WO2024070415A1

WO2024070415A1 - Dispersion composition, fluororesin film, metal-clad laminated board, and method for producing same

Info

Publication number: WO2024070415A1
Application number: PCT/JP2023/031255
Authority: WO
Inventors: 智典安藤; 知弥池田
Original assignee: 日鉄ケミカル＆マテリアル株式会社
Priority date: 2022-09-29
Filing date: 2023-08-29
Publication date: 2024-04-04

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

Dispersion composition, fluororesin film, metal-clad laminate, and method for producing same

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

In recent years, with the progress of miniaturization, weight saving, and space saving of electronic devices, there is an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow three-dimensional and high-density mounting even in a limited space, their applications are expanding to include wiring for electronic devices such as HDDs, DVDs, and smartphones, as well as components such as cables and connectors.

FPCs are manufactured by etching and wiring the metal layer of metal-clad laminates such as copper-clad laminates (CCL). Currently, metal-clad laminates that use highly heat-resistant polyimide for the insulating resin layer that contacts the metal foil are widely used. However, with the increasing speed of communication devices in recent years, 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 because of their low dielectric tangent and the potential for reducing signal transmission loss.

For example, Patent Document 1 discloses a method (casting method) for producing a fluororesin film by using a dispersion composition in which a fluororesin powder is uniformly dispersed and applying the composition to a substrate.

International Publication No. WO2021/235252

Since fluororesins have a large coefficient of thermal expansion (CTE), inorganic fillers are blended into the dispersion composition to achieve low thermal expansion, a required characteristic for insulating materials for circuit boards, while taking advantage of the characteristic of low dielectric tangent. However, when inorganic fillers are blended at high concentrations, voids are formed around the fillers due to the difference in the coefficient of thermal expansion with the matrix resin, which reduces the density of the film and is a concern for reducing peel strength and electrical properties. In addition, at the stage when a dispersion composition containing fluororesin powder is applied, many voids and cracks exist between the powder particles in the coating film. It is possible to fill most of these voids by performing a heat treatment to melt the fluororesin powder, but if volatile solvents, dispersants, or decomposition products of dispersants remain even after heating, the volatile solvents and decomposition products of dispersants remaining in the film will gasify in the subsequent process, generating new voids. In particular, when fine inorganic fillers are blended at high concentrations and uniformly, the distance between the inorganic fillers is small, making it difficult for the gasified components to escape outside the film and easier for them to remain in the film. Patent Document 1 also states that gas generated during the formation of the fluororesin layer by the casting method causes swelling and cracks, and proposes providing a heating and compression process to reduce voids in the film and form a dense film.

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

The object of the present invention is therefore 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 almost free of not only large voids and cracks but also microbubbles, and a metal-clad laminate that uses the fluororesin film as an insulating resin layer, as well as methods for producing the same.

The present inventors have investigated the cause of the generation of microbubbles and have obtained the following findings (1) to (3).
(1) When heated, the dispersant in the coating film decomposes into low molecular weight compounds and gasifies, causing microbubbles.
(2) In a film that contains fine inorganic fillers uniformly and at a high concentration, microbubbles are particularly likely to be generated.
(3) After the coating is melt-heat-treated at a temperature equal to or higher than the melting point of the fluororesin to form a film, the dispersant remains, generating microscopic air bubbles during the heating and pressurizing process.
Based on these findings, the present inventors conducted intensive research to reduce microbubbles, and as a result, they 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.

That is, the dispersion composition of the present invention comprises the following components (A) to (D):
(A) a fluorine-based resin powder,
(B) an inorganic filler;
(C) a dispersant,
(D) A dispersion composition containing an organic solvent.
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) _D10 is in the range of 0.1 to 3 μm, _D50 is in the range of 5 to 15 μm, and the proportion of particles having a size of 5 μm or more is 60% by volume or more;
It satisfies the following.

The dispersion composition of the present invention may have a content of component (C) in the range of 1 to 10% by weight based on the total amount of components (A) and (B).

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 composition.

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

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

The fluorine-based resin film of the present invention comprises the following component (A1) and component (B);
(A1) a fluorine-based resin,
(B) an inorganic filler;
Contains
Based on the total amount of components (A1) and (B), 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.

The fluororesin film of the present invention is characterized in that the 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) _D10 is in the range of 0.1 to 3 μm, _D50 is in the range of 5 to 15 μm, and the proportion of particles having a size of 5 μm or more is 60% by volume or more;
In addition, 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 in thermogravimetric and differential thermal analyses.

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 fluororesin layer made of the above-mentioned fluororesin film.

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 a 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) to form a fluororesin layer on the metal foil;
Contains:

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, comprising the steps of:
a step of placing the insulating resin layers of two single-sided metal-clad laminates manufactured by the manufacturing method of the single-sided metal-clad laminate facing each other and performing thermocompression bonding;
Contains:

The dispersion composition of the present invention contains, as the inorganic filler of component (B) which satisfies conditions (i) and (ii) in a predetermined blend ratio, the decomposition products of the dispersant of component (C) can be efficiently removed outside the film during the melt heat treatment process.
Therefore, the fluororesin film obtained by using the dispersion composition of the present invention is a dense film that is free of not only large voids and cracks, but also microbubbles, and has ensured adhesion to the metal layer, achieving both excellent dielectric properties due to the fluororesin and low thermal expansion properties due to the addition of a high concentration of inorganic filler.
Therefore, the metal-clad laminate obtained by using the dispersion composition of the present invention is useful as a material for, for example, circuit boards compatible with high-speed communication standards.

The dispersion composition according to one embodiment of the present invention comprises the following components (A) to (D):
(A) a fluorine-based resin powder,
(B) an inorganic filler;
(C) a dispersant,
In the dispersion composition, the components (A) and (B) are dispersed in the dispersion medium (D) by the dispersant (C).

Component (A):
Component (A) is a fluororesin powder. Here, "powder" means, for example, an aggregate of particles having an average particle size (D ₅₀ ) 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. The average particle size (D ₅₀ ) of the fluororesin powder can be determined, for example, by measuring the particle size distribution of the powder particles by a laser diffraction/scattering method, determining a cumulative curve with the total volume of the powder particles as 100%, and determining the particle size at the point on the cumulative curve where the cumulative volume is 50%.

The fluororesin is a polymer 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), polyvinylidene fluoride (PVDF), etc. Two or more of these may be used in combination, and the fluororesin may contain a monomer unit based on a perfluoroolefin having a functional group as part of the fluororesin. As the functional group, a carbonyl group-containing group, a hydroxyl group, an epoxy group, an amide group, an amino group, and an isocyanate group are preferred.

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 tangents.

Component (B):
Component (B) is an inorganic filler, and the type is not particularly limited, but 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 preferable. These may be used in combination of two or more. Among these, silicon dioxide (silica), aluminum oxide, boron nitride, glass, etc. are more preferable as those having a low thermal expansion coefficient.

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.

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 peak of the particle size distribution within the above range, small diameter fillers can easily enter between large diameter fillers in the film state, the intervals between the fillers become smaller, and high density packing is possible. Note that "large diameter" and "small diameter" are used in a relative sense (hereinafter the same). As the above knowledge (2) shows, in a film containing fine inorganic fillers homogeneously and at a high concentration, microbubbles are particularly likely to remain, so it is thought that microbubbles can be suppressed by lowering the amount of inorganic filler filled (i.e., increasing the ratio of fluorine-based resin to a certain level or more), but this narrows the range of thermal expansion coefficient control, which is the purpose of blending inorganic fillers, and is restricted. 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 blending ratio of fluorine-based resin, and high density packing of inorganic fillers is possible, and the degree of freedom in thermal expansion coefficient control can be maintained.

Condition (ii):
_D10 is within the range of 0.1 to 3 μm, _D50 is within the range of 5 to 15 μm, and the proportion of particles having a particle size of 5 μm or more is 60 volume % or more.
As the findings of (1) and (2) above show, the cause of microbubbles is the gas of low molecular weight compounds generated by the decomposition of the dispersant of component (C), and it is considered that the gas of low molecular weight compounds is difficult to escape to the outside of the film in a film containing fine inorganic fillers homogeneously and at a high concentration, so that the generation of microbubbles is particularly frequent. On the other hand, if a large amount of relatively large fillers with a particle size of 5 μm or more are present in the coating film coated with the resin composition, the voids and cracks generated between the fillers at the coating stage are likely to be larger than those when only fine fillers are used. As described below, such voids and cracks become a path (path) that promotes the gas of low molecular weight compounds to escape to the outside of the film in 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, so that the removal of low molecular weight compounds by volatilization is promoted in the melt heat treatment process even when the inorganic filler is mixed at a high density. On the other hand, if the condition (ii) is not satisfied, for example, if the ratio of particles having a particle size of 5 μm or more is less than 60 vol %, then large voids and cracks will be reduced at the coating stage, and the gas of the low molecular weight compound generated in the melt heat treatment step will be more likely to remain in the film, causing microbubbles.

The particle size distribution of the inorganic filler can be measured, for example, by a laser diffraction/scattering method. It is possible to measure the particle size distribution, obtain a cumulative curve with the total volume of the powder particles set at 100%, and obtain the particle diameter (D ₁₀ ) at the point where the cumulative volume is 10% on the cumulative curve, and the particle diameter (D ₅₀ ) at the point where the cumulative volume is 50%. In addition, the particle diameter means a value calculated as a sphere-equivalent diameter in the case of particles other than spherical.

In order to satisfy conditions (i) and (ii), for example, it is preferable to mix large-diameter fillers whose peak top is in the range of 8 to 15 μm in particle size distribution measurement with small-diameter fillers whose peak top is 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.

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

The shape of component (B) is not particularly limited, but for example, a spherical shape, a crushed spherical shape, etc. are preferred because they can reduce the difference in thermal expansion coefficient between the thickness direction and the surface direction. Component (B) may also be hollow.

When silica is used as component (B), it may be either crystalline or amorphous silica, but amorphous silica is preferred from the viewpoint that it is possible to reduce the thermal expansion coefficient without impairing the dielectric properties in the film state, and in particular to reduce the difference in the thermal expansion coefficient between the thickness direction and the surface direction, and spherical amorphous silica is particularly preferred.

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

Component (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 having a double bond in the molecule is more preferred.

Component (D):
The type of organic solvent of 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, dimethylsulfoxide (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, N-methyl-2-pyrrolidone (NMP), etc. are more preferred.

The dispersion composition may contain optional components such as organic fillers, hardeners, plasticizers, elastomers, coupling agents, pigments, flame retardants, and resin components other than fluorine-based resins.

(Composition ratio)
The weight ratio of the fluororesin powder of component (A) in the dispersion composition is in the range of 15 to 40% by weight, preferably 20 to 35% by weight, based on the total amount of components (A) and (B) in order to reduce the dielectric tangent when the film is made and to correspond to high frequency signal transmission. If the content of component (A) is less than 15% by weight, the film will not have a sufficiently low dielectric tangent, and voids and cracks around the filler due to the difference in thermal expansion coefficient with the resin will be easily generated. On the other hand, if the content of component (A) exceeds 40% by weight, the amount of component (B) blended will be relatively small, and the range of thermal expansion coefficient control will be narrow when the film is made.
From the viewpoint of achieving both the desired dielectric properties and low thermal expansion, the total amount of component (A) and component (B) is preferably 50% by weight or more, more preferably in the range of 60 to 99% by weight, and most preferably in the range of 70 to 99% by weight, based on 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.

The weight ratio of the inorganic filler of component (B) in the dispersion composition is in the range of 60 to 85% by weight, preferably 65 to 80% by weight, based on the total amount of components (A) and (B), from the viewpoint of lowering the thermal expansion coefficient when made into a film and ensuring dimensional stability when applied to a circuit board. If the content of component (B) is less than 60% by weight, the range of thermal expansion coefficient control when made into a film becomes narrow, and if it exceeds 85% by weight, it becomes difficult to make the film have a low dielectric tangent, and voids and cracks around the filler due to the difference in thermal expansion coefficient with the resin are likely to occur. In this embodiment, by using a component (B) that satisfies conditions (i) and (ii), it is possible to achieve high-density filling while preventing relatively large voids and cracks, and also suppressing the generation of microbubbles.

In addition, the weight ratio of component (C) in the dispersant in the dispersion composition is preferably within the range of 1 to 10% by weight, and more preferably within the range of 1 to 5% by weight, based on the total amount of components (A) and (B), from the viewpoint of ensuring the dispersibility of components (A) and (B). If the weight ratio of component (C) is less than 1% by weight, a sufficient dispersion effect cannot be obtained, and if it exceeds 10% by weight, the amount of component (C) or its decomposition products remaining in the film increases, which is likely to cause the generation of microbubbles.

The amount of organic solvent in component (D) is not limited as long as the viscosity of the dispersion composition can be adjusted to the desired value, as described later. However, to obtain good dispersibility and good coatability, it is advisable to adjust and incorporate the organic solvent 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 composition.

(viscosity)
The viscosity of the dispersion composition is not particularly limited, but for example, when the purpose is to coat a thick film of 30 μm or more, it is preferably in the range of 500 to 50,000 cP, 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. In addition, 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 and it becomes 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.

(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 it becomes homogeneous. During kneading, component (D) may be added in small amounts.

[Fluoroplastic film]
The fluororesin 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 component (A1) and component (B);
(A1) a fluorine-based resin,
(B) an inorganic filler;
Contains:

The fluororesin film of the present embodiment is in the form of a solid film 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) in the same manner 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) _D10 is in the range of 0.1 to 3 μm, _D50 is in the range of 5 to 15 μm, and the proportion of particles having a 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.

In the fluororesin film of the present embodiment, the content of component (A1) is within the range of 15 to 40% by weight, preferably within the range of 20 to 35% by weight, and the content of component (B) is within the range of 60 to 85% by weight, preferably within the range of 65 to 80% by weight, based on the total amount of components (A1) and (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.
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.

In addition, the fluororesin film does not substantially contain the dispersant of component (C). This is because most of the component (C) is thermally decomposed in the melt heat treatment process as described below. The phrase "substantially does not contain 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 mostly volatilized and removed in the melt heat treatment process, and decomposition products having high affinity for fluororesins remain in the film. Thus, the fluororesin film of the present embodiment has the characteristic of not substantially containing low molecular weight compounds generated by thermal decomposition.
That is, the fluororesin film of the present 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 is confirmed in thermogravimetric and differential thermal analysis. This state is not preferable because it generates microbubbles in a subsequent process involving heating.

In addition, in the fluororesin film of the present embodiment, since component (B) satisfies condition (i), small diameter fillers are inserted between large diameter fillers, the intervals between the fillers are reduced, and the film is densely packed. Since 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, and the film is dense with very few large voids, cracks, and microbubbles. Therefore, even if the fluororesin film of the present embodiment is heated and pressurized 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 is 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 parts and other parts in a cross-sectional observation image in the thickness direction of the fluororesin film (inorganic filler-containing fluororesin layer) 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 any five images (each image is about 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, ensures adhesion to the metal layer, and achieves a balance between the excellent dielectric properties of the fluororesin and the low thermal expansion properties achieved by the addition of a high concentration of inorganic filler.

After conditioning for 24 hours at a temperature of 24-26°C and a humidity of 45-55%, the fluororesin film has a dielectric loss tangent (Df) at 60 GHz or less, measured using a split cylinder resonator, of preferably 0.0025 or less, more preferably 0.0020 or less, and even more preferably 0.0015 or less. In addition, 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 an increase in dielectric loss when applied to a circuit board, and is likely to cause inconveniences such as electrical signal loss on the transmission path of high-frequency signals in the GHz range (e.g., 1-80 GHz).

In addition, to ensure dimensional stability, the thermal expansion coefficient of the fluororesin film is preferably within the range of 10 to 40 ppm/K, and more preferably within the range of 15 to 30 ppm/K.

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

In addition, any resin layer may be laminated on the fluororesin film of this embodiment.

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

The material of the metal layer is not particularly limited, but examples 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.

The surface roughness of the metal layer is not particularly limited, but from the viewpoint of ensuring adhesion to the fluororesin layer while reducing conductor loss, it is preferable for the metal layer to have a roughened surface with a ten-point average roughness (Rzjis) in the range of 0.3 μm to 1.5 μm.

The thickness of the metal layer is not particularly limited, but when a metal foil such as a copper foil is used, the thickness is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoints of production stability and handling, the lower limit of the thickness of the metal foil is preferably 5 μm.
When a copper foil is used as the metal foil, it may be a rolled copper foil or an electrolytic copper foil, and may be, for example, a 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, a commercially available copper foil may be used as the copper foil.

The metal foil may be surface-treated with, for example, siding, aluminum alcoholate, aluminum chelate, silane coupling agent, etc., for the purpose of, for example, rust prevention or improving adhesion.

The configuration and thickness of the fluororesin layer in the metal-clad laminate are the same as those of the fluororesin film. Note that the metal-clad laminate of this embodiment may include any resin layer other than the fluororesin layer.

The metal-clad laminate of this 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 manufactured.

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

(Coating film forming 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 an arbitrary substrate 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 can be intentionally formed at the coating stage, and the coating density can be kept 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 on the substrate is not particularly limited, and it is possible to coat it with a coater such as a comma, die, knife, or lip.

(Melting heat treatment process)
In this step, the coating film obtained in the coating film forming step is heat-treated to form a fluororesin layer.
That is, the coating film is heat-treated together with the substrate to remove the solvent remaining in the film, and the fluororesin powder of component (A) is melted to form a film, thereby forming a fluororesin layer on the substrate. The heat treatment temperature for melting the fluororesin powder may be equal to or higher than the melting point of the fluororesin, and is preferably in a temperature range of 20°C to 80°C higher than the melting point.
In addition, since the purpose of this process is also to remove the decomposition products of component (C), it is preferable to perform heat treatment at a temperature at which component (C) is thermally decomposed and the volatile components (low molecular weight compounds) generated by the decomposition can be removed. Here, when comparing the thermal decomposition temperature of component (C) with the temperature at which the generated volatile components volatilize and are removed from the coating film, the latter temperature may be higher. Therefore, when the thermal decomposition onset temperature (Td5: 5 wt% weight loss temperature) of component (C) 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 process, component (B) satisfies condition (ii), which promotes the release of volatile components outside the film.

In addition, when using metal foil as the substrate, the melt heat treatment process is preferably carried out in an inert gas atmosphere, and more preferably in a nitrogen atmosphere, to prevent oxidation.

When forming multiple fluororesin layers, the melt heat treatment may be performed each time the dispersion composition is applied and dried, or the process of applying and drying the dispersion composition may be repeated multiple times and then the melt heat treatment may be performed all at once.

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

In this manufacturing method, by using metal foil as the substrate, a metal-clad laminate having a fluororesin layer and a metal layer can be manufactured. For example, when metal foil is used as the substrate, it becomes a single-sided metal-clad laminate having a fluororesin layer on one side of the metal layer. It is also possible to use metal foil as the substrate and form another metal layer on the side of the fluororesin film opposite the substrate to produce a double-sided metal-clad laminate.

It is also possible to manufacture a double-sided metal-clad laminate by bonding together single-sided metal-clad laminates having a metal layer and a fluororesin layer. For example, a double-sided metal-clad laminate can be manufactured by using a metal foil as a substrate, carrying out the above-mentioned coating film forming step and melt heat treatment step to manufacture 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 manufactured facing each other and performing thermocompression bonding.
The thermocompression bonding conditions are preferably, for example, a temperature in the range of 10°C to 80°C higher than the melting point of the fluororesin. The pressure is preferably, for example, in the range of 2MPa to 30MPa. The fluororesin layer of the single-sided metal-clad laminate uses the dispersion composition of the present invention, and the melt heat treatment process is carried out under the above conditions, so that volatile components caused by the thermal decomposition of component (C) are sufficiently removed. Therefore, even during thermocompression bonding, where gas is difficult to escape due to the metal foils present on both sides, the generation of microbubbles is almost suppressed. Therefore, the obtained double-sided metal-clad laminate has almost no voids or cracks, including microbubbles, in the fluororesin layer, and the adhesion with the metal layer is ensured, and both excellent dielectric properties due to the fluororesin and low thermal expansion properties due to the addition of a high concentration of inorganic filler are achieved.

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

[Circuit board]
By subjecting the metal layer of the metal-clad laminate of the present embodiment thus obtained 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.

The following examples are provided to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, unless otherwise specified, the various measurements and evaluations are as follows.

[Measurement of particle size of amorphous silica]
The particle size was measured by a laser diffraction/scattering method using a laser diffraction particle size distribution analyzer (Malvern, product name: Mastersizer3000) with water as the 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 a tapping mode 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) in an area of 80 μm × 80 μm on the copper foil surface, and the ten-point average roughness (Rzjis) was calculated.

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

[Measurement of coefficient of thermal expansion (CTE)]
The fluororesin film obtained from the double-sided copper-clad laminate cut to a size of 3 mm x 20 mm was set in a thermomechanical analyzer (Hitachi High-Technologies Corporation (formerly Seiko Instruments Inc.), product name: TMA/SS7100). At this time, the distance between the device jigs (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 load of 5.0 g, and then the temperature was held for 10 minutes, and then cooled at a rate of 5°C/min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 200°C to 100°C.

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

[Peel strength measurement]
The copper foil on one side of the double-sided copper-clad laminate was circuit-processed to a width of 1 mm at 10 mm intervals in the coating direction of the fluororesin, and then cut to a width of 8 cm and a length of 4 cm. At this time, the copper foil on the other side was left entirely without circuit processing. The peel strength was measured using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D), with the copper foil of the cut measurement sample left entirely fixed to an aluminum plate with double-sided tape, and the circuit-processed copper foil was peeled off in the 180° direction at a speed of 50 mm/min, and the median strength when 10 mm was peeled off from the fluororesin layer was obtained, which was taken as the peel strength.

[Weight reduction rate]
(1) Weight loss rate of a fluororesin film obtained from a single-sided copper-clad laminate between 150°C and 420°C [ΔTG'(150-420)]:
A fluororesin film weighing 10 to 20 mg obtained from a single-sided copper-clad laminate was measured for its weight change when the film 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). At this time, the weight reduction rate [100×(weight at 150° C.−weight at 420° C.)/weight at 150° C.] (unit: weight %) calculated from the weight reduction from 150° C. to 420° C. was calculated based on the weight at 150° C., and this was designated as ΔTG'(150-420).
(2) Weight loss rate of the fluororesin film obtained from the double-sided copper-clad laminate between 150 ° C. and 420 ° C. [ΔTG (150-420)]:
A fluororesin film weighing 10 to 20 mg obtained from a double-sided copper-clad laminate was measured for its weight change when it was heated from 30° C. to 550° C. at a rate of 10° C./min under a nitrogen atmosphere using a differential thermal thermogravimetry device (TG/DTA6200) manufactured by Hitachi High-Tech Science. At this time, the weight reduction rate [100×(weight at 150° C.−weight at 420° C.)/weight at 150° C.] (unit: weight %) calculated from the weight reduction from 150° C. to 420° C. was calculated based on the weight at 150° C., and this was designated as ΔTG(150-420).

[Void evaluation]
The double-sided copper-clad laminate thus produced was polished to produce a precise cross section perpendicular to the double-sided copper-clad laminate using a cross-section polisher, and five random images of the inorganic filler-containing fluororesin layer were obtained at a magnification of 2000 times using a scanning electron microscope (SEM). Next, the void portion and the other portion of the obtained images were binarized to calculate the volume ratio of the 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 any 5 images (each image is about 300 μm × 100 μm). In this case, the case where there were no voids with a diameter of more than 1 μm and the porosity was less than 3 vol.% was rated as ○ (good), and the case where the porosity was 3 vol.% or more or the case where there were voids with a diameter of more than 1 μm was rated as × (bad).

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 Co., Ltd., with a specific surface area of 1.1 m ² /g, which was treated with 0.12% by weight of silica with hexamethyldisilazane.
Silica filler (2): SPH507-05: Amorphous silica filler manufactured by Nippon Steel Chemical & Material Co., Ltd., with a specific surface area of 9.4 m ² /g, which was treated with 1.03% by weight of silica with hexamethyldisilazane.
Silica filler (3): SP60-05: Amorphous silica filler manufactured by Nippon Steel Chemical & Material Co., Ltd., with a specific surface area of 9.0 m ² /g, which was treated with 0.98% by weight of silica with hexamethyldisilazane.
Silica filler (4): Silica filler (1) and silica filler (2) mixed in a volume ratio of 80:20.
Silica filler (5): Silica filler (1) and silica filler (2) mixed 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): Silica filler (1) and silica filler (2) mixed in a volume ratio of 45:55.
Dispersant (1): Futergent 710FL: nonionic fluorine-containing dispersant manufactured by Neos (dispersant component: 50% by weight, ethyl acetate: 50% by weight)
DMAc: N,N-dimethylacetamide

(Silica filler evaluation)
Table 1 shows the presence or absence of peaks of 0.1 to 5 μm and 8 to 15 μm for silica filler (1) to silica filler (7) measured using a laser diffraction particle size distribution analyzer, D ₁₀ , D ₅₀ calculated on a volume basis, and the proportion of particles having a particle size of 5 μm or more.

(Dispersion Composition Preparation Example 1)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side walls of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side walls of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (4) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (4) to the total amount was 85% by weight, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 1-1 was obtained. Dispersion composition 1-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 1-1 was gradually diluted and stirred with DMAc so that the combined ratio of fluororesin powder (1) and silica filler (4) was 67.5% by weight, and dispersion composition 1-2 was obtained, with a viscosity of 890 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 2)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side wall of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side wall of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (5) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (5) to the total amount was 86 wt %, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 2-1 was obtained. Dispersion composition 2-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 2-1 was gradually diluted and stirred with DMAc so that the total ratio of the fluororesin powder (1) and the silica filler (5) was 67.5% by weight, and dispersion composition 2-2 was obtained with a viscosity of 1020 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 3)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side walls of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side walls of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (6) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was checked. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (6) to the total amount was 85 wt %, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 3-1 was obtained. Dispersion composition 3-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 3-1 was gradually diluted and stirred with DMAc so that the total ratio of the fluororesin powder (1) and the silica filler (6) was 67.5% by weight, and dispersion composition 3-2 was obtained, with a viscosity of 840 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 4)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side walls of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side walls of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (4) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (4) to the total amount was 87% by weight, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 4-1 was obtained. Dispersion composition 4-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 4-1 was gradually diluted and stirred with DMAc so that the total ratio of fluororesin powder (1) and silica filler (4) was 70.0% by weight, and dispersion composition 4-2 was obtained, with a viscosity of 1210 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 5)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side wall of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side wall of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (7) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (7) to the total amount was 86 wt %, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 5-1 was obtained. Dispersion composition 5-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 5-1 was gradually diluted and stirred with DMAc so that the total ratio of fluororesin powder (1) and silica filler (7) was 67.5% by weight, and dispersion composition 5-2 was obtained, with a viscosity of 1060 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 6)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side wall of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side wall of the container after the device was stopped were carried out three times.

Next, in order to finely adjust 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 product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of fluororesin powder (1) and silica filler (1) to the total amount was 86 wt %, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 6-1 was obtained. Dispersion composition 6-1 had no fluidity and viscosity could not be measured, so it was determined to be a "solid".

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

(Dispersion Composition Preparation Example 7)
In a container of T.K.HIVIS MIX (model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 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 and stirred at 20 rpm for 5 minutes. The device was then stopped, and the kneaded material was scraped off from the stirring blades and the side walls of the container. The above stirring and scraping off of the kneaded material from the stirring blades and the side walls of the container after the device was stopped were carried out three times.

Next, in order to finely adjust the ratio of the total amount of the fluororesin powder (1) and the silica filler (2) to the total amount of the composition, a small amount of DMAc was added to the kneaded product, which was then stirred at 30 rpm for 5 minutes, and the state of the kneaded product was confirmed. This operation was repeated until the kneaded product became lumpy with no powdery parts. In this study, the kneaded product became lumpy when the total ratio of the fluororesin powder (1) and the silica filler (2) to the total amount was 86 wt %, and no powdery parts were observed inside the kneaded product lumps. When the kneaded product became lumpy, kneading at 30 rpm was started, and the kneaded product was stopped at 15-minute intervals, and the kneaded product was scraped off from the stirring blades and the side wall of the container. This operation was performed four times for a total of 60 minutes, and dispersion composition 7-1 was obtained. Dispersion composition 7-1 had no fluidity and the viscosity could not be measured, so it was determined to be a "solid".

Then, dispersion composition 7-1 was gradually diluted and stirred with DMAc so that the total ratio of fluororesin powder (1) and silica filler (2) was 67.5% by weight, and dispersion composition 7-2 was obtained, with a viscosity of 970 cP when measured at 100 rpm.

Example 1
Dispersion composition 1-2 was applied onto copper foil (electrolytic copper foil, thickness: 12 μm, ten-point average roughness (Rzjis) of the resin layer side: 0.6 μm), and then dried at 80 ° C. for 1 minute and 120 ° C. for 3 minutes using a hot air oven in an air atmosphere. Next, a nitrogen heat treatment was performed by increasing the temperature from 40 ° C. to 240 ° C. at 10 ° C./min and from 240 ° C. to 360 ° C. at 5 ° C./min using a hot air oven in a nitrogen atmosphere (oxygen concentration 0.1 vol.% or less), holding at 360 ° C. for 5 minutes, and then cooling to 40 ° C. to obtain a single-sided copper-clad laminate 1.
Next, the copper foil of the single-sided copper-clad laminate 1 was etched away using an aqueous solution of ferric chloride 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 0.24% by weight.

Next, two single-sided copper-clad laminates 1 were prepared, and the resin surfaces were placed together in a batch press machine, where they were heated to 360°C under vacuum. 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, resulting in a value of 0.49 kN/m.

Then, the copper foil of the double-sided copper-clad laminate 1 was etched away using an aqueous solution of ferric chloride 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% by weight, and the voids confirmed from the cross section of the fluororesin film were less than 3 vol.% (○).

<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 in the same manner as in Example 1, except that the type of dispersant composition was changed. The evaluation results of the obtained materials are shown in Table 2.

The above describes in detail an embodiment of the present invention for illustrative purposes, but the present invention is not limited to the above embodiment and various modifications are possible.

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

Claims

The following components (A) to (D):
(A) a fluorine-based resin powder,
(B) an inorganic filler;
(C) a dispersant,
(D) a dispersion composition containing an organic solvent,
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) D10 is in the range of 0.1 to 3 μm, D50 is in the range of 5 to 15 μm, and the proportion of particles having a size of 5 μm or more is 60% by volume or more;
A dispersion composition characterized by satisfying the above.
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).
The dispersion composition according to claim 1, wherein the content of component (D) is within the range of 25 to 50% by weight of the entire composition.
The dispersion composition according to claim 1, wherein component (B) is spherical amorphous silica.
The dispersion composition according to claim 1, wherein component (A) is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).
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) D10 is in the range of 0.1 to 3 μm, D50 is in the range of 5 to 15 μm, and the proportion of particles having a 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.
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.
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 steps of:
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 a 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) to form a fluororesin layer on the metal foil;
A method for producing a single-sided metal-clad laminate, comprising:
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 the steps of:
A step of placing the insulating resin layers of two single-sided metal-clad laminates manufactured by the method according to claim 8 face to face with each other and performing thermocompression bonding;
A method for producing a double-sided metal-clad laminate, comprising: