Thermally conductive composition

Abstract

A sheet-like thermal conductive composition comprising a resin composition containing silicone and a thermally conductive filler, wherein the Shore 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 respect to water is 95° or more.

Description

Technical Field

[0001] The present invention relates to a thermally conductive composition. This application claims priority based on Japanese Application No. 2024-125925 filed on August 1, 2024, and incorporates all the descriptions set forth in the above Japanese application.

Background Art

[0002] For heat-generating members such as IC chips, a heat-dissipating member such as a heat sink is usually attached via a thermal conductive material (TIM: Thermal Interface Material). The heat generated by the heat-generating member is conducted to the heat-dissipating member through the above thermal conductive material. As the above thermal conductive material, for example, Patent Document 1 proposes a thermally conductive sheet containing a resin and a particulate inorganic material.

Prior Art Documents

Patent Documents

[0006] Furthermore, when attaching thermal conductive sheets to mating materials such as heat-generating components, it is sometimes necessary to be able to easily peel them off and reattach them to correct misalignment; in other words, reworkability is required. On the other hand, once a soft thermal conductive sheet is attached, it is very difficult to peel it off from the mating material, and if it is forcibly peeled off, a part of the thermal conductive sheet may remain on the mating material. [Means for solving the problem]

[0007] Under these circumstances, the present inventors have conducted extensive research and aim to provide a sheet-like thermal conductive composition that is soft yet reworkable.

[0008] A thermally conductive composition according to one aspect of the present invention is a sheet-like thermally conductive composition comprising a resin composition containing silicone and a thermally conductive filler, The Shore hardness of a sheet-like material is 75 or less. The apparent thermal conductivity when compressed by 20% is 5 W / mK or higher. The contact angle of the sheet-like material's surface with respect to water is 95° or greater.

[0009] This sheet-like thermal conductive composition has a contact angle of 95° or more with water on its surface, thus ensuring thermal conductivity while maintaining reworkability despite its softness. [Effects of the Invention]

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

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically showing 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. [Figure 2] FIG. 2A is a perspective view schematically showing an example of a sheet-like thermally conductive composition according to an embodiment of the present invention. FIG. 2B is a partial enlarged view of the cross section taken along line A-A of FIG. 2A. [Figure 3] FIG. 3 shows a schematic cross-sectional view of the tip portion of an extruder and a T-die used in the production of a sheet-like thermally conductive composition according to an embodiment of the present invention. [Figure 4] 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. [Figure 5] FIG. 5 is a front view schematically showing a cutting machine equipped with a band knife. <{ [Figure 6] FIG. 6 is a partial cross-sectional view taken along line C-C of FIG. 5.

Embodiments for Carrying Out the Invention

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

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

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

[0015] Hereinafter, the details of the embodiments of the present invention will be described. The sheet-like heat-conductive composition according to the embodiment of the present invention is a member provided between an IC chip and a heat sink. The heat-conductive composition is composed of a resin composition containing silicone and a heat-conductive filler. Here, silicone is a high molecular 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 through a sheet-like heat-conductive composition according to an embodiment of the present invention. FIG. 2A is a perspective view schematically showing an example of the sheet-like heat-conductive composition according to an embodiment of the present invention, and FIG. 2B is a partially enlarged view of the cross-section taken along the line A-A of FIG. 2A. Note that all the drawings in the present application are schematic diagrams and do not accurately reflect the actual dimensions of each member.

[0016] As shown in FIG. 1, the sheet-like heat-conductive composition 1 (hereinafter also referred to as the heat-conductive sheet 1) is disposed between the IC chip 11 and the heat sink 12. The heat-conductive sheet 1 is used by bringing one surface into contact with the IC chip 11 and the other surface into contact with the heat sink 12. Thereby, the heat sink 12 is attached to the IC chip 11 through the heat-conductive sheet 1. Therefore, the heat generated by the IC chip 11 is radiated to the outside of the housing (not shown) by the heat sink 12.

[0017] FIG. 1 shows the usage mode of the heat-conductive sheet 1 attached to the upper surface of one IC chip 11. On the other hand, the sheet-like heat-conductive composition (heat-conductive sheet) according to the embodiment of the present invention may be a heat-conductive sheet attached so as to simultaneously cover heat-generating members such as a plurality of IC chips.

[0018] The Shore 00 hardness of the heat-conductive sheet 1 is 75 or less. Therefore, the thermal conductive sheet 1 is soft, which reduces the load on the mating material during installation. Furthermore, it exhibits good conformability to the mating material. The lower limit of the Shore hardness of the thermally conductive sheet 1 is, for example, 5. The preferred Shore hardness of the thermally conductive sheet 1 is between 10 and 73.

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

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

[0021] The apparent thermal conductivity of thermal conductive sheet 1 is the thermal resistance value (Kcm) measured when the sheet was compressed to a thickness of "pre-measurement thickness × 0.8" (20% compression). 2 The thermal conductivity (W) can be calculated from the thermal conductivity (W) and the thickness of the thermal conductive sheet (cm) at the time of measurement, based on the following formula (1).

[0022] Apparent thermal conductivity (W / mK) = Thickness of the thermally conductive sheet at the time of measurement (cm) ÷ Thermal resistance value (Kcm) when compressed and deformed by 20% 2 / W)×100···(1)

[0023] The thermal resistance value when compressed by 20% is measured using a thermal conductivity measuring device (for example, TIMtester1400 (manufactured by AnalysisTech)) while the thermal conductive sheet 1 is compressed by 20%.

[0024] The contact angle of the thermally conductive sheet 1 with respect to water is 95° or greater. In this invention, the above contact angle is the static contact angle. The above contact angle is measured using a contact angle measuring device such as the automatic contact angle meter DM-501 (manufactured by Kyowa Interface Science Co., Ltd.). The above contact angle is measured by dropping the liquid onto the front or back surface of the thermal conductive sheet 1. In this case, deionized water is used as the dropper solution. The upper limit of the contact angle of the thermal conductive sheet 1 with respect to water is, for example, 150°. Therefore, the contact angle of the thermal conductive sheet 1 with respect to water is, for example, between 95° and 150°.

[0025] The thermal conductive sheet 1 only needs to have a contact angle of 95° or more on either its front or back surface, but it is preferable that the contact angle of both sides of the thermal conductive sheet 1 be 95° or more. In this case, the sheet can be used without worrying about its orientation.

[0026] The thermal conductive sheet 1 has a surface with a contact angle of 95° or more with respect to water. Therefore, the thermal conductive sheet 1 is reworkable. When the surface with the above-mentioned contact angle of 95° or more is attached to the mating material, the thermal conductive sheet 1 is suitable for being peeled off and reattached after being attached.

[0027] The inventors have discovered that the reworkability of a thermal conductive sheet can be improved by reducing the surface free energy of the sheet's surface, thereby decreasing its wettability to mating materials such as heat sinks. Furthermore, the inventors focused on the contact angle with water as an alternative indicator to surface free energy, and found that good reworkability can be ensured by setting the contact angle of the thermal conductive sheet 1 with water to 95° or more.

[0028] On the surface of the thermal conductive sheet 1 with a contact angle of 95° or more, the adhesion to the mating material is moderately suppressed. Therefore, the thermal conductive sheet 1 can be peeled off the mating material without damaging the thermal conductive sheet 1 after the surface with a contact angle of 95° or more has been attached to the mating material. On the other hand, in the case of a thermal conductive sheet having a surface with a contact angle of less than 95° to water, if the surface with a contact angle of less than 95° is peeled off after being attached to the mating material, cohesive failure will occur on the attached surface.

[0029] From the viewpoint of ensuring good reworkability, a mating material made of aluminum (or an aluminum alloy) is preferred for the thermal conductive sheet 1.

[0030] The thickness of the thermal conductive sheet 1 is not particularly limited, but for example, it is 0.01 mm or more and 3.0 mm or less. In this case, the thermal conductive sheet 1 can be suitably used as a component that efficiently transfers heat between the IC chip 11 and the heat sink 12. The thickness of the thermal conductive sheet 1 is preferably between 0.01 mm and 2.5 mm. This ensures that the sheet conforms to the shape of the IC chip 11 and the heat sink 12 while also ensuring superior heat dissipation performance. On the other hand, if the thickness of the thermal conductive sheet 1 is less than 0.01 mm, it may not be able to conform to the shape of the IC chip 11 and the heat sink 12. Also, if the thickness exceeds 2.5 mm, the heat dissipation performance may be inferior due to the thermal resistance of the sheet itself.

[0031] The planar shape of the thermally conductive sheet 1 is, for example, rectangular. In this case, the vertical and horizontal dimensions of the thermal conductive sheet 1 can be determined by considering the dimensions of the component to which the thermal conductive sheet 1 is attached, such as the IC chip 11. For example, both the vertical and horizontal dimensions are independently 10 mm or more and 120 mm or less. The planar shape of the thermal conductive sheet 1 is not limited to a rectangle; it may be a circle, an ellipse, or any other shape. In the case of a circle, for example, the diameter is 10 mm or more and 120 mm or less. In the case of an ellipse, for example, the major axis or minor axis is 10 mm or more and 120 mm or less.

[0032] As shown in Figures 2A and 2B, the thermally conductive sheet 1 contains a matrix component 2 and a thermally conductive filler 4. In thermal conductive sheet 1, components other than the thermal conductive filler are collectively referred to as matrix components. The thermally conductive sheet 1 may also have weld lines formed almost in the thickness direction.

[0033] Matrix component 2 contains silicone. Therefore, the thermally conductive sheet 1 has excellent heat resistance. In embodiments of the present invention, the silicone may contain a crosslinked silicone (hereinafter also referred to as crosslinked silicone), but from the viewpoint of easily ensuring flexibility, it is preferable that the main component be uncrosslinked silicone. Here, "mainly composed of uncrosslinked silicone" means that the proportion of uncrosslinked silicone in the total silicone is 50% by mass or more. The above silicone may consist solely of uncrosslinked silicone.

[0034] As the uncrosslinked silicone, polydimethylsiloxane is preferred, which is a silicone in which all side chains are methyl groups and do not contain unsaturated groups. The above silicone preferably contains 50% by mass or more of the above 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 described above is a polymer with poor 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 mentioned above may be an oil or a millable type. It should be selected for its good moldability when manufacturing the thermally conductive sheet 1 by the method described later.

[0036] The molecular weight of the above polydimethylsiloxane is preferably 40,000 to 700,000 as a mass-average molecular weight (MW). If the mass-average molecular weight (MW) of the polydimethylsiloxane is less than 40,000, the polydimethylsiloxane is more likely to bleed 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 when manufacturing the thermal conductive sheet 1 tend to be poor.

[0037] In this invention, the mass-average molecular weight (MW) of polydimethylsiloxane is the mass-average molecular weight measured using gel permeation chromatography (GPC) with polystyrene as the standard substance, in accordance with JIS-K7252-1:2008 "Plastics - Method for determining the average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 1: General rules".

[0038] The kinematic viscosity of the above polydimethylsiloxane was 3000 mmHg, measured at 25°C using a Ubberohde viscometer. 2 / s or more 300000mm 2 A value of / s or less is preferable. The above kinematic viscosity is 3000 mm 2 Below / s, polydimethylsiloxane is more likely to bleed from the thermally conductive sheet 1. On the other hand, when the above kinematic viscosity is 300,000 mm 2 If the temperature exceeds / s, the hardness of the thermal conductive sheet 1 increases, and when placed between the IC chip and the heatsink, it may have poor adhesion and conformability to the contact surface with the IC chip and the heatsink.

[0039] If the above-mentioned silicone contains crosslinked silicone, the crosslinked silicone may be peroxide-crosslinked or crosslinked by an addition reaction, but peroxide-crosslinked silicone is preferred. This is because crosslinked silicone crosslinked by peroxide crosslinking has superior heat resistance. Examples of the crosslinked silicones mentioned above include silicones in which a part of the side chain (including the terminal) has a crosslinkable functional group such as a vinyl group, which has been crosslinked.

[0040] The above-mentioned silicone may contain silicone having crosslinkable functional groups such as vinyl groups in an uncrosslinked state.

[0041] Matrix component 2 may contain other elastomer components, etc., to the extent that it does not impair the required properties of the thermally conductive sheet 1.

[0042] Matrix component 2 may contain common additives such as flame retardants, reinforcing agents, fillers, softeners, plasticizers, anti-aging agents, tackifiers, antistatic agents, compounding adhesives, and coupling agents. Examples of the above-mentioned flame retardants include magnesium hydroxide, aluminum hydroxide, platinum compounds, triazole compounds, iron oxides such as red iron oxide and black iron. These may be used individually or in combination of two or more.

[0043] Matrix component 2 may contain a coupling agent, such as a silane coupling agent, as an additive. If zinc oxide particles are included as a thermally conductive filler, the flexibility of the thermally conductive sheet 1 can be increased by including a silane coupling agent.

[0044] Examples of the silane coupling agents mentioned above include methyltrimethoxylane, ethyltrimethoxylane, propyltrimethoxylane, butyltrimethoxylane, pentyltrimethoxylane, hexyltrimethoxylane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxylane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane. These may be used individually 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 thermal conductive sheet 1 may contain only one type of thermal conductive filler, or it may contain two or more types of thermal conductive fillers. When two or more types of thermally conductive fillers are included, the thermally conductive filler 4 may include 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 easier to achieve both high thermal conductivity and flexibility, and the moldability during manufacturing is also good.

[0047] In thermally conductive fillers, anisotropic fillers are those with an aspect ratio of 2.0 or greater, while non-anisotropic fillers are those with an aspect ratio of less than 2.0. The aspect ratio of the thermally conductive filler mentioned above refers to the larger of the following two values: the ratio of the filler's major axis to its minor axis, and the ratio of the filler's major axis to its thickness. The major axis, minor axis, and thickness mentioned above correspond to the length, width, and height of the circumscribed rectangular prism of the filler, respectively.

[0048] The above-mentioned anisotropic fillers include fibrous fillers, flaky fillers, plate-like fillers, and thin flake-like fillers. The aspect ratio of the above-mentioned anisotropic filler is preferably 5.0 or higher. The above-mentioned anisotropic fillers include spherical fillers, amorphous fillers, and others.

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

[0050] The thermal conductive sheet 1 preferably contains an anisotropic filler. When a thermal conductive sheet containing an anisotropic filler is manufactured through a slicing process by drawing, as described later, the contact angle with water of the cut surface due to the slicing process is easily increased.

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

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

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

[0054] Next, a method for manufacturing the thermally conductive sheet 1 will be described. The thermally conductive sheet 1 can be manufactured, for example, by a first manufacturing method that performs the following steps (a) to (c). (a) A step of preparing a silicone-based composition containing silicone, a thermally conductive filler, and an optional component such as a flame retardant or a coupling agent. (b) A step of molding the prepared silicone composition, and (c) A step of slicing the molded silicone composition into a sheet.

[0055] First, step (a) is performed to prepare a silicone-based composition. Here, for example, a silicone-based composition is prepared by kneading silicone, a thermally conductive filler, and various additives 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. Step (a) may be carried out while heating. In this case, only a part of the step may be carried out while heating.

[0056] Next, the process involves (b) molding the prepared silicone composition and (c) slicing the molded product into a sheet. The above silicone-based composition may be molded, for example, using an extruder. Figure 3 is a schematic cross-sectional view showing the tip portion and T-die of an extruder used in the manufacture of the thermally conductive sheet 1 according to an embodiment of the present invention. The silicone-based 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.

[0057] The silicone-based composition, which has been stirred and kneaded in the extruder 30, is first compressed vertically (in the thickness direction) by the first gap 32 to form a thin strip. At this time, the anisotropic thermally conductive filler mixed in the silicone composition is oriented in the flow direction (extrusion direction) of the silicone 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 embodiments of the present invention, for example, carbon fibers, flaky graphite powder, or boron nitride powder correspond to anisotropic thermally conductive fillers.

[0058] When the thin resin sheet 40 with the heat-conductive filler oriented completely passes through the first gap 32, the flow direction of the sheet, which was previously limited to the extrusion direction, is released, and the flow direction changes to a direction substantially perpendicular to the extrusion direction. The resin sheet 40, whose flow direction has changed to be almost perpendicular to the extrusion direction, passes completely through the first gap 32 and is then extruded further toward the second gap 33. As a result, the resin sheets 40, which are now almost perpendicular to the extrusion direction, are folded and laminated within the second gap 33. At this time, most of the anisotropic thermal conductive fillers (carbon fibers and flaky graphite powder and boron nitride powder) are oriented in the plane direction of the resin sheet 40, so the anisotropic thermal conductive fillers in the resin sheet 40 laminated within the second gap 33 are oriented along the thickness direction (vertical direction in Figure 3).

[0059] Thus, in step (b), a silicone-based composition is extruded to form a resin sheet 40 in which anisotropic thermally conductive fillers are oriented in the extrusion direction. Then, this resin sheet 40 is folded and laminated to produce a block (laminated body). Step (b) may be carried out while heating. In this case, only a part of the step may be carried out while heating.

[0060] In the T-die described above, 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 plane of the paper in Figure 3) are substantially the same throughout the T-die. Furthermore, the dimensions of the depths 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 thermal conductive sheet 1 to be manufactured.

[0061] Subsequently, the process proceeds to step (c), in which a block of thin resin sheets 40 stacked in the extrusion direction is sliced ​​in a direction perpendicular to the thickness direction. As a result, a thermal conductive sheet 1 having a predetermined thickness and in which anisotropic thermal conductive fillers are substantially oriented in the thickness direction can be obtained.

[0062] The slicing process described above is preferably performed using a pull-cutting machine equipped with a band knife. By using a pull-cutting machine equipped with a band knife to slice the thermally conductive filler in a direction perpendicular to its orientation, it becomes easier to form a cut surface with a contact angle to water of 95° or more. This is thought to be because the heat-conductive filler, which is oriented in the thickness direction and can be cut during slicing, is less likely to fall over in a direction perpendicular to the thickness direction (plane direction), and a slicing process is more likely to form a cut surface where the cut surface of the anisotropic filler is exposed on the surface. Let me explain this in more detail.

[0063] When slicing a block of anisotropic thermally conductive filler oriented in the thickness direction along the surface direction (perpendicular to the thickness direction), comparing slicing by pulling and slicing by pushing, slicing by pushing places a greater load on the anisotropic filler during processing. Therefore, slicing by push cutting makes it easier for the anisotropic filler to tilt so that it faces the surface direction during processing. Here, tilting so that the anisotropic filler faces the surface direction means that the anisotropic filler tilts so that the angle between the major axis of the anisotropic filler and the surface direction becomes small. In other words, slicing by pulling makes it less likely for the anisotropic filler to tilt in the direction of the surface 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 anisotropic fillers tilt towards the surface direction during processing, the orientation of the anisotropic fillers, which were oriented in the thickness direction of the block before processing, will decrease. This decrease in orientation leads to a decrease in thermal conductivity. Therefore, slicing by pull cutting is more likely to ensure high thermal conductivity.

[0065] Such differences in the resistance of anisotropic fillers to collapsing, due to processing methods, are particularly noticeable when slicing blocks with low hardness (blocks with a soft matrix or blocks with a low filler content). When slicing hard blocks (blocks with a hard matrix or blocks with a high filler content), even if a push-cutting method is used, which places a heavy load on the anisotropic filler during processing, the hardness of the block (mixture of matrix and filler) prevents the anisotropic filler from tipping over, and most of the anisotropic filler is cut without tipping. Therefore, when a hard block is sliced, there is no significant difference in the degree to which the anisotropic filler is exposed on the cut surface of the block, regardless of whether a push-cut or pull-cut slicing method is used.

[0066] In contrast, when slicing a block with low hardness, using a pull-cut slicing method makes it less likely for the anisotropic filler to tilt in the direction of the surface during processing, and more anisotropic filler is cut without tilting compared to using a push-cut slicing method. Therefore, with a pull-cut slicing method, the cut surface of the anisotropic filler is more likely to be exposed on the cut surface of the block. In other words, with a push-cut slicing method, the surface (uncut surface) of the anisotropic filler is more likely to be exposed on the cut surface of the block. In particular, when manufacturing soft thermal conductive sheets, such as thermal conductive sheets with a Shore hardness of 75 or less, using a slicing process by drawing the material makes it easier to expose the cut surface of the anisotropic filler on the cut surface.

[0067] Furthermore, when slicing is performed by pulling, as described above, the cut surfaces of the anisotropic filler are easily exposed on the cut surface of the block. In this case, the surface of the thermal conductive sheet has fine irregularities due to the presence of the cut surfaces of the anisotropic filler, and the surface area becomes larger. Therefore, the surface of the thermal conductive sheet 1, combined with the fact that the matrix is ​​silicone, has a higher contact angle with water, making it easier to secure the above-mentioned contact angle of 95° or more.

[0068] The pull-cutting machine equipped with the band knife described above comprises a pair of pulleys and an endless band knife stretched across this 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 described above is equipped with a cutting blade on one end face 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 0.4 mm to 1.0 mm.

[0069] Preferably, the pull-cutting machine equipped with the band knife described above is further equipped with a sharpening mechanism (also called a dressing mechanism). In this case, the cutting edge of the cutting blade is continuously sharpened, allowing slicing to be performed while maintaining a sharp cutting edge. A specific example of a pull-cutting machine equipped with a band knife will be discussed later.

[0070] In the pull-cutting machine equipped with the band knife described above, the rotational speed of the band knife is preferably 0.3 m / min or more and 400 m / min or less. In this case, it 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 will vibrate more, and the slice thickness may not be stable.

[0071] The method for manufacturing the thermally conductive sheet 1 is not limited to the first manufacturing method described above, but may also be a second manufacturing method that involves the following steps (d) to (f). Figures 4A to 4D illustrate the second manufacturing method.

[0072] (d) A step of preparing a silicone-based composition containing silicone, a thermally conductive filler, and an optional component such as a flame retardant or a coupling agent. (e) A step of molding the prepared silicone composition, and (f) A step of slicing the molded silicone composition into a sheet.

[0073] First, step (d) is performed to prepare a silicone-based composition. Here, for example, silicone, a thermally conductive filler, and various additives added as needed are mixed using two rolls 51. After that, the mixture is dispensed into a sheet to produce a resin sheet 50 (see Figure 4A). In this case, some or all of the components may be supplied in the form of a compound. Step (d) may be performed while heating. In this case, only a part of the process may be performed while heating.

[0074] Next, step (e) of molding the silicone-based composition is performed. In this step (e), resin sheets 50 made of a silicone-based composition are folded and laminated so that the resin sheets 50 are in close contact with each other (see Figure 4A). For example, by continuously supplying resin sheets 50 onto a table 53 that repeats a periodic reciprocating motion, a laminate in which the resin sheets 50 are folded and laminated can be obtained. In this case, the anisotropic thermally conductive filler is oriented in the plane direction of the resin sheet 50.

[0075] Next, the folded portion of the resin sheet 50 is cut and removed using a cutter 54 (see Figure 4B). As a result, a laminate 55 of multiple resin sheets 50 that are not connected to each other is obtained. Step (e) may be carried out while heating part or all of the process. In this case, only part of the process may be carried out while heating.

[0076] Next, the obtained laminate 55 is sliced ​​in a direction perpendicular to the plane direction of the resin sheet 50 (see Figure 4C). This allows a thermally conductive sheet 1 to be obtained (see Figure 4D). For the same reasons as in the first manufacturing method, the slicing process described above is preferably carried out using a pull-cutting machine equipped with a band knife 57. The thermally conductive sheet 1 can also be manufactured through this process. [Examples]

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

[0078] The raw materials used in the examples and comparative examples are as follows: (Matrix component) • 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 (manufactured by Dow Toray Corporation, DY32-1005U) • Silicone D: Vinyl group-containing silicone compound (manufactured by Dow & Toray Industries, Ltd., MR-53) • Peroxide: A mixture of peroxides (manufactured by Dow Toray Industries, Ltd., RC-4 50P FD). • Silane coupling agent: Octyltrimethoxysilane

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

[0080] In the above-mentioned thermally conductive fillers, the particle sizes of graphite powder, boron nitride powder A, boron nitride powder B, zinc oxide particles, and alumina particles are all median diameter (d50) values ​​of the particle size distribution measured on a volume basis using a laser diffraction / scattering particle size distribution analyzer. (Example 1) In this embodiment, the thermally conductive sheet 1 was manufactured by the first manufacturing method described above. A ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm was produced by kneading 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 using two rolls 51, and then extruding the mixture into a sheet. In this embodiment, the volume fraction of carbon fibers relative to the entire resin sheet is 30 vol%, the volume fraction of graphite powder is 10 vol%, the volume fraction of zinc oxide particles is 20 vol%, and the total volume fraction of the thermally conductive filler is 60 vol%.

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

[0082] Subsequently, the obtained block was sliced ​​perpendicular to the thickness direction to produce a 2 mm thick thermal conductive sheet 1 in which carbon fibers and graphite powder were oriented in the thickness direction. Here, the slicing of the block produced using the extruder 30 was performed using a cutting machine 60 equipped with a band knife 61.

[0083] Figures 5 and 6 illustrate 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 of Figure 5 along line CC. Figure 6 illustrates the relationship between the table 67, the band knife 61, and the feed roller 65. The cutting machine 60, equipped with a band knife 61, is a pull-cutting machine. The cutting machine 60 comprises a pair of pulleys 63A and 63B, an endless band knife 61 stretched between these pulleys 63A and 63B, a table 67 on which the workpiece to be cut (block B) is placed, a feed roller 65 for transporting the workpiece to be cut to the travel area of ​​the band knife 61, and a dressing mechanism (polishing mechanism) 69 for continuously sharpening the teeth of the band knife 61. The feed roller 65 comprises an upper feed roller 65A and a lower feed roller 65B. The dressing mechanism 69 comprises a pair of grinding rollers 69A and 69B. The teeth of the band knife 61 are double-edged.

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

[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 with a thickness of approximately 1.0 to 1.2 mm was prepared using the method described below. A ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm was produced by kneading 104 parts by mass of silicone B, 100 parts by mass of silicone C, and 450 parts by mass of boron nitride powder A using two rolls 51, and then extruding the mixture into a sheet. In this embodiment, the volume fraction of boron nitride A relative to the entire resin sheet is 49 vol%, and the total volume fraction of the thermally conductive filler is 49 vol%.

[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 with a thickness of approximately 1.0 to 1.2 mm was prepared using the method described below. A ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm was produced by kneading 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 using two rolls 51, and then extruding the mixture into a sheet. In this embodiment, the volume fraction of boron nitride powder B relative to the entire resin sheet is 40 vol%, the volume fraction of alumina particles is 15 vol%, and the total volume fraction of thermally conductive fillers is 55 vol%.

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

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

[0089] (Comparative Example 3) A ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm was prepared using the method described below, and then a block with a thickness of 10 mm was prepared in the same manner as in Example 1. A ribbon-shaped resin sheet made of a silicone-based composition with a thickness of approximately 1.0 to 1.2 mm was produced by kneading 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 using two rolls 51, and then extruding the mixture into a sheet.

[0090] Furthermore, the obtained block was crosslinked at 160°C for 40 minutes. Subsequently, the block with crosslinked matrix components was sliced ​​by push-cutting with a double-edged blade with a cutting edge angle of 30° to complete the thermally conductive sheet. In this comparative example, the volume fraction of boron nitride A relative to the entire resin sheet is 49 vol%, and the total volume fraction of the thermally conductive filler is also 49 vol%.

[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 create evaluation samples with a diameter of 33 mm and a thickness of 2 mm. A TIMtester1400 (manufactured by AnalysisTech) was used as the measuring instrument. The sheet was compressed to a thickness of "pre-measurement thickness × 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, based on the obtained thermal resistance values, the apparent thermal conductivity at 20% compression was calculated. The results are shown in Table 1.

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

[0093] (3) Contact angle with respect to water The static contact angle of the surface (cut surface by slicing) of a thermally conductive sheet with respect to water was measured using an automatic contact angle meter DM-501 (manufactured by Kyowa Interface Science Co., Ltd.). The results are shown in Table 1. Deionized water was used as the dropper solution. Measurements were taken three times, and the average value was used as the measured value.

[0094] (4) Reworkability A thermally conductive sheet was attached to an aluminum plate made of aluminum alloy (A6063). The load applied during attachment was 4 kPa. The plate was left undisturbed for 60 seconds, after which the thermally conductive sheet was peeled off the aluminum plate. The aluminum plate was observed, and its reworkability was evaluated according to the following criteria. The results are shown in Table 1. ○: The thermal conductive sheet was not present on the aluminum plate. ×: A portion of the thermal conductive sheet remained on the aluminum plate.

[0095] [Table 1]

[0096] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims and is intended to include all modifications in the meaning and scope equivalent to the claims. [Explanation of Symbols]

[0097] 1. Thermally conductive sheet (sheet-shaped thermally conductive composition) 2 Matrix Components 4. Thermally conductive fillers 4C carbon fiber 4G Graphite Powder 4Z Zinc Oxide Particles 11 IC chips 12 Heatsinks 30 Extruders 31 Flow channels 32. First Gap 33. Second Gap 34 Screw 40, 50 resin sheets 51 rolls 53 Tables 54 Cutter 55 Laminate 57, 61 Band knife 58A, 58B pulleys 59 Dressing mechanism 60 cutting machine 63A, 63B pulleys 65 Feed roller 65A Feed Roller 65B Feed Down Roller 67 Tables 69 Dressing mechanism 69A, 69B Grinding Wheel Roller

Claims

1. A sheet-like thermal conductive composition comprising a resin composition containing silicone and a thermal conductive filler, The Shore hardness of the sheet-like material is 75 or less. The apparent thermal conductivity when compressed and deformed by 20% is 5 W / mK or higher. The contact angle of the sheet-like material's surface with respect to water is between 95° and 115.6°. Thermally conductive composition.

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

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

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