JPH07286298A - Method for coating car body - Google Patents

Abstract

PURPOSE:To easily obtain a car body practically free from problem of rust preventing property, chipping resistance and finished appearance by executing the electrodeposition coating with an electrodeposition paint containing a slight amount of a flat pigment after a galvanized steel plate is defatted. CONSTITUTION:The galvanized steel plate of the car body is defat-treated. The electrodeposition coating of approximately 10 to 50mum in thickness is performed on the steel plate with the electrodeposition paint containing the 0 to 3 pts.wt. flat pigment such as clay and talc, vs. a 100 pts.wt. film-forming resin solid- -content. The electrodeposition coating is preferably the cationic electrodeposition coating. Next, a top coat is applied on the electrodeposition film via a process for applying a chipping primer and/or intermediate paint, as necessary. The coat is then dried and cured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a car body coating method in which a zinc-based plated steel sheet is degreased, then electro-deposition coating is carried out without chemical conversion treatment, and then finishes, and a car body obtained by this method.

[0002]

2. Description of the Related Art In recent years, in automobile bodies, materials have been replaced by cold rolled steel sheets and zinc-based plated steel sheets in order to improve rust prevention. In addition, it prevents damage to the coating film of the car body and the plating layer of the zinc-based plated steel sheet due to the splash of pebbles when the car is running,
That is, in order to improve chipping resistance, chipping primer is often applied.

Currently, as a coating process using a zinc-based plated steel sheet with good chipping resistance, a zinc-based plated steel sheet → degreasing → chemical conversion treatment (surface adjustment → zinc phosphate treatment) → electrodeposition coating → chipping resistant primer coating → Intermediate coating → Top coating is generally adopted.

However, in the above process, a process of painting the chipping primer is required, and
The thickness of the chipping primer is generally in the range of 3 to 10 μm from the viewpoint of chipping resistance and finished appearance, but problems in coating the chipping primer such as complicated film thickness control, and chemical conversion treatment. In the process
Control of surface conditioning bath and surface treatment bath, treatment of sludge generated, and deterioration of electrodeposition bath paint due to mixing of surface treatment liquid into electrodeposition bath which is the subsequent process There is a problem caused by the chemical conversion treatment process such as deterioration of the finished appearance of the coating film due to the above.

[0005]

Therefore, the present inventors have no problems in practical use in terms of rust resistance, chipping resistance, and finished appearance, and also have problems with the above-mentioned chipping primer coating and problems caused by the chemical conversion treatment process. As a result of studies to obtain a vehicle body coating method capable of reducing the amount of the above-mentioned substances, it was found that the above object can be achieved by omitting the chemical conversion treatment step and limiting the pigment composition of the electrodeposition coating composition, resulting in the present invention. .

That is, the present invention provides "1. After degreasing a zinc-based plated steel sheet, without performing chemical conversion treatment, the steel sheet does not contain a flat pigment or the content of the flat pigment is 100% by weight of a coating-forming resin solid content. 3 for division
The electrodeposition paint is used in an amount of less than or equal to parts by weight, and then the tipping primer is applied on the electrodeposition paint film, if necessary, and the intermediate coat paint is applied as necessary. A method for painting a vehicle body, which is characterized by applying paint. 2. The coating method according to item 1, wherein the zinc-based plated steel sheet is an iron-zinc alloy plated steel sheet. 3. 3. The coating method according to item 1 or 2 above, wherein the electrodeposition coating is cationic electrodeposition coating. 4. The coating method according to any one of the above items 1 to 3, wherein an intermediate coating composition is applied on the electrodeposition coating film, and then an overcoat composition is applied. 5. A vehicle body obtained by the coating method according to any one of items 1 to 4. Regarding

[0007]

The zinc-based plated steel sheet according to the present invention includes a galvanized steel sheet used as an anticorrosive steel sheet for automobiles; zinc-based alloy-plated steel sheet such as nickel-zinc plating and iron-zinc plating. It may be manufactured by any plating method of plating, in particular,
An iron-zinc alloy plated steel sheet can be preferably used.

In the present invention, after the zinc-based plated steel sheet is degreased, the zinc-based plated steel sheet is subjected to electrodeposition coating without chemical conversion treatment.

The electrodeposition coating composition used for this electrodeposition coating may be either an anion type or a cation type, but in general, a cation type is preferable from the viewpoint of corrosion resistance. As the base resin, epoxy type,
Examples thereof include acrylic resins, polybutadiene resins, alkyd resins, and polyester resins. Among them, polyamine resins typified by amine-added epoxy resins are preferable.

Examples of the amine-added epoxy resin include (i) a polyepoxide compound and a primary mono- or polyamine, a secondary mono- or polyamine, or 1,
Additions with secondary mixed polyamines (eg US Pat.
984,299); (ii) Addition products of polyepoxide compounds with secondary mono- or polyamines having ketiminated primary amino groups (see, for example, US Pat.
No. 017,438); (iii) a reaction product obtained by etherification of a polyepoxide compound and a ketiminated hydroxy compound having a primary amino group (see, for example, JP-A-59-43013). Can be mentioned.

The polyepoxide compound used for producing the amine-added epoxy resin is a compound having two or more epoxy groups in one molecule, and generally has at least 20.
0, preferably 400 to 4,000, more preferably 8
Those having a number average molecular weight in the range of 00 to 2,000 are suitable, and those obtained by reacting a polyphenol compound with epichlorohydrin are particularly preferable. Examples of the polyphenol compound that can be used for forming the polyepoxide compound include bis (4-hydroxyphenyl) methane and bis (4-hydroxyphenyl)-
2,2-propane, 4,4-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis- (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-) Butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4
-Hydroxyphenyl) -1,1,2,2-ethane,
4,4-dihydroxydiphenyl sulfone, phenol novolac, cresol novolac and the like can be mentioned.

The polyepoxide compound may be partially reacted with a polyol, a polyether polyol, a polyester polyol, a polyamidoamine, a polycarboxylic acid, a polyisocyanate compound or the like, and further, ε-caprolactone, an acrylic monomer or the like. May be graft-polymerized.

The above-mentioned base resin may be either an external cross-linking type or an internal (or self) cross-linking type, and examples of the curing agent used in combination with the external cross-linking type resin include (block ) It can be a conventionally known crosslinking agent such as a polyisocyanate compound or an amino resin,
A blocked polyisocyanate compound is particularly preferable. Further, as the internal cross-linking type resin, a resin having a blocked polyisocyanate group introduced therein is preferable.

The blocked isocyanate compound that can be used in the above-mentioned external crosslinking type can be an addition reaction product of a theoretical amount of a polyisocyanate compound and an isocyanate blocking agent. Examples of the polyisocyanate compound include aromatic compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis (isocyanatomethyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and isophorone diisocyanate, or alicyclic compounds. Aliphatic polyisocyanate compounds, biuret bodies of these isocyanate compounds, cyclized polymers, and ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol in excess of these isocyanate compounds,
Examples thereof include a terminal isocyanate-containing compound obtained by reacting a low molecular weight active hydrogen-containing compound such as castor oil and water.

The above-mentioned isocyanate blocking agent is one which blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked isocyanate compound formed by the addition is stable at room temperature and blocks when heated to about 100 to 200 ° C. It is desirable that the agent can be dissociated to regenerate a free isocyanate group. Examples of the blocking agent satisfying such requirements include lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methylethylketoxime and cyclohexanone oxime; phenol compounds such as phenol, para-t-butylphenol and cresol. Aliphatic alcohols such as n-butanol and 2-ethylhexanol; aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol; ether alcohol compounds such as ethylene glycol monobutyl ether. Of these, oxime-based and lactam-based blocking agents are blocking agents that dissociate at relatively low temperatures,
It is particularly suitable from the viewpoint of curability of the electrodeposition coating composition.

As a method of introducing a blocked isocyanate group into a base resin in a type having a blocked isocyanate group in a base resin molecule and self-crosslinking, a conventionally known method can be used. For example, a partially blocked polyisocyanate compound can be used. It can be introduced by reacting the free isocyanate group therein with the active hydrogen-containing portion in the base resin.

In the case of a cationic resin, the base resin is generally neutralized and made water-soluble by neutralizing the resin with a water-soluble organic acid such as formic acid, acetic acid or lactic acid to make it water-soluble or water-dispersible. In the case of an anionic resin, it can be carried out by neutralizing with an alkali such as amine or alkali metal hydroxide in place of the water-soluble organic acid, and solubilizing / dispersing in water. .

In the present invention, the electrodeposition coating composition to be electrodeposited is optionally added with an additive usually used in the electrodeposition coating, for example, a coloring pigment such as titanium white, carbon black, red iron oxide, and yellow lead. Extender pigments such as silica, clay, mica, calcium carbonate, talc; chromium-based pigments such as strontium chromate and zinc chromate; anti-corrosion pigments such as lead-based pigments such as lead silicate, lead chromate and lead hydroxide A pigment dispersant resin, a pigment dispersant, an organic solvent, a coating surface adjusting agent, a curing catalyst, etc. may be contained. When the pigment is mixed in the paint, it is usually mixed as a pigment paste in which the pigment is dispersed in a pigment dispersion resin or the like. Conventionally, in order to improve the stress relaxation ability of the electrodeposition coating film to improve the corrosion resistance, it is generally practiced to add a flat pigment such as clay or talc. However, in the present invention, the content of the flat pigment such as clay and talc is 0 with respect to 100 parts by weight of the coating film forming resin solid content.
~ 3 parts by weight is required. If the content of these flat pigments exceeds 3 parts by weight, the chipping resistance decreases. The total amount of pigment is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less with respect to 100 parts by weight of the coating film forming resin solid content.

The electrodeposition coating of the above electrodeposition coating composition can be performed by a known method. Although the film thickness of the electrodeposition coating is not particularly limited, it is generally 10 to 50 μm, preferably 15 to 35 μm, based on the cured coating film. The baking conditions for the electrodeposition coating film differ depending on the type of the electrodeposition coating composition, but are generally 100 to 200 ° C,
It is preferable to bake at 150 to 180 ° C. for about 10 to 30 minutes.

In the method of the present invention, the topcoat paint is applied to the above electrodeposition coating film through the steps of applying a chipping primer, if necessary, and applying an intermediate paint, if necessary. As the coating finishing method applied on the electrodeposition coating film, specifically, (a) intermediate coating-top coating,
(B) Topcoat coating, (c) Chipping primer coating-intermediate coating-Topcoat coating and the like.

The chipping primer used for the above-mentioned painting finish as required is a primer for imparting chipping resistance, and various chipping primers used in the field of automobile painting can be used. The chipping primer may be water-based or organic solvent-based,
Generally, a resin having a low static glass transition temperature of −30 to −60 ° C. is a main component, and examples of the resin include a mixture of a propylene-ethylene copolymer and a chlorinated polyolefin, and propylene-ethylene. Examples thereof include modified polyolefin resins such as resins obtained by graft-polymerizing (anhydrous) maleic acid on a copolymer, acrylic resins, polyvinyl chloride resins, and alkyd resins.

The intermediate coating used for the above-mentioned coating finish includes adhesion, smoothness, sharpness, overbaking resistance,
A known intermediate coating composition having excellent weather resistance can be used. A specific example thereof is a thermosetting intermediate coating composition containing a short oil having an oil length of 30% or less, an ultra-short oil alkyd resin or an oil-free polyester resin and an amino resin as a vehicle main component.

The alkyd resin and polyester resin are preferably those having a hydroxyl value of 60 to 140, an acid value of 5 to 200, and an unsaturated oil (or unsaturated fatty acid) as a modified oil, and the amino resin is an alkyl ( Suitable are etherified melamine resins having 1 to 5 carbon atoms, urea resins and benzoguanamine resins. These compounding ratios are based on the solid content weight of alkyd resin and / or oil-free polyester resin 65-85%, especially 70-8.
It is preferably 0%, 35 to 15% of amino resin, and particularly 30 to 20%. Furthermore, at least a part of the amino resin may be replaced with a polyisocyanate compound or a blocked polyisocyanate compound.

The form of the intermediate coating composition is most preferably an organic solution type, but may be a non-aqueous dispersion liquid using the above vehicle component, a high solid type, an aqueous solution type, an aqueous dispersion type, or the like. . If necessary, an extender pigment, a coloring pigment, and other additives for paints can be added to the intermediate coating material.

The coating film thickness of the intermediate coating material is preferably in the range of 10 to 50 μm based on the cured coating film, and the curing temperature of the coating film depends on the vehicle component and is 8 when heat-cured.
It is preferable to heat at a temperature of 0 to 170 ° C, particularly 120 to 150 ° C.

The topcoat paint used for the above-mentioned paint finish is
It imparts cosmetic properties to the article to be coated. Specifically, finish appearance (vividness, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalkiness resistance, etc.), chemical resistance, water resistance, moisture resistance, curability, etc. A coating material known per se which forms an excellent coating film can be used, for example, a coating material containing a base resin such as an acrylic resin, an alkyd resin, a polyester resin or a silicone resin and a crosslinking agent as a vehicle main component. Can be mentioned. Examples of the cross-linking agent include amino resins, polyisocyanate compounds, chelate compounds, polyepoxy compounds and polycarboxylic acids.

The form of the above-mentioned top coating composition is not particularly limited, and it is an organic solution type, a non-aqueous dispersion type, an aqueous (dispersion) liquid type, a powder type,
It can be used with high solid type. The coating film is dried and cured by room temperature drying, heat drying, active energy ray irradiation and the like. In the present invention, the formed coating film of these top-coat paints preferably has a pencil hardness within the range of 2B to 3H (20 ° C).

The top coating used in the present invention is classified into an enamel coating prepared by blending a metallic pigment and / or a coloring pigment in the above-mentioned coating containing a vehicle main component, and a clear coating containing no or almost no such pigment. . Then, as a method for forming a top coating film using these paints, for example, the following methods can be mentioned:

A method in which a metallic paint containing a metallic pigment and, if necessary, a coloring pigment, or a solid color paint containing a coloring pigment is applied and cured by heating (metallic or solid color by one coat / one bake method). Finish). Apply metallic paint or solid color paint,
After curing by heating, a method of coating clear paint and curing again by heating (two-coat two-bake metallic or solid color finish). Apply metallic paint or solid color paint,
Subsequently, a method of coating a clear paint and then heating the coatings to cure them simultaneously (metallic or solid color finish by 2-coat 1-bake method).

It is preferable that these top coating materials are applied by spray coating, electrostatic coating or the like. In addition, the coating film thickness is 25 to 40 μ in the above, 10 to 30 μ in the metallic paint and the solid color paint, and 25 to 50 μ in the clear paint based on the dry coating film.
Are preferred. The heating condition can be arbitrarily selected depending on the vehicle component, but is 80 to 170 ° C., particularly 120 to 1
It is preferable to heat at 50 ° C.

By the coating finishing method (a), the conventional degreasing of galvanized steel sheet-chemical conversion treatment-electrodeposition coating-chipping primer coating-intermediate coating-top coating can be substituted, and chipping resistance can be obtained, and corrosion resistance and finish can be obtained. It is possible to obtain a coated plate that has no problem in terms of practicality. In addition, the coating finishing method (b) provides chipping resistance that can be substituted for degreasing of galvanized steel sheet-chemical conversion treatment-electrodeposition coating-chipping primer coating-top coating, and also poses practical problems in terms of rust prevention and finish. There is no coated plate. The coating finishing method (c) can further improve the chipping resistance in the method (a).

[0032]

EXAMPLES The present invention will be described in more detail by way of examples.

Example 1 Iron-zinc alloy-plated steel sheet having a thickness of 0.8 mm (area weight: about 45
g / m ² ) after degreasing, amine-added epoxy resin-polyisocyanate compound-based resin emulsion for cationic electrodeposition coating (manufactured by Kansai Paint Co., Ltd., trade name "Electron #G")
T-10F-2 clear ", solid content 35% by weight) 286
52 parts by weight of the pigment paste of the formulation 1 shown in Table 1 below was added to parts by weight, and deionized water and a neutralizing agent were added to adjust the solid content to 20% by weight and the pH to 6.1. Immerse in, energize for cationic electrodeposition coating, then 1
It was baked at 70 ° C. for 20 minutes to obtain an electrodeposition coating film having a film thickness of 20 μm. Amino-alkyd intermediate coating (Kansai Paint Co., Ltd., trade name “Amilac ES Primer TP60 Sealer”) was spray-coated on this electrodeposition coating film to a dry film thickness of about 32 μm, and then at 140 ° C. at 30 ° C. Baked for minutes. Then, an amino-alkyd-based top coating composition (manufactured by Kansai Paint Co., Ltd., trade name "Neoamilac # 6000") was spray-coated on the intermediate coating film to a dry film thickness of about 35 µm, and at 140 ° C for 30 minutes. The paint finish was completed by baking.

[0034]

[Table 1]

Example 2 A coating finish was carried out in the same manner as in Example 1 except that the intermediate coating composition was not coated but the top coating composition was directly coated on the electrodeposition coating film.

Example 3 In Example 1, a polyolefin-based chipping primer (manufactured by Kansai Paint Co., Ltd., trade name "TP" was applied on the electrodeposition coating film.
-7A primer ") was spray-coated so that the dry film thickness was about 7 µm, and then the coating finish was carried out in the same manner as in Example 1 except that an intermediate coating composition was coated on the chipping primer coating film.

Example 4 A coating finish was carried out in the same manner as in Example 1 except that the pigment paste of formulation 2 shown in Table 1 was used in place of the pigment paste of formulation 1 shown in table 1.

Example 5 A coating finish was carried out in the same manner as in Example 1 except that the pigment paste of Formulation 3 shown in Table 1 was used in place of the pigment paste of Formulation 1 shown in Table 1.

Example 6 Example 1 was repeated except that a 0.8 mm thick nickel-zinc alloy plated steel sheet (basis weight of about 45 g / m ² ) was used in place of the iron-zinc alloy plated steel sheet. The coating was finished in the same manner.

Comparative Example 1 A coating finish was carried out in the same manner as in Example 1 except that a dull finish cold rolled steel sheet having a thickness of 0.8 mm was used in place of the iron-zinc alloy plated steel sheet.

Comparative Examples 2 and 3 In each of Examples 1 and 2, instead of the iron-zinc alloy-plated steel sheet, an alloy-plated steel sheet similar to this alloy-plated steel sheet was degreased and then surface-adjusted, followed by zinc phosphate treatment. The coating finish was carried out in the same manner as in Examples 1 and 2 except that a chemical conversion treated iron-zinc alloy plated steel sheet having a zinc phosphate coating weight of about 3 g / m ² was used. Comparative Example 2 is Example 1 and Comparative Example 3 is Example 2.
Respectively correspond to.

Comparative Example 4 A coating finish was carried out in the same manner as in Example 1 except that the pigment paste of Formulation 4 shown in Table 1 was used in place of the pigment paste of Formulation 1 shown in Table 1.

Comparative Example 5 A coating finish was performed in the same manner as in Example 1 except that the pigment paste of Formulation 5 shown in Table 1 was used in place of the pigment paste of Formulation 1 shown in Table 1.

The paint finishes obtained by applying the paint finishes of Examples 1 to 6 and Comparative Examples 1 to 5 were tested for the appearance of the coated surface, salt water spray resistance, yarn rust resistance and chipping resistance. I did. The test results are shown in Table 1 below.
The test was conducted according to the following test method.

Test method Appearance of coated surface: The smoothness, sharpness and color tone of the coated surface are comprehensively examined visually and evaluated according to the following criteria. ◎: Very good ○: Good △: Poor ×: Very bad

Salt spray resistance: Cross-cut scratches were made on the coating film with a knife so as to reach the substrate, and this was JIS Z
According to 2371, a salt spray test is carried out for 720 hours, and evaluation is made by rust from knife scratches and blistering width. ⊚: The maximum width of rust or blisters is less than 1 mm from the cut part (one side). ◯: The maximum width of rust or blisters is 1 mm to 2 mm from the cut part
Less than (one side). △: The maximum width of rust or blisters is 2 mm to 3 mm from the cut part
Less than (one side). ×: The maximum width of rust or blisters is 3 mm or more from the cut portion (one side).

Thread rust resistance: The coating film of the test plate was cross-cut so as to reach the substrate. After carrying out the test for 24 hours under the same conditions as the above-mentioned salt spray resistance test,
It was washed with deionized water, then placed in a container kept at a temperature of 40 ° C. and a relative humidity of 85%, and after 480 hours had elapsed, it was taken out and the length of the thread rust from the cut portion was measured, and the maximum length was determined. evaluate. ⊚: (Very good) The maximum length of the thread rust is less than 0.5 mm. ◯: (Good) The maximum length of the thread rust is 0.5 mm or more and less than 1 mm. Δ: (Poor) The maximum length of the thread rust is 1 mm or more and less than 2 mm. X: (Very bad) The maximum length of the thread rust is 2 mm or more.

Chipping resistance: Using a Q-G-R-gravel meter (product of Q panel company), 50 g of No. 7 crushed stone was used as 4
The test plate was sprayed at an angle of 90 ° under an air pressure of kg / cm ² and a temperature condition of −20 ° C. to impact the coating film. Then, stick an adhesive gum tape to this coating film, after peeling off rapidly,
The appearance of the coating film is visually evaluated. ⊚: (Very good) Scratches due to impact are observed in a part of the top coating film, but no peeling of the electrodeposition coating film or the galvanized surface is observed. ◯: (Good) The top coating film had scratches due to impact, and the electrodeposition coating film peeled off very slightly, but peeling of the galvanized surface was not observed at all. Δ: (Poor) Many scratches due to impact are observed in the top coating film, and some peeling of the galvanized surface is observed. X: (Very bad) Many scratches due to impact are observed in the top coating film, and peeling of the galvanized surface is considerably observed.

Water-resistant secondary adhesion: The test plate was immersed in water at 40 ° C for 2
After soaking for 40 hours, JIS K5400 8.5.2.
In accordance with (1990), make a cut with a cutter knife at intervals of 2 mm to make a scoring with 100 2 x 2 mm squares, attach adhesive cellophane tape on the surface, and after peeling off rapidly Evaluate the painted surface. A: There is no peeling at all. ◯: Peeling with a peeled area of 5% or less is recognized. Δ: The peeled area is more than 5% and 20% or less. X: The peeled area exceeds 20%.

[0050]

[Table 2]

[0051]

The coating method of the present invention improves the chipping resistance by limiting the pigment composition of the electrodeposition coating except the conventional chemical conversion treatment (zinc phosphate treatment) of galvanized steel sheet. With this, the painting of the chipping primer could be omitted. By eliminating the chemical conversion treatment step, it becomes unnecessary to manage the surface conditioning bath and surface treatment bath in the chemical conversion treatment step, and the treatment of sludge generated by the chemical conversion treatment becomes unnecessary, and the electrodeposition by mixing the surface treatment bath into the electrodeposition bath is eliminated. No more worrying about deterioration of bath paint. Further, when the coating of the chipping primer is omitted, the coating process of the chipping primer is not required, so that the complicated management of the film thickness of the chipping primer is released. In addition, conversion treatment of zinc-based plated steel sheet,
According to the method of the present invention in which the coating of the chipping primer is omitted, it is possible to obtain a vehicle body having rust resistance, chipping resistance, and a finished appearance, which has no practical problems.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technology display area // B32B 15/08 G

Claims (5)

[Claims] 1. After degreasing a zinc-based plated steel sheet, without chemical conversion treatment, the steel sheet does not contain a flat pigment or the flat pigment content is 3 parts by weight based on 100 parts by weight of a coating film-forming resin solid content. Part of the electrodeposition paint is applied to the electrodeposition paint, and then the tipping primer is applied on the electrodeposition paint film, if necessary, and the intermediate paint is applied as necessary. A method for painting a vehicle body, which comprises painting 2. The coating method according to claim 1, wherein the zinc-based plated steel sheet is an iron-zinc alloy plated steel sheet. 3. The coating method according to claim 1, wherein the electrodeposition coating is cationic electrodeposition coating. 4. The coating method according to claim 1, wherein an intermediate coating composition is applied on the electrodeposition coating film, and then a top coating composition is applied. 5. A vehicle body obtained by the coating method according to any one of claims 1 to 4.