JP2002035677A - Method for forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a coating film by which an excellent finished appearance is obtained at the time of coating an automotive body, etc., in a three coat-one bake method for applying an intermediate coating, applying a base coating and a clear coating by a wet-on-wet system and baking and curing the three layers at the same time. SOLUTION: The intermediate coating, base coating and clear coating are successively applied on a base material coated by electrodeposition, and the applied three layers are simultaneously baked and cured to form the coating film. The intermediate coating consists of, by weight, 10-70% hydroxy-containing resin, 10-70% curing agent capable of reacting with the hydroxy and 18-50% nonaqueous dispersion resin, based on the total amount of solid resin, and further contains a pigment. Further, the volume contraction rate of the coating film is controlled to <=45%, when the film is cured at 140 deg.C for 30 min after coating.

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 multi-layer coating film on an electrodeposition-coated material such as an automobile body, and more particularly, to a method of applying an intermediate coating to an automobile body or the like. The present invention relates to a method of applying a base paint and a clear paint by a wet-on-wet method and baking and curing at a time to form a multilayer coating film by a so-called three-coat one-bake coating system.

[0002]

2. Description of the Related Art Automobile bodies and the like are subjected to a chemical conversion treatment using zinc phosphate or the like as a coating base on the surface of a steel sheet to be coated, and then to a base coat, a middle coat and a top coat, to form a double coat. A layer coating is formed. Of these, the coating process is usually performed by applying an undercoat by electrodeposition coating, baking and curing to form an undercoat film, applying an intermediate coating film thereon, baking and curing to form an intermediate coating film. ,
The top coat is applied, and the undercoat, intermediate coat and top coat are baked and hardened separately after each coating.

When a base paint and a clear paint are used as a top coat, an intermediate paint is applied, baked and cured, and then the base paint and the clear paint are wet-coated.
It is performed by a so-called three-coat two-bake method, in which the coating is applied by an on-wet method and then baked and cured at a time.

[0004] Such a three-coat two-bake method has a problem that the total cost is high because the coating step is long and the energy consumption is large. Japanese Patent Publication No. 59-3303
No. 3 discloses a metallic coating method in which an undercoat is applied by electrodeposition coating, baking is performed, and then an intermediate coating and a metallic coating are applied and baking is performed at the same time. However, when this method is performed using the conventional intermediate coating, there is a problem that the finished appearance is inferior to the three-coat two-bake method in which the intermediate coating is applied and then baked and cured once. Was.

[0005] Japanese Patent Application Laid-Open No. 10-5680 discloses an intermediate coating and / or a metallic base coating to which a crosslinkable polymer fine particle (microgel) is added, which is applied with a wet coating. Apply metallic base paint and clear paint in on-wet method,
A method of simultaneously baking and curing an intermediate coating, a metallic base coating, and a clear coating is described. These crosslinkable polymer fine particles (microgels) are added for the purpose of preventing each paint from being mixed at the interface of the coating to make the interface unclear, and have high sharpness and gloss. The appearance of the coating is obtained.

However, this method can provide a sufficient coating appearance when painting a small area and a portion that is not conspicuous, such as when a part of an automobile body is painted with a different color. When all the outer plates were coated by this method, the finished appearance was insufficient.

By the way, non-aqueous dispersion resin (N
AD) has been used for metallic coating of equipment, automobiles, etc. because of its low pollution, resource saving, and excellent coating workability and durability due to its flow characteristics. JP-A-57-177068 discloses a non-aqueous dispersible resin coating composition containing dispersed particles obtained by graft-polymerizing a monomer component in the presence of an acrylic copolymer. According to this, a coating film having excellent surface hardness and impact resistance can be obtained by dispersing the dispersed particles in the coating film even after curing to form a non-uniform structure.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of applying a base coat and a clear paint in a wet-on-wet system when applying an electrodeposition-coated material such as an automobile body. And a method of simultaneously baking and curing three layers of an intermediate coating, a base coating, and a clear coating. The coating can provide an excellent finished appearance equal to or better than the conventional three-coat two-bake method. An object of the present invention is to provide a film forming method.

In the case of the conventional three-coat two-bake method in which baking and curing are performed after the application of an intermediate coating, the inventors have found that the base material has high concealing properties, that is, the electrodeposition formed by the electrodeposition coating. Roughness on the surface of the paint film does not have much effect on the paint film coated with the base paint and clear paint after applying and curing the intermediate paint, but wet after applying the intermediate paint without baking and curing. -In the case of a three-coat one-bake method in which a base paint and a clear paint are applied in an on-wet method and three layers are simultaneously baked and cured, the base coat concealing property is low, and the electrodeposition coating film formed by the electrodeposition paint is used. It has been found that the rough surface greatly affects the final appearance of the finished product, and that the skin appears smooth. In order to improve the concealing property of the base for the electrodeposited coating, (1) the base paint and the clear paint in the case where the base paint and the clear paint are applied by a wet-on-wet method after applying the intermediate paint. Reducing the solvent swelling ratio of the intermediate coating by the solvent contained in the coating. (2) In the process of baking and curing the intermediate coating, the base coating, and the clear coating, the solvent evaporates and the volume of the coating decreases. (3) In the process of baking and curing the intermediate paint, base paint and clear paint, the viscosity initially decreases as the temperature rises, and increases when the curing starts. However, by reducing the minimum viscosity in the baking process, it is important that the coating film has flowability even if it shrinks in volume. Considered to be found that the inclusion of non-aqueous dispersion resin (NAD) as a component of intermediate coating, and completed the present invention.

[0010]

According to the present invention, there is provided a step of sequentially applying an intermediate coating, a base coating and a clear coating on an electrodeposited material, and baking the three coated layers at once. A method of forming a coating film comprising a step of curing, wherein the intermediate coating composition has a solid content ratio based on the total resin solid content of 10 to 70% by mass of a hydroxyl group-containing resin (a) and a curing agent capable of reacting with a hydroxyl group ( b) 10 to 70% by mass and non-aqueous dispersion resin (c) 18 to 50% by mass, further containing a pigment,
A coating film forming method characterized in that the volume shrinkage when cured at 0 ° C. for 30 minutes is 45% or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The coating film forming method of the present invention, on the electrodeposited material,
It comprises a step of sequentially applying an intermediate coating, a base coating, and a clear coating, and a step of baking and curing the three coated layers at a time.

[0012]Intermediate paint  In the present invention, the intermediate coating is based on the total resin solid content.
In terms of solid content ratio, hydroxyl group-containing resin (a) 10 to 70 mass
%, A curing agent (b) capable of reacting with a hydroxyl group, 10 to 70% by mass
And non-aqueous dispersion resin (c) 18 to 50% by mass
And further containing a pigment. The above hydroxyl
The group-containing resin (a) contains a hydroxyl group and has an intermediate coating composition.
Means those that dissolve in the medium used for the product, for example,
Acrylic resin and / or polyester resin
You. Acrylic because it can be designed with high SP value
It is preferable to use a resin. With the above polyester resin
The polyol and the polycarboxylic acid or its anhydride
Can be used.

The hydroxyl group-containing resin (a) has a hydroxyl value of 5
0-250, acid value 1-50 mgKOH / g, SP value 9.
What is 5-12 is preferable. Hydroxyl value, acid value and S
If the P value exceeds the upper limit of these ranges, the water resistance of the coating film decreases. If the hydroxyl value and the acid value are less than the lower limits, the curability of the paint will be reduced, and if the SP value is less than the lower limits, the paint will be compatible with the base paint. The hydroxyl group-containing resin (a) has a number average molecular weight of 1,000 to 1,000.
0, but preferably 1100 to 5000, more preferably 1200 to 3000. By using the one in the above range, the intermediate coating can be made a high solid type, so that the volume shrinkage upon baking and curing is reduced, and the finished appearance of the coating film can be improved.

In the present specification, the SP value is called a solubility parameter and indicates a measure of solubility. The SP value was written by SUH and CLARKE.
J. Polymer Science, A-1, 5th
Volume, pages 1671 to 1681 (1967). That is, at a measurement temperature of 20 ° C.,
As a sample, 0.5 g of a resin was weighed into a 100 mL beaker, and 10 mL of a good solvent was added using a whole pipette.
Dissolve with a magnetic stirrer. Dioxane and acetone are used as good solvents, and n
-Use hexane and ion-exchanged water. The turbid point measurement is 50
The poor solvent was added dropwise using a mL burette, and the point at which turbidity occurred was taken as the amount of addition. The SP value δ of the resin can be calculated by the following equation. δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) / (V _ml ^1/2 + V
^{_{mh 1/2) V m = V 1}} V 2 / (φ 1 V 2 + φ 2 V 1) δ m = φ 1 δ 1 + φ 2 δ 2 V i: solvent molecular volume (mL / mol) φ _i: turbidity point Δ _i : SP value of solvent ml: low SP value poor solvent mixture system MH: high SP value poor solvent mixture system

The above-mentioned hydroxyl group-containing resin (a) contains 10 to 70% by mass of the solid content based on the total solid content of the resin. When the amount is less than 10% by mass, the obtained coating film becomes brittle or the appearance of the coating film is deteriorated, so that the basic performance of the coating film is inferior. If it exceeds 70% by mass, the blending ratio of the non-aqueous dispersion resin (c) is reduced, and as a result, the finished appearance of the coating film is reduced. Preferably, it is 10 to 50% by mass, more preferably 20 to 50% by mass.

The intermediate coating composition contains a curing agent (b) which can react with a hydroxyl group. The curing agent (b) is not particularly limited, and includes, for example, a melamine resin and / or a blocked isocyanate resin. The curing agent (b) has a solid content of 10 to 7 with respect to the total resin solid content.
0% by mass. If the amount is less than 10% by mass, curing may be insufficient, and the physical properties of the coating film may be poor.
If it exceeds 70% by mass, it is uneconomical and the finished appearance of the coating film deteriorates. Preferably, 20 to 50% by mass
It is. The combination of the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with a hydroxyl group is not particularly limited,
It is preferable to combine an acrylic resin and / or a polyester resin with a melamine resin from the viewpoint of pigment dispersibility and workability.

The above intermediate coating composition contains a non-aqueous dispersion resin (c). The non-aqueous dispersion resin (c) comprises a core portion having a high SP value and a shell portion having a low SP value. Since the core has a high SP value, it is insoluble in the solvent in the paint, so that the swelling ratio due to the solvent can be reduced, and furthermore, the color reversion caused by subtle mixing with the base coating film. Can be prevented. The shell part having a low SP value functions as a dispersion stabilizer. Further, since the non-aqueous dispersion resin (c) is a non-crosslinked particle, the minimum viscosity during baking can be reduced. Also, the particles themselves can be cross-linked by the curing agent (b) capable of reacting with the above-mentioned hydroxyl group. In this case, the particles can be used as a component for forming a coating film. Accordingly, the non-aqueous dispersion resin (c) has a large undercoat concealing property of the electrodeposition coating film, can suppress unpleasant skin, and has sharpness,
A coating film appearance with high gloss can be obtained.

JP-A-10-5680 discloses the addition of crosslinkable polymer microparticles (microgels) to an intermediate coating composition, which is added as a viscosity-imparting agent and blends between layers. To prevent inversion and inversion,
The purpose of the present invention is to obtain a coating film having high sharpness and gloss. However, since the particles themselves are crosslinked and cannot be a coating film forming component, the addition amount is limited to 15% by mass or less, and as a result, the ratio contributing to the reduction of the swelling ratio due to the solvent is reduced. It was small.

The non-aqueous dispersion resin (c) of the present invention
Also acts as a viscosity-imparting agent, prevents conformation or inversion between layers, and provides a coating film with high sharpness and gloss. Furthermore, this is a non-crosslinked particle having a core portion with a high SP value, and can be added in a high amount, so that not only the ratio contributing to the reduction of the swelling ratio due to the solvent is large, but also the intermediate coating. The crosslinkable polymer fine particles (the above-described crosslinkable polymer fine particles ( Microgel).

The non-aqueous dispersion resin (c) is
The SP value is 11 to 14, and the S value of the core portion and the shell portion is
It is preferable that the difference between the P values is 0.5 to 3. If the difference in SP value is less than 0.5, the non-volatile content of the paint cannot be reduced, and the coating will dissolve and swell, and the viscosity control effect of the core portion will be low. , And furthermore, the film becomes compatible with the base paint, and a coating film having an excellent finished appearance cannot be obtained. If the SP value difference exceeds 3, dispersion may become unstable, separation may occur, or the intermediate coating and the base coating may be mixed to cause inversion or cracking. Preferably, the difference in SP value is 1-3. The relationship between the SP value of the hydroxyl group-containing resin (a) and the SP value of the non-aqueous dispersion resin (c) is such that the compatibility with the base paint can be suppressed. Is preferably higher.

The non-aqueous dispersion resin (c) has a hydroxyl value of 100 to 400, preferably 130 to 400.
300. If it is less than 100, the curability of the coating material will decrease, and if it exceeds 400, the water resistance may decrease. The acid value is from 0 to 200 mgKOH / g, preferably from 0 to 50 mgKOH / g. 200mgK
If it exceeds OH / g, the water resistance of the coating film decreases. Average particle size (D _50), 0.05 to 5 [mu] m, preferably 0.05 to 1 [mu] m. If it is less than 0.05 μm, the non-volatile content of the coating material is reduced, and if it exceeds 5 μm, the effect of controlling the viscosity is poor and the appearance is poor. The Tg of the dispersion stable resin is preferably 30 ° C. or lower. If it exceeds 30 ° C., the appearance of the coating film is inferior and the chipping resistance is reduced.

The non-aqueous dispersion resin (c) is
By polymerizing a polymerizable monomer in a mixture of a dispersion stable resin and an organic solvent, non-crosslinked resin particles insoluble in this mixture can be prepared. The dispersion-stable resin constitutes the shell part, and the copolymerized polymerizable monomer constitutes the core part.

The polymerizable monomer is preferably a monomer having a functional group. The monomer having a functional group can form a three-dimensionally cross-linked coating film by reacting the obtained non-aqueous dispersion resin with the curing agent (b) capable of reacting with the hydroxyl group. Representative examples of the polymerizable monomer having the above functional group are as follows. As those having a hydroxyl group, for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate,
Examples thereof include hydroxybutyl (meth) acrylate, hydroxymethyl (meth) acrylate, allyl alcohol, and adducts of hydroxyethyl (meth) acrylate with ε-caprolactone.

On the other hand, those having an acid group include those having a carboxyl group, a sulfonic acid group and the like, and examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propyl Acrylic acid, isopropyl acrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like can be mentioned. Examples of those having a sulfonic acid group include t-butylacrylamide sulfonic acid. When a polymerizable monomer having an acid group is used, a part of the acid group is preferably a carboxyl group. Further, a glycidyl group-containing unsaturated monomer such as glycidyl (meth) acrylate, m-isopropenyl-
Isocyanate group-containing unsaturated monomers such as α, α-dimethylbenzyl isocyanate and isocyanatoethyl acrylate are also included.

Other polymerizable monomers include, for example,
Methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate,
T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
(Meth) alkyl acrylates such as n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate and tridecyl methacrylate; acrylic acid or methacrylic acid ester monomers having an oil fatty acid and an oxirane structure (E.g., an addition reaction product of stearic acid and glycidyl methacrylate); an addition reaction product of an oxirane compound containing an alkyl group having at least C ₃ and acrylic acid or methacrylic acid; styrene, α-methylstyrene, o- Methyl styrene, m-methyl styrene, p-methyl styrene, pt-butyl styrene; benzyl (meth) acrylate; itaconic acid ester (dimethyl itaconate); maleic acid ester (dimethyl maleate); fumaric acid ester (Dimethyl fumarate, etc.); , Acrylonitrile, methacrylonitrile; methyl isopropenyl ketone; vinyl acetate; veoba monomer (trade name, manufactured by Shell Chemical Company), vinyl propionate, vinyl pivalate, vinyl propionate; ethylene, propylene, butadiene, N, N-dimethylaminoethyl Acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, vinylpyridine and the like can be mentioned. The above-mentioned polymerizable monomers can be used alone or in combination of two or more of those having a functional group and other monomers.

The above polymerizable monomer is preferably copolymerized in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2'-azobisisobutyronitrile and 2,2'-azobis (2,4-dimethylvaleronitrile); benzoyl peroxide, lauryl peroxide And a peroxide-based initiator such as t-butyl peroctoate. The amount of these initiators to be used is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 5 parts by mass per 100 parts by mass of the total of the polymerizable monomers. In general, the polymerization reaction in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

The dispersion-stable resin to be present when the above-mentioned polymerizable monomer is copolymerized is not particularly limited as long as it can stably synthesize a non-aqueous dispersion resin in an organic solvent. Specifically, the hydroxyl value is 10 to 25.
0, preferably 20 to 180. If it is less than 10, the curability, adhesion, stability and the like will be reduced, and if it exceeds 250, the dispersion will be unstable. Acid value is 0-100mgK
OH / g, preferably 0 to 50 mgKOH / g.
If it exceeds 100 mgKOH / g, the water resistance of the coating film decreases. The number average molecular weight is 2000 to 1
0000 is preferred. If it is less than 2,000, dispersion becomes unstable, and if it exceeds 10,000, the non-volatile content of the coating material decreases.

The method for producing the dispersion-stable resin is not particularly limited, and examples thereof include a method obtained by radical polymerization in the presence of a radical polymerizable initiator, a method obtained by a condensation reaction and an addition reaction, and the like. As the dispersion stable resin, an acrylic resin, a polyester resin, a polyether resin, a polycarbonate resin, a polyurethane resin, or the like can be used. The monomer used to obtain the dispersion-stable resin can be appropriately selected according to the properties of the resin, but has a functional group such as a hydroxyl group or an acid group used in the polymerizable monomer. It is preferable to use a monomer, and if necessary, a monomer having a functional group such as a glycidyl group or an isocyanate group may be used. The monomer having a functional group can form a three-dimensionally cross-linked coating film by reacting the obtained non-aqueous dispersion resin with the curing agent (b).

The monomer used to obtain the above-mentioned dispersion-stable resin preferably has a side chain having 10 or more carbon atoms in an amount of 10 to 50% by mass based on the total amount of the monomer. If the content is less than 10% by mass, conformity with the base paint occurs. If it exceeds 50% by mass, separation may occur in the intermediate coating, or the intermediate coating and the base coating may be mixed to cause inversion or cracking.

Further, it is preferable that the above monomer has a hydrophilic group in an amount of 20 to 50% by mass based on the total amount of the polymerizable monomer. If the amount is less than 20% by mass, the curability, adhesion and stability may be poor. If it exceeds 50% by mass, the dispersibility may be unstable. Examples of the hydrophilic group include a hydroxyl group, a carboxyl group, an amide group, and an ether group.

The ratio of the above-mentioned dispersion stabilizer to the above-mentioned polymerizable monomer can be arbitrarily selected according to the purpose. For example, based on the total mass of both components, the dispersion-stabilizing resin is 3%.
-80 mass%, preferably 5-60 mass%, and the polymerizable monomer is 97-20 mass%, preferably 95-40 mass%. Further, the total concentration of the dispersion stabilizer and the polymerizable monomer in the organic solvent is 30 to 80% by mass, preferably 40 to 60% by mass based on the total mass.

The non-aqueous dispersion resin (c) thus obtained contains 18 to 50% by mass of the solid content based on the total solid content of the resin. If the amount is less than 18% by mass or more than 50% by mass, the appearance of the obtained coating film deteriorates. Preferably, it is 23 to 45% by mass.

The intermediate coating composition comprises the above-mentioned hydroxyl group-containing resin (a), a curing agent (b) capable of reacting with a hydroxyl group, and a non-aqueous dispersion resin (c), and further contains a pigment. The pigment is preferably contained in an amount of 10 to 70% by mass based on the total amount of the pigment and the solid content of the resin. In the present invention, the resin solid content means the total amount of the solid content of the hydroxyl group-containing resin (a), the curing agent (b) capable of reacting with the hydroxyl group, and the non-aqueous dispersion resin (c). When the amount is less than 10% by mass, the obtained intermediate coating composition cannot be made into a high solid type, and when baked and cured, the volume shrinkage becomes large and the finished appearance may be inferior. If it exceeds 70% by mass, the appearance of the coating film is deteriorated because the amount of the pigment is too large.

The above-mentioned pigments are not particularly restricted but include those used in conventional intermediate coatings, such as azo chelate pigments, insoluble azo pigments, condensed azo pigments,
Organic color pigments such as phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like; graphite, yellow iron oxide, red iron oxide, carbon black And inorganic color pigments such as titanium dioxide. Further, extenders such as calcium carbonate, barium sulfate, clay and talc; and flat pigments such as aluminum powder and mica powder may be used in combination. As the above pigment, a standard gray intermediate paint having carbon black and titanium dioxide as main pigments can be used, or a so-called color combining a set gray or various color pigments combining lightness or hue with an overcoat paint. Intermediate paints can also be used.

In the present invention, the intermediate coating composition may contain conventionally known additives such as a viscosity control agent, an anti-bake agent and a diluting solvent. As the viscosity control agent, a swelling dispersion of fatty acid amide, amide-based fatty acid,
Polyamides such as phosphates of long-chain polyaminoamides; polyethylenes such as colloidal swelling dispersions of polyethylene oxide; organic bentonites such as organic acid smectite clay and montmorillonite; aluminum silicate, barium sulfate And the like; flat pigments which exhibit viscosity depending on the shape of the pigment.

The above-mentioned intermediate coating composition comprises a hydroxyl group-containing resin (a), a curing agent (b) and a non-aqueous dispersion resin (c) capable of reacting with a hydroxyl group, and a pigment or other components. It can be obtained by a method well-known to those skilled in the art such as kneading and dispersing. The nonvolatile content of the intermediate coating obtained in this way is 40% at the time of coating.
It is preferably about 70% by mass. If the amount is less than 40% by mass, the solvent is too large, so that a high-solids intermediate coating cannot be obtained, and the volume shrinkage increases, so that the finished appearance of the coating film may be poor. 70% by mass
If it exceeds, the viscosity of the coating is too high, so that the coating appearance is inferior,
Workability may be reduced. More preferably, 45 to
60% by mass.

In the present invention, the intermediate coating composition has a volumetric shrinkage of 45% or less when cured at 140 ° C. for 30 minutes after application. If it exceeds 45%, the base coat concealing property of the electrodeposition coating film is inferior, so that a coating film having a good finished appearance cannot be obtained. Preferably, it is at most 40%. In the present invention, the volume shrinkage when cured at 140 ° C. for 30 minutes can be obtained by the following equation. Volume shrinkage (%) = {(100-coating NV) / solvent specific gravity} / [{(100-coating NV) / solvent specific gravity} + (coating NV / dry coating specific gravity)} × 100 (wherein When the mass of the object to be coated before coating is W1, the mass of the object to which the coating is applied is W2, and the mass after drying at 140 ° C. for 30 minutes is W3, the coating NV ( %) = (W3-W1) / (W2-W1) × 1
Represents the value of the non-volatile content obtained by 00. The specific gravity of the solvent represents the specific gravity of the solvent contained in the intermediate coating composition. The specific gravity of the dried coating film is the specific gravity of the nonvolatile components in the paint, and is a value obtained by calculation from the specific gravity of each component and its ratio. )

In the method for forming a coating film of the present invention, the electrodeposition coating
On the material, apply the above intermediate paint, base paint and clear paint
-A step of sequentially applying the paint, and
Consists of baking and hardening the layers all at once.
You.Base paint  In the present invention, the base paint is not particularly limited,
For example, film-forming resins, curing agents, pigments and other additives
Those composed of additives can be mentioned. The above coating film formation
The hydrophilic resin is not particularly limited. For example, acrylic resin
Fat, polyester resin, alkyd resin, epoxy resin,
Urethane resins and the like, which are amino resins and / or
Or combined with a curing agent such as a blocked isocyanate resin
Used. In terms of pigment dispersibility and workability, acrylic
Resin and / or polyester resin and melamine resin
Combinations are preferred.

When the base paint is used as an aqueous paint, US Pat. No. 5,151,112 is used as a film-forming resin.
No. 5, No. 5,183,504 and the like can be used. In particular, US Pat.
A film-forming resin obtained by combining an acrylic resin having an acrylamide group, a hydroxyl group and an acid group described in JP-A-83504 with a melamine resin is excellent in finish and appearance performance.

The above base paint can be used as a metallic base paint by adding a glittering pigment, or by blending a coloring pigment such as red, blue or black and / or an extender pigment without blending the glittering pigment. Can be used as a solid base paint. The glitter pigment is not particularly limited, for example, a non-colored or colored metallic glitter material such as a metal or an alloy and a mixture thereof,
Examples include interference mica powder, colored mica powder, white mica powder, graphite, and colorless colored flat pigments. A non-colored or colored metallic brilliant material such as a metal or an alloy, and a mixture thereof are preferable since a coating film having excellent dispersibility and high transparency can be formed. Specific examples of the metal include aluminum, aluminum oxide,
Examples thereof include copper, zinc, iron, nickel, and tin.

The shape of the glitter pigment is not particularly limited.
Further, it may be colored, but for example, has an average particle size (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm
Is preferable. Average particle size 10-35μ
Those having a range of m are excellent in glitter and are more preferable. The pigment concentration (PWC) of the glitter pigment in the base paint is generally 23% by mass or less. When the content exceeds 23% by mass, the appearance of the coating film is deteriorated. Preferably, it is 0.01 to 20% by mass, more preferably 0.01 to 18% by mass.

As the pigments other than the above-mentioned glittering pigments, the coloring pigments and extenders described in the intermediate coating can be used. As the pigment, one or a combination of two or more of a brilliant pigment, a coloring pigment and an extender pigment can be used. Pigment concentration (PWC) in base paint including the above-mentioned brilliant pigments and all other pigments
Is generally 0.1 to 50% by mass, preferably 0.5 to 40% by mass, and more preferably 1 to 30% by mass. If it exceeds 50% by mass, the appearance of the coating film is reduced.

In general, the base paint is preferably of a solution type, and if it is a solution type, it may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion) or a non-aqueous type. As other additives used in the base paint and a method for preparing the base paint, those exemplified for the intermediate paint can be exemplified. The non-volatile content of the base paint thus obtained is 30 at the time of painting.
To 60% by mass, more preferably 4% by mass.
0 to 50% by mass. If the amount is less than 30% by mass, the amount of the solvent is too large, so that a high solid paint cannot be obtained, and the volume shrinkage becomes large, so that the finished appearance of the coating film may be poor. If it exceeds 60% by mass, the viscosity is too high, so that the appearance of the coating film may be poor or the workability may be low.

[0044]Clear paint  The clear coating film contains a glitter pigment as a base paint.
Due to glitter pigments when using tallic base paint
Smoothes the unevenness and flicker of the base coating film.
It is also formed to protect the base coating.
You. In the present invention, the clear paint is not particularly limited.
However, for example, film-forming resins, curing agents and other additives
Those composed of additives can be mentioned. The above coating film formation
The hydrophilic resin is not particularly limited. For example, acrylic resin
Fat, polyester resin, epoxy resin, urethane resin, etc.
These are amino resins and / or block resins.
Used in combination with a curing agent such as socyanate resin
You. Acrylic from the viewpoint of transparency or acid etching resistance
Of resin and / or polyester resin and amino resin
Has a combination or carboxylic acid / epoxy curing system
Acrylic resin and / or polyester resin
Is preferred.

The above-mentioned clear paint contains a viscosity control agent as an additive in order to apply it in an uncured state after applying the above-mentioned base paint, and to prevent break-in, inversion or sagging between layers. Is preferred. The amount of the viscosity control agent to be added is 0.01 to 10 parts by mass, preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the resin solid content of the clear paint.
The amount is from 02 to 8 parts by mass, more preferably from 0.03 to 6 parts by mass. If the amount is more than 10 parts by mass, the appearance is deteriorated. If the amount is less than 0.1 part by mass, the effect of controlling the viscosity cannot be obtained, which causes problems such as sagging. As the coating form of the clear coating, there are organic solvent type, aqueous type (water-soluble, water-dispersible,
Emulsion), non-aqueous dispersion type or powder type, and if necessary, a curing catalyst, a surface conditioner and the like can be used.

As a method for preparing the clear coating, the method exemplified for the intermediate coating can be exemplified.
In the case of the solution type, the non-volatile content of the clear paint is 4 at the time of painting.
It is preferably from 0 to 70% by mass, more preferably from 45 to 60% by mass. If the amount is less than 40% by mass, the amount of the solvent is too large, so that a high solid paint cannot be obtained, and the volume shrinkage becomes large, so that the finished appearance of the coating film may be poor. If it exceeds 70% by mass, the viscosity is too high, so that the appearance of the coating film may be poor or the workability may be low. In the present invention, it is more preferable to use a high solid type paint as the intermediate coating, the base coating, and the clear coating. By using high solid type base paint and clear paint as well as the above intermediate paint, the total volumetric shrinkage can be reduced when applied by 3 coats and 1 bake method. A coating film having a very excellent appearance can be obtained.

[0047]Base material  The coating film forming method of the present invention is applied to an electrodeposited material.
Applicable. Electrodeposition used for the above electrodeposition coating
Use cationic and anionic paints
Can be A coating film with excellent corrosion protection can be obtained
Thus, the cationic type is preferable. Perform electrodeposition coating
The material is not particularly limited. For example, iron, copper, aluminum
Minium, tin, zinc, etc .; alloys containing these metals and
Castings. Specifically, cars, trucks,
Automobile bodies and parts such as motorcycles and buses
You. These metals are pre-reset before electrodeposition coating is performed.
Chemical conversion treatment with phosphate, chromate, etc. is particularly preferred.
New

[0048]Painting method  The coating film forming method of the present invention comprises the above-mentioned electrodeposition-coated material.
On top, intermediate paint, base paint and clear paint
It includes the step of painting. As the above painting method
Not particularly limited, for example, commonly referred to as "react gun"
Air electrostatic spray; commonly known as "micro-micro"
(Μμ) bell ”,“ micro (μ) bell ”,
Use a rotary atomizing electrostatic coating machine called
And can be performed. Preferably, a rotary atomizing type
This is a method using an electrostatic coating machine or the like. Use the base paint
Enhance design when painting on vehicle bodies, etc.
Multi-stage painting by air electrostatic spray
Preferably, paint on two stages, or air electrostatic
Combine play with the above rotary atomizing electrostatic coating machine
It is preferable to carry out by a coating method.

The dry film thicknesses of the above-mentioned intermediate coating, base coating and clear coating vary depending on the application, but are respectively 5 to 40 μm for the intermediate coating and 5 to 35 μm for the base coating.
m, clear coating film is 10 to 70 μm. If the dry film thickness exceeds the upper limit, the sharpness may be reduced, or irregularities may occur during coating, and problems such as flow may occur.If the dry film thickness is below the lower limit, the underlayer cannot be concealed and the film may break. . In the present invention, to sequentially apply the intermediate coating, the base coating, and the clear coating means that the intermediate coating, the base coating, and the clear coating are applied in this order on a wet-on-wet basis. It suffices not to include a step of baking and curing the coating film, the base coating film, and the clear coating film separately at 100 ° C. or higher. Therefore, before applying the base coating and / or before applying the clear coating, a step of leaving the coating at room temperature for a certain period of time, or previously drying the coating by heating, for example, at a temperature lower than 60 to 100 ° C. for 2 to 10 minutes. And such a method is also one of the present invention. In particular, when the base paint is used as an aqueous paint, it is preferable to dry the coating film before applying the clear paint, since a good finished appearance can be obtained.

The method for forming a coating film of the present invention comprises the following three steps: the intermediate coating, the base coating and the clear coating.
This involves baking and hardening the layers at once.
The temperature for baking and hardening is 110 to 180.
By carrying out at a temperature of 120 ° C., preferably 120 to 160 ° C., a cured coating film having a high degree of crosslinking can be obtained. 180
If the temperature exceeds 100 ° C., the coating becomes hard and brittle, and if it is lower than 110 ° C., the curing is not sufficient. The curing time varies depending on the curing temperature, but is suitably from 120 to 160 ° C. for 10 to 60 minutes. The thickness of the multilayer coating film obtained by the coating film forming method of the present invention is usually 30 to 300 μm, preferably 50 to 25 μm.
0 μm. If it exceeds 300 μm, the physical properties of the film such as a thermal cycle decrease, and if it is less than 30 μm, the strength of the film itself decreases.

The method for forming a coating film of the present invention is excellent in base layer concealing property and can provide a coating film having a good finished appearance. Furthermore, since the baking process of the intermediate coating paint can be omitted as compared with the conventional three-coat two-bake method, the coating process can be shortened, and the energy consumption can be reduced. Can be significantly reduced.

[0052]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In Examples, "parts" represents parts by mass. Synthesis Example 1 Synthesis of Acrylic Resin 1 A container equipped with a stirrer, a temperature controller and a reflux condenser was charged with 82 parts of xylene, and then a solution having the following composition: 4.5 parts of methacrylic acid 26.0 parts of ethyl acrylate FM-1 64.5 parts (hydroxyl-containing monomer manufactured by Daicel Chemical Industries, Ltd.) MSD-100 5.0 parts (Methylstyrene dimer manufactured by Mitsui Toatsu Chemicals) 20 parts of azoisobutyronitrile 13.0 parts are added. The mixture was heated with stirring to increase the temperature. While refluxing, the remaining 93.0 of the mixed solution
Then, a solution consisting of 1.0 part of azoisobutyronitrile and 12 parts of xylene was added dropwise over 30 minutes. After the reaction solution was further stirred and refluxed for 1 hour, 63 parts of the solvent was distilled off under reduced pressure to terminate the reaction.
Acrylic resin varnish 1 having a solid content of 75% and a number average molecular weight of 2,000 was obtained.

Synthesis Example 2 Synthesis 2 of Acrylic Resin 300 parts of toluene and methyl isobutyl ketone (MIB) were placed in a vessel equipped with a stirrer, a temperature controller, and a reflux condenser.
K) 100 parts were charged and heated with stirring to raise the temperature. When the temperature rose to 105 ° C., a solution having the following composition was dropped at a constant speed over 3 hours while refluxing. Styrene 50.0 parts Methyl methacrylate 300.0 parts Ethyl methacrylate 79.0 parts Ethyl acrylate 444.0 parts 2-hydroxyethyl methacrylate 104.0 parts Methacrylic acid 23.0 parts Toluene 400.0 parts t-butyl 7.0 parts of peroxy-2-ethylhexanoate After aging for 30 minutes, a solution composed of 200 parts of toluene and 3 parts of t-butylperoxy-2-ethylhexanoate was dropped at a constant speed for 30 minutes. The reaction solution was further stirred and refluxed for 1 hour to increase the rate of change into a resin, and then the reaction was terminated to obtain an acrylic resin varnish 2 having a solid content of 50% and a number average molecular weight of 21,000.

Synthesis Example 3 Synthesis of Polyester Resin A reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen inlet pipe, a water separator, and a rectification tower was charged with 258 hexahydrophthalic anhydride.
Parts, 184 parts of isophthalic acid, trimethylolpropane 2
13 parts, 180 parts of neopentyl glycol, 72 parts of neopentyl glycol hydroxypivalate, and 94 parts of Kadura E (glycidyl versatic acid ester manufactured by Shell Chemical Co., Ltd.) were charged and heated. After the raw materials have been melted and stirred, dibutyltin oxide 0.2
And stirring was started, and the temperature of the reaction tank was raised from 180 ° C. to 2
The temperature was raised to 20 ° C. over 3 hours while maintaining a constant rate of temperature increase. The generated condensed water was distilled out of the system. When the temperature reached 220 ° C., the temperature was maintained for 1 hour, and 17 parts of xylene was gradually added as a refluxing solvent in the reaction vessel to allow the condensation reaction to proceed in the presence of the solvent. When the resin acid value reaches 10.0,
After cooling to 150 ° C., 182 parts of Praxel M (ε-caprolactone, manufactured by Daicel Chemical Industries, Ltd.) were added dropwise, and the mixture was kept warm for 1 hour and then cooled to 100 ° C. Further, 264 parts of xylene was added, the solid content was 79%, the number average molecular weight was 1,400, and the acid value was 8.
0 (mgKOH / g) and a polyester resin solution having a hydroxyl value of 210 were obtained.

Synthesis Example 4 Synthesis of Nonaqueous Dispersion Resin (a) Production of Dispersion Stable Resin A vessel equipped with a stirrer, a temperature controller and a reflux condenser was charged with 90 parts of butyl acetate, and then a solution having the following composition: Methyl methacrylate 38.9 parts Stearyl methacrylate 38.8 parts 2-Hydroxyethyl acrylate 22.3 parts 20 parts of azoisobutyronitrile 5.0 parts were added, and the mixture was heated with stirring to increase the temperature. . At 110 ° C., the remaining 85 parts of the above mixed solution was added dropwise over 3 hours, and then a solution composed of 0.5 parts of azoisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion into a resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5,600 and an SP value of 9.5.

(B) Production of Non-Aqueous Dispersion Resin 35 parts of butyl acetate is charged into a container equipped with a stirrer, a temperature controller and a cooler, and the acrylic resin 60 obtained in the above (a) production of dispersion stable resin is prepared. The department was charged. Next, a solution having the following composition: styrene 7.0 parts methacrylic acid 1.8 parts methyl methacrylate 12.0 parts ethyl acrylate 8.5 parts 2-hydroxyethyl acrylate 40.7 parts azoisobutyronitrile 1.4 parts Was added dropwise at 100 ° C. for 3 hours, and then a solution consisting of 0.1 part of azoisobutyronitrile and 1 part of butyl acetate was added to 30 parts of
In minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 0.18 μm was obtained. This emulsion is diluted with butyl acetate,
A butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a non-aqueous dispersion resin content of 40% by mass having a particle size of 0.18 μm was obtained. The Tg of this non-aqueous dispersion resin is
At 23 ° C., the hydroxyl value was 162. The SP value is 11.
The difference between the SP value of the shell portion and the SP value of the core portion, which was a dispersion-stable resin, was 2.3.

Embodiment 1Preparation of intermediate coating  The acrylic resin wafer obtained in Synthesis Example 1 was placed in a 2 L vessel.
328 parts of varnish 1 were put in, followed by CR-93 (Ishihara Sangyo
973 parts of Titanium Oxide, FW-200P (Degussa)
10 parts, and 159 parts of butyl acetate
And 82 parts of xylene. After that, the whole quality
The same amount of glass beads (product name GB503M, particle size 1.
6 mm) and dispersed for 3 hours with a desktop SG mill. The
The particle size at the end of dispersion with a lined gauge is 5 μm or less.
there were. Finally, about 10 minutes after adding 81.8 parts of xylene
Stir and filter the glass beads to make a pigment paste.
Was. The solid content ratio of the prepared paste is as shown in Table 2.
In this way, the resin, non-aqueous dispersion resin and hardener
Together, an intermediate coating was prepared.

[0058]Base paint and clear paint  As a base paint, SPM-13 having a nonvolatile content of 46%
00 black (Nippon Paint Co .; black base paint),
As a clear paint, MACO with a non-volatile content of 48%
-1330 (manufactured by Nippon Paint Co., Ltd.) was used.Dilution conditions  Each paint was diluted under the following conditions and painted. (Intermediate coating) Thinner: EEP (ethoxyethyl propionate) /
Xylene = 9/1119 seconds / No. 4 Ford Cup /
20 ° C (base paint) Thinner: EEP / S-100 (aromatic system manufactured by Exxon)
(Hydrocarbon solvent) / ethyl acetate = 8/7/5 20 seconds / No. 4 Ford cup / 20 ° C (clear paint) Thinner: EEP / S-150 (Axon aromatic product)
(Hydrocarbon solvent) = 1/122 seconds / No. 4 Fordka
/ 20 ° C

[0059]Painting method  Under the coating conditions shown in Table 1, an SPC dull steel plate (20 cm × 3
0cm x 0.8mm) Power Top V-20
Into Co., Ltd. cationic electrodeposition paint)
The electrodeposited cation-coated plate to the moving plate
Apply the intermediate coating while moving while attached, 10 minutes later
Apply base paint to the base, and base again after 2.5 minutes
Apply paint (two-stage painting), and then after 20 minutes, clear
Paint. Painted intermediate coating film, base coating film
And clear coating is baked and cured at 140 ° C for 30 minutes
I let it.

[0060]

[Table 1]

[0061]Appearance evaluation  The appearance of the painted plate is compared with Big Chemie Wave Ski
The evaluation was made based on the value of the SW of Jan. The results are shown in Table 2. Number
A smaller value indicates that a better result was obtained.

[0062]Painted NV (Nonvolatile content) measurement method  Separate for intermediate coating, base coating and clear coating
And calculated according to the following method. Instrument: 5 cm × 1 aluminum foil whose mass (w1) was measured
Mask the one covered with a 0cm square holed paper
Attach to the iron plate with tape. Operation: Move this iron plate adjacent to the painted plate during the above painting
After attaching to the moving plate and applying paint, peel off the aluminum foil from the iron plate
You. NV measurement: Measure the mass (w2) of aluminum foil with paint
After the measurement, measure the mass (w3) after drying at 140 ° C. for 30 minutes.
I do. Calculation: The coating NV (%) is calculated from the following equation. Coating NV (%) = (w3-w1) / (w2-w1) × 1
Table 2 shows the obtained results.

[0063]Volume shrinkage calculation method  The volume shrinkage (%) is calculated according to the following equation. Volume shrinkage (%) = ｛(100-coated NV) / solvent ratio
Weight｝ / [｛(100-coating NV) / solvent specific gravity （+ (coating
NV / Dry coating specific gravity) x 100 Solvent specific gravity: From the solvent composition in the coating, the intermediate coating, clear
-The paint was 0.87 and the base paint was 0.86. Dry coating specific gravity: From each coating composition, intermediate coating 1.64,
Base paint 1.23 and clear paint 1.12. Total volume shrinkage (%) = Volume shrinkage of intermediate coating
X (dry film thickness of intermediate coating film / total dry film thickness) +
Volume shrinkage of base paint x (dry film thickness of base coating / toe
Dry film thickness) + volume shrinkage of clear paint x (clear
Table 2 shows the obtained results.

[0064]Solvent resistance test method  After applying the intermediate coating on a tin plate (20μm), 80 ℃
X 10 minutes to make a product with a raised NV,
Typical paint solvents S-150, Xylol, EE
Spot one drop of P, let stand for about 45 degrees after standing for 30 seconds
Condition was observed. ：: No change Δ: Swelling X: Dissolution The results obtained are shown in Table 2.

Examples 2 to 7 and Comparative Examples 1 to 3 In the same manner as in Example 1 except that the resin, the non-aqueous dispersion resin and the curing agent were blended so that the solid content ratio was as shown in Table 2. Then, prepare and paint the intermediate coating,
Measurement and evaluation were performed. The results are shown in Table 2.

[0066]

[Table 2]

In Table 2, Cymel 254 is a methyl-butyl mixed melamine resin (manufactured by Mitsui Cytec), Uban 20N-60 is a butylated melamine resin (manufactured by Mitsui Cytec), and Sumidur BL3175 is hexamethylene diisocyanate (HMDI). ) Blocked isocyanate (Sumitomo Bayer Urethane Co.).

The intermediate coatings of Examples 1 to 7 have a small volume shrinkage and are excellent in solvent resistance. Therefore, a base coating and a clear coating are applied thereon by a wet-on-wet method and baked and cured. In this case, the finished appearance was excellent. The intermediate coatings containing no non-aqueous dispersion resin of Comparative Examples 1 and 2 were inferior in solvent resistance, and were considered to be swollen by the solvent, and a good finished appearance was not obtained. . The intermediate coating composition of Comparative Example 3 had good solvent resistance, but had a low non-volatile content and a large volume shrinkage, so that a good finished appearance could not be obtained.

[0069]

According to the method for forming a coating film of the present invention, a coating film having an excellent finished appearance can be obtained when an automobile body or the like is coated by a three-coat one-bake method.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takuhiro Kakii 1-30 Nihookicho, Minami-ku, Hiroshima-shi, Hiroshima Japan Inside Paint Co., Ltd. (72) Inventor Hiroyuki Uemura 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Tsutomu Shigenaga 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-term (reference) 4D075 AE06 BB26Z BB28Z BB89X DB02 DC12 EA10 EA43 EC11

Claims (4)

[Claims] 1. a step of sequentially applying an intermediate coating, a base coating and a clear coating on an electrodeposited material;
A coating film forming method comprising a step of baking and curing the three painted layers at a time, wherein the intermediate coating composition has a solid content ratio based on the total resin solid content, and the hydroxyl group-containing resin (a) 10 to 10; 70% by mass, 10 to 70% by mass of a curing agent (b) capable of reacting with a hydroxyl group and 18 to 50% by mass of a non-aqueous dispersion resin (c), further containing a pigment, A method for forming a coating film, wherein the volume shrinkage when cured at 140 ° C. for 30 minutes is 45% or less. 2. The method according to claim 1, wherein the pigment is contained in the intermediate coating at 10 to 70% by mass based on the total amount of the pigment and the solid content of the resin. 3. The nonvolatile matter at the time of application of the intermediate coating is 40
The method for forming a coating film according to claim 1, wherein the amount is from 70 to 70 mass%. 4. The non-volatile content at the time of application of the base paint is 30 to
The coating film forming method according to claim 1, 2 or 3, wherein the content is 60% by mass, and the non-volatile content at the time of application of the clear paint is 40 to 70% by mass.