T ITLE OF THE INVENTION

FLUORORESIN LIQUID COATING COMPOSITION

[0001] The present invention relates to a fluororesin liquid coating composition for a fluororesin coating which strongly adheres to both metal base materials and resin base materials and exhibits excellent steam resistance and corrosion resistance, a coating film formed by applying the same, and an article having the coating film.

BACKGROUND ART

[0002] Fluororesins have excellent heat resistance, chemical resistance, electrical properties, and mechanical properties as well as a very low coefficient of friction, nonadhesiveness, and water and oil repellency, and are therefore widely used in all industrial fields such as chemistry, machinery, and electrical machinery.

[0003] In particular, utilizing the non-adhesiveness and water and oil repellency of fluororesins, fluororesin coatings are used in various fields such as the coating of cooking equipment such as fry pans and rice cookers or fixing rolls/belts for fixing OA equipment toner, and the fields of use have further expanded in recent years to include inkjet nozzles, chemical plant equipment, and the like.

[0004] However, when coating various base materials with fluororesins, applying the fluororesins directly to the base materials is extremely difficult in that it results in adhesive failure due to the non-adhesive property of fluororesins. Therefore, when applying a fluororesin as a coating, an adhesive primer coating composition which is adhesive with respect to the base material and is also adhesive with respect to the fluororesin coating applied thereon has ordinarily been used.

[0005] Heat-resistant resins (so-called engineering plastics), which are adhesive with respect to base materials and can with stand high temperatures exceeding the melting point of fluororesins, are used as such primer coating compositions. For example, Patent Document 1 discloses precursors such as polyimides, polyamide imides, and polyether sulfones and fine particles such as polyphenylene sulfide.

[0006] In addition, aromatic polyether ketones are also known as similar heat- resistant resins in recent years. In Patent Document 2, for example, polyether ether ketone (PEEK) is used. Such a heat-resistant resin is called a binder.

[0007] On the other hand, an organic solvent (solvent-based coating) or water (water-based coating) is used as a medium for a fluororesin coating composition containing a primer coating composition, and water-based (aqueous) coating compositions are particularly preferably used in recent years from the perspective of environmental burden or harmfulness to the body. In an aqueous coating composition, a heat-resistant resin which imparts adhesiveness to the base material (binder) is ordinarily water-insoluble, so it is used in a form in which particles thereof are dispersed in a liquid of the coating composition.

[0008] As base materials to be coated with fluororesins - in particular, PTFE or PFA having excellent water and oil repellency - it has been common to use metal base materials capable of withstanding the process of heat-treating them to a temperature exceeding the melting point of the fluororesin to melt the materials and form a coating film, but there has recently been a demand for primer coating compositions that can be used to coat the base materials of heat-resistant engineering plastics.

[0009] In this case, it is preferable from the perspectives of coating productivity and user-friendliness for a primer coating composition to also be suitably usable for a metal base material, as in the case of conventional compositions.

[0010] The role of a primer is to bond the base material and the upper coating layer (topcoat) to one another and to maintain this bond for a long period of time, so it is considered preferable to form the coating film as thinly as possible while maintaining sufficient wear resistance or corrosion resistance. Further, from the perspective of forming a thin, smooth coating film, it is preferable to use a liquid coating rather than a powder coating. A liquid coating can also be easily applied to fine structures, which is preferable in that the versatility with respect to target products increases.

[0011] In addition, depending on the required performance, a coating composition containing a fluororesin and a binder, like a primer coating composition, may also be applied in a single layer to a base material and used directly. Such a coating composition is called a one-coat coating and has been in increasing demand in recent years.

[0012] A fluororesin coating composition using a water-soluble polyamide imide and a polyether sulfone resin has been proposed as a primer liquid coating composition exhibiting excellent steam resistance and corrosion resistance (Patent Document 3).

[0013] In addition, Patent Document 4 proposes a fluororesin coating composition in which a water-soluble polyamide imide containing 3,3'-dimethylbiphenyl-4,4'- diisocyanate and/or 3,3'-dimethylbiphenyl-4,4'-diamine as structural units is used to enhance the steam resistance or the like of the coating film that is formed.

[0014] Further, Patent Document 2 proposes a coating exhibiting sufficient adhesiveness even with respect to a stainless steel (SUS) base material, the coating containing a water-soluble polyamide imide resin, a polyether ether ketone, and a fluororesin, wherein the fluororesin is a perfluororesin.

[0015] However, with conventional binders, it has not been possible to obtain a primer coating composition or a one-coat coating that can be suitably used for both heat-resistant engineering plastic base materials and metal base materials.

(PATENT DOCUMENTS)

[0016] (PATENT DOCUMENT 1 ) Japanese Examined Patent Application Publication No. H4-71951

[0017] (PATENT DOCUMENT 2) Japanese Unexamined Patent Application Publication No. 2021-91754

[0018] (PATENT DOCUMENT 3) Japanese Patent No. 4534916

[0019] (PATENT DOCUMENT 4) WO 2016/175099

SUMMARY OF THE INVENTION

TECHNICAL PROBLEMS

[0020] An object of the present invention is to provide a fluororesin liquid coating composition for a fluororesin coating which strongly adheres to both metal base materials and resin base materials and exhibits excellent steam resistance and corrosion resistance, a coating film formed by applying the same, and an article having the coating film.

MEANS FOR SOLVING THE PROBLEM

[0021] To achieve the object described above, the fluororesin liquid coating composition of the present invention contains a fluororesin and a polyetherketoneketone (PEKK).

[0022] Specifically, the present invention is as follows.

(1) A fluororesin liquid coating composition containing a fluororesin and a polyetherketoneketone (PEKK).

(2) The fluororesin liquid coating composition according to (1 ), which is an aqueous coating composition. (3) The fluororesin liquid coating composition according to (1 ) or (2), wherein the fluororesin content is from 35 to 90 mass% of the total amount of binder resins including PEKK and other resins.

(4) The fluororesin liquid coating composition according to (1 ) to (3), wherein the fluororesin is polytetrafluoroethylene or a heat-meltable perfluoro fluororesin.

(5) The fluororesin liquid coating composition according to (1 ) to (4) containing both polytetrafluoroethylene and a heat-meltable perfluoro fluororesin as fluororesins.

(6) The fluororesin liquid coating composition according to (1 ) to (5), further containing a filler.

(7) A coating film consisting of the fluororesin liquid coating composition according to (1 ) to (6).

(8) The coating film according to (7) having a thickness of from 8 to 20 ji/m.

(9) An article having the coating film according to (7) or (8).

EFFECT OF THE INVENTION

[0023] With the present invention, it is possible to provide a fluororesin liquid coating composition containing a fluororesin and polyetherketoneketone (PEKK) which strongly adheres to both metal base materials and resin base materials and exhibits excellent steam resistance and corrosion resistance, and can also form a thin coating film. In addition, with the present invention, it is possible to provide a coating film consisting of a fluororesin liquid coating composition containing a fluororesin and polyetherketoneketone (PEKK) and an article having the coating film.

[0024] The fluororesin liquid coating composition of the present invention can use water as a medium, which makes it excellent from environmental, safety and health perspectives.

EMBODIMENTS OF THE INVENTION

[0025] The fluororesin liquid coating composition of the present invention contains a fluororesin and polyetherketoneketone (PEKK).

[0026] The present invention will be described in detail hereinafter.

Fluororesin liquid coating composition

[0027] The fluororesin liquid coating composition containing a fluororesin and polyetherketoneketone (PEKK) according to the present invention is particularly suitably used as a primer coat (undercoat) for bonding a fluororesin layer to a base material.

The composition is also preferably used as a one-coat coating.

Fluororesin

[0028] Examples of the fluororesin constituting the coating composition of the present invention include, but are not limited to, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (PFA), tetrafluoroethylene- hexafluoropropylene copolymers (FEP), tetrafluoroethylene-hexafluoropropylene- perfluoro(alkyl vinyl ether) copolymers, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polychlorotrifluoroethylene, and chlorotrifluoroethylene-ethylene copolymers. Using an ordinary fluororesin that does not have functional groups in the side chain as the fluororesin in the present invention is preferable from the perspective of coating film non-adhesiveness when used as a one-coat coating or compliance with legal regulations (in particular, food contact applications).

[0029] In the present invention, it is preferable to use a heat-meltable fluororesin which exhibits melt fluidity at a temperature exceeding the melting point from the perspective that the generation of pinholes can be suppressed when formed into a coating film and that a uniform, smooth coating film can be obtained. Of these, heat- meltable perfluororesins such as low-molecular-weight PTFE or PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymers can be suitably used from the perspectives of the non-adhesiveness and heat resistance of the coating film.

[0030] The alkyl group of the perfluoro(alkyl vinyl ether) in PFA preferably has a carbon number of from 1 to 5. Of these, perfluoro(propyl vinyl ether) (PPVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(methyl vinyl ether) (PMVE) are particularly suitable. The amount of the perfluoro(alkyl vinyl ether) in PFA is preferably in the range of from 1 to 50 wt.%.

[0031] In addition, it is also preferable to use a non-heat-meltable polytetrafluoroethylene (PTFE) in the present invention. The non-heat-meltable polytetrafluoroethylene preferably used in the present invention is a high-molecular weight polytetrafluoroethylene (PTFE) which does not exhibit melt fluidity at a temperature exceeding the melting point, and this may be either a homopolymer of tetrafluoroethylene (TFE) (TFE homopolymer) or a TFE copolymer in which monomers copolymerizable with TFE are contained within the range of 1 mass% or less (modified PTFE), or a combination thereof may also be used. This makes it possible to reduce residual stress in the coating film after heating and to reduce cost.

[0032] Further, it is more preferable to use a heat-meltable perfluororesin and a non-heat-meltable polytetrafluoroethylene (PTFE) simultaneously in that each of the advantages described above can be achieved. Other fluororesins may also be added as necessary.

[0033] The fluororesin of the present invention can be prepared by dispersing a powder obtained by isolating/drying a resin obtained by a known polymerization method, a powder prepared by further pulverizing the same, or a powder obtained by fine granulation by the method described in Japanese Examined Patent Application Publication No. S52-44576 or the like in a coating composition. A fluororesin dispersion polymerized by emulsion polymerization may also be used directly, or a composition stabilized by adding a surfactant to a fluororesin dispersion or a composition concentrated by a known technique such as the method described in U.S. Patent No. 3,037,953 to adjust the fluororesin concentration to a high level may also be used. A stabilized fluororesin dispersion is preferable in that a dispersed state can be maintained for a long period of time without the fluororesin aggregating or settling.

[0034] The concentration of the fluororesin dispersion used in the coating composition of the present invention is preferably from 20 to 70 mass%, and using a composition adjusted to 40 to 70 mass% by concentration is preferable in that it becomes easy to adjust the fluororesin concentration in the coating composition. Examples of commercially available fluororesin dispersions which may be used in the present invention include Teflon® PTFE 31 -JR, PTFE 34-JR, PFA 334-JR, PFA 335-JR, and FEP 120-JR available from Chemours-Mitsui Fluoroproducts Co., Ltd. Polyetherketoneketone (PEKK)

[0035] The "polyetherketoneketone (PEKK)" used in the present invention is a polymer compound having at least the following repeating units, and either a homopolymer or a copolymer thereof may be used. In the present invention, polyetherketoneketone (PEKK) serves the role of a main binder. CHEMICAL FORMULA 1

[0036] As a production method for the polyetherketoneketone (PEKK) used in the present invention, it is known that polyetherketoneketone can be produced by reacting a diphenyl ether and a benzene dicarboxylic acid halide in the presence of a Friedel- Crafts catalyst in accordance with Japanese Examined Patent Application Publication No. S47-31440 or Japanese Examined Patent Application Publication No. H5-13967, but examples of products that have already been placed on the market as commercially available products include KEPSTAN® available from Arkema and KSTONE® available from Shandong Kaisheng New Materials.

Other components

[0037] Various additives used in ordinary coatings may be added to the fluororesin liquid coating composition of the present invention in accordance with the desired characteristics, such as enhanced dispersibility, conductivity, foaming prevention, or wear resistance, and examples thereof include surfactants (polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether-based nonionic surfactants such as Leocol available from Lion Specialty Chemicals Co., Ltd., TRITON and TERGITOL series available from the Dow Chemical Company, and Emulgen available from the KAO Corporation, sulfosuccinates such as Lipal available from Lion Specialty Chemicals Co., Ltd. or Emal or Pelax available from the KAO Corporation, sodium alkyl ether sulfonate salts, sulfuric acid mono long chain alkyl-based anionic surfactants, carboxylates such as Leoal available from Lion Specialty Chemicals Co., Ltd. or OROTAN available from the Dow Chemical Company, acrylate-based polymer surfactants, L-77 available from Momentive, and the Surfynol series (Surfynol 420, Surfynol 440, Surfynol 465, Surfynol 485, and the like) available from EVONIK), film forming agents (for example, polymer- type film forming agents such as polyamides or polyamide imides, acrylics, and acetates, higher alcohols or ethers, and polymer surfactants having a film forming effect), and thickeners (water-soluble cellulose, solvent-dispersed thickeners, alginic acid soda, casein, casein acid soda, xanthan gum, polyacrylic acids, and acrylic acid esters).

[0038] In addition, various organic/inorganic substances may also be added to the fluororesin liquid coating composition of the present invention as fillers in accordance with the desired characteristics. Examples of inorganic substances include engineering plastics such as polyphenylene sulfides, polyether sulfones, polyphenylene sulfones, polyamides, polyimides, phenol resins, urea resins, epoxy resins, urethane resins, melamine resins, polyester resins, polyether resins, acrylic resins, acrylic silicone resins, silicone resins, and silicone polyester resins. Examples of inorganic substances include metal powders, metal oxides (aluminum oxide, zinc oxide, tin oxide, titanium oxide, and the like), glass, ceramics, silicon carbide, silicon oxide, calcium fluoride, carbon black, graphite, mica, and barium sulfate. Regarding the shapes of the fillers, substances of various forms can be used, such as particulate, fibrous, and flaky substances.

[0039] In the fluororesin liquid coating composition of the present invention, polyphenylene sulfides, polyether sulfones, polyphenylene sulfones, polyamides, polyimides, polyamide imides (PAI), phenol resins, urea resins, and epoxy resins can be used as binders to be used together with PEKK, but in the case of an aqueous coating composition using water as a solvent/dispersant of the fluororesin liquid coating composition, a water-soluble polyamide imide (PAI) is particularly preferable in that it can adhere to the base material without defect as a result of melting so as to be uniformly present in the coating film.

[0040] However, the ratio of binders other than PEKK in the entire binder resin (other binders/PEKK + other binders) is preferably not greater than 0.5 and is more preferably not greater than 0.3 or not greater than 0.2.

Aqueous medium

[0041] It is particularly preferable from an environmental perspective or a cost perspective to form an aqueous based coating composition by using water as a solvent/dispersion medium of the fluororesin liquid coating composition of the present invention. In order to appropriately adjust the rheology characteristics such as liquid viscosity or to improve the dispersibility of PEKK or fillers, it is also possible to add a polar solvent that is compatible with water or to disperse an organic solvent that is incompatible with water. Adding a polar solvent dissolves heat-resistant resins (binders) so that heat-resistant resins (binders) become more uniform in the drying process after coating, and the coating film becomes refined or heat-resistant resins (binders) more easily penetrate the recesses of irregularities in the base material so that an effect of enhancing the adhesive strength with the base material can be anticipated.

[0042] In the fluororesin liquid coating composition of the present invention, the fluororesin content is preferably from 35 to 90 mass% and particularly preferably from 45 to 80 mass% with respect to the total amount of binder resins (PEKK and other resins) and the fluororesin. When the fluororesin content is less than 35 mass%, the steam resistance and corrosion resistance of the coating film may decrease and the adhesiveness of the topcoat may be diminished, whereas when the fluororesin content exceeds 90 mass%, the corrosion resistance of the coating film may decrease and the adhesive strength to a base material or the strength of the coating film may be diminished.

Base material

[0043] The fluororesin liquid coating composition of the present invention can be suitably used for both metal base materials and plastic base materials.

[0044] Examples of metal base materials include aluminum, stainless steel (SUS), copper, iron, and various alloys.

[0045] Engineering plastics, which can withstand heat treatment for forming a coating film of a fluororesin and also have long-term durability, are preferably used as plastic base materials, and these include substances called super engineering plastics such as polyaryl ketone resins (PEK, PEEK, PEKK, and PEEKK), polyarylene sulfone resins (PPS and the like), polyimides (PI), polyether imides (PEI), and polyamide imides (PAI).

Production process for fluororesin coating composition

[0046] The fluororesin coating composition of the present invention can be prepared by a conventionally known method. For example, the composition may be obtained by appropriately mixing a fluororesin (aqueous dispersion or powder) and PEKK along with other additives or fillers which may be added as necessary. In the fluororesin coating composition of the present invention, the PEKK, fluororesin, fillers, and the like may be prepared by preparing respective dispersions (dispersion liquids) in advance and mixing the resulting dispersions.

[0047] The viscosity of the fluororesin coating composition of the present invention at 25°C is preferably from 0.1 to 50,000 mPa*s. When the viscosity is less than 0.1 mPa*s, sagging or the like tends to occur when applied to a coated product, which may make it difficult to achieve the target film thickness. When the viscosity exceeds 50,000 mPa*s, the coating operability may be diminished, which may inhibit the uniformity of the film thickness of the resulting coating film and may diminish the surface smoothness or the like. A more preferable lower limit is 1 mPa*s, and a more preferable upper limit is 30,000 mPa*s. The viscosity described above is a value obtained by measurement using a BM-type single-cylinder rotary viscometer (manufactured by Tokyo Keiki Inc.). Coating film

[0048] The "coating film" of the present invention is a coating film prepared by applying the fluororesin liquid coating composition of the present invention and can be formed as a thin coating film with a thickness not greater than 20 m - for example, from 8 to 20 pm. In addition, the "coating film" of the present invention is also excellent in terms of its appearance.

[0049] A coating film prepared by using the coating composition of the present invention as a primer layer to be bonded to a base material and applying and laminating a plurality of layers thereon is also included.

[0050] The "coating film" of the present invention can be formed by commonly used methods such as various existing coating methods, examples of which include spray coating, dip coating, and spin coating, and the coating film is preferably heated to a temperature exceeding the melting point of the fluororesin in order to enable melt fluidity and to obtain a uniform coating film.

[0051] Coating films to be used in performance evaluations were prepared according to the following procedure.

[0052] Preparation of test piece for evaluation (for aluminum base material evaluation)

[0053] First, an aluminum sheet with a thickness of 100 mm and a length of 150 mm (JIS A1050 conformant product, thickness: 1 mm) was used as a base material, and after the surface was degreased with isopropyl alcohol, masking tape was affixed to a portion from the end up to 30 mm from the end parallel to the long side of the base material. Shot blasting was performed with #60 alumina to achieve a surface roughness (Ra) of from 1 to 5 ji/m. Next, the fluororesin coating compositions of each of the examples and comparative examples were spray-coated (coating composition: 0.6-0.7 g) using a spray gun (W-101-101 G, manufactured by Anest Iwata Corporation). After the masking tape was peeled off, the sheet was dried for 10 minutes at 120°C and then 20 minutes at 300°C to form a primer layer (fluororesin coating composition layer). A PFA powder coating (Teflon® coating MJ-102 available from Chemours-Mitsui Fluoroproducts Co., Ltd.) was applied by electrostatic powder coating to the entire surface of a base material on which the primer layer was formed using a powder spray gun (GX355HW manufactured by PARKER IONICS) (coating weight: 1 .4-1 .6 g), and this was baked for 15 minutes at 400°C (base material temperature). Further, the same PFA powder coating was applied by electrostatic powder coating and backed for 10 minutes at 360°C (base material temperature) to form a topcoat layer (PFA layer). A test piece with a topcoat layer (PFA layer) thickness of from 100 to 120 ji/m, with the primer not applied to the ends, was obtained.

Preparation of test piece for evaluation (for PEEK base material evaluation) [0054] After a water dispersion of a PEEK powder was applied to an aluminum sheet with a width of 100 mm and a length of 150 mm (JIS A3004, thickness: 1 mm), it was heat-treated for approximately 15 minutes at approximately 400°C to obtain an aluminum base material with a PEEK coating film having a thickness of from 20 to 30 ji/m.

[0055] Masking tape was affixed to a portion from the end up to 120 mm from the end parallel to the long side of the obtained aluminum base material with a PEEK coating film, and a 30 mm wide unmasked section of the PEEK coating film was removed by shot blasting to expose the aluminum. The masking tape of the protected PEEK portion was peeled off, and a portion from the end up to 30 mm from the end parallel to the long side of the base material with exposed aluminum was then protected with masking tape. Next, the fluororesin coating compositions of each of the examples and comparative examples were then applied by spraying in the same manner as in the procedure for preparing a test piece for aluminum base material evaluation so as to form a topcoat layer (PFA layer) and to obtain a test piece. (Performance evaluation methods)

Steam resistance evaluation

[0056] The test piece for evaluation described above was left to stand for 100 hours in 0.4 MPa steam at 150°C and then left to cool to room temperature, and the bond strength of the coating layer was measured by the following method. Next, after the base material was heated to 200°C with a gas stove, it was rapidly cooled with water and the state of the coating film was confirmed. Cases in which swelling or blistering occurred were rejected.

Bond strength measurement method

[0057] Notches were cut into the coating film to a width of 1 cm with a cutter parallel to the short side of the test piece described above, and approximately 1 cm of the coating film in a portion where the primer was not applied at the end was peeled off to form a gripping portion for bond strength measurements.

[0058] This test piece was placed on an electronic balance, and after both ends were fixed with tape, the scale of the balance was aligned to zero. The peeled coating film described above was sandwiched with pliers and pulled at a rate of 50 mm/min, and the numerical value by which the scale decreased was read to measure the bond strength (peeling strength). The units were kgf (weight kilograms).

[0059] The measurement of bond strength was performed before and after the steam resistance evaluation described above.

EXAMPLES

Preparation of fluororesin liquid coating composition

[0060] The following reagents were used in the examples and comparative examples.

Polyetherketoneketone (PEKK) resin

PEKK powder: KSTONE® CC5601 available from Shandong Kaisheng New Materials

Other binder resins

Water-soluble polyamide imide (PAI) resin

HPC-2100D-28 available from Hitachi Chemical Co., Ltd. (solution with a PAI concentration of approximately 28 mass%, water content of from 22 to 32 mass%, and N-formylmorpholine content of from 30 to 40 mass%)

Polyether ether ketone (PEEK) resin PEEK powder: VICOTE® Coating s704 available from Victrex PLC Polyether imide (PEI) resin

PEI powder: Ultern 1000F3SP-1000 available from SABIC

Fluororesins

[0061] PFA aqueous dispersion: Teflon® PFA 335-JR available from Chemours- Mitsui Fluoroproducts Co., Ltd. (PFA concentration: 60 mass%)

[0062] PTFE aqueous dispersion: Teflon® PTFE 34-JR available from Chemours- Mitsui Fluoroproducts Co., Ltd. (PTFE concentration: 58 mass%) Example 1

[0063] First, 192 g of purified water was placed in a 1 L stainless steel container, and 18 g of a nonionic surfactant aqueous solution (concentration: 81 mass%) was added while stirring at 140 rpm using a stirrer (manufactured by YAMATO SCIENTIFIC CO., LTD.). Next, 77 g of a PEKK powder was added thereto and dispersed by stirring for 10 minutes. Further, 17 g of a nonionic surfactant aqueous solution (concentration: 90 mass%), 105 g of a carbon black aqueous dispersion (25 mass%), and 58 g of a titanium oxide aqueous dispersion (55 mass%) were added and stirred for 10 minutes. Next, a fluororesin aqueous dispersion mixed in a separate container (44 g of a PFA aqueous dispersion, 259 g of a PTFE aqueous dispersion, and 96 g of purified water) was added and stirred for 10 minutes to obtain an aqueous fluororesin coating composition.

Example 2

[0064] First, 244 g of purified water was placed in a 1 L stainless steel container, and 24 g of a nonionic surfactant aqueous solution (concentration: 81 mass%) was added while stirring at 140 rpm using a stirrer (manufactured by YAMATO SCIENTIFIC CO., LTD.). Next, 81 g of a PEKK powder was added thereto and dispersed by stirring for 10 minutes. Further, 14 g of a nonionic surfactant aqueous solution (concentration: 90 mass%), 101 g of a carbon black aqueous dispersion (25 mass%), and 54 g of a titanium oxide aqueous dispersion (55 mass%) were added and stirred for 10 minutes. Next, a fluororesin aqueous dispersion mixed in a separate container (30 g of a PFA aqueous dispersion, 223 g of a PTFE aqueous dispersion, and 21 g of purified water) was added and stirred for 10 minutes to obtain an aqueous fluororesin coating composition. Examples 3-5

[0065] Aqueous fluororesin coating compositions were obtained with the same procedure as in Example 2 by adjusting the amount of each component to obtain the coating compositions (composition ratios in the solid portion of the resin (mass%)) listed in Table 1 below.

Comparative Examples 1-4

[0066] Fluororesin coating compositions were obtained with the same procedure as in the examples by adjusting the amount of each component to obtain the coating compositions (composition ratios in the solid portion of the resin (mass%)) listed in Table 2 below.

[0067] The results of evaluating the coating compositions prepared in the examples and comparative examples are shown in Tables 1 and 2. Cases in which no swelling or blistering occurred were given an evaluation result of O, and other cases were given an evaluation result of x. Cases in which the bond strength was greater than 1 .5 kgf prior to steam pressure treatment and cases in which the bond strength was greater than 0.8 kg after steam pressure treatment were considered passing, and cases in which all of the samples passed with evaluations of O were given an overall evaluation of O, while cases which had even one x or were rejected were given an overall evaluation of x.

Table 1 Table 2

[0068] The results of Tables 1 and 2 above demonstrate that while the fluororesin liquid coating compositions of the present invention containing PEKK as a binder exhibit good performance for both metal base materials and resin base materials (Table 1), the coating compositions not containing PEKK as a binder cannot exhibit sufficient performance for both types of base materials, even if they exhibit good performance for either metal base materials or resin base materials (Table 2).