WO2025005148A1 - Aqueous primer composition, method for forming primer layer, and molded article - Google Patents

Abstract

This aqueous primer composition contains: particles A which have an average particle diameter (D50) of 1 μm or more and are formed of a fluororesin that has a melting temperature of 280-320°C and a carbonyl group-containing group; at least one of a water-soluble polymer which has a weight average molecular weight of 50,000 or more, and particles B which have an average particle diameter (D50) of less than 1 μm and are formed of a fluororesin that has a melting temperature of 320°C or less; and water.

Description

Aqueous primer composition, method for forming primer layer, and molded product

This disclosure relates to an aqueous primer composition, a method for forming a primer layer, and a molded product.

The physical properties of fluororesins are sometimes utilized as materials for forming base layers (i.e., primer layers) when forming laminated molded products. For example, in order to obtain a porous composite that is strong and resistant to delamination, it has been proposed to use a low-melting point, fine-particle tetrafluoroethylene hexafluoropropylene copolymer (hereinafter also referred to as "FEP") as a primer layer (see Patent Document 1). Furthermore, in order to obtain a composition that can form a primer layer with excellent coatability, it has been proposed to use a low-melting point, fine-particle FEP (see Patent Document 2).

JP 2018-047412 A JP 2018-048233 A

However, in Patent Documents 1 and 2, FEP with a low melting point and in the form of fine particles is used, which requires detailed adjustment of the liquid properties of the composition containing FEP, making its handling complicated. Furthermore, when a highly heat-resistant primer layer is formed using a fluororesin with a high melting point, the formation temperature becomes high, which can cause defects and flaws in the primer layer and can easily reduce its performance as a primer layer. Furthermore, when a composition for forming the primer layer is applied thinly onto a substrate in order to form an extremely thin primer layer, the particles in the composition tend to be applied sparsely onto the substrate, making the primer layer more susceptible to defects and flaws.

The present disclosure has been made in consideration of the above, and aims to provide an aqueous primer composition for obtaining a thin, highly heat-resistant primer layer that has excellent adhesion and reduced defects and imperfections, a method for forming a primer layer, and a molded product.

<1> Particles A of a fluororesin having an average particle diameter (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group;
A water-soluble polymer having a weight average molecular weight of 50,000 or more; and
At least one selected from the group consisting of fluororesin particles B having an average particle diameter (D50) of less than 1 μm and a melting temperature of 320° C. or less;
Water,
1. An aqueous primer composition comprising:
<2> An aqueous primer composition comprising: particles A of a fluororesin having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group; a water-soluble polymer having a weight-average molecular weight of 50,000 or more; and water.
<3> The aqueous primer composition according to <1> or <2>, wherein the particles A have a specific surface area of 6 m ² /g or more.
<4> The aqueous primer composition according to any one of <1> to <3>, wherein the content of the particles A is more than 0 mass% and 40 mass% or less with respect to the total mass of the aqueous primer composition.
<5> The aqueous primer composition according to any one of <1> to <4>, wherein the water-soluble polymer is at least one selected from the group consisting of an acrylic polymer, a cellulose polymer, and a vinyl polymer.
<6> A method for forming a primer layer, comprising using the aqueous primer composition according to any one of <1> to <5> to form a primer layer having an average thickness of 5 μm or less.
<7> A method for forming a primer layer, comprising: forming a primer layer having an average thickness equal to or less than an average particle diameter (D50) of the particles A, using the aqueous primer composition according to any one of <1> to <5>.
<8> A molded article comprising, in the thickness direction, a substrate, a fluororesin primer layer containing a melt of particles A of a fluororesin having a melting temperature of 280 to 320°C and a water-soluble polymer having a weight-average molecular weight of 50,000 or more, and a polytetrafluoroethylene sheet in this order.
<9> An aqueous primer composition comprising: particles A of a fluororesin having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group; particles B of a fluororesin having an average particle size (D50) of less than 1 μm and a melting temperature of 320° C. or less; and water.
<10> The aqueous primer composition according to <9>, wherein the particles A have a specific surface area of 6 m ² /g or more.
<11> The aqueous primer composition according to any one of <1> to <5>, <9>, and <10>, wherein a total amount of the content of the particles A and the content of the particles B is more than 0 mass% and 40 mass% or less with respect to a total mass of the aqueous primer composition.
<12> The aqueous primer composition according to any one of <1> to <5> and <9> to <11>, wherein the average particle diameter (D50) of the particles A is 2 to 10 times the average particle diameter (D50) of the particles B.
<13> A method for forming a primer layer, comprising using the aqueous primer composition according to any one of <9> to <12> to form a primer layer having an average thickness of 5 μm or less.
<14> A method for forming a primer layer, comprising using the aqueous primer composition according to any one of <9> to <12> to form a primer layer having an average thickness equal to or less than the average particle diameter (D50) of the particles A.
<15> A molded article comprising, in the thickness direction, a substrate, a fluororesin primer layer including a melt of particles A of a fluororesin having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group, and particles B of a fluororesin having an average particle size (D50) of less than 1 μm and a melting temperature of 320° C. or less, and a polytetrafluoroethylene sheet in this order.

The present disclosure provides an aqueous primer composition for obtaining a thin, highly heat-resistant primer layer that has excellent adhesion and suppresses defects and imperfections, a method for forming a primer layer, and a molded product.

Below, one embodiment of the present disclosure is described in detail. However, 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 otherwise. The same applies to numerical values and their ranges, and do not limit the present disclosure.

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 numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
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 composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, 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 composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In the present disclosure, the "average particle size (D50)" is the volume-based cumulative 50% diameter of particles determined by a laser diffraction/scattering method. That is, 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 being 100%, and the particle size is the point on the cumulative curve where the cumulative volume is 50%.
The average particle size (D50) of the particles 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.).
The specific surface area of the particles is determined by measurement using a surface analyzer according to the BET method.
In the present disclosure, the "melting temperature" is the temperature corresponding to the maximum value of the melting peak of a resin measured by differential scanning calorimetry (DSC).
In the present disclosure, "melt flow rate" means the melt flow rate (MFR) of a resin as defined in JIS K 7210:1999 (ISO 1133:1997).
In this disclosure, the term "glass transition temperature (Tg)" refers to a value measured by analyzing a resin using a dynamic mechanical analysis (DMA) method.
In the present disclosure, a "resin" is a compound formed by polymerizing a monomer, i.e., a "resin" has a plurality of units based on the monomer.
In the present disclosure, the term "unit" in a resin 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 resin.

<Aqueous primer composition>
The aqueous primer composition of the present disclosure (hereinafter also referred to as "the composition") contains at least one selected from the group consisting of fluororesin particles A (hereinafter also referred to as "particles A") having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group, a water-soluble polymer (hereinafter also referred to as "water-soluble polymer") having a weight average molecular weight of 50,000 or more, and fluororesin particles B (hereinafter also referred to as "particles B") having an average particle size (D50) of less than 1 μm and a melting temperature of 320° C. or less, and water. The composition may contain both the water-soluble polymer and the particles B, or may contain only one of the water-soluble polymer and the particles B.
In the present disclosure, the fluororesin having a melting temperature of 280 to 320° C. and having a carbonyl group-containing group is also referred to as “resin A”.

A preferred embodiment of the present composition is a composition containing particles A (i.e., particles of resin A), a water-soluble polymer, and water (hereinafter, also referred to as "present composition 1").
According to the present composition 1, a thin, highly heat-resistant primer layer having excellent adhesion and suppressed defects and imperfections can be obtained. The function of the present composition 1 is not clear, but is presumed to be as follows.
It is desirable that the primer layer is formed by applying a primer composition thinly and uniformly to the surface of the substrate on which the primer layer is to be formed, but this is difficult when the material forming the primer layer contains fluororesin particles and the primer composition is an aqueous composition using water as a dispersion medium. That is, the water dispersibility of the fluororesin particles is not high enough, and it is not easy to control the behavior of the applied fluororesin particles when they are packed and melted by heating to form a layer. And when the melting temperature of the fluororesin is high, this tendency is likely to be significant, and the primer layer is likely to have defects and flaws.

Therefore, the present composition 1 contains a water-soluble polymer with a large weight-average molecular weight of 50,000 or more. In the present composition 1, the water-soluble polymer functions as a thickening component, enhancing the thixotropy of the present composition 1, improving the water dispersibility of the resin A particles, and suppressing their settling, thereby enhancing the uniformity of the present composition 1. Therefore, when the present composition 1 is applied to a substrate, the resin A particles tend to be densely packed, and defects and imperfections are unlikely to occur in the primer layer even if the thickness of the primer layer is reduced.

Furthermore, since the water-soluble polymer has a large weight average molecular weight of 50,000 or more, when the present composition 1 is applied to a substrate and heated, the water-soluble polymer takes time to decompose or volatilize and tends to remain for a long time. Therefore, the water-soluble polymer promotes the melting of the particles of resin A while keeping the particles of resin A of the present disclosure in contact with each other for a certain period of time, i.e., while the water-soluble polymer functions as a binding component for the particles of resin A. Therefore, when forming a primer layer using the present composition 1, the particles of resin A tend to remain on the substrate with a uniform density, so that defects and flaws are unlikely to occur in the primer layer even if the thickness of the primer layer is reduced.

Furthermore, Resin A maintains the flexibility of the resin in the primer layer even after heating and cooling. That is, the primer layer obtained by using Composition 1 has excellent adhesion.
Incidentally, Resin A of the present disclosure has a high melting temperature of 280 to 320° C. In other words, the primer layer obtained by using Composition 1 has high heat resistance.
It should be noted that the present disclosure is in no way limited to the above presumed mechanism.

Another preferred embodiment of the present composition is a composition containing particles A (i.e., particles of resin A), particles B, and water (hereinafter, also referred to as "present composition 2").

According to the present composition 2, a thin, highly heat-resistant primer layer having excellent adhesion and suppressed defects and imperfections can be obtained. The function of the present composition 2 is not clear, but is assumed to be as follows.
That is, in the present composition 2, two types of particles of fluororesin having a high melting temperature are used in combination: particles A having a predetermined average particle size, and particles B having an average particle size smaller than that of particles A. As a result, in the present composition 2, particles A and particles B interact with each other to promote loose agglomeration, and the high water dispersibility of particles A, which are particles of fluororesin having carbonyl group-containing groups, is extended to the entire particles, improving the uniformity and liquid properties of the present composition 2. Therefore, when the present composition 2 is applied to a substrate, the particles of the fluororesin are easily densely packed, and defects and flaws are unlikely to occur in the primer layer even if the thickness of the primer layer is reduced.

Furthermore, since the primer layer is formed by melting the loose aggregates, that is, particles A and B, while remaining present on the substrate at a uniform density, when heated, defects and flaws in the primer layer are unlikely to occur even if the thickness of the primer layer is reduced. Note that this tendency is more pronounced in the present composition 2, which is prepared by mixing particles A and B in advance and subjecting them to a shearing treatment.

Furthermore, the fluororesin having a melting temperature of 280 to 320° C. ensures flexibility of the resin in the primer layer even after application to a substrate and heating. That is, the primer layer obtained by using the present composition 2 has excellent adhesion.
Incidentally, Resin A has a high melting temperature of 280 to 320° C. That is, the primer layer obtained by using Composition 2 has high heat resistance.
It should be noted that the present disclosure is in no way limited to the above presumed mechanism.

<Particles A (Particles of Resin A)>
Resin A is preferably heat-fusible. In the present disclosure, "heat-fusible" means a property that there is a temperature at which the melt flow rate (MFR) is 1 to 1000 g/10 min under a load of 49 N. From the viewpoint of suppressing defects and imperfections, the MFR of resin A is preferably 5 g/10 min or more, and more preferably 10 g/10 min or more. The MFR of resin A is preferably 100 g/10 min or less, more preferably 75 g/10 min or less, and even more preferably 20 g/10 min or less.

From the viewpoint of adhesion and high heat resistance, resin A is preferably a resin containing units based on tetrafluoroethylene (TFE) and units based on perfluoro(alkyl vinyl ether) (PAVE) (i.e., perfluoroalkoxyalkane (hereinafter also referred to as "PFA")).
The particles of resin A preferably contain a TFE resin having a carbonyl group-containing group as a main component, and the content thereof is preferably 100% by mass.

Resin A is more preferably a resin having a carbonyl group-containing group and comprising a unit based on TFE and a unit based on PAVE (i.e., a perfluoroalkoxyalkane having a carbonyl group-containing group).Resin A is particularly preferably a resin having a unit based on TFE, a unit based on PAVE and a unit based on _a monomer having a carbonyl group-containing group.Note that, as PAVE, _CF2 = _CFOCF3 , _CF2 = _CFOCF2CF3 or _CF2 = _CFOCF2CF2CF3 ( _hereinafter also referred to as "PPVE") are _preferred , and PPVE is more preferred.
Resin A may further contain units based on other comonomers.

The constituent ratio of each monomer unit in resin A is not particularly limited, but for example, when the resin contains units based on TFE, the constituent ratio of the units based on TFE is preferably 90 to 99 mol % relative to all units in the resin from the viewpoint of optimally expressing the properties due to TFE. Furthermore, for example, when the resin contains units based on PAVE, the constituent ratio of the units based on PAVE is preferably 1 to 10 mol % relative to all units in the resin from the viewpoint of optimally expressing the properties due to PAVE.

From the viewpoints of adhesiveness and high heat resistance, the carbonyl group-containing group in Resin A 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.

The carbonyl-containing group may be contained in a unit based on a monomer in resin A, or may be contained in a terminal group of the main chain of resin A, with the former being preferred. Examples of the latter include tetrafluoroethylene resins having a carbonyl-containing group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and resins obtained by subjecting tetrafluoroethylene resins to plasma treatment or ionizing radiation treatment.

As monomers having a carbonyl group-containing group, itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH") are preferred, and NAH is more preferred from the viewpoint of excellent adhesion to the substrate.

The number of carbonyl group-containing groups contained in resin A is not particularly limited. The number of carbonyl group-containing groups contained in resin A may be less than 100, 100 to 5000, or 100 to 3000 per 1 × 10 ⁶ carbon atoms in the main chain, but is preferably 100 to 5000, and more preferably 250 to 3000. The number of carbonyl group-containing groups in the resin can be quantified by the composition of the resin or the method described in WO 2020/145133.

The average particle diameter (D50) of the particles of resin A is 1 μm or more, and more preferably 1.5 μm or more, from the viewpoint of adhesion and suppression of defects and imperfections. The average particle diameter (D50) of the particles of resin A is preferably 25 μm or less, more preferably 20 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less. Particles having the above average particle diameter have excellent fluidity and tend to be distributed uniformly on the surface of the substrate. In addition, the particles are likely to exhibit high levels of heat resistance and electrical properties.

In particular, in composition 2, the average particle diameter of the particles of resin A is 1 μm or more, preferably 1.3 μm or more, more preferably 1.5 μm or more, and even more preferably 1.8 μm or more, from the viewpoint of suppressing defects and imperfections. The average particle diameter of particles A is preferably 10 μm or less, more preferably 5 μm or less, and most preferably 3 μm or less. Particles having the above average particle diameter have excellent fluidity and tend to be distributed uniformly on the surface of the substrate. In addition, the particles are likely to exhibit high levels of heat resistance and electrical properties.

In this composition, particularly in composition 2, the average particle size (D50) of the particles of resin A is preferably at least twice, and more preferably at least five times, the average particle size (D50) of particles B described below, from the viewpoint of suppressing defects and imperfections. The average particle size (D50) of particles A is preferably no more than 10 times, and more preferably no more than 8 times, the average particle size (D50) of particles B.

From the viewpoint of suppressing defects and imperfections, the specific surface area of the resin A particles is preferably 6 m ² /g or more, more preferably 8 m ² /g or more. The specific surface area of the resin A particles is preferably 40 m ² /g or less, more preferably 20 m ² /g or less. In this case, the balance between the interaction between the resin A particles and the interaction between the resin A particles and the water-soluble polymer is good, and the aggregation between the resin A particles is easily suppressed. As a result, the liquid properties of the composition are easily improved. In particular, when the content of resin A in the composition is high, such an effect is likely to be remarkable.

In the present composition, the content of resin A particles is preferably greater than 0 mass% relative to the total mass of the composition, more preferably 10 mass% or more, and particularly preferably 25 mass% or more, from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance. The content of resin A particles is preferably 60 mass% or less relative to the total mass of the composition, more preferably 40 mass% or less, and even more preferably 30 mass% or less.

Furthermore, in this composition, particularly in this composition 2, the mass content of particles A is preferably at least 0.1 times, and more preferably at least 0.2 times, the mass content of particles B described below, from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance. The mass content of particles A is preferably no more than 5 times, and more preferably no more than 2 times, the mass content of particles B.

The melting temperature of resin A of the present disclosure is high, at 280 to 320°C, from the viewpoint of adhering to a substrate having high heat resistance and from the viewpoint of forming a primer layer having high heat resistance. If a fluororesin with a low melting temperature is used for the primer layer, the primer layer will liquefy when the PTFE sheet and the primer layer are thermocompression bonded, making it difficult for the primer layer to function. From the viewpoint of adhesion, the melting temperature of resin A is more preferably 290 to 310°C.

From the viewpoint of further improving the heat resistance of the primer layer, the glass transition point of resin A is preferably 50°C or higher, and more preferably 75°C or higher. There is no particular upper limit to the glass transition point of resin A, but it is preferably 150°C or lower, and more preferably 125°C or lower.

The resin A particles can be commercially available, and the resin A powder can be, for example, EA-2000 manufactured by AGC.

<Water-soluble polymer>
In the present disclosure, water-soluble means that the water solubility at 25° C. is 1% by mass or more.
In the present composition, the water-soluble polymer preferably has at least one of a hydroxy group and a carbonyl group, and more preferably has both a hydroxy group and a carbonyl group, from the viewpoint of suppressing defects and imperfections.

The water-soluble polymer is preferably at least one selected from the group consisting of acrylic polymers, cellulose polymers, and vinyl polymers.
Examples of acrylic polymers include polyacrylic acid, polymethyl acrylate, polymethacrylic acid, polymethyl methacrylate, and polyacrylamide.
Examples of cellulose-based polymers include cellulose derivatives such as methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose, starch, and agarose. Here, the term "carboxymethylcellulose" includes carboxymethylcellulose salts such as sodium carboxymethylcellulose and ammonium carboxymethylcellulose.
Examples of the vinyl polymer include polyvinyl alcohol and polyvinylpyrrolidone.

The water-soluble polymer is more preferably an acrylic polymer, more preferably polyacrylic acid.
Preferred polyacrylic acids are homopolymers of acrylic acid, copolymers of acrylic acid and comonomers based on monomers which copolymerize with acrylic acid.
Such a comonomer is preferably hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, or acrylamide.
The polyacrylic acid preferably contains 40 to 100 mol % of units based on acrylic acid and more than 0 to 60 mol % of comonomers based on all units in the polymer.

The polyacrylic acid may be neutralized, or some or all of the carboxy groups in the polyacrylic acid may be in the form of a salt. It is preferable that the polyacrylic acid is neutralized, and it is preferable that 50% or more of the carboxy groups in the polyacrylic acid are in the form of a salt.
Specifically, the polyacrylic acid is preferably a polyacrylic acid neutralized in an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, lithium hydroxide, potassium hydroxide, etc. The degree of neutralization in this case is preferably 60 to 100%, more preferably 70 to 90%.
The polyacrylic acid may be crosslinked.
An example of the crosslinked polyacrylic acid is a polyacrylic acid obtained by copolymerizing acrylic acid with an acrylate having two or more acryloyloxy groups in an amount of 1 mol % or less based on the acrylic acid.

The weight average molecular weight (Mw) of the water-soluble polymer is calculated by gel permeation chromatography (GPC) based on the following:
・Measuring device: Pump LC-20AB (manufactured by Shimadzu Corporation)
RI detector RID-10A (Shimadzu Corporation)
Column: OHpak SB-807 HQ x 1 + OHpak SB-806M HQ x 2 Mobile phase: _Na2HPO4 50mmol/l aqueous _solution Calibration curve standard material: polyacrylic acid

The weight average molecular weight of the water-soluble polymer is 50,000 or more, more preferably 100,000 or more, and even more preferably 500,000 or more, from the viewpoint of suppressing defects and imperfections. The weight average molecular weight of the water-soluble polymer is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,250,000 or less, from the viewpoint of being unlikely to remain in the formed primer layer.

If the weight-average molecular weight (Mw) of the water-soluble polymer is large, the thixotropy of the composition is high. In other words, the particles in the composition are less likely to settle and tend to remain uniformly dispersed, the composition is more likely to be applied uniformly to the substrate, and defects and imperfections are less likely to occur in the primer layer even if the primer layer is thin.

It is preferable that the water-soluble polymer is decomposed and volatilized after being applied to the substrate and heated. The thermal decomposition rate of the water-soluble polymer when heated to 280-380°C under a nitrogen stream is preferably 25% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more. There is no particular upper limit to the thermal decomposition rate of the water-soluble polymer when heated to 280-380°C under a nitrogen stream, but it is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less.

In the present composition, the content of the water-soluble polymer is preferably greater than 0 mass% relative to the total mass of the composition, from the viewpoint of suppressing defects and imperfections, and more preferably 0.01 mass% or more. The content of the water-soluble polymer is preferably 1 mass% or less relative to the total mass of the composition, more preferably 0.5 mass% or less, and even more preferably 0.3 mass% or less.

In this composition, the mass content of the water-soluble polymer is preferably less than the mass content of the resin A particles from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance. The mass content of the water-soluble polymer is preferably 0.001 times or more, and more preferably 0.002 times or more, the mass content of the resin A particles. The mass content of the water-soluble polymer is preferably 0.05 times or less, and more preferably 0.01 times or less, the mass content of the resin A particles.

<Particle B>
The resin of the particles B is preferably heat-fusible.
The number of carbonyl-containing groups contained in the resin of particles B is preferably smaller than the number of carbonyl-containing groups contained in resin A, specifically, preferably less than 100 per 1×10 ⁶ carbon atoms in the main chain.

From the viewpoint of adhesiveness and high heat resistance, the resin of particle B is preferably a resin containing a unit based on TFE and at least one of a unit based on PAVE and a unit based on hexafluoropropylene (HFP).The resin of particle B is more preferably a resin containing a unit based on TFE and a unit based on PAVE (PFA), or a resin containing a unit based on TFE and a unit based on HFP (FEP).The resin of particle B is more preferably a perfluoroalkoxyalkane (PFA) or a tetrafluoroethylene-hexafluoropropylene copolymer (FEP).In addition, as PAVE, _CF2 = _CFOCF3 , _CF2 = _CFOCF2CF3 or _CF2 = _CFOCF2CF2CF3 ( _PPVE ) _is preferred, and _PPVE is more preferred.
The resin of the particles B may further contain units based on other comonomers.

The composition ratio of each monomer unit in the resin of particle B is not particularly limited, but for example, when the resin contains a unit based on TFE, the composition ratio of the unit based on TFE is preferably 70 to 99 mol% relative to the total units in the resin from the viewpoint of favorably expressing the characteristics due to TFE. Furthermore, for example, when the resin contains a unit based on PAVE or a unit based on HFP, the composition ratio of the unit based on PAVE or the unit based on HFP is preferably 1 to 5 mol% of the unit based on PAVE and 20 to 30 mol% of the unit based on HFP relative to the total units in the resin from the viewpoint of favorably expressing the characteristics due to PAVE or HFP.
The fluorine content of the resin of particles B is preferably 70 to 76 mass %, since this makes it easier for interaction with the PTFE sheet to occur, makes it possible to further suppress peeling of the PTFE sheet from the molded product, and further improves the heat resistance of the primer layer.

If the resin of particle B is PFA or FEP, it is preferable that particle B has PFA or FEP as the main component, respectively, and the content of PFA or FEP is preferably 100 mass%.

The average particle diameter of particles B is preferably 0.1 μm or more, and more preferably 0.2 μm or more, from the viewpoint of suppressing defects and imperfections. The average particle diameter of particles B is less than 1 μm, and is preferably 0.5 μm or less, and more preferably 0.4 μm or less.

In the present composition, the content of particle B is preferably greater than 0 mass% relative to the total mass of the composition, and more preferably 10 mass% or more, from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance. The content of particle B is preferably 40 mass% or less relative to the total mass of the composition, more preferably 30 mass% or less, and even more preferably 20 mass% or less.

From the viewpoint of adhesiveness, the melting temperature of the resin of particle B is preferably 200 to 320°C, more preferably 250 to 320°C, even more preferably 280 to 320°C, and particularly preferably 290 to 310°C. It is more preferable that the melting temperature of the resin of particle B is in the same range as the melting temperature of resin A.

From the viewpoint of further improving the heat resistance of the primer layer, the glass transition point of the resin of particle B is preferably 50°C or higher, and more preferably 75°C or higher. There is no particular upper limit to the glass transition point of the resin of particle B, but it is preferably 150°C or lower, and more preferably 125°C or lower.

From the viewpoint of suppressing defects and imperfections, the melt flow rate (MFR) of the resin of particle B is preferably 5 g/10 min or more, and more preferably 10 g/10 min or more. The melt flow rate (MFR) of the resin of particle B is preferably 30 g/10 min or less, and more preferably 20 g/10 min or less.

<Mass ratio of particles in aqueous primer composition>
In the present composition, the total content of particle A and particle B is preferably more than 0 mass%, more preferably 10 mass% or more, and even more preferably 20 mass% or more, based on the total mass of the composition, from the viewpoints of adhesion, suppression of defects and defects, and high heat resistance. The total content of particle A and particle B is preferably 40 mass% or less, more preferably 35 mass% or less, based on the total mass of the composition.

<Other ingredients>
The composition may contain a surfactant, which can improve the dispersibility and handling of the composition. The surfactant is preferably a nonionic surfactant. The hydrophilic portion of the surfactant preferably has an oxyalkylene group or an alcoholic hydroxyl group. The hydrophobic portion of the surfactant preferably has an acetylene group, a polysiloxane group, or a fluorine-containing organic group (such as a perfluoroalkyl group). In other words, the surfactant is preferably an acetylene-based surfactant, a silicone-based surfactant, or a fluorine-based surfactant.
When the present composition contains a surfactant, the content of the surfactant relative to the total mass of the present composition is preferably from 1 to 15% by mass.

The composition may contain a liquid dispersion medium. In other words, the composition can be regarded as a dispersion in which particles of resin A are dispersed in a liquid. In such a dispersion, the particles of resin A are highly and uniformly dispersed in the liquid, and the above-mentioned mechanism of action is easily manifested.
The boiling point of the liquid dispersion medium is preferably in the range of 50 to 240° C. The liquid dispersion medium may be used alone or in combination of two or more kinds. When two or more kinds of liquid dispersion media are used, it is preferable that the two or more kinds of liquid dispersion media are mutually compatible.
Examples of the liquid dispersion medium include water, alcohol, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, cyclopentanone, butyl acetate, methyl isopropyl ketone, and methyl ethyl ketone. Of these, water is preferred.
The content of the liquid dispersion medium relative to the total mass of the composition is preferably from 30 to 95 mass %, more preferably from 35 to 90 mass %.

The composition may further contain a resin (hereinafter also referred to as "different resin") different from the fluororesin constituting the resin A and the water-soluble polymer and resin B of the present disclosure. The different resin may be thermosetting or thermoplastic. One type of the different resin may be used, or two or more types may be used.
The different resin is not particularly limited as long as it is a resin other than the fluororesin that constitutes Resin A, the water-soluble polymer, and Resin B of the present disclosure, and examples thereof include tetrafluoroethylene resins, polyester resins (such as liquid crystalline aromatic polyesters), polyimide resins, epoxy resins, maleimide resins, polyurethane resins, polyphenylene ether resins, polyphenylene oxide resins, and polyphenylene sulfide resins.
When the present composition contains a different resin, the content of the different resin relative to the total mass of the present composition is preferably 0.1 to 5% by mass.

In addition to the above components, the composition may further contain other components such as a thixotropic agent, a pH adjuster, a pH buffer, 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 whitening agent, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, various inorganic fillers, or various organic fillers, to the extent that the effect of the composition is not impaired.

<Properties>
In the present disclosure, the thixotropy is evaluated by the thixotropy index calculated as the ratio (μ6 rpm/μ60 rpm) of the B-type viscosity μ6 rpm [mPa·s] measured at a temperature of 20° C. and a shear rate of 60 rpm to the B-type viscosity μ6 rpm [mPa·s] measured at a temperature of 20° C. and a shear rate of 6 rpm. Note that the term "B-type viscosity" refers to a value measured from the viscous resistance torque acting on a cylinder or disk when the cylinder or disk is rotated in a liquid using a B-type viscometer in accordance with JIS-K7117-1:1999 "Plastics - Liquid, emulsion or dispersion resins - Measurement method of apparent viscosity using a Brookfield rotational viscometer" (ISO 2555:1989).

The thixotropy index of the composition is preferably 0.8 to 4.0. The lower limit of the thixotropy index of the composition is preferably 0.9, and more preferably 1.0. On the other hand, the upper limit of the thixotropy index of the composition is preferably 3.5, more preferably 2.5, and even more preferably 2.2. By adjusting the thixotropy index of the composition to within the above range, the composition tends to have a viscosity that provides better handling properties, and tends to provide improved homogeneity when applied to a substrate.

The viscosity of the composition is preferably 100 mPa·s or more, more preferably 500 mPa·s or more. The viscosity of the composition is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, and even more preferably 2,500 mPa·s or less. In this case, in addition to excellent dispersibility, the handling property and the uniformity of application of the composition to the substrate are easily improved. Furthermore, the composition is excellent in mixability with varnishes of different resin materials. The viscosity is measured using a B-type 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 regarded as the viscosity.

<Method of forming primer layer>
The first method for forming a primer layer according to the present disclosure uses the aqueous primer composition according to the present disclosure (i.e., the present composition) to form a primer layer having an average thickness of 5 μm or less.
The second method for forming a primer layer of the present disclosure uses the aqueous primer composition of the present disclosure (i.e., the present composition) to form a primer layer having an average thickness equal to or less than the average particle diameter (D50) of the particles of Resin A.

The average thickness of the primer layer is preferably more than 0 μm, more preferably 0.1 μm or more, and even more preferably 0.5 μm or more. The average thickness of the primer layer is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less.
Specifically, the average thickness of the primer layer is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more relative to the average particle size (D50) of the particles of the resin A. The average thickness of the primer layer is preferably less than 1, more preferably 0.8, relative to the average particle size (D50) of the particles of the resin A.
More specifically, when the average particle size (D50) of the resin A particles is 1 to 6 μm, the average thickness of the primer layer is preferably 0.5 to 4 μm, and more preferably 0.8 to 2.5 μm.
In the present disclosure, the term "average thickness" refers to the average value of measurement results at three or more points measured with a thickness meter.

<Preparation of Aqueous Primer Composition>
The composition can be prepared by mixing particles of resin A, at least one selected from the group consisting of water-soluble polymers having a weight-average molecular weight of 50,000 or more and particles B, and water.

The particles of resin A may be commercially available, and an example of a powder of the particles of resin A is EA-2000 manufactured by AGC Co., Ltd. The particles of resin A may be used in the preparation of the present composition in the form of an aqueous dispersion of the particles of resin A, preferably an aqueous dispersion of the particles of resin A.
The water-soluble polymer may be commercially available. The water-soluble polymer may be used in the preparation of the present composition in the form of an aqueous dispersion of the water-soluble polymer, preferably an aqueous dispersion of the water-soluble polymer.
Commercially available particles can be used as the particles B. The particles B may be used in the preparation of the present composition in the form of an aqueous dispersion of the particles B, preferably an aqueous dispersion of the particles B.

In particular, one method for producing composition 2 is to mix particles of resin A and particles of resin B and subject them to a shearing treatment.

The mixing in the preparation of the aqueous primer composition may be carried out in a batch manner or a continuous manner.
Examples of devices that can be used for the above mixing include stirring devices equipped with blades (Henschel mixers, pressure kneaders, Banbury mixers, planetary mixers, etc.), grinding devices equipped with media (ball mills, attritors, basket mills, sand mills, sand grinders, Dyno Mills, Dispermats, SC Mills, spike mills, agitator mills, etc.), and dispersing devices equipped with other mechanisms (microfluidizers, nanomizers, ultimizers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impellers, thin film swirling type high-speed mixers, etc.).
The detailed conditions for the above mixing are not particularly limited.

Examples of devices that can be used for the shearing include a mixer, a colloid mill, and a homogenizer.
The detailed conditions for the shearing are not particularly limited.

<Granting>
The method for applying the present composition to a substrate is not particularly limited, but examples thereof include flow coating, dip coating, spin coating, spray coating, flexographic printing, screen printing, gravure printing, roll coating, meniscus coating, and die coating.
The application of the present composition to a substrate may be carried out in a batch manner or a continuous manner, but the continuous manner is preferred from the viewpoint of easily suppressing uneven application of the present composition to a substrate and improving productivity.

<Heating>
The heating of the present composition applied to the substrate preferably includes heating for baking the particles of Resin A. In addition, the heating of the present composition applied to the substrate preferably includes heating for evaporating a liquid dispersion medium that may be contained in the present composition.
In particular, the heat treatment for evaporating the water-soluble polymer and the liquid dispersion medium in the present composition 1 may be carried out by holding the substrate to which the present composition 1 has been applied at a temperature equal to or higher than the volatilization temperature of the water-soluble polymer and the liquid dispersion medium, and drying the liquid coating applied to the substrate. In the heat treatment, it is not necessary to completely evaporate the water-soluble polymer and the liquid dispersion medium. Specifically, the amount of the water-soluble polymer and the liquid dispersion medium to be evaporated is preferably 50% by mass or more, and more preferably 80% by mass or more, of the water-soluble polymer and the liquid dispersion medium contained in the present composition 1.

The heat treatment for evaporating the liquid dispersion medium in this composition may be carried out in one step at a constant temperature, or in two or more steps at different temperatures. The heating temperature is preferably 50 to 280°C. The heating time is preferably 0.1 to 30 minutes.

Examples of the heat treatment for firing include a method using an oven, a method using a ventilated drying furnace, and a method using heat rays such as infrared rays. A combination of infrared heating and hot air heating may also be used.
The firing may be carried out under either normal pressure or reduced pressure, and the firing atmosphere may be any of an oxidizing gas atmosphere, a reducing gas atmosphere, and an inert gas atmosphere.
The baking temperature is preferably 300 to 350° C., and more preferably 310 to 340° C. The baking time is preferably 30 seconds to 30 minutes, and more preferably 1 to 15 minutes. The baking temperature usually means the temperature of a dry atmosphere.

The composition can be applied to the substrate and heated by using an apparatus having a dip coater and a baking furnace. An example of the baking furnace is a vertical baking furnace. Another example of such an apparatus is a glass cloth coating device manufactured by Tabata Machinery Co., Ltd.

<Substrate>
Examples of the material of the substrate include metal substrates (metal foils such as copper, nickel, aluminum, titanium, and alloys thereof), resin films (films such as polyimide, polyarylate, polysulfone, polyarylsulfone, polyamide, polyetheramide, polyphenylene sulfide, polyaryletherketone, polyamideimide, liquid crystal polyester, and liquid crystal polyesteramide), and prepregs (precursors of fiber-reinforced resin substrates). The shape of the substrate may be flat, curved, or uneven, and may be any of foil, plate, film, and fiber.

<Molded products>
One embodiment of the molded product of the present disclosure comprises a substrate, a fluororesin primer layer containing a melt of particles of resin A and a water-soluble polymer having a weight-average molecular weight of 50,000 or more, and a polytetrafluoroethylene sheet, in this order in the thickness direction. The explanations of the "substrate", "particles of resin A" and "water-soluble polymer" in such a molded product are the same as those described in the sections "Aqueous primer composition" and "Method of forming primer layer", including definitions, examples, and preferred embodiments.

Another embodiment of the molded product of the present disclosure comprises a substrate, a fluororesin primer layer containing a melt of particles of resin A and particles B (i.e., particles B) of a fluororesin having an average particle diameter (D50) of less than 1 μm and a melting temperature of 320° C. or less, and a polytetrafluoroethylene sheet, in this order in the thickness direction. The explanations of "substrate", "particles A of resin A" and "particles B" in such a molded product are the same as those described in the sections "Aqueous primer composition" and "Method of forming primer layer", including definitions, examples, and preferred embodiments.

<Polytetrafluoroethylene sheet>
The polytetrafluoroethylene (PTFE) sheet is preferably a sheet containing PTFE as a main component, and more preferably 80 mass % or more of the total mass of the sheet is PTFE.

Furthermore, it is preferable that the PTFE is non-thermofusible. Note that "non-thermofusible" means that it is not melt-moldable, in other words, it does not exhibit melt fluidity. Specifically, this means that the melt flow rate measured in accordance with ASTM D3307 at a measurement temperature of 372°C and a load of 49N is less than 0.5 g/10 min.

The thickness of the PTFE sheet is preferably 25 μm or more, and more preferably 50 μm or more. The thickness of the PTFE sheet is preferably 1000 μm or less, and more preferably 500 μm or less.

<Production of Molded Product>
The molded article of the present disclosure can be produced by, for example, thermocompression bonding a PTFE sheet to a substrate on which a fluororesin primer layer has been formed. The thermocompression bonding conditions are preferably changed appropriately depending on the thickness of the molded article to be produced, and are, for example, a temperature of 170 to 450°C, a pressure of 1.5 to 5 MPa, and a time of 60 to 150 minutes.

The above molded products are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry products, paints, cosmetics, etc., and specifically 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 and fuel cells, etc.), copy rolls, furniture, automobile dashboards, covers for home appliances, etc., sliding parts (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, etc.

One embodiment of the present disclosure is described in detail below, but the present disclosure is not limited to these embodiments.

<Particles of Resin A>
[Particle A1] Particles (average particle size: 2.0 μm, specific surface area: 7.2 m 2 /g) made of a resin (melting temperature: 300° C.) containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having 1,000 carbonyl-containing groups per 1×10 ^{6 main} chain carbon atoms.
[Particle A2] Particles (average particle size: 1.2 μm, specific surface area: 5.4 m 2 /g) made of a resin (melting temperature: 300° C.) containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having 1,000 carbonyl-containing groups per 1×10 ⁶ carbon atoms in the ^main chain.
[Particle A3] Particles (average particle size: 1.2 μm, specific surface area: 27.6 m 2 /g) made of a resin (melting temperature: 300° C.) containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having 1,000 carbonyl-containing groups per 1×10 ⁶ carbon atoms in the ^main chain.
[Particle 4] Particles of a resin (melting temperature: 300° C.) containing 97.5 mol % of a unit based on TFE and 2.5 mol % of a unit based on PPVE, in that order, and having no oxygen-containing polar group (i.e., PFA particles, average particle size: 2.0 μm, specific surface area: 9.3 m ² /g).

<Water-soluble polymer>
[Water-soluble polymer 1] A water-soluble polymer having a weight-average molecular weight of 1,000,000 (neutralization degree 80%) obtained by neutralizing polyacrylic acid crosslinked with 1 mol% or less of polyethylene glycol diacrylate relative to acrylic acid with an aqueous sodium hydroxide solution.
[Water-soluble polymer 2] A water-soluble polymer having a weight-average molecular weight of 40,000 (neutralization degree 80%) obtained by neutralizing polyacrylic acid with an aqueous sodium hydroxide solution.

<Particle B>
Particles of a resin (melting temperature: 300° C.) containing 97.5 mol % of a unit based on TFE and 2.5 mol % of a unit based on PPVE, in that order (i.e., PFA particles, average particle size: 0.3 μm)
The number of carbonyl-containing groups contained in the resin of the particles B is smaller than the number of carbonyl-containing groups contained in the resin of any of the particles A1 to A3.

<Substrate>
aluminum

<Production of aqueous primer composition (part 1)>
[Aqueous primer composition 11] An aqueous dispersion of particles A1 and water-soluble polymer 1 were mixed in a bead mill to prepare aqueous primer composition 11 containing 20% by weight of particles A1 and 0.1% by weight of water-soluble polymer 1.
[Aqueous primer composition 12] An aqueous dispersion of particles A2 and water-soluble polymer 1 were mixed in a bead mill to prepare aqueous primer composition 12 containing 20% by weight of particles A2 and 0.1% by weight of water-soluble polymer 1.
[Aqueous primer composition 13] An aqueous dispersion of particles A3 and water-soluble polymer 1 were mixed in a bead mill to prepare aqueous primer composition 13 containing 20% by weight of particles A3 and 0.1% by weight of water-soluble polymer 1.
[Aqueous primer composition 14] An aqueous dispersion of particles A1 and water-soluble polymer 2 were mixed in a bead mill to prepare aqueous primer composition 14 containing 20% by weight of particles A1 and 0.1% by weight of water-soluble polymer 2.
[Aqueous primer composition 15] An aqueous dispersion of particles 4 and water-soluble polymer 1 were mixed in a bead mill to prepare aqueous primer composition 15 containing 20% by weight of particles 4 and 0.1% by weight of water-soluble polymer 1.
[Aqueous primer composition 16] An aqueous dispersion of particles 4 and water-soluble polymer 2 were mixed in a bead mill to prepare an aqueous primer composition 16 containing 20% by weight of particles 4 and 0.1% by weight of water-soluble polymer 2.

<Example 1-1>
A primer layer having a thickness of 1 μm was obtained by applying the aqueous primer composition 11 to an aluminum substrate by gravure printing, drying at 180° C., and then melt-sintering for 5 minutes at 350° C. Furthermore, a PTFE sheet was thermocompressed to the obtained primer layer under conditions of a pressure of 1 MPa and a temperature of 350° C. to produce a molded product.

<Example 1-2 to Example 1-6>
A primer layer having a thickness of 1 μm was obtained and a molded product was produced in the same manner as in Example 1-1, except that the aqueous primer composition used was aqueous primer composition 12 in Example 1-2, aqueous primer composition 13 in Example 1-3, aqueous primer composition 14 in Example 1-4, aqueous primer composition 15 in Example 1-5, and aqueous primer composition 16 in Example 1-6.

<Evaluation of defects and imperfections>
The surfaces of the primer layers obtained in each example were observed and evaluated based on the following evaluation criteria, and the results are summarized in Table 1. In this disclosure, a defect refers to a state in which the primer layer has pinholes, and a defect refers to a state in which the primer layer has streaks and uneven thickness.
(Evaluation Criteria)
A: No defects or imperfections were found even when examined under a microscope.
B: Minor defects visible under a microscope.
C: There was a visible defect.

<Evaluation of Adhesion>
The molded product produced in each example was cut into a test piece having a length of 100 mm and a width of 10 mm. The test piece was fixed from one end in the length direction to a position 50 mm away, and the aluminum substrate and the PTFE sheet were peeled from the other end of the test piece under the conditions of a pulling speed of 50 mm/min and a peeling angle of 90°. The maximum load (N/cm) during peeling was measured and evaluated based on the following evaluation criteria, and the results are summarized in Table 1.
(Evaluation Criteria)
A: The maximum load was 10 N/cm or more.
B: The maximum load was less than 10 N/cm.

<Production of aqueous primer composition (part 2)>
[Aqueous primer composition 21] An aqueous dispersion of particles A1 and an aqueous dispersion of particles B were mixed by shearing in a bead mill to prepare an aqueous primer composition 21 containing 15% by mass each of particles A1 and particles B.
[Aqueous primer composition 22] An aqueous dispersion of particles A2 and an aqueous dispersion of particles B were mixed by shearing in a bead mill to prepare an aqueous primer composition 22 containing 15% by mass of particles A2 and 15% by mass of particles B, respectively.
[Aqueous primer composition 23] An aqueous dispersion of particles A3 and an aqueous dispersion of particles B were mixed by shearing in a bead mill to prepare an aqueous primer composition 23 containing 15% by mass each of particles A3 and particles B.
[Aqueous primer composition 24] Particles A1 and water were mixed to prepare an aqueous primer composition 24 containing 30% by mass of particles A1.
[Aqueous primer composition 25] Particles B and water were mixed to prepare an aqueous primer composition 25 containing 30% by mass of particles B.

<Example 2-1>
Aqueous primer composition 21 was applied to an aluminum substrate by gravure printing, and then dried at 180° C., followed by melt-sintering for 5 minutes at 350° C. to obtain a primer layer having a thickness of 1 μm. A PTFE sheet was then thermocompressed to the obtained primer layer under conditions of a pressure of 1 MPa and a temperature of 350° C. to produce a molded product.

<Example 2-2 to Example 2-5>
A primer layer having a thickness of 1 μm was obtained and a molded product was produced in the same manner as in Example 2-1, except that in Example 2-2, aqueous primer composition 22, in Example 2-3, aqueous primer composition 23, in Example 2-4, aqueous primer composition 24, and in Example 2-5, aqueous primer composition 25 were used as the aqueous primer composition.

The results of the "evaluation of defects and imperfections" and "evaluation of adhesion" carried out for the primer layers or molded products obtained in each example according to the procedures described above are summarized in Table 2.

The disclosures of Japanese Patent Application No. 2023-107568, filed on June 29, 2023, and Japanese Patent Application No. 2023-107569, filed on June 29, 2023, are incorporated herein by reference in their entirety. In addition, 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 (15)

Particles A of a fluororesin having an average particle diameter (D50) of 1 μm or more, a melting temperature of 280 to 320° C., and a carbonyl group-containing group;
A water-soluble polymer having a weight average molecular weight of 50,000 or more; and
At least one selected from the group consisting of fluororesin particles B having an average particle diameter (D50) of less than 1 μm and a melting temperature of 320° C. or less;
Water,
1. An aqueous primer composition comprising: An aqueous primer composition comprising particles A of a fluororesin having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320°C, and a carbonyl group-containing group, a water-soluble polymer having a weight-average molecular weight of 50,000 or more, and water. The aqueous primer composition according to claim 1 or 2, wherein the particles A have a specific surface area of 6 m ² /g or more. The aqueous primer composition according to claim 1 or 2, wherein the content of the particles A is more than 0% by mass and not more than 40% by mass with respect to the total mass of the aqueous primer composition. The aqueous primer composition according to claim 1 or 2, wherein the water-soluble polymer is at least one selected from the group consisting of acrylic polymers, cellulose polymers, and vinyl polymers. A method for forming a primer layer, comprising using the aqueous primer composition according to claim 1 or 2 to form a primer layer having an average thickness of 5 μm or less. A method for forming a primer layer, comprising using the aqueous primer composition according to claim 1 or 2 to form a primer layer having an average thickness equal to or less than the average particle diameter (D50) of the particles A. A molded article comprising, in the thickness direction, a substrate, a fluororesin primer layer containing a melt of fluororesin particles A having a melting temperature of 280-320°C and a water-soluble polymer having a weight-average molecular weight of 50,000 or more, and a polytetrafluoroethylene sheet, in this order. An aqueous primer composition comprising: fluororesin particles A having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320°C, and carbonyl-containing groups; fluororesin particles B having an average particle size (D50) of less than 1 μm and a melting temperature of 320°C or less; and water. The aqueous primer composition according to claim 9, wherein the particles A have a specific surface area of 6 m ² /g or more. The aqueous primer composition according to claim 1 or 9, wherein the total mass content of the particles A and the mass content of the particles B is more than 0 mass% and not more than 40 mass% with respect to the total mass of the aqueous primer composition. The aqueous primer composition according to claim 1 or 9, wherein the average particle diameter (D50) of the particles A is 2 to 10 times the average particle diameter (D50) of the particles B. A method for forming a primer layer, comprising using the aqueous primer composition according to claim 9 or 10 to form a primer layer having an average thickness of 5 μm or less. A method for forming a primer layer, comprising using the aqueous primer composition according to claim 9 or 10 to form a primer layer having an average thickness equal to or less than the average particle diameter (D50) of the particles A. A molded article comprising, in the thickness direction, a substrate, a fluororesin primer layer containing a melt of fluororesin particles A having an average particle size (D50) of 1 μm or more, a melting temperature of 280 to 320°C, and carbonyl group-containing groups, and fluororesin particles B having an average particle size (D50) of less than 1 μm and a melting temperature of 320°C or less, and a polytetrafluoroethylene sheet in this order.