JP2015048414A - Insulating heat-conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulating heat-conductive sheet with improved heat radiation properties and insulation properties.SOLUTION: This insulating heat-conductive sheet comprises: a fluorine resin including polytetrafluoroethylene; and a heat-conductive filler. The heat-conductive filler includes diamond particles, and heat-conductive inorganic particles other than the diamond particles. For example, boron nitride particles are suitably used as the heat-conductive inorganic particles.

Description

  The present invention relates to an insulating heat conductive sheet.

  In an electronic device typified by a mobile computer and a mobile phone, “heat dissipation” has become a major issue due to heat generation of the member itself due to improved processing capability and high-density mounting accompanying downsizing. Therefore, as a heat radiating member that has high heat dissipation performance and mechanical strength, and has excellent handling properties without adverse effects when applied to electronic devices, insulation with thermally conductive inorganic particles dispersed in a fluororesin matrix A heat conductive sheet has been proposed (Patent Document 1).

  In recent years, hybrid vehicles and electric vehicles have been developed from the viewpoint of environmental friendliness. A motor is used for such a vehicle drive system, and the motor is required to have a high output. When the motor output is increased, the amount of heat generated increases. Therefore, as a means for cooling the vehicle motor, a heat radiating member using an insulating heat conductive sheet in which heat conductive inorganic particles are dispersed in a fluororesin matrix has been proposed (Patent Document 2). Thus, the insulating heat conductive sheet can also be used for cooling the vehicle motor.

JP 2010-137562 A JP2013-208159A

  In recent years, further improvements in heat dissipation and insulation have been demanded for heat dissipation members used for electronic devices and vehicles. Therefore, in order to meet such a high demand, an object of the present invention is to provide an insulating heat conductive sheet having further improved heat dissipation and insulation.

The present invention
An insulating heat conductive sheet comprising a fluororesin containing polytetrafluoroethylene (hereinafter referred to as PTFE) and a heat conductive filler,
The thermally conductive filler includes diamond particles and thermally conductive inorganic particles excluding the diamond particles.
An insulating heat conductive sheet is provided.

  The insulating heat conductive sheet of the present invention contains two or more different particles of diamond particles and heat conductive inorganic particles as a heat conductive filler. By adding the diamond particles as a filler, it is possible to further improve the insulating properties while realizing the high thermal conductivity of the insulating thermal conductive sheet. Therefore, according to the present invention, it is possible to realize an insulating heat conductive sheet in which both heat dissipation and insulation are improved.

It is a figure which shows the thermal-characteristic evaluation apparatus used in the Example, (a) is a front view, (b) is a side view.

  Hereinafter, embodiments of the insulating heat conductive sheet of the present invention will be described. The following description does not limit the present invention.

  The insulating heat conductive sheet of this embodiment contains the fluororesin containing PTFE and a heat conductive filler. That is, the insulating heat conductive sheet has a configuration in which a heat conductive filler is dispersed in a matrix containing a fluororesin (fluororesin matrix). In addition to the heat conductive inorganic particles (excluding diamond particles), diamond particles are added to the insulating heat conductive sheet as a heat conductive filler. By adding diamond particles in addition to the thermally conductive inorganic particles, the insulating property can be improved while realizing high heat dissipation of the insulating thermally conductive sheet.

  The heat conductive inorganic particles are not particularly limited, as long as they can impart sufficient heat conductivity to the insulating heat conductive sheet and can form a sheet by being mixed with a fluororesin. Thermally conductive inorganic particles having a thermal resistance of, for example, 0.6 K / W or less, preferably 0.5 K / W or less can be used.

About the electroconductive performance of a heat conductive inorganic particle, it can determine suitably according to a use. Thermally conductive inorganic particles formed of a material having a volume resistivity of, for example, about 10 ¹⁰ to 10 ¹⁷ Ω · cm, preferably 10 ¹⁴ Ω · cm or more can be used. As such an insulating material, at least one selected from the group consisting of boron nitride, aluminum nitride, alumina, silicon nitride, and magnesium oxide can be used.

  Boron nitride is preferably used for the thermally conductive inorganic particles because of its high thermal conductivity and high electrical resistivity. Therefore, it is preferable that the insulating heat conductive sheet of this embodiment contains a diamond particle and a boron nitride particle as a heat conductive filler. For example, the heat conductive filler contained in the insulating heat conductive sheet may be composed of diamond particles and boron nitride particles.

  The shape of the heat conductive inorganic particles is not particularly limited. Spherical and non-spherical particles can be used as the thermally conductive inorganic particles. Especially, since heat conduction anisotropy can be provided by aligning in a surface direction by rolling treatment, it is preferable to use tabular and scale-like heat conductive inorganic particles. For the same reason, it is preferable that the thermally conductive inorganic particles themselves have thermal conductivity anisotropy. Moreover, in order to improve the heat conductivity of the insulating heat conductive sheet in the thickness direction, commercially available aggregated heat conductive inorganic particles may be used.

  The particle size of the heat conductive inorganic particles is not particularly limited, but is about 0.2 to 500 μm and it is necessary not to fall off the fluororesin matrix. Here, the particle diameter is a value measured by a laser diffraction / scattering particle diameter / particle size distribution measuring device (microtrack).

  The shape of the diamond particles is not particularly limited. Spherical and non-spherical diamond particles can be used. The particle size of the diamond particles is not particularly limited, and is about 0.1 to 500 μm.

  The content of the heat conductive filler is preferably 50 to 95% by mass, more preferably 70 to 90% by mass, and 80 to 90% by mass with respect to the total mass of the insulating heat conductive sheet. More preferably. The higher the content of the thermally conductive filler, the higher the thermal conductivity performance, but there is a problem that molding becomes difficult.

  The content of the diamond particles is preferably 5 to 50% by mass, more preferably 5 to 30% by mass, and more preferably 5 to 10% by mass with respect to the total mass of the insulating heat conductive sheet. Further preferred. By setting the content of diamond particles in the range of 5 to 50% by mass, higher heat dissipation can be realized.

  The fluororesin includes PTFE. When the fluororesin contains PTFE, the insulating heat conductive sheet can contain the heat conductive filler at a higher ratio. The fluororesin may be composed only of PTFE, or may be a mixture of PTFE and another fluororesin. As the other fluororesin, a meltable fluororesin is preferably used. By using a meltable fluororesin, it becomes easier to form a sheet containing a fluororesin and a thermally conductive filler. As the meltable fluororesin, those having good compatibility with PTFE are preferable. For example, perfluoroalkoxy fluororesin (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferably used.

  Although content of a fluororesin is suitably adjusted according to the quantity of a heat conductive filler, it is preferable that it is 5-50 mass% with respect to the total mass of an insulating heat conductive sheet. Moreover, when using it combining PTFE and a meltable fluororesin, 5-70 mass% is preferable and, as for the ratio of the meltable fluororesin with respect to the total mass of a fluororesin, 10-50 mass% is more preferable.

  The insulating heat conductive sheet may have a porous structure. There is no restriction | limiting in particular about this porous structure. For example, as described later, a porous structure can be obtained by preparing a sheet-like molded body containing a fluororesin, a thermally conductive filler, and a molding aid (volatile material), and then removing the molding aid. it can. In order to suppress an increase in thermal resistance due to the porous structure, the insulating heat conductive sheet may be impregnated with an impregnation material. Since the impregnating material is contained in the holes, the thermal conductivity in the holes is lowered, so that the thermal resistance of the entire insulating heat conductive sheet can be kept small. The impregnating material is not particularly limited because it can be appropriately selected according to the use of the insulating heat conductive sheet. However, for the impregnating material, for example, a material that does not have volatility and has an insulating property is preferably used. It is also possible to use an adhesive material as the impregnation material. Since the impregnating material needs to be included in the holes of the insulating heat conductive sheet, it preferably has a viscosity of 1 to 100,000 mPa · s, and more preferably has a viscosity of 1 to 1000 mPa · s. The lower the viscosity, the easier the impregnation material can be contained in the pores.

  The electrical insulation and thermal conductivity of the impregnating material are not particularly limited, but the higher the better.

  Examples of the impregnating material include acrylic and silicone oils, and adhesives such as thermosetting adhesives (for example, epoxy resins) and hot melt adhesives. These oils and adhesives are publicly known and are also commercially available. What is necessary is just to select the kind of impregnation material suitably according to the use of an insulating heat conductive sheet, and also the desired insulation and heat dissipation.

  The insulating heat conductive sheet of this embodiment can satisfy both high heat dissipation and high insulating properties, and has, for example, a thermal resistance of less than 0.55 K / W and a dielectric breakdown voltage of 50 kV / mm or more. Can do. Since the insulating heat conductive sheet of this embodiment can implement | achieve both such a low thermal resistance and a high dielectric breakdown voltage, even if it is thin, it can exhibit the outstanding heat dissipation and insulation. Therefore, the thickness of the insulating heat conductive sheet can be set to 1 mm or less, and handling properties can be improved. In addition, although the thickness of the insulating heat conductive sheet of this embodiment is not specifically limited, From the height of handling property, it can be set as about 0.05-3 mm, for example, Preferably it is 0.1-1 mm. is there.

  Next, a method for manufacturing the insulating heat conductive sheet of the present embodiment will be described.

The manufacturing method of the insulating heat conductive sheet of this embodiment is, for example,
(I) A step of preparing a plurality of sheet-like molded bodies containing a fluororesin containing PTFE, a thermally conductive inorganic filler (including diamond particles and thermally conductive inorganic particles excluding diamond particles), and a molding aid. When,
(II) a step of superposing and rolling a plurality of the sheet-like molded bodies,
(III) removing the molding aid;
including.

  Moreover, you may further include the process (process (IV)) of pressure-molding the sheet-like material obtained by process (III). In step (IV), it is desirable to perform pressure molding at a temperature within the PTFE firing temperature range.

  When manufacturing an insulating heat conductive sheet impregnated with an impregnating material, after the step (III) (after the step (IV) when the step (IV) is performed), the obtained sheet-like material A step of impregnating the impregnating material (step (V)) is performed.

  An example of the step (I) will be described. The fluororesin containing PTFE and the thermally conductive filler are as described above. First, a heat conductive filler and a molding aid are mixed in a fluororesin to produce a paste-like mixture. At this time, it is desirable to carry out under the conditions that suppress fiber formation of PTFE as much as possible. Specifically, it is desirable to reduce the number of rotations, shorten the mixing time, and mix without kneading so as not to apply a shearing force to PTFE. If fiber formation of PTFE occurs at the stage of mixing the materials, there is a possibility that the PTFE fiber already formed is cut and the PTFE network structure is destroyed when rolling in the step (II). It may be difficult to maintain the sheet shape. Therefore, by mixing so as to suppress the fiberization of PTFE as in the present embodiment, processing of a sheet-like material using a fluororesin as a matrix in the subsequent step is facilitated.

  As the molding aid, for example, saturated hydrocarbons such as dodecane and decane can be used. What is necessary is just to add a shaping | molding adjuvant so that it may become 20 to 55 weight% with respect to the total weight of a mixture. A mother sheet obtained by forming such a mixture into a sheet by extrusion molding and roll rolling can be used as a sheet-like molded body (first example of a sheet-like molded body). The thickness of the sheet-like molded body thus obtained is, for example, 0.5 to 5 mm.

  Moreover, as another example of the sheet-like molded body prepared in the step (I), a laminated sheet (second example of the sheet-like molded body) obtained by rolling a plurality of the above-described mother sheets is also given. It is done. The number of laminated sheets is not particularly limited, and can be appropriately determined in consideration of the number of constituent layers of the insulating heat conductive sheet to be manufactured (number of layers constituting the insulating heat conductive sheet). .

  In addition, even if the sheet-like molded object may contain other materials other than a fluororesin, a heat conductive filler, and a shaping | molding adjuvant, it may be produced only with the fluororesin, the heat conductive filler, and the shaping aid. Good.

  Next, an example of the step (II) will be described. In step (II), the plurality of sheet-like molded bodies prepared in step (I) are overlaid and rolled. Specifically, a plurality of sheet-like molded bodies prepared in step (I) are laminated, and the laminate is rolled to obtain a laminated sheet. As described above, the sheet-like molded body may be the mother sheet (sheet-like molded body of the first example) or a laminated sheet (first sheet) obtained by rolling a plurality of mother sheets. The sheet-like molded body of the example of 2) may be used. The number of the sheet-like molded bodies to be overlapped in the step (II) is not particularly limited, and can be, for example, about 2 to 10 sheets. In order to achieve high strength, it is desirable to roll the sheet-like molded bodies on top of each other.

  As another example of the method of superposing a plurality of sheet-like molded bodies, a method of folding the sheet-like molded bodies can also be mentioned. The number of sheet-shaped molded bodies to be folded (the number of sheet-shaped molded bodies to be stacked) is not particularly limited, and is, for example, about 2 to 10 sheets. By folding and rolling the sheet-like molded body, the sheet strength can be improved and the thermally conductive filler can be firmly fixed to the fluorine matrix. As a result, a flexible sheet with a high blending ratio of the heat conductive filler can be produced.

  Step (I) and step (II) may be alternately repeated. A specific example in this case will be described below.

  First, a plurality of (for example, 2 to 10) mother sheets are prepared (step (I)). Next, a plurality of mother sheets are overlapped, and the obtained laminate is rolled to obtain a laminated sheet (first laminated sheet) (step (II)). A plurality of (for example, 2 to 10) first laminated sheets obtained here are further prepared, and the first laminated sheets are used as the sheet-like molded body in the step (I). Next, a plurality of (for example, 2 to 10) first laminated sheets are overlapped, and the obtained laminate is rolled to obtain a laminated sheet (second laminated sheet) (step (II)). Furthermore, a plurality of (for example, 2 to 10) second laminated sheets obtained are prepared, and the second laminated sheet is used as a sheet-like molded body in step (I). Next, a plurality of (for example, 2 to 10) second laminated sheets are overlapped, and the obtained laminate is rolled to obtain a laminated sheet (third laminated sheet) (step (II)). Thus, the step (I) and the step (II) can be alternately repeated until the desired number of constituent layers of the insulating heat conductive sheet is reached. In the example described here, the lamination sheets having the same number of laminations (first lamination sheets, second lamination sheets, etc.) are overlapped and rolled, but the lamination numbers are different from each other. It is also possible to roll the sheets by overlapping them.

  It is desirable to change the rolling direction when repeating the step (II). For example, in rolling performed to obtain the second laminated sheet, the rolling direction may be changed by 90 degrees from the direction of rolling performed to obtain the first laminated sheet. By rolling while changing the direction in this way, the PTFE network extends vertically and horizontally, and the strength of the sheet can be improved and the heat conductive filler can be firmly fixed to the PTFE matrix.

  When the number of constituent layers of the insulating heat conductive sheet is represented by the total number of mother sheets included in the insulating heat conductive sheet, the number of constituent layers can be, for example, 2 to 5000 layers. In order to increase the sheet strength, the number of layers is preferably 200 or more. Further, in order to reduce the thickness (for example, a sheet having a thickness of 1 mm or less), the number of layers is preferably 1500 layers or less. The greater the number of constituent layers, the higher the strength of the resulting sheet.

  At the beginning of rolling (the stage where the total number of mother sheets included is small), it is difficult to withstand high-strength rolling with low strength. And the solid fixation of the thermally conductive filler to the PTFE matrix becomes possible. The laminated structure (number of constituent layers) is also related to the thermal conductivity and insulating properties of the obtained sheet. Therefore, in order to obtain a sheet having sufficient thermal conductivity and insulation, the number of constituent layers is preferably 10 to 1000.

  Finally, a sheet having a target thickness, for example, about 0.1 to 3 mm, is produced, and then the forming aid is removed in step (III). Can be obtained. The removal of the molding aid in step (III) can be carried out according to a method appropriately selected from known methods according to the molding aid used. For example, a sheet-like material obtained by rolling may be heated to remove the molding aid by drying.

  After removing the molding aid, the sheet-like material obtained in step (III) may be pressure-molded (step (IV)). By including such a pressure forming step, the porosity of the insulating heat conductive sheet can be lowered, and the heat conductivity can be improved. The porosity of the sheet-like material after carrying out the step (II) is usually about 50 to 80%, but the porosity of the sheet-like material is reduced to 40% or less by carrying out the step (IV). Can be made. Furthermore, through this pressure forming step, the heat conductive fillers are more densely present, and the thermal resistance of the insulating heat conductive sheet can be further reduced. The pressure molding can be performed, for example, by pressing the sheet-like material at a temperature of 320 to 400 ° C. and a pressure of 0.05 to 50 MPa for 1 to 15 minutes. In addition, the porosity here is a value calculated | required by the measuring method performed in the below-mentioned Example.

  When impregnating the insulating heat conductive sheet with the impregnating material, the sheet-like material obtained by the step (III) (if the step (IV) is carried out, the sheet-like material obtained by the step (IV)) And impregnating the impregnating material (step (V)). The impregnating material is as described above.

  In the step (V), since it is easy to impregnate the impregnating material at a high impregnation rate in a short time, the sheet-like material obtained by the step (III) (when the step (IV) is performed, The sheet-like material obtained in the step (IV) is preferably immersed in an impregnating material and pressurized. Such an operation can be performed using a pressurized container.

  After taking out the sheet-like material from the pressurized container, the impregnating material on the surface is wiped off.

  Although the insulating heat conductive sheet of this embodiment can be obtained as mentioned above, the manufacturing method of the insulating heat conductive sheet of this embodiment is not restricted above.

  The insulating heat conductive sheet of this embodiment has favorable heat conductivity and insulation. Furthermore, since the insulating heat conductive sheet of this embodiment uses a fluororesin having high oil resistance, it is suitable for use in an oil environment. Therefore, the insulating heat conductive sheet according to the present embodiment is optimal as a heat radiating member for a motor for a vehicle (for example, a hybrid car and an electric car). It can be cooled with high efficiency over a long period of time. Moreover, the insulating heat conductive sheet of this embodiment can be used as a heat radiating member of a heat sink. The usage pattern in the vehicle motor is not limited to this. The insulating heat conductive sheet of this embodiment can be used also as a heat radiating member other than a vehicle motor (for example, a generator, an electronic device, etc.).

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these Examples. First, the evaluation method performed in this example will be described.

(Thermal resistance)
The heat dissipation of the insulating heat conductive sheets of Examples and Comparative Examples was evaluated by their thermal resistance. The measurement of thermal resistance was performed using the thermal characteristic evaluation apparatus 10 shown in FIGS. 1 (a) and 1 (b). The thermal property evaluation apparatus 10 has a heating element (heater block) 11 in the upper part and a radiator (cooling base plate configured to circulate cooling water) 12 in the lower part. The heating element 11 and the radiator 12 each have a rod 13 made of aluminum (A5052, thermal conductivity: 140 W / m · K) formed so as to be a cube having one side of 20 mm. A pair of pressure adjusting screws 14 penetrating the heat generating body 11 and the heat radiating body 12 are provided on the side portions of the pair of rods 13. A load cell 15 is provided between the pressure adjusting screw 14 and the heating element 11, whereby the pressure when the pressure adjusting screw 14 is tightened is measured. Three probes 16 (diameter 1 mm) of a contact displacement meter 17 are installed inside the rod 13 on the side of the radiator 12. The upper end portion of the probe 16 is in contact with the lower surface of the rod 13 on the upper side (the heating element 11 side) when the sample (insulating heat conductive sheet of each example and comparative example) is not disposed between the rods 13. The distance between the upper and lower rods 13 (the thickness of the sample) can be measured. A temperature sensor 18 of a thermometer 19 is attached to the back side of the heating element 11 and the upper and lower rods 13. Specifically, temperature sensors 18 are attached to one place of the heating element 11 and five places at equal intervals in the vertical direction of each rod 13.

First, the sample 20 (20 mm × 20 mm) was sandwiched between the pair of rods 13 from above and below. The pressure adjusting screw 14 was tightened, pressure was applied to the sample 20 to set the temperature of the heating element 11 to 150 ° C., and 20 ° C. cooling water was circulated through the radiator 12. Then, after the temperatures of the heating element 11 and the upper and lower rods 13 were stabilized, the temperature of the upper and lower rods 13 was measured by each temperature sensor 18. The heat flux passing through the sample 20 was calculated from the thermal conductivity (W / m · K) of the upper and lower rods 13 and the temperature gradient, and the temperature at the interface between the upper and lower rods 13 and the sample 20 was calculated. And using these, the thermal resistance (K / W) in the said pressure was computed using the thermal conductivity equation (Fourier's law). In addition, the thermal resistance was calculated | required about the case where the pressure of 200N was applied to the sample 20. FIG.
Q = −λgradT
R = 1 / λ (L / A)
Q: thermal flow rate per unit area gradT: temperature gradient L: thickness of sample (insulating thermal conductive sheet) A: rod area λ: thermal conductivity R: thermal resistance

(Break Down Voltage (BDV))
The insulating properties of the insulating heat conductive sheets of Examples and Comparative Examples were evaluated by their dielectric breakdown voltages. The dielectric breakdown voltage of the insulating heat conductive sheet of an Example and a comparative example was measured by the method based on the standard of JISC2110. The breakdown voltage was measured at a boosting rate of 1 kV / sec.

(Porosity)
The weight and volume of the insulating heat conductive sheet were measured, and the actual density was obtained from the result. Using this measured density and true density, the porosity was determined by the following equation.
Porosity (%) = (1−actual density / true density) × 100

Example 1
Boron nitride particles (Mizushima Alloy Iron Co., Ltd., product number “HP-40”, particle size 30 to 60 μm) as thermally conductive inorganic particles, and diamond particles (Henan Huanghe Shunfu Co., Ltd., product number “HHM-C”, Particle size 8-16 μm) and PTFE powder (manufactured by Daikin Industries, Ltd., product number “MP-104U”) were mixed at a mass ratio of 87.5: 2.5: 10. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading.

  The obtained paste-like mixture was rolled with a rolling roll to obtain a mother sheet (sheet-like formed body) having a thickness of 0.6 mm. A laminate obtained by superimposing the two mother sheets on each other was rolled through the rolling rolls to produce a laminate sheet (first laminate sheet). Next, two sheets of the obtained first laminated sheet were prepared as sheet-like molded bodies. These two first laminated sheets were superposed and laminated, and this laminate was rolled to produce a new laminated sheet (second laminated sheet). Next, two sheets of the obtained second laminated sheet were prepared as sheet-like molded bodies. These two second laminated sheets were laminated and laminated, and this laminate was rolled in a direction changed by 90 degrees from the first rolling direction to produce a new laminated sheet (third laminated sheet). . In this way, the process of superposing and rolling the obtained laminated sheet as a sheet-like formed body is repeated 6 times while changing the rolling direction by 90 degrees, and finally rolled with a thickness of about 0.25 mm. A sheet was obtained.

  Next, the obtained rolled sheet was dried at 150 ° C. for 30 minutes to remove the molding aid. Next, this rolled sheet was pressed at 380 ° C. and 7 MPa for 1 minute to obtain an insulating heat conductive sheet having a thickness of about 0.2 mm. The porosity of this insulating heat conductive sheet was 24%.

  Furthermore, in this example, the obtained insulating heat conductive sheet was impregnated with silicone oil as an impregnating agent. Specifically, silicone oil (Momentive Performance Materials Japan GK, product number “PDMS 100-J”) was added into the pressurized container, and the insulating heat conductive sheet was immersed therein. Compressed air was fed into the container, pressurized to 0.5 MPa, and held for 10 minutes to impregnate the insulating heat conductive sheet with silicone oil. After impregnation, the silicone oil on the surface of the insulating heat conductive sheet was wiped off to obtain an insulating heat conductive sheet impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 214 μm. The thermal resistance measured by the above method was 0.52 K / W, and the dielectric breakdown voltage was 58.4 kV / mm.

(Example 2)
Boron nitride particles (Mizushima Alloy Iron Co., Ltd., product number “HP-40”, particle size 30 to 60 μm) as thermally conductive inorganic particles, and diamond particles (Henan Huanghe Shunfu Co., Ltd., product number “HHM-C”, Particle size 8-16 μm) and PTFE powder (manufactured by Daikin Industries, Ltd., product number “MP-104U”) were mixed at a mass ratio of 85: 5: 10. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading. Using the obtained paste-like mixture, an insulating heat conductive sheet was produced by the same method as in Example 1. The porosity of this insulating heat conductive sheet was 26%.

  Furthermore, also in this example, as in Example 1, the insulating heat conductive sheet was impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 214 μm. The thermal resistance measured by the above method was 0.50 K / W, and the dielectric breakdown voltage was 58.4 kV / mm.

Example 3
Boron nitride particles (Mizushima Alloy Iron Co., Ltd., product number “HP-40”, particle size 30 to 60 μm) as thermally conductive inorganic particles, and diamond particles (Henan Huanghe Shunfu Co., Ltd., product number “HHM-C”, A particle ratio of 8 to 16 μm), PTFE powder (manufactured by Daikin Industries, product number “MP-104U”), and PFA powder (manufactured by Mitsui DuPont Fluorochemical Co., Ltd., product number “MP-10”). It was mixed at a ratio of 85: 5: 8: 2. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading. Using the obtained paste-like mixture, an insulating heat conductive sheet was produced by the same method as in Example 1. The porosity of this insulating heat conductive sheet was 32%.

  Furthermore, also in this example, as in Example 1, the insulating heat conductive sheet was impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 203 μm. The thermal resistance measured by the above method was 0.50 K / W, and the dielectric breakdown voltage was 57.0 kV / mm.

Example 4
Boron nitride particles (Mizushima alloy iron, product number “HP-40”, particle size 30-60 μm) as heat conductive inorganic particles and diamond particles (product number “HHM-C”, particle size “HHM-C”, particle size) 54-84 μm) and PTFE powder (product number “MP-104U” manufactured by Daikin Industries, Ltd.) were mixed at a mass ratio of 85: 5: 10. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading. Using the obtained paste-like mixture, an insulating heat conductive sheet was produced by the same method as in Example 1. The porosity of this insulating heat conductive sheet was 24%.

  Furthermore, also in this example, as in Example 1, the insulating heat conductive sheet was impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 210 μm. The thermal resistance measured by the above method was 0.53 K / W, and the dielectric breakdown voltage was 50.0 kV / mm.

(Comparative Example 1)
Boron nitride particles (Mizushima alloy iron, product number “HP-40”, particle size 30 to 60 μm), PTFE particles (manufactured by Daikin Industries, product number “MP-104U”) and PFA powder as thermally conductive inorganic particles (Mitsui / DuPont Fluoro Chemical Co., Ltd., product number “MP-10”) was mixed at a mass ratio of 90: 8: 2. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading. Using the obtained paste-like mixture, an insulating heat conductive sheet was produced by the same method as in Example 1. The porosity of this insulating heat conductive sheet was 31%.

  Further, in this comparative example, as in Example 1, the insulating heat conductive sheet was impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 252 μm. The thermal resistance measured by the above method was 0.55 K / W, and the dielectric breakdown voltage was 48.0 kV / mm.

(Comparative Example 2)
Boron nitride particles (Mizushima alloy iron, product number “HP-40”, particle size 30-60 μm) as thermally conductive inorganic particles, and silicon nitride particles (electrochemical industry, product number “NP” as thermally conductive inorganic particles) -200 ", average particle size 1 μm), PTFE powder (product number" MP-104U "manufactured by Daikin Industries, Ltd.) and PFA powder (product number" MP-10 "manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) The mass ratio was 85: 5: 8: 2. A paste-like mixture was obtained by adding 40 parts by mass of decane as a molding aid to 100 parts by mass of the mixture and kneading. Using the obtained paste-like mixture, an insulating heat conductive sheet was produced by the same method as in Example 1. The porosity of this insulating heat conductive sheet was 34%.

  Further, in this comparative example, as in Example 1, the insulating heat conductive sheet was impregnated with silicone oil. The insulating heat conductive sheet impregnated with silicone oil had a thickness of 225 μm. The thermal resistance measured by the above method was 0.61 K / W, and the dielectric breakdown voltage was 64.9 kV / mm.

  The above results are summarized in Table 1.

  The insulating heat conductive sheets of Examples 1 to 4 in which diamond particles and boron nitride particles are included as fillers are compared with the insulating heat conductive sheet of Comparative Example 1 in which only boron nitride particles are included as fillers. The thermal resistance was low (high heat dissipation) and the dielectric breakdown voltage was high (high insulation). In addition, the insulating heat conductive sheet of Comparative Example 2 including silicon nitride particles instead of diamond particles in addition to the boron nitride particles had a higher dielectric breakdown voltage than the insulating heat conductive sheet of Comparative Example 1. The heat resistance of things has also increased. Thus, the insulating heat conductive sheet of the present invention containing diamond particles and heat conductive inorganic particles excluding diamond particles as a filler is more in comparison with the conventional insulating heat conductive sheet not containing diamond particles. It was confirmed that both high insulation and higher heat dissipation can be realized.

  Since the insulating heat conductive sheet of the present invention has high heat dissipation and high insulation and is excellent in handling properties, it can be suitably used as a heat dissipation member for electronic devices and vehicles.

DESCRIPTION OF SYMBOLS 10 Thermal characteristic evaluation apparatus 11 Heat generating body 12 Heat radiating body 13 Rod 14 Pressure adjusting screw 15 Load cell 16 Probe 17 Contact-type displacement meter 18 Temperature sensor 19 Thermometer 20 Sample

Claims (4)

An insulating heat conductive sheet comprising a fluororesin containing polytetrafluoroethylene and a heat conductive filler,
The thermally conductive filler includes diamond particles and thermally conductive inorganic particles excluding the diamond particles.
Insulating heat conductive sheet. The thermally conductive inorganic particles are boron nitride particles;
The insulating heat conductive sheet according to claim 1. The thermal resistance is less than 0.55 K / W, and the dielectric breakdown voltage is 50 kV / mm or more.
The insulating heat conductive sheet according to claim 1 or 2. The insulating heat conductive sheet has a porous structure;
Further comprising an impregnation material impregnated in the insulating heat conductive sheet,
The insulating heat conductive sheet according to any one of claims 1 to 3.

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