Aqueous coating composition set and method for forming multi-layer coating film using the same

Abstract

To provide an aqueous coating composition which enables formation of a metallic coating film having high designability, and enables formation of a coating film exhibiting good coating film physical property.SOLUTION: An aqueous coating composition set for multilayer coating film formation contains a first base coating composition forming a first base coating film, and a second base coating composition forming a second base coating film, wherein the first base coating composition contains a first coating film forming resin, a first curing agent, a first inorganic brightener and a first hydrophobic association type viscous agent, the first inorganic brightener is one or more kinds selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth, the second base coating composition contains a second coating film forming resin, a second curing agent, a second bright material, a second inorganic viscous agent, a second hydrophobic association type viscous agent, and a second dispersion agent, and the second inorganic viscous agent contains a layered material having such a laminated structure that a large number of inorganic crystal layers are laminated.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an aqueous coating composition set and a method for forming a multilayer coating film using the same. [Background technology]

[0002] For example, in the coating appearance of automobile paints, coating films with metallic luster have attracted attention. Such coating films are required to have high flip-flop properties (so-called FF properties). To enhance the flip-flop properties, the pigments must be present in the paint with a certain orientation. Furthermore, it is preferable that coating films with metallic luster do not exhibit a grainy feel (glare) and have a dense feel.

[0003] JP 2006-95522 A (Patent Document 1) discloses a method for forming a metallic, highly decorative coating film, in which an aqueous base coat paint (A1) adjusted to have a solids content of 20 to 40% by weight is applied to a substrate to a dry film thickness of 1 to 15 μm, and then an aqueous base coat paint (A2) adjusted to have a solids content of 2 to 15% by weight is applied on top of the uncured coating film to a dry film thickness of 0.1 to 5 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-95522 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the water-based base coat paint (A1) and water-based base coat paint (A2) shown in Patent Document 1 are used, the orientation of the luster pigment tends to be insufficient, which may cause unevenness in the appearance of the coating film. Furthermore, if the orientation of the luster pigment is insufficient, diffuse reflection of light is likely to occur, which may reduce the design properties.

[0006] Recently, industrial products such as automobiles have adopted designs that incorporate many curved surfaces. This has created a need for coatings that can be easily applied to even complex shaped substrates and have a beautiful metallic luster.

[0007] Furthermore, automotive coating compositions are required to be able to improve the physical properties of the coating film, such as chipping resistance and water resistance.

[0008] In the painting line for automobile exterior panels, if the baked and hardened base coat has defects such as dust particles or paint defects, the affected areas are often polished and corrected before the top coat (base coat and clear coat) is applied. In this process, the polishing marks (streaks that appear when sanded with sandpaper, etc.) can appear on the top coat after application (a phenomenon known as base coat transfer). This base coat transfer is particularly likely to occur when the top coat contains a lustrous material. Therefore, with metallic and mica-based paint colors in particular, paint workability requires a coating that is less susceptible to base coat transfer (base coat transferability).

[0009] However, in the coating composition for forming the metallic coating film shown in Patent Document 1, only the improvement of the design is focused on, and the assurance of the above-mentioned coating film physical properties is left to another coating film. For this reason, for example, the coating composition must be prepared taking into consideration the relationship between the coating film that ensures the coating film physical properties and the coating film that exhibits the metallic design. As a result, an excellent metallic coating film may not be obtained. In addition, the process of forming the multilayer coating film becomes complicated. To solve these problems, there is a need for a coating composition that can form a metallic coating film with high designability and that can also form a coating film that exhibits good coating film properties.

[0010] In view of the above-mentioned current situation, the present disclosure provides an aqueous coating composition set for forming a multilayer coating film, which can form a coating film with excellent design and metallic luster, and which also has coating film physical properties such as improved chipping resistance and substrate transferability. Furthermore, the aqueous coating composition set for forming a multilayer coating film of the present disclosure can form a multilayer coating film with excellent water resistance. A further object of the present disclosure is to provide a method for forming a multi-layer coating film using the aqueous coating composition set. [Means for solving the problem]

[0011] In order to solve the above problems, the present disclosure provides the following aspects. [1] This disclosure An aqueous coating composition set for forming a multilayer coating film having a first base coating film and a second base coating film, The aqueous coating composition set includes a first base coating composition that forms a first base coating film and a second base coating composition that forms a second base coating film, the first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic glossing agent, and a first hydrophobic association-type viscosity-improving agent; the first inorganic brightener comprises one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth; the second base coating composition comprises a second film-forming resin, a second curing agent, a second luster material, a second inorganic viscous agent, a second hydrophobic association-type viscous agent, and a second dispersant; The second inorganic viscosity agent contains a layered material having a laminated structure of inorganic crystal layers. [2] In one embodiment, the second glitter comprises a surface-treated glitter. [3] In one embodiment, the second lustrous material includes a lustrous material having a scaly shape and an aspect ratio of 5 to 2,000. [4] In one embodiment, the second base coating composition comprises a second inorganic viscosity-improving agent in an amount of 1 part by weight to 7 parts by weight per 100 parts by weight of the total resin solids of the second film-forming resin and the second curing agent; The second hydrophobic association type viscosity modifier is contained in an amount of 1 part by mass to 15 parts by mass per 100 parts by mass of the total resin solid content of the second coating film-forming resin and the second curing agent. [5] In one embodiment, the second base coating composition further comprises a second inorganic gloss agent; the amount of the first inorganic gloss agent contained in the first base coating composition is (Am1) relative to 100 parts by mass of the total resin solids of the first coating film-forming resin and the first curing agent, When the amount of the second inorganic gloss agent contained in the second base coating composition is (Am2) relative to 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent, The ratio (Am1) / (Am2) of (Am1) to (Am2) may be 2.0 or more. [6] In one embodiment, the non-volatile content (NV1) of the first base coating composition is 10% or more and 45% or less. [7] In one embodiment, the non-volatile content (NV2) of the second base coating composition is 3% or more and 18% or less. [8] In one embodiment, the first base coating composition further comprises at least one of a first glittering material and a first inorganic viscosity agent. [9] In one embodiment, the second film-forming resin comprises at least one selected from an acrylic resin, a urethane resin, and a polyester resin.

[10] In one embodiment, the second inorganic viscosity agent is a silicate layer compound.

[11] In one embodiment, at least one of the first hydrophobic association type viscous agent and the second hydrophobic association type viscous agent comprises a urethane-based hydrophobic association type viscous agent.

[12] In one embodiment, the first base coating composition further comprises a first dispersant; At least one of the first dispersant and the second dispersant includes a polymeric dispersant having at least one group selected from an anionic group, a cationic group, and a nonionic group.

[13] In one embodiment, the first inorganic brightener comprises a surface positively charged inorganic brightener.

[14] In one embodiment, the second inorganic brightener comprises a surface positively charged inorganic brightener.

[15] In one embodiment, the thickness of the first inorganic viscosity agent is 100 nm or less.

[16] In one embodiment, the thickness of the second inorganic viscosity agent is 100 nm or less.

[17] In another embodiment, the present disclosure provides a method for forming a multi-layer coating film using an aqueous coating composition set for forming a multi-layer coating film, comprising: The method for forming a multi-layer coating film is as follows: A step of applying a first base coating composition to an object to be coated to form an uncured first base coating film; A step of applying a second base coating composition onto the uncured first base coating film to form an uncured second base coating film; A step of applying a clear coating composition for forming a clear coating film onto the uncured second base coating film to form an uncured clear coating film; The method includes a step of simultaneously baking and curing an uncured first base coating film, an uncured second base coating film, and an uncured clear coating film to form a multi-layer coating film, The film thickness (t1) of the heat-cured first base coating film formed from the first base coating composition is 1 μm or more and 35 μm or less, The film thickness (t2) of the heat-cured second base coating film formed from the second base coating composition is 1 μm or more and 20 μm or less.

[18] In one embodiment, the film thickness (t1) of the heat-cured first base coating film and the film thickness (t2) of the heat-cured second base coating film satisfy the relationship (t1)≧(t2). [Effects of the Invention]

[0012] The aqueous coating composition set for forming a multilayer coating film of the present disclosure can form a coating film with excellent metallic design, and can also form a coating film with good coating film properties such as chipping resistance and water resistance. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, the process leading to the present disclosure will be described. In general, in aqueous coating compositions that form single-layer coating films with metallic luster, the solid content (also called nonvolatile (NV) content) of the coating composition is set high (e.g., NV content = 25%). Increasing the NV content increases the viscosity of the coating, preventing the coating composition from flowing and also preventing the luster material from settling.

[0014] However, aqueous coating compositions with a high NV content also have high viscosity, which makes it difficult for the luster pigment to be uniformly oriented. For example, when a coating film is formed using an aqueous coating composition with an NV content of about 25%, the luster pigment is not oriented uniformly, resulting in a grainy appearance (glare) in the coating film and possibly a reduction in the hiding power of the base.

[0015] To solve these problems, it has been proposed to stack multiple thin layers formed from aqueous coating compositions with high NV content. This is expected to improve the orientation of the luster pigment. However, as mentioned above, the orientation of the luster pigment has not yet improved, and a good metallic coating film has not been obtained.

[0016] Furthermore, when a multilayer coating film is formed using an aqueous coating composition, for example, by wet-on-wet coating, a mixed phase may occur near the interface of the layers. However, attempts to suppress the mixed phase may result in a decrease in design and coating film physical properties. For this reason, the present inventors have intensively studied a coating composition that can form a coating film having a good balance between high design and coating film physical properties, and have completed the present disclosure.

[0017] The aqueous coating composition set of the present disclosure, which solves all of these problems, is as follows: An aqueous coating composition set for forming a multilayer coating film having a first base coating film and a second base coating film, The aqueous coating composition set includes a first base coating composition that forms the first base coating film and a second base coating composition that forms the second base coating film, the first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic glossing agent, and a first hydrophobic association-type viscosity-improving agent; the first inorganic brightener comprises one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth; the second base coating composition comprises a second film-forming resin, a second curing agent, a second luster material, a second inorganic viscous agent, a second hydrophobic association-type viscous agent, and a second dispersant; The second inorganic viscosity-imparting agent contains a layered material having a laminated structure in which many inorganic crystal layers are stacked.

[0018] The aqueous coating composition set for forming a multilayer coating film according to the present disclosure improves the orientation of the luster material (luster pigment). Therefore, diffused reflection of light can be suppressed, and an excellent metallic coating film with sufficient highlight brightness can be formed. Furthermore, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure can be easily applied to even substrates with complex shapes, and a coating film with a beautiful metallic luster can be formed. Furthermore, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure forms a coating film having excellent coating film properties such as good chipping resistance, weather resistance, water resistance, and high-temperature water resistance. Furthermore, the coating film has excellent substrate transferability and also excellent substrate hiding power. While not wishing to be limited to any particular theory, the present disclosure provides a method for preparing a coating composition comprising: 2B Base paint The combination with the composition controls light transmission, which is presumably what contributes to the excellent weather resistance of the multi-layer coating film.

[0019] Furthermore, although not limited to a specific theory, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure has a predetermined structure for each coating composition, which significantly suppresses the interphase that may occur between the first base coating composition and the second base coating composition according to the present disclosure. Therefore, for example, a multilayer coating film can be formed using wet-on-wet coating. Therefore, the number of steps required for coating film formation can be reduced, thereby reducing the environmental impact. Furthermore, since the second inorganic viscous agent contains a layered material having a laminated structure of inorganic crystal layers, although interpretation should not be limited to a specific theory, structuring (cohesion) occurs due to the interaction between the second luster material and the second inorganic viscous agent, preventing the second luster material from becoming disoriented in the second base coating film, resulting in the formation of an excellent metallic coating film. Furthermore, the resulting coating film has excellent water resistance. In one embodiment, even when the concentration of the second luster material (PWC: Pigment weight concentration) contained in the second base coating composition is high, the stability of the second base coating composition can be easily maintained by including the second inorganic viscosity-improving agent according to the present disclosure within the range described herein. Furthermore, the cohesive strength of the second base coating film is further improved, making it easy to form a coating film with excellent design properties, coating film properties, and water resistance.

[0020] The aqueous coating composition set according to the present disclosure and the method for forming a multilayer coating film using the same will be described in detail below.

[0021] <First base coating composition> The first base coating composition of the present disclosure comprises a first film-forming resin, a first curing agent, a first inorganic brightening agent, and a first hydrophobic association-type viscous agent. If the aqueous coating composition set according to the present disclosure contains a first base coating composition having such a composition and further comprising a predetermined second base coating composition described below, it is possible to form a multilayer coating film (a lustrous multilayer coating film) that has a beautiful metallic feel in addition to excellent base hiding power, chipping resistance, etc.

[0022] In one embodiment, the first base coating composition further comprises at least one of a first luster material and a first inorganic viscosity-improving agent. For example, the first base coating composition can further improve its base hiding power by including the first luster material. Furthermore, together with the second base coating film, a multi-layer coating film can be formed that exhibits a deeper metallic appearance. In an embodiment in which the first base coating composition contains a first luster material, the first base coating composition may contain a first inorganic viscosity agent. By using the first luster material and the first inorganic viscosity agent in combination in the first base coating composition, it is possible to prevent the first luster material from settling during coating film formation and to prevent the coating film from becoming cloudy. In addition, because the first luster material is more uniformly oriented, a first base coating film with even better design properties and a multilayer coating film containing this first base coating film can be obtained.

[0023] In some embodiments, the non-volatile content (NV1) of the first base coating composition is 10% to 45%, for example, 10% to 35%. In some embodiments, (NV1) is 10% to 30%, for example, 15% to 25%.

[0024] The nonvolatile content (NV1) is a value calculated by [(mass of the first base coating composition after drying) / (mass of the first base coating composition before drying)] × 100 (%). The nonvolatile content can be controlled by adjusting the amount of solvent in the coating composition. By ensuring that the non-volatile content (NV1) is within the above range, the volume shrinkage rate of the first base coating film and the second base coating film according to the present disclosure can be maintained within a sufficient range, and a multi-layer coating film with a good metallic luster can be formed. Furthermore, good coating film properties can be obtained, for example, the sagging properties of the first base coating composition can be improved, and further, coating workability can be improved. The non-volatile content can be measured by the method of JIS K5601-1-2 (heating residue).

[0025] The dry film thickness (t1) of the first base coating film formed is 1 μm or more and 35 μm or less, for example, 1 μm or more and 30 μm or less. In another embodiment, the film thickness of the first base coating film is 1 μm or more and 16 μm or less. Furthermore, the first base coating composition according to the present disclosure can prevent the coating composition from dripping and the first luster material, which is added as needed, from settling. Furthermore, even on substrates with complex shapes incorporating many curved surfaces, a coating film with a beautiful, uniform metallic luster can be formed.

[0026] (1st coating film forming resin) In one embodiment, the first coating film-forming resin in the present disclosure is a resin having a number average molecular weight of 5,000 or more and 30,000 or less, for example, 7,000 or more and 25,000 or less. Having a number average molecular weight within this range allows for good workability and also allows for curability suitable for the multilayer coating film according to the present disclosure. In this specification, the molecular weight is determined by the GPC method using a styrene polymer as the standard.

[0027] In one embodiment, the first film-forming resin has a hydroxyl value of 20 to 180, for example, 30 to 160. When the hydroxyl value of the first film-forming resin is within this range, the first base coating can have sufficient water resistance, for example, excellent high-temperature water resistance (80°C), and also have good coating curability.

[0028] In one embodiment, the first film-forming resin has an acid value of 10 mgKOH / g or more and 80 mgKOH / g or less, for example, 15 mgKOH / g or more and 70 mgKOH / g or less. When the acid value of the first film-forming resin is within this range, the first base coating can have sufficient water resistance, for example, excellent high-temperature water resistance (80°C), and also have good coating curability.

[0029] Examples of the first film-forming resin include acrylic resins, polyester resins, alkyd resins, polyether resins, polyolefin resins, urethane resins, melamine resins, etc. These resins may be contained alone or in combination of two or more. For example, it is preferable to use a first film-forming resin selected from acrylic resins, polyester resins, melamine resins, urethane resins, and mixtures thereof, from the viewpoint of film strength, weather resistance, water resistance, etc. For example, the first film-forming resin includes at least one selected from acrylic resins, urethane resins, and polyester resins. In one embodiment, an acrylic resin and a urethane resin may be used in combination, in which case the acrylic resin may be contained in a solid content of 40 to 60 parts by mass, and the urethane resin may be contained in a solid content of 1 to 20 parts by mass, relative to 100 parts by mass of the total resin solid content of the first coating film-forming resin and the first curing agent. When multiple types of acrylic resins are used, the total parts by mass of the acrylic resins can be appropriately adjusted so that it falls within the above range. Similarly, when multiple types of urethane resins are used, the total parts by mass of the urethane resins can be appropriately adjusted so that it falls within the above range. In this disclosure, the first film-forming resin and the first film-curing agent are sometimes collectively referred to as the "first main resin." Furthermore, the "resin solids mass of the first main resin" refers to the total solids mass of the first film-forming resin and the first curing agent. For example, 100 parts by mass of the resin solids mass of the "first main resin" corresponds to 100 parts by mass of the combined resin solids mass of the first film-forming resin and the first curing agent.

[0030] (First hardener) The first base coating composition according to the present disclosure contains a first curing agent that is appropriately suited to the type of curable functional group possessed by the first film-forming resin. The first curing agent can be a known one, and includes, for example, an amino resin, a blocked isocyanate resin, an epoxy compound, an aziridine compound, a carbodiimide compound, an oxazoline compound, etc. From the viewpoints of the performance properties of the resulting coating film and cost, an amino resin and / or a blocked isocyanate resin is preferred.

[0031] The amino resin contained in the first curing agent is not particularly limited, and a water-soluble melamine resin and / or a water-insoluble melamine resin can be used.

[0032] Blocked isocyanate resins can be prepared by adding a blocking agent having an active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. When heated, the blocking agent dissociates to generate isocyanate groups, which then react with functional groups in the resin component to cure.

[0033] The amount of the first curing agent blended is, for example, 5 to 50 parts by mass, for example, 5 to 40 parts by mass, per 100 parts by mass of the resin solids of the first main resin (first film-forming resin and first curing agent). By blending the amount of the first curing agent within this range, sufficient coating film curability can be obtained.

[0034] (First inorganic brightener) The first inorganic brightener is one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth. By including the first inorganic brightener, the first base paint composition can improve the gloss of the entire multilayer coating film, and can form a multilayer coating film with excellent design properties, for example, an excellent metallic finish.

[0035] Although not intended to be limited to any particular theory, when a second base paint composition is applied onto a coating film (first base paint film) formed by a first base paint composition, the first inorganic brightening agent attempts to adsorb the solvent contained in the second base paint composition. As the solvent moves, the second luster pigment moves, improving its orientation. Furthermore, the viscosity of the second base paint composition increases, making it easier to maintain the orientation of the second luster pigment. As a result, the orientation of the second luster pigment in the second base paint film improves. By improving the orientation of the luster pigment, an excellent metallic coating film can be formed with reduced diffuse reflection of light.

[0036] Furthermore, the first inorganic brightener can contribute to suppressing interphase formation between the first and second base coating films, which suppresses interphase formation, thereby preventing deterioration in the appearance of the coating film and maintaining better coating film properties such as chipping resistance.

[0037] In one embodiment, the first inorganic brightening agent includes an inorganic brightening agent having a positively charged surface, which, in addition to the above-mentioned effects, can further improve the orientation of the first brightening material contained in the first base coating composition.

[0038] Furthermore, in an embodiment in which the first base coating composition contains a first luster material, the first inorganic brightening agent promotes uniform dispersion of the first luster material and can suppress localization of the first luster material.Furthermore, the first inorganic brightening agent can suppress unevenness in the first base coating film. The first inorganic brightener can also impart impact stress dispersion capabilities to the first base coating film according to the present disclosure, so that, for example, the first base coating film formed from the first base paint composition having a predetermined composition can have good chipping resistance.

[0039] In some embodiments, the first inorganic brightener comprises a surface positively charged inorganic brightener, for example, the first inorganic brightener comprises barium sulfate. For example, by including barium sulfate in the first inorganic brightening agent, it is possible to more effectively prevent interphase formation with the second base coating composition. Furthermore, since the second base coating composition in which interphase formation is prevented includes the specific second inorganic viscosity-improving agent according to the present disclosure, cohesion (structuring) is generated in the second base coating film, and the orientation disorder of the second brightening agent is more effectively prevented. Thus, in one embodiment, when the first inorganic glossing agent contains barium sulfate, the effect of preventing intermixing between the first base coating film and the second base coating film is enhanced, and the orientation disorder of the second glossing material in the second base coating film is more effectively prevented.

[0040] In one embodiment, the average primary particle size of the first inorganic brightener is 1 μm or less, for example, 0.01 μm or more and 0.8 μm or less, for example, 0.05 μm or more and 0.5 μm or less. The average primary particle size can be measured according to a known method.

[0041] The amount of the first inorganic glossing agent is, for example, 1 part by mass or more and 40 parts by mass or less, for example, 5 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the resin solid content of the first coating film-forming resin and the first curing agent. In one embodiment, the amount of the first inorganic glossing agent is 7 parts by mass or more and 35 parts by mass or less, per 100 parts by mass of the resin solid content. By keeping the amount of the first inorganic glossing agent within this range, interphase formation is further suppressed, making it easy to form a coating film with good gloss.

[0042] (First hydrophobic association type viscosity agent) The first hydrophobic association viscosity agent according to the present disclosure can increase the viscosity of the first base coating composition through hydrophobic interaction between at least one of the hydrophobic groups contained in at least one of the group consisting of the first film-forming resin, the first curing agent, and the first inorganic glossing agent contained in the first base coating composition. By including the first hydrophobic association viscosity agent, the first base coating composition can suppress coating defects such as cissing and dents in the first base coating film and can improve the smoothness of the interface between the first base coating film and the second base coating film. Furthermore, it is possible to suppress the disorder of the orientation of the first luster material in the vicinity of the interface, and to form a multi-layer coating film with luster and excellent metallic appearance.

[0043] Examples of the first hydrophobic association type viscous agent include polyacrylic acid-based viscous agents copolymerized with hydrophobic monomers, polyurethane-based viscous agents having hydrophobic chains in the molecule, urethane-urea-based viscous agents in which at least a portion of the main chain is a hydrophobic urethane chain, amide-urea-based viscous agents in which at least a portion of the main chain is a hydrophobic amide chain, and other viscous agents.

[0044] In one embodiment, the first hydrophobic association type thickener includes a polyurethane-based thickener having a hydrophobic chain in the molecule, or a urethane-urea-based thickener in which at least a portion of the main chain is a hydrophobic urethane chain. In addition to the above-mentioned effects, the inclusion of such a hydrophobic association type thickener can more effectively exhibit excellent anti-settling and anti-sagging properties in systems containing aqueous materials, such as the first base coating composition. For example, urethane-based hydrophobic association viscosity agents, such as polyurethane-based viscosity agents and urethane-urea-based viscosity agents, have the property of easily developing viscosity at low shear and not easily developing viscosity at high shear, resulting in excellent thixotropy. Due to these properties, the first base coating composition of the present disclosure can be suitably used for, for example, spray coating. Furthermore, a first base coating film formed from a first base coating composition containing such a hydrophobic association viscosity agent can have excellent water resistance and high-temperature water resistance.

[0045] Commercially available examples of the first hydrophobic association type viscosity agent include BYK-425 (urea-modified urethane compound: manufactured by BYK-Chemie), BYK-420 (urethane-urea compound: manufactured by BYK-Chemie), BYK-430 (amide-urea compound: manufactured by BYK-Chemie), PU 1250 (polyurethane polymer: manufactured by BASF), SN Thickener-660T, SN Thickener-665T (urethane-based: manufactured by San Nopco), RHEOLATE 216 (urethane-urea compound: manufactured by ELEMENTIS), Primal RM-12W, Primal RM-895 (urethane-based: manufactured by The Dow Chemical Company), and Disparlon AQ-021 (Kusumoto Chemicals).

[0046] The first base coating composition of the present disclosure contains the first hydrophobic association type viscous agent in an amount of 0.1 parts by mass or more and 5.0 parts by mass or less, for example, 0.1 parts by mass or more and 4.0 parts by mass or less, per 100 parts by mass of the total resin solids content of the first coating film-forming resin and the first curing agent. Preferably, the first hydrophobic association type viscosity modifier is contained in an amount of 0.2 parts by mass or more and 3.5 parts by mass or less, for example, 0.2 parts by mass or more and 3.0 parts by mass or less, per 100 parts by mass of the total resin solids content of the first coating film-forming resin and the first curing agent.

[0047] By including the first hydrophobic association type viscosity agent in such a range, it becomes easier to avoid the first inorganic gloss agent and the first lustrous material, which is added if desired, settling during the formation of the first base coating film, and the occurrence of turbidity in the first base coating film. Furthermore, since the first lustrous material, which is added if desired, can be more uniformly oriented, it is easy to obtain a first base coating film and a multi-layer coating film with excellent design, especially an excellent metallic tone. Furthermore, since the first base coating film can have excellent water resistance and even excellent high-temperature water-resistant adhesion, the water resistance and high-temperature water resistance of the entire multi-layer coating film can be further improved.

[0048] (First dispersant) The first base coating composition of the present disclosure may contain a first dispersant, which improves the dispersion stability of the various components contained in the first base coating composition.

[0049] In one embodiment, the first dispersant has a substituent that provides dispersion stability to the metal or metal oxide. By having such a substituent, the first dispersant can effectively coat, for example, the first inorganic brightening agent and the first luster material that may be added if desired. Furthermore, depending on the molecular weight of the first dispersant, the steric hindrance of the first inorganic brightening agent and the first luster material can be increased, thereby suppressing their aggregation. Furthermore, such a first dispersant can improve the dispersibility of the first inorganic brightening agent and the first luster material.

[0050] In one embodiment, the first dispersant may have a highly hydrophobic side chain. In this case, the first dispersant may be dissolved in an organic solvent having a water solubility of 0.01% by mass or more and 5.0% by mass or less, such as an alcohol-based organic solvent or a glycol ether-based organic solvent.

[0051] The first dispersant may be either a polymeric dispersant or a low-molecular surfactant-type dispersant. For example, a polymeric dispersant is preferred from the viewpoint of preventing aggregation of the first lustrous material. The polymeric dispersant is preferably a polymeric dispersant having at least one group selected from an anionic group, a cationic group, or a nonionic group, and more preferably at least one group selected from a polymeric dispersant having a highly hydrophobic side chain and an anionic group, a polymeric dispersant having a nonionic group, and a mixture thereof. Examples of anionic groups include phosphate groups and carboxylic acid groups. Examples of nonionic groups include polyoxyalkylene groups. However, the present invention is not limited to these groups.

[0052] As described above, the polymer dispersant may be a known dispersant such as an anionic, cationic, or nonionic acrylic copolymer, block copolymer, etc. In one embodiment, from the viewpoint of dispersion stability, a polymer having anionic or nonionic properties is preferred, and an acrylic copolymer or block copolymer is preferred.

[0053] As the polymer dispersant, known dispersants can be used, and commercially available products may also be used. Examples include the DISPERBYK series manufactured by BYK-Chemie, such as DISPERBYK, DISPERBYK-194, DISPERBYK-194N, and DISPERBYK-192; and Solsperse 41000, Solsperse 43000, Solsperse 44000, and Solsperse 47000 manufactured by Lubrizol. DISPERBYK-192, DISPERBYK-194N, and DISPERBYK are preferably used.

[0054] The amount of the first dispersant can be 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of the resin solids of the first coating film-forming resin and the first curing agent. This range further enhances the dispersion stability of the various components contained in the first base coating composition, effectively suppressing aggregation of each component during the process of forming the first base coating film. In one embodiment, aggregation of the first lustrous material can be effectively prevented, and the dispersibility of the first lustrous material can be improved.

[0055] (1st bright material) In one embodiment, the first base coating composition includes at least one of a first luster material and a first inorganic viscosity agent. Depending on the desired metallic appearance, the first base coating composition may include a first luster material. The first luster material in the present disclosure is a pigment that imparts a metallic luster to the coating film. The first base coating composition may contain one type of first luster material alone, or may contain a combination of multiple types of first luster materials.

[0056] The mass concentration (PWC) (%) of the first luster material in the first base coating composition is calculated using the following formula: PWC = (total mass of first lustrous material) / [(total mass of resin solid content of first coating film-forming resin and resin solid content of first curing agent) + (total mass of first lustrous material)] × 100 It is shown as follows. In this case, the PWC range may be 0% or more and 30% or less, for example, 1% or more and 30% or less, and in some embodiments, 5% or more and 20% or less, for example, 5% or more and 15% or less. By having the mass concentration of the first lustrous material within the above range, the first lustrous material is more uniformly oriented after coating film formation, making it possible to easily form a coating film with excellent lustrous properties and excellent design. Furthermore, the resulting coating film can have good base hiding power.

[0057] The first lustrous material may be the same lustrous material as the second lustrous material described below. In this embodiment, the detailed description of the properties of the first lustrous material can be found in the description of the second lustrous material described below. The first luster material may also be a luster material that has been surface-treated, for example, a luster material that has been surface-treated for use in an aqueous coating composition. In one aspect, surface treatment of aluminum luster pigments has the advantage of suppressing gassing (generation of hydrogen gas due to oxidation of the aluminum surface by water) in aqueous coating compositions. Examples of surface treatments include silica treatment (silane coupling agent coating), molybdenum treatment (molybdic acid coating), and organic treatment (resin coating).

[0058] The first lustrous material and the surface-treated first lustrous material may be commercially available lustrous materials, for example, METALURE manufactured by Ecart Co., Ltd. (登録商標) Series, SILVERSHINE (登録商標) Series, HYDROSHINE (登録商標) Series, Liquid Black k、 PLISMATIC (登録商標) series, the FD series, GX series, BS series, and WA series manufactured by Asahi Kasei Chemicals Corporation, and the 46 series, 63 series, WL series, WM series, and EMERAL series manufactured by Toyo Aluminum Co., Ltd.

[0059] (First inorganic viscosity agent) The first inorganic viscosity agent according to the present disclosure is preferably a layered substance having a laminated structure in which many inorganic crystal layers are stacked on top of one another. This layered structure of the first inorganic viscosity agent swells in the first base coating composition to form a house-of-cards structure, thereby imparting an appropriate viscosity to the first base coating composition and resulting in excellent coating film strength.

[0060] The shape of the primary particles of the first inorganic viscosity agent may be disc-shaped, plate-shaped, spherical, granular, cubic, needle-shaped, rod-shaped, amorphous, etc., with disc-shaped or plate-shaped being preferred.

[0061] The thickness of the first inorganic viscous agent is preferably 100 nm or less. This makes it easier to control the viscosity of the first base coating composition within an appropriate range. The thickness of the first inorganic viscous agent is more preferably 50 nm or less, even more preferably 10 nm or less, and particularly preferably 5 nm or less. The thickness of the first inorganic viscous agent may be, for example, 0.1 nm or more, or 0.3 nm or more.

[0062] The thickness of the first inorganic viscous agent other than the disk-shaped or plate-shaped one is synonymous with the average diameter of the primary particles. The average diameter is the 50% average particle diameter (D50) in the volume-based particle size distribution obtained by the laser diffraction / scattering method. The thickness of the disk-shaped or plate-shaped first inorganic viscous agent is the length of the first inorganic viscous agent in the direction perpendicular to its main surface. The same applies to the thickness of the second inorganic viscous agent.

[0063] Inorganic viscosity agents according to the present disclosure include silicate layer compounds (silicate minerals), halide minerals, oxide minerals, carbonate minerals, borate minerals, sulfate minerals, molybdate minerals, tungstate minerals, phosphate minerals, arsenate minerals, vanadate minerals, etc. Such inorganic viscosity agents impart appropriate viscosity and excellent coating strength to the first base coating composition. For example, the combined use of an inorganic viscosity agent and a first hydrophobic association type viscosity agent can provide the first base coating film with excellent water resistance and high-temperature water resistance, thereby maintaining good water resistance and high-temperature water resistance for the entire multi-layer coating film. In one embodiment, the first inorganic viscosity agent comprises a silicate layer compound.

[0064] Specific examples of silicate layer compounds include natural or synthetic smectite clay minerals such as hectorite, saponite, stevensite, hydrite, montmorillonite, nontrite, and bentonite; swelling mica clay minerals such as Na-type tetrasilicic fluormica, Li-type tetrasilicic fluormica, Na-type fluortaeniolite, and Li-type fluortaeniolite; vermicularite; kaolinite; or mixtures thereof.

[0065] Examples of commercially available inorganic viscosity agents include Laponite XLG (a synthetic hectorite-like substance manufactured by BYK), Laponite RD (a synthetic hectorite-like substance manufactured by BYK), Laponite EP (a synthetic hectorite-like substance manufactured by BYK), Laponite RDS (a synthetic hectorite-like substance manufactured by BYK), Optigel WX (a sodium-substituted bentonite manufactured by BYK), Thermavis (a synthetic hectorite-like substance manufactured by Henkel), and Sumecton SA-1 (a saponin-like substance manufactured by Kunimine Industries Co., Ltd.). These include montmorillonite-like substance), Bengel (natural bentonite sold by Hojun Co., Ltd.), Kunibia F (natural montmorillonite sold by Kunimine Kogyo Co., Ltd.), Veegum (natural hectorite manufactured by Vanderbilt Corporation in the United States), Dimonite (synthetic swelling mica manufactured by Topy Industries Co., Ltd.), Somasif (synthetic swelling mica manufactured by Co-op Chemical Co., Ltd.), SWN (synthetic smectite manufactured by Co-op Chemical Co., Ltd.), SWF (synthetic smectite manufactured by Co-op Chemical Co., Ltd.), etc.

[0066] In one embodiment, the first base coating composition of the present disclosure contains the first inorganic viscous agent in an amount of 0 to 10 parts by weight, for example, 0.5 to 10 parts by weight, per 100 parts by weight of the total resin solids of the first film-forming resin and the first curing agent (per 100 parts by weight of the total resin solids of the first film-forming resin and the first curing agent). In one embodiment, the first base coating composition of the present disclosure contains the first inorganic viscous agent in an amount of 0 to 10 parts by weight, per 100 parts by weight of the total resin solids of the first film-forming resin and the first curing agent. By including the component in such an amount, a coating film having good water resistance can be formed.

[0067] By including the first inorganic viscosity agent in such a range, it becomes easier to avoid the first lustrous material, which is added as needed, from settling during the formation of the first base coating film, and a coating film with excellent design properties, particularly an excellent metallic tone, can be easily obtained.

[0068] <Second base coating composition> The second base coating composition of the present disclosure comprises a second film-forming resin, a second curing agent, a second lustrous material, a second inorganic viscous agent, a second hydrophobic association-type viscous agent, and a second dispersant. Furthermore, the second inorganic viscous agent includes a layered material having a laminated structure of inorganic crystal layers. In this specification, the expression "the second inorganic viscous agent includes a layered material having a laminated structure in which many inorganic crystal layers are stacked" is synonymous with "the second inorganic viscous agent includes a layered material having a laminated structure of inorganic crystal layers." The aqueous coating composition set according to the present disclosure, which includes the second base coating composition having such a predetermined composition and the above-mentioned predetermined first base coating composition, can form an excellent metallic coating film with improved orientation of the luster material and suppressed diffuse reflection of light. Furthermore, even substrates with complex shapes can be easily coated, and a coating film with a beautiful metallic luster can be formed. Furthermore, the aqueous coating composition set for forming multilayer coating films according to the present disclosure can form a coating film with good physical properties such as good chipping resistance, water resistance, and high-temperature water resistance. Another advantage is that it has excellent substrate transferability. Therefore, the aqueous paint composition set for forming a multilayer coating film according to the present disclosure can form a metallic multilayer coating film (a lustrous multilayer coating film) that has excellent design properties and good coating film properties.

[0069] In some embodiments, the non-volatile content (NV2) of the second base coating composition is 3% or more and 18% or less, for example, 4% or more and 17% or less, and in some embodiments, NV2 is 5% or more and 15% or less.

[0070] The nonvolatile content (NV2) is a value calculated by [(mass of the second base coating composition after drying) / (mass of the second base coating composition before drying)] × 100 (%). The nonvolatile content can be controlled by adjusting the amount of solvent in the second base coating composition.

[0071] By ensuring that the non-volatile content (NV2) is within the above range, the volume shrinkage rate of the second base coating film according to the present disclosure can be maintained within a sufficient range, and a multi-layer coating film with good metallic luster can be easily formed. Furthermore, good coating film properties can be obtained, for example, the sagging properties of the second base coating composition can be improved, and furthermore, coating workability can be improved. The non-volatile content can be measured by the method of JIS K5601-1-2 (heating residue).

[0072] The second base coating composition according to the present disclosure can prevent the sedimentation of the second lustrous material and the flow of the coating composition, despite its low non-volatile content (NV2). Furthermore, the second base coating composition according to the present disclosure can form a thin film, allowing the second lustrous material to be more uniformly oriented. Therefore, an excellent metallic coating film can be easily obtained. Furthermore, the second base coating composition according to the present disclosure can be applied to substrates with complex shapes without causing sagging. Moreover, because the second base coating composition according to the present disclosure is water-based, it places less strain on the environment and workers.

[0073] As described above, the second base coating composition according to the present disclosure exhibits a low non-volatile content (NV2), allowing the coating film to be thin and uniform in thickness. In one embodiment, the coating film thickness (t2) of the second base coating film is 1 μm or more and 20 μm or less, for example, 2 μm or more and less than 15 μm. In another embodiment, the coating film thickness of the second base coating film is 3 μm or more and 7 μm or less. Furthermore, when a coating film is formed from a second base coating composition with a low NV content, the volume shrinkage of the second base coating composition after application allows the second luster material to be more uniformly oriented, resulting in high flip-flop properties. In other words, unlike conventional aqueous coating compositions with a high NV content (e.g., NV content = 25%), the second base coating composition of the present disclosure can freely form a thin film with a uniform thickness and can form a coating film with high flip-flop properties.

[0074] Furthermore, with the aqueous paint composition set of the present disclosure, the interaction achieved by the combination of the specified first base paint composition and second base paint composition according to the present disclosure, and the low non-volatile content (NV2) of the second base paint composition, allows the second lustrous material to be more uniformly oriented, resulting in higher flip-flop properties and a lower G value (graininess).

[0075] Furthermore, despite having such a low NV amount, the second base coating composition according to the present disclosure can prevent sagging of the second base coating composition and settling of the second luster material. Furthermore, even on substrates with complex shapes incorporating many curved surfaces, a second base coating film and a multi-layer coating film with a uniform, beautiful metallic luster can be formed.

[0076] (Second coating film forming resin) The second film-forming resin in the present disclosure may contain the same type of resin as the first film-forming resin, a different type of resin, or a mixture thereof. For example, the second film-forming resin may contain the same type of resin as the first film-forming resin.

[0077] In one embodiment, the second coating film-forming resin has a number average molecular weight of 5,000 to 30,000, for example, 7,000 to 25,000. Having a number average molecular weight within this range allows for good workability and also allows for curability suitable for the multi-layer coating film according to the present disclosure.

[0078] In one embodiment, the second film-forming resin has a hydroxyl number of 20 or greater and 180 or less, for example, 30 or greater and 160 or less. In some embodiments, the second film-forming resin has an acid number of from 10 mg KOH / g to 80 mg KOH / g, for example, from 15 mg KOH / g to 70 mg KOH / g. When the hydroxyl value and / or acid value of the second film-forming resin is within this range, the second base coating film can have sufficient water resistance, for example, excellent high-temperature water resistance (80°C), and also have good coating curability.

[0079] Examples of the second film-forming resin include acrylic resins, polyester resins, alkyd resins, polyether resins, polyolefin resins, urethane resins, melamine resins, etc. These resins may be contained alone or in combination of two or more. For example, it is preferable to use a first film-forming resin selected from acrylic resins, polyester resins, melamine resins, urethane resins, and mixtures thereof, from the viewpoints of film strength, weather resistance, water resistance, etc. For example, the second film-forming resin includes at least one selected from acrylic resins, urethane resins, and polyester resins. In one embodiment, an acrylic resin and a urethane resin may be used in combination. In this case, the acrylic resin may be contained in an amount of 40 to 60 parts by mass in terms of solid content, and the urethane resin may be contained in an amount of 1 to 20 parts by mass in terms of solid content, relative to 100 parts by mass of the total resin solid content of the second coating film-forming resin and the second curing agent. When multiple types of acrylic resins are used, the total parts by mass of the acrylic resins can be appropriately adjusted so that it falls within the above range. Similarly, when multiple types of urethane resins are used, the total parts by mass of the urethane resins can be appropriately adjusted so that it falls within the above range. For example, "mass of resin solids of the second main resin" refers to the total solid content of the second film-forming resin and the second curing agent. For example, 100 parts by mass of resin solids of the "second main resin" corresponds to 100 parts by mass of the combined resin solids of the second film-forming resin and the second curing agent.

[0080] (Second curing agent) The second base coating composition according to the present disclosure contains a curing agent that appropriately corresponds to the type of curable functional group possessed by the second film-forming resin. The second base coating composition may contain the same type of resin as the first curing agent described above, a different type of curing agent, or a mixture thereof. For example, the second base coating composition contains the same type of curing agent as the first curing agent. The type, amount, etc. of the second curing agent can be determined from the description of the first curing agent above, and the compound, amount, etc. can be selected appropriately.

[0081] (Second bright material) The second base coating composition according to the present disclosure contains a second luster material. The second luster material according to the present disclosure is a pigment that imparts a metallic luster to the coating film. The second base coating composition according to the present disclosure may use one type of second luster material alone, or may use a combination of multiple types of second luster materials.

[0082] In the second base coating composition according to the present disclosure, the mass concentration (PWC) (%) of the second luster material in the second base coating composition is calculated by the following formula: PWC = (total mass of second luminous material) / [(total mass of resin solids of second coating resin and resin solids of second curing agent) + (total mass of second luminous material)] x 100 It is shown as follows. In this case, the PWC range is 5% to 40%, for example, 10% to 40%. In one embodiment, the PWC range is 15% to 40%, for example, 20% to 40%. By having the mass concentration of the second luster pigment within the above range, the orientation of the luster pigment is easily improved, making it easy to form an excellent metallic coating film. In particular, since the present disclosure relates to an aqueous coating composition set containing a predetermined first base coating composition and a predetermined second base coating composition according to the present disclosure, the predetermined first base coating composition and the predetermined second base coating composition can interact with each other, making it easier to more uniformly orient the second luster pigment. This makes it possible to form an excellent metallic coating film with reduced diffuse reflection of light.

[0083] The second lustrous material in the present disclosure has, for example, an average particle size (D50) of 3 μm or more and 25 μm or less. In another embodiment, the average particle size may be 3 μm or more and 20 μm or less, for example, 5 μm or more and 18 μm or less. The average particle size can usually be measured using a wet flow particle size and shape analyzer, for example, an FPIA-3000S (manufactured by SYSMEX Corporation).

[0084] The second lustrous material in the present disclosure may have an average thickness of 3 μm or less, for example, 1 μm or less. In some embodiments, the second lustrous material has a thickness of 500 nm or less, for example, 250 nm or less, and in some embodiments, 100 nm or less. Preferably, the second lustrous material has an average thickness of 10 nm or more, for example, 20 nm or more. Here, the average thickness of the lustrous material can be calculated from the water surface diffusion (covering) area according to JIS K5906.

[0085] When the second lustrous material has a thickness within this range and is contained in the second base coating composition according to the present disclosure, the second lustrous material is more likely to be uniformly oriented as the second base coating composition shrinks in volume after application, making it possible to easily form a coating film that has excellent metallic luster and high flip-flop properties. Furthermore, since the thickness of the second lustrous material is within the above range, light scattering in the visible light range is less likely to occur due to the end surfaces of the lustrous materials where the lustrous materials overlap, so that a dense design (smooth design) with a low graininess can be achieved, and a high metallic feel can be obtained. Therefore, the second base coating film and the multi-layer coating film exhibit low graininess values ​​and have a dense design with little graininess.

[0086] In one embodiment, the second lustrous material has a scaly shape. For example, the aspect ratio of the second lustrous material is 5 or more and 2000 or less, and may be 10 or more and 2000 or less. In another embodiment, the aspect ratio of the second luster material is 10 or more and 1000 or less, for example, 10 or more and 800 or less. By including a second lustrous material having such a shape, the second lustrous material is more likely to be uniformly oriented as the volume of the second base paint composition shrinks after application. This makes it possible to easily form a coating film that has excellent metallic luster and high flip-flop properties. Furthermore, the adhesion between the coating and the substrate is less likely to be adversely affected. In particular, the present disclosure relates to an aqueous coating composition set containing a predetermined first base coating composition and a predetermined second base coating composition, and the interaction between the predetermined first base coating composition and the predetermined second base coating composition can make the orientation of the second luster material more uniform, thereby easily forming a coating film with excellent metallic luster and reduced diffuse reflection of light. When a commercially available product is used as the second lustrous material, the aspect ratio may be expressed as an average aspect ratio. It is sufficient that the average aspect ratio of the second lustrous material falls within the above range.

[0087] In one embodiment, the second lustrous material has a thickness of 10 nm or more and 250 nm or less, and an aspect ratio of 10 or more and 1000 or less. In another embodiment, the second lustrous material has a thickness of 10 nm or more and 150 nm or less, and an aspect ratio of 10 or more and 1000 or less. In yet another embodiment, the second shiny material has a thickness of 10 nm or more and less than 150 nm, and an aspect ratio of 10 or more and 800 or less. Because the second lustrous material has such a shape, it is possible to easily form a second base coating film and a multi-layer coating film that have excellent metallic luster and high flip-flop properties. Furthermore, it is possible to suppress the scattering of visible light, resulting in a high metallic feel for the second base coating film and the multi-layer coating film. It is also possible to easily form a second base coating film and a multi-layer coating film that exhibit a low graininess value and have a dense design (smooth design) with little graininess.

[0088] The second lustrous material may contain, for example, a pigment selected from metal flakes, metal oxide flakes, pearl pigments, and mixtures thereof. Examples of metal flakes include aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel chromium, and stainless steel. Examples of metal oxide flakes include oxides of the above metal flakes, such as alumina, chromium oxide, and mica.

[0089] In some embodiments, the second glitter comprises a surface-treated glitter. For example, in order to prevent gas generation due to reaction of metal flakes, metal oxide flakes, pearl pigments, etc. with water, metal coatings such as coatings of metal compounds of molybdic acid, chromic acid, yttrium, rare earth metals, etc., or organic polymer coatings such as coatings of organic polymers prepared using polymerizable monomers, etc., may be formed on the metal flakes, metal oxide flakes, and pearl pigments. For example, glittering materials such as metal flakes, metal oxide flakes, and pearls may have a coating comprising silicon dioxide, zirconium oxide, aluminum oxide, chromium oxide, polymerized synthetic resin, vanadium oxide, molybdenum oxide and / or molybdenum peroxide, phosphate, phosphite, borate, chromate, or mixtures or combinations thereof. For example, when chromium oxide or the like is used, its toxicity can be removed by chemically inactivating it.

[0090] The second lustrous material may contain a vapor-deposited metal pigment. Such a second lustrous material is generally obtained by depositing a thin metal film (a thin metal oxide film) on a base film, peeling off the base film, and then pulverizing the vapor-deposited metal film into metal flakes (metal oxide flakes).

[0091] The metal material to be vapor-deposited is not particularly limited, but the materials described above for the metal flakes and metal oxide flakes can be used, for example. Preferably, the second lustrous material includes a vapor-deposited aluminum pigment, a vapor-deposited chromium pigment, a vapor-deposited alumina pigment, or a vapor-deposited chromium oxide pigment. The vapor-deposited metal pigment can also have a coating such as that described above on its surface, if desired.

[0092] The second luster material may also be, for example, a luster material that has been surface-treated for use in an aqueous coating composition. In one aspect, gassing (the generation of hydrogen gas due to oxidation of the aluminum surface by water) in aqueous coating compositions can be suppressed by surface treatment of the aluminum luster material. Examples include silica treatment (silane coupling agent coating), molybdenum treatment (molybdic acid coating), and organic treatment (resin coating).

[0093] The second lustrous material and the surface-treated second lustrous material may be commercially available lustrous materials, for example, METALURE manufactured by Ecart Co., Ltd. (登録商標) Series, SILVERSHINE (登録商標) Series, HYDROSHINE (登録商標) Series, Liquid Black (登録商標) , PLISMATIC(登録商標) series, the FD series, GX series, BS series, and WA series manufactured by Asahi Kasei Chemicals Corporation, and the 46 series, 63 series, WL series, WM series, and EMERAL series manufactured by Toyo Aluminum Co., Ltd.

[0094] (Second inorganic viscosity agent) The second inorganic viscosity agent in the present disclosure comprises a layered substance having a laminated structure in which many inorganic crystal layers are stacked on top of one another. The second inorganic viscosity agent having such a layered structure swells in the second base coating composition to form a house-of-cards structure, thereby imparting an appropriate viscosity to the second base coating composition and resulting in excellent coating film strength.

[0095] Furthermore, the second inorganic viscosity agent maintains the orientation of the second luster pigment well. While not limited to a specific theory, the second inorganic viscosity agent imparts thixotropy to the second base coating composition. As described above, when the second base coating composition is applied onto the first base coating film, solvent migration can occur. However, because the second base coating composition is provided with thixotropy by the second inorganic viscosity agent, its viscosity is low in the low shear region, and the orientation of the second luster pigment is well maintained. As a result, an excellent metallic coating film with reduced diffuse reflection of light can be formed.

[0096] In addition, although not limited to a particular theory, it is believed that the inclusion of the second inorganic viscous agent in the second base coating composition leads to structuring due to the interaction between the luster material (e.g., aluminum) and the second inorganic viscous agent, preventing orientation disorder due to the cohesive force (structuring) of the second base coating composition. Furthermore, the stability of the second base coating composition, which contains a luster material with a high PWC, can be improved.

[0097] The second inorganic viscosity-improving agent also contributes to the prevention of interphase formation between the first and second base coating films, which prevents deterioration of the coating film's appearance and allows the coating film's physical properties, such as chipping resistance, to be maintained at a higher level.

[0098] The shape of the primary particles of the second inorganic viscosity increasing agent may be disc-shaped, plate-shaped, spherical, granular, cubic, needle-shaped, rod-shaped, amorphous, etc., with disc-shaped or plate-shaped being preferred.

[0099] The thickness of the second inorganic viscous agent is preferably 100 nm or less. This makes it easier to prevent the orientation of the lustrous material from being disturbed. The thickness of the second inorganic viscous agent is more preferably 50 nm or less, even more preferably 10 nm or less, and particularly preferably 5 nm or less. The thickness of the second inorganic viscous agent may be, for example, 0.1 nm or more, or 0.3 nm or more.

[0100] The second inorganic viscosity modifier in the present disclosure includes silicate layer compounds (silicate minerals), halide minerals, oxide minerals, carbonate minerals, borate minerals, sulfate minerals, molybdate minerals, tungstate minerals, phosphate minerals, arsenate minerals, vanadate minerals, and the like.

[0101] In one embodiment, the second inorganic viscosity enhancer comprises a silicate layer compound. The inclusion of the silicate layer compound provides the second base coating composition with appropriate viscosity and excellent coating strength. Furthermore, the second base coating film formed from the second base coating composition exhibits excellent water resistance and can also exhibit excellent high-temperature water resistance (up to 80°C) by using the second inorganic viscosity enhancer in combination with the second hydrophobic association viscosity enhancer described below.

[0102] Specific examples of silicate layer compounds include natural or synthetic smectite clay minerals such as hectorite, saponite, stevensite, hydrite, montmorillonite, nontrite, and bentonite; swelling mica clay minerals such as Na-type tetrasilicic fluormica, Li-type tetrasilicic fluormica, Na-type fluortaeniolite, and Li-type fluortaeniolite; vermicularite; kaolinite; or mixtures thereof.

[0103] In one embodiment, the silicate layered compound comprises at least one smectite clay mineral selected from the group consisting of natural or synthetic hectorite, saponite, stevensite, hydrite, montmorillonite, nontrite, and bentonite. In another embodiment, the silicate layered compound comprises at least one smectite clay mineral selected from the group consisting of hectorite, saponite, montmorillonite, and bentonite. Although interpretation should not be limited to any particular theory, it is believed that the silicate layer compound contains such minerals, and that, for example, due to a synergistic effect with certain components contained in the first base coating composition, such as the first inorganic gloss agent described above, the orientation of the second lustrous material in the second base coating film can be improved, and further, the interphase that may occur between the first base coating film and the second base coating film can be more effectively suppressed. As a result, the orientation of the luster pigment is improved, and an excellent metallic coating film can be formed with reduced diffused reflection of light. Furthermore, deterioration of the coating film's appearance due to interphase mixing can be suppressed, and coating film physical properties such as chipping resistance can be maintained at a good level.

[0104] Examples of commercially available second inorganic viscosity agents include Laponite XLG (a synthetic hectorite-like substance manufactured by BYK), Laponite RD (a synthetic hectorite-like substance manufactured by BYK), Laponite RDS (a synthetic hectorite-like substance manufactured by BYK), Laponite EP (a synthetic hectorite-like substance manufactured by BYK), Optigel WX (a sodium-substituted bentonite manufactured by BYK), Thermavis (a synthetic hectorite-like substance manufactured by Henkel), and Sumecton SA-1 (a support manufactured by Kunimine Industries Co., Ltd.). These include bentonite-like substances), Bengel (natural bentonite sold by Hojun Co., Ltd.), Kunibia F (natural montmorillonite sold by Kunimine Kogyo Co., Ltd.), Veegum (natural hectorite manufactured by Vanderbilt Corporation in the United States), Dimonite (synthetic swelling mica manufactured by Topy Industries Co., Ltd.), Somasif (synthetic swelling mica manufactured by Co-op Chemical Co., Ltd.), SWN (synthetic smectite manufactured by Co-op Chemical Co., Ltd.), SWF (synthetic smectite manufactured by Co-op Chemical Co., Ltd.), etc.

[0105] In one embodiment, the second base coating composition according to the present disclosure comprises a second inorganic viscosity agent in an amount of 1 to 7 parts by weight per 100 parts by weight of the total resin solids of the film-forming resin and curing agent. In one embodiment, the second base coating composition according to the present disclosure preferably contains the second inorganic viscosity-improving agent in an amount of 1 to 7 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 2 to 5 parts by mass, per 100 parts by mass of the total resin solids content of the film-forming resin and curing agent. By including the second inorganic viscosity agent in such a range, it becomes easier to avoid settling of the second lustrous material during the formation of the second base coating film and the occurrence of turbidity in the second base coating film, and furthermore, it becomes possible to more effectively suppress the occurrence of interphase between the first and second base coating films. Furthermore, since the second luster material can be uniformly oriented, a second base coating film having excellent design properties, particularly an excellent metallic tone, can be obtained.

[0106] For example, the second base coating composition contains a second inorganic viscosity agent and a second hydrophobic association-type viscosity agent in a predetermined relationship. In one embodiment, the second base coating composition contains the second inorganic viscous agent in an amount of 1 to 7 parts by mass per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent. Furthermore, the second base coating composition contains the second hydrophobic association type viscous agent described below in an amount of 1 to 15 parts by mass, for example, 1 to 15 parts by mass, per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent. The second base coating composition may contain the second inorganic viscosity modifier in an amount of 2 parts by mass or more and 7 parts by mass or less, for example, 2 parts by mass or more and 5 parts by mass or less.

[0107] The second base coating composition of the present disclosure contains the second inorganic viscosity agent and the second hydrophobic association viscosity agent in predetermined parts by mass per 100 parts by mass of the total resin solids of the film-forming resin and curing agent, as described above, thereby effectively preventing the second lustrous material from settling during coating film formation and preventing the second base coating film from becoming cloudy. Furthermore, the second lustrous material can be uniformly oriented, making it easier to obtain a coating film with excellent design properties. Furthermore, the second base coating film has excellent water resistance and can also have excellent high-temperature water resistance (up to 80°C).

[0108] In the second base coating composition of the present disclosure, as long as the second inorganic viscosity agent and the second hydrophobic association type viscosity agent are used in combination, the content ratio (mass ratio) of the second inorganic viscosity agent to the second hydrophobic association type viscosity agent is not particularly limited. For example, the content ratio (mass ratio) of the second inorganic viscosity agent to the second hydrophobic association type viscosity agent may be second inorganic viscosity agent / second hydrophobic association type viscosity agent = 1 / 1 to 5 / 1, or in another aspect, second inorganic viscosity agent / second hydrophobic association type viscosity agent = 1 / 1 to 1 / 5.

[0109] In one embodiment, in the aqueous coating composition set according to the present disclosure, the amount of the first inorganic glossing agent per 100 parts by mass of the total resin solids of the first film-forming resin and the first curing agent is less than the amount of the second inorganic viscous agent per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent. By including the second inorganic viscosity agent and the first inorganic gloss agent in this relationship, the aqueous coating composition set according to the present disclosure can form a coating film with a metallic luster that has even better design properties, and can also produce a multi-layer coating film that has improved coating film properties such as chipping resistance, water resistance, and high-temperature water resistance, as well as excellent substrate transferability.

[0110] (Second hydrophobic association type viscosity agent) The second hydrophobic association type viscous agent according to the present disclosure can increase the viscosity of the second base coating composition through hydrophobic interactions that occur between the second hydrophobic association type viscous agent and at least one of the hydrophobic groups contained in at least one of the group consisting of the second film-forming resin, the second curing agent, the second lustrous material, the second inorganic viscous agent, and the second dispersant contained in the second base coating composition. By including the second hydrophobic association type viscosity agent, coating defects such as cissing and dents in the second base coating film can be suppressed, and high smoothness can be achieved between the second base coating film and the first base coating film. Furthermore, since the second base coating composition contains a second inorganic viscosity agent and a second hydrophobic association viscosity agent, it is possible to more effectively prevent the second lustrous material from settling during coating film formation and prevent the second base coating film from becoming cloudy. Furthermore, since the second lustrous material can be uniformly oriented, a coating film with excellent design properties can be obtained. Furthermore, the second base coating film has excellent water resistance, including excellent high-temperature water resistance (up to 80°C).

[0111] Particularly preferred second hydrophobic association type thickeners include polyacrylic acid-based thickeners copolymerized with hydrophobic monomers, polyurethane-based thickeners having hydrophobic chains in the molecule, urethane-urea-based thickeners in which at least a portion of the main chain is a hydrophobic urethane chain, amide-urea-based thickeners in which at least a portion of the main chain is a hydrophobic amide chain, and other thickeners.

[0112] In one embodiment, the second hydrophobic association type thickener includes a polyurethane-based thickener having a hydrophobic chain in the molecule, or a urethane-urea-based thickener having a hydrophobic urethane chain at least part of the main chain. In addition to the above-mentioned effects, the inclusion of such a second hydrophobic association type thickener can more effectively exhibit excellent anti-settling and anti-sagging properties in systems containing aqueous materials, such as the second base coating composition. For example, urethane-based hydrophobic association viscosity agents, such as polyurethane-based viscosity agents and urethane-urea-based viscosity agents, have the property of easily developing viscosity at low shear and not easily developing viscosity at high shear, resulting in excellent thixotropy. Due to these properties, the second base coating composition of the present disclosure can be suitably used for, for example, spray coating. Furthermore, a second base coating film formed from a second base coating composition containing such a hydrophobic association viscosity agent can have excellent water resistance and high-temperature water resistance.

[0113] Commercially available examples of the second hydrophobic association type viscosity enhancer include BYK-425 (urea-modified urethane compound: manufactured by BYK-Chemie), BYK-420 (urethane-urea compound: manufactured by BYK-Chemie), BYK-430 (amide-urea compound: manufactured by BYK-Chemie), PU 1250 (polyurethane polymer: manufactured by BASF), SN Thickener-660T, SN Thickener-665T (urethane-based: manufactured by San Nopco), RHEOLATE 216 (urethane-urea compound: manufactured by ELEMENTIS), Primal RM-12W, Primal RM-895 (urethane-based: manufactured by The Dow Chemical Company), and Disparlon AQ-021 (Kusumoto Chemicals).

[0114] The aqueous coating composition of the present disclosure contains the second hydrophobic association type viscous agent in an amount of 1 to 15 parts by mass, for example, 1 to less than 15 parts by mass, per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent. In one embodiment, the second hydrophobic association type viscous agent is contained in an amount of 2 to 15 parts by mass, for example, 2 to less than 15 parts by mass, in one embodiment, 2 to 10 parts by mass, and in another embodiment, 2 to 5 parts by mass, per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent. By including the second hydrophobic association type viscous agent in this range, it is possible to more effectively prevent the second lustrous material from settling during the formation of the second base coating film and prevent the second base coating film from becoming cloudy. Furthermore, since the second lustrous material can be uniformly oriented, it is easy to obtain a coating film with excellent design properties, especially an excellent metallic tone. Furthermore, by incorporating a predetermined amount of the second hydrophobic association type viscous agent, the second base coating film and the multilayer coating film can have excellent water resistance and also excellent high-temperature water-resistant adhesion.

[0115] (2nd inorganic brightener) The second base coating composition may optionally contain a second inorganic brightener, which may be the same as or different from the first inorganic brightener. For example, the second inorganic brightener is one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth. In one embodiment, the first inorganic brightener comprises a positively charged inorganic brightener, such as barium sulfate. The second inorganic brightener may be one described above as the first inorganic brightener. By including the second inorganic brightener, the gloss of the second base coating film can be adjusted to a desired range.

[0116] In one embodiment, the second base coating composition may contain a second inorganic brightener of the same type as the first inorganic brightener. Although not intended to be limited to a particular theory, if the first inorganic brightener and the second inorganic brightener are the same type, interference unevenness due to the refractive index difference that may occur between the second base coating film and the first base coating film can be further reduced.

[0117] The second base coating composition may contain 0.01 to less than 10 parts by mass of the second inorganic brightener per 100 parts by mass of the total resin solids of the second film-forming resin and the second curing agent, for example, 0.01 to 5 parts by mass. In one embodiment, the second inorganic brightener is contained in less than 0.1 part by mass per 100 parts by mass of the resin solids, for example, 0.01 to less than 0.1 part by mass. By containing the second inorganic brightener in such a range, an excellent metallic coating film can be formed. Here, in the present disclosure, the amount of the second inorganic glossing agent can be selected depending on the type (e.g., size, thickness) of the lustrous material contained in the second base paint composition, thereby further improving the design.

[0118] In one embodiment, the second base coating composition may include a second inorganic brightener. In an embodiment in which the second base coating composition contains a second inorganic glossing agent, for example, if the amount of the first inorganic glossing agent contained in the first base coating composition per 100 parts by mass of the total resin solids of the first coating film-forming resin and the first curing agent is (Am1), and the amount of the second inorganic glossing agent contained in the second base coating composition per 100 parts by mass of the total resin solids of the second coating film-forming resin and the second curing agent is (Am2), it is preferable that the ratio of the amount of (Am1) to the amount of (Am2), (Am1) / (Am2), is 2.0 or more. By satisfying this relationship, it is possible to further reduce interference unevenness due to the difference in refractive index that may occur between the second base coating film and the first base coating film.

[0119] (Second dispersant) The second base coating composition of the present disclosure includes a second dispersant. By including the second dispersant, the dispersion stability of the various components contained in the second base coating composition is improved.

[0120] In one embodiment, the second dispersant has a substituent that provides dispersion stability to the metal or metal oxide. By having such a substituent, the second dispersant can effectively coat the second lustrous material. Furthermore, depending on the molecular weight of the second dispersant, the second dispersant can increase steric hindrance of the second lustrous material, thereby suppressing aggregation of the second lustrous material. Furthermore, such a second dispersant can improve the dispersibility of the second lustrous material.

[0121] In one embodiment, the second dispersant may have a highly hydrophobic side chain, which allows the second dispersant to dissolve in solvents such as 2-ethylhexyl alcohol (2EHOH) and monoethylene glycol mono-2-ethylhexyl ether (EHG).

[0122] The second dispersant may be either a polymeric dispersant or a low-molecular surfactant-type dispersant. For example, a polymeric dispersant is preferred from the viewpoint of preventing aggregation of the second lustrous material. The polymeric dispersant is preferably a polymeric dispersant having at least one group selected from an anionic group, a cationic group, or a nonionic group, and more preferably at least one group selected from a polymeric dispersant having a highly hydrophobic side chain and an anionic group, a polymeric dispersant having a nonionic group, and a mixture thereof. Examples of anionic groups include phosphate groups and carboxylic acid groups. Examples of nonionic groups include polyoxyalkylene groups. However, the present invention is not limited to these groups.

[0123] As described above, the polymer dispersant may be a known dispersant such as an anionic, cationic, or nonionic acrylic copolymer, block copolymer, etc. In one embodiment, from the viewpoint of dispersion stability, a polymer having anionic or nonionic properties is preferred, and an acrylic copolymer or block copolymer is preferred.

[0124] As the polymer-type dispersant, known dispersants can be used, and may include, for example, the commercially available products described as the first dispersant.

[0125] The amount of the second dispersant can be 1 to 15 parts by weight per 100 parts by weight of the total resin solids of the second film-forming resin and the second curing agent. In one embodiment, the amount of the second dispersant is 1 to 12 parts by weight, for example, 3 to 12 parts by weight, per 100 parts by weight of the total resin solids of the second film-forming resin and the second curing agent. By using the second dispersant in such an amount, the dispersion stability of the various components contained in the second base coating composition is improved, and aggregation of the components can be suppressed during the process of forming the second base coating film. Furthermore, aggregation of the second lustrous material can be more effectively prevented, and the dispersibility of the second lustrous material can be improved.

[0126] <Organic solvents> At least one of the first base coating composition and the second base coating composition according to the present disclosure may contain an organic solvent. For example, an alcohol-based organic solvent having a solubility in water of 0.01% by mass to 5.0% by mass and a boiling point of 160°C to 200°C may be included, and optionally, a glycol ether-based organic solvent having a solubility in water of 0.01% by mass to 5.0% by mass and a boiling point of 205°C to 240°C may also be included. Known solvents may be used in combination or alone. The solubility is the mass of the organic solvent dissolved in 100 parts by mass of water at 20°C, expressed as a percentage. Furthermore, the first base coating composition and the second base coating composition may contain the same type of organic solvent.

[0127] The solubility of the alcohol-based organic solvent in water within the above range has the advantage of being able to better adjust the paint viscosity and coating workability, etc. The solubility of the alcohol-based organic solvent in water is preferably 0.05% by mass or more and 3.0% by mass or less.

[0128] The boiling point of the alcohol-based organic solvent within the above range has the advantage of ensuring good coating workability, particularly resistance to foaming and sagging. The boiling point of the alcohol-based organic solvent is preferably 170°C or higher and 190°C or lower.

[0129] The alcohol-based organic solvent (solubility, boiling point) is selected from the group consisting of heptanol (0.5% by mass, 168°C), 2-ethylhexyl alcohol (0.1% by mass, 184°C), and cyclohexanol (4.0% by mass, 161°C), and from the viewpoint of the stability (particle size) of the resin aqueous dispersion, 2-ethylhexyl alcohol (2EHOH) is preferred.

[0130] The content of the alcohol-based organic solvent in the aqueous coating composition is, for example, from 10 to 150 parts by mass, and preferably from 50 to 100 parts by mass, per 100 parts by mass of the total resin solids content of the film-forming resin and curing agent. When the content is within this range, the effect of preventing aggregation of the scaly pigment is likely to be enhanced, and coating workability, such as roll-up resistance, is likely to be improved. When a plurality of organic solvents are used, the total amount of each organic solvent can be adjusted to fall within the above range.

[0131] Addition of the alcohol-based organic solvent to the aqueous coating composition improves atomization during coating, thereby significantly preventing aggregation of the scaly pigment.

[0132] If necessary, a glycol ether organic solvent having a solubility in water of 0.01% by mass or more and 5.0% by mass or less and a boiling point of 205°C or more and 240°C or less may be added to the aqueous coating composition of the present disclosure.

[0133] When the solubility of the glycol ether organic solvent in water is 0.01% by mass or more and 5.0% by mass or less, it is easy to adjust the viscosity of the aqueous coating composition to a level suitable for coating. The solubility of the glycol ether organic solvent in water is preferably 0.05% by mass or more and 3.0% by mass or less.

[0134] When the boiling point of the glycol ether organic solvent is 205°C or higher and 240°C or lower, coating workability, particularly resistance to foaming and sagging, is likely to be improved. The boiling point of the glycol ether organic solvent is preferably 210°C or higher and 230°C or lower.

[0135] The glycol ether organic solvent (solubility, boiling point) is selected from the group consisting of ethylene glycol monohexyl ether (hexyl glycol, 1.0 mass%, 208°C), ethylene glycol mono 2-ethylhexyl ether (2-ethylhexyl glycol (EHG), 0.2 mass%, 225°C), and dipropylene glycol monobutyl ether (5.0 mass%, 215°C), and the acrylic emulsion hmm, From the viewpoint of stability (particle size) of the hydrophobic melamine resin aqueous dispersion, ethylene glycol mono 2-ethylhexyl ether (EHG) is preferred.

[0136] The content of glycol ether organic solvent in the aqueous coating composition is, for example, from 10 to 150 parts by mass, preferably from 50 to 100 parts by mass, per 100 parts by mass of the total resin solids of the film-forming resin and curing agent. When the content is within this range, the effect of preventing aggregation of the scaly pigment is likely to be enhanced, and coating workability, such as release properties, is likely to be improved. When a plurality of organic solvents are used, the total amount of each organic solvent can be adjusted to fall within the above range.

[0137] When the aqueous coating composition of the present disclosure contains an alcohol-based organic solvent and a glycol ether-based organic solvent, the mass ratio of the alcohol-based organic solvent to the glycol ether-based organic solvent is preferably 1 / 1 to 3 / 1. When the mass ratio is in this range, an excessive decrease in the viscosity of the coating is suppressed, improving coating workability and also facilitating improvement in the stability of the coating composition over time.

[0138] Alternatively, the glycol ether organic solvent may be added alone to the aqueous coating composition.

[0139] <Other ingredients> At least one of the first base coating composition and the second base coating composition according to the present disclosure may contain, in addition to the above components, water, an antifoaming agent, a coloring pigment, an extender pigment, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, crosslinked resin particles, a surface conditioner, a film-forming aid, an anti-rust pigment, an anti-rust agent, etc.

[0140] <Method of manufacturing base coating composition> The method for producing the first and second base coating compositions is not particularly limited as long as it can uniformly disperse the above components. The first and second base coating compositions can be prepared by methods known to those skilled in the art, such as using a kneader, mill, or roll mill.

[0141] <First coating film and second coating film> A first coating film can be formed from the first base coating composition according to the present disclosure, and a second base coating film can be formed from the second base coating composition according to the present disclosure. Such a multi-layer coating film comprising the first and second base coating films has a high degree of orientation of the luster material, resulting in suppressed diffused reflection of light and an excellent metallic appearance. Furthermore, the multi-layer coating film has excellent physical properties such as chipping resistance, water resistance, and high-temperature water resistance, as well as workability. Therefore, the multi-layer coating film formed from the aqueous coating composition set for forming a multi-layer coating film according to the present disclosure has an excellent metallic feel and also has good coating film properties.

[0142] In one embodiment, the film thickness (t1) of the first base coating is 1 μm or more and 35 μm or less, for example, 1 μm or more and 30 μm or less, or 1 μm or more and 16 μm or less, or 2 μm or more and 15 μm or less. In another embodiment, the film thickness of the first base coating is 2.5 μm or more and 11 μm or less. By ensuring that the thickness of the first base coating film is within this range, it is possible to form a multi-layer coating film that is particularly excellent in chipping resistance, substrate transferability, and design. Note that the above-mentioned film thickness is the film thickness after heat curing.

[0143] In one embodiment, the thickness (t2) of the second base coating is 1 μm or more and 20 μm or less, for example, 2 μm or more and less than 15 μm. In another embodiment, the thickness of the second base coating is 3 μm or more and 7 μm or less. By ensuring that the thickness of the second base coating film is within this range, it is possible to form a multi-layer coating film that is excellent in terms of sagging prevention and design. Note that the above-mentioned thickness is the thickness after heat curing.

[0144] For example, the film thickness (t1) of the first base coating film formed from the first base coating composition and heat-cured and the film thickness (t2) of the second base coating film formed from the second base coating composition and heat-cured have the relationship (t1) ≧ (t2). This relationship allows the formation of a multilayer coating film with a superior metallic finish. Furthermore, it is possible to form a multilayer coating film that has excellent physical properties such as chipping resistance and excellent substrate transferability as coating workability without compromising the excellent metallic finish. Furthermore, it is possible to form a multilayer coating film that also has excellent water resistance and high-temperature water resistance.

[0145] <Method for forming multi-layer coating film> The present disclosure further provides a method for forming a multilayer coating film using an aqueous coating composition set comprising a first base coating composition and a second base coating composition according to the present disclosure, comprising: A step of applying a first base coating composition to an object to be coated to form an uncured first base coating film; A step of applying a second base coating composition onto the uncured first base coating film to form an uncured second base coating film; A step of applying a clear coating composition for forming a clear coating film onto the uncured second base coating film to form an uncured clear coating film; The method includes a step of simultaneously baking and curing an uncured first base coating film, an uncured second base coating film, and an uncured clear coating film to form a multi-layer coating film. A method for forming a multi-layer coating film, The film thickness of the first base coating film formed from the first base coating composition and heat-cured is 1 μm or more and 35 μm or less, The present invention provides a method for forming a multi-layer coating film, in which the second base coating film formed from the second base coating composition and cured by heating has a thickness of 1 μm or more and 20 μm or less.

[0146] In another aspect, the present disclosure provides: A step of applying an aqueous intermediate coating composition to an object to be coated to form an uncured intermediate coating film; A step of applying a first base coating composition onto the uncured intermediate coating film to form an uncured first base coating film; A step of applying a second base coating composition onto the uncured first base coating film to form an uncured second base coating film; A step of applying a clear coating composition for forming a clear coating film onto the uncured second base coating film to form an uncured clear coating film; The method includes a step of simultaneously baking and curing an uncured intermediate coating film, an uncured first base coating film, an uncured second base coating film, and an uncured clear coating film to form a multi-layer coating film. A method for forming a multi-layer coating film, The film thickness of the first base coating film formed from the first base coating composition and heat-cured is 1 μm or more and 35 μm or less, The thickness of the heat-cured second base coating film formed from the second base coating composition is 1 μm or more and 20 μm or less. below The present invention provides a method for forming a multi-layer coating film,

[0147] Before applying the aqueous coating composition according to the present disclosure to a substrate, an intermediate coating film may be formed on the substrate in order to further improve the hiding power of the substrate surface, adhesion to the substrate, and chipping resistance. The intermediate coating film has a dry thickness of, for example, 10 μm to 50 μm. The intermediate coating composition used to form the intermediate coating film contains a coating film-forming component, and known compositions can be used, such as those containing a hydroxyl group-containing polyester resin and / or a hydroxyl group-containing acrylic resin, and a melamine resin and / or a blocked polyisocyanate. These are dried or cured at room temperature or by heating after application, depending on the form of the intermediate coating composition used. The first base coating composition according to the present disclosure can also be applied by so-called wet-on-wet application without curing the intermediate coating film.

[0148] The substrate according to the present disclosure is not particularly limited, and examples thereof include iron, copper, aluminum, tin, zinc, and alloys containing these metals, as well as plated or vapor-deposited products made of these metals, plastics, and foams. The substrate may have a cured electrodeposition coating film formed on its surface. The cured electrodeposition coating film is formed by electrodeposition coating an electrodeposition paint on the substrate and then heat curing. The electrodeposition paint is not particularly limited, and known cationic electrodeposition paints or anionic electrodeposition paints can be used. The electrodeposition coating method and heat curing of the electrodeposition-coated coating film can be carried out by methods and conditions commonly used for electrodeposition coating automobile bodies. The method for forming a multilayer coating film (glossy multilayer coating film) according to the present disclosure is preferably applied to, for example, molded articles made of these metals, such as the outer panels of automobile bodies.

[0149] The clear coating composition used in the present disclosure can be a coating composition known as a clear coating composition for automobile bodies. Examples of such clear coating compositions include those containing a clear coating film-forming resin dispersed or dissolved in a medium, and optionally a curing agent and other additives. Examples of clear coating film-forming resins include acrylic resins, polyester resins, epoxy resins, and urethane resins. These can be used in combination with curing agents such as amino resins and / or isocyanate resins. From the perspectives of transparency and acid etching resistance, it is preferable to use a combination of an acrylic resin and / or polyester resin with an amino resin, or an acrylic resin and / or polyester resin having a carboxylic acid-epoxy curing system. For example, by including a predetermined amount of an ultraviolet absorber and a light stabilizer in addition to the above resin components, the clear coating composition can achieve good adhesion to the anticorrosion coating. Furthermore, the use of such clear coating compositions is preferable because they can prevent corrosion even when used in areas prone to salt damage.

[0150] The film thickness (t1) of the first base coating film is 1 μm or more and 35 μm or less, for example, 1 μm or more and 30 μm or less, or 1 μm or more and 16 μm or less. The film thickness (t1) of the first base coating film may also be 2 μm or more and 15 μm or less. In another embodiment, the film thickness of the first base coating film is 2.5 μm or more and 11 μm or less. By ensuring that the thickness of the first base coating film is within this range, it is possible to form a multi-layer coating film that is particularly excellent in chipping resistance, substrate transferability, and design. Note that the above-mentioned film thickness is the film thickness after heat curing.

[0151] The thickness of the second base coating is 1 μm or more and 20 μm or less, for example, 2 μm or more and less than 15 μm. In another embodiment, the thickness of the second base coating is 3 μm or more and 7 μm or less. By ensuring that the thickness of the second base coating film is within this range, it is possible to form a multi-layer coating film that is excellent in terms of sagging prevention and design. Note that the above-mentioned thickness is the thickness after heat curing.

[0152] For example, the film thickness (t1) of the first base coating film formed from the first base coating composition and heat-cured and the film thickness (t2) of the second base coating film formed from the second base coating composition and heat-cured have the relationship (t1) ≧ (t2). This relationship allows the formation of a multilayer coating film with a superior metallic feel, and also allows the formation of a multilayer coating film that is excellent in physical properties such as chipping resistance and in substrate transferability for paint workability. Furthermore, a multilayer coating film that is also excellent in water resistance and high-temperature water resistance can be formed. The resulting thin film has excellent gloss and high flip-flop properties (so-called FF properties), and is a metallic coating film that is dense and does not exhibit a grainy feel (glare), and also has good hiding power.

[0153] The means for applying the base coating composition of the present disclosure is not particularly limited, and examples thereof include commonly used coating methods such as immersion, brushing, roller coating, roll coating, air spraying, airless spraying, curtain flow coating, roller curtain coating, and die coating. These can be appropriately selected depending on the substrate. For example, the aqueous coating composition may be applied using an electrostatic coating machine. In addition, conditions such as the amount of coating discharged can be appropriately set depending on the required coating thickness.

[0154] After application of the base coating composition, it is preferable to carry out a step of volatilizing the water at 40°C to 100°C for 1 minute to 10 minutes. By setting the curing temperature after clear coating to 80°C to 180°C, preferably 120°C to 160°C, a cured coating film with a high degree of crosslinking can be obtained. When the curing temperature is within this range, the resulting coating film is sufficiently cured, but excessive crosslinking can also occur. hardening The curing time varies depending on the curing temperature, but a temperature of 120°C to 160°C and a time of 10 to 30 minutes is appropriate. [Example]

[0155] The present disclosure will be described in more detail with reference to the following examples, but the present disclosure is not limited thereto. In the examples, "parts" and "%" are by mass unless otherwise specified.

[0156] (Examples 1 to 37, Comparative Examples 1 to 4) <Preparation of Resin Composition 1> Resin composition 1 (main component) contained in the first and second base coating compositions was prepared. Specifically, the following materials were used. (1) Nippon Paint Acrylic Emulsion hmm( Average particle size 150 nm, non-volatile content 20%, solid content acid value 20 mg KOH / g, hydroxyl value 40 mg KOH / g) 236 parts (2) 10 parts of 10% by weight aqueous solution of dimethylethanolamine (3) 28.3 parts of water-soluble acrylic resin (non-volatile content 30%, solid acid value 40 mg KOH / g, hydroxyl value 50 mg KOH / g) manufactured by Nippon Paint Co., Ltd. (4) 8.6 parts of "Primepol PX-1000" manufactured by Sanyo Chemical Industries, Ltd. (bifunctional polyether polyol, number average molecular weight 400, hydroxyl value 278 mg KOH / g, primary / secondary hydroxyl value ratio = 63 / 37, non-volatile content 100%) (5) 21.5 parts of "Cymel 204" manufactured by Mitsui Chemicals, Inc. (mixed alkylated melamine resin, non-volatile content 100%) (6) Avecia "Neolet's R-9603" (polycarbonate urethane emulsion) hmm, Non-volatile content 33%) 26 parts (7) Lauryl acid phosphate 0.2 parts (8) 2-Ethylhexanol 60 parts (9) Mono 2-ethylhexyl ether 30 parts In the resin composition, the total solid content mass of the coating film-forming resin and the solid content mass of the curing agent (solid content amount of the main resin) was 100 parts by mass.

[0157] <Preparation of First Base Coating Composition> The components shown below were blended with the above resin composition 1 as shown in Table 1, and diluted with water to obtain a first base water-based coating composition.

[0158] In the table, the non-volatile content (NV1), the PWC of the first brightening material, and the PWC of the first inorganic brightening agent were calculated by the following formula. Non-volatile content (NV1) = [(mass of first base coating composition after drying) / (mass of first base coating composition before drying)] × 100 (%)

[0159] Mass concentration of first lustrous material (PWC) = (total mass of first lustrous material) / [(total mass of resin solid content of first coating film-forming resin and resin solid content of first curing agent) + (total mass of first lustrous material)] × 100 (%) The mass concentration (PWC) of the first inorganic brightening agent was also calculated by replacing the first brightening material in the above formula for calculating the (PWC) of the first brightening material with the first inorganic brightening agent.

[0160] (1st bright material) CP-315 (Asahi Kasei Chemicals aluminum pigment, thickness 0.17 μm, aspect ratio 88)

[0161] (First inorganic brightener) Barium sulfate (Sakai Chemical Industry Co., Ltd., average particle size: 30 nm)

[0162] (First hydrophobic association type viscosity agent) BYK-425 (urea-modified urethane compound: manufactured by BYK-Chemie, 1 part by mass per 100 parts by mass of the solid content of the main resin)

[0163] <Preparation of second base coating composition> The components shown below were blended with the above resin composition 1 as shown in Table 1, and diluted with water to obtain a second base water-based coating composition.

[0164] In the table, the non-volatile content (NV2), the PWC of the second luster material, and the PWC of the second inorganic brightening agent were calculated in the same manner as described above for the preparation of the first base coating composition.

[0165] (Second bright material) SB10 (Asahi Kasei Chemicals Corporation, aluminum pigment, thickness 0.06 μm, average aspect ratio 170) FD-508H (Asahi Kasei Chemicals Corporation, aluminum pigment, thickness 0.08 μm, average aspect ratio 96) FD-5090 (Asahi Kasei Chemicals Corporation, aluminum pigment, thickness 0.11 μm, average aspect ratio 80) WM2068 (Toyo Aluminum, aluminum pigment, thickness 0.15 μm, average aspect ratio 110) WA3180 (Asahi Kasei Chemicals Corporation, aluminum pigment, thickness 0.25 μm, average aspect ratio 55) WS-3001 (Ecart, aluminum pigment, thickness 0.03 μm, average aspect ratio 500)

[0166] (2nd inorganic brightener) Barium sulfate: Varifine BF-20 (Sakai Chemical Industry Co., Ltd., average particle size 30 nm)

[0167] (Second inorganic viscosity agent) Laponite RD (BYK synthetic hectorite-like material, thickness: 0.9 nm to 1.0 nm) Laponite EP (BYK synthetic hectorite-like material, thickness: 0.9 nm to 1.0 nm) Optigel WX (BYK sodium-substituted bentonite) In the table, "Lapo" means Laponite and "Opte" means Optigel.

[0168] (Second hydrophobic association type viscosity agent) BYK-425 (urea-modified urethane compound: manufactured by BYK-Chemie) Adekanol UH550 (urethane compound: manufactured by Adeka Corporation) Disparlon AQ021 (urethane compound: Kusumoto Chemical) Seisha Made in In the table, "425" means BYK-425, "UH550" means Adekanol UH550, and "AQ021" means Disparlon AQ021.

[0169] (Second dispersant) DISPERBYK-192 (BYK-Chemie) SURFYNOL-465 (EVONIK) SURFYNOL-440 (EVONIK) In the table, "192" means DISPERBYK-192, "465" means SURFYNOL-465, and "440" means SURFYNOL-440. DISPERBYK-192 is an anionic dispersant, while SURFYNOL is a nonionic dispersant (a polyether adduct of an acetylene diol compound).

[0170] <Example of coating production> A zinc phosphate-treated SPCC-SD steel plate (dull steel plate) measuring 70 x 150 mm and 0.8 mm thick was electrocoated with cationic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.) to a dry film thickness of 20 μm and baked at 160°C for 30 minutes. A gray primer paint "Orga P-30" (a polyester-melamine paint manufactured by Nippon Paint Co., Ltd.) pre-diluted to a viscosity of 25 seconds (measured at 20°C using a No. 4 Ford cup) was then electrostatically coated onto the coated plate to a dry film thickness of 35 μm and baked at 140°C for 30 minutes to create a substrate.

[0171] The first base coating composition of each Example and Comparative Example was applied onto the obtained substrate using a cartridge bell (a rotary atomizing coater manufactured by ABB) to the dry film thickness shown in Table 1. Next, after preheating at 80°C for 3 minutes, the second base coating composition was applied using a cartridge bell (a rotary atomizing coating machine manufactured by ABB) to the dry film thickness shown in Table 1. Next, the substrate was preheated at 80°C for 3 minutes, and then a wet-on-wet clear paint "Macflow O-1820 Clear" (manufactured by Nippon Paint Co., Ltd., epoxy-cured acrylic resin paint) was applied using a rotary atomizing electrostatic coater to a dry film thickness of 35 μm. After painting, the coating was baked at 140°C for 30 minutes to obtain multi-layer coating films according to each of the examples and comparative examples.

[0172] <Evaluation> The physical properties of the multi-layer coating film, the first base coating composition and the second base coating composition were evaluated based on the following criteria. The results are shown in Table 1.

[0173] (sedimentation) The second base coating composition was placed in a 50 mL sample can and allowed to stand at room temperature for 10 days, after which the degree of settling was evaluated according to the following criteria. ○: No pigments have settled and no separation is observed. △: Pigments have settled slightly and the supernatant is cloudy ×: Pigments have settled and the supernatant liquid is clear

[0174] (dispersion stability) 250 mL of the obtained second base coating composition was placed in a 500 mL beaker, stirred at 30°C for 7 days, and then filtered through a 200 mesh filter, and the degree of aggregation of the second lustrous pigment was evaluated. ○: The second luminous material is not aggregated ×: The second luminous material is aggregated

[0175] (Sauce-like properties) The obtained first base coating composition and second base coating composition were applied to a coated plate having an electrodeposition coating film and an intermediate coating film (formed from Orga P-30) with a hole of 5 mm diameter, using a cartridge bell (a rotary atomizer coating machine manufactured by ABB) to the dry film thickness shown in the table below.The plate was preheated at 80°C for 3 minutes, and then heat-cured at 140°C for 30 minutes, and the length of the sagging below the hole was measured. The smaller these values ​​are, the better the sagging resistance is. A value of 5 mm or less was rated as good sagging resistance (◯), and a value of more than 5 mm was rated as NG sagging resistance (×). The symbol (△) indicates that even when the same coating composition was used, there were cases where the sagging properties were good and cases where the sagging properties were poor.

[0176] (Hiding property of second base coating composition) The resulting second base coating composition was applied to a black and white opacity test paper using a Cartridge Bell (ABB, rotary atomizer coater) to the dry film thickness shown in the table below. After preheating at 80°C for 3 minutes, the coating was heat-cured at 140°C for 30 minutes. The degree of hiding of the resulting sample was evaluated visually. Those that were completely concealed were marked with (◯), and those in which the base was visible were marked with (×). In addition, a symbol (◎) for hiding power means that even higher hiding power is exhibited. Furthermore, the hiding power (Δ) means that even when the same coating composition is used, the hiding power is (◯) in some places and (×) in only a few places.

[0177] (Base transferability) An intermediate coating film (formed from Orga P-30) was formed on the substrate, and the intermediate coating film of the resulting coated plate was wet-sanded with #800 wet sandpaper until the gloss at 60 degrees was 50%. Next, a first base coating film, a second base coating film, and a clear coating film were formed according to the same procedure as in the above-mentioned coating film production example, to form a composite coating film. Thereafter, the presence or absence of transfer of the sanding marks was visually confirmed. The evaluation criteria are as follows: ○: No grinding marks △: Slight grinding marks were observed ×: Grinding marks were observed on the entire surface

[0178] (Metallic feel) An electrodeposition coating film and an intermediate coating film were formed on the substrate. On top of that, a multi-layer coating film was formed, which consisted of a first base coating film, a second base coating film, and a clear coating film. The obtained multi-layer coating film was referred to as "BYK-mac i The FI value (flip-flop property) and G value (graininess) were measured using a BYK-Gardner tester to evaluate the design. The higher the flip-flop property and the denser the graininess, the better the metallic feel. ◎: FI value is 20 or more and G value is 3.0 or less ○: FI value is 20 or more and G value is 3.5 or less △: FI value is 15 or more and G value is 4.0 or less ×: FI value less than 15 or G value 4.0 or more

[0179] (Water-resistant adhesion) An electrodeposition coating film and an intermediate coating film were formed on a substrate. A multi-layer coating film consisting of a first base coating film, a second base coating film, and a clear coating film was then formed on top of the electrodeposition coating film. The resulting test pieces were immersed in water at 40°C for 240 hours, after which the appearance of the coating film was visually observed and the adhesion test described below was carried out. The evaluation criteria were as follows:

[0180] (High temperature and water resistant adhesion) An electrodeposition coating film and an intermediate coating film were formed on a substrate. A multi-layer coating film consisting of a first base coating film, a second base coating film, and a clear coating film was then formed on top of the electrodeposition coating film. The resulting test pieces were immersed in 80°C water for 120 hours, after which the appearance of the coating film was visually observed and the adhesion test described below was carried out. The evaluation criteria were as follows:

[0181] (Adhesion test) Make 10 cuts in the coating of the test piece at 1mm intervals with a cutter, and then apply cellophane tape on top of the cuts. (登録商標) (manufactured by Nichiban Co., Ltd.) was applied to the surface, and then peeled off, and the number of peeled squares out of 100 squares was counted (also known as a cross-cut test). This test confirmed whether the coating film had peeled off. For example, if the result of the cross-cut test is 100 / 100, this means that the peeled area of ​​the coating film is 100%, and the coating film has peeled off.

[0182] (Evaluation of chipping resistance) An electrodeposition coating film and an intermediate coating film were formed on the substrate. Furthermore, a multi-layer coating film was formed on top of that, comprising a first base coating film, a second base coating film, and a clear coating film, each formed from the base coating composition of each Example and Comparative Example. The resulting test plate was subjected to a stone chipping test under the following conditions (simulating an automobile hood) using a Grarobe tester KSS-1 (manufactured by Suga Test Instruments Co., Ltd.). <Test Method> Stone type: Basalt No. 7 Stone size: 3~4mm Stone quantity: 100g Distance: 35cm Shot pressure: 0.3MPa Shot angle: 30° Test temperature: -20℃ The test panels after the stone chipping test were evaluated according to the following criteria. ○: Maximum peeling diameter is 1.0 mm or less △: Maximum peeling diameter is over 1.0 mm and 3.0 mm or less ×: The maximum peeling diameter exceeds 3.0 mm

[0183] [Table 1]

[0184] [Table 2]

[0185] [Table 3]

[0186] [Table 4]

[0187] The aqueous coating composition set for forming a multilayer coating film according to the present disclosure improves the orientation of the luster pigment, thereby suppressing diffuse reflection of light and forming an excellent metallic coating film with sufficient highlight brightness. Furthermore, the multi-layer coating film formed from the composition set of the present disclosure also has excellent weather resistance. Furthermore, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure can form a coating film that has good physical properties such as chipping resistance, water resistance, and high-temperature water resistance, as well as excellent substrate transferability in terms of coating workability. Therefore, the aqueous paint composition set for forming a multilayer coating film according to the present disclosure can form a metallic multilayer coating film that has excellent design properties, particularly an excellent metallic look, and also has good coating film properties. Furthermore, since a multi-layer coating film can be formed using wet-on-wet coating, the number of steps in the coating film formation process can be reduced, thereby reducing the environmental load.

[0188] On the other hand, in Comparative Example 1, since the second inorganic viscosity agent according to the present disclosure was not included, the sedimentation property of the second coating composition was poor and the dispersion stability was also reduced. Furthermore, the water resistance (40°C) and high-temperature water resistance (80°C) of the obtained coating film were both insufficient. In Comparative Example 2, the second coating composition did not contain the second hydrophobic association type viscosity agent according to the present disclosure, and therefore the sedimentation property of the second coating composition was poor and the dispersion stability was also reduced. Furthermore, the metallic feel did not meet the standard values ​​for both the FI value and the G value. In Comparative Example 3, since the first inorganic brightener was not contained, the G value did not satisfy the standard value, and the multilayer coating film had a poor metallic appearance. [Industrial Applicability]

[0189] The aqueous coating composition set for forming a multilayer coating film according to the present disclosure improves the orientation of the luster pigment. Therefore, diffused reflection of light can be suppressed, and an excellent metallic coating film with sufficient highlight brightness can be formed. Furthermore, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure can form a coating film with excellent physical properties such as good chipping resistance and excellent substrate transferability for coating workability.

[0190] This application claims priority based on Japanese Patent Application No. 2019-232918, filed on December 24, 2019, the entire contents of which are incorporated herein by reference.

Claims

1. A coating composition comprising: a first base coating film formed on a substrate using a first base coating composition; a second base coating film formed on the first base coating film using a second base coating composition; and a clear coating film formed on the second base coating film; the first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic glossing agent, and a first hydrophobic association-type viscosity-improving agent; the first inorganic brightener comprises one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth; the second base coating composition comprises a second film-forming resin, a second curing agent, a second luster material, a second inorganic viscous agent, a second hydrophobic association-type viscous agent, and a second dispersant; the second inorganic viscosity agent contains a layered material having a laminated structure of inorganic crystal layers, The non-volatile content NV1 in the first base coating composition is 10% or more and 45% or less, The non-volatile content NV2 in the second base coating composition is 3% or more and 18% or less, A multi-layer coating film, wherein the non-volatile content NV1 and the non-volatile content NV2 satisfy the relationship NV1>NV2.

2. The multi-layer coating film according to claim 1 , wherein the second luster material comprises a surface-treated luster material.

3. The multilayer coating film according to claim 1 or 2, wherein the second lustrous material has a scale-like shape and includes a lustrous material having an aspect ratio of 5 to 2000.

4. the second base coating composition contains the second inorganic viscosity agent in an amount of 1 part by mass or more and 7 parts by mass or less per 100 parts by mass of the total resin solids of the second coating film-forming resin and the second curing agent; The multilayer coating film according to any one of claims 1 to 3, wherein the second hydrophobic association type viscous agent is contained in an amount of 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the total resin solid content of the second coating film-forming resin and the second curing agent.

5. The second base coating composition further comprises a second inorganic gloss agent, the amount of the first inorganic gloss agent contained in the first base coating composition is defined as Am1 relative to 100 parts by mass of the total resin solids of the first film-forming resin and the first curing agent; When the amount of the second inorganic gloss agent contained in the second base coating composition is Am2 relative to 100 parts by mass of the total resin solids of the second coating film-forming resin and the second curing agent, 5. The multilayer coating film according to claim 1, wherein the ratio of Am1 to Am2, (Am1) / (Am2), is 2.0 or more.

6. The multi-layer coating film according to any one of claims 1 to 5, wherein the first base coating composition further comprises at least one of a first luster material and a first inorganic viscosity improving agent.

7. The multi-layer coating film according to claim 1 , wherein the second coating film-forming resin comprises at least one selected from an acrylic resin, a urethane resin, and a polyester resin.

8. The multi-layer coating film according to claim 1 , wherein the second inorganic viscosity-improving agent comprises a silicate layer compound.

9. The multilayer coating film according to any one of claims 1 to 8, wherein at least one of the first hydrophobic association type viscous agent and the second hydrophobic association type viscous agent includes a urethane-based hydrophobic association type viscous agent.

10. The first base coating composition further comprises a first dispersant; 10. The multilayer coating film according to claim 1, wherein at least one of the first dispersant and the second dispersant comprises a polymer-type dispersant having at least one selected from an anionic group, a cationic group, and a nonionic group.

11. The multi-layer coating film according to claim 1 , wherein the first inorganic brightening agent comprises an inorganic brightening agent having a positively charged surface.

12. The multi-layer coating film according to claim 5 , wherein the second inorganic brightener comprises an inorganic brightener having a positively charged surface.

13. The multi-layer coating film according to claim 6, wherein the thickness of the first inorganic viscosity agent is 100 nm or less.

14. The multilayer coating film according to any one of claims 1 to 13, wherein the thickness of the second inorganic viscosity agent is 100 nm or less.

15. A method for using an aqueous coating composition set for forming a multi-layer coating film having a first base coating film and a second base coating film, comprising: The aqueous coating composition set includes a first base coating composition that forms the first base coating film and a second base coating composition that forms the second base coating film, the first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic glossing agent, and a first hydrophobic association-type viscosity-improving agent; the first inorganic brightener comprises one or more selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth; the second base coating composition comprises a second film-forming resin, a second curing agent, a second luster material, a second inorganic viscous agent, a second hydrophobic association-type viscous agent, and a second dispersant; the second inorganic viscosity agent contains a layered material having a laminated structure of inorganic crystal layers, The non-volatile content NV1 in the first base coating composition is 10% or more and 45% or less, The non-volatile content NV2 in the second base coating composition is 3% or more and 18% or less, The non-volatile content NV1 and the non-volatile content NV2 satisfy the relationship NV1>NV2, A method for using a set of aqueous coating compositions, wherein the second base coating composition is applied after the first base coating composition.

16. A method for using the aqueous paint composition set described in Claim 15, wherein the film thickness t1 of the first base coating film and the film thickness t2 of the second base coating film have the relationship (t1) ≧ (t2).

Images