JP3275317B2 - Clear finish coating method for metal substrates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel and useful clear finish coating method which is excellent in long-term weather resistance and is particularly useful as a method for coating a metal substrate.

More specifically, when a clear paint containing a hydroxyl group-containing fluororesin and a curing agent as main components is applied to a metal base material, the hydroxyl group-containing fluororesin is specified to contain no chlorine atom. And an improved clear finish coating method comprising the use of the above resin.

[0003]

2. Description of the Related Art Conventionally, metal substrates used for roofing materials, exterior wall materials, vehicles or sashes are usually colored so as to impart aesthetics thereto or to protect such substrates. Painting paints has been performed.

[0004] However, in recent years, it would be the specifications that take advantage of the beautiful metal feel of the original metal substrate is preferred, as it is, there is also carried out to be used as a non-coated substrate
Is Domo, when used outdoors, gradually, dust in the air, or contaminated by, such as sulfur dioxide or nitrogen oxide, with or affected, resulting in a sense metal is lost.

[0005] To this end, it has been known to apply a clear finish coating with various clear paints such as acrylic resin, polyester resin or polyurethane resin to protect the metal substrate. It has been done.

[0006] In recent years, the demand for long-term durability of these metal substrates has been increasing more and more. However, the above-mentioned acrylic resin, polyester resin or polyurethane resin-based clear paint, if used outdoors and for a long time, inevitably because the weather resistance of the coating film is insufficient. However, the gloss disappeared, and after all, it could not meet the demand.

[0007] Therefore, attempts have been made to carry out this clear finish with a fluororesin-based paint having good long-term weather resistance. However, conventional polyvinylidene fluoride-based paint is a is insufficient transparency, inevitably, there is a fundamental problem that the metal substrate original metal feeling can not be obtained.

[0008] In recent years, a solvent-soluble fluororesin has been developed, and by using such a solvent-soluble fluororesin, a transparent and glossy clear finish has become possible for the first time.

[0009]

However, the clear finish using such a solvent-soluble fluororesin causes a new problem that the metal substrate surface is corroded and discolored when used outdoors for a long period of time. did.

This is because this kind of solvent-soluble fluororesin itself contains a chlorine atom in a molecule and has a very high light transmittance, so that ultraviolet rays in sunlight are
It is easy to reach the interface between the metal surface and the coating film. As a result, the transmitted ultraviolet light decomposes the bond between the chlorine atom and the carbon atom, which has a weak bonding force, and generates chloride and / or fluoride. Is considered to cause corrosion and discoloration of the metal surface.

Various proposals have been made to solve this kind of problem. That is, mixing an epoxy compound or applying an acrylic resin-based clear to the surface of a metal base material in advance, and then applying a fluororesin clear paint, however, both methods have a long-lasting effect. Because of the lack of sexuality, the ultimate solution could never be a fundamental solution.

However, the present inventors have proposed a novel and novel coating method which is completely free from the problem of corrosion and discoloration of the surface of a metal substrate even for long-term outdoor use.
In particular, we have begun research to provide a novel form of clear paint finishing.

Accordingly, an object of the present invention is to provide a novel method of coating a metal substrate, which is completely free from corrosion and discoloration on the surface of the metal substrate even in long-term outdoor use. It is an object of the present invention to provide a new and useful clear finish coating method which is excellent in long-term weather resistance.

[0014]

The inventors of the present invention have made intensive studies and studies mainly on the problems to be solved by the present invention as described above. The present inventors have found that by coating and curing a clear coating containing a polymer as an essential component, a coated product having extremely excellent long-term weather resistance and also excellent gloss can be obtained. Was completed.

That is, in the present invention, when a clear coating mainly containing a hydroxyl group-containing fluororesin (A) and a curing agent (B) is directly applied to a metal substrate, the hydroxyl group-containing fluororesin (A) Fluorine resin (A-1) containing no chlorine atom and having an average of two or more hydroxyl groups in one molecule and having a carboxyl group [hereinafter abbreviated as "hydroxyl group-containing fluororesin". ] The use of a specific clear paint is intended to provide an improved clear finish coating method.

Hereinafter, the present invention will be described in more detail. First, here, the above-mentioned "metal substrate" refers to various metals such as iron, zinc, aluminum, magnesium, copper, brass, stainless steel or zinc; or an alloy of these various and other metals. And various alloys, such as alloys of aluminum with other metals, as well as alloys of magnesium with other metals;

[0017] A plated product of these various metals, or a low-temperature sprayed iron, anodized aluminum, anodized aluminum or stainless steel, or a chemical conversion treatment with chromic acid, phosphoric acid, or the like. It refers to the applied iron or aluminum.

Next, the above-mentioned clear paint will be described. Of course, the clear paint used in the method of the present invention does not contain a coloring agent. Also included are so-called color clears which contain a coloring agent to such an extent that the feeling is not impaired.

It is important that the hydroxyl group-containing fluororesin (A-1) used in preparing the clear coating composition does not contain any chlorine atom in the molecule. It is necessary that the compound has two or more hydroxyl groups on average.

If the number of hydroxyl groups is less than 2, the durability of the coating film will necessarily decrease, which is not preferable. Further, such a hydroxyl group-containing fluororesin (A-
1) contains a carboxyl group in the molecule from the viewpoint of compatibility with a curing agent, adhesion to a metal substrate, and the like.

As a method for introducing and including such a carboxyl group in the molecule of the hydroxyl group-containing fluororesin (A-1), the carboxyl group-containing vinyl monomer is used for preparing the resin (A-1). Or copolymerize

Various polycarboxylic anhydrides such as succinic anhydride and phthalic anhydride may be added to a copolymer of a hydroxyl group-containing vinyl monomer,

Alternatively, various known and commonly used polycarboxylic acids may be added to a copolymer of an epoxy group-containing monomer, and any of these methods is possible.

The hydroxyl group-containing fluororesin (A-1) includes 15 to 75% by weight of the fluorine-containing vinyl monomer (a-1) and 5 to 40% by weight of the hydroxyl group-containing vinyl monomer (a-2).
% And 5 to 85% by weight of the other monomer (a-3) copolymerizable with (a-1) and (a-2).
Those obtained by copolymerizing the above are particularly typical examples.

If the amount of the fluorine-containing vinyl monomer (a-1) is less than the above-mentioned range, the durability of the coating film and the like will be reduced. If the ratio exceeds the above range, the coating workability will be reduced, and in either case, it is not preferable.

Also, a hydroxyl group-containing vinyl monomer (a-2)
If the amount of used is less than the above range,
The solvent resistance and durability of the coating film will decrease,
On the other hand, if it exceeds the above range, the flexibility and the like of the coating film will be reduced, and neither is preferable.

The fluorine-containing vinyl monomer (a-1), of course, does not contain a chlorine atom in the molecule, but if only typical ones among them are exemplified, the fluorine-containing vinyl monomer (a-1) can be used. Vinyl chloride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, pentafluoropropylene or hexafluoropropylene,
Fluorine-containing α-olefins; or a perfluoroalkyl perfluorovinyl ether such as trifluoromethyltrifluorovinylether, pentafluoroethyltrifluorovinylether or heptafluoropropyltrifluorovinylether, or
(Per) fluoroalkyl vinyl ether (provided that the number of carbon atoms in the alkyl group is in the range of 1 to 18), and among others, use of vinyl fluoride, vinylidene fluoride or hexafluoropropylene is preferred. .

The hydroxyl group-containing vinyl monomer (a-
If only typical examples are exemplified as 2), 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxy Various hydroxyl-containing vinyl ethers such as -2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether or 6-hydroxyhexyl vinyl ether;

Alternatively, various vinyl ethers listed above and ε
Addition reaction products with caprolactone; 2-hydroxyethyl (meth) allyl ether, 3-hydroxypropyl (meth) allyl ether, 2-hydroxypropyl (meth) allyl ether, 4-hydroxybutyl (meth) allyl ether; Various hydroxyl-containing allyls such as -hydroxybutyl (meth) allyl ether, 2-hydroxy-2-methylpropyl (meth) allyl ether, 5-hydroxypentyl (meth) allyl ether or 6-hydroxyhexyl (meth) allyl ether ether;

Alternatively, addition products of the above-mentioned various allyl ethers with ε-caprolactone; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth)
Various hydroxyl group-containing (meth) acrylates such as acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate or polypropylene glycol mono (meth) acrylate;

Further, there are main components (main adducts) of the above-mentioned various (meth) acrylates and ε-caprolactone addition reaction. If only typical examples of the other copolymerizable monomer (a-3) described above are given as examples, first, a hydroxyl group-containing fluororesin (A-
In contrast to 1), only typical carboxyl group-containing vinyl monomers used for introducing and containing a carboxyl group are exemplified by (meth) acrylic acid, crotonic acid and itacone. Acid, maleic acid or fumaric acid,

In addition, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether,
Isobutyl vinyl ether, tert- butyl bi Nirue <br/> ether, n- pentyl vinyl ether, n- hexyl vinyl ether, n- octyl vinyl ether, such as 2-ethylhexyl vinyl ether, base down Jill vinyl or phenyl vinyl ether, various alkyl vinyl ethers or Various substituted alkyl vinyl ethers;

Cycloalkyl vinyl ethers such as cyclopentyl vinyl ether, cyclohexyl vinyl ether or methylcyclohexyl vinyl ether;
Vinyl-2,2-dimethylpropanoate, vinyl-
2,2-dimethylbutanoate, vinyl-2,2-dimethylpentanoate, vinyl-2,2-dimethylhexanoate, vinyl-2-ethyl-2-methylbutanoate, vinyl-2-ethyl- Introduction <br/> 2-methylpentanoate er DOO, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl or vinyl stearate laurate or C, vinyl ₉ comprising branched aliphatic carboxylic acids, various aliphatic carboxylic acid vinyl ethers such as branched aliphatic carboxylic acid vinyl consisting branched aliphatic carboxylic acids vinyl or C ₁₁ C becomes _10;

Vinyl esters of carboxylic acids having a cyclic structure, such as vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinylbenzoate or vinyl p-tert-butylbenzoate;

Acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate or cyclohexyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate;
Methacrylates such as cyclohexyl methacrylate or benzyl methacrylate;

Ethylene, propylene or butene-1
And various α-olefins; styrene, tert
Various aromatic vinyl compounds such as -butylstyrene, α-methylstyrene or vinyltoluene;

Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinylmethyldiethoxysilane, vinyltris (β-methoxyethoxy) silane, allyltrimethoxysilane, trimethoxysilylethylvinylether, triethoxysilylethylvinylether, Methyldimethoxysilylethyl vinyl ether, trimethoxysilylpropyl vinyl ether, triethoxysilylpropyl vinyl ether,
Methyldiethoxysilylpropyl vinyl ether, γ-
Monomers containing various hydrolyzable silyl groups, such as (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane or γ- (meth) acryloyloxypropylmethyldimethoxysilane;

Glycidyl (meth) acrylate, β-
Various epoxy group-containing monomers such as methyl glycidyl (meth) acrylate or (meth) allyl glycidyl ether;

Various amino group-containing amides such as N-dimethylaminoethyl (meth) acrylamide, N-diethylaminoethyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide or N-diethylaminopropyl (meth) acrylamide Unsaturated monomers;

Various dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate or diethylaminoethyl (meth) acrylate;

Alternatively, tert-butylaminoethyl (meth) acrylate, tert-bitylaminopropyl (meth) acrylate, aziridinylethyl (meth)
Various amino group-containing monomers such as acrylate, pyrrolidinylethyl (meth) acrylate and piperidinylethyl (meth) acrylate.

From the viewpoint of increasing the polymerization yield of the hydroxyl group-containing fluororesin (A-1) itself, alkyl vinyl ethers, cycloalkyl vinyl ethers and / or
Or the use of vinyl carboxylate is desirable, furthermore, from the viewpoint of coating workability and coating film performance such as weather resistance, the type of the monomer and the amount used, as appropriate.
It is preferable to determine.

Of course, the hydroxyl group-containing fluororesin (A-
In order to include a carboxyl group in 1), it is not possible to use a carboxyl group-containing vinyl monomer or a glycidyl group-containing monomer, respectively, in a method selected from the various methods described above. Needless to say.

To prepare the hydroxyl group-containing fluororesin (A-1) component, a radical polymerization initiator is used to make full use of known techniques such as emulsion polymerization, suspension polymerization, bulk polymerization or solution polymerization. , A polymerization reaction may be performed,

Examples of the radical polymerization initiator include various diacyl peroxides such as acetyl peroxide and benzoyl peroxide; various ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide;

Various hydroperoxides such as hydrogen peroxide, tert-butyl hydroperoxide or cumene hydroperoxide; di-tert
Various dialkyl peroxides, such as butyl peroxide or dicumyl peroxide;

Alkyl peroxyesters such as tert-butyl peroxyacetate or tert-butyl peroxypivalate;

Various azo compounds such as azobisisobutyronitrile or azobisisovaleronitrile;

Or various persulfates such as potassium persulfate or ammonium persulfate. As the polymerization reaction method, there are various known and commonly used methods as described above. Among them, bulk polymerization and solution polymerization are preferable, and furthermore, the obtained copolymer is used as it is, for example, In view of the fact that it can be used as a resin composition for a solution type paint, the solution polymerization method is particularly desirable.

Particularly typical solvents used for preparing the hydroxyl group-containing fluororesin by the solution polymerization method include various aromatic hydrocarbons such as benzene, toluene and xylene; n-pentane; n-
Various aliphatic hydrocarbons, such as hexane or n-octane;

Such as cyclopentane, cyclohexane, methylcyclohexane or ethylcyclohexane;
Various alicyclic hydrocarbons; such as mineral spirits,
Various mixed hydrocarbons;

Methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, n-hexanol, n-octanol,
Various alcohols such as ethylhexanol, cyclohexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether;

Dimethoxyethane, tetrahydrofuran,
Dioxane, diisopropyl ether or di-n-
Various ethers such as butyl ether; acetone,
Various ketones such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl amyl ketone, cyclohexanone or isophorone;

Methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate or ethylene Various esters, such as glycol monobutyl ether acetate;

Alternatively, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, ethylene carbonate and the like can be mentioned. Such organic solvents may be used alone or in combination of two or more.

In order to prepare the hydroxyl group-containing fluororesin (A-1) from the various monomer components as described above by a solution polymerization method, all the monomers, polymerization initiators and solvents are used. , Batch polymerization in a reaction vessel,

Into a reaction vessel charged with a fluorine-containing vinyl monomer and a solvent, a monomer other than the fluorine-containing vinyl monomer and a polymerization initiator are continuously added, respectively.
Or, it is divided and added and polymerized,

Further, all the monomers and the polymerization initiators are added to the reaction vessel charged only with the solvent, continuously or in a divided manner, and polymerized.
Various methods can be applied.

In the above description, the description has been made mainly of the solvent-soluble type hydroxyl group-containing fluororesin. Of course, the resin may be in the form of a so-called non-aqueous dispersion in a form dispersed in a solvent. But you can

Alternatively, it may be in a form containing partially gelled particles. Next, the curing agent (B), which is another essential component of the clear paint used in the method of the present invention, is the above-mentioned hydroxyl group-containing fluororesin (A-1).
As long as the resin (A-1) can be cured by reacting with a hydroxyl group therein, it can be used naturally.

For example, various chelating agents such as acetylacetone or ethyl acetoacetate are reacted with isocyanate compounds, amino resins, polycarboxylic acid compounds, polyvalent metal alkoxides, etc., and polyvalent metal alkoxides. Particularly, a polyvalent metal chelate compound obtained by the above method is exemplified. From the viewpoint of curability, it is preferable to use an isocyanate compound or an amino resin.

First, if only typical representative examples of the above-mentioned isocyanate compound are given, various aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate;

Various cycloaliphatic diisocyanates, such as xylylene diisocyanate or isophorone diisocyanate;

Or like tolylene diisocyanate or 4,4'-diphenylmethane diisocyanate,
Including various organic diisocyanates such as various aromatic diisocyanates,

Alternatively, adducts of these organic diisocyanates with a polyhydric alcohol, a low molecular weight polyester resin (polyester polyol) or water,

Further, there are polymers such as the above-mentioned organic diisocyanates (including isocyanurate-type polyisocyanate compounds), isocyanate biuret bodies, and the like.

Further, there are also obtained those obtained by blocking various polyisocyanate compounds as described above with a known and commonly used blocking agent,

Examples of particularly typical commercial products of such various polyisocyanate compounds include "Vanock D".
-750, D-800, DN-950, DN-980,
DN-990, DN-981 or DN-992 "
[Products of Dainippon Ink and Chemicals, Inc.], “Desmodur L, N, HL or LL” (manufactured by Bayer AG, West Germany), “Takenate D-102, D-202, D
-110N or D-140N "(product of Takeda Pharmaceutical Co., Ltd.)," Coronate L, HL, EH or 203 "(product of Nippon Polyurethane Industry Co., Ltd.) or" Duranate 24A-90EX or X-67. "
9 "[a product of Asahi Kasei Corporation].

Examples of commercial products which are particularly typical examples of the blocked polyisocyanate compound include "Barnock D-550" and "Barnock B7-887-".
60 or B9-282 "(product of Dainippon Ink and Chemicals, Inc.)," B-1370 "(product of Huls, Germany)," Takenate D-815-N "(product of Takeda Pharmaceutical Co., Ltd.)," Additol
VXL-80 "(manufactured by Hoechst Synthesis Co., Ltd.) or" Coronate 2507 "(manufactured by Nippon Polyurethane Industry Co., Ltd.).

As typical examples of the amino resin, only typical ones are exemplified. An amino group-containing compound such as melamine, urea, acetoguanamine, benzoguanamine, sterogamine or spiroguanamine, and formaldehyde, paraformaldehyde, acetaldehyde or glyoxal And an aldehyde compound component such as
By a conventional method, such as a condensate obtained by reacting,

Alternatively, there may be mentioned those obtained by etherifying each of these condensates with alcohols. If the condensates are usually used for paints,
Of course, both can be used.

Among them, preferred is a form partially or completely etherified with C _{1 to} C ₄ alcohols.

Specific examples of such aminoplasts include:
Hexamethyletherified methylolmelamine, hexabutyletherified methylolmelamine, methylbutyl mixed etherified methylolmelamine, methyletherified methylolmelamine, butyletherified methylolmelamine or isobutyletherified methylolmelamine, or condensates thereof are particularly typical. It is.

The desired clear coating composition is prepared using the hydroxyl group-containing fluororesin (A-1) and the curing agent (B), which are essential components of the clear coating composition, according to a conventional method. What is necessary is just to mix these two components simply.

The mixing ratio of the curing agent (B) and the hydroxyl group-containing fluororesin (A-1) is (A-1) /
(B) = 100/3 to 100 (weight ratio)
It is desirable from the viewpoint of the performance of the coating film.

That is, the hydroxyl group-containing fluororesin (A-
When the amount of the curing agent (B) used is less than 3 parts by weight with respect to 100 parts by weight of 1), it is difficult to obtain a film having sufficient coating performance, while the amount exceeds 100 parts by weight. When it comes to, the coating film is likely to become brittle,
Either case is not preferred.

The hydroxyl group-containing fluororesin (A)
In preparing a clear coating using -1) and the curing agent (B), it is, of course, possible to use known and commonly used curing catalysts, if necessary.

If only isocyanate compounds are used as the curing agent (B), dibutyltin dilaurate, dibutyltin diacetate, tin dioctylate, or the like may be used. Various organometallic compounds, such as cobalt naphthenate; or 1,4-diazabicyclo- (2.2.2)-
Octane or 1,8-diazabicyclo- (5.4.
And various amine compounds such as 0) -undecene-7.

When an amino resin is used as the curing agent (B), p-toluenesulfonic acid, phosphoric acid or mono- or dialkyl esters of phosphoric acid, or “Nailure 155, 2500X, X-49-1”
10, 3525 or 5225 "(product of King Company of the United States) and the like, as well as dodecylbenzenesulfonic acid and organic amine blocking compounds thereof.

Further, a coloring pigment and / or a metal powder can be used to such an extent that the transparency of the obtained coating film is not impaired. Furthermore, if necessary, including various resins and solvents, a flow regulator, a color separation inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer or a silane coupling agent, etc. It goes without saying that various additives can be added.

Examples of the above-mentioned various resins include, in particular, various cellulose-based resins such as nitrocellulose or cellulose acetate butyrate.
There are a ketone resin, a petroleum resin, an acrylic polymer, an oil-free alkyd resin, an alkyd resin and an epoxy resin, and among others, the use of an acrylic resin is suitable in terms of compatibility and the like.

As the above-mentioned solvents, the above-mentioned various solvents, such as those used for preparing the above-mentioned hydroxyl group-containing fluororesin (A-1), and mixtures thereof are used.

The coating in the practice of the method of the present invention includes:
Using the clear paint described above, in the same manner as before,
That is, it is performed in accordance with a conventional method. That is, as an object to be coated, if necessary, a clear paint adjusted to a desired viscosity on a metal substrate subjected to a surface treatment, and a dry film thickness of 5 to 5.
Paint to 100 microns (μm).

The method for applying the clear paint may be any of known and commonly used means such as a roll coater, air spray or airless spray, or an ordinary method such as electrostatic coating.

After coating, at room temperature for 3 days or 6
A cured coating film can be obtained by drying or baking at a temperature of 0 to 300 ° C. for several seconds to 60 minutes.

However, when a blocked isocyanate compound is used, it should be dried at a temperature of 140 ° C. or higher.

[0087]

Next, the present invention will be described more specifically with reference examples, examples and comparative examples. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Hydroxy group-containing fluororesin (A-
Preparation Example of 1)] In a 1-liter stainless steel autoclave sufficiently purged with nitrogen gas, 100 mL of ethyl vinyl ether was placed.
Parts, "VeoVa 9" 45 parts (manufactured by The Netherlands Shell, vinyl esters of branched fatty acids having C ₈ comprising alkyl group), 4-hydroxybutyl vinyl ether 50
Parts, 5 parts of monobutyl maleate, 210 parts of xylene
Parts, 5 parts of tert-butyl peroxyoctoate,
5 parts of azobisisovaleronitrile and 1,2,2
1.5 parts of 2,6,6-pentamethylpiperidine were charged.

Next, 300 parts of the liquefied and collected hexafluoropropylene was injected under pressure and stirred at 60 ° C. for 1 hour.
After reacting for 5 hours, 280 parts of xylene was added, and the reaction was further performed for 2 hours, and the nonvolatile content (N
A solution of the target resin having a V) of 50% was obtained. Hereinafter, this is abbreviated as resin (A-1-1).

Reference Examples 2 to 5 (same as above) A hydroxyl group-containing fluororesin was prepared in the same manner as in Reference Example 1, except that the monomers used were changed as shown in Table 1.

[0091]

[Table 1]

Reference Example 6 (Preparation Example of Hydroxyl Group-Containing Fluororesin Containing Chlorine Atom) A simple resin comprising 52 parts of chlorotrifluoroethylene, 21 parts of 4-hydroxybutyl vinyl ether, 17 parts of cyclohexyl vinyl ether and 10 parts of ethyl vinyl ether. The mixture of monomers was prepared according to the method described in JP-A-57-34107, with an NV of 50%.
A xylene solution of a control hydroxyl group-containing fluororesin was obtained. Hereinafter, this is abbreviated as resin (A-1′-1).

Examples 1 to 5 and Comparative Examples Various components as shown in Table 2 were stirred and mixed to prepare various clear coatings.

Further, a predetermined metal substrate was spray-coated so as to have a dry film thickness of 40 μm. After being left at room temperature for 30 minutes, it was dried under predetermined conditions.

[0095]

[Table 2]

Footnotes in Table 2 Note 1) Curing agent (B-1); “Takenate D-140N” [Isocyanate compound manufactured by Takeda Pharmaceutical Co., Ltd.] 〃 (B-2); “Duranate X-679” [Isocyanate compound manufactured by Asahi Kasei Kogyo Co., Ltd.] 〃 (B-3); “B-1370” (isocyanate compound manufactured by Huls GmbH, Germany) 〃 (B-4); “Cymel 303” [Mitsui Cyanamid amino resin]

Note 2) "A-187"; [silane coupling agent manufactured by Nippon Unica Ltd.] Note 3) "Tinuvin 900"; (manufactured by Ciba Geigy, Switzerland) Note 4) "Tinuvin 292"; )

Note 5) Diluent solvent: xylene / butyl acetate = 50/50 (weight ratio) Note 6) Metal substrate: M-1; stainless steel "SUS304" (2B finish) 〃 ... M-2: Chromated aluminum (A5052P) 〃 ………… M-3: Galvanized steel sheet (all 0.8 mm thick)

APPLICATION EXAMPLES 1-5 AND COMPARATIVE APPLICATION Various metal substrates obtained in Examples 1-5 and Comparative Example, each of which has been subjected to a coating finish with a clear, are used for evaluation tests of various coating film properties. Provided.

The results are collectively shown in Table 3.

[0101]

[Table 3]

[0102]

As is clear from the test results in Table 3,
It was confirmed that the metal substrate obtained by the clear finish coating method of the present invention did not show any corrosion discoloration even in a long-term weather resistance test, and was able to maintain gloss for a long period of time.

On the other hand, in the case of using a conventional chlorine atom-containing hydroxyl group-containing fluororesin, corrosion discoloration could not be prevented.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-40269 (JP, A) JP-A-61-46283 (JP, A) JP-A-61-283380 (JP, A) JP-A-63-283 296873 (JP, A) JP-A-1-304161 (JP, A) JP-A-2-97582 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 7/24, 7 / 14 B32B 15/08 102 C09D 127/12

Claims (5)

(57) [Claims] 1. A hydroxyl group-containing fluororesin (A) on a metal substrate
When directly applying a clear coating mainly composed of a curing agent (B) and the above, the hydroxyl group-containing fluororesin (A) does not contain a chlorine atom and has an average of two or more per molecule. have a hydroxyl group, and a fluorine resin have a carboxyl group (a-1) [hereinafter referred to as "hydroxyl-containing fluororesin (a-1)". ], And a clear finish coating method for a metal substrate. 2. The hydroxyl group-containing fluororesin (A-
1) is 15 to 75 of the fluorine-containing vinyl monomer (a-1);
% By weight and 5 to 4 of the hydroxyl group-containing vinyl monomer (a-2).
0% by weight and 1-2% by weight of the carboxyl group-containing monomer
And 5 to 8 of other monomers (a-3) capable of being copolymerized.
The clear finish coating method for a metal substrate according to claim 1, which is obtained by copolymerizing 5% by weight. 3. The hydroxyl group-containing fluororesin (A-
1) is obtained by using at least one compound selected from the group consisting of hexafluoropropylene, vinyl fluoride and vinylidene fluoride as the above-mentioned fluorine-containing vinyl monomer (a-1), The clear finish coating method for a metal substrate according to claim 1 or 2. 4. The method according to claim 1, wherein the curing agent (B) is an isocyanate compound and / or an amino resin. 5. The clear coating mainly comprising the hydroxyl group-containing fluororesin (A) and the curing agent (B), further comprising a silane coupling agent, an ultraviolet absorber and a light stabilizer. A clear finish coating method for a metal substrate according to any one of claims 1 to 4.