Thermally conductive sheet

Abstract

A thermally conductive sheet made of a resin composition containing silicone and a thermally conductive filler, which is reproducible and maintains thermal conductivity of 90% or more after a single regeneration.

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet. This application claims priority from Japanese Application No. 2023-166156, filed September 27, 2023, and incorporates by reference all of the contents of the above-mentioned Japanese application. [Background technology]

[0002] A heat-generating component such as an IC chip is usually attached to a heat-dissipating component such as a heat sink via a thermal interface material (TIM), and the heat generated by the heat-generating component is conducted to the heat-dissipating component via the thermal interface material. As the thermally conductive material, a thermally conductive sheet in which a thermally conductive filler is blended in a resin matrix is known.

[0003] Many conventional thermally conductive sheets are made of resins whose resin matrix is fully cross-linked. In this case, it is difficult to recycle the finished product. In this respect, thermally conductive sheets made of resins whose resin matrix is cross-linked have a large environmental impact.

[0004] Meanwhile, Patent Document 1 proposes a recyclable, highly thermally conductive elastomer composition and a sheet made of the same. This highly thermally conductive elastomer composition uses SB (styrene-butadiene rubber), SBS (styrene-butadiene-styrene rubber), SIS (styrene-isoprene-styrene rubber), or the like as a matrix component. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-37916 Summary of the Invention [Problem to be solved by the invention]

[0006] The highly thermally conductive elastomer composition described in Patent Document 1 is said to be recyclable, but its performance after recycling is unclear. [Means for solving the problem]

[0007] Under these circumstances, the present inventors have conducted extensive research and have come up with a solution to provide a thermally conductive sheet that has high material recyclability and maintains good thermal conductivity even after recycling.

[0008] A thermally conductive sheet according to one aspect of the present invention comprises: The resin composition comprises a silicone and a thermally conductive filler, It is reproducible, After one re-production, the thermal conductivity remains at over 90%. [Effects of the Invention]

[0009] The thermally conductive sheet according to one aspect of the present invention can be reproduced (level material recycling) while maintaining good thermal conductivity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an IC chip to which a heat sink is attached via a thermally conductive sheet according to an embodiment of the present invention. [Figure 2] FIG. 2A is a perspective view schematically illustrating an example of a thermally conductive sheet according to an embodiment of the present invention, and FIG. 2B is a partially enlarged cross-sectional view taken along line AA in FIG. 2A. [Figure 3] FIG. 3 is a cross-sectional schematic view showing the tip portion of an extruder and a T-die used in an example of a method for producing a thermally conductive sheet according to an embodiment of the present invention. [Figure 4] 4A to 4D are schematic views showing another example of the method for producing a thermally conductive sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The outline of the embodiments of the present invention will be listed and explained. (1) A resin composition containing silicone and a thermally conductive filler, It is reproducible, A thermally conductive sheet that maintains over 90% of its thermal conductivity when reproduced once.

[0012] (2) The thermally conductive sheet of (1) above preferably has a viscosity of 100 kPa·s or more and 300 kPa·s or less, measured with a capillary rheometer at a shear rate of 10 (1 / s) and a temperature of 30°C.

[0013] (3) In the thermally conductive sheet of (1) or (2) above, the content of the thermally conductive filler is preferably 50% by volume or more and 70% by volume or less.

[0014] (4) In the thermally conductive sheet of any one of (1) to (3) above, the silicone preferably contains 90% by mass or more of polydimethylsiloxane having a mass average molecular weight MW of 60,000 or more and 700,000 or less.

[0015] (5) In the thermally conductive sheet of any one of (1) to (4) above, the silicone is preferably composed solely of uncrosslinked silicone.

[0016] (6) In the thermally conductive sheet of any one of (1) to (5) above, the thermally conductive filler preferably contains an anisotropic thermally conductive filler and a non-anisotropic thermally conductive filler.

[0017] (7) In the thermally conductive sheet of (6), the anisotropic thermally conductive filler is one or both of carbon fiber and flake graphite powder; The non-anisotropic thermally conductive filler is preferably at least one selected from the group consisting of zinc oxide particles, aluminum nitride particles, aluminum oxide particles, and magnesium hydroxide particles.

[0018] (8) In the thermally conductive sheet of (3), the silicone contains 90% by mass or more of polydimethylsiloxane having a mass average molecular weight MW of 60,000 or more and 700,000 or less, The thermally conductive filler is carbon fiber, flake graphite powder, or a non-anisotropic thermally conductive filler; The carbon fiber content is 30% by volume or more and 40% by volume or less, The content of the graphite powder is preferably 5% by volume or more and 25% by volume or less.

[0019] Hereinafter, an embodiment of the present invention will be described. In the invention of the present disclosure, the term "thermally conductive sheet" is a concept that includes both a block-shaped product obtained after molding by extrusion molding or the like, and cut products (including sliced sheet-shaped products) obtained by appropriately cutting the block-shaped product. Here, an embodiment of the thermally conductive sheet will be described using a sliced sheet as an example.

[0020] The thermally conductive sheet according to this embodiment is a component provided between an IC chip and a heat sink. The thermally conductive sheet is made of a resin composition containing silicone and a thermally conductive filler. Here, silicone is a polymer compound having a main skeleton formed by siloxane bonds. Fig. 1 is a cross-sectional view schematically showing an IC chip to which a heat sink is attached via a thermally conductive sheet according to an embodiment of the present invention. Fig. 2A is a perspective view schematically showing an example of a thermally conductive sheet according to an embodiment of the present invention. Fig. 2B is a partially enlarged view of the cross section taken along line AA in Fig. 2A. In the drawings of the present application, all of FIGS. 1 to 4 are schematic diagrams and do not accurately reflect the actual dimensions of each member.

[0021] As shown in Fig. 1, the thermally conductive sheet 1 is disposed between the IC chip 11 and the heat sink 12. The thermally conductive sheet 1 is used with one surface in contact with the IC chip 11 and the other surface in contact with the heat sink 12. In this way, the heat sink 12 is attached to the IC chip 11 via the thermally conductive sheet 1. Therefore, the heat generated by the IC chip 11 is dissipated by the heat sink 12 to the outside of the housing (not shown).

[0022] 1 shows a usage example of a thermally conductive sheet 1 attached to the top surface of a single IC chip 11. On the other hand, the thermally conductive sheet according to the embodiment of the present invention may be a thermally conductive sheet attached so as to simultaneously cover heat-generating components such as multiple IC chips.

[0023] The thermally conductive sheet 1 can be reproduced (level material recycling), and is therefore environmentally friendly. The thermal conductive sheet 1 maintains 90% or more of its thermal conductivity after each reproduction. In other words, the thermal conductivity decreases by 10% or less after each reproduction compared to the thermal conductivity before reproduction. The thermal conductive sheet 1 has excellent material recyclability.

[0024] As shown in FIGS. 2A and 2B, the thermally conductive sheet 1 contains a matrix component 2 and a thermally conductive filler 4. In the thermally conductive sheet 1, the components other than the thermally conductive filler are collectively referred to as matrix components. In the thermally conductive sheet 1, weld lines may be formed in the thickness direction.

[0025] The matrix component 2 contains silicone, which gives the thermally conductive sheet 1 excellent heat resistance. In this embodiment, the silicone is mainly composed of uncrosslinked silicone. Here, the phrase "mainly composed of uncrosslinked silicone" means that the silicone may be partially crosslinked, as long as the recyclability is not impaired. The silicone is preferably composed of only uncrosslinked silicone. The silicone composition used to form the thermally conductive sheet 1 preferably does not contain a crosslinking agent.

[0026] As the uncrosslinked silicone, polydimethylsiloxane, which is a silicone in which all side chains are methyl groups and which does not contain unsaturated groups, is preferred. The silicone preferably contains 50% by mass or more of the polydimethylsiloxane, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The polydimethylsiloxane is a polymer with low reactivity and excellent stability. Therefore, by increasing the proportion of polydimethylsiloxane in silicone, the thermal conductivity of the thermally conductive sheet 1 can be maintained at a high level when recycled. In addition, increasing the proportion of polydimethylsiloxane is suitable for providing a thermally conductive sheet 1 with excellent flexibility. The polydimethylsiloxane may be an oil or a millable type.

[0027] The molecular weight of the polydimethylsiloxane is preferably 60,000 or more and 700,000 or less in terms of mass average molecular weight MW. If the mass average molecular weight MW of the polydimethylsiloxane is less than 60,000, the polydimethylsiloxane tends to bleed out from the thermally conductive sheet 1. On the other hand, if the mass average molecular weight MW of the polydimethylsiloxane exceeds 700,000, the moldability and processability during production of the thermally conductive sheet 1 tend to be poor.

[0028] In the presently disclosed invention, the mass average molecular weight MW of polydimethylsiloxane is the mass average molecular weight measured using gel permeation chromatography (GPC) using polystyrene as the standard substance in accordance with JIS-K7252-1:2008 "Plastics - Determination of average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 1: General rules."

[0029] The kinematic viscosity of the polydimethylsiloxane is preferably 10,000 cps or more and 100,000 cps or less at 25° C. as measured with an Ubbelohde viscometer. If the kinematic viscosity is less than 10,000 cps, the polydimethylsiloxane will easily bleed from the thermally conductive sheet 1. On the other hand, if the kinematic viscosity is more than 100,000 cps, the hardness of the thermally conductive sheet 1 will increase, and when placed between an IC chip and a heat sink, the thermally conductive sheet 1 may have poor adhesion and conformability to the contact surfaces of the IC chip and the heat sink.

[0030] The silicone may contain silicone having a crosslinkable functional group such as a vinyl group in an uncrosslinked state.

[0031] The matrix component 2 may contain other elastomer components and the like to the extent that the required properties of the thermally conductive sheet 1 are not impaired.

[0032] The matrix component 2 may contain general additives such as flame retardants, reinforcing agents, fillers, softeners, plasticizers, antioxidants, tackifiers, antistatic agents, kneaded adhesives, and coupling agents. Examples of the flame retardant include aluminum hydroxide, platinum compounds, triazole compounds, iron oxides such as red iron oxide and black iron, etc. These may be used alone or in combination of two or more.

[0033] The matrix component 2 preferably contains a coupling agent such as a silane coupling agent as an additive, particularly when zinc oxide particles are contained as the thermally conductive filler. By using zinc oxide particles and a silane coupling agent in combination, the flexibility of the thermally conductive sheet 1 can be increased.

[0034] Examples of the silane coupling agent include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, etc. These may be used alone or in combination of two or more.

[0035] The thermally conductive sheet 1 contains a thermally conductive filler 4 . The thermally conductive filler 4 preferably contains an anisotropic thermally conductive filler (hereinafter also referred to as an anisotropic filler) and a non-anisotropic thermally conductive filler (hereinafter also referred to as a non-anisotropic filler). In this case, it is easy to ensure both high thermal conductivity and flexibility, and the moldability during manufacturing is also good. On the other hand, if the thermally conductive sheet 1 contains only an anisotropic filler, cracks are likely to occur in the molded product during the manufacturing process (including the recycling process).Furthermore, if the thermally conductive sheet 1 contains only a non-anisotropic filler, it is difficult to increase the thermal conductivity of the thermally conductive sheet 1.

[0036] When the thermally conductive sheet 1 contains an anisotropic filler and a non-anisotropic filler, it is preferable that the particle size of the anisotropic filler is larger than the particle size of the non-anisotropic filler, which is suitable for ensuring excellent thermal conductivity.

[0037] In the thermally conductive filler, an anisotropic filler refers to a filler having an aspect ratio of 2.0 or more, and a non-anisotropic filler refers to a filler having an aspect ratio of less than 2.0. The aspect ratio of the thermally conductive filler refers to the larger of the ratio of the major axis of the filler to the minor axis of the filler and the ratio of the major axis of the filler to the thickness of the filler. The above-mentioned major axis, minor axis, and thickness correspond to the length, width, and height of the circumscribed rectangular parallelepiped of the filler, respectively.

[0038] The anisotropic filler includes fibrous fillers, scaly fillers, plate-like fillers, thin flake fillers, and the like. The aspect ratio of the anisotropic filler is preferably 5.0 or more. The non-anisotropic filler includes spherical fillers and irregularly shaped fillers.

[0039] The thermally conductive sheet 1 preferably contains, as the thermally conductive filler, a fibrous filler, a scaly filler, and a non-anisotropic filler. In this case, the thermal conductivity of the thermally conductive sheet 1 is easily increased.

[0040] In this case, the content of the fibrous filler is preferably greater than both the content of the scaly filler and the content of the non-anisotropic filler. In this case, the thermal conductivity of the thermally conductive sheet 1 is easily increased.

[0041] The thermally conductive sheet 1 contains, as thermally conductive fillers, for example, carbon fibers 4C, flaky graphite powder 4G, and non-anisotropic fillers 4P such as zinc oxide particles, aluminum nitride particles, aluminum oxide particles, or magnesium hydroxide particles. In this case, it is preferable that the carbon fibers 4C and graphite powder 4G of the thermally conductive sheet 1 are oriented substantially in the thickness direction of the thermally conductive sheet 1, and the non-anisotropic filler 4P is dispersed throughout the thermally conductive sheet 1. A thermally conductive sheet 1 having such a configuration is particularly suitable for increasing thermal conductivity.

[0042] The fiber length of the carbon fiber 4C is preferably 20 μm or more. If the fiber length is less than 20 μm, it may be difficult to form a heat conduction path, and the heat conductivity of the thermally conductive sheet 1 may be poor. On the other hand, the preferred upper limit of the fiber length of carbon fiber 4C is 500 μm from the viewpoint of ease of filling the thermally conductive sheet with the carbon fiber. The fiber length of the carbon fiber 4C is more preferably 50 μm or more and 300 μm or less, and further preferably 100 μm or more and 300 μm or less.

[0043] The fiber diameter of the carbon fiber 4C is preferably 5 μm or more. If the fiber diameter is less than 5 μm, it is difficult to form a heat conduction path, and the heat conductivity of the thermally conductive sheet 1 may be poor. A preferred upper limit of the fiber diameter of the carbon fibers 4C is 20 μm from the viewpoint of processability when producing the thermally conductive sheet 1 (including when recycling).

[0044] The fiber length of a fibrous filler such as carbon fiber refers to the arithmetic mean value of the length in the fiber direction determined using a microscopic image of the fibrous filler. The fiber diameter of a fibrous filler refers to the arithmetic mean value of the diameter direction dimension determined using a microscopic image of the fibrous filler. The above fiber length and the above fiber diameter are determined based on the measurement results obtained by obtaining a microscopic image of the fibrous filler, randomly selecting 20 fibrous fillers from the image, measuring the length in the fiber direction and the dimensions in the radial direction of the selected fibrous fillers.

[0045] As the carbon fiber 4C, one type of carbon fiber may be used, or two or more types of carbon fiber may be used. Carbon fibers with different thermal conductivities may be used in combination as the carbon fiber 4C. When carbon fibers with high thermal conductivity are used, the thermal conductivity increases, but flexibility tends to decrease. Therefore, by using carbon fibers with different thermal conductivities in combination, it becomes easier to increase both the thermal conductivity and flexibility of the thermally conductive sheet 1.

[0046] The graphite powder 4G is preferably in the form of flakes, which is suitable for aligning in the thickness direction of the thermally conductive sheet 1 and increasing the thermal conductivity in the thickness direction. The thermally conductive sheet 1 may contain graphite powder in a shape other than flakes as the graphite powder 4G. A combination of flake graphite powder and graphite powder in a shape other than flakes may also be used.

[0047] The particle size of the flake graphite powder 4G is preferably 5 μm or more and 50 μm or less. If the particle size of the flake graphite powder 4G is less than 5 μm, it is difficult to form a heat conduction path within the thermal conductive sheet 1. On the other hand, if the particle size of the flake graphite powder 4G is more than 50 μm, it is difficult to pack it densely. The particle size of the scaly graphite powder 4G is preferably 10 μm or more and 30 μm or less.

[0048] The particle size of a scaly filler such as scaly graphite powder refers to the D50 (50% median diameter) of the maximum length in the plate surface direction determined using a microscope image for measuring the particle size of the scaly filler. The particle size is determined by obtaining a microscopic image of the scale-like filler particles for particle size measurement, randomly selecting 20 scale-like fillers from the image, measuring the maximum length of the selected scale-like fillers in the plate surface direction, and then based on the measurement results.

[0049] The zinc oxide particles are preferably irregular in shape. In this case, the zinc oxide particles are less likely to damage the components of the manufacturing equipment.

[0050] The particle size of the zinc oxide particles is preferably 0.1 μm or more and 10 μm or less. If the particle size of the zinc oxide particles is less than 0.1 μm, it is difficult to form a heat conduction path. On the other hand, if the particle size of the zinc oxide particles exceeds 10 μm, the orientation of the carbon fiber 4C and the scaly graphite powder 4G is likely to be hindered. In addition, the zinc oxide particles are likely to damage the steel components of the manufacturing equipment.

[0051] The aluminum nitride particles are preferably irregular in shape. In this case, the aluminum nitride particles are less likely to damage the components of the manufacturing equipment.

[0052] The particle size of the aluminum nitride particles is preferably 0.1 μm or more and 10 μm or less. If the particle size of the aluminum nitride particles is less than 0.1 μm, it is difficult to form a heat conduction path. On the other hand, if the particle size of the aluminum nitride particles exceeds 10 μm, the orientation of the carbon fiber 4C and the scaly graphite powder 4G is likely to be hindered. In addition, the aluminum nitride particles are likely to damage the steel components of the manufacturing equipment.

[0053] The aluminum oxide particles (also called alumina particles) preferably have a spherical shape. In this case, it is easier to fill the thermally conductive sheet with alumina particles than with other shapes, and the alumina particles are less likely to damage the components of the manufacturing equipment.

[0054] The particle size of the alumina particles is preferably 1 μm or more and 10 μm or less. If the particle size of the alumina particles is less than 1 μm, it is difficult to form a heat conduction path. On the other hand, if the particle size of the alumina particles exceeds 10 μm, the orientation of the carbon fiber 4C and the graphite powder 4G is likely to be hindered. In addition, the alumina particles are likely to damage the steel components of the manufacturing equipment.

[0055] The magnesium hydroxide particles are preferably irregular in shape. In this case, the magnesium hydroxide particles are less likely to damage the components of the manufacturing equipment.

[0056] The particle size of the magnesium hydroxide particles is preferably 1 μm or more and 10 μm or less. If the particle size of the magnesium hydroxide particles is less than 1 μm, it is difficult to form a heat conduction path. On the other hand, if the particle size of the magnesium hydroxide particles exceeds 10 μm, the orientation of the carbon fiber 4C and the graphite powder 4G is likely to be hindered. In addition, the magnesium hydroxide particles are likely to damage the steel components of the manufacturing equipment.

[0057] In the embodiment of the present invention, the particle size of the thermally conductive filler other than the fibrous filler and the scaly filler refers to the value of the median diameter (d50) measured by a laser diffraction / scattering method.

[0058] The content of the thermally conductive filler 4 in the thermally conductive sheet 1 is preferably 50% by volume or more and 70% by volume or less. In particular, when the thermally conductive filler 4 contains carbon fiber 4C, scaly graphite powder 4G, and non-anisotropic filler 4P, the preferred content of the thermally conductive filler 4 in the thermally conductive sheet 1 is 50% by volume or more and 70% by volume or less of the total content of the carbon fiber 4C, scaly graphite powder 4G, and non-anisotropic filler 4P. If the total content of the carbon fiber 4C, the scaly graphite powder 4G, and the non-anisotropic filler 4P is less than 50% by volume, sufficient thermal conductivity may not be ensured. On the other hand, if the total content exceeds 70% by volume, the thermal conductive sheet 1 becomes too hard and may not be able to conform to the shape of the component to which the thermal conductive sheet 1 is attached, such as an IC chip, during installation. Furthermore, when the thermal conductive sheet 1 is bent, cracks may easily occur in the thermal conductive sheet 1. Furthermore, during the slicing process, which is one step in the manufacturing process of the thermal conductive sheet 1, cracks may occur in the sheet during molding, making it impossible to maintain the sheet shape. In the thermally conductive sheet 1, the total content of the carbon fibers 4C, the scaly graphite powder 4G, and the non-anisotropic filler 4P is preferably 55% by volume or more and 70% by volume or less, which is more suitable for achieving both good thermal conductivity and appropriate hardness.

[0059] The content of carbon fiber 4C in thermally conductive sheet 1 is preferably 30% by volume or more and 40% by volume or less, which is suitable for ensuring good thermal conductivity of thermally conductive sheet 1. When the content of carbon fiber 4C in thermally conductive sheet 1 is 30% by volume or more and 40% by volume or less, the content of graphite powder 4G is preferably 5% by volume or more and 25% by volume or less. By keeping the total content of the thermally conductive filler between 50% and 70% by volume and keeping the content of carbon fiber 4C and flake graphite powder 4G within the above ranges, it is possible to maintain good thermal conductivity even after recycling.

[0060] The total content of the scaly graphite powder 4G and the non-anisotropic filler 4P in the thermally conductive sheet 1 is preferably 20% by volume or more and 35% by volume or less, from the viewpoint of ensuring good thermal conductivity.

[0061] The thermally conductive sheet 1 preferably has a viscosity measured by a capillary rheometer at a shear rate of 10 (1 / s) and a temperature of 30°C (hereinafter also referred to as viscosity measured by a capillary rheometer) of 100 kPa·s or more and 300 kPa·s or less. In this case, it is suitable to maintain the thermal conductivity of 90% or more when the thermal conductive sheet 1 is reproduced.

[0062] If the viscosity measured with the capillary rheometer is less than 100 kPa·s, the silicone composition will have poor moldability, making it difficult to mold into the thermally conductive sheet 1. Even if molding is possible, the orientation of the anisotropic filler will be poor. If the viscosity measured by the capillary rheometer exceeds 300 kPa·s, the thermal conductivity decreases due to reproduction, making it difficult to maintain the thermal conductivity at 90% or more. One reason why the thermal conductivity decreases each time the silicone composition is recycled is thought to be that the thermally conductive filler is damaged during the process of reformulating the silicone composition (the kneading process) and during the process of extruding the resulting silicone composition (the extrusion molding process). In particular, when a fibrous filler such as carbon fiber is contained as the thermally conductive filler, the fibrous filler is prone to breakage during the kneading process or the extrusion molding process, and when the fibrous filler breaks, the thermal conductivity is likely to decrease significantly. In contrast, if the composition of the thermally conductive sheet 1 is such that the viscosity measured by the capillary rheometer is 300 kPa·s or less, the thermally conductive filler is less likely to be damaged during the kneading process and extrusion molding process for reproducing the thermally conductive sheet 1, and the thermal conductivity is less likely to decrease even when the thermally conductive sheet is reproduced. Furthermore, if the viscosity measured with the capillary rheometer exceeds 300 kPa·s, the composition will have poor fluidity and will be prone to agglomerates during the kneading process during reproduction, making it difficult to reproduce the sheet. Also, when the silicone composition is molded into a sheet, it may be difficult to orient the anisotropic filler. Furthermore, a thermally conductive sheet 1 having a viscosity of more than 300 kPa·s as measured by the capillary rheometer is prone to cracking when bent, and in this respect, may be difficult to handle. The viscosity measured by the capillary rheometer is more preferably 150 kPa·s or more and 250 kPa·s or less.

[0063] The viscosity measured with a capillary rheometer is measured using a measurement sample made by breaking down the thermally conductive sheet 1 into small pieces, with the capillary rheometer. The viscosity measurement using the capillary rheometer is carried out in accordance with JIS K 7199 (1999), with the shear rate set to 10 (1 / s) and the measurement temperature set to 30°C.

[0064] The apparent thermal conductivity of the thermally conductive sheet 1 is preferably 10 W / mK or more. The apparent thermal conductivity is the apparent thermal conductivity when the thermal conductive sheet 1 is compressed and deformed by 20% in the thickness direction (hereinafter, also simply referred to as apparent thermal conductivity). The apparent thermal conductivity is the thermal resistance (Kcm) measured when the thermal conductive sheet is compressed to a thickness of "thickness before measurement x 0.8" (20% compression). 2 / W) and the thickness (cm) of the thermally conductive sheet 1 at the time of measurement, according to the following calculation formula (1).

[0065] Apparent thermal conductivity (W / mK) = thickness of thermal conductive sheet at time of measurement (cm) ÷ thermal resistance value when compressed and deformed by 20% (Kcm 2 / W)×100 (1) The apparent thermal conductivity is more preferably 25 W / mK or more, and even more preferably 32 W / mK or more.

[0066] The thickness of the thermally conductive sheet 1 is not particularly limited, but is, for example, 0.05 mm to 3.0 mm. In this case, the thermally conductive sheet 1 can be suitably used as a member that efficiently transfers heat between the IC chip 11 and the heat sink 12. The thickness of the thermally conductive sheet 1 is preferably 0.05 mm or more and 2.5 mm or less. This ensures better heat dissipation performance while ensuring conformability to the contact surfaces of the IC chip 11 and the heat sink 12. On the other hand, if the thickness of the thermally conductive sheet 1 is less than 0.05 mm, it may not be able to conform fully to the contact surfaces of the IC chip 11 and the heat sink 12. Furthermore, if the thickness exceeds 2.5 mm, the heat dissipation performance may be poor due to the thermal resistance of the sheet itself.

[0067] The thermally conductive sheet 1 has, for example, a rectangular shape in plan view. In this case, the vertical and horizontal dimensions of the thermally conductive sheet 1 may be determined taking into consideration the dimensions of the component to which the thermally conductive sheet 1 is attached, such as the IC chip 11, and for example, both the vertical and horizontal dimensions are independently 10 mm or more and 120 mm or less. The planar shape of the thermally conductive sheet 1 is not limited to a rectangle, and may be a shape other than a rectangle, such as a circle or an ellipse. In the case of a circle, the diameter is, for example, 10 mm or more and 120 mm or less. In the case of an ellipse, the major axis or minor axis is, for example, 10 mm or more and 120 mm or less.

[0068] The thermally conductive sheet 1 is prepared, for example, by producing a large thermally conductive sheet by the manufacturing method described below, and then punching the obtained large thermally conductive sheet into sheets of a predetermined dimension and size. In the embodiment of the present invention, the remaining portion of the large thermal conductive sheet after the thermal conductive sheet 1 has been punched out to a predetermined shape and size can be used as a material for remanufacturing, enabling level material recycling. In this respect, the embodiment of the present invention is environmentally friendly.

[0069] Next, a method for producing the thermally conductive sheet 1 will be described. The thermally conductive sheet 1 can be produced, for example, by a first production method that includes the following steps (a) to (c). (a) preparing a silicone composition containing uncrosslinked silicone, a thermally conductive filler, and optional components such as a flame retardant and a coupling agent; (b) molding the prepared silicone composition; and (c) A step of slicing the molded silicone composition into sheets.

[0070] First, step (a) of preparing a silicone-based composition is carried out. Here, for example, the silicone composition is prepared by kneading uncrosslinked silicone, a thermally conductive filler, and various additives added as needed, using a two-roll mill. In this case, some or all of the components may be supplied in the form of a compound.

[0071] Next, the prepared silicone composition is molded in step (b), and the molded product is sliced into sheets in step (c). The silicone composition may be molded using, for example, an extruder. FIG. 3 is a cross-sectional schematic view showing the tip portion of an extruder and a T-die used in the production of a thermally conductive sheet 1 according to an embodiment of the present invention. The silicone composition introduced into the extruder 30 is stirred and kneaded by the screw 34 and introduced into the first gap 32 of the T-die along the flow path 31 .

[0072] The silicone composition that has been stirred and kneaded in the extruder 30 is first squeezed in the vertical direction (thickness direction) by the first gap 32 into a thin strip shape. At this time, the anisotropic thermally conductive filler mixed in the silicone-based composition is oriented in the flow direction (extrusion direction) of the silicone-based composition. Therefore, in the thin resin sheet 40 formed by passing through the first gap 32, the anisotropic thermally conductive filler is oriented in the plane direction of the resin sheet 40. In this embodiment, for example, carbon fiber or flake graphite powder corresponds to the anisotropic thermally conductive filler.

[0073] When the thin resin sheet 40 with the thermally conductive filler oriented therein passes completely through the first gap 32, the flow direction of the sheet, which had been limited to the extrusion direction, is released and the flow direction changes to a direction approximately perpendicular to the extrusion direction. The resin sheet 40, whose flow direction has changed to a direction approximately perpendicular to the extrusion direction, passes completely through the first gap 32 and is then further extruded toward the second gap 33. As a result, the resin sheet 40, now approximately perpendicular to the extrusion direction, is folded and stacked in the second gap 33. At this time, most of the anisotropic thermally conductive filler (carbon fiber and flake graphite powder) is oriented in the plane direction of the resin sheet 40, so that the anisotropic thermally conductive filler in the resin sheet 40 stacked in the second gap 33 is oriented along the thickness direction (the vertical direction in FIG. 3 ).

[0074] Thus, in step (b), the silicone composition is extruded to form a resin sheet 40 in which the anisotropic thermally conductive filler is oriented in the extrusion direction, and then this resin sheet 40 is folded and stacked to form a block. The silicone composition may be extruded in a heated environment of, for example, 30 to 150°C.

[0075] In the T-die, the depths of the first gap 32 and the second gap 33 (i.e., the dimensions of the first gap 32 and the second gap 33 in the direction perpendicular to the paper surface in FIG. 3) are substantially uniform throughout the T-die. Furthermore, the depth dimensions of the first gap and the second gap are not particularly limited, and various design changes are possible depending on the product width of the thermally conductive sheet 1 to be manufactured.

[0076] Then, in step (c), the block formed by stacking the thin resin sheets 40 is sliced in a direction perpendicular to the thickness direction, resulting in a thermally conductive sheet 1 having a predetermined thickness and in which the anisotropic thermally conductive filler is substantially oriented in the thickness direction. The block of resin sheet 40 produced in step (b) itself can also be used as a sheet-like thermally conductive sheet according to an embodiment of the present invention. The slicing process can be carried out using, for example, an ultrasonic cutter.

[0077] The method for producing the thermally conductive sheet 1 is not limited to the first production method described above, and may be, for example, a second production method in which the following steps (d) to (f) are carried out. 4A to 4D are diagrams illustrating the second manufacturing method.

[0078] (d) preparing a silicone composition containing uncrosslinked silicone, a thermally conductive filler, and optional components such as a flame retardant and a coupling agent; (e) molding the prepared silicone composition; and (f) A step of slicing the molded silicone composition into sheets.

[0079] First, step (d) of preparing a silicone-based composition is carried out. Here, for example, uncrosslinked silicone, a thermally conductive filler, and various additives added as needed are kneaded with two rolls 51. After that, a sheet is formed to produce a resin sheet 50 (see FIG. 4A). In this case, some or all of the components may be supplied in the form of a compound. The kneading may be carried out by heating the roll 51 to, for example, 30 to 150°C.

[0080] Next, step (e) is carried out to mold the silicone composition. In this step (e), resin sheets 50 made of a silicone-based composition are folded and stacked so that the resin sheets 50 are in close contact with each other (see FIG. 4A). For example, by continuously supplying resin sheets 50 onto a table 53 that repeats cyclic reciprocating motion, a laminate in which resin sheets 50 are stacked while being folded can be obtained. At this time, the anisotropic thermally conductive filler is oriented in the plane direction of the resin sheet 50.

[0081] Thereafter, the folded portion of the resin sheet 50 is cut and removed using a cutter 54 (see FIG. 4B). As a result, a laminate 55 of a plurality of resin sheets 50 that are not connected to one another is obtained.

[0082] Next, step (f) is performed in which the obtained laminate 55 is sliced using a cutter 57 in a direction perpendicular to the surface direction of the resin sheet 50 (see FIG. 4C), thereby obtaining a thermally conductive sheet 1 (see FIG. 4D). The thermally conductive sheet 1 can also be manufactured through these steps. The slicing process can be performed in the same manner as in the first manufacturing method.

[0083] Next, a method for reproducing the thermally conductive sheet 1 will be described. First, the finished thermally conductive sheet 1 is cut. Next, the cut thermally conductive sheet is kneaded using two rolls to prepare a silicone composition. Thereafter, similar to the first or second manufacturing method, the steps of molding the silicone composition and slicing the molded product into sheets are carried out to reproduce the thermally conductive sheet. At this time, fragments of the thermally conductive sheet generated during the manufacturing process of the thermally conductive sheet 1, such as fragments of the thermally conductive sheet generated when punching out the thermally conductive sheet 1 into the specified shape and dimensions described above, and silicone-based composition that did not constitute the thermally conductive sheet 1, etc., can also be recovered and used as materials for reproducing the thermally conductive sheet 1. [Example]

[0084] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples.

[0085] The raw materials used in the examples and comparative examples are as follows. (Silicone (matrix component)) Silicone (A): Silicone oil (Shin-Etsu Chemical Co., Ltd., KF-96-100,000cs) Silicone (B): Vinyl-containing compound (MR-53, manufactured by Dow Toray Industries, Inc.) Peroxide: (RC-4 50P FD, manufactured by Dow Toray Industries, Inc.)

[0086] (thermal conductive filler) Carbon fiber (A): Mitsubishi Chemical Corporation, K223HM (fibrous, fiber length: 200 μm / fiber diameter: 11 μm) Carbon fiber (B): Mitsubishi Chemical Corporation, K23EHM (fibrous, fiber length: 200 μm / fiber diameter: 11 μm) Graphite powder: Nippon Graphite Industries Co., Ltd., CPB (flake-shaped, particle size: 22 μm) Alumina particles: Denka Co., Ltd., ASFP-09S (spherical, particle size: 1 μm) Zinc oxide particles: Sakai Chemical Industry Co., Ltd., zinc oxide type 1 (irregular shape, particle size: 0.8 μm) Magnesium hydroxide particles: EP-1A (irregular shape, particle size: 2 μm), manufactured by Konoshima Chemical Co., Ltd. Aluminum nitride particles: HF01Da (irregular shape, particle size: 1 μm) manufactured by Tokuyama Corporation

[0087] Example 1 In this example, a thermally conductive sheet was manufactured by the first manufacturing method. 100 parts by mass of silicone (A), 118 parts by mass of carbon fiber (A), 60 parts by mass of carbon fiber (B), 60 parts by mass of graphite powder, 309 parts by mass of zinc oxide particles, and 16 parts by mass of magnesium hydroxide particles were kneaded using two rolls 51, and then sheeted out to produce a ribbon-shaped sheet (silicone-based composition) with a thickness of approximately 1.0 to 1.2 mm.

[0088] Next, the ribbon-shaped sheet thus produced was extruded into a 10 mm thick sheet (block) in a rubber single-screw extruder 30 using a mold having a first gap of 1 mm and a second gap of 10 mm (see FIG. 3). At this time, the temperature inside the extruder was adjusted to 100°C. The resulting sheet was then sliced perpendicular to the thickness direction to produce a thermally conductive sheet with a thickness of 2 mm. The slicing was performed using a single-edged fixed blade that was subjected to ultrasonic vibration. In this example, the volume fraction of carbon fiber (A) relative to the entire thermally conductive sheet is 20 volume %, the volume fraction of carbon fiber (B) is 10 volume %, the volume fraction of graphite powder is 10 volume %, the volume fraction of zinc oxide particles is 20 volume %, the volume fraction of magnesium hydroxide particles is 2.5 volume %, and the total volume fraction of the thermally conductive fillers is 62.5 volume %.

[0089] Example 2 A thermally conductive sheet was produced in the same manner as in Example 1, except that a ribbon-shaped sheet having a thickness of about 1.0 to 1.2 mm was produced by the following method. 100 parts by mass of silicone (A), 150 parts by mass of carbon fiber (A), 100 parts by mass of graphite powder, 14 parts by mass of magnesium hydroxide particles, and 18 parts by mass of aluminum nitride particles were kneaded using two rolls 51, and then the mixture was sheeted out to produce a ribbon-shaped sheet (silicone-based composition) having a thickness of approximately 1.0 to 1.2 mm. In this example, the volume fraction of carbon fiber (A) relative to the entire thermally conductive sheet is 30 volume %, the volume fraction of graphite powder is 20 volume %, the volume fraction of magnesium hydroxide particles is 2.5 volume %, and the volume fraction of aluminum nitride particles is 2.5 volume %, and the total volume fraction of the thermally conductive fillers is 55.0 volume %.

[0090] Example 3 In this example, a thermally conductive sheet was manufactured by the first manufacturing method. 100 parts by mass of silicone (A), 0.53 parts by mass of silicone (B), 0.23 parts by mass of peroxide, and 225 parts by mass of graphite powder were kneaded using two rolls 51, and then the mixture was sheeted out to produce a ribbon-shaped sheet (silicone-based composition) with a thickness of approximately 1.0 to 1.2 mm.

[0091] Next, the ribbon-shaped sheet thus produced was extruded into a 10 mm thick sheet (block) in a rubber single-screw extruder 30 using a mold having a first gap of 1 mm and a second gap of 10 mm (see FIG. 3). At this time, the temperature inside the extruder was adjusted to 100°C. Subsequently, the obtained sheet (block) was subjected to a heat treatment at 170° C. for 40 minutes for crosslinking treatment. The resulting sheet was then sliced perpendicular to the thickness direction to produce a thermally conductive sheet with a thickness of 2 mm. The slicing was performed using a single-edged fixed blade that was subjected to ultrasonic vibration. In this example, the volume fraction of the graphite powder relative to the entire thermally conductive sheet is 50.4% by volume, and the total volume fraction of the thermally conductive filler is 50.4% by volume.

[0092] (Comparative Example 1) A thermally conductive sheet was produced in the same manner as in Example 1, except that a ribbon-shaped sheet having a thickness of about 1.0 to 1.2 mm was produced by the following method. 100 parts by mass of silicone (A), 330 parts by mass of carbon fiber (A), 110 parts by mass of carbon fiber (B), 175 parts by mass of alumina particles, and 525 parts by mass of zinc oxide particles were kneaded using two rolls 51, and then sheeted out to produce a ribbon-shaped sheet (silicone-based composition) with a thickness of approximately 1.0 to 1.2 mm. In this comparative example, the volume fraction of carbon fiber (A) relative to the entire thermally conductive sheet is 33.75% by volume, the volume fraction of carbon fiber (B) is 11.25% by volume, the volume fraction of alumina particles is 10% by volume, and the volume fraction of zinc oxide particles is 20% by volume, and the total volume fraction of the thermally conductive fillers is 75.0% by volume.

[0093] (Comparative Example 2) A thermally conductive sheet was produced in the same manner as in Example 3, except that a ribbon-shaped sheet having a thickness of about 1.0 to 1.2 mm was produced by the following method. 100 parts by mass of silicone (A), 1.6 parts by mass of silicone (B), 0.68 parts by mass of peroxide, and 225 parts by mass of graphite powder were kneaded using two rolls 51, and then the mixture was sheeted out to produce a ribbon-shaped sheet (silicone-based composition) with a thickness of approximately 1.0 to 1.2 mm. In this comparative example, the volume fraction of the graphite powder relative to the entire thermally conductive sheet is 50% by volume, and the total volume fraction of the thermally conductive filler is 50.0% by volume.

[0094] [Evaluation test] (1) Apparent thermal conductivity at 20% compression The thermally conductive sheets produced in the examples and comparative examples were further cut to prepare evaluation samples having a diameter of 33 mm and a thickness of 2 mm. Using a TIMtester1400 (manufactured by AnalysisTech) as the measuring device, the sheet was compressed to a thickness of "thickness before measurement x 0.8" (20% compression), and the thermal resistance was measured in that state. Furthermore, based on the obtained thermal resistance values, the apparent thermal conductivity at 20% compression was calculated. The results are shown in Table 1.

[0095] (2) Viscosity measured by capillary rheometer The thermally conductive sheet was cut into small pieces, and a sufficient number of pieces to fill the barrel were prepared as measurement samples. The viscosity of the sample was measured at a shear rate of 10 (1 / s) using a capillary rheometer (RHEOGRAPH 75, manufactured by GOETTFERT). The results are shown in Table 1. Other measurement conditions are as follows: Short die L / D=0 / 1 (L=0.2mm) Barrel diameter: 15mm ·Measurement temperature: 30℃

[0096] (3) The handling properties of the sheet were evaluated according to the following criteria. Good: Can be used as a sheet without any problems. Bad: When handling the sheet, even slight bending causes the sheet to crack.

[0097] (4) Recyclability (thermal conductivity retention rate) The obtained thermally conductive sheet was cut into small pieces, kneaded with two rolls 51, and then released into a sheet to produce a ribbon-shaped sheet having a thickness of approximately 1.0 to 1.2 mm. Thereafter, the method employed in each of the examples and comparative examples was repeated to reproduce the thermally conductive sheet. The thermal conductivity of the obtained thermal conductive sheet (apparent thermal conductivity when compressed by 20%) was measured again, and the maintenance rate (%) of the apparent thermal conductivity relative to the previous value was calculated using the following formula. The results are shown in Table 1. Maintenance rate (%) = (apparent thermal conductivity at second time / apparent thermal conductivity at first time) x 100

[0098] [Table 1]

[0099] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0100] 1. Thermally conductive sheet 2. Matrix Components 4. Thermally conductive filler 4C Carbon Fiber 4G Graphite powder 4P Non-anisotropic filler 11 IC chip 12 Heat sink 30 Extruder 31 Flow path 32 First Gap 33 Second Gap 34 Screw 40, 50 Resin sheet 51 rolls 53 Table 54, 57 Cutter 55 Laminate

Claims

1. The adhesive layer is made of a resin composition containing silicone and a thermally conductive filler, The content of the thermally conductive filler is 50% by volume or more and 70% by volume or less, The viscosity measured by a capillary rheometer at a shear rate of 10 (1 / s) and a temperature of 30°C is 100 kPa s or more and 300 kPa s or less, It is reproducible, A thermally conductive sheet that maintains thermal conductivity of 90% or more when reproduced once.

2. A thermally conductive sheet as described in claim 1, excluding those containing the resin composition containing a copolymer having a (meth)acrylic monomer unit having an anionic group, a (meth)acrylic monomer unit having a cationic group, and a silicone (meth)acrylic monomer unit.

3. The thermally conductive sheet according to claim 1 or 2, wherein the silicone contains 90 mass % or more of polydimethylsiloxane having a mass average molecular weight MW of 60,000 or more and 700,000 or less.

4. The thermally conductive sheet according to claim 1 or 2, wherein the silicone is composed solely of uncrosslinked silicone.

5. The thermally conductive sheet according to claim 1 , wherein the thermally conductive filler contains an anisotropic thermally conductive filler and a non-anisotropic thermally conductive filler.

6. the anisotropic thermally conductive filler is one or both of carbon fiber and flake graphite powder; 6. The thermally conductive sheet according to claim 5, wherein the non-anisotropic thermally conductive filler is at least one selected from the group consisting of zinc oxide particles, aluminum nitride particles, aluminum oxide particles, and magnesium hydroxide particles.

7. The silicone contains 90% by mass or more of polydimethylsiloxane having a mass average molecular weight MW of 60,000 or more and 700,000 or less, The thermally conductive filler is carbon fiber, flake graphite powder, or a non-anisotropic thermally conductive filler; The content of the carbon fiber is 30% by volume or more and 40% by volume or less, 3. The thermally conductive sheet according to claim 1, wherein the content of the graphite powder is 5% by volume or more and 25% by volume or less.

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