Composition, dense sheet, and method for producing the same

Abstract

To provide a composition comprising a thermally fusible tetrafluoroethylene-based polymer that enables formation of molded products such as dense sheets which exhibit excellent mechanical strength and heat resistance, a low linear expansion coefficient, a low dielectric constant, and a low dielectric dissipation factor, and in particular, excel in thermal conductivity while preserving electrical insulating properties, thereby being suitably applicable to heat-radiating insulating sheets and the like as thermal interface materials.SOLUTION: The composition contains particles of a thermally fusible tetrafluoroethylene-based polymer, an anisotropic filler in the form of primary particles or aggregates thereof, and a spherical filler whose average particle diameter is 0.2 or less of the major axis of the anisotropic filler primary particles, wherein the anisotropic filler content relative to the content of the tetrafluoroethylene-based polymer particles exceeds 2.4 in volume ratio, and the total of the tetrafluoroethylene-based polymer particles, the anisotropic filler, and the spherical filler in the solid content to 90 vol.% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composition containing a tetrafluoroethylene-based polymer and a plurality of predetermined fillers, a dense sheet, and a method for producing the same. [Background technology]

[0002] Thermal interface materials (TIMs) are used as heat dissipation materials to dissipate the large amounts of heat generated by electronic components such as computer chips (CPUs), video graphics arrays, servers, game consoles, smartphones, and LED boards, as well as semiconductor modules containing power semiconductors used in inverters and converters in electric vehicles and power transmission systems.TIMs typically transfer excess heat from electronic components to a heat spreader, and then transfer the heat to a heat sink. Conventionally, phase-change materials such as paraffin wax, grease-like materials, and elastomer tapes have been used as TIMs because they can spread in a very thin layer and provide intimate contact between adjacent surfaces. However, these materials have the problem of being poor in heat resistance (thermal stability) and prone to performance degradation. As a heat dissipation material applicable to TIM, for example, Patent Document 1 proposes an insulating sheet containing a predetermined polymer having an aromatic skeleton, a predetermined epoxy compound and / or oxetane compound, a curing agent, and multiple types of fillers having specific shapes, blended in a predetermined ratio. Patent Documents 2 and 3 propose thermosetting resin compositions containing a thermosetting resin and multiple secondary particles formed from primary particles of boron nitride with different aspect ratios or average major axes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-144072 [Patent Document 2] International Publication No. 2014 / 199650 [Patent Document 3] JP 2011-6586 A Summary of the Invention [Problem to be solved by the invention]

[0004] All of the prior art documents describe thermosetting sheets or resin compositions. There is still room for further study to achieve the electrical insulation, heat resistance, thermal conductivity, and mechanical properties required for TIMs with compositions containing thermoplastic resins (thermofusible resins) and inorganic fillers. The present inventors have discovered that a composition containing a heat-fusible tetrafluoroethylene-based polymer, a specific anisotropic filler, and a specific spherical filler in a predetermined ratio has excellent dispersibility, and that molded products such as sheets formed from such compositions have excellent mechanical properties and heat resistance, a low linear expansion coefficient, a low dielectric constant, and a low dielectric loss tangent, and in particular, excellent thermal conductivity while maintaining electrical insulation, thereby completing the present invention. It is an object of the present invention to provide such a composition, a dense sheet formed from the composition, and a method for making the dense sheet. [Means for solving the problem]

[0005] The present invention has the following aspects. [1] A composition comprising particles of a heat-fusible tetrafluoroethylene-based polymer, an anisotropic filler which is a primary particle or an aggregate thereof, and spherical filler having an average particle size which is 0.2 or less times the major axis of the primary particle of the anisotropic filler, wherein the volume ratio of the content of the anisotropic filler to the content of the tetrafluoroethylene-based polymer particles is more than 2.4, and the total amount of the tetrafluoroethylene-based polymer particles, the anisotropic filler, and the spherical filler in the solid content is 90 volume % or more. [2] The composition of [1], wherein the content of the anisotropic filler is 50% by volume or more. [3] The composition of [1] or [2], wherein the aspect ratio of the primary particles of the anisotropic filler is 5 or more and 1,000 or less. [4] The composition of any one of [1] to [3], wherein the major axis of the primary particles of the anisotropic filler is 2 μm or more and 10 μm or less, and the average particle diameter of the spherical filler is 0.05 μm or more and 2 μm or less. [5] The composition according to any one of [1] to [4], wherein the anisotropic filler has a Mohs hardness of 3 or less, and the spherical filler has a Mohs hardness of more than 3. [6] The composition according to any one of [1] to [5], wherein the average particle size of the tetrafluoroethylene polymer particles is less than 10 μm. [7] The composition according to any one of [1] to [6], further comprising a liquid dispersion medium. [8] A dense sheet comprising a heat-fusible tetrafluoroethylene-based polymer, an anisotropic filler which is a primary particle or an aggregate thereof, and a spherical filler whose average particle diameter is 0.2 or less relative to the major axis of the primary particle of the anisotropic filler, wherein the volume ratio of the content of the anisotropic filler to the content of the tetrafluoroethylene-based polymer is more than 2.4, and the porosity is less than 10%. [9] The dense sheet according to [8], wherein the content of the anisotropic filler is 50% by volume or more.

[10] The dense sheet according to [8] or [9], wherein the aspect ratio of the primary particles of the anisotropic filler is 5 or more and 1000 or less.

[11] The dense sheet according to any one of [8] to

[10] , wherein the long diameter of the primary particles of the anisotropic filler is 2 μm or more and 10 μm or less, and the average particle diameter of the spherical filler is 0.05 μm or more and 2 μm or less.

[12] The dense sheet according to any one of [8] to

[11] , wherein the anisotropic filler has a Mohs hardness of 3 or less, and the spherical filler has a Mohs hardness of more than 3.

[13] A dense sheet of any of [8] to

[12] that is a long sheet.

[14] A dense sheet of any of [8] to

[13] having a thickness of 50 μm or more and 1000 μm or less.

[15] A method for producing a dense sheet, comprising extruding any one of the compositions [1] to [7] or placing it on the surface of a substrate to form a layer, and pressing the layer at a temperature equal to or higher than the melting point of the tetrafluoroethylene-based polymer and at a pressure exceeding 10 MPa to obtain any one of the dense sheets [8] to

[14] . [Effects of the Invention]

[0006] According to the present invention, there is provided a composition containing a heat-meltable tetrafluoroethylene-based polymer, a predetermined anisotropic filler, and a predetermined spherical filler in a predetermined ratio, and having excellent dispersibility. From this composition, a molded product such as a dense sheet can be formed that has excellent mechanical properties and heat resistance, a low linear expansion coefficient, a low dielectric constant, and a low dielectric loss tangent, and in particular, excellent thermal conductivity while maintaining electrical insulation, and is suitable for use as a thermal interface material, such as a heat dissipation insulation sheet. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following terms have the following meanings: "Volume" is a value calculated by dividing the mass of an object by its specific gravity. "Average particle size (D50)" is the volume-based cumulative 50% diameter of particles determined by laser diffraction / scattering. In other words, particle size distribution is measured by laser diffraction / scattering, and a cumulative curve is calculated with the total volume of the particle group as 100%. The average particle size (D50) is the particle size at the point on the cumulative curve where the cumulative volume is 50%. The D50 of particles is determined by dispersing the particles in water and analyzing them by the laser diffraction / scattering method using a laser diffraction / scattering particle size distribution measuring device (LA-920 measuring device, manufactured by Horiba, Ltd.). The "melting temperature" is the temperature corresponding to the maximum value of the melting peak of a polymer as measured by differential scanning calorimetry (DSC). The "glass transition temperature (Tg)" is a value measured by analyzing a polymer using the dynamic mechanical analysis (DMA) method. The term "unit" in a polymer refers to an atomic group based on a monomer formed by polymerization of the monomer. The unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a portion of the unit is converted into a different structure by processing the polymer. Hereinafter, a unit based on monomer a will also be referred to simply as a "monomer a unit."

[0008] The composition of the present invention (hereinafter also referred to as "the composition") comprises particles (hereinafter also referred to as "F particles") of a heat-fusible tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer"), an anisotropic filler which is a primary particle or an aggregate thereof (hereinafter also referred to as "anisotropic filler"), and a spherical filler (hereinafter also referred to as "spherical filler") whose average particle diameter is 0.2 or less relative to the major axis of the primary particles of the anisotropic filler, wherein the volume ratio of the content of the anisotropic filler to the content of the F particles is more than 2.4, and the total amount of the F particles, the anisotropic filler, and the spherical filler in the solid content is 90 volume % or more. The present invention also relates to a dense sheet (hereinafter also referred to as "the dense sheet") comprising an F polymer, an anisotropic filler, and a spherical filler, wherein the volume ratio of the anisotropic filler content to the F polymer content is greater than 2.4, and the porosity is less than 10%.

[0009] This composition has excellent dispersibility, and the physical properties of the F polymer, anisotropic filler, and spherical filler are highly combined, and it is easy to form molded articles such as this dense sheet, which has excellent mechanical properties, heat resistance, a low linear expansion coefficient, a low dielectric constant, and a low dielectric loss tangent, and in particular, excellent thermal conductivity while maintaining electrical insulation. The reasons for this are not entirely clear, but are thought to be as follows.

[0010] F polymer has low surface tension and low affinity with other materials. Therefore, in a molded product formed from a composition containing F polymer and a thermally conductive inorganic filler, the interaction between the components is insufficient, making it difficult for the physical properties of each component to be fully expressed. In particular, when the filler is an agglomerated particle such as the anisotropic filler described above, the voids present within it tend to reduce the thermal conductivity of the molded product. Furthermore, particulate fillers such as spherical fillers tend to aggregate, making it difficult for them to exhibit their physical properties, and therefore reducing the mechanical properties of the resulting molded product. This composition contains F particles, an anisotropic filler, and spherical fillers whose average particle diameter is 0.2 or less relative to the major axis of the anisotropic filler's primary particles. The content of the anisotropic filler relative to the F particle content is within a specific range, and the total amount of the F particles, anisotropic filler, and the spherical fillers in the solid content is 90 volume% or more. This not only facilitates the formation of heat conduction paths through contact between the anisotropic fillers, which serve as host particles, but also facilitates the presence of spherical fillers on or near the surface of the anisotropic fillers, which is believed to facilitate the formation of a state in which filler aggregation is highly suppressed. Furthermore, if the filler is in this state in the composition, its surface area is relatively increased, promoting interactions between components and thereby improving the uniform dispersibility of the composition. Preferably, in molded articles such as the dense sheet formed from this composition, the anisotropic fillers are packed together by the heat pressing during the production of the dense sheet, further promoting the formation of heat conduction paths. Furthermore, the spherical fillers are efficiently and densely packed into the gaps between the packed anisotropic fillers, facilitating the formation of high-level filler paths. This is thought to improve the heat resistance, linear expansion coefficient, and electrical properties, particularly electrical insulation, of the molded article while improving its thermal conductivity. Furthermore, the contact interface between the F polymer and the anisotropic filler and the spherical filler is enlarged, which is thought to improve the mechanical properties, such as the bending strength, of the molded article.

[0011] This tendency becomes even more pronounced when the content of the anisotropic filler in the composition is 50% by volume or more, and the composition contains an anisotropic filler whose primary particle aspect ratio is 5 to 1000 and whose Mohs hardness is 3 or less, and a spherical filler whose Mohs hardness is greater than 3. In particular, because the spherical filler has high hardness, the disintegration of agglomerated particles of the anisotropic filler is more likely to proceed by hot pressing in the production of the dense sheet, and the resulting molded product, such as a dense sheet, is thought to have excellent mechanical properties and heat resistance, and a low linear expansion coefficient, dielectric constant, and dielectric dissipation factor, and in particular, to be likely to have excellent thermal conductivity while maintaining electrical insulation.

[0012] The F polymer in the present invention is a heat-fusible polymer containing units (hereinafter also referred to as "TFE units") based on tetrafluoroethylene (hereinafter also referred to as "TFE"). Here, the heat-fusible polymer means a polymer that has a temperature at which the melt flow rate is 1 to 1000 g / 10 min under a load of 49 N. The melting temperature of the F polymer is preferably above 100° C., more preferably at least 180° C., and even more preferably at least 200° C. The melting temperature of the F polymer is preferably at most 325° C., more preferably at most 320° C. In this case, the composition tends to have excellent processability, and molded articles formed from the composition tend to have excellent heat resistance.

[0013] The glass transition point of the F polymer is preferably 50° C. or higher, more preferably 75° C. or higher. The glass transition point of the F polymer is preferably 150° C. or lower, more preferably 125° C. or lower. The fluorine content of the F polymer is preferably 70% by mass or more, more preferably 72 to 76% by mass. The surface tension of the F polymer is preferably 16 to 26 mN / m. The surface tension of the F polymer can be measured by placing a droplet of a mixture for wetting tension testing (manufactured by Wako Pure Chemical Industries, Ltd.) specified in JIS K 6768 on a flat plate made of the F polymer.

[0014] The F polymer is preferably polytetrafluoroethylene (PTFE), a polymer containing TFE units and units based on ethylene (ETFE), a polymer containing TFE units and units based on propylene, a polymer containing TFE units and units based on perfluoro(alkyl vinyl ether) (PAVE) (PAVE units) (PFA), or a polymer containing TFE units and units based on hexafluoropropylene (FEP), with PFA and FEP being more preferred, and PFA being even more preferred. These polymers may further contain units based on other comonomers. PAVE is preferably CF2=CFOCF3, CF2=CFOCF2CF3, or CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE"), and PPVE is more preferred.

[0015] The F polymer preferably has an oxygen-containing polar group, more preferably has a hydroxyl-containing group or a carbonyl-containing group, and even more preferably has a carbonyl-containing group. In this case, the F polymer easily interacts with the anisotropic filler and the spherical filler, resulting in the composition having excellent dispersibility. Furthermore, the composition can be easily used to produce molded articles such as the dense sheet, which have low linear expansion coefficients, dielectric constants, and dielectric loss tangents, as well as excellent heat resistance and thermal conductivity. The hydroxyl group-containing group is preferably a group containing an alcoholic hydroxyl group, more preferably -CF2CH2OH and -C(CF3)2OH. The carbonyl group-containing group is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.), a formyl group, a halogenoformyl group, a urethane group (-NHC(O)O-), a carbamoyl group (-C(O)-NH), a ureido group (-NH-C(O)-NH), an oxamoyl group (-NH-C(O)-C(O)-NH), or a carbonate group (-OC(O)O-), and more preferably an acid anhydride residue. When the F polymer has an oxygen-containing polar group, the number of oxygen-containing polar groups in the F polymer is 1×10 6The number per unit is preferably 10 to 5000, more preferably 100 to 3000. The number of oxygen-containing polar groups in the F polymer can be quantified based on the polymer composition or the method described in WO 2020 / 145133.

[0016] The oxygen-containing polar group may be contained in a unit derived from a monomer in the F polymer, or may be contained in a terminal group of the main chain of the F polymer, the former being preferred. Examples of the latter include an F polymer having an oxygen-containing polar group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer obtained by subjecting an F polymer to plasma treatment or ionizing radiation treatment. The monomer having a carbonyl group-containing group is preferably itaconic anhydride, citraconic anhydride, or 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH"), and more preferably NAH.

[0017] The F polymer is preferably a polymer having a carbonyl group-containing group containing TFE units and PAVE units, more preferably a polymer containing TFE units, PAVE units, and units based on a monomer having a carbonyl group-containing group, in which the total units contain 90 to 99 mol%, 0.99 to 9.97 mol%, and 0.01 to 3 mol%, respectively, in that order. Specific examples of such F polymers include the polymers described in WO 2018 / 16644.

[0018] In the present invention, the F polymer is preferably contained as particles (hereinafter also referred to as "F particles") having an average particle diameter (D50) of less than 10 μm. The F particles may be solid particles or pellets. The D50 of the F particles is preferably 1 μm or more. The D50 of the F particles is preferably 6 μm or less, more preferably 4 μm or less. In this case, the composition is likely to have excellent dispersibility and processability. Furthermore, the composition is likely to produce molded products such as the dense sheet, which have a low linear expansion coefficient, dielectric constant, and dielectric loss tangent, and are excellent in heat resistance and thermal conductivity. The specific surface area of F particles is 1 to 25 m 2 / g is preferred, and 3 to 15m 2 / g is more preferred.

[0019] The F particles are particles containing an F polymer, and preferably consist of an F polymer. The F particles are more preferably particles of a heat-fusible F polymer having an oxygen-containing polar group and a melting temperature of 100 to 320° C. In this case, the above-mentioned mechanism of action is more effectively exerted, and aggregation of the F particles is more easily suppressed. The F particles may contain a resin or an inorganic compound other than the F polymer, may form a core-shell structure with an F polymer as the core and a resin other than the F polymer or an inorganic compound as the shell, or may form a core-shell structure with an F polymer as the shell and a resin other than the F polymer or an inorganic compound as the core. Here, examples of resins other than F polymer include aromatic polyester, polyamideimide, polyimide, and maleimide, and examples of inorganic compounds include silica and boron nitride.

[0020] One type of F particle may be used, or two or more types may be used. The F particles may also be used in combination with particles of a non-thermofusible tetrafluoroethylene-based polymer. The F particles are preferably particles of a heat-fusible F polymer having a melting temperature of 100 to 325°C, more preferably particles of a heat-fusible F polymer having a melting temperature of 180 to 320°C and containing oxygen-containing polar groups, and the non-thermofusible tetrafluoroethylene-based polymer particles are preferably particles of non-thermofusible PTFE. In this case, the aggregation-inhibiting effect of the heat-fusible F polymer particles and the retention effect of the non-thermofusible tetrafluoroethylene-based polymer due to fibrillation are balanced, which tends to improve the dispersibility of the composition. Furthermore, the electrical properties of the non-thermofusible tetrafluoroethylene-based polymer are likely to be highly expressed in molded articles such as dense sheets obtained therefrom.

[0021] The anisotropic filler contained in the present composition is in the form of primary particles or aggregates thereof. Here, "aggregates" refers to a mass formed by aggregation of primary particles, and it is more preferable that the aggregates are sintered bodies that have been subjected to firing. The shape of the anisotropic filler may be granular, needle-like (fibrous), or plate-like, and specifically may be scale-like, layer-like, leaf-like, apricot-like, columnar, cockscomb-like, equiaxed, leaf-like, micaceous, block-like, flat, wedge-like, rosette-like, mesh-like, or prismatic. In particular, the shape of the anisotropic filler is preferably non-spherical, and more preferably scaly or columnar. In this case, it is thought that the anisotropic filler is more likely to adopt a house-of-cards structure and form a heat conduction path in the present composition and, preferably, in a molded product such as the present dense sheet formed from the present composition. As a result, the present composition has excellent dispersibility, and the molded product such as the present dense sheet is more likely to have excellent thermal conductivity (thermal conductivity) and low linear expansion.

[0022] Examples of the anisotropic filler include nitrogen compounds such as boron nitride and aluminum nitride, and silicon compounds such as talc, silicon nitride, mica and wollastonite. One type of anisotropic filler may be used, or two or more types may be used in combination. Among these, the anisotropic filler is preferably boron nitride, aluminum nitride or silicon nitride, and more preferably boron nitride.

[0023] Specific examples of boron nitride fillers include the "HP-40MF" series and "HP-40J" series (both manufactured by JFE Mineral Co., Ltd.), the "UHP" series (manufactured by Showa Denko K.K.), and the "GP" and "HGP" grades of the "Denka Boron Nitride" series (manufactured by Denka Company Limited). Specific examples of aluminum nitride fillers include the "High Purity Aluminum Nitride" series (Tokuyama Corporation) and the "Toyal Tech Filler TFZ" series (Toyo Aluminum Co., Ltd.). Specific examples of silicon nitride fillers include the "Denka Silicon Nitride" series (manufactured by Denka Co., Ltd.) and the "UBE Silicon Nitride" series (manufactured by UBE Co., Ltd.).

[0024] The major axis of the primary particles of the anisotropic filler is preferably 2 μm or more and 10 μm or less. The aspect ratio of the primary particles of the anisotropic filler is preferably 5 or more and 1,000 or less, and more preferably 10 or more and 100 or less. The D50 of the anisotropic filler, which is a primary particle or an aggregate thereof, is preferably 10 μm or more, more preferably 20 μm or more, and more preferably 30 μm or more. The D50 of the anisotropic filler is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. The Mohs hardness of the anisotropic filler is preferably 3 or less, more preferably 2.5 or less. The Mohs hardness of the anisotropic filler is preferably 1 or more, more preferably 1.5 or more. Even if the anisotropic filler is brittle and has a Mohs hardness within this range, the affinity between the anisotropic filler and the F particles makes the composition excellent in dispersion stability, and the physical properties of the filler in the molded product are likely to be improved. The true density of anisotropic fillers is 0.2 to 1 g / cm 3 is preferred. The bulk density of the anisotropic filler is 0.1 to 0.5 g / cm 3 is preferred. The pressure resistance strength of the anisotropic filler is preferably 30 to 200 MPa, as measured in accordance with ASTM D 3102-78.

[0025] The surface of the anisotropic filler may be surface-treated with a silane coupling agent. Examples of the silane coupling agent include vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-isocyanatepropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, p-styryltrimethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, N-2-(aminomethyl)-8-aminooctyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0026] The spherical filler particles contained in the present composition may be ellipsoidal, but are preferably substantially spherical. Here, substantially spherical means that, when the filler is observed under a scanning electron microscope (SEM), 95% or more of the particles have a ratio of minor axis to major axis of 0.7 or greater. In this case, the present composition is likely to have excellent dispersibility and processability. Furthermore, in a molded product such as a sheet formed from the present composition, the spherical filler particles are efficiently arranged and densely packed into the gaps between the packed anisotropic fillers, easily forming heat conduction paths. This facilitates the production of molded products such as the present dense sheet, which have excellent mechanical properties, a low linear expansion coefficient, a low dielectric constant, and a low dielectric loss tangent, and, in particular, excellent thermal conductivity while maintaining electrical insulation.

[0027] The spherical filler is preferably a filler that has not been surface-treated, from the viewpoint that in a molded product such as the dense sheet, gaps filled with the packed anisotropic filler are filled more densely to form a heat conduction path for the filler, and that the physical properties of the spherical filler itself are highly expressed, thereby further improving the thermal conductivity, etc. of the molded product. Note that "surface treatment" includes surface treatment using an organic surface treatment agent such as a silane coupling agent, an inorganic surface treatment agent such as an inorganic acid, or a physical operation.

[0028] Examples of spherical fillers include metal oxides such as aluminum oxide, zinc oxide, titanium oxide, cerium oxide, beryllium oxide, magnesium oxide, nickel oxide, vanadium oxide, copper oxide, iron oxide, and silver oxide; silicon compounds such as quartz powder, silica, and silicon carbide; aluminum nitride; carbon allotropes such as graphite, graphene, and carbon nanotubes; and metals such as silver and copper. One type of spherical filler may be used, or two or more types may be used in combination. Among them, spherical fillers include aluminum oxide, aluminum nitride, silica, and silicon carbide. Preferably, the material is aluminum, graphite, silver or copper, more preferably aluminum oxide or aluminum nitride. In this case, it is easy to obtain a molded product such as a dense sheet from the composition, which has excellent electrical properties, low linear expansion and thermal conductivity.

[0029] In this composition, the average particle size (D50) of the spherical filler is 0.2 or less, preferably 0.1 or less, relative to the major axis of the primary particles of the anisotropic filler. The D50 of the spherical filler is preferably 0.01 or more, relative to the major axis of the primary particles of the anisotropic filler. Specifically, it is preferable that the major axis of the primary particles of the anisotropic filler is 2 μm or more and 10 μm or less, and the average particle size of the spherical filler is 0.05 μm or more and 2 μm or less. The D50 of the spherical filler is more preferably 0.08 μm or more, and even more preferably 0.1 μm or more, and more preferably 1.6 μm or less, and even more preferably 1 μm or less. The major axis of the primary particles of the anisotropic filler can be calculated by observing 50 or more randomly selected anisotropic fillers with a scanning electron microscope (SEM).

[0030] In the present composition, it is preferable that the Mohs hardness of the anisotropic filler is 3 or less, and the Mohs hardness of the spherical filler is greater than 3. Specifically, the Mohs hardness of the spherical filler is preferably 3.3 or more, more preferably 3.5 or more. The Mohs hardness of the spherical filler is preferably 6 or less. When the Mohs hardness of the anisotropic filler and spherical filler contained in the present composition is within the above-mentioned range, the high hardness of the spherical filler facilitates the disintegration of the anisotropic filler agglomerates during the hot pressing process for producing the present dense sheet described below, and it is presumed that the above-mentioned mechanism of action is more likely to be realized. As a result, the resulting molded product, such as the present dense sheet, is likely to have excellent thermal conductivity, low linear expansion, and electrical properties. The true density of the spherical filler is 0.2 to 1 g / cm 3 is preferred. The bulk density of the spherical filler is 0.1 to 0.5 g / cm 3 is preferred. The pressure resistance strength of the spherical filler is preferably 30 to 200 MPa, as measured in accordance with ASTM D 3102-78.

[0031] Specific examples of fillers of aluminum oxide, aluminum nitride, silica, silicon carbide, graphite, silver, or copper having such a D50 include "TM-5D" (manufactured by Taimei Chemical Co., Ltd., aluminum oxide, D50: 0.2 μm, oval shape), "HF-01D" (manufactured by Tokuyama Corporation, D50: 0.6 to 1.2 μm), and "UCP-030N" (manufactured by Sumitomo Metal Mining Co., Ltd., copper powder, D50: 0.27 μm, oval shape).

[0032] In the present composition, the anisotropic filler and the spherical filler are preferably of different types whose D50 and Mohs hardness satisfy the above-mentioned relationship.

[0033] The thermal conductivity of each of the anisotropic filler and spherical filler contained in the composition alone is preferably 20 W / m K or more, and more preferably 30 W / m K or more. There is no particular upper limit to the thermal conductivity of each of the anisotropic filler and spherical filler alone, and the higher the better, but generally it is preferably 3000 W / m K or less, and more preferably 2500 W / m K or less. The specific gravity of each of the anisotropic filler and spherical filler contained in the composition is preferably 2.3 or more, more preferably 3 or more. The upper limit of the specific gravity of each of the anisotropic filler and spherical filler is preferably 10.

[0034] In the present composition, the volume ratio of the content of the anisotropic filler to the content of the F particles is more than 2.4, and the total amount of the F particles, anisotropic filler, and spherical filler in the solid content is 90% by volume or more. The volume ratio of the anisotropic filler content to the F particle content is preferably 2.5 or more, more preferably 3.0 or more, and is preferably 10 or less. When the present composition further contains a liquid dispersion medium described below, the total volume of the F particles, anisotropic filler, and spherical filler described below in the solid content is 90% by volume or more.

[0035] The content of the anisotropic filler in the composition is preferably 50% by volume or more, more preferably 60% by volume or more, in which case the content of the F particles in the composition is preferably less than 40% by volume, more preferably 30% by volume or less, and the content of the spherical filler is preferably less than 20% by volume, more preferably 10% by volume or less. When the volume concentration is within this range, the composition is likely to have excellent dispersibility. In addition, the composition is likely to produce a molded product such as a dense sheet that has a low linear expansion coefficient, dielectric constant, and dielectric loss tangent, and that has excellent thermal conductivity while maintaining electrical insulation.

[0036] In the present composition, the total amount of the anisotropic filler and spherical filler in the total amount of the F particles, anisotropic filler, and spherical filler is preferably more than 50% by volume, more preferably 60% by volume or more, and is preferably 95% by volume or less in the total amount of the F particles, anisotropic filler, and spherical filler. In the present composition, the amount of the anisotropic filler in the total amount of the anisotropic filler and the spherical filler is preferably 40% by volume or more, more preferably 50% by volume or more, and is preferably 95% by volume or less in the total amount of the anisotropic filler and the spherical filler. In this case, heat conduction paths between the anisotropic fillers are more likely to be formed, the spherical fillers are more likely to be densely packed into the gaps between the packings of the anisotropic fillers, and a molded product such as the present dense sheet having high physical properties of each filler is more likely to be formed. Furthermore, the interaction between different fillers is enhanced, and aggregation of the anisotropic filler and the spherical filler is more likely to be suppressed, which tends to improve the dispersibility of the present composition.

[0037] The present composition may further contain another resin different from the F polymer, provided that the effects of the present invention are not impaired. Such another resin may be contained in the present composition as non-hollow particles, or, when the present composition contains a liquid dispersion medium described below, may be contained in the form of a solution or dispersion in the liquid dispersion medium. Examples of other resins include fluororesins other than F polymers, polyester resins such as liquid crystalline aromatic polyesters, polyimide resins, polyamide-imide resins, epoxy resins, maleimide resins, urethane resins, polyphenylene ether resins, polyphenylene oxide resins, and polyphenylene sulfide resins. The other resin is preferably an aromatic polymer, more preferably at least one aromatic imide polymer selected from the group consisting of aromatic polyimide, aromatic polyamic acid, aromatic polyamideimide, and a precursor of aromatic polyamideimide. The aromatic polymer is preferably contained in the composition as a varnish dissolved in a liquid dispersion medium.

[0038] The composition may be in a powder form, or may further contain a liquid dispersion medium and be in a liquid form. The liquid dispersion medium is preferably a compound that is liquid at 25°C under atmospheric pressure and has a boiling point of 50 to 240°C. One type of liquid dispersion medium may be used, or two or more types may be used. When two types of liquid dispersion medium are used, the two types of liquid dispersion medium are preferably compatible with each other.

[0039] The liquid dispersion medium is preferably a compound selected from the group consisting of water, hydrocarbons, amides, ketones and esters. Examples of hydrocarbons include alicyclic hydrocarbons such as hexane, heptane, octane, decane, and methylcyclohexane, and aromatic hydrocarbons such as toluene, ethylbenzene, and xylene. Examples of amides include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropanamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N-diethylformamide, hexamethylphosphoric triamide, and 1,3-dimethyl-2-imidazolidinone. Examples of ketones include acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl n-pentyl ketone, methyl isopentyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, and cycloheptanone. Examples of the ester include methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethyl 3-ethoxypropionate, γ-butyrolactone, and γ-valerolactone.

[0040] When the composition contains a liquid dispersion medium, the content of the liquid dispersion medium is preferably 10% by volume or more, more preferably 20% by volume or more, and preferably 60% by volume or less, more preferably 50% by volume or less. When the composition contains a liquid dispersion medium, the solid content of the composition is preferably 50% by volume or more. The solid content is preferably 90% by volume or less. The solid content refers to the total amount (total mass or total volume) of substances that form the solid content in a molded product formed from the composition. Specifically, the F particles, anisotropic filler, and spherical filler are solids, and when the composition contains other resins, the other resins are also solids, and the total volume concentration of these components is the solid content of the composition.

[0041] The present composition, particularly the present composition containing a liquid dispersion medium, preferably further contains a nonionic surfactant from the viewpoint of improving the dispersion stability of the F particles, anisotropic filler, and spherical filler. Examples of nonionic surfactants include glycol surfactants, acetylene surfactants, silicone surfactants, and fluorine surfactants. When the present composition contains a nonionic surfactant, the content of the nonionic surfactant in the present composition is preferably 1 to 15% by volume.

[0042] The present composition may further contain additives such as a thixotropic agent, a viscosity modifier, an antifoaming agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a whitening agent, a colorant, a conductive agent, a mold release agent, and a flame retardant.

[0043] When the composition contains a liquid dispersion medium, the viscosity of the composition is preferably 10 mPa·s or more, more preferably 100 mPa·s or more, and is preferably 10,000 mPa·s or less, more preferably 3,000 mPa·s or less. When the present composition contains a liquid dispersion medium and is in a liquid state, the thixotropy ratio thereof is preferably 1.0 to 3.0.

[0044] The composition can be obtained by mixing F particles, anisotropic filler, and spherical filler, and, if necessary, other resins, liquid dispersion media, surfactants, additives, etc. The composition may be obtained by mixing the F particles, anisotropic filler, and spherical filler all at once, or by mixing them separately in order, or by preparing a masterbatch of these in advance and mixing this with the remaining components. The order of mixing is not particularly limited, and the mixing method may be either mixing all at once or mixing in multiple batches. Examples of mixing devices for obtaining the present composition include agitators equipped with blades, such as a Henschel mixer, pressure kneader, Banbury mixer, and planetary mixer; grinding devices equipped with media, such as a ball mill, attritor, basket mill, sand mill, sand grinder, Dyno Mill, Dispermat, SC Mill, spike mill, and agitator mill; and dispersing devices equipped with other mechanisms, such as a microfluidizer, nanomizer, ultimizer, ultrasonic homogenizer, dissolver, disper, high-speed impeller, thin film swirling high-speed mixer, planetary mixer, and V-type mixer.

[0045] A preferred method for producing the present composition containing a liquid dispersion medium is to first add the anisotropic filler to the liquid dispersion medium containing the F particles, and then add the spherical filler and mix them, from the viewpoint of improving the dispersibility of the F particles, the anisotropic filler, and the spherical filler. More specifically, the F particles and a portion of the liquid dispersion medium are dissolved in advance, and then the anisotropic filler and the spherical filler are sequentially added and kneaded, and the resulting kneaded mixture is added to the remaining liquid dispersion medium to obtain the present composition. The liquid dispersion mediums used in the kneading and addition may be the same or different liquid dispersion mediums. Other resins, surfactants, and additives may be mixed during the kneading or addition.

[0046] The kneaded product obtained by kneading may be in a paste form (such as a paste having a viscosity of 1000 to 100,000 mPa·s) or in a wet powder form (such as a wet powder having a viscosity measured by capillograph of 10,000 to 100,000 Pa·s). The viscosity measured by capillograph is measured using a capillary with a capillary length of 10 mm and a capillary radius of 1 mm, with a furnace diameter of 9.55 mm, a load cell capacity of 2 t, a temperature of 25°C, and a shear rate of 1 s -1 The value measured as:

[0047] The mixing during kneading is preferably carried out using a planetary mixer, which is a stirring device having two stirring blades that rotate and revolve around each other. The mixing during addition is preferably carried out using a thin film swirl type high-speed mixer, which is a stirring device that spreads a kneaded mixture containing F particles, anisotropic filler, and spherical filler and a liquid dispersion medium on the inner wall surface of a cylindrical stirring vessel, swirls the mixture in the form of a thin film, and mixes the mixture while applying centrifugal force.

[0048] From this composition, a molded product having a thermal conductivity of 10 W / m·K or more can be easily obtained. The thermal conductivity of such a molded product is preferably 10 W / m·K or more and 100 W / m·K or less. In particular, in the dense sheet described below, which is obtained by pressing a layer formed from this composition at a pressure of more than 10 MPa, the porosity can be reduced, and many thermal conduction paths can be formed for the filler contained in this composition, making it easy to increase thermal conductivity. The dielectric constant of the molded article obtained from the composition is preferably 2.4 or less, more preferably 2.0 or less, and preferably greater than 1.0. The dielectric loss tangent of the molded article is preferably 0.0022 or less, more preferably 0.0020 or less, and preferably greater than 0.0010.

[0049] By subjecting this composition to a molding method such as extrusion, a molded product such as a sheet containing the F polymer, anisotropic filler, and spherical filler can be obtained. When the composition contains a liquid dispersion medium and is in a liquid state, it is preferable to extrude the composition into a sheet. The extruded sheet may be further cast by press molding, calendar molding, or the like. The sheet is preferably further heated to remove the liquid dispersion medium. When the composition is in powder form, it is preferable to melt-extrude the composition, which can be carried out using a single-screw extruder, a multi-screw extruder, or the like. The composition may also be injection molded to obtain a molded article. When forming a molded product, the present composition may be directly melt extruded or injection molded, or the present composition may be melt kneaded to form pellets, and the pellets may be melt extruded or injection molded to obtain a molded product such as a sheet. The thickness of the sheet obtained from the present composition is preferably 50 μm or more, more preferably 75 μm or more, and even more preferably 100 μm or more, and preferably 1000 μm or less. The suitable ranges of the thermal conductivity, dielectric constant, and dielectric dissipation factor of the sheet are the same as those of the molded product described above. Note that the thermal conductivity of the sheet means the thermal conductivity in the in-plane direction of the sheet. The linear expansion coefficient of the sheet is preferably 100 ppm / °C or less, more preferably 80 ppm / °C or less. The lower limit of the linear expansion coefficient of the sheet is 30 ppm / °C. The linear expansion coefficient refers to the value measured for a test piece in the range of 25°C or more and 260°C or less according to the measurement method specified in JIS C 6471:1995.

[0050] The laminate can be formed by laminating the sheet on a substrate. Examples of methods for producing the laminate include a method using a co-extruder as the extruder to extrude the composition together with the raw materials for the substrate, a method of extruding the composition onto the substrate, and a method of thermocompression bonding the sheet and the substrate. Examples of the substrate include metal substrates such as metal foils of copper, nickel, aluminum, titanium, alloys thereof, etc.; films of preferably heat-resistant resins such as polyester, polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyamideimide, liquid crystalline polyester, and tetrafluoroethylene-based polymers; prepreg substrates (precursors of fiber-reinforced resin substrates), ceramic substrates such as silicon carbide, aluminum nitride, and silicon nitride; and glass substrates.

[0051] The shape of the substrate may be flat, curved, or uneven, and may be any of foil, plate, film, and fiber. The ten-point average roughness of the surface of the substrate is preferably 0.01 to 0.05 μm. The peel strength between the sheet and the substrate is preferably 10 N / cm or more, more preferably 15 N / cm or more, and is preferably 100 N / cm or less.

[0052] By disposing this composition on the surface of a substrate and forming a polymer layer containing the F polymer, anisotropic filler, and spherical filler, a laminate having a substrate layer composed of the substrate and a polymer layer can be obtained. The polymer layer is preferably formed by disposing this composition containing a liquid dispersion medium on the surface of the substrate and heating it to remove the dispersion medium. By separating the substrate from such a laminate, a sheet containing the F polymer, anisotropic filler, and spherical filler can be obtained. Examples of the substrate include the same substrates as those that can be laminated with the above-mentioned sheet, and the preferred embodiments thereof are also the same.

[0053] The composition can be applied by coating, droplet discharging, immersion, or the like, with roll coating, knife coating, bar coating, die coating, or spraying being preferred. Heating for removing the liquid dispersion medium is preferably performed at 100 to 200°C for 0.1 to 30 minutes. During this heating, a polymer layer is formed by packing the F polymer, anisotropic filler, and spherical filler. During heating, air may be blown onto the surface to promote removal of the liquid dispersion medium by air drying. Examples of the heating device include an oven and a ventilation drying furnace. The heat source in the device may be a contact type heat source (hot air, hot plate, etc.) or a non-contact type heat source (infrared rays, etc.). The heating may be carried out under normal pressure or under reduced pressure. The atmosphere during heating may be either an air atmosphere or an inert gas atmosphere (helium gas, neon gas, argon gas, nitrogen gas, etc.).

[0054] The polymer layer is formed through the steps of applying and heating the composition. These steps may be performed once, or may be repeated two or more times. For example, the composition may be applied to the surface of a substrate and heated to form a polymer layer, and then the composition may be applied to the surface of the polymer layer and heated to form a second polymer layer. Alternatively, the composition may be applied to the surface of a substrate and heated to remove the liquid dispersion medium, and then the composition may be applied to the surface of the substrate and heated to form a polymer layer.

[0055] The composition is useful as a material for imparting insulating properties, heat resistance, corrosion resistance, chemical resistance, water resistance, impact resistance, and thermal conductivity. Specifically, the composition can be used in printed wiring boards, thermal interface materials, power module substrates, coils used in power devices such as motors, automotive engines, heat exchangers, vials, syringes, ampoules, medical wires, secondary batteries such as lithium ion batteries, primary batteries such as lithium batteries, radical batteries, solar cells, fuel cells, lithium ion capacitors, hybrid capacitors, capacitors (aluminum electrolytic capacitors, tantalum electrolytic capacitors, etc.), electrochromic elements, electrochemical switching elements, electrode binders, electrode separators, and electrodes (positive electrodes, negative electrodes). The composition is also useful as an adhesive for bonding parts. Specifically, the composition can be used to bond ceramic parts, metal parts, electronic parts such as IC chips, resistors, and capacitors on substrates for semiconductor elements and module parts, circuit boards and heat sinks, and LED chips to substrates.

[0056] This composition is particularly suitable for use as a thermal interface material (TIM) for dissipating the large amounts of heat generated by electronic components such as computer chips (CPUs), video graphics arrays, servers, game consoles, smartphones, and LED boards, as well as semiconductor modules containing power semiconductors used in electric vehicles, inverters, and converters in power transmission systems. TIMs containing this composition possess the excellent physical properties of the F polymer, anisotropic filler, and spherical filler, and exhibit excellent mechanical properties and heat resistance, a low linear expansion coefficient, dielectric constant, and dielectric dissipation factor, and particularly excellent thermal conductivity.

[0057] Details of the F polymer, anisotropic filler, spherical filler, and other optional components in the dense sheet of the present invention are the same as those described above in the description of the composition. The content of the anisotropic filler in the dense sheet is preferably 50% by volume or more, more preferably 60% by volume or more, and even more preferably 75% by volume or more. The dense sheet is preferably a long sheet. The thickness of the dense sheet is preferably 50 μm or more and 1000 μm or less, and more preferably 100 μm or more and 200 μm or less. The porosity of the dense sheet is preferably in the range of 0.1% to 2.5%. The preferred ranges of the thermal conductivity, dielectric constant, dielectric loss tangent, and linear expansion coefficient of the dense sheet are the same as those described above, and the dense sheet can be suitably used as a TIM.

[0058] The dense sheet is preferably formed from the composition. Specifically, the composition is extruded or placed on the surface of a substrate to form a layer, and then pressed at a pressure above the melting point of the F polymer and exceeding 10 MPa to obtain the dense sheet. Details of the method for extruding the composition and the method for placing the composition on the surface of a substrate are as described above. The pressing temperature after layer formation is preferably equal to or higher than the melting temperature of the F polymer. The pressing pressure is preferably 100 MPa or less. By setting the pressing temperature and pressure within the above ranges, it is easy to obtain a dense sheet with low porosity, excellent thermal conductivity, electrical properties, and a low linear expansion coefficient.

[0059] Molded articles such as the dense sheet and laminates formed from the composition are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sporting goods, food industry products, heat dissipation parts, and the like. Specifically, these include electric wire coating materials (aircraft electric wires, etc.), enameled wire coating materials used in motors for electric vehicles, etc., electrical insulating tape, insulating tape for oil drilling, oil transport hoses, hydrogen tanks, materials for printed circuit boards, separation membranes (microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, gas separation membranes, etc.), electrode binders (for lithium secondary batteries, fuel cells, etc.), copy rolls, furniture, automobile dashboards, covers for home appliances, etc., sliding components (load bearings, yaw bearings, sliding shafts, valves, bearings, bushings, seals, thrust washers, wear rings, etc.), and many other applications. useful in applications such as: pistons, slide switches, gears, cams, conveyor belts, food transport belts, tension ropes, wear pads, wear strips, tube lamps, test sockets, wafer guides, wear parts for centrifugal pumps, chemical and water supply pumps, tools (shovels, files, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, dies, toilets, container coatings, heat dissipation substrates for mounting power devices, heat dissipation components for wireless communication devices, transistors, thyristors, rectifiers, transformers, power MOS FETs, CPUs, heat dissipation fins, metal heat sinks, blades for wind turbines, wind power generation equipment, aircraft, etc., housings for personal computers and displays, electronic device materials, interior and exterior parts of automobiles, sealing materials for processing machines and vacuum ovens that perform heat treatment under low oxygen conditions, plasma processing equipment, heat dissipation components in processing units for sputtering and various dry etching equipment, and electromagnetic wave shielding.

[0060] Molded articles such as the dense sheet and laminates formed from the composition are useful as electronic substrate materials such as flexible printed wiring boards and rigid printed wiring boards, protective films, and heat dissipation substrates, particularly heat dissipation substrates for automobiles. When using the present dense sheet as a TIM, the present dense sheet may be attached directly to the target substrate, or may be attached to the target substrate via an adhesive layer such as a silicone-based adhesive layer. [Example]

[0061] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of each ingredient [F Polymer] F particle 1: Contains 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units, in that order, and has a carbonyl group-containing group with a main chain carbon number of 1×10 6 Tetrafluoroethylene polymer particles (melting temperature: 300°C) with 1000 particles per particle (D50: 2.1 μm, solid) [Anisotropic filler] Anisotropic filler 1: Boron nitride, product name "HP-40MF100" (manufactured by JFE Mineral Co., Ltd., D50: 36 μm, aspect ratio 20, aggregated structure, primary particle long diameter (average long diameter) 7 μm) [Spherical filler] Spherical filler 1: Alumina, product name "TM-5D" (manufactured by Taimei Chemical Co., Ltd., D50: 0.2 μm) Spherical filler 2: Aluminum nitride, product name "HF-01Da" (manufactured by Tokuyama Corporation, D50: 1 μm) Spherical filler 3: Alumina, product name "AA-3" (manufactured by Sumitomo Chemical Co., Ltd., D50: 3 μm) Spherical filler 4: Aluminum nitride, product name "TFZ-A10P" (manufactured by Toyo Aluminum Co., Ltd., D50: 10 μm)

[0062] 2. Example of composition production [Example 1] F particles 1, anisotropic filler 1, and spherical filler 1 were sequentially added to N-methylpyrrolidone and kneaded for 1 minute at 2000 rpm using a planetary centrifugal mixer (Thinky Corporation, trade name "Awatori Rentaro (registered trademark) ARE-310") to obtain composition 1. Composition 1 was in the form of a slurry, and of the solid content of composition 1, F particles 1 accounted for 25 vol%, anisotropic filler 1 for 68 vol%, and spherical filler 1 for 7 vol%. [Examples 2-5] Compositions 2 to 5 were obtained in the same manner as in Example 1, except that the type of spherical filler used and the volume ratio of F particles 1, anisotropic filler, and spherical filler were changed as shown in Table 1.

[0063] 3. Sheet manufacturing Composition 1 was applied to the surface of a copper foil with a thickness of 0.2 μm using an applicator to form a wet film. The copper foil substrate on which this wet film had been formed was then passed through a drying oven at 120°C for 3 minutes to dry it, forming a dry film. The copper foil substrate with the dry film was cut into a 3 cm × 3 cm piece and heat-pressed at 350°C and 50 MPa for 3 minutes. After that, the copper foil was removed by immersing it in an aqueous ferric chloride solution for 2 hours to obtain Sheet 1. Sheets 2 to 5 were produced from compositions 2 to 5 in the same manner as for Sheet 1. When producing Sheet 5, the heat pressing conditions were changed to 350°C and 5 MPa.

[0064] 4. Evaluation 4-1. Sheet porosity A 10 mm × 10 mm square test piece was cut out from each sheet, and the thickness and mass of each test piece were measured using a micrometer. The mass was divided by the volume measured with the micrometer to determine the density, and the porosity of each sheet was calculated using the specific gravity and volume of the F particles 1, anisotropic filler, and spherical filler that constituted each composition used in producing each sheet. 4-2. Thermal conductivity of the sheet The thermal conductivity (W / m K) in the in-plane direction of each sheet specimen cut out in 4-1 was measured at 25°C using a xenon flash analyzer (Netsch, LFA467 HyperFlash). The density required for calculating thermal conductivity was calculated by dividing the mass by the volume measured with the micrometer in 4-1 above. The above results are summarized in Table 1.

[0065] [Table 1] [Industrial Applicability]

[0066] This composition can be used to form molded products such as dense sheets that exhibit excellent thermal conductivity, heat resistance, and electrical insulation properties by highly exhibiting the physical properties of the tetrafluoroethylene-based polymer, anisotropic filler, and spherical filler, and can be effectively used as a thermal interface material for heat dissipation and insulation sheets, etc.

Claims

1. A composition comprising particles of a heat-fusible tetrafluoroethylene-based polymer, an anisotropic filler which is primary particles or aggregates thereof, and spherical fillers whose average particle size is 0.2 or less relative to the major axis of the primary particles of the anisotropic filler, wherein the volume ratio of the content of the anisotropic filler to the content of the tetrafluoroethylene-based polymer particles is more than 2.4, and the total amount of the tetrafluoroethylene-based polymer particles, the anisotropic filler, and the spherical fillers in the solid content is 90 volume % or more.

2. The composition according to claim 1 , wherein the content of the anisotropic filler is 50% by volume or more.

3. The composition according to claim 1 , wherein the anisotropic filler has a primary particle aspect ratio of 5 or more and 1,000 or less.

4. 2. The composition according to claim 1, wherein the major axis of the primary particles of the anisotropic filler is 2 μm or more and 10 μm or less, and the average particle diameter of the spherical filler is 0.05 μm or more and 2 μm or less.

5. The composition of claim 1 , wherein the anisotropic filler has a Mohs hardness of 3 or less and the spherical filler has a Mohs hardness of greater than 3.

6. 2. The composition of claim 1, wherein the particles of the tetrafluoroethylene-based polymer have an average particle size of less than 10 μm.

7. The composition of claim 1 further comprising a liquid dispersion medium.

8. A dense sheet comprising a heat-fusible tetrafluoroethylene-based polymer, an anisotropic filler which is a primary particle or an aggregate thereof, and a spherical filler having an average particle size which is 0.2 or less times the major axis of the primary particle of the anisotropic filler, wherein the volume ratio of the content of the anisotropic filler to the content of the tetrafluoroethylene-based polymer is more than 2.4, and the porosity is less than 10%.

9. 9. The dense sheet according to claim 8, wherein the content of the anisotropic filler is 50% by volume or more.

10. 9. The dense sheet according to claim 8, wherein the anisotropic filler has a primary particle aspect ratio of 5 or more and 1000 or less.

11. 9. The dense sheet according to claim 8, wherein the major axis of the primary particles of the anisotropic filler is 2 μm or more and 10 μm or less, and the average particle diameter of the spherical filler is 0.05 μm or more and 2 μm or less.

12. 9. The dense sheet according to claim 8, wherein the anisotropic filler has a Mohs hardness of 3 or less, and the spherical filler has a Mohs hardness of more than 3.

13. The dense sheet according to claim 8, which is a long sheet.

14. The dense sheet according to claim 8, having a thickness of 50 μm or more and 1000 μm or less.

15. A method for producing a dense sheet, comprising extruding the composition according to any one of claims 1 to 7 or placing it on the surface of a substrate to form a layer, and pressing the layer at a pressure equal to or higher than the melting point of the tetrafluoroethylene-based polymer and exceeding 10 MPa to obtain the dense sheet according to claim 8.

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