JP2023071105A - Heat-conductive silicone rubber composition - Google Patents

Abstract

To provide a heat-conductive silicone rubber composition from which is obtained a cured product that is highly heat-conductive and has, by post-curing at a low temperature, a sufficient low-molecular siloxane removing effect and sufficient hardness.SOLUTION: A heat-conductive silicone rubber composition comprises: (A) 100 pts.mass of an organopolysiloxane having an average degree of polymerization of 3,000-10,000 and a total content of a diorganocyclopolysiloxane having 3 to 10 silicon atoms of 500 ppm or less; (B) 10-100 pts.mass of an organopolysiloxane having alkenyl groups only at both ends of a molecular chain having an average degree of polymerization of 2-2,000 and; (C) 500-2,700 pts.mass of a heat-conductive filler; and (D) an effective amount of a curing agent.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a thermally conductive silicone rubber composition and a heat-dissipating molding using this composition.

Semiconductors such as transistors and diodes used in electronic devices such as converters and power supplies generate a large amount of heat as they become more sophisticated, faster, smaller and more highly integrated. Due to this, the temperature rise of the equipment may cause malfunction or destruction. Therefore, many heat dissipation methods and heat dissipation members used therefor have been proposed to suppress the temperature rise of semiconductors during operation.

For example, a heat sink using a metal plate with high thermal conductivity such as aluminum or copper is used in order to suppress temperature rise of a semiconductor during operation in an electronic device or the like. This heat sink conducts the heat generated by the semiconductor and releases the heat from the surface due to the temperature difference with the outside air. On the other hand, the semiconductor and the heat sink must be electrically insulated, so a plastic film or the like is interposed between the heat-generating electronic component and the heat sink. However, the plastic film has a very low thermal conductivity and significantly impedes the transfer of heat to the heat sink.

Therefore, a thermally conductive sheet has been developed in which a thermally conductive resin is laminated on a glass cloth in order to impart thermal conductivity and resistance to tearing. For example, there is a thermally conductive sheet in which silicone rubber containing boron nitride powder and spherical silica powder as thermally conductive fillers is laminated on glass cloth (Patent Document 1). However, in the case of arranging a planar heat-dissipating sheet, there is a problem that the creepage distance for insulation becomes too large.

For the reasons described above, a proposal has been made to wrap electronic components using a heat-dissipating molding molded in the shape of a tube or a cap (Patent Document 2). However, when the thermally conductive filler is highly filled in order to increase the thermal conductivity, the elasticity and elongation of the molded product are reduced, and the molded product may be torn, cracked, or cut when the molded product is attached to the electronic component. there was a problem with In addition, in the application of heat-dissipating molded products to electronic parts, in order to prevent contact failures caused by low-molecular-weight siloxane, the heat-dissipating-molded product must be subjected to high-temperature post-curing to remove low-molecular-weight siloxane. However, this post-curing causes the molding to become more brittle, making it difficult to attach it to electronic parts.

JP-A-9-199880 Japanese Utility Model Laid-Open No. 57-2666

The present invention has been made in view of the above circumstances, and provides a thermally conductive silicone rubber composition which, when post-cured at a low temperature and has high thermal conductivity, yields a cured product having a sufficient low-molecular-weight siloxane-removing effect and strength. With the goal. Another object of the present invention is to provide a heat-dissipating molded article that contains a small amount of low-molecular-weight siloxane and that can be easily mounted on electronic parts using the present thermally-conductive silicone rubber composition.

In order to solve the above problems, in the present invention,
(A) an organopolysiloxane having an average degree of polymerization of 3,000 to 10,000 and a total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms of 500 ppm or less: 100 parts by mass;
(B) an organopolysiloxane having an average degree of polymerization of 2 to 2,000 and having alkenyl groups only at both ends of the molecular chain: 10 to 100 parts by mass;
(C) a thermally conductive filler: 500 to 2,700 parts by mass; and (D) a curing agent: an effective amount.

With the thermally conductive silicone rubber composition of the present invention, a cured product having high thermal conductivity and sufficient low-molecular-weight siloxane removal effect and strength can be obtained by post-curing at a low temperature.

（式中、Ｒ^５は独立して炭素原子数１～４のアルキル基であり、ｄは５～１００の整数である。）
で表される片末端がトリアルコキシシリル基で封鎖されたジメチルポリシロキサン
のうちから選択される１つ以上を、有機ケイ素化合物成分の合計量中、０．０１～３０質量％含むものであることが好ましい。 The thermally conductive silicone rubber composition of the present invention further comprises (E) (E1) the following formula (1):
R ² _b R ³ _c Si(OR ⁴ ) _4-bc (1)
(wherein R ² is independently an alkyl group having 6 to 15 carbon atoms, R ³ is independently an alkyl group having 1 to 5 carbon atoms, R ⁴ is independently a ~4 alkyl group, b is an integer from 1 to 3, c is 0, 1 or 2, with the proviso that b+c is from 1 to 3.)
and (E2) the following formula (2):

(Wherein, R ⁵ is independently an alkyl group having 1 to 4 carbon atoms, and d is an integer of 5 to 100.)
0.01 to 30 mass% of the total amount of the organosilicon compound components is preferably one or more selected from dimethylpolysiloxane whose one end is blocked with a trialkoxysilyl group represented by .

With such a thermally conductive silicone rubber composition, filling of the organosilicon compound component with the non-spherical thermally conductive filler is facilitated, and the strength of the resulting cured product is sufficient.

In the present invention, the plasticity of the thermally conductive silicone rubber composition is preferably 100-800.

With such a thermally conductive silicone rubber composition, the composition is non-sticky, can be easily handled in rolling operations, and can be easily kneaded.

The present invention also provides a cured product obtained by curing the thermally conductive silicone rubber composition.

With such a cured product, sufficient low-molecular-weight siloxane removal effect and strength can be obtained by post-curing at a high heat conductivity and at a low temperature.

Furthermore, the present invention provides a heat-dissipating molded article comprising the cured product, wherein the cured material has a thermal conductivity of 1.5 W/m·K or more.

Such a heat-dissipating molded product has suitable heat-dissipating performance, contains a small amount of low-molecular-weight siloxane, and can be easily mounted on electronic components.

In the heat-dissipating molded product of the present invention, the cured product preferably has a type A durometer hardness of 60 to 96 according to JIS K6253-3:2012.

With such a heat-dissipating molding, the surface of the cured product layer is less likely to be scratched during handling, the surfaces of the cured product do not fuse or deform during molding, and the product is excellent in flexibility. Cracks do not occur when the molding is handled.

It is preferable that the heat-dissipating molding has a withstand voltage of 4.5 kV or more when the cured product has a thickness of 0.45 mm.

With such a heat-dissipating molded product, dielectric breakdown of the sheet does not occur under high voltage when the molded product is mounted on an electronic component.

In addition, it is preferable that the content of diorganocyclopolysiloxane having 3 to 10 silicon atoms in the heat-dissipating molded article is 100 ppm or less after being post-cured at 150° C. for 1 hour.

With such a heat-dissipating molded product, it is possible to effectively prevent the occurrence of contact failure due to volatilization of low-molecular-weight siloxane over time.

The thermally conductive silicone rubber composition of the present invention can sufficiently reduce the low-molecular-weight siloxane content even when subjected to a post-curing process at a low temperature. In addition, a heat-dissipating molded article formed from a cured product molded using the present composition can be prevented from embrittlement due to high-temperature post-curing. The obtained heat-dissipating molded product has excellent thermal conductivity, strength, and insulating properties, and has a low content of low-molecular-weight siloxane, so that it can be easily mounted on electronic parts and can prevent contact failure.

FIG. 4 is a diagram showing the shape of a heat-generating electronic component cover produced in an example.

The inventors of the present invention have made intensive studies to achieve the above object, and as a result, have found a thermally conductive silicone rubber composition obtained by adding and mixing a thermally conductive filler to an organopolysiloxane having a low-molecular-weight siloxane content of a certain value or less. is used to form a heat-dissipating molded product, and post-curing at a low temperature can produce a heat-dissipating molded product with a sufficiently reduced low-molecular-weight siloxane content without embrittlement. I came up with the invention.

That is, the present invention is a thermally conductive silicone rubber composition characterized by containing the following (A) to (D).
(A) Organopolysiloxane having an average degree of polymerization of 3,000 to 10,000 and a total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms of 500 ppm or less: 100 parts by mass (B) Average polymerization Organopolysiloxane having alkenyl groups only at both ends of the molecular chain with a degree of 2 to 2,000: 10 to 100 parts by mass (C) Thermally conductive filler: 500 to 2,700 parts by mass (D) Curing agent: Effective amount

The thermally conductive silicone rubber composition and heat-dissipating molding of the present invention will be described in detail below, but the present invention is not limited to them.

The present invention provides a low temperature curable thermally conductive silicone rubber composition.
The thermally conductive silicone rubber composition of the present invention is characterized by containing specific components (A) to (D) described below. If necessary, components other than these may be further included. These components are described below.

[(A) Organopolysiloxane having an average degree of polymerization of 3,000 to 10,000]
Component (A) is the main component of the thermally conductive silicone rubber composition, and preferably has an average compositional formula represented by the following formula (3).
_{RnSiO (4-n)/2} (3)

In the above formula (1), R is independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group, a vinyl group, an alkenyl group such as an allyl group, Aryl groups such as a phenyl group and a tolyl group, cycloalkyl groups such as a cyclohexyl group and a cyclopentyl group, and the like can be mentioned. Moreover, those obtained by substituting some or all of the hydrogen atoms directly attached to the carbon atoms of these groups with halogen atoms such as chlorine and fluorine may also be used. A methyl group, a phenyl group, a trifluoropropyl group and a vinyl group are preferred. Also, n is a positive number between 1.85 and 2.10.

Organopolysiloxane preferably has a linear molecular structure, but may have a partially branched structure in the molecule. Furthermore, the organopolysiloxane preferably has a molecular chain end capped with a triorganosilyl group or a hydroxyl group. Examples of the triorganosilyl group include trimethylsilyl group, dimethylvinylsilyl group, trivinylsilyl group, methylphenylvinylsilyl group, methyldiphenylsilyl group, dimethylphenylsilyl group and dimethylhydroxysilyl group.

The average degree of polymerization of component (A) is 3,000 to 10,000, preferably 5,000 to 10,000.

The average degree of polymerization referred to in this specification refers to the average degree of polymerization obtained from the number average molecular weight obtained by gel permeation chromatography (GPC) using polystyrene as a standard substance.

In component (A), the total content of diorganocyclopolysiloxanes having 3 to 10 silicon atoms is 500 ppm or less, more preferably 300 ppm or less. If the total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms exceeds 500 ppm, high-temperature post-curing is required to remove low-molecular-weight substances from the molded article, and the resulting molded article may become brittle. Low-molecular-weight siloxane volatilizes from the molded product over time, which may cause contact failure.
In this specification, the total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms can be determined by measuring the object to be measured by gas chromatography analysis.

[(B) Organopolysiloxane having an average degree of polymerization of 2 to 2,000 and having alkenyl groups only at both ends of the molecular chain]
Component (B) is a component that undergoes a cross-linking reaction in the thermally conductive silicone rubber composition. It is an organopolysiloxane having an average degree of polymerization of 2 to 2,000 and having alkenyl groups only at both ends of the molecular chain. The alkenyl group is preferably an alkenyl group having 2 to 8 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl and the like. Among them, lower alkenyl groups having 2 to 4 carbon atoms such as vinyl group and allyl group are preferred, and vinyl group is particularly preferred. The (B) component organopolysiloxane may be used singly or in combination of two or more having different average degrees of polymerization.

The average degree of polymerization of component (B) is 2 to 2,000, preferably 10 to 2,000.

The blending amount of component (B) is preferably 10 to 100 parts by mass, more preferably 30 to 70 parts by mass, per 100 parts by mass of component (A).

（式中、Ｒ^１は独立に脂肪族不飽和結合を有さない１価炭化水素基であり、Ｘはアルケニル基であり、ａは０～１９９８の数である。） Specific examples of component (B) include those represented by the following general formula (4).

(Wherein, R ¹ is independently a monovalent hydrocarbon group having no aliphatic unsaturation, X is an alkenyl group, and a is a number from 0 to 1998.)

Examples of R ¹ in the above formula include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group and octyl group. , nonyl, decyl, and dodecyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups; , phenylethyl group, phenylpropyl group, methylbenzyl group and other aralkyl groups having 1 to 10 carbon atoms, particularly 1 to 6 carbon atoms. Groups in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms such as fluorine and chlorine may also be used. For example, chloromethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, 3,3,4,4,5,5,6,6,6-nonafluoro such as a hexyl group. Among these, alkyl groups having 1 to 3 carbon atoms such as methyl group, ethyl group, propyl group, chloromethyl group and 3,3,3-trifluoropropyl group, and phenyl group, chlorophenyl group and fluorophenyl group are preferred. and aryl groups such as groups. In addition, all R ^1s may be the same or different.

Examples of alkenyl groups for X include those having about 2 to 8 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups. Among them, a lower alkenyl group such as a vinyl group or an allyl group is preferred, and a vinyl group is particularly preferred.

In general formula (4), a is a number from 0 to 1998, preferably a number satisfying 10≦a≦1998, more preferably a number satisfying 10≦a≦1,000. The organopolysiloxane represented by the general formula (4) is preferably added in an amount of 10 to 100 parts by weight, particularly 30 to 70 parts by weight, per 100 parts by weight of the organopolysiloxane of component (A).

[(C) Thermally conductive filler]
Component (C) is a component used as a filler that imparts thermal conductivity in the thermally conductive silicone rubber composition. The component (C) may have thermal conductivity, and preferably has electrical insulation. Although not particularly limited, examples include metal oxides such as alumina, silica, magnesia, red iron oxide, beryllia, titania, and zirconia; metal nitrides such as aluminum nitride, silicon nitride, and boron nitride; metal hydroxides such as magnesium hydroxide; Substances generally regarded as thermally conductive fillers, such as synthetic diamond or silicon carbide, can be used.

The blending amount of component (C) is preferably 500 to 2,700 parts by mass, more preferably 600 to 2,500 parts by mass, per 100 parts by mass of component (A).

These thermally conductive fillers include silane coupling agents or partial hydrolysates thereof, alkylalkoxysilanes or partial hydrolysates thereof, organic silazanes, organopolysiloxane oils, and hydrolyzable functional group-containing organopolysiloxanes. It may be surface-treated by the like. These treatments may be carried out in advance on the thermally conductive filler itself, or may be carried out at the time of mixing the organopolysiloxane of component (A) or component (B) with the thermally conductive filler (C). .

In the thermally conductive silicone rubber composition, the thermally conductive filler is (1) a powder having an average particle size of 5 to 60 μm, preferably 5 μm or more and less than 50 μm, and (2) a powder having an average particle size of 0.5 to 50 μm. 4 μm, preferably 0.5 μm or more and less than 3 μm, and preferably the ratio of component (1) and component (2) is (1):(2)=9:1 to 4:6; More preferably 8:2 to 5:5. When the ratio of components (1) and (2) is within this range, the thermally conductive filler can be effectively dispersed and filled in the silicone, and the plasticity of the thermally conductive silicone rubber composition can be improved in workability. can be kept within a good range. Also, the surface of the heat-dissipating molding can be made smoother.

The average particle diameter can be usually determined as a cumulative volume average diameter D ₅₀ (or median diameter) in particle size distribution measurement by laser light diffraction. It is the value of the volume-based cumulative 50% particle diameter (D ₅₀ ) measured by the MT3000II particle size distribution analyzer.

[(D) Curing agent]
Component (D) is a component necessary for curing the thermally conductive silicone rubber composition. The curing agent is appropriately selected according to the mechanism of the cross-linking reaction of the composition.

When curing is carried out by an addition reaction, an organohydrogenpolysiloxane is used as the curing agent (D) and the reaction is carried out in the presence of a platinum-based catalyst. In the case of curing with peroxides, organic peroxides are used as curing agents (D).

Here, when the composition is cured by an addition reaction (hydrosilylation reaction), the curing agent comprises an organohydrogenpolysiloxane having an average of two or more silicon-bonded hydrogen atoms per molecule and a platinum-based catalyst. The one consisting of is blended.

The silicon-bonded groups in the organohydrogenpolysiloxane are exemplified by straight-chain alkyl groups, branched-chain alkyl groups, cyclic alkyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups, and are preferred. is an alkyl group or an aryl group, particularly preferably a methyl group or a phenyl group. The kinematic viscosity of this organohydrogenpolysiloxane at 25° C. is not particularly limited, but is preferably in the range of 5 to 300 mm ² /s, particularly preferably in the range of 10 to 200 mm ² /s.
In the present invention, kinematic viscosity refers to a value measured at 25° C. using a Canon-Fenske viscometer according to JIS Z8803:2011.

The molecular structure of this organohydrogenpolysiloxane is not limited, and examples thereof include linear, branched, partially branched linear, cyclic, and dendritic (dendrimer). This organohydrogenpolysiloxane may be, for example, a homopolymer having these molecular structures, a copolymer consisting of these molecular structures, or a mixture thereof.

Examples of such organohydrogenpolysiloxanes include dimethylpolysiloxane blocked at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer blocked at both molecular chain ends with trimethylsiloxy groups, and dimethylhydrogensiloxane at both molecular chain ends. Gensiloxy group-blocked dimethylsiloxane/methylhydrogensiloxane copolymer, a siloxane unit represented by the formula: (CH ₃ ) ₃ SiO _1/2 and a siloxane unit represented by the formula: (CH ₃ ) ₂ HSiO _1/2 and the formula : SiO _4/2 , and mixtures of two or more thereof.

In the thermally conductive silicone rubber composition, the content of the organohydrogenpolysiloxane is an amount (effective amount) necessary for curing the composition. The amount of silicon-bonded hydrogen atoms in this component is preferably in the range of 0.8 to 10 mol, more preferably in the range of 1 to 8 mol, per 1 mol of silicon-bonded alkenyl groups. is preferable, and an amount within the range of 1.2 to 5 mol is particularly preferable. When the content of this component is at least the lower limit of the above range, curing is sufficient to obtain sufficient sheet strength, and oil bleeding can be suppressed. , foaming does not occur.

The platinum-based catalyst is a catalyst for accelerating the curing of the present composition, and examples thereof include chloroplatinic acid, chloroplatinic acid alcohol solutions, platinum olefin complexes, platinum alkenylsiloxane complexes, platinum carbonyl complexes, and the like. is mentioned.

Also, when the composition is cured by a free radical reaction with an organic peroxide, the curing agent is an organic peroxide. Examples of organic peroxides include benzoyl peroxide, di(p-methylbenzoyl) peroxide, di(o-methylbenzoyl) peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis( t-butylperoxy)hexane, di-t-butylperoxide, t-butylperoxybenzoate.

The content of the organic peroxide is an amount (effective amount) necessary for curing the present composition, and specifically, it is 0.5 to 20 parts by mass based on 100 parts by mass of the organosilicon compound component. An amount of 1 to 10 parts by mass is particularly preferable. When the content of this component is at least the lower limit of the above range, curing is sufficient to obtain sufficient sheet strength, and oil bleeding can be suppressed. , foaming does not occur.

[(E) component]
The thermally conductive silicone rubber composition of the present invention can further contain component (E) described below as an organosilicon compound component.
The (E) component is one or more selected from the following (E1) and (E2) components. The component (E) improves the wettability of, for example, the non-spherical thermally conductive filler (C) to facilitate the filling of the organosilicon compound component with the thermally conductive filler. Material loading can be increased.

((E1) component)
The (E1) component is an alkoxysilane represented by the following formula (1).
R ² _b R ³ _c Si(OR ⁴ ) _4-bc (1)
(wherein R ² is independently an alkyl group having 6 to 15 carbon atoms, R ³ is independently an alkyl group having 1 to 5 carbon atoms, R ⁴ is independently a ~4 alkyl group, b is an integer from 1 to 3, c is 0, 1 or 2, with the proviso that b+c is from 1 to 3.)

In formula (1) above, the alkyl group represented by R ² includes, for example, hexyl group, octyl group, nonyl group, decyl group, dodecyl group and tetradecyl group. When the number of carbon atoms in the alkyl group represented by R ² is from 6 to 15, the wettability of the non-spherical thermally conductive filler (C) is sufficiently improved to form a thermally conductive silicone rubber composition. The filling of the thermally conductive filler becomes easy, and the low-temperature properties of the composition become good.

Examples of the alkyl group represented by R ³ include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group and neopentyl group. In particular, alkyl groups having 1 to 3 carbon atoms such as methyl group, ethyl group and propyl group are preferred.

Examples of alkyl groups represented by R ⁴ include alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, propyl group and butyl group.

b is an integer from 1 to 3 and c is 0, 1 or 2; However, b+c is 1-3.

（式中、Ｒ^５は独立して炭素原子数１～４のアルキル基であり、ｄは５～１００の整数である。） ((E2) component)
The (E2) component is a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group represented by the following formula (2).

(Wherein, R ⁵ is independently an alkyl group having 1 to 4 carbon atoms, and d is an integer of 5 to 100.)

Examples of the alkyl group represented by R ⁵ include those similar to the alkyl group represented by R ⁴ in the above formula (1).

d is an integer of 5-100, preferably an integer of 10-50.

When the component (E) is blended, the blending amount is preferably 0.01 to 30% by mass, more preferably 1 to 20% by mass, based on the total amount of the organosilicon compound components. When the above amount is at least the above lower limit, filling of the non-spherical thermally conductive filler into the organosilicon compound component is facilitated. When the above amount is equal to or less than the above upper limit, the resulting cured product will have sufficient strength.

（式中、ｅは５～５００の整数、好ましくは５０～４００の整数である。） [(F) component]
The thermally conductive silicone rubber composition of the present invention may further contain the following component (F) as an organosilicon compound component. Component (F) is a plasticizer, which is dimethylsiloxane represented by the following formula (5).

(Wherein, e is an integer of 5 to 500, preferably an integer of 50 to 400.)

When the component (F) is blended, the blending amount is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, based on the total amount of the organosilicon compound components. If the above amount is equal to or more than the above lower limit, the sheet will not become brittle due to high hardness. When the above amount is equal to or less than the above upper limit, sufficient sheet strength can be obtained and oil bleeding can be suppressed.

[Other ingredients]
If necessary, the thermally conductive silicone rubber composition of the present invention may further contain other components. For example, optional components such as reinforcing silica, silicone oil, silicone wetter, flame retardant, addition reaction controller, colorant, heat resistance improver, and internal release agent, which will be described later, can be added.

[Preparation of Thermally Conductive Silicone Rubber Composition]
The thermally conductive silicone rubber composition can be prepared as follows. (A), (B), (C) components and, if blended, components (E), (F), etc. are heated to a temperature of 100° C. or higher using a mixer such as a kneader or a Banbury mixer, if necessary. while kneading. In this kneading step, if desired, reinforcing silica such as fumed silica and precipitated silica; silicone oil, silicone wetter and the like; flame retardants such as platinum, titanium oxide and benzotriazole may be added. After the uniform mixture obtained in the kneading step is cooled to room temperature, it is filtered through a strainer or the like, and then a required amount of the curing agent (D) is added to the mixture using a two-roll kneader, Banbury mixer or the like. Add and knead again. In this second kneading step, if desired, an acetylene compound-based addition reaction controller such as 1-ethynyl-1-cyclohexanol, a coloring agent such as an organic pigment or an inorganic pigment, or a heat resistance improver such as iron oxide or cerium oxide. , and an internal release agent may be added.

The curing conditions for the above thermally conductive silicone rubber composition are, for example, in the case of curing by addition reaction, 80 to 180° C., especially 100 to 160° C., for 30 seconds to 20 minutes, especially 1 minute to 10 minutes. In the case of curing with an organic peroxide, it is preferably 100 to 180° C., particularly 110 to 170° C., for 30 seconds to 20 minutes, particularly preferably 1 minute to 10 minutes. Furthermore, it is preferable to perform post-curing at 100 to 170° C. as necessary. If the post-cure temperature is too high, the elongation of the molded product may be reduced and the molded product may become brittle.

As described above, the thermally conductive silicone rubber composition of the present invention can be cured at a low temperature of 180° C. or less in both addition reaction curing and organic peroxide curing, and low-molecular-weight siloxane does not need to be removed at a high temperature. Therefore, it is possible to obtain a cured product (a molded product, particularly a heat-dissipating molded product) that has sufficient low-molecular-weight siloxane-removing effect to prevent contact failure and has high thermal conductivity and excellent strength.

The plasticity of the thermally conductive silicone rubber composition is preferably 100-800. If the plasticity is within the above range, the composition will not become sticky and difficult to handle in rolling work or the like, and the composition will be easily kneaded. The degree of plasticity can be measured by a method based on JIS K6249:2003 using an automatic William Plastometer VR-6155 manufactured by Ueshima Seisakusho Co., Ltd.

A cured product of the thermally conductive silicone rubber composition has a thermal conductivity of 1.5 W/m·K or more, preferably 1.8 W/mK or more, and still more preferably 2.0/mK or more. The thermal conductivity can be measured by the hot disk method (ISO 22007-2 compliant) using TPS-2500S manufactured by Kyoto Electronics Industry Co., Ltd.

The type A durometer hardness according to JIS K6253-3:2012 of the cured product of the thermally conductive silicone rubber composition is in the range of 60-96, more preferably 70-93. If the hardness is 60 or more, the surface of the cured product layer is less likely to be damaged during handling, and the surfaces of the cured product are not fused together or deformed during molding. On the other hand, if the hardness is 96 or less, the flexibility is excellent, and cracks do not occur when the molding is handled.

When the cured product of the thermally conductive silicone rubber composition has a thickness of 0.45 mm, the withstand voltage is 4.5 kV or more. If the withstand voltage is 4.5 kV or higher, dielectric breakdown of the sheet will not occur under high voltage when the molding is mounted on an electronic component. The withstand voltage is approximately proportional to the thickness of the cured product. The withstand voltage can be measured by a method conforming to JIS C2110-1:2016.

The cured product of the thermally conductive silicone rubber composition has a diorganocyclopolysiloxane content of 3 to 10 silicon atoms of 100 ppm or less, more preferably 50 ppm or less after post-curing at 150° C. for 1 hour. be. If the content of the diorganocyclopolysiloxane having 3 to 10 silicon atoms is 100 ppm or less, it is possible to prevent the occurrence of contact failure due to volatilization of the low-molecular-weight siloxane over time.

As described above, the thermally conductive silicone rubber composition of the present invention can be cured at a low temperature even in a system with a high filler content by suppressing the amount of low-molecular-weight siloxane. A good molded product can be obtained. Therefore, the above composition is suitable for producing heat-dissipating moldings such as heat-generating electronic component covers.

EXAMPLES The present invention will be specifically described below by showing examples and comparative examples, but the present invention is not limited to the following examples.
The average degree of polymerization was obtained from the number average molecular weight by GPC using polystyrene as a standard substance. The average particle diameter is a cumulative volume average diameter _D50 in particle size distribution measurement by laser light diffraction, and was measured with a particle size distribution analyzer MT3000II manufactured by Microtrack Bell Co., Ltd.

[Preparation of Thermally Conductive Silicone Rubber Composition]
(1) The components (A) to (C) shown below and the optional components (E) and (F) are put into a 5 L heat treatment kneader (manufactured by Inoue Seisakusho) and heated at 25 to 40 ° C. for 30 Mix for a minute. Then, after confirming that the temperature of the composition reached 170° C. by heating the inside of the kneader, heating and stirring were further performed for 2 hours.

(A) Component:
(A-1) Dimethylpolysiloxane terminated at both ends with dimethylvinyl groups having an average degree of polymerization of 8,000; total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms; 100 ppm
(A-2) Dimethylpolysiloxane terminated at both ends with dimethylvinyl groups having an average degree of polymerization of 8,000; total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms; 4700 ppm
The total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms was measured by gas chromatography analysis described later.

(B) Component:
Dimethylpolysiloxane terminated at both ends with dimethylvinyl groups, with an average degree of polymerization of 1,000

(C) Thermally conductive filler:
(C-1) Average particle size: 1 μm: Crushed alumina (C-2) Average particle size: 1 μm: Spherical alumina (C-3) Average particle size: 10 μm: Spherical alumina (C-4) Average particle size: 45 μm : Spherical alumina (C-5) Average particle size: 9.3 µm: Crushed aluminum hydroxide (C-6) Average particle size: 1.3 µm: Crushed aluminum hydroxide

Component (E): A dimethylpolysiloxane having an average degree of polymerization of 30 and having one end blocked with a trimethoxysilyl group, represented by the following formula (6)

（式中、ｆ＝３００） (F) component: dimethylpolysiloxane represented by the following formula (7)

(where f = 300)

(2) After heating and stirring, the mixture was cooled to around room temperature (25°C) and the kneaded compound was taken out. Furthermore, using a twin roll (Daishin Kikai Co., Ltd.), the following (D) as a curing agent was kneaded into the compound to prepare a thermally conductive silicone rubber composition.

(D) component: organic peroxide represented by the following formula (8)

[Plasticity measurement]
The plasticity of the resulting thermally conductive silicone rubber composition was measured using an automatic William Plastometer VR-6155 manufactured by Ueshima Seisakusho Co., Ltd. according to JIS K6249:2003. Table 1 shows the results.

[Thermal conductivity measurement]
The resulting thermally conductive silicone rubber composition was pressed into a mold of 60 mm × 60 mm × 6 mm, the pressure was adjusted so that the thickness after curing was 6 mm, and a high-pressure press (manufactured by Shoji Iron Works Co., Ltd.) was applied. was press-cured at 165° C. and 100 kgf/cm ² for 10 minutes to prepare a sheet having a thickness of 6 mm. Further, after performing secondary vulcanization at 150° C./1 hour or 200° C./1 hour, it was cooled to room temperature. Two 6 mm thick sheets were used, and a probe was sandwiched between the two sheets to measure the thermal conductivity at 25° C. by the hot disk method (according to ISO 22007-2). Table 1 shows the results.

[Hardness]
The resulting thermally conductive silicone rubber composition was pressed into a mold of 60 mm × 60 mm × 6 mm with a pressure adjusted so that the thickness after curing was 6 mm, followed by a high-pressure press (manufactured by Shoji Iron Works Co., Ltd.). was press-cured at 165° C. and 100 kgf/cm ² for 10 minutes to prepare a sheet having a thickness of 6 mm. Further, after performing secondary vulcanization at 150° C./1 hour or 200° C./1 hour, it was cooled to room temperature. A durometer A hardness tester was used to measure the hardness of a test piece obtained by stacking two sheets having a thickness of 6 mm. Table 1 shows the results.

[Withstand voltage]
The resulting thermally conductive silicone rubber composition was placed in a mold of 100 mm x 100 mm x 0.45 mm, the pressure was adjusted so that the thickness after curing was 0.45 mm, and a high pressure press (Shoji Iron Works ( Co., Ltd.) was used to press cure at 165° C. and 100 kgf/cm ² for 10 minutes to prepare a sheet with a thickness of 0.45 mm. Further, after performing secondary vulcanization at 150° C./1 hour or 200° C./1 hour, it was cooled to room temperature. Air withstand voltage was measured according to JIS C2110-1:2016 using the 0.45 mm thick sheet thus produced. Table 1 shows the results.

[Low-molecular-weight siloxane content]
The resulting thermally conductive silicone rubber composition was placed in a mold of 100 mm x 100 mm x 0.45 mm, the pressure was adjusted so that the thickness after curing was 0.45 mm, and a high pressure press (Shoji Iron Works ( Co., Ltd.) was used to press cure at 165° C. and 100 kgf/cm ² for 10 minutes to prepare a sheet with a thickness of 0.45 mm. Further, after performing secondary vulcanization (post-curing) at 150° C./1 hour or 200° C./1 hour, it was cooled to room temperature. A small piece of this sheet was taken and immersed in acetone to extract low-molecular-weight siloxane, and the total content (mass ppm) of diorganocyclopolysiloxane having 3 to 10 silicon atoms was measured by gas chromatography analysis. Table 1 shows the results.

[Strength]
The resulting thermally conductive silicone rubber composition was pressed into a mold of 100 mm x 100 mm x 2 mm with a pressure adjusted so that the thickness after curing was 2 mm, followed by a high-pressure press (manufactured by Shoji Iron Works Co., Ltd.). was press-cured at 165° C. and 100 kgf/cm ² for 10 minutes to prepare a sheet having a thickness of 2 mm. Further, after performing secondary vulcanization at 150° C./1 hour or 200° C./1 hour, it was cooled to room temperature. Using the 2 mm thick sheet produced, the tensile strength, elongation at break, and tear strength were measured according to JIS K6249:2003. Table 1 shows the results.

[Molding of cover for exothermic electronic parts]
The thermally conductive silicone rubber composition after kneading is hot-pressed at 165° C. and 100 kgf/cm ² for 10 minutes using a transfer molding machine (manufactured by PRC Co., Ltd.) consisting of a piston, a pot, a medium mold, and a lower mold. Molded. After demolding, the molded product was subjected to secondary vulcanization at 150° C./1 hour to produce a heat-generating electronic component cover. FIG. 1 shows the shape of the heat-generating electronic component cover. The dimensions (unit: mm) are also shown in the figure.

[Cracking resistance when molding is mounted]
A 15 mm × 4.5 mm × height 20 mm electrode (manufactured by Safe Co., Ltd.) was fitted with the exothermic electronic component covers prepared in Examples 1 to 3 and Comparative Examples 2 and 3, and a voltage of 4.5 kV was applied for 10 minutes. Seconds were applied, and the presence or absence of leakage current was measured. If cracks occur during mounting, leak current is generated. Thirty pieces were measured, and the number of cracks among the 30 pieces is shown in Table 1.

As shown in Table 1, in Examples 1 to 3, the strength of the moldings and crack resistance during installation were good, and the low-molecular-weight siloxane content was low. In Comparative Example 1, a thermally conductive silicone rubber composition could not be obtained because the amount of the thermally conductive filler was too large. In Comparative Example 2, even after post-curing (150° C. for 1 hour), the low-molecular-weight siloxane could not be reduced to the desired amount, and the tensile strength was poor. On the other hand, in Comparative Example 3, the high-temperature post-cure (200° C. for 1 hour) to prevent contact failure caused by low-molecular-weight siloxane caused embrittlement of the sheet, and the sheet was cut during installation and handling of the molded product. Since the crack occurred, a leak current occurred. In other words, Comparative Examples 2 and 3 cannot prevent contact failure caused by low-molecular-weight siloxane.

As described above, the thermally conductive silicone rubber composition of the present invention can be cured at a low temperature, and the low-molecular-weight siloxane content can be sufficiently reduced even when subjected to a low-temperature post-curing process. For this reason, the thermally conductive silicone rubber composition of the present invention can obtain a sufficient effect of removing low-molecular-weight siloxane even without a post-curing step or even with post-curing at a low temperature, resulting in a cured product ( molded body) can be given.
In addition, a heat-dissipating molded article formed from a cured product molded using the present composition can be prevented from embrittlement due to high-temperature post-curing. The heat-dissipating molded article thus obtained has excellent thermal conductivity, strength, and insulation properties, and has a low content of low-molecular-weight siloxane.

In addition, this invention is not limited to the said embodiment. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

Claims (8)

(A) an organopolysiloxane having an average degree of polymerization of 3,000 to 10,000 and a total content of diorganocyclopolysiloxane having 3 to 10 silicon atoms of 500 ppm or less: 100 parts by mass;
(B) an organopolysiloxane having an average degree of polymerization of 2 to 2,000 and having alkenyl groups only at both ends of the molecular chain: 10 to 100 parts by mass;
(C) a thermally conductive filler: 500 to 2,700 parts by mass; and (D) a curing agent: an effective amount. Furthermore, (E) (E1) the following formula (1):
R ² _b R ³ _c Si(OR ⁴ ) _4-bc (1)
(wherein R ² is independently an alkyl group having 6 to 15 carbon atoms, R ³ is independently an alkyl group having 1 to 5 carbon atoms, R ⁴ is independently a ~4 alkyl group, b is an integer from 1 to 3, c is 0, 1 or 2, with the proviso that b+c is from 1 to 3.)
and (E2) the following formula (2):

(Wherein, R ⁵ is independently an alkyl group having 1 to 4 carbon atoms, and d is an integer of 5 to 100.)
0.01 to 30% by mass of the total amount of the organosilicon compound components, one or more selected from dimethylpolysiloxane whose one end is blocked with a trialkoxysilyl group represented by The thermally conductive silicone rubber composition according to claim 1, wherein 3. The thermally conductive silicone rubber composition according to claim 1, wherein the thermally conductive silicone rubber composition has a plasticity of 100-800. A cured product obtained by curing the thermally conductive silicone rubber composition according to any one of claims 1 to 3. 5. A heat-dissipating molded product made of the cured product according to claim 4, wherein the cured product has a thermal conductivity of 1.5 W/m·K or more. 6. The heat-dissipating molded product according to claim 5, wherein said cured product has a type A durometer hardness of 60 to 96 according to JIS K6253-3:2012. 7. The heat-dissipating molded article according to claim 5, wherein the heat-dissipating molded article has a withstand voltage of 4.5 kV or higher when the thickness of the cured product is 0.45 mm. The heat-dissipating molded article according to any one of claims 5 to 7, wherein the content of diorganocyclopolysiloxane having 3 to 10 silicon atoms after post-curing at 150°C for 1 hour is A heat-dissipating molded article characterized by having a concentration of 100 ppm or less.

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