JP7762314B2 - Dispersion composition, fluorine-based resin film, metal-clad laminate, and method for producing the same - Google Patents

Description

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 advancement of 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 highly durable even when repeatedly bent. Because FPCs enable three-dimensional, high-density mounting even in limited spaces, their applications are expanding to include wiring for electronic devices such as hard disk drives (HDDs), DVDs, and smartphones, as well as components such as cables and connectors.

FPCs are manufactured by etching the metal layer of metal-clad laminates such as copper-clad laminate (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 speeds of communication devices, development of 5G and even 6G communications is progressing, and circuit board materials are being considered 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 dissipation factor 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 fluororesin powder is uniformly dispersed and coating this on a substrate.

International Publication No. WO2021/235252

Fluoropolymers have a large coefficient of thermal expansion (CTE). To achieve the low thermal expansion required for insulating materials for circuit boards while taking advantage of their low dielectric loss tangent, inorganic fillers are typically blended into the dispersion composition. However, blending high concentrations of inorganic fillers can lead to voids forming around the filler due to differences in the thermal expansion coefficient between the filler and the matrix resin, reducing the film's density and potentially reducing peel strength and electrical properties. Furthermore, when a dispersion composition containing fluoropolymer powder is 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 fluoropolymer powder, if volatile solvents, dispersants, or dispersant decomposition products remain after heating, these will gasify in subsequent processes, creating new voids. In particular, when fine inorganic fillers are blended in at a high concentration and uniformly, the distance between the inorganic fillers is small, so that the gasified components are less likely to escape to the outside of the film and are more likely to remain in the film. Patent Document 1 also states that swelling and cracks occur due to the gas generated when forming a fluororesin layer by a casting method, and proposes providing a heat compression process to reduce voids in the film and form a dense film.

However, while voids that occur around the filler due to differences in thermal expansion coefficients and voids caused by solvent gas can be reduced by heating and compression, it has become clear that relatively small voids, for example, microvoids with diameters of 1 μm or less, still remain in the film. Hereinafter, these microvoids will be referred to as "microbubbles" to distinguish them from relatively large voids around the filler, voids 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 obtained using this dispersion composition that is substantially free of not only large voids and cracks but also microbubbles, a metal-clad laminate plate having the fluororesin film as an insulating resin layer, and methods for producing the same.

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 film decomposes into low molecular weight compounds and gasifies, causing microbubbles.
(2) In a film containing 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 microbubbles 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.

That is, the dispersion composition of the present invention comprises the following components (A) to (D):
(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 particle 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 weight % relative to 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 weight % relative to 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-containing resin film of the present invention comprises the following component (A1) and component (B):
(A1) a fluorine-based resin,
(B) an inorganic filler;
Contains
The content of component (A1) is in the range of 15 to 40% by weight, and the content of component (B) is in the range of 60 to 85% by weight, based on the total amount of component (A1) and component (B).

The fluorine-containing resin film of the present invention is characterized in that the 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 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 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 fluorine-based resin layer made of the above-mentioned fluorine-based resin 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 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:

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 the two single-sided metal-clad laminates;
Contains:

The dispersion composition of the present invention contains an inorganic filler of component (B) that satisfies conditions (i) and (ii) in a predetermined blending ratio, and therefore 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 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.

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

Component (A):
Component (A) is a fluororesin powder. Here, "powder" refers to, for example, an aggregate of particles having an average particle diameter (D ₅₀ ) in the range of 0.05 to 100 μm, preferably 0.5 to 50 μm, and more preferably 0.5 to 10 μm. The average particle diameter (D ₅₀ ) of the fluororesin powder can be determined, for example, by measuring the particle size distribution of the powder particles by laser diffraction/scattering, determining 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%.

Fluorine-based resins are polymers containing fluorine atoms. While there are no particular limitations on the type, 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 with two or more types, and the fluororesin may contain a monomer unit based on a perfluoroolefin having a functional group as part of the fluororesin. Preferred functional groups include carbonyl-containing groups, hydroxy groups, epoxy groups, amide groups, amino groups, and isocyanate groups.

Of these fluorine-based resins, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are more preferred as they exhibit low dielectric tangents.

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.

Component (B) satisfies the following conditions (i) and (ii) when the particle size distribution is measured on a volume basis using 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 particle size distribution peak within the above range, small-diameter fillers can easily penetrate between large-diameter fillers in the film state, reducing the spacing between fillers and enabling high-density packing. Note that "large diameter" and "small diameter" are used in relative terms (the same applies below). As noted in (2) above, in films containing fine inorganic fillers homogeneously and at high concentrations, microbubbles are particularly likely to remain. Therefore, it is thought that microbubbles can be suppressed by reducing the inorganic filler loading amount (i.e., increasing the fluororesin ratio above a certain level). However, this narrows and restricts the range of thermal expansion coefficient control, which is the purpose of inorganic filler blending. 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 fluororesin blending ratio, enabling high-density packing of inorganic fillers and maintaining the freedom of thermal expansion coefficient control.

Condition (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 particle size of 5 μm or more is 60% by volume or more.
As seen in the findings of (1) and (2) above, microbubbles are caused by the gas of a low molecular weight compound generated by the decomposition of the dispersant of component (C). It is believed that the gas of the low molecular weight compound is difficult to escape from the film in a film containing a homogeneous and high concentration of fine inorganic filler, which leads to particularly frequent generation of microbubbles. 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 formed by coating the resin composition, the voids and cracks that form between the fillers at the coating stage are more likely to be larger than those formed when only fine fillers are used. As will be described later, these voids and cracks serve as paths that promote the escape of the gas of the low molecular weight compound to the outside of 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 promoting the removal of the low molecular weight compound by volatilization during the melt heat treatment process, even when the inorganic filler is blended at a high density. On the other hand, if the 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 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 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 ) at the point where the cumulative volume is 10% and the particle diameter (D ₅₀ ) at the point where the cumulative volume is 50% on the cumulative curve can be calculated. For particles other than those of a spherical shape, the particle diameter refers to the value calculated as the spherical equivalent diameter.

To satisfy conditions (i) and (ii), for example, it is preferable to blend 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 it is more preferable to blend them in 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 spherical or crushed spherical shapes are preferred, as they minimize the difference in thermal expansion coefficient between the thickness direction and the plane 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, with spherical amorphous silica being particularly preferred, as it allows the thermal expansion coefficient to be reduced without impairing the dielectric properties when formed into a film, and in particular, it allows the difference in the thermal expansion coefficient between the thickness direction and the plane direction to be reduced.

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 for component (D) is not particularly limited, but is preferably an organic solvent that is liquid at 25° C., 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.

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

(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 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, 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.

Furthermore, the weight proportion of the inorganic filler (component (B)) in the dispersion composition is within the range of 60 to 85 weight percent, preferably 65 to 80 weight percent, 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 weight percent, the range of control over the thermal expansion coefficient when formed into a film becomes narrow. If the content of component (B) exceeds 85 weight percent, 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 filling is possible while not only preventing relatively large voids and cracks but also suppressing the generation of microbubbles.

In addition, 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, and more preferably within the range of 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 dispersing effect will not be obtained, and if it exceeds 10% by weight, a large amount of component (C) or its decomposition products will remain in the film, which will likely cause the generation of microbubbles.

Furthermore, there are no restrictions on the amount of organic solvent (component (D)) blended, as long as the viscosity of the dispersion composition can be adjusted to the desired value, as described later. However, in order to obtain good dispersibility and good coatability, it is advisable to blend it in such a way that it is preferably in the range of 25 to 50% by weight, and more preferably in the range of 30 to 40% by weight, of the total composition.

(viscosity)
The viscosity of the dispersion composition is not particularly limited, but when the objective is to coat a thick film of 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.

(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.

[Fluorine-based resin 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 component (A1) and component (B):
(A1) a fluorine-based resin,
(B) an inorganic filler;
Contains:

The fluororesin film of this 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) 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) _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 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.

In the fluororesin film of this 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.
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.

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) is thermally decomposed in the melt-heat treatment step. The phrase "substantially free of the dispersant of component (C)" means that the content of component (C) in the film is 0.3 wt % 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 step, 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, as determined by thermogravimetry 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 remain, a weight loss of more than 0.3% by weight will be confirmed by thermogravimetry and differential thermal analysis. This state is not preferable because it will generate microbubbles in a subsequent step involving heating.

Furthermore, in the fluororesin film of the present embodiment, because component (B) satisfies condition (i), small-diameter fillers are embedded between large-diameter fillers, reducing the spaces 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-mentioned 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.

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, measured using a split cylinder resonator after 24 hours of conditioning at a temperature of 24-26°C and a humidity of 45-55%. Furthermore, 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 will lead to increased dielectric loss when applied to circuit boards, making it more likely to experience problems such as electrical signal loss in the transmission path of high-frequency signals in the GHz range (e.g., 1-80 GHz).

In addition, in order to ensure dimensional stability, the thermal expansion coefficient of the fluorine-based resin film is preferably in the range of 10 to 40 ppm/K, and more preferably in the range of 15 to 30 ppm/K.

There are no particular limitations on the thickness of the fluororesin film, but when used as an insulating resin layer for a circuit board, taking into account its application to high-frequency signal transmission, it is preferably in the range of 30 to 150 μm, more preferably 75 to 150 μm.

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

<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.

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. Of these, copper or copper alloys are particularly preferred.

The surface roughness of the metal layer is not particularly limited, but from the perspective of ensuring adhesion with the fluororesin layer and 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, or may be, for example, a peelable copper foil having a thickness of 5 μm or less and a release layer formed between the copper foil and a carrier foil. In addition, commercially available copper foils can 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 purposes of 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 described above. 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-containing resin film using the dispersion composition of the present invention is not particularly limited, but the following method can be exemplified.

(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.

(Melting 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 to 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 may be equal to or higher than the melting point of the fluororesin, and is preferably in a temperature range higher than the melting point by 20°C to 80°C.
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.

In addition, when using metal foil as the substrate, the melting heat treatment process is preferably carried out under an inert gas atmosphere, more preferably under 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 mixture is cooled and solidified, and the substrate is peeled off as needed to obtain a fluororesin film. Because component (B) satisfies condition (i), the fluororesin film obtained in this manner has small-diameter fillers embedded between the large-diameter fillers, reducing the spaces between the fillers and resulting in a densely packed state.

This manufacturing method uses metal foil as the substrate, allowing the production of a metal-clad laminate comprising a fluororesin layer and a metal layer. For example, when metal foil is used as the substrate, the resulting laminate is a single-sided metal-clad laminate with a fluororesin layer on one side of the metal layer. It is also possible to produce a double-sided metal-clad laminate by using metal foil as the substrate and forming another metal layer on the side of the fluororesin film opposite the substrate.

It is also possible to produce 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 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, within the range of 2 MPa to 30 MPa. The fluororesin layer of the single-sided metal-clad laminate uses the dispersion composition of the present invention and undergoes 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 foil 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.

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

[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.

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 these examples. In the following examples, unless otherwise specified, the various measurements and evaluations were performed as follows.

[Measurement of particle size of amorphous silica]
Using a laser diffraction particle size distribution analyzer (Malvern, trade name: Mastersizer 3000), 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 a tapping mode over an area of 80 μm × 80 μm on the copper foil surface using an AFM (manufactured by Bruker AXS, trade name: Dimension Icon type SPM) and a probe (manufactured by Bruker AXS, trade name: TESPA (NCHV), tip curvature radius 10 nm, spring constant 42 N/m), 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)]
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 (trade name: TMA/SS7100, manufactured by Hitachi High-Technologies Corporation (formerly Seiko Instruments Inc.)). 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 after further holding at that temperature for 10 minutes, it 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.

[Measurement of dielectric properties]
The relative permittivity (Dk) and dielectric loss tangent (Df) of the fluororesin film obtained from the double-sided copper-clad laminate 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 a temperature of 24 to 26° C. and a humidity of 45 to 55%, before the measurement.

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

[Weight reduction rate]
(1) Weight loss rate of fluororesin film obtained from 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 heated from 30°C to 550°C at a rate of 10°C/min under a nitrogen atmosphere using a differential thermal/thermogravimetric analyzer (TG/DTA6200) manufactured by Hitachi High-Tech Science, and the change in weight was measured. 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, based on the weight at 150°C, and this was designated as ΔTG'(150-420).
(2) Weight loss rate of fluororesin film obtained from 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 heated from 30°C to 550°C at a rate of 10°C/min under a nitrogen atmosphere using a differential thermal thermogravimetry analyzer (TG/DTA6200) manufactured by Hitachi High-Tech Science, and the change in weight was measured. The weight loss rate [100 × (weight at 150°C - weight at 420°C)/weight at 150°C] (unit: wt%) calculated from the weight loss 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 a precise cross section perpendicular to the laminate using a cross-section polisher, and five random images of the inorganic filler-containing fluororesin layer were taken at a magnification of 2000 times using a scanning electron microscope (SEM). Next, the void portions and other portions 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 case in which 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 a case in which the porosity was 3 vol.% or more or there were voids with a diameter of more than 1 μm was rated × (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, 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, 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, treated with hexamethyldisilazane in an amount of 0.98% by weight of 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: a 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 fillers (1) to (7), D ₁₀ and D ₅₀ calculated on a volume basis, and the proportion of particles having a particle size of 5 μm or more, measured using a laser diffraction particle size distribution analyzer.

(Dispersion Composition Preparation Example 1)
Into a container of a 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 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 device were performed three times.

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 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% by weight of the total amount, and no powdery parts were observed within the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was initiated, and the kneading was stopped at 15-minute intervals to scrape off the kneaded mixture 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 1-1. Dispersion Composition 1-1 lacked fluidity and viscosity could not be measured, so it was deemed a "solid."

Subsequently, dispersion composition 1-1 was gradually diluted and stirred with DMAc so that the total proportion of fluorine-based resin powder (1) and silica filler (4) was 67.5% by weight of the total amount, and dispersion composition 1-2 was obtained, having a viscosity of 890 cP when measured at 100 rpm.

(Dispersion Composition Preparation Example 2)
Into a container of a 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 the stirring blades and the side walls of the container. The above stirring and scraping of the kneaded material from the stirring blades and the side walls of the container after stopping the device were performed three times.

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 mixture became lumpy and free of powdery components. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (5) reached 86% by weight of the total amount, and no powdery components were observed within the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was initiated, stopping at 15-minute intervals and scraping the mixture off the stirring blades and 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 deemed a "solid."

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

(Dispersion Composition Preparation Example 3)
Into a container of a 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 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 device were performed three times.

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 mixture became lumpy and free of powdery components. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (6) reached 85% by weight of the total amount, and no powdery components were observed within the kneaded mixture. Once the mixture had formed lumps, kneading at 30 rpm was initiated, stopping at 15-minute intervals and scraping the mixture off the stirring blades and side walls of the container. This process was repeated four times for a total of 60 minutes, yielding Dispersion Composition 3-1. Dispersion Composition 3-1 lacked fluidity and viscosity could not be measured, so it was deemed a "solid."

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

(Dispersion Composition Preparation Example 4)
Into a container of a T.K. HIVIS MIX (Model 2P-03) manufactured by Primix Corporation (formerly Tokushu Kika Kogyo Co., Ltd.), 82.3 g of fluorine-based resin 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 the stirring blades and side walls of the container. This stirring and scraping of the kneaded material off the stirring blades and side walls of the container after stopping the device were performed three times.

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 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% by weight of the total amount, and no powdery parts were observed within the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was initiated, and the kneading was stopped at 15-minute intervals to scrape off the kneaded mixture 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 viscosity could not be measured, so it was deemed to be a "solid."

Subsequently, dispersion composition 4-1 was gradually diluted and stirred with DMAc so that the total proportion of fluorine-based resin powder (1) and silica filler (4) was 70.0% by weight of the total amount, and dispersion composition 4-2 was obtained, having a viscosity of 1210 cP when measured at 100 rpm.

(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 a container of a T.K. HIVIS 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. The above stirring and scraping of the kneaded material off the stirring blades and the side walls of the container after stopping the apparatus were performed three times.

Next, to fine-tune the ratio of the total amount of fluororesin powder (1) and silica filler (7) to the total 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 mixture became lumpy and free of powdery components. In this study, the mixture became lumpy when the total weight of fluororesin powder (1) and silica filler (7) reached 86% by weight, and no powdery components were observed within the kneaded mixture. Once the mixture had formed lumps, kneading at 30 rpm was initiated, stopping at 15-minute intervals and scraping the mixture 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 viscosity measurements were not possible, so it was deemed a "solid."

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

(Dispersion Composition Preparation Example 6)
Into a container of a 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 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 device were performed three times.

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 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) to the total amount reached 86 wt %, and no powdery parts were observed within the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was initiated, and the mixture was stopped at 15-minute intervals to scrape off the kneaded mixture 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 viscosity could not be measured, so it was deemed a "solid."

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

(Dispersion Composition Preparation Example 7)
Into a container of a 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 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 device were performed three times.

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 mixture became lumpy and free of powdery components. In this study, the mixture became lumpy when the total ratio of fluororesin powder (1) and silica filler (2) reached 86% by weight of the total amount, and no powdery components were observed within the kneaded mixture. Once the mixture became lumpy, kneading at 30 rpm was initiated, stopping at 15-minute intervals and scraping the mixture off the stirring blades and 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 a "solid."

Dispersion composition 7-1 was then gradually diluted and stirred with DMAc so that the total proportion of fluorine-based resin powder (1) and silica filler (2) was 67.5% by weight of the total amount, and dispersion composition 7-2 was obtained, having a viscosity of 970 cP when measured at 100 rpm.

Example 1
Dispersion composition 1-2 was coated onto copper foil (electrolytic copper foil, thickness: 12 μm, ten-point average roughness (Rzjis) on the resin layer side: 0.6 μm), and then dried using a hot air oven in an air atmosphere at 80 ° C. for 1 minute and 120 ° C. for 3 minutes. Next, using a hot air oven in a nitrogen atmosphere (oxygen concentration 0.1 vol% 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 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 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 0.24 wt%.

Next, two single-sided copper-clad laminates 1 were prepared, and placed in a batch press with the resin surfaces facing each other. They were then 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 pattern, and the peel strength was measured, resulting in a value of 0.49 kN/m.

Next, the copper foil of double-sided copper-clad laminate 1 was etched away using an aqueous ferric chloride solution to prepare fluororesin film 1. The CTE of 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.% (○).

<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. Table 2 shows the evaluation results of the obtained materials.

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 (9)

The following components (A) to (D):
(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 particle size of 5 μm or more is 60% by volume or more;
A dispersion composition characterized by satisfying the above. The dispersion composition described in claim 1, wherein the content of component (C) is within the range of 1 to 10 weight % relative to the total amount of components (A) and (B). The dispersion composition described in claim 1, wherein the content of component (D) is within the range of 25 to 50 weight % of the total composition. The dispersion composition described in claim 1, wherein component (B) is spherical amorphous silica. The dispersion composition described in 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 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. 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 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: 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: