Dispersion composition, fluorine-based resin film, metal-clad laminate, and method for producing the same

Abstract

A dispersion composition containing (A) a fluororesin powder, (B) an inorganic filler, (C) a dispersant, and (D) an organic solvent, wherein the dispersion composition satisfies that the content of component (A) is 15-40 wt% and the content of component (B) is 60-85 wt% relative to the total weight of component (A) and component (B), and, when the volume-based particle size distribution is measured by a laser diffraction / scattering method, component (B) has (i) at least one or more peak tops each between 8-15 μm and 0.1-5 μm and (ii) D10 is within the 0.1-3 μm range, D50 is within the 5-15 μm range, and the proportion of particles having a particle size of 5 μm or more is 60 vol% or more.

Description

[Technical Field]

[0001] The present invention relates to a dispersion composition, a fluororesin film, a metal-clad laminate, and a method for producing the same. [Background technology]

[0002] In recent years, with the progress in miniaturization, weight reduction, and space-saving of electronic devices, there has been an increasing demand for flexible printed circuits (FPCs), which are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow for three-dimensional, high-density packaging even in limited spaces, their applications are expanding to include wiring for electronic devices such as hard disk drives, DVDs, and smartphones, as well as components such as cables and connectors.

[0003] FPCs are manufactured by etching the metal layer of metal-clad laminates such as copper-clad laminates (CCL) to create wiring. Currently, metal-clad laminates that use highly heat-resistant polyimide for the insulating resin layer that contacts the metal foil are commonly used. However, with the recent increase in speed of communication devices, development of 5G and even 6G communications is progressing, and circuit board materials are being investigated for millimeter-wave radar boards and antenna boards that are compatible with high-speed communication standards. Among such materials, fluororesins have attracted attention due to their low dielectric loss tangent and the potential for reducing signal transmission loss.

[0004] For example, Patent Document 1 discloses a method (casting method) for producing a fluororesin film by using a dispersion composition in which fluororesin powder is uniformly dispersed and applying this to a substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. WO2021 / 235252 Summary of the Invention [Problem to be solved by the invention]

[0006] Because fluororesins have a large coefficient of thermal expansion (CTE), inorganic fillers are often incorporated into dispersion compositions to achieve the low thermal expansion required for insulating materials for circuit boards while taking advantage of their low dielectric loss tangent. However, when inorganic fillers are incorporated at high concentrations, voids form around the fillers due to differences in the thermal expansion coefficient between the fillers and the matrix resin, reducing the film's density and potentially reducing peel strength and electrical properties. Furthermore, when dispersion compositions containing fluororesin powder are applied, numerous voids and cracks exist between the powder particles in the coating. While it is possible to fill most of these voids by performing a heat treatment to melt the fluororesin powder, if volatile solvents, dispersants, or dispersant decomposition products remain in the film after heating, they can gasify and create new voids in subsequent processes. In particular, when fine inorganic fillers are incorporated at high concentrations and uniformly, the small distance between the inorganic fillers makes it difficult for gasified components to escape from the film, making them more likely to remain within the film. The above-mentioned Patent Document 1 also states that swelling and cracks occur due to gas generated when a fluororesin layer is formed by a casting method, and proposes providing a heat compression process to reduce voids in the film and form a dense film.

[0007] However, although the voids that occur around the filler due to differences in thermal expansion coefficients and the voids that occur due to solvent gas can be reduced by heating and compression, it has become clear that relatively small voids, for example, microvoids with a diameter of 1 μm or less, still remain in the film. Hereinafter, these microvoids will be referred to as "microbubbles" to distinguish them from the relatively large voids around the filler, voids due to solvent gas, cracks, etc.

[0008] Therefore, an object of the present invention is to provide a dispersion composition that can minimize voids such as microbubbles in a fluororesin film when the film is formed by a casting method, and further to provide a dense fluororesin film that is obtained using this dispersion composition and is substantially free of not only large voids and cracks but also microbubbles, a metal-clad laminate that uses the fluororesin film as an insulating resin layer, and methods for producing the same. [Means for solving the problem]

[0009] The present inventors have investigated the causes of the generation of microbubbles and have obtained the following findings (1) to (3). (1) When heated, the dispersant in the coating decomposes into low molecular weight compounds and gasifies, causing microbubbles. (2) Microbubbles are particularly likely to occur in films that contain fine inorganic fillers uniformly and at high concentrations. (3) After the coating is melt-heat treated at a temperature above the melting point of the fluororesin to form a film, the dispersant remains, generating micro-bubbles during the heating and pressurizing process. Based on these findings, the present inventors have conducted extensive research to reduce microbubbles, and have found that the above-mentioned problems can be solved by using an inorganic filler with a controlled particle size distribution to be blended into the dispersion composition and by carrying out a melt heat treatment under conditions that allow the decomposition products of the dispersant to be efficiently removed outside the film, thereby completing the present invention.

[0010] That is, the dispersion composition of the present invention comprises the following components (A) to (D): (A) Fluorine-based resin powder, (B) inorganic filler; (C) a dispersant, (D) Organic solvent The dispersion composition contains: The dispersion composition of the present invention has a content of component (A) in the range of 15 to 40% by weight and a content of component (B) in the range of 60 to 85% by weight, based on the total amount of component (A) and component (B); When the particle size distribution of component (B) is measured on a volume basis by a laser diffraction / scattering method, the following conditions (i) and (ii) are satisfied: (i) having at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm; (ii)D 10 is in the range of 0.1 to 3 μm, and D 50 is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more; It satisfies the following.

[0011] In the dispersion composition of the present invention, the content of component (C) may be within the range of 1 to 10% by weight based on the total amount of components (A) and (B).

[0012] The dispersion composition of the present invention may have a content of component (D) in the range of 25 to 50% by weight based on the total weight of the composition.

[0013] In the dispersion composition of the present invention, the component (B) may be spherical amorphous silica.

[0014] In the dispersion composition of the present invention, the component (A) may be a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0015] The fluorine-containing resin film of the present invention comprises the following component (A1) and component (B); (A1) Fluorine-based resin, (B) inorganic filler; Contains The content of component (A1) is within the range of 15 to 40% by weight, and the content of component (B) is within the range of 60 to 85% by weight, based on the total amount of component (A1) and component (B).

[0016] The fluorine-containing resin film of the present invention is characterized in that component (B) satisfies the following conditions (i) and (ii) when the particle size distribution on a volume basis is measured by a laser diffraction / scattering method: (i) having at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm; (ii)D 10 is in the range of 0.1 to 3 μm, and D 50 is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more; Furthermore, the fluororesin film of the present invention has a weight loss rate of 0.3% by weight or less between 150°C and 420°C when heated in a nitrogen atmosphere from 30°C to 550°C at a rate of 10°C / min, as measured by thermogravimetry and differential thermal analysis.

[0017] The metal-clad laminate of the present invention is a metal-clad laminate comprising an insulating resin layer consisting of a single layer or multiple layers, and a metal layer laminated on one side or both sides of the insulating resin layer, At least one of the insulating resin layers is a fluorine-based resin layer made of the above fluorine-based resin film.

[0018] The method for producing a single-sided metal-clad laminate of the present invention is a method for producing a single-sided metal-clad laminate consisting of a single layer or multiple layers, and including an insulating resin layer having at least one fluorine-based resin layer, and a metal layer laminated on one side of the insulating resin layer. The method for producing a single-sided metal-clad laminate of the present invention comprises the following steps a and b: a) applying the dispersion composition onto a metal foil to form a coating film; b) a step of subjecting the obtained coating film to heat treatment in a nitrogen atmosphere at a temperature within a range of 20 to 80°C higher than the melting point of the fluororesin, thereby removing volatile components produced by thermal decomposition of component (C) and melting the fluororesin powder of component (A), thereby forming a fluororesin layer on the metal foil; Contains:

[0019] The method for producing a double-sided metal-clad laminate of the present invention is a method for producing a double-sided metal-clad laminate in which metal layers are laminated on both sides of an insulating resin layer, and includes the steps of: a step of placing the insulating resin layers of two single-sided metal-clad laminates manufactured by the method for manufacturing a single-sided metal-clad laminate face to face with each other and thermocompression bonding them; Contains: [Effects of the Invention]

[0020] The dispersion composition of the present invention contains an inorganic filler (component (B)) that satisfies conditions (i) and (ii) in a predetermined blending ratio, and therefore the decomposition products of the dispersant (component (C)) can be efficiently removed outside the film during the melt heat treatment process. Therefore, the fluororesin film obtained using the dispersion composition of the present invention is a dense film that is free of not only large voids and cracks but also almost no microbubbles, and has ensured adhesion to the metal layer, achieving both excellent dielectric properties due to the fluororesin and low thermal expansion due to the addition of a high concentration of inorganic filler. Therefore, the metal-clad laminate obtained using the dispersion composition of the present invention is useful as a material for, for example, circuit boards that are compatible with high-speed communication standards. DETAILED DESCRIPTION OF THE INVENTION

[0021] The dispersion composition according to one embodiment of the present invention comprises the following components (A) to (D): (A) Fluorine-based resin powder, (B) inorganic filler; (C) a dispersant, (D) Organic solvent In this dispersion composition, component (A) and component (B) are dispersed in component (D), which is a dispersion medium, by the dispersant (C).

[0022] Component (A): Component (A) is a fluorine-based resin powder. Here, "powder" refers to, for example, a powder having an average particle diameter (D 50 ) of the fluorine-based resin powder is in the range of 0.05 to 100 μm, preferably in the range of 0.5 to 50 μm, and more preferably in the range of 0.5 to 10 μm. 50) can be calculated by, for example, measuring the particle size distribution of powder particles using laser diffraction / scattering, calculating a cumulative curve with the total volume of the powder particles as 100%, and then determining the particle diameter at the point on the cumulative curve where the cumulative volume is 50%.

[0023] Fluorine-based resins are polymers containing fluorine atoms, and the type is not particularly limited, but examples include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-tetrafluoroethylene-hexafluoropropylene copolymer (EFEP), polyvinyl fluoride (PVF), and polyvinylidene fluoride (PVDF). These may be used in combination of two or more types, or the fluororesin may contain a monomer unit based on a perfluoroolefin having a functional group as part of the fluororesin. Preferred functional groups are carbonyl-containing groups, hydroxy groups, epoxy groups, amide groups, amino groups, and isocyanate groups.

[0024] Among these fluorine-based resins, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are more preferable as they exhibit low dielectric tangent.

[0025] Ingredient (B): Component (B) is an inorganic filler, and the type thereof is not particularly limited. However, from the viewpoint of reducing the thermal expansion coefficient of the resin film, for example, silicon dioxide (silica), aluminum oxide (alumina), magnesium oxide (magnesia), beryllium oxide, niobium oxide, titanium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, potassium silicofluoride, talc, glass, barium titanate, etc. are preferred. These may be used in combination of two or more. Among these, silicon dioxide (silica), aluminum oxide, boron nitride, glass, etc. are more preferred because they have a low thermal expansion coefficient.

[0026] Component (B) satisfies the following conditions (i) and (ii) when the particle size distribution is measured on a volume basis by a laser diffraction / scattering method.

[0027] Condition (i): It has at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm. By having a particle size distribution peak within the above range, small-diameter fillers can easily penetrate between large-diameter fillers in the film, reducing the spacing between fillers and enabling high-density packing. Note that the terms "large diameter" and "small diameter" are used in relative terms (the same applies below). As noted in (2) above, microbubbles are particularly likely to remain in films containing homogeneously high concentrations of fine inorganic fillers. Therefore, it is thought that microbubbles can be suppressed by reducing the inorganic filler loading (i.e., increasing the proportion of fluororesin above a certain level). However, this narrows and limits the scope for controlling the thermal expansion coefficient, which is the purpose of incorporating inorganic fillers. In the present invention, by using an inorganic filler with a particle size distribution that satisfies condition (i), it is not necessary to increase the proportion of fluororesin, and high-density packing of inorganic fillers is possible, maintaining the flexibility of controlling the thermal expansion coefficient.

[0028] Condition (ii): D 10 is in the range of 0.1 to 3 μm, and D 50is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more. As noted above in (1) and (2), microbubbles are caused by low-molecular-weight compound gases generated by the decomposition of the dispersant (component (C)). It is believed that the generation of microbubbles is particularly prevalent in films containing a homogeneous and high concentration of fine inorganic fillers, since the low-molecular-weight compound gases are less likely to escape from the film. On the other hand, when a large amount of relatively large fillers with particle sizes of 5 μm or more are present in a coating film formed by applying a resin composition, the voids and cracks that form between the fillers at the coating stage tend to be larger than when only fine fillers are used. As described below, these voids and cracks act as paths that facilitate the escape of low-molecular-weight compound gases from the film during the melt-heat treatment process. Therefore, by satisfying condition (ii), large voids and cracks are intentionally formed at the coating stage, and the coating density is deliberately kept low, thereby facilitating the removal of low-molecular-weight compounds by volatilization during the melt-heat treatment process, even when the inorganic filler is blended at a high density. On the other hand, if condition (ii) is not satisfied, for example, if the proportion of particles having a particle size of 5 μm or more is less than 60% by volume, there will be fewer large voids and cracks in the coating film stage, and the gas of low-molecular-weight compounds generated in the melt heat treatment process will be more likely to remain in the film, causing microbubbles.

[0029] The particle size distribution of the inorganic filler can be measured, for example, by laser diffraction / scattering. The particle size distribution is measured, and a cumulative curve is calculated with the total volume of the powder particles set to 100%. The particle diameter (D 10 ), and the particle diameter at the 50% point (D 50 In addition, when the particle shape is other than spherical, the particle diameter means the value calculated as the diameter equivalent to a sphere.

[0030] To satisfy conditions (i) and (ii), for example, it is preferable to blend large-diameter fillers having a peak top in the range of 8 to 15 μm in particle size distribution measurement with small-diameter fillers having a peak top in the range of 0.1 to 5 μm in a volume ratio of 70:30 to 98:2, and more preferably a volume ratio of 80:20 to 95:5.

[0031] The specific surface area of ​​component (B) is not particularly limited, but is preferably 0.1 to 20 m from the viewpoint of suppressing deterioration of the dielectric loss tangent. 2 / g, preferably 0.1 to 10 m 2 The specific surface area can be measured by the BET method.

[0032] The shape of component (B) is not particularly limited, but is preferably, for example, spherical or crushed spherical, since this reduces the difference in thermal expansion coefficient between the thickness direction and the plane direction. Component (B) may also be hollow.

[0033] When silica is used as component (B), either crystalline silica or amorphous silica may be used. However, amorphous silica is preferred, and spherical amorphous silica is particularly preferred, from the viewpoint that the thermal expansion coefficient can be reduced without impairing the dielectric properties in the film state, and in particular, the difference between the thermal expansion coefficients in the thickness direction and the in-plane direction can be reduced.

[0034] Component (B) is preferably surface-treated with a coupling agent, etc. Examples of coupling agents used for the surface treatment include 3-aminopropylethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropylethoxysilane, 3-isocyanatopropylethoxysilane, and hexamethyldisilazane.

[0035] Ingredients (C): The dispersant for component (C) is not particularly limited as long as it has a dispersing effect on components (A) and (B), but from the viewpoint of efficiently dispersing the fluororesin, for example, a fluorosurfactant is preferred. As the fluorosurfactant, for example, a nonionic fluorosurfactant having a perfluoroalkenyl structure with a double bond in the molecule is more preferred.

[0036] Ingredients (D): The type of organic solvent for component (D) is not particularly limited, but an organic solvent that is liquid at 25°C is preferred, such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, methanol, ethanol, isopropanol, methyl ethyl ketone, cyclohexanone, γ-butyrolactone, etc. Among these, high-boiling point solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, and N-methyl-2-pyrrolidone (NMP) are more preferred.

[0037] The dispersion composition may contain, as optional components, for example, organic fillers, curing agents, plasticizers, elastomers, coupling agents, pigments, flame retardants, resin components other than fluorine-based resins, and the like.

[0038] (composition ratio) The weight proportion of the fluororesin powder (component (A)) in the dispersion composition is in the range of 15 to 40 wt %, preferably 20 to 35 wt %, of the total amount of components (A) and (B) from the viewpoint of reducing the dielectric loss tangent when formed into a film and making it compatible with high-frequency signal transmission. If the content of component (A) is less than 15 wt %, the film will not have a sufficiently low dielectric loss tangent, and voids and cracks will be more likely to occur around the filler due to the difference in thermal expansion coefficient with the resin. On the other hand, if the content of component (A) exceeds 40 wt %, the amount of component (B) will be relatively small, narrowing the range of control over the thermal expansion coefficient when formed into a film. From the viewpoint of achieving both the desired dielectric properties and low thermal expansion, the total amount of components (A) and (B) is preferably 50% by weight or more, more preferably 60 to 99% by weight, and most preferably 70 to 99% by weight, of the total solid content in the dispersion composition. Here, the solid content in the dispersion composition means the total of the components excluding the solvent.

[0039] Furthermore, the weight proportion of the inorganic filler (component (B)) in the dispersion composition is within the range of 60 to 85 wt %, preferably 65 to 80 wt %, of the total amount of components (A) and (B) from the viewpoint of reducing the thermal expansion coefficient when formed into a film and ensuring dimensional stability when applied to a circuit board. If the content of component (B) is less than 60 wt %, the range of control of the thermal expansion coefficient when formed into a film becomes narrow. If the content of component (B) is more than 85 wt %, it becomes difficult to achieve a low dielectric loss tangent of the film and voids and cracks are likely to occur around the filler due to the difference in the thermal expansion coefficient with the resin. In this embodiment, by using component (B) that satisfies conditions (i) and (ii), high-density packing is possible while not only preventing relatively large voids and cracks but also suppressing the generation of microbubbles.

[0040] Furthermore, from the viewpoint of ensuring the dispersibility of components (A) and (B), the weight proportion of component (C) in the dispersant in the dispersion composition is preferably within the range of 1 to 10% by weight, more preferably 1 to 5% by weight, relative to the total amount of components (A) and (B). If the weight proportion of component (C) is less than 1% by weight, a sufficient dispersion effect cannot be obtained, and if it exceeds 10% by weight, a large amount of component (C) or its decomposition products remains in the film, which is likely to cause the generation of microbubbles.

[0041] Furthermore, the amount of organic solvent used as component (D) is not limited as long as it is possible to adjust the viscosity of the dispersion composition to the desired value, as will be described later. However, in order to obtain good dispersibility and good coatability, it is advisable to adjust and blend the amount so that it is preferably in the range of 25 to 50% by weight, more preferably in the range of 30 to 40% by weight, based on the total weight of the composition.

[0042] (viscosity) The viscosity of the dispersion composition is not particularly limited, but when the objective is to coat a thick film of, for example, 30 μm or more, it is preferably in the range of 500 to 50,000 cP, and more preferably in the range of 500 to 30,000 cP. If the viscosity is less than 500 cP, the fluidity becomes too high when the dispersion composition is cast onto any substrate, making it difficult to form a thick coating film. In particular, it becomes impossible to form a relatively thick coating film in the range of 30 to 150 μm for high-frequency transmission applications. Furthermore, if the viscosity is less than 500 cP, sedimentation or aggregation of solids may occur. On the other hand, if the viscosity of the dispersion composition exceeds 50,000 cP, the viscosity is too high, making it difficult to form a coating film by casting. The viscosity of the dispersion composition can be measured at a temperature of 25°C using an E-type viscometer.

[0043] (Preparation of Dispersion Composition) The dispersion composition can be produced by mixing components (A) to (D). Each component is preferably kneaded in the presence of the organic solvent of component (D) until a homogeneous state is achieved. During kneading, component (D) may be added in small amounts at a time.

[0044] [Fluoropolymer film] The fluorine-based resin film of the present embodiment is obtained by processing the above-mentioned dispersion composition into a film shape. That is, the fluorine-based resin film comprises the following components (A1) and (B): (A1) Fluorine-based resin, (B) inorganic filler; Contains:

[0045] The fluororesin film of this embodiment is in the form of a solid film that is substantially free of the organic solvent of component (D), and the fluororesin powder of component (A) in the dispersion composition becomes amorphous and becomes the fluororesin of component (A1) (the main component of the matrix resin). The fluororesin film contains component (B) as well as the dispersion composition. Component (B) satisfies the following conditions (i) and (ii) when the particle size distribution is measured on a volume basis by a laser diffraction / scattering method: (i) having at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm; (ii)D 10 is in the range of 0.1 to 3 μm, and D 50 is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more; The phrase "substantially free of organic solvent of component (D)" means that the content of component (D) in the film is 0.1% by weight or less.

[0046] In the fluororesin film of the present embodiment, the content of component (A1) is in the range of 15 to 40% by weight, preferably 20 to 35% by weight, and the content of component (B) is in the range of 60 to 85% by weight, preferably 65 to 80% by weight, based on the total amount of component (A1) and component (B). If the content of component (A1) is less than 15% by weight, the dielectric loss tangent of the film becomes insufficient, and if the weight ratio of component (B) is less than 60% by weight, it becomes difficult to control the thermal expansion coefficient. Furthermore, from the viewpoint of achieving both the desired dielectric properties and low thermal expansion, the total amount of component (A1) and component (B) is preferably 50% by weight or more, more preferably in the range of 60 to 100% by weight, and most preferably in the range of 70 to 100% by weight, based on the total weight of the fluororesin film.

[0047] Furthermore, the fluororesin film is substantially free of the dispersant of component (C). This is because, as will be described later, most of the component (C) undergoes thermal decomposition during the melt-heat treatment process. The phrase "substantially free of the dispersant of component (C)" means that the content of component (C) in the film is 0.3% by weight or less. Among the thermal decomposition products of component (C), low-molecular-weight compounds such as volatile hydrocarbons are largely volatilized and removed during the melt-heat treatment process, while decomposition products with a high affinity for the fluororesin remain in the film. Thus, the fluororesin film of this embodiment is characterized by being substantially free of low-molecular-weight compounds produced by thermal decomposition. That is, the fluororesin film of this embodiment is characterized in that, when heated in a nitrogen atmosphere from 30°C to 550°C at a rate of 10°C / min, the weight loss rate between 150°C and 420°C is 0.3% by weight or less, preferably 0.1% by weight or less, in thermogravimetric and differential thermal analysis. If component (C) remains in the film as is or if a large amount of low-molecular-weight compounds generated by thermal decomposition remains, a weight loss of more than 0.3% by weight will be confirmed in thermogravimetric and differential thermal analysis. This state is not preferable because it will generate microbubbles in a subsequent heating process.

[0048] Furthermore, in the fluororesin film of the present embodiment, because component (B) satisfies condition (i), small-diameter fillers are inserted between large-diameter fillers, reducing the spacing between the fillers and resulting in high-density packing. Furthermore, because component (B) satisfies condition (ii), there is almost no residue of component (C) itself or volatile low-molecular-weight compounds generated by its thermal decomposition, resulting in a dense film with very few large voids, cracks, or microbubbles. Therefore, even if the fluororesin film of the present embodiment is subjected to a heat-pressure treatment in a state where volatile components are difficult to remove, such as when metal foils are laminated on both sides, the generation of microbubbles is suppressed. The above facts are reflected in the low porosity of the fluororesin film of this embodiment. That is, the porosity of the fluororesin film of this embodiment is preferably less than 3 vol.%, more preferably 1 vol.% or less. Here, as shown in the Examples described later, the porosity can be calculated by the following formula after binarizing the void portions and other portions in a cross-sectional observation image of the fluororesin film (inorganic filler-containing fluororesin layer) in the thickness direction at a magnification of 350 times using a scanning electron microscope (SEM). Porosity (vol.%)=X / Y (Here, X means the volume of the void portion in the image, and Y means the volume of the inorganic filler-containing fluorine-based resin layer in the image.) The porosity in the examples is the average value of the porosity calculated based on the above formula for five arbitrary images (each image is approximately 300 μm×100 μm). As described above, the fluororesin film of the present embodiment is a dense film that is almost free of not only large voids and cracks but also microbubbles, and ensures adhesion to the metal layer, achieving both excellent dielectric properties due to the fluororesin and low thermal expansion due to the addition of a high concentration of inorganic filler.

[0049] The fluororesin film preferably has a dielectric loss tangent (Df) of 0.0025 or less, more preferably 0.0020 or less, and even more preferably 0.0015 or less at frequencies up to 60 GHz, as measured using a split cylinder resonator after 24 hours of conditioning at a temperature of 24 to 26°C and a humidity of 45 to 55%. The relative dielectric constant (Dk) measured under the same conditions is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. If the dielectric loss tangent (Df) and relative dielectric constant (Dk) exceed the above values, this leads to increased dielectric loss when the film is applied to a circuit board, which can easily cause problems such as electrical signal loss in the transmission path of high-frequency signals in the GHz frequency range (e.g., 1 to 80 GHz).

[0050] Furthermore, in order to ensure dimensional stability, the thermal expansion coefficient of the fluorine-based resin film is preferably within a range of 10 to 40 ppm / K, and more preferably within a range of 15 to 30 ppm / K.

[0051] The thickness of the fluororesin film is not particularly limited, but when used as an insulating resin layer of a circuit board, taking into consideration application to high-frequency signal transmission, the thickness is preferably within the range of 30 to 150 μm, more preferably within the range of 75 to 150 μm.

[0052] The fluorine-based resin film of the present embodiment may have any resin layer laminated thereon.

[0053] <Metal-clad laminate> The metal-clad laminate of this embodiment comprises an insulating resin layer consisting of a single layer or multiple layers and metal layers laminated on one or both sides of the insulating resin layer, and at least one of the insulating resin layers is a fluororesin layer made of the above-mentioned fluororesin film. The metal-clad laminate of this embodiment may be a single-sided metal-clad laminate or a double-sided metal-clad laminate.

[0054] The material of the metal layer is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or copper alloys are particularly preferred.

[0055] The surface roughness of the metal layer is not particularly limited, but from the viewpoint of ensuring adhesion to the fluororesin layer and reducing conductor loss at the same time, it is preferable that the metal layer has a roughened surface with a ten-point average roughness (Rzjis) in the range of 0.3 μm to 1.5 μm.

[0056] The thickness of the metal layer is not particularly limited, but when a metal foil such as copper foil is used, it is preferably 35 μm or less, more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and handling, the lower limit of the thickness of the metal foil is preferably 5 μm. When copper foil is used as the metal foil, it may be rolled copper foil or electrolytic copper foil, or may be peelable copper foil having a release layer formed between a copper foil having a thickness of 5 μm or less and a carrier foil. In addition, commercially available copper foils can be used as the copper foil.

[0057] The metal foil may be subjected to a surface treatment using, for example, siding, aluminum alcoholate, aluminum chelate, or a silane coupling agent for the purpose of, for example, rust prevention or improving adhesive strength.

[0058] The configuration and thickness of the fluororesin layer in the metal-clad laminate are the same as those of the fluororesin film. The metal-clad laminate of the present embodiment may include any resin layer other than the fluororesin layer.

[0059] The metal-clad laminate of the present embodiment is preferably used as a circuit board material. That is, by processing the metal layers on one or both sides of the metal-clad laminate into wiring circuits by etching or the like, circuit boards such as single-sided circuit boards or double-sided circuit boards can be produced.

[0060] [Method of manufacturing fluororesin film and metal-clad laminate] The method for producing a fluorine-containing resin film using the dispersion composition of the present invention is not particularly limited, but the following method can be exemplified.

[0061] (Coating film formation process) In this step, the dispersion composition of the present invention is applied to any substrate to form a coating film. That is, the dispersion composition is applied to a substrate of any type so as to have a desired thickness after the melt-heat treatment step, and then dried to form a coating film on the substrate. When component (B) satisfies condition (ii), large voids and cracks are intentionally formed in the coating film stage, thereby making it possible to keep the coating film density low. The substrate used for coating is not particularly limited, but it is preferable to use a heat-resistant material such as a metal foil such as copper foil, a copper foil with an adhesive layer, or a polyimide film. The method for coating the dispersion composition onto the substrate is not particularly limited, and it can be coated using a coater such as a comma, die, knife, or lip.

[0062] (melt heat treatment process) In this step, the coating film obtained in the coating film forming step is heat treated to form a fluorine-based resin layer. That is, the coating film and the substrate are heat-treated to remove the solvent remaining in the film and melt the fluororesin powder of component (A) to form a film, thereby forming a fluororesin layer on the substrate. The heat treatment temperature for melting the fluororesin powder should be equal to or higher than the melting point of the fluororesin, and is preferably in the range of 20°C to 80°C higher than the melting point. Furthermore, since this step also aims to remove decomposition products of component (C), it is preferable to carry out heat treatment at a temperature at which component (C) is thermally decomposed and the volatile components (low molecular weight compounds) produced by the decomposition can be removed. Here, when comparing the thermal decomposition temperature of component (C) with the temperature at which the produced volatile components volatilize and are removed from the coating film, the latter temperature may be higher. Therefore, when the thermal decomposition onset temperature of component (C) (Td5: 5 wt% weight loss temperature) is used as the standard for the heat treatment temperature, it is preferable to set the temperature range to be 50°C to 150°C higher than the thermal decomposition onset temperature. In the melt heat treatment step, component (B) satisfying condition (ii) promotes the release of volatile components outside the film.

[0063] Furthermore, when a metal foil is used as the substrate, the melting heat treatment step is preferably carried out in an inert gas atmosphere, more preferably in a nitrogen atmosphere, in order to prevent oxidation.

[0064] When forming a plurality of fluororesin layers, the melting heat treatment may be carried out each time the dispersion composition is applied and dried, or the process of applying and drying the dispersion composition may be repeated a plurality of times and then the melting heat treatment may be carried out all at once.

[0065] After the melt-heat treatment, the film is cooled and solidified, and the substrate is peeled off as needed to obtain a fluororesin film. Since component (B) satisfies condition (i), the fluororesin film thus obtained has small-diameter fillers interspersed between large-diameter fillers, reducing the spaces between the fillers and resulting in a densely packed state.

[0066] In this manufacturing method, by using a metal foil as the substrate, a metal-clad laminate having a fluororesin layer and a metal layer can be manufactured. For example, when a metal foil is used as the substrate, a single-sided metal-clad laminate having a fluororesin layer on one side of the metal layer is obtained. Furthermore, by using a metal foil as the substrate and forming another metal layer on the side of the fluororesin film opposite the substrate, a double-sided metal-clad laminate can also be obtained.

[0067] It is also possible to produce a double-sided metal-clad laminate by bonding together single-sided metal-clad laminates each having a metal layer and a fluororesin layer. For example, a double-sided metal-clad laminate can be produced by using a metal foil as a substrate, carrying out the coating film forming step and the melt heat treatment step to produce a single-sided metal-clad laminate, and then further carrying out a step of placing the insulating resin layers of the two single-sided metal-clad laminates thus produced face to face and performing thermocompression bonding. The thermocompression bonding conditions are preferably, for example, a temperature 10°C to 80°C higher than the melting point of the fluororesin. The pressure is preferably, for example, 2 MPa to 30 MPa. The fluororesin layer of the single-sided metal-clad laminate uses the dispersion composition of the present invention and is subjected to a melt heat treatment process under the above conditions, so volatile components resulting from the thermal decomposition of component (C) are sufficiently removed. Therefore, even during thermocompression bonding, when gas escape is difficult due to the metal foils present on both sides, the generation of microbubbles is almost completely suppressed. Therefore, the resulting double-sided metal-clad laminate is almost free of voids or cracks, including microbubbles, in the fluororesin layer, ensuring adhesion to the metal layer and achieving both the excellent dielectric properties of the fluororesin and the low thermal expansion properties due to the high concentration of inorganic filler added.

[0068] The metal-clad laminate of this embodiment is useful mainly as a circuit board material for FPCs, rigid-flex circuit boards, and the like.

[0069] [Circuit board] By subjecting the metal layer of the metal-clad laminate of the present embodiment obtained as described above to wiring circuit processing such as etching, a circuit board such as a single-sided circuit board or a double-sided circuit board can be manufactured. [Example]

[0070] The features of the present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[0071] [Measurement of amorphous silica particle size] Using a laser diffraction particle size distribution analyzer (Malvern, trade name: Mastersizer3000), particle size was measured by laser diffraction / scattering method under the condition of water as a dispersion medium and a particle refractive index of 1.54. [Measurement of copper foil surface roughness] The surface roughness of the copper foil was measured in tapping mode over an area of ​​80 μm × 80 μm on the copper foil surface using an AFM (manufactured by Bruker AXS, product name: Dimension Icon type SPM) and a probe (manufactured by Bruker AXS, product name: TESPA (NCHV), tip curvature radius 10 nm, spring constant 42 N / m), and the ten-point average roughness (Rzjis) was calculated.

[0072] [Viscosity measurement] The viscosity at 25°C was measured using an E-type viscometer (manufactured by Brookfield, trade name: DV-II+Pro).

[0073] [Measurement of coefficient of thermal expansion (CTE)] A fluororesin film obtained from a double-sided copper-clad laminate cut to a size of 3 mm x 20 mm was set in a thermomechanical analyzer (Hitachi High-Technology Corporation (formerly Seiko Instruments Inc.), product name: TMA / SS7100). The distance between the device and the jig (effective measurement length) was 15 mm. Next, the temperature was raised from 30°C to 260°C at a constant heating rate while applying a 5.0 g load, and then held at that temperature for 10 minutes. After that, the temperature was cooled at a rate of 5°C / min, and the average thermal expansion coefficient (thermal expansion coefficient) from 200°C to 100°C was determined.

[0074] [Measurement of dielectric properties] The dielectric constant (Dk) and dielectric loss tangent (Df) of fluororesin films obtained from double-sided copper-clad laminates were measured at 60 GHz using a split cylinder resonator (SCR resonator). The film used for the measurement was left to stand for 24 hours under conditions of temperature: 24 to 26°C and humidity: 45 to 55%, before the measurement.

[0075] [Peel strength measurement] The copper foil on one side of the double-sided copper-clad laminate was circuitized at 10 mm intervals in the direction of the fluororesin coating to a width of 1 mm, and then cut into a width of 8 cm and a length of 4 cm. The copper foil on the other side was left uncircuited. Peel strength was measured using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D). The side of the cut measurement sample with the copper foil remaining on the entire surface was fixed to an aluminum plate with double-sided tape, and the circuit-processed copper foil was peeled off in a 180° direction at a rate of 50 mm / min. The median strength when 10 mm had been peeled off from the fluororesin layer was determined and used as the peel strength.

[0076] [Weight reduction rate] (1) Weight loss rate of fluororesin film obtained from single-sided copper-clad laminate between 150℃ and 420℃ [ΔTG'(150-420)]: A 10-20 mg fluororesin film obtained from a single-sided copper-clad laminate was heated from 30°C to 550°C at a rate of 10°C / min under a nitrogen atmosphere using a Hitachi High-Tech Science differential thermal / thermogravimetric analyzer (TG / DTA6200). The weight change was measured when the temperature was raised from 30°C to 550°C at a rate of 10°C / min. The weight loss rate (100 × (weight at 150°C - weight at 420°C) / weight at 150°C) (unit: wt%) was calculated and designated as ΔTG'(150-420). (2) Weight loss rate of fluororesin film obtained from double-sided copper-clad laminate between 150℃ and 420℃ [ΔTG(150-420)]: A 10-20 mg fluororesin film obtained from a double-sided copper-clad laminate was heated from 30°C to 550°C at a rate of 10°C / min under a nitrogen atmosphere using a Hitachi High-Tech Science differential thermal thermogravimetry analyzer (TG / DTA6200). The weight change was measured when the temperature was raised from 30°C to 550°C at a rate of 10°C / min. The weight loss rate (100 × (weight at 150°C - weight at 420°C) / weight at 150°C) (unit: wt%) was calculated from the weight loss from 150°C to 420°C, and this was defined as ΔTG(150-420).

[0077] [Void evaluation] A cross-section polisher was used to precisely polish a cross section perpendicular to the double-sided copper-clad laminate, and five random images of the inorganic filler-containing fluororesin layer were taken of this cross section at a magnification of 2000x using a scanning electron microscope (SEM). Next, the void and other parts of the obtained images were binarized to calculate the volume fraction of voids in the inorganic filler-containing fluororesin layer. Porosity (vol.%)=X / Y (Here, X means the volume of the void portion in the image, and Y means the volume of the inorganic filler-containing fluorine-based resin layer in the image.) The porosity is the average value of the porosities calculated based on the above formula for five arbitrary images (each image is approximately 300 μm × 100 μm). In this case, a sample with no voids exceeding 1 μm in diameter and a porosity of less than 3 vol.% was rated as ○ (good), and a sample with a porosity of 3 vol.% or more or with voids exceeding 1 μm in diameter was rated × (bad).

[0078] The compounds used in the synthesis examples and dispersion composition preparation examples are shown below. Fluorine-based resin powder (1): Fluon+ (Fluon is a registered trademark) EA-2000PW 10: Fluorine-based resin powder manufactured by AGC, average particle size: 2 to 3 μm, melting point: 300° C. Silica filler (1): SC70-2: Amorphous silica filler manufactured by Nippon Steel Chemical & Material, specific surface area 1.1 m 2 / g, treated with 0.12 wt% hexamethyldisilazane based on the silica weight. Silica filler (2): SPH507-05: Amorphous silica filler manufactured by Nippon Steel Chemical & Material, specific surface area 9.4 m 2 / g, treated with 1.03 wt% hexamethyldisilazane based on the silica weight. Silica filler (3): SP60-05: Amorphous silica filler manufactured by Nippon Steel Chemical & Material, specific surface area 9.0 m 2 / g, treated with 0.98 wt% hexamethyldisilazane based on the silica weight. Silica filler (4): A mixture of silica filler (1) and silica filler (2) in a volume ratio of 80:20. Silica filler (5): A mixture of silica filler (1) and silica filler (2) in a volume ratio of 95:5. Silica filler (6): A mixture of silica filler (1), silica filler (2), and silica filler (3) in a volume ratio of 80:10:10. Silica filler (7): A mixture of silica filler (1) and silica filler (2) in a volume ratio of 45:55. Dispersant (1): Futergent 710FL: Neos nonionic fluorine-containing dispersant (dispersant component: 50% by weight, ethyl acetate: 50% by weight) DMAc: N,N-dimethylacetamide

[0079] (Silica filler evaluation) Using a laser diffraction particle size distribution analyzer, the presence or absence of peaks of 0.1 to 5 μm and 8 to 15 μm of silica fillers (1) to (7) and D determined on a volume basis were 10 , D 50 Table 1 shows the percentage of particles having a particle size of 5 μm or more.

[0080] [Table 1]

[0081] (Dispersion Composition Preparation Example 1) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (4), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0082] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (4) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (4) reached 85 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes to obtain Dispersion Composition 1-1. Dispersion Composition 1-1 lacked fluidity and viscosity could not be measured, so it was determined to be a "solid."

[0083] Thereafter, the dispersion composition 1-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (4) was 67.5% by weight, thereby obtaining a dispersion composition 1-2 having a viscosity of 890 cP when measured at 100 rpm.

[0084] (Dispersion Composition Preparation Example 2) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (5), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0085] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (5) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (5) reached 86 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, and the kneading was stopped every 15 minutes. The kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 2-1. Dispersion Composition 2-1 lacked fluidity and viscosity could not be measured, so it was determined to be a "solid."

[0086] Thereafter, the dispersion composition 2-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (5) was 67.5% by weight, thereby obtaining a dispersion composition 2-2 having a viscosity of 1020 cP when measured at 100 rpm.

[0087] (Dispersion Composition Preparation Example 3) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (6), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0088] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (6) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (6) reached 85 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes to obtain Dispersion Composition 3-1. Dispersion Composition 3-1 lacked fluidity and viscosity could not be measured, so it was determined to be a "solid."

[0089] Thereafter, the dispersion composition 3-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (6) was 67.5% by weight, thereby obtaining a dispersion composition 3-2 having a viscosity of 840 cP when measured at 100 rpm.

[0090] (Dispersion Composition Preparation Example 4) 82.3 g of fluororesin powder (1), 157.7 g of silica filler (4), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0091] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (4) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (4) reached 87 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 4-1. Dispersion Composition 4-1 lacked fluidity and its viscosity could not be measured, so it was determined to be a "solid."

[0092] Thereafter, the dispersion composition 4-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (4) was 70.0 wt % of the total amount, thereby obtaining a dispersion composition 4-2 having a viscosity of 1210 cP when measured at 100 rpm.

[0093] (Dispersion Composition Preparation Example 5) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (7), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0094] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (7) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (7) reached 86 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 5-1. Dispersion Composition 5-1 lacked fluidity and its viscosity could not be measured, so it was deemed to be a "solid."

[0095] Thereafter, the dispersion composition 5-1 was gradually diluted with DMAc and stirred so that the total proportion of the fluorine-based resin powder (1) and the silica filler (7) was 67.5% by weight, thereby obtaining a dispersion composition 5-2 having a viscosity of 1060 cP when measured at 100 rpm.

[0096] (Dispersion Composition Preparation Example 6) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (1), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0097] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (1) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (1) reached 86 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 6-1. Dispersion Composition 6-1 lacked fluidity and its viscosity could not be measured, so it was determined to be a "solid."

[0098] Thereafter, the dispersion composition 6-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (1) was 67.5% by weight, and a dispersion composition 6-2 having a viscosity of 810 cP when measured at 100 rpm was obtained.

[0099] (Dispersion Composition Preparation Example 7) 70.4 g of fluororesin powder (1), 169.6 g of silica filler (2), 12 g of dispersant (1) (6 g of dispersant component), and 14.7 g of DMAc were added to the container of a TKHIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), and the mixture was stirred at 20 rpm for 5 minutes. The apparatus was then stopped, and the kneaded material was scraped off the stirring blades and the side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were repeated three times.

[0100] Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (2) to the total amount of the composition, a small amount of DMAc was added to the kneaded mixture, which was then stirred at 30 rpm for 5 minutes. The state of the kneaded mixture was then confirmed. This process was repeated until the kneaded mixture became lumpy and free of powdery parts. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (2) reached 86 wt% of the total amount, and no powdery parts were observed inside the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was started, stopped every 15 minutes, and the kneaded mixture was scraped off from the stirring blades and the side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 7-1. Dispersion Composition 7-1 lacked fluidity and viscosity could not be measured, so it was deemed to be a "solid."

[0101] Thereafter, dispersion composition 7-1 was gradually diluted with DMAc and stirred so that the total ratio of the fluorine-based resin powder (1) and the silica filler (2) was 67.5% by weight, thereby obtaining dispersion composition 7-2 having a viscosity of 970 cP when measured at 100 rpm.

[0102] Example 1 Dispersion composition 1-2 was applied to copper foil (electrolytic copper foil, thickness: 12 μm, ten-point average roughness (Rzjis) on the resin layer side: 0.6 μm), and then dried in a hot air oven in an air atmosphere at 80 ° C. for 1 minute and at 120 ° C. for 3 minutes. Next, in a nitrogen atmosphere (oxygen concentration 0.1% by volume or less), the temperature was increased from 40 ° C. to 240 ° C. at 10 ° C. / min, from 240 ° C. to 360 ° C. at 5 ° C. / min, and then held at 360 ° C. for 5 minutes, followed by nitrogen heat treatment to cool to 40 ° C., to obtain single-sided copper-clad laminate 1. Next, the copper foil of the single-sided copper-clad laminate 1 was etched away using an aqueous ferric chloride solution to prepare a fluororesin film 1'. The weight loss rate of the fluororesin film 1' was measured, and the weight loss rate ΔTG'(150-420) between 150°C and 420°C was found to be 0.24 wt%.

[0103] Next, two single-sided copper-clad laminates 1 were prepared, and the laminates were placed with the resin surfaces facing each other in a batch press. They were then heated to 360°C under vacuum, and after reaching 360°C, they were pressed at a pressure of 8 MPa for 5 minutes to obtain a double-sided copper-clad laminate 1 with a dielectric thickness of 100 μm. The copper foil on one side of the obtained double-sided copper-clad laminate 1 was processed into a 1 mm wiring shape, and the peel strength was measured and found to be 0.49 kN / m.

[0104] Next, the copper foil of the double-sided copper-clad laminate 1 was etched away using an aqueous ferric chloride solution to prepare a fluororesin film 1. The CTE of the fluororesin film 1 was 33.3 ppm / K, Dk=2.9, and Df=0.0010. Furthermore, the weight loss rate was measured, and the weight loss rate ΔTG(150-420) between 150°C and 420°C was 0.21 wt%, and the voids confirmed from the cross section of the fluororesin film were less than 3 vol.% (◯).

[0105] <Examples 2 to 4 and Comparative Examples 1 to 3> Single-sided copper-clad laminates 2 to 7, fluororesin films 2' to 7', double-sided copper-clad laminates 2 to 7, and fluororesin films 2 to 7 were produced using the same method as in Example 1, except that the type of dispersant composition was changed. Table 2 shows the evaluation results of the obtained materials.

[0106] [Table 2]

[0107] Although the embodiments of the present invention have been described in detail above for the purpose of illustration, the present invention is not limited to the above-described embodiments and various modifications are possible.

[0108] This application claims priority based on Japanese Patent Application No. 2022-156031, filed on September 29, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. The following components (A) to (D): (A) fluorine-based resin powder, (B) an inorganic filler; (C) a dispersant, (D) Organic Solvent A dispersion composition comprising: the content of component (A) is within the range of 15 to 40% by weight and the content of component (B) is within the range of 60 to 85% by weight, based on the total amount of component (A) and component (B); When the particle size distribution of component (B) is measured on a volume basis by a laser diffraction / scattering method, the following conditions (i) and (ii) are satisfied: (i) having at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm; (ii) D １０ is in the range of 0.1 to 3 μm, and D ５０ is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more; A dispersion composition characterized by satisfying the above.

2. 2. The dispersion composition according to claim 1, wherein the content of component (C) is within the range of 1 to 10% by weight based on the total amount of components (A) and (B).

3. 2. The dispersion composition according to claim 1, wherein the content of component (D) is in the range of 25 to 50% by weight based on the total weight of the composition.

4. 2. The dispersion composition according to claim 1, wherein component (B) is spherical amorphous silica.

5. 2. The dispersion composition according to claim 1, wherein component (A) is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

6. The following components (A1) and (B): (A1) a fluorine-based resin, (B) an inorganic filler; Contains the content of component (A1) is within the range of 15 to 40% by weight and the content of component (B) is within the range of 60 to 85% by weight, based on the total amount of component (A1) and component (B); When the particle size distribution of component (B) is measured on a volume basis by a laser diffraction / scattering method, the following conditions (i) and (ii) are satisfied: (i) having at least one peak top between 8 and 15 μm and at least one peak top between 0.1 and 5 μm; (ii) D １０ is in the range of 0.1 to 3 μm, and D ５０ is in the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60% by volume or more; and A fluororesin film that, when heated in a nitrogen atmosphere from 30°C to 550°C at a rate of 10°C / min in thermogravimetry and differential thermal analysis, exhibits a weight loss rate of 0.3% or less between 150°C and 420°C.

7. A metal-clad laminate comprising an insulating resin layer consisting of a single layer or multiple layers, and a metal layer laminated on one side or both sides of the insulating resin layer, 7. A metal-clad laminate, wherein at least one of the insulating resin layers is a fluororesin layer made of the fluororesin film according to claim 6.

8. A method for producing a single-sided metal-clad laminate comprising a single layer or multiple layers, an insulating resin layer having at least one fluorine-based resin layer, and a metal layer laminated on one side of the insulating resin layer, comprising: The following steps a and b: a) applying the dispersion composition according to any one of claims 1 to 5 onto a metal foil to form a coating film; b) a step of subjecting the obtained coating film to heat treatment in a nitrogen atmosphere at a temperature within a range of 20 to 80°C higher than the melting point of the fluororesin, thereby removing volatile components produced by thermal decomposition of component (C) and melting the fluororesin powder of component (A), thereby forming a fluororesin layer on the metal foil; A method for producing a single-sided metal-clad laminate, comprising:

9. A method for producing a double-sided metal-clad laminate in which metal layers are laminated on both sides of an insulating resin layer, comprising: a step of placing the insulating resin layers of two single-sided metal-clad laminates manufactured by the method of claim 8 face to face with each other and thermocompression bonding them; A method for producing a double-sided metal-clad laminate, comprising:

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