JP7270792B2 - Thermally conductive silicone rubber sheet with thermally conductive adhesive layer - Google Patents

Description

The present invention relates to a thermally conductive silicone rubber sheet excellent in workability, reworkability, and heat dissipation properties, suitable as a heat dissipation insulating sheet for heat-generating electronic parts and the like.

Heat-generating electronic parts such as power transistors and thyristors used in various electronic devices, and integrated circuit elements such as ICs, LSIs, CPUs, and MPUs, are subject to deterioration in characteristics and shortening of the life of the elements due to heat generation. Therefore, in order to smoothly dissipate heat, the arrangement within the electronic equipment is considered. In addition, specific parts or the entire device are forcibly cooled with cooling fins, and for integrated circuit elements, heat is released to cooling members, substrates, and housings via heat radiation sheets (hereinafter referred to as heat radiation sheets). Consideration is also being given to

In recent years, however, electronic devices such as personal computers have become more highly integrated, and as the amount of heat generated by the above-mentioned exothermic components and integrated circuit elements in the devices increases, conventional forced air cooling methods and heat dissipation sheets cannot be used for these components and devices. cooling or heat dissipation may be insufficient. In particular, portable laptop or notebook personal computers require a cooling method other than the forced air cooling method. As for heat dissipation sheets, the printed circuit boards on which the elements are formed are made of glass-reinforced epoxy resin or polyimide resin, which have poor thermal conductivity. can't escape to Therefore, a heat sink such as a natural cooling type or forced cooling type heat radiating fin or heat pipe is installed near the element, and the heat generated by the element is transferred to the heat sink via a heat radiating medium to dissipate the heat. there is

Thermally conductive grease for heat dissipation or a heat dissipation sheet with a thickness of about 0.2 to 10.0 mm is used as a heat dissipation medium in this system in order to improve heat conduction between the element and the radiator. As a thermally conductive grease for heat radiation, for example, a thermally conductive silicone grease containing silicone oil mixed with a thermally conductive filler such as silica fiber, zinc oxide, or aluminum nitride is known (Patent Document 1). There is a danger of sagging, the workability of assembling electronic parts is reduced, and heat history causes voids to occur, resulting in a reduction in thermal conductivity. On the other hand, as a heat-dissipating sheet, a highly-filled, high-hardness silicone rubber layer reinforced with a cloth-like reinforcing material such as glass cloth is well known (Patent Document 2). This type of heat-dissipating sheet has a rubber layer with a high degree of hardness, and is extremely useful because it not only conducts heat but also ensures insulation. However, since the heat dissipation sheet has almost no surface tack, it is very difficult to mount and fix the heat dissipation sheet to the heating element.

In order to improve the workability of mounting and fixing, a heat-dissipating sheet with an adhesive layer on one or both sides of a high-hardness thermally conductive silicone rubber sheet, and the adhesive layer surface is protected with a release protective sheet such as release paper. are also available on the market, but in the case of this composite type heat dissipation sheet, there are cases where the adhesive strength of the adhesive layer is stronger than the desired adhesive strength. Or, the adhesive layer may be destroyed during rework. Furthermore, if a silicone adhesive layer is used on one or both sides of a silicone rubber sheet, the adhesive component of the silicone will migrate into the silicone heat-dissipating rubber sheet over time, resulting in a decrease in surface adhesive strength. I had a problem. Furthermore, in order to avoid this phenomenon, it is possible to increase the thickness of the silicone adhesive layer.

Also, there has been reported a heat-dissipating sheet in which an acrylic adhesive layer having a higher thermal conductivity than silicone is laminated on one or both sides of a thermally conductive silicone rubber sheet (Patent Document 3). However, in terms of manufacturing method, the acrylic adhesive layer is cured on the separator, and the silicone heat-dissipating rubber sheet material is applied and cured on top of it. It was difficult to provide a reinforcing material such as glass cloth for the purpose. Furthermore, in order to obtain adhesion between the acrylic adhesive layer and the thermally conductive silicone rubber sheet, it was necessary to add a primer to the acrylic adhesive layer or add an adhesive component to the material of the silicone heat-dissipating rubber sheet. components may bleed over time and contaminate the actual machine. Moreover, since the acrylic pressure-sensitive adhesive layer does not have excellent heat resistance, it has the disadvantage that it is difficult to adapt to applications requiring high heat resistance.

There is also disclosed a heat-dissipating sheet in which a low-hardness thermally conductive silicone rubber layer is laminated on a high-hardness thermally conductive silicone rubber sheet reinforced with a reinforcing material as described above (Patent Document 5). However, in the case of this composite heat-dissipating sheet, it is not possible to obtain a sheet with an overall thickness of less than 0.45 mm due to manufacturing problems. However, there was a drawback that a thin composite product as a whole could not be obtained and the thermal resistance increased. In addition, in the case of conventional composite heat dissipation sheets, in order to improve the workability of low-hardness sheets, high-hardness sheets are generally laminated, and consist of a thick low-hardness layer and a thin high-hardness layer. rice field. However, in the case of this configuration, the low-hardness layer is compressed and deformed by pressure, so it may be difficult to guarantee insulation by guaranteeing space.

Therefore, by laminating a thin, low-hardness, and slightly sticky thermally conductive silicone rubber layer, heat conductivity is improved through good contact without sacrificing workability and insulation assurance. A heat-dissipating sheet to which workability and reworkability are imparted by adhesion is also disclosed (Patent Document 6). However, although the low-hardness silicone rubber layer has excellent reworkability, it has poor cohesive force, so that the adhesive force obtained is very poor, and depending on the mounting situation, it was difficult to temporarily fix it to the heating element. Moreover, this patent does not describe the peel force when peeling is performed at a pulling speed of 300 mm/min conforming to JIS C 2107, which is an important index of adhesive force.

Japanese Patent Publication No. 57-36302 JP-A-56-161140 JP-A-2001-348542 JP 2009-132752 A JP-A-06-155517 JP 2014-193598 A

As described above, the conventional high-hardness silicone heat-dissipating sheet is excellent in insulation reliability in addition to heat-dissipating properties due to its strength, but is disadvantageous in mounting workability. In addition, when a pressure-sensitive adhesive layer is provided on one or both sides to improve mounting workability, especially when a silicone pressure-sensitive layer is used, the pressure-sensitive adhesive component migrates to the interior of the silicone heat dissipation sheet over time. A decrease in strength was observed. In addition, when an acrylic adhesive layer is used, a complicated manufacturing method of using a primer component is required in order to improve adhesion to the silicone heat-dissipating sheet. Furthermore, the acrylic pressure-sensitive adhesive layer also has the drawback that it is difficult to apply it to high heat resistance applications.

On the other hand, in the case of composite sheets with low hardness and high hardness, it is difficult to make them thin, and it is difficult to guarantee space and insulation under high pressure because of their structure. In addition, there is a drawback that the manufacturing process is complicated and changes over time cannot be suppressed. Furthermore, since the low-hardness layer lacks cohesion, there have been cases where the desired adhesiveness cannot be obtained under the mounting conditions, resulting in insufficient temporary fixing to the actual machine.

An object of the present invention is to provide a composite heat-dissipating sheet that is excellent in thermal conductivity and insulation and has sufficient adhesion to actual equipment, low thermal resistance, reworkability, and reliability of adhesion. Another object of the present invention is to provide the heat-dissipating sheet with a simpler manufacturing process.

In view of such circumstances, the present inventors conducted intensive research and found that a thermally conductive silicone rubber layer having a high hardness having a durometer A hardness of 60 to 96 and preferably having a thickness of 50 to 900 μm, A thermally conductive silicone rubber sheet having, on at least one surface of the thermally conductive silicone rubber layer, a silicone pressure-sensitive adhesive layer having the following specific configuration, preferably having a thickness of 2 to 40 μm, is sufficiently thermally conductive. The inventors have found that the adhesive strength, reworkability, and adhesive strength over time are excellent, and have completed the present invention.

That is, the present invention provides a thermally conductive silicone rubber sheet comprising a laminate of at least one thermally conductive silicone rubber layer having a durometer A hardness of 60 to 96 and at least one silicone adhesive layer,
The silicone adhesive layer is a cured product of an addition reaction-curable silicone adhesive composition containing the following components (a), (c), (b), (d), (e), and (f), The thermally conductive silicone rubber sheet is provided, wherein the silicone adhesive layer has a thickness of 2 to 15 μm.
(a) an organopolysiloxane having at least one silicon-bonded alkenyl group and having 2 to 20% of the total number of silicon-bonded phenyl groups with respect to the total number of silicon-bonded substituents; : 100 parts by mass,
(c) a thermally conductive filler having an average particle size of less than 10 μm, an amount of particles with a particle size of 20 μm or greater in an amount of 0-3% by weight, and an amount of particles with a particle size of 40 μm or greater in an amount of 0% by weight; Material: 100 to 800 parts by mass,
(b) organohydrogenpolysiloxane: an amount such that the ratio of the number of silicon-bonded hydrogen atoms in component (b) to the number of alkenyl groups in component (a) is 0.5 to 30;
(d) addition reaction catalyst: catalyst amount, (e) addition reaction control agent: 0.01 to 1 part by mass, and (f) R ₃ SiO _1/2 unit (R has an aliphatic unsaturated bond unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms) and SiO _4/2 units, and the number ratio of R ₃ SiO _1/2 units to SiO _4/2 units is 0. 5 to 2.5, silicone resin: 50 to 300 parts by mass.

Since the thermally conductive silicone rubber sheet of the present invention has a thermally conductive silicone rubber layer with high hardness, it is excellent in workability, insulation assurance and thermal conductivity. Furthermore, by having a thin silicone adhesive layer with better heat resistance than the acrylic adhesive layer, it can be used satisfactorily even at high temperatures. In addition, by having the silicone adhesive layer of the present invention, the change in adhesive strength over time is suppressed, the thermal conductivity of the adhesive layer is enhanced, and the increase in thermal resistance of the sheet is suppressed. Furthermore, since the thermally conductive silicone rubber sheet of the present invention is molded by directly applying the silicone pressure-sensitive adhesive composition to the thermally conductive silicone rubber layer, it is easier than the conventional lamination method using a primer or the like. It can be manufactured in a process.

The present invention will be described in detail below.
[Thermal conductive silicone rubber layer]
The thermally conductive silicone rubber sheet of the present invention has a high hardness thermally conductive silicone rubber layer with a durometer A hardness of 60-96. The thermally conductive silicone rubber composition that provides the high-hardness thermally conductive silicone rubber layer may have the hardness described above, and may be an addition reaction-curable thermally conductive silicone rubber composition or a peroxide-curable thermally conductive silicone. Any rubber composition may be used. The addition reaction-curable silicone rubber composition may be a composition containing an alkenyl group-containing organopolysiloxane, an organohydrogensiloxane, an addition reaction catalyst, a thermally conductive filler, and a surface treatment agent. The peroxide-curable silicone rubber composition may be a composition containing an alkenyl group-containing organopolysiloxane, an organic peroxide, a thermally conductive filler, and a surface treatment agent. The durometer A hardness can be adjusted by adjusting the amount of a curing agent or the like to be described later.
Each component will be described in more detail below.

In the addition reaction-curable silicone rubber composition and the peroxide-curable silicone rubber composition, the alkenyl group-containing organopolysiloxane has an average composition formula: R ¹ _a SiO _(4-a)/2 (wherein R ¹ is independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and a is a number of 1.90 to 2.05). is.

R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, and an alkyl group; , cycloalkyl groups, aryl groups, aralkyl groups, alkenyl groups, and groups in which some or all of the hydrogen atoms bonded to these carbon atoms are substituted with halogen atoms, cyano groups, or the like. For example, alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, and octadecyl group; cycloalkyl groups such as cyclopentyl group and cyclohexyl group; aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group; aralkyl groups such as benzyl group, phenethyl group and 3-phenylpropyl group; 3,3,3-trifluoropropyl group, 3-chloropropyl group and the like and alkenyl groups such as a vinyl group, an allyl group, a butenyl group, a pentenyl group and a hexenyl group. However, at least one of R ¹ is an alkenyl group.

The alkenyl group-containing organopolysiloxane generally has a main chain composed of dimethylsiloxane units, or a portion of the methyl groups in the main chain is a vinyl group, a phenyl group, a 3,3,3-tri Those substituted with a fluoropropyl group or the like are preferred. Moreover, the terminal of the molecular chain is preferably capped with a triorganosilyl group or a hydroxyl group, and examples of the triorganosilyl group include trimethylsilyl group, dimethylvinylsilyl group and trivinylsilyl group.

The average degree of polymerization of the alkenyl group-containing organopolysiloxane is preferably 20 to 12,000, more preferably 50 to 10,000. The organopolysiloxane may be oily or gum-like, and may be selected according to the molding method and the like.

In the case of the addition reaction-curable silicone rubber composition, the organopolysiloxane preferably has 2 or more, preferably 5 to 100 silicon-bonded alkenyl groups per molecule. If the content of silicon-bonded alkenyl groups is less than the lower limit of the above range, the resulting composition will not cure sufficiently. A vinyl group is preferable as the alkenyl group bonded to the silicon atom. The alkenyl group may be present at either or both of the molecular chain terminal and the side chain, and preferably at least one alkenyl group is bonded to the silicon atom at the molecular chain terminal.

Examples of the alkenyl group-containing organopolysiloxane in the addition reaction-curing silicone rubber composition include dimethylsiloxane-methylvinylsiloxane copolymer having both molecular chain terminals blocked with trimethylsiloxy groups, and methylvinylpolysiloxane having both molecular chain terminals blocked with trimethylsiloxy groups. Siloxane, dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer with trimethylsiloxy group-blocked at both molecular chain ends, dimethylpolysiloxane with dimethylvinylsiloxy group-blocked at both molecular chain ends, methylvinylpolysiloxane with dimethylvinylsiloxy group-blocked at both molecular chain ends , dimethylsiloxane/methylvinylsiloxane copolymer with dimethylvinylsiloxy group-blocked at both molecular chain ends, dimethylsiloxane/methylvinylsiloxane-methylphenylsiloxane copolymer with dimethylvinylsiloxy group-blocked at both molecular chain ends, trivinylsiloxy at both molecular chain ends Group-blocked dimethylpolysiloxane and the like can be mentioned. These can be used singly or in combination of two or more.

The addition reaction-curable silicone rubber composition further comprises an organohydrogenpolysiloxane having an average of two or more silicon-bonded hydrogen atoms per molecule and an addition reaction catalyst. The organohydrogenpolysiloxane reacts with the alkenyl group-containing organopolysiloxane to form a crosslinked structure. Examples of organohydrogenpolysiloxanes include methylhydrogenpolysiloxane with trimethylsiloxy group-blocked at both molecular chain ends, dimethylsiloxane-methylhydrogensiloxane copolymer with trimethylsiloxy group-blocked at both molecular chain ends, and trimethylsiloxy group at both molecular chain ends. Blocking dimethylsiloxane/methylhydrogensiloxane/methylphenylsiloxane copolymer, dimethylpolysiloxane blocking both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane/methylhydrogensiloxane copolymer blocking both molecular chain ends with dimethylhydrogensiloxy groups , a dimethylsiloxane-methylphenylsiloxane copolymer having both molecular chain terminals blocked with dimethylhydrogensiloxy groups, and a methylphenylpolysiloxane having both molecular chain terminals blocked with dimethylhydrogensiloxy groups. The organohydrogenpolysiloxane may be used alone or in combination of two or more.

The amount of organohydrogenpolysiloxane may be appropriately adjusted in accordance with conventionally known addition reaction-curable silicone compositions. For example, if the ratio of the number of silicon-bonded hydrogen atoms to the number of silicon-bonded alkenyl groups in the alkenyl group-containing organopolysiloxane is 0.1 to 4.0, preferably 0.3 to 2.0. good. A thermally conductive silicone rubber layer having the durometer A hardness described above can be obtained by reacting within this range. If the amount of organohydrogenpolysiloxane is too small, the resulting silicone rubber composition may not cure sufficiently. On the other hand, if the amount is too high, the cured silicone rubber will become very hard, and problems such as the formation of many cracks on the surface may occur.

The addition reaction catalyst may be any known catalyst. Examples thereof include platinum-based catalysts such as chloroplatinic acid, alcohol solutions of chloroplatinic acid, olefin complexes of platinum, alkenylsiloxane complexes of platinum, and carbonyl complexes of platinum. The content of the platinum-based catalyst is not particularly limited, and may be an effective amount for advancing the addition reaction. For example, the amount of platinum metal in the catalyst should be 0.01 to 1,000 ppm, preferably 0.1 to 500 ppm, relative to the alkenyl group-containing organopolysiloxane. If the amount of the catalyst is too small, the silicone rubber composition will not be sufficiently cured, and if the amount of the catalyst is too large, the resulting silicone rubber composition will not cure at a faster rate, which may be economically disadvantageous.

In the case of the peroxide-curable silicone rubber composition, the alkenyl group-containing organopolysiloxane is not particularly limited, but preferably has at least two alkenyl groups per molecule. Examples include dimethylpolysiloxane with both molecular chain ends blocked with dimethylvinylsiloxy groups, dimethylpolysiloxane with both molecular chain ends blocked with methylphenylvinylsiloxy groups, dimethylsiloxane/methylphenylsiloxane copolymer with both molecular chain ends blocked with dimethylvinylsiloxy groups, molecular chains. dimethylvinylsiloxy group-blocked dimethylsiloxane/methylvinylsiloxane copolymer at both ends, dimethylsiloxane/methylvinylsiloxane copolymer blocked at both molecular chain ends with trimethylsiloxy groups, methyl vinylsiloxy group-blocked at both ends of the molecular chain (3,3, 3-trifluoropropyl) polysiloxane, both molecular chain ends silanol group-blocked dimethylsiloxane/methylvinylsiloxane copolymer, and molecular chain both ends silanol group-blocked dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer, etc. mentioned. These may be used singly or in combination of two or more.

Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butylperoxide, and t- butyl perbenzoate and the like. These may be used singly or in combination of two or more. The amount of the organic peroxide to be added is generally 0.1 to 5 parts by mass, preferably 0.5 to 3 parts by mass, per 100 parts by mass of the alkenyl group-containing organopolysiloxane. A thermally conductive silicone rubber layer having the durometer A hardness described above can be obtained by reacting within this range.

Thermally conductive fillers contained in the thermally conductive silicone rubber composition include, for example, inorganic powders such as aluminum oxide, zinc oxide, silicon oxide, silicon carbide, aluminum nitride, and boron nitride. These may be used singly or in combination of two or more.

The average particle size of the thermally conductive filler is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less. In the present invention, the average particle size is a value measured on a volume basis using a Microtrac particle size distribution analyzer MT3300EX (Nikkiso Co., Ltd.). If the average particle size exceeds the above upper limit, the surface of the sheet may be roughened and the thermal resistance may increase.

The content of the thermally conductive filler in the thermally conductive silicone rubber composition is preferably 200 to 3,000 parts by mass, more preferably 400 to 2 parts by mass, per 100 parts by mass of the alkenyl group-containing organopolysiloxane. ,000 parts by mass. If the content of the thermally conductive filler is too small, the thermal conductivity of the silicone rubber layer tends to be insufficient. On the other hand, if the amount of the thermally conductive filler to be blended is too large, it may become difficult to uniformly blend the filler into the composition, which may result in poor moldability.

（式中、Ｒ^５は、互いに独立に、炭素原子数１～６のアルキル基であり、ｃは５～１００の整数であり、好ましくは８～５０の整数である） The thermally conductive silicone rubber composition preferably further contains a surface treatment agent. Examples of the surface treatment agent include alkoxysilanes represented by the following general formula (1), and dimethylpolysiloxanes having a trialkoxy group at one molecular chain end represented by the following general formula (2). These surface treatment agents may be used alone or in combination of two or more. An alkoxysilane represented by the following formula (1) and a dimethylpolysiloxane represented by the following formula (2) may be used in combination.

R ² _a R ³ _b Si(OR ⁴ ) _4-ab (1)

(In the formula, R ² is each independently an alkyl group having 6 to 15 carbon atoms, and R ³ is each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms. , R ⁴ are each independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, provided that a+b is an integer of 1 to 3 be)

(Wherein R ⁵ is independently an alkyl group having 1 to 6 carbon atoms, c is an integer of 5 to 100, preferably an integer of 8 to 50)

R ² is an alkyl group having 6 to 15 carbon atoms. When the number of carbon atoms is within this range, the wettability of the thermally conductive filler is sufficiently improved, the handleability is good, and the low-temperature properties of the composition are good. Examples of alkyl groups include hexyl, octyl, nonyl, decyl, dodecyl, and tetradecyl groups.

R ³ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms. For example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, etc. cycloalkyl groups such as alkyl groups, cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; aryl groups such as phenyl groups, tolyl groups, xylyl groups, naphthyl groups and biphenylyl groups; benzyl groups, phenylethyl groups, phenylpropyl groups and methylbenzyl groups; aralkyl groups such as groups, and groups in which some or all of the hydrogen atoms to which carbon atoms are bonded to these groups are substituted with halogen atoms such as fluorine, chlorine, and bromine, and cyano groups, such as chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6, 6-nonafluorohexyl group and the like. It is preferably a substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, particularly preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms. More preferred are methyl group, ethyl group, propyl group, chloromethyl group, bromoethyl group, 3,3,3-trifluoropropyl group, cyanoethyl group, phenyl group, chlorophenyl group and fluorophenyl group.

R ⁴ and R ⁵ are each independently an alkyl group having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and pentyl. group, preferably a methyl group or an ethyl group.

Examples of the alkoxysilane represented by formula (1) include the following compounds. The alkoxysilanes may be used singly or in combination of two or more.
_{C6H13Si ( OCH3} ) _{3
C10H21Si ( OCH3} ) _{3
C12H25Si ( OCH3} ) _{3
C12H25Si ( OC2H5 ) 3
C10H21Si ( CH3} )( _OCH3 ) _{2
C10H21Si ( C6H5} ) _{( OCH3} ) _{2
C10H21Si ( CH3 )} ( _OC2H5 ) _2
C10H21Si (CH _{= CH2} )( _OCH3 ) _{2
C10H21Si ( CH2CH2CF3} ) _{( OCH3 ) 2}

Examples of the dimethylpolysiloxane represented by formula (2) include the following.

The amount of the surface treatment agent in the thermally conductive silicone rubber composition is preferably 5 to 80 parts by mass, more preferably 10 to 75 parts by mass, based on 100 parts by mass of the alkenyl group-containing organopolysiloxane. , more preferably 10 to 50 parts by mass. If the amount of the surface treatment agent is too large, the surface treatment agent may bleed oil over time and contaminate the actual machine. On the other hand, if the amount is too small, the thermally conductive filler may not be filled into the thermally conductive silicone rubber composition.

Other additives can be blended into the thermally conductive silicone rubber composition as long as the objects of the present invention are not impaired. Other additives include reinforcing silica such as fumed silica and precipitated silica; plasticizers such as silicone oil and silicone wetter; flame retardants such as platinum, titanium oxide and benzotriazole; - acetylene compound-based addition reaction controller such as cyclohexanol; coloring agents such as organic pigments and inorganic pigments; heat resistance improvers such as iron oxide and cerium oxide; internal release agents; can.

[Formation of high-hardness thermally conductive silicone rubber layer]
A high-hardness thermally conductive silicone rubber layer can be obtained by heat-curing the thermally conductive silicone rubber composition having a high hardness. The thermally conductive silicone rubber layer of the present invention has a durometer A hardness of 60-96, preferably 80-96. The high hardness can be obtained by mixing each of the above components in the amounts within the ranges described above. In particular, it can be obtained by adjusting the amount of the curing agent to be added within the range described above. If the hardness is lower than the above lower limit, the surface of the rubber layer may be easily scratched during handling, or the surfaces of the rubber layer may fuse together when wound into a roll during continuous molding. is difficult to guarantee. On the other hand, if the hardness is higher than the above upper limit, the flexibility of the sheet will be poor, and cracks may occur when the sheet is folded. In the present invention, the hardness of the silicone rubber layer is measured at 25° C. using a durometer A hardness tester with two 6 mm-thick cured products of the thermally conductive silicone rubber composition stacked.
The thermally conductive silicone rubber layer of the present invention can contain glass cloth or polyimide as an intermediate reinforcing layer. It is the hardness measured as an object.

In the thermally conductive silicone rubber sheet of the present invention, the thermally conductive silicone rubber layer preferably has a thickness of 50 μm or more and 900 μm or less, more preferably 60 μm or more and 700 μm or less. As described above, if the thickness of the high-hardness thermally conductive silicone rubber layer is thin, the included thermally conductive filler protrudes from the surface, impairing the smoothness of the coating surface, and lamination of the silicone adhesive layer, which will be described later, is not possible. becomes difficult.

The thermally conductive silicone rubber layer preferably has a thermal conductivity of 1.0 W/m·K or more, more preferably 1.2 W/m·K or more. If the thermal conductivity is less than 1.0 W/m·K, the thermal conductivity may be insufficient.

The thermally conductive silicone rubber layer of the present invention can contain glass cloth or polyimide as an intermediate reinforcing layer in order to improve strength. However, when the glass cloth is used as the intermediate layer, it is necessary to perform a sealing step, which will be described later. The glass cloth preferably has a thickness of 30 μm or more and 50 μm or less and a weight of 30 g/m ² or less. More preferably, the thickness is 30 μm or more and 45 μm or less and the weight is 25 g/m ² or less. Since the glass cloth has a relatively low thermal conductivity, it is preferable that the thickness of the cloth is thin in consideration of heat conduction. However, if the thickness is too thin, the strength will decrease and the film will be easily broken, or the moldability will be poor.

The thermal conductivity of the thermally conductive silicone resin that seals the glass cloth is preferably 1.0 W/mK or more. If it is less than 1.0 W/mK, the thermal conductivity of the glass cloth sealed with the thermally conductive silicone resin will deteriorate, and the thermal conductivity of the entire thermally conductive silicone rubber sheet will deteriorate. The thermally conductive silicone resin for sealing may be the thermally conductive silicone rubber composition described above. The thickness after filling is preferably 100 μm or less, more preferably 90 μm or less. If the thickness of the sealed glass cloth exceeds 100 μm, the ratio of the thickness of the high thermal conductive silicone rubber layer to the entire thermal conductive silicone rubber sheet becomes small, which is disadvantageous when considering the overall thermal conductivity. .

The thermally conductive silicone rubber layer of the present invention is preferably non-sticky. In the present invention, "non-adhesive" means having an adhesive strength of 0.01 N/25 m or less, particularly a state in which the adhesive strength is below the detection limit. When the above-described thermally conductive silicone rubber layer of the present invention has a durometer A hardness of around 90, the thermally conductive silicone rubber layer loses its surface tackiness and has the adhesive force as described above, which is a so-called non-adhesive property. Become.

[Silicone adhesive layer]
The thermally conductive silicone rubber sheet of the present invention is formed by laminating at least one thermally conductive silicone rubber layer and at least one silicone adhesive layer. The silicone pressure-sensitive adhesive layer is a cured product of an addition reaction-curable or peroxide-curable silicone pressure-sensitive adhesive composition, characterized by containing the following components (a), (c) and (f): .
(a) an organopolysiloxane having at least one silicon-bonded alkenyl group and having 2 to 20% of the total number of silicon-bonded phenyl groups with respect to the total number of silicon-bonded substituents; : 100 parts by mass,
(c) a thermal conductivity having an average particle size of less than 10 μm, an amount of particles with a particle size of 20 μm or more in an amount of 0 to 3% by weight, and an amount of particles with a particle size of 40 μm or more in an amount of 0 to 0.01% by weight; and (f) R ₃ SiO _1/2 units (R is an unsubstituted or substituted monovalent carbon number of 1 to 10 having no aliphatic unsaturation a hydrogen group) and SiO _4/2 units, and the number ratio of R ₃ SiO _1/2 units to SiO _4/2 units is 0.5 to 2.5: 50 to 300 parts by mass.

The silicone pressure-sensitive adhesive composition may be addition reaction-curable or peroxide-curable.
The addition reaction-curable silicone pressure-sensitive adhesive composition preferably has the following structure.
(a) an organopolysiloxane having at least one silicon-bonded alkenyl group and having 2 to 20% of the total number of silicon-bonded phenyl groups with respect to the total number of silicon-bonded substituents; : 100 parts by mass (c) having an average particle size of less than 10 μm, containing 0 to 3% by mass of particles having a particle size of 20 μm or more, and containing 0 to 0.01% by mass of particles having a particle size of 40 μm or more Thermally conductive filler: 100 to 800 parts by mass (b) organohydrogenpolysiloxane: the ratio of the number of silicon-bonded hydrogen atoms in component (b) to the number of alkenyl groups in component (a) is 0.5 to 50,
(d) addition reaction catalyst: catalytic amount,
(e) Addition reaction controller: 0.01 to 1 part by mass, and (f) R ₃ SiO _1/2 unit (R is an unsubstituted or substituted C1 10 monovalent hydrocarbon groups) and SiO _4/2 units, wherein the number ratio of R ₃ SiO _1/2 units to SiO _4/2 units is 0.5 to 2.5: 50 to 300 parts by mass.

The peroxide-curable silicone pressure-sensitive adhesive composition preferably has the following structure.
(a) an organopolysiloxane having at least one silicon-bonded alkenyl group and having 2 to 20% of the total number of silicon-bonded phenyl groups with respect to the total number of silicon-bonded substituents; : 100 parts by mass (c) having an average particle size of less than 10 μm, containing 0 to 3% by mass of particles having a particle size of 20 μm or more, and containing 0 to 0.01% by mass of particles having a particle size of 40 μm or more 100 to 800 parts by mass (f) R ₃ SiO _1/2 units (R is an unsubstituted or substituted, 1 to 10 carbon atoms having no aliphatic unsaturation a valent hydrocarbon group) and SiO _4/2 units, wherein the number ratio of R ₃ SiO _1/2 units to SiO _4/2 units is 0.5 to 2.5, silicone resin: 50 to 300 mass and (g) organic peroxide: 0.1 to 10 parts by mass per 100 parts by mass of component (a).
Each component will be described in more detail below.

[(a) Alkenyl Group-Containing Organopolysiloxane]
Component (a) is an organopolysiloxane having at least one, preferably two or more, silicon-bonded alkenyl groups per molecule. Usually, the main chain portion basically consists of repeating diorganosiloxane units, but it may contain a branched structure as part of the molecular structure, or it may be a cyclic body. In particular, linear diorganopolysiloxane is preferred from the viewpoint of physical properties such as mechanical strength of the cured product. The kinematic viscosity of the organopolysiloxane at 25° C. is preferably 100 to 50,000 mm ² /s, preferably 1,000 to 30,000 mm ² /s. The viscosity is measured by an Ostwald viscometer.

The present invention is characterized in that the component (a) contains 2 to 20% of the total number of silicon-bonded phenyl groups with respect to the total number of silicon-bonded substituents. It is preferably 4 to 18%, more preferably 7 to 15%. If the phenyl group content is less than the above lower limit, the adhesive strength decreases over time when the silicone adhesive layer is laminated on the thermally conductive silicone rubber layer. Moreover, if the content of the phenyl group exceeds the above upper limit, both the initial adhesive strength and the adhesive strength over time of the silicone adhesive layer are remarkably lowered, which is not preferable. The substituents bonded to silicon atoms are phenyl groups, alkenyl groups, and other substituents.

Alkenyl groups preferably have 2 to 8 carbon atoms and include, for example, vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups. Among them, a vinyl group and a lower alkenyl group such as an allyl group are preferred, and a vinyl group is particularly preferred.

Substituents other than alkenyl groups and phenyl groups bonded to silicon atoms may be organic groups bonded to silicon atoms of general alkenyl group-containing organopolysiloxanes. Preferably, it is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 3 carbon atoms, and an alkyl group, cyclo Examples include alkyl groups, aryl groups, aralkyl groups, and groups in which some or all of the hydrogen atoms bonded to these carbon atoms are substituted with halogen atoms, cyano groups, or the like. For example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, etc. cycloalkyl groups such as alkyl groups, cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; aryl groups such as tolyl groups, xylyl groups, naphthyl groups and biphenylyl groups; Aralkyl groups, and groups in which some or all of the hydrogen atoms to which carbon atoms are bonded to these groups are substituted with halogen atoms such as fluorine, chlorine, and bromine, and cyano groups, such as chloromethyl groups, 2 -bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6,6-nona A fluorohexyl group and the like can be mentioned. Particularly preferred are methyl group, ethyl group, propyl group, chloromethyl group, bromoethyl group, 3,3,3-trifluoropropyl group, cyanoethyl group, chlorophenyl group and fluorophenyl group. Moreover, it is not limited that all the functional groups other than the alkenyl group bonded to the silicon atom are the same.

式（３）中、Ｒ^７は互いに独立に、脂肪族不飽和結合を含有しない非置換又は置換の、炭素原子数１～１０の１価炭化水素基あるいは水素原子であり、但し、少なくとも２個は水素原子であり、ｎは１以上の整数であり、好ましくはｎは１～１００の整数であり、より好ましくは５～５０の整数である。 [(b) Organohydrogenpolysiloxane]
Component (b) is an organohydrogenpolysiloxane and preferably has an average of 2 or more, preferably 2 to 100, hydrogen atoms (Si--H) directly bonded to silicon atoms per molecule. The (b) component functions as a cross-linking agent for the (a) component. A hydrosilylation reaction between Si—H in component (b) and alkenyl groups in component (a) gives a three-dimensional network structure having a crosslinked structure. If the average number of Si—H groups is less than 1, there is a possibility that the composition will not be cured. The organohydrogenpolysiloxane may be a conventionally known compound, and can be represented, for example, by the following general formula (3).

In formula (3), each R ⁷ is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom containing no aliphatic unsaturated bonds, provided that at least two is a hydrogen atom, n is an integer of 1 or more, preferably an integer of 1-100, more preferably an integer of 5-50.

For R ⁷ , as an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic unsaturated bond and having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, , for example methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, etc. cycloalkyl groups such as alkyl groups, cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; aryl groups such as phenyl groups, tolyl groups, xylyl groups, naphthyl groups and biphenylyl groups; benzyl groups, phenylethyl groups, phenylpropyl groups and methylbenzyl groups; aralkyl groups such as groups, and groups in which some or all of the hydrogen atoms to which carbon atoms are bonded to these groups are substituted with halogen atoms such as fluorine, chlorine, and bromine, and cyano groups, such as chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6, 6-nonafluorohexyl group and the like. Among them, more preferred are methyl group, ethyl group, propyl group, chloromethyl group, bromoethyl group, 3,3,3-trifluoropropyl group, cyanoethyl group, phenyl group, chlorophenyl group and fluorophenyl group. ^R7 may be the same or different, provided that at least two ^R7 are hydrogen atoms.

The amount of component (b) is such that the ratio of the number of Si—H groups in component (b) to the number of alkenyl groups in component (a) is 0.1 to 30, preferably 0.5. to 15, more preferably 1.0 to 5. If the amount of component (b) is less than the above lower limit, curing of the adhesive layer will be insufficient, resulting in poor reworkability. On the other hand, when the above upper limit is exceeded, the flexibility of the cured product is remarkably lowered, and the adhesive strength is greatly lowered, which is not preferable.

[(c) Thermally conductive filler]
The thermally conductive filler contained in the silicone pressure-sensitive adhesive composition has an average particle size of less than 10 μm, the amount of particles with a particle size of 20 μm or more is 0 to 3% by mass, and the amount of particles with a particle size of 40 μm or more is is 0 to 0.01% by mass. If the particle size is out of this range, the surface condition of the thermally conductive adhesive layer will not be smooth and the contact will be poor, so that the desired adhesive strength cannot be obtained and the thermal resistance will increase. The average particle size is preferably 1-10 μm, more preferably 1-5 μm. The average particle size in the present invention is a value (volume basis) determined using Microtrac MT3300EX (Nikkiso), which is a laser diffraction/scattering particle size distribution analyzer. When two or more thermally conductive fillers are used in combination, each thermally conductive filler may satisfy the particle size requirements described above.

The amount of particles with a particle size of 20 μm or more and the amount of particles with a particle size of 40 μm or more in the thermally conductive filler (c) are determined as follows. 10 g of the filler is collected, placed in an arbitrary amount of water and ultrasonically dispersed. Sieves with mesh openings of 20 μm and 40 μm are piled up and set in a sieve shaker, and the thermally conductive filler dispersed in water is put into the shaker. The filler remaining on each sieve is dried and weighed.

As the thermally conductive filler, for example, at least one selected from alumina, aluminum hydroxide, aluminum nitride, boron nitride, zinc oxide, and metallic aluminum is preferable. From a practical point of view, alumina is particularly preferred.

The amount of component (c) is 100 to 800 parts by mass, preferably 200 to 500 parts by mass, per 100 parts by mass of component (a). If the filling amount is less than the above lower limit, sufficient thermal conductivity cannot be imparted to the adhesive layer. On the other hand, if the above upper limit is exceeded, the filler becomes too dense, and when the composition is coated to obtain a thermally conductive sheet, the smoothness of the sheet surface is impaired, the heat resistance increases, and the adhesive strength increases. can lead to decline.

[(d) addition reaction catalyst]
The component (d) is an addition reaction catalyst which promotes the addition reaction between the alkenyl group derived from the component (a) and the Si—H group derived from the component (b). A well-known catalyst is mentioned. For example, platinum-based metal catalysts, such as platinum (including platinum black), rhodium, and platinum group metal simple substances such as palladium, H ₂ PtCl ₄ ·nH ₂ O, H ₂ PtCl ₆ · nH ₂ O, NaHPtCl ₆ · nH ₂ O _{, KaHPtCl6.nH2O , Na2PtCl6.nH2O , K2PtCl4.nH2O , PtCl4.nH2O , PtCl2 , Na2HPtCl4.nH2O (} wherein _, n is an integer of 0 to 6, preferably 0 or 6); platinum chloride, chloroplatinic acid and chloroplatinates; ), a complex of chloroplatinic acid and an olefin (see U.S. Pat. Nos. 3,159,601, 3,159,662 and 3,775,452), platinum black, A platinum group metal such as palladium supported on a carrier such as alumina, silica, carbon, etc., rhodium-olefin complex, chlorotris(triphenylphosphine) rhodium (Wilkinson's catalyst), platinum chloride, chloroplatinic acid or chloroplatinate and a vinyl group-containing siloxane, particularly a vinyl group-containing cyclic siloxane. The amount of the component (d) may be a so-called catalytic amount, and is usually about 0.1 to 2000 ppm as the amount of the platinum group metal element relative to the component (a).

[(e) addition reaction control agent]
Component (e) is not particularly limited as long as it is a known addition reaction inhibitor used in ordinary addition reaction curing silicone compositions. Examples thereof include acetylene compounds such as 1-ethynyl-1-hexanol, 3-butyn-1-ol and ethynylmethylidenecarbinol, various nitrogen compounds, organic phosphorus compounds, oxime compounds, and organic chloro compounds. The amount is desirably about 0.01 to 1 part by mass per 100 parts by mass of component (a).

[(f) silicone resin]
(f) A silicone resin is added to impart cohesiveness to the silicone pressure-sensitive adhesive composition. By containing the component (f) in the following specific amount, it is possible to provide the silicone rubber sheet with appropriate adhesive strength and excellent reworkability. The silicone resin is a copolymer of R ₃ SiO _1/2 units (M units) and SiO _4/2 units (Q units), and the ratio (molar ratio) between M units and Q units is M/Q=0. 0.5 to 2.5, preferably 0.6 to 1.4, more preferably 0.7 to 1.3. When M/Q is less than 0.5, or when M/Q exceeds 1.5, desired cohesion cannot be obtained.

R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms and containing no aliphatic unsaturation. For example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, etc. cycloalkyl groups such as alkyl groups, cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; aryl groups such as phenyl groups, tolyl groups, xylyl groups, naphthyl groups and biphenylyl groups; benzyl groups, phenylethyl groups, phenylpropyl groups and methylbenzyl groups; aralkyl groups such as groups, and 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, chlorine, and bromine, and cyano groups, such as chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6, 6-nonafluorohexyl group and the like. It preferably has 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms. Among them, preferred are methyl group, ethyl group, propyl group, chloromethyl group, bromoethyl group, 3,3,3-trifluoropropyl group, cyanoethyl group, phenyl group, chlorophenyl group and fluorophenyl group. In addition, although all R may be the same or different, it is desirable that they are the same substituents as R ¹ . In particular, as with R ¹ described above, unless special properties such as solvent resistance are required, for reasons such as cost, availability, chemical stability, and environmental load, all R are methyl. It is preferably a group.

The amount of component (f) added is 50 to 300 parts by mass, preferably 60 to 250 parts by mass, more preferably 60 to 200 parts by mass, still more preferably 70 parts by mass, based on 100 parts by mass of component (a). ~150 parts by mass. If the amount of the component (f) added is less than the above lower limit, the cohesive strength is reduced, resulting in a reduced adhesive strength. On the other hand, if the above upper limit is exceeded, reworking of the actual machine becomes difficult due to an increase in adhesive strength. Component (f) itself is a solid or viscous liquid at room temperature, but it can also be used in a state of being dissolved in a solvent. In that case, the amount added to the composition is determined by the amount excluding the solvent content. Toluene, xylene, or the like can be used as the solvent.

[(g) organic peroxide]
Component (g) is an organic peroxide that decomposes under specific conditions to generate free radicals, and can be used alone or in combination of two or more. For example, peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, p-menthane hydroperoxide , hydroperoxide such as diisopropylbenzene hydroperoxide, dicumyl peroxide, dialkyl peroxide such as t-butylcumyl peroxide, dibenzoyl peroxide, diacyl peroxide such as disuccinic acid peroxide, t-butyl peroxyacetate , t-butyl peroxybenzoate and the like, and peroxydicarbonates such as diisopropyl peroxydicarbonate. In particular, peroxyketals, hydroperoxides, dialkyl peroxides, and peroxyesters, which have relatively high decomposition temperatures, are preferably used from the viewpoint of handling and storage. These organic peroxides may be used after being diluted with any organic solvent, hydrocarbon, liquid paraffin, inert solid, or the like. Component (g) is added in an amount of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, per 100 parts by mass of component (a). If the amount is less than the above lower limit, curing of the molded product will not proceed satisfactorily, and if the amount exceeds the above upper limit, the molded product will be brittle and difficult to handle, and a large amount of Decomposition residue reduces reliability.

[Adjustment of Silicone Adhesive Composition]
The silicone pressure-sensitive adhesive composition described above is prepared by charging components (a) to (f) or components (a), (c), (f) and (g) described above into a mixer or the like and mixing them. The silicone pressure-sensitive adhesive composition (that is, coating liquid) may be diluted with a solvent such as xylene or toluene, if necessary. The viscosity of the silicone pressure-sensitive adhesive composition (coating liquid) at 25° C. is preferably 200 to 900 mPa·s, preferably 300 to 700 mPa·s, more preferably 400 to 600 mPa·s. If the viscosity is less than the above lower limit, the coating liquid will drip in a coater and the thickness of the adhesive layer will tend to vary. On the other hand, if the viscosity exceeds the above upper limit, voids are likely to be contained in the coating liquid, which may cause an increase in heat resistance and poor appearance when the silicone adhesive layer is formed. In the present invention, the viscosity of the silicone pressure-sensitive adhesive composition is the absolute viscosity measured at 25°C using a rotational viscometer.

In the silicone rubber sheet of the present invention, the silicone adhesive layer preferably has a thickness of 2-40 μm, preferably 5-30 μm. If it is less than the above lower limit, it is impossible to obtain the desired adhesive strength to the actual machine. If the thickness exceeds the above upper limit, the thermal resistance will increase significantly. Moreover, reworkability deteriorates because the adhesive strength becomes excessive.

The silicone adhesive layer preferably has the following adhesive strength.
That is, according to JIS C 2107: 2011, the width of the thermally conductive silicone rubber sheet having the silicone adhesive layer is set to 25 mm, and a 2 kg roller is reciprocated 5 times against a 10 mm thick SUS plate to remove the silicone adhesive layer side. is attached to the SUS plate. After leaving this at 25° C. for 30 minutes, the stress (adhesive strength) when the thermally conductive silicone rubber sheet was peeled off by 200 mm at a constant speed tensile tester at a tensile speed of 300 mm/min was 0.05 to 0.05. It is preferably 1.0 (N/25 mm), more preferably 0.1 to 0.5 (N/25 mm). If the adhesive strength is less than the above lower limit, the adhesive strength is insufficient, making it difficult to attach the sheet to a desired mounting position. On the other hand, when the above upper limit is exceeded, the reworkability in an actual machine is deteriorated.

[Preparation of Thermally Conductive Silicone Rubber Composition]
The organopolysiloxane and the thermally conductive filler are kneaded using a mixer such as a kneader, Banbury mixer, planetary mixer, Shinagawa mixer, etc. while heating to a temperature of about 100° C. or higher as necessary. In this kneading step, if desired, reinforcing silica such as fumed silica, precipitated silica, etc.; silicone oil, silicone wetter, etc.; platinum, titanium oxide, benzotriazole, etc. A fuel or the like may be added or mixed.

After the uniform mixture obtained in the kneading step is cooled to room temperature, it is filtered through a strainer or the like. , to knead. In this second kneading step, if desired, acetylene compound-based addition reaction controllers such as 1-ethynyl-1-cyclohexanol, colorants such as organic pigments and inorganic pigments, heat resistance improvers such as iron oxide and cerium oxide. , an internal release agent, etc. may be added and mixed. The composition obtained in this second kneading step may be used as a coating material and directly subjected to the next step. It can be used as a coating material (thermally conductive silicone rubber composition) by mixing it with

[Method for producing thermally conductive silicone rubber layer]
As described above, the thermally conductive silicone rubber layer of the present invention preferably contains glass cloth or polyimide as an intermediate reinforcing layer. Such a thermally conductive silicone rubber layer may be produced, for example, by the method described later. If the intermediate reinforcing layer is not provided, the thermally conductive silicone rubber composition alone may be cured by heating and molded into a sheet.

[Method for producing glass cloth sealed with thermally conductive silicone rubber composition]
The thermally conductive silicone rubber composition (coating material) obtained by the above process is applied to a glass cloth. After coating the glass cloth continuously using a coating device such as a comma coater, knife coater, or kiss coater equipped with a drying oven, a heating oven, and a winding device, the solvent, etc., is dried and evaporated, followed by addition reaction curing. In the case of a mold, it is heated to 80 to 200°C, preferably about 100 to 150°C, for about 5 to 20 minutes, while in the case of a peroxide curing type, it is heated to 100 to 200°C, preferably 110 to 180°C. A glass cloth sealed with a thermally conductive silicone rubber composition is obtained by heating for about 2 to 15 minutes.

The thermally conductive silicone rubber composition (coating material) described above is applied to one side (surface) of the glass cloth sealed with the thermally conductive silicone resin obtained by the above process. Using a coating device such as a comma coater, knife coater, or kiss coater equipped with a drying oven, a heating oven, and a winding device, apply a solvent, etc. is dried and evaporated, and in the case of an addition reaction curing type, it is laminated by heating at 80 to 200° C., preferably about 100 to 150° C. for about 5 to 20 minutes. In the case of the peroxide curing type, the lamination is performed by heating at 100 to 200° C., preferably 110 to 180° C., for 2 to 15 minutes. As a result, a high-hardness thermally conductive silicone rubber layer having a glass cloth is obtained.
Furthermore, the heat conductive silicone rubber composition is applied to the other side (back side) of the sealed glass cloth obtained in the same manner as described above to similarly form a high hardness heat conductive silicone rubber layer. The compositions of the high-hardness thermally conductive silicone rubber sheets on the front and back surfaces do not need to be the same and may be different.

[Preparation of thermally conductive silicone rubber sheet]
The thermally conductive silicone rubber sheet of the present invention is obtained by applying the above silicone pressure-sensitive adhesive composition (coating liquid) to at least one surface of the above-mentioned high hardness thermally conductive silicone rubber layer and curing it. The coating and curing steps may be performed according to conventionally known methods. For example, using a coating device such as a comma coater, knife coater, or kiss coater equipped with a drying oven, a heating oven, and a winding device, the above silicone pressure-sensitive adhesive composition (coating liquid) is continuously coated with a high-hardness thermally conductive silicone. After coating on at least one side of the rubber layer, the solvent or the like is dried/evaporated and cured by heating at 80 to 180° C., preferably 100 to 150° C. for about 2 to 20 minutes to obtain a thermally conductive silicone rubber. you can get a sheet.

The thermally conductive silicone rubber sheet further has a protective sheet, the surface of the silicone adhesive layer that is not in contact with the thermally conductive silicone rubber sheet is covered with the protective sheet, and the thermally conductive sheet is wound into a roll. It may be a silicone rubber sheet. The protective sheet may be, for example, a PET film or release paper.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

・可塑剤：下記式（５）で表されるジメチルポリシロキサン

[High-hardness thermally conductive silicone rubber layer]
Components used in Examples and Comparative Examples are as follows.
・Dimethylpolysiloxane end-capped with dimethylvinyl groups (average degree of polymerization: 8000)
・Organic peroxide: (2-methylbenzoyl) peroxide ・Thermal conductive filler:
(z-1) crushed alumina (average particle size: 1 μm)
(z-2) Spherical alumina (average particle size: 10 μm)
(z-3) Crushed boron nitride (average particle size: 15 μm)
- Surface treatment agent: dimethylpolysiloxane represented by the following formula (4) and blocked at one end with a trimethoxysilyl group

- Plasticizer: dimethylpolysiloxane represented by the following formula (5)

The components described above were put into a Banbury mixer according to the composition shown in Table 1 below, and kneaded for 20 minutes to obtain Thermally Conductive Silicone Rubber Compositions 1 to 6.

A glass cloth having a thickness of 38 μm and a weight of 24 g/m ² was coated with the thermally conductive silicone rubber composition by the following method.
Toluene was added to the thermally conductive silicone rubber composition so as to make it 22 wt %, and the mixture was kneaded using a planetary mixer to obtain a thermally conductive silicone coating material. The thermally conductive silicone coating material was applied onto a glass cloth using a comma coater. The comma coater used has a width of 1300 mm and an effective oven length of 15 m. The 15m oven is divided into three zones of 5m each, and the temperature can be adjusted for each zone. min. A thermally conductive silicone coating material was continuously applied to a glass cloth and wound up to obtain a glass cloth sealed with a thermally conductive silicone resin. The thickness of the sealed glass cloth was 80 μm.
Furthermore, a thermally conductive silicone rubber composition having the same composition as the thermally conductive silicone rubber composition used for filling the glass cloth was used, toluene was added so as to be 15 wt%, and the mixture was coated using a planetary mixer. A working solution was prepared. The coating liquid is applied to one side of the sealed glass cloth using the comma coater and wound up, and the back side is similarly coated and wound up to obtain a high hardness heat conduction cloth with a total thickness of 200 μm. A flexible silicone rubber layer was obtained. Coating was performed under the same coating conditions using the comma coater used for filling the glass cloth.

Evaluation of Thermally Conductive Silicone Rubber Layer (1) Hardness Measurement Each of the above thermally conductive silicone rubber compositions 1 to 6 was cured under curing conditions of 140° C./10 minutes to form a sheet with a thickness of 6 mm, and two sheets were stacked. The hardness was measured using a durometer A hardness tester. The results are shown in Tables 2 and 3 below. None of the thermally conductive silicone rubber layers had a tacky feel on the surface, and the adhesive force was below the detection limit.
(2) Thermal Conductivity Each of the above thermally conductive silicone rubber compositions 1 to 6 was cured into a 6 mm thick sheet under curing conditions of 140° C./10 minutes to obtain a thermally conductive silicone rubber layer. The thermal conductivity of the thermally conductive silicone rubber layer was measured using a thermal conductivity measuring device (TPA-501, manufactured by Kyoto Electronics Industry Co., Ltd.). The results are shown in Tables 2 and 3 below.

（ｃ）熱伝導性充填材
（ｃ－１）不定形アルミナ（平均粒径：１μｍ、粒径２０μｍ以上の粒子の量：３質量％以下、粒径４０μｍ以上の粒子の量：０％）
（ｃ－２）不定形窒化アルミ（平均粒径：５μｍ、粒径２０μｍ以上の粒子の量：３質量％以下、粒径４０μｍ以上の粒子の量：０％）
（ｃ－３）破砕状酸化亜鉛（平均粒径：２μｍ、粒径２０μｍ以上の粒子の量：３％以下、粒径４０μｍ以上の粒子の量：０％）
比較用（ｃ－４）不定形アルミナ（平均粒径：１μｍ、粒径２０μｍ以上の粒子の量：１０質量％、粒径４０μｍ以上の粒子の量：３質量％）
比較用（ｃ－５）不定形アルミナ（平均粒径：１５μｍ、粒径２０μｍ以上の粒子の量：３％以下、粒径４０μｍ以上の粒子の量：０％）
（ｄ）付加反応触媒：５％塩化白金酸２－エチルヘキサノール溶液
（ｅ）付加反応制御剤：エチニルメチリデンカルビノール
（ｆ）シリコーンレジン：（ＣＨ_３）_３ＳｉＯ_１／２単位及びＳｉＯ_４／２単位からなり、ＳｉＯ_４／２単位に対する（ＣＨ_３）_３ＳｉＯ_１／２単位の個数比が１．１５であるシリコーンレジンのキシレン溶液（不揮発分６０％、Ｍ／Ｑ（モル比）＝１．１５）
（ｇ）有機過酸化物：１，１－ジ（ｔ－ブチルパーオキシ）シクロヘキサン

[Silicone adhesive composition]
Each component used in the preparation of the silicone pressure-sensitive adhesive composition is as follows.
In the following, the content ratio (%) of phenyl groups is the percentage of the number of phenyl groups bonded to silicon atoms with respect to the total number of substituents bonded to silicon atoms. In the following, the viscosity of the organopolysiloxane is the kinematic viscosity at 25° C. measured with an Ostwald viscometer. The average particle size is the volume average particle size measured by Microtrac MT3300EX (Nikkiso).
(a) Alkenyl group-containing organopolysiloxane (a-1) Organopolysiloxane having vinyl groups and containing 5% phenyl groups (5000 mm ² /s)
(a-2) Organopolysiloxane having vinyl groups and containing 20% phenyl groups (2000 mm ² /s)
Comparative (a-3) organopolysiloxane having vinyl groups and containing 0.5% phenyl groups (8000 mm ² /s)
Comparative (a-4) Organopolysiloxane having vinyl groups and containing 30% phenyl groups (1600 mm ² /s)
(b) organohydrogenpolysiloxane represented by the following formula (1500 mPa s)

(c) Thermally conductive filler (c-1) amorphous alumina (average particle size: 1 μm, amount of particles with a particle size of 20 μm or more: 3% by mass or less, amount of particles with a particle size of 40 μm or more: 0%)
(c-2) Irregular aluminum nitride (average particle size: 5 μm, amount of particles with a particle size of 20 μm or more: 3% by mass or less, amount of particles with a particle size of 40 μm or more: 0%)
(c-3) Crushed zinc oxide (average particle size: 2 μm, amount of particles with a particle size of 20 μm or more: 3% or less, amount of particles with a particle size of 40 μm or more: 0%)
Comparative (c-4) amorphous alumina (average particle size: 1 μm, amount of particles with a particle size of 20 μm or more: 10% by mass, amount of particles with a particle size of 40 μm or more: 3% by mass)
Comparative (c-5) amorphous alumina (average particle size: 15 μm, amount of particles with a particle size of 20 μm or more: 3% or less, amount of particles with a particle size of 40 μm or more: 0%)
(d) Addition reaction catalyst: 5% chloroplatinic acid 2-ethylhexanol solution (e) Addition reaction controller: ethynylmethylidenecarbinol (f) Silicone resin: (CH ₃ ) ₃ SiO _1/2 units and SiO _{4/ 2} units, and the number ratio of (CH ₃ ) ₃ SiO _1/2 units to SiO _4/2 units is 1.15. .15)
(g) organic peroxide: 1,1-di(t-butylperoxy)cyclohexane

[Examples 1 to 5 and Comparative Examples 1 to 6]
The above components (a), (c), (d), and (f) were charged into a Shinagawa universal stirrer so as to have the composition shown in Table 2 or 3 below, mixed for 30 minutes, and then the component (e). was added and mixed uniformly, and then (b) was added and mixed uniformly to obtain an addition-curable silicone pressure-sensitive adhesive composition having a viscosity of 500 mPa·s.
[ Reference example 6]
The above components (a), (c), and (f) were charged into a Shinagawa universal stirrer so as to have the composition shown in Table 2 below, mixed for 30 minutes, and then the component (g) was added and uniformly mixed. After mixing, a peroxide-curable silicone pressure-sensitive adhesive composition having a viscosity of 400 mPa·s was obtained.
All the viscosities of the above silicone pressure-sensitive adhesive compositions are absolute viscosities measured using a rotational viscometer at 25°C. Also, the parts by mass of the silicone resin shown in Tables 2 and 3 are the amount of the resin in the xylene solution.

Each of the above silicone pressure-sensitive adhesive compositions (coating liquids) was coated on one side of the high-hardness thermally conductive silicone rubber layer obtained above using the above-described comma coater. The drying zones were set to 80° C., 120° C., and 140° C. from the side closer to the comma, and the coating speed was set to 4 m/min. A silicone adhesive layer was formed by continuously coating and curing a high-hardness thermally conductive silicone rubber layer.
After that, the surface of the silicone adhesive layer was covered with a release silicone-treated PET film (protective film, commercially available product) and then wound up to obtain a high-hardness thermally conductive silicone rubber sheet wound into a roll. The thickness of the silicone adhesive layer can be adjusted to a desired thickness by adjusting the gap of the head portion of the comma coater.

[Evaluation method]
Each thermally conductive silicone rubber sheet obtained above was evaluated by the following methods. Results are shown in Tables 2 and 3.
(1) Thickness of Adhesive Layer The thickness of the entire thermally conductive silicone rubber sheet including the silicone adhesive layer (but not including the protective film) was measured using a microgauge. The thickness of the silicone adhesive layer was calculated by subtracting the thickness of the thermally conductive silicone rubber layer (200 μm) from the obtained value.
(2) Adhesive strength In accordance with JIS C 2107: 2011, the adhesive layer side with the protective film removed from the thermally conductive silicone rubber sheet (width 25 mm) is attached to a stainless steel plate (SUS plate), and the adhesive layer is adhered for 25 ° C./30 min. After standing, a 180° peel test was performed to measure the force (peeling force) required to peel off the stainless steel plate (SUS plate) by 200 mm at a pulling speed of 300 mm/min. The peel strength is defined as the initial adhesive strength of the silicone adhesive layer, and is shown in Tables 2 and 3.
(3) Stability of adhesive layer over time After aging at 60° C. for 2 months with a protective film attached to the surface of the adhesive layer of the thermally conductive silicone rubber sheet, remove the protective film and repeat the same procedure as in (2) above. The peel force was measured using The peel strength is shown in Tables 2 and 3 as adhesive strength after 60° C./2 months.
(4) Reworkability During the peel test described in (2) above, it was observed whether there was a residue of the adhesive layer with a diameter of 1 mm or more on the SUS plate. When there was no residue, the reworkability was judged to be good (○), and when there was a residue, the reworkability was judged to be poor (x). Results are shown in Tables 2 and 3. In addition, in the thermally conductive silicone rubber sheet of Comparative Example 4, there was a residue with a diameter of 1 mm or more, and it was impossible to measure the adhesive force.
(5) Thermal Resistance The thermal resistance of the thermally conductive silicone rubber sheet was measured by a method conforming to ASTM D5470. After storing the thermally conductive silicone rubber sheet at 60° C. for 2 months, the thermal resistance was measured according to ASTM D5470.

As shown in Table 2 above, in Comparative Example 1, the amount of phenyl groups in the alkenyl group-containing organopolysiloxane in the silicone adhesive layer was too small, so the adhesive strength decreased over time. In Comparative Example 2, the desired adhesive strength could not be obtained because the amount of phenyl groups in the alkenyl group-containing organopolysiloxane in the silicone adhesive layer was too large. In the silicone adhesive composition of Comparative Example 3, the thermally conductive filler contains particles with a particle size of 20 μm or more in an amount of 3% by mass or more, and has an amount of particles with a particle size of 40 μm or more in an amount of 0.01% by mass or more. Therefore, the surface precision of the adhesive layer was lowered, and the desired adhesive strength could not be obtained. In the silicone pressure-sensitive adhesive composition of Comparative Example 4, since the thermally conductive filler had an average particle size of 10 μm or more, the surface accuracy of the pressure-sensitive adhesive layer was low, and reworkability was poor, so the pressure-sensitive adhesive strength could not be measured. Furthermore, since the composition of Comparative Example 5 contained too little silicone resin, the cohesive force was insufficient and the adhesive force was lowered. Since the composition of Comparative Example 6 contained too much silicone resin, the adhesive strength increased and the reworkability decreased. Also, there is no significant increase in heat resistance over time, excellent reworkability, no change in adhesive strength over time, and excellent reliability.

The thermally conductive silicone rubber sheet of the present invention has excellent workability and thermal conductivity, suppresses change in adhesive strength over time, exhibits excellent reworkability, and suppresses an increase in thermal resistance of the sheet. Furthermore, the thermally conductive silicone rubber sheet of the present invention can be produced by a simpler process than the conventional lamination method using a primer or the like.

Claims (9)

A thermally conductive silicone rubber sheet comprising a laminate of at least one thermally conductive silicone rubber layer having a durometer A hardness of 60 to 96 and at least one silicone adhesive layer,
The silicone adhesive layer is a cured product of an addition reaction-curable silicone adhesive composition containing the following components (a), (c), (b), (d), (e), and (f), The thermally conductive silicone rubber sheet (a) has at least one silicon-bonded alkenyl group and a silicon-bonded phenyl group, wherein the silicone adhesive layer has a thickness of 2 to 15 μm. Organopolysiloxane having a number that is 2 to 20% of the total number of substituents bonded to silicon atoms: 100 parts by mass,
(c) a thermally conductive filler having an average particle size of less than 10 μm, an amount of particles with a particle size of 20 μm or greater in an amount of 0-3% by weight, and an amount of particles with a particle size of 40 μm or greater in an amount of 0% by weight; Material: 100 to 800 parts by mass,
(b) organohydrogenpolysiloxane: an amount such that the ratio of the number of silicon-bonded hydrogen atoms in component (b) to the number of alkenyl groups in component (a) is 0.5 to 30;
(d) addition reaction catalyst: catalyst amount, (e) addition reaction control agent: 0.01 to 1 part by mass, and (f) R ₃ SiO _1/2 unit (R has an aliphatic unsaturated bond unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms) and SiO _4/2 units, and the number ratio of R ₃ SiO _1/2 units to SiO _4/2 units is 0. 5 to 2.5, silicone resin: 50 to 300 parts by mass. 2. The thermally conductive silicone rubber sheet according to claim 1, wherein said thermally conductive filler is at least one selected from alumina, aluminum hydroxide, aluminum nitride, boron nitride, zinc oxide, and metallic aluminum. 3. The thermally conductive silicone rubber layer according to claim 1, wherein said thermally conductive silicone rubber layer has an adhesive strength of 0.01 N/25 m or less, and a silicone adhesive layer is laminated on one side of said thermally conductive silicone rubber layer. Thermally conductive silicone rubber sheet. The thermally conductive silicone rubber sheet according to any one of claims 1 to 3, wherein said thermally conductive silicone rubber layer has a thickness of 50 to 900 µm. An addition-curable thermally conductive silicone rubber composition in which the thermally conductive silicone rubber layer contains an alkenyl group-containing organopolysiloxane, an organohydrogenpolysiloxane, an addition reaction catalyst, a thermally conductive filler, and a surface treatment agent. The thermally conductive silicone rubber sheet according to any one of claims 1 to 4, which is a cured product. The thermally conductive silicone rubber layer is a cured product of a peroxide-curable thermally conductive silicone rubber composition containing an alkenyl group-containing organopolysiloxane, an organic peroxide, a thermally conductive filler, and a surface treatment agent. The thermally conductive silicone rubber sheet according to any one of claims 1 to 4. The thermally conductive silicone rubber sheet according to any one of claims 1 to 6, wherein said thermally conductive silicone rubber layer has a thermal conductivity of 1.0 W/m·K or more. The thermally conductive silicone rubber sheet further has a protective sheet, and the surface of the silicone adhesive layer not in contact with the thermally conductive silicone rubber sheet is covered with the protective sheet and wound into a roll. 8. The thermally conductive silicone rubber sheet according to any one of 1 to 7. 9. The method for producing a thermally conductive silicone rubber sheet according to any one of claims 1 to 8, wherein the silicone adhesive composition is applied to at least one surface of the thermally conductive silicone rubber layer and cured by heating. to obtain the thermally conductive silicone rubber sheet.