Aqueous single coating composition, single coating film, and method for forming coating film

Abstract

Problem: To provide an aqueous single-coat coating composition that forms a coating film having excellent adhesion after a water resistance test and a high brightness value, and a cured single-coat coating film obtained from such an aqueous single-coat coating composition. Solution: An aqueous single coat coating composition containing an acrylic resin (A) having a hydroxyl group, a hardener (B), and a coloring pigment (C), in which the acrylic resin (A) having a hydroxyl group is an acrylic resin having a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen 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 DEG C to 40 DEG C, and when formed on an undercoat film having a lightness value L45 of 40 to obtain a dry film thickness of 30 m, a cured single coat coating film formed from the aforementioned aqueous single coat coating composition has a 60 DEG glossiness value > = 85, a lightness value 20 value L45 of 60-95, and an infrared solar reflectance (IRSR) > = 60%.

Description

Technical Field

[0001] This invention relates to water-based single-coat coating compositions, single-coat coating films, and methods for forming coating films. Background Technology

[0002] For automotive exterior panel components, coating processes are known, including those involving applying a base coat (such as a cationic electrodeposited coating composition) and an intermediate coat, followed by applying a top coat (such as a solid type) on top of the coating film, and those involving applying the top coat directly on top of the base coat (such as a cationic electrodeposited coating composition). These processes form a top coat coating film as a single layer; therefore, they offer advantages such as fewer steps, higher productivity, and energy savings.

[0003] For example, Patent Document 1 discloses that a coating film with excellent recoating adhesion can be formed by means of a white coating material for a water-based single-coat topcoat, characterized in that the white coating material contains (A) a polyester having a specified hydroxyl value and acid value, (B) a water-based melamine resin, and (C) a white coloring pigment.

[0004] Furthermore, for example, Patent Document 2 discloses that a coating film with excellent recoating adhesion, water resistance, weather resistance and crack resistance can be formed from an aqueous single-coat topcoat coating composition, characterized in that the aqueous single-coat topcoat coating composition contains (A) a polyester resin having a specified acid value, hydroxyl value and benzene ring concentration; (B) a hardener; (C) a coloring pigment; and (D) an acrylic resin for pigment dispersion obtained by copolymerizing a specified polymerizable unsaturated monomer. Existing technical documents

[0005] [Patent Literature]

[0006] [Patent Document 1] JP 2003-206439 A

[0007] [Patent Document 2] JP 2003-292884 A Summary of the Invention

[0008] The problem that this invention aims to solve

[0009] However, when a coating film with a high brightness value is required, a topcoat coating film with the characteristic of being able to cover the color of the underlying coating film is needed. In particular, when using a single-coat topcoat coating (such as those described in Patent Documents 1 and 2 above), in order to cover the color of the underlying coating film, it is necessary to increase the amount of pigment (especially white pigment) in the coating composition.

[0010] However, when the pigment content in the coating composition of either Patent Document 1 or Patent Document 2 is increased, the adhesion of the resulting coating film after the water resistance test may decrease.

[0011] Therefore, an object of the present invention is to provide waterborne single-coat coating compositions that can form coating films with excellent adhesion and high brightness values ​​after water resistance testing, and single-coat coating films obtained from such waterborne single-coat coating compositions. Another object of the present invention is to provide a method for forming coating films using such waterborne single-coat coating compositions. Problem-solving methods

[0012] As a result of in-depth research into solving the aforementioned problems, the inventors of this invention have improved the invention with the following findings: the above problems can be solved by waterborne single-coat coating compositions comprising: an acrylic resin (A) containing hydroxyl groups, having specified hydroxyl value, acid value, Hansen solubility parameter (HSP), mass average molecular weight, and glass transition temperature; a hardener (B); and a coloring pigment (C), wherein the waterborne single-coat coating composition is used when a specified lightness value L is present. When a 45-layer coating is formed on a lower coating film to achieve a specified dry film thickness, a gloss value of 60° and a lightness value of L are obtained. A waterborne single-coat coating composition with a single-coat coating film of 45 and infrared solar reflectance (IRSR).

[0013] Therefore, the above-mentioned problems solved by the present invention are solved by waterborne single-coat coating compositions containing the following: an acrylic resin (A) having hydroxyl groups, a hardener (B), and a coloring pigment (C), wherein the acrylic resin (A) having hydroxyl groups is an acrylic resin having a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen 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°C-40°C; and when the lightness value L is 40, the acrylic resin is also a waterborne single-coat coating composition containing the following: an acrylic resin (A) ... When a dry film thickness of 30 µm is obtained by forming a lower coating film on a 45-degree base coat, the cured single-coat coating film has a 60° gloss value ≥85 and a lightness value L. 45 is 60-95, and the infrared solar reflectance (IRSR) is ≥ 60%.

[0014] Furthermore, the waterborne single-coat coating composition of the present invention is preferably a waterborne single-coat coating composition in which the content of hydroxyl-containing acrylic resin (A) in 100 parts by weight of total resin solids is 50-90 parts by weight.

[0015] Furthermore, the waterborne single-coat coating composition of the present invention is preferably a waterborne single-coat coating composition in which the hardener (B) is melamine resin.

[0016] Furthermore, the waterborne single-coat coating composition of the present invention is preferably a waterborne single-coat coating composition in which the coloring pigment (C) is a white pigment, which may be further combined with coloring pigments selected from the group consisting of: red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments and black pigments.

[0017] Furthermore, the problem solved by this invention is also addressed by a cured single-coat coating film obtained from an aqueous single-coat coating 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 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°C-40°C; a curing agent (B); and a coloring pigment (C). The cured single-coat coating film has a 60° gloss value ≥ 85 and a lightness value L of 60-95. 45. And ≥ 60% infrared solar reflectance (IRSR).

[0018] Furthermore, the problem solved by the present invention is also solved by a method for forming a cured single-coat coating film, wherein a cured electrodeposited coating film is formed by coating an electrodeposited coating composition onto a metal substrate to coat and cure it, and then the above-mentioned water-based single-coat coating composition is directly coated onto it and cured. Invention Effects

[0019] The waterborne single-coat coating composition of the present invention can form a coating film with excellent adhesion and high brightness value after water resistance testing. Furthermore, the coating film obtained using the waterborne single-coat coating composition of the present invention also exhibits excellent heat-shielding properties. Detailed Implementation

[0020] The water-based single-coat coating composition of the present invention contains an acrylic resin (A) having hydroxyl groups, a hardener (B), and a coloring pigment (C). In the present invention, "water-based" means that the resin, hardener, etc. contained herein are in a stable soluble or dispersible state in water or in a mixture of water and an organic solvent.

[0021] The hydroxyl-containing acrylic resin (A) used in this invention is a water-soluble or water-dispersible acrylic resin, which can be obtained from a free radical polymerizable monomer as a starting component by using known methods of free radical polymerization.

[0022] Monomers capable of free radical polymerization include, for example, (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 free radical polymerizable monomers can be used alone or in combination of two or more.

[0023] The hydroxyl value of the hydroxyl-containing acrylic resin (A) used in this invention is preferably 60-100 mgKOH / g; 65-95 mgKOH / g is more preferred, and 70-90 mgKOH / g is particularly preferred. By making the hydroxyl value of the hydroxyl-containing acrylic resin (A) 60-100 mgKOH / g, a coating film with sufficient crosslinking density can be obtained, which also exhibits excellent adhesion after water resistance testing.

[0024] In this invention, the hydroxyl value of the acrylic resin (A) having hydroxyl groups (which is the number of milligrams of potassium hydroxide equivalent to the number of hydroxyl groups in 1 g of sample) is calculated from the monomer formulation of the acrylic resin.

[0025] Furthermore, the acid value of the hydroxyl-containing acrylic resin (A) used in this invention is preferably 10-30 mgKOH / g; 13-27 mgKOH / g is more preferred, and 15-25 mgKOH / g is particularly preferred. By setting the acid value of the hydroxyl-containing acrylic resin (A) to 10-30 mgKOH / g, the hydroxyl-containing acrylic resin (A) exhibits stability in water without any problem. Moreover, the resulting coating film exhibits excellent adhesion after water resistance testing.

[0026] In this invention, the acid value of the acrylic resin (A) having hydroxyl groups (which is the number of milligrams of potassium hydroxide required to neutralize the free acid in 1 g of sample) is calculated from the monomer formulation of the acrylic resin.

[0027] The Hansen solubility parameter (HSP) of the hydroxyl-containing acrylic resin (A) used in this invention is preferably 9.8-10.8; 9.9-10.7 is more preferred, and 10.0-10.6 is particularly preferred. By setting the Hansen solubility parameter (HSP) of the hydroxyl-containing acrylic resin (A) to 9.8-10.8, excellent pigment dispersibility and a coating film with excellent gloss value can be obtained.

[0028] The Hansen solubility parameter (HSP) was developed by CM Hansen and is a parameter used to indicate the solubility of a substance (CM Hansen, Hansen Solubility Parameters: A User's Handbook, 1999). In this invention, the Hansen solubility parameter (HSP) is estimated using the group contribution method proposed by DW van Krevelen and PJ Hoftyzer (DW van Krevelen, PJ Hoftyzer, Properties of Polymers 2nd Edition, 1976).

[0029] The hydroxyl-containing acrylic resin (A) used in this invention preferably has a mass-average molecular weight of 10,000-100,000; 15,000-80,000 is more preferred, and 20,000-60,000 is particularly preferred. Having a mass-average molecular weight of 10,000-100,000 for the hydroxyl-containing acrylic resin (A) means that it can be coated with the coating composition without causing any problems. The resulting coating film also exhibits excellent adhesion after water resistance testing.

[0030] In this invention, the mass-average molecular weight was found to be a value calculated from data measured by gel permeation chromatography (GPC) using the mass-average molecular weight of polystyrene as a standard, at a temperature of 40°C and a flow rate of 1 mL / min, with tetrahydrofuran (THF) as the eluent. In this GPC, a combination of TSK gels G2000HXL, G3000HXL, G4000HXL, and G5000HXL (proprietary name, Tosoh Corp.) was used as the chromatographic column.

[0031] Furthermore, the glass transition temperature of the hydroxyl-containing acrylic resin (A) used in this invention is preferably 0°C-40°C; 5°C-35°C is more preferred, and 10°C-30°C is particularly preferred. Setting the glass transition temperature of the hydroxyl-containing acrylic resin (A) to 0°C-40°C means that the coating composition can be applied without causing any problems. The resulting coating film exhibits excellent adhesion after water resistance testing.

[0032] In this invention, the glass transition temperature is derived from the monomer formulation of the acrylic resin by the following equation.

[0033] 1 / Tg = ∑(Wi / Tgi)

[0034] Tg: Glass transition temperature (absolute temperature) of the copolymer.

[0035] Wi: Mass percentage of monomer component i

[0036] Tgi: Glass transition temperature (absolute temperature) of the homopolymer of monomer component i.

[0037] In the waterborne single-coat coating composition of the present invention, the content of hydroxyl-containing acrylic resin (A) in 100 parts by weight of total resin solids in the composition is preferably 50-90 parts by weight; 55-85 parts by weight is more preferred, and 60-80 parts by weight is particularly preferred. By setting the content of hydroxyl-containing acrylic resin (A) to 50-90 parts by weight, coating films with sufficient crosslinking density can be obtained, and these coating films also exhibit excellent adhesion after water resistance testing.

[0038] As the hydroxyl-containing acrylic resin (A) used in this invention, a single resin can be used, or a combination of two or more can be used.

[0039] Furthermore, the curing agents (B) that can be used in this invention include, for example, amino resins, polyisocyanate compounds, terminally capped polyisocyanate compounds, polycarbodiimide compounds, etc. Among these curing agents, amino resins are particularly preferred. These curing agents (B) can be used alone, or a combination of two or more can be used.

[0040] Amino resins are a general term for resins formed by the condensation of formaldehyde with amino-containing compounds. Amino resins include, for example, melamine resins, urea resins, and guanidine resins. Among these amino resins, melamine resin is particularly preferred.

[0041] Melamine resins include, for example, partially or fully hydroxymethylated melamine resins obtained by reacting melamine with formaldehyde; partially or fully alkylated melamine resins obtained by partially or fully etherifying the alcohol component and hydroxymethyl group of the hydroxymethylated melamine resin; melamine resins containing imino groups; and mixed melamine resins as mixtures of two or more of these melamine resins. Alkylated melamine resins include, for example, methylated melamine resins, butylated melamine resins, and alkylated melamine resins with a methyl / butyl mixture.

[0042] Polyisocyanate compounds include, for example, aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer diisocyanate; aromatic diisocyanates such as xylene diisocyanate (XDI), trilene diisocyanate (TDI), and 4,4'-diphenylmethane diisocyanate (MDI); alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI; and diisocyanate dimers, trimers, or compounds containing more diisocyanates, such as urethdione structures, urethane structures, adduct structures, biuret structures, isocyanurate structures, and iminooxadiazine dione structures. Furthermore, some of these isocyanate groups can be modified using silane coupling agents containing amino groups.

[0043] End-capped polyisocyanate compounds include, for example, polyisocyanate compounds having isocyanate groups that are end-capped by: alcohols, such as butanol; oximes, such as butyl ethyl ketone oxime; lactams, such as ε-caprolactam; active methylene compounds, such as malonate, acetoacetate, etc.; pyrazoles, such as 3,5-dimethylpyrazole, etc.; imidazoles, such as imidazole, 2-ethylimidazole, etc.; or phenols, such as m-cresol, etc.

[0044] Hydrophilic carbodiimide compounds are preferred as polycarbodiimide compounds. Hydrophilic carbodiimide compounds include, for example, compounds obtained by reacting a polycarbodiimide compound having at least two isocyanate groups in its molecule with a polyol having terminal hydroxyl groups to obtain an NCO / OH molar ratio exceeding 1, and then reacting a hydrophilizing agent having active hydrogen and a hydrophilic moiety with the reaction product.

[0045] In the waterborne single-coat coating composition of the present invention, the content of hardener (B) in 100 parts by weight of total resin solids in the composition is preferably 10-50 parts by weight; 15-45 parts by weight is more preferred, and 20-40 parts by weight is particularly preferred. By setting the content of hardener (B) to 10-50 parts by weight, coating films with sufficient crosslinking density can be obtained, and these coating films also exhibit excellent adhesion after water resistance testing.

[0046] The coloring pigment (C) used in this invention is preferably at least one selected from the group consisting of white pigment, red pigment, orange pigment, yellow pigment, green pigment, blue pigment, purple pigment and black pigment.

[0047] The coloring pigment (C) is particularly preferably a white pigment; only one white pigment may be used, or a combination of white pigment and other coloring pigments selected from the group consisting of red, orange, yellow, green, blue, purple and black pigments may be used.

[0048] White pigments used as coloring pigments (C) in this invention include, for example, titanium dioxide.

[0049] The red pigments used as coloring pigments (C) in this invention include, for example, azo pigments, anthrone pigments, anthraquinone pigments, perylene pigments, quinacridone pigments, diketopyrrolopyrrole pigments, iron oxide pigments, etc.

[0050] Orange pigments used as coloring pigments (C) in this invention include, for example, azo pigments, anthraquinone pigments, perinone pigments, quinacridone pigments, and composite oxide pigments.

[0051] Yellow pigments used as coloring pigments (C) in this invention include, for example, isoindoline pigments, azomethyl pigments, anthrone pigments, benzimidazolone pigments, quinoxaline dione pigments, isoindolineone pigments, iron oxide pigments, composite oxide pigments, etc.

[0052] Green pigments used as coloring pigments (C) in this invention include, for example, phthalocyanine pigments, azobenzene pigments, and composite oxide pigments.

[0053] Blue pigments used as coloring pigments (C) in this invention include, for example, phthalocyanine pigments, threne pigments, indigo pigments, composite oxide pigments, etc.

[0054] Purple pigments used as coloring pigments (C) in this invention include, for example, dioxazine pigments, perylene pigments, quinacridone pigments, composite oxide pigments, etc.

[0055] The black pigments used as coloring pigments (C) in this invention include, for example, carbon black, azo pigments, perylene pigments, and composite oxide pigments. It should be noted that the use of carbon black is an alternative, and the use of black pigments (such as azo pigments, perylene pigments, and composite oxide pigments) is more preferred because when these pigments are used, the resulting multilayer coating film exhibits excellent heat shielding performance.

[0056] There is no particular limitation on the total content of one or more coloring pigments (C) in the water-based single-coat coating composition of the present invention, but preferably it is 10-200 parts by weight of total resin solids in 100 parts by weight of the composition; 35-160 parts by weight is more preferred, and 60-120 parts by weight is particularly preferred.

[0057] The aqueous single-coat coating composition of the present invention may further comprise luminescent pigments. Luminescent pigments include, for example, uncolored or colored aluminum pigments, vapor-deposited metal flake pigments, interference pigments of transparent or translucent base materials coated with metal oxides, etc. A single such luminescent pigment may be used, or a combination of both or more may be used.

[0058] There is no particular limitation on the total content of one or more luminescent pigments in the water-based single-coat coating composition of the present invention, but preferably it is 0-2.0 parts by weight in 100 parts by weight of total resin solids in the composition; 0-1.0 parts by weight is more preferred, and 0-0.5 parts by weight is particularly preferred.

[0059] Optionally, the coating film properties of the aqueous single-coat coating composition of the present invention can be adjusted by adding one or more other resins. Other resins include, for example, polyester resins, polyurethane resins, polyurea resins, urethane-polyurethane resins, polyolefin resins (including chlorinated and / or modified resins), epoxy resins, etc. Furthermore, other resins can be partially cross-linked particles, or core / shell particles comprising an inner (core) and an outer (shell). Particulate-based polymers include, for example, polyurethane-polyurea particles, urethane core / acrylate shell particles, acrylate core / urethane shell particles, etc. It should be noted that in the case of partially cross-linked resin particles, this portion is insoluble in organic solvents (gel portion), and therefore the gel fraction, indicating the proportion of gel in the solid resin particles, can be measured. Furthermore, other resins preferably have hydroxyl and / or carboxyl groups as functional groups. Other resins can be used alone or in combination of both or more.

[0060] The waterborne single-coat coating composition of the present invention may optionally include suitable solvents such as water and / or organic solvents, various coating additives such as rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoamers, antioxidants, UV absorbers, extender pigments, etc. Organic solvents include, for example, aromatic hydrocarbons such as toluene, xylene, aromatic naphtha, etc.; ketones such as acetone, methyl ethyl ketone, methyl amyl ketone, etc.; esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, amyl acetate, ethyl ethoxypropionate, etc.; alcohols such as isopropanol, butanol, 2-butoxyethanol, 2-ethylhexanol, etc.; ethers; aliphatic hydrocarbons, including chlorinated hydrocarbons; or mixtures thereof. Organic solvents may be used alone or in combination of both or more thereof.

[0061] Although there is no particular limitation on the content of non-volatile components in the water-based single-coat coating composition of the present invention during application, the content is preferably 30-70% by mass; 40-60% by mass is more preferred, and 45-55% by mass is particularly preferred. Setting the content of non-volatile components to 30-70% by mass means that the coating composition can be applied without causing any problems.

[0062] A cured single-coat coating film can be obtained by applying the water-based single-coat coating composition of the present invention onto a substrate and then baking (heating).

[0063] There are no particular limitations on the substrates to which the waterborne single-coat coating compositions of the present invention can be applied; examples include components made of metals (such as iron, zinc, aluminum, magnesium, etc.), components made of alloys of these metals, components on which these metals are plated or vapor-deposited, components made of glass, plastics, foams of various materials, etc. Among these examples, metal and plastic substrates constituting automobile bodies are preferred. Optionally, these components can be subjected to suitable treatments, such as degreasing, surface treatment, etc.

[0064] Furthermore, the substrate to which the water-based single-coat coating composition of the present invention can be applied includes the aforementioned component on which a base coating film is formed. The base coating film is applied to the surface of the component because it can cover the surface of the component and impart corrosion resistance, rust prevention, adhesion, etc.; the base coating film can be formed by applying a base coating material and then curing or drying it. There are no particular limitations on the base coating material; the base coating material itself can be known; for example, electrodeposited coating compositions, solvent-based base paints, water-based base paints, etc., can be used. Among these base coating materials, cationic electrodeposited coating compositions that form a cured electrodeposited coating film by coating and curing on a metal substrate are preferred. Furthermore, it is particularly preferred that the cured cationic electrodeposited coating film has a lightness value of at least 40 L. 45.

[0065] The water-based single-coat coating composition of the present invention can be applied by electrostatic coating, air spraying, airless spraying, etc.

[0066] Although there are no particular limitations on the dry film thickness of the cured single-coat coating film, the dry film thickness is preferably 10-50 µm, more preferably 20-40 µm, and even more preferably 25-35 µm.

[0067] In this invention, baking (heating) can be performed by known means, such as using a drying oven, including hot air ovens, electric ovens, infrared induction heating ovens, etc. While there are no particular limitations on the curing temperature, it is preferably 100°C-160°C; 120°C-155°C is more preferred, and 130°C-150°C is particularly preferred. By setting the curing temperature to 100°C-160°C, the curing reaction can be sufficiently promoted. Furthermore, while there are no particular limitations on the heating time, it is preferably 10-50 minutes; 15-45 minutes is more preferred, and 20-40 minutes is particularly preferred.

[0068] The 60° gloss value of the cured single-coat coating film of the waterborne single-coat coating composition of the present invention is preferably ≥85, ≥87 is more preferred, and ≥90 is particularly preferred. In the present invention, the 60° gloss value is a value measured using a Micro-tri-gloss gloss meter (proprietary name, BYK-Gardner GmbH).

[0069] With a lightness value of 40 L On a base coating film of 45, the lightness value L of the cured single-coat coating film of the waterborne single-coat coating composition of the present invention, formed to obtain a dry film thickness of 30 µm, is... 45 is preferably 60-95; 65-92 is more preferred, and 70-90 is particularly preferred. This results in a lightness value L of the cured single-coat paint film. A value of 45 (for a coating thickness of 60-95) indicates that the cured single-coat paint film exhibits excellent heat shielding performance. Here, the brightness value L... 45 is the lightness value in the CIE LAB color system, based on the spectral reflectance of light incident at an angle of 45° relative to the vertical line of the coating film and received at an angle deviating 45° from the direction of specular reflection to the direction of incident light. It should be noted that the CIE LAB color system was defined by the International Commission on Illumination (CIE) in 1976 and is the color system used in JIS Z 8781-4:2013. In this invention, the lightness value L... 45 is the value measured using a BYK maci multi-angle spectrophotometer (proprietary name, BYK Gardner Ltd.).

[0070] Furthermore, the infrared solar reflectance (IRSR) of the cured single-coat coating film obtained from the above-described water-based single-coat coating composition is preferably ≥ 60%; ≥ 63% is more preferred, and ≥ 65% is particularly preferred. An infrared solar reflectance (IRSR) of ≥ 60% for the cured single-coat coating film means that the cured single-coat coating film exhibits excellent heat shielding performance. It should be noted that in this invention, the infrared solar reflectance (IRSR) value is measured using a UV-3600 UV / visible / near-IR spectrophotometer (proprietary name, Shimadzu Corp.).

[0071] The waterborne single-coat coating composition of the present invention and the method for forming a coating film using the waterborne single-coat coating composition are effective for vehicle bodies, parts and components of buses, trucks, motorcycles, public buses, etc., and are particularly effective for metal car bodies. Example

[0072] The invention is described more specifically below with the aid of practical examples; however, the invention is not limited to these examples. Furthermore, unless otherwise stated, in the examples, “parts” means “parts by mass”; and regarding content, “%” means “% by mass”.

[0073] <Production Example 1-1: Production of Acrylic Resin Aqueous Dispersion AC-1>

[0074] Ninety-four parts of deionized water were placed in a flask equipped with two dropping devices, a reflux condenser, a thermometer, a stirrer, and a nitrogen inlet tube, and the temperature was raised to 80°C under a nitrogen atmosphere. Then, using one dropping device, a mixture of free radical polymerizable monomers containing the following was added dropwise at a uniform rate over 3 hours: 13.68 parts styrene, 18.52 parts 2-hydroxyethyl methacrylate, 16.03 parts n-butyl acrylate, 49.21 parts n-butyl methacrylate, and 2.56 parts acrylic acid; 4.0 parts n-dodecyl mercaptan as an emulsion polymerization regulator; and 2.0 parts sodium methacryloyloxy polyoxypropylene sulfate (proprietary name, Sanyo Chemical Industries, Ltd.), containing the reactive anionic emulsifier Eleminol RS-3000; and the reactive nonionic emulsifier ADEKA REASOAP NE20 (proprietary name, ADEKA Corporation). A mixed emulsifier solution containing 1.0 part of Corp. and 15 parts of deionized water was added dropwise simultaneously using the above-mentioned dropping device. A polymerization initiator solution containing 0.30 parts of ammonium persulfate in 15 parts of deionized water was then added dropwise over 3 hours using another dropping device at a uniform rate. After the dropwise addition was complete, stirring was continued for 1 hour, followed by cooling to 40°C to obtain an aqueous dispersion of acrylic resin AC-1 with the property values ​​shown in Table 1.

[0075] <Production Examples 1-2 to 1-19: Production of Aqueous Dispersions of Acrylic Resins AC-2 to AC-19>

[0076] The acrylic resin aqueous dispersions AC-2 to AC-19 having the property values ​​shown in Tables 1 and 2 were obtained by following the formulations shown in Table 1 using the same method as in Production Example 1-1.

[0077] [Table 1]

[0078]

[0079] [Table 2]

[0080]

[0081] (Note 1) Emulsion polymerization regulator: n-Dodecyl mercaptan

[0082] (Note 2) Reactive anionic emulsifier Eleminol RS-3000 (proprietary name, Sanyo Chemical Industries, Ltd., sodium methacryloyloxy polyoxypropylene sulfate)

[0083] (Note 3) Reactive nonionic emulsifier: ADEKA REASOAP NE20 (proprietary name, ADEKA Corporation)

[0084] <Production Example 2: Production of Aqueous Acrylic-Ethyl Carbamate Resin Dispersion AU-1>

[0085] 2-1 Production of Polyester Polyol PE-1

[0086] Under a nitrogen stream, 49.9 parts of adipic acid, 18.5 parts of 1,6-hexanediol, and 31.6 parts of neopentyl glycol were placed in a flask equipped with a reflux condenser, which included a separator for reaction water, a thermometer, a stirrer, and a nitrogen inlet. Stirring was performed while the temperature was raised to 160°C. After maintaining the temperature at 160°C for 1 hour, the temperature was raised to 230°C over a period of 5 hours. The acid value was measured at regular intervals while maintaining the temperature at 230°C, and the mixture was cooled to ≤ 80°C when the acid value reached 3.5 mg KOH / g. Finally, 21.9 parts of methyl ethyl ketone were added to obtain polyester polyol PE-1. The characteristic values ​​of polyester polyol PE-1 were an acid value of 3.5 mg KOH / g, a hydroxyl value of 155 mg KOH / g, and 80% by mass resin solids.

[0087] 2-2 Production of Aqueous Acrylic-Ethyl Carbamate Resin Dispersion AU-1

[0088] Under a nitrogen flow, 420.0 parts of polyester polyol PE-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 obtained in Production Example 2-1 were loaded into a flask equipped with two dropping devices, a reflux condenser, a thermometer, a stirring device, and a nitrogen inlet pipe, and stirred to obtain a homogeneous mixture.

[0089] Then, 259.9 parts of isophorone diisocyanate were added to the resulting solution. After the exothermic reaction subsided, the reaction mixture was gradually heated to 80°C while stirring, and stirring continued at this temperature until the isocyanate content became 2.2% by mass. Then, 66.7 parts of trimethylolpropane were added, followed by stirring at 80°C until no free isocyanate groups were detected in the solution. Then, 248.9 parts of methyl ethyl ketone were added to the resulting polyurethane solution.

[0090] Then, the temperature was adjusted to 82°C, and a monomer mixture capable of free radical polymerization, comprising 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 over 3 hours at a uniform rate using a dripping device. Simultaneously, a polymerization initiator solution comprising 22.8 parts of 2,2'-azobis(methylbutyronitrile) and 152.3 parts of methyl ethyl ketone was added dropwise over 3.5 hours using another dripping device at a uniform rate.

[0091] After the monomer mixture and polymerization initiation solution were added dropwise, the resulting reaction mixture was stirred at 82°C for 2.5 hours, and 56.9 parts of dimethylethanolamine and 2242 parts of deionized water were added. The separation tube was then fitted into a reflux condenser, and the solvent was removed under reduced pressure at 45°C until the resin solids in the dispersion reached 40% by mass, yielding an aqueous acrylate-urethane resin dispersion AU-1. The resulting aqueous acrylate-urethane resin dispersion AU-1 had an acid value of 32 mgKOH / g, a hydroxyl value of 57 mgKOH / g, and a pH of 8.1.

[0092] <Production Example 3: Production of Black Pigment Paste P-1>

[0093] 100.0 parts of an aqueous acrylate-urethane resin dispersion AU-1, 40.0 parts of perylene black pigment Spectrasense Black L0086 (proprietary name, Sun ChemicalColors & Effects GmbH) and 60.0 parts of deionized water were mixed and then dispersed by an electric mill to obtain a black pigment paste P-1.

[0094] <Production Example 4: Production of Blue Pigment Paste P-2>

[0095] 100.0 parts of aqueous acrylate-urethane resin dispersion AU-1, 40.0 parts of cobalt blue pigment HEUCODUR Blue 2R (proprietary name, HEUBACH GmbH), and 60.0 parts of deionized water were mixed and then dispersed by an electric mill to obtain blue pigment paste P-2.

[0096] <Production Example 5: Production of Red Pigment Paste P-3>

[0097] 100.0 parts of aqueous acrylate-urethane resin dispersion AU-1, 40.0 parts of red iron oxide pigment 100ED (proprietary name, Toda Kogyo Corp.) and 60.0 parts of deionized water were mixed and then dispersed by an electric mill to obtain red pigment paste P-3.

[0098] <Production Example 6-1: Production of Waterborne Single-Coat Coating Composition WB-1>

[0099] 55.30 parts of aqueous acrylic resin dispersion AC-1 were used as the dispersion resin, and 84.92 parts of titanium dioxide pigment TI-PURE R-706 (proprietary name, The Chemours Company) were added to it, along with 8.50 parts of 2-butoxyethanol for viscosity adjustment and 21.20 parts of deionized water, and dispersed by an electric mill to obtain a pigment paste.

[0100] Then, 169.92 parts of the above pigment paste were stirred in a dissolving apparatus, and the following were added: 3.30 parts of waterborne acrylic resin dispersion AC-111, 12.50 parts of melamine resin solution CYMEL 325 (proprietary name, ALLNEX GmbH, non-volatile content 80% by mass), 20.80 parts of melamine resin solution CYMEL 203 (proprietary name, ALLNEX GmbH, 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 UV absorber TINUVIN 384-2 (proprietary name, BASF Japan, Ltd.), 2.00 parts of light stabilizer TINUVIN 292 (proprietary name, BASF Japan, Ltd.), and thickener RHEOVISHS. 2.00 parts of l152 (proprietary name, BASF Japan Ltd.), 1.00 part of surface conditioner BYK-346 (proprietary name, BYK-Chemie GmbH) and 10.00 parts of deionized water are added and mixed in this order.

[0101] Finally, it was diluted with deionized water to obtain a viscosity of 120 mPa·s at 20°C and a viscosity of 1000 s⁻¹. -1 The shear rate (using an R180 portable rotational viscometer (proprietary name, porRheo GmbH)) was determined to obtain the waterborne single-coat coating composition WB-1 with the formulation shown in Table 3.

[0102] <Production Examples 6-2 to 6-22: Production of Waterborne Single-Coat Coating Compositions WB-2 to WB-22>

[0103] The waterborne single-coat coating compositions WB-2 to WB-22 were obtained using the formulations shown in Tables 3-5, in the same manner as in Production Example 6-1.

[0104] [Table 3]

[0105]

[0106] [Table 4]

[0107]

[0108] [Table 5]

[0109]

[0110] (Note 4) Titanium oxide pigment: TI-PURE R-706 (proprietary name, Chemours)

[0111] (Note 5) Melamine resin solution: CYMEL 325 (proprietary name, ALLNEX GmbH, non-volatile content 80% by mass)

[0112] (Note 6) Melamine resin solution: CYMEL 203 (proprietary name, ALLNEX GmbH, non-volatile content 72% by mass)

[0113] (Note 7) UV absorber: TINUVIN 384-2 (proprietary name, BASF Japan Ltd.)

[0114] (Note 8) Light stabilizer: TINUVIN 292 (proprietary name, BASF Japan Ltd.)

[0115] (Note 9) Thickener: RHEOVIS HS l152 (proprietary name, BASF Japan Ltd.)

[0116] (Note 10) Surface conditioner: BYK-346 (proprietary name, BYK Chemicals Ltd.)

[0117] <Examples 1 to 14 and Comparative Examples 1 to 8>

[0118] (1) Evaluation of the production and appearance of the test sheet

[0119] Electrodeposition coating of zinc phosphate-treated soft steel sheets was performed using Cathogard 500 cationic electrodeposition coating (proprietary name, BASF Japan Ltd.) to provide a dry film thickness of 20 µm, and cured at 175°C for 25 minutes to obtain the electrodeposited coated sheet. The lightness value L of the resulting electrodeposited coating film was measured using a BYK mac i multi-angle spectrophotometer (proprietary name, BYK Gardner Ltd.). 45 is 40.

[0120] The water-based single-coat coating compositions WB-1 to WB-22 were then sprayed onto electrodeposited coated sheets to obtain a dry film thickness of 30 µm. After standing at room temperature for 3 minutes, the sheets were heated at 140°C for 30 minutes to produce cured single-coat coating film test sheets. The appearance of the resulting coating films was visually evaluated using the following criteria, and the results are shown in Tables 6 and 7.

[0121] ○: No abnormalities found in the coating film

[0122] ×: Small bubbles or pinholes (holes) exist in the coating film.

[0123] (2) Evaluation of cured single-coat coating film

[0124] Test sheets of cured single-coat coating films (Examples 1 to 14, Comparative Examples 1, 3 and 5 to 8) that were rated ○ in the above appearance assessment were subjected to the following measurements and assessments (2)-1 to (2)-4, and the results are shown in Tables 6 and 7.

[0125] (2) -1 60° gloss value

[0126] The 60° gloss value was measured using a Micro-tri-gloss gloss meter (proprietary name, Bick Gardner Ltd.).

[0127] (2)-2 Brightness value L 45 measurement

[0128] Lightness value L was measured using a BYK mac i multi-angle spectrophotometer (proprietary name, BYK Gardner Ltd.). 45.

[0129] (2)-3 Measurement of Infrared Solar Reflectance (IRSR)

[0130] Infrared solar reflectance (IRSR) was measured using a UV-3600 UV / Visible / Near-IR spectrophotometer (proprietary name, Shimadzu Corporation).

[0131] (2)-4 Adhesion measurement after water resistance test

[0132] The test sheets were immersed in warm water at 40°C for 10 days, then removed and dried. The adhesion of these test sheets was then evaluated according to JIS K5400-8.5 (cross-cut test). Therefore, lines were cut into the surface of the coating film of the test sheet using a cutter down to the underlying material to obtain 100 squares of 2 mm × 2 mm size; Sellotape® was then adhered to this surface and abruptly removed at 45°C at 20°C. Evaluation was based on the number of squares remaining on the coating film, according to the following criteria.

[0133] ○: The number of squares of remaining coating film is 100 (without removal).

[0134] ×: The number of squares of remaining coating film is 99 or less.

[0135] [Table 6]

[0136]

[0137] [Table 7]

[0138]

[0139] In the foregoing, the invention designed by the inventors has been described with reference to actual examples and specific terms. However, it is unnecessary to repeat the above examples, and various modifications can be made within the scope of the essence of the invention.

Claims

1. A water-based single-coat coating composition comprising an acrylic resin (A) having hydroxyl groups, a hardener (B), and a coloring pigment (C). in, 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 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°C-40°C. And when L has a lightness value of 40 When a dry film thickness of 30 µm is obtained by forming a base coating film at 45, the cured single-coat coating film formed from the aforementioned water-based single-coat coating composition has a 60° gloss value ≥ 85 and a lightness value L. 45 is 60-95, and the infrared solar reflectance (IRSR) is ≥ 60%.

2. The water-based single-coat coating composition according to claim 1, wherein, In 100 parts by weight of total resin solids, the content of the hydroxyl-containing acrylic resin (A) is 50-90 parts by weight.

3. The water-based single-coat coating composition according to claim 1 or 2, wherein, The aforementioned hardener (B) is melamine resin.

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

5. A single-coat coating film obtained from the aqueous single-coat coating composition according to claim 1 or 2.

6. A method for forming a cured single-coat paint film, wherein, A cured electrodeposited coating film is formed by coating a metal substrate with a cationic electrodeposited coating composition for coating and curing, and then the aqueous single-coat coating composition according to claim 1 or 2 is directly coated onto it and cured.

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