Thermal conductive sheet

Abstract

To provide a thermally conductive sheet with excellent handling properties. [Solution] The thermal conductive sheet 1 has a maximum valley depth Sv of 15 μm or more and 50 μm or less on one side, and a minimum autocorrelation length Sal of 100 μm or more and less than 1500 μm. On the other side of the thermal conductive sheet 1, the maximum valley depth Sv of 1 μm or more and less than 15 μm, and a minimum autocorrelation length Sal of 1500 μm or more and 3500 μm or less. The thermal conductive sheet 1 includes, for example, a binder component 11 and a thermal conductive filler 12.

Description

Technical Field

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

Background Art

[0002] In recent years, with the progress of electronics, many heat-generating components have been used in electronic devices such as power devices. When controlling an electronic circuit, it is important to dissipate heat from these heat-generating components to cool the entire system. A thermally conductive sheet (heat dissipation sheet) is installed, for example, between a heat-generating component and a heat dissipation fin or a metal plate, and is adhered to the heat-generating component without gaps by pressure bonding, and exhibits thermal conductivity to transfer the heat generated from the heat-generating component to the heat dissipation fin or the like, thereby removing heat from the entire system.

[0003] The above thermally conductive sheet is composed of, for example, a thermally conductive inorganic filler and a resin. As the inorganic filler, inexpensive aluminum hydroxide, aluminum oxide (alumina), silicon carbide, boron nitride, aluminum nitride, etc., which are expected to have higher thermal conductivity, are used.

[0004] As the above thermally conductive sheet, for example, those disclosed in Patent Documents 1 and 2 are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Thermally conductive sheets are often sold in a three-layer structure with release films laminated to both sides of the sheet. When using such a thermally conductive sheet, one of the release films is peeled off and the exposed sheet surface is attached to the heating element. However, peeling off the release film is often difficult, resulting in poor handling. Poor handling necessitates careful peeling of the release film to avoid deformation or damage to the thermally conductive sheet, which increases the time required for the process. Patent documents 1 and 2 state that a smaller difference between the surface roughness Sa of one layer and the surface roughness Sa of the other layer is desirable, but they do not mention the peelability of the release film.

[0007] Therefore, the object of the present invention is to provide a thermally conductive sheet that is easy to handle. [Means for solving the problem]

[0008] In this invention, the maximum valley depth Sv of one surface is 15 μm or more and 50 μm or less, and the minimum autocorrelation length Sal is 100 μm or more and less than 1500 μm. The present invention provides a thermally conductive sheet in which the maximum valley depth Sv of the other surface is 1 μm or more and less than 15 μm, and the minimum autocorrelation length Sal is 1500 μm or more and 3500 μm or less.

[0009] The difference between the maximum valley depth Sv of one surface and the maximum valley depth Sv of the other surface is preferably 5 μm or more.

[0010] The ratio of the maximum valley depth Sv of one surface to the maximum valley depth Sv of the other surface is preferably greater than 1.0 and less than or equal to 10.0.

[0011] The difference between the minimum autocorrelation length Sal of one of the above-mentioned surfaces and the minimum autocorrelation length Sal of the other surface is preferably 1300 μm or more.

[0012] The ratio of the minimum autocorrelation length Sal of the other surface to the minimum autocorrelation length Sal of the other surface is preferably greater than 1.0 and less than or equal to 10.0.

[0013] A release film is provided on one of the above surfaces and the other of the above surfaces. On one of the above surfaces, when the above release film is peeled 200 mm under the conditions of room temperature, tensile speed of 1000 mm / min, and peel angle of 170°, the minimum value of the first peel strength is 5 mN / cm or more and less than 50 mN / cm, and the maximum value is 50 mN / cm or more and less than 100 mN / cm. It is preferable that the second peel strength on the other surface described above, when the release film is peeled off by 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170°, is between 50 mN / cm and 150 mN / cm, with a maximum value of between 100 mN / cm and 200 mN / cm.

[0014] The ratio of the maximum value of the second peeling strength to the maximum value of the first peeling strength is preferably greater than 1.0 and less than or equal to 10.0.

[0015] The ratio of the minimum value of the second peeling strength to the minimum value of the first peeling strength is preferably greater than 1.0 and less than or equal to 5.0.

[0016] The above-mentioned thermally conductive sheet preferably contains a binder component and a thermally conductive filler.

[0017] The binder component described above is preferably a silicone resin. [Effects of the Invention]

[0018] The thermally conductive sheet of the present invention offers excellent handling properties. Therefore, when attempting to peel one of the release films from the thermally conductive sheet sandwiched between two release films, the peeling of the release film is easy, allowing for efficient work. [Brief explanation of the drawing]

[0019] [Figure 1] This is a partial cross-sectional view showing one embodiment of the thermally conductive sheet of the present invention. [Modes for carrying out the invention]

[0020] [Thermal Conductive Sheet] The thermal conductive sheet (heat dissipation sheet) of the present invention may be in a form without a base material (base material layer), so-called "base material-less", or may be a thermal conductive sheet provided on at least one side of the base material. Note that the above "base material (base material layer)" does not include a release film that is peeled off during the use of the thermal conductive sheet.

[0021] The above thermal conductive sheet may be provided with a release film. The above release film may be provided on only one surface of the above thermal conductive sheet, or may be provided on both surfaces. Examples of the above release film include a film formed from a low-adhesive resin, and a sheet including a release treatment layer provided on the surface of the film. The above release film is peeled off and removed when the above thermal conductive sheet is used.

[0022] FIG. 1 is a schematic cross-sectional view showing an embodiment of the thermal conductive sheet of the present invention. As shown in FIG. 1, release films 2 and 3 are provided on both surfaces of the thermal conductive sheet 1, and the thermal conductive sheet 1 is sandwiched between two release films 2 and 3. Specifically, the thermal conductive sheet 1 has a first surface 1a and a second surface 1b, and the release treatment surface of the release film 2 is bonded to the first surface 1a, which is one surface of the thermal conductive sheet 1, and the release treatment surface of the release film 3 is bonded to the second surface 1b, which is the other surface of the thermal conductive sheet 1. Further, the thermal conductive sheet 1 includes a binder component 11 as a matrix component and a thermal conductive filler 12 dispersed in the binder component 11.

[0023] The maximum valley depth Sv of one surface (the first surface 1a) of the thermal conductive sheet 1 is 15 μm or more and 50 μm or less (15 to 50 μm), preferably 15 to 40 μm, and more preferably 20 to 30 μm.

[0024] The minimum autocorrelation length Sal of one of the surfaces (first surface 1a) of the thermally conductive sheet 1 is 100 μm or more and less than 1500 μm, preferably 200 to 1000 μm, and more preferably 300 to 800 μm.

[0025] The maximum valley depth Sv of the other surface (second surface 1b) of the thermal conductive sheet 1 is 1 μm or more and less than 15 μm, preferably 2 to 12 μm, and more preferably 3 to 10 μm.

[0026] The minimum autocorrelation length Sal of the other surface (second surface 1b) of the thermally conductive sheet 1 is 1500 to 3500 μm, preferably 1700 to 3300 μm, and more preferably 2000 to 3000 μm.

[0027] The maximum valley depth Sv represents the absolute value of the maximum distance from the average plane to the valley on the thermal conductive sheet surface; a larger value indicates deeper valleys on the thermal conductive sheet surface. On the other hand, the minimum autocorrelation length Sal represents the horizontal distance in the direction in which the autocorrelation function decays most quickly to a specific value; a larger value indicates smoother irregularities. Because the maximum valley depth Sv and minimum autocorrelation length Sal of the first and second surfaces of the thermal conductive sheet are within the above ranges, the adhesion force between the second surface and the release film laminated to the second surface is moderately higher than the adhesion force between the first surface and the release film laminated to the first surface. This allows for easy peeling of the release film on the first surface side, and then easy peeling of the release film on the second surface side when the thermal conductive sheet is laminated to the substrate, resulting in excellent handling of the thermal conductive sheet.

[0028] The maximum valley depth Sv of the first surface is higher than the maximum valley depth Sv of the second surface. The difference between the maximum valley depth Sv of the first surface and the maximum valley depth Sv of the second surface [(maximum valley depth Sv of the first surface) - (maximum valley depth Sv of the second surface)] is preferably 5 μm or more, and more preferably 10 μm or more. The higher the above difference, the easier it is to peel the release film from the first surface side of the thermal conductive sheet. The above difference is, for example, 100 μm or less.

[0029] The ratio of the maximum valley depth Sv of the first surface to the maximum valley depth Sv of the second surface [(maximum valley depth Sv of the first surface) / (maximum valley depth Sv of the second surface)] is preferably greater than 1.0 and less than or equal to 10.0, more preferably between 1.5 and 8.0, and even more preferably between 2.0 and 6.0. When the above ratio is within the above range, the handling properties are superior.

[0030] The minimum autocorrelation length Sal of the second surface is longer than the minimum autocorrelation length Sal of the first surface. The difference between the minimum autocorrelation length Sal of the first surface and the minimum autocorrelation length Sal of the second surface [(minimum autocorrelation length Sal of the second surface) - (minimum autocorrelation length Sal of the first surface)] is preferably 1300 μm or more, and more preferably 1500 μm or more. The longer the above difference, the easier it is to peel the release film from the first surface side of the thermal conductive sheet. The above difference is, for example, 5000 μm or less.

[0031] The ratio of the minimum autocorrelation length Sal of the second surface to the minimum autocorrelation length Sal of the first surface [(minimum autocorrelation length Sal of the second surface) / (minimum autocorrelation length Sal of the first surface)] is preferably greater than 1.0 and less than or equal to 10.0, more preferably between 1.5 and 9.0, and even more preferably between 2.0 and 8.0. When the above ratio is within the above range, the handling properties are superior.

[0032] The arithmetic mean height Sa of one surface (first surface 1a) and the other surface (second surface 1b) of the thermal conductive sheet 1 is preferably 0.2 to 10 μm, respectively. When the arithmetic mean height Sa is within this range, the release film can be peeled off more easily and the adhesion to the adherend is excellent. The arithmetic mean height Sa of one surface (first surface 1a) is preferably 0.5 to 8 μm, more preferably 1.5 to 6 μm. The arithmetic mean height Sa of the other surface (second surface 1b) is preferably 0.3 to 5 μm, more preferably 0.5 to 3 μm. It is preferable that the arithmetic mean height Sa of one surface (first surface 1a) is higher than the arithmetic mean height Sa of the other surface (second surface 1b).

[0033] The arithmetic mean height Sa of the first surface is higher than the arithmetic mean height Sa of the second surface. The difference between the arithmetic mean height Sa of the first surface and the arithmetic mean height Sa of the second surface [(arithmetic mean height Sa of the first surface) - (arithmetic mean height Sa of the second surface)] is preferably 0.5 μm or more, and more preferably 1.0 μm or more. When the above difference is 0.5 μm or more, the release film on the first surface side can be peeled off more easily from the thermal conductive sheet. From the viewpoint of superior thermal conductivity, the above difference is, for example, 20 μm or less.

[0034] The above-mentioned thermally conductive sheet preferably contains a binder component and a thermally conductive filler.

[0035] (Binder component) The above-mentioned binder component is a component that forms the matrix of the above-mentioned thermally conductive sheet. Examples of the above-mentioned binder component include thermoplastic resins, thermosetting resins, active energy ray curable resins, and other resins (binder resins). Only one type of the above-mentioned binder component may be used, or two or more types may be used.

[0036] Examples of the thermoplastic resins mentioned above include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g., polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, and acrylic resins. Only one type of thermoplastic resin may be used, or two or more types may be used.

[0037] The above-mentioned thermosetting resins include both thermosetting resins and resins obtained by curing the above-mentioned thermosetting resins. Examples of the above-mentioned thermosetting resins include silicone resins, phenolic resins, epoxy resins, urethane resins, urethane urea resins, melamine resins, alkyd resins, polyimide resins, and acrylic resins. Only one type of the above-mentioned thermosetting resin may be used, or two or more types may be used.

[0038] The above-mentioned active energy ray curable resin includes both a resin that can be cured by irradiation with active energy rays (active energy ray curable resin) and a resin obtained by curing the above-mentioned active energy ray curable resin. The above-mentioned active energy ray curable resin is not particularly limited, but for example, a polymer of a polymerizable compound having at least two (meth)acryloyloxy groups in its molecule can be used. The above-mentioned active energy ray curable resin may be used by one type only, or by two or more types.

[0039] Among the binder resins mentioned above, thermosetting resins are preferred. Furthermore, silicone resins are preferred as the binder resin from the viewpoint of excellent thermal conductivity, heat resistance, and insulation properties. As the silicone resin, known or conventional silicone resins used in thermally conductive sheets can be used. As the silicone resin, two-component curing type silicone resins are preferred from the viewpoint of being able to disperse thermally conductive fillers well without using solvents. One type of silicone resin may be used, or two or more types may be used.

[0040] The content of the above binder component is preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the total amount of the thermal conductive sheet. When the content is 2% by mass or more, the thermal conductive sheet is less likely to become brittle and has excellent moldability. The content is preferably 40% by mass or less. When the content is 40% by mass or less, the thermal conductivity of the thermal conductive sheet is further improved. In particular, it is preferable that the content of silicone resin be within the above range.

[0041] (Thermal conductive filler) The above-mentioned thermally conductive filler is a filler (particle) that has thermal conductivity and is a component that exhibits thermal conductivity in the above-mentioned thermally conductive sheet. Examples of the above-mentioned thermally conductive filler include metal particles, ceramic fillers, and inorganic fillers such as carbon fillers. Only one type of the above-mentioned thermally conductive filler may be used, or two or more types may be used.

[0042] Examples of metals that make up the above metal particles include gold, silver, copper, aluminum, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these (such as solder). Only one of the above metals may be used, or two or more may be used.

[0043] Examples of the above-mentioned metal particles include, specifically, silver particles, copper particles, aluminum particles, nickel particles, tin particles, solder particles, and particles in which these particles are coated with a metal. Gold, silver, copper, nickel, and tin are preferred as coating metals.

[0044] Examples of the above ceramic fillers include metal oxides such as alumina (aluminum oxide), titania (titanium oxide), magnesia (magnesium oxide), zirconia (zirconium oxide), and zinc oxide; nitrides such as aluminum nitride, titanium nitride, and boron nitride; metal hydroxides such as aluminum hydroxide; carbides such as silicon carbide; silicon compounds such as glass, silica, silicon carbide, silicon nitride, and silicon; and minerals such as steatite, forsterite, sialon, perlite, mullite, and zeolite.

[0045] Examples of the carbon filler mentioned above include carbon fibers, carbon nanotubes, and carbon material-containing particles such as diamond. The carbon filler may also be coated with a metal. Preferred coating metals include gold, silver, copper, nickel, and tin.

[0046] Among the above-mentioned thermally conductive fillers, metal oxides and nitrides are preferred, and metal oxides are more preferred.

[0047] The shape of the above-mentioned thermally conductive filler is not particularly limited and can be spherical (including perfect spheres and ellipsoids), flake-like (scale-like), dendritic, lumpy, flattened, needle-like, polyhedron, or irregular. Among these, a spherical shape is preferred from the viewpoint of achieving higher filling properties in the thermally conductive sheet and superior thermal conductivity.

[0048] The above-mentioned thermal conductive filler preferably contains two or more (more preferably three or more) thermal conductive fillers with different median diameters, from the viewpoint of increasing the filling rate of the thermal conductive filler and improving the thermal conductivity of the thermal conductive sheet. That is, the above-mentioned thermal conductive filler preferably has two or more (preferably three or more) peak tops in its particle size distribution.

[0049] The above-mentioned thermally conductive filler may or may not be surface-treated. Examples of surface treatment agents include silane coupling agents. When the surface is treated with a silane coupling agent, the thermally conductive filler disperses well in the binder component (especially the silicone resin) which is the matrix of the thermally conductive sheet, resulting in superior filling and moldability. One type of silane coupling agent may be used, or two or more types may be used.

[0050] Examples of the silane coupling agents mentioned above include silane coupling agents having functional groups other than alkoxy groups, such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane (functional group-containing silane coupling agents); and silane coupling agents not having functional groups other than alkoxy groups, such as n-octyltriethoxysilane and n-decyltrimethoxysilane (functional group-free silane coupling agents). Among these, functional group-free silane coupling agents are preferred from the viewpoint of good wettability with metal oxides and the expected improvement of bulk strength and flexibility of the thermally conductive sheet, more preferably silane coupling agents in which the terminal other than the alkoxy group is an alkyl group (terminal alkyl group-containing silane coupling agent), and particularly preferably n-octyltriethoxysilane.

[0051] The above-mentioned thermal conductive filler preferably includes a thermal conductive filler with a median diameter of 20 to 100 μm. Including such a thermal conductive filler improves the thermal conductivity of the thermal conductive sheet. In this specification, a thermal conductive filler with a median diameter of 20 to 100 μm may be referred to as "thermal conductive filler (A)". The median diameter of thermal conductive filler (A) is preferably 25 to 90 μm, more preferably 30 to 80 μm.

[0052] As the thermal conductive filler (A), any of the types and shapes exemplified and described above can be appropriately selected. Among these, aluminum oxide is preferred for the thermal conductive filler (A). Furthermore, a spherical shape is preferred for the thermal conductive filler (A). By using such a thermal conductive filler (A), the thermal conductivity of the thermal conductive sheet is further improved.

[0053] The above-mentioned thermal conductive filler preferably includes a thermal conductive filler with a median diameter of 1 to 20 μm. Including such a thermal conductive filler improves the thermal conductivity of the thermal conductive sheet. In particular, including it together with thermal conductive filler (A) increases the filling rate of the thermal conductive filler in the thermal conductive sheet, further improving the thermal conductivity of the thermal conductive sheet. In this specification, a thermal conductive filler with a median diameter of 1 to 20 μm may be referred to as "thermal conductive filler (B)". The median diameter of thermal conductive filler (B) is preferably 2 to 15 μm.

[0054] As the thermal conductive filler (B), any of the types and shapes exemplified and described above can be appropriately selected. Among these, aluminum oxide is preferred for the thermal conductive filler (B). Furthermore, a spherical shape is preferred for the thermal conductive filler (B). By using such a thermal conductive filler (B), the thermal conductivity of the thermal conductive sheet is further improved.

[0055] The above-mentioned thermal conductive filler may include thermal conductive fillers with a median diameter of less than 1 μm. Including such thermal conductive fillers improves the thermal conductivity of the thermal conductive sheet. In particular, including it together with thermal conductive filler (A) and / or thermal conductive filler (B) increases the filling density of the thermal conductive filler in the thermal conductive sheet, further improving the thermal conductivity of the thermal conductive sheet. In this specification, thermal conductive fillers with a median diameter of less than 1 μm may be referred to as "thermal conductive filler (C)". The median diameter of thermal conductive filler (C) is preferably 0.01 μm or more and less than 1 μm, more preferably 0.1 to 0.6 μm.

[0056] Furthermore, the above-mentioned thermal conductive filler may also include a thermal conductive filler with a median diameter greater than 100 μm and less than or equal to 200 μm. Including such a thermal conductive filler improves the thermal conductivity of the thermal conductive sheet. In particular, including it together with thermal conductive filler (A) and / or thermal conductive filler (B) further improves the thermal conductivity of the thermal conductive sheet. In this specification, a thermal conductive filler with a median diameter greater than 100 μm and less than or equal to 200 μm may be referred to as "thermal conductive filler (D)". The median diameter of thermal conductive filler (D) is preferably 110 to 150 μm.

[0057] As the thermal conductive filler (D), any of the types and shapes exemplified and described above can be appropriately selected. Among these, aluminum nitride is preferred as the thermal conductive filler (D). Furthermore, a spherical shape is preferred for the thermal conductive filler (D). By using such a thermal conductive filler (D), the thermal conductivity of the thermal conductive sheet is further improved.

[0058] The total amount of one or more thermal conductive fillers selected from the group consisting of (A) to (D) in the thermal conductive sheet is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, based on 100% by mass of the total amount of thermal conductive fillers contained in the thermal conductive sheet.

[0059] In this specification, the median diameter (D50) of the thermally conductive filler is the number-based average primary particle diameter measured by laser diffraction-scattering.

[0060] The total amount of the thermal conductive filler in the thermal conductive sheet is preferably 70 to 95% by volume, and more preferably 75 to 90% by volume, based on 100% by volume of the total amount of the thermal conductive sheet. When the total amount is 70% by volume or more, the filling rate of the thermal conductive filler in the thermal conductive sheet is high, resulting in superior thermal conductivity. When the total amount is 95% by volume or less, the thermal conductive sheet is less likely to become brittle, and the moldability during the manufacturing of the thermal conductive sheet is excellent.

[0061] (Thermal conductive sheet) The above-mentioned thermal conductive sheet may contain a coloring agent. Including a coloring agent can impart opacity to the thermal conductive sheet. The above-mentioned coloring agent can be appropriately selected depending on the purpose, and examples include black coloring agents, cyan coloring agents, magenta coloring agents, yellow coloring agents, etc. For example, as the above-mentioned black coloring agent, black pigments or mixed pigments that have been blackened by subtractive mixing of multiple pigments can be used. Examples of the above-mentioned black pigments include carbon black, Ketjen black, perylene black, titanium black, iron black, and aniline black. The above-mentioned coloring agent may be used by one or two or more types.

[0062] The total amount of the coloring agent in the thermal conductive sheet is, for example, 0.2 to 10% by mass, preferably 0.4 to 8% by mass, based on 100% by mass of the total amount of the thermal conductive sheet.

[0063] The above-mentioned thermal conductive sheet may contain other components in addition to the various components described above. Examples of these other components include thixotropy imparters, dispersants, curing agents, curing accelerators, curing retarders, tackifiers, plasticizers, flame retardants, antioxidants, and stabilizers. Only one of these other components may be used, or two or more may be used.

[0064] The thickness of the above-mentioned thermal conductive sheet is, for example, 10 to 6000 μm, preferably 100 to 3000 μm.

[0065] The above-mentioned thermal conductive sheet preferably has a thermal conductivity in the thickness direction of 2.5 W / mK or more, more preferably 4.0 W / mK or more, and may also have a thermal conductivity of 6.0 W / mK or more, or 9.0 W / mK or more. When the above-mentioned thermal conductivity is 2.5 W / mK or more, it exhibits excellent thermal conductivity and heat dissipation in the thickness direction. The specific method for measuring the above-mentioned thermal conductivity is as described in the examples below.

[0066] When the above-mentioned thermal conductive sheet is provided with a release film on one side (first side 1a), the minimum value of the peel strength (first peel strength) when the release film is peeled off 200 mm under the conditions of room temperature, tensile speed of 1000 mm / min, and peel angle of 170° is preferably 5 mN / cm or more and less than 50 mN / cm, more preferably 8 to 45 mN / cm, and even more preferably 10 to 40 mN / cm. When the minimum value of the first peel strength is within the above range, the release film on the first side can be easily peeled off, and the thermal conductive sheet has excellent handling properties.

[0067] When the above-mentioned thermal conductive sheet is provided with a release film on one side (first surface 1a), the maximum value of the first peel strength is preferably 50 mN / cm or more and less than 100 mN / cm, more preferably 55 to 90 mN / cm, and even more preferably 60 to 80 mN / cm. When the maximum value of the first peel strength is within the above range, the release film on the first surface can be easily peeled off, and the thermal conductive sheet has excellent handling properties.

[0068] When the above-mentioned thermal conductive sheet is provided with a release film on the other side (second side 1b), the minimum value of the peel strength (second peel strength) when the release film is peeled off 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170° is preferably 50 to 150 mN / cm, more preferably 60 to 120 mN / cm, and even more preferably 70 to 100 mN / cm. When the minimum value of the second peel strength is within the above range, the release film on the second side can be peeled off moderately and easily, and the thermal conductive sheet has excellent handling properties.

[0069] When the thermal conductive sheet is provided with a release film on the other side (second side 1b), the maximum value of the second peel strength is preferably 100 to 200 mN / cm, more preferably 110 to 180 mN / cm, and even more preferably 120 to 160 mN / cm. When the maximum value of the second peel strength is within the above range, the release film on the second side can be peeled off moderately and easily, resulting in excellent handling of the thermal conductive sheet.

[0070] The specific methods for measuring the first peel strength and the second peel strength are as described in the examples below.

[0071] The minimum value of the second peel strength is preferably greater than the minimum value of the first peel strength. The ratio of the minimum value of the second peel strength to the minimum value of the first peel strength [(minimum value of second peel strength) / (minimum value of first peel strength)] is preferably greater than 1.0 and 5.0 or less, more preferably 1.2 to 4.0, and even more preferably 1.5 to 3.0. When the ratio is within the above range, the handling properties are superior.

[0072] The maximum value of the second peel strength is preferably greater than the maximum value of the first peel strength. The ratio of the maximum value of the second peel strength to the maximum value of the first peel strength [(maximum value of second peel strength) / (maximum value of first peel strength)] is preferably greater than 1.0 and 10.0 or less, more preferably 1.5 to 8.0, and even more preferably 2.0 to 6.0. When the ratio is within the above range, the handling properties are superior.

[0073] [Release film] Preferably, the release film described above has an uneven surface on the side that is bonded to the thermal conductive sheet. By using a release film with the above-mentioned uneven surface, a shape derived from the uneven surface is transferred to the surface of the thermal conductive sheet. The uneven surface of the release film can be created by known or conventional methods such as sandblasting, embossing, or particle kneading. By appropriately adjusting the sandblasting conditions and the size of the embedded particles, the surface parameters of the thermal conductive sheet surface, such as Sv, Sal, and Sa, can be adjusted. Commercially available release films can also be used.

[0074] A release treatment layer may be provided on the surface of the above-mentioned release film that has an uneven shape. Examples of the above-mentioned release treatment layer include a layer formed by surface treatment with a release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. When a release treatment layer is provided, the thickness and shape of the release treatment layer are appropriately set so that the uneven shape of the surface does not disappear, that is, the release film retains the above-mentioned uneven shape.

[0075] [Method for manufacturing a thermally conductive sheet] The method for molding the above-mentioned thermal conductive sheet is not particularly limited, and known or conventional molding methods for molded bodies can be used. Among these, molding by roll-to-sheet is preferred from the viewpoint of continuous molding and excellent productivity.

[0076] The above-mentioned thermal conductive sheet can be obtained, for example, by placing a composition containing the various components described above between the release surfaces of two release films with flat release surfaces, and curing the composition by heating and pressurizing to form the sheet. Alternatively, the release film on one side (especially the first side) may then be peeled off, and the low-molecular-weight components in the thermal conductive sheet may be removed by heating with one side of the thermal conductive sheet exposed. When the release film used during molding is peeled off, the thermal conductive sheet can be manufactured by attaching a release film having a release surface with an uneven shape for transferring the shape to one side (especially the first side) to the exposed surface of the thermal conductive sheet. In a thermal conductive sheet formed by layering a release film with an uneven shape after molding, the surface parameters of the release film and the thermal conductive sheet may not necessarily be close in value, and may differ by orders of magnitude, because the uneven shape of the release film is transferred after molding. In this way, the surface parameters of the thermal conductive sheet can be adjusted by selecting whether the step of laminating the release film having an uneven shape to the thermal conductive sheet is performed before or after molding. Furthermore, by laminating the release film having an uneven shape after molding, an appropriate uneven shape can be transferred to the thermal conductive sheet, resulting in a thermal conductive sheet with excellent handling properties and thermal conductivity. The thermal conductive sheet may be manufactured by (i) placing the above composition between the release treatment surfaces of two release films having an uneven shape and molding, or (ii) placing the composition between the release treatment surfaces of two release films with flat release treatment surfaces and molding, and then replacing both the first and second side release films with release films having release treatment surfaces with an uneven shape for shape transfer.

[0077] The above composition includes, for example, the binder component and the thermally conductive filler. If multiple types of thermally conductive fillers are used, they may be mixed beforehand and then mixed with the binder component, or multiple types of thermally conductive fillers and the binder component may be mixed simultaneously. The above composition is preferably in the form of a paste that does not contain organic solvents.

[0078] The apparatus for producing the film of the above composition is not particularly limited, and a known molding apparatus such as a roll laminator, roll press, hot press molding machine, or extruder can be used, by placing the material between release films coated with a release agent. [Examples]

[0079] The embodiments of the present invention will be described in more detail below based on the examples, but the present invention is not limited to these examples. Unless otherwise specified, the content of each component listed in the table is expressed in "parts by mass".

[0080] Example 1 Alumina particles (A2), alumina particles (B2), alumina particles (C1), and titanium black were mixed in the mass ratios shown in Table 1. A silane coupling agent (a silane coupling agent having an ethoxy group and an alkyl group) was then added, and the particles were surface-treated by a dry method to prepare a particle composition. A resin paste was prepared by mixing the above particle composition with a thermosetting silicone resin (a two-component addition reaction type silicone resin having a mechanism of crosslinking by hydrosilylation of a polymer having vinyl groups and a polymer having Si-H groups under a platinum catalyst) as a binder component in the mass ratio shown in Table 1. Next, the resin paste was placed between two release films (B1), and a sheet-like resin paste layer was formed using a roll press. Then, the resin paste layer was placed in a heating furnace and heated at 90°C for 30 minutes to heat-cur it and mold a thermally conductive sheet. After that, one side of the release film (B1) was peeled off the molded thermally conductive sheet, and the low molecular weight siloxane in the thermally conductive sheet was removed by heating at 150°C for 90 minutes. Then, the thermally conductive sheet was removed from the heating furnace, and the release-treated surface of the release film (A1) was placed on top of the exposed surface of the thermally conductive sheet. In this way, a thermal conductive sheet (thickness of thermal conductive sheet: 1 mm) of Example 1 was fabricated as a laminate of [release film (A1) / thermal conductive sheet / release film (B1)], with a release film (A1) on the first side of the thermal conductive sheet and a release film (B1) on the second side of the thermal conductive sheet.

[0081] Example 2 The thermal conductive sheet of Example 2 was prepared in the same manner as in Example 1, except that the formulation of the thermal conductive sheet and the types of release films used on the first and second surfaces were changed as shown in Table 1.

[0082] Comparative Example 1 The resin paste prepared in Example 1 was placed between the release surface of release film (B1) and the release surface of release film (A2), and a sheet-like resin paste layer was formed using a roll press. Next, the resin paste layer was placed in a heating furnace and heated at 90°C for 30 minutes to heat-cur it, thereby forming a thermally conductive sheet. In this way, a thermally conductive sheet of Comparative Example 1 (thickness of thermally conductive sheet: 1 mm) was prepared as a laminate of [release film (A2) / thermally conductive sheet / release film (B1)], with release film (A2) on the first side of the thermally conductive sheet and release film (B1) on the second side of the thermally conductive sheet.

[0083] Comparative Example 2 The thermal conductive sheet of Comparative Example 2 was prepared in the same manner as Comparative Example 1, except that the types of release films used on the first and second surfaces were changed as shown in Table 1. However, since the release surfaces of release films (A2) and (C) are relatively flat, they do not adhere properly when bonded to the thermal conductive sheet after molding, resulting in a large amount of air trapped between the release film and the thermal conductive sheet. Therefore, in Comparative Examples 1 and 2, the thermal conductive sheets were prepared without replacing the release films.

[0084] The various raw materials shown in the table are as follows. The Sv and Sal values ​​on the release side of the release film are as shown in the table. <Thermal conductive filler> Aluminum nitride particles (D): median diameter 120 μm, spherical Alumina particles (A1): Median diameter 42.8 μm, spherical Alumina particles (A2): Median diameter 46.1 μm, spherical Alumina particles (B1): Median diameter 6.8 μm, spherical Alumina particles (B2): Median diameter 6.4 μm, spherical Alumina particles (C1): Median diameter 0.4 μm, spherical Alumina particles (C2): median diameter 0.4 μm, polyhedron <Release film> Release film (A1): Unoriented polypropylene (CPP) film with a release treatment layer, 40 μm thick. Release film (A2): Polyethylene terephthalate (PET) film with a release treatment layer, 50 μm thick. Release film (B1): PET film with a release treatment layer, 100 μm thick. Release film (B2): A film made by bonding an ETFE film (12 μm) with a release treatment layer and a PET film (50 μm) with adhesive, with a thickness of 65 μm. Release film (C): PET film with release treatment layer, 75 μm thick

[0085] (evaluation) The raw materials and release films used in the examples and comparative examples, as well as the thermally conductive sheets obtained in the examples and comparative examples, were evaluated as follows. The evaluation results are shown in the table.

[0086] (1) Median diameter (D50) The median diameter (D50) of the thermally conductive filler was measured using a particle size distribution analyzer (product name "MT3300EXII", manufactured by Microtrac Co., Ltd.). Specifically, alumina particles were dispersed in a 0.2% by mass aqueous solution of sodium hexametaphosphate. The suspension containing the dispersed alumina particles was subjected to a 150W ultrasonic bath dispersion treatment for 1 minute before being used for measurement.

[0087] (2) Surface parameters of the release film Using a 3D shape measuring machine (product name "VR-5000," manufactured by Keyence Corporation), the maximum groove depth Sv and minimum autocorrelation length Sal were measured on the release surface of the release film (before use) in low-magnification camera mode at 12x magnification. A 50mm x 50mm piece of release film was used as a sample. A reference surface was established at a total of five points: the center of the sample and the four center points when the sample was divided into four sections. A 30mm x 10mm area with no unevenness was selected as the analysis range based on visual observation. After surface shape correction, waviness removal, and screen correction with correction strength 5, measurements were taken. For transparent release films, the side opposite the release surface was blackened by spraying it with black spray (DGF spray, manufactured by Nippon Marine Tools Co., Ltd.) before measurement.

[0088] (3) Surface parameters of the thermally conductive sheet Using a 3D shape measuring machine (product name "VR-5000", manufactured by Keyence Corporation), the release film was peeled off the thermal conductive sheet in low-magnification camera mode x12, and the maximum valley depth Sv, minimum autocorrelation length Sal, and arithmetic mean height Sa were measured on the exposed surface of the thermal conductive sheet. A 50mm x 50mm piece of release film was used as a sample, and a reference plane was established at a total of 5 points: the center of the sample and the center points of the four divisions of the sample. A 30mm x 30mm area that appeared uniform upon visual observation was selected as the analysis range, and measurements were performed after surface shape correction, waviness removal, and screen correction with a correction strength of 5.

[0089] (4) Thermal conductivity By adjusting the gap of the roll press machine, thermal conductive sheets of three different thicknesses—1.0 mm, 1.5 mm, and 2.0 mm—were fabricated for each example. The release film was then peeled off the thermal conductive sheets, and the thermal resistance of the three thicknesses was measured using a thermal property measuring device (product name "DynTIM," manufactured by Siemens K.K.) after compressing them by 10% in the thickness direction (i.e., to 90% of the original thickness). The thermal conductivity was calculated from the slope of the extrapolation line of the thermal resistance values ​​obtained for each thickness of thermal conductive sheet.

[0090] (5) Peel strength For each example, the heat-conductive sheet was cut to a size of 10 mm x 200 mm. Using a product name "Peel Strength Tester PFT-50S" (manufactured by Palmec Co., Ltd.), one of the release films was peeled off the heat-conductive sheet at a length of 200 mm under conditions of a tensile speed of 1000 mm / min and a peeling angle of 170°. The minimum and maximum peel strengths under stable conditions were measured. This measurement was performed five times, and the average value was used as the evaluation result.

[0091] (6) Handling For each sample obtained from the thermal conductive sheet, the sheet was cut into 10mm x 20mm pieces. Three workers were instructed to peel off the release film from the first side of the sheet, bond it to a glass epoxy substrate, and then peel off the release film from the second side of the bonded thermal conductive sheet. The time taken to complete the above process for all 15 samples was measured, and the average time taken by the three workers was used as the evaluation result.

[0092] [Table 1]

[0093] As can be seen from Table 1, the thermal conductive sheets of the examples were judged to have excellent handling properties, with short working times in the handling evaluation. On the other hand, when the maximum groove depth Sv on the first surface was low and the minimum autocorrelation length Sal was long (Comparative Example 1), the working time in the handling evaluation was long, and the sheet was judged to have poor handling properties. Furthermore, in Comparative Example 2, the smoothness of the first and second surfaces was high, making it impossible to measure the maximum groove depth Sv and the minimum autocorrelation length Sal. In addition, in Comparative Example 2, the release film adhered well to the thermal conductive sheet, requiring careful peeling to avoid damaging the thermal conductive sheet, resulting in a long working time in the handling evaluation and a judgment of poor handling properties.

[0094] The following describes variations of the invention according to the present invention. [Note 1] On one side, the maximum valley depth Sv is between 15 μm and 50 μm, and the minimum autocorrelation length Sal is between 100 μm and 1500 μm. A thermally conductive sheet having a maximum valley depth Sv of 1 μm or more and less than 15 μm on the other side, and a minimum autocorrelation length Sal of 1500 μm or more and 3500 μm or less. [Note 2] The thermal conductive sheet as described in Note 1, wherein the difference between the maximum valley depth Sv of one surface and the maximum valley depth Sv of the other surface is 5 μm or more. [Note 3] The thermal conductive sheet according to Note 1 or 2, wherein the ratio of the maximum valley depth Sv of one surface to the maximum valley depth Sv of the other surface is greater than 1.0 and less than or equal to 10.0. [Note 4] The difference between the minimum autocorrelation length Sal of one surface and the minimum autocorrelation length Sal of the other surface is 1300 μm or more, as described in any one of Notes 1 to 3. [Note 5] The ratio of the minimum autocorrelation length Sal of the other surface to the minimum autocorrelation length Sal of the one surface is greater than 1.0 and less than or equal to 10.0, as described in any one of Notes 1 to 4. [Note 6] The one surface and the other surface are provided with a release film. On one of the aforementioned surfaces, when the release film is peeled 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170°, the minimum value of the first peel strength is 5 mN / cm or more and less than 50 mN / cm, and the maximum value is 50 mN / cm or more and less than 100 mN / cm. A thermally conductive sheet as described in any one of the appendices 1 to 5, wherein the second peel strength on the other surface, when the release film is peeled 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170°, is 50 mN / cm or more and 150 mN / cm or less, with a maximum value of 100 mN / cm or more and 200 mN / cm or less. [Note 7] The thermal conductive sheet as described in Note 6, wherein the ratio of the maximum value of the second peel strength to the maximum value of the first peel strength is greater than 1.0 and less than or equal to 10.0. [Note 8] The thermal conductive sheet according to Note 6 or 7, wherein the ratio of the minimum value of the second peel strength to the minimum value of the first peel strength is greater than 1.0 and 5.0 or less. [Note 9] A thermally conductive sheet as described in any one of Notes 1 to 8, comprising a binder component and a thermally conductive filler. [Note 10] The thermal conductive sheet described in Note 9, wherein the binder component is silicone resin. [Explanation of Symbols]

[0095] 1. Thermally conductive sheet 1a Front page 1b Second side 2,3 Release film 11 Binder components 12 Thermally conductive fillers

Claims

1. On one side, the maximum valley depth Sv is between 15 μm and 50 μm, and the minimum autocorrelation length Sal is between 100 μm and less than 1500 μm. A thermally conductive sheet having a maximum valley depth Sv of 1 μm or more and less than 15 μm on the other side, and a minimum autocorrelation length Sal of 1500 μm or more and 3500 μm or less.

2. The thermal conductive sheet according to claim 1, wherein the difference between the maximum valley depth Sv of one surface and the maximum valley depth Sv of the other surface is 5 μm or more.

3. The thermally conductive sheet according to claim 1 or 2, wherein the ratio of the maximum valley depth Sv of one surface to the maximum valley depth Sv of the other surface is greater than 1.0 and less than or equal to 10.

0.

4. The thermally conductive sheet according to claim 1 or 2, wherein the difference between the minimum autocorrelation length Sal of one surface and the minimum autocorrelation length Sal of the other surface is 1300 μm or more.

5. The thermally conductive sheet according to claim 1 or 2, wherein the ratio of the minimum autocorrelation length Sal of the other surface to the minimum autocorrelation length Sal of the one surface is greater than 1.0 and less than or equal to 10.

0.

6. The one surface and the other surface are provided with a release film, On one of the aforementioned surfaces, when the release film is peeled 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170°, the minimum value of the first peel strength is 5 mN / cm or more and less than 50 mN / cm, and the maximum value is 50 mN / cm or more and less than 100 mN / cm. The thermally conductive sheet according to claim 1 or 2, wherein the second peel strength on the other surface, when the release film is peeled off by 200 mm under the conditions of room temperature, a tensile speed of 1000 mm / min, and a peel angle of 170°, is 50 mN / cm or more and 150 mN / cm or less, with a maximum value of 100 mN / cm or more and 200 mN / cm or less.

7. The thermal conductive sheet according to claim 6, wherein the ratio of the maximum value of the second peel strength to the maximum value of the first peel strength is greater than 1.0 and less than or equal to 10.

0.

8. The thermal conductive sheet according to claim 6, wherein the ratio of the minimum value of the second peel strength to the minimum value of the first peel strength is greater than 1.0 and less than or equal to 5.

0.

9. A thermally conductive sheet according to claim 1 or 2, comprising a binder component and a thermally conductive filler.

10. The thermally conductive sheet according to claim 9, wherein the binder component is a silicone resin.

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