Aqueous epoxy resin-based primer coating composition and anticorrosive coating method

Abstract

To provide an environmentally considerate aqueous epoxy resin-based primer coating composition capable of forming a coating film having excellent chemical resistance (acid and alkali resistance) and excellent long-term corrosion protection, and also having excellent compatibility with both the substrate and an overcoated paint, and also to provide an anticorrosive coating method.SOLUTION: An aqueous epoxy resin-based primer coating composition comprises an epoxy resin, an amine compound, an anticorrosive pigment, and water, wherein the anticorrosive pigment contains a molybdate, and the water-soluble content of the anticorrosive pigment is 0.01 to 1.0 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous epoxy resin-based undercoat paint composition and an anticorrosion coating method, and more particularly to an aqueous epoxy resin-based undercoat paint composition and an anticorrosion coating method that are environmentally friendly, can form a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion prevention properties, and are highly compatible with substrates and topcoats. [Background technology]

[0002] Anticorrosion paints have been developed to maintain the corrosion resistance of large steel structures such as bridges, steel towers, ships, and plants. From an environmental perspective, the anticorrosion paint is preferably an aqueous coating composition. Patent Documents 1 and 2, for example, disclose aqueous coating compositions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-149791 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-221464 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the coating compositions described in Patent Documents 1 and 2 do not provide sufficient chemical resistance to the resulting coating film, and there is room for improvement in long-term corrosion prevention. In order to enhance the corrosion prevention effect of the aqueous coating composition, it is conceivable to increase the water-soluble content of the anti-rust pigment. However, an increase in the water-soluble content tends to decrease chemical resistance, making it difficult to achieve both.

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide an aqueous epoxy resin-based primer coating composition and anticorrosion coating method which are environmentally friendly, provide a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion resistance, and are compatible with substrates and topcoats. [Means for solving the problem]

[0006] The present inventors have discovered that by incorporating a specific amount of molybdate into an anti-rust pigment and designing the content of water-soluble components to be low, it is possible to obtain a coating film that maintains excellent chemical resistance while also achieving long-term corrosion prevention, and have completed the present invention.

[0007] The aqueous epoxy resin-based primer coating composition and anticorrosion coating method of the present invention, which solve the above problems, mainly include the following components.

[0008] (1) A water-based epoxy resin-based primer coating composition comprising an epoxy resin, an amine compound, an anti-rust pigment, and water, wherein the anti-rust pigment comprises a molybdate salt, and the water-soluble content of the anti-rust pigment is 0.01 to 1.0 mass%.

[0009] According to this configuration, the aqueous epoxy resin-based primer coating composition is environmentally friendly and can form a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion resistance. In addition, the aqueous epoxy resin-based primer coating composition has excellent compatibility with substrates and topcoats.

[0010] (2) The aqueous epoxy resin-based primer coating composition according to (1), wherein the content of the molybdate salt, calculated as the amount of molybdenum oxide, in the rust-preventive pigment is 0.1 to 5.0 mass %.

[0011] With this configuration, the aqueous epoxy resin-based primer coating composition can form a coating film with better chemical resistance and better long-term corrosion resistance.

[0012] (3) The aqueous epoxy resin-based undercoat coating composition according to (1) or (2), wherein the equivalent ratio of the epoxy resin to the amine compound is 0.4 to 0.7.

[0013] With this configuration, the aqueous epoxy resin-based primer coating composition can form a coating film with excellent moisture resistance.

[0014] (4) The aqueous epoxy resin-based undercoat coating composition according to any one of (1) to (3), wherein the amine compound comprises an aliphatic polyamine or a polyamidoamine.

[0015] With this configuration, the aqueous epoxy resin-based primer coating composition can form a coating film that has excellent adhesion to the substrate and chemical resistance.

[0016] (5) A corrosion-protective coating method comprising the steps of: applying an aqueous epoxy resin-based undercoat coating composition according to any one of (1) to (4) onto a metal substrate to form an undercoat coating film; and applying an aqueous coating composition onto the undercoat coating film to form a topcoat coating film.

[0017] According to this configuration, the corrosion-protective coating method is environmentally friendly because it uses the above-mentioned aqueous epoxy resin-based undercoat coating composition, and can form a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion protection. Furthermore, because the corrosion-protective coating method uses the above-mentioned aqueous epoxy resin-based undercoat coating composition, the resulting undercoat coating film and topcoat coating film are highly compatible. Furthermore, the resulting coated product has a good coating film appearance and excellent weather resistance.

[0018] (6) A corrosion-protective coating method comprising the steps of: applying an aqueous epoxy resin-based undercoat coating composition according to any one of (1) to (4) onto a metal substrate to form an undercoat coating film; applying an epoxy resin-based aqueous coating composition onto the undercoat coating film to form an intermediate coating film; and applying a fluororesin-based or urethane resin-based aqueous coating composition onto the intermediate coating film to form a topcoat coating film.

[0019] According to this configuration, the corrosion-protective coating method is environmentally friendly because it uses the above-mentioned aqueous epoxy resin-based undercoat coating composition, and can form a coating film with superior chemical resistance (acid resistance and alkali resistance) and long-term corrosion protection. Furthermore, because the corrosion-protective coating method uses the above-mentioned aqueous epoxy resin-based undercoat coating composition, the compatibility of the resulting undercoat coating film and topcoat coating film is superior. Furthermore, the resulting coated product has a better coating film appearance and superior weather resistance. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an aqueous epoxy resin-based primer coating composition and anticorrosion coating method which are environmentally friendly, provide a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion resistance, and are compatible with substrates and topcoats. DETAILED DESCRIPTION OF THE INVENTION

[0021] <Water-based epoxy resin-based primer coating composition> An aqueous epoxy resin-based primer coating composition (hereinafter also referred to as a coating composition) according to one embodiment of the present invention contains an epoxy resin, an amine compound, an anti-rust pigment, and water. The anti-rust pigment contains a molybdate. The water-soluble content of the anti-rust pigment is 0.01 to 1.0 mass %. Each of these components will be described below.

[0022] (epoxy resin) Epoxy resins are cured by drying under various conditions to become a component that forms a coating film. The epoxy resin is not particularly limited. Examples of epoxy resins include bisphenol-type epoxy resins, novolac-type epoxy resins, aromatic epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins, glycidyl ester-type epoxy resins, and glycidyl amine-type epoxy resins.

[0023] Examples of bisphenol epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol AD ​​epoxy resins, bisphenol S epoxy resins, and their brominated and hydrogenated products. Examples of novolac epoxy resins include phenol novolac epoxy resins and cresol novolac epoxy resins. Examples of aromatic epoxy resins include trisphenolmethane triglycidyl ether.

[0024] Examples of alicyclic epoxy resins include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, bis(3,4-epoxycyclohexyl)adipate, bis(3,4-epoxycyclohexylmethyl adipate), bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxycyclohexanone-meta-dioxane), and bis(2,3-epoxycyclopentyl)ether.

[0025] Examples of aliphatic epoxy resins include diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of polypropylene glycol, and polyglycidyl ethers of long-chain polyols including polyoxyalkylene glycols containing an alkylene group having 2 to 9 carbon atoms and polytetramethylene ether glycol.

[0026] Examples of glycidyl ester type epoxy resins include phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, diglycidyl-p-oxybenzoic acid, glycidyl ether-glycidyl ester of salicylic acid, and dimer acid glycidyl ester.

[0027] Examples of glycidylamine type epoxy resins include triglycidyl isocyanurate, N,N'-diglycidyl derivatives of cyclic alkylene urea, N,N,O-triglycidyl derivatives of p-aminophenol, and N,N,O-triglycidyl derivatives of m-aminophenol.

[0028] Among these, the epoxy resin is preferably a bisphenol type epoxy resin, and more preferably a bisphenol A type epoxy resin, because the coating film has excellent chemical resistance and flexibility and has excellent adhesion to the substrate.

[0029] The weight-average molecular weight (Mw) of the epoxy resin is not particularly limited. For example, Mw is preferably 400 or more, more preferably 500 or more. Furthermore, Mw is preferably 4000 or less, more preferably 3000 or less. When the Mw of the epoxy resin is within the above range, the resulting coating film tends to have excellent coating strength, processability, and smoothness. In the present embodiment, Mw can be measured by gel permeation chromatography (GPC) or the like. More specifically, Mw can be calculated in terms of polystyrene by measuring the difference in refractive index using a GPC apparatus (HLC-8220; manufactured by Tosoh Corporation) equipped with a differential refractometer (RI) detector.

[0030] The epoxy equivalent (solid content) of the epoxy resin is not particularly limited. For example, the epoxy equivalent (solid content) is preferably 250 g / eq or more, more preferably 400 g / eq or more. The epoxy equivalent (solid content) is preferably 1500 g / eq or less, more preferably 750 g / eq or less. When the epoxy equivalent (solid content) is within the above range, the coating composition has the advantage of excellent adhesion and flexibility of the coating film.

[0031] The content (solid content) of the epoxy resin is not particularly limited. For example, the content (solid content) of the epoxy resin in the coating composition is preferably 10% by mass or more, and more preferably 15% by mass or more. Furthermore, the content (solid content) of the epoxy resin in the coating composition is preferably 40% by mass or less, and more preferably 35% by mass or less. When the content (solid content) of the epoxy resin is within the above range, the coating composition has excellent adhesion of the coating film and workability during coating.

[0032] (amine compounds) The amine compound is blended to cure the epoxy resin. The amine compound is not particularly limited. Examples of the amine compound include aliphatic polyamines such as trimethylenediamine, ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and pentaethylenehexamine; alicyclic polyamines such as menthanediamine and isophoronediamine; heterocyclic polyamines such as piperidine, piperazine, methylmorpholine, and ethylmorpholine; aromatic polyamines such as phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, benzylmethylamine, dimethylbenzylamine, m-xylenediamine, and pyridine; modified polyamines such as epoxy compound-added polyamines; and polyamidoamines such as those obtained by reacting carboxylic acid compounds such as aliphatic dicarboxylic acids, fatty acids, and dimer acids, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and azelaic acid, with aliphatic polyamines or polyamines having a polyoxyalkylene chain.

[0033] Among these, the amine compound preferably contains an aliphatic polyamine or a polyamidoamine, which enables the coating composition to form a coating film that has excellent adhesion to the substrate and chemical resistance.

[0034] Regarding the blending ratio of the epoxy resin and the amine compound, the equivalent ratio, expressed as the amount of active hydrogen of the amine compound per epoxy group of the epoxy resin, is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. The equivalent ratio is preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.65 or less. By keeping the equivalent ratio within the above range, the coating composition can form a coating film with excellent moisture resistance.

[0035] (Anti-rust pigment) The anti-rust pigment comprises a molybdate, which is preferably a metal salt of molybdic acid.

[0036] The molybdate is not particularly limited. For example, the molybdate may be a salt of a Group 2 element (e.g., magnesium) of molybdic acid, aluminum molybdate, zinc molybdate, etc. The molybdate may be a single compound or multiple compounds. The valence of the molybdate is either 4 or 6. The molybdic acid may include condensed molybdic acids such as orthomolybdic acid, metamolybdic acid, and paramolybdic acid.

[0037] The molybdate content in the anti-rust pigment is preferably 0.1% by mass or more. Furthermore, the molybdate content in the anti-rust pigment is preferably 5.0% by mass or less, and more preferably 3.0% by mass or less. By keeping the molybdate content within the above range, the coating composition can form a coating film with superior chemical resistance and long-term corrosion prevention. In this embodiment, the molybdate content is a value converted into the amount of molybdenum oxide (MoO3) according to the following procedure. Specifically, 20 mL of a 10% aqueous solution of sodium hydroxide is added to approximately 0.3 g of the anti-rust pigment and heated to a boil. 20 mL of a 20% aqueous solution of nitric acid is added to this, followed by approximately 70 mL of water, and the mixture is heated until transparent. After cooling, the mixture is transferred to a 250 mL volumetric flask and water is added up to the mark. 10 mL of this mixture is then transferred to a 100 mL volumetric flask, 2.5 mL of a 20% aqueous solution of nitric acid is added, and water is added up to the mark. This is then subjected to ICP optical emission spectroscopy (ICP-OES, Agilent Technologies "5900 ICP-OES") to measure the Mo emission wavelength of 202.032 nm. The amount of molybdenum in the anti-corrosion pigment is determined from the molybdenum calibration curve measured at the same time, and calculated as the amount of molybdenum oxide (MoO3).

[0038] Returning to the explanation of the anti-rust pigment as a whole, the anti-rust pigment may contain, in addition to the molybdate described above, metal oxides and / or metal nitrates, metal carbonates, metal phosphates, fluorine-containing metal compounds, ammonium complex salts, zinc powder, etc. of one or more metal elements selected from zinc, calcium, aluminum, magnesium, titanium, manganese, strontium, barium, iron, zirconium, cerium, etc.

[0039] Among these, the anti-rust pigment preferably contains a metal phosphate, metal phosphite, or metal tripolyphosphate containing one of the metal elements zinc, calcium, and aluminum, from the viewpoint of providing the resulting coated article with better corrosion resistance and improved durability, and more preferably contains a phosphate or metal phosphite containing at least one of the metal elements zinc or calcium.

[0040] The water-soluble content of the anti-rust pigment may be 0.01% by mass or more. The water-soluble content of the anti-rust pigment may be 1.0% by mass or less, and preferably 0.7% by mass or less. If the water-soluble content is less than 0.01% by mass, the coating composition will have poor corrosion resistance. On the other hand, if the water-soluble content exceeds 1.0% by mass, the coating composition will have poor chemical resistance (acid resistance, alkali resistance, etc.) and moisture resistance. In this embodiment, the water-soluble content can be measured in accordance with "JIS K 5101-16-2."

[0041] The content of the anti-rust pigment is not particularly limited. For example, the content of the anti-rust pigment in the coating composition is preferably 1.0 mass% or more, and more preferably 3.0 mass% or more. The content of the anti-rust pigment in the coating composition is preferably 15 mass% or less, and more preferably 10 mass% or less. When the content of the anti-rust pigment is within the above range, the coating composition can form a coating film with better chemical resistance and better long-term corrosion prevention.

[0042] The coating composition of this embodiment is characterized in that the anti-rust pigment contains molybdate in the amount described above. As described above, the coating composition of this embodiment contains a relatively small and specific amount of molybdate, and is designed to have a low water-soluble content as described above, which makes it possible to obtain a coating film that maintains excellent chemical resistance while also achieving long-term corrosion prevention.

[0043] The method for preparing the anti-rust pigment is not particularly limited. For example, the anti-rust pigment can be prepared by reacting or mixing a molybdate and another pigment, and then drying or pulverizing the mixture as appropriate.

[0044] The coating composition of the present embodiment may contain other pigments in addition to the above-described anti-rust pigments. The other pigments are not particularly limited. Examples of the other pigments include various color pigments and extender pigments.

[0045] The color pigment is not particularly limited, and examples of the color pigment include titanium oxide, carbon black, and ferric oxide.

[0046] The extender pigment is not particularly limited, and examples thereof include talc, barium sulfate, mica, and calcium carbonate.

[0047] (water) The water content is not particularly limited and is adjusted appropriately taking into consideration the heating residue of the coating composition and workability during application. For example, the heating residue of the coating composition is preferably 30% by mass or more, and more preferably 40% by mass or more, of the coating composition. Furthermore, the heating residue of the coating composition is preferably 70% by mass or less, and more preferably 60% by mass or less, of the coating composition. When the heating residue of the coating composition is within the above range, the coating composition has excellent workability during application.

[0048] Returning to the explanation of the coating composition as a whole, the coating composition of this embodiment may contain, as necessary, dyes, thickeners, dispersants, matting agents, antifoaming agents, leveling agents, anti-sagging agents, surface conditioners, viscosity conditioners, waxes, silane coupling agents, rust inhibitors other than the rust-preventive pigment, preservatives, antifreeze agents, film-forming aids, anti-cister agents, and the like.

[0049] The viscosity of the coating composition at 23°C is preferably 1.0 Pa·s or more, and more preferably 3.0 Pa·s or more. Furthermore, the viscosity of the coating composition at 23°C is preferably 10.0 Pa·s or less, and more preferably 7.0 Pa·s or less. When the viscosity of the coating composition is within the above range, the coating composition exhibits excellent coating workability and penetration. In this embodiment, the viscosity can be measured, for example, using a TVB-10 viscometer manufactured by Toki Sangyo Co., Ltd., at 23°C, 60 rpm, and rotor No. M4.

[0050] The pigment volume concentration (PVC) in the nonvolatile content of the coating composition is preferably 20% or more, more preferably 25% or more. The PVC of the coating composition is preferably 40% or less, more preferably 35% or less. When the PVC of the coating composition is within the above range, the coating composition has excellent corrosion resistance, coating workability, and adhesion to the substrate. The term "pigment" as used herein refers to all pigments contained in the coating composition, and the PVC can be calculated from the blending amounts and specific gravities of the components that make up the nonvolatile content.

[0051] The method for preparing the coating composition is not particularly limited. For example, the coating composition can be prepared by mixing and stirring the above-mentioned components. The coating composition may be a one-component type or a two-component type.

[0052] As described above, the coating composition of this embodiment is environmentally friendly and can form a coating film that has excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion resistance. In addition, the coating composition has excellent compatibility with substrates and overcoats.

[0053] <Corrosion prevention coating method and manufacturing method of coated products> (First embodiment) A corrosion-protective coating method according to one embodiment of the present invention comprises the steps of applying the above-described aqueous epoxy resin-based undercoat coating composition to a metal substrate to form an undercoat coating film, and applying an aqueous coating composition to the undercoat coating film to form a topcoat coating film. A method for producing a coated article according to one embodiment of the present invention comprises the steps of applying the above-described aqueous epoxy resin-based undercoat coating composition to a metal substrate to form an undercoat coating film, and applying an aqueous coating composition to the undercoat coating film to form a topcoat coating film. Each of these steps will be explained below. In the following explanation, the matters described above in relation to the embodiment of the aqueous epoxy resin-based undercoat coating composition will be omitted as appropriate.

[0054] ·Undercoat film formation process The primer coating film forming step is a step in which the above-mentioned aqueous epoxy resin-based primer coating composition is applied to a metal substrate to form a primer coating film. If there is an old coating film on the metal substrate, it is appropriately scraped off and then painted to form a primer coating film.

[0055] The aqueous epoxy resin-based primer coating composition is applied to a metal substrate of a steel structure such as a steel tower, a bridge, a tank, or a plant. The metal constituting the metal substrate is not particularly limited. Examples of metals constituting the metal substrate include steel, galvanized steel, stainless steel, magnesium alloy, aluminum, and aluminum alloy.

[0056] The shape of the metal substrate is not particularly limited, and may be, for example, a plate, sheet, foil, or the like.

[0057] The metal substrate may be subjected to various surface treatments, such as oxidation treatment, such as anodizing, phosphate treatment, chromate treatment, and non-chromate treatment.

[0058] The method for applying the aqueous epoxy resin-based primer coating composition to the metal substrate is not particularly limited, and examples of the application method include known methods such as spray coating, roller coating, brush coating, and flow coating.

[0059] The drying conditions for the applied aqueous epoxy resin-based primer coating composition are not particularly limited, and may be, for example, at a humidity of 85% or less, at 5 to 35°C, for about 12 to 48 hours.

[0060] The dry film thickness of the resulting primer coating film is not particularly limited. For example, the dry film thickness is preferably 20 μm or more, more preferably 45 μm or more. Furthermore, the dry film thickness is preferably 200 μm or less, more preferably 120 μm or less. When the dry film thickness is within the above range, the resulting coated product has excellent corrosion resistance and chemical resistance.

[0061] Topcoat film formation process The topcoat film forming step is a step of applying an aqueous coating composition onto an undercoat film to form a topcoat film. An intermediate coating film may be formed between the undercoat film and the topcoat film.

[0062] The aqueous coating composition that is the topcoat coating composition is not particularly limited. Examples of aqueous coating compositions include acrylic resin-based coating compositions, urethane resin-based coating compositions, epoxy resin-based coating compositions, chlorinated polyolefin-based coating compositions, silicone resin-based coating compositions, fluororesin-based coating compositions, and phthalic acid resin-based coating compositions. Among these, the aqueous coating compositions are preferably urethane resin-based coating compositions, epoxy resin-based coating compositions, silicone resin-based coating compositions, and fluororesin-based coating compositions, in view of their superior coating film appearance and weather resistance.

[0063] The method for applying the aqueous coating composition is not particularly limited, and examples of the application method that can be used include known methods such as spray coating, roller coating, brush coating, and flow coating.

[0064] The aqueous coating composition is applied and dried as appropriate under drying conditions of a humidity of 85% or less, at 5 to 35°C, for about 4 to 48 hours.

[0065] The dry film thickness of the resulting topcoat coating film is not particularly limited. For example, the dry film thickness is preferably 5 μm or more, more preferably 10 μm or more. Furthermore, the dry film thickness is preferably 100 μm or less, more preferably 50 μm or less. When the dry film thickness is within the above range, the resulting coated product has better corrosion resistance, weather resistance, and water resistance.

[0066] As described above, the corrosion-protective coating method and coated article manufacturing method of this embodiment use the above-mentioned aqueous epoxy resin-based undercoat coating composition, which is environmentally friendly and allows for the formation of a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion protection. Furthermore, because the corrosion-protective coating method and coated article manufacturing method use the above-mentioned aqueous epoxy resin-based undercoat coating composition, the resulting undercoat coating film and topcoat coating film have excellent compatibility. Furthermore, the resulting coated article has a good coating film appearance and excellent weather resistance.

[0067] (Second embodiment) A corrosion-protective coating method according to one embodiment of the present invention includes the steps of applying the above-described aqueous epoxy resin-based undercoat coating composition to a metal substrate to form an undercoat coating film, applying an epoxy resin-based aqueous coating composition to the undercoat coating film to form an intermediate coating film, and applying a fluororesin- or urethane resin-based aqueous coating composition to the intermediate coating film to form a topcoat coating film. A method for producing a coated article according to one embodiment of the present invention includes the steps of applying the above-described aqueous epoxy resin-based undercoat coating composition to a metal substrate to form an undercoat coating film, applying an epoxy resin-based aqueous coating composition to the undercoat coating film to form an intermediate coating film, and applying a fluororesin- or urethane resin-based aqueous coating composition to the intermediate coating film to form a topcoat coating film. In the following description, the details described above in relation to the embodiment of the aqueous epoxy resin-based undercoat coating composition and the first embodiment of the corrosion-protective coating method will be omitted as appropriate.

[0068] ·Undercoat film formation process The undercoat film forming step is a step of applying the above-mentioned aqueous epoxy resin-based undercoat coating composition to a metal substrate to form an undercoat film. The undercoat film forming step is as described above in relation to the first embodiment of the corrosion-protective coating method.

[0069] Intermediate coating film formation process The intermediate coating film forming step is a step in which an epoxy resin-based water-based paint composition is applied on the undercoat coating film to form an intermediate coating film.

[0070] The epoxy resin constituting the epoxy resin-based aqueous coating composition is not particularly limited. Examples of epoxy resins include bisphenol-type epoxy resins, novolac-type epoxy resins, glycidyl ether-type epoxy resins, glycidyl ester-type epoxy resins, and alicyclic epoxy resins. The epoxy resin may be a modified epoxy resin modified with an alkylphenol or a fatty acid, or may be an alkylphenyl glycidyl ether obtained by reacting an alkylphenol with epichlorohydrin, or an alkylphenol novolac-type epoxy resin obtained by reacting a novolac-type alkylphenol resin with epichlorohydrin.

[0071] The epoxy resin-based aqueous coating composition may contain, as necessary, coloring pigments, extender pigments, anti-rust pigments, dyes, curing agents, thickeners, dispersants, matting agents, defoaming agents, leveling agents, anti-sagging agents, surface conditioners, viscosity adjusters, waxes, silane coupling agents, anti-rust agents other than anti-rust pigments, preservatives, antifreezing agents, film-forming aids, anti-cistering agents, etc.

[0072] The pigment volume concentration (PVC) in the nonvolatile matter of the epoxy resin-based aqueous coating composition is preferably 20% or more, more preferably 25% or more. The PVC of the coating composition is preferably 40% or less, more preferably 35% or less. By having the PVC of the coating composition within the above range, the coating composition has excellent corrosion resistance, coating workability, and interlayer adhesion.

[0073] The method for applying the epoxy resin-based aqueous coating composition is not particularly limited, and examples of the application method that can be used include known methods such as spray coating, roller coating, brush coating, and flow coating.

[0074] The epoxy resin-based water-based coating composition is applied as appropriate under coating conditions of humidity of 85% or less, at 5 to 35°C, and for about 12 to 48 hours, and then dried.

[0075] The dry film thickness of the resulting intermediate coating film is not particularly limited. For example, the dry film thickness is preferably 5 μm or more, more preferably 10 μm or more. Furthermore, the dry film thickness is preferably 100 μm or less, more preferably 50 μm or less. When the dry film thickness is within the above range, the resulting coated product has better corrosion resistance and interlayer adhesion.

[0076] Topcoat film formation process The topcoat film forming step is a step in which a fluororesin-based or urethane resin-based aqueous coating composition is applied on the intermediate coating film to form a topcoat film.

[0077] The fluororesin-based aqueous coating composition may be either a one-component type or a two-component type.

[0078] The fluororesin is not particularly limited. Examples of the fluororesin include PTFE (polytetrafluoroethylene resin), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), polyvinylidene fluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinyl fluoride (PVF), fluoroolefin-vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer. Among these, the fluororesin is preferably PTFE, PVDF, or fluoroolefin-vinyl ether copolymer, because of its superior weather resistance.

[0079] The urethane resin-based aqueous coating composition is not particularly limited. Examples of the urethane resin-based aqueous coating composition include a polyurethane resin coating composition, a polyester urethane resin coating composition, a moisture-curing polyurethane resin coating composition, an epoxy urethane coating composition, and a modified epoxy urethane resin coating composition.

[0080] The polyurethane resin coating composition is, for example, a two-component polyurethane resin coating composition containing an aliphatic and / or alicyclic polyisocyanate as the isocyanate component, or a one-component polyurethane resin coating composition containing a urethane emulsion.

[0081] Aliphatic polyisocyanates include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate (HDI).

[0082] Alicyclic polyisocyanates include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

[0083] The aliphatic or alicyclic polyisocyanate may be modified into a biuret type, an adduct type, an isocyanurate type, or the like, or may be a prepolymer.

[0084] Fluororesin-based or urethane resin-based aqueous coating compositions may contain, as necessary, coloring pigments, extender pigments, anti-rust pigments, dyes, curing agents, thickeners, dispersants, matting agents, defoaming agents, leveling agents, anti-sagging agents, surface conditioners, viscosity adjusters, waxes, silane coupling agents, anti-rust agents other than anti-rust pigments, preservatives, antifreezing agents, film-forming aids, anti-cising agents, ultraviolet absorbers, light stabilizers, and the like.

[0085] The pigment volume concentration (PVC) in the nonvolatile matter of a fluororesin- or urethane-resin-based aqueous coating composition is preferably 10% or more, more preferably 15% or more. The PVC of the coating composition is preferably 25% or less, more preferably 20% or less. By having the PVC of the coating composition within the above range, the coating composition has excellent coating appearance, coating workability, and interlayer adhesion.

[0086] The PVC of the coating composition used in the undercoat coating film forming step and the intermediate coating film forming step is preferably higher than the PVC of the coating composition used in the topcoat coating film forming step. When the PVC of the coating composition satisfies the above relationship, the coating composition has excellent coating appearance, coating workability, and interlayer adhesion.

[0087] The method for applying the fluororesin-based or urethane resin-based aqueous coating composition is not particularly limited, and examples of the application method include known methods such as spray coating, roller coating, brush coating, and flow coating.

[0088] A fluororesin-based or urethane resin-based aqueous coating composition is applied and dried as appropriate under drying conditions of humidity of 85% or less, at 5 to 35°C for about 4 to 48 hours.

[0089] The dry film thickness of the resulting topcoat coating film is not particularly limited. For example, the dry film thickness is preferably 5 μm or more, more preferably 10 μm or more. Furthermore, the dry film thickness is preferably 100 μm or less, more preferably 50 μm or less. When the dry film thickness is within the above range, the resulting coated product has better corrosion resistance, weather resistance, and water resistance.

[0090] As described above, the corrosion-protective coating method and coated article manufacturing method of this embodiment use the above-mentioned aqueous epoxy resin-based undercoat coating composition, which is environmentally friendly and allows for the formation of a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion protection. Furthermore, because the corrosion-protective coating method and coated article manufacturing method use the above-mentioned aqueous epoxy resin-based undercoat coating composition, the resulting undercoat coating film and topcoat coating film have excellent compatibility. Furthermore, the resulting coated article has a good coating film appearance and excellent weather resistance. [Example]

[0091] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. Unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0092] The raw materials used are shown below. Epoxy resin 1: Bisphenol A epoxy resin (ADEKA Corporation, ADEKA Resin EM-101-50, epoxy equivalent (solid content) 535 g / eq, solid content 50%) Anti-rust pigments 1-7 and 9 were prepared by reacting and / or mixing aluminum tripolyphosphate, zinc oxide, precipitated barium, and zinc molybdate, adjusting the molybdate content and water-soluble content as appropriate. The reaction was carried out in water as appropriate, and the resulting composition was dried and then pulverized to obtain an anti-rust pigment. For example, Anti-rust pigment 2 was prepared by reacting 78 parts of aluminum tripolyphosphate and 22 parts of zinc oxide in water, spray-drying the resulting composition, mixing the resulting composition with 85% by mass, 5% by mass of zinc molybdate, and 10% by mass of precipitated barium sulfate, and pulverizing the mixture. Anti-rust pigment 4 was prepared by reacting 90 parts of aluminum tripolyphosphate and 10 parts of zinc oxide in water, spray-drying the resulting composition, mixing the resulting composition with 76% by mass, 8% by mass of zinc oxide, 10% by mass of zinc molybdate, and 6% by mass of precipitated barium sulfate, and pulverizing the mixture. Anti-rust pigment 5 was prepared by reacting 59 parts of aluminum tripolyphosphate and 41 parts of zinc oxide in water, spray-drying the resulting composition (86 mass %), mixing with 11 mass % of zinc molybdate, and 3 mass % of precipitated barium sulfate, and pulverizing the mixture. Anti-rust pigment 6 was prepared by reacting 59 parts of aluminum tripolyphosphate and 41 parts of zinc oxide in water, spray-drying the resulting composition (96 mass %), mixing with 1 mass % of zinc molybdate, and 3 mass % of precipitated barium sulfate, and pulverizing the mixture. Anti-rust pigment 7 was prepared by reacting 82 parts of aluminum tripolyphosphate and 18 parts of zinc oxide in water, spray-drying the resulting composition (93 mass %), mixing with 1 mass % of zinc molybdate, and 6 mass % of precipitated barium sulfate, and pulverizing the mixture. Anti-rust pigment 9 was prepared by reacting 90 parts of aluminum tripolyphosphate and 10 parts of zinc oxide in water, spray-drying the resulting mixture, and mixing and pulverizing the mixture with 68% by mass of a composition obtained by the reaction, 7% by mass of zinc oxide, 20% by mass of zinc molybdate, and 5% by mass of precipitated barium sulfate. Anti-rust pigment 8: Kikuchi Color Co., Ltd., PW-2 (zinc phosphate) Other pigment 1: Titanium oxide (CRISTAL, TiONA 595) Other pigment 2: Talc (Talc MS412, manufactured by Fuji Talc Industries Co., Ltd.) Other pigment 3: Precipitated barium sulfate (Sakai Chemical Industry Co., Ltd., Precipitated barium sulfate 100) Additive 1: Dispersant (BYK Japan, DISPERBYK-2010) Additive 2: Antifoaming agent (BYK-024, manufactured by BYK Japan Co., Ltd.) Additive 3: Leveling agent (BYK-348, manufactured by BYK Japan Co., Ltd.) Additive 4: Antifreeze (ADEKA Corporation, propylene glycol) Additive 5: Rust inhibitor other than anti-rust pigment (Kiresutoru Light WC-L, manufactured by KIRESUTO Co., Ltd.) Amine compound 1: Modified aliphatic polyamine (Fujicure FXH-935, manufactured by T&K TOKA Corporation, active hydrogen equivalent (solid content) 213, solid content 80%) Amine compound 2: Polyamidoamine (T&K TOKA Corporation, Tomide TXS-53-C, active hydrogen equivalent (solid content) 525, solid content 40%) Amine compound 3: Modified aliphatic polyamine emulsion (Fujicure FXS-918-FA, manufactured by T&K TOKA Corporation, active hydrogen equivalent (solid content) 500, solid content 60%)

[0093] ·Measuring method for water-soluble content of anti-rust pigments The water-soluble content of the anti-rust pigment was measured in accordance with "JIS K 5101-16-2". -Method for measuring the amount of molybdenum oxide in anti-rust pigments The molybdate content in the anti-rust pigment was measured in terms of molybdenum oxide using the following method. Approximately 0.3 g of the anti-rust pigment was added to 20 mL of 10% aqueous sodium hydroxide solution and heated to a boil. To this was added 20 mL of 20% aqueous nitric acid solution, followed by approximately 70 mL of water and heated until transparent. After cooling, the mixture was transferred to a 250 mL volumetric flask and water was added up to the mark. A 10 mL aliquot was placed in a 100 mL volumetric flask, to which 2.5 mL of 20% aqueous nitric acid solution was added, followed by water up to the mark. This mixture was then analyzed using inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-OES, Agilent Technologies, Inc., 5900 ICP-OES). The amount of molybdenum in the anti-rust pigment was calculated using a simultaneously measured molybdenum calibration curve and calculated as molybdenum oxide (MoO3).

[0094] Example 1 The resin, anti-rust pigment and other pigments listed in Table 1 were dispersed in water, and then additives were added and the mixture was stirred with water to prepare a water-based epoxy resin-based primer coating composition.

[0095] <Examples 2 to 10 and Comparative Examples 1 to 3> Aqueous epoxy resin-based undercoat coating compositions were prepared in the same manner as in Example 1, except that the formulation and conditions were changed to those shown in Table 1.

[0096] [Table 1]

[0097] The resulting aqueous epoxy resin primer coating compositions were evaluated for coating appearance, drying properties (semi-curing properties), cyclic corrosion resistance, acid resistance, alkali resistance, and moisture resistance using the following evaluation methods. The results are shown in Table 1.

[0098] <Painting conditions for test panels> (Painting specification 1 (single film)) Base material: SPCC-SB (cold-rolled steel plate) specified in "JIS G 3141" Film thickness: 60±5μm Drying conditions: Natural drying (JIS K 5600-1-1 3.3.8) for 7 days. (Painting specification 2 (single film)) Substrate: 150mm x 70mm x 3.2mm SS400 steel plate specified in "JIS G 3101", which was blasted. The blasting conditions were as follows: Degree of rust removal: Sa 2 1 / 2 or more as specified in JIS Z 0313 Abrasive: Grid Surface roughness: 25 μm Rzjis was used as standard. Film thickness: 60±5μm Drying conditions: Natural drying (JIS K 5600-1-1 3.3.8) for 7 days. (Painting specification 3 (multi-layer film)) ·undercoat Substrate: SPCC-SB (cold-rolled steel plate) specified in "JIS G 3141" prepared (by polishing) according to "JIS K 5600-1-4 5.1.5". The size was 150 mm x 70 mm x 0.8 mm. The abrasive paper used for polishing was waterproof abrasive paper P280 specified in "JIS R 6253". Film thickness: 60±5μm Drying conditions: Natural drying according to JIS K 5600-1-1 3.3.8, cured for one day. Undercoat Water-based epoxy resin intermediate coating composition: SWET intermediate coating A (main agent) white and B (hardener), manufactured by Tohpe Corporation Film thickness: 30±5μm Drying conditions: Natural drying according to JIS K 5600-1-1 3.3.8, cured for one day. Top coat Water-based fluororesin topcoat paint composition: SWET Topcoat FA (main agent) white and B (hardener), manufactured by Tohpe Corporation Film thickness: 25±5μm Drying conditions: Natural drying (JIS K 5600-1-1 3.3.8) for 7 days.

[0099] <Test conditions and evaluation criteria> (Coating appearance) Test panels with coating specification 1 (single film) were used. The appearance of the coating film was visually observed and classified according to the following evaluation criteria. ⊚: The coating surface was smooth and the coating appearance was excellent. ×: Coating defects such as repellency, bumps, and blisters were observed on the coating surface. (Drying (semi-curing)) Test panels with coating specification 1 (single film) were used. Evaluation was carried out in accordance with "JIS K 5600-1-1 4.3.5", with a pass being indicated by ⊚ and a fail being indicated by ×. (cyclic corrosion) Test panels with coating specification 2 (single film) were used. Tests were conducted according to the test method of "JIS K 5551 7.17" and classified according to the following evaluation criteria. The test equipment used was a combined cycle tester CYP-90L manufactured by Suga Test Instruments Co., Ltd. ⊚: No rust, swelling, cracking or peeling was observed. ○: Rust, swelling, cracking and peeling were observed in a small area. ×: Rust, swelling, cracking and peeling were observed. (acid resistance) Test panels with coating specification 3 (multi-layer film) were used. Tests were conducted according to the test method of "JIS K 5659 7.17" and classified according to the following evaluation criteria. ⊚: The degree of color change was not great, and no swelling, cracking, peeling, or holes were observed. ◯: The degree of color change was not great, and no cracks, peeling, or holes were observed, but a small amount of swelling was observed. ×: Color change, cracks, peeling and holes were observed. (alkali resistance) Test panels with coating specification 3 (multi-layer film) were used. Tests were conducted according to the test method of "JIS K 5659 7.16" and classified according to the following evaluation criteria. ⊚: The degree of color change was not great, and no swelling, cracking, peeling, or holes were observed. ◯: The degree of color change was not great, and no cracks, peeling, or holes were observed, but a small amount of swelling was observed. ×: Color change, cracks, peeling and holes were observed. (moisture resistance) Test panels with paint specification 2 (single layer) were used. Tests were conducted according to the test method of "Metropolitan Expressway Co., Ltd. Civil Engineering Materials Common Specifications, May 2023, 6.10 Water-based Epoxy Resin Paint SDK W-513 (May 2023) (14) Moisture Resistance," and the results were classified according to the following evaluation criteria. The test equipment used was a humidity tester CT-3 manufactured by Suga Testing Instruments Co., Ltd. ⊚: No rust, swelling, cracking or peeling was observed. ○: Rust, swelling, cracking and peeling were observed in a small area. ×: Rust, swelling, cracking and peeling were observed.

[0100] As shown in Table 1, the aqueous epoxy resin primer coating composition of the present invention was able to form a coating film with excellent chemical resistance (acid resistance and alkali resistance) and long-term corrosion prevention. Furthermore, the aqueous epoxy resin primer coating composition of the present invention was highly compatible with the substrate and the topcoat paint, and had a good appearance.

Claims

1. The composition contains an epoxy resin, an amine compound, a rust-preventive pigment, and water, The anti-rust pigment comprises a molybdate; The water-soluble content of the anti-rust pigment is 0.01 to 1.0 mass %.

2. 2. The aqueous epoxy resin-based primer coating composition according to claim 1, wherein the content of the molybdate salt, calculated as the amount of molybdenum oxide, in the rust-preventive pigment is 0.1 to 5.0 mass %.

3. 3. The aqueous epoxy resin-based primer coating composition according to claim 1, wherein the equivalent ratio of said epoxy resin to said amine compound is 0.4 to 0.

7.

4. 3. The aqueous epoxy resin-based primer coating composition according to claim 1, wherein the amine compound comprises an aliphatic polyamine or a polyamidoamine.

5. a step of applying the aqueous epoxy resin-based primer coating composition according to claim 1 or 2 onto a metal substrate to form an primer coating film; and a step of applying an aqueous coating composition onto the undercoat coating to form a topcoat coating.

6. a step of applying the aqueous epoxy resin-based primer coating composition according to claim 1 or 2 onto a metal substrate to form an primer coating film; a step of applying an epoxy resin-based aqueous coating composition on the undercoat coating to form an intermediate coating; and a step of applying a fluororesin-based or urethane resin-based aqueous coating composition on the intermediate coating to form a top coating.

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