JPH0326771A - Coating method - Google Patents

Abstract

PURPOSE:To perform coating giving coated film without generation of intercoat adhesion failure by a substrate with specific urethane resin paint as a primer and coating said primer with second urethane resin paint. CONSTITUTION:A substrate to be coated is coated with urethane resin paint containing (A) urethane prepolymer having isocyanate group terminal composed of (i) alpha,alpha,alpha',alpha'-tetramethylxylylene diisocyanate and (ii) a compound having >=2 active hydrogen within a molecule (preferably polyol) and (B) a resin having active hydrogen within molecule (preferably polyester polyol resin) and further the coated surface is repeatedly coated with urethane resin paint to perform the aimed painting.

Description

[Detailed Description of the Invention] The present invention relates to a coating method, for example, after applying a urethane resin paint as a primer to a substrate to be coated, a coating is applied on top of it at a considerable interval. This invention relates to a coating method that allows repeated coating without causing delamination even when a second urethane resin Mr1 paint is applied.

Conventionally, urethane resins have been widely used in fields such as paints, printing inks, and adhesives due to their excellent toughness, chemical resistance, adhesion, and gloss.

However, in the field of paints, when the paint film is completely cured, the cohesive force of the urethane bonds is strong, so a second layer appears on the paint film.
When urethane resin paints are applied over and over again, the adhesion of the paint films to each other is poor, often causing peeling between the eyebrows. Therefore, conventionally, when applying multiple urethane resin paints, the second layer is applied within a limited time after the first layer is applied. In particular, when the object to be coated is plastic, concrete, etc., the time during which the second N layer can be coated after the first layer is coated is very limited, which poses a problem in workability.

As a result of intensive research in order to solve the above-mentioned problems in overcoating urethane resin paints, the inventors of the present invention decided to use a specific polyisocyanate prebolimer and active hydrogen as the first layer or undercoat paint. The present invention was developed based on the discovery that when using a urethane resin paint containing a resin having a polyurethane resin, the time allowed until the second layer of the urethane resin paint is applied is significantly extended.

1. The coating method according to the present invention for increasing the divination to ``2'' uses a terminal isocyanate 1. The method is characterized in that after a urethane resin paint containing a base urethane prepolymer and a resin having active hydrogen in the molecule is applied to a substrate to be coated, a further urethane resin paint is applied thereon.

The above urethane polymer used in the present invention is α, α
, α゛,α''-tetramethylxylylene diisocyanate (hereinafter abbreviated as TMXDI) and a compound having two or more active hydrogens in the molecule (hereinafter referred to as an active hydrogen compound) with respect to active hydrogen. It can be obtained by reacting under conditions with an excess of isocyanate groups, and has an isocyanate group at the terminal.TMXI)r is as follows:
Either p- or m-form may be used, or a mixture thereof may be used. In addition, two scenes of TMXDI,
Polymerized TMXDI, such as the triacetate, can also be used.

Examples of the active hydrogen compounds used to produce such a urethane prepolymer include ethylene glycol, propylene glycol, 1l3=butylene glycol, 1,4-butylene glycol, 2,3-butylene gelicol, neopentyl glycol, 2 ,2. 4-
1-limethyl-1,3-pentanediol, 1,6-
Low molecular weight polyols such as hexamethylene glycol, cyclohexanedimethanol, cyclohexanediol, trimethylolpropane, glycerin, 1,2,6-hexanetriol, hydrogenated bisphenol A1 sorbitol, sorbitol, sucrose, pentaerythritol, quadrol, and polyesters. Examples include polyols having a relatively high molecular weight of about 500 to 3,000, such as polyols, polyether polyols, acrylic polyols, and epoxy resins.

Furthermore, water and boric acid compounds such as ethylenediamine can also be used as active hydrogen compounds.

TMX as described above for producing urethane prepolymer
The reaction between DI and an active hydrogen compound can be carried out without a solvent, but usually, for example, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and ethers such as cellosolve acetate are used. It is preferable to carry out the reaction in an organic solvent without active hydrogen, such as the following. The reaction may be carried out by a conventional method. If necessary, a normal urethanization reaction catalyst,
For example, metal compounds, organometallic compounds, tertiary organic a5
You may also use a button etc.

Further, after the reaction between TMXDI and the active hydrogen compound is completed, it is preferable to remove unreacted TMXDI by a method such as extraction or distillation. However, the unreacted TMXDI is 5
% or less, there is no particular need to remove it and it can be used as is.

Next, examples of the resin having two or more active hydrogens in the molecule (hereinafter referred to as active hydrogen resin) used in the present invention include polyester polyol resin, polyether polyol resin, polyether polyester polyol resin, and acrylic polyol resin. All resins, epoxy polyol resins and their modified resins, polyamide polyamine resins, etc.
Mention may be made of mixtures of these. Furthermore, in addition to the above, polyurethane polyol resin, castor oil, polybutadiene polyol resin, borilactone polyol resin,
Hydroxyl group-containing vinyl resins, carboxyl group-containing polyester polyol resins, etc. can also be used.

The above-mentioned polyester polyol resin can be obtained by condensing a polybasic acid and a polyol by a conventional method under conditions in which there is an excess of hydroxyl groups. Examples of the polybasic acids include maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, phthalic acid, isophthalic acid, terephthalic acid, and trimellitic acid. Examples of the polyols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, L4-7'tanediol, 1.5-pentanediol, neopentyl glycol, .6-hexamethylene glycol, decamethylene glycol, hydroquinone bis(hydroxyethyl ether), 2,4.4-trimethyl-1,3-pentanediol, hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, hexanetriol,
Examples include glycerin, pentaerythritol, tris(hydroxyethyl)isocyanurate, cyclohexanediol, cyclohexanedimethanol, xylylene glycol, quadrol, and the like. Also, for example, higher fatty acids such as coconut oil fatty acid, linseed oil fatty acid, soybean oil fatty acid, cottonseed oil fatty acid, tung oil fatty acid, castor oil fatty acid, etc. are blended into the acid component to make an oil-modified polyester polyol resin. is also used.

Such polyester polyol resin has a molecular weight of about 50
0 to 50,000, preferably about 2,000 to 10,000,
Hydroxyl value is about 10-300, preferably about 20-200
, the acid value is in the range of about 1 to 100, preferably about 5 to 50.

The polyether polyol resin is obtained by ring-opening addition polymerization of, for example, ethylene oxide, propylene oxide, or a mixture thereof to an initiator such as ethylene glycol, propylene glycol, glycerin, or pentaerythritol. or polytetramethylene ether glycol obtained by ring-opening polymerization of tetrahydrofuran.

Examples of polyether polyester polyol resins include those obtained by reacting the polyether polyol resin described above with a polybasic acid to form a polyester, as well as those obtained by ring-opening copolymerization reaction of an epoxy compound and an acid anhydride. Mention may be made of those having both polyether and polyester segments.

Examples of the acrylic polyol resin include those obtained by copolymerizing a vinyl monomer having a hydroxyl group and an α,β monoethylenically unsaturated monomer having copolymerizability therewith.

A vinyl monomer having a hydroxyl group can be obtained, for example, by reacting an unsaturated carboxylic acid, which may or may not have a hydroxyl group, with a polyhydric alcohol, an alkylene oxide, a glycidyl compound, or the like. Examples of the unsaturated carboxylic acid include 2-hydroxyethyl acrylate},
2-hydroxybrobyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, cinnamic alcohol, crotonyl alcohol, or acrylic acid, methacrylic acid, maleic acid, fumaric acid, Examples of the polyhydric alcohol, alkylene oxide, glycidyl compound, etc. include crotonic acid, itaconic acid, etc. Examples of the polyhydric alcohol, alkylene oxide, glycidyl compound, etc. Dimethanol, phenyl glycidyl ether, glycidyl decanoate and the like can be mentioned.

α having copolymerizability with the vinyl monomer having a hydroxyl group
, β-ethylenically unsaturated monomers include, for example, acrylics such as methyl acrylate, ethyl acrylate, n-probyl acrylate, isobrobyl acrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate. acid esters, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isobrobyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate,
Vinyl aromatic monomers such as styrene, vinyltoluene, α-methylstyrene, other acrylic acid, methacrylic acid,
Vinyl acetate, vinyl probionate, vinyl stearate, acrylonitrile, methacrylic nitrile, allyl acetate, diallyl adipate, dimethyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, ethylene,
Examples include propylene, glycidyl methacrylate, acrylamide, N-methylolacrylamide, N-butoxymethylacrylamide, diacetone acrylamide, and the like.

The acrylic polyol resin thus obtained has a molecular weight of about 1,000 to 100,000, preferably about 500.
0 to 50,000, and the hydroxyl value is preferably in the range of about 1O to 300, preferably about 20 to 200.

Epoxy polyol resin is an epoxy resin having at least two hydroxyl groups in its molecule, and can usually be obtained by reacting bisphenol A and shrimp chlorohydrin. Such epoxy polyol resin has the following chemical structure.

Among such epoxy polyol resins, n is 2
It is preferably about 12 to 12, especially about 2 to 10, and the epoxy equivalent is preferably about 425 to ioooo, especially about 425 to 4000. Furthermore, in addition to such epoxy polyol resins, for example, epoxy ester resins obtained by reacting soybean oil fatty acids with epoxy resins, and modified resins obtained by reacting epoxy resins with amines, phenols, etc. Epoxy resins can also be used.

Polyamide polyamine resin is obtained by reacting a polybasic acid with an excess of polyamine, and it contains polyamine resin in the molecule.
It has a primary amino group and/or a secondary amino group. Examples of the polyamines include ethylenediamine, diethylenetriamine, triethylenetetra, tetraethylenepentamine, pentaethylenehexamine, xylylenediamine, hexamethylenediamine, 4,4'-methylenebis(cyclohexylamine), 3- Aminomethyl-1-3,5. 5-}trimethylcyclohexylamine, bis(aminomethyl)cyclohexane, l-methyl-2,4-diaminocyclohexane, and the like. Examples of the polybasic acids include adipic acid, azelaic acid, sebacic acid, dodecanoic acid, and polymerized vegetable oil (
dimer acid), etc.

A polyamide boryan resin can be obtained by mixing such a polybasic acid and a polyamine and heating the mixture to about 150 to 200° C. while removing raw or filtered water. In this reaction, an appropriate catalyst such as an organic acid may be used as necessary.

In the method of the present invention, the urethane resin paint used for the first layer or undercoat contains the thus obtained TMXDI urethane prepolymer and active hydrogen resin, but if necessary, polyisocyanate or a preform thereof may also be used. It may also contain a polymer.

Such polyisocyanates are not particularly limited as long as they have two or more isocyanate groups in the molecule and are used as crosslinking agents in the technical field of paints. Thus, for example, tolylene diisocyanate, 4,4''-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated 4,4''-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, isophorone diisocyanate, Trimethylhexamethylene diisocyanate, dimer acid diisocyanate, etc. are preferably used.

Furthermore, polymerized polyisocyanates such as dimers and trimers of these diisocyanates, and polymerized polyisocyanates such as dimers and trimers of these diisocyanates, which are obtained by reacting these polyisocyanates with the above-mentioned active hydrogen compound under conditions with an excess of isocyanate groups, contain two or more Prebolimers having isocyanate groups and biuret compounds obtained by reacting these diisocyanates with water are also used.

Among these, non-yellowing polyisocyanates with excellent weather resistance such as hexamethylene diisocyanate, isophorone diisocyanate, and lysine diisocyanate, their polymerized polyisocyanates, and prepolymers of these polyisocyanates and active hydrogen compounds are used. and biuret compounds are preferably used.

Such a urethane resin paint used for the first layer or undercoat in the method of the present invention is a blend of TMXDI prepolymer, if necessary, other polyisocyanate or polypolymer, and active hydrogen resin. However, the blending ratio is the equivalent ratio of isocyanate group/active hydrogen,
That is, the equivalent ratio of NCO group/active hydrogen is about 0.2 to 3.0.
, particularly preferably in the range of about 0.7 to 1.5.

In addition, as mentioned above, when polyisocyanate or its prepolymer is used together with TMXDI Brepolymer, the blending ratio is such that TMX
The content of the DI prepolymer is preferably 20% by weight or more, particularly preferably 40% by weight or more.

In the present invention, the urethane resin paint used for the first layer or undercoat can be used as it is as a clear paint, but if necessary, color pigments, IJI materials, silicone-based, amine-based, polyether-based, etc. Various dispersants such as polyester, castor oil, wax, and bentonite, antifoaming agents, abrasives, leveling agents, thixotropic agents, penzotriazole, hindered agone, hindered phenyl, etc. It may contain various stabilizers, various reaction catalysts such as tin-based, lead-based, zinc-based, etc.

According to the method of the present invention, after the urethane resin paint obtained as described above is applied to a substrate to be coated, a second urethane resin paint is applied thereon.

Here, the means for applying the first and second urethane resin paints is not particularly limited, and includes, for example, an air spray gun, an airless spray gun, a brush,
It can be applied using a roll coater, flow coater, dipping, electrostatic coating, etc.

According to the method of the present invention, the urethane resin paint containing the TMXDI prepolymer and the active hydrogen resin has excellent recoatability, and can be advantageously used as a primer for coated substrates made of plastic, for example. can. According to the method of the present invention, a urethane resin paint containing a TMXDI prepolymer and an active hydrogen resin is applied as a first layer or undercoat to a substrate to be coated, and after drying and baking to form a coating film, For example, even after 5 days or more, a second urethane resin paint can be applied as a second layer or top coat to create a recoated urethane resin paint that has excellent adhesion between the two and does not cause delamination. can be obtained.

In the method of the present invention, the second urethane resin paint may be of a one-component type or a two-component type. The one-component type is called a moisture-curable urethane resin paint, and is made of a prebolimer having a isocyanate group. Obtainable. Here, as the above-mentioned free polyisocyanate, as mentioned above,
Polyisocyanates, which may be used in combination with the TMXDI prepolymer, are preferably used. TMXDI is also suitably used as polyisocyanate. The above active hydrogen-containing compound also has a molecular weight of 300 to 10,000.
, polyether polyols, polyester polyols, polyether polyester polyols, etc. having 2 to 4 functional groups are preferably used.

On the other hand, two-component urethane resin paints consist of a main agent consisting of a polyol having two or more hydroxyl groups in the molecule, and a polyol having two or more hydroxyl groups in the molecule.
This is a two-component paint containing a curing agent made of polyisocyanate having more than 100 isocyanate groups.

Here, as the above-mentioned polyol, the aforementioned polyester polyol resin, polyether polyol resin, polyether polyester polyol resin, acrylic polyol resin, epoxy polyol resin, etc. are used,
In particular, polyester polyol resins and acrylic polyol resins are preferably used. Further, as the polyisocyanate, a polyisocyanate that may be used in combination with the TMXDI prebolymer as described above is preferably used. TMXDI is also suitably used as polyisocyanate.

Such urethane resin paints are used as clear paints and color paints.

As described above, according to the method of the present invention, first, a terminal isocyanate a urethane prepolymer consisting of TMXD I and a compound having two or more active hydrogens in the molecule is applied to the substrate to be coated. After applying the first urethane resin paint containing a resin with active hydrogen in its molecules, the second urethane resin paint is further applied on top of it, so that the first layer of paint and the second urethane resin paint are
The adhesion of the coating film is good, so if the second coating film is usually formed 5 days or more after the first coating film is formed,
However, according to the method of the present invention, delamination between the coating films does not occur even in such cases.

EXAMPLES The present invention will be described below with reference to examples as well as reference examples, but the present invention is not limited to these examples in any way. In the following, parts and % mean parts by weight and % by weight, respectively.

Reference Example 1 (Production of Prepolymer A) 8 parts of m-TMXD 1 1 6 2, 44.7 parts of trimethylolpropane, and 0.0 parts of dibutyltin dilaurate.
05 parts by weight was charged into a reaction vessel, and the reaction was carried out at 80 to 85°C for 3 hours under stirring in a nitrogen stream.

Next, unreacted m-TMXDI is distilled off using a thin film evaporator, and 0. A prebolimer containing 5% free #m-TMXDI was obtained. This m-TMXDI/trimethylolprobane prebomer was diluted with ethyl acetate and the solid content was 75%.
, TMXDI prebolimer solution A having an isocyanate group content of 10.0% was obtained.

(Production of Prepolymer B) 5 parts of m-TMXD I 1 4 6, 1000 parts of polypropylene glycol (molecular weight 1000), 268 parts of trimethylolpropane, and 0 parts of dibutyltin dilaurate.
．． 06 parts by weight and 91) parts of cellosolve acetate were charged into a reaction vessel, and the reaction was carried out at 80 to 85°C for 4 hours under stirring in a nitrogen stream to obtain a solid content of 75% and an isocyanate group content of 4.6%. TMXDI polymer? A solution B was obtained.

Moreover, the following was used as a curing agent.

Curing agent A Prepolymer solution? &A was used as is. Solid content 75%
, isocyanate group content 1 0. 0%.

Curing agent B Brevolimer solution B was used as is. Solid content 75%,
Isocyanato group content: 4.6%.

Curing agent C (comparison) Takefuto D-165N-900X (HMDI biuret type isocyanate curing agent manufactured by Takeda Pharmaceutical Co., Ltd.) was used as it was. Solid content 90%, isocyanato group content 21
．． 0%.

Curing agent D: Prepared by sufficiently mixing and stirring 00 parts of curing agent AI and 0,125 parts of curing agent. Solids content 83.3%, isocyanate group content 16. ■%.

Curing agent E 100 parts of curing agent B and curing agent C 8 3. Three parts were thoroughly mixed and stirred to prepare. Solid content 81.8%, contains isocyanate groups ffi 1 2. 1%.

Example 1 A substrate to be coated was prepared by degreasing a polyurethane resin molded article for an automobile bumper in trichloroethane vapor for 1 minute.

100 parts of Soflex Fish 100 Primer Gray main agent (Kansai Pain L-T'+L 2-component primer for polyurethane resin, polyester polyol resin system) and hardening agent E 1 9. 3 parts (equivalent ratio) and thinner (
14 at xylene/methyl ethyl ketone ratio 60/40)
s/FC#4 (20°C).

The paint thus diluted was quickly air-sprayed onto the substrate to be coated to a dry film thickness of 25 μm, and baked and dried at 80° C. for 30 minutes to obtain a primer.

After baking, place in an atmosphere at 30°C, and after 3, 5, 7, and 10 days, apply 20% soft
0 White (a two-component urethane type solid color paint for bumpers manufactured by Kansai Paint, polyester polyol resin type) was air-sprayed to a dry film thickness of 35 μm, and baked and dried at 80° C. for 30 minutes.

After cooling to room temperature, regarding the coating film between the brimer and topcoat,
A grid adhesion test was conducted. The results are shown in Table 1.

Example 2 The same coated substrate as in Example 1 was prepared.

Soflex Kan 100 Brimar Gray base agent 100 parts and catalyst (Neostane, tin-based catalyst manufactured by Nitto Kaoru) 0.00
5 parts and curing agent 8 5 0. Example l
The mixture was diluted in the same manner as in Example 1 to obtain a paint, which was applied onto the above-mentioned substrate to be coated and baked to dry.

After baking, a top coat was applied in the same manner as in Example 1, baked and dried, and a grid adhesion test was conducted. Results first
Shown in the table.

Example 3 The same coated substrate as in Example 1 was prepared.

Soflex LTL000 Primer (Kansai Paint■
Lacquer-type primer for polyurethane resin) was coated on the above coated substrate and dried to obtain a brimer-coated plate.

Soflex lh200 white base agent 100 parts and hardening agent D
1 3. 7 parts (equivalent ratio) and thinner (xylene/methyl ethyl ketone ratio 60/40) to 16
s/FC#4 (20°C).

The paint diluted in this way was air-sprayed onto the primer coated plate so that the dry film thickness was 35 μm, and the paint was heated at 80°C.
Baked and dried for 30 minutes.

After baking, place in an atmosphere of 30℃, 3 days later, 5 days later,
After 7 and 10 days, half of the painted surface was masked with masking tape, and the dry film thickness of Soflex Hiro 400 Silver (2-component urethane type paint for metallic head coat for bumpers manufactured by Kansai Paint ■, polyester polyol resin type) was applied. Air spraying was performed so that the thickness was 15 μm.

Next, the masking tape was peeled off, and the product was baked and dried at 80° C. for 30 minutes to obtain a two-tone painted board.

After cooling to room temperature, a grid adhesion test was conducted. Results first
Shown in the table.

Example 4 A primer coated plate was prepared in the same manner as in Example 3.

On this primer coated plate, Soflex Nl400 Silhar was air-sprayed to a dry film thickness of 15 μm and set for 5 minutes.

100 parts of Soflex Aim 500 Clear main agent and hardening agent D 2 7. 3 parts (equivalent ratio) and thinner (
17 at xylene/methyl ethyl ketone ratio 60/40)
s/FC#4 (20°C).

The paint diluted in this way was air-sprayed onto the above silver so that the dry film thickness was 30 μm, and the paint was heated at 80°C.
Baked and dried for 30 minutes.

After cooling to room temperature, place in an atmosphere of 30'C, and after 3 days,
After 1 day, 7 days, and 10 days, a freshly prepared silver clear coat as described above was coated again and baked and dried to obtain a recoat coated board.

After cooling to room temperature, a checkerboard adhesion test (recoat adhesion) was conducted. The results are shown in Table 1.

Comparative example 1 A coated substrate was prepared in the same manner as in Example 1.

Soflex 100 parts Primer Gray base agent 100 parts and hardening agent CI 1. 1 part (equivalent ratio) and diluted with thinner (xylene/methyl ethyl ketone ratio 60/40) to 14 seconds/FC#4 (20''C).

The paint diluted in this manner was applied onto the substrate to be coated and baked to dry in the same manner as in Example 1.

After baking, place in an atmosphere of 30'C, and after 3 days,
Dry Soflex Magnetic 200 White after 7 days and 10 days +15! It was air-sprayed to a thickness of 35 μm and baked and dried at 80'C for 30 minutes.

After cooling to room temperature, the coating film between the primer and topcoat,
A grid adhesion test was conducted. The results are shown in Table 1.

Comparative example 2 A primer coated plate was prepared in the same manner as in Example 3.

Soflex llh200 white base agent 100 parts and hardening agent C
I 0. 5 parts (equivalent ratio) and thinner (xylene/methyl ethyl ketone ratio 60/40) to 16
s/FC#4 (20°C).

The paint diluted in this way was air-sprayed onto the primer coated plate so that the dry film thickness was 30 μm, and the paint was heated at 80°C.
Baked and dried for 30 minutes.

After this, in the same manner as in Example 3, Soflex 1) h4
00 Silver and Soflex 500 Clear were applied and baked, and a grid adhesion test was conducted. The results are shown in Table 1.

Comparative example 3 A primer coated plate was prepared in the same manner as in Example 4.

Air spray Soflex Aim 400 Silver onto this primer coated plate to a dry film thickness of 15 μm.
Set for 5 minutes.

Soflex Aim 500 Clear base agent 100 parts and hardening agent C
21.0 parts (equivalent ratio) and mixed with thinner (xylene/methyl ethyl ketone ratio 60/40) for 17 seconds/
Diluted to FC#4 (20°C).

The thus diluted paint was air-sprayed onto the primer-coated plate to a dry film thickness of 30 μm, and baked and dried at 80° C. for 30 minutes.

After this, in the same manner as in Example 4, Soflex Nll4
00 silver and Soflex ik500 clear were applied and baked, and a grid adhesion test was conducted. Results first
Shown in the table.

Claims (3)

[Claims] (1) A urethane prepolymer with terminal isocyanate groups consisting of α, α, α′, α′-tetramethylxylylene diisocyanate and a compound having two or more active hydrogens in the molecule, and a resin having active hydrogens in the molecule. A coating method characterized by applying a urethane resin paint containing the urethane resin paint to a substrate to be coated, and then applying another layer of urethane resin paint thereon. (2) The coating method according to claim 1, wherein the compound having active hydrogen is a polyol. (3) The coating method according to claim 1, wherein the resin having active hydrogen is a polyester polyol resin.