WO2025033551A1 - Aqueous dispersion and method for producing laminate - Google Patents

Abstract

An aqueous dispersion contains: particles containing a hot-melt tetrafluoroethylene polymer, a poly (meth) acrylic acid having a weight average molecular weight of 200,000 or more; a pH buffer having a pH optimum range of 4-10, and water; wherein the aqueous dispersion has a pH of 4-10.

Description

Aqueous dispersion and method for producing laminate

This disclosure relates to an aqueous dispersion and a method for producing a laminate.

Fluorine resins are used in various fields because of their excellent physical properties such as electrical characteristics, water and oil repellency, chemical resistance, heat resistance, etc. In particular, tetrafluoroethylene-based polymers are excellent in physical properties such as mold releasability, electrical insulation, water and oil repellency, chemical resistance, weather resistance, heat resistance, etc., and are used by being processed into various molded articles.
For example, Patent Document 1 describes a fluororesin aqueous dispersion containing fluororesin particles having a volume average particle size within a specific range, and it is described that the fluororesin aqueous dispersion preferably contains a water-soluble thickener from the viewpoints of improving dispersibility and redispersibility and suppressing sedimentation.

JP 2019-052211 A

In Patent Document 1, the addition of a water-soluble thickener improves the dispersibility of the fluororesin particles and inhibits settling, but it has been found that even with this configuration, the fluororesin particles settle over time, causing changes in viscosity. When the viscosity of the aqueous dispersion changes, it can become difficult to handle.

In view of this situation, one embodiment of the present disclosure relates to providing an aqueous dispersion in which viscosity change over time is suppressed, and a method for producing a laminate using the aqueous dispersion.

The present disclosure includes the following aspects.
<1> An aqueous dispersion containing particles containing a heat-fusible tetrafluoroethylene-based polymer, poly(meth)acrylic acid having a weight-average molecular weight of 200,000 or more, a pH buffer having an optimum pH range of 4 to 10, and water, the aqueous dispersion having a pH of 4 to 10.
<2> The aqueous dispersion according to <1>, having a viscosity of 500 mPa·s or more at 25° C.
<3> The aqueous dispersion according to <1> or <2>, wherein the heat-meltable tetrafluoroethylene-based polymer contains a unit based on tetrafluoroethylene and at least one of a unit based on perfluoro(alkyl vinyl ether) and a unit based on hexafluoropropylene.
<4> The aqueous dispersion according to any one of <1> to <3>, wherein the heat-fusible tetrafluoroethylene polymer has a carbonyl group-containing group.
<5> The aqueous dispersion according to any one of <1> to <4>, wherein the heat-fusible tetrafluoroethylene polymer has 10 to 5,000 carbonyl-containing groups per 1×10 ⁶ carbon atoms in the main chain.
<6> The aqueous dispersion according to any one of <1> to <5>, wherein the particles containing the heat-fusible tetrafluoroethylene polymer have an average particle size of 10 μm or less.
<7> The aqueous dispersion according to any one of <1> to <6>, wherein the particles containing a heat-fusible tetrafluoroethylene-based polymer have a specific surface area of more than 6 m ² /g.
<8> The aqueous dispersion according to any one of <1> to <7>, wherein a content of the particles containing the heat-fusible tetrafluoroethylene-based polymer is 60 mass % or less.
<9> The aqueous dispersion according to any one of <1> to <8>, wherein the poly(meth)acrylic acid has a weight average molecular weight of 500,000 to 1,500,000.
<10> The aqueous dispersion according to any one of <1> to <7>, wherein the poly(meth)acrylic acid has at least one unit selected from the group consisting of units based on a compound represented by general formula (I) and units based on a compound represented by general formula (II):


In general formula (I), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, a trialkylsilyl group having 3 to 9 carbon atoms, a group represented by the following general formula (IA) or a group represented by the following general formula (IB):


In formula (IA), R ³ represents an alkylene group having 1 to 4 carbon atoms, R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 2 to 20.


In formula (IB), R ⁵ to R ⁷ each independently represent an alkyl group having 1 to 3 carbon atoms, and R ⁸ represents an alkylene group having 1 to 3 carbon atoms.


In formula (II), R ¹¹ represents a hydrogen atom or a methyl group, and R ¹² and R ¹³ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
<11> The aqueous dispersion liquid according to any one of <1> to <10>, wherein the pH buffer includes at least one selected from the group consisting of carbonic acid, phosphoric acid, boric acid, formic acid, oxalic acid, acetic acid, citric acid, isocitric acid, lactic acid, and ammonium salts thereof, as well as sulfonic acids and amino acids.
<12> The aqueous dispersion according to any one of <1> to <11>, having a viscosity at 25°C of 10,000 mPa·s or less.
<13> The aqueous dispersion according to any one of <1> to <12>, further comprising a surfactant having no fluorine atom.
<14> A method for producing a laminate, comprising applying the aqueous dispersion according to any one of <1> to <13> to a substrate, heating the substrate to remove the water, and further heating the substrate to melt and sinter the particles containing the heat-fusible tetrafluoroethylene-based polymer.

According to one embodiment of the present disclosure, there is provided an aqueous dispersion in which the change in viscosity over time is suppressed, and a method for producing a laminate using the aqueous dispersion.

Below, the form for carrying out the embodiment of the present disclosure will be described in detail. However, the embodiment of the present disclosure is not limited to the following embodiment. In the following embodiment, the components (including element steps, etc.) are not essential unless specifically stated. The same applies to the numerical values and their ranges, and they do not limit the embodiment of the present disclosure.

In the present disclosure, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
In the present disclosure, the numerical ranges indicated using "to" include the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, each component may contain multiple types of the corresponding substance. When multiple substances corresponding to each component are present in the aqueous dispersion, the content or amount of each component means the total content or amount of the multiple substances present in the aqueous dispersion, unless otherwise specified.
In the present disclosure, multiple types of particles corresponding to each component may be included. When multiple types of particles corresponding to each component are present in the aqueous dispersion, the particle size of each component means the value for a mixture of the multiple types of particles present in the aqueous dispersion, unless otherwise specified.
In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
In this disclosure, the term "lamination" refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
In the present disclosure, 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 treating the polymer. Hereinafter, a unit based on monomer a is also simply referred to as a "monomer a unit."

In this disclosure, the "melting temperature" of a tetrafluoroethylene-based polymer is the temperature corresponding to the maximum value of the melting peak of the polymer as measured by differential scanning calorimetry (DSC).
In this disclosure, the "melt flow rate" of a tetrafluoroethylene-based polymer means the melt mass flow rate of the polymer as defined in JIS K 7210-1:2014 (ISO1133-1:2011).
In the present disclosure, the "glass transition temperature (Tg)" of a tetrafluoroethylene-based polymer is a value measured by analyzing the polymer by dynamic mechanical analysis (DMA).

In the present disclosure, the "weight average molecular weight" of poly(meth)acrylic acid is determined as a polystyrene-equivalent weight average molecular weight in gel permeation chromatography (GPC) analysis.
In the present disclosure, the average particle diameter of particles means the volume average particle diameter (D50), which is the volume-based cumulative 50% diameter of particles obtained by a laser diffraction/scattering method. That is, the particle size distribution is measured by a laser diffraction/scattering method, a cumulative curve is obtained with the total volume of the particle group being 100%, and the particle diameter is the point on the cumulative curve where the cumulative volume is 50%. The D50 of particles is obtained 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 (for example, a laser diffraction/scattering particle size distribution measuring device "LS-13 320" manufactured by Beckman Coulter, Inc.).

In this disclosure, "specific surface area" is a value calculated by measuring particles using the gas adsorption (constant volume) BET multipoint method, and is determined using a BET specific surface area measuring device (e.g., NOVA4200e (manufactured by Quantachrome Instruments)).

In the present disclosure, the "viscosity" of the aqueous dispersion is determined by measuring the aqueous dispersion 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 calculated.
In the present disclosure, the "thixotropy ratio" of an aqueous dispersion is a value calculated by dividing the viscosity _η1 of the aqueous 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.

<Aqueous Dispersion>
The aqueous dispersion of the present disclosure contains particles containing a heat-fusible tetrafluoroethylene-based polymer, poly(meth)acrylic acid having a weight-average molecular weight of 200,000 or more, a pH buffer having an optimum pH range of 4 to 10, and water.
Hereinafter, the heat-fusible tetrafluoroethylene polymer will also be referred to as "F polymer", and particles containing the heat-fusible tetrafluoroethylene polymer will also be referred to as "F particles". Poly(meth)acrylic acid having a weight-average molecular weight of 200,000 or more will also be referred to as "specific poly(meth)acrylic acid". A pH buffer having an optimum pH range of 4 to 10 will also be abbreviated as "pH buffer".
In the aqueous dispersion having the above-described structure, the settling of the F particles is suppressed, and the change in viscosity over time is suppressed. The reason for this is not clear, but is presumed to be as follows.

The pH of an aqueous dispersion containing F particles is likely to decrease over time. Poly(meth)acrylic acid is a substance that exhibits a high degree of thickening function due to its functional groups, but it is also likely to be denatured by changes in the pH of the aqueous dispersion over time. In addition, when poly(meth)acrylic acid contains units based on (meth)acrylate as a copolymer component, hydrolysis of the ester moiety is likely to proceed. It is believed that the thickening function of poly(meth)acrylic acid decreases over time due to these factors.
Therefore, it is presumed that the thickening function of poly(meth)acrylic acid can be maintained over time by setting the weight-average molecular weight of poly(meth)acrylic acid to 200,000 or more, increasing the number of constituent units to increase the absolute number of functional groups that exhibit a thickening function, and simultaneously using a pH buffer having an optimum pH range of 4 to 10 to maintain the pH of the aqueous dispersion within the range of 4 to 10.
The inventors have found that such effects are more likely to be manifested significantly when the average particle size of the F particles is small or the specific surface area of the F particles is large, resulting in a strong interaction between the F particles and water, or when the content of the F particles in the aqueous dispersion is within a certain range, the liquid viscosity of the aqueous dispersion is low, and the F particles themselves have a high degree of freedom.
Each component contained in the aqueous dispersion will be described below.

(F particle)
The F polymer contained in F particle is a polymer that contains units (hereinafter also referred to as "TFE units") based on tetrafluoroethylene (hereinafter also referred to as "TFE units"). The content of TFE units in F polymer is preferably 50 mol% or more, more preferably 90 mol% or more, based on the total units in F polymer, from the viewpoint of favorably expressing the characteristics of TFE units. The content can be 99 mol% or less, or 98 mol% or less.

The F polymer is heat-meltable. A heat-meltable polymer means a polymer that has a temperature at which the melt flow rate is 1 to 1000 g/10 min under a load of 49 N.
From the viewpoint of heat resistance, the melting temperature of the F polymer is preferably 200° C. or higher, more preferably 260° C. or higher. From the viewpoint of ease of processing, the melting temperature of the F polymer is preferably 325° C. or lower, more preferably 320° C. or lower.

From the viewpoint of heat resistance, the glass transition point of the F polymer is preferably 50° C. or higher, and more preferably 75° C. or higher. From the viewpoint of ease of processing, the glass transition point of the F polymer is preferably 150° C. or lower, and more preferably 125° C. or lower.
The fluorine content of the F polymer is preferably 70% by mass or more, more preferably 72 to 76% by mass, from the viewpoint of favorable expression of properties due to fluorine atoms, such as electrical properties and heat resistance.
The surface tension of the F polymer is preferably 16 to 26 mN/m. The surface tension of the F polymer can be measured by placing a droplet of a wettability index reagent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) on a flat plate made of the F polymer.

F polymer is preferably polytetrafluoroethylene (PTFE), the polymer that comprises TFE unit and the unit based on ethylene, the polymer that comprises TFE unit and the unit based on propylene, the polymer that comprises TFE unit and the unit based on perfluoro(alkyl vinyl ether) (PAVE) (PAVE unit) (PFA), and the polymer that comprises TFE unit and the unit based on hexafluoropropylene (FEP), more preferably the polymer that comprises TFE unit and at least one of PAVE unit and the unit based on hexafluoropropylene, and from the viewpoint of properties such as adhesiveness and processability, more preferably PFA and FEP, and more preferably PFA.These polymers may further comprise the unit based on other comonomers.
PAVE is preferably CF ₂ ═CFOCF ₃ , CF ₂ ═CFOCF ₂ CF ₃ or CF ₂ ═CFOCF ₂ CF ₂ CF ₃ (hereinafter also referred to as “PPVE”), and more preferably PPVE.

In particular, from the viewpoint of obtaining an aqueous dispersion with high uniformity and improving the adhesiveness of the molded article obtained therefrom, the F polymer preferably has an oxygen-containing polar group, more preferably has a hydroxyl group-containing group or a carbonyl group-containing group, and even more preferably has a carbonyl group-containing group.

The hydroxyl-containing group is preferably a group containing an alcoholic hydroxyl group, more preferably --CF ₂ CH ₂ OH or --C(CF ₃ ) ₂ OH.
The carbonyl group-containing group 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-), and 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, 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 carbonyl group-containing group may be contained in a unit based on a monomer in the F polymer, or may be contained in a terminal group of the main chain of the F polymer, the former being preferred. Examples of the latter include an F polymer having a carbonyl group-containing group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer obtained by subjecting an F polymer to plasma treatment or ionizing radiation treatment.

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"), with NAH being more preferred.

The F polymer is preferably a polymer having a carbonyl group-containing group, including TFE units and PAVE units, and more preferably a polymer containing TFE units, PAVE units, and units based on a monomer having a carbonyl group-containing group, and containing these units in the order of 90 to 99 mol%, 0.99 to 9.97 mol%, and 0.01 to 3 mol% of the total units. Specific examples of such F polymers include the polymers described in WO 2018/016644.

F particles are particles that contain an F polymer, and preferably have an F polymer as the main component, and preferably consist of an F polymer. Having an F polymer as the main component means that the content of the F polymer is relatively high compared to the content of each of the other components on a volume basis.

From the viewpoint of dispersion stability, the D50 of the F particles is preferably 0.1 μm or more, more preferably more than 0.3 μm, and even more preferably 1 μm or more. From the viewpoint of dispersion stability, the D50 of the F particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 5 μm or less.

The specific surface area of the F particles is preferably 1 to 50 m ² /g, and more preferably 1 to 25 m ² /g. The specific surface area of the F particles is more preferably more than 6 m ² /g, even more preferably 7 m ² /g or more, and particularly preferably 8 m ² /g or more. The specific surface area of the F particles is preferably 25 m ² /g or less. In this case, the above-mentioned mechanism of action is more easily manifested.

F particles may be used alone or in combination of two or more types. When two or more types of F particles are used in combination, different F particles refer to F particles that differ in average particle size, different types of F polymer, different content of F polymer, different presence or absence of other components other than F polymer, different content of other components, or a combination thereof.

The content of F particles in the aqueous dispersion is preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 40% by mass or more. The content of F particles in the aqueous dispersion is preferably 75% by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less. From the viewpoint of making it easier for the above-mentioned mechanism of action to be expressed, the content of F particles in the aqueous dispersion is preferably 30 to 60% by mass.

(Specific poly(meth)acrylic acid)
The specific poly(meth)acrylic acid has a weight average molecular weight of 200,000 or more. From the viewpoint of further suppressing viscosity change over time, the weight average molecular weight of the specific poly(meth)acrylic acid is preferably 500,000 or more, more preferably 750,000 or more. From the viewpoint of dispersibility of the specific poly(meth)acrylic acid, the weight average molecular weight of the specific poly(meth)acrylic acid is preferably 1,500,000 or less, more preferably 1,250,000 or less.

The specific poly(meth)acrylic acid may be at least one selected from the group consisting of a homopolymer, a copolymer, and a crosslinked product of the homopolymer or the copolymer.
The specific poly(meth)acrylic acid preferably has at least one unit selected from the group consisting of units based on a compound represented by the following general formula (I) and units based on a compound represented by the following general formula (II):

In general formula (I), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, a trialkylsilyl group having 3 to 9 carbon atoms, a group represented by the following general formula (IA) or a group represented by the following general formula (IB):

In formula (IA), R ³ represents an alkylene group having 1 to 4 carbon atoms, R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 2 to 20.

In formula (IB), R ⁵ to R ⁷ each independently represent an alkyl group having 1 to 3 carbon atoms, and R ⁸ represents an alkylene group having 1 to 3 carbon atoms.

In formula (II), R ¹¹ represents a hydrogen atom or a methyl group, and R ¹² and R ¹³ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

As the alkyl group having 1 to 20 carbon atoms in ^R2 of the general formula (I), those having 1 to 10 carbon atoms are preferable.

The alkylene group in R ³ of formula (IA) is preferably an ethylene group, a trimethylene group, a propylene group, or a tetramethylene group, more preferably an ethylene group or a propylene group, and particularly preferably an ethylene group.
R ⁴ in formula (IA) is preferably a hydrogen atom or a methyl group.
In formula (IA), n is preferably an integer of from 2 to 10, and more preferably an integer of from 4 to 10.

Among the above, R ² represented by general formula (I) is preferably a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a group represented by general formula (IA).

R ¹¹ in formula (II) is preferably a hydrogen atom.
R ¹² in formula (II) is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom.
R ¹³ in formula (II) is more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

The specific poly(meth)acrylic acid may have one type of unit based on the compound represented by general formula (I) alone or two or more types. The specific poly(meth)acrylic acid may have one type of unit based on the compound represented by general formula (II) alone or two or more types.
The specific poly(meth)acrylic acid may be a homopolymer composed of units based on the compound represented by general formula (I) or a homopolymer composed of units based on the compound represented by general formula (II), or may be a copolymer having units based on the compound represented by general formula (I) and units based on the compound represented by general formula (II), or may be a crosslinked product of these homopolymers or copolymers.

The crosslinked material is preferably crosslinked with a (meth)acrylate compound having 2 to 4 (meth)acryloyl groups or a (meth)acrylamide compound having 2 to 4 (meth)acryloyl groups.

The specific poly(meth)acrylic acid may be neutralized, that is, some or all of the carboxy groups may be in the form of a salt, and it is preferable that all of the carboxy groups are in the form of a salt.

The content of the specific poly(meth)acrylic acid in the aqueous dispersion is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, from the viewpoint of effectively suppressing the viscosity change of the aqueous dispersion over time. The above content of the specific poly(meth)acrylic acid is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of workability, preventing the viscosity of the aqueous dispersion from becoming too high.

(pH Buffer)
The pH buffer has an optimum pH range of 4 to 10. The optimum pH range refers to the range in which the pH buffer can exert its buffering function. The pH buffer according to the present disclosure may have an optimum pH range that falls within at least a part of the range of 4 to 10. The optimum pH range of the pH buffer is preferably 7 to 10.
The pH buffer preferably contains at least one selected from the group consisting of carbonic acid (about 5.4 to 7.4), phosphoric acid (about 5.4 to 7.4), boric acid (about 8.2 to 10.2), formic acid (about 2.6 to 4.6), oxalic acid (about 2.8 to 4.8), acetic acid (about 3.8 to 5.8), citric acid (about 3.8 to 5.8), isocitric acid (about 3.8 to 5.8), lactic acid (about 2.7 to 4.7), and ammonium salts thereof, as well as sulfonic acids and amino acids. The numerical value in parentheses indicates the optimum pH range.

Sulfonic acids and amino acids include 2-morpholinoethanesulfonic acid, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, N-(2-acetamido)-2-aminoethanesulfonic acid, 2-hydroxy-3-morpholinopropanesulfonic acid, 2-hydroxy-N-tris(hydroxymethyl)methyl-3-aminopropanoic acid, N-tris(hydroxymethyl)methyl-3-aminopropanoic acid, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid, 3-morpholinopropanesulfonic acid, N -Tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid, N-[tris(hydroxymethyl)methyl]glycine, tris(hydroxymethyl)aminomethane, N,N-bis(2-hydroxyethyl)glycine, glycylglycine, N-cyclohexyl-2-aminoethanesulfonic acid, N-cyclohexyl-3-aminopropanesulfonic acid, and ethylenediaminetetraacetic acid.

The pH buffer is preferably an ammonium salt of a compound selected from the group consisting of carbonic acid, phosphoric acid, boric acid, formic acid, oxalic acid, acetic acid, citric acid, and lactic acid, more preferably ammonium formate, ammonium oxalate, ammonium acetate, triammonium citrate, diammonium hydrogen phosphate, triammonium phosphate, ammonium borate, ammonium hydrogen carbonate, or ammonium carbonate, and even more preferably ammonium hydrogen carbonate, ammonium carbonate, or ammonium acetate.

From the viewpoint of effectively suppressing viscosity changes over time of the aqueous dispersion, the content of the pH buffer in the aqueous dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more. The above content of the pH buffer is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less.

(water)
The aqueous dispersion of the present disclosure uses water as a dispersion medium. The content of water can be appropriately adjusted in consideration of the coating method, the thickness of the molded product to be produced, and the like. For example, the content of water is preferably more than 40% by mass, more preferably 50% by mass or more, and even more preferably 55% by mass or more, based on the total volume of the aqueous dispersion. The content of water is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total volume of the aqueous dispersion. Specifically, the content of water in the aqueous dispersion is preferably 40 to 65% by mass. In this case, the above-mentioned mechanism of action is more easily manifested.

The aqueous dispersion of the present disclosure may further contain a water-soluble dispersion medium other than water as a dispersion medium. As the water-soluble dispersion medium, a water-soluble compound that is liquid at 25°C and classified as polar under atmospheric pressure is preferable, such as N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and N-methyl-2-pyrrolidone.

The solids concentration in the aqueous dispersion is preferably 20% by volume or more, more preferably 40% by volume or more, based on the total volume of the aqueous dispersion. The solids concentration is preferably 80% by volume or less. The solids content refers to the total amount of substances that form the solids in the molded product formed from the aqueous dispersion. Specifically, the F particles, the specific poly(meth)acrylic acid, and the pH buffer are included in the solids content, and if the aqueous dispersion contains other resins, the other resins are also included in the solids content.

(Surfactant)
The aqueous dispersion may further contain a surfactant, and preferably contains a surfactant that does not have a fluorine atom. When the aqueous dispersion contains a surfactant, the surfactant is nonionic, and the hydrophobic portion of the surfactant preferably contains an acetylene group or a polysiloxane group, and the hydrophilic portion preferably contains an oxyalkylene group or an alcoholic hydroxyl group.
That is, when the aqueous dispersion liquid further contains a surfactant, a nonionic surfactant is preferred, and a polyoxyalkylene alkyl ether, an acetylene surfactant, or a silicone surfactant is more preferred. These surfactants preferably have an alcoholic hydroxyl group. In addition, these surfactants may be used alone or in combination of two or more. From the viewpoint that the polyoxyalkylene alkyl ether stabilizes the long-term dispersibility of F particles and improves the liquid properties such as the viscosity of the aqueous dispersion liquid, and the silicone surfactant improves the initial dispersibility of F particles, it is preferred to use a polyoxyalkylene alkyl ether and a silicone surfactant in combination.
When the aqueous dispersion further contains a surfactant, the amount of the surfactant is preferably 1 to 15% by mass based on the total mass of the aqueous dispersion, in which case the affinity between the components is enhanced and the dispersion stability of the aqueous dispersion is more likely to be improved.

Specific examples of silicone surfactants include "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", and "BYK-3456" (all manufactured by BYK Japan), "KF-6011", and "KF-6043" (all manufactured by Shin-Etsu Chemical Co., Ltd.).

Specific examples of polyoxyalkylene alkyl ethers include "Tergitol TMN-100X" (manufactured by The Dow Chemical Company), "Lutensol TO8", "Lutensol XL70", "Lutensol XL80", "Lutensol XL90", "Lutensol XP80", and "Lutensol M5" (all manufactured by BASF), "Newcoal 1305", "Newcoal 1308FA", and "Newcoal 1310" (all manufactured by Nippon Nyukazai Co., Ltd.), "Leocol TDN-90-80", and "Leocol SC-90" (all manufactured by Lion Specialty Chemicals).

The aqueous dispersion may further contain at least one nonionic water-soluble polymer selected from the group consisting of polyvinyl alcohol-based polymers, polyvinylpyrrolidone-based polymers, and polysaccharides. In this case, not only the dispersion stability of the aqueous dispersion but also the rheological properties are improved, and the handling properties of the aqueous dispersion, such as film-forming properties, are likely to be further improved. As a result, it is easier to form a thick molded product or a molded product of any shape from the aqueous dispersion. In particular, if the water-soluble polymer has a nonionic hydroxyl group, this tendency is likely to be remarkable.
The polyvinyl alcohol based polymer may be a partially acetylated or partially acetalized polyvinyl alcohol.

Examples of polysaccharides include glycogens, amicropectins, dextrins, glucans, fructans, chitins, amyloses, agaroses, amicropectins, and celluloses. Examples of celluloses include methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose.
The nonionic water-soluble polymer is preferably a nonionic polysaccharide, more preferably a nonionic cellulose, and further preferably hydroxymethyl cellulose, hydroxyethyl cellulose or hydroxypropyl cellulose.
Specific examples of such nonionic polysaccharides include the "Sunrose (registered trademark)" series (manufactured by Nippon Paper Industries Co., Ltd.), the "Metolose (registered trademark)" series (manufactured by Shin-Etsu Chemical Co., Ltd.), and "HEC CF Grade" (manufactured by Sumitomo Seika Chemicals Co., Ltd.).

When the aqueous dispersion further contains a nonionic water-soluble polymer, the content of the nonionic water-soluble polymer is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, relative to the total amount of the aqueous dispersion. The content is preferably less than 1% by mass. The ratio of the mass of the water-soluble polymer to the mass of the F particles in the aqueous dispersion is preferably 0.001 or more, and more preferably 0.01 or more. The ratio is preferably less than 0.1.

(Other ingredients)
The aqueous dispersion may be used in combination with particles of other fluororesins than F polymer (hereinafter also referred to as "other F particles"). Examples of other fluororesins include melt-type fluororesins other than F polymer and non-melt-type fluororesins, and from the viewpoint of moldability, melt-type fluororesins other than F polymer are preferred. The melt-type fluororesins other than F polymer are melt-type fluororesins that do not contain TFE units.
When F particles are used in combination with other F particles, the proportion of the other F particles in the total amount of the F particles and the other F particles is preferably less than 50% by mass, more preferably 25% by mass or less. The proportion is preferably 0.1% by mass or more, more preferably 1% by mass or more.

The aqueous dispersion may contain a resin other than the fluororesin. The other resin may be contained in the aqueous dispersion as powder particles, or may be dissolved or dispersed in water.
Examples of the other resin include polyester resins such as liquid crystalline aromatic polyesters, imide resins, epoxy resins, maleimide resins, urethane resins, polyphenylene ether resins, polyphenylene oxide resins, and polyphenylene sulfide resins. The other resin is preferably an aromatic polymer, and more preferably at least one aromatic imide polymer selected from the group consisting of aromatic polyimides, aromatic polyamic acids, aromatic polyamideimides, and aromatic polyamideimide precursors. The aromatic polymer is preferably contained in the aqueous dispersion as a varnish dissolved in water.
Specific examples of aromatic imide polymers include the "UPIA-AT" series (manufactured by Ube Industries, Ltd.), the "NEOPLUMI (registered trademark)" series (manufactured by Mitsubishi Gas Chemical Company, Inc.), the "SPIXELIA (registered trademark)" series (manufactured by Somar), the "Q-PILON (registered trademark)" series (manufactured by PI Technical Research Institute, Ltd.), the "WINGO" series (manufactured by Wingo Technology Co., Ltd.), the "TOMAID (registered trademark)" series (manufactured by T&K TOKA Corporation), the "KPI-MX" series (manufactured by Kawamura Sangyo Co., Ltd.), "HPC-1000", and "HPC-2100D" (all manufactured by Resonac Corporation).

If the aqueous dispersion contains other resins, the content of the other resins relative to the F particles is preferably 0.1% by volume or more, and more preferably 1% by volume or more. The content is preferably 15% by volume or less, and more preferably 10% by volume or less.

The aqueous dispersion may further contain an inorganic filler, in which case the molded product produced from the aqueous dispersion tends to have excellent electrical properties and low linear expansion.
The inorganic filler is preferably a nitride filler or an inorganic oxide filler, more preferably a boron nitride filler, a beryllia filler (a beryllium oxide filler), a silicate filler (a silica filler, a wollastonite filler, a talc filler), or a metal oxide (cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, etc.) filler, and even more preferably a silica filler.

It is preferable that at least a portion of the surface of the inorganic filler is surface-treated with a silane coupling agent (3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, etc.).

The inorganic filler preferably has a D50 of 20 μm or less, more preferably 10 μm or less, and more preferably has a D50 of 0.01 μm or more, more preferably 0.1 μm or more.
The shape of the inorganic filler may be any of granular, needle-like (fibrous) and plate-like.Specific shapes of the inorganic filler include spherical, scale-like, layered, leaf-like, apricot kernel-like, columnar, cockscomb-like, equiaxial, leaf-like, micaceous, block-like, flat, wedge-like, rosette-like, net-like and prismatic shapes.

The inorganic filler may be used alone or in combination of two or more types. When the aqueous dispersion further contains an inorganic filler, the content of the inorganic filler is preferably 1 to 50 mass % and more preferably 5 to 40 mass % based on the total aqueous dispersion.

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

The aqueous dispersion may further contain a silane coupling agent from the viewpoint of further improving the miscibility between the F polymer and the inorganic filler.
Examples of the silane coupling agent include the same silane coupling agents as those that may be used in the surface treatment of the inorganic filler, and the preferred ranges thereof are also the same.
When the aqueous dispersion contains a silane coupling agent, the content of the silane coupling agent in the aqueous dispersion (excluding the silane coupling agent used for surface treatment of the inorganic filler) is preferably 1 to 10% by volume based on the total volume of the aqueous dispersion.

The aqueous dispersion may further contain additives such as thixotropic agents, viscosity regulators, defoamers, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, colorants, conductive materials, release agents, surface treatment agents, flame retardants, conductive fillers, and preservatives.

(Physical properties of aqueous dispersion)
The pH of the aqueous dispersion is from 4 to 10, more preferably from 7 to 10, and even more preferably from 8 to 10. When preparing the aqueous dispersion, in addition to the above-mentioned pH buffer, another basic compound such as ammonia or an amine may be used in combination.
The viscosity of the aqueous dispersion at 25° C. is preferably 10,000 mPa·s or less, and more preferably 3,000 mPa·s or less. The viscosity of the aqueous dispersion at 25° C. is preferably 500 mPa·s or more, and more preferably 600 mPa·s or more.
When the aqueous dispersion is stored in a container at 25° C. for one month, the rate of change in viscosity before and after storage, represented by the following formula (hereinafter also referred to as "viscosity maintenance rate"), is preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.
Viscosity retention rate = viscosity after storage (mPa·s) / viscosity before storage (mPa·s) × 100

The thixotropy ratio of the aqueous dispersion is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. The thixotropy ratio of the aqueous dispersion is preferably 1 or more, and more preferably 2 or more. When the thixotropy ratio of the aqueous dispersion is within the above range, the settling of F particles is more easily suppressed.

<Method of producing aqueous dispersion>
The aqueous dispersion of the present disclosure can be obtained by mixing F particles, a specific poly(meth)acrylic acid, a pH buffer, and water, and, if necessary, additives such as other resins, surfactants, silane coupling agents, etc. The order of mixing is not particularly limited, and the mixing method may be a lump mix or a multiple-part mix.

Mixing devices for obtaining the aqueous dispersion of the present disclosure include blade-equipped stirring devices such as Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers; media-equipped grinding devices such as ball mills, attritors, basket mills, sand mills, sand grinders, Dyno Mills, Dispermats, SC Mills, spike mills, and agitator mills; and dispersing devices equipped with other mechanisms such as microfluidizers, nanomizers, ultimizers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impellers, thin-film swirling high-speed mixers, planetary agitators, and V-type mixers.

<Applications of aqueous dispersions>
The use of the aqueous dispersion of the present disclosure is not particularly limited, and can be used, for example, for the production of molded products. In particular, the aqueous dispersion of the present disclosure is suitable for applications in which it is desired to favorably express the properties of the F polymer contained in the aqueous dispersion.

The aqueous dispersion is useful as a material for imparting insulating properties, heat resistance, corrosion resistance, chemical resistance, water resistance, impact resistance, and the like.
Specifically, the aqueous dispersion can be used in printed wiring boards, thermal interface materials, substrates for power modules, coils used in power devices such as motors, in-vehicle engines, heat exchangers, vials, syringes, ampoules, medical wires, secondary batteries such as lithium ion batteries, primary batteries such as lithium batteries, radical batteries, solar cells, fuel cells, lithium ion capacitors, hybrid capacitors, capacitors (aluminum electrolytic capacitors, tantalum electrolytic capacitors, etc.), electrochromic elements, electrochemical switching elements, electrode binders, electrode separators, electrodes (positive electrodes, negative electrodes), and the like.
The aqueous dispersion is also useful as an adhesive for bonding parts. Specifically, the aqueous dispersion can be used for bonding ceramic parts, metal parts, electronic parts such as IC chips, resistors, and capacitors on substrates of semiconductor elements and module parts, bonding circuit boards and heat sinks, bonding LED chips to substrates, and the like.

<Laminate and method for producing laminate>
The method for producing the laminate of the present disclosure involves applying the aqueous dispersion of the present disclosure to a substrate, heating to remove the water, and further heating to melt and sinter the F particles.

Substrates include metal substrates (metal foils such as copper, nickel, aluminum, titanium, and alloys thereof), heat-resistant resin films (heat-resistant resin films such as polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyamideimide, liquid crystalline polyester, and tetrafluoroethylene polymers), prepreg substrates (precursors of fiber-reinforced resin substrates), ceramic substrates (ceramic substrates such as silicon carbide, aluminum nitride, and silicon nitride), and glass substrates.

The shape of the substrate may be flat, curved or uneven, and may be any of foil, plate, film and fiber (woven fabric, nonwoven fabric, etc.).
The ten-point average roughness of the surface of the substrate is preferably 0.01 to 0.05 μm.
The surface of the substrate may be surface-treated with a silane coupling agent or plasma-treated. Examples of such silane coupling agents include the same silane coupling agents as those that may be used for surface treatment of inorganic fillers.
The peel strength between the fluororesin layer and the substrate is preferably 10 N/cm or more, more preferably 15 N/cm or more, and is preferably 100 N/cm or less.

Examples of the method for applying the aqueous dispersion include a coating method, a droplet discharging method, and a dipping method, and preferably a roll coating method, a knife coating method, a bar coating method, a die coating method, or a spray method.
Heating for removing water is preferably performed at 100 to 200° C. for 0.1 to 30 minutes. In this heating, it is not necessary to completely remove water, but it is sufficient to remove water to the extent that the layer formed by packing of the F particles and the composite particles can maintain a self-supporting film. In addition, when heating, air may be blown to promote removal of water by air drying.
The heating for baking the F polymer is preferably carried out at a temperature equal to or higher than the baking temperature of the F polymer, more preferably at 360 to 400° C. for 0.1 to 30 minutes.
The heating device for each heating may be an oven or a ventilated drying furnace. The heat source in the device may be a contact type heat source (hot air, hot plate, etc.) or a non-contact type heat source (infrared rays, etc.).
The heating may be carried out under normal pressure or under reduced pressure.
The atmosphere in each heating step may be either an air atmosphere or an inert gas atmosphere (helium gas, neon gas, argon gas, nitrogen gas, etc.).

The fluororesin layer is formed through the steps of applying an aqueous dispersion and heating. These steps may be performed once each, or may be repeated two or more times. For example, an aqueous dispersion may be applied to the surface of a substrate and heated to form a fluororesin layer, and an aqueous dispersion may be applied to the surface of the fluororesin layer and heated to form a second fluororesin layer. In addition, after an aqueous dispersion is applied to the surface of a substrate and heated to remove water, an aqueous dispersion may be applied to the surface and heated to form a fluororesin layer.
The aqueous 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 and a fluororesin layer on one surface of the substrate layer is obtained, and in the latter case, a laminate having a substrate layer and a fluororesin layer on both surfaces of the substrate layer is obtained.

The thickness of the fluororesin layer can be appropriately selected depending on the application, and may be, for example, 25 μm or more, 30 μm or more, or 40 μm or more. The thickness of the fluororesin layer may be 200 μm or less.

Specific examples of suitable laminates include a metal-clad laminate having a metal foil and a fluororesin layer on at least one surface of the metal foil, and a multilayer film having a polyimide film and a fluororesin layer on both surfaces of the polyimide film.

Laminates formed from aqueous dispersions are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sporting goods, food industry products, heat dissipation parts, and the like.
Specifically, these include electric wire coating materials (aircraft electric wires, etc.), enameled wire coating materials used in motors for electric vehicles, etc., electrical insulating tape, insulating tape for oil drilling, oil transport hoses, hydrogen tanks, 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, yaw bearings, sliding shafts, valves, bearings, bushings, seals, thrust washers, wear rings, etc.), and other applications. and the like), tension ropes, wear pads, wear strips, tube lamps, test sockets, wafer guides, wear parts of centrifugal pumps, chemical and water supply pumps, tools (shovels, files, hacksaws, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, dies, toilets, container coating materials, heat dissipation boards mounted for power devices, heat dissipation members for wireless communication devices, transistors, thyristors, rectifiers, transformers, power MOS FETs, CPUs, heat dissipation fins, metal heat sinks, blades for windmills, wind power generation equipment, aircraft, etc., housings for personal computers and displays, electronic device materials, interior and exterior parts of automobiles, processing machines and vacuum ovens that perform heat treatment under low oxygen conditions, sealing materials for plasma treatment devices, heat dissipation parts in treatment units for sputtering and various dry etching devices, electromagnetic wave shields, etc.

Laminates formed from the aqueous dispersion of the present disclosure are useful as electronic substrate materials such as flexible printed wiring boards and rigid printed wiring boards, as protective films and heat dissipation substrates, particularly heat dissipation substrates for automobiles.

Next, the embodiments of the present disclosure will be specifically described using examples, but the embodiments of the present disclosure are not limited to these examples.

The following F particles were prepared.
F Particle 1: Particles of tetrafluoroethylene polymer (melting temperature: 300° C.) containing TFE units, NAH units and PPVE units and having 1,000 carbonyl group-containing groups per 1×10 ⁶ main chain carbon atoms (D50: 2.1 μm, specific surface area: 8 m ² /g)
F Particles 2: Particles of a tetrafluoroethylene polymer (melting temperature: 300° C.) containing TFE units and PPVE units and having 250 carbonyl-containing groups per 1×10 ⁶ main chain carbon atoms (D50: 1.6 μm, specific surface area: 16 m ² /g)
F Particles 3: Particles of a tetrafluoroethylene polymer (melting temperature: 300° C.) containing TFE units and PPVE units and having 250 carbonyl group-containing groups per 1×10 ⁶ main chain carbon atoms (D50: 3.6 μm, specific surface area: 6 m ² /g)

The following polyacrylic acids were prepared:
PAA1: A polyacrylic acid having a weight average molecular weight Mw of 1,000,000, which is a copolymer of acrylic acid and 2-hydroxyethyl acrylate in a molar ratio of 1:1 and is crosslinked with polyethylene glycol diacrylate. PAA2: A polyacrylic acid having a weight average molecular weight Mw of 250,000, which is a copolymer of acrylic acid and 2-hydroxyethyl acrylate in a molar ratio of 1:1 and is not crosslinked with polyethylene glycol diacrylate. PAA3: A polyacrylic acid having a weight average molecular weight Mw of 150,000, which is a copolymer of acrylic acid and 2-hydroxyethyl acrylate in a molar ratio of 1:1 and is not crosslinked with polyethylene glycol diacrylate.

(Example 1)
An aqueous dispersion 1 containing 40% by mass of F particles 1, 0.1% by mass of PAA1, and ammonium bicarbonate (optimum pH range: 9.0 to 10.0) and having a pH adjusted to 9 with ammonia was prepared by shear stirring treatment.

(Example 2)
Aqueous dispersion 2 was prepared in the same manner as in Example 1, except that PAA1 was replaced with PAA2 having a Mw of 250,000.

(Example 3)
Aqueous dispersion 3 was prepared in the same manner as in Example 1, except that PAA1 was replaced with PAA3 having a Mw of 150,000.

(Example 4)
Aqueous dispersion 4 was prepared in the same manner as in Example 1, except that only ammonia was used instead of the combined use of ammonium bicarbonate and ammonia.

(Example 5)
Aqueous Dispersion 5 was prepared in the same manner as in Example 1, except that ammonium bicarbonate and ammonia were not added.

<Evaluation (Part 1)>
The pH of the resulting aqueous dispersions 1 to 5 was measured.
The obtained aqueous dispersions 1 to 5 were stored in a container at 25° C. for one month, and the viscosity was measured before and after storage. The results are shown in Table 1.

<Evaluation (part 2)>
Aqueous dispersions 6 to 12 were prepared in the same manner as in Example 1, except that the type and content of F particles were changed as shown in Table 2 below. Each of the aqueous dispersions 1 and 6 to 12 was stored at 25° C. for one month, and the viscosity was measured before and after storage. The viscosity change rate (viscosity after storage/viscosity before storage×100) was evaluated as "A" if it was 90% or more and less than 90%, as "B" if it was 80% or more and less than 80%, and as "C" if it was 50% or more and less than 80%. The results are shown in Table 2. The viscosity of each of the aqueous dispersions before storage was 500 to 2000 mPa·s.

The disclosure of Japanese Patent Application No. 2023-131640 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims (14)

An aqueous dispersion containing particles containing a heat-fusible tetrafluoroethylene polymer, poly(meth)acrylic acid having a weight-average molecular weight of 200,000 or more, a pH buffer having an optimum pH range of 4 to 10, and water, and having a pH of 4 to 10. The aqueous dispersion according to claim 1, having a viscosity of 500 mPa·s or more at 25°C. The aqueous dispersion according to claim 1 or 2, wherein the heat-fusible tetrafluoroethylene-based polymer contains units based on tetrafluoroethylene and at least one of units based on perfluoro(alkyl vinyl ether) and units based on hexafluoropropylene. The aqueous dispersion according to claim 1 or 2, wherein the heat-fusible tetrafluoroethylene polymer has a carbonyl group-containing group. 3. The aqueous dispersion according to claim 1, wherein the heat-fusible tetrafluoroethylene polymer has 10 to 5,000 carbonyl-containing groups per 1×10 ⁶ carbon atoms in the main chain. The aqueous dispersion according to claim 1 or 2, wherein the particles containing the heat-fusible tetrafluoroethylene polymer have an average particle size of 10 μm or less. The aqueous dispersion according to claim 1 or 2, wherein the particles containing the heat-fusible tetrafluoroethylene-based polymer have a specific surface area of more than 6 m ² /g. The aqueous dispersion according to claim 1 or 2, wherein the content of particles containing the heat-fusible tetrafluoroethylene-based polymer is 60 mass% or less. The aqueous dispersion according to claim 1 or 2, wherein the weight average molecular weight of the poly(meth)acrylic acid is 500,000 to 1,500,000. The aqueous dispersion according to claim 1 or 2, wherein the poly(meth)acrylic acid has at least one unit selected from the group consisting of units based on a compound represented by the following general formula (I) and units based on a compound represented by the following general formula (II):


In general formula (I), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, a trialkylsilyl group having 3 to 9 carbon atoms, a group represented by the following general formula (IA) or a group represented by the following general formula (IB):


In formula (IA), R ³ represents an alkylene group having 1 to 4 carbon atoms, R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 2 to 20.


In formula (IB), R ⁵ to R ⁷ each independently represent an alkyl group having 1 to 3 carbon atoms, and R ⁸ represents an alkylene group having 1 to 3 carbon atoms.


In formula (II), R ¹¹ represents a hydrogen atom or a methyl group, and R ¹² and R ¹³ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. The aqueous dispersion according to claim 1 or 2, wherein the pH buffer comprises at least one selected from the group consisting of carbonic acid, phosphoric acid, boric acid, formic acid, oxalic acid, acetic acid, citric acid, isocitric acid, lactic acid, and ammonium salts thereof, as well as sulfonic acids and amino acids. The aqueous dispersion according to claim 1 or 2, having a viscosity of 10,000 mPa·s or less at 25°C. The aqueous dispersion according to claim 1 or 2, further comprising a surfactant that does not have a fluorine atom. A method for producing a laminate, comprising applying the aqueous dispersion according to claim 1 or 2 to a substrate, heating to remove the water, and further heating to melt and sinter the particles containing the heat-fusible tetrafluoroethylene-based polymer.