Method for manufacturing a laminate, method for manufacturing a sheet, and sheet

Abstract

To provide a method for producing a sheet that comprises a thermofusible tetrafluoroethylene-based polymer and an inorganic filler and has a high heat-transfer coefficient.SOLUTION: Provided is a method for producing a laminate, comprising: forming, on a surface of a substrate, a layer comprising a powder of a tetrafluoroethylene-based polymer comprising a thermofusible tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio exceeding 1; forming a layer comprising a burned product of the powder and the inorganic filler; and pressing the layer and the substrate in either process, the laminate comprising the substrate and the layer comprising the burned product and the inorganic filler formed on the surface of the substrate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a laminate having a layer containing a fired product of particles of a predetermined tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio greater than 1, a method for producing a sheet containing the fired product and the inorganic filler, and a sheet containing the fired product and the inorganic filler.

Background Art

[0002] Tetrafluoroethylene-based polymers are excellent in physical properties such as electrical insulation, water and oil repellency, chemical resistance, and heat resistance, and are widely used in parts for electronic devices, parts for automobiles, and the like. In particular, tetrafluoroethylene-based polymers are used as various electronic members in the form of coatings, laminates, sheets, or films, taking advantage of their low dielectric constant and low dielectric tangent.

[0003] On the other hand, electronic components tend to be highly densified, highly integrated, and high-output, and measures against heat generation from these electronic components have become important. In particular, power semiconductors such as LEDs generate a large amount of heat, so improvement of heat dissipation performance is particularly important. Patent Documents 1 and 2 disclose sheets obtained by injection molding a powder composition containing a tetrafluoroethylene-based polymer and a boron nitride filler, and attempts have been made to improve the thermal conductivity of the sheets.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, due to the higher functionality of electrical equipment, its power consumption has increased, and the requirements for the heat dissipation performance of electronic components are becoming increasingly high. The sheets disclosed in Patent Documents 1 and 2 still do not have sufficient heat dissipation performance.

[0006] The inventors of the present invention have considered a manufacturing method in which inorganic fillers are highly oriented for the purpose of developing a sheet containing a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler and having high thermal conductivity, and have completed the present invention.

[0007] The present invention provides a manufacturing method for providing a laminate having a layer with high thermal conductivity and a sheet made of the layer by improving the orientation of inorganic fillers in a layer containing a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler, and a sheet with high thermal conductivity.

Means for Solving the Problems

[0008] [1] A method for manufacturing a laminate having a base material and a layer formed on the surface of the base material and containing a fired product of the powder and the inorganic filler, the method comprising forming a layer containing a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio of more than 1 on the surface of the base material, and pressing the layer and the base material in any process of forming a layer containing the fired product of the powder and the inorganic filler. [2] The manufacturing method according to [1] above, wherein the powder of the tetrafluoroethylene-based polymer contains particles of a heat-meltable tetrafluoroethylene-based polymer and particles of a non-heat-meltable tetrafluoroethylene-based polymer. [3] The manufacturing method according to [1] or [2] above, wherein the heat-meltable tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer having a carbonyl group-containing group or a hydroxyl group-containing group and a melting temperature of 200°C or higher and 320°C or lower. [4] The production method according to any one of [1] to [3], wherein the mass ratio of the thermoplastic tetrafluoroethylene-based polymer to the inorganic filler in the layer is such that the mass of the inorganic filler is from 0.2 to 2 with the mass of the thermoplastic tetrafluoroethylene-based polymer being 1. [5] The production method according to any one of [1] to [4], wherein the average particle diameter of the particles of the thermoplastic tetrafluoroethylene-based polymer is smaller than the average particle diameter of the inorganic filler. [6] The production method according to any one of [1] to [5], wherein the content of the inorganic filler in the layer containing the particles of the thermoplastic tetrafluoroethylene-based polymer and the inorganic filler is 60% by mass or less. [7] The production method according to any one of [1] to [6], wherein the inorganic filler contains at least one of boron nitride or silicon oxide. [8] The production method according to any one of [1] to [7], wherein the layer containing the powder and the inorganic filler further contains a silane coupling agent. [9] The production method according to any one of [1] to [8], wherein the layer containing the powder and the inorganic filler and the base material are pressed.

[10] The production method according to any one of [1] to [9], wherein the pressure of the pressing is 0.2 MPa or more and 10 MPa or less.

[11] The production method according to any one of [1] to

[10] , wherein the temperature of the pressing is equal to or lower than the melting temperature of the thermoplastic tetrafluoroethylene-based polymer.

[12] The production method according to any one of [1] to

[11] , wherein a liquid composition containing the powder of the tetrafluoroethylene-based polymer, the inorganic filler, and a liquid dispersion medium is coated on the surface of the base material, and at least a part of the liquid dispersion medium is removed to form a layer containing the powder and the inorganic filler.

[13] The production method according to

[12] , wherein the liquid composition further contains a silane coupling agent.

[14] A method for producing a sheet including a fired product and an inorganic filler, the method including: forming a layer including a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio greater than 1 on a surface of a substrate; and in any process of forming a fired product of the powder and the layer including the inorganic filler, pressing the layer and the substrate to obtain a laminate having the substrate and the layer including the fired product and the inorganic filler formed on the surface of the substrate, and then removing the substrate.

[15] A sheet having a thickness of 50 μm or more and a thermal conductivity of more than 5 W / m·K, the sheet including a fired product of a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio greater than 1.

Advantages of the Invention

[0009] According to the present invention, the orientation of the inorganic filler in the layer including the tetrafluoroethylene-based polymer and the inorganic filler can be improved, and a laminate having a layer with high thermal conductivity and a sheet made of the layer can be manufactured. Further, according to the present invention, a sheet with high thermal conductivity including a tetrafluoroethylene-based polymer and an inorganic filler is provided.

Modes for Carrying Out the Invention

[0010] The following terms have the following meanings. The "heat-meltable tetrafluoroethylene-based polymer" is a polymer containing units based on tetrafluoroethylene (hereinafter also referred to as TFE units), and means a polymer having a melt flowability such that, under the condition of a load of 49 N, there is a temperature at which the melt flow rate becomes 1 to 1000 g / 10 min at a temperature 20°C or higher than the melting temperature of the polymer. The "non-heat-meltable tetrafluoroethylene-based polymer" is a polymer containing TFE units, and means a non-melt-flowable polymer in which there is no temperature at which the melt flow rate exceeds 1 g / 10 min under the condition of a load of 49 N. "The glass transition temperature (Tg) of a polymer" is a value measured by analyzing the polymer using the dynamic viscoelasticity measurement (DMA) method. "The melting temperature (melting point) of a polymer" is the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC) method. "D50" is the average particle diameter of particles or inorganic fillers, and is the volume-based cumulative 50% diameter of particles or inorganic fillers determined by the laser diffraction / scattering method. That is, the particle size distribution of particles or inorganic fillers is measured by the laser diffraction / scattering method, a cumulative curve is obtained with the total volume of the population of particles or fillers as 100%, and it is the particle diameter at the point where the cumulative volume becomes 50% on the cumulative curve. "D90" is the cumulative volume particle diameter of particles or inorganic fillers, and is the volume-based cumulative 90% diameter of particles determined in the same manner as "D50". "Viscosity" is a value measured for a liquid composition at room temperature (25 °C) under the condition of a rotation speed of 30 rpm using a B-type viscometer. The measurement is repeated three times, and the average value of the three measurement values is taken. "Thixotropy ratio" is a value calculated by dividing the viscosity obtained by measuring the liquid composition under the condition of a rotation speed of 30 rpm by the viscosity obtained by measuring under the condition of a rotation speed of 60 rpm. "Unit based on a monomer" means an atomic group based on the monomer formed by the polymerization of the monomer. The unit may be a unit directly formed by a polymerization reaction, or a unit in which a part of the unit has been converted to another structure by treating the polymer. Hereinafter, the unit based on monomer a is also simply referred to as "monomer a unit".

[0011] The manufacturing method of the present invention (hereinafter also referred to as "this method") is a method of forming a layer containing powder of a tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer") (hereinafter also referred to as "this powder") containing particles of a heat-meltable tetrafluoroethylene-based polymer (hereinafter also referred to as "melt F polymer") (hereinafter also referred to as "melt particles") and an inorganic filler with an aspect ratio greater than 1 (hereinafter also referred to as "this inorganic filler"), and in any process of forming a fired product of this powder and a layer containing the inorganic filler, pressing the layer and the base material, to obtain a laminate (hereinafter also referred to as "this laminate") having the base material and the layer containing the fired product and the inorganic filler formed on the surface of the base material.

[0012] This powder is an aggregate of particles containing melt particles, and may consist only of melt particles, or may contain melt particles and other particles. As other particles, particles of a non-heat-meltable tetrafluoroethylene-based polymer (hereinafter also referred to as "non-melt F polymer") (hereinafter also referred to as "non-melt particles") are preferable, and it is preferable to contain melt particles and non-melt particles. In the latter case, due to the progress of fibrillation of the non-heat-meltable F polymer in the pressing of the layer and the base material, the inorganic filler is likely to be carried in the layer, and the strength of the layer is more likely to be further improved. In this case, the content of non-melt particles in the total amount of this powder is preferably 50% by mass or more. The non-melt F polymer is preferably non-heat-meltable polytetrafluoroethylene. The D50 of the non-melt particles is preferably from 0.1 to 1 μm. When this powder is an aggregate of melt particles and non-melt particles, the content of melt particles and non-melt particles in this powder is preferably such that the total mass of the content of melt particles and non-melt particles is 100% by mass with the mass of this powder being 100% by mass. When this powder is an aggregate of melt particles and non-melt particles, the content of melt particles in this powder is preferably from 5 to 80% by mass, more preferably from 10 to 60% by mass, with the total mass of the content of melt particles and non-melt particles being 100% by mass.

[0013] The melting temperature of the molten F polymer is preferably 200 °C or higher, more preferably 250 °C or higher, and even more preferably 280 °C or higher. From the viewpoint of moldability, 320 °C or lower is preferable.

[0014] The glass transition point of the molten F polymer is preferably from 30 to 150 °C, more preferably from 75 to 125 °C. As the molten F polymer, a polymer containing a TFE unit and a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as PAVE) (hereinafter also referred to as PAVE unit) (hereinafter also referred to as PFA) or a copolymer containing a TFE unit and a unit based on hexafluoropropylene (hereinafter also referred to as FEP) is preferable, and PFA is particularly preferable. These polymers may further contain units based on other comonomers.

[0015] As PAVE, CF2=CFOCF3, CF2=CFOCF2CF3 or CF2=CFOCF2CF2CF3 (hereinafter also referred to as PPVE) is preferable, and PPVE is more preferable. The molten F polymer preferably has a polar functional group. The molten F polymer having a polar functional group is more likely to further improve the adhesiveness to a substrate, the peel strength of the laminate, the water resistance, and other reliability.

[0016] The polar functional group may be contained in the monomer unit in the molten F polymer or may be contained in the end group of the main chain of the molten F polymer. As the latter embodiment, a molten F polymer having a polar functional group as an end group derived from a polymerization initiator, a chain transfer agent, etc., and a molten F polymer having a polar functional group obtained by subjecting the molten F polymer to plasma treatment or ionizing radiation treatment can be mentioned. The polar functional group is preferably a hydroxyl group-containing group or a carbonyl group-containing group, and particularly preferably a carbonyl group-containing group.

[0017] The hydroxyl group-containing group is preferably a group containing an alcoholic hydroxyl group, and more preferably -CF2CH2OH or -C(CF3)2OH. The carbonyl group-containing group is a group containing a carbonyl group (>C(O)), and a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH2), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.) or a carbonate group (-OC(O)O-) is preferable, and an acid anhydride residue is particularly preferable.

[0018] Preferable embodiments of the molten F polymer include a polymer (1) containing TFE units and PAVE units and having a polar functional group, or a polymer (2) containing TFE units and PAVE units, containing 2.0 to 5.0 mol% of PAVE units based on all monomer units, and having no polar functional group. Polymer (1) is preferred. Since these polymers form microspherulites in the product, the properties of the resulting product are likely to be improved.

[0019] Polymer (1) is preferably a polymer containing TFE units, PAVE units, and a monomer having a hydroxyl group-containing group or a carbonyl group-containing group. Polymer (1) preferably contains 90 to 99 mol% of TFE units, 0.5 to 9.97 mol% of PAVE units, and 0.01 to 3 mol% of units based on the monomer, respectively, based on all units. The monomer is preferably itaconic anhydride, citraconic anhydride or 5-norbornene-2,3-dicarboxylic anhydride (also known as: hymic anhydride; hereinafter also referred to as "NAH"). Specific examples of polymer (1) include the polymers described in International Publication No. 2018 / 16644.

[0020] Polymer (2) consists only of TFE units and PAVE units, and preferably contains 95.0 to 98.0 mol% of TFE units and 2.0 to 5.0 mol% of PAVE units based on all monomer units. The content of PAVE units in polymer (2) is preferably 2.1 mol% or more, more preferably 2.2 mol% or more, based on all monomer units. Note that the fact that the polymer (2) has no polar functional groups means that the number of polar functional groups in the polymer is less than 500 per 1×106 carbon atoms constituting the polymer main chain. The number of polar functional groups is preferably 100 or less, more preferably less than 50. The lower limit of the number of polar functional groups is usually 0.

[0021] The polymer (2) may be produced using a polymerization initiator, a chain transfer agent, etc. that do not generate polar functional groups as end groups of the polymer chain, or may be produced by fluorinating a molten F-polymer having polar functional groups. Examples of the fluorination method include a method using fluorine gas (see JP-A-2019-194314, etc.).

[0022] When the molten F-polymer has a carbonyl group-containing group or a hydroxyl group-containing group, the number of carbonyl group-containing groups or hydroxyl group-containing groups in the molten F-polymer is preferably 10 or more and 5000 or less, more preferably 50 or more and 4000 or less, and even more preferably 100 or more and 2000 or less per 1×106 main chain carbon atoms. In this case, the molten F-polymer easily interacts with this inorganic filler, and the dispersibility of this inorganic filler in the resulting layer is likely to be excellent. Note that the number of carbonyl group-containing groups or hydroxyl group-containing groups in the molten F-polymer can be quantified from the composition of the polymer. Also, the carbonyl group-containing group can be quantified by the method described in WO 2020 / 145133.

[0023] The molten particles are particles containing a molten F-polymer, and the amount of the molten F-polymer in the molten particles is preferably 80% by mass or more, more preferably 100% by mass. The D50, which is the average particle size of the molten particles, is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 8 μm or less. The D50 of the molten particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 1 μm or more. Further, the D90 of the molten particles is preferably less than 100 μm, and more preferably 90 μm or less. If the D50 and D90 of the molten particles are within such ranges, their surface area will increase, and the dispersibility of the molten particles will be more easily improved.

[0024] The molten particles may contain another resin or inorganic substance different from the molten F polymer. Specific examples of the other resin include aromatic polymers such as aromatic polyimide, aromatic maleimide, styrene elastomer, and aromatic polyamic acid. Specific examples of the inorganic substance include silica.

[0025] This inorganic filler is an inorganic filler with an aspect ratio greater than 1, and its shape may be any of granular, needle-like, fibrous, or plate-like. Specific shapes of this inorganic filler include spherical, scaly, layered, flaky, almond-shaped, columnar, cockscomb-shaped, equiaxed, leaf-shaped, mica-shaped, block-shaped, flat plate-shaped, wedge-shaped, rosette-shaped, reticular, and prismatic. In addition to the above shapes, this inorganic filler may have various shapes such as plate-shaped, hollow-shaped, and honeycomb-shaped. The aspect ratio of this inorganic filler is preferably 5 or more, and more preferably 10 or more. Also, the aspect ratio of this inorganic filler is preferably 1000 or less.

[0026] Examples of this inorganic filler include aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon oxide, and silicon carbide. Among these, from the viewpoint of thermal conductivity, alumina, boron nitride, and silicon oxide are preferred, boron nitride and silicon oxide are more preferred, and boron nitride, particularly hexagonal boron nitride, is even more preferred.

[0027] This inorganic filler is preferably surface-treated with a silane coupling agent. In this case, the inorganic filler and the molten particles can act well with each other, and the dispersibility of the inorganic filler in the resulting layer is likely to be excellent. Also, the adhesion between the powder and the inorganic filler is improved, and peeling of the powder or the inorganic particles in the powder layer is likely to be suppressed. A silane coupling agent is a compound having a hydrolyzable silyl group and an organic group. The silane coupling agent may be partially reacted or may form a polysiloxane skeleton.

[0028] As the hydrolyzable silyl group, a monoalkoxysilyl group, a dialkoxysilyl group, or a trialkoxysilyl group is preferable, and a trialkoxysilyl group is more preferable. The hydrolyzable silyl group may be hydrolyzed. Examples of the organic group include a vinyl group, an epoxy group, a styryl group, an acryloyloxy group, a methacryloyloxy group, an amino group, an isocyanate group, a mercapto group, a benzotriazole group, and an acid anhydride group. An epoxy group, a benzotriazole group, a phenyl group, or a ureido group is preferable, and an epoxy group is more preferable. The silane coupling agent may have a plurality of different types of organic groups or a plurality of the same type of organic groups. The silane coupling agent preferably is a compound having a trialkoxysilyl group and a benzotriazole group or an epoxy group, and more preferably is a compound having a trialkoxysilyl group and an epoxy group.

[0029] Examples of the silane coupling agent include a compound having a benzotriazole group and a trimethoxysilyl group at both ends of the main chain, a compound having three epoxy groups in the main chain and a plurality of triethoxysilyl groups in the side chain, a compound having a siloxane structure in the main chain and amino groups at both ends of the main chain, a compound having a butadiene structure in the main chain and one acid anhydride group and one trimethoxysilyl group in the side chain, and a compound having an alkoxysiloxane structure in the main chain and a plurality of epoxy groups in the side chain. Specific examples of the silane coupling agent include N-phenyl-3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, p-styryltrimethoxysilane, 3-trimethoxysilylpropyl succinic anhydride, N-2-(aminomethyl)-8-aminooctyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0030] Specific products of the silane coupling agent include "KBM-573", "KBM-403", "KBM-903", "KBE-903", "KBM-1403", "X-12-967C", "X-12-1214A", "X-12-984S", "X-12-1271A", "KBP-90", "KBM-6803", "X-12-1287A", "KBM-402", "KBE-402", "KBE-403", "KR-516", "KBM-303", "KBM-4803", "KBM-3063", and "KBM-13" (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0031] As a method for surface-treating the present inorganic filler with a silane coupling agent, there is a method of mixing and treating a solution containing the silane coupling agent and the inorganic filler and then drying them. In the mixing treatment, the mixture of the solution and the inorganic filler may be heated or hydrated to promote the reaction of the silane coupling agent. Also, the reaction of the silane coupling agent may be accelerated by a reaction catalyst. Further, after drying, the inorganic filler surface-treated with the silane coupling agent may be crushed or classified.

[0032] The D50 of the present inorganic filler is preferably from 0.1 to 50 μm, and it is more preferable to use inorganic fillers with different D50s. When using inorganic fillers with different D50s, a mixture of a coarse powder with a D50 of 10 to 50 μm and a fine powder with a D50 of 0.5 to 4 μm is preferable. By using a mixture of a coarse powder and a fine powder as the present inorganic filler, the fine powder can be filled between the coarse powders, thereby increasing the filling rate of the present inorganic filler in the resulting layer. When the present inorganic filler is formed of a coarse powder and a fine powder, the blending ratio of the coarse powder is preferably 70% or more, more preferably 75% or more. If the ratio of the coarse powder is within this range, the present inorganic filler in the resulting layer tends to be densely filled.

[0033] The D50, which is the average particle size of the molten particles, is preferably smaller than the D50 of the present inorganic filler, and the D50 of the molten particles is preferably 0.1 or more and 0.6 or less of the D50 of the present inorganic filler. When using inorganic fillers with different D50s, specifically even when using the above-mentioned coarse powder and fine powder, the D50 of the molten particles is preferably smaller than the D50 of the fine powder.

[0034] This method forms a layer containing the present powder and the present inorganic filler on the surface of the substrate. Examples of the substrate include a metal substrate or a resin substrate. The metal substrate is preferably a metal foil. Examples of the metal constituting the metal foil include copper, copper alloy, stainless steel, nickel, nickel alloy, aluminum, aluminum alloy, titanium, and titanium alloy. As the metal foil, a copper foil is preferable, a rolled copper foil without distinction between the front and back or an electrolytic copper foil with distinction between the front and back is more preferable, and a rolled copper foil is even more preferable. As the resin substrate, a polyimide film is more preferable. The surface of the substrate may be surface-treated with a silane coupling agent or the like. The ten-point average roughness of the surface of the substrate is preferably 0.01 to 0.05 μm.

[0035] A method for forming a layer containing the present powder and the present inorganic filler (hereinafter, also referred to as "powder layer") on the surface of the base material includes, for example, a method of extruding a powder composition containing the present powder and the present inorganic filler onto the base material, a method of co-extruding the base material and a powder composition containing the present powder and the present inorganic filler, a method of creating a sheet containing the present powder and the present inorganic filler and joining the base material and the obtained sheet by adhesion or crimping, etc., a method of coating the surface of the base material with a liquid composition containing the present powder, the present inorganic filler and a liquid dispersion medium and removing at least a part of the liquid dispersion medium by heating, and the like.

[0036] When extrusion-molding a powder composition containing the present powder and the present inorganic filler, the powder composition may further contain a thermoplastic resin, a thermosetting resin, or a semi-cured thermoplastic resin. The powder composition may be pellets containing the present powder, the present inorganic filler, and these resins. Examples of such resins include polyolefins such as polyethylene, polypropylene, ABS resin, polymethyl methacrylate, polystyrene, ethylene-vinyl acetate copolymer, modified polyolefin, etc., tetrafluoroethylene-based polymers, polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyester elastomer, etc., polyamides such as nylon 6, nylon 66, nylon 610, nylon 612, nylon 12, aromatic amorphous nylon, methoxymethylated polyamide resin, polyamide elastomer, etc., engineering plastics such as polycarbonate, polyacetal, polyarylate, polysulfone, etc., polyurethane, polyurethane elastomer, or polymer blends or alloys thereof.

[0037] When coating the surface of the base material with a liquid composition containing the present powder, the present inorganic filler, and a liquid dispersion medium and removing at least a part of the liquid dispersion medium by heating to form a powder layer, the liquid dispersion medium may be water or a non-aqueous dispersion medium. The liquid dispersion medium may also be an aprotic dispersion medium or a protic dispersion medium. Note that "liquid" means a state where the viscosity is 10 mPa·s or less at 25°C. The liquid dispersion medium is more preferably at least one selected from the group consisting of water, amides, ketones, esters, and glycols. Specific examples of the liquid dispersion medium include water, N-methyl-2-pyrrolidone, γ-butyrolactone, methyl ethyl ketone, cyclohexanone, cyclopentanone, ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol. One kind of the liquid dispersion medium may be used, or two or more kinds may be used. In the case of using two or more kinds, it is preferable that the different liquid dispersion media are compatible.

[0038] When coating this dispersion liquid, coating methods such as spray method, roll coating method, spin coating method, gravure coating method, microgravure coating method, gravure offset method, knife coating method, kiss coating method, bar coating method, die coating method, fountain Meyer bar method, and slot die coating method can be used.

[0039] When using the liquid dispersion medium, from the viewpoint of further improving the dispersion stability and handleability of the liquid composition, a nonionic surfactant may be further contained. As the surfactant, an acetylene-based surfactant, a silicone-based surfactant, or a fluorine-based surfactant is preferable, and a silicone-based surfactant is more preferable.

[0040] Specific examples of such surfactants include the "Fujent" series (manufactured by Neos Co., Ltd., Fujent is a registered trademark), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd., Surflon is a registered trademark), the "Megafac" series (manufactured by DIC Corporation, Megafac is a registered trademark), the "Unidine" series (manufactured by Daikin Industries, Ltd., Unidine is a registered trademark), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by BYK-Chemie Japan Co., Ltd.), "KF-6011", and "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.). When containing a surfactant, the content of the surfactant in the liquid composition is preferably 1% by mass or more and 15% by mass or less. In this case, the affinity between components increases, and the dispersion stability and handling properties of the liquid composition are more likely to be improved.

[0041] The liquid composition may contain an aromatic polymer. As the aromatic polymer, aromatic polyimide, aromatic polyamideimide, a precursor of aromatic polyamideimide, aromatic maleimide, aromatic elastomer (such as styrene elastomer), aromatic polyamic acid or polyphenylene ether is preferable, and aromatic polyimide, aromatic polyamideimide, a precursor of aromatic polyamideimide or aromatic polyamic acid is more preferable. The aromatic polyimide may be thermoplastic or thermosetting. The thermoplastic polyimide means a polyimide in which imidization is completed and no further imidization reaction occurs.

[0042] Specific examples of the aromatic polyimide include "Neoprim (registered trademark)" series (manufactured by Mitsubishi Gas Chemical Company), "Spixelia (registered trademark)" series (manufactured by Somal Co., Ltd.), "Q-PILON (registered trademark)" series (manufactured by PI Technology Research Institute), "WINGO" series (manufactured by Wingo Technology Co., Ltd.), "Tomide (registered trademark)" series (manufactured by T&K Toka Co., Ltd.), "KPI-MX" series (manufactured by Kawamura Sangyo Co., Ltd.), "UPIA (registered trademark)-AT" series (manufactured by Ube Industries, Ltd.), "HPC-1000", "HPC-2100D" (both manufactured by Showa Denko Materials Co., Ltd.).

[0043] The liquid composition preferably contains a silane coupling agent. In this case, the adhesion between the present powder and the present inorganic filler is improved, and peeling of the present powder or the present inorganic particles in the powder layer is likely to be suppressed. The silane coupling agent may be mixed in the liquid composition and contained in the liquid composition, or may be contained in the liquid composition as a surface treatment agent for the present inorganic filler.

[0044] As the silane coupling agent contained in the liquid composition, a compound having a trialkoxysilyl group and a phenyl group, vinyl group, epoxy group, acryloyloxy group, methacryloyloxy group, amino group, ureido group, mercapto group or isocyanate group is preferable, and a compound having a trialkoxysilyl group and an amino group is more preferable.

[0045] The thermal decomposition temperature of the silane coupling agent contained in the liquid composition is preferably 200°C or higher, more preferably 300°C or higher. The upper limit of the thermal decomposition temperature is preferably 400°C. In this case, the heat resistance of the obtained laminate is more likely to be improved. The thermal decomposition temperature of the silane coupling agent is the temperature at which the mass becomes 50% of that at the start of temperature increase when the silane coupling agent is heated from 50°C to 400°C at a rate of 5°C / min in a nitrogen atmosphere.

[0046] Specific examples of the silane coupling agent contained in the liquid composition include methyltrimethoxysilane, methyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxyxypropyltrimethoxysilane, n-phenyl-3-aminopropyltrimethoxysilane. The above-mentioned silane coupling agent may be used as a surface treatment agent for the inorganic filler, or may be mixed and used in the liquid composition.

[0047] When obtaining a liquid composition containing a silane coupling agent by mixing the silane coupling agent, it is preferable to obtain the liquid composition by adding the silane coupling agent to the present inorganic filler, further adding the present powder, and performing a mixing process. When adding the silane coupling agent, the present inorganic filler may be dispersed in a liquid dispersion medium, and the silane coupling agent may be diluted with a liquid dispersion medium. Further, in the mixing process, the liquid composition containing the silane coupling agent, the present inorganic filler, and the present powder may be heated or hydrated to promote the reaction of the silane coupling agent. Further, the reaction of the silane coupling agent may be accelerated by a reaction catalyst.

[0048] When the liquid composition contains a surfactant, an aromatic polyimide, or a silane coupling agent, its content is preferably 1 to 10% by mass, respectively independently, based on the content of the present powder.

[0049] The content of the liquid dispersion medium in the liquid composition is preferably 30% by mass or more. The content of the liquid dispersion medium is preferably 90% by mass or less, and more preferably 80% by mass or less. Regarding the solid content in the liquid composition, with the total mass of the liquid composition being 100%, the solid content concentration is preferably 20% by mass or more, and more preferably 30% by mass or more. Also, from the viewpoint of the dispersibility of the liquid composition, the solid content mass is preferably 60% by mass or less, and more preferably 50% by mass or less. Also, the liquid dispersion medium is preferably deaerated from the viewpoint of suppressing a decrease in the uniformity of the component distribution and voids in the powder layer.

[0050] The viscosity of the liquid composition is preferably 10 mPa·s or more, and more preferably 100 mPa·s or more. The viscosity of the liquid composition is preferably 10000 mPa·s or less, and more preferably 1000 mPa·s or less. In this case, the liquid composition has excellent coatability. The thixotropy ratio of the liquid composition is preferably 1 or more. The thixotropy ratio of the liquid composition is preferably 3 or less, and more preferably 2 or less. In this case, the liquid composition not only has excellent coatability but also excellent homogeneity.

[0051] After coating the liquid composition on the substrate, at least a part of the liquid dispersion medium is removed by heating to form a powder layer. The heating may be carried out until at least a part of the liquid dispersion medium is removed, and the liquid dispersion medium may be removed to such an extent that the present powder and the inorganic filler maintain a layered shape. It is preferable that 80% by mass or more of the liquid dispersion medium contained in the liquid composition is removed. The liquid dispersion medium may be completely removed.

[0052] The temperature for removing the liquid dispersion medium is preferably a temperature equal to or lower than the melting temperature of the molten F polymer and equal to or lower than the boiling point of the liquid dispersion medium, and more preferably a temperature equal to or lower than a temperature 100 °C lower than the melting temperature of the molten F polymer and from 10 °C to 100 °C lower than the boiling point of the liquid dispersion medium. For example, when using a molten F polymer with a melting temperature of 300 °C and N-methyl-2-pyrrolidone with a boiling point of about 200 °C, the temperature for removing the liquid dispersion medium is preferably 150 °C or lower, and more preferably 100 to 120 °C. From the viewpoint of forming a powder layer with excellent smoothness, it is preferable to blow air onto the surface of the formed powder layer during the removal of the liquid dispersion medium.

[0053] The content mass ratio of the molten F polymer and the present inorganic filler in the powder layer obtained by the above method is preferably such that the content mass of the inorganic filler is 0.2 or more, more preferably 0.5 or more, with the content mass of the molten F polymer being 1. Also, the content mass of the inorganic filler is preferably 2 or less, more preferably 1.5 or less. Also, the content of the present inorganic filler in the powder layer is preferably 60% by mass or less, more preferably 50% by mass or less, with the total mass of the powder layer being 100% by mass. When forming a powder layer using the liquid composition, the total mass of the powder layer is the mass when 80% by mass or more of the liquid dispersion medium is removed. The content mass ratio of the molten F polymer and the present inorganic filler and the content of the present inorganic filler in the powder layer can be within the above range by appropriately setting the mass ratio and content of the present powder and the present inorganic filler in the composition or the liquid composition.

[0054] The obtained powder layer may contain a third component in addition to the present powder and the present inorganic filler. Examples of the third component include a silane coupling agent, an ultraviolet absorber, and other resins different from the tetrafluoroethylene-based polymer. The powder layer preferably contains a resin other than the silane coupling agent or the tetrafluoroethylene-based polymer, and more preferably contains a resin other than the silane coupling agent and the tetrafluoroethylene-based polymer. In this case, the adhesion between the present powder and the present inorganic filler is improved, and peeling of the present powder or the present inorganic particles in the powder layer is likely to be suppressed. The silane coupling agent may be contained in the powder layer as a surface treatment agent for the present inorganic filler. When forming the powder layer using the liquid composition, the powder layer containing the silane coupling agent may be obtained by forming the powder layer from the liquid composition mixed with the silane coupling agent.

[0055] As the ultraviolet absorber, an ultraviolet absorber having a phenolic hydroxyl group and a nitrogen-containing heterocyclic structure is preferable, and an ultraviolet absorber having a hydroxybenzophenone structure or an ultraviolet absorber having a phenolic hydroxyl group and a triazine structure or a benzotriazole structure is more preferable. The latter ultraviolet absorber preferably has a hydroxyphenyltriazine structure or a structure in which various substituents are substituted on the hydroxyphenyl structure. Examples of other resins different from the F polymer include the above-mentioned aromatic polymers.

[0056] In addition to the third component, the powder layer may further contain additives such as a thixotropy-imparting agent, a viscosity regulator, an antifoaming agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightening agent, a colorant, a conductive agent, a mold release agent, a surface treatment agent, a flame retardant, and various fillers.

[0057] The obtained powder layer is further fired to form a fired product of the present powder (hereinafter, also referred to as "the present fired product") and a layer containing the present inorganic filler (hereinafter, also referred to as "the fired product layer"). The present powder may be completely fired or partially fired. The firing temperature only needs to be equal to or higher than the melting point of the molten F polymer, for example, in the range of 300 to 400 °C.

[0058] When the powder layer is formed on the surface of the substrate by the method of melt extrusion, the method of co-extrusion, or the method of bonding to the substrate, a fired layer can be formed by firing the substrate and the powder layer in the above-mentioned firing temperature range. When the powder layer is formed on the surface of the substrate by coating the liquid composition on the substrate and removing at least a part of the liquid dispersion medium by heating, a fired layer can be formed by subsequently firing in the above-mentioned firing temperature range. The liquid dispersion medium may be completely removed before firing.

[0059] The fired layer may contain, for example, the surfactant, the third component, the additive, and its residue. Also, the content mass ratio of the molten F polymer and the present inorganic filler in the fired layer is preferably 0.2 or more, more preferably 0.5 or more, with the content mass of the molten F polymer being 1, similar to the powder layer. Also, the content mass of the present inorganic filler is preferably 2 or less, more preferably 1.5 or less. Also, the content of the present inorganic filler in the fired layer is preferably 60 mass% or less, more preferably 50 mass% or less, with the total mass of the fired layer being 100 mass%.

[0060] In this method, the layer and the substrate are pressed in any process of forming the powder layer and forming the fired layer. When the powder layer is formed on the surface of the substrate by the method of melt extrusion, the method of co-extrusion, or the method of bonding to the substrate, the pressing is preferably performed at any stage of (1) the stage of forming the powder layer on the surface of the substrate, (2) the stage after forming the powder layer and before firing, (3) the firing stage, and (4) the stage after forming the fired layer until the fired layer is cooled. In the stage (2), the powder layer may be cooled once or fired as it is without cooling. Pressing is preferably carried out at the stage of (1) or (2) above, and more preferably at the stage of (2). Pressing may be carried out at a plurality of the above stages.

[0061] When the powder layer is formed on the surface of the substrate by a method of coating the liquid composition on the surface of the substrate and removing at least a part of the liquid dispersion medium by heating, pressing is carried out at any one of the following stages: (11) a stage immediately after a part of the liquid dispersion medium is removed by heating and a powder layer is formed; (21) a stage before further heating the powder layer to form a fired layer after the powder layer is formed; (31) a stage in which the powder layer is fired and a fired layer is formed; and (41) a stage until the fired layer is cooled after firing. In the above (11), it is preferable that 80% by mass or more of the liquid dispersion medium contained in the liquid composition is removed. In the stage of (21) above, after the powder layer is formed, the powder layer may be cooled once, or may be fired without cooling after the powder layer is formed. Pressing is more preferably carried out at the stage of (11) or (21) above, and even more preferably carried out at the stage of (21). Pressing may be carried out at a plurality of the above stages.

[0062] Pressing is preferably carried out in an atmosphere of reduced pressure from atmospheric pressure, and more preferably carried out in an atmosphere of atmospheric pressure. The pressure of pressing is preferably 0.2 MPa or more, and more preferably 0.5 MPa or more. The pressure is preferably 10 MPa or less, and more preferably 5 MPa or less.

[0063] The temperature of pressing is preferably higher than the glass transition temperature of the molten F polymer, and more preferably 30°C or more higher than the glass transition temperature. Also, the temperature of pressing is preferably lower than the melting temperature of the molten F polymer, and more preferably 100°C or more lower than the melting temperature. The temperature of pressing is preferably higher than the glass transition temperature of the molten F polymer and 100°C or more lower than the melting temperature of the molten F polymer.

[0064] The pressing method includes passing the powder layer or the fired layer and the base material between a pair of heated rolls during any process from the formation of the powder layer to the formation of the fired layer, blowing hot air while passing the powder layer or the fired layer and the base material between a pair of rolls, and pressing the powder layer or the fired layer and the base material with a hot plate. Preferably, the ratio of the thickness of the powder layer or the fired layer after pressing to the thickness of the powder layer or the fired layer before pressing is from 0.5 to 0.9. For example, the ratio of the thickness of the powder layer after pressing to the thickness of the powder layer before pressing is preferably from 0.5 to 0.9, or the ratio of the thickness of the fired layer after pressing to the thickness of the fired layer before pressing is preferably from 0.5 to 0.9.

[0065] From the viewpoint of suppressing the adhesion of the powder layer or the fired layer to the roll or the hot plate during pressing, a release film may be disposed between the surface of the powder layer or the fired layer and the roll or the hot plate, or the surface of the roll or the hot plate may be surface-treated with a release agent. When passing between a pair of rolls for pressing, the release film preferably contacts the powder layer or the fired layer only on the pressure-applying surface of the roll and is peeled off when the powder layer or the fired layer separates from the roll. The thickness of the release film is preferably from 50 to 150 μm. Examples of the release film include polyimide films, and specific examples include "Apical NPI" (manufactured by Kaneka Corporation), "Kapton EN" (Toray DuPont Company), and "U-Pirex S" (Ube Industries, Ltd.).

[0066] In the present invention, in the process of forming the powder layer until the fired layer is formed, it can also be considered that the inorganic filler is in a state of flowing and dispersing in the molten F polymer. It is considered that the pressing of the layer in this state exhibits the effect of orienting the long axis direction of the inorganic filler in the horizontal direction of the substrate surface. In particular, the powder layer can also be regarded as a state in which the inorganic filler is dispersed in the voids formed by the packing of the powder. If the powder layer in such a state is pressed, it is considered that the voids are crushed and the long axis direction of the inorganic filler becomes more likely to be oriented in the horizontal direction of the substrate. As a result, according to the present method, it is considered that a dense laminate containing the inorganic filler with the long axis direction oriented and dispersed in the horizontal direction of the substrate is obtained in the molten F polymer.

[0067] By the present method, the present laminate including the fired layer in which the inorganic filler is highly oriented and the substrate can be obtained. The thickness of the fired layer is preferably 50 μm or more, more preferably 75 μm or more. The upper limit of the thickness is preferably 500 μm, more preferably 250 μm.

[0068] By removing the substrate from the present laminate obtained by the present method, a sheet containing the present fired product and the inorganic filler can be produced. Examples of the removal method include peeling or etching. The sheet thus obtained has the voids between the present fired products crushed, the voids in the layer reduced, and the inorganic filler oriented in the plane, and is excellent in thermal conductivity.

[0069] The sheet of the present invention (hereinafter also referred to as "the present sheet") contains a fired product of a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio of more than 1, has a thickness of 50 μm or more, and a thermal conductivity of more than 5 W / m·K. Regarding the heat-meltable tetrafluoroethylene-based polymer, the powder containing it, the tetrafluoroethylene-based polymer, the powder containing it, and the fired product, they are the same as the molten F polymer, the molten particles, the F polymer, the present powder, and the fired product. In addition, the inorganic filler with an aspect ratio exceeding 1 is the same as the present inorganic filler.

[0070] The thickness of this sheet is preferably 50 μm or more, more preferably 75 μm or more. The upper limit of the thickness is preferably 500 μm, more preferably 250 μm. The thermal conductivity of this sheet measured by the method described later is preferably more than 5 W / m·K, more preferably 8 W / m·K or more. The upper limit of the thermal conductivity of this sheet is not particularly limited and is 100 W / m·K.

[0071] Since this laminate and this sheet are excellent in thermal conductivity, they can be suitably used as a thermally conductive insulating sheet for heat dissipation of electronic components, a metal base substrate provided with a thermally conductive insulating layer, and a circuit board. In particular, since the inorganic filler in this laminate and this sheet is highly oriented, the heat dissipation direction can be controlled. For example, after laminating a plurality of these sheets, an insulating sheet obtained by slicing this laminate in the thickness direction so that the cut end face is a plane is a sheet in which the present inorganic filler is oriented in the thickness direction of the insulating sheet. Such a sheet is useful when heat dissipation in the thickness direction is required because the heat conduction in the thickness direction is high.

[0072] This laminate and this sheet are useful as electronic substrate materials such as flexible printed wiring boards and rigid printed wiring boards, protective films, heat dissipation substrates, particularly heat dissipation substrates for automobiles. Specifically, the present laminate and the present sheet can also be suitably used as a heat dissipation member for a wireless communication device. For example, in a wireless communication device having a base material made of resin or the like, an antenna pattern formed on the base material, and an RFIC package which is a power supply circuit connected to the antenna pattern, if the present laminate or the present sheet is disposed around the RFIC package, heat dissipation of the RFIC package can be promoted and its temperature rise can be effectively suppressed. In this case, from the viewpoint of not disturbing the radiation of the antenna, it is preferable to dispose the present laminate or the present sheet on the surface of the RFIC package opposite to the surface on which the antenna pattern is provided. Examples of such wireless communication devices include the wireless communication devices described in International Publication No. WO2020 / 008691 and International Publication No. WO2020 / 031419. Further, the present laminate and the present sheet can also be suitably used as a mounting heat dissipation substrate for a power device. When using the present laminate or the present sheet as these members, the present laminate or the present sheet may be directly bonded to the target substrate, or the present laminate or the present sheet may be bonded to the target substrate via an adhesive layer such as a silicone-based adhesive layer.

[0073] As described above, the present method, the method for manufacturing a sheet for removing a base material from the laminate obtained by the present method, and the present sheet have been described. However, the present invention is not limited to the configurations of the above-described embodiments. For example, the present method and the method for manufacturing a sheet for removing a base material from the laminate obtained by the present method may have any other arbitrary steps added in the configuration of the above-described embodiment, or may be replaced with any arbitrary steps that produce the same effect. Further, in the configuration of the above-described embodiment, any other arbitrary configuration may be added to the present sheet, or it may be replaced with any arbitrary configuration that exhibits the same function.

Examples

[0074] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto. 1. Preparation of Each Component [Powder] Powder 1: Composed of melt particles (D50: 2.1 μm) made from a polymer containing 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units in this order, having 1000 carbonyl group-containing groups per 1×106 main chain carbons, and a melting temperature of 300 °C Powder 2: Non-melt particles (D50: 0.3 μm) made of non-thermally meltable polytetrafluoroethylene [Inorganic filler] Filler 1: Scaly boron nitride filler (aspect ratio: greater than 1, D50: 14.6 μm) [Liquid compound] NMP: N-Methyl-2-pyrrolidone

[0075] 2. Production examples of the dispersion [Example 1] Into a pot, a varnish of thermoplastic aromatic polyimide (PI1), NMP, and an aminosilane coupling agent were charged and mixed. Further, a powder mixture of Powder 1 and Filler 1 was charged into the pot and mixed to prepare a composition. This composition was kneaded in a planetary mixer and then taken out to obtain Kneaded Powder 1 containing 50 parts by mass of Powder 1, 40 parts by mass of Filler 1, 6 parts by mass of PI1, 1 part by mass of the aminosilane coupling agent, and 30 parts by mass of NMP. Kneaded Powder 1 was in a lump and clay-like form. While adding NMP to Kneaded Powder 1 in multiple portions, it was stirred in a planetary mixer at 2000 rpm while defoaming. Further, NMP was stirred in multiple portions, and a total of 80 parts by mass of NMP was added to Kneaded Powder 1 to prepare a dispersion, obtaining Dispersion 1. The viscosity of Dispersion 1 was 300 mPa·s.

[0076] [Example 2] In the preparation of the composition of Example 1, further using Powder 2, a kneaded powder 2 containing 25 parts by mass of Powder 1, 25 parts by mass of Powder 2, 40 parts by mass of Filler 1, 6 parts by mass of PI1, 1 part by mass of an amino silane coupling agent, and 30 parts by mass of NMP was obtained. While adding NMP to the kneaded powder 2 in multiple portions, it was stirred at 2000 rpm with defoaming using a planetary mixer. Further, NMP was stirred in multiple portions, and a total of 80 parts by mass of NMP was added to the kneaded powder 2 to prepare a dispersion, and Dispersion 2 was obtained.

[0077] 3. Manufacturing Examples of Laminates [Laminate 1] On the surface of a long copper foil with a thickness of 18 μm, Dispersion 1 was applied using a bar coater to form a wet film. Next, the copper foil on which this wet film was formed was passed through a drying furnace at 110°C for 5 minutes to be dried, and a powder layer 1 containing Powder 1 and Filler 1, which is a dry film, was formed on the substrate surface. This substrate was passed between a pair of rolls heated to 120°C, which was adjusted to press the powder layer 1 at 0.5 MPa, to press the powder layer 1. Thereafter, the substrate was further heated in a nitrogen oven at 380°C for 3 minutes. As a result, a laminate 1 having a copper foil and a polymer layer with a thickness of 200 μm as a molded product containing a molten sintered product of Powder 1, Filler 1, and PI1 on its surface was manufactured. [Laminate 2] The substrate on which the powder layer 1 was formed was heated at 380°C as it was without passing between a pair of rolls, and a laminate 2 having a copper foil and a polymer layer with a thickness of 200 μm as a molded product containing a molten sintered product of Powder 1, Filler 1, and PI1 on its surface was obtained. [Laminate 3] A laminate 3 was manufactured in the same manner as the manufacture of laminate 1 except that Dispersion 1 was changed to Dispersion 2.

[0078] 4. Evaluation 4-1. Evaluation of Linear Expansion Coefficient of Sheet For each laminate, the copper foil of the laminate was removed by etching with an aqueous ferric chloride solution to produce a sheet that was a single polymer layer. A 180 mm square test piece was cut out from the produced sheet, and the coefficient of linear expansion of the test piece in the range of 25°C to 260°C was measured according to the measurement method specified in JIS C 6471:1995. As a result, the coefficients of linear expansion of the sheets obtained from laminate 1 and laminate 3 were each 50 ppm / °C or less, and the coefficient of linear expansion of the sheet obtained from laminate 2 exceeded 75 ppm / °C.

[0079] 4-2. Evaluation of Thermal Conductivity of Sheet For each laminate, the copper foil of the laminate was removed by etching with an aqueous ferric chloride solution to produce a sheet that was a single polymer layer. A 10 mm × 10 mm square test piece was cut out from the center of the produced sheet, and the in-plane thermal conductivity (W / m·K) was measured. As a result, the thermal conductivities of the sheets obtained from laminate 1 and laminate 3 were each 10 W / m·K, and the thermal conductivity of the sheet obtained from laminate 2 was 5 W / m·K or less.

[0080] Furthermore, the sheet obtained from laminate 3 was superior in bendability and sheet strength compared to the sheet obtained from laminate 1.

Industrial Applicability

[0081] As is clear from the above results, there were no voids in the sheet cross-section of the sheet produced by this method and it was dense, and since the inorganic filler was highly oriented, the sheet obtained by this method was excellent in thermal conductivity.

Claims

1. A method for manufacturing a laminate having a base material and a layer formed on the surface of the base material and containing a fired product of the powder and the inorganic filler, the method comprising: forming a layer containing a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer on the surface of the base material and an inorganic filler having an aspect ratio of more than 1, the inorganic filler being aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon oxide, or silicon carbide; and pressing the layer containing the inorganic filler and the base material at a temperature equal to or lower than the melting temperature of the heat-meltable tetrafluoroethylene-based polymer in any process of forming the layer containing the fired product of the powder and the inorganic filler.

2. The manufacturing method according to claim 1, wherein the powder of the tetrafluoroethylene-based polymer contains particles of a heat-meltable tetrafluoroethylene-based polymer and particles of a non-heat-meltable tetrafluoroethylene-based polymer.

3. The manufacturing method according to claim 1 or 2, wherein the heat-meltable tetrafluoroethylene-based polymer has a carbonyl group-containing group or a hydroxyl group-containing group and has a melting temperature of 200°C or higher and 320°C or lower.

4. The manufacturing method according to any one of claims 1 to 3, wherein the content mass ratio of the heat-meltable tetrafluoroethylene-based polymer and the inorganic filler in the layer is such that the content mass of the inorganic filler is from 0.2 to 2 with the content mass of the heat-meltable tetrafluoroethylene-based polymer being 1.

5. The manufacturing method according to any one of claims 1 to 4, wherein the average particle diameter of the particles of the heat-meltable tetrafluoroethylene-based polymer is smaller than the average particle diameter of the inorganic filler.

6. The manufacturing method according to any one of claims 1 to 5, wherein the content of the inorganic filler in the layer containing the particles of the heat-meltable tetrafluoroethylene-based polymer and the inorganic filler is 60% by mass or less.

7. The manufacturing method according to any one of claims 1 to 6, wherein the inorganic filler contains at least one of boron nitride or silicon oxide.

8. The manufacturing method according to any one of claims 1 to 7, wherein the layer containing the powder and the inorganic filler further contains a silane coupling agent.

9. The manufacturing method according to any one of claims 1 to 8, wherein the layer containing the powder and the inorganic filler and the base material are pressed.

10. The manufacturing method according to any one of claims 1 to 9, wherein the pressure of the pressing is 0.2 MPa or more and 10 MPa or less.

11. The manufacturing method according to any one of claims 1 to 10, wherein a liquid composition containing the powder of the tetrafluoroethylene-based polymer, the inorganic filler, and a liquid dispersion medium is coated on the surface of a substrate, and at least a part of the liquid dispersion medium is removed to form a layer containing the powder and the inorganic filler.

12. The manufacturing method according to claim 11, wherein the liquid composition further contains a silane coupling agent.

13. A method for manufacturing a sheet containing the fired product and the inorganic filler, comprising: forming a layer containing a powder of a tetrafluoroethylene-based polymer containing particles of a heat-meltable tetrafluoroethylene-based polymer and an inorganic filler having an aspect ratio greater than 1, such as aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon oxide, or silicon carbide, on the surface of a substrate; and pressing the layer containing the inorganic filler and the substrate at a temperature below the melting temperature of the heat-meltable tetrafluoroethylene-based polymer in any process to obtain a laminate having the substrate and the layer containing the fired product and the inorganic filler formed on the surface of the substrate, and then removing the substrate.