Water-based coating agent for steel, coating film, method of coating steel and steel

Abstract

This water-based coating for steel comprises polyurethane resin particles (A-1) and ethylene-unsaturated carboxylic acid copolymer resin particles (A-2), silicon oxide particles (B) having a mode diameter of 5 to 20 nm, an organic titanium compound (C), and a phthalocyanine pigment (F) coated with at least one of a resin and a surfactant, wherein the content of the phthalocyanine pigment (F) is 0.01 to 10 parts by mass per 100 parts by mass of the total of the resin particles (A-1) and the resin particles (A-2), and the primary particle size is 0.01 to 1.0 μm.

Description

Technology Field

[0001] The present invention relates to an aqueous coating agent for steel, a coating film, a method for coating steel, and steel.

[0002] The present application claims priority based on Japanese Patent Application No. 2020-176150 filed in Japan on October 20, 2020, and incorporates the contents thereof herein by reference. Background Technology

[0003] Conventionally, chromate treatment is known as a treatment to impart corrosion resistance to steel or plated steel. After chromate treatment, the surface of the steel retains its metallic luster while exhibiting a yellowish tint. On the other hand, since the hexavalent chromium used in chromate treatment is toxic, non-chromium treatments that do not contain chromium have also been used in recent years (see, for example, Patent Document 1). Prior art literature

[0004] Japanese Patent Publication No. 2004-190121 The problem to be solved

[0005] Since the surface of steel treated with a non-chrome finish is colorless and transparent, unlike that of chromate treatment, it is difficult to visually determine whether the treatment has been applied. Although methods such as surface analysis or the use of marking devices exist to verify the presence of the treatment, they present the problem of increased costs due to the addition of processes.

[0006] For this reason, coloring the surface of steel that has undergone a non-chrome treatment can be considered. In this case, it is desirable to impart an aesthetically pleasing appearance to the steel surface with vivid color tones while maintaining the steel's characteristic metallic luster. However, when coloring steel in non-chrome treatment, simply adding pigments to the treatment agent resulted in a decrease in the performance of the formed film, such as corrosion resistance and weather resistance. Furthermore, there was a problem where the pigments agglomed within the film, causing the color to be indistinct and resulting in an appearance that lacked metallic luster.

[0007] The present invention is made in consideration of the above and aims to provide a water-based coating agent for steel, a coating, a method for coating steel, and steel that can maintain the corrosion resistance and weather resistance of the formed coating and also impart desirable ornamentation to the metal surface.

[0008] In addition, the present invention aims to provide a coating for steel, a method for coating steel, and steel that can maintain corrosion resistance and weather resistance and also impart desirable ornamentation to the metal surface. means of solving the problem

[0009] (1) The present invention relates to an aqueous coating agent for steel, each comprising: a polyurethane resin particle (A-1) and an ethylene-unsaturated carboxylic acid copolymer resin particle (A-2) having a median diameter of 20 to 100 nm and having at least one of a silanol group and an alkoxysilyl group; a silicon oxide particle (B) having a median diameter of 5 to 20 nm; an organic titanium compound (C); and a phthalocyanine pigment (F) coated with at least one of a resin and a surfactant, wherein the content of the phthalocyanine pigment (F) is 0.01 to 10 parts by mass per 100 parts by mass of the total of the polyurethane resin particle (A-1) and the ethylene-unsaturated carboxylic acid copolymer resin particle (A-2), and the primary particle size is 0.01 to 1.0 μm.

[0010] According to the invention of (1), a water-based coating agent for steel can be provided that maintains the corrosion resistance and weather resistance of the formed coating and also provides a desirable design on the metal surface.

[0011] (2) The phthalocyanine in the above phthalocyanine pigment (F) is at least one of metallic phthalocyanine and non-metallic phthalocyanine, and the metal of the above metallic phthalocyanine is any one of Ca, Ba, Cd, Na, Cu, Ni, Co, Fe, Mg, Zn, Al, Mn, V, Ti and Sn, a water-based coating agent for steel described in (1).

[0012] According to the invention of (2), the effect of maintaining the corrosion resistance and weather resistance of the formed film is more preferably obtained, and the desirable design of the metal surface can be maintained.

[0013] (3) A water-based coating agent for steel described in (1) or (2), having a viscosity of 100 mPa·s or less at 20°C.

[0014] According to the invention of (3), desirable paintability of the water-based coating agent for steel is obtained, paint non-uniformity is eliminated, and desirable design properties can be imparted to the metal surface.

[0015] (4) A water-based coating agent for steel described in any one of claims (1) to (3), wherein the mass ratio of the polyurethane resin particles (A-1) and the ethylene-unsaturated carboxylic acid copolymer resin particles (A-2) is (A-1):(A-2)=20:80 to 90:10.

[0016] According to the invention of (4), a film with excellent solvent resistance and alkali resistance can be formed.

[0017] (5) A water-based coating for steel described in any one of claims (1) to (4), further having silicon oxide particles (E) with a mode diameter of 70 to 200 nm.

[0018] According to the invention of (5), the hardness of the formed film can be improved and the friction coefficient can be adjusted to a suitable range, so the anti-abrasion properties of the film can be improved.

[0019] (6) A coating formed by a water-based coating agent for steel described in any one of (1) to (5), having a chroma C* of 2.0 or more and 50 or less.

[0020] According to the invention of (6), desirable design properties can be imparted to steel by a film formed by a water-based coating agent for steel.

[0021] (7) A method for coating steel by applying a water-based coating agent for steel described in any one of (1) to (5) to the surface of steel to form a coating.

[0022] According to the invention of (7), a coating can be formed that maintains corrosion resistance and weather resistance on the surface of the steel and also provides a desirable design on the surface of the metal.

[0023] (8) Steel having a film formed on its surface by a water-based coating agent for steel described in any one of (1) to (5), and a 60° gloss of 50% or more.

[0024] According to the invention of (8), a steel material with desirable design properties can be provided.

[0025] (9) The steel described in (8) is either hot-dip galvanized steel or aluminum-containing galvanized steel.

[0026] According to the invention of (9), a steel material with desirable design properties can be provided. Specific details for implementing the invention

[0027] Hereinafter, an embodiment of the present invention will be described. The present invention is not limited to the following embodiments.

[0028] Water-based coating for steel

[0029] The water-based coating agent for steel according to the present embodiment comprises polyurethane resin particles (A-1) (hereinafter simply referred to as “resin particles (A-1)”), ethylene-unsaturated carboxylic acid copolymer resin particles (A-2) (hereinafter simply referred to as “resin particles (A-2)”), silicon oxide particles (B), an organic titanium compound (C), and a phthalocyanine pigment (F). Additionally, it may include wax particles (D) and silicon oxide particles (E).

[0030] The polyurethane resin particles (A-1) have a median diameter of 20 to 100 nm and also have at least one of a silanol group and an alkoxysilyl group. As for the resin particles (A-1), they are not particularly limited, but, for example, polycarbonate-based polyurethane is preferred in that it has excellent solvent resistance and alkali resistance. The polycarbonate-based polyurethane resin particles are obtained, for example, by the following method. First, a polyurethane prepolymer is prepared by reacting an isocyanate group-containing compound, a polycarbonate polyol, a low molecular weight polyol, and a compound having an active hydrogen group and a hydrophilic group. Next, the hydrophilic group is neutralized by a neutralizing agent. Next, the neutralized prepolymer is dispersed in water containing an alkoxysilane and an amine containing an active hydrogen group, and by chain extension, polycarbonate-based polyurethane resin particles having at least one of a silanol group and an alkoxysilyl group are obtained.

[0031] Examples of the above isocyanate group-containing compounds include, but are not particularly limited, aliphatic diisocyanates such as hexamethylene diisocyanate, 1,3-cyclohexanediisocyanate, isophorone diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, alicyclic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate, 4,4-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate or mixtures thereof, aromatic diisocyanates such as 4,4-toluidine diisocyanate, etc.

[0032] The above polycarbonate polyol is not particularly limited, but examples include one obtained by reacting one or more glycols selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol-A, and hydrogenated bisphenol-A with dimethyl carbonate, diphenyl carbonate, ethylene carbonate, phosgene, etc.

[0033] The above low molecular weight polyols are not particularly limited, but examples include glycols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol, glycerin, trimethylolpropane, pentaerythritol, etc.

[0034] Compounds having the above active hydrogen group and hydrophilic group are not particularly limited, but examples include compounds containing sulfonic acid groups such as 2-hydroxyethanesulfonic acid, derivatives thereof, or compounds containing carboxyl groups such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, or derivatives thereof. When manufacturing the above polyurethane resin particles, these compounds may be used alone or in combination of two or more types. It is preferable to neutralize the hydrophilic groups, such as the carboxyl group or sulfonic acid group, using a neutralizing agent in order to effectively disperse the polyurethane prepolymer in water.

[0035] The above neutralizing agent is not particularly limited, but examples include tertiary amines such as ammonia, triethylamine, and dimethyl ethanolamine, or alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. These may be used alone or in combination of two or more.

[0036] The alkoxysilanes containing the above active hydrogen group are not particularly limited, but examples include amino group-containing silanes such as γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane, and mercapto group-containing silanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldiethoxysilane.

[0037] The amines used for the above chain extension are not particularly limited, but examples include diamines such as ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, and piperazine; polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine; and hydrazines. These may be used alone or in combination of two or more.

[0038] The reaction to obtain a polyurethane prepolymer from the above isocyanate group-containing compound and an active hydrogen compound such as a polyol is preferably carried out at a reaction temperature of, for example, 30 to 100°C. The above reaction may be carried out in the presence of an organic solvent or without it. As for the organic solvent, an organic solvent with relatively high solubility in water is preferred, and examples include acetone, methyl ethyl ketone, acetonitrile, N-methylpyrrolidone, etc.

[0039] As a method for dispersing the above-mentioned neutralized prepolymer in water, although not particularly limited, methods using a homogenizer, a mixer, etc., may be cited. At this time, the temperature is preferably, for example, above room temperature and below 70°C.

[0040] If an organic solvent is used in the reaction to obtain a polyurethane prepolymer, the organic solvent may be removed by distillation under reduced pressure if necessary.

[0041] The ethylene-unsaturated carboxylic acid copolymer resin particles (A-2) have a median diameter of 20 to 100 nm and also have at least one of a silanol group and an alkoxysilyl group. As for the resin particles (A-2), although not particularly limited, for example, resin particles obtained by reacting an epoxy group-containing alkoxysilane with a resin liquid in which an ethylene-methacrylic acid copolymer resin is neutralized and water-oxidized with at least one of an alkali metal hydroxide, ammonia, and an amine are preferred in that they can form a high-performance film in the form of fine particles.

[0042] The above ethylene-methacrylic acid copolymer resin is not particularly limited, but for example, it is preferable that the ethylene content be 70 to 90 mass% and the methacrylic acid content be 10 to 30 mass%. The above ethylene-methacrylic acid copolymer resin may contain monomers other than ethylene and methacrylic acid, but it is preferable that the content of the above other monomers be 10 mass% or less. The method of manufacturing the above ethylene-methacrylic acid copolymer resin is not particularly limited and can be manufactured by known methods such as polymerization using a high-pressure method low-density polyethylene manufacturing apparatus.

[0043] The above-mentioned epoxy group-containing alkoxysilanes are not particularly limited, but examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. These may be used alone or in combination of two or more types.

[0044] It is preferable to use 0.1 to 20 parts by mass of the above epoxy group-containing alkoxysilanes for every 100 parts by mass of the solid content of the above water-oxidized ethylene-methacrylic acid copolymer resin, and more preferable to use 1 to 10 parts by mass. If less than 0.1 parts by mass of the above epoxy group-containing alkoxysilanes are used, the alkali resistance of the film formed on the surface of the steel or the adhesion to curable resins such as paints is reduced. Similarly, if more than 20 parts by mass are used, the bath stability of the water-based coating agent for steel may be reduced.

[0045] A polyfunctional epoxy compound may be used in combination with the above-mentioned water-oxidized ethylene-methacrylic acid copolymer resin and the above-mentioned epoxy group-containing alkoxysilanes during the reaction. The above-mentioned polyfunctional epoxy compound is not particularly limited, but examples include sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, propylene glycol diglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanurate, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, etc. These may be used alone or in combination of two or more types.

[0046] It is preferable to carry out the reaction between the above-mentioned water-oxidized ethylene-methacrylic acid copolymer resin and the above-mentioned epoxy group-containing alkoxysilanes and polyfunctional epoxy compounds for 0.5 to 12 hours under temperature conditions of 50 to 100°C.

[0047] It is preferable that the mass ratio of the resin particle (A-1) and the resin particle (A-2) be (A-1):(A-2) = 20:80 to 90:10. If the resin particle (A-1) is less than 20 parts by mass for every 100 parts by mass of the total resin particle (A-1) and the resin particle (A-2), the hydrophobicity of the film increases, tape peelability decreases, or solvent resistance against high hydrophilic solvents such as white gasoline decreases. If the resin particle (A-1) exceeds 90 parts by mass, the hydrophilicity of the film increases, alkali resistance decreases, solvent resistance against high hydrophilic solvents such as ethanol decreases, or corrosion resistance of the processed part deteriorates due to the film becoming brittle.

[0048] A composite film is formed by the reaction of silicon oxide particles (B) and an organic titanium compound (C) by the resin particles (A-1) and resin particles (A-2) having at least one of a silanol group and an alkoxysilyl group. By doing so, the solvent resistance and alkali resistance of the film formed by the water-based coating agent for steel can be improved.

[0049] The particle diameters of the resin particles (A-1) and resin particles (A-2) are both 20 to 100 nm. The particle diameter is a median diameter (D50) measured by dynamic light scattering. If the particle diameter is less than 20 nm, the paintability is reduced due to reasons such as the viscosity of the water-based coating agent for steel becoming high or bath stability decreasing. If the particle diameter exceeds 100 nm, the tape peelability or solvent resistance of the film formed by the water-based coating agent for steel is reduced.

[0050] The particle size of the resin particles (A-1) can be adjusted by changing the amount of hydrophilic functional groups introduced to obtain water dispersibility, such as carboxyl groups and sulfonic acid groups, and the type or amount of a neutralizing agent that neutralizes the hydrophilic functional groups. The particle size of the resin particles (A-2) can be adjusted by changing the type of neutralizing agent, the conditions of water dispersibility, the type or amount of epoxy group-containing alkoxysilanes, and the type or amount of a polyfunctional epoxy compound.

[0051] The silicon oxide particles (B) have a particle diameter of 5 to 20 nm. The particle diameter is the mode diameter (most frequent particle diameter) measured by the dynamic light scattering method. Since light is transmitted when the particle diameter is within this range, desirable design properties (gloss and saturation) are obtained. As for the silicon oxide particles (B), colloidal silica, fumed silica, etc., can be used, although they are not particularly limited. Specifically, examples include Snowtex N, Snowtex C (Nissan Kagaku High School), Aderite AT-20N, AT-20A (Asahi Denka High School), Cataloid S-20L, Cataloid SA (Shokubai Kase High School), etc. These may be used individually or in combination of two or more types.

[0052] The content of silicon oxide particles (B) is preferably 5 to 100 parts by mass with respect to a total of 100 parts by mass of resin particles (A-1) and resin particles (A-2), and more preferably 10 to 50 parts by mass. If the content of silicon oxide particles (B) is less than 5 parts by mass, the hardness or corrosion resistance of the film formed by the water-based coating material for steel may decrease. If it exceeds 100 parts by mass, the film-forming ability or water resistance of the film may decrease.

[0053] Organic titanium compounds (C) are not particularly limited, but examples include dipropoxybis(triethanolaminato)titanium, dipropoxybis(diethanolaminato)titanium, dibutoxybis(triethanolaminato)titanium, dibutoxybis(diethanolaminato)titanium, dipropoxybis(acetylacetonato)titanium, dibutoxybis(acetylacetonato)titanium, dihydroxybis(lact)titanium monoammonium salt, dihydroxybis(lact)titanium diammonium salt, propanedioxytitanium bis(ethylacetoacetate), oxotitanium bis(monoammonium oxalate), etc. These may be used alone or in combination of two or more.

[0054] The content of the organic titanium compound (C) is preferably 0.05 to 3 parts by mass in terms of titanium atoms, and more preferably 0.1 to 2 parts by mass, with respect to 100 parts by mass of the total of the resin particles (A-1) and resin particles (A-2). If the content of the organic titanium compound (C) is less than 0.05 parts by mass, the compounding of each component within the film formed by the aqueous coating agent for steel becomes insufficient, and the performance of the film may be reduced. If it exceeds 3 parts by mass, the hydrophilicity of the film becomes too high, and the performance of the film may be reduced, and the bath stability of the aqueous coating agent for steel may be reduced.

[0055] In order to lower the kinetic friction coefficient of the film formed by the water-based coating agent for steel and to improve the lubricity of the film surface, wax particles (D) may be added. In that case, it is preferable that the particle size is 0.5 to 4 μm and the softening point is 100 to 140°C. As for the wax particles (D), they are not particularly limited, but polyolefin wax particles (D) are preferred from the perspective of improving the aesthetic appearance (gloss and saturation). As for the polyolefin wax particles (D), they are not particularly limited, but examples include hydrocarbon-based waxes such as paraffin, microcrystalline, and polyethylene, and derivatives thereof. As for the derivatives, they are not particularly limited, but examples include carboxylated polyolefins and chlorinated polyolefins.

[0056] When the above wax particles (D) are added to an aqueous coating agent for steel, the particle size is not particularly limited, but is preferably 0.5 to 4 μm. The above particle size is a median diameter (D50) measured by dynamic light scattering. If the above particle size is less than 0.5 μm, the lubricity of the formed coating may be insufficient. If the above particle size exceeds 4 μm, there is a possibility that problems such as uneven distribution of the wax particles (D) and detachment from the coating may occur.

[0057] In the aqueous coating agent for steel of the present embodiment, silicon oxide particles (E) with a particle size (mode diameter) of 70 to 200 nm may be included in addition to silicon oxide particles (B) with a particle size (mode diameter) of 5 to 20 nm. The particle size is the mode diameter (mode particle size) measured by dynamic light scattering. By including silicon oxide particles (E) in the aqueous coating agent for steel, the hardness of the coating can be improved, and the coefficient of friction can be adjusted to a suitable range. Accordingly, the anti-abrasion properties of the coating can be improved, thereby preventing coil deformation of the coated steel or load collapse of the cutting plate, and thus improving the handling properties of the coated steel.

[0058] By making the particle size of the silicon oxide particles (E) 70 nm or larger, the hardness and friction coefficient of the coating can be improved. In addition, by making the particle size 200 nm or smaller, the silicon oxide particles (E) are less likely to settle in the water-based coating agent for steel, thereby ensuring dispersibility.

[0059] Silicon oxide particles (E) have a larger particle size (mode diameter) than silicon oxide particles (B). As for the silicon oxide particles (E), they are not particularly limited and known ones may be used. Examples include ST-ZL, MP-1040 (manufactured by Nissan Kagaku High School), PL-7 (manufactured by Fuso Kagaku High School), SI-80P (manufactured by Shokubai Kase High School), etc. These may be used individually or two or more types may be used in combination.

[0060] The content of silicon oxide particles (E) is preferably 1 to 20 parts by mass with respect to a total of 100 parts by mass of resin particles (A-1) and resin particles (A-2), and more preferably 1 to 10 parts by mass. If the content of silicon oxide particles (E) is less than 1 part by mass, it is difficult to obtain the effect of adjusting the friction coefficient, so it is sufficient to include 1 part by mass or more. In addition, if the content of silicon oxide particles (E) exceeds 20 parts by mass, there is a risk that the film-forming properties or water resistance of the coating will decrease.

[0061] The phthalocyanine pigment (F) imparts a desirable chromaticity C* to the formed film while maintaining the glossiness of the coated steel. In the phthalocyanine pigment (F), the phthalocyanine is preferably at least one of metallic phthalocyanine and non-metallic phthalocyanine. As for the metal of the metallic phthalocyanine, it is preferably any one of, for example, Ca, Ba, Cd, Na, Cu, Ni, Co, Fe, Mg, Zn, Al, Mn, V, Ti, and Sn. As for the phthalocyanine, it is more preferable that the metal is metallic phthalocyanine in which the metal is either Cu or Sn. The crystal structure of the phthalocyanine is not particularly limited and may use the generally used α-type or β-type, or may use one having other crystal structures.

[0062] The method for obtaining the above-mentioned phthalocyanine is not particularly limited, but for example, known methods for obtaining copper phthalocyanine include the urea method (Weiler method), in which phthalic acid or its derivative, urea or its derivative is heated and reacted in an organic solvent in the presence of a copper compound and a catalyst, and the phthalodinitrile method, in which phthalodinitrile is heated and reacted in an organic solvent in the presence of a copper compound.

[0063] Since the phthalocyanine obtained by the above method forms aggregates of fine pigments, phthalocyanine particles having a very fine primary particle size, a narrow distribution width, and a sharp particle size distribution can be obtained by using known methods such as acid pasting or solvent salt milling as a micronization method. In addition, to prevent re-aggregation of phthalocyanine particles, a resin and / or a surfactant may be added. By coating, a phthalocyanine dispersion is obtained.

[0064] The method of coating the above-mentioned phthalocyanine with a resin or surfactant is not particularly limited, but for example, in a solvent salt milling method, phthalocyanine, a resin and / or surfactant, a water-soluble inorganic salt, and a water-soluble organic solvent can be mixed using a kneader, an extruder, etc., thereby allowing the phthalocyanine to be micronized and the resin or surfactant to be uniformly coated on the surface of the phthalocyanine. When micronizing the phthalocyanine by a method other than the above, the resin and / or surfactant may be added to coat the surface of the phthalocyanine, or the resin and / or surfactant may be added after micronization to coat the surface of the phthalocyanine. By doing so, desirable dispersibility of the phthalocyanine (F) in the aqueous coating agent for steel is obtained, and as a result, desirable color saturation and gloss of the film formed by the aqueous coating agent for steel and the steel coated with said film are obtained.

[0065] The above resin has a pigment-affinity site having the property of adsorbing to the pigment and a site compatible with the colorant carrier, and functions to stabilize the dispersion of the pigment on the colorant carrier by adsorbing to the pigment. It is not particularly limited and may use natural resins, modified natural resins, synthetic resins such as acrylic resins, or synthetic resins modified by natural resins. Rosin is a representative example of a natural resin, and rosin derivatives, cellulose derivatives, rubber derivatives, protein derivatives, and their oligomers are used as modified natural resins. Examples of synthetic resins include epoxy resin, acrylic resin, maleic acid resin, butyral resin, polyester resin, melamine resin, phenolic resin, polyurethane resin, and polyamide resin. Examples of synthetic resins modified by natural resins include rosin-modified maleic acid resin, rosin-modified fumaric acid resin, and rosin-modified phenolic resin.

[0066] Specifically, an oily dispersant such as a polycarboxylic acid ester including polyurethane or polyacrylate, an unsaturated polyamide, a polycarboxylic acid, a polycarboxylic acid (partial)amine salt, an ammonium polycarboxylic acid salt, an alkylamine polycarboxylic acid salt, a polysiloxane, a long-chain polyaminoamide phosphate, a hydroxyl group-containing polycarboxylic acid ester or a modified product thereof, an amide or a salt thereof formed by the reaction of a poly(lower alkyleneimine) and a polyester having a free carboxyl group; Water-soluble resins or water-soluble polymer compounds such as (meth)acrylic acid-styrene copolymer, (meth)acrylic acid-(meth)acrylic acid ester copolymer, styrene-maleic acid copolymer, polyvinyl alcohol, and polyvinylpyrrolidone, polyester-based, modified polyacrylate-based, ethylene oxide / propylene oxide addition compounds, and phosphate ester-based compounds are used, and these can be used alone or in a mixture of two or more types.

[0067] The above surfactant is not particularly limited and conventionally known anionic surfactants, nonionic surfactants, cationic surfactants, cationic surfactants, etc. may be used.

[0068] Specifically, examples of anionic surfactants include sodium lauryl sulfate, polyoxyethylene alkyl ether sulfate, sodium dodecylbenzene sulfonic acid, alkali salt of styrene-acrylic acid copolymer, sodium stearate, sodium alkylnaphthalene sulfonate, sodium alkyldiphenyl ether disulfonate, monoethanolamine lauryl sulfate, triethanolamine lauryl sulfate, ammonium lauryl sulfate, monoethanolamine stearate, sodium stearate, sodium lauryl sulfate, monoethanolamine of styrene-acrylic acid copolymer, polyoxyethylene alkyl ether phosphate ester, etc. Examples of nonionic surfactants include polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene alkyl ether phosphate ester, polyoxyethylene sorbitan monostearate, polyethylene glycol monolaurate, acetylene glycol, polyoxyethylene acetylene glycol, etc. Examples of cationic surfactants include alkyl quaternary ammonium salts or their ethylene oxide adducts. Examples of cationic surfactants include alkyl betaines such as alkyldimethylaminoacetic acid betaine, alkylimidazoline, etc. These may be used alone or in a mixture of two or more.

[0069] The content of the phthalocyanine pigment (F) is 0.01 to 10 parts by mass per 100 parts by mass of the total of the resin particles (A-1) and the resin particles (A-2). The above content of the phthalocyanine pigment (F) is preferably 0.05 to 5 parts by mass. If the content of the phthalocyanine pigment (F) is less than 0.01 parts by mass, the desired chromaticity of the formed film may not be obtained. If it exceeds 10 parts by mass, the glossiness of the steel material with the formed film may decrease.

[0070] The particle size of the phthalocyanine pigment (F) is 0.01 to 1.0 μm. The above particle size is the primary particle size measured by an electron microscope. The above primary particle size is preferably 0.05 to 1.0 μm. If the primary particle size of the phthalocyanine pigment (F) is less than 0.01 μm, desirable dispersibility in the water-based coating agent for steel is not obtained, and chromaticity and gloss may not be obtained. If the primary particle size exceeds 1.0 μm, diffuse reflection of light occurs in the film, and desirable chromaticity of the film may not be obtained. In addition, desirable gloss of the steel coated with the film may not be obtained.

[0071] In addition, the water-based coating agent for steel according to the present embodiment preferably includes at least one anti-corrosion agent selected from the group consisting of phosphoric acid compounds, thiocarbonyl compounds, niobium oxide, and guanidine compounds. By doing so, excellent corrosion resistance of the steel coated with the film is obtained.

[0072] Examples of the above phosphoric acid compounds include phosphates such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and phosphoric acid, and phosphates such as triammonium phosphate, diammonium hydrogen phosphate, trisodium phosphate, and disodium hydrogen phosphate. These may be used individually or in combination of two or more types. By using the above phosphoric acid compounds, phosphate ions form a phosphate layer on the surface of the steel to passivate it, thereby improving the corrosion resistance of the steel.

[0073] The content of the above phosphoric acid compound is preferably 0.01 to 5 parts by mass in terms of phosphoric acid, and more preferably 0.05 to 3 parts by mass, based on a total of 100 parts by mass of resin particles (A-1) and resin particles (A-2). If it is less than 0.01 parts by mass, the corrosion resistance becomes insufficient, and if it exceeds 5 parts by mass, depending on the aqueous dispersion resin used, it may gel and become impossible to apply.

[0074] The above thiocarbonyl compounds, niobium oxide, and guanidine compounds are effective, in particular, in preventing white rust on zinc steel and similar materials, just like chromium compounds that have been conventionally used to impart corrosion resistance. The above thiocarbonyl compounds are compounds having a thiocarbonyl group and are represented, for example, by the following general formula (1).

[0075]

[0076] In the above formula (1), X and Y represent a hydrocarbon group having 1 to 15 carbon atoms, having H, OH, SH, or NH2 as a substituent, or having -O-, -NH-, -S-, -CO-, or -CS- as a substituent. X and Y may be combined to form a ring. For the thiocarbonyl compound represented by the above formula (1), it is preferable to have a nitrogen atom or an oxygen atom.

[0077] As for the thiocarbonyl compound, in addition to the above, a compound capable of forming a thiocarbonyl group-containing compound in an aqueous solution or in the presence of an acid or alkali may be used. Examples include thiourea and its derivatives, such as methylthiourea, dimethylthiourea, trimethylthiourea, ethylthiourea, diethylthiourea, 1,3-dibutylthiourea, phenylthiourea, diphenylthiourea, 1,3-bis(dimethylaminopropyl)-2-thiourea, ethylenethiourea, propylenethiourea, etc.

[0078] As for the thiocarbonyl compound, in addition to the above, carbothio acids and their salts may be used. Examples include thioacetic acid, thiobenzoic acid, dithioacetic acid, sodium methyl dithiocarbamate, sodium dimethyl dithiocarbamate, triethylamine dimethyl dithiocarbamate, sodium diethyl dithiocarbamate, piperidine pentamethylene dithiocarbamate, pipecholine pipecholyl dithiocarbamate, potassium o-ethylxantogenate, etc.

[0079] These thiocarbonyl compounds may be used alone or in combination of two or more. In addition, among the above thiocarbonyl compounds, those with low solubility in water may be dissolved in a solvent such as an alkaline solution and then incorporated into an aqueous coating agent for steel.

[0080] The content of the above thiocarbonyl compound is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the total of resin particles (A-1) and resin particles (A-2), and more preferably 0.2 to 5 parts by mass. If it is less than 0.1 parts by mass, the corrosion resistance becomes insufficient, and if it exceeds 10 parts by mass, the corrosion resistance becomes saturated and uneconomical, and depending on the aqueous dispersion resin used, it may gel and become impossible to apply.

[0081] The niobium oxide is preferably niobium oxide colloidal particles. This allows for further improvement in the corrosion resistance of the formed film. The niobium oxide colloidal particles preferably have a particle size of 100 nm or less, from the perspective of forming a film containing more stable and dense niobium oxide and providing stable rust prevention to the workpiece. The particle size is the mode diameter (most frequent particle size) measured by dynamic light scattering. The particle size is more preferably 2 to 50 nm, and even more preferably 2 to 20 nm.

[0082] The above niobium oxide colloidal particles represent an oxide of niobium dispersed in water in a fine particulate state. For example, the above includes, for instance, an amorphous state in an intermediate state between niobium hydroxide and niobium oxide, where strictly speaking, niobium oxide is not formed. The above niobium oxide colloidal particles are not particularly limited, and niobium oxide sol prepared by a known method may be used.

[0083] The content of the niobium oxide above is preferably 0.1 to 5 parts by mass in Nb2O5 equivalent with respect to 100 parts by mass of the total of resin particles (A-1) and resin particles (A-2), and more preferably 0.2 to 3 parts by mass. If it is less than 0.1 parts by mass, sufficient corrosion resistance is not obtained and is undesirable. Even if it exceeds 5 parts by mass, no improvement in effect is seen and there is a concern that it may not be economical.

[0084] The above guanidine compounds are not particularly limited, but examples include guanidine, aminoguanidine, guanyltiourea, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, 1,3-diphenylguanidine, etc. The above guanidine compounds may be used alone or in combination of two or more types.

[0085] The content of the above guanidine compound is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the total of resin particles (A-1) and resin particles (A-2), and more preferably 0.2 to 3 parts by mass. If it is less than 0.1 parts by mass, the corrosion resistance becomes insufficient, and if it exceeds 5 parts by mass, the corrosion resistance becomes saturated and uneconomical, and depending on the aqueous dispersion resin used, it may gel and become impossible to apply.

[0086] The water-based coating agent for steel according to the present embodiment may include components other than those mentioned above, provided that such components do not impede the effects of the present invention. For example, it may include defoaming agents, organic solvents, leveling agents, etc. As for organic solvents, they are not particularly limited as long as they are generally used in paints, and examples include hydrophilic solvents such as alcohol-based, ketone-based, ester-based, and ether-based solvents. As for leveling agents, they are not particularly limited, and examples include leveling agents such as silicone-based and fluorine-based agents.

[0087] The solvent for the water-based coating agent for steel according to the present embodiment may be water, a mixture of water and various alcohols, etc.

[0088] The water-based coating agent for steel according to the present embodiment preferably has a viscosity of 100 mPa·s or less at 20°C. If the viscosity at 20°C exceeds 100 mPa·s, for example during painting, the coating agent transferred from the coating roll to the workpiece is prone to becoming a cobweb-shaped droplet, and uneven painting is prone to occur. It is more preferable that the viscosity of the water-based coating agent for steel be 50 mPa·s or less. The lower limit of the viscosity of the water-based coating agent for steel is not particularly limited, but, for example, it may be 3 mPa·s or more, or 5 mPa·s or more.

[0089] <Film formed by water-based coating agent for steel>

[0090] The film formed by the water-based coating agent for steel according to the present embodiment (hereinafter referred to simply as "film") is composed of a composite resin in which each of the above components is composited. That is, the functional groups of each component form bonds and are in a composited state. The above bonds are formed by the reaction of at least one of the Si-OH groups and Si-OR groups of the resin particles (A-1) and (A-2), the silicon oxide particles (B), the Si-OH groups on the surface of (E), and at least one of the Ti-OH and Ti-OR' groups of the organic titanium compound (C). The above bonds are considered to be, for example, Si-O-Si bonds, Si-O-Ti-O-Si bonds, and the organic resin particles and inorganic particles form a chemically strong bond.

[0091] The film of the present embodiment comprises a resin including polyurethane resin particles and ethylene-unsaturated carboxylic acid copolymer resin particles, silicon oxide particles, Ti, and a phthalocyanine pigment, wherein the content of the phthalocyanine pigment is 0.01 to 10 parts by mass per 100 parts by mass of the total of polyurethane resin particles and ethylene-unsaturated carboxylic acid copolymer resin particles, and the particle size (primary particle size) of the phthalocyanine pigment is 0.01 to 1.0 μm. The silicon oxide particles include those with a particle size (mode diameter) of 5 to 20 nm, and may also include silicon oxide particles with a particle size (mode diameter) of 70 to 200 nm. The Ti is derived from the above-mentioned organic titanium compound (C). That is, the film of the present embodiment contains Ti as an element. In addition, the presence of phthalocyanine pigment can be confirmed by verifying that phthalocyanine is contained within the film. Furthermore, the film may contain the aforementioned rust inhibitor or other additive components.

[0092] The above film has a chroma C* of 2.0 or higher and 50 or lower. It is desirable for the film's chroma C* to be 2.0 or higher, as this results in a vivid hue and good color development. It is more preferable for the chroma C* to be 5.0 or higher. Additionally, the chroma C* should be 50 or lower. It is more preferable for the chroma C* to be less than 50. If the chroma C* is less than 2.0, there is a possibility that the color development of the film may decrease. The chroma C* can be measured using a commercially available colorimeter, for example, using the spectrophotometer SE6000 manufactured by Nippon Tenshoku Kogyo Co., Ltd. The chroma C* can be calculated using the following formula. In the following formula, a* and b* represent the colors in the L*a*b* color system, where a* represents the red direction, -a* represents the green direction, b* represents the yellow direction, and -b* represents the blue direction.

[0093]

[0094] The above film preferably has a film content of 0.5 to 3 g / m², and more preferably 0.5 to 2 g / m². If the film content is less than 0.5 g / m², corrosion resistance or alkali resistance may decrease. On the other hand, if the film content is too high, not only is adhesion to the substrate reduced, but it is also uneconomical.

[0095] Steel Coating Method

[0096] A method for coating steel involves applying a water-based coating agent for steel to a metal surface to form a film, and includes a coating process and a heat curing process.

[0097] In the coating process, the above-mentioned aqueous coating agent for steel is uniformly applied to the metal surface. The coating method is not particularly limited, and commonly used methods such as roll coating, air spraying, airless spraying, and immersion may be appropriately employed. To enhance the hardness of the film, the steel to be coated may be heated in advance.

[0098] In the heat curing process, the steel coated with the above-mentioned water-based coating agent for steel is heated to form a film on the surface of the steel. The heating temperature of the steel to be coated is 50 to 250°C, preferably 70 to 220°C. If the heating temperature is below 50°C, the evaporation rate of moisture is slow and sufficient film formation is not obtained, resulting in reduced solvent resistance or alkali resistance. On the other hand, if the temperature exceeds 250°C, thermal decomposition of the resin occurs, the physical properties of the film deteriorate, leading to a decrease in various performance characteristics and also worsening of the appearance, such as yellowing. The heat curing time is preferably 1 second to 5 minutes.

[0099] In addition, the method for coating the steel may include, in addition to the above, a topcoat coating process in which a topcoat paint is applied onto the film. Examples of topcoat paints used in the topcoat coating process include paints composed of acrylic resin, acrylic-modified alkyd resin, epoxy resin, urethane resin, melamine resin, phthalic acid resin, amino resin, polyester resin, vinyl chloride resin, etc. The film thickness of the topcoat paint is appropriately determined by the application of the anti-corrosion metal product and the type of topcoat paint used, and is not particularly limited. Typically, it is about 5 to 300 μm, more preferably about 10 to 200 μm. The formation of the topcoat paint film can be performed by applying the topcoat paint onto the film formed by the above-mentioned water-based coating agent for steel, and then heating to dry and cure it. The heating temperature can be, for example, 50 to 250°C, and the heating time can be 5 minutes to 1 hour.

[0100] Steel coated with a water-based coating for steel

[0101] The steel material according to the present embodiment comprises a steel material (substrate), a plating layer disposed on the steel material (substrate), and a coating disposed on the surface of the plating layer. As described above, the coating comprises a resin comprising polyurethane resin particles and ethylene-unsaturated carboxylic acid copolymer resin particles, silicon oxide particles, Ti, and a phthalocyanine pigment. The content of the phthalocyanine pigment is 0.01 to 10 parts by mass per 100 parts by mass of the total of the polyurethane resin particles and the ethylene-unsaturated carboxylic acid copolymer resin particles. In addition, the primary particle size of the phthalocyanine pigment is 0.01 to 1.0 μm.

[0102] The steel material on which a film is formed on the surface by the aqueous coating agent for steel according to the present embodiment is not particularly limited, but includes, for example, zinc-based plated steel such as aluminum-containing galvanized steel, galvanized steel, zinc-nickel plated steel, zinc-iron plated steel, zinc-chromium plated steel, zinc-titanium plated steel, zinc-magnesium plated steel, zinc-manganese plated steel, zinc-aluminum-magnesium plated steel, and zinc-aluminum-magnesium-silicon plated steel. Furthermore, the plating layer may contain a small amount of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, etc., and may also include inorganic materials such as silica, alumina, and titania dispersed therein. Furthermore, it is applicable to multilayer plating combined with other types of plating such as iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc. Furthermore, it is also applicable to plating with aluminum or aluminum-based alloys. The plating method is not particularly limited and may be any known method, such as electroplating, hot-dip plating, deposition plating, dispersion plating, or vacuum plating. As for the steel material, it is preferable to use aluminum-containing zinc-plated steel.

[0103] The steel material having a coating formed on its surface according to the present embodiment preferably has a 60° glossiness of 50% or more. The 60° glossiness is more preferably 50 to 200%, and even more preferably 60 to 150%. If the 60° glossiness is less than 50%, a desirable appearance of the steel material is not obtained. Furthermore, the 60° glossiness is more preferably set to 200% or less from the upper limit of the 60° glossiness of general plated steel materials. However, it is possible to exceed 200% by applying a special manufacturing method or polishing after manufacturing to the steel material, and it may exceed 200%. The 60° glossiness can be measured based on the method specified in JIS Z 8741, and can be measured using a commercially available gloss meter (e.g., VG2000 manufactured by Nippon Tenshoku Kogyo Co., Ltd.).

[0104] The steel material having a coating formed on its surface according to the present embodiment maintains corrosion resistance and accelerated weathering resistance, while also possessing desirable gloss and saturation, and obtaining an appearance with excellent design qualities.

[0105] Examples

[0106] The contents of the present invention will be explained in more detail below based on examples. The contents of the present invention are not limited to the description of the following examples.

[0107] <Preparation of aqueous dispersion of resin particles (A-1)>

[0108] (Preparation Example 1)

[0109] 4,4-methylenebis(cyclohexyl isocyanate), polycarbonate diol with a molecular weight of 2000, neopentyl glycol, dimethylolpropionic acid, and N-methylpyrrolidone as a solvent were added to a reaction vessel and stirred at 80°C for 6 hours, then neutralized with dimethyl ethanolamine to obtain a polyurethane prepolymer solution. Next, the polyurethane prepolymer solution obtained by the above reaction was dispersed in water containing hydrazine and γ-(2-aminoethyl)aminopropyltriethoxysilane using a homodisperser to obtain an aqueous dispersion of polycarbonate-based polyurethane resin particles containing silanol groups and / or ethoxysilyl groups. The solid content concentration was 30 mass%, and the median diameter measured by dynamic light scattering was 39 nm.

[0110] (Preparation Example 2)

[0111] A polyurethane prepolymer obtained in the same manner as in Preparation Example 1 was dispersed using a homodisperser in water containing hydrazine and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, thereby obtaining an aqueous dispersion of polycarbonate-based polyurethane resin particles containing silanol groups and / or ethoxysilyl groups. The solid content concentration was 30 mass%, and the median diameter measured by dynamic light scattering was 20 nm.

[0112] (Preparation Example 3)

[0113] 4,4-methylenebis(cyclohexyl isocyanate), dimethylolpropionic acid, and acetone were added to a reaction vessel and heated to 50°C under stirring to react; subsequently, a polyester polyol with a molecular weight of 2000, obtained by reacting adipic acid, neopentyl glycol, and ethylene glycol, was added and reacted to obtain a polyurethane prepolymer solution. Next, the polyurethane prepolymer solution obtained by the above reaction was dispersed using a homodisperser in water containing dimethylethanolamine, γ-(2-aminoethyl)aminopropyltriethoxysilane, and 2-(2-aminoethylamino)ethanol, and the acetone was removed by distillation under heating to obtain an aqueous dispersion of polyester-based polyurethane resin particles containing silanol groups and / or ethoxysilyl groups. The solid content concentration was 30 mass%, and the median diameter was 32 nm.

[0114] <Preparation of aqueous dispersion of resin particles (A-2)>

[0115] (Preparation Example 4)

[0116] In a reaction vessel, an ethylene-methacrylic acid copolymer resin (methacrylic acid content of 20 mass%), sodium hydroxide equivalent to 5.6 mass% relative to the resin, and deionized water were added, and by stirring at 95°C for 6 hours, a water-dispersible resin solution with a solid content of 20 mass% was obtained. To this water-dispersible resin solution, 0.8 mass% of γ-glycidoxypropyltrimethoxysilane and 0.8 mass% of glycerol polyglycidyl ether were also added, and by reacting at 85°C for 2 hours, a water-dispersible solution of ethylene-methacrylic acid copolymer resin particles having silanol groups and / or methoxysilyl groups was obtained. The solid content concentration was 21 mass%, and the median diameter was 50 nm.

[0117] (Preparation Example 5)

[0118] In a reaction vessel, ethylene-methacrylic acid copolymer resin (methacrylic acid content of 20 mass%), 3.7 mass% sodium hydroxide, 6.3 mass% ammonia water, and deionized water were added relative to the resin, and stirred at 95°C for 6 hours to obtain a water-dispersible resin solution with a solid content of 20 mass%. To this water-dispersible resin solution, 1.2 mass% of γ-glycidoxypropyltriethoxysilane and 0.6 mass% of pentaerythritol polyglycidyl ether were also added, and reacted at 85°C for 2 hours to obtain a water-dispersible resin solution of ethylene-methacrylic acid copolymer resin particles having silanol groups and / or methoxysilyl groups. The solid content concentration was 21 mass%, and the median diameter was 100 nm.

[0119] (Preparation Example 6)

[0120] In a reaction vessel, an ethylene-methacrylic acid copolymer resin (methacrylic acid content of 20 mass%), sodium hydroxide equivalent to 4.7 mass% relative to the resin, and deionized water were added, and by stirring at 95°C for 2 hours, a water-dispersible resin solution with a solid content of 20 mass% was obtained. To this water-dispersible resin solution, 1.2 mass% of γ-glycidoxypropyltrimethoxysilane and 1.2 mass% of hydrogenated bisphenol A diglycidyl ether were also added, and by reacting at 85°C for 2 hours, a water-dispersible solution of ethylene-methacrylic acid copolymer resin particles having silanol groups and / or methoxysilyl groups was obtained. The solid content concentration was 21 mass%, and the median diameter was 70 nm.

[0121] (Preparation Example 7)

[0122] In a reaction vessel, an ethylene-methacrylic acid copolymer resin (methacrylic acid content of 20 mass%), 21.0 mass% of ammonia water and deionized water relative to the resin were added, and by stirring at 95°C for 2 hours, a water-dispersible resin solution with a solid content of 20 mass% was obtained. To this water-dispersible resin solution, 1.2 mass% of γ-glycidoxypropyltrimethoxysilane and 1.2 mass% of hydrogenated bisphenol A diglycidyl ether were also added, and by reacting at 85°C for 2 hours, a water-dispersible solution of ethylene-methacrylic acid copolymer resin particles having silanol groups and / or methoxysilyl groups was obtained. The solid content concentration was 21 mass%, and the median diameter was 150 nm.

[0123] (Preparation Example 8)

[0124] In a reaction vessel, an ethylene-methacrylic acid copolymer resin (methacrylic acid content of 27 mass%), 28.0 mass% of ammonia water and deionized water relative to the resin were added, and by stirring at 95°C for 2 hours, a water-dispersible resin solution with a solid content of 20 mass% was obtained. To this water-dispersible resin solution, 1.6 mass% of γ-glycidoxypropyltrimethoxysilane and 1.6 mass% of hydrogenated bisphenol A diglycidyl ether were also added, and by reacting at 85°C for 2 hours, a water-dispersible solution of ethylene-methacrylic acid copolymer resin particles having silanol groups and / or methoxysilyl groups was obtained. The solid content concentration was 21 mass%, and the median diameter was 14 nm.

[0125] (Preparation Example 9)

[0126] 190 parts by mass of a bisphenol F epichlorohydrin-type epoxy resin with an epoxy equivalent of 190, 30 parts by mass of diethanolamine, and 110 parts by mass of propylene glycol monomethyl ether acetate were added to a reaction vessel and reacted at 100°C for 2 hours to obtain a modified epoxy resin with a solid content concentration of 70%. 100 parts by mass of a trimethylolpropane 2,4-toluene diisocyanate prepolymer with an NCO of 13.3% and a non-volatile content of 75%, 44 parts by mass of nonylphenol, 5 parts by mass of dimethylbenzylamine, and 65 parts by mass of propylene glycol monomethyl ether acetate were mixed in a reaction vessel and reacted at 80°C for 3 hours under a nitrogen atmosphere to obtain a half-blocked polyisocyanate with a solid content concentration of 70% and an NCO of 20%. 70 parts by mass of the above modified epoxy resin and 30 parts by mass of the above half-blocked polyisocyanate were mixed and reacted by stirring at 80°C for 4 hours, after which it was confirmed by infrared spectroscopic analysis that the absorption of NCO groups was completely eliminated. Subsequently, an aqueous epoxy resin was obtained by diluting with ion-exchanged water. The solid content concentration was 25 mass%, and the median diameter was 600 nm.

[0127] <Preparation of Water-based Coating Agents for Steel Materials According to Examples and Comparative Examples>

[0128] (Example 1)

[0129] 80 parts by mass of the aqueous dispersion of the resin particles (A-1) of Preparation Example 1 and 20 parts by mass of the aqueous dispersion of the resin particles (A-2) of Preparation Example 4 were used in terms of solid content. As silicon oxide particles (B), particles with a particle size (mode diameter) of 15 nm were used. As the organic titanium compound (C), dipropoxybis(triethanolaminato)titanium was used. As the wax particles (D), polyethylene particles with a particle size (median diameter) of 1.0 μm and a softening point of 115°C were used. As the silicon oxide particles (E), particles with a particle size (mode diameter) of 100 nm were used. As the phthalocyanine pigment (F), Cu phthalocyanine (primary particle size 0.26 μm) using a surfactant as a coating agent was used. As the rust inhibitor (G), phosphate and thiourea were used. The content of each component is in parts by mass relative to 100 parts by mass of the total of resin particles (A-1) and resin particles (A-2), and the amount shown in Table 6 was used to prepare the steel coating adjuster according to Example 1. In addition, the content of the organic titanium compound (C) shown in Table 6 is in parts by mass equivalent to titanium atoms.

[0130] (Examples 2 to 18 and Comparative Examples 1 to 21)

[0131] Coating adjusters for steel materials according to Examples 2 to 18 and Comparative Examples 1 to 20 were prepared in the same manner as Example 1, except that the raw materials shown in Table 6 were used. In addition, Comparative Example 12 was adjusted to a high viscosity by aging it at 60°C and designated as Comparative Example 21. Furthermore, the types of silicon oxide particles (B), organic titanium compound (C), silicon oxide particles (E), phthalocyanine pigment (F), and rust inhibitor (G) shown in Table 6, and the corresponding symbols shown in Table 6, are shown in Tables 1 to 5 below.

[0132] In addition, the details of the phthalocyanine pigment (F) shown in Table 4 are as follows.

[0133] Type k: Made by Mikuni Shikiso Kabushiki Kaisha "SA Blue 5204"

[0134] Type l: Toyo Color Co., Ltd. "LIOFAST SF670 Blue"

[0135] Type m: Mikuni Shikiso Kabushiki Kaisha "SA Blue 5205"

[0136] Type n: Dainichi Sekka High School Kabushiki Kaisha "DP Color 1737 Blue"

[0137] Type o: Dainichi Sekka High School Kabushiki Kaisha "DP Color 1534 Blue"

[0138] Type p: Dainichi Sekka High School Kabushiki Kaisha Production "DP-1957 Yellow"

[0139] Type q: Dainichi Sekka High School Kabushiki Kaisha "NAF Color NAF1032 Red"

[0140] Type r: Toyo Color Co., Ltd. "LIOFAST BLUE G227"

[0141] Type s: Toyo Color Co., Ltd. "EMF BLUE HG"

[0142] Type t: Mikuni Shikiso Kabushiki Kaisha "PSM Sky Blue FG"

[0143] Type u: Dainichi Sekka High School Kabushiki Kaisha "TB Color TB-700 Blue GA"

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150] <Production of Coated Steel Sheets for Evaluation>

[0151] Using the water-based coating agents for steel of Examples 1 to 18 and Comparative Examples 1 to 21 above, a coating was formed on the surface of hot-dip galvanized steel sheets and aluminum-containing galvanized steel, and evaluation samples were prepared. The water-based coating agent for steel was applied using a bar coater to achieve a dry film weight of 1 g / m², and a test plate was prepared by baking it to a target plate temperature of 150°C using a hot air drying oven with an atmosphere temperature of 500°C.

[0152] <Evaluation>

[0153] Using test plates of the above-prepared examples and comparative examples, alkali resistance, solvent resistance, ablation resistance, planar corrosion resistance, weather resistance (change in saturation), gloss, saturation, and paintability were evaluated under the following conditions. The results are shown in Table 7.

[0154] (Alkali resistant)

[0155] The test plate was immersed for 2 minutes while stirring in a 2 mass% aqueous solution (pH 12.5) of an alkaline degreasing agent (Surf Cleaner 53, manufactured by Nippon Paint Co., Ltd.) at 55°C. After tape sealing the edges and back of the test plate, a salt spray test (JIS-Z-2371) was performed. The occurrence of white rust after 72 hours was observed and evaluated according to the following criteria, with 3 being deemed a pass. The results are shown in Table 7.

[0156] 3: Almost no white or blue

[0157] 2: White blue area less than 30%

[0158] 1: White blue area 30% or more

[0159] (Content)

[0160] After placing the test plate in a rubbing tester, the plate was rubbed 5 times (reciprocating) with a load of 0.5 kgf / ㎠ using cotton swabs impregnated with ethanol, methyl ethyl ketone (MEK), or white gasoline. Subsequently, the edges and back of the test plate were sealed with tape, and a salt spray test (JIS-Z-2371) was performed. The occurrence of white rust after 72 hours was observed and evaluated according to the following criteria, with 3 being deemed a pass. The results are shown in Table 7.

[0161] 3: Almost no white or blue

[0162] 2: White blue area less than 30%

[0163] 1: White blue area 30% or more

[0164] (Abduction [sliding movement])

[0165] A load of 10 g / cm² was applied to the test plate through corrugated cardboard, and an elliptical motion of 360 times / min was applied to induce abrasion (wear scratches) on the sliding part. After conducting the test for 10 minutes, the condition of the test plate surface was observed and evaluated according to the following criteria, with 3 being considered a pass. The results are shown in Table 7.

[0166] 3: Almost no darkening

[0167] 2: Less than 50% of the sliding surface area is blackened

[0168] 1: More than 50% of the surface area of ​​the sliding part is blackened

[0169] (Corrosion resistance of flat surfaces)

[0170] The test plates were tape-sealed on their edges and back sides, and a salt spray test (SST, JIS-Z-2371) was performed. The occurrence of white rust was observed after 72 hours for the hot-dip galvanized specimens and after 120 hours for the aluminum-containing galvanized specimens, and evaluated according to the following criteria, with 3 being deemed acceptable. The results are shown in Table 7.

[0171] 3: Almost no white or blue

[0172] 2: White blue area less than 30%

[0173] 1: White blue area 30% or more

[0174] (Weather resistance [change in saturation])

[0175] The test plate was placed in a Sunshine Weather Meter tester, and an accelerated weathering test was conducted for 500 hours. The initial value and the change in chroma after the test were measured. Chromata was calculated as Chromata C* using the same method as the chroma measurement shown below. The change in Chromata C* was calculated using the following Equation (2), and evaluated according to the following criteria, with 3 being deemed acceptable. A Sunshine Weather Meter manufactured by Suga Shikenki Co., Ltd. was used as the tester. The results are shown in Table 7.

[0176] Change (%) = Saturation C* after test / Initial saturation C* × 100 … (2)

[0177] 3: Change (%) = 95% to 100%

[0178] 2: Change (%) = 90% to less than 95%

[0179] 1: Change (%) = 80% to less than 90%

[0180] (Gloss [design])

[0181] Using a gloss meter (VG2000 manufactured by Nippon Tenshoku Kogyo Co., Ltd.), the 60° glossiness (%) of the test plate surface was measured based on the method specified in JIS Z 8741. Evaluation was performed according to the following criteria, and 2 was deemed acceptable. The results are shown in Table 7.

[0182] 2: 50 to 200%

[0183] 1: Less than 50%

[0184] (Saturation [Design])

[0185] Using a spectrophotometer (SE6000 manufactured by Nippon Tenshoku Kogyo Co., Ltd.), the L*a*b* values ​​of the test plate surface were measured, and the chroma C* was calculated using the following formula. Evaluation was performed based on the following criteria, and 3 was deemed passing. The results are shown in Table 7.

[0186] 3: C*=2.0 to 50

[0187] 2: C*=greater than 50, less than 100

[0188] 1: C*=less than 2.0

[0189]

[0190] (Dojangseong)

[0191] Water-based coating agent for steel was applied using an automatic bar coater (Yasuda Seki Seisakusho No. 542-AB), and the non-uniformity of the coating appearance was evaluated according to the following criteria, with 2 being accepted. The results are shown in Table 7.

[0192] 2: No non-uniformity

[0193] 1: Non-uniformity exists

[0194]

[0195] From the results of Table 7 above, it was confirmed that the steel plates coated with the water-based coating agents for steel of Examples 1 to 18 had excellent gloss and color saturation compared to the steel plates coated with the water-based coating agents for steel of Comparative Examples 1 to 21, and exhibited excellent design properties. In addition, the steel plates coated with the water-based coating agents for steel of Examples 1 to 18 showed excellent results in alkali resistance, solvent resistance, sliding mobility, corrosion resistance of flat surfaces, weather resistance, and paintability.

Claims

Claim 1 Each comprises polyurethane resin particles (A-1) and ethylene-unsaturated carboxylic acid copolymer resin particles (A-2), each having a median diameter of 20 to 100 nm and also having at least one of a silanol group and an alkoxysilyl group; silicon oxide particles (B) having a median diameter of 5 to 20 nm; an organic titanium compound (C); a phthalocyanine pigment (F) coated with at least one of a resin and a surfactant; and at least one anti-corrosion agent (G) selected from the group consisting of a phosphate compound, a thiocarbonyl compound, niobium oxide, and a guanidine compound, wherein the content of the phthalocyanine pigment (F) is 0.01 to 10 parts by mass per 100 parts by mass of the total of the polyurethane resin particles (A-1) and the ethylene-unsaturated carboxylic acid copolymer resin particles (A-2), and the primary particle diameter is A water-based coating agent for steel having a thickness of 0.01 to 1.0 μm. Claim 2 A water-based coating agent for steel according to claim 1, wherein the phthalocyanine in the phthalocyanine pigment (F) is at least one of metallic phthalocyanine and non-metallic phthalocyanine, and the metal of the metallic phthalocyanine is any one of Ca, Ba, Cd, Na, Cu, Ni, Co, Fe, Mg, Zn, Al, Mn, V, Ti, and Sn. Claim 3 A water-based coating agent for steel according to claim 1, having a viscosity of 100 mPa·s or less at 20°C. Claim 4 A water-based coating agent for steel according to claim 1, wherein the mass ratio of the polyurethane resin particles (A-1) and the ethylene-unsaturated carboxylic acid copolymer resin particles (A-2) is (A-1):(A-2)=20:80 to 90:

10. Claim 5 A water-based coating for steel according to claim 1, further comprising silicon oxide particles (E) having a mode diameter of 70 to 200 nm. Claim 6 A water-based coating agent for steel according to claim 1, wherein, for every 100 parts by mass of the total of the polyurethane resin particles (A-1) and the ethylene-unsaturated carboxylic acid copolymer resin particles (A-2), the phosphoric acid compound is 0.01 to 5 parts by mass in terms of phosphoric acid equivalent, the thiocarbonyl compound is 0.1 to 10 parts by mass, the niobium oxide is 0.1 to 5 parts by mass in terms of Nb2O5 equivalent, and the guanidine compound is 0.1 to 5 parts by mass. Claim 7 A coating formed by a water-based coating agent for steel described in any one of claims 1 to 6, having a chroma C* of 2.0 or more and 50 or less. Claim 8 A method for coating steel by applying a water-based coating agent for steel described in any one of claims 1 to 6 to the surface of steel to form a coating. Claim 9 A steel material having a film formed on its surface by a water-based coating agent for steel material described in any one of claims 1 to 6, and having a 60° gloss of 50% or more. Claim 10 In paragraph 9, the steel is a steel that is either hot-dip galvanized steel or aluminum-containing galvanized steel.

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