JP2023024371A - Aqueous clear coating material - Google Patents

Abstract

To provide a coating material capable of forming a coating excellent in coating film physical properties such as whitening resistance.SOLUTION: An aqueous clear coating material contains a resin component and a crosslinking agent. The resin component (A) contains: an acrylic resin (A1) in which the content of a carboxyl group-containing monomer in a resin-constituting component is 5 wt.% or less; and an acrylic resin (A2) in which the content of a carboxy group-containing monomer in a resin-constituting component is higher than that in the acrylic resin (A1). The crosslinking agent is a carbodiimide compound. The carbodiimide compound is contained in an amount of 0.1-10 pts.wt. in terms of solid content based on 100 pts.wt. of the solid content of the resin component (A).SELECTED DRAWING: None

Description

The present invention relates to a novel water-based clear coating material.

In recent years, environmental concerns such as the reduction of volatile organic compounds (VOC) have been increasing, and in the coating field, there is a shift from solvent-based coating materials using organic solvents to water-based coating materials.

One of the problems with water-based coating materials such as those described above is the improvement of physical properties of coating films such as stain resistance and water resistance. Techniques related to introduction of a cross-linking agent have been proposed to address such problems (for example, Patent Document 1). However, by simply introducing a cross-linking agent, whitening resistance may not be obtained, or a rigid coating film may be formed, resulting in poor conformability to the substrate. In particular, when the clear coating material (topcoat) is insufficient in whitening resistance and conformability to the substrate, there is a risk of impairing the design of the substrate, and there is room for improvement.

WO2017/006950

SUMMARY OF THE INVENTION It is an object of the present invention to provide a water-based clear coating material capable of exhibiting excellent coating film physical properties such as whitening resistance.

In order to solve the above-mentioned problems, the inventors of the present invention, as a result of intensive studies, have conceived of a water-based clear coating material containing a specific acrylic resin as a resin component and a carbodiimide compound as a cross-linking agent in a specific weight ratio. The invention has been perfected.

That is, the present invention has the following features.
1. A water-based clear coating material containing a resin component (A) and a cross-linking agent (B),
The resin component (A) includes an acrylic resin (A1) in which the content of the carboxy group-containing monomer in the resin component is 5% by weight or less, and the acrylic resin in which the content of the carboxy group-containing monomer in the resin component is the acrylic resin Containing more acrylic resin (A2) than (A1),
The cross-linking agent (B) is a carbodiimide compound,
A water-based clear coating material characterized by containing 0.1 to 10 parts by weight of a carbodiimide compound in terms of solid content with respect to 100 parts by weight of the solid content of the resin component (A).
2. 1. The solid content of the resin component (A) contains 55% by weight or more of the acrylic resin (A1) in terms of solid content. The water-based clear coating material described in .
3. 1. Further, the organic amine compound is included as the basic organic compound (C). or 2. The water-based clear coating material described in .

According to the coating material of the present invention, it is possible to form a coating excellent in coating film physical properties such as whitening resistance and substrate followability.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated.

The present invention relates to a water-based clear coating material (hereinafter also simply referred to as "coating material"), characterized by containing a resin component (A) and a cross-linking agent (B).

The resin component (A) (hereinafter also referred to as "(A) component") of the present invention is an acrylic resin (A1) (hereinafter referred to as " (Also referred to as "(A1) component"), and an acrylic resin (A2) (hereinafter also referred to as "(A2) component") in which the content of the carboxy group-containing monomer in the resin component is higher than that of the acrylic resin (A1) characterized by comprising By including such components (A1) and (A2) in combination, it is possible to exhibit excellent effects in whitening resistance and the like.

The (A1) component of the present invention contains a (meth)acrylic acid alkyl ester as a main component of the resin component, and as other monomer components, the content of a carboxy group-containing monomer is 5% by weight or less (more preferably 0 to 4.8% by weight, more preferably 0.05 to 4.5% by weight, particularly preferably 0.1 to 3% by weight). In such a range, good physical properties of the film can be obtained. When the component (A1) has a carboxyl group-containing monomer, the whitening resistance can be further enhanced by cross-linking the component (B), which will be described later. In the present invention, alkyl acrylate and alkyl methacrylate are collectively referred to as alkyl (meth)acrylate. Moreover, a monomer is a general term for compounds having a polymerizable unsaturated double bond. In the present invention, "α to β" has the same meaning as "more than or equal to α and less than or equal to β".

Examples of (meth)acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) Acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, cyclohexyl (meth)acrylate and the like can be mentioned, and one or more of these can be used.

Examples of carboxyl group-containing monomers include
Carboxy group-containing monomers such as (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, isocrotonic acid, salicylic acid and the like can be mentioned, and one or more of these can be used.

Specific examples of other monomers include, for example,
aromatic monomers such as styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, divinylbenzene, phenyl (meth)acrylate, benzyl (meth)acrylate;
Nitrile group-containing monomers such as (meth)acrylonitrile, vinylidene cyanide, α-cyanoethyl (meth)acrylate;
Maleic acid amide, (meth)acrylamide, N-monoalkyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide, 2-(dimethylamino)ethyl (methacrylate), N-[3-(dimethylamino)propyl] Amide group-containing monomers such as (meth)acrylamide and vinylamide;
Carbonyl group-containing monomers such as acrolein, diacetone (meth)acrylamide, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone;

aminomethyl acrylate, aminoethyl acrylate, aminopropyl (meth)acrylate, amino-n-butyl (meth)acrylate, butylvinylbenzylamine, vinylphenylamine, p-aminostyrene, N-methylaminoethyl (meth)acrylate, N - amino group-containing monomers such as t-butylaminoethyl (meth)acrylate;
glycidyl (meth) acrylate, diglycidyl fumarate, 3,4-epoxycyclohexyl (meth) acrylate, 3,4-epoxyvinylcyclohexane, allyl glycidyl ether, ε-caprolactone-modified glycidyl (meth) acrylate, β-methylglycidyl (meth) ) epoxy group-containing monomers such as acrylates;
hydroxyl group-containing monomers such as hydroxypropyl (meth)acrylate, ethylene glycol mono (meth) acrylate, glycerol mono (meth) acrylate;
vinylidene halide-based monomers such as vinylidene fluoride;
Alkoxysilyl groups such as vinyltrimethoxysilane, vinyltriethoxysilane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, γ-(meth)acryloyloxypropylmethyldimethoxysilane, etc. contained monomers;
ethylene, propylene, isoprene, butadiene, vinyl ether, vinyl ketone; and the like. These can be used singly or in combination of two or more.

In the present invention, the other monomer component is preferably an acrylic silicone resin containing an alkoxysilyl group-containing monomer. In such a case, film physical properties such as weather resistance, stain resistance and water resistance can be enhanced.

Examples of the form of the component (A1) include water-soluble resins, water-dispersible resins, and composites thereof. In the present invention, a water-dispersible resin (resin emulsion) is preferred.

Component (A1) can be produced by a single-stage or multi-stage (two-stage, or three-stage or more) emulsion polymerization method or the like from a group of monomers obtained by appropriately mixing the above-mentioned monomers. As the polymerization method, a known method may be adopted, and in addition to ordinary emulsion polymerization, soap-free emulsion polymerization, feed emulsion polymerization, seed emulsion polymerization, and the like can also be adopted. At the time of polymerization, emulsifiers, initiators, dispersants, polymerization inhibitors, polymerization inhibitors, buffers, chain transfer agents and the like can be used.

As the emulsifier, various surfactants that can be used for emulsion polymerization can be used, and these may be reactive type having a polymerizable unsaturated double bond (reactive surfactant). As emulsifiers, anionic surfactants and nonionic surfactants are preferably used alone or in combination.

The glass transition temperature (hereinafter simply referred to as “Tg”) of the component (A1) is preferably set to −5° C. to 80° C. (more preferably 0 to 60° C.). If Tg is within such a range, the effects of the present invention can be stably obtained. In addition, Tg in the present invention is a value obtained by the Fox formula.

The average particle size of the acrylic resin of component (A1) is preferably 300 nm or less (more preferably 20 to 200 nm). If the average particle size is within such a range, the water resistance, weather resistance, chemical resistance, etc. of the coating can be improved. The average particle size referred to here is a value measured by a dynamic light scattering method.

Furthermore, the pH of the emulsion solution of component (A1) is preferably 7.0 or higher (more preferably 7.5 to 12, and still more preferably 8.0 to 11). In such a range, the stability of the covering material can be ensured.

The content of the component (A1) is preferably 55% by weight or more (more preferably 60 to 99.99% by weight, more preferably 60 to 99.99% by weight, more preferably 80 to 99.98% by weight, particularly preferably 90 to 99.95% by weight). The component (A1) is a main binder component in the component (A), and when the component (A1) satisfies the above range, it is advantageous for whitening resistance. In addition, it is possible to sufficiently secure film physical properties such as substrate followability, weather resistance, stain resistance, and water resistance.

The (A2) component of the present invention contains a (meth)acrylic acid alkyl ester as a main component of the resin component, and has a higher content of carboxy group-containing monomers in the resin component than the (A1) component ( preferably 3 to 80% by weight, more preferably 6 to 70% by weight, still more preferably 10 to 60% by weight). Within such a range, whitening resistance can be improved by a cross-linking reaction with a cross-linking agent (B) described later.

Examples of the form of the component (A2) include water-soluble resins, water-dispersible resins, and composites thereof. In the present invention, a water-dispersible resin (resin emulsion) is preferred. In addition, the (A2) component can be produced by the same method as for the (A1) component. The average particle size of the acrylic resin of component (A2) is preferably 300 nm or less (more preferably 20 to 200 nm). The average particle size referred to here is a value measured by a dynamic light scattering method.

Further, the component (A2) is preferably a resin (alkali-soluble or alkali-swellable resin) that dissolves or swells with alkali (neutralization). Thereby, the whitening resistance can be further improved. This mechanism of action is not limited to the following, but in the embodiment containing the (A1) component and the (A2) component having different contents of the carboxy group-containing monomer, the dissolved or swollen (A2) component is the above (A1 ), it is considered that the crosslinked structure of the film becomes partially dense when crosslinked with the crosslinking agent (B), which will be described later. This makes it possible to improve the whitening resistance without impairing the physical properties of the film such as the conformability to the substrate imparted by the component (A1).

The pH of the emulsion solution before neutralization of the component (A2) is preferably less than 7 (more preferably 6 or less, more preferably 1 to 4), and by mixing with the component (A1), dissolution or It swells and the above effect can be obtained. The average particle size of the acrylic resin of the component (A2) is a measured value before being dissolved or swollen by alkali (neutralization).

The content of the component (A2) is 45 wt% or less (more preferably 0.01 to 40 wt%, preferably 0.02 ~20% by weight, more preferably 0.05 to 10% by weight). The above component (A2) is a binder component that acts auxiliary to the above component (A1). When the above range is satisfied, it is advantageous for whitening resistance, and whitening resistance is achieved by crosslinking of the component (B) described later. can be further enhanced.

In the present invention, a carbodiimide compound is included as the cross-linking agent (B), and the carbodiimide compound is added in an amount of 0.1 to 10 parts by weight (preferably 0.1 to 10 parts by weight in terms of solid content) per 100 parts by weight of the solid content of the resin component (A). 2 to 5 parts by weight). In such a case, a coating excellent in whitening resistance and the like can be formed by cross-linking reaction with the resin component (A) (the (A1) component and the (A2) component).

Examples of such carbodiimide compounds include carbodiimide group-containing resins, N,N-dicyclohexylcarbodiimide, and N,N-diisopropylcarbodiimide. Examples of the carbodiimide group-containing resin include those described in JP-A-10-60272, JP-A-10-316930, JP-A-11-60667, WO2017/006950, and the like. The form of the carbodiimide compound is preferably water-soluble or water-dispersible, and the water-dispersible form is particularly advantageous in terms of storage stability.

The carbodiimide equivalent of the carbodiimide compound is preferably 100-500 (more preferably 150-400). Within such a range, the effect of the present invention can be sufficiently obtained.

In the present invention, in addition to the above components, it is preferable to include a basic organic compound (C) (hereinafter also referred to as “component (C)”). Component (C) includes, for example, alkylamines [e.g., monomethylamine, dimethylamine, trimethylamine, monoethylamine, triethylamine, monoisopropylamine, diisopropylamine, butylamine, diethylenetriamine, triethylenetriamine, triethylenetetramine, etc.], alcohol Amines (aminoalcohols) [e.g., monoethanolamine, methylethanolamine, ethylethanolamine, mono-n-butylethanolamine, aminoethylpropanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, dimethylethanolamine, 2-aminomethylpropanol, etc.], heterocycle-containing amines [eg, morpholine, methylmorpholine, piperazine, hydroxyethylpiperazine, etc.]. These can be used singly or in combination of two or more. The component (C) may be added as a neutralizing agent during the production of the component (A). In the present invention, alcoholamines (aminoalcohols) are preferred, and 2-aminomethylpropanol, diethanolamine, monoethanolamine and the like are particularly preferred.

The boiling point of the organic amine compound is preferably 80° C. or higher (more preferably 100° C. or higher, more preferably 150° C. or higher). When the above range is satisfied, the rate of volatilization during film formation becomes moderate, so a film with excellent whitening resistance can be formed.

By containing the component (C), a dense coating can be formed. Although this action mechanism is not limited to the following, the cross-linking reaction of the carbodiimide compound (B) tends to speed up as the pH decreases. On the other hand, when a basic organic compound is added, its volatilization rate is moderate, so the cross-linking reaction (curing rate) due to a rapid decrease in pH is suppressed. A cross-linking reaction occurs. As a result, a dense coating can be formed, and whitening resistance can be further improved.

The content of component (C) is 0.01 to 5 parts by weight (0.02 to 3 parts by weight) per 100 parts by weight of the solid content of component (A). In the case of such a range, the above effects can be sufficiently exhibited.

The coating material of the present invention can be produced by uniformly mixing the above components by a known method, but if necessary, other components that are commonly used in coating materials can also be mixed. Examples of such components include coloring pigments, extender pigments, fibers, film-forming aids, thickeners, leveling agents, coupling agents, plasticizers, antifreeze agents, pH adjusters, preservatives, and antifungal agents. , anti-algae agents, antibacterial agents, dispersants, antifoaming agents, ultraviolet absorbers, light stabilizers, antioxidants, water, and the like.

The coating material of the present invention is a water-based clear coating material that forms a transparent coating, that is, a coating that transmits visible light. As a result, it is possible to form a laminated film having transparency, and to obtain a finish that takes advantage of the design of the base. The transparency may be such that the color and pattern of the base can be visually recognized, and the coating may be either colorless and transparent, or colored and transparent. (including split gloss etc.). A colored transparent film can be formed from a coating material containing, for example, a coloring pigment, a dye, or the like. A matte coating can be formed by a coating material containing, for example, an extender, a matting agent, or the like.

The degree of visible light transmission can be indicated by visible light transmittance. Visible light transmittance is preferably 30% or more, more preferably 35 to 100%, still more preferably 40 to 95%. The visible light transmittance is a value obtained by measuring the transmittance of light with a wavelength of 580 nm for a film with a thickness of 30 μm using a spectrophotometer (transmittance is 100% when there is no film (air)). be.

In order to obtain such visible light transmittance, for example, the coloring pigment ratio in the covering material should be set low. The coloring pigment ratio in the coating material is preferably 10% by weight or less, more preferably 5% by weight or less, and still more preferably 0 to 3% by weight. Embodiments in which the coating material does not contain a coloring pigment are also suitable.

In the present invention, a transparent film can be formed by applying a water-based clear coating material to the underlying surface. The aqueous clear coating material of the present invention can be suitably used as a topcoat material. The base surface is not particularly limited, but a patterned coated surface provided on a substrate (for example, a patterned coated surface having a colored pattern) is suitable. By applying the water-based clear coating material of the present invention to such a base surface, the resistance to whitening is enhanced, and the design (colored pattern) of the base surface can be maintained for a long period of time.

Examples of the substrate include concrete, mortar, and plate-like substrates. Among these, plate-like substrates include, for example, cement boards, extruded boards, slate boards, PC boards, ALC boards, fiber-reinforced cement boards, metal siding boards, ceramic siding boards, ceramic boards, calcium silicate boards, Examples include plastic boards, hardwood cement boards, PVC extruded siding boards, and plywood. The surface of these substrates may have been subjected to some surface treatment (for example, sealer, surfacer, filler, etc.), or may have a coating film already formed, or may have wallpaper attached. .

A colored pattern is a pattern in which at least two or more colors are visible in a mixed state. For example, a pattern in which spots of two or more colors are mixed, and spots (one color or two or more colors) are scattered on a background color. Patterns, patterns that are painted in two or more colors (e.g., island pattern, line pattern, tile pattern, brick pattern, stone pattern, rock pattern, wood pattern, geometric pattern, striped pattern) , lattice pattern, random pattern, etc.). Such a multicolor pattern may be formed by various printing methods (inkjet printing, etc.), or may be formed by a decorative coating agent such as a stone-like finish coating material or multicolored pattern paint. may be

In applying the water-based clear coating material of the present invention, a known coating tool can be used. Examples of coating tools that can be used include sprays, rollers, and brushes. The coating amount of the aqueous clear coating material is preferably 0.05-0.8 kg/m ² (more preferably 0.08-0.5 kg/m ² ). The number of times of coating is preferably 1 to 3 times. At the time of coating, the water-based clear coating material can be diluted as needed. Drying after application of the water-based clear coating material may be carried out at room temperature (preferably 0 to 50°C, more preferably 5 to 45°C), and heating can be performed if necessary.

Examples are shown below to further clarify the features of the present invention.

・Manufacturing of water-based clear coating material
Based on the formulation shown in Table 1, each raw material was mixed by a conventional method to produce a water-based clear coating material.
In addition, each component used the following.

(A) Resin component Resin 1: Acrylic resin emulsion (cyclohexyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, emulsion polymer of acrylic acid, content of carboxy group-containing monomer: 0.5% by weight, average particle size: 120 nm , solid content: 50% by weight, medium: water, pH = 8.5)
・Resin 2: Acrylic resin emulsion (emulsion polymer of cyclohexyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid, γ-methacryloyloxypropyltrimethoxysilane, content of carboxy group-containing monomer: 0.5% by weight, average Particle diameter: 120 nm, solid content: 50% by weight, medium: water, pH = 8.5)
Resin 3: Acrylic resin emulsion (emulsion polymer of cyclohexyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid, γ-methacryloyloxypropyltrimethoxysilane, content of carboxy group-containing monomer: 0.1% by weight, average Particle diameter: 120 nm, solid content: 50% by weight, medium: water, pH = 8.5)
・ Resin 4: Acrylic resin emulsion (emulsion polymer of cyclohexyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid, γ-methacryloyloxypropyltrimethoxysilane, content of carboxy group-containing monomer: 1.5% by weight, average Particle diameter: 120 nm, solid content: 50% by weight, medium: water, pH = 8.5)
・ Resin 5: Acrylic resin emulsion (emulsion polymer of cyclohexyl methacrylate, 2-ethylhexyl acrylate and methyl methacrylate, content of carboxy group-containing monomer: 0% by weight, average particle size: 120 nm, solid content: 50% by weight, medium: water, pH=8.5)
・ Resin 6: Acrylic resin emulsion (cyclohexyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, emulsion polymer of acrylic acid, content of carboxy group-containing monomer: 6% by weight, average particle size: 120 nm, solid content: 50% by weight , medium: water, pH = 8.5)
Resin 7: Alkali-swellable acrylic resin emulsion (emulsion polymer of ethyl acrylate, ethyl methacrylate, methacrylic acid, content of carboxy group-containing monomer: 30% by weight, average particle size: 80 nm, solid content: 30% by weight, medium : water, pH = 3.0)

(B) Crosslinking Agent/Crosslinking Agent 1: Carbodiimide resin aqueous dispersion (solid content: 40% by weight, carbodiimide equivalent: 310)
· Cross-linking agent 2: carbodiimide resin aqueous dispersion (solid content: 40% by weight, carbodiimide equivalent: 230)
· Crosslinking agent 3: carbodiimide resin aqueous solution (solid content: 40% by weight, carbodiimide equivalent: 335)
· Crosslinking agent 4: carbodiimide resin aqueous dispersion (solid content: 40% by weight, carbodiimide equivalent: 450)
(C) basic organic compound/basic organic compound 1: 2-aminomethylpropanol (boiling point: 165°C)
・ Basic organic compound 2: 25% ammonia water (boiling point: 100 ° C.)
(others)
・Matting agent: acrylic bead powder (average particle size: 10 μm)
・Additives (urethane associative thickeners, defoaming agents, UV absorbers, etc.)
・Media: Water, hydrophilic solvent

・Production of stone-like finish coating material 200 parts by weight of acrylic resin emulsion (solid content: 50% by weight), 210 parts by weight of calcium carbonate, aggregate (yellow aggregate, black aggregate, brown aggregate, mixture of Kansui stone) 550 parts by weight, 10 parts by weight of film-forming aid, 4 parts by weight of viscosity modifier, 2 parts by weight of antifoaming agent, and 110 parts by weight of water were uniformly mixed by a conventional method to obtain a stone-like finish coating material.

(Examples 1 to 16, Comparative Examples 1 to 3)
A stone-like finish coating material was spray-coated onto a base material (slate plate: 45×30 cm) at a coating amount of 5.0 kg/m ² and dried at 23° C. for 24 hours. Then, the water-based clear coating material was spray-coated with a spray gun at a coating amount of 0.3 kg/m ² , dried and cured at 23°C for 24 hours to form a test sample [I]. The following whitening resistance evaluation was performed on the produced test specimen [I]. Results are shown in Table 1.

<Whitening resistance evaluation 1>
Specimen [I] was immersed in water (23° C.) for 7 days, and the presence or absence of whitening immediately after pulling out was checked. As the evaluation criteria, a 4-grade evaluation (excellent: A>B>C>D: poor) was used, with "A" indicating no whitening and "D" indicating whitening of the entirety.

<Whitening resistance evaluation 2>
Specimen [I] was immersed in water (23°C) for 7 days, pulled out, dried for 24 hours (23°C), and then examined for whitening. The evaluation criteria are the same as those for whitening resistance evaluation 1.

In Examples 1 to 16, sufficient whitening resistance could be obtained. In particular, in Examples 7 to 13, whitening resistance evaluations 1 and 2 were both "A" evaluations.

Next, for Examples 1 to 16, film physical property evaluation (stain resistance evaluation, conformability evaluation) was performed. Results are shown in Table 1.
<Stain resistance evaluation 1>
A contaminant (15% by weight carbon aqueous solution) is spotted on the film surface of the test sample [I], dried for 24 hours (23 ° C.), washed with water for 10 minutes on the surface, and then washed for 6 hours (23 ° C.). After drying, the staining condition was evaluated. The evaluation criteria were as follows: "AA" for maintaining excellent aesthetics without surface contamination; "A" for maintaining excellent aesthetics with almost no surface contamination; A 5-grade evaluation (excellent: AA>A>B>C>D: inferior) was made with "D" indicating staining.

<Stain resistance evaluation 2>
A specimen [II] was used as the specimen after the whitening resistance evaluation 2, and the stain resistance evaluation was conducted. The evaluation method and evaluation criteria are the same as those of the contamination resistance evaluation 1.

<Stain resistance evaluation 3>
Specimen [III] was formed in the same manner as Specimen [I] except that an aqueous clear coating material stored at 50° C. for 30 days was used, and stain resistance evaluation was performed. The evaluation method and evaluation criteria are the same as those of the contamination resistance evaluation 1.

<Follow-up evaluation>
<Preparation of test sample [IV]>
A slate plate (45×30 cm) was spray-coated with a stone-like finishing coating material at a coating amount of 5.0 kg/m ² and dried at 23° C. for 24 hours. Two slate plates with this stone-like coating film are placed side by side, and the connection between the plates (width 20 mm) is filled with a modified silicone sealant (resin component: alkoxysilyl group-containing polyether polymer) to be painted. was used as the base material.
A water-based clear coating material was spray-coated on the entire surface of the base material with a spray gun at a coating amount of 0.1 kg/m ² and dried for 3 days (5 ° C., humidity 30%). ]. With respect to the prepared test specimen [IV], the appearance of the film was confirmed, and the state of occurrence of defects (swelling, peeling, cracking, etc.) was evaluated. The evaluation was made into a four-grade evaluation (excellent: A>B>C>D: poor), with "A" indicating that no problem occurred and "D" indicating that a problem clearly occurred.

In Examples 1 to 15, sufficient stain resistance and followability could be obtained. In addition, even the coating film after being immersed in water could maintain stain resistance. Moreover, in Examples 1 to 12 and 14, the stain resistance was sufficiently maintained even after the aqueous coating material was stored.

Claims (3)

A water-based clear coating material containing a resin component (A) and a cross-linking agent (B),
The resin component (A) includes an acrylic resin (A1) in which the content of the carboxy group-containing monomer in the resin component is 5% by weight or less, and the acrylic resin in which the content of the carboxy group-containing monomer in the resin component is the acrylic resin Containing more acrylic resin (A2) than (A1),
The cross-linking agent (B) is a carbodiimide compound,
A water-based clear coating material characterized by containing 0.1 to 10 parts by weight of a carbodiimide compound in terms of solid content with respect to 100 parts by weight of the solid content of the resin component (A). 2. The water-based clear coating material according to claim 1, wherein the solid content of the resin component (A) contains 55% by weight or more of the acrylic resin (A1) in terms of solid content. 3. The water-based clear coating material according to claim 1, further comprising an organic amine compound as the basic organic compound (C).