JP2002035680A - Method for forming coating film, material to be coated and intermediate coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a coating film by which a coating film excellent in finished appearance and chipping resistance 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, 40-80% hydroxy-containing resin and 20-60% curing agent capable of reacting with the hydroxy, based on the total amount of solid resin component, and further contains 0.05-3% sulfonic-acid catalyst, based on the solid resin component.

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. A method in which a base paint and a clear paint are applied by a wet-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, and a coating material obtained by the method. And an intermediate coating composition.

[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. As the painting process,
Normally, an undercoat is applied by electrodeposition coating and baked and cured to form an undercoat film, an intermediate coat is applied thereon, and baked and cured to form an intermediate coat, followed by overcoating. Undercoating, intermediate coating and topcoating are separately baked and hardened 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. Of these, the intermediate coating is applied to conceal the base, secure the surface smoothness after the top coating, and impart coating properties such as impact resistance and chipping resistance. When chipping property is particularly required, an intermediate coating for chipping resistance has been widely used.

In Japanese Patent Publication No. 59-33033, an undercoat is applied by electrodeposition coating and baked for the purpose of solving the problem of the three-coat two-bake method in which the coating process is long and energy consumption is large. Thereafter, a metallic coating method is disclosed in which an intermediate paint and a metallic paint are applied and baked simultaneously. However, since this method applies a metallic paint without baking and hardening after applying the intermediate paint, when using an intermediate paint for chipping resistance that has been widely used in a three-coat two-bake coating system, The intermediate coating and the metallic coating were mixed at the interface of the coating, resulting in inferior finished appearance, which was not suitable for use.

[0005]

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. It is possible to obtain an excellent finished appearance equal to or more than that of the conventional three-coat two-bake method,
Further, it is an object of the present invention to provide a method for forming a coating film having excellent chipping resistance, an object to be coated obtained by the method, and an intermediate coating composition.

The inventors of the present invention have proposed an intermediate coating composition comprising a hydroxyl group-containing resin and a curing agent capable of reacting with a hydroxyl group, further containing a sulfonic acid-based catalyst. In the three-coat one-bake method, a base coat and a clear paint are applied in a wet-on-wet system without baking and hardening after applying the intermediate coating, and three layers are simultaneously baked and hardened. It was found that a coating film excellent in chipping resistance and finished appearance was obtained, and the present invention was completed.

[0007]

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 40 to 80% by weight of a hydroxyl group-containing resin (a) and a curing agent capable of reacting with a hydroxyl group ( b) A coating film forming method comprising 20 to 60% by weight, and further comprising 0.05 to 3% by weight of a sulfonic acid-based catalyst based on the solid content of the resin.

[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, 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. The intermediate coating composition comprises a hydroxyl group-containing resin (a) and a curing agent (b) capable of reacting with a hydroxyl group. The hydroxyl group-containing resin (a) means a resin containing a hydroxyl group and soluble in a medium used for the 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.

[0010] 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) has a solid content of 40% based on the total solid content of the resin, that is, the total amount of the solid content of the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with the hydroxyl group. ８０80% by weight. When the amount is less than 40% 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 80% by weight, the proportion of the curing agent (b) that can react with a hydroxyl group decreases, resulting in insufficient curing. Preferably, it is 45 to 75% by weight.

The curing agent (b) capable of reacting with the hydroxyl group 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 20 to 20% based on the total resin solid content.
60% by weight. If the amount is less than 20% by weight, the curing may be insufficient and the physical properties of the coating film may be poor.
If it exceeds 60% by weight, it is uneconomical and the finished appearance of the coating film deteriorates. Preferably, it is 25 to 55% 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.

In the present invention, the intermediate coating composition further contains a sulfonic acid-based catalyst in the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with the hydroxyl group. With the sulfonic acid-based catalyst, the crosslink density of the coating film can be increased and the tensile strength can be improved.
In the coat 1 bake method, excellent chipping resistance can be exhibited.

The sulfonic acid catalyst is preferably an organic sulfonic acid catalyst, and more preferably at least one selected from the group consisting of paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid and salts thereof. . As the above salt,
Amine salts and metal salts. The metal salt is not particularly limited, and examples thereof include metals such as zinc, magnesium, and tin. The amine salt is not particularly limited, and examples thereof include salts of organic amines such as triethylamine, dimethylethanolamine, and diethanolamine. The above sulfonic acid-based catalysts can be used alone or in combination of two or more.

The sulfonic acid-based catalyst is used in an amount of 0.05 to 3% by weight based on the solid content of the resin. 0.0
If it is less than 5% by weight, a coating film having excellent chipping resistance cannot be obtained. If it exceeds 3% by weight, the content is too large, and the appearance of the coating film is rather poor. Preferably,
0.5 to 2% by weight. In the present invention, the resin solid content means the solid content of the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with the hydroxyl group. When the intermediate coating contains a non-aqueous dispersion resin (c) to be described later, the hydroxyl-containing resin (a), the curing agent (b) capable of reacting with the hydroxyl group, and the solid of the non-aqueous dispersion resin (c) are used. It means minute.

In the present invention, it is preferable that the non-aqueous dispersion resin (c) is further contained in the intermediate coating composition. 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. Furthermore,
Since the non-aqueous dispersion resin (c) is a non-crosslinked particle, the coating film can be imparted with flexibility, so that the chipping resistance can be further improved. 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 undercoat concealing property of the electrodeposition coating film, can suppress the occurrence of skin irregularities, has excellent clarity and gloss, and has excellent resistance. A coating film having chipping properties can be obtained.

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.

As the polymerizable monomer, a monomer having a functional group is preferable. 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 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 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 between the above-mentioned dispersion stabilizer and 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 non-aqueous dispersion resin (c) thus obtained preferably contains 5 to 50% by weight of solid content based on the total solid content of the resin. If the amount is less than 5% by weight or more than 50% by weight, the appearance of the obtained coating film deteriorates. Preferably, it is 18 to 45% by weight. When the intermediate coating composition contains a non-aqueous dispersion resin (c), the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with the hydroxyl group each have a solid content ratio based on the total resin solid content. 10 to 70% by weight and 1
It is preferably from 0 to 70% by weight. An intermediate coating composition comprising 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 containing a sulfonic acid-based catalyst is also provided by the present invention. One.

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.
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 above-mentioned pigments are not particularly limited, and include those used in conventional intermediate coatings, for example, 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, for example, a viscosity controlling agent, an anti-bake agent, a diluting solvent and the like. 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.

[0033] The intermediate coating composition is a resin containing a hydroxyl group (a).
And a curing agent (b) capable of reacting with a hydroxyl group and, if desired, a non-aqueous dispersion resin (c), and a pigment or other components kneaded or dispersed using a kneader or a roll. Can be obtained by any method. The nonvolatile content of the thus obtained intermediate coating composition 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, 4
5 to 60% by weight.

In the present invention, the intermediate coating composition preferably 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 hiding power of the electrodeposition coating film is inferior, and as a result, a coating film having a good finished appearance may not be obtained. More preferably, it is 40% or less.

In the present invention, the volume shrinkage when cured at 140 ° C. for 30 minutes can be determined 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. )

[0036]Base paint  In the coating film forming method of the present invention, a special
Not limited to, for example, film-forming resin, curing agent, pigment
And other additives.
You. The film-forming resin is not particularly limited, for example,
For example, acrylic resin, polyester resin, alkyd resin,
Epoxy resins, urethane resins, etc. are listed.
Hardness of mino resin and / or blocked isocyanate resin
Used in combination with an agent. Pigment dispersibility and workability
From the viewpoint, acrylic resin and / or polyester resin
Combinations with lamin resins are preferred.

When the above-mentioned base paint is used as a water-based paint, US Pat.
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 may 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 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.

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) and 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 weight, more preferably 4% by weight.
0 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.

[0042]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.

As the clear paint, a viscosity control agent is added as an additive in order to apply the base paint described above in an uncured state after the application, 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.

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 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.

[0045]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

[0046]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 thickness of the above-mentioned intermediate coating, base coating and clear coating varies depending on the intended use, but is 5 to 40 μm for the intermediate coating and 5 to 35 μm for the base coating, respectively.
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 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 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.

[0050]

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 Nonaqueous 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.
Resin, non-aqueous dispersion resin, curing agent and
An intermediate coating was prepared by blending a sulfonic acid-based catalyst.
Sulfonic acid-based catalysts include dinonyl naphthalenedis
Zinc sulfonate (Zn (DNDNSA)_Two )It was used.

[0054]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 = 9/11 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 ℃

[0055]Painting method  Under the coating conditions shown in Table 1, an SPC dull steel plate (20 cm × 3
Power Top V-6 (0cm x 0.8mm)
To a dry film thickness of 20 μm.
The electrodeposited cation electrodeposited plate to the moving plate
While applying and moving, apply the intermediate coating and after 10 minutes
Apply base paint.
Paint (2 stage paint), then 20 minutes later clear
-Painted. Painted intermediate coat, base coat and
And clear coating is baked and cured at 140 ° C for 30 minutes.
I let you.

[0056]

[Table 1]

[0057]Appearance evaluation  The appearance of the painted plate is compared with Big Chemie Wave Ski
The evaluation was made based on the value of LW of Jan. The results are shown in Table 2. Number
A smaller value indicates that a better result was obtained.

[0058]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.

[0059]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.

[0060]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.

[0061]Test method for chipping resistance  0.8mm thick SPC dull steel sheet treated with zinc phosphate
(20cm x 30cm x 0.8mm) cationic electrodeposition coating
Film (Power Top U-50 manufactured by Nippon Paint Co., Ltd.)
Electrodeposited to a thickness of about 25 μm, 160 ° C x 3
Bake in 0 minutes, then apply the intermediate coating to a dry film thickness of about 35
It was spray-coated so as to have a thickness of μm. 10 minutes later, base
Spray paint to dry film thickness of about 16μm
After setting for about 7 minutes, clear paint is dried
Is spray-coated so that the thickness becomes about 40 μm,
What was baked for 20 minutes was used as a test coated plate. Stepping stone testing machine
Cooled to -30 ° C in the sample holder of Suga Test Instruments Co., Ltd.
Attach the coating film so that the angle of approach of the stone is 60 °,
100 g of No. 7 crushed stone at 3 kg / cm^Two Injection with air pressure
Then, the crushed stones collided with the painted plate. About the peeling wound at that time
The degree (number and size) was evaluated. ：: almost no peeling scratches ○: slight peeling scratches slightly △: spot peeling scratches in some places ×: peeling scratches all over

Example 2, Comparative Examples 1-2 Except that the resin, the non-aqueous dispersion resin, the curing agent and the sulfonic acid-based catalyst were blended so that the solid content ratio was as shown in Table 2, In the same manner as in the above, an intermediate coating was prepared and applied, and measurement and evaluation were performed. The results are shown in Table 2.

[0063]

[Table 2]

In Table 2, Cymel 254 is a methyl-butyl mixed melamine resin (manufactured by Mitsui Cytec). The intermediate coating containing the sulfonic acid-based catalyst of Examples 1 and 2,
The chipping resistance was good. In particular, since the intermediate coating composition of Example 1 further contains a non-aqueous dispersion resin, not only the chipping resistance can be further improved, but also the solvent resistance is excellent, so that the wet coating -Excellent finish appearance when base paint and clear paint were applied by on-wet method and baked and cured. The intermediate coatings of Comparative Examples 1 and 2 that did not contain the sulfonic acid catalyst did not have good chipping resistance.

[0065]

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

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4D075 AE06 CA04 DB02 DC22 EA43 EB22 EB32 EB33 EB35 EB36 EB38 EB52 EB54 EB55 EB56 EC37 EC54 4J038 CG001 CG002 CG141 CG142 CH121 CH122 CJ011 CJ012 CJ04 CJ031J04 CJ031 DD04 DG192 DG301 GA03 GA05 GA06 GA07 GA09 GA11 GA13 JB03 JC13 JC14 KA03 KA04 MA08 MA10 NA01 NA27 PA15 PA19 PB07

Claims (6)

[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 coated layers at a time, wherein the intermediate coating composition has a hydroxyl group-containing resin (a) of 40 to 40 at a solid content ratio based on the total resin solid content. 80% by weight and 20 to 60% by weight of a curing agent (b) capable of reacting with a hydroxyl group, and further comprising 0.05 to 3% by weight of a sulfonic acid-based catalyst based on the solid content of the resin. Film formation method. 2. The sulfonic acid-based catalyst is at least one organic sulfonic acid-based catalyst selected from the group consisting of paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, and salts thereof. The method for forming a coating film according to the above. 3. The intermediate coating composition further comprises, as a resin component,
3. The method for forming a coating film according to claim 1, wherein the coating film contains 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. 5. A hydroxyl group-containing resin (a) in an amount of 10 to 70% by weight, a curing agent capable of reacting with hydroxyl groups (b) in an amount of 10 to 70% by weight, and a non-aqueous dispersion resin (a solid content ratio based on the total solid content of the resin). c) An intermediate coating composition comprising 5 to 50% by weight, and further containing 0.05 to 3% by weight of a sulfonic acid-based catalyst based on the solid content of the resin. 6. The sulfonic acid-based catalyst is at least one organic sulfonic acid-based catalyst selected from the group consisting of paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, and salts thereof. The intermediate coating composition according to the above.