Heat conductive sheet

Abstract

To provide a heat conductive sheet which is excellent in a product life cycle.SOLUTION: A heat conductive sheet contains a resin, and a heat conductive filler, wherein when a ratio R40 / R20 of a heat resistance value R40 per 1 mm measured by applying a fastening torque of 40 cN m to a heat resistance value R20 per 1 mm measured by applying a fastening torque of 20 cN m is 0.62 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] As heat-generating electronic components, such as central processing units (CPUs) in personal computers, become smaller and more powerful, the amount of heat generated per unit area by these components has become extremely large. This amount of heat can reach approximately 20 times that of an iron. To prevent these heat-generating electronic components from breaking down over the long term, they must be cooled. Metal heat sinks and housings are used for cooling. However, when a heat-generating electronic component is placed directly in contact with a heat sink, microscopic air exists at the interface, which can impede heat conduction. Therefore, to efficiently transfer heat, a thermally conductive material is often placed between the heat-generating electronic component and the heat sink.

[0003] Thermally conductive materials include thermally conductive spacers, thermally conductive sheets, and thermally conductive greases, which are made by filling thermosetting resins with thermally conductive fillers. Thermally conductive spacers are thick, highly flexible sheets that can conform to the uneven shapes of mating materials. Thermally conductive sheets are relatively thin sheets that are easy to handle and can improve the thermal conductivity between heat-generating electronic components and heat sinks while ensuring insulation. Thermally conductive grease is made by filling a fluid resin with a thermally conductive filler, which allows for a high degree of freedom in application shape and can reduce thermal resistance by applying it thinly.

[0004] For example, a known thermally conductive sheet has a configuration in which silicone composition layers containing a thermally conductive filler are laminated on both sides of a reinforcing layer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-126642 Summary of the Invention [Problem to be solved by the invention]

[0006] With the rapid miniaturization, high integration, and high output of electronic components in recent years, the operating temperatures of heat-generating electronic components have risen, and higher voltages are being applied between the heat-generating electronic components and heat sinks. Therefore, there is a demand for further improvements in thermal conductivity and insulation, especially for thinly molded thermally conductive sheets.

[0007] Furthermore, gaps between heat-generating electronic components and thermally conductive sheets, or between heat sinks and thermally conductive sheets, reduce thermal conductivity. Therefore, thermally conductive sheets are sometimes fastened to heat-generating electronic components to ensure close contact between the heat-generating electronic components and heat sinks. However, fastening a thermally conductive sheet with high torque can cause fastening components to sink into the thermally conductive sheet at the fastened portion or cause the heat-generating electronic component to lift off the thermally conductive sheet at a distance from the fastened portion, resulting in reduced thermal resistance and insulation. Alternatively, fastening a thermally conductive sheet with high torque can cause localized stress concentrations, resulting in marks or tears on the thermally conductive sheet, potentially shortening its product lifespan.

[0008] Therefore, there is a need for a thermally conductive sheet that, when tightened to a heat-generating electronic component with a torque applied to achieve a predetermined thermal resistance, can achieve high heat dissipation even with a low torque, thereby reducing the risk of marks or tears at the tightened portion and providing a long product life.

[0009] The present invention has been made in view of the above problems, and has an object to provide a thermally conductive sheet having an excellent product life. [Means for solving the problem]

[0010] That is, the present invention is as follows. [1] resin and a thermally conductive filler, The ratio R40 / R20 of the thermal resistance per 1 mm measured with a tightening torque of 20 cN m to the thermal resistance per 1 mm measured with a tightening torque of 40 cN m is 0.62 or less. Thermally conductive sheet. [2] The thermal resistance value R20 is 0.50°C / W·mm or less. The thermally conductive sheet according to [1]. [3] The thermal resistance value R40 is 0.30°C / W mm or less. The thermally conductive sheet according to [1] or [2]. [4] A reinforcing material and a resin layer laminated on the front and back surfaces of the reinforcing material, the resin layer contains the resin and the thermally conductive filler; The thermally conductive sheet according to any one of [1] to [3]. [5] The thermally conductive filler contains agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less. The thermally conductive sheet according to any one of [1] to [4]. [6] the ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN m is 0.65 or more; The thermally conductive sheet according to any one of [1] to [5]. [7] The thermal resistance value R60 per mm measured with a tightening torque of 60 cN m is 0.25°C / W mm or less. The thermally conductive sheet according to any one of [1] to [6]. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a thermally conductive sheet having an excellent product life. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view illustrating an example of a thermally conductive sheet according to an embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view showing an example of a use of the thermally conductive sheet of the present embodiment. [Figure 3] 1 is a graph showing changes in thermal resistance value with respect to tightening torque in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below, but the present invention is not limited to this and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0014] 1. Thermally conductive sheet The thermally conductive sheet of this embodiment contains a resin and a thermally conductive filler, and has a ratio R40 / R20 of 0.62 or less between the thermal resistance value R20 per mm measured when a tightening torque of 20 cN m is applied and the thermal resistance value R40 per mm measured when a tightening torque of 40 cN m is applied.

[0015] A schematic cross-sectional view showing an example of the thermally conductive sheet of this embodiment is shown in Fig. 1. As shown in Fig. 1, the thermally conductive sheet 1 of this embodiment is not particularly limited as long as it is a sheet containing a resin and a thermally conductive filler, but may be in an embodiment having a resin layer 10 containing a resin and a thermally conductive filler, or in an embodiment further having a reinforcing material 20, with the resin layer 10 laminated on the front and back surfaces of the reinforcing material 20.

[0016] Figure 2 shows a cross-sectional view of a thermally conductive sheet in use. As shown in Figure 2, the thermally conductive sheet 1 is positioned between a heat-generating electronic component 2 and a heat sink 3. If there is a gap between the heat-generating electronic component 2 and the thermally conductive sheet 1, or between the heat sink 3 and the thermally conductive sheet 1, the thermal resistance at these interfaces increases, reducing overall thermal conductivity. Therefore, to ensure close contact between the heat-generating electronic component 2 and the heat sink 3, the thermally conductive sheet 1 is sometimes fastened to the heat-generating electronic component 2 or the heat sink 3 using fastening screws 4 or similar. However, if the thermally conductive sheet is fastened with a high torque, the fastening parts may sink into the thermally conductive sheet at the fastened area, or the heat-generating electronic component may lift off the thermally conductive sheet at a distance from the fastened area. Furthermore, if the thermally conductive sheet is fastened with a high torque, it cannot withstand localized stress concentrations, causing the thermally conductive sheet 1 to deteriorate, such as leaving marks or tearing, at the fastened area, shortening its product lifespan.

[0017] In this embodiment, "tightening torque" refers to the rotational moment (cN·m) required when tightening a fastening screw.

[0018] As such, even when using the same thermally conductive sheet, the thermal conductivity exhibited varies depending on the tightening torque, so in order to achieve a predetermined thermal conductivity, the thermally conductive sheet must be fixed with a tightening torque of a certain level or more. However, if the tightening torque is too high, the thermally conductive sheet may be torn or damaged, or the insulating properties may be reduced at such damaged locations, thereby shortening the product life of the thermally conductive sheet.

[0019] In contrast, in this embodiment, the ratio R40 / R20, between the thermal resistance per mm R20 measured when a tightening torque of 20 cN m is applied and the thermal resistance per mm R40 measured when a tightening torque of 40 cN m is applied, is reduced, thereby specifying that thermal conductivity can be achieved even with a low tightening torque. This makes it difficult for the product life of the thermal conductive sheet to be impaired, even when tightened with a specified tightening torque to achieve the specified thermal conductivity. The configuration of the thermal conductive sheet is described in detail below.

[0020] 1.1.Thermal resistance value for tightening torque The ratio R40 / R20 of the thermal resistance per mm R20 measured when a tightening torque of 20 cN m is applied to the thermal resistance per mm R40 measured when a tightening torque of 40 cN m is 0.62 or less, and is preferably 0 to 0.60, 0.10 to 0.58, 0.20 to 0.56, or 0.30 to 0.54. When the ratio R40 / R20 is 0.62 or less, a predetermined thermal conductivity can be exhibited even when tightened with a low tightening torque, which in turn tends to further improve the product life.

[0021] Furthermore, the ratio R60 / R40 of the thermal resistance R40 to the thermal resistance R60 per mm measured when a tightening torque of 60 cN·m is preferably 0.65 or greater, 0.70 to 1.00, 0.75 to 0.96, 0.80 to 0.94, or 0.85 to 0.92. An R60 / R40 ratio of 0.65 or greater indicates that the upper limit at which thermal conductivity does not increase easily even with an increased tightening torque is being approached. This eliminates the need to tighten with an unnecessarily high tightening torque in order to improve thermal conductivity, which in turn tends to improve product life.

[0022] Furthermore, the ratio R60 / R20 of the thermal resistance value R20 to the thermal resistance value R60 is preferably 0.36 to 0.54, 0.38 to 0.52, 0.40 to 0.50, or 0.42 to 0.48. When the ratio R60 / R20 is within the above range, the thermal conductivity tends to be further improved depending on the tightening torque.

[0023] The thermal resistance value R20 is preferably 0.50°C / W mm or less, 0 to 0.46°C / W mm, 0.10 to 0.42°C / W mm, or 0.20 to 0.40°C / W mm. When the thermal resistance value R20 is 0.50°C / W mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which tends to further improve the product life.

[0024] The thermal resistance value R40 is preferably 0.30°C / W·mm or less, 0 to 0.28°C / W·mm, 0.05 to 0.26°C / W·mm, 0.10 to 0.24°C / W·mm, or 0.15 to 0.22°C / W·mm. When the thermal resistance value R40 is 0.30°C / W·mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a relatively low fastening torque, which in turn tends to further improve the product life.

[0025] The thermal resistance value R60 is preferably 0.25°C / W mm or less, 0.05 to 0.23°C / W mm, 0.10 to 0.21°C / W mm, or 0.15 to 0.19°C / W mm. When the thermal resistance value R60 is 0.25°C / W mm or less, if the tightening torque is increased, a correspondingly high thermal conductivity tends to be exhibited.

[0026] The ratio (R40 / R20) / (R60 / R40) of the ratio (R40 / R20) to the ratio (R60 / R40) is preferably 1.10 or greater, 1.15 to 2.50, 1.20 to 2.25, 1.25 to 2.00, 1.30 to 1.95, 1.35 to 1.90, or 1.40 to 1.85. When the ratio (R40 / R20) / (R60 / R40) is 1.10 or greater, the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN·m to 40 cN·m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN·m to 60 cN·m. This means that a predetermined thermal conductivity can be achieved even when tightened with a relatively low tightening torque, which in turn tends to improve the product life.

[0027] The difference between the ratio (R60 / R40) and the ratio (R40 / R20), {(R60 / R40) - (R40 / R20)}, is preferably 0.06 or greater, 0.08 to 0.80, 0.10 to 0.75, 0.12 to 0.70, 0.14 to 0.65, 0.18 to 0.60, or 0.22 to 0.5. When the difference {(R60 / R40) - (R40 / R20)} is 0.06 or greater, the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN m to 40 cN m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN m to 60 cN m. This means that the specified thermal conductivity can be achieved even when tightened with a relatively low tightening torque, which in turn tends to improve the product life.

[0028] The thermal resistance values ​​R20, R40, and R60 are not particularly limited, and can be measured, for example, by the method described in the Examples. The thermal resistance values ​​R20, R40, and R60 can be adjusted by the crushing strength and particle size of the thermally conductive filler used, and the amount and viscosity of the silicone oil used, which will be described later.

[0029] 1.2.Resin layer The resin layer contains a resin and a thermally conductive filler, and may contain silicone oil or a surfactant, if necessary. When the thermally conductive sheet of this embodiment further includes a reinforcing material 20, the resin layer 10 may be disposed on one surface of the reinforcing material 20, or on both surfaces thereof, as shown in FIG.

[0030] The thickness of the resin layer is preferably 50 to 200 μm, 75 to 150 μm, or 100 to 125 μm. The thinner the resin layer, the more improved the thermal conductivity, and the thicker the resin layer, the more improved the insulating properties. Furthermore, the presence of a reinforcing material allows the mechanical strength of the thermally conductive sheet to be maintained, so the thickness of the resin layer can be made thinner. Note that the thickness of the resin layer refers to the thickness of each resin layer when a reinforcing material is used and the resin layer is present on both sides of the reinforcing material, as described below.

[0031] Resin The resin is not particularly limited, but examples thereof include silicone resin, silicone rubber, epoxy resin, acrylic resin, phenolic resin, melamine resin, unsaturated polyester, fluororesin, polyimide resin, polyamideimide resin, polyetherimide resin, polyester resin, polyphenylene ether resin, etc. These resins may be used alone or in combination of two or more.

[0032] Among these, silicone resins and silicone rubbers are preferred. These silicone resins and silicone rubbers may be peroxide-curable, condensation-curable, addition-curable, or ultraviolet-curable, or may be those cured by these curing reactions. By using such resins, the mechanical strength and flexibility of the thermally conductive sheet are further improved, and the handling properties are further improved, and the thermal conductivity and insulating properties tend to be further improved.

[0033] The resin content is preferably 25 to 55 volume %, 30 to 50 volume %, or 35 to 45 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. When the resin content is within the above range, thermal conductivity and insulation properties tend to be further improved.

[0034] 1.2.2.Thermal Conductive Filler The thermally conductive filler is not particularly limited, but examples thereof include boron nitride, aluminum nitride, aluminum oxide, silicon nitride, silicon oxide, zinc oxide, silica, aluminum hydroxide, magnesium oxide, and carbon.

[0035] Among these, boron nitride or aluminum oxide is preferred, boron nitride is more preferred, and hexagonal boron nitride is more preferred. By using such a thermally conductive filler, thermal conductivity and insulating properties tend to be further improved.

[0036] The thermally conductive filler may be secondary particles formed by agglomeration of primary particles (hereinafter also referred to as "aggregated particles"). For example, by using a thermally conductive filler having anisotropy in thermal conductivity as agglomerated particles, the thermal conductivity due to contact between the thermally conductive fillers is improved and a thermal conduction path in any direction is easily formed, which tends to further improve the thermal conductivity.

[0037] When agglomerated particles are used, the crushing strength thereof is preferably 6.0 MPa or less, 0.1 to 5.0 MPa or less, 0.5 to 4.0 MPa or less, or 1.0 to 3.0 MPa or less. A crushing strength of 6.0 MPa or less tends to further decrease R40 / R20 and further improve R40 / R20. Furthermore, the agglomerated particles are appropriately loosened in response to the tightening torque, thereby forming an appropriate heat conduction path. Therefore, high thermal conductivity can be achieved even with a low tightening torque. Furthermore, a crushing strength of 0.1 MPa or more tends to prevent unintended destruction of the agglomerated particles during the molding process of the thermally conductive sheet.

[0038] The thermally conductive filler preferably contains agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less as agglomerated particles. By using such agglomerated particles of boron nitride having a low crushing strength, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which tends to further improve the product life.

[0039] The thermally conductive filler preferably has an average particle size of 70 to 170 μm, 80 to 160 μm, 90 to 150 μm, 100 to 140 μm, or 110 to 130 μm. When the average particle size of the thermally conductive filler is within the above range, the dispersibility and packing of the thermally conductive filler in the thermally conductive sheet tend to be improved. Furthermore, the desired thermal conductivity can be achieved even when fastened with a low fastening torque, which tends to further improve the product life.

[0040] In this embodiment, the average particle size refers to the median diameter D50. When the thermally conductive filler is in the form of agglomerated particles, the average particle size refers to the particle size of the agglomerated particles (secondary particles).

[0041] The total content of the thermally conductive filler is preferably 35 to 75 volume %, 40 to 70 volume %, 45 to 65 volume %, or 50 to 60 volume %, relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. When the total content of the thermally conductive filler is within the above range, thermal conductivity and insulating properties tend to be further improved. While a high loading of the thermally conductive filler is preferable from the viewpoint of improving thermal conductivity, the higher the total content of the thermally conductive filler, the higher the porosity and the lower the insulating properties tend to be. Therefore, the present invention, which can reduce the porosity and improve insulating properties, is useful.

[0042] Silicone oil The thermally conductive sheet of this embodiment, particularly the resin layer, may further contain silicone oil. Examples of silicone oils include, but are not limited to, peroxide-curable, condensation-curable, addition-curable, and ultraviolet-curable non-reactive compounds without curable functional groups. Examples of such silicone oils include, but are not limited to, dimethylpolysiloxane and diphenylpolysiloxane.

[0043] The viscosity of the silicone oil at 23°C is preferably 5.0 x 10 3 mm 2 / s or more, and 1.0 × 10 4 ~2.5×10 7 mm 2 / s, which is 5.0 × 10 4 ~2.0×10 7 mm 2 / s, which is 1.0 × 10 5 ~1.5×10 7 mm 2 / s, which is 5.0 × 10 5 ~1.0×10 7 mm 2 / s. The viscosity of silicone oil at 23°C is 5.0 x 10 3 mm 2 / s or more, the R40 / R20 tends to decrease further and the R40 / R20 tends to improve further. Furthermore, when the viscosity of the silicone oil at 23°C is within the above range, the desired thermal conductivity can be achieved even when tightened with a low tightening torque, and there is no need to tighten with an unnecessarily high tightening torque in order to improve thermal conductivity, which in turn tends to improve the product life.

[0044] The silicone oil may be used alone or in combination of two or more types with different structures, viscosities, etc.

[0045] The content of the silicone oil is preferably 0.5 to 5.0 volume %, 0.5 to 2.5 volume %, or 0.5 to 1.5 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. When the content of the silicone oil is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0046] Surfactants The surfactant is not particularly limited, but for example, a polymer having a silicone (meth)acrylic monomer unit γ is preferred, and a copolymer having a (meth)acrylic monomer unit α having an anionic group, a (meth)acrylic monomer unit β having a cationic group, and a silicone (meth)acrylic monomer unit γ is more preferred. The use of such a surfactant tends to improve the dispersibility of the thermally conductive filler component and further reduce the thermal resistance.

[0047] The content of the surfactant is 1.0 to 8.0 volume %, 2.0 to 6.0 volume %, 3.0 to 6.0 volume %, or 4.0 to 5.0 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. By keeping the content of the surfactant within the above range, the dispersibility of the thermally conductive filler component is improved, and the thermal resistance tends to be further reduced.

[0048] The surfactant will be described in more detail below. In this embodiment, a "monomer" refers to a monomer having a polymerizable unsaturated bond before polymerization, and a "monomer unit" refers to a repeating unit that constitutes a part of the surfactant after polymerization and is derived from a specific monomer. Furthermore, (meth)acrylic includes acrylic and methacrylic, and (meth)acrylic monomers include (meth)acrylate and (meth)acrylamide. Furthermore, hereinafter, "(meth)acrylic monomer unit α" and the like will also be simply referred to as "unit α" and the like.

[0049] The (meth)acrylic monomer unit α is a repeating unit having an anionic group. The anionic group is not particularly limited, but examples thereof include a carboxy group, a phosphate group, a phenolic hydroxy group, and a sulfonic acid group. Among these, one or more groups selected from the group consisting of a carboxy group, a phosphate group, and a phenolic hydroxy group are preferred. The presence of such a group tends to further improve the dispersibility of the filler component.

[0050] Such a (meth)acrylic monomer is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, acid phosphooxypropyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate, acid phosphooxypolyoxypropylene glycol monomethacrylate, phosphoric acid-modified epoxy acrylate, 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 4-hydroxyphenyl acrylate, 4-hydroxyphenyl methacrylate, 2-methacryloyloxyethyl succinic acid, and 2-acrylamido-2-methylpropanesulfonic acid.

[0051] The (meth)acrylic monomer unit β is a repeating unit having a cationic group. The cationic group is not particularly limited, but is preferably, for example, one or more selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium salt. Among these, a tertiary amino group is more preferred. The presence of such a group tends to further improve the dispersibility of the filler component.

[0052] Such (meth)acrylic monomers are not particularly limited, but examples thereof include 1-aminoethyl acrylate, 1-aminopropyl acrylate, 1-aminoethyl methacrylate, 1-aminopropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl (meth)acrylate, dimethylaminoethyl methacrylate quaternary salt, 1,2,2,6,6-pentamethyl-4-piperidyl acrylate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0053] The (meth)acrylic monomer unit γ is a silicone (meth)acrylic monomer unit, which is a (meth)acrylic monomer that does not contain a cationic group or an anionic group in the molecule but has a silicone group.

[0054] The (meth)acrylic monomer γ preferably has a skeleton that has high affinity or compatibility with other matrix components. The (meth)acrylic monomer γ has such a skeleton as a silicone skeleton such as dimethylsiloxane, methylphenylsiloxane, or diphenylsiloxane. By having such a skeleton, compatibility with other matrix components is improved, and the dispersibility of the filler component in the thermal grease tends to be improved.

[0055] Such a (meth)acrylic monomer is not particularly limited, but examples thereof include (meth)acrylic monomers having a siloxane skeleton such as α-butyl-ω-(3-methacryloxypropyl)polydimethylsiloxane. The unit γ may be used alone or in combination of two or more.

[0056] 1.3.Reinforcement The presence of a reinforcing material in the thermally conductive sheet tends to further improve the mechanical strength of the thermally conductive sheet and improve its handling. The position of the reinforcing material 20 is not particularly limited, but it is preferable that it is located at the center of the thermally conductive sheet in the thickness direction, for example. In other words, it is preferable that the reinforcing material 20 is not present on either surface of the cross section in the thickness direction. This allows resin layers to be disposed on the front and back surfaces of the thermally conductive sheet, and the resin layers come into contact with the heat-generating electronic component and the heat sink, which tends to further improve thermal conductivity and insulation.

[0057] The reinforcing material is not particularly limited, but examples thereof include glass cloth; organic fiber cloths such as cotton, hemp, aramid fiber, cellulose fiber, nylon fiber, polyolefin fiber, aramid fiber, cellulose fiber, nylon fiber, and polyolefin fiber; inorganic fiber cloths such as stainless steel, copper, and aluminum; nonwoven fabrics; resin films; and metal foils such as copper foil, nickel foil, and aluminum foil. Among these, glass cloth is preferred. The use of such reinforcing materials tends to further improve insulation and thermal conductivity.

[0058] The thickness of the reinforcing material is preferably 10 to 150 μm, 20 to 100 μm, or 30 to 75 μm. When the thickness of the reinforcing material is within the above range, the thermal conductive sheet can be configured to be thin while maintaining mechanical strength, which tends to further improve thermal conductivity.

[0059] Thickness The thickness of the thermally conductive sheet of this embodiment is preferably 100 to 800 μm, 125 to 600 μm, or 150 to 400 μm. The thinner the thermally conductive sheet, the more improved the thermal conductivity, and the thicker the thermally conductive sheet, the more improved the insulating properties. Furthermore, the presence of a reinforcing material allows the mechanical strength of the thermally conductive sheet to be maintained, allowing the thickness of the thermally conductive sheet to be made thinner.

[0060] 1.5.Durometer A hardness The thermally conductive sheet of this embodiment preferably has a durometer A hardness of 65 to 90, 70 to 88, 75 to 86, or 80 to 84. When the durometer A hardness is within the above range, the thermally conductive sheet is less susceptible to damage, and the product life tends to be further improved.

[0061] 1.6.Thermal Conductivity The thermal conductivity of the thermally conductive sheet of this embodiment is preferably 5.0 to 15.0 W / mK, 6.0 to 15.0 W / mK, or 7.0 to 15.0 W / mK.

[0062] 2. Manufacturing method of thermal conductive sheet The method for manufacturing the thermally conductive sheet of this embodiment is not particularly limited, but may, for example, include a resin layer forming step in which a resin layer is formed from a resin composition containing a resin and a thermally conductive filler, and if the thermally conductive sheet has a reinforcing material, may include a pressurizing step in which two resin layers are formed in the resin layer forming step, the reinforcing material is sandwiched between the two obtained resin layers, and heating and pressurizing are applied to form the thermally conductive sheet.

[0063] 2.1.Resin layer molding process The resin layer forming step is a step of forming a resin layer from a resin composition containing a resin and a thermally conductive filler. The resin composition contains a resin and a thermally conductive filler, and may also contain a solvent such as toluene, a dispersant for the thermally conductive filler, and the like, as necessary.

[0064] The method for forming the resin layer is not particularly limited, but for example, a method in which a resin composition is applied to a release film such as a PET film and dried at room temperature or under heat can be mentioned.

[0065] The coating method is not particularly limited, and known coating methods such as a doctor blade method, a comma coater method, a screen printing method, a roll coater method, etc. Among these, the doctor blade method and the comma coater method are preferred from the viewpoint of thickness accuracy of the resin layer.

[0066] 2.2.Pressure process The pressurizing step is a step of sandwiching a reinforcing material between two resin layers obtained in the resin layer forming step, and then heating and pressurizing the reinforcing material to form a thermally conductive sheet having resin layers on both sides of the reinforcing material. During this process, at least a portion of the resin component of the resin layer melts or deforms and penetrates into the fibers of the reinforcing material. Note that a thermally conductive sheet having a resin layer on one side of the reinforcing material may be formed by pressing and heating one resin layer against one side of the reinforcing material.

[0067] The heating and pressurizing conditions are not particularly limited. For example, the heating temperature is preferably 100 to 200°C, and 125 to 175°C. The pressing pressure is preferably 7.5 to 12.5 MPa, and 5 to 15 MPa. The heating and pressurizing time is preferably 30 to 90 minutes, and 45 to 75 minutes. [Example]

[0068] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, all operations were carried out at 23°C and 50% humidity.

[0069] Example 1 Boron nitride agglomerated particles (low-strength BN, crushing strength: 2 MPa, average particle size D50: 120 μm), silicone resin (peroxide-curable silicone, Toray Dow Corning Silicone Co., Ltd., product name "CF3110"), surfactant, toluene, curing agent (2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, Kayaku Nouryon Co., Ltd., product name "Trigonox 101"), and silicone oil KF-96H-1 million CS, Shin-Etsu Chemical Co., Ltd., viscosity 1 million mm 2 The resin composition was coated onto a PET film by a doctor blade method and left to stand at room temperature for 1 hour to volatilize the toluene, forming a resin layer with a thickness of 150 μm.

[0070] The surfactant used above was prepared as follows: First, 100 parts by mass of a (meth)acrylic monomer consisting of 48.4 mol % acrylic acid (manufactured by Toagosei Co., Ltd.), 1.6 mol % 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (manufactured by ADEKA Corporation, "ADEKA STAB LA-82"), and 50.0 mol % α-butyl-ω-(3-methacryloxypropyl)polydimethylsiloxane (weight average molecular weight 5,000, manufactured by JNC Corporation, "Silaplane FM-0721") was added to an autoclave equipped with a stirrer. Next, 0.05 parts by mass of azobisisobutyronitrile (Tokyo Chemical Industry Co., Ltd.) was added as an initiator to 100 parts by mass of the total (meth)acrylic monomers, and 1,000 parts by mass of a mixed solution of toluene (special reagent grade) and 2-propanol (special reagent grade) in a volume ratio of 7:3 was added as a solvent, and the autoclave was purged with nitrogen. The autoclave was then heated in an oil bath at 65°C for 20 hours to carry out radical polymerization. After polymerization was completed, the mixture was degassed under reduced pressure at 120°C for 1 hour to obtain a surfactant copolymer.

[0071] A glass cloth reinforcing material (trade name "H25" manufactured by Unitika Ltd.) was sandwiched between the two resin layers, and heated and pressurized at 150°C, 10 MPa, and 1 hour to form a thermally conductive sheet with a resin layer on both sides of the reinforcing material. The thickness of the thermally conductive sheet obtained was 300 μm.

[0072] The components used and the contents of boron nitride agglomerated particles 1 and 2, boron nitride flake particles, silicone resin, and silicone oil in the thermally conductive sheet obtained by the above procedure are shown in Table 1. The contents are shown as the percentage of the volume obtained by subtracting the volume of the reinforcing material from the total volume of the thermally conductive sheet, i.e., 100% by volume of the resin layer.

[0073] The crushing strength of agglomerated boron nitride particles was measured in accordance with JIS R1639-5:2007. Specifically, boron nitride particles were dispersed onto the sample stage of a microcompression tester (MCT-211, Shimadzu Corporation). 20 agglomerated boron nitride particles were selected from the boron nitride particles and subjected to a compression test individually. The crushing strength (σ: MPa) was calculated using the equation σ = α × P / (π × d²) based on the dimensionless number (α = 2.48), which varies with position within the particle, the crushing test force (P: N), and the particle size (d: μm). A Weibull plot of the crushing strengths of 20 inorganic filler components was performed in accordance with JIS R1625:2010, and the crushing strength at which the cumulative failure rate reached 63.2% was defined as the crushing strength of the boron nitride particles.

[0074] A thermally conductive sheet was placed between the TO-3 model heater and the copper plate. The thermally conductive sheet was then fastened using M3mm screws with a tightening torque of 20cN·m, 40cN·m, and 60cN·m. The contact area between one TO-3 model heater and the heat dissipation sheet was approximately 6cm. 2 After that, a power supply (Kikusui Electronics Co., Ltd., model number: PMC35-3) was used to apply 15 W of power to the TO-3 model heater. Then, 10 minutes after the application of 15 W of power, the temperature of the TO-3 model heater (T1) and the temperature of the copper plate (T2) were measured, and the thermal resistance was calculated using the following formula. Thermal resistance (℃ / W)=(T1-T2) / 15

[0075] The thermal resistance per unit thickness (°C / W·mm) was calculated by dividing the obtained thermal resistance by the thickness of the sheet.

[0076] The durometer A hardness of the thermally conductive sheet was measured by a method conforming to JIS K 6253. Specifically, the heat dissipation sheet material was cut into a size of 25 mm x 25 mm and stacked to a height of 12 mm or more, and the hardness was measured using a durometer type A (manufactured by Mitutoyo Corporation).

[0077] Example 2 Silicone oil (KF-96H-1 million CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1 million mm2 / s), silicone oil (KF-96H-100,000 CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 100,000 mm 2 A thermally conductive sheet of Example 2 was produced in the same manner as in Example 1, except that a thermally conductive sheet (aluminum fluoride / s) was used.

[0078] Example 3 Silicone oil (KF-96H-1 million CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1 million mm 2 The thermally conductive sheet of Example 3 was produced in the same manner as in Example 1, except that the amount of cellulose acetate / s used was 6.8 vol% and the amount of silicone resin (peroxide-curable silicone, manufactured by Dow Corning Toray Silicones Co., Ltd., product name "CF3110") used was 33.7 vol%.

[0079] (Comparative Example 1) A thermally conductive sheet of Comparative Example 1 was produced by the same procedure as in Example 1, except that boron nitride agglomerated particles (high-strength BN, crushing strength: 8 MPa, average particle size D50: 80 μm) were used instead of the boron nitride agglomerated particles (low-strength BN, crushing strength: 2 MPa, average particle size D50: 120 μm).

[0080] (Comparative Example 2) A thermally conductive sheet of Comparative Example 2 was produced in the same manner as in Comparative Example 1, except that silicone oil and surfactant were not used and the amount of silicone resin used was as shown in Table 1.

[0081] (Comparative Example 3) A thermally conductive sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that silicone oil was not used and the amount of silicone resin used was as shown in Table 1.

[0082] Comparative Example 4 Silicone oil (KF-96H-1 million CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1 million mm 2 / s), silicone oil (KF-96-1000CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1,000 mm 2A thermally conductive sheet of Comparative Example 4 was produced in the same manner as in Example 1, except that a thermally conductive sheet (aluminum fluoride / s) was used.

[0083] (evaluation) (product life) A thermally conductive sheet was sandwiched between the TO-220 package and the heat sink, and torque was applied so that the thermal resistance of the thermally conductive sheet was 0.27°C / W mm, as measured by the thermal resistance measurement method described in the examples (thermal resistance measurement using a TO-3 heater), and the sheet was left for one hour.The thermally conductive sheet was then removed and left for another hour, after which it was checked to see if there were any traces of the fastening material sinking in around the fastening part of the thermally conductive sheet. A: No marks remain and continued use will not affect the product's lifespan. B: Slight marks remain, but continued use will not affect the product's lifespan. C: Marks remain clearly, and there are concerns about the product's lifespan if it is used continuously.

[0084] [Table 1]

[0085] Figure 3 is a graph showing the change in thermal resistance value with respect to the tightening torque for Example 1 and Comparative Example 1. As shown in Figure 3, it can be seen that in the example, high thermal resistance can be achieved with a low tightening torque, even without applying a physical load to the thermal conductive sheet by tightening. [Industrial Applicability]

[0086] INDUSTRIAL APPLICABILITY The present invention has industrial applicability as a thermally conductive sheet having excellent thermal conductivity and electrical insulation properties.

Claims

1. resin and a thermally conductive filler, The ratio R40 / R20 of the thermal resistance value R20 per mm measured when a tightening torque of 20 cN m is applied to the thermal resistance value R40 per mm measured when a tightening torque of 40 cN m is applied is 0.62 or less. Thermally conductive sheet.

2. The thermal resistance value R20 is 0.50 ° C. / W mm or less, The thermally conductive sheet according to claim 1 .

3. The thermal resistance value R40 is 0.30°C / W mm or less. The thermally conductive sheet according to claim 1 .

4. A reinforcing material and a resin layer laminated on the front and back surfaces of the reinforcing material, the resin layer contains the resin and the thermally conductive filler; The thermally conductive sheet according to claim 1 .

5. the thermally conductive filler comprises agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less; The thermally conductive sheet according to claim 1 .

6. The ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN m is 0.65 or more, The thermally conductive sheet according to claim 1 .

7. The thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN m is 0.25°C / W mm or less. The thermally conductive sheet according to claim 1 .

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