JPH11319707A - Coating by using water coating-composition having high water-resistant secondary adhesion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make workability good in broad humidity conditions ranging from a high humidity to a low humidity by a method wherein, after forming an under coat on a material to be coated, a water coating-composition having a specific composition of which water resistant secondary adhesion is improved is applied, cured and thereafter, a coating-composition for a clear coat is applied thereonto to be cured. SOLUTION: An under coat is formed on a material to be coated, and a water coating-composition containing 30 to 90 wt.% of a film forming polymer containing hydroxyl group and carboxyl group, 10 to 50 wt.% of an amino resin curing agent, and 3 to 30 wt.% of a polymer to be obtained by an addition polymerizable oxazoline represented by the formula is applied onto the coating film, and cured. Thereafter, a coating-composition for a clear coat is applied onto the water-based coating composition, and allowed to be cured. In the formula, R<1> to R<5> are respectively independently hydrogen, a halogen, an alkyl, phenyl or a substituted phenyl group, and R<5> is an acyclic organic group having an addition polymerizable unsaturated bond.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an aqueous coating composition which has good workability under a wide range of humidity conditions from high humidity to low humidity and has good water-resistant secondary adhesion of a composite coating film. The present invention relates to a coating method and a coated product obtained thereby.

[0002]

2. Description of the Related Art Conventionally, in the coating of automobile parts and the like, a metallic pigment-containing metallic base paint called a top coat is applied to a base plate and a middle coated plate without being cured. A two-coat, one-bake method, in which a clear paint is applied repeatedly by a wet-on-wet method, and finally, both the clear paint film and the metallic base paint film are cured.

[0003] In the two-coat one-bake method as described above, organic solvent type paints have been mainly used. However, from the viewpoints of safety at the time of coating, reduction of environmental pollution, resource saving, and the like, in recent years, there has been a strong demand for a shift to a water-based paint having a low solvent content or containing no solvent. For this reason, various water-based paints for automobiles have been developed.

[0004] For example, Japanese Patent Application Laid-Open No. Hei 4-25582 discloses an aqueous metallic base coating composition containing, as a main component, an aqueous dispersion of an amide group-containing acidic resin and a hydrophilic group-carrying polyurethane resin. Japanese Patent Application Laid-Open No. 7-74320 discloses that a water-dispersed resin composition in which an acrylic resin is used as a core and a polyester resin is provided in a shell is used to perform good work under a wide range of humidity conditions from high humidity to low humidity. A water-based coating composition having properties has been proposed.

However, these aqueous metallic base coating compositions are solubilized or dispersed in water by neutralizing a carboxyl group with a base, so that the carboxyl group may remain even after the formation of a coating film. Due to this, the water resistance secondary adhesion of the composite coating film was low.

[0006]

By adding an oxazoline polymer component capable of reacting with a carboxyl group to the above-mentioned aqueous metallic base coating composition, water-resistant adhesiveness and chipping resistance of the composite coating film after heat curing are obtained. Was found to be significantly improved.

[0007]

SUMMARY OF THE INVENTION The present invention relates to
After forming an undercoat and, if necessary, an intermediate coating film, a water-based coating composition having a specific composition with improved water-resistant secondary adhesion is applied, and the coating film of the water-based coating composition is not cured or cured. After that, a coating method for applying a coating composition for a clear coat on the coating composition and curing both a coating film of the aqueous coating composition and / or a coating film of the coating composition for clear coating is provided. The present invention further provides a coated article including a coating film formed by the above coating method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the coating method of the present invention, first, (I) an undercoat and, if necessary, an intermediate coating film are formed on an object to be coated. The coating object suitable for use in the present invention is not particularly limited as long as it can be used by heating and curing an aqueous coating composition described below, for example, an automobile body, a wheel,
Automobile parts such as bumpers; home electric appliances such as air conditioner outdoor units; and building materials such as outer wall materials. As the undercoat paint used in the above step (I) and the intermediate paint optionally used, any paint composition known in the art can be used, and can be applied and dried and cured by a conventional method. The film thickness of the formed undercoat film and the intermediate coat film formed as necessary is not particularly limited as long as it is within a range desired for the object to be coated.

In the coating method of the present invention, the step (II) comprises:
An aqueous coating composition of a specific component is applied on the formed undercoat or intermediate coat. Aqueous coating compositions suitable for use in the present invention include (A) a film-forming polymer containing hydroxyl and carboxyl groups, (B) an amino resin curing agent, and (C) a formula (a):

Embedded image (Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen, halogen, alkyl, phenyl or substituted phenyl group, and R ⁵ represents an addition polymerizable unsaturated bond. Or an addition-polymerizable oxazoline polymer represented by the formula (1), or a polymer obtained by polymerizing the oxazoline and (b) one or more monomers other than those described above. Hereinafter, the water-based coating composition preferably used in the method of the present invention will be described.

[0010] Film-forming polymer (A) Film-forming polymer which can be contained in the aqueous coating composition
(A) is an acrylic resin (A-1) and a polyester resin (A-
Can be synthesized from 2). As the acrylic resin (A-1), to copolymerize an ethylenic monomer having a saturated hydrocarbon group having 6 to 18 carbon atoms, a hydroxyl group-containing ethylenic monomer, an acidic group-containing ethylenic monomer and other ethylenic monomers Is obtained by

The ethylenic monomer having a saturated hydrocarbon group having 6 to 18 carbon atoms is not particularly limited. For example, an acrylic acid ester having 6 to 18 carbon atoms at the ester site (specifically, Specifically, hexyl acrylate, cyclohexyl acrylate, ethyl hexyl acrylate, lauryl acrylate, lauryl stearyl acrylate, etc.); methacrylates (hexyl methacrylate, cyclohexyl methacrylate, ethylhexyl methacrylate, lauryl methacrylate, lauryl methacrylate) Stearyl, etc.). Or
The monomer () may be a reaction product of a functional group-containing ethylenic monomer and a compound having a saturated hydrocarbon group having 6 to 18 carbon atoms which reacts with the functional group. Examples of such a monomer include a reaction product of glycidyl methacrylate with lauric acid or stearic acid, and a reaction product of methacrylic isocyanate with lauryl alcohol or stearyl alcohol. In the present invention, since the monomer () has an appropriate bulkiness, the structural viscosity of the paint using the obtained thermosetting aqueous resin can be made suitable.

In the acrylic resin (A-1), suitable hydroxyl-containing ethylenic monomers () are not particularly limited, but include, for example, 2-hydroxyethyl acrylate, 4-hydroxyethyl acrylate, and 4-hydroxyethyl acrylate. Hydroxybutyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,4-dihydroxy-
4'-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide and the like can be mentioned.

The acidic group-containing ethylenic monomer ()
Although is not particularly limited, for example, a carboxyl group-containing monomer (specifically, acrylic acid,
Methacrylic acid, crotonic acid, isocrotonic acid, 3-vinylsalicylic acid; styrene derivatives such as 3-vinylacetylsalicylic acid). Alternatively, the monomer () is a half ester of a dibasic acid monomer,
It may be a half amide or a half thioester. Examples thereof include maleic acid, fumaric acid, half esters of itaconic acid, half thioesters, and the like. In this case, the alcohol that forms the half ester includes, for example, one having 1 carbon atom such as methanol, ethanol, propanol, butanol, methyl cellosolve, ethyl cellosolve, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, and propargyl alcohol. And -12 alcohols. Among these, in the acrylic resin (A-1), suitable monomers () include butanol, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol,
Propagyl alcohol is preferred.

Examples of the mercaptan forming the half ester include mercaptans having 1 to 12 carbon atoms such as ethyl mercaptan, propyl mercaptan and butyl methyl captan. Examples of the amine forming the half amide include ethylamine,
Examples thereof include amines having 1 to 12 carbon atoms such as diethylamine, butylamine, cyclohexylamine, aniline, and naphthylamine. Among the half esters, half amides and half thioesters of the dibasic acid monomers, the half thioester has a problem in terms of odor. Half esters and half amides can be suitably used because they do not have such a problem. In the half ester, half amide, and half thioester of the dibasic acid monomer, each reaction of half esterification, half amidation, and half thioesterification can be performed by a usual method, for example, a temperature range of room temperature to 120 ° C. Can be performed using a tertiary amine as a catalyst, if necessary.

The other ethylenic monomer () constituting the acrylic resin (A-1) is not particularly limited, and the above-mentioned ethylenic monomer having a saturated hydrocarbon group having 6 to 18 carbon atoms is used. , A hydroxyl group-containing ethylenic monomer, and other than the acidic group-containing ethylene monomer, which may be an ethylenic monomer having no reactive functional group, such as styrene, α
-Styrenes such as -methylstyrene; methyl acrylate,
Acrylic esters such as ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate; methacryl such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, p-butyl methacrylate, and 2-ethylhexyl methacrylate Acid esters;
Nitriles such as acrylonitrile; olefins such as ethylene and propylene; further,
An amide group-containing ethylenic monomer such as acrylamide, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, and N, N-dibutylacrylamide may be used.

The film-forming polymer (A) in the aqueous coating composition used in the present invention comprises the monomer component (モ ノ マ ー)
) Is replaced by a known polymerization method (for example, a radical polymerization method, etc.)
Can be obtained by copolymerization using In the polymer (A), the content of the ethylenic monomer () having a saturated hydrocarbon group having 6 to 18 carbon atoms is from 30 to
It is 80% by weight, more preferably 40-60% by weight. In the film-forming polymer (A), when the content of the monomer () is less than 30% by weight, the interaction between particles is weak and "sagging" is easily generated. Since the amounts of the hydroxyl group-containing ethylenic monomer () and the acidic group-containing ethylenic monomer () contained in the component (A-1) are both insufficient, the curability of the obtained aqueous coating composition and water content It is not preferable because the dispersion stability decreases.

Another component of the film-forming polymer (A) is a polyester resin having a hydroxyl group at a terminal (A-
2). Such a polyester resin (A-2) may be any resin having a hydroxyl group at the terminal, and can be obtained by polyesterification of a polyol with a polycarboxylic acid or an acid anhydride. As the polyol,
Although not particularly limited, for example, tetraols such as dimers of pentaerythritol and trimethylolpropane; triols such as trimethylolpropane and Heiantriol; 1,9-nonanediol, 2-methyl-1,8 -
Octanediol, neopentyl glycol, hydroxypiparic neopentyl glycol, 3-methyl-1,5-
Pentanediol, 1,6-hexanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,3-propylene glycol, propylene glycol, hexylene glycol, ethylene glycol, diethylene glycol, hydrogenated bisphenol A, caprolactone diol,
Examples thereof include diols such as bishydroxyethyl taurine. The polycarboxylic acid is not particularly limited and includes, for example, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, adipic acid, trimellitic acid, azelaic acid, sebacic acid, succinic acid, cyclohexanedicarboxylic acid, maleic acid, and the like. Can be mentioned. The acid anhydride is not particularly limited, and examples thereof include an acid anhydride of the polycarboxylic acid.

The polyester resin (A-2) has a number average molecular weight of 500 to 4,000, an acid value of less than 15, and a hydroxyl value of 50 to 20.
It is preferred to have 0. If the number average molecular weight of the polyester resin is less than 500, the hardness and water resistance of the coating film of the obtained water-based coating composition will decrease, and if it exceeds 4,000, the smoothness of the coating film obtained will decrease. Further, when the acid value of the polyester resin is 15 or more, the water resistance of the obtained coating film is reduced. Further, when the hydroxyl value of the polyester resin is less than 50, the curability of the obtained coating film decreases, and when it exceeds 200, the water resistance of the obtained coating film decreases.

By adding the above polyester resin (A-2) as a component in a preferred aqueous coating composition to be used in the present invention, flexibility and flexibility are imparted to a coating film of the obtained aqueous coating composition. can do. Further, since the polyester resin is a hydrophobic resin, the workability, particularly the stiffness, can be improved.

A monoepoxy compound may be added to the polyester resin (A-2) in order to further increase the flexibility of the resulting coating film. Suitable monoepoxy compounds include, for example, Cardura E10, YOA10, YOA20,
YOA30 (manufactured by Daicel Chemical Industries, aliphatic monoepoxy compound) and the like.

In the film-forming polymer (A) in the aqueous coating composition which can be used in the present invention, the acrylic resin component (A-1) and the polyester resin component (A-2) having a hydroxyl group at the terminal are It may be contained in an amount of 50 to 90% by weight and 50 to 10% by weight, more preferably 60 to 80% by weight and 40 to 20% by weight, respectively, based on the total amount of resin solids in the paint. In the aqueous coating composition, the acrylic resin component
When the content of (A-1) is less than 50% by weight and the content of the polyester resin (A-2) exceeds 50% by weight, the hydrophilic portion which is responsible for water dispersibility of the film-forming polymer (A) Is insufficient, the aqueous dispersion stability is reduced. Alternatively, in the aqueous coating composition, the content of the acrylic resin (A-1) exceeds 90% by weight and the content of the polyester resin (A-2) is 1%.
If the amount is less than 0% by weight, the properties of the polyester resin are not utilized, and workability and water dispersibility are undesirably reduced.

The film-forming polymer (A) in the aqueous coating composition suitable for use in the present invention is obtained by subjecting the polyester resin component (A-2) to a transesterification reaction or a urethanation reaction with diisocyanate. It is characterized in that it is grafted to the acrylic resin component (A-1), and at least a part of the acidic groups in the film-forming polymer (A) is neutralized by a base.

As one embodiment of such a film-forming polymer (A), in a water-based coating composition, the hydrophobic polyester resin component (A-2) is used as a core, and the hydrophilic acrylic resin component (A- Core-shell type particles having 1) as a shell are exemplified. In such particles, the components (A-1) and (A-2) are preferably tightly bound to such an extent that they cannot be easily separated, and by adopting such a structure, The film-forming polymer (A) can avoid direct contact of the polyester resin (A-2) with water, thereby eliminating the possibility of hydrolysis of the polyester resin. That is, by forming the film-forming polymer (A) into particles having a core-shell structure, high water resistance can be imparted to a coating film composed of an aqueous coating composition containing the particles.

The film-forming polymer (A) is prepared by first mixing the desired amounts of the acrylic resin component (A-1) and the polyester resin component (A-2) in an organic solvent at 130 to 200 ° C., preferably A graft copolymer resin can be obtained by causing a heat reaction at 140 to 180 ° C. and copolymerizing using a known polymerization initiator by an ordinary method (for example, a radical polymerization method). The organic solvent used in the graft copolymerization reaction is not particularly limited, and examples thereof include aromatic hydrocarbons such as Solvesso 150 (S-150) (manufactured by Shoei Chemical Industry Co., Ltd.) and xylene; esters such as butyl acetate; γ-butyrolactone; ethers such as dibutyl ether and ethylene glycol diethyl ether; ketones such as methyl isobutyl ketone; ether esters such as propylene glycol monomethyl ether acetate; amides such as N-methylpyrrolidone; . These can be used in combination of two or more. In the heating reaction, if the temperature is lower than 130 ° C., the progress of the reaction is not sufficient, so that the stability of the obtained film-forming polymer (A) is not improved. If the temperature exceeds 200 ° C., the obtained polymer ( A) is not preferred because it causes the coloring of A) and deteriorates the appearance when a coating film of the aqueous coating composition is formed.

The film-forming polymer (A) can be converted into an aqueous dispersion by graft copolymerization and then neutralizing at least a part of the acidic groups contained in the obtained resin with a base. it can.

The hydroxyl value of the film-forming polymer (A) obtained as described above is 50 to 200, more preferably 60 to 1
50. If the hydroxyl value is less than 50, the curability of the coating film of the obtained water-based coating composition will decrease, and if it exceeds 200, the water resistance of the coating film will decrease. The above hydroxyl value can be achieved by adjusting the content of the hydroxyl group-containing ethylenic monomer () contained in the acrylic resin (A-1) to 2 to 40% by weight.

The acid value of the film-forming polymer (A) is 10
It is preferably from 100 to 100, particularly preferably from 20 to 60. If the acid value is less than 10, the water dispersibility decreases, and if it exceeds 100,
The water resistance of the coating film decreases. The acid value of the film-forming polymer (A) is such that the content of the acidic group-containing ethylenic monomer () contained in the acrylic resin (A-1) is 2%.
-60% by weight, more preferably 4-40% by weight.

The number average molecular weight of the film-forming polymer (A) is from 5,000 to 100,000, preferably from 10,000 to 60,000.
It is. When the number average molecular weight is less than 5,000, the hardness and water resistance of the coating film decrease, and when it exceeds 100,000, atomization during spray coating cannot be performed, so that the smoothness of the obtained coating film decreases. Not preferred. The film-forming polymer (A) is composed of the above monomer components (to
) Is copolymerized by a known method. For example, the film-forming polymer (A) can be obtained by dropping and copolymerizing the polymerization initiator and the monomer mixture while the heated solvent is further heated and stirred. In a preferred embodiment in this case, in a solution containing the polyester resin having a hydroxyl group at the terminal (A-2), the polymerization initiator and the monomer mixture are simultaneously added to the solution.
5 hours, preferably dropping over 2 to 3 hours, then
Maintaining the polymerization temperature for 0 to 4 hours, preferably 1 to 2 hours.

The above-mentioned film-forming polymer (A) contained in the aqueous coating composition preferably used in the present invention, after polymerization,
At least a part of the acidic groups contained in the polymer (A) is neutralized with a base. The base used for the neutralization is not particularly limited, for example, ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine,
Examples thereof include dimethylethanolamine, diethanolamine, and triethanolamine. Of these, diethanolamine, dimethylethanolamine,
Triethanolamine is preferred. The polymer (A)
It is preferable to neutralize the acidic group contained therein with the above base to such an extent that can be dispersed in water. The ratio of such acidic groups to be neutralized may be about 50%, for example, a molar ratio of 0.4 to 2.0, preferably 0.6 to 1.4, based on the total number of moles of the acidic groups contained. The amine can be suitably neutralized.

Another embodiment (A) of the film-forming polymer suitable for use in the coating method of the present invention includes: an amide group-containing monomer, an acidic group-containing monomer, a hydroxyl group-containing monomer, and It is obtained by copolymerizing a monomer other than the above, and has a number average molecular weight of 6,000 to 50,000, an acid value of 10 to 100, and a hydroxyl value of 50 to 50.
200, and at least a part of the acidic group is neutralized with a base.

In the above embodiment, the amide group-containing monomer (') which is a copolymer component of the film-forming polymer (A') is usually a (meth) acrylamide compound, for example, acrylamide, methacrylamide, N,
N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-dibutylacrylamide, N, N-dibutylmethacrylamide, N, N-dioctylacrylamide, N, N-dioctylmethacrylamide, N, N-monobutylacrylamide , N, N-monobutylmethacrylamide, N-monooctylacrylamide, N-monooctylmethacrylamide and the like. More preferred amide group-containing monomer (') is acrylamide or methacrylamide.

The details of the acidic group-containing monomer ('), the hydroxyl group-containing monomer ('), and the monomer (') other than those described above, which are copolymer components of the film-forming polymer (A'), are described in detail above. ~).

The above-mentioned film-forming polymer (A ') can be obtained by radical copolymerization of the above-mentioned monomer components ('-'). In this case, in the copolymerization, the amide group-containing monomer component (') is used in an amount of 5 to 40% by weight, preferably 8 to 30% by weight of the whole. When the amount of the amide group-containing monomer component (') is less than 5% by weight, the appearance of the coating film of the obtained water-based coating composition decreases, and when it exceeds 40% by weight, the water resistance of the coating film decreases. Are not preferred. In the above copolymerization, the amount of the acidic group-containing monomer (') used is 3 to 15
%, Preferably 5 to 13% by weight. When the amount of the monomer component (') is less than 3% by weight, the water dispersibility of the aqueous coating composition decreases, and when the amount exceeds 15% by weight, the water resistance when the composition is used as a coating film decreases. I do.
The amount of the hydroxyl group-containing monomer component (') used may be in the range of 10 to 40% by weight, preferably 13 to 30% by weight. When the amount of the monomer component (') is less than 10% by weight of the entire monomer components constituting the film-forming polymer (A'), the curability of the coating film is reduced. Any of these is not preferred because the properties are reduced.

Regarding the formation of the film-forming polymer (A ') using the monomer components (' to '), it is preferable to carry out a copolymerization reaction under the same conditions as those described for the film-forming polymer (A). .

The number average molecular weight of the film-forming polymer (A ′) copolymerized to satisfy the above conditions is from 6,000 to 50,000.
0, preferably in the range of 8,000 to 30,000. When the number average molecular weight is less than 6,000, both the workability as an aqueous coating composition and the curability of the obtained coating film are not sufficient,
Alternatively, if it exceeds 50,000, the non-volatile content of the coating composition at the time of coating is too low, and this also leads to a reduction in workability.

Suitable amino resin curing agents (B) contained in the aqueous coating composition suitable for use in the method of the present invention include, for example, dimethylolmelamine, trimethylolmelamine, tetramethylolmelamine, pentamer Methylol melamine, hexamethylol melamine; alkyl ethers thereof such as methyl ether, ethyl ether, propyl ether, isopropyl ether, butyl ether, isobutyl ether; urea-formamide condensate; urea-melamine condensate; and mixtures thereof. be able to.

In the aqueous coating composition, since the film-forming polymer (A) or (A ′) has a grafted structure, even when hydrophobic melamine is used as the curing agent (B), the polymer is used. It can be stably dispersed in water.

The component (C) contained in the aqueous coating composition is represented by the following formula (a):

Embedded image (Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen, halogen, alkyl, phenyl or substituted phenyl group, and R ⁵ represents an addition polymerizable unsaturated bond. And a polymer curing agent obtained by (b) polymerizing one or more monomers other than those described above, if necessary. Examples of the addition-polymerizable oxazoline (a) include,
Vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl
Examples thereof include 2-oxazoline and 2-isopropenyl-5-ethyl-2-oxazoline, and one or a mixture of two or more selected from these groups can be used.
Among them, 2-isopropenyl-2-oxazoline is preferred because it is the most commercially available. Such an addition-polymerizable oxazoline (a) may account for 5% by weight or more of the curing agent component (C) from the viewpoints of durability and water resistance of the resulting aqueous coating composition as a coating film. preferable.

The other monomer (b) which can be copolymerized with the addition-polymerizable oxazoline (a) is not reacted with an oxazoline group, and
The monomer is not particularly limited as long as it is a monomer copolymerizable with (a). Examples of such monomers (b) include methyl (meth) acrylate, butyl (meth) acrylate, (meth)
(Meth) acrylic acid esters such as 2-ethylhexyl acrylate; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene; and the like, and one or a mixture of two or more thereof may be used. May be.

In the present invention, the curing agent component (C)
Is obtained by polymerizing an addition-polymerizable oxazoline (a) and, if necessary, one or more other monomers (b) by a conventionally known polymerization method. The most preferred embodiment is an emulsion polymerization method from the viewpoint of easy conversion to water. In such an emulsion polymerization method, a so-called monomer dropping method, a multi-stage polymerization method, a pre-emulsion method, or the like can be applied using a conventionally known polymerization catalyst and a surfactant.

In the aqueous coating composition suitable for use in the present invention, the film-forming polymer (A) containing a hydroxyl group and a carboxyl group is 30 to 90% by weight, and the amino resin curing agent (B) is 10% by weight. -50% by weight, and 3-30% by weight of the curing agent component (C).

The aqueous coating composition may further contain a pigment. Examples of pigments that can be added include coloring pigments such as titanium dioxide, graphite, chromium oxide, iron oxide, graphite, carbon black, phthalocyanine pigments, and quinacridone; calcium carbonate, magnesium carbonate, barium sulfate, silicate, and aluminum water. Extenders such as hydrates and calcium sulfate; When using an aqueous coating composition that can contain a pigment as an intermediate coating,
Some of the pigments include barium sulfate, calcium carbonate, clay,
It is desirable to contain an inorganic pigment such as titanium oxide as a coloring pigment. Further, the aqueous coating composition may further contain a glitter pigment as a pigment other than the above. By including a glitter pigment in the coating composition, an aqueous metallic coating composition can be obtained. Examples of such glitter pigments include aluminum foil, alumina flake, mica, tin foil, gold foil, metal titanium foil, nickel foil and the like. The glitter pigment, the resin solid content in the coating composition is 100 parts by weight, 5 to 60
It is preferable to include the parts by weight. The resulting aqueous metallic coating composition can be suitably used as a base coat coating.

The aqueous coating composition used in the present invention can ensure better dispersion stability and workability by incorporating a polymer thickener. Examples of such a polymer thickener include acrylic resin particles. The polymer thickener is preferably added in an amount of 60% by weight or less based on the solid content of the resin in the aqueous coating composition. When the content of the polymer thickener exceeds 60% by weight, the smoothness of the coating film of the obtained water-based coating composition is reduced.

The water-based coating composition may further contain, as additives other than the above-mentioned components, for example, silicone-based and acrylic-based antifoaming agents; dispersants; silicon-based, acrylic-based, fluorine-based, and other surface modifiers; A curing catalyst such as a phosphoric acid type or an onium salt type may be added.

The aqueous coating composition used in the present invention may be an aqueous solid coating composition having a high solid content.

Aqueous coating compositions suitable for use in the method of the present invention are those based on water, preferably deionized water, but may optionally further comprise a small amount of an organic solvent. It may be added. Organic solvents that can be added include
For example, ether alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether; alcohols such as methanol, ethanol, isopropanol, n-butanol, sec-butanol and t-butanol; esters Type; ketone type and the like.

The aqueous coating composition having the above composition can be applied to the undercoat or intermediate coat obtained above by a known coating method, for example, spray coating, brush coating, dip coating, roll coating or It can be painted by sink painting or the like.

The coating film of the aqueous coating composition applied by the above-mentioned coating method preferably has a wet film thickness in the range of 5 to 100 μm, but the coated material including the coating film exhibits desired properties. The film thickness is not limited to the above range as long as the film thickness is necessary.

In the coating method of the present invention, in the step (III), after the coating film of the aqueous coating composition is cured, a coating composition for a clear coat is applied thereon. In this process,
The coating film of the aqueous coating composition can be coated with a clear coating composition without being cured. The clearcoat coating composition suitable for use in the method of the present invention may or may not contain an aminoplast curing agent such as a melamine resin.
Examples of such a coating composition include a coating composition for a clear coat having both a carboxyl group-containing resin and an epoxy group-containing resin. Further, the coating composition for clear coat may be composed of a half-esterified copolymer, an acrylic resin containing an epoxy group, or may be in a powder form.

In the step (III) of the present invention, when the coating film composed of the aqueous coating composition is cured, and then the coating composition for a clear coat is applied thereon, the coating film of the aqueous coating composition is According to the usual method, 10 minutes to 1 at 100 to 160 ° C
Can cure under time conditions.

In the step (IV) of the method of the present invention, the coating film of the aqueous coating composition and the coating film of the clear coating composition which have not been cured in the step (II) can be cured. When the coating film of the aqueous coating composition is cured in the step (II), only the coating film of the clear coating composition is cured. When simultaneously curing the coating film of the water-based coating composition and the coating film of the coating composition for clear coat (that is, two-coat one-bake method), the entire coated product including the coating film is subjected to 100 to 160 by a conventional method. 10 ° C
It can be cured under the conditions of minutes to 1 hour. Alternatively, when only the coating film of the coating composition for a clear coat is cured, the painted material is cured under the same conditions as described above.

[0052]

The aqueous coating composition of the present invention comprises a polymer (A) having both a hydroxyl group and a carboxyl group as main components, and an amino resin curing agent (B) and an oxazoline group as a curing agent for curing the polymer (A). Contains polymer (C). The hydroxyl group and the carboxyl group in the polymer (A) are effective to make the paint components water-soluble and to give a homogeneous water-dispersed paint. However,
After applying the aqueous coating composition, the polymer (A)
Is cured under predetermined conditions by the amine resin curing agent (B), but a large number of unreacted carboxyl groups remain in the polymer (A) at the time of curing. Since the presence of such a carboxyl group causes the coating film to become water-soluble and, in effect, can reduce the water resistance and storage stability of the coating film, it is important that the carboxyl group be eliminated when the coating film is cured. In the present invention, in the aqueous coating composition, under the curing conditions, the remaining carboxyl group can be eliminated by the reaction shown in the following scheme with the oxazoline group in the polymer (C).

Embedded image That is, since there is no carboxyl group in the formed coating film, the water resistance and chipping resistance are remarkably improved as compared with the conventional aqueous coating composition.

[0053]

The present invention will be described below with reference to examples.
The present invention is not limited to the following examples. In the following Production Examples, Examples, and Comparative Examples, all percentages and parts are by weight unless otherwise specified. Production Example 1: Production of polyester resin (a) 613 parts by weight of 1,9-nonanediol, 114 parts by weight of trimethylolpropane, 105 parts by weight of adipic acid and phthalic anhydride
536 parts by weight were charged into a reactor together with 30 parts by weight of xylene, the temperature was raised to the reflux temperature, and water generated by the reaction was removed while azeotroping with xylene. The temperature was set at 190 ° C over about 2 hours from the start of reflux, and the acid value equivalent to carboxylic acid was 85%.
Stirring and dehydration were continued until the temperature reached, and then cooled to 140 ° C. While maintaining this temperature, 205 parts by weight of Cajura E10 (glycidyl versatate: manufactured by Shell Co.) was added dropwise over 30 minutes, and then stirring was continued for 2 hours to complete the reaction. Acid value 5, hydroxyl value 120, number average molecular weight 2,3
50 polyester resins (a) were obtained.

Production Example 2: Production of film-forming polymer (1) 400 parts by weight of Solvesso 150 (S-150), 200 parts by weight of methyl isobutyl ketone and 200 parts by weight of the polyester resin (a) obtained in Production Example 1 were charged. Under stirring at 100 ° C., a monomer mixture consisting of 166 parts by weight of hydroxyethyl acrylate, 61 parts by weight of methacrylic acid, 520 parts by weight of ethylhexyl methacrylate and 53 parts by weight of styrene was obtained.
A solution obtained by adding 10 parts by weight of t-butylperoxy-2-ethylhexanoate (Kayaester O: manufactured by Kayaku Akzo Co., Ltd.) was dropped at a constant speed in 3 hours. After 30 minutes, 50 parts by weight of S-150 and 4 parts by weight of Kayaester O were added dropwise over 30 minutes, and the mixture was further reacted at that temperature for 1 hour to obtain an ester having an acid value of 41, a hydroxyl value of 96 and a number average molecular weight of 10,000. An acrylic resin mixture was obtained.

This resin mixture was heated to 140 ° C. while stirring, and subjected to a transesterification reaction at that temperature for 4 hours. As a film-forming polymer, an acid value of 41, a hydroxyl value of 96 and a number average molecular weight were obtained.
As a result, 10,000 film-forming polymers (a), which are polyester-grafted acrylic resins, were obtained. In the present specification,
This polyester graft acrylic resin is called “polyester acrylic resin”. The obtained film-forming polymer (a) was heated and stirred at 65 ° C., and 90 parts by weight of dimethylethanolamine and 2274 parts by weight of deionized water were added thereto.
By making it water-soluble, an emulsion-colored viscous aqueous dispersion solution was obtained (solid content: 25%).

Production Example 3: Production of film-forming polymer (2) In a 1 L reaction vessel equipped with a nitrogen inlet tube, a stirrer, a temperature controller and a cooling tube, 76 parts by weight of ethylene glycol monobutyl ether were charged, and further 15 parts by weight of styrene. Parts, methyl methacrylate 63 parts by weight, 2-hydroxyethyl methacrylate 48 parts by weight, N-butyl acrylate 117 parts by weight,
61 parts by weight of a monomer solution comprising 27 parts by weight of methacrylic acid, 30 parts by weight of acrylamide and 3 parts by weight of azobisisobutyronitrile were added, and the temperature was adjusted to 120 ° C. with stirring. After adding 245 parts by weight of the monomer solution in 3 hours, stirring was continued for 1 hour. Further, 28 parts by weight of dimethylethanolamine and 200 parts by weight of deionized water were added to obtain a film-forming polymer (b) having a nonvolatile content of 50%, a resin number average molecular weight of 12,000, a hydroxyl value of 70 and an acid value of 58.

Production Example 4: Diethylene glycol monobutyl ether 400 in a dispersing resin reactor
100 parts by weight of styrene, 172 parts by weight of methyl methacrylate, 230 parts by weight of lauryl acrylate, 219 parts by weight of methyl acrylate, Plaxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.) 218 under stirring at 100 ° C. Parts by weight, a monomer mixture consisting of 61 parts by weight of methacrylic acid and 10 parts by weight of Kayaester O were dropped at a constant speed over 3 hours, and after 30 minutes, 50 parts by weight of diethylene glycol monobutyl ether and 3 parts by weight of Kayaester O were added for 30 minutes. Then, the mixture was further reacted at that temperature for 1 hour to obtain an acrylic resin having an acid value of 40, a hydroxyl value of 50 and a number average molecular weight of 17,000. Hereinafter, this acrylic resin is referred to as a dispersing resin. The obtained resin for dispersion was heated and stirred at 85 ° C., and 87 parts by weight of triethylamine and 2952 parts by weight of deionized water were added thereto, and the mixture was made water-soluble.
A clear, viscous aqueous solution was obtained. The solid content of the obtained aqueous solution is
22%.

Production Example 5: Thickening resin 180 parts by weight of deionized water, 10 parts by weight of styrene, 0.7 parts by weight of methacrylic acid and 0.7 parts by weight of dimethanolamine were charged into a reactor and heated to 83 ° C. Next, 4,4'-azobis-
0.5 parts by weight of 4-cyanovaleric acid was neutralized with 0.87 parts by weight of dimethylethanolamine and dissolved in 5 parts by weight of deionized water was added dropwise over 20 minutes. In addition, styrene 84.3
Parts by weight, a mixture consisting of 5 parts by weight of methacrylic acid and 5 parts by weight of dimethylethanolamine, and 0.5 parts by weight of 4,4'-azobis-4-cyanovaleric acid in dimethylethanolamine
A solution neutralized with 0.27 parts by weight and dissolved in 40 parts by weight of deionized water was added dropwise over 2 hours, and stirring was continued for 1 hour to obtain a white emulsion [solid content: 30%, particle size: 330 nm]
(By laser light scattering method)]. This emulsion,
Hereinafter, it is referred to as a thickening resin.

Production Example 6: 89 parts by weight of the dispersing resin obtained in Production Example 4 and Perind Maroon R-6424 [manufactured by Bayer AG, Maroon (red pigment)] in a 1.5 L pigment dispersible paste in a sealable stainless steel container. Weigh 21 parts by weight and 28 parts by weight of deionized water, add 480 cc of glass beads,
After premixing with a stirrer, use a pent conditioner for 2 minutes.
After mixing and dispersing for a time, a pigment-dispersed paste was obtained.

Example 1 An aqueous metallic base paint [1] was prepared according to the composition and amount shown in Table 1. First, 5 parts by weight of an aluminum pigment (aluminum paste NW-91-2061, aluminum metal pigment 62%, manufactured by Toyo Aluminum Co., Ltd.) is uniformly mixed in advance with 71 parts by weight of the dispersing resin prepared in Production Example 4 to obtain a dispersion. And Next, 700 parts by weight of the film-forming polymer (a) and a curing agent (C-212:
A melamine resin curing agent (manufactured by Mitsui Cytec Co., Ltd.) was previously mixed and made water-soluble, and then mixed with the dispersion to obtain an aqueous dispersion. Furthermore, an antifoaming agent (BY
K-341: 2 parts by weight by Big Chemie Japan) and 84 parts by weight of the thickening resin obtained in Production Example 5, and oxazoline-containing polymer: Epocross K-1010E (Nippon Shokubai) 19
A water-based metallic base coating composition [1] was prepared by adding parts by weight and stirring and mixing at room temperature using a stirrer.

Examples 2 to 5 and Comparative Examples 1 and 2 Water-based metallic base coatings [2] to [7] were prepared in the same procedure as in Example 1 according to the compositions and amounts shown in Table 1. Here, when the film-forming polymer (a) was used (that is, Examples 2 and 3 and Comparative Example 1),
After mixing the polymer (a) with a curing agent (C-212: a melamine resin curing agent manufactured by Mitsui Cytec Co., Ltd.) and making it water-soluble, the pigment was previously dispersed and added to the dispersing resin obtained in Preparation Example 4; Was uniformly mixed to obtain an aqueous dispersion. On the other hand, when the film-forming polymer (b) was used (Examples 4 and 5 and Comparative Example 2), the resin for dispersion or the resin for dispersion and the pigment obtained in Production Example 6 were simply added together with a curing agent. An aqueous dispersion was obtained by mixing with the paste. Further, to the aqueous dispersion, a commercially available antifoaming agent as an additive and the thickening resin obtained in Production Example 5, and for Examples 2 to 5, a commercially available oxazoline-containing polymer were further added. In the above, aqueous metallic base coating compositions [2] to [7] were respectively manufactured by stirring and mixing using a stirrer.

[0062]

[Table 1] ¹⁾ : Melamine resin curing agent, manufactured by Mitsui Cytec Co., Ltd. ²⁾ : Prepared in Production Example 6 ³⁾ : Prepared in Production Example 4 ⁴⁾ : Aluminum paste NW-91-2061, 62% of aluminum metal pigment,
Toyo Aluminum ⁵⁾ : Silicone defoamer, manufactured by Big Chemie Japan ⁶⁾ : Prepared in Production Example 5 ⁷⁾ : Trade name "Epocross", Nippon Shokubai ⁸⁾ : Trade name "Epocross", Nippon Shokubai Co., Ltd.

Production Example 7: Preparation of coating composition for clear coat
Preparation (1) A reaction vessel was charged with 900 parts by weight of xylene and heated to 100 ° C., and then 12 parts by weight of methacrylic acid, 264 parts by weight of styrene, 264 parts by weight of methyl methacrylate, 360 parts by weight of n-butyl acrylate, 2 parts by weight A mixed solution composed of 100 parts by weight of hydroxyethyl acrylate and 10 parts by weight of azobisbutyronitrile was dropped at a constant speed over 3 hours, and a solution composed of 3 parts by weight of azobisbutyronitrile and 100 parts by weight of xylene was further added for 30 minutes. Was dropped. The reaction was continued for another 2 hours to obtain an acrylic resin solution having a nonvolatile content of 50% and a number average molecular weight of 8,000.

To 100 parts by weight of this acrylic resin solution, 36 parts by weight of Uban 20SE-60 (a melamine resin curing agent manufactured by Mitsui Toatsu Chemicals) and 0.5 part by weight of Modaflow (a leveling agent manufactured by Monsanto Co., Ltd.) were blended for clearing. A coating composition (a) for coating was prepared. The paint composition (a) for clear coat thus obtained is thinner (composition: S-100 / S) before use.
-150 = 1/1) and diluted to the desired paint viscosity (= 25 seconds / Ford Cup No. 4/20 ° C.) before use.

Examples 6 to 10 and Comparative Examples 3 and 4 The aqueous metallic base coating compositions [1] to [7] obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were added to NACU.
RE5225 (Amine blocked acid catalyst: King Industries
Inc.) (1 part by weight). Then ford cup
No. 4 diluted with deionized water so as to be 60 seconds, each coating composition obtained by adjusting the viscosity, so that the dry film thickness is 10 ~ 50μm on a steel plate which has been pre-coated Was spray painted. Then, it was dried at 80 ° C. for 10 minutes. The coating conditions were 25% humidity and 65% and 85% humidity.
We performed at two levels. Next, the coating composition for clear coat prepared in Production Example 7 was applied on the coating film of the coating composition so as to have a dry film thickness of 40 μm. After setting for 5 minutes, the coating film of the coating composition and the coating film of the clear coating composition were simultaneously baked at 140 ° C. for 30 minutes.

The finished appearance, water resistance and solvent resistance of each coating film obtained in Examples 6 to 10 and Comparative Examples 3 and 4 were
The following method evaluated. Table 4 shows the evaluation results.

Evaluation method 1. Sagging limit film thickness In Examples 6 to 10 and Comparative Examples 3 and 4,
Each of the metallic base coating compositions was subjected to oblique coating so as to have a thickness of 10 μm in the thin film portion and 50 μm in the thick film portion, and the maximum thickness of the obtained coating film without sagging coating defects was defined as the sagging limit film thickness. The sagging limit film thickness of 25 μm or more was judged as acceptable. 2. Waki limit film thickness In Examples 6 to 10 and Comparative Examples 3 and 4,
Each of the metallic base coating compositions was subjected to oblique coating so as to have a thickness of 10 μm in the thin film portion and 50 μm in the thick film portion. A film thickness of at least 25 μm was judged to be acceptable. 3. The appearance of each coating film obtained in Examples 6 to 10 and Comparative Examples 3 and 4 was visually observed, and the following evaluation criteria were used together with the flip value measured by a metallic ambience tester. Was determined according to Evaluation criteria: good (the orientation of aluminum is good and the flip value is 30 or more): ○ Slightly inferior (the orientation of aluminum is slightly inferior and the flip value is 25 or more and less than 30): 不良 poor (the orientation of aluminum) Is disturbed and the flip value is less than 25.): ×

[0068] 4. Solvent resistance In each of the coating films obtained in Examples 6 to 10 and Comparative Examples 3 and 4, a predetermined amount (about 1 g) of the cured coating film was obtained by using a Soxhlet extractor under reflux in an acetone solution. The soluble part was extracted under the condition of time. The case where the extraction rate was less than 5% was regarded as pass (○), and the case where the extraction rate was higher than 5% was rejected (×). 5. Water resistance (appearance evaluation) In Examples 6 to 10 and Comparative Examples 3 and 4,
Each of the obtained cured coating films was immersed in warm water at 40 ° C. for 10 days, and the water resistance of the coated surface was evaluated by observing the change in the coated surface. No abnormality was indicated by "O", and glossy or discolored cases were indicated by "X". 6. Storage stability In the resin solids used in each of the metallic base coating compositions prepared in Examples 1 to 5 and Comparative Examples 1 and 2, the initial stability immediately after dilution with deionized water and the resin after dilution were reduced by 40%. A change in stability over time after standing at 10 ° C. for 10 days was visually determined, and indicated as “uniform” or “non-uniform”.

[0069] 7. Chipping Resistance Each of the coating films obtained in Examples 6 to 10 and Comparative Examples 3 and 4 was subjected to a stepping stone test under the following conditions using a Gravelo tester (manufactured by Suga Test Instruments Co., Ltd.). Stone size: No. 7 crushed stone Amount of stone: 50 g Distance: 35 cm Air pressure: 4.0 kg / cm ² Angle: 45 ° Test temperature: -20 ° C The chipping resistance is as follows by visual inspection of the degree of peeling of the coating film. The evaluation was made in four steps according to the evaluation criteria. Evaluation criteria: no peeling. : が あ る Slight peeling (small peeling area): 剥離 Peeling occurred. : △ Significant peeling has occurred. : × (maximum peeling area)

[0070] 8. Water-resistant secondary adhesion On a pre-coated intermediate coated steel plate, apply the base by spray coating so that the dry film thickness is 12 to 15 μm, and at 80 ° C
Dried for 10 minutes. Next, each clear was painted under each predetermined condition and baked to obtain a test piece. The test piece was immersed in warm water at 40 ° C. for 10 days, taken out, and subjected to an adhesion test within one hour. The adhesion test is
Hold the cutting edge of a cutter (NT cutter S type, A type or equivalent) on the painted surface of the above test piece at an angle of about 30 degrees to the painted surface, and 11 parallel lines at 2 mm intervals reaching the substrate I pulled. A cross-cut was formed by drawing another 11 parallel lines at 2 mm intervals perpendicular to the parallel lines. An adhesive tape (manufactured by Nichiban, cellophane tape for industrial use) is evenly pressed on the grid with a fingertip so that no foaming remains. Immediately after that, one end of the adhesive 4 tape was held, and the tape was peeled off from the test piece by suddenly pulling the tape at an angle of about 45 degrees with respect to the coated surface. ).

Table 2 summarizes the above evaluation results.

[Table 2] ⁺⁾ : Judgment result based on flip value measured by metallic ambience tester

Production Example 8: Preparation of coating composition for clear coat
Preparation (2) Charge 500 parts by weight of butyl acetate into a reaction vessel, raise the temperature to 125 ° C., and then add 50 parts by weight of styrene and glycidyl methacrylate.
400 parts by weight, methyl methacrylate 26.4 parts by weight, 2-ethylhexyl acrylate 200 parts by weight, 2-hydroxyethyl acrylate 350 parts by weight, and t-butyl peroxy-2-
A mixed solution consisting of 70 parts by weight of ethyl hexanoate (Kayaester O) was dropped at a constant speed over 3 hours. After dropping, 12
After holding at 5 ° C. for 30 minutes, a solution comprising 10 parts by weight of Kayaester O and 250 parts by weight of xylene was added dropwise over 80 minutes. After the completion of the dropwise addition, the reaction was continued at 125 ° C. for 2 hours to obtain an acrylic resin solution having a nonvolatile content of 59% and a number average molecular weight of 4,000.

A reaction vessel was charged with 80 parts by weight of xylene, and
After heating to 5 ° C., 25 parts by weight of styrene, 21 parts by weight of N-butyl acrylate, 95 parts by weight of n-butyl methacrylate,
A mixed solution consisting of 34 parts by weight of ethylhexyl acrylate, 50 parts by weight of itaconic anhydride, 100 parts by weight of propylene glycol monomethyl ether acetate and 10 parts by weight of Kayaester O was dropped at a constant rate over 3 hours. After dropping,
Stirring was further continued at 115 ° C. for 2 hours to obtain a polymer having an anhydrous carboxyl group having a nonvolatile content of 53% and a number average molecular weight of 5,500.

The above carboxyl group-containing polymer 38
To 5 parts by weight, 1.35 parts by weight of triethylamine dissolved in 35 parts by weight of butyl acetate, and 18.2 parts by weight of methanol were added.
For 12 hours, and after confirming that the absorption (1785 nm ^-1 ) based on the acid anhydride group had completely disappeared by IR, a half-esterified polymer was obtained.

In a stainless steel container, 100 parts by weight of the acrylic resin varnish prepared above, 133 parts by weight of the half-esterified polymer, 0.3 parts by weight of tetrabutylammonium bromide, and Tinuvin-900 (a benzotriazole-based ultraviolet absorber manufactured by Ciba Geigy) 1.2 parts by weight, SANOL LS-292
0.6 parts by weight of a hindered amine light stabilizer (manufactured by Sankyo Co., Ltd.) was stirred with an experimental stirrer to produce a clear coat coating composition (b). This is converted to butyl acetate / xylene =
Using a thinner consisting of 1/1, the desired paint viscosity (=
25 seconds / Ford Cup No. 4/20 ° C.).

Examples 11 and 12 and Comparative Example 5 The aqueous metallic base coating composition [1] prepared above,
To [4] and [6], 1 part by weight of NACURE5225 (amine-blocked acid catalyst: manufactured by KIng Industries Inc.) was added, and the mixture was diluted with deionized water to 60 seconds using Ford Cup No. 4. The viscosity was adjusted. The aqueous metallic base coating compositions [1 ′] and [4 ′] whose viscosity was adjusted in this manner.
And [6 '] are each applied by spray coating on a steel plate which has been previously subjected to intermediate coating so as to have a dry film thickness of 10 to 50 [mu] m, and dried at 80 [deg.] C. for 10 minutes to obtain an aqueous metallic base coating composition. Was obtained. Then, on the coating film,
Clearcoat paint composition (b) prepared in Production Example 8
Was applied to a dry film thickness of 40 μm. The coating was performed at a temperature of 25 ° C. and two levels of humidity of 65% and 85%. After setting for 5 minutes, the metallic base coating film and the clear coat are simultaneously
Bake at 0 ° C. for 30 minutes. Each of the obtained coating films was evaluated for the finished appearance (evaluated by sagging and armpit critical film thickness, and flip value), solvent resistance, water resistance, storage stability, chipping resistance and secondary adhesion resistance, respectively. Performed in the same manner as in Example 6. Table 3 shows the results.

Production Example 9: Paint clear coat paint composition
A reaction vessel was charged with 630 parts by weight of xylene and heated to 130 ° C. Using a dropping funnel, a mixed solution composed of 200 parts by weight of styrene, 450 parts by weight of glycidyl methacrylate, 270 parts by weight of methyl methacrylate, 80 parts by weight of isobutyl methacrylate, and 75 parts by weight of Kayaester O was dropped at a constant rate over 3 hours. After the completion of the dropwise addition, the mixture was kept for 30 minutes, and then a solution comprising 1 part by weight of Kayaester O and 70 parts by weight of xylene was added dropwise over 30 minutes. After dropping, 130 ° C for 1 hour
, The xylene was removed by distillation under reduced pressure to obtain an acrylic resin varnish.

[0078] 70 parts by weight of the obtained acrylic resin varnish, 19.1 parts by weight of decanedicarboxylic acid, 0.11 part by weight of CF-1056 (manufactured by Toray Dow Corning Silicon) and 0.89 parts by weight of benzoin were put into a Henschel mixer (manufactured by Mitsui Miike Seisakusho). hand,
The mixture was dry-mixed, and then dissolved and dispersed at a temperature of 100 ° C. in a co-kneader PR-46 (Bus, Switzerland) and cooled. After cooling, the coating composition was pulverized with a hammer mill and classified with a 150-mesh wire net to obtain a coating composition for a powder acrylic clear coat.

Examples 13 to 15 and Comparative Example 6 The aqueous metallic base coating composition [2] prepared above,
After adding 1 part by weight of NACURE 5225 (amine-blocked acid catalyst: manufactured by KIng Industries Inc.) to [3], [5] and [7], deionize the mixture with Ford Cup No. 4 for 60 seconds. It was diluted with water to adjust the viscosity. The water-based metallic base coating compositions [2 '], [3'], [5 '] and [7'] each having the viscosity adjusted in this way were
It was applied on a steel sheet which had been subjected to intermediate coating in advance by spray coating so as to have a dry film thickness of 10 to 50 μm, and dried at 80 ° C. for 10 minutes to obtain a coating film of an aqueous metallic base coating composition. Next, the coating composition for powder clear coat prepared in Production Example 9 was electrostatically coated on the above coating film so that the dry film thickness became 40 μm. The coating was performed at a temperature of 25 ° C. and two levels of humidity of 65% and 85%. After setting for 5 minutes, the metallic base coating film and the powder clear coat were simultaneously baked at 150 ° C. for 30 minutes. Finish appearance of each coating film obtained (evaluation by sagging and waki limit film thickness and flip value), solvent resistance,
Evaluations on water resistance, storage stability, chipping resistance and secondary adhesion resistance were performed in the same manner as in Example 6. Table 3 shows the results.

[0080]

[Table 3] ⁺⁾ : Judgment result based on flip value measured by metallic ambience tester

[0081]

According to the present invention, an aqueous coating composition, particularly an aqueous metallic base coating composition, contains an oxazoline polymer component capable of reacting with a carboxyl group as a curing agent so that a clear coat thereon can be formed. The water-resistant secondary adhesion and chipping resistance after heat curing of the composite coating film can be significantly improved.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09D 139/04 C09D 139/04 161/20 161/20 167/02 167/02 201/06 201/06

Claims (10)

[Claims] 1. An undercoat and, if necessary, a step of forming an intermediate coating film on an object to be coated. (II) On the coating film, (A) a film containing a hydroxyl group and a carboxyl group. 30-90% by weight of forming polymer, (B) 10-50% by weight of amino resin curing agent, and (C) (a) formula: (Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen, halogen, alkyl, phenyl or substituted phenyl group, and R ⁵ represents an addition polymerizable unsaturated bond. Aqueous polymer containing an addition-polymerizable oxazoline represented by the formula (1) and, if necessary, (b) 3 to 30% by weight of a polymer obtained by polymerizing one or more monomers other than the above. A step of applying a coating composition, (III) a step of applying a clear coat coating composition thereon without or after curing the coating film of the aqueous coating composition (IV) of the aqueous coating composition A coating method including a step of curing a coating film and / or a coating film of a clear coating composition. 2. The film-forming polymer (A) in the aqueous coating composition comprises: (A-1) an ethylenic monomer having a saturated hydrocarbon group having 6 to 18 carbon atoms, a hydroxyl group-containing ethylenic monomer, and an acidic group-containing Acrylic resin obtained by copolymerizing an ethylenic monomer and another ethylenic monomer 50 to 90% by weight, and (A-2) 50 to 10% by weight of a polyester resin having a hydroxyl group at a terminal, and The polyester resin (A-2) is grafted to the acrylic resin (A-1) by a reaction, and at least a part of the acidic groups in the film-forming polymer (A) is neutralized with a base. The coating method according to claim 1, wherein 3. The film-forming polymer (A) in the aqueous coating composition has an average molecular weight of 5,000 to 100,000, an acid value of 10 to 100, and a hydroxyl value of 50 to 200.
The painting method described. 4. The film-forming polymer (A) in the aqueous coating composition, wherein the content of the ethylenic monomer having a saturated hydrocarbon group having 6 to 18 carbon atoms is 30 to 80% by weight. The coating method according to claim 2, wherein 5. The film-forming polymer (A) in the aqueous coating composition, wherein the polyester resin (A-2) has an average molecular weight of 500 to 4,000, an acid value of less than 15, and a hydroxyl value of 50 to 200. The coating method according to claim 1, wherein: 6. The film-forming polymer (A ′) in the aqueous coating composition is obtained by copolymerizing an amide group-containing monomer, an acidic group-containing monomer, a hydroxyl group-containing monomer, and a monomer other than those described above. Number average molecular weight 6,000-5
The coating method according to claim 1, wherein the coating method has a molecular weight of 10,000, an acid value of 10 to 100 and a hydroxyl value of 50 to 200, and at least a part of the acidic group is neutralized with a base. 7. The coating method according to claim 1, wherein the aqueous coating composition further contains a pigment. 8. The coating method according to claim 7, wherein the pigment is a glitter pigment. 9. A coated article comprising a coating film formed by the method according to claim 1. 10. (A) 30 to 90% by weight of a film-forming polymer containing a hydroxyl group and a carboxyl group, (B) 10 to 50% by weight of an amino resin curing agent, and (C) (a) a formula: (Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen, halogen, alkyl, phenyl or substituted phenyl group, and R ⁵ represents an addition polymerizable unsaturated bond. Aqueous polymer containing an addition-polymerizable oxazoline represented by the formula (1) and, if necessary, (b) 3 to 30% by weight of a polymer obtained by polymerizing one or more monomers other than the above. Paint composition.