Method for producing a laminate having a layer containing a heat-fusible tetrafluoroethylene polymer

Abstract

[Problem] To provide a production method for providing a laminate which exhibits excellent peeling strength and reliability such as water resistance, and improves adhesion between a substrate and a layer which has a tetrafluoroethylene polymer. [Solution] A method for producing a laminate which has a layer containing a thermofusible tetrafluoroethylene polymer, said method involving the formation of a layer containing a thermofusible tetrafluoroethylene polymer by coating a substrate with a dispersion containing a powder of a thermofusible tetrafluoroethylene polymer, forming a coating film by drying the same, and heating the obtained coating film, wherein the steps from at least forming the coating film until after the layer has been formed involve heating and compressing the substrate and the coating film or layer.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a laminate having a layer containing a heat-fusible tetrafluoroethylene-based polymer. [Background technology]

[0002] Tetrafluoroethylene-based polymers have excellent physical properties such as electrical insulation, water and oil repellency, chemical resistance, and heat resistance, and are widely used in electronic equipment parts, automobile parts, etc. In particular, tetrafluoroethylene-based polymers have excellent low dielectric properties and low dielectric loss tangent, and their use in the electronic equipment field is attracting attention due to their excellent properties.

[0003] For example, laminates in which a tetrafluoroethylene-based polymer is laminated with a metal substrate such as copper, or laminates in which a tetrafluoroethylene-based polymer is laminated with a polyimide resin having excellent heat resistance, are used as printed circuit boards. However, since the tetrafluoroethylene-based polymer has poor adhesiveness to other resins and metals, various attempts have been made to improve the adhesiveness.

[0004] For example, Patent Document 1 describes a method for producing a laminate in which a dispersion containing a tetrafluoroethylene-based polymer powder is applied to a substrate and heated to form a layer containing a tetrafluoroethylene-based polymer. However, the layer formed by this production method may blister or crack due to gases or the like generated during heating. This is known to result in uneven layer thickness and variations in electrical properties (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 159102 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-222899 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, laminates in which a dispersion containing a tetrafluoroethylene-based polymer is applied to a substrate of other resin or metal and heated to form a layer containing a tetrafluoroethylene-based polymer have been required to have improved adhesion between the layer containing a tetrafluoroethylene-based polymer and the substrate, improved water resistance and peel strength of the laminate, and suppressed deterioration of peel strength and the like during use, i.e., improved reliability of the laminate during use.

[0007] The present inventors aimed to provide a laminate having improved adhesion between a layer containing a tetrafluoroethylene-based polymer and a substrate, and excellent peel strength and water resistance. As a result, they investigated methods for producing a laminate having the layer and a substrate, and completed the present invention.

[0008] The present invention provides a manufacturing method that improves the adhesion between a layer containing a tetrafluoroethylene-based polymer and a substrate, and gives a laminate that is excellent in peel strength and water resistance. [Means for solving the problem]

[0009] The present invention has the following aspects. A method for producing a laminate having a layer containing a heat-fusible tetrafluoroethylene-based polymer, comprising: applying a dispersion containing a powder of a heat-fusible tetrafluoroethylene-based polymer onto a substrate, drying the dispersion to form a coating film, further heating the resulting coating film to form a layer containing the heat-fusible tetrafluoroethylene-based polymer, and heat-compressing the coating film or the layer and the substrate at least during the process from the formation of the coating film to the end of the formation of the layer. [2] The method for producing a laminate according to the above [1], wherein the heat-meltable tetrafluoroethylene-based polymer is a polymer containing units based on perfluoro(alkyl vinyl ether) and having a polar functional group, or a polymer containing 2 to 5 mol% of units based on perfluoro(alkyl vinyl ether) based on the total units and having no polar functional group. [3] The method for producing a laminate according to [1] or [2] above, wherein the substrate is a copper foil or a polyimide film. [4] The method for producing a laminate according to any one of [1] to [3], wherein the temperature of the heat-compression is equal to or higher than the glass transition temperature of the heat-fusible tetrafluoroethylene-based polymer and is equal to or lower than a temperature 100°C higher than the melting temperature of the heat-fusible tetrafluoroethylene-based polymer. [5] The method for producing a laminate according to any one of [1] to [4], wherein the pressure of the heat compression is 0.2 MPa or more and 10 MPa or less. [6] The method for producing a laminate according to any one of [1] to [5], wherein the heat compression is carried out when forming the layer. [7] The method for producing a laminate according to any one of [1] to [6] above, wherein the ratio of the thickness of the coating film after the heat-compression to the thickness of the coating film before the heat-compression, or the ratio of the thickness of the layer after the heat-compression to the thickness of the layer before the heat-compression, is 0.1 to 0.8. [8] The method for producing a laminate according to any one of [1] to [7], wherein the thickness of the layer after the heat compression is 40 μm or more. [9] The method for producing a laminate according to any one of [1] to [8] above, wherein the dispersion further contains an inorganic filler.

[10] The method for producing a laminate according to any one of [1] to [9] above, wherein the dispersion further contains an inorganic filler that has been surface-treated with a silane coupling agent.

[11] The method for producing a laminate according to any one of [1] to

[10] above, wherein the dispersion contains an inorganic filler having an average particle size of 10 μm or more.

[12] The method for producing a laminate according to any one of [9] to

[11] above, wherein the mass ratio of the inorganic filler to the heat-fusible tetrafluoroethylene-based polymer in the dispersion is 0.5 to 1.5.

[13] The method for producing a laminate according to any one of [1] to

[12] above, wherein the dispersion further contains a non-thermofusible polytetrafluoroethylene powder.

[14] The method for producing a laminate according to any one of [1] to

[13] above, wherein the dispersion further contains an aromatic polymer.

[15] The method for producing a laminate according to any one of [1] to

[14] above, wherein the dispersion further contains a silane coupling agent. [Effects of the Invention]

[0010] According to the present invention, it is possible to improve the adhesion between a layer containing a tetrafluoroethylene-based polymer and various substrates, and to produce a laminate having excellent peel strength and water resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following terms have the following meanings: The term "thermally meltable tetrafluoroethylene-based polymer" refers to a polymer containing units (hereinafter also referred to as TFE units) based on tetrafluoroethylene (hereinafter also referred to as TFE), and a melt-flowable polymer that has a temperature at which the melt flow rate is 1 to 1000 g / 10 min under a load of 49 N. The "glass transition temperature (Tg) of a polymer" is a value measured by analyzing a polymer using dynamic mechanical analysis (DMA). The "melting temperature (melting point) of a polymer" is the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). "D50" is the average particle size of a target substance (powder or inorganic filler), and is the cumulative 50% diameter based on volume of the target substance determined by laser diffraction / scattering. In other words, the particle size distribution of the target substance is measured by laser diffraction / scattering, and a cumulative curve is calculated with the total volume of the target substance group as 100%. D50 is the particle size at the point on that cumulative curve where the cumulative volume is 50%. "D90" is the cumulative volume particle size of the object, and is the volume-based cumulative 90% diameter of the object that can be determined in the same manner as "D50". The "viscosity of the dispersion" is a value measured for the dispersion using a Brookfield 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 measured values ​​is used. The "thixotropy ratio of the dispersion" is a value calculated by dividing the viscosity obtained by measuring the dispersion at a rotation speed of 30 rpm by the viscosity obtained by measuring the dispersion at a rotation speed of 60 rpm. The term "unit based on a monomer" refers to an atomic group based on the monomer formed by polymerization of the monomer. The unit may be a unit formed directly by the polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by treating the polymer. Hereinafter, a unit based on monomer a may also be simply referred to as a "monomer a unit."

[0012] The manufacturing method of the present invention (hereinafter also referred to as this method) is a method in which a dispersion (hereinafter also referred to as this dispersion) containing a powder (hereinafter also referred to as this powder) of a heat-fusible tetrafluoroethylene-based polymer (hereinafter also referred to as F polymer) is applied to a substrate, dried to form a coating film, the resulting coating film is further heated to form a layer containing the heat-fusible tetrafluoroethylene-based polymer, and at least at any stage from the formation of the coating film to the stage after the formation of the layer, the coating film or the layer and the substrate are heated and compressed to obtain a laminate (hereinafter also referred to as this laminate).

[0013] The melting temperature of the F polymer contained in the present powder is preferably 200° C. or higher, more preferably 250° C. or higher, and even more preferably 280° C. or higher. From the viewpoint of moldability, the melting temperature of the F polymer is preferably 325° C. or lower.

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

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

[0016] The polar functional group may be contained in a monomer unit in the F polymer or in a terminal group of the main chain of the polymer. Examples of the latter include an F polymer having a polar functional group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer having a polar functional group obtained by subjecting an F polymer to plasma treatment or ionizing radiation treatment. The polar functional group is preferably a hydroxyl group-containing group or a carbonyl group-containing group, and particularly preferably a carbonyl group-containing group. When the F polymer has an oxygen-containing polar group, the number of oxygen-containing polar groups in the F polymer is 1×10 6 The number of oxygen-containing polar groups per unit is preferably 10 to 5000, more preferably 100 to 3000. The number of oxygen-containing polar groups in the F polymer can be quantified by the composition of the polymer or the method described in WO 2020 / 145133.

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

[0018] Suitable embodiments of the F polymer include polymer (1) containing TFE units and PAVE units and having a polar functional group, or polymer (2) containing TFE units and PAVE units, with 2 to 5 mol% of PAVE units relative to the total monomer units, and having no polar functional group. These polymers form microspherulites in the product, which tends to improve the properties of the resulting product.

[0019] Polymer (1) is preferably a polymer containing TFE units, PAVE units, and units derived from a monomer having a hydroxyl group-containing group or a carbonyl group-containing group, and preferably contains 90 to 99 mol% TFE units, 0.5 to 9.97 mol% PAVE units, and 0.01 to 3 mol% units derived from the monomer, based on all units. The monomer is preferably itaconic anhydride, citraconic anhydride, or 5-norbornene-2,3-dicarboxylic anhydride (also known as himic acid anhydride; hereinafter also referred to as "NAH"). Specific examples of polymer (1) include the polymers described in WO 2018 / 16644.

[0020] The polymer (2) is composed of only TFE units and PAVE units, and preferably contains 95 to 98 mol % of TFE units and 2 to 5 mol % of PAVE units based on the total monomer units. The content of PAVE units in the polymer (2) is preferably 2.1 mol % or more, more preferably 2.2 mol % or more, based on the total monomer units. The term "polymer (2) has no polar functional group" means that the number of carbon atoms constituting the polymer main chain is 1 × 106 This means that the number of polar functional groups that the polymer has is less than 500 per unit area. The number of polar functional groups is preferably 100 or less, and more preferably less than 50. The lower limit of the number of polar functional groups is usually 0.

[0021] Polymer (2) may be produced using a polymerization initiator or chain transfer agent that does not generate a polar functional group as the terminal group of the polymer chain, or may be produced by fluorinating an F polymer having a polar functional group. Fluorination methods include methods using fluorine gas (see, for example, JP 2019-194314 A).

[0022] The present powder is a powder containing an F polymer, and the amount of the heat-fusible F polymer in the powder is preferably 80% by mass or more, and more preferably 100% by mass. The D50 of the present powder is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 8 μm or less. The D50 of the present powder is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 1 μm or more. The D90 of the present powder is preferably less than 100 μm, and more preferably 90 μm or less. If the D50 and D90 of the present powder are within these ranges, the surface area will be large, and the dispersibility of the present powder will likely be further improved.

[0023] The powder may contain other resins or inorganic substances different from the F polymer. Specific examples of other resins include aromatic polymers such as aromatic polyimide, aromatic maleimide, styrene elastomer, and aromatic polyamic acid. A specific example of the inorganic material is silica. The powder may form a core-shell structure with an F polymer as the core and a resin or inorganic compound other than an F polymer as the shell, or may form a core-shell structure with an F polymer as the shell and a resin or inorganic compound other than an F polymer as the core. The content of F powder in the present dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 60% by mass or less, more preferably 40% by mass or less.

[0024] In this method, the present powder is dispersed in a dispersion medium, which is then applied to a substrate. The dispersion medium is preferably degassed to prevent the formation of voids and reduce the uniformity of the component distribution in the molded product. The dispersion medium is liquid, preferably a low-viscosity liquid or a high-viscosity liquid, more preferably a low-viscosity liquid. The dispersion medium may consist of one type of liquid or a mixture of multiple liquids.

[0025] A low-viscosity liquid is a liquid compound with a viscosity at 25°C of more than 0 mPa·s and less than 10 mPa·s, which does not react with F polymers or other resins. The boiling point of a low-viscosity liquid is preferably 75°C or higher, more preferably 100°C or higher. The boiling point of a low-viscosity liquid is preferably 300°C or lower, more preferably 250°C or lower. The low-viscosity liquid may be water or a non-aqueous dispersion medium, preferably an amide, ketone, or ester, more preferably N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, or cyclopentanone.

[0026] A highly viscous liquid is a liquid compound that has a viscosity of more than 10 mPa·s at 25°C and does not react with F polymers or other resins. The viscosity of a highly viscous liquid is preferably 200 mPa·s or less. The boiling point of a highly viscous liquid is preferably 100°C or higher. The boiling point of a highly viscous liquid is preferably 350°C or less, more preferably 300°C or less. The highly viscous liquid is preferably a glycol, glycol ether or glycol acetate, more preferably a glycol monoalkyl ether, glycol monoaryl ether, glycol monoalkyl ether acetate or glycol monoaryl ether acetate, and even more preferably a glycol monoalkyl ether. Specific examples of highly viscous liquids include ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol monobutyl ether, propylene glycol monophenyl ether, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0027] The content of the dispersion medium in the dispersion liquid is preferably 30% by mass or more, and more preferably 90% by mass or less, and more preferably 80% by mass or less. The solid content of the dispersion is preferably 20% by mass or more, and more preferably 30% by mass or more, where the total mass of the dispersion is 100%. From the viewpoint of dispersibility of the dispersion, the solid content is preferably 60% by mass or less, and more preferably 50% by mass or less. The solid content of the dispersion means the total amount of substances that form the solid content in the molded product formed from the dispersion. For example, when the dispersion contains the F polymer, an inorganic filler and an aromatic polymer, which will be described later, the total content of these components is the solid content of the dispersion.

[0028] The dispersion is a liquid containing the present powder, and is a liquid composition in which the present powder is dispersed. The dispersion may contain a third component other than the powder, such as an inorganic filler for improving the electrical properties of the laminate and the low linear expansion of the F polymer-containing layer in the laminate, a surfactant for improving dispersion stability and handleability, or an aromatic polymer for improving the peel strength and processability of the laminate.

[0029] The inorganic filler is preferably a nitride filler or an inorganic oxide filler, more preferably a boron nitride filler, beryllia filler (beryllium oxide filler), silicate filler (silica filler, wollastonite filler, talc filler, steatite filler), metal oxide filler such as cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, or titanium oxide, further preferably a silica filler, steatite filler, or boron nitride filler, and particularly preferably a silica filler. The silica content in the silica filler is preferably 50% by mass or more, more preferably 75% by mass or more, and is preferably 100% by mass or less, more preferably 90% by mass or less.

[0030] The inorganic filler is preferably at least partially surface-treated. Examples of surface treatment agents used for such surface treatment include polyhydric alcohols such as trimethylolethane, pentaerythritol, and propylene glycol, saturated fatty acids such as stearic acid and lauric acid, esters thereof, alkanolamines, amines such as trimethylamine and triethylamine, paraffin wax, silane coupling agents, silicones, and polysiloxanes. The silane coupling agent is preferably a silane coupling agent having a functional group such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatopropyltriethoxysilane. When the inorganic filler is surface-treated with a silane coupling agent having a functional group, voids are less likely to occur in the layer containing the F polymer in the present laminate, and the present laminate tends to have excellent water resistance. In addition, the inorganic filler is less likely to peel off from the layer containing the F polymer.

[0031] The average particle size D50 of the inorganic filler is preferably 30 μm or less, more preferably 20 μm or less, and is preferably 0.1 μm or more, more preferably 1 μm or more. When the dispersion contains an inorganic filler, the inorganic filler preferably has a D50 of 10 μm or more. In this case, voids are less likely to occur in the layer containing the F polymer in the laminate, and the laminate is more likely to have excellent water resistance. In addition, since the surface area of ​​the inorganic filler is small, resistance at the interface with the F polymer is less likely to occur, and the laminate is more likely to have excellent electrical properties. The shape of the inorganic filler may be any of granular, needle-like (fibrous), and plate-like. Specific shapes of the inorganic filler include spherical, scale-like, layer-like, leaf-like, apricot-like, columnar, cockscomb-like, equiaxial, leaf-like, mica-like, block-like, flat, wedge-like, rosette-like, net-like, and prismatic shapes, with spherical and scale-like shapes being preferred. In addition to the above shapes, the inorganic filler may have various shapes such as a plate shape, a hollow shape, a honeycomb shape, and the like. When a hollow filler is used, the hollowness (average volume ratio of voids per particle) is preferably 40 to 80%. The particle strength of the hollow filler is preferably 20 MPa or more. The particle strength is the particle strength when the remaining rate of the hollow filler after pressure pressing is 50%. The particle strength can be calculated from the apparent density of the hollow filler and the apparent density of the pellet obtained by pressure pressing the hollow filler.

[0032] The inorganic filler may be a single inorganic filler or a combination of two or more inorganic fillers. In the latter case, it is preferable to use at least a silica filler. In the latter case, it is also preferable to use a hollow filler and a non-hollow filler in combination. Specific preferred examples of inorganic fillers include silica fillers (such as the "Admafine" series manufactured by Admatechs Co., Ltd.), zinc oxide surface-treated with an ester such as propylene glycol dicaprate (such as the "FINEX" series manufactured by Sakai Chemical Industry Co., Ltd.), spherical fused silica fillers (such as the "SFP" series manufactured by Denka Corporation), rutile-type titanium oxide fillers coated with a polyhydric alcohol and an inorganic substance (such as the "Tipaque" series manufactured by Ishihara Sangyo Kaisha), rutile-type titanium oxide fillers surface-treated with an alkylsilane (such as the "JMT" series manufactured by Teika Corporation), steatite fillers (such as the "BST" series manufactured by Nippon Talc Co., Ltd.), and boron nitride fillers (such as the "UHP" series manufactured by Showa Denko KK, and the "HGP" series and "GP" series manufactured by Denka).

[0033] When the dispersion contains an inorganic filler, the content is preferably 1% by mass or more, and more preferably 5% by mass or more. The content is preferably 40% by mass or less, and more preferably 30% by mass or less. The mass ratio of the inorganic filler content to the F polymer content in the dispersion is preferably 0.5 or more, and more preferably 0.7 or more. The mass ratio is preferably 1.5 or less, and more preferably 1.2 or less. In this case, the dispersion stability of the dispersion is more likely to be improved, and the electrical properties of the laminate are more likely to be improved.

[0034] The surfactant is preferably a nonionic surfactant. The hydrophilic portion of the surfactant preferably has an oxyalkylene group or an alcoholic hydroxyl group. The oxyalkylene group may be composed of one type or two or more types, and in the latter case, the different types of oxyalkylene groups may be arranged randomly or in blocks. The oxyalkylene group is preferably an oxyethylene group.

[0035] The hydrophobic portion of the surfactant preferably has an acetylene group, a polysiloxane group, a perfluoroalkyl group, or a perfluoroalkenyl group. The surfactant is preferably a glycol surfactant, an acetylene surfactant, a silicone surfactant or a fluorine surfactant, and more preferably a silicone surfactant. One or more types of nonionic surfactants may be used. When two types of nonionic surfactants are used, the nonionic surfactants are preferably a silicone-based surfactant and a glycol-based surfactant. The fluorosurfactant is preferably a fluorosurfactant having a hydroxyl group, particularly an alcoholic hydroxyl group or an oxyalkylene group, and a perfluoroalkyl group or a perfluoroalkenyl group. Specific examples of such surfactants include the "Ftergent" series (manufactured by Neos Corporation, Ftergent is a registered trademark), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd., Surflon is a registered trademark), the "Megafac" series (manufactured by DIC Corporation, Megafac is a registered trademark), the "Unidyne" series (manufactured by Daikin Industries, Ltd., Unidyne is a registered trademark), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", and "BYK-3456" (manufactured by BYK Japan), "KF-6011", and "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by The Dow Chemical Company, such as "Tergitol TMN-100X", Tergitol is a registered trademark). When the present dispersion contains a surfactant, the content thereof is preferably 1 to 15% by mass, which increases the affinity between the components and tends to further improve the dispersion stability of the present dispersion.

[0036] The aromatic polymer is preferably an aromatic polyimide, an aromatic polyamideimide, an aromatic maleimide, an aromatic elastomer (such as a styrene elastomer), an aromatic polyamic acid, or a polyphenylene ether, and more preferably an aromatic polyimide or an aromatic polyamic acid. The aromatic polyimide may be thermoplastic or thermosetting. A thermoplastic polyimide refers to a polyimide in which imidization is complete and no further imidization reaction occurs.

[0037] Specific examples of aromatic polyimides include the "Neoprim (registered trademark)" series (manufactured by Mitsubishi Gas Chemical Company, Inc.), the "Spixeria (registered trademark)" series (manufactured by Somar), the "Q-PILON (registered trademark)" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology Co., Ltd.), the "Tomide (registered trademark)" series (manufactured by T&K TOKA Corporation), the "KPI-MX" series (manufactured by Kawamura Sangyo Co., Ltd.), and the "UPIA (registered trademark)-AT" series (manufactured by Ube Industries, Ltd.). Specific examples of aromatic polyamideimides include "HPC-1000" and "HPC-2100D" (both manufactured by Showa Denko Materials Co., Ltd.). When the present dispersion contains an aromatic polymer, the content thereof is preferably from 1 to 30% by mass, more preferably from 5 to 20% by mass, which tends to improve the peel strength and UV processability of the present laminate.

[0038] In addition to the third component, the dispersion may contain non-thermofusible polytetrafluoroethylene (hereinafter also referred to as PTFE). In this case, the physical properties based on the non-thermofusible PTFE are well exhibited, and the laminate is likely to have excellent electrical properties. Furthermore, when the layer containing the F polymer in the laminate further contains an inorganic filler and non-thermofusible PTFE, the non-thermofusible PTFE is partially fibrillated when the layer containing the F polymer and the substrate are heated and compressed, resulting in a high degree of inorganic filler support and suppressed powder fall-off, which is preferable. Note that non-thermofusible PTFE means PTFE at which there is no temperature at which the melt flow rate becomes 1 to 1000 g / 10 min under a load of 49 N. Non-thermofusible PTFE may be a TFE homopolymer, or may be a modified PTFE such as a copolymer having, in addition to TFE units, a trace amount of units based on PAVE, hexafluoropropylene (hereinafter also referred to as "HFP") or fluoroalkyl ether (hereinafter also referred to as "FAE"). The dispersion preferably contains the non-thermofusible PTFE as a non-thermofusible PTFE powder, the D50 of which is preferably between 0.1 and 1 μm. When the dispersion contains non-thermofusible PTFE, the content of the non-thermofusible PTFE powder is preferably 1% by mass or more, more preferably 10% by mass or more. This content is preferably 60% by mass or less, more preferably 40% by mass or less. The ratio of the content of the non-thermofusible PTFE powder in the dispersion to the content of the F powder is preferably 1% by mass or more, more preferably 3% by mass or more. This ratio is preferably 100 or less. In this case, the laminate tends to have excellent electrical properties and water resistance.

[0039] The dispersion may also contain a silane coupling agent from the viewpoint of adhesiveness of the layer containing the F polymer. In this case, the dispersion is likely to have excellent dispersion stability and film-forming properties. Furthermore, when the dispersion contains an inorganic filler, the F powder and the inorganic filler are more firmly bonded together, and as a result, the inorganic filler is less likely to fall off from the laminate. Examples of the silane coupling agent include compounds similar to the silane coupling agents used in the surface treatment of the inorganic filler.

[0040] When the dispersion contains a silane coupling agent, the content is preferably 0.1% by mass or more, more preferably 1% by mass or more, and is preferably 20% by mass or less, more preferably 10% by mass or less. Furthermore, when the dispersion contains a silane coupling agent, the ratio of the content of the silane coupling agent to the content of the F powder is preferably 0.01 or more, more preferably 0.05 or more, relative to the content of the F powder being 1. The ratio of the content of the silane coupling agent to the content of the F powder is preferably 0.3 or less, more preferably 0.1 or less. When the content of the silane coupling agent is within the above range, the dispersion tends to have excellent dispersion stability. Preferred examples of the silane coupling agent include the silane coupling agents used in the surface treatment of the inorganic filler.

[0041] In this method, the dispersion is applied to a substrate and dried to form a coating film. The substrate may be a metal substrate or a resin substrate. The metal substrate is preferably a metal foil. By processing the metal foil, the molded article of the present invention can be suitably used as a printed circuit board. Examples of metals constituting the metal foil include copper, copper alloys, stainless steel, nickel, nickel alloys, aluminum, aluminum alloys, titanium, and titanium alloys. As the metal foil, copper foil is preferred, with rolled copper foil with no front or back distinction or electrolytic copper foil with front and back distinction being more preferred, and rolled copper foil being even more preferred. Rolled copper foil has a small surface roughness, so that transmission loss can be reduced even when the laminate is processed into a printed circuit board. Furthermore, rolled copper foil is preferably used after immersing in a hydrocarbon organic solvent to remove rolling oil. The ten-point average roughness of the surface of the metal foil is preferably 0.01 to 0.05 μm.

[0042] The metal substrate may also be a metal foil with a carrier containing two or more layers of metal foil, such as a copper foil with a carrier consisting of a carrier copper foil with a thickness of 10 to 35 μm and an ultra-thin copper foil with a thickness of 2 to 5 μm laminated on the carrier copper foil via a release layer. By simply peeling off the carrier copper foil from the carrier-attached copper foil, a laminate having an ultra-thin copper foil can be easily formed. Using this laminate, it is possible to form fine patterns by the MSAP (modified semi-additive) process, using the ultra-thin copper foil layer as a plating seed layer. From the viewpoint of heat resistance, the release layer is preferably a metal layer containing nickel or chromium, or a multilayer metal layer formed by laminating such metal layers. Such a release layer allows the carrier metal foil to be easily peeled from the ultrathin metal foil even after processing at 300°C or higher. A specific example of the metal foil with a carrier is "FUTF-5DAF-2" manufactured by Fukuda Metal Foil and Powder Co., Ltd.

[0043] The resin substrate is preferably a layer containing polyimide, more preferably a polyimide film. The polyimide is preferably a polyimide obtained by reacting a diamine with a carboxylic dianhydride to synthesize a polyamic acid, and then imidizing the polyamic acid by a thermal imidization method or a chemical imidization method. The polyimide is particularly preferably an aromatic polyimide. The surface of the substrate may be surface-treated with a silane coupling agent or the like.

[0044] The dispersion is applied to the substrate and dried to remove the dispersion medium, forming a coating film containing the F polymer. It is sufficient that a coating film is formed on at least one surface of the substrate, and a coating film may be formed on only one surface of the substrate, or on both surfaces of the substrate. Alternatively, drying may be performed until the dispersion medium is completely removed to form a coating film that does not contain the dispersion medium, or until most of the dispersion medium is removed to form a coating film that contains a trace amount of the dispersion medium. In the latter coating film formation, it is preferable to remove at least 90% by mass of the dispersion medium contained in the dispersion. The coating preferably contains the F polymer in an unmelted state, and more preferably is formed by packing the present powder in an unmelted state.

[0045] The dispersion can be applied by any of the following coating methods: spraying, roll coating, spin coating, gravure coating, microgravure coating, gravure offset, knife coating, kiss coating, bar coating, die coating, fountain-meyer bar coating, and slot die coating.

[0046] The temperature for removing the dispersion medium is preferably a temperature below the melting temperature of the F polymer and below the boiling point of the dispersion medium, and more preferably a temperature below 100°C lower than the melting temperature of the F polymer and below 10°C to 100°C lower than the boiling point of the dispersion medium. For example, when using an F polymer with a melting temperature of 300°C and N-methyl-2-pyrrolidone with a boiling point of approximately 200°C, the temperature for removing the dispersion medium is preferably 150°C or lower, more preferably 100 to 120°C. From the viewpoint of forming a coating film with excellent smoothness, it is preferable to blow air onto the surface of the coating film to be formed when removing the dispersion medium.

[0047] The formed coating film is further heated to melt and sinter the F polymer to form a layer containing the F polymer (hereinafter also referred to as the F layer). The F polymer in the F layer may be completely melt-sintered or partially melt-sintered. The thickness of the F layer is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 50 μm or more. The upper limit of the thickness is preferably 300 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Within this range, an F layer with excellent crack resistance can be easily formed. The peel strength between the F layer and the substrate is preferably 10 N / cm or more, more preferably 15 N / cm or more. The peel strength is preferably 100 N / cm or less.

[0048] The F layer is formed through the steps of applying the present dispersion and heating as described above, but these steps may be repeated two or more times. For example, the present dispersion may be applied to the surface of a substrate and heated to form an F layer, and then the present dispersion may be applied to the surface of the F layer and heated to form a second F layer. Alternatively, the present dispersion may be applied to the surface of a substrate and heated to remove the liquid dispersion medium, and then the present dispersion may be applied to the surface and heated to form an F layer.

[0049] In this method, the coating film or the F layer and the substrate are heated and compressed at least during the process from the formation of the coating film to the formation of the F layer, and the heating and compression is preferably carried out after the formation of the coating film or the F layer. As described above, the formation of a coating film means that the dispersion liquid applied to the substrate is dried to remove the dispersion medium, thereby forming a coating film containing the F polymer. As mentioned above, the formation of the F layer refers to further heating the coating to melt and bake the F polymer to form the F layer, and this is the period up to the completion of cooling after baking. Cooling after melting and baking can be either forced cooling using cold air or cold water, or natural cooling by leaving it at around room temperature, but cooling is considered complete when the temperature of the laminate with the F layer has dropped to ambient temperature. The above-mentioned heat compression is preferably carried out when the F layer is formed, and is preferably carried out after the F layer is formed, preferably before the above-mentioned cooling is completed, and more preferably immediately after the F polymer is baked. When the F layer is formed by repeating the steps of applying the present dispersion and heating two or more times as described above, the heat-compression may be performed after the first application, or after any of the second or subsequent application and heating steps. Heat-compression may also be performed sequentially after each step, or several steps may be performed without heat-compression. Heat-compression may also be performed after all of the steps of applying the present dispersion and heating.

[0050] The above-mentioned heat compression may be carried out, for example, as follows: (1) Immediately after the dispersion is dried and a coating film is formed (2) After the coating film is formed, but before the coating film is further heated to form the F layer, (3) The coating film is further heated, the F polymer is melted and baked, and the F layer is formed. (4) The stage in which the F polymer is melted and sintered and the formed F layer is cooled. It is preferable to carry out the heating and compression at one of the above stages. The temperature of the coating film in the above (1) is preferably the temperature at which the dispersion medium is removed. Furthermore, in the above stage (2), the coating film may be cooled once after formation, or may be further heated without cooling after formation of the coating film. It is more preferable that the heating and compression be carried out in the above stage (3) or (4), and even more preferable that it be carried out in the above stage (4). The heating and compression may be carried out in more than one of the above stages.

[0051] The temperature of the heat compression is preferably higher than the glass transition temperature of the F polymer, and more preferably 30°C or more higher than the glass transition temperature. The temperature of the heat compression is preferably not higher than 100°C higher than the melting temperature of the F polymer, more preferably lower than the melting temperature, and even more preferably not higher than 100°C lower than the melting temperature. The temperature of the heat compression is preferably higher than the glass transition temperature of the F polymer and not lower than 100°C or more lower than the melting temperature of the F polymer.

[0052] The heat compression is preferably carried out in an atmosphere of atmospheric pressure or reduced pressure, and more preferably in an atmosphere of atmospheric pressure. The pressure for the heat compression is preferably 0.2 MPa or more, more preferably 0.5 MPa or more, and is preferably 10 MPa or less, more preferably 5 MPa or less.

[0053] The above-mentioned hot compression method includes a method in which the coating film or F layer and the substrate are passed between a pair of heated rolls at any stage from the formation of the coating film to the formation of the F layer, a method in which hot air is blown onto the coating film or F layer and the substrate while passing them between a pair of rolls, and a method in which the coating film or F layer and the substrate are pressed with a heated press. A roll press is preferably used as a method for passing the material between a pair of rolls. The pair of rolls may be a pair of metal rolls, or a metal roll and a rubber roll. The linear pressure applied between the pair of rolls is preferably 1 to 20 tf / m, more preferably 2 to 10 tf / m. The roll temperature is preferably not more than a temperature 70°C higher than the melting point of the F polymer, more preferably not more than a temperature 50°C higher than the melting point of the F polymer. The roll temperature is preferably not less than a temperature 70°C lower than the melting point of the F polymer, more preferably not less than a temperature 50°C lower than the melting point of the F polymer. The roll temperature is preferably not less than 250°C, more preferably not less than 300°C. The roll temperature is preferably not more than 370°C, more preferably not more than 350°C. When the F layer and the substrate are passed between a pair of rolls, in order to prevent the F layer from adhering to the roll, it is preferable to place a release film between the surface of the F layer and the roll, or to surface-treat the surface of the roll with a release agent. The release film preferably comes into contact with the F layer only on the pressure surface of the roll, and is peeled off when the F layer leaves the roll. The thickness of the release film is preferably 50 to 150 μm. Examples of release films include polyimide films, and specific examples include "Apical NPI" (manufactured by Kaneka Corporation), "Kapton EN" (DuPont-Toray Co., Ltd.), and "Upilex S" (Ube Industries, Ltd.).

[0054] When the thickness of the coating film or F layer before the heat compression is 10 to 300 μm, the thickness of the coating film or F layer after the heat compression is preferably 5 to 200 μm. The above-mentioned heat-compression preferably results in a ratio of the thickness of the coating film or F layer after heat-compression to the thickness of the coating film or F layer before heat-compression of 0.1 to 0.8. For example, the ratio of the thickness of the coating film after heat-compression to the thickness of the coating film before heat-compression is preferably 0.1 to 0.8, or the ratio of the thickness of the F layer after heat-compression to the thickness of the F layer before heat-compression is preferably 0.1 to 0.8. Furthermore, according to this method, even if the thickness of the F layer is increased, the powder or the inorganic filler in the resulting laminate is prevented from falling off, so the thickness of the F layer after heat compression can be increased. A laminate with a thick F layer has improved electrical properties and water resistance. From this perspective, the thickness of the F layer after heat compression is preferably 40 μm or more. The thickness of the F layer after heat compression is usually 200 μm or less.

[0055] When a laminate having a layer containing an F polymer is produced by applying, drying, and heating a dispersion containing an F polymer powder, the powder initially accumulates in the coating film, resulting in voids between the powder. The coating film is further heated to melt the powder and form a layer, but it is difficult to completely fill the voids. However, it is believed that in laminates obtained by a production method including a heat compression step, as in the above method, the voids are crushed and the voids in the layer are reduced.

[0056] The present laminate can be obtained by the above-described method. The porosity of the F layer in this laminate is preferably 5% or less, more preferably 4% or less. The porosity is preferably 0.01% or more, more preferably 0.1% or more. The porosity is determined by determining the void areas of the F layer through image processing of an SEM photograph of the cross section of the molded product observed using a scanning electron microscope (SEM), and then dividing the area occupied by the void areas by the area of ​​the F layer (%). The area occupied by the void areas is determined by approximating the void areas as circles. The present laminate may be a laminate having a substrate and an F layer on one side of the substrate, or a laminate having a substrate and an F layer on both sides of the substrate.

[0057] The surface of the F layer of the laminate may be further subjected to a surface treatment to improve its adhesiveness. Examples of surface treatments include plasma treatments such as corona discharge treatment, atmospheric plasma discharge treatment, or vacuum plasma discharge treatment, plasma graft polymerization treatment, light irradiation treatments such as electron beam irradiation and excimer UV light irradiation, flame-based Itro treatment, and wet etching treatment using metallic sodium, with vacuum plasma discharge treatment being preferred. Vacuum plasma discharge treatment can be carried out using known equipment. From the viewpoint of treatment efficiency, the vacuum plasma discharge treatment is preferably a glow discharge treatment, so-called low-temperature plasma treatment, in which sustained discharge occurs at a gas pressure of 0.1 to 1330 Pa, preferably 1 to 266 Pa. Under such gas pressure, stable glow discharge can be achieved by applying 10 W to 100 kW of power at a frequency of 10 kHz to 2 GHz between the discharge electrodes. The discharge power density of the vacuum plasma discharge treatment is 5 to 400 W·min / m 2 Gases used in the vacuum plasma discharge treatment include helium gas, neon gas, argon gas, nitrogen gas, oxygen gas, carbon dioxide gas, hydrogen gas, air, and water vapor. Two or more of these gases may be mixed. From the viewpoint of improving adhesion strength, the gas is preferably a mixed gas of argon gas, carbon dioxide gas, oxygen gas, or nitrogen gas with hydrogen gas, more preferably a mixed gas of argon gas and hydrogen gas. The gas flow rate during treatment is preferably 500 to 10,000 sccm.

[0058] When the present laminate is further laminated with other layers, the structure may be, for example, metal substrate / F layer / other base layer / F layer / metal substrate, metal substrate layer / other base layer / F layer / other base layer / metal substrate layer, etc. Each layer may further contain glass cloth or filler. The laminate is useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry supplies, paints, cosmetics, etc., and specifically as wire coating materials for aircraft wires and the like, electrical insulating tape, insulating tape for oil drilling, materials for printed circuit boards, separation membranes such as microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, and gas separation membranes, electrode binders for lithium secondary batteries or fuel cells, copy rolls, covers for furniture, automobile dashboards, and home appliances, etc., sliding members such as load bearings, sliding shafts, valves, bearings, gears, cams, belt conveyors, and food transport belts, tools such as shovels, files, saws, and the like, boilers, hoppers, pipes, ovens, baking molds, chutes, dies, toilets, and container coating materials.

[0059] As described above, this method improves the adhesion between the F layer and the substrate, and makes it possible to produce a laminate that is excellent in water resistance and peel strength and is resistant to deterioration, in other words, highly reliable.

[0060] Although the present invention has been described above, it is not limited to the configuration of the above-described embodiment. For example, the method may include any other step in addition to the configuration of the above embodiment, or may be replaced with any other step that produces a similar effect.Furthermore, the laminate may include any other step in addition to the configuration of the above embodiment, or may be replaced with any other step that produces a similar function. [Example]

[0061] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of each ingredient [powder] Powder 1: Powder consisting of F polymer 1 (melting temperature: 300°C, glass transition point: 85°C) containing 98.0 mol% TFE units, 0.1 mol% NAH units, and 1.9 mol% PPVE units, in that order, and having an oxygen-containing polar group (D50: 2.0 μm, 98% particle size: 4.9 μm). Powder 2: Powder made of non-thermoplastic PTFE (D50: 0.3 μm)

[0062] [Inorganic filler] Filler 1: Made of silicon oxide, specific surface area 7m 2 / g of approximately spherical silica filler (D50: 0.4 μm, 98% particle size: 1.0 μm) surface-treated with vinyltrimethoxysilane (hereinafter also referred to as vinylsilane). Filler 2: Made of silicon oxide, specific surface area 7m 2 / g of non-surface-treated, nearly spherical silica filler (D50: 0.4 μm, 98% particle size: 1.0 μm) Filler 3: Made of silicon oxide, with a specific surface area of ​​3m 2 / g of nearly spherical silica filler (D50: 16 μm, 98% particle size: 20 μm) surface-treated with vinylsilane

[0063] [Non-aqueous solvent] NMP: N-methyl-2-pyrrolidone [Surfactants] Surfactant 1: Copolymer of (meth)acrylate having a perfluoroalkenyl group and (meth)acrylate having a hydroxyl group and an oxyethylene group [Varnishes made from other polymers] Varnish 1: Varnish in which thermoplastic polyimide (PI1) is dissolved in NMP

[0064] 2. Dispersion liquid production example (Example 1) First, Powder 1, Varnish 1, Surfactant 1, and NMP were placed in a pot, and then zirconia balls were placed in the pot. The pot was then rolled at 150 rpm for 1 hour to prepare a liquid composition. Next, Filler 1, Surfactant 1, and NMP were placed in a pot, and then zirconia balls were placed in the pot. Thereafter, the pot was rolled at 150 rpm for 1 hour to prepare a liquid composition. Both liquid compositions were then poured into a pot, followed by the addition of zirconia balls, and the pot was rolled at 150 rpm for 1 hour to obtain Dispersion 1 containing Powder 1 (11 parts by mass), Filler 1 (11 parts by mass), PI 1 (7 parts by mass), Surfactant 1 (4 parts by mass), and NMP (67 parts by mass) and having a viscosity of 400 mPa.

[0065] (Example 2) Dispersion 2 having a viscosity of 400 mPa and containing Powder 1 (11 parts by mass), Filler 1 (11 parts by mass), Surfactant 1 (4 parts by mass), and NMP (74 parts by mass) was obtained in the same manner as in Example 1, except that Varnish 1 was not used and the amount of NMP was changed. (Example 3) Dispersion 3 containing Powder 1 (11 parts by mass), Filler 2 (11 parts by mass), PI1 (7 parts by mass), Surfactant 1 (4 parts by mass), and NMP (67 parts by mass) and having a viscosity of 700 mPa s was obtained in the same manner as in Example 1, except that Filler 1 was changed to Filler 2.

[0066] (Example 4) Dispersion 4 having a viscosity of 400 mPa was obtained in the same manner as in Example 1, except that Filler 1 was changed to Filler 3, and contained Powder 1 (11 parts by mass), Filler 3 (11 parts by mass), PI1 (7 parts by mass), Surfactant 1 (4 parts by mass), and NMP (67 parts by mass).

[0067] (Example 5) Dispersion 5 having a viscosity of 500 mPa and containing Powder 1 (2 parts by mass), Powder 2 (9 parts by mass), Filler 3 (11 parts by mass), PI1 (7 parts by mass), Surfactant 1 (4 parts by mass), and NMP (67 parts by mass) was obtained in the same manner as in Example 1, except that the 11 parts by mass of Powder 1 was changed to 2 parts by mass of Powder 1 and 9 parts by mass of Powder 2.

[0068] 3. Example of laminate manufacturing (Production of laminate 1) Dispersion 1 was applied to the surface of a long copper foil with a thickness of 18 μm using a bar coater. The copper foil coated with Dispersion 1 was then passed through a drying oven at 120°C for 5 minutes and dried by heating to obtain a coating film. The thickness of the formed coating film was 12 μm. Immediately after drying, the coating film was heated and compressed by roller pressure at a temperature of 150°C and a pressure of 0.6 MPa in an atmospheric pressure atmosphere until the coating film cooled to 25°C until the coating film thickness reached 8 μm. The coating film was then heated at 380°C for 3 minutes in a nitrogen oven. This produced Laminate 1, which had copper foil and a 7 μm-thick F layer on its surface as a molded product containing a fused and fired product of Powder 1, Filler 1, and PI1. A reduction in voids in the coating film was confirmed before and after heat compression.

[0069] (Production of laminate 2) A coating film was obtained on the surface of the copper foil in the same manner as in Laminate 1. The thickness of the formed coating film was 15 μm. The coating film was then heated at 380°C for 3 minutes in a nitrogen oven to obtain a copper foil and a 12 μm-thick F layer on its surface, which contained a molten and baked product of Powder 1, Filler 1, and PI1. Immediately after heating, while the F layer was cooling to 25°C, it was heat-pressed using a vacuum press at a temperature of 330°C and a pressure of 0.2 MPa in a vacuum atmosphere to heat-compress the F layer until it became 8 μm thick, thereby obtaining Laminate 2. A decrease in the voids in the F layer was confirmed before and after heat-compression.

[0070] (Production of laminate 3) Laminate 3 was produced in the same manner as laminate 2, except that dispersion 1 was changed to dispersion 2 and the heat pressing conditions were changed to a temperature of 330°C and 0.6 MPa. A decrease in the voids in layer F was confirmed before and after heat compression.

[0071] (Production of laminate 4) Laminate 4 was produced in the same manner as laminate 3, except that the heat pressing conditions were changed to a temperature of 330°C and 1.0 MPa, and the F layer was heated and compressed until it had a thickness of 5 μm. A decrease in the voids in the F layer was confirmed before and after heat compression.

[0072] (Production of laminate 5) Laminate 5 was produced in the same manner as laminate 3, except that the hot pressing conditions were changed to a temperature of 380° C. and a pressure of 0.6 MPa. A decrease in the voids in layer F was confirmed before and after hot compression.

[0073] (Production of laminate 6) Laminate 6 was produced in the same manner as laminate 3, except that the heat pressing was not carried out.

[0074] (Production of laminate 7) Laminate 7 was produced in the same manner as laminate 1, except that dispersion 1 was changed to dispersion 3. A decrease in the voids in layer F was confirmed before and after heat compression.

[0075] (Production of laminate 8) Laminate 8 was produced in the same manner as laminate 1, except that dispersion 1 was changed to dispersion 4. A decrease in voids in layer F was confirmed before and after heat compression.

[0076] (Production of laminate 9) Laminate 8 was produced in the same manner as laminate 1, except that dispersion 1 was changed to dispersion 5. A decrease in voids in layer F was confirmed before and after heat compression.

[0077] (Production of laminate 10) A laminate 10 was produced in the same manner as the laminate 1, except that the thickness of the F layer was changed to 100 μm.

[0078] (Production of laminate 11) Laminate 11 was produced in the same manner as laminate 1, except that the thickness of layer F was changed to 100 μm and heat pressing was not performed.

[0079] (Production of laminate 12) A coating film was obtained on the surface of the copper foil in the same manner as in Laminate 1. The thickness of the formed coating film was 15 μm. The coating film was then heated at 380°C for 3 minutes in a nitrogen oven to obtain a laminate having a copper foil and a 12 μm-thick F layer on its surface, which contained a molten and baked product of Powder 1, Filler 1, and PI1. Immediately after heating, the obtained laminate was passed between a pair of metal rolls at 330°C in an atmospheric pressure environment until the F layer was cooled to 25°C. At this time, the laminate was passed while a polyimide film was sandwiched between the surface of the F layer and the metal rolls as a release film. This heated and compressed the F layer to obtain Laminate 12. A decrease in the voids in the F layer was confirmed before and after the heat compression, and the void ratio of the F layer was between 0.1% and 4%. The laminates 1 to 12 were evaluated for peel strength, water resistance, electrical properties and warpage based on the following criteria.

[0080] 3. Measurement and Evaluation 3-1.Water resistance evaluation Each laminate was etched with an aqueous solution of ferric chloride to remove the copper foil, thereby obtaining the F layer alone. This F layer was pre-dried at 50°C for 48 hours in accordance with ASTM D570, and then immersed in pure water at 23°C for 24 hours. The mass of the F layer was measured before and after immersion in pure water, and the water absorption rate was calculated based on the following formula and evaluated according to the following criteria. Water absorption rate (%) = (mass after immersion in water - mass after pre-drying) / mass after pre-drying x 100 Good: Water absorption rate is 0.05% or less. △: Water absorption rate is more than 0.05% and 0.1% or less. ×: The water absorption rate is more than 0.1%.

[0081] 3-2. Evaluation of peel strength after high temperature and humidity treatment A rectangular test piece 100 mm long and 10 mm wide was cut out from each laminate and held in an atmosphere of 85°C and 85% relative humidity for 72 hours, after which the copper foil and the F layer were peeled from one end of the test piece to a position 50 mm from one end in the longitudinal direction, and one end of the peeled copper foil and F layer was attached to each chuck of a tensile tester (manufactured by Orientec Co., Ltd.) The peel strength (N / cm) between the copper foil and the F layer in the unpeeled portion of the test piece was then measured using the tensile tester and evaluated according to the following criteria. ○: Peel strength ≧ 10N / cm ×: Peel strength ≦ 10N / cm

[0082] 3-3.Evaluation of dielectric loss tangent after high temperature and high humidity treatment A rectangular test piece measuring 100 mm in length and 50 mm in width was cut from each laminate and etched with an aqueous ferric chloride solution to remove the copper foil, yielding an F layer alone. After storing the F layer alone in an atmosphere of 85°C and 85% relative humidity for 72 hours, the dielectric loss tangent (measurement frequency: 10 GHz) of the multilayer film was measured using the split post dielectric resonance (SPDR) method and evaluated according to the following criteria. ◯: The dielectric loss tangent is less than 0.0020. △: The dielectric loss tangent is 0.0020 or more and 0.0040 or less. ×: The dielectric loss tangent is more than 0.0040.

[0083] 3-4. Evaluation of warpage after high temperature and humidity treatment A square test piece measuring 180 mm square was cut out from each laminate and kept in an atmosphere of 85% relative humidity for 72 hours. The test piece was then placed on a smooth glass surface and visually evaluated according to the following criteria. ◯: No warping (waviness) was observed in the test piece. △: Warpage (waviness) was observed in the test piece, but the test piece was not curled. ×: Warpage (waviness) was observed in the test piece, and the test piece was curled up. The results are shown in Table 1 below.

[0084] [Table 1]

[0085] Each of the laminates 8 to 10 was superior to the laminate 1 in terms of the physical properties of the laminate in the following respects. The laminate 8 had a lower dielectric loss tangent itself and was excellent in electrical properties. In the laminates 9 and 10, the inorganic filler was less likely to fall off as powder, making them easy to handle, and the surface smoothness of the layers was also high. Compared to the laminate 2, the laminate 12 had a lower water absorption rate in the evaluation of water resistance, and was excellent in water resistance.

[0086] As is clear from the above results, the laminate produced by this method has a dense cross section with no voids, low water absorption, excellent peel strength, excellent electrical properties, and little warping. Therefore, the laminate produced by this method has excellent adhesion to various substrates, excellent peel strength, and excellent water resistance.

Claims

1. A method for producing a laminate having a layer containing a heat-fusible tetrafluoroethylene-based polymer, comprising: applying a dispersion containing a powder of a heat-fusible tetrafluoroethylene-based polymer, a silica filler that has been surface-treated with a silane coupling agent, and an aromatic polymer that is an aromatic polyimide, an aromatic polyamideimide, an aromatic maleimide, a styrene elastomer, an aromatic polyamic acid, or polyphenylene ether, wherein the mass ratio of the silica filler to the heat-fusible tetrafluoroethylene-based polymer is 0.5 to 1.5, onto a substrate and drying the dispersion to form a coating film; further heating the resulting coating film to form a layer containing the heat-fusible tetrafluoroethylene-based polymer; and heat-compressing the coating film or the layer and the substrate at least during the process from the formation of the coating film to the process after the formation of the layer.

2. 2. The method for producing a laminate according to claim 1, wherein the heat-meltable tetrafluoroethylene-based polymer is a polymer containing a unit based on perfluoro(alkyl vinyl ether) and having a polar functional group, or a polymer containing 2 to 5 mol% of a unit based on perfluoro(alkyl vinyl ether) relative to all units and having no polar functional group.

3. 3. The method for producing a laminate according to claim 1, wherein the substrate is a copper foil or a polyimide film.

4. 4. The method for producing a laminate according to claim 1, wherein the temperature of the heat-compression is equal to or higher than the glass transition temperature of the heat-fusible tetrafluoroethylene polymer and is equal to or lower than a temperature 100°C higher than the melting temperature of the heat-fusible tetrafluoroethylene polymer.

5. The method for producing a laminate according to any one of claims 1 to 4, wherein the pressure of the heat compression is 0.2 MPa or more and 10 MPa or less.

6. The method for producing a laminate according to claim 1 , wherein the heat compression is carried out when the layer is formed.

7. 7. The method for producing a laminate according to claim 1, wherein a ratio of the thickness of the coating film after the heat-compression to the thickness of the coating film before the heat-compression, or a ratio of the thickness of the layer after the heat-compression to the thickness of the layer before the heat-compression, is 0.1 to 0.

8.

8. The method for producing a laminate according to any one of claims 1 to 7, wherein the thickness of the layer after the heat compression is 40 µm or more.

9. The method for producing a laminate according to claim 1 , wherein the dispersion contains a silica filler having an average particle size of 10 μm or more.

10. The method for producing a laminate according to any one of claims 1 to 9, wherein the dispersion further contains a non-thermofusible polytetrafluoroethylene powder.

11. The method for producing a laminate according to claim 1 , wherein the dispersion further contains a silane coupling agent.

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