Thermally conductive composition

Abstract

Disclosed is a sheet-shaped thermally conductive composition which is composed of a resin composition that contains a silicone and a thermally conductive filler. The sheet-shaped material has a Shore 00 hardness of 75 or less, and has an apparent thermal conductivity of 5W / mK or more when compressed and deformed by 20%. The contact angle of the surface of the sheet-shaped material with water is 95° or more.

Description

Thermally conductive composition

[0001] The present application claims priority to Japanese Application No. 2024-125925, filed August 1, 2024, and incorporates by reference the entire contents of said Japanese application.

[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). Heat generated in the heat-generating component is conducted to the heat-dissipating component via the thermal interface material. For example, Patent Document 1 proposes a thermally conductive sheet containing a resin and a particulate inorganic material as the thermally conductive material.

[0003] JP 2019-108497 A

[0004] Thermally conductive sheets are components that are required to have excellent thermal conductivity, and their thermal conductivity can be increased by increasing the amount of thermally conductive filler they contain. On the other hand, thermally conductive sheets tend to become harder as the content of thermally conductive filler increases. Thermally conductive sheets used on IC chips are attached to the IC chips while applying a predetermined compressive load. Furthermore, the harder the thermally conductive sheet, the greater the compressive load that must be applied when attaching it to the IC chip.

[0005] Therefore, when attaching a hard thermally conductive sheet with high thermal conductivity to an IC chip, a relatively large compressive load must be applied. On the other hand, a large compressive load places a large load on the IC chip. If the compressive load applied during attachment is maintained thereafter, the IC chip will continue to be subjected to a load. The application of a large load to the IC chip continuously can cause the IC chip to fail. For this reason, a soft thermally conductive sheet is required.

[0006] Furthermore, when attaching a thermally conductive sheet to a mating member such as a heat-generating component, it is sometimes required to have reworkability, i.e., the ability to easily peel it off and reattach it in order to correct misalignment. On the other hand, once attached, a soft thermally conductive sheet is very difficult to peel off from the mating member, and if it is forcibly peeled off, part of the thermally conductive sheet may remain on the mating member.

[0007] The present inventors have conducted extensive research under these circumstances and have an object to provide a sheet-shaped thermally conductive composition that is soft but has reworkability.

[0008] A thermally conductive composition according to one embodiment of the present invention is a sheet-shaped thermally conductive composition made of a resin composition containing silicone and a thermally conductive filler, wherein the sheet-shaped material has a Shore 00 hardness of 75 or less, an apparent thermal conductivity when compressed and deformed by 20% of 5 W / mK or more, and a contact angle of the surface of the sheet-shaped material with water of 95° or more.

[0009] This sheet-shaped thermally conductive composition has a surface with a contact angle of 95° or more with water, and therefore, despite its softness, it has good thermal conductivity and reworkability.

[0010] The thermally conductive composition according to one aspect of the present invention has reworkability, and can be reattached if misalignment occurs during attachment.

[0011] FIG. 1 is a cross-sectional view schematically illustrating an IC chip to which a heat sink is attached via a sheet-like thermally conductive composition according to an embodiment of the present invention. FIG. 2A is a perspective view schematically illustrating an example of a sheet-like thermally conductive composition according to an embodiment of the present invention. FIG. 2B is a partially enlarged view of the cross section along line A-A in FIG. 2A. FIG. 3 is a cross-sectional schematic diagram of the tip portion of an extruder and a T-die used in producing a sheet-like thermally conductive composition according to an embodiment of the present invention. FIGS. 4A to 4D are schematic views showing another example of a method for producing a sheet-like thermally conductive composition according to an embodiment of the present invention. FIG. 5 is a front view schematically illustrating a cutter equipped with a band knife. FIG. 6 is a partial cross-sectional view along line C-C in FIG. 5.

[0012] The outline of the embodiments of the present invention will be described below: (1) A thermally conductive composition according to one aspect of the present invention is a sheet-shaped thermally conductive composition made of a resin composition containing silicone and a thermally conductive filler, wherein the sheet-shaped material has a Shore 00 hardness of 75 or less, an apparent thermal conductivity when compressed and deformed by 20% of 5 W / mK or more, and a contact angle of the surface of the sheet-shaped material with water of 95° or more.

[0013] (2) In the thermally conductive composition of (1) above, the resin composition preferably contains polydimethylsiloxane as the silicone.

[0014] (3) In the thermally conductive composition of (1) or (2) above, the resin composition preferably contains an anisotropic thermally conductive filler as the thermally conductive filler.

[0015] Detailed descriptions of embodiments of the present invention are provided below. A sheet-shaped thermally conductive composition according to an embodiment of the present invention is a component disposed between an IC chip and a heat sink. The thermally conductive composition is a resin composition containing silicone and a thermally conductive filler. Here, silicone is a polymeric compound having a main skeleton formed by siloxane bonds. FIG. 1 is a cross-sectional view schematically illustrating an IC chip to which a heat sink is attached via a sheet-shaped thermally conductive composition according to an embodiment of the present invention. FIG. 2A is a perspective view schematically illustrating an example of a sheet-shaped thermally conductive composition according to an embodiment of the present invention, and FIG. 2B is a partially enlarged view of the cross section taken along line A-A in FIG. 2A. Note that all drawings in this application are schematic diagrams and do not accurately reflect the actual dimensions of each component.

[0016] As shown in Fig. 1, a sheet-like thermally conductive composition 1 (hereinafter also referred to as thermally conductive sheet 1) is placed between an IC chip 11 and a 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, heat generated by the IC chip 11 is dissipated by the heat sink 12 to the outside of a housing (not shown).

[0017] 1 shows a usage mode of the thermally conductive sheet 1 attached to the upper surface of one IC chip 11. On the other hand, the sheet-shaped thermally conductive composition (thermally conductive sheet) according to an embodiment of the present invention may be a thermally conductive sheet that is attached so as to simultaneously cover heat-generating components such as multiple IC chips.

[0018] The thermal conductive sheet 1 has a Shore 00 hardness of 75 or less. Therefore, the thermal conductive sheet 1 is soft and can reduce the load on the mating material during attachment. It also has good conformability to the mating material. The lower limit of the Shore 00 hardness of the thermal conductive sheet 1 is, for example, 5. The preferred Shore 00 hardness of the thermal conductive sheet 1 is 10 or more and 73 or less.

[0019] The Shore 00 hardness of the thermally conductive sheet 1 may be measured using a durometer for measuring Shore 00 hardness, such as GS-754G, Type 00 (manufactured by Teclock). In measuring the Shore 00 hardness, the thickness of the thermally conductive sheet 1 to be measured is 12 mm or more. If the thickness of the thermally conductive sheet 1 to be measured is less than 12 mm, multiple thermally conductive sheets 1 are stacked to achieve a thickness of 12 mm or more before measurement.

[0020] The thermal conductive sheet 1 has an apparent thermal conductivity of 5 W / mK or more when compressed and deformed by 20% in the thickness direction. By setting the apparent thermal conductivity to 5 W / mK or more, the thermal conductivity of the thermal conductive sheet 1 is ensured. The apparent thermal conductivity of the thermal conductive sheet 1 is preferably 6 W / mK or more.

[0021] The apparent thermal conductivity of the thermal conductive sheet 1 is calculated by the thermal resistance (Kcm) measured when the 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 at the time of measurement, according to the following calculation formula (1).

[0022] 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)

[0023] The thermal resistance value when the thermal conductive sheet 1 is compressed and deformed by 20% is measured using a thermal conductivity measuring device (for example, TIMtester 1400 (manufactured by AnalysisTech)) in a state where the thermal conductive sheet 1 is compressed and deformed by 20%.

[0024] The contact angle of the thermally conductive sheet 1 with water is 95° or more. In the present invention, the contact angle is a static contact angle. The contact angle is measured using a contact angle measuring device such as an automatic contact angle meter DM-501 (manufactured by Kyowa Interface Science Co., Ltd.). The contact angle is measured by dropping a liquid onto the front or back surface of the thermally conductive sheet 1. In this case, ion-exchanged water is used as the dropped liquid. The upper limit of the contact angle of the thermally conductive sheet 1 with water is, for example, 150°. Therefore, the contact angle of the thermally conductive sheet 1 with water is, for example, 95° or more and 150° or less.

[0025] The contact angle of either the front or back surface of the thermally conductive sheet 1 may be 95° or more, but it is preferable that the contact angle of both surfaces of the thermally conductive sheet 1 is 95° or more. In this case, the sheet can be used without worrying about the orientation.

[0026] The thermally conductive sheet 1 has a surface that has a contact angle with water of 95° or more. Therefore, the thermally conductive sheet 1 has reworkability. When the surface of the thermally conductive sheet 1 having the contact angle of 95° or more is attached to a mating material, the thermally conductive sheet 1 is suitable for being peeled off and reattached after being attached once.

[0027] The present inventors have found that reworkability of a thermally conductive sheet can be imparted by reducing the surface free energy of the surface of the thermally conductive sheet and thereby reducing its wettability with a mating material such as a heat sink. Furthermore, the present inventors have focused on the contact angle with water as an alternative index of surface free energy and have found that good reworkability can be ensured by making the contact angle with water of the thermally conductive sheet 1 95° or more.

[0028] The surface of the thermally conductive sheet 1 having the contact angle of 95° or more has moderately reduced adhesion to the mating material. Therefore, once the surface of the thermally conductive sheet 1 having the contact angle of 95° or more is attached to the mating material, it can be peeled off from the mating material without causing damage to the thermally conductive sheet 1. On the other hand, if a thermally conductive sheet having a surface having a contact angle of less than 95° with water is once attached to the mating material and then peeled off, cohesive failure occurs on the attached surface.

[0029] The mating material of the thermally conductive sheet 1 is preferably made of aluminum (or an aluminum alloy) from the viewpoint of being suitable for exhibiting good reworkability.

[0030] The thickness of the thermally conductive sheet 1 is not particularly limited, but is, for example, 0.01 mm or more and 3.0 mm or less. 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 0.01 mm or more and 2.5 mm or less. This ensures superior heat dissipation performance while ensuring conformability to the shapes 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 0.01 mm, it may not be able to fully conform to the shapes of the IC chip 11 and the heat sink 12. Furthermore, if the thickness exceeds 2.5 mm, the thermal resistance of the sheet itself may result in poor heat dissipation performance.

[0031] The planar shape of the thermally conductive sheet 1 is, for example, rectangular. In this case, the vertical and horizontal dimensions of the thermally conductive sheet 1 may be determined taking into consideration the dimensions of the member 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 to 120 mm. The planar shape of the thermally conductive sheet 1 is not limited to rectangular, and may be a shape other than rectangular, such as circular or elliptical. In the case of a circular shape, the diameter is, for example, 10 mm to 120 mm. In the case of an elliptical shape, the major axis or minor axis is, for example, 10 mm to 120 mm.

[0032] 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, all components other than the thermally conductive filler are collectively referred to as the matrix component. The thermally conductive sheet 1 may have weld lines formed in the thickness direction.

[0033] The matrix component 2 contains silicone. Therefore, the thermally conductive sheet 1 has excellent heat resistance. In an embodiment of the present invention, the silicone may contain a cross-linked silicone (hereinafter also referred to as cross-linked silicone), but from the viewpoint of ensuring flexibility, it is preferable that the silicone is primarily composed of uncross-linked silicone. Here, "primarily composed of uncross-linked silicone" means that the proportion of uncross-linked silicone in the total silicone is 50 mass % or more. The silicone may be composed solely of uncross-linked silicone.

[0034] The uncrosslinked silicone is preferably polydimethylsiloxane, which is a silicone whose side chains are all methyl groups and contain no unsaturated groups. 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 the polydimethylsiloxane in the silicone, the flexibility of the thermally conductive sheet 1 can be improved.

[0035] The polydimethylsiloxane may be an oil or a millable type, and it is only necessary to select one that has good moldability when producing the thermally conductive sheet 1 by the method described below.

[0036] The molecular weight of the polydimethylsiloxane is preferably 40,000 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 40,000, the polydimethylsiloxane tends to bleed out from the thermal 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 thermal conductive sheet 1 tend to be poor.

[0037] In the present invention, the weight average molecular weight MW of the polydimethylsiloxane is a weight average molecular weight measured using gel permeation chromatography (GPC) using polystyrene as a 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."

[0038] The kinematic viscosity of the polydimethylsiloxane was 3000 mm at 25°C as measured with an Ubbelohde viscometer. ２ / s or more 300000mm ２ The kinematic viscosity is preferably 3000 mm / s or less. ２ If the kinematic viscosity is less than 300,000 mm / s, polydimethylsiloxane will easily bleed out from the thermally conductive sheet 1. ２ If the hardness exceeds 1 / s, the thermal conductive sheet 1 becomes too hard, and when placed between an IC chip and a heat sink, the sheet may have poor adhesion and conformability to the contact surfaces of the IC chip and the heat sink.

[0039] When the silicone contains a crosslinked silicone, the crosslinked silicone may be one that has been crosslinked by peroxide or one that has been crosslinked by an addition reaction, but one that has been crosslinked by peroxide is preferred. This is because crosslinked silicones that have been crosslinked by peroxide crosslinking have better heat resistance. Examples of the crosslinked silicone include those obtained by crosslinking silicones that have crosslinkable functional groups such as vinyl groups in part of their side chains (including terminals).

[0040] The silicone may contain silicone having a crosslinkable functional group such as a vinyl group in an uncrosslinked state.

[0041] 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.

[0042] The matrix component 2 may contain common additives such as flame retardants, reinforcing agents, fillers, softeners, plasticizers, antioxidants, tackifiers, antistatic agents, kneaded adhesives, and coupling agents. Examples of the flame retardants include magnesium hydroxide, aluminum hydroxide, platinum-based compounds, triazole-based compounds, iron oxides such as red iron oxide and black iron. These may be used alone or in combination of two or more.

[0043] The matrix component 2 may contain a coupling agent such as a silane coupling agent as an additive. When zinc oxide particles are contained as the thermally conductive filler, the flexibility of the thermally conductive sheet 1 can be increased by adding a silane coupling agent.

[0044] 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.

[0045] The thermally conductive sheet 1 contains a thermally conductive filler 4. The thermally conductive filler 4 may be a conductive filler such as carbon fiber, or an insulating filler such as boron nitride.

[0046] The thermally conductive sheet 1 may contain only one type of thermally conductive filler, or may contain two or more types of thermally conductive fillers. When two or more types of thermally conductive fillers are contained, the thermally conductive filler 4 may contain 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 formability during manufacturing is also good.

[0047] In the thermally conductive filler, an anisotropic filler refers to a filler with an aspect ratio of 2.0 or more, and a non-anisotropic filler refers to a filler with 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 major axis, minor axis, and thickness correspond to the length, width, and height, respectively, of the circumscribed rectangular parallelepiped of the filler.

[0048] The anisotropic filler includes fibrous fillers, scaly fillers, plate-like fillers, flaky fillers, etc. The aspect ratio of the anisotropic filler is preferably 5.0 or more. The non-anisotropic filler includes spherical fillers, irregular fillers, etc.

[0049] Examples of the thermally conductive filler include carbon fiber, graphite powder, boron nitride powder, zinc oxide particles, aluminum nitride particles, aluminum oxide particles, and magnesium hydroxide particles.

[0050] The thermally conductive sheet 1 preferably contains an anisotropic filler. When a thermally conductive sheet containing an anisotropic filler as the thermally conductive filler is manufactured through a slicing process by pull-cutting, which will be described later, the contact angle of the cut surface with water due to the slicing process is likely to be increased.

[0051] An example of a preferred thermally conductive filler 4 is one containing carbon fibers 4C, scaly graphite powder 4G, and zinc oxide particles 4Z (see FIG. 2B ). In this case, it is preferable that the carbon fibers 4C and graphite powder 4G are oriented substantially in the thickness direction of the thermally conductive sheet 1, and the non-anisotropic filler is dispersed throughout the thermally conductive sheet 1. A thermally conductive sheet 1 having such a configuration is particularly suitable for increasing thermal conductivity.

[0052] Another preferred example of the thermally conductive filler 4 is one containing boron nitride powder and aluminum oxide particles, which results in a thermally conductive sheet with good thermal conductivity and insulating properties.

[0053] The content of the thermally conductive filler 4 in the thermally conductive sheet 1 is preferably 45% by volume or more and 70% by volume or less. If the total content of the thermally conductive filler 4 is less than 45% by volume, sufficient thermal conductivity may not be ensured. On the other hand, if the total content exceeds 70% by volume, the thermally conductive sheet 1 may become too hard. A more preferred content of the thermally conductive filler 4 is 45% by volume or more and 65% by volume or less.

[0054] Next, we will explain the method for producing the thermally conductive sheet 1. The thermally conductive sheet 1 can be produced, for example, by a first production method that involves the following steps (a) to (c): (a) preparing a silicone-based composition containing silicone, a thermally conductive filler, and optional components such as a flame retardant and a coupling agent; (b) molding the prepared silicone-based composition; and (c) slicing the molded silicone-based composition into sheets.

[0055] First, step (a) of preparing a silicone-based composition is carried out. Here, the silicone-based composition is prepared, for example, by kneading silicone, a thermally conductive filler, and various additives added as needed using a twin roll mill. At this time, some or all of the components may be compounded and supplied. This step (a) may be carried out while heating. At this time, only part of the step may be carried out while heating.

[0056] Next, the prepared silicone composition is molded in step (b) and sliced ​​into sheets in step (c). The silicone composition can be molded, for example, using an extruder. Figure 3 is a cross-sectional schematic diagram showing the tip of an extruder and a T-die used in the manufacture 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 a screw 34 and introduced into a first gap 32 of the T-die along a flow path 31.

[0057] The silicone-based composition stirred and kneaded in the extruder 30 is first squeezed in the vertical direction (thickness direction) by the first gap 32 to form a thin strip. 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 after passing through the first gap 32, the anisotropic thermally conductive filler is oriented in the plane direction of the resin sheet 40. In embodiments of the present invention, for example, carbon fiber, scaly graphite powder, or boron nitride powder corresponds to the anisotropic thermally conductive filler.

[0058] When the thin resin sheet 40 in which the thermally conductive filler is oriented passes completely through the first gap 32, the flow direction of the sheet, which was limited to the extrusion direction, is released and the flow direction changes to a direction approximately perpendicular to the extrusion direction. After completely passing through the first gap 32, the resin sheet 40, whose flow direction has changed to a direction approximately perpendicular to the extrusion direction, is 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 fillers (carbon fiber and flake graphite powder or boron nitride powder) are oriented in the plane direction of the resin sheet 40, so that the anisotropic thermally conductive fillers in the resin sheet 40 stacked in the second gap 33 are oriented along the thickness direction (the vertical direction in FIG. 3 ).

[0059] 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 laminated to produce a block (laminate). Step (b) may be performed while heating. In this case, only part of the step may be performed while heating.

[0060] 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.

[0061] Then, in step (c), the block in which the thin resin sheets 40 are stacked in the extrusion direction 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.

[0062] The slicing process is preferably carried out using a slicing machine equipped with a band knife. Using a slicing machine equipped with a band knife to slice in a direction perpendicular to the orientation direction of the thermally conductive filler makes it easier to form a cut surface with a contact angle of 95° or more with respect to water. This is thought to be because the thermally conductive filler, which is oriented in the thickness direction and can be cut during slicing, is less likely to fall in a direction perpendicular to the thickness direction (plane direction), making it easier to form a cut surface by slicing in which the cut surface of the anisotropic filler is exposed on the surface. This will be explained in more detail below.

[0063] When a block in which anisotropic thermally conductive fillers are oriented in the thickness direction is sliced ​​along the surface direction (perpendicular to the thickness direction), comparing slicing by pull-cutting and slicing by push-cutting, the load on the anisotropic filler during processing is greater with slicing by push-cutting. Therefore, with slicing by push-cutting, the anisotropic filler is more likely to tip toward the surface direction during processing. Here, "the anisotropic filler tipping toward the surface direction" refers to the anisotropic filler tilting so that the angle between the major axis of the anisotropic filler and the surface direction becomes smaller. In other words, with slicing by pull-cutting, the anisotropic filler is less likely to tip toward the surface direction during processing, and the cut surface of the anisotropic filler is more likely to be exposed on the cut surface of the block that appears after slicing.

[0064] Furthermore, if the anisotropic filler particles fall toward the surface during processing, the orientation of the anisotropic filler particles, which were oriented in the thickness direction of the block before processing, will decrease. This decrease in orientation will lead to a decrease in thermal conductivity. Therefore, slicing by pulling cuts makes it easier to ensure high thermal conductivity.

[0065] Such differences in the resistance of anisotropic fillers to collapse due to the processing method are particularly noticeable when slicing a block with low hardness (a block with a soft matrix itself or a block with a low filler content). When slicing a block with high hardness (a block with a hard matrix itself or a block with a high filler content), even if a push-cut slicing process is used, which places a large load on the anisotropic filler during processing, the block (a mixture of matrix and filler) is hard, so the anisotropic filler is less likely to collapse, and most of the anisotropic filler is cut without collapsing. Therefore, when slicing a block with high hardness, there is no significant difference in the degree of exposure of the cut surface of the anisotropic filler at the cut surface of the block, depending on whether a push-cut slicing process or a pull-cut slicing process is used.

[0066] In contrast, when slicing a block with low hardness, the anisotropic filler is less likely to tip toward the surface during processing when slicing by pull-cutting is used, and more of the anisotropic filler is cut without tipping compared to when slicing by push-cutting is used. Therefore, the cut surface of the anisotropic filler is more likely to be exposed on the cut surface of the block when slicing by pull-cutting. In other words, the surface (uncut surface) of the anisotropic filler is more likely to be exposed on the cut surface of the block when slicing by push-cutting. In particular, when manufacturing a soft thermal conductive sheet such as a thermal conductive sheet with a Shore 00 hardness of 75 or less, using the slicing by pull-cutting makes it easier to expose the cut surface of the anisotropic filler on the cut surface.

[0067] Furthermore, when slicing by pull-cutting is used, as described above, the cut surfaces of the anisotropic filler tend to be exposed on the cut surfaces of the block, and in this case, the surface of the thermally conductive sheet has fine irregularities due to the presence of the cut surfaces of the anisotropic filler, increasing the surface area. Therefore, combined with the fact that the matrix is ​​silicone, the surface of the thermally conductive sheet 1 increases the contact angle with water, making it easier to ensure the contact angle of 95° or more.

[0068] The cutting machine equipped with the band knife includes a pair of pulleys and an endless band knife stretched across the pair of pulleys. The band knife rotates around the pair of pulleys in accordance with the rotation of the pulleys. The band knife is made of, for example, steel. The band knife has a cutting blade on one end surface in the width direction. This cutting blade may be single-edged or double-edged. The dimensions of the band knife are not particularly limited, but the width of the band knife is, for example, 20 mm to 100 mm, and the thickness of the band knife is, for example, 0.4 mm to 1.0 mm.

[0069] The above-mentioned band knife-equipped sliding cutter preferably further includes a grinding mechanism (also called a dressing mechanism). In this case, the cutting edge of the cutting blade is continuously sharpened, allowing the cutting edge to be kept sharp during slicing. Specific examples of band knife-equipped sliding cutters will be described later.

[0070] In the above-mentioned band knife-equipped sliding cutter, the rotation speed of the band knife is preferably 0.3 m / min or more and 400 m / min or less. This is suitable for forming a cut surface with low surface roughness. If the rotation speed is less than 0.3 m / min, it may not be possible to slice the block. On the other hand, if the rotation speed exceeds 400 m / min, the knife may vibrate excessively, causing the slice thickness to become unstable.

[0071] The method for manufacturing the thermally conductive sheet 1 is not limited to the first manufacturing method described above, but may be, for example, a second manufacturing method in which the following steps (d) to (f) are performed. Figures 4A to 4D are diagrams illustrating the second manufacturing method.

[0072] (d) preparing a silicone-based composition containing silicone, a thermally conductive filler, and optional components such as a flame retardant and a coupling agent; (e) molding the prepared silicone-based composition; and (f) slicing the molded silicone-based composition into sheets.

[0073] First, step (d) of preparing a silicone-based composition is carried out. Here, for example, silicone, a thermally conductive filler, and various additives added as needed are kneaded using a twin roll 51. Then, a sheet is formed to produce a resin sheet 50 (see FIG. 4A). At this time, some or all of the components may be compounded and supplied. This step (d) may be carried out while heating. At this time, only part of the step may be carried out while heating.

[0074] Next, step (e) of molding the silicone-based composition is performed. In this step (e), resin sheets 50 made of the 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 the resin sheets 50 onto a table 53 that periodically reciprocates, a laminate can be obtained in which the resin sheets 50 are stacked while being folded. At this time, the anisotropic thermally conductive filler is oriented in the plane direction of the resin sheets 50.

[0075] 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 multiple resin sheets 50 that are not connected to each other is obtained. This step (e) may be performed while heating is applied to part or all of the step. In this case, heating may be applied to only part of the step.

[0076] Next, step (f) is performed in which the obtained laminate 55 is sliced ​​in a direction perpendicular to the surface of the resin sheet 50 (see FIG. 4C). This allows the thermally conductive sheet 1 to be obtained (see FIG. 4D). For the same reasons as in the first manufacturing method, the slicing is preferably performed using a pull-cutting machine equipped with a band knife 57. The thermally conductive sheet 1 can also be manufactured through these steps.

[0077] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples.

[0078] The raw materials used in the examples and comparative examples are as follows: (Matrix components) Silicone A: silicone oil (polydimethylsiloxane with a mass average molecular weight of 100,000) Silicone B: silicone oil (polydimethylsiloxane with a mass average molecular weight of 40,000) Silicone C: silicone rubber (DY32-1005U, manufactured by Dow Toray Industries, Inc.) Silicone D: vinyl group-containing silicone compound (MR-53, manufactured by Dow Toray Industries, Inc.) Peroxide: mixture of (RC-4 50P FD, manufactured by Dow Toray Industries, Inc.) Silane coupling agent: octyltrimethoxysilane

[0079] (Thermal conductive filler) Carbon fiber: Mitsubishi Chemical Corporation, K223HM (fibrous, fiber length: 200 μm / fiber diameter: 11 μm) Graphite powder: Nippon Graphite Industries Co., Ltd., CPB, flaky, particle size: 22 μm) Boron nitride powder A: Dandong Chemical Engineering Institute Co., Ltd., HSL100, flaky, 30 μm) Boron nitride powder B: Dandong Chemical Engineering Institute Co., Ltd., HSPD50, flaky, 50 μm) Zinc oxide particles: Sakai Chemical Industry Co., Ltd., zinc oxide type 1 (irregular, particle size: 0.8 μm) Alumina particles: Sumitomo Chemical Co., Ltd., irregular, NXA-100

[0080] In the thermally conductive filler, the particle sizes of the graphite powder, boron nitride powder A, boron nitride powder B, zinc oxide particles, and alumina particles are all median diameters (d50) of particle size distributions measured on a volume basis using a laser diffraction / scattering particle size distribution analyzer. (Example 1) In this example, a thermally conductive sheet 1 was produced using the first manufacturing method described above. 100 parts by mass of silicone A, 4 parts by mass of silane coupling agent, 177 parts by mass of carbon fiber, 60 parts by mass of graphite powder, and 304 parts by mass of zinc oxide particles were kneaded using a two-roll mill 51 and then sheeted out to produce a ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm. In this example, the volume fraction of the carbon fiber, graphite powder, and zinc oxide particles in the entire resin sheet was 30% by volume, 10% by volume, and 20% by volume, respectively, for a total volume fraction of the thermally conductive fillers of 60% by volume.

[0081] Next, the ribbon-shaped resin sheet thus produced was fed into an extruder 30, and a block having a thickness of 10 mm was produced using a T-die (see FIG. 3) having a first gap 32 having a thickness of 1 mm and a second gap 33 having a thickness of 10 mm. In this block, the carbon fiber and graphite powder were oriented in the thickness direction.

[0082] The obtained block was then sliced ​​in a direction perpendicular to the thickness direction to produce a 2 mm thick thermally conductive sheet 1 in which the carbon fibers and graphite powder were oriented in the thickness direction. Here, the block produced using the extruder 30 was sliced ​​using a cutter 60 equipped with a band knife 61.

[0083] Figures 5 and 6 are diagrams illustrating a cutting machine 60 equipped with a band knife 61. Figure 5 is a front view of the cutting machine 60, and Figure 6 is a partial cross-sectional view taken along line CC in Figure 5. Figure 6 is a diagram illustrating the relationship between a table 67, the band knife 61, and a feed roller 65. The cutting machine 60 equipped with the band knife 61 is a sliding cutter. The cutting machine 60 includes a pair of pulleys 63A and 63B, an endless band knife 61 stretched across the pair of pulleys 63A and 63B, a table 67 on which the workpiece (block B) is placed, a feed roller 65 for transporting the workpiece to the travel area of ​​the band knife 61, and a dressing mechanism (grinding mechanism) 69 for continuously sharpening the teeth of the band knife 61. The feed roller 65 includes an upper feed roller 65A and a lower feed roller 65B. The dressing mechanism 69 includes a pair of grinding rollers 69A and 69B. The teeth of the band knife 61 are double-edged.

[0084] In this process, the block B was sliced ​​using a cutting machine 60 shown in Figures 5 and 6. Specifically, the block B was placed on a table 67 and sliced ​​with a band knife 61 while being transported by a feed roller 65. In Figure 6, the band knife 61 rotates in a direction penetrating the page from the front to the back. At this time, the rotation speed of the band knife 61 was set to 226 m / min. Processing was performed with the dressing mechanism 69 driven.

[0085] Example 2 A thermally conductive sheet was completed in the same manner as in Example 1, except that a ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm was prepared by the following method. 104 parts by mass of silicone B, 100 parts by mass of silicone C, and 450 parts by mass of boron nitride powder A were kneaded using two rolls 51 and then sheeted out to prepare a ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm. In this example, the volume fraction of boron nitride A relative to the entire resin sheet was 49% by volume, and the total volume fraction of the thermally conductive filler was 49% by volume.

[0086] Example 3 A thermally conductive sheet was completed in the same manner as in Example 1, except that a ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm was prepared using the following method. 100 parts by mass of silicone A, 6 parts by mass of silane coupling agent, 220 parts by mass of boron nitride powder B, and 145 parts by mass of alumina particles were kneaded using two rolls 51 and then sheeted out to prepare a ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm. In this example, the volume fraction of boron nitride powder B relative to the entire resin sheet was 40% by volume, the volume fraction of alumina particles was 15% by volume, and the total volume fraction of the thermally conductive filler was 55% by volume.

[0087] Comparative Example 1 A thermally conductive sheet was completed in the same manner as in Example 1, except that push-cutting with a blade was selected instead of pull-cutting (slicing) with a band knife. Here, a double-edged blade with a cutting edge angle of 30° was used as the blade.

[0088] (Comparative Example 2) A thermally conductive sheet was completed in the same manner as in Example 2, except that push-cutting with a blade was selected instead of pull-cutting (slicing) with a band knife. Here, a double-edged blade with a cutting edge angle of 30° was used as the blade.

[0089] Comparative Example 3 A ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm was produced by the method described below, and then a block having a thickness of 10 mm was produced in the same manner as in Example 1. 100 parts by mass of silicone B, 100 parts by mass of silicone C, 3.2 parts by mass of silicone D, 1.4 parts by mass of peroxide, and 450 parts by mass of boron nitride powder A were kneaded using two rolls 51, and then the mixture was sheeted out to produce a ribbon-shaped resin sheet made of a silicone-based composition and having a thickness of approximately 1.0 to 1.2 mm.

[0090] The resulting block was then cross-linked at 160°C for 40 minutes. The cross-linked block was then sliced ​​using a double-edged blade with a 30° cutting angle to produce a thermally conductive sheet. In this comparative example, the volume fraction of boron nitride A relative to the entire resin sheet was 49% by volume, and the total volume fraction of the thermally conductive filler was 49% by volume.

[0091] [Evaluation Test] (1) Thermal Resistance and Apparent Thermal Conductivity at 20% Compression The thermally conductive sheets prepared in the Examples and Comparative Examples were further cut to prepare evaluation samples with a diameter of 33 mm and a thickness of 2 mm. Using a TIMtester 1400 (manufactured by AnalysisTech), 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. The sample temperature during measurement was 25°C. The results are shown in Table 1. Furthermore, the apparent thermal conductivity at 20% compression was calculated based on the obtained thermal resistance values. The results are shown in Table 1.

[0092] (2) Shore 00 Hardness Six thermally conductive sheets were stacked to form a laminate with a total thickness of 12 mm, and the Shore 00 hardness was measured using a GS-754G, Type 00 (manufactured by Teclock). The results are shown in Table 1. The measurement was performed three times, and the average value was used as the measured value.

[0093] (3) Contact angle with water The static contact angle with water of the surface (cut surface by slicing) of the thermally conductive sheet was measured using an automatic contact angle meter DM-501 (manufactured by Kyowa Interface Science Co., Ltd.). The results are shown in Table 1. Ion-exchanged water was used as the dropping liquid. The measurement was performed three times, and the average value was taken as the measured value.

[0094] (4) Reworkability A thermally conductive sheet was attached to an aluminum plate made of aluminum alloy (A6063). A load of 4 kPa was applied during attachment. The attached sheet was left standing for 60 seconds, and then the thermally conductive sheet was peeled off from the aluminum plate. The aluminum plate was observed, and the reworkability was evaluated according to the following criteria. The results are shown in Table 1. ◯: No thermally conductive sheet remained on the aluminum plate. ×: Part of the thermally conductive sheet remained on the aluminum plate.

[0095]

[0096] 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.

[0097] REFERENCE SIGNS LIST 1 Thermally conductive sheet (sheet-shaped thermally conductive composition) 2 Matrix component 4 Thermally conductive filler 4C Carbon fiber 4G Graphite powder 4Z Zinc oxide particles 11 IC chip 12 Heat sink 30 Extruder 31 Flow path 32 First gap 33 Second gap 34 Screw 40, 50 Resin sheet 51 Roll 53 Table 54 Cutter 55 Laminate 57, 61 Band knife 58A, 58B Pulley 59 Dressing mechanism 60 Cutting machine 63A, 63B Pulley 65 Feed roller 65A Upper feed roller 65B Lower feed roller 67 Table 69 Dressing mechanism 69A, 69B Grindstone roller

Claims

1. A thermally conductive composition in sheet form, comprising a resin composition containing silicone and a thermally conductive filler, wherein the Shore 00 hardness of the sheet is 75 or less, the apparent thermal conductivity when compressed and deformed by 20% is 5 W / mK or more, and the contact angle of the surface of the sheet with water is 95° or more.

2. The thermally conductive composition according to claim 1, wherein the resin composition contains polydimethylsiloxane as the silicone.

3. The thermally conductive composition according to claim 1 or 2, wherein the resin composition contains an anisotropic thermally conductive filler as the thermally conductive filler.

Images