JP7539276B2 - 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.

In recent years, in the field of automotive painting, coatings with high design properties have been developed. For example, there is a tendency to prefer paint colors that change in brightness depending on the viewing angle, rather than solid colors that are a single color. Furthermore, due to diversifying consumer tastes and a desire for originality, there is a demand for more unique designs rather than just simple brightness changes, for example.

Patent No. 5765741 (Patent Document 1) describes a method for forming a multi-layer coating film with high design, in which a metallic base coating film containing a color pigment and a lustrous material, a colored base coating film containing a color pigment, and a clear coating film are formed on the surface of a coated object, in which the light reflectance of the single metallic base coating film is 45-50% at wavelengths of 650-700 nm, and 20% or less at wavelengths of 410-440 nm and 510-590 nm, and the light transmittance of the single colored base coating film is 50-70% at wavelengths of 400-700 nm, 88-92% at wavelengths of 650-700 nm, and 20-60% at wavelengths of 410-440 nm and 510-590 nm. The multi-layer coating film with high design formed by this method is a so-called candy color coating film, in which the hues of the first and second layers are similar.

Patent No. 6411343 (Patent Document 2) describes a coating composition that contains a chlorine-process titanium oxide pigment, a yellow iron oxide pigment, a carbon black pigment with a primary average particle size in the range of 15 to 80 nm, and a resin composition that is a vehicle-forming component, and the coating composition is applied to a cured coating film of 25 μm, and the coating film has an average light transmittance of 0.1 to 1.0% at wavelengths of 420 nm to 480 nm, and the cured coating film has an L* value of 80 to 95, an a* value of -2.0 to 2.0, and a b* value of 0.1 to 5.0 in the L*a*b* color system. The invention described in Patent Document 2 aims to provide a coating composition that can form a coating film with high brightness and low ultraviolet transmittance in the wavelength range of 420 to 480 nm, and a coating film formation method in which a color base coating film is laminated on the coating film obtained by applying the coating composition to a substrate (paragraph [0005]).

Patent No. 5765741 specification Patent No. 6411343 specification

The multilayer coating film of the above-mentioned Patent Document 1 is described as being less prone to color unevenness, having high saturation and brightness, and having a sense of depth in color. Also, the coating composition of Patent Document 2 is described as being high brightness yet having low ultraviolet transmittance, and therefore not peeling off during accelerated weathering tests.
In response to this, the present invention aims to provide a unique design that differs from conventional designs in a multi-layer coating film having a first coating film with a low lightness L* value.

In order to solve the above problems, the present invention provides the following aspects.
[1]
A multi-layer coating film having at least a first coating film and a second coating film,
The first coating film is a cured coating film of a first coating composition containing a first coating film-forming resin and a color 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 first coating film has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and a receiving angle of 45°,
The second coating film is a multi-layer coating film having a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film.
[2]
The multilayer coating film according to [1], wherein the second coating film, as a single coating film, has a hue of 1R to 10R in the Munsell color system.
[3]
The light reflectance of the multilayer coating film is less than 0.4% at a wavelength of 420 to 570 nm, and is 0.4% or more and 2% or less at a wavelength of 580 to 700 nm.
The multilayer coating film according to [1] or [2].
[4]
The amount of the glittering pigment contained in the first coating film is 3 parts by mass or less per 100 parts by mass of the resin solid content.
[1] to [3] The multilayer coating film according to any one of the above.
[5]
The second coating film contains a red pigment, and the amount of the red pigment contained in the second coating film is 0.1 to 6 parts by mass per 100 parts by mass of resin solids.
[1] to [4] The multilayer coating film according to any one of the above.
[6]
The multilayer coating film according to any one of [1] to [5], wherein the flip-flop value of the multilayer coating film is 1.05 or more and less than 2.
[7]
A method for forming a multi-layer coating film by successively coating a first coating composition and a second coating composition on a substrate, comprising the steps of:
The first coating composition comprises a first film-forming resin and a color pigment,
The second coating composition comprises a second film-forming resin and a color pigment,
The first coating film obtained by curing the first coating composition has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and an acceptance angle of 45°,
The second coating film obtained by curing the second coating composition has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film.
A method for forming a multi-layer coating film.
[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 color pigment,
The second coating composition comprises a second film-forming resin and a color pigment,
The first coating film obtained by curing the first coating composition has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and an acceptance angle of 45°,
The second coating film obtained by curing the second coating composition has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film.
A method for forming a multi-layer coating film.
[9]
The light reflectance of the multilayer coating film is less than 0.4% at a wavelength of 420 to 570 nm, and is 0.4% or more and 2% or less at a wavelength of 580 to 700 nm.
The method for forming a multilayer coating film according to [7] or [8].
[10]
[1] to [6] An article having a multilayer coating film according to any one of the above.

The above multi-layer coating film has a first coating film with a low lightness L* value of 10 or less, and while the multi-layer coating film as a whole is recognized as having a black color tone, it can create a unique design in which the perceived color impression changes depending on the intensity and angle of incident light.

First, we will explain how we arrived at the present invention. The researchers of the present invention have conducted research with the aim of developing a coating film with a unique design in dark tones such as black. In the process, they have investigated methods for imparting a sense of shadow and depth not found in conventional solid colors to monochromatic color coating films with black tones, known as solid colors.

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.

However, when aluminum pigment, a type of photoluminescent pigment, was added to the black coating to impart a sense of shadow, it was found that the color of the aluminum pigment itself was added, increasing the brightness and giving the coating a gray hue. Furthermore, by adding aluminum pigment, the granular texture of the photoluminescent pigment became visible, resulting in the design of a so-called metallic coating. On the other hand, further investigation revealed that when mica was added to the coating as a photoluminescent pigment, the entire coating became cloudy, losing the sense of firmness that the black coating has. Thus, it was difficult to impart a sense of shadow and depth to a coating with a black color tone using conventional technology.

The inventors conducted extensive research to solve the above problems. Through experiments, they discovered that by laminating coating films of different hues, it is possible to impart a sense of shadow and depth to a coating film with a black color tone, and this led to the completion of the present invention.

The multilayer coating film in this disclosure is a multilayer coating film having at least a first coating film and a second coating film provided on the first coating film. The first coating film has a chroma C* of 10 or less and a lightness L* of 10 or less, and the second coating film has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film. The first coating composition forming the first coating film and the second coating composition forming the second coating film are described below 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 color 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 can be carried out by any conventional method without any particular limitations. 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 under 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 3,000 or less. The acrylic resin emulsion preferably has a hydroxyl value (solid content hydroxyl value) of 20 mg KOH/g or less and 180 mg KOH/g or less, and an acid value (solid content acid value) of 1 mg KOH/g or less and 80 mg KOH/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 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 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 acrylic resin emulsion, and then dispersing the monomer in water with a basic compound.

Polyester resin dispersions can be prepared, for example, by condensing a polyhydric alcohol component with 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, 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, isophorone diisocyanate, etc. In such blocked isocyanate resins, the blocking agent dissociates when heated 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 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. The pigment may further contain an anti-rust pigment as necessary.

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:

The first paint composition may contain a luster pigment, if necessary, to the extent that the effect of the present invention is not impaired. The luster pigment referred to here is a pigment having a scale shape and an aspect ratio (average maximum diameter of the pigment/average thickness of the pigment) of 10 or more. 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. When the luster pigment is contained, it may be contained in an amount of, for example, 0.1 to 3 parts by mass per 100 parts by mass of resin solids (solids of the coating film-forming components), provided that the luster pigment is contained within a range that does not impair the effect of the present invention.

The average maximum diameter and average thickness of the pigment at the above aspect ratios can be measured by observing the pigment with a shape analysis laser microscope (such as Keyence VK-X 250) and calculating the number average of the maximum length (long diameter) of 100 arbitrarily selected pigments.

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, color pigment, hardener, 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 color 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).

As the polyester resin, for example, a hydroxyl-containing polyester resin can be used. 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 color pigment. The color 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, an antioxidant, and other additives that are commonly used by those skilled in the art.

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, for example, the color 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 paint 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.

In the present disclosure, the second coating film formed by applying and curing the second coating composition has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film. The second coating composition that forms such a second coating film preferably contains a red pigment. Examples of red pigments include iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, and perylene maroon.

The amount of red pigment contained in the second paint composition is preferably an amount such that the amount of red pigment contained in the second coating film is 0.1 to 6 parts by mass per 100 parts by mass of resin solids. The above content is more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass. By having the amount of red pigment in the above range, it is possible to form a second coating film with high saturation and transparency, and there is an advantage in that a multi-layer coating film having the desired design can be formed.

The second paint composition may contain other pigments in addition to the red pigment. Examples of other pigments include the extender pigments and anti-rust pigments exemplified in the first paint composition. The second paint composition is preferably such that the total content of the red pigment and other pigments in the second coating is 0.5 to 10 parts by mass, and more preferably 2 to 7 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 at least a first coating film which is a cured coating film of the first coating composition, and a second coating film which is a cured coating film of the second coating composition, in that order.

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 of sequentially coating the first and second coating compositions on a substrate. 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. Alternatively, the first coating composition may be coated, and the coated coating film may be uncured, and the second coating composition may be coated wet-on-wet, and then heat cured. In the wet-on-wet coating, preheating may be performed between coatings as necessary. Alternatively, the first coating composition and the second coating composition may be coated sequentially, and then dried at room temperature to form a multi-layer coating film. In the coating, a clear coating may be further provided as necessary.
A method of successively applying a first coating composition, a second coating composition, and a clear coating composition to a substrate in a wet-on-wet manner. More specifically, this method involves successively applying a first coating composition, a second coating composition, and a clear coating in a wet-on-wet manner 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 coater.

The first coating composition is preferably applied so that the dry film thickness is within the range of 3 to 20 μm, and more preferably within the range of 5 to 10 μm. The second coating composition is preferably applied so that the dry film thickness is within the range of 3 to 20 μm, and more preferably within the range of 5 to 10 μm.

When applying and heat-curing the first and second coating compositions, the heating temperature and time can be appropriately selected depending on 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 in terms 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 according to the coating form of the clear coating composition. The dry film 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 multi-layer 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 reaction-curing clear coating composition may be applied to provide a clear coating film.

In the multilayer coating film disclosed herein, the first coating film obtained by curing the first paint composition has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and an acceptance angle of 45°.

The chroma C* and lightness L* are parameters in the L*C*h color system and can be determined in accordance with JIS Z8729. The 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. The chroma C* indicates that the brighter the measured material is as its value increases, and that the duller it is as its value decreases. The lightness L* indicates that the brighter the measured material is as its value increases, and that the darker it is as its value decreases. The chroma C* and lightness L* can be measured using a commercially available multi-angle spectrophotometer. An example of a multi-angle spectrophotometer is the MA-68II (manufactured by X-Rite).

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

In this specification, the chroma C* and lightness L* of the first coating film refer to values measured using a coating film of the first coating composition with a film thickness of 8 μm. More specifically, a steel plate coated with a cationic electrodeposition coating composition is coated with a dark gray cured undercoat coating film, and the first coating composition is spray-coated on the coated plate so that the dry film thickness is 8 μm, and then the first coating film is heated and cured at 140°C for 20 minutes to obtain the first coating film.

As a method for adjusting the chroma C* and lightness L* of the first coating film to the above range, for example,
A method using a black pigment as a coloring pigment;
A method of mixing two or more pigments selected from the group consisting of red pigments, yellow pigments, orange pigments, blue pigments, green pigments, purple pigments, etc., as color pigments by a subtractive color mixing method to achieve a black color tone; and a combination of the above methods;
etc.

In the multilayer coating film disclosed herein, the second coating film obtained by curing the second coating composition has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as compared to 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-3310 spectrophotometer (Hitachi) in wavelength scan mode in the range of 410 to 700 nm at a scan speed of 300 nm/min and a sampling interval of 0.5 nm.

In the multilayer coating film disclosed herein, the light transmittance of the second coating film alone, measured as described above, is 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm. Having the light transmittance of the second coating film alone within the above ranges in each wavelength range has the advantage of improving the design of the multilayer coating film.

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 coating film thickness. Specifically, for example, the color pigment is one or more selected from the group consisting of iron oxide pigments, perylene pigments, azo pigments, and quinacridone pigments, such as iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake (Mn salt), perylene red, and perylene maroon, and the content of the color pigment is 0.1 to 6 parts by mass per 100 parts by mass of resin solids. By providing a second coating film having a dry film thickness of 3 to 20 μm using a second coating composition, the light transmittance of the second coating film can be suitably adjusted, which has the advantage of being able to satisfactorily obtain a multilayer coating film having the design desired in this disclosure.

In the multilayer coating film of the present disclosure, the second coating film, as a single coating film, preferably has a hue of 1R to 10R in the Munsell color system. When the light transmittance of the single coating film of the second coating film satisfies the above conditions and the hue of the Munsell color system satisfies the above conditions, it can be said that the hue of the single second coating film is a hue that is particularly suitable for expressing the design in the multilayer coating film of the present disclosure, and there is an advantage in that a more suitable design can be achieved in the multilayer coating film.

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, "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 case where the hue of the Munsell color system in the single coating film of the second coating film is 1R to 10R, the single coating film of the second coating film can be said to have a hue that is recognized as red.

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.

In the present disclosure, the light reflectance of the multilayer coating film is preferably less than 0.4% at wavelengths of 420 to 570 nm, and 0.4% to 2% at wavelengths of 580 to 700 nm.

The light reflectance of the multilayer coating film is measured as follows. 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 8 μm, the second coating composition is spray-coated wet-on-wet to a dry film thickness of 8 μm, and the clear coating composition is spray-coated wet-on-wet to a dry film thickness of 35 μm. The uncured three-layer coating film is then heated and cured at 140°C for 20 minutes to obtain a multilayer coating film, which is then used for measurement.

The light reflectance can be determined by measuring the ratio of the light irradiated from the light source to the intensity of the light reflected by the multilayer coating film using a U-3310 spectrophotometer (Hitachi) in wavelength scan mode over the range of 420 to 700 nm at a scan speed of 300 nm/min and a sampling interval of 0.5 nm.

In a multi-layer coating film, by having the light reflectance in the above wavelength range being within the above range, the multi-layer coating film as a whole appears black, while the advantage is that under certain conditions, the characteristic of the color impression perceived by the eye changing is preferably obtained. This is thought to be because, for example, the light reflectance of the multi-layer coating film increases slightly in the wavelength range of 580 to 700 nm, so that the color in this wavelength range is perceived slightly to the extent that the color impression changes when viewed with the naked eye.

The cured coating film of the coating composition preferably has a flip-flop value of 1.05 or more and 2.0 or less. In this specification, the flip-flop value (sometimes referred to as FF value) is a value indicating 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 the light receiving angle of 15 degrees is specifically the L* value for the 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 relative to the axis perpendicular to the measurement target surface (incident angle 45 degrees). The L* value at an acceptance angle of 110 degrees (L*(110°) value) is the L* value for light received at an angle of 110° from the specular reflection angle in the direction of the measurement light when measurement light is similarly irradiated.

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.

A larger FF value indicates a larger change in the L* value (brightness) depending on the observation angle (light receiving angle), and a smaller FF value indicates a smaller change in the L* value (brightness) depending on the observation angle (light receiving angle). In general metallic coatings, the larger the FF value and the larger the change in brightness depending on the viewing angle, the greater the sense of shadow as a metallic coating. On the other hand, the multilayer coating of the present disclosure is not designed with a metallic luster (metallic feel) brought about by a photoluminescent pigment, so the FF value is not large, falling in the range of about 2.0 or less.

For example, in the conventional automotive coating field, the base coating film, which greatly affects the design, can be roughly divided into a coating film that does not contain a glittering pigment, which is called a solid color, and a coating film that contains a glittering pigment and has a metallic luster (metallic feel). In contrast, the multilayer coating film of the present disclosure has the above-mentioned configuration, which is characterized by a unique design. More specifically, the multilayer coating film of the present disclosure has a characteristic that the impression of the color perceived by the eye changes subtly depending on the intensity and incident angle of the light incident on the multilayer coating film. When strong light is incident on the multilayer coating film of the present disclosure in visual observation, a brown color that is more saturated than black and does not turbidity can be seen in the highlights. In addition, in the shade, the amount of light seen may be reduced, and black is seen. And, when weak light is incident on the multilayer coating film of the present disclosure, black is seen even in the highlights.

In the multilayer coating film of the present disclosure, the above-mentioned change in color impression is an extremely delicate change, so that it is difficult to quantify the changing color itself using a spectrophotometer or the like with current technology, but it is a change that can be recognized by the naked eye. The design of the multilayer coating film of the present disclosure is not a design that can be grasped at a glance, but it is a delicate design like a craftwork made by precise manual work, in which the impression of the color perceived by the naked eye changes subtly depending on the intensity and angle of the incident light. The design of the multilayer coating film of the present disclosure is not a design like a metallic luster (metallic feel) brought about by a glittering pigment, nor is it a design like a conventional solid color without changes in brightness and hue. The design of the multilayer coating film of the present disclosure is different from the design of conventional solid colors, and is a design like a craftwork, so to speak, and can be called an artistic solid color.

Without being bound by theory, the inventors believe that the reason why the above-mentioned change in color impression can be recognized in the multilayer coating film of the present disclosure is as follows.
The multilayer coating film of the present disclosure has at least a first coating film and a second coating film. The first coating film has a chroma of C*10 or less and a brightness of L*10 or less, and is recognized as being almost black, and the second coating film is a sheer red coating film (red clear coating film) that partially transmits visible light and has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm and 85 to 95% at wavelengths of 650 to 700 nm as a single coating film.
When light is irradiated (incident) on the multilayer coating film having the above-mentioned configuration, at least a part of the incident light is scattered or reflected in the second coating film layer at the time when the light of each wavelength constituting the incident light is incident on the second coating film portion. The scattered light, reflected light, etc. generated in the second coating film becomes weak visible light in various wavelength ranges, and becomes visible light with saturation.
In the multilayer coating film having the above configuration, when the intensity of the light irradiated (incident) to the multilayer coating film is strong, it is believed that chromatic colors other than black are confirmed by visually observing weak visible light in various wavelength ranges based on the scattered light, reflected light, etc. generated in the second coating film. This is believed to be because when the intensity of the light irradiated (incident) to the multilayer coating film is strong, the absolute amount of light is large, and therefore the amount of light scattered and reflected in the second coating film is also large.
On the other hand, when the intensity of the light irradiated (incident) to the multi-layer coating film is weak, the absolute amount of light is small, so the amount of scattered and reflected light going out from the second coating film is small. This is because a certain amount of scattered and reflected light is absorbed in the second coating film. As a result, the amount of weak visible light in various wavelength ranges is not enough to be visually observable, and it is believed that chromatic colors other than black cannot be confirmed. In this way, in the multi-layer coating film of the present disclosure, the impression of the visible color changes depending on the intensity and angle of the incident light, which is thought to bring about a unique design in the multi-layer coating film of the present disclosure. And it is thought that such a change in impression brings about a sense of shadow and depth to the coating film with a black color tone.

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 40 parts of ethoxypropanol were charged into a 1-L reaction vessel equipped with a stirrer, a temperature regulator, and a cooling tube, 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 were 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: 10.4 parts of carbon black (Raven 5000 Ultra (trade name)) as a color pigment, 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 the 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%), 38 parts of the above color pigment dispersion paste, 5 parts of the phosphate 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), and 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.
The amount of carbon black contained in the first coating composition was 6 parts by mass per 100 parts by mass of the resin solid content.

Preparation of the second coating composition
Color pigment dispersion paste: 15.7 parts of red color pigment (PERIINDO MAROON 179), 39.3 parts of pigment dispersant Disperbyk 190, 43.7 parts of ion-exchanged water, and 0.5 parts of defoamer BYK-011 were mixed with a stirrer such as a Disper, and then dispersed with a disperser filled with zirconia beads as a medium to obtain a color pigment dispersion paste.

182 parts of the acrylic resin emulsion of the second 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%), 14 parts of the above color pigment dispersion paste, 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), and 3 parts of linoleic acid (manufactured by Kishida Chemical Co., Ltd.) were uniformly dispersed and dimethylaminoethanol was added to the pH to 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.
The amount of the color pigment contained in the second coating composition was 2.25 parts by mass per 100 parts by mass of the resin solid content.

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 15 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% to a dry film thickness of 15 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.

Example 2
A second coating composition was prepared in the same manner as in Example 1, except that the amount of the color pigment dispersion paste was changed from 14 parts to 28 parts in the preparation of the second coating composition.
A multi-layer coating film was formed in the same manner as in Example 1, except that the second coating composition obtained above was used.

Example 3
The first coating composition was prepared by the same procedure as in Example 1, except that the amount of the color pigment dispersion paste used in the preparation of the first coating composition was adjusted so that the amount of carbon black contained in the first coating composition was 4 parts by mass per 100 parts by mass of the resin solids.
A multi-layer coating film was formed in the same manner as in Example 1, except that the first coating composition obtained above was used.

Comparative Example 1
A second coating composition was prepared in the same manner as in Example 1, except that the color pigment dispersion paste was not used in the preparation of the second coating composition.
A multi-layer coating film was formed in the same manner as in Example 1, except that the second coating composition obtained above was used.

Comparative 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%), 9 parts of aluminum paste 93-0647 (ground aluminum bright pigment, manufactured by Toyo Aluminum, active ingredient 61%, ground aluminum pigment) per 100 parts by mass of resin solids, 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 solids), 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 a first coating composition having a resin solids concentration of 33% by mass.

Preparation of second coating composition A color pigment dispersion paste for preparing a second coating composition was prepared in the same manner as in Example 1, except that 10.3 parts of carbon black was used instead of 15.7 parts of the red color pigment (PERIINDO MAROON).
A second coating composition was prepared in the same manner as in Example 1, except that 0.04 parts of the color pigment dispersion paste obtained above was added. The amount of color pigment (carbon black) contained in the obtained second coating composition was 0.01 parts per 100 parts of resin solids.

Comparative Example 3
A multi-layer coating film was formed in the same manner as in Example 1, except that Vibrant Red (a red base coating composition manufactured by Nippon Paint Automotive Coatings) was used as the second coating composition.

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

Measurement of chroma C* and lightness L* of the first coating
Preparation of test plate having first 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 having a thickness of 0.8 mm, length of 30 cm and width of 40 cm, 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 Dark 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 dark gray color tone (lightness 30).
Next, the first coating composition used in the Examples or Comparative Examples was air-spray coated to a dry film thickness of 15 μm under conditions of room temperature 23° C. and humidity 68%. After setting for 7 minutes, the coated plate was baked in a dryer at 140° C. for 30 minutes to obtain a test plate having a first coating film.

Using the test plate having the single first coating film obtained above, the chroma C* value and lightness L* value at an incident angle of 45° and an acceptance angle of 45° were measured using a multi-angle spectrophotometer MA-68II (manufactured by X-Rite). The measurement results are shown in the table below.

Measurement of Munsell values of second coating
Preparation of test plate having second coating film The second paint composition was spray-coated on a white polypropylene plate so that the dry coating film was 23 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.

Measurement of Munsell Value The Munsell value of the test plate having the second coating film obtained above was measured using a multi-angle spectrophotometer "CR-400" manufactured by Minolta Co., Ltd. The measurement results are shown in the table below.

Measurement of light transmittance of second coating film From the test plate having the 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 a second coating film. This second coating film was measured in wavelength scan mode in the range of 410 to 700 nm at a scan speed of 300 nm/min and a sampling interval of 0.5 nm using a U-3310 spectrophotometer (manufactured by Hitachi), and the light transmittance of the second coating film in each wavelength region was determined. The measurement results are shown in the table below.

Visual observation of change in color impression of multilayer coating film Painted test panels having the multilayer coating film formed in each example were visually observed when 100,000 lux (outdoors) as strong light was irradiated onto the multilayer coating film, and when 200 lux of weak light was irradiated onto the multilayer coating film, and evaluated according to the following criteria.

○: When weak light is applied, the highlights are observed to be black, whereas when strong light is applied, the highlights are observed to be brown with a yellow to red tint. ×: The unique design as rated ○ above cannot be seen.

Chroma C* value and lightness L* value of multi-layer coating film Using the coating test plate having the multi-layer coating film formed in each example, the chroma C* value and lightness L* value at an incident angle of 45° and an acceptance angle of 45° were measured with a multi-angle spectrophotometer MA-68II (manufactured by X-Rite Co., Ltd.). The measurement results are shown in the table below.

Measurement of FF value of multilayer coating film For the coated test panels having the multilayer coating film formed in each Example, the L* value at an incident angle of 45 degrees and 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) were measured using a multi-angle spectrophotometer MA-68II (trade name, manufactured by X-Rite Corporation), and the FF value was calculated by the following formula.
FF value = L*(15°) value/L*(110°) value

All of the multi-layer coating films of the Examples were observed to be black in highlights when irradiated with weak light, while when irradiated with strong light, they were seen to be brown with yellow to red hues in highlights, creating a unique design with a sense of shadow. The multi-layer coating films of the Examples also had a sense of depth due to the transparency, due to the above-mentioned characteristics of the single second coating film.
Comparative Example 1 is an example in which the first coating film is a black coating film and the second coating film is a clear coating film that does not contain a color pigment. In this example, the color tone of the multi-layer coating film was a color tone that is so-called black solid color. More specifically, when weak light was irradiated onto the multi-layer coating film, it was observed as black in the highlights, and when strong light was irradiated, it was a coating film that was perceived as black in the highlights.
Comparative Example 2 is an example in which the first coating contains an aluminum pigment as a glitter pigment, and the second coating contains a black pigment as a color pigment, which is a black color clear coating. In this example, the color tone of the multi-layer coating was a color tone called a metallic color. More specifically, in both cases where the multi-layer coating was irradiated with weak light and strong light, the design was a metallic dark gray coating with a grainy feel.
Comparative Example 3 is an example in which an opaque solid-color red coating film was provided as the second coating film. In this example, the color tone of the multilayer coating film was a color tone that is so-called a red solid color. More specifically, the design of the red coating film was obtained in both cases where the multilayer coating film was irradiated with weak light and strong light.

The multilayer coating film of the present disclosure has a first coating film with a low lightness L* value of 10 or less, and has a unique design in which the overall multilayer coating film is recognized as having a color tone close to black, but the visual impression of the color changes depending on the intensity and angle of incident light. The multilayer coating film can be suitably used as a design coating film for various articles.

Claims (6)

A multi-layer coating film comprising a first coating film, a second coating film provided on the first coating film, and a clear coating film provided on the second coating film ,
The first coating film is a cured coating film of a first coating composition containing a first coating film-forming resin and a color 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 first film-forming resin and the second film-forming resin are acrylic resin emulsions;
the color pigment contained in the first coating film is one or more pigments selected from the group consisting of carbon black, graphite, perylene-based black pigments, and azomethiazo-based pigments;
the color pigment contained in the second coating film is one or more kinds of red pigments selected from the group consisting of iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake, perylene red, and perylene maroon;
the amount of the red pigment contained in the second coating film is 0.1 to 6 parts by mass per 100 parts by mass of resin solids,
the dry film thickness of the first coating film and the second coating film is 3 to 20 μm;
The dry thickness of the clear coating film is 10 to 80 μm,
The first coating film has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and a receiving angle of 45°,
The second coating film has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film;
The second coating film, as a single coating film, has a hue of 1R to 10R in the Munsell color system;
The light reflectance of the multilayer coating film is less than 0.4% at a wavelength of 420 to 570 nm, and is 0.4% or more and 0.89% or less at a wavelength of 580 to 700 nm . The amount of the luster pigment contained in the first coating film is 3 parts by mass or less per 100 parts by mass of resin solids.
The multi-layer coating film according to claim 1 . The multi-layer coating film according to claim 1 or 2 , wherein the flip-flop value of the multi-layer coating film is 1.05 or more and less than 2. A method for forming a multi-layer coating film by sequentially 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 color pigment;
the second coating composition comprises a second film-forming resin and a color pigment;
the first film-forming resin and the second film-forming resin are acrylic resin emulsions;
The color pigment contained in the first coating composition is one or more pigments selected from the group consisting of carbon black, graphite, perylene-based black pigments, and azomethiazo-based pigments;
The color pigment contained in the second coating composition is one or more red pigments selected from the group consisting of iron oxide, transparent iron oxide, monoazo red, quinacridone red, azo lake, perylene red, and perylene maroon;
The amount of the red pigment contained in the second coating film obtained by curing the second coating composition is 0.1 to 6 parts by mass per 100 parts by mass of resin solids,
The first coating film obtained by curing the first coating composition has a chroma C* of 10 or less and a lightness L* of 10 or less at an incident angle of 45° and an acceptance angle of 45°,
The second coating film has a light transmittance of 3 to 35% at wavelengths of 410 to 440 nm and 510 to 590 nm, and 85 to 95% at wavelengths of 650 to 700 nm, as a single coating film;
the dry film thickness of the first coating film and the second coating film is 3 to 20 μm;
The clear coating composition is cured to give a clear coating film having a dry thickness of 10 to 80 μm.
The second coating film, as a single coating film, has a hue of 1R to 10R in the Munsell color system;
The light reflectance of the multilayer coating film is less than 0.4% at a wavelength of 420 to 570 nm, and is 0.4% or more and 0.89% or less at a wavelength of 580 to 700 nm . 5. The method for forming a multi-layer coating film according to claim 4 , wherein the first coating composition, the second coating composition and the clear coating composition are successively applied wet-on - wet to a substrate to form the multi-layer coating film. An article having the multilayer coating film according to any one of claims 1 to 3 .