Thermal Conductive Sheet

Abstract

To provide a heat-conductive sheet that excels in heat conductivity, flexibility, and insulation and can be easily molded.SOLUTION: A heat-conductive sheet is prepared by blending an acrylic resin composed of an acrylic monomer and an acrylic polymer with silicon carbide, soft ferrite and a plasticizing agent. The sheet has a heat conductivity of 2 W / m K or more, an Asker C hardness of 2 to 10, and a volume resistivity of 1010 Ω cm or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermally conductive sheet made of an acrylic resin composition for thermal dissipation materials and having excellent thermal conductivity, moldability, flexibility and insulating properties. [Background technology]

[0002] Conventionally, thermally conductive materials have been considered that are made by compounding a thermally conductive filler such as silicon carbide or alumina (aluminum oxide) with a flexible resin. Thermally conductive sheets made by forming this type of thermally conductive material into a sheet are used by being placed between a heat generating body such as an electric or electronic component and a heat dissipating body such as a heat sink or a housing panel. When the thermally conductive sheet is placed in this way, the heat generated by the heat generating body can be efficiently released to the heat dissipating body. In addition to thermal conductivity, the thermally conductive sheet is required to have insulation properties that prevent conduction between the heat generating body and the heat dissipating body when the sheet is placed, and flexibility that allows the contact area to be increased by deforming the sheet according to the surface shape of the heat conducting body.

[0003] Conventionally, silicone-based resins have often been used as flexible resins, but silicone-based resins have problems such as insufficient flexibility, expensive resin materials, time required for curing, and the possibility of poor contact due to the generation of low molecular weight siloxane. In order to solve these problems, the applicant of the present application has proposed a thermally conductive material in which a thermally conductive filler is blended with an acrylic resin obtained by polymerizing a monomer containing an acrylic acid ester (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-7129 A Summary of the Invention [Problem to be solved by the invention]

[0005] Silicon carbide, which has been generally used as a thermally conductive filler, has very good thermal conductivity but poor insulation. Therefore, in a thermally conductive material in which a large amount of silicon carbide is blended with an acrylic resin, the thermal conductivity is improved but the insulation is reduced. In addition, alumina, which has been generally used as another thermally conductive filler, has relatively good thermal conductivity and excellent insulation, although it is inferior to silicon carbide. However, a thermally conductive material in which a large amount of alumina is blended with an acrylic resin has a problem of insufficient viscosity and poor formability. Therefore, the present invention aims to provide an acrylic resin thermally conductive sheet that is excellent in thermal conductivity, flexibility, insulation, and formability into a sheet. [Means for solving the problem]

[0006] The present invention, which has solved the above-mentioned problems, is a thermally conductive sheet obtained by blending silicon carbide, soft ferrite, and a plasticizer with an acrylic resin consisting of 20 to 35 mass% of an acrylic monomer and 65 to 80 mass% of an acrylic polymer, wherein 230 to 250 mass parts of the silicon carbide, 10 to 20 mass parts of the soft ferrite, and 40 to 55 mass parts of the plasticizer are blended with 100 mass parts of the acrylic resin, and the sheet after curing has a thermal conductivity of 2 W / m K or more, an Asker C hardness of 2 to 10, and a volume resistivity of 10 10 It is characterized by a resistance of Ω·cm or more.

[0007] The present invention may further include the following configurations or characteristics. The soft ferrite may be a Ni-Zn ferrite powder having a median diameter of 20 to 40 μm as measured by a laser diffraction apparatus. The silicon carbide may be a powder having a median diameter of 60 to 80 μm as measured by a laser diffraction apparatus, and the plasticizer may be a trimellitic acid alkyl ester. The thermal conductive material of the thermal conductive sheet before curing may have a viscosity of 100 to 200 Pa s as measured by a Brookfield viscometer under conditions of rotor No. 7, a rotation speed of 2 rpm, and 25° C.

[0008] The applicant of the present application has developed a thermal conductive material made of acrylic resin and silicon carbide, which has a thermal conductivity of 2 W / m K or more and a thermal conductivity of 10 10 They discovered that it is possible to easily mold a flexible thermally conductive sheet with an Asker C hardness of 2 to 10 while still having a volume resistivity of Ω·cm or more.

[0009] Thermally conductive sheets can be produced in a short time by applying a thermally conductive material using a coater or the like, and then forming and curing the material into a sheet. However, in order to apply the material using a coater or the like, it is preferable that the viscosity of the material to be applied is within a certain range. The applicant of the present application discovered that by blending soft ferrite in addition to silicon carbide and a plasticizer, it is possible to adjust the viscosity of the thermally conductive material to the range of 100 to 200 Pa s, and form the material into a thick thermally conductive sheet of 2 mm or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The thermally conductive sheet (or thermally conductive material) of the present invention contains, as essential components, a conventionally known acrylic resin, silicon carbide, soft ferrite, and a plasticizer.

[0011] The acrylic resin of the present invention is obtained by radical (co)polymerization of a conventionally known acrylic monomer and an acrylic polymer.

[0012] As the acrylic resin in the present invention, various resins containing acrylic acid esters can be used. For example, acrylic resins such as ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-hexyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, octyl (meth)acrylate, i-octyl (meth)acrylate, i-myristyl (meth)acrylate, lauryl (meth)acrylate, nonyl (meth)acrylate, i-nonyl (meth)acrylate, i-decyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, and i-stearyl (meth)acrylate can be used. These acrylic resins may be used alone or in combination of two or more.

[0013] The acrylic resin in the present invention is obtained by (co)polymerizing an acrylic monomer and an acrylic polymer obtained by polymerizing the acrylic monomer by a known polymerization method. The acrylic monomer and the acrylic polymer in the acrylic resin are preferably contained in an amount of 20 to 35 mass% and 65 to 80 mass%, respectively, and more preferably contained in an amount of 25 to 30 mass% and 70 to 75 mass%, respectively.

[0014] Silicon carbide in the present invention is a thermally conductive filler that is blended to increase the thermal conductivity of the thermally conductive sheet. Silicon carbide is a substance that has a thermal conductivity of 200 W / m·K or more by itself, and the more silicon carbide is blended with the acrylic resin, the higher the thermal conductivity of the resulting thermally conductive sheet. However, silicon carbide is a semiconductor (e.g., volume resistivity: about 10 8 It is also a material with a high hardness (for example, Vickers hardness: 23.0 GPa) and a low viscosity (Ω·cm) of acrylic resin. Therefore, if the amount of silicon carbide mixed with the acrylic resin is too high, problems may occur with the insulation and flexibility of the thermal conductive sheet.

[0015] The silicon carbide used in the present invention is a powder for grinding and abrasives known in the art, and has a median diameter (D50) measured by a laser diffraction device of 60 to 80 μm, more preferably 65 to 75 μm. When the median diameter of silicon carbide is within the above range, the thermally conductive sheet of the present invention can have a thermal conductivity of 2 W / m·K or more and a viscosity that allows it to be molded into a sheet of a certain thickness (for example, 2 mm or more). If the median diameter of silicon carbide is smaller than the above range, a high thermal conductivity path cannot be formed in the thermally conductive sheet of the present invention, and there is a risk that the thermal conductivity of 2 W / m·K or more cannot be obtained. In addition, if the median diameter of silicon carbide is larger than the above range, there is a risk that clogging occurs in a coater device or the like when applying the thermally conductive material, or that voids (holes) generated during the molding of the sheet cannot be removed.

[0016] Soft ferrite has magnetic properties and is generally used to impart magnetism to things it is mixed with. However, the soft ferrite in the present invention is a filler that is mixed in small amounts to adjust the thermal conductivity, insulation, and flexibility of the thermal conductive sheet and the viscosity of the thermal conductive material before it is molded and cured into a thermal conductive sheet, and is different from soft ferrite that is mixed in large amounts with the intention of imparting magnetism to the thermal conductive sheet.

[0017] The soft ferrite used in the present invention is a Ni-Zn-based soft magnetic ferrite powder, and has a median diameter (D50) measured by a laser diffraction device of 20 to 40 μm, more preferably 25 to 35 μm. When the median diameter of the soft ferrite is within the above range, the thermal conductive material of the present invention has appropriate thermal conductivity, insulating properties, and viscosity, and can be easily formed into a sheet. When the median diameter of the soft ferrite is smaller than the above range, the viscosity of the thermal conductive material of the present invention cannot be sufficiently increased, and it may not be possible to form it into a sheet. When the median diameter of the soft ferrite is larger than the above range, a conductive path is easily formed in the thermal conductive sheet of the present invention, and the thermal conductive material has a certain level of insulating properties (for example, volume resistivity; 10 10 There is a risk that the material will no longer have a dielectric constant (Ω·cm or more).

[0018] The plasticizer used in the present invention is a non-radically polymerizable trimellitic acid alkyl ester that does not radically polymerize with acrylic monomers or acrylic polymers. The plasticizer affects the viscosity of the thermal conductive material and the moldability and flexibility (or hardness) of the thermal conductive sheet.

[0019] The thermally conductive material or thermally conductive sheet of the present invention may contain a polymerization initiator and an antioxidant. The polymerization initiator affects the reaction rate of the thermally conductive material and can improve the productivity of the thermally conductive sheet. The antioxidant suppresses the oxidation of the thermally conductive material in air and can adjust the usable time (pot life) of the thermally conductive material.

[0020] The thermally conductive material or thermally conductive sheet of the present invention may contain conventionally known additives to the extent that they do not interfere with the object of the present invention, such as polyfunctional fillers, reinforcing fibers, release agents, defoamers, dispersants, organic flame retardants, inorganic flame retardants such as metal hydroxides, coupling agents, pigments, and antistatic agents.

[0021] [How to mix ingredients] The materials used in the present invention were subjected to a conventional kneading machine to obtain a thermal conductive material. Examples of the kneading machine include a mixer, a roll mill, a Banbury mixer, a kneader, a pressure kneader, a continuous kneader such as a twin-screw kneader, etc., but these machines are not particularly limited. In addition, when kneading the materials, it is possible to reduce pressure or degas the material, if necessary.

[0022] [Method of manufacturing thermal conductive sheets] The thermally conductive material obtained by kneading the various materials used in the present invention with a kneader was coated on a PET film to a specified thickness with a conventionally known coater device, etc., and formed into a sheet. The thermally conductive material formed into a sheet was then heated and cured in a heating furnace at a specified temperature and time to obtain a thermally conductive sheet.

[0023] [Viscosity of thermal conductive material before curing] After kneading the various materials used in the present invention with a kneader, the thermally conductive material in a state before being molded and cured into a sheet by a coater or the like was subjected to viscosity measurement under conditions of a temperature of 25°C, using a Brookfield viscometer (B-type rotational viscometer) with a rotor No. 7 and a rotation speed of 2 revolutions per minute. In order to mold the thermally conductive sheet of the present invention, it is preferable that the viscosity of the thermally conductive material before molding is 100 to 200 Pa·s. When the viscosity is within the above range, the thermally conductive material of the present invention can be easily molded into a sheet by a coater or the like and its shape can be easily maintained. When the viscosity is lower than the above range, the fluidity is high, making it difficult to maintain the shape as a sheet or to create a thick sheet. When the viscosity is higher than the above range, the fluidity is low, making it difficult to apply the material by a coater or the like and to remove voids (holes) mixed inside the sheet.

[0024] [Sheet hardness (flexibility)] The hardness (flexibility) of the molded and cured thermally conductive sheet was measured using a durometer (manufactured by Kobunshi Keiki Co., Ltd.; product name "Asker Rubber Hardness Meter C Type") in accordance with the standard of JIS K7312 under the condition of a temperature of 25°C. The thermally conductive sheet of the present invention preferably has an Asker C hardness value of 2 or more and 10 or less. The lower the hardness value, the higher the flexibility, and when the thermally conductive sheet is attached to a heat generating body or a heat dissipating body, the thermally conductive sheet deforms according to the surface shape of the heat generating body or the heat dissipating body, and the contact area can be increased (thermal conduction efficiency can be increased). When the Asker C hardness is within the above range, the thermally conductive sheet of the present invention can deform according to the shape of the heat generating body or the heat dissipating body even if the surface of the heat generating body or the heat dissipating body has an uneven shape, and a sufficient contact area can be secured. When the Asker C hardness value is higher than the above range, depending on the surface shape of the heat generating body or the heat dissipating body, the contact area with the thermally conductive sheet cannot be secured sufficiently, and it becomes difficult to achieve the expected thermal conduction efficiency. When the Asker C hardness value is lower than the above range, although the flexibility is high, the durability of the thermally conductive sheet is low and it is easily torn.

[0025] [Thermal conductivity of sheet (thermal conductivity)] The thermal conductivity of the molded and cured thermally conductive sheet was measured at a temperature of 25°C using a rapid thermal conductivity meter (Kyoto Electronics Manufacturing Co., Ltd.; model number "QTM-500"). The thermally conductive sheet of the present invention preferably has a thermal conductivity of 2 W / m·K or more. In a thermally conductive sheet, the higher the thermal conductivity, the better, but if the thermal conductivity is lower than the above range, heat cannot be sufficiently conducted from the heat generating body to the heat dissipating body, and there is a risk of problems such as thermal runaway occurring.

[0026] [Volume resistivity of sheet (insulation)] The volume resistivity of the molded and cured thermally conductive sheet was measured at a temperature of 25° C. in accordance with the JIS K6911 standard using a resistivity meter (manufactured by Mitsubishi Chemical Corporation; product number "MCP-HT450"). 10 It is preferable that the volume resistivity is Ω·cm or more. The higher the volume resistivity, the higher the insulating property, and when the thermally conductive sheet is placed between a heating element and a heat sink, it is possible to make it difficult for a current generated from either the heating element or the heat sink to be transmitted to the other (to suppress conduction). In the thermally conductive sheet of the present invention, the higher the volume resistivity, the more preferable it is. However, if the volume resistivity is lower than the above range, for example, a current generated outside the electronic / electrical device (the heat sink side) may be transmitted to the inside of the electronic / electrical device (the heating element side) where an IC chip is located, which may cause problems such as damage to the device or malfunction. EXAMPLES

[0027] The present invention will be described in more detail below with reference to examples. However, the examples described below do not limit the present invention, and all modifications that do not deviate from the spirit of the present invention are considered to be included in the technical scope of the present invention. In addition, the formulations and characteristic evaluation results of the examples and comparative examples described below are shown in Tables 1 to 6. The unit of formulation in Tables 1 to 6 is "parts by mass" unless otherwise specified. Regarding the "thermal conductivity evaluation" in Tables 1 to 6, those that have a thermal conductivity of 2 W / m·K or more that is 10 times higher than that of an acrylic resin that does not contain any filler (about 0.2 W / m·K) and can suitably dissipate heat from a heat generating body to a heat sink side are marked as "○", and those that are less than 2 W / m·K are marked as "×". Regarding the "volume resistivity evaluation" in Tables 1 to 6, those that have a thermal conductivity of 10 times higher than that of an acrylic resin that does not contain any filler (about 0.2 W / m·K), and can suitably dissipate heat from a heat generating body to a heat sink side are marked as "○", and those that are less than 2 W / m·K are marked as "×". In addition, regarding the "volume resistivity evaluation" in Tables 1 to 6, 10 Those with a resistance of Ω·cm or more are marked with a "○", and those with a resistance of 10 10 Those with a resistance of less than Ω·cm were marked as "X".

[0028] [Examples 1 to 9 and Comparative Examples 1 to 10] To 100 parts by mass of acrylic resin (manufactured by Nippon Shokubai Co., Ltd.; product name "HD-A218") formed by polymerization of acrylic monomer and acrylic polymer, 220 to 260 parts by mass of SiC for grinding and abrasives (manufactured by Pacific Random Co., Ltd.; product name "NG F180") as silicon carbide, 0 to 25 parts by mass of soft magnetic ferrite (manufactured by Toda Kogyo Co., Ltd.; product name "BSN-714") as soft ferrite, and 40 parts by mass of trimellitic acid alkyl ester (manufactured by ADEKA; product name "C-880") as plasticizer were added, and a thermal conductive material was formed using a kneader, and the thermal conductive sheet was obtained by molding and curing using a coater device or the like. The composition and the evaluation results are shown in Table 1.

[0029] [Examples 10 to 18 and Comparative Examples 11 to 18] To 100 parts by mass of acrylic resin, 220 to 260 parts by mass of silicon carbide, 10 to 25 parts by mass of soft ferrite, and 45 parts by mass of plasticizer were added, and a thermally conductive material was prepared using a kneader, which was then molded and cured using a coater or the like to obtain a thermally conductive sheet. The formulation and the evaluation results are shown in Table 2.

[0030] [Examples 19 to 27 and Comparative Examples 19 to 26] To 100 parts by mass of acrylic resin, 220 to 260 parts by mass of silicon carbide, 10 to 25 parts by mass of soft ferrite, and 50 parts by mass of plasticizer were added, and a thermally conductive material was prepared using a kneader, and the material was molded and cured using a coater or the like to obtain a thermally conductive sheet. The formulation and the evaluation results are shown in Table 3.

[0031] [Examples 28 to 36 and Comparative Examples 27 to 34] To 100 parts by mass of acrylic resin, 220 to 260 parts by mass of silicon carbide, 10 to 25 parts by mass of soft ferrite, and 55 parts by mass of plasticizer were added, and a thermally conductive material was prepared using a kneader, which was then molded and cured using a coater or the like to obtain a thermally conductive sheet. The formulation and the evaluation results are shown in Table 4.

[0032] [Comparative Examples 35 to 45] To 100 parts by mass of acrylic resin, 230 to 260 parts by mass of silicon carbide, 10 to 25 parts by mass of soft ferrite, and 60 parts by mass of plasticizer were added, and a thermally conductive material was prepared using a kneader, and the material was molded and cured using a coater or the like to obtain a thermally conductive sheet. The formulation and the evaluation results are shown in Table 5.

[0033] [Comparative Examples 46 to 51] To 100 parts by mass of acrylic resin, 260 parts by mass of silicon carbide, 10 to 30 parts by mass of alumina (product name "AX35-125", average particle size 35 μm, manufactured by Nippon Steel Chemical & Material Co., Ltd.) for comparison with soft ferrite, and 40 to 60 parts by mass of plasticizer were added, and a thermal conductive material was obtained using a kneader. The composition and evaluation results are shown in Table 6.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] [Table 4]

[0038] [Table 5]

[0039] [Table 6]

[0040] From Comparative Examples 1 to 3 in Table 1, it was found that in the composition of the present invention, in order to form a thermally conductive sheet, the content of soft ferrite needs to be at least 10 parts by mass.

[0041] From the comparison between Example 1 and Comparative Example 3 in Table 1, the comparison between Example 10 and Comparative Example 11 in Table 2, the comparison between Example 19 and Comparative Example 19 in Table 3, the comparison between Example 28 and Comparative Example 27 in Table 4, and the comparison between Comparative Example 36 and Comparative Example 37 in Table 5, it can be seen that in the composition of the present invention, when the amount of silicon carbide blended was 260 parts by mass, the volume resistivity of the thermal conductive sheet was 10 10 It has been confirmed that the volume resistivity of the thermal conductive paste is less than 10 Ω·cm, and when the amount of silicon carbide blended is 260 parts by mass or more, 10 It was found that the resistivity was less than Ω·cm.

[0042] From the comparison of Examples 3, 6, 9 and Comparative Example 9 with Comparative Examples 4-6 and Comparative Example 10 in Table 1, the comparison of Examples 12, 15, 18 and Comparative Example 17 with Comparative Examples 12-14 and Comparative Example 18 in Table 2, the comparison of Examples 21, 24, 27 and Comparative Example 25 with Comparative Examples 20-22 and Comparative Example 26 in Table 3, the comparison of Examples 30, 33, 36 and Comparative Example 33 with Comparative Examples 28-30 and Comparative Example 34 in Table 4, and the comparison of Comparative Examples 38, 41 and Comparative Example 44 with Comparative Examples 39, 42 and Comparative Example 45 in Table 5, it was confirmed that in the formulation of the present invention, when the blending amount of soft ferrite was 25 parts by mass, the Asker C hardness of the thermal conductive sheet exceeded 10, and when the blending amount of soft ferrite was 25 parts by mass or more, the Asker C hardness of the thermal conductive sheet exceeded 10. In addition, when combined with the results obtained from the above-mentioned Comparative Examples 1-3, it was found that the blending amount of soft ferrite blended in the thermal conductive sheet of the present invention is preferably 10 to 20 parts by mass.

[0043] From Comparative Examples 7 to 10 in Table 1, Comparative Examples 15 to 18 in Table 2, Comparative Examples 23 to 26 in Table 3, and Comparative Examples 31 to 34 in Table 4, it was confirmed that in the formulation of the present invention, when the amount of silicon carbide was 220 parts by mass, the thermal conductivity of the thermal conductive sheet was less than 2 W / m·K, and when the amount of silicon carbide was 220 parts by mass or less, the thermal conductivity of the thermal conductive sheet was less than 2 W / m·K. In addition, when combined with the result when the amount of silicon carbide was 260 parts by mass, it was found that the amount of silicon carbide blended in the thermal conductive sheet of the present invention is preferably 230 to 250 parts by mass. However, in Comparative Examples 43 to 45 in Table 5, the thermal conductivity of the thermal conductive sheet was less than 2 W / m·K despite the amount of silicon carbide being 230 parts by mass. This is thought to be because when a large amount of plasticizer is blended, the filler in the thermal conductive sheet becomes unevenly distributed (settled due to gravity), making it impossible to form an efficient thermal conduction path.

[0044] From Comparative Examples 46 to 51 in Table 6, it was found that when alumina was added in the same amount as soft ferrite in the formulation of the present invention, the viscosity of the thermal conductive material was insufficient and it was difficult to form it into a sheet.

[0045] From the above, it has been found that the present invention provides a thermally conductive sheet molded from a thermally conductive material containing 100 parts by mass of acrylic resin, 230 to 250 parts by mass of silicon carbide, 10 to 20 parts by mass of soft ferrite, and 40 to 55 parts by mass of plasticizer, which has excellent flexibility, thermal conductivity, and insulation properties.

Claims

1. A thermally conductive sheet comprising an acrylic resin containing 20 to 35 mass% of an acrylic monomer and 65 to 80 mass% of an acrylic polymer, and further including silicon carbide, soft ferrite, and a plasticizer; Relative to 100 parts by mass of the acrylic resin, 230 to 250 parts by mass of the silicon carbide; 10 to 20 parts by mass of the soft ferrite; and 40 to 55 parts by mass of the plasticizer, After curing, the thermal conductivity of the sheet is 2 W / m K or more, the Asker C hardness is 2 to 10, and the volume resistivity is 10 １０ A thermally conductive sheet having a resistivity of Ω·cm or more.

2. 2. The thermal conductive sheet according to claim 1, wherein the soft ferrite is a Ni-Zn ferrite powder having a median diameter of 20 to 40 μm as measured by a laser diffraction device.

3. 3. The thermal conductive sheet according to claim 1, wherein the silicon carbide is a powder having a median diameter of 60 to 80 μm as measured by a laser diffraction device.

4. The thermal conductive sheet according to any one of claims 1 to 3, wherein the plasticizer is an alkyl trimellitate ester.

5. The thermal conductive material of the thermal conductive sheet before curing has a viscosity of 100 to 200 Pa s measured by a Brookfield viscometer under conditions of rotor No. 7, a rotation speed of 2 rpm, and 25 ° C. The thermal conductive sheet according to any one of claims 1 to 4.

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