Method for manufacturing insulating heat dissipation sheet

Abstract

To provide a method for manufacturing an insulating heat dissipation sheet having heat transfer properties, good insulating properties, and uniform in-plane dielectric strength, and being finishable in a roll form with high productivity.SOLUTION: The method for manufacturing an insulating heat dissipation sheet includes the step of continuously pressing, using a double-belt press machine, a silicone B-stage sheet containing (A) a silicone component and (B) a thermally conductive filler under the conditions that the temperature is in the range of 100°C to 250°C and the pressure is 2 MPa to 20 MPa, to form the sheet into a roll shape.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a manufacturing method capable of producing a roll of insulating and heat-dissipating sheet that has thermal conductivity and insulating properties and is used to transfer heat from heat-generating components to heat-dissipating components in electrical equipment, electronic devices, light-emitting devices, integrated circuits, etc. In particular, the present invention relates to a manufacturing method capable of supplying a roll of insulating and heat-dissipating sheet that has excellent insulating properties, heat-dissipating characteristics, and in-plane uniformity, even when a nitride, which has poorer packing properties than an oxide, is used as a thermally conductive filler. [Background technology]

[0002] In recent years, as electronic devices have become more powerful, the density and packaging of semiconductor elements have become increasingly high. This has led to an increase in the amount of heat generated by the electronic components that make up these devices, making efficient heat dissipation important. To address this issue, heat dissipators such as heat sinks are commonly used to dissipate the heat generated by heat-generating elements. It is known that a heat dissipation sheet is placed between the heat-generating element and the heat dissipating element to improve heat transfer efficiency.

[0003] In particular, the electrification of automobiles has become significant. To overcome the challenges of shortening battery charging times, downsizing powertrains, and improving performance, active research is being conducted into higher voltages. This has led to a growing demand for heat-dissipating sheets with high thermal conductivity and in-plane insulation. To meet these requirements, heat-dissipating sheets with fillers dispersed in resin or rubber are widely used. Aluminum oxide, which is inexpensive and easily dispersed in rubber, is commonly used in such heat-dissipating sheets. In particular, in recent years, nitrides such as boron nitride, aluminum nitride, and silicon nitride, which have high thermal conductivity and insulating properties, have increasingly been used as insulating and thermally conductive fillers in high-thermal-conductivity and high-insulation heat-dissipating sheets.

[0004] For example, a thermally conductive sheet has been proposed in which silicone rubber containing boron nitride powder and spherical silica powder as thermally conductive fillers is laminated onto glass cloth (Patent Document 1). When manufacturing this sheet, it is necessary to prepare a sheet of an appropriate size and apply pressure using a press molding machine or the like. This requires batch production, and the completed thermally conductive sheet cannot be rolled up. This is extremely inefficient in terms of productivity and yield, and the size of the raw sheet is limited, which also limits the packaging size.

[0005] An alternative continuous molding method is coating molding. For example, thermally conductive sheets can be continuously produced by sealing glass cloth with thermally conductive silicone resin and then coating it with a thermally conductive silicone rubber layer. Coating molding is highly efficient because the completed sheet can be continuously wound up. Furthermore, while the width of the sheet is limited by the coating equipment, there is no limit to the length in the longitudinal direction, which allows for much greater freedom in sheet size compared to press molding. However, coating molding has poorer surface accuracy than press molding, resulting in higher contact thermal resistance. Furthermore, since no pressure is applied, it is difficult to increase the density of the thermally conductive silicone rubber layer. Therefore, it was not suitable as a method for producing sheets with high thermal conductivity.

[0006] To solve this problem, it has been investigated to use a thermally conductive composition highly filled with spherical aluminum oxide containing few coarse particles in the coating process (Patent Document 2). However, although a high filling rate of spherical aluminum oxide increases the thermal conductivity of the sheet, it also reduces the fluidity of the thermally conductive composition, resulting in uneven distribution of voids within the sheet. This has led to the problem of variations in the insulating properties within the surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-199880 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-233104 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the present invention aims to provide a highly productive method for producing an insulating and heat-dissipating sheet that uses an insulating and thermally conductive filler and does not have the above-mentioned problems, i.e., that has heat conductivity, good insulation properties, and uniform in-plane insulation strength, and can be finished in roll form. In particular, the present invention aims to provide a production method that can produce a roll-shaped insulating and heat-dissipating sheet that has excellent insulation properties, heat dissipation characteristics, and uniform in-plane insulation strength, even when a nitride, which has inferior filling properties compared to oxides, is used as a thermally conductive filler. [Means for solving the problem]

[0009] As a result of extensive research into solving the above problems, the inventors discovered that by continuously pressing a silicone B-stage sheet containing an insulating and thermally conductive filler in a double belt press at a temperature of 100 to 250°C and a pressure of 2 to 20 MPa, an insulating and heat-dissipating sheet formed into a roll can be obtained, thereby solving the above problems and leading to the creation of the present invention.

[0010] Accordingly, the present invention provides the following production method. 1. A method for producing an insulating and heat-dissipating sheet, in which a silicone B-stage sheet containing (A) a silicone component and (B) a non-thermally conductive filler is continuously pressed in a double belt press at a temperature of 100 to 250°C and a pressure of 2 to 20 MPa to form it into a roll. 2. The method for producing an insulating and heat-dissipating sheet according to 1, wherein the (B) insulating and thermally conductive filler contains aluminum oxide in an amount of 400 to 2,000 parts by mass per 100 parts by mass of the (A) silicone component. 3. The method for producing an edge heat dissipation sheet according to 1, wherein the (B) insulating thermally conductive filler contains a nitride. 4. The method for producing an insulating and heat-radiating sheet according to 3, wherein the nitride is at least one selected from aluminum nitride and silicon nitride, and the amount thereof is 330 to 1,650 parts by mass per 100 parts by mass of the (A) silicone component. 5. The method for producing an insulating and heat-radiating sheet according to 3, wherein the nitride is boron nitride, and the amount of boron nitride is 100 to 300 parts by mass per 100 parts by mass of the (A) silicone component. 6. The method for producing an insulating and heat-radiating sheet according to any one of 1 to 5, wherein the temperature of the B-stage sheet immediately before it is released from the press is less than 150°C. [Effects of the Invention]

[0011] According to the method for producing an insulating and heat-dissipating sheet of the present invention, it is possible to provide a highly productive method for producing an insulating and heat-dissipating sheet that has heat conductivity, good insulation properties, uniform in-plane insulation strength, and can be finished in roll form. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a double belt press used in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. [Silicone B-stage sheet] The silicone B-stage sheet of the present invention is a silicone B-stage sheet containing (A) silicone component and (B) intrinsically thermally conductive filler (B), and is a tack-free sheet that appears cured, uncured, or semi-cured. This B-stage sheet can further contain a peroxide crosslinking agent, and the crosslinking reaction can be fully promoted by heating above the decomposition temperature of the peroxide crosslinking agent.

[0014] [(A) Silicone component] The silicone component is not particularly limited as long as it can be molded after being brought into a B-stage state, and can be used alone or in combination of two or more. Various organopolysiloxanes can be used, and a specific example that is preferably used is (A-1) an organopolysiloxane having the average composition formula shown in the following average composition formula (1). R 1 a SiO (4-a) / 2 (1) (In the formula, R 1 are the same or different unsubstituted or substituted monovalent hydrocarbon groups, and a is a positive number of 1.85 to 2.10.

[0015] In the above formula (1), R 1 are the same or different unsubstituted or substituted monovalent hydrocarbon groups, preferably monovalent hydrocarbon groups having 1 to 8 carbon atoms. The monovalent hydrocarbon groups may be substituted, for example, with halogen atoms and / or cyano groups. 1 Examples of the monovalent hydrocarbon group represented by the formula (R) include alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl and tolyl; cycloalkyl groups such as cyclohexyl and cyclopentyl; and groups in which some or all of the hydrogen atoms directly bonded to the carbon atoms of these groups have been substituted with halogen atoms or cyano groups, such as chloromethyl, chloroethyl, trifluoropropyl, cyanoethyl, and cyanopropyl groups. 1 is preferably a methyl group, a phenyl group, a trifluoropropyl group, or a vinyl group, and a is a positive number of 1.85 to 2.10.

[0016] The average degree of polymerization of the silicone component is preferably 3,000 to 10,000, and more preferably 5,000 to 10,000. In the present invention, the degree of polymerization can be determined, for example, as a polystyrene-equivalent value in gel permeation chromatography (GPC) analysis using toluene as a developing solvent, and it is usually preferable to determine the average degree of polymerization as a number-average degree of polymerization or the like (the same applies hereinafter). [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6mL / min Detector: Refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperH4000(6.0mmI.D.×15cm×1) TSKgel SuperH3000(6.0mmI.D.×15cm×1) TSKgel SuperH2000(6.0mmI.D.×15cm×2) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 20 μL (0.5% by mass THF solution)

[0017] Also included is (A-2) dimethylpolysiloxane in which one molecular chain terminal is blocked with a trialkoxy group, represented by the following general formula (2). [ka] (In the formula, R 2 are independently alkyl groups having 1 to 6 carbon atoms, and c is an integer of 5 to 100.

[0018] In the above general formula (2), R 2 Examples of the alkyl group represented by the formula (I) include alkyl groups such as 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, and a hexyl group, and some or all of the hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom such as fluorine, chlorine, or bromine, a cyano group, or the like.

[0019] A specific example of a suitable component (A-2) is one represented by the following formula (3): [ka] (In the formula, c is an integer of 5 to 100.)

[0020] When the components (A-1) and (A-2) are used in combination, the (A-1):(A-2) ratio is preferably 80:20 to 99:1, and more preferably 80:20 to 85:15.

[0021] [(B) Thermally conductive filler] As the thermally conductive filler, insulating and thermally conductive materials can be used as appropriate, and they can be used alone or in combination of two or more. For example, aluminum oxide (alumina), which has excellent filling properties, and nitrides, which have excellent thermal conductivity, are suitable. As nitrides, aluminum nitride, silicon nitride, boron nitride, etc. are preferred in terms of thermal conductivity, insulating properties, and availability. Among them, boron nitride is known to be flaky, and by orienting it in the plane direction, it is expected to improve the uniformity of insulation properties and in-plane insulation strength.

[0022] The optimal amount of the insulating and thermally conductive filler varies depending on the type of the filler, since the filling ability varies depending on the shape. In order to obtain the desired heat transfer properties, the amount is preferably equal to or greater than the lower limit shown below, and in order to obtain a more uniform composition, the amount is preferably equal to or less than the upper limit shown below. The amount of aluminum oxide is preferably 400 to 2,000 parts by mass, and more preferably 1,000 to 2,000 parts by mass, per 100 parts by mass of the silicone component (A). The amount of aluminum nitride or silicon nitride is preferably 330 to 1,650 parts by mass, and more preferably 820 to 1,650 parts by mass, per 100 parts by mass of the silicone component (A). The amount of boron nitride is preferably 100 to 300 parts by mass, more preferably 150 to 300 parts by mass, per 100 parts by mass of the silicone component (A).

[0023] [(C) Peroxide Crosslinker] Generally, a peroxide crosslinking agent is used to convert the silicone component (A) into a B-stage sheet by press heat vulcanization. The peroxide crosslinking agent can be used alone or in combination of two or more. For example, when the crosslinking reaction is a radical reaction, an organic peroxide is used as the crosslinking agent. Specific examples include benzoyl peroxide, monochlorobenzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, o-methylbenzoyl peroxide, p-methylbenzoyl peroxide, di(tert-butyl)perbenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and di(tert-butyl)peroxide.

[0024] The amount of the peroxide crosslinking agent is preferably 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the silicone component (A).

[0025] [Other ingredients] In addition to the above components, the composition of the B-stage sheet used in the present invention can contain other components as needed, provided that the effects of the present invention are not impaired. Examples of other components that can be included include filler reinforcement agents, dispersants, flame retardant aids, heat resistance aids, coloring pigments, reaction inhibitors such as ethynylmethyldecylcarbinol and ethynylcyclohexanol, plasticizers, oils that act as wettability improvers, and coupling agents. When these optional components are included, their amount is preferably 35% by mass or less, more preferably 30% by mass or less, of the total composition. Furthermore, the viscosity can be adjusted to the desired level using an organic diluting solvent such as xylene.

[0026] If necessary, the insulating and heat-dissipating sheet can also contain glass fiber cloth or various films that serve as the framework during molding, or glass fiber cloth impregnated with a composition containing a thermally conductive filler. Examples of such thermally conductive fillers include metal oxides such as aluminum oxide, silica, magnesia, red iron oxide, beryllia, titania, and zirconia, nitrides such as aluminum nitride, silicon nitride, and boron nitride, artificial diamond, and silicon carbide, which are generally considered to be thermally conductive fillers. These may be used alone or in combination. It is also possible to use two or more types of particles with different average particle sizes.

[0027] [Production of B-stage sheets] B-stage sheets can be obtained by molding an (organopolysiloxane) composition containing the above components into a sheet at a temperature below the decomposition temperature of the peroxide crosslinking agent used, if a peroxide crosslinking agent is used. For example, the organopolysiloxane composition can be coated onto a processing film such as polyethylene terephthalate (PET), dried by heating, and then cured at a temperature preferably between 50°C and 100°C to obtain a B-stage sheet. By setting the temperature at 50°C or higher, the weak addition crosslinking reaction does not proceed, which further suppresses cracking and shedding during the molding process from drying and curing to press heat vulcanization. On the other hand, by setting the temperature at 100°C or lower, the crosslinking reaction caused by the peroxide can be suppressed to a certain extent, allowing sufficient pressing during press heat vulcanization and achieving better thermal conductivity and insulation.

[0028] [Double belt press processing (press heat vulcanization process)] The resulting B-stage sheet can be subjected to a double-belt press process to undergo a curing reaction, resulting in an insulating and heat-dissipating sheet. Double-belt press (DBP) processing is a method for obtaining an insulating and heat-dissipating sheet by sandwiching the B-stage sheet between two belts and passing it through a heating process while applying pressure. The double-belt press has a mechanism for continuously pressing the B-stage sheet while handling it, thereby improving the insulating properties and uniformity of the in-plane insulating strength of the insulating and heat-dissipating sheet. Figure 1 is a schematic diagram of the double-belt press used in the examples of the present invention. Rotating the rollers allows for pressure and heating, making it possible to adjust the pressure and temperature. Furthermore, by cooling the insulating and heat-dissipating sheet before it is released from the press, it is also possible to adjust the temperature of the B-stage sheet just before it is released from the press.

[0029] The pressing conditions are a temperature of 100 to 250°C and a pressure of 2 to 20 MPa, with 170 to 200°C and a pressure of 5 to 8 MPa being preferred. Under these conditions, the time required for the thermal vulcanization step can be shortened, the insulating and heat-dissipating sheet can have uniform insulating properties and in-plane insulating strength, and productivity can be increased.

[0030] Furthermore, the temperature immediately before the B-stage sheet is released from the press is preferably less than 150° C., and more preferably between 80° C. and 150° C. Under these conditions, the temperature difference when the sheet is released from the press is small, which reduces temperature-induced shrinkage stress even when an inexpensive processing film such as PET film is used, and prevents deformation of the insulating and heat-dissipating sheet.

[0031] [Thermal resistance of insulating heat dissipation sheet] The thermal resistance of the insulating and heat-dissipating sheet obtained by the manufacturing method of the present invention is 0.01 to 3.00 (cm) at 50°C and 689.5 kPa in thermal resistance measurement according to ASTM D 5470. 2 ·K / W) is preferable, and 0.01 to 2.50 (cm 2 K / W) is more preferable, and 0.01 to 2.0 (cm 2The thickness of the insulating and heat-dissipating sheet is preferably 0.1 to 2.0 mm, and more preferably 0.1 to 1.0 mm.

[0032] As described above, the method for producing an insulating and heat-dissipating sheet of the present invention allows for the high productivity production of an insulating and heat-dissipating sheet that has heat conductivity, good insulation properties, and uniform in-plane insulating strength. Therefore, the resulting insulating and heat-dissipating sheet is useful for transferring heat from heat-generating components such as electrical equipment, electronic devices, light-emitting devices, and integrated circuits to heat-dissipating components. Furthermore, the production method of the present invention uses double-belt press thermal vulcanization, allowing for continuous molding and finishing into a roll, which makes it possible to supply the sheet in an optimal shape regardless of the user's desired size, thereby also improving yield. [Example]

[0033] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0034] [Examples and Comparative Examples] The materials used in the examples and comparative examples are as follows. (A) Component: Silicone component: (A-1) Dimethylpolysiloxane with an average degree of polymerization of 6,000, both ends of which are capped with dimethylvinyl groups (A-2) Dimethylpolysiloxane represented by the following formula (4), having an average degree of polymerization of 30 and having one end blocked with a trimethoxysilyl group: [ka]

[0035] (B) Component: Insulating and thermally conductive filler (B-1) Crushed aluminum oxide powder with an average particle size of 1.5 μm (B-2) Spherical aluminum oxide powder with an average particle size of 12 μm (B-3) Crushed aluminum nitride powder with an average particle size of 1.5 μm (B-4) Crushed aluminum nitride powder with an average particle size of 20 μm (B-5) Boron nitride powder with an average particle size of 15 μm

[0036] Component (C): Peroxide crosslinker component: (C-1) 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane ( Nippon Oil & Fats Co., Ltd., Perhexa 25B) (C-2) Di(4-methylbenzoyl) peroxide (manufactured by Shin-Etsu Chemical Co., Ltd., C-23N: di(4-methylbenzoyl) peroxide, concentration 50% by mass). The amounts in the table are the amounts of each component.

[0037] Glass cloth: thickness 40 μm, mass 26 g / m 2 Glass cloth Xylene: Dilution solvent

[0038] [Preparation of Thermally Conductive Silicone Composition and Diluted Solution] A thermally conductive silicone composition was prepared by adding components (A) to (C) in the amounts (parts by mass) shown in Table 1 to a Banbury mixer and kneading for 20 minutes. To this was added xylene in the amount (parts by mass) shown in Table 1, and the mixture was kneaded using a planetary mixer to prepare a diluted thermally conductive silicone solution for coating.

[0039] [Production of B-stage sheets] The thermally conductive silicone diluted solution was applied to one side of a glass cloth using a comma coater, and then heated and dried at 80°C for 10 minutes to seal the glass cloth. Furthermore, both sides of the sealed glass cloth obtained above were coated using a comma coater so that the thickness after double belt press molding would be 0.20 mm. The glass cloth was then heated and dried at 80°C for 10 minutes and wound up to obtain a B-stage sheet. The thickness of both sides of the glass cloth was adjusted to be uniform.

[0040] [Press-molded sheet production] The resulting B-stage sheet was press-cured using a double-belt press or hydraulic sheet-fed press under the molding conditions listed in Tables 2 and 3. Takaline Corporation's FL1-01 release film was used to prevent the B-stage sheet from sticking to the press. After press-curing, the release film was peeled off to obtain a 0.20 mm thick insulating and heat-dissipating sheet. The double-belt press shown in Figure 1 was used. The B-stage sheet (1) was heated and pressurized, and then heated (cooled) and heated again to obtain the insulating and heat-dissipating sheet (2). The temperature just before the insulating and heat-dissipating sheet was released from the press was adjusted by adjusting the temperature, pressure, etc.

[0041] [Preparation of Fully Cured Sheet (for Comparative Example)] The diluted thermally conductive silicone solution was applied to one side of a glass cloth using a comma coater, and then the glass cloth was sealed by heating and drying at 80°C for 10 minutes and 180°C for 15 minutes. The sealed glass cloth was then coated on both sides using a comma coater so that the thickness after molding would be 0.20 mm, and the sheet was then heated and dried at 80°C for 10 minutes and 180°C for 15 minutes, after which it was wound up to obtain an insulating and heat-dissipating sheet with a thickness of 0.20 mm.

[0042] [evaluation] The thermal resistance of the obtained insulating and heat-dissipating sheet was evaluated as a measure of heat transfer. Specifically, the thermal resistance was measured at 50°C and 689.5 kPa using a TIM Tester manufactured by Analysis Tech. To evaluate the insulation properties, a voltage withstand test was conducted in accordance with JIS C 2110. In addition, to evaluate the uniformity of the in-plane insulation strength, a voltage withstand test was conducted on the entire surface of the sheet. Specifically, a 4kV DC voltage was applied to both sides of the insulating heat dissipation sheet for 10 seconds using 200mm x 300mm electrodes, and the number of sheets that shorted out of 50 was counted. As the production volume per unit time, the maximum production area is shown in the table as a ratio when the maximum production area per unit time at a double belt press thermal vulcanization temperature of 180°C is set to 1. Regarding the possibility of finishing into a roll after pressing, those that could be finished into a sheet of 10 m or more in length after pressing were rated as "yes," and those that could not be finished were rated as "no."

[0043] [Table 1]

[0044] [Table 2]

[0045] [Table 3]

[0046] The insulating and heat-dissipating sheets of the examples all had a withstand voltage of 3 kV or more (insulation), low thermal resistance (heat conductivity), and uniform in-plane insulation strength.Furthermore, they could be roll-finished, and were highly productive. In Comparative Example 1, the press temperature was low and thermal vulcanization was insufficient, resulting in poor sheet release from the release film, high thermal resistance, and low voltage resistance. In Comparative Example 2, the pressure was too low, so the sheet was not densified, resulting in non-uniform in-plane insulation strength and high thermal resistance. In Comparative Examples 3, 5, and 7, press heat vulcanization was not performed, so the sheets were not densified, resulting in low withstand voltage and high thermal resistance. In Comparative Examples 4, 6, and 8, press heat vulcanization was performed using a hydraulic sheet press, resulting in a withstand voltage of 3 kV and low thermal resistance, but it was not possible to press continuously and perform roll finishing.Furthermore, the production volume per unit time was 0.6, resulting in low productivity. [Explanation of symbols]

[0047] 1 B Stage Seat 2. Insulating heat dissipation sheet

Claims

1. A method for producing an insulating and heat-dissipating sheet, comprising continuously pressing a silicone B-stage sheet containing (A) a silicone component and (B) a non-thermally conductive filler in a double belt press at a temperature of 100 to 250°C and a pressure of 2 to 20 MPa to form it into a roll.

2. 2. The method for producing an insulating and heat-dissipating sheet according to claim 1, wherein the (B) insulating and heat-conductive filler contains aluminum oxide in an amount of 400 to 2,000 parts by mass per 100 parts by mass of the (A) silicone component.

3. The method for manufacturing an edge heat dissipation sheet according to claim 1 , wherein the insulating thermally conductive filler (B) comprises a nitride.

4. The method for producing an insulating and heat-dissipating sheet according to claim 3, wherein the nitride is one or more selected from aluminum nitride and silicon nitride, and the amount thereof is 330 to 1,650 parts by mass per 100 parts by mass of the (A) silicone component.

5. 4. The method for producing an insulating and heat-radiating sheet according to claim 3, wherein the nitride is boron nitride, and the amount of boron nitride is 100 to 300 parts by mass per 100 parts by mass of the silicone component (A).

6. The method for producing an insulating and heat-radiating sheet according to any one of claims 1 to 5, wherein the temperature of the B-stage sheet immediately before it is released from the press is less than 150°C.

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