JP7074710B2 - Painting method - Google Patents

Description

The present invention relates to a method for painting an automobile body including a steel plate member and a resin member.

Generally, in an automobile body, a resin member such as a plastic bumper or a plastic fender is attached to a metal member such as a vehicle frame (for example, a steel plate member).
Conventionally, in the painting of automobile bodies, the heat resistance of the resin member is lower than that of the metal member. After painting, the resin member is assembled to the metal member.

That is, in the painting process of the metal member, the paint for the metal member that cures at a relatively high temperature is applied to the metal member and cured, and in the coating process of the resin member, the paint for the resin member that cures at a relatively low temperature is applied. The paint is applied to the resin member and cured.

As a method of painting the metal member and the resin member in a separate process as described above, for example, in Patent Document 1, a colored base paint for a metal steel plate and a clear paint are applied to an automobile body made of a metal steel plate to obtain 120 to 140. A vehicle painting method has been proposed in which a bumper made of a resin material is baked at ° C, and a colored base paint for resin members and a clear paint are applied and baked at 90 to 110 ° C.

However, in the vehicle painting method described in Patent Document 1, since the paints used in the painting process of the metal steel plate portion and the resin material portion are different from each other, the color tone of the coating film of the metal steel plate portion and the coating film of the resin material portion are different. It is difficult to match the color tones of these, and there is a limit to reducing those color differences.

Therefore, in Patent Document 2, the same water-based coloring base paint is used for both the steel plate member and the resin member, and the coating film on the steel sheet member and the coating film on the resin member are coated on each of them. A method for reducing the color difference of the above is described.

Japanese Unexamined Patent Publication No. 2011-25153 Japanese Unexamined Patent Publication No. 2016-117031

However, according to the study by the present inventors, in the method described in Patent Document 2, the color tone of the resin member coating color may become whitish, especially when a light-colored paint such as pink is used. That is, even though the same paint was used for the steel plate member and the resin member, the color of the steel sheet member and the color of the resin member may be different.

The present invention has been made in view of the above-mentioned conventional circumstances, and is a method for painting an automobile body including a steel plate member and a resin member, which is a light-colored water-based base paint while reducing the load in the painting process. It is an object of the present invention to provide a coating method capable of reducing the difference in color of the coating film on both members after coating even when the above is used.

As a result of diligent studies to achieve the above object, the present inventors have found that the above problems can be solved by the following coating method, and have completed the present invention.
<1> A method of applying a single water-based light-colored base paint on the surface of an automobile body including a steel plate member and a resin member.
The content of titanium oxide in the water-based light-colored base paint is 15 to 30 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The content of the chromatic pigment in the water-based light-colored base paint is 2.5 to 4.5 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The content of the glycol ether-based hydrophilic organic solvent in the water-based light-colored base paint is 45 to 65 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The difference between the surface temperature of the steel plate member and the surface temperature of the resin member at the time of painting the aqueous light color base paint is 10 to 30 ° C.
The difference between the viscosity of the steel plate member after 1 minute of application of the water-based light-colored base paint and the viscosity of the resin member after 1 minute of application of the water-based light-colored base paint is 70 Pa · s or less. Painting method.
<2> The steel sheet member is a steel sheet to which electrodeposition coating and water-based intermediate coating are sequentially applied.
The coating method according to <1>, wherein a clear paint is applied onto a coating film formed by the water-based light color base paint and existing on the steel plate member.
<3> The resin member is a resin material coated with a water-based primer.
The coating method according to <1> or <2>, wherein the clear paint is applied onto the coating film formed by the water-based light-colored base paint and existing on the resin member.

According to the coating method of the present invention, a single water-based base paint is applied to the surface of an automobile body including a steel plate member and a resin member, so that a light-colored water-based base paint is used while reducing the load on the painting process. However, it is possible to reduce the difference in color of the coating film on both members after painting.

Hereinafter, the present invention will be described in detail, but these are examples of desirable embodiments, and the present invention is not specified in these contents.

The coating method of the present invention includes a step of applying a single water-based light-colored base paint on the surface of an automobile body including a steel plate member and a resin member.

In the present invention, the water-based light color base paint is L ^* a ^* b ^* specified in JIS Z8781-4 (2013) calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter. It means a water-based paint having an L ^* value as lightness of 45 to 65 in a color system.

The water-based light-colored base paint contains a water-soluble or water-dispersible resin component (hydrophilic resin component), a curing agent, a pigment, an organic solvent, and the like. The aqueous light color base paint can be prepared, for example, by dissolving or dispersing a hydrophilic resin component, a curing agent, a pigment, an organic solvent, or the like in water.

Examples of the hydrophilic resin component include a hydrophilic group (for example, a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, a polyoxyethylene bond, etc.) and a functional group that reacts with a curing agent (for example, a hydroxyl group). Examples thereof include resins having the above. Specific examples thereof include known hydrophilic resins such as acrylic resin, polyester resin, alkyd resin, chlorinated polyolefin resin, epoxy resin and polyurethane resin.

The content of the hydrophilic resin component in the water-based light-colored base paint is preferably 100 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint from the viewpoint of coating performance such as weather resistance and water resistance. It is 50 to 90 parts by mass, more preferably 55 to 85 parts by mass, and further preferably 60 to 80 parts by mass.

Examples of the curing agent include melamine resin, polyisocyanate compound, blocked polyisocyanate compound, carbodiimide group-containing compound and the like.

The content of the curing agent in the water-based light-colored base paint is preferably 10 to 10 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint from the viewpoint of coating performance such as weather resistance and water resistance. It is 50 parts by mass, more preferably 15 to 45 parts by mass, and further preferably 20 to 40 parts by mass.

Examples of the pigment include a coloring pigment, an extender pigment, a brilliant pigment and the like.
Examples of the coloring pigment include chromatic pigments, titanium oxide, and carbon black pigments. The chromatic pigment is a coloring pigment that exhibits a color other than white and black.
Examples of chromatic pigments include azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindolin pigments, isoindolinone pigments, and metal chelate azo pigments. Organic pigments such as system pigments, phthalocyanine pigments, indanslon pigments, dioxazine pigments, slene pigments, and indigo pigments; metal oxide pigments such as iron oxide can be mentioned.

Examples of the extender pigment include talc, clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, silica, alumina white and the like.

Glittering pigments include, for example, aluminum (including vaporized aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, titanium oxide or iron oxide coated aluminum oxide, titanium oxide or iron oxide coated. Examples thereof include mica, glass flakes, hologram pigments and the like.
These pigments can be used alone or in combination of two or more.

The content of the pigment in the water-based light-colored base paint is preferably 17 with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint from the viewpoint of protecting the steel plate member and the resin member and giving an aesthetic appearance. It is .5 to 40 parts by mass, more preferably 18 to 35 parts by mass, and further preferably 20 to 30 parts by mass.

In the present invention, the aqueous light color base paint contains at least titanium oxide and a chromatic pigment.
The content of titanium oxide in the water-based light-colored base paint is 15 to 30 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint. When the content of titanium oxide is 15 parts by mass or more, the hiding power of the coating film is improved and color unevenness can be prevented. When the content of titanium oxide is 30 parts by mass or less, the L ^* value of the coating film does not become too high. Therefore, it is not necessary to add a chromatic pigment in order to lower the L ^* value of the coating film, and the pigment concentration does not increase and the viscosity and the paint solid content do not increase.
The titanium oxide content is preferably 15 to 25 parts by mass, more preferably 17 to 23 parts by mass, from the viewpoint of reducing the difference in color of the coating film on the steel plate member and the resin member after painting. be.

The content of the chromatic pigment in the water-based light-colored base paint is 2.5 to 4.5 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint. When the content of the chromatic pigment is 2.5 parts by mass or more, it is possible to prevent the L ^* value of the coating film from becoming too high and improve the design of the automobile body. When the content of the chromatic pigment is 4.5 parts by mass or less, the L ^* value of the coating film is prevented from becoming too low, the content of titanium oxide does not need to be increased, and the appropriate viscosity and paint solid content are not required. It becomes.
The content of the chromatic pigment is preferably 3.0 to 4.0 parts by mass from the viewpoint of reducing the difference in color of the coating film on the steel plate member and the resin member after painting.

Examples of the organic solvent include glycol ether-based hydrophilic organic solvents such as ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether; hydrocarbon-based organic solvents such as toluene, xylene, hexane, and heptane; acetic acid. Ester-based organic solvents such as ethyl, butyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl acetate; alcohol-based organic solvents such as butanol, propanol, octanol, cyclohexanol, and diethylene glycol; methyl ethyl ketone, methyl isobutyl ketone , Cyclohexanone, a ketone-based organic solvent such as isophorone, and the like.

In the present invention, the aqueous light color base paint contains at least a glycol ether-based hydrophilic organic solvent.
The content of the glycol ether-based hydrophilic organic solvent in the water-based light-colored base paint is 45 to 65 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint. When the content of the glycol ether-based hydrophilic organic solvent is 45 parts by mass or more, it is possible to prevent the occurrence of armpits (coating film defects such as pinholes) during painting and baking. When the content of the glycol ether-based hydrophilic organic solvent is 65 parts by mass or less, the stability of the aqueous resin in the coating material is improved.
The content of the glycol ether-based hydrophilic organic solvent is preferably 50 to 60 parts by mass from the viewpoint of reducing the difference in color of the coating film on the steel plate member and the resin member after coating.

In addition to the above components, for example, a curing catalyst, a viscosity modifier, and other paint additives can be added to the aqueous light color base paint in an appropriate ratio, if necessary.

Further, in the present invention, the difference between the surface temperature of the steel plate member and the surface temperature of the resin member at the time of coating the water-based light-colored base paint is 10 to 30 ° C.
Either the surface temperature of the steel plate member or the surface temperature of the resin member may be higher.

The surface temperature can be measured by a non-contact thermometer. For example, a radiation thermometer "AD-5616" (manufactured by A & D Company Limited) can be used.

Further, in the present invention, the difference between the viscosity of the steel sheet member after 1 minute of application of the water-based light color base paint and the viscosity of the resin member after 1 minute of application of the water-based light color base paint is 70 Pa · s or less. Is. When the viscosity difference is 70 Pa · s or less, the difference in convection between titanium oxide and the chromatic pigment in the coating film after coating is reduced, and the difference in the color of the coating film can be reduced.

In order to make the viscosity difference 70 Pa · s or less, for example, a method of adjusting the content of the glycol ether-based hydrophilic organic solvent can be mentioned.
The viscosity of the steel plate member after 1 minute of application of the water-based light-colored base paint and the viscosity of the resin member after 1 minute of application of the water-based light-colored base paint should be either within the above range. It may be expensive.

The viscosity of the steel plate member and the resin member after 1 minute of application of the water-based light-colored base paint can be measured by the following operations (1) to (3).
(1) A water-based light-colored base paint is applied onto each member under the conditions of a temperature of 23 ° C. and a humidity of 75% so that the dry film thickness is 15 μm.
(2) After 1 minute has passed since the water-based light color base paint was applied, a part of the coating film was scraped off with a spatula or the like and collected.
(3) Using a viscoelasticity measuring device, the viscosity at 0.1 sec ^-1 when the shear rate was changed from 10000 sec ^-1 to 0.0001 sec ^-1 at a temperature of 23 ° C. was measured 1 minute after the above coating. Let it be viscosity.

As the viscoelasticity measuring device, for example, "HAAKE RheoStress RS150" (trade name, manufactured by HAAKE) can be used.

Examples of the method of applying the water-based light-colored base paint to the steel plate member and the resin member include an air spray method, an airless spray method, and an electrostatic coating method.
The coating film thickness of the aqueous light color base paint is, for example, 10 to 30 μm, preferably 10 to 20 μm as a dry film thickness.

After the water-based light-colored base paint is applied, it can be allowed to stand still and preheated by a known means. Preheating can be performed, for example, at 40 to 90 ° C., preferably 50 to 80 ° C., for example, 1 to 10 minutes, preferably 1 to 5 minutes.

The automobile body in the present invention includes a steel plate member and a resin member, and it is preferable that the painted surface thereof is configured so as to partially contain both of the above members.
The form containing both members and the content ratio of both members are not limited. However, it is preferable that 20% or more of the painted surface is occupied by 5 to 95% of the steel plate member and 95 to 5% of the resin member.

The automobile body can be obtained by assembling the steel plate member and the resin member by a known method.
In the present invention, from the viewpoint of facilitating the control of the temperature difference, after individually performing the steps of applying the water-based light-colored base paint to the steel plate member and the steps of applying the water-based light-colored base paint to the resin member, the above-mentioned It is preferable to assemble.

Further, in the present invention, it is preferable that the steel sheet member is formed by sequentially electrodeposition coating and water-based intermediate coating on the steel sheet from the viewpoint of corrosion resistance.
Specifically, it is preferable that the steel sheet is subjected to chemical conversion treatment and then coated with an electrodeposition paint (electrodeposition coating), and the baking-cured coating film surface of the electrodeposition paint is coated with a water-based intermediate coating paint. ..

Examples of the chemical conversion treatment include phosphate treatment such as zinc phosphate treatment and iron phosphate treatment, composite oxide film treatment, chromium phosphate treatment, chromate treatment and the like.

Electrodeposition coating is performed by applying a cationic electrodeposition paint to a steel sheet member.
For example, an electrodeposition bath made of a cationic electrodeposition paint having a solid content concentration of 5 to 40% by mass and a pH adjusted to a range of 5.5 to 9.0 by diluting with deionized water or the like is used at a bath temperature. This can be done by adjusting the temperature to 15 to 35 ° C. and energizing a steel plate member as a cathode under the condition of a load voltage of 100 to 400 V.

As the cationic electrodeposition coating material, for example, a known coating material obtained by blending an aqueous solution or a dispersion liquid of a cationic polymer compound with a cross-linking agent, various pigments, and other additives can be used. ..

Examples of the cationic polymer compound include those in which an amino group is introduced into an acrylic resin or an epoxy resin having a crosslinkable functional group such as a hydroxyl group. By neutralizing this with an organic acid, an inorganic acid or the like to make it water-soluble or water-dispersible, an aqueous solution or dispersion of a cationic polymer compound can be obtained.
As the cross-linking agent, a blocked polyisocyanate compound or an alicyclic epoxy compound can be used.

After electrodeposition coating, wash with extra filtrate (UF filtrate), reverse osmosis permeation water (RO water), industrial water, pure water, etc. to remove excess cationic electrodeposition paint adhering to the steel sheet member. May be good.

For baking and drying of the coating film by electrodeposition coating, the surface temperature of the coating film is 110 to 200 ° C., preferably 140 to 180 ° C., 10 to 10 to, using a drying facility such as an electric hot air dryer or a gas hot air dryer. The coating can be heated for 180 minutes, preferably 20 to 50 minutes.

The coating film thickness of the cationic electrodeposition paint is, for example, 10 to 30 μm, preferably 15 to 25 μm as a dry film thickness.

The water-based intermediate coating paint contains a water-soluble or water-dispersible resin component (hydrophilic resin component), a curing agent, and the like. The water-based intermediate coating paint can be prepared, for example, by dissolving or dispersing a hydrophilic resin component, a curing agent, or the like in water.

As the hydrophilic resin component and the curing agent, the same ones used in the aqueous light color base paint can be used.

In addition to the above components, for example, a coloring pigment, an extender pigment, a curing catalyst, an organic solvent, and other paint additives can be added to the water-based intermediate coating paint in an appropriate ratio, if necessary.

The water-based intermediate coating paint is specified in JIS Z8781-4 (2013) calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter from the viewpoint of giving a light-colored finish to the steel plate member. It is preferable that the L ^* value as the lightness in the L ^* a ^* b ^* color system is 80 or more.

Examples of the method of applying the water-based intermediate coating paint to the steel sheet member include an air spray method, an airless spray method, and an electrostatic coating method.
The coating film thickness of the water-based intermediate coating paint is, for example, 10 to 40 μm, preferably 13 to 30 μm as the dry film thickness.

After the water-based intermediate coating paint is applied, it can be allowed to stand still and preheated by a known means. Preheating can be performed, for example, at 40 to 90 ° C., preferably 50 to 80 ° C., for example, 1 to 10 minutes, preferably 1 to 5 minutes.

Further, in the present invention, the resin members include polypropylene resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS), polycarbonate resin, polyamide resin, polyacetal resin, polybutylene terephthalate resin, polyftalamide resin, and polyphenylene. Resin materials such as a sulfide resin, a polyether ether ketone resin, a thermoplastic polyimide resin, a polysulphon resin, and a polyetherimide resin can be used.
Among these, polypropylene resin, which is soft and has high fatigue resistance, is preferable.

Further, the resin member is preferably a resin material coated with a water-based primer from the viewpoint of improving the adhesion to the water-based light-colored base paint.
Specifically, it is preferable that the resin material is subjected to a treatment such as degreasing and then coated with a water-based primer paint (water-based primer coating).

The water-based primer coating material contains a water-soluble or water-dispersible resin component (hydrophilic resin component), a curing agent, and the like. The water-based primer coating material can be prepared, for example, by dissolving or dispersing a hydrophilic resin component, a curing agent, or the like in water.

As the hydrophilic resin component and the curing agent, the same ones used in the aqueous light color base paint can be used.

In addition to the above components, for example, a conductive pigment, a coloring pigment, an extender pigment, a curing catalyst, an organic solvent, and other paint additives can be added to the water-based primer paint in an appropriate ratio, if necessary. ..

The water-based primer paint is L specified in JIS Z8781-4 (2013) calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter from the viewpoint of giving a light-colored finish to the resin member. ^* A ^* b ^* It is preferable that the L ^* value as the lightness in the color system is 80 or more.

Examples of the method of applying the water-based primer paint to the resin member include an air spray method, an airless spray method, and an electrostatic coating method.
The coating film thickness of the water-based primer paint is, for example, 5 to 20 μm, preferably 6 to 15 μm as a dry film thickness.

After the water-based primer paint is applied, it can be allowed to stand still and preheated by a known means. Preheating can be performed, for example, at 40 to 90 ° C., preferably 50 to 80 ° C., for example, 1 to 10 minutes, preferably 1 to 5 minutes.

In the present invention, it is preferable to apply the clear paint to at least a part of the coating film formed by the water-based light-colored base paint and existing on the steel plate member and the resin member.

Further, from the viewpoint of improving the smoothness and vividness of the coating film, the coating film formed by the water-based light-colored base paint and present on the steel plate member and the coating film formed by the water-based light-colored base paint and present on the resin member. It is more preferable to apply a clear paint to both of the coating films to be applied.

As the clear paint, a solvent-based and two-component thermosetting clear paint composition known for painting automobile bodies can be used.
The solvent system is a term that is contrasted with water-based and means that the solvent does not substantially contain water.
Examples of the two-component thermosetting clear coating composition include an organic solvent-type thermosetting coating composition containing a two-component resin (main agent) having a crosslinkable functional group and a crosslinking agent. It can be used by mixing the above two liquids immediately before painting.

Examples of the crosslinkable functional group contained in the substrate resin include a carboxyl group, a hydroxyl group, an epoxy group and a silanol group.

Examples of the type of the substrate resin include acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, and fluororesin.

Examples of the cross-linking agent include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

If necessary, the clear paint can contain a coloring pigment, a brilliant pigment, a dye, etc. to the extent that the transparency is not impaired, and further, an extender pigment, an ultraviolet absorber, a light stabilizer, and a defoaming agent. , Thickener, rust preventive, surface conditioner and the like can be appropriately contained.

Examples of the method for applying the clear paint include an air spray method, an airless spray method, and an electrostatic coating method.

Each member coated with the clear paint can be heated and baked and cured by a known method. The baking temperature is, for example, 80 to 170 ° C., preferably 120 to 160 ° C. for steel sheet members, and, for example, 50 to 130 ° C., preferably 70 to 120 ° C. for resin members. The baking time is, for example, 20 to 40 minutes.

The coating film thickness of the clear paint is, for example, 10 to 60 μm, preferably 25 to 50 μm as the dry film thickness.

Hereinafter, the present invention will be described in more detail with reference to examples. The scope of the present invention is not limited to these examples. Further, "part" in the embodiment indicates "part by mass".

[Test board]
As a steel plate member, a cationic electrodeposition paint (trade name "Electron 9900", manufactured by Kansai Paint Co., Ltd.) is primed on a steel plate (450 mm x 300 mm x 0.8 mm) by electrodeposition coating and baked to a thickness of about 20 μm. The one on which the electrodeposition coating film was formed was prepared.
A polypropylene plate (trade name "TOP-6", manufactured by Onda Kasei Co., Ltd.) was prepared as a resin member.

[Aqueous light color base paint]
(Aqueous light color base paint 1)
Aqueous light-colored base paint containing acrylic resin, polyester resin, urethane resin and melamine resin as resin components and iron oxide, quinacridone-based pigment and titanium oxide as pigments (trade name "WBC713D-3", manufactured by Kansai Paint Co., Ltd.) I prepared.
Using the base paint, the iron oxide (red) content is 0.5 parts, the quinacridone-based red pigment content is 3 parts, and the titanium oxide content is 100 parts of the total resin solid content in the base paint. An aqueous light-colored base paint 1 having a content of 25 parts and a content of the hydrophilic solvent ethylene glycol monobutyl ether of 55 parts was prepared.

(Aqueous light color base paint 2)
A water-based light color base paint "WBC713D-3" was prepared.
Using the base paint, the content of iron oxide (red) is 0.3 parts, the content of quinacridone-based red pigment is 3.5 parts, and oxidation is performed with respect to 100 parts of the total resin solid content in the base paint. A water-based light-colored base paint 2 having a titanium content of 20 parts, an aluminum pigment content of 1.5 parts, and a hydrophilic solvent ethylene glycol monopropyl ether content of 50 parts was prepared.

(Aqueous light color base paint 3)
A water-based light color base paint "WBC713D-3" was prepared.
Using the base paint, the iron oxide (red) content is 0.5 parts, the quinacridone-based red pigment content is 3 parts, and the titanium oxide content is 100 parts of the total resin solid content in the base paint. An aqueous light-colored base paint 3 having a content of 25 parts and a content of the hydrophilic solvent ethylene glycol monobutyl ether of 60 parts was prepared.

(Aqueous light color base paint 4)
A water-based light color base paint "WBC713D-3" was prepared.
Using the base paint, the iron oxide (red) content is 0.5 parts, the quinacridone-based red pigment content is 3 parts, and the titanium oxide content is 100 parts of the total resin solid content in the base paint. An aqueous light-colored base paint 4 having a content of 40 parts and a content of the hydrophilic solvent ethylene glycol monobutyl ether of 55 parts was prepared.

(Aqueous light color base paint 5)
A water-based light color base paint "WBC713D-3" was prepared.
Using the above base paint, the content of iron oxide (red) is 0.5 parts, the content of quinacridone-based red pigment is 3 parts, and the content of titanium oxide is 100 parts of the total resin solid content in the base paint. An aqueous light-colored base paint 5 having a content of 25 parts and a content of the hydrophilic solvent ethylene glycol monobutyl ether of 35 parts was prepared.

L ^* a ^* b ^* color specified in JIS Z8781-4 (2013) calculated from the reflectance of water-based light color base paints 1 to 5 measured at a reflection angle of 45 degrees using a spectrocolorimeter. The L ^* value as the lightness in the system was measured. The results are shown in Table 1.

[Aqueous intermediate paint]
As a resin component, a water-based intermediate coating paint (trade name "WP555D-3", manufactured by Kansai Paint Co., Ltd.) containing an acrylic resin, a polyester resin, a urethane resin and a melamine resin was prepared. Titanium oxide, iron oxide and carbon were blended as pigments so that the L ^* value could be adjusted to obtain a water-based intermediate coating paint 1.

The coating viscosity (No. 4 Ford cup, 20 ° C.) of the water-based intermediate coating paint 1 was 20 to 24 seconds. This water-based intermediate coating paint is JIS Z8781-4 (2013) calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter (trade name "CM512m3", manufactured by Konica Minolta, sample diameter 50 mm). ), The L ^* value as the lightness in the L ^* a ^* b ^* colorimetric system was 82.

[Aqueous primer paint]
As a resin component, a water-based primer paint containing an olefin resin, a urethane resin and an acrylic resin (trade name "Ascarex 380-1", manufactured by Kansai Paint Co., Ltd.) was prepared. Titanium oxide, iron oxide and carbon were blended as pigments so that the L ^* value could be adjusted to obtain a water-based primer paint 1.

The coating viscosity (No. 4 Ford cup, 20 ° C.) of the water-based primer coating material 1 was 45 to 55 seconds. This water-based primer paint is JIS Z8781-4 (2013) calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter (trade name "CM512m3", manufactured by Konica Minolta, sample diameter 50 mm). The L ^* value as the lightness in the L ^* a ^* b ^* colorimetric system specified in 1 was 82.

[Example 1]
(Steel steel member painting process)
Aqueous intermediate coating paint 1 (“WP555D-3”, resulting in L ^* value 82) was applied to the steel sheet member obtained above so that the cured film thickness was 17 μm, set for 3 minutes, and set at 75 ° C. Preheated at 25 ° C. for 3 minutes and cooled at 25 ° C. for 3 minutes.

The surface temperature of the steel sheet member after the water-based intermediate coating was measured by a radiation thermometer (trade name "AD-5616", manufactured by A & D Company Limited). The results are shown in Table 2.

Then, the water-based light color base paint 1 is applied under the conditions of a temperature of 23 ° C. and a humidity of 75% so that the cured film thickness is 15 μm, set for 3 minutes, preheated at 75 ° C. for 3 minutes, and at 25 ° C. for 5 minutes. Cooled.

After 1 minute has passed since the water-based light color base paint was applied, a part of the coating film was scraped off with a spatula to collect it, and a viscoelasticity measuring device (trade name "HAAKE RheoStress RS150", manufactured by HAAKE) was used. At a temperature of 23 ° C., the viscosity at 0.1 sec ^-1 when the shear rate was changed from 10000 sec ^-1 to 0.0001 sec ^-1 was determined 1 minute after the application of the water-based light-colored base paint 1 on the steel plate member. The viscosity was used. The results are shown in Table 2.

Then, an acid epoxy-based clear paint (trade name "DKC-K12-1", manufactured by Kansai Paint Co., Ltd.) was applied, and after setting for 10 minutes, baking was performed at 140 ° C. for 30 minutes.

(Resin member painting process)
Aqueous primer paint 1 (“Ascarex 380-1”, resulting in L ^* value 82) is applied to the above resin member so that the cured film thickness is 8 μm, set for 3 minutes, and set at 75 ° C. for 3 minutes. It was preheated and cooled at 25 ° C. for 3 minutes.

The surface temperature of the resin member after coating with the water-based primer was measured with a radiation thermometer (trade name "AD-5616", manufactured by A & D Company Limited). The results are shown in Table 2.
Further, the difference between the surface temperature of the resin member after the water-based primer coating and the surface temperature of the steel sheet member after the water-based intermediate coating was determined. The results are shown in Table 2.

Then, the water-based light color base paint 1 is applied under the conditions of a temperature of 23 ° C. and a humidity of 75% so that the cured film thickness is 15 μm, set for 3 minutes, preheated at 75 ° C. for 3 minutes, and at 25 ° C. for 5 minutes. Cooled.

After 1 minute has passed since the water-based light color base paint was applied, a part of the coating film was scraped off with a spatula to collect it, and a viscoelasticity measuring device (trade name "HAAKE RheoStress RS150", manufactured by HAAKE) was used. At a temperature of 23 ° C., the viscosity at 0.1 sec ^-1 when the shear rate was changed from 10000 sec ^-1 to 0.0001 sec ^-1 was determined 1 minute after the application of the water-based light color base paint 1 on the resin member. The viscosity was used. The results are shown in Table 2.
Further, the difference between the viscosity of the water-based light-colored base paint 1 after 1 minute of coating on the resin member and the viscosity of the water-based light-colored base paint 1 after 1 minute of coating on the steel plate member was determined. The results are shown in Table 2.

Then, an acrylic / isocyanate-based two-component clear paint (trade name "Soflex 8538D", manufactured by Kansai Paint Co., Ltd.) was applied, and after setting for 5 minutes, baking was performed at 100 ° C. for 30 minutes.

(Evaluation of the difference in the color of the coating film on each member)
The L ^* value (L1) and a ^* value (a1) of the coating film on the steel sheet member before the application of the acid epoxy clear paint and after the cooling after the application of the water-based light color base paint 1 are as follows. Measured by method. That is, three locations on the steel plate member were randomly selected. Using an integrating sphere-type spectrocolorimeter (trade name "CM512m3", manufactured by Konica Minolta, sample diameter 50 mm), the L ^* and a ^* values at these three locations were measured at a light receiving angle of 45 degrees (on the coated surface). On the other hand, the vertical direction was set to 0 degrees.) It was calculated from the spectral reflectance measured at a reflection angle of 45 degrees.
The average value of the L ^* values at the three locations was L1, and the average value of the a ^* values at the three locations was a1.

L ^* value (L2) and a ^* value (a2) of the coating film on the resin member before applying the acrylic / isocyanate-based two-component clear paint and after cooling after applying the water-based light-colored base paint 1. Was measured according to the above-mentioned measuring methods of L1 and a1.

ΔL ^* (L2-L1) and Δa ^* (a2-a1) were determined. The results are shown in Table 2.

Further, after applying the clear paint and baking and drying, the coating film surfaces on the steel plate member and the resin member were observed, and the difference in the color of the coating film on each member was evaluated according to the following criteria. The results are shown in Table 2.
◎: I did not feel any difference in color.
◯: I hardly felt the difference in color.
×: I felt a difference in color.

[Examples 2 and 3 and Comparative Examples 1 and 2]
The surface temperature of the steel plate member after the water-based intermediate coating and the water-based light color of the steel plate member are the same as in Example 1 except that the water-based light color base paint 1 is changed to the water-based light color base paint shown in Table 2. The viscosity of the base paint 1 minute after coating, the surface temperature of the resin member after the water-based primer coating, and the viscosity of the water-based light-colored base paint on the resin member 1 minute after coating were measured. The results are shown in Table 2.
Further, in the same manner as in Example 1, the difference in the color of the coating film on each member was evaluated. The results are shown in Table 2.

From the results in Table 2, it was found that the difference in the color of the coating film was small between the steel plate member and the resin member painted by the coating method of the present invention.

Claims (3)

A method of applying a single water-based light-colored base paint to the surface of an automobile body including steel plate members and resin members.
The content of titanium oxide in the water-based light-colored base paint is 15 to 30 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The content of the chromatic pigment in the water-based light-colored base paint is 2.5 to 4.5 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The content of the glycol ether-based hydrophilic organic solvent in the water-based light-colored base paint is 45 to 65 parts by mass with respect to 100 parts by mass of the total resin solid content in the water-based light-colored base paint.
The difference between the surface temperature of the steel plate member and the surface temperature of the resin member at the time of painting the aqueous light color base paint is 10 to 30 ° C.
The difference between the viscosity of the steel plate member after 1 minute of application of the water-based light-colored base paint and the viscosity of the resin member after 1 minute of application of the water-based light-colored base paint is 70 Pa · s or less. Painting method. The steel sheet member is a steel sheet in which electrodeposition coating and water-based intermediate coating are sequentially applied.
The coating method according to claim 1, wherein a clear paint is applied onto a coating film formed by the water-based light color base paint and existing on the steel plate member. The resin member is a resin material coated with a water-based primer.
The coating method according to claim 1 or 2, wherein the clear paint is applied onto the coating film formed by the water-based light-colored base paint and existing on the resin member.