阅读说明：本技术 多层涂膜形成方法 (Method for forming multilayer coating film ) 是由 冈崎纮和 成田信彦 于 2019-05-20 设计创作，主要内容包括：本发明目的在于提供一种光辉性优异的多层涂膜形成方法。具体而言,作为解决方法,提供有一种多层涂膜形成方法,依次包含下述的工序(1)～(3)：(1)在被涂覆物上涂覆基底涂料(X)来形成基底涂膜的工序；(2)涂覆光辉性颜料分散体(Y)来形成光辉性涂膜的工序；(3)涂覆透明涂料(Z)来形成透明涂膜的工序,光辉性颜料分散体(Y)为含有鳞片状光辉性颜料(A)的光辉性颜料分散体,鳞片状光辉性颜料(A)的厚度T为1～65nm,在将存在于多层涂膜的全部光辉性颜料投影到多层涂膜的表面上时,光辉性颜料投影在多层涂膜表面上的部分所占的面积占有率R为0.1～50％,且所述T及R满足以下的主要条件(1),T(nm)×R(％)≦2000…(1)。(The invention aims to provide a method for forming a multilayer coating film with excellent brilliance. Specifically, as a solution, there is provided a multilayer coating film forming method comprising the following steps (1) to (3) in this order: (1) a step of applying a base coat (X) to an object to be coated to form a base coat; (2) a step of forming a bright coating film by applying a bright pigment dispersion (Y); (3) and (c) applying a clear coating material (Z) to form a clear coating film, wherein the bright pigment dispersion (Y) is a bright pigment dispersion containing a scaly bright pigment (a), the thickness T of the scaly bright pigment (a) is 1 to 65nm, and when all the bright pigments present in the multilayer coating film are projected onto the surface of the multilayer coating film, the area occupancy R of the portion of the bright pigment projected onto the surface of the multilayer coating film is 0.1 to 50%, and T and R satisfy the following main condition (1), T (nm) xr (%) < 2000 … (1).)

1. A multilayer coating film forming method comprising the following steps (1) to (3) in this order:

(1) a step of applying a base coat (X) to an object to be coated to form a base coat;

(2) a step of forming a bright coating film by applying a bright pigment dispersion (Y);

(3) a step of forming a clear coating film by applying a clear coating material (Z),

the bright pigment dispersion (Y) is a bright pigment dispersion containing a scaly bright pigment (A) having a thickness T of 1 to 65nm,

when the entire bright pigment existing in the multilayer coating film is projected on the surface of the multilayer coating film, the area occupancy rate R of the portion of the bright pigment projected on the surface of the multilayer coating film is 0.1 to 50%,

and T and R satisfy the following main condition (1),

T(nm)×R(％)≦2000…(1)。

2. the method of claim 1, wherein a Y value (Y5) indicating luminance in an XYZ chromaticity system based on a spectral reflectance when light applied to the multilayer coating film at an angle of 45 ° with respect to a normal reflection light is received at an angle of 5 ° in an incident light direction is 20 to 1500.

3. The method of claim 1 or 2, wherein the multilayer coating film has an HG value in the range of 5 to 66.

4. The method of forming a multilayer coating film according to any one of claims 1 to 3, wherein the content of the flaky bright pigment (A) is 0.2 to 80 parts by mass based on 100 parts by mass of the total solid content in the bright pigment dispersion (Y).

5. The method of forming a multilayer coating film according to any one of claims 1 to 4, wherein the bright pigment dispersion (Y) contains a viscosity modifier.

6. The method of forming a multilayer coating film according to any one of claims 1 to 5, wherein the clear coating material (Z) is a 2-liquid clear coating material containing a hydroxyl group-containing resin and a polyisocyanate compound.

7. A coated article having on its surface a multilayer coating film obtained by the multilayer coating film forming method according to any one of claims 1 to 6.

8. A multilayer coating film comprising a base coating film, a bright coating film containing a bright pigment (A) in the form of flakes, and a clear coating film formed on the surface of an object to be coated in this order,

the thickness T of the flaky bright pigment (A) is 1-65 nm,

when the entire bright pigment existing in the multilayer coating film is projected on the surface of the multilayer coating film, the area occupancy rate R of the portion of the bright pigment projected on the surface of the multilayer coating film is 0.1 to 50%,

and T and R satisfy the following main condition (1),

T(nm)×R(％)≦2000…(1)。

Technical Field

The present invention relates to a method for forming a multilayer coating film, a coated article, and a multilayer coating film, which can form a metal coating film having less graininess and excellent metallic luster.

Background

The purpose of the coating is mainly to protect raw materials and to impart aesthetic appeal. Among industrial products, from the viewpoint of enhancing the commercial appeal thereof, the aesthetic feeling, particularly "texture", is very important.

In recent years, although a very high brightness is obtained by dazzling a highlight, a design is required in which the brightness is drastically decreased by slightly inclining the coating surface, and this design is attractive (aesthetic) because of the change in brightness.

A coating film of such a design is usually formed from a multilayer coating film comprising a metal coating film by using a bright coating composition comprising a bright pigment.

As the metallic coating film, a metallic glossy coating film having a texture characterized in that there is no feeling of graininess on the surface like a mirror surface, and the vicinity of regular reflection light (high light) of the coating plate shines and appears dark in an oblique direction (shade), that is, a difference in luminance between a high light region and a dark region is large, and the like has attracted attention.

Patent document 1 discloses a multilayer coating film comprising: a colored base layer containing a coloring material formed directly or indirectly on a surface of an object to be coated; and a layer of a glow-containing material which is superimposed on the colored base layer and contains a scaly glow material and a coloring material, wherein the colored base layer has a surface smoothness as measured by Wave Scan DOI (trade name) manufactured by BYK-Gardner of 8 or less, the scaly glow material has a thickness of 25nm to 200nm, preferably 80 to 150nm, the layer of the glow-containing material has a thickness of 1.5 μm or more and 6 μm or less, and when all the glow materials present in the layer of the glow-containing material are projected on the surface of the layer of the glow-containing material, the area occupancy of the portion of the glow material projected on the surface is 30% or more and 90% or less.

However, the multilayer coating film specifically disclosed in patent document 1 is insufficient in that the granular feeling is too noticeable and the luminance difference between the highlight region and the shadow region is small because aluminum flakes having a thickness of 110nm are used as a bright material.

Patent document 2 discloses a multilayer coating film comprising: a lower layer coating film formed directly or indirectly on a surface of an object to be coated; and an upper coating film laminated on the lower coating film, wherein the lower coating film has a luminance L value of 30 or less, the upper layer coating film contains a large number of aluminum flakes as a bright material, the aluminum flakes have a surface roughness Ra of 30nm or less, the aluminum flakes have a thickness of 70nm to 150nm, and the aspect ratio of the long diameter to the short diameter of the aluminum flakes contained in the upper coating film is 3 or less, when the square root of the product of the major axis and the minor axis is defined as the particle diameter, the average particle diameter is 7 to 15 μm, the standard deviation of the particle diameter distribution is 30% or less of the average particle diameter, when all the aluminum flakes contained in the upper coating film are projected onto the surface of the upper coating film, the projected area occupancy of the portion of the aluminum scale projected on the surface is 40% to 90%.

However, the thickness of the flaky bright pigment used in the multilayer coating film described in patent document 2 is 70nm or more, and the thickness T of the flaky bright pigment of the present invention is 1 to 65nm, which is a technical idea different from the present invention.

Patent document 3 discloses a method for forming a multilayer coating film by heating an uncured colored coating film, an uncured bright coating film and an uncured clear coating film formed by sequentially applying a colored coating material (X), a bright pigment dispersion (Y) and a clear coating material (Z) on an object to be coated, and simultaneously curing the 3 coating films, wherein the bright pigment dispersion (Y) contains water, a specific surface conditioner, a scaly bright pigment and a viscosity conditioner, and the light transmittance at a wavelength of 550nm of a film obtained by applying the bright pigment dispersion (Y) so that the cured film thickness is 0.2 μm is 10 to 50%.

However, although the multilayer coating film forming method described in patent document 3 uses 50nm aluminum-deposited flakes as the scaly bright pigment, nothing is described about the area occupancy of the portion of the multilayer coating film surface on which the bright pigment is projected when the entire bright pigment present in the multilayer coating film is projected onto the surface of the multilayer coating film. Further, there is no description about the case where the relationship between the thickness of the aluminum deposited flake and the area occupancy of the portion of the multilayer coating film surface on which the bright pigment is projected falls within the specific range specified in the present invention.

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-019147

Patent document 2: international publication No. 2017/146150

Patent document 3: international publication No. 2017/022698

Disclosure of Invention

The first object of the present invention is to provide a method for forming a multilayer coating film which can form a multilayer coating film having less graininess and excellent metallic luster.

A second object of the present invention is to provide a coated article having a multilayer coating film with less graininess and excellent metallic luster on the surface, which is obtained by the above multilayer coating film forming method.

The third object of the present invention is to provide a multilayer coating film having less graininess and excellent metallic luster.

According to the first aspect of the present invention, there is provided a method for forming a multilayer coating film according to any one of items 1 to 6 below.

Item 1: a multilayer coating film forming method comprising the following steps (1) to (3) in this order:

(1) a step of applying a base coat (X) to an object to be coated to form a base coat;

(2) a step of forming a bright coating film by applying a bright pigment dispersion (Y);

(3) a step of forming a clear coating film by applying a clear coating material (Z),

the bright pigment dispersion (Y) is a bright pigment dispersion containing a scaly bright pigment (A) having a thickness T of 1 to 65nm,

when the entire bright pigment existing in the multilayer coating film is projected on the surface of the multilayer coating film, the area occupancy rate R of the portion of the bright pigment projected on the surface of the multilayer coating film is 0.1 to 50%,

and T and R satisfy the following main condition (1),

T(nm)×R(％)≦2000…(1)。

item 2: the method of forming a multilayer coating film according to item 1, wherein a Y value (Y5) indicating luminance in an XYZ colorimetric system based on a spectral reflectance when light irradiated at an angle of 45 ° to regular reflection light is received at an angle of 5 ° in an incident light direction is 20 to 1500.

Item 3: the method of forming a multilayer coating film according to item 1 or 2, wherein the HG value of the multilayer coating film is in the range of 5 to 66.

Item 4: the method of forming a multilayer coating film according to any one of items 1 to 3, wherein the content of the flaky bright pigment (A) is 0.2 to 80 parts by mass relative to 100 parts by mass of the total solid content in the bright pigment dispersion (Y).

Item 5: the method of forming a multilayer coating film according to any one of claims 1 to 4, wherein the bright pigment dispersion (Y) contains a viscosity modifier.

Item 6: the method of forming a multilayer coating film according to any one of claims 1 to 5, wherein the clear coating material (Z) is a 2-liquid clear coating material containing a hydroxyl group-containing resin and a polyisocyanate compound.

Further, according to a second aspect of the present invention, there is provided a coated article having on a surface thereof a multilayer coating film obtained by the multilayer coating film forming method of the first aspect.

Further, according to a third aspect of the present invention, there is provided a multilayer coating film comprising a base coating film, a bright coating film containing a bright pigment (A) in the form of a scale, and a clear coating film formed on the surface of an object in this order,

the thickness T of the flaky bright pigment (A) is 1-65 nm,

when the entire bright pigment existing in the multilayer coating film is projected on the surface of the multilayer coating film, the area occupancy rate R of the portion of the bright pigment projected on the surface of the multilayer coating film is 0.1 to 50%,

and T and R satisfy the following main condition (1),

T(nm)×R(％)≦2000…(1)。

according to the method for forming a multilayer coating film of the present invention, a multilayer coating film having less graininess and excellent metallic luster can be obtained.

The coated article of the present invention has a multilayer coating film with less graininess and excellent metallic luster on the surface.

The multilayer coating film of the present invention has less graininess and excellent metallic luster.

Drawings

Fig. 1 is a graph showing the relationship between the thickness t (nm) of the flaky bright pigment (a) contained in the bright pigment dispersion (Y) forming the bright coating film and the area occupancy R (%) of the portion of the bright pigment projected on the surface of the multilayer coating film when all the bright pigments present in the multilayer coating film are projected on the surface of the multilayer coating film in examples and comparative examples.

Detailed Description

First form

The first embodiment of the present invention will be explained.

[1-1. Process (1) ]

The step (1) is a step of applying a base coating material (X) to an object to be coated to form a base coating film.

< coated article >

In the multilayer coating film forming method of the present invention, examples of the material of the coating object include metals such as iron, zinc, aluminum, and titanium, alloys containing the metals, glass, ceramics, inorganic materials, various plastics, and wood. Further, a composite of plastic and various fibers (carbon fibers, glass fibers, metal fibers, organic fibers, and the like) may be used. Examples of the shape of the coated object include a plate shape (sheet shape), a cylindrical shape, a linear shape, a belt shape, a foam shape, a combination thereof, and a molded article obtained by molding at least 1 or more of the above raw materials. Depending on the raw materials, degreasing treatment or surface treatment may be appropriately performed as the coating object. Examples of the surface treatment include phosphate treatment, chromate treatment, and complex oxide treatment. Further, if the material of the coating object is a metal, it is preferable to form a cationic electrodeposition coating film on the surface-treated metal material by a cationic electrodeposition paint. An intermediate coating film may be formed on the cationic electrodeposition coating film. The intermediate coating film is preferably colored from the viewpoint of substrate hiding properties, weather resistance, and the like. In particular, when the base coat (X) described later is transparent, a colored intermediate coating film is preferably formed from the viewpoint of base hiding property, weather resistance, and the like.

When the material of the object to be coated is plastic, it is preferable to form a primer coating film on the plastic material after the degreasing treatment by a primer coating.

< base coating (X) >

As the base paint (X), a thermosetting paint which is known per se and mainly contains a solvent and a thermosetting resin can be specifically used. The thermosetting paint may include a paint called an intermediate paint. The base coating (X) may be clear or colored.

Examples of the solvent used for the base paint (X) include organic solvents and/or water.

As the organic solvent used for the base coating material (X), specifically, an organic solvent generally used for coating materials can be used.

Examples thereof include hydrocarbons such as toluene, xylene, hexane and heptane; esters such as ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and the like; ethers such as ethylene glycol monomethyl ether, diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol dibutyl ether, and the like; alcohols such as butanol, propanol, octanol, cyclohexanol, and diethylene glycol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, and isophorone. These may be used alone or in combination of 2 or more.

The thermosetting resin used for the primer (X) is preferably a base resin and a crosslinking agent in combination from the viewpoints of water resistance, chemical resistance, weather resistance, and the like.

The matrix resin is preferably a resin having good weather resistance, transparency, and the like, and specifically, acrylic resin, polyester resin, epoxy resin, polyurethane resin, and the like can be mentioned.

Examples of the acrylic resin include resins obtained by copolymerizing (meth) acrylates having functional groups such as a carboxyl group, a hydroxyl group, an amide group, and a methylol group, other (meth) acrylates, styrene, and the like.

As the polyester resin, a polyester resin obtained by condensation reaction of a polybasic acid, a polyhydric alcohol, and a modified oil by a conventional method can be used.

Examples of the epoxy resin include epoxy ester resins obtained by a method of synthesizing an epoxy ester by a reaction between an epoxy group and an unsaturated fatty acid and adding an α, β -unsaturated acid to the unsaturated group, a method of esterifying a hydroxyl group of an epoxy ester with a polybasic acid such as phthalic acid or trimellitic acid, and the like.

Examples of the urethane resin include a compound obtained by an addition reaction of a polyisocyanate compound such as a diisocyanate compound and a polyol such as a diethanol, and a urethane resin obtained by reacting a polyisocyanate compound such as a diisocyanate compound with the acrylic resin, the polyester resin, or the epoxy resin to increase the molecular weight thereof.

The base coating material (X) may be either a water-based coating material or a solvent-based coating material, and is preferably a water-based coating material from the viewpoint of reducing VOC of the coating material. When the base coating material (X) is an aqueous coating material, the base resin may contain a hydrophilic group, such as a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, a polyoxyethylene group, or the like, most commonly a carboxyl group, in an amount sufficient to make the resin water-soluble or water-dispersible by neutralizing the hydrophilic group to form an alkali metal salt. The amount of the hydrophilic group such as a carboxyl group in this case is not particularly limited, and may be arbitrarily selected depending on the degree of water solubility or water dispersibility, but may be usually about 10mgKOH/g or more, preferably in the range of 30 to 200mgKOH/g, based on the acid value. Examples of the basic substance used for neutralization include sodium hydroxide and amine compounds.

The resin may be dispersed in water by emulsion polymerization of the monomer component in the presence of a surfactant or a water-soluble resin. The resin may be obtained by dispersing the resin in water in the presence of an emulsifier or the like. In the case of this water dispersion, the hydrophilic group may be not contained at all in the matrix resin, or may be contained in an amount smaller than that of the water-soluble resin.

The crosslinking agent is a component for crosslinking and curing the above-mentioned base resin by heating, and examples thereof include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, epoxy group-containing compounds, carboxyl group-containing compounds, carbodiimide group-containing compounds, hydrazide group-containing compounds, and aminourea group-containing compounds. Among them, preferred are amino resins, polyisocyanate compounds and blocked polyisocyanate compounds which are reactive with hydroxyl groups, and carbodiimide group-containing compounds which are reactive with carboxyl groups. As the polyisocyanate compound and the blocked polyisocyanate compound, those described in the section of the clear coating material (Z) to be described later can be used. The above-mentioned crosslinking agents may be used alone or in combination of 2 or more.

Specifically, amino resins obtained by condensation or co-condensation of melamine, benzoguanamine, urea, or the like with formaldehyde, or further etherification with a lower 1-valent alcohol, or the like are preferably used. Further, a polyisocyanate compound or a blocked polyisocyanate compound can also be preferably used.

The proportions of the above-mentioned respective components in the base coating material (X) may be arbitrarily selected as required, but from the viewpoint of water resistance, handling properties and the like, the former is preferably 60 to 90% by mass, particularly preferably 70 to 85% by mass, and the latter is preferably 10 to 40% by mass, particularly preferably 15 to 30% by mass, based on the total mass of the two components.

If necessary, a pigment dispersant, an anti-settling agent, an antifoaming agent, an ultraviolet absorber, and the like may be further appropriately blended in the base paint (X).

Examples of the pigment include a coloring pigment, an extender pigment, a bright pigment, and an anticorrosive pigment, and among them, a coloring pigment is preferably used, and a pigment of a desired color is more preferably used from the viewpoint of obtaining a coating film excellent in substrate hiding property and design property.

The aforementioned pigments may be used in an appropriate combination depending on light transmittance, concealing property of the substrate, desired color, and the like.

The amount of the pigment used may be such that the light transmittance in the wavelength range of 400 to 700nm in the cured coating film formed from the base coating material (X) is 10% or less, preferably 5% or less, from the viewpoint of base hiding property, weather resistance and the like. Further, when the base paint (X) is transparent, the pigment may be in an amount within a range that does not impair the transparency of the base paint (X).

From the viewpoint of base hiding properties, when the base coating material (X) is colored, the brightness L value of the obtained coating film is preferably adjusted to be in the range of 0.1 to 95, preferably 0.1 to 70, and more preferably 0.1 to 60 by adjusting the kind and blending amount of the pigment.

As the coloring pigment, there can be mentioned, for example, composite metal oxide pigments, black iron oxide pigments, black titanium oxide pigments, pyrene black pigments, carbon black pigments, titanium white, zinc molybdate, calcium molybdate, Prussian blue, ultramarine, cobalt blue, copper phthalocyanine blue, indanthrone blue, chrome yellow, synthetic yellow iron oxide, bismuth vanadate, titanium yellow, zinc yellow (zinc yellow), monoazo yellow, ochre yellow, disazo yellow, isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, benzimidazolone yellow, iron oxide red, monoazo red, non-substituted phthalocyanine red, azo lake red (Mn salt), quinacridone magenta, anthraquinonyl orange, dianthraquinone red, pyrene brown red, pyrene red, diketopyrrolopyrrole molybdate red, chlorinated phthalocyanine green, brominated phthalocyanine green, or pyrazolone orange, benzimidazolone orange, oxazine violet, pyrene violet, and the like, any 1 of them or a combination thereof may be used.

Further, a transparent coloring pigment may be used as the coloring pigment.

The transparent coloring pigment may be any 1 or a combination of 1 or more selected from complex metal oxide pigments such as titanium yellow, azo pigments, phthalocyanine pigments, diketopyrrolopyrrole pigments, pyrene ketone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal complex azo pigments, phthalocyanine pigments, indanthrone pigments, dioxane pigments, and indigo pigments.

The extender pigment may be used in any one or combination of 1 or more selected from barium sulfate, barium carbonate, calcium carbonate, aluminum silicate, silica, magnesium carbonate, talc, alumina white, and the like.

Examples of the bright pigment include a metal in a particle form or a flake form (flake form or flake form), a glass or a metal oxide in a flake form (flake form or flake form), a ground product of a vapor deposited film, and an oxide coating material thereof.

The particulate or scaly (scaly or flaky) metal may be used in any 1 kind or combination of metal particles such as aluminum, copper, zinc, nickel, chromium, stainless steel, brass, and nickel alloy, or scales.

The glass or metal oxide in the scaly form (scaly or flaky form) may be used in any 1 kind or in combination, for example, from among glass flakes, natural mica, artificial mica, alumina flakes, silica flakes, and the like.

The ground product of the vapor deposited film may be a ground product of a vapor deposited film known as a vapor deposited metal flake pigment, and any 1 or more of the ground products obtained by vapor depositing a metal such as aluminum, gold, silver, copper, brass, titanium, chromium, nickel, nichrome, or stainless steel on a substrate such as a film, peeling the substrate, and then grinding the vapor deposited metal film may be used, or any combination thereof may be used.

The oxide coating material may be one in which the particulate or scaly (scale-like, flake-like) metal, the scaly (scale-like, flake-like) glass or metal oxide, or a ground product of the vapor deposited film is coated with an oxide such as alumina (aluminum oxide), silica (silicon oxide), mica, titanium oxide, and/or iron oxide, and any 1 or more thereof may be used from among them or a combination thereof.

The rust preventive pigment may be any one or a combination of 1 or more selected from zinc, zinc chromate, strontium chromate, calcium chromate, lead cyanamide, calcium plumbate, and zinc phosphate.

The pigment may be used in an appropriate combination in terms of light transmittance, substrate hiding property, desired hue, and the like, and the amount thereof used is preferably 10% or less, preferably 5% or less, in terms of substrate hiding property, weather resistance, and the like, in the cured coating film formed from the base coating material (X) having a light transmittance in the wavelength range of 400 to 700 nm.

The light transmittance of the coating film is a spectral light transmittance measured in a wavelength range of 400 to 700nm by using a self-counting spectrophotometer (EPS-3T type, manufactured by hitachi corporation) using the coating film as a sample, wherein the coating film is obtained by applying a coating material to a glass plate so as to form a predetermined film thickness on the basis of a cured coating film, curing the coating film, immersing the coating film in warm water at60 to 70 ℃, and peeling and drying the coating film. When there is a difference in the measured wavelength (400 to 700nm), the maximum value is taken as the light transmittance.

When the base paint (X) is colored, the black-and-white hiding film thickness of the base paint (X) is preferably 40 μm or less, more preferably 5 to 35 μm, and still more preferably 10 to 30 μm, from the viewpoint of color stability and the like. In the present specification, the "black-and-white masking film thickness" refers to a value obtained by applying a masking test paper of black-and-white municipality pattern defined in 4.1.2 of JIS K5600-4-1 onto a steel plate, coating the steel plate with a coating material in an inclined manner so that the film thickness changes continuously, drying or curing the coated steel plate, observing the coated surface with eyes under diffuse sunlight, and measuring the minimum film thickness of the black-and-white boundary of the municipality pattern where the masking test paper is not visible with an electromagnetic film thickness meter.

When the pigment is used in the base coating material (X), a desired amount of the pigment may be used according to the purpose or the like. The amount of the base coating material (X) is preferably in the range of 0.01 to 70 parts by mass, preferably 0.1 to 50 parts by mass, and more preferably 0.2 to 40 parts by mass, based on 100 parts by mass (solid content) of the base coating material (X).

The base coating material (X) in this case has a solid content of 10 to 60 mass% and a viscosity of 200 to 5000 mPas as measured at a temperature of 20 ℃ with a B-type viscometer at 6rpm after 1 minute. In the present specification, "LVDV-I" (trade name, manufactured by BROOKFIELD) is used as a type B viscometer.

< application of base coating (X) >

The base paint (X) may be applied by a conventional method, and in the case where the base paint (X) is an aqueous paint, for example, deionized water and, if necessary, additives such as a thickener and a defoaming agent may be added to the base paint (X), and after the solid content and viscosity are adjusted, the base paint (X) may be applied by spraying, spin coating, or the like on the surface of the object to be coated. When coating, static electricity can be applied as required.

The cured film thickness of the base coating film obtained from the base coating material (X) may be 0.1 to 35 μm, preferably 5 to 30 μm, and more preferably 10 to 25 μm, from the viewpoints of light transmittance, base hiding property, and brilliance.

[1-2. Process (2) ]

The step (2) is a step of forming a bright coating film by applying the bright pigment dispersion (Y) after forming the base coating film in the step (1).

Further, a step of applying a colorless clear paint, a colored clear paint, a bright clear paint, a colored bright paint or the like to form a desired coating film may be provided between the steps (1) and (2) as necessary, and a step of adjusting and/or preheating and/or curing the bright coating film may be provided.

< Bright pigment Dispersion (Y) >

The bright pigment dispersion (Y) contains water and a flaky bright pigment (A).

The bright pigment dispersion (Y) may further contain a viscosity modifier (B) and/or a surface modifier (C), if necessary.

From the viewpoint of obtaining a multilayer coating film having less graininess and excellent metallic luster, it is preferable that the bright pigment dispersion (Y) contain the viscosity modifier (B) and the surface modifier (C).

(Scale-like lustrous pigment (A))

The scaly bright pigment (A) may be selected from 1 or 2 or more kinds in combination from among the light-reflective pigments and the light-interference pigments.

The thickness T of the flaky bright pigment (A) is an average thickness, and may be 1 to 65nm, preferably 5 to 60nm, and more preferably 10 to 50 nm.

As the flaky bright pigment (a), it is difficult to obtain a flaky bright pigment having a thickness T of less than 1nm, and it is difficult to obtain a multilayer coating film having a small granular feel and excellent metallic luster with a flaky bright pigment having a thickness of more than 65 nm.

The average particle diameter of the flaky bright pigment (A) varies depending on the kind of the flaky bright pigment (A), but may be 0.1 to 100 μm, usually 0.1 to 50 μm, preferably 1.0 to 23 μm, and more preferably 5.0 to 20 μm.

The average thickness is defined as the average of 100 or more measured values obtained by observing and measuring a cross section of a coating film containing the flaky bright pigment (A) with a Transmission Electron Microscope (TEM).

The average particle diameter is a median diameter of a volume-based particle size distribution measured by a laser diffraction scattering method using a Microtrac particle size distribution measuring apparatus MT3300 (trade name, manufactured by japan ltd).

Specific examples of the flaky bright pigment (a) include a flaky metallic pigment such as aluminum, copper, chromium, nickel alloy, and stainless steel, a flaky metallic pigment coated with a metal oxide on the surface, a light-reflective pigment such as a flaky metallic pigment having a coloring pigment chemically adsorbed or bonded on the surface, and an interference pigment such as a metal oxide-coated mica pigment, a metal oxide-coated alumina flake pigment, a metal oxide-coated glass flake pigment, and a metal oxide-coated silica flake pigment.

The flaky bright pigment (A) is not particularly limited as long as the thickness T is 1 to 65 nm.

When a light-reflective pigment is used as the scaly bright pigment (a), a metal flake pigment deposited by evaporation is preferably used from the viewpoint of easy availability, granular feel, and finished appearance.

The metal flake pigment to be deposited can be obtained by depositing metal flakes on a base material, peeling the base material, and then pulverizing the metal flakes to be deposited. Examples of the substrate include a film.

The material of the metal is not particularly limited, but examples thereof include aluminum, gold, silver, copper, brass, titanium, chromium, nickel, nichrome, and stainless steel. Among them, aluminum and chromium are particularly preferable from the viewpoint of easy availability and easy handling. In the present specification, a metal deposition scale pigment obtained by depositing aluminum is referred to as an "aluminum deposition scale pigment", and a metal deposition scale pigment obtained by depositing chromium is referred to as an "deposited chromium scale pigment".

Examples of commercially available products that can be used as the aluminum deposited flake pigment include "Hydroshine WS" series (trade name, manufactured by ECKART), "Decome" series (trade name, manufactured by SCHLENK), and "Metashen" series (trade name, manufactured by BASF).

Examples of commercially available products that can be used as the above-mentioned evaporated chromium scale pigment include "metallic Liquid Black" series (trade name, product of ECKART corporation).

The average primary particle diameter (D50) of the deposited metal flake pigment is preferably 0.1 to 50 μm, more preferably 1 to 23 μm, and most preferably 5 to 20 μm, from the viewpoints of stability in a paint, color tone of a coating film to be formed, and handling properties.

When an aluminum deposited flake pigment is used as the metal deposited flake pigment, it is preferable to subject the surface of the aluminum deposited flake pigment to a silica treatment from the viewpoint of obtaining a coating film excellent in storage stability and brilliance.

As the flaky bright pigment (a), a flaky aluminum pigment produced by pulverizing and grinding aluminum in a ball mill or an attritor mill in the presence of a pulverizing medium using a pulverizing aid can be used. Here, as the grinding aid, in addition to higher fatty acids such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid, myristic acid, fatty amines, fatty amides, fatty alcohols, and the like can be used. As the pulverization medium, an aliphatic hydrocarbon such as mineral spirits can be used.

Depending on the kind of the pulverization aid, the flaky aluminum pigment can be roughly classified into a floating type and a non-floating type. When the aluminum pigment is blended into a coating composition, the floating type can be aligned (floated) on the surface of a coating film obtained by coating, a finished product having a strong metallic feeling can be obtained, and a heat reflection effect can be exerted, and rust preventive ability can be exerted, but when the scaly aluminum pigment of this type is used, it is necessary to pay attention to the effect of the surface tension of the grinding aid, depending on the blending amount thereof, in the process of forming the coating film, thereby hiding the entire surface and making the coating film easily peelable. From this viewpoint, a non-leafing type scaly aluminum pigment is preferably used.

When a light-reflective pigment is used as the scaly bright pigment (a), 1 or more selected from the group consisting of an aluminum vapor deposition scaly pigment, a chromium vapor deposition scaly pigment, an aluminum vapor deposition scaly pigment having a surface treated with silica, a non-floating aluminum scaly pigment, and a non-floating aluminum scaly pigment having a surface treated with silica can be preferably used.

When a light interference pigment is used as the flaky bright pigment (a), specifically, a pigment in which a translucent base material such as natural mica, artificial mica, alumina flakes, silica flakes, or glass flakes is coated with a metal oxide can be used.

The optical interference pigment may be subjected to a surface treatment for improving dispersibility, water resistance, chemical resistance, weather resistance, and the like.

The metal oxide-coated mica pigment is a pigment in which natural mica or artificial mica is used as a base material and a metal oxide is coated on the surface of the base material.

The natural mica is a scaly substrate obtained by pulverizing mica ore (mica), and the artificial mica is SiO₂、MgO、Al₂0₃、K₂SiF₆、Na₂SiF₆And the synthetic mica, which is synthesized by heating industrial raw materials, melting them at a high temperature of about 1500 ℃, cooling them, and crystallizing them, has fewer impurities and more uniform size and thickness than natural mica.

Specifically, fluorophlogopite (KMg) is known₃AlSi₃O₁₀F₂) Tetrasilicosylvite mica (KMg)_2.5AlSi₄O₁₀F₂) Tetrasilicic sodium mica (NaMg)_2.5AlSi₄O₁₀F₂) And Na-type tridentate (Na-taeniolite) (NaMg)₂LiSi₄O₁₀F₂) Or tridentigen Lina (LiNaMg)₂LiSi₄O₁₀F₂) And the like.

Examples of the coating metal oxide include titanium oxide, iron oxide, and aluminum oxide. By coating the metal oxide, an interference color can be expressed.

The metal oxide coated aluminum oxide flake pigment is a pigment which takes aluminum oxide flakes as a base material and is coated with metal oxide on the surface of the base material. The aluminum oxide scale is scaly (flaky) aluminum oxide, and is colorless and transparent. The alumina need not be a single component, and may contain oxides of other metals. Examples of the coating metal oxide include titanium oxide and iron oxide. By coating the metal oxide, an interference color can be expressed.

The metal oxide-coated silica flake pigment is a pigment in which a base material having a smooth surface and a uniform thickness, that is, a flake silica, is coated with a metal oxide having a refractive index different from that of the base material. Examples of the coating metal oxide include titanium oxide, iron oxide, and aluminum oxide. By coating the metal oxide, an interference color can be expressed.

The metal oxide-coated glass flake pigment is a pigment in which a scaly glass substrate is coated with a metal oxide, and since the surface of the substrate is smooth, the granular feeling can be expressed by strong reflection of light. Examples of the coating metal oxide include titanium oxide and iron oxide. By coating the metal oxide, an interference color can be expressed.

In the case of an optical interference pigment based on natural mica, artificial mica, alumina flakes or silica flakes, the particle size of the optical interference pigment is preferably in the range of 5 to 30 μm, particularly preferably 7 to 25 μm, in terms of the finished appearance and granular feel of the coating film.

In the case of a light interference pigment based on glass flakes, a particle size having an average particle size of 15 to 100 μm, particularly preferably 17 to 45 μm, can be used from the viewpoint of the granular feel of the coating film.

When the average particle size exceeds the upper limit, the feeling of particles due to the light interference pigment passing through the multilayer coating film may be excessive, which is not preferable in terms of design, and when the average particle size is less than the lower limit, luminance may be insufficient.

When a light interference pigment is used as the flaky bright pigment (a), it is preferable to use 1 or more selected from the group consisting of a metal oxide-coated mica pigment, a metal oxide-coated alumina flake pigment, a metal oxide-coated glass flake pigment and a metal oxide-coated silica flake pigment.

From the viewpoint of obtaining a multilayer coating film excellent in the brilliance, the bright pigment dispersion (Y) may contain the above-mentioned flaky bright pigment (a) in an amount of 0.2 to 80 parts by mass, particularly 0.5 to 25 parts by mass, and preferably 0.7 to 20 parts by mass, based on 100 parts by mass (solid content) of the bright pigment dispersion.

(viscosity modifier (B))

As the viscosity modifier (B) in the bright pigment dispersion (Y), known viscosity modifiers can be used, but examples thereof include silica-based fine powders, mineral-based viscosity modifiers, barium sulfate fine particles, polyamide-based viscosity modifiers, organic resin fine particle viscosity modifiers, diurea-based viscosity modifiers, polyurethane-complex viscosity modifiers, acrylic swelling type, i.e., polyacrylic viscosity modifiers, and cellulose-based viscosity modifiers. Among them, mineral-based viscosity modifiers, polyacrylic-based viscosity modifiers, and cellulose-based viscosity modifiers are particularly preferably used from the viewpoint of obtaining a coating film having excellent brilliance.

Examples of the mineral viscosity modifier include those having a crystal structure of 2: a swellable layered silicate having a type 1 structure. Specific examples thereof include smectite clay minerals such as natural or synthetic montmorillonite, saponite, hectorite, stevensite (beidellite), nontronite, bentonite, and artificial lithium magnesium silicate (laponite), swellable mica clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na-salt onyx fluorine mica, and Li-type onyx fluorine mica, and vermiculite, and substituted or derived products thereof, and mixtures thereof.

Examples of the polyacrylic acid viscosity modifier include sodium polyacrylate, polyacrylic acid- (meth) acrylate copolymer, and the like.

The polyacrylic acid viscosity modifier may have an acid value as an active ingredient of 30 to 300mgKOH/g, preferably 80 to 280 mgKOH/g.

Examples of commercially available polyacrylic viscosity modifiers include "Primal ASE-60", "Primal TT 615", "Primal RM 5" (trade name) manufactured by DOW CHEMICAL, and "SN Thickner 613", "SN Thickner 618", "SN Thickner 630", "SN Thickner 634", and "SN Thickner 636" (trade name) manufactured by SAN NOPCO.

Examples of the cellulose-based viscosity modifier include carboxymethyl cellulose, methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, and cellulose nanofibers, and among these, cellulose nanofibers are preferably used from the viewpoint of obtaining a coating film having excellent brilliance.

The cellulose nanofibers are also referred to as cellulose fibrils, fibrillated cellulose, or nanocellulose crystals.

The cellulose nanofibers preferably have a number average fiber diameter in the range of 2 to 500nm, more preferably 2 to 250nm, and even more preferably 2 to 150nm, from the viewpoint of obtaining a coating film having excellent brilliance. The number average fiber length is preferably in the range of 0.1 to 20 μm, more preferably 0.1 to 15 μm, and still more preferably 0.1 to 10 μm.

The number average fiber diameter and the number average fiber length can be measured and calculated, for example, from an image obtained by dispersing a sample of cellulose nanofibers diluted with water, casting the sample on a hydrophilized carbon film-coated grid, and observing the resulting product with a Transmission Electron Microscope (TEM).

The cellulose nanofibers may be cellulose nanofibers obtained by fluffing a cellulose material and stabilizing the cellulose material in water.

Here, the cellulose material refers to a material having various forms mainly composed of cellulose, and specific examples thereof include pulp (pulp derived from herbs such as wood pulp, jute, abaca, and kenaf); natural cellulose such as cellulose produced by microorganisms; regenerated cellulose spun by dissolving cellulose in a solvent such as a copper ammonia solution or a morpholine derivative; and fine cellulose obtained by depolymerizing cellulose by subjecting the cellulose raw material to mechanical treatment such as hydrolysis, alkaline hydrolysis, enzymatic hydrolysis, bursting treatment, or a vibratory ball mill.

Further, the cellulose raw material may be subjected to various treatments by anion modification using a known method, and further, an aqueous dispersion dispersed in an aqueous solvent may be used. For example, a modified cellulose obtained by introducing a group such as a carboxyl group, a carboxymethyl group, or a phosphoric group into a cellulose raw material by a known method is washed to prepare a dispersion of the modified cellulose, and a mechanical shearing force is applied to the dispersion to thereby disintegrate the cellulose, and then cellulose nanofibers are used.

Examples of commercially available cellulose nanofibers include RHEOCRYSTA (registered trademark) manufactured by first industrial pharmaceutical co. In the present invention, for example, cellulose nanofibers prepared as follows can be used.

The cellulose nanofibers can be produced, for example, by the following method.

The method of defibering the cellulose material is not particularly limited as long as the cellulose material can maintain a fibrous state, but examples thereof include a mechanical defibering treatment using a homogenizer, a grinder, or the like, a chemical treatment using an oxidation catalyst, or a biological treatment using a microorganism.

Further, as the cellulose nanofibers, anion-modified cellulose nanofibers can be used. Examples of the anion-modified cellulose nanofibers include carboxylated cellulose nanofibers, carboxymethylated cellulose nanofibers, and cellulose nanofibers containing phosphoric acid groups. The anion-modified cellulose nanofibers can be obtained by, for example, introducing a functional group such as a carboxyl group or a carboxymethyl group into a cellulose raw material by a known method, washing the obtained modified cellulose, preparing a dispersion of the modified cellulose, and then defibering the obtained dispersion. The above carboxylated cellulose is also called oxidized cellulose.

The oxidized cellulose can be obtained, for example, by oxidizing the cellulose raw material in water using an oxidizing agent in the presence of a compound selected from an N-oxyl compound, a bromide, an iodide, or a mixture thereof.

The amount of the N-oxyl compound to be used is not particularly limited as long as it is an amount of a catalyst capable of causing cellulose to be nanofibrillated. The amount of bromide or iodide used may be appropriately selected within a range that can promote the oxidation reaction.

As the oxidizing agent, known oxidizing agents can be used, and examples thereof include chlorine, hypochlorous acid, chlorous acid, perchloric acid, salts thereof, oxychlorides, peroxides, and the like. The amount of carboxyl groups in the oxidized cellulose is preferably set to 0.2mmol/g or more based on the mass of the solid content of the oxidized cellulose. The amount of carboxyl groups can be adjusted by adjusting the time of the oxidation reaction; adjusting the oxidation reaction temperature; adjusting the pH value during the oxidation reaction; the amount of the N-oxyl compound, bromide, iodide, an oxidizing agent, etc. is adjusted.

The introduction of the carboxymethyl group can be carried out as follows.

The cellulose material is mixed with a solvent, and an alkali treatment is performed using an alkali metal hydroxide as an alkalinizing agent in an amount of 0.5 to 20 times by mol per glucose residue of the cellulose material at a reaction temperature of 0 to 70 ℃ for 15 minutes to 8 hours. Then, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times by mol per glucose residue, and the resulting mixture is reacted at a reaction temperature of 30 to 90 ℃ for 30 minutes to 10 hours to introduce a carboxymethyl group into a hydroxyl group in a cellulose molecule.

The modified cellulose obtained by introducing a carboxymethyl group into the cellulose material preferably has a degree of substitution per unit of carboxymethyl group per glucose of 0.02 to 0.50.

The modified cellulose obtained as described above is dispersed in an aqueous solvent to form a dispersion, and then defibered by using a pulverizer. The pulverizer used may be any of a high-speed shearing type, an impact type, a bead mill type, a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, and an ultrasonic type. Further, a plurality of them may be used in combination. Among them, from the viewpoint that a stronger shearing force can be handled under the condition that the risk of contamination of the medium is low, a fluffer of a high-speed shearing type, a collision type, and a high-speed rotation type is preferably used.

The viscosity modifiers may be used singly or in combination of 2 or more.

(surface conditioner (C))

Preferably, the bright pigment dispersion (Y) further contains a surface conditioner (C). When the bright pigment dispersion (Y) is applied to a coating object, a surface conditioner is used in order to help align the scaly bright pigment (a) dispersed in water uniformly on the coating object. If the scaly bright pigment (A) can be uniformly oriented on the object to be coated, a multilayer coating film having less graininess and excellent metallic luster can be obtained.

The surface conditioner (C) is preferably a liquid mixed at a ratio of isopropyl alcohol/water/surface conditioner (C) of 4.5/95/1, the viscosity of the liquid is adjusted to 150mPa · s at a temperature of 20 ℃ and a rotation speed of 60rpm on a B-type viscometer, 10 μ L is dropped on a preliminarily degreased tin plate (manufactured by PALTEK), and a contact angle with respect to the tin plate is measured after 10 seconds, and is 8 to 20 °, preferably 9 to 19 °, and more preferably 10 to 18 °. At this time, a viscosity modifier "ASE-60" (polyacrylic viscosity modifier, manufactured by DOW CHEMICAL Co., Ltd., solid content: 28%) was used for viscosity adjustment.

The ratio of isopropyl alcohol/water/surface conditioner (C) was 4.5/95/1, which corresponds to the ratio of the components of the bright pigment dispersion (Y) for evaluation of the surface conditioner (C). The viscosity at60 rpm of the rotor of the type B viscometer was 150 mPas, which is a value generally used when the coating material was applied. The contact angle of the tin plate of 8 to 20 ° means wet spreading of the liquid under standard coating conditions. When the contact angle is 8 ° or more, the liquid can be coated on the coated object without being excessively diffused, and when it is 20 ° or less, the liquid can be uniformly coated on the coated object without being excessively depressed.

Examples of the surface conditioner (C) include surface conditioners (C) such as silicones, acetylene glycols, acrylics, ethylenes, and fluorines. The surface conditioning agents (C) can be used singly or in appropriate combination of 2 or more.

Examples of commercially available surface conditioner (C) include BYK series available from BYK-Chemie, Tego series available from Evonik Industries, Surfynol series, Dynol series available from Kyoho chemical, Glanol series available from Polyflow series available from Kyoho chemical, and Disparlon series available from Nanzhi chemical.

Among them, silicone-based surface control agents and acetylene glycol-based surface control agents are preferable as the surface control agent (C) from the viewpoint of metallic luster and water resistance of the obtained coating film. As the silicone-based surface conditioner, polydimethylsiloxane or a modified silicone obtained by modifying the polydimethylsiloxane can be used. Examples of the modified silicone include polyether modified products, acrylic modified products, and polyester modified products. The acetylene glycol surface-modifying agent may be a surface-modifying agent obtained by adding an oxyalkylene to acetylene glycol.

As the surface conditioner (C), a surface conditioner having a dynamic surface tension of preferably 50 to 70mN/m, more preferably 53 to 68mN/m, and still more preferably 55 to 65mN/m can be used. In the present specification, the dynamic surface tension refers to a surface tension value at a frequency of 10Hz measured by the maximum bubble pressure method.

The dynamic surface tension was measured using a SITA measuring apparatus (SITAt 60, inc., hong fine products).

Further, as the surface conditioner (C), a surface conditioner having a static surface tension of preferably 15 to 30mN/m, more preferably 18 to 27mN/m, and still more preferably 20 to 24mN/m may be used.

The static surface tension can be measured using a surface tension meter (DCAT 21, engelhardson co.).

Further, as the surface conditioner (C), a surface conditioner having a length of the thin layer (Lamella) of preferably 6.0 to 9.0mm, more preferably 6.5 to 8.5mm, and still more preferably 7.0 to 8.0mm may be used.

The bright pigment dispersion (Y) may contain a matrix resin and a crosslinking agent from the viewpoint of adhesion of the obtained coating film.

Examples of the matrix resin include acrylic resins, polyester resins, alkyd resins, and polyurethane resins. They may be aqueous dispersions or solutions.

Examples of the crosslinking agent include melamine resins, melamine resin derivatives, urea resins, (meth) acrylamides, polyaziridines, polycarbodiimides, and polyisocyanate compounds which may or may not be blocked. They may be used alone or in combination of 2 or more.

If necessary, a pH adjuster, an organic solvent, a coloring pigment, an extender pigment, a bright pigment other than the flaky bright pigment (a), a pigment dispersant, an anti-settling agent, an antifoaming agent, an ultraviolet absorber, and the like may be further appropriately blended in the bright pigment dispersion (Y).

As the pH adjuster to be added to the bright pigment dispersion (Y) as needed, specifically, a pH adjuster generally used for paints can be used.

The pH adjuster may be any of an inorganic acid, an inorganic base, an organic acid, and an organic base. They may be used alone or in combination of 2 or more.

As the organic solvent to be blended in the bright pigment dispersion (Y) as required, specifically, an organic solvent generally used for paints can be used.

Examples of the organic solvent include the same organic solvents as those optionally blended in the base coat (X). They may be used alone or in combination of 2 or more.

The content of the organic solvent in the bright pigment dispersion (Y) may be 0 to 40 parts by mass, particularly 0 to 30 parts by mass, and preferably 0 to 20 parts by mass, based on 100 parts by mass of the bright pigment dispersion.

The coloring pigment to be blended in the bright pigment dispersion (Y) as required may contain 1 or a combination of 2 or more kinds of conventionally known pigments for ink, paint and plastic coloring.

Examples of the color pigment include the same color pigments as those optionally blended in the base coat (X). By using these alone or 2 or more in combination, a desired color tone can be realized.

Examples of the extender pigment include barium sulfate, barium carbonate, calcium carbonate, aluminum silicate, silica, magnesium carbonate, talc, and alumina white.

(blending amount of each component of the bright pigment dispersion (Y))

The bright pigment dispersion (Y) contains water and a flaky bright pigment (A). In the bright pigment dispersion (Y), the blending ratio of each component is preferably in the following range from the viewpoint of obtaining a coating film excellent in bright property,

based on 100 parts by mass of the total amount of water and the flaky bright pigment (A),

water: 70 to 99.999 parts by mass, preferably 80 to 99.999 parts by mass, more preferably 90 to 99.995 parts by mass,

flaky bright pigment (a): 30 to 0.001 parts by mass, preferably 20 to 0.001 parts by mass, and more preferably 10 to 0.005 parts by mass (mass of solid content).

When the bright pigment dispersion (Y) contains the viscosity modifier (B), the viscosity modifier (B) may be contained in an amount of 0.1 to 50 parts by mass, particularly 1 to 35 parts by mass, and preferably 5 to 25 parts by mass in terms of solid content, based on 100 parts by mass (solid content) of the bright pigment dispersion, from the viewpoint of obtaining a multilayer coating film having excellent bright properties.

When the viscosity modifier (B) contains a cellulose-based viscosity modifier, the content of the cellulose-based viscosity modifier is preferably in the range of 2 to 100 parts by mass, more preferably in the range of 5 to 70 parts by mass, and particularly preferably in the range of 8 to 60 parts by mass, based on 100 parts by mass (solid content) of the bright pigment dispersion, from the viewpoint of obtaining a multilayer coating film having excellent brilliance.

When the bright pigment dispersion (Y) contains the surface conditioner (C), the surface conditioner (C) may be contained in an amount of 1 to 50 parts by mass, particularly 5 to 45 parts by mass, and preferably 8 to 40 parts by mass in terms of solid content, based on 100 parts by mass (solid content) of the bright pigment dispersion, from the viewpoint of obtaining a multilayer coating film having excellent bright properties.

(coating of Bright pigment Dispersion (Y))

The bright pigment dispersion (Y) can be prepared by mixing and dispersing the aforementioned components.

From the viewpoint of obtaining a coating film excellent in brilliance, the solid content at the time of coating is preferably adjusted to 0.1 to 15 mass%, preferably 0.2 to 10 mass%, based on the brilliant pigment dispersion (Y).

From the viewpoint of obtaining a coating film excellent in the brilliance, the viscosity of the bright pigment dispersion (Y) is preferably 60 to 1500mPa · s, preferably 60 to 1000mPa · s, and more preferably 60 to 500mPa · s, at a temperature of 20 ℃, after 1 minute at60 rpm as measured with a B-type viscometer (sometimes referred to as "B60 value" in the present specification). At this time, the viscometer used was LVDV-I (trade name, model B viscometer manufactured by BROOKFIELD).

The bright pigment dispersion (Y) can be applied by electrostatic coating, air spraying, airless spraying, or the like. In the multilayer coating film forming method of the present invention, rotary atomizing electrostatic coating is particularly preferred.

The bright coating film obtained by applying the bright pigment dispersion (Y) is preferably subjected to an appropriate method after application, for example, a method of leaving at room temperature for 15 to 30 minutes, a method of preheating at 50 to 100 ℃ for 30 seconds to 10 minutes, or the like.

The thickness of the bright coating film is preferably 0.02 to 6.5 μm, more preferably 0.04 to 5.0. mu.m, still more preferably 0.12 to 3.0. mu.m, particularly preferably 0.12 to 2.0. mu.m, and most preferably 0.12 to 1.0. mu.m, as the cured film thickness.

When the thickness of the bright coating film is less than 0.02 μm, it is difficult to form a bright coating film, and the amount of the bright pigment contained per unit area of the multilayer coating film is small, which is not preferable because the reflection intensity is lowered. When the cured film thickness of the bright coating film exceeds 6.5 μm, the alignment of the bright pigment is lowered, which is not preferable.

[1-3. Process (3) ]

The step (3) is a step of forming a clear coating film by applying the clear coating material (Z) on the bright coating film formed in the step (2).

Further, a step of applying a colorless clear paint, a colored clear paint, a bright clear paint, a colored bright clear paint, or the like to form a desired coating film may be provided between the steps (2) and (3) as necessary, and a step of adjusting and/or preheating and/or curing the bright coating film may be provided.

< clear coating Material (Z) >

The clear coating (Z) may be any known thermosetting clear coat coating composition. Examples of the thermosetting clear coat coating composition include a base resin having a crosslinkable functional group, and an organic solvent-based thermosetting coating composition, an aqueous thermosetting coating composition, a powder thermosetting coating composition, and the like containing a crosslinking agent.

Examples of the crosslinkable functional group having the matrix resin include a carboxyl group, a hydroxyl group, an epoxy group, and a silanol group. Examples of the type of the matrix resin include acrylic resins, polyester resins, alkyd resins, polyurethane resins, epoxy resins, and fluorine resins. Examples of the crosslinking agent include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

The combination of the base resin/crosslinking agent of the clear coating material (Z) is preferably a carboxyl group-containing resin/epoxy group-containing resin, a hydroxyl group-containing resin/polyisocyanate compound, a hydroxyl group-containing resin/blocked polyisocyanate compound, a hydroxyl group-containing resin/melamine resin, or the like.

The clear coating (Z) may be a 1-liquid type coating or a multi-liquid type coating such as a 2-liquid type urethane resin coating.

From the viewpoint of the adhesion of the obtained coating film, the clear coating material (Z) is preferably a 2-liquid type clear coating material containing a hydroxyl group-containing resin and an isocyanate group-containing compound.

When a 2-liquid type clear coating material containing a hydroxyl group-containing resin and an isocyanate group-containing compound is used as the clear coating material (Z), it is preferable that the hydroxyl group-containing resin and the polyisocyanate compound are in a separate form from each other and are mixed immediately before use, from the viewpoint of storage stability.

When a 1-liquid type coating material is used as the clear coating material (Z), the combination of the base resin/the crosslinking agent in the 1-liquid type coating material includes a carboxyl group-containing resin/an epoxy group-containing resin, a hydroxyl group-containing resin/a blocked polyisocyanate compound, a hydroxyl group-containing resin/a melamine resin, and the like. When a 1-liquid type coating material is used as the clear coating material (Z), it is preferable that the clear coating material (Z) contains a self-crosslinkable component from the viewpoint of adhesion.

Examples of the self-crosslinkable component include melamine resins, melamine resin derivatives, (meth) acrylamides, polyaziridines, polycarbodiimides, and polyisocyanates which may or may not be blocked. They may be used alone or in combination of 2 or more.

In the clear coating material (Z), if necessary, a solvent such as water or an organic solvent, a curing catalyst, an antifoaming agent, an ultraviolet absorber and other additives can be appropriately blended.

(hydroxyl group-containing resin)

As the hydroxyl group-containing resin, any conventionally known resin can be used without limitation as long as it contains a hydroxyl group. Examples of the hydroxyl group-containing resin include a hydroxyl group-containing acrylic resin, a hydroxyl group-containing polyester resin, a hydroxyl group-containing polyether resin, and a hydroxyl group-containing polyurethane resin, preferred examples of the hydroxyl group-containing resin include a hydroxyl group-containing acrylic resin and a hydroxyl group-containing polyester resin, and particularly preferred examples of the hydroxyl group-containing resin include a hydroxyl group-containing acrylic resin.

The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 80 to 200mgKOH/g, more preferably 100 to 180 mgKOH/g. When the hydroxyl value is 80mgKOH/g or more, the crosslinking density is high, and therefore, the abrasion resistance is sufficient. Further, when the content is 200mgKOH/g or less, the water resistance of the coating film can be maintained.

The hydroxyl group-containing acrylic resin preferably has a weight average molecular weight of 2500 to 40000, more preferably 5000 to 30000. When the weight average molecular weight is 2500 or more, the coating film performance such as acid resistance is good, and when the weight average molecular weight is 40000 or less, the handling property is good because smoothness of the coating film can be maintained.

In the present specification, the average molecular weight is a value calculated from a chromatogram measured by gel permeation chromatography based on the molecular weight of standard polystyrene. The gel permeation chromatography used was "HLC 8120 GPC" (manufactured by Tosoh corporation). As the column, 4 columns of "TSKgel G-4000 HXL", "TSKgel G-3000 HXL", "TSKgel G-2500 HXL" and "TSKgel G-2000 HXL" (trade name, manufactured by Tosoh Corp.) were used, and in the mobile phase: tetrahydrofuran, measurement temperature: 40 ℃, flow rate: 1 cc/min, detector: under the condition of RI.

The glass transition temperature of the hydroxyl-containing acrylic resin is preferably in the range of-40 ℃ to 20 ℃, particularly preferably in the range of-30 ℃ to 10 ℃. When the glass transition temperature is-40 ℃ or higher, the hardness of the coating film is sufficient, and when the glass transition temperature is 20 ℃ or lower, the smoothness of the coated surface of the coating film can be maintained.

(polyisocyanate Compound)

The polyisocyanate compound is a compound having at least 2 isocyanate groups in 1 molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates.

Examples of the aliphatic polyisocyanate include aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1, 2-propylene diisocyanate, 1, 2-butylene diisocyanate, 2, 3-butylene diisocyanate, 1, 3-butylene diisocyanate, 2, 4, 4-or 2, 2, 4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and 2, 6-diisocyanatomethylhexanoate (generic name: lysine diisocyanate); aliphatic triisocyanates such as 2-isocyanatoethyl 2, 6-diisocyanatohexanoate, 1, 6-diisocyanato-3-isocyanatomethylhexane, 1, 4, 8-triisocyanatooctane, 1, 6, 11-triisocyanatoundecane, 1, 8-diisocyanato-4-isocyanatomethyloctane, 1, 3, 6-triisocyanatohexane and 2, 5, 7-trimethyl-1, 8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate include 1, 3-cyclopentane diisocyanate, 1, 3-cyclopentene diisocyanate, 1, 4-cyclohexane diisocyanate, 1, 3-cyclohexane diisocyanate, 3-isocyanatomethylene-3, 5, 5-trimethylcyclohexyl isocyanate (generic name: isophorone diisocyanate), 4-methyl-1, 3-cyclohexylxylene diisocyanate (generic name: hydrogenated TDI), 2-methyl-1, 3-cyclohexylxylene diisocyanate, 1, 3-or 1, 4-bis (isocyanatomethyl) cyclohexane (generic name: hydrogenated xylene diisocyanate) or a mixture thereof, dimethylene (4, 1-cyclohexanediyl) diisocyanate (generic name: hydrogenated MDI), and mixtures thereof, Alicyclic diisocyanates such as norbornane diisocyanate; 1, 3, 5-triisocyanatocyclohexane, 1, 3, 5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2, 6-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanato ethyl) -2-isocyanato-3- (3-isocyanatopropyl) -heptane, Alicyclic triisocyanates such as 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane and 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane.

Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylenebis (4, 1-phenylene) diisocyanate (common name: MDI), 1, 3-or 1, 4-xylylene diisocyanate or a mixture thereof, ω' -diisocyanato-1, 4-diethylbenzene, 1, 3-or 1, 4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; and araliphatic triisocyanates such as 1, 3, 5-triisocyanatomethylbenzene.

Examples of the aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4' -diphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 2, 4-toluene diisocyanate (common name: 2, 4-TDI), 2, 6-toluene diisocyanate (common name: 2, 6-TDI) or a mixture thereof, 4' -toluidine diisocyanate, 4' -diphenyl ether diisocyanate, and the like; aromatic triisocyanates such as triphenylmethane-4, 4', 4 ″ -triisocyanate, 1, 3, 5-triisocyanatophenyl ester, 2, 4, 6-toluene triisocyanate and the like; and aromatic tetraisocyanates such as 4, 4' -diphenylmethane-2, 2', 5, 5' -tetraisocyanate.

Further, as the derivative of the polyisocyanate, there can be mentioned, for example, a dimer, trimer, biuret, allophanate, uretdione, uretonimine, isocyanurate, oxazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), crude TDI and the like of the above-mentioned polyisocyanate.

The above polyisocyanates and derivatives thereof may be used alone or in combination of 2 or more.

Among aliphatic diisocyanates, hexamethylene diisocyanate-based compounds and 4, 4' -dimethylene (cyclohexyl isocyanate) among alicyclic diisocyanates can be preferably used. Among these, a derivative of hexamethylene diisocyanate is particularly preferable from the viewpoint of adhesion, compatibility, and the like.

Further, as the polyisocyanate compound, the polyisocyanate and its derivative, and a prepolymer obtained by reacting a compound having an active hydrogen group such as a hydroxyl group or an amino group with the polyisocyanate under a condition of an excess of isocyanate groups can be used. Examples of the compound capable of reacting with the polyisocyanate include polyols, low molecular weight polyester resins, amines, water, active hydrogen group-containing resins (acrylate polyols, polyolefin polyols, polyurethane polyols, polyether polyols, and polyester polyols), and the like.

Further, as the polyisocyanate compound, a blocked polyisocyanate compound, which is a compound obtained by blocking an isocyanate group in the polyisocyanate or the derivative thereof with a blocking agent, may be used.

Examples of the blocking agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybenzyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactams such as epsilon-caprolactam, delta-valerolactam, gamma-butyrolactam and beta-propiolactam; aliphatic alcohols such as methanol, ethanol, propanol, butanol, pentanol, and lauryl alcohol; ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethyl alcohol; alcohols such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methyl acrylate; oximes such as formamide oxime, acetamide oxime, acetyl oxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene groups such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; amides such as acetanilide, acetoxyaniline, acetyltoluidine, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; imides such as succinimide, phthalimide, and maleimide; amines such as diphenylamine, phenylnaphthylamine, dimethylaniline, N-phenyldimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylaniline; imidazoles such as imidazole and 2-methylimidazole; ureas such as urea, thiourea, ethylene urea, ethylene thiourea and diphenylurea; carbamates such as phenyl N-phenylcarbamate; imines such as ethyleneimine and propyleneimine; sulfites such as sodium bisulfite and potassium bisulfite; azole compounds, and the like. Examples of the azole compound include pyrazole or pyrazole derivatives such as pyrazole, 3, 5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3, 5-dimethylpyrazole, 4-nitro-3, 5-dimethylpyrazole, 4-bromo-3, 5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole and 2-phenylimidazole; imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline, and the like.

When the block formation (reaction of the block agent) is carried out, a solvent may be added as necessary. As the solvent used in the blocking reaction, a solvent which is unreactive to an isocyanate group is preferable, and examples thereof include ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and solvents such as N-methyl-2-pyrrolidone (NMP).

The polyisocyanate compounds may be used singly or in combination of 2 or more.

When a 2-liquid type clear coating material containing a hydroxyl group-containing resin and an isocyanate group-containing compound is used as the clear coating material (Z), the equivalent ratio (NCO/OH) of the hydroxyl group-containing resin to the isocyanate group of the polyisocyanate compound is preferably in the range of 0.5 to 2.0, and more preferably in the range of 0.8 to 1.5, from the viewpoints of curability, abrasion resistance, and the like of a coating film.

The clear coating material (Z) may contain a pigment such as a coloring pigment, a bright pigment or an extender pigment, a dye or the like as appropriate within a range not to impair the transparency.

The coloring pigment may be 1 or a combination of 2 or more conventionally known pigments for ink and paint.

As such a coloring pigment, the coloring pigment used in the base coat (X) can be used.

As the bright pigment, conventionally known bright pigments can be used.

The bright pigment may be the bright pigment used in the bright pigment dispersion (Y), and the bright pigment may be used in any thickness. It may be particularly preferred to use a light interference pigment.

Specifically, the dye may be any 1 or more of azo dyes and triphenylmethane dyes having excellent weather resistance, or a combination thereof.

The amount of the pigment added when the clear coating material (Z) contains a pigment may be appropriately determined, but is preferably 10 parts by mass or less, and more preferably 0.01 to 5 parts by mass, based on 100 parts by mass of the resin solid content in the clear coating material (Z).

The form of the clear coating (Z) is not particularly limited, but it is usually used as an organic solvent-based coating composition. As the organic solvent used in this case, various organic solvents for coating materials such as aromatic or aliphatic hydrocarbon solvents; an ester solvent; a ketone solvent; ether solvents, and the like. The organic solvent used may be the same as that used in the preparation of the hydroxyl group-containing resin or may be added as appropriate.

The solid content concentration of the clear coating material (Z) is preferably in the range of 30 to 70 mass%, more preferably 40 to 60 mass%.

After the bright coating film is formed, the clear coating material (Z) may be applied on the bright coating film or on an arbitrary coating film provided on the bright coating film.

The application of the clear coat (Z) is not particularly limited, and can be carried out by the same method as the undercoat, and for example, it can be carried out by a coating method such as air spraying, airless spraying, rotary atomizing coating, curtain coating, or the like. These coating methods may also be applied with static electricity, as required. Among them, the rotary atomization coating with the application of static electricity is preferable.

The amount of the clear coating (Z) applied is preferably 10 to 50 μm as the cured film thickness.

When the cured film thickness of the transparent coating film is less than 15 μm, the surface smoothness is undesirably reduced. When the cured film thickness of the clear coating film exceeds 50 μm, sagging occurs during application of the clear coating material, and surface smoothness is undesirably reduced.

When the clear coating material (Z) is applied, it is preferable to adjust the viscosity of the clear coating material (Z) in advance to a viscosity range suitable for the application method using a solvent such as an organic solvent, for example, in the case of electrostatic imprint-applied rotary atomization coating, the viscosity range is 15 to 60 seconds at 20 ℃ as measured by a Ford cup (FordCup) No.4 viscometer.

After the transparent coating film is formed by applying the transparent coating material (Z), preheating may be performed at a temperature of 50 to 80 ℃ for 3 to 10 minutes, for example, in order to promote volatilization of volatile components.

The transparent coating film may have 1 layer or 2 or more layers. When the clear coating film has 2 or more layers, the 1 st and 2 nd layers may be the same clear coating material (Z) or different clear coating materials (Z). When different clear coating materials (Z) are used, from the viewpoint of smoothness and adhesion of the coating film, it is preferable that the clear coating material (Z1) containing a hydroxyl group-containing acrylic resin and a melamine resin is used as the clear coating material of the 1 st layer, and the clear coating material (Z2) containing a hydroxyl group-containing acrylic resin and a polyisocyanate compound is used as the clear coating material of the 2 nd layer to obtain smoothness and adhesion of the coating film.

[ formation of multilayer coating film ]

The method for forming a multilayer coating film can be a known method.

Specifically, the following is made.

On the coated article after degreasing treatment and surface treatment (phosphate treatment, chromate treatment, complex oxide treatment, etc.) as required, 1 or more kinds of coating films such as 1 or more electrodeposition coating films (cationic electrodeposition coating film, anionic electrodeposition coating film), primer coating film, colored intermediate coating film, transparent intermediate coating film, etc. are formed as required.

Next, a base coating film of a desired color tone is formed through the step (1).

Then, as necessary, 1 or more coating films such as a colorless clear coating film, a colored clear coating film, a bright clear coating film, a colored coating film, and a colored bright coating film are formed.

Next, a bright coating film is formed in step (2).

Then, as necessary, 1 or more coating films such as a colorless clear coating film, a colored clear coating film, a bright clear coating film, a colored coating film, and a colored bright coating film are formed.

Next, a transparent coating film is formed by the step (3).

If necessary, a top clear coating film of 1 layer or more may be formed on the clear coating film formed in step (3) to form a multilayer coating film.

When a coating film is formed on a coating film, the coating film may be formed on a wet coating film or on a coating film after conditioning and/or preheating and/or curing.

In the case of forming a coating film, the coating film may be cured by heating each time each coating film is formed, or a plurality of cured coating films may be simultaneously formed by simultaneously heating arbitrary plurality of uncured coating films.

Preferably, the step of simultaneously curing the 3 coating films by heating the uncured multilayer coating film comprising the uncured base coating film, the uncured photoluminescent coating film and the uncured clear coating film formed in the steps (1) to (3). Even when the bright pigment dispersion (Y) does not contain the matrix resin or the crosslinking agent, the bright coating film may be cured by transition of the resin component from the upper layer and/or the lower layer.

Heating for forming a coating film can be performed by a known means, and for example, a drying furnace such as an air heating furnace, an electric furnace, or an infrared induction heating furnace can be used.

The heating temperature is not particularly limited, but is preferably in the range of 70 to 150 ℃, preferably 80 to 140 ℃.

The heating time is not particularly limited, but is preferably 10 to 40 minutes, and more preferably 20 to 30 minutes.

By sequentially performing the above-described steps (1) to (3), a multilayer coating film can be formed.

The thickness T and the area occupancy R of the obtained multilayer coating film satisfy the following main condition (1):

T(nm)×R(％)≦2000…(1)，

the thickness T is the thickness T of the flaky bright pigment (a) contained in the bright pigment dispersion (Y), and the area occupancy R is the area occupancy R of the portion of the multilayer coating film where the bright pigment is projected when the entire bright pigment present in the multilayer coating film is projected onto the surface of the multilayer coating film.

In the present invention, the thickness T of the flaky bright pigment (A) is 1 to 65nm, and the area occupancy R is 0.1 to 50%.

When the product of T (nm) and R (%) is 2000 or less (T.times.R ≦ 2000), a metallic coating film having less graininess and excellent metallic luster can be formed on the coated object.

As described above, the thickness T of the flaky bright pigment (A) is an average thickness and may be 1 to 65nm, preferably 5 to 60nm, and more preferably 10 to 50 nm.

As described above, the average thickness can be defined as an average value of 100 or more measured values obtained by observing and measuring a cross section of a coating film containing the flaky bright pigment (a) with a Transmission Electron Microscope (TEM).

When all the bright pigments present in the multilayer coating film are projected on the surface of the multilayer coating film, the area occupancy R of the portion of the bright pigments projected on the surface of the multilayer coating film is the area occupancy of the portion of the bright pigments projected on the surface of the multilayer coating film when all the bright pigments present in the multilayer coating film are projected on the surface of the multilayer coating film. The area occupancy R can be obtained from the obtained image by imaging the multilayer coating film from the surface side thereof.

In the present invention, the area occupancy (R) may be 0.1 to 50%, preferably 1 to 40%, and more preferably 5 to 30%.

The Y5 value in XYZ chromaticity system of the obtained multilayer coating film can be 20-1500, preferably 50-1500, and more preferably 65-1500.

The Y5 value in the XYZ colorimetric system is the luminance in the XYZ colorimetric system when light irradiated from an angle of 45 degrees to the coating film is received at an angle of 5 degrees with respect to the regular reflection light.

In the present specification, the Y5 value was measured using a multiangle spectrophotometer ("GCMS-4", trade name, manufactured by Colorkungunya Technique Co., Ltd.).

The multilayer coating film obtained preferably has an HG value representing a grainy feel of 5 to 66, preferably 5 to 50, and more preferably 5 to 40.

The HG value indicating Graininess is abbreviated as Hi-light grain value. The HG value is one of the scales of the texture at the microscopic observation, that is, the microscopic brilliance, and is a parameter indicating the graininess on the highlight side (the coating film is observed from the vicinity of regular reflection with respect to the incident light). The measurement parameter can be obtained by imaging the coating film with a CCD camera at an incident angle of 15 degrees/a reception angle of 0 degrees, performing two-dimensional fourier transform processing on two-dimensional luminance distribution data as obtained digital image data, extracting only a spatial frequency region corresponding to the granular sensation from the obtained power spectrum image, and further setting the calculated measurement parameter to a value of 0 to 100 while maintaining linearity with the granular sensation.

In the present invention, the product of the thickness T and the area occupancy R of the flaky bright pigment (a) is set to the following main condition (1):

t (nm). times.R (%). ltoreq.2000 2000 … (1). The present inventors have also found that a multilayer coating film having less graininess and excellent metallic luster can be easily formed by correlating the L × 25 value described below.

The obtained multilayer coating film had a value of L × 25, which is a value of L × a b in a chromaticity system when light irradiated from an angle of 45 ° to the multilayer coating film was received at an angle of 25 ° in the incident light direction with respect to the normally reflected light.

Here, the color system L a b is a color system specified by the international commission on illumination in 1976 and used in japanese industrial standard JIS Z8781-4 and japanese industrial standard JIS Z8781-5, and L is a numerical value indicating brightness.

The L × 25 value is the brightness of highlight, and is a value measured by irradiating a measurement light from an axis perpendicular to a measurement target surface at an angle of 45 ° using a multi-angle spectrophotometer ("CM-512 m 3", trade name, manufactured by KONICAMINOLTA corporation) and measuring light received at an angle of 25 ° from a normal reflection angle in the direction of the measurement light. A higher value of L25 means a higher brightness.

In the present invention, in a super-dense color system luminance region (black region) where the L × 25 value is 19 or less (L × 25 ≦ 19), by setting the T × R range to 2000 or less, preferably 1 to 1000, and more preferably 5 to 500, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a dark color system luminance region where the L × 25 value is greater than 19 and not more than 50 (19< L × 25 ≦ 50), by setting the T × R range to 2000 or less, preferably 100 to 2000, and more preferably 200 to 1800, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in an intermediate luminance region where the L × 25 value is more than 50 and 75 or less (50< L × 25 ≦ 75), by setting the T × R range to 2000 or less, preferably 100 to 2000, and more preferably 250 to 2000, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a light-colored luminance region where the L × 25 value is in a range of more than 75 and 90 or less (75< L × 25 ≦ 90), by setting the T × R in a range of 2000 or less, preferably 10 to 1000, and more preferably 50 to 600, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a super-pale luminance region (white region) where the L × 25 value is greater than 90 (90< L × 25), the T × R is in the range of 2000 or less, preferably 10 to 1000, and more preferably 50 to 1000, whereby a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, the range of T × R is not greatly affected by hue and chroma.

In the present invention, although the multilayer coating film having less graininess and excellent metallic luster differs depending on the color tone and the like, the Y5 value, which is the brightness of high light, is generally high, and the HG value, which indicates graininess, is low.

In the present invention, the multilayer coating film obtained can be made to have less graininess and excellent metallic luster by adjusting the range of T × R, preferably the range of T × R and the Y5 value and/or HG value, and further preferably adjusting the range of T × R and L × 25 value, and more preferably adjusting 2 or more values selected from the range of T × R and L × 25 value, Y5 value, and HG value.

Second form

Next, a second aspect of the present invention will be explained.

A second aspect of the present invention is a coated article having on a surface thereof a multilayer coating film obtained by the multilayer coating film forming method of the first aspect.

The coated article obtained by the method for forming a multilayer coating film of the present invention is a coated article having a multilayer coating film provided on the coated article described in the first embodiment by the method for forming a multilayer coating film of the first embodiment.

Examples of applications of the coating material obtained by the method for forming a multilayer coating film of the present invention include automobile bodies and automobile parts such as automobiles, trucks, and motorcycles, and the shape of the coating material is preferably a shape (plate shape, molded product, etc.) used for the above applications.

The method of forming each coating film, the film thickness of each coating film, the relationship between the film thicknesses of the coating films, the L × 25 value, the Y5 value, the HG value of the multilayer coating film, the relationship therebetween, and the like are the same as those described in the first embodiment.

The coated article obtained by the method for forming a multilayer coating film of the present invention has a multilayer coating film with less graininess and excellent metallic luster, and can be an industrial product with excellent aesthetic feeling.

The third form

Next, a third aspect of the present invention will be explained.

The third aspect of the present invention is a multilayer coating film comprising a base coating film, a bright coating film containing a bright pigment (a) in the form of a scale, and a clear coating film formed on the surface of an object to be coated in this order,

the thickness T of the flaky bright pigment (A) is 1 to 65nm,

when the entire bright pigment existing in the multilayer coating film is projected on the surface of the multilayer coating film, the area occupancy rate R of the portion of the bright pigment projected on the surface of the multilayer coating film is 0.1 to 50%,

the aforementioned T and R satisfy the following main condition (1).

T(nm)×R(％)≦2000…(1)

In the present invention, the thickness T of the flaky bright pigment (a) is defined as described in the first embodiment.

In the present invention, the area occupancy R of the portion of the multilayer coating film surface on which the bright pigment is projected is defined as the same as that described in the first embodiment.

When the product of T and R of the flaky bright pigment (a) contained in the bright pigment dispersion (Y) is 2000 or less (T × R ≦ 2000), a metallic coating film having less graininess and excellent metallic luster can be formed from the multilayer coating film.

The layered coating film of the present invention may be provided on an object to be coated. Here, the coated object is the same as the coated object described in the first embodiment.

The base coating film constituting the laminated coating film of the present invention is the same as the base coating film described in the first embodiment.

The bright coating film constituting the laminated coating film of the present invention may be the same as the bright coating film described in the first embodiment, and the flaky bright pigment (a) contained in the bright coating film may be the same as the flaky bright pigment (a) described in the first embodiment.

The clear coating film may be the same as that described in the first embodiment.

The method of forming the multilayer coating film may be the same as that described in the first embodiment.

The film thickness of the base coating film, the film thickness of the photoluminescent coating film, the film thickness of the transparent coating film, the film thickness of the multilayer coating film, and the optical characteristics (color tone, etc.) may be the same as those described in the first embodiment.

An optional layer or coating film may be provided between the object to be coated and the base coating film, between the base coating film and the bright coating film, between the bright coating film and the clear coating film, or on the clear coating film, as required.

The Y5 value in the XYZ chromaticity system of the multilayer coating film of the present invention is 20 to 1500, preferably 50 to 1500, and more preferably 65 to 1500.

The definition of the Y5 value in the XYZ colorimetric system is the same as that described in the first embodiment.

In the present specification, the value of Y5 was measured using a multiangle spectrophotometer ("GCMS-4", trade name, manufactured by Colorkungunya Technique Co., Ltd.) as in the first embodiment.

The multilayer coating film of the present invention has a luminance L value (L25 value) in a chromaticity system of L a b when light irradiated from an angle of 45 DEG is received at an angle of 25 DEG with respect to a normal reflection light in an incident light direction, the luminance L value being in a range of 1 to 95.

Here, the color system L a b is a color system specified by the international commission on illumination in 1976 and used in japanese industrial standard JIS Z8729, and L is a numerical value representing luminance.

The L × 25 value is the brightness of highlight, and is a value measured by irradiating a measurement light from an axis perpendicular to a measurement target surface at an angle of 45 ° using a multi-angle spectrophotometer ("CM-512 m 3", trade name, manufactured by KONICA MINOLTA corporation) and measuring light received at an angle of 25 ° from a normal reflection angle in the direction of the measurement light. A higher value of L25 means a higher brightness.

The multilayer coating film of the present invention preferably has an HG value representing a grainy feel of 5 to 66, preferably 5 to 50, and more preferably 5 to 40.

The HG value indicating Graininess is abbreviated as Hi-light grain value. The HG value is defined as the same value as described in the first embodiment.

In the present invention, the product of the thickness T and the area occupancy R of the flaky bright pigment (a) is set to the following main condition (1):

t (nm). times.R (%). times.in the range of 2000 … (1), and the inventors have found that a multilayer coating film having less graininess and excellent metallic luster can be easily formed by correlating the value of L.times.25 with the above value.

In the present invention, in a super-deep color system luminance region (black region) where the L × 25 value is 19 or less (L × 25 ≦ 19), by setting the T × R value to 2000 or less, preferably 1 to 1000, and more preferably 5 to 500, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a dark-color luminance region where the L × 25 value is greater than 19 and not more than 50 (19< L × 25 ≦ 50), by setting the T × R range to 2000 or less, preferably 100 to 2000, and more preferably 200 to 1800, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in an intermediate luminance region where the L × 25 value is in a range of more than 50 and 75 or less (50< L × 25 ≦ 75), by setting the T × R range to 2000 or less, preferably 100 to 2000, and more preferably 250 to 2000, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a pale color luminance region where the L25 value is more than 75 and 90 or less (75< L25 ≦ 90), by setting the T × R range to 2000 or less, preferably 10 to 1000, and more preferably 50 to 600, a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, in a super-pale luminance region (white region) where the L × 25 value is greater than 90 (90< L × 25), the T × R is in the range of 2000 or less, preferably 10 to 1000, and more preferably 50 to 1000, whereby a multilayer coating film having less graininess and excellent metallic luster can be formed.

In the present invention, the relationship between the range of T × R and the range of L × 25 values is not greatly affected by the hue and chroma.

In the present invention, although the multilayer coating film having less graininess and excellent metallic luster differs depending on the color tone and the like, the Y5 value, which is the brightness of high light, is generally high, and the HG value, which indicates graininess, is low.

In the present invention, the multilayer coating film obtained can be a multilayer coating film having less graininess and excellent metallic luster by adjusting the range of T × R, preferably the range of T × R and the L × 25 value, and more preferably by adjusting the values of Y5 and HG in addition thereto.

Examples

The present invention will be described more specifically below with reference to examples and comparative examples. However, the present invention is not limited to these examples. "part(s)" and "%" are based on mass.

(production of acrylic resin aqueous Dispersion)

Production example 1

A reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube, and a dropping device was charged with 128 parts of deionized water and 2 parts of "Adeka Reasoap SR-1025" (trade name, manufactured by ADEKA, emulsifier, active ingredient 25%) and stirred and mixed in a nitrogen stream to raise the temperature to 80 ℃.

Next, 5.3 parts of a 6% aqueous ammonium persulfate solution and 1% of the total amount of the monomer emulsion for core described below were introduced into a reaction vessel and held at 80 ℃ for 15 minutes. Thereafter, the remaining monomer emulsion for core part was dropped into the reaction vessel kept at the same temperature over 3 hours, and aging was performed for 1 hour after completion of the dropping. Then, the monomer emulsion for the shell described below was added dropwise over 1 hour, and after 1 hour of aging, 40 parts of 5% 2- (dimethylamino) ethanol aqueous solution was gradually added to the reaction vessel while cooling to 30 ℃ and filtered with 100 mesh nylon cloth and discharged to obtain an aqueous acrylic resin dispersion having an average particle diameter of 100nm and a solid content of 28%. The obtained acrylic resin aqueous dispersion had an acid value of 33mgKOH/g and a hydroxyl value of 25 mgKOH/g.

By mixing the core with a monomer emulsion: 40 parts of deionized water, 2.8 parts of Adeka Reasoap SR-1025', 2.1 parts of methylene bisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, 28 parts of ethyl acrylate and 21 parts of n-butyl acrylate are mixed and stirred to obtain a monomer emulsion for the core part.

By mixing a shell with a monomer emulsion: 17 parts of deionized water, 1.2 parts of Adeka Reasoap SR-1025', 0.03 part of ammonium persulfate, 3 parts of styrene, 5.1 parts of 2-hydroxyethyl acrylate, 5.1 parts of methacrylic acid, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate and 9 parts of n-butyl acrylate are mixed and stirred to obtain a monomer emulsion for the shell.

(production of Bright pigment Dispersion (Y))

Production example 2

0.13 parts by mass of "Hydroshine WS-6001" (trade name, aluminum vapor deposited flake pigment for aqueous use, manufactured by Eckart corporation, solid content: 10% by mass, internal solvent: isopropyl alcohol 70.0% by mass, butyl glycol 20.0% by mass, average particle diameter D50: 10 μm, thickness: 13.5nm, surface-treated with silica), "RHEOCRICTAS" (cellulose nanofiber viscosity modifier, manufactured by first Industrial pharmaceutical Co., Ltd., solid content: 0.5%) 74.06 parts by mass, surface modifier "Dynol 604" (trade name, manufactured by Nisin chemical industry Co., Ltd., acetylene glycol surface modifier, HLB: 8, nonvolatile content: 100% by mass), 2.2 parts by mass of the aqueous acrylic resin dispersion obtained in the above production example 1, 0.01 parts by mass of dimethylethanolamine, 0.49 parts by mass of aqueous solvent, and 22.8 parts by mass of distilled water (100 parts by mass in total) were mixed with stirring, a bright pigment dispersion (Y-1) was prepared.

Production examples 3 to 25

Bright pigment dispersions (Y-2) to (Y-24) were obtained in the same manner as in production example 2, except that the formulations described in Table 1 were all prepared.

The details of the raw materials in the table are as follows.

WS-6001

Trade name "Hydroshine WS-6001", manufactured by Eckart corporation, aqueous aluminum flake pigment for evaporation, solid content 10.0%, internal solvent isopropyl alcohol 70.0%, butyl glycol 20.0%, average particle diameter (D50): 10.0 μm, thickness: 13.5nm, surface treated with silica

Liquid Black

The trade name "metallic Liquid Black", manufactured by Eckart corporation, aqueous vapor-deposited chromium oxide flake pigment, solid content: 10.0%, internal solvent 1-methoxy-2-propanol 90.0%, average particle diameter (D50): 14.0 μm, thickness: 20.0nm

WS-4140

Trade name "Hydroshine WS-4140", manufactured by Eckart corporation, aqueous aluminum flake pigment evaporated by evaporation, solid content 10.0%, internal solvent isopropanol 70.0%, butyl glycol 20.0%, average particle diameter (D50): 14.0 μm, thickness: 22.5nm, surface treated with silicon dioxide

WS-4001

Trade name "Hydroshine WS-4001", manufactured by Eckart corporation, aluminum flake pigment for aqueous vapor deposition, solid content: 10.0%, internal solvent: isopropyl alcohol 70.0%, butyl glycol 20.0%, average particle diameter (D50): 10.5 μm, thickness: 22.5nm, surface treated with silicon dioxide

WS-3004

Trade name "Hydroshine WS-3004", manufactured by Eckart corporation, aluminum flake pigment for water-based vapor deposition, solid content: 10.0%, internal solvent: isopropanol 90.0%, average particle size (D50): 11.0 μm, thickness: 50.0nm, surface treated with silica

WS-3001

Trade name "Hydroshine WS-3001", manufactured by Eckart corporation, aluminum flake pigment for water-based vapor deposition, solid content: 10.0%, internal solvent: isopropanol 90.0%, average particle size (D50): 11.1 μm, thickness: 50.0nm, surface treated with silica

S 1500

Trade name "STAPA IL HYDROOLAN S1500", manufactured by Eckart corporation, ground aluminum flake pigment, solid content: 20.0%, internal solvent: isopropanol 80.0%, average particle size (D50): 15.0 μm, thickness: 50.0nm, surface treated with silica

S 1100

Trade name "STAPA IL HYDROOLAN S1100", manufactured by Eckart corporation, ground aluminum flake pigment, solid content: 50.0%, internal solvent: isopropyl alcohol 50.0%, average particle diameter (D50): 11.0 μm, thickness: 80.0nm, surface treated with silica

S 2100

Trade name "STAPA IL HYDROOLAN S2100", manufactured by Eckart corporation, ground aluminum flake pigment, solid content: 60.0%, internal solvent: isopropyl alcohol 40.0%, average particle diameter (D50): 22.0 μm, thickness: 130nm, surface treated with silicon dioxide

RHEOCRYSTA

The trade name "RHEOCRYSTA", manufactured by first industrial pharmaceutical company, cellulose-based viscosity modifier ═ cellulose nanofiber gel, solid content 0.5%.

ASE-60

The product name is Acrysol ASE-60, manufactured by DOW CHEMICAL, polyacrylic acid viscosity regulator, 28% of solid content

Dynol 604

The product name is "Dynol 604", manufactured by EVONIK INDUSTRIES, acetylene glycol surface conditioner, HLB value is 8, and non-volatile component is 100% by mass

Colored pigment dispersion liquid

The following hydroxyl group-containing acrylic resin was used and produced by the following method.

(production of hydroxyl-containing acrylic resin)

After 35 parts by mass of propylene glycol monopropyl ether was charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen gas inlet tube, and a dropping device and heated to 85 ℃, a mixture containing 32 parts by mass of methyl methacrylate, 27.7 parts by mass of n-butyl acrylate, 20 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of 4-hydroxybutyl acrylate, 3 parts by mass of hydroxypropyl acrylate, 6.3 parts by mass of acrylic acid, 1 part by mass of 2-acryloyloxyethyl phosphate, 15 parts by mass of propylene glycol monopropyl ether, and 2.3 parts by mass of 2, 2' -bisazo (2, 4-dimethylpentanenitrile) was dropped over 4 hours and aged for 1 hour after completion of the dropping. Then, a mixture of 10 parts by mass of propylene glycol monopropyl ether and 1 part by mass of 2, 2' -bisazo (2, 4-dimethylvaleronitrile) was added dropwise over 1 hour, and aging was performed for 1 hour after completion of the addition. Then, 7.4 parts by mass of diethanolamine was added to obtain a hydroxyl group-containing acrylic resin solution having a solid content of 55%. The hydroxyl group-containing acrylic resin thus obtained had an acid value of 51mgKOH/g and a hydroxyl value of 52 mgKOH/g.

(production of color pigment Dispersion)

25.4 parts by mass (14.0 parts by mass of a solid content) of the above hydroxyl-containing acrylic resin, 7 parts by mass of RAVEN 5000ULTRA III (trade name, carbon black pigment, manufactured by BIRLA corporation) and 66.6 parts by mass of deionized water were put into a stirring and mixing vessel, and mixed uniformly, and 2- (dimethylamino) ethanol was added thereto to adjust the pH to 7.5. The obtained mixture was charged into a 225ml resinous bottle, 130 parts by mass of zirconia beads having a diameter of 1.5mm were charged and stoppered, and dispersed for 120 minutes using a vibration type paint mixer (paint conditioner). After the dispersion, the resultant was subjected to 100-mesh wire gauze filtration to remove zirconia beads, thereby obtaining a black pigment dispersion having a solid content of 20.9 mass%.

(Table 1)

(preparation of coated article)

Coated object 1

On a degreased and zinc phosphate-treated steel sheet (Japanese Industrial Standard JISG3141, size 400 mm. times.300 mm. times.0.8 mm), a cationic electrodeposition paint "ELECRON GT-10" (trade name: manufactured by Wasse paint Co., Ltd., a blocked polyisocyanate compound was used as a crosslinking agent in an epoxy polyamine cationic resin) was subjected to electrodeposition coating so that the film thickness was 20 μm based on the cured coating film, and the coating film was heated at 170 ℃ for 20 minutes to be crosslinked and cured, thereby forming an electrodeposition coating film as the coated article 1.

(preparation of test plate)

Example 1

A base coating material (X-1) was electrostatically coated on the above-mentioned object 1 by using a rotary atomizing Bell (Bell) type coating machine so that the cured film thickness became 20 μm, and the resultant was left for 3 minutes to form a base coating film, wherein the base coating material (X-1) was color-matched so that L45, a 45 and b 45 of the base coating film were values shown in Table 2 and based on a polyester resin type aqueous intermediate coating material (WP-522H) manufactured by Kyowa coating Co., Ltd.

The bright pigment dispersion (Y-1) prepared as described above was adjusted to the coating viscosity described in Table 1, and coated on the base coating film under conditions of room temperature of 23 ℃ and humidity of 68% so as to form a cured coating film of 1.5 μm using Robot Bell manufactured by ABB. Left to stand for 3 minutes, and thereafter preheated at 80 ℃ for 3 minutes to form a bright coating film.

Subsequently, a clear coating film was formed by applying a clear coating material (Z-1) "KINO 6510" (trade name, hydroxyl/isocyanate-based curable acrylic resin, urethane resin-based 2-liquid organic solvent-based coating material, manufactured by seiki paint corporation) onto the bright coating film so as to form a cured coating film of 35 μm under conditions of room temperature of 23 ℃ and a humidity of 68% using a Robot Bell manufactured by ABB corporation. After coating, the plate was left at room temperature for 7 minutes, and then heated at 140 ℃ for 30 minutes in a hot air circulation type drying oven to simultaneously cure the multilayer coating film.

Here, the film thickness of the cured coating film can be calculated by the following equation. The same applies to the following examples.

x＝sc/sg/S*10000

x: film thickness [ mu m ]

sc: coating solid component [ g ]

sg: specific gravity of coating film [ g/cm [)³]

S: evaluation area of coating solid component [ cm ]²]

Examples 2 to 28 and comparative examples 1 to 6

Test plaques were obtained in the same manner as in example 1, except that the values of L × 45, a × 45, and b × 45 of the base coating film were changed to the values described in table 2, and the photoluminescent pigment dispersion (Y) described in tables 2 and 3 was used to form a multilayer coating film as a photoluminescent coating film having a cured film thickness described in tables 2 and 3.

Evaluation of coating film

The multilayer coating film was evaluated for each test panel obtained as described above, and the results are shown in tables 2 and 3 in total.

(Table 2)

(Table 3)

Value of L45

The L x 45 value is a luminance in the L a b chromaticity system, and is a L value measured by irradiating a measurement light from an angle of 45 ° to an axis perpendicular to a surface to be measured of the surface of the base coating film using a multi-angle spectrophotometer ("CM-512 m 3", product name, manufactured by KONICA MINOLTA corporation) and receiving light from a regular reflection angle at an angle of 45 ° in the direction of the measurement light.

a 45 value

The a × 45 value is the luminance in the L × a × b chromaticity system, and is a value measured by irradiating a measurement light from an angle of 45 ° to an axis perpendicular to a measurement target surface of the base coating film using a multi-angle spectrophotometer ("CM-512 m 3", product name, manufactured by KONICA MINOLTA corporation) and receiving light from a regular reflection angle at an angle of 45 ° in the direction of the measurement light.

b 45 value

The b 45 value is a luminance in the L a b chromaticity system, and is a b value measured by irradiating a measurement light from an angle of 45 ° to an axis perpendicular to a measurement target surface of the base coating film using a multi-angle spectrophotometer ("CM-512 m 3", product name, manufactured by KONICA MINOLTA corporation) and receiving light from a regular reflection angle at an angle of 45 ° in the direction of the measurement light.

Value L25

The L25 value is a luminance in the L a b chromaticity system, and is a L value measured by irradiating a measurement light from an angle of 45 ° to an axis perpendicular to a measurement target surface of the multilayer coating film using a multi-angle spectrophotometer ("CM-512 m 3", product name, manufactured by KONICA MINOLTA corporation) and receiving light from a regular reflection angle at an angle of 25 ° in the direction of the measurement light. A higher value of L25 means a higher brightness.

Y5 value

The Y5 value is the luminance in the XYZ colorimetric system, and is a Y value measured by irradiating a measurement light from an angle of 45 ° to an axis perpendicular to a measurement target surface of the multilayer coating film surface using a multi-angle spectrophotometer ("GCMS-4", trade name, manufactured by mura color technology research institute), and measuring the light received at an angle of 5 ° in the direction of the measurement light from the regular reflection angle. A larger value of Y5 means a higher gloss of the coating film.

HG value

The HG value is an abbreviation for the Hi-light gradient value. The HG value is one of the scales of microscopic brilliance when microscopic observation is performed on the coating surface, and indicates an index of a high brilliance graininess. The HG value may be calculated as follows. First, a CCD camera is used to pick up images of the multilayer coating film at an incident angle of light of 15 degrees/a reception angle of 0 degrees, and the obtained digital image data (two-dimensional luminance distribution data) is subjected to two-dimensional fourier transform processing to obtain a power spectrum image. Then, only the spatial frequency region corresponding to the graininess is extracted from the obtained power spectrum image, the calculated measurement parameter is further set to a value of 0 to 100, and the value is converted to the HG value while maintaining linearity with the graininess. The HG value is a value of 0 when the graininess of the bright pigment is completely absent and 100 when the graininess of the bright pigment is the maximum.

While the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, the configurations, methods, steps, shapes, materials, numerical values, and the like recited in the above embodiments and examples are merely examples, and configurations, methods, steps, shapes, materials, numerical values, and the like different from those described above may be used as necessary.

The configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described embodiments may be combined with each other without departing from the spirit of the present invention.