JPS6224018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to water-soluble coating compositions. Conventionally, water-soluble paint compositions are obtained by mixing and kneading water-soluble resins with water, extender pigments, dry powdered titanium dioxide pigments, coloring pigments, amine additives, and various other additives. is widely used. Since these water-soluble coating compositions use water as a dispersion system, the surface tension of the water is high, which was thought to be a contributing factor to the occurrence of repellency on the surface of the coating film. In order to compensate for this coating film defect, anti-cissing agents or water-soluble solvents (hydrophilic solvents) have been used in combination. Furthermore, when lipophilic colored pigments are used, color separation tends to occur, which limits the selection of colored pigments and narrows the range of hues. In addition, as the prices of raw materials for paints have soared in recent years, it has become possible to improve the performance of the coating film if the same amount of raw materials are used, or to reduce the amount of raw materials used and create coatings that are equal to or better than conventional ones. There is an increasing demand for coating compositions with film performance. For example, regarding titanium dioxide pigment, which is used in a relatively large amount in paint compositions, if the amount used is the same, it will improve the hiding properties, gloss, sharpness, etc. of the paint film, or the amount used will increase. There is a growing demand for something that provides the same level of concealment performance as the conventional technology, even when there is only a small number of charges. However, conventional dry powdered titanium dioxide pigments have not been able to sufficiently meet the above requirements. The present inventors have arrived at the present invention as a result of extensive research into a water-soluble coating composition that eliminates the above-mentioned drawbacks and satisfies the above requirements. In other words, the present invention improves the water-soluble solvent used in order to suppress color separation and repellency and improve wetting of the coated surface or pigment compared to conventional water-soluble paint compositions using water-soluble resins. It is an object of the present invention to provide a water-soluble paint composition that can reduce the amount used and further improve hiding properties, gloss, and sharpness. That is, the present invention provides a slurry or wet cake with a moisture content of 40% by weight or less containing (a) a water-soluble synthetic resin and (b) titanium dioxide obtained in a wet finishing step of a pigment-grade titanium dioxide production process, and a condensed phosphate. A pigment-grade titanium dioxide slurry obtained by adding a dispersant containing a combination of polyacrylate and/or polyoxyethylene alkyl ether to form a fluid slurry, and then dispersing by wet grinding, (c) water, and ( d) If necessary, it relates to a water-soluble coating composition comprising an extender, various coloring pigments other than titanium dioxide, various additives, and a water-soluble solvent. The water-soluble synthetic resin as component (a) used in the present invention includes (1) polybasic acids such as phthalic anhydride, trimellitic anhydride, etc., ethylene glycol, neopentyl glycol, pentaerythritol, glycerin, etc. , polyhydric alcohol and soybean oil,
A carboxyl group in a reaction product having an acid value of 35 to 100 obtained by reacting an oil such as linseed oil or these fatty acids by a conventional condensation reaction with an amine such as triethylamine, dimethylethanolamine, etc. , water-soluble alkyd resins obtained by neutralizing with alkali metal hydroxides or ammonia, (2) acrylic acid, methacrylic acid, maleic acid, styrene, vinyltoluene, alkyl esters of (meth)acrylic acid, (meth) ) Acrylic acid hydroxyalkyl ester, etc., acid value 35-100
A water-soluble acrylic resin obtained by neutralizing the carboxyl groups in the copolymer with amine or ammonia, etc. (3) A reaction product with an acid value of 35 to 100 obtained by reacting oil or polybutadiene with maleic acid. Water-soluble maleated resins obtained by neutralizing with amines or ammonia, etc.; (4) Water-soluble maleated resins obtained by neutralizing with amines or ammonia, etc.; Examples include modified water-soluble resins obtained by neutralizing resins with amines or ammonia, etc., (5) water-soluble amino resins obtained by methyl etherifying polymethylolmelamine with methanol, and (6) water-soluble phenolic resins. These may be used alone or as a mixture of two or more. In addition, as the slurry of pigment grade titanium dioxide (JIS K5116), which is the component (b) used in the present invention, the slurry of pigment-grade titanium dioxide (JIS K5116) used in Japanese Patent Application No. 195143 (Sho 56-195143) previously filed by the applicant of the present invention (method for manufacturing titanium dioxide slurry) , Japanese Patent Publication No. 1983-
99121) is used. That is, a slurry or wet cake containing titanium dioxide and having a water content of 40% by weight or less (i.e., solid content of 60% by weight or more) obtained in the wet finishing step of the pigment-grade titanium dioxide manufacturing process is mixed with a condensed phosphate and a polyacrylate. A pigment-grade titanium dioxide slurry obtained by adding a dispersant containing and/or polyoxyethylene alkyl ether to form a fluid slurry and then dispersing it by wet grinding is used as the component (b). In other words, titanium dioxide crude pigment (obtained by the sulfuric acid method or chlorine method) → Wet grinding → Classification (omitted in some cases) → Coating with an inorganic surface treatment agent (further coating treatment with an organic agent is included if necessary) →・Use products manufactured through the process of washing and dehydration → addition of dispersant → wet grinding → pigment grade titanium dioxide slurry. In addition, in order to obtain a slurry or filtrate (wet cake) with a low water content before adding a dispersant in the above step, after coating with an inorganic surface treatment agent (further coating treatment with an organic agent as necessary), a wet process is performed. A pigment-grade titanium dioxide slurry prepared by passing through a grinding process, filtering, washing, and dehydrating, adding a dispersant, and then wet grinding may also be used. The reason why the solid content concentration of the slurry containing titanium dioxide is set to 60% by weight or more is that a slurry with a low solid content concentration naturally does not have a high water content. This is because the water balance in the system is disrupted, resulting in disadvantages such as unusability. In addition, the dispersant added in the slurry step is:
It is a combination of condensed phosphate, polyacrylate and/or polyoxyethylene alkyl ether. This combination makes it possible to obtain a titanium dioxide slurry with little tendency to thicken (low viscosity, high solid content) even when the solid content is high as described above. Examples of the condensed phosphate dispersant include sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, and sodium pyrophosphate, and the amount of these added is preferably based on the solid material (titanium dioxide treated with an inorganic surface coating). is 0.3 to 1.5% by weight, more preferably 0.5 to 1% by weight. Examples of the polyacrylates include sodium polyacrylate and ammonium polyacrylate, and commercially available products include Nobuco SN-5040 (San Nopco), Aquaric DL-40 (Nippon Shokubai), and Poise 530 (Kao Atlas). ), Aron T-40 (Toagosei), and Demol P (Kao Atlas). Examples of polyoxyethylene alkyl ethers include those in which the alkyl group is lauryl, cetyl, stearyl, oleyl, etc., and commercially available products include Emulgen various types (Kao Atlas), Neoneugen 140A (Daiichi Kogyo Seiyaku), etc. .
The addition rate of both polyacrylate and polyoxyethylene alkyl ether is preferably 0.1 to 1.5% by weight, more preferably 0.2 to 1% by weight, in terms of solids. Furthermore, the combination of the above-mentioned inorganic surface treatment coating agent and dispersant is one of three types, condensed phosphate type, polyacrylate type, and polyoxyethylene alkyl ether, for surface treatment of hydrated titania, hydrated silica, and hydrated alumina. For surface treatment of hydrated titania-hydrated alumina or hydrated alumina alone, it is preferable to add condensed phosphates and polyacrylates, and for surface treatment of a large amount of hydrated silica-hydrated alumina, condensed phosphates are preferred. Particularly preferred are polyoxyethylene alkyl ether and polyoxyethylene alkyl ether. In addition, as the extender pigment which is the component (2) which is added as necessary in the water-soluble paint composition of the present invention, such as barite, talc, mica, clay, calcium carbonate, barium sulfate, etc., are commonly added to the water-soluble paint composition. All the extender pigments used can be used without any problems. These extender pigments can be used alone or as a mixture of two or more. Furthermore, in the composition of the present invention, as component (2), coloring pigments other than titanium dioxide pigments, such as carbon black, red iron, vermilion, molybdenum red, yellow lead, phthalocyanine blue, phthalocyanine green, etc., are usually water-soluble paints. Organic or inorganic coloring pigments used in; such as methanol, ethanol, isopropanol, etc.
Alcohol solvents, ether alcohols or ether solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, dioxane, etc., ether ester solvents such as diethylene glycol monomethyl acetate, ethylene glycol monomethyl ether acetate, etc., acetone, diacetone Water-soluble solvents such as alcohols, ketone solvents, etc.; Various additives generally used in water-soluble paint compositions, such as anti-skinning agents, anti-cissing agents, anti-color separation agents, dispersants, etc. agents etc. are used. These can be used alone or as a mixture of two or more. Conventional water-soluble paint compositions have the required quality,
Alternatively, the formulation varies depending on the application, and it is difficult to make a general statement about the formulation, but for example, in the case of a glossy top coat, the paint composition should contain 5 to 25% by weight of titanium dioxide pigment and 30 to 30% by weight of a water-soluble synthetic resin (solid content).
40% by weight, extender pigment 0-10% by weight, coloring pigment 0-10% by weight
One example of a known composition is 10% by weight of a water-soluble solvent, 5-20% by weight of a water-soluble solvent, 0.1-0.5% by weight of a color separation inhibitor, 0.05-0.2% by weight of an anti-cissing agent, and the balance of water and other additives. Therefore, in the case of the water-soluble coating composition of the present invention,
With a similar formulation, it is possible to reduce the titanium dioxide pigment and water-soluble solvent in the above composition by 10% or more, and the amount of various additives by 10% or more, sometimes nearly 50%. For example, titanium dioxide pigment is 5-22% by weight.
In addition, the water-soluble solvent can also be added in an amount of 5 to 10% by weight. Furthermore, the amount of the color separation inhibitor can be about 0.1 to 0.2% by weight, and the amount of the anti-cissing agent can be about 0.02 to 0.1% by weight. All of these effects are due to the use of a specific pigment grade titanium dioxide slurry. The water-soluble coating composition of the present invention as described above is advantageously produced by the following method. First, a water-soluble synthetic resin is dissolved in water and, if necessary, a water-soluble solvent, and then the pigment-grade titanium dioxide slurry, extender pigment, other coloring pigments, various additives, etc. are simply mixed and prepared to form a water-soluble paint. A composition can be obtained. In other words, by using a specific pigment-grade titanium dioxide slurry, the conventional strong dispersion process (e.g., long kneading using a ball mill, high-speed disperser, etc.) for dispersing dry powder titanium dioxide pigment can be omitted. be able to. The thus obtained water-soluble coating composition of the present invention is applied to various substrates by conventional coating methods such as electrodeposition coating, dipping coating, spray coating, electrostatic coating, roller coating, brush coating, etc., and is coated at room temperature. Alternatively, it is formed into a film by heating and drying. Hereinafter, the details of the present invention will be explained with reference to Examples. Reference example 1 50kg of sulfuric acid method rutile crude pigment (primary particle size 0.25μ) crushed with a roller mill was revalved with water to 400g.
g/slurry (Nopco SN-5040 as dispersant)
(0.1% addition to _TiO2 ) and vibration mill grinding (media, alumina balls, residence time 30 min)
After that, the slurry concentration was lowered to 200g/ and classified, and only the fine slurry was collected and the concentration was adjusted (220g/), and 1136 (TiO ₂ 250Kg) was sent to an inorganic surface treatment process. Heat the slurry to 70℃ and add titanyl sulfuric acid solution (100g/ _TiO2 )25
was added and aged for 20 minutes, then a sodium silicate solution (SiO ₂ 60g/21) was added and aged for 20 minutes, and then a sodium aluminate solution (as Al ₂ O ₃₎ was added.
After adding 100g/) 55 and aging for 20 minutes, it was neutralized using dilute sulfuric acid (200g/), aged for 20 minutes, and filtered, washed, and dehydrated using a high-pressure press filter. The solids concentration of the slag was 64%. Transfer 156 kg of this slag (100 kg of TiO ₂ ) to a kneader, add 0.7 kg of sodium tripolyphosphate, 0.2 kg of Poise 530 (polyacrylate dispersant manufactured by Kao Atlas), and 0.2 kg of Emulgen L-40 (polyoxyethylene alkyl ether type manufactured by Kao Atlas). Pour 0.2Kg of dispersion into the
After kneading and fluidizing, it is completely slurried with a disperser, then sand milled (media, glass beads), and aged with gentle stirring for 24 hours to produce a pigment grade titanium dioxide slurry with a solid content of 64% by weight. I got (A). Reference example 2 500 kg of sulfuric acid method rutile coarse pigment (primary particle size 0.23μ) crushed with a roller mill was revalved with water.
400g/slurry (Nopco SN- as a dispersant)
5040 was added (0.15% based on TiO ₂ ), a fine slurry was obtained in the same manner as in Reference Example 1, the concentration was adjusted (220 g/), and 1136 (250 kg of TiO ₂ ) was sent to the inorganic surface treatment process. Heat the slurry to 70℃ and add titanyl sulfuric acid solution ( _100g /TiO2)
After adding 25 and aging for 20 minutes, then adding aluminum sulfate solution (Al ₂ O ₃ 108g/) 51 and aging for 20 minutes, neutralizing with caustic soda solution (200g/) and aging for 20 minutes, It was filtered, washed, and dehydrated using a high-pressure press filter. The solids concentration of the slag was 65%. Transfer 152 kg of this slag (100 kg of TiO ₂ ) to a kneader, and add 0.7 kg of sodium tripolyphosphate as a dispersant.
Pigment-grade titanium dioxide slurry (B) with a solid content of 65% was prepared in the same manner as in Reference Example 1, except that 1kg of Aron T-40 (sodium polyacrylate manufactured by Toagosei; non-volatile content 40% by weight) was used. Obtained. Reference Example 3 Fine slurry was obtained in the same manner as in Reference Example 2 using rutile coarse pigment, and the concentration was adjusted (220 g/
) and sent 1136 (250Kg of TiO ₂ ) to the inorganic surface treatment process. The slurry was heated to 70℃ and a sodium silicate solution (60g/SiO ₂ ) was added.
Aged for 20 min, then treated with aluminum sulfate solution (as _{Al2O3 )}
After adding 108 g/) 46 and aging for 20 minutes, it was neutralized using dilute sulfuric acid (200 g/), and after aging for 20 minutes, it was filtered, washed, and dehydrated using a high-pressure press filter. The solids concentration of the slag was 62%. This slag 161Kg
(TiO ₂ 100Kg) was transferred to a kneader, and 0.5Kg of sodium tripolyphosphate and Emulgen L-40 were added as dispersants.
A pigment-grade titanium dioxide slurry (C) with a solid content of 62% by weight was obtained using the same procedure as in Reference Example 1 except that 0.5 kg was used. Example 1 In a reaction vessel, 23 parts by weight of soybean oil fatty acid, 8 parts by weight of pentaerythritol, and ethylene glycol.
0.5 parts by weight, 10 parts by weight of phthalic anhydride, 1 part by weight of xylene
After dehydrating at 220°C until the acid value reaches 17, the mixture was cooled to 100°C, and reacted at 100°C for 4 hours while adding 8.5 parts by weight of methyl methacrylate and 1.5 parts by weight of acrylic acid dropwise. A resin with an acid value of 38 was obtained. After the reaction was completed, 3.5 parts by weight of triethylamine was added to neutralize the mixture, and then 15 parts by weight of ethylene glycol monobutyl ether and 30 parts by weight of tap water were added to dissolve and dilute. After dissolving 61 kg of the water-soluble acrylic modified alkyd resin solution () obtained in the above reaction in a mixture of 2 kg of tap water and 8 kg of isopropanol, 16.1 kg of the pigment grade titanium dioxide slurry (C), 3 kg of red iron oxide, 9 kg of precipitated barium sulfate, Add 5 kg of kaolin one by one,
Disperse using a high speed stirrer. Next, a lead naphthenate dryer (metal content 15%) 1.5 kg, a cobalt naphthenate dryer (metal content 5%) 0.5 kg, anti-skinning agent (product name Disparon #501 manufactured by Kusumoto Kasei) 0.3
Kg, 0.1 Kg of anti-cissing agent (trade name Sanfinol 104 manufactured by Nissin Chemical Co., Ltd.), 0.1 Kg of antifoaming agent (trade name Formaster NS manufactured by San Nopco Co., Ltd.) and 1.5 Kg of water were thoroughly stirred with a disper. An air-drying acrylic modified alkyd resin coating composition was obtained. Examples 2 and 3 Water-soluble air-drying acrylic modified alkyd resin paints were obtained in the same manner as in Example 1 using the formulations shown in Table 1.

[Table] Comparative Example 1 After mixing 9.5 kg of tap water, 8 kg of isopropanol, 61 kg of water-soluble acrylic modified alkyd resin solution (), 10 kg of powdered titanium dioxide pigment, 3 kg of red iron, 9 kg of precipitated barium sulfate, and 5 kg of kaolin, use a sand mill. It was dispersed. Next, 1.5 kg of lead naphthenate dryer (15%) and 0.5 kg of cobalt phthenate dryer (5%) were added, and further 0.3 kg of anti-skinning agent (same as Example 1) and antifoaming agent (same as Example 1) were added. ) 0.1Kg and anti-cissing agent (Example 1)
0.15 kg (same as the above) were mixed and prepared to obtain a water-soluble air-drying type acrylic modified alkyd resin paint of a comparative example.
The coating composition is one that has been commonly used in the past. Comparative Examples 2 and 3 Based on the formulations shown in Table 2, water-soluble air-drying acrylic modified alkyd resin paints were obtained in the same manner as in Comparative Example 1.

[Table] Table 3 shows the results of a comparative test using the water-soluble air-drying acrylic modified alkyd resin paints obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The coating method, film thickness (coating amount), drying conditions, etc. were all in accordance with JIS as indicated for each test method.

[Table] It is clear from Table 3 that when comparing Comparative Example 1 (conventional product) and Example 1 (using titanium dioxide slurry and reducing the amount of anti-cissing agent added), Example 1 has higher gloss. , color separation properties were excellent, and no change in cissing properties was observed even when the amount of the anti-cissing agent was reduced. In addition, in Example 2 (using titanium dioxide slurry) and Comparative Example 2 (using powdered titanium oxide), the amount of anti-cissing agent added and the water-soluble solvent isopropanol were reduced.
Example 2 was extremely excellent in gloss, color separation, and repellency. Furthermore, Example 3 (using titanium dioxide slurry)
In Comparative Example 3 and Comparative Example 3 (using powdered titanium dioxide), the coloring pigment was changed to phthalocyanine blue, but Example 3 had very good color separation and repellency. Example 4 In a reaction vessel, 10 parts by weight of linseed oil, 1,2-polybutadiene (trade name NISSO-PB- manufactured by Nippon Soda)
3000), 9 parts by weight of maleic anhydride, 0.2 parts by weight of antioxidant, and 0.5 parts by weight of xylene were mixed, and the reaction was continued at 190°C for 5 hours to obtain a resin with an acid value of 72. Then, it was diluted with 20 parts by weight of ethylene glycol monoethyl ether. Further, 5 parts by weight of triethylamine was added to neutralize the mixture, and 25 parts by weight of tap water was added to dissolve the mixture to obtain a water-soluble maleated polybutadiene resin solution (2). The water-soluble maleated polybutadiene resin solution 15
Kg, water-soluble alkyd resin solution (Dainippon Ink & Chemicals, trade name Watersol S199: acid value
43: Non-volatile content 60% by weight), 10 kg of tap water, 29.2 kg of the pigment grade titanium dioxide slurry (C), 6 kg of precipitated barium sulfate, and 5 kg of ethylene glycol monobutyl ether were mixed in sequence and dispersed using a high-speed stirrer. Next, 3 kg of isopropanol, 0.5 kg of triethylamine, 6.8 kg of tap water, and a water-soluble melamine resin solution (trade name: Nikaratsuku MW manufactured by Sanwa Chemical Co., Ltd.)
-22: Non-volatile content 70% by weight) 1.7 kg were mixed and sufficiently stirred to obtain a stoving type water-soluble paint composition of the present invention. Example 5 To 15 kg of the water-soluble maleated polybutadiene resin solution () obtained in Example 4, 25 kg of water-soluble alkyd resin solution (same as in Example 4) and 11 kg of tap water were added.
After sequentially mixing 25 kg of the pigment grade titanium dioxide slurry (A), 7 kg of precipitated barium sulfate, and 5 kg of ethylene glycol monobutyl ether and dispersing with a high-speed stirrer, 3 kg of isopropanol, 0.5 kg of triethylamine, 7.8 kg of tap water and Mix 1.7 kg of water-soluble melamine resin solution (same as Example 4),
A stoving type water-soluble coating composition of the present invention was obtained. Example 6 6 parts by weight of acrylic acid, 14 parts by weight of 2-hydroxyethyl methacrylate, 40 parts by weight of methyl methacrylate, 40 parts by weight of ethyl acrylate, and polymerization catalyst
1.5 parts by weight were mixed and a 10 hour reaction was carried out at 100°C in a reaction vessel to obtain an acrylic resin with an acid value of 47. After the reaction was completed, 35 parts by weight of ethylene glycol monoethyl ether and 5 parts by weight of triethylamine were added to neutralize the mixture, and then diluted with 60 parts by weight of tap water to obtain a water-soluble acrylic resin solution (). 60 kg of this water-soluble acrylic resin solution (), 17.7 kg of the pigment-grade titanium dioxide slurry (C), 4 naphthol-based red pigments (product name: FB Conc, manufactured by Sanyo Shiki)
Kg, anti-cissing agent (product name L- manufactured by Nippon Unica)
5310) 0.02Kg and dispersed with a high-speed disperser, water-soluble melamine resin solution (same as Example 4)
11 kg of dimethylethanolamine, 0.5 kg of isopropanol, and 4.3 kg of tap water were successively added and mixed with thorough stirring to obtain a water-soluble stoving type acrylic melamine resin paint of the present invention. Comparative Example 4 A water-soluble alkyd resin solution (Example 4) was added to 15 kg of the water-soluble maleated polybutadiene resin solution ().
), 20 kg of tap water, 19 kg of powdered titanium dioxide pigment, 6 kg of precipitated barium sulfate, and 2.5 kg of ethylene glycol monobutyl ether were mixed in sequence and dispersed in a sand mill, followed by 2 kg of isopropanol, 0.5 kg of triethylamine, and tap water. 10.5
Kg and 1.7 Kg of water-soluble melamine resin solution (same as Example 4) were added to obtain a conventional water-soluble resin paint. Comparative Example 5 To 60 kg of the water-soluble acrylic resin solution (), 11 kg of powdered titanium dioxide pigment, 4 kg of naphthol-based red pigment (same as Example 6), 0.05 kg of anti-cissing agent (same as Example 6), and tap water. 6 kg was added, mixed and dispersed with a sand mill. After kneading, 11 kg of a water-soluble melamine resin solution (same as in Example 4), 0.5 kg of dimethylethanolamine, 3 kg of isopropanol, and 5 kg of tap water were added and mixed to obtain a conventional water-soluble baking type acrylic melamine resin paint. The water-soluble paints obtained in Examples 4 to 6 and Comparative Examples 4 to 5 were applied by air spray onto a zinc phosphate treated steel plate to a dry film thickness of 25 microns. After coating, Examples 4, 5 and Comparative Example 4 were 140
℃ for 20 minutes, Example 6 and Comparative Example 5 at 150℃
A test piece was obtained by baking and drying for 20 minutes. The test results are shown in Table 4.

【table】

[Table] From Table 4 above, it is clear that the conventional product (Comparative Example 4)
The composition of the present invention (Example 4), which uses a titanium dioxide slurry and reduces the amount of a water-soluble solvent with wettability, has improved gloss and hiding properties, and has improved coating surface condition (repellency). The image quality was also good, and the image clarity was further improved. In addition, the composition of the present invention (Example 5), in which the titanium dioxide pigment content was reduced compared to the conventional product, exhibited excellent performance in terms of gloss, sharpness, and hiding power. Furthermore, compared to the conventional product (Comparative Example 5), the composition of the present invention (Example 6) uses titanium dioxide slurry and reduces the amount of anti-cissing agent added.
As in Example 4, the coating film surface condition was excellent, and in particular, the prevention of repelling and color separation properties were also excellent.

Claims (1)

[Claims] 1. (a) Water-soluble synthetic resin; (b) Condensed phosphoric acid is added to a slurry or wet cake containing titanium dioxide with a water content of 40% by weight or less obtained in the wet finishing step of the pigment-grade titanium dioxide manufacturing process. A pigment-grade titanium dioxide slurry obtained by adding a dispersant consisting of a salt and a combination of polyacrylate and/or polyoxyethylene alkyl ether to form a fluid slurry, and then dispersing it by wet grinding; (iii) water; (iv) A water-soluble paint composition consisting of an extender, various coloring pigments other than titanium dioxide, various additives, and a water-soluble solvent, if necessary.