Multilayer coating film, and multilayer coating film formation method

Abstract

To provide a multilayer coating film having excellent jet-blackness of shade and both blackness of highlight and dense pearl feeling, and a multilayer coating film formation method.SOLUTION: A multilayer coating film has a first colored coating film, a second colored coating film, and a clear coating film in this order on a black substrate layer, wherein the first colored coating film contains a coating film formation resin, a silver pearl pigment, a black pigment, and a purple pigment, the second colored coating film contains 0.02 to 0.10 pts.mass of a black pigment with respect to 100 pts.mass of the total amount of the coating film formation resin and a coating film formation resin solid content, Mc75 value indicating jet-blackness of shade of the multilayer coating film is 215.0 or more, L*15 value indicating brightness of highlight is 30.0 or less, and SG15 value indicating brightness of pearl is 3.0 to 4.0.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a black multilayer coating film and a method for forming the multilayer coating film.

Background Art

[0002] In recent years, especially in the fields such as automobiles, black-colored coatings with low brightness, especially those with high jet-blackness, have become popular from the perspective of a high-class feeling. On the other hand, from the perspective of texture, a silky feeling, that is, a pearl feeling including an optically interfering pigment whose color changes depending on the observation angle, and among them, in particular, a design with a dense pearl feeling is gathering popularity. Then, there is a demand for a multilayer coating film and a method for forming the multilayer coating film that have both of these characteristics, namely, high jet-blackness and a dense pearl feeling. However, a coating film having a dense pearl feeling has a high highlight brightness and a hue that is contrary to jet-blackness, so it has been difficult to achieve both.

[0003] For example, in Patent Document 1, a dark color paint containing 0.1 to 10 parts by weight of a coloring pigment, 1 to 20 parts by weight of an interfering pigment, and 0.1 to 4 parts by weight of carbon black per 100 parts by weight (solid content) of a resin component is applied, and then a color clear paint containing 0.01 to 5 parts by weight of carbon black and 0 to 5 parts by weight of a coloring pigment per 100 parts by weight (solid content) of a resin component is applied to the coated surface, and a coating film forming method is disclosed.

[0004] Further, in Patent Document 2, a multilayer coating film having a first coating film, a second coating film, and a clear coating film in this order, wherein the first coating film is a cured coating film of a first paint composition containing a first coating film forming resin and a bright pigment, the second coating film is a cured coating film of a second paint composition containing a second coating film forming resin and a coloring pigment, the bright pigment contained in the first coating film includes a flaky aluminum pigment, the content of the coloring pigment contained in the second coating film is in the range of 1.5 to 6 parts by mass with respect to 100 parts by mass of the resin solid content contained in the coating film, and a multilayer coating film in which the bright area Sa(45°) value, the bright intensity Si(15°) value, and the L*(25°) value of the multilayer coating film are respectively in a specific range is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the coating film forming method of Patent Document 1, the blackness is insufficient, and even higher blackness is required.

[0007] Also, while the multi - layer coating film of Patent Document 2 has low lightness and chroma such that it is recognized as a black coating film, although a multi - layer coating film with recognized luminance can be obtained, it does not have a pearlescent feeling.

[0008] Therefore, an object of the present invention is to provide a multi - layer coating film and a multi - layer coating film forming method that are excellent in the blackness of the shade and have both the blackness of the highlight and a dense pearlescent feeling.

Means for Solving the Problems

[0009] As a result of intensive research to solve the above problems, the present inventors have found that in a multi - layer coating film having, in this order, a first colored coating film containing a coating film - forming resin, a silver pearl pigment, a black pigment, and a purple pigment, a second colored coating film containing a coating film - forming resin and a specific amount of black pigment, and a clear coating film on a black underlayer, by setting the Mc75 value representing the blackness of the shade, the L*15 value representing the lightness of the highlight, and further the SG15 value representing the brilliance of the pearl within a specific range, the above problems can be solved, and thus the present invention has been completed.

[0010] That is, the above problems of the present invention are solved by a multilayer coating film having a first colored coating film, a second colored coating film, and a clear coating film in this order on a black base layer, wherein the first colored coating film contains a film-forming resin, a silver pearl pigment, a black pigment, and a purple pigment, the second colored coating film contains a film-forming resin and 0.02 to 0.10 parts by mass of a black pigment based on 100 parts by mass of the total amount of the film-forming resin solid content, the Mc75 value representing the jet blackness of the shade of the multilayer coating film represented by the following formula 1 is 215.0 or more, the L*15 value representing the lightness of the highlight is 30.0 or less, and the SG15 value representing the brilliance of the pearl is 3.0 to 4.0. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Formula 1) (However, X75, Y75, and Z75 respectively represent the tristimulus values in the XYZ color system based on the spectral reflectance of the reflected light received at an angle of 75 degrees with respect to the incident light direction with respect to the specular reflection angle when the incident light irradiated at an angle of 45 degrees with respect to the perpendicular to the surface of the multilayer coating film.)

[0011] Furthermore, in the multilayer coating film of the present invention, it is preferable that the first colored coating film contains 5.0 to 30.0 parts by mass of a silver pearl pigment based on 100 parts by mass of the total amount of the film-forming resin solid content, and the average particle diameter D50 of the silver pearl pigment is 4.0 to 12.0 μm.

[0012] Furthermore, in the multilayer coating film of the present invention, it is preferable that the purple pigment contained in the first colored coating film is a dioxazine violet pigment.

[0013] Also, the problems of the present invention include a step (1) of coating a first colored paint composition (BC1) on a black base layer to form an uncured first colored coating film, a step (2) of coating a second colored paint composition (BC2) on the uncured first colored coating film obtained in step (1) to form an uncured second colored coating film, a step (3) of coating a clear paint composition (CC) on the uncured second colored coating film obtained in step (2) to form an uncured clear coating film, A method for forming a multilayer coating film, comprising a step (4) of simultaneously curing an uncured first colored coating film, an uncured second colored coating film, and an uncured clear coating film formed in steps (1) to (3). The first colored coating composition (BC1) contains a film-forming resin, a silver pearl pigment, a black pigment, and a purple pigment. The second colored coating composition (BC2) contains a film-forming resin and 0.02 to 0.10 parts by mass of a black pigment based on 100 parts by mass of the total amount of the film-forming resin solids. The problem is also solved by a method for forming a multilayer coating film in which the Mc75 value representing the jet blackness of the obtained multilayer coating film represented by the following formula 1 is 215.0 or more, the L*15 value representing the lightness of the highlight is 30.0 or less, and the SG15 value representing the brilliance of the pearl is 3.0 to 4.0. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Formula 1) (However, X75, Y75, and Z75 represent the tristimulus values in the XYZ color system based on the spectral reflectance of the reflected light received at an angle of 75 degrees with respect to the incident light direction with respect to the normal of the multilayer coating film surface when the incident light irradiated at an angle of 45 degrees with respect to the normal of the multilayer coating film surface is received.)

[0014] Furthermore, in the method for forming a multilayer coating film of the present invention, the first colored coating composition (BC1) preferably contains 5.0 to 30.0 parts by mass of a silver pearl pigment based on 100 parts by mass of the total amount of the film-forming resin solids, and the average particle diameter D50 of the silver pearl pigment is preferably 4.0 to 12.0 μm.

[0015] Furthermore, in the method for forming a multilayer coating film of the present invention, the purple pigment contained in the first colored coating composition (BC1) is preferably a dioxazine violet pigment.

Advantages of the Invention

[0016] By the multilayer coating film and the method for forming a multilayer coating film of the present invention, a multilayer coating film excellent in the jet blackness of the shade and having both the blackness of the highlight and a dense pearl feeling can be obtained.

Mode for Carrying Out the Invention

[0017] [Object to be Coated] The multilayer coating film of the present invention is formed on a black underlayer formed on an object to be coated. The object to be coated in the present invention is not particularly limited, and examples thereof include members made of metals such as iron, zinc, aluminum, and magnesium, members made of alloys of these metals, members plated or vapor-deposited with these metals, members made of glass, plastic, foams of various materials, etc. Among them, steel materials and plastic materials constituting an automobile body are preferable. These members can be appropriately subjected to treatments such as degreasing treatment and surface treatment as necessary.

[0018] In addition, in the present invention, those in which an undercoat film is formed on the above member can also be used as the object to be coated. The undercoat film is applied to the member surface in order to conceal the member surface or impart corrosion resistance, rust prevention, adhesion, conductivity, etc. to the member, and can be formed by applying an undercoat paint and curing or drying it. This undercoat paint is not particularly limited, and known ones per se, for example, electrodeposition paints, solvent-based primers, water-based primers, etc. can be used.

[0019] [Black Underlayer] The black underlayer used in the multilayer coating film of the present invention may be the above undercoat film directly formed on the object to be coated, or may be a coating film formed with an undercoat film interposed therebetween on the object to be coated. The black underlayer is formed by a paint composition for black underlayer containing a film-forming resin and a coloring pigment.

[0020] As the film-forming resin of the paint composition for black underlayer of the present invention, a thermosetting resin composition in which a cross-linking reaction proceeds by heating after coating to form a coating film may be used, or a thermoplastic resin composition in which a coating film is formed by volatilization of a solvent may be used. The film-forming resin can be used by dissolving or dispersing it in a solvent such as an organic solvent and / or water.

[0021] As the thermosetting resin composition in the paint composition for the black underlayer of the present invention, for example, a thermosetting resin composition containing a base resin and a curing agent can be used. The content of the curing agent in this resin composition (base resin + curing agent) is not particularly limited, but it is preferably 0.1 to 50.0 parts by mass, more preferably 5.0 to 45.0 parts by mass, and particularly preferably 10.0 to 40.0 parts by mass with respect to 100 parts by mass of the total amount of the resin solids forming the coating film. When the paint composition for the black underlayer of the present invention is a thermosetting resin composition, it may be a one-component paint composition in which the base resin and the curing agent are mixed in advance, or a two-component paint composition in which the base resin and the curing agent are mixed immediately before painting.

[0022] Examples of the base resin of the thermosetting resin composition in the paint composition for the black underlayer of the present invention include acrylic resin, polyester resin, polyurethane resin, polyurea resin, acrylic urethane resin, polyurethane polyurea resin, polyolefin resin (including chlorinated and / or modified ones), epoxy resin, etc. Further, the base resin may be partially crosslinked particles, or core / shell type particles composed of an inner (core part) and an outer (shell part). Examples of the particulate base resin include polyurethane-polyurea particles, urethane core / acrylic shell type particles, acrylic core / urethane shell type particles, etc. When a part of the base resin particles is crosslinked, that part becomes a part insoluble in the organic solvent (gel part), so the gel fraction, which is a value indicating the ratio of the gel part in the solid content of the base resin particles, can be measured. Also, the base resin preferably has a hydroxyl group and / or a carboxyl group as a functional group. These base resins may be used alone or in combination of two or more.

[0023] Examples of the curing agent for the thermosetting resin composition in the coating composition for the black underlayer of the present invention include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, polycarbodiimide compounds, and the like. Among these, amino resins and blocked polyisocyanate compounds are particularly preferred. These curing agents may be used alone or in combination of two or more.

[0024] An amino resin is a general term for resins obtained by adding and condensing formaldehyde to a compound containing an amino group. Examples of amino resins include melamine resins, urea resins, guanamine resins, etc. Among these, melamine resins are particularly preferred.

[0025] Examples of melamine resins include partially or completely methylolated melamine resins obtained by reacting melamine with formaldehyde, partially or completely alkyl ether type melamine resins obtained by partially or completely etherifying the methylol groups of methylolated melamine resins with an alcohol component, imino group-containing melamine resins, and mixed type melamine resins obtained by mixing two or more of these melamine resins. Further, examples of alkyl ether type melamine resins include methylated melamine resins, butylated melamine resins, methyl / butyl mixed alkyl ether type melamine resins, and the like.

[0026] Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; aromatic diisocyanates such as xylylene diisocyanate (XDI), tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI; and compounds composed of dimers, trimers, or more of these diisocyanates, such as uretdione, allophanate, adduct, biuret, isocyanurate, and iminooxadiazinedione forms. Further, a part of these isocyanate groups may be modified with an amino group-containing silane coupling agent or the like.

[0027] Examples of the blocked polyisocyanate compound include those obtained by blocking the isocyanate groups of the above polyisocyanate compounds with alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ε-caprolactam, active methylenes such as malonic diester and acetoacetic ester, pyrazoles such as 3,5-dimethylpyrazole, imidazoles such as imidazole and 2-ethylimidazole, and phenols such as m-cresol.

[0028] As the polycarbodiimide compound, a hydrophilic carbodiimide compound is preferred. Examples of the hydrophilic carbodiimide compound include those obtained by reacting a polycarbodiimide compound containing at least two isocyanate groups in one molecule with a polyol having a hydroxyl group at the molecular end at a ratio such that the molar ratio of NCO / OH exceeds 1, and then reacting the resulting reaction product with a hydrophilizing agent having an active hydrogen and a hydrophilic moiety.

[0029] Examples of the thermoplastic resin composition used in the paint composition for the black underlayer of the present invention include a thermoplastic resin composition containing a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, a polyolefin resin (including chlorinated and / or modified ones), and an epoxy resin, which has a mass average molecular weight of 30,000 or more.

[0030] Examples of the coloring pigment used in the paint composition for the black underlayer of the present invention include inorganic pigments such as composite oxide pigments such as titanium oxide, iron oxide, and titanium yellow, and organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments, and indigo pigments, and carbon black. These coloring pigments may be used alone or in combination of two or more.

[0031] The total content of the coloring pigment contained in the paint composition for the black underlayer of the present invention is not particularly limited, but is preferably 20.0 to 180.0 parts by mass, more preferably 40.0 to 150.0 parts by mass, and particularly preferably 60.0 to 120.0 parts by mass with respect to 100 parts by mass of the total amount of the resin solids forming the coating film.

[0032] The paint composition for the black underlayer of the present invention may further contain, as required, solvents such as organic solvents and / or water, rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoaming agents, antioxidants, ultraviolet absorbers, and other various paint additives, extender pigments, etc. as appropriate. Examples of organic solvents include organic solvents commonly used in the production of colored paint compositions, such as aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone, esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate, alcohols such as isopropanol, butanol, 2-butoxyethanol, and 2-ethylhexanol, ethers, aliphatic hydrocarbons containing chlorinated hydrocarbons, or mixtures thereof. Among these, when using a polyisocyanate compound (including blocked ones) as a curing agent, a smooth curing reaction can be achieved by restricting the use of alcohols and water in the organic solvent.

[0033] The content of non-volatile components (coating film-forming resin solids + coloring pigment + paint additive solids + extender pigment) during the coating of the paint composition for the black underlayer of the present invention is not particularly limited, but is preferably 10.0 to 65.0% by mass, more preferably 15.0 to 63.0% by mass, and particularly preferably 20.0 to 60.0% by mass.

[0034] The paint composition for the black underlayer of the present invention can be applied by methods such as electrostatic coating, air spraying, and airless spraying. The dry film thickness of the black underlayer coating film is not particularly limited, but is preferably 3.0 to 50.0 μm, more preferably 4.0 to 45.0 μm, and particularly preferably 5.0 to 40.0 μm.

[0035] The black underlayer obtained from the paint composition for the black underlayer of the present invention preferably has an N value in the range of 1.5 to 4.5 on the Munsell chart.

[0036] [First Colored Coating Film] The first colored coating film used in the multilayer coating film of the present invention is formed from a first colored paint composition containing a film-forming resin, a silver pearl pigment, a black pigment, and a purple pigment.

[0037] As the film-forming resin of the first colored paint composition of the present invention, it may be a thermosetting resin composition that forms a coating film by the progress of a crosslinking reaction by heating after coating, or it may be a thermoplastic resin composition that forms a coating film by the evaporation of a solvent. The film-forming resin can be used by dissolving or dispersing it in a solvent such as an organic solvent and / or water.

[0038] As the thermosetting resin composition in the first colored paint composition of the present invention, for example, a thermosetting resin composition containing a base resin and a curing agent can be used. The content of the curing agent in this resin composition (base resin + curing agent) is not particularly limited, but it is preferably 0.1 to 50.0 parts by mass, more preferably 5.0 to 45.0 parts by mass, and particularly preferably 10.0 to 40.0 parts by mass with respect to 100 parts by mass of the total amount of the film-forming resin solid content. When the first colored paint composition of the present invention is a thermosetting resin composition, it may be a one-component paint composition in which the base resin and the curing agent are mixed in advance, or a two-component paint composition in which the base resin and the curing agent are mixed immediately before coating.

[0039] Examples of the base resin of the thermosetting resin composition in the first colored paint composition of the present invention can be the same as those exemplified as the base resin of the thermosetting resin composition in the black underlayer paint composition. When both the black underlayer paint composition and the first colored paint composition of the present invention are thermosetting resin compositions, the base resin may be the same or different.

[0040] Examples of the curing agent for the thermosetting resin composition in the first colored paint composition of the present invention can be the same as those exemplified as the curing agent for the thermosetting resin composition in the paint composition for the black underlayer. When both the paint composition for the black underlayer and the first colored paint composition of the present invention are thermosetting resin compositions, the same curing agent may be used, or different ones may be used.

[0041] Examples of the thermoplastic resin composition in the first colored paint composition of the present invention can be the same as those exemplified as the thermoplastic resin composition in the paint composition for the black underlayer. When both the paint composition for the black underlayer and the first colored paint composition of the present invention are thermoplastic resin compositions, the same one may be used, or different ones may be used.

[0042] The first colored paint composition of the present invention contains a silver pearl pigment that exhibits a silver-white color. In addition to the silver type, pearl pigments include an iridescent type generated by light interference, a colored type in which titanium oxide is coated and then further coated with iron oxide, etc. However, as the pearl pigment used in the first colored paint composition of the present invention, the silver type is particularly preferred. Examples of commercially available silver pearl pigments include, for example, Xirallic T61-10 WNT Mircro Silver, Iriodin 121 Rutile Luster Satin WNT, Iriodin 111 Rutile Fine Satin WNT (trade names, manufactured by Merck), Glacier Exterior Silk White S1303V, Mearlin Exterior CFS Bright Silver 1303Z, Mearlin Exterior CFS Fine Pearl 1303V (trade names, manufactured by Sun Chemical Colors & Effects), Automotive Rutile Ultra Silk A-903M, Automotive Rutile Fine White A-903D, Automotive Splendor White A-901K (trade names, manufactured by CQV), etc.

[0043] The average particle size D50 of the above silver pearl pigment is preferably 4.0 to 12.0 μm, and particularly preferably 6.0 to 10.0 μm. By setting the average particle size D50 of the silver pearl pigment to 4.0 to 12.0 μm, a multilayer coating film having a dense pearl feeling can be obtained.

[0044] In addition, the average particle size D50 in the present invention is the particle size at which the cumulative volume of particles integrated from the small particle size side to a certain particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method (static light scattering method) is expressed as a percentage of the total volume of the particles, and the value is 50%. Examples of the laser diffraction / scattering method (static light scattering method) particle size distribution measuring device include Partica LA-960V2 series (trade name, manufactured by Horiba, Ltd.), SALD-2300 (trade name, manufactured by Shimadzu Corporation), MT3000II series (trade name, manufactured by Microtrac Bell Corporation), and the like.

[0045] The content of the silver pearl pigment in the first colored paint composition of the present invention is preferably 5.0 to 30.0 parts by mass, more preferably 10.0 to 25.0 parts by mass, and particularly preferably 15.0 to 20.0 parts by mass with respect to 100 parts by mass of the total amount of the film-forming resin solid content. By setting the content of the silver pearl pigment to 5.0 to 30.0 parts by mass, a multilayer coating film having a dense pearl feeling can be obtained.

[0046] The first colored paint composition of the present invention contains a black pigment. The black pigment in the first colored paint composition of the present invention is not particularly limited as long as it is black. Examples include carbon black, graphite, iron black, composite metal oxides such as iron chromium and bismuth manganese, perylene-based black pigments, azomethiazole-based pigments, etc. Preferred black pigments include carbon black. These black pigments may be used alone or in combination of two or more.

[0047] In the first colored paint composition of the present invention, the content of the black pigment is preferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and particularly preferably 5.0 to 10.0 parts by mass with respect to 100 parts by mass of the total amount of the film-forming resin solids. By setting the content of the black pigment to 1.0 to 20.0 parts by mass, a multi-layer coating film excellent in jet blackness can be obtained.

[0048] The first colored paint composition of the present invention contains a purple pigment. The purple pigment in the first colored paint composition of the present invention is not particularly limited as long as it is purple. For example, dioxazine violet pigments such as Color Index (C.I.) Pigment Violet 23 (C.I. No. 51319), C.I. Pigment Violet 37 (C.I. No. 51345), etc., perylene violet pigments such as C.I. Pigment Violet 29 (C.I. No. 71129), quinacridone violet pigments such as C.I. Pigment Violet 19 (C.I. No. 73900), etc. can be mentioned. Examples of commercially available dioxazine violet pigments include Hostaperm Violet P-RL, Hostaperm Violet RL 02, Hostaperm Violet BL 01, Hostaperm Violet RL Special 01 (trade name, manufactured by HEUBACH), Cromophtal Violet D 5700, Cromophtal Violet D 5800, Cromophtal Violet K 5700, Cromophtal Violet K 5800, Cromophtal Violet L 5805 (trade name, manufactured by Sun Chemical Colors & Effects), etc. Examples of commercially available perylene violet pigments include Corimax Violet 5011 (trade name, manufactured by Zeya Chemicals), etc. Examples of commercially available quinacridone violet pigments include Cinquasia Violet K 5340 FK, Cinquasia Violet K 5350, Cinquasia Violet K 5350 FP, Cinquasia Violet L 5110, Cinquasia Violet L 5120, Cinquasia Violet L 5125 (trade name, manufactured by Sun Chemical Colors & Effects), etc. Among these, preferred purple pigments include dioxazine violet pigments. These purple pigments may be used alone or in combination of two or more.

[0049] In the first colored paint composition of the present invention, the content of the purple pigment is preferably 0.10 to 0.90 parts by mass, more preferably 0.15 to 0.70 parts by mass, and particularly preferably 0.20 to 0.50 parts by mass with respect to 100 parts by mass of the total amount of the film-forming resin solid content. By setting the content of the purple pigment to 0.10 to 0.90 parts by mass, it is possible to cancel out the complementary green color and obtain a multi-layer coating film excellent in blackness.

[0050] The first colored paint composition of the present invention may further contain a coloring pigment other than the above black pigment and purple pigment. Examples of the coloring pigment other than the black pigment and purple pigment include white pigments, red pigments, orange pigments, yellow pigments, green pigments, and blue pigments. More specific examples include inorganic pigments such as composite oxide pigments such as titanium oxide, iron oxide, cobalt blue, and titanium yellow, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments, indigo pigments and other organic pigments. Among these, it is particularly preferable to contain a phthalocyanine-based or threne-based blue pigment because it is possible to cancel out the complementary orange color and obtain a multi-layer coating film excellent in blackness. These coloring pigments may be used alone or in combination of two or more.

[0051] The first colored paint composition of the present invention may further contain, as required, solvents such as organic solvents and / or water, rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoaming agents, antioxidants, ultraviolet absorbers, and various other paint additives, extender pigments, etc., as appropriate. Examples of organic solvents include aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, which are commonly used in the production of colored paint compositions; ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone; esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate; alcohols such as isopropanol, butanol, 2-butoxyethanol, and 2-ethylhexanol; ethers; aliphatic hydrocarbons including chlorinated hydrocarbons; or mixtures thereof. Among these, when a polyisocyanate compound (including blocked ones) is used as a curing agent, a smooth curing reaction can be achieved by restricting the use of alcohols and water as organic solvents.

[0052] The content of non-volatile components (coating film-forming resin solids + pearl pigment + colored pigment + paint additive solids + extender pigment) during the coating of the first colored paint composition of the present invention is not particularly limited, but is preferably 10.0 to 60.0% by mass, more preferably 12.5 to 50.0% by mass, and particularly preferably 15.0 to 40.0% by mass.

[0053] The first colored paint composition of the present invention can be applied by methods such as electrostatic coating, air spraying, and airless spraying. The dry film thickness of the first colored coating film is not particularly limited, but is preferably 3.0 to 15.0 μm, more preferably 3.0 to 12.0 μm, and particularly preferably 3.0 to 10.0 μm.

[0054] [Second Colored Coating Film] The second colored coating film used in the multilayer coating film of the present invention is formed from a second colored paint composition containing a coating film-forming resin and a black pigment. By inserting the second colored coating film between the first colored coating film and the clear coating film, a multilayer coating film having both high blackness and a dense pearl feeling can be obtained.

[0055] As the film-forming resin of the second colored coating composition of the present invention, a thermosetting resin composition that forms a coating film by the progress of a crosslinking reaction upon heating after coating may be used, or a thermoplastic resin composition that forms a coating film by the volatilization of a solvent may be used. The film-forming resin can be used by dissolving or dispersing it in a solvent such as an organic solvent and / or water.

[0056] As the thermosetting resin composition in the second colored coating composition of the present invention, for example, a thermosetting resin composition containing a base resin and a curing agent can be used. The content of the curing agent in this resin composition (base resin + curing agent) is not particularly limited, but it is preferably 0.1 to 50.0 parts by mass, more preferably 5.0 to 45.0 parts by mass, and particularly preferably 10.0 to 40.0 parts by mass with respect to 100 parts by mass of the total amount of the film-forming resin solid content. In the case where the second colored coating composition of the present invention is a thermosetting resin composition, it may be a one-component coating composition in which the base resin and the curing agent are mixed in advance, or a two-component coating composition in which the base resin and the curing agent are mixed immediately before coating.

[0057] Examples of the base resin of the thermosetting resin composition in the second colored coating composition of the present invention include the same ones as those exemplified as the base resin of the thermosetting resin composition in the black underlayer coating composition or the first colored coating composition. In the case where the black underlayer coating composition or the first colored coating composition of the present invention is a thermosetting resin composition, the base resin of the second colored coating composition may be the same or different.

[0058] Examples of the curing agent of the thermosetting resin composition in the second colored coating composition of the present invention include the same ones as those exemplified as the curing agent of the thermosetting resin composition in the black underlayer coating composition or the first colored coating composition. In the case where the black underlayer coating composition or the first colored coating composition of the present invention is a thermosetting resin composition, the curing agent of the second colored coating composition may be the same or different.

[0059] Examples of the thermoplastic resin composition in the second colored paint composition of the present invention include the same ones as those listed as examples of the thermoplastic resin composition in the black undercoat paint composition or the first colored paint composition. When the black undercoat paint composition or the first colored paint composition of the present invention is a thermoplastic resin composition, the second colored paint composition may use the same one or a different one.

[0060] The second colored paint composition of the present invention contains a black pigment. The black pigment in the second colored paint composition of the present invention is not particularly limited as long as it is black. Examples include the same black pigments as those shown in the first colored paint composition, and the same black pigment as that used in the first colored paint composition may be used, or a different one may be used. Preferred black pigments include carbon black. The black pigment may be used alone or in combination of two or more.

[0061] The content of the black pigment in the second colored paint composition of the present invention is preferably 0.02 to 0.10 parts by mass, more preferably 0.04 to 0.10 parts by mass, and particularly preferably 0.06 to 0.10 parts by mass with respect to 100 parts by mass of the total amount of the resin solids forming the coating film. By setting the content of the black pigment to 0.02 to 0.10 parts by mass, a multi-layer coating film with little color change can be obtained even when the film thickness fluctuates, and a multi-layer coating film excellent in the blackness of the highlight can be obtained. Furthermore, the SG15 value representing the luster of the pearl of the multi-layer coating film can also be adjusted to an appropriate value by the content of the black pigment.

[0062] The second colored paint composition of the present invention may further contain a coloring pigment other than the above black pigment. Examples of coloring pigments other than the black pigment include, for example, white pigments, red pigments, orange pigments, yellow pigments, green pigments, blue pigments, and purple pigments. More specific examples include inorganic pigments such as composite oxide pigments such as titanium oxide, iron oxide, cobalt blue, and titanium yellow, and organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments, and indigo pigments. Among these, it is particularly preferable to add a dioxazine-based purple pigment and / or a phthalocyanine-based or threne-based blue pigment because it can cancel out the complementary green-based and / or orange-based colors and obtain a multilayer coating film with excellent jet blackness. These coloring pigments may be used alone or in combination of two or more.

[0063] The second colored paint composition of the present invention may further appropriately contain solvents such as organic solvents and / or water, rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoamers, antioxidants, ultraviolet absorbers, and other various paint additives, extender pigments, etc., as needed. Examples of organic solvents include organic solvents commonly used in the production of colored paint compositions, such as aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone, esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate, alcohols such as isopropanol, butanol, 2-butoxyethanol, and 2-ethylhexanol, ethers, aliphatic hydrocarbons containing chlorinated hydrocarbons, or mixtures thereof. Among these, when using a polyisocyanate compound (including blocked ones) as a curing agent, a smooth curing reaction can be carried out by restricting the use of alcohols and water in the organic solvent.

[0064] The content rate of the non-volatile components (coating film-forming resin solid content + coloring pigment + coating additive solid content + extender pigment) during the coating of the second colored coating composition of the present invention is not particularly limited, but is preferably 10.0 to 60.0% by mass, more preferably 12.5 to 50.0% by mass, and particularly preferably 15.0 to 40.0% by mass.

[0065] The second colored coating composition of the present invention can be coated by methods such as electrostatic coating, air spraying, and airless spraying. The dry film thickness of the second colored coating film is not particularly limited, but is preferably 3.0 to 15.0 μm, more preferably 3.0 to 12.0 μm, and particularly preferably 3.0 to 10.0 μm.

[0066] [Clear coating film] The clear coating film used in the multilayer coating film of the present invention is formed by a clear coating composition containing a coating film-forming resin.

[0067] As the coating film-forming resin of the clear coating composition of the present invention, a thermosetting resin composition that forms a coating film by the progress of a crosslinking reaction by heating after coating is preferable. The coating film-forming resin can be used by being dissolved or dispersed in a solvent such as an organic solvent and / or water.

[0068] As the thermosetting resin composition in the clear coating composition of the present invention, for example, a thermosetting resin composition containing a base resin and a curing agent can be used. The content of the curing agent in this resin composition (base resin + curing agent) is not particularly limited, but is preferably 0.1 to 50.0 parts by mass, more preferably 5.0 to 45.0 parts by mass, and particularly preferably 10.0 to 40.0 parts by mass with respect to 100 parts by mass of the total amount of the coating film-forming resin solid content. In addition, the clear coating composition of the present invention may be a one-component coating composition in which the base resin and the curing agent are mixed in advance, or a two-component coating composition in which the base resin and the curing agent are mixed immediately before coating.

[0069] Examples of the base resin in the clear coating composition of the present invention include acrylic resins, polyester resins, polyurethane resins, acrylic urethane resins, and the like. Further, the base resin preferably has one or more selected from hydroxyl groups, carboxyl groups, and epoxy groups as functional groups. These base resins may be used alone or in combination of two or more.

[0070] Examples of the curing agent in the clear coating composition of the present invention include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, and the like. These curing agents may be used alone or in combination of two or more.

[0071] Examples of the amino resin, polyisocyanate compound, and blocked polyisocyanate compound, which are the curing agents in the clear coating composition of the present invention, may be the same as those listed in the examples of the curing agents of the thermosetting resin composition in the black underlayer coating composition, the first colored coating composition, or the second colored coating composition. When any of the black underlayer coating composition, the first colored coating composition, or the second colored coating composition of the present invention is a thermosetting resin composition, the same or different curing agents may be used for the clear coating composition.

[0072] The clear coating composition of the present invention may further contain, as required, solvents such as organic solvents and / or water, rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoaming agents, antioxidants, ultraviolet absorbers, and other various paint additives, extender pigments, coloring pigments in an amount that does not impair transparency, etc., as appropriate. Examples of organic solvents include aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, which are commonly used in the production of colored coating compositions, ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone, esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate, alcohols such as isopropanol, butanol, 2-butoxyethanol, and 2-ethylhexanol, ethers, aliphatic hydrocarbons containing chlorinated hydrocarbons, or mixtures thereof. Among these, when a polyisocyanate compound (including blocked ones) is used as a curing agent, smooth curing reaction can be achieved by restricting the use of alcohols and water in the organic solvent.

[0073] The content of non-volatile components (coating film-forming resin solids + paint additive solids + extender pigment + coloring pigment) during the coating of the clear coating composition of the present invention is not particularly limited, but is preferably 30.0 to 65.0% by mass, more preferably 35.0 to 63.0% by mass, and particularly preferably 40.0 to 60.0% by mass.

[0074] The clear coating composition of the present invention can be applied by methods such as electrostatic coating, air spraying, and airless spraying. The dry film thickness of the clear coating film is not particularly limited, but is preferably 15.0 to 60.0 μm, more preferably 20.0 to 55.0 μm, and particularly preferably 25.0 to 50.0 μm.

[0075] In the present invention, the Mc75 value representing the blackness of the shade of the multilayer coating film represented by the following formula 1 is preferably 215.0 or more, and particularly preferably 218.0 or more. By setting the Mc75 value to 215.0 or more, a multilayer coating film excellent in the blackness of the shade can be obtained. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Equation 1)

[0076] Here, X75, Y75, and Z75 respectively represent the three stimulus values in the XYZ color system based on the spectral reflectance of the reflected light that receives the incident light irradiated at an angle of 45 degrees with respect to the perpendicular line of the multi-layer coating surface and forms an angle of 75 degrees with the incident light direction with respect to the specular reflection angle.

[0077] In the present invention, X75, Y75, and Z75 were measured using a multi-angle colorimeter BYKmac i (trade name, manufactured by BYK-Gardner).

[0078] In the present invention, the L*15 value representing the lightness in the CIE LAB color system based on the spectral reflectance of the reflected light that receives the incident light irradiated at an angle of 45 degrees with respect to the perpendicular line of the multi-layer coating surface and forms an angle of 15 degrees with the incident light direction with respect to the specular reflection angle is preferably 30.0 or less, and particularly preferably 28.0 or less. By setting the L*15 value to 30.0 or less, a multi-layer coating film excellent in the blackness of highlights can be obtained.

[0079] The CIE LAB color system is a color system defined by the International Commission on Illumination (CIE) in 1976 and also adopted in JIS Z 8781-4:2013. The lightness L*15 value in the present invention is a numerical value measured using a multi-angle colorimeter BYKmac i (trade name, manufactured by BYK-Gardner).

[0080] In the present invention, the SG15 value representing the brilliance of the pearls in the multilayer coating film is preferably from 3.0 to 4.0, and particularly preferably from 3.1 to 3.8. When the SG15 value is lower than 3.0, it becomes difficult to feel the brilliance of the pearls, and when the SG15 value is higher than 4.0, it becomes difficult to feel blackness because the brilliance of the pearls is too high. That is, by setting the SG15 value to 3.0 to 4.0, a multilayer coating film having both the blackness of the highlight and the pearl feeling can be obtained. The SG15 value in the present invention is a numerical value measured as the Sparkle Grade using a multi-angle colorimeter BYKmac i (trade name, manufactured by BYK-Gardner). In this colorimeter, the SG15 value of the Sparkle Grade is obtained from the Sparkle area Sa15 value and the Sparkle intensity Si15 value obtained by illuminating the sample surface at an angle of 15 degrees with respect to the perpendicular line of the multilayer coating film surface and taking an image with a vertically arranged CCD chip.

[0081] Here, the Mc75 value, L*15 value, and SG15 value can be adjusted to preferable values by appropriately adjusting the types and contents of the silver pearl pigment, black pigment, purple pigment in the first colored coating film, or the black pigment in the second colored coating film.

[0082] In the method for forming a multilayer coating film of the present invention, a first colored coating composition, a second colored coating composition, and a clear coating composition are used.

[0083] First, as step (1), the first colored coating composition is applied onto a black underlayer to form an uncured first colored coating film. After applying the first colored coating composition, heating (flash-off) may be performed at 70 to 80°C for 3 to 5 minutes in order to volatilize the solvent contained in the first colored coating film, or it may simply be left at room temperature without performing heating. When performing flash-off, the temperature and time range are selected with the above range as a reference so that the coating film is not completely cured.

[0084] Next, as step (2), a second colored paint composition is applied onto the uncured first colored coating film obtained in step (1) to form an uncured second colored coating film. After the application of the second colored paint composition, heating (flash-off) may be performed at 70 to 80°C for 3 to 5 minutes in order to volatilize the solvent contained in the second colored coating film, or it may simply be left at room temperature without heating. When performing flash-off, the temperature and time range are selected based on the above range so that the coating film does not cure completely.

[0085] Next, as step (3), a clear paint composition is applied onto the uncured second colored coating film obtained in step (2) to form an uncured clear coating film. Generally, after the application of the clear paint composition, it is left at room temperature for 5 to 20 minutes and then heat-cured.

[0086] Finally, as step (4), the uncured first colored coating film, the uncured second colored coating film, and the uncured clear coating film formed in steps (1) to (3) are heated to cure these three layers simultaneously.

[0087] In the present invention, heating (baking) can be performed by known means. For example, drying furnaces such as hot air furnaces, electric furnaces, and infrared induction heating furnaces can be used. The baking temperature is not particularly limited, but it is preferably 70 to 160°C, more preferably 75 to 155°C, and particularly preferably 80 to 150°C. By setting the baking temperature to 70 to 160°C, the curing reaction can proceed sufficiently. Also, the heating time is not particularly limited, but it is preferably 10 to 50 minutes, more preferably 15 to 45 minutes, and particularly preferably 20 to 40 minutes.

[0088] The multi-layer coating film and the multi-layer coating film forming method of the present invention are applicable to vehicle bodies, members, and parts such as passenger cars, trucks, motorcycles, and buses, and are particularly effective for use on metal automobile bodies and plastic automobile parts.

Examples

[0089] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" unless otherwise specified, and "%" regarding the blending amount and the content means "% by mass".

[0090] [Method for Measuring Resin Characteristic Values] In the present invention, the resin characteristic values were measured by the following methods. 1. Weight-average molecular weight The weight-average molecular weight was determined as the value obtained by converting the data measured at a temperature of 40°C and a flow rate of 1 m / min by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the eluent, based on the weight-average molecular weight of polystyrene. Here, the columns for gel permeation chromatography (GPC) were used in combination of TSKgel G2000HXL, G3000HXL, G4000HXL, and G5000HXL (trade names, manufactured by Tosoh Corporation). 2. Acid value It was measured in accordance with JIS-K5601-2-1:1999. 3. Hydroxyl value It was measured in accordance with JIS-K1557-1:2007. 4. Resin solid content The resin solid content was determined by measuring the mass of 1.0 g of the sample after heating at 130°C for 60 minutes.

[0091] [Production Example 1: Production of Polyurethane Resin Dispersion Liquid PU-1 for Aqueous Colored Paint Composition] 1-(1) Production of Polyester Polyol Solution PP-1 In a flask equipped with a reflux condenser attached with a reaction water separation tube, a thermometer, a stirring device, and a nitrogen gas introduction tube, 35.0 parts of dimer acid PRIPOL1017 (trade name, manufactured by Croda), which is mainly composed of a dicarboxylic acid having 36 carbon atoms produced by dimerization of an unsaturated fatty acid having 18 carbon atoms, 30.0 parts of isophthalic acid, 0.6 part of adipic acid, 33.6 parts of 1,6 - hexanediol, and 0.8 part of trimethylolpropane were charged. After heating the temperature to 120 °C to dissolve the raw materials, the temperature was raised to 160 °C while stirring. After holding at 160 °C for 1 hour, the temperature was raised to 230 °C over 5 hours. While maintaining at 230 °C, the resin acid value was periodically measured. When the resin acid value reached 4 mgKOH / g, it was cooled to 80 °C or lower. Finally, 60.8 parts of methyl ethyl ketone was added to obtain a polyester polyol solution PP - 1. The characteristic values of the polyester polyol solution PP - 1 were a mass average molecular weight of 7,200, an acid value of 4 mgKOH / g, a hydroxyl value of 62 mgKOH / g, and a resin solid content of 60 mass%.

[0092] 1-(2) Production of polyurethane resin dispersion liquid PU-1 In a flask equipped with a thermometer, a stirring device, and a nitrogen gas introduction tube, 110.0 parts of the polyester polyol solution PP - 1 obtained in Production Example 1-(1), 4.5 parts of dimethylolpropionic acid, 2.0 parts of neopentyl glycol, and 20.3 parts of methyl ethyl ketone were charged, and the temperature was raised to 80 °C while stirring. When the temperature reached 80 °C, 24.0 parts of isophorone diisocyanate was added. While maintaining 80 °C, when the isocyanate amount in the solution reached 0.40 mmol / g, 3.2 parts of trimethylolpropane was added and 80 °C was maintained. When the isocyanate amount in the solution reached 0.03 mmol / g, 5.2 parts of butyl cellosolve was added, and after cooling to 50 °C, 3.3 parts of dimethylethanolamine was added to neutralize the acid groups, and 150.0 parts of deionized water was added. Then the temperature was raised to 100 °C, and methyl ethyl ketone was removed under reduced pressure conditions to obtain a polyurethane resin dispersion liquid PU - 1. The characteristic values of the polyurethane resin dispersion liquid PU - 1 were a mass average molecular weight of 71,000, an acid value of 21 mgKOH / g, a hydroxyl value of 21 mgKOH / g, and a resin solid content of 38 mass%.

[0093] <Production Example 2: Production of Polyester Resin Solution PE-1 for Aqueous Colored Paint Composition> Into a flask equipped with a reflux condenser with a reaction water separation tube, a thermometer, a stirring device, and a nitrogen gas introduction tube, 15.0 parts of the above dimer acid PRIPOL1017 (trade name, manufactured by Croda), 30.0 parts of phthalic anhydride, 3.1 parts of adipic acid, 31.5 parts of 1,6 - hexanediol, and 10.3 parts of trimethylolpropane were charged. After heating the raw materials to dissolve them up to 120°C, the temperature was raised to 160°C while stirring. After holding at 160°C for 1 hour, the temperature was raised to 230°C over 5 hours. After holding at 230°C for 2 hours, it was cooled to 180°C. Next, 10 parts of trimellitic anhydride was added, and while maintaining at 180°C, the resin acid value was periodically measured. When the resin acid value reached 25 mgKOH / g, it was cooled to 80°C or lower. After adding 25 parts of butyl cellosolve, 3.2 parts of dimethylethanolamine was added to neutralize the acid groups, and 34.1 parts of deionized water was added to obtain a polyester resin solution PE-1. The characteristic values of the polyester resin solution PE-1 were a mass average molecular weight of 15,000, an acid value of 25 mgKOH / g, a hydroxyl value of 90 mgKOH / g, and a resin solid content of 60 mass%.

[0094] <Production Example 3: Production of Acrylic Urethane Resin Dispersion AU-1 for Aqueous Colored Paint Composition> 3-(1) Production of Polyester Polyol Solution PP-2 Into a flask equipped with a reflux condenser with a reaction water separation tube, a thermometer, a stirring device, and a nitrogen gas introduction tube, 49.9 parts of adipic acid, 18.5 parts of 1,6 - hexanediol, and 31.6 parts of neopentyl glycol were charged. Under a nitrogen stream, the temperature was raised to 160°C while stirring. After holding at 160°C for 1 hour, the temperature was raised to 230°C over 5 hours. While holding at 230°C, the resin acid value was periodically measured. When the resin acid value reached 3.5 mgKOH / g, it was cooled to 80°C. Finally, 21.9 parts of methyl ethyl ketone was added to obtain a polyester polyol solution PP-2. The characteristic values of the polyester polyol solution PP-2 were an acid value of 3.5 mgKOH / g, a hydroxyl value of 155 mgKOH / g, and a resin solid content of 80 mass%.

[0095] Production of Acrylic Urethane Resin Dispersion Liquid AU-1 in 3-(2) Into a flask equipped with two dropping devices, a reflux condenser, a thermometer, a stirring device, and a nitrogen gas inlet tube, 420.0 parts of the polyester polyol solution PP-2 obtained in Production Example 3-(1), 31.0 parts of neopentyl glycol, 27.8 parts of trimethylolpropane monoallyl ether, 0.5 part of dibutyltin dilaurate, and 195.7 parts of methyl ethyl ketone were charged, and the mixture was stirred under a nitrogen stream until it became uniform.

[0096] Next, 259.9 parts of isophorone diisocyanate were added to the obtained solution. After the exothermic reaction subsided, the reaction mixture was gradually heated to 80 °C while stirring, and at this temperature, stirring was continued until the isocyanate amount in the solution reached 0.60 mmol / g. Next, 66.7 parts of trimethylolpropane were added, and stirring was carried out at 80 °C until free isocyanate groups in the solution could no longer be detected. Thereafter, 248.9 parts of methyl ethyl ketone were added to the obtained polyurethane solution.

[0097] Subsequently, the temperature was adjusted to 82 °C, and a radical polymerizable monomer mixture consisting of 312.5 parts of n-butyl acrylate, 312.5 parts of methyl methacrylate, 74.7 parts of 2-hydroxypropyl methacrylate, and 58.4 parts of acrylic acid was dropped at a constant rate over 3 hours using one of the dropping devices. Simultaneously with the dropping by the above dropping device, a polymerization initiator solution consisting of 22.8 parts of 2,2'-azobis(methylbutyronitrile) and 152.3 parts of methyl ethyl ketone was dropped at a constant rate over 3.5 hours using the other dropping device.

[0098] After the dropping of the monomer mixture and the polymerization initiator solution was completed, the obtained reaction mixture was stirred at 82 °C for an additional 2.5 hours, and 56.9 parts of dimethylethanolamine and 2242 parts of deionized water were added. Thereafter, a separation tube was attached to the reflux condenser, and the solvent was removed under reduced pressure at 45 °C until the resin solid content of the dispersion reached 40% by mass to obtain an acrylic urethane resin aqueous dispersion AU-1. The obtained acrylic urethane resin dispersion AU-1 had an acid value of 32 mgKOH / g and a hydroxyl value of 57 mgKOH / g.

[0099] <Production Example 4: Production of Black Pigment Paste WP-1 for Aqueous Coloring Paint Composition> 100.0 parts of acrylic urethane resin dispersion liquid AU-1 as a dispersion resin, 40.0 parts of Mitsubishi Carbon Black MA-100 (trade name, manufactured by Mitsubishi Chemical Corporation), and 60.0 parts of deionized water were mixed, and then dispersed with a motor mill to obtain an aqueous black pigment paste WP-1.

[0100] <Production Example 5: Production of Blue Pigment Paste WP-2 for Aqueous Coloring Paint Composition> 100.0 parts of acrylic urethane resin dispersion liquid AU-1 as a dispersion resin, 40.0 parts of Heliogen Blue L 6900 (trade name, manufactured by Sun Chemical Colors & Effects), and 60.0 parts of deionized water were mixed, and then dispersed with a motor mill to obtain an aqueous blue pigment paste WP-2.

[0101] <Production Example 6: Production of Purple Pigment Paste WP-3 for Aqueous Coloring Paint Composition> 100.0 parts of acrylic urethane resin dispersion liquid AU-1 as a dispersion resin, 40.0 parts of Hostaperm Violet P-RL (trade name, manufactured by HEUBACH), and 60.0 parts of deionized water were mixed, and then dispersed with a motor mill to obtain an aqueous purple pigment paste WP-3.

[0102] <Production Examples 7 to 10: Production of Aqueous First Coloring Paint Compositions WBBC1-1 to WBBC1-4> The components listed in Table 1 were mixed in the order described, and further stirred for 30 minutes. Next, dimethylethanolamine was added to adjust the pH to 8.2. Then, deionized water was added, and using a rotational viscometer Rheomat RM180 (trade name, manufactured by METTLER TOLEDO), the viscosity measured at 20 °C and a shear rate of 1000 s -1 was adjusted to 100 mPa·s.

[0103]

Table 1

[0104] 1) Melamine resin solution: Cymel 327 (trade name, manufactured by Allnex, resin solid content 90% by mass) 2) Inorganic thickener: A mixture of 3 parts by mass of Laponite RD (trade name, manufactured by BYK-Chemie), 3 parts by mass of Pluriol P900 (trade name, manufactured by BASF), and 94 parts by mass of deionized water 3) Alkali-swellable emulsion: Rheovis AS 1130 (trade name, manufactured by BASF) 4) Surface conditioner: Surfynol 104PA (trade name, manufactured by Evonik Industries, active ingredient 50% by mass) 5) Silver pearl pigment: Iriodin 121 Rutile Luster Satin WNT (trade name, manufactured by Merck, D50 = 10 μm)

[0105] <Production Examples 11 to 15: Production of Aqueous Second Coloring Paint Compositions WBBC2-1 to WBBC2-5> The components listed in Table 2 were mixed in the order described and further stirred for 30 minutes. Next, dimethylethanolamine was added to adjust the pH to 8.2. Then, deionized water was added, and using a rotational viscometer Rheomat RM180 (trade name, manufactured by METTLER TOLEDO), the viscosity measured at 20 °C and a shear rate of 1000 s -1 was adjusted to 100 mPa·s.

[0106]

Table 2

[0107] <Examples 1 to 5 and Comparative Examples 1 to 4> [Preparation of Test Plates] A phosphated cold-rolled steel sheet (150 mm × 75 mm × 0.8 mm) was electrocoated with a cationic electrodeposition paint, Cathoguard No. 500 (trade name, manufactured by BASF Japan Ltd.) to a dry film thickness of 20 μm, and then heated at 170 °C for 30 minutes to cure. Thereafter, as a black undercoat paint composition, an aqueous paint composition, ProBloc N-3000 N2.0-3 (W) (trade name, manufactured by BASF Japan Ltd.) was electrostatically applied to a dry film thickness of 20 μm and left at room temperature for 5 minutes. One of the plurality of test panels thus prepared was heated at 140 °C for 30 minutes to cure for measuring the N value of the Munsell chart, and the N value of the obtained black undercoat layer on the Munsell chart was 2.0.

[0108] Next, the above unheated test panel was electrostatically coated with the aqueous first color paint composition WBBC1 shown in Table 3 to a dry film thickness of 8 μm, left at room temperature for 3 minutes, and then electrostatically coated with the aqueous second color paint composition WBBC2 shown in Table 3 to a dry film thickness of 8 μm, left at room temperature for 5 minutes, and then pre-dried (flash-off) at 80 °C for 3 minutes. In Comparative Example 1, after coating with the aqueous first color paint composition BC1, it was left at room temperature for 5 minutes without coating with the aqueous second color paint composition BC2, and then pre-dried (flash-off) at 80 °C for 3 minutes. Next, a solvent-based clear paint composition, ProGloss HD-N (W) (trade name, manufactured by BASF Japan Ltd., two-component acrylic / urethane paint) was electrostatically applied to a dry film thickness of 35 μm, left at room temperature for 10 minutes, and then heated at 140 °C for 30 minutes to obtain a test coated panel on which a multi-layer coating film was formed.

[0109] [Evaluation] The test panels prepared as described above were evaluated as follows, and the results are shown in Table 3.

[0110] <Mc75 value (blackness of the shade)> Using a multi-angle colorimeter BYKmac i (trade name, manufactured by BYK-Gardner), X75, Y75, and Z75 were measured, and the Mc75 value was determined from the following Equation 1. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Equation 1)

[0111] Note that the evaluation was carried out as follows, and ◎ and 〇 were set as the passing ranges. ◎: 218.0 ≦ Mc75 〇: 215.0 ≦ Mc75 < 218.0 ×: Mc75 < 215.0

[0112] <L*15 value (brightness of highlight)> The L*15 value was measured using a multi-angle colorimeter BYKmac i (product name, manufactured by BYK-Gardner). Note that the evaluation was carried out as follows, and ◎ and 〇 were set as the passing ranges. ◎: L*15 ≦ 28.0 〇: 28.0 < L*15 ≦ 30.0 ×: 30.0 < L*15

[0113] <SG15 value (pearl brilliance)> The SG15 value was measured using a multi-angle colorimeter BYKmac i (product name, manufactured by BYK-Gardner). Note that the evaluation was carried out as follows, and ◎ and 〇 were set as the passing ranges. ◎: 3.1 ≦ SG15 ≦ 3.8 〇: 3.0 ≦ SG15 < 3.1 or 3.8 < SG15 ≦ 4.0 ×: SG15 < 3.0 or 4.0 < SG15

[0114] <Visual evaluation score for pearl compactness> The pearl compactness was evaluated visually. That is, a 5-point evaluation (5 points, 4 points, 3 points, 2 points, 1 point in descending order of compactness) was carried out by a total of 5 people, 2 designers and 3 engineers with more than 3 years of experience in color development. The average value of 3 people excluding the maximum and minimum values was used as the visual evaluation score, and ◎ and 〇 were set as the passing ranges as follows. ◎: 4.0 ≦ visual evaluation score 〇: 3.0 ≦ visual evaluation score < 4.0 ×: visual evaluation score < 3.0

[0115]

Table 3

[0116] <Production Example 16: Production of Polyester Resin Solution PE-2 for Solvent-Based Colored Paint Composition> Into a flask equipped with a reflux condenser with a reaction water separation tube, a thermometer, a stirring device, and a nitrogen gas introduction tube, 25.0 parts of adipic acid, 16.0 parts of phthalic anhydride, 16.0 parts of isophthalic acid, 13.0 parts of 1,6-hexanediol, 13.0 parts of neopentyl glycol, 11.0 parts of trimethylolpropane, and 6.0 parts of glycerin were charged. After heating the temperature to 120 °C to dissolve the raw materials, the temperature was raised to 160 °C while stirring. After holding at 160 °C for 1 hour, the temperature was gradually raised to 230 °C over 5 hours. The reaction was continued while holding at 230 °C, and when the resin acid value reached 6 mg KOH / g, it was cooled to 80 °C or lower. Then, it was diluted with a mixed solvent of n-butyl acetate / Solvesso #100 (trade name, manufactured by ExxonMobil, aromatic naphtha) = 1 / 1 (mass ratio) so that the resin solid content became 55% by mass, and a polyester resin solution PE-2 having characteristic values of a hydroxyl value of 107 mg KOH / g, an acid value of 5 mg KOH / g, and a mass average molecular weight of 36,000 was obtained.

[0117] <Production Example 17: Production of Black Pigment Paste SP-1 for Solvent-Based Colored Paint Composition> After mixing 100.0 parts of polyester resin solution PE-2 as a dispersion resin, 55.0 parts of Mitsubishi Carbon Black MA-100 (trade name, manufactured by Mitsubishi Chemical Corporation), and 120.0 parts of xylene, it was dispersed with a motor mill to obtain a solvent-based black pigment paste SP-1.

[0118] <Production Example 18: Production of Blue Pigment Paste SP-2 for Solvent-Based Colored Paint Composition> As the dispersion resin, 100.0 parts of polyester resin solution PE-2, 55.0 parts of Heliogen Blue L 6900 (trade name, manufactured by Sun Chemical Colors & Effects), and 120.0 parts of xylene were mixed, and then dispersed with a motor mill to obtain a solvent-based blue pigment paste P-2.

[0119] <Production Example 19: Production of Solvent-Based Colored Paint Composition Purple Pigment Paste SP-3> As the dispersion resin, 100.0 parts of polyester resin solution PE-2, 55.0 parts of Hostaperm Violet P-RL (trade name, manufactured by HEUBACH), and 120.0 parts of xylene were mixed, and then dispersed with a motor mill to obtain a solvent-based purple pigment paste SP-3.

[0120] <Production Example 20: Production of Solvent-Based First Colored Paint Composition SBBC1> The components listed in Table 4 were mixed in the order described. Next, the viscosity was adjusted to 12 seconds under the conditions of Ford Cup #4 and 20 °C with a mixed solvent composed of n-butyl acetate / Solvesso #100 (trade name, manufactured by ExxonMobil, aromatic naphtha) (mixed mass ratio: 1 / 1).

[0121]

Table 4

[0122] 6) Cellulose acetate butyrate solution: A solution obtained by dissolving CAB-381-2BP (trade name, manufactured by Eastman Chemical) in n-butyl acetate so that the resin solid content is 15%. 7) Polyisocyanate compound solution: A solution obtained by dissolving Desmodur N3300 (trade name, manufactured by Covestro, NCO content 21.8% by mass) in xylene so that the resin solid content is 75%.

[0123] <Production Example 21: Production of Solvent-Based Second Colored Paint Composition SBBC2> The components listed in Table 5 were mixed in the order of description. Next, the viscosity was adjusted to 12 seconds under the conditions of Ford Cup #4 and 20°C using a mixed solvent composed of n-butyl acetate / Solvesso #100 (trade name, manufactured by ExxonMobil, aromatic naphtha) (mixed mass ratio: 1 / 1).

[0124] [Table 5]

[0125] [Example 6] [Preparation of Test Plate] On a polypropylene plate (150 mm × 70 mm × 3 mm), as a paint composition for a black underlayer, a solvent-based conductive primer paint composition, Primerac No. 1501, Primer E-DG N2 (trade name, manufactured by BASF Japan Ltd.), was applied by air spray so that the dry film thickness became 7 μm, and it was left at room temperature for 2 minutes. When one of the plurality of prepared test plates was heated at 90°C for 30 minutes for N value measurement of the Munsell chart and cured, the N value of the obtained black underlayer in the Munsell chart was 2.0.

[0126] Next, on the unheated test plate, the solvent-based first coloring paint composition SBBC1 described in Table 6 was electrostatically applied so that the dry film thickness became 8 μm, left at room temperature for 3 minutes, and then the water-based second coloring paint composition BC2 described in Table 6 was electrostatically applied so that the dry film thickness became 8 μm, and it was left at room temperature for 5 minutes. Then, a solvent-based clear paint composition, ProGloss N-2000 (W) (trade name, manufactured by BASF Japan Ltd., two-component acrylic / urethane paint), was electrostatically applied so that the dry film thickness became 30 μm, left at room temperature for 10 minutes, and then heated at 90°C for 30 minutes to obtain a test coated plate on which a multilayer coating film was formed.

[0127] [Evaluation] The evaluation of the multilayer coating film obtained from the solvent-based first coloring paint composition and the solvent-based second coloring paint composition was the same as the evaluation of the multilayer coating film obtained from the water-based first coloring paint composition and the water-based second coloring paint composition, and the results are shown in Table 6.

[0128]

Table 6

[0129] As described above, the invention made by the present inventors has been specifically described based on the embodiments. However, it goes without saying that the present invention is not limited to the above embodiments and can be variously modified without departing from the gist thereof.

Claims

1. A multilayer coating film having a first colored coating film, a second colored coating film, and a clear coating film in this order on a black underlayer, wherein the first colored coating film contains a coating film-forming resin, a silver pearl pigment, a black pigment, and a purple pigment, the second colored coating film contains a coating film-forming resin and 0.02 to 0.10 parts by mass of a black pigment with respect to 100 parts by mass of the total amount of the coating film-forming resin solid content, a multilayer coating film in which the Mc75 value representing the jet blackness of the shade of the multilayer coating film represented by the following formula 1 is 215.0 or more, the L*15 value representing the lightness of the highlight is 30.0 or less, and the SG15 value representing the brilliance of the pearl is 3.0 to 4.

0. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Formula 1) (However, X75, Y75, and Z75 represent the tristimulus values in the XYZ color system based on the spectral reflectance of the reflected light received at an angle of 75 degrees with respect to the incident light direction with respect to the normal of the multilayer coating film surface when the incident light irradiated at an angle of 45 degrees with respect to the normal of the multilayer coating film surface is received, respectively.)

2. The multilayer coating film according to claim 1, wherein the first colored coating film contains 5.0 to 30.0 parts by mass of a silver pearl pigment with respect to 100 parts by mass of the total amount of the coating film-forming resin solid content, and the average particle diameter D50 of the silver pearl pigment is 4.0 to 12.0 μm.

3. The multilayer coating film according to claim 1 or claim 2, wherein the purple pigment contained in the first colored coating film is a dioxazine violet pigment.

4. Step (1) of coating a first colored paint composition on a black underlayer to form an uncured first colored coating film, Step (2) of coating a second colored paint composition on the uncured first colored coating film obtained in step (1) to form an uncured second colored coating film, Step (3) of coating a clear paint composition on the uncured second colored coating film obtained in step (2) to form an uncured clear coating film, A method for forming a multilayer coating film, comprising a step (4) of simultaneously curing the uncured first colored coating film, the uncured second colored coating film, and the uncured clear coating film formed in steps (1) to (3). The first colored coating composition contains a film-forming resin, a silver pearl pigment, a black pigment, and a purple pigment. The second colored coating composition contains a film-forming resin and 0.02 to 0.10 parts by mass of a black pigment based on 100 parts by mass of the total amount of the film-forming resin solids. A method for forming a multilayer coating film, wherein the Mc75 value representing the jet blackness of the shade of the multilayer coating film represented by the following formula 1 is 215.0 or more, the L*15 value representing the lightness of the highlight is 30.0 or less, and the SG15 value representing the pearlescent luster is 3.0 to 4.

0. Mc75 = 100×(log(94.81 / X75) - log(107.34 / Z75) + log(100 / Y75)) (Formula 1) (However, X75, Y75, and Z75 respectively represent the tristimulus values in the XYZ color system based on the spectral reflectance of the reflected light received at an angle of 75 degrees with respect to the incident light direction with respect to the specular reflection angle of the incident light irradiated at an angle of 45 degrees with respect to the perpendicular to the surface of the multilayer coating film.)

5. The method for forming a multilayer coating film according to claim 4, wherein the first colored coating composition contains 5.0 to 30.0 parts by mass of a silver pearl pigment based on 100 parts by mass of the total amount of the film-forming resin solids, and the average particle diameter D50 of the silver pearl pigment is 4.0 to 12.0 μm.

6. The method for forming a multilayer coating film according to claim 4 or claim 5, wherein the purple pigment contained in the first colored coating composition is a dioxazine violet pigment.

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