JP7771961B2 - Manufacturing method of laminated film and laminated film - Google Patents

Description

The present invention relates to a method for manufacturing a laminated film, which is formed by applying a liquid composition containing a liquid dispersion medium with a predetermined surface tension to the surface of a polymer film that has been treated to increase its surface tension, to obtain a laminated film having a polymer layer with reduced increase in thickness at the edges, and to a laminated film having a polymer layer in which the ratio of the edge thickness to the central thickness is adjusted to be within a predetermined range.

Printed circuit boards used for transmitting high-frequency signals are required to have excellent transmission characteristics. Tetrafluoroethylene-based polymers, which have low relative permittivity and dielectric loss tangent, have attracted attention as insulating layer materials for printed circuit boards with high transmission characteristics. A liquid composition containing tetrafluoroethylene-based polymer powder and a liquid dispersion medium is known as a material for forming an insulating layer containing such a polymer.
Patent Documents 1 and 2 describe a laminated film having tetrafluoroethylene polymer layers on both sides of a polyimide film, which is formed by applying such a liquid composition to the surface of the polyimide film and then heating it.

Japanese Patent Application Publication No. 9-157418 Japanese Patent Application Laid-Open No. 2005-35300

On the other hand, because tetrafluoroethylene-based polymers are non-sticky, adhesion between the polyimide film and the tetrafluoroethylene-based polymer layer in such laminate films is generally low. Therefore, the inventors attempted to improve the adhesion of laminate films by surface-treating the polyimide film. However, the inventors newly discovered that this method easily causes unevenness in the thickness of the laminate film, particularly the tendency for the edges of the laminate film to bulge. Therefore, the inventors newly discovered that when a long piece of such laminate film is wound into a roll, the laminate film wrinkles and stretches, reducing yields when used as a printed circuit board material, etc.

As a result of extensive research, the inventors have found that a liquid composition containing a liquid dispersion medium having a surface tension within a predetermined range also has excellent dispersion stability, wets and spreads more uniformly on the surface of a polymer film that has been treated to increase the surface tension, and can form a laminated film with little thickness variation and high adhesion strength.
The present invention was made based on this finding, and its object is to provide a laminated film having a polymer layer with excellent adhesion and in which the ratio of the thickness of the edge to the thickness of the center is adjusted to a predetermined range, and a method for producing the same.

The present invention has the following aspects.
<1> A method for producing a laminated film, comprising: applying a liquid composition containing a tetrafluoroethylene-based polymer powder and a liquid dispersion medium having a surface tension of 30 mN/m or more to the surface of a polymer film that has been treated to increase the surface tension, the liquid composition containing the powder in an amount of 10 mass% or more; and heating the applied composition to obtain a laminated film in which a polymer layer is formed on the surface of the polymer film.
<2> The manufacturing method of <1>, wherein the treatment is at least one hydrophilization treatment selected from the group consisting of a corona treatment and a plasma treatment.
<3> The manufacturing method of <1> or <2>, wherein the surface tension of the surface of the polymer film that has been subjected to the treatment is greater than the surface tension of the liquid dispersion medium.
<4> The manufacturing method according to any one of <1> to <3>, wherein the polymer film has a surface with an arithmetic mean roughness Ra of 0.01 to 5 μm.
<5> The method of any one of <1> to <4>, wherein a polar functional group is present on the surface of the polymer film that has been subjected to the treatment.
<6> The method of any one of <1> to <5>, wherein the powder has an average particle size of 0.1 to 10 μm.
<7> The method of any one of <1> to <6>, wherein the tetrafluoroethylene-based polymer has a melting temperature of 260 to 320°C.
<8> The method according to any one of <1> to <7>, wherein the tetrafluoroethylene-based polymer contains units based on perfluoro(alkyl vinyl ether), and the content of units based on perfluoro(alkyl vinyl ether) is 1.5 to 5.0 mol % based on all units.
<9> The method of any one of <1> to <8>, wherein the liquid composition contains an aromatic polymer.
<10> The method of any one of <1> to <9>, wherein the polymer film contains an aromatic polyimide.
<11> The manufacturing method according to any one of <1> to <10>, wherein the polymer film has an average thickness of 10 μm or more, and the polymer layer has an average thickness of 10 μm or more.
<12> A laminated film comprising: a polymer film having a surface that has been treated to increase surface tension; and a polymer layer formed on the surface and containing a tetrafluoroethylene-based polymer, wherein the ratio of the thickness of the end portion to the thickness of the center portion of the polymer layer is 1.1 or less.
<13> The laminate film according to <12>, wherein the laminate film is pre-dried under conditions of 50°C for 48 hours, and then immersed in pure water at 23°C for 24 hours. When the mass of the laminate film is measured before and after immersion in the pure water, the water absorption calculated according to the following formula is 0.1% or less.
Water absorption rate (%) = (mass after immersion in pure water - mass after pre-drying) / mass after pre-drying x 100
<14> The laminate film according to <12> or <13>, wherein the polymer film has an average thickness of 10 μm or more, and the polymer layer has an average thickness of 10 μm or more.
<15> The laminate film according to any one of <12> to <14>, wherein the polymer layer is provided on both sides of the polymer film.

The present invention provides a laminated film having a polymer layer with excellent adhesion and in which the ratio of edge thickness to central thickness is adjusted to a predetermined range.

The following terms have the following meanings:
The "average particle diameter (D50)" is the volume-based cumulative 50% diameter of a target object (powder or inorganic filler) determined by a laser diffraction/scattering method. That is, the particle size distribution of the target object is measured by a laser diffraction/scattering method, and a cumulative curve is calculated with the total volume of the target particle population set to 100%, and the "average particle diameter (D50)" is the particle diameter at the point on the cumulative curve where the cumulative volume is 50%.
"D90" is the volume-based cumulative 90% diameter of the object, measured in the same manner.
"Melting temperature (melting point)" is the temperature corresponding to the maximum value of the melting peak of a polymer as measured by differential scanning calorimetry (DSC).
The "glass transition temperature (Tg)" is a value measured by analyzing a polymer using dynamic mechanical analysis (DMA) method.
The "specific surface area" is a value determined by measuring a powder using a NOVA4200e (manufactured by Quantachrome Instruments) by the gas adsorption (constant volume method) BET multipoint method.
The "viscosity" is a value determined by measuring the liquid composition using a Brookfield viscometer at 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" is a value (η 1 /η ₂ ) calculated by dividing the viscosity η ₁ obtained by measuring the liquid composition at a rotation speed of 30 rpm by the viscosity η ₂ obtained by measuring the liquid composition at a rotation speed of ₆₀ rpm.
The "yield strength" refers to the stress at which, as the strain increases, the relationship between the strain and the stress becomes no longer proportional, and the phenomenon of the strain remaining even after the stress is removed begins to occur. The "yield strength" is defined as the value of the "stress at 5% strain" when the tensile modulus of the film is measured according to ASTM D882.
"Low plastic deformation resistance" means a property in which stress increases when the support layer is plastically deformed, or a property in which a large stress is required when the support layer is plastically deformed, and is defined as the value of "stress at 15% strain" when the tensile modulus of the film is measured in accordance with ASTM D882.
The "tensile modulus" is a value measured on a film at a measurement frequency of 10 Hz using a wide-range viscoelasticity measuring device.
The "average thickness" is the average value of the measured values obtained by measuring the film thickness at 10 points using a contact thickness gauge DG-525H (manufactured by Ono Sokki Co., Ltd.) with a probe AA-026 (Φ10 mm, SR7).
"Ten-point average roughness (Rzjis) of the surface of a metal foil (metal substrate)" is a value specified in Annex JA of JIS B 0601:2013 (ISO 4287:1997, Amd.1:2009).
"Arithmetic mean roughness Ra" is a value on the surface of the film measured in accordance with JIS B 0601:2013 (ISO 4287:1997, Amd.1:2009).
The "unit" in a polymer may be an atomic group formed directly from a monomer, or may be an atomic group in which a part of the structure is converted by treating the obtained polymer with a predetermined method. A unit based on monomer A contained in a polymer may also be simply referred to as a "monomer A unit."

The production method of the present invention (hereinafter also referred to as "this method") is a method of applying a liquid composition containing tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer") powder and a liquid dispersion medium having a surface tension of 30 mN/m or more to the surface of a polymer film that has been treated to increase its surface tension, and the liquid composition contains 10 mass % or more of F polymer powder (hereinafter also referred to as "F powder"), and then heating the applied composition to obtain a laminated film in which a polymer layer is formed on the surface of the polymer film.
Therefore, the resulting laminate film is a laminate having a polymer film with a surface treated to increase surface tension and a polymer layer containing the F polymer formed on the surface. In such a laminate film, the ratio of the thickness of the edge to the thickness of the center of the polymer layer is within a predetermined range (preferably 1.1 or less). In other words, the variation in the thickness of the polymer layer is small. The reason for this is not necessarily clear, but is thought to be as follows.

In this method, in order to improve the adhesion between the polymer film and the polymer layer, the surface of the polymer film is treated to increase its surface tension prior to coating with the liquid composition. However, when a liquid composition containing F powder is applied to the surface of a polymer film that has been treated in this way, as the composition flows from the center to the edges and spreads, the flow may stop near the edges (pinning phenomenon), causing the coating film to bulge. If the coating film (liquid composition) is heated in this state, the shape of the edges will be maintained, and the thickness of the resulting polymer layer at the edges will be greater than the thickness at the center.
Therefore, in this method, a liquid composition containing a liquid dispersion medium with a surface tension of 30 mN/m or more is used, which is thought to increase the wettability of the liquid composition to the surface of the polymer film, allowing it to wet and spread evenly to the edges of the polymer film, thereby reducing variation in the thickness of the resulting polymer layer.

The F polymer in this method is a polymer containing units based on tetrafluoroethylene (TFE) (TFE units).
The F polymer is preferably heat-meltable, and its melting temperature is preferably 260 to 320° C., more preferably 285 to 320° C. Use of such an F polymer makes it easy to form a dense polymer layer with excellent adhesion, and to easily obtain a laminated film with excellent heat resistance.
The glass transition point (Tg) of the F polymer is preferably from 75 to 125°C, more preferably from 80 to 100°C.
The melt viscosity of the F polymer at 380° C. is preferably 1×10 ² to 1×10 ⁶ Pa·s, more preferably 1×10 ³ to 1×10 ⁶ Pa·s.

The surface tension of the F polymer is preferably 16 to 26 mN/m, more preferably 16 to 20 mN/m. The surface tension of the F polymer can be measured by placing a droplet of a mixture for wetting tension testing (manufactured by Wako Pure Chemical Industries, Ltd.) specified in JIS K 6768 on a flat plate made of the F polymer.
The fluorine content of the F polymer is preferably 70% by mass or more, more preferably 72 to 76% by mass.
F polymers have low surface tension and a high fluorine content, and are excellent in physical properties such as electrical properties, but have extremely low dispersion stability in liquid compositions. However, in the liquid composition of the present method, the dispersion stability of such F polymers is improved by using the above-mentioned liquid dispersion medium.

F polymer can be enumerated as polytetrafluoroethylene (PTFE), the polymer that comprises TFE unit and the unit based on ethylene, the polymer that comprises TFE unit and the unit based on propylene, the polymer that comprises TFE unit and the unit based on perfluoro (alkyl vinyl ether) (PAVE) (PAVE unit) (PFA), the polymer that comprises TFE unit and the unit based on hexafluoropropylene (FEP), the polymer that comprises TFE unit and the unit based on fluoroalkylethylene, the polymer that comprises TFE unit and the unit based on chlorotrifluoroethylene, preferably PFA or FEP, more preferably PFA.Above-mentioned polymer can also comprise the unit based on other comonomer.
As the PAVE, CF ₂ ═CFOCF ₃ , CF ₂ ═CFOCF ₂ CF ₃ or CF ₂ ═CFOCF ₂ CF ₂ CF ₃ (hereinafter also referred to as “PPVE”) is preferred, and PPVE is more preferred.

The F polymer preferably has a polar functional group, in which case the polymer layer tends to have excellent physical properties such as electrical properties and surface smoothness.
The polar functional group may be contained in a unit contained in the F polymer, or may be contained in a terminal group of the F polymer main chain. Examples of the latter F polymer include polymers having a polar functional group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and polymers having a polar functional group prepared by plasma treatment or ionizing radiation treatment.

As the polar functional group, a hydroxyl group-containing group, a carbonyl group-containing group, and a phosphono group-containing group are preferred, a hydroxyl group-containing group and a carbonyl group-containing group are more preferred, and a carbonyl group-containing group is even more preferred.
As the hydroxyl group-containing group, an alcoholic hydroxyl group-containing group is preferred, and —CF ₂ CH ₂ OH, —C(CF ₃ ) ₂ OH and a 1,2-glycol group (—CH(OH)CH ₂ OH) are more preferred.
The carbonyl group-containing group is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH ₂ ), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.) or a carbonate group (-OC(O)O-), and more preferably an acid anhydride residue.

When the F polymer has a polar functional group, the number of polar functional groups in the F polymer is preferably 10 to 5000, more preferably 100 to 3000, per 1 × ¹⁰ carbon atoms in the main chain. The number of polar functional groups in the F polymer can be quantified by the composition of the polymer or the method described in WO 2020/145133.

The F polymer is preferably a tetrafluoroethylene-based polymer containing PAVE units and containing 1.5 to 5.0 mol% of PAVE units relative to all units, and more preferably a polymer (1) containing PAVE units and having a polar functional group, or a polymer (2) containing PAVE units and containing 2.0 to 5.0 mol% of PAVE units relative to all monomer units but not having a polar functional group. These polymers form microspherulites in the polymer layer, which tends to improve the physical properties of the resulting polymer layer.

The polymer (1) preferably contains, based on all units, 90 to 98 mol % of TFE units, 1.5 to 9.97 mol % of PAVE units, and 0.01 to 3 mol % of units derived from a monomer having a polar functional group.
Furthermore, as the monomer having a polar functional group, itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH") are preferred.
Specific examples of the polymer (1) include the polymers described in WO 2018/16644.

The polymer (2) is composed of only TFE units and PAVE units, and preferably contains 95.0 to 98.0 mol % of TFE units and 2.0 to 5.0 mol % of PAVE units based on the total 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 all units.
The phrase "polymer (2) has no polar functional groups" means that the number of polar functional groups that the polymer has is less than 500 per 1 × ¹⁰ carbon atoms constituting the polymer main chain. The number of polar functional groups is preferably 100 or less, more preferably less than 50. The lower limit of the number of polar functional groups is usually 0.

The polymer (2) may be produced using a polymerization initiator, a chain transfer agent, or the like that does not generate a polar functional group as a terminal group of the polymer chain, or may be produced by fluorinating a polymer having a polar functional group (e.g., a polymer having a polar functional group derived from a polymerization initiator at the terminal group of the polymer chain).
Examples of the fluorination treatment method include a method using fluorine gas (see JP 2019-194314 A, etc.).

The F powder in this method is a powder containing an F polymer, and the content of the F polymer is preferably 80% by mass or more, more preferably 100% by mass.
The F powder may contain other polymers besides the F polymer, such as aromatic polyesters, polyamideimides, polyimides, polyphenylene ethers, polyphenylene oxides, and maleimides.

The F powder may contain an inorganic substance. Examples of inorganic substances include oxides, nitrides, metal elements, alloys, and carbon. Silicon oxide (silica), metal oxides (beryllium oxide, cerium oxide, alumina, soda alumina, magnesium oxide, zinc oxide, titanium oxide, etc.), boron nitride, and magnesium metasilicate (steatite) are more preferred. Silica and boron nitride are even more preferred, and silica is particularly preferred. This tends to improve the dispersion stability of the F powder in the liquid composition.
The inorganic-containing F powder preferably has an F polymer core and an inorganic substance on the surface of the core, and is obtained, for example, by coalescence (collision, aggregation, etc.) of an F polymer powder and an inorganic substance powder.

The D50 of the F powder is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less. The D50 of the F powder is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 1 μm or more.
Furthermore, D90 of the F powder is preferably less than 100 μm, and more preferably 90 μm or less.
The specific surface area of the F powder is preferably 1 to 8 m ² /g, more preferably 1 to 5 m ² /g, and even more preferably 1 to 3 m ² /g.
When the D50, D90, and specific surface area of the F powder are within the above ranges, the dispersion stability of the F powder in the liquid composition is likely to be excellent. In addition, the resulting polymer layer is dense, which tends to improve water resistance (low water absorption).

One type of F powder may be used, or two or more types may be used. When two types of F powders are used, the F powders are preferably a powder of a heat-fusible F polymer (such as a powder of a heat-fusible F polymer having a carbonyl group-containing group containing TFE units and PAVE units) and a powder of a non-heat-fusible F polymer (such as a powder of non-heat-fusible PTFE).
The proportion of the former powder in the total amount of the two types of F powder is preferably 50% by mass or less, more preferably 25% by mass or less, and is preferably 0.1% by mass or more, more preferably 1% by mass or more.
It is also preferable that the D50 of the former powder is 1 to 4 μm, and the D50 of the latter powder is 0.1 to 1 μm.

The liquid dispersion medium used in this method has a surface tension of 30 mN/m or more, preferably 35 mN/m or more, and more preferably 40 mN/m or more. The surface tension is preferably 75 mN/m or less, and more preferably 55 mN/m or less. Use of a liquid dispersion medium with such a surface tension provides excellent dispersion stability for the F powder, making it easy to obtain a liquid composition that uniformly wets and spreads on the surface of the polymer film that has been subjected to the above treatment.
Specific examples of liquid dispersion media include N-methyl-2-pyrrolidone (NMP: 41), cyclohexanone (CHN: 35.2), dimethyl sulfoxide (DMSO: 43.5), diethylene glycol (DEG: 45.2), bromobenzene (35.75), and water (72.8). The numbers in parentheses indicate the surface tension (unit: mN/m) of each liquid dispersion medium.
The liquid dispersion medium may be used alone or in combination of two or more kinds.

The content of F powder in the liquid composition is 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. The content of F powder is preferably 60% by mass or less, and more preferably 40% by mass or less. According to the present invention, even when a liquid composition with a high content of F powder is used, a polymer layer with little thickness variation can be formed, so that a polymer layer of any thickness, particularly a thick polymer layer, can be easily formed.
The content of the liquid dispersion medium in the liquid composition is preferably 40% by mass or more, more preferably 50% by mass or more, and is preferably 80% by mass or less.

The liquid composition used in this method preferably contains an aromatic polymer (hereinafter referred to as "AR polymer"). In this case, the resulting polymer layer can be imparted with properties derived from the F polymer (electrical properties, adhesiveness, low water absorption, etc.) and properties derived from the AR polymer (low linear expansion, UV absorption, etc.). The AR polymer may be dissolved or dispersed in a liquid dispersion medium.
The glass transition point of the AR polymer is preferably 300 to 350° C., more preferably 315 to 335° C. In this case, the linear expansion coefficient of the polymer layer (laminated film) is reduced, making it easy to prevent or suppress deformation due to heating.
The 5% weight loss temperature of the AR polymer is preferably 260° C. or higher, more preferably 300° C. or higher, and even more preferably 320° C. or higher. The 5% weight loss temperature of the AR polymer is preferably 600° C. or lower. Within the above range, bubbles caused by decomposition gas of the AR polymer and bubbles caused by gas produced as a by-product accompanying the reaction of the AR polymer itself are reduced, making it easy to effectively suppress roughening of the interface between the polymer layer and the polymer film in the laminate film.

The AR polymer is preferably thermoplastic, since the plasticity of such an AR polymer improves dispersibility in the polymer layer, making it easier to form a dense and uniform polymer layer.
The AR polymer is preferably at least one selected from the group consisting of aromatic polyimide, aromatic maleimide, aromatic polyphenylene ether, aromatic styrene elastomer, and liquid crystal polyester, and more preferably aromatic polyimide. Here, the thermoplastic polyimide means a polyimide in which imidization has been completed and no further imidization reaction occurs.
Use of such an AR polymer not only tends to improve the adhesion of the polymer layer to the polymer film, but also tends to improve the physical properties of the film (such as UV absorbency).

Specific examples of AR polymers include aromatic polyamideimides such as the "HPC" series (manufactured by Hitachi Chemical Co., Ltd.), and aromatic polyimides such as the "Neoprim" series (manufactured by Mitsubishi Gas Chemical Company, Inc.), the "Spixeria" series (manufactured by Somar), the "Q-PILON" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology), the "Tomido" series (manufactured by T&K Toka Corporation), the "KPI-MX" series (manufactured by Kawamura Sangyo Kaisha), and the "UPIA-AT" series (manufactured by Ube Industries, Ltd.).
As the aromatic polyimide which is the AR polymer, the aromatic polyimide which will be explained later in connection with the polymer film may be used.

A preferred embodiment of the F polymer and AR polymer in this method is one in which the melting temperature of the F polymer is 285 to 320°C and the glass transition point of the AR polymer is 315 to 335°C.
In the above embodiment, not only are the F polymer and the AR polymer uniformly dispersed in the polymer layer, which tends to improve the film properties, but also, in a high-temperature environment, the F polymer and the AR polymer highly interact with each other, which tends to further improve the heat resistance of the polymer layer.

In the liquid composition of this method, the content of the AR polymer relative to the total content of the F polymer and the AR polymer is preferably 10% by mass or less, more preferably 7.5% by mass or less, and even more preferably 5% by mass or less, and the content of the AR polymer is preferably 0.1% by mass or more.
When the contents of the F polymer and the AR polymer in the liquid composition satisfy the above ratio and the content of the AR polymer is low relative to the content of the F polymer, the AR polymer is likely to be highly dispersed in the F polymer in the resulting polymer layer, and as a result, the physical properties (electrical properties, low water absorption, etc.) based on the F polymer are likely to be highly exhibited in the polymer layer.

The liquid composition used in this method may further contain an inorganic filler from the viewpoint of improving the electrical properties and low linear expansion of the polymer layer.
The inorganic filler is preferably a nitride filler or an inorganic oxide filler, more preferably a boron nitride filler, a beryllia filler (a beryllium oxide filler), a silicate filler (a silica filler, a wollastonite filler, a talc filler), or a metal oxide filler (cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, etc.), and even more preferably a silica filler. The inorganic filler is preferably surface-treated with a silane coupling agent.

The inorganic filler preferably has a D50 of 20 μm or less, more preferably 10 μm or less, and preferably has a D50 of 0.01 μm or more, more preferably 0.1 μm or more.
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, micaceous, block-like, flat, wedge-like, rosette-like, net-like, and prismatic shapes.

Specific examples of suitable inorganic fillers include silica fillers (such as the "Admafine (registered trademark)" series manufactured by Admatechs Co., Ltd.), zinc oxide fillers surface-treated with esters such as propylene glycol dicaprate (such as the "FINEX (registered trademark)" series manufactured by Sakai Chemical Industry Co., Ltd.), spherical fused silica fillers (such as the "SFP (registered trademark)" series manufactured by Denka Co., Ltd.), titanium oxide fillers coated with polyhydric alcohols and inorganic substances (such as the "Tipaque (registered trademark)" series manufactured by Ishihara Sangyo Kaisha, Ltd.), and rutile-type titanium oxide fillers surface-treated with alkylsilanes. Examples of fillers include hollow silica fillers (such as the "JMT (registered trademark)" series manufactured by Teika Corporation), hollow silica fillers (such as the "E-SPHERES" series manufactured by Taiheiyo Cement Corporation, the "Silinax" series manufactured by Nittetsu Mining Co., Ltd., and the "Ecocospher" series manufactured by Emerson & Cumming Co., Ltd.), talc fillers (such as the "SG" series manufactured by Nippon Talc Co., Ltd.), 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 "Denka Boron Nitride" series ("GP" and "HGP" grades) manufactured by Denka Company, Ltd.).

The liquid composition in this method may further contain a surfactant from the viewpoint of improving dispersibility and handling properties.
The surfactant is preferably nonionic.
The hydrophilic portion of the surfactant preferably has an oxyalkylene group or an alcoholic hydroxyl group.
The hydrophobic portion of the surfactant preferably has an acetylene group, a polysiloxane group, a perfluoroalkyl group, or a perfluoroalkenyl group. In other words, the surfactant is preferably an acetylene-based surfactant, a silicone-based surfactant, or a fluorine-based surfactant, and more preferably a silicone-based surfactant.
The surfactant may be a glycol-based surfactant.
The surfactant may be used alone or in combination of two or more. When two surfactants are used, it is preferable to use a silicone surfactant and a glycol surfactant.

In addition to the above components, the liquid composition used in this method may also contain additives such as silane coupling agents, dehydrating agents, antifoaming agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, colorants, conductive agents, release agents, surface treatment agents, flame retardants, and organic fillers.

The viscosity of the liquid composition is preferably 100 mPa·s or more, more preferably 250 mPa·s or more, and is preferably 100,000 mPa·s or less, more preferably 10,000 mPa·s or less, particularly preferably 3,000 mPa·s.
The thixotropy ratio of the liquid composition is preferably 1.0 to 2.0.
A liquid composition having such a viscosity and thixotropy ratio tends to wet and spread more uniformly on the surface of a polymer film.

In this method, the treatment applied to the surface of the polymer film is preferably a hydrophilization treatment, which can relatively easily increase the surface tension of the polymer film surface.
The hydrophilization treatment is preferably a physical activation treatment such as a corona treatment, a plasma treatment, a glow treatment, or a UV ozone treatment, and more preferably at least one treatment selected from the group consisting of a corona treatment and a plasma treatment. These treatments allow the hydrophilization treatment to be carried out relatively easily and reliably.

The corona treatment is preferably carried out in the presence of a flammable gas (vinyl acetate, etc.) from the viewpoint of efficiently introducing polar functional groups.
Examples of plasma irradiation devices for plasma treatment include high frequency induction type, capacitively coupled electrode type, corona discharge electrode-plasma jet type, parallel plate type, remote plasma type, atmospheric pressure plasma type, and ICP high density plasma type.
The gas used in the plasma treatment is preferably a rare gas, hydrogen gas, or nitrogen gas, and specific examples of such gas include argon gas, a mixed gas of hydrogen gas and nitrogen gas, and a mixed gas of hydrogen gas, nitrogen gas, and argon gas.

The surface of the polymer film subjected to the above treatment preferably contains polar functional groups. The presence of polar functional groups on the surface of the polymer film increases the surface tension (wettability) and adhesiveness of the surface. This improves the uniformity of the thickness of the resulting polymer layer and further increases the adhesive strength between the polymer film and the polymer layer. The effect of reducing the linear expansion coefficient of the polymer film can also be expected.
The polar functional group present on the surface of the polymer film is preferably a hydroxyl group-containing group or a carbonyl group-containing group.
Furthermore, the polymer film may be subjected to an annealing treatment to adjust the residual stress thereof. The annealing treatment is preferably performed at a temperature of 120 to 180° C., under a pressure of 0.005 to 0.015 MPa for a time of 30 to 120 minutes.

The surface tension of the surface of the polymer film that has been subjected to the above treatment is preferably greater than the surface tension of the liquid dispersion medium, in which case the liquid composition can more smoothly and uniformly wet and spread over the surface of the polymer film.
Specifically, the difference in surface tension between the surface of the treated polymer film and the surface tension of the liquid dispersion medium is preferably 10 mN/m or more, more preferably 20 mN/m or more, and is preferably 50 mN/m or less, more preferably 40 mN/m or less.
The arithmetic mean roughness Ra of the surface of the polymer film is preferably 0.01 to 5 μm, more preferably 0.03 to 1 μm, in which case there are fewer steps that serve as starting points for the pinning phenomenon, making it easier for the liquid composition to wet and spread more uniformly over the surface of the polymer film.

When the liquid composition (polymer layer) contains an AR polymer, the absolute value of the difference between the glass transition point of the base polymer contained in the polymer film and the glass transition point of the AR polymer contained in the liquid composition (polymer layer) is preferably 20° C. or less, more preferably 10° C. or less. The absolute value of the difference in glass transition point may be 0° C. In this case, the glass transition points of the base polymer and the AR polymer become closer to each other, making the laminate film as a whole less susceptible to deformation due to heating.
The specific value of the glass transition point of the base polymer contained in the polymer film is preferably 230 to 340° C., more preferably 250 to 320° C. In this case, the degree of deformation of the polymer film due to heating is sufficiently low.

When the absolute value of the difference in glass transition temperature and the specific value of the glass transition temperature of the base polymer satisfy the above ranges, the occurrence of wrinkles on the surface of the obtained laminated film can be prevented or suppressed.
The base polymer contained in the polymer film is preferably an aromatic polyimide, since the use of an aromatic polyimide tends to reduce the degree of deformation of the polymer film due to heating.
The content of the base polymer in the polymer film is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass.

Base polymers include polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyamideimide, liquid crystalline polyester, and tetrafluoroethylene-based polymers, with aromatic polyimide being preferred.

The imide group density of the aromatic polyimide base polymer is preferably 0.20 to 0.35. If the imide group density is equal to or less than the upper limit, the water absorption rate of the polymer film is lowered, and changes in the dielectric properties of the laminated film are easily suppressed. If the imide group density is equal to or greater than the lower limit, the imide groups function as polar groups, which not only improves the adhesion between the polymer film and the polymer layer but also tends to significantly reduce the water absorption rate.
Furthermore, if the imide group density is within this range, wrinkles are less likely to occur in the laminated film, which is less likely to occur when the glass transition temperature of the aromatic polyimide in the polymer film is high.

The imide group density is the molecular weight per unit of the imide group portion (140.1) in a polyimide obtained by imidizing a polyimide precursor, divided by the molecular weight per unit of the polyimide. For example, the imide group density of a polyimide (molecular weight per unit: 382.2) obtained by imidizing a polyimide precursor consisting of two components, 1 mole of pyromellitic dianhydride (molecular weight: 218.1) and 1 mole of 3,4'-oxydianiline (molecular weight: 200.2), is 0.37, which is the value obtained by dividing 140.1 by 382.2.

Examples of aromatic polyimides include polyimides obtained by reacting diamine with carboxylic dianhydride to synthesize polyamic acid, and then imidizing the polyamic acid by thermal imidization or chemical imidization.
Examples of solvents for synthesizing polyamic acid include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

Diamines include 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 4,4'-oxydianiline, 3,3'-oxydianiline, 3,4'-oxydianiline, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 1,4-diaminobenzene (p-phenylenediamine), 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)biphenyl, Examples of the diamine component include 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 3,3'-dihydroxy-4,4'-diamino-1,1'-biphenyl, and 2,4-diaminotoluene. These diamine components may be used alone or in combination of two or more.

Carboxylic acid dianhydrides include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenylethertetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3 Examples of the dicarboxylic acid component include 1,3-bis(3,4-dicarboxyphenyl)methane dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3,2',3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldicyclohexane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride. These dicarboxylic acid components may be used alone or in combination of two or more.

Furthermore, the total moles of oxygen atoms derived from ether bonds contained in the diamine and the carboxylic acid dianhydride relative to the total moles of the diamine and the carboxylic acid dianhydride is preferably 35 to 70%, more preferably 45 to 65%. In this case, the flexibility of the polymer main chain of the aromatic polyimide is increased, the stackability of the aromatic rings is improved, and the adhesion between the polymer film and the polymer layer is further improved. In addition, in this case, the UV processability of the laminated film is also improved.
An inorganic filler may be added to such a polymer film for the purpose of improving properties such as yield strength, resistance to plastic deformation, thermal conductivity, loop stiffness, etc. Examples of such inorganic fillers include silicon oxide, titanium oxide, aluminum oxide, silicon nitride, boron nitride, calcium hydrogen phosphate, and calcium phosphate.

The polymer film preferably has a high yield strength. Specifically, the stress at 5% strain of the polymer film is preferably 180 MPa or more, more preferably 210 MPa or more. The stress at 5% strain is preferably 500 MPa or less.
Furthermore, the polymer film is preferably resistant to plastic deformation. Specifically, the stress at 15% strain of the polymer film is preferably 225 MPa or more, more preferably 245 MPa or more. The stress at 15% strain is preferably 580 MPa or less.
If the polymer film has high yield strength, particularly low plastic deformation resistance, the absolute value of the linear expansion coefficient of the laminated film can be easily made sufficiently low, and warping can be more reliably prevented.

The tensile modulus of the polymer film at 320° C. is preferably 0.2 GPa or more, more preferably 0.4 GPa or more, and is preferably 10 GPa or less, more preferably 5 GPa or less.
In this case, the laminate film has excellent handleability even when heated and cooled during processing. In other words, if the tensile modulus of the polymer film is equal to or greater than the above-mentioned lower limit, the shrinkage of the polymer layer during heating and cooling during processing is effectively alleviated by the elasticity of the polymer film, making the laminate film less likely to wrinkle, and the physical properties (surface smoothness, etc.) of the resulting laminate film are likely to be improved. This tendency becomes more pronounced when the content of the F polymer in the polymer layer or the thickness of the polymer layer is high. Furthermore, if the tensile modulus of the polymer film is equal to or less than the above-mentioned upper limit, the flexibility of the laminate film is likely to be further improved.

It is preferable that the polymer film be in direct contact with the polymer layer. That is, it is preferable that the polymer layer be formed (laminated) directly on the surface of the polymer film without surface treatment using a silane coupling agent, adhesive, etc. In this case, the physical properties of the resulting laminated film are less likely to deteriorate. Furthermore, with the above-mentioned configuration, high adhesion is achieved between the polymer film and the polymer layer even when they are in direct contact.

The method for applying the liquid composition to the polymer film may be any method that forms a stable liquid coating of the liquid composition on the surface of the polymer film, and includes 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.

When heating a polymer film on which a liquid coating has been formed, it is preferable to maintain the temperature in the low temperature range to remove the liquid dispersion medium, i.e., to dry the film. This results in a dried coating. The temperature in the low temperature range is preferably 80°C or higher and lower than 180°C. The temperature in the low temperature range refers to the temperature of the atmosphere during drying.
The temperature retention in the low temperature range may be carried out in one stage, or in two or more stages at different temperatures.
The atmosphere in which the temperature is maintained in the low temperature range may be either atmospheric pressure or reduced pressure, and may be any of an oxidizing gas atmosphere such as oxygen gas, a reducing gas atmosphere such as hydrogen gas, or an inert gas atmosphere such as a rare gas or nitrogen gas.

In this method, it is preferable to further heat the dried coating in a temperature range (hereinafter also referred to as the "baking range") that exceeds the holding temperature in the low temperature range, and bake the F powder (F polymer) to form a polymer layer on the surface of the polymer film. The temperature in the baking range means the temperature of the atmosphere during baking.
The formation of the polymer layer is thought to proceed as the particles of the F powder pack closely together and the F powder (F polymer) fuses together. When the liquid composition contains a heat-fusible AR polymer, a polymer layer consisting of a mixture of the F polymer and the AR polymer is formed, and when the liquid composition contains a thermosetting AR polymer, a polymer layer consisting of the F polymer and a cured product of the AR polymer is formed.

The firing atmosphere may be either normal pressure or reduced pressure, and may be any of an oxidizing gas atmosphere such as oxygen gas, a reducing gas atmosphere such as hydrogen gas, or an inert gas atmosphere such as a rare gas or nitrogen gas.
The firing atmosphere is preferably an inert gas atmosphere with a low oxygen concentration, and more preferably a nitrogen gas atmosphere with an oxygen concentration (volume basis) of less than 500 ppm. The oxygen concentration (volume basis) is typically 1 ppm or more. Within this range, oxidative decomposition of the polymer component is suppressed, while the adhesiveness of the polymer layer is likely to be improved.
The temperature in the baking zone is preferably equal to or higher than the melting temperature of the F polymer, more preferably 300 to 380°C.
The time for maintaining the temperature of the baking zone is preferably 30 seconds to 5 minutes, and particularly preferably 1 to 2 minutes.

When forming polymer layers on both sides of a polymer film, it is preferable to apply a liquid composition to one surface of the polymer film, heat it to remove the liquid dispersion medium, apply a liquid composition to the other surface of the polymer film, heat it to remove the liquid dispersion medium, and further heat it to bake the F polymer, thereby forming each polymer layer and obtaining a laminated film.
A laminated film having polymer layers on both sides of a polymer film may be obtained by applying a liquid composition to both surfaces of a polymer film, heating to remove the liquid dispersion medium, and further heating to bake the F polymer, thereby simultaneously forming polymer layers on both surfaces.

A laminated film having polymer layers on both sides of a polymer film is preferably obtained by immersing a polymer film in a liquid composition to apply the liquid composition to both surfaces of the polymer film, and then passing the film through a baking furnace and heating it. Specifically, it is more preferable to obtain the film by immersing a polymer film in the liquid composition, and then passing the polymer film through a baking furnace while pulling it out of the liquid composition.
The polymer film is preferably pulled up vertically and passed through the baking furnace in an upward direction. In this case, a smooth polymer layer is likely to be formed. After the polymer film is pulled up vertically, it may be further heated while being pulled down vertically, or it may be pulled down vertically without being heated.
The amount of the liquid composition applied to the polymer film can be adjusted by passing the polymer film with the liquid composition adhered thereto between a pair of rolls.
Such a laminated film can be suitably produced using an apparatus having a dip coater and a baking furnace, such as a vertical baking furnace or a glass cloth coating machine manufactured by Tabata Kikai Kogyo Co., Ltd.

The average thickness of the polymer film is preferably 10 μm or more, more preferably 15 μm or more, and is preferably 500 μm or less, more preferably 100 μm or less.
The average thickness of the polymer layer is preferably 10 μm or more, more preferably 15 μm or more. The average thickness of the polymer layer is preferably 500 μm or less, more preferably 100 μm or less. By using the liquid composition in this method, a relatively thick polymer layer with little thickness variation can be formed.
The average thickness of the laminate film is preferably 30 μm or more, more preferably 40 μm or more, and is preferably 1000 μm or less, more preferably 200 μm or less.

The laminate film of the present invention (hereinafter also referred to as "the present laminate film") comprises a polymer film having a surface treated to increase surface tension, and a polymer layer formed on the surface and containing an F polymer. In the present laminate film, the ratio of the thickness of the edge portion to the thickness of the center portion of the polymer layer is 1.1 or less, preferably 1.07 or less, and more preferably 1.04 or less. A polymer layer that satisfies this thickness relationship can be said to have little variation in thickness.
The present laminate film is preferably long. In this case, it is preferable that the ratio of the thickness at the center of the present laminate film in the width direction (short direction: CD direction) to the thickness at the end in the width direction satisfies the above-mentioned relationship. In this case, when the present long laminate film is wound into a roll and stored, wrinkles are less likely to occur at the end in the width direction if the thickness of the polymer layer satisfies the above-mentioned relationship.

The length of the long present laminate film in the longitudinal direction (MD direction) is preferably 1 to 1,000 m, and the length in the transverse direction (CD direction) is preferably 100 to 10,000 mm.
The definitions and ranges of the F polymer and AR polymer in the present laminate film, including preferred embodiments thereof, are the same as those in the present method. The ranges of the configuration and physical properties of the present laminate film, including preferred embodiments thereof, are also the same as those in the present method.
The present laminate film may have a polymer layer on only one side of the polymer film, or may have polymer layers on both sides of the polymer film, the latter being preferred, as this makes it easier to prevent warping of the present laminate film.

When the present laminate film has polymer layers on both sides of the polymer film, the ratio of the average thickness of the combined two polymer layers to the average thickness of the polymer film is preferably 1 or greater. This ratio is preferably 3 or less. In this case, a good balance is likely to be achieved between the properties of the base polymer in the polymer film (high yield strength, low plastic deformation, etc.) and the properties of the F polymer in the polymer layer (electrical properties such as low dielectric constant and low dielectric tangent, low water absorption, etc.). Furthermore, even in the present laminate film with a large ratio and thick polymer layers, warping and peeling are likely to be suppressed. This tendency is particularly pronounced when the tensile modulus of the polymer film is equal to or greater than the lower limit mentioned above.

It is also preferable that the thicknesses of the two polymer layers are equal, since in this case the linear expansion coefficients of the two polymer layers become closer to each other, making the laminate film even less susceptible to warping.
The dielectric constant of the present laminated film is preferably 2.0 to 3.0, making the present laminated film suitable for use as a printed circuit board material or the like that requires a low dielectric constant.
The dielectric loss tangent of the present laminated film is preferably 0.0001 to 0.0020.

The absolute value of the linear expansion coefficient of the present laminate film is preferably 30 ppm/°C or less, more preferably 20 ppm/°C or less, and even more preferably 10 ppm/°C or less. In this case, the occurrence of warping of the present laminate film is effectively prevented regardless of the temperature of the atmosphere in which the present laminate film is placed. The lower limit of the absolute value of the linear expansion coefficient of the present laminate film is 0 ppm/°C.
The peel strength between the polymer layer and the polymer film in the present laminate film is preferably 10 N/cm or more, more preferably 15 N/cm or more, and even more preferably 20 N/cm or more. The upper limit of the peel strength of the present laminate film is 100 N/cm.

Furthermore, this laminated film exhibits low water absorption (high water barrier properties), which is believed to be due to the fact that the polymer layer and polymer film are not integrated together in a compatible manner but exist independently of each other, and therefore the low water absorption of the F polymer complements the high water absorption of the base polymer.
Specifically, the present laminate film was pre-dried under conditions of 50°C for 48 hours, and then immersed in pure water at 23°C for 24 hours. When the mass of the present laminate film was measured before and after immersion in pure water, the mass of the present laminate film was calculated based on the following formula:
Water absorption rate (%) = (mass after immersion in pure water - mass after pre-drying) / mass after pre-drying x 100

The water absorption rate determined based on the above formula is preferably 0.1% or less, more preferably 0.07% or less, and even more preferably 0.05% or less. The lower limit of the water absorption rate of the present laminated film is 0%.
The present laminated film with such low water absorption is less likely to deform due to water absorption, and is therefore suitable for use as a printed circuit board material, etc.

Furthermore, this laminate film containing an AR polymer in the polymer layer has high ultraviolet (UV) absorption properties and is suitable for processing with a laser such as a UV-YAG laser. This is thought to be due to the fact that the AR polymer is highly dispersed in the polymer layer, forming a type of matrix and being uniformly distributed, which allows the aromatic rings in the AR polymer to exhibit good UV absorption properties.
Such a polymer layer allows via holes with good shapes to be easily formed by laser processing, and therefore the present laminate film having this polymer layer is particularly suitable for use as a printed circuit board material.

This laminate film, in which the polymer film is an aromatic polyimide film, is useful as a release film or carrier film. This laminate film has excellent adhesion between the polymer layer and the polymer film, making it resistant to delamination, allowing it to be used repeatedly as a carrier film. Furthermore, the polymer layer has excellent heat resistance, so its release properties are unlikely to deteriorate even with repeated use.

Specifically, a dispersion or varnish containing a resin or inorganic filler is applied to the surface of the polymer layer of the present laminate film, dried to form a coating film, and then the present laminate film is peeled off from the coating film to obtain an independent coating film. For example, after forming the coating film on the surface of the polymer layer of the present laminate film, the coating film side of the present laminate film having such a coating film is attached to another substrate, and the present laminate film is peeled off to obtain a laminate of the other substrate and the coating film.
When forming a coating on the surface of the polymer layer of the present laminate film, for example, during drying, the film may be heated at a temperature below the melting point of the F polymer. The present laminate film has excellent heat resistance and is therefore less likely to deform even after repeated heat treatments.

Specifically, the present laminate film is useful as a carrier film for forming ceramic green sheets, a carrier film for forming secondary batteries, a carrier film for forming solid polymer electrolyte membranes, and a carrier film for forming catalysts for solid polymer electrolyte membranes.
When the present laminate film is used as a carrier film, from the viewpoint of obtaining a coating film with a uniform thickness, the ratio of the thickness of the edge portion to the thickness of the center portion of the present laminate film is preferably 1.1 or less, more preferably 1.07 or less, and even more preferably 1.04 or less. The thickness ratio is 1 or more.

The present laminate film can be easily and firmly bonded to other substrates due to the excellent adhesiveness of the polymer layer surface. Examples of other substrates include metal foils and metal conductors. For example, by attaching metal foils to both sides of the present laminate film, a metal clad laminate can be obtained. The metal foils can then be processed to easily form the metal clad laminate into a printed circuit board.
Examples of metals that can be used to form the metal foil include copper, copper alloys, stainless steel, nickel, nickel alloys (including alloy 42), aluminum, aluminum alloys, titanium, and titanium alloys.
As the metal foil, copper foil is preferred, and rolled copper foil with no front and back distinction or electrolytic copper foil with front and back distinction is more preferred, and rolled copper foil is even more preferred. Rolled copper foil has small surface roughness, so that transmission loss can be reduced even when the metal clad 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 4 μm, in which case the adhesion to the polymer layer is good and a printed circuit board with excellent transmission characteristics is easily obtained.
The surface of the metal foil may be roughened by a method such as forming a roughened layer, dry etching, or wet etching.
The thickness of the metal foil may be any thickness that allows the metal clad laminate to exhibit sufficient functionality in its intended use, and is preferably less than 20 μm, more preferably 2 to 15 μm.
The surface of the metal foil may be partially or entirely treated with a silane coupling agent.

In the metal clad laminate, a method of laminating a metal foil on the surface of a polymer layer includes a method of hot pressing the present laminate film and the metal foil.
The pressing temperature in the heat press is preferably 310 to 400°C.
The heat pressing is preferably carried out at a vacuum of 20 kPa or less in order to prevent the inclusion of air bubbles and to prevent deterioration due to oxidation.
Furthermore, it is preferable to heat the heat press after the above-mentioned degree of vacuum is reached. If the temperature is raised before the above-mentioned degree of vacuum is reached, the polymer layer will be pressed in a softened state, i.e., in a state where it has a certain degree of fluidity and adhesiveness, which may cause bubbles.
The pressure in the hot press is preferably 0.2 to 10 MPa from the viewpoint of preventing damage to the metal foil and firmly adhering the polymer layer to the metal foil.
In particular, when the tensile modulus of the polymer film is equal to or greater than the above-mentioned lower limit, the occurrence of wrinkles due to heating and cooling in the heat press can be easily suppressed.

The metal clad laminate can be used in the manufacture of printed circuit boards as a flexible copper clad laminate or a rigid copper clad laminate.
The printed circuit board can be manufactured, for example, by processing the metal foil in the metal clad laminate into a conductor circuit (pattern circuit) of a predetermined pattern by etching or the like, or by processing the metal clad laminate of the present invention into a pattern circuit by electroplating (semi-additive process (SAP process), modified semi-additive process (MSAP process), etc.).
In the manufacture of a printed circuit board, after forming a pattern circuit, an interlayer insulating film may be formed on the pattern circuit, and a conductor circuit may further be formed on the interlayer insulating film, or a solder resist may be laminated on the pattern circuit, or a coverlay film may be laminated on the pattern circuit. The interlayer insulating film, solder resist, and coverlay film may each be formed from the above-mentioned liquid composition.

In metal clad laminates, the peel strength between the metal foil and the present laminate film is preferably 10 N/cm or more, more preferably 15 N/cm or more, and even more preferably 20 N/cm or more. The upper limit of the peel strength between the metal foil and the present laminate film is typically 100 N/cm. Because the present laminate film suppresses deformation during thermocompression bonding, it is bonded to the metal foil with high adhesion, making it easy to obtain a metal clad laminate with high peel strength.

Although the laminate film and the manufacturing method of the laminate film of the present invention have been described above, the present invention is not limited to the configurations of the above-described embodiments.
For example, in the laminated film of the present invention, any other configuration may be added to the configuration of the above-described embodiment, or any other configuration that exhibits the same function may be substituted.
Furthermore, in the method for producing the laminated film of the present invention, any other steps may be added to the configuration of the above-described embodiment, or any other steps that exhibit the same function may be substituted.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
1. Preparation of each component [F polymer]
F Polymer 1: A PFA-based polymer containing 98.0 mol%, 0.1 mol%, and 1.9 mol% of TFE units, NAH units, and PPVE units, in that order, and having 1,000 carbonyl group-containing groups per 1 x ¹⁰⁶ main chain carbon atoms (melting temperature: 300°C).
F Polymer 2: PFA-based polymer containing 97.5 mol% TFE units and 2.5 mol% PPVE units, in that order, and having 25 carbonyl group-containing groups per 1 x ¹⁰⁶ main chain carbon atoms (melting temperature: 305°C)
[powder]
Powder 1: Powder made of F polymer 1 with a D50 of 1.9 μm. Powder 2: Powder made of F polymer 2 with a D50 of 2.0 μm.

[Liquid dispersion medium]
Liquid dispersion medium 1: N-methyl-2-pyrrolidone (NMP: surface tension 41 mN/m)
Liquid dispersion medium 2: Toluene (Tol: surface tension 27 mN/m)
[Surfactant]
Surfactant 1: A nonionic polymer which _is a copolymer of _CH2 =C( _CH3 )C(O) _OCH2CH2 ( _CF2 ) _6F and _CH2 =C( _CH3 )C(O)( _OCH2CH2 ) _23OH and has a fluorine content of ₃₅ % by mass [AR polymer varnish]
Varnish 1: NMP solution (solid content: 10% by mass) containing AR polymer 1, which is an aromatic polyimide (glass transition point: 315°C).
[Polymer film]
Polyimide film 1: Aromatic polyimide film having a thickness of 50 μm, a glass transition point of 315° C., an imide group density of 0.25, and a tensile modulus at 320° C. of 0.3 GPa

2. Preparation of Liquid Composition (Liquid Composition 1)
67 parts by mass of liquid dispersion medium 1, 3 parts by mass of surfactant 1, and 30 parts by mass of powder 1 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 disperse powder 1, thereby obtaining liquid composition 1.
(Liquid composition 2)
87 parts by mass of liquid dispersion medium 1, 3 parts by mass of surfactant 1, and 10 parts by mass of powder 1 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 disperse powder 1, thereby obtaining liquid composition 2.

(Liquid composition 3)
Liquid composition 3 was prepared in the same manner as liquid composition 1, except that powder 1 was changed to powder 2.
(Liquid composition 4)
Liquid composition 4 was prepared in the same manner as liquid composition 3, except that liquid dispersion medium 1 was changed to liquid dispersion medium 2.
(Liquid composition 5)
70 parts by mass of liquid dispersion medium 1 and 30 parts by mass of powder 2 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 disperse powder 2, thereby obtaining liquid composition 5.
(Liquid composition 6)
57 parts by mass of liquid dispersion medium 1, 10 parts by mass of varnish 1, 3 parts by mass of surfactant 1, and 30 parts by mass of powder 1 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 disperse powder 1, thereby obtaining liquid composition 6.

3. Manufacturing of laminated film (Example 1)
First, both surfaces of the polyimide film 1 (surface tension: 35 mN/m, arithmetic mean roughness of the surface: 0.05 μm) were subjected to a corona treatment to introduce polar functional groups into the surface. The surface tension of the polyimide film 1 after the corona treatment was 78 mN/m.
Next, Liquid Composition 1 was applied to one side of Polyimide Film 1 by a small diameter gravure reverse method, and the film was passed through a forced air drying oven (oven temperature: 150°C) for 3 minutes to remove the NMP and form a dry coating.
Furthermore, the liquid composition 1 was similarly applied to the other surface of the polyimide film 1 and dried to form a dry film.
Next, the polyimide film 1 having the dry coating formed on both sides thereof was passed through a far-infrared oven (oven temperature: 320°C) for 20 minutes to melt and bake the powder 1. As a result, a polymer layer (thickness: 25 µm) containing F polymer 1 was formed on both sides of the polyimide film 1, and a long laminated film 1 was obtained in which the polymer layer, the polyimide film 1, and the polymer layer were directly formed in this order.

(Example 2)
Except for using Liquid Composition 2 instead of Liquid Composition 1, a polymer layer (thickness: 25 μm) containing F polymer 1 was formed on both sides of polyimide film 1 in the same manner as in Example 1, and a long laminated film 2 was obtained in which the above polymer layer, the above polyimide film 1, and the above polymer layer were directly formed in this order.
In the case of the laminated film 2, the process of applying the liquid composition 1 and melt-baking had to be repeated twice to form a polymer layer having a thickness of 25 μm.
(Example 3)
Except for using Liquid Composition 3 instead of Liquid Composition 1, a polymer layer (thickness: 25 μm) containing F polymer 2 was formed on both sides of polyimide film 1 in the same manner as in Example 1, and a long laminated film 3 was obtained in which the above polymer layer, the above polyimide film 1, and the above polymer layer were directly formed in this order.

(Example 4)
Except for using Liquid Composition 4 instead of Liquid Composition 1, a polymer layer (thickness: 25 μm) containing F polymer 2 was formed on both sides of polyimide film 1 in the same manner as in Example 1, and a long laminated film 4 was obtained in which the above polymer layer, the above polyimide film 1, and the above polymer layer were directly formed in this order.
(Example 5)
Except for using Liquid Composition 5 instead of Liquid Composition 1 and omitting the corona treatment on the surface of Polyimide Film 1, the same procedure as in Example 1 was repeated to form polymer layers (thickness: 25 μm) containing F Polymer 2 on both sides of Polyimide Film 1, and a long laminated film 5 was obtained in which the polymer layer, Polyimide Film 1, and Polymer layer were directly formed in this order.
(Example 6)
Except for using Liquid Composition 6 instead of Liquid Composition 1, polymer layers (thickness: 25 μm) containing F polymer 1 and AR polymer 1 were formed on both sides of Polyimide Film 1 in the same manner as in Example 1, and a long laminated film 6 was obtained in which the polymer layer, the polyimide film 1, and the polymer layer were directly formed in this order.

4. Evaluation 4-1. Appearance of Polymer Layer The surface of the polymer layer of each laminate film was visually observed and evaluated according to the following criteria.
[Evaluation criteria]
◯: The surface of the polymer layer is smooth with no irregularities observed.
x: The surface of the polymer layer is uneven and not smooth.

4-2. Uniformity of Thickness of Polymer Layer For each laminate film, the thickness of one polymer layer at the center and at the ends in the short direction was measured, and the ratio of the end thickness to the center thickness was calculated and evaluated according to the following criteria.
[Evaluation criteria]
Good: The thickness ratio is 1.07 or less.
Δ: The thickness ratio is greater than 1.07 and equal to or less than 1.1.
×: The thickness ratio is more than 1.1.

Each laminate film 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 laminate film was measured before and after immersion in pure water, and the water absorption was calculated based on the following formula and evaluated according to the following criteria.
Water absorption rate (%) = (mass after immersion in pure water - mass after pre-drying) / mass after pre-drying x 100
[Evaluation criteria]
⊚: Water absorption rate is 0.05% or less.
Good: The water absorption rate is more than 0.05% and not more than 0.07%.
△: The water absorption rate is more than 0.07% and 0.1% or less.
×: The water absorption rate is more than 0.1%.

4-4. Peel Strength A rectangular test piece measuring 100 mm in length and 10 mm in width was cut out from each laminate film. The polyimide film 1 and the polymer layer were then peeled from one end of the test piece in the longitudinal direction to a position 50 mm from the end. Next, using a tensile tester (manufactured by Orientec Co., Ltd.), the test piece was peeled at a 90-degree angle at a pulling rate of 50 mm/min, with the center being a position 50 mm from one end of the longitudinal direction. The maximum load was taken as the peel strength (N/cm), and the peel strength was evaluated according to the following evaluation criteria.
[Evaluation criteria]
Good: Peel strength is 15 N/cm or more.
Δ: Peel strength is 10 N/cm or more and less than 15 N/cm.
×: Peel strength is less than 10 N/cm.

4-5. Dielectric Loss Tangent The dielectric loss tangent of each laminate film was measured at 10 GHz by the SPDR (split post dielectric resonance) method and evaluated according to the following evaluation criteria.
[Evaluation criteria]
⊚: The dielectric loss tangent is 0.0015 or less.
Good: The dielectric loss tangent is greater than 0.0015 and equal to or less than 0.0020.
Δ: The dielectric loss tangent is more than 0.0020 and not more than 0.0030.
×: The dielectric loss tangent is more than 0.0030.
The results are shown in Table 1 below.

The laminated film of the present invention has excellent peel strength (adhesion) and high uniformity in the thickness of the polymer layer. Therefore, such laminated films can be processed and used for antenna parts, printed circuit boards, aircraft parts, automobile parts, etc.

Claims (10)

A method for manufacturing a laminated film, comprising: applying a liquid composition containing a tetrafluoroethylene-based polymer powder and a liquid dispersion medium having a surface tension of 30 mN/m or more to the surface of a polymer film that has been treated to increase its surface tension, the liquid composition containing the powder in an amount of 10 mass% or more; and heating the applied composition to obtain a laminated film having a polymer layer formed on the surface of the polymer film; wherein the surface tension of the surface of the treated polymer film is greater than the surface tension of the liquid dispersion medium . The manufacturing method described in claim 1, wherein the treatment is at least one hydrophilization treatment selected from the group consisting of corona treatment and plasma treatment. 3. The method according to claim 1 , wherein the polymer film has a surface with an arithmetic mean roughness Ra of 0.01 to 5 μm. The method according to any one of claims 1 to 3 , wherein polar functional groups are present on the surface of the polymer film that has been subjected to the treatment. The method according to any one of claims 1 to 4 , wherein the powder has an average particle size of 0.1 to 10 µm. The method according to any one of claims 1 to 5 , wherein the tetrafluoroethylene polymer has a melting temperature of 260 to 320°C. The method according to any one of claims 1 to 6 , wherein the tetrafluoroethylene-based polymer contains units based on perfluoro(alkyl vinyl ether), and the content of units based on perfluoro(alkyl vinyl ether) is 1.5 to 5.0 mol% based on all units. The method according to any one of claims 1 to 7 , wherein the liquid composition contains an aromatic polymer. The method according to any one of claims 1 to 8 , wherein the polymer film contains an aromatic polyimide. The method according to any one of claims 1 to 9 , wherein the polymer film has an average thickness of 10 µm or more, and the polymer layer has an average thickness of 10 µm or more.