JP7042027B2 - A two-component reaction-curing water-based paint composition for topcoat paints, and a multi-layer film forming method and coating body using the same. - Google Patents

Description

The present invention relates to a two-component reaction-curing water-based coating composition for a top coat, a multi-layer film forming method using the same, and a coated body.

In recent years, the development of water-based paints has been promoted in order to protect the environment, safety workers, and reduce odors to the surroundings. On the other hand, in the market, there has been a demand for a painting system in which the number of paintings is reduced by reducing the number of processes for the purpose of reducing the labor of painting and shortening the construction period.

As one means for realizing the process saving, for example, a method of using a paint capable of forming a thick film as an undercoat paint or a topcoat paint can be mentioned. As means for enabling such thick film formation, for example, a method of increasing the content of the coating film forming component and selecting a specific viscosity modifier (Patent Document 1), or a method of containing hollow particles (Patent Document 1). Patent Document 2) is known. These are effective methods for epoxy resin paints mainly used as undercoat paints and one-component paints.

As the water-based topcoat paint, a fluororesin paint, a silicone resin paint, a urethane resin paint, or an acrylic resin paint is generally used. As a method for providing a coating film performance having particularly high weather resistance while using such a paint, a method of containing polyisocyanate as a curing agent in a two-component reaction curing type paint (Patent Documents 3 and 4) is known. Is.

Japanese Unexamined Patent Publication No. 2016-186021 Japanese Patent No. 5475917 Japanese Unexamined Patent Publication No. 2005-187517 Japanese Unexamined Patent Publication No. 2014-88495

As a method for forming a thick film, for example, a method of devising a pigment and / or an additive to be added to a paint is known. However, when this method is applied to a topcoat paint, when a general isocyanate-curable water-based topcoat paint, which is a two-component reaction-curable paint capable of forming a high-performance topcoat, is applied with a high film thickness, the drying time is long. For a long time, the isocyanate group also reacts with the moisture in the paint to generate carbon dioxide gas, so that it is easy to cause a paint film defect that bubbles are generated in the paint film, especially in the thick film portion. As a result, the durability of the coating film is lowered and the appearance of the coating film is impaired. Further, the obtained high-thickness coating film is required to have excellent coating workability at the time of forming the coating film and also excellent leveling property.

The present invention has been made in view of the above problems, and even if it is formed with a high film thickness, firstly, coating film defects such as bubbles generated in the coating film are less likely to occur, and secondly, coating work is performed. Provided are a two-component reaction-curing water-based coating composition for a topcoat paint, which has excellent properties and leveling properties and gives a topcoat coating film in which brush marks and roller marks are inconspicuous, and a multi-layer film forming method and a coating body using the same. The purpose is to do.

According to the studies by the present inventors, a two-component reaction-curing coating composition containing a carbodiimide group-containing compound as at least a part of the curing agent and reacting the curing agent with a carboxyl group in the main agent to obtain a coating film. It was found that when the above was used, no bubbles were generated in the coating film, and a thick film coating film having excellent durability and appearance could be formed. According to the additional studies by the present inventors, by setting the non-volatile content, viscosity, and surface tension of the coating composition to appropriate values, a thick film coating film using the above-mentioned curing system can be applied with a brush or a roller. And / or it was found that it can be formed by on-site coating by spraying, and it is possible to obtain a thick topcoat coating film in which brush marks and roller marks are inconspicuous. As described above, the present inventors have combined a main agent having a carboxyl group and a curing agent containing a carbodiimide group-containing compound to set the non-volatile content, viscosity, and surface tension of the obtained coating composition within a specific range. We have found that the above problems can be solved by making adjustments, and have completed the present invention.

That is, the two-component reaction-curing water-based coating composition for a top coat according to the present invention contains (A) a carboxyl group-containing resin, (B) a curing agent, (C) a pigment, and (D) water. ,
(B) The curing agent contains a carbodiimide group-containing compound and contains.
In the coating composition, the non-volatile content is 40 to 60% by mass, and the content is 40 to 60% by mass.
The coating composition has a viscosity of 90 to 1000 Pa · s at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C., and a viscosity of 0.3 to 3 Pa · s at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C. can be,
The surface tension of the coating composition is 55 to 80 mN / m.

In a preferred example of the coating composition according to the present invention, the coating composition further contains (E) a viscosity modifier.

In another preferred example of the coating composition according to the present invention, the (A) carboxyl group-containing resin contains a carboxyl group-containing fluororesin.

The method for forming a multi-layer film according to the present invention is to apply an undercoat paint to a substrate and dry it to form an undercoat film, and to apply a topcoat paint to the undercoat paint and dry it to form a topcoat film. Including that
The topcoat paint comprises the paint composition according to the present invention.

In a preferred example of the method for forming a multi-layer film according to the present invention, the undercoat paint comprises a two-component reaction-curable water-based paint composition containing an epoxy resin.

The coated body according to the present invention includes a base material, an undercoat coating film arranged on the base material, and a topcoat coating film arranged on the undercoat coating film.
The topcoat coating film is formed of a topcoat paint made of the coating composition according to the present invention.

In a preferred example of the coated body according to the present invention, the undercoat coating film is formed of an undercoat paint made of a two-component reaction-curable water-based paint composition containing an epoxy resin.

According to the present invention, even if it is formed with a high film thickness, firstly, it is difficult for a coating film defect that bubbles are generated in the coating film to occur, and secondly, it is excellent in coating workability and leveling property, and it is brush-coated. It is possible to provide a two-component reaction-curing water-based coating composition for a topcoat coating material that gives a topcoat coating film in which marks and roller marks are inconspicuous, and a multi-layer film forming method and a coating body using the same.

≪Two-component reaction-curing water-based paint composition for topcoat paint≫
The two-component reaction-curing water-based coating composition for a topcoat coating material according to the present invention is a topcoat coating material containing (A) a carboxyl group-containing resin, (B) a curing agent, (C) a pigment, and (D) water. A two-component reaction-curing water-based paint composition for use.
(B) The curing agent contains a carbodiimide group-containing compound and contains.
In the coating composition, the non-volatile content is 40 to 60% by mass, and the content is 40 to 60% by mass.
The coating composition has a viscosity of 90 to 1000 Pa · s at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C., and a viscosity of 0.3 to 3 Pa · s at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C. can be,
The surface tension of the coating composition is 55 to 80 mN / m. By adopting the above structure, the coating film composition is less likely to cause coating film defects such as bubbles generated in the coating film even if it is formed with a high film thickness, and secondly, coating workability and coating workability and It has excellent leveling properties and can provide a topcoat coating film in which brush marks and roller marks are inconspicuous. Unless otherwise noted, surface tension is measured at 23 ° C.

In the above coating composition, the non-volatile content is preferably 40 to 60% by mass, more preferably 45 to 55% by mass, and even more preferably 47 to 53% by mass. When the content of the non-volatile component is within the above range, it is easy to obtain a topcoat film having a sufficient film thickness. In the present specification, the non-volatile component contained in the water-based paint composition for topcoat paint refers to a component remaining after drying the paint composition in an oven at 110 ° C. for 3 hours.

The coating composition contains (A) a carboxyl group-containing resin. (A) The carboxyl group-containing resin has a carboxyl group as a reactive site that reacts with a curing agent or the like. Examples of the (A) carboxyl group-containing resin include resins containing a structural unit derived from a monomer containing a carboxyl group. The (A) carboxyl group-containing resin is a resin having at least one carboxyl group in one molecule, and the acid value of the non-volatile component is preferably in the range of 5 mgKOH / g to 80 mgKOH / g. Hereinafter, the acid value of the non-volatile component is expressed in the unit of "mgKOH / g-nonvolatile component". The (A) carboxyl group-containing resin may be used alone or in combination of two or more.

(A) As the carboxyl group-containing resin, a carboxyl group-containing water-soluble resin (hereinafter, may be simply referred to as “water-soluble resin”) and a carboxyl group-containing water-dispersible resin (hereinafter, simply “water dispersion”). It may be described as "sexual resin"). Each of the water-soluble resin and the water-dispersible resin preferably has at least two carboxyl groups in one molecule. Each of the water-soluble resin and the water-dispersible resin may be used alone or in combination of two or more. Further, one kind or two or more kinds of the water-soluble resin and one kind or two or more kinds of the water-dispersible resin may be mixed and used.

The form, type, etc. of the water-soluble resin are particularly limited as long as it contains a carboxyl group, has water solubility, and cures by reacting with the carbodiimide group in the curing agent (B). For example, a carboxyl group-containing styrene acrylic resin having a nonionic functional group, a cationic functional group, or an anionic functional group, a nonionic functional group, a cationic functional group, or a carboxyl group-containing acrylic resin having an anionic functional group. , A carboxyl group-containing polyester resin having a nonionic functional group, a cationic functional group, or an anionic functional group, and the like. Examples of the nonionic functional group include an amide group and a polyoxyalkylene group. Examples of the cationic functional group include an amino group, an imino group, a hydrazino group and the like. Examples of the anionic functional group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group and the like. Each of the nonionic functional group, the cationic functional group, and the anionic functional group may be used alone or in combination of two or more. As the water-soluble resin, a commercially available product can be preferably used.

The form of the water-soluble resin is not particularly limited, and examples thereof include a form dissolved in an aqueous medium such as water and a form dispersed in an aqueous medium such as water, and more specifically, a carboxyl group-containing water-soluble resin aqueous solution. Can be mentioned.

As long as the water-dispersible resin contains a carboxyl group, has water dispersibility, and is cured by reacting with the carbodiimide group in the curing agent (B), its form, type, etc. are particularly high. Not limited to, for example, carboxyl group-containing styrene acrylic resin, carboxyl group-containing acrylic resin, carboxyl group-containing urethane resin, carboxyl group-containing silicone resin, carboxyl group-containing acrylic silicon resin, carboxyl group-containing acrylic urethane resin, carboxyl group-containing polyester resin. , Carboxyl group-containing fluororesin, carboxyl group-containing acrylic fluororesin, and the like, and carboxyl group-containing fluororesin is preferable from the viewpoint of long-term durability and weather resistance. As the water-dispersible resin, a commercially available product can be preferably used.

The form of the water-dispersible resin is not particularly limited, and can be obtained by forced emulsion, self-emulsification, suspension polymerization, emulsion polymerization, miniemulsion polymerization, etc., and is an aqueous medium such as water due to the action of emulsifiers, hydrophilic groups, etc. Examples thereof include a form dispersed therein, and more specific examples thereof include a carboxyl group-containing water-dispersible resin emulsion and a carboxyl group-containing water-dispersible resin dispersion. In the present specification, the carboxyl group-containing water-dispersible resin emulsion means an emulsion in which a carboxyl group-containing water-dispersible resin is dispersed in an aqueous medium containing water as a main component, and contains a carboxyl group. The water-dispersible resin dispersion means a dispersion liquid in which a carboxyl group-containing water-dispersible resin is dispersed in an aqueous medium containing water as a main component. The carboxyl group-containing water-dispersible resin emulsion is not particularly limited, but can be used in an aqueous medium containing water as a main component by a normal emulsion polymerization method, a forced emulsification method (a method using an emulsifier, a high-speed stirrer, etc.), or the like. It is prepared by emulsifying a carboxyl group-containing water-dispersible resin. Here, examples of the emulsifier include polyethers such as polyoxyethylene alkylphenol ether-based nonionic surfactants and polyoxyethylene / polyoxypropylene block copolymers; at least one of the nonionic surfactants and the polyethers. Examples thereof include an adduct of the diisocyanate compound and the diisocyanate compound. The emulsifier may be used alone or as a blend of two or more.

In the present specification, the (A) carboxyl group-containing resin tends to have a high initial gloss, and it is easy to obtain a topcoat coating film having excellent durability. Therefore, a carboxyl group-containing water-dispersible resin emulsion and a carboxyl group It is preferably in combination with a water-soluble resin and / or a water-dispersible resin containing a carboxyl group.

(A) The weight average molecular weight Mw of the carboxyl group-containing resin is preferably 1,000 or more, more preferably 2,000 or more, and more preferably 5,000 or more, from the viewpoint of coating film performance and the like. Is even more preferable.

The carboxyl group-containing resin (A) preferably contains a carboxyl group-containing fluororesin. Examples of the carboxyl group-containing fluororesin include a carboxyl group-containing resin containing a structural unit derived from a fluorine-containing monomer, and more specifically, a structural unit derived from a carboxyl group-containing monomer and a fluorine-containing monomer. Examples thereof include a resin containing a constituent unit from which it is derived. Examples of the fluorine-containing monomer include vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, bromotrifluoroethylene, chlorotrifluoroethylene, pentafluoropropylene, hexafluoropropylene, and (per) fluoroalkyltrifluoro. The vinyl ether [(per) fluoroalkyl group has 1 to 18 carbon atoms. ] Etc. can be mentioned.

Examples of the monomer containing a carboxyl group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and carboxylalkylallyl esters.

(A) For the polymerization of the carboxyl group-containing resin, a polymerizable monomer other than the above-mentioned fluorine-containing monomer and the monomer containing a carboxyl group may be used. Such polymerizable monomers include hydroxyl group-containing polymerizable monomers, vinyl ethers, olefins, allyl ethers, vinyl esters, allyl esters, (meth) acrylic acid esters, (meth) acrylic acid amides, and cyano groups. Examples thereof include monomers, dienes and the like, and crotonic acid esters and the like.

Specifically, examples of the hydroxyl group-containing polymerizable monomer include allyl alcohol; hydroxyalkyl vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, and 4-hydroxycyclohexylvinyl ether; 2-hydroxy. Hydroxyalkylallyl ethers such as ethylallyl allyl ether, 3-hydroxypropylallyl ether, 4-hydroxybutylallyl ether, 4-hydroxycyclohexylallyl ether; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate; Esters of hydroxyalkyl carboxylic acids such as vinyl hydroxyacetate, vinyl hydroxyisobutyrate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxycyclohexylcarboxylate and vinyl alcohol; hydroxyethyl allyl ester, hydroxypropyl allyl Examples thereof include hydroxyalkylallyl esters such as esters, hydroxybutylallyl esters, and hydroxyisobutylallyl esters.

Specific examples of the above-mentioned fluorine-containing monomer, carboxyl group-containing monomer, and polymerizable monomer other than the hydroxyl group-containing polymerizable monomer include methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, chloroethyl vinyl ether and the like. Alkyl vinyl ethers; olefins such as ethylene, propylene, 1-butene, isobutylene, cyclohexene, vinyl chloride, vinylidene chloride; styrene-based monomers such as styrene and α-methylstyrene; methylallyl ether, ethylallyl ether, butylallyl Alkyl allyl ethers such as ethers and cyclohexyl allyl ethers; carboxylic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl hexanoate, vinyl octanate, vinyl versatic acid (preferably fatty acids). ) Vinyl esters; Allyl esters of carboxylic acids (preferably fatty acids) such as allyl propionate and allyl acetate; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) (Meta) acrylic acid esters such as cyclohexyl acrylate; (meth) acrylic acid amides such as (meth) acrylate amide; cyano group-containing monomers such as acrylonitrile and 2,4-dicyanobutene-1; isoprene, butadiene and the like. Dienes; examples thereof include crotonic acid esters such as 2-hydroxyethyl crotonate and 4-hydroxybutyl crotonate.

Further, for the polymerization of the (A) carboxyl group-containing resin, a polymerizable monomer having a hydroxyl group and a reactive group other than the carboxyl group may be used. Examples of such a reactive group include functional groups such as an amide group, an amino group, a nitrile group, a glycidyl group and an isocyanate group.

Specific examples of the amino group-containing polymerizable monomer include aminoalkyl vinyl ethers and aminoalkylallyl ethers, and examples of the amide group-containing polymerizable monomer include (meth) acrylamide and N-methyl (meth) acrylamide. Examples of the nitrile group-containing polymerizable monomer include (meth) acrylonitrile, and examples of the glycidyl group-containing polymerizable monomer include glycidyl allyl ether and glycidyl (meth) acrylate. Examples thereof include vinyl isocyanate and isocyanatoethyl acrylate.

The carboxyl group-containing fluororesin preferably has a fluorine content of 1 to 60% by mass, more preferably 2 to 50% by mass. When the fluorine content of the carboxyl group-containing fluororesin is 1% by mass or more, it is easy to impart sufficient weather resistance to the topcoat coating film obtained from the coating composition of the present invention. Further, when the fluorine content of the carboxyl group-containing fluororesin is 60% by mass or less, it is easy to impart sufficient chemical resistance to the topcoat coating film.

The above-mentioned carboxyl group-containing fluororesin is blended in the form of, for example, a carboxyl group-containing fluororesin emulsion and / or a carboxyl group-containing fluororesin dispersion, and the initial gloss tends to be high, and a topcoat coating film having excellent durability can be obtained. Since it is easy to obtain, it is preferable to use a combination of a carboxyl group-containing fluororesin emulsion and a carboxyl group-containing fluororesin dispersion. In the present invention, the carboxyl group-containing fluorine resin emulsion means an emulsion in which a carboxyl group-containing fluorine resin is dispersed in an aqueous medium containing water as a main component, and is referred to as a carboxyl group-containing fluorine resin dispersion. Means a dispersion liquid in which a carboxyl group-containing fluororesin is dispersed in an aqueous medium containing water as a main component. The above-mentioned carboxyl group-containing fluororesin emulsion is not particularly limited, but can be subjected to a carboxyl group in an aqueous medium containing water as a main component by a normal emulsion polymerization method, a forced emulsification method (a method using an emulsifier, a high-speed stirrer, etc.) or the like. It is prepared by emulsifying the contained fluororesin. The emulsifier is as described above.

In the non-volatile content contained in the coating composition, the content of the (A) carboxyl group-containing resin is preferably 20 to 80% by mass, preferably 30 to 80% by mass, from the viewpoint of curability, corrosion resistance and the like of the topcoat film. It is more preferably 70% by mass, and even more preferably 40 to 60% by mass.

The coating composition contains (B) a curing agent. The curing agent (B) is not particularly limited as long as it contains a carbodiimide group-containing compound. (B) The curing agent may be used alone or in combination of two or more. Examples of the carbodiimide group-containing compound include a carbodiimide group-containing resin, N, N-dicyclohexylcarbodiimide, N, N-diisopropylcarbodiimide and the like. Various types of carbodiimide group-containing resins are known, and for example, those obtained by the production methods described in JP-A-6-56950, JP-A-9-77839 and the like can be used. Examples of commercially available products include trade names "carbodilite E-02" and "carbodilite E-03A" (all manufactured by Nisshinbo Chemical Co., Ltd.). The carbodiimide group-containing compound may be used alone or in combination of two or more.

The carbodiimide group-containing resin is preferably blended in the form of a carbodiimide group-containing resin emulsion, a carbodiimide group-containing resin dispersion, and / or a carbodiimide group-containing resin aqueous solution. In the present invention, the carbodiimide group-containing resin emulsion means an emulsion in which a carbodiimide group-containing resin is dispersed in an aqueous medium containing water as a main component, and the carbodiimide group-containing resin dispersion is a carbodiimide. It means a dispersion liquid in which a group-containing resin is dispersed in an aqueous medium containing water as a main component. As the carbodiimide group-containing resin emulsion, the carbodiimide group-containing resin dispersion, and the carbodiimide group-containing resin aqueous solution, available commercially available products can be preferably used.

In the (B) curing agent, the curing agent other than the carbodiimide group-containing compound is not particularly limited as long as the effect of the present invention is not impaired, and examples thereof include an oxazoline group-containing compound and a hydrazide compound. (B) The content of the carbodiimide group-containing compound in the curing agent is preferably 50 to 100% by mass, more preferably 70 to 100, because bubbles are less likely to occur in the coating film and a good appearance can be easily maintained. It is by mass, and even more preferably 90 to 100% by mass.

In the non-volatile content contained in the coating composition, the content of the (B) curing agent is preferably 1 to 40% by mass, preferably 2 to 30% by mass, from the viewpoint of curability, coatability, etc. of the topcoat coating film. It is more preferably%, and even more preferably 3 to 20% by mass.

The coating composition contains (C) a pigment. The pigment (C) is not particularly limited, and examples thereof include colored pigments, rust preventive pigments, extender pigments and the like commonly used in the paint industry. Specific examples of coloring pigments, rust preventive pigments, and extender pigments include titanium oxide, red iron oxide, yellow iron oxide, carbon black, aluminum tripolyphosphate, zinc phosphate, condensed aluminum phosphate, barium metaborate, calcium carbonate, and sulfuric acid. Inorganic pigments such as barium, kaolin, talc, clay, mica, alumina, myoban, white clay, magnesium hydroxide, and magnesium oxide, phthalocyanine blue, phthalocyanine green, naphthol red, quinacridon red, benzimidazolone yellow, Hansa yellow, benz Examples thereof include organic pigments such as imidazolone orange and dioxazine violet. (C) The pigment may be used alone or in combination of two or more.

In the non-volatile content contained in the coating composition, the pigment volume concentration (PVC) is preferably 2 to 40%, more preferably 3 to 30%, and even more preferably 4 to 25%. preferable. When the pigment volume concentration (PVC) is 2% or more, the hiding property of the coating film is unlikely to be insufficient, and when it is 40% or less, the weather resistance is unlikely to decrease.

The coating composition contains (D) water. In the coating composition, (D) water functions as the main dispersion medium. From the viewpoint of reducing environmental load and odor, the content of (D) water is preferably 50 to 100% by mass in the volatile content of the coating composition (that is, the components other than the non-volatile content in the coating composition). It is more preferably 75 to 100% by mass, and even more preferably 90 to 100% by mass.

The coating composition may further contain (E) a viscosity modifier so as to facilitate the formation of a thicker topcoat film. (E) The viscosity adjusting agent is not particularly limited, and a known viscosity adjusting agent can be used. Specifically, a cellulose-based viscosity adjusting agent, an organic bentonite, an amide-based viscosity adjusting agent, and an alkali-soluble type viscosity can be used. Examples thereof include an adjusting agent and a urethane-associated viscosity adjusting agent. (E) The viscosity modifier may be used alone or in combination of two or more.

In the non-volatile content contained in the coating composition, the content of the (E) viscosity modifier is preferably 0.05 to 5% by mass, more preferably 0.1 to 4% by mass, and 0. It is even more preferably .15 to 3% by mass. (E) When the content of the viscosity adjusting agent is 0.05 to 5% by mass, it is easy to form a thicker topcoat film.

In addition to the above-mentioned components, the above-mentioned coating composition includes (A) a binder resin other than a carboxyl group-containing resin, an organic solvent, a diluent, a rust preventive, a dispersant, a defoaming agent, an anti-settling agent, and a surface conditioner. , Leveling agent, antifungal agent, preservative, ultraviolet absorber, light stabilizer, pH adjuster and the like may be appropriately contained as needed.

The coating composition has (1) a viscosity at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C. and (2) a viscosity at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C., respectively, (1) 90 to 1000 Pa. s and (2) 0.3 to 3 Pa · s, preferably (1) 100 to 500 Pa · s and (2) 0.4 to 2 Pa · s, and (1) 200 to 300 Pa · s and (1) 200 to 300 Pa · s and ( 2) It is more preferably 0.5 to 1 Pa · s. When the viscosities of the above (1) and (2) are within the above ranges, the coating composition tends to have high pseudoplasticity, so that it is easy to obtain a topcoat coating film having a sufficient film thickness from the coating composition. Examples of the method for adjusting the viscosity of the above (1) and (2) include a method of adjusting the blending amount of the viscosity adjusting agent and water in the above coating composition.

The surface tension of the coating composition is 55 to 80 mN / m, preferably 60 to 75 mN / m, and more preferably 65 to 70 mN / m. When the surface tension is 55 to 80 mN / m, the obtained topcoat coating film tends to be excellent in coating workability and leveling even if it is formed with a high film thickness. Examples of the method for adjusting the surface tension include a method of adjusting the type and / or amount of the resin and / or the surface adjusting agent, and / or the blending amount of the pigment and / or water in the above-mentioned coating composition.

The coating composition according to the present invention is a two-component reaction-curing water-based coating composition in which (A) a carboxyl group-containing resin and (B) a curing agent are mixed immediately before coating. Since both (A) the carboxyl group-containing resin and (B) the curing agent are non-hazardous substances, the coating composition according to the present invention is excellent in safety. The coating composition according to the present invention contains (A) a carboxyl group-containing resin and (B) a curing agent separately at the time of storage, and these are mixed immediately before coating. (A) The carboxyl group-containing resin is usually stored in combination with water or various components appropriately selected as needed, and this is referred to as a main agent. Further, (B) the curing agent is also usually stored in combination with water and various components appropriately selected as needed, and this is referred to as a curing agent mixture. In addition, in order to adjust the viscosity of the coating composition according to the present invention, water may be further added after mixing the main agent and the curing agent mixture. By mixing the main agent and the curing agent mixture, crosslinks are formed at room temperature and the curing reaction proceeds. Since the (A) carboxyl group-containing resin and (B) curing agent do not generate gas during the curing reaction, the obtained topcoat coating film is less likely to cause coating film defects even when it is formed of a thick film.

≪Multi-layer film formation method≫
The method for forming a multi-layer film according to the present invention is to apply an undercoat paint to a substrate and dry it to form an undercoat film, and to apply a topcoat paint to the undercoat paint and dry it to form a topcoat film. Including that
The topcoat paint comprises the paint composition according to the present invention.

The base material is not particularly limited, and examples thereof include metal base materials such as steel, zinc, aluminum, copper, and tin; concrete base materials; and plastic base materials such as polyvinyl chloride, polycarbonate, polyolefin, acrylic, and ABS. Be done. Further, a steel base material or the like which has been subjected to a base treatment for the purpose of further improving the corrosion resistance can also be applied. Examples of the base treatment include zinc rich paint, zinc plating, and metal spraying. As the shape of the base material, there are various shapes depending on the use thereof, and examples thereof include a plate shape and a tubular shape. The above-mentioned base material may be used alone or in combination of two or more.

The undercoat paint is not particularly limited, and examples thereof include epoxy resin-based paints, urethane resin-based paints, acrylic resin-based paints, etc. , Epoxy resin-based paint is preferable. The undercoat paint may be used alone or in combination of two or more.

The thickness of the undercoat film is preferably 30 to 300 μm, more preferably 60 to 130 μm. When the thickness of the undercoat coating film is 30 to 300 μm, the corrosion resistance and chemical resistance of the undercoat coating film are likely to be improved.

The thickness of the topcoat film is preferably 25 to 100 μm, more preferably 40 to 80 μm, and even more preferably 50 to 70 μm. When the thickness of the topcoat coating film is 25 to 100 μm, the concealing property is excellent, the weather resistance is improved, and the life of the coating film as a multilayer body can be maintained for a long time. Further, usually, an intermediate coating film is applied between the undercoat coating film and the topcoat coating film, but since the above-mentioned advantages can be achieved, this intermediate coating film can be eliminated, and the coating process can be performed. Can be shortened.

Both the thickness of the undercoat film and the thickness of the topcoat film refer to the dry film thickness. As used herein, the dry film thickness refers to the film thickness after drying for 168 hours under the conditions of 23 ° C. and 50% relative humidity.

The undercoat film may be a single layer or a plurality of layers. Even when the undercoat coating film has multiple layers, the thickness of the undercoat coating film is as described above. The case where the undercoat coating film has multiple layers is, for example, the case where the undercoat coating film has two layers consisting of a first undercoat coating film and a second undercoat coating film (however, the second undercoat coating film is a topcoat coating film). It comes in contact with.). In this case, the multi-layer film formed is a multi-layer film in which the first undercoat coating film, the second undercoat film, and the topcoat coating film are laminated in this order. The first undercoat coating film and the second undercoat coating film correspond to the undercoat coating film and the intermediate coating film in the three-layer multi-layer film composed of the undercoat coating film, the intermediate coating film and the topcoat coating film, respectively.

In the above-mentioned method for forming a multi-layer film, the coating of the undercoat paint and the coating of the topcoat paint are not particularly limited, and known coating means such as air spray coating, airless spray coating, brush coating, roller coating and the like can be used. .. The drying temperature of the paint is preferably 5 to 35 ° C. The drying time of the paint is preferably 2 to 24 hours, more preferably 2 to 16 hours, for example, at 23 ° C. and 50% relative humidity. When the paint of the next step is applied again in order to form the multi-layer film, for example, at 23 ° C. and 50% relative humidity, it can be applied without any problem by drying for 4 hours to 10 days. Further, from the viewpoint of repair, when the undercoat paint used in the present invention is applied onto a substrate, there may be a coating film (old coating film) that already covers the substrate to be coated.

Regarding (1) the viscosity of the topcoat paint at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C. and (2) the viscosity of the top coat at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C., the same viscosities of the paint composition have already been obtained. As explained.

≪Painted body≫
The coating body according to the present invention is a coating body including a base material, an undercoat coating film arranged on the base material, and a topcoat coating film arranged on the undercoat coating film, and the topcoat coating film is a coating body. It is formed of a top coat coating material comprising the coating film composition according to the present invention. This coated body is formed, for example, by applying an undercoat paint to a base material and drying it to form an undercoat coating film, and by applying a topcoat paint to the undercoat coating film and drying it to form a topcoat coating film. be able to.

The base material and the coating method are as described above in the method for forming a multi-layer film according to the present invention. Further, other points, for example, the thickness of the undercoat coating film, the thickness of the topcoat coating film, and the point that the topcoat coating film may be a single layer or a multi-layer, are also related to the multi-layer film according to the present invention. As already explained in the forming method.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. In the following Examples and Comparative Examples, "parts" and "%" regarding the amount of the component represent "parts by mass" and "% by mass", respectively.

<Example 1>
In the mixer, in 11.3 parts of ion-exchanged water, 0.05 part of hydroxyethyl cellulose (viscosity adjuster), 0.2 part of DISPERBYK-190 (pigment dispersant manufactured by BYK), SN deformer 1312 (consumer manufactured by San Nopco Ltd.) 0.2 part of foaming agent) and 27.0 parts of titanium oxide were gradually added under a stirring environment and mixed until the particle size became 15 μm or less to obtain a mixture. Next, 159.1 parts of the acrylic resin emulsion, 2.0 parts of the film forming aid, and 0.1 part of the surface adjusting agent were gradually added to the above mixture under a stirring environment, and the mixture was stirred for 10 minutes. The main agent of Example 1 was prepared. Separately, in a mixer, 50.0 parts of carbodilite E-02A (carbodiimide group-containing compound manufactured by Nisshinbo Chemical Co., Ltd.) was gradually added to 50.0 parts of ion-exchanged water under a stirring environment for 30 minutes. Stirring was performed to prepare the curing agent of Example 1. Immediately before painting, the main agent and the curing agent were mixed at a mass ratio of 85:15 to prepare the coating material of Example 1.

<Examples 2 to 18, Comparative Examples 1 to 13>
According to the formulation shown in Table 1 or 2, a main agent and a curing agent are prepared in the same manner as in Example 1, and the main agent and the curing agent are mixed to be used in Examples 2 to 18 and Comparative Examples 1 to 12. The paint was prepared. The paint of Comparative Example 13 was "Aqueous V Freon # 100H Topcoat", which is an isocyanate-curable water-based fluororesin topcoat manufactured by Dai Nippon Toryo Co., Ltd.

(Note 1) Acryset EMN-260E (acrylic resin emulsion manufactured by Nippon Shokubai Co., Ltd .; non-volatile content 44%, acid value 40 mgKOH / g-non-volatile content)
(Note 2) WEM-200U (Urethane acrylic resin emulsion manufactured by Taisei Fine Chemicals Co., Ltd .; non-volatile content 38%, acid value 16 mgKOH / g-non-volatile content)
(Note 3) WBR-016U (Polyurethane resin dispersion manufactured by Taisei Fine Chemicals Co., Ltd .; non-volatile content 30%, acid value 23 mgKOH / g-nonvolatile content)
(Note 4) Lumiflon FD1000 (Fluororesin dispersion manufactured by Asahi Glass Co., Ltd .; non-volatile content 40%, acid value 15 mg KOH / g-non-volatile content)
(Note 5) BYK-307 (surface conditioner manufactured by BYK; non-volatile content 97%)
(Note 6) BYK-3455 (surface conditioner manufactured by BYK; non-volatile content 94%)
(Note 7) DISPERBYK-190 (pigment dispersant manufactured by BYK; non-volatile content 40%)
(Note 8) SN Deformer 1312 (Antifoaming agent manufactured by San Nopco Ltd .; 100% non-volatile content)
(Note 9) Hydroxyethyl cellulose (cellulose-based viscosity modifier; 100% non-volatile content)
(Note 10) SN thickener 617 (viscosity adjuster manufactured by San Nopco Ltd .; non-volatile content 20%)
(Note 11) Dalpad C (Dow Chemical's film forming aid)
(Note 12) Carbodilite E-02A (carbodiimide group-containing compound manufactured by Nisshinbo Chemical Co., Ltd .; non-volatile content 40%, carbodiimide equivalent 445 g / eq-nonvolatile content)
(Note 13) Carbodilite E-03A (carbodiimide group-containing compound manufactured by Nisshinbo Chemical Co., Ltd .; non-volatile content 40%, carbodiimide equivalent 365 g / eq-nonvolatile content)

Tables 3 to 8 show the results of evaluating the characteristics of the paints of Examples 1 to 18 and Comparative Examples 1 to 13 as follows.

<Non-volatile content>
For the paints of Examples 1-18 and Comparative Examples 1-13, each of them was precisely weighed in a 2 g aluminum cup, dried in an oven at 110 ° C. for 3 hours, and then the mass of the residue was precisely weighed to the original. The ratio of the mass of the residue to the mass was determined as the non-volatile content (mass%).

<Surface tension>
After adjusting the liquid temperature of the paint to 23 ° C., the surface tension was measured by the platinum plate method using an automatic surface tension meter CBVP-Z type manufactured by Kyowa Interface Science Co., Ltd.

<Viscosity>
After adjusting the liquid temperature of the paint to 23 ° C., the viscosity of the shear rate of 0.1 s ^-1 and the viscosity of the shear rate of 1,000 s ^-1 were measured using a Leometer ARES manufactured by TA Instruments.

<Appearance of coating film 1 (leveling property)>
The paints of Examples 1 to 18 and Comparative Examples 1 to 13 were each applied to a glass plate (2 × 70 × 150 mm) using a brush so that the dry film thickness was 50 to 60 μm. The obtained coating film was dried at room temperature for 1 week, and the appearance of the coating film was visually evaluated based on the following criteria.
〇: The surface of the coating film was smooth and the appearance of the coating film was excellent.
Δ: The surface of the coating film had minute irregularities, and the appearance of the coating film was slightly inferior.
X: The surface of the coating film had clear irregularities, and the appearance of the coating film was inferior.

<Coating film appearance 2 (foaming)>
The paints of Examples 1 to 18 and Comparative Examples 1 to 13 were each applied to a glass plate (2 × 70 × 150 mm) using a film applicator so that the dry film thickness was 150 to 250 μm. The obtained coating film was dried at room temperature for 1 week, and the appearance of the coating film was visually evaluated based on the following criteria.
〇: There was no foaming inside the coating film, the surface of the coating film was smooth, and the appearance of the coating film was excellent.
X: There was clear unevenness due to foaming inside the coating film, and the appearance of the coating film was inferior.

<Painting workability>
The coating workability when the paints of Examples 1 to 18 and Comparative Examples 1 to 13 were applied to a tin plate with a roller and a brush so that the dry film thickness was 50 to 60 μm was evaluated according to the following criteria. ..
〇: There was no problem with the painting work.
Δ: The paint was liable to drip or the coated surface was liable to be inhomogeneous, so that the painting work required skill.
X: The roller and / or the brush was heavy or too light, so that a uniform painted surface could not be formed.

<Sagging>
Using the paints of Examples 1 to 18 and Comparative Examples 1 to 13, a coating film was prepared according to the sagging property test method of JIS K 5551 7.9, and the obtained coating film was dried at room temperature for 1 week. , The thickness of the coating film was measured using an electromagnetic film thickness meter, and the maximum film thickness was evaluated based on the following criteria. The test plate was a tin plate (0.3 × 150 × 150 mm).
⊚: The maximum film thickness was 70 μm or more.
◯: The maximum film thickness was 50 μm or more and less than 70 μm.
Δ: The maximum film thickness was 25 μm or more and less than 50 μm.
X: The maximum film thickness was less than 25 μm.

<Moisture resistance>
"Water-based", a water-based epoxy resin undercoat paint manufactured by Dainippon Paint Co., Ltd., is applied to a steel plate (3.2 x 70 x 150 mm) that has been grit-blasted so that the cleanliness is ISO Sa2.5 and the surface roughness is 25 μm with Rz _JIS . "Epool" was spray-coated on both sides of the test plate so that the dry film thickness was 60 μm, dried for 24 hours under the conditions of 23 ° C. and 50% relative humidity, and then on one side of Examples 1 to 18 and Comparative Examples 1 to 1. Each of the 13 paints was spray-coated so that the dry film thickness was 55 μm. After another 24 hours, the side surface of the test plate was coated with "aqueous epool" and then dried under the same conditions for 6 days to obtain the desired coated plate. The obtained coated plate was tested for 120 hours according to the long-term durability and moisture resistance (continuous dew condensation method) of the coating film of JIS K 5600-7-2. After the test, the cells were allowed to stand for 2 hours under the conditions of 23 ° C. and 50% relative humidity, and visually evaluated based on the following criteria.
〇: No abnormalities such as cracks, blisters, and peeling were observed on the surface of the coating film.
X: Abnormalities such as cracks, blisters, and peeling were observed on the surface of the coating film.

<Weather resistance>
The paints of Examples 1 to 18 and Comparative Examples 1 to 13 were spray-coated on an aluminum plate (1 × 70 × 150 mm) so as to have a dry film thickness of 55 μm. The obtained coating film was dried at room temperature for 1 week to obtain a desired coated plate. The dried coating film of the produced coated plate is tested according to the cycle A of the long-term durability, accelerated weathering resistance and accelerated light resistance (xenon lamp method) of the JIS K 5600-7-7 coating film. The gloss retention rate and the appearance of the coating film were visually determined. The gloss retention rate was calculated by measuring the 60 ° mirror glossiness of the coating film before and after the test with a gloss meter (BYK Gardner Micro-Gloss) manufactured by BYK Gardner.
* Gloss retention rate (%) = Mirror gloss of the coating film after the test (60 °) / Mirror gloss of the coating film before the test (60 °) x 100
⊚: The gloss retention rate at a test time of 2000 hours was 80% or more.
◯: The gloss retention rate at a test time of 500 hours was 80% or more, and the gloss retention rate at a test time of 2000 hours was less than 80%.
X: The gloss retention rate at a test time of 500 hours was less than 80%.

Claims (6)

It is a multi-layer film forming method including coating a base material with an undercoat paint and drying it to form an undercoat film, and coating the undercoat paint with a topcoat paint and drying it to form a topcoat film. hand,
The topcoat paint is a two-component reaction-curable water-based paint composition for a topcoat paint containing (A) a carboxyl group-containing resin, (B) a curing agent, (C) a pigment, and (D) water. ,
(B) The curing agent contains a carbodiimide group-containing compound (however, the general formula (1):

{In the formula, p indicates an integer from 1 to 5, and the two R ^1s are independently general formula (2) :.

(In the formula, the number average repetition number q is in the range of 6 to 40, and R ² indicates an alkyl group or a phenyl group having 1 to 8 carbon atoms.) Residues of polyethylene glycol monoalkyl ether represented by and / Or general formula (3):

(In the formula, the number average repetition number r is in the range of 4 to 14, and R ³ indicates an alkyl group or a phenyl group having 1 to 8 carbon atoms.) It is a residue of a polypropylene glycol monoalkyl ether represented by. .. }
(Excluding carbodiimide compounds represented by),
In the coating composition, the non-volatile content is 40 to 60% by mass, and the content is 40 to 60% by mass.
The coating composition has a viscosity of 90 to 1000 Pa · s at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C., and a viscosity of 0.3 to 3 Pa · s at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C. can be,
The surface tension of the coating composition is 55 to 80 mN / m .
The undercoat paint is a method comprising a two-component reaction-curable water-based paint composition containing an epoxy resin . The method according to claim 1 , wherein the top coat further contains (E) a viscosity modifier. The method according to claim 1 or 2, wherein the (A) carboxyl group-containing resin in the topcoat paint contains a carboxyl group-containing fluororesin. A coating body including a base material, an undercoat coating film arranged on the base material, and a topcoat coating film arranged on the undercoat coating film.
The topcoat coating film is a two-component reaction-curing water-based paint composition for a topcoat paint containing (A) a carboxyl group-containing resin, (B) a curing agent, (C) a pigment, and (D) water. hand,
(B) The curing agent contains a carbodiimide group-containing compound (however, the general formula (1):

{In the formula, p indicates an integer from 1 to 5, and the two R ^1s are independently general formula (2) :.

(In the formula, the number average repetition number q is in the range of 6 to 40, and R ² indicates an alkyl group or a phenyl group having 1 to 8 carbon atoms.) Residues of polyethylene glycol monoalkyl ether represented by and / Or general formula (3):

(In the formula, the number average repetition number r is in the range of 4 to 14, and R ³ indicates an alkyl group or a phenyl group having 1 to 8 carbon atoms.) It is a residue of a polypropylene glycol monoalkyl ether represented by. .. }
(Excluding carbodiimide compounds represented by),
In the coating composition, the non-volatile content is 40 to 60% by mass, and the content is 40 to 60% by mass.
The coating composition has a viscosity of 90 to 1000 Pa · s at a shear rate of 0.1 s ^-1 and a temperature of 23 ° C., and a viscosity of 0.3 to 3 Pa · s at a shear rate of 1,000 s ^-1 and a temperature of 23 ° C. can be,
The surface tension of the coating composition is formed from a topcoat coating material composed of a coating composition having a surface tension of 55 to 80 mN / m .
The undercoat coating film is a coating body formed of an undercoat paint made of a two-component reaction-curable water-based paint composition containing an epoxy resin . The coated body according to claim 4, wherein the topcoat paint further contains (E) a viscosity modifier. The coated body according to claim 4 or 5, wherein the (A) carboxyl group-containing resin in the topcoat paint contains a carboxyl group-containing fluororesin.