JPH0833865A - Wet on wet coating method - Google Patents

Abstract

PURPOSE:To obtain a coating film excellent in the appearance and smoothness of the coating film by specifying neutralization number of a base material resin of a water-miscible coating material in the case of wet on wet coating using plural thermosetting water-miscible coating materials. CONSTITUTION:A surface coated with a thermosetting water-miscible coating material A is wet on wet coated with another thermosetting water-miscible coating material B before cured. In this case, the neutralization number of the base material resin of the coating material A is controlled to 10-40KOHmg/g and the neutralization number of the base material resin of the coating material B is controlled to 10-20KOHmg/g higher than that of the coating material A. The excellent coating film is obtained without causing mixing or inversion between both coating films even at the time of wet on wet coating with plural thermosetting water-miscible coating materials in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel coating method by which a plurality of water-based paints can be applied by a wet-on-wet method to form a multi-layer paint film having excellent paint film appearance and smoothness.

[0002]

2. Description of the Related Art A plurality of thermosetting water-based paints have been conventionally applied in a wet-on-wet system. For example, in painting car bodies,
Body parts of car bodies (eg doors,
Panel hood, panel roof, panel trunk lid,
The thermosetting water-based intermediate coating composition (a) is spray-painted on the fender, etc., and it is almost the same color as the top coating film on the outer panel on the inner panel (for example, inside the hood, trunk room, door, etc.) without curing. After applying a thermosetting water-based intermediate coating composition (b) toned to the above, it is heated and the water-based intermediate coating composition (ii) is heated.
It has been practiced to cure both the coating films of (b) and (b) and then apply a top coat paint to the outer plate portion. In this case, it can be avoided that the intermediate coating material (a) is applied to the inner plate portion near the outer plate portion and the intermediate coating material (b) is applied to the outer plate portion near the inner plate portion. Therefore, at the boundary portion between the outer plate portion and the inner plate portion, the intermediate coating paints (a) and (b) overlap each other in a wet-on-wet manner.

Further, the center pillar portion of the automobile body is coated with a thermosetting water-based intermediate coating material after cationic electrodeposition coating, and the thermosetting water-based black top coating material is applied only to the center pillar portion without curing. There is.

However, in the conventional method in which a plurality of thermosetting water-based paints are applied by the wet-on-wet method as described above, a mixed layer or inversion occurs between the wet coating layers, resulting in the coating film of the multilayer coating film. Defects such as a decrease in appearance and smoothness, and skin defects on the coating film have occurred. In many cases, such a defect cannot be eliminated even by forming a top coating film on the defect.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel coating method in which the above-mentioned defects in the coating method in which a plurality of thermosetting water-based coating materials are applied wet-on-wet are eliminated.

Another object of the present invention is to coat a plurality of thermosetting water-based paints in a wet-on-wet manner without causing mixed layers or inversion between the two paint films and having excellent paint film appearance and smoothness. It is an object of the present invention to provide a novel coating method capable of obtaining a film.

These and other objects of the invention will be apparent from the following description.

The present invention is a wet-on-wet coating method in which a thermosetting water-based paint (A) is applied and the thermosetting water-based paint (B) is applied to the coated surface without curing. The neutralization value of the base resin of A) is 10-40.
KOHmg / g, and the neutralization value of the base resin of the water-based paint (B) is 10 to 20 KOHm higher than that of the water-based paint (A).
The present invention provides a coating method characterized by increasing g / g.

The present inventor, as a result of earnest research to eliminate the above-mentioned drawbacks of the prior art, adjusts the neutralization value of the base resin in both thermosetting water-based paints to be applied in a wet-on-wet manner within a specific range. It has been found that the above-mentioned defects are eliminated and the object is achieved. The present invention has been completed based on this new finding.

The thermosetting water-based paint (A) is a paint which is applied to the surface to be coated in advance prior to the coating of the thermosetting water-based paint (B). In the present invention, the base of the water-based paint (A) is used. It is necessary that the neutralization value of the resin is in the range of 10 to 40 KOHmg / g, preferably 20 to 30 KOHmg / g. The neutralization value of the base resin is 10 KOHm
When it is less than g / g, the water dispersion stability is lowered and the coating layer of the water-based paint (B) is easily mixed or inverted,
On the other hand, if it exceeds 40 KOHmg / g, the coating workability
Both are not preferable because the water resistance of the coating film is reduced.

In the present invention, the "neutralization value" of the base resin means the amount of neutralized carboxyl groups among the carboxyl groups contained in 1 g of the base resin, converted into mg of KOH. . This neutralization may be all or part of the carboxyl groups of the base resin.
Therefore, when all the carboxyl groups of the base resin are neutralized, the neutralization value of the base resin becomes a value equal to its acid value. Further, when a part of the carboxyl groups of the base resin is neutralized, the neutralization value of the base resin becomes a value smaller than its acid value.

The thermosetting water-based paint (A) of the present invention has the above-mentioned predetermined neutralization value,
Conventionally known paints can be used. That is, the thermosetting water-based coating material (A) is obtained by dissolving or dispersing a base resin and a crosslinking agent in water, and further, if necessary, a coloring pigment, a metallic pigment,
It is a thermosetting water-based coating composition containing an extender pigment, various additives, an organic solvent and the like.

The above-mentioned base resin, which is a main component for forming the coating film of the water-based paint (A), may be a known one having a crosslinkable functional group and a carboxyl group in its molecule. Here, the carboxyl group is for making the base resin aqueous by neutralization. Examples of the crosslinkable functional group include a hydroxyl group, an epoxy group, an isocyanate group,
Examples thereof include amino groups, and these may be used alone or in combination of two or more. The functional group is the base resin 1
It is preferable that two or more are bonded per molecule. The introduction of the carboxyl group and the crosslinkable functional group is performed by a known method.

As the base resin, for example, one kind or two kinds or more selected from an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin and a modified resin thereof having a carboxyl group and a crosslinkable functional group are used. It can be preferably used, and their number average molecular weight is about 1,0.
00 to 100,000, especially about 2,000 to 30,000
A range of 0 is suitable. An aqueous emulsion of three-dimensionally crosslinked polymer particles having a carboxyl group and a crosslinkable functional group can also be used as the base resin.

The amount of carboxyl groups in the base resin of the water-based paint (A) is 10 to 50K based on the acid value in the unneutralized state.
It is preferably OH mg / g, particularly 20 to 30 KOH mg / g. Then, by neutralizing a part or all of the carboxyl groups in the resin and adjusting the neutralization value to the above-mentioned predetermined range, a base resin applicable to the water-based paint (A) is obtained.

The neutralizing agent used for neutralizing the carboxyl group is, for example, ammonia; ethylamine, propylamine, butylamine, benzylamine,
Monoethanolamine, neopentanolamine, 2-
First of aminopropanol, 3-aminopropanol, etc.
Grade monoamine; diethylamine, diethanolamine,
Secondary monoamines such as di-n-propanolamine, di-iso-propanolamine, N-methylethanolamine, N-ethylethanolamine; dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, dimethylaminoethanol. Etc. tertiary monoamines; amino compounds such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine and methylaminopropylamine, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, calcium hydroxide, Alkaline earth metal hydroxides such as barium hydroxide can be used.

The cross-linking agent is for three-dimensionally cross-linking and curing the above-mentioned base resin, and is one or two selected from, for example, amino resins and polyisocyanate compounds.
More than one species can be used. Here, as the amino resin, a methylolated amino resin obtained by reacting an amino component such as melamine, urea, benzoguanamine and the like with formaldehyde, a part or all of the methylol group of the resin is changed to a monoalcohol having 1 to 5 carbon atoms. Examples thereof include etherified products. Examples of the polyisocyanate compound include aliphatic, alicyclic and aromatic polyisocyanate compounds having two or more isocyanate groups in one molecule. A blocked polyisocyanate compound obtained by reacting these compounds with a blocking agent may be used.

The mixing ratio of the base resin and the cross-linking agent in the water-based paint (A) is not particularly limited, but the base resin is 50 to 90% by weight, preferably 60 to 80% by weight based on the total weight of both components. The crosslinking agent is 50 to 10% by weight, preferably 40 to 20% by weight.

The water-based paint (A) can be directly applied to a metal or plastic object to be coated such as an automobile body. These objects to be coated are, for example, a primer such as a cationic electrodeposition coating. If necessary, it is preferable to apply it beforehand.

The water-based paint (A) has a viscosity of 20 to 200.
Seconds, preferably 30-100 seconds / Ford Cup # 4 /
Adjust the temperature to 20 ℃ and spray paint, electrostatic paint, etc.
It is preferable to apply a film having a thickness of 10 to 60 μm based on the cured coating film.

The thermosetting water-based paint (B) is a paint to be applied on the uncured coating surface of the above-mentioned water-based paint (A). In the present invention, the neutralization value of the base resin of the water-based paint (B) is used. Is required to be 10 to 20 KOHmg / g larger than that of the water-based paint (A). The difference between the neutralization value of the base resin of the water-based paint (B) and the neutralization value of the base resin of the water-based paint (A) is 10
If it is smaller than KOHmg / g, both coatings are likely to be mixed layers or invert, while if the difference is larger than 20KOHmg / g, coating workability and water resistance of the coating are deteriorated.

As the thermosetting water-based paint (B) in the present invention, a conventionally known paint can be used as long as it has the above-mentioned predetermined neutralization value. That is, the thermosetting water-based paint (B) is prepared by dissolving or dispersing a base resin and a cross-linking agent in water and, if necessary, further containing a coloring pigment, an extender pigment, various additives, an organic solvent and the like. It is a thermosetting water-based paint.

The above-mentioned base resin, which is a main component for forming the coating film of the water-based paint (B), may be a known one having a crosslinkable functional group and a carboxyl group in its molecule. Examples of the crosslinkable functional group include a hydroxyl group, an epoxy group, an isocyanate group, and an amino group, and these may be used alone or in combination of two or more. Further, it is preferable that two or more functional groups are bonded per molecule of the base resin. The introduction of the carboxyl group and the crosslinkable functional group is performed by a known method.

As the base resin, for example, one kind or two kinds or more selected from an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin and a modified resin thereof having a carboxyl group and a crosslinkable functional group are used. It can be preferably used, and their number average molecular weight is about 1,0.
00 to 100,000, especially about 2,000 to 30,000
A range of 0 is suitable. An aqueous emulsion of three-dimensionally crosslinked polymer particles having a carboxyl group and a crosslinkable functional group can also be used as the base resin.

The amount of carboxyl groups in the base resin of the water-based paint (B) is 20 to 60K based on the acid value in the unneutralized state.
It is preferably OH mg / g, particularly 30 to 50 KOH mg / g. Then, by neutralizing a part or all of the carboxyl groups in the resin and adjusting the neutralization value to the above-mentioned predetermined range, a base resin applicable to the water-based paint (B) can be obtained. For this neutralization, the same neutralizing agent as in the case of the water-based paint (A) can be used.

The cross-linking agent is used for three-dimensionally cross-linking and curing the above-mentioned base resin, and is, for example, one or two selected from amino resins and polyisocyanate compounds.
More than one species can be used. Specific examples of these cross-linking agents are the same as in the case of the water-based paint (A).

The mixing ratio of the base resin and the crosslinking agent in the water-based paint (B) is not particularly limited, but the base resin is 50 to 90% by weight, preferably 60 to 80% by weight, based on the total weight of the both components. The crosslinking agent is 50 to 10% by weight, preferably 40 to 20% by weight.

The water-based paint (B) is applied to the uncured surface of the water-based paint (A). For example, apply water-based paint (A),
It is preferable to apply the water-based paint (B) after standing at room temperature for several minutes.

The water-based paint (B) has a viscosity of 20 to 200.
Seconds, preferably 30-100 seconds / Ford Cup # 4 /
Adjust the temperature to 20 ℃ and spray paint, electrostatic paint, etc.
It is preferable to apply a film having a thickness of 10 to 60 μm based on the cured coating film.

The coating method of the present invention comprises the above water-based paint (A).
Is applied, and the water-based paint (B) is applied to the coated surface by a wet-on-wet coating method without crosslinking and curing.

Specific examples of such a coating method include the following cases.

Water-based intermediate coatings (a) and (b) on the outer and inner plates of the car body that have been subjected to cationic electrodeposition coating, respectively.
In the case of using the water-based intermediate coating material (A) as the water-based intermediate coating material (A) and the water-based intermediate coating material (B) as the water-based intermediate coating material (B) in the step of applying the above. That is, the water-based intermediate coating material (A) is spray-coated on the outer plate portion and is not cured, and then the water-based intermediate coating material (B) toned to the same color as the top coating film of the outer plate portion is applied on the inner plate portion. Then, in the step of simultaneously heating and curing both of the intermediate coating films, at the boundary portion between the outer plate portion and the inner plate portion and at the dust portion where the water-borne coating material (A) is scattered on the inner plate portion, The water-based paint (B) is overlapped on the uncured coating film surface in a wet-on-wet state. Moreover, the scattered particles of the water-based paint (B) are
It may be applied to the surface of the uncured coating film.

In order to apply an aqueous black topcoat paint only to the center pillar portion of the outer plate portion without curing, after coating the automobile body by cationic electrodeposition, the entire surface of the outer plate portion is coated with the above waterborne intermediate coating material (a). In the case of using the water-based paint (A) as the water-based intermediate paint (a) and the water-based paint (B) as the water-based black top coating, respectively.

When a water-based metallic paint or a water-based colored paint and a water-based clear paint are applied in a two-coat, one-bake system, the water-based metallic paint or the water-based colored paint is the water-based paint (A), and the water-based clear paint is the water-based paint (B). When using each.

In the present invention, the coating of the water-based paint (A) and the water-based paint (B) can be carried out by any method depending on the purpose, for example, air spray, airless spray, electrostatic coating, dip coating, It is preferably performed by electrodeposition coating or the like. The coating film thickness can be appropriately selected, but a range of 10 to 60 μm, particularly 20 to 40 μm is suitable based on the cured coating film. Also, after applying the water-based paint (A),
It is preferable that the aqueous coating material (B) is applied after being left at room temperature for about 1 to 10 minutes and dried without causing a crosslinking reaction. After that, both coatings are simultaneously crosslinked and cured by heating at about 110 to 160 ° C. for about 20 to 60 minutes. here,
Predrying at about 40 to 70 ° C. for about 1 to 30 minutes before heat-curing is effective in preventing cracking.

[0036]

According to the coating method of the present invention, the following remarkable effects can be obtained.

(1) Water-based paint (A) and water-based paint (B)
Since the neutralization value of each base resin of the above was adjusted as described above, even if the both coating materials were applied wet-on-wet, no mixed layer or inversion occurred between both layers, and the coating film appearance of the obtained coating film It is possible to prevent the deterioration of smoothness and smoothness, and to prevent the occurrence of skin marks on the coated surface.

(2) In the wet-on-wet coating of the conventional water-based base coating / water-based clear coating, it took a long time to evaporate water and the like in the water-based coating, but the method of the present invention provides a water-based coating. When the water-based paint (A) and the water-based paint (B) are used as the water-based clear paint, the water-based paint (B) remains on the wet coating film of the water-based paint (A).
Since it can be painted, the process can be simplified.

[0039]

EXAMPLES The present invention will be described more specifically below with reference to production examples, examples and comparative examples.

Production Example 1 Preparation of thermosetting water-based paint (A-1) 1,000 parts of polyester resin (weight of solid content, the same hereinafter), 40 parts of dimethylaminoethanol, methyl etherified melamine resin containing imino group (Mitsui Cytec Co., Ltd.) (stock)
Made, product name "Cymel 703") 300 parts, titanium white pigment (made by Sakai Chemical Industry Co., Ltd., product name "R-41") 1,5
00 parts and 4.5 parts of carbon black (trade name "Mitsubishi Carbon Black M-100" manufactured by Mitsubishi Chemical Co., Ltd.) are mixed and dispersed in 1,720 parts of deionized water to prepare a thermosetting water-based paint (A-1. ) Was prepared.

The above polyester resin is neopentyl glycol 0.75 mol, trimethylolpropane 0.2
5 mol, adipic acid 0.4 mol and phthalic anhydride 0.5
Mol to the reaction vessel and allowed to react at 220 ° C. for 5 hours, and then 0.035 mol of trimellitic anhydride was added.
It was obtained by reacting at 0 ° C. for 1 hour, and has a number average molecular weight of about 6,000, an acid value of 25 KOHmg / g, and a hydroxyl value of 110 KOHmg / g. Further, this polyester resin has one equivalent of its carboxyl groups neutralized in the coating material by dimethylaminoethanol as a neutralizing agent, and has a neutralization value of 25 KOHmg / g.

Production Example 2 Preparation of thermosetting water-based paint (B-1) 1,000 parts of polyester resin, 56 parts of dimethylaminoethanol, imino group-containing methyl etherified melamine resin (Mitsui Cytec Co., Ltd., trade name " Cymel 70
3 ") 300 parts, barium sulfate 540 parts and carbon black (Mitsubishi Chemical Co., Ltd., trade name" Mitsubishi Carbon Black M-100 ") 60 parts are mixed and dispersed in 1,720 parts of deionized water and thermosetting. An aqueous paint (B-1) was prepared.
The polyester resin is neopentyl glycol 0.
87 mol, 0.13 mol of trimethylolpropane, 0.45 mol of adipic acid and 0.5 mol of phthalic anhydride were added to a reaction vessel and reacted at 220 ° C. for 5 hours, and then trimellitic anhydride of 0.05 mol was added. It was obtained by adding and reacting at 160 ° C. for 1 hour. The number average molecular weight was about 8.0.
00, acid value 35 KOHmg / g, hydroxyl value 52 KOHm
It is g / g. Further, this polyester resin has a carboxyl group neutralized by 1 equivalent with dimethylaminoethanol in a coating material, and has a neutralization value of 35 KOHmg / g.

Production Example 3 Preparation of Thermosetting Waterborne Coating (B-2) In Production Example 2, the amount of trimellitic anhydride used as the raw material for the polyester resin was changed to 0.06 mol to give an acid value of 40.
A thermosetting aqueous solution was prepared in the same manner as in Production Example 2 except that a polyester resin having KOHmg / g and a hydroxyl value of 50KOHmg / g was prepared and neutralized with 1 equivalent of dimethylaminoethanol to give a neutralization value of 40KOHmg / g. Paint (B-2)
Was prepared.

Production Example 4 Preparation of Thermosetting Waterborne Coating (B-3) Production except that the polyester resin in Production Example 2 was replaced with the polyester resin in Production Example 1 and the amount of dimethylaminoethanol used was 40 parts. A thermosetting aqueous coating material (B-3) was prepared in the same manner as in Example 2.

Production Example 5 Preparation of thermosetting water-based paint (B-4) In Production Example 2, the amount of trimellitic anhydride used as the polyester resin raw material was changed to 0.04 mol to give an acid value of 30.
A thermosetting aqueous coating material was prepared in the same manner as in Production Example 2 except that a polyester resin having KOH mg / g and a hydroxyl value of 55 KOH mg / g was prepared and neutralized with diethylaminoethanol at 1 equivalent to give a neutralization value of 30 KOH mg / g. (B-4)
Was prepared.

Production Example 6 Preparation of thermosetting water-based paint (B-5) In Production Example 2, the amount of trimellitic anhydride used as the raw material for the polyester resin was changed to 0.12 mol to give an acid value of 50.
A thermosetting aqueous coating material was prepared in the same manner as in Production Example 2 except that a polyester resin having KOHmg / g and a hydroxyl value of 47KOHmg / g was prepared and neutralized to 1 equivalent with diethylaminoethanol to give a neutralization value of 50KOHmg / g. (B-5)
Was prepared.

Production Example 7 Preparation of Thermosetting Waterborne Coating (B-6) The polyester resin used in Production Example 3 (acid value 40 KOHm
(g / g, hydroxyl value 50 KOH mg / g) is neutralized with diethylaminoethanol at 0.625 equivalent to give a neutralization value of 25 KO.
A thermosetting water-based paint (B-6) was prepared in the same manner as in Production Example 3 except that Hmg / g was used.

Production Example 8 Preparation of Thermosetting Aqueous Paint (B-7) The polyester resin used in Production Example 3 (acid value 40 KOHm
(g / g, hydroxyl value 50 KOH mg / g) is neutralized with diethylaminoethanol at 0.375 equivalent to give a neutralization value of 15 KO.
A thermosetting water-based coating material (B-7) was prepared in the same manner as in Production Example 3 except that Hmg / g was used.

Examples 1 to 2 and Comparative Examples 1 to 5 Dull steel plates (the surface of which is treated with zinc phosphate) are coated with an epoxy resin-based cationic electrodeposition coating (“Electron # 9800”, trade name,
(Kansai Paint Co., Ltd.) is electro-deposited (film thickness 25 μm, the same applies hereinafter) and heat-cured, and then the thermosetting water-based paint (A) prepared above is applied to the entire surface of the electro-deposition coated surface. Is spray-coated (film thickness 30 to 35 μm) and left at room temperature for 3 minutes.
Spray coating to incline to m, leave at room temperature for 7 minutes, pre-dry at 60 ° C for 10 minutes, then at 140 ° C for 3 minutes.
Both coatings were simultaneously cured by heating for 0 minutes.

In the above coating, the viscosity of the water-based coating (A) during coating was 50 seconds / Ford cup # 4/20 ° C.
The viscosity of the water-based paint (B) during coating was adjusted to 50 seconds / Ford cup # 4/20 ° C., respectively.

The coating surface condition of the coating film obtained above was examined for the film forming portion, the inclined portion and the dust portion as follows.

Here, the film forming portion is a thermosetting water-based coating (A).
The portion where the thermosetting water-based paint (B) is applied to the coating surface of the above in a film thickness of 20 μm, and the inclined portion have a film thickness of the water-based paint (B) of 2
Water-based paint (A) for the part that is inclined from 0 to 0 μm and the dust part
The part in which the water-based paint (B) adheres to the coated surface in the form of particles (dust). As for the evaluation criteria, ◯ indicates good gloss (visual evaluation) and smoothness (visual evaluation) on the entire coating surface, and Δ indicates that gloss decreases on a part of the coating surface and smoothness is not sufficient.
X indicates that gloss and smoothness are significantly inferior.

Further, the coating workability during the above coating was examined as follows. That is, both coating films coated in the same manner as above and before baking were left at a temperature of 60 ° C. after leaving the wet coated plate vertically for 7 minutes.
It was pre-dried for 10 minutes, immediately baked at 140 ° C. for 30 minutes, and evaluated based on the following criteria.

◯: Even when the wet coating surface (30 μm as a cured coating film) of the water-based coating material (A) is coated with the water-based coating material (B) as a cured coating film from 20 μm to 50 μm, sagging or cracking occurs on the coating surface. No, when the wet coating surface (30 μm as a cured coating film) of the water-based coating surface (A) is coated with the aqueous coating material (B) as a cured coating film in an amount of 20 μm or more, sagging or cracking is observed on the coating surface. Even when the water-based paint (B) is applied to the wet coating surface (30 μm as a cured coating film) of 20 μm or less as a cured coating film on the wet coating surface of the water-based coating material (A), the occurrence of sagging, cracks, etc. is observed on the coating surface. Are shown respectively.

Table 1 below shows the coating process, the coating surface condition of the obtained coating film, and the test results of the coating workability during coating.

[0056]

[Table 1]

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C09D 201/02 PDE (72) Inventor Naoshi Isaka 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. Within

Claims (6)

[Claims] 1. A wet-on-wet coating method in which a thermosetting water-based paint (A) is applied and the thermosetting water-based paint (B) is applied to the coated surface without curing. Neutralization value of base resin of 10-40KOHmg
/ G, and making the neutralization value of the base resin of the water-based paint (B) 10 to 20 KOHmg / g larger than that of the water-based paint (A). 2. The coating method according to claim 1, wherein the neutralization value of the base resin of the water-based paint (A) is 20 to 30 KOHmg / g. 3. The coating method according to claim 1, wherein the water-based paint (A) is a paint containing a base resin having a carboxyl group and a crosslinkable functional group and a crosslinking agent. 4. The acid value of the base resin of the water-based paint (A) is
The coating method according to claim 1, which is 10 to 50 KOHmg / g. 5. The coating method according to claim 1, wherein the water-based paint (B) is a paint containing a base resin having a carboxyl group and a crosslinkable functional group, and a crosslinking agent. 6. The acid value of the base resin of the water-based paint (A) is
The coating method according to claim 1, which is 20 to 60 KOHmg / g.