Method for forming multilayer coating film

Abstract

To provide a method for forming a multilayer coating film excellent in finishing properties without performing a putty coating process SOLUTION: A method for forming a multilayer coating film, the method comprising a step (1) of applying a primer coating composition to a substrate to form an undercoating film, a step (2) of applying an undercoating composition to the undercoating film to form an undercoating film having a thickness of 50 to 1000 μ m, and a step (3) of applying an intermediate coating composition to the undercoating film to form an intermediate coating film, the undercoat paint composition is a multi-component polyurethane paint composition obtained by mixing a base component containing an acrylic polyol, a pigment composition, and an organic solvent, and a curing agent component (A-II) containing a polyisocyanate compound, the solids concentration of the undercoat paint composition (A) during application is 70% by mass or more based on the total mass of the undercoat paint composition (A), and the intermediate paint composition (B) is a multi-component polyurethane paint composition or a multi-component polyurea paint composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for forming a multi-layer coating film. [Background technology]

[0002] Painting the exterior panels or parts of large car bodies and vehicles such as railway cars generally involves applying primer paint, putty paint, surfacer paint, intermediate paint, and top coat paint in that order to the object to be painted. Depending on the process, multiple coats of paint may be required to ensure performance.

[0003] The above process involves many steps, and some require multiple coats of paint, resulting in a lot of labor and time for the painting process. Furthermore, the paint film applied in the previous step must be sufficiently dry before moving on to the next step, which takes time. When heat drying is performed after painting, the amount of energy consumed during heat drying is enormous because the objects to be coated are large. To solve these issues, there is a need for process and energy savings.

[0004] Patent Document 1 discloses a method for forming a coating film, in which a first coating film is formed on an object using a coating composition, and a second coating film is formed on the first coating film, wherein the coating composition contains a solids content including a resin material and additives, and 30 to 70 wt % of a solvent component, in which the solvent component contains 70 to 98 wt % of a highly volatile solvent component having an evaporation rate of 0.5 or more relative to butyl acetate as 1, and 2 to 30 wt % of a low volatile solvent component having an evaporation rate of less than 0.5 relative to butyl acetate as 1. Focusing on the surfacer coating and undercoat coating steps, wet-on-wet coating is used to reduce the cost and time of the coating process, but there is no difference in the number of coats applied, and further process reductions are desired.

[0005] Patent Document 2 discloses a method for forming a putty coating on the surface of a railway vehicle exterior panel by spraying a putty composition consisting of a base component essentially containing an unsaturated polyester resin, a vinyl monomer, and a filler, and a curing agent component essentially containing an organic peroxide. The method comprises: introducing the base component, which is pressurized at a pressure suitable for spray coating, the curing agent component, which is pressurized by compressed air, and separately compressed air, into a spray gun separately; premixing the curing agent component pressurized by the compressed air and a portion of the separately compressed air through a nozzle provided at the rear inside of the spray gun; merging the premix with the remaining portion of the separately compressed air at the front inside of the spray gun and colliding with an impact material; and spraying the mixture of the curing agent component and the separately compressed air, which has been homogeneously mixed, at the tip of the spray gun while merging and mixing with the base component. Although applying a putty film using a spray gun significantly improves painting workability, it still requires three to five applications to fill in any unevenness, and polishing is required after applying the putty, resulting in significant time and workload issues. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-134606 [Patent Document 2] Japanese Patent Application Publication No. 10-80666 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and aims to provide a method for forming a multi-layer coating film that provides an excellent finish without the need for a putty coating process. By applying a thick surfacer instead of the putty coating process, the present invention aims to improve the ease of painting, reduce the time required for drying, and reduce the energy required for heating and drying. [Means for solving the problem]

[0008] As a result of intensive research into solving the above problems, the inventors have discovered a method for forming a multilayer coating film, comprising: step (1) of applying a primer coating composition (D) to an object to be coated to form a primed coating film (D'); step (2) of applying a primer coating composition (A) on the primed coating film (D') to form a primed coating film (A') having a thickness of 50 to 1000 μm; and step (3) of applying an intermediate coating composition (B) on the primer coating film (A') to form an intermediate coating film (B'), wherein the primer coating composition (A) is a base composition comprising an acrylic polyol (Aa), a pigment composition (Ab), and an organic solvent (Ac). The present inventors have discovered that the above-mentioned problems can be solved by a method for forming a multi-layer coating film, which comprises mixing an organic solvent-based multi-component polyurethane coating composition obtained by mixing a curing agent component (A-II) containing a polyisocyanate compound (Ad), wherein the solids concentration of the primer coating composition (A) at the time of application is 70 mass% or more based on 100 mass parts of the total mass of the primer coating composition (A), and the intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition or an organic solvent-based multi-component polyurea coating composition, and have completed the present invention. That is, the present invention provides the following multi-layer coating film forming method. Item 1. Step (1) of applying a primer coating composition (D) to an object to be coated to form a primer coating film (D'); Step (2) of applying a primer coating composition (A) onto the primer-treated coating film (D') to form a primer coating film (A') having a thickness of 50 to 1000 μm; Step (3) of applying an intermediate coating composition (B) onto the undercoat coating film (A') to form an intermediate coating film (B'); A method for forming a multilayer coating film, comprising: The primer coating composition (A) is an organic solvent-based multi-component polyurethane coating composition obtained by mixing a main component (AI) containing an acrylic polyol (Aa), a pigment composition (Ab) and an organic solvent (Ac), and a curing agent component (A-II) containing a polyisocyanate compound (Ad), The solid content concentration of the primer coating composition (A) at the time of application is 70 mass% or more based on 100 mass parts of the total mass of the primer coating composition (A), The intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition or an organic solvent-based multi-component polyurea coating composition. A method for forming multi-layer coating films. Item 2. The method for forming a multi-layer coating film according to Item 1, wherein the acrylic polyol (Aa) contained in the primer coating composition (A) contains an acrylic polyol (A-a1) having a glass transition temperature of from -20°C to 60°C, an acid value of from 1 mgKOH / g to 25 mgKOH / g, and a hydroxyl value of from 100 mgKOH / g to 200 mgKOH / g. Item 3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the content of the pigment composition (Ab) in the undercoat paint composition (A) is 100 to 500 parts by mass based on 100 parts by mass of the solid content of all resin components contained in the main component (AI) and the curing agent component (A-II). Item 4. The method for forming a multi-layer coating film according to any one of Items 1 to 3, wherein the solids concentration of the intermediate coating composition (B) at the time of application is 70 mass% or more based on 100 mass parts of the total mass of the intermediate coating composition (B). Item 5. The intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition (B1) obtained by mixing a main component (B1-I) containing a hydroxyl group-containing resin (B1-a), a pigment composition (B1-b), an organic solvent (B1-c) and a catalyst (B1-e), and a curing agent component (B1-II) containing a polyisocyanate compound (B1-d), 5. The method for forming a multi-layer coating film according to any one of items 1 to 4, wherein the content of the catalyst (B1-e) is 0.1 to 5 parts by mass based on 100 parts by mass of the solid content of the hydroxyl group-containing resin (B1-a). Item 6. The method for forming a multilayer coating film according to Item 5, wherein the hydroxyl group-containing resin (B1-a) contains an acrylic polyol (B1-a1) and a polyester polyol (B1-a2), and the solid content ratio of the acrylic polyol (B1-a1) to the polyester polyol (B1-a2) is 50 / 50 to 95 / 5 by mass. Item 7. The intermediate coating composition (B) is an organic solvent-based multi-component polyurea coating composition (B2) obtained by mixing a main component (B2-I) containing a polyaspartic acid ester (B2-a), a pigment composition (B2-b) and an organic solvent (B2-c), and a curing agent component (B2-II) containing a polyisocyanate compound (B2-d), 7. The method for forming a multi-layer coating film according to any one of items 1 to 6, wherein the water content of the main component (B-II) is 5000 ppm or less. Item 8. The method for forming a multilayer coating film according to Item 7, wherein the main component (B2-I) contains a dehydrating agent (B2-e), and the content of the dehydrating agent (B2-e) is 5 to 30 parts by mass based on 100 parts by mass of the solid content of all resin components contained in the main component (B2-I). Item 9. After the step (3), a topcoat paint composition (C) is applied onto the intermediate coating film (B') to form a topcoat coating film (C'). A method for forming a multilayer coating film according to any one of items 1 to 8, comprising the step (4). Item 10. The topcoat paint composition (C) is an aqueous multi-component polyurethane paint composition obtained by mixing a main component (CI) containing a hydroxyl group-containing resin (Ca), a pigment composition (Cb) and water, and a curing agent component (C-II) containing a polyisocyanate compound (Cd), Item 10. The method for forming a multilayer coating film according to Item 9, wherein the hydroxyl group-containing resin (Ca) contains an acrylic polyol (C-a1) and a polyester polyol (C-a2), and the solid content ratio of the acrylic polyol (C-a1) to the polyester polyol (C-a2) is 40 / 60 to 90 / 10 by mass. Item 11. The method for forming a multilayer coating film according to any one of Items 1 to 10, wherein the coating in steps (1), (2), and (3) is carried out by airless spraying. Item 12. The method for forming a multilayer coating film according to any one of Items 1 to 11, wherein the substrate is a railway vehicle, industrial machinery, construction machinery, a large vehicle, a ship, a building, or a structure. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for forming a multi-layer coating film that has an excellent finish while improving coating workability, reducing the time required for drying, and reducing the energy required for heating and drying by eliminating the putty coating process. DETAILED DESCRIPTION OF THE INVENTION

[0010] Each step of the present invention will be described below.

[0011] <1. Step (1) of forming primer coating film (D')> The method for forming a multi-layer coating film of the present invention comprises the step (1) of applying a primer coating composition (D) to an article to be coated to form a primed coating film (D').

[0012] <Object to be coated> Examples of substrates to be coated include metal substrates, plastic substrates, and composite substrates thereof, as well as wood, glass, cloth, concrete, and ceramic materials. Metal substrates include metals such as iron, steel, copper, aluminum, tin, and zinc, and alloys containing these metals. Metal substrates may be plated with zinc, copper, chromium, or the like, or may be surface-treated using a surface treatment agent such as chromate, zinc phosphate, or zirconium salt. Examples of plastic substrates include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The surfaces of these metal or various plastic substrates may be surface-treated, such as by degreasing with a detergent or solvent, phosphate treatment, chromate treatment, complex oxide treatment, blasting, cleaning, or polishing.

[0013] The substrate may be a molded article containing the above-mentioned substrate. Examples of molded articles include various molded articles such as automobile bodies, various vehicle bodies, and parts for home appliances. Among these, industrial machinery, construction machinery, railway vehicles, large vehicles, ship bodies, buildings, and structures are preferred, and railway vehicles are particularly preferred.

[0014] <Primer coating composition (D)> The primer coating composition (D) can be any conventionally known primer coating, and can be selected appropriately depending on the material of the substrate to be coated. For example, a primer coating having rust prevention and adhesion-improving properties is preferred for metal substrates, and an primer coating having adhesion-improving properties is preferred for plastic substrates.

[0015] Specific examples of the components of the primer coating composition (D) include coating compositions containing a film-forming resin, a crosslinking agent, a coloring pigment, an extender pigment, a luster pigment, an anti-rust pigment, and a conductive pigment. Furthermore, coating additives such as an ultraviolet absorber, a light stabilizer, a curing catalyst, a plasticizer, an adhesion promoter, a compatibilizer, an anti-foaming agent, a viscosity modifier, an anti-rust agent, and a surface conditioner can be appropriately added. When the substrate to be coated is a metal substrate, it is preferable to contain an epoxy resin as the film-forming resin, and it is preferable to contain an anti-rust pigment. Furthermore, when the substrate to be coated is a plastic substrate, it is preferable to contain a polyolefin resin as the film-forming resin.

[0016] <Method for applying primer coating composition (D)> In the present invention, the primer coating composition (D) is applied to the above-mentioned substrate to form a primed coating film (D').

[0017] The primer coating composition (D) can be applied by a conventionally known coating method, with airless spray coating being particularly preferred.

[0018] The relative humidity (hereinafter sometimes abbreviated as RH) during coating is preferably 80% or less, particularly 70% or less.

[0019] There are no particular limitations on the drying method after coating, and a coating film can be obtained by drying at room temperature, but there are no particular problems with heat drying or forced drying depending on the coating environment, etc. When heat drying is used, drying can be carried out at a temperature in the range of 25 to 80°C, preferably 40 to 60°C, for 0.5 to 6 hours. If necessary, air drying using a blower or the like can be used. When drying at room temperature, a coating film can be obtained by drying for 6 to 48 hours in an environment of, for example, 5 to 45°C.

[0020] In the case of forced drying, in terms of finish, it is recommended to set the material at room temperature for 2 to 30 minutes before heat curing. It may also be left to stand.

[0021] The film thickness can be adjusted as appropriate depending on the condition of the surface to be coated, but generally, a dry film thickness in the range of 5 to 150 μm, particularly 10 to 120 μm, is suitable.

[0022] <2. Step (2) of forming primer coating film (A')> The method for forming a multilayer coating film of the present invention comprises the step (2) of applying an undercoat paint composition (A) onto the undercoat treated coating film (D') to form an undercoat coating film (A') having a thickness of 50 to 1000 μm.

[0023] <Undercoat paint composition (A)> The primer coating composition (A) is an organic solvent-based multi-component polyurethane coating composition obtained by mixing a base component (AI) containing an acrylic polyol (Aa), a pigment composition (Ab), and an organic solvent (Ac), with a curing agent component (A-II) containing a polyisocyanate compound (Ad). The primer coating composition (A) is a two-component composition in which each component is stored separately. The components are generally mixed immediately before application, and the viscosity is adjusted with a diluting thinner as needed before use. The primer coating composition (A) can also be a multi-component composition obtained by mixing three or more components, including components other than the base component (AI) and curing agent component (A-II), if necessary.

[0024] The primer coating composition (A) is suitably prepared by blending the main component (AI) and the curing agent component (A-II) in such a ratio that the amount of isocyanate groups in the curing agent component (A-II) is 0.5 to 4.0 equivalents, preferably 0.7 to 3.0 equivalents, per equivalent of hydroxyl groups in the main component (AI).

[0025] The primer coating composition (A) has a solids concentration at the time of application of 70 mass % or more, more preferably 75 mass % or more, based on 100 parts by mass of the total mass of the primer coating composition (A).

[0026] <Main ingredient (AI)> The main component (AI) contains an acrylic polyol (Aa), a pigment composition (Ab), and an organic solvent (Ac).

[0027] The non-volatile content of the main component (AI) is preferably within the range of 70 to 99.9 mass %, particularly 75 to 90 mass %, from the viewpoints of ease of application and finish of the formed coating film.

[0028] The main component (AI) can have a low viscosity relative to its solids concentration, enabling excellent coating workability. Specifically, the viscosity measured with a Brookfield viscometer in the storage state (sealed can) can be in the range of 2,000 to 15,000 mPa·s. Unless otherwise specified in this specification, the viscosity is measured on a sample adjusted to 25°C.

[0029] <Acrylic polyol (Aa)> The primer coating composition (A) contains an acrylic polyol (Aa) in a main component (AI).

[0030] The acrylic polyol (Aa) is a component that can serve as a polyurethane film-forming component together with the polyisocyanate compound (Ad) described below. Any conventionally known acrylic polyol can be used without limitation as long as it has organic solvent dilutability and film-forming ability, and can be, for example, a copolymer of polymerizable unsaturated monomers containing a hydroxyl group-containing polymerizable unsaturated monomer as an essential component and at least one (meth)acryloyl group-containing monomer.

[0031] Examples of hydroxyl group-containing polymerizable unsaturated monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; ε-caprolactone-modified products of the above hydroxyalkyl (meth)acrylates; hydroxyl group-containing (meth)acryloyl monomers such as polyoxyethylene chain-containing (meth)acrylates whose molecular terminals are hydroxyl groups; and allyl alcohol, and these can be used alone or in combination of two or more.

[0032] Examples of the polymerizable unsaturated monomer to be copolymerized with the hydroxyl group-containing polymerizable unsaturated monomer include linear or branched alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; cyclohexyl (meth)acrylate; acrylate, alicyclic alkyl (meth)acrylate such as isobornyl (meth)acrylate; aralkyl (meth)acrylate such as benzyl (meth)acrylate; alkoxyalkyl (meth)acrylate such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate; perfluoroalkyl (meth)acrylate; N,N-dialkylaminoalkyl (meth)acrylate such as N,N-diethylaminoethyl (meth)acrylate; (meth)acrylamide; allyl (meth)acrylate acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate (Meth)acryloyl monomers having at least two polymerizable unsaturated groups in one molecule, such as glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, and 1,1,1-trishydroxymethylpropane tri(meth)acrylate; (meth)acrylic acid; carbonyl group-containing (meth)acryloyl monomers, such as acetoacetoxyethyl (meth)acrylate and diacetone (meth)acrylamide;Examples of the epoxy group-containing (meth)acryloyl monomers include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, and 3,4-epoxycyclohexylpropyl (meth)acrylate; isocyanato group-containing (meth)acryloyl monomers such as isocyanatoethyl (meth)acrylate; alkoxysilyl group-containing (meth)acryloyl monomers such as γ-methacryloyloxypropyltrimethoxysilane and γ-methacryloyloxypropyltriethoxysilane; and oxidatively curable group-containing (meth)acryloyl monomers such as dicyclopentenyloxyethyl (meth)acrylate, dicyclopentenyloxypropyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. These may be used alone or in combination of two or more.

[0033] Examples of copolymerizable polymerizable unsaturated monomers other than (meth)acryloyl monomers include (meth)acrylonitrile; vinyl ester compounds such as vinyl acetate and vinyl propionate; vinyl aromatic compounds such as styrene and α-methylstyrene; polyvinyl compounds having at least two polymerizable unsaturated groups in one molecule such as triallyl isocyanurate, diallyl terephthalate and divinylbenzene; carboxyl group-containing polymerizable unsaturated monomers such as maleic acid, crotonic acid and β-carboxyethyl acrylate; (meth)acrolein, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone and vinyl ethyl ketone), vinyl butyl ketone, etc.), acetoacetoxy allyl ester, and other carbonyl group-containing polymerizable unsaturated monomers; allyl glycidyl ether, and other epoxy group-containing polymerizable unsaturated monomers; m-isopropenyl-α,α-dimethylbenzyl isocyanate, and other isocyanato group-containing polymerizable unsaturated monomers; vinyltrimethoxysilane, vinyltriethoxysilane, and other alkoxysilyl group-containing polymerizable unsaturated monomers; and oxidatively curable group-containing polymerizable unsaturated monomers, such as reaction products of epoxy group-containing polymerizable unsaturated monomers or hydroxyl group-containing polymerizable unsaturated monomers with unsaturated fatty acids. These may be used alone or in combination of two or more.

[0034] The acrylic polyol (Aa) can be synthesized by a conventionally known method, for example, by polymerizing a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer in the presence of an organic solvent using a polymerization initiator.

[0035] As the polymerization initiator, any known polymerization initiator can be used without any limitation, and examples thereof include peroxide-based polymerization initiators and azo-based polymerization initiators.

[0036] As the organic solvent used in the polymerization, any known organic solvent can be used without limitation, and examples thereof include alcohol-based organic solvents, ether-based organic solvents, hydrocarbon-based organic solvents, aromatic organic solvents, ketone-based organic solvents, ester-based organic solvents, etc. These can be used alone or in combination of two or more.

[0037] The acrylic polyol (Aa) contains an acrylic polyol (A-a1) having a glass transition temperature of -20°C or higher and 60°C or lower, an acid value of 1 mgKOH / g or higher and 25 mgKOH / g or lower, and a hydroxyl value of 100 mgKOH / g or higher and 200 mgKOH / g or lower. The acrylic polyol (A-a1) is suitably contained in the acrylic polyol (Aa) in an amount of 75% by mass or higher, preferably 85% by mass or higher.

[0038] From the viewpoint of suppressing skinning, the acrylic polyol (A-a1) has a glass transition temperature of 60° C. or lower, and preferably 50° C. or lower. From the viewpoint of polishability, the glass transition temperature is −20° C. or higher, preferably −10° C. or higher, and preferably 0° C. or higher.

[0039] In this specification, the glass transition temperature (Tg) is a value calculated by the following formula. 1 / Tg(K)=W1 / T1+W2 / T2+...Wn / Tn Tg(℃)=Tg(K)-273 where W1, W2, ... Wn are the mass fractions of each monomer, and T1, T2, ... Tn are the glass transition temperatures Tg (K) of the homopolymers of each monomer. The glass transition temperatures of the homopolymers of each monomer are values ​​taken from POLYMER HANDBOOK Fourth Edition, edited by J. Brandrup, Eh Immergut, and E.A. Grulke (1999). The glass transition temperatures of monomers not listed in this document are taken as the static glass transition temperatures when the homopolymers of the monomers are synthesized so as to have a weight-average molecular weight of about 50,000.

[0040] In this specification, the static glass transition temperature of a resin can be measured, for example, by placing a sample in a measuring cup, vacuum suctioning the sample to completely remove the solvent, and then measuring the change in heat quantity in the range of −100° C. to 150° C. at a temperature rise rate of 3° C. / min using a differential scanning calorimeter "DSC-50Q" (trade name, manufactured by Shimadzu Corporation), and defining the first change point in the baseline on the low temperature side as the static glass transition temperature.

[0041] The acrylic polyol (A-a1) has an acid value of 1 mgKOH / g or more, preferably 2 mgKOH / g or more, and more preferably 3 mgKOH / g or more from the viewpoint of pot life, and an acid value of 25 mgKOH / g or less, preferably 20 mgKOH / g or less, and more preferably 15 mgKOH / g or less from the viewpoint of suppressing scumming.

[0042] The acrylic polyol (A-a1) has a hydroxyl value of 100 mgKOH / g or more, preferably 110 mgKOH / g or more, and more preferably 120 mgKOH / g or more from the viewpoint of curability, and 200 mgKOH / g or less, preferably 190 mgKOH / g or less, and more preferably 180 mgKOH / g or less from the viewpoint of water resistance and pot life.

[0043] From the viewpoint of suppressing skinning, the acrylic polyol (A-a1) preferably has a weight average molecular weight of 1,000 or more and 10,000 or less, more preferably 1,500 or more and 8,000 or less, and even more preferably 2,000 or more and 5,000 or less.

[0044] In this specification, the weight-average molecular weight and number-average molecular weight are values ​​measured using a gel permeation chromatograph ("HLC8120GPC" manufactured by Tosoh Corporation) and converted based on the weight-average molecular weight and number-average molecular weight of polystyrene. Four columns, "TSKgel G-4000HxL," "TSKgel G-3000HxL," "TSKgel G-2500HxL," and "TSKgel G-2000HxL" (all manufactured by Tosoh Corporation), were used, and the measurement was performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 ml / min, and detector: RI.

[0045] The acrylic polyol (Aa) is suitably contained in an amount of 75% by mass or more, preferably 85% by mass or more, of the resin solid content contained in the main component (AI).

[0046] In this specification, the term "solid content" or "non-volatile content" refers to the residue remaining after removing the volatile components, and the residue may be solid or liquid at room temperature. For example, the term refers to the residue remaining after treating a sample at 105°C for 3 hours to remove the volatile components.

[0047] The content of the acrylic polyol (Aa) in the main component (AI) is typically within the range of 10 to 50 parts by mass, preferably 15 to 45 parts by mass, and more preferably 20 to 40 parts by mass, in terms of non-volatile content, per 100 parts by mass of the total mass of the main component (AI).

[0048] <Pigment composition (Ab)> The main component (AI) includes a pigment composition (Ab).

[0049] It is preferable for the pigment composition (Ab) to contain a body pigment as part of its components. Specific examples of the body pigment include calcium carbonate, talc, clay, barium sulfate, barium carbonate, aluminum silicate, gypsum, silica, white carbon, diatomaceous earth, magnesium carbonate, alumina white, gloss white, and mica powder. These can be used alone or in combination of two or more. Among these, it is preferable to contain at least one of calcium carbonate, talc, clay, and barium sulfate, and calcium carbonate is particularly preferable. As the body pigment, any of those known as body pigments in the paint industry can be used. These can be synthetic or natural products, and may be surface-treated as necessary. There are also no limitations on the shape or size of the body pigment.

[0050] From the viewpoint of thick coating properties and polishing properties, the content of the extender pigment is preferably in the range of 100 to 500 parts by mass, and more preferably in the range of 120 to 300 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing agent component (A-II).

[0051] From the viewpoint of coating workability, the pigment composition (Ab) preferably contains at least one of bentonite, montmorillonite, beidellite, nottronite, saponite, hectorite, and stevensite. The content is preferably in the range of 0.5 to 10 parts by mass, and more preferably in the range of 1 to 8 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing agent component (A-II).

[0052] Furthermore, the pigment composition (Ab) may contain known pigments such as color pigments and anti-rust pigments, if necessary.

[0053] Examples of color pigments include white pigments such as titanium dioxide; black pigments such as carbon black, acetylene black, lamp black, bone black, graphite, iron black, and aniline black; yellow pigments such as yellow iron oxide, titanium yellow, monoazo yellow, condensed azo yellow, azomethine yellow, bismuth vanadate, benzimidazolone, isoindolinone, isoindoline, quinophthalone, benzidine yellow, and permanent yellow; orange pigments such as permanent orange; red iron oxide, naphthol AS-based azo red, anthanthrone, anthraquinonyl red, and perilemma. Examples of pigments that can be used include red pigments such as rune, quinacridone red pigments, diketopyrrolopyrrole, watching red, and permanent red; purple pigments such as cobalt purple, quinacridone violet, and dioxazine violet; blue pigments such as cobalt blue, phthalocyanine blue, and threne blue; green pigments such as phthalocyanine green; metallic pigments such as aluminum powder, bronze powder, copper powder, tin powder, iron phosphide, and zinc powder; and pearlescent pigments such as metal oxide-coated mica powder and mica-like iron oxide. These pigments can be used alone or in combination of two or more.

[0054] When the undercoat paint composition (A) of the present invention contains a coloring pigment, it is preferable that the mass of the coloring pigment is 1 or more and less than 100 parts by mass, preferably 2 to 80 parts by mass, and more preferably 3 to 60 parts by mass, based on 100 parts by mass of the total of the extender pigments, from the viewpoint of thick coating properties and the finished appearance of the top coat.

[0055] In the present invention, the content of the pigment composition (Ab) is suitably within the range of 100 parts by mass or more and 500 parts by mass or less, and preferably 120 parts by mass or more and 400 parts by mass or less, based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing component (A-II), from the viewpoints of the adhesion strength of the primer coating film and the finished appearance after the topcoat coating.

[0056] <Organic solvent (Ac)> The organic solvent (Ac) can be, for example, an organic compound having a molecular weight in the range of 58 to 220, particularly 72 to 200, and any organic solvent known in the field of paints can be used without limitation. However, it is desirable that the organic solvent contains at least one organic solvent selected from, for example, ester-based organic solvents and ketone-based organic solvents.

[0057] Examples of such ester-based organic solvents include ethyl acetate, butyl acetate, isobutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and diethylene glycol monoethyl ether acetate. Examples of ketone-based organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl amyl ketone, ethyl isoamyl ketone, diisobutyl ketone, methyl hexyl ketone, and isophorone. These can be used alone or in combination of two or more.

[0058] The amount of at least one organic solvent selected from such ester-based organic solvents and ketone-based organic solvents used is desirably 5% by mass or more, and particularly 20% by mass or more, of the total organic solvents contained in the primer coating composition (A).

[0059] In the present invention, examples of organic solvents other than the above-mentioned ester-based organic solvents and ketone-based organic solvents include linear alkanes such as n-butane, n-hexane, n-heptane, n-pentane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, and n-heptadecane; 2-methylbutane, 2,2-dimethylpropane, 2-methylpentane; hexane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 3,4-diethylhexane, 2,6-dimethyloctane, 3,3-dimethyloctane, 3,5-dimethyloctane, 4,4-dimethyloctane, 3-ethyl-3- branched alkanes such as methylheptane, 2-methylnonane, 3-methylnonane, 4-methylnonane, 5-methylnonane, 2-methylundecane, 3-methylundecane, and 2,2,4,6,6-pentamethylheptane; aliphatic hydrocarbon organic solvents such as cyclic alkanes such as cyclopentane, t-decalin, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, propylcyclohexane, isopropylcyclohexane, 1,2-methylethylcyclohexane, 1,3-methylethylcyclohexane, 1,4-methylethylcyclohexane, 1,2,3-trimethylcyclohexane, 1,2,4-trimethylcyclohexane, and 1,3,5-trimethylcyclohexane; and aromatic hydrocarbon organic solvents such as toluene and xylene.Dioxane, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono Examples of the organic solvent include ether-based organic solvents such as tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol monoisopropyl ether; and alcohol-based organic solvents such as methanol, isopropanol, tert-butanol, secondary butanol, isobutanol, n-butanol, 2-ethylhexanol, n-octanol, and benzyl alcohol.

[0060] The organic solvent (Ac) can be blended as a polymerization solvent or dilution solvent in the production of the acrylic polyol (Aa), or as a dilution solvent in the production of the main component (AI).

[0061] <Hardening agent component (A-II)> The curing agent component (A-II) contains a polyisocyanate compound (Ad).

[0062] From the viewpoints of workability and miscibility with the main component (AI), it is preferable that the curing agent component (A-II) contains an organic solvent. The organic solvent can be appropriately selected from the compounds exemplified in the description of the organic solvent (Ac) above. From the viewpoints of coating workability and the finish of the formed coating film, the non-volatile content of the curing agent component (A-II) is suitably in the range of 70 to 100 mass%, particularly 75 to 100 mass%.

[0063] <Polyisocyanate compounds (Ad)> The polyisocyanate compound (Ad) is a polyisocyanate compound having two or more isocyanate groups in one molecule. Specific examples thereof include diisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, xylylene diisocyanate, meta-tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, lysine diisocyanate, butane diisocyanate, and pentyl diisocyanate; 1,8-diisocyanato-4-isocyanatomethyloctane, (2S)-2,6-diisocyanatohexanoic acid 2-isocyanatoethyl (trivial name: lysine triisocyanate), 2,6-diisocyanato-4-isocyanatomethyloctane, 2-isocyanatoethyl (2S)-2,6-diisocyanatohexanoate (trivial name: lysine triisocyanate), and 2,6-diisocyanato-4-isocyanatomethyloctane. Examples of the polyisocyanate include triisocyanate compounds such as 2-isocyanatoethyl isocyanatohexanoate, 1,6,11-triisocyanatoundecane, 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and polyisocyanate compounds, or adducts of these polyisocyanates with polyhydric alcohols, low-molecular-weight polyester resins, or water, or cyclized polymers of the above-mentioned polyisocyanates, and further isocyanate-biuret compounds, and these may be used alone or in combination of two or more.

[0064] In the present invention, the curing agent component (A-II) preferably contains a polyisocyanate compound (A-d1) having a viscosity of 100 to 1500 mPa·s as measured at 25°C with an E-type viscometer. By using a polyisocyanate with a viscosity within this range, the viscosity of the coating composition is reduced, enabling the coating composition to have a high solid content. From the viewpoint of coating workability, a viscosity of 100 to 1000 mPa·s is particularly preferred.

[0065] In this specification, when measuring viscosity with an E-type viscometer, the RE215 model manufactured by Toki Sangyo Co., Ltd. is used, and the measurement is carried out at 25°C.

[0066] From the viewpoint of curability and coating film hardness, it is preferable to further contain an alicyclic polyisocyanate compound (A-d2) in addition to the polyisocyanate compound (A-d1). Specific examples of the alicyclic polyisocyanate compound (A-d2) include alicyclic diisocyanates such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, and norbornane diisocyanate; , 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyanato and alicyclic triisocyanates such as 2-isocyanatoethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0067] <Other additives for primer coating composition (A)> The primer coating composition (A) may further contain, as appropriate, paint additives such as viscosity modifiers, curing catalysts, modifying resins other than the acrylic polyol (Aa), such as cellulose acetate butyrate and its modified products, polyester resins, alkyd resins, and polyurethane resins, pigment dispersants, surface conditioners, and resin particles. These additives may be contained in either the main component (AI) or the curing agent component (A-II), but from the viewpoint of storage stability, it is preferable that additives capable of directly reacting with isocyanate compounds be contained in the main component (AI).

[0068] The primer coating composition (A) preferably contains an amide-based rheology control agent. The use of an amide-based rheology control agent improves the storage stability of the main component (AI) and the application workability of the primer coating composition (A), while also improving the adhesion strength of the primer coating composition (A) to the intermediate coating film (B'). The amide-based rheology control agent may be contained in either the main component (AI) or the curing agent component (A-II), but is preferably contained in the main component (AI) because of its effect on the storage stability of the main component (AI).

[0069] As such an amide-based rheology control agent, any agent known in the field of coatings can be used without any limitation, and the synthesis method, materials used, etc. are not particularly limited, and commercially available products can also be used.

[0070] Specific examples include fatty acid monoamides synthesized by dehydration of fatty acid ammonium salts or ammonolysis of fats and oils (esters); fatty acid diamides (bisamides) synthesized by the condensation reaction of fatty acid amides and formaldehyde, the thermal condensation reaction of monocarboxylic acids and diamines, or the thermal condensation reaction of dibasic acids and monoamines; fatty acid polyamides obtained by polycondensation of dibasic acids and diamines, polycondensation of diamine derivatives and dibasic acids, polycondensation of diamines and dibasic acid derivatives or dimer acids obtained by dimerization of unsaturated fatty acids, or ring-opening polymerization of lactams.

[0071] Such an amide-based rheology control agent may be diluted with a diluting medium such as an organic solvent. In the present invention, the content of the active ingredients (components other than the diluting medium) of the amide-based rheology control agent is desirably within a range of 0.5 to 10 parts by mass, preferably 1 to 8 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing agent component (A-II).

[0072] From the viewpoint of suppressing foaming, the undercoat paint composition (A) preferably contains an antifoaming agent. The antifoaming agent may be contained in either the main component (AI) or the curing agent component (A-II), but is preferably contained in the main component (AI).

[0073] Any defoaming agent known in the field of coatings can be used without any restrictions, and there are no particular restrictions on the synthesis method, materials used, etc., and commercially available products can also be used.Specific examples of commercially available products include Dappo SN-348, Dappo SN-352, Dappo SN-359, Dappo SN-368 (manufactured by San Nopco), Flowlen AC-202, Flowlen AC-262H, Flowlen AC-300, Flowlen AC-300HF, Flowlen AC-326F, Flowlen AC-901, Flowlen AC-901HF, Flowlen AC-902, Flowlen AC-903, and Flowlen AC-904. LEN AC-903HF, FLOWEREN AC-950, FLOWEREN AC-1160, FLOWEREN AC-1160HF, FLOWEREN AC-1190, FLOWEREN AC-1190HF, FLOWEREN AC-2000, FLOWEREN AC-2000HF, FLOWEREN AC-2200HF, FLOWEREN AO-82, FLOWEREN AO-98, FLOWEREN AO-108, AQUALEN 8020, AQUALEN 8021N, AQUALEN SB-520, Aqualene SB-630, Aqualene HS-01, Florene AO-5 (manufactured by Kyoeisha Chemical Co., Ltd.), BYK-051N, BYK-052N, BYK-055, BYK-065, BYK-077, BYK-081, BYK-088, BYK-354, BYK-1752, BYK-011, BYK-012, BYK-014, BYK-017, BYK-021, BYK-022, BYK-024, BYK-025, BYK-044 , BYK-093, BYK-1610, BYK-1640, BYK-1650, BYK-1785 (manufactured by BYK), Disparlon OX-880EF, Disparlon OX-70, Disparlon OX-77EF, Disparlon OX-710, Disparlon OX-66, Disparlon OX-66EF, Disparlon 1952, Disparlon 1958, Disparlon 1930N, Disparlon 1934 (manufactured by Kusumoto Chemicals), TEGO Examples of such foams include Airex 910, TEGO Airex 920, TEGO Airex 931, TEGO Airex 940, TEGO Airex 950, TEGO Airex 901W, TEGO Airex 902W, TEGO Airex 904W, TEGO Foamex 800, TEGO Foamex 815N, TEGO Foamex 840, TEGO Foamex 1488, TEGO Foamex 1495, and TEGO Foamex 8030 (manufactured by Evonik).

[0074] The content of the antifoaming agent is preferably in the range of 0.05 to 3 parts by mass, and more preferably in the range of 0.1 to 2 parts by mass, of the active ingredient based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing agent component (A-II).

[0075] From the viewpoint of improving adhesion, the undercoat paint composition (A) preferably contains a silane coupling agent. The type of silane coupling agent is not particularly limited, but examples thereof include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)methyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)methyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)methyldimethoxysilane; 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2 Examples of suitable silane coupling agents include amino group-containing silane coupling agents such as (aminoethyl) 3-aminopropyltrimethoxysilane and N-2(aminoethyl) 3-aminopropylmethyldimethoxysilane; mercapto group-containing silane coupling agents such as 3-mercaptopropyltrimethoxysilane; vinyl group-containing silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(methoxyethoxy)silane; and (meth)acryloyl group-containing silane coupling agents such as 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, and 3-(meth)acryloyloxypropyldimethoxymethylsilane. Two or more of these can also be used in combination. Among these, it is preferable to use an epoxy group-containing silane coupling agent.

[0076] The content of the silane coupling agent is preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass, based on 100 parts by mass of the solid content of the resin components contained in the main component (AI) and the curing agent component (A-II).

[0077] When the silane coupling agent does not have a hydroxyl group, the curing agent component (A-II) preferably contains the silane coupling agent.

[0078] Furthermore, as the curing catalyst, any conventionally known urethane catalyst can be used without any particular limitation, and examples thereof include metal compounds such as bismuth nitrate, lead oleate, tin octoate, dibutyltin dilaurate, dibutyltin bis(acetylacetonate), dibutyltin diacetate, dibutyltin octanoate, dioctyltin dilaurate, dioctyltin dineodecanoate, titanium tetrachloride, dibutyltitanium dichloride, tetrabutyl titanate, iron trichloride, and zinc octoate, as well as tertiary amines.

[0079] The curing catalyst may be contained in either the main component (AI) or the curing agent component (A-II). When the curing catalyst is contained in the main component (AI), the content of the curing catalyst is suitably in the range of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the solid content of the acrylic polyol (Aa), from the viewpoints of curability of the composition of the present invention and suppression of viscosity increase after mixing of the main component (AI) and the curing agent component (A-II).

[0080] <Method for forming primer coating film (A')> In the present invention, the primer coating composition (A) is applied onto the above-mentioned primer-treated coating film (D') to form the primer coating film (A').

[0081] The primer coating composition (A) can be applied by a conventionally known coating method, with airless spray coating being particularly suitable. The primer coating composition (A) can be applied in a thick film, with the primer coating film (A') having a dry film thickness of 50 to 1000 μm, preferably 100 to 800 μm. The primer coating composition (A) has excellent coating workability because a primer coating film (A') with a thickness of 50 to 300 μm can be obtained in a single application by airless spray coating.

[0082] The coating film after application can be dried, for example, at a temperature of 5 to 80°C, preferably 10 to 60°C, for 10 to 120 minutes, particularly 20 to 90 minutes.

[0083] The primer coating composition (A) has excellent finish properties, so that after the coating film has dried, the next step can be carried out without polishing, but polishing may be carried out to obtain a coating film with even better finish properties.

[0084] <3. Step (3) of forming intermediate coating film (B')> The method for forming a multilayer coating film of the present invention comprises a step (3) of applying an intermediate coating composition (B) onto the undercoat coating film (A') to form an intermediate coating film (B').

[0085] From the viewpoint of shortening the drying time of the coating film, the intermediate coating composition (B) preferably has a solids concentration at the time of application of 70 mass % or more based on the total mass of the intermediate coating composition (B).

[0086] The intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition (B1) or an organic solvent-based multi-component polyurea coating composition (B2), each of which will be explained below.

[0087] <Organic solvent-based multi-component polyurethane coating composition (B1)> The multi-component polyurethane coating composition (B1) is obtained by mixing a main component (B1-I) containing a hydroxyl group-containing resin (B1-a), a pigment composition (B1-b), an organic solvent (B1-c), and a catalyst (B1-e), and a curing agent component (B1-II) containing a polyisocyanate compound (B1-d). The multi-component polyurethane coating composition (B1) can also be a multi-component composition obtained by mixing three or more components, including components other than the main component (B1-I) and the curing agent component (B1-II), as needed.

[0088] The multi-component polyurethane coating composition (B1) is suitably prepared by blending a main component (B1-I) and a curing agent component (B1-II) in such a ratio that the amount of isocyanate groups in the curing agent component (B1-II) is 0.2 to 3.0 equivalents, preferably 0.5 to 1.5 equivalents, per equivalent of hydroxyl groups in the main component (B1-I).

[0089] <Main ingredient (B1-I)> The main component (B1-I) contains a hydroxyl group-containing resin (B1-a), a pigment composition (B1-b), an organic solvent (B1-c), and a catalyst (B1-e).

[0090] The non-volatile content of the main component (B1-I) is suitably in the range of 70 to 90 mass %, particularly 75 to 85 mass %, from the viewpoints of ease of application and finish of the formed coating film.

[0091] The main component (B1-I) can have a low viscosity relative to its solid content concentration, and can exhibit excellent coating workability. Specifically, the viscosity measured with a Stormer viscometer in the storage state (sealed can) can be in the range of 55 to 80 KU, particularly 60 to 75 KU.

[0092] <Hydroxyl group-containing resin (B1-a)> Specific examples of the hydroxyl group-containing resin (B1-a) include acrylic resin, polyester resin, alkyd resin, urethane resin, fluororesin, epoxy resin, silicone resin, polyether resin, acrylic silicone resin, and vinyl acetate / Beova resin. These may be used alone or in combination of two or more. Among these, it is preferable to contain an acrylic polyol (B1-a1) and a polyester polyol (B1-a2). When the acrylic polyol (B1-a1) and the polyester polyol (B1-a2) are contained, the content ratio thereof is preferably 50 / 50 to 95 / 5 in terms of the solid content ratio based on mass.

[0093] <Acrylic polyol (B1-a1)> As the acrylic polyol (B1-a1), those described above as the acrylic polyol (Aa) can be suitably used. Among them, from the viewpoint of the finish of the coating film, those containing styrene and a polymerizable unsaturated monomer having a bridged alicyclic hydrocarbon group as a constituent monomer component are particularly preferred.

[0094] Examples of polymerizable unsaturated monomers having a bridged alicyclic hydrocarbon group include compounds having a bridged alicyclic hydrocarbon group having 10 to 20 carbon atoms and a polymerizable unsaturated group, and typical examples of bridged alicyclic hydrocarbon groups having 10 to 20 carbon atoms include an isobornyl group, a tricyclodecanyl group, and an adamantyl group. Specific examples of such monomers include isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, adamantyl (meth)acrylate, 3,5-dimethyladamantyl (meth)acrylate, and 3-tetracyclododecyl (meth)acrylate, and these can be used alone or in combination of two or more.

[0095] The total content of styrene and polymerizable unsaturated monomers having a bridged alicyclic hydrocarbon group in the acrylic polyol (B1-a1) is preferably 30 parts by mass or more, and more preferably 45 parts by mass or more, based on 100 parts by mass of the constituent monomer components, from the viewpoints of finish quality and hardness.

[0096] From the viewpoint of finished quality, the content of styrene is preferably within the range of 5 to 60 parts by mass, and more preferably 10 to 50 parts by mass, based on 100 parts by mass of the constituent monomer components.

[0097] From the viewpoint of finished quality, the content of the polymerizable unsaturated monomer having a bridged alicyclic hydrocarbon group is preferably within a range of 5 to 50 parts by mass, and more preferably 10 to 40 parts by mass, based on 100 parts by mass of the constituent monomer components.

[0098] From the viewpoint of coating workability, the acrylic polyol (B1-a1) preferably has a weight average molecular weight in the range of 2,000 to 40,000, and more preferably 6,000 to 15,000.

[0099] The acrylic polyol (B1-a1) preferably has a hydroxyl value in the range of 20 to 200 mgKOH / g, preferably 30 to 170 mgKOH / g, from the viewpoint of the curability and finish of the coating film.

[0100] The glass transition temperature of the acrylic polyol (B1-a1) is preferably in the range of 30 to 90°C, and more preferably 40 to 80°C, from the viewpoint of the hardness of the coating film.

[0101] <Polyester polyol (B1-a2)> The polyester polyol (B1-a2) can be produced by subjecting a polybasic acid component and a polyhydric alcohol component to a condensation reaction according to a conventionally known method.

[0102] The polybasic acid component is typically a dibasic acid selected from the group consisting of phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, hexahydroterephthalic acid, succinic acid, fumaric acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, and 1,4-cyclohexanedicarboxylic acid. Optionally, a trivalent or higher polybasic acid, such as trimellitic anhydride, methylcyclohexene tricarboxylic acid, pyromellitic anhydride, or ethylene glycol bisanhydrotrimellitate, can also be used in combination with the polybasic acid component. When sulfonic acid groups are introduced, a sulfonate group-containing polybasic acid, such as sodium 5-sulfoisophthalate, can also be used in combination.

[0103] As an acid component other than the polybasic acid component, optionally, a monobasic acid such as benzoic acid, crotonic acid, p-tert-butylbenzoic acid, etc. can also be used in combination. These acid components can be used alone or in combination of two or more.

[0104] Examples of polyhydric alcohol components that are primarily used include dihydric alcohols such as ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 1,4-dimethylolcyclohexane, and 1,4-cyclohexanedimethanol. Optionally, trihydric or higher polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol can also be used in combination. These polyhydric alcohols can be used alone or in combination of two or more. Furthermore, if necessary, fatty acids such as dehydrated castor oil fatty acid, linseed oil fatty acid, soybean oil fatty acid, tall oil fatty acid, monobasic acids such as benzoic acid, and fats and oils can be used as copolymerization components.

[0105] The polyester polyol (B1-a2) preferably has a number average molecular weight in the range of 500 to 10,000, more preferably in the range of 1,000 to 5,000. If the number average molecular weight of the polyester polyol (B1-a2) is less than 500, the drying properties of the coating film may be significantly reduced, while if it exceeds 10,000, the viscosity of the coating composition increases, which undesirably reduces coating workability or reduces the non-volatile content during coating.

[0106] The hydroxyl value of the polyester polyol (B1-a2) is preferably in the range of 0.5 to 200 mgKOH / g, particularly 40 to 140 mgKOH / g. If the hydroxyl value of the polyester polyol (B1-a2) is less than 0.5 mgKOH / g, the adhesion and water resistance of the coating film may decrease, while if it exceeds 200 mgKOH / g, the viscosity of the coating composition increases, which undesirably reduces coating workability or reduces the non-volatile content during coating.

[0107] The glass transition temperature of the polyester polyol (B1-a2) is preferably within the range of −70 to 0° C., and more preferably within the range of −65 to −10° C. If the glass transition temperature of the polyester polyol (B1-a2) is less than −70° C., the drying properties of the coating film will be reduced, while if it exceeds 0° C., coating workability will be reduced, which is undesirable.

[0108] <Pigment composition (B1-b)> As the pigment composition (B1-b), pigments such as coloring pigments and extender pigments described above for the pigment composition (Ab) can be used without any particular restrictions. In particular, including an extender pigment as part of the components is preferred, as it reduces the viscosity of the coating composition, improves coating workability, and provides a good finish. When an extender pigment is included, its amount is suitably in the range of 0.5 to 80% by mass, particularly 1 to 60% by mass, of the total pigment composition (B1-b).

[0109] The amount of pigment composition (B1-b) to be added can be adjusted appropriately depending on the type of pigment, and is generally within the range of 1 to 250 mass %, preferably 2 to 240 mass %, based on the total mass of the resins contained in the multi-component polyurethane coating composition (B1).

[0110] <Organic solvents (B1-c)> As the organic solvent (B1-c), those described above as the organic solvent (Ac) can be used without any particular limitation. Among them, it is preferable to use a ketone-based organic solvent as part of the components in an amount of 1 to 50 mass %, preferably 2 to 40 mass %, because the viscosity of the coating composition can be reduced.

[0111] <Catalyst (B1-e)> As the catalyst (B1-e), conventionally known urethane catalysts can be used without particular limitation. Specific examples include tin octoate, dibutyltin di(2-ethylhexanoate), dioctyltin di(2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, dibutyltin fatty acid salts, lead 2-ethylhexanoate, zinc octoate, zinc naphthenate, zinc fatty acids, cobalt naphthenate, calcium octoate, copper naphthenate, and tetra(2-ethylhexyl) titanate. These can be used alone or in combination. If necessary, known urethane curing catalysts such as tertiary amines and phosphate compounds can also be used in combination. Among these, tin compounds and calcium compounds are preferred from the viewpoint of improving surface drying properties.

[0112] From the viewpoint of drying properties, the content of the catalyst (B1-e) is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4.5 parts by mass, based on 100 parts by mass of the solid content of the hydroxyl group-containing resin (B1-a).

[0113] <Hardening agent component (B1-II)> The curing agent component (B1-II) contains a polyisocyanate compound (B1-d).

[0114] From the viewpoints of workability and miscibility with the main component (B1-I), it is preferable that the curing agent component (B1-II) contains an organic solvent. The organic solvent can be appropriately selected from the compounds exemplified in the description of the organic solvent (Ac) above. From the viewpoints of coating workability and the finish of the formed coating film, the non-volatile content of the curing agent component (B1-II) is suitably in the range of 30 to 70 mass%, particularly 40 to 60 mass%.

[0115] <Polyisocyanate compound (B1-d)> As the polyisocyanate compound (B1-d), those described above as the polyisocyanate compound (Ad) can be used without any particular limitation.

[0116] <Other additives for multi-component polyurethane coating composition (B1)> The multi-component polyurethane coating composition (B1) may further contain paint additives such as viscosity modifiers, cellulose acetate butyrate and its modified products, modifying resins other than the hydroxyl group-containing resin (B1-a), pigment dispersants, surface conditioners, resin particles, etc. These additives may be contained in either the main component (B1-I) or the curing agent component (B1-II), but from the viewpoint of storage stability, it is preferable that the main component (B1-I) contains additives that can react directly with isocyanate compounds.

[0117] <Organic solvent-based multi-component polyurea coating composition (B2)> The multi-component polyurea coating composition (B2) is obtained by mixing a main component (B2-I) containing a polyaspartic acid ester (B2-a), a pigment composition (B2-b), and an organic solvent (B2-c), and a curing agent component (B2-II) containing a polyisocyanate compound (B2-d). The multi-component polyurea coating composition (B2) can also be a multi-component composition obtained by mixing three or more components, including components other than the main component (B2-I) and the curing agent component (B2-II), as needed.

[0118] The multi-component polyurea coating composition (B2) is suitably prepared by blending a main component (B2-I) and a curing agent component (B2-II) in such a ratio that 1 equivalent of amino groups in the main component (B2-I) contains 0.5 to 2.0 equivalents, preferably 0.8 to 1.5 equivalents, of isocyanate groups in the curing agent component (B2-II).

[0119] <Main ingredient (B2-I)> The main component (B2-I) contains a polyaspartic acid ester (B2-a), a pigment (B2-b), and an organic solvent (B2-c).

[0120] The non-volatile content of the main component (B2-I) is preferably in the range of 70 to 90 mass %, particularly 75 to 85 mass %, from the viewpoints of ease of application and finish of the formed coating film.

[0121] The main component (B2-I) can have a low viscosity relative to its solid content concentration, and can exhibit excellent coating workability. Specifically, the viscosity measured with a Stormer viscometer in the storage state (sealed can) can be in the range of 50 to 70 KU, particularly 53 to 68 KU.

[0122] From the viewpoint of pot life, the main component (B2-I) preferably has a water content of 5000 ppm or less.

[0123] In this specification, the water content can be measured by Karl Fischer coulometric titration. Specifically, the water content can be measured using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name "MKC-610") with the temperature of the moisture vaporizer (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name "ADP-611") attached to the meter set to 130°C.

[0124] <Polyaspartic acid ester (B2-a)> As the polyaspartic acid ester (B2-a), a polyaspartic acid ester having a secondary amino group is preferred from the viewpoints of reactivity and coating workability.

[0125] Specifically, the following formula (1) TIFF2026006814000001.tif30122

[0126] (wherein X is an n-valent cyclic or chain aliphatic hydrocarbon group or a polyoxyalkylene polyamine residue having a number average molecular weight of 25 to 5,000, and R 1 and R 2 are each independently an organic group inactive to an isocyanate group, and n is an integer of 2 or more.

[0127] X is an n-valent group having a number average molecular weight of 25 to 5,000, and the number average molecular weight is preferably 50 to 3,000, and more preferably 100 to 2,000.

[0128] X is an aliphatic hydrocarbon group or a polyoxyalkylene polyamine residue.

[0129] The aliphatic hydrocarbon group may be an alicyclic hydrocarbon group, a chain hydrocarbon group, or a group having both an alicyclic portion and a chain portion.

[0130] The alicyclic hydrocarbon group may have a side chain. The chain hydrocarbon group may be a straight-chain hydrocarbon group or a branched hydrocarbon group.

[0131] X is preferably a divalent aliphatic hydrocarbon group. Examples of the divalent aliphatic hydrocarbon group include alkylene, cycloalkylene, cycloalkylalkylene, alkylcycloalkylene, alkylenebiscycloalkylene, alkylenebis(alkylcycloalkylene), and cycloalkylenebisalkylene.

[0132] Here, alkylene is preferably alkylene having 1 to 8 carbon atoms, cycloalkylene is preferably cycloalkylene having 5 to 6 carbon atoms, alkyl is preferably alkyl having 1 to 8 carbon atoms, and cycloalkyl is preferably cycloalkyl having 5 to 6 carbon atoms.

[0133] The polyoxyalkylene polyamine residue refers to a group obtained by removing primary amino groups at both ends of a polyoxyalkylene polyamine. The polyoxyalkylene polyamine residue may have a side chain. The polyoxyalkylene polyamine residue is preferably a polyoxyethylene polyamine residue, a polyoxypropylene polyamine residue, a polyoxybutylene polyamine residue, or a polyoxyethylene polyoxypropylene polyamine residue. The polyoxyalkylene polyamine residue is more preferably -(CH(CH3)-CH2-O)x-CH2-CH(CH3)- (wherein x is an integer of 3 to 6).

[0134] In formula (1), R 1 and R 2 R is each independently an organic group that is inert to an isocyanate group. 1 and R 2 is preferably alkyl having 1 to 15 carbon atoms, more preferably alkyl having 1 to 8 carbon atoms, further preferably methyl or ethyl, and most preferably ethyl.

[0135] In formula (1), n ​​is an integer of 2 or more. n is preferably an integer of 2 to 6, more preferably an integer of 2 to 4, and most preferably 2.

[0136] Compounds of formula (1) can be synthesized, for example, by reacting an optionally substituted maleic or fumaric acid ester with a polyamine.

[0137] Specific examples of the compound represented by formula (1) include, but are not limited to, tetraethyl N,N'-[methylenebis(cyclohexane-4,1-diyl)]bisaspartate, tetraethyl N,N'-(hexane-1,6-diyl)bisaspartate, tetrabutyl N,N'-(2-methylpentane-1,5-diyl)bisaspartate, tetraethyl N,N'-[methylenebis(3-methylcyclohexane-4,1-diyl)]bisaspartate, tetraethyl N,N and at least one selected from the group consisting of tetraethyl N,N'-(bis-2-propyl)polypropylene glycol 300-O,O'-diylbisaspartate, tetraethyl N,N'-(butane-1,4-diyl)bisaspartate, tetraethyl N,N'-(2,2-dimethylpropane-1,3-diyl)bisaspartate, tetraethyl N,N'-(2,4-dimethylhexane-1,6-diyl)bisaspartate, and mixtures thereof. Among these, tetraethyl N,N'-[methylenebis(cyclohexane-4,1-diyl)]bisaspartate, tetrabutyl N,N'-(2-methylpentane-1,5-diyl)bisaspartate, and tetraethyl N,N'-[methylenebis(3-methylcyclohexane-4,1-diyl)]bisaspartate are preferred.

[0138] Commercially available polyaspartic acid esters (B2-a) include "Desmophen NH1420," "Desmophen NH1423LF," "Desmophen NH 1520," and "Desmophen NH 1220" (all trade names, manufactured by Sumika Bayer Co., Ltd.), "FEISOARTIC F420," "FEISOARTIC F220," and "FEISOARTIC F520" (all trade names, manufactured by Feiyang Chemical Industry Co., Ltd.), and the like.

[0139] <Pigment composition (B2-b)> As the pigment composition (B2-b), pigments such as color pigments and extender pigments described above for the pigment composition (Ab) can be used without any particular restrictions.

[0140] The amount of pigment composition (B2-b) can be adjusted appropriately depending on the type of pigment, and is generally within the range of 1 to 250 mass %, preferably 2 to 240 mass %, based on the total mass of the resins contained in the multi-component polyurea coating composition (B2).

[0141] <Organic solvents (B2-c)> As the organic solvent (B2-c), any of the organic solvents described above as the organic solvent (Ac) can be used without any particular limitation.

[0142] <Dehydrating agent (B2-e)> In order to improve the pot life, the multi-component polyurea coating composition (B2) preferably contains a dehydrating agent (B2-e) in addition to the main component (B2-I). As the dehydrating agent, conventionally known ones can be used without limitation, and specific examples include anhydrous gypsum, hemihydrate gypsum (calcined gypsum), zeolite, orthoesters (methyl orthoformate, methyl orthoacetate, orthoborate ester, etc.), silicates, isocyanates, etc., and one type may be used alone, or two or more types may be used in combination. Among these, it is preferable to contain zeolite.

[0143] Zeolite is a general term for crystalline aluminosilicates, and its constituent elements are Al, Si, O, and cations (positive ions), and it has a tetrahedral structure (Si) formed from SiO4 and AlO4. 4+ or Al 3+ Zeolite is a compound with a basic structure of a tetrahedron (a tetrahedron formed around a center). These tetrahedrons are connected in a complex and regular pattern, forming one-, two-, or three-dimensional regular pores with diameters of several Å to several dozen Å, roughly the same size as small molecules. This is the characteristic of zeolites.

[0144] Cations exist within the pores of zeolites, and the various functions of zeolites are based on these cations. Because only molecules smaller than the diameter of the pores of zeolites can enter, and they can be screened out from larger molecules, some zeolites are called molecular sieves.

[0145] There are two types of zeolites: natural zeolites, which are primarily composed of hydrous aluminosilicates, and synthetic zeolites, which are primarily composed of Na2O·Al2O3·xSiO2·yH2O. Synthetic zeolites, also known as palmitites, are produced by a dry process in which sodium carbonate, silica, alumina, or kaolin are eutectic, or by a wet process in which sodium silicate and sodium aluminate are mixed together to precipitate a gel.

[0146] Both natural and synthetic zeolites have ion exchange capacity, their crystalline structure remains unchanged even after dehydration, and they have large adsorption capacity due to the formation of molecular-sized pores after dehydration. Furthermore, zeolites obtained by hydrothermal synthesis, where sodium aluminosilicate gel is crystallized and dehydrated, are generally called molecular sieves.

[0147] From the viewpoints of pot life and corrosion resistance, zeolites generally referred to as molecular sieves can be preferably used. Zeolites molded into powder or pellet form are commercially available, and depending on the type of raw zeolite, molecular sieves such as molecular sieve 3A, molecular sieve 4A, molecular sieve 5A, and molecular sieve 13X are commercially available. The numbers indicate the approximate pore diameter (angstroms) of the pores, and the capital letters indicate the type of zeolite, with A representing LTA zeolite and X representing FAU zeolite.

[0148] Of the above molecular sieves, molecular sieve 3A, molecular sieve 4A, and molecular sieve 5A are preferred from the viewpoint of finished appearance, with molecular sieve 5A being particularly suitable.

[0149] The effective diameter of the pores in the molecular sieve crystal varies depending on the location and size of the metal cations near the pores. For example, molecular sieve 5A is molecular sieve 4A in which the sodium ions are replaced with calcium ions.

[0150] From the viewpoint of finished appearance, the pore size (effective diameter of the pores) of the zeolite is preferably in the range of 0.50 nm or less, particularly preferably in the range of 0.10 to 0.50 nm, and even more particularly preferably in the range of 0.20 to 0.50 nm.

[0151] The pore size of the zeolite can be measured by nitrogen gas adsorption method.

[0152] When zeolite is used in the multi-component polyurea coating composition (B2), the amount used is preferably within the range of 5 to 30 mass %, particularly 10 to 20 mass %, based on the total solid content of the polyaspartic acid ester (B2-a) and the polyisocyanate compound (B2-d), from the viewpoints of pot life and finished appearance.

[0153] <Hardening agent component (B2-II)> The curing agent component (B2-II) contains a polyisocyanate compound (B2-d).

[0154] The nonvolatile content of the curing agent component (B2-II) is suitably in the range of 30 to 100 mass %, particularly 40 to 100 mass %, from the viewpoints of coating workability and the finish of the formed coating film.

[0155] <Polyisocyanate compound (B2-d)> As the polyisocyanate compound (B2-d), those described above as the polyisocyanate compound (Ad) can be used without any particular limitation.

[0156] <Other additives for multi-component polyurea coating composition (B2)> The multi-component polyurethane coating composition (B2) may further contain paint additives such as viscosity modifiers, cellulose acetate butyrate and its modified products, modifying resins other than the polyaspartic acid ester (B2-a), pigment dispersants, surface conditioners, resin particles, catalyst compounds, etc. These additives may be contained in either the main component (B2-I) or the curing agent component (B2-II), but from the viewpoint of storage stability, it is preferable that additives capable of directly reacting with isocyanate compounds be contained in the main component (B2-I).

[0157] <Method for forming intermediate coating film (B')> In the present invention, the intermediate coating composition (B) is applied on the undercoat coating film (A') to form the intermediate coating film (B').

[0158] The intermediate coating composition (B) is a two-component composition in which each component is stored separately, and is generally mixed immediately before application, with the viscosity adjusted using thinner as needed, before use.

[0159] From the viewpoint of concealing the polishing marks of the primer coating film, the intermediate coating composition (B) preferably has a solids concentration at the time of application of 70 mass % or more, more preferably 75 mass % or more, based on 100 mass parts of the total mass of the intermediate coating composition (B).

[0160] The intermediate coating composition (B) can be applied by a conventionally known coating method, with airless spray coating being particularly suitable.

[0161] There are no particular limitations on the drying method after coating, and a coating film can be obtained by drying at room temperature, but there are no particular problems with heat drying or forced drying depending on the coating environment, etc. When heat drying is used, drying can be carried out for 5 to 20 minutes at a temperature ranging from 25 to 80°C, preferably from 40 to 60°C. If necessary, air drying using a blower or the like can be used. When drying at room temperature, a coating film can be obtained by drying for 0.5 to 1 hour in an environment of, for example, 5 to 45°C.

[0162] The film thickness can be adjusted as appropriate depending on the condition of the surface to be coated, but a dry film thickness of 5 to 100 μm, particularly 10 to 80 μm, is generally suitable.

[0163] The intermediate coating composition (B) has excellent drying properties, so it hardens in a relatively short time even when dried at room temperature, making it possible to carry out polishing work.

[0164] <4. Step (4) of forming topcoat coating film (C')> The method for forming a multi-layer coating film of the present invention may include a step (4) of applying a topcoat paint composition (C) onto the intermediate coating film (B') to form a topcoat coating film (C').

[0165] <Topcoat paint composition (C)> The topcoat paint composition (C) can be a conventionally known topcoat paint, such as a water-based paint, an organic solvent-based paint, a solventless paint, etc. Among these, from the viewpoint of drying speed and consideration of environmental pollution and the effects on the human body, it is preferable to use an aqueous multi-component polyurethane paint composition obtained by mixing a main component (CI) containing a hydroxyl group-containing resin (Ca), a pigment composition (Cb), and water, and a curing agent component (C-II) containing a polyisocyanate compound (Cd).

[0166] The hydroxyl-containing resin (Ca) contained in the main component (CI) preferably contains a self-emulsifying emulsion. In this specification, a self-emulsifying emulsion refers to an emulsion obtained by dropping and mixing a resin having ionic functional groups such as carboxyl groups, synthesized without a solvent or in the presence of an appropriate organic solvent, into water, and dispersing the resin by optionally removing excess organic solvent, or by dispersing the resin by adding water after a polymerization reaction and optionally removing excess organic solvent. Because no emulsifier is used, the coating film performance, particularly water resistance and weather resistance, is excellent. Furthermore, because it is not produced from an aqueous medium, it is easy to obtain fine particles with a relatively low molecular weight and a small, well-balanced particle size. When applied as a water-based paint, the paint is extremely easy to handle, such as easy to stir by hand, and has excellent drying properties and a glossy finish. Furthermore, despite being a water-based paint, it can achieve an excellent coating film appearance, and its excellent reactivity with polyisocyanate compounds allows for the production of coating films with excellent weather resistance.

[0167] From the viewpoints of drying speed, finish, weather resistance, and water resistance, the hydroxyl-containing resin (Ca) contained in the main component (CI) preferably contains an acrylic polyol (C-a1) and a polyester polyol (C-a2). The solid content ratio of the acrylic polyol (C-a1) and the polyester polyol (C-a2) is preferably 40 / 60 to 90 / 10, particularly preferably 50 / 50 to 80 / 20, by mass.

[0168] The acrylic polyol (C-a1) is preferably a resin emulsion in which a hydroxyl group-containing resin is dispersed in water, but any conventionally known acrylic polyol can be used without limitation as long as it has the ability to form a coating film, and the resins may be used alone or in combination of two or more.

[0169] The weight average molecular weight of the acrylic polyol (C-a1) is preferably within the range of 5,000 to 150,000, particularly 5,000 to 50,000, and more particularly 10,000 to 40,000.

[0170] When the acrylic polyol (C-a1) is an emulsion, the average particle size of the resin particles contained therein is preferably within a range of 50 to 300 nm, particularly 100 to 200 nm, from the viewpoints of storage stability and the finished appearance of the resulting coating film.

[0171] In this specification, the average particle size of an emulsion is the volume average particle size measured by the Coulter Counter method at a measurement temperature of 20° C. Measurement by the Coulter Counter method can be performed using, for example, a "COULTER N4" (trade name, manufactured by Beckman Coulter, Inc.).

[0172] The acrylic polyol (C-a1) preferably has a glass transition temperature in the range of 30 to 80°C, particularly 50 to 70°C, from the viewpoint of coating film hardness.

[0173] From the viewpoints of water resistance and coating workability, the acrylic polyol (C-a1) preferably has a hydroxyl value in the range of 50 to 250 mgKOH / g, particularly 100 to 200 mgKOH / g, and an acid value in the range of 5 to 50 mgKOH / g, particularly 5 to 35 mgKOH / g.

[0174] When the acrylic polyol (C-a1) contains an acrylic polyol emulsion, the method for dispersing the acrylic polyol in water or the method for producing the acrylic polyol emulsion are not limited, but examples thereof include a method of polymerizing a polymerizable unsaturated compound component containing a (meth)acryloyl compound as an essential component and containing other polymerizable unsaturated compounds in one step or multiple steps in the presence of an organic solvent to obtain an acrylic polyol and dispersing the resulting acrylic polyol in water; and a method of emulsion-polymerizing a polymerizable unsaturated compound component containing a (meth)acryloyl compound as an essential component and containing other polymerizable unsaturated compounds in one step or multiple steps in the presence of water and a dispersion stabilizer.

[0175] The (meth)acryloyl compounds and other polymerizable unsaturated compounds that are copolymerization components of the acrylic polyol (C-a1) can be, for example, those described above for the acrylic polyol (Aa), which can be used alone or in combination of two or more. Among these, preferred is an acrylic polyol obtained by dispersing in water an acrylic polyol obtained by multi-stage polymerization of a polymerizable unsaturated compound component (1) containing an epoxy group-containing polymerizable unsaturated compound and a polymerizable unsaturated compound component (2) containing a carboxyl group-containing polymerizable unsaturated compound in the presence of an organic solvent. In this case, a hydroxyl group-containing polymerizable unsaturated compound is contained in either (1) or (2), or in both (1) and (2).

[0176] In the acrylic polyol emulsion, the resin can be dispersed in water by neutralizing some or all of the anionic groups, such as carboxyl groups, contained in the acrylic polyol with a basic compound and then dispersing the resultant in water, or by adding the acrylic polyol to an aqueous medium containing a basic compound and dispersing the resultant.

[0177] In the present invention, it is preferable to contain a polyester polyol (C-a2) because it provides excellent coating film appearance, and in particular it is suitable to contain a polyester polyol emulsion. Regarding the polyester polyol emulsion, there are no limitations on the method for dispersing the polyester polyol in water or the method for producing the polyester polyol emulsion, but examples include a method in which a polyester resin obtained by polymerizing components essentially comprising a polybasic acid component and a polyhydric alcohol component through an ester reaction in one stage or multiple stages is dispersed in water.

[0178] The polyester polyol (C-a2) may be, for example, an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins, such as a urethane-modified polyester resin or a urethane-modified alkyd resin. Of these polyester resins, oil-free polyester resins are preferably used from the viewpoint of the weather resistance of the resulting coating film. Oil-free polyester resins are generally esters of polybasic acids and polyhydric alcohols.

[0179] As the polybasic acid component and polyhydric alcohol component, for example, the polybasic acids and polyhydric alcohols described above for the polyester polyol (B1-a2) can be used without any particular limitation.

[0180] The esterification reaction of both components can be carried out by a known method.

[0181] The oil-free polyester resin can also be obtained by carrying out a transesterification reaction using an alkyl ester of a polybasic acid (e.g., methyl ester, ethyl ester, etc.) instead of the polybasic acid in the above-mentioned esterification reaction. The transesterification reaction of both components can be carried out by a known method.

[0182] The oil-modified alkyd resin is a resin obtained by reacting the acid component and alcohol component of the oil-free polyester resin with an oil fatty acid by a known method.

[0183] Examples of oil fatty acids include coconut oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, safflower oil fatty acids, tall oil fatty acids, dehydrated castor oil fatty acids, and tung oil fatty acids.

[0184] The urethane-modified polyester resin is a resin obtained by reacting the oil-free polyester resin with a polyisocyanate compound by a known method, and the urethane-modified alkyd resin is a resin obtained by reacting the alkyd resin with a polyisocyanate compound by a known method.

[0185] Examples of polyisocyanate compounds used in producing urethane-modified polyester resins and urethane-modified alkyd resins include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 2,4,6-triisocyanatotoluene.

[0186] The hydroxyl group-containing resin (Ca) contained in the main component (CI) may also contain a commercially available resin emulsion.

[0187] Specific commercially available product names include "Bayhydrol A145," "Bayhydrol A2290," "Bayhydrol A2427," "Bayhydrol A2470," "Bayhydrol A2542," "Bayhydrol A2546," "Bayhydrol A2601," and "Bayhydrol A242" manufactured by Covestro; "Barnock WE-303," "Barnock WE-304," "Barnock WE-306," "Barnock WE-308," and "Barnock WE-313" manufactured by DIC Corporation; and "Lumiflon FE-4200," "Lumiflon FE-4300," "Lumiflon FE-4400," and "Lumiflon FE-4500" manufactured by Asahi Glass Co., Ltd.

[0188] The pigment composition (Cb) contained in the main component (CI) can be any pigment such as the color pigments and extender pigments described in the pigment composition (Ab) above, without any particular restrictions, and it is particularly preferable to include barium sulfate as an extender pigment.

[0189] The polyisocyanate compound (Cd) contained in the curing agent component (C-II) may suitably be any of the polyisocyanate compounds described above as the polyisocyanate compound (Ad), as well as polyisocyanate compounds for water-based paints, such as hydrophilized polyisocyanate compounds in which a hydrophilic group has been introduced into a polyisocyanate compound, and water-dispersible polyisocyanate compounds in which a polyisocyanate compound can be made to be dispersed in water using a surfactant.

[0190] Examples of the hydrophilic group include anionic groups such as acid groups and nonionic groups containing polyoxyalkylene (polyether chain) units. Examples of the acid group include carboxyl groups, phosphate groups, and sulfonic acid groups.

[0191] The content of the polyisocyanate compound (Cd) in the aqueous multi-component polyurethane coating composition is adjusted as appropriate so that the equivalent ratio (NCO / OH) of the isocyanate groups of the polyisocyanate compound to the hydroxyl groups of the hydroxyl-containing resin (Ca) is generally in the range of 0.5 to 5.0, but from the viewpoints of coating appearance, coating workability, and coating hardness, it is preferably 1.0 to 3.0, more preferably 1.1 to 2.5, and even more preferably 1.2 to 2.0. By keeping the equivalent ratio (NCO / OH) within the above preferred range, there is an advantage that the curing reactivity of the aqueous multi-component polyurethane coating composition can be improved.

[0192] <Method for forming topcoat film (C')> In the present invention, the topcoat paint composition (C) is applied on the intermediate paint film (B') to form the topcoat paint film (C').

[0193] The topcoat paint composition (C) is a two-component composition in which each component is stored separately, and is generally prepared by mixing the components together immediately before application, adjusting the viscosity with water or thinner as needed, and then using the mixture.

[0194] The topcoat paint composition (C) can be applied by a conventionally known application method, with air spray application being particularly preferred.

[0195] There are no particular limitations on the drying method after coating, and a coating film can be obtained by drying at room temperature, but there are no particular problems with heat drying or forced drying depending on the coating environment, etc. When heat drying is used, drying can be carried out at a temperature in the range of 25 to 80°C, preferably 40 to 60°C, for 0.5 to 3 hours. If necessary, air drying using a blower or the like can be used. When drying at room temperature, a coating film can be obtained by drying for 1 to 7 days in an environment of, for example, 5 to 45°C.

[0196] The film thickness can be adjusted as appropriate depending on the condition of the surface to be coated, but a dry film thickness of 5 to 100 μm, particularly 10 to 80 μm, is generally suitable.

[0197] Furthermore, from the viewpoint of imparting weather resistance and antifouling properties, after step (4) of forming the topcoat coating film (C'), a step of subsequently applying a top clear coating composition to the entire surface and drying it to form the outermost clear coating film may be included.

[0198] As the top clear coat, conventionally known water-based paints, organic solvent-based paints, solventless paints, etc. can be used. Among them, water-based paints are preferred from the viewpoint of consideration of environmental pollution and effects on the human body. In such cases, it is preferred that the top coat paint composition (C) is also a water-based paint. [Example]

[0199] The present invention will be further described below with reference to examples, in which "parts" and "%" mean "parts by mass" and "% by mass", respectively.

[0200] <Production of primer coating composition (A)> Production Example 1 Synthesis of acrylic polyol (A-a1) A reaction vessel was charged with 52 parts of butyl acetate and heated to 110°C with stirring. A monomer mixture consisting of 30 parts of styrene, 14.5 parts of i-butyl methacrylate, 22 parts of 2-ethylhexyl acrylate, 1 part of acrylic acid, 32.5 parts of 2-hydroxyethyl methacrylate, and 1.0 part of azobisisobutyronitrile and a polymerization initiator was added dropwise at a constant rate over 3 hours using a dropping pump at temperatures below 110°C. After the dropwise addition, the mixture was maintained at 110°C for 60 minutes and stirring was continued. Subsequently, an additional catalyst, a solution of 0.5 parts of azobisisobutyronitrile in 7 parts of butyl acetate, was added dropwise at a constant rate over 60 minutes. After the dropwise addition, the mixture was maintained at 110°C for 60 minutes to terminate the reaction. The resulting acrylic polyol (A-a1) was a homogeneous, yellow, transparent solution with a non-volatile content of 65%. The resin had a weight-average molecular weight of 8,000, a glass transition temperature (Tg) of 33°C, an acid value (AV) of 7.8 mgKOH / g, and a hydroxyl value (OHV) of 140 mgKOH / g.

[0201] Production Examples 2 to 6 Synthesis of Acrylic Polyols (A-a2) to (A-a6) Acrylic polyol solutions (A-a2) to (A-a6) were obtained in the same manner as in Production Example 1 above, except that the blending compositions shown in Table 1 were used.

[0202] [Table 1]

[0203] Production Example 7 Preparation of primer coating composition (A-1) To 100 parts of the acrylic polyol solution (A-a1) (65 parts solids), 100 parts of calcium carbonate, 30 parts of titanium white, 0.3 parts of carbon, 5 parts of methyl amyl ketone, 1 part (solids) of a pigment dispersant (manufactured by BYK under the trade name "BYK-161"), 1 part (solids) of an antifoaming agent (manufactured by BYK under the trade name "BYK-052N"), 1 part (solids) of a surface conditioner (manufactured by BYK under the trade name "BYK-320"), 2 parts of montmorillonite (manufactured by ELEMENTIS under the trade name "BENTONE27"), 3 parts (solids) of an amide-based thickener (fatty acid amide, amide-based rheology control agent), and 0.1 parts (solids) of dioctyltin dilaurate were sequentially blended, mixed, stirred, and dispersed for 30 minutes to obtain a main component. A curing agent component was obtained by mixing and stirring 35 parts (solid content) of a polyisocyanate compound ("Desmodur ULTRA N3900", product name, manufactured by Sumika Covestro Urethane Co., Ltd.) and 1.5 parts (solid content) of γ-glycidoxypropyltrimethoxysilane (silane coupling agent). The main component and the curing agent component were mixed immediately before use so that the solid content of the acrylic polyol contained in the main component and the solid content of the polyisocyanate compound contained in the curing agent component were in a ratio of 65:35 by mass, and the paint viscosity was adjusted with dilution thinner so that the viscosity measured at 60 rpm with a Brookfield viscometer was 0.3 Pa·s, thereby obtaining an undercoat paint composition (A-1).

[0204] Production Examples 8 to 16 Preparation of primer coating compositions (A-2) to (A-10) Primer coating compositions (A-2) to (A-10) were obtained in the same manner as in Production Example 7 above, except for using the formulations shown in Table 2. However, primer coating composition (A-10) was diluted to a viscosity of 0.1 Pa s. The numerical values ​​for the blending amounts in the table are those for the solid content or active ingredients.

[0205] [Table 2]

[0206] (Note 1) Desmodur ULTRA N3900: Product name, manufactured by Sumika Covestro Urethane Co., Ltd., aliphatic polyisocyanate compound, viscosity measured with an E-type viscometer at 25°C: 730 mPa·s (Note 2) Desmodur ULTRA Z4470BA: Product name, manufactured by Sumika Covestro Urethane Co., Ltd., alicyclic polyisocyanate compound, viscosity measured at 25°C with an E-type viscometer of 600 mPa·s.

[0207] <Production of intermediate coating composition (B1)> Production Example 17 Synthesis of acrylic polyol (B1-a1-1) A reaction vessel equipped with a stirrer, thermometer, reflux condenser, thermostat, and dropping pump was charged with 60 parts of butyl acetate and heated to 125°C with stirring. A mixture of the following monomers and polymerization initiator was added dropwise at a constant rate over 3 hours using the dropping pump. After the addition was complete, the mixture was aged at the same temperature for 2 hours to complete the reaction. The resin solution was then diluted with butyl acetate to adjust the nonvolatile content to 65%. 38 parts styrene Isobornyl acrylate 20 parts Isobutyl methacrylate 5 parts 2-Ethylhexyl acrylate 10 parts 2-Hydroxyethyl methacrylate 20 parts 2-Hydroxyethyl acrylate 7 parts t-Butyl peroxyhexanoate 6.1 parts The weight average molecular weight of the obtained acrylic polyol (B1-a1-1) was 10,000, the hydroxyl value was 120 mgKOH / g, and the glass transition temperature was 48°C.

[0208] Production Example 18 Synthesis of polyester polyol (B1-a2-1) The following components were charged into a reactor equipped with a heating device, a thermometer, a stirrer, a rectification column, and a reflux condenser equipped with a water separator, and the temperature was raised from 160°C to 230°C over 3 hours. 1,4-cyclohexanedicarboxylic acid 23.5 parts Adipic acid 34.2 parts Neopentyl glycol 37 parts Trimethylolpropane 5.3 parts This was maintained at 230°C for 1 hour, and the resulting condensation water was distilled off using a rectification column. Next, 5 parts of butyl acetate were added, and the butyl acetate and condensation water were refluxed, and the water was removed using a water separator. Two hours after the addition of butyl acetate, the acid value was measured. When the acid value reached 2 or less, the mixture was cooled to 120°C and diluted with butyl acetate to a nonvolatile content of 70%, yielding a polyester polyol (B1-a2-1) solution. The resulting polyester polyol (B1-a2-1) had a number average molecular weight of 3,800, a hydroxyl value of 52 mgKOH / g, and a glass transition temperature of -50°C.

[0209] Production Example 19 Preparation of intermediate coating composition (B1-1) 100 parts of the acrylic polyol (B1-a1-1) solution obtained in Production Example 17 (65 parts resin solids), 14.3 parts of the polyester polyol (B1-a2-1) solution obtained in Production Example 18 (10 parts resin solids), 60 parts of titanium white, 20 parts of barium sulfate, 1 part of a pigment dispersant ("BYK-161", trade name, manufactured by BYK-chemie), 0.2 parts of montmorillonite ("BENTONE27", trade name, manufactured by ELEMENTIS), 2 parts of an ultraviolet absorber ("TINUVIN 400", trade name, manufactured by BASF, hydroxyphenyltriazine ultraviolet absorber), 2 parts of a light stabilizer ("TINUVIN A mixture of 2 parts of an antifoaming agent ("BYK-052N", trade name, manufactured by BYK-chemie, alkyl vinyl ether copolymer), 0.1 parts of a surface conditioner ("BYK-300", trade name, manufactured by BYK-chemie), and 0.2 parts of dioctyltin dilaurate was stirred to obtain the base component of an intermediate coating composition (B1-1). In the above, 60 parts of titanium white and 20 parts of barium sulfate were added and mixed as a pigment dispersion paste prepared using 61.5 parts of acrylic polyol (B1-a1-1) solution (40 parts of resin solids) and 1 part of pigment dispersant. A polyisocyanate compound ("Desmodur ULTRA N3300", trade name, manufactured by Sumika Covestro Urethane Co., Ltd.) was used as the curing agent component of the intermediate coating composition (B1-1). The base agent and curing agent were mixed according to the formulation shown in Table 3 below, and diluted with thinner (Kansai Paint Co., Ltd., product name: Retan PG Eco Thinner 20) to a non-volatile content of 80% by mass to prepare an intermediate coating paint composition (B1-1).

[0210] Production Examples 20 to 21 Preparation of Intermediate Coating Compositions (B1-2) and (B1-3) Coating compositions (B1-2) and (B1-3) were obtained in the same manner as in Production Example 19 above, except for using the formulations shown in Table 3. The numerical values ​​for the blending amounts in the table are the values ​​for the solid content or active ingredients.

[0211] [Table 3]

[0212] <Production of intermediate coating composition (B2)> Production Examples 22 to 23 Preparation of intermediate coating compositions (B2-1) and (B2-2) Polyaspartic acid ester ("Desmophen NH-1420", trade name, manufactured by Covestro, amine value 201, molecular weight 554.7) 55 parts (resin solids content 49.5 parts), polyol compound ("Desmophen XP-2488", trade name, manufactured by Covestro, polyester polyol, hydroxyl value 528) 55 parts (resin solids content 5.5 parts), titanium white 60 parts, barium sulfate 20 parts, pigment dispersant ("BYK-161", trade name, manufactured by BYK-chemie) 1 part, dehydrating agent ("Molecular Sieve 5A", trade name, manufactured by Union Showa, sodium calcium amino silicate, pore size 0.42 nm) 10 parts, ultraviolet absorber ("TINUVIN 400", trade name, manufactured by BASF, hydroxyphenyltriazine ultraviolet absorber) 2 parts, light stabilizer ("TINUVIN 2 parts of "BYK-123", trade name, manufactured by BASF, hindered amine light stabilizer), 0.1 parts of antifoaming agent ("BYK-052N", trade name, manufactured by BYK-chemie, alkyl vinyl ether copolymer), and 0.1 parts of surface conditioner ("BYK-300", trade name, manufactured by BYK-chemie) were mixed and stirred to obtain the main component of the intermediate coating composition (B2-1). In the above, 60 parts of titanium white and 20 parts of barium sulfate were added and mixed as a pigment dispersion paste prepared using 20 parts of polyaspartic acid ester (18 parts of resin solid content) and 1 part of pigment dispersant. A polyisocyanate compound ("Desmodur ULTRA N3900", trade name, manufactured by Sumika Covestro Urethane Co., Ltd.) was used as the curing agent component of the intermediate coating composition (B2-1). The base resin and curing agent were mixed according to the formulation shown in Table 4 below, and diluted with thinner (Kansai Paint Co., Ltd., product name: Retan PG Eco Thinner 20) to a non-volatile content of 80% by mass to prepare an intermediate coating paint composition (B2-1).

[0213] An intermediate coating composition (B2-2) was also obtained in the same manner as above, except for using the formulation shown in Table 4. The numerical values ​​for the blending amounts in the table are the values ​​for the solid content or active ingredients.

[0214] [Table 4]

[0215] <Production of topcoat paint composition (C)> Production Example 24: Production of Water-Based Top Coating Composition (C-1) 50 parts of propylene glycol monopropyl ether was placed in a four-necked glass flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet, and the temperature was raised to 120 ° C. under a nitrogen stream while stirring. When the temperature reached 120 ° C., a mixed solution of 13.5 parts of styrene, 13.5 parts of methyl methacrylate, 16.9 parts of i-butyl methacrylate, 13.5 parts of n-butyl methacrylate, 3.5 parts of n-butyl acrylate, 24.0 parts of 2-hydroxyethyl methacrylate, 1.5 parts of glycidyl methacrylate, and 1.5 parts of t-butylperoxy-2-ethylhexanoate as a polymerization initiator was added dropwise over 4 hours, and after the dropwise addition, the temperature was maintained at 120 ° C. for 1 hour. While maintaining the temperature at 120°C, a premixed solution containing 1.5 parts styrene, 1.5 parts methyl methacrylate, 1.5 parts i-butyl methacrylate, 1.5 parts n-butyl methacrylate, 1.5 parts n-butyl acrylate, 4.0 parts 2-hydroxyethyl methacrylate, 3.0 parts acrylic acid, and 0.3 parts t-butylperoxy-2-ethylhexanoate was added dropwise to the flask over 1 hour. After the addition, the mixture was maintained at 120°C for 1.5 hours to obtain an acrylic polyol solution. Subsequently, propylene glycol monopropyl ether was distilled off from the resulting acrylic polyol solution under reduced pressure until the nonvolatile content reached 85%. The mixture was cooled to 95°C, the pH was adjusted to 8.0 with dimethylethanolamine, and the mixture was stirred for 30 minutes. Furthermore, deionized water was added dropwise over 2 hours with stirring to obtain an acrylic polyol emulsion (C-a1-1) with a nonvolatile content of 50%. The acrylic polyol emulsion (C-a1-1) had a weight average molecular weight of 23,000, an acid value of 21 mg KOH / g, a hydroxyl value of 121 mg KOH / g, and a glass transition temperature of 54 ° C. A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a water separator was charged with 175 parts of trimethylolpropane, 314 parts of neopentyl glycol, 281 parts of adipic acid, 177 parts of isophthalic acid, and 99 parts of 1,2-cyclohexanedicarboxylic anhydride, and the temperature was raised from 160 ° C to 230 ° C over 3 hours, and then a condensation reaction was carried out at 230 ° C for 4 hours while the produced condensation water was distilled off using the water separator.Next, 58 parts of trimellitic anhydride was added to the resulting condensation reaction product to add carboxyl groups, and the mixture was allowed to react at 170°C for 30 minutes. After neutralization, an equal amount of 2-(dimethylamino)ethanol was added to the acid groups, and deionized water was gradually added to disperse the mixture in water, yielding a polyester polyol emulsion (C-a2-1) with a solids concentration of 45% and a pH of 7.2. The polyester polyol emulsion (C-a2-1) had a number average molecular weight of 1,425, an acid value of 35 mg KOH / g, a hydroxyl value of 130 mg KOH / g, and a glass transition temperature of -12°C.

[0216] 100 parts of deionized water, 5 parts of a pigment dispersant ("DISPER BYK-190", product name, manufactured by BYK-chemie), 60 parts of titanium white, 20 parts of barium sulfate, and 1 part of an antifoaming agent ("BYK-015", product name, manufactured by BYK-chemie) were blended and stirred at room temperature, followed by pigment dispersion to prepare a pigment dispersion paste. A mixture of 186 parts of the pigment dispersion paste, 60 parts (30 parts solids) of a 50% nonvolatile acrylic polyol emulsion (C-a1-1), 66.7 parts (30 parts solids) of a polyester polyol emulsion (C-a2-1), 1 part of a surface conditioner (BYK-348, product name, manufactured by BYK-chemie), 2 parts (1 part solids) of an ultraviolet absorber (TINUVIN384-2, product name, manufactured by BASF, a benzotriazole-based ultraviolet absorber), 2 parts of a light stabilizer (TINUVIN292, product name, manufactured by BASF, a hindered amine-based light stabilizer), and 0.6 parts of a thickener (ACRYSOL ASE60, product name, manufactured by The Dow Chemical Company, an alkali-swellable thickener) was mixed at room temperature and stirred. Dimethylethanolamine was added dropwise to the mixture until the pH reached 8.0, producing the main component (CI).

[0217] In a separate container, 40 parts of a polyisocyanate compound (Bayhydur XP2655, product name, manufactured by Sumika Covestro Urethane Co., Ltd., a hexamethylene diisocyanate-based polyisocyanate having sulfonic acid groups), 10 parts of ethyl ethoxypropionate, and 10 parts of ethylene glycol monobutyl ether acetate were blended and mixed until uniform, to prepare a curing agent component (C-II).

[0218] The base resin and curing agent were mixed according to the formulation shown in Table 5 below, and deionized water was added so that the non-volatile content was 40%, followed by stirring to obtain a water-based topcoat paint composition (C-1).

[0219] Production Examples 25-26 Production of Water-Based Top Coating Compositions (C-2)-(C-3) Water-based topcoat paint compositions (C-2) to (C-3) were obtained in the same manner as in Production Example 24 above, except for using the formulations shown in Table 5. The numerical values ​​for the blending amounts in the table are the values ​​for the solid content or active ingredients.

[0220] [Table 5]

[0221] <Creating multi-layer coatings> Example 1: Preparation of multilayer coated plate 1 An aluminum plate measuring 300 x 150 x 2.0 mm was airless spray coated with "Epomarine GX" (an epoxy resin primer coating composition manufactured by Kansai Paint Co., Ltd.) to a dry film thickness of approximately 60 μm and dried at 20°C for 16 hours. An undercoat coating composition (A-1) was airless spray coated onto the coated surface to a dry film thickness of approximately 500 μm, followed by drying at 60°C for 30 minutes. An intermediate coating composition (B1-1) was then airless spray coated onto the coated surface to a dry film thickness of 50 μm. The coated surface was then left for 4 hours at room temperature (23°C, 50% RH), after which it was sanded with #400 sandpaper, dried at room temperature, and degreased and cleaned using KAR Silicon Off. An aqueous topcoat coating composition (C-2) was then air spray coated to a dry film thickness of 40 μm and dried at 60°C for 40 minutes, yielding a multilayer coating plate 1.

[0222] Examples 2 to 19 and Comparative Examples 1 to 3: Preparation of multilayer coated plates 2 to 22 Multilayer coated plates 2 to 22 were prepared in the same manner as above, except for using the coating compositions and film thicknesses listed in Table 6. For the topcoat coating composition, "Rethan PG Ecofleet #531 White" (Kansai Paint Co., Ltd., two-component urethane resin-based topcoat coating) was used for the levels listed as "solvent."

[0223] Example 20: Preparation of multilayer coated plate 23 An aluminum plate measuring 300 x 150 x 2.0 mm was spray-painted with "Epomarine GX" (an epoxy resin primer paint composition manufactured by Kansai Paint Co., Ltd.) to a dry film thickness of approximately 60 μm and dried at 20°C for 16 hours. The primer paint composition (A-1) was spray-painted onto the coated surface to a dry film thickness of approximately 500 μm and then dried at 60°C for 30 minutes. Next, an intermediate paint composition (B1-1) was spray-painted onto the coated surface to a dry film thickness of 50 μm. The coated surface was then left for 4 hours at room temperature (23°C, 50% RH), after which it was sanded with #400 sandpaper, dried at room temperature, and degreased and cleaned using KAR Silicon Off. Finally, "Retan WB Eco EV #539 White HS Base" (a water-based metallic base paint for automotive refinishing manufactured by Kansai Paint Co., Ltd.) was spray-painted to a dry film thickness of 20 μm and dried with an air blower. "Retan WB Eco EV EQ Clear" (a water-based clear paint for automotive repairs, manufactured by Kansai Paint Co., Ltd.) was spray-painted to a dry film thickness of 40 μm, and then heated and dried at 60°C for 20 minutes to obtain a multi-layer coating plate 23.

[0224] <Performance test> The results of various performance tests conducted on the multilayer coating films obtained in the examples and comparative examples are shown in Table 6. If the multilayer coating film receives a rating of "C" or "D" in any one of the following performance tests, the multilayer coating film fails.

[0225] [Table 6]

[0226] Paint film appearance The appearance of each multi-layer coating film obtained in the Examples and Comparative Examples was visually inspected for unevenness, popping, shrinkage, smoothness, gloss, etc., and evaluated according to the following evaluation criteria. S: The appearance of the coating is very good. A: Almost no unevenness, wrinkles or shrinkage are observed, and the smoothness and gloss are good, with no practical problems. B: A slight decrease in smoothness and loss of gloss are observed, but unevenness, underarms, and shrinkage are hardly observed, and the level is not problematic for practical use. C: Significant unevenness, underarms, shrinkage, loss of shine, etc. are evident, and there is a clear problem.

[0227] Corrosion resistance In accordance with JIS K 5600-7-1, each test coated plate had a cross-cut made in the test coating surface that reached the base material, and was sprayed with a 5% aqueous solution of sodium chloride adjusted to a pH of 7.0 in an atmosphere of 35°C for 168 hours, after which the width of the blister on one side from the cut was evaluated. S: Less than 1.0 mm, A: 1.0mm or more and less than 2.0mm, B: 2.0mm or more and less than 3.0mm, C: 3.0mm or more, D: 3.0mm or more and cracks occur.

[0228] water resistance Each multilayer coating film obtained in the Examples and Comparative Examples was immersed in a 40°C thermostatic water bath for 10 days, then removed and the surface moisture was wiped off. Immediately after wiping off the moisture, 100 2mm x 2mm cross-hatched patterns (total number) were formed on the coating surface in accordance with JIS K 5600-5-6 (1990). Adhesive tape was applied to the cross-hatched surface and quickly peeled off, and the number of cross-hatched coating films remaining on the coating surface (remaining number) was evaluated according to the following criteria. S: Remaining number / total number = 100 / 100 with no chipped edges A: Remaining number / total number = 100 / 100 with chipped edges. B: Remaining number / total number = 99-90 / 100 C: Remaining number / total number = 89 or less / 100.

[0229] weather resistance Each multilayer coating film obtained in the Examples and Comparative Examples was subjected to an accelerated weathering test in accordance with JIS K 5600-7-7 using a "Super Xenon Weather Meter" (a weathering tester manufactured by Suga Test Instruments Co., Ltd.) under conditions of a test piece wetting cycle of 18 minutes / 2 hours and a black panel temperature of 61 to 65° C. Next, when the lamp irradiation time reached 1,000 hours, the appearance of the test coated plate was evaluated visually. S: No change at all before and after the test. A: After the test, some gloss loss or discoloration is observed. B: Loss of gloss or discoloration is observed after testing. C: Significant loss of gloss or discoloration is observed after the test.

Claims

1. A step (1) of applying a primer coating composition (D) to an object to be coated to form a primed coating film (D'); Step (2) of applying a primer coating composition (A) onto the primer-treated coating film (D') to form a primer coating film (A') having a thickness of 50 to 1000 μm; Step (3) of applying an intermediate coating composition (B) onto the undercoat coating film (A') to form an intermediate coating film (B'); A method for forming a multilayer coating film, comprising: The primer coating composition (A) is an organic solvent-based multi-component polyurethane coating composition obtained by mixing a main component (AI) containing an acrylic polyol (A-a), a pigment composition (A-b) and an organic solvent (A-c), and a curing agent component (A-II) containing a polyisocyanate compound (A-d), The solids concentration of the primer coating composition (A) at the time of application is 70 mass% or more based on the total mass of the primer coating composition (A), The intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition or an organic solvent-based multi-component polyurea coating composition, A method for forming multi-layer coating films.

2. The method for forming a multilayer coating film according to claim 1, wherein the acrylic polyol (A-a) contained in the undercoat paint composition (A) contains an acrylic polyol (A-a1) having a glass transition temperature of -20°C or higher and 60°C or lower, an acid value of 1 mgKOH / g or higher and 25 mgKOH / g or lower, and a hydroxyl value of 100 mgKOH / g or higher and 200 mgKOH / g or lower.

3. The method for forming a multilayer coating film according to claim 1, wherein the content of the pigment composition (A-b) in the undercoat paint composition (A) is 100 to 500 parts by mass based on 100 parts by mass of the solid content of all resin components contained in the main component (AI) and the curing agent component (A-II).

4. 2. The method for forming a multilayer coating film according to claim 1, wherein the solids concentration of the intermediate coating composition (B) at the time of application is 70 mass% or more based on the total mass of the intermediate coating composition (B).

5. The intermediate coating composition (B) is an organic solvent-based multi-component polyurethane coating composition (B1) obtained by mixing a main component (B1-I) containing a hydroxyl group-containing resin (B1-a), a pigment composition (B1-b), an organic solvent (B1-c) and a catalyst (B1-e), and a curing agent component (B1-II) containing a polyisocyanate compound (B1-d), 2. The method for forming a multi-layer coating film according to claim 1, wherein the content of the catalyst (B1-e) is 0.1 to 5 parts by mass based on 100 parts by mass of the solid content of the hydroxyl group-containing resin (B1-a).

6. The method for forming a multilayer coating film according to claim 5, wherein the hydroxyl group-containing resin (B1-a) contains an acrylic polyol (B1-a1) and a polyester polyol (B1-a2), and the solid content ratio of the acrylic polyol (B1-a1) to the polyester polyol (B1-a2) is 50 / 50 to 95 / 5 by mass.

7. The intermediate coating composition (B) is an organic solvent-based multi-component polyurea coating composition (B2) obtained by mixing a main component (B2-I) containing a polyaspartic acid ester (B2-a), a pigment composition (B2-b), and an organic solvent (B2-c), and a curing agent component (B2-II) containing a polyisocyanate compound (B2-d), 2. The method for forming a multilayer coating film according to claim 1, wherein the water content of the main component (B-II) is 5000 ppm or less.

8. The method for forming a multilayer coating film according to claim 7, wherein the main component (B2-I) contains a dehydrating agent (B2-e), and the content of the dehydrating agent (B2-e) is 5 to 30 parts by mass based on 100 parts by mass of the solid content of all resin components contained in the main component (B2-I).

9. The method for forming a multilayer coating film according to claim 1, further comprising a step (4) of applying a topcoat paint composition (C) onto the intermediate coating film (B') after the step (3) to form a topcoat coating film (C').

10. The topcoat paint composition (C) is an aqueous multi-component polyurethane paint composition obtained by mixing a main component (C-I) containing a hydroxyl group-containing resin (C-a), a pigment composition (C-b) and water, and a curing agent component (C-II) containing a polyisocyanate compound (C-d), The method for forming a multilayer coating film according to claim 9, wherein the hydroxyl group-containing resin (Ca) contains an acrylic polyol (Ca1) and a polyester polyol (Ca2), and the solid content ratio of the acrylic polyol (Ca1) and the polyester polyol (Ca2) is 40 / 60 to 90 / 10 by mass.

11. 2. The method for forming a multilayer coating film according to claim 1, wherein the coating in steps (1), (2), and (3) is carried out by airless spraying.

12. The method for forming a multilayer coating film according to any one of claims 1 to 11, wherein the object to be coated is a railway vehicle, industrial machinery, construction machinery, a large vehicle, a ship, a building, or a structure.

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