Aqueous coating composition, coating film, base material with laminate coating film, and method for producing base material with laminate coating film

Abstract

To provide an aqueous coating composition which enables formation of a coating film containing titanium oxide and having a hiding ratio of 90% or more, while having a long pot life even under a high temperature and high humidity condition, in a coating state suitable for coating, and enables formation of a coating film that hardly causes foaming even if a coating film is formed on an undercoating film formed of an aqueous undercoating composition, and is excellent in adhesion to the undercoating film.SOLUTION: An aqueous coating composition containing titanium oxide contains a first agent containing an aqueous polyol resin (A) and a second agent containing an isocyanate compound (B), wherein a blending ratio of the titanium oxide is 40 to 78 mass% with respect to 100 mass% of a solid content of the aqueous polyol resin (A).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous coating composition, a coating film, a substrate with a multilayer coating film, and a method for producing a substrate with a multilayer coating film. [Background technology]

[0002] Conventionally, (large steel) structures such as ships, bridges, tanks, containers, plants, marine buoys, and undersea pipelines have been coated with coating films of various specifications in order to impart various functions such as corrosion resistance. Specifically, an undercoat coating film is formed on these structures, and then a topcoat coating film is formed on top of that in order to improve design, weather resistance, etc.

[0003] As the topcoat paint composition that forms the topcoat paint film, two-component urethane paint compositions are widely used in the field of heavy-duty corrosion protection because they can form paint films that are excellent in appearance gloss, weather resistance, corrosion resistance, etc. As such two-component urethane coating compositions, in recent years, two-component water-based urethane coating compositions have been developed in order to be environmentally friendly coating compositions.

[0004] As an example of the two-component water-based urethane coating composition, Patent Document 1 discloses a two-component curing water-based coating composition consisting of a base agent containing a specific aqueous polymer polyol and a curing agent containing a water-dispersible polyisocyanate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-257141 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has been found that the conventional two-component water-based urethane coating compositions described in Patent Document 1 and elsewhere have a short usable life when in a paint state suitable for coating, particularly under high temperature and high humidity conditions (e.g., 35°C, 85% RH), which requires management of the coating environment and conditions, and may limit the environments in which coating is applicable. The topcoat film is sometimes required to have a hiding power of 90% or more, but it has been found that conventional topcoat paint compositions that contain titanium oxide and are capable of forming topcoat films with a hiding power of 90% or more have a short usable life, particularly under high-temperature, high-humidity conditions, when in a paint state suitable for painting.

[0007] Furthermore, in recent years, from the viewpoints of environmental conservation and safety of the working environment, there has been a demand for the use of water-based undercoat paint compositions as the undercoat paint compositions for forming the undercoat paint film. However, when a primer coating film is formed using such an aqueous primer coating composition and then a topcoat coating film is formed on top of it using a conventional two-component aqueous urethane coating composition as described in Patent Document 1, etc., it has been found that foaming is likely to occur on the surface of the topcoat coating film, and that depending on the type of primer coating film, adhesion to the topcoat coating film may be poor.

[0008] The present invention has been made in view of the above, and aims to provide an aqueous coating composition which, when in a paint state suitable for painting, is an aqueous coating composition which has a long pot life even under high-temperature, high-humidity conditions, contains titanium oxide, and is capable of forming a coating film with a hiding power of 90% or more, is less likely to cause foaming when a coating film is formed on an undercoat coating film formed from the aqueous primer coating composition, and is capable of forming a coating film which has excellent adhesion to the undercoat coating film. [Means for solving the problem]

[0009] As a result of extensive research into methods for solving the above problems, the inventors have found that the above problems can be solved by the following configuration examples, and have thus completed the present invention. An example of the configuration of the present invention is as follows.

[0010] [1] An aqueous coating composition containing titanium dioxide, a first agent containing an aqueous polyol resin (A); A second agent containing an isocyanate compound (B); Including, The blending ratio of the titanium oxide is 40 to 78 mass% relative to 100 mass% of the solid content of the aqueous polyol resin (A). Water-based paint composition.

[0011] [2] The aqueous coating composition according to [1], wherein the aqueous polyol resin (A) is an aqueous (meth)acrylic polyol resin.

[0012] [3] The elastic modulus of a 50 μm thick coating film formed from the first agent at 90 ° C is 0.5 N / mm 2 The aqueous coating composition according to [1] or [2] above.

[0013] [4] The aqueous coating composition according to any one of [1] to [3], which is for use in containers.

[0014] [5] A coating film formed from the aqueous coating composition according to any one of [1] to [4]. [6] A substrate with a multilayer coating film, comprising a substrate on which an undercoat coating film has been formed and the coating film described in [5].

[0015] [7] A method for producing a substrate with a multilayer coating film, comprising the following steps 1 and 2: Step 1: A step of applying at least one primer coating selected from a water-based epoxy primer, a water-based (meth)acrylic-modified epoxy primer, and a water-based (meth)acrylic primer to a substrate to form a primer coating film. Step 2: A step of applying the aqueous coating composition described in any one of [1] to [4] onto the undercoat coating film formed in Step 1 to form a topcoat coating film. [Effects of the Invention]

[0016] According to the present invention, an aqueous coating composition in a paint state suitable for painting has a long pot life (e.g., 3 hours or more) even under high-temperature, high-humidity conditions (e.g., 35°C, 85% RH), yet it is possible to form a coating film that contains titanium oxide and has a hiding power of 90% or more. Furthermore, the aqueous coating composition of the present invention is less likely to foam when a coating film is formed on a primer coating film formed from a water-based primer coating composition, and it is possible to form a coating film that has excellent adhesion to the primer coating film. DETAILED DESCRIPTION OF THE INVENTION

[0017] ≪Water-based paint composition≫ The aqueous coating composition according to the present invention (hereinafter also referred to as "the composition") contains titanium oxide, a first agent containing an aqueous polyol resin (A); A second agent containing an isocyanate compound (B); Including, The blending ratio of the titanium oxide is 40 to 78 mass % relative to 100 mass % of the solid content of the aqueous polyol resin (A). The composition can also be described as a multi-component water-based urethane coating composition.

[0018] A preferred embodiment of the composition is An aqueous coating composition containing titanium oxide, a first agent containing an aqueous polyol resin (A); A second agent containing an isocyanate compound (B); Including, the content of the solid content of the aqueous polyol resin (A) is 35 to 50 mass% relative to 100 mass% of the nonvolatile content of the composition; the content of the solid content of the isocyanate compound (B) is 10 to 20 mass% relative to 100 mass% of the nonvolatile content of the composition; The blending ratio of the titanium oxide is 40 to 78 mass % relative to 100 mass % of the solid content of the aqueous polyol resin (A).

[0019] The present composition is not particularly limited as long as it is a multi-component composition containing the first and second agents, and depending on the components used, it may also be a three- or more-component composition that includes a third agent other than the first and second agents. These first, second and third agents (hereinafter collectively referred to as "agent n") are usually stored, preserved, transported, etc. in separate containers, and are mixed to form the present composition when the composition is to be used (e.g., immediately before painting). In other words, these agents n can be said to be components of a kit for preparing the present composition, or in other words, the present composition can be said to be a kit for an aqueous paint composition that includes the first and second agents.

[0020] The present composition is prepared by mixing the agent n, but may be diluted after or during this preparation depending on the coating method and other factors. All descriptions in this specification, except for those relating to such dilution, are descriptions of the product before dilution.

[0021] In a paint state suitable for application, the pot life of the composition under high temperature and high humidity conditions (for example, 35°C, 85% RH) is preferably 3 hours or more. If the pot life is within the above range, strict control of the coating environment and coating conditions is not required, and the environment in which coating can be applied is not easily limited, which is preferable. The pot life is specifically measured by the method described in the examples below. A paint state suitable for application includes, for example, a paint state suitable for application methods such as the application method in Step 2 below. A specific example is a state in which the viscosity of the composition at 35°C is 1 Pa·s.

[0022] The time required for the composition to reach a fully cured state (drying time) according to ASTM D5895 is preferably 120 minutes or less, more preferably 90 minutes or less. If the time required to reach a completely cured state (drying property) is within the above range, the desired coating film can be formed in a short time, which is preferable in terms of coating workability and the like. The drying property is specifically measured by the method described in the examples below.

[0023] The content of nonvolatile matter in the present composition is preferably 40% by mass or more, more preferably 50% by mass or more. The upper limit of the content of nonvolatile matter in the present composition is not particularly limited, but is preferably 80% by mass or less.

[0024] The content of nonvolatile matter in this composition can be calculated as the mass percentage of the heating residue of this composition by measuring 1±0.1 g of this composition (the composition immediately after mixing with agent n) onto a flat-bottomed dish, spreading it evenly using a wire of known mass, and heating it at a heating temperature of 125°C for 1 hour (at normal pressure), and then measuring the heating residue (nonvolatile matter) and the mass of the wire, and calculating the mass percentage of the heating residue of this composition from the masses before and after heating. Furthermore, the solid content of each component below (for example, the solid content of the aqueous polyol resin (A)) refers to the components other than the solvent and dispersion medium in each component. The nonvolatile content of the present composition is approximately equal to the sum of the solid contents of the components used in preparing the present composition, and therefore can also be calculated from the solid contents of the components used in preparing the present composition.

[0025] The present composition is an aqueous coating composition, which is different from so-called organic solvent-based coating compositions. The aqueous coating composition is a composition in which the water content is preferably 60% by mass or more, more preferably 75% by mass or more, relative to 100% by mass of the total of the solvent and dispersion medium in the composition. The upper limit of the water content may be 100% by mass. The content of water in the present composition is preferably 30 to 60 mass %, more preferably 35 to 50 mass %.

[0026] The present composition is suitable for use on substrates such as steel (iron, steel, ferroalloy, carbon steel, mild steel, alloy steel, etc.), non-ferrous metals (zinc, aluminum, copper, brass, zinc plating, zinc thermal spraying, etc.), and stainless steel (SUS304, SUS410, etc.), and is particularly suitable for use on substrates made of steel or stainless steel. Specific examples of such substrates include ships, bridges, and other structures, and suitable examples include (large) steel or stainless steel structures such as ships, bridges, marine structures, plants, tanks, and containers. In particular, the composition is preferably used for containers (container boxes) and more preferably for the outer surface of reefer containers, in order to more effectively exhibit the effects of the present invention. The present composition is suitably used as a topcoat paint for the above-mentioned substrates, particularly for the substrates on which an undercoat paint film has been formed.

[0027] <Titanium oxide> The present composition contains titanium oxide. Since the titanium oxide is preferably dispersed in the present composition, it is preferably blended into the first agent, but it may also be blended into the third agent to form a paste-like third agent. One type of titanium oxide may be used, or two or more types differing in shape, average particle size, etc. may be used.

[0028] As the titanium oxide, known titanium oxides used as color pigments and the like can be used, and any of rutile, anatase, brookite, etc. may be used, but the rutile type is preferred from the viewpoint of stability, etc.

[0029] Furthermore, titanium oxide that has been surface-treated for the purpose of obtaining effects such as improved dispersibility in resin binders, improved light resistance and improved appearance of the coating film, may also be used. Whether or not titanium oxide has been surface-treated can be determined by analysis using an analytical method such as X-ray diffraction.

[0030] The surface treatment may be, for example, a surface treatment of titanium oxide with one or more surface treatment compounds. Examples of the surface treatment compound include silicon compounds such as silica, hydrous silica, sodium silicate, potassium silicate, and polysiloxane; zirconium compounds such as zirconium chloride, zirconium oxychloride, zirconium sulfate, zirconium nitrate, zirconium acetate, and zirconium dioxide; zinc compounds such as zinc chloride and zinc acetate; aluminum compounds; antimony compounds; tin compounds; cerium compounds; iron compounds; sulfur compounds; fluorine compounds; phosphate esters; alcohols; and organic acids.

[0031] Examples of methods for surface treatment of titanium oxide include those described in JP-A-3-23221, JP-A-6-49388, JP-A-6-345438, JP-A-7-292276, JP-A-7-292277, JP-A-9-48931, JP-A-9-124968, JP-A-10-158015, and JP-A-2001-2417.

[0032] When titanium oxide is surface-treated with a surface-treatment compound, the content of the surface-treatment compound relative to 100% by mass of the entire surface-treated titanium oxide is, for example, 0.1 to 10% by mass.

[0033] The average particle size of titanium oxide is not particularly limited, but is preferably 0.01 to 10 μm, and more preferably 0.05 to 5 μm, from the viewpoints that the present composition having excellent coating workability can be easily obtained and a coating film having a higher hiding power can be easily formed. The average particle size of titanium oxide can be measured by a method such as laser diffraction / scattering, or can be measured based on an electron microscope image.

[0034] In the present composition, the blending ratio of titanium oxide is 40 to 78 mass % relative to 100 mass % of the solid content of the aqueous polyol resin (A). By having the titanium oxide content within this range, the aqueous coating composition can be in a paint state suitable for painting, and can form a coating film with a hiding power of 90% or more, even when it is in a long usable state under high-temperature, high-humidity conditions. Furthermore, when the composition has a titanium oxide content within this range, foaming and other problems are unlikely to occur when a coating film is formed on a primer coating film formed from the aqueous primer coating composition, and a coating film with excellent adhesion to the primer coating film can be formed. The blending ratio of titanium oxide is preferably 40 to 60 mass% relative to 100 mass% of the solid content of the aqueous polyol resin (A) from the viewpoint of obtaining an aqueous coating composition in a coating state suitable for coating and having a longer usable life even under high-temperature and high-humidity conditions, and is preferably 60 to 78 mass% relative to 100 mass% of the solid content of the aqueous polyol resin (A) from the viewpoint of forming a coating film with higher hiding power. In order to achieve the above effects, the amount of titanium oxide to be blended is preferably 10 to 40% by mass, and more preferably 15 to 35% by mass, relative to 100% by mass of the nonvolatile content of the composition.

[0035] <First agent> The first part of the composition contains an aqueous polyol resin (A).

[0036] The first agent preferably has a modulus of elasticity of 0.5 N / mm at 90°C of a 50 μm thick first agent coating film formed from the first agent. 2 More preferably, 0.55 to 1.5 N / mm 2 It is desirable that the agent be such that By using a first agent that can form a first agent coating film with an elastic modulus within the above range, it is possible to easily form a coating film that is less likely to foam, particularly for an undercoat coating film formed from a water-based undercoat paint composition. The elastic modulus varies mainly depending on the molecular weight of the aqueous polyol resin (A) used in the first agent, and can be measured by the method described in the examples below.

[0037] [Water-based polyol resin (A)] The aqueous polyol resin (A) may be a resin having two or more —OH groups in one molecule. The aqueous polyol resin (A) used in the present composition (first part) may be one type or two or more types.

[0038] The weight average molecular weight (Mw) of the solid content of the aqueous polyol resin (A) is preferably 10,000 or more, more preferably 15,000 to 650,000, still more preferably 100,000 to 600,000, and particularly preferably 200,000 to 550,000. By using an aqueous polyol resin (A) having an Mw within the above range, a first agent having an elastic modulus within the above range can be easily obtained, and in particular, a coating film that is less likely to foam can be easily formed when compared to an undercoat coating film formed from an aqueous undercoat paint composition.

[0039] The hydroxyl value of the solid content of the aqueous polyol resin (A) is preferably 30 to 200 mgKOH / g, more preferably 50 to 100 mgKOH / g, from the viewpoints that the present composition having excellent storage stability can be easily obtained and a coating film having excellent film properties such as weather resistance can be easily formed.

[0040] Examples of the aqueous polyol resin (A) include water or a polyol resin that uses water as the main solvent or dispersion medium, or a polyol resin that can be mixed with water (can be diluted with water), and more specifically, examples thereof include a water-dispersed polyol resin, a water-soluble polyol resin, and an emulsion-type polyol resin.

[0041] The polyol resin is not particularly limited, and examples thereof include (meth)acrylic polyol resins, polyester polyol resins, polyether polyol resins, polyurethane polyol resins, and polycarbonate polyol resins. Among these, (meth)acrylic polyol resins are preferred because they can easily form a coating film that is excellent in appearance, weather resistance, chemical resistance, etc. In this specification, "(meth)acrylic" means acrylic and / or methacrylic, and similar expressions such as "(meth)acrylate" below have the same meaning.

[0042] Examples of the (meth)acrylic polyol resin include homopolymers or copolymers of (meth)acrylic compounds having hydroxyl groups, copolymers obtained using (meth)acrylic compounds having hydroxyl groups and other compounds copolymerizable with said compounds, and modified products of these (co)polymers.

[0043] Examples of the (meth)acrylic compound having a hydroxyl group include compounds represented by the following formula (1), and specific examples include 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate. The (meth)acrylic compound having a hydroxyl group may be used alone or in combination of two or more kinds.

[0044] [ka]

[0045] In formula (1), R is a hydrogen atom or a methyl group. In formula (1), L is a divalent linking group, and is preferably an alkylene group (for example, an alkylene group having 1 to 10 carbon atoms).

[0046] Examples of the other compounds include unsaturated carboxylic acid compounds such as (meth)acrylic acid, 2-ethylacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, stearyl (meth)acrylate, and isostearate. (Meth)acrylic acid alkyl esters such as tearyl (meth)acrylate, cetyl (meth)acrylate, and lauryl (meth)acrylate; (meth)acrylic compounds having a fluorine atom such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, 1H,1H,5H-octafluoropentyl (meth)acrylate, and 2-(perfluorooctyl)ethyl (meth)acrylate; isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, and dicyclohexyl (meth)acrylate. (meth)acrylic compounds having an alicyclic structure such as cyclopentanyl (meth)acrylate and dicyclopentenyloxyethyl (meth)acrylate; (meth)acrylic compounds having an ether bond such as polyethylene glycol mono(meth)acrylate, methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate and methoxypolyethylene glycol (meth)acrylate; benzyl (meth)acrylate; 2-ethyl-2-methyl-[1,3]-dioxolan-4-yl-methyl (meth)acrylate; dimethylaminoethyl (meth)acrylate; unsaturated carboxylic acid ester compounds such as diethyl maleate and diethyl phthalate; vinyl compounds such as styrene, α-methylstyrene, vinyl acetate, vinyl benzoate, vinyltoluene, acrylonitrile, methacrylonitrile, vinylpyridine, vinylpyrrolidone and vinyl chloride; and (meth)acrylamide compounds such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide. The other compounds may be used alone or in combination of two or more.

[0047] The modified product is not particularly limited, but examples thereof include alkyd resin-modified (meth)acrylic polyol resins and fatty acid-modified (meth)acrylic polyol resins. The modified product refers to a resin in which the proportion of structural units derived from the modified component is less than 50% by mass.

[0048] The solid content of the aqueous polyol resin (A) is preferably 20 to 70 mass %, more preferably 30 to 60 mass %, and even more preferably 35 to 50 mass %, relative to 100 mass % of the nonvolatile content of the composition. The solid content of the aqueous polyol resin (A) is preferably 20 to 80 mass %, more preferably 30 to 70 mass %, and even more preferably 40 to 60 mass %, relative to 100 mass % of the solid content of the first agent. When the content of the aqueous polyol resin (A) is within the above range, a coating film excellent in appearance, weather resistance, corrosion resistance, foaming resistance, etc. can be easily formed.

[0049] As the aqueous polyol resin (A) used as a raw material when preparing the present composition and the first agent, an aqueous dispersion of the resin is preferred, an emulsion or dispersion is more preferred, and an emulsion is even more preferred, from the viewpoints that the present composition, which is an aqueous paint composition, can be easily prepared and a coating film having the desired physical properties can be easily formed.

[0050] From the viewpoint of the stability of the emulsion, the solid content in the emulsion is preferably 30% by mass or more, more preferably 35% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less.

[0051] The average particle size of the polyol resin in the emulsion is preferably 0.05 to 0.9 μm, more preferably 0.1 to 0.8 μm, from the viewpoints of excellent emulsion stability and easy production of the present composition having excellent film-forming properties. The term "average particle size" in this specification refers to the particle size (median size, d50) corresponding to 50% of the volume-based cumulative particle size distribution measured based on the "Particle size analysis - Laser diffraction and scattering method" specified in JIS Z 8825:2013.

[0052] The viscosity of the emulsion (25° C.) is preferably 10 to 10,000 mPa·s, and more preferably 20 to 7,000 mPa·s, from the viewpoint that the present composition having excellent film-forming properties can be easily obtained.

[0053] The water dispersion (emulsion) is a dispersion in which a resin is dispersed in a dispersion medium containing water (hereinafter also referred to as an "aqueous medium"). The aqueous medium is not particularly limited as long as it contains water, but the content of water in the aqueous medium is preferably 50 to 100% by mass, more preferably 60 to 100% by mass.

[0054] The aqueous medium may contain a medium other than water, and examples of such a medium include acetone, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diacetone alcohol, dioxane, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monohexyl ether. These may be used alone or in combination of two or more.

[0055] The emulsion can be prepared, for example, by emulsifying a polyol resin with one or more surfactants to form an emulsion, or by directly emulsion polymerization of the monomers that form the polyol resin.

[0056] [Other ingredients] The first agent may contain other components other than titanium oxide, the aqueous polyol resin (A), and the isocyanate compound (B), such as dispersants, flash rust inhibitors, antifoaming agents, pigments, film-forming aids, thickeners (anti-sagging agents, anti-settling agents, thixotropic agents), water, leveling agents, plasticizers, surfactants, (organic) solvents, light stabilizers, ultraviolet absorbers, pH adjusters, and other conventionally known components, as needed, within the scope of not impairing the effects of the present invention. These other components may each be used alone or in combination of two or more.

[0057] ·solvent The first agent may contain a solvent (organic solvent). Examples of the solvent include conventionally known organic solvents such as aromatic, aliphatic, ketone, ether, ester, and alcohol solvents. Specific examples include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as mineral spirits and cyclohexane; ketone solvents such as methyl isobutyl ketone and cyclohexanone; ether or ester solvents such as butyl acetate, propylene glycol monomethyl ether, dipropylene glycol dimethyl ether, and propylene glycol monomethyl ether acetate; and alcohol solvents such as n-butyl alcohol and isopropyl alcohol.

[0058] The solvent is preferably used in an amount such that the VOC content in the composition is preferably 200 g / L or less, more preferably 150 g / L or less, and even more preferably 100 g / L or less.

[0059] The VOC content in the composition can be calculated from the specific gravity of the composition, the heating residue (mass ratio of non-volatile content), and the moisture content using the following formulas (2) and (3). The specific gravity of the composition, the heating residue, and the moisture content may be measured values ​​or values ​​calculated from the raw materials used. VOC content (mass%) = (100-heating residue rate-moisture rate) / 100...(2) VOC content (g / L) = Composition specific gravity x 1000 x (100 - heating residual fraction - moisture percentage) / 100... (3)

[0060] The first agent may contain a solvent (organic solvent), but the content of the solvent (organic solvent) in the first agent is preferably 15% by mass or less, and more preferably 10% by mass or less.

[0061] Dispersant Since the titanium oxide is preferably dispersed in the present composition, it is preferable to add a dispersant to the n-th agent containing titanium oxide. The dispersant is not particularly limited, but examples thereof include various dispersants such as copolymers having a pigment-adsorbing group (pigment-affinity group) such as a carboxyl group, a phosphate group, an amino group, a salt group of these, or an ammonium base, and having a compatible chain such as a fatty acid, polyamino, polyether, polyester, polypolyurethane, or polyacrylate.

[0062] When a dispersant is blended into the present composition, the amount of solid content of the dispersant blended is preferably 0.1 to 3 mass %, more preferably 0.1 to 2 mass %, relative to 100 mass % of the nonvolatile content of the present composition, in order to facilitate the formation of a coating film with excellent smoothness and in which titanium oxide and pigments are uniformly dispersed.

[0063] Flash rust inhibitor When the present composition is applied to a metal surface, the rust on the metal surface may bleed to the surface of the coating film, causing rust spots (flash rust), and this can be prevented by incorporating a flash rust inhibitor into the present composition. The flash rust inhibitor is not particularly limited as long as it is a component that can inhibit flash rust, and any known flash rust inhibitor can be used.

[0064] Examples of flash rust inhibitors include nitrites such as sodium nitrite, potassium nitrite, calcium nitrite, strontium nitrite, barium nitrite, and ammonium nitrite; benzoates such as sodium benzoate, potassium benzoate, calcium benzoate, and ammonium benzoate; phytates such as sodium phytate and potassium phytate; salts of fatty acids such as sebacic acid and dodecanoic acid; phosphoric acid derivatives such as alkyl phosphates and polyphosphates; tannates; metal sulfonates; N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid, and the like. Examples of suitable chelating agents include amine-based chelating agents such as alkali metal salts of EDTA, diethylenetriaminepentaacetic acid (DTPA), propylenediaminetetraacetic acid (PDTA), iminodiacetic acid, nitrilotriacetic acid (NTA), and diethylenetriaminepentamethylenephosphonic acid (DTPMP); addition reaction products of 4-methyl-γ-oxo-benzenebutanoic acid and N-ethylmorpholine; intercalation compounds obtained by intercalating monoalkylamines, polyamines, quaternary ammonium ions, etc. into layered phosphates such as aluminum dihydrogen triphosphate; and hydrazine derivatives such as hydrazide compounds, semicarbazide compounds, and hydrazone compounds.

[0065] When a flash rust inhibitor is incorporated into the present composition, the amount of the flash rust inhibitor incorporated is preferably 0.01 to 5 mass %, more preferably 0.05 to 3 mass %, relative to 100 mass % of the nonvolatile content of the present composition, in order to facilitate the inhibition of flash rust, etc.

[0066] Defoaming agent As the defoaming agent, various known defoaming agents such as polymer-based, acrylic-based, silicone-based, mineral oil-based, and olefin-based defoaming agents can be used, with silicone-based defoaming agents being preferred.

[0067] When an antifoaming agent is blended into the present composition, the amount of the solid content of the antifoaming agent is preferably 0.01 to 2.0 mass%, more preferably 0.1 to 1.5 mass%, relative to 100 mass% of the nonvolatile content of the present composition, from the viewpoints of being able to suppress foam generation during the production or application of the present composition and being able to break any foam that has generated in the present composition.

[0068] Pigments Examples of the pigment include conventionally known color pigments and extender pigments. Examples of color pigments include inorganic pigments such as carbon black, red iron oxide, iron hydroxide, and ultramarine; and organic pigments such as phthalocyanine blue and phthalocyanine green. Examples of extender pigments include barium sulfate (including precipitated barium sulfate and elutriated barium sulfate), calcium carbonate, potassium feldspar, kaolin, clay, talc, mica, bentonite, magnesium carbonate, and silica.

[0069] When a pigment is blended into the present composition, the amount of the pigment blended is preferably 1 to 35 mass %, more preferably 5 to 30 mass %, relative to 100 mass % of the nonvolatile content of the present composition, in order to easily obtain a coating film that has an excellent balance between flexibility and adhesion to the primer coating film.

[0070] The pigment volume concentration (PVC) in the composition is preferably 10 to 25%, more preferably 10 to 20%, from the viewpoint of being able to easily form a coating film that has a good balance between flexibility and adhesion to the undercoat coating film.

[0071] The PVC refers to the total volume concentration of titanium oxide and pigment relative to the volume of nonvolatile matter in the composition. Specifically, the PVC can be calculated using the following formula: PVC [%] = Total volume of all titanium oxides and pigments in the composition × 100 / Volume of non-volatile matter in the composition

[0072] The volume of the nonvolatile content in the composition can be calculated from the mass and true density of the nonvolatile content of the composition. The mass and true density of the nonvolatile content may be measured values ​​or values ​​calculated from the raw materials used. The volume of the titanium oxide and pigment can be calculated from the mass and true density of the titanium oxide and pigment used. The mass and true density of the titanium oxide and pigment may be measured values ​​or values ​​calculated from the raw materials used. For example, the volume can be calculated by separating the titanium oxide and pigment from other components from the nonvolatile content of the composition and measuring the mass and true density of the separated titanium oxide and pigment.

[0073] Film-forming agents Since the present composition contains water, the composition may freeze in winter, etc., and from the viewpoint of improving film-forming properties at low temperatures and the finished appearance of the resulting coating film, a film-forming aid may be blended therein.

[0074] Examples of the film-forming aid include conventionally known alcohols, glycol ethers, and esters, such as alcohols such as 2,2,4-trimethylpentanediol and benzyl alcohol; glycol ethers such as ethylene glycol diethyl ether, diethylene glycol diethyl ether, propylene glycol diethyl ether, dipropylene glycol diethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, dipropylene glycol n-butyl ether, ethylene glycol monobenzyl ether, and ethylene glycol monophenyl ether; and esters such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethylpentanediol diisobutyrate.

[0075] When a film-forming aid is blended into the present composition, the blending amount of the film-forming aid is preferably 1 to 10 mass %, more preferably 2 to 8 mass %, relative to 100 mass % of the present composition, in order to facilitate the formation of a coating film that has excellent film-forming properties at low temperatures and excellent appearance.

[0076] Thickener Examples of thickeners include organic clay salts such as stearate salts of Al, Ca, and Zn, lecithin salts, and alkylsulfonates; clays such as bentonite clay and hectorite clay, and organically modified versions of these clays (e.g., organically modified hectorite clay); polyethylene wax, oxidized polyethylene wax, ethylene-vinyl acetate wax, polyamide wax, hydrogenated castor oil wax, synthetic finely powdered silica, urea thickeners, and urethane thickeners.

[0077] When a thickener is blended in the present composition, the blending amount of the thickener is preferably 0.01 to 0.4 mass %, more preferably 0.05 to 0.35 mass %, relative to 100 mass % of the nonvolatile content of the present composition.

[0078] ·water The first agent preferably contains water. The raw materials used in preparing the first agent, such as the aqueous polyol resin (A), may contain water. When using such water-containing raw materials, it is not necessary to use water other than the water contained in the raw materials. However, it is preferable to use water in addition to the water that may be contained in the raw materials, such as the aqueous polyol resin (A), in order to make it easier to prepare the present composition and to easily obtain the present composition having better coating workability. The water to be further used is not particularly limited, and tap water or the like may be used, but ion-exchanged water or the like is preferably used.

[0079] The water content in the first agent (including water that may be contained in raw materials such as the aqueous polyol resin (A)) is preferably used so that the water content in the composition falls within the above-mentioned range, specifically, preferably 30 to 60% by mass, more preferably 35 to 50% by mass, relative to 100% by mass of the first agent. Furthermore, the content of water in the first agent is preferably 50% by mass or more, more preferably 70 to 100% by mass, and particularly preferably 80 to 100% by mass, relative to 100% by mass of the total amount of the dispersion medium and solvent in the first agent, so that the desired composition can be easily obtained.

[0080] <Second agent> The second part of the composition contains an isocyanate compound (B).

[0081] [Isocyanate compound (B)] The isocyanate compound (B) is not particularly limited, but is preferably a polyisocyanate compound having two or more isocyanate groups in one molecule, and more preferably a water-dispersible polyisocyanate compound. The isocyanate compound (B) used in the present composition (second agent) may be one type or two or more types.

[0082] Examples of the isocyanate compound (B) include aliphatic polyisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, and dicyclohexylmethane diisocyanate; Isocyanates: aromatic polyisocyanates such as diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, phenylene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, and dianisidine diisocyanate; and dimers or trimers (biuret-modified products, isocyanurate-modified products, and adducts) of the above polyisocyanates. Among these, hexamethylene diisocyanate is preferred as the isocyanate compound (B) from the viewpoints of ultraviolet resistance, yellowing resistance, and the like.

[0083] Furthermore, the isocyanate compound (B) may be an isocyanate compound having a hydrophilic group, since it can exist relatively stably in water. Examples of the isocyanate compound having a hydrophilic group include compounds obtained by modifying the above-mentioned polyisocyanates with a hydrophilic compound.

[0084] Examples of the hydrophilic compound include polyalkylene glycol compounds, and suitable examples thereof include polyethylene glycol and compounds in which one end of polyethylene glycol is blocked with an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group.

[0085] The solid content of the isocyanate compound (B) is preferably 5 to 30 mass %, more preferably 10 to 25 mass %, and even more preferably 10 to 20 mass %, relative to 100 mass % of the nonvolatile content of the composition. The solid content of the isocyanate compound (B) is preferably 30 to 100 mass%, more preferably 40 to 100 mass%, and even more preferably 50 to 100 mass%, relative to 100 mass% of the solid content of the second part. When the content of the isocyanate compound (B) is within the above range, a coating film excellent in foaming resistance, weather resistance, corrosion resistance, etc. can be easily formed.

[0086] Furthermore, the content of the isocyanate compound (B) in the present composition is preferably an amount such that the reaction ratio represented by the following formula is preferably 0.4 to 2, more preferably 0.8 to 1.5, in order to easily obtain a coating film that has a good balance of foaming resistance, weather resistance, and corrosion resistance. Reaction ratio = NCO equivalent of isocyanate compound (B) / OH equivalent of aqueous polyol resin (A)

[0087] [Additives] The second agent may contain additives other than titanium oxide, the aqueous polyol resin (A), and the isocyanate compound (B), such as dispersants, flash rust inhibitors, antifoaming agents, pigments, film-forming aids, thickeners (anti-sagging agents, anti-settling agents, thixotropic agents), water, leveling agents, plasticizers, surfactants, (organic) solvents, light stabilizers, ultraviolet absorbers, pH adjusters, and other conventionally known additives, as needed, within the scope of not impairing the effects of the present invention. These additives may be used alone or in combination of two or more. Specific examples of these additives are the same as those described in the section for the first agent.

[0088] <Method for preparing the present composition> The first and second agents can be prepared by mixing (kneading) the components to be blended into these agents. During this mixing (kneading), the components may be added and mixed all at once, or may be added and mixed in multiple batches. The present composition can be prepared by mixing (kneading) the first agent, the second agent, and other agents (for example, a third agent) that are used as needed. The mixing (kneading) can be carried out using a conventionally known device such as a mixer, disperser, or stirrer, and examples of such devices include a disperser, a mixing / dispersing mill, a mortar mixer, a roll, a paint shaker, and a homogenizer. The mixing (kneading) may be carried out while heating or cooling depending on the season, environment, etc.

[0089] <<Coated film, substrate with multi-layered coating>> The coating film according to the present invention (hereinafter also referred to as "the present coating film") is formed from the present composition, and is usually formed on a substrate. The substrate with a multilayer coating film according to the present invention has a substrate on which an undercoat coating film has been formed and a main coating film, and is usually produced by forming a main coating film on a substrate on which an undercoat coating film has been formed using the present composition.

[0090] The thickness of the coating film is usually 20 to 200 μm, preferably 50 to 100 μm, in terms of dry film thickness.

[0091] The hiding power of the coating film, measured in accordance with JIS K 5600-4-1:1999, is preferably 90% or more, more preferably 92% or more, and even more preferably 93% or more. The present coating film having a hiding ratio within the above range can be suitably used as a topcoat coating on the following substrates, etc. Specifically, the hiding rate is measured by the method described in the examples below.

[0092] The material of the substrate is not particularly limited, and examples thereof include steel (iron, steel, ferroalloy, carbon steel, mild steel, alloy steel, etc.), non-ferrous metals (zinc, aluminum, copper, brass, zinc plating, zinc thermal spraying, etc.), and stainless steel (SUS304, SUS410, etc.), with steel or stainless steel being preferred. Specifically, the substrate is preferably a ship, a bridge, or other structures, more preferably a (large) steel or stainless steel structure such as a ship, a bridge, a marine structure, a plant, a tank, or a container, further preferably a container (container box), and particularly preferably the outer surface of a reefer container.

[0093] The substrate may have an undercoat coating film for the purpose of improving adhesion to the substrate and corrosion resistance, and it is preferable that the substrate has such an undercoat coating film. In this specification, the term "undercoat coating film" refers to a coating film provided between the main coating film and the substrate (a coating film provided below the main coating film), and includes not only known undercoat coating films (primer coating films) in the narrow sense, but also known coating films known as so-called intermediate coating films. The undercoat film may be one layer or two or more layers.

[0094] Examples of the undercoat coating film include coating films formed from various known undercoat coating compositions such as epoxy primer, (meth)acrylic-modified epoxy primer, and (meth)acrylic primer.

[0095] When an organic solvent-based primer coating composition is used as the primer coating composition to form a primer coating film, forming a topcoat coating film on top of it using a conventional two-component water-based urethane coating composition may not cause problems with foaming or adhesion, but when an aqueous primer coating composition is used to form a primer coating film and then a conventional two-component water-based urethane coating composition to form a topcoat coating film on top of that, problems with foaming and adhesion tend to occur. On the other hand, when an aqueous primer coating composition is used to form a primer coating film, forming a topcoat coating film on top of that using this composition is less likely to cause problems with foaming or adhesion. For this reason, an organic solvent-based primer coating composition may be used as the primer coating composition, but it is preferable to use a water-based primer coating composition in order to more effectively exhibit the effects of the present invention.

[0096] The water-based primer coating composition may be a one-component coating composition or a multi-component coating composition containing a main component and a curing agent component. In order to better demonstrate the effects of the present invention, the multi-component coating composition is preferably a coating composition other than a coating composition in which both the main component and the curing agent component contain emulsions. The aqueous undercoat paint composition is preferably a one-component (meth)acrylic primer; an epoxy primer other than a paint composition in which both the main component and the curing agent component contain an emulsion; or a (meth)acrylic-modified epoxy primer, in order to more effectively exhibit the effects of the present invention.

[0097] The curing agent component of the epoxy primer may be, for example, an amine emulsion or an aqueous amine.

[0098] In this specification, the term "amine emulsion" refers to a liquid mixture obtained by mixing a component containing an amine compound with water so that the solid content is 50% by mass at 23°C, or by volatilizing the solvent / dispersion medium, followed by thorough stirring and allowing to stand at 23°C for 1 hour, in which 80% by mass or more of the solid content of the component mixed with water is stably present in water and the liquid mixture is maintained in an emulsion state.

[0099] In the present invention, aqueous amine refers to a liquid mixture obtained by mixing a component containing an amine compound with water so that the solid content is 3% by mass at 23°C, thoroughly stirring the mixture, and allowing it to stand at 23°C for 1 hour, in which 90% by mass or more of the solid content of the component mixed with water is stably present in the water, and the solid content of the component mixed with water is present in a state where the average particle size of the solid content measured with a laser diffraction particle size distribution analyzer (e.g., Mastersizer 3000 (manufactured by Spectris Inc.)) is less than 10 nm.

[0100] The thickness of the undercoat coating is usually 20 to 200 μm, preferably 50 to 100 μm, in terms of dry film thickness.

[0101] The substrate may be a substrate that has been subjected to a pretreatment such as a cleaning treatment or a blasting treatment to remove rust, dirt, paint (old paint film), etc. adhering to the substrate, or a substrate on which the primer coating film has been formed after the pretreatment.

[0102] The substrate with the multilayer coating film can be produced, for example, by a method including the following steps 1 and 2. Step 1: A step of applying at least one primer coating selected from a water-based epoxy primer, a water-based (meth)acrylic-modified epoxy primer, and a water-based (meth)acrylic primer to a substrate to form a primer coating film. Step 2: Applying the composition to the primer coating film formed in Step 1 to form the main coating film (top coating film).

[0103] Examples of the coating method in steps 1 and 2 include brush coating, air spray coating, airless spray coating, and roll coater coating. Spray coating is preferred because it is excellent in workability and productivity, and can easily coat a large-area substrate. The undercoat film and main coating film having the above thickness may be formed by one coating, or by two or more coatings (two or more coatings).

[0104] The conditions for forming the undercoat film and main coating film are not particularly limited and may be set appropriately depending on the coating film formation method, type of substrate, application, coating environment, etc., but the drying temperature is usually 5 to 40° C. when drying at room temperature, and usually 30 to less than 100° C., more preferably 40 to 80° C. when forced drying is performed using a hot air dryer or the like. The present composition can be dried and cured even by drying at room temperature. The drying time varies depending on the drying method of the coating film, and is, for example, about 1 to 7 days when drying at room temperature, and about 5 to 60 minutes when forced drying is used. [Example]

[0105] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0106] [Example 1] A mill base was prepared by adding 10 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant, 0.1 part by mass of flash rust inhibitor, 0.3 part by mass of antifoaming agent 1, 18.0 parts by mass of titanium oxide, and 4.0 parts by mass of extender pigment to a container and dispersing the mixture using a paint shaker until the particle gauge was 20 μm or less. To the obtained mill base, 54.0 parts by mass of aqueous polyol resin A-1, 3.7 parts by mass of film-forming aid, 0.4 parts by mass of antifoaming agent 2, 0.4 parts by mass of thickener, and 8.1 parts by mass of ion-exchanged water were added, and then mixed with a high-speed disper to prepare the first agent. 90 parts by mass of the prepared first agent and 10 parts by mass of the second agent (isocyanate compound B-1) were mixed using a high-speed disper until homogeneous to prepare an aqueous coating composition.

[0107] [Examples 2 to 6 and Comparative Examples 1 to 6] The main agent was prepared in the same manner as in Example 1, except that the types and amounts of each component constituting the first agent were changed as shown in Table 1 below. The prepared base agent and curing agent were mixed in the mixing ratio by mass shown in Table 1 using a high-speed disper to prepare an aqueous coating composition. The components listed in Table 1 are explained in Table 2.

[0108] <Coating film elasticity modulus of the first agent> The prepared first agent was applied to a 200 mm x 200 mm polyethylene sheet using an air sprayer so that the dry film thickness was 50 μm. The applied first agent was dried at room temperature for 10 minutes and then hot-air dried at 50°C for 30 minutes. It was then dried for 7 days in an environment of 23°C and 50% relative humidity, and the dried coating film was peeled off from the polyethylene sheet to form a first agent coating film with a dry film thickness of 50 μm. The stress of the formed first-component coating film was measured at a strain of 0 to 10% using an autograph AGX-V and a thermostatic bath TCE-N-300A manufactured by Shimadzu Corporation at a temperature of 90°C and a tension speed of 1 mm / s. The elastic modulus was calculated from the slope of the resulting stress-strain curve. The results are shown in Table 1. The first agent coating film obtained using the first agent obtained in Comparative Example 5 had a very low modulus of elasticity, making it impossible to measure the modulus of elasticity.

[0109] <Pot life> The prepared aqueous coating composition was diluted with ion-exchanged water until its viscosity (measured at 35°C with a Viscotester VT-06 (manufactured by Rion Co., Ltd.) at a rotor speed of 62.5 rpm) reached 1 Pa·s. The diluted solution was kept in a thermo-hygrostat at 35°C and 85% RH (the start of this holding period was considered the start of the test), and the coating viscosity was measured every hour using the Viscotester VT-06 (rotor speed 62.5 rpm). The time immediately before the viscosity of the aqueous coating composition reached twice its viscosity at the start of the test was taken as the pot life, and the pot life was evaluated according to the following evaluation criteria. The results are shown in Table 1. Evaluation criteria ○: Pot life is 3 hours or more ×: Usable time is 2 hours or less

[0110] <Drying> According to ASTM D5895, 100% by weight of the prepared aqueous coating composition was diluted with 5% by weight of ion-exchanged water, and the aqueous coating composition was applied to a 350mm x 25mm glass plate using an applicator with a 0.2mm gap, and then dried under an environment of 23°C and 50% relative humidity. The time until the coating surface reached a dry-through state (dry-through) was measured using a drying time recorder. The results are shown in Table 1.

[0111] <Concealment rate> According to Method B (opacity test paper) of JIS K 5600-4-1:1999, Part 4: Visual Properties of Coating Films, Section 1: Hiding Power (for Light Color Paints), an aqueous coating composition prepared by diluting 100% by weight of the aqueous coating composition with 5% by weight of ion-exchanged water was applied to a black-and-white opacity test paper (manufactured by Nippon Test Panel Co., Ltd.) using an applicator with a 0.15 mm gap and allowed to dry at 23°C and 50% relative humidity. After drying, the tristimulus value Y was measured using a colorimeter CR-400 (manufactured by Konica Minolta, Inc.). The opacity was calculated from the measured tristimulus value Y and evaluated according to the following criteria. The results are shown in Table 1. Evaluation criteria ○: Concealment rate is 90% or more ×: Concealment rate is less than 90%

[0112] <Recoatability and adhesion> The following (meth)acrylic primer was applied to a 150 mm x 70 mm JIS G 3141:2017 (SPCC-SB) cold-rolled steel plate using an applicator with a 0.4 mm gap, and then dried for 4 hours in an environment of 23°C and 50% relative humidity to form a primer coating film. An aqueous coating composition prepared by mixing 5% by mass of ion-exchanged water with 100% by mass of the prepared aqueous coating composition was applied onto the formed undercoat coating film using an applicator with a gap of 0.4 mm, and the coating was dried in an environment of 35°C and a relative humidity of 85% to form a topcoat coating film, thereby producing a substrate with a multilayer coating film.

[0113] Five days after the topcoat coating was formed, the laminated coating film was visually observed and the recoatability was evaluated according to the following evaluation criteria. The results are shown in Table 1. Further, similar evaluations were carried out using the following (meth)acrylic modified epoxy primer, epoxy primer A, or epoxy primer B instead of the (meth)acrylic primer. The results are shown in Table 1. Evaluation criteria (recoatability) ○: No bubbles are generated in the laminated coating film ×: Bubbles occurred in the laminated coating film

[0114] In addition, 5 days after the topcoat coating was applied, the coating surface of the laminated coating substrate was subjected to a 25-grid, 2mm x 2mm, cross-cut adhesion test (cross-cut method) in accordance with JIS K 5600-5-6:1999. The cross-cuts were deep enough to reach the primer coating from the surface of the topcoat coating. The percentage of the area of ​​the peeled coating, with the total coating area of ​​the 25 grids taken as 100%, was measured, and the adhesion (between the topcoat coating and the primer coating) was evaluated according to the following criteria. The results are shown in Table 1. Further, similar evaluations were carried out using the following (meth)acrylic modified epoxy primer or epoxy primer A instead of the (meth)acrylic primer. The results are shown in Table 1. Evaluation criteria (adhesion) ○: The area of ​​peeled coating is 15% or less ×: The area of ​​peeled coating is greater than 15%

[0115] [(Meth)acrylic primer] A container was charged with 14.0 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant, 0.1 part by mass of flash rust inhibitor, 0.1 part by mass of antifoaming agent, 10.0 parts by mass of coloring pigment, 24.0 parts by mass of extender pigment, and 0.2 parts by mass of anti-settling agent, and the mixture was dispersed using a high-speed disperser until the particle gauge became 40 μm or less, to prepare a mill base. To the obtained mill base, 44.0 parts by mass of acrylic resin, 4.0 parts by mass of film-forming aid, 0.2 parts by mass of antifoaming agent, 0.4 parts by mass of thickener, and 2.0 parts by mass of ion-exchanged water were added, and then mixed using a high-speed disper to prepare a (meth)acrylic primer.

[0116] [(Meth)acrylic modified epoxy primer] A mill base was prepared by adding 14.0 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant, 0.1 part by mass of flash rust inhibitor, 0.1 part by mass of antifoaming agent, 10.0 parts by mass of color pigment, 27.0 parts by mass of extender pigment, and 0.2 parts by mass of anti-settling agent to a container and dispersing the mixture using a high-speed disperser until the particle gauge was 40 μm or less. To the obtained mill base, 33.0 parts by mass of acrylic resin, 2.7 parts by mass of amine resin 1, 1.5 parts by mass of film-forming agent, 0.2 parts by mass of antifoaming agent, 0.5 parts by mass of thickener, and 9.7 parts by mass of ion-exchanged water were added, and then mixed using a high-speed disper to prepare the first agent. 74.0 parts by mass of epoxy resin 2 and 26.0 parts by mass of film-forming aid were added to a container, and then mixed with a high-speed disper to prepare a second part. Thereafter, 95 parts by mass of the first part obtained as described above and 5 parts by mass of the second part were mixed in a high-speed disper until uniform, to prepare a (meth)acrylic-modified epoxy primer.

[0117] [Epoxy Primer A] A mill base was prepared by adding 15.0 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant, 0.1 part by mass of flash rust inhibitor, 0.1 part by mass of antifoaming agent, 10.0 parts by mass of color pigment, 27.0 parts by mass of extender pigment, and 0.2 parts by mass of anti-settling agent to a container and dispersing the mixture using a high-speed disperser until the particle gauge was 40 μm or less. To the obtained mill base, 38.0 parts by mass of epoxy resin 1, 0.3 parts by mass of antifoaming agent, 0.5 parts by mass of thickener, and 7.8 parts by mass of ion-exchanged water were added, and then mixed using a high-speed disper to prepare the first agent. 43.0 parts by mass of amine resin 1 and 57.0 parts by mass of ion-exchanged water were added to a container, and then mixed with a high-speed disper to prepare a second part. Thereafter, 92 parts by mass of the first part obtained as described above and 8 parts by mass of the second part were mixed with a high-speed disper until homogeneous, thereby preparing an epoxy primer A.

[0118] [Epoxy Primer B] A mill base was prepared by adding 15.0 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant, 0.1 part by mass of flash rust inhibitor, 0.1 part by mass of antifoaming agent, 10.0 parts by mass of color pigment, 27.0 parts by mass of extender pigment, and 0.2 parts by mass of anti-settling agent to a container and dispersing the mixture using a high-speed disperser until the particle gauge was 40 μm or less. To the obtained mill base, 38.0 parts by mass of epoxy resin 1, 0.3 parts by mass of antifoaming agent, 0.5 parts by mass of thickener, and 7.8 parts by mass of ion-exchanged water were added, and then mixed using a high-speed disper to prepare the first agent. 94.0 parts by mass of amine resin 2 and 6.0 parts by mass of ion-exchanged water were added to a container, and then mixed with a high-speed disper to prepare a second part. Thereafter, 92 parts by mass of the first part obtained as described above and 8 parts by mass of the second part were mixed with a high-speed disper until homogeneous, thereby preparing an epoxy primer B.

[0119] Details of the (meth)acrylic primer, (meth)acrylic-modified epoxy primer, epoxy primer A and epoxy primer B are shown in Table 3. Further, the explanation of each component listed in Table 3 is shown in Table 4.

[0120] [Table 1]

[0121] [Table 2]

[0122]

Table 3

[0123]

Table 4

Claims

1. An aqueous coating composition containing titanium oxide, a first agent containing an aqueous polyol resin (A); a second agent containing an isocyanate compound (B); Including, The blending ratio of the titanium oxide is 40 to 78 mass% relative to 100 mass% of the solid content of the aqueous polyol resin (A). Water-based paint composition.

2. 2. The aqueous coating composition according to claim 1, wherein the aqueous polyol resin (A) is an aqueous (meth)acrylic polyol resin.

3. The elastic modulus of the coating film having a thickness of 50 μm formed from the first agent at 90° C. is 0.5 N / mm ２ The aqueous coating composition according to claim 1, wherein

4. The aqueous coating composition according to claim 1, which is for use in containers.

5. A coating film formed from the aqueous coating composition according to any one of claims 1 to 4.

6. A substrate with a multi-layer coating film, comprising a substrate on which an undercoat coating film has been formed and the coating film according to claim 5.

7. A method for producing a substrate with a multilayer coating film, comprising the following steps 1 and 2: Step 1: A step of applying at least one primer coating selected from a water-based epoxy primer, a water-based (meth)acrylic-modified epoxy primer, and a water-based (meth)acrylic primer to a substrate to form a primer coating film. Step 2: A step of applying the aqueous coating composition according to any one of claims 1 to 4 onto the undercoat coating film formed in step 1 to form a topcoat coating film.

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