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

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

[0001] The present disclosure relates to an aqueous primer composition, a method for forming a primer layer, and a molded article.

[0002] Fluorine resins are sometimes used as materials for forming base layers (i.e., primer layers) when forming laminated molded products, taking advantage of their physical properties. For example, in order to obtain a porous composite that is excellent in strength and is resistant to delamination, it has been proposed to use a low-melting-point, particulate 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, particulate FEP (see Patent Document 2).

[0003] JP 2018-047412 A JP 2018-048233 A

[0004] However, Patent Documents 1 and 2 use a low-melting-point, particulate FEP, 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 high-melting-point fluororesin, the formation temperature becomes high, which can cause defects and flaws in the primer layer and reduce its performance as a primer layer. Furthermore, when a composition for forming the primer layer is thinly applied to a substrate to form an extremely thin primer layer, the particles in the composition tend to be applied sparsely to the substrate, making the primer layer more susceptible to defects and flaws.

[0005] The present disclosure has been made in view 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 suppressed defects and imperfections, a method for forming a primer layer, and a molded product.

[0006] <1> 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; at least one selected from the group consisting of a water-soluble polymer having a weight-average molecular weight of 50,000 or more, 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 water. <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> A specific surface area of ​​the particles A is 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 not more than 40 mass% relative 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 acrylic polymers, cellulose polymers, and vinyl polymers. <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 using the aqueous primer composition according to any one of <1> to <5> to form a primer layer having an average thickness of not more than the average particle diameter (D50) of the particles A. <8> A molded article comprising, in this order 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. <9> An aqueous primer composition comprising: 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; 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 water. <10> A water-based primer composition comprising particles A of a fluororesin having 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 the total amount of the content by mass of the particles A and the content by mass 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. <12> The aqueous primer composition according to any one of <1> to <5> and <9> to <11>, wherein the average particle size (D50) of the particles A is 2 to 10 times the average particle size (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 of not more than the average particle size (D50) of the particles A. <15> A molded article comprising, in this order in the thickness direction, a substrate; a fluororesin primer layer containing 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.

[0007] According to the present disclosure, there are provided an aqueous primer composition for obtaining a thin, highly heat-resistant primer layer that has excellent adhesion and suppressed defects and imperfections, a method for forming a primer layer, and a molded product.

[0008] An embodiment of the present disclosure will be described in detail below. 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 otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0009] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. 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 contained. 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, "average particle size (D50)" is the volume-based cumulative 50% diameter of particles determined by laser diffraction / scattering method. That is, the particle size distribution is measured by a laser diffraction / scattering method, and a cumulative curve is calculated with the total volume of the particle group as 100%. 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 particle size distribution measuring device (LA-920 measuring instrument, 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 this disclosure, the "melting temperature" refers to the temperature corresponding to the maximum value of the melting peak of the resin measured by differential scanning calorimetry (DSC). In this disclosure, the "melt flow rate" refers to the melt flow rate (MFR) of the resin as defined in JIS K 7210:1999 (ISO 1133:1997). In this disclosure, the "glass transition temperature (Tg)" refers to a value measured by analyzing the resin using a dynamic mechanical analysis (DMA) method. In the present disclosure, a "resin" is a compound obtained 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 refers to 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.

[0010] <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 particles A (hereinafter also referred to as "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 carbonyl group-containing groups; water-soluble polymers (hereinafter also referred to as "water-soluble polymers") having a weight-average molecular weight of 50,000 or more; and particles B (hereinafter also referred to as "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. The composition may contain both the water-soluble polymer and particles B, or may contain only one of the water-soluble polymer and particles B. In this disclosure, the fluororesin having a melting temperature of 280 to 320°C and carbonyl group-containing groups is also referred to as "resin A."

[0011] 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"). Composition 1 provides a thin, highly heat-resistant primer layer with excellent adhesion and reduced defects and imperfections. The function of composition 1 is unclear, but is presumed to be as follows. A primer layer is preferably formed by applying a primer composition thinly and uniformly to the surface of a substrate on which the primer layer is to be formed. However, 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. This is because the water dispersibility of the fluororesin particles is not sufficiently high, and the applied fluororesin particles are packed together and it is difficult to control their behavior when they melt upon heating to form a layer. Furthermore, this tendency is likely to become more pronounced when the melting temperature of the fluororesin is high, making the primer layer more susceptible to defects and imperfections.

[0012] Therefore, Composition 1 contains a water-soluble polymer with a large weight-average molecular weight of 50,000 or more. In Composition 1, the water-soluble polymer functions as a thickening component, enhancing the thixotropy of Composition 1, improving the aqueous dispersibility of Resin A particles, and suppressing their settling, thereby enhancing the uniformity of Composition 1. Therefore, when Composition 1 is applied to a substrate, the Resin A particles tend to be densely packed, and defects and imperfections in the primer layer are less likely to occur even if the thickness of the primer layer is reduced.

[0013] Furthermore, because 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 present on the substrate at a uniform density, so that defects and imperfections are less likely to occur in the primer layer even if the thickness of the primer layer is reduced.

[0014] Furthermore, Resin A maintains the flexibility of the resin in the primer layer even after heating and cooling. That is, the primer layer obtained using Composition 1 has excellent adhesion. Resin A of the present disclosure has a high melting temperature of 280 to 320°C. That is, the primer layer obtained using Composition 1 has high heat resistance. The present disclosure is not limited in any way to the above-mentioned presumed mechanism.

[0015] 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 "composition 2").

[0016] Composition 2 provides a thin, highly heat-resistant primer layer with excellent adhesion and reduced defects and imperfections. The function of Composition 2 is unclear, but is presumed to be as follows. Composition 2 contains two types of high-melting-temperature fluororesin particles: Particles A with a predetermined average particle size and Particles B with an average particle size smaller than Particles A. As a result, Particles A and B interact with each other in Composition 2 to promote loose agglomeration, extending the high water dispersibility of Particles A, which are fluororesin particles having carbonyl groups, to the entire particle mass, thereby improving the uniformity and liquid properties of Composition 2. Therefore, when Composition 2 is applied to a substrate, the fluororesin particles tend to be densely packed, making the primer layer less susceptible to defects and imperfections, even when the primer layer is thin.

[0017] Furthermore, since the primer layer is formed by melting the loose aggregates, i.e., particles A and B, while remaining present on the substrate at a uniform density, upon heating, defects and flaws are unlikely to occur in the primer layer even if the thickness of the primer layer is reduced. Note that this tendency is more pronounced in Composition 2, which is prepared by premixing particles A and B and subjecting them to shearing treatment.

[0018] Furthermore, fluororesins having a melting temperature of 280 to 320°C ensure the flexibility of the resin in the primer layer even after application to a substrate and heating. That is, the primer layer obtained using composition 2 has excellent adhesiveness. Resin A has a high melting temperature of 280 to 320°C. That is, the primer layer obtained using composition 2 has high heat resistance. The present disclosure is not limited in any way to the above-mentioned assumed mechanism.

[0019] <Particles A (Particles of Resin A)> Resin A is preferably heat-fusible. In the present disclosure, "heat-fusible" refers to the property of having 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, 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.

[0020] From the viewpoint of adhesiveness and high heat resistance, resin A is preferably a resin containing a unit based on tetrafluoroethylene (TFE) and a unit 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-based resin having a carbonyl group-containing group as the main component, and the content thereof is preferably 100% by mass.

[0021] Resin A is more preferably a resin having a carbonyl group-containing group and containing 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 containing a unit based on TFE, a unit based on PAVE, and a unit based on a monomer having a carbonyl group-containing group.In addition, PAVE is preferably CF ２ = CFOCF ３ , C.F. ２ = CFOCF ２ CF ３ or CF ２ = CFOCF ２ CF ２ CF ３ (hereinafter also referred to as "PPVE") is preferred, and PPVE is more preferred. Resin A may further contain units based on other comonomers.

[0022] 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 favorably exhibiting 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 favorably exhibiting the properties due to PAVE.

[0023] From the viewpoint of adhesiveness and high heat resistance, the carbonyl group-containing group in the resin A is a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (—OC(O)NH ２ ), acid anhydride residue (—C(O)OC(O)—), imide residue (—C(O)NHC(O)—, etc.) and carbonate group (—OC(O)O—), and acid anhydride residue is more preferred.

[0024] The carbonyl group-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, the former being preferred. Examples of the latter include tetrafluoroethylene resins having a carbonyl group-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.

[0025] As the monomer 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.

[0026] 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 is 1×10 ６The number may be less than 100, 100 to 5000, or 100 to 3000, 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.

[0027] The average particle diameter (D50) of the resin A particles is 1 μm or more, more preferably 1.5 μm or more, from the viewpoint of adhesiveness and suppression of defects and imperfections. The average particle diameter (D50) of the resin A particles 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 uniformly distributed on the surface of the substrate. Furthermore, the particles are likely to exhibit high heat resistance and electrical properties.

[0028] In particular, in Composition 2, the average particle size 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 size of Particle 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 size have excellent fluidity and tend to be uniformly distributed on the surface of the substrate. Furthermore, the particles are likely to exhibit high heat resistance and electrical properties.

[0029] In this composition, particularly in this 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 of the particles B described below, from the viewpoint of suppressing defects and imperfections. The average particle size (D50) of the particles A is preferably not more than 10 times, and more preferably not more than 8 times, the average particle size (D50) of the particles B.

[0030] From the viewpoint of suppressing defects and imperfections, the specific surface area of ​​the particles of Resin A is 6 m ２ / g or more is preferable, and 8m ２ The specific surface area of ​​the particles of resin A is preferably 40 m / g or more. ２ / g or less is preferable, and 20m ２ / g or less is more preferable. In this case, the balance between the interaction between the particles of resin A and the interaction between the particles of resin A and the water-soluble polymer is improved, and aggregation between the particles of resin A is likely to be suppressed. As a result, the liquid properties of the composition are likely to be improved. In particular, when the content of resin A in the composition is high, this effect is likely to be significant.

[0031] In the present composition, from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance, the content of resin A particles is preferably more than 0% by mass, more preferably 10% by mass or more, and particularly preferably 25% by mass or more, relative to the total mass of the present composition. The content of resin A particles is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to the total mass of the present composition.

[0032] Furthermore, in the present composition, particularly in the present 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 adhesiveness, suppression of defects and imperfections, and high heat resistance. The mass content of particles A is preferably at most 5 times, and more preferably at most 2 times, the mass content of particles B.

[0033] 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. The melting temperature of Resin A is more preferably 290 to 310°C from the viewpoint of adhesion.

[0034] From the viewpoint of further improving the heat resistance of the primer layer, the glass transition point of the 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 the resin A, but it is preferably 150° C. or lower, and more preferably 125° C. or lower.

[0035] The particles of resin A can be commercially available, and as a powder of particles of resin A, for example, EA-2000 manufactured by AGC can be used.

[0036] <Water-soluble polymer> In the present disclosure, water-soluble means that the water solubility is 1% by mass or more at 25° C. In the present composition, from the viewpoint of suppressing defects and imperfections, 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.

[0037] 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 polymers include cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose, starch, and agarose. Here, "carboxymethyl cellulose" encompasses carboxymethyl cellulose salts such as sodium carboxymethyl cellulose and ammonium carboxymethyl cellulose. Examples of vinyl polymers include polyvinyl alcohol and polyvinylpyrrolidone.

[0038] The water-soluble polymer is more preferably an acrylic polymer, and more preferably polyacrylic acid. The polyacrylic acid is preferably a homopolymer of acrylic acid or a copolymer of a comonomer based on acrylic acid and a monomer copolymerizable with acrylic acid. The 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.

[0039] The polyacrylic acid may be neutralized, or some or all of the carboxy groups of the polyacrylic acid may be in the form of a salt. Neutralization is preferred, and it is preferable that 50% or more of the carboxy groups of the polyacrylic acid be in the form of a salt. Specifically, the polyacrylic acid is preferably polyacrylic acid neutralized in an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, lithium hydroxide, or potassium hydroxide. The degree of neutralization in this case is preferably 60 to 100%, more preferably 70 to 90%. The polyacrylic acid may be crosslinked. Examples of crosslinked polyacrylic acids include polyacrylic acids obtained by copolymerizing acrylic acid with an acrylate having two or more acryloyloxy groups in an amount of 1 mol% or less relative to the acrylic acid.

[0040] The weight average molecular weight (Mw) of the water-soluble polymer is calculated by gel permeation chromatography (GPC) based on the following: Measuring equipment: Pump LC-20AB (Shimadzu Corporation) RI detector RID-10A (Shimadzu Corporation) Column: OHpak SB-807 HQ x 1 + OHpak SB-806M HQ x 2 Mobile phase: Na ２ HPO ４ 50mmol / l aqueous solution - Calibration curve standard material: polyacrylic acid

[0041] From the viewpoint of suppressing defects and imperfections, 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 preventing the water-soluble polymer from remaining in the formed primer layer, 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.

[0042] When the weight-average molecular weight (Mw) of the water-soluble polymer is large, the thixotropy of the composition is high, i.e., the particles in the composition are less likely to settle and are more likely to remain uniformly dispersed, the composition is more likely to be applied uniformly to a substrate, and defects and imperfections in the primer layer are less likely to occur even when the primer layer is thin.

[0043] The water-soluble polymer is preferably decomposed and volatilized after being applied to a substrate and heated. The thermal decomposition rate of the water-soluble polymer when heated to 280 to 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. The upper limit of the thermal decomposition rate of the water-soluble polymer when heated to 280 to 380°C under a nitrogen stream is not particularly limited, but is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less.

[0044] In the present composition, the content of the water-soluble polymer is preferably more than 0% by mass, more preferably 0.01% by mass or more, relative to the total mass of the composition, from the viewpoint of suppressing defects and imperfections. The content of the water-soluble polymer is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, relative to the total mass of the composition.

[0045] In the present composition, from the viewpoints of adhesion, suppression of defects and imperfections, and high heat resistance, the mass content of the water-soluble polymer is preferably less than the mass content of the particles of resin A. The mass content of the water-soluble polymer is preferably 0.001 times or more, more preferably 0.002 times or more, the mass content of the particles of resin A. The mass content of the water-soluble polymer is preferably 0.05 times or less, more preferably 0.01 times or less, the mass content of the particles of resin A.

[0046] <Particles B> The resin of particles B is preferably heat-fusible. The number of carbonyl group-containing groups contained in the resin of particles B is preferably smaller than the number of carbonyl group-containing groups contained in resin A, specifically, when the number of carbon atoms in the main chain is 1×10 ６ Preferably, there are less than 100 per unit.

[0047] 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 (PFA) containing a unit based on TFE and a unit based on PAVE, or a resin (FEP) containing a unit based on TFE and a unit based on HFP.The resin of particle B is more preferably a perfluoroalkoxyalkane (PFA) or a tetrafluoroethylene-hexafluoropropylene copolymer (FEP).Incidentally, as PAVE, CF ２ = CFOCF ３ , C.F. ２ = CFOCF ２ CF ３ or CF ２ = CFOCF ２ CF ２ CF ３ (PPVE) is preferred, and PPVE is more preferred. The resin of particles B may further contain units based on other comonomers.

[0048] The constituent ratio of each monomer unit in the resin of particle B 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 70 to 99 mol% relative to the total units in the resin, from the viewpoint of favorably exhibiting the properties of TFE. Furthermore, for example, when the resin contains units based on PAVE or units based on HFP, the constituent ratio of the units based on PAVE or units based on HFP is preferably 1 to 5 mol% relative to the total units in the resin, and 20 to 30 mol% relative to the total units in the resin, from the viewpoint of favorably exhibiting the properties of PAVE or HFP. The fluorine content of the resin of particle B is preferably 70 to 76 mass%, because this facilitates interaction with the PTFE sheet, can further suppress peeling of the PTFE sheet from the molded product, and can further improve the heat resistance of the primer layer.

[0049] When the resin of particles B is PFA or FEP, particles B preferably contain PFA or FEP as the main component, and the content of PFA or FEP is preferably 100% by mass.

[0050] From the viewpoint of suppressing defects and imperfections, the average particle size of particles B is preferably 0.1 μm or more, more preferably 0.2 μm or more. The average particle size of particles B is less than 1 μm, preferably 0.5 μm or less, more preferably 0.4 μm or less.

[0051] In the present composition, from the viewpoints of adhesiveness, suppression of defects and imperfections, and high heat resistance, the content of particles B is preferably more than 0 mass% and more preferably 10 mass% or more relative to the total mass of the composition, and the content of particles B is preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less relative to the total mass of the composition.

[0052] From the viewpoint of adhesiveness, the melting temperature of the resin of particles 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 particles B is in the same range as the melting temperature of resin A.

[0053] From the viewpoint of further improving the heat resistance of the primer layer, the glass transition temperature of the resin of particles B is preferably 50° C. or higher, and more preferably 75° C. or higher. The upper limit of the glass transition temperature of the resin of particles B is not particularly limited, but is preferably 150° C. or lower, and more preferably 125° C. or lower.

[0054] From the viewpoint of suppressing defects and imperfections, the melt flow rate (MFR) of the resin of particles B is preferably 5 g / 10 min or more, more preferably 10 g / 10 min or more, and is preferably 30 g / 10 min or less, more preferably 20 g / 10 min or less.

[0055] <Mass Ratio of Particles in Aqueous Primer Composition> In the present composition, the total mass of the particles A and the particles 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 imperfections, and high heat resistance. The total mass of the particles A and the particles B is preferably 40 mass% or less, more preferably 35 mass% or less, based on the total mass of the composition.

[0056] <Other Components> The composition may contain a surfactant, which can improve the dispersibility and handleability 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 composition contains a surfactant, the content of the surfactant relative to the total mass of the composition is preferably 1 to 15 mass%.

[0057] The composition may contain a liquid dispersion medium. In other words, the composition can be considered a dispersion in which resin A particles are dispersed in a liquid. In such a dispersion, the resin A particles are highly and uniformly dispersed in the liquid, which makes it easier for the above-described mechanism of action to be significantly exhibited. The boiling point of the liquid dispersion medium is preferably in the range of 50 to 240°C. A single liquid dispersion medium may be used, or two or more liquid dispersion media may be used in combination. When two or more liquid dispersion media are used, the two or more liquid dispersion media are preferably mutually compatible. Examples of liquid dispersion media 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. Among 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 %.

[0058] The present composition may further contain a resin (hereinafter also referred to as "different resin") different from the fluororesin constituting Resin A, the water-soluble polymer, and Resin B of the present disclosure. The different resin may be thermosetting or thermoplastic. One type of 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 constituting Resin A, the water-soluble polymer, and Resin B of the present disclosure, and examples thereof include tetrafluoroethylene-based 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 mass%.

[0059] In addition to the above components, the present composition may further contain other components such as a thixotropy-imparting agent, a pH adjuster, a pH buffer, a viscosity modifier, 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 brightener, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, various inorganic fillers, or various organic fillers, provided that the effects of the present composition are not impaired.

[0060] <Properties> In the present disclosure, thixotropy is evaluated by the thixotropy index, which is calculated as the ratio (μ6 rpm / μ60 rpm) of the Brookfield viscosity μ60 rpm [mPa s] measured at a temperature of 20°C and a shear rate of 60 rpm to the Brookfield viscosity μ6 rpm [mPa s] measured at a temperature of 20°C and a shear rate of 6 rpm. Note that "B-type viscosity" refers to a value measured in accordance with JIS-K7117-1:1999 "Plastics - Liquid, emulsion or dispersion resins - Measurement of apparent viscosity using a Brookfield rotational viscometer" (ISO 2555:1989) from the viscous resistance torque acting on a cylinder or disk when the cylinder or disk is rotated in a liquid using a Brookfield rotational viscometer.

[0061] 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 fall within the above range, the composition tends to have a viscosity that improves handleability, and tends to achieve improved uniformity when applied to a substrate.

[0062] 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, not only is the dispersibility excellent, but the handleability and the uniformity of application of the composition to the substrate are also easily improved. Furthermore, the composition has excellent miscibility with varnishes of different resin materials. The viscosity is determined by measuring the 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 measurements is taken as the viscosity.

[0063] <<Method for forming a primer layer>> A 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. A second 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 the average particle diameter (D50) of the resin A particles or less.

[0064] The average thickness of the primer layer is preferably greater than 0 μm, more preferably 0.1 μm or greater, and even more preferably 0.5 μm or greater. 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 greater, more preferably 0.2 or greater, and even more preferably 0.3 or greater, relative to the average particle diameter (D50) of the resin A particles. Furthermore, the average thickness of the primer layer is preferably less than 1, more preferably 0.8, relative to the average particle diameter (D50) of the resin A particles. More specifically, when the average particle diameter (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 even more preferably 0.8 to 2.5 μm. In this disclosure, "average thickness" refers to the average value of three or more measurement results measured using a film thickness meter.

[0065] <Preparation of aqueous primer composition> This 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.

[0066] Commercially available resin A particles can be used, and an example of a powder of resin A particles is EA-2000 manufactured by AGC. The resin A particles may be used in the preparation of the composition in the form of an aqueous dispersion of resin A particles, preferably an aqueous dispersion of resin A particles. The water-soluble polymer may be commercially available. The water-soluble polymer may be used in the preparation of the composition in the form of an aqueous dispersion of water-soluble polymer, preferably an aqueous dispersion of water-soluble polymer. The particles B may be commercially available. The particles B may be used in the preparation of the composition in the form of an aqueous dispersion of particles B, preferably an aqueous dispersion of particles B.

[0067] In particular, the method for producing the composition 2 includes mixing particles of resin A and particles of resin B and subjecting the mixture to a shearing treatment.

[0068] The mixing in the preparation of the aqueous primer composition may be carried out batchwise or continuously. Examples of equipment that can be used for the mixing include agitators 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 high-speed mixers, etc.). The detailed conditions for the mixing are not particularly limited.

[0069] Furthermore, examples of devices that can be used for the shearing include a mixer, a colloid mill, a homogenizer, etc. The detailed conditions for the shearing are not particularly limited.

[0070] <Application> The method for applying the present composition to a substrate is not particularly limited, and 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 batchwise or continuously, but a continuous method is preferred from the viewpoint of easily suppressing uneven application of the present composition to the substrate and improving productivity.

[0071] <Heating> Heating the composition applied to the substrate preferably includes heating for baking the particles of resin A. Heating the composition applied to the substrate preferably includes heating for evaporating the liquid dispersion medium that may be contained in the composition. In particular, the heat treatment for evaporating the water-soluble polymer and liquid dispersion medium in composition 1 can be carried out by holding the substrate to which composition 1 has been applied at a temperature equal to or higher than the volatilization temperature of the water-soluble polymer and liquid dispersion medium, and drying the liquid coating applied to the substrate. The heat treatment does not necessarily require complete evaporation of the water-soluble polymer and liquid dispersion medium. Specifically, the amounts of the water-soluble polymer and liquid dispersion medium to be evaporated are preferably 50% by mass or more, and more preferably 80% by mass or more, of the water-soluble polymer and liquid dispersion medium contained in composition 1.

[0072] The heat treatment for evaporating the liquid dispersion medium in the present 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.

[0073] Examples of heat treatment for firing include a method using an oven, a method using a ventilation drying furnace, and a method using heat rays such as infrared rays, and a method combining infrared heating and hot air heating may also be used. Firing may be carried out under either normal pressure or reduced pressure. The firing atmosphere may be any of an oxidizing gas atmosphere, a reducing gas atmosphere, and an inert gas atmosphere. The firing temperature is preferably 300 to 350°C, more preferably 310 to 340°C. The firing time is preferably 30 seconds to 30 minutes, more preferably 1 to 15 minutes. The firing temperature usually refers to the temperature of a dry atmosphere.

[0074] The application and heating of the composition to the substrate can be suitably carried out using an apparatus equipped with a dip coater and a baking furnace. Examples of the baking furnace include a vertical baking furnace and a glass cloth coating machine manufactured by Tabata Kikai Kogyo Co., Ltd.

[0075] <Substrate> Examples of the material for 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 crystalline polyester, and liquid crystalline polyesteramide), and prepregs (precursors of fiber-reinforced resin substrates). The shape of the substrate may be flat, curved, or uneven, and may further be any of foil, plate, film, and fiber.

[0076] One embodiment of the molded product of the present disclosure comprises, in this order in the thickness direction, 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. The explanations of the "substrate," "particles of resin A," and "water-soluble polymer" in such a molded product are the same as those given in the sections "Aqueous primer composition" and "Method for forming a primer layer," including definitions, examples, and preferred embodiments.

[0077] Another embodiment of the molded product of the present disclosure comprises, in this order in the thickness direction, 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. The explanations of "substrate," "particles A of resin A," and "particles B" in such a molded product are the same as those given in the sections "Aqueous primer composition" and "Method for forming a primer layer," including definitions, examples, and preferred embodiments.

[0078] <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.

[0079] Furthermore, the PTFE is preferably non-thermofusible. The term "non-thermofusible" means that the PTFE is not melt-moldable, i.e., does not exhibit melt flowability. Specifically, this means that the melt flow rate measured in accordance with ASTM D3307 at a temperature of 372°C and a load of 49N is less than 0.5 g / 10 min.

[0080] The thickness of the PTFE sheet is preferably 25 μm or more, more preferably 50 μm or more, and is preferably 1000 μm or less, more preferably 500 μm or less.

[0081] <Production of Molded Article> The molded article of the present disclosure can be produced by, for example, thermocompression bonding a PTFE sheet to a substrate having a fluororesin primer layer formed thereon. The thermocompression bonding conditions are preferably changed appropriately depending on the thickness of the molded article to be produced, but for example, the temperature is 170 to 450°C, the pressure is 1.5 to 5 MPa, and the time is 60 to 150 minutes.

[0082] The molded articles are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sports equipment, food industry supplies, paints, cosmetics, and the like, and specifically as electric wire coating materials (aircraft electric wires, etc.), electrical insulating tape, insulating tape for oil drilling, 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, covers for furniture, automobile dashboards, home appliances, etc., sliding members (load bearings, sliding shafts, valves, bearings, gears, cams, belt conveyors, food transport belts, etc.), tools (shovels, files, saws, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, dies, toilets, and container coating materials, and the like.

[0083] An embodiment of the present disclosure will be described in detail below, but the present disclosure is not limited to these embodiments.

[0084] <Particles of Resin A> [Particle A1] Particles A1 containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having a carbonyl group-containing group with a main chain carbon number of 1×10６ Particles (average particle diameter: 2.0 μm, specific surface area: 7.2 m) made of resin (melting temperature: 300°C) with 1000 particles per particle ２ / g) [Particle A2] Particles containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having a carbonyl group-containing group with a main chain carbon number of 1×10 ６ Particles (average particle diameter: 1.2 μm, specific surface area: 5.4 m) made of resin (melting temperature: 300°C) with 1000 particles per particle ２ / g) [Particle A3] Particles containing 97.9 mol %, 0.1 mol %, and 2.0 mol % of units based on TFE, NAH, and PPVE, respectively, and having a carbonyl group-containing group with a main chain carbon number of 1×10 ６ Particles (average particle diameter: 1.2 μm, specific surface area: 27.6 m) made of resin (melting temperature: 300°C) with 1000 particles per particle ２ / g) [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 this order and having no oxygen-containing polar group (i.e., PFA particles, average particle diameter: 2.0 μm, specific surface area: 9.3 m ２ / g)

[0085] <Water-soluble polymers> [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.

[0086] <Particles B> Particles (i.e., PFA particles, average particle size: 0.3 μm) of a resin (melting temperature: 300° C.) containing 97.5 mol % of units based on TFE and 2.5 mol % of units based on PPVE, in that order. The number of carbonyl group-containing groups contained in the resin of particles B is smaller than the number of carbonyl group-containing groups contained in any of the resins of particles A1 to A3.

[0087] <Base material> Aluminum

[0088] <Preparation 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 mass of particles A1 and 0.1% by mass 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 mass of particles A2 and 0.1% by mass 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 mass of particles A3 and 0.1% by mass 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 mass of particles A1 and 0.1% by mass 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 mass% of particles 4 and 0.1 mass% 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 aqueous primer composition 16 containing 20 mass% of particles 4 and 0.1 mass% of water-soluble polymer 2.

[0089] Example 1-1 Aqueous primer composition 11 was applied to an aluminum substrate by gravure printing, dried at 180° C., and then melt-baked 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., thereby producing a molded product.

[0090] <Examples 1-2 to 1-6> A primer layer having a thickness of 1 μm was obtained and a molded article 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.

[0091] <Evaluation of Defects and Flaws> The surfaces of the primer layers obtained in each example were observed and evaluated based on the following evaluation criteria, which are summarized in Table 1. In this disclosure, a defect is a state in which there are pinholes in the primer layer, and a defect is a state in which there are streaks in the primer layer and the thickness is uneven. (Evaluation Criteria) A: No defects or imperfections were found even when examined under a microscope. B: Minute defects were found that could be seen under a microscope. C: Visible defects were found.

[0092] <Evaluation of Adhesion> The molded product produced in each example was cut into a test piece 100 mm long and 10 mm wide. The test piece was fixed from one end to a position 50 mm in the longitudinal direction, and the aluminum substrate and the PTFE sheet were peeled from the other end of the test piece at a pulling rate of 50 mm / min and a peel angle of 90°. The maximum load (N / cm) during peeling was measured and evaluated based on the following evaluation criteria, which 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.

[0093]

[0094] <Preparation of Aqueous Primer Composition (Part 2)> [Aqueous Primer Composition 21] Aqueous dispersions of particles A1 and particles B were mixed by shearing in a bead mill to prepare aqueous primer composition 21 containing 15% by mass of particles A1 and particles B, respectively. [Aqueous Primer Composition 22] Aqueous dispersions of particles A2 and particles B were mixed by shearing in a bead mill to prepare aqueous primer composition 22 containing 15% by mass of particles A2 and particles B, respectively. [Aqueous Primer Composition 23] Aqueous dispersions of particles A3 and particles B were mixed by shearing in a bead mill to prepare aqueous primer composition 23 containing 15% by mass of particles A3 and particles B, respectively. [Aqueous Primer Composition 24] Particles A1 and water were mixed to prepare aqueous primer composition 24 containing 30% by mass of particles A1. [Aqueous Primer Composition 25] Particles B and water were mixed to prepare aqueous primer composition 25 containing 30% by mass of particles B.

[0095] Example 2-1 Aqueous primer composition 21 was applied to an aluminum substrate by gravure printing, dried at 180° C., and then melt-baked 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., thereby producing a molded product.

[0096] <Examples 2-2 to 2-5> A primer layer having a thickness of 1 μm was obtained and a molded article was produced in the same manner as in Example 2-1, except that aqueous primer composition 22 was used in Example 2-2, aqueous primer composition 23 in Example 2-3, aqueous primer composition 24 in Example 2-4, and aqueous primer composition 25 in Example 2-5 were used as the aqueous primer composition.

[0097] The primer layers or molded articles obtained in each example were subjected to "evaluation of defects and imperfections" and "evaluation of adhesion" according to the procedures described above. The results are summarized in Table 2.

[0098]

[0099] 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 were specifically and individually stated to be incorporated by reference.

Claims

1. An aqueous primer composition comprising: at least one selected from the group consisting 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; a water-soluble polymer having a weight-average molecular weight of 50,000 or more; 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 water.

2. An aqueous primer composition comprising 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 water.

3. The specific surface area of ​​the particle A is 6 m ２ The aqueous primer composition according to claim 1 or 2, wherein the viscosity is 100 MPa or more.

4. An aqueous primer composition as described in claim 1 or 2, wherein the content of particles A is more than 0 mass% and not more than 40 mass% relative to the total mass of the aqueous primer composition.

5. 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.

6. 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.

7. 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.

8. 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 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 specific surface area of ​​the particle A is 6 m ２ The aqueous primer composition according to claim 9, wherein the molecular weight of the aqueous primer composition is 1 / g or more.

11. An aqueous primer composition as described in claim 1 or 9, wherein the total amount of the content by mass of said particles A and the content by mass of said particles B is more than 0 mass% and not more than 40 mass% relative to the total mass of said aqueous primer composition.

12. The aqueous primer composition according to claim 1 or 9, wherein the average particle diameter (D50) of said particles A is 2 to 10 times the average particle diameter (D50) of said particles B.

13. 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.

14. 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.

15. A molded article comprising, in the thickness direction, a substrate, a fluororesin primer layer containing 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.

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