Resin film, metal-clad laminate, circuit board, and method for manufacturing resin film

Abstract

The objective is to provide a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments. [Solution] A resin film containing at least a fluororesin, wherein the water contact angle of the surface of the resin film is 55° or more and 105° or less, and the surface of the resin film is measured according to JIS Z8781-4:2013 before and after heat treatment of the resin film at 180°C for 10 minutes, CIE1976(L * ,a * ,b * ) chromaticity difference Δb in color space * The color difference ΔE is 0.5 or less. * A resin film in which the ratio is 0.8 or less.

Description

Technical Field

[0001] The present disclosure relates to a resin film, a metal foil laminated body, a circuit board, and a method for manufacturing a resin film.

Background Art

[0002] In order to achieve high-speed communication by next-generation information communication (for example, high-frequency 5G), dielectric materials of printed circuit boards used for antennas and transmission lines are required to have low transmission loss characteristics. Against this background, fluororesin materials with excellent electrical properties have attracted attention as insulating materials for printed circuit boards. Since fluororesin materials generally have poor adhesiveness with other materials, surface modification techniques are used to improve adhesiveness. For example, Patent Document 1 describes performing corona discharge treatment on a long roll film. Patent Document 2 describes a resin film mainly composed of a fluororesin and having a pretreated surface on at least one surface. Patent Document 3 describes a fluororesin film having a modified surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a resin film capable of sufficiently maintaining adhesive strength with other materials even in a high-temperature environment, and a method for manufacturing the same. Another object of the present disclosure is to provide a metal foil laminated body and a circuit board capable of sufficiently maintaining interlayer adhesive strength even in a high-temperature environment. [Means for solving the problem]

[0005] This disclosure relates to a resin film comprising at least a fluororesin, wherein the water contact angle of the surface of the resin film is 55° or more and 105° or less, and the surface of the resin film is measured according to JIS Z8781-4:2013 before and after heat treatment of the resin film at 180°C for 10 minutes, and CIE1976(L * ,a * ,b * ) chromaticity difference Δb in color space * The color difference ΔE is 0.5 or less. * It is a resin film in which the ratio is 0.8 or less.

[0006] It is preferable that the water contact angle of the surface of the resin film after heat treatment of the resin film at 180°C for 10 minutes is 60° or more and 105° or less. The amount of components eluted from the resin film into the tetrahydrofuran, as measured by immersing the resin film in tetrahydrofuran, is preferably 900 ppm or less relative to the mass of the resin film. It is preferable that at least one surface of the resin film has a modified layer. The modified layer is preferably a layer formed by plasma treatment under a monomer-containing inert gas atmosphere. The monomers contained in the monomer-containing inert gas atmosphere preferably include aliphatic vinyl compounds. The fluororesin is preferably a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. Preferably, the adhesive strength to the copper foil, as measured by a 90-degree peel test using a laminate formed by bonding the resin film and copper foil at 200°C, is 2 N / cm or more, and the retention rate of the adhesive strength after leaving the laminate in a 290°C environment for 1 minute is 80% or more. The fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and has a plasma polymerization layer of vinyl acetate on at least one surface of the resin film, and the chromaticity difference Δb * is 0.0 or more and 0.5 or less, and the color difference ΔE * is preferably 0.0 or more and 0.7 or less.

[0007] This disclosure is also a metal-clad laminate including the resin film described above and a metal foil. The surface roughness (Rz) of the metal foil is preferably 1.5 μm or less. The metal-clad laminate preferably further includes a base material.

[0008] This disclosure is also a circuit board formed from the metal-clad laminate described above.

[0009] This disclosure is a method for manufacturing a resin film including at least a fluororesin, including a plasma treatment step of subjecting at least one surface of a fluororesin layer containing the fluororesin to plasma treatment under predetermined conditions in a monomer-containing inert gas atmosphere, where the predetermined conditions are conditions of a frequency of the applied voltage of 1 to 100 kHz and an electric field strength of 5 to 50 kV / mm, and is also a method for manufacturing a resin film.

[0010] The water contact angle of the surface of the resin film is 55° or more and 105° or less, and the chromaticity difference Δb * ,a * ,b * ) in the CIE1976 (L * space of the surface of the resin film, measured before and after heat-treating the resin film at 180° C. for 10 minutes in accordance with JIS Z8781-4:2013, is 0.5 or less, and the color difference ΔE * is preferably 0.8 or less. The fluororesin is preferably a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. It is preferable that the monomers contained in the monomer-containing inert gas atmosphere polymerize through the plasma treatment, thereby forming a polymer layer on the fluororesin layer. The monomer contained in the monomer-containing inert gas atmosphere is an aliphatic vinyl compound, and the concentration of the aliphatic vinyl compound in the monomer-containing inert gas atmosphere is preferably 0.1 to 5% by volume. The inert gas contained in the monomer-containing inert gas atmosphere is preferably one or more selected from the group consisting of nitrogen, argon, and helium. It is preferable that the plasma treatment is continuously performed on the surface of the fluororesin layer while the fluororesin layer is being conveyed by a roll-to-roll system. The fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and the plasma treatment is continuously performed on the surface of the fluororesin layer while the fluororesin layer is conveyed by roll-to-roll, and the monomer contained in the monomer-containing inert gas atmosphere polymerizes due to the plasma treatment, thereby forming a polymer layer on the fluororesin layer, the monomer contained in the monomer-containing inert gas atmosphere is vinyl acetate, the concentration of vinyl acetate in the monomer-containing inert gas atmosphere is 0.30 to 1.0 volume%, and the predetermined conditions are preferably a voltage frequency of 20 to 60 kHz and an electric field strength of 5 to 30 kV / mm. [Effects of the Invention]

[0011] The resin film of this disclosure and the resin film manufactured by the manufacturing method of this disclosure can maintain sufficient adhesive strength with other materials even in high-temperature environments. Furthermore, the metal-clad laminate and the circuit board of this disclosure can maintain sufficient interlayer adhesive strength even in high-temperature environments. [Modes for carrying out the invention]

[0012] The present disclosure will be explained in detail below. Fluoropolymer materials generally have poor adhesion to other materials, so surface modification technologies such as plasma treatment are used to improve adhesion. Conventional surface-modified resin films have a problem in that their adhesion to other materials tends to decrease, especially in high-temperature environments. The cause is speculative and not definitive, but it is thought that monomer-derived residues (e.g., by-products, more specifically decomposition products of monomers and / or aggregates of monomer homopolymers, etc.) generated during the surface modification process remain on the surface and / or inside the resin film, and that heat causes oxidation of the resin film. If a part of the resin film decomposes due to oxidation, it leads to the peeling of other materials from the resin film.

[0013] In light of the above issues, the resin film manufacturing method of this disclosure includes surface modification treatment under predetermined conditions. By treating under predetermined conditions, the generation of monomer-derived residues is suppressed, and a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments can be manufactured.

[0014] Furthermore, according to the resin film manufacturing method of this disclosure, it is presumed that by processing under predetermined conditions, functional groups that are resistant to thermal degradation (e.g., amide groups, imide groups, etc.) are imparted to the modified layer formed by monomer polymerization. As a result, it is presumed that the heat resistance of the manufactured resin film is improved, and the oxidative degradation of the resin film due to heat can be reduced. This point is also considered to contribute to maintaining the adhesive strength with other materials in high-temperature environments.

[0015] Furthermore, some conventional surface-modified resin films exhibit reduced wettability due to the volatilization of the modified layer itself during heat treatment. While such surface-modified resin films exhibit wettability immediately after modification, their wettability significantly decreases with heat treatment. On the other hand, resin films manufactured by the manufacturing method of this disclosure retain a sufficient modified layer even after heat treatment, thus maintaining sufficient wettability even in high-temperature environments. This also contributes to maintaining adhesive strength with other materials in high-temperature environments.

[0016] Furthermore, the inventors have found that the less the color change (especially the yellowing) of the resin film due to oxidation caused by heat, the less residue tends to be present. The degree of color change of the resin film serves as an indicator of the amount of residue in the resin film. Based on this finding, the resin film of this disclosure has a predetermined chromaticity difference Δb * and color difference ΔE * The resin film of this disclosure shall satisfy a predetermined chromaticity difference Δb * and color difference ΔE * By satisfying these requirements, the amount of monomer-derived residue is reduced, and the heat resistance of the resin film is improved, allowing sufficient adhesive strength to be maintained with other materials even in high-temperature environments.

[0017] [Resin film] The resin film of this disclosure will be described in detail below. The resin film of this disclosure contains at least a fluororesin. The water contact angle of the surface of the resin film is 55° to 105°. The surface temperature of the resin film is measured according to JIS Z8781-4:2013 before and after heat treatment of the resin film at 180°C for 10 minutes, according to CIE1976(L * ,a * ,b * ) chromaticity difference Δb in color space * The color difference ΔE is 0.5 or less. * The ratio is 0.8 or less. The resin film of this disclosure having the above characteristics tends to have little color change and therefore less resin film residue. As a result, the resin film of this disclosure can maintain sufficient adhesive strength with other materials even in high-temperature environments. Hereinafter, "heat treatment of the resin film at 180°C for 10 minutes" may be referred to as "specified heat treatment".

[0018] The surface properties of the resin film of this disclosure are described below. On at least one surface (one side or both sides) of the resin film of this disclosure, the chromaticity difference Δb * and color difference ΔE * The following conditions are met. In this disclosure, the surface of the resin film on which the following parameters are measured is the chromaticity difference Δb * and color difference ΔE *The surface to be measured is the same as the surface to be measured. In the resin film of this disclosure, it is preferable that at least one surface (one or both sides) is the measurement surface and satisfies the parameters shown below. If the resin film is subjected to a surface treatment such as plasma treatment, it is preferable that the surface-treated surface is the measurement surface and satisfies the parameters shown below.

[0019] <Chromaticity difference Δb * and color difference ΔE * > In this disclosure, brightness L * , chromaticity a * , and chromaticity b * (Hereafter simply "L * "a * " and "b * (Sometimes it is written as ") is measured according to JIS Z8781-4:2013 CIE1976 (L * ,a * ,b * ) This is a value in the color space. L * a * , and b * This is measured using a colorimeter (Konica Minolta "CR-400") capable of measuring according to JIS Z8781-4:2013.

[0020] In this disclosure, the chromaticity difference Δb * (Hereafter simply "Δb * (It is sometimes written as "Δb") is the formula "Δb * = (After specified heat treatment b * )-(before specified heat treatment b) * Δb is calculated from ")". * A larger value indicates a greater degree of yellowing after the specified heat treatment.

[0021] Color difference ΔE * (Hereafter simply "ΔE * The chromaticity difference ΔL (sometimes described as ") is calculated from the following formula. In this disclosure, the chromaticity difference ΔL in the following formula is calculated from the following formula. * (Hereafter simply "ΔL * (It is sometimes written as "ΔL") is the formula "ΔL * =(L after specified heat treatment) * )-(L before specified heat treatment)* It is calculated from the chromaticity difference Δa in the formula below. * (Hereafter simply "Δa * (It is sometimes written as "Δa") is the formula "Δa * = (a after predetermined heat treatment) * )-(a before specified heat treatment) * It is calculated from ").

[0022]

number

[0023] ΔE * An example of the criteria for making this judgment (Source: "Color Science Handbook," Author: Color Science Association of Japan, Publisher: University of Tokyo Press, 3rd edition published April 15, 2011) is shown in Table 1.

[0024] [Table 1]

[0025] As already mentioned, the Δb of the surface of the resin film before and after the predetermined heat treatment * It is 0.5 or less. From the viewpoint of maintaining sufficient adhesive strength with other materials even in high-temperature environments, the Δb of the surface of the resin film before and after the specified heat treatment is considered. * The Δb of the surface of the resin film before and after the predetermined heat treatment is preferably 0.4 or less, more preferably 0.3 or less, even more preferably 0.2 or less, and even more preferably 0.1 or less. * The lower limit is not particularly limited, but for example, it is 0.0 or greater.

[0026] As already mentioned, the ΔE of the resin film surface before and after the predetermined heat treatment * It is 0.8 or less. From the viewpoint of maintaining sufficient adhesive strength with other materials even in high-temperature environments, the ΔE of the resin film surface before and after the specified heat treatment is considered. *The ΔE of the surface of the resin film before and after the predetermined heat treatment is preferably 0.7 or less, more preferably 0.6 or less, even more preferably 0.5 or less, even more preferably 0.4 or less, and still more preferably 0.3 or less. * The lower limit is not particularly limited, but for example, it is 0.0 or greater.

[0027] The resin film disclosed herein has a surface Δb * is 0.5 or less, and ΔE * The value is 0.8 or less, and there is little change in color tone in high-temperature environments. Therefore, the resin film of this disclosure also has the advantage of being able to maintain the transparency of the resin film even in high-temperature environments.

[0028] <Water contact angle> In this disclosure, the water contact angle refers to the static contact angle of water. The water contact angle in this disclosure is measured using a fully automatic contact angle meter, DropMaster700 (manufactured by Kyowa Interface Chemical Co., Ltd.), by dropping 2 μL of water from a microsyringe onto a resin film placed horizontally and capturing a still image 1 second after dropping with a video microscope. In this disclosure, the water contact angle is the average value (numerical mean) of the values ​​measured at 15 measurement points on the surface of the resin film.

[0029] As already mentioned, the water contact angle of the resin film surface is 55° or higher. Preferably, the water contact angle of the resin film surface is 60° or higher, more preferably 70° or higher, even more preferably 80° or higher, and even more preferably 85° or higher. If the water contact angle is 55° or higher, the resin film can be given appropriate wettability. Furthermore, when a polymer layer is formed by the polymerization of monomers described later, if the water contact angle is 55° or higher, excessive self-polymerization of monomers is suppressed, and a sufficient amount of monomer-derived substituents that contribute to adhesion can be present on the surface of the resin film. Therefore, the adhesive strength of the resin film is less likely to decrease. On the other hand, as already mentioned, the water contact angle of the resin film surface is 105° or lower. When a surface modification treatment is applied to the resin film, the water contact angle of the resin film surface tends to be 105° or lower. In terms of giving the resin film appropriate wettability, it is more preferable that the water contact angle of the resin film surface is 100° or lower. Unless otherwise specified, the water contact angle of the resin film surface refers to the water contact angle of the resin film surface before the specified heat treatment.

[0030] The water contact angle of the resin film surface after predetermined heat treatment is preferably 60° or higher, more preferably 65° or higher, even more preferably 70° or higher, even more preferably 80° or higher, and even more preferably 85° or higher. If the water contact angle after predetermined heat treatment is 60° or higher, the resin film can be given appropriate wettability even in a high-temperature environment. Furthermore, when a polymer layer is formed by monomer polymerization as described later, if the water contact angle after predetermined heat treatment is 60° or higher, excessive self-polymerization of monomers is suppressed, and a sufficient amount of monomer-derived substituents that contribute to adhesion can be present on the surface of the resin film. Therefore, the adhesive strength of the resin film is less likely to decrease. On the other hand, from the viewpoint of the resin film maintaining an adhesive strength of a predetermined level or higher even in a high-temperature environment, the water contact angle of the resin film surface after predetermined heat treatment is preferably 105° or lower, and more preferably 100° or lower.

[0031] <Elution amount> The amount of components leached from the resin film into tetrahydrofuran (THF), as measured by immersing the resin film in THF, is preferably 900 ppm or less relative to the mass of the resin film. Hereinafter, "amount of components leached from the resin film into THF" may be referred to as "leached amount."

[0032] The amount of elution from the resin film is measured by the following method: Immerse a resin film in THF to a concentration of 100 g / L at 25°C for 100 hours. Hereinafter, "Immerse a resin film in THF to a concentration of 100 g / L at 25°C for 100 hours" may be referred to as "prescribed immersion." After prescribed immersion, remove the resin film from the THF. After immersion, concentrate the THF-containing liquid under reduced pressure using an evaporator, and then dry it at 90°C for 96 hours to collect the eluted material from the resin film into the THF. Dry the collected eluted material until it is completely dry, and measure the mass of the eluted material. Calculate the elution amount (in %) using the formula "elution amount = 100 × mass of eluted material / mass of resin film before immersion," and convert it to elution amount (in ppm).

[0033] The amount of leaching from the resin film is an indicator of the amount of residue remaining on the resin film. The less leaching from the resin film, the less residue tends to be left on the resin film. To reduce residue on the resin film and maintain sufficient adhesive strength with other materials even in high-temperature environments, the amount of leaching from the resin film is preferably 800 ppm or less, more preferably 700 ppm or less, even more preferably 600 ppm or less, even more preferably 500 ppm or less, even more preferably 400 ppm or less, and particularly preferably 300 ppm or less. The lower limit of the amount of leaching from the resin film is not particularly limited, but for example, it is 0 ppm or more.

[0034] <Adhesive strength> From the viewpoint of maintaining sufficient adhesive strength with other materials, the adhesive strength of the resin film to the copper foil is preferably 0.5 N / cm or more, more preferably 1 N / cm or more, even more preferably 2 N / cm or more, even more preferably 3 N / cm or more, even more preferably 4 N / cm or more, and particularly preferably 5 N / cm or more. The upper limit of the adhesive strength of the resin film to the copper foil is not particularly limited, but for example, it is 20 N / cm or less.

[0035] The adhesive strength between the copper foil and the resin film is measured by a 90-degree peel test using a laminate (hereinafter sometimes referred to as the "laminated material for peel testing") formed by bonding the resin film and copper foil at 200°C. Details of the measurement method will be described later in the examples.

[0036] From the viewpoint of maintaining sufficient adhesive strength with other materials even in high-temperature environments, it is preferable that the retention rate of adhesive strength after leaving the above-mentioned laminate for peel testing in a 290°C environment for 1 minute is 80% or more, more preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more. Hereinafter, "leaving the laminate for peel testing in a 290°C environment for 1 minute" may be referred to as "specified high-temperature standing." The upper limit of the retention rate of adhesive strength after specified high-temperature standing is not particularly limited, but for example, it is 100% or less.

[0037] The retention rate of adhesive strength after a predetermined high-temperature standing period is measured by the following method. First, the adhesive strength of the resin film and copper foil before the predetermined high-temperature standing period (adhesion strength before predetermined high-temperature standing period) is measured by the method described above. Next, the laminate for the peel test is subjected to a predetermined high-temperature standing period. Then, the adhesive strength of the resin film and copper foil after the predetermined high-temperature standing period (adhesion strength after predetermined high-temperature standing period) is measured by the method described above. The retention rate of adhesive strength after predetermined high-temperature standing period (in %) is calculated from the formula "Retention rate = 100 × Adhesion strength after predetermined high-temperature standing period / Adhesion strength before predetermined high-temperature standing period".

[0038] <Fluororesin> The resin film of this disclosure comprises at least a fluororesin. The fluororesin is not particularly limited and may be any polymer that partially contains fluorine atoms. Preferably, the fluororesin is a melt-mold fluororesin. Examples of melt-mold fluororesins include tetrafluoroethylene (TFE)-perfluoroalkyl vinyl ether (PAVE) copolymer [PFA], copolymer having chlorotrifluoroethylene (CTFE) units [CTFE copolymer], tetrafluoroethylene (TFE)-hexafluoropropylene (HFP) copolymer [FEP], tetrafluoroethylene (TFE)-ethylene copolymer [ETFE], polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), tetrafluoroethylene (TFE)-hexafluoropropylene (HFP)-vinylidene fluoride copolymer [THV], and tetrafluoroethylene (TFE)-vinylidene fluoride copolymer. By using a melt-mold fluororesin, melt molding can be performed, thus reducing processing costs compared to using PTFE. Furthermore, it improves adhesion when bonding with metal foil.

[0039] In particular, the fluororesin is preferably PFA or FEP, and more preferably PFA.

[0040] The melting point of PFA is preferably 180 to 340°C, more preferably 230 to 330°C, and even more preferably 280 to 320°C. The melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10°C / min using a differential scanning calorimeter (DSC).

[0041] While there are no particular limitations on the PFA, copolymers with a molar ratio of TFE units to PAVE units (TFE units / PAVE units) of 70 / 30 or more and less than 99.5 / 0.5 are preferred. More preferably, the molar ratio of TFE units to PAVE units (TFE units / PAVE units) is 70 / 30 or more and 98.9 / 1.1 or less, and even more preferably 80 / 20 or more and 98.5 / 1.5 or less. The higher the number of TFE units, the better the mechanical properties of the PFA tend to be. The lower the number of TFE units, the less the melting point of the PFA tends to be, and the better the moldability tends to be. Examples of PAVE units include perfluoropropyl vinyl ether (PPVE) units.

[0042] PFA may be a copolymer containing only TFE and PAVE. Alternatively, PFA may be a copolymer in which monomer units derived from monomers copolymerizable with TFE and PAVE amount to 0.1 to 10 mol%, and the total amount of TFE units and PAVE units is 90 to 99.9 mol%. Examples of monomers copolymerizable with TFE and PAVE include HFP, vinyl monomers represented as CZ3Z4=CZ5(CF2)nZ6 (wherein Z3, Z4, and Z5 are the same or different hydrogen atoms or fluorine atoms, Z6 is a hydrogen atom, fluorine atom, or chlorine atom, and n is an integer from 2 to 10), and alkyl perfluorovinyl ether derivatives represented as CF2=CF-OCH2-Rf7 (wherein Rf7 is a perfluoroalkyl group having 1 to 5 carbon atoms). Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group. Examples of acid anhydride monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, and maleic anhydride. One acid anhydride monomer may be used alone, or two or more may be used in combination.

[0043] The PFA preferably has a melt flow rate (MFR) of 0.1 to 100 g / 10 min, more preferably 0.5 to 90 g / 10 min, and even more preferably 1.0 to 85 g / 10 min. In this specification, the MFR is the value obtained by measuring under conditions of 372°C and a load of 5.0 kg in accordance with ASTM D3307.

[0044] Fluororesins are preferable to have fewer functional groups, and especially fewer unstable end groups. Such fluororesins can be produced by adjusting the conditions during manufacturing (polymerization reaction), or by reducing the number of unstable end groups by performing fluorine gas treatment, heat treatment, or supercritical gas extraction on the polymerized fluororesin. Fluorine gas treatment is preferred due to its excellent processing efficiency and the fact that some or all of the unstable end groups are converted to -CF3, becoming stable end groups. Fluorination treatment can be performed by contacting an unfluorinated fluororesin with a fluorine-containing compound. Using fluororesins with a reduced number of unstable end groups in this way is preferable because it reduces the electrostatic loss tangent and decreases the loss of electrical signals.

[0045] The number of unstable end groups mentioned above is not particularly limited, but for fluororesins with a main chain of 10 carbon atoms... 6 The value per unit is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. Considering the effect of reducing dielectric loss tangent, it is preferably less than 10, and even more preferably 5 or less.

[0046] Examples of unstable end groups include functional groups such as -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), hydroxyl groups (-CH2OH, etc.), -CONH2, -COOR (R=CH3, etc.), -CF2H, and -OCOO-R (n-propyl carbonate, etc.).

[0047] The number of unstable end groups is measured specifically by the following method. First, the above-mentioned fluororesin is melted and compressed to produce a film with a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain the infrared absorption spectrum of the above-mentioned fluororesin, and a difference spectrum is obtained from the base spectrum, which is completely fluorinated and does not contain any functional groups. From the absorption peak of a specific functional group that appears in this difference spectrum, the number of carbon atoms in the above-mentioned fluororesin is calculated according to the following formula (A): 1 × 10 6 Calculate the number of unstable terminals per unit. N = I × K / t (A) I: Absorbance K: Correction coefficient t: Film thickness (mm)

[0048] The fluororesin film of this disclosure may contain components other than fluororesin. The components that can be contained are not particularly limited and include fillers such as silica particles and glass short fibers, thermosetting resins that do not contain fluorine, and thermoplastic resins that do not contain fluorine. The content of components other than fluororesin is preferably 5% by mass or less (more preferably 3% or less, 1% or less, etc.).

[0049] Fluororesins can be produced by conventionally known methods, such as emulsion polymerization or suspension polymerization, by appropriately mixing monomers that form their constituent units and additives such as polymerization initiators as needed. Among these, fluororesins obtained by emulsion polymerization are preferred.

[0050] <Composition of resin film> The resin film of this disclosure is preferably elongated. Elongated means that the size in the length direction of the resin film is longer than the size in the width direction. The length of the resin film may be 0.3 m or more, 1 m or more, 50 m or more, 100 m or more, 200 m or more, 1000 m or more, 2000 m or more, or 5000 m or more. The upper limit of the length of the resin film is not particularly limited, but for example it may be 50000 m or less. The lower limit of the width of the resin film is not particularly limited, but for example it may be 200 mm or more, or 400 mm or more. The upper limit of the width of the resin film is not particularly limited, but for example it may be 2000 mm or less.

[0051] The thickness of the resin film of this disclosure is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The thickness of the resin film of this disclosure is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. The thickness of the resin film can be measured by reflection spectroscopy using the film thickness measurement system F20 (manufactured by Filmetrics).

[0052] The resin film of this disclosure preferably comprises a fluororesin layer and a modified layer. It is preferable that the modified layer be on at least one surface (one side or both sides) of the resin film. The fluororesin layer and the modified layer will be described below.

[0053] The fluororesin layer contains a fluororesin. The fluororesin described above is preferred. The fluororesin content in the fluororesin layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, and still more preferably 99.5% by mass or more. The fluororesin layer may also contain only fluororesin. The fluororesin content in the fluororesin layer may be 100% by mass.

[0054] The modified layer of this disclosure is extremely thin, and its thickness is preferably 1 nm to 100 nm, more preferably 1 nm to 50 nm, and even more preferably 1 nm to 20 nm. The thickness of the modified layer is measured by observing a cross-section of the resin film using an electron microscope (a field emission transmission electron microscope JEM-ARM200F manufactured by JEOL Ltd.).

[0055] The modified layer is preferably a polymer layer. The polymer layer is a layer formed by the polymerization of monomers (monomer polymerization layer). Preferably, the polymer layer is a layer formed by plasma treatment in a monomer-containing inert gas atmosphere (monomer plasma polymerization layer). Details of the plasma treatment will be described later. The polymer layer is preferably provided directly on top of the fluororesin layer. The polymer layer also functions as an adhesive layer to bond other materials to the resin film.

[0056] The polymer layer may completely cover the surface of the fluororesin layer. However, in many cases, the polymer layer does not completely cover the surface of the fluororesin layer to the extent that the fluorine element concentration on the surface of the resin film can be measured, and a portion of the fluororesin layer is exposed on the surface of the resin film. One example of a state in which a portion of the fluororesin layer is exposed on the surface of the resin film is when the fluororesin layer is exposed through gaps between substituents derived from numerous monomers introduced on the surface of the fluororesin layer.

[0057] Examples of monomers for forming the polymer layer include polymerizable or nonpolymerizable organic compounds containing oxygen atoms. Specific examples of monomers for forming the polymer layer include vinyl compounds such as aliphatic vinyl compounds; acrylic acid esters such as glycidyl methacrylate; carboxylic acids such as acetic acid and formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; carboxylic acid esters such as ethyl acetate and ethyl formate; and acrylic acids such as acrylic acid and methacrylic acid. Of these, vinyl compounds, acrylic acid esters, and ketones are preferred, with vinyl compounds being more preferred, due to their resistance to deactivation of the modified surface, long lifespan, and ease of handling.

[0058] From the viewpoint of achieving both polymerizability of monomers and adhesion to other materials, suitable examples of vinyl compounds that can be used as monomers include aliphatic vinyl compounds. Aliphatic vinyl compounds are aliphatic compounds having a vinyl group. The carbon chain of an aliphatic compound may be linear or branched. Furthermore, the carbon-carbon bond of the carbon chain of an aliphatic compound may be saturated or unsaturated. In addition, the carbon chain of an aliphatic compound may have heteroatoms such as oxygen atoms in addition to carbon atoms. From the viewpoint of achieving both polymerizability of monomers and adhesion to other materials, suitable examples of aliphatic vinyl compounds include those with the general formula (1) "H2C=CH-OR 1 Examples of compounds represented by " are shown. R in general formula (1) 1 This is an alkyl group having 1 to 6 carbon atoms, or the general formula (2) "-CO-R 2 This represents the base represented by " in general formula (2). 2 R represents a hydrogen atom, a C1-C6 alkyl group, or a C2-C6 alkenyl group. C1-C6 alkyl groups are linear or branched. C2-C6 alkenyl groups are linear or branched and may have one or more (e.g., two or three) double bonds. In general formula (1), R represents a hydrogen atom, a C1-C6 alkyl group, or a C2-C6 alkenyl group. 1The alkyl group having 1 to 6 carbon atoms represented by is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 or 2 carbon atoms. 2 The alkyl group having 1 to 6 carbon atoms represented by is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 or 2 carbon atoms. 2 As the alkenyl group having 2 to 6 carbon atoms represented by , an alkenyl group having 2 to 5 carbon atoms is preferred.

[0059] As compounds represented by general formula (1) that can be used as aliphatic vinyl compounds, vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, and vinyl sorbate; and ethers such as vinyl ethyl ether and vinyl methyl ether are desirable. Among these, aliphatic vinyl compounds consisting of vinyl acetate, vinyl propionate, vinyl formate, etc. are particularly preferred. When the vinyl compound contains aliphatic vinyl compounds such as vinyl acetate, vinyl propionate, and vinyl formate, the proportion of the aliphatic vinyl compound in the vinyl compound is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, even more preferably 99 mol% or more, and particularly preferably 100 mol%.

[0060] The resin constituting the polymer layer has units derived from the above-mentioned monomers as constituent units. Preferably, the resin constituting the polymer layer has units derived from vinyl compounds as constituent units, more preferably from aliphatic vinyl compounds, and even more preferably from vinyl acetate. In the resin constituting the polymer layer, the content of units derived from vinyl compounds is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, even more preferably 99 mol% or more, and particularly preferably 100 mol% of the total number of constituent units.

[0061] [Method for manufacturing resin film] This disclosure also relates to a method for manufacturing a resin film. The manufacturing method of this disclosure is a method for manufacturing a resin film that includes at least a fluororesin. By the manufacturing method of this disclosure, for example, the resin film of this disclosure described above can be manufactured.

[0062] The manufacturing method of the present disclosure includes a plasma treatment step. The manufacturing method of the resin film of the present disclosure includes, if necessary, a step of forming a fluororesin layer. However, if a commercially available fluororesin film is used as the fluororesin layer, the step of forming the fluororesin layer can be omitted.

[0063] <Fluororesin layer formation process> In the process of forming the fluororesin layer, a fluororesin layer containing fluororesin is formed. Examples of fluororesins used in forming the fluororesin layer include those described above. The fluororesin used in forming the fluororesin layer is preferably PFA or FEP, and more preferably PFA. The molding method for forming the fluororesin layer into a sheet is not particularly limited, but examples include a melt molding method and a casting method. An example of a melt molding method is extrusion molding. An example of a casting method is to prepare a solution or dispersion containing fluororesin, and then coat and dry it on a substrate such as metal such as copper foil or aluminum foil, or resin. The fluororesin layer formed on the substrate may be used together with the substrate or peeled off and used. Furthermore, the fluororesin layer may be formed by uniaxial stretching or biaxial stretching of the fluororesin, or it may be unstretched.

[0064] <Plasma treatment process> In the plasma treatment process, at least one surface of a fluororesin layer containing fluororesin is plasma treated under predetermined conditions in a monomer-containing inert gas atmosphere. The predetermined conditions are an applied voltage frequency of 1 to 100 kHz and an electric field strength of 5 to 50 kV / mm.

[0065] In the manufacturing method disclosed herein, plasma treatment is performed under conditions of an applied voltage frequency of 1 to 100 kHz and an electric field strength of 5 to 50 kV / mm. It is presumed that by treating under these conditions, monomers are efficiently decomposed, monomer-derived substituents are introduced into the main chain of the fluororesin, and a modified layer is formed. As a result, residual material in the resin film is reduced, hydrolysis of the resin film is suppressed, and a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments can be manufactured.

[0066] The plasma treatment may be performed on one side of the fluororesin layer or on both sides.

[0067] It is preferable to perform surface treatment by exposing the surface to be modified to an atmosphere of organic compound-containing inert gas, which includes an organic compound and an inert gas, inducing a discharge by applying a high-frequency voltage between electrodes, thereby generating active species on the surface, and then introducing functional groups of the organic compound or graft polymerization of a polymerizable organic compound. More specifically, it is preferable to form a polymer layer on the fluororesin layer by polymerization of monomers contained in the monomer-containing inert gas through plasma treatment. In detail, plasma of monomers contained in the monomer-containing inert gas is generated by corona discharge. The generated monomer plasma polymerizes (e.g., graft polymerization), forming a polymer layer on the surface of the fluororesin layer.

[0068] In terms of production efficiency and manufacturing cost, when the fluororesin layer is in a long shape, it is preferable to continuously perform plasma treatment on the surface of the fluororesin layer while conveying the long fluororesin layer by roll-to-roll, rather than by batch processing. Roll-to-roll is a processing method in which a roll of fluororesin layer is unwound, the unwound fluororesin layer is passed through a processing section (e.g., a plasma processing section), and the plasma-treated fluororesin layer, which is a resin film, is wound back into a roll shape.

[0069] In terms of improving processing continuity, the transport speed of the fluororesin layer is preferably 1 m / min or more and 100 m / min or less, more preferably 1 m / min or more and 50 m / min or less, and even more preferably 2.5 m / min or more and 25 m / min or less.

[0070] Plasma treatment may be carried out, for example, under atmospheric pressure (equivalent to 1 atmosphere, 1013 hPa) or a pressure close to it. However, plasma treatment is not limited to an atmospheric pressure environment, and may be carried out under a pressurized or depressurized environment in the range of 500 to 2000 hPa. Pressurization can prevent unintended gases (e.g., oxygen from the air) from entering the plasma atmosphere.

[0071] Examples of monomers included in the monomer-containing inert gas atmosphere include those similar to the monomers used to form the polymer layer described above. From the standpoint of the modified surface being less prone to deactivation and having a long lifespan, and ease of handling, the monomers included in the monomer-containing inert gas atmosphere are preferably vinyl compounds (preferably aliphatic vinyl compounds). When the monomer contains a vinyl compound, the proportion of the vinyl compound in the monomer is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, even more preferably 99 mol% or more, and particularly preferably 100 mol%. The vinyl compound is preferably an aliphatic vinyl compound. When the vinyl compound contains an aliphatic vinyl compound, the proportion of the aliphatic vinyl compound in the vinyl compound is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, even more preferably 99 mol% or more, and particularly preferably 100 mol%.

[0072] The concentration of monomer in the monomer-containing inert gas atmosphere varies depending on the type of monomer, the type of fluororesin to be surface-modified, etc., but is preferably 0.1 to 5% by volume, more preferably 0.1 to 3.0% by volume, even more preferably 0.1 to 1.0% by volume, even more preferably 0.15 to 1.0% by volume, and particularly preferably 0.30 to 1.0% by volume.

[0073] Examples of inert gases included in the monomer-containing inert gas atmosphere include nitrogen gas, helium gas, and argon gas. In order to stabilize the discharge and enable more uniform surface modification within the plane, it is preferable that the inert gas be one or more (for example, one to three) selected from the group consisting of nitrogen, argon, and helium, and more preferably nitrogen gas.

[0074] The inert gas contained in the monomer-containing inert gas atmosphere is preferably heated before mixing with the monomer. Heating the inert gas tends to reduce residual material in the resin film, making it possible to produce a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments. The temperature of the inert gas is, for example, 0°C to 150°C, preferably 20°C to 120°C, more preferably 40°C to 100°C, and even more preferably 50°C to 90°C.

[0075] The monomer-containing inert gas may contain carbon dioxide, but it is preferable that it does not contain carbon dioxide in order to suppress the carbonization of the monomer.

[0076] Plasma treatment can be performed, for example, using a corona discharge device. A corona discharge device comprises, for example, a discharge electrode and a ground electrode (for example, a roll-shaped ground electrode).

[0077] From the viewpoint of reducing resin film residue and manufacturing a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments, the frequency of the applied voltage, which is the discharge condition, is 1 kHz or higher, preferably 10 kHz or higher, more preferably 15 kHz or higher, even more preferably 20 kHz or higher, and even more preferably 25 kHz or higher. From the viewpoint of reducing resin film residue and manufacturing a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments, the frequency of the applied voltage is 100 kHz or lower, preferably 80 kHz or lower, more preferably 70 kHz or lower, even more preferably 60 kHz or lower, even more preferably 50 kHz or lower, even more preferably 40 kHz or lower, and particularly preferably 30 kHz or lower. The above applied voltage frequencies are relatively low, and it is presumed that this contributes to reducing resin film residue. The type of applied voltage is not particularly limited, but for example, it is an AC voltage.

[0078] From the viewpoint of reducing resin film residue and manufacturing a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments, the discharge condition, which is the electric field strength, is preferably 5kV / mm or more, and more preferably 10kV / mm or more. From the viewpoint of reducing resin film residue and manufacturing a resin film that can maintain sufficient adhesive strength with other materials even in high-temperature environments, the discharge condition, which is the electric field strength, is preferably 50kV / mm or less, more preferably 40kV / mm or less, and more preferably 30kV / mm or less.

[0079] The processing temperature can be any temperature within the range of 0°C to 100°C. To reduce stretching and wrinkling of the resin film, the processing temperature is preferably 80°C or lower. Note that when heat treatment is performed when laminating the resin film with other materials such as metal foil, the amount of oxygen on the surface of the resin film may decrease due to the heat treatment. Therefore, it is preferable to perform surface modification under conditions that ensure a sufficient amount of surface oxygen at the time the resin film and other materials such as metal foil are bonded together.

[0080] <Annealing process> The method for manufacturing a fluororesin film according to this disclosure may include an annealing step after the plasma treatment step, if necessary. Annealing can further reduce residual material in the resin film. If annealing is performed, it can be carried out by heat treatment. Heat treatment can be carried out, for example, by passing the film through a heating furnace in a roll-to-roll manner. Heat treatment may also be performed by placing the film in a batch-type drying oven.

[0081] However, the manufacturing method of this disclosure does not require an annealing process. As described above, by performing the plasma treatment process under predetermined conditions, residual resin film is reduced, and sufficient adhesive strength with other materials can be maintained even in high-temperature environments. Therefore, the manufacturing method of this disclosure can obtain the desired adhesive strength even without an annealing process. Furthermore, if annealing is omitted, the manufacturing method of this disclosure can shorten the production time.

[0082] The above describes an example of a method for manufacturing the resin film of this disclosure. However, the resin film of this disclosure described above is not limited to those manufactured by the above manufacturing method. For example, the resin film of this disclosure may be surface-treated by conventional methods such as corona discharge treatment, glow discharge treatment, plasma discharge treatment other than those described above, sputtering treatment, etc.

[0083] The resin film of this disclosure has the advantage of being able to maintain sufficient adhesive strength with other materials even in high-temperature environments. For this reason, the resin film of this disclosure can be suitably used in metal-clad laminates and circuit boards (especially circuit boards for high-frequency circuits). The resin film of this disclosure also has the advantage of being able to maintain its transparency even in high-temperature environments. For this reason, the resin film of this disclosure can be applied to various flexible devices, and is specifically useful in various display devices (e.g., liquid crystal display devices, organic EL display devices, touch panels, liquid crystal displays, organic EL displays, color filters, electronic paper, etc.), glass laminated transparent antennas, transparent antenna films, antenna-on displays, surface protective films for solar panels, substrate materials for solar cells, foldable displays, or components thereof.

[0084] [Metal-clad laminate] The present disclosure also relates to a metal-clad laminate. The metal-clad laminate of the present disclosure comprises the resin film of the present disclosure described above and a metal foil. Because it comprises the resin film of the present disclosure which can sufficiently maintain adhesive strength with other materials even in high-temperature environments, the metal-clad laminate of the present disclosure can sufficiently maintain interlayer adhesive strength even in high-temperature environments. Preferably, the metal-clad laminate further comprises a substrate.

[0085] <Metal foil> The metal foil is provided directly or indirectly on the resin film. The metal foil may be provided on both sides of the resin film or on one side. Examples of metals that make up the metal foil include copper, aluminum, stainless steel (SUS), nickel, and gold. Alloys of these may also be used. From the viewpoint of conductivity and circuit processability, copper foil is preferred as the metal foil.

[0086] The surface roughness (Rz) of the metal foil is preferably 1.5 μm or less, and more preferably 1.0 μm or less. The resin film of this disclosure described above also exhibits excellent adhesion to metal foil with a high degree of smoothness, such as Rz of 1.5 μm or less. The metal foil only needs to have an Rz of 1.5 μm or less on at least the surface that adheres to the resin film described above, and the Rz of the other surface is not particularly limited. The lower limit of the Rz of the metal foil is not particularly limited, but for example, it is 0.1 μm or more. The Rz of the metal foil is the sum of the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv). The Rz of the metal foil is the ten-point average roughness specified in JIS-B0601. In this disclosure, the Rz of the metal foil is the value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0087] The copper foils that can be used for metal foils are not particularly limited, and examples include rolled copper foil and electrolytic copper foil. The copper foil with an Rz of 1.5 μm or less is not particularly limited, and for example, unroughened copper foil that has not undergone roughening treatment can be used. Furthermore, the copper foil with an Rz of 1.5 μm or less is not particularly limited, and commercially available products can be used. Examples of commercially available copper foils with an Rz of 1.5 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm, Rz 0.85 μm) (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.).

[0088] When the metal foil is directly mounted on the resin film, the adhesive strength between the metal foil and the resin film is preferably 0.5 N / cm or more, more preferably 1 N / cm or more, even more preferably 2 N / cm or more, even more preferably 3 N / cm or more, even more preferably 4 N / cm or more, and particularly preferably 5 N / cm or more, as these materials are suitable for use as metal-clad laminates and circuit boards. The upper limit of the adhesive strength between the metal foil and the resin film is not particularly limited, but is, for example, 20 N / cm or less. The adhesive strength between the metal foil and the resin film is measured by a 90-degree peel test using a laminate formed by bonding the resin film and the metal at 200°C. Details of the measurement method will be described later in the examples.

[0089] The thickness of the metal foil is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm, and even more preferably in the range of 9 to 35 μm.

[0090] The metal foil may be surface-treated to enhance its adhesive strength with the resin film of this disclosure. The surface treatment of the metal foil is not particularly limited, but examples include plasma treatment, corona treatment, UV treatment, electron beam treatment, etc.

[0091] From the viewpoint of improving adhesion with the resin film, the metal foil may have a roughened layer on its surface. However, if the roughening treatment may reduce the performance required in this disclosure, the amount of roughened particles electrodeposited on the metal foil surface may be reduced as needed, or the metal foil may be in an unroughened state.

[0092] From the viewpoint of improving various properties, one or more layers selected from the group consisting of a heat-resistant treatment layer (nickel plating, titanium plating, etc.), a rust-preventive treatment layer, and a chromate treatment layer may be provided between the metal foil and the surface treatment layer. These layers may be a single layer or multiple layers.

[0093] <Base material> The base material is not particularly limited, but examples include fabrics made of glass fibers, glass nonwoven fabrics, and resin film layers. The fabrics made of glass fibers may be in the form of a prepreg impregnated with resin. Examples of resin films used as the base material include heat-resistant resin films and thermosetting resin films. Examples of heat-resistant resin films include polyimide, liquid crystal polymers, polyphenylene sulfide, cycloolefin polymers, and polystyrene. Examples of thermosetting resin films include epoxy resins, polyphenylene oxide, polyphenylene ethers, polybutadiene, and divinylbenzene. The heat-resistant resin film and thermosetting resin film may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but examples include glass cloth, and low-dielectric types are particularly preferred. The thickness of the base material is preferably in the range of 12 to 200 μm.

[0094] In the metal-clad laminate of this disclosure, the lamination order and manufacturing method of the metal foil layer, substrate layer, and the resin film described above are not particularly limited, and the layer configuration can be adapted to the purpose. Specifically, examples of lamination orders include those consisting of a substrate layer / resin film / metal layer, a metal layer / resin film / substrate layer / resin film / metal layer, a metal layer / substrate layer / resin film / substrate layer / metal layer, and a metal layer / substrate layer / resin film / metal layer. Alternatively, the lamination order may consist of a metal layer / resin film / metal layer. Furthermore, other layers may be included as needed.

[0095] <Method for manufacturing metal-clad laminates> The metal-clad laminate of this disclosure has a metal layer formed on the surface of a resin film. The metal layer may be formed on one or both sides of the resin film. Examples of methods for forming the metal layer include laminating a metal foil onto the surface of the resin film, vapor deposition, and plating.

[0096] There are no particular limitations on the method for compounding metal foil, other layers, and resin films, but two examples include the following: (i) A method of laminating metal foil, other layers, and pre-formed resin films by applying pressure under heating using a roll-to-roll process or a press. The layer facing the metal foil may be any other layer or a resin film. (ii) A method of manufacturing a laminate by adhering a resin film to one side of a metal foil, and laminating the resin side not facing the metal foil with the other layers by applying pressure under heating.

[0097] The metal-clad laminate of this disclosure can maintain sufficient interlayer adhesion strength even in high-temperature environments. Because it can maintain surface smoothness of the interlayer adhesion surfaces, the metal-clad laminate of this disclosure has the advantage of low transmission loss. Therefore, the metal-clad laminate of this disclosure can be suitably used in the circuit substrates described below.

[0098] [Circuit board] This disclosure also relates to a circuit board formed from the metal-clad laminate described above. Since the metal-clad laminate of this disclosure can maintain sufficient interlayer adhesion strength even in high-temperature environments, the circuit board of this disclosure can also maintain sufficient interlayer adhesion strength even in high-temperature environments, resulting in low transmission loss.

[0099] The method for manufacturing the circuit board of this disclosure is not particularly limited and can be manufactured by a general method using the metal-clad laminate described above. In one example, the circuit board of this disclosure can be manufactured by etching the metal-clad laminate. By etching, a pattern is printed onto the metal foil of the metal-clad laminate to form a printed circuit board. Examples of etching solutions include acidic or alkaline chemical solutions, and more specifically, aqueous ferric chloride solutions. After etching, the circuit board may be washed and dried as needed. In addition, dry etching using gas may be performed instead of wet etching using an etching solution. Furthermore, the specific method of etching is not particularly limited and can be carried out by any known method.

[0100] The circuit boards of this disclosure can be suitably used as printed circuit boards. A printed circuit board is a plate-shaped component used to electrically connect electronic components such as semiconductors and capacitor chips, and to arrange and fix them within a limited space. The configuration of the printed circuit board is not particularly limited. The printed circuit board may be a rigid board, a flexible board, or a rigid-flexible board. Furthermore, the printed circuit board may be a single-sided board, a single-sided board, a double-sided board, or a multilayer board (such as a pull-up board).

[0101] The circuit board of this disclosure is particularly suitable for use as a circuit board for high-frequency circuits. In this disclosure, a high-frequency circuit includes not only circuits that simply transmit high-frequency signals, but also circuits that have transmission lines for transmitting non-high-frequency signals on the same plane, such as transmission lines that convert high-frequency signals to low-frequency signals and output the generated low-frequency signals to the outside, and transmission lines that supply power for driving high-frequency compatible components. Furthermore, the circuit board of this disclosure can also be used as a circuit board for antennas, filters, and the like.

[0102] While embodiments of this disclosure have been described above, it will be understood that a variety of modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0103] The present disclosure will be described below in detail based on examples, but the present disclosure is not limited in any way to the examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0104] The fluororesins used in the examples and comparative examples are shown below. Fluorinated PFA: Terminally fluorinated TFE / PPVE copolymer (Composition: TFE / PPVE = 96.1 / 3.9 (mass%), MFR: 16.0 g / 10 min, Melting point: 305°C, Number of unstable end groups: Undetectable (Main chain carbon number 10) 6 (Less than 1 per unit) PFA: Untreated TFE / PPVE copolymer (Composition: TFE / PPVE = 95.4 / 4.6 (mass%), MFR: 15.8 g / 10 min, Melting point: 305°C, Number of unstable end groups: 10 carbon atoms in the main chain) 6 (297 pieces per unit)

[0105] [Example 1] <Manufacturing of fluororesin sheets> F-type PFA was fed into a 360°C extruder, extruded through a 1700mm wide T-die, taken up onto a metal cooling roll, and then wound onto a winding core to obtain a roll of fluororesin sheet (equivalent to a fluororesin layer) with a width of 1300mm and a thickness of 12μm.

[0106] <Plasma Treatment> A roll-shaped fluororesin sheet was plasma-treated on both sides while being conveyed by a roll-to-roll system. Specifically, under atmospheric pressure, a monomer-containing inert gas containing 0.5% by volume of vinyl acetate and nitrogen gas was flowed near the discharge electrode of a corona discharge device and the roll-shaped ground electrode, while the fluororesin sheet, which was aligned with the roll-shaped ground electrode, was continuously passed between the electrodes. The nitrogen gas was heated to 50°C before mixing with vinyl acetate. Both sides of the fluororesin sheet were plasma-treated by applying corona discharge under conditions of an electric field strength of 17.1 kV / mm and an applied voltage frequency of 20 kHz. The plasma-treated fluororesin sheet was wound into a roll to obtain the resin film of Example 1.

[0107] [Examples 2-6 and Comparative Examples 1-2] Except for the fluororesin used in the manufacture of the fluororesin sheet, and the frequency of the applied voltage, electric field strength, type of inert gas, and temperature of the inert gas used in the plasma treatment, which are as shown in Tables 2 and 3 described later, resin films of Examples 2 to 6 and Comparative Examples 1 to 2 were obtained in the same manner as in Example 1.

[0108] [Reference example] As a reference example resin film, a fluororesin sheet made from the F-type PFA of Example 1 was used without plasma treatment.

[0109] [Specified heat treatment] The obtained resin film was cut to a predetermined size (100 mm x 200 mm), placed on a metal plate covered with PTFE-impregnated glass cloth, and heated in an electric furnace under an air atmosphere at 180°C for 10 minutes without any load. The heated film was removed and allowed to stand for at least 30 minutes in an environment of 25°C, and then cooled to 25°C.

[0110] [Method for measuring color changes] Using a colorimeter capable of measurement according to JIS Z8781-4:2013 (Konica Minolta "CR-400"), CIE1976 (L * ,a * ,b * ) L in the color space * a * , and b * The following measurements were taken. The plasma-treated surface of the resin film was used as the measurement surface, and the resin film was placed on a white calibration plate (Konica Minolta "CR-A43"), and measurements were taken under the following conditions. The modified surface of the resin film before the predetermined heat treatment and the modified surface of the resin film after the predetermined heat treatment were measured. * a * , and b * Measure Δb * And ΔE was calculated. (Measurement conditions) • Light source: Auxiliary illuminant C (C light source) for color measurement as defined in JIS Z8720:2012 • Vision: 2 times • The stimulus values ​​X, Y, and Z obtained when measuring the color of the white calibration plate are normalized so that they fall within ±0.03 of the reference value.

[0111] [Method for measuring the water contact angle] The water contact angle was measured using a fully automatic contact angle meter, DropMaster700 (manufactured by Kyowa Interface Chemical Co., Ltd.), in the following manner. 2 μL of water was dropped onto a horizontally placed resin film from a microsyringe, and a still image was captured 1 second after dropping using a video microscope. Measurements were obtained at 15 points on the surface of the resin film (5 points every 2 mm in the width direction of the resin film, and 3 points every 2 mm in the length direction of the resin film), and the average value was defined as the water contact angle. The water contact angle was measured for both the resin film before and after the predetermined heat treatment.

[0112] [Elution amount (extraction amount)] 20 g of resin film was immersed in 200 mL of THF at 25°C for 100 hours. After immersion, the resin film was removed from the THF. The THF-containing solution was concentrated under reduced pressure using an evaporator, and then dried in an oven at 90°C for 96 hours to completely remove the THF and obtain the eluate. The eluate was dried until completely dry, and its mass was measured. The eluate amount (in %) was calculated using the formula "eluate amount = 100 × mass of eluate / mass of resin film before immersion," and converted to the eluate amount (extraction amount in Tables 2 and 3, in ppm).

[0113] [90-degree peel test] (Method for manufacturing laminates for peel testing) Using a resin film and electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm, Rz 0.85 μm, unroughened copper foil) (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.), the copper foil, resin film, and copper foil were stacked in that order, and the laminates were heat-pressed in a vacuum heat press machine (model number: MKP-1000HVWH-S7 / manufactured by Mikado Technos Co., Ltd.) at a press temperature of 200°C, a preheating time of 120 seconds, a pressurizing pressure of 3 MPa, and a pressurizing time of 15 minutes to obtain a laminate for peel testing. The size of the resin film was 1 cm (length direction of the resin film) x 10 cm (width direction of the resin film).

[0114] (Peel test method) An aluminum plate was attached to the underside of the laminate for the peel test using adhesive tape. Using a precision universal testing machine Autograph AGS-X 100N (manufactured by Shimadzu Corporation), the copper foil was gripped and pulled at a speed of 50 mm per minute at a 90-degree angle to the plane of the laminate for the peel test and in the direction of the long side of the laminate (the width direction of the resin film). The peel strength of the copper foil was measured, and the obtained value was defined as the adhesive strength. The peel surface was the interface between the copper foil on the upper side of the peel test sample and the resin film.

[0115] (Adhesive strength) Using the peel test method described above, the adhesive strength was measured at five locations on the surface of the resin film (five locations spaced 200 mm apart in the width direction of the resin film), and the average value was defined as the adhesive strength.

[0116] (retention rate) The laminate for the peel test was left to stand in an environment of 290°C for 1 minute (predetermined high-temperature standing). The adhesive strength of the resin film after predetermined high-temperature standing (adhesive strength after predetermined high-temperature standing) was measured using the peel test method described above. The retention rate (in %) of the adhesive strength after predetermined high-temperature standing was calculated using the formula "Retention rate = 100 × Adhesive strength after predetermined high-temperature standing / Adhesive strength before predetermined high-temperature standing".

[0117] The measurement results for the resin films of Examples 1-6, Comparative Examples 1-2, and the Reference Example are shown in Tables 2 and 3.

[0118] [Table 2]

[0119] [Table 3]

[0120] As is clear from Tables 2 and 3, the resin films of the examples had a high retention rate of adhesive strength and were able to maintain sufficient adhesive strength with other materials even in high-temperature environments. [Industrial applicability]

[0121] The resin film of this disclosure can be suitably used as a circuit board.

Claims

1. A resin film containing at least a fluororesin, The water contact angle of the surface of the resin film is 55° or more and 105° or less. The surface of the resin film is measured according to JIS Z8781-4:2013 before and after heat treatment of the resin film at 180°C for 10 minutes, according to CIE1976(L ＊ , a ＊ , b ＊ ) chromaticity difference Δb in color space ＊ The color difference ΔE is 0.5 or less. ＊ A resin film in which the ratio is 0.8 or less.

2. The resin film according to claim 1, wherein the water contact angle of the surface of the resin film after heat treatment at 180°C for 10 minutes is 60° or more and 105° or less.

3. The resin film according to claim 1 or 2, wherein the amount of components eluted from the resin film into the tetrahydrofuran, as measured by immersing the resin film in tetrahydrofuran, is 900 ppm or less relative to the mass of the resin film.

4. The resin film according to claim 1 or 2, wherein at least one surface of the resin film has a modified layer.

5. The resin film according to claim 4, wherein the modified layer is a layer formed by plasma treatment under a monomer-containing inert gas atmosphere.

6. The resin film according to claim 5, wherein the monomer contained in the monomer-containing inert gas atmosphere includes an aliphatic vinyl compound.

7. The resin film according to claim 1 or 2, wherein the fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer.

8. The adhesive strength to the copper foil, as measured by a 90-degree peel test using a laminate formed by bonding the resin film and copper foil at 200°C, is 2 N / cm or more. The resin film according to claim 1 or 2, wherein the retention rate of the adhesive strength after the laminate is left standing in an environment of 290°C for 1 minute is 80% or more.

9. The aforementioned fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, The resin film has a plasma polymerization layer of vinyl acetate on at least one surface, The chromaticity difference Δb ＊ The color difference ΔE is 0.0 or more and 0.5 or less. ＊ The resin film according to claim 1 or 2, wherein the ratio is 0.0 or more and 0.7 or less.

10. A metal-clad laminate comprising a resin film according to claim 1 or 2 and a metal foil.

11. The metal-clad laminate according to claim 10, wherein the surface roughness (Rz) of the metal foil is 1.5 μm or less.

12. The metal-clad laminate according to claim 10, further comprising a base material.

13. A circuit board formed from a metal-clad laminate as described in claim 10.

14. A method for producing a resin film containing at least a fluororesin, The process includes a plasma treatment step in which at least one surface of the fluororesin layer containing the fluororesin is plasma treated under predetermined conditions in a monomer-containing inert gas atmosphere. A method for manufacturing a resin film, wherein the predetermined conditions are that the applied voltage has a frequency of 1 to 100 kHz and an electric field strength of 5 to 50 kV / mm.

15. The water contact angle of the surface of the resin film is 55° or more and 105° or less. The chromaticity difference Δb in the CIE1976 (L ＊ , a ＊ , b ＊ ) color space of the surface of the resin film, measured in accordance with JIS Z8781-4:2013, before and after heat-treating the resin film at 180°C for 10 minutes, is 0.5 or less, and the color difference ΔE ＊ is 0.8 or less. The method for producing a resin film according to claim ＊ 14.

16. The method for producing a resin film according to claim 14 or 15, wherein the fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer.

17. A method for producing a resin film according to claim 14 or 15, wherein a polymer layer is formed on the fluororesin layer by polymerization of monomers contained in the monomer-containing inert gas atmosphere through the plasma treatment.

18. The method for producing a resin film according to claim 14 or 15, wherein the monomer contained in the monomer-containing inert gas atmosphere is an aliphatic vinyl compound, and the concentration of the aliphatic vinyl compound in the monomer-containing inert gas atmosphere is 0.1 to 5% by volume.

19. The method for producing a resin film according to claim 14 or 15, wherein the inert gas contained in the monomer-containing inert gas atmosphere is one or more selected from the group consisting of nitrogen, argon, and helium.

20. A method for manufacturing a resin film according to claim 14 or 15, wherein the plasma treatment is continuously performed on the surface of the fluororesin layer while the fluororesin layer is being conveyed by roll-to-roll.

21. The aforementioned fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, While the fluororesin layer is being conveyed by a roll-to-roll mechanism, the plasma treatment is continuously performed on the surface of the fluororesin layer. The plasma treatment causes polymerization of monomers contained in the monomer-containing inert gas atmosphere, thereby forming a polymer layer on the fluororesin layer. The monomer contained in the monomer-containing inert gas atmosphere is vinyl acetate. The concentration of vinyl acetate in the monomer-containing inert gas atmosphere is 0.30 to 1.0% by volume. The method for manufacturing a resin film according to claim 14 or 15, wherein the predetermined conditions are that the applied voltage has a frequency of 20 to 60 kHz and an electric field strength of 5 to 30 kV / mm.

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