JP2778749B2 - Painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of applying a two-coat one-bake (2C1B) method using a water-based paint as a base coat and an organic solvent-based paint as a top coat.

<Conventional technology and its problems> A thermosetting water-based coloring paint (base coat) is applied and, without curing, an acid catalyst-containing thermosetting organic solvent-based clear coating (top coat) is applied to the coated surface. A coating method based on the so-called 2C1B method, in which both the coating films are cured by heating, is already known.

However, the coating film formed by such a method has insufficient curing properties of the clear coating film as compared with those using an organic solvent-based base coat, and based on this, weather resistance, solvent resistance, water resistance, and It has a defect that the adhesion between layers is inferior and the finished appearance such as sharpness and smoothness also deteriorates.

It is thought that these are caused by bleeding of the amine as a neutralizing agent contained in the water-based coloring paint into the clear paint. Therefore, even if an attempt is made to evaporate the amine by heating and drying the aqueous metallic paint before applying the clear paint, the amine forms a salt with the carboxyl group of the resin, and the amine remains in the coating film considerably. It cannot solve the above problem.

<Means for Solving the Problems> The inventors of the present invention have conducted intensive studies for the purpose of resolving the above-mentioned defects, and as a result, the use of a water-based paint neutralized with dialkanolamine to achieve an object. The inventors have found out what can be achieved and completed the present invention.

That is, the present invention applies a thermosetting colored water-based paint (A) and cures the organic solvent-based thermosetting clear paint mainly containing an acrylic resin, hexaalkoxymethylmelamine and an acid catalyst on the coated surface without curing. (B) is coated, and then heated to cure both coating films. This is a coating method by a two-coat one-bake method, wherein the water-based coating material (A) is a neutralizing agent containing dialkanolamine as a main component. The present invention relates to a coating method characterized by being neutralized.

The feature of the present invention is that an aqueous solvent as a base coat is neutralized with a dialkanolamine, and a top coat is an organic solvent-based paint mainly containing an acrylic resin, hexaalkoxymethylmelamine and an acid catalyst.
We were painting with the 2C1B method, and as a result, the following technical effects were obtained.

(1) Since a water-based paint is used as the base coat,
It is effective in saving resources and preventing pollution, and in the metallic finish, the flaky metallic pigment is easily oriented parallel to the coating surface, and has an excellent metallic feeling.

(2) Since hexaalkoxymethylmelamine is used in the top coat, it is easy to make a high solid content type paint.

(3) The use of dialkanolamine as a neutralizing agent in the aqueous coating of the base coat completely prevents the curability of the clear coating film from being impaired, and provides weather resistance, solvent resistance, water resistance, interlayer adhesion and finished appearance. Etc. could be improved.
Such technical effects have not been obtained with other neutralizing agents such as, for example, alkylamines, monoalkanolamines and trialkanolamines. Although the reason for this has not been fully elucidated, dialkanolamine reacts with the resin component in the base coat, so that the amine does not bleed into the clear coating film, while other neutralizing agents do not. It is speculated that the reaction does not proceed and bleeds into the clear coating film to reduce the function of the acid catalyst.

The thermosetting colored aqueous coating composition (A) and the organic solvent-based thermosetting clear coating composition (B) used in the present invention will be specifically described.

Thermosetting colored water-based paint (A): a paint to be applied prior to the clear paint (B), which is a water-soluble base material neutralized with a dialkanolamine, a crosslinking agent, a coloring material, and water as main components. Or a water-dispersible paint. This is a base coat paint in the 2C1B system.

(1) Substrate resin: a basic component of a cured base coat film, for example, an acrylic resin, an alkyd resin (containing polyester resin, the same applies hereinafter), an epoxy resin, a fluorine-containing resin, etc., and a carboxyl group in these resins And the like are neutralized with dialkanolamine to make them water-soluble or water-dispersed. Of these, acrylic resins are preferred.

(I) Water-soluble acrylic resin Acid value obtained by copolymerizing carboxyl group-containing vinyl monomer (M-1), hydroxyl group-containing vinyl monomer (M-2) and other vinyl monomer (M-3) is about 20 to about
150, hydroxyl value about 20 to about 200, number average molecular weight about 3,000 to about 1
A neutralized acrylic resin of 00,000 can be used.

The carboxyl group-containing vinyl monomer (M-1) is a compound having one or more carboxyl groups and one polymerizable unsaturated bond in one molecule, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and And conic acid.

The hydroxyl group-containing vinyl monomer (M-2) is a compound having one hydroxyl group and one polymerizable unsaturated bond in one molecule, and the hydroxyl group mainly acts as a functional group that reacts with a crosslinking agent. As the monomer, specifically, acrylic acid or methacrylic acid and 2 to 10 carbon atoms
Monoesters with two dihydric alcohols are preferred, for example 2-hydroxyethyl acrylate, 2-hydroxyethyl acrylate
Examples thereof include hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

The other vinyl monomer (M-3) is a compound other than the above both monomers (M-1) and (M-2) and has one polymerizable unsaturated bond in one molecule. Examples are listed below.

Acrylic acid or methacrylic acid with 1 to 20 carbon atoms
Monoesters with a polyhydric alcohol: For example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-
Ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate and the like.

Aromatic vinyl monomers: for example, styrene, α-methylstyrene, vinyltoluene and the like.

Glycidyl group-containing vinyl monomer: a compound having one glycidyl group and one polymerizable unsaturated bond in one molecule,
Specifically, glycidyl acrylate, glycidyl methacrylate and the like.

Nitrogen-containing alkyl (C1-20) acrylate: for example, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and the like.

Amide compounds containing a polymerizable unsaturated bond: for example, acrylamide, methacrylamide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-
Butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide and the like.

Vinyl compounds: for example, vinyl acetate, vinyl propionate, vinyl chloride and the like.

Nitrile compounds containing a polymerizable unsaturated bond: for example, acrylonitrile, methacrylonitrile and the like.

Diene compounds: for example, butadiene, isoprene and the like.

One or more of these other vinyl monomers (M-3) can be used.

The copolymerization reaction of the vinyl monomer can be performed by a known method, for example, azobisisobutyronitrile, benzoyl peroxide, dibutyl peroxide, ammonium persulfate, potassium persulfate, sodium pyrosulfite, t-butyl hydroperoxide And a radical polymerization catalyst such as cumene hydroperoxide in an organic solvent compatible with water such as butyl cellosolve. If the acid value of the resin is less than about 20, it is difficult to dissolve in water, about 15
If it exceeds 0, the coating film performance may be reduced due to the effect of the residual carboxyl group.

The acrylic resin thus obtained can be made water-soluble by neutralization with a dialkanolamine.

General formula HNROH as dialkanolamine)
₂ (R is an alkylene group having 1 to 20 carbon atoms), for example, diethanolamine, diisopropanolamine, etc., and one or more of these can be used.

The neutralization amount is generally in the range of 0.3 to 1.5 equivalents to the resin acid value.

(Ii) Water-dispersible acrylic resin A fine-particle acrylic resin having an average particle diameter of 0.05 to 1.0 μm obtained by emulsion-polymerizing a vinyl monomer in the presence of a dispersion stabilizer such as a surfactant. Become.

The vinyl monomer to be emulsion-polymerized is selected from each of the carboxyl group-containing vinyl monomer (M-1), hydroxyl group-containing vinyl monomer (M-2), and other vinyl monomers (M-3) exemplified for the water-soluble acrylic resin. When a small amount of a polyvinyl compound (M-4) having two or more polymerizable unsaturated bonds in one molecule is used in combination, a water-dispersible acrylic resin crosslinked in the particles is obtained. It is preferable because the film performance is further improved.

Examples of the polyvinyl compound (M-4) having two or more polymerizable unsaturated bonds in one molecule include ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1 , 6-hexanediol diacrylate, divinylbenzene, trimethylolpropane triacrylate, and the like. In each compound, it is preferable that the reactivity of two or more unsaturated bonds contained in each compound does not greatly differ. Does not include system compounds.

The water-dispersible acrylic resin produced here is also neutralized with the dialkanolamine.

(Iii) Water-dispersible acrylic resin This is an aqueous dispersion in which acrylic resin fine particles dispersed in water are stabilized by a stabilizer polymer. The water-dispersible acrylic resin has a core portion containing the particles and a shell portion containing the stabilizer polymer. It is a core / shell type emulsion.

Specifically, first, a vinyl monomer component containing no or almost no carboxyl group-containing vinyl monomer (M-1) is emulsion-polymerized, and thereafter, a vinyl monomer containing a large amount of the carboxyl group-containing vinyl monomer (M-1) It is obtained by emulsion polymerization with the addition of components, which is preferred from the viewpoint of coating workability because it is thickened by neutralization with a neutralizing agent. As the neutralizing agent, the dialkanolamine is used.

(Iv) water-dispersible acrylic resin core / shell type in which polymer particles (core portion) are cross-linked and there is a polymer (shell portion) for stabilizing the polymer particles (core portion); Emulsion.

In particular, the method of bonding the core and the shell is such that a hydrolyzable functional group or a silanol group is provided on the surface of the core, a polymerizable unsaturated bond is introduced into these groups, and carboxyl is added to the unsaturated bond. Group-containing vinyl monomer (M-
A copolymer obtained by copolymerizing a vinyl monomer component containing 1) (forming a shell portion) and then neutralizing a carboxyl group of the shell portion is preferable.

Since it is thixotropic (thixotropic), the coating film hardly sags even under high humidity, no abnormality is recognized even when an organic solvent is blended, smoothness, gloss, water resistance In addition, it has characteristics such as excellent adhesion.

This core / shell type emulsion is obtained by the following steps.

(I): a silane monomer having a hydrolyzable functional group and / or a silanol group and a polymerizable unsaturated bond
(Simply referred to as "silane-based monomer") (M-5), hydroxyl group-containing vinyl monomer (M-2) and other vinyl monomer (M-6) in an aqueous medium to cause a three-dimensional crosslinking reaction. To produce an emulsion in which the particulate polymer is dispersed in water. These fine particles form the core.

(II): A silane monomer (M-5) and / or an allyl (meth) acrylate (M-7) are reacted with the fine particle polymer in the emulsion.

In (II), the silane monomer (M-5) undergoes a condensation reaction with a functional group on the surface of the fine particle polymer, and the allyl (meth) acrylate (M-7) reacts with the unreacted polymer remaining in the fine particle polymer. It is thought that the polymerizable unsaturated bond is copolymerized with the polymerizable unsaturated bond, and the polymerizable unsaturated bond can be introduced into the surface of the fine particle polymer by any of these methods.

(III): In the emulsion after the reaction of the above (II), a vinyl monomer component (M-8) containing a carboxyl group-containing vinyl monomer (M-1) is copolymerized, and the carboxyl group is further neutralized. This neutralized copolymer is a stabilizing polymer for stabilizing the dispersion of the fine particle polymer, and corresponds to a shell portion. In (III), the vinyl monomer component (M-8) is added to the silane-based monomer (M-5) and / or allyl (meth) acrylate (M-7) on the surface of the fine particle polymer after the reaction of (II). Copolymerizes with a polymerizable unsaturated bond derived therefrom.

The silane monomer (M-5) used in the step (I) is
A compound in which three hydrolyzable functional groups and / or silanol groups in one molecule and one residue having one polymerizable unsaturated bond are bonded to Si, and represented by the general formula (R ₁ ) ₃ -Si-X
(R ₁ is a hydrolyzable functional group and / or a silanol group, and X is a residue having a polymerizable unsaturated bond). The silane-based monomer (M-5) mainly has a function of forming a core portion by internal crosslinking.

In this general formula, examples of the hydrolysis functional group of R ₁ include an alkoxy group having 1 to 12 carbon atoms, an alkoxyalkoxy group having 3 to 15 carbon atoms, and an alkanoyloxy group having 1 to 12 carbon atoms. , CH ₂ = CH- and R ₂ is H or CH ₃ —, and n is an integer of 2 to 10.

As the silane-based monomer (M-5), specifically,
Vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane, acryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, acryloxypropyltriethoxysilane, methacryloxypropyltriethoxy Silane, vinyltris (β-methoxyethoxy) silane and the like. Among them, particularly preferred silane-based monomers include vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane and the like. Can be mentioned.

In the step (I), the hydroxyl-containing vinyl monomer (M-
As for 2), those described above can be used, and the “other vinyl monomer (M-6)” can be any of the monomers (M-1) to (M-
5) except (M-5) and (M-2).

The silane-based monomer (M-5), the hydroxyl-containing vinyl monomer (M-2) and the other vinyl monomer (M-6) in the step (I) are copolymerized in an aqueous medium and cross-linked three-dimensionally. The method for obtaining the fine particle polymer can be carried out, for example, by the following emulsion polymerization methods known per se.

(I) The mixture of the monomers is copolymerized at a predetermined temperature while gradually dropping the mixture of the monomers into a stirring aqueous medium in which a surfactant is mixed with water under an inert gas atmosphere.

(Ii) A mixture of the above-mentioned monomers is emulsified in an aqueous medium in advance, and the mixture is copolymerized at a predetermined temperature while being gradually dropped into water under stirring.

(Iii) In any of the above, a small amount of a monomer (either a mixture or a single monomer may be used) is taken out and subjected to seed polymerization in advance, and then emulsion polymerization is carried out according to the above methods (i) and (ii). Good.

Among them, (iii) is preferable from the viewpoint that the particle diameter can be reduced and sagging resistance, smoothness and the like are improved.

All of these emulsion polymerizations are preferably performed in the presence of a radical polymerization initiator.

Here, constituent ratios of various monomers used in the steps (I) and (III) will be described. The composition ratio of all the monomers in the step (I) and all the monomers in the step (III) is 30% based on the total weight of both monomers.
Preferred is from about 95 to about 95% by weight, especially from about 60 to about 90% by weight, and the total monomer in step (III) is from about 70 to about 5% by weight, especially from about 40 to 10% by weight.

Further, all the monomers in the step (I) are composed of a silane-based monomer (M-5), a hydroxyl group-containing vinyl monomer (M-2) and another vinyl monomer (M-6),
Based on the total weight of these monomers, the silane monomer (M-5) is 0.5 to 20% by weight, particularly 1 to 10% by weight,
1 to 30% by weight of a hydroxyl group-containing vinyl monomer (M-2),
Particularly, 2 to 20% by weight of the other vinyl monomer (M-
6) is preferably 98.5 to 50% by weight, particularly 97 to 70% by weight.

Further, all monomers in the step (III) are composed of a vinyl monomer component (M-8) containing a carboxyl group-containing vinyl monomer (M-1), and the monomer (M-1) is included in the monomer component (M-8). 1 to 50% by weight, especially 3 to 30% by weight
Is preferred. The monomer component (M-8) is composed of the monomer (M
-1) is used in combination with one or more kinds selected from the hydroxyl group-containing vinyl monomer (M-2) and the above-mentioned monomers (M-3). Of these, the content of the monomer (M-2) was 30% in the monomer component (M-8).
% By weight or less, particularly preferably 25% by weight or less.

The monomer component (M-8) may be used in combination with a silane monomer (M-5) or a polyvinyl compound (M-4).
% By weight or less is suitable.

The emulsion obtained in the step (I) is obtained by dispersing a particulate polymer obtained by a three-dimensional crosslinking reaction of the monomers (M-5), (M-2) and (M-6) in an aqueous medium. It is. The cross-linking reaction of these monomers is mainly carried out by copolymerization by polymerizable unsaturated bonds contained in the monomers, and condensation including hydrolysis by hydrolyzable functional groups and / or silanol groups in the silane monomer (M-5). The reaction and the like are performed together, and the reaction between the silane-based monomer (M-5) and the hydroxyl group contained in the hydroxyl-containing vinyl monomer (M-2) may be involved.
As a result, the fine-particle polymer mainly contains carbon-carbon bonds formed by polymerizable unsaturated bonds and silane-based monomers (M-
It is presumed that a three-dimensional cross-linking reaction is caused by both the -Si-O-Si- bond according to 5). Then, on the surface of the fine particle polymer, the silane-based monomer (M-
It is considered that the hydrolyzable functional group and / or silanol group based on 5) are bonded in an unreacted state. Further, a hydroxyl group based on the monomer (M-2) also exists on the surface. The particle size of the fine particle polymer obtained in the step (I) varies depending on the type and amount of the surfactant and the like, and the polymerization method, but is preferably from 10 to 500 nm, particularly preferably from 30 to 300 nm.

Step (II): The silane-based monomer (M-5) and / or allyl (meth) acrylate (M-7) are reacted with the fine particle polymer in the emulsion of the above step (I). This is because a polymerizable unsaturated bond is introduced into the surface of the fine particle polymer. The particulate polymer obtained by introducing the polymerizable unsaturated bond obtained in the step (II) is hereinafter abbreviated as “unsaturated particulate polymer”.

First, looking at the silane-based monomer (M-5),
The silane monomer (M-5) reacts with the unreacted hydrolyzable functional group and / or silanol group or hydroxyl group based on vinyl monomer (M-2) bonded to the surface of the fine particle polymer in step (I). At least, a polymerizable unsaturated bond is introduced into the surface of the fine particle polymer.

Specifically, a silane-based monomer (M-5) is blended in the emulsion obtained in the step (I),
The above reaction is performed simultaneously with the adsorption of the silane-based monomer (M-5) on the surface of the fine particle polymer in the emulsion, thereby introducing a polymerizable unsaturated bond.

The ratio between the fine particle polymer and the silane monomer (M-5) in the step (II) is not particularly limited, but the ratio in the step (II) per 1 mol of the silane-based monomer (M-5) used in the step (I) is not limited. The silane monomer (M-5) used
The range of 0.5 to 2 mol (usually 50 to 200 parts by weight per 100 parts by weight of the former) is preferable. When the amount of the silane-based monomer of the latter is less than the amount, the amount of the polymerizable double bond introduced is reduced and the stability of the present composition is stabilized. There is a possibility that the property may be deteriorated, and if it is more than one, the fine particle polymer may be easily aggregated.

Further, comparing the polymerizability of the allylic double bond and the acrylic double bond contained in the monomer (M-7), the latter is more easily polymerized. The monomer (M-7) is blended into the aqueous dispersion obtained in the step (I), and heated to 40 to 90 ° C., whereby the acrylic double bond of the monomer (M-7) is dispersed in the aqueous dispersion. It is presumed that it polymerizes with the unreacted monomer contained in the particulate polymer in the liquid, and as a result, an allylic double bond having poor polymerization reactivity remains on the surface of the particulate polymer in an unreacted state. Monomers (M-5) and (M
When -7) is used in combination, the above reactions are thought to occur concurrently. The ratio of the monomer (M-7) is preferably 0.5 to 5 parts by weight per 100 parts by weight of the fine particle polymer.

It is preferable to use the monomer (M-5) and the monomer (M-7) in combination, and the above-mentioned composition ratios of these fine particles of the polymer can be applied.

Step (III): The unsaturated particulate polymer obtained in step (II) is added to a vinyl monomer having a carboxyl group (M
In this step, a vinyl monomer component (M-8) containing -1) is copolymerized, and then the carboxyl group is neutralized to form a shell portion.

Vinyl monomer component (M-8) in step (III)
The copolymerization reaction of (i) and (ii) can be applied mutatis mutandis. The vinyl monomer component (M-8) is blended into the emulsion of the unsaturated particulate polymer obtained in step (II). This reaction is preferably carried out in the presence of the radical polymerization initiator, if necessary.

This step is for chemically bonding a linear copolymer (corresponding to a shell part) mainly composed of a vinyl monomer component (M-8) to the unsaturated fine particle polymer (corresponding to the core part) of the step (II). belongs to. The process (II
When a silane-based monomer (M-5) or a polyvinyl compound (M-4) is used in combination in I), the linear copolymer becomes a network, which may be chemically bonded. Specifically, in the unsaturated particulate polymer of the step (II), the silane-based monomer (M-
The above vinyl monomer is added to the polymerizable unsaturated bond based on 5) and / or the polymerizable unsaturated bond remaining in the allyl (meth) acrylate (M-7) copolymerized with the unreacted monomer remaining in the fine particle polymer. This is a reaction for copolymerizing the components. As a result, the copolymer (shell portion) of the vinyl monomer component (M-8) is chemically bonded to the surface of the fine particle polymer (core portion) in step (I).

The step (III) includes copolymerizing an unsaturated particulate polymer with a vinyl monomer component to form a shell portion, and further neutralizing a carboxyl group in the shell portion.
This neutralization is performed by mixing a neutralizing agent in the reaction system, and the dialkanolamine is used as the neutralizing agent.

Among the above base resins, (iv) a water-dispersible acrylic resin was most suitable.

Further, it is preferable that the water-soluble acrylic resin and the water-dispersible acrylic resin coexist, and the ratio thereof is 1 to 60% for the former and 99 to 40% for the latter based on the total weight of both components. Is preferred.

(2) Cross-linking agent A cross-linking agent for reacting with the base resin to form a three-dimensionally cross-linked and cured base coat film, which is uniformly dissolved or dispersed in the base resin and has a cross-linking reactive functional group. Things.

Specifically, methylolated products of amino resins such as melamine resin, benzoguanamine resin and urea resin, furthermore, alkyl etherified products thereof, phenol formaldehyde resin, and blocked polyisocyanate compound can be applied.

The compounding amount of the crosslinking agent is preferably from 10 to 50%, particularly preferably from 15 to 40%, based on the total solid weight with the base resin.

(3) Colorant: for coloring the base coat film, which also contains a metallic pigment. Examples of the metallic pigments include aluminum flakes, copper block flakes, mica-like iron oxide, mica flakes, mica-like iron oxide coated with a metal oxide, mica flakes coated with a metal oxide, and the like. Examples of pigments include inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate, and carbon black; phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, flavanthrone yellow, isoindoline yellow, and induthrone blue. And organic pigments such as quinacridone violet.

The aqueous paint (A) used in the method of the present invention can be obtained by mixing and dispersing the above-mentioned base resin, curing agent and coloring agent in water, and further blending an antifoaming agent, a fungicide and the like as necessary. You may. Further, an organic solvent can be blended.

Organic solvent-based thermosetting clear coating (B): A coating applied to the uncured coating surface of the aqueous coating (A), and forms a transparent coating film.

The clear paint (B) is a liquid paint mainly composed of an acrylic resin, hexaalkoxymethylmelamine, an acid catalyst and an organic solvent, and includes a non-aqueous dispersion type and the like.

The acrylic resin is mainly composed of a monoesterified product of acrylic acid or methacrylic acid and a monohydric alcohol having 1 to 20 carbon atoms and a hydroxyl group-containing vinyl monomer, and further contains a carboxyl group-containing vinyl monomer or other vinyl monomers as necessary. It is obtained by polymerization using a number average molecular weight of about 1,000 to 100,000 and a hydroxyl value of 50 to
Acrylic resins having an acid value of 200 and an acid value of 0 to 50 are preferred.

Further, the acrylic resin may be modified with a reaction product of ε-caprolactone and a hydroxyl group-containing vinyl monomer, or a ring-opened polyester of ε-caprolactone may be used in combination.

Hexaalkoxymethylmelamine is a crosslinking agent for the acrylic resin, and is obtained by fully etherifying hexamethylolmelamine with a monohydric alcohol having 1 to 4 carbon atoms. It is necessary that all the six methylol groups of one triazine nucleus are alkyl etherified, and the alkyl groups in one nucleus may be the same or different. Particularly preferred alkyl groups include, for example, a methyl group, an ethyl group, an n-butyl group and an isobutyl group.

The acid catalyst is for accelerating the crosslinking reaction between the acrylic resin and hexaalkoxymethylmelamine, and examples thereof include dodecylbenzenesulfonic acid, paratoluenesulfonic acid, and dinonylnaphthalenedisulfonic acid. You can also use those that are blocked by kind.

The organic solvent is obtained by dissolving or dispersing each of the above-mentioned components, and is used, for example, in one or more paints selected from hydrocarbons, alcohols, esters, ketones, and ethers. Is preferred.

In the clear paint (B), the composition ratio of the acrylic resin and hexaalkoxymethylmelamine is preferably 45 to 85%, and the latter is preferably 55 to 15%, based on the total weight ratio of both components. The acid catalyst is suitably used in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the total of the above two components. Further, the solid content concentration of the clear coating (B) at the time of coating can be arbitrarily selected depending on the coating material and the like, but is preferably in the range of 40 to 65% by weight.

In the clear coating (B), the above-mentioned components can be further blended with the above-mentioned components, if necessary, to such an extent that the transparency is not impaired. Additives such as an ultraviolet absorber, a light stabilizer and a surface conditioner are also appropriately added. Can be used.

The feature of the method of the present invention resides in that the above water-based paint (A) and clear paint (B) are used, and both paints are applied based on a two-coat one-bake method.

As an object to be coated in the method for forming a coating film of the present invention, particularly a passenger car,
Although an automobile outer panel such as a bus, a truck, and a motorcycle is preferable, it is also suitable for an object to be coated, such as an outer panel of an electric product, in which the appearance of a finished paint is important. These objects to be coated can be previously subjected to chemical conversion treatment, undercoating (eg, electrodeposition coating), intermediate coating, or the like, if necessary.

First, a water-based paint (A) is applied to the object to be coated. As the coating machine, it is preferable to use an atomization type coating machine, for example, an air spray coating machine, an airless spray coating machine, an air atomization type or a rotary electrostatic coating machine, and the like. It is preferable to adjust to about 800 to 5,000 cps / 6 rpm (B-type viscometer), and the coating film thickness is about 10 to about 50 μm, especially about 15 to about 50 μm based on the heat-cured film thickness.
30μ is suitable.

Next, the coating film of the water-based paint (A) is air-dried without crosslinking and curing, for example, at room temperature or at a temperature of 100 ° C. or less. % Or less, and then the clear paint (B) is applied to the coating surface. The clear paint (B) is adjusted to have a solid content concentration of 20 to 70% by weight.

As the coating machine, an appropriate one can be selected from those exemplified in the application of the water-based paint (A). The coating thickness of the clear paint (B) is preferably about 10 to 80 μm (after curing).

After applying the clear paint (B), apply 10 to 90 at about 60 to 170 ° C.
It is preferable to heat the two coating films by heating for about a minute.

Examples Next, the present invention will be described more specifically with reference to Production Examples, Examples, and Comparative Examples. In addition, all parts and% are based on weight.

I Production Example (1) Production of Core / Shell Type Emulsion It was produced according to the following steps using the components shown in Table 1.

Step (I): Place 120 parts of deionized water in a flask, heat it to 80 to 85 ° C., drop 2 parts of the first pre-emulsion shown in Table 1 while stirring, ripen it for 20 minutes, and then The remaining pre-emulsion was dropped at a constant speed over a period of 3 hours to obtain an aqueous dispersion of a core portion formed by a three-dimensional crosslinking reaction.

Step (II): Immediately after the completion of the first pre-emulsion dropping, the silane-based monomer and allyl methacrylate are dropped at 80 to 85 ° C. for 1 hour to react the silane-based monomer and allyl methacrylate on the surface of the core. I was sorry.

Step (III): 50 parts of deionized water were blended, and the second pre-emulsion was dropped at 80 to 85 ° C. at a constant speed over 1 hour.

Then, hold at the same temperature for 1 hour, then quench to room temperature,
Deionized water was added to a solids content of 30%.
The polymer particles obtained are insoluble in organic solvents. Thereafter, deionized water was added, EM-1 to EM-3 were neutralized with diethanolamine, and EM-4 to 6 were neutralized with diisopropanolamine, respectively, and adjusted to a solid content of 20% to obtain a core / shell emulsion EM-1. 6 was obtained.

(2) Manufacture of aluminum pigment concentrate Liquid paste aluminum paste (metal content 65
%) And 25 parts of butyl cellosolve were added and stirred for 1 hour to obtain an aluminum pigment concentrate (P-1).

(3) Production of Colored Water-based Paint (A) A colored water-based paint for base coat (A) was obtained using the emulsion, the pigment dispersion, and the like obtained in the above Production Examples.

The composition of the water-based paint (A) is as shown in Table 2.

Each component is uniformly mixed and dispersed.
E-60 "(Rohm and Haas Co., thickener) 2.9 to 2.1
The resulting mixture was adjusted to an apparent viscosity of 3,000 cps / 6 rpm (B-type viscometer) and a pH of 7.80 to obtain an aqueous paint.

In Table 2, EM-1 'in the water-dispersed resin is the neutralizing agent of EM-1.
EM-2 'for EM-2 neutralizing agent for diethylaminoethanol, EM-3' for EM-3
Dimethylaminoethanol as neutralizing agent, EM-4 'is EM
-4 is neutralized with monoethanolamine, EM-5 'is EM
-5 neutralizer is triethanolamine, EM-6 'is EM
The neutralizing agent of -6 was replaced with triethylamine, all of which are for comparative examples.

 Water-soluble resin S-1 was produced by the following method.

60 parts of butyl cellosolve and 15 parts of isobutyl alcohol are added to the reaction vessel and heated to 115 ° C. in a nitrogen stream. 115 ° C
When reached, a mixture of 26 parts of n-butyl acrylate, 47 parts of methyl methacrylate, 10 parts of styrene, 10 parts of 2-hydroxylethyl methacrylate, 6 parts of acrylic acid and 1 part of azoisobutyronitrile is taken over 3 hours. Add. 115 after addition
The mixture was aged at 39 ° C for 39 minutes, a mixture of 1 part of azobisisobutyronitrile and 115 parts of butyl cellosolve was added over 1 hour, and after aging for 30 minutes, the mixture was passed through a 200 mesh nylon cloth at 50 ° C. The acid value of the resulting reaction product 48 and a viscosity of Z ₄ Gardener bubble viscometer) and a nonvolatile matter of 55%. This was neutralized with an equivalent amount of diethanolamine, and deionized water was added to obtain a 50% acrylic resin aqueous solution. S
-1 'is obtained by replacing the above diethanolamine with dimethylaminoethanol.

In the crosslinking agent, H-1: Cymel 350 (hexamethoxymethylmelamine,
H-2: Cymel 370 (partially methoxylated methylol melamine, same as above) (4) Manufacture of acrylic resin Charge 40 parts of cellosolve acetate into a reaction vessel, heat and stir, reach the temperature of 185 ° C. The monomer mixture was added over 8 hours.

Styrene 10 parts i-butyl methacrylate 80 parts n-butyl methacrylate 12 parts 2-ethylhexyl methacrylate 20 parts 2 hydroxyethyl methacrylate 25 parts methacrylic acid 8 parts cellosolve acetate 50 parts α, α'-azobisisobutyronitrile 4 parts One hour after the addition of the monomer mixture, the reaction was continued at 185 ° C., after which 10 parts of cellosolve acetate, α, α′-
A mixture consisting of 0.6 parts of azobisisobutyronitrile was added to 1
The addition took 80 minutes to complete. Then, after reacting for 2 hours, cellosolve acetate was distilled off under reduced pressure to remove the resin component concentration.
It was adjusted to 65% to produce an acrylic resin solution. The number average molecular weight of the resin component of the acrylic resin solution is 4,800.

(5) Production of non-aqueous dispersion of acrylic resin 35 parts of Cymel 235 (detailed later), 103 parts of n-heptane,
0.15 parts of benzoyl peroxide was charged into a reaction vessel, which was heated to 95 ° C., and the following monomer mixture was added dropwise over 8 hours.

Styrene 15 parts Acrylonitrile 9 parts Methyl methacrylate 13 parts Methyl acrylate 15 parts n-butyl methacrylate 1.8 parts 2-hydroxyethyl methacrylate 10 parts Acrylic acid 1.2 parts Benzoyl peroxide 0.5 parts n-butanol 5 parts Shellsol 140 30 parts n-heptane 9 Part 1 hour after the completion of dropping of the monomer mixture, t-
Butyl peroctoate 0.65 parts, Shellsol 140 3.5
Parts of the mixture were added dropwise over 1 hour. Then 95
Stirring was continued for 2 hours while maintaining the temperature at ° C. Thereafter, the pressure was reduced to remove 34 parts of the solvent, and an acrylic resin non-aqueous dispersion having a resin content of 60% and a varnish viscosity of A (Gardner bubble viscosity) was obtained.

(6) Production of acrylic resin In an organic solvent containing 85 parts of xylol and 15 parts of n-butanol, 30 parts of styrene, 40 parts of n-butyl methacrylate, 10 parts of 2-ethylhexyl acrylate, 18 parts of 2-hydroxyethyl acrylate, and 2 parts of acrylic acid Parts of the monomers were reacted to obtain an acrylic resin solution having a number average molecular weight of 4,600, a resin solid content of 50%, and an acrylic resin solution.

(7) Production of acrylic resin Swazole-1000 (Cosmo Oil Co., Ltd. product,
30 parts of an aromatic hydrocarbon solvent), 20 parts of xylol, and 15 parts of n-butanol were charged and heated and stirred. After the temperature reached 130 ° C., the following monomer mixture was added over 3 hours.

Styrene 20 parts n-butyl methacrylate 22 n-butyl acrylate 20 2-hydroxyethyl acrylate 16 TONE M-100 20 acrylic acid 2 α, α-azobisisobutyronitrile 2.2 After addition of the above monomer mixture, 1 Time 130 ℃
Then, a mixture of 1 part of t-butyl peroctoate and 10 parts of xylol was added over 1 hour. Then 2
After keeping stirring at 130 ° C. for a time, the mixture was cooled and xylol was added thereto to obtain an acrylic resin solution having a solid content of 50% by weight. This acrylic resin had a number average molecular weight (w) of 7,500 and a hydroxyl value of 110.

TONE M-100 is a trade name of Union Carbide (USA), a monomer obtained by adding 2 mol of ε-caprolactone to 1 mol of 2-hydroxyethyl acrylate.

(8) Production of clear paint (B) An organic solvent-based clear paint (B) for a top coat was obtained using the acrylic resin obtained in Production Examples (4) and (7). The composition is shown in Table 3.

The alkoxymelamine and acid catalyst in Table 3 are as follows.

Alkoxy melamine M-1: Cymel 303 (trade name, manufactured by Mitsui Cyanamid Co., Ltd., hexamethoxymethyl melamine) M-2: Cymel 235 (trade name, manufactured by Mitsui Cyanamid Co., Ltd., hexaalkoxy (mixture of methoxy / butoxy) methylmelamine) Acid catalyst CAT- 1: Catalyst 6000 (manufactured by Mitsui Toatsu Chemicals, trade name, dodecylbenzenesulfonic acid) CAT-2: Nacure5225 (King Industries (US),
Product name, dodecylbenzenesulfonic acid amine block) CAT-3: Nacure 2500 (King Industries (US),
(Trade name, amine block of P-toluenesulfonic acid) III Example The aqueous paint (A) and the clear paint (B) obtained in the above Production Examples (3) and (8) were applied by a 2C1B method.

An epoxy resin-based cationic electrodeposition paint is electrodeposited on a 0.8 mm thick dull copper plate that has been subjected to zinc phosphate conversion treatment to a cured coating of about 20μ, baked at 170 ° C for 20 minutes, and # 400 sandpaper And degrease by wiping with petroleum benzene. Next, apply the intermediate coating surfacer for automobiles to the dry coating film.
Air-sprayed to 25μ, baked at 140 ° C for 80 minutes, water-sanded with # 400 sandpaper, drained and dried. Then, it is degreased with petroleum benzene to make it a test material.

To this material, an aqueous paint (A) adjusted to a viscosity of 2,000 to 4,000 cps was applied using BEA (manufactured by Nippon Randsburg Co., Ltd., electrostatic air spray) so that the dry film thickness became 10 to 15 μm. After drying at ℃ 15 minutes, viscosity with Ford Cup No.4
The clear paint (B) adjusted to 20-25 seconds has a dry film thickness of 35
Apply using mini-bell G to make ~ 40μ. And ten
After leaving at room temperature for minutes, it was cured by heating with an electric hot air dryer at 140 ° C. for 30 minutes.

Table 4 shows the combination of the water-based paint (A) and the clear paint (B) and the performance test results of the obtained coating films.

The test method is as follows.

Weather resistance: Based on a QUV-accelerated backpack test using an accelerated weather resistance tester manufactured by Q Panel.

Test conditions: UV irradiation 16H / 60 ° C water condensation 9H / 50 ° C as one cycle, and the coating film was evaluated for 3,600 hours (150 cycles).

◎ The gloss is almost the same as the initial one.

△ Degradation of gloss was observed, but no defect such as cracking or whitening.

× Significant decrease in gloss, cracking, whitening (chalking)
Phenomenon was recognized and failed.

Solvent resistance: Gauze impregnated with xylol is pressed with a finger, and the coated surface is strongly rubbed back and forth 20 times. Good in the degree of melting of the painted surface, scratches and swelling Between markedly inferior (x) Judgment in 5 steps.

Water resistance: Evaluation of coated surface after immersion at 40 ° C for 10 days. ○ indicates that no abnormality was observed at all, △ indicates that some swelling was observed, and X indicates that swelling was significantly generated.

Interlayer adhesion: with a cutter knife to reach the substrate
At the approximate center of the test piece, make a parallel line of 11
Pull at intervals of 1mm scratch cut in a grid pattern so as to be 100 squares in 1 cm ^2, and adhering the adhesive cellophane tape to the coated surface, Coban eyes after peeling it rapidly The painted surface was evaluated. ○ indicates that no peeling of the coating film was observed,
Δ indicates that some peeling was observed between the metallic coating and the clear coating, and x indicates that many interlayer peeling was observed.

Sharpness: Measured with an image clarity meter (IMAGE CLARITY METER: manufactured by Suga Test Instruments Co., Ltd.). Numbers in the table are ICM values from 0 to 100%
The value of the range of, the larger the numerical value is sharpness (image clarity)
And an ICM value of 80 or more indicates that the sharpness is extremely excellent.

 Smoothness: Visual evaluation Metallic feeling: Visual evaluation

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI B05D 7/24 303 B05D 7/24 303E (58) Fields investigated (Int.Cl. ⁶ , DB name) B05D 1/00-7 / 26 C09D 1/00-9/04

Claims (1)

(57) [Claims] 1. An organic solvent-based thermosetting clear coating material comprising an acrylic resin, hexaalkoxymethylmelamine and an acid catalyst as main components without coating and curing a thermosetting colored aqueous coating material (A). (B) is coated, and then heated to cure both coating films. This is a coating method by a two-coat one-bake method, wherein the water-based coating material (A) is a neutralizing agent containing dialkanolamine as a main component. A coating method characterized by being neutralized.