JPH0975837A - Method for forming double-layered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cured coating film with excellent mechanical physical properties, scratch resistance, weatherability etc., by applying a water-based base coat resin compsn. and performing powder coating of a powder coating resin compsn. contg. a specified epoxy group-contg. vinyl polymer and an aliph. dibasic acid as essential components. SOLUTION: When a double-layered coating film is formed on an automotive car body, after a water-based base coat resin compsn. is applied on an article to be coated, a powder coating resin compsn. contg. a vinyl polymer contg. epoxy groups in a molecule obtd. by using a polymerizable monomer of the formula (wherein R1 is hydrogen atom or a methyl group) as an essential monomer component and polymerizing it and an aliph. clibasic acid as essential film forming components is applied thereon and this is baked and dried. As the vinyl polymer with epoxy groups, such a polymer that has a softening point based on a ring and ball softening point method in the range of about 80 - about 150 deg.C and has a number average MW in the range of about 1,000 - about 10,000, is used.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel and useful method for forming a multilayer coating film. More specifically, the present invention comprises coating an aqueous basecoat resin composition containing an aqueous resin as an essential component on an article to be coated, and then adding an epoxy group-containing vinyl polymer (B), A specific resin composition for powder coating, which contains an aliphatic dibasic acid (C) as an essential component, is applied, baked, and dried.

In particular, it provides a coating film excellent in appearance, mechanical properties, weather resistance and scratch resistance.
The present invention relates to a novel method for forming a multilayer coating film, and more particularly to a novel and useful coating film forming method capable of obtaining a multilayer coating film having extremely high practicality when formed on an automobile body.

[0003]

2. Description of the Related Art Powder coating is one form of coating that does not contain an organic solvent. In recent years, however, the pollution-free nature of the powder coating has attracted attention from the viewpoint of environmental problems such as air pollution. In addition, the amount used has been increasing year by year.

As for the kind of binder resin used in this kind of powder coating, various polymer compounds have been used depending on the application, for example, acrylic copolymer having a glycidyl group in the molecule. The composition obtained by incorporating an aliphatic dibasic acid into the coalescence,

When compared with other resin compositions for powder coatings, for example, a resin composition for powder coatings obtained by using a block / isocyanate-curable polyester resin as a binder composition,

Since the coating film obtained there is excellent in transparency, hardness, weather resistance and the like, a resin for powder coating, which is particularly used outdoors, for transparent (clear) coating. It is suitable as a composition.

Further, from the aspect of the method of painting the car body, let's take a look at the conventional technique. As a technique that is a conventional technique but has been inherited up to the present First, the base coat resin composition in a form containing an organic solvent is coated on the intermediate coating film, and similarly, the organic solvent-based transparent top coat resin composition is coated, and these two layers are formed. The so-called two-coat one-bake method of simultaneously baking and drying is widely adopted and applied even today.

In that case, since the volatilization of the organic solvent is unavoidable, there is a problem to be solved from the viewpoint of environmental protection to suppress the generation of such volatile components. As a possible means for solving such a problem, it is conceivable to use a resin composition for powder coating material having no volatile content,

Even if a conventional resin composition for powder coating is applied as a base coating coating as described above, especially as a base coating coating containing metallic powder, the end result is good. To obtain a coating film of extremely high practicality that gives a coating film appearance of
It can be said that it is difficult.

Therefore, at present, the most excellent coating system in terms of environmental hygiene is limited to a coating system using a so-called water-based base coat resin composition with water as a diluent. This is a system in which a resin composition is coated, and then a resin composition for powder coating is further powder coated thereon.

However, a resin composition for powder coatings, which is required and required for a coating film for an automobile body, can realize a high degree of smoothness and sharpness,
The fact is that it has not been obtained.

[0012]

As described above, as long as the conventional techniques as described above are followed, a coating film excellent in appearance, mechanical properties, weather resistance and scratch resistance, among others, is inevitable. It can be said that it is extremely difficult to provide a coating film forming method capable of obtaining a multi-layer coating film having extremely high practicality.

However, the present inventors have diligently started research in order to solve various problems in the conventional technique as described above. Therefore, the problem to be solved by the present invention depends on, among other things, the appearance of the coating film,
An object of the present invention is to provide a coating film forming method capable of obtaining a multi-layer coating film having extremely high practicality such that a coating film excellent in mechanical properties, weather resistance and scratch resistance can be provided. In particular, it is an object of the present invention to provide a method for forming a multi-layer coating film, which is extremely highly practical and is capable of giving a coating film excellent in various physical properties or various performances.

[0014]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of diligently studying in order to solve various problems (solving problems) in the conventional technique as described above and solve them, as a result, after coating the aqueous base coat resin composition, the co-weight of specific components An extremely excellent coating film appearance can be achieved by powder-coating a transparent resin composition for top coat powder coating in the form of blending an aliphatic dibasic acid, baking and drying. In addition to the above, in addition to finding that the weather resistance of the coating film is also extremely excellent, here, a novel coating film forming method, that is, the multilayer coating film of the present invention is provided. It came to complete the forming method.

That is, in the present invention, basically, an aqueous base coat resin composition (I), which is an aqueous resin (A), is applied as an indispensable film-forming component to an object to be coated, and then the following general formula

[0016]

Embedded image

(In the formula, R _{1 s} are the same or different and each represents a hydrogen atom or a methyl group.)

A vinyl polymer (B) having an epoxy group in the molecule, which is obtained by polymerizing the polymerizable monomer (b-1) represented by the formula (b-1) as an essential monomer component, An object of the present invention is to provide a method for forming a multilayer coating film, which comprises coating a resin composition (II) for powder coating material containing an aliphatic dibasic acid (C) as an essential film-forming component component, followed by baking and drying. To do.

The present invention will be described in more detail below. That is, the method for forming a multilayer coating film of the present invention will be described in more detail.

Here, first, the above-mentioned aqueous base coat resin composition (I) referred to in the present invention means, for example, a so-called water-dilutable resin composition comprising water as an essential solvent component. As the resin composition, a known and commonly used resin composition can be used as it is.

Of these, only typical ones are exemplified, that is, a so-called water-soluble resin is used as a binder, and a so-called dispersion type (water dispersion type) resin is used as a binder. And a so-called emulsion polymer as a binder.

First, to exemplify only typical ones of the above-mentioned types, by completely neutralizing an acrylic resin having an acid group in the molecule with an amine, a completely water-soluble acrylic resin is obtained. Such as those that have been garbled,

Then, only representative examples of the above-mentioned type will be illustrated. For example, the so-called anion-forming property in a molecule as disclosed in Japanese Patent Publication No. 3-45755. A water-dispersible polyurethane resin having a group,

Further, only the representative ones of the above-mentioned type will be illustrated, for example, JP-A-56 / 56
As disclosed in Japanese Patent Application Laid-Open No. 157358, there is one which is composed of a so-called emulsion polymer aqueous solution in the form of containing so-called crosslinkable polymer fine particles.

On the other hand, the resin composition (II) for powder coating referred to in the present invention has the following general formula:

[0026]

Embedded image

(In the formula, R _{1 s} are the same or different and each represents a hydrogen atom or a methyl group.)

The vinyl monomer (b-1) represented by
As an essential monomer component, it can be polymerized or even
If necessary, it can be obtained by copolymerizing the vinyl-based monomer (b-1) with another polymerizable monomer (b-2) that can be copolymerized, that is, in the molecule, A specific type of resin composition comprising a vinyl-based (co) polymer (B) having an epoxy group and an aliphatic dibasic acid (C) as essential film-forming components. It is a thing.

Here, the above-mentioned vinyl-based (co) polymer having a specific epoxy group in the molecule means that the terminal or side chain of the molecule is represented by the above-mentioned general formula [I]. A compound having a specific epoxy group of the form

The (co) polymer (B) [hereinafter, also referred to as vinyl polymer (B) or epoxy group-containing vinyl polymer (B). ] Is, for example, the vinyl-based monomer (b-1) represented by the above general formula [I].
In particular, “R ₁ ” in this general formula [I] is “−
By homopolymerizing a vinyl monomer of the form "CH ₃ ",

Alternatively, the monomer (b-1) and another polymerizable monomer (b) copolymerizable with the monomer (b-1)
-2), among other things, a method such as copolymerization with vinyl monomers,

By modifying the vinyl-based copolymer, the copolymer can be prepared by a method such as introducing a specific epoxy group into the copolymer as represented by the above-mentioned general formula [I]. I can.

In the case of the above method, etc.,
For example, there is a method of previously synthesizing a vinyl copolymer having an isocyanate group in the molecule, and further reacting this copolymer with methylglycidol. However, it is recommended because it is simple.

A polymerizable monomer having an epoxy group in the molecule, which is used when the epoxy group-containing vinyl polymer (B) is prepared by the above-mentioned method, especially in the molecule. As the vinyl monomer (b-1) having an epoxy group, only typical ones are β-methylglycidyl (meth) acrylate.

Further, such a vinyl monomer (b-1) having an epoxy group in the molecule, that is, a monomer having a specific epoxy group as represented by the above general formula [I]. Of course, other polymerizable monomers (b-2) that can be copolymerized with can also be used.

Such an epoxy group-containing vinyl monomer (b
-1) and other polymerizable monomers that can be copolymerized with (b-
As only 2), only typical ones are listed. Various (meth) acrylic acid esters of glycidol such as glycidyl (meth) acrylate; various kinds such as allyl glycidyl ether or allyl methyl glycidyl ether. Allyl glycidyl ethers of
Various vinyl monomers having an alicyclic epoxy group in the molecule, such as 3,4-epoxycyclohexyl acrylate or 3,4-epoxycyclohexyl methacrylate;

Various acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate or cyclohexyl acrylate; various methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate or benzyl methacrylate; Di-methyl fumarate, di-methyl fumarate,
Di-n-butyl fumarate, di-n-butyl malate,
Various dialkyl esters of α, β-ethylenically unsaturated dibasic acids such as di-octyl fumarate or di-octyl malate;

In addition to various carboxyl group-containing monomers such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid, further itaconic acid, maleic acid or fumaric acid Various polyvalent carboxyl group-containing monomers with 1 to 18 carbon atoms
Monoesters with monoalkyl alcohols

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; tert-butylaminoethyl (meth)
Various amino group-containing monomers such as acrylate, tert-butylaminopropyl (meth) acrylate, aziridinylethyl (meth) acrylate, pyrrolidinylethyl (meth) acrylate or piperidinylethyl (meth) acrylate Kind;

Ethylene, propylene or butene-1
Various α-olefins, such as vinyl chloride or vinylidene chloride, various halogenated olefins other than fluoroolefins, such as styrene, α-methylstyrene or vinyltoluene, various aromatic vinyls Compound;

Containing various hydrolyzable silyl groups such as γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane or γ- (meth) acryloyloxypropylmethyldimethoxysilane. Monomers;

Various fluorine-containing α-olefins such as vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, bromotrifluoroethylene, pentafluoropropylene or hexafluoropropylene. ;
Or various perfluoroalkyl perfluorovinyl ethers such as trifluoromethyl trifluorovinyl ether, pentafluoroethyl trifluorovinyl ether or heptafluoropropyl trifluorovinyl ether or (per) fluoroalkyl vinyl ethers (provided that the above alkyl group The number of carbon atoms is within a certain range of 1 to 18), and various fluorine-containing vinyl monomers;

Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, C ₉ branched aliphatic (also called branched aliphatic, hereinafter The same) various aliphatic vinyl carboxylates such as vinyl carboxylate, C ₁₀ branched aliphatic vinyl carboxylate, C ₁₁ branched aliphatic vinyl carboxylate or vinyl stearate;

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

Thus, the above-mentioned general formula [I], which is an essential component of the epoxy group-containing vinyl (co) polymer (B) used in preparing the resin composition (II) for powder coating, is used. The amount of the epoxy group-containing vinyl monomer (b-1) used is

Needless to say, the so-called epoxy group-containing vinyl monomer (b-
1) In particular, only the vinyl-based monomer in which “R ₁ ” in the general formula [I] is “—CH ₃ ”, that is,
It means that it can be used in the form of 100% by weight,

Each of the above-mentioned vinyl monomers (b
When the -1) and the polymerizable monomer (b-2) are used in combination, based on the total amount of all vinyl-based monomers used in the preparation of the (co) polymer (B), Usually about 10
To about 70% by weight is suitable, and preferably 20 to 50% by weight.

In particular, when these monomers (b-1) and (b-2) are used in combination, this monomer (b- represented by the above-mentioned general formula [I] is used. When the amount of 1) used is less than about 10% by weight, the resulting coating film, in particular, the mechanical properties are likely to deteriorate, so that the effects of the present invention are sufficiently exerted. I can't do it easily,

On the other hand, when the content is too much higher than about 70% by weight, the smoothness of the coating film is apt to be deteriorated, and it is difficult to obtain a coating film having a good appearance. Therefore, also in this case, the effect of the present invention cannot easily be achieved sufficiently, and therefore, in any case, it is not preferable.

The softening point of the epoxy group-containing vinyl (co) polymer (B) by the ring and ball method is about 80 to about 1.
The range of 50 ° C is suitable. This softening point is about 80 ℃
If it is lower than 100 ° C, the powder coating tends to be inferior in blocking resistance and the like, while if it is too high than about 150 ° C, the coating film is particularly deteriorated. In either case, the smoothness is likely to be inferior, which is not preferable.

The number average molecular weight of the (co) polymer (B) is appropriately in the range of about 1,000 to about 10,000, and preferably 1,500 to 6,000.
A range of 0 is suitable.

When the number average molecular weight is less than about 1,000, the mechanical properties of the coating film tend to be inferior, and on the other hand, about 10,
If it is too large than 000, in particular, the smoothness of the coating film will be deteriorated, which is not preferable.

In order to obtain the (co) polymer (B) using various polymerizable monomers listed above as examples, various known and conventional methods are used and applied. However, the solution radical polymerization method is particularly recommended because it is simple and easy.

The above-mentioned resin composition for powder coating (I) used for carrying out the method for forming a multilayer coating film of the present invention.
The aliphatic dibasic acid (C), which is an essential component of I), refers to a compound having a form represented by the following general formula [II], for example.

[0056]

[Chemical Formula 5] HOOC-R-COOH ... [II]

(However, R in the formula has 1 to 20 carbon atoms.
It represents a straight-chain or branched alkylene group. )

Of these compounds, succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, brassylic acid, and the like can be given as only representative ones.

Among these various compounds listed above, especially from the viewpoint of the appearance of the coating film, the above-mentioned general formula [II]
It is desirable to use a form in which "R" has a carbon number of 8 or more.

The above-mentioned resin composition for powder coating (I) used for carrying out the method for forming a multilayer coating film of the present invention.
Regarding the usage ratio of the epoxy group-containing vinyl (co) polymer (B) and the aliphatic dibasic acid (C), which are the essential constituents of I), the epoxy equivalent number of the former (B) component is When "a" is used and the number of equivalents of the latter component (C) is "b", it is appropriate that the ratio a / b is within the range of about 0.5 to about 2.

As a method for producing an intended powder coating from each of the essential constituents of the resin composition (II) for powder coating, various known and conventional methods are used and applied. Of these, only to exemplify a particularly representative method, first, each of the essential components as listed above, further, if necessary, also mixed with a pigment or a leveling agent, Further, there is a so-called mechanical pulverization method in which the mixture thus obtained is melt-kneaded, and after that, each step of fine pulverization and classification is performed to form a powder coating.

At that time, the resin composition for powder coating (I
In addition to I), various known additives such as organic or inorganic pigments, flow regulators, ultraviolet absorbers, antioxidants, etc .; nitrocellulose or cellulose acetate butyrate. It is needless to say that various kinds of fibrin derivatives such as those mentioned above; or various kinds of resins such as chlorinated polyethylene, chlorinated polypropylene, petroleum resin, epoxy resin or chlorinated rubber can be added.

Thus, the method for forming a multilayer coating film of the present invention is
First, the aqueous base coat resin composition (I) described above is
The method comprises coating the base material to be coated, then coating the resin composition (II) for powder coating described above, and then baking and drying.

Here, to exemplify only the representative ones of the above-mentioned base materials to be coated, automobile bodies, automobile (use) parts, motorcycles or parts for motorcycles, household appliances, etc. Also, various building materials such as fences; various building interior and exterior materials such as aluminum sashes; and various ferrous or non-ferrous metal materials or products such as aluminum foil.

[0065]

BEST MODE FOR CARRYING OUT THE INVENTION The first aspect of the present invention is to first coat an aqueous basecoat resin composition (I) containing an aqueous resin (A) as an essential film-forming component on a substrate to be coated. After coating, the polymerizable monomer (b-1) represented by the above-mentioned general formula [I] is used as an essential monomer component, especially the epoxy represented by the general formula [I]. Epoxy group-containing vinyl (co) polymer (B) obtained by polymerizing the group-containing vinyl monomer (b-1)
And a dibasic acid (C) and an aliphatic dibasic acid (C) as essential film-forming components are coated on the resin composition (II) for powder coating, followed by baking and drying. Is that

The above-mentioned epoxy group-containing vinyl type (co)
As the polymer (B), especially the above-mentioned general formula [I]
The polymerizable monomer (b-1) represented by the formula (b-1), especially the epoxy group-containing vinyl monomer represented by the general formula (I) (b-
About 10 to about 70 parts by weight of 1) and about 3 of the other polymerizable monomer (b-2) copolymerizable with the monomer (b-1).
0 to about 90 parts by weight, and the total amount of these two monomers is 10
0 parts by weight, that is, about 10 to about 70% by weight of the monomer (b-1) and about 30 to about 90% by weight of the monomer (b-2) are copolymerized. It is a method for forming a multilayer coating film, which comprises using a specific shape obtained by

Alternatively, the above-mentioned epoxy group-containing vinyl polymer (B) has a softening point by the ring and ball method of about 80 to about 150 ° C. and a number average molecular weight of about 1,000 to A method for forming a multilayer coating film, which comprises using a specific embodiment having a range of about 10,000.

[0068]

EXAMPLES Next, the present invention will be described more specifically with reference examples, examples and comparative examples. However, the present invention is by no means limited to only these illustrative examples. Absent. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation Example of Aqueous Resin (A)] First, a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet is used.

250 parts of styrene, 157 parts of methyl methacrylate, 63 parts of 2-hydroxyethyl methacrylate and 30 parts of methacrylic acid, and 8 parts of tert-butyl peroxyoctoate (hereinafter abbreviated as TBPO). And a mixture of 75 parts of this mixture and 5 parts of methyl ethyl ketone (MEK).
00 parts was charged into a reaction vessel as described above, and the mixture was kept at 75 ° C. for 30 minutes while stirring under a nitrogen blanket.

The remaining mixture was added dropwise over 2 hours,
After the dropping, the reaction is carried out at the same temperature for 12 hours to obtain a nonvolatile content of 50% and a solution acid value of 19%.
Thus, a solution of an acrylic resin having a solution hydroxyl value of 26 and a Gardner viscosity at 25 ° C. (hereinafter the same) of Z was obtained.

After adding 31 parts of dimethylaminoethanol to 1,000 parts of the resin solution thus obtained,
By adding water, an aqueous solution of an aqueous acrylic resin having a concentration of 55% in nonvolatile content (also referred to as solid content) was obtained. Hereinafter, this is abbreviated as an aqueous resin (A-1).

Reference Example 2 (Same as above) 680 parts of deionized water was placed in the same reaction vessel as in Reference Example 1.
2 parts of ammonium persulfate and "Triton x-
15 parts of "200" were added and heated to 95 ° C. Then
An aqueous emulsion containing an acrylic monomer component as shown below was added dropwise to this reaction system at 95 ° C. over 4 hours, and after the completion of the addition, it was held for 3 hours.

After that, the reaction solution was cooled, and 5 parts of dimethylethanolamine and 40 parts of deionized water were added. Thus, a milky white dispersion of a stable aqueous acrylic resin having a solid content of 45% was obtained. Hereinafter, this is abbreviated as an aqueous resin (A-2).

Methyl methacrylate 450 parts Ethyl acrylate 350 parts 2-Hydroxyethyl methacrylate 150 parts Acrylic acid 20 parts Ethylene glycol dimethacrylate 30 parts

5 parts of n-octyl mercaptan

Ammonium persulfate 4 parts

“Triton X-200” 15 parts “Emulgen 840s” 10 parts

Deionized water 530 parts

Here, the above-mentioned "Triton X-
"200" means Rohm and Haas (Rohm)
& Haas) is a trade name of an anionic surfactant, and "Emulgen 840s" is a trade name of a nonionic surfactant manufactured by Kao Atlas Co., Ltd.

Reference Example 3 (Preparation Example of Thickener) 64 parts of “Acrysol ASE-60” (trade name of thickener manufactured by Rohm and Haas Co .; solid content = 28%) was added to dimethylethanolamine. And 530 parts of deionized water were added to obtain the target product having a solid content of 3%. Hereinafter, this thickener is abbreviated as (P).

Reference Example 4 (Preparation Example of Metallic Paint for Aqueous Base Coat) To 100 parts of the aqueous resin (A-1) obtained in Reference Example 1,
10 parts of the thickener (P) obtained in Reference Example 3, 6 parts of "Cymel 300" [trade name of hexamethoxymethylated melamine manufactured by Mitsui Cyanamid], and 1 part of paratoluenesulfonic acid , "Aluminum paste dispersion # 49
19 "[trade name of aluminum paste manufactured by Toyo Aluminum Co., Ltd.] and" Aluminum paste dispersion liquid # 5 "
5-519 "(trade name of the same company) and 12 parts of isopropanol were mixed, and the viscosity of the Ford Cup No. 4 at 20 ° C was 16 seconds with deionized water. Adjusted to. Hereinafter, this is abbreviated as water-based base coat paint (X-1).

Reference Example 5 (same as above) To 100 parts of the aqueous resin (A-2) obtained in Reference Example 2,
10 parts of the thickener (P) obtained in Reference Example 3, 5 parts of "Cymel 300", 1 part of paratoluenesulfonic acid,
3 parts of "Aluminum paste dispersion # 4919" and 1.5 parts of "Aluminum paste dispersion # 55-519" were mixed with 12 parts of isopropanol, and the mixture was mixed with deionized water to obtain Ford at 20 ° C.・ Cup No
The viscosity according to No. 4 was adjusted to 16 seconds. Hereinafter, this is abbreviated as water-based base coat paint (X-2).

Reference Example 6 [Preparation Example of Vinyl Polymer (B)] In a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet, 500 parts of xylene was charged, and the mixture was placed in a nitrogen atmosphere at 130 ° C. The temperature is raised to 0 ° C. and 250 parts of methyl methacrylate, 100 parts of n-butyl methacrylate and 150 parts of β-methylglycidyl methacrylate, 3 parts of azobisisobutyronitrile and 20 parts of TBPO are added thereto. The mixture was added dropwise over 4 hours, and after the completion of the addition, the temperature was kept at the same temperature for 10 hours.

After the completion of the polymerization reaction, the resin solution thus obtained was kept under a reduced pressure of about 30 Torr to distill off xylene to obtain a nonvolatile content of 99.5%.
The softening point by ring and ball method is 117 ° C, and the epoxy equivalent is 55.
A solid product of the target copolymer (B) having a number average molecular weight of 0 and a number average molecular weight of 4,700 was obtained. Hereinafter, this is abbreviated as polymer (B-1).

Reference Examples 7 to 9 (same as above) Except that the monomer mixture to be used was changed to one shown in Table 1, the same procedure as in Reference Example 6 was carried out. Copolymers (B-2) to (B-4) were obtained.

[0087]

[Table 1]

<< Footnote in Table 1 >> 1) Abbreviation of styrene

2) Abbreviation of methyl methacrylate

3) Abbreviation for n-butyl methacrylate

4) Abbreviation for di-n-butyl fumarate

5) Abbreviation for β-methylglycidyl methacrylate

6) Abbreviation for glycidyl methacrylate

Reference Examples 10 and 11 [Preparation Example of Control Vinyl Polymer (B ')] The monomer mixture to be used was changed to that shown in Table 2, and one reference Only in the case of Example 11, the vinyl copolymers (B'-1) and (B'-) for control were used in the same manner as in Reference Example 6 except that the amount of TBPO used was changed to 60 parts. 2) was obtained.

[0095]

[Table 2]

Reference Examples 12 to 17 [Preparation Examples of Clear Powder Coating for Top Coat and Control Clear Powder Coating]

First, the respective components were mixed in accordance with the blending ratio as shown in Table 3, and the mixture was further mixed with "Cokneader" (trade name of uniaxial kneader manufactured by Buss Co., Ltd. in Switzerland. "PR-46 type" is used) and kneaded by heating. Then, thus obtained,
Each kneaded product was coarsely pulverized and then finely pulverized to prepare various powder coatings having an average particle diameter of 30 to 40 μm.

[0098]

[Table 3]

<< Footnote in Table 3 >> 1) Abbreviation of decanedicarboxylic acid

2) Trade name of extender manufactured by Monsanto, USA

In Examples 1 to 4 and Comparative Examples 1 and 2, the coating films shown in Tables 4 and 5 were formed in accordance with the method for forming a multilayer coating film shown below, and each of them was formed. It is for showing the place where the test of evaluation judgment of various performances about the coating film was conducted.

That is, for that purpose, first, the multi-layer coating film forming method of the present invention is fully utilized, and the desired multi-layer coating film and the control multi-layer coating film are respectively prepared by the following methods. A film was formed.

That is, using the metallic paint for aqueous base coat prepared in Reference Example 1 or 2 and the powder coating for top clear obtained in Reference Examples 12 to 17, two coats were prepared by the following method. 1 bake coating was performed. The substrate to be coated at that time was used after the following pretreatment.

That is, "Bondelight # 3030"
[Product name of mild steel plate treated with zinc phosphate-based treatment agent manufactured by Nippon Parkerizing Co., Ltd.] is electrodeposited with an epoxy resin-based cationic electrodeposition coating, and then,
An amino / polyester resin-based intermediate coating was used.

It should be noted that in these various examples,
The specific coating method using the two-coat one-bake method is as follows.

First, in a coating atmosphere in which the metallic coating composition for water-based base coat (X-1) is at a temperature of 25 ° C. and a relative humidity of 65 to 70%, a dry film thickness of 2 is obtained.
The coating was applied in two times so that the thickness became 0 μm. I set a setting for 2 minutes between these two paintings.

At the time of the first coating, the air pressure of the spray gun was 5 kg / cm ^2, and the flow velocity of the coating was 400 m /
On the other hand, the flow rate of the paint at the time of the second coating was 200 m / min, and the distance between the substrate to be coated and the spray gun was 40 cm. The substrate for coating was held correctly so that the coated surface on the substrate for coating was always perpendicular to the ejection direction.

After such two coatings, the substrate to be coated was air dried at a temperature of 30 ° C. for 5 minutes.
Further, after cooling to room temperature, powder coating T1 for top clear or the like was applied by electrostatic powder coating so as to have a dry film thickness of 60 μm, and baked at 150 ° C. for 20 minutes. .

The thus-obtained cured coating films were subjected to comparative tests for evaluation and evaluation of various properties. The results are collectively shown in Tables 4 and 5.

[0110]

[Table 4]

<< Footnote in Table 4 >>

Smoothness ………… Evaluation was made visually.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙

20 degree gloss: The 20 degree specular reflectance (%) was measured and this value was displayed.

Metallic feeling ......... "ALCOPE LM
R-100 ”(trade name of metallic feeling measuring device manufactured by Kansai Paint Co., Ltd.) was used for evaluation, and evaluation was made according to the IV value obtained.

Excellent: When the value exceeds 250 Good: When the value is 200 or more and less than 250 Bad: When the value is less than 200

DuPont impact: This is an evaluation judgment (1/2 inch) by a DuPont impact tester, and is a height (cm) that does not cause defects such as cracks in the coating film when a load of 500 g is dropped. However, the larger this value, the better the impact resistance.

Erichsen value: This is an evaluation judgment by an Erichsen tester. The larger this value, the better the flexibility of the coating film.

Scratch resistance: Using a rubbing flannel containing a 5% aqueous cleanser solution, a rubbing tester was used to apply a load of 1.5 kg to perform rubbing 20 times. At that time, the gloss retention (%) with respect to the initial gloss was measured, and this value was displayed. The higher the value, the better the scratch resistance.

Adhesion between layers: The coated plate is immersed in warm water at 40 ° C. for 10 days and then pulled up to 3
After 0 minutes, a cross cut was put in and a peeling test using an adhesive tape was performed.

◯: No peeling was observed at all Δ: Peeling was observed between the base coat and the top coat X: When significant delamination was observed

Water resistance: The coated plate was immersed in warm water of 40 ° C. for 10 days, and the gloss retention rate (%) was used for evaluation and judgment. .

⊚: When the gloss retention rate exceeds 80% ○: When the gloss retention rate is 60% to less than 80% ×: When the gloss retention rate is less than 60%

Weather resistance: According to the sunshine weather meter [trade name of Suga Test Instruments Co., Ltd.],
After 1000 hours of accelerated weather resistance test, the gloss retention rate (%) was used for evaluation and judgment, and the value was displayed. The higher the value, the better the weather resistance. It means that.

[0125]

[Table 5]

[0126]

From the above detailed description,
As is apparent, the coating film obtained by the method for forming a multilayer coating film of the present invention is particularly excellent in the appearance of the coating film, and in addition, in particular, mechanical properties, flexibility, and scratch resistance. It is also excellent in various physical properties such as weather resistance. Therefore, according to the method of the present invention, a cured coating film having an extremely high practicality can be provided.

Claims (3)

[Claims] 1. An aqueous basecoat resin composition (I) containing an aqueous resin (A) as an essential component is applied onto an article to be coated, and then the following general formula: (However, R ₁ in the formula, which may be the same or different, each represents a hydrogen atom or a methyl group.) Polymerizes the polymerizable monomer (b-1) A resin composition for powder coating (II) containing, as an essential component, a vinyl polymer (B) having an epoxy group and an aliphatic dibasic acid (C), which are obtained at most, is applied and baked. A method for forming a multilayer coating film, which comprises drying. 2. The above-mentioned vinyl polymer (B) having an epoxy group is represented by the following general formula: (However, R ₁ in the formula, which may be the same or different, each represents a hydrogen atom or a methyl group.) About the polymerizable monomer (b-1) represented by 1
0 to about 70 parts by weight and about 30 to about 90 of the other polymerizable monomer (b-2) copolymerizable with the monomer (b-1).
The method according to claim 1, which is obtained by copolymerizing with 1 part by weight. 3. The above-mentioned vinyl polymer (B) having an epoxy group has a softening point by the ring and ball method within the range of about 80 to about 150 ° C., and further about 1,000 to about 1.
The method according to claim 1 or 2, which has a number average molecular weight in the range of 10,000.