Multi-liquid type water-based coating composition, multilayer coating film and method for forming multilayer coating film

Abstract

To provide a multi-liquid type water-based coating composition from which a coating film that is excellent in surface dryness and adhesion of the coating films even when an interval of a plurality of coating steps is long can be obtained.SOLUTION: A multi-liquid type water-based coating composition contains a main agent containing a carboxy group-containing water-based acrylic resin (A1) and a modified epoxy resin (A2), and a curing agent containing a hydrophilized modified carbodiimide compound (B1), wherein the modified epoxy resin (A2) has an anionic group and has no ester bond produced by reaction of an epoxy group and a fatty acid-derived carboxy group, and has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less and an average particle diameter of 30 nm or more and 2,000 nm or less, and a ratio (Wac / Wep) of a solid content mass Wac of the carboxy group-containing water-based acrylic resin (A1) to a solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a multi-liquid type aqueous paint composition, a multi-layer coating film, and a method for forming the multi-layer coating film.

Background Art

[0002] Patent Document 1 discloses a two-liquid type aqueous paint composition containing an aqueous acrylic resin having a carboxyl group and a carbodiimide compound. Patent Documents 2 and 3 disclose using a carbodiimide compound as a curing agent in an aqueous material containing a vinyl-modified epoxy resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a multi-liquid type aqueous paint composition capable of obtaining a coating film excellent in surface drying property and also excellent in adhesion to other coating films even when the interval between a plurality of coating steps is long.

Means for Solving the Problems

[0005] To solve the above problems, the present invention provides the following aspects. [1] A main agent containing a carboxyl group-containing aqueous acrylic resin (A1) and a modified epoxy resin (A2), and A curing agent containing a hydrophilically modified carbodiimide compound (B1), The modified epoxy resin (A2) has an anionic group, does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less, A two-component type aqueous paint composition, wherein the ratio (Wac / Wep) of the solid content mass Wac of the carboxy group-containing aqueous acrylic resin (A1) to the solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5. [2] The carboxy group-containing aqueous acrylic resin (A1) in the two-component type aqueous paint composition according to [1] above has a solid content acid value of 3 mgKOH / g or more and 50 mgKOH / g or less, and a glass transition point of -25°C or more and 50°C or less. [3] The main agent further contains an organic solvent (A3) having a boiling point of 150°C or more and 300°C or less in the two-component type aqueous paint composition according to [1] or [2] above. [4] In the two-component type aqueous paint composition according to [3] above, the content of the organic solvent (A3) is 1 part by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the total solid content of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2). [5] In the two-component type aqueous paint composition according to [1] or [2] above, the equivalent ratio (carboxy group / carbodiimide group) of the total carboxy group of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2) to the carbodiimide group of the hydrophilically modified carbodiimide compound (B1) is 0.4 or more and 2.2 or less. [6] It is for forming an intermediate coat film, In the two-component type aqueous paint composition according to [1] or [2] above, a top coat film formed by an aqueous top coat paint composition is formed on the intermediate coat film. [7] It is for forming an intermediate coat film, In the two-component type aqueous paint composition according to [1] or [2] above, the intermediate coat film is formed on a primer coat film formed by an aqueous primer paint composition. [8] An undercoat coating film disposed on an object to be coated, An intermediate coat coating film disposed on the undercoat coating film and formed from the two-component aqueous coating composition of [1] or [2] above, And a topcoat coating film disposed on the intermediate coat coating film, the multi-layer coating film comprising the same. [9] The undercoat coating film is formed from an aqueous undercoat coating composition comprising a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin, The topcoat coating film is formed from an aqueous topcoat coating composition comprising a main agent containing a carboxyl group-containing aqueous acrylic resin and a curing agent containing a hydrophilic-modified carbodiimide compound, the multi-layer coating film of [8] above.

[10] Coating an aqueous undercoat coating composition on an object to be coated to form an undercoat coating film, Coating the two-component aqueous coating composition of [1] or [2] above on the undercoat coating film to form an intermediate coat coating film, Coating an aqueous topcoat coating composition on the intermediate coat coating film to form a topcoat coating film, a method for forming a multi-layer coating film comprising the same. [Advantages of the Invention]

[0006] According to the present invention, there is provided a two-component aqueous coating composition capable of obtaining a coating film excellent in surface drying property and excellent in adhesion to other coating films even when the interval between a plurality of coating steps is long. [Embodiments for Carrying Out the Invention]

[0007] From the viewpoints of corrosion resistance and design, a multi-layer coating film is formed on large structures such as ships, bridges, buildings, tanks, and plants. When forming a multi-layer coating film on a large structure, usually, a long interval (coating interval) occurs between coating steps. During the period until the next coating step, the previously formed coating film (the lower coating film) is exposed to ultraviolet rays and deteriorates. It is difficult for the subsequently formed coating film (the upper coating film) to adhere to the deteriorated lower coating film.

[0008] According to the multi-liquid type aqueous coating composition of the present disclosure (hereinafter, may be simply referred to as an aqueous coating composition), even when the interval between a plurality of coating steps is long, the adhesion between the coating film formed by the aqueous coating composition and the underlying coating film, and the adhesion between the coating film formed by the aqueous coating composition and the overlying coating film are improved. The case where the interval is long is, for example, when there is an interval of about 10 days.

[0009] Hereinafter, the adhesion between coating films when the interval between a plurality of coating steps is long is referred to as interval adhesion. The coating film formed by the aqueous coating composition of the present disclosure may be referred to as an intermediate coating film. The aqueous coating composition of the present disclosure may be referred to as an intermediate coating composition. Based on the intermediate coating film, the coating film disposed adjacent to the lower layer of the intermediate coating film is referred to as an undercoat film, and the coating film disposed adjacent to the upper layer of the intermediate coating film is referred to as a topcoat film. The interval adhesion between the undercoat film and the intermediate coating film is referred to as under-intermediate interval adhesion. The interval adhesion between the intermediate coating film and the topcoat film is referred to as intermediate-top interval adhesion.

[0010] Since the acrylic resin is excellent in weather resistance, it contributes to the suppression of deterioration of the coating film. On the other hand, the acrylic resin has a small effect of enhancing the interval adhesion. In the present disclosure, a specific modified epoxy resin is used together with a carboxyl group-containing aqueous acrylic resin as the main agent in a curing system in which a carboxyl group and a carbodiimide group are involved.

[0011] The usage amount of the specific modified epoxy resin is set to be equal to or less than that of the acrylic resin. Thereby, the surface drying property is improved together with the interval adhesion. Specifically, the ratio (Wac / Wep) of the solid content mass Wac of the carboxyl group-containing aqueous acrylic resin (A1) to the solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5.

[0012] The specific modified epoxy resin used in the present disclosure has an anionic group, does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less.

[0013] Epoxy resins have hydroxyl groups due to their synthesis method. Due to the action such as hydrogen bonding by the hydroxyl groups, epoxy resins can strongly adhere to other coating films. In addition, the above-mentioned modified epoxy resin does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid. Aliphatic groups are generally hydrophobic. Therefore, the intermediate coating composition or intermediate coating film having no such ester bond (in other words, fatty acid residue) is particularly compatible with the undercoat film formed by an aqueous coating composition and / or an aqueous topcoat composition. Thereby, it is considered that the interval adhesion between the intermediate coating film and other coating films is improved.

[0014] The upper interval adhesion in the intermediate coating film formed by the aqueous coating composition of the present disclosure is exhibited even when it is painted and sufficiently dried and then left outdoors in summer for 10 days. Further, even when the obtained multilayer coating film is immersed in water after the topcoat film is formed, high upper interval adhesion can be obtained. The adhesion is evaluated according to the cross-cut method of JIS K5600-5-6. When 25 squares are formed at a cut interval of 3 mm in the multilayer coating film including the intermediate coating film formed by the aqueous coating composition of the present disclosure, the number of squares where the intermediate coating film is peeled off is 10 or less. The lower-middle interval adhesion between the undercoat film and the intermediate coating film is also excellent.

[0015] Large structures are usually painted outdoors. Therefore, there are cases where an insufficiently dried coating film is exposed to rain. In this case, the coating film can greatly expand and cracks and blisters can occur. Hereinafter, the water resistance of a coating film that is not completely cured but has no stickiness is referred to as initial water resistance.

[0016] In the present disclosure, an epoxy resin having a solid acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less is used. Thereby, the initial rain resistance of the intermediate coat film is improved. The initial rain resistance of the intermediate coat film is exhibited even when it is dried at a low temperature (10°C or lower) and rained on. When the aqueous coating composition of the present disclosure is dried at 5°C for 6 hours and the obtained semi-dry coating film is immersed in water at 5°C for 16 hours, the crack density evaluated in accordance with JIS K 5600-8-4 is 2 or less. Hereinafter, the initial rain resistance when dried at a low temperature (10°C or lower) and rained on is referred to as low-temperature initial rain resistance.

[0017] The surface drying property of the intermediate coat film is high even at a low temperature (10°C or lower). When a coating film obtained by drying the aqueous coating composition of the present disclosure at 5°C for 16 hours was tested in accordance with the surface drying property (Barotini method) in accordance with JIS K 5600-3-2, it was possible to remove Barotini (glass beads) leaving only 5 or less without scratching.

[0018] Hereinafter, the aqueous resin refers to a water-soluble resin or a water-dispersible resin (including dispersion form and emulsion form). Aqueous conversion means making the resin water-soluble or water-dispersible.

[0019] The aqueous coating composition contains water as a solvent. The proportion of water in all solvents is 50% by mass or more, and may be 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0020] The weight average molecular weight and the number average molecular weight are measured by polystyrene standard by GPC (gel permeation chromatography) method.

[0021] Tg may be determined by calculation from the types and amounts of raw material monomers, or may be measured by a differential scanning calorimeter (DSC).

[0022] The solid content acid value can be measured by a known method described in JIS K 0070:1992. The solid content acid value may be calculated from the blending amount of the unsaturated monomer in the raw material monomer of the target resin.

[0023] The epoxy equivalent is determined in accordance with JIS K 7236.

[0024] The average particle diameter is the 50% average particle diameter (D50) in the volume-based particle size distribution using a particle size distribution measuring device of the laser diffraction / scattering method.

[0025] [Two-component aqueous coating composition] The aqueous coating composition of the present disclosure includes a main agent containing a carboxy group-containing aqueous acrylic resin (A1) and a modified epoxy resin (A2), and a curing agent containing a hydrophilically modified carbodiimide compound (B1). The aqueous coating composition is a two-component type containing the main agent and the curing agent. The aqueous coating composition may further include a third agent containing other components.

[0026] The aqueous coating composition of the present disclosure is suitable for forming an intermediate coating film. The intermediate coating film is disposed between the other two coating films (the primer coating film and the topcoat film). The adhesiveness between the intermediate coating film and the other coating films affects the performance of the multi-layer coating film. Since the aqueous coating composition of the present disclosure forms a coating film excellent in interval adhesiveness, it is particularly suitable for forming an intermediate coating film of a large structure.

[0027] The aqueous coating composition cures (dries) by the reaction between the carboxy group and the carbodiimide group. The curing system involving the carboxy group and the carbodiimide group improves the surface drying property of the aqueous coating composition. The above curing system exhibits excellent surface drying property even at low temperatures. Therefore, even if an operator walks on the intermediate coating film with insufficient drying in winter, it is difficult for shoe marks to be formed on the coating film, and peeling of the coating film is reduced. Thereby, the coating workability and appearance are improved.

[0028] · Carboxy group-containing aqueous acrylic resin (A1) The carboxy group-containing aqueous acrylic resin (A1) (hereinafter, may be simply referred to as aqueous acrylic resin (A1)) reacts with a carbodiimide compound (B1) to form a crosslinked structure at a temperature from low temperature to normal temperature (for example, 5°C or higher and 30°C or lower).

[0029] The solid content acid value of the aqueous acrylic resin (A1) may be 3 mgKOH / g or more and 50 mgKOH / g or less. When the solid content acid value of the aqueous acrylic resin (A1) is 3 mgKOH / g or more, the corrosion resistance of the coating film is likely to increase. When the solid content acid value of the aqueous acrylic resin (A1) is 50 mgKOH / g or less, the water resistance (especially, the initial low-temperature rain resistance) and the corrosion resistance of the coating film are likely to improve.

[0030] The solid content acid value of the aqueous acrylic resin (A1) may be 5 mgKOH / g or more, and may be 10 mgKOH / g or more. The solid content acid value of the aqueous acrylic resin (A1) may be 45 mgKOH / g or less, may be 40 mgKOH / g or less, and may be 20 mgKOH / g or less.

[0031] The glass transition point (Tg) of the aqueous acrylic resin (A1) may be -25°C or higher and 50°C or lower. When the Tg of the aqueous acrylic resin (A1) is -25°C or higher, the surface drying property of the aqueous coating composition from low temperature to normal temperature is likely to improve. When the Tg of the aqueous acrylic resin (A1) is 50°C or lower, the water resistance (especially, the initial low-temperature rain resistance) of the coating film is likely to improve.

[0032] The Tg of the aqueous acrylic resin (A1) may be -15°C or higher, may be -5°C or higher, and may be 5°C or higher. The Tg of the aqueous acrylic resin may be 40°C or lower, may be 30°C or lower, and may be 20°C or lower.

[0033] The aqueous acrylic resin (A1) may have a solid content acid value of 3 mgKOH / g or more and 50 mgKOH / g or less, and a glass transition point of -25°C or higher and 50°C or lower.

[0034] The aqueous acrylic resin (A1) may be water-soluble or water-dispersible. The aqueous acrylic resin (A1) may be an acrylic resin emulsion.

[0035] The aqueous acrylic resin (A1) is obtained by copolymerizing a carboxyl group-containing α,β-ethylenically unsaturated monomer and other α,β-ethylenically unsaturated monomers. When these monomers are emulsion-polymerized, an acrylic resin emulsion is obtained.

[0036] Examples of the carboxyl group-containing α,β-ethylenically unsaturated monomer include (meth)acrylic acid, (meth)acrylic acid dimer, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, and itaconic acid. These may be used alone or in combination of two or more. Among them, (meth)acrylic acid may be used. (meth)acrylic acid represents acrylic acid and methacrylic acid.

[0037] Examples of other α,β-ethylenically unsaturated monomers include (meth)acrylic acid methyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth)acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate; polymerizable amide compounds such as (meth)acrylamide, N-methylol(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N,N-dioctyl(meth)acrylamide, N-monobutyl(meth)acrylamide, N-monooctyl(meth)acrylamide, 2,4-dihydroxy-4'-vinylbenzophenone, N-(2-hydroxyethyl)acrylamide, and N-(2-hydroxyethyl)methacrylamide; polymerizable aromatic compounds such as styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, p-chlorostyrene, and vinyl naphthalene; polymerizable nitriles such as acrylonitrile and methacrylonitrile; α-olefins such as ethylene and propylene; vinyl esters such as vinyl acetate and vinyl propionate; and dienes such as butadiene and isoprene. These may be used alone or in combination of two or more.

[0038] As other α,β-ethylenically unsaturated monomers, crosslinkable monomers may be used. A crosslinkable monomer is a compound having two or more radically polymerizable ethylenically unsaturated groups in the molecule. Examples of the crosslinkable monomer include divinylbenzene, ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, allyl (meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate and other divinyl compounds; triallyl cyanurate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate and other monomers having a functionality of 3 or more. These may be used alone or in combination of two or more. Among them, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, and divinylbenzene may be used.

[0039] Additionally, a hydroxyl group-containing α,β-ethylenically unsaturated monomer may be used. Examples of the hydroxyl group-containing α,β-ethylenically unsaturated monomer include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methacryl alcohol, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone. These may be used alone or in combination of two or more. Among them, hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone may be used.

[0040] The method of emulsion polymerization is not particularly limited. For example, an emulsifier is dissolved in an aqueous medium containing water or, if necessary, an organic solvent such as alcohol, ether (e.g., dipropylene glycol methyl ether, propylene glycol methyl ether, etc.), and each α,β-ethylenically unsaturated monomer and polymerization initiator are dropped while heating and stirring. Each α,β-ethylenically unsaturated monomer may be pre-emulsified with an emulsifier.

[0041] As the polymerization initiator and emulsifier, those commonly used by those skilled in the art can be used. If necessary, the molecular weight may be adjusted using a chain transfer agent such as mercaptan (e.g., lauryl mercaptan) and α-methylstyrene dimer. The reaction temperature, reaction time, etc. can be appropriately selected within the range commonly used by those skilled in the art.

[0042] The obtained acrylic resin emulsion is neutralized with a basic compound if necessary. By neutralization, the pH of the aqueous paint composition can be adjusted to 5 - 10. Examples of the basic compound include amines such as ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, diethylaminoethanol, triethanolamine, tetraethylammonium hydroxide, propylamine, dipropylamine, tripropylamine, butylamine, dibutylamine, tributylamine; and hydroxides of alkali metals such as sodium hydroxide.

[0043] The average particle diameter of the acrylic resin emulsion may be, for example, 0.01 μm or more and 1.0 μm or less. When the average particle diameter of the acrylic resin emulsion is within the above range, the paint stability is improved, and the smoothness of the obtained paint film is also improved. The average particle diameter can be adjusted, for example, by the monomer composition and the conditions of emulsion polymerization.

[0044] After solution-polymerizing the above monomer and then forcibly dispersing it, an acrylic resin dispersion can be obtained. The number average molecular weight (Mn) of the acrylic resin dispersion is, for example, 4,000 or more and 20,000 or less. When the Mn of the acrylic resin dispersion is 4,000 or more, the hardness and weather resistance of the resulting coating film are likely to be improved. When the Mn of the acrylic resin dispersion is 20,000 or less, an excessive increase in the viscosity of the aqueous coating composition is likely to be suppressed.

[0045] · Modified epoxy resin (A2) The modified epoxy resin (A2) (hereinafter, may be simply referred to as modified epoxy resin (A2)) has an anionic group, does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, and has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less.

[0046] Examples of the anionic group include a carboxy group, a phosphoric acid group, a phosphorous acid group, a carboxymethyl group, and a sulfo group. The anionic group is typically a carboxy group. The carboxy group of the modified epoxy resin (A2) can react with the carbodiimide compound (B1) to form a crosslinked structure. A part of the anionic group is neutralized to render the modified epoxy resin (A2) water-borne.

[0047] The solid content acid value of the modified epoxy resin (A2) is 5 mgKOH / g or more and 50 mgKOH / g or less. Thereby, the paint stability and water resistance (especially, initial rain resistance) are improved. The solid content acid value of the modified epoxy resin (A2) may be 10 mgKOH / g or more, may be 15 mgKOH / g or more, and may be 20 mgKOH / g or more from the viewpoint of paint stability. The solid content acid value of the modified epoxy resin (A2) may be 45 mgKOH / g or less, may be 40 mgKOH / g or less, and may be 30 mgKOH / g or less from the viewpoint of water resistance.

[0048] The number average molecular weight Mn of the modified epoxy resin (A2) is 1,000 or more and 15,000 or less. Thereby, paint stability and water resistance (particularly, initial rainfall resistance) are improved. The Mn of the modified epoxy resin (A2) may be 1,200 or more, may be 2,000 or more, and may be 3,000 or more from the viewpoint of water resistance. The Mn of the modified epoxy resin (A2) may be 13,000 or less, may be 10,000 or less, and may be 6,000 or less from the viewpoint of paint stability.

[0049] The average particle diameter of the modified epoxy resin (A2) is 30 nm or more and 2,000 nm or less. Thereby, paint stability and water resistance (particularly, initial rainfall resistance) are improved. The average particle diameter of the modified epoxy resin (A2) may be 50 nm or more, may be 80 nm or more, and may be 100 nm or more from the viewpoint of water resistance. The average particle diameter of the modified epoxy resin (A2) may be 1,500 nm or less, may be 1,200 nm or less, may be 1,000 nm or less, and may be 500 nm or less from the viewpoint of paint stability.

[0050] The modified epoxy resin (A2) does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid. In other words, when preparing the modified epoxy resin (A2), a fatty acid is not used as a compound that reacts with the epoxy group contained in the raw material epoxy resin. In particular, the modified epoxy resin (A2) does not use a long-chain fatty acid having 13 to 21 carbon atoms as a reaction material with the raw material epoxy resin.

[0051] The modified epoxy resin (A2) is not particularly limited as long as it has the above structure and physical properties. The modified epoxy resin (A2) may be a vinyl-modified epoxy resin, may be a vinyl graft-amine-modified epoxy resin, or may be an acrylic-modified epoxy resin from the viewpoint of improving interval adhesion.

[0052] <Synthesis Method 1> The vinyl graft-amine modified epoxy resin (A2a) is obtained, for example, by copolymerizing an anionic group-containing vinyl monomer (y) with a reaction product (x) of an epoxy resin (1) as a raw material (hereinafter referred to as the raw material epoxy resin (1)), a glycidyl group-containing vinyl monomer (2), and an amine compound (3).

[0053] For the synthesis of the vinyl graft-amine modified epoxy resin (A2a), for example, the methods described in JP-A-2009-24118 and WO 2007 / 004436 can be referred to.

[0054] The epoxy group of the raw material epoxy resin (1) is ring-opened by the amino group of the amine compound (3), and an amino group is introduced into the raw material epoxy resin (1). The amino group reacts with the epoxy group of the glycidyl group-containing vinyl monomer (2), and a vinyl group is introduced into the raw material epoxy resin (1). The vinyl group and the anionic group-containing vinyl monomer (y) are copolymerized to obtain an epoxy resin (A2a) in which a vinyl group is grafted via an amine group.

[0055] The raw material epoxy resin (1) is not particularly limited as long as it does not have a vinyl group. The epoxy equivalent of the raw material epoxy resin (1) may be, for example, 170 or more and 3,000 or less. Examples of the raw material epoxy resin (1) include aromatic epoxy resins such as bisphenol type, novolac type, biphenyl type, and naphthalene type; and aliphatic epoxy resins such as dicyclopentadiene type and glycidyl ethers of polyhydric alcohols. These may be used alone or in combination of two or more.

[0056] Examples of the bisphenol type epoxy resin include bisphenol A type, bisphenol F type, bisphenol S type, bisphenol AD type, diglycidyl ethers of alkylene oxide adducts of these bisphenol type epoxy resins, and hydrogenated bisphenol type obtained by adding hydrogen to these bisphenol type epoxy resins.

[0057] Examples of novolak type epoxy resins include phenol novolak type, cresol novolak type, and novolak type of bisphenol A.

[0058] Examples of biphenyl type, naphthalene type, and dicyclopentadiene type resins include resins in which one or more glycidyl ether groups are substituted at any position of biphenyl, naphthalene, or dicyclopentadiene.

[0059] The raw material epoxy resin (1) is produced, for example, by a known method. For example, bisphenol A type epoxy resin can be obtained by condensing a halogenated product of bisphenol A with epichlorohydrin or β-methylepihalohydrin.

[0060] Among them, in terms of further improving the interval adhesion, it may be an aromatic epoxy resin, may be a bisphenol type epoxy resin, and may be a bisphenol A type epoxy resin.

[0061] Examples of the glycidyl group-containing vinyl monomer (2) include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, and (meth)allyl glycidyl ether. These can be used alone or in combination of two or more. (Meth)acrylate represents acrylate and methacrylate.

[0062] Examples of the amine compound (3) include alkanolamines, aliphatic amines, aromatic amines, alicyclic amines, and aromatic nucleus-substituted aliphatic amines. Examples of the alkanolamine include ethanolamine, diethanolamine, diisopropanolamine, di-2-hydroxybutylamine, N-methylethanolamine, N-ethylethanolamine, and N-benzyethanolamine. Examples of the aliphatic amine include primary amines such as ethylamine, propylamine, butylamine, hexylamine, laurylamine, stearylamine, palmitylamine, oleylamine, and elsylamine; and secondary amines such as diethylamine, dipropylamine, and dibutylamine. Examples of the aromatic amine include toluidine, xylidine, cumidine (isopropyl aniline), hexylaniline, nonylaniline, and dodecylaniline. Examples of the alicyclic amines include cyclopentylamine, cyclohexylamine, and norbornylamine. Examples of the aromatic nucleus-substituted aliphatic amines include benzylamine and phenethylamine. These may be used alone or in combination of two or more.

[0063] Examples of the vinyl monomer (y) containing an anionic group include (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, and itaconic acid. These may be used alone or in combination of two or more.

[0064] Other components may be used as raw materials for the vinyl graft-amine modified epoxy resin (A2a). However, fatty acids are not used as compounds that react with the epoxy groups contained in the raw material epoxy resin (1). The residue of the fatty acid may be contained as a substituent of each raw material (the above (1) to (3)). Examples of the other components include (meth)acrylates having no glycidyl group, styrenes, and (meth)acrylic silane coupling agents. These may be used alone or in combination of two or more.

[0065] Examples of (meth)acrylates having no glycidyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and diacrylates of acrylic esters. Examples of styrenes include styrene, vinyltoluene, and α-methylstyrene. Examples of acrylic silane coupling agents include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane. These may be used alone or in combination of two or more.

[0066] The reaction conditions are appropriately set according to the types of raw materials and the like. A polymerization initiator may be used. Examples of the polymerization initiator include known organic peroxides and azo compounds. As the polymerization method, for example, the solution polymerization method is adopted.

[0067] The mass ratio (x / y) of the reactant (x) to the vinyl monomer (y) containing an anionic group is appropriately set according to the solid content acid value of the vinyl graft-amine modified epoxy resin (A2a). The mass ratio (x / y) may be, for example, 99 / 1 to 50 / 50, 97 / 3 to 70 / 30, or 90 / 10 to 80 / 20.

[0068] <Synthesis Method 2> The acrylic-modified epoxy resin (A2b) is obtained, for example, by polymerizing an acidic group-containing radically polymerizable unsaturated compound (4) (hereinafter referred to as the acidic group-containing monomer (4)) in the presence of the above-mentioned raw material epoxy resin (1). The acrylic-modified epoxy resin (A2b) may be a reaction product of the raw material epoxy resin (1), the acidic group-containing monomer (4), and a radically polymerizable unsaturated compound having no acidic group.

[0069] For the synthesis of the acrylic-modified epoxy resin (A2b), for example, the method described in Japanese Patent No. 6158971 can be referred to.

[0070] The acidic group-containing monomer (4) has, as the acidic group, for example, at least one of a carboxyl group, a sulfonic acid group (-SO 3 H), and a phosphoric acid group (H 2 PO 4 - ).

[0071] Examples of the carboxyl group-containing monomer (4a) include compounds containing a carboxyl group and a (meth)acryloyl group such as acrylic acid and methacrylic acid; compounds containing at least one carboxyl group and an ethylenic unsaturated bond such as maleic acid, itaconic acid, monoethyl maleate, monobutyl maleate, monoethyl itaconate, and monobutyl itaconate. These can be used alone or in combination of two or more.

[0072] Examples of the sulfonic acid group-containing monomer (4b) include acrylamido t-butyl sulfonic acid, 2-acrylamido-2-methylsulfonic acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, and bis(3-sulfopropyl) itaconate. These can be used alone or in combination of two or more.

[0073] Examples of the phosphoric acid group-containing monomer (4c) include compounds represented by the general formula: CH 2 =C(R a )COO-(CH 2 CHR b O)n-P(=O)(OH) 2 (wherein R a is H or CH 3 , R b is H, CH 3 or CHCl, and n is 1 to 6).

[0074] Examples of radical polymerizable unsaturated compounds having no acidic group include alkyl esters of α,β-ethylenically unsaturated aliphatic carboxylic acids such as ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, and N,N-dimethylaminoethyl acrylate; glycidyl esters of α,β-ethylenically unsaturated aliphatic carboxylic acids such as glycidyl acrylate and glycidyl methacrylate; vinyl esters of saturated aliphatic carboxylic acids such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene, α-methylstyrene, and vinyltoluene; alkyl esters of α,β-ethylenically unsaturated aliphatic carboxylic acids having a hydroxyl group such as 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, or a reaction product of 2-hydroxyethyl methacrylate and ε-caprolactone; and ethylenically unsaturated compounds having an amide group such as acrylamide, methacrylamide, N-methylolacrylamide, N-methoxybutylacrylamide, diacetoneacrylamide, and N,N-dimethylaminopropylacrylamide. These may be used alone or in combination of two or more.

[0075] The mass ratio of the raw material epoxy resin (1) to the acidic group-containing monomer (4) ((1):(4)) is, for example, 95:5 to 60:40. The mass ratio ((1):(4)) may be 90:10 to 65:35, and may be 90:10 to 70:30.

[0076] The number average molecular weight of the acrylic-modified epoxy resin (A2b) is, for example, 3,000 or more and 30,000 or less. The number average molecular weight of the acrylic-modified epoxy resin (A2b) may be 5,000 or more, and may be 7,000 or more. The number average molecular weight of the acrylic-modified epoxy resin (A2b) may be 25,000 or less, and may be 20,000 or less.

[0077] The solid content acid value of the acrylic-modified epoxy resin (A2b) is, for example, 10 mgKOH / g or more and 70 mgKOH / g or less. The solid content acid value of the acrylic-modified epoxy resin (A2b) may be 15 mgKOH / g or more, may be 20 mgKOH / g or more, may be 25 mgKOH / g or more, may be 30 mgKOH / g or more. The solid content acid value of the acrylic-modified epoxy resin (A2b) may be 65 mgKOH / g or less, may be 60 mgKOH / g or less, may be 55 mgKOH / g or less, may be 50 mgKOH / g or less.

[0078] The modified epoxy resin (A2) can be dispersed in water by neutralizing part of the anionic groups. The neutralization rate is adjusted so that the solid content acid value of the modified epoxy resin (A2) is 5 mgKOH / g or more and 50 mgKOH / g or less. Examples of the neutralizing agent include those exemplified as the neutralizing agent for the acrylic resin emulsion.

[0079] The ratio (Wac / Wep) of the solid content mass Wac of the aqueous acrylic resin (A1) to the solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5. When Wac is equal to or more than Wep, the surface drying property (especially the low-temperature surface drying property) and the initial rain resistance (especially the low-temperature initial rain resistance) are improved. When the proportion of Wep is 5% by mass or more of the total of the aqueous acrylic resin (A1) and the modified epoxy resin (A2), the interval adhesion and the anticorrosion property are improved. The ratio (Wac / Wep) may be 60 / 40 to 90 / 10, may be 70 / 30 to 90 / 10, may be 80 / 20 to 90 / 10.

[0080] · Organic solvent (A3) The aqueous coating composition may contain, as a solvent, an organic solvent (A3) (hereinafter, may be referred to as a high-boiling solvent (A3)) having a boiling point of 150°C or more and 300°C or less together with water. The high-boiling solvent (A3) is considered to mainly lower the Tg of various resins contained in the main agent and promote the fusion and mutual diffusion of resin particles. Further, the high-boiling solvent (A3) can impart flexibility to the coating film and further improve the low-temperature initial rain resistance of the intermediate coating film.

[0081] The boiling point of the high-boiling solvent (A3) may be 160°C or higher, may be 200°C or higher, and may be 220°C or higher from the viewpoints of water resistance (particularly, initial rain resistance) and corrosion resistance. The boiling point of the high-boiling solvent (A3) may be 290°C or lower, and may be 280°C or lower from the viewpoints of surface drying property and corrosion resistance.

[0082] Examples of the high-boiling solvent (A3) include ethylene glycol monobutyl ether (boiling point 171°C), diethylene glycol monobutyl ether (boiling point 230°C), ethylene glycol monobutyl ether acetate (boiling point 192°C), diethylene glycol monobutyl ether acetate (boiling point 247°C), diethylene glycol monomethyl ether (boiling point 193°C), 2,2,4-trimethylpentane-1,3-diol monoisobutyrate (common name Texanol, boiling point 244°C), 1-hexanol (boiling point 157°C), diisobutyl adipate (boiling point 293°C), 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (boiling point 281.5°C), and tripropylene glycol butyl ether (boiling point 274°C). These may be used alone or in combination of two or more.

[0083] The content of the high-boiling solvent (A3) may be 1 part by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the total solid content of the aqueous acrylic resin (A1) and the modified epoxy resin (A2). When the content of the high-boiling solvent (A3) is 1 part by mass or more, the water resistance and corrosion resistance can be further improved. When the content of the high-boiling solvent (A3) is 25 parts by mass or less, the surface drying property and corrosion resistance can be further improved.

[0084] The content of the high-boiling solvent (A3) may be 1.5 parts by mass or more, may be 2 parts by mass or more, and may be 3 parts by mass or more. The content of the high-boiling solvent (A3) may be 20 parts by mass or less, may be 15 parts by mass or less, and may be 10 parts by mass or less.

[0085] · Hydrophilic-modified carbodiimide compound (B1) The hydrophilic modified carbodiimide compound (B1) has at least one carbodiimide group in the molecule. The carbodiimide group reacts with the carboxyl groups of the aqueous acrylic resin (A1) and the modified epoxy resin (A2) to form a crosslinked structure.

[0086] The content of the hydrophilic modified carbodiimide compound (B1) is set such that the equivalent ratio of the total carboxyl groups of the aqueous acrylic resin (A1) and the modified epoxy resin (A2) to the carbodiimide groups of the carbodiimide compound (B1) (carboxyl group / carbodiimide group) is, for example, 0.4 or more and 2.2 or less. Thereby, the interval adhesion can be further improved.

[0087] The hydrophilic modified carbodiimide compound (B1) is, for example, represented by the following general formula (1):

Chemical formula

[0088] In the general formula (1), p is an integer of 1 to 5, and the two Rs 1 are each independently a residue of a polyethylene glycol monoalkyl ether represented by the following general formula (2) and / or a residue of a polypropylene glycol monoalkyl ether represented by the following general formula (3).

[0089] The general formula (2) is as follows.

Chemical formula

[0090] The general formula (3) is as follows.

Chemical formula

[0091] The molar ratio of the residue of the polyethylene glycol monoalkyl ether represented by the general formula (2) to the residue of the polypropylene glycol monoalkyl ether represented by the general formula (3) is, for example, 1:1 to 1:15.

[0092] The hydrophilically modified carbodiimide compound (B1) represented by the general formula (1) can be produced, for example, as follows. First, isocyanate-terminated dicyclohexylmethane carbodiimide represented by the following general formula (5) is synthesized by a condensation reaction involving decarboxylation of 4,4-dicyclohexylmethane diisocyanate represented by the following general formula (4). Next, the isocyanate-terminated dicyclohexylmethane carbodiimide is reacted with a mixture of polyethylene glycol monoalkyl ether and polypropylene glycol monoalkyl ether.

[0093] The general formula (4) is as follows. [Chemical formula]

[0094] The general formula (5) is as follows. [Chemical formula] (In the formula, p represents an integer of 1 to 5.)

[0095] The isocyanate-terminated dicyclohexylmethane carbodiimide represented by the general formula (5) can be obtained by a known method for producing carbodiimide. Methods for producing carbodiimide are known, for example, from U.S. Patent No. 2,941,956, Japanese Patent Publication No. 47-33279, J. Org. Chem., 28, 2069-2076 (1963), and Chemical Review 1981, vol. 81, No. 4, 619-4,621.

[0096] As the hydrophilically modified carbodiimide compound (B1), the carbodiimide compound described in Japanese Patent No. 5101747 can be referred to.

[0097] · Other main component The aqueous coating composition may contain other main components other than the aqueous acrylic resin (A1) and the modified epoxy resin (A2). Examples of other main components include polyester resin, polyether resin, polyolefin resin, polyurethane resin, polycarbonate resin, melamine resin, and fluororesin. These can be used alone or in combination of two or more. The content of other main components may be less than 10 parts by mass, may be 5 parts by mass or less, and may be 0.1 parts by mass or less with respect to 100 parts by mass of the solid content of the main agent.

[0098] · Other curing component The aqueous coating composition may contain other curing components other than the hydrophilically modified carbodiimide compound (B1). Examples of other curing components include polyisocyanate curing agents (including blocked polyisocyanate curing agents), amino resins, epoxy compounds, aziridine compounds, and oxazoline compounds. These can be used alone or in combination of two or more. The content of other curing components may be less than 10 parts by mass, may be 5 parts by mass or less, and may be 0.1 parts by mass or less with respect to 100 parts by mass of the solid content of the curing agent.

[0099] · Pigment The aqueous coating composition may contain a pigment. Examples of the pigment include a coloring pigment, a rust preventive pigment, and an extender pigment. These may be used singly or in combination of two or more.

[0100] · Additive The aqueous coating composition may contain various additives as required. Examples of the additive include an ultraviolet absorber, a viscosity modifier, an antioxidant, an antifoaming agent, a surface conditioner, a pinhole preventive agent, a silane coupling agent, a pigment dispersant, and a sedimentation preventive agent. These may be used singly or in combination of two or more.

[0101] · Solvent The aqueous coating composition contains water as a solvent. The aqueous coating composition may contain other organic solvents together with the high-boiling solvent (A3) or in place of the high-boiling solvent (A3). Examples of other organic solvents include hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, cyclobutane; aromatic solvents such as toluene, xylene; ether solvents such as ethylene glycol monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-n-butyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, dioxane; ester solvents such as methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, methyl acetoacetate, ethylene glycol monomethyl ether acetate, butyl carbitol acetate; ketone solvents such as acetone, acetylacetone, diacetone alcohol, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone; alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, n-pentanol. These are used alone or in combination of two or more kinds.

[0102] · Method for preparing an aqueous coating composition The aqueous coating composition can be prepared by known methods. The main agent is prepared by mixing a carboxy group-containing aqueous acrylic resin (A1), a modified epoxy resin (A2), an organic solvent (A3) as required, and other components. The curing agent is separately prepared by mixing a hydrophilized modified carbodiimide compound (B1) and other components as required. The aqueous coating composition is prepared by mixing the main agent, the curing agent, and other components as required. For mixing, commonly used mixing devices such as paint shakers and mixers are used. The mixing of the main agent and the curing agent is usually carried out immediately before use (for example, used within 60 minutes after mixing).

[0103] [Multi-layer coating film] The multi-layer coating film of the present disclosure includes an undercoat film disposed on an object to be coated, a middle coat film disposed on the undercoat film and formed by the above-mentioned multi-liquid type aqueous coating composition, and a top coat film disposed on the middle coat film.

[0104] The middle coat film and the top coat film are excellent in interval adhesion. The undercoat film and the middle coat film are also excellent in interval adhesion. Therefore, the restrictions on the painting work are reduced.

[0105] The undercoat film and the top coat film may be formed using an aqueous coating composition. In this case, since the entire multi-layer coating film can be formed with aqueous paints, the environmental load is reduced and the safety during painting is enhanced. The modified epoxy resin (A2) of the middle coat paint composition does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, so it has good compatibility with other aqueous coating compositions. Therefore, the multi-layer coating film formed entirely with aqueous paints is even more excellent in interval adhesion.

[0106] ·Object to be coated The multilayer coating film of the present disclosure is mainly applied outdoors and is further suitable for coating articles to be coated that are mainly used or installed outdoors. Examples of the articles to be coated include steel structures such as bridges, buildings, tanks, plants, and towers, ships, vehicles, and roofs. The object of coating is typically a metal surface. Examples of the metal include iron, steel, aluminum, stainless steel, and plated steel sheets such as zinc plating and aluminum plating. Other objects of coating include coating films formed on metal surfaces. The multi-component aqueous coating composition according to the present disclosure can be used for repainting the coated metal surface.

[0107] · Primer coating film The primer coating film is formed by an aqueous primer coating composition containing, for example, a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin. As the above aqueous primer coating composition, the aqueous coating composition described in Japanese Patent No. 5612667 can be referred to.

[0108] (Amine-modified aqueous epoxy resin) The amine-modified aqueous epoxy resin has one or more primary amino groups and / or secondary amino groups in the molecule. The amine-modified aqueous epoxy resin imparts corrosion resistance to the primer coating film.

[0109] The amine-modified aqueous epoxy resin may be bisphenol A type or bisphenol F type. The amine-modified aqueous epoxy resin may be bisphenol A type.

[0110] The amine-modified aqueous epoxy resin can be obtained, for example, by a method of adding a primary amino group-containing polyamine to a raw material epoxy resin or a method of adding a ketimized amino group-containing compound to a raw material epoxy resin. The amine-modified aqueous epoxy resin may further be obtained by reacting a compound having a functional group such as an epoxy group, an acid anhydride group, an acid halogen group, or an isocyanate group with a part of the primary amino group, secondary amino group, and / or hydroxyl group.

[0111] The epoxy equivalent of the raw material epoxy resin may be 180 g / eq or more and 3,800 g / eq or less. When the epoxy equivalent of the raw material epoxy resin is 180 g / eq or more, the initial rain resistance of the undercoat film can be improved. When the epoxy equivalent of the raw material epoxy resin is 3,800 g / eq or less, the undercoat paint composition is easily made aqueous, and the water resistance of the undercoat film can be improved. The epoxy equivalent of the raw material epoxy resin may be 400 g / eq or more, and may be 700 g / eq or more. The epoxy equivalent of the raw material epoxy resin may be 3,200 g / eq or less.

[0112] The amine-modified aqueous epoxy resin used in the undercoat paint composition may have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid. In this case, a fatty acid is added to the raw material epoxy resin before amine modification.

[0113] ((Meth)acryloyl group-containing compound) (Meth)acryloyl group-containing compounds have one or more (meth)acryloyl groups in the molecule. The number of (meth)acryloyl groups is 1 or more, and may be 2 to 4. The number of (meth)acryloyl groups is appropriately set according to the desired film physical properties.

[0114] (Meth)acryloyl group-containing compounds may have a molecular weight of, for example, 150 or more and 2,000 or less. The molecular weight can be calculated from the chemical formula.

[0115] Examples of the (meth)acryloyl group-containing compound include polymerizable unsaturated monocarboxylic acid ester compounds of polyhydric alcohols such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, pentaerythritol diacrylate, pentaerythritol dimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, glycerol diacrylate, glycerol dimethacrylate, glycerol acryloxydimethacrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane dimethacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethane trimethacrylate, 1,1,1-trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethylpropane dimethacrylate; adducts of epoxy group-containing ethylenically unsaturated monomers and carboxy group-containing ethylenically unsaturated group monomers such as reaction products of glycidyl acrylate, glycidyl methacrylate with acrylic acid, methacrylic acid, crotonic acid, maleic acid; polymerizable unsaturated monocarboxylic acid amide compounds of polyvalent amines such as ethylenediamine diacrylate. These may be used alone or in combination of two or more kinds.

[0116] (Meth)acryloyl group-containing compounds may be modified with polyethylene oxide. As a result, the primer coating composition is liable to be made aqueous.

[0117] (Aqueous epoxy resin) The aqueous epoxy resin has two or more epoxy groups in the molecule. The aqueous epoxy resin may be, for example, an aqueous product of the above raw material epoxy resin (1). The aqueous epoxy resin may be in the form of an emulsion dispersed in an aqueous medium such as water. The aqueous epoxy resin in the form of an emulsion may be a forced emulsification type or a self-emulsification type.

[0118] Forced emulsification is carried out, for example, by stirring the raw material epoxy resin (1) together with an emulsifier in an aqueous medium. Self-emulsification is carried out, for example, by introducing a hydrophilic site into the raw material epoxy resin (1) and emulsifying it in an aqueous medium. Examples of the hydrophilic site include a side chain having a hydroxyl group or a carboxyl group, and a nonionic polyalkylene oxide skeleton.

[0119] The epoxy equivalent of the aqueous epoxy resin is, for example, 150 g / eq or more and 1,200 g / eq or less. The number average molecular weight of the aqueous epoxy resin is, for example, 300 or more and 3,000 or less.

[0120] The thickness of the primer coating film is appropriately set according to the use and the like. The thickness of the primer coating film after drying may be, for example, 20 μm or more and 150 μm or less.

[0121] · Intermediate coating film The intermediate coating film is formed by the above multi-component type aqueous coating composition.

[0122] The thickness of the intermediate coating film is appropriately set according to the use and the like. The thickness of the intermediate coating film after drying may be, for example, 20 μm or more and 100 μm or less.

[0123] · Topcoat film The topcoat film is formed by an aqueous topcoat paint composition containing, for example, a main agent containing a carboxy group-containing aqueous acrylic resin and a curing agent containing a hydrophilized modified carbodiimide compound. As the above aqueous topcoat paint composition, reference can be made to the two-component aqueous paint composition described in Japanese Patent No. 5101747.

[0124] Examples of the carboxy group-containing aqueous acrylic resin and the hydrophilized modified carbodiimide compound include those exemplified in the above multi-component aqueous paint composition.

[0125] The thickness of the topcoat film is appropriately set according to the use and the like. The thickness of the topcoat film after drying may be, for example, 10 μm or more and 100 μm or less.

[0126] [Method for forming a multi-layer coating film] The multi-layer coating film is formed by a method comprising: applying a primer paint composition onto an object to be coated to form a primer coating film; applying the above multi-component aqueous paint composition onto the primer coating film to form an intermediate coating film; and applying a topcoat paint composition onto the intermediate coating film to form a topcoat film.

[0127] The coating method for each paint composition is appropriately selected according to the type, size, etc. of the object to be coated. Examples of the coating method include brush coating, roller coating, spray coating, and flow coating. The coating amount of each paint composition is appropriately set so as to obtain a desired film thickness. The coating amount of each paint composition may be, for example, 30 g / m 2 or more and 400 g / m 2 or less.

[0128] Each paint composition dries (cures) by being left in an outdoor environment for a certain period after coating. The drying temperature can be, for example, 5°C or more and 30°C or less. The leaving period can be, for example, 3 days or more and 10 days. The multi-component aqueous paint composition of the present disclosure has excellent surface drying properties even at low temperatures. Even when the multi-component aqueous paint composition of the present disclosure is coated at low temperatures, the resulting coating film has excellent interval adhesion and initial rain resistance.

Examples

[0129] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the Examples in any way. In the Examples, "parts" and "%" are based on mass unless otherwise specified.

[0130] [Production Example A1-1] · Production of aqueous acrylic resin (A1-1) 198 parts of deionized water was charged into a reactor equipped with a stirrer, a nitrogen inlet tube, a temperature controller, a condenser, and a dropping funnel, and the temperature was raised to 80 °C while stirring under a nitrogen atmosphere. 385.5 parts of 2-ethylhexyl acrylate (2-EHA), 401.6 parts of methyl methacrylate (MMA), 200 parts of styrene (ST), 12.8 parts of acrylic acid (AA), and 100 parts of an emulsifier (trade name: Latemul PD-104, manufactured by Kao Corporation, 20% aqueous solution) were added to 579.4 parts of deionized water to obtain a pre-emulsion. 3 parts of ammonium persulfate was dissolved in 150 parts of deionized water to obtain an initiator aqueous solution. The pre-emulsion and the initiator aqueous solution were dropped into the above reactor over 2 hours.

[0131] After completion of the dropping, the reaction was continued at 80 °C for 1 hour and then cooled. Subsequently, 10 parts of N,N-dimethylaminoethanol was added to obtain an acrylic emulsion (A1-1) having a resin solid content of 50% by mass. The solid content acid value of this acrylic emulsion calculated from the monomer composition was 10 mgKOH / g, and the Tg was 10 °C.

[0132] [Production Examples A1-2 to 9] Acrylic emulsions (A1-2 to 9) were obtained in the same manner as in Production Example A1-1 except that the blending amounts of the raw material monomers were changed as shown in Table 1. The physical properties of each acrylic emulsion are shown in Table 1.

[0133]

Table 1

[0134] [Production Example A2b-1] Production of modified epoxy resin Into a reactor equipped with a heating device, a stirrer, a reflux condenser, and a dropping funnel, 90 parts of bisphenol A type epoxy resin (raw material epoxy resin (1), trade name: Epotote YD-017, manufactured by Nippon Steel Chemical & Material Co., Ltd.) were charged. 15 parts of butyl carbitol, 30 parts of methyl isobutyl ketone, and 60 parts of methoxypropanol were added to the reactor. Next, while stirring the obtained mixture, the temperature was raised to 120 °C to dissolve the bisphenol A type epoxy resin. Subsequently, the obtained epoxy solution was cooled to 110 °C.

[0135] A monomer mixture consisting of 3.9 parts of methacrylic acid, 2.1 parts of ethyl acrylate, 4.0 parts of styrene, and 10 parts of methyl isobutyl ketone was prepared. An initiator solution a was prepared by dissolving 2 parts of a polymerization initiator (benzoyl peroxide) in 19 parts of methyl isobutyl ketone.

[0136] The monomer mixture and the initiator solution a were dropped into the epoxy solution in parallel from separate dropping funnels over 2 hours. After the dropping was completed, the mixed solution was kept at 110 °C for 30 minutes. Next, an initiator solution b prepared by dissolving 0.2 part of a polymerization initiator (benzoyl peroxide) in 2 parts of methyl isobutyl ketone was dropped into the mixed solution over 30 minutes. Thereafter, the mixed solution was kept at 110 °C for an additional 3 hours to obtain a solution (non-volatile content 43.8%) containing an acrylic-modified epoxy resin (A2b-1) having no ester bond. The acrylic-modified epoxy resin (A2b-1) had a solid acid value of 25 mgKOH / g, a number average molecular weight of 4,000, and an average particle diameter of 150 nm.

[0137] The acrylic-modified epoxy resin (A2b-1) was cooled to 60 °C, and a solution containing 197 parts of deionized water and 4.6 parts of a basic substance (triethylamine) was dropped over 2 hours for neutralization. After the dropping was completed, it was kept at 60 °C for 30 minutes. Finally, the organic solvent was removed under reduced pressure to obtain an aqueous dispersion of the acrylic-modified epoxy resin (A2b-1). The aqueous dispersion had a non-volatile content of 34.5% and a pH of 7.54.

[0138] [Production Examples A2b-2 to 7, Comparative Production Examples a2-1 to 4] Production of Modified Epoxy Resin Except for changing the raw material epoxy resin etc. as shown in Table 2 or Table 3, in the same manner as in Production Example A2-1, an aqueous dispersion of the acrylic-modified epoxy resin having no ester bond (A2b-2 to A2b-7, a2-1 to a2-4) was obtained. The details of the raw material epoxy resin used are as follows. The physical properties of each modified epoxy resin are shown in Table 2 and Table 3.

[0139] · Trade name Epotote YD-017: Manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol A type, number average molecular weight 3,700 · Trade name Epotote YD-012: Manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol A type, number average molecular weight 1,200 · Trade name Epotote YD-20H: Manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol A type, number average molecular weight 11,000 · Trade name Epotote YP-50S: Manufactured by Nippon Steel Chemical & Material Co., Ltd., phenoxy type, number average molecular weight 14,000 · Trade name Epotote YD-011: Manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol A type, number average molecular weight 900 · Trade name 4275: Manufactured by Mitsubishi Chemical Corporation, phenoxy type, number average molecular weight 18,000

[0140]

Table 2

[0141]

Table 3

[0142] In Table 2, the modified epoxy resins (A2a-1, A2a-2) are commercially available products, and the details are as follows. · Modified epoxy resin (A2a-1): Vinyl graft-amine modified epoxy resin, trade name KA1851L, manufactured by Arakawa Chemical Industries, Ltd. · Modified epoxy resin (A2a-2): Vinyl graft-amine modified epoxy resin, trade name Modipics 304, manufactured by Arakawa Chemical Industries, Ltd.

[0143] [Production Example a2-5] Production of Modified Epoxy Resin Having the Above Ester Bond Into a four-necked flask equipped with a stirrer, thermometer, temperature controller, and nitrogen inlet tube, 150 parts of dehydrated castor oil fatty acid, 50 parts of soybean oil fatty acid, 500 parts of bisphenol A type epoxy resin (raw material epoxy resin (1), trade name: Epotote YD-011, manufactured by Nippon Steel Chemical & Material Co., Ltd.), and 60.2 parts of p-tert-butylbenzoic acid were charged.

[0144] Next, 0.02 part of triethylamine was charged into the above flask, and the temperature was raised to 180 °C while stirring. While confirming the dehydrated state, the temperature was raised to 220 °C to proceed with the esterification. The reaction was carried out for about 3 hours until the solid acid value of the content became 1 or less. Subsequently, the temperature was lowered to 150 °C, and 253.4 parts of butyl cellosolve was added to obtain a fatty acid ester of epoxy resin (non-volatile content 75% solution).

[0145] Separately, a mixture of 120 parts of ST, 49.8 parts of 2-ethylhexyl methacrylate, 40 parts of AA, and 30 parts of a monoester compound of polyethylene glycol with a molecular weight of 400 and methacrylic acid was prepared. The above flask was maintained at 125 °C, and the above mixture, 5 parts of t-butylperoxy-2-ethylhexanoate, and 3 parts of di-t-butylperoxy ether were added over 1 hour. Subsequently, the reaction was carried out at the same temperature for 10 hours to carry out a vinylation reaction on the fatty acid ester of epoxy resin, and a vinyl-modified epoxy resin (a2-5) (non-volatile content 80% solution) having the above ester bond was obtained.

[0146] The total amount of the vinyl compound was about 24% of 100 parts by weight of the total amount of the fatty acid ester of epoxy resin and the vinyl compound. The obtained vinyl-modified epoxy resin (a2-5) had a solid acid value of 30 mgKOH / g.

[0147] 54 g of a basic substance (triethylamine) was added to the above flask and mixed well. Then, while stirring, 1550 g of ion-exchanged water was added little by little for neutralization to obtain an aqueous dispersion of the vinyl-modified epoxy resin (a2-5). The aqueous dispersion had a non-volatile content of 35% and a pH of 9.2.

[0148] [Production Example B1] Production of a hydrophilized modified carbodiimide compound (B1) 25 parts of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) was added to 2500 parts of 4,4-dicyclohexylmethane diisocyanate, and the reaction was carried out at 170 °C until the isocyanate equivalent reached 436 to obtain a carbodiimide compound having isocyanate groups at both ends. The carbodiimide compound had 2.8 carbodiimide groups per molecule.

[0149] Next, 567 parts of polypropylene glycol monobutyl ether (trade name: Newpol LB-65, manufactured by Sanyo Chemical Industries, Ltd., number-average repeating number 5) and 225 parts of polyethylene glycol monomethyl ether (trade name: MPG-081, manufactured by Nippon Emulsion Co., Ltd., number-average repeating number 15) were added to 872 parts of the carbodiimide compound, and the reaction was carried out at 160 °C until the absorption derived from the isocyanate group disappeared by IR. Then, it was cooled to 60 °C, and 2496 parts of deionized water was gradually added to emulsify the carbodiimide compound to obtain an aqueous dispersion (non-volatile content 40%) of the hydrophilized modified carbodiimide compound (B1).

[0150] [Example 1] (1) Preparation of the main agent 11.5 parts of deionized water, 1.9 parts of a pigment dispersant (trade name: DISPERBYK-190, manufactured by BYK-Chemie), 0.3 part of an antifoaming agent (trade name: BYK-019, manufactured by BYK-Chemie), 13.7 parts of titanium oxide, 5.2 parts of calcium carbonate, and 20.5 parts of talc were mixed in a sand mill to obtain a pigment dispersion paste. To 53.1 parts of the pigment dispersion paste, 5.0 parts of deionized water, 40.0 parts of acrylic emulsion (A1-1), 9.4 parts of modified epoxy resin (A2b-2), 1.2 parts of high-boiling solvent (A3-1), 0.5 part of thickener (trade name: Adekanol UH-550, manufactured by Adeka), 0.3 part of thickener (trade name: Primar RM-12W, manufactured by Rohm and Haas), and 0.2 part of defoamer (trade name: SN Deformer 1315, manufactured by San Nopco) were added to obtain the main agent (I-1).

[0151] (2) Preparation of the aqueous coating composition To 109.7 parts of the main agent (I-1), 12.2 parts of the carbodiimide compound aqueous dispersion B1 was mixed to obtain the aqueous coating composition.

[0152] [Example 2-31, Comparative Examples 1-8] Except that the components of the main agent were changed as shown in the following table, aqueous coating compositions were obtained in the same manner as in Example 1.

[0153] The details of the high-boiling solvents in the table are as follows. · A3-1: Trade name CS-16, manufactured by JNC · A3-2: Trade name Dowanol TM MA, glycol ether, manufactured by The Dow Chemical Company · A3-3: Trade name Dowanol TM PnB, glycol ether, manufactured by The Dow Chemical Company · A3-5: Trade name COASOL 290 Plus, manufactured by Chemoxy

[0154] [Evaluation] Test panels were prepared using the aqueous coating composition, and the following evaluations were conducted. The evaluation results are shown in Tables 3 to 8.

[0155] (1) Intermittent adhesion in the middle and lower parts The aqueous primer coating composition (including a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin) described in Japanese Patent No. 5612667 was applied using a brush at an application amount of 200 g / m2 It was applied to a sandblasted steel plate of 150 mm × 70 mm × 1.6 mm and dried at 23°C for 24 hours. Subsequently, the coated plate was left outdoors for 10 days. Subsequently, the aqueous coating composition obtained in the example or comparative example was applied to the above coated plate using a brush at an application rate of 130 g / m 2 and dried at 23°C for 7 days to obtain a test plate.

[0156] The test plate was immersed in water at 23°C for 7 days. The test plate was pulled out, and immediately thereafter, the cross-cut method was carried out in accordance with JIS K5600-5-6 under the conditions of a gap interval of 3 mm and 25 meshes. The results were evaluated according to the following criteria. Criteria A and B indicate excellent interval adhesion between the undercoat film and the intermediate coat film, and criterion C indicates low interval adhesion between the undercoat film and the intermediate coat film and is not practical.

[0157] Evaluation criteria A: 0 to 3 mesh peeling B: 4 to 10 mesh peeling C: 11 to 25 mesh peeling

[0158] (2) Upper interval adhesion The aqueous undercoat paint composition described in Japanese Patent No. 5612667 (including a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin) was applied to a sandblasted steel plate of 150 mm × 70 mm × 1.6 mm using a brush at an application rate of 200 g / m 2 and dried at 23°C for 24 hours. Next, the aqueous coating composition obtained in the example or comparative example was applied to the above coated plate using a brush at an application rate of 130 g / m 2 and dried at 23°C for 7 days. Thereafter, the coated plate was left outdoors for 10 days. Subsequently, the aqueous topcoat paint composition described in Japanese Patent No. 5101747 (including a main agent containing a carboxyl group-containing aqueous acrylic resin and a curing agent containing a hydrophilically modified carbodiimide compound) was applied using a brush at 120 g / m 2It was applied to the above painted board and dried at 23°C for 7 days to obtain a test board.

[0159] The test board was immersed in water at 23°C for 7 days. The test board was pulled out, and immediately afterwards, the cross-cut method was carried out in accordance with JIS K5600-5-6 under the conditions of a gap interval of 3 mm and 25 meshes. The results were evaluated according to the same criteria as above. Criteria A and B indicate excellent interval adhesion between the intermediate coating film and the top coating film, and criterion C indicates low and impractical interval adhesion between the intermediate coating film and the top coating film.

[0160] (3) Low-temperature surface drying property The aqueous coating composition obtained in the example or comparative example was applied to a glass plate using a film applicator with a gap of 150 μm and dried at 5°C for 16 hours to obtain a test board. The test board was tested in accordance with the surface drying property (Barotini method) compliant with JIS K 5600-3-2:1999. The results were evaluated according to the following criteria. Criteria A and B indicate excellent low-temperature surface drying property, and criterion C indicates low and impractical low-temperature surface drying property.

[0161] Evaluation criteria A: All Barotini (glass beads) are removed without damage. B: When trying to remove without damage, 1 to 5 Barotini grains remain. C: When trying to remove without damage, 6 or more Barotini grains remain.

[0162] (4) Low-temperature initial rain resistance The aqueous primer coating composition described in Japanese Patent No. 5612667 (including a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin) was applied to a sandblasted steel plate of 150 mm × 70 mm × 1.6 mm with a coating amount of 200 g / m 2 using a brush and dried at 23°C for 24 hours. Next, the aqueous coating composition obtained in the example or comparative example was applied using a brush with a coating amount of 130 g / m 2It was applied to the above coated plate and dried at 5°C for 6 hours. Subsequently, the above coated plate was immersed in water at 5°C for 16 hours. The coated plate was pulled out and dried at room temperature of 5°C and humidity of 50% RH for 24 hours to obtain a test plate. The crack density of the coating film of the test plate was determined in accordance with JIS K 5600-8-4. The results were evaluated according to the following criteria. Criteria A and B indicate excellent low-temperature initial rain resistance, and criterion C indicates low low-temperature initial rain resistance and being not practical.

[0163] Evaluation Criteria A: No cracks B: Crack density is 1 - 2 C: Crack density is 3 - 5

[0164] (5) Composite film corrosion resistance The aqueous undercoat paint composition described in Japanese Patent No. 5612667 (including a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin) was applied to a sandblasted steel plate of 150 mm × 70 mm × 1.6 mm with a coating amount of 200 g / m 2 using spray and dried at 23°C for 24 hours. Next, the aqueous paint composition obtained in the example or comparative example was applied to the above coated plate with a coating amount of 130 g / m 2 using spray and dried at 23°C for 24 hours. Subsequently, the aqueous topcoat paint composition described in Japanese Patent No. 5101747 (including a main agent containing a carboxyl group-containing aqueous acrylic resin and a curing agent containing a hydrophilically modified carbodiimide compound) was applied to the above coated plate with a coating amount of 120 g / m 2 using spray and dried at 23°C for 7 days to obtain a test plate.

[0165] A cycle corrosion test in accordance with JIS K5600 7-7 was performed on the test plate for 500 cycles. Thereafter, the rust grade of the test plate was determined in accordance with JIS K 5600-8-3. The results were evaluated according to the following criteria. Criteria A and B indicate excellent corrosion resistance, and criterion C indicates low corrosion resistance and being not practical.

[0166] Evaluation criteria A: Grade Ri 0 to Ri 1 (rust area 0 to 0.05%) B: Grade Ri 2 to Ri 3 (rust area 0.5 to 1%) C: Grade Ri 4 to Ri 5 (rust area 8 to 50%)

[0167]

Table 4

[0168]

Table 5

[0169]

Table 6

[0170]

Table 7

[0171]

Table 8

[0172] The present invention includes the following aspects. [1] A main agent containing a carboxy group-containing aqueous acrylic resin (A1) and a modified epoxy resin (A2), A curing agent containing a hydrophilically modified carbodiimide compound (B1), and The modified epoxy resin (A2) has an anionic group, does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less, A two-component aqueous coating composition in which the ratio (Wac / Wep) of the solid content mass Wac of the carboxy group-containing aqueous acrylic resin (A1) to the solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5. [2] The carboxy group-containing aqueous acrylic resin (A1) in the above [1] two-component aqueous coating composition has a solid content acid value of 3 mgKOH / g or more and 50 mgKOH / g or less, and a glass transition point of -25°C or more and 50°C or less. [3] The main agent further contains an organic solvent (A3) having a boiling point of 150°C or more and 300°C or less in the two-component aqueous coating composition of the above [1] or [2]. [4] In the two-component aqueous coating composition of the above [3], the content of the organic solvent (A3) is 1 part by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the total solid content of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2). [5] In the two-component aqueous coating composition of any one of the above [1] to [4], the equivalent ratio (carboxy group / carbodiimide group) of the total carboxy group of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2) to the carbodiimide group of the hydrophilically modified carbodiimide compound (B1) is 0.4 or more and 2.2 or less. [6] For forming an intermediate coating film, In the two-component aqueous coating composition of any one of the above [1] to [5], a topcoat film formed by an aqueous topcoat coating composition is formed on the intermediate coating film. [7] For forming an intermediate coating film, In the two-component aqueous coating composition of any one of the above [1] to [6], the intermediate coating film is formed on a primer coating film formed by an aqueous primer coating composition. [8] A primer coating film disposed on an object to be coated, An intermediate coating film disposed on the primer coating film and formed by the two-component aqueous coating composition of any one of the above [1] to [7], A multilayer coating film comprising a topcoat film disposed on the intermediate coat film. [9] The primer coating film is formed from an aqueous primer coating composition containing a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin. The topcoat film of the multilayer coating film according to the above [8] is formed from an aqueous topcoat coating composition containing a main agent containing a carboxyl group-containing aqueous acrylic resin and a curing agent containing a hydrophilically modified carbodiimide compound.

[10] Coating an aqueous primer coating composition on an object to be coated to form a primer coating film. Coating any of the multi-component aqueous coating compositions of the above [1] to [7] on the primer coating film to form an intermediate coat film. A method for forming a multilayer coating film, comprising coating an aqueous topcoat coating composition on the intermediate coat film to form a topcoat film.

Industrial Applicability

[0173] According to the multi-component aqueous coating composition of the present disclosure, a coating film having excellent surface drying properties and excellent adhesion between coating films even when the interval between a plurality of coating steps is long is provided. Therefore, the multi-component aqueous coating composition of the present disclosure is mainly suitable for use as an intermediate coat for objects to be coated that are coated outdoors a plurality of times.

Claims

1. A main agent containing a carboxy group-containing aqueous acrylic resin (A1) and a modified epoxy resin (A2), and a curing agent containing a hydrophilically modified carbodiimide compound (B1), wherein the modified epoxy resin (A2) has an anionic group, does not have an ester bond formed by the reaction of an epoxy group and a carboxy group derived from a fatty acid, has a solid content acid value of 5 mgKOH / g or more and 50 mgKOH / g or less, a number average molecular weight of 1,000 or more and 15,000 or less, and an average particle diameter of 30 nm or more and 2,000 nm or less, and a ratio (Wac / Wep) of the solid content mass Wac of the carboxy group-containing aqueous acrylic resin (A1) to the solid content mass Wep of the modified epoxy resin (A2) is 50 / 50 to 95 / 5, a two-component type aqueous paint composition.

2. The carboxy group-containing aqueous acrylic resin (A1) has a solid content acid value of 3 mgKOH / g or more and 50 mgKOH / g or less, and a glass transition point of -25°C or more and 50°C or less. The two-component type aqueous paint composition according to Claim 1.

3. The main agent further contains an organic solvent (A3) having a boiling point of 150°C or more and 300°C or less. The two-component type aqueous paint composition according to Claim 1 or 2.

4. The content of the organic solvent (A3) is 1 part by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the total solid content of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2). The two-component type aqueous paint composition according to Claim 3.

5. The equivalent ratio (carboxy group / carbodiimide group) of the total carboxy group of the carboxy group-containing aqueous acrylic resin (A1) and the modified epoxy resin (A2) to the carbodiimide group of the hydrophilically modified carbodiimide compound (B1) is 0.4 or more and 2.2 or less. The two-component type aqueous paint composition according to Claim 1 or 2.

6. For forming an intermediate coat film, and a top coat film formed by an aqueous top coat paint composition is formed on the intermediate coat film. The two-component type aqueous paint composition according to Claim 1 or 2.

7. For forming an intermediate coat film, and the intermediate coat film is formed on a primer coat film formed by an aqueous primer paint composition. The two-component type aqueous paint composition according to Claim 1 or 2.

8. A primer coat film disposed on an object to be coated, and an intermediate coat film disposed on the primer coat film and formed by the two-component type aqueous paint composition according to Claim 1 or 2, A multilayer coating film comprising a topcoat film disposed on the intermediate coat film.

9. The undercoat film is formed from an aqueous undercoat paint composition comprising a main agent containing an amine-modified aqueous epoxy resin and a curing agent containing at least one of a (meth)acryloyl group-containing compound and an aqueous epoxy resin, The topcoat film is formed from an aqueous topcoat paint composition comprising a main agent containing a carboxy group-containing aqueous acrylic resin and a curing agent containing a hydrophilically modified carbodiimide compound, the multilayer coating film according to claim 8.

10. Coating an aqueous undercoat paint composition on an object to be coated to form an undercoat film, Coating the multi-liquid type aqueous paint composition according to claim 1 or 2 on the undercoat film to form an intermediate coat film, Coating an aqueous topcoat paint composition on the intermediate coat film to form a topcoat film, a method for forming a multilayer coating film.

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