JP6448736B2 - Thermally conductive sheet - Google Patents

Description

The present invention relates to a heat conductive sheet. In particular, the present invention relates to a heat conductive sheet used as a heat transfer material that can be interposed between a heat generating electronic component and a heat dissipating member such as a heat sink.

Semiconductors such as transistors and diodes used in electronic devices such as converters and power supplies themselves generate a large amount of heat as their performance, speed, size, and integration increase. The temperature rise of the equipment caused by malfunction causes malfunction or destruction. Therefore, many heat dissipating methods for suppressing the temperature rise of the semiconductor during operation and heat dissipating members used therefor have been proposed.

For example, a heat sink using a metal plate having a high thermal conductivity such as aluminum or copper is used to suppress a temperature rise of a semiconductor in operation in an electronic device or the like. The heat sink conducts heat generated by the semiconductor and releases the heat from the surface due to a temperature difference from the outside air. On the other hand, the semiconductor and the heat sink must be electrically insulated. For this reason, a plastic film or the like is interposed between the heat-generating electronic component and the heat sink. However, plastic films have a very low thermal conductivity, which significantly impedes heat transfer to the heat sink. Also, when a semiconductor such as a transistor is fixed to a heat sink with a screw, the screw needs to penetrate the plastic film. At that time, a hole is formed in the film, and the film is broken and the insulation cannot be maintained. This problem occurs. The inability to maintain insulation is fatal for transistors and diodes.

Accordingly, in order to impart heat conductivity that is not easily torn, a heat conductive sheet in which a heat conductive resin is laminated on a glass cloth has been developed. For example, there is a thermally conductive sheet in which a silicone rubber containing boron nitride powder and spherical silica powder as a thermally conductive filler is laminated on a glass cloth (Patent Document 1). The sheet is pressed during manufacture. In order to pressurize, it is necessary to prepare a sheet of an appropriate size and use a press molding machine or the like, and since batch production is performed, the completed heat conductive sheet cannot be wound into a roll. This is very inefficient from the viewpoint of productivity and yield, and the size of the original fabric sheet is limited, so that the size when mounting is also limited.

An example of the continuous molding method is coating molding. For example, a thermally conductive sheet can be continuously produced by sealing one side of a glass cloth with a thermally conductive silicone resin and forming a thermally conductive silicone rubber layer on the sealed glass cloth by coating. it can. The coating molding is very efficient because the finished sheet can be wound up continuously. In addition, although the length in the width direction of the sheet is limited by the size of the coating apparatus, the length in the length direction is not limited, so that the degree of freedom in size during mounting is markedly increased compared to press molding. However, in the coating molding, since the surface accuracy is worse than that in the press molding, the contact thermal resistance is increased. Further, since no pressure is applied, the density of the silicone rubber layer is difficult to increase. Therefore, it was unsuitable as a method for producing a sheet having high thermal conductivity.

JP-A-9-199880

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sheet that can be continuously produced by coating molding and wound into a roll, and that has high thermal conductivity and high insulation. And

As a result of intensive studies, the present inventors have found that in the heat conductive sheet having the cured layer of the heat conductive silicone composition on both sides or one side of the glass cloth affixed with the heat conductive resin composition, When the heat-sensitive silicone composition contains a heat conductive filler having a specific particle size in a specific amount, a heat conductive sheet having high heat conductivity can be produced by continuous molding. We have found that this has been achieved and have reached the present invention.

The present invention is a method for producing a thermally conductive sheet comprising a glass cloth and a thermally conductive cured layer that are sealed with a thermally conductive resin composition ,
A step of applying a thermally conductive silicone composition to both or one side of the glass cloth and heating the composition to form the thermally conductive cured layer, wherein the thermally conductive silicone composition comprises a silicone component and a thermally conductive material. Conductive filler (C), the amount of the thermally conductive filler (C) is 1200 to 2000 parts by mass with respect to 100 parts by mass of the silicone component, and the thermally conductive filler (C) is less than 15 μm. In the thermally conductive filler (C), the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass, and the amount of particles having a particle size of 75 μm or more is 0 to 0.001. It is the manufacturing method of the said heat conductive sheet characterized by the place which is 01 mass%.

The heat conductive sheet of the present invention can be continuously produced by coating molding and wound into a roll, and has high heat conductivity and high insulation.

The sheet | seat of this invention has the layer (it may be called a heat conductive hardening layer) by which the heat conductive silicone composition was hardened on both surfaces or one side of the glass cloth sealed with the heat conductive resin composition.

The said heat conductive silicone composition contains a silicone component and a heat conductive filler (C). The composition may contain a component (A) described below as the silicone component.

（式中、Ｒ¹は独立して、置換または非置換の炭素原子数１〜１０、好ましくは１〜８の１価炭化水素基を表わし、aは１．９０〜２．０５である）を有し、１分子中に少なくとも２個の、ケイ素原子に結合したアルケニル基を有するオルガノポリシロキサンである。（Ａ）成分は好ましくは、重合度が２０〜１２，０００、より好ましくは５０〜１０，０００である。 The component (A) has the following average composition formula:

Wherein R ¹ independently represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and a is 1.90 to 2.05. And an organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule. The component (A) preferably has a degree of polymerization of 20 to 12,000, more preferably 50 to 10,000.

Examples of R ¹ include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and octadecyl; cyclopentyl and cyclohexyl Cycloalkyl groups such as phenyl groups, tolyl groups, xylyl groups and naphthyl groups; aralkyl groups such as benzyl groups, phenethyl groups and 3-phenylpropyl groups; 3,3,3-trifluoropropyl groups and 3 -Halogenated alkyl groups such as chloropropyl group; and alkenyl groups such as vinyl group, allyl group, butenyl group, pentenyl group and hexenyl group. The component (A) may be in the form of oil or gum.

The component (A) is a component that is cured by addition reaction or peroxide, and has 2 or more, preferably 3 or more alkenyl groups bonded to a silicon atom in one molecule. When the content of the alkenyl group bonded to the silicon atom is less than the above range, the resulting composition is not sufficiently cured when the curing is performed by an addition reaction. The alkenyl group is preferably a vinyl group. The alkenyl group may be bonded to either the silicon atom at the molecular chain terminal or a silicon atom other than the molecular chain terminal, and preferably at least one alkenyl group is bonded to the silicon atom at the molecular chain terminal. .

Specific examples of the component (A) when curing is carried out by addition reaction include, for example, a molecular chain both-end trimethylsiloxy group-capped dimethylsiloxane / methylvinylsiloxane copolymer, a molecular chain both-end trimethylsiloxy group-capped methylvinylpolysiloxane Molecular chain both ends trimethylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxane copolymer, molecular chain both ends dimethylvinylsiloxy group-blocked dimethylpolysiloxane, molecular chain both ends dimethylvinylsiloxy group-blocked methylvinylpolysiloxane, Dimethylsiloxane / methylvinylsiloxane copolymer with dimethylvinylsiloxy group blocked at both ends of molecular chain, dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxa copolymer with dimethylvinylsiloxy group blocked at both ends of molecular chain It can be mentioned copolymers and both molecular chain terminals by trimethylsiloxy blocked with dimethylvinylsiloxy groups and the like. These can be used alone or in combination of two or more.

Specific examples of the component (A) when curing is performed using a peroxide include, for example, molecular chain both ends dimethylvinylsiloxy group-capped dimethylpolysiloxane, molecular chain both ends methylphenylvinylsiloxy group-capped dimethylpolysiloxane , Dimethylvinylsiloxy group-capped dimethylsiloxane / methylphenylsiloxane copolymer, molecular chain both ends dimethylvinylsiloxy group-capped dimethylsiloxane / methylvinylsiloxane copolymer, molecular chain both ends trimethylsiloxy group-capped dimethylsiloxane, Methylvinylsiloxane copolymer, molecular chain both ends dimethylvinylsiloxy group-blocked methyl (3,3,3-trifluoropropyl) polysiloxane, molecular chain both ends silanol group-blocked dimethylsiloxane / methylvinylsiloxane copolymer and molecular chain Both End silanol dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers. These can be used alone or in combination of two or more.

When curing is performed by addition reaction, the reaction is performed in the presence of a platinum catalyst using organohydrogenpolysiloxane as the curing agent (B). In the case of curing with a peroxide, an organic peroxide is used as the curing agent (B). As the curing agent and the catalyst, those well known in the art can be used.

The thermally conductive silicone composition may further contain a component (D) described below as a silicone component.

The component (D) is one or more selected from the following components (D1) and (D2). The component (D) can improve the wettability of the heat conductive filler (C) to facilitate the filling of the silicone component with the filler, and thus can increase the filling amount of the filler.

（式中、Ｒ^２は独立して炭素原子数６〜１５のアルキル基であり、Ｒ^３は独立して非置換または置換の炭素原子数１〜１２の１価炭化水素基であり、Ｒ^４は独立して炭素原子数１〜６のアルキル基であり、ａは１〜３の整数であり、ｂは０〜２の整数であり、但しａ＋ｂは１〜３である。）
で表されるアルコキシシランである。 The component (D1) is represented by the following formula (1):

(Wherein R ² is independently an alkyl group having 6 to 15 carbon atoms, R ³ is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and R ⁴ Is 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 1 to 3).
It is the alkoxysilane represented by these.

In the above formula (1), examples of the alkyl group represented by R ² include hexyl group, octyl group, nonyl group, decyl group, dodecyl group, and tetradecyl group. When the alkyl group represented by R ² has 6 to 15 carbon atoms, the wettability of the thermally conductive filler (C) is sufficiently improved, and the filler is filled into the thermally conductive silicone composition. In addition, the low temperature characteristics of the composition are improved.

Examples of the unsubstituted or substituted monovalent hydrocarbon group represented by R ³ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, Hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group and other alkyl groups, cyclopentyl group, cyclohexyl group, cycloheptyl group and other cycloalkyl groups, phenyl group, tolyl group, xylyl group, naphthyl group and biphenylyl Aryl groups such as aralkyl groups, aralkyl groups such as benzyl groups, phenylethyl groups, phenylpropyl groups and methylbenzyl groups, and some or all of the hydrogen atoms of these groups are halogen atoms such as fluorine, chlorine and bromine or cyano groups For example, chloromethyl group, 2-bromoe Group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6,6-nonafluoro A hexyl group etc. are mentioned. R ³ preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and in particular, methyl group, ethyl group, propyl group, chloromethyl group, bromoethyl group, 3,3,3- Examples thereof include unsubstituted or substituted alkyl groups having 1 to 3 carbon atoms such as a trifluoropropyl group and a cyanoethyl group, and unsubstituted or substituted phenyl groups such as a phenyl group, a chlorophenyl group and a fluorophenyl group.

Examples of the alkyl group represented by R ⁴ include alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl and hexyl.

（式中、Ｒ^５は独立して炭素原子数１〜６のアルキル基であり、ｃは５〜１００の整数である。）で表される、分子鎖片末端がトリアルコキシ基で封鎖されたジメチルポリシロキサンである。Ｒ^５で表されるアルキル基としては、上記式（１）中のＲ^４で表されるアルキル基と同種のものが挙げられる。 The component (D2) is represented by the following formula (2):

(Wherein R ⁵ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100), and one end of the molecular chain is blocked with a trialkoxy group. Dimethylpolysiloxane. Examples of the alkyl group represented by R ⁵ include the same type as the alkyl group represented by R ⁴ in the above formula (1).

（式中、ｒは５〜５００の整数である。）で表わされるジメチルシロキサンである。 The said heat conductive silicone composition may contain the following component (E) as a silicone component. Component (E) is a plasticizer and has the following formula (4):

(Wherein, r is an integer of 5 to 500).

The heat conductive filler (C) may be a commonly used material such as non-magnetic metals such as copper and aluminum, and metal oxides such as alumina, silica, magnesia, bengara, beryllia, titania and zirconia. Metal nitrides such as aluminum nitride, silicon nitride and boron nitride, metal hydroxides such as magnesium hydroxide, artificial diamond, and silicon carbide. These can be used alone or in combination of two or more.

The heat conductive filler (C) has an average particle size of less than 15 μm, preferably less than 10 μm, and the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass, preferably 0 to 2.5% by mass. The amount of particles having a particle size of 75 μm or more is 0 to 0.01% by mass, preferably 0% by mass. When any one of the average particle size, the amount of particles having a particle size of 45 μm or more and the amount of particles having a particle size of 75 μm or more exceeds the upper limit, when a thermally conductive sheet is obtained by coating the thermally conductive silicone composition, The filler may protrude from the surface of the coating film and the smoothness of the sheet surface may be impaired. This leads to an increase in contact thermal resistance when mounted, which is disadvantageous in terms of thermal conductivity.

The heat conductive filler (C) is preferably alumina in consideration of heat conductivity, electrical insulation and price. In particular,
(C1) An average particle size of 0.1 μm or more and less than 5 μm, preferably 0.5 μm or more and less than 2 μm, the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass, and particles having a particle size of 75 μm or more Alumina having an amount of 0 to 0.01% by mass, and (C2) an average particle size of 5 μm or more and less than 15 μm, preferably 5 μm or more and less than 10 μm, and the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass. The amount of particles having a particle size of 75 μm or more is 0 to 0.01% by mass, the amount of the component (C1) is 20 to 50% by mass, preferably 20 to 40% by mass, and (C2 ) Thermally conductive fillers with a component content of 50-80% by weight, preferably 60-80% by weight are preferred.

From the viewpoint of smoothing the surface of the heat conductive sheet, the heat conductive filler (C) is preferably spherical. In particular, if the relatively large filler having an average particle size of 5 μm or more and less than 15 μm, for example, the component (C2) is spherical, the surface of the heat conductive sheet can be made smoother.

The average particle diameter in the present invention is a value (volume basis) determined using Microtrac MT3300EX (Nikkiso), which is a laser diffraction / scattering particle diameter distribution measuring apparatus.

The amount of particles having a particle size of 45 μm or more and the amount of particles having a particle size of 75 μm or more in the heat conductive filler (C) are determined as follows. 10 g of filler is sampled and placed in an arbitrary amount of water and ultrasonically dispersed. The sieves with openings of 45 μm and 75 μm are stacked and set on 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.

(C) The quantity of a component is 1200-2000 mass parts with respect to a total of 100 mass parts of the quantity of a silicone component, Preferably it is 1200-1600 mass parts. When the filling amount is less than the lower limit, sufficient thermal conductivity cannot be obtained. If the above upper limit is exceeded, it will be difficult to fill the silicone, and even if it can be filled, the filler will become too dense, and when the composition is coated to obtain a thermally conductive sheet, Smoothness may be impaired, leading to an increase in thermal resistance. The total amount of silicone component is the sum of component (A) and, if present, component (D), component (E), and organohydrogenpolysiloxane as the curing agent (B) described above. Means.

(D) It is preferable that the quantity of a component is 0.01-60 mass% of the total of the quantity of a silicone component, More preferably, it is 5-50 mass%. When the amount is less than the lower limit, it may be difficult to fill the silicone component of the thermally conductive filler (C). When the said amount exceeds the said upper limit, the intensity | strength of the hardened | cured material obtained may become inadequate.

(E) It is preferable that the quantity of a component is 5-25 mass% of the sum total of the quantity of a silicone component.

The thermally conductive silicone composition preferably has a cured product having a thermal conductivity of 3.0 W / mK or more. Moreover, it is preferable that the durometer A hardness of the said hardened | cured material is 60-96, More preferably, it is 80-96. If the hardness is too low, the surface of the cured product layer may be easily damaged during handling, or the cured product layer surfaces may be fused when wound into a roll during continuous molding. In addition, when the heat conductive sheet of the present invention is fixed between the heat generation part and the cooling part of the electronic device by screwing, if the hardness is low, the sheet is deformed by the pressure applied by the screwing and the heat generation part and the cooling part are It becomes difficult to secure a space between the two, and hence it becomes difficult to maintain insulation. On the other hand, if the hardness is too high, the flexibility is poor and cracking may occur when the sheet is folded.

The heat conductive sheet of this invention has the said heat conductive hardening layer on both surfaces or one side of the glass cloth sealed by the heat conductive resin composition. As the glass cloth, a commercially available one is sufficient, and for example, one having a weight of 30 g / m ² or less is used. The thickness of the glass cloth is preferably 60 μm or less, more preferably 30 to 50 μm, and still more preferably 30 to 45 μm. Since the glass cloth has a relatively low thermal conductivity, it is preferable that the glass cloth is thin when high thermal conductivity is desired. However, if it becomes too thin, the strength decreases.

The thermally conductive resin composition for sealing the glass cloth preferably has a thermal conductivity of 1.2 W / mK or more.

Examples of the thermally conductive resin composition used for sealing include those obtained by adding a thermally conductive filler to a thermosetting resin, for example, thermal conductivity for the thermally conductive cured layer. The composition containing the (A)-(C) component mentioned above regarding the silicone composition is included. Here, it is preferable that the quantity of a heat conductive filler (C) is 200-2000 mass parts with respect to a total of 100 mass parts of quantity of a silicone component. When the amount of the filler is less than the above lower limit, it is difficult to make the thermal conductivity of the sealing material 1.2 W / mK or more. The particle size of the heat conductive filler (C) is not limited. The thermally conductive resin composition for sealing may be the same as the thermally conductive silicone composition for the thermally conductive cured layer.

The sealing is preferably performed so that the thickness of the sheet obtained by sealing the glass cloth (referred to as a sealed glass cloth sheet) is 100 μm or less, more preferably 90 μm or less, and even more preferably 85 μm or less. . When trying to manufacture a heat conductive sheet with a predetermined thickness, if the thickness of the above-mentioned glass cloth sheet is too thick, the thickness of the heat conductive hardened layer becomes thin, which is the heat conduction of the heat conductive sheet. Reduce sex. Moreover, it is preferable that the thickness of a heat conductive sheet is 200 micrometers or more from the point of ensuring insulation. When the thickness of the thermally conductive sheet is 200 μm, the thickness of the thermally conductive cured layer on both sides thereof is less than 50 μm when the thickness of the glass cloth sheet that has been stopped is made to exceed 100 μm. Then, the heat conductive filler contained in the heat conductive hardened layer protrudes to the surface and the smoothness of the surface is impaired, and as a result, the heat conductivity is lowered.

As will be described later, the thermally conductive sheet of the present invention is obtained by applying and curing the thermally conductive silicone composition on both sides or one side of the sealed glass cloth sheet to form a cured product layer. . The application is preferably performed so that the thickness of the cured product layer after curing is 50 μm or more and 400 μm or less, more preferably 60 μm or more and 350 μm or less. As described above, if the thickness of the cured product layer is too thin, the thermally conductive filler contained therein protrudes and the smoothness of the surface of the thermally conductive cured layer is impaired. Preferably, the resulting heat conductive sheet has a total sheet thickness of 130 to 900 μm, more preferably 150 to 800 μm, when the heat conductive cured layer is provided on both sides of the glass cloth. When it has on one side, it is 80-500 micrometers, More preferably, it is 90-450 micrometers.

The thermally conductive silicone composition can be prepared as follows. (A) and (C) components, optionally together with (D) and (E) components, using a mixer such as a kneader, Banbury mixer, planetary mixer, Shinagawa mixer, etc. While kneading, knead. In this kneading step, if desired, reinforcing silica such as fumed silica and precipitated silica; silicone oil, silicone wetter, etc .; difficulty such as platinum, titanium oxide and benzotriazole A flame retardant or the like may be added. The homogeneous mixture obtained in the kneading step is cooled to room temperature, filtered through a strainer, etc., and then a required amount of curing agent (B) is added to the mixture using a two-roll, Shinagawa mixer, etc. Knead again. In this re-kneading step, if desired, an acetylene compound-based addition reaction control agent such as 1-ethynyl-1-cyclohexanol, a colorant such as an organic pigment or an inorganic pigment, and a heat resistance improver such as iron oxide or cerium oxide , And an internal release agent or the like may be added. The heat conductive silicone composition thus obtained may be directly used for the next step as a coating material, but if necessary, a solvent such as toluene may be further added.

When the thus obtained thermally conductive silicone composition is used as a sealing material, a conventional coating apparatus such as a comma coater, knife coater or kiss coater equipped with a drying furnace, a heating furnace and a winding device is used. In this case, after the composition is continuously applied to the glass cloth, the solvent is dried and evaporated, and in the case of curing by addition reaction, the peroxide is about 80 to 200 ° C., preferably about 100 to 150 ° C. In the case of curing by heating, it is heated to about 100 to 200 ° C., preferably about 110 to 180 ° C., to obtain a sealed glass cloth.

The thermally conductive sheet of the present invention is continuously produced by coating the thermally conductive silicone composition on both sides or one side of a sealed glass cloth sheet to form a thermally conductive cured layer. For example, using a conventional coating apparatus such as a comma coater, knife coater, kiss coater equipped with a drying furnace, a heating furnace, and a winding device, the thermally conductive silicone composition obtained above is sealed with a glass cloth. In the case of curing by addition reaction, 80 to 200 ° C., preferably about 100 to 150 ° C. In the case of curing by heating, a heat conductive cured layer is formed by heating to 100 to 200 ° C., preferably about 110 to 180 ° C. When coating on both surfaces, a heat conductive sheet is obtained by forming a heat conductive hardened layer on the other surface (the back side) of the glass cloth in the same manner as the surface. Coating on the front side and coating on the back side may be performed at once. The completed heat conductive sheet is continuously wound into a roll. The front and back conductive silicone compositions may be the same or different.

The thermal conductive sheet thus obtained preferably has a thermal resistance of 1.8 cm ² · K / W or less when the total thickness is 0.2 mm as measured according to ASTM D5470. Preferably, the dielectric breakdown voltage when the total thickness is 0.2 mm is 6 kV or more when measured according to JIS K6249. The thermal resistance and breakdown voltage are substantially proportional to the thickness of the thermal conductive sheet.

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

The materials used in Examples and Comparative Examples are as follows.
(A) component:
(A-1) Dimethylpolysiloxane having both average terminals with dimethylvinyl groups having an average degree of polymerization of 8000 (A-2) Dimethylpolysiloxane having both average terminals having 3000 degrees of polymerization with dimethylvinyl groups

(B) component: 2-methylbenzoyl peroxide

Component (C):
(C-1) Amorphous alumina (C-2) average in which the average particle size is 1 μm, the amount of particles having a particle size of 45 μm or more is 3% by mass or less, and the amount of particles having a particle size of 75 μm or more is 0% Spherical alumina (C-3) having a particle size of 10 μm, an amount of particles having a particle size of 45 μm or more being 3% by mass or less, and an amount of particles having a particle size of 75 μm or more being 0% (for comparison) 10 μm, the amount of particles having a particle size of 45 μm or more is 10% by mass, and the amount of particles having a particle size of 75 μm or more is 3% by mass. Spherical alumina (C-4) (for comparison) The average particle size is 20 μm Yes, the amount of particles having a particle size of 45 μm or more is 3% or less, the amount of particles having a particle size of 75 μm or more is 0%, the average particle size of amorphous alumina (C-5) is 1 μm, and the particle size is 45 μm or more The amount of particles is 3% or less, and the amount of particles having a particle size of 75 μm or more is 0%.

Component (D): dimethylpolysiloxane having the following formula (3), an average degree of polymerization of 30, and one end blocked with a trimethoxysilyl group

（式中、ｒ＝３００） Component (E): Dimethylpolysiloxane having the following formula (4)

(Where r = 300)

Glass cloth: thickness is 40 μm and weight is 26 g / m ²

Examples 1-4 and Comparative Examples 1-5
[Preparation of thermally conductive silicone composition]
The components (parts by mass) shown in Table 1 were charged into a Banbury mixer and kneaded for 20 minutes to prepare thermally conductive silicone compositions (A) to (F).

The thermal conductivity and hardness of the cured product of the obtained silicone composition were measured by the following methods. The results are shown in Table 1.
Thermal conductivity The obtained silicone composition was press-molded at 160 ° C. for 10 minutes using a 60 × 60 × 6 mm mold and the pressure was adjusted so that the thickness after curing was 6 mm. Cured into a sheet. Using a thermal conductivity meter (TPA-501, trade name manufactured by Kyoto Electronics Industry Co., Ltd.), the thermal conductivity of the sheet was measured by sandwiching a probe between the two sheets.
Hardness The obtained silicone composition was press-molded at 160 ° C. for 10 minutes using a 60 × 60 × 6 mm mold, the pressure after curing was 6 mm, and a 6 mm thick sheet Cured. Hardness was measured using a durometer A hardness tester with a test piece obtained by stacking two sheets.

[Manufacture of thermal conductive sheet]
Sealing of glass cloth The thermally conductive silicone composition obtained above was used as a sealing composition, and 20% by mass of toluene was added to the composition, and a planetary mixer was used. A coating material was prepared by kneading. The coating material was coated on one side of the glass cloth using a comma coater to seal the glass cloth. The comma coater used has a width of 1300 mm and an effective oven length of 15 m. The 15 m oven was divided into three zones of 5 m each, and the temperature could be adjusted for each zone. The temperatures were 80 ° C., 150 ° C. and 180 ° C. from the side close to the comma portion. The coating speed was 2 m / min. The above-mentioned coating material was continuously applied to a glass cloth and wound up to obtain a sealed glass cloth. The thickness of the sealed glass cloth was 80 μm.

Coating on sealed glass cloth Obtained by adding 20% by mass of toluene to the thermally conductive silicone composition obtained above and kneading using a planetary mixer. The coating material was applied to one side (surface) of the obtained glass cloth obtained above by using a comma coater so that the thickness after curing was 60 μm and wound. Subsequently, the other surface (back surface) was similarly coated and wound to obtain a heat conductive sheet having a total thickness of 200 μm. The comma coater used and the coating conditions are the same as those used in the above-mentioned sealing. In Comparative Example 5, coating on the sealed glass cloth was performed as follows. The oven temperature was 60 ° C., 80 ° C. and 80 ° C. from the side close to the comma portion, and the coating speed was 2 m / min. The temperature of the oven was reduced to a temperature at which toluene was volatilized and (B) peroxide was not decomposed, thereby obtaining an unvulcanized product. This unvulcanized product is cut out to an appropriate size, the pressure is adjusted using a press molding machine so that the thickness after curing is 200 μm, and press molding is performed at 170 ° C./10 minutes. A conductive sheet was obtained.

The thermal resistance and dielectric breakdown voltage of the obtained heat conductive sheet were measured by the following methods. The results are shown in Table 2.
Thermal resistance was measured according to ASTM D 5470.
Dielectric breakdown voltage was measured according to JIS K 6249.

The heat conductive sheet of the present invention was continuously produced by coating molding and wound into a roll. As is apparent from Table 2, when the total thickness is 0.2 mm, 1.8 cm ² -It has a low thermal resistance of K / W or less and a high breakdown voltage of 6 kV or more.

On the other hand, in the sheet of Comparative Example 1, the amount of the thermally conductive filler (C) was less than the range of the present invention, and as a result, the thermal resistance was large. In Comparative Example 2 in which the amount of particles having a particle size of 45 μm or more and the amount of particles having a particle size of 75 μm or more are larger than the range of the present invention, these particles having a large particle size protrude on the surface of the sheet and the surface smoothness is impaired. , Heat resistance increased. Even in Comparative Example 3 in which the average particle size is larger than the range of the present invention and Comparative Example 4 in which the amount of the filler is large, the smoothness of the sheet surface is impaired and the thermal resistance is increased. The sheet of Comparative Example 5 differs from Comparative Example 2 only in that it was press-molded instead of coating molding. By press molding, a sheet having low thermal resistance was obtained, but in press molding, the sheet cannot be continuously produced and wound into a roll.

Claims (12)

A method for producing a thermally conductive sheet comprising a glass cloth and a thermally conductive cured layer sealed with a thermally conductive resin composition ,
A step of applying a thermally conductive silicone composition to both or one side of the glass cloth and heating the composition to form the thermally conductive cured layer, wherein the thermally conductive silicone composition comprises a silicone component and a thermally conductive material. Conductive filler (C), the amount of the thermally conductive filler (C) is 1200 to 2000 parts by mass with respect to 100 parts by mass of the silicone component, and the thermally conductive filler (C) is less than 15 μm. In the thermally conductive filler (C), the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass, and the amount of particles having a particle size of 75 μm or more is 0 to 0.001. The manufacturing method of the said heat conductive sheet characterized by being 01 mass%. In the manufacturing method, the thermally conductive sheet is obtained by forming a thermally conductive cured layer by continuously applying and curing a thermally conductive silicone composition on at least one surface of a glass cloth by coating molding. Item 2. A method for producing a thermally conductive sheet according to Item 1. The manufacturing method of the heat conductive sheet of Claim 2 which further includes the process of winding up the obtained heat conductive sheet continuously in roll shape after forming the said heat conductive hardening layer. The silicone component is
(A) The following average composition formula:
R ¹ _a SiO _{(4-a) / 2}
Wherein R ¹ independently represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is 1.90 to 2.05, and one molecule The method for producing a thermally conductive sheet according to any one of claims 1 to 3 , which is an organopolysiloxane having at least two alkenyl groups bonded to silicon atoms. The thermally conductive silicone composition as the silicone component,
(D) one or more selected from the following (D1) and (D2),
(D1) The following formula (1):
R ² _a R ³ _b Si (OR ⁴ ) _4-ab (1)
(Wherein R ² is independently an alkyl group having 6 to 15 carbon atoms, R ³ is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and R ⁴ Is 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 1 to 3). And (D2) the following formula (2):

(Wherein, R ⁵ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100), and one end is blocked with a trialkoxy group. ,
The manufacturing method of the heat conductive sheet of Claim 4 which further contains these. (D) The manufacturing method of the heat conductive sheet of Claim 5 whose quantity of a component is 0.01-60 mass% of the sum total of the quantity of a silicone component. In the cross section of the heat conductive sheet, the thickness of the glass cloth layer is 60 μm or less, and the thickness of the entire heat conductive sheet is the both sides of the glass cloth with the cured layer of the heat conductive silicone composition as a target. The method for producing a thermally conductive sheet according to any one of claims 1 to 6 , wherein the heat conductive sheet has a thickness of 130 to 900 µm when it is contained on one side and 80 to 500 µm when it is on one side. The manufacturing method of the heat conductive sheet of any one of Claims 1-5 in which the hardened | cured material of the said heat conductive silicone composition has a heat conductivity of 3.0 W / m * K or more. The thermally conductive filler (C) is
(C1) The average particle size is 0.1 μm or more and less than 5 μm, the amount of particles having a particle size of 45 μm or more is 0 to 3% by mass, and the amount of particles having a particle size of 75 μm or more is 0 to 0.01% by mass. 20 to 50 mass% of alumina, and (C2) the amount of particles having an average particle diameter of 5 μm or more and less than 15 μm, the particle diameter of 45 μm or more being 0 to 3 mass%, and the particle diameter of 75 μm or more Is 0 to 0.01% by mass of alumina 50 to 80% by mass
The manufacturing method of the heat conductive sheet of any one of Claims 1-8 which consists of. The method for producing a thermally conductive sheet according to claim 9 , wherein the component (C2) is spherical alumina. The thermal conductivity according to any one of claims 1 to 10 , wherein the thermal resistance when the total thickness is 0.2 mm is 1.8 cm ² · K / W or less as measured according to ASTM D5470. Sheet manufacturing method . The method for producing a thermally conductive sheet according to any one of claims 1 to 11 , wherein a dielectric breakdown voltage when the total thickness is 0.2 mm is 6 kV or more when measured according to JIS K6249.