Coating composition and coated article

Abstract

The present invention provides a coating composition capable of inhibiting foaming in the composition, thereby capable of forming a coating with good film properties, and a coated article. A coating composition characterized in that a heat-resistant resin (A), a non-melt-processible fluorine-containing polymer (B), and a melt-processible fluorine-containing polymer (C) are dispersed in a water medium, the average particle diameter of the resin particles of (A) to (C) is 0.1 to 10 μm, and the coating composition substantially does not contain methyl cellulose.

Description

TECHNICAL FIELD

[0001] The present application relates to a coating composition and a coated article. BACKGROUND

[0002] Fluororesins such as polytetrafluoroethylene, tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, etc. have low friction coefficient, and excellent properties such as non-stickiness, heat resistance, etc., and thus are widely used for surface processing of food industry articles, cooking utensils such as frying pans, pots, etc., household articles such as irons, etc., electrical industry articles, mechanical industry articles, etc.

[0003] Patent Document 1 discloses a coating composition containing a polyether sulfone resin, a polyimide-based resin, a non-melt-processable fluoropolymer, and a melt-processable fluoropolymer.

[0004] Patent Document 2 discloses a coating composition containing a fluororesin, a heat-resistant binder, and a heat stabilizer.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2020-176216

[0008] Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2003-53261 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] An object of the present application is to provide a coating composition and a coated article which can suppress foaming in the composition, and thus can form a coating having good film properties.

[0011] MEANS FOR SOLVING THE PROBLEMS

[0012] The present application relates to a coating composition characterized in that a heat-resistant resin (A), a non-melt-processable fluoropolymer (B), and a melt-processable fluoropolymer (C) are dispersed in a water medium,

[0013] The average particle diameter of the resin particles of (A) to (C) is 0.1 to 10 μm, and the coating composition substantially does not contain methyl cellulose.

[0014] The above heat-resistant resin (A) is preferably a polyamide-imide and / or a polyimide (A-1).

[0015] The above heat-resistant resin (A) is preferably a polyamide-imide and / or a polyimide (A-1) and a polyether sulfone (A-2).

[0016] The heat-resistant resin (A) is preferably a polyamide-imide and / or polyimide (A-1) and a polyether sulfone (A-2) in a mass ratio ((A-1) : (A-2)) of 85 : 15 to 65 : 35.

[0017] The polyether sulfone and the polyamide-imide and / or polyimide (A) are in a mass ratio ((A) : (B) + (C)) of 15 : 85 to 35 : 65 relative to the total amount of the non-melt-processible fluorine-containing polymer (B) and the melt-processible fluorine-containing polymer (C).

[0018] The non-melt-processible fluorine-containing polymer (B) is preferably polytetrafluoroethylene and / or modified polytetrafluoroethylene.

[0019] The melt-processible fluorine-containing resin polymer (C) is preferably tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and / or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0020] The coating composition preferably further contains a non-ionic surfactant having an HLB of 10 or less.

[0021] The coating composition is preferably directly applied to a substrate composed of a metal or a non-metal inorganic material or to a layer composed of a heat-resistant resin.

[0022] The present application also relates to a coated article characterized by having: a substrate; a base coat layer formed by directly applying the coating composition to the substrate; and a top coat layer containing a fluorine-containing polymer.

[0023] The coated article can further have a middle coat layer between the base coat layer and the top coat layer.

[0024] Effects of the Invention

[0025] According to the present application, a coating having excellent film properties can be formed. DETAILED DESCRIPTION

[0026] The present application will be described in detail below.

[0027] The present application relates to a coating composition in which a heat-resistant resin (A), a non-melt-processible fluorine-containing polymer (B), and a melt-processible fluorine-containing polymer (C) are dispersed in an aqueous medium,

[0028] The resin particles of (A) to (C) have an average particle diameter of 0.1 μm to 10 μm, and

[0029] The coating composition substantially does not contain methyl cellulose.

[0030] In order to ensure the paintability, the coating composition containing the components of (A) to (C) described above generally adds methyl cellulose as a thickening agent. However, the coating composition containing such methyl cellulose generates foaming in the spray process, which sometimes adversely affects the coating film properties.

[0031] Therefore, the present application is characterized by substantially not containing methyl cellulose. Thus, surprisingly, it is possible to suppress the foaming of the paint at the time of spraying. The methyl cellulose dissolves in the medium to increase the viscosity of the medium, and stabilizes the generated bubbles, but it is presumed that the viscosity of the medium is reduced by substantially not containing methyl cellulose, and the bubble breaking is accelerated. It is also preferable from the aspect of not generating problems such as deterioration of the coating film properties due to foaming. Specifically, if the foaming is less, the voids of the coating film are reduced, and thus the corrosion resistance of the coating film is improved. Here, substantially not containing methyl cellulose means that the amount of methyl cellulose is less than 0.050 mass% with respect to the total amount of the paint. The amount of the above-described methyl cellulose is more preferably 0.025 mass% or less. In addition, it is also possible not to contain methyl cellulose.

[0032] As described above, the coating composition of the present application substantially does not contain methyl cellulose, and thus, if the viscosity is excessively reduced, the painting becomes difficult. Therefore, in order to adjust the viscosity, it is preferable to contain a nonionic surfactant having an HLB of 10 or less. By using such a lipophilic nonionic surfactant, the viscosity of the coating composition is increased, and thus, it is preferable from the aspect of good paintability. Furthermore, it also has the effect of improving the mechanical stability of the fluorine-containing polymer and the heat-resistant resin dispersed in water, and improving the wettability to the metal to be coated at the time of painting.

[0033] In the present application, the HLB is a value obtained by Griffin's method from the following formula.

[0034] HLB = 20 x [(molecular weight of the hydrophilic group contained in the surfactant) / (molecular weight of the surfactant)]

[0035] In the coating composition of the present application, the chemical structure of the nonionic surfactant is not particularly limited, and specifically, non-alkyl phenol type nonionic surfactants and the like can be given.

[0036] The non-alkyl phenol type nonionic surfactant is a nonionic surfactant that does not contain a benzene ring in the structure. For example, nonionic surfactants using natural alcohol of a polyoxyethylene alkyl ether system as a raw material and the like can be given.

[0037] The non-alkyl phenol type nonionic surfactant (b) is preferably the following general formula (I):

[0038] R-O-A-H (I)

[0039] (wherein R represents a linear or branched, saturated or unsaturated, non-cyclic aliphatic hydrocarbon group having 8 to 19 carbon atoms or a saturated cyclic aliphatic hydrocarbon group having 8 to 19 carbon atoms. A represents a polyoxyalkylene chain having 3 to 25 ethylene oxide units and 0 to 5 propylene oxide units).

[0040] As the nonionic surfactant represented by the above general formula (I), the following general formula (II) is preferable:

[0041] C x H 2x+1 CH(C y H 2y+1 )C z H 2z O(C2H4O) n H(II)

[0042] a polyoxyethylene alkyl ether surfactant represented by the following general formula (III) :

[0043] the following general formula (III) :

[0044] C x H 2x+1 -O-A-H(III)

[0045] a polyoxyethylene alkyl ether surfactant represented by the following general formula (III) :

[0046] In the coating composition of the present application, the mixing amount of the nonionic surfactant having an HLB of 10 or less is preferably 2.0 to 10.0 mass% relative to the total amount of the coating composition. The above lower limit is preferably 2.5 mass%, further preferably 3.0 mass%. The above upper limit is preferably 9.0 mass%, further preferably 8.0 mass%. The mixing amount of the nonionic surfactant having an HLB of 11 or more is not particularly limited, and is preferably 1.0 to 5.0 mass% relative to the total amount of the coating composition.

[0047] The coating composition of the present application is in a state where the heat-resistant resin (A), the non-melt-processable fluorine-containing polymer (B), and the melt-processable fluorine-containing polymer (C) are dispersed in a water medium. Furthermore, the average particle diameter of the resin particles of these (A) to (C) is 0.1 to 10 μm. By being in this range, good dispersibility can be obtained, the stability of the composition can be obtained, and the properties of the coating film can be improved.

[0048] The specific method for making the average particle diameter of the resin particles of (A) to (C) 0.1 to 10 μm is not particularly limited, and can be performed by combining each component of (A) to (C) used as a raw material, each of which is in the range of 0.1 to 10 μm.

[0049] The average particle diameter of the resin particles was measured by a particle size distribution measuring device based on laser diffraction (Microtrac MT-3000EXII manufactured by Microtrac BEL Corp.). The average particle diameter (50% cumulative particle diameter) was automatically calculated by the device.

[0050] Hereinafter, each component of (A) to (C) is described in detail.

[0051] The heat-resistant resin (A) refers to a resin that can be continuously used under conditions of 150°C or higher. As such a resin, a resin other than a fluorine-containing resin can be cited. Note that the fluorine-containing resin corresponding to (B), (C) does not correspond to the heat-resistant resin (A).

[0052] More specifically, aromatic polyether ketone resins such as polyether ether ketone resin, polyphenylene sulfide resin, polyaryl ether ketone (PAEK), polyether ketone ketone (PEKK), polyether ketone (PEK), and polyether ether ketone ketone (PEEKK), polyether sulfone (PES), liquid crystal polymer (LCP), polysulfone (PSF), amorphous polyarylate (PAR), polyether nitrile (PEN), thermoplastic polyimide (TPI), polyimide (PI), polyether imide (PEI), polyamide imide (PAI), and the like can be cited.

[0053] Among them, polyamide imide and / or polyimide (A-1) is particularly preferable from the aspect of excellent adhesion to metals.

[0054] Further, the heat-resistant resin (A) can be used in combination of polyamide imide and / or polyimide (A-1) and polyether sulfone (A-2). By using these resins in combination, it is preferable from the aspect that the corrosion resistance and the steam resistance of the coating can be balanced.

[0055] In this case, the mass ratio of polyamide imide and / or polyimide (A-1) to polyether sulfone (A-2) ((A-1):(A-2)) is preferably 85:15 to 65:35. By being in this range, it is preferable from the aspect that the corrosion resistance and the steam resistance of the coating are good. The above range is more preferably 80:20 to 70:30.

[0056] The above-mentioned polyamide-imide (PAI) is a resin composed of a polymer having an amide bond and an imide bond in the molecular structure. As the PAI, there are no particular limitations, and examples that can be given include resins composed of a high-molecular-weight polymer obtained by each reaction such as a reaction of an aromatic diamine having an amide bond in the molecule with an aromatic tetracarboxylic acid such as pyromellitic acid, a reaction of an aromatic tri-carboxylic acid such as trimellitic anhydride with a diamine such as 4,4-diaminophenyl ether or a diisocyanate such as diphenylmethane diisocyanate, and a reaction of a dibasic acid having an aromatic imide ring in the molecule with a diamine. From the aspect that the heat resistance is excellent, as the PAI, a polymer having an aromatic ring in the main chain is preferable.

[0057] The above-mentioned polyimide (PI) is a resin composed of a polymer having an imide bond in the molecular structure. As the PI, there are no particular limitations, and examples that can be given include resins composed of a high-molecular-weight polymer obtained by a reaction of an aromatic tetracarboxylic anhydride such as pyromellitic anhydride, and the like. From the aspect that the heat resistance is excellent, as the PI, a polymer having an aromatic ring in the main chain is preferable.

[0058] The above-mentioned polyether sulfone resin (PES) is a resin composed of a polymer having a repeating unit represented by the formula:

[0059] [Chemical Formula 1]

[0060]

[0061] The above-mentioned polyether sulfone resin (PES) is a resin composed of a polymer having a repeating unit represented by the formula:

[0062] The above-mentioned aromatic polyether ketone resin is a resin including a repeating unit composed of an arylene group, an ether group [-0-], and a carbonyl group [-C(=0)-]. As the aromatic polyether ketone resin, polyether ketone resin (PEK), polyether ether ketone resin (PEEK), polyether ether ketone ketone resin (PEEKK), polyether ketone ester resin, and the like can be exemplified. The above-mentioned aromatic polyether ketone resin can be used alone as one kind or in combination as two or more kinds.

[0063] As the aromatic polyether ketone resin, at least one kind selected from the group consisting of PEK, PEEK, PEEKK, and polyether ketone ester resin is preferable, and PEEK is more preferable.

[0064] The coating composition of the present application further comprises a non-melt processable fluoropolymer (B). "Non-melt processable" refers to the property that the melt flow rate cannot be measured at a temperature higher than the melting point according to ASTM D-1238 and D-2116.

[0065] The aforementioned non-melt-processable fluorine-containing polymer (B) is preferably non-melt-processable polytetrafluoroethylene (PTFE).

[0066] The aforementioned non-melt-processable PTFE preferably has fibrillation property. The aforementioned fibrillation property refers to a property of being easily fiberized to form fibrils. Whether or not the non-melt-processable PTFE has fibrillation property can be determined by a representative method of molding a powder made of a polymer of TFE, i.e., "high molecular weight PTFE powder", i.e., "paste extrusion". This is because, generally, when paste extrusion is possible, the high molecular weight PTFE has fibrillation property. In a case where the un-baked molded product obtained by the paste extrusion does not have substantial strength or elongation, for example, in a case where the elongation is 0% and the product is broken if stretched, it can be considered that the non-melt-processable PTFE does not have fibrillation property.

[0067] The aforementioned non-melt-processable PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.230. The aforementioned SSG is more preferably 2.130 to 2.190, and further preferably 2.140 to 2.170. When the SSG of the aforementioned non-melt-processable PTFE is within the aforementioned range, a coating film having more excellent corrosion resistance can be formed. The SSG is a value determined in accordance with ASTM D 4895.

[0068] The aforementioned non-melt-processable PTFE preferably has a peak top (DSC melting point) of 333°C to 347°C in a heat of fusion curve obtained by using a differential scanning calorimeter at a temperature increase rate of 10°C / minute for the aforementioned non-melt-processable PTFE without heating to a temperature of 300°C or more. The peak top is more preferably 333°C to 345°C, and further preferably 340°C to 345°C. When the peak top (DSC melting point) is within the aforementioned range, a coating film having more excellent corrosion resistance can be formed.

[0069] If explained more specifically, for example, in the aforementioned differential scanning calorimetry (DSC), RDC220 (manufactured by SII Nanotechnology Inc.) that has been temperature-calibrated in advance using indium, lead as standard samples is used, about 3 mg of PTFE powder is charged into an aluminum pan (crimped container), and temperature increase is performed at a temperature range of 250°C to 380°C at 10°C / minute under an air flow of 200 ml / minute. Note that the heat calibration is performed using indium, lead, tin as standard samples, and the aforementioned aluminum pan that is empty in the measurement reference is sealed and used. For the obtained heat of fusion curve, using Muse standard analysis software (manufactured by SII Nanotechnology Inc.), the temperature at which the peak of the heat of fusion is shown is taken as the DSC melting point.

[0070] The non-melt-processable PTFE is preferably at least one selected from the group consisting of a tetrafluoroethylene homopolymer (hereinafter also referred to as "homopolymer PTFE") and a modified polytetrafluoroethylene (hereinafter also referred to as "modified PTFE").

[0071] The modified PTFE is a modified PTFE composed of tetrafluoroethylene (TFE) and a monomer other than TFE (hereinafter also referred to as "modified monomer").

[0072] As the modified monomer, there is no particular limitation as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrofluoroolefins such as trifluoroethylene, vinylidene fluoride (VDF); perfluorovinyl ethers; perfluoroalkyl ethylenes; and ethylene. In addition, the modified monomer used can be one or a plurality of types.

[0073] As the perfluorovinyl ether, there is no particular limitation, and examples thereof include perfluoro unsaturated compounds represented by the following general formula (1)

[0074] CF2=CF-ORf 1 (1)

[0075] (in the formula, Rf 1 represents a perfluoro organic group) and the like. In the present specification, the "perfluoro organic group" means an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group can have an ether oxygen.

[0076] As the perfluorovinyl ether, there is no particular limitation, and examples thereof include perfluoro(alkyl vinyl ethers) (PAVE) in which Rf 1 in the above general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms of the perfluoroalkyl group is preferably 1 to 5.

[0077] As the perfluoroalkyl group in the PAVE, examples thereof include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, and the like, and the perfluoroalkyl group is preferably a perfluoropropyl group. That is, the PAVE is preferably perfluoropropyl vinyl ether (PPVE).

[0078] As the perfluorovinyl ether, there is no particular limitation, and examples thereof include perfluoro(alkyl vinyl ethers) (PAVE) in which Rf 1 in the above general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms of the perfluoroalkyl group is preferably 1 to 5. 1 is the following formula:

[0079] [Chem. 2]

[0080]

[0081] a perfluoro vinyl ether represented by a group represented by the formula: CF3(CF2)„CF=CF2 (in the formula, m represents 0 or an integer of 1 to 4) ; Rf 1 is the following formula:

[0082] [Chemical 3]

[0083]

[0084] a perfluoro vinyl ether represented by a group represented by the formula: CF3(CF2)„CF=CF2 (in the formula, m represents 0 or an integer of 1 to 4) ; Rf

[0085] As the perfluoroalkyl ethylene (PFAE), for example, perfluoro butyl ethylene (PFBE), perfluoro hexyl ethylene, and the like can be given.

[0086] As the modified monomer in the above modified PTFE, at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene is preferable. PAVE is more preferable, and PPVE is further preferable.

[0087] The above homopolymer PTFE contains substantially only TFE units, and for example, a homopolymer PTFE obtained without using a modified monomer is preferable.

[0088] The modified monomer unit of the above modified PTFE is preferably 0.001 to 2 mol%, and more preferably 0.001 to 1 mol%.

[0089] The content of each monomer unit of the above non-melt-processable fluorine-containing polymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescence X-ray analysis according to the kind of the monomer.

[0090] The coating composition of the present application further contains a melt-processable fluorine-containing polymer (C). The above "melt-processability" means that the polymer can be melted and processed using existing processing equipment such as an extruder and an injection molding machine. Therefore, the melt flow rate (MFR) of the above melt-processable fluorine-containing polymer is usually 0.01 to 100 g / 10 minutes.

[0091] In the present specification, the above MFR is a value obtained by measuring the mass (g / 10 minutes) of the polymer flowing out from a nozzle having an inner diameter of 2 mm and a length of 8 mm per 10 minutes at a measurement temperature (for example, 372°C in the case of PFA and FEP, and 297°C in the case of ETFE) and a load (for example, 5 kg in the case of PFA, FEP, and ETFE) determined according to the kind of the fluorine-containing polymer in accordance with ASTM D 1238 using a melt flow indexer (manufactured by Seishin Enterprise Co., Ltd.), and taking the obtained value as the MFR.

[0092] The melting point of the melt-processable fluorine-containing polymer (C) is preferably 100°C to 333°C, more preferably 140°C or higher, further preferably 160°C or higher, particularly preferably 180°C or higher. In addition, it is more preferably 332°C or lower, further preferably less than 322°C, particularly preferably 320°C or lower.

[0093] In the present specification, the melting point of the melt-processable fluorine-containing polymer is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is raised at a rate of 10°C / minute using a differential scanning calorimeter [DSC].

[0094] As the melt-processable fluorine-containing polymer, at least one selected from the group consisting of low molecular weight PTFE, TFE / PAVE copolymer (PFA), TFE / HFP copolymer (FEP), ethylene (Et) / TFE copolymer (ETFE), Et / TFE / HFP copolymer, polychlorotrifluoroethylene (PCTFE), CTFE / TFE copolymer, Et / CTFE copolymer, and polyvinylidene fluoride (PVDF) can be given.

[0095] From the viewpoint of obtaining a coating film having more excellent corrosion resistance, the melt-processable fluorine-containing polymer (C) is preferably at least one selected from the group consisting of FEP and PFA, more preferably FEP.

[0096] The FEP is not particularly limited, and a copolymer having a molar ratio of TFE units to HFP units (TFE units / HFP units) of 70 / 30 or higher and less than 99 / 1 is preferred. A more preferred molar ratio is 70 / 30 or higher and 98.9 / 1.1 or lower, and a further preferred molar ratio is 80 / 20 or higher and 98.9 / 1.1 or lower. If the TFE units are too few, the mechanical properties tend to decrease, and if they are too many, the melting point is too high and the moldability tends to decrease. The FEP is also preferably a copolymer in which the monomer units derived from a monomer copolymerizable with TFE and HFP are 0.1 mol% to 10 mol%, and the TFE units and the HFP units in total are 90 mol% to 99.9 mol%. As the monomer copolymerizable with TFE and HFP, PAVE, CF2=CF-OCH2-Rf 2 (In the formula, Rf 2 represents a perfluoroalkyl group having 1 to 5 carbon atoms) and the like.

[0097] The melting point of the FEP is preferably 150°C to less than 322°C, more preferably 200°C to 320°C, and further preferably 240°C to 320°C.

[0098] The MFR of the FEP is preferably 1 g / 10 minutes to 100 g / 10 minutes.

[0099] The thermal decomposition initiation temperature of the aforementioned FEP is preferably 360°C or higher. More preferably, it is 380°C or higher, and even more preferably, it is 390°C or higher.

[0100] In this specification, the thermal decomposition onset temperature is determined by using a differential thermal-thermogravimetric analysis (TG-DTA) device (trade name: TG / DTA6200, manufactured by SEIKO Electronics Co., Ltd.) to heat 10 mg of the sample from room temperature at a heating rate of 10 °C / min, resulting in a temperature reduction of 1% by mass of the sample.

[0101] The PFA is not particularly limited, but preferably a copolymer with a TFE unit to PAVE unit molar ratio (TFE unit / PAVE unit) of 70 / 30 or more and less than 99 / 1. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and a further preferred molar ratio is 80 / 20 or more and 98.9 / 1.1 or less. If there are too few TFE units, the mechanical properties tend to decrease; if there are too many, the melting point is too high, and the moldability tends to decrease. The PFA is also preferably a copolymer from monomers capable of copolymerizing with TFE and PAVE in which the monomer units are 0.1 mol% to 10 mol%, and the total TFE and PAVE units are 90 mol% to 99.9 mol%. Examples of monomers capable of copolymerizing with TFE and PAVE include HFP and CZ. 1 Z 2 =CZ 3 (CF2) n Z 4 (where Z) 1 Z 2 and Z 3 Same or different, indicating hydrogen or fluorine atoms, Z 4 Vinyl monomers (representing hydrogen, fluorine, or chlorine atoms, where n represents an integer from 2 to 10) and CF2=CF-OCH2-Rf 2 (where Rf) 2 Alkyl perfluorovinyl ether derivatives, etc., representing perfluoroalkyl groups with 1 to 5 carbon atoms.

[0102] The melting point of the PFA is preferably 180℃ to less than 322℃, more preferably 230℃ to 320℃, and even more preferably 280℃ to 320℃.

[0103] The melt flow rate (MFR) of the above-mentioned PFA is preferably 1 g / 10 min to 100 g / 10 min.

[0104] The thermal decomposition initiation temperature of the aforementioned PFA is preferably 380°C or higher. More preferably, it is 400°C or higher, and even more preferably 410°C or higher.

[0105] The content of each monomer unit of the above-mentioned melt-processible fluoropolymer can be calculated by suitably combining NMR, FT-IR, elemental analysis, and fluorescence X-ray analysis according to the kind of the monomer.

[0106] The average particle diameter of the above-mentioned non-melt-processible fluoropolymer and the above-mentioned melt-processible fluoropolymer is preferably 0.01 μm to 40 μm from the viewpoint of dispersion stability in the above-mentioned coating composition and surface smoothness of the resulting coating film. The average particle diameter is more preferably 0.05 μm or more and more preferably 20 μm or less, further preferably 10 μm or less, particularly preferably 5 μm or less.

[0107] The above-mentioned average particle diameter can be measured by a laser scattering method.

[0108] The mass ratio of the total amount of the above-mentioned PES and the above-mentioned polyimide-based resin to the total amount of the above-mentioned non-melt-processible fluoropolymer and the above-mentioned melt-processible fluoropolymer is preferably 15 / 85 to 35 / 65 from the viewpoint of obtaining a coating film having more excellent corrosion resistance. The mass ratio is more preferably 20 / 80 or more and more preferably 30 / 70 or less.

[0109] In addition, the mass ratio of the above-mentioned non-melt-processible fluoropolymer to the above-mentioned melt-processible fluoropolymer is preferably 5 / 95 to 95 / 5 from the viewpoint of obtaining a coating film having more excellent corrosion resistance. The mass ratio is more preferably 20 / 80 or more, further preferably 30 / 70 or more, still more preferably 40 / 60 or more, particularly preferably 50 / 50 or more, and more preferably 90 / 10 or less, further preferably 80 / 20 or less, particularly preferably 70 / 30 or less.

[0110] The coating composition of the present application is in a state where the above-mentioned resin particles are dispersed in an aqueous medium.

[0111] The coating composition of the present application can contain an organic solvent. The above-mentioned organic solvent is an organic compound, and is preferably a liquid at ordinary temperature of about 20°C.

[0112] As the above-mentioned organic solvent, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-alkoxy-N,N-dimethylpropionamide, γ-butyrolactone, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, dimethylacetamide, dimethylformamide, N-formylmorpholine, N-acetylmorpholine, dimethylpropylurea, anisole, diethyl ether, ethylene glycol, phenylacetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, xylene, toluene, ethanol, 2-propanol, and the like can be given, and one or two or more kinds thereof can be used.

[0113] The above organic solvent is preferably at least one selected from the group consisting of N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-alkyloxy-N,N-dimethylpropanamide, gamma-butyrolactone, dimethylsulfoxide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, dimethylacetamide, dimethylformamide, N-formylmorpholine, N-acetylmorpholine, dimethylpropylene urea, anisole, diethyl ether, ethylene glycol, acetophenone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, xylene, toluene, ethanol and 2-propanol, more preferably at least one selected from the group consisting of N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-alkyloxy-N,N-dimethylpropanamide, gamma-butyrolactone, dimethylsulfoxide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, dimethylacetamide, dimethylformamide, N-formylmorpholine, N-acetylmorpholine and dimethylpropylene urea, further preferably at least one selected from the group consisting of N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-alkyloxy-N,N-dimethylpropanamide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, N-formylmorpholine, N-acetylmorpholine and dimethylpropylene urea.

[0114] The above 3-alkyloxy-N,N-dimethylpropanamide is represented by N(CH3)2COCH2CH2OR 11 (R 11 is an alkyl group. The alkoxy group (R 11 The alkoxy group (R

[0115] The above organic solvent is also preferably one having a boiling point of 150°C or higher, more preferably 170°C or higher, further preferably 210°C or higher. This can delay the drying speed at the time of coating and improve the surface smoothness of the coating film.

[0116] The above boiling point is a value measured at 1 atmosphere (atm).

[0117] The above coating composition preferably has a solid content concentration of 5 to 70 mass%, more preferably 10 mass% or higher, more preferably 60 mass% or lower, further preferably 50 mass% or lower, particularly preferably 40 mass% or lower.

[0118] The coating composition of the present application can further contain various additives. As the above-mentioned additives, there are no particular limitations, and examples thereof include a filler, a leveling agent, a solid lubricant, an anti-settling agent, a moisture absorbent, a surfactant, a surface modifier, a thixotropy imparting agent, a viscosity modifier, an anti-gelation agent, a UV absorber, a light stabilizer, a plasticizer, an anti-tarnish agent, an anti-skinning agent, an anti-chip agent, an anti-mold agent, an antibacterial agent, an antioxidant, an antistatic agent, a silane coupling agent, a coloring agent (iron oxide, titanium dioxide, etc.), and the like.

[0119] In the coating composition of the present application, in order to impart properties, improve physical properties, increase thickness, and the like to the resulting coated article, as the above-mentioned additives, a filler can be contained. As the above-mentioned properties and physical properties, there are no particular limitations, and examples thereof include strength, durability, weather resistance, flame retardancy, aesthetic properties, and the like.

[0120] As the above-mentioned filler, there are no particular limitations, and examples thereof include wood flour, quartz sand, carbon black, clay, talc, diamond, fluorinated diamond, corundum, silica, boron nitride, boron carbide, silicon carbide, fused alumina, tourmaline, jadeite, germanium, zirconia, zirconium carbide, chrysoberyl, topaz, zoizite, garnet, body pigments, lustrous flat pigments, flaky pigments, glass, glass powder, mica powder, metal powder (gold, silver, copper, platinum, stainless steel, aluminum, and the like), various reinforcing materials, various thickening materials, electrically conductive fillers, and the like.

[0121] The content of the above-mentioned additives is preferably 0.01 to 10.0% by mass, and more preferably 0.1 to 5.0% by mass, relative to the above-mentioned coating composition.

[0122] The coating composition of the present application is more preferably a coating composition having a viscosity of 100 to 300 cP at 25°C at the time of application. By being substantially free of methyl cellulose, such a viscosity range can particularly suitably achieve the objects of the present application.

[0123] The coating composition of the present application can be used as a coating composition for forming a base coat layer in a coating method for forming a base coat layer and then a top coat layer containing a fluorine-containing polymer on a substrate. Hereinafter, such a coated article is sometimes referred to as a first coated article.

[0124] The above-mentioned first coated article can further have a middle coat layer between the above-mentioned base coat layer and the above-mentioned top coat layer. As the above-mentioned middle coat layer, there are no particular limitations, and it can be formed from a publicly known middle coat paint.

[0125] The coating composition of the present application can also be used as a coating composition for forming a middle coat layer of a multilayer coating film composed of a base coat layer containing a heat-resistant resin, a middle coat layer, and a top coat layer containing a fluorine-containing polymer. Hereinafter, such a coated article is sometimes referred to as a second coated article.

[0126] Note that this method of use is the same as in Japanese Patent Application Publication No. 2020-176216 filed by the present applicant, and the method of use can be the same as that described in the prior document.

[0127] As the substrate, for example, a substrate composed of a metallic or non-metallic inorganic material, preferably a substrate composed of a metal, more preferably a substrate composed of aluminum or stainless steel, can be used.

[0128] As the metal, metallic elements such as iron, aluminum, copper, and alloys thereof can be given. As the alloy, stainless steel and the like can be given.

[0129] As the non-metallic inorganic material, enamel, glass, ceramic, and the like can be given.

[0130] The substrate can contain other materials in addition to the metallic or non-metallic inorganic material.

[0131] The substrate can be subjected to surface treatment such as degreasing treatment, surface roughening treatment, and the like as needed. The method of surface roughening treatment is not particularly limited, and chemical etching using an acid or a base, anodizing (acid-resistant aluminum treatment), sandblasting, and the like can be given. The surface treatment can be appropriately selected depending on the kind of the substrate, the kind of the coating composition, and the like, and for example, sandblasting is preferred.

[0132] The substrate can also be subjected to degreasing treatment in which impurities such as oil are thermally decomposed and removed by air baking at 380°C. In addition, an aluminum substrate subjected to surface roughening treatment using an alumina abrasive after surface treatment can also be used.

[0133] The method of applying the coating composition to the substrate or the heat-resistant layer is not particularly limited, and in the case where the coating composition is in a liquid state, for example, spray coating, roll coating, coating using a doctor blade, dip coating, immersion coating, spin coating, curtain coating, and the like can be given, with spray coating being preferred. In the case where the coating composition is in a powder form, electrostatic coating, flow dip method, rotary inner liner method, and the like can be given, with electrostatic coating being preferred.

[0134] As described above, the present application achieves the inhibition of foaming by substantially not containing methyl cellulose, but the problem caused by foaming is particularly significantly generated in the case where spray coating is performed using a low-pressure atomizing coating gun having an atomizing pressure of less than 0.2 MPa. Therefore, the effect can be particularly appropriately exerted in the case where coating is performed by spray using a low-pressure atomizing gun.

[0135] After the coating of the above-mentioned coating composition, drying can be performed. The above-mentioned drying is preferably performed at a temperature of 70°C to 300°C for 5 minutes to 60 minutes. Further, baking at a temperature of 260°C to 410°C for 10 minutes to 30 minutes is preferred.

[0136] In the above-mentioned first coated article, when the coating composition of the present application is used for the formation of the primer layer, the film thickness of the primer layer is preferably 5 μm to 90 μm. If the film thickness is too thin, pinholes are likely to occur, and the corrosion resistance of the coated article can decrease. If the film thickness is too thick, cracks are likely to occur, and the water vapor resistance of the coated article can decrease. The more preferable upper limit of the film thickness when the primer layer is formed from a liquid composition is 60 μm, and the further preferable upper limit is 50 μm. The more preferable upper limit of the film thickness when the primer layer is formed from a powder-like composition is 80 μm, and the further preferable upper limit is 70 μm.

[0137] The above-mentioned first coated article has a primer layer and a top coat layer containing a fluorine-containing polymer. The above-mentioned top coat layer can be the same as the fluorine-containing layer described in detail in Japanese Patent Application Publication No. 2020-176216 filed by the present applicant.

[0138] The film thickness of the fluorine-containing layer is preferably 5 μm to 90 μm. If the film thickness is too thin, the corrosion resistance of the coated article can decrease. If the film thickness is too thick, in the case where the coated article is in the presence of water vapor, water vapor is likely to remain in the coated article, and the water vapor resistance can sometimes be poor. The more preferable upper limit of the film thickness when the fluorine-containing layer is formed from a liquid composition is 60 μm, the further preferable upper limit is 50 μm, and the particularly preferable upper limit is 40 μm. The more preferable upper limit of the film thickness when the fluorine-containing layer is formed from a powder-like composition is 80 μm, the further preferable upper limit is 75 μm, and the particularly preferable upper limit is 70 μm.

[0139] The primer layer is preferably in direct contact with the above-mentioned substrate.

[0140] The fluorine-containing layer can be in direct contact with the primer layer or can be in contact through another layer, and is preferably in direct contact.

[0141] The coating composition of the present application can provide a coating film having excellent corrosion resistance, and the first and second coated articles have excellent corrosion resistance. Therefore, the coating composition of the present application, and the first and second coated articles can be applied to all fields requiring corrosion resistance. The application is not particularly limited, and can be exemplified by applications utilizing the non-stickiness, heat resistance, slidability, etc. of fluorine-containing polymers. For example, as applications utilizing non-stickiness, there can be exemplified cooking utensils such as frying pans, pressure cookers, pots, striped frying pans, rice cookers, ovens, hot plates, toasters, kitchen knives, gas stoves, etc.; kitchenware such as electric kettles, ice-making trays, molds, range hoods, etc.; food industry parts such as mixing rolls, calender rolls, conveyors, feed hoppers, etc.; industrial goods such as OA (Office Automation) rolls, OA tapes, OA separating claws, papermaking rolls, calender rolls for film manufacturing, etc.; molds for foamed styrene molding, etc.; release of molding molds such as plywood / decorative board manufacturing release plates, etc.; industrial containers (particularly for semiconductor industry), etc., and as applications utilizing slidability, there can be exemplified medical guide wires, catheters, sheaths, catheter sheaths, etc., tools such as saws, files, etc.; household goods such as irons, scissors, kitchen knives, etc.; metal foils; electric wires; sliding bearings of food processors, packaging machines, textile machines, etc.; sliding parts of cameras / clocks; automobile parts such as tubes, valves, bearings, etc.; snow shovels; hoes; parachutes, etc.

[0142] The coating composition of the present application, and the first and second coated articles are preferably used for cooking utensils or kitchenware, more preferably for cooking utensils, and further preferably for rice cookers.

[0143] The first and second coated articles are also preferably cooking utensils, kitchenware, or constituent parts thereof, more preferably cooking utensils or constituent parts thereof, and further preferably rice cookers or constituent parts thereof.

[0144] Examples

[0145] The present application will be specifically described below based on examples.

[0146] In the following examples, "parts", "%" respectively mean "mass parts", "mass %", unless otherwise specified.

[0147] The average particle diameter was measured by a particle size distribution measuring device (Microtrac MT-3000EXII manufactured by Microtrac BEL) utilizing laser diffraction. The film thickness was measured using a high-frequency film thickness meter (trade name: LZ-300C, manufactured by Kett Science Institute).

[0148] Preparation of polyamide-imide resin aqueous dispersion (1)

[0149] A polyamide-imide resin [PAI] varnish (containing N-methyl-2-pyrrolidone (hereinafter referred to as NMP) 71%) having a solid content of 29% was put into water to precipitate the PAI. This was pulverized in a ball mill for 48 hours to obtain a PAI aqueous dispersion (average particle diameter 2 μm). The solid content of the obtained PAI aqueous dispersion was 20%.

[0150] Preparation of polyether sulfone resin aqueous dispersion (1) of Production Example 2

[0151] Polyether sulfone resin [PES] having a number average molecular weight of about 24,000 (60 parts) and deionized water (60 parts) were stirred in a ceramic ball mill for about 10 minutes until particles composed of the PES were completely pulverized. Next, NMP (180 parts) was added and further pulverized for 48 hours to obtain a dispersion. The obtained dispersion was further pulverized with a sand mill for 1 hour to obtain a PES aqueous dispersion (average particle diameter 2 μm) having a PES concentration of about 20%.

[0152] Production Example 3 (coating composition of the present application: Example 1)

[0153] To the PAI aqueous dispersion obtained in Production Example 1 was added a tetrafluoroethylene homopolymer [TFE homopolymer, hereinafter referred to as PTFE] aqueous dispersion (average particle diameter 0.28 μm, solid content 60%, containing a non-alkyl phenol type polyether nonionic surfactant as a dispersant at 6% relative to PTFE) and a tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter referred to as FEP) aqueous dispersion (average particle diameter 0.20 μm, solid content 60%, containing a non-alkyl phenol type polyether nonionic surfactant as a dispersant at 5% relative to FEP) so that the FEP was 8.4% of the PTFE in terms of the mass ratio of the solid contents, and a non-alkyl phenol type polyether nonionic surfactant (HLB value 9.5) as a thickening agent was added at 11% relative to the solid content of the polymers so as to be added at 25% of the total solid content of the PAI, PTFE and FEP, to obtain an aqueous dispersion having a solid content of 37% of the polymers (primer coating composition (1)).

[0154] Production Example 4 (coating composition of the present application: Examples 2, 3, 5)

[0155] The PES aqueous dispersion obtained in Production Example 2 and the PAI aqueous dispersion obtained in Production Example 1 were mixed so that PES was 75% of the total amount of solid components of PES and PAI, to which was added an aqueous dispersion of a tetrafluoroethylene homopolymer [TFE homopolymer, hereinafter referred to as PTFE] (average particle diameter 0.28 μm, solid component 60%, containing 6% of a non-alkyl phenol type polyether nonionic surfactant as a dispersant with respect to PTFE) and an aqueous dispersion of a tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter referred to as FEP) (average particle diameter 0.20 μm, solid component 60%, containing 5% of a polyether nonionic surfactant as a dispersant with respect to FEP) so that FEP was 50% of PTFE in terms of mass ratio of solid components, and PES and PAI were 25% of the total amount of solid components of PES, PAI, PTFE and FEP, and a non-alkyl phenol type polyether nonionic surfactant (HLB value 9.5) as a thickening agent was added at 11% with respect to the solid components of the polymers, to obtain an aqueous dispersion of 37% of the solid components of the polymers (primer coating covering composition (2)).

[0156] Production Example 5 (covering composition of the application: Example 4)

[0157] A primer coating covering composition (3) of 36% of the solid components of the polymers was obtained in the same manner as in Production Example 4 except that 0.068% of methyl cellulose was added with respect to the solid components of the polymers in Production Example 4.

[0158] Comparative Production Example 1

[0159] A primer coating covering composition (4) of 33% of the solid components of the polymers was obtained in the same manner as in Production Example 3 except that the thickening agent was replaced by a non-alkyl phenol type polyether nonionic surfactant (HLB value 9.5) and 0.61% of methyl cellulose was added with respect to the solid components of the polymers.

[0160] Comparative Production Example 2

[0161] A primer coating covering composition (5) of 33% of the solid components of the polymers was obtained in the same manner as in Production Example 4 except that the thickening agent was replaced by a non-alkyl phenol type polyether nonionic surfactant (HLB value 9.5) and 0.61% of methyl cellulose was added with respect to the solid components of the polymers.

[0162] Comparative Production Example 3

[0163] A primer coating covering composition (6) of 36% of the solid components of the polymers was obtained in the same manner as in Production Example 4 except that 0.14% of methyl cellulose was added with respect to the solid components of the polymers in Production Example 4.

[0164] <Manufacture of test panel>

[0165] The surface of an aluminum plate (A-1050P) cut into a length of 5 cm and a width of 10 cm and having a thickness of 1.5 mm was degreased with acetone, and then sandblasted so as to have a surface roughness Ra value of 2.5 μm to 4.0 μm as measured in accordance with JIS B 1982. After removing dust from the surface by air blowing, the base coating composition obtained in the production example and the comparative production example was sprayed so as to have a dry film thickness of about 10 μm using an RG-2 type gravity spray gun (trade name, manufactured by ANEST IWATA Co., Ltd., nozzle diameter 1.0 mm) at a spray pressure of 0.2 MPa. The coating film on the obtained aluminum plate was dried at 80°C to 100°C for 15 minutes, and cooled to room temperature.

[0166] On the obtained coating film, PTFE aqueous paint (Polyflon PTFE K-3700C21R manufactured by Daikin Industries, Ltd.) or PFA powder paint (Neoflon PFA ACX-34 manufactured by Daikin Industries, Ltd.) was applied.

[0167] As the intermediate coating of Example 5, a coating layer in which 2.0 mass% of silicon carbide was mixed in ACX-34 was applied, and as the top coating, a coating layer in which 1.5 mass% of glass flakes and 1.0 mass% of diamond powder were mixed in ACX-34 was applied.

[0168] In the case of the PTFE aqueous paint, spraying was performed using an RG-2 type gravity spray gun (trade name, manufactured by ANEST IWATA Co., Ltd., nozzle diameter 1.0 mm) at a spray pressure of 0.2 MPa, and baking was performed at 380°C for 20 minutes, and cooling was performed, and a PTFE layer having a film thickness of about 20 μm was formed as the top coating, whereby a test coated panel was obtained. The obtained test coated panel had a base coating layer and a top coating layer composed of PTFE formed on the aluminum plate.

[0169] In the case of the top coating being ACX-34, electrostatic coating was performed under conditions of an applied voltage of 40 KV and a pressure of 0.08 MPa, and baking was performed at 380°C for 20 minutes, and cooling was performed, and a PFA layer having a film thickness of about 40 μm was formed as the top coating, whereby a test coated panel was obtained. The obtained test coated panel had a base coating layer and a top coating layer composed of PFA formed on the aluminum plate.

[0170] In the case of the powder coating containing the filler material for the intermediate coating, ACX-34 containing silicon carbide was electrostatically coated under the conditions of an applied voltage of 40 KV and a pressure of 0.08 MPa, and then the top coating of ACX-34 containing glass flakes and diamond powder was electrostatically coated in the same manner. The test coated plate was obtained by baking at 380°C for 20 minutes, cooling, forming a layer of the PFA containing filler material (containing PFA 98% and silicon carbide 2%) having a film thickness of about 40 μm for the intermediate coating, and forming a layer of the PFA containing filler material (containing PFA 97.5%, glass flakes 1.5%, and diamond powder 1.0%) having a film thickness of about 5 μm for the top coating. The obtained test coated plate had a primer layer, an intermediate coating layer composed of PFA and silicon carbide, and a top coating layer composed of PFA, glass flakes, and diamond powder, formed on the aluminum plate. The corrosion resistance test was performed using the above obtained coated plate.

[0171] <evaluation method>

[0172] The following evaluations were performed.

[0173] (coating test of the primer coating composition)

[0174] After the surface of an aluminum plate (A-1050P) having a thickness of 1.5 mm cut into a length of 5 cm and a width of 10 cm was degreased with acetone, the primer coating composition obtained in the examples and comparative examples was spray coated using a W-101 type gravity spray gun (trade name, manufactured by ANEST IWATA Co., Ltd., nozzle diameter 1.2 mm) at a spray pressure of 0.1 MPa in such a manner that the dry film thickness was about 10 μm. The number of blisters immediately after coating was investigated.

[0175] (corrosion resistance test of the coated plate)

[0176] A cross cut reaching the substrate was formed on the coated film surface of the obtained test coated plate using a cutting knife. The test plate was immersed in a solution in which 20 g of the raw material of the relevant instant noodle (manufactured by Aiseibishoku Co., Ltd.) was dissolved in 1 liter of water, and the test plate on which the cross cut was made using the cutting knife was immersed at 70°C for 1000 hours, and the number of swellings at the cross cut portion was counted.

[0177] The score was given as follows.

[0178] 5 points: no swelling

[0179] 4 points: swelling (3 mm or less) of 3 or less

[0180] 3 points: swelling of 4 to 6, or swelling of 4 mm or more

[0181] 2 points: swelling of 7 to 10, or swelling of 10 mm or more, or swelling of 4 mm or more of 3 or more

[0182] 1 minute expansion is 11 or more

[0183] (coating viscosity)

[0184] The viscosity was measured using a B-type viscometer (TVB10 type, manufactured by Tokimec Industry Co., Ltd.) under the conditions of No. 2 rotor, 60 rpm, and 25°C.

[0185]

[0186] As shown by the results of Table 1 above, the coating composition of the present application suppresses foaming. Thus, a coating film having excellent coating film properties can be obtained.

[0187] Industrial applicability

[0188] The coating composition of the present application can be suitably used for applications requiring corrosion resistance, and can be particularly suitably used for cooking appliances or kitchenware.

Claims

1. A coating composition characterized in that, the heat-resistant resin (A), the non-melt-processable fluorine-containing polymer (B), and the melt-processable fluorine-containing polymer (C) are dispersed in a water medium, the average particle diameter of the resin particles of (A) to (C) is 0.1 μm to 10 μm, and a non-ionic surfactant having an HLB of 10 or less is contained, the coating composition substantially does not contain methyl cellulose.

2. The coating composition of claim 1, wherein, the heat-resistant resin (A) is a polyamide-imide and / or a polyimide (A-1).

3. The coating composition of claim 1, wherein, the heat-resistant resin (A) is a polyamide-imide and / or a polyimide (A-1) and a polyether sulfone (A-2).

4. The coating composition of claim 3, wherein, the mass ratio (A-1):(A-2) of the polyamide-imide and / or polyimide (A-1) to the polyether sulfone (A-2) is 85:15 to 65:35, the mass ratio (A):(B)+(C) of the total amount of the polyether sulfone to the polyamide-imide and / or polyimide (A) to the total amount of the non-melt-processable fluorine-containing polymer (B) and the melt-processable fluorine-containing polymer (C) is 15:85 to 35:

65.

5. The coating composition according to any one of claims 1 to 4, wherein the non-melt-processable fluorine-containing polymer (B) is a polytetrafluoroethylene and / or a modified polytetrafluoroethylene.

6. The coating composition according to any one of claims 1 to 5, wherein the melt-processable fluorine-containing resin polymer (C) is a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and / or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

7. The coating composition according to any one of claims 1 to 6, which is directly applied to a substrate composed of a metal or a non-metal inorganic material, or to a layer composed of a heat-resistant resin.

8. A coated article, characterized by, having: a substrate; a base coat layer formed by directly applying the coating composition according to any one of claims 1 to 7 to the substrate; and a top coat layer containing a fluorine-containing polymer.

9. The coated article according to claim 8, further having a middle coat layer between the base coat layer and the top coat layer.

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