Multilayer coating film and method for producing the same

Abstract

A multilayer coating film comprising a colored coating film formed on an object to be coated and containing a white pigment and a black pigment, a glitter coating film formed on the colored coating film and containing a glitter material and a black pigment, and a clear coating film formed on the glitter coating film, wherein light I irradiated from an angle of 45 degrees with respect to the surface of the multilayer coating film 45 is the lightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light * 45 is greater than or equal to 1 and less than 40, and the light I 45 is the lightness L based on the spectral reflectance received at an angle of 5 degrees with respect to the specularly reflected light * 5 and the light I 45 is the lightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light * 45, and the ratio (L * 5 / L * 45) is greater than or equal to 4.0 and less than or equal to 10.0, and the occupancy rate of the glitter material as viewed from the normal direction of the surface of the multilayer coating film is greater than or equal to 30% and less than or equal to 80%. Multilayer coating film.

Description

Technical Field

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

Background Art

[0002] In recent years, due to technological advancements, multilayer coating films having various colors and textures for automobiles have been proposed. Among them, coating films having a texture like that of metal have attracted attention. Patent Document 1 discloses a method for forming a multilayer coating film using two types of pearlescent pigments.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a multilayer coating film in which high lightness change and metallic texture are compatible in the gray color gamut.

Means for Solving the Problems

[0005] To solve the above problems, the present invention provides the following aspects. [1] A colored coating film formed on an object to be coated and containing a white pigment and a black pigment, A pearlescent coating film formed on the colored coating film and containing a pearlescent material and a black pigment, A clear coating film formed on the pearlescent coating film, and a multilayer coating film comprising: Light I irradiated at an angle of 45 degrees with respect to the surface of the multilayer coating film 45 Based on the lightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light, * L45 is 1 or more and less than 40, The light I 45The brightness L based on the spectral reflectance received at an angle of 5 degrees with respect to the specularly reflected light * 5 and the light I 45 The brightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light * 45 and the ratio (L * 5 / L * 45) is 4.0 or more and 10.0 or less, The occupancy rate of the brightening material as viewed from the normal direction of the surface of the multilayer coating film is 30% or more and 80% or less. Multilayer coating film [2] The graininess on the surface of the multilayer coating film is 4.0 or more and 8.0 or less. The multilayer coating film of the above [1] [3] The light IC irradiated from an angle of 45 degrees with respect to the surface of the colored coating film 45 The brightness CL based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light * 45 is 0 or more and 45 or less. The multilayer coating film of the above [1] or [2] [4] The thickness of the brightening coating film is 0.05 μm or more and 1.0 μm or less. The multilayer coating film of any one of the above [1] to [3] [5] The brightening material contains aluminum particles. The multilayer coating film of any one of the above [1] to [4] [6] Coating a colored paint containing a white pigment and a black pigment on an object to be coated to form an uncured colored coating film, Coating a brightening pigment dispersion containing a brightening material and a black pigment on the uncured colored coating film to form an uncured brightening coating film, Coating a clear paint on the uncured brightening coating film to form an uncured clear coating film, Curing the uncured colored coating film, the uncured brightening coating film, and the uncured clear coating film to obtain a multilayer coating film. And The light I irradiated from an angle of 45 degrees with respect to the surface of the multilayer coating film 45 The brightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light * 45 is 1 or more and less than 40, The light I45 The lightness L based on the spectral reflectance obtained by receiving light at an angle of 5 degrees with respect to the specularly reflected light * 5 and the light I 45 The lightness L based on the spectral reflectance obtained by receiving light at an angle of 45 degrees with respect to the specularly reflected light * 45 and the ratio (L * 5 / L * 45) is 4.0 or more and 10.0 or less, The occupancy rate of the brightening material as viewed from the normal direction of the surface of the multilayer coating film is 30% or more and 80% or less. A method for producing a multilayer coating film. [7] The clear paint is a two-component paint containing a hydroxyl group-containing resin and a polyisocyanate compound. The method for producing a multilayer coating film according to [6] above. [8] The solid content concentration of the brightening pigment dispersion is 0.1% by mass or more and 12.0% by mass or less. The method for producing a multilayer coating film according to [6] or [7] above. [9] The brightening pigment dispersion contains cellulose nanofibers. The method for producing a multilayer coating film according to any one of [6] to [8] above. [Advantages of the Invention]

[0006] According to the present invention, it is possible to provide a multilayer coating film in which high lightness change and metallic texture are compatible in the gray color gamut, and a method for producing the same. [Brief Description of the Drawings]

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

[0008] A. Multilayer Coating The multilayer coating according to the present disclosure includes a colored coating formed on an object to be coated and containing a white pigment and a black pigment, a glossy coating formed on the colored coating and containing a brightening agent and a black pigment, and a clear coating formed on the glossy coating. The multilayer coating is provided, for example, as part or all of the exterior of an automobile body.

[0009] Light I irradiated at an angle of 45 degrees with respect to the surface of the multilayer coating (that is, the surface on the clear coating side of the multilayer coating; the same applies hereinafter). 45 The lightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light. * 45 is greater than or equal to 1 and less than 40. In the above coating configuration, the lightness L * The multilayer coating having 45 is recognized as gray.

[0010] Light I 45 The lightness L based on the spectral reflectance received at an angle of 5 degrees with respect to the specularly reflected light. * 5 and light I 45 The lightness L based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light. * 45 and the ratio (L * 5 / L * 45) is greater than or equal to 4.0 and less than or equal to 10.0. The ratio (L * 5 / L * 45) indicates the change in lightness when the composite coating is viewed from two predetermined directions. The ratio (L * 5 / L * 45) being greater than or equal to 4.0 and less than or equal to 10.0 means that the change in lightness when viewed at an angle of 5 degrees with respect to the specularly reflected light and when viewed at an angle of 45 degrees with respect to the specularly reflected light is large.

[0011] The occupancy rate of the brightening agent as viewed from the normal direction of the multilayer coating is 30% or more and 80% or less. Thereby, the white pigment and the black pigment contained in the colored coating can be visually recognized without passing through the brightening agent. Therefore, a gray color tone is more felt.

[0012] Generally, the coating film in the gray color gamut tends to have a low overall brightness, and the brightness change is small. The multi-layer coating film of the present disclosure has a metallic texture in the gray color gamut, while having a large brightness change from the highlight area to the face area.

[0013] The highlight area refers to the range of -25 degrees or more and less than 25 degrees with respect to the specular reflection light of the light incident at an angle of 45 degrees (when the traveling direction of the specular reflection light is set as 0 degrees, the area between the position advanced 25 degrees in the surface direction of the multi-layer coating film and the position advanced 25 degrees in the direction opposite to the surface of the multi-layer coating film). The shade area refers to the range of 75 degrees or more with respect to the specular reflection light of the light incident at an angle of 45 degrees (starting from the position advanced 75 degrees in the direction opposite to the surface of the multi-layer coating film as described above, and further advancing in the direction opposite to the surface of the multi-layer coating film from the starting point). The face area is the range between the highlight area and the shade area (more than 25 degrees and less than 75 degrees with respect to the specular reflection light). In the present disclosure, as the highlight area, the point of 5 degrees with respect to the specular reflection light, which can also be called the super-highlight area, is observed. In the present disclosure, as the face area, the point of 45 degrees with respect to the specular reflection light, which is equal to the normal direction of the multi-layer coating film, is observed.

[0014] · Brightness L * 45 Brightness L * 45 is from 1 or more and less than 40. Brightness L * 45 may be 5 or more, may be 10 or more, and may be 15 or more. Brightness L * 45 may be 35 or less, and may be 25 or less.

[0015] · Ratio (L * 5 / L * 45) Ratio (L * 5 / L * 45) is from 4.0 or more and 10.0 or less. Ratio (L * 5 / L * 45) being within this range results in a large change between the brightness in the super-highlight area and the brightness in the face area. That is, while a high metallic texture can be obtained in the super-highlight area, the gray color tone is strengthened in the face area. Ratio (L * 5 / L* 45) may be 5.0 or more, and may be 6.0 or more. Ratio (L * 5 / L * 45) may be 9.0 or less, and may be 8.0 or less.

[0016] Brightness L * 5 is the L calculated from the spectral reflectance obtained by receiving the above light I 45 at an angle of 5 degrees with respect to the specularly reflected light. * a * b * Color system (CIE1976L * a * b * in the color space). * is the brightness L. * 45 is similarly the L calculated from the spectral reflectance obtained by receiving the above light I 45 at an angle of 45 degrees with respect to the specularly reflected light. * a * b * in the color system. * is the brightness L. * 5, L * 45 can all take values of 0 or more. * Brightness L can be obtained using a variable-angle colorimeter (for example, product name: Gonio-Spectrophotometer GSP-1, manufactured by Murakami Color Research Laboratory Co., Ltd.). * Brightness L is the average value of the brightness L of five different samples. *

[0017] Brightness L * 5 is not particularly limited. In terms of enhancing the brilliance, * brightness L 5 may be 80 or more, and may be 100 or more. * Brightness L 5 may be 150 or less, and may be 130 or less.

[0018] · Occupancy rate ​The occupancy rate of the brightening material is the area ratio of the brightening material to the area of the multilayer coating film as viewed from the normal direction of the surface of the multilayer coating film. When the occupancy rate of the brightening material is 30.0% or more and 80.0% or less, a metallic texture can be obtained, and since the white pigment and black pigment of the colored coating film can be visually recognized, the multilayer coating film can be recognized as being in the gray color gamut. The occupancy rate of the brightening material may be 35.0% or more, and may be 40.0% or more. The occupancy rate of the brightening material may be 75.0% or less, may be 70.0% or less, and may be 60.0% or less.

[0019] Specifically, the occupancy rate of the brightening material is obtained as follows. First, the multilayer coating film is observed with an electron microscope from its normal direction. In the observation field of view, the region corresponding to the brightening material and the other regions are binarized by image processing software. With the area of the observation field of view taken as 100%, the area ratio of the brightening material is calculated. The magnification of the electron microscope is not particularly limited, and for example, it may be about 100 times or more and 200 times or less. The size of the observation field of view is also not particularly limited, and for example, it may be about 500 nm or more and 1000 nm or less in the vertical direction and 1000 nm or more and 1500 nm or less in the horizontal direction. As the electron microscope, an industrial microscope (for example, ECLIPSE LV150N manufactured by Nikon Instech Co., Ltd.) is used. As the image processing software, for example, NIS-Elements (image comprehensive software manufactured by Nikon Corporation), NIS-A AMEAS (software for distance measurement and area calculation manufactured by Nikon Corporation) are used. The occupancy rate is the average value of the occupancy rates in five different observation fields of view.

[0020] · Graininess Graininess is known as an index for evaluating the brightness of a coating film (see, for example, Japanese Patent Laid-Open No. 2019-71825). The smaller the graininess, the stronger the impression that the composite coating film is dense, and the higher the metallic texture. The graininess (Graininess. Hereinafter referred to as graininess G) of the multilayer coating film is 4.0 or more and 8.0 or less. Graininess G may be 4.5 or more, and may be 5.0 or more. Graininess G may be 7.0 or less, and may be 6.0 or less.

[0021] The particle feeling G is obtained by imaging a composite coating film irradiated with diffused light and analyzing it with a specific image analysis algorithm. Specifically, diffused light is irradiated onto the composite coating film from a light source installed inside a white-painted hemisphere. The composite coating film is imaged with a CCD camera from its normal direction and obtained by analyzing it with a specific image analysis algorithm. The particle feeling G can be obtained using a multi-angle colorimeter (for example, product name: BYK-mac i 23mm, manufacturing No. 1238698, catalog No. 7030, manufactured by BYK-Gardner). The particle feeling G is the average value of the particle feeling G of five different samples.

[0022] In terms of further improving the metallic texture, the glitter coating film may contain a glitter material arranged in parallel with the coating film. Among them, 80.0% or more of the number of glitter materials contained in the glitter coating film may be arranged in parallel with the surface of the multilayer coating film. Parallel means that in the cross-section of the multilayer coating film, the acute angle θ formed by the surface of the glitter coating film and the glitter material is 0 degrees or more and 30 degrees or less.

[0023] ·Glitter intensity The arrangement of the glitter material is indicated by, for example, the sparkle intensity of the multilayer coating film. The glitter intensity (hereinafter referred to as the Si 15 value) of the light received in the normal direction of the coating film from the light irradiated from a direction inclined 15 degrees with respect to the normal direction of the coating film is smaller, the more glitter materials are arranged in parallel with the glitter coating film. The Si 15 value is known as an index for evaluating the glitter property of the coating film (see, for example, International Publication No. 2022 / 176336).

[0024] In the present disclosure, the Si 15 value of the composite coating film can be 3.0 or more and 10.0 or less. When the Si 15 value is within this range, it can be said that 80% or more of the number of glitter materials contained in the glitter coating film are arranged in parallel with the surface of the glitter coating film. The Si 15 value may be 4.0 or more, and may be 5.0 or more. The Si 15 value may be 9.0 or less, and may be 7.0 or less.

[0025] Si 15 The value is obtained by imaging the light irradiated from a direction inclined 15 degrees with respect to the normal direction of the multilayer coating film from the normal direction of the multilayer coating film and analyzing it with a specific image analysis algorithm. A histogram of brightness levels is used as the image analysis algorithm. Si 15 The value can be obtained using a multi-angle colorimeter (for example, product name: BYK-mac i 23mm, manufacturing No. 1238698, catalog No. 7030, manufactured by BYK-Gardner). Si 15 The value is the Si of five different samples 15 and is the average value of the values.

[0026] In particular, the arrangement of the flaky pearlescent pigment (hereinafter referred to as the flaky pearlescent material) can also be confirmed from the cross-section of the multilayer coating film. The acute angle θ is obtained from the cross-section of the multilayer coating film as follows. First, image the cross-section of the multilayer coating film with an electron microscope. Place the obtained cross-section on a two-dimensional coordinate (xy coordinate) and obtain an approximate straight line L0 of the surface of the pearlescent coating film. Similarly, obtain an approximate straight line L1 of the surface of the flaky pearlescent material. The surface of the flaky pearlescent material is the main surface closer to the clear coating film. The angle formed by the approximate straight line L0 and the approximate straight line L1 is the angle θ. The ratio of the flaky pearlescent material parallel to the pearlescent coating film is obtained by dividing the number of flaky pearlescent materials that are arranged parallel to the pearlescent coating film and can be entirely confirmed in the observation field of view by the number of pearlescent materials that can be entirely confirmed in the observation field of view.

[0027] In the above observation with an electron microscope, the magnification is not particularly limited. The magnification of the electron microscope may be, for example, about 100 times or more and 200 times or less. The size of the observation field of view is also not particularly limited and may be, for example, about 500 nm or more and 1000 nm or less in the vertical direction and 1000 nm or more and 1500 nm or less in the horizontal direction. In the following observation with an electron microscope, the magnification and the observation field of view may be the same as above.

[0028] In a brilliant coating film, it is preferable that the flaky brilliant materials do not overlap with each other. Thereby, the flaky brilliant materials are likely to be arranged in parallel with the brilliant coating film. Further, even when the occupancy rate of the brilliant material is low, the impression that the coating film is dense is enhanced, and the metallic texture is improved. That the flaky brilliant materials do not overlap with each other means that in the cross section of the multilayer coating film, a part or all of the flaky brilliant material and other flaky brilliant materials do not overlap in the thickness direction. It is not necessary for the flaky brilliant materials to be in contact with each other. For example, when the multilayer coating film is viewed from the normal direction, if a part or all of the flaky brilliant materials appear to overlap, the flaky brilliant materials overlap in the thickness direction.

[0029] Among them, it is preferable that 80% or more of the number of flaky brilliant materials contained in the brilliant coating film do not overlap with other flaky brilliant materials. The overlapping ratio of the flaky brilliant materials is obtained as follows. First, the cross section of the multilayer coating film is imaged with an electron microscope. In the obtained cross section, one or more flaky brilliant materials on the clearest coating film side of the brilliant coating film are used as reference brilliant materials. Mark the flaky brilliant materials that overlap with the reference brilliant material in the thickness direction. Further, mark the flaky brilliant materials that overlap with the marked flaky brilliant material in the thickness direction. Count all the flaky brilliant materials (hereinafter sometimes referred to as overlapping brilliant materials) that are marked and whose entirety can be confirmed in the observation field of view. At this time, one overlapping brilliant material is not counted multiple times. The ratio of the overlapping brilliant materials is obtained by dividing the number of the overlapping brilliant materials by the number of flaky brilliant materials (that is, the total of the reference brilliant material and the overlapping brilliant materials) whose entirety can be confirmed in the observation field of view.

[0030] ·Specular glossiness The specular glossiness of the multilayer coating film is not particularly limited. The 60-degree specular glossiness of the multilayer coating film may be 80.0% or more and 100% or less. The 60-degree specular glossiness is measured in accordance with JIS Z 8741 Specular glossiness - Measuring method. Specifically, light is irradiated at an incident angle of 60 degrees with respect to the normal of the multilayer coating film, and the luminous flux φ S of the reflected light at a reflection angle of 60 degrees is measured. Under the same conditions, light is irradiated onto the plane of glass with a refractive index of 1.567, and the luminous flux φ0 of the reflected light is measured. The luminous flux φS The value obtained by multiplying by 100 after removing the light beam φ0 is the 60-degree specular gloss. The 60-degree specular gloss is the average value of the 60-degree specular glosses of five different samples.

[0031] Figure 1 is a diagram for explaining the light-receiving angle of spectral reflectance. Light I irradiated from an angle of 45 degrees with respect to the surface of the multilayer coating 45 The specularly reflected light is indicated by R0. Light I 45 The light received at an angle of 5 degrees with respect to the specularly reflected light of Light I is indicated by R5. Light I 45 The light received at an angle of 15 degrees with respect to the specularly reflected light of Light I is R 15 as indicated. Light I 45 The light received at an angle of 45 degrees with respect to the specularly reflected light of Light I is R 45 as indicated.

[0032] <Workpiece> The material of the workpiece is not particularly limited. Examples of the workpiece include metal materials containing iron, copper, aluminum, tin, zinc, or alloys thereof. The shape of the workpiece is also not particularly limited. The workpiece may be plate-shaped or may have a three-dimensional shape. The workpiece may constitute at least a part of the body of a passenger car, truck, bus, etc.

[0033] The workpiece may be degreased and / or surface-treated. Examples of the surface treatment include phosphate treatment, chromate treatment, zirconium chemical conversion treatment, and composite oxide treatment. After the surface treatment, the metal material may be undercoated with an electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0034] <Colored coating film> The colored coating film conceals the texture and color of the workpiece and gives the multilayer coating film a gray color tone.

[0035] The thickness of the colored coating film is not particularly limited. From the perspective of hiding power, the thickness of the colored coating film may be 1 μm or more and 20 μm or less, may be 3 μm or more and 18 μm or less, or may be 5 μm or more and 15 μm or less. When the thickness of the colored coating film is within this range, the texture and color of the object to be coated are easily hidden without being transparent through the colored coating film. The thickness of the colored coating film is measured, for example, by an electromagnetic thickness gauge. The thickness of the colored coating film is the average value of the thicknesses of the colored coating films in five different samples. The thicknesses of other layers can also be measured and calculated in the same manner.

[0036] The black-and-white hiding film thickness of the colored coating film may be 80 μm or less, may be 10 μm or more and 70 μm or less, or may be 15 μm or more and 60 μm or less. The black-and-white hiding film thickness is measured using the black-and-white checkered hiding rate test paper specified in 4.1.2 of JIS K5600-4-1. Specifically, the hiding rate test paper is attached to a steel plate, and the paint is applied in a slanting manner so that the film thickness changes continuously. After the paint is dried or cured, the painted surface is visually observed under diffused daylight. The minimum film thickness at which the black-and-white boundary of the checkered pattern of the hiding rate test paper cannot be seen is the black-and-white hiding film thickness. This film thickness can also be measured by an electromagnetic thickness gauge in the same manner.

[0037] The brightness CL based on the spectral reflectance at which the light IC irradiated at an angle of 45 degrees with respect to the surface of the colored coating film 45 is received at an angle of 45 degrees with respect to the specularly reflected light * CL45 may be 0 or more and 45 or less. Thereby, the multilayer coating film can be recognized as a gray color. Brightness CL * CL45 may be 2 or more, may be 3 or more, or may be 10 or more. Brightness CL * CL45 may be 40 or less, may be 30 or less, or may be 20 or less.

[0038] (White pigment) The colored coating film contains a white pigment. The white pigment is not particularly limited. Examples of the white pigment include titanium dioxide, zinc oxide, and silica. These may be used alone or in combination of two or more. It may be titanium dioxide in terms of high refractive index. The titanium dioxide may be of the rutile type or the anatase type. Among them, from the viewpoint of weather resistance, it may be rutile-type titanium dioxide. The surface of the titanium dioxide may be treated with an inorganic compound such as silica, zirconium, or aluminum.

[0039] The primary particle diameter of the white pigment is not particularly limited. From the viewpoint of hiding power, the primary particle diameter of the white pigment may be 100 nm or more and 500 nm or less, or may be 200 nm or more and 400 nm or less. The primary particle diameter can be measured using image processing software from an electron microscope image of the cross-section of the multilayer coating film.

[0040] The amount of the white pigment is not particularly limited. The white pigment is added so that the lightness L * 45 is 1 or more and less than 40. Specifically, the amount of the white pigment may be 5.0% by mass or more and 40.0% by mass or less of the colored coating film. The amount of the white pigment may be 10% by mass or more, or 15.0% by mass or more of the colored coating film. The amount of the white pigment may be 30.0% by mass or less, or 25.0% by mass or less of the colored coating film. The amount of the white pigment may be 50.0 parts by mass or more and 200.0 parts by mass or less with respect to 100 parts by mass of the first resin described later.

[0041] (Black pigment) The colored coating film contains a black pigment. The black pigment is not particularly limited. Examples of the black pigment include carbon black; composite metal oxides such as iron chromium and bismuth manganese; perylene pigments; azomethiazole pigments. These may be used alone or in combination of two or more. The black pigment may be carbon black.

[0042] The primary particle diameter of the black pigment is not particularly limited. From the perspective of hiding power, the primary particle diameter of the black pigment may be 20.0 nm or more and 70.0 nm or less, and may be 30.0 nm or more and 60.0 nm or less.

[0043] The amount of the black pigment is not particularly limited. The black pigment is added so that the lightness L * is 1 or more and less than 40. Specifically, the amount of the black pigment may be 2.0% by mass or more and 10.0% by mass or less of the colored coating film. The amount of the black pigment may be 3.0% by mass or more of the colored coating film, and may be 4.0% by mass or more. The amount of the black pigment may be 9.0% by mass or less of the colored coating film, and may be 8.0% by mass or less. The amount of the black pigment may be 20.0 parts by mass or more and 30.0 parts by mass or less with respect to 100 parts by mass of the first resin described later.

[0044] The mixing ratio (white:black) of the white pigment and the black pigment may be, for example, 94.9:5.1 to 99.9:0.1 by mass ratio. The mixing ratio (white:black) may be 96:4 to 99.8:0.2.

[0045] (First resin) The colored coating film contains, for example, a first resin as a vehicle. The white pigment and the black pigment are dispersed in the first resin.

[0046] The first resin is not particularly limited. The first resin may include a cured product of a first thermosetting resin. The first resin is obtained, for example, by curing a first thermosetting resin formed by a crosslinkable functional group and a base resin. A first curing agent may be used for the curing.

[0047] Examples of the crosslinkable functional group include a carboxy group, a hydroxy group, an epoxy group, a silanol group, and a (meth)acryloyl group.

[0048] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, polyurethane resin, epoxy resin, and fluororesin. The epoxy resin may be a urethane-modified epoxy resin. The polyester resin may be a urethane-modified polyester resin. The acrylic resin may be a urethane-modified acrylic resin. Each urethane-modified resin has a urethane bond in the resin skeleton. These may be used alone or in combination of two or more. Among them, acrylic resin and urethane-modified polyester may be used in terms of improving chipping resistance.

[0049] The acrylic resin is obtained, for example, by copolymerizing (meth)acrylic acid esters having functional groups such as α,β-ethylenically unsaturated carboxylic acid, hydroxyl group, amide group, and methylol group, other (meth)acrylic acid esters, and styrene.

[0050] The urethane-modified polyester is obtained by reacting a hydroxyl group-containing polyester with an aliphatic diisocyanate compound. The hydroxyl group-containing polyester is prepared by polycondensing an acid component such as a polyvalent carboxylic acid and / or acid anhydride with a polyhydric alcohol. Examples of the aliphatic diisocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, and methylcyclohexane diisocyanate. These may be used alone or in combination of two or more.

[0051] The amount of the first resin is not particularly limited. In terms of easy formation of a uniform coating film, the amount of the first resin may be 60.0% by mass or more and 95.0% by mass or less of the colored coating film, may be 70.0% by mass or more and 90.0% by mass or less, and more preferably 75.0% by mass or more and 85.0% by mass or less.

[0052] The glass transition temperature (Tg) of the first resin is not particularly limited. From the viewpoints of coating film hardness and smoothness, the Tg of the first resin may be -40°C or higher and 20°C or lower, and may be -30°C or higher and 10°C or lower. The Tg is measured by a differential scanning calorimeter (DSC) conforming to JIS K 7121.

[0053] (Others) The colored coating film may further contain other pigments according to hiding power and the like. Examples of other pigments include metallic pigments, rust preventive pigments, colored pigments (colored pigments) other than white pigments and black pigments, and extender pigments. Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc. These may be used alone or in combination of two or more.

[0054] The amount of the colored pigment is not particularly limited as long as it does not significantly affect the lightness. The amount of the colored pigment may be, for example, 0.1% by mass or more and 1.0% by mass or less of the colored coating film. The amount of the colored pigment may be 10.0% by mass or less, 8.0% by mass or less, or 0% by mass of the colored coating film. The amount of the colored pigment may be 1.0% by mass or more and 10.0% by mass or less with respect to 100 parts by mass of the first resin described later.

[0055] The colored coating film may also contain various additives as necessary. Examples of the additives include ultraviolet absorbers, antioxidants, defoamers, surface modifiers, dispersants, and pinhole preventives.

[0056] <Glossy coating film> The glossy coating film gives a metallic texture to the multi-layer coating film.

[0057] The thickness of the glossy coating film is not particularly limited. The thickness of the glossy coating film may be 0.05 μm or more and 1.0 μm or less. Thereby, it becomes easy for the brightening material to be arranged in parallel with the coating film. Therefore, the change in lightness becomes even larger, and the ratio (L * 5 / L *)(45) is likely to be in the range of 4.0 or more and 10.0 or less. It is possible. The thickness of the brightening coating film may be 0.1 μm or more, and may be 0.3 μm or more. The thickness of the brightening coating film may be 0.8 μm or less, and may be 0.7 μm or less.

[0058] (Brightening material) The brightening coating film contains a brightening material. The brightening material is not particularly limited as long as it reflects light. Among them, in terms of being able to make the brightening coating film thin and the metallic texture being likely to be improved, it may be a scaly brightening material. The aspect ratio of the scaly brightening material is, for example, 2 or more. The aspect ratio is the ratio (major axis / thickness) of the major axis of one main surface of the scaly brightening material to the distance (thickness) between the two main surfaces of the scaly brightening material. The aspect ratio of the scaly brightening material may be 10 or more and 1000 or less.

[0059] The brightening coating film may contain, together with the scaly brightening material, other brightening materials (brightening materials with an aspect ratio of less than 2) other than the scaly brightening material. However, the content of the other brightening material may be 10.0% by mass or less of the total brightening material, and may be 5.0% by mass or less. Thereby, the scaly brightening material is more likely to be arranged in parallel with the coating film.

[0060] The major axis of the brightening material is not particularly limited. In terms of being easy to adjust the occupancy rate, the major axis of the brightening material may be 1.0 μm or more and 80.0 μm or less, and may be 3.0 μm or more and 50.0 μm or less. The above major axis is calculated by observing the multilayer coating film with an electron microscope from its normal direction. In the observation field of view, the region corresponding to the brightening material and the other regions are binarized by image processing software. Next, 20 brightening materials are arbitrarily selected, and their longest diameters are measured respectively. The average value of these measured values is the major axis of the brightening material.

[0061] The thickness of the brightening material, particularly the flaky brightening material, may be 0.05 μm or more and 0.3 μm or less. Thereby, the brightening coating film can be made thinner. The thickness of the brightening material may be 0.25 μm or less, and may be 0.2 μm or less. The above thickness may be calculated by observing the cross-section of the multilayer coating film with an electron microscope. In the observation field of view, the region corresponding to the brightening material and the other regions are binarized by image processing software. Next, 20 brightening materials are arbitrarily selected, and the length of the thickest part of each is measured. The average value of these measurement values is the thickness of the brightening material.

[0062] The average particle size of the brightening material is not particularly limited. In terms of being easy to improve the brightening feeling, the average particle size of the brightening material may be 2.0 μm or more and 50.0 μm or less, and may be 5.0 μm or more and 35.0 μm or less. The average particle size means the volume average particle size D50. The volume average particle size D50 can be measured using a laser Doppler particle size analyzer (for example, manufactured by Nikkiso Co., Ltd., "Microtrac UPA150").

[0063] The brightening material is not particularly limited. L * 5 / L * In terms of being easy to increase 45, it may be a brightening material that does not use multiple reflection interference as a coloring function. Examples of such brightening materials include metal particles. Specifically, particles of aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and alloys containing these can be mentioned. The brightening material may be colored. These are used alone or in combination of two or more. As a brightening material that uses multiple reflection interference as a coloring function, mica is typical.

[0064] Among them, they may be flaky metal particles. In terms of obtaining a high brightening feeling with a small amount, they may be flaky aluminum particles.

[0065] The amount of the total brightening material may be 3.0% by mass or more and 30.0% by mass or less of the brightening coating film, and may be 5.0% by mass or more and 25.0% by mass or less. Thereby, the above occupancy rate of the brightening material is likely to be 30.0% or more and 80.0% or less.

[0066] (Black pigment) The brightening coating film contains a black pigment. The black pigment is not particularly limited, and examples thereof include the same black pigments as those exemplified for the colored coating film. The black pigments contained in the colored coating film and the brightening coating film may be the same or different.

[0067] The amount of the black pigment is not particularly limited. The black pigment is added so that the lightness L * 45 is 1 or more and less than 40 (furthermore, the lightness CL * 45 is 0 or more and 45 or less). Specifically, the amount of the black pigment may be 30.0% by mass or more and 80.0% by mass or less of the brightening coating film. The amount of the black pigment may be 35.0% by mass or more of the brightening coating film, and may be 40.0% by mass or more. The amount of the black pigment may be 75.0% by mass or less of the brightening coating film, and may be 70.0% by mass or less. The amount of the black pigment may be 10.0 parts by mass or more and 30.0 parts by mass or less with respect to 100 parts by mass of the second resin described later.

[0068] The mixing ratio of the brightening material and the black pigment (brightening material: black) may be, for example, 80:20 to 20:80 by mass ratio. The mixing ratio (brightening material: black) may be 60:40 to 40:60, and may be 50:50 to 40:60.

[0069] (Viscosity regulator) The brightening coating film may contain a viscosity regulator. The viscosity regulator adjusts the viscosity of the brightening pigment dispersion (Y) which is a material of the brightening coating film. In the brightening pigment dispersion (Y) immediately after coating, the brightening material is arranged in parallel with the coating film. However, when the liquid component contained in the brightening pigment dispersion (Y) flows, the brightening material also flows and its arrangement is disturbed. By appropriately adjusting the viscosity of the brightening pigment dispersion (Y), in the brightening coating film after coating and before curing, the flow of the liquid component is suppressed and the disturbance of the arrangement of the brightening material is also suppressed. Therefore, the brightening material is easily held in a state arranged in parallel with the coating film.

[0070] The viscosity modifier is not particularly limited. Examples of the viscosity modifier include silica-based fine powder, mineral-based viscosity modifier, micronized barium sulfate powder, polyamide-based viscosity modifier, organic resin fine particle viscosity modifier, diurea-based viscosity modifier, urethane association type viscosity modifier, polyacrylic acid-based viscosity modifier which is an acrylic swelling type, and cellulose-based viscosity modifier. These may be used alone or in combination of two or more. Among them, a cellulose-based viscosity modifier may be used in terms of easy dispersion of the brightening material and excellent quick-drying property.

[0071] Examples of the mineral-based viscosity modifier include swelling layered silicates having a 2:1 type crystal structure. Specifically, smectite group clay minerals such as natural or synthetic montmorillonite, saponite, hectorite, stibnite, beidellite, nontronite, bentonite, laponite; swelling mica group clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na salt type fluorine teniolite, Li-type fluorine teniolite; vermiculite; and their substituents and derivatives. These may be used alone or in combination of two or more.

[0072] Examples of the polyacrylic acid-based viscosity modifier include sodium polyacrylate and polyacrylic acid-(meth)acrylate copolymer. Examples of commercially available products of the polyacrylic acid-based viscosity modifier include Primar ASE-60, Primar TT615, Primar RM5 (all manufactured by Dow Chemical Company), SN Thickeners 613, SN Thickeners 618, SN Thickeners 630, SN Thickeners 634, SN Thickeners 636 (all manufactured by San Nopco Limited). These may be used alone or in combination of two or more. The solid content acid value of the polyacrylic acid-based viscosity modifier is not particularly limited. The above solid content acid value may be 30 mgKOH / g or more and 300 mgKOH / g or less, or may be 80 mgKOH / g or more and 280 mgKOH / g or less.

[0073] Examples of the cellulose-based viscosity modifiers include cellulose acetate butyrate (CAB), carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and cellulose nanofibers (CNF). These may be used alone or in combination of two or more. Among them, it may be CAB or CNF, and it may be CNF.

[0074] The amount of the viscosity modifier is not particularly limited. The amount of the viscosity modifier may be, for example, 0.05 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the bright pigment dispersion. Thereby, the disorder of the arrangement of the brightening material is likely to be suppressed. The above amount of the viscosity modifier may be 0.07 parts by mass or more, may be 0.1 parts by mass or more, and may be 0.15 parts by mass or more. The above amount of the viscosity modifier may be 5.0 parts by mass or less, and may be 3.0 parts by mass or less.

[0075] (Second resin) The brightening coating film may contain a resin component (second resin). The second resin includes, for example, a cured product of a thermosetting resin similar to the first resin. However, it is desirable that the amount of the second resin is small. When the amount of the second resin is small, it becomes easy to make the brightening coating film thin. When the brightening coating film is thin, the disorder of the orientation of the brightening material is likely to be suppressed, and the brightening material is likely to be arranged in parallel with the surface of the coating film.

[0076] The amount of the second resin may be 15.0% by mass or less, may be 10.0% by mass or less, and may be 5.0% by mass or less of the bright pigment dispersion in terms of being easy to form a thin brightening coating film.

[0077] (Others) The brilliant coating film may contain pigments other than the brilliance material and the black pigment according to concealment and the like. Examples of other pigments include rust preventive pigments, coloring pigments (including white pigments and colored pigments), and the above-described extender pigments. Among them, the brilliant coating film may contain a white pigment (particularly titanium dioxide). In terms of facilitating the parallel arrangement of the scaly brilliance material with the coating film, the content of other pigments (particularly titanium dioxide) may be 10.0% by mass or less of the brilliant pigment dispersion, and may be 2.0% by mass or less. The content of other pigments (particularly titanium dioxide) may be 0.01% by mass or more of the brilliant pigment dispersion, and may be 0.1% by mass or more.

[0078] The brilliant coating film may contain various additives as required. Examples of the additives include ultraviolet absorbers, antioxidants, defoamers, anti-settling agents, dispersants, and surface modifiers.

[0079] <Clear Coating Film> The clear coating film protects the colored coating film and the brilliant coating film. The clear coating film is not particularly limited and has the same configuration as a conventionally known clear coating film.

[0080] The thickness of the clear coating film is not particularly limited. From the viewpoint of scratch resistance, the thickness of the clear coating film may be 10 μm or more, and may be 15 μm or more. In terms of being less likely to impair whiteness and metallic texture, the thickness of the clear coating film may be 50 μm or less, and may be 40 μm or less.

[0081] (Third Resin) The clear coating film contains, for example, a third resin. The third resin may include a cured product of a third thermosetting resin. Specifically, the third resin is obtained by curing a third thermosetting resin formed by a crosslinkable functional group and a base resin. A second curing agent may be used for the curing.

[0082] Examples of the third thermosetting resin include the same resins as those exemplified as the first thermosetting resin. The Tg of the third resin is not particularly limited. From the viewpoints of the coating film hardness and smoothness, the Tg of the third resin may be -40°C or higher and 20°C or lower, and may be -30°C or higher and 10°C or lower.

[0083] (Others) The clear coating film may contain a pigment as long as the transparency is not impaired. The pigment is not particularly limited, and one or a combination of two or more conventionally known pigments can be used. The addition amount of the pigment is not particularly limited. The addition amount of the pigment may be, for example, 30.0 parts by mass or less, and may be 0.01 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the solid content of the third resin.

[0084] The clear coating film may contain various additives as needed. Examples of the additives include an ultraviolet absorber, an antioxidant, an antifoaming agent, a surface conditioner, and a pinhole preventive agent.

[0085] FIG. 2 is a cross-sectional view schematically showing a part of a coated article including a multilayer coating film according to the present disclosure. The coated article 100 includes a substrate 10 and a multilayer coating film 20. The multilayer coating film 20 includes a colored coating film 21, a glitter coating film 22, and a clear coating film 23 in this order. The glitter coating film 22 contains a glitter material 221.

[0086] FIG. 3 is a cross-sectional view schematically showing a part of the glitter coating film in the present disclosure. In the illustrated example, the acute angle formed by the approximate straight line L0 on the surface of the glitter coating film 22 and the approximate straight line L1 on the surface of the glitter material 221 is approximately 0 degrees. That is, the glitter material 221 is parallel to the surface of the glitter coating film 22.

[0087] B. Method for manufacturing a multilayer coating film The above-mentioned multilayer coating film is manufactured by forming a colored coating film, a glossy coating film, and a clear coating film on an object to be coated in this order. When the glossy coating film is formed, the colored coating film may be cured or uncured. When the clear coating film is formed, the glossy coating film may be cured or uncured. Among them, from the viewpoints of productivity, adhesion, and water resistance, after laminating the respective coating films without curing them, they may be heated to simultaneously cure these three uncured coating films.

[0088] In this specification, curing is a concept including solidification. That is, curing in this specification means that the coating film loses its fluidity regardless of whether a chemical reaction is involved. Specifically, curing in this specification is synonymous with "curing and drying" defined in JIS K 5500 (Paint Terms). That is, curing means a) strongly squeezing the center of the test piece with the thumb and index finger, no depression due to fingerprints appears on the painted surface, no movement of the coating film is felt, and also, rapidly and repeatedly rubbing the painted surface with the fingertip, and no rubbing marks appear (dry hard). Uncured in this specification is a state other than the above-mentioned curing and includes a semi-cured state.

[0089] The multilayer coating film is preferably manufactured by the following method. That is, the manufacturing method of the multilayer coating film includes coating a colored paint on an object to be coated to form an uncured colored coating film, coating a glossy pigment dispersion on the uncured colored coating film to form an uncured glossy coating film, coating a clear paint on the uncured glossy coating film to form an uncured clear coating film, and curing the uncured colored coating film, the uncured glossy coating film, and the uncured clear coating film to obtain a multilayer coating film. FIG. 4 is a flowchart showing a method for manufacturing a multilayer coating film according to the present disclosure.

[0090] (1) Formation of an uncured colored coating film (S11) A colored paint (X) is coated on an object to be coated to form an uncured colored coating film.

[0091] The painting method is not particularly limited. Examples of the painting method include air spray painting, airless spray painting, rotary atomization painting, and curtain coating. These methods may be combined with electrostatic painting. Among them, from the viewpoint of coating efficiency, it may be rotary atomization electrostatic painting. For rotary atomization electrostatic painting, for example, a rotary atomization type electrostatic painting machine called "micro-micro bell (μμ bell)", "micro bell (μ bell)", "metallic bell (meta bell)" and the like is used.

[0092] The coating amount of the colored paint (X) is not particularly limited. The colored paint (X) is applied, for example, so that the thickness of the cured colored paint film is 1 μm or more and 20 μm or less.

[0093] After applying the colored paint (X), pre-drying (also referred to as pre-heating) may be performed. Thereby, the boiling over of the solvent contained in the colored paint film in the curing process is suppressed, and the generation of blisters is easily suppressed. Furthermore, pre-drying suppresses the mixing of the uncured colored paint film and the bright paint, and it becomes difficult to form a mixed layer. Therefore, the appearance of the obtained multilayer paint film is easily improved.

[0094] The conditions for pre-drying are not particularly limited. Examples of pre-drying include a method of leaving it for 15 minutes or more and 30 minutes or less under temperature conditions of 20°C or more and 25°C or less, and a method of heating it for 30 seconds or more and 10 minutes or less under temperature conditions of 50°C or more and 100°C or less.

[0095] <Colored paint (X)> The colored paint (X) contains the above white pigment, black pigment, and first thermosetting resin. The colored paint (X) contains, if necessary, a first curing agent, a first solvent, various additives, and the like. The colored paint (X) is prepared by diluting a mixture of a white pigment, a black pigment, a first thermosetting resin, a first curing agent, and various additives with a first solvent. The colored paint (X) may be a one-component paint or a multi-component paint such as a two-component paint.

[0096] The viscosity of the colored paint (X) is not particularly limited. The viscosity of the colored paint (X) measured by a B-type viscometer at 20°C is, for example, 500 cps / 6 rpm or more and 6000 cps / 6 rpm or less.

[0097] The solid content concentration of the colored paint (X) is not particularly limited. The solid content concentration of the colored paint (X) may be 30.0% by mass or more and 70.0% by mass or less. The solid content of the colored paint (X) is all components obtained by removing the first solvent from the colored paint (X).

[0098] (First thermosetting resin) The first thermosetting resin is formed by a crosslinkable functional group and a base resin. Details of the crosslinkable functional group and the base resin are as described above.

[0099] The amount of the first thermosetting resin is not particularly limited. When the first curing agent is included, the solid content mass of the first thermosetting resin may be 60.0% by mass or more and 90.0% by mass or less, and may be 70.0% by mass or more and 85.0% by mass or less, of the total of the solid content mass of the first thermosetting resin and the solid content mass of the first curing agent.

[0100] (First curing agent) The first curing agent is not particularly limited and may be appropriately selected according to the first thermosetting resin. Examples of the first curing agent include amino resins, urea resins, polyisocyanate compounds, epoxy group-containing compounds, carboxy group-containing compounds, carbodiimide group-containing compounds, hydrazide group-containing compounds, and semicarbazide group-containing compounds. The polyisocyanate compound includes a blocked polyisocyanate compound in which the isocyanate group is blocked with a blocking agent. These may be used alone or in combination of two or more. Among them, amino resins and polyisocyanate compounds may be used in terms of various performances and costs of the obtained coating film. The amino resin is obtained, for example, by condensing an amino compound such as melamine, benzoguanamine, or urea with formaldehyde and further etherifying with a lower monohydric alcohol. Details of the polyisocyanate compound will be described later.

[0101] The amount of the first curing agent is not particularly limited. In terms of curability, the solid content mass of the first curing agent may be 10.0% by mass or more and 40.0% by mass or less, may be 15.0% by mass or more and 30.0% by mass or less, and may be 15.0% by mass or more and 25.0% by mass or less of the total of the solid content mass of the first thermosetting resin and the solid content mass of the first curing agent.

[0102] (The first solvent) The first solvent is not particularly limited. The first solvent may be water (deionized water), may be an organic solvent, or may be a combination thereof. Among them, from the viewpoint of low VOC (Volatile Organic Compounds), it may be water. The proportion of water in the first solvent may be 50.0% by mass or more, and may be 80.0% by mass or more.

[0103] Examples of the organic solvent include ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol -t- butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as swazol, shellzol, and mineral spirit; and aromatic solvents such as xylene, toluene, Solvesso - 100 (S - 100), and Solvesso - 150 (S - 150). These may be used alone or in combination of two or more.

[0104] The amount of the first solvent is not particularly limited and is appropriately set according to the solid content, viscosity, etc. of the colored paint (X). For example, when the solid content of the colored paint (X) is 30.0% by mass or more and 70.0% by mass or less, and the viscosity of the colored paint (X) measured by a B-type viscometer at 20°C is 500 cps / 6 rpm or more and 6000 cps / 6 rpm or less, the first solvent is added.

[0105] When water is used as the first solvent, a first thermosetting resin having a hydrophilic group may be used. By neutralizing the hydrophilic group of the first thermosetting resin to form an alkali salt, the first thermosetting resin is solubilized or dispersed in water. Examples of the hydrophilic group include a carboxy group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, and a polyoxyethylene bond. Examples of the neutralizing agent include alkaline substances such as sodium hydroxide and amine compounds.

[0106] The first thermosetting resin can be prepared in a water-dispersed state by emulsion polymerization of the raw material monomers of the first thermosetting resin in the presence of a surfactant or a water-soluble resin. Alternatively, the first thermosetting resin may be dispersed in water with an emulsifier. In these cases, the first thermosetting resin may not contain a hydrophilic group, or may contain a small amount of a hydrophilic group.

[0107] (Others) The colored paint (X) contains, as other components, pigments and various additives exemplified as those contained in the colored paint film.

[0108] (2) Formation of an uncured glossy paint film (S12) A glossy pigment dispersion (Y) is applied onto the uncured colored paint film to form an uncured glossy paint film.

[0109] The coating method is not particularly limited. Examples of the coating method include the same methods as those for coating the colored paint. Among them, from the viewpoint of coating efficiency, it may be rotary atomization electrostatic coating.

[0110] The coating amount of the bright pigment dispersion (Y) is not particularly limited. The bright pigment dispersion (Y) is applied, for example, so that the thickness of the bright coating film in the resulting multilayer coating film is 0.05 μm or more and 1.0 μm or less.

[0111] After applying the bright pigment dispersion (Y), pre-drying may be performed. Thereby, the fluidity of the bright coating film rapidly decreases, and the flow of the bright material is also easily suppressed. The conditions for pre-drying are not particularly limited and may be the same as those for pre-drying the colored coating film.

[0112] <Bright pigment dispersion (Y)> The bright pigment dispersion (Y) contains a bright material and a black pigment. The bright pigment dispersion (Y) contains, if necessary, a viscosity modifier, a second solvent, and the like. The bright pigment dispersion (Y) is prepared by diluting a mixture of a bright material, a black pigment, a viscosity modifier, various additives, etc. with a second solvent.

[0113] The viscosity of the bright pigment dispersion (Y) is not particularly limited. The viscosity of the bright pigment dispersion (Y) may be such that the disorder of the arrangement of the bright material is easily suppressed, and the viscosity measured by a B-type viscometer at 20°C may be 20 cps / 6 rpm or more and 3000 cps / 6 rpm or less.

[0114] The solid content concentration of the bright pigment dispersion (Y) may be 0.1 mass% or more and 12.0 mass% or less. Thereby, it becomes easy to form a thin bright coating film, and the ratio (L * 5 / L * 45) is likely to be in the range of 4.0 or more and 10.0 or less. The solid content concentration of the bright pigment dispersion (Y) may be 9.0 mass% or less, may be 8.0 mass% or less, and may be 7.5 mass% or less. The solid content of the bright pigment dispersion (Y) is all the components obtained by removing the second solvent from the bright pigment dispersion (Y).

[0115] Among them, when the fluorescent pigment dispersion (Y) is aqueous, that is, when the second solvent contains 50.0 mass% or more of water, the solid content concentration of the fluorescent pigment dispersion (Y) may be 3.5 mass% or more, may be 4.0 mass% or more, and may be 4.5 mass% or more. When the second solvent contains 50.0 mass% or more of water, the solid content concentration of the fluorescent pigment dispersion (Y) may be 11.0 mass% or less, may be 10.5 mass% or less, and may be 10.0 mass% or less.

[0116] When the fluorescent pigment dispersion (Y) is solvent-based, that is, when the second solvent contains 50.0 mass% or more of an organic solvent, the solid content concentration of the fluorescent pigment dispersion (Y) may be 1.0 mass% or more and may be 2.0 mass% or more. When the second solvent contains 50 mass% or more of an organic solvent, the solid content concentration of the fluorescent pigment dispersion (Y) may be 5.0 mass% or less and may be 3.5 mass% or less.

[0117] The amount of the brightening material may be, for example, 0.1 mass% or more and 5.0 mass% or less of the fluorescent pigment dispersion (Y). Thereby, the above occupancy rate of the brightening material is likely to be 30.0% or more and 80.0% or less. The above amount of the brightening material may be 0.5 mass% or more and may be 1.0 mass% or more. The above amount of the brightening material may be 3.0 mass% or less, may be 2.5 mass% or less, and may be 1.8 mass% or less.

[0118] The amount of the black pigment may be, for example, 0.1 mass% or more and 5.0 mass% or less of the fluorescent pigment dispersion (Y). The above amount of the black pigment may be 0.5 mass% or more and may be 1.0 mass% or more. The above amount of the black pigment may be 3.0 mass% or less, may be 2.5 mass% or less, and may be 1.8 mass% or less.

[0119] (The second solvent) The second solvent is not particularly limited. The second solvent may be water, may be an organic solvent, or may be a combination thereof. Among these, from the perspective of low VOC, it may be water. The proportion of water in the second solvent may be 50.0% by mass or more, and may be 80.0% by mass or more. Examples of the organic solvent used in the second solvent include the same organic solvents as those exemplified as the first solvent.

[0120] The amount of the second solvent is not particularly limited and is appropriately set according to the solid content, viscosity, etc. of the fluorescent pigment dispersion (Y). For example, the second solvent is added so that the solid content of the fluorescent pigment dispersion (Y) is 0.1% by mass or more and 12.0% by mass or less, and the viscosity of the fluorescent pigment dispersion (Y) measured by a B-type viscometer at 20°C is 20 cps / 6 rpm or more and 3000 cps / 6 rpm or less.

[0121] (Others) The fluorescent pigment dispersion material (Y) further contains various additives exemplified as those contained in the fluorescent coating film.

[0122] For example, a dispersant is added to enhance the dispersibility of the fluorescent material. The dispersant is not particularly limited and is appropriately selected according to the second solvent, the fluorescent material, etc.

[0123] When the fluorescent pigment dispersion (Y) is aqueous, examples of the dispersant include inorganic dispersants such as phosphates and polyphosphates; polymer dispersants such as polycarboxylic acid-based, polyethylene glycol-based, and naphthalenesulfonic acid formalin condensate-based; and low-molecular dispersants such as alkylsulfonic acid-based, quaternary ammonium-based, and higher alcohol alkylene oxide-based. Examples of the phosphate include sodium hexametaphosphate, sodium pyrophosphate, and sodium phosphate.

[0124] When the fluorescent pigment dispersion (Y) is solvent-based, examples of the dispersant include polymer dispersants such as polycarboxylic acid partial alkyl ester-based, polyether-based, and polyalkylene polyamine-based.

[0125] The amount of the dispersant is not particularly limited. The amount of the dispersant may be, for example, 0.01% by mass or more and 3.0% by mass or less of the luminescent pigment dispersion (Y), and may be 0.1% by mass or more and 1.0% by mass or less.

[0126] The surface conditioner is added to control the surface tension of the luminescent coating film. Thereby, the luminescent material is likely to be arranged in parallel with the coating film. Furthermore, the adhesion between layers is improved.

[0127] The surface conditioner is not particularly limited. Examples of the surface conditioner include silicone-based, acrylic-based, vinyl-based, and fluorine-based surface conditioners. These may be used alone or in combination of two or more. Among them, from the viewpoints of the luminescence and water resistance of the luminescent coating film, etc., it may be a silicone-based surface conditioner. Examples of the silicone-based surface conditioner include polydimethylsiloxane and modified silicone obtained by modifying this. Examples of the modified silicone include polyether-modified products, acrylic-modified products, and polyester-modified products.

[0128] Examples of commercially available surface conditioners include BYK series (manufactured by BYK Chemie), Tego series (manufactured by Evonik), Granol series, Polyflow series (all manufactured by Kyoeisha Chemical Co., Ltd.), and Disparon series (manufactured by Kusumoto Chemicals, Ltd.).

[0129] The amount of the surface conditioner is not particularly limited. The amount of the surface conditioner may be 0.1% by mass or more and 10.0% by mass or less of the luminescent pigment dispersion (Y), may be 0.2% by mass or more and 8.0% by mass or less, and may be 0.4% by mass or more and 6.0% by mass or less. When the surface conditioner is within this range, the surface tension of the luminescent coating film decreases, and the wettability with respect to the uncured colored coating film of the luminescent pigment dispersion (Y) is likely to be improved.

[0130] (3) Formation of an uncured clear coating film (S13) A clear paint (Z) is applied onto the luminescent coating film to form an uncured clear coating film.

[0131] The coating method is not particularly limited. Examples of the coating method include the same methods as those for coating colored paints. Among them, from the viewpoint of coating efficiency, it may be rotary atomization electrostatic coating.

[0132] The coating amount of the clear paint (Z) is not particularly limited. The clear paint (Z) is applied, for example, so that the thickness of the clear paint film after curing is 25 μm or more and 45 μm or less.

[0133] <Clear paint (Z)> The clear paint (Z) is not particularly limited, and conventionally known clear paints can be used. The form of the clear paint (Z) is also not particularly limited. The clear paint (Z) may be a powder, an aqueous system, or a solvent system.

[0134] The clear paint (Z) contains the above-mentioned third thermosetting resin. The clear paint (Z) contains, if necessary, a second curing agent, a third solvent, various additives, etc. The clear paint (Z) is prepared by diluting a mixture of the third thermosetting resin, the second curing agent, and various additives, etc. with the third solvent. The clear paint (Z) may be a one-component paint or a multi-component paint such as a two-component paint.

[0135] The viscosity of the clear paint (Z) is not particularly limited. The viscosity of the clear paint (Z) measured by a B-type viscometer at 20°C is, for example, 500 cps / 6 rpm or more and 6000 cps / 6 rpm or less.

[0136] The solid content of the clear paint (Z) is not particularly limited. The solid content of the clear paint (Z) is, for example, 40.0 mass% or more and 60.0 mass% or less.

[0137] (Third thermosetting resin) The third thermosetting resin is formed by a crosslinkable functional group and a base resin. The details of the crosslinkable functional group and the base resin are as described above.

[0138] The one - component clear coating (Z) contains, as the third thermosetting resin, for example, a polyepoxide and a polyacid. Specifically, the one - component clear coating (Z) contains, as the third thermosetting resin, an acrylic resin (1) containing an acid anhydride group, a polyester resin (2) containing a carboxyl group, and an acrylic resin (3) containing a hydroxyl group and an epoxy group. From the viewpoint of storage stability, the acid anhydride group of the acrylic resin (1) may be half - esterified with a low - molecular - weight alcohol or the like. Hereinafter, such a third thermosetting resin is referred to as an acid - epoxy curing resin composition. The acid - epoxy curing resin composition is liable to increase the solid - content concentration of the clear coating (Z). Furthermore, according to the acid - epoxy curing resin composition, a clear coating film excellent in acid resistance is liable to be obtained.

[0139] The acid - epoxy curing resin composition cures as the above - mentioned three types of polymers react with each other. The curing mechanism of the acid - epoxy curing resin composition is as follows. First, by heating, the acid anhydride group in the acrylic resin (1) reacts with the hydroxyl groups in the polyester resin (2) and the acrylic resin (3), and a carboxyl group is formed. The carboxyl group and the carboxyl group in the polyester resin (2) react with the epoxy group present in the acrylic resin (3), and a cross - linking point is formed. Starting from this cross - linking point, a cross - linking reaction occurs.

[0140] The blending of the acrylic resin (1), the polyester resin (2) and the acrylic resin (3) is not particularly limited. The blending of the acid - epoxy curing resin composition is carried out in amounts and methods well - known to those skilled in the art.

[0141] Among them, the molar ratio of the carboxyl group of the acrylic resin (1) and the polyester resin (2) to the epoxy group of the acrylic resin (3) may be 1.0 / 1.4 or more and 1.0 / 0.6 or less, and may be 1.0 / 1.2 or more and 1.0 / 0.8 or less. Thereby, the curability of the clear coating (Z) is liable to be improved. Furthermore, a clear coating film that is difficult to yellow is liable to be obtained.

[0142] The molar ratio of the carboxy groups of the acrylic resin (1) to the hydroxyl groups of the polyester resin (2) and the acrylic resin (3) may be 1.0 / 2.0 or more and 1.0 / 0.5 or less, and may be 1.0 / 1.5 or more and 1.0 / 0.7 or less. Thereby, the curability of the clear paint (Z) is likely to be improved. Further, a clear paint film excellent in water resistance is likely to be obtained.

[0143] The two-component clear paint (Z) is preferable in that the physical properties of the paint film are likely to be improved. The two-component clear paint (Z) contains a separated third thermosetting resin and a second curing agent. The third thermosetting resin and the second curing agent are mixed immediately before use. Examples of the combination of the third thermosetting resin / the second curing agent include a carboxy group-containing resin / an epoxy group-containing resin, a hydroxyl group-containing resin / a polyisocyanate compound, a hydroxyl group-containing resin / a blocked isocyanate compound, and a hydroxyl group-containing resin / a melamine resin. These are particularly suitable for forming a clear paint film.

[0144] Among them, the two-component clear paint (Z) may contain a hydroxyl group-containing resin as the third thermosetting resin and a polyisocyanate compound as the second curing agent, in that the physical properties of the paint film are likely to be improved.

[0145] Specific 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. Among them, a hydroxyl group-containing acrylic resin and a hydroxyl group-containing polyester resin may be used, and a hydroxyl group-containing acrylic resin may be used. These may be used alone or in combination of two or more.

[0146] The hydroxyl value of the hydroxyl group-containing acrylic resin is not particularly limited. From the viewpoints of scratch resistance and water resistance of the paint film, the hydroxyl value of the hydroxyl group-containing acrylic resin may be 80 mgKOH / g or more and 200 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 180 mgKOH / g or less.

[0147] The weight average molecular weight of the hydroxyl group-containing acrylic resin is not particularly limited. From the viewpoints of acid resistance and smoothness of the coating film, the weight average molecular weight of the hydroxyl group-containing acrylic resin may be 2,500 or more and 40,000 or less, and may be 5,000 or more and 30,000 or less. The weight average molecular weight can be calculated based on the molecular weight of standard polystyrene from the chromatogram measured by gel permeation chromatography. As the gel permeation chromatography, for example, HLC8120GPC (manufactured by Tosoh Corporation) is used. As the columns, TSKgel G-4000HXL, TSKgel G-3000HXL, TSKgel G-2500HXL, and TSKgel G-2000HXL (all manufactured by Tosoh Corporation) are used. The chromatography is carried out, for example, under the conditions of using tetrahydrofuran as the mobile phase, a differential refractive index detector (RI) as the detector, a measurement temperature of 40 °C, and a flow rate of 1 cc / min.

[0148] (Second curing agent) The second curing agent is not particularly limited and may be appropriately selected according to the third thermosetting resin. Examples of the second curing agent include the same curing agents as those exemplified as the first curing agent.

[0149] For example, the polyisocyanate compound has at least two isocyanate groups in one molecule. Examples of the polyisocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having an aromatic ring not bonded to the isocyanate group in the molecule (aromatic aliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates.

[0150] 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, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate); and 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, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0151] Examples of alicyclic polyisocyanates include alicyclic diisocyanates such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylene bis(4,1-cyclohexane diyl) diisocyanate (common name: hydrogenated MDI), norbornane diisocyanate, 4,4'-methylene bis(cyclohexyl isocyanate), etc.; alicyclic triisocyanates such as 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)-heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, etc.

[0152] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylene bis(4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,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 aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0153] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0154] Examples of the derivative of the polyisocyanate include a dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI of the above-mentioned polyisocyanate.

[0155] The polyisocyanate compound is used alone or in combination of two or more thereof.

[0156] Among them, from the viewpoints of adhesiveness and compatibility, etc., it may be hexamethylene diisocyanate or 4,4'-methylenebis(cyclohexyl isocyanate), and may be a derivative of hexamethylene diisocyanate.

[0157] As the polyisocyanate compound, a prepolymer of the above polyisocyanate or its derivative may be used. The prepolymer is obtained by reacting a polyisocyanate or its derivative with a compound capable of reacting therewith under conditions of an excess of isocyanate groups. The compound capable of reacting with the polyisocyanate or its derivative is a compound having an active hydrogen group such as a hydroxyl group or an amino group. Examples of the above compound include polyhydric alcohols, low molecular weight polyester resins, amines, and water.

[0158] As the polyisocyanate compound, a blocked polyisocyanate compound may be used. The blocked polyisocyanate compound is obtained by blocking the isocyanate groups in the above polyisocyanate or its derivative with a blocking agent.

[0159] Examples of the blocking agent include phenol compounds, lactam compounds, alcohols, ethers, oxime compounds, compounds having an active methylene group, mercaptan compounds, acid amide compounds, imide compounds, amine compounds, imidazole compounds, urea compounds, carbamic acid esters, imine compounds, sulfites, azole compounds, and ketone compounds.

[0160] Examples of the phenol compound include phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate.

[0161] Examples of the lactam compound include ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam.

[0162] Examples of the alcohol include methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol, 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 methacrylate.

[0163] Examples of the ether include 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 methoxymethanol.

[0164] Examples of the oxime compound include formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monoxime, benzophenone oxime, and cyclohexanone oxime.

[0165] Examples of the compound having an active methylene group include dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone.

[0166] Examples of the mercaptan compound include butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methyl thiophenol, and ethyl thiophenol.

[0167] Examples of the acid amide compound include acetanilide, acetanisidide, acetotoluidide, acrylamide, methacrylamide, acetamide, stearic acid amide, and benzamide.

[0168] Examples of imide compounds include succinimide, phthalimide, and maleimide.

[0169] Examples of amine compounds include diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine.

[0170] Examples of imidazole compounds include imidazole and 2-ethylimidazole.

[0171] Examples of urea compounds include urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea.

[0172] Examples of carbamic acid esters include phenyl N-phenylcarbamate.

[0173] Examples of imine compounds include ethyleneimine and propyleneimine.

[0174] Examples of sulfites include sodium bisulfite and potassium bisulfite.

[0175] Examples of azole compounds 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, 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0176] Examples of ketone compounds include methyl ethyl ketone and methyl isobutyl ketone.

[0177] Examples of commercially available blocked isocyanate compounds include, for example, the Duranate (blocked hexamethylene diisocyanate) series (manufactured by Asahi Kasei Corporation), Sumidule BL3175, Desmodule BL3272MPA, Desmodule BL3475 BA / SN, Desmodule BL3575 / 1 MPA / SN, Desmodule BL4265 SN, Desmodule BL5375 MPA / SN, Desmodule VP LS2078 / 2 (all manufactured by Bayer Corporation).

[0178] The equivalent ratio (=OH / NCO) of the hydroxyl group of the hydroxyl group-containing resin to the isocyanate group of the polyisocyanate compound is not particularly limited. From the viewpoints of the curability and scratch resistance of the coating film, etc., the above equivalent ratio (=OH / NCO) may be 0.5 or more and 2.0 or less, and may be 0.8 or more and 1.5 or less.

[0179] (Third solvent) The clear paint (Z) contains a third solvent, if necessary. The third solvent is not particularly limited. The third solvent may be water, an organic solvent, or a combination thereof. Among them, from the viewpoint of low VOC, it may be water. The proportion of water in the third solvent may be 50.0% by mass or more, and may be 80.0% by mass or more. Examples of the organic solvent used for the third solvent include the same organic solvents as those exemplified as the first solvent.

[0180] The amount of the third solvent is not particularly limited and is appropriately set according to the solid content and viscosity of the clear paint (Z), etc. The third solvent is added, for example, so that the solid content of the clear paint (Z) is 40.0% by mass or more and 60.0% by mass or less.

[0181] (4) Curing (S14) The uncured colored coating film, the uncured glossy coating film, and the uncured clear coating film are cured at once. Each coating film can be cured by heating.

[0182] The heating conditions are appropriately set according to the composition of each coating film and the like. The heating temperature is, for example, 70°C or higher and 150°C or lower, and may be 80°C or higher and 140°C or lower. The heating time is, for example, 10 minutes or longer and 40 minutes or shorter, and may be 20 minutes or longer and 30 minutes or shorter. Examples of the heating device include drying furnaces such as hot air furnaces, electric furnaces, and infrared induction heating furnaces.

[0183] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited only to these Examples. Note that both "parts" and "%" are based on mass.

[0184] [Evaluation] (1) Lightness L * 5, L * 45, CL * 45 Using a variable-angle spectrophotometer (Gonio-Spectrophotometer GSP-1, manufactured by Murakami Color Research Laboratory Co., Ltd.), the spectral reflectance of the light I irradiated onto the coating film at an angle of 45 degrees was measured at predetermined angles (5 degrees, 45 degrees) with respect to the specularly reflected light. From this spectral reflectance, L 45 a * b * The respective lightnesses L in the colorimetric system * were calculated. The average values of five different samples were taken as the lightnesses L * 5, L * 45, CL * 45, respectively. *

[0185] (2) L * 5 / L * 45 Using a variable-angle spectrophotometer (Gonio-Spectrophotometer GSP-1, manufactured by Murakami Color Research Laboratory Co., Ltd.), the spectral reflectances of the light I irradiated onto the coating film at an angle of 45 degrees were measured at angles of 5 degrees and 15 degrees with respect to the specularly reflected light, respectively. From this spectral reflectance, L 45 a * b * The lightness L in the colorimetric system * 5 and the lightness L * 5 and the lightness L * ​45 was calculated. The average value of five different samples was taken as the lightness L * 5 and the lightness L * 45. The lightness L * 5 was divided by the lightness L * 45 to obtain L * 5 / L * 45.

[0186] (3) Graininess G Using a multi-angle colorimeter (product name: BYK-mac i 23mm, manufacturing No. 1238698, catalog No. 7030, manufactured by BYK-Gardner), the graininess G was obtained. The average value of five different samples was taken as the graininess G

[0187] (4) Thickness of the glossy coating Using an electromagnetic film thickness gauge (product name: FISCHERSCOPE (registered trademark) MMS PC2, manufactured by Fischer Instruments Co., Ltd.), the thickness of the glossy coating was measured. The average value of five different samples was taken as the thickness of the glossy coating

[0188] (5) Occupancy rate The multi-layer coating was imaged from its normal direction using an industrial microscope (product name: ECLIPSE LV150N, manufactured by NIKON), and the area corresponding to the brightening material and the other areas were binarized using image processing software. With the area of the observation field of view taken as 100%, the area ratio of the brightening material was calculated. The magnification in imaging was 200 times. The observation field of view was 480 nm in the vertical direction and 720 nm in the horizontal direction. The average value in five different observation fields of view was taken as the occupancy rate

[0189] (6) Si 15 value Using a multi-angle colorimeter (product name: BYK-mac i 23mm, manufacturing No. 1238698, catalog No. 7030, manufactured by BYK-Gardner), by imaging and analyzing the light irradiated from a direction inclined 15 degrees with respect to the normal direction of the multi-layer coating from the normal direction of the multi-layer coating, the Si 15 value was obtained. The average value of five different samples was taken as the Si 15 value.

[0190] (7) Orientation of the flaky brightening material The cross-section of the multilayer coating film was imaged with an industrial microscope (product name: ECLIPSE LV150N, manufactured by NIKON Corporation). The angles θ formed between the surface of the brightening coating film and the flaky brightening material within the observation field of view were calculated respectively by the above method. When the angle θ was 30 degrees or less, it was considered that the surface of the brightening coating film and the flaky brightening material were parallel.

[0191] (8) Arrangement of the brightening material The cross-section of the multilayer coating film was imaged with an industrial microscope (product name: ECLIPSE LV150N, manufactured by NIKON Corporation). The number of overlapping brightening materials within the observation field of view was calculated respectively by the above method.

[0192] [Example 1] (I) Preparation of the object to be coated As the object to be coated, a zinc phosphate-treated steel sheet provided with a cured electrodeposition coating film was prepared. The cured electrodeposition coating film was formed by electrocoating a cationic electrodeposition paint composition (product name: Power Niks) manufactured by Nippon Paint Co., Ltd. on the zinc phosphate-treated steel sheet so that the dry film thickness was 20 μm, and then heating at 160 °C for 30 minutes.

[0193] (II) Preparation of the paint (II-1) Preparation of the colored paint 130.5 parts of a white pigment dispersion paste and 2.5 parts of a black pigment dispersion paste manufactured as follows, 73.9 parts of a hydroxyl group-containing acrylic resin emulsion resin (30 parts in terms of resin solid content) and 60 parts of a hydroxyl group-containing polyester resin (30 parts in terms of resin solid content), 100 parts of a hydroxyl group-containing polyurethane resin (manufactured by Nippon Paint Automotive Coatings Co., Ltd.) (20 parts in terms of resin solid content), and 22.2 parts of Cymel 327 (manufactured by Nippon Cytec Industries Co., Ltd., melamine resin) as the first curing agent were mixed. Then, 40 parts of ion-exchanged water was added to the mixture and further mixed. Subsequently, 3.3 parts of Biscarex HV-30 (manufactured by BASF, a polycarboxylic acid-based viscosity modifier, non-volatile content 30%) was added to the mixture as a viscosity modifier, and further mixed and stirred to obtain a colored paint (X-1).

[0194] (Manufacture of White Pigment Dispersion Paste) 4.5 parts of a dispersant (trade name: Disperbyk 190, manufactured by BYK Chemie GmbH, nonionic-anionic dispersant), 0.5 part of an antifoaming agent (trade name: BYK-011, manufactured by BYK Chemie GmbH), 22.9 parts of ion-exchanged water, and 72.1 parts of titanium dioxide were preliminarily mixed. Then, a glass bead medium was added in a paint conditioner and mixed at room temperature until the secondary particle diameter of titanium dioxide became 5 μm or less to obtain a white pigment dispersion paste.

[0195] (Manufacture of Black Pigment Dispersion Paste) 18.6 parts of a dispersant (trade name: DIPEX ULTRA PA4550, manufactured by BASF Japan Ltd.), 0.5 part of an antifoaming agent (trade name: BYK-011, manufactured by BYK Chemie GmbH), 36.0 parts of ion-exchanged water, 10.4 parts of a black pigment (carbon black), and 34.5 parts (30 parts in terms of resin solid content) of a hydroxyl group-containing acrylic resin emulsion were preliminarily mixed. Then, a glass bead medium was added in a paint conditioner and mixed at room temperature until the secondary particle diameter of the black pigment (carbon black) became 60 nm or less to obtain a black pigment dispersion paste.

[0196] (Manufacture of Hydroxyl Group-Containing Acrylic Resin Emulsion) Into a normal reaction vessel for producing an acrylic resin emulsion equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen inlet tube, etc., 445 parts of water and 5 parts of an emulsifier (trade name: Newcol 293, manufactured by Nippon Emulsifier Co., Ltd.) were charged, and while stirring these, the temperature was raised to 75°C. A monomer mixture containing 145 parts of methyl methacrylate, 50 parts of styrene, 220 parts of ethyl acrylate, 70 parts of 2-hydroxyethyl methacrylate, and 15 parts of methacrylic acid, a mixture of 240 parts of water and 30 parts of an emulsifier (trade name: Newcol 293) were emulsified using a homogenizer to obtain a monomer pre-emulsion. While stirring the inside of the above reaction vessel, the monomer pre-emulsion was dropped over 3 hours. In parallel with the dropping of the monomer pre-emulsion, an aqueous solution in which 1 part of APS (ammonium persulfate) as a polymerization initiator was dissolved in 50 parts of water was evenly dropped into the above reaction vessel until the dropping of the monomer pre-emulsion was completed. After the dropping of the monomer pre-emulsion was completed, the reaction was continued at 80°C for 1 hour. After cooling the reaction product, an aqueous solution in which 2 parts of dimethylaminoethanol were dissolved in 20 parts of water was added to the above reaction vessel to obtain a hydroxyl group-containing acrylic resin emulsion with a solid content concentration of 40.6% by mass.

[0197] Regarding the solid content of the obtained hydroxyl group-containing acrylic resin emulsion, the acid value was 20 mgKOH / g, the hydroxyl value was 60 mgKOH / g, and the glass transition temperature (Tg) was 30°C. The solid content concentration was measured according to the JIS K 5601-1-2 heating residue measurement method.

[0198] (Production of Hydroxyl Group-Containing Polyester Resin) 25.6 parts of isophthalic acid, 22.8 parts of phthalic anhydride, 5.6 parts of adipic acid, 19.3 parts of trimethylolpropane, 26.7 parts of neopentyl glycol, 17.5 parts of ε-caprolactone and 0.1 part of dibutyltin oxide were added to the reactor, and while mixing and stirring these, the temperature was raised to 170 °C. Then, while raising the temperature of the reaction product to 220 °C over 3 hours, water generated by the condensation reaction was removed until the acid value reached 8. Next, 7.9 parts of trimellitic anhydride was added to the reactor and reacted at 150 °C for 1 hour to obtain a polyester resin with an acid value of 40. Further, after cooling the polyester resin to 100 °C, 11.2 parts of butyl cellosolve was added and stirred until it became uniform. Subsequently, the polyester resin was cooled to 60 °C, and then 98.8 parts of ion-exchanged water and 5.9 parts of dimethylethanolamine were added. Thereby, a hydroxyl group-containing polyester resin with a solid content of 50 mass% was obtained. Regarding the solid content of the hydroxyl group-containing polyester resin, the acid value was 40 mgKOH / g, the hydroxyl value was 110 mgKOH / g, the number average molecular weight was 2870, and the glass transition temperature (Tg) was -3 °C. The above glass transition temperature (Tg) was measured using a differential scanning calorimeter (DSC220C) manufactured by Seiko Instruments (SII). The measurement conditions were a sample amount of 10 mg, a heating rate of 10 °C / min, and a measurement temperature from -20 °C to 100 °C.

[0199] (II-2) Preparation of the fluorescent pigment dispersion To 0.10 part of CAB, 0.10 part of cellulose nanofiber, 1.50 parts of scaly aluminum particles (trade name "EMR-D4670", manufactured by Toyo Aluminum Co., Ltd., thickness 0.16 μm, average particle diameter 8 μm), 6.55 parts of aluminum dissolution thinner, 0.51 part of titanium dioxide, 1.20 parts of black pigment (carbon black), 1.49 parts of acrylic resin, 1.82 parts of thermosetting resin, 1.20 parts of phosphoric acid, 0.13 part of amine, 0.01 part of antifoaming agent, deionized water was added so that the total amount became 100 parts and stirred to obtain a fluorescent pigment dispersion (Y-1). The solid content concentration of the fluorescent pigment dispersion (Y-1) was 10.0%.

[0200] (II-3) Preparation of the clear paint As the clear paint (Z-1), PU Excel O-2100 (manufactured by Nippon Paint Co., Ltd., a two-component clear paint containing a hydroxyl group-containing resin and a polyisocyanate compound) was prepared.

[0201] (III) Formation of an uncured colored coating film On the object to be coated, the colored paint (X-1) was applied using a metabell.

[0202] (IV) Formation of an uncured glossy coating film On the uncured colored coating film, the glossy pigment dispersion (Y-1) was applied using a metabell.

[0203] (V) Formation of an uncured clear coating film On the uncured glossy coating film, the clear paint (Z-1) was applied using a micrometabell.

[0204] (VI) Curing After the formation of the clear coating film (V), it was heated at 140 °C for 20 minutes to obtain an object to be coated provided with a multilayer coating film A1. In the multilayer coating film A1, the thickness of the colored coating film was 6 μm, the black-and-white hiding film thickness of the colored coating film was 10 μm, the thickness of the glossy coating film was 0.5 μm, and the thickness of the clear coating film was 30 μm.

[0205] (VII) Evaluation The above evaluation was performed on the multilayer coating film A1. The results of evaluations (1) to (5) are shown in Table 1. Regarding evaluation (6), the Si 15 value of the multilayer coating film A1 was 6.2. Regarding evaluation (7) of the multilayer coating film A1, 80% or more of the scaly brightening materials were arranged parallel to the surface of the glossy coating film. Regarding evaluation (8) of the multilayer coating film A1, 80% or more of the scaly brightening materials did not overlap with other scaly brightening materials.

[0206] [Comparative Example 1] An object to be coated provided with a multilayer coating film B1 was obtained and evaluations (1) to (5) were performed in the same manner as in Example 1 except that the amount of the brightening material in the glossy pigment dispersion was reduced. The results are shown in Table 1.

[0207] [Comparative Example 2] A coated object with a multilayer coating film B2 was obtained and evaluations (1) to (5) were performed in the same manner as in Example 1, except that the amount of the black pigment in the colored paint was reduced. The results are shown in Table 1.

[0208] [Comparative Example 3] A coated object with a multilayer coating film B3 was obtained and evaluations (1) to (5) were performed in the same manner as in Example 1, except that the black pigment dispersion paste was not blended in the colored paint. The results are shown in Table 1.

[0209] [Comparative Example 4] A coated object with a multilayer coating film B4 was obtained and evaluations (1) to (5) were performed in the same manner as in Example 1, except that the thickness of the glossy coating film was set to 1.5 μm. The results are shown in Table 1.

[0210] [Comparative Example 5] A coated object with a multilayer coating film B5 was obtained and evaluations (1) to (5) were performed in the same manner as in Example 1, except that the solid content concentration of the glossy pigment dispersion was adjusted to 15.0%. The results are shown in Table 1.

[0211]

Table 1

[0212] The multilayer coating film of Example 1 had a large change in lightness and had a dense metallic texture. The multilayer coating film of Comparative Example 1 had a small change in lightness and lacked a metallic texture. This is considered to be because both the ratio (L * 5 / L * 45) and the occupancy rate of the brightening material were small. The multilayer coating film of Comparative Example 2 had a small change in lightness and had a hue that was recognized as silver rather than gray. This is considered to be because the ratio (L * 5 / L * 45) was even smaller than that of Comparative Example 1. The multilayer coating film of Comparative Example 3 had a small change in lightness, lacked a metallic texture, and had a hue that was recognized as white. This is because L *45 is large, and the ratio (L * 5 / L * 45) is considered to be even smaller than that of Comparative Example 2. The multilayer coating film of Comparative Example 4 had a small change in lightness and lacked a metallic texture. This is considered to be because the ratio (L * 5 / L * 45) was small. The multilayer coating film of Comparative Example 5 had a small change in lightness and lacked density. This is considered to be because the ratio (L * 5 / L * 45) was small. In addition, it is considered that the large particle feeling G also has an influence.

Industrial Applicability

[0213] The multilayer coating film and the method for producing the multilayer coating film of the present invention are particularly suitable for the outer panel of an automobile body.

[0214] This application claims priority based on Japanese Patent Application No. 2023-192023 filed in Japan on November 10, 2023, and all of the described contents are incorporated herein by reference.

Explanation of Signs

[0215] 100 Coated article 10 Object to be coated 20 Multilayer coating film 21 Colored coating film 22 Glossy coating film 221 Glossy material 23 Clear coating film

Claims

1. A colored coating film formed on a substrate and containing a white pigment and a black pigment; a glittering coating film formed on the colored coating film and containing a glittering material and a black pigment; A multi-layer coating film comprising a clear coating film formed on the glossy coating film, Light I was irradiated at an angle of 45 degrees onto the surface of the multilayer coating film. ４５ The brightness L based on the spectral reflectance of light received at an angle of 45 degrees to the regular reflected light ＊ 45 is equal to or greater than 1 and less than 40, The light I ４５ The brightness L based on the spectral reflectance of light received at an angle of 5 degrees with respect to the regular reflection light ＊ 5 and the light I ４５ The brightness L based on the spectral reflectance of light received at an angle of 45 degrees to the regular reflected light ＊ Ratio to 45 (L ＊ 5 / L ＊ 45) is 4.0 or more and 10.0 or less, A multi-layer coating film, wherein the occupancy rate of the lustrous material as viewed from the normal direction of the surface of the multi-layer coating film is 30% or more and 80% or less.

2. The multi-layer coating film according to claim 1, wherein the graininess of the surface of the multi-layer coating film is 4.0 or more and 8.0 or less.

3. The surface of the colored coating is irradiated with light at an angle of 45 degrees. ４５ The brightness CL based on the spectral reflectance of light received at an angle of 45 degrees to the regular reflected light ＊ The multilayer coating film according to claim 1 or 2, wherein 45 is 0 or more and 45 or less.

4. The multi-layer coating film according to claim 1 or 2, wherein the thickness of the glittering coating film is 0.05 μm or more and 1.0 μm or less.

5. The multi-layer coating film according to claim 1 or 2, wherein the luster material contains aluminum particles.

6. A colored coating material containing a white pigment and a black pigment is applied onto an object to form an uncured colored coating film; Coating the uncured colored coating film with a glittering pigment dispersion containing a glittering material and a black pigment to form an uncured glittering coating film; Applying a clear coating to the uncured glossy coating film to form an uncured clear coating film; and curing the uncured color coating film, the uncured glitter coating film, and the uncured clear coating film to obtain a multi-layer coating film. Light I was irradiated at an angle of 45 degrees onto the surface of the multilayer coating film. ４５ The brightness L based on the spectral reflectance of light received at an angle of 45 degrees to the regular reflected light ＊ 45 is equal to or greater than 1 and less than 40, The light I ４５ The brightness L based on the spectral reflectance of light received at an angle of 5 degrees with respect to the regular reflection light ＊ 5 and the light I ４５ The brightness L based on the spectral reflectance of light received at an angle of 45 degrees to the regular reflected light ＊ Ratio to 45 (L ＊ 5 / L ＊ 45) is 4.0 or more and 10.0 or less, A method for producing a multilayer coating film, wherein the occupancy rate of the luster material as viewed from a normal direction of a surface of the multilayer coating film is 30% or more and 80% or less.

7. The method for producing a multi-layer coating film according to claim 6, wherein the clear coating is a two-component coating containing a hydroxyl group-containing resin and a polyisocyanate compound.

8. The method for producing a multilayer coating film according to claim 6 or 7, wherein the solid content concentration of the glittering pigment dispersion is 0.1% by mass or more and 12.0% by mass or less.

9. The method for producing a multilayer coating film according to claim 6 or 7, wherein the glittering pigment dispersion contains cellulose nanofibers.

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