Sheet

Abstract

This invention provides a sheet comprising unfired polytetrafluoroethylene (PTFE) and inorganic particles; the inorganic particles of this sheet are not easily peeled off and possess excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials. The solution is as follows: a sheet comprising unfired PTFE, inorganic particles, and a resin, wherein the resin has at least one functional group selected from the group consisting of carbonyl groups, hydroxyl groups, epoxy groups, and amine groups; and the total content of the aforementioned PTFE, inorganic particles, and resin is 90% by mass or more.

Description

Technical Field

[0001] The present invention relates to a predetermined sheet comprising unfired polytetrafluoroethylene, a method for manufacturing the sheet, and a method for manufacturing a laminate comprising the sheet. Prior Technology

[0002] Polytetrafluoroethylene (PTFE) has attracted much attention as a dielectric layer material for printed circuit boards due to its excellent low dielectric constant or low dielectric tangent isoelectric properties. Patent Document 1 describes forming a dielectric layer from a sheet composed of PTFE and inorganic particles. Patent Document 2 describes a dielectric layer reinforced with a reinforcing fabric, wherein the dielectric layer comprises PTFE, inorganic particles, and a reinforcing fabric. Previous technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2021-061406 Patent Document 2: Japanese Patent Publication No. 2020-507888 Summary of the Invention

[0004] The problem the invention aims to solve When forming a layered product containing layers of PTFE and inorganic particles from a sheet containing unfired PTFE and inorganic particles, the inorganic particles tend to agglomerate, making it difficult to fully exhibit their physical properties. Furthermore, during processing, the inorganic particles tend to peel off, and the sheet lacks sufficient physical strength, such as toughness, leading to breakage. Moreover, the sheet is required to adhere to other substrate layers such as metal foil, but this adhesion is currently insufficient. The inventors have discovered that a sheet containing unburned polytetrafluoroethylene, inorganic particles, and a resin having predetermined functional groups in a predetermined ratio has inorganic particles that are not easily peeled off, and also has excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials, thus achieving the present invention.

[0005] The means to solve the problem The present invention has the following characteristics. [1] A sheet comprising: unburned polytetrafluoroethylene, inorganic particles and resin, wherein the resin has at least one functional group selected from the group consisting of carbonyl groups, hydroxyl groups, epoxy groups and amine groups; and the total content of the aforementioned polytetrafluoroethylene, the aforementioned inorganic particles and the aforementioned resin is 90% by mass or more. [2] The sheet as described in [1] above, wherein the aforementioned inorganic particles include particles selected from at least one inorganic material in the group consisting of silicon dioxide, boron nitride and titanium dioxide. [3] The sheet as described in [1] or [2] above, wherein the resin comprises at least one of the following: a hot-melt tetrafluoroethylene polymer; and an aromatic polymer or a precursor thereof. [4] The sheet as described in any of [1] to [3] above, wherein the resin comprises: a hot-melt tetrafluoroethylene polymer; and an aromatic polymer or a precursor thereof. [5] The sheet as described in [3] or [4] above, wherein the melting temperature of the aforementioned hot-melt tetrafluoroethylene polymer is 260 to 320°C. [6] The sheet as described in [3] or [4] above, wherein the aforementioned aromatic polymer or its precursor is polyimide, polyamide-imide, polyimide precursor or polyamide-imide precursor. [7] The sheet material as described in any of [1] to [6] above, wherein the content of the aforementioned polytetrafluoroethylene is 10% by mass or more. [8] The sheet as described in any of [1] to [7] above, wherein the content of the aforementioned resin is 5% by mass or more. [9] The sheet as described in any of [1] to [8] above, wherein the ratio of the content of the aforementioned inorganic particles to the total content of the aforementioned polytetrafluoroethylene and the aforementioned resin is 0.1 or more.

[10] The sheet as described in any of [1] to [9] above has a thickness of 50µm or more.

[11] A method for manufacturing a sheet involves casting a liquid composition comprising the aforementioned polytetrafluoroethylene particles, the aforementioned inorganic particles and the aforementioned resin to obtain a sheet as described in any one of [1] to

[10] .

[12] The manufacturing method described above in

[11] , wherein the average particle size of the aforementioned polytetrafluoroethylene particles is 0.1 to 10 µm.

[13] As described in

[11] or

[12] above, the manufacturing method involves casting the aforementioned liquid components to obtain cast materials that are stacked and bonded together.

[14] A method for manufacturing a sintered sheet is to heat a sheet as described in any one of [1] to

[10] above to sinter the aforementioned polytetrafluoroethylene.

[15] A method for manufacturing a laminate is to hot press a sheet as described in any one of [1] to

[10] above with a substrate to obtain a laminate having a substrate layer and a polymer layer.

[0006] Invention Effects According to the present invention, a sheet comprising unburned polytetrafluoroethylene, inorganic particles and a resin having predetermined functional groups can be obtained. The inorganic particles of the sheet are not easily peeled off and have excellent electrical properties, low linear expansion, physical strength and adhesion to other materials. Implementation

[0007] The following terms have the following meanings. The term "tetrafluoroethylene polymer" refers to polymers containing units primarily composed of tetrafluoroethylene (hereinafter also denoted as "TFE"). The term "thermally molten tetrafluoroethylene polymer" refers to a tetrafluoroethylene polymer that, under a load of 49N, exhibits a melt flow rate of 1 to 1000 g / 10 minutes. "Melting temperature (melting point) of a polymer" refers to the temperature at which the maximum value of the polymer's melting peak is determined by differential scanning calorimetry (DSC). "Glass transfer point (Tg) of polymers" refers to the value measured by analyzing polymers using the dynamic viscoelasticity assay (DMA). "D50 of the particle" refers to the average particle size, which is the cumulative 50% particle size based on the particle volume standard obtained by laser diffraction scattering. That is, by measuring the particle size distribution of the particles using laser diffraction scattering, and calculating the cumulative curve with the total volume of the particle group as 100%, the particle size at the point where the cumulative volume becomes 50% on the cumulative curve is obtained. "D90 of the particle" refers to the cumulative volume diameter of the particle, which is the cumulative 90% of the particle's volume diameter obtained in the same way as "D50". The viscosity of the liquid composition was measured using a Type B viscometer at room temperature (25°C) and a rotation speed of 30 rpm. The measurement was repeated three times, and the average of the three measurements was taken. The term "monomer-based unit" refers to a group of atoms formed by the polymerization of monomers, with the aforementioned monomers as the main component. A unit can be formed directly through a polymerization reaction, or it can be a unit formed by processing the polymer to transform a portion of the aforementioned unit into a different structure. Hereinafter, a unit based on monomer 'a' will be simply referred to as "monomer 'a' unit."

[0008] The sheet material of the present invention (hereinafter also referred to as "the sheet material") comprises: unfired polytetrafluoroethylene (hereinafter also referred to as "PTFE", and unfired polytetrafluoroethylene as "unfired PTFE"), inorganic particles, and resin (hereinafter also referred to as "the resin material"), wherein the resin has at least one functional group selected from the group consisting of carbonyl groups, hydroxyl groups, epoxy groups, and amine groups; and the total content of unfired PTFE, inorganic particles, and the resin material is 90% by mass or more. In other words, the sheet material is a self-supporting film-like sheet material with unfired PTFE, inorganic particles, and the resin material as the main components.

[0009] We believe that in this sheet, the resin containing the aforementioned functional groups interacts with inorganic particles, thereby not only inhibiting the aggregation of inorganic particles and promoting their uniform dispersion within the sheet, but also acting as a binder component to strongly support the unburned PTFE and inorganic particles. In other words, this sheet uses this resin as a matrix and has a structure in which unburned PTFE and inorganic particles are strongly held and uniformly dispersed within the resin. As a result, this sheet can inhibit the peeling of inorganic particles, highly exhibiting the physical properties of both PTFE and inorganic particles, thereby improving physical strength. Furthermore, by containing this resin with the aforementioned functional groups, this sheet also exhibits excellent affinity with other substrates such as metal foil, thereby improving its adhesion.

[0010] The PTFE used in this invention can be a homopolymer of TFE, or a copolymer of TFE with trace amounts of perfluoro(alkyl vinyl ether) (hereinafter also denoted as "PAVE"), hexafluoropropylene (hereinafter also denoted as "HFP"), fluoroalkyl vinyl ether, etc., i.e., the so-called modified PTFE. The proportion of TFE units in the PTFE should preferably be 99.5 mol% or more, more preferably 99.9 mol% or more.

[0011] PTFE should be PTFE with a molecular weight Mn of more than 200,000 calculated according to the following formula (1). Mn=2.1×10 10×ΔHc -5 . 16··· (1) In equation (1), Mn represents the number average molecular weight of PTFE, and ΔHc represents the heat of crystallization of PTFE (cal / g) determined by differential scanning calorimetry.

[0012] In this invention, unfired PTFE refers to PTFE that has not been exposed to temperatures above the melting temperature of PTFE after polymerization. Fired PTFE refers to PTFE that has been exposed to temperatures above the melting temperature of PTFE after polymerization. Furthermore, in this specification, the melting temperature of PTFE is set to 327°C.

[0013] Unfired PTFE can be in either fibrillary or non-fibrillary form, but fibrillary is preferable. If unfired PTFE is in fibrillary form, it easily supports inorganic particles within the sheet, making them less likely to peel off. Furthermore, unfired PTFE readily entangles with inorganic particles or the resin, thus improving the sheet's toughness. In other words, fibrillary unfired PTFE can also be considered as readily agglomerating with inorganic particles or the resin.

[0014] The unburned PTFE in this sheet should preferably be in granular form. In this case, the unburned PTFE particles should preferably be the same as the unburned PTFE particles contained in the liquid composition described later. Unfired PTFE can be obtained through emulsion polymerization or suspension polymerization. From the perspective of lower crystallinity and easier improvement of sheet toughness, PTFE obtained through emulsion polymerization is preferable.

[0015] The inorganic particles in this invention are preferably spherical, needle-like, or plate-like, more preferably spherical, scale-like, or layered, and even more preferably spherical or scale-like. Spherical inorganic particles should ideally be approximately true spherical. "Approximately true spherical" means that, when observed using a scanning electron microscope (SEM), the ratio of the minor axis to the major axis of the inorganic particles is 0.7 or higher. The proportion of approximately true spherical inorganic particles should ideally be 95% or higher. The aspect ratio of non-spherical inorganic particles should preferably be 2 or higher, and preferably 5 or higher. The aspect ratio should preferably be below 10000.

[0016] Inorganic particles can also be hollow. In this case, the sheet material easily possesses excellent electrical properties. Inorganic particles are particles containing at least one inorganic substance, preferably particles containing carbon, inorganic nitrides, or inorganic oxides. Specific examples of inorganic substances include: carbon, boron nitride, aluminum nitride, beryllium oxide, silicon dioxide, silash, talc, cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, and titanium dioxide. From the viewpoint of improving the electrical properties and low linear expansion of this sheet material, the inorganic particles should preferably include particles selected from at least one inorganic compound formed by silicon dioxide, boron nitride, and titanium dioxide. Silicon dioxide should preferably be amorphous silicon dioxide. Boron nitride should preferably be hexagonal boron nitride. Titanium dioxide should preferably be rutile titanium dioxide.

[0017] The D50 of inorganic particles should preferably be below 20µm, and more preferably below 10µm. The D50 should preferably be above 0.01µm, and more preferably above 0.1µm. The specific surface area of ​​inorganic particles should be between 1 and 20 m² / g.

[0018] The surface of the inorganic particles can also be surface-treated with a silane coupling agent. This increases the affinity between the inorganic particles, unburned PTFE, and the resin, making it less likely for the inorganic particles to peel off from the sheet. Furthermore, the sheet readily exhibits excellent electrical properties and low linear expansion. The preferred silane coupling agent is a silane coupling agent with a functional group, such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatepropyltriethoxysilane.

[0019] Specific examples of products containing silicon dioxide particles include the "Admafine" series (manufactured by Admatechs), the "SFP" series (manufactured by Denka), and the "E-SPHERES" series (manufactured by Pacific Cement Corporation). Specific examples of titanium dioxide particles include the "TIPAQUE" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Tayca Co., Ltd.). Specific examples of particles containing boron nitride include the "UHP" series (manufactured by Showa Denko) and the "GP" and "HGP" grades of the "Denka Boron Nitride" series (manufactured by Denka).

[0020] One type of inorganic particle may be used, or two or more types may be used. For example, silicon dioxide particles, boron nitride particles, and titanium dioxide particles may be used together as inorganic particles. In this case, the proportions of silicon dioxide particles, boron nitride particles, and titanium dioxide particles in the total amount of inorganic particles should preferably be 10 to 60% by mass, 10 to 60% by mass, and 5 to 40% by mass, respectively.

[0021] The resin is a resin having at least one functional group (hereinafter also referred to as "the functional group") selected from the group consisting of carbonyl groups, hydroxyl groups, epoxy groups and amine groups, preferably a resin having the functional group selected from the group consisting of at least one of the following resins: fluororesins, polyester resins such as liquid crystal aromatic polyesters, amide resins, epoxy resins, maleimide resins, ethyl carbamate resins, polyphenylene ether resins, polyoxyphenylene oxide resins and polyphenylene sulfide resins.

[0022] A group containing a hydroxyl group is a group containing a hydroxyl group, preferably a group containing an alcoholic hydroxyl group. A carbonyl group is a group containing a carbonyl group, which can be listed as: carboxyl, alkoxycarbonyl, amide, isocyanate, carbamate (-OC(O)NH 2), acid anhydride residue (-C(O)OC(O)-), amide-imine residue (-C(O)NHC(O)-, etc.) and carbonate (-OC(O)O-), preferably a carboxyl, amide, amide, or acid anhydride residue.

[0023] The resin preferably contains at least one of the following: a hot-melt tetrafluoroethylene polymer having the functional group (hereinafter also referred to as "F polymer"); or, an aromatic polymer having the aforementioned functional group or a precursor of the aforementioned aromatic polymer (hereinafter also referred to as "AR polymer"), preferably including F polymer and AR polymer.

[0024] The melting temperature of polymer F should preferably be above 200℃, and more preferably above 260℃. The melting temperature of polymer F should preferably be below 325℃, and more preferably below 320℃. At this temperature, the sheet material easily exhibits excellent heat resistance, low linear expansion, and processability. The glass transition point of polymer F should preferably be above 50°C, and more preferably above 75°C. The glass transition point of polymer F should preferably be below 150°C, and more preferably below 125°C. The fluorine content of polymer F should preferably be above 70% by mass, and more preferably 72% to 76% by mass. At this level, polymer F interacts more easily with unfired PTFE. The surface tension of polymer F should be between 16 and 26 mN / m. Furthermore, the surface tension of polymer F can be measured by placing a droplet of the wetting index reagent (manufactured by Wako Pure Chemical Industries, Ltd.) onto a plate made of polymer F.

[0025] Polymer F is preferably: a polymer containing TFE units and ethylene-based units; a polymer containing TFE units and propylene-based units; a polymer containing TFE units and PAVE-based units (PAVE units) (PFA); a polymer containing TFE units and HFP-based units (FEP), with PFA and FEP being more preferred, and PFA being even more preferred. These polymers may also further contain units based on other comonomers.

[0026] PAVE should be CF 2=CFOCF 3, CF 2=CFOCF 2CF 3 and CF 2=CFOCF 2CF 2CF 3 (hereinafter also referred to as "PPVE"), with PPVE being more appropriate. The functional groups of polymer F should preferably be hydroxyl-containing groups or carbonyl-containing groups, with carbonyl-containing groups being more preferred. In this case, the interaction between polymer F and unfired PTFE or inorganic particles will not only be enhanced, but the adhesion of the sheet will also be improved more easily.

[0027] The hydroxyl groups in polymer F should preferably be -CF2CH2OH and C(CF3)2OH. The carbonyl groups in polymer F should preferably be: carboxyl, alkoxycarbonyl, amide, isocyanate, carbamate, anhydride residue, amide residue, or carbonate, with anhydride residue being more preferred.

[0028] When polymer F contains hydroxyl or carbonyl groups, the number of hydroxyl or carbonyl groups in polymer F, measured by the number of carbon atoms in the main chain, is preferably 10 to 5000 per 1 × 10⁶ carbon atoms, more preferably 100 to 3000. Furthermore, the number of hydroxyl or carbonyl groups in polymer F can be quantified by means of the polymer composition or by the methods described in International Publication No. 2020 / 145133.

[0029] The functional group of polymer F can be contained in the monomer-dominated unit of polymer F, or it can be contained in the terminal group of the main chain of polymer F, with the former being preferable. Examples of the latter include: polymer F with oxygen-containing polar groups as terminal groups derived from polymerization initiators, chain transfer agents, etc., and polymer F obtained by plasma treatment or free radiation treatment of polymer F. Monomers containing carbonyl groups are preferably itanic anhydride, citraconic anhydride, and 5-norconene-2,3-dicarboxylic anhydride (hereinafter also denoted as "NAH"), with NAH being the most suitable.

[0030] Polymer F is preferably a polymer containing carbonyl groups, comprising TFE units and PAVE units, and more preferably a polymer comprising TFE units, PAVE units, and units mainly composed of monomers containing carbonyl groups, and comprising, in sequence, 90 to 99 mol%, 0.99 to 9.97 mol%, and 0.01 to 3 mol% of these units relative to all units. Specific examples of polymer F may be found in International Publication No. 2018 / 16644.

[0031] The F polymer in this sheet can be granular or non-granular. The F polymer can also aggregate with unfired PTFE or inorganic particles. When the F polymer is granular, the particles of the F polymer should preferably be the same as the particles of the F polymer that can also be included in the liquid composition, as described later.

[0032] AR polymers can be thermosetting or thermoplastic. The functional groups of the AR polymer are preferably amine groups or carbonyl groups, and more preferably selected from at least one group composed of amine, amide, carboxyl, and amide-imine residues. In this case, the interaction between the AR polymer and unfired PTFE or inorganic particles is not only enhanced, but the adhesion of the sheet is also easily improved. Examples of AR polymers include: aromatic polyimides, aromatic polyimide precursors of polyamides or their salts, aromatic polyamide-imides, aromatic polyamide-imides, aromatic polyether-imides, and aromatic polyether-imides, with aromatic polyimides, polyamides or their salts being more preferred.

[0033] AR polymers can also be water-soluble. Examples of water-soluble AR polymers include water-soluble aromatic polyimide precursors, water-soluble polyamide-imides, and their precursors. Water-soluble aromatic polyimide precursors can be polyamides and their salts, which are formed by the polymerization of diamines and tetracarboxylic dianhydrides. Water-soluble aromatic polyamide-imide or its precursor can be obtained by reacting at least one of a diisocyanate or a diamine with a tricarboxylic acid anhydride.

[0034] Examples of tetracarboxylic dianhydrides include pyrolithic anhydride and biphenyl tetracarboxylic anhydride. Diamines include phenylenediamine, 3,3'-dimethylbiphenyl-4,4'-diamine, 4,4'-diamine diphenylmethane, and 4,4'-diamine diphenyl ether. Examples of diisocyanates include 4,4'-diphenylmethane diisocyanate, succinic diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, and 3,3'-diphenylmethane diisocyanate.

[0035] The number average molecular weight (Mn) of AR polymers should preferably be between 5,000 and 50,000. The acid value of AR polymers should be between 20 and 100 mg / KOH. Furthermore, the acid value of the AR polymer was determined by titrating a mixed solution of 0.5 g of AR polymer, 0.15 g of 1,4-diazabicyclo[2.2.2]octane, 60 g of N-methyl-2-pyrrolidone, and 1 mL of deionized water using a potentiometric titration apparatus with a 0.05 mole / L ethanolic potassium hydroxide solution. Additionally, when the AR polymer contains anhydride groups, the acid value after ring-opening of the anhydride groups was used as the acid value of the AR polymer.

[0036] Specific examples of AR polymers include: the "UPIA-AT" series (manufactured by Ube Industries), the "Neopulim" series (manufactured by MITSUBISHI GAS CHEMICAL), the "SPIXAREA" series (manufactured by SOMAR), the "Q-PILON" series (manufactured by PI Technology Research Institute), the "WINGO" series (manufactured by Wingo Technology), the "Tohmide" series (manufactured by T&K TOKA), the "KPI-MX" series (manufactured by Kawamura Industries), "HPC-1000", and "HPC-2100D" (all manufactured by SHOWA DENKO MATERIALS). In this sheet material, the AR polymer can be granular or non-granular, but is preferably non-granular. The AR polymer can also aggregate with unfired PTFE and inorganic particles.

[0037] The resin in this sheet material preferably contains any of the following: an F polymer and an aromatic polymer having the functional group; an F polymer and a precursor of an aromatic polymer having the functional group; or an F polymer, an aromatic polymer having the functional group, and a precursor of an aromatic polymer having the functional group. In this case, a strong matrix from the resin will be formed in the sheet material, which can easily and uniformly support unburned PTFE and inorganic particles, thereby improving the physical properties and adhesion of the sheet material. In particular, if the resin contains both an F polymer and an AR polymer, this tendency becomes more pronounced because the F polymer, which has a high affinity for PTFE, highly supports unburned PTFE, and the AR polymer can improve the bonding effect between components. Furthermore, when the resin contains both an F polymer and an AR polymer, the F polymer and the AR polymer can also form crosslinks in the sheet material.

[0038] The total content of unburned PTFE, inorganic particles, and this resin in this sheet material is 90% by mass or more, preferably 95% by mass or more. The upper limit of the total content is 100% by mass. In other words, the content of components different from unburned PTFE, inorganic particles, and this resin in this sheet material is less than 10% by mass, preferably less than 5% by mass. Examples of different components include reinforcing fibers. The lower limit of the content of the aforementioned different components is 0% by mass. Through the above-described mechanism, even at the aforementioned component content ratios, this sheet material possesses excellent softness, toughness, and other physical properties, and can highly balance the physical properties of PTFE and inorganic particles.

[0039] The content of unfired PTFE in this sheet should preferably be 10% by mass or more, and more preferably 15% by mass or more. The content of unfired PTFE should preferably be 60% by mass or less, and more preferably 40% by mass or less. The content of inorganic particles in this sheet should preferably be 20% by mass or more, and more preferably 40% by mass or more. The content of inorganic particles should preferably be below 80% by mass, and more preferably below 70% by mass.

[0040] In this sheet material, the ratio of inorganic particle content to the total content of unfired PTFE and inorganic particles should preferably be 0.1 or higher, more preferably 0.2 or higher, and even more preferably 0.3 or higher. This ratio should preferably be less than 1, more preferably less than 0.8, and even more preferably less than 0.6. Through the aforementioned mechanism, even at the higher values ​​mentioned above, the physical properties of the inorganic particles in the sheet material are still readily and effectively represented.

[0041] The content of this resin in this sheet should preferably be 0.1% by mass or more, and more preferably 5% by mass or more. The content of this resin should preferably be 60% by mass or less, and more preferably 30% by mass or less. In this sheet material, the ratio of the content of this resin to the total content of unfired PTFE should preferably be 0.05 or higher, more preferably 0.2 or higher, and even more preferably 0.5 or higher. This ratio should preferably be less than 1, and more preferably less than 0.5.

[0042] When the resin is an F polymer, the F polymer content in the sheet should preferably be 10% by mass or more, and more preferably 15% by mass or more. The F polymer content should preferably be 60% by mass or less, and more preferably 30% by mass or less. The AR polymer content in this sheet should preferably be 0.1% by mass or more, and more preferably 1% by mass or more. The AR polymer content should preferably be less than 10% by mass, and more preferably less than 5% by mass. When this resin contains both F polymer and AR polymer, the ratio of the content of F polymer to the total content of AR polymer in this resin should preferably be 0.6 or more, and more preferably 0.9 or more. This ratio should preferably be less than 1, and more preferably less than 0.99.

[0043] When the content of unburned PTFE, inorganic particles, and this resin in the sheet is within the range described above, the aforementioned mechanism is more likely to be exhibited. This sheet material may also further contain, within a range of less than 10% by mass, the following other components: liquid lubricant, liquid dispersion medium, coagulant, nonionic surfactant, pH adjuster and pH buffer, or organic particles, organic pigments, metallic soaps, lubricants, organic monomers, organic oligomers with a degree of polymerization of less than 50, thixotropic agents, viscosity modifiers, defoamers, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive agents, release agents, surface treatment agents, flame retardants, etc.

[0044] The thickness of this sheet material is preferably 50µm or more, and more preferably 100µm or more. The thickness of this sheet material is preferably 1000µm or less, and more preferably 500µm or less. Through the aforementioned mechanism, even at the aforementioned thicknesses, this sheet material still possesses excellent physical strength, such as toughness. The tensile strength of this sheet should preferably be above 200 MPa, and more preferably above 300 MPa. The tensile strength of this sheet should preferably be below 800 MPa. Furthermore, the tensile strength can be measured using TENSILON (manufactured by TOYO BALDWIN CO., LTD., model: UTM-5T) under the conditions of a load cell with a rated weighing capacity of 5000 kg, a clamping distance of 110 mm, and a speed of 10 mm / min.

[0045] This sheet material is preferably obtained by casting a liquid composition (hereinafter also referred to as "this composition") containing unfired PTFE particles, inorganic particles, and this resin. Furthermore, casting means spreading out a fluid composition, and casting can be carried out by the methods described later. The D50 of the unburned PTFE particles in this composition should preferably be 10µm or less, and more preferably 1µm or less. The D50 of the unburned PTFE particles should preferably be 0.1µm or more. Furthermore, the D90 of the unburned PTFE particles should preferably be 20µm or less. At this point, the unburned PTFE, inorganic particles, and the resin can easily interact, thus easily obtaining a sheet material with excellent uniformity of composition distribution. The inorganic particles in this composition should be the same as the inorganic particles contained in the sheet material described above.

[0046] The resin in this composition may be granular, non-granular, or soluble in this composition. When this resin contains polymer F, the polymer F in this composition should preferably be in granular form. The D50 of the polymer F particles (hereinafter also referred to as "F particles") in this composition should preferably be 0.1µm or more, and more preferably 1µm or more. The D50 of the F particles should preferably be 8µm or less. The specific surface area of ​​F particles should be between 1 and 25 m² / g. At this point, the F polymer, unfired PTFE, and inorganic particles easily interact, making it easy to obtain a sheet material with excellent uniformity of composition distribution.

[0047] When this resin contains AR polymer, the AR polymer is preferably in a liquid state or soluble in a liquid dispersion medium described later in this composition. In this case, the AR polymer readily functions as a binder for unburned PTFE and inorganic particles, thereby readily and firmly supporting the unburned PTFE and inorganic particles in the sheet. Unburned PTFE, inorganic particles, and this resin can also be aggregated together to form composite particles, which are included in this composition. The composite particles can also form the following core-shell structure: with any one of unburned PTFE, inorganic particles, and this resin as the core, and the components of unburned PTFE, inorganic particles, and this resin not included in the core as the shell.

[0048] This composition is preferably obtained by mixing unburned PTFE particles, inorganic particles, this resin, and a liquid lubricant. It is also preferable to mix the aggregates of unburned PTFE particles, inorganic particles, and this resin with a liquid lubricant. In this case, the components are easily and uniformly dispersed in the sheet. This composition can be obtained by distilling off the liquid dispersion medium from a state containing unburned PTFE particles, inorganic particles, and the resin, and a liquid dispersion medium or liquid lubricant. Alternatively, it can be obtained by adding a trace amount of the aforementioned liquid component to a mixed powder containing unburned PTFE particles, inorganic particles, and the resin, but not containing a liquid dispersion medium or liquid lubricant.

[0049] Liquid lubricants should preferably be liquid compounds that can be removed by means of heating, distillation, or extraction, and preferably liquid compounds that can be removed by heating and have a boiling point below 300°C. Liquid lubricants include naphtha, white oil, liquid paraffin, toluene, xylene, hexane, n-decane, tetradecane, dodecane, and polyethylene glycol, with tetradecane or dodecane being preferable. One type of liquid lubricant may be used, or two or more types may be used. The content of liquid lubricant in this composition should preferably be 10 to 60% by mass, more preferably 20 to 40% by mass.

[0050] Examples of mixing devices used to obtain this composition include: Heinz mixers, pressure kneaders, Bambury closed mixers, and planetary mixers with impellers; ball mills, grinding mills, basket mills, sand mixers, sand mills, Dyno-Mills, Dispermats, SC-Mills, spike mills, and stirred mills with media pulverizing devices; microfluidic homogenizers, nanomizers, ultra-thinners, ultrasonic homogenizers, dissolvers, dispersers, high-speed impeller dispersers, thin-film rotary high-speed mixers, self-rotating and revolution-rotating mixers, and V-type mixers with other mechanisms, preferably V-type mixers.

[0051] The aggregates of unburned PTFE particles, inorganic particles, and the resin can be obtained, for example, by removing the liquid dispersion medium from a dispersion containing unburned PTFE particles, inorganic particles, the resin, and the liquid dispersion medium. Liquid dispersion media are compounds that are liquid at atmospheric pressure and 25°C. One or more liquid dispersion media may be used. When using two liquid dispersion media, they should ideally be miscible.

[0052] The liquid dispersion medium should preferably be a compound selected from the group consisting of water, amides, ketones, esters, and ethylene glycol. Specifically, water, N-methyl-2-pyrrolidone, γ-butyrolactone, methyl ethyl ketone, cyclohexanone, cyclopentanone, ethylene glycol, and propylene glycol are examples, with water being the most suitable. This readily yields a sheet material with a uniform dispersion of unburned PTFE particles, inorganic particles, and the resin. The content of liquid dispersion medium in the dispersion should preferably be 40% by mass or more, and more preferably 60% by mass or more. The content of liquid dispersion medium should preferably be 90% by mass or less, and more preferably 80% by mass or less.

[0053] To further enhance dispersion stability, the dispersion may also contain nonionic surfactants. Nonionic surfactants are preferably ethylene glycol-based, acetylene-based, polysiloxane-based, or fluorine-based surfactants, with polysiloxane-based surfactants being more preferred. One or more nonionic surfactants may be used. When using two nonionic surfactants, a polysiloxane-based surfactant and an ethylene glycol-based surfactant are preferred.

[0054] Specific examples of nonionic surfactants include: the "Ftergent" series (manufactured by NEOS), the "Surflon" series (manufactured by AGC SEIMI CHEMICAL), the "MEGAFACE" series (manufactured by DIC), the "UNIDYNE" series (manufactured by Daikin Industries), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by BYK Japan), "KF-6011", "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by Dow Chemical Company, "Tergitol TMN-100X", etc.). When the dispersion contains a nonionic surfactant, the content of the nonionic surfactant in the dispersion should preferably be 1 to 15% by mass.

[0055] When the liquid dispersion medium is water, the dispersion may also contain a pH adjuster or a pH buffer. This easily improves the stability of the dispersion. Examples of pH adjusters include amines, ammonia, and citric acid. Examples of pH buffers include trihydroxymethylaminomethane, ethylenediaminetetraacetic acid, ammonium bicarbonate, ammonium carbonate, and ammonium acetate. The dispersion may further contain other components mentioned above that may also be included in the sheet.

[0056] The dispersion is obtained by mixing unburned PTFE, inorganic particles, this resin, and a liquid dispersion medium. When this resin contains F polymer, the dispersion is preferably obtained by mixing a mixture containing unburned PTFE and a liquid dispersion medium with a mixture containing inorganic particles, F polymer particles and a liquid dispersion medium. When this resin contains AR polymer, the dispersion should preferably be obtained by mixing an unburned PTFE, AR polymer and liquid dispersion medium with inorganic particles. The mixing apparatus used to obtain the dispersion can be the same as the mixing apparatus described above that can be used to obtain this composition, preferably a planetary mixer.

[0057] The removal of the liquid dispersion medium from a dispersion containing unburned PTFE, inorganic particles, this resin, and the liquid dispersion medium can be carried out by filtration, heating, distillation, etc., with heating being preferable. The removal of liquid dispersion media should preferably be carried out by adding a flocculant to the dispersion, removing the liquid dispersion media, and removing the flocculant as needed. When removal is carried out by heating, the heating temperature should preferably be above the boiling point of both the liquid dispersion media and the flocculant. The coagulant should preferably be a primary alcohol, with methanol, ethanol, isopropanol and butanol being more suitable. The amount of primary alcohol should be added relative to the content of liquid dispersion medium in the dispersion to make the mass ratio between 0.2 and 1.

[0058] This sheet material is preferably obtained by casting the composition. In this process, unfired PTFE is easily fibrillated, resulting in a sheet material in which inorganic particles are less likely to peel off. Furthermore, it is easy to obtain a sheet material with excellent electrical properties and toughness. The casting of this composition is preferably carried out by compression molding, extrusion molding, or calendering, with calendering being more suitable. Furthermore, calendering refers to a method in which the composition is rolled between multiple rolls.

[0059] The casting of this composition can be performed using one forming method or a combination of two or more forming methods. Furthermore, the casting process can be repeated multiple times using a single forming method. For example, the master sheet obtained by extruding this composition can be further calendered for casting, or the master sheet obtained by calendering this composition can be further calendered for casting. In this way, it is easy to obtain a sheet of any thickness with excellent toughness and uniformity. For burnishing forming, multiple rollers can be used, but it is advisable to use a combination of 4 rollers. The arrangement of 4 rollers can be I-type, S-type, inverted L-type, Z-type, and oblique Z-type. The casting of this composition can be carried out while heating at a temperature lower than the melting temperature of unfired PTFE, or it can be carried out without heating.

[0060] This sheet can also be obtained by casting the composition into layers and then bonding them together. In this case, the toughness of the sheet is easily improved. This method can be exemplified by laminating and rolling multiple sheet-like cast materials. The lamination and rolling processes can also be repeated to adjust the thickness or properties of the resulting sheet material. When repeatedly layering and rolling, it is advisable to change the casting direction of the cast material. Specifically, the following method can be used: stack the surfaces of one cast material in such a way that their casting directions intersect each other perpendicularly, and then cast the composition.

[0061] The number of layers of the cast material should be between 10 and 1000. The casting ratio of the cast material should be between 100 and 20000. At this point, the casting process can also be carried out using the same method as casting the composition, preferably by burnishing.

[0062] When this composition contains a liquid lubricant, the sheet should preferably be obtained by casting the composition and removing the liquid lubricant. Methods for removing the liquid lubricant include heating, distillation, and extraction; heating is preferred. The liquid lubricant may also be partially removed, until the total content of unburned PTFE, inorganic particles, and the resin in the sheet reaches 90% by mass or more, and the sheet can form a sheet from its self-supporting film form. The heating temperature should preferably be between 100 and 200°C. Heating devices can include ovens and ventilated drying furnaces. The heat source in the device can be a contact heat source such as hot air or heating plates, or a non-contact heat source such as infrared rays. Furthermore, each heating process can be carried out under normal pressure or under reduced pressure. Furthermore, the gas environment during each heating process can be any of the following inert gas environments: air, helium, neon, argon, or nitrogen.

[0063] If this sheet is heated above the melting temperature of PTFE, a sheet containing sintered PTFE can be obtained (hereinafter also referred to as "sintered sheet"). Like this sheet, the inorganic particles of the sintered sheet are not easily peeled off, and it has excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials. The heating temperature should be above the melting temperature of PTFE, preferably 360 to 400°C. The heating time should be 0.1 to 30 minutes. The heating method and conditions can be the same as those used for heating to remove liquid lubricants.

[0064] The thickness of the sintered sheet should preferably be 50µm or more, and more preferably 100µm or more. The thickness of the sintered sheet should preferably be less than 500µm, and more preferably less than 300µm. At this thickness, it is easier to balance the mechanical strength with the physical properties such as low linear expansion and electrical properties of the sintered sheet. If this sheet and the substrate are hot-pressed together, a laminate containing a substrate layer and a polymer layer containing PTFE and inorganic particles can be obtained.

[0065] Examples of substrates include: metal substrates such as metal foils made of copper, nickel, aluminum, titanium, and their alloys; heat-resistant resin films made of heat-resistant resin films such as polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyamide-imide, liquid crystal polyester, and tetrafluoroethylene polymers; prepreg substrates that are precursors to fiber-reinforced resin substrates; ceramic substrates made of silicon carbide, aluminum nitride, or silicon nitride; and glass substrates. The shape of the substrate can be planar, curved, or uneven. Furthermore, the shape of the substrate can also be any of the following: foil, plate, film, or fibrous. The average roughness of the substrate surface at ten points should be between 0.01 and 0.05 µm.

[0066] The surface of the substrate can be treated with a silane coupling agent or with plasma. The preferred silane coupling agent is a silane coupling agent with a functional group, such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatepropyltriethoxysilane.

[0067] Methods of hot pressing include: applying clamping pressure to the substrate and the sheet using a pair of opposing heating plates; passing the substrate and the sheet between a pair of opposing rollers; and applying pressure to the substrate and the sheet using rollers on a heating plate. The hot-pressing temperature should preferably be above 200℃, more preferably above the melting temperature of PTFE, and even more preferably above 350℃. The hot-pressing temperature should preferably be below 400℃. PTFE should be fired by heating during hot pressing.

[0068] Hot pressing can also be performed under reduced pressure. In this case, from the viewpoint of suppressing the deterioration caused by oxidation of the substrate and the sheet, it is advisable to perform the process under a vacuum of 20 kPa or less. Hot pressing is preferably performed by vacuum pressing. From the viewpoint of preventing the sheet from adhering to the heating plate or rollers during hot pressing, it is advisable to place a release film between the surface of the sheet and the heating plate or rollers, or to treat the surface of the heating plate or rollers with a release agent.

[0069] The thickness of the release film should be 50 to 150 µm. Release films can be made of polyimide, and specific examples include "APICAL NPI" (manufactured by Kaneka Corporation), "Kapton EN" (Dupont-Toray Corporation), and "UPILEX S" (Ube Industries).

[0070] This sheet material can be hot-pressed onto only one surface of the substrate, or it can be hot-pressed onto both sides of the substrate. In the former case, a laminate having a substrate layer and a polymer layer located on one surface of the substrate layer can be obtained; in the latter case, a laminate having a substrate layer and polymer layers located on both surfaces of the substrate layer can be obtained. Suitable examples of laminates include: metal-coated laminates having a metal foil and a polymer layer on at least one surface of the metal foil, and multilayer films having a polyimide film and polymer layers on both surfaces of the polyimide film. The peel strength between the polymer layer and the substrate layer should be 10 to 100 N / cm. The substrate layer can also be further removed from the laminate to obtain a sheet containing PTFE, inorganic particles and this resin.

[0071] This sheet, sintered sheet, and laminate with a substrate layer and a polymer layer can be effectively used as antenna parts, printed circuit boards, aerospace parts, automotive parts, sporting goods, food industry products, heat dissipation parts, coatings, cosmetics, etc. Specifically, it can be effectively used as: wire sheathing material for aircraft wires, enameled wire sheathing material for motors used in electric vehicles, electrical insulation tape, oil drilling insulation tape, oil delivery hoses, hydrogen tanks, materials for printed circuit boards, separation membranes such as microporous filter membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes and gas separation membranes, electrode and electrolyte binders for lithium batteries and fuel cells, replica rollers, housings for furniture, automotive dashboards, and home appliances, sliding components, tension cables, wear-resistant pads, wear-resistant strips, lamps, test sockets, wafer guides, wear parts for centrifugal pumps, and pharmaceutical supplies. Pumps and water pumps, tools such as shovels, files, cones and saws; boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, molds, toilets, container coverings, power devices, transistors, thyristors, rectifiers, transformers, power MOSFETs, CPUs, heat sinks, metal heat sinks, windmills or wind power generation equipment or aircraft blades, computer or monitor housings, electronic device materials, automotive interior and exterior parts, processing machines or vacuum ovens that undergo heat treatment in low oxygen conditions, sealing materials for plasma treatment equipment, heat dissipation parts in sputtering or various dry etching equipment, electromagnetic wave shielding components. Sliding components include: load-bearing bearings, yaw bearings, sliding shafts, valves, bearings, bushings, seals, thrust washers, wear rings, pistons, slide switches, gears, cams, conveyor belts and food conveyor belts.

[0072] The above describes the sheet material, the manufacturing method of the sheet material, and the manufacturing method of the laminate containing the sheet material. However, the present invention is not limited to the above-described embodiments. For example, this sheet material can be supplemented with any other components in the above-described embodiments, or it can be replaced with any other components that perform the same function. Furthermore, the manufacturing method of this sheet material and the manufacturing method of the laminate containing this sheet material can be supplemented with any other steps in the above-described embodiments, or it can be replaced with any other steps that can produce the same effect.

[0073] Example The present invention will be described in detail below by way of examples, but the present invention is not limited thereto. 1. Preparation of each component and part [Dispersion] Dispersion 1: An aqueous dispersion containing 60% by mass of particles (D50: 0.3µm) of unburned PTFE (PTFE1; melt temperature: 327°C) (AD-911E manufactured by AGC). [Inorganic particles] Inorganic particles 1: Spherical silicon dioxide (D50: 1µm) [Resin particles] Resin particle 1: Particles composed of tetrafluoroethylene-based polymers (F resin 1; melt temperature: 300℃) (D50: 2.1µm), which contain TFE units, NAH units, and PPVE units in sequence at 97.9 mol%, 0.1 mol%, and 2.0 mol%, and have 1000 carbonyl groups per 1×10⁶ carbon atoms in the main chain. Resin particle 2: consists of particles (D50: 1.8µm) composed of tetrafluoroethylene-based polymers (F resin 2; melt temperature: 305℃), containing TFE units and PPVE units in sequence at 98.7 mol% and 1.3 mol%, and lacking carbonyl groups, hydroxyl groups, epoxy groups, and amine groups. Resin particles 3: Particles composed of powdered, unburned PTFE obtained by removing water from dispersion 1. [Resin Varnish] Varnish 1: A water-based varnish containing an aromatic polyamide amide precursor (PAI1; containing carboxyl and amide groups; acid value: 50 mg KOH / g). [Surfactants] Surfactant 1: Polyoxyethyl-modified polydimethylsiloxane with dimethylsiloxane units in the main chain and oxyethyl groups in the side chains. [Glass cloth] Fiberglass cloth 1: Fiberglass cloth (manufactured by Arisawa Fiber Glass Co., Ltd. "1078")

[0074] 2. Examples of sheet manufacturing (Example 1) The dry admixtures of inorganic particles 1 and resin particles 1, water, and surfactant 1 are added to a planetary mixer and kneaded. Next, the mixture of dispersion 1 and varnish 1, along with water, is added repeatedly and stirred to obtain mixture 1. While stirring mixture 1, methanol is added, and agglomerate 1 containing PTFE particles 1, inorganic particles 1, resin particles 1, and PAI 1 is recovered. This agglomerate 1 is formed from a composition 1 consisting of 20 parts by mass of PTFE 1, 60 parts by mass of inorganic particles 1, 18.5 parts by mass of resin particles 1, 1.5 parts by mass of PAI 1, 1 part by mass of surfactant 1, 100 parts by mass of water, and 70 parts by mass of methanol. The condensate 1, which was heated under vacuum and at 60°C for 24 hours, was added to a V-type mixer and mixed for 5 minutes at 24°C and 10 rpm to obtain a paste-like liquid composition 1.

[0075] Liquid component 1 is cast between a pair of rolling rolls to obtain a master sheet 1 with a thickness of 3 mm. The master sheet 1 is then cast using an inverted L-shaped calender, and further heated at 150°C for 30 minutes to remove dodecane, resulting in a sheet 1 with a thickness of 200 µm. In sheet 1, the total content of PTFE 1, inorganic particles 1, F resin 1, and polyamide-imide, a reactant of PAI 1 or PAI 1, is 98% by mass or more; the content of PTFE 1 is 15% by mass or more; the total content of F resin 1 and polyamide-imide, a reactant of PAI 1 or PAI 1, is 15% by mass or more; and the content of inorganic particles is 50% by mass or more.

[0076] (Example 2) Except that resin particles 1 are replaced with resin particles 2, mixture 2 is obtained in the same manner as in Example 1. Mixture 2 is used to replace mixture 1, and sheet 2 is obtained in the same manner as in Example 1. (Example 3) Except for changing resin particles 1 to resin particles 2 and not using varnish 1, sheet 3 is obtained in the same manner as in Example 1. (Example 4) After impregnating the glass cloth 1 with the mixture 2, it is heated at 100°C to dry it, thereby obtaining a master sheet in which the glass cloth 1 is impregnated with PTFE particles 1. The aforementioned master sheet is then cast using an inverted L-shaped calender to obtain a sheet 4 with a thickness of 200µm and a glass cloth 1 content of more than 10 by mass. (Example 5) 15 parts by weight of resin particles 3, 13 parts by weight of resin particles 1, 60 parts by weight of inorganic particles 1, 2 parts by weight of PAI1 and 10 parts by weight of tetradecane were added to a Heinz mixer and stirred at 1000 rpm for 2 minutes to obtain aggregate 5. Except that aggregate 5 was replaced with aggregate 1, sheet 5 was obtained in the same manner as in Example 1.

[0077] 3. Evaluation Examples of Sheets 3-1. Assessment of Flexural Resistance Cut 50mm × 100mm rectangular test pieces from sheets 1 to 5. For each test piece, bend it at a 180° angle along a 2mm mandrel, following the method specified in JIS K 5600-5-1. Visually inspect the bent test pieces and evaluate their flexural strength according to the following criteria. [Evaluation Benchmarks] 〇: No cracks were confirmed on the test piece. ×: Cracks were confirmed in the test piece.

[0078] 3-2. Assessment of Follower Loss After performing the 3-1 evaluation, remove each sheet from the mandrel. Visually inspect the powder adhesion to the mandrel and assess the ease of powder removal according to the following criteria: [Evaluation Criteria] 〇: No powder was confirmed to be adhering to the spindle. ×: Powder is confirmed to be adhering to the mandrel.

[0079] 3-3. Adhesion Assessment Sheets 1 to 5 are each stacked with a strip of copper foil (thickness: 18µm, average surface roughness of ten points: 0.8µm), and hot-pressed under vacuum at 380°C to obtain laminates 1 to 5 having a polymer layer of copper foil and a sintered material containing PTFE particles 1 on its surface. Rectangular test pieces, 100 mm long and 10 mm wide, were cut from laminates 1 to 5 respectively. After fixing the test piece at a position 50 mm from one end along its length, the copper foil was peeled from the polymer layer at a stretching speed of 50 mm / min from one end along its length at a 90° angle relative to the test piece. The maximum load during peeling was taken as the peel strength (N / cm), and the adhesion of the sheet was evaluated according to the following criteria. [Evaluation Benchmarks] 〇: Peel strength is above 12N / cm. △: Peel strength is above 10 N / cm and less than 12 N / cm. ×: Peel strength is less than 10 N / cm.

[0080] 3-4. Evaluation of Electrical Characteristics For laminates 1 to 4, copper foil was removed by etching with ferric chloride aqueous solution to obtain sintered sheets 1 to 4 consisting of individual polymer layers. The dielectric constant and dielectric tangent of the sintered sheets were determined by SPDR (separated dielectric resonator) method (measurement frequency: 10 GHz). The evaluation results of each are summarized and displayed in Table 1 below.

[0081] [Table 1]

[0082] Industrial availability The above results clearly demonstrate that the sheet material of the present invention possesses excellent flexural strength and adhesion, and is not prone to powdering. Furthermore, the sintered sheets obtained from the sheet material of the present invention exhibit excellent low dielectric constant and low dielectric tangent. Therefore, it can be considered that the sheet material of the present invention has excellent uniformity of compositional distribution and highly exhibits the properties of unsintered PTFE, inorganic particles, and the resin itself. The sheet material of the present invention, or the sintered sheets and laminates obtained from the sheet material of the present invention, have inorganic particles that are not easily peeled off, and possess excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials, making them effective as printed circuit board materials.

Claims

1. A sheet comprising: unburned polytetrafluoroethylene, inorganic particles, and a hot-melt tetrafluoroethylene-based polymer, wherein the hot-melt tetrafluoroethylene-based polymer has at least one functional group selected from the group consisting of carbonyl groups, hydroxyl groups, epoxy groups, and amine groups; and wherein the content of the inorganic particles is 20% by mass or more, the total content of the polytetrafluoroethylene, the inorganic particles, and the hot-melt tetrafluoroethylene-based polymer is 90% by mass or more, the hot-melt tetrafluoroethylene-based polymer comprises units mainly composed of perfluorinated (alkyl vinyl ethers), and the inorganic particles comprise particles selected from at least one inorganic material selected from the group consisting of silicon dioxide, boron nitride, and titanium dioxide.

2. The sheet as claimed in claim 1, wherein the melting temperature of the aforementioned thermoplastic tetrafluoroethylene polymer is 260 to 320°C.

3. The sheet material as requested in item 1, wherein the content of the aforementioned polytetrafluoroethylene is 10% by mass or more.

4. The sheet material as requested in item 1, wherein the content of the aforementioned hot-melt tetrafluoroethylene polymer is 5% by mass or more.

5. The sheet of claim 1, wherein the ratio of the content of the aforementioned inorganic particles to the total content of the aforementioned polytetrafluoroethylene and the aforementioned hot-melt tetrafluoroethylene polymer is 0.1 or more.

6. The sheet material as requested in item 1 has a thickness of 50µm or more.

7. A method for manufacturing a sheet, comprising casting a liquid composition including the aforementioned polytetrafluoroethylene particles, the aforementioned inorganic particles and the aforementioned thermomeltable tetrafluoroethylene polymer to obtain the sheet as claimed in claim 1.

8. The manufacturing method of claim 7, wherein the average particle size of the aforementioned polytetrafluoroethylene particles is 0.1 to 10 µm.

9. The manufacturing method of claim 7 or 8, wherein the aforementioned liquid composition is cast and the resulting cast materials are stacked and bonded together.

10. A method for manufacturing a fired sheet, comprising heating a sheet as claimed in any one of claims 1 to 6 to fire the aforementioned polytetrafluoroethylene.

11. A method for manufacturing a laminate, comprising hot-pressing a sheet as claimed in any one of claims 1 to 6 with a substrate to obtain a laminate having a substrate layer and a polymer layer.