Multilayer coating film

Abstract

[Problem] The purpose of the present disclosure is to provide a multilayer coating film which has a light sensation and is capable of achieving both masking properties and chroma of the coating film. [Solution] This multilayer coating film is provided with an intermediate coat layer, a first base layer laminated on the intermediate coat layer, and a second base layer laminated on the first base layer, the intermediate coat layer having a 45-degree viewing angle lightness L * of 80 or more, the first base layer having a transmittance in the visible light region of 5-30%, and the second base layer having a transmittance in the visible light region of 5-30%. The transmittance of the second base layer in the visible light region is 60% or more, and the second base layer contains a brilliant pigment.

Description

Technical Field

[0001] The present disclosure relates to a multilayer coating film. Background Art

[0002] On the surface of an object to be coated such as an automobile body, a plurality of coating films (multilayer coating film) having various functions are successively formed. While protecting the object to be coated, a beautiful appearance and excellent design are imparted. As a method for forming such a multilayer coating film, a method is generally used in which an undercoat coating film such as an electrodeposition coating film is formed on an object to be coated having excellent conductivity, and a middle coat coating film and a top coat coating film are successively formed thereon as needed. Among these coating films, the coating film that particularly significantly affects the appearance and design of the coating film is the top coat coating film including the base coating film. Especially for automobiles, the appearance and design of the top coat coating film formed on the vehicle body are extremely important.

[0003] The base coating film can be roughly classified into a coating film containing no scaly pigment called so-called solid color and a coating film containing scaly pigment called so-called metallic color having a shiny feeling. As a representative example of the scaly pigment contained in the coating film having a shiny feeling, scaly aluminum pigment can be cited. By making the base coating film contain scaly aluminum pigment, a metallic-like luster (metallic feeling) can be exhibited.

[0004] The appearance of the coating film formed on an automobile is greatly related to the appearance value such as the high-class feeling of the automobile. In addition, customers (consumers) who purchase automobiles tend to seek automobiles having a coating film with excellent design. Due to such diversification of consumer preferences and originality intentions, a more unique design is sought.

[0005] Patent Document 1 describes the following coating film structure in which a coating film realized by a colored base coating material containing a coloring pigment, a coating film realized by a metal-based coating material, and a top transparent coating film are laminated on a substrate, and the difference in lightness between the metal-based coating material and the coating film realized by the colored base coating material is 30 or less, the color difference is 50 or less, and the chroma difference is 30 or less.

[0006] Patent Document 2 describes the following laminated coating object having a colored base layer formed on a substrate and a mica base layer formed on the colored base layer. The shielding film thickness of the mica base layer is greater than the coating film thickness of the mica base layer and within 10 times the coating film thickness, and the colored base layer has a lightness that is 10 to 30 lower in terms of L value than the lightness of the mica base layer.

[0007] Patent Document 3 describes the following method for forming a multilayer coating film. After applying a cationic electrodeposition coating and heating and curing it, a first colored coating, a thermosetting aqueous second colored coating, and a thermosetting aqueous transparent coating are applied, and then heated to simultaneously cure the three coating films. Subsequently, a thermosetting transparent coating is applied and heated and cured. The first colored coating contains as essential components a neutralized product of a polycarboxylic acid resin having an acid value of 5 to 100 and an amino resin, and has substrate hiding properties of an organic solvent type or a non-aqueous dispersion type thermosetting.

[0008] Patent Document 4 describes the following method for forming a bright multilayer coating film. A bright multilayer coating film having a red to yellow hue is formed on a substrate to be coated, and it is described that: a step of applying a colored base coating on the substrate to be coated to form a colored base coating film; a step of applying a bright coating on the colored base coating film to form a bright coating film; a step of applying a top transparent coating on the bright coating film to form a top transparent coating film; setting the interference color of the high-luminance part of the bright coating film and the colored base coating film color to be the same series of colors within the range of Munsell hue of 10RP to 10Y, etc.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-205262

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 1-215380

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 11-104550

[0014] Patent Document 4: Japanese Patent Application Laid-Open No. 2006-289247 Summary of the Invention

[0015] Problems to be Solved by the Invention

[0016] However, if the chroma of the coating film is increased, the hiding property decreases. Conversely, if the hiding property of the coating film is to be increased, there is a relationship of decreasing chroma. In the multilayer coating films described in the conventionally known Patent Documents 1 to 4, a coating film having a bright feeling sometimes cannot sufficiently balance the hiding property and chroma of the coating film.

[0017] An object of the present disclosure is to provide a multilayer coating film having a bright feeling and capable of balancing the hiding property and chroma of the coating film.

[0018] Means for Solving the Problems

[0019] The present disclosure provides the following aspects.

[0020] [1] A multilayer coating film, which comprises an intermediate coating layer, a first base layer laminated on the intermediate coating layer, and a second base layer laminated on the first base layer.

[0021] The lightness L* of the intermediate coating layer at a 45-degree viewing angle is 80 or more.

[0022] The transmittance of the first base layer in the visible light region is 5% or more and 30% or less.

[0023] The transmittance of the second base layer in the visible light region is 60% or more.

[0024] The second base layer contains a brightening pigment.

[0025] [2] The multilayer coating film according to [1], wherein the absolute value of the difference between the hue h1 of the first base layer and the hue h2 of the multilayer coating film is 20 or less.

[0026] [3] The multilayer coating film according to [1] or [2], wherein the chroma C1 of the first base layer is 60 or more.

[0027] [4] The multilayer coating film according to any one of [1] to [3], wherein the chroma C2 of the multilayer coating film is 60 or more.

[0028] [5] The multilayer coating film according to any one of [1] to [4], wherein the glossiness Si15 value of the multilayer coating film is 15 or more.

[0029] [6] The multilayer coating film according to any one of [1] to [5], wherein the first base layer contains a coloring pigment.

[0030] In 100 parts by mass of the total solid content of the first base layer, the content of the coloring pigment is 5 parts by mass or more and 60 parts by mass or less.

[0031] [7] The multilayer coating film according to any one of [1] to [6], wherein the second base layer contains a coloring pigment.

[0032] In 100 parts by mass of the total solid content of the second base layer, the content of the coloring pigment is 2 parts by mass or less.

[0033] [8] The multilayer coating film according to any one of [1] to [7], wherein in 100 parts by mass of the total solid content of the second base layer, the content of the black pigment in the second base coating film is 0 part by mass or more and 0.1 part by mass or less.

[0034] [9] The multilayer coating film according to any one of [1] to [8], wherein, in 100 parts by mass of the total amount of the solid components of the second base layer, the content of the mica-based pigment in the second base coating film is 0.1 part by mass or more and 15 parts by mass or less.

[0035]

[10] The multilayer coating film according to any one of [1] to [9], wherein a first transparent layer is further provided between the first base layer and the second base layer.

[0036]

[11] The multilayer coating film according to any one of [1] to

[10] , further comprising a second transparent layer laminated on the second base layer.

[0037] Advantages of the Invention

[0038] The present disclosure provides a multilayer coating film having a bright feeling and capable of achieving both the hiding power and chroma of the coating film. Detailed Description of the Invention

[0039] The multilayer coating film of the present disclosure includes an intermediate coating layer, a first base layer laminated on the intermediate coating layer, and a second base layer laminated on the first base layer.

[0040] The lightness L* at a 45-degree viewing angle of the intermediate coating layer is 80 or more.

[0041] The transmittance of the first base layer in the visible light region is 5% or more and 30% or less.

[0042] The transmittance of the second base layer in the visible light region is 60% or more.

[0043] The second base layer contains a brightening pigment.

[0044] The multilayer coating film of the present disclosure has a bright feeling and is capable of achieving both the hiding power and chroma of the coating film. Although the present disclosure should not be construed in terms of a specific theory, the reason why the multilayer coating film of the present disclosure can exhibit such an effect can be considered as follows. That is, it can be considered that since the lightness of the intermediate coating layer of the multilayer coating film of the present disclosure is 80 or more, the influence of the undercoat layer on the appearance can be suppressed to a certain extent. And by laminating a first base layer having transparency and a second base layer having a higher transparency than the first base layer and containing a brightening pigment on the intermediate coating layer, the hiding power of the coating film as a whole is good, and a multilayer coating film having chroma and a bright feeling can be obtained.

[0045] In the present disclosure, the "intermediate coating film" may be a layer disposed below the first base layer, that is, on the substrate side.

[0046] In one mode, the multi-layer coating film of the present disclosure can be used for automotive applications. In this mode, the multi-layer coating film of the present disclosure can be disposed on an undercoat, and the undercoat can be disposed on a substrate.

[0047] The above-mentioned substrate only needs to have a matrix layer such as a metal layer, a plastic layer, a foam layer, etc.

[0048] Examples of the metal for forming the above-mentioned metal layer include iron, copper, aluminum, tin, zinc, and their alloys. The aforementioned metal layer can be in the form of a plate or a molded article. Specific examples of the aforementioned molded article include automotive bodies and components such as sedans, trucks, motorcycles, buses, etc.

[0049] The above-mentioned metal layer (preferably the base layer side of the aforementioned metal layer) can be subjected to chemical conversion treatment in advance using phosphates, zirconates, chromates, etc., and then an electrodeposited coating film layer is formed as the undercoat. Examples of the electrodeposition coating composition that can be used to form the aforementioned electrodeposited coating film layer include cationic electrodeposition coating compositions and anionic electrodeposition coating compositions.

[0050] Examples of the resin for forming the above-mentioned plastic layer include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin. The aforementioned plastic layer can be in the form of a plate or a molded article. Examples of the aforementioned molded article include automotive components such as spoilers, bumpers, rearview mirror covers, grilles, door handles, etc. On the aforementioned plastic layer (preferably the base layer side of the aforementioned plastic layer), a primer layer can be provided as the undercoat.

[0051] (Multi-layer coating film)

[0052] The multi-layer coating film of the present disclosure includes an intermediate coat, a first base layer laminated on the above-mentioned intermediate coat, and a second base layer laminated on the above-mentioned first base layer. The multi-layer coating film of the present disclosure can further include a first transparent layer between the first base layer and the second base layer. In addition, the multi-layer coating film of the present disclosure can further include a second transparent layer laminated on the above-mentioned second base layer.

[0053] (Intermediate coat)

[0054] Typically, the intermediate coat can be a layer disposed on the undercoat. The intermediate coat, for example, protects the undercoat and can impart chipping resistance to the multi-layer coating film, but is not limited thereto.

[0055] The lightness L* at a 45-degree viewing angle of the above-mentioned intermediate coat is 80 or more, preferably 80 or more and 100 or less. By making the lightness L* at a 45-degree viewing angle of the intermediate coat within this range, the lightness chroma and hiding power of the obtained multi-layer coating film become good.

[0056] In the present disclosure, the lightness L* at a 45-degree viewing angle can be measured in accordance with JIS Z 8723.

[0057] The above-mentioned intermediate coat film is formed from an intermediate coat paint composition containing an intermediate coat film-forming resin, a coloring pigment, an extender pigment, and the like. As the above-mentioned film-forming resin, the compounds exemplified in the film-forming resin (A) used in the first base paint composition or the second base paint composition described later can be used. As the film-forming resin used in the above-mentioned intermediate coat paint composition, from the viewpoints of various properties of the intermediate coat film, a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate is preferably used.

[0058] Examples of the coloring pigment contained in the above-mentioned intermediate coat paint composition include pigments having no chroma such as carbon black and titanium dioxide, and pigments having a chroma for compensating the hue of the base layer. When the above-mentioned intermediate coat paint composition contains a pigment, the content of the pigment is preferably 0.1 part by mass or more and preferably 50 parts by mass or less relative to 100 parts by mass of the resin solid content.

[0059] In a preferred embodiment, the content of a white coloring pigment such as titanium dioxide is preferably 20 parts by mass or more and more preferably 25 parts by mass or more relative to 100 parts by mass of the resin solid content, the content of a black coloring pigment such as carbon black is preferably 0.1 part by mass or less and more preferably 0.05 part by mass or less relative to 100 parts by mass of the resin solid content, and the content of other colored coloring pigments is preferably 0.2 part by mass or less and more preferably 0.1 part by mass or less relative to 100 parts by mass of the resin solid content. By making the content range of the pigment fall within this range, it is easy to set the lightness of the intermediate coat layer within a desired range.

[0060] The thickness of the above-mentioned intermediate coat film is, for example, preferably 3 to 50 μm, more preferably 5 to 30 μm.

[0061] (First base layer)

[0062] The above-mentioned first base layer is laminated on the intermediate coat layer. The above-mentioned first base layer can be directly contacted and laminated on the intermediate coat layer, or can be laminated on the intermediate coat layer via another layer provided on the intermediate coat layer. The first base layer can, for example, impart color to the multilayer film, but is not limited thereto.

[0063] The transmittance of the above-mentioned first base layer in the visible light region is 5% or more and 30% or less, preferably 9% or more and 20% or less.

[0064] In the present disclosure, the transmittance in the visible light region means the transmittance for light having a wavelength of 400 nm or more and 700 nm or less. The transmittance in this visible light region can be measured in accordance with JIS R 32124.

[0065] The above-mentioned first base layer preferably contains a coloring pigment. Examples of such coloring pigments include organic coloring pigments such as azo chelate pigments, azomethine azo pigments, azo lake pigments, insoluble azo pigments, condensed azo pigments, monoazo pigments, indanthrone pigments, bisazo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, quinophthalone pigments, isoindolinone pigments, naphthol pigments, pyrazolone pigments, anthanthrone pigments, anthraquinone pigments, anthrapyrimidine pigments, metal complex pigments, etc.; inorganic coloring pigments such as chrome yellow, iron oxide, iron oxide yellow, transparent iron oxide, iron black, iron chromium, bismuth manganese, bismuth vanadate, chromium oxide, molybdenum orange, iron oxide red, titanium yellow, zinc white, zinc yellow, yellowish brown, carbon black, titanium dioxide, cobalt green, phthalocyanine green, ultramarine, cobalt blue, phthalocyanine blue, cobalt violet, etc.; graphite pigments, other colored and colored flat pigments, etc.

[0066] The above-mentioned coloring pigments can be colored or achromatic, and can be colors such as red, blue, yellow, green, purple, brown, white, black, gray, etc.

[0067] In the above-mentioned first base layer, in 100 parts by mass of the total solid content of the first base layer, the content of the coloring pigment is preferably 5 parts by mass or more and 60 parts by mass or less, more preferably 10 parts by mass or more and 50 parts by mass or less. By making the content of the coloring pigment in the first base layer within this range, the color stability when the film thickness varies becomes good.

[0068] In the present disclosure, the solid content refers to the heating residue defined in JIS K 5601-1-2:2008, and is calculated by measuring the percentage of the mass of the residue after heating at 105°C for 60 minutes relative to the original mass.

[0069] The thickness of the aforementioned first base layer is, for example, 3 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less.

[0070] The above-mentioned first base layer can be formed using a first base coating composition. The first base coating composition contains a film-forming resin (A1) and a curing agent (B1). In one mode, the above-mentioned first base coating composition further contains a coloring pigment (C1), and in other modes, the above-mentioned first base coating composition does not contain a coloring pigment (C1).

[0071] (Film-forming resin (A1))

[0072] The above-mentioned film-forming resin (A) is a resin capable of forming a film by reacting with a curing agent (B1) described later, and preferably contains one or more selected from acrylic resins, polyol resins, polyester resins, polyurethane resins, epoxy resins, fluororesins, and silicone resins, and more preferably contains one or more selected from acrylic resins, polyol resins, and polyester resins. The above-mentioned film-forming resin (A1) preferably has a hydroxyl group.

[0073] The above-mentioned film-forming resin (A1) preferably contains an aqueous resin. An aqueous resin is a resin dispersed in an aqueous medium and can be an emulsion or a dispersion. Examples of the aqueous resin include acrylic resin aqueous dispersions, polyester resin aqueous dispersions, polyurethane resin aqueous dispersions, and epoxy resin aqueous dispersions.

[0074] The above-mentioned film-forming resin (A1) preferably contains an acrylic resin, and more preferably contains an acrylic resin aqueous dispersion. The acrylic resin aqueous dispersion can be either an acrylic resin emulsion or an acrylic resin dispersion, and is preferably an acrylic resin emulsion. The acrylic resin contained in the acrylic resin aqueous dispersion can be in the form of particles in the aqueous medium.

[0075] Typically, the above-mentioned acrylic resin is obtained in the form of a polymer of a monomer mixture containing (meth)acrylic monomers, and the acrylic resin aqueous dispersion can be obtained by emulsion polymerization of the above-mentioned monomer mixture. The above-mentioned monomer mixture preferably contains a hydroxyl group-containing monomer and may also contain an acid group-containing monomer and other monomers. In one embodiment, the above-mentioned monomer mixture preferably contains (meth)acrylic alkyl esters, a hydroxyl group-containing monomer, and an acid group-containing monomer, and more preferably contains (meth)acrylic alkyl esters, a hydroxyl group-containing monomer, an acid group-containing monomer, and styrene-based monomers.

[0076] In the present disclosure, (meth)acrylic acid means acrylic acid and methacrylic acid.

[0077] The above-mentioned (meth)acrylic alkyl ester is a (meth)acrylic alkyl ester having no acid group and no hydroxyl group. By making the above-mentioned monomer mixture contain (meth)acrylic alkyl esters, the main skeleton of the acrylic resin can be well formed.

[0078] Examples of the above-mentioned (meth)acrylic alkyl ester include, for example, (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid tert-butyl ester, (meth)acrylic acid hexyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid octyl ester, (meth)acrylic acid nonyl ester, (meth)acrylic acid decyl ester, (meth)acrylic acid dodecyl ester, (meth)acrylic acid stearyl ester, etc. As the (meth)acrylic alkyl ester, only one kind can be used, or two or more kinds can be used in combination.

[0079] As the hydroxyl group-containing monomer, (meth)acrylic monomers having a hydroxyl group can be mentioned. Specifically, hydroxyl group-containing alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, etc.; ε-caprolactone-modified (meth)acrylic monomers, etc.

[0080] As the ε-caprolactone-modified (meth)acrylic monomer, commercially available products can be used. As such commercially available products, for example, PLACCEL FA-1, PLACCEL FA-2, PLACCEL FA-3, PLACCEL FA-4, PLACCEL FA-5, PLACCEL FM-1, PLACCEL FM-2, PLACCEL FM-3, PLACCEL FM-4, and PLACCEL FM-5 (all manufactured by Daicel Chemical Industries, Ltd.) etc. can be mentioned. As the hydroxyl group-containing monomer, only 1 kind can be used, or 2 or more kinds can be used in combination.

[0081] By making the above monomer mixture contain a hydroxyl group-containing monomer, hydrophilicity can be imparted to the resulting acrylic resin, and the curing reactivity of the acrylic resin with the curing agent (B) described later can be improved.

[0082] The acid group-containing monomer can be a (meth)acrylic monomer having an acid group, and this acid group can be a carboxyl group, a sulfonic acid group, or a phosphoric acid group. From the viewpoint of improving the dispersion stability and promoting the curing reaction function, a carboxyl group is preferred. By making the above monomer mixture contain an acid group-containing monomer, various stabilities such as the storage stability, mechanical stability, and stability to freezing of the resulting acrylic resin can be improved, and the curing reaction of the acrylic resin with the curing agent (B) during film formation can be promoted.

[0083] As the acid group-containing monomer, carboxyl group-containing monomers such as (meth)acrylic acid, crotonic acid, isocrotonic acid, ethylacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, and fumaric acid can be mentioned; sulfonic acid group-containing monomers such as p-vinylbenzenesulfonic acid, p-acrylamidopropanesulfonic acid, and tert-butylacrylamidesulfonic acid; phosphoric acid group-containing monomers such as the phosphoric acid monoester of 2-hydroxyethyl (meth)acrylate and the phosphoric acid monoester of 2-hydroxypropyl (meth)acrylate, etc. As the acid group-containing monomer, only 1 kind can be used, or 2 or more kinds can be used in combination.

[0084] As the above-mentioned other monomers, at least one monomer selected from styrene-based monomers, (meth)acrylonitrile, and (meth)acrylamide can be cited, etc. As the styrene-based monomers, styrene, α-methylstyrene, etc. can be cited. The other monomers can be used alone or in combination of two or more.

[0085] The above monomer mixture may further contain crosslinkable monomers such as carbonyl group-containing monomers, monomers containing hydrolyzable silyl groups, and various polyfunctional vinyl monomers. By making the monomer mixture contain crosslinkable monomers, self-crosslinkability can be imparted to the resulting acrylic resin. The crosslinkable monomers can be used alone or in combination of two or more.

[0086] As the above carbonyl group-containing monomers, monomers containing a ketone group such as acrolein, diacetone (meth)acrylamide, (meth)acrylic acid acetoacetoxyethyl ester, formylstyrene, and alkyl vinyl ketones having 4 to 7 carbon atoms (for example, methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone) can be cited.

[0087] As the above monomers containing hydrolyzable silyl groups, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, etc. can be cited.

[0088] The above polyfunctional vinyl monomers are compounds having two or more ethylenically unsaturated groups capable of radical polymerization in the molecule. As specific examples of the polyfunctional vinyl monomers, polyfunctional vinyl compounds such as divinylbenzene, ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, (meth)allyl acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate can be cited; polyfunctional monomers such as triallyl cyanurate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate can be cited.

[0089] The crosslinkable monomers can be used alone or in combination of two or more. As preferred crosslinkable monomers, (meth)allyl acrylate, ethylene glycol di(meth)acrylate, divinylbenzene, etc. can be cited, for example. By using these crosslinkable monomers, there is an advantage that the average particle diameter of the acrylic resin contained in the resulting acrylic resin aqueous dispersion can be suitably controlled to 100 nm or less.

[0090] Based on the total amount of the monomer mixture, the amount of the crosslinkable monomer is preferably 0.2 to 20% by mass, more preferably 0.5 to 20% by mass. By including the crosslinkable monomer in the monomer mixture within the above range, there is an advantage that the average particle diameter of the acrylic resin contained in the prepared acrylic resin aqueous dispersion can be suitably controlled to 100 nm or less.

[0091] In the film-forming resin (A1), the acrylic resin contained in the acrylic resin aqueous dispersion may be in the form of particles, and the average particle diameter of the particles is preferably 0.01 μm or more and 1.0 μm or less.

[0092] It should be noted that in the present disclosure, the average particle diameter is the volume average particle diameter determined by the dynamic light scattering method. Specifically, an electrophoretic light scattering photometer ELSZ series (manufactured by Otsuka Electronics Co., Ltd.) or the like can be used for measurement.

[0093] In the film-forming resin (A1), the acrylic resin contained in the acrylic resin aqueous dispersion may be core-shell type particles.

[0094] In the film-forming resin (A1), the acid value of the acrylic resin contained in the acrylic resin aqueous dispersion is preferably 1 mgKOH / g or more and 80 mgKOH / g or less, more preferably 2 mgKOH / g or more and 70 mgKOH / g or less, and still more preferably 3 mgKOH / g or more and 60 mgKOH / g or less.

[0095] In the film-forming resin (A1), the hydroxyl value of the acrylic resin contained in the acrylic resin aqueous dispersion is preferably 30 mgKOH / g or more and 120 mgKOH / g or less, more preferably 35 mgKOH / g or more and 100 mgKOH / g or less. By being within the above range, there is an advantage that the curing reaction proceeds sufficiently and the hardness of the obtained film becomes good.

[0096] It should be noted that in the present disclosure, both the acid value and the hydroxyl value are values in terms of solid content and are measured by the method based on JIS K 0070.

[0097] In the film-forming resin (A1), the weight average molecular weight of the acrylic resin contained in the acrylic resin aqueous dispersion is preferably 50,000 or more and 5,000,000 or less, more preferably 50,000 or more and 1,000,000 or less. By being within the above range, various properties such as the hardness, adhesion, and water resistance of the obtained film become good.

[0098] It should be noted that in the present disclosure, the weight average molecular weight is a value obtained by converting the measurement result of gel permeation chromatography (GPC) based on polystyrene standards.

[0099] In the solid content of the above-mentioned film-forming resin (A1), the content of the solid content of the acrylic resin aqueous dispersion is preferably 30% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 85% by mass or less, and still more preferably 50% by mass or more and 80% by mass or less. By being within the above range, there are advantages that the curing reaction proceeds sufficiently and the hardness of the obtained film becomes good.

[0100] The acrylic resin aqueous dispersion can be produced by heating and stirring the above monomer mixture in an aqueous medium in the presence of a radical polymerization initiator and an emulsifier, and carrying out emulsion polymerization. The reaction temperature can be, for example, about 30 to 100 °C. The reaction time can be appropriately selected according to the reaction scale and reaction temperature, and can be, for example, about 1 to 10 hours. In emulsion polymerization, for example, the monomer mixture or monomer pre-emulsion can be added all at once to a reaction vessel containing water and an emulsifier, or it can also be added dropwise temporarily. By appropriately selecting such steps, the reaction temperature can be adjusted. The above monomer pre-emulsion can be prepared by emulsifying the monomer mixture with at least a part of water and an emulsifier.

[0101] As the above radical polymerization initiator, known initiators used in the emulsion polymerization of acrylic resins can be used. The radical polymerization initiator is preferably a water-soluble radical polymerization initiator. For example, persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate can be used in the form of an aqueous solution. In addition, a so-called redox initiator obtained by combining an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide with a reducing agent such as sodium bisulfite, sodium thiosulfate, Rongalite, and ascorbic acid can also be used in the form of an aqueous solution.

[0102] As the radical polymerization initiator, only one kind can be used, or two or more kinds can be used in combination.

[0103] As the above emulsifier, for example, an anionic or nonionic emulsifier selected from micelle compounds having a hydrocarbon group with 6 or more carbon atoms in the same molecule and having a hydrophilic part such as a carboxylate, sulfonate, or sulfate partial ester can be used. As the anionic emulsifier, alkali metal salts or ammonium salts of sulfuric acid half esters of alkylphenols or higher alcohols; alkali metal salts or ammonium salts of alkyl sulfonates or allyl sulfonates; alkali metal salts or ammonium salts of sulfuric acid half esters of polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers, etc. can be cited. As the nonionic emulsifier, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers, etc. can be cited. In addition, as other examples of the emulsifier, various anionic and nonionic reactive emulsifiers having groups such as (meth)acrylic acid-based, propenyl-based, allyl-based, allyl ether-based, and maleic acid-based groups having a radically polymerizable unsaturated double bond in the molecule can be cited.

[0104] Commercially available products can be used as the emulsifier. Examples of commercially available products include, for example, Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), ELEMINOL JS-2 (manufactured by Sanyo Chemical Industries, Ltd.), ADEKA REASOAP SR-10 (manufactured by ADEKA Corporation), Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like.

[0105] Only one kind of emulsifier can be used, or two or more kinds can be used in combination.

[0106] In emulsion polymerization, if necessary, mercaptan compounds, lower alcohols, and other additives (chain transfer agents) for adjusting the molecular weight can be used. By using these additives, emulsion polymerization can be carried out appropriately. In addition, the smooth and uniform formation of the coating film can be promoted, and the adhesion of the coating film to the object to be coated can be improved.

[0107] As the emulsion polymerization, any polymerization method such as a single-stage continuous monomer uniform dropping method, a core-shell polymerization method as a multi-stage monomer feeding method, and a power feeding polymerization method in which the monomer composition fed is continuously changed during polymerization can be appropriately selected.

[0108] A neutralizing agent can be added to the obtained acrylic resin aqueous dispersion to neutralize at least a part of the acid groups that may be contained in the acrylic resin. The stability of the acrylic resin aqueous dispersion can be improved by neutralization. As the neutralizing agent, basic compounds can be cited. As the basic compounds, for example, ammonia; organic amines such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine (dimethylaminoethanol); inorganic bases such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. As the neutralizing agent, only one kind can be used, or two or more kinds can be used in combination.

[0109] The above-mentioned polyol resin is a resin having two or more hydroxyl groups in the molecule, and examples thereof include polyether polyols and polycarbonate polyols. As the above-mentioned polyol resin, polyether polyols such as polypropylene glycol are preferred.

[0110] In the above-mentioned first base coating composition, the content of the solid component of the above-mentioned polyol resin is preferably 1 part by mass or more and 70 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and still more preferably 10 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass in total of the solid components of the above-mentioned acrylic resin aqueous dispersion.

[0111] A polyester resin aqueous dispersion can be prepared, for example, by condensing a polyol component and a polyacid component and dispersing it in water using a basic compound. A polyurethane resin aqueous dispersion can be prepared, for example, by polymerizing a polyol compound, a compound having an active hydrogen group and a hydrophilic group in the molecule, and an organic polyisocyanate as needed using a chain extender and a polymerization inhibitor, and dispersing the resulting polymer in water.

[0112] In the above first base coating composition, the content of the solid component of the above polyester resin aqueous dispersion is preferably 10 parts by mass or more and 90 parts by mass or less, more preferably 20 parts by mass or more and 80 parts by mass or less, and still more preferably 30 parts by mass or more and 70 parts by mass or less, relative to 100 parts by mass in total of the solid components of the above acrylic resin aqueous dispersion.

[0113] The hydroxyl value of the film-forming resin (A1) is preferably 30 mgKOH / g or more and 120 mgKOH / g or less, more preferably 35 mgKOH / g or more and 100 mgKOH / g or less. By being within the above range, there are advantages that the curing reaction proceeds sufficiently and the hardness of the resulting film becomes good.

[0114] In 100 mass% of the solid components of the aqueous first base coating composition, the content rate of the solid components of the above film-forming resin (A1) is preferably 10 mass% or more and 90 mass% or less, more preferably 15 mass% or more and 85 mass% or less, and still more preferably 20 mass% or more and 80 mass% or less.

[0115] (Curing agent (B1))

[0116] The above curing agent (B1) can be a compound having two or more groups capable of reacting with the film-forming resin (A1) in one molecule, and belongs to the film-forming components together with the film-forming resin (A1). As the above curing agent (B1), one or two or more selected from amino resins (melamine resins, urea resins, benzoguanamine resins, etc.), blocked isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and metal ions can be used.

[0117] In one mode, the above curing agent (B1) preferably contains an amino resin, more preferably contains a melamine resin. By containing a melamine resin, a film can be formed by means of the self-polymerization of the melamine resin and the reaction of the amino groups contained in the melamine resin with the hydroxyl groups that may be contained in the film-forming resin (A1).

[0118] Melamine resin can be obtained by modifying a condensate of an amino compound such as melamine and an aldehyde compound such as formaldehyde or acetaldehyde with a lower alcohol such as methanol, ethanol, propanol, or butanol. The melamine resin is preferably a compound having three reactive functional groups represented by the following formula in one triazine nucleus as a reactive functional group or a polycondensate thereof.

[0119] -NX 1 X 2

[0120] [X 1 、X 2 each independently represents a hydrogen atom, a hydroxymethyl group, or -CH2-OR 1 .

[0121] R 1 represents an alkyl group having 1 to 8 carbon atoms, preferably a linear or branched alkyl group having 1 to 8 carbon atoms.

[0122] In the case where a molecule contains a plurality of -CH2-OR 1 , the plurality of R 1 may be the same or different. ]

[0123] Examples of the melamine resin include a fully alkylated type containing only -N(CH2OR 1 )2 as a reactive functional group; a hydroxymethyl type containing -N(CH2OR 1 )(CH2OH) as a reactive functional group; an imino type containing -N(CH2OR 1 )(H) as a reactive functional group; and a hydroxymethyl / imino type containing -N(CH2OR 1 )(CH2OH) and -N(CH2OR 1 )(H) or containing -N(CH2OH)(H), a total of four types. In the above-mentioned fully alkylated type, hydroxymethyl type, imino type, or hydroxymethyl / imino type melamine resin, R 1 is preferably an alkyl group having 1 to 4 carbon atoms, preferably methyl, n-butyl, or isobutyl. In one embodiment, methyl and butyl can be mixed. In other embodiments, it can be only methyl, or in other embodiments, it can be only butyl.

[0124] As the melamine resin, commercially available products can be used. Examples of commercially available products include hydroxymethyl-imino type methyl / butyl mixed etherified melamine resins such as CYMEL 202; imino type methyl / butyl mixed etherified melamine resins such as CYMEL 204, CYMEL 211, CYMEL 250, CYMEL 254, Mycoat 212, Mycoat 518, Mycoat 525; fully alkyl type methylated melamine resins such as CYMEL 350; imino type methylated melamine resins such as CYMEL 325, CYMEL 327, CYMEL 385, CYMEL 701, CYMEL 712, Mycoat 723, Mycoat 776; imino type butylated melamine resins such as Mycoat 508, hydroxymethyl type methylated melamine resins such as CYMEL 370, hydroxymethyl type methyl / isobutyl mixed etherified melamine resins such as Mycoat 2677 (the above are manufactured by Allnex Japan Co., Ltd.), etc.

[0125] In the total 100% by mass of the solid content of the above-mentioned curing agent (B1), the content of the solid content of the above-mentioned melamine resin can be 0% by mass, preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and further preferably 95% by mass or more and 100% by mass or less.

[0126] In the total 100 parts by mass of the solid content of the above-mentioned film-forming resin (A1) and the solid content of the curing agent (B1), the content of the above-mentioned melamine resin can be 0 parts by mass, preferably 10 parts by mass or more and 90 parts by mass or less, and further can be 20 parts by mass or more and 80 parts by mass or less. Thus, there is an advantage that various physical properties such as the hardness, adhesion, and water resistance of the obtained film become good.

[0127] The blocked isocyanate compound can be prepared by adding a blocking agent having an active hydrogen to a polyisocyanate containing trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. This blocked isocyanate resin dissociates the blocking agent by heating, generates an isocyanate group, and reacts with the functional groups in the above resin components to cure.

[0128] In the total 100% by mass of the solid content of the film-forming resin (A1) and the solid content of the curing agent (B1), the content of the solid content of the curing agent (B1) in the aqueous first base coating composition is preferably 20% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 40% by mass or less.

[0129] (Colored pigment (C1))

[0130] As the above coloring pigments, there is no particular limitation, and examples thereof include azo chelate pigments, azomethine azo pigments, azo lake pigments, insoluble azo pigments, condensed azo pigments, monoazo pigments, indanthrone pigments, bisazo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, quinophthalone pigments, isoindolinone pigments, naphthol pigments, pyrazolone pigments, anthanthrone pigments, anthraquinone pigments, anthrapyrimidine pigments, metal complex pigments and other organic coloring pigments; chrome yellow, iron oxide, iron oxide yellow, transparent iron oxide, iron black, iron chromium, bismuth manganese, bismuth vanadate, chromium oxide, molybdenum orange, iron oxide red, titanium yellow, zinc white, zinc yellow, tan, carbon black, titanium dioxide, cobalt green, phthalocyanine green, ultramarine, cobalt blue, phthalocyanine blue, cobalt violet and other inorganic coloring pigments; graphite pigments, other colored and colored flat pigments, etc.

[0131] The above coloring pigments can be chromatic or achromatic, and can be colors such as red, blue, yellow, green, purple, brown, white, black, gray, etc.

[0132] As the above coloring pigment (C1), from the viewpoint of improving weather resistance and ensuring hiding power, a coloring pigment is preferably used. In particular, titanium dioxide is more preferably used because of its excellent coloring and hiding properties and low price. In addition, as the pigment, a standard gray coating composition containing carbon black and titanium dioxide as the main pigments can be used. In addition, it can also be a coating composition whose lightness or hue matches that of the second base coating composition, and a coating composition combined with various coloring pigments. The first base coating composition of the present disclosure can function as a primer when coating the second base coating composition, and can also function as a colored substrate when containing a coloring pigment.

[0133] In the first base coating composition, the pigment mass concentration of the above pigment (the ratio of the mass of the pigment to the total solid content of the first base coating composition (PWC)) is preferably 5% by mass or more and 60% by mass or less. By setting the PWC to 5% by mass, it is easier to improve the hiding power. By setting the PWC to 60% by mass or less, it is possible to more easily suppress the increase in viscosity during curing, and therefore, it is easier to ensure fluidity and obtain a good coating film appearance.

[0134] (Brightness pigment)

[0135] The above-mentioned first base coating composition may further contain a brightening pigment. In one embodiment, the above-mentioned first base coating composition contains a brightening pigment, and in other embodiments, the above-mentioned first base coating composition does not contain a brightening pigment.

[0136] Examples of brightening pigments include metallic brightening pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and their alloys; mica pigments such as interference mica pigments and muscovite pigments; graphite pigments; glass flake pigments, etc.

[0137] The average particle size of the above-mentioned brightening pigment is preferably 1 μm or more and 30 μm or less, more preferably 5 μm or more and 25 μm or less. The average thickness of the above-mentioned brightening pigment is preferably 0.01 μm or more and 6 μm or less, more preferably 0.1 μm or more and 5 μm or less.

[0138] In the present disclosure, the average particle size of the brightening pigment refers to the average major axis. In the measurement of the average particle size, a shape analysis laser microscope (e.g., VK-X 250 manufactured by KEYENCE Corporation, etc.) can be used to observe the brightening pigment, and the arithmetic mean value of the maximum lengths (major axes) of any 100 pigments can be obtained, thereby enabling the measurement.

[0139] In addition, in the present disclosure, the average thickness t of the above-mentioned brightening pigment can be calculated according to the water surface spreading area (WCA: m 2 / g) per 1 g of the brightening pigment and using the following formula.

[0140] t (μm) = 0.4 / [WCA (m 2 / g)]

[0141] In the present disclosure, the water surface spreading area can be measured in accordance with JIS K 5906.

[0142] The water surface spreading area (WCA) of the above-mentioned brightening pigment is preferably 0.06 m 2 / g or more and 40 m 2 / g or less, more preferably 0.08 m 2 / g or more and 4 m 2 / g or less. By making the water surface spreading area of the brightening pigment within the above range, the resulting coating film can obtain an appearance with a high degree of graininess.

[0143] When the above-mentioned brightening pigment is an aluminum pigment, surface treatment can be carried out as needed. Examples of surface treatments that can be performed on aluminum pigments include surface treatment using metal oxide-based compounds, surface treatment using phosphorus compounds, surface treatment using amine compounds, surface treatment using silane compounds, etc.

[0144] As the above metal oxide-based compound, for example, metal oxides containing at least a transition metal element as a constituent metal, alkali metal salts thereof, ammonium salts thereof, etc. can be cited. Specifically, molybdenum trioxide, molybdic acid, alkali metal molybdates, ammonium molybdates, vanadic acid, alkali metal vanadates, ammonium vanadates, etc. can be cited. It should be noted that the above alkali metal is not particularly limited, and for example, sodium, potassium, etc. can be cited. Among them, as the above metal oxide-based compound, it is preferable to use one or two or more metal oxide-based compounds selected from molybdic acid, alkali metal molybdates, ammonium molybdates, vanadic acid, alkali metal vanadates, and ammonium vanadates.

[0145] As the above phosphorus compound, for example, organic phosphates, organic phosphites, organic phosphonic acids, and amine salts of these compounds can be cited. These phosphorus compounds can be used alone or in combination of two or more.

[0146] As the above amine compound, for example, linear or branched primary amines, linear or branched secondary amines, linear or branched tertiary amines, alicyclic primary amines, alicyclic secondary amines, alicyclic tertiary amines, primary amines containing an aromatic group, secondary amines containing an aromatic group, tertiary amines containing an aromatic group, etc. can be cited. These amine compounds may have substituents (such as hydroxyl groups, etc.) as needed. These amine compounds can be used alone or in combination of two or more.

[0147] As the above silane compound, for example, alkoxysilane compounds, silane coupling agents containing vinyl, silane coupling agents containing epoxy groups, silane coupling agents containing styryl groups, silane coupling agents containing (meth)acryloyl groups, silane coupling agents containing amino groups, silane coupling agents containing isocyanate groups, silane coupling agents containing ureido groups, silane coupling agents containing mercapto groups, silane coupling agents containing acid anhydride groups, and partial condensates thereof, etc. can be cited. These silane compounds can be used alone or in combination of two or more.

[0148] The above surface treatment can be carried out under treatment conditions commonly adopted by those skilled in the art. The above surface treatment can be carried out only one kind, or two or more kinds can be used in combination.

[0149] As the above brightening pigment, commercially available products can be used. As commercially available products, for example, Alpaste 93-0647, 06-0672, TCR-2020, MG1000, etc. (all manufactured by Toyo Aluminium Co., Ltd.); Alumin paste MH-9901, etc. (manufactured by Asahi Kasei Co., Ltd.), etc. can be cited.

[0150] In one mode, the above-mentioned bright pigment is preferably 1 part by mass or more and 45 parts by mass or less, more preferably 2 parts by mass or more and 35 parts by mass or less, based on 100 parts by mass of the resin solid content of the film-forming resin (A1). The pigment mass concentration of the above-mentioned bright pigment in the aqueous first base coating composition is preferably 2% by mass or more and 40% by mass or less, more preferably 2.5% by mass or more and 35% by mass, and further preferably 3% by mass or more and 30% by mass or less.

[0151] It should be noted that the above-mentioned aqueous first base coating composition may not contain a bright pigment. In other modes, the pigment mass concentration of the bright pigment in the first base coating composition may be 0% by mass.

[0152] The above-mentioned coloring pigment (C1) and bright pigment can be used to prepare the first base coating composition after being made into a pigment dispersion paste. The pigment dispersion paste can be obtained by pre-dispersing at least a small amount of the pigment, a pigment dispersant, and a part of the film-forming resin (A1) used as needed in an aqueous medium. The pigment dispersant can be a resin having a structure containing a pigment-affinitive part and a hydrophilic part. As the pigment-affinitive part and the hydrophilic part, for example, nonionic, cationic, and anionic functional groups can be cited. The pigment dispersant can have two or more of the above-mentioned functional groups in one molecule.

[0153] As the nonionic functional group, for example, a hydroxyl group, an amide group, a polyoxyalkylene group, etc. can be cited. As the cationic functional group, for example, an amino group, an imino group, a hydrazino group, etc. can be cited. In addition, as the anion functional group, for example, a carboxyl group, a sulfo group, a phosphoric acid group, etc. can be cited. Such a pigment dispersant can be manufactured by a method well known to those skilled in the art.

[0154] The pigment dispersant is not particularly limited as long as it does not contain a volatile basic substance or the content is 3% by mass or less in its solid content. It is preferable to be able to effectively disperse the pigment with a small amount of the pigment dispersant. Commercially available products can be used as the pigment dispersant. As examples of commercially available products, for example, Disperbyk-180, Disperbyk-190 (both manufactured by BYK-Chemie), EFKAPOLYMER4550 (manufactured by BASF), EFKAPOLYMER4585 (manufactured by BASF) as an anionic / nonionic dispersant; Solsperse27000 (manufactured by Avecia) as a nonionic dispersant; Solsperse 41000, Solsperse 53095 (both manufactured by Avecia) as an anionic dispersant; Disperbyk-2015 (manufactured by BYK-Chemie) as a polymer copolymer, etc. can be cited.

[0155] The weight-average molecular weight of the pigment dispersant is preferably 1,000 or more and 100,000 or less, more preferably 2,000 or more and 100,000 or less, and still more preferably 4,000 or more and 50,000 or less.

[0156] The pigment dispersion paste can be prepared by mixing and dispersing a pigment dispersant, a pigment, and a part of the film-forming resin (A1) used as needed according to a known method. The proportion of the pigment dispersant in the pigment dispersion paste during the production of the pigment dispersion paste is preferably 1% by mass or more and 50% by mass or less based on the solid content of the pigment dispersion paste. By making the proportion of the pigment dispersant within the above range, the pigment dispersion stability and the physical properties of the resulting coating film can be maintained within a better range. The above proportion of the pigment dispersant is more preferably 3% by mass or more, and more preferably 5% by mass or less.

[0157] The first base coating composition of the present disclosure preferably contains an aqueous medium. The aqueous medium in the present disclosure can be water; a hydrophilic solvent; a mixture of water and a hydrophilic solvent. Examples of the above hydrophilic solvent include glycol solvents such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, and triethylene glycol; glycol ether solvents such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol monoethyl ether; alcohol solvents such as methanol, ethanol, isopropyl alcohol, and benzyl alcohol; cyclic ether solvents such as dioxane and tetrahydrofuran; ketone solvents such as acetone; and N-methyl-2-pyrrolidone.

[0158] (Other components)

[0159] In the first base coating composition, on the basis of containing the above components, additives commonly used by those skilled in the art can be included within a range that does not affect the coating film performance and the coating film appearance. Examples of the above additives include pigments such as extender pigments, coloring pigments, and rust-inhibiting pigments; anti-sagging and anti-settling agents; curing catalysts (organometallic catalysts); anti-color separation agents; dispersants; defoaming and anti-cratering agents; surface modifiers; viscosity modifiers; thickeners; leveling agents; matting agents; antioxidants; ultraviolet light protectants; plasticizers; film-forming aids; defoamers; and organic compounds containing a phosphate group.

[0160] Examples of the above extender pigments include titanium oxide, calcium carbonate, barium sulfate, barium carbonate, magnesium silicate, clay, talc, silica, and calcined kaolin.

[0161] (Viscosity modifier)

[0162] The first base coating composition of the present disclosure preferably contains a viscosity modifier. By including the viscosity modifier, thixotropy is imparted to the first base coating composition, the coating workability becomes good, and the appearance of the obtained multilayer coating film becomes good.

[0163] Examples of the viscosity modifier include organic viscosity modifiers and inorganic viscosity modifiers. Examples of the organic viscosity modifiers include crosslinked or non-crosslinked resin particles; swelling dispersions of fatty acid amides, amide-based fatty acids, polyamide-based viscosity modifiers such as phosphates of long-chain polyaminoamides; polyethylene-based viscosity modifiers such as colloidal swelling dispersions of polyethylene oxide. Examples of the inorganic viscosity modifiers include organophilic montmorillonite clays such as organic bentonite viscosity modifiers of organic acid montmorillonite clay, montmorillonite, etc.

[0164] Examples of the above thickeners include, for example, associative nonionic urethane thickeners, alkali-swellable thickeners, bentonite as an inorganic intercalation compound, etc.

[0165] In the first base coating composition, the solid content concentration (total content rate of the solid content) is 15% by mass or more and 40% by mass or less, more preferably 18% by mass or more and 35% by mass or less, and still more preferably 20% by mass or more and 30% by mass or less.

[0166] The above first base coating composition can be manufactured by a method commonly used by those skilled in the art, such as kneading / dispersing the film-forming resin (A1) and the curing agent (B1), and the coloring pigment (C1), brightening pigment, other components, and additives used as needed, using a disperser, homogenizer, kneader, etc.

[0167] In the above manufacturing method, for example, it is preferable to prepare in advance a paste containing the coloring pigment (C1) or the brightening pigment and a pigment dispersant used as needed and mix them. As the pigment dispersant, the above-mentioned commercially available pigment dispersants, etc. can be used.

[0168] (First transparent layer)

[0169] The above first transparent layer is preferably disposed between the above first base layer and the above second base layer. By including the first transparent layer, unevenness and the like caused by the first base coating film can be smoothed, the first base coating film can be protected, and aesthetics can be imparted. In one aspect, the multilayer coating film of the present disclosure includes the first transparent layer, and in other aspects, the multilayer coating film of the present disclosure does not include the first transparent layer.

[0170] The thickness of the above first transparent layer is preferably 15 μm or more and 40 μm or less, more preferably 20 μm or more and 30 μm or less.

[0171] The above-mentioned first transparent layer can be formed from a first transparent coating composition. As the above-mentioned first transparent coating composition, a transparent coating composition containing a film-forming resin, a curing agent, etc. can be used. If it is within the range that does not interfere with the design of the substrate, a coloring component can also be contained. In addition, in order to obtain a film having a desired gloss (gloss value, for example, from full gloss to full matte), a matting agent can also be contained. As the form of the transparent coating composition, solvent-based, water-based, and powder-based types can be cited.

[0172] As a preferred example of the solvent-based transparent coating composition, from the viewpoints of transparency, acid etching resistance, etc., a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate, or a carboxylic acid / acrylic resin having an epoxy curing system and / or a polyester resin, etc. can be cited.

[0173] As an example of the water-based transparent coating composition, a composition containing a resin obtained by neutralizing the film-forming resin contained in the substances cited as examples of the above-mentioned solvent-based transparent coating with a base to make it water-based can be cited. This neutralization can be carried out by adding a tertiary amine such as dimethylethanolamine and triethylamine before or after polymerization.

[0174] As the powder-based transparent coating composition, ordinary powder coatings such as thermoplastic and thermosetting powder coatings can be used. In order to obtain a film having good physical properties, a thermosetting powder coating is preferred. As a specific example of the thermosetting powder coating, powder transparent coating compositions such as epoxy-based, acrylic-based, and polyester-based can be cited, and an acrylic-based powder transparent coating composition having good weather resistance is particularly preferred.

[0175] In order to ensure the coating workability, the first transparent coating composition is preferably added with a viscosity control agent. As the viscosity control agent, a substance that generally exhibits thixotropy can be used. As such a substance, for example, publicly known substances can be used. The first transparent coating composition can contain a curing catalyst, a surface modifier, etc. as needed.

[0176] (Second base layer)

[0177] The second base layer is laminated on the first base layer. The above-mentioned second base layer can be directly in contact with and laminated on the first base layer, or can be laminated on the first base layer via another layer provided on the first base layer, such as the first transparent layer. The second base layer can, for example, impart a gloss feeling to the multilayer film, but is not limited thereto.

[0178] The transmittance of the above-mentioned second base layer in the visible light region is 60% or more, preferably 65% or more and 100% or less, more preferably 70% or more and 100% or less, and further preferably 75% or more and 100% or less.

[0179] The above-mentioned second base layer contains a brightening pigment (C2). Examples of such brightening pigments include metallic brightening pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, and their alloys; mica pigments such as interference mica pigments and muscovite pigments; graphite pigments; and glass flake pigments. From the viewpoint of imparting transparency to the resulting multilayer coating film, the above-mentioned second base layer preferably contains mica pigments.

[0180] Among the above-mentioned brightening pigments (C2), in the total 100% by mass of the solid content of the brightening pigment (C2), the content of the mica pigment is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and still more preferably 95% by mass or more and 100% by mass or less.

[0181] The average particle size of the above-mentioned brightening pigment (C2) is preferably 1 μm or more and 30 μm or less, more preferably 5 μm or more and 25 μm or less. The average thickness of the above-mentioned brightening pigment (C1) is preferably 0.01 μm or more and 6 μm or less, more preferably 0.1 μm or more and 5 μm or less.

[0182] When the above-mentioned brightening pigment (C2) is an aluminum pigment, surface treatment can be carried out as needed. Examples of surface treatments that can be carried out on aluminum pigments include surface treatment using metal oxide-based compounds, surface treatment using phosphorus compounds, surface treatment using amine compounds, surface treatment using silane compounds, etc. As the above-mentioned metal oxide-based compounds, the above-mentioned phosphorus compounds, the above-mentioned amine compounds, and the above-mentioned silane compounds, the same compounds as those exemplified in the description of the brightening pigments used in the above-mentioned first base coating composition can be used. The above-mentioned surface treatment can be carried out under treatment conditions commonly used by those skilled in the art. The above-mentioned surface treatment can be carried out only one kind, or two or more kinds can be used in combination.

[0183] As the above-mentioned brightening pigment, commercially available products can be used. Examples of commercially available products include Alpaste 93-0647, 06-0672, TCR-2020, MG1000, etc. (all manufactured by Toyo Aluminium Co., Ltd.), and Alumin Paste MH-9901, etc. (manufactured by Asahi Kasei Corporation), etc.

[0184] In the second base layer, in 100 parts by mass of the solid content of the second base layer, the content of the brightening pigment (C2) is preferably 0.1 part by mass or more and 15 parts by mass or less, more preferably 0.5 part by mass or more and 10 parts by mass or less, and still more preferably 1 part by mass or more and 5 parts by mass or less.

[0185] In the second base layer, in 100 parts by mass of the solid components of the second base layer, the content of mica pigment is preferably 0.1 part by mass or more and 15 parts by mass or less, more preferably 0.5 part by mass or more and 10 parts by mass or less, and still more preferably 1 part by mass or more and 5 parts by mass or less.

[0186] The above-mentioned second base layer may contain a coloring pigment. As this coloring pigment, the same pigments as those exemplified as the coloring pigments optionally contained in the above-mentioned first base layer can be used.

[0187] In the second base layer, in 100 parts by mass of the total amount of the solid components of the second base layer, the content of the coloring pigment is preferably 2 parts by mass or less, more preferably 0.001 part by mass or more and 1 part by mass or less, and still more preferably 0.01 part by mass or more and 0.1 part by mass or less. By making the content of the coloring pigment in the second base layer within this range, the transparency and hue variability become good.

[0188] In the above-mentioned second base layer, the content of the black pigment is preferably small. For example, in the above-mentioned second base layer, in 100 parts by mass of the total amount of the solid components of the second base layer, the content of the black pigment is preferably 0 part by mass or more and 0.1 part by mass or less, more preferably 0 part by mass or more and 0.05 part by mass or less, and still more preferably 0 part by mass or more and 0.001 part by mass or less. By making the content of the black pigment within this range, it is easy to improve the transparency of the obtained multilayer coating film.

[0189] The thickness of the aforementioned second base layer is, for example, 0.1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and for example, 50 μm or less, preferably 30 μm or less, more preferably 20 μm or less.

[0190] The above-mentioned second base layer can be formed using a second base coating composition. The second base coating composition contains a film-forming resin (A2) and a curing agent (B2). In one mode, the above-mentioned second base coating composition further contains a brightening pigment (C2). In this mode, the second base coating composition may or may not contain a coloring pigment. In other modes, the above-mentioned second base coating composition does not contain a brightening pigment (C2). In this mode, the second base coating composition may or may not contain a coloring pigment.

[0191] (Film-forming resin (A2))

[0192] The above-mentioned film-forming resin (A2) is a resin capable of forming a film by reacting with a curing agent (B2) described later, and any of the resins described as the film-forming resin (A1) can be used. The resin composition of the film-forming resin (A1) and the resin composition of the film-forming resin (A2) may be the same or different.

[0193] The above film-forming resin (A2) preferably contains an acrylic resin, and more preferably contains an aqueous acrylic resin dispersion. By making both the film-forming resin (A1) and the film-forming resin (A2) contain an acrylic resin, and by making the film-forming resin (A2) contain an acrylic resin, various physical properties such as the storage stability of the resulting coating composition, the water resistance and weather resistance of the resulting film become good. In addition, the adhesion between the first base film and the second base film becomes good. As the above acrylic resin and aqueous acrylic resin dispersion, the resins and aqueous dispersions described as the acrylic resin and aqueous acrylic resin dispersion in the film-forming resin (A1) can be used, and they can be manufactured by the same method.

[0194] In the film-forming resin (A2), the acrylic resin contained in the aqueous acrylic resin dispersion may be in the form of particles, and the average particle size of the particles is preferably 0.01 μm or more and 1.0 μm or less.

[0195] In the film-forming resin (A2), the acrylic resin contained in the aqueous acrylic resin dispersion may be core-shell type particles.

[0196] In the film-forming resin (A2), the acid value of the acrylic resin contained in the aqueous acrylic resin dispersion is preferably 1 mgKOH / g or more and 80 mgKOH / g or less, more preferably 2 mgKOH / g or more and 70 mgKOH / g or less, and further preferably 3 mgKOH / g or more and 60 mgKOH / g or less.

[0197] In the film-forming resin (A2), the hydroxyl value of the acrylic resin contained in the aqueous acrylic resin dispersion is preferably 30 mgKOH / g or more and 120 mgKOH / g or less, more preferably 35 mgKOH / g or more and 100 mgKOH / g or less. By being within the above range, there is an advantage that the curing reaction proceeds sufficiently and the hardness of the resulting film becomes good.

[0198] In the film-forming resin (A2), the weight average molecular weight of the acrylic resin contained in the aqueous acrylic resin dispersion is preferably 50,000 or more and 5,000,000 or less, more preferably 50,000 or more and 1,000,000 or less. By being within the above range, there is an advantage that various properties such as the hardness, adhesion, and water resistance of the resulting film become good.

[0199] In the solid content of the above film-forming resin (A2), the content of the solid content of the acrylic resin aqueous dispersion is preferably 20% by mass or more and 90% by mass or less, more preferably 25% by mass or more and 85% by mass or less, and further preferably 30% by mass or more and 80% by mass or less. By being within the above range, there are advantages that the curing reaction proceeds sufficiently and the hardness of the obtained film becomes good.

[0200] In the above second base coating composition, the content of the solid content of the above polyol resin is preferably 1 part by mass or more and 90 parts by mass or less, more preferably 10 parts by mass or more and 70 parts by mass or less, and further preferably 30 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass in total of the solid content of the above acrylic resin aqueous dispersion.

[0201] In the above second base coating composition, the content of the solid content of the above polyester resin aqueous dispersion is preferably 20 parts by mass or more and 80 parts by mass or less, more preferably 30 parts by mass or more and 70 parts by mass or less, and further preferably 40 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass in total of the solid content of the above acrylic resin aqueous dispersion.

[0202] The above film-forming resin (A2) preferably has a hydroxyl group. The hydroxyl value of the film-forming resin (A2) is preferably 30 mgKOH / g or more and 120 mgKOH / g or less, more preferably 35 mgKOH / g or more and 100 mgKOH / g or less. By being within the above range, there are advantages that the curing reaction proceeds sufficiently and the hardness of the obtained film becomes good.

[0203] In 100% by mass of the solid content of the aqueous second base coating composition, the content of the solid content of the above film-forming resin (A2) is preferably 10% by mass or more and 90% by mass or less, more preferably 15% by mass or more and 85% by mass or less, and further preferably 20% by mass or more and 80% by mass or less.

[0204] (Curing agent (B2))

[0205] The above curing agent (B2) can be a compound having two or more groups capable of reacting with the film-forming resin (A2) in one molecule, and belongs to the film-forming components together with the film-forming resin (A2). As the above curing agent (B2), the compounds described as the curing agent (B1) can all be used. The curing agent (B1) and the curing agent (B2) can be the same or different.

[0206] In one mode, the above-mentioned curing agent (B2) preferably contains an amino resin, and more preferably contains a melamine resin. By containing the melamine resin, a coating film can be formed by means of the self-polymerization of the melamine resin and the reaction between the amino group contained in the melamine resin and the hydroxyl group that may be contained in the coating film-forming resin (A2).

[0207] In the total 100% by mass of the solid content of the above-mentioned curing agent (B2), the content of the solid content of the above-mentioned melamine resin may be 0% by mass, preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and further preferably 95% by mass or more and 100% by mass or less.

[0208] In the total 100 parts by mass of the solid content of the above-mentioned coating film-forming resin (A2) and the solid content of the curing agent (B2), the content of the above-mentioned melamine resin may be 0 parts by mass, preferably 10 parts by mass or more and 80 parts by mass or less, and further may be 20 parts by mass or more and 70 parts by mass or less. Thus, there is an advantage that various physical properties such as the hardness, adhesion, and water resistance of the obtained coating film become good.

[0209] In the total 100% by mass of the solid content of the coating film-forming resin (A2) and the solid content of the curing agent (B2), the content of the solid content of the curing agent (B2) in the aqueous second base coating composition is preferably 20% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less.

[0210] (Brightening pigment (C2))

[0211] The brightening pigment (C2) has the same meaning as the brightening pigment (C2) that may be contained in the second base layer.

[0212] The second base coating composition of the present disclosure contains an aqueous medium. This aqueous medium has the same meaning as the aqueous medium that may be contained in the first base coating composition.

[0213] (Other components)

[0214] In the second base coating composition, on the basis of containing the above-mentioned components, additives commonly used by those skilled in the art may be contained within a range that does not affect the coating film performance and coating film appearance. As the above-mentioned additives, one or more substances such as those used in the first base coating composition may be appropriately contained.

[0215] (Viscosity regulator)

[0216] The second base coating composition of the present disclosure preferably contains a viscosity regulator. The viscosity regulator may appropriately contain one or more substances used as the first base coating composition.

[0217] The above-mentioned second base layer preferably contains a coloring pigment. As such a coloring pigment, one or more substances used in, for example, the first base coating composition can be appropriately included.

[0218] As the above-mentioned extender pigment, one or more substances used in, for example, the first base coating composition can be appropriately included.

[0219] As the above-mentioned pigment, from the viewpoint of improving weather resistance and ensuring hiding power, a coloring pigment is preferred. In particular, titanium dioxide is more preferred because of its excellent coloring and hiding properties and low price. In addition, as the pigment, a standard gray coating composition having carbon black and titanium dioxide as main pigments can be used. In addition to this, a coating composition having a lightness or hue matching that of the second base coating composition and a coating composition combining various coloring pigments can also be used. The first base coating composition of the present disclosure can function as a primer when coating the second base coating composition, and can also function as a colored base by containing a coloring pigment.

[0220] The above-mentioned brightening pigment (C2) and the above-mentioned coloring pigment can be used for preparing the second base coating composition after being made into a pigment dispersion paste. The pigment dispersion paste can be obtained by previously dispersing at least a small amount of a pigment, a pigment dispersant, and a part of a film-forming resin (A2) used as required in an aqueous medium. As the pigment dispersant, the compounds and materials described as the pigment dispersants that can be used in the first base coating composition can all be used.

[0221] Examples of the above-mentioned thickener include associative nonionic urethane thickeners, alkali-swellable thickeners, bentonite as an inorganic intercalation compound, and the like.

[0222] In the second base coating composition, the solid content concentration is 15% by mass or more and 40% by mass or less, preferably 18% by mass or more and 35% by mass or less, more preferably 20% by mass or more and 30% by mass or less.

[0223] The above-mentioned second base coating composition can be manufactured by a method commonly used by those skilled in the art, such as kneading / dispersing the film-forming resin (A2), the curing agent (B2), and, if necessary, the brightening pigment (C2), other components, and additives using a disperser, a homogenizer, a kneader, etc.

[0224] In the above-mentioned manufacturing method, for example, it is preferred to previously prepare a paste containing the brightening pigment (C2) and a pigment dispersant used as required and mix them. As the pigment dispersant, the above-mentioned commercially available pigment dispersants and the like can be used.

[0225] (Second transparent layer)

[0226] The above-mentioned second transparent layer is preferably laminated on the above-mentioned second base layer. By including the second transparent layer, unevenness and the like caused by the second base coating film can be smoothed, the second base coating film can be protected, and aesthetics can be imparted. In one aspect, the multilayer coating film of the present disclosure includes a second transparent layer.

[0227] The thickness of the above-mentioned second transparent layer is 10 μm or more and 80 μm or less, preferably 20 μm or more and 60 μm or less. By making the thickness of the second transparent layer within this range, unevenness can be sufficiently masked, and defects such as craters or runs during coating can be suppressed.

[0228] The above-mentioned second transparent layer can be formed from a second transparent coating composition. As the above-mentioned second transparent coating composition, a transparent coating composition containing a film-forming resin, a curing agent, and the like can be used. If it is within the extent that does not interfere with the substrate design, a coloring component can also be included. In addition, in order to obtain a coating film with a desired gloss (gloss value, for example, full gloss to full matte), a matting agent can also be included. As the form of the transparent coating composition, solvent-based, water-based, and powder-based types can be cited.

[0229] As a preferred example of the solvent-based transparent coating composition, from the viewpoints of transparency or acid etching resistance, etc., a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate, or a carboxylic acid / acrylic resin having an epoxy curing system and / or a polyester resin, etc. can be cited.

[0230] As an example of the water-based transparent coating composition, a composition containing a resin obtained by neutralizing the film-forming resin contained in the substances cited as examples of the above-mentioned solvent-based transparent coating with a base to make it water-based can be cited. This neutralization can be carried out by adding a tertiary amine such as dimethylethanolamine and triethylamine before or after polymerization.

[0231] As the powder-based transparent coating composition, ordinary powder coatings such as thermoplastic and thermosetting powder coatings can be used. In order to obtain a coating film with good physical properties, a thermosetting powder coating is preferred. As a specific example of the thermosetting powder coating, epoxy-based, acrylic-based, and polyester-based powder transparent coating compositions, etc. can be cited, and an acrylic-based powder transparent coating composition with good weather resistance is particularly preferred.

[0232] In order to ensure coating workability, the second transparent coating composition is preferably added with a viscosity control agent. As the viscosity control agent, substances that generally exhibit thixotropy can be used. As such substances, for example, publicly known substances can be used. The first transparent coating composition can contain a curing catalyst, a surface modifier, etc. as needed.

[0233] The absolute value |h2 - h1| of the difference between the hue h1 of the first base layer and the hue h2 of the multi-layer coating film is preferably 20 or less, more preferably 0 or more and 5 or less, and still more preferably 0 or more and 3 or less. By making the absolute value of the hue difference fall within this range, it becomes easy to obtain the target hue and the coating workability becomes good.

[0234] In the present disclosure, the hue is a parameter in the L*C*H* colorimetric system and can be measured in accordance with JIS Z8729. In addition, the hue h1 of the first base layer can be measured in a state where the first base layer is formed on the intermediate coat before forming the second base layer.

[0235] The chroma C1 of the first base layer is preferably 30 or more, more preferably 45 or more and 100 or less, and still more preferably 60 or more and 100 or less. By making the chroma of the first base layer fall within this range, the chroma of the obtained multi-layer coating film can be improved.

[0236] The chroma C1 of the multi-layer coating film is preferably 30 or more, more preferably 45 or more and 100 or less, and still more preferably 60 or more and 100 or less.

[0237] In the present disclosure, the chroma can be measured in accordance with JIS Z8729 in the same manner as the hue.

[0238] The specular gloss value Si15 of the multi-layer coating film is preferably 15 or more.

[0239] (Method for manufacturing a multi-layer coating film)

[0240] The multi-layer coating film of the present disclosure includes:

[0241] A step of coating an intermediate coat coating composition on an object to be coated to form an intermediate coat;

[0242] A first base coating film forming step of coating a first base coating composition on the intermediate coat to form a first base coating film;

[0243] A second base coating film forming step of coating an aqueous second base coating composition on the first base coating film to form a second base coating film; and

[0244] A heat curing step of heat curing at least the first base coating film and the second base coating film to form a multi-layer coating film.

[0245] For example, the intermediate coat can be formed by applying an intermediate coat paint composition to form an intermediate coat paint film, and the intermediate coat is formed by heating and curing the intermediate coat paint film. The heating temperature and time for heating and curing the intermediate coat paint film can be appropriately selected according to the composition of the paint composition (aqueous or solvent-based) and the type of the object to be coated. The heating temperature can be appropriately selected, for example, in the range of 80 to 180°C, preferably in the range of 100 to 160°C. The heating time can be appropriately selected, for example, in the range of 5 minutes to 60 minutes, preferably in the range of 10 minutes to 30 minutes.

[0246] The temperature for preheating the intermediate coat paint film can be, for example, 30 to 80°C, and the preheating time can be, for example, 1 minute to 60 minutes.

[0247] As the above-mentioned object to be coated, it can be used for various substrates, such as metal molded products, plastic molded products, foams, etc. The aqueous base paint composition of the present disclosure can be applied to the exterior panel coating of automotive bodies, automotive parts, etc. As the metal molded product, for example, plates and molded products made of iron, copper, aluminum, tin, zinc, etc. and alloys containing these metals can be cited. Specifically, automotive bodies and parts such as sedans, trucks, motorcycles, buses, etc. can be cited.

[0248] The above-mentioned metal molded product can be subjected to chemical conversion treatment with phosphates, zirconium salts, chromates, etc. in advance, and then an electrodeposition paint film is formed as the undercoat. As the electrodeposition paint composition that can be used to form the electrodeposition paint film, cationic electrodeposition paint compositions and anionic electrodeposition paint compositions can be cited.

[0249] As the above-mentioned plastic molded product, for example, plates and molded products of polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, etc. can be cited. As specific examples of plastic molded products, automotive parts such as splash guards, bumpers, rearview mirror covers, grilles, door handles, etc. can be cited. Among these plastic molded products, as the undercoat, primer coating for enabling electrostatic coating can be applied.

[0250] The above-mentioned first base paint composition and second base paint composition can be used to coat the object to be coated by methods commonly used in the paint field. As the coating method, for example, air spray coating, airless spray coating, electrostatic spray coating, multi-stage coating based on air-electrostatic spray coating (preferably two-stage coating), coating combining air-electrostatic spray coating with a rotary atomizing electrostatic coater, etc. can be cited.

[0251] When applying and heat-curing the above first base coating composition and second base coating composition, the heating temperature and time can be appropriately selected according to the composition of the coating composition (aqueous or solvent-based) and the type of the object to be coated. The heating temperature can be appropriately selected, for example, in the range of 80 to 180 °C, preferably in the range of 100 to 160 °C. The heating time can be appropriately selected, for example, in the range of 5 minutes to 60 minutes, preferably in the range of 10 minutes to 30 minutes.

[0252] When preheating the first base coating film or the second base coating film, the temperature can be, for example, 30 to 80 °C, and the preheating time can be, for example, 1 minute to 60 minutes.

[0253] The above first base coating composition is preferably applied in such a manner that the dry film thickness t1 of the cured first base coating film is in the range of 8 to 20 μm, more preferably in the range of 10 to 15 μm. In addition, the second base coating composition is preferably applied in such a manner that the dry film thickness of the cured second base coating film t2 is in the range of 8 to 20 μm, more preferably in the range of 10 to 15 μm.

[0254] The above manufacturing method may further include: a first transparent coating film forming step of applying a first transparent coating on the first base coating film to form a first transparent coating film after forming the first base coating film and before forming the second base coating film. That is, the uncured first base coating film may not be heat-cured, and a transparent coating is applied thereon by wet-on-wet to form an uncured first transparent coating film. In the heat-curing step, the uncured first base coating film and the first transparent coating film can be heat-cured simultaneously to form a multilayer coating film including a first base layer and a first transparent layer. By forming the first transparent coating film, the unevenness and the like caused by the first base coating film can be smoothed, protection can be carried out, and beauty can be imparted.

[0255] The above manufacturing method may further include: a second transparent coating film forming step of applying a second transparent coating on the second base coating film to form a second transparent coating film after forming the second base coating film and before heat-curing. That is, the uncured second base coating film may not be heat-cured, and a transparent coating is applied thereon by wet-on-wet to form an uncured second transparent coating film. In the heat-curing step, the uncured second base coating film and the second transparent coating film can be heat-cured simultaneously to form a multilayer coating film including a second base layer and a second transparent layer. By forming the second transparent coating film, the unevenness and the like caused by the second base coating film can be smoothed, protection can be carried out, and beauty can be imparted. The above manufacturing method may include both the first transparent coating film forming step and the second transparent coating film forming step.

[0256] As a method of applying a clear coating material, a coating method using a rotary atomization type electrostatic coating machine called MICRO MICRO BELL or MICRO BELL can be mentioned.

[0257] When the clear coating film forming step is included, the heat curing temperature in the heat curing step is preferably 80 to 180° C., more preferably 120 to 160° C., from the viewpoint of curability and physical properties of the obtained multilayer coating film. The heat curing time can be arbitrarily set according to the above temperature, and the heat curing temperature is 80 to 160° C. and the time is 10 to 30 minutes.

[0258] The multilayer coating film disclosed in the present invention has a glossy feel and can achieve both hiding power and chroma of the coating film, and can be preferably used for coating of automobile bodies and the like.

[0259] Example

[0260] The present invention will be described in more detail below with reference to the following examples, but the present invention is not limited thereto.

[0261] [Example 1]

[0262] (I) Preparation of the object to be coated

[0263] As a coating object, a zinc phosphate treated steel sheet having a cured electrodeposition coating film was prepared. The cured electrodeposition coating film can be formed by applying a cationic electrodeposition coating composition "Panicon" manufactured by Nippon Pent Corporation to the zinc phosphate treated steel sheet by electrodeposition coating to a dry film thickness of 20 μm, and then heating at 160° C. for 30 minutes.

[0264] (II) Preparation of coating

[0265] (II-1) Preparation of midcoat

[0266] 51.0 parts by mass of a thermosetting polyester resin (manufactured by Nippon Pent Co., Ltd., with a hydroxyl value of 80, an acid value of 8 mgKOH / g, a number average molecular weight of 1800, and a solid content of 70% by mass) and 49 parts by mass of a titanium dioxide pigment "CR-97" (manufactured by Ishihara Sangyo Co., Ltd.) were added and uniformly dispersed, and then 25.5 parts by mass of a melamine resin "Yuban 128" (manufactured by Mitsui Science Co., Ltd., with a solid content of 60% by mass) were added and uniformly dispersed to obtain a white mid-coat paint.

[0267] (II-2) Preparation of base coating composition

[0268] In the preparation of the base coating composition, an aqueous resin composition mixed with the following (1) to (9) is used.

[0269] Prepare a base coating composition containing the following components:

[0270] (1) 236 parts of an acrylic emulsion resin manufactured by Nippon Paint Co., Ltd. (average particle size: 150 nm, non-volatile content: 20% by mass, solid component acid value: 20 mg KOH / g, hydroxyl value: 40 mg KOH / g);

[0271] (2) 10 parts by mass of a 10% by mass aqueous solution of dimethylethanolamine;

[0272] (3) 28.3 parts by mass of a water-soluble acrylic resin manufactured by Nippon Paint Co., Ltd. (non-volatile content: 30% by mass, solid component acid value: 40 mg KOH / g, hydroxyl value: 50 mg KOH / g);

[0273] (4) 8.6 parts by mass of "Primepole PX-1000" manufactured by Sanyo Chemical Industries, Ltd. (bifunctional polyether polyol, number average molecular weight: 400, hydroxyl value: 278 mg KOH / g, primary hydroxyl / secondary hydroxyl value ratio = 63 / 37, non-volatile content: 100%);

[0274] (5) 21.5 parts by mass of "CYMEL 204" manufactured by Mitsui Chemicals, Inc. (mixed alkylated melamine resin, non-volatile content: 100% by mass);

[0275] (6) 26 parts by mass of "Neorets R-9603" manufactured by Avecia Co., Ltd. (polycarbonate-based urethane emulsion resin, non-volatile content: 33% by mass);

[0276] (7) 0.2 part by mass of lauryl acid phosphate;

[0277] (8) 10 parts by mass of 2-ethylhexanol;

[0278] (9) 25 parts by mass of mono-2-ethylhexyl ether,

[0279] The total of the solid component mass of the film-forming resin and the solid component mass of the curing agent in the above aqueous resin composition (the solid component amount of the main resin) is 100 parts by mass.

[0280] Add the pigments shown in Table 1 to the above aqueous resin composition so as to achieve the contents (PWC) shown in Table 1, to obtain a first base coating composition and a second base coating composition.

[0281] The mass concentration of the pigment is calculated by the following formula:

[0282] The mass concentration of pigment (PWC) = (mass of pigment) / [(total mass of resin solid components of film-forming resin, resin solid components of curing agent, and solid components of additives) + (total mass of pigment)] × 100 (%).

[0283] (II-3) Preparation of transparent coating

[0284] As the transparent coating, an acid epoxy-curing type transparent coating (trade name: Mac Flow O-1820 Clear, manufactured by NIPPON PAINT AUTOMOTIVE COATINGS Co., Ltd.) was prepared.

[0285] (III) Formation of multi-layer coating film

[0286] Using an air spray gun W-101-132G manufactured by Anest Iwata Co., Ltd., the intermediate coating (pre-diluted to 25 seconds (measured at 20 °C using a No. 4 Ford cup)) was air spray-coated on the object to be coated so that the dry film thickness became 35 μm. The coated panel was heated at 140 °C for 30 minutes using a dryer to obtain a coated article with an intermediate coating film.

[0287] Next, the first base coating was air spray-coated at a dry film thickness of 15 μm under the conditions of a room temperature of 23 °C and a humidity of 68%. After 3 minutes of setting, preheating was carried out at 80 °C for 4 minutes. The coated panel was cooled to room temperature, and the transparent coating was air spray-coated at a dry film thickness of 25 μm, followed by 7 minutes of setting. The coated panel was heated at 140 °C for 30 minutes using a dryer to obtain a coated article with the first base layer.

[0288] Next, the second base coating was air spray-coated at a dry film thickness of 15 μm under the conditions of a room temperature of 23 °C and a humidity of 68%. After 3 minutes of setting, preheating was carried out at 80 °C for 4 minutes. The coated panel was cooled to room temperature, and the transparent coating was air spray-coated at a dry film thickness of 35 μm, followed by 7 minutes of setting. Finally, the coated panel was heated at 140 °C for 30 minutes using a dryer to obtain a coated article with a multi-layer coating film.

[0289] (IV) Evaluation

[0290] The following evaluations were carried out on the coated articles. The results of evaluations (1) to (6) are shown in Table 1.

[0291] (1) Lightness L*45

[0292] Using a spectrophotometer (BYK Gardner Co., Ltd., BYK-mac i), the lightness L*45 of the intermediate coating was obtained.

[0293] (2) Chroma C*45

[0294] Using a spectrophotometer (manufactured by BYK Gardner, model: BYK-mac i), obtain the lightness C*45 of the first base layer and the multi-layer coating film.

[0295] (3) Glossiness Si15 value

[0296] Using a spectrophotometer (manufactured by BYK Gardner, model: BYK-mac i), obtain the glossiness Si15 value of the multi-layer coating film.

[0297] (4) Hue h15

[0298] Using a spectrophotometer (manufactured by BYK Gardner, model: BYK-mac i), obtain h15. Set the hue of the first base coating film as h1 and the hue of the multi-layer coating film as h2, and calculate the difference h1 - h2.

[0299] (5) Transmittance in the visible light region

[0300] Regarding the light transmittance of the first base coating film and the second base coating film alone, using a spectrophotometer (manufactured by Hitachi, trade name: U-4100), in the wavelength range of 400 - 700 nm, measure under the conditions of wavelength scanning mode, scanning speed of 60 nm / minute, and sampling interval of 2 nm. The average transmittance is obtained by averaging the transmittance every 10 nm.

[0301] (6) Color stability when the thickness of the masking film changes

[0302] Produce a coated article with a multi-layer coating film whose film thickness of the base coating film changes by ±20%, compare it with the coated article produced with the normal film thickness, and visually evaluate whether there is a sense of incongruity in color.

[0303] ○: Almost no sense of incongruity

[0304] ×: Sense of incongruity is felt

[0305] [Example 2, Comparative Examples 1 - 7]

[0306] Change the pigment composition in the first base coating and the second base coating to the pigment composition shown in Table 1. Except for this, operate in the same way as in Example 1 to obtain a multi-layer coating film and conduct evaluation.

[0307]

[0308] Examples 1 and 2 are examples of the present disclosure, and it can be confirmed that they have a sense of glossiness and can balance the masking property and chroma of the coating film.

[0309] Comparative Examples 1 and 2 are examples where the lightness at a 45-degree angle of the intermediate coat is less than 80, the color stability when the film thickness varies is insufficient, and the chroma is not sufficiently satisfactory.

[0310] Comparative Example 3 is an example where the transmittance in the visible light region of the second base layer is less than 60%, the color stability when the film thickness varies is insufficient, and the chroma is not sufficiently satisfactory.

[0311] Comparative Example 4 is an example where the second base layer does not contain a brightening pigment, and the coated film does not exhibit a bright feeling.

[0312] Comparative Example 5 is an example where the transmittance of visible light of the first base layer exceeds 30%, the color stability when the film thickness varies is insufficient, and the chroma is not sufficiently satisfactory.

[0313] Industrial Applicability

[0314] The multi-layer coated film of the present disclosure has a bright feeling, can balance the hiding power and chroma of the coated film, and can be preferably used for coating automobile bodies and the like.

Claims

1. A multilayer coating film comprising a midcoat layer, a first base layer laminated on the midcoat layer, and a second base layer laminated on the first base layer, The 45-degree viewing angle brightness L* of the middle coating is greater than 80, The transmittance of the first base layer in the visible light region is greater than or equal to 5% and less than or equal to 30%. The transmittance of the second base layer in the visible light region is greater than 60%. The second base layer contains a bright pigment.

2. The multilayer coating film according to claim 1, wherein An absolute value of a difference between the hue h1 of the first base layer and the hue h2 of the multilayer coating film is 20 or less.

3. The multilayer coating film according to claim 1, wherein The chroma C1 of the first base layer is 60 or more.

4. The multilayer coating film according to claim 1, wherein The chroma C2 of the multilayer coating film is 60 or more.

5. The multilayer coating film according to claim 1, wherein The glossiness Si15 value of the multilayer coating film is greater than 15.

6. The multilayer coating film according to claim 1, wherein The first base layer comprises a coloring pigment, The content of the coloring pigment is 5 parts by mass or more and 60 parts by mass or less in 100 parts by mass of the total solid content of the first base layer.

7. The multilayer coating film according to claim 1, wherein The second base layer comprises a coloring pigment, The content of the coloring pigment is 2 parts by mass or less based on 100 parts by mass of the total solid content of the second base layer.

8. The multilayer coating film according to claim 1, wherein The content of the black pigment in the second base coating film is 0 parts by mass or more and 0.1 parts by mass or less in 100 parts by mass of the total solid content of the second base layer.

9. The multilayer coating film according to claim 1, wherein The content of the mica-based pigment in the second base coating film is 0.1 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the total solid content of the second base layer.

10. The multilayer coating film according to any one of claims 1 to 9, wherein A first transparent layer is further provided between the first base layer and the second base layer. 11 . The multilayer coating film according to claim 10 , further comprising a second transparent layer laminated on the second base layer.

Images