JP2017019882A - Aqueous coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use an aqueous coating for adding good metallic glossiness same as conventional coating using organic solvents, increasing solid component concentration in the coating for shortening drying time and reducing usage rate of brilliant pigments.SOLUTION: A composition containing a brilliant pigment as a metal piece by pulverizing a vapor deposited metal film or the like and cellulose acetate is used as an aqueous coating. A substitution degree of the cellulose acetate is 0.5 to 1.2.SELECTED DRAWING: None

Description

The present invention relates to an aqueous coating composition capable of imparting a metallic luster close to the metallic luster possessed by metal plating, metal foil, and the like.

As a paint capable of imparting a metallic luster close to the metallic luster possessed by metal plating, metal foil, etc. by forming a coating film, a paint composition comprising a glittering pigment obtained by pulverizing a deposited metal film into a metal piece Known (for example, Patent Document 1). In such a coating composition, the content of the glitter pigment is set to 15% or more in terms of PWC (ratio in the solid content in the paint), and a large amount of solvent is used so that the glitter pigment is applied to the surface of the object to be coated. It is oriented in a planar shape on the top. In this way, the glossy pigment having a very thin thickness is orientated in a planar shape along the surface of the base material, so that metallic gloss can be imparted to the object to be coated.

According to Patent Document 2, in such a conventional coating composition, an organic solvent is used as a solvent, and after coating the coating material on the object to be coated, the organic solvent in the coating film volatilizes. The film thickness of the coating film on the object to be coated decreases rapidly, and the inclination of the glitter pigment contained in the coating film with respect to the base material becomes gentle. As a result, the glitter pigment is oriented in a planar shape. To do. That is, such a coating composition contains a large amount of an organic solvent because it requires a drastic reduction in the thickness of the coating film in order to orient the glitter pigment in a planar shape.

However, in recent years, from the viewpoints of improving the working environment and protecting the environment, there has been a demand for water-based paints that do not use organic solvents or reduce the amount of organic solvents used as much as possible. Such water-based coatings are variously studied for metallic coatings using aluminum flakes obtained by pulverizing metal powder or metal foil with a ball mill or the like.

Examples of the aqueous metallic paint containing an aqueous cellulose derivative include a paint composition disclosed in Patent Document 2 and a paint composition disclosed in Patent Document 3.

In paragraph [0042] of Patent Document 2, it is disclosed that the aqueous cellulose derivative is used in a proportion of 1 to 30% by weight with respect to the resin solid content of the aqueous resin. Further, paragraph [0033] of Patent Document 3 discloses that the acrylic resin solid content and the cellulose acetate butyrate resin solid content are used in a weight ratio of 100: 45 to 55.

However, even if the formulation proposed in the conventional water-based metallic paint composition including the paint compositions disclosed in Patent Document 2 and Patent Document 3 is applied to the paint composition exhibiting the above metallic gloss. A good metallic luster could not be obtained.
Japanese Patent Laid-Open No. 11-80620 JP 2009-15537 A JP 7-331118 A JP 2006-297268 A

An object of the present invention is to provide an aqueous coating composition capable of imparting good metallic gloss. Another object of the present invention is to increase the solids concentration in the paint in order to shorten the drying time. Another object of the present invention is to reduce the usage rate of the luster pigment in order to save resources and reduce costs.

The water-based paint composition of the present invention is characterized by containing a glittering pigment made into a metal piece by pulverizing a deposited metal film and cellulose acetate having a substitution degree of 0.5 to 1.2.

By using the water-based coating composition of the present invention, a good metallic gloss can be imparted to the coating film. Moreover, drying time can be shortened by using the water-based coating composition of this invention. Furthermore, the use rate of a luster pigment can be reduced by using the water-based coating composition of this invention.

In the present invention, cellulose acetate having a substitution degree of 0.5 to 1.2 is used as the binder resin. By using such cellulose acetate as a binder resin, the glitter pigment in the coating film can be oriented in a planar state in a good state, and a good metallic gloss can be obtained. Moreover, by using such cellulose acetate as a binder resin, the solid content concentration in the coating can be increased, and the drying time can be shortened. Furthermore, by using such cellulose acetate as a binder resin, the dispersion of the glitter pigment can be improved, and the usage rate of the glitter pigment can be reduced.

The cellulose acetate in this invention has the substitution degree of 0.5-1.2 as mentioned above. If the degree of substitution is too high or too low, the water-solubilizing ability is low and the water-based paint cannot be obtained. In addition, if the degree of substitution is too high, the interfacial energy with the metal pieces increases, the dispersibility and orientation ability of the metal pieces decrease, the metallic gloss is impaired, and the solid content concentration in the paint cannot be increased. The PWC of the glitter pigment cannot be reduced. A more preferable range of substitution degree of cellulose acetate is 0.6 to 1.0.

Specific examples of the cellulose acetate as described above can be obtained by, for example, using cellulose acetate having a substitution degree of about 2.5 as a raw material, dissolving it in hydrous acetic acid, and deacetylating with a sulfuric acid catalyst to adjust the substitution degree. Soluble cellulose acetate (hereinafter, WSCA) having a water substitution degree of 0.5 to 1.2 is raised.

The weight average degree of polymerization (DPw) of WSCA measured by GPC-MALLS is, for example, 50 to 250, the degree of dispersion (DPw / DPn) is, for example, 1.2 to 6, and the fluctuation of the degree of substitution between molecules is intermolecular substitution. The half-value width of the degree distribution curve was divided by the theoretical value of the half-value width of the intermolecular substitution degree distribution curve that inevitably occurs in the reaction probability theory derived from the average substitution degree and the weight average molecular weight by the binomial theorem. For example, the index is 1.2 to 2.7 using an index (hereinafter, composition distribution index or CDI) as an index. In relation to the water solubilization ability, the composition distribution index is preferably small, for example, 1.2 to 2.0.

In addition to the WSCA, other cellulose derivatives can be used in combination. Other cellulose derivatives are not particularly limited, and carboxymethyl cellulose acetate butyrate can be mentioned as a preferable one.

The glitter pigment used in the present invention is a glitter pigment obtained by pulverizing a deposited metal film into a metal piece. Such a luster pigment can be generally obtained by vapor-depositing a metal film on a base film, peeling off the base film, and then pulverizing the deposited metal film into a metal piece. The average thickness of the glitter pigment is preferably in the range of 0.01 to 0.1 μm. Moreover, it is preferable that an average particle diameter (median value) is the range of 5-100 micrometers. The average particle diameter can be measured by a laser diffraction method.

The material of the deposited metal film is not particularly limited, and examples thereof include metal films such as aluminum, gold, silver, copper, brass, titanium, chromium, nickel, nickel chromium, and stainless steel. Among these, aluminum is particularly preferable. Accordingly, the glitter pigment of the present invention is preferably an aluminum pigment.

It is known that when an aluminum pigment is blended in an aqueous paint, metal aluminum reacts with moisture to generate hydrogen. Therefore, the aluminum pigment used in the present invention is preferably one in which such generation of hydrogen is suppressed. Examples thereof include an aluminum pigment coated with an organic film or an inorganic film.

Organic coatings include monomeric or polymer (oligomer) type fatty acids such as dimer acid, organic phosphates, phosphate ester compounds, organic phosphonic acid compounds (esters), organosilane compounds such as aminosilane compounds and silane coupling agents. Examples of inorganic coatings include borate, phosphate, phosphite, silicate, molybdate, vanadate, chromium oxide, zirconium oxide, and aluminum oxide. .

Use of such an aluminum pigment whose surface of the metal pigment is stabilized is preferred because generation of hydrogen gas in the aqueous base coating composition can be suppressed.

The aluminum pigment used in the present invention preferably has a hydrogen gas generation amount described below of 3 ml or less per 1 g of aluminum pigment. By using such an aluminum pigment, generation of hydrogen gas in the aqueous base coating composition can be suppressed, and safety when the coating is stored can be improved.

The hydrogen gas generation amount is the hydrogen gas generation amount when a 2.5% by mass paint containing an aluminum pigment is prepared and 10 days have elapsed after preparation of the paint at 50 ° C. Since the amount of hydrogen gas generated is easily affected by the aqueous solvent in the paint, it was measured here with a nonvolatile content of 2.5% by mass.

In the aqueous coating composition of the present invention, when this is used as a so-called base coating, the content of the glitter pigment is preferably in the range of 10 to 30% by mass in terms of PWC. By increasing the PWC in the coating composition, the planar orientation of the glitter pigment can be promoted, and better metallic gloss can be imparted. However, if the PWC is too high, the adhesion in the laminated coating, that is, the adhesion to the underlying coating layer and the clear coating layer tends to be reduced. A more preferable range of PWC is 15 to 40% by mass.

In the aqueous coating composition of the present invention, WSCA is used as a binder resin. However, if necessary, another binder resin may be further contained, and the other binder resin may be a main component. Examples of such other binder resins include at least one selected from the group consisting of acrylic resins, melamine resins, urethane resins, and polyester resins. These resins are generally used as water-soluble resins or water-based emulsion resins. Preferable examples include acrylic resin, melamine resin and polyester resin, but those having high affinity with the surface of the aluminum pigment, for example, functional groups such as amino group, carboxyl group, phosphoric acid group or silicic acid group It is preferable to use one having This is because cohesive failure in the base coating layer can be suppressed.

The function of WSCA is to improve the “wetting” or “affinity” of a piece of metal such as an aluminum pigment to a paint solvent or binder resin. For example, Patent Document 2 describes the importance of orientation of scaly aluminum pieces in the process from coating application to drying in obtaining a metallic glossy coating film. It is not fully considered whether it is dominated by. The inventors of the present invention have found that such orientation behavior is related to the “wetting” of the aluminum pieces and the affinity with the “binder resin”, and have completed the present invention. In so-called solvent-based paints using a conventional organic solvent as a main solvent, for example, the free energy at the interface between cellulose acetate butyrate and aluminum is low, and adding cellulose acetate butyrate to the binder resin can wet the aluminum pieces in the paint. Improved and good dispersion of aluminum pieces. In the drying process of the paint and the completion of the coating film, a specific interaction between the aluminum piece and cellulose acetate butyrate occurs, and the aluminum piece is also oriented following the formation of the cellulose acetate butyrate film. . In the absence of such specific interaction, the aluminum pieces are more energetically stable in contact with the air than in contact with the paint solvent or other binder resin, so that in the coating film forming process, the aluminum pieces Will be exposed and the metallic luster will be impaired. Therefore, in developing water-based paints for the purpose of solvent removal, an aluminum piece “wetting” improver is required to replace water-insoluble cellulose acetate butyrate. The inventors of the present invention were published in non-patent literature (van Oss C. J., Chaudhury M. K., Good R. J., Chem. Rev., 88, 927-941 (1988)). As a result of searching for a “wetting” improver for metal pieces for water-based paints with reference to the theory, it was found that WSCA was most suitable.

In order to develop the function of WSCA, it is sufficient that WSCA is present in an amount of 10 to 80% in the solid content of the coating composition, and it is not necessarily the main component when using a plurality of binder resins. When the ratio of WSCA is larger than this range, there is no room for a bright pigment or other binder resin, and the purpose of the paint may not be achieved. Further, when the ratio of WSCA is less than this range, the “wetting” and “affinity” of the glitter pigment are deteriorated, and it becomes impossible to orientate in a plane state in a good state, and the metallic gloss is lowered. .

The aqueous coating composition of the present invention can be prepared by mixing a glitter pigment, WSCA, and other binder resin as necessary in an aqueous solvent.

The aqueous solvent other than water used in the aqueous coating composition of the present invention is not particularly limited, but a solvent having high water solubility is desirable. Examples include isopropyl alcohol, methanol, methyl glycol, methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, methyl diglycol, hexyl glycol, methylpropylene glycol, methoxypropanol (propylene glycol monomethyl ether), methylpropylene diglycol, and the like. .

The aqueous paint composition of the present invention may be prepared in a state where the concentration of components other than the aqueous solvent is high, and when applying the paint, an aqueous solvent may be added and diluted to a predetermined concentration. The aqueous coating composition of the present invention is preferably in a state where it can be applied diluted to a paintable viscosity, that is, the coating material non-volatile content at the time of application is 10% by mass or less.
By reducing the non-volatile content in this way, the coating workability such as spray coating is improved, the coating film surface can be smoothed, and a good metallic gloss can be easily obtained.

Moreover, in the water-based coating composition of the present invention, as necessary, waxes such as polyethylene wax and polypropylene wax, drying agents, dispersants, thickeners, ultraviolet absorbers, and light stabilizers may be used as additives. Further, an antioxidant, a curing catalyst and the like can be blended.

The concentration of the binder resin (WSCA and other binder resins) in the aqueous coating composition of the present invention is preferably in the range of 30 to 80% by mass, more preferably in the range of 60 to 75% by mass. preferable.

The coating film obtained with the aqueous coating composition of the present invention can be used as, for example, one layer of a laminated coating film. For example, a base coating layer formed on a substrate, a base coating layer formed on the base coating layer by applying the aqueous coating composition of the present invention, and a base coating layer It can be used as a layer of a laminated coating film including a clear coating film layer.

The metal-tone laminated coating film obtained with the aqueous coating composition of the present invention has a structure in which a base coating film layer, a base coating film layer, and a clear coating film layer are laminated as described above, for example. The base coating film layer is formed from the aqueous coating composition of the present invention, and the glitter pigment is in a state of being oriented in a planar shape. For this reason, favorable metallic luster is shown.

The base material on which the aqueous coating composition of the present invention is applied is not particularly limited, and a base material that requires metallic gloss can be used as the base material. For example, the water-based coating composition of the present invention can be applied to various parts such as automobile parts such as automobile wheels and handles, automobile bodies, electrical appliances, and cellular phones to form a metal-tone laminated coating film.

The base coating layer on which the aqueous coating composition of the present invention is applied is preferably a colored coating, and its color is preferably black. By making the base coating layer black, the reflection of light transmitted through the base coating layer is reduced, it is difficult to become white, and good metallic luster is exhibited.

The thickness of the base coating film layer is not particularly limited, but is generally in the range of 10 to 30 μm. In addition, the thickness of the clear coating layer in the present invention is not particularly limited, but generally the thickness is preferably in the range of 15 to 40 μm.

The thickness of the base coating layer formed by applying the aqueous coating composition of the present invention is preferably as thin as possible, generally 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less. Although not particularly limited, it is generally 0.1 μm or more.

The base coating and clear coating combined with the aqueous coating composition of the present invention may be a solvent-based coating or a water-based coating. Moreover, a powder coating material may be sufficient. The clear paint may be a so-called colored clear paint.

In the application of the aqueous coating composition of the invention as a base coating, for example, the aqueous coating composition can be applied after applying a base coating and baking and curing. By baking and curing the base coating, it is possible to prevent the glitter pigment in the aqueous coating composition from sinking into the base coating layer when the aqueous coating composition is applied thereon.

In the application of the aqueous coating composition of the invention as a base coating, for example, the aqueous coating composition is applied, preliminarily dried, then the clear coating is applied, and then the base coating layer and the clear coating layer are applied. May be baked and cured at the same time. In this way, the coating process can be simplified by performing the coating and baking hardening process by a so-called two-coat one-bake method. However, it is not always necessary to use the 2-coat 1-bake method, and after applying the aqueous base paint, it may be pre-dried and baked and cured, and then the clear paint may be applied.

In the application of the aqueous coating composition of the invention as a base coating, for example, a base coating is applied and pre-dried, and then the aqueous coating composition is applied and pre-dried, and then a clear coating is applied thereon. The base coating layer, the base coating layer, and the clear coating layer may be simultaneously baked and cured. That is, you may perform a painting and baking hardening process by what is called a 3 coat 1 bake system. Thus, a manufacturing process can be simplified by forming a coating film by a 3 coat 1 baking system.

The conditions for preliminary drying of the paint are not particularly limited, but it is generally preferable to dry at a temperature in the range of 60 to 90 ° C. for 1 to 10 minutes. This drying time also depends on the solid content in the coating, and generally a short predrying time can be obtained by increasing the solid content. For this purpose, the solid content of the aqueous coating composition of the present invention is preferably 5 to 10%.

The conditions of the bake curing treatment are appropriately selected according to the binder resin used for each paint,
Generally, it is baked and cured by heating at a temperature of 120 to 160 ° C. for 10 to 40 minutes.

ADVANTAGE OF THE INVENTION According to this invention, favorable metal-like glossiness can be provided with respect to various articles | goods using an aqueous coating composition. Also, the drying time can be shortened by increasing the solid content concentration in the paint. Furthermore, the usage rate of the luster pigment can be reduced.

Hereinafter, the present invention will be described in detail with specific examples, but the present invention is not limited to the following examples.

[Darkness pigment]
As the glitter pigment, an aluminum powder paste containing aluminum powder obtained by pulverizing aluminum vapor-deposited powder was used. Specifically, the trade name “HYDROSHINEWS3001” (manufactured by Big Chemie) was used.

[Synthesis Example 1 of water-soluble cellulose acetate (WSCA)]
5.1 parts by weight of acetic acid and 2.0 parts by weight with respect to 1 part by weight of cellulose acetate (manufactured by Daicel, trade name “L-50”, acetyl group total substitution degree 2.43, 6% viscosity: 110 mPa · s) A part by weight of water was added and stirred at 40 ° C. for 5 hours to obtain a solution having a uniform appearance. 0.13 parts by weight of sulfuric acid was added to this solution, and the resulting solution was kept at 70 ° C. to carry out hydrolysis (partial deacetylation reaction; aging). In this aging process, water was added to the system twice in the middle. That is, 0.67 parts by weight of water was added 1 hour after the reaction was started, and 1.67 parts by weight of water was added after another 2 hours, and the reaction was further continued for 3 hours. The total hydrolysis time is 6 hours. The first aging from the start of the reaction to the first water addition, the second aging from the first water addition to the second water addition, the reaction from the second water addition to the end of the reaction (ripening completed) This is called the third aging. After carrying out the hydrolysis, the temperature of the system is cooled to room temperature (about 25 ° C.), and 15 parts by weight of acetone / methanol = 1/2 (weight ratio) mixed solvent (precipitating agent) is added to the reaction mixture to cause precipitation. Was generated. The precipitate was recovered as a wet cake having a solid content of 15% by weight, and washed by adding 8 parts by weight of methanol and draining to a solid content of 15% by weight. This was repeated three times. The washed precipitate was further neutralized by washing twice with 8 parts by weight of methanol containing 0.004% by weight of potassium acetate, and dried to obtain water-soluble cellulose acetate (WSCA).

[Synthesis Examples 2 to 9 of WSCA]
WSCA was obtained in the same manner as in Synthesis Example 1 except that the reaction temperature, first aging time, second aging time, third aging time, and precipitating agent were changed as shown in Table 1.

The total acetyl group substitution degree (hereinafter simply referred to as substitution degree or DS), weight average polymerization degree (DPw), degree of dispersion (DPw / DPn), and composition distribution index (CDI) of WSCA obtained in each synthesis example. It measured by the following method. The production conditions and the measurement results (analytical values) of the physical properties of the obtained WSCA are shown in Table 1. The “sample number” in Table 1 means the sample number of the obtained WSCA.

[Measurement of substitution degree (DS)]
The unsubstituted hydroxyl group of the WSCA sample was propionylated according to the method of Tezuka (Carbohydr. Res., 273, 83 (1995)). The total degree of acetyl group substitution of propionylated WSCA was determined from a signal of 169 to 171 ppm of acetylcarbonyl and a signal of 172 to 174 ppm of propionylcarbonyl in ¹³ C-NMR according to the method of Tezuka (same as above).

[Measurement of weight average degree of polymerization (DPw), degree of dispersion (DPw / DPn)]
The weight average polymerization degree and dispersion degree of WSCA were determined by conducting GPC-light scattering measurement under the following conditions after being led to propionylated low-substituted cellulose acetate.
Equipment: GPC “SYSTEM-21H” manufactured by Shodex
Solvent: Acetone Column: 2 GMHxl (Tosoh), same guard column Flow rate: 0.8 ml / min
Temperature: 29 ° C
Sample concentration: 0.25% (wt / vol)
Injection volume: 100 μl
Detection: MALLS (multi-angle light scattering detector) (manufactured by Wyatt, “DAWN-EOS”)
MALLS correction standard substance: PMMA (molecular weight 27,600)

[Measurement of composition distribution index (CDI)]
The CDA of WSCA was determined by conducting HPLC analysis under the following conditions after being led to propionylated low substituted cellulose acetate.
Equipment: Agilent 1100 Series
Column: Waters Nova-Pak phenyl 60Å 4 μm (150 mm × 3.9 mmΦ) + guard column Column temperature: 30 ° C.
Detection: Varian 380-LC
Injection volume: 5.0 μL (sample concentration: 0.1% (wt / vol))
Eluent: Liquid A: MeOH / H ₂ O = 8/1 (v / v), Liquid B: CHCl ₃ / MeOH = 8/1 (v / v)
Gradient: A / B = 80/20 → 0/100 (28 min); Flow rate: 0.7 mL / min
First, a calibration curve of elution time versus DS was created by HPLC analysis of a sample with known DS in the range of 0 to 3 acetyl DS (acetyl group total substitution degree). Based on the calibration curve, the elution curve (time vs. detected intensity curve) of the unknown sample is converted to the DS vs. detected intensity curve (composition distribution curve), and the uncorrected half-value width X of this composition distribution curve is determined. The corrected half width Z of the distribution was determined.
Z = (X ² −Y ² ) ^1/2
Y is a device constant defined by the following equation.
Y = ax + b
a: X value of a sample with acetyl DS = 3 b: X value of a sample with acetyl DS = 0 x: Acetyl DS of unknown sample
From the corrected half width Z, the composition distribution index (CDI) was determined by the following formula.
CDI = Z / Z ₀
Here, Z ₀ is the composition distribution generated when acetylation and partial deacetylation in the preparation of all partially substituted cellulose acetates occur with equal probability for all hydroxyl groups (or acetyl groups) of all molecules. Yes, defined by
DPw: weight average polymerization degree p: (acetyl DS of unknown sample) / 3
q: 1-p

[Carboxymethylcellulose acetate butyrate (CMCAB)]
Carboxymethylcellulose acetate butyrate (trade name “CMCA B-641-0.2”, acid value 40 mg KOH / g, manufactured by Eastman Chemical Company) was used.

[Synthesis of acrylic resin]
40 parts by mass of propylene glycol monoethyl ether is charged into a Kolben equipped with a stirrer, a temperature controller, and a cooling pipe, and 8.86 parts by mass of styrene, 8.27 parts by mass of ethylhexyl acrylate, 15.00 parts by mass of lauryl methacrylate, 2 -Hydroxyethyl methacrylate 34.80 parts by mass, methacrylic acid 3.07 parts by mass, acid phosphooxyhexa (oxypropylene) monomethacrylate (JAMP-100N, Johoku Chemical Co., Ltd.) 30.00 parts by mass, mixed monomer solution 100 parts by mass, And 43 parts by mass of an initiator solution of 3.0 parts by mass of tertiary butyl peroctoate (Kayaester O) and 40 parts by mass of propylene glycol monoethyl ether were added dropwise at 115 ° C. over 3 hours, and then stirring was continued for 30 minutes. , Then tertiary butyl peroctoate (Kaya ester O) 0.3 parts by weight was added dropwise in 1 hour initiator solution 20.3 parts by weight of 20 parts by mass of propylene glycol monoethyl ether, and further stirring continued for 1.5 hours. The obtained product was a phosphoric acid group-containing acrylic resin having an acid value of 106 mgKOH / g, an acid value of 86 mgKOH / g from a phosphoric acid group, a hydroxyl value of 150, and a number average molecular weight of 5000, and the nonvolatile content was 49%.

[Preparation of aqueous base coating composition]
A predetermined cellulose derivative is dispersed in 4.5 times (mass) of a predetermined solvent, and an aluminum powder paste (trade name WS-3001: nonvolatile content of 10% by mass, solvent: propyl alcohol), melamine resin (in order to obtain a predetermined configuration) The product name “Cymel 325” (manufactured by Nippon Cytec Industries, non-volatile content 80% by mass) or the above acrylic resin was added and stirred, and then 2.4 times the amount of dimethylmethanolamine diluted with 10% by mass water (vs. cellulose) Derivative, mass) was added with stirring, and then 20 times the amount of water (vs. cellulose derivative, mass) was gradually added.

The dispersion was diluted with a mixed diluent (a diluent in which water and propylene glycol monomethyl ether were mixed at a ratio of 4: 1) so as to have a predetermined nonvolatile content to obtain an aqueous coating composition.
The paint composition of these water-based paint compositions is shown in Table 2.

[Formation of laminated coating film]
Cationic electrodeposition paint (trade name “Power Top U-50”, a cation type electrodeposition paint manufactured by Nippon Paint Co., Ltd.) is dried on a dull steel sheet with a thickness of 0.8 mm, 10 cm × 30 cm treated with zinc phosphate. After electrodeposition coating so that the film thickness was 20 μm, baking was performed at 170 ° C. for 30 minutes. On the substrate electrodeposited as described above, as a base paint, water-based paint (trade name “AR-2000 Black”, manufactured by Nippon Paint Co., Ltd., is spray-coated so that the dry film thickness is 20 μm. After pre-drying at 80 ° C. for 5 minutes, baking and curing treatment was performed at 140 ° C. for 20 minutes.

Next, the aqueous coating composition is spray-coated so that the dry film thickness is 0.5 μm, preliminarily dried at 80 ° C. for a predetermined time, and then the clear paint is spray-coated so that the dry film thickness is 30 μm. Set for 10 minutes. Then, the baking process was performed at 140 degreeC for 20 minute (s), and the laminated coating film was formed.

As the clear paint, acrylic melamine paint (trade name “Super Lac O-200 Clear”, manufactured by Nippon Paint Co., Ltd.) was used.

About the obtained coating film, the following methods evaluated the external appearance (metallic gloss), gloss (angle 45 degrees), and initial adhesiveness.

[Appearance of coated film (metallic luster)]
The appearance of the coating film was evaluated by the naked eye according to the following criteria.
5: Metal gloss is very strong 4: Metal gloss is strong 3: Metal gloss is 2: Metal gloss is slightly felt 1: Metal luster is not felt so much

[Glossy (45 °)]
The gloss at an incident angle and an output angle of 45 ° was evaluated using a gloss meter (Nippon Denshoku Industries Co., Ltd. PG-II).

[Initial adhesion]
Hold the cutting blade of the cutter (NT cutter S type, A type or equivalent) at about 30 degrees with respect to the coating film, draw 11 parallel lines with an interval of 2 mm to reach the substrate, and then parallel Eleven parallel lines with an interval of 2 mm perpendicular to the line were drawn to form 100 grids on the coating film. After the adhesive tape (industrial adhesive tape manufactured by Nichiban Co., Ltd.) is uniformly pressed with fingertips on this grid so that no air bubbles remain, immediately hold one end of the adhesive tape and approximately 45 degrees to the coating surface. The tape was peeled off from the coating film at a sharp angle, and the number of grids in which 100 coating films were not removed was measured. These test results are listed in Table 3.

As is apparent from the results shown in Table 3, in Examples 1 to 12, particularly Examples 1 to 3 and 5 to 11 according to the present invention, good metallic gloss was obtained and excellent in initial adhesion. ing. In Example 2, good results were obtained while suppressing the usage rate of the aluminum pigment. In Example 3, good results were obtained while shortening the drying time.

As described above, according to the present invention, it is possible to obtain a good metallic gloss similar to that of a conventional solvent-based paint using an aqueous paint.

Claims (6)

A water-based paint composition comprising a glittering pigment formed into a metal piece by pulverizing a deposited metal film and cellulose acetate having a substitution degree of 0.5 to 1.2. The aqueous coating composition according to claim 1, wherein the cellulose acetate has a substitution degree of 0.6 to 1.0. The aqueous coating composition according to claim 2, further comprising another binder resin. The aqueous coating composition according to claim 3, wherein the other binder resin is at least one selected from the group consisting of an acrylic resin, a melamine resin, a urethane resin, and a polyester resin. The aqueous paint composition according to any one of claims 1 to 4, wherein the glitter pigment is an aluminum pigment. 6. The aqueous paint composition according to claim 5, wherein the aluminum pigment is an aluminum pigment coated with an organic coating or an inorganic coating.