Multi-layer coating

Abstract

A multilayer coating film having a small hue difference from the first base coating film and having high flip-flop properties. 【Solution means】It includes a first base coating film, a second base coating film, and a clear coating film. The first base paint contains a bright pigment and two or more kinds of coloring pigments, and the solid content concentration NV1 is 20 to 35% by mass, and the PWC of the bright pigment G1 is 1 to 25%, and the PWC of the coloring pigment C1 is 0.1 to 5.0%. The second base paint contains a bright pigment and coloring pigments having the same Color Index name as two or more kinds of the first base paint compositions, and the solid content concentration NV2 is 7 to 30% by mass, and the PWC of the bright pigment G2 is 5 to 35%, and the PWC of the coloring pigment C2 is 0.5 to 20.0%. Furthermore, the ratio (T1 / T2) of the thickness T1 of the first base coating film to the thickness T2 of the second base coating film is 1.5 / 1 to 5 / 1, (NV1 / NV2) is 1.3 / 1 to 3 / 1, (PWC G1 / PWC G2 ) is 1 / 10 to 1 / 1, (PWC C1 / PWC C2 ) is 1 / 5 to 1 / 1.

Description

[Technical Field]

[0001] This invention relates to a multi-layer coating film. [Background technology]

[0002] Automobile bodies are constructed with multiple layers of coatings (multilayer coatings). These multilayer coatings protect the body while simultaneously providing the automobile with superior aesthetic appeal. In a multilayer coating, for example, a first base coating, a second base coating, and a clear coating are layered in this order. Traditionally, automobiles have been expected to have a luxurious appearance, and designs with a strong metallic finish and high flip-flop appeal are preferred. Therefore, the second base coating typically contains a glossy pigment.

[0003] Multilayer coatings are mainly formed on the outer panels of the vehicle body. In many cases, multilayer coatings are not formed on the inner panels. For example, only the first base coating used for painting the outer panels is formed on the inner panels. Because the final coatings formed on the inner and outer panels are different, a color difference may occur between the inner and outer panels. This color difference can cause, for example, streaky unevenness in the paint on the inner panels. Streaky unevenness is formed when the first base paint composition for the first base coating and the second base paint composition for the second base coating are applied to the outer panels after the inner panels have been painted, and the second base paint composition is scattered onto the inner panels. Conventionally, this problem has been solved by using a paint composition specifically for the inner panels, but this is inefficient and increases costs. If the first and second base coatings are formed with the same paint composition, the desired flip-flop properties cannot be obtained.

[0004] In this regard, Patent Document 1 discloses a method for controlling the discharge amount of the second base coating composition and the movement speed of the spray gun. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-126528 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present disclosure aims to provide a multilayer coating (corresponding to the outer panel) that, when the same first base coating composition is used to form the first base coating on the outer and inner panels, exhibits a small difference in hue between the first base coating and a single film (corresponding to the inner panel), and provides high flip-flop properties. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides the following embodiments. [1] A first base coating film formed on the object to be coated with a first water-based base coating composition, The first base coating film is formed with a second base coating film made of an aqueous second base coating composition, The second base coating film comprises a clear coating film formed with a clear coating composition, The aqueous first base paint composition comprises a luminous pigment and two or more coloring pigments. The solid content concentration NV1 is 20-35% by mass. PWC of the aforementioned luminous pigment G1 The percentage is 1-25%, PWC of the aforementioned colored pigment C1 The percentages are 0.1-5.0%. The aqueous second base coating composition comprises a luminous pigment and two or more color pigments with the same color index name as the color pigments contained in the aqueous first base coating composition, The solid content concentration NV2 is 7-30% by mass. PWC of the aforementioned luminous pigment G2 The percentage is 5-35%. PWC of the aforementioned colored pigment C2 The percentages are 0.5-20.0%. The ratio (T1 / T2) of the thickness T1 of the first base coating to the thickness T2 of the second base coating is 1.5 / 1 to 5 / 1. The ratio (NV1 / NV2) of the solid content concentration NV1 to the solid content concentration NV2 is 1.3 / 1 to 3 / 1, the PWC of the bright pigment G1 and the PWC of the bright pigment G2 The ratio (PWC G1 / PWC G2 ) is 1 / 10 to 1 / 1, the PWC of the colored pigment C1 and the PWC of the colored pigment C2 The ratio (PWC C1 / PWC C2 ) is 1 / 5 to 1 / 1, a multilayer coating film. [2] For the light I irradiated at an angle of 45 degrees with respect to the surface of the coating film 45 Based on the spectral reflectance received at an angle of 25 degrees with respect to the specularly reflected light, the lightness L * 25 value, and the lightness L * 25 value and a * 25 value and b * 25 value, the color difference E * 25 value, in The value ΔL * 25 obtained by subtracting the lightness Lbc * 25 of the first base coating film from the lightness Lm * 25 of the multilayer coating film is 0 to 10, The difference ΔE * 25 between the color difference Em * 25 of the multilayer coating film and the color difference Ebc * 25 of the first base coating film is 10 or less, For the light I irradiated at an angle of 45 degrees with respect to the surface of the coating film 45 Based on the spectral reflectance received at an angle of 45 degrees with respect to the specularly reflected light, the lightness L * 45 value, and the lightness L * 45 value and a * 45 value and b * 45 value, the color difference E * 45 value, in The value ΔL * 45 obtained by subtracting the lightness Lbc * 45 of the first base coating film from the lightness Lm * 45 of the multilayer coating film is -10 to 0, The color difference Em of the multi-layer coating film * 45 value and the color difference Ebc of the first base coating film * Difference from 45 ΔE * The multilayer coating described in [1] above, wherein 45 is 10 or less. [3] The multilayer coating film according to [1] or [2] above, wherein the difference between the average particle size of the lustrous pigment contained in the aqueous first base coating composition and the average particle size of the lustrous pigment contained in the aqueous second base coating composition is 5 μm or less. [Effects of the Invention]

[0008] According to this disclosure, a multilayer coating film is provided that has a small difference in hue from the first base coating film and high flip-flop properties. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic perspective view showing the coating method for test plates used to evaluate dust streaks in the examples. [Modes for carrying out the invention]

[0010] To minimize the hue difference between the first base coating and the multi-layer coating comprising the first base coating, the second base coating, and the clear coating, two or more color pigments having the same color index name are incorporated into both the water-based first base coating composition and the water-based second base coating composition. As a result, when the same first base coating composition as the outer coating is used to form the inner panel, the hue difference between the outer panel and the inner panel is reduced.

[0011] Exterior panels are typically the parts of a car that are visible from the outside. Specifically, these include the outer doors, roof, front fenders, outer side panels, and hood. Interior panels are typically the parts of a car that are not visible from the outside. Specifically, these include the inner doors, pillars, and floor.

[0012] As described above, the difference in hue manifests as streaky paint irregularities (hereinafter also referred to as dust streaks) formed on the inner panels of the vehicle body. In the painting process of an automobile body, first, the first base paint composition is applied to the inner panels. Next, the first base paint composition and the second base paint composition are applied to the outer panels. The second base paint composition is applied when the doors are not completely closed. As a result, the second base paint composition is scattered onto the pillars, forming dust streaks. Because the difference in hue between the first base coating and the multi-layer coating in this disclosure is small, the occurrence of dust streaks is suppressed, resulting in a finish that does not look out of place.

[0013] The Colour Index is a database that organizes and classifies industrially manufactured and sold synthetic dyes and pigments based on their species, hue, and chemical structure. The Colour Index includes Colour Index Generic Names, which are classified by species and hue for each chemical structure, and Colour Index Constitution Numbers, which are classified by chemical structure. In this disclosure, the Colour Index Names are used.

[0014] Color indexes are published by the Society of Dyers and Colourists (SDC) and the American Association of Textile Chemists and Colourists (AATCC). Many manufacturers also list the color index name alongside the product name on their products or catalogs. From this information, it is possible to obtain the color index name of a pigment.

[0015] According to the "Colour Index™ Online" (https: / / colour-index.com / colour-index-generic-name) published by SDC and AATCC, the color index names distinguish multiple pigments with the same chemical structure but different crystal forms by adding a number after a colon (:). For example, copper phthalocyanine blue has multiple color index names: "PB 15:1," "PB 15:3," and "PB 15:6." These copper phthalocyanine blues have α-type, β-type, and ε-type crystal forms, respectively.

[0016] In this disclosure, "color pigments having the same color index name" means color pigments that have the same chemical structure (the same symbol before the colon), regardless of differences in crystal form (i.e., even if the numbers after the colon are different). In the case of copper phthalocyanine blue above, even if the numbers after the colon are different, multiple pigments whose symbol before the colon is "PB 15" are considered "color pigments having the same color index name". Hereinafter, "color pigments having the same color index name" may be referred to as "similar colors" for convenience.

[0017] To achieve high flip-flop properties (FF properties) while minimizing the above-mentioned hue differences, the ratio of the thickness of each coating film is further controlled, as well as the ratio of PWC (polycrystalline crystalline solids) of the coloring pigment and luminescence pigment in each paint composition, and the ratio of solid content mass.

[0018] Flip-flop property refers to the property where the brightness of a coating surface changes depending on the viewing angle. In this disclosure, light I irradiated from a 45-degree angle onto the surface of a multilayer coating film. 45 L is calculated from the spectral reflectance when light is received at an angle of 15 or 75 degrees relative to specularly reflected light. * a * b * Color system (CIE1976L) * a * b * Lightness L in the color space * (L * 15,L *75) ratio (L * 15 / L * 75) is used as an indicator of FF properties. Ratio (L * 15 / L * The larger the value of 75), the better the FF performance.

[0019] • Ratio of coating film thickness The ratio (T1 / T2) of the thickness T1 of the first base coating to the thickness T2 of the second base coating is 1.5 / 1 to 5 / 1. That is, the first base coating is thicker than the second base coating. When T1 / T2 is within this range, the orientation of the luminous pigment is enhanced, improving the flip-flop properties. T1 / T2 may be between 1.5 / 1 and 3 / 1.

[0020] • PWC ratio of coloring pigments PWC C1 and the coloring pigments contained in the water-based second base paint composition (hereinafter sometimes collectively referred to as the second coloring pigments) in the PWC C2 Ratio to (PWC) C1 / PWC C2 ) is 1 / 5 to 1 / 1. PWC C1 / PWC C2 Within this range, the difference in hue between the first base coating and the multi-layer coating becomes smaller. In other words, the occurrence of dust streaks is suppressed. PWC C1 / PWC C2 It may be between 1 / 3 and 1 / 1.1, or between 1 / 2.5 and 1 / 1.25.

[0021] • PWC ratio of luminous pigments PWC G1 and the luminous pigment contained in the water-based second base paint composition (hereinafter sometimes referred to as the second luminous pigment) in PWC G2 Ratio to (PWC) G1 / PWC G2 ) is 1 / 10 to 1 / 1. PWC G1 / PWC G2Within this range, the orientation of the luminous pigment increases, improving the flip-flop properties. G1 / PWC G2 It may be between 1 / 5 and 1 / 1.1, or between 1 / 3 and 1 / 1.25.

[0022] • Ratio of solid content The ratio (NV1 / NV2) of the solid content concentration NV1 of the first aqueous base coating composition to the solid content concentration NV2 of the second aqueous base coating composition is 1.3 / 1 to 3 / 1. That is, the solid content of the first aqueous base coating composition is greater than that of the second aqueous base coating composition. When NV1 / NV2 is within this range, the orientation of the luminous pigment is enhanced, improving the flip-flop properties. NV1 / NV2 may be between 1.3 / 1 and 2.5 / 1.

[0023] • Brightness difference and color difference between the first base coating and the multi-layer coating. If both the difference in brightness and the difference in color between the first base coating and the multi-layer coating are within a predetermined range, then the difference in hue between the two can be said to be small.

[0024] Brightness and color difference are measured using light I, which is shone onto the surface of the coating film at a 45-degree angle. 45 L is calculated from the spectral reflectance of light received at a predetermined angle relative to specularly reflected light. * a * b * Color system (CIE1976L) * a * b * Lightness L in the color space * and color difference E * Chromatic difference E * The value is brightness L * Value and a * Value and b * The value is calculated using the following formula. Color difference E * =√{(L * ) 2 +(a * ) 2 +(b * ) 2}

[0025] The light I irradiated on the surface of the multilayer coating 45 Lm based on the spectral reflectance received at an angle of 25 degrees with respect to the specular reflection light * From the 25 value, the light I irradiated on the surface of the first base coating 45 Lbc based on the spectral reflectance received at an angle of 25 degrees with respect to the specular reflection light * The value ΔL obtained by subtracting the 25 value * 25 is from 0 to 10. ΔL * 25 may be from 0 to 6.

[0026] The light I irradiated on the surface of the multilayer coating 45 Lm based on the spectral reflectance received at an angle of 45 degrees with respect to the specular reflection light * From the 45 value, the light I irradiated on the surface of the first base coating 45 Lbc based on the spectral reflectance received at an angle of 45 degrees with respect to the specular reflection light * The value ΔL obtained by subtracting the 45 value * 45 is from -10 to 0. ΔL * 45 may be from -6 to 0.

[0027] Lm * The color difference Em of the multilayer coating calculated by the above formula from the 25 value * The 25 value and Lbc * The color difference Ebc of the first base coating calculated by the above formula from the 25 value * The difference ΔE between the 25 value * 25 is 10.0 or less. ΔE * 25 may be 6.0 or less.

[0028] Lm * The color difference Em of the multilayer coating calculated by the above formula from the 45 value * The 45 value and Lbc * The color difference Ebc of the first base coating calculated by the above formula from the 45 value * The difference ΔE between the 45 value * 45 is 10.0 or less. ΔE * 45 may be 6.0 or less.

[0029] ΔL * 25 is from 0 to 10, and ΔL *The fact that 45 is between -10 and 0 means that the difference in brightness is very small. ΔE * 25 is less than or equal to 10, and ΔE * A value of 45 being 10 or less means that the difference in color is very small. Because the difference in brightness and color between the multi-layer coating and the first base coating is small, the difference in hue is perceived as small.

[0030] Lightness L * and color difference E * This can be obtained using a multi-angle colorimeter (for example, the "BYK-mac i" product from BYK). Brightness L * and color difference E * This is the average value of five different samples or any five points from the same sample.

[0031] Brightness L of the first water-based coating film * and color difference E * This measurement is performed using a coating film formed on the same substrate on which the multi-layer coating film is formed, under the same conditions as when the first base coating film and the clear coating film constituting the multi-layer coating film are formed.

[0032] Brightness L of the water-based first base coating and multi-layer coating * and color difference E * This corresponds to the brightness and color difference of the inner and outer panels of the vehicle body, respectively. The brightness and color difference of the inner panels (typically pillars) and outer panels (typically door outers) of the vehicle body correspond to the brightness L of the water-based first base coating and the multi-layer coating. * and color difference E * It is acceptable to consider it as such.

[0033] In terms of brightness and color difference between the inner and outer panels of the vehicle body, ΔL * 25 is 0-10, ΔL * 45 is -10 to 0, ΔE * 25 is 10.0 or less, and ΔE *If 45 is 10.0 or less, the inner and outer panels are likely to be formed of the aqueous first base coating composition and the aqueous second base coating composition used in this disclosure. The lightness of the inner and outer panels of the vehicle body is the average value of any five points on the inner panel and any five points on the outer panel of the same vehicle body.

[0034] In this specification, the glass transition temperature (Tg) of a resin can be calculated from the type and amount of raw material monomers used in the production of the resin in question. Tg may be measured by a differential scanning calorimeter (DSC).

[0035] The number-average molecular weight (Mn) and weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC) using a polystyrene standard sample after removing moisture by vacuum drying or other methods.

[0036] The hydroxyl value (OHV) and acid value (AV) are determined based on the solid content mass. The hydroxyl value (OHV) and acid value (AV) can be measured by known methods described in JIS K 0070:1992. The hydroxyl value (OHV) and acid value (AV) may also be calculated from the amount of unsaturated monomers in the raw material monomers of the resin in question.

[0037] Solids are also called non-volatile components. In specific cases, the solids of a paint composition are all the components of the paint composition excluding the solvent. The solids concentration is determined by dividing the total mass of the solids (excluding the solvent) by the total mass of the paint composition. The solids concentration can also be calculated from the residue when the paint composition is heated to 140°C, in accordance with JIS K 5601-1-2, the method for measuring residual residue after heating. Specifically, the solids of an aqueous paint composition are the aqueous resin, hardener, glossy pigment, coloring pigment, and other solid components added as needed, as described later.

[0038] The resin solids are the resin components among the solids mentioned above. Specifically, the solids of the aqueous paint composition are the aqueous resin, curing agent, and other resins described later.

[0039] The PWC (mass%) of a pigment (e.g., a luminous pigment) is calculated by dividing the mass of the pigment in question by the total mass of all pigments and resin solids contained in the paint composition (see formula below). The pigment in question may include multiple types. For example, the PWC of the first coloring pigment... C1 This is calculated from the total mass of multiple coloring pigments contained in the aqueous first base paint composition. TIFF2026092509000002.tif15117

[0040] The thickness of the coating can be measured using an electromagnetic film thickness gauge (for example, SANKO's SDM-miniR). The coating thickness is the average value of the coating thickness at any five points.

[0041] The average particle size is the 50% average particle size (D50) in the volume-based particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. An example of a particle size distribution analyzer is the UPA-150 (Nikkiso Co., Ltd., Microtrac particle size distribution analyzer).

[0042] Water-based resins are generally classified into water-soluble and water-dispersible types. Water-dispersible resins are further divided into colloidal dispersion type and emulsion type. Colloidal dispersion type (hereinafter simply referred to as dispersion type) water-based resins are typically obtained by partially dissolving a resin synthesized in an organic solvent (solution-polymerized resin) in water using a neutralizing agent. Emulsion type water-based resins are typically produced by emulsion polymerization or by mechanical forced emulsification.

[0043] In the case of water-based acrylic resins, those with an Mw (mold value) exceeding 100,000 can be considered emulsion type, while those with an Mw of 100,000 or less can be considered colloidal dispersion type. Measuring Mw becomes difficult when it exceeds 1,000,000. Water-based acrylic resins for which Mw cannot be measured can be considered emulsion type. Water-based resins include water-soluble resins, dispersion-type resins, and emulsion-type resins.

[0044] [Multi-layer coating] The multi-layer coating comprises a first base coating formed on the object to be coated with a first water-based base coating composition, a second base coating formed on the first base coating with a second water-based base coating composition, and a clear coating formed on the second base coating with a clear coating composition.

[0045] Brightness Lm of multi-layer coating * 25 is, for example, between 35 and 110. (Brightness Lm) * 25 may be 40 or greater, 45 or greater, or 55 or greater. Brightness Lm * 25 may be less than or equal to 100, less than or equal to 95, or less than or equal to 90.

[0046] Brightness Lm of multi-layer coating * 45 is, for example, between 10 and 60. (Brightness Lm) * 45 may be 15 or greater, 20 or greater, 25 or greater, or 30 or greater. Brightness Lm * 45 may be 50 or less, 45 or less, or 40 or less.

[0047] • Water-based first base coating The dry thickness of the first water-based coating is, for example, 5 to 15 μm. The dry thickness of the second water-based coating is, for example, 2 to 8 μm. The dry thickness of the clear coating is, for example, 10 to 60 μm.

[0048] Brightness Lbc of the first water-based coating film * 25 is, for example, between 30 and 100. Brightness Lbc * 25 may be 40 or higher, 45 or higher, or 50 or higher. Brightness Lbc * 25 may be 90 or less, 80 or less, or 65 or less.

[0049] Brightness Lbc of the first water-based coating film * 45 is, for example, between 10 and 60. Brightness Lbc *45 may be 20 or greater, and may be 30 or greater. Brightness Lbc * 45 may be 55 or less, 50 or less, or 40 or less.

[0050] • Water-based first base paint composition The first water-based paint composition includes, for example, a water-based resin, a curing agent, a glossy pigment, and a coloring pigment.

[0051] The solid content concentration NV1 of the aqueous first base coating composition is 20 to 35% by mass. When the solid content concentration NV1 is 20% by mass or more, the coating efficiency is improved. When the solid content concentration NV1 is 35% by mass or less, the appearance is improved. The solid content concentration NV1 may be 25% by mass or more. The solid content concentration NV1 may be 30% by mass or less.

[0052] (Water-based resin) Examples of water-based resins include water-based acrylic resins, water-based polyester resins, polyether polyols, and water-based polyurethane resins. These can be used individually or in combination of two or more types.

[0053] The ratio of aqueous resin to the mass of resin solids in the first aqueous base coating composition is, for example, 50 to 90% by mass. This makes it easier to achieve both storage stability and curing properties in the first aqueous base coating composition. The above ratio of aqueous resin may be 60% by mass or more. The above ratio of aqueous resin may be 85% by mass or less.

[0054] • Water-based acrylic resin The aqueous acrylic resin may be an emulsion-type acrylic resin. The emulsion-type acrylic resin (acrylic resin emulsion) has hydroxyl groups and carboxyl groups. The hydroxyl groups of the acrylic resin emulsion react with the curing agent to form a crosslinked structure.

[0055] The Mw of the acrylic resin emulsion is 100,000 or more. The Mw of the acrylic resin emulsion may be 100,000 or more, and may be 200,000 or more. There is no upper limit to the Mw of the acrylic resin emulsion.

[0056] The OHV of the acrylic resin emulsion is, for example, 10 mg KOH / g or more and 100 mg KOH / g or less. This increases the crosslinking density and further improves chipping resistance. The OHV of the acrylic resin emulsion may be 20 mg KOH / g or more, or 30 mg KOH / g or more. The OHV of the acrylic resin emulsion may be 90 mg KOH / g or less, or 80 mg KOH / g or less.

[0057] The acid value (AV) of the acrylic resin emulsion is, for example, 5 mg KOH / g or more and 50 mg KOH / g or less. The AV of the acrylic resin emulsion may be 10 mg KOH / g or more, and may be 15 mg KOH / g or more. The AV of the acrylic resin emulsion may be 40 mg KOH / g or less, and may be 30 mg KOH / g or less.

[0058] The Tg of the acrylic resin emulsion is, for example, between -15°C and 60°C. This makes it easy for the Tg of the first base coating film to be above 60°C. The Tg of the acrylic resin emulsion may be above -10°C or above, or above 25°C. The Tg of the acrylic resin emulsion may be below 55°C or below, or below 50°C.

[0059] The average particle size of the acrylic resin emulsion is, for example, 20 nm to 200 nm. The average particle size of the acrylic resin emulsion may be 180 nm or less, 160 nm or less, 150 nm or less, or 100 nm or less. The average particle size of the acrylic resin emulsion may be 25 nm or more, or 30 nm or more.

[0060] The solid content of the acrylic resin emulsion is 8 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the resin solid content of the aqueous first base coating composition. The above content of the acrylic resin emulsion may be 10 parts by mass or more. The above content of the acrylic resin emulsion may be 15 parts by mass or less, and may be 12 parts by mass or less.

[0061] Acrylic resin emulsions are used individually or in combination of two or more types. When multiple types of aqueous acrylic resins are included, the OHV, AV, and Tg of the aqueous acrylic resins are average values ​​calculated based on the OHV, AV, Tg, and mass ratio of each aqueous acrylic resin.

[0062] Aqueous acrylic resins can be obtained, for example, by copolymerizing monomers containing α,β-ethylenically unsaturated monomers having hydroxyl groups and α,β-ethylenically unsaturated monomers having carboxyl groups.

[0063] Examples of α,β-ethylenically unsaturated monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, allyl alcohol, methacrylic alcohol, and adducts of hydroxyethyl (meth)acrylate with ε-caprolactone. Alternatively, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, or adducts of hydroxyethyl (meth)acrylate with ε-caprolactone may also be used.

[0064] "(Meth)acrylic acid" includes both acrylic acid and methacrylic acid.

[0065] Examples of α,β-ethylenically unsaturated monomers having a carboxyl group include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, maleic acid, fumaric acid, and itaconic acid. Acrylic acid or methacrylic acid may also be used.

[0066] Other α,β-ethylenically unsaturated monomers may be used as copolymerization components. Examples of other α,β-ethylenically unsaturated monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth)acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate; and polymerizable amide compounds such as (meth)acrylamide, N-methylol(meth)acrylamide, and N-butoxymethyl(meth)acrylamide.

[0067] Other α,β-ethylenically unsaturated monomers may be crosslinkable monomers. Crosslinkable monomers have two or more radically polymerizable ethylenically unsaturated groups in their molecule. Examples of crosslinkable monomers include divinylbenzene, allyl (meth)acrylate, and ethylene glycol di(meth)acrylate.

[0068] Acrylic resin emulsions are typically synthesized by emulsion polymerization. The emulsion polymerization method is not particularly limited. For example, an emulsifier is dissolved in an aqueous medium containing water, or optionally an organic solvent such as alcohol or ether (e.g., dipropylene glycol methyl ether, propylene glycol methyl ether, etc.), and the raw material monomers and polymerization initiators are added dropwise under heating and stirring. The raw material monomers may be emulsified beforehand with an emulsifier.

[0069] Examples of polymerization initiators include azo-based oily compounds such as azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), and 2,2'-azobis(2,4-dimethylvaleronitrile); aqueous compounds such as anionic 4,4'-azobis(4-cyanovaleric acid), 2,2-azobis(N-(2-carboxyethyl)-2-methylpropionamidine), and cationic 2,2'-azobis(2-methylpropionamidine); redox-based oily peroxides such as benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, and t-butyl perbenzoate; and aqueous peroxides such as potassium persulfate and ammonium persulfate.

[0070] The emulsifier is not particularly limited. Examples of emulsifiers include reactive emulsifiers. Examples of reactive emulsifiers include Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminor JS-2 (manufactured by Sanyo Chemical Industries, Ltd.), Adekarya Soap NE-20 (manufactured by ADEKA Corporation), Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and Latemul PD-104 (manufactured by Kao Corporation). To adjust the molecular weight, chain transfer agents such as mercaptans (e.g., lauryl mercaptan) and α-methylstyrene dimers may be used.

[0071] The reaction temperature is determined according to the polymerization initiator. For example, when using an azo initiator or peroxide, the reaction temperature is 60-90°C. When using a redox initiator, the reaction temperature is 30-70°C. The reaction time is 1-8 hours. The amount of polymerization initiator per 100 parts by mass of the monomer mixture is 0.1-5% by mass. Emulsion polymerization can be carried out in multiple steps, for example, in two steps. In two-step polymerization, a portion of the raw material monomers is emulsion-polymerized, and then the remaining raw material monomers are polymerized.

[0072] Acrylic resin emulsions may be neutralized with basic compounds for storage stability. Acrylic resin emulsions have a pH of 5-10. Neutralization is performed before or after emulsion polymerization.

[0073] The basic compound is not particularly limited and, for example, at least one selected from the group consisting of ammonia and amine compounds. Examples of amine compounds include dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, isopropylamine, triallylamine, triethylenediamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, aminoethanolamine, N-methyl-N,N-diethanolamine, iminobispropylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, methylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, allylmorpholine, N-methylmorpholine, and N-ethylmorpholine. These can be used individually or in combination of two or more.

[0074] Acrylic resin emulsions can also be obtained by solution polymerization and neutralization. Solution polymerization is carried out by known methods.

[0075] Water-soluble acrylic resins can be prepared, for example, by solution polymerization of the above-mentioned α,β-ethylenically unsaturated monomers and then making them water-soluble using a basic compound.

[0076] • Water-based polyester resin The aqueous polyester resin may be of the dispersion type. The aqueous polyester resin may have hydroxyl groups and carboxyl groups.

[0077] The OHV of the aqueous polyester resin is, for example, 50 to 150 mgKOH / g. The above OHV may be 70 mgKOH / g or more. The above OHV may be 120 mgKOH / g or less, and may be 100 mgKOH / g or less.

[0078] The AV of the aqueous polyester resin is, for example, 20 to 80 mg KOH / g. The above AV may be 25 mg KOH / g or more. The above AV may be 50 mg KOH / g or less, and 40 mg KOH / g or less.

[0079] The manganese (Mn) content of water-based polyester resin is, for example, 500 to 20,000. If the Mn content of the water-based polyester resin is 500 or higher, storage stability is improved. If the Mn content of the water-based polyester resin is 20,000 or lower, viscosity increase is suppressed, and painting workability is improved. The Mn content of the water-based polyester resin may be 1,500 or higher. The Mn content of the water-based polyester resin may be 10,000 or lower.

[0080] The Tg of a water-based polyester resin is, for example, -20 to 80°C. If the Tg of the water-based polyester resin is -20°C or higher, the hardness of the resulting coating film will be higher. If the Tg of the water-based polyester resin is 80°C or lower, the ability to conceal the substrate (opacity) will be improved. The Tg of the water-based polyester resin may be 0°C or higher. The Tg of the water-based polyester resin may be 60°C or lower.

[0081] Aqueous polyester resins are obtained by neutralizing polyester resin with a basic compound. Polyester resins are produced, for example, by the condensation of a polyhydric alcohol component and a polybasic acid component.

[0082] Examples of polyhydric alcohol components include hydroxycarboxylic acid components such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, neopentyl glycol ester of hydroxypivalate, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethylpentanediol. These can be used individually or in combination of two or more.

[0083] Examples of polybasic acid components include aromatic polycarboxylic acids and acid anhydrides such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrachlorophthalic anhydride, and pyromellitic anhydride; alicyclic polycarboxylic acids and anhydrides such as hexahydrophthalic anhydride, tetrahydrophthalic anhydride, and 1,4- and 1,3-cyclohexanedicarboxylic acid; and aliphatic polycarboxylic acids and anhydrides such as maleic anhydride, fumaric acid, succinic anhydride, adipic acid, and sebacic acid. These can be used individually or in combination of two or more.

[0084] If necessary, monobasic acids such as benzoic acid and t-butylbenzoic acid may be used in combination.

[0085] Monohydric alcohols, monoepoxide compounds such as Cardura E (trade name: Oxalis Chemicals), and lactones such as β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, ε-caprolactone, and γ-caprolactone may be used in combination as reaction components. These may be used individually or in combination of two or more.

[0086] Furthermore, fatty acids such as castor oil, dehydrated castor oil, and one or more of these fatty acids may be added to the reaction system.

[0087] The polyester resin may be grafted with aqueous acrylic resin and / or vinyl resin, or may be reacted with a polyisocyanate compound.

[0088] • Polyether polyol Polyether polyols are resins other than those mentioned above, and have two or more hydroxyl groups in one molecule. Polyether polyols may have an average of three or more hydroxyl groups per molecule. This can further increase the strength of the coating film. Polyether polyols may be in emulsion form and may be water-soluble.

[0089] The manganese (Mn) of polyether polyols is, for example, 300 to 2000. When the Mn of polyether polyols is 300 or higher, the coating performance improves. When the Mn of polyether polyols is 2000 or lower, the appearance of the coating improves. The Mn of polyether polyols may be 400 or higher, or 500 or higher. The Mn of polyether polyols may be 1800 or lower, or 1500 or lower.

[0090] Polyether polyols can be obtained, for example, by addition polymerization of an alkylene oxide such as ethylene oxide, propylene oxide, or tetrahydrofuran to a polyhydric alcohol. Polyether polyols may be polyether diols having two hydroxyl groups in one molecule.

[0091] Examples of polyetherdiols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and polyoctamethylene ether glycol.

[0092] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and their block forms. Polyether polyols can be obtained, for example, by adding ethylene oxide and / or propylene oxide to a polyhydric alcohol compound.

[0093] Examples of commercially available polyether polyols include the Sannix series manufactured by Sanyo Chemical Industries, Ltd. Specifically, these include Sannix GP-250, Sannix GP-400, Sannix PP-200, and Sannix GP-600.

[0094] • Water-based polyurethane resin The aqueous polyurethane resin may be water-soluble and water-dispersible. The aqueous polyurethane resin may be of the dispersion type. The aqueous polyurethane resin may be used alone or in combination of two or more types.

[0095] Water-based polyurethane resins fuse with themselves and other components to strengthen the coating film and enhance its shock absorption. Water-based polyurethane resins also improve the chipping resistance and adhesion of multi-layer coatings.

[0096] The OHV of the water-based polyurethane resin is, for example, 0 mgKOH / g or more and 50 mgKOH / g or less. This improves the strength of the coating film. The OHV of the water-based polyurethane resin may be 5 mgKOH / g or more, and may be 10 mgKOH / g or more. The OHV of the water-based polyurethane resin may be 40 mgKOH / g or less, and may be 30 mgKOH / g or less.

[0097] The AV of the aqueous polyurethane resin is, for example, 0 mg KOH / g or more and 20 mg KOH / g or less. This improves water resistance. The OHV of the aqueous polyurethane resin may be 5 mg KOH / g or more and may be 10 mg KOH / g or more. The AV of the aqueous polyurethane resin may be 17 mg KOH / g or less and may be 15 mg KOH / g or less.

[0098] The Tg of the aqueous polyurethane resin is, for example, -20°C or lower. A Tg of -20°C or lower further improves chipping resistance. The Tg of the aqueous polyurethane resin may be -30°C or lower, or -50°C or lower. There is no particular lower limit to the Tg of the aqueous polyurethane resin. The Tg of the aqueous polyurethane resin may be, for example, -90°C or higher.

[0099] The weight-average molecular weight (Mw) of the water-based polyurethane resin is, for example, 20,000 or more. This increases the strength of the coating film and improves adhesion. The Mw of the water-based polyurethane resin may be 150,000 or more, or 250,000 or more. There is no particular upper limit to the Mw of the water-based polyurethane resin. The Mw of the water-based polyurethane resin may be, for example, 1,000,000 or less.

[0100] Aqueous polyurethane resins can be obtained, for example, by forcibly emulsifying the polyurethane resin using a surfactant, or by neutralizing the polyurethane resin with a base or acid.

[0101] Polyurethane resins can be obtained, for example, by the reaction of polyols, compounds having active hydrogen groups and hydrophilic groups in their molecules, polyisocyanate compounds described later, and, if necessary, chain extenders and polymerization inhibitors. Chain extenders and polymerization inhibitors may be used as needed.

[0102] Examples of polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyacrylate polyols, and polyhydric alcohols. These can be used individually or in combination of two or more. In particular, the polyol may be a polyether polyol.

[0103] Examples of compounds having an active hydrogen group and a hydrophilic group within the molecule include compounds containing an active hydrogen group and an anionic group, a cationic group, or a nonionic hydrophilic group. Anionic groups include anionic groups and anion-forming groups. Anion-forming groups are groups that can react with a base to form an anionic group, specifically by neutralization with a base before, during, or after the urethane reaction to form an anionic group.

[0104] Examples of compounds containing active hydrogen and an anionic group are described in the specifications of Japanese Patent Publication No. 42-24192 and Japanese Patent Publication No. 55-41607, specifically α,α-dimethylolpropionic acid and α,α-dimethylolbutyric acid. Examples of compounds having active hydrogen and a cationic group are described in the specifications of Japanese Patent Publication No. 43-9076. Examples of compounds having active hydrogen and a nonionic hydrophilic group are described in Japanese Patent Publication No. 48-41718, specifically polyethylene glycol and alkyl alcohol alkylene oxide adducts.

[0105] (Hardening agent) Examples of curing agents include blocked isocyanate compounds, melamine resins, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and metal ions. These can be used individually or in combination of two or more. The curing agent may be a melamine resin, a blocked isocyanate compound, a carbodiimide compound, or a melamine resin.

[0106] The ratio of the crosslinking agent to the resin solids mass of the first aqueous base coating composition is, for example, 10 to 50% by mass. The above ratio of the crosslinking agent may be 15% by mass or more. The above ratio of the aqueous resin may be 40% by mass or less.

[0107] Melamine resin Melamine resin has three nitrogen atoms (N) around a triazine ring (triazine core). 1 ~N 3 Six substituents R 1 ~R 6 A structure formed by the bonding of (-N 1 (R 1 )(R 2 ), -N 2 (R 3 )(R 4 ), -N 3 (R 5 )(R 6 )) includes.

[0108] Melamine resin is, for example, the following general formula (1):

[0109] [ka] (In the formula, substituent R 1 ~R 6 Each of these independently represents a hydrogen atom, an alkyl ether group, a methylol group, or a bond to another triazine ring. It is represented as follows.

[0110] Alkyl ether (-CH2-OR 7 ) constitutes an alkyl group (R 7 The number of carbon atoms in ) may be 1 to 8, or 1 to 4. 7 It may be linear or branched. 7 This may be a methyl group, an ethyl group, a propyl group, or a butyl group.

[0111] Melamine resin may be composed of a multinuclear body in which multiple triazine rings are bonded together, or it may be a mononuclear body consisting of a single triazine ring.

[0112] Examples of melamine resins include -N(-CH2-OR 7 Methylol group having (-CH2OH); -N(-CH2-OR 7 Imino group having )(H);-N(-CH2-OR 7 )(-CH2OH) and -N(-CH2-OR 7 A methylol / imino group having (H), substituent R 1 ~R 6 One example is the fully alkyl type, which has only alkyl ether groups.

[0113] The Mw of the melamine resin may be between 400 and 2000. This keeps the viscosity of the first water-based paint composition low, improving the appearance of the coating film. The Mw of the melamine resin may be 1500 or less, or 1300 or less. The Mw of the melamine resin may be 500 or more, or 600 or more.

[0114] · Blocked isocyanate compounds Blocked isocyanate compounds can be prepared by blocking polyisocyanate compounds with a blocking agent.

[0115] Polyisocyanate compounds have at least two isocyanate groups in one molecule. Examples of polyisocyanate compounds include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having aromatic rings not bonded to isocyanate groups in the molecule (aroliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specifically, examples include aromatic polyisocyanates such as tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; and polymers of these, such as biuret type, nurate type, and adduct type. These can be used individually or in combination of two or more.

[0116] Examples of blocking agents include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylcarbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycolphenol; polyester-type terminal polyols obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam. As a blocking agent, active hydrogen compounds such as methyl diketones, methyl ketoesters, and methyl diester compounds, such as alkyl esters including acetylacetone, ethyl acetoate, and diethyl malonate, may be used. Alternatively, blocked isocyanates using pyrazole compounds or imidazole compounds as blocking agents may be used.

[0117] It is preferable that the blocking rate of the blocked isocyanate compound is 100%. This enhances the storage stability of the first base coating composition.

[0118] • Carbodiimide compounds Carbodiimide compounds have at least two carbodiimide groups (-N=C=N-) in their molecule.

[0119] Examples of carbodiimide compounds include poly(4,4′-diphenylmethanecarbodiimide), poly(3,3′-dimethyl-4,4′-biphenylmethanecarbodiimide), poly(tolylcarbodiimide), poly(p-phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly(naphthylenecarbodiimide), poly(1,6-hexamethylenecarbodiimide), poly(4,4′-methylenebiscyclohexylcarbodiimide), poly(1,4-tetramethylenecarbodiimide), poly(1,3-cyclohexylenecarbodiimide), poly(1, Examples include poly(4-cyclohexylenecarbodiimide), poly(1,3-diisopropylphenylenecarbodiimide), poly(1-methyl-3,5-diisopropylphenylenecarbodiimide), poly(1,3,5-triethylphenylenecarbodiimide), and poly(triisopropylphenylenecarbodiimide).

[0120] (First-grade luminous pigment) The first luminous pigment is not particularly limited. The first luminous pigment is, for example, at least one selected from the group consisting of aluminum flake pigments, metal oxide coated alumina flake pigments, metal oxide coated silica flake pigments, graphite pigments, interference mica pigments, colored mica pigments, metallic titanium flake pigments, stainless steel flake pigments, plate-like iron oxide pigments, metal-plated glass flake pigments, metal oxide coated glass flake pigments, hologram pigments, and flake-like pigments made of cholesteric liquid crystal polymers.

[0121] PWC of the first luminous pigment G1 The range is 1-25%. G1 If it is 1% or more, sufficient concealment can be achieved. G1 If the amount is 25% or less, good coating film properties can be obtained. G1 It may be 2.0% or more, and may be 5.0% or more. G1 It may be 20.0% or less, 15.0% or less, or 10.0% or less.

[0122] The average particle size of the first luminous pigment is not particularly limited. The average particle size of the first luminous pigment may be, for example, 8 to 25 μm, as this easily improves the luminosity.

[0123] (First coloring pigment) The first coloring pigment contains two or more coloring pigments of the same color as the second coloring pigment. That is, the first water-based base paint composition contains at least one coloring pigment X' of the same color as coloring pigment X contained in the second water-based base paint composition, and one coloring pigment Y' of the same color as coloring pigment Y (which is not of the same color as coloring pigment X) contained in the second water-based base paint composition. This reduces the difference in hue between the multi-layer coating (corresponding to the outer panel) and the first base coating (corresponding to the inner panel). Three or more coloring pigments of the same color may be included.

[0124] The first coloring pigment is not particularly limited. Examples of the first coloring pigment include organic pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, phthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, benzimidazolon pigments, diketopyrrolopyrrole pigments, and metal complex pigments; and inorganic pigments such as yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. Two or more of these are used in combination.

[0125] PWC (Personal Water Container) C1 The range is 0.1-5.0%. C1 If the concentration is 0.1% or higher, the hue of the first base coating becomes easier to adjust, and the color difference with the multi-layer coating tends to be smaller. PWC C1 If the amount is 5.0% or less, the flip-flop properties of the first base coating may improve. C1 It may be 0.3% or more, and may be 0.5% or more. C1 It may be 4.0% or less, or 3.0% or less.

[0126] (Extender pigments) The first water-based paint composition may contain an extender pigment. Examples of extender pigments include talc, calcium carbonate, precipitated barium sulfate, and silica. The PWC of the extender pigment is not particularly limited.

[0127] (solvent) The first aqueous base coating composition contains water as a solvent. The first aqueous base coating composition may also contain an organic solvent along with the aqueous solvent. In the first aqueous base coating composition, the proportion of water in the solvent is, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more.

[0128] Examples of organic solvents include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, cellosolve acetate, and butyl cellosolve, and alcohols. Among these, hydrophilic organic solvents, such as alcohols, are also acceptable.

[0129] Examples of hydrophilic organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, 2-butyl alcohol, 3-butyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, hexylene glycol, 2,5-hexanediol, and dipropylene glycol.

[0130] (others) The aqueous first base coating composition may further contain additives. Examples of additives include anti-settlement agents, curing catalysts, UV absorbers, antioxidants, leveling agents, surface modifiers such as silicones and organic polymers, anti-sagging agents, thickeners, defoaming agents, pigment dispersants, lubricants, and crosslinkable polymer particles (microgels).

[0131] (Preparation method) The first aqueous base coating composition is prepared by mixing the above components by a known method. The first aqueous base coating composition is diluted with a solvent such as water as needed and then used for coating.

[0132] • Water-based second base paint composition The aqueous second base coating composition includes, for example, an aqueous resin, a curing agent, a second bright pigment, and a second coloring pigment, similar to those of the aqueous first base coating composition. The aqueous second base coating composition may optionally include extender pigments and additives similar to those of the aqueous first base coating composition.

[0133] The second coloring pigment contains two or more coloring pigments of the same color as the first coloring pigment. It may contain three or more coloring pigments of the same color.

[0134] The solid content concentration NV2 of the water-based second base coating composition is 7.0 to 30.0% by mass. When the solid content concentration NV2 is 7.0% by mass or higher, the coating efficiency is improved. When the solid content concentration NV2 is 30.0% by mass or lower, the FF performance is improved. The solid content concentration NV2 may be 15.0% by mass or higher. The solid content concentration NV2 may be 20.0% by mass or lower.

[0135] The aqueous second base coating composition may contain a wettability enhancer such as a fluorine-containing compound or a silicone compound. This may reduce the surface tension of the aqueous second base coating composition and improve its wettability to the first base coating film. The amount of wettability enhancer may be 0.1 to 5.0 parts by mass per 100 parts by mass of the resin solids content of the aqueous second base coating composition.

[0136] Examples of fluorine-containing compounds include fluorinated alkyl carboxylates, fluorinated alkyl alkoxylates, and fluorinated alkyl esters.

[0137] Examples of silicone-based additives include polyether-modified polymethylalkylsiloxane, polyether-modified polydimethylsiloxane, polyester-modified polymethylalkylsiloxane, silicone-modified polyacrylic, and aralkyl-modified polymethylalkylsiloxane.

[0138] (PWC of second-grade luminous pigments) G2 ) PWC of second-order bright pigments G2 The range is 5.0-35.0%. G2 If the content is 5.0% or higher, sufficient brilliance can be obtained. G2 A good appearance is obtained when the percentage is 35.0% or less. G2 It may be 7.0% or more, and may be 9.0% or more. G2 It may be 30% or less, and 25.0% or less.

[0139] The average particle size of the secondary luminescence pigment is not particularly limited. The average particle size of the secondary luminescence pigment may be, for example, 8.0 to 25 μm, as this easily improves the luminescence.

[0140] The difference between the average particle size of the first luminous pigment and the average particle size of the second luminous pigment may be 5.0 μm or less. This may further reduce the difference in hue. The difference in average particle size may be 3.0 μm or less, 1.0 μm or less, or 0 μm.

[0141] (PWC of the second coloring pigment) C2 ) PWC (Personal Water Container) for the second coloring pigment C2 The range is 0.5-20.0%. C2 If the concentration is 0.5% or higher, the hue of the second base coating becomes easier to adjust, and the color difference with the multi-layer coating tends to be smaller. PWC C2 If the ratio is 20.0% or less, the flip-flop properties of the multi-layer coating may improve. C2 It may be 1.0% or more, and may be 1.5% or more. C2 It may be 10.0% or less, 7.0% or less, or 5.0% or less.

[0142] • Clear paint composition The clear coating composition may be solvent-based, water-based, or in powder form. The clear coating composition may be solvent-based. The clear coating composition may contain the above-mentioned coloring pigments to the extent that transparency is not impaired.

[0143] The clear coating composition may be, for example, an acid epoxy curing type containing a polyepoxide and a polycarboxylic acid, or a urethane curing type containing a hydroxyl group-containing resin and a polyisocyanate compound. The urethane curing type clear coating composition may be a two-component type.

[0144] An acid epoxy curing clear coating composition includes, for example, (a) an acid anhydride group-containing aqueous acrylic resin, (b) a carboxyl group-containing polyester resin, and (c) an aqueous acrylic resin having hydroxyl groups and epoxy groups. From the viewpoint of storage stability, the acid anhydride groups of (a) the acid anhydride group-containing aqueous acrylic resin may be half-esterified with a low molecular weight alcohol or the like. The carboxyl group-containing polyester resin may further have hydroxyl groups.

[0145] The resins (a) to (c) described above are blended such that, for example, the molar ratio of carboxyl groups contained in (a) aqueous acrylic resin and (b) polyester resin to epoxy groups contained in (c) aqueous acrylic resin is 1 / 1.4 to 1 / 0.6 (preferably 1 / 1.2 to 1 / 0.8), and the molar ratio of carboxyl groups derived from acid anhydride groups contained in (a) aqueous acrylic resin to hydroxyl groups contained in (b) polyester resin and (c) aqueous acrylic resin is 1 / 2.0 to 1 / 0.5 (preferably 1 / 1.5 to 1 / 0.7).

[0146] A urethane-curing clear coating composition includes, for example, a hydroxyl group-containing resin and a polyisocyanate compound. Examples of polyisocyanate compounds include those listed above. Examples of hydroxyl group-containing resins include polyester resins, polyurethane resins, aqueous acrylic resins, and polyols containing hydroxyl groups.

[0147] The OHV of the hydroxyl group-containing resin is, for example, 20 mg KOH / g or more and 200 mg KOH / g or less. The above OHV may be 30 mg KOH / g or more. The above OHV may be 180 mg KOH / g or less. The Mw of the hydroxyl group-containing resin is, for example, 1000 or more and 20000 or less. The above Mw may be 2000 or more. The above Mw may be 15000 or less. The AV of the hydroxyl group-containing resin is, for example, 0 mg KOH / g or more and 30 mg KOH / g or less. The above AV may be 25 mg KOH / g or less.

[0148] The hydroxyl group-containing resin and the polyisocyanate compound are blended, for example, such that the equivalent ratio of isocyanate groups (NCO) to hydroxyl groups (OH) (NCO / OH) is between 0.5 and 1.7. The above equivalent ratio may be 0.7 or higher. The above equivalent ratio may be 1.5 or lower.

[0149] Alternatively, an acrylic melamine-curing type clear coating composition may be used. The clear coating composition may be a commercially available product.

[0150] The resin solids content concentration of the clear coating composition is not particularly limited and is set appropriately according to the painting conditions. For example, the resin solids content concentration of the clear coating composition is 40 to 70% by mass.

[0151] (subject to be coated) The material of the object to be coated is not particularly limited. Examples of materials to be coated include metal, resin, and glass.

[0152] The shape of the object to be painted is not particularly limited. Specifically, the objects to be painted include automobile bodies and parts for automobile bodies such as passenger cars, trucks, motorcycles, and buses, as well as automobile parts such as spoilers, bumpers, mirror covers, grilles, and door handles.

[0153] Examples of metals include iron, copper, aluminum, tin, zinc, or alloys thereof (e.g., steel). Typical examples of metals to be coated include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy plated steel sheets, zinc-aluminum-magnesium alloy plated steel sheets, aluminum plated steel sheets, aluminum-silicon alloy plated steel sheets, and tin plated steel sheets.

[0154] Metallic workpieces may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, metallic workpieces may be further coated with electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0155] Examples of resins include polyethylene resin, EVA resin, polyolefin resin (polyethylene resin, polypropylene resin, etc.), vinyl chloride resin, styrene resin, polyester resin (including PET resin, PBT resin, etc.), polycarbonate resin, acrylic resin, acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene (AS) resin, polyamide resin, acetal resin, phenolic resin, fluororesin, melamine resin, urethane resin, epoxy resin, and polyphenylene oxide (PPO). The resin-coated object may be degreased. The resin part may be primed.

[0156] [Method for forming multi-layer coatings] A multi-layer coating can be formed by a method comprising: applying an aqueous first base coating composition onto a workpiece to form an uncured first base coating; applying an aqueous second base coating composition on the uncured first base coating to form an uncured second base coating; applying a clear coating composition on the uncured second base coating to form an uncured clear coating; and heating the uncured first base coating, the uncured second base coating, and the uncured clear coating.

[0157] When the second base coating composition is applied, the first base coating film may be cured or uncured.

[0158] In other words, a multi-layer coating may be manufactured by a method (3-coat 1-bake method) comprising the steps of sequentially applying a first base coating composition, a second base coating composition, and a clear coating composition onto a substrate to form uncured first base coatings, second base coatings, and clear coatings in that order, and curing the uncured first base coatings, second base coatings, and clear coatings at once.

[0159] Examples of painting methods include air spray painting, airless spray painting, electrostatic spray painting, multi-stage painting using air electrostatic spray painting (preferably two-stage painting), and painting combining air electrostatic spray painting with a rotary atomizing electrostatic painting machine.

[0160] The curing of each coating composition is carried out, for example, under conditions of a heating temperature of 80°C to 180°C and a heating time of 5 to 60 minutes (preferably 10 to 30 minutes).

[0161] Preheating may be performed between the application of the first base coating composition and the application of the second base coating composition, and between the application of the second base coating composition and the application of the clear coating composition. Preheating can be performed, for example, by leaving the mixture at a temperature of 20°C to 25°C for 5 to 15 minutes, or by heating it at a temperature of 50°C to 80°C for 30 seconds to 10 minutes. Preheating is not required between the application of the first base coating composition and the application of the second base coating composition.

[0162] In preheating, at least some of the solvent is intentionally removed. Failure to preheat means that no work is performed to intentionally remove the solvent from the uncured first base coating before applying the second base coating composition. Methods for intentionally removing the solvent (i.e., preheating methods) include, for example, air drying and heat drying. In air drying, for example, the uncured first base coating is left at a temperature of 20°C to 25°C for 5 to 15 minutes. Heat drying is performed under conditions where the curing reaction by the coating-forming components does not proceed, or at least the curing reaction is not completed. In heat drying, for example, the uncured first base coating is heated at a temperature of 50°C to 80°C for 30 seconds to 10 minutes. [Examples]

[0163] The details of each component of the paint composition used in the examples are as follows. • Water-based resin 1 (acrylic resin emulsion) Add 126.5 parts of deionized water to the reaction vessel and raise the temperature to 80°C while mixing and stirring under a nitrogen atmosphere. The mixture was heated. Then, 100 parts of a monomer mixture consisting of 27.61 parts methyl acrylate, 53.04 parts ethyl acrylate, 4.00 parts styrene, 9.28 parts 2-hydroxyethyl methacrylate, 3.07 parts methacrylic acid, and 3.00 parts allyl methacrylate, 0.7 parts Aqualon HS-10 (polyoxyethylene alkylpropenylphenyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.5 parts Adekarya Soap NE-20 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd.), and 80 parts deionized water were added dropwise to the reaction vessel in parallel over 2 hours. An initiator solution consisting of 0.3 parts ammonium persulfate and 10 parts deionized water was added dropwise. After the dropwise addition was complete, the mixture was allowed to mature at the same temperature for 2 hours. Next, the mixture was cooled to 40°C, filtered through a 400-mesh filter, and then 70 parts of deionized water and 0.32 parts of dimethylaminoethanol were added to adjust the pH to 6.5.

[0164] The resulting acrylic resin emulsion was a single-layer type with an average particle size of 150 nm, a non-volatile content of 20%, a solid content acid value of 20 mg KOH / g, and a hydroxyl value of 40 mg KOH / g.

[0165] • Water-based resin 2 (water-soluble acrylic resin) 23.89 parts of tripropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to the reaction vessel, and the mixture was heated to 105°C while being mixed and stirred under a nitrogen atmosphere. Next, a monomer mixture was prepared containing 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, and 6.9 parts of methacrylic acid. An initiator solution consisting of 100 parts of this monomer mixture, 10 parts of tripropylene glycol methyl ether, and 1 part of tert-butyl peroxy 2-ethylhexanoate was added dropwise to the reaction vessel in parallel over 3 hours. After the addition was complete, the mixture was aged at the same temperature for 0.5 hours. Furthermore, an initiator solution consisting of 5 parts of tripropylene glycol methyl ether and 0.3 parts of tert-butyl peroxy 2-ethylhexanoate was added dropwise to the reaction vessel over 0.5 hours. After the addition was complete, the mixture was aged at the same temperature for 2 hours. Using a solvent removal apparatus, 16.1 parts of the solvent were removed by distillation under reduced pressure (70 torr) at 110°C, after which 204 parts of deionized water and 7.1 parts of dimethylaminoethanol were added.

[0166] The obtained water-soluble acrylic resin (B) had a non-volatile content of 30.0%, a solid content acid value of 40 mg KOH / g, and a hydroxyl value of 50 mg KOH / g.

[0167] • Water-based resin 3 (polyether polyol) Product name "Primepol PX-1000" manufactured by Sanyo Chemical Industries, Ltd., bifunctional polyether polyol, number average molecular weight 400, hydroxyl value 278 mgKOH / g, primary / secondary hydroxyl value ratio = 63 / 37, non-volatile content 100%.

[0168] • Water-based resin 4 (urethane resin emulsion) Abyssia Co., Ltd. product name "NeoLets R-9603", polycarbonate-based urethane emulsion resin, non-volatile content 33%

[0169] • Hardener Product name "Cymel 204" manufactured by Mitsui Chemicals, Inc., mixed alkylated melamine resin, 100% non-volatile content.

[0170] • Luminous pigment 1 Product name "Alpaste (registered trademark) 06-0672" manufactured by Toyo Aluminum Co., Ltd., silver color, average particle size 17 μm • Luminous pigment 2 Product name "Alpaste (registered trademark) WM-2025" manufactured by Toyo Aluminum Co., Ltd., silver color, average particle size 15 μm • Luminous pigment 3 Product name "ALPASE (registered trademark) WL-4690" manufactured by Toyo Aluminum Co., Ltd., silver color, average particle size 7 μm

[0171] • Coloring pigment 1 (Color index name: P.BK.7) Product name "Raven 5000 Black" by Birla, black color. • Coloring pigment 2 (Color index name: PB15:1) Product name "Cyanine Blue G-314" manufactured by Sanyo Pigment Co., Ltd., blue color. • Coloring pigment 3 (Color index name: PB15:3) This product, "Cyanine Blue 3011," manufactured by Sanyo Pigment Co., Ltd., is blue and is the same color as coloring pigment 2. • Coloring pigment 4 (Color index name: PV19Y) DIC Corporation's product name "FASTOGEN SUPER RED 400RG", red. • Coloring pigment 5 (Color index name: P.BR.7) Lanxess brand product name "Bayferrox 120NM", red. • Coloring pigment 6 (Color index name: PW6) Product name "Tipaaque CR-97" manufactured by Ishihara Sangyo Co., Ltd., white. • Coloring pigment 7 (Color index name: PV23) Clariant's product name "Violet RL-NF" (violet color)

[0172] • Tertiary amines (neutralizing agents) 10% by mass aqueous solution of dimethylethanolamine

[0173] • Clear paint Product name "Macflow O-1810 Clear" manufactured by Nippon Paint Automotive Coatings Co., Ltd., an acid epoxy curing acrylic resin-based paint.

[0174] ·Base material Zinc phosphate treated SPCC-SD steel plate, dimensions 20cm x 30cm x 0.8cm thick

[0175] ·Multi-angle colorimeter Product name "BYK-mac i" manufactured by BYK Corporation

[0176] [Examples 1-6 and Comparative Examples 1-5] (1) Preparation of the first base coating composition (1bc) In addition to the glossy pigments and coloring pigments in the formulations (PWC) shown in Tables 1 and 2, the following amounts of resin components, curing agents, and tertiary amines were added and uniformly dispersed to obtain the first base coating composition.

[0177] Water-based resin 1:200 parts by mass (non-volatile content 40 parts by mass) Water-based resin 2:16.7 parts by mass (non-volatile content 5 parts by mass) Water-based resin 3:10 parts by mass (non-volatile content 10 parts by mass) Water-based resin 4:5 parts by mass (non-volatile content 1.65 parts by mass) Hardener: 15.2 parts by mass (non-volatile content 15.2 parts by mass) Tertiary amine: 40 parts by mass (concentration 10% by mass) Corrosion inhibitor: 0.2 parts by mass (non-volatile content 0.1 parts by mass)

[0178] (2) Preparation of the second base coating composition (2bc) The luminous pigments and coloring pigments were blended as shown in Tables 1 and 2, and the same amounts of resin components, curing agents, and tertiary amines as the first base coating composition were blended and uniformly dispersed to obtain the second base coating composition. The solid content concentration was adjusted by the amount of solvent.

[0179] (3) Formation of multi-layer coating The substrate (steel plate) was coated with cationic electrodeposition paint (product name "Power Top V-50", manufactured by Nippon Paint Automotive Coatings Co., Ltd.) and an intermediate coating paint (product name "OP-30", manufactured by Nippon Paint Automotive Coatings Co., Ltd.) to prepare the object to be coated. The first base coating composition was applied to the workpiece using a spray gun to a dry film thickness of 12 μm. Subsequently, the second base coating composition was applied using a spray gun to a dry film thickness of 4 μm, and the workpiece was preheated at 80°C for 3 minutes.

[0180] Next, the clear coating composition was applied to a dry film thickness of 35 μm. Finally, the mixture was heated at 140°C for 30 minutes to form a multilayer coating having a first base coating, a second base coating, and a clear coating.

[0181] [Comparative Example 6] The first and second base coating compositions were prepared in the same manner as in Example 1, except that the luminous pigments and coloring pigments were blended as shown in Tables 1 and 2.

[0182] A multilayer coating film was obtained in the same manner as in Example 1, except that the obtained first base coating composition and second base coating composition were applied to a dry film thickness of 7.5 μm.

[0183] [evaluation] • Brightness and color difference The first base coating for evaluation was prepared as follows. First, a cationic electrodeposition paint (product name: "Power Top V-50", manufactured by Nippon Paint Automotive Coatings Co., Ltd.) and an intermediate paint (product name: "OP-30", manufactured by Nippon Paint Automotive Coatings Co., Ltd.) were applied to a substrate (steel plate) to prepare a coated object. The first base paint composition was applied onto the coated object with a spray gun to a dry film thickness of 10 μm, and preheated at 80°C for 3 minutes to form an uncured first base paint film. Subsequently, the above clear paint composition was applied to a dry film thickness of 10 μm. Finally, it was heated at 140°C for 30 minutes.

[0184] Using a multi-angle colorimeter, the Lbc * 25 value, Lbc * 45 value, Ebc * 25 value, and Ebc * 45 value of the first base paint film for evaluation, and the Lm * 25 value, Lm * 45 value, color difference Em * 25 value, and color difference Em * 45 value of the above multi-layer paint film were measured, and ΔL * 25, ΔL * 45, ΔE * 25, and ΔE * 45 were calculated.

[0185] ·FF property Using a multi-angle colorimeter, light I 45 irradiated from an angle of 45 degrees with respect to the surface of the multi-layer paint film was received at an angle of 15 degrees or 75 degrees with respect to the specularly reflected light to measure the brightness Lm * 15, Lm * 75), respectively. From these values, the ratio (Lm * 15 / Lm * 75) was calculated, and the FF property was evaluated according to the following criteria. The larger the ratio (Lm * 15 / Lm * 75), the better the FF property. A: Ratio (Lm * 15 / Lm * 75) is 4 or more B: Ratio (Lm * 15 / Lm * 75) is less than 4

[0186] · Dust streak The inner panel test plate 1 corresponding to the inner panel and the outer panel test plates (the outer panel test plate 2A assuming the front door and the outer panel test plate 2B assuming the rear door) corresponding to the outer panel were produced as follows.

[0187] (a) Production of the inner panel test plate 1 Three coated objects were prepared by coating a substrate (steel plate) with a cationic electrodeposition paint (product name: "Power Top V-50", manufactured by Nippon Paint Automotive Coatings Co., Ltd.) and an intermediate paint (product name: "OP-30", manufactured by Nippon Paint Automotive Coatings Co., Ltd.). On one of the coated objects, the first base paint composition was sprayed with a spray gun to a dry film thickness of 10 μm to form an uncured first base paint film. This was used as the inner panel test plate 1 corresponding to the inner panel.

[0188] (b) Production of the outer panel test plate Next, as shown in Fig. 1, another coated object A was placed above the inner panel test plate 1 so that the height from the surface of the inner panel test plate 1 to the surface of the coated object A was 25 mm. Further, another coated object B was placed so that the height from the surface of the inner panel test plate 1 to the surface of the coated object B was 10 mm. The distance between the coated object A and the coated object B was set to 10 mm.

[0189] Subsequently, under standard robot coating conditions, from the left end of the coated object A to the right end of the coated object B in Fig. 1, the first base paint composition and the second base paint composition were sequentially applied so that the dry film thicknesses were 12 μm and 4 μm, respectively. Then, it was preheated at 80 °C for 3 minutes. Thereafter, the clear paint composition was applied to a dry film thickness of 30 μm. Finally, it was baked at 140 °C for 30 minutes to form a multilayer paint film having a first base paint film, a second base paint film, and a clear paint film on the coated object A and the coated object B. From the coated object A, the outer panel test plate 2A assuming the front door was produced, and from the coated object B, the outer panel test plate 2B assuming the rear door was produced.

[0190] The surface of the inner panel test plate 1 described above was visually inspected, and dust streaks were evaluated according to the following criteria. An A rating indicates that the difference in hue between the first base coating and the multi-layer coating has been reduced. A: Depending on the viewing angle, slight dust streaks can be seen, but it's not particularly noticeable. B: Dust streaks can be seen depending on the viewing angle, which is unusual. C: Dust streaks are easily visible, indicating a clear abnormality.

[0191] [Table 1]

[0192] [Table 2]

[0193] In Examples 1-6, the difference in hue between the first base coating and the multi-layer coating was small, and the occurrence of dust streaks was reduced. In addition, the FF properties were also excellent. Comparative Example 1 showed dust streaks because the ratio of PWC to luminous pigment was outside the specified range. Comparative Examples 2 and 3 showed dust streaks because the ratio of PWC to colored pigment was outside the specified range. Comparative Examples 4 and 5 showed dust streaks because there was only one type of colored pigment of the same color, or none at all. Comparative Example 6 had poor FF properties because the first base coating composition and the second base coating composition were identical. [Industrial applicability]

[0194] The present invention provides a multi-layer coating film in which the difference in hue between the first base coating film and the multi-layer coating film is small, and in addition, high flip-flop properties are obtained. The present invention is suitable for painting the exterior of an automobile body when the same first base coating composition is used to form the first base coating film on the exterior and interior of the automobile body. [Explanation of Symbols]

[0195] A,B Coated object 1. Inner plate test plate 2A Outer panel test plate 2B Outer panel test plate

Claims

1. A first base coating film formed on the object to be coated with a first water-based base coating composition, The first base coating film is formed with a second base coating film made of an aqueous second base coating composition, The second base coating film comprises a clear coating film formed with a clear coating composition, The aqueous first base paint composition comprises a luminous pigment and two or more coloring pigments. The solid content concentration NV1 is 20-35% by mass. PWC of the aforementioned luminous pigment Ｇ１ The percentage is 1-25%, PWC Ｃ１ The percentages range from 0.1% to 5.0%. The aqueous second base coating composition comprises a luminous pigment and two or more colored pigments with the same color index name as the colored pigments contained in the aqueous first base coating composition, The solid content concentration NV2 is 7 to 30% by mass. PWC of the aforementioned luminous pigment Ｇ２ The percentages range from 5% to 35%. PWC Ｃ２ The percentages range from 0.5% to 20.0%. The ratio (T1 / T2) of the thickness T1 of the first base coating to the thickness T2 of the second base coating is 1.5 / 1 to 5 / 1. The ratio of the solid content concentration NV1 to the solid content concentration NV2 (NV1 / NV2) is between 1.3 / 1 and 3 / 1. PWC of the aforementioned luminous pigment Ｇ１ and the PWC of the aforementioned luminous pigment Ｇ２ Ratio to (PWC) Ｇ１ PWC Ｇ２ ) is between 1 / 10 and 1 / 1, PWC of the coloring pigment Ｃ１ and the PWC of the coloring pigment Ｃ２ and the ratio (PWC Ｃ１ / PWC Ｃ２ ) is 1 / 5 to 1 / 1, a multilayer coating film.

2. Light I irradiated onto the surface of the coating film at a 45-degree angle ４５ The brightness L is based on the spectral reflectance obtained by receiving light at an angle of 25 degrees to specularly reflected light. ＊ 25 values, and the aforementioned brightness L ＊ 25 values ​​and a ＊ 25 values ​​and b ＊ Color difference E calculated from 25 values ＊ In the 25-value system, Brightness Lm of the aforementioned multilayer coating film ＊ The brightness Lbc of the first base coating film is obtained from the 25 value. ＊ ΔL (the value obtained by subtracting 25) ＊ 25 is between 0 and 10, Color difference Em of the multi-layer coating film ＊ 25 value and the color difference Ebc of the first base coating film ＊ Difference from 25 ΔE ＊ 25 is less than or equal to 10, Light I irradiated onto the surface of the coating film at a 45-degree angle ４５ The brightness L is based on the spectral reflectance obtained by receiving light at a 45-degree angle to specularly reflected light. ＊ 45 value, and the aforementioned brightness L ＊ 45 values ​​and a ＊ 45 values ​​and b ＊ Color difference E calculated from 45 values ＊ In the 45 value, Brightness Lm of the aforementioned multilayer coating film ＊ The brightness Lbc of the first base coating film is obtained from the 45 value. ＊ ΔL (the value obtained by subtracting 45) ＊ 45 is between -10 and 0. Color difference Em of the multi-layer coating film ＊ 45 value and the color difference Ebc of the first base coating film ＊ Difference ΔE from 45 ＊ The multilayer coating film according to claim 1, wherein 45 is 10 or less.

3. The multilayer coating film according to claim 1 or 2, wherein the difference between the average particle size of the lustrous pigment contained in the first aqueous base coating composition and the average particle size of the lustrous pigment contained in the second aqueous base coating composition is 5 μm or less.

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