JP4521937B2 - Anisotropic heat transfer sheet manufacturing method and anisotropic heat transfer sheet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an anisotropic heat transfer sheet that transfers heat generated from components such as semiconductor elements, power supplies, and light sources used in electronic equipment.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is a heat transfer sheet that transfers heat generated from a semiconductor element or the like used in an electronic device to a heat sink or the like. Among heat transfer sheets, there is an anisotropic heat transfer sheet in which thermally conductive fibers having anisotropic thermal conductivity are oriented in the same direction. This utilizes the property that the thermal conductivity is higher in the axial direction than in the radial direction of the thermally conductive fibers.
[0003]
Several methods for producing anisotropic heat transfer sheets have been reported. For example, the thermally conductive fibers are dispersed in the polymer composition, and the thermally conductive fibers are flow-oriented using extrusion molding, calender molding, etc., and then the polymer composition is solidified to form an anisotropic heat transfer sheet. There is a manufacturing method.
[0004]
A method for producing an anisotropic heat transfer sheet in which fibers are oriented in the thickness direction of the sheet is described in JP-A-11-302545. This is to produce a composite block in which thermally conductive long fibers are oriented in one direction in liquid silicone rubber and cured, and further, the composite block is cut perpendicularly to the orientation direction of the thermally conductive long fibers. This is a method for producing an anisotropic heat transfer sheet.
[0005]
[Problems to be solved by the invention]
However, after dispersing thermally conductive fibers in the polymer composition and orienting the thermally conductive fibers using extrusion molding, calendering, etc., the polymer composition is solidified to produce an anisotropic heat transfer sheet. In this method, it is difficult to orient the fibers in the thickness direction of the heat transfer sheet. In addition, in the method in which liquid silicone rubber is impregnated with heat conductive long fibers and the silicone rubber is cured into blocks and cut, It is possible to produce an anisotropic heat transfer sheet in which the fibers are oriented in the thickness direction of the heat transfer sheet at low cost due to the difficulty of cutting the block thinly to a thickness of about several mm while maintaining the orientation. was difficult.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention uses anisotropic flocking as a method for orienting fibers in the thickness direction of the heat transfer sheet, and is anisotropic with high thermal conductivity in the thickness direction at any thickness. The present invention provides a method for easily producing a heat conductive sheet.
[0007]
That is, a method for producing an anisotropic heat transfer sheet in which heat conductive fibers are oriented in a thickness direction in a polymer sheet, and manufacturing an anisotropic heat transfer sheet in which heat conductive fibers are oriented by electrostatic flocking Is the method.
[0008]
Furthermore, the method for producing an anisotropic heat transfer sheet in which the heat conductive fibers are oriented in the thickness direction in the polymer sheet, wherein the heat conductive fibers are oriented on the surface of the hair-implanted layer by electrostatic flocking, and are liquid. This is a method for producing an anisotropic heat transfer sheet in which a polymer is impregnated between oriented heat conductive fibers and then solidified.
[0009]
Furthermore, the method for producing an anisotropic heat transfer sheet in which the heat conductive fibers are oriented in the thickness direction in the polymer sheet, wherein the heat conductive fibers are oriented on the surface of the hair-implanted layer by electrostatic flocking, and are liquid. This is a method for producing an anisotropic heat transfer sheet in which a polymer is impregnated between oriented heat conductive fibers and then solidified, and then the planted layer is peeled off.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
In the method for producing an anisotropic heat transfer sheet of the present invention, the heat conductive fibers can be easily oriented in the thickness direction of the heat transfer sheet by orienting the heat conductive fibers by electrostatic flocking.
In a typical embodiment of the present invention, as shown in FIG. 4, the thermally conductive fiber 1 is oriented upright on the surface of the to-be-grafted layer 2 by electrostatic flocking, and then the to-be-grafted layer is solidified. Next, as shown in FIG. 5, the liquid polymer 3 is applied and impregnated between oriented heat conductive fibers, and then solidified to produce an anisotropic heat transfer sheet. Subsequently, as shown in FIG. 6, the to-be-grafted layer 2 is peeled. Through the above steps, an anisotropic heat transfer sheet 5 in which the heat conductive fiber end portions 4 are exposed on both surfaces of the heat transfer sheet as shown in FIG. 7 is obtained.
[0011]
The electrostatic flocking of the present invention may be any conventional method such as an up method, a down method, a side method, or a spraying method in which air is sprayed onto a coated surface by a jet, Then, heat conductive fibers that are flocks are blown between the electrodes, and are oriented upright on the surface of the to-be-grafted layer. It is most preferable from the efficiency of heat conduction that the implanted thermal conductive fiber is implanted in the vertical direction with respect to the surface of the planted layer, but if it is implanted obliquely, the pressure from the vertical direction is buffered. You can also
Furthermore, it is also preferable to apply vibration to the high voltage electrode plate or to stir and vibrate the flocs when planting.
[0012]
In the impregnation of the liquid polymer of the present invention, it is necessary to cure with 100 to 20000 cP of liquid polymer in order to impregnate between the electrostatically implanted thermal conductive fibers. ˜1500 cP, more preferably, it is possible to use a liquid polymer having a high viscosity to some extent by diluting with an organic solvent to temporarily lower the viscosity, and removing the organic solvent by scattering after impregnation. Further, in order to promote the impregnation, it is also effective to carry out under reduced pressure.
[0013]
As long as the heat conductive fiber of the present invention is a fiber having a heat conductivity of 50 W / m · K or more, the diameter and surface state of the fiber are not specified, but the fiber length used for flocking is aligned. Preferably it is. The type of heat conductive fiber is not particularly limited, but is preferably at least one fiber selected from carbon fiber, graphite fiber, metal fiber, polyethylene fiber, polybenzazole fiber, and ceramic fiber. In particular, pitch-based carbon fibers having high thermal conductivity are most preferable. Furthermore, it is preferable that the aspect ratio of the heat conductive fiber used is 7.2 to 25000. Furthermore, in order to charge the conductive carbon fiber, it is preferable that the surface of the carbon fiber is treated with a material that is easily charged. Furthermore, it is preferable that the resistance of the carbon fiber surface-treated is 50 to 10 × 10 ¹⁰ Ω.
[0014]
The polymer sheet of the present invention is a polymer sheet made of a known organic polymer, and is preferably a heat-resistant thermosetting organic polymer. The types of organic polymers include silicone rubber, fluoro rubber, urethane rubber, chlorinated polyethylene, ethylene propylene rubber, epoxy resin, urethane resin, silicone resin, polyimide resin, phenol resin, unsaturated polyester resin, diallyl phthalate resin, benzo Thermosetting polymers such as cyclobutene resin, thermosetting polyphenylene ether, and modified PPE resin can be used, and alloy materials thereof can also be used. The polymer sheet may contain a reinforcing agent, a flame retardant, a colorant, a heat resistance improver, an adhesive, a plasticizer, an oil, a curing retarder, and the like.
[0015]
Furthermore, a heat conductive filler may be dispersed and blended in the polymer sheet of the present invention. Thermal conductivity can be increased by blending a thermally conductive filler. Thermally conductive fillers include metal oxides such as aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon carbide, aluminum hydroxide, metal nitride, metal carbide, metal hydroxide, gold, silver, copper, A filler such as a spherical shape, a powder shape, a fiber shape, a needle shape, a scale shape, a whisker shape, a pellet shape, or the like made of at least one of metals and alloys such as aluminum and magnesium, and diamond and graphite is preferable. Among these thermally conductive fillers, at least one kind of thermally conductive filler selected from aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, aluminum hydroxide, and silicon carbide, which is excellent in electrical insulation and inexpensive, is more preferable. .
[0016]
The to-be-grafted layer of the present invention is a thin layer for fixing electrostatically-planted thermally conductive fibers in an upright state. By using a material that can be peeled from the liquid polymer for the grafted hair layer, the grafted layer is removed after the liquid polymer is cured, and the ends of the thermally conductive fibers are displayed on both surfaces of the anisotropic heat transfer sheet. Therefore, the thermal conductivity of the obtained anisotropic heat transfer sheet is not lowered. In addition, if the above-described thermally conductive filler is dispersed and blended in the flocked layer, the influence on the thermal conductivity of the flocked layer is reduced, so that after the liquid polymer is solidified, the flocked layer is laminated without peeling. An anisotropic heat transfer sheet may be used as it is. Further, the above-described reinforcing agent, flame retardant, colorant, heat resistance improver, pressure-sensitive adhesive, plasticizer, oil, curing retarder and the like may be contained in the to-be-grafted layer. At this time, when the hair-implanted layer is an electrical insulating layer, an anisotropic heat transfer sheet having an electrically insulating surface on the hair-implanted layer side is obtained.
[0017]
[Example 1]
A liquid addition type silicone rubber (manufactured by GE Toshiba Silicone Co., Ltd.) was coated on a release sheet coated with Teflon as a flocking layer by screen printing to a thickness of 60 μm, and polybenzazole having a length of 1 mm by electrostatic flocking by the up method. After orienting the heat conductive fibers 1 made of short fibers (Zylon AS manufactured by Toyobo Co., Ltd.) on the surface of the flocked layer, the liquid addition type silicone rubber was heated and cured.
[0018]
Further, a liquid polymer made of uncured epoxy resin (manufactured by Hitachi Chemical Co., Ltd.) is impregnated in the gap between the heat conductive fibers so that the tip of the heat conductive fiber 1 is not completely hidden, and the surface is flattened. The epoxy resin was heat cured. Silicone rubber which is a to-be-planted layer was peeled off to obtain an anisotropic heat transfer sheet 5 having a thickness of 1 mm. FIG. 1 shows a cross-sectional view of an anisotropic heat transfer sheet according to the first embodiment. It is the anisotropic heat-transfer sheet | seat 5 which the heat conductive fiber edge part 4 has exposed on the front and back. The volume ratio of the polybenzazole short fibers to the epoxy resin was 3.8% by volume, and the thermal conductivity was 1.5 W / m · K.
[0019]
[Example 2]
On a Teflon-coated release sheet, a silicone compound in which aluminum oxide powder (spherical alumina A-20 made by Showa Denko KK) is blended as a heat conductive filler 6 in a liquid addition type silicone gel (GE Toshiba Silicone Co., Ltd.) Short fiber graphite having a thermal conductivity in the fiber length direction of 1000 W / m · K (Melbron milled by Petka Co., Ltd .: diameter 9 μm, average length 100 μm) The thermal conductive fiber 1 made of the above was oriented upright on the surface of the to-be-grafted layer 2 by electrostatic flocking using the up method, and then the silicone compound was cured.
[0020]
Further, after impregnating the liquid polymer composed of the silicone compound having the same composition as described above in the gap between the heat conductive fibers so that the tip of the heat conductive fiber 1 is not completely hidden, the surface is flattened, and then the silicone compound is added. Heat cured. An anisotropic heat transfer sheet 5 having a thickness of 220 μm was obtained. FIG. 2 shows a cross-sectional view of the anisotropic heat transfer sheet according to the second embodiment. The thermally conductive fiber end 4 is exposed on one side, and the one side is an electrically insulating anisotropic heat transfer sheet 5. The volume ratio of the short carbon fibers to the silicone compound was 3.6% by volume, and the thermal conductivity was 5.0 W / m · K.
[0021]
[Example 3]
On a Teflon-coated release sheet, a silicone compound in which aluminum oxide powder (spherical alumina A-20 made by Showa Denko KK) is blended as a heat conductive filler 6 in a liquid addition type silicone gel (GE Toshiba Silicone Co., Ltd.) Short fiber graphite having a thermal conductivity in the fiber length direction of 1000 W / m · K (Melbron milled by Petka Co., Ltd .: diameter 9 μm, average length 100 μm) The thermal conductive fiber 1 made of the above was oriented upright on the surface of the to-be-grafted layer 2 by electrostatic flocking using the up method, and then the silicone compound was cured.
[0022]
Furthermore, liquid addition silicone rubber (manufactured by GE Toshiba Silicone Co., Ltd.) is impregnated in the gaps between the heat conductive fibers so that the tips of the heat conductive fibers 1 are not completely hidden, and the surface is flattened. Was cured by heating. An anisotropic heat transfer sheet 5 having a thickness of 200 μm was obtained. FIG. 2 shows a cross-sectional view of the anisotropic heat transfer sheet according to the second embodiment. The thermally conductive fiber end 4 is exposed on one side, and the one side is an electrically insulating anisotropic heat transfer sheet 5. The volume ratio of the short carbon fibers to the silicone compound was 3.6% by volume, and the thermal conductivity was 6.1 W / m · K.
[0023]
[Example 4]
UV curable ink (produced by Teikoku Mfg. Co., Ltd.) was applied onto a PET sheet as a to-be-implanted layer by screen printing to a thickness of 60 μm, and high-strength polyethylene short fibers having a length of 0.5 mm by electrostatic flocking using the up method. After orienting the heat conductive fiber 1 made of (Toyobo Co., Ltd.) on the surface of the to-be-grafted layer, it was cured by irradiation with ultraviolet rays.
[0024]
Furthermore, the gap between the heat conductive fibers is impregnated with a liquid polymer made of an uncured epoxy resin (manufactured by Hitachi Chemical Co., Ltd.) so that the tip of the heat conductive fiber 1 is not completely hidden, and the surface is flattened. The epoxy resin was heat cured. The to-be-grafted layer was peeled off to obtain an anisotropic heat transfer sheet 5 having a thickness of 1 mm. FIG. 1 shows a cross-sectional view of an anisotropic heat transfer sheet according to the first embodiment. It is the anisotropic heat-transfer sheet | seat 5 which the heat conductive fiber edge part 4 has exposed on the front and back. The volume ratio of the high-strength polyethylene to the epoxy resin was 4.0% by volume, and the thermal conductivity was 1.1 W / m · K.
[0025]
[Example 5]
On a Teflon-coated release sheet, a silicone compound in which aluminum oxide powder (spherical alumina A-20 made by Showa Denko KK) is blended as a heat conductive filler 6 in a liquid addition type silicone gel (GE Toshiba Silicone Co., Ltd.) It is applied by screen printing to a thickness of 60 μm as the flocked layer 2, and a carbon long fiber (k6371T manufactured by Mitsubishi Chemical Corporation) having a thermal conductivity of 140 W / m · K in the fiber length direction is cut to a length of 0.5 mm. The thermally conductive fiber 1 was oriented upright on the surface of the to-be-grafted layer 2 by electrostatic flocking using the up method, and then the silicone compound was cured.
[0026]
Furthermore, liquid addition silicone rubber (manufactured by GE Toshiba Silicone Co., Ltd.) is impregnated in the gaps between the heat conductive fibers so that the tips of the heat conductive fibers 1 are not completely hidden, and the surface is flattened. Was cured by heating. An anisotropic heat transfer sheet 5 having a thickness of 500 μm was obtained. FIG. 2 shows a cross-sectional view of the anisotropic heat transfer sheet according to the second embodiment. The thermally conductive fiber end 4 is exposed on one side, and the one side is an electrically insulating anisotropic heat transfer sheet 5. The volume ratio of the short carbon fibers to the silicone compound was 3.2% by volume, and the thermal conductivity was 3.8 W / m · K.
[0027]
[Example 6]
UV-curable ink (manufactured by Teikoku Ink Manufacturing Co., Ltd.) was coated on a PET sheet as a flocking layer by screen printing to a thickness of 60μm, and 1mm long copper was manufactured by chatter vibration cutting by up electrostatic flocking. After orienting the heat conductive fibers 1 made of short fibers (diameter 9 μm) on the surface of the to-be-grafted layer, they were cured by irradiation with ultraviolet rays.
[0028]
Furthermore, the gap between the heat conductive fibers is impregnated with a liquid polymer made of an uncured epoxy resin (manufactured by Hitachi Chemical Co., Ltd.) so that the tip of the heat conductive fiber 1 is not completely hidden, and the surface is flattened. The epoxy resin was heat cured. The to-be-grafted layer was peeled off to obtain an anisotropic heat transfer sheet 5 having a thickness of 1 mm.
FIG. 1 shows a cross-sectional view of an anisotropic heat transfer sheet according to the first embodiment. It is the anisotropic heat-transfer sheet | seat 5 which the heat conductive fiber edge part 4 has exposed on the front and back. The volume ratio of the high-strength polyethylene to the epoxy resin was 6.0% by volume, and the thermal conductivity was 8.1 W / m · K.
[0029]
[Comparative Example 1]
Liquid addition type silicone gel (GE Toshiba Silicone Co., Ltd.), aluminum oxide powder (Spherical Alumina A-20, Showa Denko Co., Ltd.) Silicone Compound 50% by volume and short fiber graphite (Petka Co., Ltd.) as heat conductive filler 6 A silicone compound was prepared by blending 50% by volume of heat conductive fiber 1 having a diameter of 9 μm and an average length of 100 μm, and a sheet having a thickness of 1 mm was obtained by press molding.
FIG. 3 shows a cross-sectional view of Comparative Example 1. The thermal conductivity was 1.8 W / m · K.
[0030]
Since the heat conductive fibers can be oriented by electrostatic flocking, the thickness of the heat transfer sheet can be adjusted by the fiber length, which makes it very easy to form a thin sheet. Furthermore, the heat conductive fibers are anisotropic heat transfer sheets. By passing through, high thermal conductivity was obtained while keeping thermal resistance low. The anisotropic heat transfer sheets shown in Examples 1 to 6 had a thermal conductivity equal to or higher than that of Comparative Example 1 although the fiber concentration contained in the sheet was very low compared to Comparative Example 1. .
[0031]
【The invention's effect】
According to the present invention, an anisotropic heat transfer sheet in which the heat conductive fibers are oriented in the thickness direction of the heat transfer sheet can be obtained very simply as compared with the prior art.
In the present invention, by using the method of electrostatic flocking for fiber orientation, an anisotropic heat transfer sheet in which thermally conductive fibers are easily oriented can be obtained, and further by selecting the fiber length used for electrostatic flocking. The sheet can be designed to an arbitrary thickness.
[Brief description of the drawings]
1 is a longitudinal sectional view of an anisotropic heat transfer sheet according to Example 1, FIG. 2 is a longitudinal sectional view of an anisotropic heat transfer sheet according to Example 2, and FIG. 3 is a longitudinal sectional view of Comparative Example 1. 4 is a longitudinal cross-sectional view of the process of the present invention. FIG. 5 is a vertical cross-sectional view of the process of the present invention. FIG. 6 is a vertical cross-sectional view of the process of the present invention. Longitudinal section of the process 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Thermal conductive fiber 2 Flocked layer 3 Liquid polymer 4 Thermal conductive fiber edge part 5 Anisotropic heat transfer sheet 6 Thermal conductive filler

Claims (10)

A method for producing an anisotropic heat transfer sheet in which heat conductive fibers are oriented in a thickness direction in a polymer sheet,
Orient the surface of the non-solidified hair transplantation layer in which the heat conductive filler is dispersed and blended by electrostatic flocking so that the tip is immersed in the planted hair layer and does not penetrate through the hair transplantation layer. After being allowed to solidify the flocked layer to make an electrically insulating layer,
A method for producing an anisotropic heat transfer sheet, further comprising impregnating a liquid polymer between the oriented heat conductive fibers and then solidifying the polymer.   The method for producing an anisotropic heat transfer sheet according to claim 1, wherein a heat conductive filler is dispersed and blended in a liquid polymer impregnated between heat conductive fibers.   The method for producing an anisotropic heat transfer sheet according to claim 1 or 2, wherein the thermally conductive filler is any one of aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, aluminum hydroxide, and silicon carbide. . Thermally conductive fibers oriented in the thickness direction in the polymer sheet by electrostatic flocking;
A polymer sheet that is a cured body of a liquid polymer filled between the thermally conductive fibers;
Laminated on one side of the polymer sheet, an electrically insulating hair-implanted layer in which a thermally conductive filler is dispersed and blended;
An anisotropic heat transfer sheet comprising:   The anisotropic heat transfer sheet according to claim 4, wherein a heat conductive filler is dispersed and blended in the polymer sheet.   The anisotropic heat transfer sheet according to claim 4 or 5, wherein the thermally conductive filler is any one of aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, aluminum hydroxide, and silicon carbide.   The anisotropic heat-transfer sheet | seat of any one of Claims 4-6 in which the said heat conductive fiber is immersed in the to-be-grafted layer.   The anisotropic heat transfer sheet according to any one of claims 4 to 7, wherein the heat conductive fibers are pitch-based carbon fibers.   The anisotropic heat transfer sheet according to any one of claims 4 to 8, wherein the thermally conductive fibers are oriented obliquely with respect to the anisotropic heat transfer sheet surface.   The anisotropic heat transfer sheet according to any one of claims 4 to 9, wherein the flocked layer is a cured product of liquid addition type silicone rubber.

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