Multilayer coating film and method for forming a multilayer coating film

Abstract

To provide: a multilayer coating film which exhibits excellent jet-blackness of shade portions and exhibits both highlight blackness and dense pearlescence and a method for producing a multilayer coating film. [Solution] A multilayer coating film having a first colored coating film, a second colored coating film and a clear coating film in the stated order on a black underlayer. The first colored coating film contains a coating film-forming resin, a silver pearl pigment, a black pigment and a violet pigment. The second colored coating film contains a coating film-forming resin and a black pigment at a quantity of 0.02-0.10 parts by mass relative to a total of 100 parts by mass of solid resin content of the coating film-forming resin. The Mc75 value, which indicates the jet-blackness of shade portions of the multilayer coating film, is 215.0 or more. The L*15 value, which indicates the lightness of highlights, is 30.0 or less. The SG15 value, which indicates pearlescent brilliance, is 3.0-4.0.

Description

Title of the Invention: Multilayer coating film and method for forming a multilayer coating film [Technical Field]

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

[0002] In fields such as the automotive field in particular, black coatings having low lightness and high jet-blackness in particular have become popular in recent years from the perspective of imparting a sense of luxury. From the perspective of feel, however, designs which have a silky feel, that is, have a pearlescent feel and contain optical interference pigments whose color changes with the angle of observation, and especially designs having dense pearlescence, are becoming increasingly popular. Therefore, there is a need for multilayer coating films and methods for forming multilayer coating films that combine these properties and have high jet-blackness and dense pearlescence. However, because coating films having dense pearlescence have high highlight lightness and a hue that runs counter to jetblackness, it was difficult to achieve this combination of properties.

[0003] For example, Patent Document 1 discloses a method for forming a coating film, the method being characterized by coating a dark colored coating that contains 0.1-10 parts by weight of a coloring pigment, 1-20 parts by weight of an interference pigment and 0.1-4 parts by weight of carbon black relative to a total of 100 parts by weight of (solid content of) a resin component, and then coating the coated surface with a colored clear coating that contains 0.01-5 parts by weight of carbon black and 0-5 parts by weight of a coloring pigment relative tal of 100 parts by weight of (solid content of) a resin component.In addition, Patent Document 2 discloses a multilayer coating film having a first coating film, a second coating film and a clear coating film in the stated order, wherein the first coating film is a cured coating film of a first coating composition containing a first coating film-forming resin and a brilliant pigment, the second coating film is a cured coating film of a second coating composition containing a second coating film-forming resin and a coloring pigment, the brilliant pigment contained in the first coating film contains a flaky aluminum pigment, the content of the coloring pigment contained in the second coating film falls within the range of 1.5-6 parts by mass relative to 100 parts by mass of solid resin content contained in the coating film, and the sparkle area Sa (45°) value, sparkle intensity Si (15°) value and L* (25°) value of the multilayer coating film fall within specified ranges.[Citation List][Patent Literature]

[0005] [Patent Document 1] Japanese Patent No. 3946837[Patent Document 2] Japanese Patent Application Publication No. 2022-175163[Summary of Invention] em to be Solved by the Invention]However, in the coating film formation method in Patent Document 1 , jet-blackness is insufficient and needs to be higher.

[0007] In addition, the multilayer coating film in Patent Document 2 has a sufficiently low lightness and chroma to be recognized as a black coating film, but although a multilayer coating film recognized as being brilliant is obtained, the multilayer coating film does not exhibit pearlescence.

[0008] Therefore, the purpose of the present invention is to provide a multilayer coating film which exhibits excellent jet-blackness of shade portions and exhibits both highlight blackness and dense pearlescence, and a method for producing said multilayer coating film.[Means for Solving the Problem]

[0009] As a result of diligent research carried out in order to solve the problems mentioned above, the inventors of the present invention found that the problem mentioned above could be solved by a multilayer coating film having: a first colored coating film that contains a coating film-forming resin, a silver pearl pigment, a black pigment and a violet pigment, a second colored coating film that contains a coating film-forming resin and a specified quantity of a black pigment, and a clear coating film in the stated order on a black underlayer, wherein the Mc75 value, which indicates the jet-blackness of shade portions, the L*15 value, which indicates the lightness of highlights, and the SG15 value, which indicates pearlescent brilliance, fall within specified ranges, and thereby completed the present invention.

[0010] That is, the problem to be addressed by the present invention can be solved by a multilayer coating film having a first colored coating film, a second colored coating film and a clear coating film in the stated 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 violet pigment, the second colored coating film contains a coating film-forming resin and a black pigment at a quantity of 0.02-0.10 parts by mass relative to a total of 100 parts by mass of solid resin content in the coating film-forming resin, the Mc75 value, which indicates the jetblackness of shade portions of the multilayer coating film and is represented by formula 1below, is 215.0 or more, the L*15 value, which indicates the lightness of highlights, is 30.0 or less, and the SG15 value, which indicates pearlescent brilliance, is 3.0-4.0.Mc75=100x(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )(Here, X75, Y75 and Z75 denote tristimulus values in an XYZ color system based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is measured at an angle of 75° (incident light direction) relative to the angle of specular reflection.)

[0011] Furthermore, the multilayer coating film of the present invention is preferably such that the first colored coating film contains a silver pearl pigment at a quantity of 5.0-30.0 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, and the average particle diameter D50 of the silver pearl pigment is 4.0-12.0 pm.

[0012] Furthermore, in the multilayer coating film of the present invention, the violet pigment ned in the first colored coating film is preferably a dioxazine violet pigment.In addition, the problem to be addressed by the present invention can be solved by a method for producing a multilayer coating film, the method being characterized by including: a step (1 ) for coating a first colored coating composition (BC1) on a black underlayer to form an uncured first colored coating film, a step (2) for coating a second colored coating composition (BC2) on the uncured first colored coating film obtained in step (1) to form an uncured second colored coating film, a step (3) for coating a clear coating composition (CC) on the uncured second colored coating film obtained in step (2) to form an uncured clear coating film, and a step (4) for simultaneously heating and curing the uncured first colored coating film, uncured second colored coating film and uncured clear coating film formed in steps (1) to (3), where the first colored coating composition (BC1 ) contains a coating film-forming resin, a silver pearl pigment, a black pigment and a violet pigment, the second colored coating composition (BC2) contains a coating film-forming resin and a black pigment at a quantity of 0.02-0.10 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, the Mc75 value, which indicates the jet-blackness of shade portions of the obtained multilayer coating film and is represented by formula 1 below, is 215.0 or more, the L*15 value, which indicates the lightness of highlights, is 30.0 or less, and the SG15 value, which indicates pearlescent brilliance, is 3.0-4.0.Mc75=100x(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )(Here, X75, Y75 and Z75 denote tristimulus values in an XYZ color system based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is measured at an angle of 75° (incident light direction) relative to the angle of specular reflection.)Furthermore, the method for producing a multilayer coating film of the present invention is preferably such that the first colored coating composition (BC1) contains a silver pearl pigment at a quantity of 5.0-30.0 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, and the average particle diameter D50 of the pearl pigment is 4.0-12.0 pm.Furthermore, in the method for forming a multilayer coating film of the present invention, the violet pigment contained in the first colored coating composition (BC1) is preferably a dioxazine violet pigment. ntageous Effects of the Invention]According to the multilayer coating film and method for producing a multilayer coating film of the present invention, it is possible to obtain a multilayer coating film which exhibits excellent jet-blackness of shade portions and exhibits both highlight blackness and dense pearlescence.[Description of Embodiments]

[0017] [Object to be coated]The multilayer coating film of the present invention can be formed on a black underlayer that is formed on an object to be coated. In the present invention, the object to be coated is not particularly limited, and examples thereof include members comprising metals such as iron, zinc, aluminum or magnesium, members comprising alloys of these metals, members on which these metals are plated or vapor deposited, and members comprising glass, plastics and foams of various materials, and of these, steel materials and plastic materials that constitute motor vehicle bodies are preferred. If necessary, these members can be subjected to treatments such as degreasing and surface treatments as appropriate.

[0018] In the present invention, an object obtained by forming an undercoat film on the aforementioned members can be used as the object to be coated. The undercoat film can be applied to a surface of a member in order to conceal the surface of the member or to impart the member with anti-corrosion properties, rust-proofing properties, adhesive properties, electrical conductivity, and so on, and it is possible to coat an undercoating material and then cure or dry the undercoating material. This undercoating material is notparticularly limited, and it is possible to use materials that are already known, such as electrodeposition coating materials, solvent-based primers, water-based primers, and the like.

[0019] [Black underlayer]The black underlayer used in the multilayer coating film of the present invention may be the aforementioned undercoat film formed directly on the object to be coated, but may also be a coating film formed on the object to be coated via an undercoat film. The black underlayer is formed from a black underlayer-forming coating composition that contains a coating filmg resin and a coloring pigment.The coating film-forming resin in the black underlayer-forming coating composition in the present invention may be a thermosetting resin composition that forms a coating film as a result of a crosslinking reaction progressing through heat after being coated, but may also be a thermoplastic resin composition that forms a coating film as a result of a solvent evaporating. The coating film-forming resin can be used by being dissolved or dispersed in a solvent such as an organic solvent and / or water.

[0021] The thermosetting resin composition in the black underlayer-forming coating composition in the present invention can be, for example, a thermosetting resin composition that contains a base resin and a curing agent. The content of the curing agent in this resin composition (base resin+curing agent) is not particularly limited, but is preferably 0.1-50.0 parts by mass, more preferably 5.0-45.0 parts by mass, and particularly preferably 10.0-40.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. Moreover, in a case where the black underlayer-forming coating composition in the present invention is a thermosetting resin composition, this composition may be a one-liquid type coating composition in which a base resin and a curing agent are mixed in advance or a two-liquid type coating composition in which a base resin and a curing agent are mixed immediately before the composition is coated.Examples of the base resin in the thermosetting resin composition in the black underlayerforming coating composition in the present invention include acrylic resins, polyester resins, polyurethane resins, polyurea resins, acrylic urethane resins, polyurethane polyurea resins, polyolefin resins (including chlorinated and / or modified polyolefin resins) and epoxy resins. Furthermore, the base resin may be partially crosslinked particles or core / shell type particles in which particles comprise an inner side (a core portion) and an outer side (a shell portion). Examples of particulate base resins include polyurethane-polyurea particles, urethane core / acrylic shell type particles and acrylic core / urethane shell type particles. Moreover, ina case where base resin particles are partially crosslinked, crosslinked parts form parts that are insoluble in organic solvents (gel parts), and it is possible to measure the gel fraction, which is a value that indicates the proportion of gel parts in solid content of base resin particles. In addition, the base resin preferably has a hydroxyl group and / or a carboxyl group as a functional group. It is possible to use one of these base resins in isolation, or a combination of two or more types thereof.

[0023] Examples of the curing agent in the thermosetting resin composition in the black underlayerforming coating composition in the present invention include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds and polycarbodiimide compounds. Of these, amino resins and blocked polyisocyanate compounds are particularly preferred. It is possible to use one of these curing agents in isolation, or a combination of two or more types thereof.

[0024] The term “amino resin” is a generic term for resins obtained by adding formaldehyde to an amino group-containing compound and condensing. Examples of amino resins include melamine resins, urea resins and guanamine resins, and of these, melamine resins are particularly preferred.

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

[0026] Examples of polyisocyanate compounds 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, diisocyanate dimers and trimers, such as uretdiones, allophanates, adducts, biurets, isocyanurates and iminooxadiazinediones of these diisocyanates, and other compounds comprising these diisocyanates. Furthermore some isocyanate groups in these diisocyanates may be modified with an amino group-containing silane coupling agent or the like.

[0027] Examples of blocked polyisocyanate compounds include compounds obtained by blocking isocyanate groups in the polyisocyanate compounds mentioned above with, for example, an alcohol such as butanol, an oxime compound such as methyl ethyl ketoxime, a lactam compound such as s-caprolactam, an active methylene compound such as a malonic acid diester or an acetoacetic acid ester, a pyrazole compound such as 3,5-dimethylpyrazole, an imidazole compound such as imidazole or 2-ethylimidazole, and a phenol compound such as m-cresol.

[0028] A hydrophilic carbodiimide compound is preferred as the polycarbodiimide compound. Examples of hydrophilic carbodiimide compounds include compounds obtained by reacting a polycarbodiimide compound having two or more isocyanate groups per molecule and a polyol having a hydroxyl group at a molecular terminal at proportions so that the NCO / OH molar ratio is greater than 1, and then reacting the thus obtained reaction product with a philizing agent having an active hydrogen and a hydrophilic moiety.Examples of thermoplastic resin compositions in the black underlayer-forming coating composition in the present invention include thermoplastic resin compositions containing resins having a mass average molecular weight of 30 000 or more, such as acrylic resins, polyester resins, alkyd resins, urethane resins, polyolefin resins (including chlorinated and / or modified polyolefin resins) and epoxy resins.

[0030] Examples of coloring pigments in the black underlayer-forming coating composition in the present invention include inorganic pigments such as complex oxide pigments, such as titanium oxide, iron oxide and titanium yellow, organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perynone 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. It is possible to use one e coloring pigments in isolation, or a combination of two or more types thereof.The total content of coloring pigments contained in the black underlayer-forming coating composition in the present invention is not particularly limited, but is preferably 20.0-180.0 parts by mass, more preferably 40.0-150.0 parts by mass, and particularly preferably 60.0- 120.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin.

[0032] If necessary, the black underlayer-forming coating composition in the present invention may also contain a variety of additives, such as solvents such as organic solvents and / or water, rheology controlling agents, pigment dispersing agents, anti-settling agents, curing catalysts, anti-foaming agents and antioxidants, and body pigments and the like as appropriate. Examples of organic solvents include organic solvents commonly used in the production of colored coating 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 including chlorinated hydrocarbons, and mixtures of these. Of these, in a case where a polyisocyanate compound (including a blocked polyisocyanate compound) is used as a curing agent, a curing reaction progresses smoothly if use of water and alcoholic organic solvents is moderated.The content of involatile components (coating film-forming solid resin content+coloring pigment+coating material additive solid content+body pigment) when the black underlayerforming coating composition in the present invention is coated is not particularly limited, but is preferably 10.0-65.0 mass%, more preferably 15.0-63.0 mass%, and particularly ably 20.0-60.0 mass%.The black underlayer-forming coating composition in the present invention can be coated using a method such as electrostatic coating, air spraying or airless spraying. The dried film thickness of the coating film for the black underlayer is not particularly limited, but is preferably 3.0-50.0 pm, more preferably 4.0-45.0 pm, and particularly preferably 5.0-40.0 pm.

[0035] The black underlayer obtained from the black underlayer-forming coating composition in the present invention preferably has an N value of 1.5-4.5 on a Munsell chart.[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 coating composition that contains a coating film-forming resin, a silver pearl pigment, a black pigment and a violet pigment.The coating film-forming resin in the first colored coating composition in the present invention may be a thermosetting resin composition that forms a coating film as a result of a crosslinking reaction progressing through heat after being coated, but may also be athermoplastic resin composition that forms a coating film as a result of a solvent evaporating. The coating film-forming resin can be used by being dissolved or dispersed in a solvent such as an organic solvent and / or water.

[0038] The thermosetting resin composition in the first colored coating composition in the present invention can be, for example, a thermosetting resin composition that contains a base resin and a curing agent. The content of the curing agent in this resin composition (base resin+curing agent) is not particularly limited, but is preferably 0.1-50.0 parts by mass, more preferably 5.0-45.0 parts by mass, and particularly preferably 10.0-40.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. Moreover, in a case where the first colored coating composition is a thermosetting resin composition in the present invention, this composition may be a one-liquid type coating composition in which a base resin and a curing agent are mixed in advance or a two-liquid type coating composition in which a base resin and a curing agent are mixed immediately the composition is coated.Examples of the base resin in the thermosetting resin composition in the first colored coating composition in the present invention include the same types as those listed as examples of the base resin in the thermosetting resin composition in the black underlayer-forming coating composition. In a case where the black underlayer-forming coating composition and the first colored coating composition in the present invention are both thermosetting resin compositions, the base resins in the two compositions may be the same as, or different from, each other.

[0040] Examples of the curing agent in the thermosetting resin composition in the first colored coating composition in the present invention include the same types as those listed as examples of the curing agent in the thermosetting resin composition in the black underlayerforming coating composition. In a case where the black underlayer-forming coating composition and the first colored coating composition in the present invention are both thermosetting resin compositions, the curing agents in the two compositions may be the same as, or different from, each other.

[0041] Examples of the thermoplastic resin composition in the first colored coating composition in the present invention include the same types as those listed as examples of the thermoplastic resin composition in the black underlayer-forming coating composition. In a case where the black underlayer-forming coating composition and the first colored coating composition in the present invention are both thermoplastic resin compositions, these thermoplastic resin compositions may be the same as, or different from, each other.

[0042] The first colored coating composition in the present invention contains a silver pearl pigment having a silvery white color. In addition to silver types, pearl pigments include iridescent types involving light interference and coloring types obtained by coating titanium oxide and then coating iron oxide or the like, but a silver type is particularly preferred as the pearl pigment used in the first colored coating composition in the present invention. Examples of commercially available silver pearl pigments include Xirallic T61-10 WNT Micro Silver, Iriodin 121 Rutile Luster Satin WNT and Iriodin 111 Rutile Fine Satin WNT (produced by Merck), Glacier Exterior Silk White S1303V, Mearlin Exterior CFS Bright Silver 1303Z and Mearlin Exterior CFS Fine Pearl 1303V (produced by Sun Chemical Colors & Effects), and Automotive Rutile Ultra Silk A-903M, Automotive Rutile Fine White A-903D and Automotive Splendor White A-901K (produced by CQV).

[0043] The average particle diameter D50 of the silver pearl pigment is preferably 4.0-12.0 pm, and particularly preferably 6.0-10.0 pm. By setting the average particle diameter D50 of the silver pearl pigment to be 4.0-12.0 pm, it is possible to obtain a multilayer coating film having dense pearlescence.

[0044] Moreover, in the present invention, when the total volume of particles accumulated from the small particle diameter size is expressed as a percentage relative to the volume of all particles in a volume-based particle diameter distribution measured using a laser diffraction / scattering method (a static light scattering method), the average particle diameter D50 is the particle diameter where this percentage reaches 50%. Examples of particle diameter distribution measurement apparatuses that use a laser diffraction / scattering method (a static light scattering method) include the Partica LA-960V2 series (produced by Horiba, Ltd.), SALD-2300 (produced by Shimadzu Corporation), and the MT3000II series (produced by MicrotracBEL Corp.).

[0045] The content of the silver pearl pigment in the first colored coating composition in the present invention is preferably 5.0-30.0 parts by mass, more preferably 10.0-25.0 parts by mass, and particularly preferably 15.0-20.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. By setting the content of the silver pearl pigment to be 5.0-30.0 parts by mass, it is possible to obtain a multilayer coating film having dense pearlescence.The first colored coating composition in the present invention contains a black pigment. The black pigment in the first colored coating composition in the present invention is not particularly limited as long as this is black in color, but examples thereof include carbonblack, graphite, iron black, complex metal oxides such as iron-chromium and bismuthmanganese, perylene type black pigments and azomethine azo type pigments, with carbon black being a preferred black pigment. It is possible to use one of these black pigments in isolation, or a combination of two or more types thereof.The content of the black pigment in the first colored coating composition in the present invention is preferably 1.0-20.0 parts by mass, more preferably 3.0-15.0 parts by mass, and particularly preferably 5.0-10.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. By setting the content of the black pigment to be 1.0-20.0 parts by mass, it is possible to obtain a multilayer coating film having excellent jet-blackness.

[0048] The first colored coating composition in the present invention contains a violet pigment. The violet pigment in the first colored coating composition in the present invention is not particularly limited as long as this is violet in color, but examples thereof include dioxazine violet pigments such as Color Index (C.l.) Pigment Violet 23 (C.l. No. 51319) and C.l. Pigment Violet 37 (C.l. No. 51345), perylene violet pigments such as C.l. Pigment Violet 29 (C.l. No. 71129), and quinacridone violet pigments such as C.l. Pigment Violet 19 (C.l. No. 73900). Examples of commercially available dioxazine violet pigments include Hostaperm Violet P-RL, Hostaperm Violet R L 02, Hostaperm Violet BL 01 and Hostaperm Violet RL Special 01 (produced by HEUBACH), and Cromophtal Violet D 5700, Cromophtal Violet D 5800, Cromophtal Violet K 5700, Cromophtal Violet K 5800 and Cromophtal Violet L 5805 (produced by Sun Chemical Colors & Effects). Examples of commercially available perylene violet pigments include Corimax Violet 5011 (produced by Zeya Chemicals). 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 and Cinquasia Violet L 5125 (produced by Sun Chemical Colors & Effects). Of these, dioxazine violet pigments are preferred as the violet pigment. It is possible to use one of these violet pigments in isolation, or a combination of two or more types thereof.The content of the violet pigment in the first colored coating composition in the present invention is preferably 0.10-0.90 parts by mass, more preferably 0.15-0.70 parts by mass, and particularly preferably 0.20-0.50 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. By setting the content of the violet pigment to be 0.10-0.90 parts by mass, it is possible to eliminate a green color that is a complementary color and obtain a multilayer coating film having excellent jet-blackness.

[0050] The first colored coating composition in the present invention can further contain coloring pigments in addition to the black pigment and violet pigment mentioned above. Examples of coloring pigments other than black pigments and violet pigments include white pigments, red pigments, orange pigments, yellow pigments, green pigments and blue pigments, and specific examples thereof include inorganic pigments such as complex oxide pigments, such as titanium oxide, iron oxide and titanium yellow, and organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perynone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments and indigo pigments. Of these, incorporating a phthalocyanine type or threne type blue pigment is particularly preferred from the perspective of being able to eliminate an orange color that is a complementary color and obtain a multilayer coating film having excellent jet-blackness. It is possible to use one of coloring pigments in isolation, or a combination of two or more types thereof.If necessary, the first colored coating composition in the present invention may also contain a variety of additives, such as solvents such as organic solvents and / or water, rheology controlling agents, pigment dispersing agents, anti-settling agents, curing catalysts, antifoaming agents and antioxidants, and body pigments and the like as appropriate. Examples of organic solvents include organic solvents commonly used in the production of colored coating 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 including chlorinated hydrocarbons, and mixtures of these. Of these, in a case where a polyisocyanate compound (including a blocked polyisocyanate compound) is used as a curing agent, a curing reaction progresses smoothly if use of water and alcoholic organic solvents is moderated.The content of involatile components (coating film-forming solid resin content+pearl pigment+coloring pigment+coating material additive solid content+body pigment) when the first colored coating composition in the present invention is coated is not particularly limited, but is preferably 10.0-60.0 mass%, more preferably 12.5-50.0 mass%, and particularly ably 15.0-40.0 mass%.The first colored coating composition in the present invention can be coated using a method such as electrostatic coating, air spraying or airless spraying. The dried film thickness of thefirst colored coating film is not particularly limited, but is preferably 3.0-15.0 pm, more preferably 3.0-12.0 pm, and particularly preferably 3.0-10.0 pm.

[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 coating composition that contains a coating film-forming resin and a black pigment. By interposing the second colored coating film between the first colored coating film and the clear coating film, it is possible to obtain a multilayer coating film having both highlight blackness and dense pearlescence.The coating film-forming resin in the second colored coating composition in the present invention may be a thermosetting resin composition that forms a coating film as a result of a crosslinking reaction progressing through heat after being coated, but may also be a thermoplastic resin composition that forms a coating film as a result of a solvent evaporating. The coating film-forming resin can be used by being dissolved or dispersed in a solvent such as an organic solvent and / or water.

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

[0057] Examples of the base resin in the thermosetting resin composition in the second colored coating composition in the present invention include the same types as those listed as examples of the base resin in the thermosetting resin composition in the black underlayerforming coating composition or the first colored coating composition. In a case where the black underlayer-forming coating composition or the first colored coating composition in the present invention is a thermosetting resin composition, the base resin in the second colored coating composition may be the same as, or different from, the base resin in the black underlayer-forming coating composition or the first colored coating composition.

[0058] Examples of the curing agent in the thermosetting resin composition in the second colored coating composition in the present invention include the same types as those listed as examples of the curing agent in the thermosetting resin composition in the black underlayerforming coating composition or the first colored coating composition. In a case where the black underlayer-forming coating composition or the first colored coating composition in the present invention is a thermosetting resin composition, the curing agent in the second colored coating composition may be the same as, or different from, the curing agent in the black underlayer-forming coating composition or the first colored coating composition.

[0059] Examples of the thermoplastic resin composition in the second colored coating composition in the present invention include the same types as those listed as examples of the thermoplastic resin composition in the black underlayer-forming coating composition or the first colored coating composition. In a case where the black underlayer-forming coating composition or the first colored coating composition in the present invention is a thermoplastic resin composition, the thermoplastic resin composition of the second colored coating composition may be the same as, or different from, that of the black underlayerforming coating composition or the first colored coating composition.

[0060] The second colored coating composition in the present invention contains a black pigment. The black pigment in the second colored coating composition in the present invention is not particularly limited as long as this is black in color, and examples thereof include the same black pigments as those given as examples of the black pigment in the first colored coating composition, and the black pigment in the second colored coating composition may be the same as, or different from, the black pigment in the first colored coating composition. Carbon black can be given as an example of a preferred black pigment. It is possible to use one of these black pigments in isolation, or a combination of two or more types thereof.

[0061] The content of the black pigment in the second colored coating composition in the present invention is preferably 0.02-0.10 parts by mass, more preferably 0.04-0.10 parts by mass, and particularly preferably 0.06-0.10 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. By setting the content of the black pigment to be 0.02-0.10 parts by mass, it is possible to obtain a multilayer coating film in which there is little change in color even if the film thickness changes and also possible to obtain a multilayer coating film having excellent highlight blackness. Furthermore, at this black pigment content, it is possible to adjust the SG15 value, which indicates pearlescent brilliance of the multilayer coating film, to an appropriate value.

[0062] The second colored coating composition in the present invention can further contain coloring pigments in addition to the black pigment. Examples of coloring pigments other than black pigments include white pigments, red pigments, orange pigments, yellow pigments, green pigments, blue pigments and violet pigments, and specific examples thereof include inorganic pigments such as complex oxide pigments, such as titanium oxide, iron oxide and titanium yellow, and organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perynone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments and indigo pigments. Of these, adding a dioxazine type violet pigment and / or a phthalocyanine type or threne type blue pigment is particularly preferred from the perspective of being able to eliminate a green color and / or an orange color that are complementary colors and obtain a multilayer coating film having excellent jet-blackness. It is possible to use one of these coloring pigments in isolation, or a combination of two or more types thereof.

[0063] If necessary, the second colored coating composition in the present invention may also contain a variety of additives, such as solvents such as organic solvents and / or water, rheology controlling agents, pigment dispersing agents, anti-settling agents, curing catalysts, anti-foaming agents and antioxidants, and body pigments and the like as appropriate. Examples of organic solvents include organic solvents commonly used in the production of colored coating 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 including chlorinated hydrocarbons, and mixtures of these. Of these, in a case where a polyisocyanate compound (including a blocked polyisocyanate compound) is used as a curing agent, a curing reaction sses smoothly if use of water and alcoholic organic solvents is moderated.The content of involatile components (coating film-forming solid resin content+coloring pigment+coating material additive solid content+body pigment) when the second colored coating composition in the present invention is coated is not particularly limited, but is preferably 10.0-60.0 mass%, more preferably 12.5-50.0 mass%, and particularly preferably 15.0-40.0 mass%.

[0065] The second colored coating composition in the present invention can be coated using a method such as electrostatic coating, air spraying or airless spraying. The dried film thickness of the second colored coating film is not particularly limited, but is preferably 3.0- m, more preferably 3.0-12.0 pm, and particularly preferably 3.0-10.0 pm.[Clear coating film]The clear coating film used in the multilayer coating film of the present invention is formed from a clear coating composition containing a coating film-forming resin.The coating film-forming resin in the clear coating composition in the present invention is preferably a thermosetting resin composition that forms a coating film by being coated and then crosslinked by being heated. The coating film-forming resin can be used by being dissolved or dispersed in a solvent such as an organic solvent and / or water.The thermosetting resin composition in the clear coating composition in the present invention can be, for example, a thermosetting resin composition that contains a base resin and a curing agent. The content of the curing agent in this resin composition (base resin+curing agent) is not particularly limited, but is preferably 0.1-50.0 parts by mass, more preferably 5.0-45.0 parts by mass, and particularly preferably 10.0-40.0 parts by mass, relative to a total of 100 parts by mass of solid content of the coating film-forming resin. Moreover, the clear coating composition in the present invention may be a one-liquid type coating composition in which a base resin and a curing agent are mixed in advance or a two-liquid type coating composition in which a base resin and a curing agent are mixed iately before the composition is coated.Examples of the base resin in the clear coating composition in the present invention include acrylic resins, polyester resins, polyurethane resins and acrylic urethane resins. In addition, the base resin preferably has one or more groups selected from among a hydroxyl group, a carboxyl group and an epoxy group as a functional group. It is possible to use one of these base resins in isolation, or a combination of two or more types thereof.

[0070] Examples of the curing agent in the clear coating composition in the present invention include amino resins, polyisocyanate compounds and blocked polyisocyanate compounds. It is possible to use one of these curing agents in isolation, or a combination of two or more types thereof.

[0071] Examples of amino resins, polyisocyanate compounds and blocked polyisocyanate compounds that are curing agents in the clear coating composition in the present invention include the same types as those given as examples of curing agents in the thermosetting resin compositions in the black underlayer-forming coating composition, the first colored coating composition and the second colored coating composition. In a case where the black underlayer-forming coating composition, the first colored coating composition or the second colored coating composition in the present invention is a thermosetting resin composition, the curing agent in the clear coating composition may be the same as, or different from, the curing agent in the black underlayer-forming coating composition, the first colored coating composition or the second colored coating composition.

[0072] If necessary, the clear coating composition in the present invention may also contain a variety of additives, such as solvents such as organic solvents and / or water, rheology controlling agents, pigment dispersing agents, anti-settling agents, curing catalysts, antifoaming agents and antioxidants, body pigments, coloring pigments at quantities that do not impair transparency, and the like, as appropriate. Examples of organic solvents include organic solvents commonly used in the production of colored coating 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 including chlorinated hydrocarbons, and mixtures of these. Of these, in a case where a polyisocyanate compound (including a blocked polyisocyanate compound) is used as a curing agent, a curing reaction progresses smoothly if use of water and alcoholic organic solvents is moderated.

[0073] The content of involatile components (coating film-forming solid resin content+coating material additive solid content+body pigment+coloring pigment) when the clear coating composition in the present invention is coated is not particularly limited, but is preferably 30.0-65.0 mass%, more preferably 35.0-63.0 mass%, and particularly preferably 40.0-60.0 mass%.

[0074] The clear coating composition in the present invention can be coated using a method such as electrostatic coating, air spraying or airless spraying. The dried film thickness of the clear coating film is not particularly limited, but is preferably 15.0-60.0 pm, more preferably 20.0- 55.0 pm, and particularly preferably 25.0-50.0 pm.

[0075] In the present invention, the Mc75 value, which indicates the jet-blackness of shade portions of the obtained multilayer coating film and is represented by formula 1 below, is preferably 215.0 or more, and particularly preferably 218.0 or more. By setting the Mc75 value to be 215.0 or more, it is possible to obtain a multilayer coating film having excellent jet-blackness of shade portions.Mc75=100*(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )

[0076] Here, X75, Y75 and Z75 denote tristimulus values in an XYZ color system based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is measured at an angle of 75° (incident light direction) relative to the angle of specular reflection.

[0077] In the present invention, X75, Y75 and Z75 values were measured using a multi-angle meter BYKmac i (produced by BYK-Gardner).In the present invention, in the CIE LAB system, which is based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is received so as to form an angle of 15° with the incident light direction relative to the regular reflection angle, the L*15 value, which indicates lightness, is preferably 30.0 or less, and particularly preferably 28.0 or less. If the L*15 value is 30.0 or less, it is possible to obtain a multilayer coating film having excellent highlight blackness.

[0079] Moreover, the CIE LAB color system is a color system defined by the International Commission on Illumination (CIE) in 1976 and is also used in JIS Z 8781-4: 2013. In the present invention, the L*15 lightness value is a numerical value measured using a multiangle colorimeter BYKmac i (produced by BYK-Gardner).

[0080] In the present invention, the SG15 value, which indicates the pearlescent brilliance of the multilayer coating film, is preferably 3.0-4.0, and particularly preferably 3. 1-3.8. It is difficult to sense pearlescent brilliance if the SG15 value is less than 3.0, and it is difficult to sense blackness because pearlescent brilliance is excessively high if the SG15 value is more than 4.0. That is, by setting the SG15 value to be 3.0-4.0, it is possible to obtain a multilayer coating film that exhibits both highlight blackness and pearlescence. In the present invention, the SG15 value is a numerical value measured as sparkle grade using a multiangle colorimeter BYKmac i (produced by BYK-Gardner). When using this colorimeter, a sample surface is irradiated at an angle of 15° relative to the perpendicular line to the surfaceof the multilayer coating film, an image is acquired by a CCD chip disposed perpendicularly to determine the sparkle area Sa15 value and the sparkle intensity Si15 value, and the sparkle grade SG15 value is obtained from these.

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

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

[0083] First, as a step (1), the first colored coating composition is formed on the black underlayer to form an uncured first colored coating film. After coating the first colored coating composition, the first colored coating film may be heated for 3-5 minutes at 70-80°C (flash- off) or left at room temperature without being heated in order to evaporate off solvent contained in the first colored coating film. In the case of flash-off, these ranges are used as guidelines for selecting ranges for temperature and time within which flash-off is carried out t the coating film is not completely cured.Next, as a step (2), the second colored coating composition is coated on the uncured first colored coating film obtained in the step (1) so as to form an uncured second colored coating film. After coating the second colored coating composition, the second colored coating film may be heated for 3-5 minutes at 70-80°C (flash-off) or left at room temperature without being heated in order to evaporate off solvent contained in the second colored coating film. In the case of flash-off, these ranges are used as guidelines for selecting ranges for temperature and time within which flash-off is carried out so that the coating film is not completely cured.Next, as a step (3), the clear coating composition is coated on the uncured second colored coating film obtained in the step (2) so as to form an uncured clear coating film. In general, after the clear coating composition is coated, the film is allowed to stand at room temperature for 5-20 minutes, after which thermal curing is carried out.Finally, as a step (4), the uncured first colored coating film, uncured second colored coating film and uncured clear coating film formed in steps (1 ) to (3) are heated so as to simultaneously cure these three layers.

[0087] In the present invention, heating (baking) can be carried out using a well-known means, and it is possible to use a drying oven such as a hot blast oven, an electric oven or an infrared induction heating oven. The baking temperature is not particularly limited, but is preferably 70-160°C, more preferably 75-155°C, and particularly preferably 80-150°C. By setting the baking temperature to be 70-160°C, a curing reaction can progress sufficiently. In addition, the heating time is not particularly limited, but is preferably 10-50 minutes, more preferably 15-45 minutes, and particularly preferably 20-40 minutes.

[0088] The multilayer coating film and method for producing a multilayer coating film of the present invention can be used for vehicle bodies, members and components of passenger cars, trucks, motorcycles, buses, and the like, and are particularly effective when used for metal motor vehicle bodies and plastic motor vehicle components.[Working Examples]The present invention will now be explained in greater detail through the use of working examples, but is not limited to these working examples. In the working examples, the term "parts" means "parts by mass" and use of the symbol "%" relating to blending quantities and content values means "mass%", unless explicitly indicated otherwise.[Methods for measuring resin property values]In the present invention, resin property values were measured using the following methods.1. Mass average molecular weightBy carrying out gel permeation chromatography (GPC) using tetrahydrofuran (THF) as an eluent, mass average molecular weight was determined as a value obtained when data measured at a temperature of 40°C and a flow rate of 1 m / min were converted on the basis of the mass average molecular weight of polystyrene. Here, a combination of TSKgel G2000HXL, G3000HXL, G4000HXL and G5000HXL (produced by Tosoh Corporation) were used as columns in the gel permeation chromatography (GPC).2. Acid valueAcid value was measured in accordance with JIS-K5601-2-1: 1999.3. Hydroxyl valueHydroxyl value was measured in accordance with JIS-K1557-1: 2007.4. Solid resin contentSolid resin content was determined by measuring the mass after heating 1.0 g of a sample for 60 minutes at 130°C.

[0091] Production Example 1: Production of polyurethane resin-dispersed solution PU-1 forwater- based colored coating composition>1-(1) Production of polyester polyol solution PP-135.0 parts of a dimer acid whose primary component was a dicarboxylic acid having 36 carbon atoms obtained through dimerization of an unsaturated fatty acid having 18 carbon atoms PRIPOL 1017 (produced by Croda Inc.), 30.0 parts of isophthalic acid, 0.6 parts of adipic acid, 33.6 parts of 1 ,6-hexane diol and 0.8 parts of trimethylolpropane were placed in a flask equipped with a reflux condenser having a reaction water separation pipe, a temperature gauge, a stirring device and a nitrogen gas inlet pipe, after which the temperature was increased to 120°C to dissolve the raw materials, and the temperature was then increased to 160°C while stirring. The temperature was maintained at 160°C for 1 hour, and then increased to 230°C over a period of 5 hours. The resin acid value was periodically measured while maintaining a temperature of 230°C, and when the resin acid value reached 4 mg KOH / g, the temperature was lowered to 80°C or lower. Finally, 60.8 parts of methyl ethyl ketone was added to obtain polyester polyol solution PP-1. Polyester polyol solution PP-1 had a mass average molecular weight of 7200, an acid value of 4 mg KOH / g, a hydroxyl value of 62 mg KOH / g, and a solid resin content of 60 mass%.

[0092] 1-(2) Production of polyurethane resin-dispersed solution PU-1110.0 parts of 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 placed in a flask equipped with a temperature gauge, a stirring device and a nitrogen gas inlet pipe, and the temperature was increased to 80°C while stirring. When the temperature reached 80°C, 24.0 parts of isophorone diisocyanate was added, the temperature was maintained at 80°C, and when the isocyanate amount in the solution reached 0.40 mmol / g, 3.2 parts of trimethylolpropane was added and the temperature was maintained at 80°C. When the isocyanate amount in the solution reached 0.03 mmol / g, 5.2 parts of butyl cellosolve was added, the temperature was lowered to 50°C, acid groups were neutralized by adding 3.3 parts of dimethylethanolamine, and 150.0 parts of deionized water was then added. The temperature was then increased to 100°C, and methyl ethyl ketone was removed under reduced pressure conditions to obtain polyurethane resin-dispersed solution PU-1. Polyurethane resin-dispersed solution PU-1 had a mass average molecular weight of 71 000, an acid value of 21 mg KOH / g, a hydroxyl value of 21 mg KOH / g, and a esin content of 38 mass%.Production Example 2: Production of polyester resin solution PE-1 for water-based colored coating composition>15.0 parts of the dimer acid mentioned above PRIPOL 1017 (produced by Croda Inc.), 30.0 parts of phthalic acid anhydride, 3.1 parts of adipic acid, 31.5 parts of 1,6-hexane diol and 10.3 parts of trimethylolpropane were placed in a flask equipped with a reflux condenser having a reaction water separation pipe, a temperature gauge, a stirring device and a nitrogen gas inlet pipe, after which the temperature was increased to 120°C to dissolve the raw materials, and the temperature was then increased to 160°C while stirring. The temperature was maintained at 160°C for 1 hour, and then increased to 230°C over a period of 5 hours. The temperature was maintained at 230°C for 2 hours, and then lowered to 180°C. Next, 10 parts of trimellitic anhydride was added, the resin acid value was periodically measured while maintaining a temperature of 180°C, and when the resin acid value reached 25 mg KOH / g, the temperature was lowered to 80°C or lower. 25 parts of butyl cellosolve was added, acid groups were neutralized by adding 3.2 parts of dimethylethanolamine, and 34.1 parts of deionized water were added to obtain polyester resin solution PE-1. Polyester resin solution PE-1 had a mass average molecular weight of 15 000, an acid value of 25 mg KOH / g, a hydroxyl value of 90 mg KOH / g, and a solid resin content of 60 mass%.

[0094] Production Example 3: Production of polyurethane resin-dispersed solution AU-1 for waterbased colored coating composition>3-(1) Production of polyester polyol solution PP-249.9 parts of adipic acid, 18.5 parts of 1 ,6-hexane diol and 31.6 parts of neopentyl glycol were placed in a flask equipped with a reflux condenser having a reaction water separation pipe, a temperature gauge, a stirring device and a nitrogen gas inlet pipe, after which the temperature was increased to 160°C while stirring in a nitrogen stream. The temperature was maintained at 160°C for 1 hour, and then increased to 230°C over a period of 5 hours. The resin acid value was periodically measured while maintaining a temperature of 230°C, and when the resin acid value reached 3.5 mg KOH / g, the temperature was lowered to 80°C. Finally, 21.9 parts of methyl ethyl ketone was added to obtain polyester polyol solution PP-2. Polyester polyol solution PP-2 had an acid value of 3.5 mg KOH / g, a hydroxyl value mg KOH / g, and a solid resin content of 80 mass%.3-(2) Production of acrylic urethane resin-dispersed solution AU-1420.0 parts of 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 parts of dibutyl tin dilaurate and 195.7 parts of methyl ethyl ketone were placed in a flask equipped with two dropping devices, a reflux condenser, a temperature gauge, a stirring device and a nitrogen gas inlet pipe, after which the contents of the flask were stirred and homogenized in a nitrogen stream.

[0096] Next, 259.9 parts of isophorone diisocyanate were added to the obtained solution. Once an exothermic reaction had subsided, the temperature was increased to 80°C while the reaction was stirred, and stirring was continued at this temperature 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. Next, 248.9 parts of methyl ethyl ketone were added to the obtained polyurethane solution.

[0097] Next, the temperature was adjusted to 82°C, and a radical-polymerizable monomer mixture comprising 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 added dropwise over a period of 3 hours using one of the dropping devices. While the dropwise addition was being carried out using the dropping device, a polymerization initiator solution comprising 22.8 parts of 2,2’-azobis(methylbutyronitrile) and 152.3 parts of methyl ethyl ketone was added dropwise over a period of 3.5 hours using the other dropping device.

[0098] Once the dropwise addition of the monomer mixture and the polymerization initiator solution was complete, the obtained reaction mixture was stirred for 2.5 hours at 82°C, and 56.9 parts of dimethylethanolamine and 2242 parts of deionized water were added. Next, a separation pipe was attached to the reflux condenser, and desolvation was carried out at 45°C under reduced pressure until the solid resin content in the dispersion reached 40 mass%, thereby obtaining acrylic urethane resin-dispersed solution AU-1. The obtained acrylic urethane resin-dispersed solution AU-1 had an acid value of 32 mg KOH / g and a yl value of 57 mg KOH / g.Production Example 4: Production of black pigment paste WP-1 for water-based colored coating composition>Water-based black pigment paste WP-1 was obtained by mixing 100.0 parts of acrylic urethane resin-dispersed solution AU-1 as a dispersed resin, 40.0 parts of Mitsubishi carbon black MA-100 (produced by Mitsubishi Chemical Corporation) and 60.0 parts of deionized water and dispersing using a motor mill.

[0100] Production Example 5: Production of blue pigment paste WP-2 for water-based colored coating composition>Water-based blue pigment paste WP-2 was obtained by mixing 100.0 parts of acrylic urethane resin-dispersed solution AU-1 as a dispersed resin, 40.0 parts of Heliogen Blue L6900 (produced by Sun Chemical Colors & Effects) and 60.0 parts of deionized water and dispersing using a motor mill.

[0101] Production Example 6: Production of violet pigment paste WP-3 for water-based colored coating composition>Water-based violet pigment paste WP-3 was obtained by mixing 100.0 parts of acrylic urethane resin-dispersed solution AU-1 as a dispersed resin, 40.0 parts of Hostaperm Violet P-RL (produced by HEUBACH) and 60.0 parts of deionized water and dispersing using a motor mill.

[0102] Production Examples 7-10: Production of water-based first colored coating compositions WBBC1-1 to WBBC1-4>Components listed in Table 1 were mixed using the stated procedure and stirred for 30 minutes. Next, the pH was adjusted to 8.2 by adding dimethylethanolamine. Next, deionized water was added and the viscosity, as measured at a shearing rate of 1000 s1and a temperature of 20°C using a rotational viscometer Rheomat RM180 (produced by METTLER TOLEDO), was adjusted to 100 mPa s.

[0103] [Table 1]T able 1 . Formulations of Production Examples 7 to 10

[0104] 1) Melamine resin solution: Cymel 327 (produced by Allnex GMBH, solid resin content: 90 mass%)2) Inorganic thickener: A mixture of 3 parts by mass of Laponite RD (produced by BYK), 3 parts by mass of Pluriol P900 (produced by BASF) and 94 parts by mass of deionized water3) Alkali-swelling emulsion: Rheovis AS 1130 (produced by BASF)4) Surface conditioner: Surfynol 104 PA (produced by Evonik Industries, active ingredient content: 50 mass%)5) Silver pearl pigment: Iriodin 121 Rutile Luster Satin WNT (produced by Merck, D50=10 pm)

[0105] Production Examples 11-15: Production of water-based second colored coating compositions WBBC2-1 to WBBC2-5>Components listed in Table 2 were mixed using the stated procedure and stirred for 30 minutes. Next, the pH was adjusted to 8.2 by adding dimethylethanolamine. Next, deionized water was added and the viscosity, as measured at a shearing rate of 1000 s1and a temperature of 20°C using a rotational viscometer Rheomat RM180 (produced by METTLER TOLEDO), was adjusted to 100 mPa s.

[0106] [Table 2]Table 2. Formulations of Production Examples 11 to 15

[0107] <Working Examples 1-5 and Comparative Examples 1-4>[Preparation of test sheet] A cationic electrodeposition coating material Cathoguard No. 500 (produced by BASF Japan) was coated by electrodeposition on a zinc phosphate-treated cold rolled steel sheet(150 mm*75 mm*0.8 mm) so as to attain a dried film thickness of 20 m, and the coating material was then cured by being heated for 30 minutes at 170°C. Next, a water-based coating composition ProBloc N-3000 N2.0-3(W) (produced by BASF Japan) was electrostatically coated as a black underlayer-forming coating composition so as to attain a dried film thickness of 20 pm, and then left to stand for 5 minutes at room temperature. When one of these prepared test sheets was cured by being heated for 30 minutes at 140°C in order to measure the N value on a Munsell chart, the obtained black underlayer had an N value of 2.0 on a Munsell chart.

[0108] Next, a water-based first colored coating composition WBBC1 shown in Table 3 was electrostatically coated on the unheated test sheet so as to attain a dried film thickness of 8 pm and then left to stand for 3 minutes at room temperature, after which a water-based second colored coating composition WBBC2 shown in Table 3 was electrostatically coated so as to attain a dried film thickness of 8 pm and then left to stand for 5 minutes at room temperature, and pre-drying (flash-off) was then carried out for 3 minutes at 80°C. Moreover, in Comparative Example 1 , the water-based first colored coating composition BC1 was coated and left to stand for 5 minutes at room temperature without coating the water-based second colored coating composition BC2, and pre-drying (flash-off) was then carried out for 3 minutes at 80°C. Next, a solvent-based clear coating composition ProGloss HD-N(W) (produced by BASF Japan; two-component acrylic / urethane coating material) was electrostatically coated so as to attain a dried film thickness of 35 pm, left to stand for 10 minutes at room temperature, and then heated for 30 minutes at 140°C to obtain a test coated sheet having a multilayer coating film formed thereon.

[0109] [Evaluations]Test sheets produced in the manner described above were subjected to the following evaluations, and the results of these evaluations are shown in Table 3.

[0110] <Mc75 value (jet-blackness of shade portions)>X75, Y75 and Z75 values were measured using a multi-angle colorimeter BYKmac i (produced by BYK-Gardner), and the Mc75 value was determined using formula 1 below. Mc75=100x(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )

[0111] Moreover, evaluations were carried out as follows, with © and O taken to be an acceptable range.©: 218.0<Mc75O: 215.0<Mc75<218.0 x: Mc75<215.0

[0112] <L*15 value (highlight lightness)>The L*15 value was measured using a multi-angle colorimeter BYKmac i (produced by BYK- Gardner). Moreover, evaluations were carried out as follows, with © and O taken to be an acceptable range.©: L*15<28.0O: 28.0<L*15<30.0 x: 30.0<L*15

[0113] <SG15 value (pearlescent brilliance)>The SG15 value was measured using a multi-angle colorimeter BYKmac i (produced by BYK-Gardner). Moreover, evaluations were carried out as follows, with © and O taken to be an acceptable range.©: 3.1<SG15<3.8O: 3.0<SG15<3.1 or 3.8<SG15<4.0 x: SG15<3.0 or 4.0<SG15

[0114] <Visual evaluation score of dense pearlescence>Dense pearlescence was visually evaluated. That is, two designers and three technicians, all of whom had been involved in color development for three years or longer, gave a five- point evaluation (five, four, three, two and one points in decreasing order of excellent denseness), and the average values from three people, excluding the maximum and minimum values, was taken to be the visual evaluation score, with © and O taken to be an acceptable range.©: 4.0< visual evaluation scoreO: 3.0< visual evaluation score <4.0 x: visual evaluation score <3.0

[0115] [Table 3]Table 3. Evaluation results for Working Examples 1 to 5 and Comparative Examples 1 to 4

[0116] Production Example 16: Production of polyester resin solution PE-2 for solvent-based colored coating composition>25.0 parts of adipic acid, 16.0 parts of phthalic acid anhydride, 16.0 parts of isophthalic acid, 13.0 parts of 1,6-hexane diol, 13.0 parts of neopentyl glycol, 11.0 parts of trimethylolpropane and 6.0 parts of glycerin were placed in a flask equipped with a reflux condenser having a reaction water separation pipe, a temperature gauge, a stirring device and a nitrogen gas inlet pipe, after which the temperature was increased to 120°C to dissolve the raw materials, and the temperature was then increased to 160°C while stirring. The temperature was maintained at 160°C for 1 hour, and then gradually increased to 230°C over a period of 5 hours. A reaction was continued while maintaining a temperature of 230°C, and when the resin acid value reached 6 mg KOH / g, the temperature was lowered to 80°C or lower. Next, dilution was carried out using a mixed solvent of n-butyl acetate / Solvesso #100 (produced by Exxon Mobil; aromatic naphtha) at a mass ratio of 1 / 1 to attain a solid resin content of 55 mass%, thereby obtaining polyester resin solution PE-2, which had 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.

[0117] Production Example 17: Production of black pigment paste SP-1 for solvent-based colored coating composition>Solvent-based black pigment paste SP-1 was obtained by mixing 100.0 parts of polyester resin solution PE-2 as a dispersed resin, 55.0 parts of Mitsubishi carbon black MA-100 (produced by Mitsubishi Chemical Corporation) and 120.0 parts of xylene and dispersing using a motor mill.

[0118] Production Example 18: Production of blue pigment paste SP-2 for solvent-based colored coating composition>Solvent-based blue pigment paste P-2 was obtained by mixing 100.0 parts of polyester resin solution PE-2 as a dispersed resin, 55.0 parts of Heliogen Blue L 6900 (produced by Sun Chemical Colors & Effects) and 120.0 parts of xylene and dispersing using a motor mill.Production Example 19: Production of violet pigment paste SP-3 for solvent-based colored coating composition>Solvent-based violet pigment paste SP-3 was obtained by mixing 100.0 parts of polyester resin solution PE-2 as a dispersed resin, 55.0 parts of Hostaperm Violet P-RL (produced by ACH) and 120.0 parts of xylene and dispersing using a motor mill.Production Example 20: production of solvent-based first colored coating composition SBBC1>Components listed in Table 4 were mixed using the stated procedure. Next, a mixed solvent of n-butyl acetate / Solvesso #100 (produced by Exxon Mobil; aromatic naphtha) at a mass ratio of 1 / 1 was used to adjust to a viscosity of 12 seconds at 20°C using a No. 4 Ford cup.

[0121] [Table 4]Table 4. Formulation of Production Example 20

[0122] 6) Cellulose acetate butyrate solution: CAB-381-2BP (produced by Eastman Chemical); a solution obtained by dissolving in n-butyl acetate at a solid resin content of 15%7) Polyisocyanate compound solution: Desmodur N3300 (produced by Covestro, NCO content: 21.8 mass%); a solution obtained by dissolving in xylene at a solid resin content of 75%

[0123] Production Example 21: production of solvent-based second colored coating composition SBBC2>Components listed in Table 5 were mixed using the stated procedure. Next, a mixed solvent of n-butyl acetate / Solvesso #100 (produced by Exxon Mobil; aromatic naphtha) at a mass ratio of 1 / 1 was used to adjust to a viscosity of 12 seconds at 20°C using a No. 4 Ford cup.

[0124] [Table 5]Table 5. Formulation of Production Example 21

[0125] <Working Example 6>[Preparation of test sheets]A solvent-based electrically conductive primer coating composition Primac No. 1501 Primer E-DG N2 (produced by BASF Japan) was coated as a black underlayer-forming coating composition on a polypropylene sheet (150 mm*70 mm><3 mm) so as to obtain a dried film thickness of 7 pm, and then left to stand for 2 minutes at room temperature. When one of these prepared test sheets was cured by being heated for 30 minutes at 90°C in order to measure the N value on a Munsell chart, the obtained black underlayer had an N value of 2.0 on a Munsell chart.

[0126] Next, solvent-based first colored coating composition SBBC1 shown in Table 6 was electrostatically coated on the unheated test sheet so as to attain a dried film thickness of 8 pm and then left to stand for 3 minutes at room temperature, after which water-based second colored coating composition BC2 shown in Table 6 was electrostatically coated so as to attain a dried film thickness of 8 pm and then left to stand for 5 minutes at room temperature. Next, a solvent-based clear coating composition ProGloss N-2000(W) (produced by BASF Japan; two-component acrylic / urethane coating material) was electrostatically coated so as to attain a dried film thickness of 30 pm, left to stand for 10 minutes at room temperature, and then heated for 30 minutes at 90°C to obtain a test coated sheet having a multilayer coating film formed thereon.

[0127] [Evaluations]Multilayer coating films obtained from solvent-based first colored coating compositions and solvent-based second colored coating compositions were evaluated in the same way as multilayer coating films obtained from water-based first colored coating compositions and water-based second colored coating compositions, and the results of these evaluations are shown in Table 6.

[0128] [Table 6]Table 6. Evaluation results for Working Example 6

[0129] The invention achieved by the inventors of the present invention has been explicitly described above by means of embodiments, but the present invention is not limited to these embodiments, and it goes without saying that a variety of alterations are possible as long as these do not deviate from the gist of the invention.

Claims

[CLAIMS]

1. A multilayer coating film having a first colored coating film, a second colored coating film and a clear coating film in the stated 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 violet pigment, the second colored coating film contains a coating film-forming resin and a black pigment at a quantity of 0.02-0.10 parts by mass relative to a total of 100 parts by mass of solid resin content of the coating film-forming resin, the Mc75 value, which indicates the jet-blackness of shade portions ofthe multilayer coating film and is represented by formula 1 below, is 215.0 or more, the L*15 value, which indicates the lightness of highlights, is 30.0 or less, and the SG15 value, which indicates pearlescent brilliance, is 3.0-4.0.Mc75=100x(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )(Here, X75, Y75 and Z75 denote tristimulus values in an XYZ color system based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is measured at an angle of 75° (incident light direction) relative to the angle of specular reflection.)

2. The multilayer coating film as claimed in claim 1 , wherein the first colored coating film contains a silver pearl pigment at a quantity of 5.0-30.0 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, and the average particle diameter D50 of the silver pearl pigment is 4.0-12.0 pm.

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

4. A method for producing a multilayer coating film, the method being characterized by including: a step (1 ) for coating a first colored coating composition on a black underlayer to form an uncured first colored coating film, a step (2) for coating a second colored coating composition on the uncured first colored coating film obtained in step (1 ) to form an uncured second colored coating film, a step (3) for coating a clear coating composition on the uncured second colored coating film obtained in step (2) to form an uncured clear coating film, and a step (4) for simultaneously heating and curing the uncured first colored coating film, uncured second colored coating film and uncured clear coating film formed in steps (1) to (3),where the first colored coating composition contains a coating film-forming resin, a silver pearl pigment, a black pigment and a violet pigment, the second colored coating composition contains a coating film-forming resin and a black pigment at a quantity of 0.02-0.10 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, the Mc75 value, which indicates the jet-blackness of shade portions ofthe multilayer coating film and is represented by formula 1 below, is 215.0 or more, the L*15 value, which indicates the lightness of highlights, is 30.0 or less, and the SG15 value, which indicates pearlescent brilliance, is 3.0-4.0.Mc75=100*(log(94.81 / X75)-log(107.34 / Z75)+log(100 / Y75)) (formula 1 )(Here, X75, Y75 and Z75 denote tristimulus values in an XYZ color system based on spectral reflectance of reflected light, where incident light landing at an angle of 45° relative to the perpendicular line to the surface of the multilayer coating film is measured at an angle of 75° (incident light direction) relative to the angle of specular reflection.)

5. The method for producing a multilayer coating film as claimed in claim 4, wherein the first colored coating composition contains a silver pearl pigment at a quantity of 5.0-30.0 parts by mass relative to a total of 100 parts by mass of solid content of the coating film-forming resin, and the average particle diameter D50 of the silver pearl pigment is 4.0-12.0 pm.

6. The method for producing a multilayer coating film as claimed in claim 4 or claim 5, wherein the violet pigment contained in the first colored coating composition is a dioxazine violet pigment.

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