JP2002035681A - Method for forming coating film and material to be coated - 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, and the applied three layers are simultaneously baked and cured to form the coating film. In this case, the surface roughness (Ra) is limited to conform to 0.05<=Ra<=0.35, and the appearance (SW) of the surface of the coating film obtained by the baking and curing is controlled to SW<=20.

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 automobile body or the like.
A method in which a base paint and a clear paint are applied by an on-wet method and baked and cured at a time to form a multilayer coating film by a so-called three-coat one-bake coating system;
Further, the present invention relates to an object to be coated obtained thereby.

[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, in this method, since the metallic paint is applied without baking and hardening after the intermediate coating is applied, the finished appearance is compared with the three-coat two-bake method in which the intermediate coating is applied and then baked and hardened once. The problem that it was inferior was produced.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for applying a base coat and a clear paint in a wet-on-wet system by applying an intermediate coat when coating a material such as an automobile body. A method of simultaneously baking and curing three layers of a base paint and a clear paint, wherein a method of forming a coating film capable of obtaining an excellent or better finished appearance as compared with a conventional three-coat two-bake method,
Further, it is an object of the present invention to provide an object to be coated obtained thereby.

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 material, such as a coating film, does not have much effect on the coating film coated with the base paint and the clear paint after applying and curing the intermediate coating, but it does not perform baking and curing after applying the intermediate coating. In the case of a three-coat one-bake method in which a base paint and a clear paint are applied in a wet-on-wet method and three layers are simultaneously baked and cured, the undercoat concealment is low, and the surface roughness of the material surface is reduced to the final appearance. , Which greatly affected the appearance of the skin. Then, in the case of the three-coat one-bake method, it was found that the base concealing property had a high correlation with the surface roughness of the material itself, and the present invention was completed.

[0007]

According to the present invention, there is provided a method of manufacturing a material comprising:
A method for forming a coating film comprising 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, wherein the surface roughness (Ra) of the material is 0.05 ≦ Ra ≦ 0.35, and the appearance (SW) of the surface of the coating film obtained by baking and curing is SW ≦ 20.

[0008]

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 comprises a step of sequentially applying an intermediate coating, a base coating and a clear coating on a material, and a step of baking and curing the three coated layers at once.

In the present invention, the surface roughness (Ra) of the material is 0.05 ≦ Ra ≦ 0.35. In the case of the three-coat one-bake method, the surface roughness of the material has a great effect on the obtained multilayer coating film. Therefore, in the present invention, the material before the intermediate coating, the base coating and the clear coating are applied. By setting the surface roughness (Ra) of the above to the above range, the finished appearance of the multilayer coating film obtained by applying the intermediate coating material, the base coating material and the clear coating material and then baking and hardening at once is improved. Can be. Therefore, when the Ra of the material exceeds 0.35, a multilayer coating film having an excellent appearance cannot be obtained. Materials with Ra less than 0.05 are difficult to obtain in practice and are not practical.

Preferably, the surface roughness (Ra) of the material is 0.05 ≦ Ra ≦ 0.32. The surface roughness (Ra) is measured by Handysurf E-
30A (manufactured by Tokyo Seimitsu Co., Ltd.).

The raw material is not particularly limited as long as the surface roughness (Ra) is within the above range, and examples thereof include metal, glass, plastic, and foam. Examples of the metal products include iron, copper, aluminum, tin,
Zinc and the like; alloys and castings containing these metals; Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals may be previously subjected to a chemical conversion treatment with a phosphate, a chromate, or the like, and an electrodeposition coating film may be formed thereon by an electrodeposition paint. As the electrodeposition coating, a cationic type and an anion type can be used, but a cationic type electrodeposition coating is preferable because of its excellent anticorrosion property.

The electrodeposition paint is not particularly limited as long as the surface roughness (Ra) of the material on which the electrodeposition coating film is formed is within the above range, and a commercially available product can be used.

In the case of using an electrodeposited material as the above-mentioned material, it is preferable that the material is applied and then baked and cured at 150 ° C. or higher. For example, in the case of baking at 140 ° C. for about 10 minutes, the electrodeposition coating film swells due to the solvent in the intermediate coating applied thereon and the boundary surface becomes unclear, and the appearance of the obtained multilayer coating film is reduced. May be inferior. More preferably, it is baked and cured at 160 to 210 ° C. for 10 to 30 minutes.

In the present invention, the appearance (SW) of the surface of the coating film obtained by the above-mentioned baking and curing is such that SW ≦ 20. When the appearance (SW) of the surface of the obtained coating film exceeds 20, the skin becomes mushy and cannot be used for applications such as automobiles requiring a high appearance. Appearance (S
W) is a value measured by a wave scan manufactured by Big Chemie.

[0015]Intermediate paint  In the present invention, as the intermediate coating, a resin solid content
The hydroxyl group-containing resin (a) 10 to 10 in terms of solid content ratio based on the total amount
70% by weight, a hardener capable of reacting with a hydroxyl group (b) 10 to 7
0% by weight and non-aqueous dispersion resin (c) 18-5
Those comprising 0% by weight are preferred. The above non-water disperser
By using one containing John resin (c),
Solvent swelling of intermediate coating by solvent contained in base coating
Rate and the interface between the intermediate paint and the base paint
Can be prevented from mixing.
A coated film having an excellent finished appearance can be obtained.

The hydroxyl group-containing resin (a) means a resin containing a hydroxyl group and soluble in a medium used for an intermediate coating, and examples thereof include an acrylic resin and / or a polyester resin. It is preferable to use an acrylic resin because it can be designed to have a high SP value. As the polyester resin, a resin composed of a polyol and a polycarboxylic acid or an anhydride thereof 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 hydroxyl group-containing resin (a) is preferably contained in a solid content of 10 to 70% by weight based on the total solid content of the resin. If the content is less than 10% by weight, 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 weight, the blending ratio of the non-aqueous dispersion resin (c) is reduced, so that the finished appearance of the coating film is reduced. Preferably, 10 to 50
%, More preferably 20 to 50% by weight.

The above 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.
It is preferably contained at 0% by weight. If the amount is less than 10% by weight, the curing may be insufficient, and the physical properties of the coating film may be poor. If it exceeds 70% by weight, it is uneconomical and the finished appearance of the coating film deteriorates. More preferably, 20 to 5
0% by weight. 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, but from the viewpoint of pigment dispersibility and workability, an acrylic resin and / or a polyester resin is combined with a melamine resin. Is preferred.

The 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 coating film forming component, so that the amount of the particles can be increased. Therefore, the non-aqueous dispersion resin (c) has a large base concealing property, can suppress the occurrence of unpleasant skin, and can provide a coated film with high sharpness and gloss.

Japanese Patent Application Laid-Open No. 10-5680 discloses the addition of cross-linkable polymer fine particles (microgel) 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 cross-linked and cannot be a coating film forming component, the addition amount is limited to 15% by weight 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 microparticles (microgel) can be reduced in that the minimum viscosity at the time of baking of the paint can be reduced, so that the base material has a large concealing property and a coating film having an excellent finished appearance can be obtained. Are different.

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 coating material cannot be reduced, and the coating swells or dissolves, and the viscosity control effect of the core portion is reduced. Adaptation occurs 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 to
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 Co., Ltd.), 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 used is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total polymerizable monomer. 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 at the time of copolymerizing the polymerizable monomer is not particularly limited as long as the non-aqueous dispersion resin can be stably synthesized 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 weight based on the total amount of the monomer. If the content is less than 10% by weight, compatibility with the base paint occurs. If it exceeds 50% by weight, 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 weight based on the total amount of the polymerizable monomer. If it is less than 20% by weight, curability, adhesion and stability may be poor. If it exceeds 50% by weight, 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 weight of both components, the dispersion-stabilizing resin is 3%.
-80% by weight, preferably 5-60% by weight, and the polymerizable monomer is 97-20% by weight, preferably 95-40% by weight. Further, the total concentration of the dispersion stabilizer and the polymerizable monomer in the organic solvent is 30 to 80% by weight, preferably 40 to 60% by weight based on the total weight.

The thus obtained non-aqueous dispersion resin (c) preferably contains 18 to 50% by weight of solid content based on the total solid content of the resin. 18% by weight
If it is less than 50% by weight, or if it exceeds 50% by weight, the appearance of the resulting coating film is deteriorated. Preferably, 23 to 45% by weight
It is.

The above-mentioned intermediate coating usually contains a pigment. The pigment is preferably contained in an amount of 10 to 70% by weight based on the total amount of the pigment and the solid content of the resin.
In this specification, 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 content is less than 10% by weight, 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 poor. If it exceeds 70% by weight, the appearance of the coating film is deteriorated because the amount of the pigment is too large.

The pigment is not particularly limited, and includes 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, conventionally known additives, for example, a viscosity controlling agent, an anti-bake agent, a diluting solvent and the like can be added to the intermediate coating composition. 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.

As the coating form of the intermediate coating, a solution type is preferably used, and examples of the solution type include an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion) and a non-aqueous type. No. The intermediate coating composition comprises a hydroxyl group-containing resin (a) and a curing agent capable of reacting with a hydroxyl group (b).
And the non-aqueous dispersion resin (c), and the pigment and other components can be obtained by a method known to those skilled in the art, such as kneading and dispersing using a kneader, a roll, or the like.

The nonvolatile content of the intermediate coating material thus obtained is preferably 40 to 70% by weight at the time of application. If the content is less than 40% by weight, the solvent is too large, so that a high-solids intermediate coating 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 weight, the viscosity is too high, so that the appearance of the coating film may be poor or the workability may be low. More preferably, it is 45 to 60% by weight.

In the present invention, it is preferable that the intermediate coating material has a volume shrinkage of 45% or less when cured at 140 ° C. for 30 minutes after application. If it exceeds 45%, the resulting film may be inferior in base layer concealing property, and as a result, a coated film having a good finished appearance may not be obtained. More preferably, 4
0% or less. 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 weight of the object to be coated before coating is W1, the weight of the object to which the coating is applied is W2, and the weight 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 indicates the specific gravity of the solvent contained in the intermediate coating. 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. )

[0043]Base paint  In the present invention, a non-aqueous dispersion
Those containing John resin can be suitably used
You. In the present invention, a non-aqueous
It is preferable to use one containing a sparging resin
However, more preferably, both the intermediate paint and the base paint are used.
By using one containing non-aqueous dispersion resin
You.

As the non-aqueous dispersion resin,
The non-aqueous dispersion resin (c) described in the above-mentioned intermediate coating composition can be used. The resin and the curing agent used together with the non-aqueous dispersion resin are also those described in the above intermediate coating composition. Can be mentioned. In the base paint, the compounding amount of the non-aqueous dispersion resin is preferably 5 to 50% by weight in terms of solids based on the total amount of resin solids. 5
When the amount is less than 50% by weight or more than 50% by weight, the appearance of the obtained coating film deteriorates. More preferably, 18-
45% by weight.

The above-mentioned base paint can be used as a metallic base paint by blending 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 weight or less. When the content exceeds 23% by weight, the appearance of the coating film is deteriorated. Preferably, it is 0.01 to 20% by weight, more preferably 0.01 to 18% by weight.

As the pigments other than the above-mentioned brilliant 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 weight, preferably 0.5 to 40% by weight, and more preferably 1 to 30% by weight. If it exceeds 50% by weight, the appearance of the coating film will be reduced.

As the form of the base paint, a solution type is preferably used, and examples of the solution type include an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion) and a non-aqueous type. Can be 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 preferably 30 to 60% by weight at the time of coating,
More preferably, it is 40 to 50% by weight. If the amount is less than 30% by weight, 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 weight, the viscosity is too high, so that the appearance of the coating film may be poor or the workability may be low.

[0049]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 clear paint contains a viscosity control agent as an additive in order to apply it in an uncured state after the above-mentioned base paint is applied, 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 weight, preferably 0.1 to 100 parts by weight, based on 100 parts by weight of the resin solid content of the clear paint.
The amount is from 02 to 8 parts by weight, more preferably from 0.03 to 6 parts by weight. If the amount is more than 10 parts by weight, the appearance deteriorates. If the amount is less than 0.1 part by weight, 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.

Examples of the method for preparing the clear coating include those exemplified for the intermediate coating.
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 weight, more preferably from 45 to 60% by weight. If the amount is less than 40% by weight, 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 weight, 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.

[0052]Painting method  The method for forming a coating film of the present invention comprises the steps of:
Paint, base paint and clear paint
Including. The above coating method is particularly limited
For example, air static called "react gun"
Electrospray; commonly known as “micro / micro (μμ)
"", "Micro (μ) bell", "meta bell", etc.
By using a rotary atomizing electrostatic coating machine
be able to. Preferably, a rotary atomizing type electrostatic coating machine or the like
It is a method using. Apply the above base paint to automobile body etc.
When painting on the other hand, air
-Multi-stage painting by electrostatic spraying, preferably 2
Paint with a stove or air electrostatic spray and above
Coating method combined with a rotary atomizing type electrostatic coating machine
More preferably, it is performed.

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 according to the present invention comprises the three steps of the intermediate coating, base coating and clear coating applied as described above.
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 film 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.

[0056]

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 the examples, "parts" represents parts by weight. 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 of Nonaqueous Dispersion Resin (a) Production of Dispersion-Stable Resin A container 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 the solution.
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 particle size of 0.18 μm and a nonaqueous dispersion resin content of 40% by weight 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 full weight
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.

[0060]Preparation of base paint  The acrylic resin wafer obtained in Synthesis Example 1 was placed in a 2 L vessel.
500 copies of varnish 1, DISPERBYK161 (Big
320 parts of Chemie's dispersing aid), followed by Mona
Arc 1400 (Carbot carbon black) 10
Parts, then 31 parts of butyl acetate and 31 parts of xylene.
Was. After that, the same amount of glass beads (product
(GB503M, particle size 1.6 mm)
Dispersed in a mill for 3 hours. Dispersion end by grind gauge
Upon completion, the particle size was 5 μm or less. After dispersion is complete, glass
The beads were filtered to obtain a pigment paste. Page made
Resin and non-water so that the solid content ratio is as shown in Table 2.
Mixing dispersion resin and curing agent, base coating
A preparation was prepared.

[0061]Clear 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 = 9/11 19 seconds / No. 4 Ford cup / 20 ° C (base paint) Thinner: EEP / S-100 (exxon aromatic resin)
(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) = 1/1 22 seconds / No. 4 Ford cup / 20 ℃

[0062]Painting method  Using the following materials, paint with 3 coats and 1 bake coating system
Was done. Surface roughness (Ra) of each material is
Cut-off using F-30A (manufactured by Tokyo Seimitsu).
The measurement was performed at a setting of 5 μm. Material 1: Polished steel plate (Ra: 0.05 μm) Material 2: On SPC steel plate (zinc, nickel alloy plating)
Power Top V-20 (Cation electrodeposition manufactured by Nippon Paint Co., Ltd.)
Paint) with a dry film thickness of 20 μm (Ra:
Material 3: Powertop U-60 on SPC bright steel plate
0 (cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd.)
Material coated at 0 μm (Ra: 0.38 μm) Material 4: Powertop V-6 on SPC dull steel plate (Japan
Paint Co., Ltd. cationic electrodeposition paint) with a dry film thickness of 20 μm
Painted (Ra: 0.42 μm)

Under the coating conditions shown in Table 1, the intermediate coating is applied while the coating plate is being moved by attaching the coating plate to the moving plate, the base coating is applied after 10 minutes, and the base coating is applied again after 2.5 minutes. Painting (2 stage painting), then 2
After 0 minute, the clear paint was applied. The coated intermediate coating film, base coating film and clear coating film were baked and cured at 140 ° C. for 30 minutes.

[0064]

[Table 1]

[0065]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 smaller the value, the better
Indicates that the result was obtained. Table 2 shows the results.
FIG. 1 shows the relationship between the surface roughness (Ra) and the SW of the coating film.
Was.

[0066]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 x 1 aluminum foil whose weight (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 weight (w2) of aluminum foil with paint
After drying, measure the weight (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.

[0067]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: 0.8% for the intermediate coating, based on the solvent composition in the coating.
7. The base paint was 0.86. Dry coating specific gravity: From each coating composition, intermediate coating 1.64,
The base paint was 1.23. Table 2 shows the obtained results.

[0068]Solvent resistance test method  Apply intermediate paint and base paint on tin plate respectively
After that (20 μm), it was dried at 80 ° C. × 10 minutes to increase NV.
And S-1 which is a typical paint solvent
50, spot 1 drop of xylol and EEP and let stand for 30 seconds
After the placement, the state was observed at an angle of about 45 degrees. ：: No change Δ: Swelling X: Dissolution The results obtained are shown in Table 2.

Example 2 An intermediate paint and a base paint were prepared and coated in the same manner as in Example 1 except that the resin and the curing agent were blended so that the solid content ratio was as shown in Table 2. The measurement and evaluation were performed. The results are shown in Table 2 and FIG.

[0070]

[Table 2]

In Table 2, Cymel 254 is a methyl-butyl mixed melamine resin (manufactured by Mitsui Cytec). In Examples 1, materials 1 and 2 having a surface roughness of 0.35 or less
Was used, the appearance (SW) of the coating film obtained by the three-coat one-bake coating system was excellent. In Example 2 using the intermediate paint and the base paint containing no non-aqueous dispersion resin, a coating film having an excellent appearance was obtained when the material 1 was used, but a good coating film was obtained when the material 2 was used. No appearance coating film was obtained.

[0072]

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.

[Brief description of the drawings]

FIG. 1 shows the surface roughness (Ra) of a material and the appearance (SW) of a coating film obtained by a three-coat one-bake method in Examples 1 and 2.
It is a graph showing the relationship with.

Claims (4)

[Claims] 1. A method for forming a coating film comprising: a step of sequentially applying an intermediate coating, a base coating, and a clear coating on a material; and a step of baking and curing the three coated layers at once. The surface roughness (Ra) of the material is 0.05 ≦ Ra ≦ 0.35, and the appearance (SW) of the coating film surface obtained by baking and curing is SW ≦ 20. Coating method. 2. The method according to claim 1, wherein the surface roughness (Ra) of the material is 0.05 ≦ Ra ≦ 0.32. 3. The intermediate coating composition has a hydroxyl group-containing resin (a) in an amount of 10 to 70% by weight based on the total solid content of the resin.
3. The coating film forming method according to claim 1, comprising 10 to 70% by weight of a curing agent (b) capable of reacting with a hydroxyl group and 18 to 50% by weight of a non-aqueous dispersion resin (c). 4. An object to be coated obtained by the method for forming a coating film according to claim 1, 2 or 3.