Multi-layer coating film and method for forming the same

Abstract

To provide a multilayer coating film which has low lightness and high chroma, and is composed of a first coating film, a second coating film and a clear coating film.SOLUTION: A multilayer coating film has a first coating film, a second coating film and a clear coating film in this order, in which the first coating film is a cured coating film of a first coating composition containing a first coating film formation resin and a brilliant pigment, the second coating film is a cured coating film of a second coating composition containing a second coating film formation resin and a coloring pigment, the multilayer coating film has C*15 / L*15 at an incident angle of 45° and a light receiving angle of 15° of 3 or more, a C*value at an incident angle of 45° and a light receiving angle of 15° of 70 or more, and a granular value (G value) at an incident angle of 45°of 1 or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] On the surface of an object to be coated such as an automobile body, a plurality of coating films having various functions are sequentially formed to protect the object to be coated and at the same time give a beautiful appearance and an excellent design. As a method for forming such a plurality of coating films, a method of forming an undercoat coating film such as an electrodeposition coating film on an object to be coated having excellent conductivity, and then sequentially forming an intermediate coating film and a top coating film as required is common. Among these coating films, it is the top coating film composed of a base coating film and a clear coating film that particularly greatly affects the appearance and design of the coating film. Especially in automobiles, the appearance and design of the top coating film composed of the base coating film and the clear coating film formed on the vehicle body are extremely important.

[0003] The appearance of the coating film formed on an automobile is greatly related to the appearance value such as the luxury of the automobile. In addition, customers who purchase automobiles tend to seek automobiles having a coating film with excellent design. Due to the diversification of consumers' preferences and the trend towards uniqueness, more unique designs are required.

[0004] For example, in Japanese Patent Application Laid-Open No. 2016-107256 (Patent Document 1), there is a method of sequentially coating a substrate with a first colored paint (X), a second colored paint (Y), and a clear paint (Z) to form a multilayer coating film including a first colored coating film, a second colored coating film, and a clear coating film; the first colored paint (X) contains a film-forming resin (A1), a scaly bright pigment (B1), and a coloring pigment (C1), and the total amount of the scaly bright pigment (B1) and the coloring pigment (C1) is 40 to 120 parts by mass based on 100 parts by mass of the solid content of the film-forming resin (A1); the second colored paint (Y) contains a film-forming resin (A2), a scaly bright pigment (B2), and a coloring pigment (C2), and the total amount of the scaly bright pigment (B2) and the coloring pigment (C2) is 1 to 20 parts by mass based on 100 parts by mass of the solid content of the film-forming resin (A2); based on a total of 200 parts by mass of 100 parts by mass of the solid content of the film-forming resin (A1) and 100 parts by mass of the solid content of the film-forming resin (A2), the total amount of the scaly bright pigment (B1), the coloring pigment (C1), the scaly bright pigment (B2), and the coloring pigment (C2) is 60 to 120 parts by mass, and a method for forming a multilayer coating film is described (Claim 1). Patent Document 1 describes that by this method, a multilayer coating film having high chroma and excellent adhesion and finish can be formed.

[0005] In Japanese Patent Application Laid-Open No. 2008-62198 (Patent Document 2), there is described a method for forming a laminated coating film by forming a first base coating film and a first clear coating film by wet-on-wet coating, baking and curing, and then forming a second base coating film and a second clear coating film by wet-on-wet coating and baking and curing (Claim 1). This Patent Document 2 describes that by the above-described forming method, a method for forming a laminated coating film having a sense of depth, excellent design, and small hue variation due to film thickness variation can be provided.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] According to the invention of Patent Document 1 above, it is described that a multilayer coating film having high color density and excellent adhesion and finish can be formed. Here, both the first colored paint (X) and the second colored paint (Y) used in forming the multilayer coating film of Patent Document 1 are paints containing both a coloring pigment and a bright pigment. Further, according to the invention of Patent Document 2 above, it is described that a laminated coating film having excellent design with a sense of depth and a small hue change due to film thickness variation can be formed. The laminated coating film of this Patent Document 2 is a coating film composed of four layers, and is formed by applying and baking and curing the first base and the first clear, and then applying and baking and curing the second base and the second clear.

[0008] In contrast to the above patent documents, an object of the present invention is to provide a multilayer coating film composed of three layers of a first coating film, a second coating film, and a clear coating film, which has low lightness and high color density. MEANS FOR SOLVING THE PROBLEMS

[0009] To solve the above problems, the present invention provides the following aspects. [1] 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, and the multilayer coating film has C*15 / L*15 of 3 or more at an incident angle of 45° and a light receiving angle of 15°, a C* value of 70 or more at an incident angle of 45° and a light receiving angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°. [2] The above multilayer coating film is the multilayer coating film of [1] with a C*15 / FF of 15 or more at an incident angle of 45° and a light receiving angle of 15°. [3] The above second coating film, as a single coating film, has an average light transmittance of 30% or less in the wavelength range of 400 nm or more and 700 nm or less. [1] or the multilayer coating film of [2]. [4] The film thickness of the above first coating film is in the range of 1 to 9 μm. The luminescent pigment contained in the above first coating film has an average particle diameter in the range of 2 to 13 μm, an average thickness in the range of 0.01 to 0.1 μm, and an aspect ratio in the range of 50 to 300. [1] to [3] any one of the multilayer coating films. [5] The above multilayer coating film has a hue of 1B to 10PB in the Munsell color system, and is any one of the multilayer coating films of [1] to [4]. [6] The content of the luminescent pigment in the above second coating composition is less than 0.5 part by mass with respect to 100 parts by mass of the resin solid content. [1] to [5] any one of the multilayer coating films. [7] A method of forming a multilayer coating film by sequentially coating a first coating composition, a second coating composition, and a clear coating composition on an object to be coated. The above first coating composition contains a first coating film-forming resin and a luminescent pigment. The above second coating composition contains a second coating film-forming resin and a coloring pigment. The above multilayer coating film has a C*15 / L*15 of 3 or more at an incident angle of 45° and a light receiving angle of 15°, a C* value of 70 or more at an incident angle of 45° and a light receiving angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°. A method for forming a multilayer coating film. [8] A method of forming a multilayer coating film by sequentially coating a first coating composition, a second coating composition, and a clear coating composition on an object to be coated in a wet-on-wet manner. The above first coating composition contains a first coating film-forming resin and a luminescent pigment. The above second coating composition contains a second coating film-forming resin and a coloring pigment. The above-mentioned multilayer coating film has a C*15 / L*15 of 3 or more at an incident angle of 45° and a receiving angle of 15°, a C* value of 70 or more at an incident angle of 45° and a receiving angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°. Method for forming a multilayer coating film. [9] An article having any one of the multilayer coating films of [1] to [6].

Effect of the Invention

[0010] According to the present disclosure, it is possible to form a multilayer coating film having a deep color tone that is low in lightness and high in chroma.

Mode for Carrying Out the Invention

[0011] The researchers of the present invention have conducted research aiming to develop a coating film having a high-chroma color tone (dark and vivid color tone) in a dark color with low lightness. For this reason, in a single-color so-called solid color, a method for forming a coating film having low lightness, high chroma, and a sense of depth has been studied.

[0012] As one method for imparting a sense of depth to the coating film, there is a method of changing the reflection intensity lightness at the highlight position and the shade position to increase the flip-flop value. As a result, the lightness of the coating film changes depending on the viewing angle, a shadow effect is generated, and a sense of depth can be felt.

[0013] However, for the purpose of imparting a shadow effect to a dark coating film, when an aluminum pigment, which is a type of bright pigment, is added to the coating film, the lightness increases due to the addition of the color tone (silver color) of the aluminum pigment itself. In addition, by adding the aluminum pigment, the granularity of the bright pigment is visually recognized, resulting in a so-called metallic tone coating film. On the other hand, for example, when mica is added to the coating film as a bright pigment, cloudiness such as clouding occurs throughout the coating film, and the chroma decreases. Thus, it has been difficult to impart a shadow effect and a sense of depth while maintaining high chroma in a coating film having a dark color tone with low lightness.

[0014] The inventors of the present invention conducted research with the aim of solving the above problems. As a result of experiments, they found that by combining specific first and second coatings, it is possible to provide a multilayer coating composed of three layers, namely a first coating, a second coating, and a clear coating, which has low lightness and high chroma, and thus completed the present invention. Hereinafter, the first coating composition for forming the first coating and the second coating composition for forming the second coating will be sequentially described.

[0015] First coating composition The first coating in the present disclosure is a cured coating of the first coating composition. The above first coating composition is a coating composition containing a first coating-forming resin and a bright pigment.

[0016] The above first coating composition contains a first coating-forming resin. Examples of the first coating-forming resin include acrylic resin, polyester resin, polyurethane resin, epoxy resin, fluororesin, silicone resin, and the like. The above first coating composition may be an aqueous coating composition or a solvent-based coating composition.

[0017] When the above first coating composition is an aqueous coating composition, examples of the first coating-forming resin preferably include acrylic resin emulsion (including acrylic silicone resin emulsion, acrylic urethane resin emulsion, etc.), acrylic resin dispersion (including acrylic silicone resin dispersion, acrylic urethane resin dispersion, etc.), water-soluble acrylic resin, polyester resin dispersion, polyurethane resin dispersion, epoxy resin dispersion, and the like. These resins may be used alone or in combination of two or more. The above resins can be prepared by methods commonly used by those skilled in the art. Commercially available products may be used as the above resins.

[0018] As a preferred embodiment, for example, an embodiment using either or both of an acrylic resin emulsion and a water-soluble acrylic resin, an embodiment using an acrylic resin emulsion, a water-soluble acrylic resin, and a polyester resin dispersion, an embodiment using an acrylic resin emulsion, a water-soluble acrylic resin, and a polyurethane resin dispersion, and the like can be mentioned.

[0019] The acrylic resin emulsion can be prepared, for example, by emulsion polymerization of a mixture of α,β-ethylenically unsaturated monomers. Preferred α,β-ethylenically unsaturated monomers used in the preparation of the acrylic resin emulsion include, for example, (meth)acrylate esters, α,β-ethylenically unsaturated monomers having an acid group, and α,β-ethylenically unsaturated monomers having a hydroxyl group.

[0020] Examples of the above (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, dihydrodicyclopentadienyl (meth)acrylate, and the like. In this specification, the (meth)acrylate ester means both an acrylate ester and a methacrylate ester.

[0021] Examples of α,β-ethylenically unsaturated monomers having an acid group include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acrylamido-2-methylpropanesulfonic acid, p-hydroxystyrene, 2,4-dihydroxy-4'-vinylbenzophenone, and the like.

[0022] Examples of α,β-ethylenically unsaturated monomers having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts thereof with ε-caprolactone. Preferred among these are hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethyl (meth)acrylate, and adducts thereof with ε-caprolactone.

[0023] The above α,β-ethylenically unsaturated monomer mixture may further contain other α,β-ethylenically unsaturated monomers. Examples of other α,β-ethylenically unsaturated monomers include polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds. The above α,β-ethylenically unsaturated monomers can be variously selected according to the purpose as needed.

[0024] The acrylic resin emulsion can be prepared by emulsion polymerization of the above α,β-ethylenically unsaturated monomer mixture. The emulsion polymerization is not particularly limited and can be carried out using a conventional method. Specifically, for example, an emulsifier is dissolved in an aqueous medium containing water or, if necessary, an organic solvent such as alcohol, ether (e.g., dipropylene glycol methyl ether, propylene glycol methyl ether, etc.), and the above α,β-ethylenically unsaturated monomer mixture and a polymerization initiator are dropped while heating and stirring. It can also be carried out by dropping an α,β-ethylenically unsaturated monomer mixture pre-emulsified with an emulsifier and water in the same manner.

[0025] As the above polymerization initiator and emulsifier, those commonly used by those skilled in the art can be used. If necessary, the molecular weight may be adjusted using a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer. The reaction temperature, reaction time, etc. can be appropriately selected within the range commonly used by those skilled in the art. The acrylic resin emulsion obtained by the reaction may be neutralized with a base if necessary.

[0026] The above acrylic resin emulsion preferably has a lower limit of the number average molecular weight of 3000. Further, the above acrylic resin emulsion preferably has a hydroxyl value (solid content hydroxyl value) with a lower limit of 20 mgKOH / g and an upper limit of 180 mgKOH / g, and an acid value (solid content acid value) with a lower limit of 1 mgKOH / g and an upper limit of 80 mgKOH / g.

[0027] In this specification, the number average molecular weight is a value determined by the GPC method using polystyrene as a standard. In this specification, the acid value and hydroxyl value are values calculated from the monomer composition used in the preparation based on the provisions of JIS.

[0028] Water-soluble acrylic resins can be prepared, for example, by solution polymerization of a monomer mixture containing α,β-ethylenically unsaturated monomers that can be used in the preparation of the above acrylic resin emulsion, and solubilizing with a basic compound. Acrylic resin dispersions can be prepared, for example, by solution polymerization of a monomer mixture containing α,β-ethylenically unsaturated monomers that can be used in the preparation of the above acrylic resin emulsion, and dispersing with a basic compound.

[0029] Polyester resin dispersions can be prepared, for example, by condensing a polyhydric alcohol component and a polybasic acid component, and dispersing with a basic compound. Polyurethane resin dispersions can be prepared, for example, by polymerizing a polyol compound, a compound having an active hydrogen group and a hydrophilic group in the molecule, and an organic polyisocyanate, optionally using a chain extender and a polymerization terminator, and dissolving or dispersing the resulting polymer in water.

[0030] When the above first paint composition is an aqueous paint composition, it is preferable to use a curing agent that reacts with the above first film-forming resin. Such a curing agent is a film-forming component that reacts with the above first film-forming resin to form a coating film. As the curing agent, a melamine resin, a blocked isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, an oxazoline compound, metal ions, etc. can be used. These may be used alone or in combination of two or more. The above components can be prepared by methods commonly used by those skilled in the art. Commercially available products may be used as the above components. It is more preferable to use either or both of a melamine resin and a blocked isocyanate compound as the curing agent.

[0031] Melamine resin can be a water-soluble melamine resin and / or a water-insoluble melamine resin. The melamine resin has a structure in which hydrogen atoms or substituents (such as alkyl ether groups, methylol groups, etc.) are bonded via three nitrogen atoms around a melamine nucleus (triazine nucleus). Generally, the above melamine resin is composed of a polynuclear body in which a plurality of melamine nuclei are bonded to each other. On the other hand, the above melamine resin may be a mononuclear body composed of one melamine nucleus.

[0032] Commercially available products may be used as the above melamine resin. Specific examples of commercially available products include, for example, the Cymel series (trade name) manufactured by Allnex, specifically, Cymel 202, Cymel 204, Cymel 211, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 250, Cymel 251, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cymel 285, Cymel 301, Cymel 303, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 701, Cymel 703, Cymel 1141; and the Uban (trade name) series manufactured by Mitsui Chemicals, etc. These may be used alone or in combination of two or more.

[0033] The blocked isocyanate compound can be prepared by adding a blocking agent having an active hydrogen to a polyisocyanate composed of trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Such a blocked isocyanate resin dissociates the blocking agent by heating to generate isocyanate groups, which react with the functional groups in the above resin component to cure.

[0034] The amount of the curing agent is preferably 10 to 80% by mass, more preferably 15 to 60% by mass, based on the solid content mass of the coating resin (the solid content mass of the coating film forming component including the above coating film forming resin and the curing agent).

[0035] The above-mentioned first coating composition contains a bright pigment. Examples of bright pigments include metallic bright pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and alloys thereof, and interference mica pigments, white mica pigments, graphite pigments, glass flake pigments, and the like. In the first coating composition of the present disclosure, it is preferable that the bright pigment is an aluminum pigment from the viewpoint of the design property of the obtained multilayer coating film.

[0036] The above-mentioned bright pigment preferably has an average particle size of 2 to 13 μm, more preferably 4 to 11 μm. The above-mentioned bright pigment also preferably has an average thickness of 0.01 to 0.1 μm, more preferably 0.02 to 0.08 μm. By satisfying the above conditions for the average particle size and average thickness of the bright pigment, a good denseness is brought to the first coating film, and thereby there is an advantage that the desired design can be suitably obtained in the multilayer coating film.

[0037] The average particle size of the above-mentioned bright pigment means the average major axis. The measurement of the average particle size can be carried out by observing the bright pigment using a shape analysis laser microscope (such as VK-X 250 manufactured by Keyence Corporation, etc.) and obtaining the number average value of the maximum length (major axis) of 100 arbitrarily selected pigments.

[0038] The average thickness of the above-mentioned bright pigment can be measured by forming a coating film containing the above-mentioned bright pigment, measuring the cross-section of the obtained coating film using a transmission electron microscope (TEM), and obtaining the average value of the measured values.

[0039] The above-mentioned bright pigment also preferably has an aspect ratio (average of the maximum diameter of the pigment / average of the thickness of the pigment) in the range of 50 to 300, preferably in the range of 100 to 200.

[0040] When the above-mentioned luminous pigment is an aluminum pigment, surface treatment may be carried out if necessary. Examples of surface treatments that can be applied to aluminum pigments include surface treatments using metal oxide-based compounds, surface treatments using phosphorus compounds, surface treatments using amine compounds, surface treatments using silane compounds, and the like.

[0041] Examples of the above-mentioned metal oxide-based compounds include metal oxides containing at least transition metal elements as constituent metals, alkali metal salts thereof, and ammonium salts thereof. Specifically, molybdenum trioxide, molybdic acid, alkali metal molybdates, ammonium molybdates, vanadic acid, alkali metal vanadates, ammonium vanadates, and the like can be mentioned. The alkali metal is not particularly limited, and examples include sodium, potassium, and the like. Among them, as the metal oxide-based compound, it is preferable to use one or more metal oxide-based compounds selected from the group consisting of molybdic acid, alkali metal molybdates, ammonium molybdates, vanadic acid, alkali metal vanadates, and ammonium vanadates.

[0042] Examples of the above-mentioned phosphorus compounds include organic phosphates, organic phosphites, organic phosphonic acids, and amine salts of these compounds. These phosphorus compounds may be used alone or in combination of two or more.

[0043] Examples of the above-mentioned amine compounds include linear or branched primary amines, linear or branched secondary amines, linear or branched tertiary amines, alicyclic primary amines, alicyclic secondary amines, alicyclic tertiary amines, aromatic group-containing primary amines, aromatic group-containing secondary amines, aromatic group-containing tertiary amines, and the like. These amine compounds may have substituents (such as hydroxyl groups, etc.) if necessary. These amine compounds may be used alone or in combination of two or more.

[0044] As the above silane compound, for example, alkoxysilane compounds, vinyl group-containing silane coupling agents, epoxy group-containing silane coupling agents, styryl group-containing silane coupling agents, (meth)acrylic group-containing silane coupling agents, amino group-containing silane coupling agents, isocyanate group-containing silane coupling agents, ureido group-containing silane coupling agents, mercapto group-containing silane coupling agents, acid anhydride group-containing silane coupling agents, and partial condensates thereof, etc. may be mentioned. These silane compounds may be used alone or in combination of two or more.

[0045] The above surface treatment can be carried out under the treatment conditions usually used by those skilled in the art. The above surface treatment may be carried out only one kind or two or more kinds may be used in combination.

[0046] In particular, when the bright pigment contained in the above first paint composition is an aluminum pigment and the average particle diameter is, for example, 2 to 13 μm, more preferably 4 to 11 μm, by carrying out the above surface treatment, there are advantages such as the stability of the first paint composition becoming better without impairing the appearance of the formed multilayer coating film.

[0047] Commercially available products may be used as the above bright pigment. As commercially available products, for example, Alpaste 46 series, 97 series (such as 97-0510, etc.) of Toyo Aluminium Co., Ltd., 01 series (such as 01-0651, etc.); Alpaste FD series of Asahi Kasei Co., Ltd., etc.; Metallux 4860 of Eckart Co., Ltd., etc.; may be mentioned

[0048] The amount of the above bright pigment is preferably in the range of 5 to 45 parts by mass, more preferably in the range of 15 to 35 parts by mass, based on 100 parts by mass of the resin solid content of the first film-forming resin.

[0049] In addition to the above-described bright pigment, the first coating composition may contain other pigments as required. However, these other pigments are subject to the condition that they are in an amount that does not impair the performance of the first coating film. Examples of other pigments include coloring pigments and extender pigments. Examples of extender pigments include calcium carbonate, barium sulfate, clay, talc, and the like. The above pigments may further contain rust preventive pigments as required.

[0050] As the coloring pigment, various inorganic coloring pigments and organic coloring pigments can be used. In this specification, the "coloring pigment" includes colored coloring pigments and achromatic coloring pigments. As the coloring pigment, for example, black pigments such as carbon black, graphite, iron black, composite metal oxides such as iron chromium and bismuth manganese, perylene-based black pigments, azomethiazole-based pigments; Blue pigments such as ultramarine blue, ultramarine, cobalt blue, copper phthalocyanine blue, indanthrone blue; Yellow pigments such as lead yellow, synthetic yellow iron oxide, bismuth vanadate, titanium yellow, zinc yellow, ocher, monoazo yellow, disazo yellow, isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, benzimidazolone yellow; Red pigments such as iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, perylene maroon; Orange pigments such as quinacridone magenta, anthraquinone orange, dianthraquinonyl red, pyrazolone orange, benzimidazolone orange, diketopyrrolopyrrole chrome vermilion; Green pigments such as chlorinated phthalocyanine green, brominated phthalocyanine green; Violet pigments such as dioxazine violet, perylene violet; White pigments such as titanium dioxide; and the like can be mentioned.

[0051] In addition to the above components, the aqueous first coating composition may contain additives commonly used by those skilled in the art, such as surface modifiers, viscosity control agents, thickeners, antioxidants, ultraviolet light inhibitors, defoamers, etc. For example, by using a viscosity control agent, thixotropic properties can be imparted and the coating workability can be adjusted. Examples of viscosity control agents include polyamide-based ones such as crosslinked or non-crosslinked resin particles, swollen dispersions of fatty acid amides, amide-based fatty acids, phosphates of long-chain polyaminoamides, polyethylene-based ones such as colloidal swollen dispersions of polyethylene oxide, and organophilic bentonite-based ones such as organic acid smectite clay and montmorillonite. When using these additives, they can be used in amounts commonly used by those skilled in the art.

[0052] The above aqueous first coating composition may further contain a phosphate group-containing organic compound in addition to the above components, if necessary.

[0053] The above aqueous first coating composition may contain water as a solvent and, if necessary, a water-soluble or water-miscible organic solvent.

[0054] The production of the above aqueous first coating composition can be carried out by methods commonly used by those skilled in the art, such as kneading and dispersing the first coating film-forming resin, the bright pigment, the curing agent, and other components and additives, if necessary, using a disper, a homogenizer, a kneader, etc. In the above production method, for example, it is preferable to prepare and mix a paste containing a bright pigment and a pigment dispersant, if necessary. As the pigment dispersant, commercially available pigment dispersants can be used.

[0055] When the above first coating composition is a solvent-based coating composition, examples of the first coating film-forming resin include acrylic resins, polyester resins (including urethane-modified polyester resins, etc.). These resins may be used alone or in combination of two or more.

[0056] The acrylic resin can be prepared, for example, by solution polymerization of a monomer mixture containing α,β-ethylenically unsaturated monomers. The acrylic resin preferably has a number average molecular weight of 1,000 to 20,000. The acrylic resin also preferably has an acid value (solid content acid value) of 1 to 80 mgKOH / g, more preferably 10 to 45 mgKOH / g. Further, the hydroxyl value (solid content hydroxyl value) is preferably 10 to 200 mgKOH / g.

[0057] Commercially available products may be used as the acrylic resin. Examples of commercially available products include the Dianal HR series manufactured by Mitsubishi Rayon Co., Ltd.

[0058] The amount of the acrylic resin is preferably 30 to 80% by mass, more preferably 35 to 70% by mass, based on the solid content mass of the coating resin (solid content mass of the film-forming components).

[0059] As the polyester resin, for example, a hydroxyl group-containing polyester resin can be used. The hydroxyl group-containing polyester resin can be prepared by polycondensing an acid component such as a polyvalent carboxylic acid and / or an acid anhydride with a polyhydric alcohol.

[0060] When the first coating composition is a solvent-based coating composition, it is preferable to use a curing agent that reacts with the first film-forming resin. As the curing agent, a melamine resin, a blocked isocyanate compound, etc. can be used. These may be used alone or in combination of two or more. The above components can be prepared by methods commonly used by those skilled in the art. Commercially available products may be used as the above components.

[0061] The above hardener preferably contains a melamine resin. The melamine resin is not particularly limited, and methylated melamine resin, butylated melamine resin, methyl-butyl mixed type melamine resin, etc. can be used. For example, the Cymel series commercially available from Allnex, the Uban series commercially available from Mitsui Chemicals, etc. can be mentioned. The amount of the melamine resin is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, based on the solid content mass of the coating resin (the solid content mass of the coating film forming components including the above coating film forming resin and hardener).

[0062] The above hardener preferably further contains a blocked isocyanate compound. The blocked isocyanate compound can be prepared by adding a blocking compound such as a compound having an active methylene group, a ketone compound or a caprolactam compound to a polyisocyanate by an addition reaction. Commercially available products may be used as the blocked isocyanate compound. Examples of commercially available products include the Duranate series manufactured by Asahi Kasei Corporation, the Sumidur series manufactured by Sumika Covestro Urethane Co., Ltd., etc.

[0063] The amount of the blocked isocyanate compound contained in the first coating composition is preferably 10 to 30% by mass, more preferably 15 to 25% by mass, based on the solid content mass of the coating resin (the solid content mass of the coating film forming components including the above coating film forming resin and hardener).

[0064] The solvent-based first coating composition contains the above first coating film forming resin and a bright pigment. The same bright pigment as the above can be used as the bright pigment. In addition to the above components, the solvent-based first coating composition may contain additives usually used by those skilled in the art, such as a curing catalyst, a surface conditioner, an ultraviolet absorber, an antioxidant, etc., additives usually used by those skilled in the art.

[0065] The solvent-based first coating composition can appropriately adjust the solid content concentration and viscosity by diluting with an organic solvent during coating. Examples of the organic solvents that can be used include ester solvents, ether solvents, alcohol solvents, ketone solvents, aliphatic hydrocarbon solvents, aromatic solvents, and the like.

[0066] The above solvent-based first coating composition may further contain a phosphoric acid group-containing organic compound in addition to the above components, if necessary.

[0067] The production of the above solvent-based first coating composition can be carried out by a method commonly used by those skilled in the art, such as kneading and dispersing a first coating film-forming resin, a curing agent, a pigment, a phosphoric acid group-containing organic compound, and an additive using a disper, a homogenizer, a kneader, etc. In the above production method, for example, it is preferable to prepare and mix a paste containing a bright pigment and a pigment dispersant as required in advance.

[0068] Second coating composition The second coating film in the present disclosure is a cured coating film of a second coating composition. The above second coating composition is a coating composition containing a second coating film-forming resin and a coloring pigment. The second coating composition may be an aqueous coating composition or a solvent-based coating composition, similar to the above first coating composition. Such a second coating composition can be prepared by the same procedure as the first coating composition.

[0069] As the second coating film-forming resin, the same resin as the above first coating film-forming resin can be used. The above first coating film-forming resin and the second coating film-forming resin may have the same resin composition or different resin compositions.

[0070] The second coating composition contains a pigment. Examples of the pigment include coloring pigments, extender pigments, and the like. Examples of the extender pigment include calcium carbonate, barium sulfate, clay, talc, and the like.

[0071] As coloring pigments contained in the second coating composition, various inorganic coloring pigments and organic coloring pigments can be used. As the coloring pigments, the above-mentioned coloring pigments can be used. The coloring pigments can be appropriately selected according to the color tone of the multilayer coating film. For example, when the hue of the multilayer coating film in the Munsell color system is 1B to 10PB, Blue pigments such as cyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, indanthrone blue, etc.; Green pigments such as chlorinated phthalocyanine green, brominated phthalocyanine green, etc.; Violet pigments such as dioxazine violet, perylene violet, etc. are used as the main pigments. If necessary, carbon black, graphite, iron black (iron oxide black), composite metal oxides such as iron chromium and bismuth manganese, perylene-based black pigments, azomethiazole-based pigments, etc. black pigments; Red pigments such as iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, perylene maroon, etc.; Yellow pigments such as lead yellow, synthetic yellow iron oxide, bismuth vanadate, titanium yellow, zinc yellow (zinc yellow), ocher, monoazo yellow, disazo yellow, isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, benzimidazolone yellow, etc.; Orange pigments such as quinacridone magenta, anthraquinone orange, dianthraquinonyl red, pyrazolone orange, benzimidazolone orange, diketopyrrolopyrrole chrome vermilion, etc.; etc. are preferably used as appropriate.

[0072] In the present disclosure, the second coating film formed by applying and curing the second coating composition preferably has an average light transmittance in the range of 400 nm or more and 700 nm or less of 30% or less as the light transmittance of the single coating film. The second coating composition for forming such a second coating film preferably contains the above blue pigment as a coloring pigment, and more preferably contains one or more of phthalocyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue.

[0073] The suitable amount of the coloring pigment contained in the second coating composition is preferably appropriately selected according to the type of the coloring pigment and the like. For example, the amount of the coloring pigment contained in the second coating film can be selected such that it is 1 to 25 parts by mass with respect to 100 parts by mass of the resin solid content. The above content may be, for example, 2 to 20 parts by mass. By appropriately selecting the amount of the coloring pigment contained in the second coating film according to the type of the coloring pigment and by having the first coating film of the present disclosure, it is possible to design such that C*15 / L*15 of the obtained multilayer coating film is 3 or more, the C* value is 70 or more, and the granularity value (G value) is 1 or less. Thereby, a multilayer coating film having high chroma and the desired design can be formed.

[0074] The above second coating composition may contain other pigments other than the above coloring pigment. Examples of other pigments include extender pigments and rust preventive pigments exemplified in the above first coating composition.

[0075] In the present disclosure, the second coating composition preferably does not substantially contain a pearlescent pigment. For example, the content of the pearlescent pigment in the second coating composition is preferably less than 0.5 part by mass, more preferably less than 0.3 part by mass, and even more preferably less than 0.1 part by mass with respect to 100 parts by mass of the resin solid content.

[0076] Formation of a multilayer coating film The multilayer coating film of the present disclosure is a coating film having, in this order, a first coating film which is a cured coating film of the above first coating composition, a second coating film which is a cured coating film of the above second coating composition, and a clear coating film.

[0077] In the formation of the multilayer coating film of the present disclosure, the object to be coated with the above coating composition is not particularly limited, and examples thereof include metals, plastics, foams, and the like. The above coating composition can be advantageously used particularly for metals and castings, and can be particularly preferably used for metals that can be electrodeposited. Examples of such metals include iron, copper, aluminum, tin, zinc, and alloys containing these metals. These objects to be coated may be molded articles. Specific examples of the molded articles include automobile bodies such as passenger cars, trucks, motorcycles, buses, and their parts. It is more preferable that the object to be coated such as the above metal is subjected to a chemical conversion treatment in advance with a phosphoric acid-based chemical conversion treatment agent, a zirconium-based chemical conversion treatment agent, or the like before electrodeposition coating. It is preferable that a cured electrodeposition coating film is formed on the object to be coated that has been subjected to the necessary chemical conversion treatment. As the electrodeposition coating composition used for the formation of the cured electrodeposition coating film, both cationic and anionic types can be used. It is preferable to use a cationic electrodeposition coating composition as the electrodeposition coating composition because a coating film having more excellent corrosion resistance can be formed.

[0078] The above object to be coated may further have an intermediate coating film formed thereon as necessary. An intermediate coating composition is used for the formation of the intermediate coating film. As the intermediate coating composition, for example, a coating composition containing a film-forming resin, a curing agent, various coloring components of organic and / or inorganic systems, and a extender pigment can be used. The film-forming resin and the curing agent are not particularly limited, and specifically, the film-forming resin and the curing agent mentioned in the above aqueous coating composition can be used. From the viewpoint of various performances of the obtained intermediate coating film, a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate is preferably used as the film-forming resin of the intermediate coating composition.

[0079] Examples of the method for forming a coating film using the above first coating composition and second coating composition include the following methods. · A method of sequentially coating a substrate with the above first coating composition and second coating composition, and then coating with a clear coating composition. In such coating, the first coating composition may be coated and heat-cured, and then the second coating composition may be coated and heat-cured. Also, the first coating composition may be coated, and while the coated coating film is in an uncured state, the second coating composition may be coated wet-on-wet, and then heat-cured. In the above wet-on-wet coating, preheating may be performed as necessary during coating. Also, the first coating composition and the second coating composition may be sequentially coated and dried at room temperature. And a clear coating composition is coated on the second coating film obtained by coating the second coating composition to provide a clear coating film. · A method of sequentially coating a substrate with a first coating composition, a second coating composition, and a clear coating composition wet-on-wet. Specifically, this coating is a method of sequentially coating a first coating composition, a second coating composition, and a clear coating film wet-on-wet to form uncured first, second, and clear coating films, and then heat-curing these uncured coating films all at once. In the above wet-on-wet coating, preheating may be performed as necessary during coating.

[0080] The above first coating composition and second coating composition can be applied to the substrate by methods commonly used in the coating field. Examples of coating methods include multi-stage coating (preferably two-stage coating) by air spray coating, airless spray coating, electrostatic spray coating, air electrostatic spray coating, and coating by combining air electrostatic spray coating and a rotary atomization type electrostatic coater.

[0081] The above first coating composition is preferably applied so that the film thickness of the cured first coating film is in the range of 1 to 9 μm, and more preferably in the range of 2 to 7 μm. Also, the second coating composition is preferably applied so that the film thickness of the cured second coating film is in the range of 7 to 30 μm, and more preferably in the range of 10 to 25 μm.

[0082] When applying and heat-curing the above-described first coating composition and second coating composition, the heating temperature and time can be appropriately selected according to the composition of the coating composition (aqueous or solvent-based) and the type of the object to be coated. The heating temperature can be appropriately selected, for example, in the range of 80 to 180 °C, preferably in the range of 100 to 160 °C. The heating time can be appropriately selected, for example, in the range of 5 minutes to 60 minutes, preferably in the range of 10 minutes to 30 minutes.

[0083] The above-described clear coating composition is not particularly limited, and examples thereof include solvent-based, aqueous-based, and powder-based clear coating compositions.

[0084] Preferred examples of the above-described solvent-based clear coating composition include, from the viewpoints of transparency or acid etching resistance, etc., combinations of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate, or acrylic resins and / or polyester resins having a carboxylic acid / epoxy curing system, etc.

[0085] Examples of the aqueous-based clear coating composition include those containing a resin obtained by neutralizing a film-forming resin, which is exemplified as an example of the above-described solvent-based clear coating composition, with a base to make it aqueous. This neutralization can be carried out by adding a tertiary amine such as dimethylethanolamine and triethylamine before or after polymerization.

[0086] These solvent-based clear coating compositions and aqueous-based clear coating compositions preferably contain a viscosity control agent in order to ensure coating workability. As the viscosity control agent, those generally showing thixotropy can be used. As examples of the viscosity control agent, for example, those exemplified in the case of aqueous coating compositions can be used. In addition, additives generally used in the coating field may be contained as necessary.

[0087] As the powder-type clear coating composition, for example, powder coating compositions generally used in the coating field such as thermoplastic powder coating compositions and thermosetting powder coating compositions can be used. Among these, from the viewpoint of coating film physical properties and the like, thermosetting powder coating compositions are preferred. Specific examples of thermosetting powder coating compositions include epoxy-based, acrylic-based, and polyester-based powder clear coating compositions.

[0088] The coating of the clear coating composition can be carried out using a coating method known to those skilled in the art according to the coating form of the clear coating composition. The dry film thickness of the clear coating film formed by coating the above clear coating composition is generally preferably 10 to 80 μm, and more preferably 20 to 60 μm.

[0089] By heat-curing the uncured clear coating film obtained by coating the clear coating composition, a cured clear coating film can be formed. When the clear coating composition is coated on the uncured second base coating film, by heating, these uncured coating films will be heat-cured. From the viewpoints of curability and the physical properties of the resulting multilayer coating film, the heat-curing temperature is preferably set at 80 to 180°C, and more preferably set at 120 to 160°C. The heat-curing time can be arbitrarily set according to the above temperature. Examples of the heat-curing conditions include conditions such as heating at a heat-curing temperature of 120°C to 160°C for 10 to 30 minutes. In addition, depending on the type of the coating composition, after coating the above coating composition, it may be dried at room temperature to form a coating film, and then, for example, a reaction-curing type clear coating composition may be coated to provide a clear coating film.

[0090] The multilayer coating film of the present disclosure is conditioned that C*15 / L*15 at an incident angle of 45° and a light-receiving angle of 15° is 3 or more. The above-mentioned chroma C* and lightness L* are parameters in the L*C*h color system, and can be obtained in accordance with JIS Z8729. This L*C*h color system is a color system defined by the International Commission on Illumination and is described in Section 4.2 of CIE Publication 15.2(1986). In the L*C*h color system, L* represents lightness, C* represents chroma, and h represents hue angle. The chroma C* means that the vividness of the substance to be measured increases as the numerical value increases, and the dullness increases as the numerical value decreases. The lightness L* means that the brightness of the substance to be measured increases as the numerical value increases, and the darkness increases as the numerical value decreases. The above-mentioned chroma C* and lightness L* can be measured using a commercially available multi-angle spectrophotometer. Examples of the multi-angle spectrophotometer include BYK-maci (manufactured by BYK).

[0091] Regarding the chroma C* and lightness L* at the above incident angle of 45° and light-receiving angle of 15°, specifically, the position of the specular reflection light of the light irradiated from the 45° angle of the cured coating film is set to 0°, and the light-receiving angle at the position 15° from the specular reflection light in the incident angle direction is meant.

[0092] In this specification, the measurement of the chroma C* and lightness L* of the multilayer coating film refers to the values measured using the multilayer coating film composed of the cured coating film of the first coating composition, the cured coating film of the second coating composition, and the clear coating film. More specifically, on a steel plate coated with a cationic electrodeposition coating composition, on a coated plate formed with a dark gray-based curing intermediate coating film, the first coating composition is spray-coated so that the dry film thickness becomes 4 μm, then the second coating composition is spray-coated wet-on-wet so that the dry film thickness becomes 12 μm, and then the clear coating composition is spray-coated wet-on-wet so that the dry film thickness becomes 35 μm, and then the measurement is performed using the multilayer coating film obtained by heating and curing the uncured three-layer coating film at 140°C for 20 minutes.

[0093] The above-mentioned multilayer coating film has a C*15 / L*15 value of 3 or more at an incident angle of 45° and a light-receiving angle of 15°. It is more preferable that this C*15 / L*15 value is within the range of 4 to 7. When C* / L* is less than 3, in the case of light reception of the shade, it may have a dark, turbid or hazy feeling and may become a color without a sense of depth.

[0094] The above-mentioned multilayer coating film also has a C* value of 70 or more at an incident angle of 45° and a light-receiving angle of 15°. It is preferable that the above C* value is 80 or more, and it is preferable that the upper limit value of C* is 130. It is more preferable that the above C* is within the range of 90 to 120. By the C* value satisfying the above conditions, it is shown that the multilayer coating film has high color saturation.

[0095] The multilayer coating film of the present disclosure preferably also has a C*15 / FF value of 15 or more at an incident angle of 45° and a light-receiving angle of 15°.

[0096] The above FF value is a flip-flop value and is a value indicating the degree of change in the intensity of reflected light according to the viewing angle (light-receiving angle). The FF value is obtained by measuring the L* value (L*(15°) value) at a light-receiving angle of 15 degrees and the L* value (L*(110°) value) at a light-receiving angle of 110 degrees, and using the following formula FF value = L*(15°) value / L*(110°) value to calculate. Specifically, the L* value (L*(15°) value) at the above light-receiving angle of 15 degrees is the L* value of the light received at a position 15 degrees in the direction of the measurement light from the specular reflection angle with respect to the incident angle, when the measurement light is irradiated at an angle of 45 degrees with respect to the axis perpendicular to the measurement target surface (incident angle 45 degrees). Also, the L* value (L*(110°) value) at the above light-receiving angle of 110 degrees is the L* value of the light received at an angle of 110° in the direction of the measurement light from the specular reflection angle, when the measurement light is irradiated in the same manner.

[0097] The above L* value (L*(15°) value) at a light-receiving angle of 15 degrees and the L* value (L*(110°) value) at a light-receiving angle of 110 degrees can be measured using a commercially available multi-angle spectrocolorimeter.

[0098] The larger the FF value, the greater the change in the L* value (lightness) due to the observation angle (light-receiving angle). When the FF value is small, it indicates that the change in the L* value (lightness) due to the observation angle (light-receiving angle) is small. In a general metallic coating film, when the FF value is large and the change in lightness depending on the viewing angle is large, there is often a high sense of shadow as a metallic coating film.

[0099] In the multilayer coating film of the present disclosure, the fact that C*15 / FF is 15 or more means that the value of C*15 is sufficiently high with respect to the change in lightness of highlight / shade that the FF value represents, and it becomes one of the indicators of being low in lightness and high in chroma.

[0100] The multilayer coating film of the present disclosure is also conditioned that the granularity value (G value) at an incident angle of 45° is 1 or less. The above granularity value (G value) is a value obtained by quantifying granularity through diffused illumination measurement. The above granularity value (G value) acquires an image with a CCD chip under diffused illumination within a white-painted hemisphere, analyzes the acquired image using a histogram of brightness levels, and represents the uniformity of the light and dark regions as a value indicating one granularity. The granularity value (G value) is represented in the range of 0 to 30, and the smaller the value, the finer it is, and the larger the value, the more granular it is. In the multilayer coating film of the present disclosure, when the granularity value (G value) is 1 or less, it can be said that the coating film has almost no visible granularity of luminance.

[0101] The above granularity value (G value) can be measured using a glossiness measuring instrument. Examples of the glossiness measuring instrument capable of measuring these include BYK-maci (manufactured by BYK).

[0102] In this specification, the measurement of the granularity value (G value) refers to a value measured using a multi-layer coating film composed of a cured coating film of the first coating composition with a film thickness of 4 μm, a cured coating film of the second coating composition with a film thickness of 12 μm, and a clear coating film with a film thickness of 35 μm. More specifically, on a steel plate coated with a cationic electrodeposition coating composition, on a coated plate formed with a dark gray-based curing intermediate coating film, the first coating composition is spray-coated so that the dry film thickness is 4 μm, then the second coating composition is spray-coated wet-on-wet so that the dry film thickness is 12 μm, and then the clear coating composition is spray-coated wet-on-wet so that the dry film thickness is 35 μm. Thereafter, the measurement is performed using a multi-layer coating film obtained by heat-curing the uncured three-layer coating film at 140 °C for 20 minutes.

[0103] In the multi-layer coating film of the present disclosure, the second coating film obtained by curing the second coating composition preferably has an average light transmittance of 30% or less in the wavelength range of 400 nm or more and 700 nm or less as a single coating film.

[0104] The measurement of the light transmittance of the second coating film is performed as follows. The prepared second coating composition is spray-coated on a polypropylene plate so as to have a predetermined dry film thickness, and after heat-curing at 140 °C for 20 minutes, the coating film is peeled off from the polypropylene plate to prepare a single second coating film. The single second coating film used for measuring the light transmittance means a coating film film obtained by peeling only the second coating film from the substrate as described above.

[0105] The light transmittance can be obtained by measuring the intensity ratio of the transmitted light when the incident light passes through the single second coating film under the conditions of a scan speed of 300 nm / min and a sampling interval of 10 nm in the wavelength range of 400 to 700 nm using a U-4100 type spectrophotometer (manufactured by Hitachi, Ltd.) for the prepared single second coating film, and calculating the average value of the measured values in the above wavelength range.

[0106] In the multilayer coating film of the present disclosure, by the light transmittance of the single coating film of the second coating film measured as described above being 30% or less in terms of the average light transmittance in the wavelength range of 400 nm or more and 700 nm or less, there is an advantage that the appearance of the multilayer coating film composed of the first coating film, the second coating film, and the clear coating film can be improved in design properties with low lightness and high chroma.

[0107] Adjustment of the light transmittance of the second coating film is performed by adjusting the type and pigment mass concentration of the coloring pigment contained in the second paint, and adjusting the film thickness of the coating film. Specifically, a second coating film having a film thickness of 7 to 30 μm is provided using a second paint composition in which the coloring pigment contains one or more selected from the group consisting of, for example, cyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue, and the content of the coloring pigment is 1 to 25 parts by mass with respect to 100 parts by mass of the resin solid content. Thereby, the light transmittance of the second coating film can be suitably adjusted, and as a result, there is an advantage that a multilayer coating film having the intended design in the present disclosure can be obtained favorably.

[0108] In the multilayer coating film of the present disclosure, the hue in the Munsell color system is preferably 1B to 10PB. In the multilayer coating film of the present disclosure, when the above conditions are satisfied and the hue in the Munsell color system satisfies the above conditions, it can be said that the above hue is particularly suitable in the intended design of low lightness and high chroma in the present disclosure.

[0109] The Munsell color system is well known to those skilled in the art as the "method of expressing colors by three attributes" (JIS Z 8721), and colors are classified by the three attributes of color, hue (H), and lightness and chroma.

[0110] In the Munsell color system, the hue (H) is indicated by a combination of the symbols (R, Y, G, B, and P) and numbers (such as 5 and 10) on the Munsell color wheel. In the Munsell color wheel, "R" indicates red, "Y" indicates yellow, "G" indicates green, "B" indicates blue, and "P" indicates purple. Also, among these intermediate hues, "YR" indicates yellow-red, "GY" indicates green-yellow, "BG" indicates blue-green, "PB" indicates purple-blue, and "RP" indicates red-purple. The above 10 colors are the 10 hues of the Munsell color wheel. By dividing each of these 10 hues into 10 equal parts, a 100-color wheel of the Munsell color wheel (Munsell color wheel 100) is obtained. In the multilayer coating film of the present disclosure, when the hue in the Munsell color system is 1B to 10PB, it can be said that the multilayer coating film has a hue recognized as blue.

[0111] In the present disclosure, the hue (H) in the Munsell color system can be measured, for example, by a multi-angle spectrophotometer "CR-400" manufactured by Minolta Co., Ltd.

[0112] The multilayer coating film of the present disclosure has a C*15 / L*15 of 3 or more and a C* value of 70 or more, resulting in a coating film that is vivid, dark, and has a high chroma while having a low lightness. The multilayer coating film of the present disclosure also has a G value of 1 or less, resulting in a coating film with a calm design with almost no granular glossiness.

[0113] The multilayer coating film of the present disclosure has such a dark color with a sense of depth. Examples of the colors of the multilayer coating film of the present invention include colors with low lightness and high chroma, such as red, blue, and green. Among these, a blue-based multilayer coating film in which the hue in the Munsell color system is indicated by 1B to 10PB is more preferable.

Example

[0114] The present invention will be described more specifically by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0115] Production Example 1: Production of an acrylic resin emulsion (film-forming resin) 633 parts of deionized water was added to the reaction vessel, and the temperature was raised to 80 °C while mixing and stirring in a nitrogen stream. Next, a first-stage monomer mixture of 75.65 parts by mass of styrene (ST), 178.96 parts by mass of methyl methacrylate (MMA), 75.94 parts by mass of n-butyl acrylate (BA), 64.45 parts by mass of 2-ethylhexyl acrylate (2-EHA), 105.00 parts by mass of hydroxyethyl methacrylate (HEMA), 25.00 parts of Aqualon HS-10 (polyoxyethylene alkyl propenyl phenyl ether sulfate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 25.00 parts of Adeka Resorcinol NE-20 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd.), and 400 parts of deionized water, a monomer emulsion composed of 1.2 parts of ammonium persulfate and 500 parts of deionized water, and an initiator solution were added dropwise to the reaction vessel in parallel over 1.5 hours. After completion of the dropwise addition, aging was carried out at the same temperature for 1 hour. Furthermore, at 80 °C, a second-stage monomer mixture of 53.65 parts by mass of styrene (ST), 178.96 parts by mass of methyl methacrylate (MMA), 75.94 parts by mass of n-butyl acrylate (BA), 64.45 parts by mass of 2-ethylhexyl acrylate (2-EHA), 105.00 parts by mass of hydroxyethyl methacrylate (HEMA), and 22 parts by mass of acrylic acid, a monomer emulsion composed of 10 parts of Aqualon HS-10 and 250 parts of deionized water, and an initiator solution composed of 3.0 parts of ammonium persulfate and 500 parts of deionized water were added dropwise to the reaction vessel in parallel over 1.5 hours. After completion of the dropwise addition, aging was carried out at the same temperature for 2 hours. Next, it was cooled to 40 °C, filtered through a 400-mesh filter, and then 100 parts of deionized water and 1.6 parts of dimethylaminoethanol were added to adjust the pH to 6.5, obtaining an acrylic resin emulsion having an average particle diameter of 150 nm, a non-volatile content of 35%, a solid acid value of 20 mg KOH / g, and a hydroxyl value of 100 mg KOH / g.

[0116] Production Example 2: Production of a phosphoric acid group-containing organic compound 40 parts of ethoxypropanol were charged into a 1-liter reaction vessel equipped with a stirrer, a temperature regulator, and a cooling pipe. To this, 121.7 parts of a monomer solution consisting of 4 parts of styrene, 35.96 parts of n-butyl acrylate, 18.45 parts of ethylhexyl methacrylate, 13.92 parts of 2-hydroxyethyl methacrylate, 7.67 parts of methacrylic acid, 20 parts of ethoxypropanol, 40 parts of a solution in which 20 parts of Hostamer PP (acid phosphooxyhexa(oxypropylene) monomethacrylate manufactured by Uni-Chemical Co., Ltd.) was dissolved, and 1.7 parts of azobisisobutyronitrile were added dropwise at 120°C for 3 hours, and then stirring was continued for 1 hour. The obtained phosphoric acid group-containing organic compound had an acid value of 105 mgKOH / g, of which the phosphoric acid group value was 55 mgKOH / g, the hydroxyl value was 60 mgKOH / g, the number average molecular weight was 6000, and the non-volatile content was 63%.

[0117] In the examples of this specification, the number average molecular weight was measured using a GPC apparatus "HLC8220GPC" (trade name, manufactured by Tosoh Corporation), four columns "Shodex KF-606M" and "Shodex KF-603" (both manufactured by Showa Denko K.K., trade name), with a mobile phase of tetrahydrofuran, a measurement temperature of 40°C, a flow rate of 0.6 cc / min, and a detector of RI. In the examples of this specification, the acid value and the phosphoric acid group value of the phosphoric acid group-containing organic compound were calculated based on the definition of the acid value in JIS K5601 2-1 (the number of mg of potassium hydroxide (KOH) required to neutralize the free acid in 1 g of the sample (non-volatile matter)). The hydroxyl value was calculated based on the definition of the hydroxyl value in JIS K0070 (the number of mg of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl group when 1 g of the sample was acetylated).

[0118] Example 1 Preparation of the first coating composition Colored pigment dispersion paste 20 parts of Shanin Blue G314, which is a coloring pigment, and 5 parts of Hostaperm Violet NFVP336, and Dispex, which is a pigment dispersant (登録商標)18.6 parts of Ultra PA 4550 (manufactured by BASF), 36.0 parts of ion-exchanged water, and 0.5 part of BYK-011 as an antifoaming agent were mixed and dispersed with a stirrer such as a disper to obtain a colored pigment dispersion paste.

[0119] First coating composition 182 parts of the acrylic resin emulsion of Production Example 1, 2.2 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90%), 122 parts of the above colored pigment dispersion paste, 22.2 parts of aluminum paste SB-10 (ground aluminum bright pigment, manufactured by Asahi Kasei, average particle size 10 μm, average thickness 0.06 μm, active ingredient 65%) based on 100 parts by mass of the resin solid content, 5 parts of the phosphate group-containing organic compound of Production Example 2, 0.4 part of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts (3 parts in terms of solid content) of Neugen EA-207D (amphiphilic compound, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%), and 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed, and dimethylaminoethanol was added so that the pH became 8.1, and then diluted with deionized water to prepare an aqueous coating composition having a resin solid content concentration of 12% by mass.

[0120] Preparation of the second coating composition 182 parts of the acrylic resin emulsion of Production Example 1, 2.2 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90%), 90 parts of the colored pigment dispersion paste prepared in the preparation of the above first coating composition, 5 parts of the phosphate group-containing organic compound of Production Example 2, 0.4 part of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts (3 parts in terms of solid content) of Neugen EA-207D (amphiphilic compound, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%), and 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed, and dimethylaminoethanol was added so that the pH became 8.1, and then diluted with deionized water to prepare an aqueous coating composition having a resin solid content concentration of 19% by mass.

[0121] Formation of a multilayer coating film On a zinc phosphate-treated mild steel plate with a thickness of 0.8 mm, a length of 30 cm, and a width of 40 cm, the cationic electrodeposition coating composition "Power Top U-50)" (manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was electrodeposition coated so that the dry film thickness was 20 μm, and the coated plate was baked at 160 °C for 30 minutes. Then, the intermediate coating composition "OP-30P Middle Gray" (manufactured by Nippon Paint Automotive Coatings Co., Ltd., polyester-melamine-based paint, diluted in advance for 25 seconds (using a No. 4 Ford cup and measured at 20 °C)) was air spray coated using an Anest Iwata air spray gun W-101-132G so that the dry film thickness was 35 μm, and then baked and cured at 140 °C for 30 minutes to form a cured intermediate coating film with a lightness of 60. Next, the first paint composition was air spray coated under the conditions of a room temperature of 23 °C and a humidity of 68% so that the dry film thickness was 4 μm. After setting for 4 minutes, preheating was carried out at 80 °C for 5 minutes. After preheating, the second paint composition was air spray coated wet-on-wet under the conditions of a room temperature of 23 °C and a humidity of 68% so that the dry film thickness was 12 μm. After setting for 4 minutes, preheating was carried out at 80 °C for 5 minutes. After preheating after coating with the second paint composition, the coated plate was allowed to cool to room temperature, and MacFlow-O-1810 (a solvent-based clear paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was air spray coated as a clear paint so that the dry film thickness was 35 μm, and setting was carried out for 7 minutes. Then, the coated plate was baked in a dryer at 140 °C for 30 minutes to obtain a coated test plate having a multilayer coating film.

[0122] When the Munsell value of the formed multilayer coating film was measured with a multi-angle spectrophotometer "CR-400" manufactured by Minolta, it was 7.5PB2 / 8.

[0123] Example 2 Preparation of the first coating composition 182 parts of the acrylic resin emulsion of Production Example 1, 2.2 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90%), 30.0 parts of aluminum paste SB-10 (ground aluminum bright pigment, manufactured by Asahi Kasei, average particle diameter 10 μm, average thickness 0.06 μm, active ingredient 65%) based on 100 parts by mass of the resin solid content, 5 parts of the phosphate group-containing organic compound of Production Example 2, 0.4 part of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts (3 parts in terms of solid content) of Neugen EA-207D (amphiphilic compound, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%), 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed, and dimethylaminoethanol was added so that the pH became 8.1, and it was diluted with deionized water to prepare a first coating composition having a resin solid content concentration of 33% by mass.

[0124] Preparation of the second coating composition In the preparation of the second coating composition, the second coating composition was prepared in the same procedure as in Example 1, except that the amount of the pigment dispersion paste was changed to 180 parts.

[0125] Formation of a multilayer coating film A multilayer coating film was formed in the same procedure as in Example 1, except that the first coating composition and the second coating composition obtained above were used.

[0126] When the Munsell value of the formed multilayer coating film was measured with a multi-angle spectrophotometer "CR-400" manufactured by Minolta, it was 7.5PB 2 / 7.

[0127] Comparative Example 1 Preparation of the first coating composition In the preparation of the first coating composition, the first coating composition was prepared in the same procedure as in Example 1, except that T-8650 (ground aluminum bright pigment, manufactured by Nippon Boshitsu Kogyo Co., Ltd., average particle diameter 18 μm) was used in an amount of 3.3 parts based on 100 parts by mass of the resin solid content.

[0128] Preparation of the second coating composition 182 parts of the acrylic resin emulsion of Production Example 1, 2.2 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90%), 65 parts of the colored pigment dispersion paste prepared in Example 1, 0.01 part of 09-0645 (aluminum glitter pigment, manufactured by Nippon Boshitsu Kogyo Co., Ltd., average particle size 20 μm) which is a glitter pigment, 0.4 part of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts of Neugen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) (3 parts in terms of solid content), 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed, and dimethylaminoethanol was added so that the pH became 8.1, and it was diluted with deionized water to prepare an aqueous paint composition having a resin solid content concentration of 18% by mass.

[0129] Formation of a multilayer coating film A multilayer coating film was formed in the same procedure as in Example 1, except that the first paint composition and the second paint composition obtained above were used.

[0130] When the Munsell value of the formed multilayer coating film was measured with a multi-angle spectrophotometer "CR-400" manufactured by Minolta, it was 7.5PB.

[0131] Comparative Example 2 Preparation of the first coating composition In the preparation of the first paint composition, the first paint composition was prepared in the same procedure as in Example 1, except that 94-0642 (aluminum glitter pigment, manufactured by Toyo Aluminum Co., Ltd., average particle diameter 17 μm) was used in an amount of 2.0 parts per 100 parts by mass of the resin solid content as the glitter pigment.

[0132] Preparation of the second coating composition In the preparation of the second paint composition, the second paint composition was prepared in the same procedure as in Example 1, except that the amount of the pigment dispersion paste was changed from 90 parts to 50 parts.

[0133] Formation of a multilayer coating film A multilayer coating film was formed in the same procedure as in Example 1, except that the first coating composition and the second coating composition obtained above were used.

[0134] When the Munsell value of the formed multilayer coating film was measured with a multi-angle spectrophotometer "CR-400" manufactured by Minolta Co., Ltd., it was 7.5PB.

[0135] Comparative Example 3 Preparation of a coating composition 182 parts of the acrylic resin emulsion of Production Example 1, 2.2 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90%), 20 parts of the colored pigment dispersion paste prepared in Example 1, 10.0 parts of MH-8801 (ground aluminum glitter pigment, manufactured by Toyo Aluminum Co., Ltd., average particle diameter 15 μm) which is a glitter pigment, 0.4 part of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts of Neugen EA-207D (amphiphilic compound, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) (3 parts in terms of solid content), and 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed, and dimethylaminoethanol was added so that the pH became 8.1, and it was diluted with deionized water to prepare an aqueous coating composition having a resin solid content concentration of 18% by mass.

[0136] Formation of a multilayer coating film On a phosphatized cold-rolled steel sheet with a thickness of 0.8 mm, a length of 30 cm, and a width of 40 cm, "Power Top U-50)" which is a cationic electrodeposition coating composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was electrodeposition-coated so that the dry film thickness became 20 μm, and the coated plate was baked at 160 °C for 30 minutes. The intermediate coating composition "OP-30P Middle Gray" (manufactured by Nippon Paint Automotive Coatings Co., Ltd., polyester-melamine-based paint, diluted in advance for 25 seconds (measured at 20 °C using a No. 4 Ford cup)) was air-sprayed using an Anest Iwata air spray gun W-101-132G so that the dry film thickness became 35 μm, and then baked and cured at 140 °C for 30 minutes to form a cured intermediate coating film having a lightness of 60. Next, the paint composition prepared above was air-sprayed under the conditions of a room temperature of 23 °C and a humidity of 68% to a dry film thickness of 12 μm. After setting for 4 minutes, preheating was carried out at 80 °C for 5 minutes. After the above preheating, the painted plate was allowed to cool to room temperature, and MacFlow - O - 1810 (a solvent-based clear paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was air-sprayed as a clear paint to a dry film thickness of 35 μm and set for 7 minutes. Then, the painted plate was baked at 140 °C for 30 minutes in a dryer to obtain a painted test plate having a multilayer coating film.

[0137] When the Munsell value of the formed multilayer coating film was measured with a multi-angle spectrophotometer "CR - 400" manufactured by Minolta, it was 7.5PB 8 / 4.

[0138] Using the multilayer coating films formed in the above examples and comparative examples, the following evaluations were performed. The evaluation results are shown in the following table.

[0139] Measurement of the chroma C* of the multilayer coating film and calculation of C*15 / L*15 Using the painted test plates having the multilayer coating films formed in each example and comparative example, the chroma C* value and lightness L* value at an incident angle of 45° and a receiving angle of 15° were measured with a multi-angle spectrophotometer BYK-maci (manufactured by BYK). Using the chroma C* value and lightness L* value measured above, C*15 / L*15 was calculated.

[0140] Calculation of C* / FF of the multilayer coating film Measurement of the FF value of the multilayer coating film Regarding the painted test plates having the multilayer coating films formed in each example and comparative example, using a multi-angle spectrophotometer BYK-maci (manufactured by BYK), the L* value (L*(15°) value) at a receiving angle of 15° and the L* value (L*(110°) value) at a receiving angle of 110° at an incident angle of 45° were measured, and the FF value was determined by the following formula. FF value = L*(15°) value / L*(110°) value

[0141] Using the obtained FF value and the C*15 value measured above, C*15 / FF was calculated.

[0142] Measurement of the light transmittance of the second coating film On a white polypropylene plate, the second coating composition was spray-coated so that the dry coating film would be 12 μm thick, and then heat-cured at 140 °C for 20 minutes in a hot air drying furnace to obtain a test plate having a single second coating film formed on the white polypropylene plate. From the test plate having the single second coating film formed on the white polypropylene plate formed above, the second coating film was peeled off from the polypropylene plate to obtain a single second coating film. Using a U-3310 type spectrophotometer (manufactured by Hitachi), this single second coating film was measured in the wavelength scan mode in the range of 400 to 700 nm at a scan speed of 300 nm / min and a sampling interval of 10 nm. After that, the light transmittance of the single second coating film in each wavelength region was measured, and the average value of the measured values in the above wavelength range was calculated. The measurement results are shown in the following table.

[0143] Evaluation of the depth perception of the multilayer coating film The painted test plates having the multilayer coating films formed in each example and comparative example were visually observed and evaluated according to the following criteria. ○: A smooth depth feeling like a mirror surface can be felt from the multilayer coating film. ×: A smooth depth feeling like a mirror surface cannot be felt from the multilayer coating film.

[0144]

Table 1

[0145] For all the multilayer coating films of the examples, C*15 / L*15 was 3 or more, the C* value was 70 or more, and the granularity value (G value) was 1 or less. And all of the above multilayer coating films were of low lightness but high chroma, and a depth feeling was felt. Comparative Example 1 is a multilayer coating film in which C*15 / L*15 is less than 3, the C* value is less than 70, and the granularity value (G value) exceeds 1. In this Comparative Example 1, the second coating film contains a bright pigment. The multilayer coating film of Comparative Example 1 is a coating film in which the grain shape of the bright pigment is visible, has a slightly high lightness, and is inferior in depth. Comparative Example 2 is a multilayer coating film in which C*15 / L*15 is less than 3 and the granularity value (G value) exceeds 1. The multilayer coating film of Comparative Example 2 had a high chroma while also having a high lightness and was inferior in depth. Comparative Example 3 is a multilayer coating film composed of two layers, a first coating film and a clear coating film. The multilayer coating film of Comparative Example 3 had a low C*15 / L*15 and C* value and a high G value. The multilayer coating film of Comparative Example 3 is a coating film in which the grain shape of the bright pigment is visible, has a low chroma, a high lightness, and is inferior in depth.

Industrial Applicability

[0146] The multilayer coating film of the present disclosure is a coating film with excellent design properties, having a low lightness while having a high chroma, a smooth depth like a mirror surface, and a sense of thickness. The above multilayer coating film can be suitably used as a decorative coating film for various articles (for example, automobile bodies such as passenger cars, trucks, motorcycles, buses, and their parts).

Claims

1. 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 coating composition containing a first coating film-forming resin and a bright 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 multilayer coating film has a C*15 / L*15 of 3 or more at an incident angle of 45° and a light-receiving angle of 15°, a C* value of 70 or more at an incident angle of 45° and a light-receiving angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°, the second coating film, as a single coating film, has an average light transmittance of 19% or less in the wavelength range of 400 nm or more and 700 nm or less, and the content of the bright pigment in the second coating composition is less than 0.5 parts by mass with respect to 100 parts by mass of the resin solid content.

2. The multilayer coating film according to Claim 1, wherein the multilayer coating film has a C*15 / FF of 15 or more at an incident angle of 45° and a light-receiving angle of 15°.

3. The film thickness of the first coating film is in the range of 1 to 9 μm, the bright pigment contained in the first coating film has an average particle diameter in the range of 2 to 13 μm, an average thickness in the range of 0.01 to 0.1 μm, and an aspect ratio in the range of 50 to 300, The multilayer coating film according to Claim 1 or 2.

4. The multilayer coating film according to any one of Claims 1 to 3, wherein the hue of the multilayer coating film in the Munsell color system is 1B to 10PB.

5. A method for forming a multilayer coating film by sequentially coating an object to be coated with a first coating composition, a second coating composition, and a clear coating composition, wherein the first coating composition contains a first coating film-forming resin and a bright pigment, the second coating composition contains a second coating film-forming resin and a coloring pigment, the multilayer coating film has a C*15 / L*15 of 3 or more at an incident angle of 45° and a light-receiving angle of 15°, a C* value of 70 or more at an incident angle of 45° and a light-receiving angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°, the second coating film formed by curing the second coating composition, as a single coating film, has an average light transmittance of 19% or less in the wavelength range of 400 nm or more and 700 nm or less, and the content of the bright pigment in the second coating composition is less than 0.5 parts by mass with respect to 100 parts by mass of the resin solid content.

6. A method for forming a multilayer coating film by sequentially coating an object to be coated with a first coating composition, a second coating composition, and a clear coating composition in a wet-on-wet manner, The first coating composition contains a first film-forming resin and a bright pigment. The second coating composition contains a second film-forming resin and a colored pigment. In the multilayer coating film, C*15 / L*15 at an incident angle of 45° and a light-receiving angle of 15° is 3 or more, the C* value at an incident angle of 45° and a light-receiving angle of 15° is 70 or more, and the granularity value (G value) at an incident angle of 45° is 1 or less. The second coating film formed by curing the second coating composition has an average light transmittance of 19% or less in the wavelength range of 400 nm or more and 700 nm or less as a single coating film. A method for forming a multilayer coating film, wherein the content of the bright pigment in the second coating composition is less than 0.5 parts by mass with respect to 100 parts by mass of the resin solid content.

7. An article having the multilayer coating film according to any one of Claims 1 to 4.

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