JPH09173956A - Formation of coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a double coating film improved in finished coating film appearance and acid rain resistance. SOLUTION: In this foaming method of the coating film by applying a metallic or solid base coating material and further applying a 1st clear coating material and a 2nd clear coating material and baking them, the 1st clear coating material is a thermosetting clear coating material containing an acrylic resin, which is obtained by polymerizing a monomer containing a secondary hydroxyl group and has the OH value of at least 20 originating from the secondary hydroxyl group, and a melamine resin, 10-20wt.% of which has the number average molecular weight of 2000. Besides the 2nd clear coating material is a thermosetting clear coating material performing the reaction of a polyepoxy with a poly-acid, preferably the reaction of an acid anhydride modified group with an epoxy group, and the reaction of an acid anhydride group or the acid anhydride modified group with the epoxy group and the reaction of the acid anhydride group or the acid anhydride modified group with the hydroxyl group as the main reaction of hardening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film, and more particularly to a method for forming a coating film having a good finished appearance and good acid resistance.

[0002]

2. Description of the Related Art Generally, a top coating for automobiles is made by applying a metallic base paint or a solid base paint, and then applying a clear paint wet on wet to protect the metallic base paint. , A top coat film is formed. Further, by applying the clear paint repeatedly, a high appearance of the object to be coated can be obtained. However, when the paint is applied twice, the first clear paint is applied, followed by curing and baking, and then the second clear paint. Paint and bake.

As a conventional clear coating composition, a combination of a hydroxyl group-containing polymer and a melamine resin curing agent is generally used. The outermost top coating film obtained from a coating material using this melamine resin curing agent is generally inferior in acid resistance, and acid rain, which has become a big problem in recent years, may cause a loss of the top surface coating film. there were. This poor acid resistance is considered to be caused by the triazine nuclei in the melamine resin, and this drawback cannot be solved as long as the melamine resin is used for the outermost top coating film.

Therefore, the "thermosetting composition" of JP-A-2-45577 and the "thermosetting resin composition" of JP-A-3-287650 have good acid resistance without using a melamine resin. As a clear coating composition, a thermosetting resin composition containing a polymer containing an acid anhydride group half ester and a hydroxy compound and an epoxy compound has been proposed.

[0005]

However, since the clear coating material comprising the above thermosetting resin composition has a high free energy on the surface (interface) of the clear coating material, it is different from the first clear coating film which has been previously formed. However, there is a problem in that the adhesiveness with the second clear coating film that is applied over the first clear coating film is reduced.

In such a case, in order to improve the adhesion between the first clear coating film and the second clear coating film, the first clear coating film may be water-polished and then the second clear coating film may be applied. Conceivable.

However, this water-research process is economical,
It is difficult to be adopted due to process problems.

Therefore, it is possible to use a second clear coating composition comprising an acid / epoxy-containing thermosetting resin composition which forms a coating film having good acid resistance, without the need for a water polishing step for the first clear coating film. The advent of a so-called "clear coating capable of non-sand coating (referred to as" non-sand adhesion "), which improves the adhesion to the second clear, is desired.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to form a coating film having a good finished appearance and good acid resistance, and the adhesion between the first clear coating film and the second clear coating film. To provide an improved coating film forming method.

[0010]

In order to achieve the above-mentioned object, the method for forming a coating film of the present invention is a method in which a metallic base paint or a solid base paint is applied and then a metallic base paint or a solid base paint is applied. In the coating film forming method of applying 1 clear coating material, then applying 2nd clear coating material and baking, (a) 1st clear coating material is (A)
The above-mentioned 2 obtained by polymerizing a monomer containing a secondary hydroxyl group.
A thermosetting clear coating composition containing an acrylic resin having an OH value derived from a primary hydroxyl group of at least 20 and (B) a melamine resin having a number average molecular weight of 2,000 or more in 10 to 20% by weight of the melamine resin. And (b) the second clear coating material is a thermosetting clear coating material containing a polyepoxy and a polyacid, and preferably (A) an acid anhydride-modified group in which an acid anhydride group is half-esterified and an epoxy group. And the reaction between (B) the acid anhydride group or the acid anhydride-modified group and the epoxy group and the reaction between the acid anhydride group or the acid anhydride-modified group and the hydroxyl group are the main reactions for curing. It is a thermosetting clear paint.

Therefore, according to the second clear coating composition (b) used in the present invention, a melamine resin is not contained and a solid cured product is obtained after coating and curing baking from polyepoxy and polyacid curing coating film. A top coat film having excellent properties and a high finish appearance can be obtained. Furthermore, when a second clear coating composition is applied on the first clear coating film and then cured and baked, the hydroxyl groups derived from the thermosetting resin of the first clear coating composition (a) used in the present invention are changed to the second clear coating composition ( The second clear coating composition (b) has a carboxyl group derived from the thermosetting resin of the first clear coating composition (a) while being bound to an acid anhydride-modified group (e.g., ester group) derived from the thermosetting resin composition of b). The first clear coating film (a) and the second clear coating film (b) are combined with the epoxy group derived from the thermosetting resin.
The adhesion to and becomes strong.

Wet on after the first clear coating
The second clear coating film can be formed by wet, but it is preferable in the present invention to form the second clear coating film after preheating (40 to 120 ° C.) or baking and curing the first clear coating film.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In describing the embodiments of the present invention, first, the steps of a coating system for an automobile to which the embodiments of the present invention are most applied will be described.

Before coating, the material is first subjected to chemical conversion treatment. Next, electrodeposition coating is performed, and then intermediate coating is performed. afterwards,
Preferably, it is baked and cured, and then a metallic paint or a solid paint is applied. However, it is also possible to apply metallic paint or solid paint after the intermediate coating with wet on wet. Then, the first clear coating material used in the present embodiment is applied wet-on-wet on the metallic coating film or the solid coating film,
Preferably, it is hardened and baked. Then, the second clear paint used in the present embodiment is applied onto the first clear paint and cured and baked to form a laminated coating film.

Here, in the coating film forming method of the present embodiment, the outline of the coating material formed under the clear coating film is as follows.

The electrodeposition paint is a paint which uses various ordinary anion type and cation type resins as vehicles. Further, the intermediate coating is a polyhydric alcohol, a polyester resin composed of a polybasic acid, and an alkyd resin modified with an oil or the like, or an acrylic resin composed of acrylic acid and a crosslinking agent such as a melamine resin or a block polyisocyanate. Is a vehicle, and a rust preventive pigment, a chipping resistant pigment, and other materials are appropriately mixed with the vehicle. Further, as the metallic paint or solid paint, a polyester resin composed of a polyhydric alcohol and a polybasic acid, and an alkyd resin modified with an oil or the like, or an acrylic resin composed of acrylic acid, an acrylic ester, etc. and a melamine resin or a block This is a coating material in which a cross-linking agent such as polyisocyanate is used as a vehicle, and a bright pigment such as a coloring pigment, an aluminum foil or a mica pigment is appropriately mixed therein.

Next, the coating film forming method according to the present invention will be described.

As described above, in the method for forming a coating film according to the present invention, the metallic base paint or the solid base paint is applied, and then the first clear paint is applied on the metallic base paint or the solid base paint. Is a method for forming a coating film in which a second clear paint is applied and baked after curing and baking, and the first clear paint (a) shown below is used.
And a second clear coating composition (b).

The first clear paint (a) and the second clear paint (b) will be described in detail below. The top coating method using the first clear paint (a) and the second clear paint (b) will be described later.

First Clear Coating (a) The first clear coating (a) is obtained by polymerizing (A) a monomer having a secondary hydroxyl group and OH derived from the secondary hydroxyl group.
Having a valency of at least 20 and 10 to 20% by weight of the (B) melamine resin have a number average molecular weight of 2,000.
It is a thermosetting clear coating material containing the above melamine resin.

Acrylic resin (A) The acrylic resin (A) has an OH value (hydroxyl value) of preferably 90 to 150, and the OH value derived from the secondary hydroxyl group is at least 20. preferable.
When the OH value of the acrylic resin (A) is less than 90 and when the OH value derived from the secondary hydroxyl group is less than 20 in the OH value, non-sand adhesion between the first clear coating film and the second clear coating film Deteriorates. On the other hand, when the OH value exceeds 150, and the OH value derived from the secondary hydroxyl group is 9
If it exceeds 0, the water resistance and durability of the first clear coating film may deteriorate.

The acid value of the acrylic resin (A) is preferably 3-10. When the acid value of the acrylic resin (A) is less than 3, the thermosetting reaction between the acrylic resin and the melamine resin does not proceed sufficiently, and the coating strength and finished appearance of the first clear coating film deteriorate. On the other hand, when the acid value exceeds 10, the thermosetting reaction between the acrylic resin and the melamine resin proceeds too much, the functional groups in the surface layer of the first clear coating film decrease, the wettability with the second clear film decreases and the second clear film decreases. It cannot bond with a functional group (for example, an epoxy group or a hydroxyl group) of the interface layer of the coating film, resulting in a decrease in non-sand adhesion.

The acrylic resin (A) is preferably (i)
(Meth) acrylic acid ester, wherein the position of the carbon atom farthest from the (meth) acryloyloxy group is 4 or less in terms of the number of atoms directly bonded to the (meth) acryloyloxy group (meta). ) 30 to 84.9% by weight, preferably 40 to 70% by weight of acrylate, and (ii) an α, β-ethylenically unsaturated monomer which comprises an α, β-ethylenically unsaturated group The position of the furthest carbon atom is within 6 in terms of the number of atoms counted from the atom directly bonded to the α, β-ethylenically unsaturated group, other than the above-mentioned (i), short-chain α, β-ethylenically unsaturated monovalent 0-40% by weight, preferably 5-30% by weight, (iii) at least 1
A hydroxyl group-containing ethylenically unsaturated monomer containing a secondary ethylenically unsaturated monomer having a secondary hydroxyl group, or a mixture thereof,
40%, preferably 20 to 30% by weight, (iv) 0.1 to 5% by weight of acid group-containing ethylenically unsaturated monomer, preferably 0.3 to 3% by weight, and (v) the above ( It is a polymer obtained by polymerizing 0 to 34.9% by weight, preferably 5 to 25% by weight of an ethylenically unsaturated monomer other than i) to (iv). The polymerization percentage of the resin is based on the total solid content of the resin composition.

In the short-chain (meth) acrylic acid ester (a) (A) (i), the position of the carbon atom farthest from the (meth) acryloyloxy group is counted from the atom directly bonded to the (meth) acryloyloxy group. A short chain (meth) acrylic acid ester having 4 or less atoms is preferable,
Suitable specific examples include acrylic acid esters (for example, methyl acrylate, ethyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate,
Cyclohexyl acrylate, isobornyl acrylate),
Further, methacrylic acid esters (for example, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate) and the like can be mentioned. When the position of the carbon atom farthest from the (meth) acryloyloxy group is greater than 4 in terms of the number of atoms directly bonded to the (meth) acryloyloxy group, the coating film strength is deteriorated, which is not preferable.

When the amount of the short chain (meth) acrylic acid ester (a) (A) (i) is less than 30% by weight based on the acrylic resin (A), the surface free energy of the clear coating film is It is not preferable because it lowers the adhesiveness. On the other hand, when the amount of the short chain (meth) acrylic acid ester exceeds 84.9% by weight with respect to the acrylic resin (A), the flexibility of the coating film is lowered and the coating film is apt to crack. Become.

In the above α, β-ethylenically unsaturated monomer (a) (A) (ii), the position of the carbon atom farthest from the α, β-ethylenically unsaturated group is α, β-ethylenic. An α, β-ethylenically unsaturated monomer having 6 or less atoms counted from the atoms directly bonded to the unsaturated group is preferable, and preferable specific examples include styrene and α-methylstyrene.
Examples thereof include styrene derivatives such as pt-butylstyrene. When the position of the carbon atom farthest from the α, β-ethylenically unsaturated group is greater than 6 in terms of the number of atoms directly bonded to the α, β-ethylenically unsaturated group, the surface free energy It is not preferable because it causes a decrease.

When the amount of the α, β-ethylenically unsaturated monomer (a) (A) (ii) exceeds 40% by weight with respect to the acrylic resin (A), the flexibility of the coating film deteriorates. Is not preferred.

The hydroxyl group-containing ethylenically unsaturated monomer (a) (A) (iii) containing at least one secondary hydroxyl group-containing ethylenically unsaturated monomer is specifically acrylic. Acid 2-hydroxyethyl, acrylic acid 2-
Hydroxypropyl, 2-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate and the like are preferable. Moreover, the mixture means the mixture of the said specific example.

When the amount of the above-mentioned hydroxyl group-containing ethylenically unsaturated monomer (a) (A) (iii) is less than 15% by weight with respect to the acrylic resin (A), the acrylic resin (A) contains The OH value derived from the secondary hydroxyl group is lowered, and the non-sand adhesion between the first clear coating film and the second clear coating film is deteriorated. On the other hand, the hydroxyl group-containing ethylenically unsaturated monomer (a)
If the amount of (A) (iii) exceeds 40% by weight with respect to the acrylic resin (A), the OH value derived from the secondary hydroxyl group in the acrylic resin (A) becomes excessive, and the water resistance of the first clear coating film is increased. , Durability deteriorates.

Specific examples of the acid group-containing ethylenically unsaturated monomer (a) (A) (iv) include acrylic acid,
Methacrylic acid, crotonic acid, itaconic acid, maleic acid,
Fumaric acid and the like are preferred.

When the amount of the above-mentioned acid group-containing ethylenically unsaturated monomer (a) (A) (iv) is less than 0.1% by weight with respect to the acrylic resin (A), the thermosetting reaction will occur. It is not preferable because it does not proceed sufficiently and the coating strength and the finished appearance deteriorate. On the other hand, the acid group-containing ethylenically unsaturated monomer (a)
If the amount of (A) and (iv) exceeds 5% by weight with respect to the acrylic resin (A), the thermosetting reaction proceeds too much to bond with the functional groups of the interface layer of the first clear coating film, Non-sand adhesion tends to decrease.

Further, as the ethylenically unsaturated monomers other than the above-mentioned (i) to (iv) of (a), (A) and (v), for example, 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate can be used. , Lauryl acrylate, lauryl methacrylate, acrylamide, methacrylamide and the like.

When the amount of (a) (A) (v) exceeds 34.9% by weight with respect to the acrylic resin (A), the non-sand adhesion of the first clear coating film and the second clear coating film is improved. descend.

The acrylic resin (A) can be obtained by a usual polymerization method. It is carried out by a known method such as solution polymerization such as radical polymerization, and the polymerization temperature is 10
The polymerization can be performed at 0 to 150 ° C. for 3 to 8 hours. The initiator may be an azo type (for example, dimethyl-2,
2'-azobisisobutyrate and the like or peroxide type (for example, t-butylperoxy-2-ethylhexanoent and the like) initiators are preferable. The number average molecular weight of the obtained polymer is 500 to 40,000, especially 1.0
It is preferably from 00 to 20,000. When the number average molecular weight exceeds 40,000, the polymer viscosity becomes high, and it becomes difficult to prepare a coating composition having a high solid content. On the other hand, when the number average molecular weight is less than 500, the curability of the curable resin composition becomes insufficient. The molecular weight is determined by the GPC method.

Melamine resin (B) Melamine resin (B) is 10 to 2 in the melamine resin.
It is preferable that 0% by weight has a number average molecular weight of 2,000 or more. For example, "Super Peckamine 13-548" manufactured by Dainippon Ink and Co., Ltd. or "Uban XM-40" manufactured by Mitsui Toatsu Co., Ltd. is suitable. is there.

When the polymer having a number average molecular weight of 2,000 or more in the melamine resin (B) is less than 10% by weight, the amount of functional groups on the surface of the first clear coating film decreases,
Adhesion to the clear coating film is reduced. On the other hand, when the number average molecular weight of the melamine resin is 2,000 or more,
If it exceeds 0% by weight, the curability of the first clear coating film decreases, the coating strength of the first clear coating film decreases, and the finished appearance deteriorates.

Weight of acrylic resin (A) / melamine resin
Ratio (B) The weight ratio of acrylic resin (A) / melamine resin (B) is
It is preferably 80/20 to 50/50, and 75 /
25-60 / 40 is more preferable. When the weight ratio of (A) / (B) exceeds 80/20, the curability of the first clear coating film decreases, while the weight ratio of (A) / (B) is 50/50.
If it is less than the above, the curing reaction of the first clear coating film proceeds too much, and the adhesion to the first clear coating film deteriorates.

Additives The resin component used in the above-mentioned first clear paint (a) includes
In order to improve the weather resistance of the coating film, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant and the like may be added. Further, crosslinked resin particles as a rheology control agent and a silicone-based or acrylic-based surface modifier for adjusting the appearance may be added. Furthermore, as a diluent for adjusting viscosity, an alcohol solvent (for example,
Solvents such as methanol, ethanol, propanol, and butanol), hydrocarbon-based and ester-based solvents can be used.

Second Clear Paint (b) The second clear paint (b) is a thermosetting clear paint containing a polyepoxy and a polyacid, and preferably (A) an acid anhydride group is half-esterified. Of an acid anhydride-modified group with an epoxy group, and (B) reaction of an acid anhydride group or the acid anhydride-modified group with an epoxy group, and an acid anhydride group or the acid anhydride-modified group with a hydroxyl group It is a thermosetting clear paint whose reaction is the main reaction for curing.

The second clear paint (b) is specifically
The above-mentioned JP-A-2-45577 or 3-28.
A thermosetting clear coating composition comprising the thermosetting resin composition described in Japanese Patent Publication No. 7650.

For example, (I) a copolymer of a radical-polymerizable monomer having an acid anhydride and another copolymerizable monomer, in which the acid anhydride group is half-esterified and does not have an acid anhydride group. A thermosetting resin composition (C) containing a polymer and a compound having both an epoxy group and a hydroxyl group in the molecule (II) (JP-A-3-287650),
(I) A copolymer having no acid anhydride group, wherein the acid anhydride group in the copolymer of a radically polymerizable monomer having an acid anhydride and another copolymerizable monomer is half-esterified,
(II) hydroxy compound, (III) epoxy compound,
Thermosetting resin composition (D) containing (Japanese Patent Laid-Open No. 2-4557)
No. 7) is preferable. Further, as a more preferred embodiment of the thermosetting resin composition (C), (E) (i) (1) acid anhydride group-containing ethylenically unsaturated monomer 15 to 40% by weight
And (2) other copolymerizable ethylenically unsaturated monomer 6
Acid anhydride group-containing polymer obtained by copolymerizing 0 to 85% by weight with (ii) a monoalcohol containing 1 to 12 carbon atoms, and an acid anhydride group / hydroxyl group molar ratio. And a polymer having a carboxyl group and a carboxylic acid ester group, obtained by reacting in an amount of 1/10 to 1/1, and (F) (i) formula (I)

Embedded image [In the formula, R is a hydrogen atom or a methyl group, X is a linear or branched alkyl or hydroxyalkyl, and m is 2-8.
And n is an integer of 3 to 7 and q is an integer of 0 to 4] 5 to 60% by weight of a hydroxyl group-containing ethylenically unsaturated monomer having a structure shown in (ii) epoxy group-containing A hydroxyl group and an epoxy group, which are obtained by copolymerizing 10 to 605 wt% of an ethylenically unsaturated monomer, and (iii) 0 to 85 wt% of another copolymerizable ethylenically unsaturated monomer, if necessary, are added. The coating composition containing the polymer contained therein, and the coating composition (G) having a ratio of 50 to 250 parts by weight of the component (F) to 100 parts by weight of the component (E) is more preferable.

Next, the above-mentioned thermosetting resin composition (C),
The thermosetting resin composition (D) and the coating composition (G) will be described.

Thermosetting composition (C) Copolymer (I) Radical-polymerizable monomers containing an acid anhydride group for forming the above copolymer (I) include itaconic anhydride and maleic anhydride. , Citraconic anhydride and the like. On the other hand, other copolymerizable monomers include styrene, α-methylstyrene, acrylates (for example, methyl acrylate, ethyl acrylate, propyl acrylate, acrylate-n, i, and t-butyl, 2-ethylhexyl acrylate, lauryl acrylate, etc.),
Methacrylic acid esters (eg, methyl methacrylate, ethyl methacrylate, propyl methacrylate, methacrylic acid-n, i, and t-butyl, methacrylic acid 2-
Ethylhexyl, lauryl methacrylate, etc.), acrylamide, methacrylamide, etc. In the composition of the reactant in the copolymerization reaction, the radical-polymerizable monomer containing the acid anhydride is 10 to 40 wt% based on all the monomers.
% Is preferred.

The copolymerization is carried out by a known method, for example, solution polymerization such as radical polymerization. The number average molecular weight of the copolymer is preferably 500 to 40,000. If it is more than 40,000, the viscosity of the copolymer becomes high, and it is difficult to form a high solid content thermosetting composition. On the other hand, if it is less than 500, the curability is not sufficient, and the molecular weight is determined by the GPC method. The acid anhydride group has at least two, preferably 2 to 15 in one molecule. If the number is less than 2, there is a drawback that the curability is not sufficient.

Half-esterification is performed after polymerizing. The half-esterifying agent used for half-esterification is a low-molecular alcohol, specifically, methanol, ethanol, n-butanol, i-butanol, t
-Butanol, methyl cellosolve, ethyl cellosolve,
There are dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, propargyl alcohol and the like. Particularly preferred compounds are acetol, allyl alcohol, propargyl alcohol, and methanol. This is because alcohol is volatilized at the time of heating and it is good for regenerating the acid anhydride group.

The half-esterification reaction is carried out according to a conventional method at a temperature of room temperature to 120 ° C. in the presence of a catalyst. Examples of the catalyst include tertiary amines (eg, triallylamine, tributylamine, etc.) and quaternary ammonium salts (eg, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, benzyltributylammonium chloride, benzyltributylammonium bromide). Can be mentioned.

Having both an epoxy group and a hydroxyl group in the molecule
Compound (II) The compound (II) has 2 to 10 epoxy groups and 2 to 12 hydroxyl groups in the molecule. The epoxy equivalent is 100 to 800 and the hydroxy equivalent is 200 to 1,200.
It is. If the epoxy equivalent is less than the above lower limit, the curability will not be sufficient, while if it is greater than the upper limit, the curing will be excessive and the weather resistance will be poor, such being undesirable. The hydroxy equivalent is 20
When it is less than 0, the water resistance of the cured coating film is not sufficient, and when it exceeds 1,200, it is difficult to obtain a high solid content, which is not preferable.

The compound (II) may have a low molecular weight or a high molecular weight. Examples of the low molecular weight compound include trimethylolpropane diglycidyl ether and the like. Examples of the polymer compound include (i) 30 to 70% by weight of a radical polymerizable monomer having an epoxy group, and (ii) a radical polymerizable monomer having a hydroxyl group 10.
To 50 wt% and (iii) an epoxy equivalent of 200 obtained by copolymerizing a monomer composition containing the balance of other radical-polymerized monomers (however,% is based on the total amount of monomers).
Resin compositions containing a copolymer having a molecular weight of 1,200 and a molecular weight of 500,000 (hereinafter, referred to as "copolymer (II ')").

Examples of the monomer (i) include glycidyl (meth) acrylate and 3,4-epoxycyclohexanyl methacrylate.

Examples of the monomer (ii) include 2-hydroxyethyl (meth) acrylate, acrylic acid 4 and the like.
-Hydroxyethyl, "Placcel FM-1" (manufactured by Daicel Chemical Industries, Ltd.) and the like.

Examples of the monomer (iii) include those exemplified as "other copolymerizable monomers" in the copolymer (I).

The copolymer (II ') is obtained by radical polymerization of a monomer composition containing the above-mentioned monomers (i) to (iii) and a radical polymerization initiator.

The copolymer (I
I ′) is an epoxy equivalent of 100 to 800, a hydroxy equivalent of 200 to 1,200, and a molecular weight of 500 to 40,000.
Has zero. Total number of epoxy groups of compound (II) / total number of half-esterified acid anhydride groups of copolymer (I) =
The total number of hydroxyl groups of compound (II) / the total number of half-esterified acid anhydride groups of copolymer (I) = 0.1 to 1.5 is preferable. Specifically, the compounding amount of the compound (II) that gives such a ratio is preferably, for example, 50 to 250 parts by weight with respect to 100 parts by weight of the copolymer (I). If the amount of the compound (II) used is less than 50 parts by weight, sufficient curing will not be carried out and the water resistance, weather resistance, etc. of the cured coating film will decrease, which is not preferable. On the other hand, when it exceeds 250 parts by weight, unreacted carboxyl group remains, which is not preferable because the chemical resistance is lowered.

Since the thermosetting composition composition (D) copolymer (I) copolymer (I) is the same as that shown in the above "thermosetting resin composition (C)", its explanation is omitted. To do.

Hydroxy Compound (II) As the hydroxy compound (II), various compounds can be mentioned, but those having two or more hydroxy groups in the molecule are preferable. Examples of such things include, for example, 1,
5-pentadiol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, dipentaerythritol, triethylene glycol, triethanolamine, tripropanolamine, etc., The following high molecular weight compounds are included. Examples of the high molecular weight compound include acrylic polyol, polyester polyol, polyether polyol, polyurethane polyol and the like. These can of course be used as a mixture.

The hydroxy compound (II) has a hydroxy equivalent weight of 30 to 1,000. When it is less than 30, the water resistance of the cured coating film is not sufficient, while when it exceeds 1,000, high solid content is unlikely to occur.

The equivalent ratio of the modified (half-esterified) acid anhydride group in the copolymer (I) / hydroxy group in the hydroxy compound (II) is 0.3 / 1 to 10/1.
When the equivalence ratio is lower than 0.3 / 1, curability is lowered, while when the equivalence ratio is higher than 10/1, water resistance is lowered.

[0058] Epoxy compound (III) Examples of the epoxy compound (III), ring aliphatic epoxy resins, for example, US U. C. ERL423 commercially available from Company C
4, ERL4299, ERL4221, ERL4206
Glycidyl ester-based epoxy resin (eg, diglycidyl phthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, dimethylglycidyl phthalate, dimethylglycidyl hexahydrophthalate, dimer acid glycidyl ester, aromatic diglycidyl ester, etc.), glycidyl Ether-based epoxy resins (eg, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, diglycerol triglycidyl ether, sorbitol polyglycidyl ether, etc.), glycidyl group-containing acrylic polymers (eg, radical copolymerizable unsaturated bond and glycidyl) And a radical-polymerized monomer having a group with a copolymerizable monomer).

Examples of the glycidyl group-containing monomer include glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether.
Examples of the copolymerizable monomer include the above-mentioned "copolymer (I)"
The above-mentioned monomers are mentioned as "other copolymerizable monomers".

Among the above epoxy compounds (III), preferred are glycidyl ester epoxy resins, glycidyl ether epoxy resins, and glycidyl group-containing acrylic polymers.

Oxirane group in epoxy compound (III) /
The equivalent ratio of the modified (half-esterified) acid anhydride group in the copolymer (I) / hydroxy group in the hydroxy compound (II) is 0.3 / 1 to 5/1. Equivalent ratio is 0.3
When it is lower than / 1, the water resistance decreases, while when the equivalent ratio is higher than 5/1, unreacted oxirane groups remain and the chemical resistance deteriorates.

Coating Composition (G) Polycarbonate Having Carboxyl Group and Carboxylic Acid Ester Group
The polymer (E) having a carboxyl group and a carboxylic acid ester group is a half ester obtained by reacting an acid anhydride group-containing polymer (e) (i) with a monoalcohol (e) (ii). It is a group-containing polymer.

The acid anhydride group-containing polymer (e) (i) is an acid anhydride group-containing ethylenically unsaturated monomer (e) (i) (1) 15-4.
It is obtained by copolymerizing 0% by weight with 60 to 85% by weight of another copolymerizable ethylenically unsaturated monomer (e) (i) (2). If the amount of the acid anhydride group-containing ethylenically unsaturated monomer (e) (i) (1) is less than 15% by weight, the curability is insufficient, and if it exceeds 40% by weight, the resulting coating film becomes too hard and brittle. It is not preferable because it lacks the property.

Acid anhydride group-containing ethylenically unsaturated monomer
Specific examples of (e) (i) (1) are the same as the monomers given in the above-mentioned "radical polymerizable monomer containing an acid anhydride group of the copolymer (I)", and therefore, the explanation here Is omitted. In addition, other copolymerizable ethylenically unsaturated monomer (e) (i)
The specific example of (2) is also the same as the monomer described as "other copolymerizable monomer" for preparing the above-mentioned copolymer (I), and therefore the description thereof is omitted here.

The above-mentioned copolymerization is carried out by a known method such as solution polymerization such as radical polymerization. The number average molecular weight of the obtained polymer is preferably 1,500 to 8,000. When the number average molecular weight exceeds 8,000, the polymer viscosity becomes high, and it becomes difficult to prepare a coating composition having a high solid content. On the other hand, when the number average molecular weight is less than 1,500, the curability of the curable resin composition becomes insufficient. The resulting polymer has an average of at least 2 and preferably 2 to 15 acid anhydride groups per molecule. When the number of acid anhydride groups contained in one molecule is less than 2, the curability of the curable resin composition becomes insufficient. If it exceeds 15, it becomes too hard and brittle, and the weather resistance is insufficient.

Then, the obtained polymer is reacted with the monoalcohol (e) (ii) in an amount such that the acid anhydride group / hydroxyl group molar ratio is 1/10 to 1/1 to give a carboxyl group. And a polymer (E) having a carboxylic acid ester group is prepared. If this ratio exceeds 1/10, the excess alcohol is too much and causes cracking during curing. On the other hand, if it is less than 1/1, unreacted anhydride groups remain and storage stability deteriorates. Also, monoalcohol (e) (ii)
The low molecular weight alcohols mentioned in the above "half-esterification agent for copolymer (I)" can be used.

Polymer containing hydroxyl group and epoxy group
The polymer (F) having a hydroxyl group and an epoxy group (F) is 1
The molecule preferably has 2 to 10 epoxy groups on average and at least 2 to 12 hydroxyl groups on average. Also,
The epoxy equivalent is preferably 100-800. When the epoxy equivalent is larger than the above upper limit, the curability of the curable resin composition becomes insufficient. Further, if smaller than the above lower limit,
It is not preferable because it becomes too hard and the coating film becomes brittle. When the hydroxy equivalent is less than 200, the water resistance of the cured coating film is not sufficient, and when it exceeds 1,200, the curability is insufficient, which is not preferable.

Such a polymer (F) has, for example, the formula (I)

Embedded image [In the formula, R is a hydrogen atom or a methyl group, X is a linear or branched alkyl or hydroxyalkyl, and m is 2-8.
And n is an integer of 3 to 7 and q is an integer of 0 to 4], a hydroxyl group-containing ethylenically unsaturated monomer (f) (i) having a structure of 5 to 60% by weight, Epoxy group-containing ethylenically unsaturated monomer (f) (ii) 10 to 60% by weight, and optionally other copolymerizable ethylenically unsaturated monomer (f) (iii) 0 to 85% by weight, It can be obtained by polymerizing. If the hydroxyl group-containing ethylenically unsaturated monomer (f) (i) is less than 5% by weight, curability is insufficient,
If it exceeds 60% by weight, the compatibility is insufficient and the reaction does not proceed sufficiently, which is not preferable. If the amount of the epoxy group-containing ethylenically unsaturated monomer (f) (ii) is less than 10% by weight, the curability will be insufficient, and if it exceeds 60% by weight, it will be too hard and the weather resistance will be insufficient, such being undesirable.

If the hydroxyl group-containing alkyl chain of the hydroxyl group-containing ethylenically unsaturated monomer (f) (i) that can be used for preparing the polymer (F) containing a hydroxyl group and an epoxy group is too short, The flexibility in the vicinity of the cross-linking points is lost, so that it becomes too hard, and if it is too long, the molecular weight between cross-linking points tends to be too large. Therefore, the hydroxyl group-containing alkyl chain preferably has 4 to 20 carbon atoms. Specific examples include compounds such as 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and reaction products thereof with ε-caprolactone. Such compounds are commercially available, for example, "Braxel F" manufactured by Daicel Chemical Industries, Ltd.
"M-1", "Braxel FA-1", etc. are mentioned. Alternatively, such a compound esterifies (meth) acrylic acid with a large excess (for example, 1.5 times (mol) or more) of a diol (for example, 1,4-butanediol, 1,6-hexanediol). It is prepared by

Epoxy group-containing ethylenically unsaturated monomer
Examples of (f) (ii) include glycidyl (meth) acrylate and 3,4-epoxycyclohexanylmeryl (meth) acrylate.

Other copolymerizable ethylenically unsaturated monomers (f) (iii) include the acid anhydride group-containing polymer (e)
Examples of the "other copolymerizable ethylenically unsaturated monomer (e) (i) (2)" for adjusting (i) include the monomers described above.

The above-mentioned copolymer is formed by a known method such as solution polymerization such as radical polymerization. The polymer obtained preferably has a number average molecular weight of 500 to 8,000.

Additives A thermosetting resin composition (C), a thermosetting resin composition (D) and a polymer (E) having a carboxyl group and a carboxylic acid ester group, which are used in the above-mentioned second clear coating composition (b). Each of the resin components of the coating composition (G) containing the polymer (F) containing a hydroxyl group and an epoxy group, an "additive" and a quaternary ammonium salt that can be optionally blended with the above-mentioned first clear coating (a). A curing catalyst such as

Manufacturing Method The manufacturing method of the first clear coating material (a) and the second clear coating material (b) of this embodiment is not particularly limited, and any method known to those skilled in the art can be used. The solid content of both clear paints of the present embodiment is preferably in the range of 30 to 80% by weight at the time of production and 20 to 70% by weight at the time of coating.

Coating Method The coating method of the present invention is applied in the steps described above for coating automobiles.

The first clear coating material (a) and the second clear coating material (b) used in this embodiment are arbitrary substrates such as wood, metal, glass, cloth, plastic, foam, and the like.
In particular it can be applied to plastic and metal surfaces such as steel, aluminum and their alloys.

The dry film thickness of each of the first clear paint (a) and the second clear paint (b) and the film can be varied over a wide range depending on the desired application, but the film thickness is often 20 to. 80 μm is useful.

According to the coating method of this embodiment, after coating the substrate, the coating film is cured. Curing is 100-180 ° C,
Preferably, a cured coating film having a high degree of crosslinking can be obtained at a temperature of 120 to 160 ° C. The curing time varies depending on the curing temperature and the like, but generally, it is suitable to cure at a temperature of 120 to 160 ° C. for 10 to 30 minutes.

Further, other preferable embodiments of the present invention other than those described in the claims will be shown below.

1. In the method for forming a coating film, the acrylic resin (A) in the first clear coating composition (a) has an OH value (hydroxyl value) of 90 to 150, and the OH value derived from the secondary hydroxyl group is 20 to 90 is a coating film forming method.

2. In the coating film forming method, the acrylic resin (A) contained in the first clear coating material (a) is (i)
(Meth) acrylic acid ester, wherein the position of the carbon atom farthest from the (meth) acryloyloxy group is 4 or less in terms of the number of atoms directly bonded to the (meth) acryloyloxy group (meta). ) 40 to 70% by weight of acrylic acid ester, and (ii) α, β-ethylenically unsaturated monomer, wherein the position of the carbon atom farthest from the α, β-ethylenically unsaturated group is α, 5 to 30% by weight of a short chain α, β-ethylenically unsaturated monomer other than the above (i) having 6 or less atoms counted from the atoms directly bonded to the β-ethylenically unsaturated group, (iii) 20 to 30% of a hydroxyl group-containing ethylenically unsaturated monomer containing at least one secondary hydroxyl group-containing ethylenically unsaturated monomer or a mixture thereof,
(Iv) 0.3 to 3% by weight of an ethylenically unsaturated monomer containing an acid group, and (v) 5 to 25% by weight of an ethylenically unsaturated monomer other than the above (i) to (iv). Is a polymer obtained by polymerizing a.

3. In the coating film forming method, the weight ratio of acrylic resin (A) / melamine resin (B) in the first clear coating material (a) is 75/25 to 60/40. is there.

4. In the coating film forming method, the second clear coating composition (b) is obtained by half-esterifying the acid anhydride group in the copolymer of (I) a radical-polymerizable monomer having an acid anhydride and another copolymerizable monomer. And a thermosetting resin composition (C) containing a copolymer having no acid anhydride group and a compound (II) having both an epoxy group and a hydroxyl group in the molecule. It is a method of forming a coating film.

5. In the coating film forming method, the second clear coating composition (b) is obtained by half-esterifying the acid anhydride group in the copolymer of (I) a radical-polymerizable monomer having an acid anhydride and another copolymerizable monomer. A method for forming a coating film, which comprises a thermosetting resin composition (D) containing a copolymer having no acid anhydride group, (II) a hydroxy compound, and (III) an epoxy compound. Is.

6. In the method for forming a coating film, the second clear coating material (b) is (E) (i) (1) 15-40% by weight of an acid anhydride group-containing ethylenically unsaturated monomer, and (2) other copolymerizable An acid anhydride group comprising an acid anhydride group-containing polymer obtained by copolymerizing 60 to 85% by weight of an ethylenically unsaturated monomer, and (ii) a monoalcohol containing 1 to 12 carbon atoms. / Hydroxyl molar ratio is 1/10 to 1
A polymer having a carboxyl group and a carboxylic acid ester group, which is obtained by reacting in an amount of / 1 /, and (F) (i) formula (I)

Embedded image [In the formula, R is a hydrogen atom or a methyl group, X is a linear or branched alkyl or hydroxyalkyl, and m is 2-8.
And n is an integer of 3 to 7 and q is an integer of 0 to 4] 5 to 60% by weight of a hydroxyl group-containing ethylenically unsaturated monomer having a structure shown in (ii) epoxy group-containing A hydroxyl group and an epoxy group, which are obtained by copolymerizing 10 to 605 wt% of an ethylenically unsaturated monomer, and (iii) 0 to 85 wt% of another copolymerizable ethylenically unsaturated monomer, if necessary, are added. A coating composition containing a polymer contained therein, characterized in that the coating composition (G) has a ratio of 50 to 250 parts by weight of the component (F) to 100 parts by weight of the component (E). It is a method of forming a coating film.

[0086]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

Examples 1 to 13 and Comparative Examples 1 to 13 (1) Preparation of coated plate: A phosphoric acid conversion treated steel plate was coated with "Power Top U-8", a cationic electrodeposition coating manufactured by Nippon Paint Co., Ltd.
"0", and then coated with Nippon Paint Co., Ltd.'s intermediate coating "Olga P-2" on the process test plate, Nippon Paint Co., Ltd.'s metallic base coating "Superlac M311" Was applied, and then the first clear paint was applied wet-on-wet, followed by baking and drying.
Then, the second clear coating material was applied on the first clear coating film and baked and dried. The plate on which the coating film was formed as described above was used as an evaluation plate.

(2) Preparation of first clear paint (a): a) Synthesis of acrylic resin (A): Production example 1. A 2 liter separable Kolben equipped with a reflux condenser, a dropping roW, a thermometer, and a stirring blade was charged with 440 g of xylol and 160 g of n-butanol, and 1
After heating to 20 ° C., 160 g of styrene, 221.1 g of ethyl acrylate, 200 of ethyl methacrylate
g, 2-hydroxypropyl acrylate 222.7
g, 6.2 g of methacrylic acid, and 16 g of azobisisobutyronitrile were added dropwise at a constant rate for 3 hours through a dropping funnel, and an aging time of 30 minutes was set. Then, a mixed solution of 50 g of xylol and 1 g of benzoyl peroxide was added dropwise, followed by aging for 2 hours, and then diluted with 150 g of xylol to terminate the reaction.

According to the above synthetic method, the acrylic resin (A) was prepared according to the compounding ratio of the monomers of Production Examples 2 to 9 shown in Table 1.
Was synthesized. The acrylic synthetic resin (A) was used in Examples 1 to 13 and Comparative Examples 1 to 5 described later. Further, the acrylic resin (A ') synthesized according to the above-mentioned synthesis method with the monomer mixing ratios of Production Examples 10 to 16 in Table 1 is
It provided for Comparative Examples 6-13 mentioned later.

[0090]

[Table 1] Note) * 1: Styrene (α, β-ethylenically unsaturated monomer
(Belonging to (a) (A) (ii)) * 2: Methyl methacrylate (belonging to short-chain (meth) acrylic acid ester (a) (A) (i)) * 3: Ethyl acrylate (above (a) (Belonging to (A) (i)) * 4: Ethyl methacrylate (belonging to (a) (A) (i) above) * 5: n-Butyl acrylate (belonging to (a) (A) (i) above ) * 6: n-butyl methacrylate (belonging to (a) (A) (i) above) * 7: Cyclohexyl methacrylate (belonging to (a) (A) (i) above) * 8: Lauryl methacrylate ( (Belongs to (a) (A) (v) above) * 9: 2-ethylhexyl methacrylate ((a) (A) (v) above)
* 10: 2-hydroxypropyl acrylate ((a) (A) above)
(Belonging to (iii)) * 11: 2-hydroxybutyl acrylate ((a) (A) (ii) above)
i)) * 12: 2-hydroxyethyl methacrylate ((a) (A) above)
(belonging to (iii)) * 13: Methacrylic acid (belonging to (a) (A) (iv) above) * 14: Azobisisobutyronitrile b) Preparation of first clear coating (a): As a curing agent n
-Butoxymethylol melamine, "Univan 20SE-
60 "(manufactured by Mitsui Toatsu Chemicals, Inc., number average molecular weight (Mn) =
1,200) and "Univan XM-40" (Mitsui Toatsu Chemical Co., Ltd., Mn = 2,500) are used, and the curing agent and the synthesized acrylic resin (A) are mixed to obtain a first clear coating. Created.

(3) Evaluation: The examples and comparative examples shown in Tables 2 and 3 below are the evaluation results of the test plates on which the first clear paint was applied and baked, and then the second clear paint was applied and baked.

The second clear paints shown in Tables 2 and 3 are as follows.

Second clear paint A: "Macflow O-
570 clear "(manufactured by Nippon Paint Co., Ltd., copolymerized with (I) a radical-polymerizable monomer having an acid anhydride and another copolymerizable monomer, in which the acid anhydride group is half-esterified) Clear coating containing the combination and (II) a copolymer containing a hydroxy group and an epoxy group) Second clear coating B: "Superlac O-150 clear" (manufactured by Nippon Paint Co., Ltd., acrylic / melamine curing) system coating) evaluation method: acid _{resistance: 10% H 2 SO 4 70} ℃ in aqueous × 15
Went in minutes.

(Evaluation: Good: Good, Fair: Average, Poor: Bad) Adhesion: JIS K-5400 6.15 Residual number appearance: JIS K-5400 6.7 Gloss and water resistance: JIS K-5400 7. 2 (evaluation; ◯: good, Δ: average, x: bad) Impact resistance: JIS K-5400 6.13 Load 500 g

[Table 2]

[Table 3] From these results, according to the coating film forming method of the present invention, it is possible to form a coating film having a good finished appearance and good acid resistance, and the adhesion between the first clear coating film and the second clear coating film is conventional. It was found to be improved compared to.

[0095]

As described above, according to the coating film forming method of the present invention, since the second clear coating composition (b) does not contain a melamine resin, the acid resistance is improved.

By adjusting the surface free energy of the first clear coating material (a), the wettability with the second clear coating material (b) is ensured, and the second clear coating material (a) is covered with the second clear coating material. When the coating material (b) is applied and then cured and baked, the hydroxyl group derived from the thermosetting resin of the first clear coating material (a) becomes an acid anhydride group derived from the thermosetting resin of the second clear coating material (b). At the same time as binding, for example, a carboxyl group derived from the thermosetting resin of the first clear paint (a) is bound to an epoxy group derived from the thermosetting resin of the second clear paint (b), the first clear coating film ( The adhesion between a) and the second clear coating film (b) becomes strong.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 7/24 301 B05D 7/24 301R 302 302P 302S 302U

Claims (5)

[Claims] 1. A metallic base paint or a solid base paint is applied, and then a first clear paint is applied on the metallic base paint or the solid base paint, and a second base paint is applied.
In the method of forming a coating film by coating and baking a clear coating material, (a) the first clear coating material is obtained by polymerizing (A) a monomer having a secondary hydroxyl group, and OH derived from the secondary hydroxyl group.
Having a valency of at least 20 and 10 to 20% by weight of the (B) melamine resin have a number average molecular weight of 2,000.
A melamine resin as described above, which is a thermosetting clear coating containing (b) a second clear coating, which is a thermosetting clear coating containing polyepoxy and polyacid. Forming method. 2. The coating film forming method according to claim 1, wherein the second clear coating composition (b) comprises (A) an acid anhydride-modified group obtained by half-esterifying an acid anhydride group and an epoxy group. The reaction, and the heat (B) the reaction of the acid anhydride group or the acid anhydride-modified group with the epoxy group and the reaction of the acid anhydride group or the acid anhydride-modified group with the hydroxyl group as the main reaction for curing. A method for forming a coating film, which is a curable clear coating material. 3. A method for forming a coating film, which comprises applying the first clear paint (a) according to claim 1 or 2 and preheating. 4. A method for forming a coating film, which comprises coating the first clear coating composition (a) according to claim 1 or 2 and curing and baking. 5. The coating film forming method according to claim 1, wherein the acrylic resin (A) contained in the first clear coating composition (a) has an OH value of 90 to 150. An acid value of 3 to 10, (i) a (meth) acrylic acid ester, and (meth)
30 to 84.9% by weight of a short-chain (meth) acrylic acid ester in which the position of the carbon atom farthest from the acryloyloxy group is 4 or less in terms of the number of atoms directly bonded to the (meth) acryloyloxy group. (Ii) an α, β-ethylenically unsaturated monomer,
The position of the carbon atom farthest from the β-ethylenically unsaturated group is within 6 in terms of the number of atoms directly bonded to the α, β-ethylenically unsaturated group, and is short chain α other than (i) above. , Β-ethylenically unsaturated monomer in an amount of 0 to 40% by weight, and (iii) a hydroxyl group-containing ethylenically unsaturated monomer containing at least one secondary hydroxyl group-containing ethylenically unsaturated monomer or a mixture thereof. 15 to 40%, (iv) 0.1 to 5% by weight of an acid group-containing ethylenically unsaturated monomer, (v) an ethylenically unsaturated monomer other than the above (i) to (iv) Is a polymer obtained by polymerizing 0 to 34.9% by weight of acrylic resin (A)
/ Melamine resin (B) weight ratio is 80/20 to 50/5
A coating film forming method, wherein the coating film forming method is 0.