Water-based glossy paint composition and method for forming a multi-layer coating film

Abstract

To provide an aqueous glossy paint composition (X) that can produce a metallic design and form a paint film with suppressed paint streaks, a method for forming a multi-layer paint film, and a multi-layer paint film. [Solution] An aqueous glossy coating composition (X) for inkjet coating containing indium particles (x1), a surface modifier (x2), a pigment dispersant (x3), a viscosity modifier (x4), and water (x5), A water-based glossy coating composition (X) for inkjet coating, comprising 0.1 to 25 parts by mass of solids per 100 parts by mass of the total components of the water-based glossy coating composition (X).

Description

[TECHNICAL FIELD]

[0001] The present invention relates to an aqueous glittering coating composition and a method for forming a multilayer coating film. [BACKGROUND ART]

[0002] The purposes of coating are mainly to protect the material and impart aesthetic appearance. In industrial products, aesthetic appearance, particularly "texture", is important from the perspective of enhancing product competitiveness. While consumers demand various textures for industrial products, in recent years, metallic or pearlescent luster (hereinafter referred to as "metallic luster") has been required in fields such as automotive outer panels, automotive parts, and home appliances.

[0003] Metallic luster refers to a texture characterized by no grainy feel on the surface like a mirror surface, and further, it appears bright when viewed from a direction almost perpendicular to the coated plate (highlight) and dark when viewed obliquely from above the coated plate (shade), that is, a large difference in brightness between the highlight area and the shade area.

[0004] It is advantageous in terms of simplicity and cost if metallic luster can be imparted by coating. Patent Document 1 discloses a method for forming a metallic coating film characterized by coating a composition containing non-leafing aluminum flakes and an organic solvent onto an uncured coated surface, and then coating a clear coating. The coating disclosed in Patent Document 1 is a solvent-based coating. However, in recent years, from the perspective of low environmental impact, aqueous conversion has also been required in the field of metallic coatings.

[0005] Patent Document 2 discloses an aqueous base coating composition characterized by comprising a glittering pigment obtained by pulverizing a vapor-deposited metal film into metal pieces, and an aqueous cellulose derivative having an acid value of 20 to 150 mgKOH / g (solid content), wherein the aqueous cellulose derivative is used as a main binder resin, and the content of the glittering pigment is 20 to 70 mass% in terms of PWC. [PRIOR ART DOCUMENTS] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-90318 [Patent Document 2] Japanese Patent Publication No. 2009-155537 [Overview of the project] [Problems that the invention aims to solve]

[0007] Until now, rotary atomization electrostatic coating has been widely used to paint objects such as automobiles. However, due to the long automobile production lines, the need for air conditioning, and the high temperatures required for paint curing, a large amount of CO2 is emitted during the painting process. For this reason, inkjet printing and other methods are attracting attention as alternative coating methods that contribute to CO2 reduction.

[0008] Incidentally, inexpensive aluminum flake pigments have traditionally been used as the glossy pigments in aqueous paint compositions for forming coatings with a metallic appearance. However, when coatings are formed using inkjet technology from aqueous paint compositions containing aluminum flake pigments, there is a problem of paint streaks appearing.

[0009] One of the objects of the present invention is to provide an aqueous glossy paint composition (X) for inkjet coating that can produce a metallic design and form a coating film with suppressed paint streaks, a method for forming a multilayer coating film, and a multilayer coating film. [Means for solving the problem]

[0010] The following embodiments are provided according to this disclosure. Section 1. A water-based glossy coating composition (X) for inkjet coating, comprising indium particles (x1), a surface modifier (x2), a pigment dispersant (x3), a viscosity modifier (x4), and water (x5), A water-based glossy coating composition (X) for inkjet coating, comprising 0.1 to 25 parts by mass of solids per 100 parts by mass of the total components of the water-based glossy coating composition (X). Section 2. An aqueous glossy coating composition (X) for inkjet coating according to item 1, wherein the cumulative 50% volume particle size D50 of indium particles (x1) is 0.70 μm or less. Section 3. The aqueous glossy coating composition (X) for inkjet coating according to item 1 or 2, wherein the content of indium particles (x1) is 70 parts by mass or more based on 100 parts by mass of the solid content of the aqueous glossy coating composition (X). Section 4. Forming a glossy coating film on a substrate by inkjet coating with an aqueous glossy coating composition (X) for inkjet coating described in any one of items 1 to 3, and A clear coating is formed by applying a clear coating composition (Y) onto the glossy coating that is formed. A method for forming a multilayer coating film including the following. Section 5. A glossy coating film formed on a substrate, which is formed from the aqueous glossy coating composition (X) described in any one of items 1 to 3, A clear coating formed on the aforementioned glossy coating film, and a clear coating formed from a clear coating composition (Y) A multi-layer coating film equipped with the following features. Section 6. A multilayer coating film as described in item 5, wherein the thickness of the glossy coating film as a dry film thickness is 0.1 to 3.0 μm. Item 7. A multilayer coating film according to item 5 or 6, wherein the 60-degree specular gloss of the multilayer coating film is in the range of 100 to 250. [Effects of the Invention]

[0011] According to the present invention, an aqueous glossy paint composition (X) for inkjet coating and a method for forming a multi-layer coating film are obtained that can produce a metallic design and form a coating film with suppressed paint streaks. [Modes for carrying out the invention]

[0012] As used herein, the terms "comprise" and "contain" are concepts that also include "consist essentially of" and "consist of".

[0013] As used herein, "inkjet coating" refers to a coating method in which a coating composition is directly ejected from extremely fine nozzles and adhered to form a coating film on a surface to be coated. "Inkjet coating" includes liquid column ejection coating, liquid film ejection coating, and liquid droplet ejection coating. "Liquid column" refers to a columnar, linear, rod-shaped, or thread-shaped coating composition. "Liquid column ejection coating" refers to a coating method in which a coating composition is ejected from an ejection port in the form of a liquid column. "Liquid film" refers to a film-shaped or planar coating composition. "Liquid film ejection coating" refers to a coating method in which a coating composition is ejected from an ejection port in the form of a liquid film. "Liquid droplet ejection coating" refers to a coating method in which a coating composition in the form of a liquid film or liquid column is fractured by turning ejection on and off to form liquid droplets, and the liquid droplets are ejected from the ejection port in a state where the directionality of each liquid droplet is controlled. Examples of inkjet coating include coating by a robot and coating using a dispenser. In certain embodiments, inkjet coating includes coating in which a coating composition is ejected toward an object to be coated from an ejection port of a dispenser.

[0014] As used herein, "solid content" means non-volatile components such as resins, crosslinking agents, and pigments contained in a coating composition that remain after drying the coating composition at 110°C for 1 hour. The total solid content of a coating composition can be calculated by determining the ratio of the mass of components remaining after drying to the total mass of the coating composition before drying.

[0015] In the numerical ranges described stepwise in the present specification, the upper limit or lower limit of the numerical range of one step can be arbitrarily combined with the upper limit or lower limit of the numerical range of another step. In addition, in the numerical ranges described in the present specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples or a value that can be uniquely derived from the examples. Furthermore, as used herein, a numerical value connected by "~" means a numerical range that includes the numerical values before and after "~" as the lower limit and the upper limit.

[0016] Water-based glossy coating composition (X) for inkjet painting The aqueous glittering coating composition (X) for inkjet coating according to the present disclosure contains indium particles (x1), a surface conditioner (x2), a pigment dispersant (x3), a viscosity modifier (x4), and water (x5), and contains 0.1 to 25 parts by mass of solid content based on 100 parts by mass of the total of all components of the aqueous glittering coating composition (X).

[0017] Conventionally, when a coating film is formed by an inkjet method using an aqueous glittering coating composition containing a scaly aluminum pigment such as aluminum flakes as a glittering pigment, there has been a problem that coating streaks occur in the coating film.

[0018] Although the present invention does not wish to be bound by theory, from a microscopic perspective, in an inkjet method, connections of droplets (dots) of the aqueous glittering coating composition form lines, a plurality of lines overlap to form a surface, and a coated surface is formed. To form a coated surface, overlapping portions between adjacent droplets are required. However, since the viscosity of the overlapping portions is different from the viscosity of a single droplet itself, a phenomenon occurs in which the orientation of the metal particles contained in the overlapping portions is different, or the metal particles cannot be arranged neatly. This difference in the orientation of the metal particles remains even after the coated surface is formed, resulting in unevenness, which is referred to as coating streaks.

[0019] Aluminum flakes have a large average particle diameter of about 15 μm, and a dense metallic design cannot be exhibited unless they are oriented neatly. When the average particle diameter of aluminum flakes is reduced, a practical coating film cannot be produced because aluminum flakes are chemically unstable and easily corroded by acids or alkalis.

[0020] On the other hand, indium particles (x1) have a small particle diameter and are resistant to corrosion. They are also useful in terms of having millimeter-wave transmittance. It is thought that when applied, indium particles (x1) are neatly laid out in the coating film, so differences in the orientation of metal particles in droplets become inconspicuous, and coating streaks are eliminated. The aqueous glossy coating composition (X) of the present invention can be used to create a metallic-looking design and form a coating film with suppressed paint streaks. Furthermore, applying the aqueous glossy coating composition (X) of the present invention using inkjet printing contributes to reducing CO2 emissions during coating film formation.

[0021] Indium particle (x1) The indium particles (x1) are flaky particles. These flaky particles are sometimes also referred to as scale-like particles, plate-like particles, or flake-like particles.

[0022] In the present invention, "flaky particles" means particles having a substantially flat surface and a substantially uniform thickness in the direction perpendicular to the substantially flat surface. Furthermore, "flaky particles" refers to particles with a very thin thickness and a very long substantially flat surface. The length of the substantially flat surface is the diameter of a circle having the same projected area as the projected area of ​​the flaky particle.

[0023] There are no particular restrictions on the shape of the approximately flat surface, and it can be appropriately selected depending on the purpose. Examples include polygons such as approximately rectangles, approximately squares, approximately circles, approximately ellipses, approximately triangles, approximately quadrilaterals, approximately pentagons, approximately hexagons, approximately heptagons, approximately octagons, and other polygons, as well as random irregular shapes. Among these, approximately circular is preferred.

[0024] The indium particles (x1) may be a single layer, or two or more layers may be stacked to form primary particles. Furthermore, the primary indium particles (x1) may aggregate to form secondary particles.

[0025] Note that indium particles (x1) consist of indium with a purity of 95% or higher, and may contain trace amounts of impurities, but alloys with other metals are not included.

[0026] The above-mentioned indium particles (x1) can be manufactured by performing a delamination layer formation step, a vacuum deposition step, a delamination step, and other steps as necessary. For a method of manufacturing indium particles (x1) including these steps, please refer to WO2022 / 244483.

[0027] The cumulative 50% volume particle diameter D50 of the indium particles (x1) obtained by performing the above-described peel layer formation step, vacuum deposition step, peeling step, and other steps as necessary, is preferably 0.70 μm or less, more preferably 0.60 μm or less, even more preferably 0.50 μm or less, and particularly preferably 0.40 μm or less, from the viewpoint of forming a multi-layer coating film with excellent metallic luster. The lower limit of the cumulative 50% volume particle diameter D50 of the indium particles (x1) is not particularly limited, but it is preferably 0.10 μm or more. The cumulative 50% volume particle size (D50) is the particle size corresponding to 50% of the cumulative volume distribution of the particle size distribution curve obtained by the laser diffraction method, and represents the particle size of indium particles when non-spherical indium particles are measured assuming they are perfect spheres. Examples of means using the laser diffraction method include laser diffraction / scattering particle size analyzers.

[0028] Commercially available indium particles (x1) can be used. Examples of such commercially available products include "Leaf Powder 49CJ-1120", "Leaf Powder 49CJ-1150", "Leaf Powder 49BJ-1120", and "Leaf Powder 49BJ-1150" (all manufactured by Oike Metallic Design Co., Ltd.).

[0029] The content of indium particles (x1) in the aqueous glossy coating composition (X) of the present invention is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, even more preferably in the range of 60 to 95 parts by mass, and particularly preferably in the range of 65 to 90 parts by mass, based on 100 parts by mass of solid content of the aqueous glossy coating composition (X), from the viewpoint of obtaining a coating film that can exhibit a metallic design and suppresses paint streaks.

[0030] The content of indium particles (x1) in the aqueous glossy coating composition (X) of the present invention is preferably in the range of 0.1 to 15% by mass, more preferably in the range of 0.5 to 15% by mass, even more preferably in the range of 1 to 15% by mass, and particularly preferably in the range of 2 to 15% by mass, based on the total mass of the aqueous glossy coating composition (X), in order to produce a coating film that can exhibit a metallic design and suppresses paint streaks.

[0031] Surface conditioning agent (x2) The aqueous glossy coating composition (X) of the present invention contains a surface modifier (x2).

[0032] The surface modifier is used to help uniformly orient the indium particles dispersed in water onto the substrate when applying the aqueous glossy paint composition (X) to the substrate.

[0033] Examples of surface modifiers include silicone-based surface modifiers, acrylic-based surface modifiers, vinyl-based surface modifiers, fluorine-based surface modifiers, and acetylenediol-based surface modifiers. Among these, it is preferable to include a silicone-based surface modifier from the viewpoint of obtaining a coating film that can produce a metallic appearance and suppresses paint streaks. Each of the above surface modifiers can be used individually or in appropriate combinations of two or more types.

[0034] Examples of commercially available surface conditioners include the BYK series from BIC Chemie, the Tego series from Evonic, the Polyflow series from Kyoeisha Chemical, and the Disparon series from Kusumoto Chemical.

[0035] Among surface modifiers, silicone-based surface modifiers are preferred from the viewpoint of the metallic luster and water resistance of the resulting coating film. Silicone-based surface modifiers include polydimethylsiloxane and modified silicones derived from it. Examples of modified silicones include polyether-modified silicone, acrylic-modified silicone, and polyester-modified silicone.

[0036] The content of the surface modifier (x2) in the aqueous glossy coating composition (X) of the present invention is preferably in the range of 0.1 to 50 parts by mass, more preferably in the range of 1 to 30 parts by mass, and particularly preferably in the range of 5 to 20 parts by mass, based on the content of 100 parts by mass of indium particles (x1), in order to produce a metallic design and obtain a coating film in which paint streaks are suppressed.

[0037] Pigment dispersant (x3) As the pigment dispersant (x3), for example, any compound of anionic, cationic, or nonionic type can be used, but in particular, it is preferable to use an anionic compound from the viewpoint of being able to produce a metallic design and obtain a coating film in which paint streaks are suppressed.

[0038] As anionic compounds, compounds having functional groups such as phosphate groups, carboxyl groups, sulfonic acid groups, and sulfate ester groups can be used, and among these, compounds containing phosphate groups are preferred from the viewpoint of forming a coating film with excellent gloss.

[0039] The above anionic compounds can also be used after neutralization with a neutralizing agent. Examples of neutralizing agents include ammonia; primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 2-amino-2-methyl-1-propanol, and 3-aminopropanol; secondary monoamines such as diethylamine, diethanolamine, di-n- or di-iso-propanolamine, N-methylethanolamine, and N-ethylethanolamine; tertiary monoamines such as trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, and dimethylethanolamine; and polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, and methylaminopropylamine.

[0040] Examples of the above-mentioned phosphate group-containing compounds include polyoxyethylene alkyl ether phosphates, polyoxyethylene phenyl ether phosphates, alkyl phosphate esters, and alkyl phosphate ester salts.

[0041] Each of the above pigment dispersants (x3) may be used individually or in combination of two or more.

[0042] The amount of pigment dispersant (x3) contained in the aqueous glossy paint composition (X) is preferably in the range of 0.1 to 50 parts by mass, more preferably in the range of 1 to 30 parts by mass, and particularly preferably in the range of 5 to 20 parts by mass, per 100 parts by mass of indium particles (x1). Having the amount of pigment dispersant (x3) within this range has the advantage of providing good dispersion stability for the indium particles (x1) and good physical properties for the resulting coating film.

[0043] Viscosity modifier (x4) Examples of the viscosity modifier (x4) include association-type viscosity modifiers, inorganic viscosity modifiers, polyacrylic acid-based viscosity modifiers, cellulose derivative-based viscosity modifiers, protein-based viscosity modifiers, alginic acid-based viscosity modifiers, polyvinyl-based viscosity modifiers, polyether-based viscosity modifiers, maleic anhydride copolymer-based viscosity modifiers, and polyamide-based viscosity modifiers. In particular, from the viewpoint of obtaining a coating film that can produce a metallic appearance and suppresses paint streaks, it is preferable to use an association-type viscosity modifier as the viscosity modifier (x4), and it is especially preferable to use an acrylic association-type viscosity modifier, which will be described later.

[0044] Examples of the above-mentioned associated viscosity modifiers include acrylic associated viscosity modifiers, which are acrylic resins having a hydrophilic acrylic main chain and hydrophobic side chains; and urethane associated viscosity modifiers, which have a hydrophobic portion, a urethane bond, and a polyether chain in one molecule, and which exhibit an effective thickening effect by the association of the hydrophobic portions in an aqueous medium.

[0045] Examples of inorganic viscosity modifiers include silicates, metal silicates, montmorillonite, organic montmorillonite, and colloidal alumina. Examples of polyacrylic acid-based viscosity modifiers include sodium polyacrylate and polyacrylic acid-(meth)acrylic acid ester copolymers. Examples of cellulose derivative-based viscosity modifiers include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, and cellulose nanofibers.

[0046] Examples of protein-based viscosity modifiers include casein, sodium caseinate, and ammonium caseinate. Examples of alginate-based viscosity modifiers include sodium alginate. Examples of polyvinyl-based viscosity modifiers include polyvinyl alcohol, polyvinylpyrrolidone, and polyvinylbenzyl ether copolymers.

[0047] Examples of polyether-based viscosity modifiers include polyether dialkyl esters, polyether dialkyl ethers, and polyether epoxy modified products. Examples of maleic anhydride copolymer-based viscosity modifiers include partial esters of vinyl methyl ether-maleic anhydride copolymers. Examples of polyamide-based viscosity modifiers include polyamide amine salts. These viscosity modifiers (x4) can be used individually or in combination of two or more types.

[0048] The viscosity modifier (x4) content in the aqueous glossy coating composition (X) of the present invention is preferably in the range of 0.1 to 50 parts by mass, more preferably in the range of 1 to 30 parts by mass, and particularly preferably in the range of 5 to 20 parts by mass, based on the content of 100 parts by mass of indium particles (x1), in order to produce a coating film that exhibits a metallic appearance and suppresses paint streaks.

[0049] Water (x5) The amount of water (x5) in the aqueous glossy coating composition (X) can be adjusted as appropriate, for example, to 1 to 99% by mass. In some embodiments, the amount of water (x5) in the aqueous glossy coating composition (X) is 25 to 85 parts by mass per 100 parts by mass of the total components of the aqueous glossy coating composition.

[0050] The aqueous glossy coating composition (X) for inkjet coating according to this disclosure contains indium particles (x1), a surface modifier (x2), a pigment dispersant (x3), a viscosity modifier (x4), and water (x5), and contains 0.1 to 25 parts by mass of solids per 100 parts by mass of the total components of the aqueous glossy coating composition (X). The solid content of the aqueous glossy paint composition (X) is preferably 0.1 to 20% by mass, and more preferably 0.5 to 15% by mass, from the viewpoint of suppressing paint streaks.

[0051] Other ingredients The water-based glossy paint composition (X) for inkjet coating may further contain, as needed, a base resin, a crosslinking component for curing the base resin, an organic solvent, pigments other than the indium particles (x1), an anti-settlement agent, an antifoaming agent, an ultraviolet absorber, and the like.

[0052] The aqueous glossy coating composition (X) is prepared by mixing indium particles (x1), a surface modifier (x2), a pigment dispersant (x3), a viscosity modifier (x4), water (x5), and other optional components.

[0053] In some preferred embodiments, the proportions of the components of the aqueous glossy paint composition (X), indium particles (x1), surface modifier (x2), pigment dispersion (x3), viscosity modifier (x4), and water (x5), are within the following ranges, which allows for the creation of a metallic-looking coating and suppression of paint streaks. Indium particles (x1): 0.1-15% by mass Surface modifier (x2): 0.1-50% by mass Pigment dispersion (x3): 0.1-50% by mass Viscosity modifier (x4): 0.1~50% by mass and water (x5): 1~99.6% by mass

[0054] Mirror gloss (60° gloss) In the present invention, the aqueous glossy coating composition (X) is preferably applied to an intermediate coating to form a glossy coating film with a dry film thickness of 0.1 to 3.0 μm, and then a clear coating film is formed on top of the glossy coating film to obtain a multi-layer coating film in which the 60-degree specular gloss is 100 or higher. The upper limit of the 60-degree specular gloss is not particularly limited, but is, for example, 250.

[0055] In this invention, the 60-degree specular gloss of a multi-layer coating obtained by laminating a clear coating on a glossy coating obtained by coating to a dry film thickness of 0.1 to 3.0 μm is defined. However, this does not mean that the glossy coating thickness is within the above range in all cases of 0.1 to 3.0 μm. Rather, the definition refers to the 60-degree specular gloss when the film thickness is within any of the above ranges.

[0056] Specular gloss refers to the ratio of specular reflection from an object's surface to specular reflection from a reference surface (glass with a refractive index of 1.567), and is a numerical value defined in JIS-Z8741. Specifically, it is measured using a gloss meter, where a light beam with a specified angle of incidence and aperture is incident on the sample surface, and the light beam with a specified angle of aperture reflected in the specular reflection direction is measured by a light receiver. In this specification, it is defined as 60-degree specular gloss (60° gloss) measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). The higher the 60-degree specular gloss value, the higher the gloss of the coating.

[0057] Method for forming a multi-layer coating The present invention provides a method for forming a multilayer coating film, which includes applying an aqueous glossy coating composition (X) to a workpiece to form a glossy coating film, and applying a clear coating composition (Y) to the formed cured or uncured glossy coating film to form a clear coating film.

[0058] Object to be coated The object to be coated is not particularly limited. Examples of such objects include the exterior panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and the exterior panels of household electrical appliances such as mobile phones and audio equipment. Of these, the exterior panels of automobile bodies and automobile parts are preferred. The materials of these objects to be coated are not particularly limited. Examples include metallic materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; plastic materials such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various types of FRP; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Of these, metallic and plastic materials are preferred.

[0059] Furthermore, the surface to which the multi-layer coating is applied may be a metal surface such as the exterior panels of an automobile body, automobile parts, household electrical appliances, or steel plates or other metal substrates that make up these, which may have been subjected to surface treatments such as phosphate treatment, chromate treatment, or composite oxide treatment. If the material of the object to be coated is metal, it is preferable that a primer coating is formed on the surface-treated metal material. An intermediate coating may also be formed on top of the primer coating. The above-mentioned primer coating and intermediate coating can be formed, for example, if the object to be coated is an automobile body, using known primer and intermediate coating paints that are normally used in automobile body painting.

[0060] For example, an electrodeposition paint, preferably a cationic electrodeposition paint, can be used as the primer paint for forming the undercoat film.

[0061] Specifically, for forming the intermediate coating film, a thermosetting paint known to be used can be used, which mainly consists of a base resin, a binder resin such as a crosslinking agent, a pigment, and a solvent such as an organic solvent and / or water.

[0062] Examples of base resins used in intermediate coatings include thermosetting resins and room-temperature curing resins, but from the viewpoint of water resistance, chemical resistance, and weather resistance, thermosetting resins are preferable.

[0063] Suitable base resins include those with good weather resistance and transparency, such as acrylic resins, polyester resins, epoxy resins, and urethane resins.

[0064] Examples of the acrylic resins mentioned above include (meth)acrylic acid esters having functional groups such as carboxyl groups, hydroxyl groups, amide groups, methylol groups, and epoxy groups, as well as resins obtained by copolymerizing other (meth)acrylic acid esters, styrene, and the like.

[0065] As the polyester resin, for example, polyester resins obtained by the condensation reaction of polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, trimethylolpropane, and pentaerythritol with polyhydric carboxylic acid components such as adipic acid, isophthalic acid, terephthalic acid, phthalic anhydride, hexahydrophthalic anhydride, and trimellitic anhydride can be used.

[0066] Examples of epoxy resins include so-called bisphenol A type epoxy resins, which are produced by the condensation reaction of bisphenol A and epichlorohydrin.

[0067] Examples of urethane resins include compounds obtained by the addition reaction of a diisocyanate compound with a polyhydric alcohol, and compounds obtained by reacting the above-mentioned acrylic resin, polyester resin, or epoxy resin with a diisocyanate compound to increase its molecular weight.

[0068] The intermediate coating paint may be either a water-based paint or a solvent-based paint, but from the viewpoint of reducing the VOC content of the paint, a water-based paint is preferable. When the intermediate coating paint is a water-based paint, the base resin used may contain a sufficient amount of hydrophilic groups, such as carboxyl groups, hydroxyl groups, methylol groups, amino groups, sulfonic acid groups, polyoxyethylene bonds, etc., more preferably carboxyl groups or hydroxyl groups, and even more preferably carboxyl groups, to make the resin water-soluble or water-dispersible. The base resin can be made water-soluble or water-dispersible by neutralizing the hydrophilic groups to form an alkali salt. The amount of hydrophilic groups, such as carboxyl groups, is not particularly limited and can be arbitrarily selected depending on the degree of water solubility or water dispersion, but generally, it can be set to about 10 mg KOH / g or more, preferably in the range of 30 to 200 mg KOH / g, based on the acid value. Examples of alkaline substances used for neutralization include sodium hydroxide and amine compounds.

[0069] Furthermore, the aqueous dispersion of the above resin can also be carried out by emulsion polymerization of the polymerizable component in the presence of a surfactant or a water-soluble resin. Alternatively, the resin can be obtained by dispersing it in water in the presence of, for example, an emulsifier. In this aqueous dispersion, the base resin may not contain any of the hydrophilic groups, or it may contain fewer hydrophilic groups than the water-soluble resin.

[0070] The aforementioned crosslinking agent is used to crosslink and harden the above-mentioned base resin by heating, and the crosslinking component exemplified in the aqueous glossy coating composition (X) can be used.

[0071] The ratio of each component in the intermediate coating can be arbitrarily selected as needed, but from the viewpoint of water resistance, finish, etc., it is generally preferable that the base resin and crosslinking agent be in the range of 60 to 90% by mass and 10 to 40% by mass, based on the total mass of both components.

[0072] The aforementioned pigment provides color and opacity to the intermediate coating film formed by the intermediate coating paint. The type and amount of the pigment can be adjusted as appropriate according to the desired hue or brightness of the multi-layer coating film.

[0073] The cured film thickness of the intermediate coating obtained by the intermediate coating paint is preferably 3 μm to 50 μm, more preferably 5 to 45 μm, and even more preferably 8 to 40 μm, from the viewpoint of the opacity of the substrate and the metallic gloss of the multi-layer coating.

[0074] The intermediate coating can be applied according to conventional methods. If the intermediate coating is a water-based coating, for example, deionized water and, if necessary, additives such as thickeners and defoamers can be added to the intermediate coating to adjust the solid content to about 30-70% by mass and the viscosity to 500-6000 cps / 6 rpm (Type B viscometer). Then, the coating can be applied to the surface of the object to be coated by spray painting (air spray, airless spray), rotary atomization painting, inkjet painting, etc. These coating methods may also be electrostatically applied if necessary. Preferably, the method for applying the intermediate coating is electrostatically applied rotary atomization painting or inkjet painting.

[0075] After applying the intermediate coat paint, and before applying the water-based glossy paint composition (X) to the intermediate coat film, 1) the intermediate coat paint may be completely cured at a high temperature, 2) the intermediate coat paint may be partially cured at a low temperature, or 3) the intermediate coat paint may be left at ambient temperature for several minutes to allow the solvent to evaporate. Step 1) is also called baking, and the baking temperature is, for example, 120-200°C, preferably around 140°C, and the baking time is, for example, 20 minutes to 1 hour. Step 2) is also called preheating, and the preheating temperature is, for example, 50-100°C, preferably around 80°C, and the preheating time is, for example, 30 seconds to 10 minutes. Step 3) is called setting. The standing time is, for example, 15-30 minutes. The ambient temperature is, for example, 15-35°C.

[0076] Coating of a water-based glossy paint composition (X) for inkjet painting. This disclosure also provides a method for forming a multilayer coating film using the above-mentioned aqueous glossy coating composition (X) for inkjet coating.

[0077] The water-based glossy paint composition (X) for inkjet coating is applied by inkjet coating. After applying the water-based glossy paint composition (X) and before applying the clear paint composition (Y), it may be preheated and set up in the same manner as described for the intermediate coat paint.

[0078] In some preferred embodiments, an aqueous glossy paint composition (X) for inkjet coating is applied by inkjet coating using a jet dispenser. A jet dispenser is a device that continuously dispenses liquid material in droplet form at high speed. It dispenses liquid material in droplet form from a discharge port by rapidly advancing a plunger, which is a valve body, toward the discharge port within a liquid chamber having a discharge port, and then abruptly stopping it. Examples of drive methods for these plunger parts include mechanical and piezo-jet types that utilize the reciprocating motion of the plunger and rod parts by air pressure, spring force, or displacement of a piezoelectric element. A piezo type is an electromechanical conversion method or piezoelectric element method that drives a piezoelectric element to eject ink or paint inside the element as minute droplets from a nozzle.

[0079] The frequency at which liquid droplets are dispensed from the dispenser is preferably in the range of 10 to 10,000 Hz, more preferably in the range of 30 to 5,000 Hz, and even more preferably in the range of 50 to 3,000 Hz, from the viewpoint of suppressing the occurrence of paint streaks and improving painting efficiency.

[0080] When dispensing droplets from the dispenser, the distance between the dispensing port and the object to be coated is preferably in the range of 0.1 to 50 mm, more preferably in the range of 0.5 to 30 mm, and even more preferably in the range of 1 to 10 mm, from the viewpoint of suppressing the occurrence of paint streaks and improving the finish.

[0081] From the viewpoint of ensuring stable paint supply, the supply pressure is preferably in the range of 0.001 to 10 MPa, more preferably in the range of 0.005 to 5.0 MPa, and even more preferably in the range of 0.01 to 1.0 MPa.

[0082] The scanning speed of the dispenser is preferably in the range of 10 to 1500 mm / s, more preferably in the range of 50 to 1000 mm / s, and even more preferably in the range of 100 to 800 mm / s, from the viewpoint of suppressing the occurrence of paint streaks and improving painting efficiency.

[0083] The pitch when scanning the dispenser is preferably in the range of 0.001 to 1.0 mm, more preferably in the range of 0.005 to 1.0 mm, and even more preferably in the range of 0.01 to 1.0 mm, from the viewpoint of coating efficiency and the like.

[0084] The thickness of the glossy coating film is preferably 0.1 to 3.0 μm, and more preferably 0.15 to 2.5 μm, as a dry film thickness.

[0085] In the method for forming a multilayer coating film of the present invention, a clear coating film is formed by applying a clear coating composition (Y) onto a glossy coating film obtained by applying an aqueous glossy coating composition (X).

[0086] Clear coating composition (Y) The clear coating composition (Y) can be any known thermosetting clear coat coating composition. Examples of such thermosetting clear coat coating compositions include organic solvent-type thermosetting coating compositions containing a base resin having a crosslinkable functional group and a crosslinking agent, aqueous thermosetting coating compositions, powder thermosetting coating compositions, and the like.

[0087] Examples of crosslinkable functional groups in the above-mentioned base resin include carboxyl groups, hydroxyl groups, epoxy groups, and silanol groups. Examples of base resin types include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, and fluororesins. Examples of crosslinking agents include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

[0088] Preferred base resin / crosslinking agent combinations for the clear coating composition (Y) include carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / polyisocyanate compound, hydroxyl group-containing resin / blocked polyisocyanate compound, and hydroxyl group-containing resin / melamine resin.

[0089] Furthermore, the clear coating composition (Y) may be a one-component coating or a multi-component coating such as a two-component coating.

[0090] In particular, the clear coating composition (Y) is preferably a two-component clear coating containing the following hydroxyl group-containing resin and polyisocyanate compound, from the viewpoint of the adhesion of the resulting coating film.

[0091] Hydroxyl group-containing resin Any conventionally known resin containing hydroxyl groups can be used without limitation as the hydroxyl group-containing resin. Examples of such hydroxyl group-containing resins include hydroxyl group-containing acrylic resins, hydroxyl group-containing polyester resins, hydroxyl group-containing polyether resins, and hydroxyl group-containing polyurethane resins. Preferred examples include hydroxyl group-containing acrylic resins and hydroxyl group-containing polyester resins, with hydroxyl group-containing acrylic resins being particularly preferred.

[0092] The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 80 to 200 mgKOH / g, and more preferably in the range of 100 to 180 mgKOH / g, from the viewpoint of scratch resistance and water resistance of the coating film.

[0093] The weight-average molecular weight of the hydroxyl group-containing acrylic resin is preferably in the range of 2,500 to 40,000, and more preferably in the range of 5,000 to 30,000, from the viewpoint of acid resistance and smoothness of the coating film.

[0094] In this specification, the weight-average molecular weight is calculated from the chromatogram measured by gel permeation chromatography, using the molecular weight of standard polystyrene as a reference. The gel permeation chromatograph used was "HLC8120GPC" (manufactured by Tosoh Corporation). Four columns were used: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all product names manufactured by Tosoh Corporation). The measurements were performed under the following conditions: mobile phase; tetrahydrofuran, measurement temperature; 40°C, flow rate; 1 cc / min, detector; radioisotope (RI).

[0095] The glass transition temperature of the hydroxyl group-containing acrylic resin is preferably in the range of -40°C to 20°C, and particularly preferably in the range of -30°C to 10°C. If the glass transition temperature is -40°C or higher, the hardness of the coating film is sufficient, and if it is 20°C or lower, the smoothness of the coating surface can be maintained.

[0096] Polyisocyanate compounds Polyisocyanate compounds are compounds having at least two isocyanate groups in one molecule, and examples include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of said polyisocyanates.

[0097] Examples of the above aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer diisocyanate, and 2,6-methyl diisocyanatohexanoate (common name: lysine diisocyanate). Examples include aliphatic diisocyanates such as isocyanates; 2,6-diisocyanatohexanoate 2-isocyanatoethyl, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0098] Examples of the alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), and 2-methyl-1,3-cyclohexylene diisocyanate. Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, methylenebis(4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2 ,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane,2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane,3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane,5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane,6-(2-isocyana Examples include alicyclic triisocyanates such as sodium ethyl (2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0099] Examples of the aforementioned aromatic aliphatic polyisocyanates include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0100] Examples of the aromatic polyisocyanates include aromatic diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyanate, 4,4'-diphenylenediisocyanate, 1,5-naphthalenediisocyanate, 2,4-tolyleneenediisocyanate (common name: 2,4-TDI) or 2,6-tolyleneenediisocyanate (common name: 2,6-TDI) or mixtures thereof, 4,4'-toluidinediisocyanate, and 4,4'-diphenyletherdiisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0101] Furthermore, examples of polyisocyanate derivatives include the dimers, trimers, biuret, allophanate, uretodione, uretoimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), crude TDI, and others. These polyisocyanate derivatives may be used alone or in combination of two or more.

[0102] The above-mentioned polyisocyanates and their derivatives may be used individually or in combination of two or more types.

[0103] Among aliphatic diisocyanates, hexamethylene diisocyanate compounds and among alicyclic diisocyanates, 4,4'-methylenebis(cyclohexyl isocyanate) can be suitably used. In particular, derivatives of hexamethylene diisocyanate are optimal from the viewpoint of adhesion, compatibility, etc.

[0104] Furthermore, as the polyisocyanate compound, a prepolymer may be used that is obtained by reacting the above-mentioned polyisocyanate and its derivatives with a compound having an active hydrogen group, such as a hydroxyl group or an amino group, which can react with the polyisocyanate, under conditions of isocyanate group excess. Examples of compounds that can react with the polyisocyanate include polyhydric alcohols, low molecular weight polyester resins, amines, and water.

[0105] Furthermore, as the polyisocyanate compound, a blocked polyisocyanate compound can also be used, which is a compound in which the isocyanate groups in the above-mentioned polyisocyanate and its derivatives are blocked with a blocking agent.

[0106] Examples of the above-mentioned blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylolurea, methylolmelamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl acrylate. Alcohol-based compounds such as roxyethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiophenol Mercaptans such as ethylthiophenol; acid amides such as acetanilide, acetanisidide, acetotoluid, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; imides such as succinimide, phthalimide, and maleimide; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole;Examples of azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamic acid ester compounds such as phenyl N-phenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole compounds. Examples of the above-mentioned azole compounds include pyrazoles or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazoles or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0107] When performing the blocking reaction (reacting with the blocking agent), a solvent may be added as needed. Suitable solvents for the blocking reaction are those that are not reactive with isocyanate groups. Examples include acetone, ketones such as methyl ethyl ketone, esters such as ethyl acetate, and solvents such as N-methyl-2-pyrrolidone (NMP).

[0108] Polyisocyanate compounds can be used individually or in combination of two or more.

[0109] Polyisocyanate compounds can be used alone or in combination of two or more. In the present invention, from the viewpoint of curability and scratch resistance of the coating film, the equivalent ratio (OH / NCO) of the hydroxyl groups of the hydroxyl group-containing resin to the isocyanate groups of the polyisocyanate compound is preferably in the range of 0.5 to 2.0, and more preferably in the range of 0.8 to 1.5.

[0110] When using a two-component clear coating composition (Y) containing a hydroxyl group-containing resin and a polyisocyanate compound, it is preferable for the hydroxyl group-containing resin and the polyisocyanate compound to be in a separated form for storage stability, and the two are mixed immediately before use.

[0111] A one-component paint may be used as the clear coating composition (Y). Examples of base resin / crosslinking agent combinations in the one-component paint include carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / blocked polyisocyanate compound, and hydroxyl group-containing resin / melamine resin.

[0112] The clear coating composition (Y) may further contain, as needed, solvents such as water or organic solvents, curing catalysts, defoamers, ultraviolet absorbers, and other additives.

[0113] The above clear coating composition (Y) may contain coloring pigments as appropriate, within a range that does not impair transparency. As coloring pigments, one or more conventionally known pigments for inks and coatings may be used. The amount added may be determined as appropriate, but is 30 parts by mass or less, preferably 0.01 to 10 parts by mass, per 100 parts by mass of the vehicle-forming resin composition in the clear coating composition (Y).

[0114] The form of the clear coating composition (Y) is not particularly limited, but it is usually used as an organic solvent-type coating composition. In this case, various organic solvents for coatings can be used, such as aromatic or aliphatic hydrocarbon solvents; ester solvents; ketone solvents; ether solvents, etc. The organic solvent used may be the same one used in the preparation of the hydroxyl group-containing resin, etc., or additional solvents may be added as appropriate.

[0115] The solid content concentration of the clear coating composition (Y) is preferably about 30 to 70% by mass, and more preferably in the range of 40 to 60% by mass.

[0116] The aforementioned clear coating composition (Y) is applied to the glossy coating film. The application of the clear coating composition (Y) is not particularly limited and can be carried out in the same manner as the intermediate coating, for example, by spraying, rotary atomization, or curtain coating. These coating methods may be electrostatically applied if necessary. Preferably, the application method for the clear coating composition (Y) is electrostatic rotary atomization or inkjet coating. The amount of clear coating composition (Y) applied is usually preferably such that the cured film thickness is approximately 10 to 50 μm.

[0117] In some preferred embodiments, the method for forming a multilayer coating of the present invention includes applying an intermediate coating paint (X) to a workpiece to form an intermediate coating; applying an aqueous glossy coating composition (X) for inkjet painting onto the formed intermediate coating to form a glossy coating; and applying a clear coating composition (Y) onto the formed glossy coating to form a clear coating.

[0118] In some preferred embodiments, the method for forming a multilayer coating of the present invention involves, from the viewpoint of adhesion and water resistance of the multilayer coating, applying an intermediate coating to the object to be coated, applying the aqueous glossy coating composition (X) onto the formed uncured intermediate coating to form a glossy coating, applying the formed uncured glossy coating to form an uncured clear coating, and simultaneously curing these three uncured coatings by heating.

[0119] Heating can be carried out by known means, for example, drying furnaces such as hot air furnaces, electric furnaces, and infrared induction heating furnaces can be used. The heating temperature is preferably in the range of 70 to 150°C, more preferably 80 to 140°C. The heating time is not particularly limited, but is preferably in the range of 10 to 40 minutes, more preferably 20 to 30 minutes.

[0120] The present invention includes a multilayer coating comprising a glossy coating film formed from an aqueous glossy coating composition (X) on a substrate, and a clear coating film formed from a clear coating composition (Y) on the glossy coating film. The aqueous glossy coating composition (X), the clear coating composition (Y), and the method for forming the multilayer coating are as described above.

[0121] The aqueous glossy coating composition (X), the method for forming a multilayer coating film, and the multilayer coating film of the present invention can be applied to various industrial products, particularly the inner and outer panels of automobile bodies and automobile parts. The present invention is not limited to the embodiments described above, and various modifications are possible based on the technical concept of the present invention.

[0122] For example, the configurations, methods, processes, shapes, materials, and numerical values ​​listed in the above-mentioned embodiments and the following examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used as needed. Furthermore, the configurations, methods, processes, shapes, materials, and numerical values ​​listed in the above-mentioned embodiments and the following examples can be combined with each other, as long as they do not depart from the spirit of the present invention. [Examples]

[0123] The present invention will be described more specifically below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Note that "parts" and "%" are all based on mass.

[0124] [1] Preparation of base material Object to be coated A degreased and zinc-phosphate treated steel plate (JIS G3141, size 400mm x 300mm x 0.8mm) was electrodeposited with cationic electrodeposition paint "Elecron GT-10" (product name: manufactured by Kansai Paint Co., Ltd., which uses a blocked polyisocyanate compound as a crosslinking agent in an epoxy resin polyamine-based cationic resin) to a film thickness of 20 μm based on the cured coating. The coating was then heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposited coating film. The electrodeposited surface of the obtained steel plate was electrostatically coated with "WP-523H" (product name, manufactured by Kansai Paint Co., Ltd., an aqueous intermediate coating composition containing acrylic emulsion, polyester resin, and melamine) using a rotary atomizing electrostatic coating machine to achieve a cured film thickness of 20 μm. After being left at room temperature for 10 minutes, it was preheated at 80°C for 3 minutes to prepare the substrate.

[0125] [2] Preparation of paint Preparation of viscosity modifier diluent (x4-1) Manufacturing Example 1 A mixture consisting of 20 parts methacrylic acid, 19.5 parts acrylate of a 60-mol adduct of n-octadecyl alcohol ethylene oxide, 60 parts propyl acrylate, and 0.5 parts diacrylate of a 15-mol adduct of ethylene glycol ethylene oxide was added to 350 parts methyl triglycol from a dropping funnel at a constant rate over 1.5 hours, while uniformly stirring to allow the reaction to proceed. The reaction temperature was maintained at 80-90°C. After the addition was complete, the mixture was kept at the same temperature for 3 hours and then cooled to 40°C to obtain a diluted solution of acrylic aggregate viscosity modifier (x4-1) with a solid content of 20% by mass.

[0126] Manufacturing Example 2 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and two dropping devices, 15.4 parts (10 parts solids) of the following macromonomer solution, 20 parts of ethylene glycol monobutyl ether, and 30 parts of diethylene glycol monoethyl ether acetate were charged, and the temperature was raised to 85°C while blowing nitrogen gas into the solution. Next, in the reaction vessel maintained at the same temperature, a mixture consisting of 31.5 parts of N,N-dimethylacrylamide, 31.5 parts of N-isopropylacrylamide, 27 parts of 2-hydroxyethyl acrylate, 10 parts of ethylene glycol monobutyl ether, and 40 parts of diethylene glycol monoethyl ether acetate, and a mixture consisting of 0.15 parts of "Perbutyl O" (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polymerization initiator, t-butylperoxy-2-ethylhexanoate) and 20 parts of ethylene glycol monobutyl ether were simultaneously added dropwise to the reaction vessel over 4 hours. After the dropwise addition was complete, the mixture was stirred at the same temperature for 2 hours to allow it to mature. Next, a mixture consisting of 0.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) and 15 parts of ethylene glycol monobutyl ether was added dropwise to a reaction vessel maintained at the same temperature over 1 hour. After the addition was complete, the mixture was stirred at the same temperature for 1 hour to allow it to mature. Then, while adding ethylene glycol monobutyl ether, the mixture was cooled to 30°C to obtain a copolymer solution with a solid content of 35%. The weight-average molecular weight of the obtained copolymer was 310,000. 215 parts of deionized water were added to the obtained copolymer solution to obtain a diluted acrylic association type viscosity modifier solution (x4-2) with a solid content of 20%.

[0127] Macromonomer solution: In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, 16 parts of ethylene glycol monobutyl ether and 3.5 parts of 2,4-diphenyl-4-methyl-1-pentene were charged. Nitrogen gas was passed through the gas phase, and the temperature was raised to 160°C while stirring. Once 160°C was reached, a mixture consisting of 30 parts n-butyl methacrylate, 40 parts 2-ethylhexyl methacrylate, 30 parts 2-hydroxyethyl methacrylate, and 7 parts di-tert-amyl peroxide was added dropwise over 3 hours, and the mixture was stirred at the same temperature for 2 hours. The mixture was then cooled to 30°C and diluted with ethylene glycol monobutyl ether to obtain a macromonomer solution with a solid content of 65%. The obtained macromonomer had a hydroxyl value of 129 mgKOH / g and a number-average molecular weight of 2,300.

[0128] Manufacturing of a water-based glossy paint composition (X) Example 1 "Leaf Powder 49CJ-1120" (Product name, manufactured by Oike Metallic Design Co., Ltd., indium particles, cumulative 50% volume particle size (D50)) 100 parts (20 parts solids) of approximately 0.3 μm, 20% solids content, dispersed in propylene glycol monomethyl ether; 1.8 parts (1.8 parts solids) of BYK-348 (trade name, manufactured by BYK, silicone-based surface modifier, 100% solids content); 1.8 parts (1.8 parts solids) of "Prysurf A208F" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous solution of polyoxyethylene alkyl (C8) ether phosphate ester with 99% solids content); 9 parts (1.8 parts solids) of the acrylic aggregate viscosity modifier diluent (x4-1) obtained in Production Example 1; 51.9 parts of 1% dimethylethanolamine aqueous solution; and 340 parts of deionized water were added and stirred to produce an aqueous glossy coating composition (X-1) with a solids content of 5.0% by mass.

[0129] Examples 2-6, Comparative Example 1 Each aqueous glossy coating composition (X-2) to (X-7) was obtained in the same manner as in Example 1, except that the amount and composition of each component were as shown in Table 1 below. [Table 1] (*1) "Hydroshine WS-3001": Product name, water-based vapor-deposited aluminum flake pigment, manufactured by Eckart, solids content: 10%, internal solvent: isopropanol, cumulative 50% volume particle size (D50): approximately 13 μm, thickness: 0.05 μm. (*2) "BYK-381": Product name, manufactured by BYK, acrylic surface modifier, solids content 52%, internal solvent: dipropylene glycol monomethyl ether. (*3) "BYK-190": Product name, manufactured by BYK, styrene-based block copolymer, solids content 40%.

[0130] Preparation of clear coating composition (Y) Manufacturing Example 3 "KINO-6510T" (product name, manufactured by Kansai Paint Co., Ltd., an acrylic resin-based organic solvent type clear coat paint containing hydroxyl group-containing acrylic resin and polyisocyanate compound) was used as the clear coat composition (Y-1).

[0131] [3] Preparation of test board Test Example 1 The aqueous glossy paint composition (X-1) prepared in [2] above was stirred for 1 minute using an ultrasonic disperser "UH-50" (product name, manufactured by MST Corporation). Next, the aqueous glossy coating composition (X-1) prepared in [1] above was filled into an "A-430 / X JET" (product name, manufactured by SSI JAPAN, tabletop high-speed coating device and high-viscosity micro-piezo jet dispenser, discharge port diameter 70 μm). Then, the coating was applied to the workpiece under the conditions of frequency 132 Hz, speed 50 mm / s, pitch 0.3 mm, and distance between the discharge port and the workpiece 1 mm, to obtain a cured coating film thickness of 0.5 μm. After being left at room temperature for 3 minutes, preheating was performed at 80°C for 3 minutes to obtain an uncured glossy coating film.

[0132] Next, the clear coating composition (Y-1) prepared in [2] above was applied to the uncured glossy coating film using a mini-bell type rotary electrostatic coating machine under booth temperature of 23°C and humidity of 68% to a cured coating film thickness of 35 μm. After being left at room temperature for 7 minutes, it was heated in a hot air circulating drying oven at 140°C for 30 minutes to dry and cure, thereby producing the test panel of Test Example 1.

[0133] Test Examples 2-6, Comparative Test Example 1 Test panels for Test Examples 2-6 and Comparative Test Example 1 were prepared under the same conditions as Test Example 1, except that aqueous glossy paint compositions (X-2) to (X-7) were used instead of aqueous glossy paint composition (X-1) in Example 1.

[0134] Here, the film thickness of the dried glossy coating was calculated using the following formula. The same applies to the following examples. x = sc / sg / S * 10000 x: Film thickness [μm] sc: Painted solid content [g] sg: Paint film specific gravity [g / cm 3 ] S: Evaluation area of ​​coated solid content [cm²] 2 ] The solid content sc in the formula was calculated by the following method. Aluminum foil was prepared, its mass was measured, and then all areas except the 21 cm × 37 cm area were masked. In the preparation of the test plate described in [3] above, the object to be coated prepared in [1] above and the masked aluminum foil were placed side by side, and the aqueous glossy coating composition was applied to them. After that, the masking was removed, and the aluminum foil coated with the aqueous glossy coating composition was dried at 140°C for 30 minutes. After drying, the mass of the aluminum foil with the glossy coating film attached was weighed, and the solid content sc was calculated by subtracting the mass of the aluminum foil before coating. The specific gravity sg of the coating film in the formula was calculated using the specific gravity of each raw material (resin, pigment, additive, etc.) used in the water-based glossy coating composition. The specific gravity of the raw materials was determined by referring to the "Paint Raw Materials Handbook, 9th Edition" (Japan Paint Manufacturers Association), and if it was unclear, the literature value for the specific gravity of each compound was referred to. The specific gravity of resins and organic additives was approximated to 1. In the formula, the evaluation area S for the coated solid content is the area on the painted plate to which the glossy coating film is attached, and was calculated from the unmasked area of ​​the masked aluminum foil, which is 21 cm × 37 cm.

[0135] Mirror gloss (60° gloss) The 60° gloss value of the coating film on the test plate was measured using a gloss meter (micro-TRI-gloss, BYK-Gardner). A higher 60° gloss value indicates superior gloss. A value of 100 or higher was considered acceptable.

[0136] Paint streaks The test panels obtained above were visually inspected, and the paint streaks were evaluated according to the following evaluation criteria. ◎ and ○ indicate a pass. The evaluation results are shown in Table 1. -Evaluation Criteria- ◎: No paint streaks are visible at all. ○: Slight paint streaks are visible, but there are no practical problems. ×: Clear paint streaks are visible, posing a practical problem.

[0137] According to Table 1, the multi-layer coatings of Test Examples 1 to 6, formed using the aqueous glossy coating compositions (X-1) to (X-6) of Examples 1 to 6, passed both the specular gloss test and the paint streaking test. On the other hand, the multi-layer coating of Comparative Example 1, formed using Comparative Example 1's aqueous glossy coating composition (X-7), which uses vapor-deposited aluminum flake pigment as the glossy pigment in aqueous glossy coating composition (X), passed the specular gloss test but failed the paint streaking test.

Claims

1. A water-based glossy coating composition (X) for inkjet coating, comprising indium particles (x1), a surface modifier (x2), a pigment dispersant (x3), a viscosity modifier (x4), and water (x5), A water-based glossy coating composition (X) for inkjet coating, comprising 0.1 to 25 parts by mass of solids per 100 parts by mass of the total components of the water-based glossy coating composition (X).

2. The aqueous glossy coating composition (X) for inkjet coating according to claim 1, wherein the cumulative 50% volume particle size D50 of indium particles (x1) is 0.70 μm or less.

3. The aqueous glossy coating composition (X) for inkjet coating according to claim 1 or 2, wherein the content of indium particles (x1) is 70 parts by mass or more based on 100 parts by mass of the solid content of the aqueous glossy coating composition (X).

4. Forming a glossy coating film on a substrate by inkjet coating with the aqueous glossy coating composition (X) for inkjet coating described in any one of claims 1 to 3, and A clear coating is formed by applying a clear coating composition (Y) onto the glossy coating that is formed. A method for forming a multilayer coating film including the following.

5. A glossy coating film formed on a substrate, which is formed from the aqueous glossy coating composition (X) according to any one of claims 1 to 3, A clear coating formed on the aforementioned glossy coating film, and a clear coating formed from a clear coating composition (Y) A multi-layer coating film equipped with the following features.

6. The multilayer coating according to claim 5, wherein the thickness of the glossy coating as a dry film thickness is 0.1 to 3.0 μm.

7. The multilayer coating film according to claim 5, wherein the 60-degree specular gloss of the multilayer coating film is in the range of 100 to 250.

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