JP7635620B2 - Aqueous dispersion and method for producing laminate - Google Patents

Description

The present invention relates to an aqueous dispersion containing tetrafluoroethylene polymer particles, specific inorganic particles, and a specific ratio of polyhydric alcohols, and a method for producing a laminate having a polymer layer formed from the aqueous dispersion.

Tetrafluoroethylene polymers such as polytetrafluoroethylene (PTFE) have excellent physical properties such as electrical properties, water and oil repellency, chemical resistance, and heat resistance, and are used in a variety of industrial applications. Dispersions containing particles of tetrafluoroethylene polymers are known as coating agents used to impart the above physical properties to the surface of a substrate, and such dispersions are also attracting attention as materials for forming dielectric layers of printed circuit boards that correspond to high-frequency band frequencies.

On the other hand, in an attempt to improve the physical properties of such dispersions, Patent Documents 1 and 2 describe aqueous dispersions containing particles of tetrafluoroethylene-based polymers to which a specific polyhydric alcohol, depolymerizable acrylic resin particles, and a nonionic surfactant have been added.

International Publication No. 2003/011991 International Publication No. 2021/045228

Aqueous dispersions containing particles of tetrafluoroethylene-based polymers, which generally have low surface tension, tend to have poor dispersion conditions, and therefore tend to cause coarse packing of the particles when the particles are applied to a substrate and baked to form a polymer layer. As a result, problems with the density of the polymer layer tend to occur, particularly when attempting to form a thick polymer layer.
Specifically, when the polymer layer is formed on the surface of a substrate such as a metal foil by a continuous production process such as roll-to-roll, cracks and pinholes are likely to occur in the polymer layer, and the laminate consisting of the polymer layer and the substrate is likely to warp due to the low linear expansion of the tetrafluoroethylene-based polymer.
In the case where inorganic particles are blended into the aqueous dispersion to adjust the linear expansion coefficient of the formed molded product, the dispersibility and handling properties of the dispersion are reduced, and the particles and inorganic particles are likely to fall off (powder off) during coating. Also, the adhesion of the formed molded product to the substrate is likely to be reduced.
The present inventors have found that this tendency becomes more pronounced when inorganic particles having a small particle size are blended into the dispersion liquid in order to improve the electrical properties of the polymer layer, such as the dielectric constant and the dielectric loss tangent.

The present inventors have found, through intensive research, that the aqueous dispersion containing tetrafluoroethylene polymer particles and inorganic particles of a specific particle size, and the ratio of polyhydric alcohol to water is within a specific range, has excellent dispersion stability.Furthermore, they have found that this dispersion can form a thick and smooth molded product, and the molded product obtained is dense, has excellent electrical properties such as low dielectric tangent, flexibility such as bending resistance, low linear expansion, and improves adhesion and adhesion to substrates such as metal foil.
An object of the present invention is to provide a dispersion containing particles of a tetrafluoroethylene-based polymer which is excellent in dispersion stability, and which is capable of forming a thick and smooth polymer layer in the obtained molded product which is excellent in electrical properties, flexibility such as bending resistance, low linear expansion, and adhesiveness and adhesion to a substrate such as a metal foil, and a method for producing a laminate having a polymer layer formed from such a dispersion.

The present invention has the following aspects.
<1> An aqueous dispersion comprising tetrafluoroethylene polymer particles, inorganic particles having an average particle size of less than 10 μm, a polyhydric alcohol, and water, the mass ratio of the polyhydric alcohol to the water being 0.2 or more.
<2> The aqueous dispersion of <1>, wherein the tetrafluoroethylene-based polymer is a heat-fusible tetrafluoroethylene-based polymer having a carbonyl group-containing group or a hydroxyl group-containing group.
<3> The aqueous dispersion according to <1> or <2>, wherein the particles of the tetrafluoroethylene-based polymer are particles of a heat-fusible tetrafluoroethylene-based polymer and particles of a non-heat-fusible tetrafluoroethylene-based polymer.
<4> The aqueous dispersion of any one of <1> to <3>, wherein the inorganic particles are silica particles.
<5> The aqueous dispersion of any one of <1> to <4>, wherein the inorganic particles have a scale-like or substantially spherical shape.
<6> The aqueous dispersion according to any one of <1> to <5>, wherein the content of the inorganic particles is greater than the content of the tetrafluoroethylene-based polymer.
<7> The aqueous dispersion of any one of <1> to <6>, having a pH in the range of 5 to 10.
<8> The aqueous dispersion according to any one of <1> to <7>, wherein the polyhydric alcohol is an aliphatic polyhydric alcohol having a boiling point of 100° C. or higher.
<9> The aqueous dispersion of any one of <1> to <8>, further comprising an aromatic resin.
<10> The aqueous dispersion according to <9>, wherein the aromatic resin is a precursor of a water-soluble aromatic polyamideimide or a precursor of a water-soluble aromatic polyimide.
<11> The aqueous dispersion according to <9> or <10>, wherein the content of the aromatic resin is less than 10 mass% based on the particles of the tetrafluoroethylene-based polymer.
<12> The aqueous dispersion according to any one of <1> to <11>, further comprising a surfactant.
<13> A method for producing a laminate, comprising applying the aqueous dispersion of any one of <1> to <12> to a surface of a substrate, and heating the applied aqueous dispersion to form a polymer layer containing the tetrafluoroethylene-based polymer and the inorganic particles, and obtaining a laminate having the substrate and the polymer layer in this order.
<14> The manufacturing method of <13>, wherein the ten-point average roughness of the surface of the substrate is less than 0.1 μm.
<15> The method of <13> or <14>, wherein the polymer layer has a thickness of 25 μm or more.

According to the present invention, it is possible to provide a dispersion containing particles of a tetrafluoroethylene-based polymer, which has excellent dispersion stability, and a laminate having a polymer layer formed from such a dispersion. From the dispersion of the present invention, it is possible to form a molded product, particularly a thick and smooth polymer layer, which has excellent electrical properties such as low dielectric tangent, flexibility such as bending resistance, adhesion and adhesion to substrates such as metal foil, and low linear expansion. Therefore, a laminate having a polymer layer formed from the dispersion of the present invention is useful, for example, as a constituent material for a printed circuit board.

The following terms have the following meanings.
The "average particle size (D50)" is the volume-based cumulative 50% diameter of a target object (particle) determined by a laser diffraction/scattering method. In other words, the particle size distribution is measured by a laser diffraction/scattering method, a cumulative curve is calculated with the total volume of a particle group taken as 100%, and the average particle size (D50) is the particle size at the point on the cumulative curve where the cumulative volume is 50%.
The D50 of a target object is determined by dispersing the particles in water and analyzing them by a laser diffraction/scattering method using a laser diffraction/scattering type particle size distribution measuring device (LA-920 measuring device, manufactured by Horiba, Ltd.).
"Melting temperature" is the temperature corresponding to the maximum of the melting peak of a polymer as measured by differential scanning calorimetry (DSC).
The "viscosity of the dispersion liquid" is a viscosity measured using a Brookfield viscometer at 25° C. and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measured values is used.
The "thixotropy ratio" is a value calculated by dividing the viscosity _η1 of the dispersion measured at a rotation speed of 30 rpm by the viscosity _η2 measured at a rotation speed of 60 rpm. Each viscosity measurement is repeated three times, and the average value of the three measured values is used.
A "unit" in a polymer means an atomic group based on a monomer formed by polymerization of the monomer. The unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by processing the polymer. Hereinafter, a unit based on monomer a is also referred to simply as a "monomer a unit."

The aqueous dispersion of the present invention (hereinafter also referred to as "the present dispersion") contains particles (hereinafter also referred to as "F particles") of a tetrafluoroethylene polymer (hereinafter also referred to as "F polymer"), inorganic particles having an average particle size of less than 10 μm, a polyhydric alcohol, and water, and the mass ratio of the polyhydric alcohol to water is 0.2 to 0.5.

The present dispersion has excellent dispersion stability. In addition, a molded product (fired product) formed from the present dispersion has excellent physical properties based on the F polymer, such as electrical properties, and excellent physical properties based on the inorganic particles, such as linear expansion properties, and has excellent surface smoothness, flexibility, such as bending resistance, and adhesiveness and adhesion to a substrate.
The reason why the dispersion stability of the present dispersion is improved is not necessarily clear, but is presumed to be, for example, as follows.
F particles, which are particles of an F polymer having generally low surface energy, are unlikely to interact with inorganic particles, so that the F particles and inorganic particles are each considered to be in a state in which they are likely to aggregate in the dispersion. In the present dispersion, it is considered that the polyhydric alcohol acts as a dispersant for the F particles and inorganic particles in the present dispersion, suppressing their aggregation. It is also considered that the polyhydric alcohol also acts as a rheology regulator for the present dispersion, improving the dispersion stability and coatability of the present dispersion. Furthermore, it is considered that adjusting the content of the polyhydric alcohol relative to water to a predetermined range highly balances the action of suppressing the aggregation of the F particles and inorganic particles and the action of improving the rheology, improving the dispersion stability and coatability of the present dispersion. And it is also considered that the small particle size of the inorganic particles and the large surface area of the inorganic particles improve the wettability of the inorganic particles and the polyhydric alcohol, enhancing these actions.
Therefore, when this dispersion is applied and the F polymer is baked to form a molded product (polymer layer), the F particles and inorganic particles are highly packed together during application without falling off, and the polyhydric alcohol is highly removed during baking, so that a molded product with advanced physical properties is formed.
As a result, it is believed that this dispersion has excellent dispersion stability, and that it is possible to easily form molded products from this dispersion that have excellent electrical properties, bending resistance, adhesion to the substrate, low linear expansion, smoothness, etc., and are less prone to powder falling, and that highly combine the physical properties of the F polymer and the physical properties of the inorganic particles.

The F polymer in this dispersion is a polymer that contains units (TFE units) based on tetrafluoroethylene (TFE).The F polymer may be heat-meltable or non-heat-meltable, but is preferably heat-meltable.The F polymer may be used alone or in combination of two or more kinds, and in this case, it is preferable that at least one of the F polymers is heat-meltable.
In such a case, a molded product formed from the dispersion liquid is likely to have excellent flexibility and adhesiveness/cohesion to a substrate. Note that the term "thermal melt property" refers to a polymer having melt fluidity at which a melt flow rate is 1 to 1000 g/10 min at a temperature 20° C. or more higher than the melting temperature of the polymer under a load of 49 N.
When the F polymer is heat-meltable, the melting temperature is preferably 200° C. or higher, more preferably 260° C. or higher. The melting temperature of the F polymer is preferably 325° C. or lower, more preferably 320° C. or lower. In such a case, a molded product formed from the present dispersion tends to have excellent heat resistance.

The fluorine atom content in the F polymer is preferably 70% by mass or more, more preferably 70 to 76% by mass. Due to the above-mentioned mechanism of action, the present dispersion liquid is particularly likely to improve the water dispersibility of the particles of the F polymer having a high fluorine atom content.
The glass transition point of the F polymer is preferably from 75 to 125°C, more preferably from 80 to 100°C.

F polymer includes polytetrafluoroethylene (PTFE), polymers that contain TFE units and units based on ethylene (ETFE), polymers that contain TFE units and units based on perfluoro(alkyl vinyl ether) (PAVE) (PAVE units) (PFA), and polymers that contain TFE units and units based on hexafluoropropene (HFP) ₍ FEP).Each of ETFE, PFA and FEP may further contain other units.Preferably, PAVE is _CF2 = _CFOCF3 , _{CF2 = CFOCF2CF3} and _CF2 = _CFOCF2CF2CF3 (PPVE), and more preferably _PPVE .
The F polymer is preferably PFA or FEP, more preferably PFA.

At least one of the F polymers preferably has an oxygen-containing polar group. In this case, the affinity of the F polymer with the inorganic particles and the polyhydric alcohol is improved, so that the dispersion tends to have excellent dispersion stability.
The oxygen-containing polar group may be contained in the unit of the F polymer, or may be contained in the terminal group of the main chain of the F polymer. The latter embodiment includes an F polymer having an oxygen-containing polar group as an end group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer having an oxygen-containing polar group obtained by subjecting an F polymer to plasma treatment or ionizing radiation treatment. The oxygen-containing polar group is preferably a hydroxyl group-containing group, a carbonyl group-containing group, and a phosphono group-containing group, and from the viewpoint of the dispersion stability of the present dispersion, a hydroxyl group-containing group and a carbonyl group-containing group are more preferable, and a carbonyl group-containing group is even more preferable.

The hydroxyl-containing group is preferably a group containing an alcoholic hydroxyl group, and more preferably --CF ₂ CH ₂ OH, --C(CF ₃ ) ₂ OH, or a 1,2-glycol group (--CH(OH)CH ₂ OH).
The carbonyl group-containing group is a group containing a carbonyl group (>C(O)), and is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH ₂ ), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.) or a carbonate group (-OC(O)O-), more preferably an acid anhydride residue.
When the F polymer has a carbonyl group-containing group, the number of carbonyl group-containing groups in the F polymer is preferably 10 to 5000, more preferably 100 to 3000, and even more preferably 800 to 1500 per 1 × 10 ⁶ carbon atoms in the main chain. The number of carbonyl group-containing groups in the F polymer can be quantified by the composition of the polymer or the method described in WO 2020/145133.
The monomer having a carbonyl group-containing group is preferably itaconic anhydride, citraconic anhydride, or 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH").

The F polymer is preferably a polymer having a carbonyl group-containing group or a hydroxyl group-containing group, including a TFE unit and a PAVE unit, more preferably a polymer containing a TFE unit, a PAVE unit, and a unit based on a monomer having a carbonyl group-containing group or a hydroxyl group-containing group, and even more preferably a polymer containing these units in the following order of 90 to 99 mol%, 0.5 to 9.97 mol%, and 0.01 to 3 mol% relative to the total units.
Specific examples of such polymers include those described in WO 2018/16644.
These F polymers not only have excellent dispersion stability, but also tend to be distributed more densely and homogeneously in the molded product (polymer layer, etc.) obtained from the dispersion. Furthermore, they tend to form microspherulites in the molded product, and tend to have high adhesion to other components. As a result, molded products with excellent physical properties such as electrical properties are more likely to be obtained.

In this dispersion, the D50 of the F particles is preferably 0.1 to 25 μm. The D50 of the F particles is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. The D50 of the F particles is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. With a D50 in this range, the fluidity and dispersibility of the F particles tend to be good.

From the viewpoint of dispersion stability of the present dispersion, the bulk density of the F particles is preferably 0.15 g/m ² or more, and more preferably 0.20 g/m ² or more. The bulk density of the F particles is preferably 0.50 g/m ² or less, and more preferably 0.35 g/m ² or less.
The specific surface area of the F particles is preferably from 1 to 8 m ² /g, and more preferably from 1 to 3 m ² /g.

F particles may be one type or two or more types. When two types of F particles are used, the F particles preferably include particles of a non-thermofusible F polymer (preferably PTFE) and particles of an F polymer (preferably a polymer having a carbonyl group-containing group or a hydroxyl group-containing group, including the above-mentioned TFE unit and PAVE unit) whose melting temperature is 200 to 320°C. And, it is more preferable that the content mass of the former particles is larger than the content mass of the latter particles.
In this case, the ratio of the latter particles to the total of the former particles and the latter particles is preferably 25% by mass or less, more preferably 15% by mass or less, and in this case, the ratio is preferably 0.1% by mass or more, more preferably 1% by mass or more.
The present dispersion is likely to have excellent dispersion stability, ease of handling, and long-term storage stability. In addition, during preparation of the present dispersion or during formation of a molded product, the PTFE is appropriately fibrillated, so that the inorganic particles are easily supported in the molded product, and a molded product having excellent physical properties and high strength based on the PTFE is easily formed.
In this case, preferred are an embodiment in which the D50 of the particles of the non-thermofusible F polymer is 0.1 to 1 μm and the D50 of the particles of the F polymer having a melting temperature of 200 to 320° C. is 0.1 to 1 μm, and an embodiment in which the D50 of the particles of the non-thermofusible F polymer is 0.1 to 1 μm and the D50 of the particles of the F polymer having a melting temperature of 200 to 320° C. is 1 to 4 μm.

The F particles may contain a resin or an inorganic substance other than the F polymer, but preferably contain the F polymer as the main component. The content of the F polymer in the F particles is preferably 80% by mass or more, more preferably 100% by mass.
Examples of the resin include heat-resistant resins such as aromatic polyester, polyamideimide, (thermoplastic) polyimide, polyphenylene ether, polyphenylene oxide, and maleimide. Examples of the inorganic material include silicon oxide (silica), metal oxides (beryllium oxide, cerium oxide, alumina, soda alumina, magnesium oxide, zinc oxide, titanium oxide, and the like), boron nitride, and magnesium metasilicate (steatite). At least a part of the surface of the inorganic material may be surface-treated.
F particles containing a resin or inorganic substance other than an F polymer may have a core-shell structure having an F polymer as a core and a resin or inorganic substance other than an F polymer as a shell, or may have a core-shell structure having an F polymer as a shell and a resin or inorganic substance other than an F polymer as a core. Such F particles are obtained, for example, by coalescing (by collision, aggregation, etc.) particles of an F polymer with a resin or inorganic substance other than an F polymer.

The content of F particles in the present dispersion is preferably 5% by mass or more, and more preferably 10% by mass or more, based on the total mass of the present dispersion. The content of F particles is preferably 40% by mass or less, and more preferably 20% by mass or less, based on the total mass of the present dispersion.

The inorganic particles contained in the present dispersion are preferably nitride particles or inorganic oxide particles, more preferably boron nitride particles, beryllium oxide particles, silicate particles (silica particles, wollastonite particles, talc particles), metal oxide particles (cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, etc.) particles or magnesium metasilicate (steatite) particles, and even more preferably silica particles. These inorganic particles may be fired ceramic particles.
The inorganic particles may be used alone or in combination of two or more kinds. When two or more kinds of inorganic particles are used in combination, two kinds of silica particles may be used in combination, or silica particles and other inorganic particles may be used in combination.
By containing inorganic particles in the dispersion, the molded product produced from the dispersion is likely to have excellent electrical properties and low linear expansion. In addition, even if the dispersion contains inorganic particles, the dispersion is excellent in dispersion stability due to the above-mentioned mechanism of action, and it is easy to obtain a dense molded product. Therefore, it is easy to form a molded product that has high physical properties of the F polymer and the inorganic particles from the dispersion.

It is preferable that at least a portion of the surface of the inorganic particles is surface-treated with a silane coupling agent (3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, etc.). Such inorganic particles have excellent affinity with F particles, and tend to improve the dispersibility of the dispersion.

The inorganic particles contained in the dispersion have an average particle size (D50) of less than 10 μm. The inorganic particles preferably have a D50 of more than 0.1 μm and less than 10 μm. D50 is more preferably 8 μm or less, and more preferably 5 μm or less. D50 is preferably 0.25 μm or more, and more preferably 0.5 μm or more. The inorganic particles preferably have a specific surface area of 1 to 20 m ² /g, and more preferably 1 to 5 m ² /g.

The shape of the inorganic particles may be any of granular, needle-like (fibrous), and plate-like. Specific shapes of the inorganic particles include spherical, scale-like, layered, leaf-like, apricot kernel-like, columnar, cockscomb-like, equiaxial, leaf-like, mica-like, block-like, flat, wedge-like, rosette-like, mesh-like, and prismatic. The shape of the inorganic particles is preferably approximately spherical or scale-like, more preferably approximately spherical with D50 of more than 0.1 μm and less than 10 μm and substantially free of particles with a particle diameter of 3 μm or more, or scale-like with an average major axis of 1 μm or more and an aspect ratio of 5 or more, and even more preferably approximately spherical.
In addition, substantially spherical inorganic particles refer to inorganic particles in which, when observed with a scanning electron microscope (SEM), the proportion of spherical particles having a ratio of minor axis to major axis of 0.7 or more is 95% or more.
In such a case, the inorganic particles become more easily wetted in the present dispersion, and the interaction with the F particles is easily enhanced. In addition, in a molded product formed from the present dispersion, the inorganic particles and the F polymer are more easily distributed uniformly, and the physical properties of both are easily expressed in a well-balanced manner.

Specific examples of suitable inorganic particles include silica particles (such as the "Admafine (registered trademark)" series manufactured by Admatechs Co., Ltd.), zinc oxide surface-treated with esters such as propylene glycol dicaprylate (such as the "FINEX (registered trademark)" series manufactured by Sakai Chemical Industry Co., Ltd.), spherical fused silica (such as the "SFP (registered trademark)" series manufactured by Denka Co., Ltd.), titanium oxide coated with polyhydric alcohol and inorganic substances (such as the "Tipaque (registered trademark)" series manufactured by Ishihara Sangyo Kaisha, Ltd.), and rutile-type titanium oxide surface-treated with alkylsilane (such as the "Tipaque (registered trademark)" series manufactured by Teika Co., Ltd.). "JMT (registered trademark)" series by Taiheiyo Cement Corporation, hollow silica particles ("E-SPHERES" series by Taiheiyo Cement Corporation, "Silinax" series by Nippon Steel Mining Co., Ltd., "Ecocospher" series by Emerson & Cumming Co., Ltd., etc.), talc particles ("SG" series by Nippon Talc Co., Ltd., etc.), steatite particles ("BST" series by Nippon Talc Co., Ltd., etc.), boron nitride particles ("UHP" series by Showa Denko KK, "Denka Boron Nitride" series ("GP", "HGP" grades) by Denka Co., Ltd., etc.).

In the present dispersion, the content of inorganic particles is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total mass of the present dispersion, and the content of inorganic particles is preferably 70% by mass or less, more preferably 50% by mass or less.
In the present dispersion, the content of inorganic particles is preferably greater than the content of F polymer. Specifically, the ratio of the content of inorganic particles to the content of F particles in the present dispersion is greater than 1, more preferably 1.25 or more, and even more preferably 1.5 or more. The ratio is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. When it is in this range, it becomes possible to easily form a thick molded product from the present dispersion without defects such as powder falling while maintaining the dispersion stability of the F particles and inorganic particles, and the physical properties of the obtained molded product are easily improved.

The total content of the F particles and inorganic particles in the present dispersion is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total mass of the present dispersion. The total content is preferably 70% by mass or less.
In this case, a molded product such as a coating film can be formed from the dispersion liquid with a high thickness and high uniformity, and the physical properties due to the F polymer and the physical properties due to the inorganic particles are easily expressed to a high degree. That is, even when the content of the F particles and the inorganic particles is in such a high range, the dispersion liquid has excellent dispersion stability due to the above-mentioned mechanism of action, and the physical properties of the molded product can be improved.

The polyhydric alcohol contained in the present dispersion is a compound having two or more alcoholic hydroxyl groups. The polyhydric alcohol is preferably an aliphatic polyhydric alcohol having two or three alcoholic hydroxyl groups, no nitrogen atom, and a boiling point of 100° C. or higher.
The boiling point of the polyhydric alcohol is preferably 150° C. or higher, more preferably 200° C. or higher, and more preferably 340° C. or lower.
Moreover, the polyhydric alcohol is preferably one that is miscible with water.

Examples of polyhydric alcohols include ethylene glycol (198°C), 1,2-propanediol (188°C), 1,3-propanediol (214°C), 1,2-butanediol (190°C), 1,3-butanediol (208°C), 1,4-butanediol (229°C), 1,5-pentanediol (242°C), 2-butene-1,4-diol (235°C), glycerin (290°C), 2-ethyl-2-hydroxymethyl-1,3-propanediol (295°C), and 1,2,6-hexanetriol (178°C/666 Pa). The boiling points of the respective polyhydric alcohols are shown in parentheses.
The polyhydric alcohol is preferably glycerin, which improves the dispersibility of the F particles and inorganic particles in the dispersion, and improves the electrical properties, bending resistance, adhesion to the substrate, and low linear expansion of the resulting molded product, and is less likely to fall off.
The polyhydric alcohols may be used alone or in combination of two or more kinds.

In this dispersion, the polyhydric alcohol to water content mass ratio is 0.2 or more. Such a content mass ratio is more preferably 0.25 or more, and even more preferably 0.5 or more. Such a content mass ratio is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. When the content mass ratio is within this range, the aggregation suppression effect and rheology adjustment effect of the polyhydric alcohol are exhibited in a well-balanced manner, and this dispersion tends to have excellent dispersion stability.

The water content in the present dispersion is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total mass of the present dispersion, and is preferably 60% by mass or less, more preferably 50% by mass or less.
The content of the polyhydric alcohol in the present dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass of the present dispersion, and is preferably 70% by mass or less, more preferably 60% by mass or less.
Within this range, the dispersion can be handled as a liquid or paste, and its dispersion stability and coatability are more likely to be improved.

In addition to water and the polyhydric alcohol, the dispersion may further contain a compound as a liquid dispersion medium to the extent that the effect of the present invention is not impaired. Such a compound is preferably liquid at 25°C under atmospheric pressure and miscible with water. The boiling point of such a compound is preferably in the range of 50 to 240°C, and specific examples include methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

The dispersion may further include an aromatic resin. The aromatic resin may be thermoplastic or thermosetting. The aromatic resin may be included in the dispersion as a precursor thereof. The aromatic resin may be dissolved in the dispersion or may be dispersed without being dissolved. The aromatic resin is preferably water-soluble.

Examples of the aromatic resin include aromatic epoxy resins, phenolic resins, aromatic polyester resins (such as liquid crystalline aromatic polyesters), aromatic polyesteramides (such as liquid crystalline aromatic polyesteramides), aromatic maleimides, polyphenylene ethers, aromatic polyimides, aromatic polyimide precursors (polyamic acids or salts thereof), aromatic polyamideimides, aromatic polyamideimide precursors, aromatic polyetherimides, and aromatic polyetherimide precursors. Of these, aromatic polyimide precursors, aromatic polyamideimides, or aromatic polyamideimide precursors are preferred, and water-soluble aromatic polyamideimide precursors or water-soluble aromatic polyimide precursors are more preferred.
In this case, the aromatic resin easily interacts with the F polymer, and furthermore, a molded article formed from this dispersion tends to have excellent adhesion to a substrate such as a metal foil and excellent UV absorption properties.

Examples of aromatic polyimide precursors include polyamic acids obtained by polymerizing tetracarboxylic dianhydrides and diamines in a solvent, and polyamic acid salts obtained by reacting the polyamic acid with aqueous ammonia or an organic amine. An aqueous solution of polyamic acid can be prepared by dissolving the polyamic acid salt in water. Specific examples of aromatic polyimide resins or their precursors include the "Neoprim (registered trademark)" series (manufactured by Mitsubishi Gas Chemical Company, Inc.), the "Spiceria (registered trademark)" series (manufactured by Somar), the "Q-PILON (registered trademark)" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology Co., Ltd.), the "Tomide (registered trademark)" series (manufactured by T&K Toka Corporation), the "KPI-MX" series (manufactured by Kawamura Sangyo Co., Ltd.), and the "Upia (registered trademark)-AT" series (manufactured by Ube Industries, Ltd.).

Examples of aromatic polyamideimide resins or precursors thereof include polyamideimide resins or precursors thereof obtained by reacting diisocyanate and/or diamine with a tribasic acid anhydride (or tribasic acid chloride) as an acid component.
Specific examples of aromatic polyamideimide resins or precursors thereof include "HPC-1000" and "HPC-2100D" (both manufactured by Showa Denko Materials KK).

When the present dispersion further contains an aromatic resin, the content thereof is preferably 0.01% by mass or more, more preferably 1% by mass or more, based on the total mass of the present dispersion, and the content of the aromatic resin is preferably 5% by mass or less, more preferably 3% by mass or less.
The content of the aromatic resin in the dispersion is preferably less than 10% by mass, more preferably 5% by mass or less, based on the F particles in the dispersion, and is preferably 0.1% by mass or more based on the F particles.
If the content of the aromatic resin is in such a low range, the dispersion stability of the F particles is improved, and the physical properties of the molded product obtained from the dispersion liquid are likely to be improved. Although the reason for this is not necessarily clear, it is thought that the aromatic resin is likely to function highly as a dispersant and binder for the low hydrophilic F particles, that is, it adheres to the surface of the F particles and promotes dense sintering of the F particles when forming the molded product.

The present dispersion may further contain a surfactant from the viewpoint of improving the dispersibility of the F particles and the inorganic particles.
The surfactant is preferably nonionic.
The surfactant is preferably a glycol-based surfactant, an acetylene-based surfactant, a silicone-based surfactant or a fluorine-based surfactant, and more preferably a silicone-based surfactant.
The surfactant may be used alone or in combination of two or more. When two types of nonionic surfactants are used, the nonionic surfactants are preferably a silicone-based surfactant and a glycol-based surfactant.

Specific examples of surfactants include the "Ftergent" series (manufactured by Neos Co., Ltd., Ftergent is a registered trademark), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd., Surflon is a registered trademark), the "Megafac" series (manufactured by DIC Corporation, Megafac is a registered trademark), the "Unidyne" series (manufactured by Daikin Industries, Ltd., Unidyne is a registered trademark), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by BYK Japan KK), "KF-6011", "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by The Dow Chemical Company, "Tergitol TMN-100X", etc.).

From the viewpoint of improving the adhesiveness and low linear expansion of a molded article formed from the present dispersion, the present dispersion may further contain a resin material other than the F polymer and the aromatic resin described above. Such a resin material may be thermosetting or thermoplastic, may be modified, and may be dissolved in the present dispersion or may be dispersed without being dissolved.
Examples of such resin materials include non-aromatic maleimide resins, urethane resins, polyimide resins, polyamic acids, polyamideimides, and polyvinyl acetal resins.
When the present dispersion further contains a resin material, the content thereof is preferably 40% by mass or less based on the total mass of the present dispersion.

The pH of the present dispersion is preferably in the range of 5 to 10, and more preferably in the range of 7 to 9. In this case, the present dispersion tends to have excellent dispersion stability and storage stability.
The dispersion may further comprise a pH adjuster or buffer.
The pH adjuster may include amines, ammonia, and citric acid.
Examples of the pH buffer include tris(hydroxymethyl)aminomethane, ethylenediaminetetraacetic acid, ammonium hydrogen carbonate, ammonium carbonate, and ammonium acetate.
When the present dispersion further contains a pH adjuster or a pH buffer, the pH adjuster or the pH buffer may be added to water before the preparation of the present dispersion, or may be added at any stage of the preparation of the present dispersion.

In addition to the above components, the dispersion may further contain other components such as a thixotropic agent, a viscosity regulator, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightening agent, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, and various fillers, provided that the effects of the present invention are not impaired.

The viscosity of the dispersion is preferably 10 mPa·s or more, more preferably 30 mPa·s or more, and even more preferably 50 mPa·s or more. The viscosity of the dispersion is preferably 10,000 mPa·s or less, more preferably 3,000 mPa·s or less, and even more preferably 1,000 mPa·s or less.

The thixotropy ratio of the present dispersion is preferably 1.0 or more. The thixotropy ratio of the present dispersion is preferably 3.0 or less, and more preferably 2.0 or less. In this case, the present dispersion has excellent coatability and homogeneity, and is easy to form a denser molded product (polymer layer, etc.).

In this dispersion, the dispersion layer ratio is preferably 60% or more, more preferably 70% or more, and more preferably 80% or more. Here, the dispersion layer ratio is a value calculated by the following formula from the height of the entire dispersion in the screw tube and the height of the sedimentation layer (dispersion layer) before and after standing when the dispersion (18 mL) is placed in a screw tube (internal volume: 30 mL) and left at rest at 25 ° C. for 14 days. Note that if no sedimentation layer is confirmed after standing and there is no change in state, the dispersion layer ratio is considered to be 100%, assuming that there is no change in the height of the entire dispersion.
Dispersion layer rate (%) = (height of settled layer) / (total height of dispersion liquid) x 100

Due to the above-mentioned mechanism of action, this dispersion has excellent dispersion stability, particularly long-term storage stability. When this dispersion is allowed to stand at 25°C for 30 days, the fluctuation range (absolute value) of the thixotropic ratio of this dispersion is preferably 3 or less, and more preferably less than 1.

The dispersion can be prepared by mixing F particles, inorganic particles, polyhydric alcohol, and water. Examples of the mixing method include a method of adding each component all at once or sequentially and mixing; a method of mixing F particles and inorganic particles to prepare a powder composition, and further adding polyhydric alcohol and water and mixing; a method of previously mixing F particles and water or polyhydric alcohol, and inorganic particles and water or polyhydric alcohol, respectively, and further mixing the obtained two mixtures.
In addition, when a surfactant, an aromatic resin, or other resin material is further contained in the present dispersion, it is preferable to add it simultaneously when dispersing the F particles, inorganic particles, and polyhydric alcohol in water in advance, or to add it to the water in advance before dispersing the F particles and inorganic particles. When the present dispersion contains an aromatic resin, it may be mixed with the F particles as a varnish of the aromatic resin. Examples of the solvent constituting the varnish include N-methyl-2-pyrrolidone, cyclohexanone, and toluene. When the F particles contain two types of F particles, a mixture containing the second F particles and water may be added to a mixture containing the first F particles, inorganic particles, polyhydric alcohol, and water.

Examples of mixing methods for preparing the dispersion include stirring using a stirring device equipped with uniaxial or multiaxial blades (stirring blades) such as propeller blades, turbine blades, paddle blades, and shell-shaped blades, or a Henschel mixer, pressure kneader, Banbury mixer, or planetary mixer; mixing using a disperser that uses media such as a ball mill, attritor, basket mill, sand mill, sand grinder, Dyno Mill (a bead mill using grinding media such as glass beads or zirconium oxide beads), Dispermat, SC mill, spike mill, or agitator mill; and mixing using a disperser that does not use media, such as a high-pressure homogenizer such as a Microfluidizer, Nanomizer, or Ultimizer, an ultrasonic homogenizer, a Dissolver, a Disper, or a high-speed impeller disperser.

Among them, the device used for mixing is preferably a Henschel mixer, a pressure kneader, a Banbury mixer or a planetary mixer, and more preferably a planetary mixer.
The planetary mixer has two agitating blades that rotate and revolve around each other, and has a structure that agitates and kneads the kneaded material in the agitation tank. Therefore, there is little dead space in the agitation tank where the agitating blades do not reach, and the load on the blades is reduced, allowing the composition to be kneaded to a high degree. In other words, while suppressing the aggregation of the F particles, the F particles are wetted with a liquid dispersion medium, and the F particles, inorganic particles, and polyhydric alcohols can be kneaded while interacting with each other to a high degree, so that when the kneaded material is further mixed with a liquid dispersion medium, the present dispersion liquid with excellent dispersion stability is easily obtained. In addition, the component concentration of the present dispersion liquid is easily adjusted, and a thick molded product (polymer layer, etc.) with excellent surface smoothness and uniformity is easily formed from the present dispersion liquid.

The present dispersion may be prepared by mixing a composition containing F particles and a polyhydric alcohol or water to obtain a mixture, and then further adding a polyhydric alcohol or water to the mixture to adjust the viscosity.
In this case, the inorganic particles may be added to the composition before mixing, or may be added when the mixture is mixed with the polyhydric alcohol or water.

This dispersion can be used to form insulating layers for printed wiring boards, to bond ceramic and metal parts together in vehicle engines, to impart corrosion resistance to heat exchangers and the fins or tubes that make them up, to impregnate and dry coils used in thermal interface materials, power module substrates, and motors and other power devices to form thermally conductive, heat-resistant coating layers, and to coat the inside and outside of glass containers such as medical vials and syringes.

This dispersion has excellent dispersion stability and long-term storage stability, and can be used to form molded products that have excellent flexibility such as bending resistance, i.e., excellent crack resistance and low linear expansion, exhibit strong adhesion to substrates, and are resistant to powder falling.
This dispersion is applied to at least one surface of a substrate to form a liquid coating, which is then heated to remove the dispersion medium to form a dry coating, and the dry coating is further heated to bake the F polymer, thereby obtaining a laminate having a polymer layer (hereinafter also referred to as "F layer") on the surface of the substrate, which contains the F polymer and inorganic particles and preferably has a higher inorganic particle content than the F polymer content.

Examples of the substrate include metal substrates such as metal foils made of copper, nickel, aluminum, titanium, and alloys thereof, heat-resistant films made of heat-resistant resins such as tetrafluoroethylene polymers, polyimides, polyarylates, polysulfones, polyarylsulfones, polyamides, polyetheramides, polyphenylene sulfides, polyaryletherketones, polyamideimides, liquid crystal polyesters, and liquid crystal polyesteramides, and prepregs which are precursors of fiber-reinforced resin substrates. Among these, metal substrates are preferred, and copper foils are more preferred.
The ten-point average roughness of the surface of the substrate is preferably less than 0.1 μm, more preferably 0.05 μm or less. The ten-point average roughness is preferably 0.001 μm or more. Even with such a non-roughened substrate, a laminate having excellent peel strength can be obtained from the present dispersion, and a printed circuit board or the like having excellent transmission characteristics can be formed from such a laminate. The ten-point average roughness of the surface of the substrate is a value specified in Annex JA of JIS B 0601:2013.
The thickness of the substrate is preferably 2 to 100 μm. When the substrate is a metal foil, the thickness of the substrate is preferably 1 to 35 μm. The substrate may also be a metal foil with a carrier, which is an extremely thin copper foil (thickness 2 to 5 μm) laminated on a carrier copper foil via a release layer.

The method for applying the present dispersion to the surface of a metal substrate (base material) may be any method that forms a stable liquid coating (wet film) of the present dispersion on the surface of the metal substrate, and includes a coating method, a droplet ejection method, and a dipping method, with the coating method being preferred. The coating method allows the liquid coating to be efficiently formed on the surface of the metal substrate with simple equipment.
Examples of the coating method include spraying, roll coating, spin coating, gravure coating, microgravure coating, gravure offset, knife coating, kiss coating, bar coating, die coating, fountain-meyer bar, and slot die coating.

When drying the liquid coating, the liquid coating is heated at a temperature at which the water and polyhydric alcohol volatilize, and a dry coating is formed on the surface of the metal substrate (base material). The heating temperature in such drying is preferably the boiling point of the polyhydric alcohol + 50°C or less, more preferably the boiling point of the polyhydric alcohol or less, and even more preferably the boiling point of the polyhydric alcohol - 50°C or less. The drying temperature is preferably 120°C to 200°C. Air may be blown in the process of removing the water and polyhydric alcohol.
During drying, the water and polyhydric alcohol do not necessarily have to be completely evaporated, but may be evaporated to an extent that the layer shape after holding is stable and a free-standing film can be maintained.

When baking the F polymer, it is preferable to heat the dried coating to a temperature equal to or higher than the melting temperature of the F polymer. The heating temperature is preferably 380° C. or lower, more preferably 350° C. or lower.
Examples of the heating method include a method using an oven, a method using a ventilated drying furnace, and a method using heat rays such as infrared rays. Heating may be performed under either normal pressure or reduced pressure. The heating atmosphere may be any of an oxidizing gas atmosphere (oxygen gas, etc.), a reducing gas atmosphere (hydrogen gas, etc.), and an inert gas atmosphere (helium gas, neon gas, argon gas, nitrogen gas, etc.).
The heating time is preferably from 0.1 to 30 minutes, more preferably from 0.5 to 20 minutes.
By heating under the above conditions, the F layer can be suitably formed while maintaining high productivity.

The thickness of the F layer is preferably 0.1 to 200 μm, more preferably 25 μm or more, and even more preferably 50 μm or more.
In particular, the present dispersion can be suitably used for the purpose of forming a thick F layer of 25 μm or more by repeating the operation of applying it to the surface of a metal substrate and heating it several times.
The F layer is formed through the steps of coating the modified dispersion, drying, and firing as described above.
These steps may be carried out once or twice or more. From the viewpoint of obtaining a thick film having excellent smoothness, the steps of coating, drying and baking the present dispersion may be carried out multiple times.
For example, the present dispersion may be applied to a substrate, and the water and polyhydric alcohol may be removed by heating to form a film. The present dispersion may be further applied onto the formed film to remove the water and polyhydric alcohol, and the F polymer may be further baked by heating to form an F layer.

The peel strength between the F layer and the base layer is preferably 10 N/cm or more, and more preferably 15 N/cm or more. The above peel strength is preferably 100 N/cm or less. By using this dispersion, a laminate having such excellent peel strength can be easily formed without impairing the physical properties of the F polymer in the F layer.

The porosity of the F layer is preferably 30% or less, more preferably 20% or less. The porosity is preferably 0.1% or more, more preferably 1% or more. An F layer with such a low porosity can be easily formed from this dispersion. The porosity is determined by determining the void portions of the F layer by image processing from an SEM photograph of the cross section of a molded product observed with a scanning electron microscope (SEM), and is the percentage obtained by dividing the area occupied by the void portions by the area of the F layer. The area occupied by the void portions is determined by approximating the void portions as circles.

The dispersion may be applied to only one surface of the substrate, or may be applied to both surfaces of the substrate. In the former case, a laminate having a substrate layer made of the substrate and an F layer on one surface of the substrate layer is obtained, and in the latter case, a laminate having a substrate layer made of the substrate and an F layer on both surfaces of the substrate layer is obtained. The latter laminate is less likely to warp, and therefore has excellent handling properties during processing.
Specific examples of such laminates include a metal-clad laminate having a metal foil and an F layer on at least one surface of the metal foil, and a multilayer film having a polyimide film and an F layer on both surfaces of the polyimide film. These laminates are suitable as printed circuit board materials, etc., because they have excellent physical properties such as electrical properties, and can be used for producing flexible printed circuit boards and rigid printed circuit boards.

The outermost surface of the substrate may be further subjected to a surface treatment in order to further improve its low linear expansion property and adhesiveness.
Examples of the surface treatment method include annealing treatment, corona treatment, plasma treatment, ozone treatment, excimer treatment, and silane coupling treatment.
The conditions for the annealing treatment are preferably a temperature of 120 to 180° C., a pressure of 0.005 to 0.015 MPa, and a time of 30 to 120 minutes.
Examples of gases used in the plasma treatment include oxygen gas, nitrogen gas, rare gas (such as argon), hydrogen gas, ammonia gas, and vinyl acetate. These gases may be used alone or in combination of two or more.

On the outermost surface of the laminate, another substrate may be further laminated.
Other substrates include metal substrates, heat-resistant resin films, prepregs which are precursors of fiber-reinforced resin plates, laminates having a heat-resistant resin film layer, and laminates having a prepreg layer.
The metal substrate may be any of the metal substrates described above. The heat-resistant resin film is a film containing one or more types of heat-resistant resin, and examples of the heat-resistant resin include the resins described above.
As a method for lamination, a method of hot pressing the laminate and another substrate can be mentioned.

Laminates of the F layer and other substrates are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry products, paints, cosmetics, etc., and specifically, are useful as electric wire coating materials (aircraft electric wires, etc.), electrical insulating tape, oil drilling insulating tape, materials for printed circuit boards, separation membranes (microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, gas separation membranes, etc.), electrode binders (for lithium secondary batteries, for fuel cells, etc.), copy rolls, furniture, automobile dashboards, covers for home appliances, etc., sliding members (load bearings, sliding shafts, valves, bearings, gears, cams, belt conveyors, food transport belts, etc.), tools (shovels, files, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, dies, toilets, and container coating materials.

The above describes the method for producing the present dispersion and the laminate having a polymer layer formed from the present dispersion, but the present invention is not limited to the configurations of the above-mentioned embodiments. For example, the present dispersion may have any other configuration added to the configurations of the above-mentioned embodiments, or may be replaced with any configuration that exerts a similar function. Furthermore, the method for producing the laminate having a polymer layer formed from the present dispersion may have any other process added to the configurations of the above-mentioned embodiments, or may be replaced with any process that exerts a similar effect.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.
1. Details of each component [F particles]
F Particle 1: Particles (D50: 2.1 μm) made of a polymer (melting temperature: 300° C.) containing 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units, in that order, and having 1,000 carbonyl group-containing groups per 1× ¹⁰⁶ main chain carbon atoms.
F Particle 2: Particles made of non-thermofusible PTFE (D50: 0.3 μm)
[F Dispersion]
F dispersion 1: Aqueous dispersion containing 60% by mass of F particles 2 (manufactured by AGC, "product number AD-915E")
[Inorganic particles]
Inorganic particles 1: Nearly spherical silica particles (D50: 1.0 μm)
Inorganic particles 2: Nearly spherical silica particles (D50: 10.2 μm)
[Polyhydric alcohol]
gly: glycerin [surfactant]
Surfactant 1: Nonionic surfactant (manufactured by BYK Japan, "BYK-3450")
[Aromatic resin varnish]
Varnish 1: Water varnish containing a precursor of water-soluble aromatic polyamideimide (PAI1) ("HPC-1000" manufactured by Showa Denko Materials Co., Ltd.)

2. Example of production of aqueous dispersion
[Example 1-1]
Into a pot, F particles 1, inorganic particles 1, varnish 1, surfactant 1, gly, ammonia water, and ammonium hydrogen carbonate were added, and zirconia balls were then added. After that, the pot was rolled at 150 rpm for 1 hour to prepare a liquid composition.
In addition, the prepared liquid composition and F dispersion 1 were added to another pot, and zirconia balls were added. The pot was then rolled at 150 rpm for 1 hour to obtain an aqueous dispersion 1 (viscosity: 500 mPa·s, pH: 8.0) containing F particles 1 (18 parts by mass), F particles 2 (20 parts by mass), inorganic particles 1 (60 parts by mass), PAI 1 (2 parts by mass), surfactant 1 (1 part by mass), gly (48 parts by mass) and water (12 parts by mass). The content mass ratio of polyhydric alcohol to water in the aqueous dispersion 1 was 4.

[Example 1-3 ] ~ [Example 1-4 ]
Aqueous dispersions 3 to 4 were obtained in the same manner as in Example 1-1, except that the type and amount of inorganic particles, and the amounts of F particles 1, F particles 2 , varnish 1, surfactant 1, gly, and water were changed as shown in Table 1 .

3. Example of laminate production [Example 2-1]
A wet film was formed on the surface of a non-roughened copper foil (surface ten-point average roughness: 0.05 μm or less, thickness: 18 μm) by a roll-to-roll process by applying the aqueous dispersion 1 by a small diameter gravure reverse method. Then, the copper foil on which the wet film was formed was passed through a ventilated drying furnace (furnace temperature 120° C.) to form a dry film, and further passed through a baking furnace at 380° C. in a nitrogen gas atmosphere to heat and bake the F particles 1 and F particles 2.
As a result, a laminate 1 was obtained, which had a copper foil and a polymer layer (thickness: 100 μm) formed on the surface of the copper foil from the aqueous dispersion liquid 1.
[Example 2-3 ] ~ [Example 2-4 ]
Except for changing the aqueous dispersion 1 to the aqueous dispersions 3 to 4 , the same procedure as in Example 2-1 was carried out to obtain laminates 3 to 4 .

4. Evaluation 4-1. Dispersion stability of dispersion Each dispersion (18 mL) was placed in a screw tube (internal volume: 30 mL) and allowed to stand at 25° C. for 14 days. The dispersion layer ratio was calculated from the total height of the dispersion in the screw tube and the height of the sedimentation layer (dispersion layer) before and after standing using the following formula, and the dispersion stability was evaluated according to the following criteria.
[Evaluation Criteria]
◯: Dispersion layer rate is 60% or more. ×: Dispersion layer rate is less than 60%.

4-2. Film-forming ability of dispersion When a laminate was produced from each dispersion, the surface of the dried coating was visually observed, and the presence or absence of powder falling off was evaluated according to the following criteria to evaluate the film-forming ability.
[Evaluation Criteria]
◯: No powder fall was observed. △: Powder fall was observed in part of the dried coating. ×: Powder fall was observed over the entire surface of the dried coating.

The surface smoothness of the polymer layer of each laminate was evaluated by measuring the thickness of the center and ends in the short side direction of the polymer layer, calculating the ratio of the end thickness to the center thickness, and according to the following criteria.
[Evaluation Criteria]
◯: The thickness ratio is 1.07 or less. Δ: The thickness ratio is greater than 1.07 and less than 1.1. ×: The thickness ratio is greater than 1.1.

Flexibility of Laminate Each laminate was bent 180° with a radius of curvature (300 μm), a load (50 mN, 1 minute) was applied from above, and then the laminate was returned to its original state. The presence or absence of cracks on the surface of the polymer layer was visually observed and evaluated according to the following criteria.
[Evaluation Criteria]
◯: No cracks occurred ×: Cracks occurred

4-5. Interlayer adhesion of laminates A rectangular test piece (length 100 mm, width 10 mm) was cut out from each laminate, and the test piece was fixed at a position 50 mm from one end in the longitudinal direction, and the polymer layer and the copper foil were peeled off from one end in the longitudinal direction at an angle of 90° to the test piece at a pulling speed of 50 mm/min. The maximum load applied at that time was taken as the peel strength, and the interlayer adhesion was evaluated according to the following criteria.
[Evaluation Criteria]
A: The peel strength is 15 N/cm or more. B: The peel strength is 10 N/cm or more and less than 15 N/cm. C: The peel strength is less than 10 N/cm.

The copper foil of each laminate was removed by etching with an aqueous solution of ferric chloride to prepare a single polymer layer. A square test piece measuring 180 mm square was cut out from the prepared polymer layer, and the linear expansion coefficient of the test piece was measured in the range of 25°C to 260°C according to the measurement method specified in JIS C 6471:1995, and evaluated according to the following criteria.
[Evaluation Criteria for Linear Expansion Coefficient]
Good: The linear expansion coefficient is 75 ppm/° C. or less.
×: The linear expansion coefficient is more than 75 ppm/° C.

4-7. Dielectric loss tangent of laminate A rectangular test piece 100 mm long and 50 mm wide was cut out from each laminate, and the copper foil was removed by etching with an aqueous solution of ferric chloride to obtain a polymer layer alone. The dielectric loss tangent of the polymer layer (measurement frequency: 10 GHz) was measured by the SPDR (split post dielectric resonance) method and evaluated according to the following criteria. [Evaluation criteria for dielectric loss tangent]
A: The dielectric loss tangent is less than 0.0020 Δ: The dielectric loss tangent is 0.0020 or more and 0.0040 or less ×: The dielectric loss tangent is more than 0.0040 The results of the evaluations described in 4-1 to 4-6 are shown in Table 2. The relative dielectric constants of Laminates 1 and 3 measured simultaneously in the measurement of the dielectric loss tangent in 4-6 were both 2.1 or less.

The aqueous dispersion of the present invention has excellent dispersion stability and can be easily processed into films, fiber-reinforced films, prepregs, and metal laminates (metal foils coated with resin). The processed products obtained can be used as materials for antenna parts, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry products, sliding bearings, etc.

Claims (14)

An aqueous dispersion comprising particles of a tetrafluoroethylene-based polymer, inorganic particles having an average particle size of less than 10 μm, a polyhydric alcohol, and water, wherein the content of the inorganic particles is greater than the content of the tetrafluoroethylene-based polymer, and the content mass ratio of the polyhydric alcohol to water is 0.2 or more and 10 or less . The aqueous dispersion according to claim 1, wherein the tetrafluoroethylene-based polymer is a heat-fusible tetrafluoroethylene-based polymer having a carbonyl group-containing group or a hydroxyl group-containing group. The aqueous dispersion according to claim 1 or 2, wherein the tetrafluoroethylene-based polymer particles are particles of a heat-fusible tetrafluoroethylene-based polymer and particles of a non-heat-fusible tetrafluoroethylene-based polymer. The aqueous dispersion according to any one of claims 1 to 3, wherein the inorganic particles are silica particles. The aqueous dispersion according to any one of claims 1 to 4, wherein the inorganic particles are scaly or substantially spherical in shape. The aqueous dispersion according to any one of claims 1 to 5 , which has a pH in the range of 5 to 10. The aqueous dispersion according to any one of claims 1 to 6 , wherein the polyhydric alcohol is an aliphatic polyhydric alcohol having a boiling point of 100°C or higher. The aqueous dispersion according to any one of claims 1 to 7 , further comprising an aromatic resin. The aqueous dispersion according to claim 8 , wherein the aromatic resin is a precursor of a water-soluble aromatic polyamideimide or a precursor of a water-soluble aromatic polyimide. 10. The aqueous dispersion according to claim 8 , wherein the content of the aromatic resin is less than 10 mass% based on the mass of the tetrafluoroethylene-based polymer particles. The aqueous dispersion according to any one of claims 1 to 10 , further comprising a surfactant. A method for producing a laminate, comprising applying the aqueous dispersion according to any one of claims 1 to 11 to a surface of a substrate, and heating the applied aqueous dispersion to form a polymer layer containing the tetrafluoroethylene-based polymer and the inorganic particles, and obtaining a laminate having the substrate and the polymer layer in this order. The method according to claim 12 , wherein the ten-point average roughness of the surface of the substrate is less than 0.1 μm. The method according to claim 12 or 13 , wherein the polymer layer has a thickness of 25 μm or more.