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Abstract

[Problem] To provide a sheet that contains unsintered polytetrafluoroethylene and inorganic particles, in which the inorganic particles are unlikely to peel off, and that has excellent electrical properties, low linear expansion properties, physical strength, and adhesion to other materials. [Solution] This sheet contains: unsintered polytetrafluoroethylene; inorganic particles; and a resin having at least one type of functional group selected from the group consisting of a carbonyl group-containing group, a hydroxyl group-containing group, an epoxy group, and an amino group. The total content of the polytetrafluoroethylene, the inorganic particles, and the resin is at least 90 mass%.

Description

Technical Field

[0001] The present invention relates to a predetermined sheet containing unfired polytetrafluoroethylene, a method for producing the sheet, and a method for producing a laminate containing the sheet.

Background Art

[0002] Polytetrafluoroethylene is attracting attention as a material for the dielectric layer of printed circuit boards because of its excellent electrical properties such as low dielectric constant and low dielectric tangent. Patent Document 1 describes forming a dielectric layer from a sheet composed of polytetrafluoroethylene and inorganic particles. Patent Document 2 describes a dielectric layer reinforced with a reinforcing woven fabric, which includes polytetrafluoroethylene, inorganic particles, and a reinforcing woven fabric.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When forming a layered molded product having a layer containing polytetrafluoroethylene and inorganic particles from a sheet containing unfired polytetrafluoroethylene and inorganic particles, in the sheet, there are problems that the inorganic particles tend to aggregate and it is difficult to fully exhibit their physical properties. Further, when processing the sheet, there are problems that the inorganic particles tend to peel off and the physical strength such as toughness is insufficient and it is easy to break. Furthermore, such a sheet is required to have adhesiveness with other base material layers such as metal foil, but the adhesiveness is not yet sufficient. The inventors of the present invention have discovered that a sheet containing unfired polytetrafluoroethylene, inorganic particles, and a resin having a predetermined functional group in a predetermined ratio exhibits excellent properties such as resistance to peeling of the inorganic particles, electrical properties, low linear expansion, physical strength, and adhesion to other materials, leading to the present invention. [Means for solving the problem]

[0005] The present invention has the following aspects. [1] A sheet comprising uncalcined polytetrafluoroethylene, inorganic particles, and a resin having at least one functional group selected from the group consisting of carbonyl group-containing groups, hydroxyl group-containing groups, epoxy groups, and amino groups, wherein the total content of the polytetrafluoroethylene, the inorganic particles, and the resin is 90% by mass or more. [2] The sheet of [1] wherein the inorganic particles consist of at least one inorganic substance selected from the group consisting of silica, boron nitride and titanium dioxide. [3] The sheet of [1] or [2] wherein the resin comprises at least one of a heat-meltable tetrafluoroethylene polymer or an aromatic polymer or its precursor. [4] A sheet of any of the above [1] to [3], wherein the resin comprises a heat-meltable tetrafluoroethylene polymer and an aromatic polymer or its precursor. [5] The sheet according to [3] or [4], wherein the melting temperature of the heat-meltable tetrafluoroethylene polymer is 260 to 320°C. [6] The sheet of [3] or [4] wherein the aromatic polymer or its precursor is a polyimide, a polyamideimide, a polyimide precursor, or a polyamideimide precursor. [7] Any of the sheets from [1] to [6], wherein the polytetrafluoroethylene content is 10% by mass or more. [8] Any of the sheets from [1] to [7], wherein the resin content is 5% by mass or more. [9] Any of the sheets from [1] to [8] above, wherein the ratio of the content of the inorganic particles to the sum of the content of the polytetrafluoroethylene and the content of the resin is 0.1 or more.

[10] Any of the sheets described in [1] to [9] above, having a thickness of 50 μm or more.

[11] A method for producing a sheet, comprising casting a liquid composition containing polytetrafluoroethylene particles, inorganic particles, and a resin, to obtain any of the sheets described in [1] to

[10] above.

[12] The method for producing the

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

[13] A method for manufacturing the

[11] or

[12] , comprising casting the liquid composition and laminating and bonding the resulting casts together.

[14] A method for producing a fired sheet, comprising heating one of the sheets from [1] to

[10] to fire the polytetrafluoroethylene.

[15] A method for manufacturing a laminate, comprising heat-pressing any of the sheets from [1] to

[10] with a substrate to obtain a laminate having a substrate layer and a polymer layer. [Effects of the Invention]

[0006] According to the present invention, a sheet can be obtained that comprises unfired polytetrafluoroethylene, inorganic particles, and a resin having a predetermined functional group, wherein the inorganic particles are less likely to peel off, and the sheet has excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials. [Modes for carrying out the invention]

[0007] The following terms have the following meanings: A "tetrafluoroethylene polymer" is a polymer that contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE"). A "thermally meltable tetrafluoroethylene polymer" refers to a tetrafluoroethylene polymer for which there exists a temperature range where the melt flow velocity is between 1 and 1000 g / 10 min under a load of 49 N. The "melting temperature (melting point) of a polymer" is the temperature corresponding to the maximum value of the melting peak measured for the polymer using differential scanning calorimetry (DSC). The glass transition temperature (Tg) of a polymer is a value measured by analyzing the polymer using the dynamic viscoelasticity measurement (DMA) method. "Particle D50" is the average particle diameter, which is the volume-based cumulative 50% diameter of the particle determined by laser diffraction and scattering. In other words, the particle size distribution is measured by laser diffraction and scattering, the total volume of the particle collection is set to 100%, and a cumulative curve is obtained. D50 is the particle diameter at the point on that cumulative curve where the cumulative volume reaches 50%. "Particle D90" is the cumulative volume particle size of the particle, and is the volume-based cumulative 90% diameter of the particle, which is determined in the same way as "D50". The "viscosity of the liquid composition" is a value measured for the liquid composition using a B-type viscometer at room temperature (25°C) and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measurements is used. A "monomer-based unit" refers to an atomic group based on a monomer, formed by the polymerization of the monomer. The unit may be one directly formed by the polymerization reaction, or it may be a unit in which a part of the unit is converted to a different structure by processing the polymer. Hereinafter, a unit based on monomer a will also be simply referred to as a "monomer a unit."

[0008] The sheet of the present invention (hereinafter also referred to as "this sheet") comprises uncalcined polytetrafluoroethylene (hereinafter, polytetrafluoroethylene is also referred to as "PTFE," and uncalcined polytetrafluoroethylene is also referred to as "uncalcined PTFE"), inorganic particles, and a resin having at least one functional group selected from the group consisting of carbonyl group-containing groups, hydroxyl group-containing groups, epoxy groups, and amino groups (hereinafter also referred to as "this resin"), wherein the total content of uncalcined PTFE, inorganic particles, and this resin is 90% by mass or more. In other words, this sheet is a self-supporting film-like sheet mainly composed of uncalcined PTFE, inorganic particles, and this resin.

[0009] In this sheet, the resin having the functional group is considered to not only interact with the inorganic particles to suppress the aggregation of the inorganic particles and promote the uniform dispersion of the inorganic particles in the sheet, but also firmly support the unfired PTFE and the inorganic particles as a binder component. In other words, it is also considered that this sheet has a structure in which the resin is used as a matrix and the unfired PTFE and the inorganic particles are uniformly dispersed while being firmly held therein. As a result, in this sheet, exfoliation of the inorganic particles is suppressed, physical properties of both PTFE and the inorganic particles are highly expressed, and the physical strength is improved. Further, due to the inclusion of the resin having this functional group, it is considered that this sheet also has excellent affinity with other base materials such as metal foils and its adhesiveness is improved.

[0010] The PTFE in the present invention may be a homopolymer of TFE, or may be a so-called modified PTFE which is a copolymer of TFE and a comonomer such as a trace amount of perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), hexafluoropropylene (hereinafter also referred to as "HFP"), fluoroalkyl ethylene, etc. The proportion of TFE units in PTFE is preferably 99.5 mol% or more, more preferably 99.9 mol% or more, of all the units.

[0011] Preferably, the PTFE has a number average molecular weight, Mn, calculated based on the following formula (1) of 200,000 or more. Mn = 2.1×10 10 ×ΔHc -5.16 ··· (1) In formula (1), Mn represents the number average molecular weight of PTFE, and ΔHc represents the heat of crystallization (cal / g) of PTFE measured by differential scanning calorimetry.

[0012] The unfired PTFE in the present invention means PTFE that has not been exposed to a temperature above the melting temperature of PTFE after being produced by polymerization. Further, the fired PTFE means PTFE that has been exposed to a temperature above the melting temperature of PTFE after being produced by polymerization. In this specification, the melting temperature of PTFE is assumed to be 327°C.

[0013] The unfired PTFE may be fibrillar or non-fibrillar, and fibrillar is preferred. If the unfired PTFE is fibrillar, it is easy for the unfired PTFE to carry the inorganic particles in this sheet, and it is difficult for the inorganic particles to peel off from this sheet. In addition, the unfired PTFE is likely to entangle with the inorganic particles or this resin, and it is easy to improve the toughness of this sheet. In other words, the fibrillar unfired PTFE can also be regarded as being easy to adhere to the inorganic particles or this resin.

[0014] The unfired PTFE in this sheet preferably exists in a particulate state. In this case, the particles of the unfired PTFE are preferably the same particles as the particles of the unfired PTFE contained in the liquid composition described later The unfired PTFE may be PTFE obtained by an emulsion polymerization method or PTFE obtained by a suspension polymerization method. From the viewpoint of having a low crystallinity and being easy to enhance the toughness of the sheet, PTFE obtained by an emulsion polymerization method is preferred.

[0015] The shape of the inorganic particles in the present invention is preferably spherical, needle-like or plate-like, more preferably spherical, scaly or layered, and even more preferably spherical or scaly. The inorganic particles that are spherical are preferably substantially spherical. Substantially spherical means that when the inorganic particles are observed by a scanning electron microscope (SEM), the ratio of the short diameter to the long diameter is 0.7 or more. The proportion occupied by the substantially spherical inorganic particles is preferably 95% or more. The aspect ratio of the non-spherical inorganic particles is preferably 2 or more, and preferably 5 or more. The aspect ratio is preferably 10,000 or less.

[0016] The inorganic particles may be hollow. In this case, this sheet is likely to have excellent electrical properties. The inorganic particles are particles containing at least one kind of inorganic substance, and particles containing carbon, inorganic nitride or inorganic oxide are preferred. Specific examples of inorganic substances include carbon, boron nitride, aluminum nitride, beryllia, silica, wollastonite, 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 the sheet, the inorganic particles are preferably particles containing at least one inorganic substance selected from the group consisting of silica, boron nitride, and titanium dioxide. The silica is preferably amorphous silica. The boron nitride is preferably hexagonal boron nitride. The titanium dioxide is preferably rutile titanium dioxide.

[0017] The D50 of the inorganic particles is preferably 20 μm or less, and more preferably 10 μm or less. The D50 is preferably 0.01 μm or more, and more preferably 0.1 μm or more. The specific surface area of ​​inorganic particles ranges from 1 to 20 m². 2 / g is preferable.

[0018] The surface of the inorganic particles may be surface-treated with a silane coupling agent. In this case, the affinity between the inorganic particles and the unfired PTFE and the resin is improved, making it less likely for the inorganic particles to peel off the sheet. In addition, the sheet tends to have excellent electrical properties and low thermal expansion. The preferred silane coupling agent is one having a functional group such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatetopropyltriethoxysilane.

[0019] Specific examples of silica-containing particles include the "AdmaFine" series (manufactured by Admatex), the "SFP" series (manufactured by Denka), and the "E-SPHERES" series (manufactured by Taiheiyo Cement Corporation). Specific examples of particles containing titanium dioxide include the "Typeque" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Teika Co., Ltd.). Specific examples of particles containing boron nitride include the "UHP" series (manufactured by Showa Denko Corporation) and the "GP" and "HGP" grades of the "Denka Boron Nitride" series (manufactured by Denka Corporation).

[0020] One type of inorganic particle may be used, or two or more types may be used. For example, silica particles, boron nitride particles, and titanium dioxide particles may be used in combination as inorganic particles. In this case, the content of silica particles, boron nitride particles, and titanium dioxide particles in relation to the total amount of inorganic particles is preferably 10 to 60% by mass, 10 to 60% by mass, and 5 to 40% by mass, in that order.

[0021] The resin is a resin having at least one functional group selected from the group consisting of carbonyl group-containing groups, hydroxyl group-containing groups, epoxy groups, and amino groups (hereinafter also referred to as "the functional group"), and it is preferable that the resin has at least one of the functional groups selected from the group consisting of fluororesins, polyester resins such as liquid crystalline aromatic polyesters, imide resins, epoxy resins, maleimide resins, urethane resins, polyphenylene ether resins, polyphenylene oxide resins, and polyphenylene sulfide resins.

[0022] A hydroxyl group-containing group is a group containing a hydroxyl group, and a group containing an alcoholic hydroxyl group is preferred. Carbonyl group-containing groups are groups containing a carbonyl group, and include carboxyl groups, alkoxycarbonyl groups, amide groups, isocyanate groups, carbamate groups (-OC(O)NH2), acid anhydride residues (-C(O)OC(O)-), imide residues (-C(O)NHC(O)-, etc.), and carbonate groups (-OC(O)O-), with carboxyl groups, amide groups, imide residues, or acid anhydride residues being preferred.

[0023] The resin preferably contains at least one of the following: a heat-meltable tetrafluoroethylene polymer having the functional group (hereinafter also referred to as "F polymer") or an aromatic polymer having the functional group or a precursor of the aromatic polymer (hereinafter, the aromatic polymer or the precursor is also referred to as "AR polymer"), and more preferably contains both F polymer and AR polymer.

[0024] The melting temperature of the F polymer is preferably 200°C or higher, and more preferably 260°C or higher. The melting temperature of the F polymer is preferably 325°C or lower, and more preferably 320°C or lower. In this case, the sheet tends to have excellent heat resistance, low linear expansion, and processability. The glass transition temperature of the F polymer is preferably 50°C or higher, and more preferably 75°C or higher. The glass transition temperature of the F polymer is preferably 150°C or lower, and more preferably 125°C or lower. The fluorine content of the F polymer is preferably 70% by mass or more, and more preferably 72 to 76% by mass. In this case, the F polymer and uncalcined PTFE interact more readily. 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 wetting index reagent (manufactured by Wako Pure Chemical Industries, Ltd.) on a flat plate made of the F polymer.

[0025] The F polymer 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), or 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 further contain units based on other comonomers.

[0026] PAVE is preferably CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE"), with PPVE being more preferred. The functional groups of the F polymer are preferably hydroxyl group-containing groups or carbonyl group-containing groups, with carbonyl group-containing groups being more preferable. In this case, not only is the interaction of the F polymer with unfired PTFE and inorganic particles enhanced, but the adhesion of the sheet is also easily improved.

[0027] The hydroxyl group-containing groups in the F polymer are preferably -CF2CH2OH and C(CF3)2OH. The carbonyl group-containing group of the F polymer is preferably a carboxyl group, alkoxycarbonyl group, amide group, isocyanate group, carbamate group, acid anhydride residue, imide residue, or carbonate group, with acid anhydride residue being more preferred.

[0028] If the F polymer contains hydroxyl group-containing groups or carbonyl group-containing groups, the number of hydroxyl group-containing groups or carbonyl group-containing groups in the F polymer is 1 × 10⁶ carbon atoms in the main chain. 6 The number of hydroxyl group-containing groups or carbonyl group-containing groups in polymer F can be quantified by the polymer composition or by the method described in International Publication No. 2020 / 145133.

[0029] The functional group possessed by the F polymer may be included in the monomer-based units within the F polymer, or it may be included in the terminal groups of the main chain of the F polymer, with 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 plasma treatment or ionization treatment of the F polymer. The monomers having a carbonyl group are preferably itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic acid anhydride (hereinafter also referred to as "NAH"), with NAH being more preferred.

[0030] The F polymer is preferably a polymer having carbonyl group-containing groups, including TFE units and PAVE units, and more preferably a polymer containing TFE units, PAVE units, and units based on monomers having carbonyl group-containing groups, with these units present in the following proportions relative to the total number of units: 90 to 99 mol%, 0.99 to 9.97 mol%, and 0.01 to 3 mol% in that order. A specific example of such an F polymer is the polymer described in International Publication No. 2018 / 16644.

[0031] The shape of the F polymer in this sheet may be particulate or non-particulate. The F polymer may be bonded to uncalcined PTFE or inorganic particles. If the F polymer is particulate, the particles of the F polymer are preferably the same as the particles of the F polymer that may be contained in the liquid composition described later.

[0032] The AR polymer may be thermosetting or thermoplastic. The functional groups of the AR polymer are preferably amino groups or carbonyl group-containing groups, and more preferably at least one selected from the group consisting of amino groups, amide groups, carboxyl groups, and imide residues. In this case, not only is the interaction of the AR polymer with unfired PTFE and inorganic particles enhanced, but the adhesion of the sheet is also easily improved. Examples of AR polymers include aromatic polyimides, aromatic polyimide precursors which are polyamic acids or their salts, aromatic polyamideimides, aromatic polyamideimide precursors, aromatic polyetherimides, and aromatic polyetherimide precursors, with aromatic polyimides, aromatic polyimide precursors which are polyamic acids or their salts, aromatic polyamideimides, or aromatic polyamideimide precursors being more preferred.

[0033] The AR polymer may be water-soluble. Examples of water-soluble AR polymers include water-soluble aromatic polyimide precursors, water-soluble polyamide-imides, and their precursors. Examples of water-soluble aromatic polyimide precursors include polyamic acids and their salts obtained by polymerizing tetracarboxylic dianhydrides and diamines. Examples of water-soluble aromatic polyamideimides or their precursors include polyamideimides or their precursors obtained by reacting at least one of diisocyanates or diamines with a tribasic acid anhydride.

[0034] Examples of tetracarboxylic dianhydrides include pyromellitic anhydride and biphenyltetracarboxylic anhydride. Examples of diamines include phenylenediamine, 3,3'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl ether. Examples of diisocyanates include 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, and 3,3'-diphenylmethane diisocyanate.

[0035] The number-average molecular weight (Mn) of the AR polymer is preferably between 5,000 and 50,000. The acid value of the AR polymer is preferably 20 to 100 mg / KOH. The acid value of AR polymer is 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 titrator with a 0.05 mol / L ethanolic potassium hydroxide solution. If the AR polymer contains acid anhydride groups, the acid value obtained when the acid anhydride groups are ring-opened is considered the acid value of the AR polymer.

[0036] Specific examples of AR polymers include the "Yupia-AT" series (manufactured by Ube Industries), the "Neoprim®" series (manufactured by Mitsubishi Gas Chemical Company), the "Spixeria®" series (manufactured by Somar), the "Q-PILON®" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology), the "Tomide®" series (manufactured by T&K TOKA), the "KPI-MX" series (manufactured by Kawamura Industries), and "HPC-1000" and "HPC-2100D" (both manufactured by Showa Denko Materials). In this sheet, the AR polymer may be particulate or non-particulate, with non-particulate being preferred. The AR polymer may be bonded to uncalcined PTFE and inorganic particles.

[0037] The resin in this sheet preferably contains either an F polymer and an aromatic polymer having this functional group, an F polymer and a precursor of an aromatic polymer having this functional group, or an F polymer, an aromatic polymer having this functional group, and a precursor of an aromatic polymer having this functional group. In this case, a strong matrix is ​​formed in the sheet by the resin, and the unfired PTFE and inorganic particles are easily and uniformly supported thereon, further improving the physical properties and adhesiveness of the sheet. 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 the unfired PTFE, while the AR polymer enhances the binder effect between the components. Furthermore, if the resin contains both an F polymer and an AR polymer, the F polymer and the AR polymer may form a crosslinked body in the sheet.

[0038] The total content of unfired PTFE, inorganic particles, and the resin in this sheet 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 other than unfired PTFE, inorganic particles, and the resin in this sheet is less than 10% by mass, preferably 5% by mass or less. Examples of different components include reinforcing fibers. The lower limit of the content of the aforementioned different components is 0% by mass. Due to the mechanism of action described above, even with such component content ratios, this sheet exhibits excellent physical properties such as flexibility and toughness, and can express the physical properties of PTFE and inorganic particles in a highly balanced manner.

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

[0040] The ratio of the inorganic particle content to the total inorganic particle content of unfired PTFE in this sheet is preferably 0.1 or higher, more preferably 0.2 or higher, and even more preferably 0.3 or higher. Such a ratio is preferably less than 1, more preferably 0.8 or lower, and even more preferably 0.6 or lower. Due to the mechanism of action described above, even with such a high ratio, the physical properties of the inorganic particles in the sheet tend to be highly expressed.

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

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

[0043] When the content of unfired PTFE, inorganic particles, and this resin in this sheet falls within the specified range, the above-described mechanism of action is more likely to manifest. This sheet may also contain, in amounts not exceeding 10% by mass, other components such as liquid lubricants, liquid dispersion media, flocculants, nonionic surfactants, pH adjusters and pH buffers, organic particles, organic pigments, metal soaps, lubricants, organic monomers, organic oligomers with a degree of polymerization of 50 or less, thixotropic agents, viscosity modifiers, defoamers, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive agents, mold release agents, surface treatment agents, and flame retardants.

[0044] The thickness of this sheet is preferably 50 μm or more, and more preferably 100 μm or more. The thickness of this sheet is preferably 1000 μm or less, and more preferably 500 μm or less. Due to the mechanism of action described above, even at these thicknesses, this sheet exhibits excellent physical strength, such as toughness. The tensile strength of this sheet is preferably 200 MPa or higher, and more preferably 300 MPa or higher. The tensile strength of this sheet is preferably 800 MPa or lower. The tensile strength can be measured using TENSILON (manufactured by TOYO BALDWIN CO., LTD., model: UTM-5T) under the conditions of a load cell rating of 5000 kg, a chuck distance of 110 mm, and a speed of 10 mm / min.

[0045] The sheet is preferably obtained by casting a liquid composition (hereinafter also referred to as "the composition") containing unfired PTFE particles, inorganic particles, and the resin. Casting means spreading a fluid composition, and casting can be carried out by the method described later. In this composition, the D50 of the unfired PTFE particles is preferably 10 μm or less, and more preferably 1 μm or less. The D50 of the unfired PTFE particles is preferably 0.1 μm or more. Furthermore, the D90 of the unfired PTFE particles is preferably 20 μm or less. In this case, the unfired PTFE, inorganic particles, and the resin interact easily, making it easier to obtain a sheet with excellent uniformity of component distribution. In this composition, inorganic particles similar to those contained in the aforementioned sheet are preferred.

[0046] The resin in this composition may be in particulate form, non-particulate form, or dissolved in the composition. When the resin contains an F polymer, the F polymer is preferably in particulate form in this composition. The D50 of the F polymer particles (hereinafter also referred to as "F particles") in this composition is preferably 0.1 μm or larger, and more preferably 1 μm or larger. The D50 of the F particles is preferably 8 μm or smaller. The specific surface area of ​​F particles ranges from 1 to 25 m². 2 / g is preferable. In this case, the F polymer, unfired PTFE, and inorganic particles interact easily, making it easier to obtain a sheet with excellent uniformity of component distribution.

[0047] When this resin contains an AR polymer, it is preferable that the AR polymer is in liquid form in this composition or dissolved in a liquid dispersion medium described later. In this case, the AR polymer readily functions as a binder for unfired PTFE and inorganic particles, and the unfired PTFE and inorganic particles are readily supported in this sheet. Unfired PTFE, inorganic particles, and this resin may be included in this composition as composite particles bonded together. The composite particles may form a core-shell structure in which one of the unfired PTFE, inorganic particles, or this resin forms the core, and the component not included in the core from among the unfired PTFE, inorganic particles, or this resin forms the shell.

[0048] This composition is preferably obtained by mixing unfired PTFE particles, inorganic particles, this resin, and a liquid lubricant, and more preferably by mixing an aggregate of unfired PTFE particles, inorganic particles, and this resin with a liquid lubricant. In this case, each component is easily dispersed uniformly within the sheet. This composition may be obtained by distilling off the liquid dispersion medium from a state containing unfired PTFE particles, inorganic particles, and this resin, along with a liquid dispersion medium or liquid lubricant. Alternatively, it may be obtained by adding a trace amount of the liquid component to a mixed powder containing unfired PTFE particles, inorganic particles, and this resin, but without any liquid components such as a liquid dispersion medium or liquid lubricant.

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

[0050] Examples of mixing apparatus for obtaining this composition include stirring devices equipped with blades such as Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers; grinding devices equipped with media such as ball mills, attritors, basket mills, sand mills, sand grinders, Dino mills, disper mats, SC mills, spike mills, and agitator mills; and dispersion devices equipped with other mechanisms such as microfluidizers, nanomizers, ultimateizers, ultrasonic homogenizers, desolvers, dispersers, high-speed impellers, thin-film swirling high-speed mixers, rotating and revolving agitators, and V-type mixers, with V-type mixers being preferred.

[0051] Aggregates of unfired PTFE particles, inorganic particles, and the present resin can be obtained, for example, by removing the liquid dispersion medium from a dispersion containing unfired PTFE particles, inorganic particles, the present resin, and the liquid dispersion medium. The liquid dispersion medium is a compound that is liquid at atmospheric pressure and 25°C. One type of liquid dispersion medium may be used, or two or more types may be used. When two types of liquid dispersion mediums are used, it is preferable that the two liquid dispersion mediums are mutually compatible.

[0052] The liquid dispersion medium is preferably a compound selected from the group consisting of water, amides, ketones, esters, and glycols. Specifically, examples include water, N-methyl-2-pyrrolidone, γ-butyrolactone, methyl ethyl ketone, cyclohexanone, cyclopentanone, ethylene glycol, and propylene glycol, with water being more preferred. In this case, it is easy to obtain a sheet in which uncalcined PTFE particles, inorganic particles, and the resin are uniformly dispersed. The liquid dispersion medium content in the dispersion is preferably 40% by mass or more, and more preferably 60% by mass or more. The liquid dispersion medium content is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0053] The dispersion may further contain a nonionic surfactant to improve dispersion stability. The nonionic surfactant is preferably a glycol-based surfactant, acetylene-based surfactant, silicone-based surfactant, or fluorine-based surfactant, with silicone-based surfactant being more preferred. One nonionic surfactant may be used, or two or more may be used. When two nonionic surfactants are used, it is preferable that the nonionic surfactants be a silicone-based surfactant and a glycol-based surfactant.

[0054] Specific examples of nonionic surfactants include the "Futergent" series (manufactured by Neos Co., Ltd.), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd.), the "Megafac" series (manufactured by DIC Corporation), the "Unidyne" series (manufactured by Daikin Industries, Ltd.), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by Bic Chemie Japan Co., Ltd.), "KF-6011", "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by Dow Chemical Corporation, such as "Tergitol TMN-100X"). If the dispersion contains a nonionic surfactant, the content of the nonionic surfactant in the dispersion is preferably 1 to 15% by mass.

[0055] When the liquid dispersion medium is water, the dispersion may contain a pH adjuster or pH buffer. In this case, the stability of the dispersion is easily improved. Examples of pH adjusters include amines, ammonia, and citric acid. Examples of pH buffers include tris(hydroxymethyl)aminomethane, ethylenediaminetetraacetic acid, ammonium bicarbonate, ammonium carbonate, and ammonium acetate. The dispersion may further contain other components that may be present in this sheet, as described above.

[0056] The dispersion can be obtained by mixing uncalcined PTFE, inorganic particles, the resin, and a liquid dispersion medium. When the resin contains F polymer, the dispersion is preferably obtained by mixing a mixture containing uncalcined PTFE and a liquid dispersion medium with a mixture containing inorganic particles, F polymer particles, and a liquid dispersion medium. When the resin contains an AR polymer, the dispersion is preferably obtained by mixing an inorganic particle with a mixture containing uncalcined PTFE, an AR polymer, and a liquid dispersion medium. Examples of mixing equipment for obtaining a dispersion include those similar to those used to obtain the present composition, and a planetary mixer is preferred.

[0057] The liquid dispersion medium can be removed from a dispersion containing unfired PTFE, inorganic particles, this resin, and the liquid dispersion medium by filtration, heating, distillation, etc., and is preferably removed by heating. The removal of the liquid dispersion medium is preferably carried out by adding a flocculant to the dispersion, and then removing the liquid dispersion medium and, if necessary, the flocculant. When removing by heating, the heating temperature is preferably above the boiling point of the liquid dispersion medium and the flocculant. As a flocculant, primary alcohols are preferred, with methanol, ethanol, isopropanol, and butanol being more preferred. It is preferable to add primary alcohol in an amount that is 0.2 to 1 by mass relative to the liquid dispersion medium in the dispersion.

[0058] This sheet is preferably obtained by casting the composition. In this case, the uncalcined PTFE is more likely to fibrillate, and a sheet in which the inorganic particles are less likely to peel off is easily obtained. Furthermore, a sheet with excellent electrical properties and toughness is easily obtained. The composition is preferably cast by press molding, extrusion molding, or calendering, and more preferably by calendering. Calendering refers to a method of rolling the composition by passing it between multiple rolls.

[0059] The casting of this composition may be carried out using one molding method, or by combining two or more molding methods. Furthermore, the casting may be carried out by repeating one molding method multiple times. For example, a base sheet obtained by extruding this composition may be further calendered and then cast, or a base sheet obtained by calendering this composition may be further calendered and then cast. In this case, it is easy to obtain a sheet of any thickness with excellent toughness and uniformity. Multiple rolls can be used in calendering, and it is preferable to use a combination of four rolls. Possible arrangements of the four rolls include I-type, S-type, inverted L-type, Z-type, and oblique Z-type. The casting of this composition may be carried out while heating at a temperature below the melting point of uncalcined PTFE, or it may be carried out without heating.

[0060] This sheet may also be obtained by laminating and bonding together cast products obtained by casting this composition. In this case, the toughness of the sheet is likely to be improved. One method involves laminating multiple sheets of the composition and rolling them. The thickness and physical properties of the resulting sheet may be adjusted by repeating this lamination and rolling process. When repeating lamination and rolling, it is preferable to change the casting direction of the cast material. Specifically, one method is to cast the composition onto the surface of a single cast material, overlapping them so that their casting directions intersect perpendicularly to each other.

[0061] The number of layers of the cast material is preferably 10 to 1000. The casting ratio of the cast material is preferably 100 to 20000 times. The casting process in this case can be carried out in the same manner as the molding method used to cast the composition, and it is preferable to carry it out by calendering.

[0062] If the composition contains a liquid lubricant, it is preferable to obtain the sheet by casting the composition and removing the liquid lubricant. Methods for removing the liquid lubricant include heating, distillation, and extraction, with heating being preferred. The liquid lubricant does not need to be completely removed; it is sufficient if the total content of uncalcined PTFE, inorganic particles, and the resin in the sheet is 90% by mass or more, and the sheet can form a self-supporting film. The heating temperature is preferably 100 to 200°C. Examples of heating devices include ovens and forced-air drying ovens. The heat source in the device may be a contact-type heat source such as hot air or a hot plate, or a non-contact heat source such as infrared radiation. Furthermore, each heating process may be carried out under normal pressure or under reduced pressure. Furthermore, the atmosphere used for each heating process may be an air atmosphere, an inert gas atmosphere such as helium gas, neon gas, argon gas, or nitrogen gas.

[0063] If this sheet is heated to a temperature above the melting point of PTFE, a sheet containing fired PTFE (hereinafter also referred to as "fired sheet") can be obtained. Like this sheet, the fired sheet is less prone to delamination of inorganic particles and has excellent electrical properties, low thermal expansion, physical strength, and adhesion to other materials. The heating temperature should be above the melting point of PTFE, preferably between 360 and 400°C. The heating time should preferably be between 0.1 and 30 minutes. The heating method and conditions are the same as those used for heating to remove the liquid lubricant described above.

[0064] The thickness of the fired sheet is preferably 50 μm or more, and more preferably 100 μm or more. The thickness of the fired sheet is preferably 500 μm or less, and more preferably 300 μm or less. In this case, it is easier to balance the mechanical strength of the fired sheet with physical properties such as low linear expansion and electrical properties. When this sheet is heat-pressed onto a substrate, a laminate is obtained having a substrate layer and a polymer layer containing PTFE and inorganic particles.

[0065] Examples of substrates include metal substrates such as metal foils made of copper, nickel, aluminum, titanium, and their alloys; heat-resistant resin films such as polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyallyl ether ketone, polyamide-imide, liquid crystalline polyester, and tetrafluoroethylene polymers; prepreg substrates which are precursors to fiber-reinforced resin substrates; ceramic substrates such as silicon carbide, aluminum nitride, or silicon nitride; and glass substrates. The substrate can be planar, curved, or uneven. Furthermore, the substrate may be foil-like, plate-like, film-like, or fibrous. The ten-point average roughness of the substrate surface is preferably 0.01 to 0.05 μm.

[0066] The surface of the substrate may be surface-treated with a silane coupling agent or plasma-treated. The preferred silane coupling agent is one having a functional group such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatetopropyltriethoxysilane.

[0067] Methods of heat-pressure bonding include a method of sandwiching the substrate and the sheet between a pair of opposing hot plates and applying pressure, a method of passing the substrate and the sheet between a pair of opposing rolls, and a method of applying pressure to the substrate and the sheet with rolls on a hot plate. The temperature for heat bonding is preferably 200°C or higher, more preferably above the melting point of PTFE, and even more preferably 350°C or higher. A temperature of 400°C or lower is preferred. It is preferable to sinter the PTFE during the heating process.

[0068] The heat-compression bonding may be performed under reduced pressure. In this case, it is preferable to perform the bonding at a vacuum level of 20 kPa or less, from the viewpoint of suppressing deterioration due to oxidation of the substrate and the sheet. It is preferable to perform the heat-compression bonding using a vacuum press. During heat sealing, it is preferable to either place a release film between the surface of the sheet and the heat plate or roll, or to surface treat the surface of the heat plate or roll with a release agent, in order to suppress adhesion of the sheet to the heat plate or roll.

[0069] The thickness of the release film is preferably 50 to 150 μm. Polyimide films are used as release films, with specific examples including "Apical NPI" (manufactured by Kaneka Corporation), "Kapton EN" (Toray DuPont), and "Upirex S" (manufactured by Ube Industries).

[0070] This sheet may be heat-pressed onto only one surface of the substrate, or it may be heat-pressed onto both surfaces of the substrate. In the former case, a laminate is obtained having a substrate layer and a polymer layer on one surface of the substrate layer, and in the latter case, a laminate is obtained having a substrate layer and polymer layers on both surfaces of the substrate layer. Suitable examples of laminates include a metal-clad laminate having a metal foil and a polymer layer on at least one surface of the metal foil, and a polyimide film and a multilayer film having polymer layers on both surfaces of the polyimide film. The peel strength between the polymer layer and the substrate layer is preferably 10 to 100 N / cm. Furthermore, the substrate layer may be removed from the laminate to obtain a sheet containing PTFE, inorganic particles, and the resin.

[0071] This sheet, the baked sheet, and the laminate having a substrate layer and a polymer layer are useful as antenna components, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry products, heat dissipation components, paints, cosmetics, etc. Specifically, this includes wire insulation materials for aircraft and other applications, enamel wire insulation materials used in motors for electric vehicles and other applications, electrical insulation tapes, insulating tapes for oil drilling, oil transport hoses, hydrogen tanks, printed circuit board materials, separation membranes such as microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes and gas separation membranes, electrodes and electrolyte binders for lithium secondary batteries and fuel cells, copy rolls, furniture, car dashboards, covers for home appliances and other applications, sliding members, tension ropes, wear pads, wear strips, tube lamps, test sockets, wafer guides, wear parts for centrifugal pumps, chemical and water supply pumps, tools such as shovels, files, drills and saws, boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, dies, toilets, container insulation materials, power devices, transistors, thyristors, rectifiers, transformers, and power MOS It is useful in FETs, CPUs, heat sinks, metal heat sinks, blades for wind turbines, wind power generation equipment, and aircraft, casings 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 such as sputtering and various dry etching equipment, and as electromagnetic shielding. Examples of sliding members include load bearings, yaw bearings, sliding shafts, valves, bearings, bushings, seals, thrust washers, wear rings, pistons, slide switches, gears, cams, belt conveyors, and food transport belts.

[0072] Although the present invention has described the sheet, a method for manufacturing the sheet, and a method for manufacturing a laminate containing the sheet, the present invention is not limited to the configuration of the embodiments described above. For example, the sheet may have any other configurations added to the configuration of the above embodiment, or it may be replaced with any configuration that performs a similar function. Also, the method for manufacturing the sheet and the method for manufacturing a laminate containing the sheet may have any other additional steps added to the configuration of the above embodiment, or it may be replaced with any step that produces a similar effect. [Examples]

[0073] 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 component and member [Dispersion] Dispersion 1: An aqueous dispersion containing 60% by mass of particles (D50: 0.3 μm) made of uncalcined PTFE (PTFE1; melting point: 327°C) (AGC Corporation "AD-911E"). [Inorganic particles] Inorganic particle 1: Spherical silica (D50: 1 μm) [Resin particles] Resin particle 1: Contains TFE units, NAH units, and PPVE units in the following order: 97.9 mol%, 0.1 mol%, and 2.0 mol%, respectively, with carbonyl group-containing groups having a main chain of 1 × 10¹⁶ carbon atoms. 6 Particles (D50: 2.1 μm) made of a tetrafluoroethylene polymer (F resin 1; melting temperature: 300°C) with 1000 particles per unit. Resin particles 2: Particles (D50: 1.8 μm) made of a tetrafluoroethylene polymer (F resin 2; melting temperature: 305°C) containing 98.7 mol% and 1.3 mol% TFE units and PPVE units, respectively, and lacking carbonyl group-containing groups, hydroxyl groups, epoxy groups, and amino groups. Particles made of uncalcined PTFE powder obtained by removing water from a dispersion of resin particles (3 parts) to a dispersion of 1 part resin particles. [Resin varnish] Varnish 1: Water varnish containing an aromatic polyamide imide precursor (PAI1, containing carboxyl and amide groups; acid value: 50 mg KOH / g) [Surfactants] Surfactant 1: Polyoxyalkylene-modified polydimethylsiloxane having dimethylsiloxane units in the main chain and oxyethylene groups in the side chains. [Glass cloth] Glass cloth 1: Glass cloth (Arisawa Fiberglass Co., Ltd. "1078")

[0074] 2. Examples of sheet manufacturing (Example 1) A dry blend of inorganic particles 1 and resin particles 1, water, and surfactant 1 were placed in a planetary mixer and kneaded. Subsequently, a mixture of dispersion 1 and varnish 1, along with water, was added in several batches and stirred to obtain mixture 1. Methanol was added while stirring mixture 1 to recover aggregates 1 containing PTFE particles 1, inorganic particles 1, resin particles 1, and PAI 1, which were formed from 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 aggregate 1, heated under vacuum at 60°C for 24 hours, and dodecane were placed in a V-type mixer and mixed for 5 minutes at 24°C and a rotation speed of 10 rpm to obtain a paste-like liquid composition 1.

[0075] Liquid composition 1 was cast by passing it between a pair of rolling rolls to obtain a base sheet 1 with a thickness of 3 mm. Base sheet 1 was cast using an inverted L-shaped calender and further heated at 150°C for 30 minutes to remove dodecane, obtaining 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 PAI 1 or polyamide-imide (a reaction product of PAI 1) was 98% by mass or more, the content of PTFE 1 was 15% by mass or more, the total content of F resin 1 and PAI 1 or polyamide-imide (a reaction product of PAI 1) was 15% by mass or more, and the content of inorganic particles was 50% by mass or more.

[0076] (Example 2) Mixture 2 was obtained in the same manner as in Example 1, except that resin particle 1 was replaced with resin particle 2. Sheet 2 was obtained in the same manner as in Example 1, using mixture 2 instead of mixture 1. (Example 3) Sheet 3 was obtained in the same manner as in Example 1, except that resin particle 1 was changed to resin particle 2 and varnish 1 was not used. (Example 4) After immersing glass cloth 1 in mixture 2, it was heated at 100°C and dried to obtain a base sheet in which PTFE particles 1 were impregnated into the glass cloth 1. The base sheet was cast using an inverted L-shaped calender to obtain a sheet 4 with a thickness of 200 μm and a glass cloth 1 content of more than 10 mass in the sheet. (Example 5) 15 parts by mass of resin particles 3, 13 parts by mass of resin particles 1, 60 parts by mass of inorganic particles 1, 2 parts by mass of PAI 1, and 10 parts by mass of tetradecane were added to a Henschel mixer and stirred at 1000 rpm for 2 minutes to obtain aggregate 5. Sheet 5 was obtained in the same manner as in Example 1, except that aggregate 5 was replaced with aggregate 1.

[0077] 3. Example of sheet evaluation 3-1. Evaluation of flexural resistance A 50mm x 100mm rectangular test specimen was cut from each of sheets 1 through 5. Each test specimen was bent at a 180° angle along a 2mm mandrel according to the method specified in JIS K 5600-5-1. The bent specimens were visually inspected, and their bending resistance was evaluated according to the following criteria. [Evaluation Criteria] ○: No cracks were observed in the test specimen. ×: Cracks were observed in the test specimen.

[0078] 3-2. Evaluation of powder fallout After performing the evaluation in 3-1, each sheet was removed from the mandrel. The amount of powder adhering to the mandrel was visually checked, and the ease of powder removal was evaluated according to the following criteria. [Evaluation Criteria] ○: No powder was found to be adhering to the mandrel. ×: Powder adhesion to the mandrel was observed.

[0079] 3-3. Evaluation of Adhesion Each of sheets 1 to 5 was placed on top of a long copper foil (thickness: 18 μm, average surface roughness at 10 points: 0.8 μm), and the two were heat-pressed together using a vacuum press at 380°C to obtain laminates 1 to 5 having a copper foil and a polymer layer containing fired PTFE particles 1 on its surface. Rectangular test specimens, 100 mm in length and 10 mm in width, were cut from each of the laminates 1 to 5. The specimen was fixed 50 mm from one end in the longitudinal direction, and the copper foil and polymer layer were peeled off at a tensile speed of 50 mm / min, at a 90° angle to the specimen from the other end in the longitudinal direction. The maximum load at which peeling occurred was defined as the peel strength (N / cm), and the adhesion of the sheet was evaluated according to the following criteria. [Evaluation Criteria] ○: The peel strength was 12 N / cm or higher. △: The peel strength was 10 N / cm or more and less than 12 N / cm. ×: The peel strength was less than 10 N / cm.

[0080] 3-4. Evaluation of Electrical Characteristics For each of the laminates 1 to 4, the copper foil was removed by etching with an aqueous ferric chloride solution to obtain fired sheets 1 to 4, each consisting of a single polymer layer. The dielectric constant and dielectric loss tangent (measurement frequency: 10 GHz) of the fired sheets were measured using the SPDR (Split Post Dielectric Resonance) method. The evaluation results for each are summarized in Table 1 below.

[0081] [Table 1] [Industrial applicability]

[0082] As is clear from the above results, the sheet of the present invention exhibited excellent flexibility, adhesion, and low powder shedding. Furthermore, the fired sheet obtained from the sheet of the present invention exhibited excellent low dielectric constant and low dielectric loss tangent. Therefore, it is considered that the sheet of the present invention exhibits excellent uniformity of component distribution and highly exhibits the properties of unfired PTFE, inorganic particles, and the present resin. The sheet of the present invention, as well as the fired sheet and laminate obtained from the sheet of the present invention, are less prone to peeling of inorganic particles, and have excellent electrical properties, low linear expansion, physical strength, and adhesion to other materials, making them useful as printed circuit board materials.

Claims

1. A sheet comprising uncalcined polytetrafluoroethylene, inorganic particles, and a heat-meltable tetrafluoroethylene polymer having at least one functional group selected from the group consisting of carbonyl group-containing groups, hydroxyl group-containing groups, epoxy groups, and amino groups, wherein the inorganic particle content is 20% by mass or more, and the total content of the polytetrafluoroethylene, the inorganic particles, and the heat-meltable tetrafluoroethylene polymer is 90% by mass or more.

2. The sheet according to claim 1, wherein the inorganic particles are particles comprising at least one inorganic substance selected from the group consisting of silica, boron nitride, and titanium dioxide.

3. The sheet according to claim 1, wherein the melting temperature of the heat-meltable tetrafluoroethylene polymer is 260 to 320°C.

4. The sheet according to claim 1, wherein the polytetrafluoroethylene content is 10% by mass or more.

5. The sheet according to claim 1, wherein the content of the heat-meltable tetrafluoroethylene polymer is 5% by mass or more.

6. The sheet according to claim 1, wherein the ratio of the content of inorganic particles to the sum of the content of polytetrafluoroethylene and the content of the heat-meltable tetrafluoroethylene polymer is 0.1 or more.

7. The sheet according to claim 1, wherein the thickness is 50 μm or more.

8. A method for producing a sheet according to claim 1, comprising casting a liquid composition containing the polytetrafluoroethylene particles, the inorganic particles, and the heat-meltable tetrafluoroethylene polymer.

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

10. The manufacturing method according to claim 8 or 9, wherein the liquid composition is cast and the resulting casts are laminated and bonded together.

11. A method for producing a fired sheet, comprising heating the sheet according to any one of claims 1 to 7 to fire the polytetrafluoroethylene.

12. A method for producing a laminate, comprising heat-pressing a sheet and a substrate according to any one of claims 1 to 7 to obtain a laminate having a substrate layer and a polymer layer.

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