Water-based covering materials

Abstract

To provide an aqueous coating material which can exhibit excellent performance in coating film physical properties such as weather resistance.SOLUTION: An aqueous coating material contains a synthetic resin emulsion, specifically, a synthetic resin emulsion (A) and a synthetic resin emulsion (B) having a glass transition temperature lower than that of the synthetic resin emulsion (A) by 3°C or more. The respective average particle diameters of the synthetic resin emulsion (A) and the synthetic resin emulsion (B) are 320 nm or less, and the average particle diameter of the synthetic resin emulsion (B) is larger than the average particle diameter of the synthetic resin emulsion (A).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous coating material.

Background Art

[0002] Conventionally, in buildings, civil engineering structures, etc., coating is performed with various coating materials for the purposes of surface protection, improvement of aesthetics, etc. In such a coating field, due to the movement of reducing the environmental load and the like, the trend towards water-based coatings has been advancing, and various aqueous coating materials have been proposed.

[0003] As a binder in an aqueous coating material, a synthetic resin emulsion is mainly used. A synthetic resin emulsion is generally formed by dispersing resin particles on the submicron order in an aqueous medium. After being applied to a coated surface, as drying progresses, the resin particles fuse together to form a film (film formation). At that time, if the fusion of the resin particles is insufficient, it may have an adverse effect on the film physical properties. Therefore, in an aqueous coating material containing a synthetic resin emulsion, stable film-forming properties are required.

[0004] Patent Document 1 describes an aqueous coating material containing two types of emulsions having a specific average particle diameter and forming a film at a predetermined temperature or lower.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the aqueous coating material of Patent Document 1 is designed for use in building interiors and has not been considered for outdoor use. Therefore, it may be difficult to obtain sufficient performance in film physical properties such as weather resistance, and there is room for improvement.

[0007] This invention has been made in view of these points, and aims to improve the weather resistance and other film properties of aqueous coating materials containing synthetic resin emulsions. [Means for solving the problem]

[0008] To solve these problems, the inventors, after diligent research, conceived of an aqueous coating material containing two synthetic resin emulsions that satisfy specific conditions regarding glass transition temperature and average particle size, and thus completed the present invention.

[0009] In other words, the present invention has the following features. 1. An aqueous coating material containing a synthetic resin emulsion, Acrylic with a glass transition temperature of 20°C or less Resin emulsion (A), and The glass transition temperature is 3°C or more lower than that of the synthetic resin emulsion (A) described above. acrylic Contains resin emulsion (B), the above acrylic Resin emulsion (A) The average particle size is 60-200 nm. the above acrylic The average particle size of resin emulsion (B) is 、 It is below 320nm, the above acrylic The average particle size of the resin emulsion (A) is greater than the above acrylic The average particle size of resin emulsion (B) is larger. A water-based coating material characterized by the following features. 2. The above acrylic Resin emulsion (A) and the above acrylic The aqueous coating material according to claim 1, characterized in that the mixing ratio of the resin emulsion (B) component is 99 / 1 to 10 / 90 in terms of the solid content weight ratio of (A) / (B). [Effects of the Invention]

[0010] The aqueous coating material of the present invention can exhibit excellent performance in terms of film properties such as weather resistance. [Modes for carrying out the invention]

[0011] The following describes embodiments for carrying out the present invention.

[0012] The aqueous coating material of the present invention contains a synthetic resin emulsion as a binder. The synthetic resin emulsion includes synthetic resin emulsion (A) (hereinafter also referred to as "component (A)") and synthetic resin emulsion (B) (hereinafter also referred to as "component (B)") having a glass transition temperature 3°C or more lower than that of component (A), and components (A) and (B) satisfy specific conditions in terms of average particle size. In the present invention, by using these two specific types of synthetic resin emulsions, excellent performance in coating properties such as weather resistance can be achieved.

[0013] The synthetic resin emulsion in this invention is obtained by emulsifying and dispersing a resin in an aqueous medium (a medium containing water). Examples of resins in the synthetic resin emulsion include vinyl acetate resin, vinyl chloride resin, epoxy resin, alkyd resin, acrylic resin, urethane resin, silicone resin, fluororesin, etc., or composite systems thereof. These can be used individually or in combination of two or more.

[0014] In the present invention, an embodiment comprising an acrylic resin emulsion is preferred as the synthetic resin emulsion. The acrylic resin emulsion is an aqueous dispersion of polymer particles mainly composed of alkyl (meth)acrylate. Such an acrylic resin emulsion can be obtained, for example, by emulsion polymerization of a group of monomers including alkyl (meth)acrylate and, if necessary, other monomers, using a known method.

[0015] Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, and the like. These can be used alone or in combination of two or more. The compositional ratio of such (meth)acrylic acid alkyl ester is preferably 30% by weight or more, more preferably 40 to 99.9% by weight, still more preferably 50 to 99.5% by weight based on all the monomers constituting the synthetic resin. In the present invention, the acrylic acid alkyl ester and the methacrylic acid alkyl ester are collectively referred to as (meth)acrylic acid alkyl ester. Also, in the present invention, "a to b" has the same meaning as "a or more and b or less".

[0016] Examples of the other monomers include carboxyl group-containing monomers, amino group-containing monomers, piperidyl group-containing monomers, hydroxyl group-containing monomers, nitrile group-containing monomers, amide group-containing monomers, glycidyl group-containing monomers, carbonyl group-containing monomers, alkoxysilyl group-containing monomers, aromatic monomers, and the like. These can be used alone or in combination of two or more. The compositional ratio of these other monomers is preferably 0.1 to 60% by weight, more preferably 0.5 to 50% by weight based on all the monomers constituting the synthetic resin.

[0017] Specifically, examples of the carboxyl group-containing monomer include (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, isocrotonic acid, salicylic acid, cinnamic acid, etc. Examples of amino group-containing monomers include butylvinylbenzylamine, vinylphenylamine, p-aminostyrene, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, N-[2-(meth)acryloyloxyethyl]piperidine, N-[2-(meth)acryloyloxyethyl]pyrrolidine, N-[2-(meth)acryloyloxyethyl]morpholine, 4-[N,N-dimethylamino]styrene, 4-[N,N-diethylamino]styrene, 2-vinylpyridine, 4-vinylpyridine, etc. Examples of piperidyl group-containing monomers include 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloylamino-1,2,2,6,6-pentamethylpiperidine, 4-cyano-4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, and 4-(meth)acryloyloxy-1-methylcarb Moyloxy-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-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonyloxy-2,2,6,6-tetramethylpiperidine, etc. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxypentyl (meth)acrylate, 4-hydroxypentyl (meth)acrylate, 1-methyl-4-hydroxypentyl (meth)acrylate, 3-ethyl-3-hydroxyhexyl (meth)acrylate, 2-hydroxydecyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1-methyl-4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-methyl-8-hydroxyoctyl (meth)acrylate, 7-methyl-8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, hydroxymethylcyclohexyl (meth)acrylate, etc. Examples of the nitrile group-containing monomer include (meth)acrylonitrile, etc. Examples of the amide group-containing monomer include (meth)acrylamide, ethyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-n-propyl (meth)acrylamide, N-cyclopropyl (meth)acrylamide, N-(meth)acryloylpyrrolidine, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-methyl-N-ethyl (meth)acrylamide, N-methyl-N-isopropyl (meth)acrylamide, N-methyl-N-n-propyl (meth)acrylamide, N-methylol (meth)acrylamide, N-[3-(dimethylamino)propyl] (meth)acrylamide, vinylamide, N,N-methylenebisacrylamide, diacetone (meth)acrylamide, N-methylol (meth)acrylamide, acrylamide glycolic acid, methyl acrylamide glycolate, dimethoxyhydroxyethyl acrylamide, etc. Examples of glycidyl group-containing monomers include 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)acrylate, etc. Examples of carbonyl group-containing monomers include diacetone (meth)acrylate, diacetone (meth)acrylamide, acrolein, vinyl methyl ketone, vinyl ethyl ketone, vinyl (iso)butyl ketone, acetonyl acrylate, acrylic oxyalkyl propanals, methacrylic oxyalkyl propanals, 2-hydroxypropyl acrylate acetyl acetate, tandiol acrylate acetyl acetate, acetoacetoxyethyl (meth)acrylate, acetoacetoxyaryl ester, etc. Examples of monomers containing alkoxysilyl groups include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, vinyltrimethoxysisiliane, vinyltriethoxysisiliane, vinyltriisopropoxysilane, etc. Examples of aromatic monomers include styrene, 2-methylstyrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylanisole, and vinylnaphthalene. These can be used individually or in combination of two or more.

[0018] Examples of acrylic resin emulsions that can be used include acrylic styrene resin emulsion, epoxy-modified acrylic resin emulsion, silicone-modified acrylic resin emulsion, urethane-modified acrylic resin emulsion, and fluorine-modified acrylic resin emulsion. Of these, for example, acrylic styrene resin emulsion can be obtained by using aromatic monomers such as styrene as the other monomers mentioned above, epoxy-modified acrylic resin emulsion can be obtained by using glycidyl group-containing monomers as the other monomers mentioned above, and silicone-modified acrylic resin emulsion can be obtained by using alkoxysilyl group-containing monomers as the other monomers mentioned above.

[0019] The polymerization method for the synthetic resin emulsion used in this invention is not particularly limited. The synthetic resin emulsion can be produced by mixing the above-mentioned monomers with various additives as needed and polymerizing them using commonly known polymerization methods (emulsion polymerization, suspension polymerization, dispersion polymerization, etc.). Polymerization may be carried out in one step or in two or more steps. Examples of additives include water, emulsifiers, initiators, solvents, dispersants, emulsification stabilizers, polymerization inhibitors, polymerization inhibitors, buffers, crosslinking agents, pH adjusters, chain transfer agents, catalysts, etc., and the necessary amounts should be added depending on the polymerization method and purpose. It is desirable that the weight-average molecular weight of the synthetic resin emulsion be 200,000 or more.

[0020] The aqueous coating material of the present invention uses two types of synthetic resin emulsions that satisfy specific conditions in terms of glass transition temperature and average particle size. This enables the material to exhibit excellent performance in terms of film properties such as weather resistance. The reason for this is not limited to the following, but it is believed that by using two types of synthetic resin emulsions that satisfy specific conditions in terms of glass transition temperature and average particle size, sufficient fusion of the resin particles constituting the synthetic resin emulsion occurs during the film formation stage after coating with the aqueous coating material, resulting in excellent film-forming properties, the formation of a dense film, and consequently, excellent performance in terms of film properties such as weather resistance.

[0021] The aqueous coating material of the present invention comprises, as a synthetic resin emulsion, synthetic resin emulsion (A) and synthetic resin emulsion (B) having a glass transition temperature 3°C or more lower than that of component (A). The glass transition temperature is a value determined by Fox's formula.

[0022] In the present invention, the glass transition temperature of component (B) is 3°C or more lower than the glass transition temperature of component (A), and the difference between the glass transition temperatures of component (A) and component (B) is 3°C or more, preferably 4 to 40°C, more preferably 5 to 25°C, and even more preferably 6 to 18°C.

[0023] The glass transition temperature of component (A) is preferably -20 to 30°C, more preferably -10 to 20°C, and even more preferably -5 to 15°C. The glass transition temperature of component (B) is preferably -50 to 10°C, more preferably -30 to 5°C, and even more preferably -25 to 0°C. If components (A) and (B) have such glass transition temperatures, they are suitable as room-temperature drying or room-temperature curing aqueous coating materials, and the amount of film-forming aids and other additives can be reduced.

[0024] In the present invention, the average particle diameters of synthetic resin emulsion (A) and synthetic resin emulsion (B) are 320 nm or less, and the average particle diameter of synthetic resin emulsion (B) is larger than that of synthetic resin emulsion (A). The difference in average particle diameter between component (A) and component (B) is preferably 20 nm or more, more preferably 40 nm or more, and even more preferably 60 nm or more. The average particle diameter of the synthetic resin emulsion is a value measured by dynamic light scattering. Specifically, it can be measured using a dynamic light scattering measuring device (measurement temperature is 25°C).

[0025] The average particle size of component (A) is 320 nm or less, preferably 200 nm or less, more preferably 50 to 150 nm, and even more preferably 60 to 120 nm. The average particle size of component (B) is 320 nm or less, preferably 100 to 300 nm, more preferably 120 to 280 nm, and even more preferably 140 to 260 nm.

[0026] The mixing ratio of component (A) to component (B) is preferably 99 / 1 to 10 / 90 in terms of the solid content weight ratio of (A) / (B), more preferably 97 / 3 to 45 / 55, and even more preferably 95 / 5 to 65 / 35. When component (A) and component (B) are mixed in such a ratio, the coating properties such as weather resistance are even more favorable.

[0027] The aqueous coating material of the present invention may contain coloring pigments. For example, known inorganic coloring pigments, organic coloring pigments, etc., can be used as coloring pigments. By appropriately using one or more of these coloring pigments, the aqueous coating material can be set to a desired color tone, and an aqueous coating material exhibiting a single color, such as glossy synthetic resin emulsion paint (JIS K5660) or synthetic resin emulsion paint (JIS K5663), can be obtained. In the present invention, even when such coloring pigments are included, excellent performance in film properties such as weather resistance can be achieved. The mixing ratio of the coloring pigment is preferably 1 to 500 parts by weight, more preferably 5 to 200 parts by weight, and even more preferably 10 to 100 parts by weight, per 100 parts by weight of the solid content (total solid content of component (A) and component (B)) of the synthetic resin emulsion.

[0028] Examples of coloring pigments include titanium dioxide, zinc oxide, alumina, carbon black, graphite, black iron oxide, iron-manganese composite oxide, iron-copper-manganese composite oxide, iron-chromium composite oxide, iron-chromium-cobalt composite oxide, copper-chromium composite oxide, copper-manganese-chromium composite oxide, copper-magnesium composite oxide, bismuth-manganese composite oxide, ferric oxide (red iron oxide), molybdate orange, permanent red, permanent carmine, anthraquinone red, perylene red, quinacridone red, yellow iron oxide, titanium yellow, first yellow, benzoimidazolone yellow, chromium green, cobalt green, phthalocyanine green, ultramarine, Prussian blue, cobalt blue, phthalocyanine blue, quinacridone violet, dioxazine violet, aluminum pigment, pearl pigment, etc. These can be used individually or in combination of two or more. The average particle size of the coloring pigment is preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 0.01 to 0.9 μm. The average particle size of the coloring pigment is measured using a laser diffraction particle size distribution analyzer.

[0029] The aqueous coating material of the present invention may also contain components other than those listed above, such as extender pigments, dyes, aggregates, color particles, matting agents, thickeners, wetting agents, leveling agents, antifreeze agents, film-forming aids, preservatives, antifungal agents, antialgal agents, antibacterial agents, dispersants, surfactants, defoaming agents, ultraviolet absorbers, light stabilizers, antioxidants, adhesion promoters, decontamination agents, hydrophilic agents, photocatalysts, water repellents, crosslinking agents, curing agents, curing accelerators, plasticizers, coupling agents, adsorbents, pH adjusters, catalysts, water, solvents, etc. The aqueous coating material can be manufactured by uniformly mixing such components by conventional methods.

[0030] The aqueous coating material of the present invention can reduce the amount of volatile organic compounds (VOCs), such as film-forming aids. The content of volatile organic compounds in the aqueous coating material can preferably be less than 5% by weight, and more preferably less than 1% by weight. Even with such a low content of volatile organic compounds, the aqueous coating material of the present invention can exhibit excellent film-forming properties. Volatile organic compounds are organic compounds with a boiling point of 250°C or lower at standard pressure.

[0031] The aqueous coating material of the present invention can be applied, for example, to topcoats, intermediate coats, and undercoats. Among these, it is preferably applied to topcoats, and in particular, to glossy synthetic resin emulsion paints.

[0032] When the aqueous coating material of the present invention is used as a glossy synthetic resin emulsion paint, its 60-degree specular gloss is preferably 70 or higher, more preferably 75 or higher, and even more preferably 80 or higher. The 60-degree specular gloss is measured using a gloss meter after applying the sample to a glass plate using a film applicator with a gap of 150 μm and drying it for 48 hours under standard conditions (temperature 23°C, relative humidity 50%).

[0033] The aqueous coating material of the present invention can form a coating on its surface in which hard regions derived from component (A) and soft regions derived from component (B) are mixed. The area ratio of such hard regions to soft regions is preferably 99 / 1 to 10 / 90, more preferably 97 / 3 to 45 / 55, and even more preferably 95 / 5 to 65 / 35. Furthermore, the surface roughness (Ra value) of the coating made with the aqueous coating material of the present invention is preferably 10 nm or less, more preferably 8 nm or less. A coating made with the aqueous coating material of the present invention exhibiting such characteristics can demonstrate even better performance in terms of coating properties such as weather resistance. When the surface roughness is within the above range, it is also preferable in terms of improving gloss. The above-mentioned area ratio and surface roughness can be determined by observation using an atomic force microscope.

[0034] The aqueous coating material of the present invention can be applied, for example, to the surface finishing of surfaces to be coated on buildings, civil engineering structures, etc. Examples of substrates constituting the surface to be coated include concrete, mortar, porcelain tiles, fiber-reinforced cement boards, cement calcium silicate boards, slag cement perlite boards, cement boards, ALC boards, siding boards, gypsum boards, plywood, extruded boards, steel plates, plastic boards, etc. The surfaces of these substrates may have been subjected to some kind of surface treatment (for example, treatment with putty, sealer, surfacer, filler, etc.), or they may already have a coating film (old coating film, etc.) formed on them, or wallpaper, etc., attached to them.

[0035] When applying the aqueous coating material of the present invention, various painting tools such as sprayers, rollers, and brushes can be used.

[0036] When painting, it is also possible to dilute the coating with water. The amount of water to be mixed should be set appropriately considering the type of painting equipment, the condition of the surface to be painted, the temperature during painting, etc., but it is preferably 0 to 20% by weight of the total water-based coating material.

[0037] The amount of water-based coating material to be applied is preferably 0.1 to 0.8 kg / m². 2 , more preferably 0.12~0.6 kg / m 2 More preferably 0.15 to 0.4 kg / m 2 That is the case.

[0038] Drying of the water-based coating material after application is preferably carried out at room temperature (5-40°C), but heating is also possible if necessary. The drying time is preferably about 0.5-4 hours at room temperature. The number of coats can be one or two or more (preferably one to two). If the number of coats is two or more, it is desirable that the total amount applied is within the above range. [Examples]

[0039] The following examples illustrate the features of the present invention.

[0040] ○ Manufacturing of water-based coating materials A total of 200 parts by weight of synthetic resin emulsion was prepared, and each aqueous coating material was obtained by uniformly mixing it with 70 parts by weight of titanium dioxide, 3 parts by weight of dispersant, 1 part by weight of thickener, and 1 part by weight of defoamer. The synthetic resin emulsions used are listed below. The combinations of synthetic resin emulsions used for each aqueous coating material are shown in Table 1.

[0041] • [A1]: Acrylic resin emulsion (emulsion polymer of MMA-St-2EHA-AA, glass transition temperature 5°C, average particle size 80 nm, solids content 50 wt%) • [A2]: Acrylic resin emulsion (emulsion polymer of MMA-St-2EHA-AA, glass transition temperature 10°C, average particle size 80 nm, solids content 50 wt%) • [A3]: Acrylic resin emulsion (emulsion polymer of MMA-St-BA-AA, glass transition temperature 8°C, average particle size 105 nm, solids content 50 wt%) • [A4]: Acrylic resin emulsion (emulsion polymer of MMA-St-BA-AA, glass transition temperature 10°C, average particle size 350 nm, solids content 50 wt%) • [B1]: Acrylic resin emulsion (emulsion polymer of St-2EHA-AA, glass transition temperature -5°C, average particle size 200 nm, solids content 50% by weight) • [B2]: Acrylic resin emulsion (emulsion polymer of MMA-St-2EHA-AA, glass transition temperature -2°C, average particle size 160 nm, solids content 50% by weight) • [B3]: Acrylic resin emulsion (emulsion polymer of MMA-St-2EHA-AA, glass transition temperature -8°C, average particle size 220 nm, solids content 50% by weight)

[0042] The monomers constituting the above synthetic resin emulsion are as follows: • MMA: Methyl methacrylate (Tg: 105℃) St: Styrene (Tg: 100℃) BA: n-butyl acrylate (Tg: -54℃) • 2EHA: 2-Ethylhexyl acrylate (Tg: -70℃) AA: Acrylic acid (Tg: 106℃)

[0043] ○ Exam The following tests were conducted on each water-based coating material.

[0044] (1) Film-forming property A water-based coating material was applied to one side of a glass plate using a film applicator with a 150 μm gap. After drying for 48 hours in a constant temperature room at 5°C, the appearance of the coating was visually observed. The evaluation was as follows: "○" indicated no cracks were observed in the coating, and "×" indicated cracks were observed in the coating.

[0045] (2) Gloss A water-based coating was applied to one side of a glass plate using a film applicator with a 150 μm gap. After drying for 48 hours under standard conditions (23°C, 50% relative humidity), the 60-degree specular gloss of the coating was measured using a specular gloss meter. The evaluation was as follows: a 60-degree specular gloss of 80 or higher was rated "a", 75 or higher but less than 80 was rated "b", and 70 or higher but less than 75 was rated "c".

[0046] (3) Weather resistance Apply a water-based coating material to one side of the slate board at a rate of 0.25 kg / m². 2 Test specimens were obtained by coating them and drying them for 7 days under standard conditions (temperature 23°C, relative humidity 50%). The obtained test specimens were subjected to accelerated weathering tests using an iSuper UV tester (manufactured by Iwasaki Electric Co., Ltd.), with each cycle consisting of 6 hours of light irradiation and 2 hours of condensation (total 8 hours), for up to 60 cycles. The evaluation was as follows: a chalking grade (JIS K5600-8-6) of 0 or 1 after the accelerated test was rated "a", a chalking grade of 2 was rated "b", and a chalking grade of 3 or higher was rated "c" (Excellent: a > b > c: Poor).

[0047] The test results are shown in Table 1. The aqueous coating materials of the examples showed excellent results in all tests. Furthermore, observation of the coatings of the examples using an atomic force microscope revealed that in all cases, the area ratio of hard regions to soft regions on the coating surface was within the range of 95 / 5 to 65 / 45, and the surface roughness (Ra value) of the coating was 8 nm or less.

[0048] [Table 1]

Claims

1. A water-based coating material containing a synthetic resin emulsion, Acrylic resin emulsion (A) with a glass transition temperature of 20°C or less, and The above synthetic resin emulsion (A) contains an acrylic resin emulsion (B) having a glass transition temperature 3°C or more lower than the above synthetic resin emulsion (A), The average particle size of the acrylic resin emulsion (A) is 60 to 200 nm, and the average particle size of the acrylic resin emulsion (B) is 320 nm or less. The average particle size of acrylic resin emulsion (B) is larger than the average particle size of acrylic resin emulsion (A). A water-based coating material characterized by the following features.

2. The aqueous coating material according to claim 1, characterized in that the mixing ratio of the acrylic resin emulsion (A) and the acrylic resin emulsion (B) components is 99 / 1 to 10 / 90 in terms of the solid content weight ratio of (A) / (B).

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