Aqueous one-coat coating compositions, one-coat coating films, and processes for forming coating films

Abstract

To provide aqueous one-coat coating compositions which form coating films with outstanding adhesion after a water-resistance test, and high lightness value, and cured one-coat coating films obtained from such aqueous one-coat coating compositions.SOLUTION: There is provided aqueous one-coat coating compositions containing a hydroxy group-containing acrylic resin (A), a curing agent (B), a colored pigment (C), wherein the hydroxy group-containing acrylic resin (A) is an acrylic resin with a hydroxyl value of 60 to 100 mgKOH / g, an acid value of 10 to 30 mgKOH / g, a Hansen solubility parameter (HSP) of 9.8 to 10.8, a mass-average molecular weight of 10,000 to 100,000, and a glass transition temperature of 0 to 40°C, and wherein a cured one-coat coating film formed from the aqueous one-coat coating composition to achieve a dry film thickness of 30 μm on an undercoat film with a lightness value L*45 of 40 has a 60° gloss value of 85 or more, a lightness value L*45 of 60 to 95, and an infrared reflectance (IRSR) of 60% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based one-coat paint composition, a one-coat coating film, and a method for forming a coating film. [Background technology]

[0002] There are already known coating methods in which an undercoat paint and an intermediate coat paint such as a cationic electrodeposition coating composition are applied to the outer panel of an automobile, and then a topcoat paint such as a solid type is applied on the coating film to finish the coating, and a topcoat paint is applied directly on the coating film of an undercoat paint such as a cationic electrodeposition coating composition to finish the coating. These methods have the advantages of fewer steps, high productivity, and energy savings because the topcoat coating film is formed in one coat.

[0003] For example, Patent Document 1 discloses that a coating film with excellent recoat adhesion can be formed by a water-based one-coat white paint for topcoat, which is characterized by containing (A) a polyester resin having a specific hydroxyl value and acid value, (B) an aqueous melamine resin, and (C) a white coloring pigment.

[0004] Furthermore, for example, Patent Document 2 discloses that a coating film having excellent recoat adhesion, water resistance, weather resistance, and chipping resistance can be formed by using a water-based one-coat topcoat paint composition that is characterized by containing (A) a polyester resin having a specific acid value, hydroxyl value, and benzene ring concentration, (B) a curing agent, (C) a coloring pigment, and (D) an acrylic resin for pigment dispersion obtained by copolymerizing a specific polymerizable unsaturated monomer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-206439 A [Patent Document 2] JP 2003-292884 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a coating film with high brightness is required, the topcoat coating film must have the property of concealing the color tone of the base coating film. In particular, when using a topcoat one-coat paint composition as described in Patent Documents 1 and 2, it is necessary to increase the content of pigments, particularly white pigments, in the paint composition in order to conceal the color tone of the base coating film while increasing the brightness of the coating film. However, in both of the coating compositions described in Patent Documents 1 and 2, as the pigment content increases, the adhesion of the resulting coating film after a water resistance test may decrease.

[0007] Therefore, the present invention has an object to provide an aqueous one-coat paint composition capable of forming a coating film having excellent adhesion after a water resistance test and high brightness, and a one-coat coating film obtained from the aqueous one-coat paint composition. Another object of the present invention is to provide a method for forming a coating film using the aqueous one-coat paint composition. [Means for solving the problem]

[0008] As a result of intensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by an aqueous one-coat paint composition containing a hydroxyl-containing acrylic resin (A) having a specific hydroxyl value, acid value, Hansen space solubility parameter (HSP), mass average molecular weight and glass transition temperature, a curing agent (B) and a coloring pigment (C), wherein the one-coat paint film formed to a specific dry film thickness on a base coating film having a specific lightness L*45 value exhibits a specific 60° gloss value, lightness L*45 value and infrared reflectance (IRSR), and have thus completed the present invention.

[0009] That is, the above-mentioned object of the present invention is achieved by an aqueous one-coat paint composition containing a hydroxyl-containing acrylic resin (A), a curing agent (B), and a color pigment (C), in which the hydroxyl-containing acrylic resin (A) is an acrylic resin having a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen space solubility parameter (HSP) of 9.8-10.8, a mass average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40°C, and the cured one-coat paint film formed on a base coat having a lightness L*45 value of 40 and a dry film thickness of 30 μm has a 60° gloss value of 85 or more, a lightness L*45 value of 60-95, and an infrared reflectance (IRSR) of 60% or more.

[0010] Furthermore, the water-based one-coat paint composition of the present invention is preferably one in which the content of the hydroxyl-containing acrylic resin (A) is 50 to 90 parts by mass based on 100 parts by mass of the total resin solids.

[0011] Furthermore, the aqueous one-coat paint composition of the present invention is preferably an aqueous one-coat paint composition in which the curing agent (B) is a melamine resin.

[0012] Furthermore, the water-based one-coat paint composition of the present invention is preferably a water-based one-coat paint composition in which the color pigment (C) is a white pigment and can be further combined with a color pigment selected from the group consisting of a red pigment, an orange pigment, a yellow pigment, a green pigment, a blue pigment, a purple pigment, and a black pigment.

[0013] The problems of the present invention are also solved by a cured one-coat coating film obtained from an aqueous one-coat paint composition containing a hydroxyl-containing acrylic resin (A) having a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen space solubility parameter (HSP) of 9.8-10.8, a mass average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40°C, a curing agent (B), and a coloring pigment (C), the cured one-coat coating film having a 60° gloss value of 85 or more, a lightness L*45 value of 60-95, and an infrared reflectance (IRSR) of 60% or more.

[0014] Furthermore, the object of the present invention can also be achieved by a coating film forming method in which a cationic electrodeposition coating composition is applied to a metal substrate, the coating film is baked to form a cured cationic electrodeposition coating film, and then the above-mentioned water-based one-coat coating composition is applied directly thereon, and the coating film is baked to form a cured one-coat coating film. Effect of the Invention

[0015] The aqueous one-coat paint composition of the present invention can form a coating film with high brightness and excellent adhesion after a water resistance test. Furthermore, the coating film obtained by using the aqueous one-coat paint composition of the present invention also has excellent heat-shielding properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The water-based one-coat paint composition of the present invention contains a hydroxyl-containing acrylic resin (A), a curing agent (B), and a color pigment (C). In the present invention, the term "water-based" means that the resin, curing agent, etc. contained therein are in a state in which they can be stably dissolved or dispersed in water or a mixture of water and an organic solvent.

[0017] The hydroxyl-containing acrylic resin (A) used in the present invention is a water-soluble or water-dispersible acrylic resin, and can be obtained by a known method utilizing a radical polymerization reaction using radically polymerizable monomers as raw material components.

[0018] Examples of radical polymerizable monomers include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, allyl alcohol, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, styrene, cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, and (meth)acrylonitrile. These radical polymerizable monomers may be used alone or in combination of two or more.

[0019] The hydroxyl value of the hydroxyl-containing acrylic resin (A) used in the present invention is preferably 60 to 100 mgKOH / g, more preferably 65 to 95 mgKOH / g, and particularly preferably 70 to 90 mgKOH / g. By making the hydroxyl value of the hydroxyl-containing acrylic resin (A) 60 to 100 mgKOH / g, a coating film having a sufficient crosslink density can be obtained, and the coating film shows excellent adhesion even after a water resistance test.

[0020] In the present invention, the hydroxyl value, which is the number of milligrams of potassium hydroxide equivalent to the hydroxyl groups in 1 g of a sample of the hydroxyl-containing acrylic resin (A), was calculated from the monomer composition of the acrylic resin.

[0021] The acid value of the hydroxyl-containing acrylic resin (A) used in the present invention is preferably 10 to 30 mgKOH / g, more preferably 13 to 27 mgKOH / g, and particularly preferably 15 to 25 mgKOH / g. By making the acid value of the hydroxyl-containing acrylic resin (A) 10 to 30 mgKOH / g, the hydroxyl-containing acrylic resin (A) exhibits satisfactory stability in water. Furthermore, the resulting coating film exhibits excellent adhesion even after a water resistance test.

[0022] In the present invention, the acid value, which is the number of milligrams of potassium hydroxide required to neutralize the free acid in 1 g of a sample of the hydroxyl-containing acrylic resin (A), was calculated from the monomer composition of the acrylic resin.

[0023] The hydroxyl-containing acrylic resin (A) used in the present invention preferably has a Hansen space solubility parameter (HSP) of 9.8 to 10.8, more preferably 9.9 to 10.7 mgKOH / g, and particularly preferably 10.0 to 10.6 mgKOH / g. By making the Hansen space solubility parameter (HSP) of the hydroxyl-containing acrylic resin (A) 9.8 to 10.8, excellent pigment dispersibility can be obtained, and a coating film having a high gloss value can be obtained.

[0024] The Hansen space solubility parameter (HSP) is a parameter developed by C. M. Hansen to indicate the solubility of a substance (C. M. Hansen, Hansen Solubility Parameters: A User's Handbook, 1999). In the present invention, the Hansen space solubility parameter (HSP) was determined using the group contribution method proposed by D. W. van Krevelen and P. J. Hoftyzer (D. W. van Krevelen and P. J. Hoftyzer, Properties of Polymers, 2nd Edition, 1976).

[0025] The mass average molecular weight of the hydroxyl-containing acrylic resin (A) used in the present invention is preferably 10,000 to 100,000, more preferably 15,000 to 80,000, and particularly preferably 20,000 to 60,000. By making the mass average molecular weight of the hydroxyl-containing acrylic resin (A) 10,000 to 100,000, the coating composition exhibits problem-free coating workability. In addition, the obtained coating film exhibits excellent adhesion even after a water resistance test.

[0026] In the present invention, the mass average molecular weight was determined by converting data measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as an eluent at a temperature of 40° C. and a flow rate of 1 m / min into the mass average molecular weight of polystyrene. Here, a combination of TSKgel G2000HXL, G3000HXL, G4000HXL, and G5000HXL (product names, manufactured by Tosoh Corporation) was used as the gel permeation chromatography (GPC) column.

[0027] The glass transition temperature of the hydroxyl-containing acrylic resin (A) used in the present invention is preferably 0 to 40° C., more preferably 5 to 35° C., and particularly preferably 10 to 30° C. By making the glass transition temperature of the hydroxyl-containing acrylic resin (A) 0 to 40° C., the coating composition exhibits problem-free coating workability. Furthermore, the resulting coating film exhibits excellent adhesion even after a water resistance test.

[0028] In the present invention, the glass transition temperature was calculated from the monomer composition of the acrylic resin using the formula shown below. 1 / Tg = Σ (Wi / Tg i ) Tg: Glass transition temperature of the copolymer (absolute temperature) W i : Mass fraction of monomer i Tg i : Glass transition temperature of homopolymer of monomer i (absolute temperature)

[0029] In the water-based one-coat paint composition of the present invention, the content of the hydroxyl-containing acrylic resin (A) is preferably 50 to 90 parts by mass, more preferably 55 to 85 parts by mass, and particularly preferably 60 to 80 parts by mass, based on 100 parts by mass of the total resin solids content of the composition. By making the content of the hydroxyl-containing acrylic resin (A) 50 to 90 parts by mass, a coating film having sufficient crosslink density can be obtained, and excellent adhesion is exhibited even after a water resistance test.

[0030] The hydroxyl-containing acrylic resin (A) used in the present invention may be one type alone or two or more types may be used in combination.

[0031] In addition, the curing agent (B) used in the present invention may be, for example, an amino resin, a polyisocyanate compound, a blocked polyisocyanate compound, a polycarbodiimide compound, etc. Among these, an amino resin is particularly preferred. These curing agents (B) may be used alone or in combination of two or more.

[0032] The amino resin is a general term for resins obtained by condensing a compound containing an amino group with formaldehyde. Examples of the amino resin include melamine resin, urea resin, and guanamine resin, and among these, melamine resin is particularly preferred.

[0033] Examples of the melamine resin include partially or completely methylolated melamine resins obtained by reacting melamine with formaldehyde, partially or completely alkyl ether type melamine resins obtained by partially or completely etherifying the methylol groups of methylolated melamine resins with an alcohol component, imino group-containing melamine resins, and mixed melamine resins obtained by mixing two or more of these melamine resins, etc. Furthermore, examples of the alkyl ether type melamine resin include methylated melamine resins, butylated melamine resins, and methyl / butyl mixed alkyl ether type melamine resins, etc.

[0034] Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate, aromatic diisocyanates such as xylylene diisocyanate (XDI), tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI), alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI, and compounds consisting of diisocyanate dimers, trimers, or higher diisocyanates such as uretdione bodies, allophanate bodies, adduct bodies, biuret bodies, isocyanurates, and iminooxadiazinedione bodies. Furthermore, some of these isocyanate groups may be modified with an amino group-containing silane coupling agent or the like.

[0035] Examples of the blocked polyisocyanate compound include those in which the isocyanate group of the above-mentioned polyisocyanate compound is blocked with, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ε-caprolactams, active methylenes such as malonic acid diesters and acetoacetate esters, pyrazoles such as 3,5-dimethylpyrazole, imidazoles such as imidazole and 2-ethylimidazole, phenols such as m-cresol, and the like.

[0036] The polycarbodiimide compound is preferably a hydrophilic carbodiimide compound. For example, the hydrophilic carbodiimide compound may be a compound obtained by reacting a polycarbodiimide compound containing at least two isocyanate groups in one molecule with a polyol having a hydroxyl group at the molecular end in a ratio such that the molar ratio of NCO / OH exceeds 1, and reacting the resulting reaction product with a hydrophilizing agent having active hydrogen and a hydrophilic portion. In the water-based one-coat paint composition of the present invention, the content of the curing agent (B) is preferably 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, and particularly preferably 20 to 40 parts by mass, based on 100 parts by mass of the total resin solid content of the composition. By making the content of the curing agent (B) 10 to 50 parts by mass, a coating film having sufficient crosslink density can be obtained, and excellent adhesion is exhibited even after a water resistance test.

[0037] The color pigment (C) used in the present invention is preferably at least one color pigment selected from the group consisting of white pigments, red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments, and black pigments.

[0038] These color pigments (C) are particularly preferably white pigments. The white pigments may be used alone, or the white pigment may be used in combination with a color pigment selected from the group consisting of red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments, and black pigments.

[0039] Examples of the white pigment that is the color pigment (C) used in the present invention include titanium oxide.

[0040] Examples of the red pigment of the color pigment (C) used in the present invention include azo pigments, anthanthrone pigments, anthraquinone pigments, perylene pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and iron oxide pigments.

[0041] Examples of the orange pigment that is the color pigment (C) used in the present invention include azo pigments, anthraquinone pigments, perinone pigments, quinacridone pigments, and composite oxide pigments.

[0042] Examples of the yellow pigment of the color pigment (C) used in the present invention include isoindoline pigments, azomethine pigments, anthrone pigments, benzimidazolone pigments, quinoxalinedione pigments, isoindolinone pigments, iron oxide pigments, and composite oxide pigments.

[0043] Examples of the green pigment that is the color pigment (C) used in the present invention include phthalocyanine pigments, azomethine pigments, and composite oxide pigments.

[0044] Examples of the blue pigments that are the color pigments (C) used in the present invention include phthalocyanine pigments, threne pigments, indigo pigments, and composite oxide pigments.

[0045] Examples of the purple pigment that is the color pigment (C) used in the present invention include dioxazine-based pigments, perylene-based pigments, quinacridone-based pigments, and composite oxide-based pigments.

[0046] Examples of the black pigment of the color pigment (C) used in the present invention include carbon black, azo pigments, perylene pigments, composite oxide pigments, etc. It is more preferable to refrain from using carbon black and use azo, perylene, composite oxide, or other black pigments, since the resulting multilayer coating film will exhibit an excellent heat-shielding effect.

[0047] The total content of the color pigment (C) contained in the aqueous one-coat paint composition of the present invention is not particularly limited, but is preferably 10 to 200 parts by mass, more preferably 35 to 160 parts by mass, and particularly preferably 60 to 120 parts by mass, based on 100 parts by mass of the total resin solids.

[0048] The water-based one-coat paint composition of the present invention may further contain a glittering pigment. Examples of the glittering pigment include uncolored or colored aluminum pigments, vapor-deposited metal flake pigments, and light interference pigments in which a transparent or translucent substrate is coated with a metal oxide. These glittering pigments may be used alone or in combination of two or more.

[0049] The total content of the luster pigment contained in the aqueous one-coat paint composition of the present invention is not particularly limited, but is preferably 0 to 2.0 parts by mass, more preferably 0 to 1.0 parts by mass, and particularly preferably 0 to 0.5 parts by mass, based on 100 parts by mass of the total resin solids.

[0050] The water-based one-coat paint composition of the present invention may be added with other resins as necessary to adjust the coating film performance. Examples of the other resins include polyester resins, polyurethane resins, polyurea resins, acrylic urethane resins, polyurethane polyurea resins, polyolefin resins (including those that have been chlorinated and / or modified), and epoxy resins. Furthermore, the other resins may be partially crosslinked particles, or may be core / shell type particles consisting of an inner (core) and an outer (shell) part. Examples of particulate base resins include polyurethane-polyurea particles, urethane core / acrylic shell type particles, and acrylic core / urethane shell type particles. In addition, when a part of the resin particles is crosslinked, the part becomes a part (gel part) that is insoluble in an organic solvent, so that the gel fraction, which is a value indicating the proportion of the gel part in the solid content of the resin particles, can be measured. In addition, it is preferable that the other resins have a hydroxyl group and / or a carboxyl group as a functional group. The other resins may be used alone or in combination of two or more types.

[0051] The aqueous one-coat paint composition of the present invention may further contain, as necessary, solvents such as water and / or organic solvents, various paint additives such as rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoamers, antioxidants, and ultraviolet absorbers, and extender pigments. Examples of organic solvents include aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone, esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate, alcohols such as isopropanol, butanol, 2-butoxyethanol, and 2-ethylhexanol, ethers, and aliphatic hydrocarbons including chlorinated hydrocarbons, or mixtures thereof. The organic solvents may be used alone or in combination of two or more.

[0052] The non-volatile content of the water-based one-coat paint composition of the present invention at the time of application is not particularly limited, but is preferably 30 to 70 mass%, more preferably 40 to 60 mass%, and particularly preferably 45 to 55 mass%. By making the non-volatile content at the time of application 30 to 70 mass%, the paint composition shows satisfactory coating workability.

[0053] The aqueous one-coat paint composition of the present invention can be applied to an object to be coated, and then baked (heated) to obtain a cured one-coat paint film.

[0054] There are no particular limitations on the substrate to which the aqueous one-coat paint composition of the present invention can be applied, and examples thereof include members made of metals such as iron, zinc, aluminum, magnesium, etc., members made of alloys of these metals, members plated or vapor-deposited with these metals, members made of glass, plastics, foams of various materials, etc., and among these, metal and plastic substrates that constitute automobile bodies are preferred. These members can be appropriately subjected to treatments such as degreasing and surface treatments as necessary.

[0055] Further, the substrate to which the aqueous one-coat paint composition of the present invention can be applied also includes the above-mentioned substrate on which an undercoat paint film is formed. The undercoat paint film is applied to the surface of the substrate to conceal the surface of the substrate or to impart anticorrosive properties, antirust properties, adhesion, etc. to the substrate, and can be formed by applying an undercoat paint and curing or drying it. The undercoat paint is not particularly limited, and a known undercoat paint, such as an electrodeposition paint, a solvent-based primer, or a water-based primer, can be used. Among them, a metal substrate is preferably coated with a cationic electrodeposition paint composition and baked to form a cured cationic electrodeposition paint film, and it is particularly preferable that the lightness L*45 value of the cured cationic electrodeposition paint film is 40 or more.

[0056] The water-based one-coat paint composition of the present invention can be applied by electrostatic coating, air spray, airless spray or the like.

[0057] The dry film thickness of the cured one-coat coating film is not particularly limited, but is preferably from 10 to 50 μm, more preferably from 20 to 40 μm, and particularly preferably from 25 to 35 μm.

[0058] In the present invention, baking (heating) can be performed by a known means, and for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven can be used. The baking temperature is not particularly limited, but is preferably 100 to 160°C, more preferably 120 to 155°C, and particularly preferably 130 to 150°C. By setting the baking temperature to 100 to 160°C, the curing reaction can be sufficiently promoted. In addition, the heating time is not particularly limited, but is preferably 10 to 50 minutes, more preferably 15 to 45 minutes, and particularly preferably 20 to 40 minutes.

[0059] The 60° gloss value of the cured one-coat coating film obtained from the aqueous one-coat paint composition of the present invention is preferably at least 85, more preferably at least 87, and particularly preferably at least 90. The 60° gloss value in the present invention is a value measured using a Micro Trigloss gloss meter (product name, manufactured by BYK-Gardner).

[0060] The aqueous one-coat paint composition of the present invention is preferably a cured one-coat coating film formed on a base coating film having a lightness L*45 value of 40 so as to have a dry film thickness of 30 μm, and has a lightness L*45 value of 60 to 95, more preferably 65 to 92, and particularly preferably 70 to 90. By making the lightness L*45 value of the cured one-coat coating film 60 to 95, the cured one-coat coating film exhibits an excellent heat-shielding effect. Here, the lightness L*45 value is a lightness in the CIE LAB color system based on the spectral reflectance of reflected light received at an angle of 45 degrees to the incident light direction with respect to the specular reflection angle, after incident light is irradiated at an angle of 45 degrees to the normal line of the coating film layer surface. The CIE LAB color system is a color system defined by the International Commission on Illumination (CIE) in 1976 and adopted in JIS Z 8781-4:2013. The lightness L*45 value in the present invention is a value measured using a multi-angle colorimeter BYKmac i (product name, manufactured by BYK-Gardner).

[0061] The infrared reflectance (IRSR) of the cured one-coat coating film obtained from the above water-based one-coat paint composition is preferably 60% or more, more preferably 63% or more, and particularly preferably 65% ​​or more. By making the infrared reflectance (IRSR) of the cured one-coat coating film 60% or more, the cured one-coat coating film exhibits an excellent heat-shielding effect. The infrared reflectance (IRSR) in the present invention is a value measured using an ultraviolet-visible-near infrared spectrophotometer UV-3600 (product name, manufactured by Shimadzu Corporation).

[0062] The aqueous one-coat paint composition of the present invention and the coating film forming method using the same are applicable to automobile bodies, members and parts of passenger cars, trucks, motorcycles, buses and the like, and are particularly effective for use on metal automobile bodies. EXAMPLES

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" unless otherwise specified, and "%" regarding blend amounts and contents means "% by mass".

[0064] <Production Example 1-1: Production of acrylic resin aqueous dispersion AC-1> A flask equipped with two dropping devices, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas inlet tube was charged with 94 parts of deionized water and heated to 80° C. under a nitrogen atmosphere. Next, a mixture of radical polymerizable monomers consisting of 13.68 parts of styrene, 18.52 parts of 2-hydroxyethyl methacrylate, 16.03 parts of n-butyl acrylate, 49.21 parts of n-butyl methacrylate, and 2.56 parts of acrylic acid, and an emulsifier solution consisting of 4.0 parts of n-dodecyl mercaptan as an emulsion polymerization regulator, 2.0 parts of reactive anionic emulsifier Eleminol RS-3000 (trade name, manufactured by Sanyo Chemical Industries, Ltd., sodium methacryloyloxy polyoxypropylene sulfate ester), 1.0 part of reactive nonionic emulsifier Adeka Reasoap NE20 (trade name, manufactured by ADEKA Corporation), and 15 parts of deionized water was added dropwise at a constant speed over 3 hours using one of the dropping devices. Simultaneously with the dropping by the dropping device, a polymerization initiator solution consisting of 0.30 parts of ammonium persulfate and 15 parts of deionized water was dropped at a constant rate over 3 hours using the other dropping device. After the dropping was completed, the mixture was stirred for 1 hour and then cooled to 40°C to obtain an acrylic resin aqueous dispersion AC-1 having the properties shown in Table 1.

[0065] <Production Examples 1-2 to 1-19: Production of acrylic resin aqueous dispersions AC-2 to AC-19> According to the blending compositions shown in Table 1, and in the same manner as in Production Example 1-1, aqueous acrylic resin dispersions AC-2 to AC-19 having the property values ​​shown in Tables 1 and 2 were obtained.

[0066] [Table 1]

[0067] [Table 2]

[0068] (Note 1) Emulsion polymerization regulator: n-dodecyl mercaptan (Note 2) Reactive anionic emulsifier: Eleminol RS-3000 (product name, manufactured by Sanyo Chemical Industries, Ltd., sodium methacryloyloxypolyoxypropylene sulfate) (Note 3) Reactive nonionic emulsifier: Adeka Reasoap NE20 (product name, manufactured by ADEKA Corporation)

[0069] <Production Example 2: Production of acrylic urethane resin aqueous dispersion AU-1> 2-1 Preparation of polyester polyol solution PE-1 In a flask equipped with a reflux condenser with a reaction water separation tube, a thermometer, a stirrer and a nitrogen gas inlet tube, 49.9 parts of adipic acid, 18.5 parts of 1,6-hexanediol and 31.6 parts of neopentyl glycol were charged and heated to 160°C while stirring under a nitrogen stream. After holding at 160°C for 1 hour, the temperature was raised to 230°C over 5 hours. While holding at 230°C, the acid value was measured periodically, and when the acid value became 3.5mgKOH / g, it was cooled to 80°C or less. Finally, 21.9 parts of methyl ethyl ketone was added to obtain a polyester polyol solution PE-1. The characteristic values ​​of the polyester polyol solution PE-1 were an acid value of 3.5mgKOH / g, a hydroxyl value of 155mgKOH / g and a resin solid content of 80% by mass.

[0070] 2-2 Production of acrylic urethane resin aqueous dispersion AU-1 A flask equipped with two dropping apparatuses, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas inlet tube was charged with 420.0 parts of the polyester polyol solution PE-1 obtained in Production Example 2-1, 31.0 parts of neopentyl glycol, 27.8 parts of trimethylolpropane monoallyl ether, 0.5 parts of dibutyltin dilaurate, and 195.7 parts of methyl ethyl ketone, and the mixture was stirred under a nitrogen stream to make it uniform.

[0071] Next, 259.9 parts of isophorone diisocyanate were added to the resulting solution. After the exothermic reaction had subsided, the reaction mixture was gradually heated to 80° C. with stirring, and stirring was continued at this temperature until the isocyanate content of the solution was 2.2% by weight. Then, 66.7 parts of trimethylolpropane were added and stirred at 80° C. until free isocyanate groups in the solution were no longer detectable. Then, 248.9 parts of methyl ethyl ketone were added to the resulting polyurethane solution.

[0072] Then, the temperature was adjusted to 82°C, and a radical polymerizable monomer mixture consisting of 312.5 parts of n-butyl acrylate, 312.5 parts of methyl methacrylate, 74.7 parts of 2-hydroxypropyl methacrylate, and 58.4 parts of acrylic acid was added dropwise at a constant rate over 3 hours using one of the dropping devices. Simultaneously with the dropping using the dropping device, a polymerization initiator solution consisting of 22.8 parts of 2,2'-azobis(methylbutyronitrile) and 152.3 parts of methyl ethyl ketone was added dropwise at a constant rate over 3.5 hours using the other dropping device.

[0073] After the monomer mixture and the polymerization initiator solution were dropped, the resulting reaction mixture was stirred at 82°C for another 2.5 hours, and 56.9 parts of dimethylethanolamine and 2242 parts of deionized water were added. Then, a separation tube was attached to the reflux condenser, and the solvent was removed under reduced pressure at 45°C until the resin solid content of the dispersion reached 40% by mass, to obtain an acrylic urethane resin aqueous dispersion AU-1. The obtained acrylic urethane resin aqueous dispersion AU-1 had an acid value of 32 mgKOH / g, a hydroxyl value of 57 mgKOH / g, and a pH of 8.1.

[0074] <Production Example 3: Production of black pigment paste P-1> 100.0 parts of acrylic urethane resin aqueous dispersion AU-1 as a dispersing resin, 40.0 parts of perylene-based black pigment Spectrasense Black L 0086 (trade name, manufactured by Sun Chemical Colors & Effects), and 60.0 parts of deionized water were mixed and dispersed in a motor mill to obtain black pigment paste P-1.

[0075] <Production Example 4: Production of blue pigment paste P-2> 100.0 parts of acrylic urethane resin aqueous dispersion AU-1 as a dispersing resin, 40.0 parts of cobalt blue pigment HEUCODUR Blue 2R (trade name, manufactured by HEUBACH) and 60.0 parts of deionized water were mixed and dispersed in a motor mill to obtain blue pigment paste P-2.

[0076] <Production Example 5: Production of Red Pigment Paste P-3> 100.0 parts of acrylic urethane resin aqueous dispersion AU-1 as a dispersing resin, 40.0 parts of red iron oxide pigment 100ED (product name, manufactured by Toda Kogyo Co., Ltd.) and 60.0 parts of deionized water were mixed and dispersed in a motor mill to obtain red pigment paste P-3.

[0077] <Production Example 6-1: Production of Water-Based One-Coat Paint Composition WB-1> 55.30 parts of acrylic resin aqueous dispersion AC-1 was used as the dispersing resin, and 84.92 parts of titanium oxide pigment TI-PURE R-706 (product name, manufactured by CHEMOURS Corporation) was added thereto. Furthermore, 8.50 parts of 2-butoxyethanol and 21.20 parts of deionized water were added to adjust the viscosity, and the mixture was dispersed in a motor mill to obtain a pigment paste. Next, 169.92 parts of the above pigment paste was stirred with a dissolver, and 113.30 parts of acrylic resin aqueous dispersion AC-1, 12.50 parts of melamine resin solution CYMEL 325 (trade name, manufactured by ALLNEX, non-volatile content 80% by mass), 20.80 parts of melamine resin solution CYMEL 203 (trade name, manufactured by ALLNEX, non-volatile content 72% by mass), 1.26 parts of black pigment paste P-1, 6.30 parts of blue pigment paste P-2, 3.15 parts of red pigment paste P-3, 2.00 parts of ultraviolet absorber TINUVIN 384-2 (trade name, manufactured by BASF Japan Ltd.), 2.00 parts of light stabilizer absorber TINUVIN 292 (trade name, manufactured by BASF Japan Ltd.), thickener RHEOVIS HS 2.00 parts of BASF 1152 (trade name, manufactured by BASF Japan Co., Ltd.), 1.00 parts of surface conditioner BYK-346 (trade name, manufactured by BYK-Chemie Co., Ltd.), and 10.00 parts of deionized water were added in sequence and mixed. Finally, the mixture was measured using a portable rotational viscometer REOMAT R180 (trade name, manufactured by proRheo Co., Ltd.) at 20 °C and a shear rate of 1000 s -1 The viscosity was adjusted to 120 mPa·s by dilution with deionized water to obtain water-based one-coat paint composition WB-1 having the formulation shown in Table 3.

[0078] <Production Examples 6-2 to 6-22: Production of Water-Based One-Coat Paint Compositions WB-2 to WB-22> According to the blending compositions shown in Tables 3 to 5, water-based one-coat paint compositions WB-2 to WB-22 were obtained in the same manner as in Production Example 6-1.

[0079] [Table 3]

[0080] [Table 4] [Table 5]

[0081] (Note 4) Titanium oxide pigment: TI-PURE R-706 (product name, manufactured by CHEMOURS) (Note 5) Melamine resin solution: CYMEL 325 (product name, manufactured by ALLNEX, non-volatile content 80% by mass) (Note 6) Melamine resin solution: CYMEL 203 (product name, manufactured by ALLNEX, non-volatile content 72% by mass) (Note 7) UV absorber: TINUVIN 384-2 (product name, manufactured by BASF Japan Ltd.) (Note 8) Light stabilizer absorber: TINUVIN 292 (product name, manufactured by BASF Japan Ltd.) (Note 9) Thickener: RHEOVIS HS 1152 (product name, manufactured by BASF Japan Ltd.) (Note 10) Surface conditioner: BYK-346 (product name, manufactured by BYK-Chemie)

[0082] <Examples 1 to 14 and Comparative Examples 1 to 8> (1) Preparation of test panels and visual evaluation of appearance A zinc phosphate-treated mild steel plate was electrocoated using cationic electrocoating paint Cathoguard No. 500 (product name, manufactured by BASF Japan Ltd.) so that the cured film thickness was 20 μm, and the plate was baked at 175° C. for 25 minutes to obtain an electrocoated plate. The lightness L*45 value of the electrocoating layer obtained was 40, as measured using a multi-angle colorimeter BYKmac i (product name, manufactured by BYK-Gardner).

[0083] Next, the aqueous one-coat paint compositions WB-1 to WB-22 were spray-painted onto the above-mentioned electrodeposition-coated plate so that the dry film thickness was 30 μm, and after leaving it at room temperature for 3 minutes, it was heated at 140 ° C for 30 minutes to prepare a cured one-coat coating film test plate. The appearance of the obtained coating film was visually evaluated according to the following criteria, and the results are shown in Tables 6 and 7. 〇: No abnormalities in the coating ×: The coating has small bubbles or holes (also called "pull marks").

[0084] (2) Evaluation of cured one-coat coating The cured single-coat coating test panels (Examples 1 to 14, Comparative Examples 1, 3, and 5 to 8) that were judged to be ◯ in the above visual appearance evaluation were subjected to the measurements and evaluations (2)-1 to (2)-4 below. The results are shown in Tables 6 and 7.

[0085] (2)-1 60° gloss value The 60° gloss value was measured using a Micro Trigloss glossmeter (trade name, manufactured by BYK-Gardner).

[0086] (2)-2 Measurement of lightness L*45 value The lightness L*45 value was measured using a multi-angle colorimeter BYKmac i (trade name, manufactured by BYK-Gardner).

[0087] (2)-3 Infrared reflectance (IRSR) measurement The infrared reflectance (IRSR) was measured using a UV-3600 ultraviolet-visible-near infrared spectrophotometer (trade name, manufactured by Shimadzu Corporation).

[0088] (2)-4 Evaluation of adhesion after water resistance test The test plate was immersed in 40°C warm water for 10 days, pulled out and dried. Thereafter, the adhesion was evaluated according to JIS K5400-8.5 (cross-cut test). That is, a cut line was made in the coating surface of the test plate with a cutter so as to reach the substrate, 100 squares of 2mm x 2mm were made, and cellophane tape (registered trademark) was applied to the entire surface, which was then rapidly peeled off at 45° at 20°C. The evaluation was performed according to the following criteria based on the number of squares in the remaining coating film. ○: 100 squares of remaining coating (no peeling) ×: The number of remaining coating squares is 99 or less

[0089] [Table 6] [Table 7]

[0090] The invention made by the present inventors has been specifically described above based on an embodiment, but it goes without saying that the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention.

Claims

1. A water-based one-coat paint composition comprising a hydroxyl-containing acrylic resin (A), a curing agent (B), and a color pigment (C), the hydroxyl-containing acrylic resin (A) is an acrylic resin having a hydroxyl value of 60 to 100 mgKOH / g, an acid value of 10 to 30 mgKOH / g, a Hansen space solubility parameter (HSP) of 9.8 to 10.8, a mass average molecular weight of 10,000 to 100,000, and a glass transition temperature of 0 to 40° C.; A cured one-coat coating film formed from the aqueous one-coat paint composition on a base coating film having a lightness L*45 value of 40 and a dry film thickness of 30 μm has a 60° gloss value of 85 or more, a lightness L*45 value of 60 to 95, and an infrared reflectance (IRSR) of 60% or more. A water-based one-coat paint composition.

2. 2. The aqueous one-coat paint composition according to claim 1, wherein the content of said hydroxyl-containing acrylic resin (A) is 50 to 90 parts by mass based on 100 parts by mass of the total resin solids.

3. 3. The water-based one-coat paint composition according to claim 1, wherein the curing agent (B) is a melamine resin.

4. The water-based one-coat paint composition according to claim 1 or claim 2, wherein the color pigment (C) is a white pigment and can be further combined with a color pigment selected from the group consisting of a red pigment, an orange pigment, a yellow pigment, a green pigment, a blue pigment, a purple pigment, and a black pigment.

5. A cured one-coat paint film obtained from the aqueous one-coat paint composition according to claim 1 or 2.

6. A method for forming a coating film, comprising the steps of: applying a cationic electrodeposition coating composition to a metal substrate; baking the composition to form a cured cationic electrodeposition coating film; and then directly applying the aqueous one-coat coating composition according to claim 1 or 2 thereon; and baking the composition to form a cured one-coat coating film.