Water-based colored coating composition and method for forming multilayer coating film

Abstract

The purpose of the present disclosure is to provide an aqueous colored coating composition that has excellent discharge stability and has excellent drip resistance and image clarity in a coating film to be formed when coating is performed using a liquid discharge head, which controls discharging of the composition by changing the relative distance between a valve body and a discharge port.　The aqueous colored coating composition is for coating using the liquid discharge head, which controls discharging of the composition by changing the relative distance between the valve body and the discharge port, the aqueous colored coating composition having a viscosity (V1) of 20 to 100 mPa·s at a temperature of 23°C and a shear rate of 1,000 sec-1, and a viscosity (V2) of 5,000 to 40,000 mPa·s at a temperature of 23°C and a shear rate of 0.1 sec-1.

Description

[Technical Field]

[0001] The present disclosure relates to an aqueous colored coating composition and a method for forming a multilayer coating film using the aqueous colored coating composition. [Background technology]

[0002] A coating composition suitable for coating using a liquid ejection head that controls ejection by changing the relative distance between the valve body and the ejection port, and a method for forming a multilayer coating film using this coating composition have been investigated. For example, Patent Document 1 discloses a coating composition for precision coating (claim 1) that includes a film-forming resin dispersed in an aqueous medium, a crosslinking agent capable of undergoing a crosslinking reaction with the film-forming resin, a rheology modifier, a colorant, and a swelling solvent that swells the film-forming resin, wherein the solid content of the coating composition is less than 25 wt % based on the total weight of the coating composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 232011 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] The coating composition disclosed in Patent Document 1 leaves room for improvement in terms of the discharge stability of the coating composition, sagging of the coating film formed from the coating composition, and the like. Therefore, an object of the present disclosure is to provide an aqueous colored coating composition that exhibits excellent discharge stability when used in coating using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port, and that produces a coating film that exhibits excellent sagging resistance and vividness. [Means for solving the problem]

[0005] The present inventors have developed an aqueous colored coating composition that is applied using a liquid ejection head that controls ejection by changing the relative distance between a valve body and an ejection port, and the aqueous colored coating composition is applied at a temperature of 23°C and a shear rate of 1,000 sec -1 Viscosity (V1) of 20 to 100 mPa·s at a temperature of 23°C and a shear rate of 0.1 sec -1 The present inventors have discovered an aqueous colored coating composition having a viscosity (V2) of 5,000 to 40,000 mPa·s at 2000°C. [Effects of the Invention]

[0006] The aqueous colored coating composition of the present disclosure exhibits excellent discharge stability when applied using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port, and the formed coating film exhibits excellent sagging resistance and vividness. DETAILED DESCRIPTION OF THE INVENTION

[0007] Specifically, the present disclosure relates to the following aspects: [Aspect 1] An aqueous colored coating composition that is applied using a liquid ejection head that controls ejection by changing the relative distance between a valve body and an ejection port, The above aqueous colored coating composition was heated at a temperature of 23°C and a shear rate of 1,000 sec -1 Viscosity (V1) of 20 to 100 mPa·s at a temperature of 23°C and a shear rate of 0.1 sec -1 and a viscosity (V2) of 5,000 to 40,000 mPa·s. Water-based colored paint composition.

[0008] The aqueous colored coating composition has a predetermined viscosity (V1), and therefore has excellent discharge stability. If the aqueous colored coating composition has poor discharge stability, the coating film formed from the aqueous colored coating composition may have an uneven thickness, and may be inferior in smoothness, color reproducibility, etc., and may also have poor coating film performance. In addition, since the aqueous colored paint composition has a predetermined viscosity (V2), it is excellent in sag resistance and distinctness of image of the coating film formed from the aqueous colored paint composition.

[0009] [Aspect 2] The aqueous colored paint composition according to Aspect 1, wherein the solid content concentration of the aqueous colored paint composition is within the range of 10 to 25% by mass. Since the aqueous colored paint composition has a predetermined solid content concentration, it is excellent in discharge stability and distinctness of image of the coating film formed from the aqueous colored paint composition.

[0010] [Aspect 3] The aqueous colored paint composition according to Aspect 1 or 2, wherein tanδ (loss elastic modulus / storage elastic modulus) of the aqueous colored paint composition at a temperature of 23°C is within the range of 0.25 to 0.80. Since the aqueous colored paint composition has a predetermined tanδ, it is excellent in discharge stability and distinctness of image of the coating film formed from the aqueous colored paint composition.

[0011] [Aspect 4] Under the condition of a temperature of 23°C, with a shear rate of 0.1 sec -1 After holding for 50 seconds, the viscosity (V3) of the aqueous colored paint composition, changing the shear rate to 1,000 sec -1 After holding for 10 seconds, the viscosity (V4) of the aqueous colored paint composition, changing the shear rate to 0.1 sec -1 After holding for 10 seconds, the viscosity (V5) of the aqueous colored paint composition and the following formulas (1) and (2): 0.001 < V4 / V3 < 0.007 Formula (1) 30 < V5 / V4 < 200 Formula (2) satisfy The aqueous colored paint composition according to any one of Aspects 1 to 3.

[0012] Since the aqueous colored coating composition satisfies formula (1), it has a low viscosity (V4) at a shear rate when discharged from a liquid discharge head, making it easy to discharge the aqueous colored coating composition in controlled sizes from a liquid discharge head and providing excellent discharge stability.Furthermore, since the aqueous colored coating composition satisfies formula (2), the aqueous colored coating composition adhered to a substrate has a high viscosity (V5) at a shear rate corresponding to sagging, providing excellent sagging resistance for a coating film formed from the aqueous colored coating composition.

[0013] [Aspect 5] 5. The aqueous colored coating composition according to any one of Aspects 1 to 4, wherein the aqueous colored coating composition comprises an acrylic resin emulsion (A) and a viscosity modifier (B). The aqueous colored coating composition contains the acrylic resin emulsion (A) and the viscosity modifier (B), and therefore the coating film formed from the aqueous colored coating composition has excellent sagging resistance.

[0014] [Aspect 6] Step 1: A step of forming a colored coating film on a substrate by discharging the aqueous colored coating composition according to any one of Aspects 1 to 5 in proximity to the substrate using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port; Step 2: A step of applying a clear coating composition to the colored coating film to form a clear coating film; A method for forming a multilayer coating film, comprising:

[0015] The above-mentioned method for forming a multilayer coating film is excellent in the discharge stability of the aqueous colored coating composition, and the coating film formed from the aqueous colored coating composition is excellent in sagging resistance.

[0016] [Aspect 7] 7. The method for forming a multi-layer coating film according to aspect 6, wherein the colored coating film has a dry thickness in the range of 1.0 to 15.0 μm. In the above-mentioned method for forming a multilayer coating film, the colored coating film has a predetermined dry film thickness, and therefore the multilayer coating film has excellent image clarity.

[0017] The aqueous colored coating composition of the present disclosure and the method for forming a multilayer coating film using the aqueous colored coating composition (hereinafter, sometimes simply referred to as the "method for forming a multilayer coating film") will be described in detail below. [Aqueous colored paint composition] The aqueous colored coating composition of the present disclosure is applied using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port.

[0018] Examples of liquid ejection heads that control ejection by changing the relative distance between the valve body and the ejection port include those that eject the aqueous colored paint composition by shortening the relative distance between the valve body and the ejection port, and those that eject the aqueous colored paint composition by increasing the relative distance between the valve body and the ejection port.

[0019] The liquid ejection head may be of an on-demand type (for example, a piezo type, a thermal type, or a bulb type), a continuous type, or the like, with the on-demand type, and particularly the piezo type, being preferred because it has excellent ejection properties for high-viscosity aqueous colored coating compositions. An example of the piezo type liquid ejection head is the piezo jet dispenser X JET (high viscosity liquid compatible model) manufactured by SSI JAPAN.

[0020] The above aqueous colored coating composition was heated at a temperature of 23°C and a shear rate of 1,000 sec -1 The aqueous colored coating composition has a viscosity (V1) of 20 to 100 mPa·s, preferably 30 to 60 mPa·s, and more preferably 45 to 60 mPa·s, thereby providing excellent ejection stability from a liquid ejection head.

[0021] The above aqueous colored coating composition was subjected to a temperature of 23°C and a shear rate of 0.1 sec -1The aqueous colored coating composition has a viscosity (V2) of 5,000 to 40,000 mPa·s, preferably 11,000 to 35,000 mPa·s, and more preferably 25,000 to 30,000 mPa·s, thereby providing the aqueous colored coating composition with excellent discharge stability and coating films formed from the aqueous colored coating composition with excellent sagging resistance.

[0022] The aqueous colored coating composition has a tan δ (loss modulus / storage modulus) of preferably 0.25 to 0.80, more preferably 0.30 to 0.70, and even more preferably 0.35 to 0.70 at a temperature of 23° C. This provides the aqueous colored coating composition with excellent discharge stability, and the coating film formed from the aqueous coating composition with excellent image clarity. The methods for measuring the viscosity (V1), viscosity (V2) and tan δ will be explained in the examples.

[0023] The above aqueous colored coating composition was subjected to a shear rate of 0.1 sec under the condition of a temperature of 23°C. -1 The viscosity (V3) after holding at 1000 s for 50 s and the shear rate -1 The viscosity (V4) after 10 seconds was measured and the shear rate was changed to 0.1 sec. -1 and the viscosity (V5) after being held for 10 seconds, V4 / V3 is preferably greater than 0.001, more preferably greater than 0.002, and even more preferably greater than 0.003, and is preferably less than 0.007, more preferably less than 0.006, and even more preferably less than 0.005. This reduces the viscosity (V4) at the shear rate when discharged from the liquid discharge head, making it easier to discharge the aqueous colored coating composition in controlled sizes from the liquid discharge head, and resulting in excellent discharge stability of the aqueous colored coating composition.

[0024] Furthermore, V5 / V4 is preferably greater than 30, more preferably greater than 50, and even more preferably greater than 60, and is preferably less than 200, more preferably less than 180, and even more preferably less than 160. This means that the aqueous colored coating composition adhered to the substrate has a high viscosity (V5) at a shear rate corresponding to sagging, and the coating film formed from the aqueous colored coating composition has excellent sagging resistance. The methods for measuring the viscosity (V3), viscosity (V4) and viscosity (V5) will be explained in the examples.

[0025] The aqueous colored coating composition preferably has a solids concentration of 10 to 25% by mass, more preferably 10 to 20% by mass, and even more preferably 10 to 16% by mass, which provides the aqueous colored coating composition with excellent discharge stability and coating films formed from the aqueous coating composition with excellent image clarity.

[0026] In this specification, the solid content concentration can be calculated by weighing out the object to be measured (e.g., an aqueous colored paint composition) into a heat-resistant container such as an aluminum foil cup, spreading the object to be measured on the bottom of the container, drying it at 110°C for 1 hour, weighing the mass of the components in the object to be measured that remain after drying, and determining the ratio of the mass of the components in the object to the total mass of the object to be measured before drying.

[0027] The composition of the aqueous colored coating composition is not particularly limited as long as it has the above-mentioned viscosity, but it can contain a resin such as an acrylic resin, a polyester resin, an alkyd resin, a polyurethane resin, an epoxy resin, a silicone resin, or any combination thereof.

[0028] The resin can be an emulsion, and can include, for example, an acrylic resin emulsion, a polyester resin emulsion, an alkyd resin emulsion, a polyurethane resin emulsion, an epoxy resin emulsion, a silicone resin emulsion, any combination thereof, and the like. The resin preferably contains an acrylic resin emulsion (acrylic resin emulsion (A)).

[0029] The acrylic resin emulsion (A) is an acrylic resin emulsified and dispersed in an aqueous medium, and examples thereof include emulsions produced by emulsion polymerization of a polymerizable unsaturated monomer mixture. The acrylic resin emulsion (A) is preferably a core-shell emulsion consisting of a core portion made of copolymer (I) and a shell portion made of copolymer (II). Furthermore, it is preferable from the viewpoint of improving the appearance and water resistance of the resulting coating film that the copolymer (I) is obtained by copolymerizing a polymerizable unsaturated monomer (a1) having two or more polymerizable unsaturated groups in one molecule with a polymerizable unsaturated monomer (a2) other than the polymerizable unsaturated monomer (a1), and that the copolymer (II) is obtained by copolymerizing a plurality of polymerizable unsaturated monomers (a3).

[0030] Examples of the polymerizable unsaturated monomer (a1) include ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, allyl (meth)acrylate, divinylbenzene, trimethylolpropane triacrylate, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, and combinations thereof. In this specification, "(meth)acrylate" means acrylate and / or methacrylate.

[0031] The polymerizable unsaturated monomer (a2) other than the polymerizable unsaturated monomer (a1) (hereinafter, sometimes simply referred to as "polymerizable unsaturated monomer (a2)") is a monomer having one polymerizable unsaturated group copolymerizable with the polymerizable unsaturated monomer (a1) in one molecule, and includes compounds having, for example, a vinyl group, a (meth)acryloyl group, etc. as the polymerizable unsaturated group.

[0032] Specific examples of the polymerizable unsaturated monomer (a2) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. Alkyl or cycloalkyl (meth)acrylates such as acrylate, isostearyl acrylate (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, and cyclododecyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth)acrylate; vinyls such as styrene, α-methylstyrene, and vinyl toluene. Aromatic compounds; polymerizable unsaturated monomers having an alkoxysilyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, and γ-(meth)acryloyloxypropyltriethoxysilane; perfluoroalkyl (meth)acrylates, such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; polymerizable unsaturated monomers having a fluorinated alkyl group, such as fluoroolefins; maleimide groups Monomers having a photopolymerizable functional group such as those mentioned above; vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, and vinyl acetate; carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; nitrogen-containing polymerizable unsaturated monomers such as (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and adducts of glycidyl (meth)acrylate and amines;Monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; (meth)acrylic acid having a polyoxyethylene chain with a hydroxyl group at the molecular terminal; acrylates and other hydroxyl group-containing polymerizable unsaturated monomers; epoxy group-containing polymerizable unsaturated monomers such as glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, and allyl glycidyl ether; (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal; 2-acrylamido-2-methyl Sulfonic acid group-containing polymerizable unsaturated monomers such as methylpropanesulfonic acid, allylsulfonic acid, sodium styrenesulfonate, sulfoethyl methacrylate, and its sodium or ammonium salts; phosphoric acid group-containing polymerizable unsaturated monomers such as 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, and 2-methacryloyloxypropyl acid phosphate; 2-hydroxy-4-(3-methacryloyl) Monomers having an ultraviolet absorbing functional group, such as 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, and 2-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole;4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidin UV-stable monomers such as 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, and the like; carbonyl group-containing monomer compounds such as acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrene, and vinyl alkyl ketones having 4 to 7 carbon atoms (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), and the like, as well as combinations thereof;

[0033] When producing the copolymer (I), the content of the polymerizable unsaturated monomer (a1) is preferably in the range of 0.1 to 20 mass%, more preferably 0.2 to 10 mass%, and even more preferably 0.7 to 4 mass%, based on the total mass of the polymerizable unsaturated monomer (a1) and the polymerizable unsaturated monomer (a2). The content of the polymerizable unsaturated monomer (a2) is preferably in the range of 80 to 99.9 mass%, more preferably 90 to 99.8 mass%, and even more preferably 96 to 99.3 mass%, based on the total mass of the polymerizable unsaturated monomer (a1) and the polymerizable unsaturated monomer (a2), from the viewpoints of stability during production and improvement of the water resistance, weather resistance, etc. of the resulting coating film.

[0034] The polymerizable unsaturated monomers (a3) ​​forming the shell portion of the copolymer (II) can be selected from those listed for the polymerizable unsaturated monomers (a2). From the viewpoint of ensuring the stability of the resulting core-shell emulsion in an aqueous medium, it is preferable that the shell portion of the copolymer (II) contains a carboxyl group-containing monomer as the polymerizable unsaturated monomer (a3). Acrylic acid and / or methacrylic acid are particularly suitable as the carboxyl group-containing monomer. From the viewpoints of the stability of the emulsion resin in an aqueous medium and the water resistance of the resulting coating film, the amount of the carboxyl group-containing monomer is preferably 1 to 40% by mass, more preferably 6 to 25% by mass, and even more preferably 7 to 19% by mass, based on the total mass of the polymerizable unsaturated monomers (a3). This is advantageous in terms of improving storage stability and the water resistance of the resulting coating film.

[0035] Furthermore, from the viewpoint of ensuring the stability of the resulting emulsion resin in an aqueous medium, it is preferable that the multiple polymerizable unsaturated monomers (a3) ​​forming the shell portion of the copolymer (II) contain the above-mentioned hydroxyl group-containing monomer as at least a portion of their components, in order to improve the stability of the emulsion resin in an aqueous medium. Particularly suitable hydroxyl group-containing monomers are 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. From the viewpoints of the stability of the emulsion resin in an aqueous medium and the water resistance of the resulting coating film, the amount of the hydroxyl group-containing monomer is generally in the range of 1 to 40 mass%, preferably 3 to 25 mass%, and more preferably 4 to 20 mass%, based on the total mass of the multiple polymerizable unsaturated monomers (a3). This range improves storage stability and the water resistance of the resulting coating film.

[0036] The core-shell emulsion can be obtained, for example, by emulsion polymerizing a monomer mixture (1) containing the polymerizable unsaturated monomer (a1) and the polymerizable unsaturated monomer (a2) in the above-mentioned ratio to produce a copolymer (I), then adding a monomer mixture (2) containing a plurality of polymerizable unsaturated monomers (a3), and further emulsion polymerizing the resulting copolymer. The emulsion polymerization of the monomer mixture (1) can be carried out by a method known per se, for example, by using a polymerization initiator in the presence of an emulsifier. The monomer mixture (2) can optionally contain components such as a polymerization initiator, a chain transfer agent, a reducing agent, and an emulsifier.

[0037] The core-shell emulsion is a core / shell emulsion having a core consisting of a copolymer (I) formed from a monomer mixture (1) containing a polymerizable unsaturated monomer (a1) and a polymerizable unsaturated monomer (a2), and a shell consisting of a copolymer (II) formed from a monomer mixture (2) containing multiple polymerizable unsaturated monomers (a3). From the viewpoint of sagging resistance of the resulting coating film, the ratio of copolymer (I) to copolymer (II) in the core-shell emulsion is preferably generally 5 / 95 to 95 / 5, particularly 30 / 70 to 92 / 8, and more particularly 40 / 60 to 90 / 10, in terms of the solids mass ratio of copolymer (I) to copolymer (II).

[0038] As the acrylic resin emulsion (A), a single-layer type acrylic resin emulsion obtained by emulsion polymerization in one stage can also be used. The acrylic resin emulsion (A) obtained as described above has a resin acid value in the range of preferably 5 to 90 mgKOH / g, more preferably 8 to 60 mgKOH / g, and even more preferably 10 to 50 mgKOH / g from the viewpoints of storage stability, water resistance of the resulting coating film, etc. Also, the acrylic resin emulsion (A) has a resin hydroxyl value in the range of preferably 1 to 100 mgKOH / g, more preferably 2 to 90 mgKOH / g, and even more preferably 5 to 80 mgKOH / g from the viewpoints of water resistance of the resulting coating film, etc.

[0039] When the aqueous colored coating composition of the present disclosure contains the above-mentioned acrylic resin emulsion, the content of the acrylic resin emulsion (A) is preferably within the range of 15 to 60 mass%, more preferably within the range of 20 to 55 mass%, and even more preferably within the range of 25 to 45 mass%, based on the resin solid content in the aqueous colored coating composition.

[0040] The aqueous colored coating composition can further contain a curing agent. Examples of the curing agent include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, epoxy group-containing compounds, carboxyl group-containing compounds, carbodiimide group-containing compounds, hydrazide group-containing compounds, and semicarbazide group-containing compounds. Among these, amino resins, polyisocyanate compounds, and blocked polyisocyanate compounds that can react with hydroxyl groups, and carbodiimide group-containing compounds that can react with carboxyl groups are preferred.

[0041] The aqueous colored coating composition preferably further contains a viscosity modifier (B). Examples of the viscosity modifier (B) include polyacrylic acid-based viscosity modifiers, silica-based fine powders, mineral-based viscosity modifiers, barium sulfate fine powder, polyamide-based viscosity modifiers, organic resin fine particle viscosity modifiers, diurea-based viscosity modifiers, urethane association-type viscosity modifiers, and cellulose-based viscosity modifiers, with polyacrylic acid-based viscosity modifiers being preferred.

[0042] When the aqueous colored coating composition of the present disclosure contains a viscosity modifier (B), the content of the viscosity modifier (B) is preferably within the range of 0.1 to 10 mass%, more preferably within the range of 0.5 to 8 mass%, and even more preferably within the range of 1.0 to 6.0 mass%, based on the resin solid content in the aqueous colored coating composition.

[0043] The above-mentioned aqueous colored coating composition may contain various coating additives, such as color pigments, luster pigments, dyes, thickeners, curing catalysts, ultraviolet absorbers, light stabilizers, antifoaming agents, plasticizers, surface conditioners, and anti-settling agents, as necessary.

[0044] [Multi-layer coating film formation method] The method for forming a multi-layer coating film of the present disclosure includes the following steps. Step 1: A step of forming a colored coating film on a substrate by discharging a predetermined aqueous colored coating composition close to the substrate using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port. Step 2: A step of applying a clear coating composition to the colored coating film to form a clear coating film.

[0045] The liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port is as explained in the section "Water-based colored coating composition."

[0046] The dry film thickness of the colored coating film formed from the aqueous colored coating composition varies depending on the application of the substrate, etc., and is not particularly limited, but is preferably 1.0 to 15.0 μm, more preferably 3.0 to 15.0 μm, and even more preferably 5.0 to 15.0 μm, from the viewpoint of the image clarity of the multilayer coating film.

[0047] Examples of the substrate include outer panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts; and outer panels of household electrical appliances such as mobile phones and audio equipment, with outer panels of automobile bodies and automobile parts being preferred.

[0048] The material of the substrate is not particularly limited, and examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.)-plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin; plastic materials such as various fiber-reinforced plastics (FRP); inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth.

[0049] The surface of the substrate may be a metal surface such as an outer panel of an automobile body, an automobile part, a household electrical appliance, or a metal substrate such as the steel plate that constitutes these, which has been subjected to a surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0050] A coating film may be further formed on an object that may or may not have been surface-treated. For example, a substrate to be coated may be surface-treated as needed, and a primer coating film may be formed thereon, or an intermediate coating film may be formed on the primer coating film. For example, when the substrate to be coated is an automobile body, the primer coating film and intermediate coating film may be formed using known primer and intermediate coating materials that are commonly used in painting automobile bodies.

[0051] The proximity discharge is not particularly limited as long as it is the distance between the discharge port and the substrate when the above-mentioned liquid discharge head is generally used, and is preferably 0.1 to 50.0 mm, more preferably 0.5 to 30 mm, and even more preferably 1.0 to 10.0 mm. In equipment equipped with the above-mentioned liquid ejection head, the frequency at which the aqueous colored coating composition is ejected from the valve body is preferably within the range of 10 to 10,000 Hz, more preferably within the range of 30 to 5,000 Hz, and even more preferably within the range of 50 to 3,000 Hz, from the viewpoints of ejection stability and the prevention of unevenness in the coating film formed.

[0052] In the equipment equipped with the liquid ejection head, the supply pressure for supplying the aqueous colored coating composition to the liquid ejection head is preferably within the range of 0.001 to 10 MPa, more preferably within the range of 0.005 to 5.0 MPa, and even more preferably within the range of 0.01 to 1.0 MPa, from the viewpoint of supply stability, etc. In the equipment equipped with the liquid ejection head, the scanning speed of the liquid ejection head is preferably within a range of 10 to 1,500 mm / s, more preferably within a range of 50 to 1,000 mm / s, and even more preferably within a range of 100 to 800 mm / s, from the viewpoints of ejection stability and the prevention of unevenness in the formed coating film.

[0053] In equipment equipped with the above-mentioned liquid ejection head, the pitch when scanning the liquid ejection head is preferably within the range of 0.001 to 1.0 mm, more preferably within the range of 0.005 to 1.0 mm, and even more preferably within the range of 0.01 to 1.0 mm, from the viewpoint of coating efficiency, etc.

[0054] Examples of the clear coating composition include curable clear coating compositions (for example, thermosetting clear coating compositions and photocurable clear coating compositions) and non-curable clear coating compositions. Examples of the thermosetting clear coating composition include organic solvent-based thermosetting coating compositions containing a base resin having a crosslinkable functional group and a curing agent, aqueous thermosetting coating compositions, and powder thermosetting coating compositions.

[0055] Examples of crosslinkable functional groups possessed by the base resin include carboxyl groups, hydroxyl groups, epoxy groups, silanol groups, etc. Types of base resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, fluororesins, etc. Examples of curing 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.

[0056] Preferred combinations of base resin / curing agent for the above clear coating composition include hydroxyl group-containing resin / polyisocyanate compound, carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / blocked polyisocyanate compound, and hydroxyl group-containing resin / melamine resin, with hydroxyl group-containing resin / polyisocyanate compound being more preferred. The clear coating composition may be a one-component coating, or may be a multi-component coating such as a two-component urethane resin coating.

[0057] Furthermore, the above-mentioned clear coating composition may contain coloring pigments, luster pigments, dyes, etc., as needed, to the extent that transparency is not impaired, and may further contain extender pigments, ultraviolet absorbers, light stabilizers, antifoaming agents, thickeners, rust inhibitors, surface conditioners, etc., as appropriate.

[0058] The application method of the clear coating composition is not particularly limited, but a wet coating film can be formed by, for example, air spray coating, airless spray coating, rotary atomization coating, curtain coating, or other coating methods. In these coating methods, electrostatic application may be performed as necessary. Of these, air spray coating or rotary atomization coating is particularly preferred. The amount of the clear coating composition applied is usually an amount that results in a cured film thickness of 10 to 70 μm, preferably 20 to 50 μm. [Example]

[0059] The present disclosure will be explained in more detail below with reference to Production Examples, Examples, and Comparative Examples. However, the present disclosure is not limited thereto. In each example, "parts" and "%" are by mass unless otherwise specified. Furthermore, the film thickness of the coating film is based on the cured coating film.

[0060] [Production of acrylic resin emulsion (A)] [Manufacturing Example 1] A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%), and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion (1) described below and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80°C for 15 minutes. Thereafter, the remaining monomer emulsion (1) was added dropwise over 3 hours to the reaction vessel maintained at the same temperature, and the mixture was aged for 1 hour after the completion of the dropwise addition. Then, the following monomer emulsion (2) was added dropwise over 1 hour, and after aging for 1 hour, 40 parts of a 5% aqueous dimethylethanolamine solution was gradually added to the reaction vessel while cooling to 30°C, and the mixture was discharged while being filtered through a 100-mesh nylon cloth, yielding an acrylic resin emulsion (A1) with a solids concentration of 30%. The obtained acrylic resin emulsion (A1) had an acid value of 33 mg KOH / g and a hydroxyl value of 25 mg KOH / g.

[0061] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2.1 parts of methylenebisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, 28 parts of ethyl acrylate, and 21 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (1). Monomer emulsion (2): A monomer emulsion (2) was obtained by mixing and stirring 18 parts of deionized water, 0.31 parts of "Aqualon KH-10," 0.03 parts of ammonium persulfate, 5.1 parts of methacrylic acid, 5.1 parts of 2-hydroxyethyl acrylate, 3 parts of styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate, and 9 parts of n-butyl acrylate.

[0062] [Manufacturing Example 2] A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%). The mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion (3) described below and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80°C for 15 minutes. The remaining monomer emulsion (3) was then added dropwise over 3 hours to the reaction vessel maintained at the same temperature. After the addition, the reaction vessel was aged for 1 hour. Next, the monomer emulsion (4) described below was added dropwise over 1 hour. After aging for 1 hour, the reaction vessel was cooled to 30°C while gradually adding 40 parts of a 5% aqueous dimethylethanolamine solution. The mixture was then discharged while filtering through a 100-mesh nylon cloth, yielding an acrylic resin emulsion (A2) with a solids concentration of 30%. The resulting acrylic resin emulsion (A2) had an acid value of 13 mgKOH / g and a hydroxyl value of 65 mgKOH / g.

[0063] Monomer emulsion (3): A monomer emulsion (3) was obtained by mixing and stirring 46.2 parts of deionized water, 0.79 parts of "Aqualon KH-10", 7.7 parts of styrene, 16.94 parts of methyl methacrylate, 7.7 parts of n-butyl acrylate, 30.8 parts of n-butyl methacrylate, 11.55 parts of 2-hydroxyethyl methacrylate, and 2.31 parts of ethylene glycol dimethacrylate.

[0064] Monomer emulsion (4): A monomer emulsion (4) was obtained by mixing and stirring 13.8 parts of deionized water, 0.24 parts of "Aqualon KH-10", 0.03 parts of ammonium persulfate, 2.3 parts of styrene, 6.9 parts of methyl methacrylate, 4.6 parts of ethyl acrylate, 3.68 parts of n-butyl acrylate, 3.45 parts of 2-hydroxyethyl methacrylate, and 2.07 parts of methacrylic acid.

[0065] [Production of Hydroxyl-Containing Acrylic Resin (C)] [Manufacturing Example 3] A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 35 parts of propylene glycol monopropyl ether. After heating to 85°C, a mixture of 30 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 29 parts of n-butyl acrylate, 15 parts of 2-hydroxyethyl acrylate, 6 parts of acrylic acid, 15 parts of propylene glycol monopropyl ether, and 2.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 4 hours, and the mixture was aged for 1 hour after the completion of the dropwise addition. Subsequently, a mixture of 10 parts of propylene glycol monopropyl ether and 1 part of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 1 hour, and the mixture was aged for 1 hour after the completion of the dropwise addition. Further addition of 7.4 parts of diethanolamine and 13 parts of propylene glycol monopropyl ether gave a hydroxyl group-containing acrylic resin (C1) solution with a solids concentration of 55%. The resulting hydroxyl group-containing acrylic resin (C1) had an acid value of 47 mgKOH / g, a hydroxyl value of 72 mgKOH / g, and a weight average molecular weight of 58,000.

[0066] [Production of polyester resin (D)] [Manufacturing Example 4] A reactor equipped with a thermometer, stirrer, heater, and distillation column was mixed with 118 parts of 1,6-hexanediol and 102 parts of adipic acid. A small amount of xylene was added for reflux, and the mixture was gradually heated to 250°C. The mixture was maintained at this temperature for 5 hours, allowing for esterification while dehydrating to yield a polyester resin. Per 100 parts of the polyester resin, 102.5 parts of ethylene glycol monobutyl ether and 2.5 parts of orthophosphoric acid were added, and the mixture was maintained at 100°C for 3 hours to yield a polyester resin (D1) solution with a solids concentration of 50%. The number average molecular weight of the polyester resin (D1) was 4,000.

[0067] [Production of pigment dispersion] [Manufacturing Example 5] A container equipped with a stirrer was charged with 9.1 parts (5 parts solids) of the hydroxyl-containing acrylic resin (C1) solution obtained in Production Example 3, 4 parts of "Carbon MA-100" (trade name, carbon black, manufactured by Mitsubishi Chemical Corporation), and 50 parts of deionized water, and mixed uniformly to form a mixed solution. 2-Ethyl-1-hexanol was added to the mixed solution to adjust the pH to 7.5. The pH-adjusted mixed solution was then placed in a wide-mouth glass bottle, and glass beads with a diameter of approximately 1.3 mm were added as a dispersion medium, the bottle was sealed, and the bottle was dispersed for 4 hours using a paint shaker to obtain a pigment dispersion (P-1).

[0068] [Manufacturing Example 6] A container equipped with a stirrer was charged with 9.1 parts (5 parts solids) of the hydroxyl-containing acrylic resin (C1) solution obtained in Production Example 3, 7 parts of "Chlorinated Copper Cyanine Blue G-314" (trade name, manufactured by Sanyo Dish Co., Ltd., phthalocyanine blue pigment), and 50 parts of deionized water, and mixed uniformly to form a mixed solution. 2-Ethyl-1-hexanol was added to the mixed solution to adjust the pH to 7.5. The pH-adjusted mixed solution was then placed in a wide-mouth glass bottle, and glass beads with a diameter of approximately 1.3 mm were added as a dispersion medium, the bottle was sealed, and the bottle was dispersed for 4 hours using a paint shaker to obtain a pigment dispersion (P-2).

[0069] [Manufacturing Example 7] A container equipped with a stirrer was charged with 9.1 parts (5 parts solids) of the hydroxyl-containing acrylic resin (C1) solution obtained in Production Example 3, 10 parts of "PERRIND MAROON 179 229-6440" (trade name, manufactured by Sun Chemical Co., organic perylene pigment), and 50 parts of deionized water, and mixed uniformly to form a mixed solution. 2-Ethyl-1-hexanol was added to the mixed solution to adjust the pH to 7.5. The pH-adjusted mixed solution was then placed in a wide-mouth glass bottle, and glass beads with a diameter of approximately 1.3 mm were added as a dispersion medium, the bottle was sealed, and the bottle was dispersed for 4 hours using a paint shaker to obtain a pigment dispersion (P-3).

[0070] [Manufacturing Example 8] A container equipped with a stirrer was charged with 9.1 parts (5 parts solids) of the hydroxyl-containing acrylic resin (C1) solution obtained in Production Example 3, 10 parts of "YELLOW 2GLMA" (trade name, manufactured by Dominion Color Corporation, a bismuth vanadate-based yellow pigment), and 50 parts of deionized water, and mixed uniformly to form a mixed solution. 2-Ethyl-1-hexanol was added to the mixed solution to adjust the pH to 7.5. The pH-adjusted mixed solution was then placed in a wide-mouth glass bottle, and glass beads with a diameter of approximately 1.3 mm were added as a dispersion medium, the bottle was sealed, and the bottle was dispersed for 4 hours using a paint shaker to obtain a pigment dispersion (P-4).

[0071] [Preparation of aqueous colored coating composition] [Example 1] Into a stirring mixing vessel were added 63.1 parts (9 parts solids) of the pigment dispersion (P-1) obtained in Production Example 5, 116.7 parts (35.0 parts solids) of the acrylic resin emulsion (A1) obtained in Production Example 1, 16.1 parts (4.5 parts solids) of "Primal ASE-60" (trade name, manufactured by Rohm and Haas Company, polyacrylic acid-based thickener, 28% solids), 30 parts (15 parts solids) of the hydroxyl group-containing polyester resin (D1) solution obtained in Production Example 4, 42.9 parts (15 parts solids) of "U-coat UX-8100" (trade name, manufactured by Sanyo Chemical Industries, Ltd., urethane emulsion, 35% solids), 30 parts (30 parts solids) of "Cymel 350" (trade name, manufactured by Mitsui Cytec Co., Ltd., methyl etherified melamine resin, weight average molecular weight 550, 100% solids), and "TINUVIN 1.1 parts (1 part solids) of "BASF 384-2" (trade name, benzotriazole-based ultraviolet absorber, solids concentration 95%) were mixed uniformly, and 2-(dimethylamino)ethanol and deionized water were added to obtain aqueous colored coating composition No. 1 with a pH of 8.0 and a coating solids concentration of 15%.

[0072] [Examples 2 to 20 and Comparative Examples 1 to 4] Water-based colored coating compositions Nos. 2 to 24 were obtained in the same manner as in Example 1, except that the blending compositions in Example 1 were as shown in Table 1 below. The values ​​shown in Table 1 refer to solid contents.

[0073] [Paint property measurement] The paint properties of the aqueous colored paint compositions No. 1 to No. 24 obtained in Examples 1 to 20 and Comparative Examples 1 to 4 were measured according to the following methods. The evaluation results are also shown in Table 1. [Viscosity (V1) and Viscosity (V2)] At a temperature of 23°C, the shear rate is 0.0001 sec -1 From 10,000 seconds -1 The temperature was changed to 23°C and the shear rate was changed to 1,000 sec -1 Viscosity (V1) at 23°C and shear rate of 0.1 sec -1 The viscosity (V2) at the temperature of 1000°C was measured using a cone and plate viscometer "HAAKE RheoStress RS150" (trade name, manufactured by HAAKE, 35 mm diameter, 2° inclined cone and plate).

[0074] [tanδ] At a temperature of 23°C, a shear stress of 1.0 Pa, and a frequency of 0.1 Hz, tan δ (loss modulus / storage modulus) at a temperature of 23°C was measured using a "HAAKE RheoStress RS150" (trade name, manufactured by HAAKE, 35 mm diameter, 2° inclined cone and plate).

[0075] [Viscosity (V3), Viscosity (V4), and Viscosity (V5)] First, the shear rate is set to 0.1 sec -1 The viscosity (V3) was measured after holding the shear rate at 1000 sec for 50 seconds. -1 The shear rate was then changed to 0.1 sec, and the viscosity (V4) was measured after holding for 10 seconds. -1 The viscosity (V5) was measured after 10 seconds of holding the temperature at 23°C using a HAAKE RheoStress RS150 (product name, manufactured by HAAKE, 35 mm diameter, 2° inclined cone and plate).

[0076] [Discharge stability test and sagging resistance test] The aqueous colored coating compositions Nos. 1 to 24 obtained in Examples 1 to 20 and Comparative Examples 1 to 4 were subjected to a discharge stability test and a sagging resistance test.

[0077] [Discharge stability test] Each of the aqueous colored coating compositions No. 1 to No. 24 was filled into an "X JET" (trade name, manufactured by SSI JAPAN, high-viscosity micro-piezo jet dispenser, discharge orifice diameter 100 μm). Each of the aqueous colored coating compositions No. 1 to No. 24 was then applied to the substrate in a line (10 cm long) under the following conditions: frequency 350 Hz, supply pressure 0.03 MPa, speed 230 mm / s, and distance between the discharge orifice and the substrate 10 mm. The linear distortion was observed and evaluated according to the following criteria: ⊚ and ◯ indicate passing. The evaluation results are shown in Table 2. ◎: No distortion in linear objects. ◯: The linear object is partially distorted, but this does not pose a problem in practical use. △: The linear object is distorted overall, and is problematic for practical use. ×: Linear objects cannot be formed.

[0078] [Sagging resistance test] [Preparation of coated specimens for sagging resistance test] A cold-rolled steel plate measuring 11 cm x 45 cm that had been subjected to a zinc phosphate conversion treatment was electrodeposited with "Elecron 9400HB" (product name: manufactured by Kansai Paint Co., Ltd., an amine-modified epoxy resin-based cationic resin using a blocked polyisocyanate compound as a curing agent) to a dry film thickness of 20 μm, and the plate was cured by heating at 170°C for 30 minutes to obtain an electrodeposited coated steel plate. Next, 21 punch holes, each 5 mm in diameter, were punched in a row at 2 cm intervals in a section 3 cm from the end of the long side of the obtained electrodeposited coated steel plate to prepare a coated specimen for sagging resistance tests.

[0079] [Preparation of coated panels for sagging resistance tests] Aqueous colored coating compositions No. 1 to No. 24 were filled into an "X JET" (trade name, manufactured by SSI JAPAN, high-viscosity micro-piezo jet dispenser, nozzle diameter 100 μm). The coating was then applied to the sagging resistance test substrate at a frequency of 350 Hz, a supply pressure of 0.03 MPa, a distance of 10 mm between the nozzle and the substrate, and at 27°C and a relative humidity of 50%. The coating was applied with a thickness gradient of approximately 10 μm to 40 μm in the longitudinal direction. The coated plate was then placed vertically and allowed to stand for 3 minutes, after which it was preheated at 80°C for 3 minutes. After leaving the coating for 7 minutes, it was heated at 140°C for 30 minutes to cure the coating, thereby preparing a coated plate for the sagging resistance test.

[0080] For the resulting coated panels for sagging resistance testing, the film thickness at the position of the thinnest punch hole among those where sagging of the coating film was observed 5 mm or more from the bottom end of the punch hole [sagging limit film thickness (μm)] was measured and evaluated. The larger the sagging limit film thickness, the better the sagging resistance. ◎ and ○ are acceptable. The evaluation results are shown in Table 1. ⊚: The sagging limit film thickness is 20 μm or more. ◯: The sagging limit film thickness is 15 μm or more and less than 20 μm. △: The sagging limit film thickness is 10 μm or more and less than 15 μm. ×: The sagging limit film thickness is less than 10 μm.

[0081] [Table 1]

[0082] [Table 2] (Note 1) "UH-756VF": Product name, manufactured by ADEKA Corporation, urethane associative viscosity modifier, solids concentration 32%, (Note 2) "UH-752": Product name, manufactured by ADEKA Corporation, urethane associative viscosity modifier, solid content 28%, (Note 3) "Leocrysta I-2SX": Product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., cellulose nanofiber, viscosity adjuster, solids concentration 2%.

[0083] [Preparation of clear coating composition (Z-1)] [Manufacturing Example 9] In a stirring and mixing container, 233 parts (solid content 70 parts) of the acrylic resin emulsion (A2) obtained in Production Example 2 and 78.9 parts (solid content 30 parts) of "Bayhydur VPLS2310" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., blocked polyisocyanate compound, solid content concentration 38%) were uniformly mixed, and deionized water was added so that the paint solid content concentration was 40%, and the mixture was stirred to obtain a one-component water-based clear paint composition (Z-1).

[0084] [Preparation of substrate for image clarity test] [Preparation of substrate for image clarity test (O-1)] The surface of a black polypropylene plate measuring 100 mm in length, 100 mm in width, and 2 mm in thickness was wiped with gauze soaked in petroleum benzine to degrease it, and then "Ascalex #2850" (trade name, manufactured by Kansai Paint Co., Ltd., a polyolefin-containing water-based primer paint) was applied with a hand spray gun to a cured coating thickness of 15 μm. After leaving it for 5 minutes, the plate was preheated at 80°C for 3 minutes to create a coated object (O-1) for a clearness test.

[0085] [Preparation of substrate for image clarity test (O-2)] A zinc phosphate-treated galvannealed steel sheet was electrodeposited with "Elecron 9400HB" (trade name: manufactured by Kansai Paint Co., Ltd., an amine-modified epoxy resin-based cationic resin using a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm, and then heated at 170°C for 30 minutes to cure, forming an electrodeposited coating. Next, "WP-522H" (trade name: polyester resin-based water-based primer paint manufactured by Kansai Paint Co., Ltd.) was applied to the electrodeposited coating with a hand spray gun to a cured coating thickness of 15 μm, and after leaving it for 5 minutes, the coating was preheated at 80°C for 3 minutes to prepare a coated object (O-2) for a distinctness test.

[0086] [Preparation of substrate for image clarity test (O-3)] The surface of a black polypropylene plate measuring 100 mm long x 100 mm wide x 2 mm thick was degreased by wiping with gauze soaked in petroleum benzine, then "Ascalex #2850" (trade name, Kansai Paint Co., Ltd., polyolefin-containing water-based primer paint) was applied with a hand spray gun to a cured film thickness of 15 μm, left for 5 minutes, and then preheated at 80°C for 3 minutes to form an uncured primer film. To this uncured primer film, "Retan WB Eco EV Base" (trade name, Kansai Paint Co., Ltd., water-based colored base coat paint) was applied to a dry film thickness of 15 μm, left at room temperature for 5 minutes, and then preheated at 80°C for 3 minutes to form an uncured base coat film. Next, the clear coating composition (Z-1) obtained in Production Example 9 was applied to the uncured base coat film using a hand spray gun to a cured film thickness of 35 μm, and after leaving it for 7 minutes, it was heated at 120°C for 30 minutes to cure the base coat film and clear coating film, thereby producing a coated substrate (O-3) for a clearness test.

[0087] [Preparation of substrate (O-4) for image clarity test] The surface of a black polypropylene plate measuring 100 mm long x 100 mm wide x 2 mm thick was degreased by wiping with gauze soaked in petroleum benzine, then "Ascalex #2850" (trade name, Kansai Paint Co., Ltd., polyolefin-containing water-based primer paint) was applied with a hand spray gun to a cured film thickness of 15 μm, left for 5 minutes, and then preheated at 80°C for 3 minutes to form an uncured primer film. To this uncured primer film, "Retan WB Eco EV Base" (trade name, Kansai Paint Co., Ltd., water-based colored base coat paint) was applied to a dry film thickness of 15 μm, left at room temperature for 5 minutes, and then preheated at 80°C for 3 minutes to form an uncured base coat film. Next, "Retan WB Eco EV Clear" (trade name, two-component water-based clear paint, manufactured by Kansai Paint Co., Ltd.) was applied to the uncured base coat film using a hand spray gun to a cured film thickness of 35 μm, and after leaving it for 7 minutes, it was heated at 80°C for 30 minutes to cure the base coat film and clear coat film, thereby creating a coated object (O-4) for a vividness test.

[0088] [Preparation of substrate (O-5) for image clarity test] A zinc phosphate-treated galvannealed steel sheet was electrodeposited with "Elecron 9400HB" (product name: manufactured by Kansai Paint Co., Ltd., an amine-modified epoxy resin-based cationic resin using a blocked polyisocyanate compound as a curing agent) to a thickness of 20 μm, and then heated to 170°C for 30 minutes to cure, forming an electrodeposited coating. Next, "WP-522H" (product name: polyester resin-based water-based primer paint manufactured by Kansai Paint Co., Ltd.) was applied to the electrodeposited coating with a hand spray gun to a cured coating thickness of 15 μm, and after leaving it for 5 minutes, the coating was preheated at 80°C for 3 minutes to form an uncured primer coating. A "Retan WB Eco EV Base" (product name: water-based colored base coat paint manufactured by Kansai Paint Co., Ltd.) was applied to the uncured primer coating to a dry thickness of 15 μm, and the coating was left at room temperature for 5 minutes, followed by preheating at 80°C for 3 minutes to form an uncured base coat coating. Next, "Retan WB Eco EV Clear" (trade name, two-component water-based clear paint, manufactured by Kansai Paint Co., Ltd.) was applied to the uncured base coat film using a hand spray gun to a cured film thickness of 35 μm, and after leaving it for 7 minutes, it was heated at 80°C for 30 minutes to cure the base coat film and clear coat film, thereby creating a coated object (O-5) for a vividness test.

[0089] [Example 21] [Preparation of coated panels for image clarity testing] [Preparation of coated plate (S1) for image clarity test] Aqueous colored coating composition No. 1 was filled into an "X JET" (trade name, manufactured by SSI JAPAN, high-viscosity micro-piezo jet dispenser, outlet diameter 100 μm) and applied to a substrate for a distinctness test (O-1) at a frequency of 350 Hz, a supply pressure of 0.03 MPa, a distance between the outlet and the substrate of 10 mm, 27°C, and a relative humidity of 50% to a dry film thickness of 10 μm. The coating was left at room temperature for 5 minutes and then preheated at 80°C for 3 minutes to form an uncured colored coating film. Next, the clear coating composition (Z-1) obtained in Production Example 9 was applied to the uncured colored coating film using a hand spray gun to a cured film thickness of 35 μm. After leaving for 7 minutes, the coating was heated at 120°C for 30 minutes to cure the colored coating film and clear coating film, producing a coated panel for a distinctness test (S1-1).

[0090] [Preparation of coated plate (S2) for image clarity test] A coated plate for image clarity test (S2-1) was prepared according to the procedure described in "Preparation of coated plate for image clarity test (S1)," except that the coated plate for image clarity test (O-1) was changed to the coated plate for image clarity test (O-2). [Preparation of coated plate (S3) for image clarity test] A coated plate for image clarity test (S3-1) was prepared according to the procedure described in "Preparation of coated plate for image clarity test (S1)," except that the coated plate for image clarity test (O-1) was changed to the coated plate for image clarity test (O-3).

[0091] [Preparation of coated plate (S4) for image clarity test] Aqueous colored coating composition No. 1 was filled into an "X JET" (trade name, manufactured by SSI JAPAN, high-viscosity, minute-volume piezo-jet dispenser, nozzle diameter 100 μm) and applied to a substrate (O-4) for a distinctness test at a frequency of 350 Hz, a supply pressure of 0.03 MPa, a nozzle-to-substrate distance of 10 mm, 27°C, and a relative humidity of 50% to a dry film thickness of 10 μm. The coating was then left at room temperature for 5 minutes and then preheated at 80°C for 3 minutes to form an uncured colored coating. Next, "Retan WB Eco EV Clear" (trade name, two-component water-based clear coating, manufactured by Kansai Paint Co., Ltd.) (Z-2) was applied to the uncured colored coating with a hand spray gun to a cured film thickness of 35 μm. The coating was left for 7 minutes and then heated at 120°C for 30 minutes to cure the colored coating and clear coating, producing a coated panel (S4-1) for a distinctness test.

[0092] [Preparation of coated plate (S5) for image clarity test] A coated plate for image clarity test (S5-1) was prepared according to the procedure described in "Preparation of coated plate for image clarity test (S4)," except that the coated plate for image clarity test (O-4) was changed to the coated plate for image clarity test (O-5).

[0093] [Examples 22 to 44 and Comparative Examples 5 to 8] In Example 21, the same procedure as in Example 21 was used except that the combinations of aqueous colored coating compositions and film thicknesses were as shown in Table 2. Coated panels for image clarity tests (S1-2) to (S1-28), (S2-2) to (S2-28), (S3-2) to (S3-28), (S4-2) to (S4-28), and (S5-2) to (S5-28) were prepared.

[0094] [Image clarity test] The coated plates for image clarity tests obtained in Examples 21 to 44 and Comparative Examples 5 to 8 were evaluated for image clarity based on the Short Wave (SW) value measured using a "Wave Scan" (trade name, manufactured by BYK Gardner). The smaller the SW value, the higher the image clarity of the coating surface, with ◎ and ○ indicating a pass. The evaluation results are shown in Table 2. ◎: Sw value is less than 25. ○: Sw value is 25 or more and less than 30. △: Sw value is 30 or more and less than 40. ×: Sw value is 40 or more.

[0095] [Table 3]

Claims

1. An aqueous colored coating composition containing a hydroxyl group-containing acrylic resin, an acrylic resin emulsion, and a hydroxyl group-containing polyester resin, which is applied using a liquid ejection head that controls ejection by changing the relative distance between a valve body and an ejection port, The aqueous colored coating composition is heated at a temperature of 23°C and a shear rate of 1,000 sec -1 Viscosity (V) of 30 mPa or more and less than 60 mPa s 1 ) and a temperature of 23°C and a shear rate of 0.1 sec -1 Viscosity (V 2 ) and The aqueous colored coating composition has a tanδ (loss modulus / storage modulus) at a temperature of 23°C and a frequency of 0.1 Hz in the range of 0.25 to 0.80, The solid content concentration of the aqueous colored coating composition is within the range of 8 to 27% by mass. Water-based colored paint composition.

2. The aqueous colored coating composition according to claim 1, wherein the solids concentration of the aqueous colored coating composition is within the range of 10 to 20 mass%.

3. The aqueous colored coating composition according to claim 1, wherein the solid content concentration of the aqueous colored coating composition is in the range of 10 to 16 mass%.

4. Under the condition of a temperature of 23°C, the shear rate was 0.1 sec -1 The viscosity of the aqueous colored coating composition after holding for 50 seconds (V 3 ) and the shear rate is 1,000 sec -1 After changing the temperature to 100°C and holding for 10 seconds, the viscosity of the aqueous colored coating composition (V 4 ) and the shear rate is 0.1 sec -1 After changing the temperature to 100°C and holding for 10 seconds, the viscosity of the aqueous colored coating composition (V 5 ) are expressed by the following formulas (1) and (2): 0.001<V 4 / V 3 <0.007 Formula (1) 30<V 5 / V 4 <200 Formula (2) fulfill, The aqueous colored coating composition according to claim 1.

5. The aqueous colored coating composition according to claim 1, wherein the aqueous colored coating composition contains a viscosity modifier (B).

6. Step 1: A step of forming a colored coating film on a substrate by discharging the aqueous colored coating composition according to any one of claims 1 to 4 in close proximity to the substrate using a liquid discharge head that controls discharge by changing the relative distance between the valve body and the discharge port. Step 2: A step of applying a clear coating composition to the colored coating film to form a clear coating film; A method for forming a multilayer coating film, comprising:

7. 7. The method for forming a multilayer coating film according to claim 6, wherein the dry thickness of the colored coating film is in the range of 1.0 to 15.0 μm.

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