Water-based coating compositions and their applications

Abstract

This disclosure relates to aqueous coating compositions comprising a) a water-soluble or water-dispersible binder; b) cellulose nanofibers; c) a cosolvent; and d) an effect pigment. High effect pigment orientation is achieved based on the low-VOC aqueous coating compositions according to this disclosure. This disclosure further relates to a wet-on-wet method for producing multilayer coating films, and multilayer coating films that can be obtained by this method. This disclosure further relates to a method for using aqueous coating compositions for the production of pigment aqueous coating materials.

Description

[Technical Field]

[0001] This disclosure relates to aqueous coating compositions, coating films, coated articles, and methods for forming multilayer coating films. [Background technology]

[0002] In recent years, coating films with a glossy, pearlescent, and / or metallic appearance have become known and are widely used in fields such as automobiles. Such appearances can often be achieved by the use of one or more effect pigments. The term "effect pigment" refers to inorganic and / or organic pigments used in curable coating compositions to impart appearance or effect to the cured coating composition. The quality of the appearance achieved by the use of one or more effect pigments depends critically on the dispersion of pigment particles in the coating material, the size and shape of the pigment particles, the rheological properties of the coating material, the application of the coating material, and especially the orientation of the pigment particles in the coating layer.

[0003] Basecoat compositions are either water-based or organic solvent-based. Compared to water-based basecoats, organic solvent-based basecoats offer advantages in appearance. Pigment orientation can usually be improved by increasing the amount of volatile organic solvent. However, the use of such solvents increases the volatile organic compounds (VOCs) in the coating composition. Because VOCs have adverse environmental impacts, many government regulations impose limits on the amount of solvents that can be used. As VOC levels decrease, many paint properties become inferior to the original high-VOC versions, and the most typical drawback caused by reduced solvent content is the deterioration of the effective pigment orientation properties of water-based basecoats.

[0004] The current color trend in OEM (Original Equipment Manufacturer) paints is for visually "liquid-like" colors. To achieve this effect, the paint film needs to have extremely high trigger properties. This means that there are higher demands on the orientation control of the effect pigments. The effect pigments in the base coat must exhibit an orientation substantially parallel to the substrate underneath. [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, it is desirable to use coating composition components that provide good pigment orientation to the coating composition without requiring a large amount of solvent. [Means for solving the problem]

[0006] In one embodiment, this disclosure is as follows: a) Water-soluble or water-dispersible binder; b) Cellulose nanofibers; c) Cosolvent of formula (I) [ka] (In the formula, the combinations of X1 and n are (X1, n) = (H, 1) or (CH2-CH-CH2, 3), X2 and X3 are independently selected from a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, where m is an integer from 1 to 30. d) Pigments; We provide an aqueous coating composition containing the following: Here, this aqueous coating composition has a volatile organic compound content of 420 g / l or less without water; A multilayer coating film comprising a base coat layer obtained by applying this aqueous coating composition and a clear coat layer on the base coat layer has a lightness index of 0.20 or higher, where lightness index = (L * 15° -L * 25° ) / L *15° , L * 15° and L * 25° each represent lightness values measured at viewing angles of 15° and 25° according to the L*a*b* color system (CIE lab). * a * b * The foregoing aqueous coating composition is hereinafter also referred to as "the aqueous coating composition of the present disclosure", "the aqueous coating composition according to the present disclosure", "the coating composition of the present disclosure", or "the coating composition according to the present disclosure".

[0007] In another aspect, the present disclosure provides a coating film obtained from the aqueous coating composition of the present disclosure, which has a dry film thickness exceeding 5 μm.

[0008] In another aspect, the present disclosure provides a coated article comprising a cured coating film on an article, wherein the cured coating film is obtained by curing the aqueous coating composition of the present disclosure.

[0009] In another aspect, the present disclosure provides a method for manufacturing a multilayer coating film, comprising the following steps:

[0010] (1) Optionally, applying a coating material onto a substrate and then curing the composition to produce a cured first coating layer on the substrate; (2) Applying one or more identical or different aqueous base coat materials onto the coating layer obtained in step (1) to produce one or more base coat layers; (3) Applying one or more identical or different clear coat materials to produce one or more clear coat layers on one or the topmost base coat layer; and (4) Curing one or more base coat layers and one or more clear coat layers together; and providing a method for manufacturing a multilayer coating film comprising the steps. Here, at least one of the base coat materials is the aqueous coating composition of the present disclosure.

[0011] The aforementioned method for manufacturing a multilayer coated film will also be referred to hereafter as the "method of this disclosure" or the "method according to this disclosure."

[0012] In another embodiment, the Disclosure provides a multilayer coated film obtained by the method of the Disclosure described above.

[0013] In a further embodiment, the Disclosure provides a method for using the aqueous coating composition of the Disclosure for the manufacture of a pigment aqueous coating material.

[0014] Surprisingly, it has been found that highly effective pigment orientation is achieved based on the low-VOC aqueous coating compositions of this disclosure. The aqueous coating compositions of this disclosure have a higher solids content and therefore have higher transfer efficiency and a good environmental profile. The aqueous coating compositions of this disclosure have the advantages of easy preparation, low cost, efficient transfer, and wide application, and for example, different types of effect pigments, particularly non-vapor-deposited metal pigments, can be used in this disclosure. In some preferred embodiments, automotive coatings having a visually "liquid-like" appearance can be obtained using the aqueous coating compositions of this disclosure. In other preferred embodiments, this disclosure can be applied to a wet-to-wet coating process, and the resulting multilayer coating film has good performance with a good balance in appearance and mechanical properties such as hardness.

[0015] Those skilled in the art will understand that the recognized and other advantages described herein are merely illustrative and do not fully represent all the advantages of various embodiments. [Modes for carrying out the invention]

[0016] The following describes the disclosure in more detail, but only a few embodiments are shown, not all embodiments of the disclosure. In fact, the disclosure can be embodied in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided to satisfy the legal requirements to which the disclosure applies.

[0017] In the context of this disclosure, the expressions "a," "an," and "the" include both the plural and singular forms of a term when used to define that term.

[0018] In the context of this disclosure, the terms “contains,” “includes,” etc., are used interchangeably with “contains,” etc., and are to be interpreted in a non-restrictive and open manner. That is, for example, further components or elements may exist. Expressions such as “consist of,” “essentially made from,” or synonyms may be encompassed by “contains” or synonyms, where used.

[0019] In the context of this disclosure, for convenience, the term "resin" is used to encompass resins, oligomers, and polymers. "Binder" refers to the film-forming component of a coating composition. Therefore, resins and other film-forming agents are part of the binder, but crosslinking agents, solvents, pigments, additives such as antioxidants, light stabilizers (e.g., hindered amine light stabilizers, HALS), and UV absorbers are not part of the binder.

[0020] In the context of this disclosure, “CIE lab” means L * a * b * Also known as chromatic achromatic, it is a color space defined in 1976 by the International Commission on Illumination (CIE). Colors are represented by three values: L * represents perceptual brightness, and a * and b * These represent the four colors inherent to human vision: red, green, blue, and yellow.

[0021] In this disclosure, "free organic solvent" means an organic solvent present in a free state within the composition, specifically referring to an organic solvent added to the composition, excluding solvents contained in the resin or additive itself, or solvents present within them. The same applies to "free water."

[0022] In the context of this disclosure, “number-average molecular weight” is determined by gel permeation chromatography of a sample dissolved in tetrahydrofuran using a polystyrene or poly(methyl methacrylate) standard.

[0023] In the context of this disclosure, “solids” means the proportion of nonvolatile substances in a coating, paint, or other suspension that remain after the evaporation of the volatile solvent and water.

[0024] In the context of this disclosure, “acrylic resin” includes acrylic resin and methacrylic resin, “acrylic monomer” includes acrylic monomer and methacrylic monomer, “(meth)acrylate” means acrylate and methacrylate, “(meth)acrylic” means acrylic acid and methacrylic acid, and “(meth)acrylamide” means acrylamide and methacrylamide.

[0025] Throughout this specification, references to “embodiments or examples,” “one embodiment or example,” “another embodiment or example,” “other embodiments or examples,” “several embodiments or examples,” etc., mean that certain elements (e.g., features, structures, characteristics, and / or properties) described in relation to an embodiment / example are included in at least one embodiment / example described herein, and may or may not be present in other embodiments / examples. Furthermore, it should be understood that the element(s) described may be combined in any appropriate manner in various embodiments or examples unless explicitly indicated in the context.

[0026] Coating composition This disclosure is, a) Water-soluble or water-dispersible binder; b) Cellulose nanofibers; c) Cosolvent of formula (I) [ka] (In the formula, the combinations of X1 and n are (X1, n) = (H, 1) or (CH2-CH-CH2, 3), X2 and X3 are independently selected from hydrogen and alkyl groups having 1 to 8 carbon atoms, where m is an integer from 1 to 30); and d) Pigments; The present invention provides an aqueous coating composition containing the following:

[0027] In this disclosure, each component of the aqueous coating composition can be used individually or in combination of two or more components in a desired ratio.

[0028] The term "aqueous coating composition" refers to a coating composition in which more than 50% by mass of the volatile components is water.

[0029] The aqueous coating compositions of this disclosure are more environmentally friendly and have a lower volatile organic compound (VOC) content, which is 420 g / L or less without water (or without water), preferably 410 g / L or less (without water), and more particularly 407 g / L or less (without water). In some preferred embodiments, the aqueous coating compositions have a VOC content of 150 g / L or less (including water), preferably 145 g / L or less (including water), and more particularly 140 g / L or less (including water).

[0030] The aqueous coating compositions of this disclosure have a relatively high solids content. Therefore, it is preferable that the compositions have a solids content of more than 15% by mass, preferably 17-60% by mass, and more particularly 18-50% by mass, measured according to DIN EN ISO 3251 (June 2008) as detailed in the Examples section of this specification, based on the total mass of the coating material in each case. In view of the high solids content, the aqueous coating compositions of this disclosure have high transfer efficiency and a good environmental profile without adversely affecting storage stability. The disclosed compositions have a high solids content while achieving good effective pigment orientation, which is unexpected to those skilled in the art.

[0031] In some preferred embodiments, the aqueous coating composition has a thixotropy value (Ti value) of 40 or less, preferably 36 or less, and more particularly 33 or less, where Ti value = η(A) / η(B), and η(A) is 1000s -1 This is the viscosity under a shear rate of η(B), where η(B) is 1s -1 This is the viscosity under shear rate, measured at 23°C using a rotational viscometer. Low viscosity dependence improves the fluidity of aqueous coating compositions and, consequently, contributes to highly effective pigment orientation.

[0032] The aqueous coating compositions of this disclosure each have a pH, preferably in the range of 4 to 10, more preferably in the range of 5 to 10, even more preferably in the range of 7 to 10, and particularly in the range of 7 to 9, as measured at 23°C in each case.

[0033] Water-soluble or water-dispersible binder The terms "water-soluble or water-dispersible" are well known in the art. The binder can be any suitable for film formation in an aqueous coating composition. Preferably, the water-soluble or water-dispersible binder comprises at least one selected from acrylic resins, polyurethane resins, acrylic-urethane resins, polyester resins, polyether resins, alkyd resins, polycarbonate resins, and epoxy resins. These resins may be used individually or in combination of two or more. Such resins or polymers are well known in the art.

[0034] Here, there are no particular restrictions on the acrylic resin, and it may be either a water-soluble or dispersible acrylic resin. Such resins include monomers such as methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, amyl acrylate, amyl methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl acrylate, 3, These polymers can be prepared from 3,5-trimethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl acrylate or lauryl methacrylate, cycloalkyl acrylates and / or cycloalkyl methacrylates, such as cyclopentyl acrylate, cyclopentyl methacrylate, isobornyl acrylate, isobornyl methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate, and vinyl aromatic hydrocarbons, such as vinyltoluene, α-methylstyrene and styrene, and amides or nitriles, vinyl esters and vinyl ethers of acrylic acid or methacrylic acid. Any crosslinkable functional group, such as hydroxyl, amine, glycidyl, carbamate, etc., can be incorporated into the ester portion of the acrylic monomer. Non-limiting examples of hydroxy-functional acrylic monomers that can be used to form such polymers include hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate and hydroxypropyl acrylate. Examples of amino-functional acrylic monomers include t-butylaminoethyl methacrylate and t-butylaminoethyl acrylate. The glycidyl group can be incorporated, for example, by copolymerizing glycidyl methacrylate or allyl glycidyl ether. Other acrylic monomers having a crosslinkable functional group in the ester portion of the monomer are also within the scope of the art.Modified acrylic resins, such as polyester-modified acrylics, can also be used. Polyester-modified acrylics modified with e-caprolactone are described in U.S. Patent No. 4,546,046 by Etzell et al.

[0035] In one embodiment of the present disclosure, a preferred acrylic resin is typically a hydroxy-containing acrylic resin. The hydroxy-containing acrylic resin may be a copolymer product of a hydroxy-containing polymerizable unsaturated monomer and at least one unsaturated monomer copolymerizable with the hydroxy-containing polymerizable unsaturated monomer, for example, in the form of an aqueous dispersion. Hydroxy-containing polymerizable unsaturated monomers are known in the art and include, for example, monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified compounds of monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a hydroxy-terminated polyoxyethylene chain as described in US9701866B2. There are no particular limitations on the at least one unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, and it can be appropriately selected according to the properties required for the hydroxyl group-containing acrylic resin. Examples of unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer include, but are not limited to, those described in US9701866B2.

[0036] In other embodiments of the present disclosure, the hydroxy-containing acrylic resin has a number average molecular weight of 500 to 20,000, more preferably 1,500 to 10,000. Furthermore, the hydroxy-containing acrylic resin preferably has an acid value of 1 to 200 mg KOH / g, more preferably 2 to 180 mg KOH / g. The hydroxy-containing acrylic resin useful for the aqueous coating compositions according to the present disclosure may be prepared by any method known in the art, or it may be commercially available. Examples of commercially available hydroxy-containing acrylic resins useful for the aqueous coating compositions according to the present disclosure include Setaqua® 6160, Viacryl® VSC 6800W / 47WA and VIacryl® VSC 6276W / 44WA from Allnex Resins Germany GMBH, and NeoCryl XK-110 from DSM.

[0037] A suitable polyurethane resin is typically an addition polymerization product of an organic compound having at least two reactive hydrogen functional values ​​and a polyisocyanate, for example, in the form of an aqueous dispersion. Polyurethane resins may be modified to enhance hydrophilic stabilization or dispersibility in aqueous media by introducing cationic or anionic modifying groups, or ionic groups potentially convertible to cationic or anionic groups. Such polyurethane resins are often referred to in the art as ionically hydrophilically stabilized polyurethane resins. Alternatively, polyurethane resins may be modified by introducing nonionic hydrophilic modifying groups. Suitable cationic, anionic, and / or nonionic modifications of polyurethane resins are known, for example, from WO2013 / 128011A1.

[0038] In one embodiment of this disclosure, the preferably contained polyurethane resin has a number-average molecular weight of 200 to 30,000 g / mol, preferably 2,000 to 20,000 g / mol. It also has a hydroxyl value of, for example, 5 to 250 mg KOH / g, particularly 20 to 150 mg KOH / g. The acid value of the polyurethane resin is preferably 5 to 200 mg KOH / g, particularly 10 to 40 mg KOH / g. The hydroxyl value is determined according to DIN / ISO 4629, and the acid value is determined according to DIN 53402.

[0039] Polyurethane resins useful for the aqueous coating compositions according to this disclosure may be prepared by any method known in the art, or they may be commercially available. Examples of commercially available polyurethane resins useful for the aqueous coating compositions according to this disclosure include DAOTAN® TW 1237 / 32WA from Allnex Resins Germany GMBH and Basonol® PU 1035W from BASF (China) Company Ltd.

[0040] Polyester resins can also be used as binder resins in coating compositions. Polyester resins can be formulated as acid-functional or hydroxyl-functional resins. The polyester resin is preferably hydroxyl-functional, particularly preferably having an OH value in the range of 20-300 mgKOH / g, more preferably 40-150 mgKOH / g. More preferably, at least two different hydroxyl-functional polyesters are used as further binders. In one embodiment of this disclosure, the polyester resin has a number-average molecular weight of 400-5,000, more preferably 500-4,000. Polyester resins useful for aqueous coating compositions according to this disclosure may be prepared by any method known in the art, or they may be commercially available. Examples include Uralac SN800 from DSM and WATERSOL ZHW-1346 from Eternal.

[0041] In one embodiment of this disclosure, acrylic urethane resins, polyether resins, alkyd resins, polycarbonate resins, or epoxy resins can also be used as binder resins in the coating composition. Acrylic urethane resins can provide a synergistic effect between acrylic and urethane, improve compatibility when applied to acrylic resin-based coating compositions, and reduce the cost of urethane resin particles. These resins may be prepared by any method known in the art or may be commercially available.

[0042] In one embodiment of the present disclosure, for better pigment orientation, the binder comprises an acrylic resin, a polyurethane resin, and a polyester resin. Furthermore, the mass of the three resins accounts for 70% or more by mass, preferably at least 80% by mass, and more preferably 100% by mass, of the mass of the water-soluble or water-dispersible binder.

[0043] The total amount of all polymer binders based on the total mass of the aqueous coating composition of this disclosure is preferably 9 to 60% by mass, more preferably 10 to 50% by mass, and most preferably 15 to 30% by mass.

[0044] Cellulose nanofibers The term "cellulose nanofiber" is also referred to in the literature as "cellulose nanofibril," "fibrillated cellulose," or "nanocellulose crystal," all of which refer to fibrous materials. The term "cellulose nanofiber" is a general term that includes natural cellulose nanofibers and functionalized cellulose nanofibers, such as carboxylated or sulfated, or otherwise modified and / or surface-functionalized cellulose nanofibers. However, the main chain having such groups is always cellulose. Of course, non-fibrous cellulose derivatives do not fall under the term "cellulose nanofiber." In particular, hydroxyalkylcellulose that dissolves in aqueous media, for example, is not included in the term "cellulose nanofiber" as used herein. The term "cellulose nanofiber" may be referred to as CNF in this disclosure.

[0045] The inventors of this disclosure accidentally discovered that the compositions of this disclosure greatly facilitate the orientation of effect pigments by combining cellulose nanofibers with specific cosolvents. It should be noted that while the addition of cellulose nanofibers to compositions has been proposed in the literature to improve the dispersibility of pigments, this is the first time it has been reported that they work in cooperation with specific solvents to enhance the flake orientation performance.

[0046] The cellulose nanofibers used may be obtained by defiberizing cellulose material and stabilizing it in water. The cellulose material referred to here refers to various forms of cellulose as the main raw material. Specific examples include natural cellulose such as pulp (e.g., wood pulp, jute, Manila hemp, kenaf, and other herbaceous plant-derived pulp), and cellulose produced by microorganisms; regenerated cellulose obtained by dissolving cellulose in a copper ammonia aqueous solution, a morpholine derivative solvent, etc., and spinning the dissolved cellulose; and fine cellulose obtained by depolymerizing cellulose material through mechanical treatments such as hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting, and vibrating ball milling.

[0047] The method for defiberizing cellulose material is not particularly limited as long as the cellulose material remains fibrous. Examples of methods include mechanical defiberization using homogenizers, grinders, etc.; chemical treatment using oxidation catalysts, etc.; and biological treatment using microorganisms, etc.

[0048] As the cellulose nanofiber, anion-modified cellulose nanofiber can be used and is preferably used. Examples of anion-modified cellulose nanofiber include carboxylated cellulose nanofiber, carboxymethylated cellulose nanofiber, and sulfated cellulose nanofiber. Anion-modified cellulose nanofiber can be obtained, for example, by introducing functional groups such as carboxyl groups and carboxymethyl groups into a cellulose material by a known method, washing the resulting modified cellulose to prepare a dispersion of modified cellulose, and then defiberizing this dispersion. The defiberization method is not particularly limited. The amount of carboxyl groups in oxidized cerilose is preferably 0.2 mmol / g or more, based on the solid content mass of the oxidized cellulose. The amount of carboxyl groups can be adjusted by controlling the oxidation reaction time, the oxidation reaction temperature, the pH during the oxidation reaction, and the amount of N-oxyl compounds, bromides, iodides, or oxidizing agents used. The degree of carboxymethyl substitution per glucose unit of the modified cellulose obtained by introducing carboxymethyl groups into the above cellulose raw material is preferably 0.02 to 0.50.

[0049] In one embodiment of the present disclosure, the cellulose nanofibers preferably have a number-average fiber diameter in the range of 2 to 800 nm, more preferably 2 to 500 nm, even more preferably 2 to 250 nm, and most preferably 2 to 150 nm.

[0050] In another embodiment of the present disclosure, the cellulose nanofibers have a number-average fiber length preferably in the range of 0.04 to 20 μm, more preferably 0.04 to 15 μm, and even more preferably 0.04 to 10 μm. The aspect ratio, obtained by dividing the number-average fiber length by the numerically average fiber diameter, is preferably in the range of 20 to 10000, more preferably 20 to 5000, and even more preferably 20 to 1000. The number-average values ​​of the fiber length, fiber diameter, and aspect ratio of the cellulose nanofibers can be determined by SEM or AFM.

[0051] Examples of commercially available cellulose nanofibers include Rheocrysta (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Cebina Fine (length 0.5-10 μm, diameter 15-100 nm), and Celluforce NCV100 (length 44-108 nm, diameter 2.3-4.5 nm). The above powders are dispersed in deionized water, and the dispersion has a solid content of 1.0-6.0% by mass, preferably 1.0-3.0% by mass.

[0052] In one embodiment of this disclosure, in order to obtain a better synergistic effect between cellulose nanofibers and the cosolvent, the effective content of cellulose nanofibers based on the total mass of the aqueous coating composition is preferably in the range of 0.35% to 0.80% by mass, more preferably 0.40% to 0.75% by mass, and most preferably 0.55% to 0.70% by mass. The effective content is the mass amount of cellulose nanofibers contained in the cellulose nanofiber solution or dispersion. If the effective content of cellulose nanofibers is too low, it may be difficult to improve the rheological properties of the composition, and a multilayer film with good color performance cannot be obtained. There is an upper limit to the amount of cellulose nanofibers in the aqueous coating composition; if the content is too high, improvement in orientation cannot be obtained, and the cost increases.

[0053] cosolvent The term "cosolvent" refers to a solvent or diluent other than water (e.g., an acid or organic solvent) present in an aqueous composition. In this disclosure, the cosolvent is added to the composition and has the following general formula (I): [ka] (In the formula, the combinations of X1 and n are (X1, n) = (H, 1) or (CH2-CH-CH2, 3), X2 and X3 are independently hydrogen and alkyl ("C") having 1 to 8 carbon atoms. 1~8 Selected from alkyl groups (also represented as alkyl), where m is an integer from 1 to 30. The cosolvent may be used alone or in combination of two or more types.

[0054] As used herein, the term “alkyl” or “alkyl group” means a fully saturated, linear (i.e., unbranched) or branched, substituted or unsubstituted hydrocarbon chain. In some embodiments, the alkyl group comprises 1 to 6 carbon atoms, and in yet other embodiments, the alkyl group comprises 1 to 4 carbon atoms. Examples of alkyl groups include methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl, and n-octyl.

[0055] In some embodiments of this disclosure, m is an integer from 1 to 25, more preferably from 1 to 20, and particularly preferably from 1 to 15.

[0056] In some embodiments of this disclosure, the cosolvent is a diol ether compound. Preferably, the cosolvent is lipophilic and has a hydrophilic-lipophilic balance value (HLB value) of at least 9. More preferably, the cosolvent has a boiling point of at least 140°C and / or a vapor pressure of 500 Pa or less.

[0057] In one embodiment of this disclosure, X1=H, n=1, X2 and X3 are independently selected from hydrogen and alkyl groups having 1 to 8 carbon atoms, and m is an integer from 1 to 30. Preferably, X2 and X3 are independently selected from hydrogen and alkyl groups having 1 to 6 carbon atoms, and / or m is an integer from 1 to 20. More preferably, X2 and X3 are independently selected from hydrogen and alkyl groups having 1 to 5 carbon atoms, and / or m is an integer from 1 to 10. Preferred examples of cosolvents are butyl glycol, butyl diglycol, and / or ethylene glycol. Cosolvents with low molecular weights have a relatively fast evaporation rate during film drying, which is advantageous for obtaining a hard dried film.

[0058] In another embodiment of the present disclosure, X1 = CH2-CH-CH2, n = 3, X2 and X3 are independently selected from alkyl groups having hydrogen and 1 to 8 carbon atoms, and m is an integer from 1 to 30. In this embodiment, the cosolvent has the following structure.

[0059] [ka]

[0060] Preferably, X2 and X3 are independently selected from hydrogen and alkyl having 1 to 6 carbon atoms, and / or m is an integer from 1 to 20. More preferably, X2 and X3 are independently selected from hydrogen, methyl and ethyl, and / or m is an integer from 3 to 18. A preferred example of a cosolvent is polypropylene glycol, more preferably polypropylene glycol having a number average molecular weight of 500 to 3,000, most preferably 700 to 2,000, which is commercially available, for example, Nissan uniol TG1000 or BASF Pluriol P 900.

[0061] The cosolvents used in this disclosure can have a synergistic effect with CNF, which is beneficial for the orientation of the effect pigments in the compositions of this disclosure. In some comparative examples, cosolvents that did not conform to formula (I) were used, and the resulting multilayer films had poor color performance and low lightness index. Preferably, to obtain a better synergistic effect between cellulose nanofibers and the cosolvent, the mass ratio of the effective content of cellulose nanofibers to the cosolvent is 1:1 to 6:1, more preferably 1.5:1 to 5:1, and most preferably 2.5:1 to 4.5:1. In some embodiments of this disclosure, in order to reduce VOC values, the mass percentage of the cosolvent is 70.0% to 100.0% by mass, more preferably 80.0% to 100.0% by mass, and most preferably 85.0% to 100.0% by mass, based on the total free organic solvents in the aqueous coating composition. This means that, in addition to the cosolvent, the disclosed compositions preferably contain small amounts of other organic solvents, or preferably do not contain other organic solvents. In other embodiments of the present disclosure, the amount of cosolvent in the aqueous coating composition of the present disclosure is in the range of 0.6% to 5.0% by mass (for example, 0.8% by mass, 2.1% by mass, 3.0% by mass, 4.0% by mass, or 4.5% by mass), preferably in the range of 0.9% to 3.5% by mass, based on the mass of the coating composition.

[0062] Effective pigments The aqueous coating composition of this disclosure further comprises one or more effect pigments. Depending on the desired texture of the resulting coating film, one or more effect pigments may be suitably selected and used. From the viewpoint of obtaining a coating film with excellent metallic luster, non-vapor-deposited metallic pigments are preferred. From the viewpoint of obtaining a coating film with excellent pearlescent luster, mica pigments are preferred. Effect pigment (d) is preferably in flake form.

[0063] In this field, vapor-deposited aluminum flakes are often used to improve the orientation of pigments. This disclosure does not particularly limit the type of effect pigment, and preferably, non-vapor-deposited metal pigments, which are more cost-effective, can be used. The material of the metal is not particularly limited. Examples include aluminum, gold, silver, copper, brass, titanium, chromium, nickel, nickel-chromium, stainless steel, etc. Among these, aluminum or chromium are particularly preferred, for example, from the viewpoint of availability and ease of handling. Aluminum flake pigments are more preferred. Aluminum flake pigments are usually produced by grinding and grinding aluminum in a ball mill or attritor mill in the presence of a grinding liquid medium and a grinding aid. Examples of grinding aids used in the production process of aluminum flake pigments include higher fatty acids, such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid, and myristic acid; and aliphatic amines, aliphatic amides, and aliphatic alcohols. Examples of grinding liquid media used include aliphatic hydrocarbons such as mineral spirits. The aluminum flake pigment preferably has an average particle size (D50) of 1 to 50 μm, more preferably 5 to 25 μm, and particularly preferably 6 to 20 μm. The aluminum flake pigment preferably has a thickness of 0.01 to 1.0 μm, and particularly preferably 0.03 to 0.4 μm. For example, commercially available aluminum flake pigments can be used. Examples of commercially available flake aluminum pigments include the "STAPA Hydrolan" series and "STAPA Metallux" series from ECKART, and the "EMERAL EX" series from Toyal.

[0064] In this specification, "average particle size" or "D50" refers to the median diameter in a volume-based particle size distribution measured by laser diffraction scattering using a Microtrac MT3300 particle size distribution analyzer (product name, manufactured by Nikkiso Co., Ltd.). In this specification, "thickness" is defined as the average value obtained by measuring the thickness of 100 or more particles using image processing software while observing a cross-section of a coating film containing an effect pigment under a microscope.

[0065] Preferably, the amount of component (iv) in the coating composition of the present disclosure is in the range of 0.5% to 2.0% by mass, preferably 0.8% to 1.8% by mass, based on the mass of the coating composition.

[0066] From the viewpoint of forming a pearlescent coating film, the effect pigment is preferably mica, such as natural mica, synthetic mica, and / or metal oxide coated mica pigment, more preferably natural mica and / or synthetic mica. Natural mica is a flaky substrate obtained by crushing mica from ore. Synthetic mica is synthesized by heating industrial materials such as SiO2, MgO, Al2O3, K2SiF6, or NaSiF6 at a high temperature of about 1500°C to melt them, and then cooling and crystallizing them. Compared to natural mica, synthetic mica has a lower impurity content and is more uniform in size and thickness. A specific example of a synthetic mica substrate is fluorophlogopite (KMg2AlSi3O 10 F2), potassium tetrasilicon mica (KMg 2.5 AlSi4O 10 F2), sodium tetrasilicon mica (NaMg 2.5 AlSi4O 10 F2), Na teniolite (NaMg2LiSi4O 10 F2), LiNa teniolite (LiMg2LiSi4O 10 Examples include F2). Metal oxide coated mica pigments are pigments that use natural mica or synthetic mica as a base material and coat its surface with a metal oxide. From the viewpoint of obtaining a coating film with excellent pearlescent luster, the mica pigment preferably has an average particle size (D50) of 5 to 30 μm, and particularly preferably 5 to 25 μm. The mica pigment preferably has a thickness of 0.05 to 1.0 μm, and particularly preferably 0.2 to 0.7 μm.

[0067] Examples of commercially available pearl white flake paints include the "Xirallic" and "IRIODIN" series from MERCK, and the "Glacier Exterior Frost white" series from SunChemical.

[0068] The solid content of the effect pigment (d) in the aqueous coating composition of this disclosure is preferably 0.5% to 8.0% by mass, particularly preferably 1.0% to 7.0% by mass, and even more preferably 3.5% to 6.0% by mass, based on the mass of the aqueous coating composition. When the effect pigment, particularly the non-vapor-deposited metal pigment or mica pigment described above, is used in the total amount described above in combination with at least one water-soluble or water-dispersible binder, at least one cellulose nanofiber material, and at least one co-solvent, a particularly high brightness index can be obtained.

[0069] Other ingredients In addition to the essential components (a) to (d) described above, the aqueous coating compositions of this disclosure may also contain one or more further components known to those skilled in the art, such as crosslinking agents, other rheology control agents, neutralizing agents, water, surface modifiers, and ultraviolet absorbers. In some embodiments of this disclosure, the aqueous coating compositions do not contain light-scattering particles such as titanium dioxide, which may affect the orientation of the effect pigment.

[0070] Crosslinking agent In some embodiments of this disclosure, the disclosed compositions may also include a crosslinking agent for use in crosslinking and curing of the binder by heating. The crosslinking agent is preferably selected from the group consisting of melamine resins, blocked polyisocinates, and mixtures thereof. The crosslinking agent may be used alone or in combination of two or more.

[0071] Melamine resins are particularly useful in the aqueous coating compositions according to this disclosure. Particularly preferred are methylated melamine resins obtained by etherifying at least some methylol groups of a partially or completely methylolated melamine resin with methyl alcohol; butylated melamine resins obtained by etherifying at least some methylol groups of a partially or completely methylolated melamine resin with butyl alcohol; and methylated / butylated melamine resins obtained by etherifying at least some methylol groups of a partially or completely methylolated melamine resin with methyl alcohol and butyl alcohol. Examples of commercially available melamine resins useful for the aqueous basecoat compositions according to this disclosure include Cymel® 202, Cymel® 203, Cymel® 211, Cymel® 251, Cymel® 303, Cymel® 324, Cymel® 325, Cymel® 327, Cymel® 350, Cymel® 385, Cymel® 1130, Cymel® 1156, Cymel® 1116, Cymel® 1158 from Allnex USA Inc.; Cymel® 204, Cymel® 238, Cymel® 323 from Cytec Industries Inc.; and Mitsui Chemicals, Examples include U-VAN® 120, U-VAN® 20HS, U-VAN® 20SE60, U-VAN® 2021, U-VAN® 2028, and U-VAN® 28-60 from Inc.

[0072] Blocked polyisocyanates volatilize at the curing temperature, allowing for the regeneration of isocyanate groups. Suitable examples of blocked polyisocyanates include polyisocyanates and adducts thereof modified by blocking their isocyanate groups (-N=C=O groups) with a blocking agent. Blocking agents include oximes, such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; alcohols, such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol, benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, urea methylol, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; phenols, such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; ethers, such as ethylene glycol Methyl ethers, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; lactams, e.g., ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; active methylene compounds, e.g., dimethyl malonate, diethyl malonate, ethyl acetate, methyl acetate, and acetylacetone; mercaptans, e.g., butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; amides, e.g., acetanilide, acetaniside, acetoliimide, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide;Examples include imides, such as succinimide, phthalimide, and maleimide; amines, such as diphenylamine and phenylnaphthylamine; xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles or imidazole derivatives; ureas, such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamates, such as phenyl N-phenylcarbamate; imines, such as ethyleneimine and propyleneimine; sulfites, such as sodium bisulfite and potassium bisulfite; and azoles, such as pyrazoles or pyrazole derivatives. Examples of polyisocyanates include aliphatic polyisocyanates, such as trimethylene diisocyanate, 1,2-propylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 4-isocyanatomethyl-1,8-octanediisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, and α,α'-dipropyl Ropyr ether diisocyanates and transvinylidene diisocyanates; alicyclic polyisocyanates, e.g., 1,3-cyclopentylene diisocyanate, 1,2-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4-methyl-1,3-cyclohexylene diisocyanate, 4,4'-dicyclohexylene diisocyanate methane, 3,3'-dimethyl-4,4'-dicyclohexylene diisocyanate methane, norbornane diisocyanate, and isophorone diisocyanate;Aromatic polyisocyanates, such as m- and p-phenylenediisocyanates, 1,3- and 1,4-bis(isocyanate-methyl)benzene, 1,5-dimethyl-2,4-bis(isocyanate-methyl)benzene, 1,3,5-triisocyanate-benzene, 2,4- and 2,6-toluenediisocyanates, 2,4,6-toluenediisocyanate, α,α,α',α'-tetramethylo-, m- and p-xylylenediisocyanates, 4,4'-diphenylenediisocyanatemethane, 4,4'-diphenylenediisocyanate, 3,3'-dichloro-4,4'-diphenylenediisocyanate, naphthalene-1,5-diisocyanate; and combinations thereof.

[0073] Preferably, the amount of crosslinking agent in the coating composition of the present disclosure is in the range of 1% to 10% by mass (e.g., 2%, 3%, 5%, 8%), more preferably in the range of 2% to 7%, and more particularly in the range of 3% to 6%, based on the total mass of the coating composition.

[0074] Other rheology control agents The term "other rheology control agents" refers to rheology control agents other than component (b) cellulose nanofibers that can exhibit a thickening effect. In some embodiments of this disclosure, the other rheology control agents are preferably selected from (meth)acrylic acid-(meth)acrylate copolymers and / or hydrophobically modified ethoxylated polyurethanes. (meth)acrylic acid-(meth)acrylate copolymers can be obtained by the reaction of (meth)acrylic acid with (meth)acrylic acid esters. Copolymers containing only C1-C4 alkyl (meth)acrylates do not have an associative thickening effect (ASE thickening effect). Conversely, copolymers containing (meth)acrylates having a chain length of four or more carbon atoms have an associative thickening effect (HASE thickeners). Hydrophobically modified ethoxylated polyurethanes are obtained by reacting diisocyanate with a polyether, and then reacting this prepolymer with a hydrophobic alcohol. Such polyurethanes are also called HEUR thickeners. Particularly preferred is the use of a combination of a non-associative thickening (meth)acrylic acid-(meth)acrylate copolymer and a hydrophobically modified ethoxylated polyurethane.

[0075] In this context, it is preferable that at least one thickening agent, more particularly (meth)acrylic acid-(meth)acrylate copolymer and / or hydrophobically modified ethoxylated polyurethane, be present in a total amount of 0.05 to 3.0% by mass, preferably 0.1 to 2.0% by mass, and more preferably 0.2 to 1.5% by mass, based on the total mass of the coating composition.

[0076] According to one particularly preferred embodiment of the present disclosure, the aqueous coating material is free of inorganic rheology control agents and / or polyamides, and more particularly free of phyllosilicates (or layered silicates) and polyamides. This means that phyllosilicates and / or polyamides, more particularly phyllosilicates and polyamides, are present in a total amount of 0% by mass based on the total mass of the coating composition. Surprisingly, the use of cellulose nanofibers without the additional use of polyamides and / or phyllosilicates yields excellent coloration performance and stable shear viscosity.

[0077] Neutralizing agent The neutralizing agent is preferably selected from the group consisting of inorganic bases, primary amines, secondary amines, tertiary amines, and mixtures thereof, and in particular, diethylethanolamine, which has a suitable boiling point and evaporation rate. In this context, it is preferable that at least one neutralizing agent, particularly diethylethanolamine, be present in a total amount of 0.3 to 3.0% by mass, preferably 0.5 to 2.0% by mass, and more preferably 0.7 to 1.5% by mass, based on the total mass of the coating composition. By using the neutralizing agent, particularly diethylethanolamine, in the above amount range in combination with the cosolvent, sufficient solubilization of the binder is ensured, and thus good storage stability is obtained.

[0078] water The water can be selected from the group consisting of deionized water, distilled water, and pure water, and is preferably deionized water.

[0079] Preferably, the amount of free water (excluding water inside the binder and additives) in the coating composition of the present disclosure is in the range of 20% to 60% by mass (for example, 25%, 30%, 40%, 50%, or 55%), preferably in the range of 30% to 50%, and more preferably in the range of 35% to 46%, based on the total mass of the coating composition.

[0080] It should be understood that the aqueous coating compositions according to this disclosure may already contain a total amount of water medium such that a viscosity suitable for the purpose of coating is provided. Furthermore, the aqueous basecoat compositions according to this disclosure may be diluted to a suitable viscosity by the addition of further water and / or by means of a small amount of organic solvent before coating.

[0081] Surface modifiers and UV absorbers Surface modifiers primarily promote the formation of smooth and uniform films during the drying process, and examples include acrylic and silicone leveling agents. Examples of commercially available surface modifiers include the BYK series (manufactured by BYK-Chemie), the Tego series (manufactured by Evonik), and the Surfynol series (manufactured by Evonik).

[0082] Known UV absorbers can be used. Examples include benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, benzophenone absorbers, and other UV absorbers. Commercially available products include Tinuvin 384-2 and Tinuvin 123 from BASF.

[0083] The amount of surface modifier or ultraviolet absorber in the coating composition of this disclosure can be determined by those skilled in the art according to the actual application.

[0084] The method for preparing the aqueous coating composition according to this disclosure is not particularly limited. Any method known in the art can be used, such as kneading a mixture of the resin and pigment and dispersing it using a ball mill, sand mill, disperser, etc.

[0085] The aqueous coating compositions of this disclosure can be prepared by those skilled in the art using processes known in the art. For example, the coating compositions of this disclosure may be prepared by adding all components stepwise with stirring. Preferably, if the effect pigments are used in the form of dry powder or particles before forming the coating composition of this disclosure, they are pre-dispersed in a binder and / or solvent to form a pre-dispersion, respectively. The binder and solvent used to form the pre-dispersion are applicable to this disclosure. Preferably, the binder and solvent used to form the pre-dispersion are part of the binder and co-solvent in the coating composition of this disclosure. In a preferred embodiment, the effect pigments are well dispersed in the polyester resin and co-solvent, and no particles or aggregates are present in the pre-dispersion. By using the co-solvent of this disclosure, the dispersion of effect pigments, particularly non-vapor-deposited metal pigments, can be greatly improved, so there is no need to use other dispersants in the pre-dispersion of the effect pigments.

[0086] The aqueous coating compositions according to this disclosure can be applied by any conventional coating method, such as air spray coating, air atomized electrostatic coating, or rotary bell atomized electrostatic coating, preferably, for example, in an automotive painting process, after a prior application of an undercoat layer containing an electrodeposited coating material and / or sealing material.

[0087] Generally, the aqueous coating compositions according to this disclosure are applied in such a way that a coating film having a thickness of more than 5 μm, preferably 6 to 20 μm, after curing can be obtained. The coating is then cured for an appropriate time, such as 10 minutes to 1 hour, at a temperature in the range of 100 to 200°C, preferably 120 to 160°C, thereby obtaining a cured coating film. The cured coating film has a relatively high dry film thickness, which not only ensures a color development effect but also allows the film to exhibit significant mechanical properties (such as impact resistance).

[0088] The Disclosure further relates to a coated article having a cured coating film on the article, wherein the cured coating film is obtained by curing an aqueous coating composition of the Disclosure. The Disclosure can be used with many different types of objects, including metals or metallic objects such as raw steel, phosphated steel, galvanized steel, or aluminum; and non-metallic objects such as plastics and composite materials.

[0089] A further subject of this disclosure is the use of the aqueous coating compositions of this disclosure for the manufacture of pigment aqueous coating materials. Applications of pigment aqueous coating materials include, but are not limited to, automobiles, railway vehicles, bridges and pipelines, steel structures, interior and exterior walls of building engineering, furniture, and other industrial fields. Preferably, automobiles are mentioned, and more preferably, the pigment aqueous coating materials of this disclosure are suitable for automotive base coat materials.

[0090] A multilayer coating film comprising a base coat layer obtained by applying the aqueous coating composition of the present invention and a clear coat layer on the base coat layer has a lightness index of 0.20 or higher, preferably 0.22 or higher, more preferably 0.30 and / or 0.50 or lower, where lightness index = (L * 15° -L * 25° ) / L * 15° , L * 15° and L * 25° Each of them is L * a * b *The lightness values ​​are expressed according to the color system (CIE lab) and measured at viewing angles of 15° and 25°. The appropriate viewing angle in the lightness index formula is determined according to the lightness values ​​of the films obtained with different types of effect pigments. With respect to the lightness of this combination, the lightness index can achieve relatively high values, meaning that the high light reflectivity and high orientation of the effect pigments of the multilayer coating film of this disclosure are achieved in a low VOC environment containing the aqueous coating composition of this disclosure. Preferably, the multilayer coating film also has a diffusion graininess (Gdiff) of 4 or less, particularly preferably 3.7 or less (Gdiff). * ) has. This means that the film of the present disclosure has higher smoothness. In embodiments of the present disclosure, the multilayer coated film has a super-shining silver effect and G * The value is less than 4, and the corresponding brightness index is preferably greater than 0.3, L * 110° It is less than 10 (L * 110°は , L * a * b * (According to the color system (CIE lab), the lightness value is measured at a light source illuminance of 45° and a viewing angle of 110°). In another embodiment of the present disclosure, the multilayer coating film has a silky pearl white color effect, G * The value is preferably less than 2.5, and the corresponding brightness index is preferably greater than 0.2.

[0091] Manufacturing method for multilayer coated films This disclosure also provides a method for manufacturing a multilayer coated film, the method comprising the following steps: (1) A step of optionally applying a coating material to a substrate and then curing the composition to produce a first cured coating layer on the substrate; (2) A step of manufacturing one or more base coat layers by applying one or more identical or different aqueous base coat materials onto the coating layer obtained in step (1); (3) A process of manufacturing one or more clear coat layers on one or the top base coat layer by applying one or more identical or different clear coat materials; and (4) A process of curing one or more base coat layers and one or more clear coat layers together; Includes, Here, at least one of the base coat materials is the aqueous coating composition according to the present disclosure.

[0092] In the method of this disclosure, a multilayer coating system is constructed on a substrate.

[0093] In accordance with this disclosure, the substrate is selected from metal substrates, plastics, glass and ceramics, and more particularly from metal substrates. Metal substrates essentially intended include, for example, iron, aluminum, copper, zinc, magnesium and their alloys, and steel, which is any of a very diverse range of forms and compositions, or substrates made of these. Preferred substrates are iron and steel substrates, particularly typical iron and steel substrates used in the automotive industry. Prior to step (1) of the method of this disclosure, the metal substrate may be pretreated by conventional methods, for example, by washing. Preferred plastic substrates include, in principle, (i) polar plastics, such as polycarbonate, polyamide, polystyrene, styrene copolymer, polyester, polyphenylene oxide, and mixtures thereof; (ii) reactive plastics, such as PUR-RIM, SMC, BMC; and (iii) polyethylene and polypropylene type polyolefin substrates with high rubber content, such as PP-EPDM; and surface-activated polyolefin substrates, or substrates made of these. Plastics may be fiber-reinforced, in particular using carbon fibers and / or metal fibers. The plastic substrate may also be pre-treated, more particularly by washing, prior to step (1) of the method of the present disclosure, in order to improve the adhesion of the first coating layer. It is also possible to use a substrate that further contains both metal and plastic fractions. Such a substrate is, for example, a car body containing plastic parts.

[0094] Process (1) In step (1) of the method of the present disclosure, the cured first coating layer may be manufactured on a substrate by applying a coating material to the substrate and optionally curing it thereafter.

[0095] The coating material in step (1) may be an electrodeposition coating material. The first coating layer is preferably a cured electrodeposition layer having a thickness in the range of 8 to 18 μm.

[0096] Process (2) In step (2) of the method of the present disclosure, one base coat layer is manufactured (Option 1), or two or more directly continuous base coat layers are manufactured (Option 2).

[0097] These layers are produced by directly applying an aqueous coating composition to the substrate, directly applying it to the cured coating layer obtained in step (1), directly and continuously applying two or more base coat materials to the substrate, or directly and continuously applying them to the cured coating layer obtained in step (1).

[0098] Therefore, after manufacturing, the base coat layer according to option 1 of step (2) is placed directly on the cured coating layer obtained in step (1).

[0099] The direct and continuous application of two or more basecoat materials to the cured coating layer obtained in step (1) (option 2) is understood as follows: The application of the first basecoat material directly produces a first basecoat layer on the cured first coating layer of step (1). Then, at least one further basecoat layer is directly produced on the first basecoat layer. If two or more further basecoat layers are produced, they are produced directly and continuously. For example, exactly one further basecoat layer can be produced, in which case, in the final multilayer coating system, that basecoat layer is located directly beneath the first or so clearcoat layer.

[0100] The base coat materials may be the same or different. It is also possible to produce two or more base coat layers with the same base coat material and one or more further base coat layers with one or more other base coat materials. However, at least one of the aqueous base coat materials used in step (2) includes the aqueous coating composition of this disclosure.

[0101] In the context of this disclosure, preferred embodiments include the production of two or more basecoat layers according to option 2 of step (2) of the method of this disclosure. The aqueous basecoat material used in step (2) includes a primer coating material (e.g., N-3000 N6 from BASF Coatings GmbH) and the aqueous coating composition of this disclosure.

[0102] The base coat layer is cured together with the clear coat material, rather than separately. In particular, the coating material used in step (2) of the method of this disclosure is not cured separately, like the coating material referred to as a surfacer in the context of standard methods. Therefore, the base coat layer is preferably not exposed to temperatures above 100°C for more than 1 minute, and especially preferably not exposed to temperatures above 100°C at all in step (2).

[0103] After curing in step (4), the base coat material is applied such that the base coat layer and each individual base coat layer have a thickness of, for example, more than 5 μm. Preferably, the primer layer has a cured thickness in the range of 12 to 18 μm, and the aqueous coating layer cured with the aqueous coating composition according to this disclosure has a thickness of 6 to 15 μm.

[0104] Process (3) In step (3) of the method of the present disclosure, one or more clear coat layers are manufactured directly on one base coat layer or on an uppermost base coat layer by the application of one or more identical or different clear coat materials. Preferably, one clear coat layer is manufactured on one base coat layer. Suitable clear coat materials are commercially available, for example, ProGloss® from BASF Coatings GmbH.

[0105] The thickness of each clear coat layer after curing in step (4) is, for example, 15 to 80 μm, preferably 20 to 65 μm, and particularly preferably 25 to 60 μm.

[0106] Process (4) In step (4) of the method of the present disclosure, co-curing is performed between the base coat layer and the clear coat layer, or between multiple base coat layers and clear coat layers. Co-curing is performed at a temperature of preferably 100 to 250°C, preferably 100 to 180°C, for a time of 5 to 60 minutes, preferably 10 to 45 minutes. The method of the present disclosure makes it possible to manufacture a multilayer coating system on a substrate without a separate curing step.

[0107] In embodiments of this disclosure, the multilayer coating film is made by the following steps: (1) A step of applying electrodeposition coating material to the substrate of an article and drying it at a temperature of 120 to 180°C to form a first coating layer that has been cured; (2a) A step of applying a primer material to the cured first coating layer and flushing off the composition at room temperature for 3 to 6 minutes, wherein the resulting primer-dried film preferably has a thickness in the range of 12 to 18 μm; (2b) A process in which process (2a) is arbitrarily repeated; (3) A step of applying the aqueous coating composition of the Disclosure onto a primer film or a plurality of films formed in step (2a) or step (2b), and flushing off the coating composition at room temperature for 3 to 6 minutes, and then at a temperature of 50 to 80°C for 3 to 6 minutes, wherein the final coated dry film preferably has a thickness in the range of 6 to 15 μm; and (4) A step of applying a clear coat material onto the coating film formed in step (3), then flushing off the clear coat material at room temperature for 5 to 10 minutes, and then drying at a temperature of 120 to 160°C for 20 to 40 minutes to form a clear coat film preferably having a thickness in the range of 30 to 60 μm, thereby forming a multilayer coating film on the substrate. It is prepared by a process that includes [this].

[0108] Preferably, the multilayer coating film is prepared in an integrated process, and the multilayer coating film comprises one or two primer layers, one base coat layer, and one clear coat layer. This process can compress the process flow, reduce operating costs, reduce capital investment, and reduce energy consumption, while the resulting multilayer coating film has excellent color performance.

[0109] Multilayer coated film After the completion of step (4) of the method of the present disclosure, the obtained product is the multilayer coating film of the present disclosure. The present disclosure further provides a multilayer coating film having characteristic color performance. Specifically, the film has a lightness index of 0.20 or higher, preferably 0.22 or higher, where lightness index = (L * 15° -L * 25° ) / L * 15° , L * 15° and L * 25° Each of them is L * a * b *The lightness values ​​are expressed according to the color system (CIE lab) and measured at viewing angles of 15° and 25°. Regardless of whether the effect pigment of the disclosed composition is selected from metallic pigments or mica, the resulting multilayer coating film can satisfy the requirements of the lightness index. Preferably, the multilayer coating film also has a diffusion graininess (G) of 4 or less, particularly preferably 3.7 or less. * ) has.

[0110] This disclosure further relates to colored articles having multilayer coating films. The colored articles of this disclosure can be obtained by those skilled in the art by conventional procedures.

[0111] Embodiment Embodiment 1 a) Water-soluble or water-dispersible binder; b) Cellulose nanofibers; c) Cosolvent of formula (I) [ka] (In the formula, the combinations of X1 and n are (X1, n) = (H, 1) or (CH2-CH-CH2, 3), X2 and X3 are independently selected from a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, where m is an integer from 1 to 30. d) Pigments; an aqueous coating composition comprising, The aqueous coating composition has a volatile organic compound content of 420 g / l or less without water; A multilayer coating film comprising a base coat layer obtained by applying the aqueous coating composition and a clear coat layer on the base coat layer has a lightness index of 0.20 or higher, where the lightness index = (L * 15° -L * 25° ) / L * 15° And L * 15° and L * 25° Each of them is L * a* b * An aqueous coating composition representing lightness values ​​measured at viewing angles of 15° and 25° according to the color system (CIE lab).

[0112] Embodiment 2 e) The aqueous coating composition according to Embodiment 1, further comprising a crosslinking agent.

[0113] Embodiment 3 The aqueous coating composition according to Embodiment 1 or 2, wherein the water-soluble or water-dispersible binder (a) comprises at least one selected from acrylic resin, polyurethane resin, acrylic-urethane resin, polyester resin, polyether resin, alkyd resin, polycarbonate resin, and epoxy resin.

[0114] Embodiment 4 The aqueous coating composition according to any one of Embodiments 1 to 3, wherein the cosolvent (c) has a boiling point of at least 140°C and an HLB value of at least 9.

[0115] Embodiment 5 The aqueous coating composition according to any one of Embodiments 1 to 4, wherein the effect pigment (d) comprises at least one selected from non-vapor-deposited metal pigments and mica.

[0116] Embodiment 6 The aqueous coating composition according to any one of Embodiments 1 to 5, wherein the effect pigment (d) has a particle size of 5 to 25 μm.

[0117] Embodiment 7 The aqueous coating composition according to any one of Embodiments 1 to 6, wherein the crosslinking agent (e) comprises at least one selected from melamine resin and blocked polyisocyanate.

[0118] Embodiment 8 The aqueous coating composition according to any one of Embodiments 1 to 7, wherein the effective content of the cellulose nanofiber (b) is 0.35% by mass to 0.80% by mass based on the total mass of the aqueous coating composition.

[0119] Embodiment 9 The aqueous coating composition according to Embodiment 8, wherein the mass ratio of the cosolvent (c) to the effective content of the cellulose nanofiber (b) is 1:1 to 6:1.

[0120] Embodiment 10 The aqueous coating composition according to any one of Embodiments 1 to 9, wherein the mass percentage of the cosolvent (c) is 70.0% by mass to 100.0% by mass, based on the total free organic solvent in the aqueous coating composition.

[0121] Embodiment 11 An aqueous coating composition according to any one of Embodiments 1 to 10, having a solid content of more than 15% by mass.

[0122] Embodiment 12 An aqueous coating composition according to any one of Embodiments 1 to 11, having a volatile organic compound content (including water) of 150 g / L or less.

[0123] Embodiment 13 The aqueous coating composition has a thixotropy value (Ti value) of 40 or less, where Ti value = η(A) / η(B), and η(A) is measured at 23°C using a rotational viscometer and measured over 1000 s. -1 This is the viscosity under shear rate, where η(B) is measured at 23°C using a rotational viscometer, and 1s -1 An aqueous coating composition according to any one of Embodiments 1 to 12, wherein the viscosity under a shear rate is .

[0124] Embodiment 14 The multilayer coating film has a diffusion particle size of 4 or less (G * An aqueous coating composition according to any one of Embodiments 1 to 13, having )

[0125] Embodiment 15 A coating film obtained from an aqueous coating composition according to any one of Embodiments 1 to 14, wherein the dry film thickness of the coating film is greater than 5 μm.

[0126] Embodiment 16 A coated article comprising a cured coating film on the article, wherein the cured coating film is obtained by curing an aqueous coating composition according to any one of Embodiments 1 to 14.

[0127] Embodiment 17 A method for manufacturing a multilayer coated film, comprising the following steps: (1) A step of optionally applying a coating material to a substrate and then curing the composition to produce a first cured coating layer on the substrate; (2) A step of manufacturing one or more base coat layers by applying one or more identical or different aqueous base coat materials onto the coating layer obtained in step (1); (3) A process of manufacturing one or more clear coat layers on one base coat layer or an uppermost base coat layer by applying one or more identical or different clear coat materials; and (4) A process of curing one or more base coat layers and one or more clear coat layers together; Includes, A method wherein at least one of the base coat materials is an aqueous coating composition according to any one of Embodiments 1 to 14.

[0128] Embodiment 18 A multilayer coated film that can be obtained by the method described in Embodiment 17.

[0129] Embodiment 19 The multilayer coating film has a lightness index of 0.20 or more and a diffusion granularity (G * ) of 4 or less, and the lightness index = (L * 15° -L * 25° ) / L * 15° , where L * 15° and L * 25° respectively represent the lightness values measured at a viewing angle of 15° and 25° according to the L * a * b * color system (CIE lab). The multilayer coating film according to Embodiment 18.

[0130] Embodiment 20 A method of using the aqueous coating composition according to any one of Embodiments 1 to 14 for the production of a pigment aqueous coating material.

Examples

[0131] The present disclosure will be better understood by considering the following non-limiting examples. The examples do not limit the scope of the present disclosure described and claimed.

[0132] Explanation of the method Solid content (%) The solid content was measured in accordance with DIN EN ISO 3251 (date: June 2008). 1 g of the sample was weighed on a pre-dried aluminum foil, dried in a drying oven at 125°C for 60 minutes, cooled in a desiccator, and weighed again. The residue relative to the total amount of the sample used corresponds to the solid content or the non-volatile fraction.

[0133] Solid mass = Sample mass × Solid content (%) Dry film thickness The dry film thickness was measured using an FMP20 device from Helmut-Fischer in accordance with DIN EN ISO 2808:2007-05 (date: May, 20C7), Method 12A - Magnetic induction gauge.

[0134] VOC The content of volatile organic compounds (VOCs including water) was measured by gas chromatography in accordance with GB / T 23986-2009 10.3. The content of volatile organic compounds without water (VOCs without water) was measured by gas chromatography in accordance with GB / T 23986-2009 10.4.

[0135] Lightness index and diffuseness granularity (G * ) G * To measure G, a coated substrate (a multi-layer coating system as in section 2 of the following examples) was measured with diffuse illumination using BYK mac i from BYK-Chemie GmbH. To evaluate or measure granularity, the non-uniformity between the bright and dark parts was evaluated, and these parts were recorded with a CCD camera to provide a grayscale image. The uniformity of this image becomes the measurement of granularity.

[0136] To determine the lightness index, a coated substrate (a multi-layer coating system as in section 2 of the following examples) was measured at 45° with a D65 light source using BYK mac i from BYK-Chemie GmbH. The viewing angles were -15°, 15°, 25°, 45°, 75°, and 110°. From the lightness values measured at viewing angles of 15° and 25°, the lightness index can be calculated according to the following formula: Lightness index = (L * 15° - L * 25° ) / L * 15° In the formula, L * represents the lightness values measured at each measurement angle (15° and 45°).

[0137] Thixotropy value (Ti value) The Ti value was determined according to the formula: Ti value = η(A) / η(B), where η(A) is the viscosity at a shear rate of 1000 s -1 and η(B) is the viscosity at 1 s-1 This is the viscosity under shear rate, measured at 23°C using a rotational viscometer (MCR 302, manufactured by Anton Paar).

[0138] Examples Regarding the listed formulation ingredients and their quantities, the following should be considered: When referring to a marketed product or a preparation protocol described elsewhere, the reference is precisely to the product prepared using that marketed product or protocol, regardless of the primary designation chosen for the ingredient.

[0139] Therefore, if the formulation component has the primary designation "acrylic resin" and a commercially available product is indicated for this component, the acrylic resin is used precisely in the form of this commercially available product. Consequently, in order to draw conclusions about the amount of the active substance (of the acrylic resin), further components such as solvents present in the commercially available product must be considered.

[0140] Therefore, when referring to the preparation protocol of the formulation components, if such preparation results in, for example, a polymer dispersion having a defined non-volatile fraction, then this dispersion is precisely used. Most importantly, it is not the main designation chosen that is "polymer dispersion" or simply the active substance, such as "polymer," "polyester," or "polyurethane-modified polyacrylate." This point must be taken into consideration when drawing conclusions regarding the amount of the active substance (of the polymer).

[0141] 1. Preparation and evaluation of aqueous coating composition (Super Shining Silver) Preparation of pigment dispersion paste: A pigment dispersion paste was obtained by mixing 1 part co-solvent (Pluriol® P 900, manufactured by BASF), 0.8 parts polyester resin (Uralac SN800, manufactured by DSM, solids content approximately 63% by mass), and 9.7 parts aluminum flake pigment (EMR 4670, manufactured by Toyo Aluminum Co., Ltd., average particle size D50: 8 μm, particle size was tested according to ASTM D7928-16, standard test method for particle size distribution of fine-grained soil by sedimentation analysis, solids content approximately 56% by mass).

[0142] Preparation of CNF solution: The cellulose nanofiber solution (CNF solution) was prepared by gradually adding solid CNF to deionized water from dried Celluforce NCV-100 while vigorously stirring. After the desired amount of CNF in the water reached 3% by mass, stirring was continued until a clear solution was formed.

[0143] 13.9 parts polyurethane resin (DAOTAN® TW 1237 / 32WA, manufactured by Allnex, solids content approximately 32% by mass), 4.2 parts acrylic resin (NeoCryl XK-110, manufactured by DSM, solids content approximately 46% by mass), 1.4 parts type A rheology control agent (Rheovis AS 1130, manufactured by BASF, solids content approximately 29% by mass), 20.8 parts type B rheology control agent (CNF solution), 0.6 parts ultraviolet absorber (Tinuvin 123, manufactured by BASF), 0.4 parts surface modifier (BYK346, manufactured by BYK, solids content approximately 50% by mass), and 41.6 parts deionized water were introduced into the container. Next, 5.5 parts of melamine resin (Cymel 202, Cymel 303, manufactured by Allnex, with a solid content of approximately 80% by mass), 1.1 parts of diethylethanolamine, and 11.5 parts of pigment dispersion paste were added and mixed uniformly to obtain aqueous coating composition S-1.

[0144] A series of aqueous coating compositions S2 to S15 were prepared according to the components and quantities provided in Tables 1, 3, and 5, and the pH of each resulting aqueous coating composition was adjusted to 8.2.

[0145] The obtained aqueous coating compositions were applied as base coats. The solids content, viscosity, and VOC values ​​of these compositions were measured. The measurement results are shown in Tables 2, 4, and 6.

[0146] 2. Manufacturing and evaluation of multilayer coated film (Super Shining Silver) A steel panel coated with a standard cathode electrodeposition material (CathoGuard® 800 gray, manufactured by BASF Coatings) was used. A primer coating material (N-3000 N6, manufactured by BASF Coatings GmbH) was applied to the panel using an ESTA Bell (EcoBell III, manufactured by Duerr Systems AG, Germany) and flashed off at room temperature for 5 minutes. The dry primer film thickness was 15 μm.

[0147] Subsequently, an aqueous coating composition (Super Shining Silver) was applied using a rotary atomizer (EcoBell II, manufactured by Duerr Systems AG, Germany) at a temperature of 23°C and 65% humidity to achieve a dry film thickness of 7 μm (flow rate 380 mL / min, rotation speed 40,000 rpm, voltage 60 kV). After coating, the panel was left at room temperature for 5 minutes, followed by a flash-off at 70°C for 5 minutes. After cooling to 23°C, a clear coat paint (ProGloss®, manufactured by BASF Coatings GmbH) was applied to achieve a dry film thickness of 45 μm. After coating, the panel was left for 10 minutes, followed by horizontal baking at 140°C for 30 minutes to obtain a panel with a final multilayer coating film.

[0148] The color performance of the manufactured multilayer coated films was evaluated from the perspectives of lightness index and granularity. The measurement results are summarized in Tables 2, 4, and 6.

[0149] [Table 1]

[0150] [Table 2]

[0151] [Table 3]

[0152] [Table 4]

[0153] [Table 5]

[0154] [Table 6]

[0155] 3. Preparation and evaluation of aqueous coating composition (silky pearl white) A series of aqueous coating compositions (silky pearl white) M-1 to M-9 were prepared according to the components and quantities provided in Tables 7 and 8, and the pH of each resulting aqueous coating composition was adjusted to 8.2. The pigment dispersion paste was prepared by mixing pearl white flake pigment with several binder resins. The CNF solution was prepared in the same manner as in Section 1 of the Examples.

[0156] The resulting aqueous coating compositions were applied as base coats. The solids content, viscosity, and VOC values ​​of these compositions were measured. The measurement results are shown in Table 8.

[0157] 4. Manufacturing and evaluation of multilayer coated film (silky pearl white) A steel panel coated with a standard cathode electrodeposition material (CathoGuard® 800 gray from BASF Coatings) was used. Using an ESTA Bell (EcoBell III, manufactured by Duerr Systems AG, Germany), primer coating material 1 (N-3000 N8.9, manufactured by BASF Coatings GmbH) was applied to the panel, and material 1 was flashed off at room temperature for 5 minutes to form a film of primer 1. Using the same ESTA Bell, primer coating material 2 (N-3000 QAB-CB, manufactured by BASF Coatings GmbH) was applied to the film of primer 1, and material 2 was flashed off at room temperature for 5 minutes to form a film of primer 2.

[0158] Subsequently, an aqueous coating composition (silky pearl white) was applied using a rotary atomizer (EcoBell II, manufactured by Duerr Systems AG, Germany) at a temperature of 23°C and 65% humidity to achieve a dry film thickness of 10 μm (flow rate 380 mL / min, rotation speed 40,000 rpm, voltage 60 kV). After coating, the panel was left at room temperature for 5 minutes, followed by a flash-off at 70°C for 5 minutes. After cooling to 23°C, a clear coat paint (ProGloss®, manufactured by BASF Coatings GmbH) was applied to achieve a dry film thickness of 45 μm. After coating, the panel was left for 10 minutes, followed by horizontal baking at 140°C for 30 minutes to obtain a panel with a final multilayer coating film.

[0159] The color performance of the manufactured multilayer coated films was evaluated from the perspectives of lightness index and granularity. The measurement results are summarized in Tables 9 and 10.

[0160] [Table 7]

[0161] [Table 8]

[0162] [Table 9]

[0163] [Table 10]

[0164] Based on the experimental results described above, it can be concluded that the embodiments satisfying the requirements of this disclosure have low VOC values ​​and excellent color performance, regardless of whether they use aluminum sheets or mica effect pigments. Furthermore, the embodiments of this disclosure are also expected to enable a high solids content of more than 15% by mass based on the total mass of the aqueous coating composition, thereby achieving high material transfer efficiency in application.

Claims

1. a) Water-soluble or water-dispersible binder; b) Cellulose nanofibers; c) Cosolvent of formula (I) 【Chemistry 1】 (In the formula, X １ The combination of and n is (X １ ,n) = (H, 1) or (CH ２ -CH-CH ２ 3) and X ２ and X ３ (is independently selected from an alkyl group having hydrogen and 1 to 8 carbon atoms, where m is an integer from 1 to 30); and d) Effect pigments; an aqueous coating composition comprising, The aqueous coating composition has a volatile organic compound content of 420 g / l or less without water; A multilayer coating film comprising a base coat layer obtained by applying the aqueous coating composition and a clear coat layer on the base coat layer has a lightness index of 0.20 or more, where the lightness index = (L ＊ １５° − L ＊ ２５° ) / L ＊ １５° and L ＊ １５° and L ＊ ２５° each represent lightness values measured at viewing angles of 15° and 25° according to the L ＊ a ＊ b ＊ color system (CIE lab), an aqueous coating composition.

2. e) The aqueous coating composition according to claim 1, further comprising a crosslinking agent.

3. The aqueous coating composition according to claim 1 or 2, wherein the water-soluble or water-dispersible binder (a) comprises at least one selected from the following resins: acrylic resin, polyurethane resin, acrylic-urethane resin, polyester resin, polyether resin, alkyd resin, polycarbonate resin, and epoxy resin.

4. The aqueous coating composition according to claim 1 or 2, wherein the cosolvent (c) has a boiling point of at least 140°C and an HLB value of at least 9.

5. The aqueous coating composition according to claim 1 or 2, wherein the effect pigment (d) comprises at least one selected from non-vapor-deposited metal pigments and mica.

6. The aqueous coating composition according to claim 1 or 2, wherein the effect pigment (d) has a particle size of 5 to 25 μm.

7. The aqueous coating composition according to claim 1 or 2, wherein the crosslinking agent (e) comprises at least one selected from melamine resin and blocked polyisocyanate.

8. The aqueous coating composition according to claim 1 or 2, wherein the effective content of the cellulose nanofiber (b) is 0.35% by mass to 0.80% by mass based on the total mass of the aqueous coating composition.

9. The aqueous coating composition according to claim 8, wherein the mass ratio of the cosolvent (c) to the effective content of the cellulose nanofiber (b) is 1:1 to 6:

1.

10. The aqueous coating composition according to claim 1 or 2, wherein the mass percentage of the cosolvent (c) is 70.0% by mass to 100.0% by mass, based on the total free organic solvent in the aqueous coating composition.

11. The aqueous coating composition according to claim 1 or 2, having a solid content of more than 15% by mass.

12. The aqueous coating composition according to claim 1 or 2, having a volatile organic compound content (including water) of 150 g / L or less.

13. The aqueous coating composition has a thixotropy value (Ti value) of 40 or less, where Ti value = η(A) / η(B), and η(A) is measured at 23°C using a rotational viscometer and lasts for 1000 s. －１ This is the viscosity under the shear rate, where η(B) is measured at 23°C using a rotational viscometer, and 1 s －１ The aqueous coating composition according to claim 1 or 2, wherein the viscosity under a shear rate is [value missing].

14. The multilayer coating film has a diffusion particle size of 4 or less (G ＊ The aqueous coating composition according to claim 1 or 2, having )

15. A coating film obtained from the aqueous coating composition according to claim 1 or 2, wherein the dry film thickness of the coating film is greater than 5 μm.

16. A coated article comprising a cured coating film on the article, wherein the cured coating film is obtained by curing the aqueous coating composition described in claim 1 or 2.

17. A method for manufacturing a multilayer coated film, comprising the following steps: (1) A step of optionally applying a coating material to a substrate and then curing the composition to produce a first cured coating layer on the substrate; (2) A step of manufacturing one or more base coat layers by applying one or more identical or different aqueous base coat materials onto the coating layer obtained in step (1); (3) A step of manufacturing one or more clear coat layers on one base coat layer or an uppermost base coat layer by applying one or more identical or different clear coat materials; and (4) A step of curing one or more base coat layers and one or more clear coat layers together; Includes, A method wherein at least one of the base coat materials is the aqueous coating composition described in claim 1 or 2.

18. A multilayer coated film that can be obtained by the method of claim 17.

19. The multilayer coating film has a lightness index of 0.20 or higher and a diffusion granularity of 4 or lower (G ＊ ) has the lightness index = (L ＊ １５° -L ＊ ２５° ) / L ＊ １５° And L ＊ １５° and L ＊ ２５° Each of them is L ＊ a ＊ b ＊ The multilayer coated film according to claim 18, which represents lightness values ​​measured at viewing angles of 15° and 25° according to the color system (CIE Lab).

20. A method for using the aqueous coating composition according to claim 1 or 2 for the manufacture of a pigment aqueous coating material.

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