Thermal conductive sheet

Abstract

The objective is to provide a thermally conductive sheet that offers superior insulation properties in addition to thermal conductivity. [Solution] The material comprises a reinforcing material and a resin layer laminated on the front and back surfaces of the reinforcing material, wherein the resin layer contains resin and agglomerated boron nitride, and in particles of the agglomerated boron nitride with an area circle equivalent diameter in the range of 20 to 100 μm, the codispersion between the area circle equivalent diameter and the circumference circle equivalent diameter is 275 μm. 2 The following is a heat dissipation sheet.

Description

[Technical Field]

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

[0002] With the miniaturization and increased power output of heat-generating electronic components such as the CPU (Central Processing Unit) in personal computers, the amount of heat generated per unit area from these components has become extremely large. This amount of heat can reach about 20 times that of an iron. To prevent these heat-generating electronic components from failing over the long term, cooling of the heat-generating electronic components is necessary. Metal heat sinks and casings are used for cooling, but if the heat-generating electronic component and the heat sink are in direct contact, microscopic air may be present at the interface, which can hinder heat conduction. Therefore, to efficiently transfer heat, the heat-generating electronic component and the heat sink are sometimes placed with a thermally conductive material in between.

[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 sheets that are thick and highly flexible, and have excellent conformability to the uneven shape of the mating material. Thermally conductive sheets are relatively thin sheets with excellent handling properties, and can enhance the thermal conductivity between heat-generating electronic components and heat sinks while ensuring insulation. Furthermore, thermally conductive greases are greases made by filling a fluid resin with a thermally conductive filler, offering a high degree of freedom in application shape, and can also reduce thermal resistance by applying them thinly.

[0004] For example, a known thermally conductive sheet has a structure in which layers of a silicone composition 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

Summary of the Invention

Problems to be Solved by the Invention

[0006] With the recent rapid miniaturization, high integration, and high output of electronic components, the operating temperature of heat-generating electronic components has increased, and a high voltage has come to be applied between the heat-generating electronic components and the heat sink. Therefore, there is a demand for further improvement in the thermal conductivity and insulation of thermally conductive sheets, especially those formed thinly.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a thermally conductive sheet that is further excellent in insulation in addition to thermal conductivity.

Means for Solving the Problems

[0008] That is, the present invention is as follows. 〔1〕 It has a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, the resin layer contains a resin and aggregated boron nitride, in the particles included in the range of the equivalent circle diameter of the area of the aggregated boron nitride of from 20 to 100 μm, the covariance of the equivalent circle diameter of the area and the equivalent circle diameter of the circumference is 275 μm 2 or less, Heat dissipation sheet. 〔2〕 The tap density of the aggregated boron nitride is from 0.30 to 1.50 g / cm3, The heat dissipation sheet according to 〔1〕. 〔3〕 The crushing strength of the aggregated boron nitride is from 1.0 to 6.0 MPa, The heat dissipation sheet according to 〔1〕 or 〔2〕. 〔4〕 In the particles included in the range of the equivalent circle diameter of the area of the aggregated boron nitride of from 20 to 100 μm, the equivalent circle diameter D50 of the area is from 15 to 45 μm, The heat dissipation sheet according to any one of 〔1〕 to 〔3〕. [5] The content of the aggregated boron nitride is 50 to 80% by volume with respect to the total amount of the resin layer. The heat dissipation sheet according to any one of [1] to [4]. [Advantages of the Invention]

[0009] According to the present invention, it is possible to provide a thermally conductive sheet that is excellent not only in thermal conductivity but also in insulation. [Brief Description of the Drawings]

[0010] [Figure 1] It is a schematic cross-sectional view showing an example of the thermally conductive sheet of the present embodiment. [Figure 2] It is a diagram showing the relationship between the equivalent diameter of the area circle and the equivalent diameter of the perimeter circle in the range of the equivalent diameter of the area circle of 20 to 100 μm. [Modes for Carrying Out the Invention] [[ID=2​​​​​​​​​​​​​​Figure 1 shows a schematic cross-sectional view illustrating an example of the thermal conductive sheet of this embodiment. As shown in Figure 1, the thermal conductive sheet 1 of this embodiment has a reinforcing material 20 and a resin layer 10 laminated on the front and back surfaces of the reinforcing material 20.

[0014] Conventionally, aggregated boron nitride has been used as a useful thermally conductive filler from the perspective of improving thermal conductivity. However, aggregated boron nitride does not unconditionally have excellent thermal conductivity, and improvements in thermal conductivity have been made by using multiple types of aggregated boron nitride with different particle sizes from the perspective of close packing.

[0015] In this embodiment, the covariance between the area circle equivalent diameter and the circumferential circle equivalent diameter of the aggregated boron nitride is defined in the range of 20 to 100 μm. The closer the aggregated boron nitride is to a perfect circle, the more the circumferential circle equivalent diameter becomes equal to the area circle equivalent diameter. Conversely, the more irregular and uneven the aggregated boron nitride is, the more the circumferential circle equivalent diameter tends to be larger than the area circle equivalent diameter. Therefore, in this embodiment, we focus on the aggregated boron nitride particle group within a specific particle size range and define that there are fewer irregularly shaped particles that reduce the dielectric breakdown voltage based on the correlation between the circumferential circle equivalent diameter and the area circle equivalent diameter, thereby further improving thermal conductivity and insulation.

[0016] 1.1. Reinforcement materials The presence of a reinforcing material in the thermal conductive sheet improves its mechanical strength, making it possible to construct a thinner thermal conductive sheet and also tending to improve handling. The position of the reinforcing material 20 is not particularly limited, but for example, it is preferably located at the center in the thickness direction of the thermal conductive sheet, and preferably at least within a range of ±0.2d from the center in the cross-section in the thickness direction, when the thickness of the thermal conductive sheet is d. In other words, it is preferable that the reinforcing material 20 is not located within a range of 0.3d from both surfaces in the cross-section in the thickness direction. As a result, resin layers are arranged on the front and back surfaces of the thermal conductive sheet, and the resin layers come into contact with the heat-generating electronic components and the heat sink, which tends to improve thermal conductivity and insulation.

[0017] While not particularly limited, examples of reinforcing materials include glass cloth; organic fiber cloths such as cotton, hemp, aramid fibers, cellulose fibers, nylon fibers, polyolefin fibers; 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. Using such reinforcing materials tends to further improve insulation and thermal conductivity.

[0018] The thickness of the reinforcing material is preferably 10 to 150 μm, 20 to 100 μm, or 30 to 75 μm. By keeping the thickness of the reinforcing material within the above range, the thermal conductive sheet can be made thinner while maintaining mechanical strength, which tends to improve thermal conductivity.

[0019] 1.2. Resin layer The resin layer 10 comprises a resin and agglomerated boron nitride, and may optionally contain silicone oil and a silane coupling agent. The resin layer may also further contain thermally conductive fillers other than agglomerated boron nitride.

[0020] The thickness of the resin layer is preferably 50 to 250 μm, 75 to 200 μm, or 100 to 150 μm. A thinner resin layer tends to improve thermal conductivity, while a thicker resin layer tends to improve insulation. Furthermore, the presence of a reinforcing material maintains the mechanical strength of the thermally conductive sheet, allowing the resin layer to be made thinner. Note that, as described later, the thickness of the resin layer refers to the thickness of each individual resin layer when a reinforcing material is used and the resin layer exists on both sides of the reinforcing material.

[0021] 1.2.1. Resin The resin is not particularly limited, but examples include silicone resin, silicone rubber, epoxy resin, acrylic resin, phenolic resin, melamine resin, unsaturated polyester, fluororesin, polyimide resin, polyamide-imide resin, polyetherimide resin, polyester resin, and polyphenylene ether resin. These resins may be used individually or in combination of two or more.

[0022] Among these, silicone resins and silicone rubbers are preferred. These silicone resins and silicone rubbers may be peroxide-cured, condensation-cured, addition-cured, or UV-cured, and may also be in their cured state. Using such resins tends to improve the mechanical strength and flexibility of the thermally conductive sheet, enhance handling, and further improve thermal conductivity and insulation. A curing agent corresponding to each curing type may also be used.

[0023] The resin content is preferably 20-55% by volume, 25-50% by volume, or 30-45% by volume relative to the total volume of the thermal conductive sheet minus the volume of the reinforcing material, i.e., 100% by volume of the resin layer. When the resin content is within the above range, the thermal conductivity and insulation properties tend to be further improved.

[0024] 1.2.2. Agglomerated Boron Nitride In this embodiment, aggregated boron nitride having a predetermined particle shape and particle size is used. "Aggregation" refers to the state of secondary particles formed by the aggregation of primary particles. Primary boron nitride particles have a flattened shape, and tend to have poor thermal conductivity in the thickness direction and excellent thermal conductivity in the plane direction. Such flattened primary boron nitride particles tend to be oriented in the plane direction. By using boron nitride, which has anisotropy in terms of thermal conductivity, as aggregated particles, thermal conductivity is improved by contact between boron nitride particles, and it becomes easier to form heat conduction paths in any direction, thus tending to further improve thermal conductivity. In addition, by using aggregated particles, the proportion of primary particles lying flat in the plane direction of the thermal conductive sheet is reduced, and the thermal resistance in the thickness direction is decreased. The secondary particles may be spherical or irregularly shaped lumps.

[0025] Figure 2 shows the relationship between the area circle equivalent diameter and the circumferential circle equivalent diameter in the range of 20 to 100 μm for aggregated boron nitride. By measuring the area circle equivalent diameter and circumferential circle equivalent diameter for each individual aggregated boron nitride particle, plot data like that shown in Figure 2 can be obtained. From this relationship between the area circle equivalent diameter and circumferential circle equivalent diameter, the covariance, which represents how one variable changes when the other variable increases, can be calculated.

[0026] Considering the thickness of the resin layer, particles in the range of 20 to 100 μm in area circle equivalent diameter are classified as considerably large. Because these particles are large, they can efficiently transfer heat in the thickness direction, thus contributing to improved thermal conductivity. However, if their shape is distorted, the length along the long axis approaches the thickness of the resin layer, resulting in a particle size that reduces insulation.

[0027] From the above perspective, in this embodiment, the covariance between the area circle equivalent diameter and the circumference circle equivalent diameter in the area circle equivalent diameter range of 20 to 100 μm for aggregated boron nitride is 275 μm. 2 The following, preferably 250 μm 2 The following is true: 240 μm 2 The following is true: 230 μm 2 The following is true, 220 μm2 is 210 μm or less 2 is 200 μm or less 2 is 190 μm or less 2 is 180 μm or less 2 is 170 μm or less 2 is 160 μm or less 2 is 150 μm or less 2 is as follows. Further, the covariance of the equivalent circle diameter of the area and the equivalent circle diameter of the circumference in the range of 20 to 100 μm of the equivalent circle diameter of the area of the aggregated boron nitride is 50 μm 2 or more and 75 μm 2 or more and 100 μm 2 or more and 110 μm 2 or more and 120 μm 2 or more and 130 μm 2 or more. When the covariance of the equivalent circle diameter of the area and the equivalent circle diameter of the circumference is within the above range, the thermal conductivity and insulation tend to be further improved.

[0028] In addition, in this specification, the unit of covariance is the product (μm 2 ) of the equivalent circle diameter of the area (μm) and the equivalent circle diameter of the circumference (μm).

[0029] The equivalent circle diameter D10 of the area of the aggregated boron nitride in the range of the equivalent circle diameter of the area of 20 to 100 μm is preferably 10 to 35 μm, 12.5 to 32.5 μm, 15 to 30 μm, 17.5 to 27.5 μm, 20 to 25 μm. When the equivalent circle diameter D10 of the area is within the above range, the thermal conductivity and insulation tend to be further improved.

[0030] The equivalent circle diameter D50 of the area of the aggregated boron nitride in the range of the equivalent circle diameter of the area of 20 to ,100 μm is preferably 15 to 45 μm, 17.5 to 40 μm, 20 to 35 μm, 22.5 to 32.5 μm, 25 to 30 μm. When the equivalent circle diameter D50 of the area is within the above range, the thermal conductivity and insulation tend to be further improved.

[0031] The area circle equivalent diameter D90 of aggregated boron nitride in the range of 20 to 100 μm is preferably 35 to 65 μm, 40 to 60 μm, 42.5 to 57.5 μm, or 45 to 55 μm. When the area circle equivalent diameter D90 is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0032] The area circle equivalent diameter D90 / area circle equivalent diameter D10 is preferably 1.50 to 3.00, 1.75 to 2.75, or 2.00 to 2.50. When the area circle equivalent diameter D90 / area circle equivalent diameter D10 is within the above range, thermal conductivity and insulation tend to be further improved.

[0033] The number-based average of the area circle equivalent diameter of aggregated boron nitride in the range of 20 to 100 μm is preferably 20 to 45 μm, 22.5 to 42.5 μm, 25 to 40 μm, 27.5 to 37.5 μm, and 30 to 35 μm. When the number-based average of the area circle equivalent diameter is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0034] The dispersion of the area circle equivalent diameter of aggregated boron nitride in the range of 20 to 100 μm is preferably 80 to 275 μm. 2 and 90-250 μm 2 The size is 100-225 μm. 2 The size is 120-200 μm. 2 The size is 140-180 μm. 2 Therefore, when the dispersion of the area equivalent diameter falls within the above range, thermal conductivity and insulating properties tend to improve further. Note that dispersion refers to the population dispersion.

[0035] In this embodiment, the area-circle equivalent diameter is the diameter of the circle obtained when the area of ​​the particle is converted to a circle of the same area. Area-circle equivalent diameter D50 refers to the diameter at which the cumulative distribution reaches 50% in the cumulative distribution curve based on the number of aggregated boron nitride particles in the area-circle equivalent diameter range of 20 to 100 μm. Similarly, area-circle equivalent diameters D10 and D90 refer to the diameters at which the cumulative distribution reaches 10% and 90%, respectively, in the cumulative distribution curve based on the number of particles.

[0036] The equivalent circumference diameter D10 of aggregated boron nitride in the area circle equivalent diameter range of 20 to 100 μm is preferably 10 to 35 μm, 12.5 to 32.5 μm, 15 to 30 μm, 17.5 to 27.5 μm, or 20 to 25 μm. When the equivalent circumference diameter D10 is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0037] The equivalent circumference diameter D50 of aggregated boron nitride in the area circle equivalent diameter range of 20 to 100 μm is preferably 15 to 45 μm, 20 to 40 μm, 22.5 to 37.5 μm, 25 to 35 μm, or 27.5 to 32.5 μm. When the equivalent circumference diameter D50 is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0038] The equivalent diameter D90 of the circumferential circle of aggregated boron nitride in the range of area circle equivalent diameter 20 to 100 μm is preferably 40 to 70 μm, 45 to 65 μm, 47.5 to 62.5 μm, or 50 to 60 μm. When the equivalent diameter D90 of the circumferential circle is within the above range, the thermal conductivity and insulating properties tend to be further improved.

[0039] The equivalent circumference diameter D90 / D10 is preferably 1.75 to 3.00, 2.00 to 2.75, or 2.25 to 2.50. When the equivalent circumference diameter D90 / D10 is within the above range, thermal conductivity and insulation tend to be further improved.

[0040] The number-based average of the circumferential diameters in aggregated boron nitride in the area circle equivalent diameter range of 20 to 100 μm is preferably 20 to 50 μm, 22.5 to 47.5 μm, 25 to 45 μm, 27.5 to 42.5 μm, 30 to 40 μm, and 32.5 to 37.5 μm. When the number-based average of the circumferential diameters is within the above range, thermal conductivity and insulation tend to be further improved.

[0041] The dispersion of the circumferential diameter of aggregated boron nitride in the area circle equivalent diameter range of 20 to 100 μm is preferably 100 to 350 μm. 2 and 120~325μm 2 The size is 130-300 μm. 2 The size is 140-275 μm. 2 The size is 150-250 μm. 2 Therefore, when the dispersion of the equivalent diameter of the circumference is within the above range, the thermal conductivity and insulating properties tend to improve further. Note that dispersion refers to the population dispersion.

[0042] In this embodiment, the equivalent circumference diameter is the diameter of a circle obtained by converting the circumference of a particle to a circle of the same circumference. The equivalent circumference diameter D50 refers to the diameter at which the cumulative distribution reaches 50% in the cumulative distribution curve based on the number of aggregated boron nitride particles in the area equivalent diameter range of 20 to 100 μm. Similarly, the equivalent circumference diameters D10 and D90 refer to the diameters at which the cumulative distribution reaches 10% and 90%, respectively, in the cumulative distribution curve based on the number of particles.

[0043] The area circle equivalent diameter and circumference circle equivalent diameter for each particle can be measured in accordance with ISO 13322-2 using a flow-type image analysis particle size and shape measuring device that captures particles passing through a flow cell with a high-sensitivity CCD camera or similar device.

[0044] The tap density is preferably 0.30 to 1.50 g / cm³. 3 The concentration is 0.40-1.25 g / cm³. 3 The concentration is 0.45-1.00 g / cm³. 3 Therefore, 0.50~0.90 g / cm³ 3Therefore, it is 0.55~0.80 g / cm³. 3 Therefore, when the tap density is within the above range, the packing efficiency of the aggregated boron nitride is further improved, and the thermal conductivity and insulating properties tend to be further enhanced.

[0045] Tap density is calculated by placing a certain weight of powder in a container, tapping the container to fill the gaps between particles, and dividing the result by the volume of that container. It can be measured in accordance with JIS R 1628:1997.

[0046] The area circle equivalent diameter, perimeter circle equivalent diameter, and tap density can be arbitrarily adjusted by classifying the agglomerated boron nitride. Furthermore, when synthesizing agglomerated boron nitride using boron carbide as a raw material, the shape of the boron carbide used becomes the shape of the boron nitride, and the particle size becomes approximately twice that of the raw material. Therefore, by selecting the shape and particle size of the boron carbide and then synthesizing the agglomerated boron nitride, the area circle equivalent diameter, perimeter circle equivalent diameter, and tap density can also be adjusted. In addition, regarding the shape of agglomerated boron nitride, by hot-pressing boron nitride with low crystallinity, a sintered body with a certain degree of crystal orientation can be obtained, and by crushing this, agglomerated boron nitride with a high aspect ratio can be obtained.

[0047] The crushing strength is preferably 1.0 to 6.0 MPa, 1.2 to 5.0 MPa, 1.5 to 4.0 MPa, and 1.7 to 2.8 MPa. When the crushing strength is within the above range, in the pressurization step of the thermal conductive sheet manufacturing method described later, the aggregated boron nitride deforms along with the flow of the resin, making it less likely for voids to form. As a result, the thermal resistance in the thickness direction is further reduced, voids do not form, and the insulating properties tend to be further improved.

[0048] In this embodiment, the crushing strength refers to the value measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring granular properties - Part 5: Single granular crushing strength". The crushing strength σ (unit: MPa) of a single agglomerated particle is calculated using the formula σ = α × P / (π × d²) from the values ​​of the dimensionless number α (α = 2.48), which changes depending on the position within the agglomerated particle, the crushing test force P (unit: N), and the particle size d (unit: μm). The measurement shall be performed on 20 or more agglomerated particles, and the value at the point of cumulative failure rate of 63.2% shall be calculated. A micro-compression tester can be used for the measurement. For example, the "MCT-210" (product name) manufactured by Shimadzu Corporation can be used as a micro-compression tester.

[0049] The content of aggregated boron nitride is preferably 50-80% by volume, 52-75% by volume, 55-70% by volume, and 57-65% by volume, relative to the total volume of the thermal conductive sheet minus the volume of the reinforcing material, i.e., 100% by volume of the resin layer. When the content of aggregated boron nitride is within the above range, the thermal resistance tends to decrease further, void formation is less likely, and insulation performance tends to improve further.

[0050] 1.3.3. Other thermally conductive fillers The thermally conductive sheet of this embodiment may contain other thermally conductive fillers besides aggregated boron nitride. These other thermally conductive fillers are not particularly limited, but examples include aluminum nitride, aluminum oxide, silicon nitride, silicon oxide, zinc oxide, silica, aluminum hydroxide, magnesium oxide, and carbon. Among these, aluminum oxide is preferred. Using such thermally conductive fillers tends to further improve thermal conductivity and insulation.

[0051] Other thermally conductive fillers may be aggregated particles formed by the aggregation of primary particles. For example, using a thermally conductive filler with anisotropic thermal conductivity as aggregated particles improves thermal conductivity through contact between the thermally conductive fillers and facilitates the formation of heat conduction paths in any direction, thus tending to further improve thermal conductivity.

[0052] The content of other thermally conductive fillers is preferably 0 to 20% by volume, 0 to 15% by volume, 0 to 10% by volume, 0 to 5% by volume, and 0 to 3.0% by volume, relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100% by volume of the resin layer. Furthermore, other thermally conductive fillers may not be included.

[0053] 1.3.4. Silane coupling agents The thermally conductive sheet of this embodiment may contain a silane coupling agent. This further improves the adhesion between the resin and the agglomerated boron nitride, preventing void formation, resulting in superior thermal resistance and improved dielectric breakdown voltage. Furthermore, it suppresses delamination and void formation on the surface of the resin and agglomerated boron nitride due to the difference in thermal expansion coefficients between the resin and agglomerated boron nitride at high temperatures and during heat cycles, which tends to further improve long-term reliability.

[0054] Silane coupling agents are not particularly limited, but examples include alkyl silane coupling agents such as decyltrimethoxysilane; epoxy silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane; mercapto silane coupling agents such as 3-mercaptopropyltrimethoxysilane and 3-mercaptotriethoxysilane; ureido silane coupling agents such as 3-ureidopropyltriethoxysilane; and siloxane silane coupling agents containing a polyorganosiloxane skeleton. Silane coupling agents may be used individually or in combination of two or more types.

[0055] Among these, coupling agents containing a polyorganosiloxane skeleton are preferred. By using such a silane coupling agent, the adhesion between the resin and the aggregated boron nitride is further improved, and the tensile shear fracture strength can be further improved. As a result, voids are not formed, thermal resistance is excellent, and the dielectric breakdown voltage tends to be further improved.

[0056] The silane coupling agent content is preferably 0.001 to 1.0% by mass, 0.003 to 0.5% by mass, or 0.005 to 0.1% by mass, relative to 100% by mass of aggregated boron nitride. When the silane coupling agent content is within the above range, voids are not formed, thermal resistance is excellent, and the dielectric breakdown voltage tends to improve.

[0057] 1.4. Thickness The thickness of the thermal conductive sheet in this embodiment is preferably 100 to 800 μm, 125 to 600 μm, or 150 to 400 μm. The thinner the thermal conductive sheet, the better the thermal conductivity, and the thicker the thermal conductive sheet, the better the insulation tends to be. Furthermore, by including a reinforcing material, the mechanical strength of the thermal conductive sheet can be maintained, allowing the thermal conductive sheet to be made even thinner.

[0058] 1.5.Thermal resistance The thermal resistance of the thermally conductive sheet in this embodiment is preferably 0.01 to 0.90°C / W·mm, 0.02 to 0.8°C / W·mm, and 0.03 to 0.70°C / W·mm.

[0059] 2. Method for manufacturing a thermally conductive sheet The method for manufacturing the thermally conductive sheet of this embodiment is not particularly limited, but may include, for example, a resin layer molding step in which a resin layer is formed using a resin composition containing a resin and a thermally conductive filler, and a pressurizing step in which a reinforcing material is sandwiched between the two resin layers formed in the resin layer molding step, and then heated and pressurized to form a thermally conductive sheet.

[0060] 2.1.Resin layer molding process The resin layer molding process is a process of forming a resin layer using a resin composition containing a resin and a thermally conductive filler. The resin composition contains a resin and a thermally conductive filler, and may optionally contain a solvent such as toluene, a dispersant for the thermally conductive filler, etc.

[0061] The method for forming the resin layer is not particularly limited, but one example is to apply a resin composition onto a release film such as a PET film and dry it at room temperature or under heating.

[0062] The coating method is not particularly limited, but known coating methods such as the doctor blade method, comma coater method, screen printing method, and roll coater method can be used. Among these, the doctor blade method and comma coater method are preferred from the viewpoint of accuracy of the resin layer thickness.

[0063] 2.2. Pressurization Process The pressurization process involves sandwiching a reinforcing material between two resin layers obtained in the resin layer molding process, heating, and pressurizing to form a heat-conductive sheet with resin layers on both sides of the reinforcing material. During this process, at least a portion of the resin components of the resin layers melt or deform and penetrate into the fibers of the reinforcing material, but voids may inevitably be created during this process. Alternatively, a heat-conductive sheet with a resin layer on one side of the reinforcing material may be formed by pressurizing and heating one resin layer against one side of the reinforcing material.

[0064] 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 pressurizing pressure is preferably 7.5 to 12.5 MPa and 5 to 15 MPa. Furthermore, the heating and pressurizing time is preferably 30 to 90 minutes and 45 to 75 minutes. [Examples]

[0065] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples. Unless otherwise specified, each operation was carried out under conditions of 23°C and 50% humidity.

[0066] (Preparation Example 1) Boric acid, melamine, and calcium carbonate (all reagent grade) were mixed in a mass ratio of 70:50:5. The mixture was heated in a nitrogen gas atmosphere from room temperature to 1400°C in 1 hour, held at 1400°C for 3 hours, then heated to 1900°C in 4 hours, held at 1900°C for 2 hours, and then cooled to room temperature to produce hexagonal boron nitride. This mixture was then crushed, pulverized, and sieved to obtain aggregated boron nitride BN1 having the particle sizes listed in Table 1 below.

[0067] (Preparation Examples 2-5) Aggregated boron nitride BN2-5 with particle sizes listed in Table 1 below was obtained in the same manner as in Preparation Example 1, except for changes in the crushing and classification conditions.

[0068] The area circle equivalent diameter and perimeter equivalent diameter of agglomerated boron nitride in the range of 20 to 100 μm were determined by simultaneously measuring the area circle equivalent diameter and perimeter equivalent diameter using dynamic image analysis with the Microtrac-Bell product "SYNC". For the measurement, 2 mL of sodium hexametaphosphate aqueous solution and 200 mL of water were placed in a 300 mL beaker, 60 mg of agglomerated boron nitride was added, and the mixture was stirred at 100 rpm for 1 minute using a stirrer without homogenization, and the measurement was performed while agglomerated particles were present. Water was used as the dispersant, and the refractive index was set to 1.33. From the obtained particle image data, data for area circle equivalent diameters of 20 to 100 μm were extracted, and a number-based cumulative distribution curve was created from this data, and the D90, D50, D10, mean, and variance of the area circle equivalent diameter and perimeter equivalent diameter were calculated, respectively. Furthermore, using the same data, the covariance values ​​of the area circle equivalent diameter and the circumference circle equivalent diameter were determined for particles contained within the area circle equivalent diameter range of 20 to 100 μm of aggregated boron nitride.

[0069] For reference, Figure 2 shows the relationship between the area circle equivalent diameter and the circumference circle equivalent diameter in the range of 20 to 100 μm for BN1.

[0070] The tap density of aggregated boron nitride was determined in accordance with the method described in JIS R 1628:1997 "Method for Measuring the Bulk Density of Fine Ceramic Powders". Specifically, aggregated boron nitride powder was subjected to a 100 cm³ load. 3 The material was filled into a dedicated container, and after tapping under the conditions of a tapping time of 180 seconds, 180 taps, and a tap lift of 18 mm, the bulk density was measured, and the obtained value was defined as the tap density. For the measurement, a "powder tester" (product name) manufactured by Hosokawa Micron was used.

[0071] The crushing strength of aggregated boron nitride was measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring grain properties - Part 5: Single grain crushing strength". A microcompression tester (manufactured by Shimadzu Corporation, product name "MCT-210") was used for the measurement. The measurement was performed on 20 or more aggregated particles, and the value was calculated at a cumulative fracture rate of 63.2%.

[0072] [Table 1]

[0073] (Example 1) A resin composition was obtained by mixing aggregated boron nitride BN1, silicone resin (peroxide-curable silicone, manufactured by Toray Dow Corning Silicone Co., Ltd., trade name "CF3110"), silane coupling agent (decyltrimethoxysilane, manufactured by Dow Toray Corporation, trade name "Z-6210"), curing agent (2,5-dimethyl-2,5-di(t-butylperoxy)hexane, manufactured by Kayaku Nurion Co., Ltd., trade name "Trigonox 101"), and toluene.

[0074] The obtained resin composition was coated onto a PET film using the doctor blade method, and left to stand at room temperature for 1 hour to allow toluene to evaporate, forming a resin layer with a thickness of 100 μm.

[0075] A glass cloth (product name "H25" manufactured by Unitika Corporation), which serves as a reinforcing material, was sandwiched between the two resulting resin layers. The mixture was then heated and pressurized at 150°C, 10 MPa, and for 1 hour to form a thermally conductive sheet with resin layers on both sides of the reinforcing material. The thickness of the resulting thermally conductive sheet was 200 μm.

[0076] Table 2 shows the components used and their respective contents. The contents of components other than the silane coupling agent are shown as the volume obtained by subtracting the volume of the reinforcing material from the total volume of the silane coupling agent thermal conductive sheet, i.e., as a percentage of 100% of the resin layer volume. The amount of silane coupling agent used was 0.01% by mass relative to 100% by mass of the total amount of aggregated boron nitride. The amount of curing agent was 1% by mass relative to 100% by mass of the total amount of silicone resin.

[0077] (Examples 2-3, Comparative Examples 1-2) Except for using aggregated boron nitride BN2-5 instead of aggregated boron nitride BN1, thermally conductive sheets for Examples 2-3 and Comparative Examples 1-2 were prepared using the same procedure as in Example 1.

[0078] (evaluation) (thermal resistance) A thermal conductive sheet was placed between the TO-3 type model heater and the copper plate. The thermal conductive sheet was then tightened using a screw with a nominal diameter of M3 mm and a tightening torque of 0.5 N·m. The contact area between one TO-3 type model heater and the heat dissipation sheet was approximately 6 cm². Subsequently, 15 W of power was applied to the TO-3 type model heater using a power supply (manufactured by Kikusui Electronics Co., Ltd., model number: PMC35-3). The temperature of the TO-3 type model heater (T1) and the temperature of the copper plate (T2) were measured 10 minutes after the application of 15 W of power, and the thermal resistance was calculated using the following formula. Thermal resistance (℃ / W)=(T1-T2) / 15

[0079] The thermal resistance per unit thickness (°C / W·mm) was calculated by dividing the obtained thermal resistance by the thickness of the sheet.

[0080] (Dielectric breakdown voltage) The dielectric breakdown voltage of the thermal conductive sheet was measured in accordance with JIS C 2110. Specifically, the thermal conductive sheet was processed to a size of 5 cm x 5 cm.

[0081] A φ25mm columnar electrode was positioned to sandwich the test sample, and an AC voltage was applied to the test sample. The voltage applied to the test sample was increased from 0V at a rate (500V / s) such that dielectric breakdown occurred an average of 10-20 seconds after the start of voltage application. The voltage at which dielectric breakdown occurred was measured for five test samples, and the average value V5(kV) was obtained. Then, the dielectric breakdown voltage (kV / mm) was calculated by dividing the voltage V5(kV) by the thickness (mm) of the test sample.

[0082] [Table 2] *In the table, [vol%] indicates the value of each component when the total of components other than the silane coupling agent is set to 100 volume%.

[0083] Furthermore, in Examples 1-3 and Comparative Examples 1-2, compositions containing 50 vol% of agglomerated boron nitride and 50 vol% of silicone resin (Examples 1'-3', Comparative Examples 1'-2') were prepared, and their dielectric breakdown voltages were measured. Similar to Table 2 above, the results showed that Examples 1'-3' had a higher dielectric breakdown voltage than Comparative Examples 1'-2'. Similarly, in Examples 1-3 and Comparative Examples 1-2, compositions containing 70 vol% of agglomerated boron nitride and 30 vol% of silicone resin (Examples 1''-3'', Comparative Examples 1''-2'') were prepared, and their dielectric breakdown voltages were measured. Similar to Table 2 above, the results showed that Examples 1''-3'' had a higher dielectric breakdown voltage than Comparative Examples 1''-2''. [Industrial applicability]

[0084] The present invention has industrial applicability as a thermally conductive sheet with excellent thermal conductivity and insulation properties. [Explanation of symbols]

[0085] 1…Thermal conductive sheet, 10…Resin layer, 20…Reinforcement material

Claims

1. It comprises a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, The resin layer comprises a resin and aggregated boron nitride. In the particles of the aggregated boron nitride contained within the area circle equivalent diameter range of 20 to 100 μm, the codispersion between the area circle equivalent diameter and the circumference circle equivalent diameter is 275 μm. 2 The following is: Heat dissipation sheet.

2. The tap density of the aggregated boron nitride is 0.30 to 1.50 g / cm³. The heat dissipation sheet according to claim 1.

3. The crushing strength of the aggregated boron nitride is 1.0 to 6.0 MPa. The heat dissipation sheet according to claim 1.

4. In the particles of the aggregated boron nitride that are included in the area circle equivalent diameter range of 20 to 100 μm, the area circle equivalent diameter D50 is 15 to 45 μm. The heat dissipation sheet according to claim 1.

5. The content of the aggregated boron nitride is 50 to 80% by volume relative to the total amount of the resin layer. The heat dissipation sheet according to claim 1.

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