JP7688968B2 - Multi-layer coating film and method for forming multi-layer coating film - Google Patents

Description

The present invention relates to a multi-layer coating film and a method for forming a multi-layer coating film.

On the surface of a coated object such as an automobile body, multiple coating films with various functions are formed in sequence to protect the coated object while at the same time imparting a beautiful appearance and excellent design. A common method for forming such multiple coating films is to form an undercoat coating film such as an electrodeposition coating film on the substrate, which has excellent electrical conductivity, and then, on top of that, a middle coating film and a topcoat coating film are formed as required. Of these coating films, it is the topcoat coating film, which consists of a base coating film and a clear coating film, that has a major influence on the appearance and design of the coating film. In particular, in the case of automobiles, the appearance and design of the topcoat coating film, which consists of a base coating film and a clear coating film formed on the body of the vehicle, is extremely important.

The appearance of the paint film formed on an automobile plays a large role in the automobile's appearance value, such as its sense of luxury. Furthermore, automobile buyers tend to seek automobiles with paint films that excel in design. Diversifying consumer tastes and a desire for originality have created a demand for more distinctive designs.

For example, JP 2016-107256 A (Patent Document 1) describes a method for forming a multilayer coating film including a first colored coating film, a second colored coating film, and a clear coating film by sequentially coating a first colored coating film (X), a second colored coating film (Y), and a clear coating film on a substrate; the first colored coating film (X) contains a vehicle-forming resin (A1), a scaly luster pigment (B1), and a colored pigment (C1), and the total amount of the scaly luster pigment (B1) and the colored pigment (C1) is 40 to 120 parts by mass based on 100 parts by mass of the solid content of the vehicle-forming resin (A1); the second colored coating film (Y) contains a vehicle-forming resin (A1), a scaly luster pigment (B1), and a colored pigment (C1), and the total amount of the scaly luster pigment (B1) and the colored pigment (C1) is 40 to 120 parts by mass based on 100 parts by mass of the solid content of the vehicle-forming resin (A1); A method for forming a multilayer coating film is described, which contains a vehicle-forming resin (A2), a scaly luster pigment (B2), and a coloring pigment (C2), and the total amount of the scaly luster 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 vehicle-forming resin (A2); and the total amount of the scaly luster pigment (B1), the coloring pigment (C1), the scaly luster pigment (B2), and the coloring pigment (C2) is 60 to 120 parts by mass based on a total of 200 parts by mass of 100 parts by mass of the solid content of the vehicle-forming resin (A1) and 100 parts by mass of the solid content of the vehicle-forming resin (A2) (Claim 1). Patent Document 1 describes that this method can form a multilayer coating film with high saturation, excellent adhesion, and excellent finish.

JP 2008-62198 A (Patent Document 2) describes a method for forming a multilayer coating film by forming a first base coating film and a first clear coating film by wet-on-wet painting, baking and hardening them, and then forming a second base coating film and a second clear coating film by wet-on-wet painting, baking and hardening them (Claim 1). Patent Document 2 describes that the above-mentioned formation method can provide a method for forming a multilayer coating film that has a sense of depth, is excellent in design, and has little hue variation due to film thickness variation.

JP 2016-107256 A JP 2008-62198 A

The invention of Patent Document 1 above states that a multilayer coating film with high saturation and excellent adhesion and finish can be formed. Here, the first colored paint (X) and the second colored paint (Y) used in forming the multilayer coating film of Patent Document 1 are both paints containing both color pigments and luster pigments. In addition, the invention of Patent Document 2 above states that a multilayer coating film with excellent design with a sense of depth and small hue changes due to film thickness fluctuations can be formed. This multilayer coating film of Patent Document 2 is a coating film composed of four layers, and is formed by painting a first base and a first clear, baking and hardening them, and then painting a second base and a second clear, and baking and hardening them.

In contrast to the above patent documents, the present invention aims to provide a multi-layer coating film that has low brightness and high chroma and is composed of three layers: a first coating film, a second coating film, and a clear coating film.

In order to solve the above problems, the present invention provides the following aspects.
[1]
A multi-layer coating film having a first coating film, a second coating film, and a clear coating film in this order,
The first coating film is a cured coating film of a first coating composition containing a first coating film-forming resin and a luster pigment,
The second coating film is a cured coating film of a second coating composition containing a second coating film-forming resin and a color pigment,
The above multilayer coating film has a C*15/L*15 of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°.
[2]
The multilayer coating film according to [1], wherein C*15/FF at an incident angle of 45° and an acceptance angle of 15° is 15 or more.
[3]
The second coating film, as a single coating film, has an average light transmittance of 30% or less in a wavelength range of 400 nm or more and 700 nm or less.
A multi-layer coating film of [1] or [2].
[4]
The thickness of the first coating film is within the range of 1 to 9 μm,
The luster pigment contained in the first coating film has an average particle size 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] A multilayer coating film.
[5]
The multilayer coating film according to any one of [1] to [4], wherein the multilayer coating film has a hue of 1B to 10PB in the Munsell color system.
[6]
The content of the glitter pigment in the second coating composition is less than 0.5 parts by mass per 100 parts by mass of resin solids.
[1] to [5] A multilayer coating film.
[7]
A method for forming a multi-layer coating film by successively coating a first coating composition, a second coating composition and a clear coating composition on a substrate, comprising the steps of:
The first coating composition comprises a first film-forming resin and a luster pigment,
The second coating composition comprises a second film-forming resin and a color pigment,
The multilayer coating film has a C*15/L*15 of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°.
[8]
A method for forming a multi-layer coating film by successively applying a first coating composition, a second coating composition and a clear coating composition to a substrate in a wet-on-wet manner, comprising:
The first coating composition comprises a first film-forming resin and a luster pigment,
The second coating composition comprises a second film-forming resin and a color pigment,
The multilayer coating film has a C*15/L*15 ratio of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) of 1 or less at an incident angle of 45°.
A method for forming a multi-layer coating.
[9]
[1] to [6] An article having a multilayer coating film.

According to this disclosure, it is possible to form a multi-layer coating film that has low brightness but high saturation and deep color tones.

The researchers of the present invention have conducted research with the aim of developing a coating film with a high chroma tone (dark, vivid tone) in a deep color with low brightness. For this reason, they have investigated a method for forming a coating film with low brightness, high chroma, and a sense of depth in a single color known as a solid color.

One method for giving a sense of depth to a paint film is to increase the flip-flop value by changing the reflection intensity brightness of the highlight and shade positions. This causes the brightness of the paint film to change depending on the viewing angle, creating a sense of shadow and depth.

However, when aluminum pigment, a type of photoluminescent pigment, was added to a coating with the aim of imparting a sense of shadow to a dark-colored coating, the color (silver) of the aluminum pigment itself was added, which increased the brightness. Furthermore, by adding aluminum pigment, the granular texture of the photoluminescent pigment became visible, resulting in a so-called metallic-toned coating. On the other hand, when mica was added to a coating as a photoluminescent pigment, the entire coating became cloudy and the saturation decreased. Thus, it was difficult to impart a sense of shadow and depth while maintaining high saturation in a coating with a low brightness and dark tone.

The present inventors conducted research with the aim of solving the above problems. They discovered through experiments that by combining a specific first coating film and second coating film, it is possible to provide a multi-layer coating film that is low in brightness and high in chroma and is composed of three layers: a first coating film, a second coating film, and a clear coating film, and thus completed the present invention. Below, the first coating composition that forms the first coating film and the second coating composition that forms the second coating film are described in order.

First Coating Composition The first coating film in the present disclosure is a cured coating film of a first coating composition. The first coating composition is a coating composition that contains a first coating film-forming resin and a luster pigment.

The first coating composition includes a first coating film-forming resin. Examples of the first coating film-forming resin include acrylic resin, polyester resin, polyurethane resin, epoxy resin, fluororesin, and silicone resin. The first coating composition may be an aqueous coating composition or a solvent-based coating composition.

When the first coating composition is an aqueous coating composition, the first coating film-forming resin preferably contains, for example, an acrylic resin emulsion (including an acrylic silicone resin emulsion, an acrylic urethane resin emulsion, etc.), an acrylic resin dispersion (including an acrylic silicone resin dispersion, an acrylic urethane resin dispersion, etc.), a water-soluble acrylic resin, a polyester resin dispersion, a polyurethane resin dispersion, an epoxy resin dispersion, etc. These resins may be used alone or in combination of two or more kinds. The resins can be prepared by methods commonly used by those skilled in the art. Commercially available products may be used as the resins.

Preferred embodiments include, 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, and an embodiment using an acrylic resin emulsion, a water-soluble acrylic resin, and a polyurethane resin dispersion.

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)acrylic acid esters, α,β-ethylenically unsaturated monomers having an acid group, and α,β-ethylenically unsaturated monomers having a hydroxyl group.

Examples of the (meth)acrylic acid 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, and dihydrodicyclopentadienyl (meth)acrylate. In this specification, (meth)acrylic acid esters refer to both acrylic acid esters and methacrylic acid esters.

Examples of α,β-ethylenically unsaturated monomers having an acid group include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethyl phthalic acid, 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, and 2,4-dihydroxy-4'-vinylbenzophenone.

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 of these with ε-caprolactone. Among these, preferred are hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethyl (meth)acrylate, and adducts of these with ε-caprolactone.

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 selected from various types as necessary depending on the purpose.

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 added dropwise while heating and stirring. An α,β-ethylenically unsaturated monomer mixture previously emulsified using an emulsifier and water may also be added dropwise in the same manner.

The polymerization initiator and emulsifier may be those commonly used by those skilled in the art. 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. may 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.

The acrylic resin emulsion preferably has a number average molecular weight of 3000 or less. The acrylic resin emulsion preferably has a hydroxyl value (solid content hydroxyl value) of 20 mgKOH/g or less and 180 mgKOH/g or less, and an acid value (solid content acid value) of 1 mgKOH/g or less and 80 mgKOH/g or less.

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

The water-soluble acrylic resin can be prepared, for example, by solution polymerizing a monomer mixture containing an α,β-ethylenically unsaturated monomer that can be used to prepare the above-mentioned acrylic resin emulsion, and then dissolving the monomer in water with a basic compound. The acrylic resin dispersion can be prepared, for example, by solution polymerizing a monomer mixture containing an α,β-ethylenically unsaturated monomer that can be used to prepare the above-mentioned acrylic resin emulsion, and then dispersing the monomer in water with a basic compound.

The polyester resin dispersion can be prepared, for example, by condensing a polyhydric alcohol component with a polybasic acid component and dispersing with a basic compound. The polyurethane resin dispersion 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, using a chain extender and a polymerization terminator as necessary, and dissolving or dispersing the resulting polymer in water.

When the first coating composition is an aqueous coating composition, it is preferable to use a curing agent that reacts with the first coating film-forming resin. Such a curing agent is a coating film-forming component that reacts with the first coating 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, a metal ion, 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.

The melamine resin may 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 (alkyl ether groups, methylol groups, etc.) are bonded to the periphery of a melamine nucleus (triazine nucleus) via three nitrogen atoms. The above melamine resin is generally composed of a polynuclear body in which multiple melamine nuclei are bonded to each other. On the other hand, the above melamine resin may be a mononuclear body consisting of one melamine nucleus.

Commercially available products may be used as the melamine resin. Specific examples of commercially available products include the Cymel series (product 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, and Cymel 1141; and the U-Ban (product name) series manufactured by Mitsui Chemicals. These may be used alone or in combination of two or more types.

Blocked isocyanate compounds can be prepared by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, or isophorone diisocyanate. When heated, the blocking agent dissociates to generate isocyanate groups, which react with the functional groups in the resin components to harden.

The amount of hardener is preferably 10 to 80% by mass, more preferably 15 to 60% by mass, based on the paint resin solids mass (the solids mass of the film-forming components including the film-forming resin and the hardener).

The first paint composition contains a luster pigment. Examples of the luster pigment include metallic luster pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and alloys thereof, as well as interference mica pigments, white mica pigments, graphite pigments, and glass flake pigments. In the first paint composition of the present disclosure, it is preferable that the luster pigment is an aluminum pigment from the viewpoint of the design of the resulting multilayer coating film.

The above-mentioned luster pigment preferably has an average particle size of 2 to 13 μm, more preferably 4 to 11 μm. The above-mentioned luster pigment also preferably has an average thickness of 0.01 to 0.1 μm, more preferably 0.02 to 0.08 μm. When the average particle size and average thickness of the luster pigment satisfy the above conditions, a good sense of density is imparted to the first coating film, which has the advantage of allowing the desired design to be suitably obtained in the multi-layer coating film.

The average particle size of the above-mentioned glittering pigment means the average long diameter. The average particle size can be measured by observing the glittering pigment with a shape analysis laser microscope (such as Keyence VK-X 250) and calculating the number average value of the maximum length (long diameter) of 100 arbitrarily selected pigment particles.

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

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

When the above-mentioned luster pigment is an aluminum pigment, it may be subjected to a surface treatment as necessary. Examples of surface treatments that can be applied to aluminum pigments include surface treatments using metal oxide compounds, surface treatments using phosphorus compounds, surface treatments using amine compounds, and surface treatments using silane compounds.

The metal oxide compounds include, for example, metal oxides containing at least a transition metal element as a constituent metal, and their alkali metal salts and ammonium salts. Specific examples include molybdenum trioxide, molybdic acid, alkali metal molybdate salts, ammonium molybdate salts, vanadic acid, alkali metal vanadate salts, and ammonium vanadate salts. The alkali metals are not particularly limited, but include, for example, sodium and potassium. Among them, it is preferable to use, as the metal oxide compounds, one or more metal oxide compounds selected from the group consisting of molybdic acid, alkali metal molybdate salts, ammonium molybdate salts, vanadic acid, alkali metal vanadate salts, and ammonium vanadate salts.

Examples of the 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 kinds.

Examples of the 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, and aromatic group-containing tertiary amines. These amine compounds may have a substituent (e.g., a hydroxyl group, etc.) as necessary. These amine compounds may be used alone or in combination of two or more kinds.

Examples of the silane compounds include 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. These silane compounds may be used alone or in combination of two or more.

The above surface treatments can be carried out under treatment conditions commonly used by those skilled in the art. Only one of the above surface treatments may be carried out, or two or more of them may be used in combination.

In particular, when the luster pigment contained in the first coating composition is an aluminum pigment and has an average particle size of, for example, 2 to 13 μm, more preferably 4 to 11 μm, the above surface treatment has the advantage of improving the stability of the first coating composition without impairing the appearance of the multi-layer coating film that is formed.

As the above-mentioned glittering pigment, a commercially available product may be used.
Toyo Aluminum Co., Ltd.'s Alpaste 46 series, 97 series (e.g., 97-0510), 01 series (e.g., 01-0651), etc.;
Asahi Kasei aluminum paste FD series, etc.
Metallux 4860 manufactured by Ecart, etc.;
Examples include

The amount of the above-mentioned luster pigment is preferably within the range of 5 to 45 parts by mass, and more preferably within the range of 15 to 35 parts by mass, per 100 parts by mass of the resin solids content of the first coating film-forming resin.

The first coating composition may contain other pigments as required in addition to the luster pigment. However, the amount of these other pigments must not impair the performance of the first coating film. Examples of the other pigments include color pigments and extender pigments. Examples of the extender pigments include calcium carbonate, barium sulfate, clay, and talc. The pigments may further include an anti-rust pigment as required.

As the color pigment, various inorganic color pigments and organic color pigments can be used. In this specification, the term "color pigment" includes chromatic color pigments and achromatic color pigments.
Examples of color pigments include black pigments such as carbon black, graphite, iron black, composite metal oxides such as iron chromium and bismuth manganese, perylene-based black pigments, and azomethiazo-based pigments;
Blue pigments such as Prussian blue, ultramarine blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue;
yellow pigments, such as yellow lead, synthetic yellow iron oxide, bismuth vanadate, titanium yellow, zinc yellow, ochre, monoazo yellow, disazo yellow, isoindolinone yellow, metal complex azo yellow, quinophthalone yellow, and benzimidazolone yellow;
red pigments such as iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, and perylene maroon;
Orange pigments such as quinacridone magenta, anthranthrone orange, dianthraquinonyl red, pyrazolone orange, benzimidazolone orange, and diketopyrrolopyrrole chrome vermilion;
green pigments such as chlorinated phthalocyanine green and brominated phthalocyanine green;
violet pigments such as dioxazine violet and perylene violet;
White pigments such as titanium dioxide;
Some examples include:

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 conditioners, viscosity control agents, thickeners, antioxidants, UV inhibitors, and defoamers. For example, the use of a viscosity control agent can impart thixotropy and adjust the paint workability. Examples of viscosity control agents include crosslinked or non-crosslinked resin particles, polyamide-based agents such as swollen dispersions of fatty acid amides, amide-based fatty acids, and phosphates of long-chain polyaminoamides, polyethylene-based agents such as colloidal swollen dispersions of polyethylene oxide, organic acid smectite clays, and organic bentonite-based agents such as montmorillonite. When these additives are used, they can be used in amounts commonly used by those skilled in the art.

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

The aqueous first coating composition may contain water as a solvent, and optionally a water-soluble or water-miscible organic solvent.

The above-mentioned water-based first paint composition can be produced by a method commonly used by those skilled in the art, such as kneading and dispersing the first film-forming resin, the luster pigment, the curing agent, and other components and additives as required, using a disperser, homogenizer, kneader, etc. In the above-mentioned production method, it is preferable to prepare in advance a paste containing the luster pigment and, as required, a pigment dispersant, and mix them. As the pigment dispersant, a commercially available pigment dispersant can be used.

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

The acrylic resin can be prepared, for example, by solution polymerization of a monomer mixture containing an α,β-ethylenically unsaturated monomer. 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. The hydroxyl value (solid content hydroxyl value) is also preferably 10 to 200 mgKOH/g.

Commercially available acrylic resins may be used. Examples of commercially available products include the Dianale HR series manufactured by Mitsubishi Rayon Co., Ltd.

The amount of acrylic resin is preferably 30 to 80% by mass, and more preferably 35 to 70% by mass, based on the paint resin solids mass (solids mass of the coating film-forming components).

For example, a hydroxyl-containing polyester resin can be used as the polyester resin. The hydroxyl-containing polyester resin can be prepared by polycondensation of an acid component such as a polycarboxylic acid and/or an acid anhydride with a polyhydric alcohol.

When the first coating composition is a solvent-based coating composition, it is preferable to use a curing agent that reacts with the first coating film-forming resin. As the curing agent, a melamine resin, a blocked isocyanate compound, or the like can be used. These may be used alone or in combination of two or more types. 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.

The curing agent preferably contains a melamine resin. The melamine resin is not particularly limited, and methylated melamine resin, butylated melamine resin, methyl-butyl mixed melamine resin, etc. can be used. Examples include the Cymel series commercially available from Allnex, and the U-Ban series commercially available from Mitsui Chemicals. The amount of melamine resin is preferably 10 to 50% by mass, and more preferably 15 to 40% by mass, based on the paint resin solids mass (the solids mass of the coating film-forming components including the coating film-forming resin and the curing agent).

The curing agent preferably further contains a blocked isocyanate compound. The blocked isocyanate compound can be prepared by addition reaction of a blocking compound such as a compound having an active methylene group, a ketone compound, or a caprolactam compound with a polyisocyanate. A commercially available product may be used as the blocked isocyanate compound. Examples of commercially available products include the Duranate series manufactured by Asahi Kasei Corporation and the Sumidur series manufactured by Sumika Covestro Urethane Co., Ltd.

The amount of the blocked isocyanate compound contained in the first coating composition is preferably 10 to 30% by mass, and more preferably 15 to 25% by mass, based on the paint resin solids mass (the solids mass of the coating film-forming components including the coating film-forming resin and the curing agent).

The solvent-based first coating composition contains the first coating film-forming resin and a luster pigment. The luster pigment may be the same as that described above. In addition to the above components, the solvent-based first coating composition may contain additives that are commonly used by those skilled in the art, such as a curing catalyst, a surface conditioner, an ultraviolet absorber, and an antioxidant.

The solids concentration and viscosity of the solvent-based first coating composition can be appropriately adjusted by diluting it with an organic solvent when applying. Examples of organic solvents that can be used include ester-based solvents, ether-based solvents, alcohol-based solvents, ketone-based solvents, aliphatic hydrocarbon-based solvents, and aromatic solvents.

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

The above-mentioned solvent-based first paint composition can be produced by a method commonly used by those skilled in the art, such as kneading and dispersing the first film-forming resin, the curing agent, the pigment, the phosphate group-containing organic compound, and the additives using a disperser, homogenizer, kneader, etc. In the above-mentioned production method, it is preferable to prepare in advance a paste containing the glitter pigment and, if necessary, a pigment dispersant, and mix them.

Second Coating Composition The second coating film in the present disclosure is a cured coating film of the second coating composition. The 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 first coating composition. Such a second coating composition can be prepared by the same procedure as the first coating composition.

The second film-forming resin may be the same as the first film-forming resin. The first film-forming resin and the second film-forming resin may have the same resin composition or different resin compositions.

The second coating composition contains a pigment. Examples of the pigment include color pigments and extender pigments. Examples of the extender pigment include calcium carbonate, barium sulfate, clay, and talc.

As the color pigment contained in the second coating composition, various inorganic color pigments and organic color pigments can be used. As the color pigment, the above-mentioned color pigments can be used. The color pigment can be appropriately selected according to the color tone of the multi-layer coating film. For example, when the hue of the multi-layer coating film is 1B to 10PB in the Munsell color system,
blue pigments such as cyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue;
green pigments such as chlorinated phthalocyanine green and brominated phthalocyanine green;
Purple pigments such as dioxazine violet and perylene violet are used as the main pigment, and black pigments such as carbon black, graphite, iron black, composite metal oxides such as iron chromium and bismuth manganese, perylene black pigments, and azomethiazo pigments are used as necessary.
red pigments such as iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, and perylene maroon;
yellow pigments, such as yellow lead, synthetic yellow iron oxide, bismuth vanadate, titanium yellow, zinc yellow, ochre, monoazo yellow, disazo yellow, isoindolinone yellow, metal complex azo yellow, quinophthalone yellow, and benzimidazolone yellow;
Orange pigments such as quinacridone magenta, anthranthrone orange, dianthraquinonyl red, pyrazolone orange, benzimidazolone orange, and diketopyrrolopyrrole chrome vermilion;
It is preferable to use the following appropriately.

In the present disclosure, the second coating film formed by applying and curing the second paint 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 the light transmittance of the single coating film.
The second coating composition for forming such a second coating film preferably contains the above-mentioned blue pigment as a coloring pigment, and more preferably contains one or more of cyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue.

The suitable amount of the color pigment contained in the second coating composition is preferably selected appropriately depending on the type of color pigment, etc. For example, the amount of the color pigment contained in the second coating film can be selected so that it is 1 to 25 parts by mass per 100 parts by mass of resin solids. The above content may be, for example, 2 to 20 parts by mass. By appropriately selecting the amount of the color pigment contained in the second coating film depending on the type of color pigment, and by having the first coating film of the present disclosure, it is possible to design the resulting multilayer coating film so that its C*15/L*15 is 3 or more, its C* value is 70 or more, and its granularity value (G value) is 1 or less, thereby forming a multilayer coating film with high saturation and the desired design.

The second coating composition may contain pigments other than the color pigments. Examples of the pigments include the extender pigments and anti-rust pigments exemplified in the first coating composition.

In the present disclosure, it is preferable that the second coating composition is substantially free of a luster pigment. For example, the luster pigment content in the second coating composition is preferably less than 0.5 parts by mass, more preferably less than 0.3 parts by mass, and even more preferably less than 0.1 parts by mass, per 100 parts by mass of resin solids.

Multilayer Coating Film Formation 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 first coating composition, a second coating film which is a cured coating film of the second coating composition, and a clear coating film.

In forming the multilayer coating film of the present disclosure, the substrate to which the coating composition is applied is not particularly limited, and examples thereof include metals, plastics, and foams. The coating composition can be used particularly advantageously on metals and castings, and can be particularly suitably used on metals that can be electrocoated. Examples of such metals include iron, copper, aluminum, tin, zinc, and alloys containing these metals. These substrates may be molded articles. Specific examples of molded articles include automobile bodies and parts thereof, such as passenger cars, trucks, motorcycles, and buses. It is more preferable that the substrates, such as the metals, are chemically treated with a phosphoric acid-based chemical conversion treatment agent or a zirconium-based chemical conversion treatment agent before electrocoating. It is preferable that a cured electrodeposition coating film is formed on a substrate that has been subjected to chemical conversion treatment as required. Either a cationic or anionic electrodeposition coating composition can be used as the electrodeposition coating composition used to form the cured electrodeposition coating film. It is preferable to use a cationic electrodeposition coating composition as the electrodeposition coating composition, since it is possible to form a coating film with better corrosion resistance.

If necessary, the above-mentioned substrate may further have an intermediate coating film formed on the cured electrodeposition coating film. An intermediate coating composition is used to form the intermediate coating film. As the intermediate coating composition, for example, a coating composition containing a film-forming resin, a curing agent, various organic and/or inorganic coloring components and extender pigments can be used. The film-forming resin and the curing agent are not particularly limited, and specifically, the film-forming resins and curing agents listed in the above-mentioned aqueous coating composition can be used. As the film-forming resin of the intermediate coating composition, a combination of an acrylic resin and/or a polyester resin and an amino resin and/or an isocyanate is preferably used from the viewpoint of various properties of the obtained intermediate coating film.

Examples of methods for forming a coating film using the first and second coating compositions include the following methods.
- A method in which the above-mentioned first coating composition and second coating composition are applied to a substrate in sequence, and then a clear coating composition is applied. In such coating, the first coating composition may be applied and heat cured, and then the second coating composition may be applied and heat cured. Alternatively, the first coating composition may be applied, and the applied coating film may be applied wet-on-wet while the applied coating film is in an uncured state, and then the second coating composition may be applied and heat cured. In the above-mentioned wet-on-wet coating, preheating may be performed between coatings as necessary. Alternatively, the first coating composition and the second coating composition may be applied in sequence, and then dried at room temperature. Then, a clear coating composition is applied to the second coating film obtained by applying the second coating composition to provide a clear coating film.
A method of successively coating a first coating composition, a second coating composition, and a clear coating composition on a substrate by wet-on-wet coating. More specifically, this coating is a method of successively coating a first coating composition, a second coating composition, and a clear coating by wet-on-wet coating to form an uncured first coating film, a second coating film, and a clear coating film, and then heat-curing these uncured coating films at once. In the above wet-on-wet coating, preheating may be performed between coats as necessary.

The first and second coating compositions can be applied to the substrate by a method commonly used in the coating field. Examples of the coating method include air spray coating, airless spray coating, electrostatic spray coating, multi-stage coating (preferably two-stage coating) using air electrostatic spray coating, and coating using a combination of air electrostatic spray coating and a rotary atomizing electrostatic coating machine.

The first coating composition is preferably applied so that the thickness of the first coating film after curing is within the range of 1 to 9 μm, and more preferably within the range of 2 to 7 μm. The second coating composition is preferably applied so that the thickness of the second coating film after curing is within the range of 7 to 30 μm, and more preferably within the range of 10 to 25 μm.

When applying and heat-curing the first and second coating compositions, the heating temperature and time can be appropriately selected according to the composition of the coating composition (water-based or solvent-based) and the type of substrate. 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 to 60 minutes, preferably in the range of 10 to 30 minutes.

The clear coating composition is not particularly limited, and examples include solvent-based, water-based, and powder-based clear coating compositions.

Preferred examples of the above-mentioned solvent-based clear coating composition include, from the standpoint of transparency or acid etching resistance, a combination of an acrylic resin and/or a polyester resin with an amino resin and/or an isocyanate, or an acrylic resin and/or a polyester resin with a carboxylic acid/epoxy curing system.

An example of a water-based clear coating composition is one that contains a resin that has been neutralized with a base to make the film-forming resin water-based, as given above as an example of a solvent-based clear coating composition. This neutralization can be carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine before or after polymerization.

These solvent-based and water-based clear coating compositions preferably contain a viscosity control agent to ensure ease of coating work. Viscosity control agents that generally exhibit thixotropy can be used. Examples of viscosity control agents that can be used include those listed in the section on water-based coating compositions. Additionally, additives that are commonly used in the coating field may be included as necessary.

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

The clear coating composition can be applied using a coating method known to those skilled in the art in accordance with the coating form of the clear coating composition. The dry thickness of the clear coating film formed by applying the above-mentioned clear coating composition is generally preferably 10 to 80 μm, and more preferably 20 to 60 μm.

A cured clear coating film can be formed by heating and curing the uncured clear coating film obtained by coating the clear coating composition. When the clear coating composition is coated on an uncured second base coating film, the uncured coating film is heat cured by heating. From the viewpoint of curability and physical properties of the resulting multilayer coating film, the heat curing temperature is preferably set to 80 to 180°C, and more preferably set to 120 to 160°C. The heat curing time can be set arbitrarily according to the above temperature. Examples of heat curing conditions include heating at a heat curing temperature of 120°C to 160°C for 10 to 30 minutes.
Depending on the type of coating composition, the coating composition may be applied, then dried at room temperature to form a coating film, and then, for example, a reactive curing clear coating composition may be applied to provide a clear coating film.

The multilayer coating film of the present disclosure has a condition that C*15/L*15 at an incident angle of 45° and an acceptance angle of 15° is 3 or more. The chroma C* and lightness L* are parameters in the L*C*h color system and can be determined in accordance with JIS Z8729. This L*C*h color system is a color system established 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 the hue angle.
Saturation C* means that the measured substance becomes brighter as its value increases, and becomes duller as its value decreases. Lightness L* means that the measured substance becomes brighter as its value increases, and becomes darker as its value decreases. The saturation C* and lightness L* can be measured using a commercially available multi-angle spectrophotometer. An example of a multi-angle spectrophotometer is the BYK-maci (manufactured by BYK).

In the above chroma C* and lightness L* for an incidence angle of 45° and an acceptance angle of 15°, the incidence angle and acceptance angle refer to the acceptance angle at a position 15° in the direction of the incidence angle from the specularly reflected light, which is irradiated at an angle of 45° to the cured coating film, with the position of the specularly reflected light being set at 0°.

In this specification, the measurement of the chroma C* and lightness L* of the multilayer coating film refers to values measured using a 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, the first coating composition is spray-coated on a steel plate coated with a cationic electrodeposition coating composition and a dark gray cured undercoat coating film to a dry film thickness of 4 μm, then the second coating composition is spray-coated wet-on-wet to a dry film thickness of 12 μm, then the clear coating composition is spray-coated wet-on-wet to a dry film thickness of 35 μm, and then the uncured three-layer coating film is heated and cured at 140° C. for 20 minutes to obtain a multilayer coating film.

The above multi-layer coating film has a C*15/L*15 of 3 or more at an incident angle of 45° and an acceptance angle of 15°. It is more preferable that this C*15/L*15 is within the range of 4 to 7. If C*/L* is less than 3, the color received by the shade may appear dark, cloudy, or dull, and may lack depth.

The multi-layer coating film also has a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°. The C* value is preferably 80 or more, and the upper limit of C* is preferably 130. It is more preferable that the C* value is within the range of 90 to 120. If the C* value satisfies the above conditions, it is indicated that the multi-layer coating film has high chroma.

The multilayer coating film disclosed herein also preferably has a C*15/FF of 15 or greater at an incident angle of 45° and an acceptance angle of 15°.

The FF value is a flip-flop value, which indicates the degree of change in reflected light intensity according to the viewing angle (light receiving angle). The FF value is calculated 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. The L* value (L*(15°) value) at a light receiving angle of 15 degrees is specifically the L* value for light received at a position 15 degrees from the regular reflection angle relative 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). The L* value (L*(110°) value) at a light receiving angle of 110 degrees is also the L* value for light received at an angle of 110 degrees from the regular reflection angle in the direction of the measurement light, when the measurement light is irradiated in the same manner.

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

The larger the FF value, the greater the change in L* value (brightness) due to the observation angle (light receiving angle), and the smaller the FF value, the smaller the change in L* value (brightness) due to the observation angle (light receiving angle). In general metallic coatings, the larger the FF value and the greater the change in brightness due to the viewing angle, the greater the sense of shadow for the metallic coating.

In the multilayer coating film disclosed herein, a C*15/FF of 15 or more is an indicator that the C*15 value is sufficiently high relative to the change in lightness of the highlights/shades represented by the FF value, and that the coating has low lightness and high chroma.

The multi-layer coating film of the present disclosure also requires that the granularity value (G value) at an incidence angle of 45° is 1 or less. The granularity value (G value) is a value obtained by quantifying the granularity by diffuse lighting measurement. The granularity value (G value) is a value obtained by acquiring an image by a CCD chip under diffuse lighting in a white-painted hemisphere, analyzing the acquired image using a brightness level histogram, and expressing the uniformity of the light and dark areas as a value indicating a granularity. The granularity value (G value) is expressed in a range of 0 to 30, with a smaller value indicating finer particles and a larger value indicating more granular particles. In the multi-layer coating film of the present disclosure, a granularity value (G value) of 1 or less means that the coating film has almost no visible granularity in brightness.

The above granularity value (G value) can be measured using a glitter meter. An example of a glitter meter that can measure these values is the BYK-maci (manufactured by BYK).

In this specification, the granularity value (G value) is a value measured using a multilayer coating film consisting of a cured coating film of the first coating composition having a thickness of 4 μm, a cured coating film of the second coating composition having a thickness of 12 μm, and a clear coating film having a thickness of 35 μm. More specifically, the first coating composition is spray-coated to a dry thickness of 4 μm on a steel plate coated with a cationic electrodeposition coating composition and a dark gray cured undercoat coating film, and then the second coating composition is spray-coated wet-on-wet to a dry thickness of 12 μm, and then the clear coating composition is spray-coated wet-on-wet to a dry thickness of 35 μm, and then the uncured three-layer coating film is heated and cured at 140° C. for 20 minutes to obtain a multilayer coating film.

In the multilayer coating film disclosed herein, the second coating film obtained by curing the second paint 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.

The light transmittance of the second coating film is measured as follows. The prepared second paint composition is spray-coated onto a polypropylene plate to a predetermined dry film thickness, and the coating is cured by heating at 140°C for 20 minutes. The coating film is then peeled off from the polypropylene plate to prepare a second coating film alone. The second coating film alone used to measure the light transmittance means the coating film obtained by peeling off only the second coating film from the substrate, as described above.

The light transmittance can be determined by measuring the intensity ratio of the transmitted light when the incident light passes through the second coating film alone using a U-4100 spectrophotometer (Hitachi) in 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, and then calculating the average value of the measured values in the above wavelength range.

In the multilayer coating film disclosed herein, the average light transmittance of the second coating film alone measured as described above in the wavelength range of 400 nm to 700 nm is 30% or less, which has the advantage that the appearance of the coating film of the multilayer coating film composed of the first coating film, second coating film, and clear coating film described above can be improved in design with low brightness and high saturation.

The light transmittance of the second coating film is adjusted by adjusting the type and pigment mass concentration of the color pigment contained in the second paint, and by adjusting the film thickness of the coating film. Specifically, the light transmittance of the second coating film can be suitably adjusted by providing a second coating film having a film thickness of 7 to 30 μm using a second coating composition containing one or more color pigments selected from the group consisting of cyanine blue, threne blue, cobalt blue, copper phthalocyanine blue, and indanthrone blue, and having a color pigment content of 1 to 25 parts by mass per 100 parts by mass of resin solids, thereby providing an advantageous effect of favorably obtaining a multilayer coating film having the design targeted in this disclosure.

In the multilayer coating film of the present disclosure, it is preferable that the hue of the Munsell color system is 1B to 10PB. In the multilayer coating film of the present disclosure, when the above conditions are met and the hue of the Munsell color system also meets the above conditions, it can be said that the above hue is particularly suitable for the low brightness and high chroma design aimed at in this disclosure.

The Munsell color system is well known to those skilled in the art as the "method of representing color by three attributes" (JIS Z 8721), and classifies colors according to the three attributes of color: hue (H), lightness, and saturation.

In the Munsell color system, a hue (H) is represented by a combination of a symbol (R, Y, G, B, or P) on the Munsell color wheel and a number (such as 5 or 10). In the Munsell color wheel, "R" indicates red, "Y" indicates yellow, "G" indicates green, "B" indicates blue, and "P" indicates purple. In addition, intermediate hues between these, "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 on the Munsell color wheel. Then, by dividing each of these 10 hues into 10 equal parts, the 100 hue wheel of the Munsell color wheel (Munsell color wheel 100) is obtained. In the multilayer coating film of the present disclosure, when the hue of the Munsell color system is 1B to 10PB, the multilayer coating film can be said to have a hue that is recognized as blue.

In this disclosure, the hue (H) of the Munsell color system can be measured, for example, using a multi-angle spectrophotometer "CR-400" manufactured by Minolta.

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 low in brightness but high in chroma, a vivid, deep color, and a dark color. The multilayer coating film of the present disclosure also has a G value of 1 or less, resulting in a coating film with a subdued design with almost no granular shine.

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

The present invention will be described in more detail with reference to the following examples, but is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

Production Example 1 Production of Acrylic Resin Emulsion (Film-Forming Resin) 633 parts of deionized water was added to a reaction vessel and heated to 80° C. while mixing and stirring in a nitrogen stream. Next, a monomer mixture for the first stage consisting 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), and 105.00 parts by mass of hydroxyethyl methacrylate (HEMA), 25.00 parts by mass of Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 25.00 parts of Adeka Reasoap NE-20 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd.), and 400 parts of deionized water, and an initiator solution consisting of 1.2 parts of ammonium persulfate and 500 parts of deionized water were dropped into the reaction vessel in parallel over a period of 1.5 hours. After the dropwise addition was completed, the mixture was aged at the same temperature for 1 hour.
Further, 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 consisting of 10 parts of Aqualon HS-10 and 250 parts of deionized water, and an initiator solution consisting of 3.0 parts of ammonium persulfate and 500 parts of deionized water were dropped into the reaction vessel in parallel over 1.5 hours. After the dropwise addition was completed, the mixture was aged at the same temperature for 2 hours.
The mixture was then cooled to 40°C and filtered through a 400 mesh filter, after which 100 parts of deionized water and 1.6 parts of dimethylaminoethanol were added to adjust the pH to 6.5, yielding an acrylic resin emulsion having an average particle size of 150 nm, a nonvolatile content of 35%, a solid content acid value of 20 mgKOH/g, and a hydroxyl value of 100 mgKOH/g.

Production Example 2 Production of Phosphate Group-Containing Organic Compound A 1-L reaction vessel equipped with a stirrer, a temperature regulator, and a cooling tube was charged with 40 parts of ethoxypropanol, and 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, 40 parts of a solution obtained by dissolving 20 parts of Hosmer PP (acid phosphooxyhexa(oxypropylene)monomethacrylate manufactured by Unichemical Co., Ltd.) in 20 parts of ethoxypropanol, and 1.7 parts of azobisisobutyronitrile was added dropwise thereto at 120° C. for 3 hours, and stirring was further continued for 1 hour. The resulting phosphate group-containing organic compound had an acid value of 105 mgKOH/g, including a phosphate value of 55 mgKOH/g, a hydroxyl value of 60 mgKOH/g, a number average molecular weight of 6,000 and a nonvolatile content of 63%.

In the Examples of the present specification, the number average molecular weight was measured using a GPC apparatus "HLC8220GPC" (trade name, manufactured by Tosoh Corporation) and four columns, namely "Shodex KF-606M" and "Shodex KF-603" (both of which are trade names, manufactured by Showa Denko K.K.), under the conditions of 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 phosphate value of the phosphate group-containing organic compound were calculated based on the definition of acid value in JIS K5601 2-1 (the number of milligrams of potassium hydroxide (KOH) required to neutralize the free acid in 1 g of sample (non-volatile matter)). The hydroxyl value was calculated based on the definition of hydroxyl value in JIS K0070 (the number of milligrams of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl group when 1 g of sample is acetylated).

Example 1
Preparation of the first coating composition
Color pigment dispersion paste 20 parts of Shanin Blue G314 and 5 parts of Hostapalm Violet NFVP336 as color pigments, 18.6 parts of Dispex ^{(registered trademark)} Ultra PA 4550 (manufactured by BASF) as a pigment dispersant, 36.0 parts of ion-exchanged water, and 0.5 parts of BYK-011 as an antifoaming agent were mixed and dispersed with a stirrer such as a disper to obtain a color pigment dispersion paste.

182 parts of acrylic resin emulsion of the first coating composition 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 color 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%) per 100 parts by mass of resin solid content, 5 parts of phosphoric acid group-containing organic compound of Production Example 2, 0.4 parts of lauryl acid phosphate, 50 parts of butyl cellosolve, Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) To this was uniformly dispersed 5.5 parts (3 parts in terms of solids) of linoleic acid (Kishida Chemical Co., Ltd.), dimethylaminoethanol was added so that the pH was 8.1, and the mixture was diluted with deionized water to prepare an aqueous coating composition with a resin solids concentration of 12% by mass.

Preparation of second coating composition 182 parts of 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 color pigment dispersion paste prepared in the preparation of the first coating composition, 5 parts of phosphoric acid group-containing organic compound of Production Example 2, 0.4 parts of lauryl acid phosphate, 50 parts of butyl cellosolve, Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) 5.5 parts (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 was 8.1, and the mixture was diluted with deionized water to prepare an aqueous coating composition having a resin solid content concentration of 19% by mass.

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

The Munsell value of the multi-layer coating film formed was measured using a Minolta multi-angle spectrophotometer "CR-400" and found to be 7.5PB2/8.

Example 2
Preparation of first coating composition 182 parts of 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 size 10 μm, average thickness 0.06 μm, active ingredient 65%) per 100 parts by mass of resin solid content, 5 parts of phosphoric acid group-containing organic compound of Production Example 2, 0.4 parts of lauryl acid phosphate, 50 parts of butyl cellosolve, Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) A first coating composition having a resin solids concentration of 33 mass% was prepared by uniformly dispersing 5.5 parts (3 parts in terms of solids content) of cellulose acetate and 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) and adding dimethylaminoethanol to adjust the pH to 8.1. The composition was then diluted with deionized water to prepare a first coating composition having a resin solids concentration of 33 mass%.

Preparation of Second Coating Composition A second coating composition was prepared in the same manner as in Example 1, except that the amount of the pigment dispersion paste was changed to 180 parts.

Formation of a multi-layer coating film A multi-layer coating film was formed in the same manner as in Example 1, except that the first coating composition and the second coating composition obtained above were used.

The Munsell value of the multi-layer coating film formed was measured using a Minolta multi-angle spectrophotometer "CR-400" and found to be 7.5PB 2/7.

Comparative Example 1
Preparation of first coating composition In preparing the first coating composition, T-8650 (ground aluminum glitter pigment, manufactured by Nippon Boshū Kogyo Co., Ltd., average particle size 18 μm) was used as the glitter pigment in an amount of 3.3 parts per 100 parts by mass of resin solids. The first coating composition was prepared in the same manner as in Example 1.

Preparation of second coating composition 182 parts of 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 colored pigment dispersion paste prepared in Example 1, 0.01 parts of 09-0645 (aluminum bright pigment, manufactured by Nippon Boshoku Kogyo Co., Ltd., average particle size 20 μm) which is a glittering pigment, 0.4 parts of lauryl acid phosphate, 50 parts of butyl cellosolve, Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Shiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) 5.5 parts (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 was 8.1, and the mixture was diluted with deionized water to prepare an aqueous coating composition having a resin solid content concentration of 18% by mass.

Formation of a multi-layer coating film A multi-layer coating film was formed in the same manner as in Example 1, except that the first coating composition and the second coating composition obtained above were used.

The Munsell value of the multi-layer coating film was measured using a Minolta multi-angle spectrophotometer "CR-400" and found to be 7.5 PB.

Comparative Example 2
Preparation of first coating composition In preparing the first coating composition, 94-0642 (aluminum bright pigment, manufactured by Toyo Aluminum, average particle size 17 μm) was used as the luster pigment in an amount of 2.0 parts per 100 parts by mass of the resin solids. The first coating composition was prepared in the same manner as in Example 1.

Preparation of Second Coating Composition A second coating composition was prepared in the same manner as in Example 1, except that the amount of the pigment dispersion paste was changed from 90 parts to 50 parts.

Formation of a multi-layer coating film A multi-layer coating film was formed in the same manner as in Example 1, except that the first coating composition and the second coating composition obtained above were used.

The Munsell value of the multi-layer coating film was measured using a Minolta multi-angle spectrophotometer "CR-400" and found to be 7.5 PB.

Comparative Example 3
Preparation of Paint 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 bright pigment, manufactured by Toyo Aluminum, average particle size 15 μm) which is a glittering pigment, 0.4 parts of lauryl acid phosphate, 50 parts of butyl cellosolve, 5.5 parts of Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Shiyaku 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 was 8.1, and the mixture was diluted with deionized water to prepare an aqueous paint composition having a resin solid content concentration of 18% by mass.

Formation of multi-layer coating film A cationic electrodeposition coating composition "Power Top U-50" (manufactured by Nippon Paint Automotive Coatings) was electrodeposited on a zinc phosphate-treated dull steel plate measuring 0.8 mm in thickness, 30 cm in length and 40 cm in width, so that the dry film thickness was 20 μm, and the plate was baked at 160° C. for 30 minutes. On the plate, an intermediate coating composition "OP-30P Middle Gray" (manufactured by Nippon Paint Automotive Coatings, polyester-melamine paint, pre-diluted for 25 seconds (measured at 20° C. using a No. 4 Ford cup)) was air spray painted using an air spray gun W-101-132G manufactured by Anest Iwata so that the dry film thickness was 35 μm, and then the plate was baked and cured at 140° C. for 30 minutes to form a cured intermediate coating film having a brightness of 60.
Next, the coating composition prepared above was air spray coated at a room temperature of 23° C. and a humidity of 68% so as to give a dry film thickness of 12 μm. After setting for 4 minutes, the coating was preheated at 80° C. for 5 minutes.
After the preheating, the coated plate was cooled to room temperature, and a clear coating of Macflow-O-1810 (a solvent-based clear coating made by Nippon Paint Automotive Coatings Co., Ltd.) was applied by air spray to a dry film thickness of 35 μm, and the plate was left to set for 7 minutes. The coated plate was then baked in a dryer at 140° C. for 30 minutes to obtain a coated test plate having a multi-layer coating film.

The Munsell value of the multi-layer coating film formed was measured using a Minolta multi-angle spectrophotometer "CR-400" and found to be 7.5PB 8/4.

The multi-layer coating films formed in the above examples and comparative examples were used to carry out the following evaluations. The evaluation results are shown in the table below.

Measurement of chroma C* of multi-layer coating film and calculation of C*15/L*15 Using the coating test plate having the multi-layer coating film formed in each Example and Comparative Example, the chroma C* value and the lightness L* value at an incident angle of 45° and an acceptance angle of 15° were measured with a multi-angle spectrophotometer BYK-maci (manufactured by BYK Corporation). Using the chroma C* value and the lightness L* value measured above, C*15/L*15 was calculated.

Calculation of C*/FF for multi-layer coating
Measurement of FF value of multilayer coating film For the coated test panels having the multilayer coating film formed in each Example and Comparative Example, the L* value at an acceptance angle of 15 degrees (L*(15°) value) and the L* value at an acceptance angle of 110 degrees (L*(110°) value) at an incidence angle of 45 degrees were measured using a multi-angle spectrophotometer BYK-maci (manufactured by BYK Corporation), and the FF value was calculated by the following formula.
FF value = L*(15°) value/L*(110°) value

The C*15/FF was calculated using the obtained FF value and the C*15 value measured above.

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

Evaluation of Depth of Multilayer Coating Films The coated test panels having the multilayer coating films formed in each of the Examples and Comparative Examples were visually observed and evaluated according to the following criteria.

○: The multi-layer coating film gives a smooth, deep feel like a mirror surface.
×: The multi-layer coating does not give a smooth, deep, mirror-like feel.

In all of 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 multilayer coating films had low brightness but high chroma, and a sense of depth 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) is more than 1. In this Comparative Example 1, the second coating film contains a glittering pigment. The multilayer coating film of Comparative Example 1 is a coating film in which the grain shape of the glittering pigment is visible, and the coating film has a slightly high lightness and a poor sense of depth.
Comparative Example 2 is a multi-layer coating film in which C*15/L*15 is less than 3 and the granularity value (G value) exceeds 1. The multi-layer coating film of Comparative Example 2 was a coating film with high saturation but also high brightness, and poor depth.
Comparative Example 3 is a multi-layer coating film composed of two layers, a first coating film and a clear coating film. The multi-layer coating film of Comparative Example 3 had low C*15/L*15 and C* values, and a high G value. The multi-layer coating film of Comparative Example 3 was a coating film in which the particle shape of the glittering pigment was visible, and had low saturation, high brightness, and poor depth.

The multilayer coating film of the present disclosure is a coating film with low brightness but high chroma, a smooth depth and a heavy feeling like a mirror surface, and excellent design. The multilayer coating film can be suitably used as a design coating film for various articles (for example, automobile bodies such as passenger cars, trucks, motorcycles, and buses, and their parts, etc.).

Claims (7)

A multi-layer coating film having a first coating film, a second coating film, and a clear coating film in this order,
The first coating film is a cured coating film of a first coating composition containing a first coating film-forming resin and a luster pigment,
The second coating film is a cured coating film of a second coating composition containing a second coating film-forming resin and a color pigment,
The multilayer coating film has a C*15/L*15 ratio of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) at an incident angle of 45° of 1 or less ,
The second coating film, as a single coating film, has an average light transmittance of 19% or less in a wavelength range of 400 nm or more and 700 nm or less;
A multi-layer coating film , wherein the content of the luster pigment in the second coating composition is less than 0.5 parts by mass per 100 parts by mass of resin solids . The multi-layer coating film according to claim 1, wherein the C*15/FF at an incident angle of 45° and an acceptance angle of 15° is 15 or more. The thickness of the first coating film is within a range of 1 to 9 μm;
The luster pigment contained in the first coating film has an average particle size 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 . The multi-layer coating film according to any one of claims 1 to 3 , wherein the multi-layer coating film has a hue of 1B to 10PB in the Munsell color system. A method for forming a multi-layer coating film by successively coating a first coating composition, a second coating composition and a clear coating composition on a substrate, comprising the steps of:
The first coating composition comprises a first film-forming resin and a luster pigment,
the second coating composition comprises a second film-forming resin and a color pigment;
The multilayer coating film has a C*15/L*15 ratio of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) at an incident angle of 45° of 1 or less ,
The second coating film formed by curing the second coating composition has an average light transmittance of 19% or less in a wavelength range of 400 nm or more and 700 nm or less as a single coating film,
A method for forming a multi-layer coating film , wherein the content of the luster pigment in the second coating composition is less than 0.5 parts by mass per 100 parts by mass of resin solids . A method for forming a multi-layer coating film by successively applying a first coating composition, a second coating composition and a clear coating composition to a substrate in a wet-on-wet manner, comprising:
The first coating composition comprises a first film-forming resin and a luster pigment,
the second coating composition comprises a second film-forming resin and a color pigment;
The multilayer coating film has a C*15/L*15 ratio of 3 or more at an incident angle of 45° and an acceptance angle of 15°, a C* value of 70 or more at an incident angle of 45° and an acceptance angle of 15°, and a granularity value (G value) at an incident angle of 45° of 1 or less ,
The second coating film formed by curing the second coating composition has an average light transmittance of 19% or less in a wavelength range of 400 nm or more and 700 nm or less as a single coating film,
A method for forming a multi-layer coating film , wherein the content of the luster pigment in the second coating composition is less than 0.5 parts by mass per 100 parts by mass of resin solids . An article having the multilayer coating film according to any one of claims 1 to 4 .