone grease composition, a heat conductive silicone gel composition, and a heat conductive silicone potting composition is used between the heat generating part and the cooler. By interposing the silicone composition, the cooling efficiency of the part is improved and the part is protected.

For example, Patent Document 1 proposes a thermally conductive silicone composition containing an organopolysiloxane, a hydrolyzable group-containing methylpolysiloxane, a thermally conductive filler, and a curing agent. It was difficult to bring it into close contact with a part having a fine structure.
Therefore, in Patent Document 2, there is a method in which a cooler and a heat generating component are assembled in advance, a heat conductive silicone potting composition having high fluidity is poured into the cooler, and the heat generating component and the cooler are thermally connected. Proposed.
However, when the practical fluidity is maintained by the method of Patent Document 2, the thermal conductivity of about 1.0 W / m · K is the limit, and further heat generation is generated due to the recent miniaturization of equipment and parts. Not enough to cope with the increase in quantity.

As a technique for solving this problem, Patent Documents 3 and 4 propose a silicone potting composition in which a large amount of a heat conductive filler is contained to increase the heat conductivity while achieving both high fluidity.
However, since these compositions contain a large amount of alumina, they have a problem that the density is high and the total weight of the parts becomes heavy. Therefore, in order to improve the performance of the inverter, not only high thermal conductivity and high fluidity but also low-density thermally conductive silicone potting composition has been urgently desired.

Japanese Patent No. 35436663 Japanese Patent No. 5304623 JP-A-2019-077843 Japanese Unexamined Patent Publication No. 2019-07845

The present invention has been made in view of the above circumstances, and although it contains a large amount of a heat conductive filler, it has high flowability, can flow into a fine space, and has desired heat after curing. It is an object of the present invention to provide a thermally conductive silicone potting composition having conductivity and giving a low-density cured product.

As a result of diligent studies to achieve the above object, the present inventors have made a thermal conductive filler by using alumina having a predetermined average particle size and magnesium oxide in combination as the thermally conductive filler. The present invention has been completed by finding a thermally conductive silicone potting composition that gives a cured product having high flowability and low density even when a large amount of is added.

（式中、Ｒ¹は互いに独立に非置換または置換の一価炭化水素基であり、Ｒ²は互いに独立にアルキル基、アルコキシアルキル基、アルケニル基またはアシル基である。ｎは２〜１００の整数であり、ａは１〜３の整数である。）
で示されるオルガノポリシロキサン：１〜１００質量部
（Ｃ）平均粒径が０．１〜５０μｍのアルミナ粉末：１００〜２，０００質量部
（Ｄ）平均粒径が１〜１５０μｍの酸化マグネシウム粉末：１００〜２，０００質量部
（Ｅ）１分子中に少なくとも２個のＳｉＨ基を有するオルガノハイドロジェンシロキサン：０．１〜１００質量部
（Ｆ）ヒドロシリル化反応触媒
を含む熱伝導性シリコーンポッティング組成物、
２． １記載の熱伝導性シリコーンポッティング組成物を硬化してなる硬化物、
３． 熱伝導率が３．５Ｗ／ｍ・Ｋ以上であり、かつ密度が３．０以下である２記載の硬化物
を提供する。 That is, the present invention
1. 1. (A) Organopolysiloxane: 100, which has a viscosity at 25 ° C. of 0.01 to 100 Pa · s, has at least two alkenyl groups bonded to silicon atoms in one molecule, and does not have an organoxysilyl group. Part by mass (B) The following general formula (1)

(In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group ^{independently of each other, and R 2} is an alkyl group, an alkoxyalkyl group, an alkenyl group or an acyl group independently of each other. N is 2 to 100. It is an integer, and a is an integer of 1 to 3.)
Organopolysiloxane represented by: 1 to 100 parts by mass (C) Alumina powder having an average particle size of 0.1 to 50 μm: 100 to 2,000 parts by mass (D) Magnesium oxide powder having an average particle size of 1 to 150 μm: 100 to 2,000 parts by mass (E) Organohydrogensiloxane having at least two SiH groups in one molecule: 0.1 to 100 parts by mass (F) Thermally conductive silicone potting composition containing a hydrosilylation reaction catalyst ,
2. A cured product obtained by curing the thermally conductive silicone potting composition according to 1.
3. 3. The cured product according to 2 having a thermal conductivity of 3.5 W / m · K or more and a density of 3.0 or less is provided.

The thermally conductive silicone potting composition of the present invention has high flowability before curing, can flow into a fine space, obtains desired thermal conductivity after curing, and has a low density. Can contribute to protection and weight reduction. Therefore, the composition of the present invention is effective for potting when a component having a fine structure such as a transformer is fixed to a cooler, and in such a member, high thermal conductivity after curing is achieved. It is possible to efficiently transfer the heat of the parts to the cooler at a high rate, and the weight of the parts can be reduced due to the low density.

Hereinafter, the present invention will be described in more detail.
The thermally conductive silicone potting composition according to the present invention is one that cures at room temperature or at heating and adheres to a metal, an organic resin, or the like.
(A) alkenyl group-containing organopolysiloxane,
(B) Organopolysiloxane, one end of which is sealed with an alkoxysilyl group, etc.
(C) Alumina powder with an average particle size of 0.1 μm to 50 μm,
(D) Magnesium oxide powder having an average particle size of 1 μm to 150 μm,
(E) Organohydrogensiloxane,
(F) Contains a hydrosilylation reaction catalyst.

[(A) component]
The component (A) is an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule and no organoxisilyl group. The component (A) is distinguished from the component (B) in that it does not have an organoxisilyl group.

The viscosity of the component (A) at 25 ° C. is 0.01 to 100 Pa · s, preferably 0.06 to 10 Pa · s. If the viscosity at 25 ° C. is less than 0.01 Pa · s, the storage stability of the composition deteriorates, and if it exceeds 100 Pa · s, the flowability cannot be ensured. The viscosity is a value measured by a B-type rotational viscometer (hereinafter, the same applies).

Such an organopolysiloxane is not particularly limited as long as it satisfies the above viscosity and alkenyl group content, and a known organopolysiloxane can be used. Examples of the molecular structure include linear, branched chain, linear with partial branch, dendrimer (dendrimer) and the like, and preferably linear and linear with partial branch. .. Further, the component (A) may be a single polymer having these molecular structures, a copolymer having these molecular structures, or a mixture of two or more kinds of organopolysiloxanes having different viscosities.

Specifically, a linear diorganopolysiloxane in which the main chain basically consists of repeating diorganosiloxane units and both ends of the molecular chain are sealed with a triorganosyloxy group or a silanol-containing group is preferable. When the molecular structure of the organopolysiloxane of the component (A) is linear or branched, the position of the silicon atom to which the alkenyl group is bonded in the molecule of the organopolysiloxane is at the end of the molecular chain and in the middle of the molecular chain. Either one of (bifunctional diorganosiloxane unit located at the non-terminal of the molecular chain or trifunctional monoorganosylsesquioxane unit) may be located at both of them when there are two or more of them. Particularly preferable in terms of flexibility, it is a linear diorganopolysiloxane containing an alkenyl group bonded to silicon atoms at both ends of the molecular chain.

The alkenyl group bonded to the silicon atom is not particularly limited, but an alkenyl group having 2 to 10 carbon atoms is preferable, and an alkenyl group having 2 to 8 carbon atoms is more preferable.
Specific examples thereof include vinyl, allyl, 1-butenyl, 1-hexenyl groups and the like. Among these, a vinyl group is preferable from the viewpoint of ease of synthesis and cost. The number of alkenyl groups in one molecule of the component (A) is preferably 2 to 10.

The organic group bonded to the silicon atom other than the alkenyl group is not particularly limited, but a monovalent hydrocarbon group excluding the aliphatic unsaturated bond having 1 to 20 carbon atoms is preferable, and one of 1 to 10 carbon atoms is preferable. A valent hydrocarbon group is more preferred.
Specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-hexyl and n-dodecyl groups; aryl groups such as phenyl groups; 2-phenylethyl, 2-phenylpropyl groups and the like. Arylkill groups and the like can be mentioned.
Further, a part or all of the hydrogen atoms of these hydrocarbon groups may be substituted with halogen atoms such as chlorine, fluorine and bromine, and specific examples thereof include fluoromethyl, 2-bromoethyl and chloromethyl. Examples thereof include halogen-substituted monovalent hydrocarbon groups such as 3,3,3-trifluoropropyl group.
Among these, an alkyl group having 1 to 5 carbon atoms is preferable, and 90 mol% or more is more preferably a methyl group from the viewpoint of ease of synthesis and cost.

The component (A) does not contain an organoxysilyl group, and examples of the organoxy group include an alkoxy group, an alkoxyalkoxy group, an alkenyloxy group, and an asyloxy group. Examples of the alkoxy group include those having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, and examples thereof include a methoxy group and an ethoxy group. Examples of the alkoxyalkoxy group include those having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms in each alkoxy group, and examples thereof include a methoxyethoxy group and a methoxypropoxy group. Examples of the alkenyloxy group include those having 2 to 6 carbon atoms, and examples thereof include a vinyloxy group and an aryloxy group. Examples of the asyloxy group include those having 1 to 10 carbon atoms, and examples thereof include an acetyloxy group and an octanoyloxy group.

Examples of the component (A) include dimethylpolysiloxane having both ends of the molecular chain dimethylvinylsiloxy group blocked, dimethylpolysiloxane having both ends of the molecular chain methylphenylvinylsiloxy group blocking dimethylpolysiloxane, and dimethylvinylsiloxy group blocking dimethylsiloxane / methylphenyl at both ends of the molecular chain. Siloxane copolymer, dimethylvinyl siloxy group-sealed dimethylsiloxane / methylvinylsiloxane copolymer at both ends of the molecular chain, dimethylsiloxane / methylvinylsiloxane copolymer containing silanol groups at both ends of the molecular chain, dimethylsiloxane containing silanol groups at both ends of the molecular chain -Methylvinylsiloxane-Methylphenylsiloxane copolymer, trimethylsiloxy group-blocking dimethylsiloxane at both ends of the molecular chain dimethylsiloxane-Methylvinylsiloxane copolymer, dimethylvinylsiloxy group-blocking methyl at both ends of the molecular chain (3,3,3-trifluoropropyl) ) Polysiloxane, formula: (CH ₃ ) ₃ siloxane unit represented by SiO _1/2 and formula: (CH ₃ ) ₂ (CH ₂ = CH) siloxane unit represented by _{SiO 1/2 and formula: CH 3 Examples} include an organopolysiloxane copolymer composed of a siloxane unit represented by SiO 3/2 and a formula: (CH ₃ ) ₂ a siloxane unit represented by SiO _2/2 , and the component (A) is a molecular chain. A dimethylpolysiloxane having both ends sealed with a dimethylvinylsilyl group is particularly preferable.

[(B) component]
The component (B) is an organopolysiloxane represented by the following general formula (1), and has a role of lowering the viscosity of the composition and imparting flowability. The component (B) is distinguished from the component (A) in that it has ^{two −SiOR groups at one end.}

In the formula, R ¹ represents an unsubstituted or substituted monovalent hydrocarbon group independently of each other. The monovalent hydrocarbon group of R ¹ is not particularly limited, but has preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms.
Specific examples of the monovalent hydrocarbon group include alkyl, alkenyl, aryl, and aralkyl groups, and halogens in which some or all of the hydrogen atoms of these monovalent hydrocarbon groups are substituted with halogen atoms such as chlorine, fluorine, and bromine. Examples thereof include a halogenated monovalent hydrocarbon group such as an alkylated group.

The alkyl group may be linear, branched or cyclic, and specific examples thereof include linear alkyl groups such as methyl, ethyl, n-propyl, n-hexyl and n-octyl groups; isopropyl, Branched chain alkyl groups such as isobutyl, tert-butyl and 2-ethylhexyl groups; cyclic alkyl groups such as cyclopentyl and cyclohexyl groups can be mentioned.
Specific examples of the alkenyl group include vinyl, allyl, 1-butenyl, 1-hexenyl group and the like.
Specific examples of the aryl group include a phenyl group and a tolyl group.
Specific examples of the aralkyl group include 2-phenylethyl, 2-methyl-2-phenylethyl group and the like.
Specific examples of the alkyl halide group include 3,3,3-trifluoropropyl, 2- (nonafluorobutyl) ethyl, 2- (heptadecafluorooctyl) ethyl group and the like.
Among these, R ¹ is preferably a methyl group, a phenyl group, or a vinyl group.

R ² represents an alkyl group, an alkoxyalkyl group, an alkenyl group or an acyl group independently of each other. Examples of the alkyl group of R ² include unsubstituted or substituted alkyl groups having 1 to 10, preferably 1 to 6, and more preferably 1 to 3, which are the same as the group exemplified in ^{R 1 above.} The same can be mentioned. Examples of the alkoxyalkyl group include those having an alkoxy group and an alkyl group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and examples thereof include methoxyethyl and methoxypropyl groups. Examples of the alkenyl group include those having 2 to 6 carbon atoms, and examples thereof include a vinyl group and an allyl group. Examples of the acyl group include those having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and examples thereof include an acetyl group and an octanoyl group.
Among these, R ² is preferably an alkyl group, more preferably a methyl group or an ethyl group.

n is an integer of 2 to 100, preferably an integer of 5 to 80. If n is less than 2, oil bleeding is likely to occur from the composition, and the adhesive strength decreases with time. If n exceeds 100, the viscosity of the composition becomes high and the workability becomes poor.
a is an integer of 1 to 3, preferably 3.

The viscosity of the component (B) at 25 ° C. is preferably 0.005 to 10 Pa · s, more preferably 0.005 to 1 Pa · s. Within such a range, it is possible to suppress a decrease in adhesive force over time due to oil bleeding from the composition, and it is possible to prevent an increase in viscosity and a decrease in flowability.

Specific examples of the organopolysiloxane represented by the formula (1) include, but are not limited to, the following compounds.

The blending amount of the component (B) is 1 to 100 parts by mass, preferably 10 to 80 parts by mass with respect to 100 parts by mass of the component (A). If it is less than 1 part by mass, a low-viscosity composition cannot be obtained, and if it exceeds 100 parts by mass, the physical properties after curing become poor.
The component (B) may be used alone or in combination of two or more.

[(C) component]
The component (C) is an alumina powder having an average particle size of 0.1 to 50 μm, preferably 1 to 10 μm, and has a role of imparting thermal conductivity to the composition. If the average particle size is less than 0.1 μm, the particles tend to aggregate with each other and the flowability becomes poor. When the average particle size exceeds 50 μm, the flowability of the particles themselves becomes low. The shape of the component (C) is arbitrary, and may be indeterminate, spherical, or any shape. In the present invention, the average particle size is assumed to be measured as a _{volume-based median diameter (D 50} ) in the particle size distribution measurement by the laser light diffraction method.

The blending amount of the component (C) is 100 to 2,000 parts by mass, preferably 1,000 to 2,000 parts by mass, and more preferably 1, with respect to 100 parts by mass of the component (A). It is 500 to 1,800 parts by mass. If the blending amount of the component (C) is less than 100 parts by mass, the desired thermal conductivity cannot be imparted to the cured product, and if it exceeds 2,000 parts by mass, the composition does not become liquid and the composition does not become liquid. It has poor flowability.
The component (C) may be used alone or in combination of two or more.

[(D) component]
The component (D) is magnesium oxide having an average particle size of 1 to 150 μm, preferably 5 to 100 μm, and has a role of imparting thermal conductivity to the composition. If the average particle size is less than 1 μm, the particles tend to aggregate with each other and the flowability becomes poor. If the average particle size exceeds 150 μm, the flowability of the particles themselves becomes poor. The shape of the component (D) is arbitrary, and may be indeterminate, spherical, or any shape.

The blending amount of the component (D) is 100 to 2,000 parts by mass, preferably 500 to 1,800 parts by mass, and more preferably 1,000 to 1,000 parts by mass with respect to 100 parts by mass of the component (A). It is 1,500 parts by mass. If the blending amount of the component (D) is less than 100 parts by mass, the desired thermal conductivity cannot be imparted to the cured product, and if it exceeds 2,000 parts by mass, the composition does not become liquid and the composition does not become liquid. It has poor flowability.
The component (D) may be used alone or in combination of two or more.

In the present invention, by using the component (C) and the component (D) in combination, it is possible to impart flowability to the composition while imparting desired thermal conductivity.
From the viewpoint of the flowability of the composition, the ratio of the component (C) / component (D) is preferably 0.7 to 2.0, more preferably 0.7 to 1.4 by mass ratio. ..

[(E) component]
The component (E) is an organohydrogensiloxane having at least 2, preferably 3 or more, more preferably 3 to 100 SiH groups in one molecule.
The molecular structure of the organohydrogensiloxane of the component (E) may be linear, branched or network-like, and a plurality of organohydrogensiloxane chains may be bonded by a linking group. The silicon atom-bonded hydrogen atom may be present only at one of the terminal portion of the molecular chain (both ends or one end) and the non-terminal portion of the molecular chain, or may be present at both of them.
Examples of the organic group other than the hydrogen atom bonded to the silicon atom of the component (E) include a monovalent hydrocarbon group having 1 to 10 carbon atoms excluding the alkenyl group, and specific examples thereof include methyl, ethyl, propyl and the like. Alkyl groups such as butyl groups; aryl groups such as phenyl and trill groups; aralkyl groups such as phenylethyl and phenylpropyl groups; some or all of the hydrogen atoms of these groups are halogen atoms such as chlorine, fluorine and bromine. Substituted alkyl halide groups such as γ-chloropropyl and 3,3,3-trifluoropropyl groups can be mentioned. Among these, an alkyl group having 1 to 6 carbon atoms is preferable, and more preferably an alkyl group having 1 to 3 carbon atoms, and 90 mol% or more of the organic groups other than the hydrogen atom are methyl from the viewpoint of ease of synthesis and cost. More preferably it is a group.

(E) kinematic viscosity at 25 ° C. of the component, is not particularly limited, 1~10,000mm ² / s and is more preferably 1~1,000mm ² / s. The kinematic viscosity is a measured value at 25 ° C. measured by a Canon Fenceke viscometer (hereinafter, the same applies). As the component (E), several types of components (E) having different viscosities may be used in combination.

As the component (E), a compound containing a cyclic organohydrogensiloxane represented by the following general formula (2-1) and / or a cyclic organohydrogensiloxane represented by the following general formula (2-2) may be used. good. These compounds have a role of cross-linking with the component (A) and the component (B) and a role of imparting adhesiveness.

R ³ is an alkyl group having 1 to 6 carbon atoms independently of each other, and examples thereof include methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl groups. Among these, those having 1 to 3 carbon atoms are preferable, and 90 mol% or more are preferably methyl groups from the viewpoint of ease of synthesis and cost.

R ⁴ is an epoxy group or a trialkoxysilyl group that is independently bonded to a silicon atom via a carbon atom or a carbon atom and an oxygen atom. Examples of the epoxy group bonded to the silicon atom via the carbon atom or the carbon atom and the oxygen atom include 3-glycidoxypropyl, 3-glycidoxyethyl, 3,4-epoxycyclohexylethyl group and the like. Examples of the trialkoxysilyl group bonded to the silicon atom via the carbon atom or the carbon atom and the oxygen atom include trimethoxysilylpropyl, trimethoxysilylpropylmethyl, trimethoxysilylethyl, triethoxysilylpropyl and triethoxysilylpropyl. Examples thereof include methyl and triethoxysilylethyl groups.

i is an integer of 2 or more, j is an integer of 1 or more, i + j is an integer of 4 to 12, preferably an integer of 4 to 8, more preferably an integer of 4 to 6, and further. It is preferably 4.
The sequence order of the siloxane units in the formula (2-1) may be arbitrary, and may be random, block, or alternate.

（破線は珪素原子との結合手を表す。） In the formula (2-2), X is a divalent hydrocarbon group which may contain an ether bond, and is preferably a group containing a bisphenol A residue represented by the following formula (3).

(The broken line represents the bond with the silicon atom.)

k is an integer of 3 to 11 independently of each other, preferably an integer of 3 to 7, more preferably an integer of 3 to 5, and even more preferably 3.

Specific examples of the component (E) include, but are not limited to, organohydrogensiloxane represented by the following formula. The component (E) may be used alone or in combination of two or more.

The blending amount of the component (E) is 0.1 to 100 parts by mass, preferably 10 to 30 parts by mass with respect to 100 parts by mass of the component (A). If it is less than 0.1 part by mass, the hardness becomes insufficient, and if it exceeds 100 parts by mass, the physical properties after curing become poor.

[(F) component]
The component (F) is a hydrosilylation reaction catalyst. The hydrosilylation reaction catalyst may be any catalyst as long as it promotes an addition reaction between the alkenyl group of the component (A) and, in some cases, the alkenyl group of the components (A) and (B) and the Si—H group of the component (E). Known ones can be used. Specifically, it is preferable to use a platinum group metal-based catalyst, and among them, a catalyst selected from platinum and a platinum compound is preferable.

Specific examples of the catalyst include platinum (including platinum black), rhodium, palladium and other platinum group metals, H ₂ PtCl ₄ · nH ₂ O, H ₂ PtCl ₆ · H ₂ O, NaHP _{PtCl 6} · nH ₂ O. , KHPtCl ₆ · nH ₂ O, Na ₂ PtCl ₆ · nH ₂ O, K ₂ PtCl ₄ · nH ₂ O, PtCl ₄ · nH ₂ O, PtCl ₂ , Na ₂ HPtCl ₄ · nH ₂ O (However, in the formula n is an integer of 0 to 6, preferably 0 or 6), such as platinum chloride, chloroplatinic acid, chloroplatinate, alcohol-modified chloroplatinic acid, complex of chloroplatinic acid and olefin, platinum black. , Platinum group metal such as palladium supported on a carrier such as alumina, silica, carbon, rhodium-olefin complex, chlorotris (triphenylphosphine) rhodium (Wilkinson catalyst), platinum chloride, platinum chloride acid or platinum chloride acid. Examples thereof include a complex of a salt and a vinyl group-containing siloxane, and these may be used alone or in combination of two or more.

The blending amount of the component (F) is an effective amount as a catalyst, and may be any amount as long as the reaction between the component (A) and the component (E) can proceed, and may be appropriately adjusted according to the desired curing rate.
In particular, the amount of the component (A) is preferably 0.1 to 7,000 ppm based on the mass converted to the platinum group metal atom, and more preferably 1 to 6,000 ppm. When the blending amount of the component (F) is within the above range, more efficient catalytic action can be expected.

[Other ingredients]
In the thermally conductive silicone composition of the present invention, in addition to the above components (A) to (F), known additives may be added as long as the object of the present invention is not impaired.
For example, a reaction control agent may be added for the purpose of suppressing the curing reaction of the composition at room temperature and extending the shelf life and pot life. As the reaction control agent, any conventionally known reaction control agent can be used as long as it can suppress the catalytic activity of the component (F). Specific examples thereof include acetylene alcohol compounds such as 1-ethynyl-1-cyclohexanol and 3-butin-1-ol, various nitrogen compounds such as triallyl isocyanurate, organic phosphorus compounds, oxime compounds, and organic chloro compounds. These may be used alone or in combination of two or more. Among these, 1-ethynyl-1-cyclohexanol and triallyl isocyanurate are preferable.

When the reaction control agent is used, the blending amount is preferably 0.01 to 5% by mass with respect to 100 parts by mass of the component (A) in consideration of the shelf life and pot life of the composition and the curability of the composition. Parts, more preferably 0.05 to 1 part by mass.
The reaction control agent may be diluted with an organic solvent such as toluene, xylene, or isopropyl alcohol in order to improve the dispersibility in the composition.

Further, for the purpose of lowering the viscosity of the thermally conductive silicone composition of the present invention and imparting flowability, an organopolysiloxane having both ends sealed with a trialkoxysilyl group may be added.
The viscosity of the organopolysiloxane having both ends sealed with a trialkoxysilyl group at 25 ° C. is preferably 0.01 to 100 Pa · s, more preferably 0.03 to 10 Pa · s, still more preferably 0.05 to 5 Pa.・ S.

The alkoxy groups forming the trialkoxysilyl groups at both ends are preferably those having 1 to 6 carbon atoms independently of each other, and more preferably those having 1 to 4 carbon atoms, for example, a trimethoxysilyl group, a triethoxysilyl group and the like. Can be mentioned.
Substituents bonded to silicon atoms other than both ends include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl groups; cycloalkyl groups such as cyclohexyl groups; vinyl and allyl. Alkenyl groups such as groups; monovalent hydrocarbon groups having 1 to 8 carbon atoms such as aryl groups such as phenyl and trill groups, and some or all of the hydrogen atoms of these monovalent hydrocarbon groups are chlorine, fluorine, bromine and the like. Examples thereof include a halogenated monovalent hydrocarbon group such as a chloromethyl group and a trifluoromethyl group substituted with the halogen atom of.

Examples of such an organopolysiloxane include those represented by the following formula (4).

In the formula (4), R ⁵ represents an alkyl group having 1 to 4 carbon atoms independently of each other, and specific examples thereof include methyl, ethyl, n-propyl, n-butyl group and the like. Among these, a methyl group and an ethyl group are preferable.
R ⁶ represents an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms independently of each other, and specific examples thereof include methyl, ethyl, n-propyl, n-butyl, n-pentyl and n. Alkyl groups such as −hexyl and n-heptyl groups; monovalent hydrocarbon groups such as aryl groups such as phenyl and trill groups, and some or all of the hydrogen atoms of these monovalent hydrocarbon groups are chlorine, fluorine and bromine. Examples thereof include halogenated monovalent hydrocarbon groups such as chloromethyl, 3-chloropropyl and trifluoromethyl groups substituted with halogen atoms such as. Among these, a methyl group and an ethyl group are particularly preferable.
r is preferably an integer of 1-150.

When an organopolysiloxane having both ends sealed with a trialkoxysilyl group is used, the blending amount is preferably 1 to 50 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the component (A). Is.

In addition, a hindered phenolic antioxidant, a reinforcing or non-reinforcing filler such as calcium carbonate, a colorant such as a pigment or a dye can be added.

[Manufacturing method of thermally conductive silicone potting composition, etc.]
In the thermally conductive silicone potting composition of the present invention, the components (A) to (F) and, if necessary, other components are mixed by a known method using a gate mixer, a kneader, a planetary mixer or the like. Can be prepared.
The thermally conductive silicone adhesive of the present invention comprises a first agent consisting of the components (A), (B), (C), (D), (F), and if necessary, other components, and (A). , (B), (C), (D), (E) components, and if necessary, other components are prepared separately, and the first and second agents are mixed before use. It may be a two-agent type composition. In addition, there may be a component commonly used in the first agent and the second agent. By using such a two-dosage form for the composition, storage stability can be further ensured.

The viscosity of the heat conductive silicone potting composition of the present invention at 25 ° C. is preferably 1 to 100 Pa · s, more preferably 10 to 60 Pa · s, from the viewpoint of dispersibility and workability of the heat conductive filler. Is.

The thermally conductive silicone potting composition of the present invention preferably has a flowability at 23 ° C. of 100 mm or more, which will be described in detail in a later example. When the silicone potting composition is poured into a part having a fine structure such as a transformer attached to the cooler, it is preferably 120 mm or more. The higher the flowability, the more preferable the upper limit of the flowability, but since the measurement limit depends on the length of the aluminum plate, the upper limit of the measurement is 400 mm here.

The curing conditions of the heat conductive silicone potting composition of the present invention are not particularly limited, and can be the same conditions as those of conventionally known silicone gels.
The thermally conductive silicone potting composition may be cured by heat from a heat-generating component after being poured, or may be positively cured by heating. The heat curing conditions are preferably 60 to 180 ° C., more preferably 80 to 150 ° C., preferably 0.1 to 3 hours, more preferably 0.5 to 2 hours.

The thermal conductivity of the cured product at an environmental temperature of 25 ° C. is preferably 3.5 W / m · K or more, and more preferably 4.0 W / m · K or more. The upper limit is not particularly limited, but is usually 10.0 W / m · K or less.
The density of the cured product ^{is preferably 3.0 g / cm 3} or less, more preferably 2.9 g / cm ³ or less. The lower limit is not particularly limited, but is usually 1.7 g / cm ³ or more.
The hardness of the cured product is preferably 20 or more as measured by a type A durometer, and the upper limit is not particularly limited, but is usually 80 or less.

When the heat conductive silicone potting composition of the present invention is used as a filler in a case containing fine heat-generating parts, it has high flowability and therefore flows into every corner of the fine structure, and after curing, the heat-generating parts, etc. Since it adheres well to the case and has high thermal conductivity, the heat of the heat-generating component can be efficiently transferred to the case, and its reliability can be dramatically improved. Further, since the density is low, it can contribute to the weight reduction of the entire component.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Each component used in Examples and Comparative Examples is shown below.
(A) Component-A-1: Both ends are sealed with a dimethylvinylsilyl group, and dimethylpolysiloxane having a viscosity at 25 ° C. of 0.06 Pa · s-A-2: Both ends are sealed with a dimethylvinylsilyl group. , Didimethylpolysiloxane having a viscosity of 0.4 Pa · s at 25 ° C.

Component (B) B-1: Organopolysiloxane represented by the following formula (viscosity at 25 ° C.: 0.03 Pa · s)

(C) Component-C-1: Alumina powder with an average particle size of 1 μm-C-2: Alumina powder with an average particle size of 10 μm-C-3: Alumina powder with an average particle size of 45 μm-C-4: Average grain Alumina powder with a diameter of 70 μm

Component (D) -D-1: Magnesium oxide powder with an average particle size of 70 μm

・Ｅ−２：下記式で表されるオルガノハイドロジェンシロキサン（２５℃における動粘度：８００ｍｍ²／ｓ）

・Ｅ−３：下記式で表されるオルガノハイドロジェンシロキサン（２５℃における動粘度：１８ｍｍ²／ｓ）

Component (E) E-1: Organohydrogensiloxane represented by the following formula (kinematic viscosity at 25 ° C: 10 mm ² / s)

E-2: Organohydrogensiloxane represented by the following formula (kinematic viscosity at 25 ° C: 800 mm ² / s)

E-3: Organohydrogensiloxane represented by the following formula (kinematic viscosity at 25 ° C: 18 mm ² / s)

Component (F) F-1: Didimethylpolysiloxane solution of platinum-divinyltetramethyldisiloxane complex (dissolved in the same dimethylpolysiloxane as A-3 above. Contains 1% by mass as platinum atom)

Other Ingredients ・ G-1: 1-Etinyl-1-Cyclohexanol ・ G-2: Triallyl Isocyanurate

H-1: Organopolysiloxane having a viscosity of 1 Pa · s at 25 ° C. with both ends sealed with a trimethoxysilyl group.

[Examples 1 and 2, Comparative Examples 1 and 2]
The components (A) to (F) and other components were mixed as follows to obtain a silicone potting composition.
Add the components (A), (B), (C), (D) and (H-1) to a 5L gate mixer (trade name: 5L planetary mixer, manufactured by Inoue Seisakusho Co., Ltd.) in the blending amounts shown in Table 1. The mixture was heated and mixed at 150 ° C. for 2 hours. After cooling the mixture, component (F) was added and mixed at 25 ° C. for 30 minutes. Next, the reaction control agents (G-1) and (G-2) components were added and mixed at 25 ° C. for 30 minutes. Finally, the component (E) was added and mixed at 25 ° C. for 30 minutes.
The following physical characteristics of the obtained composition were measured. The results are shown in Table 1.

[1] Viscosity The viscosity of the thermally conductive silicone potting composition at 25 ° C. was measured at 20 rpm using a B-type viscometer.

[2] A flowable heat conductive silicone potting composition was weighed in 0.60 mL and dripped on an aluminum plate (JIS H 4000: 2014, width 25 x length 400 x thickness 0.5 mm). Immediately after hanging, the aluminum plate was tilted to 28 ° and left in an atmosphere of 23 ° C (± 2 ° C) for 1 hour. The length of the thermally conductive silicone potting composition after being left to stand was measured from end to end.

[3] Thermal Conductivity The thermally conductive silicone potting composition was press-cured at 120 ° C. for 10 minutes to a thickness of 2.0 mm, and further heated in an oven at 120 ° C. for 50 minutes. The thermal conductivity of the obtained cured product was measured at an ambient temperature of 25 ° C. using a hot disk method thermophysical characteristic measuring device TPA-501 (manufactured by Kyoto Denshi Kogyo Co., Ltd.) in accordance with ISO 22007-2.

[4] Density The heat conductive silicone potting composition was press-cured at 120 ° C. for 10 minutes to a thickness of 2.0 mm, and further heated in an oven at 120 ° C. for 50 minutes. The density of the obtained silicone sheet was measured according to JIS K 6251: 2017.

[5] Hardness The thermally conductive silicone potting composition was press-cured at 120 ° C. for 10 minutes to a thickness of 2.0 mm, and further heated in an oven at 120 ° C. for 50 minutes. Three obtained silicone sheets were stacked and the hardness was measured by a type A durometer specified in JIS K 6253: 2012.

[6] Elongation during cutting, tensile strength The thermally conductive silicone potting composition was press-cured at 120 ° C. for 10 minutes to a thickness of 2.0 mm, and further heated in an oven at 120 ° C. for 50 minutes. The elongation and tensile strength of the obtained silicone sheet during cutting were measured according to JIS K 6251: 2017.

[7] Tension-shear adhesive strength A heat-conducting silicone potting composition is placed between aluminum plates (JIS H 4000: 2014) having a thickness of 1.0 mm so as to have a thickness of 2.0 mm and an adhesive area of 25 mm × 10 mm. In the sandwiched state, the mixture was heated at 120 ° C. for 1 hour to cure the silicone potting composition to prepare an adhesion test piece. The tensile shear adhesive strength of the obtained test piece was measured according to JIS K 6850: 1999.

As shown in Table 1, the thermally conductive silicone potting compositions of Examples 1 and 2 have good flowability before curing, have excellent thermal conductivity, and can provide a cured product having a low density. Understand.
On the other hand, in Comparative Example 1 which does not contain the component (D), the flowability is inferior, and in Comparative Example 2 in which the amount of the component (D) added exceeds the range of the present invention, the viscosity of the composition becomes too high, so that the potting composition It was not suitable as.

Claims (3)

(A) Organopolysiloxane: 100, which has a viscosity at 25 ° C. of 0.01 to 100 Pa · s, has at least two alkenyl groups bonded to silicon atoms in one molecule, and does not have an organoxysilyl group. Part by mass (B) The following general formula (1)

(In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group ^{independently of each other, and R 2} is an alkyl group, an alkoxyalkyl group, an alkenyl group or an acyl group independently of each other. N is 2 to 100. It is an integer, and a is an integer of 1 to 3.)
Organopolysiloxane represented by: 1 to 100 parts by mass (C) Alumina powder having an average particle size of 0.1 to 50 μm: 100 to 2,000 parts by mass (D) Magnesium oxide powder having an average particle size of 1 to 150 μm: 100 to 2,000 parts by mass (E) Organohydrogensiloxane having at least two SiH groups in one molecule: 0.1 to 100 parts by mass (F) Thermally conductive silicone potting composition containing a hydrosilylation reaction catalyst .. A cured product obtained by curing the thermally conductive silicone potting composition according to claim 1. The cured product according to claim 2, which has a thermal conductivity of 3.5 W / m · K or more and a density of 3.0 or less.