Water-based paint composition set and method for forming multi-layer coating film using same

Abstract

The present invention provides a water-based paint composition with which it is possible to form a metallic coating film having excellent design properties and to form a coating film exhibiting good coating-film physical properties. Provided is a water-based paint composition set for forming a multilayer coating film, the water-based paint composition set containing a first base paint composition for forming a first base coating film and a second base paint composition for forming a second base coating film. The first base paint composition contains a first coating-film forming resin, a first hardener, a first inorganic brightener, and a first hydrophobic associative viscous agent. The first inorganic brightener is formed of one or more substances selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulphate, and diatomaceous earth. The second base paint composition contains a second coating-film forming resin, a second hardener, a second bright material, a second inorganic viscous agent, a second hydrophobic associative viscous agent, and a second dispersing agent. The second inorganic viscous agent contains a layered material having a laminated structure in which many inorganic crystal layers are laminated.

Description

[Technical field]

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

[0002] For example, in the coating film appearance of automobile paint, coating films with metallic luster are attracting attention. Such coating films are required to have high flip-flop properties (so-called FF properties). To enhance the flip-flop properties, it is necessary for the pigment to be present in the paint with a certain orientation. In addition, it is preferable that the coating film with metallic luster does not show a grainy feeling (glare) and satisfies a dense feeling.

[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 20-40% by weight is applied to a substrate to give a dry film thickness of 1-15 μm, and then an aqueous base coat paint (A2) adjusted to have a solids content of 2-15% by weight is applied on top of the uncured coating film to give a dry film thickness of 0.1-5 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-95522 A Summary of the Invention [Problem to be solved by the invention]

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

[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 objects with complex shapes 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 coating defects, the affected areas are polished and corrected before the top coat (base coat and clear coat) is applied. In this case, the polishing marks (streaks that appear in the areas polished with sandpaper, etc.) may appear on the paint film after the top coat is applied (base coat transfer). This base coat transfer is particularly likely to occur when the top coat contains a lustrous material. Therefore, particularly with metallic and mica-based paint colors, a paint film that is less likely to cause base coat transfer (base coat transferability) is required as an issue for painting workability.

[0009] However, in the coating composition forming the metallic coating film shown in Patent Document 1, only the improvement of design is focused on, and the guarantee of the coating film properties as described above is left to another coating film. For this reason, for example, the coating composition must be prepared in consideration of the relationship between the coating film that ensures the coating film properties and the coating film that shows the metallic design. As a result, there are cases where an excellent metallic coating film cannot be obtained. In addition, the process of forming the multi-layer coating film becomes complicated. In order to solve these problems, there is a need for a coating composition that can form a metallic coating film having high designability and, in addition, can 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 paint composition set for forming a multilayer coating film, which can form a coating film having excellent design and metallic luster, and further has coating film physical properties and base transferability with improved chipping resistance, etc. Also, the aqueous paint composition set for forming a multilayer coating film of the present disclosure can form a multilayer coating film having 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 for forming a first base coating film and a second base coating composition for forming a second base coating film, The first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic gloss agent, and a first hydrophobic association type viscous 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 includes 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 shiny material includes a shiny material having a scaly shape and an aspect ratio of 5 to 2,000. [4] In one embodiment, the second base coating composition contains a second inorganic viscosity modifier in an amount of 1 part by mass to 7 parts by mass per 100 parts by mass of the total resin solids of the second coating film-forming resin and the second curing agent; 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] 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 solid content 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 solid content of the second coating film-forming resin and the second curing agent, The ratio of (Am1) to (Am2), (Am1) / (Am2), may be 2.0 or more. [6] In one embodiment, the non-volatile content (NV1) of the first base coating composition is greater than or equal to 10% and less than or equal to 45%. [7] In one embodiment, the non-volatile content (NV2) of the second base coating composition is greater than or equal to 3% and less than or equal to 18%. [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 includes 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 layered 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 polymer-type 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 polishing agent comprises a surface positively charged inorganic polishing agent.

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

[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 onto a substrate 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 have a relationship of (t1)≧(t2). Effect of the Invention

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

[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 content (NV) content) of the coating composition is set high (for example, 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 high NV content have a high viscosity, which causes problems such as the luster pigment being difficult to orient evenly. For example, when a coating film is formed using an aqueous coating composition with an NV content of about 25%, the orientation of the luster pigment is not uniform, resulting in a grainy feel (glare) in the coating film, and furthermore, the hiding power of the base may be reduced.

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

[0016] In addition, when a multi-layer coating film is formed by, for example, wet-on-wet coating using an aqueous coating composition, a mixed phase may occur near the interface of the layers. However, when an attempt is made to suppress the mixed phase, there is a risk of a decrease in design and film properties. For this reason, the present inventors have intensively studied a coating composition capable of forming a coating film having a good balance between high design and film 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 gloss agent, and a first hydrophobic association type viscous 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 includes 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 layered 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, it is possible to suppress diffuse reflection of light and form an excellent metallic coating film with sufficient highlight brightness. Furthermore, the aqueous coating composition set for forming a multilayer coating film according to the present disclosure can be easily painted even on a substrate having a complex shape, and a coating film with a beautiful metallic luster can be formed. Moreover, 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, high temperature water resistance, etc. Furthermore, the coating film has excellent base transferability and also has excellent base hiding ability. While not wishing to be limited to any particular theory, the present disclosure provides a method for preparing a coating composition comprising the steps of: 2B S paint By combining with the composition, light transmission is controlled, which is presumably what contributes to the excellent weather resistance of the multi-layer coating film.

[0019] Furthermore, although it should not be interpreted as being limited to a particular theory, the aqueous coating composition set for forming a multi-layer coating film according to the present disclosure has a predetermined composition for each coating composition, so that the interphase that may occur between the layers of the predetermined first base coating composition and the predetermined second base coating composition according to the present disclosure can be greatly suppressed. Therefore, for example, a multi-layer coating film can be formed using wet-on-wet coating. Therefore, the number of steps for forming a coating film can be reduced, and the environmental load is reduced. Furthermore, since the second inorganic viscous agent contains a layered material having a laminated structure of inorganic crystal layers, although it should not be interpreted limitedly by a specific theory, structuring (cohesive force) occurs due to the interaction between the second luster material and the second inorganic viscous agent, preventing the orientation disorder of the second luster material in the second base coating film, and forming an excellent metallic coating film. Furthermore, the resulting coating film has excellent water resistance. In one embodiment, even if the concentration (PWC: Pigment weight concentration) of the second glittering material 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 agent according to the present disclosure within the range described in the present specification. Furthermore, the cohesive force of the second base coating film is further improved, and a coating film having excellent design properties, coating film properties, and water resistance can be easily formed.

[0020] The aqueous paint 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 in the present disclosure contains a first coating film-forming resin, a first curing agent, a first inorganic gloss agent, and a first hydrophobic association type viscosifier. If the first base coating composition has such a composition and further contains a specific second base coating composition described below, the aqueous coating composition set according to the present disclosure can form a multilayer coating film (a shiny multilayer coating film) that has a beautiful metallic feel in addition to excellent base hiding properties and chipping resistance.

[0022] In one embodiment, the first base coating composition further comprises at least one of a first luster material and a first inorganic viscosity agent. For example, the first base coating composition can further improve the base hiding power by including the first luster material. In addition, together with the second base coating film, a multi-layer coating film that has a deeper metallic feel can be formed. In an embodiment containing a first luster material, the first base coating composition may contain a first inorganic viscous agent. By using the first luster material and the first inorganic viscous agent in combination in the first base coating composition, it is possible to prevent the first luster material from settling during the formation of the coating film and to prevent the coating film from becoming turbid. In addition, since the first luster material is more uniformly oriented, a first base coating film having a more excellent design and a multi-layer coating film having this first base coating film can be obtained.

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

[0024] The non-volatile 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 non-volatile content can be controlled by adjusting the amount of the solvent in the coating composition. By having the non-volatile content (NV1) 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 multilayer coating film having 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. In addition, the first base coating composition according to the present disclosure can prevent the phenomenon of the coating composition dripping and the sedimentation of the first luster material added as needed. Moreover, even on a coating object having a complex shape with many curved surfaces, a coating film with a beautiful metallic luster without unevenness 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 5000 or more and 30000 or less, for example, 7000 or more and 25000 or less. By having the number average molecular weight within such a range, it is possible to have good workability and further to have 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 coating film-forming resin has a hydroxyl value of 20 to 180, for example, 30 to 160. When the hydroxyl value of the first coating film-forming resin is within such a range, the first base coating film can have sufficient water resistance, for example, excellent high-temperature water resistance (80° C.), and also has good coating film 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, an acid value of 15 mgKOH / g or more and 70 mgKOH / g or less. When the acid value of the first film-forming resin is within such a range, the first base coating film can have sufficient water resistance, for example, excellent high-temperature water resistance (80°C). In addition, the first base coating film has good coating film 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 coating film-forming resin selected from an acrylic resin, a polyester resin, a melamine resin, a urethane resin, and a mixture thereof, from the viewpoints of coating film strength, weather resistance, water resistance, etc. For example, the first coating film-forming resin includes at least one selected from an acrylic resin, a urethane resin, and a polyester resin. 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 a solid content of 40 parts by mass to 60 parts by mass, and the urethane resin may be contained in a solid content of 1 part by mass 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 respective acrylic resins can be appropriately adjusted so as to fall within the above range. Similarly, when multiple types of urethane resins are used, the total parts by mass of the respective urethane resins can be appropriately adjusted so as to fall within the above range. In the present disclosure, the first film-forming resin and the first film-curing agent may be collectively referred to as the "first main resin." In addition, the "resin solid content mass of the first main resin" refers to the total solid content of the first film-forming resin and the first curing agent. For example, 100 parts by mass of the resin solid content of the "first main resin" corresponds to 100 parts by mass of the total resin solid content 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 appropriately corresponds to the type of curable functional group possessed by the first film-forming resin. The first curing agent may 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 of the obtained coating film and the cost, an amino resin and / or a blocked isocyanate resin are 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 active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. In such blocked isocyanate resins, the blocking agent is dissociated by heating to generate isocyanate groups, which react with the functional groups in the resin components to cure.

[0033] The amount of the first curing agent is, for example, 5 parts by mass or more and 50 parts by mass or less, for example, 5 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the resin solid content of the first main resin (first coating film-forming resin and first curing agent). By having the amount of the first curing agent in this range, sufficient coating film curability can be obtained.

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

[0035] Although it should not be interpreted as being limited to a particular theory, when the second base coating composition is applied onto the coating film (first base coating film) formed by the first base coating composition, the first inorganic gloss agent tries to adsorb the solvent contained in the second base coating composition. As the solvent moves, the second luster material moves, and its orientation is improved. Furthermore, since the viscosity of the second base coating composition increases, the orientation of the second luster material is easily maintained. As a result, the orientation of the second luster material in the second base coating film is improved. By improving the orientation of the luster pigment, an excellent metallic coating film with reduced diffuse reflection of light can be formed.

[0036] Furthermore, the first inorganic gloss agent can contribute to suppression of interphase formation between the first base coating film and the second base coating film. When interphase formation is suppressed, deterioration of the appearance of the coating film is suppressed, and the coating film properties such as chipping resistance can be maintained better.

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

[0038] Furthermore, in an embodiment in which the first base coating composition contains the first luster material, the first inorganic glossing agent can promote uniform dispersion of the first luster material and suppress localization of the first luster material. Furthermore, the first inorganic glossing agent can suppress unevenness of the first base coating film. In addition, the first inorganic gloss agent can impart impact stress dispersion ability to the first base coating film according to the present disclosure. Therefore, for example, the first base coating film formed from the first base coating composition having a predetermined composition can have good chipping resistance.

[0039] In one embodiment, the first inorganic brightener comprises a surface positively charged inorganic brightener, for example, the first inorganic brightener comprises barium sulfate. For example, the first inorganic brightening agent contains barium sulfate, which can more effectively suppress interphase with the second base coating composition. In addition, the second base coating composition in which interphase is suppressed contains the specific second inorganic viscosity agent according to the present disclosure, so that cohesive force (structuring) is generated in the second base coating film, and the orientation disorder of the second brightening material is more effectively prevented. Thus, in one embodiment, since the first inorganic gloss agent contains barium sulfate, the effect of preventing inter-phase mixing between the first base coating film and the second base coating film is enhanced, and orientation disturbance of the second gloss material in the second base coating film is more effectively prevented.

[0040] In an embodiment, the average primary particle size of the first inorganic gloss agent 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, relative to 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, relative to 100 parts by mass of the resin solid content. By the amount of the first inorganic glossing agent being within such a range, it becomes easier to suppress the interphase, and it is easy to form a coating film having good gloss.

[0042] (First hydrophobic association type viscosity agent) The first hydrophobic association type viscosifier according to the present disclosure can increase the viscosity of the first base coating composition by hydrophobic interaction occurring between at least one of the hydrophobic groups of at least one of the group consisting of the first coating film-forming resin, the first curing agent, and the first inorganic gloss agent contained in the first base coating composition. By including the first hydrophobic association type viscosifier, the first base coating composition can suppress coating defects such as cissing and dents in the first base coating film, and can increase the smoothness of the interface between the first base coating film and the second base coating film. Furthermore, the orientation disorder of the first luster material in the vicinity of the interface can be suppressed, and a luster multilayer coating film having an excellent metallic feel can be formed.

[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 viscous agent includes a polyurethane-based viscous agent having a hydrophobic chain in the molecule, and a urethane-urea-based viscous agent in which at least a part of the main chain is a hydrophobic urethane chain. By including such a hydrophobic association type viscous agent, in addition to the above effects, excellent anti-settling properties and sagging properties can be more effectively exhibited in a system including a water-based material, such as the first base coating composition. For example, urethane-based hydrophobic association type viscosifiers such as polyurethane-based viscosifiers and urethane-urea-based viscosifiers have the property that viscosity is easily developed at low shear and is difficult to develop at high shear, and have excellent thixotropy. Due to such properties, the first base coating composition of the present disclosure can be suitably used for, for example, spray coating. Furthermore, the first base coating film formed from the first base coating composition containing such a hydrophobic association type viscosifier can have excellent water resistance and high temperature water resistance.

[0045] Examples of commercially available first hydrophobic association type viscosity agents 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), RHEOLATE216 (urethane-urea compound: manufactured by ELEMENTIS), Primal RM-12W, Primal RM-895 (urethane-based: manufactured by Dow Chemical), and Disparlon AQ-021 (Kusumoto Chemical).

[0046] The first base coating composition of the present disclosure contains a 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 viscous agent 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 viscous agent in such a range, it becomes easier to avoid settling of the first inorganic gloss agent and the first lustrous material, which is added if desired, during formation of the first base coating film, and the occurrence of turbidity in the first base coating film. In addition, since the first lustrous material added as desired can be more uniformly oriented, it is easy to obtain a first base coating film and a multi-layer coating film having excellent design, particularly excellent metallic tone. Furthermore, since the first base coating film can have excellent water resistance and 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. By including the first dispersant, the dispersion stability of various components contained in the first base coating composition is improved.

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

[0050] In an 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 solubility in water 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 polymer type dispersant or a low molecular weight surfactant type dispersant. For example, from the viewpoint of preventing aggregation of the first lustrous material, a polymer type dispersant is preferred. The polymer type dispersant is preferably a polymer type dispersant having at least one selected from an anionic group, a cationic group, or a nonionic group, and more preferably at least one selected from a polymer type dispersant having a highly hydrophobic side chain and having an anionic group, a polymer type dispersant having a nonionic group, and a mixture thereof. Examples of the anionic group include a phosphoric acid group and a carboxylic acid group. Examples of the nonionic group include a polyoxyalkylene group. However, the present invention is not limited to these groups.

[0052] As described above, the polymer dispersant may be a known dispersant such as 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 type dispersant, a known dispersant can be used, and a commercially available product can be used. For example, BYK-Chemie's DISPERBYK series, such as DISPERBYK, DISPERBYK-194, DISPERBYK-194N, DISPERBYK-192; Lubrizol's Solsperse 41000, Solsperse 43000, Solsperse 44000, Solsperse 47000, etc. can be mentioned. DISPERBYK-192, DISPERBYK-194N, DISPERBYK can be preferably used.

[0054] The amount of the first dispersant can be 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin solid content of the first coating film-forming resin and the first curing agent. By being in such a range, the dispersion stability of various components contained in the first base coating composition is further improved, and the aggregation of each component can be effectively suppressed in the formation process of the first base coating film. In one embodiment, the 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 comprises at least one of a first glittering material and a first inorganic viscosity agent. Depending on the desired metallic appearance, the first base coating composition may comprise a first glittering 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 glittering material in the first base coating composition is calculated by the following formula: PWC = (total mass of the first lustrous material) / [(total mass of the resin solid content of the first coating resin and the resin solid content of the first hardener) + (total mass of the first lustrous material)] × 100 As shown in the figure. In this case, the range of PWC 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 in the above range, the first lustrous material is more uniformly oriented after the coating film is formed, so that the coating film having excellent lustrous properties and excellent design can be easily formed. Furthermore, the obtained coating film can have good base hiding properties.

[0057] The first shining material may be the same shining material as the second shining material described later. In this embodiment, the detailed description of the characteristics of the first shining material can be referenced to the description of the second shining material described later. 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 embodiment, the surface treatment of the aluminum luster material has the advantage of suppressing gassing (hydrogen gas generation due to oxidation of the aluminum surface by water) in the aqueous coating composition. 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 Aluminium Co., Ltd.

[0059] (First inorganic viscosity agent) The first inorganic viscosity agent according to the present disclosure is preferably a layered material having a laminated structure in which a large number of inorganic crystal layers are stacked. The first inorganic viscosity agent having such a layered structure swells in the first base coating composition and forms a card house structure, thereby providing the first base coating composition with an appropriate viscosity and excellent coating strength.

[0060] The shape of the primary particles of the first inorganic viscosity agent may be disc-like, plate-like, spherical, granular, cubic, needle-like, rod-like, amorphous, etc., with disc-like or plate-like shapes 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, 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 is true for the thickness of the second inorganic viscous agent.

[0063] The 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 viscous agent and a first hydrophobic association type viscous agent can provide the first base coating film with excellent water resistance and high-temperature water resistance, thereby enabling the water resistance and high-temperature water resistance of the entire multi-layer coating film to be well maintained. In one embodiment, the first inorganic viscosity agent comprises a silicate layered compound.

[0064] Specific examples of the silicate layered compound 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, as well as vermicularite and 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 manufactured by Kunimine Kogyo Co., Ltd.). These include smectite-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 in the US), 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 mass, for example, 0.5 to 10 parts by mass, per 100 parts by mass of the total resin solids of the first film-forming resin and the first curing agent, for example, 0.5 to 10 parts by mass. 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 mass, for example, 0.5 to 10 parts by mass, per 100 parts by mass 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 viscous agent in such a range, it becomes easier to avoid the first lustrous material, which is added as necessary, from settling during the formation of the first base coating film, and a coating film having excellent design properties, particularly excellent metallic tones, 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 luster 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 statement "the second inorganic viscous agent includes a layered material having a laminated structure in which a large number of 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, it can be easily painted even on a coating object having a complex shape, 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 can form a coating film having physical properties such as good chipping resistance, water resistance, and high-temperature water resistance. Furthermore, it has the advantage of having excellent base 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 shiny multilayer coating film) having excellent design properties and good coating film properties.

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

[0070] The non-volatile 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 non-volatile content can be controlled by adjusting the amount of the solvent in the second base coating composition.

[0071] By having the non-volatile content (NV2) 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 having a 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 further, 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 second lustrous material from settling and the coating composition from flowing, despite its low non-volatile content (NV2). In addition, the second base coating composition according to the present disclosure can form a thin film, so that the second lustrous material can 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 a substrate having a complex shape without causing sagging. Moreover, since 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), so that the coating thickness can be made thin and uniform. In one embodiment, the coating 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 coating thickness of the second base coating is 3 μm or more and 7 μm or less. In addition, when a coating is formed from a second base coating composition with a low NV amount, the second luster material can be more uniformly oriented due to the volume shrinkage of the second base coating composition after coating, and high flip-flop properties can be obtained. In other words, unlike conventional aqueous coating compositions having 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 disclosed herein, the interaction achieved by the combination of a specific 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, allow the second luster material to be more uniformly oriented, resulting in higher flip-flop properties and a lower G value (grainy feel).

[0075] In addition, the second base coating composition according to the present disclosure can prevent the second base coating composition from dripping and the second luster material from settling, even when the substrate has a complex shape including many curved surfaces, and can form a second base coating film and a multi-layer coating film with a beautiful, uniform metallic luster.

[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 described above, may contain a different type of resin, or may be a mixture of these. For example, the second film-forming resin contains 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 5000 to 30000, for example, 7000 to 25000. By having the number average molecular weight within such a range, good workability can be obtained, and further, curability suitable for the multilayer coating film according to the present disclosure can be obtained.

[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 one embodiment, 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 coating film-forming resin is within such range, the second base coating film can have sufficient water resistance, for example, excellent high-temperature water resistance (80° C.), and also has good coating film 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 an acrylic resin, a polyester resin, a melamine resin, a urethane resin, and a mixture 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 an acrylic resin, a urethane resin, and a polyester resin. 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 respective acrylic resins can be appropriately adjusted so as to fall within the above range. Similarly, when multiple types of urethane resins are used, the total parts by mass of the respective urethane resins can be appropriately adjusted so as to fall within the above range. For example, the "resin solid content mass of the second main resin" means the total solid content mass of the second film-forming resin and the second curing agent. For example, 100 parts by mass of the resin solid content of the "second main resin" corresponds to 100 parts by mass of the total resin solid content of the second film-forming resin and the second curing agent.

[0080] (Second hardener) The second base coating composition according to the present disclosure contains a curing agent that corresponds appropriately to the type of curable functional group possessed by the second coating film-forming resin. The second base coating composition may contain the same type of resin as the first curing agent described above, may contain a different type of curing agent, or may be a mixture of these. 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 appropriately selected.

[0081] (Second bright material) The second base coating composition according to the present disclosure includes a second luster material. The second luster material in 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 glittering material in the second base coating composition is expressed by the following formula: PWC = (total mass of second luster material) / [(total mass of resin solid content of second coating resin and resin solid content of second hardener) + (total mass of second luster material)] x 100 As shown in the figure. In this case, the PWC range is 5% to 40%, for example, the PWC range is 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 material in the above range, the orientation of the luster pigment is easily improved, and an excellent metallic coating film can be easily formed. In particular, since the present disclosure is 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 for the second luster material to be more uniformly oriented. 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 type particle size shape analyzer, for example, FPIA-3000S (manufactured by SYSMEX).

[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 (coverage) area according to JIS K5906.

[0085] The second lustrous material has a thickness within this range, and is contained in the second base coating composition according to the present disclosure, so that the second lustrous material is more easily oriented with the volume shrinkage of the second base coating composition after application. Therefore, it is 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 is less likely to be scattered in the visible light range by the end faces of the lustrous materials at the overlapping parts, making it possible to achieve a dense design (smooth design) with a low graininess and a high metallic feel. Therefore, the second base coating film and the multi-layer coating film exhibit a low graininess value and have a dense design with a low graininess.

[0086] In one embodiment, the second shining material has a scaly shape. For example, the aspect ratio of the second shining 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 shiny material is 10 or more and 1000 or less, for example, 10 or more and 800 or less. By including the second lustrous material having such a shape, the second lustrous material is easily oriented uniformly with the volumetric shrinkage of the second base coating composition after application. Therefore, it is possible to easily form a coating film that has excellent metallic luster and high flip-flop properties. In addition, the adhesion between the coating film and the substrate is less likely to be adversely affected. In particular, the present disclosure relates to an aqueous coating composition set that includes a first base coating composition and a second base coating composition, and the interaction between the first base coating composition and the second base coating composition can make the orientation of the second luster material more uniform. Therefore, a coating film with excellent metallic luster and reduced diffuse reflection of light can be easily formed. When a commercially available product is used as the second lustrous material, the aspect ratio may be indicated 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 shining 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 shining 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. By having the second luster material have 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, and it is possible to obtain a high metallic feel for the second base coating film and the multi-layer coating film. In addition, it is possible to easily form a second base coating film and a multi-layer coating film that show a low graininess value and have a dense design (smooth design) with a low graininess.

[0088] The second lustrous material may include, 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 chrome, stainless steel, etc. 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 the generation of gas due to reaction of metal flakes, metal oxide flakes, pearl pigments, etc. with water, a metal coating, for example, a coating of a metal compound such as molybdic acid, chromic acid, yttrium, or rare earth metal, or an organic polymer coating, for example, a coating of an organic polymer prepared using a polymerizable monomer, 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 that includes silicon dioxide, zirconium oxide, aluminum oxide, chromium oxide, polymerized synthetic resins, vanadium oxide, molybdenum oxide and / or molybdenum peroxide, phosphates, phosphites, borates, chromates, 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 pieces (metal oxide pieces).

[0091] The metal material to be vapor-deposited is not particularly limited, but the materials described above for the metal pieces and metal oxide pieces can be used. Preferably, the second lustrous material includes vapor-deposited aluminum pigment, vapor-deposited chromium pigment, vapor-deposited alumina pigment, and vapor-deposited chromium oxide pigment. The vapor-deposited metal pigment can also have a coating film on its surface as 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 embodiment, gassing (hydrogen gas generation due to oxidation of the aluminum surface by water) in an aqueous coating composition 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 Aluminium Co., Ltd.

[0094] (Second inorganic viscosity agent) The second inorganic viscosity agent in the present disclosure includes a layered material having a laminated structure in which a large number of inorganic crystal layers are stacked. The second inorganic viscosity agent having such a layered structure swells in the second base coating composition and forms a card house structure, thereby providing the second base coating composition with an appropriate viscosity and excellent coating strength.

[0095] Furthermore, the second inorganic viscous agent maintains the orientation of the second luster material well. Although not limited to a particular theory, the second inorganic viscous 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, the solvent may move. However, since the second base coating composition is given thixotropy by the second inorganic viscous agent, the viscosity in the low shear region is small, and the orientation of the second luster material is well maintained. As a result, an excellent metallic coating film with suppressed diffuse reflection of light can be formed.

[0096] In addition, although it should not be interpreted as being limited to a particular theory, it is believed that the second base coating composition contains a second inorganic viscous agent, which causes structuring due to the interaction between the glittering material (e.g., aluminum) and the second inorganic viscous agent, and prevents the orientation disorder due to the cohesive force (structuring) of the second base coating composition. Moreover, the stability of the second base coating composition, which has a high PWC of the glittering material, can be improved.

[0097] The second inorganic viscosity modifier also contributes to suppression of interphase formation between the first base coating film and the second base coating film. When interphase formation is suppressed, deterioration of the coating film's appearance is suppressed, and coating film properties such as chipping resistance can be maintained in a better condition.

[0098] The shape of the primary particles of the second inorganic viscosity agent may be discoid, plate-like, spherical, granular, cubic, needle-like, rod-like, amorphous, etc., with discoid or plate-like shapes 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 glittering material from being disturbed. The thickness of the second inorganic viscous agent is more preferably 50 nm or less, 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 agent contains a silicate layer compound. The silicate layer compound can provide the second base coating composition with an appropriate viscosity and excellent coating strength. In addition, the second base coating film formed from the second base coating composition has excellent water resistance by using the second inorganic viscosity agent in combination with the second hydrophobic association type viscosity agent described later, and can also have excellent high temperature water resistance (80°C).

[0102] Specific examples of silicate layered 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 fluorine taeniolite, and Li-type fluorine taeniolite, as well as vermicularite and 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 not 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 a certain component contained in the first base coating composition, such as the first inorganic gloss agent described above, the second luster material can be well oriented in the second base coating film, 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 diffuse reflection of light is suppressed, resulting in the formation of an excellent metallic coating film. In addition, deterioration of the appearance of the coating film due to interphase can be suppressed, and further, the coating film 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 Kogyo Co., Ltd.). bentonite-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 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 viscous agent in an amount of 1 part by weight or more and 7 parts by weight or more per 100 parts by weight of the total resin solids of the film-forming resin and the curing agent. In one embodiment, the second base coating composition according to the present disclosure preferably contains the second inorganic viscous agent in an amount of 1 part by mass to 7 parts by mass to 100 parts by mass of the total resin solids content of the film-forming resin and the curing agent, more preferably 2 parts by mass to 7 parts by mass, and even more preferably 2 parts by mass to 5 parts by mass. By including the second inorganic viscosity agent in such a range, it is easy to prevent the second lustrous material from settling during the formation of the second base coating film, and the second base coating film from becoming turbid. In addition, it is possible to more effectively suppress the occurrence of interphase between the first base coating film and the second base coating film. 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 solid content of the second coating 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 per 100 parts by mass of the total resin solid content of the second coating film-forming resin and the second curing agent, for example, 1 to less than 15 parts by mass. The second base coating composition may contain the second inorganic viscosity agent 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 type viscosity agent in a predetermined amount per 100 parts by mass of the total resin solid content of the coating film-forming resin and the curing agent, as described above, so that the second lustrous material can be effectively prevented from settling during the formation of the coating film and the second base coating film from becoming turbid. In addition, the orientation of the second lustrous material can be made uniform, so that a coating film having excellent design properties can be easily obtained. In addition, the second base coating film has excellent water resistance, and can also have excellent high-temperature water resistance (80°C).

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

[0109] In one embodiment, in the aqueous paint composition set according to the present disclosure, the amount of the first inorganic gloss 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 containing the second inorganic viscosifier and the first inorganic gloss agent in this relationship, the aqueous paint composition set according to the present disclosure can form a coating film with a metallic luster and excellent design properties, and can also provide a multilayer coating film having improved coating film properties such as chipping resistance, water resistance, and high-temperature water resistance, as well as excellent transferability to the base.

[0110] (Second hydrophobic association type viscosity agent) The second hydrophobic association type viscosifying agent of the present disclosure can increase the viscosity of the second base coating composition due to hydrophobic interaction occurring between the second hydrophobic association type viscosifying agent and at least one of the hydrophobic groups contained in the second base coating composition, the hydrophobic association type viscosifying agent being ... By including the second hydrophobic association type viscous 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. In addition, since the second base coating composition contains a second inorganic viscosity agent and a second hydrophobic association type viscosity agent, it is possible to more effectively prevent the second lustrous material from settling during the formation of the coating film and the second base coating film from becoming turbid. Furthermore, since the second lustrous material can be uniformly oriented, a coating film having excellent design properties can be obtained. Moreover, the second base coating film has excellent water resistance and can also have excellent high-temperature water resistance (80°C).

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

[0112] In one embodiment, the second hydrophobic association type viscous agent includes a polyurethane-based viscous agent having a hydrophobic chain in the molecule, and a urethane-urea-based viscous agent in which at least a part of the main chain is a hydrophobic urethane chain. By including such a second hydrophobic association type viscous agent, in addition to the above effects, excellent anti-settling properties and sagging properties can be more effectively exhibited in a system including a water-based material, such as the second base coating composition. For example, urethane-based hydrophobic association type viscosifiers such as polyurethane-based viscosifiers and urethane-urea-based viscosifiers have the property that viscosity is easily developed at low shear and is difficult to develop at high shear, and are excellent in thixotropy. Due to such properties, the second base coating composition of the present disclosure can be suitably used, for example, in spray coating. Furthermore, the second base coating film formed from the second base coating composition containing such a hydrophobic association type viscosifier can have excellent water resistance and high temperature water resistance.

[0113] Examples of commercially available second hydrophobic association type viscosity agents 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), RHEOLATE216 (urethane-urea compound: manufactured by ELEMENTIS), Primal RM-12W, Primal RM-895 (urethane-based: manufactured by Dow Chemical), and Disparlon AQ-021 (Kusumoto Chemical).

[0114] The aqueous coating composition of the present disclosure contains the second hydrophobic association type viscous agent in an amount of 1 part by mass or more and 15 parts by mass or less, for example, 1 part by mass or more and less than 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. In one embodiment, the second hydrophobic association type viscous agent is contained in an amount of 2 parts by mass or more and 15 parts by mass or less, for example, 2 parts by mass or more and less than 15 parts by mass, in one embodiment, 2 parts by mass or more and 10 parts by mass or less, and in another embodiment, 2 parts by mass or more and 5 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. By including the second hydrophobic association type viscous agent in such a range, it is possible to more effectively prevent the second lustrous material from settling during the formation of the second base coating film and the second base coating film from becoming turbid. In addition, since the second lustrous material can be uniformly oriented, it is easy to obtain a coating film with excellent design, especially excellent metallic tone. Furthermore, by blending a predetermined amount of a predetermined second hydrophobic association type viscous agent, the second base coating film and the multi-layer coating film can have excellent water resistance and further excellent high-temperature water-resistant adhesion.

[0115] (2nd inorganic brightener) The second base coating composition may optionally contain a second inorganic gloss agent, which may be the same as or different from the first inorganic gloss agent. 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 an inorganic brightener having a positively charged surface, for example, barium sulfate. The second inorganic brightener can refer to the above-mentioned 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 the same type of second inorganic gloss agent as the first inorganic gloss agent. Although it should not be limited to a particular theory, the first inorganic gloss agent and the second inorganic gloss agent are the same type, so that the 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 the second inorganic glossing agent in an amount of 0.01 parts by mass or more and less than 10 parts by mass, for example, 0.01 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the total resin solid content of the second coating film-forming resin and the second curing agent. In one embodiment, the second inorganic glossing agent may be contained in an amount of less than 0.1 parts by mass, for example, 0.01 parts by mass or more and less than 0.1 parts by mass, based on 100 parts by mass of the resin solid content. By containing the second inorganic glossing agent in such a range, an excellent metallic coating film can be formed. Here, in the present disclosure, the amount of the second inorganic gloss agent can be selected according to the type (e.g., size, thickness) of the lustrous material contained in the second base coating composition, thereby further improving the design.

[0118] In one embodiment, the second base coating composition may include a second inorganic polishing agent. 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 is (Am1) per 100 parts by mass of the total resin solids of the first coating film-forming resin and the first curing agent, and the amount of the second inorganic glossing agent contained in the second base coating composition is (Am2) per 100 parts by mass of the total resin solids of the second coating film-forming resin and the second curing agent, it is preferable that the ratio of the amount of (Am1) to the amount of (Am2), (Am1) / (Am2), is 2.0 or more. Such a relationship can further reduce interference unevenness due to the refractive index difference 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 some embodiments, the second dispersant has a substituent that provides dispersion stability to metal or metal oxide. By having such a substituent, the second dispersant can effectively cover the second luster material, and further, depending on the molecular weight of the second dispersant, the steric hindrance of the second luster material can be increased, so that the aggregation of the second luster material can be suppressed. In addition, such a second dispersant can increase the dispersibility of the second luster material.

[0121] In an embodiment, the second dispersant may have a highly hydrophobic side chain. By having a highly hydrophobic side chain, the second dispersant can be dissolved in a solvent such as, for example, 2-ethylhexyl alcohol (2EHOH) or monoethylene glycol mono 2-ethylhexyl ether (EHG).

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

[0123] As described above, the polymer dispersant may be a known dispersant such as 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, a known dispersant can be used, and may include, for example, the commercially available products described in the first dispersant.

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

[0126] <Organic solvent> 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 or more and 5.0% by mass or less and a boiling point of 160°C to 200°C or less, and optionally a glycol ether-based 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 to 240°C or less may be included. In addition, 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 that the paint viscosity and coating workability can be better adjusted. 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] By having the boiling point of the alcohol-based organic solvent within the above range, there is an advantage that the coating workability, particularly the resistance to foaming and sagging, can be secured within a better range. 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 water dispersion, 2-ethylhexyl alcohol (2EHOH) is preferred.

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

[0131] When the above alcohol-based organic solvent is added to the aqueous coating composition, the particle size distribution during coating is improved, and therefore the aggregation of the scaly pigment can be significantly prevented.

[0132] If necessary, a glycol ether-based 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-based 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-based 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-based organic solvent is 205° C. or higher and 240° C. or lower, the coating workability, particularly the resistance to foaming and sagging, is likely to be improved. The boiling point of the glycol ether-based organic solvent is preferably 210° C. or higher and 230° C. or lower.

[0135] The glycol ether-based 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). hmm, From the viewpoint of stability (particle size) of the hydrophobic melamine resin water dispersion, ethylene glycol mono 2-ethylhexyl ether (EHG) is preferred.

[0136] The content of the glycol ether organic solvent in the aqueous coating composition is, for example, 10 to 150 parts by mass, preferably 50 to 100 parts by mass, per 100 parts by mass of the total resin solids of the coating film-forming resin and the curing agent. When the content is within this range, the effect of preventing the scale-like pigment from agglomerating is easily enhanced, and coating workability such as rollability is easily improved. When a plurality of organic solvents are used, the total amount of each organic solvent can be adjusted to be 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 / glycol ether-based organic solvent is preferably 1 / 1 to 3 / 1. When the mass ratio is within this range, an excessive decrease in the viscosity of the coating is suppressed, the coating workability is improved, and the stability of the coating composition over time is also likely to be improved.

[0138] Also, 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-mentioned 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 assistant, 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 the above components can be uniformly dispersed. The first and second base coating compositions can be prepared by a method known to those skilled in the art, for example, using a kneader, a mill, or a roll mill.

[0141] <First coating film and second coating film> The first coating film can be formed from the first base coating composition according to the present disclosure, and the second base coating film can be formed from the second base coating composition according to the present disclosure. The multi-layer coating film having such a first base coating film and a second base coating film has a high orientation of the luster material, and thus has an excellent metallic feel with suppressed diffuse reflection of light. In addition, the multi-layer coating film has excellent physical properties such as chipping resistance, water resistance, and high-temperature water resistance, and workability. Therefore, the multilayer coating film formed from the aqueous paint composition set for forming a multilayer coating film according to the present disclosure has an excellent metallic feel and also has good coating film properties.

[0142] In one embodiment, the 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 thickness of the first base coating is 2.5 μm or more and 11 μm or less. By having the thickness of the first base coating film within this range, it is possible to form a multi-layer coating film that is particularly excellent in chipping resistance, base transferability, and design. Note that the above-mentioned thickness is the 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 setting the thickness of the second base coating film within this range, a multi-layer coating film having excellent sagging prevention properties and excellent design can be formed. Note that the above-mentioned thickness is the thickness after heat curing.

[0144] For example, the thickness (t1) of the first base coating film formed from the first base coating composition and cured by heating and the thickness (t2) of the second base coating film formed from the second base coating composition and cured by heating have a relationship of (t1) ≧ (t2). By having such a relationship, a multilayer coating film having a better metallic feel can be formed, and further, a multilayer coating film having excellent physical properties such as chipping resistance and excellent base transferability as painting workability can be formed without impairing the excellent metallic feel. Furthermore, a multilayer coating film having excellent water resistance and high temperature water resistance can be formed.

[0145] <Method of forming multi-layer coating film> The present disclosure further provides a method for forming a multilayer coating film using an aqueous coating composition set including a first base coating composition and a second base coating composition according to the present disclosure, A step of applying a first base coating composition onto a substrate 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 heat-cured second base coating film is formed from a second base coating composition and has a thickness of 1 μm or more and 20 μm or less.

[0146] In another aspect, the present disclosure provides a method for the preparation of a A step of applying an aqueous intermediate coating composition onto a substrate 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 second base coating film formed from the second base coating composition and cured by heating is 1 μm to 20 μm. 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 concealing properties of the substrate surface, adhesion to the substrate, and chipping resistance. The intermediate coating film has a thickness of, for example, 10 μm to 50 μm in terms of dry film thickness. The intermediate coating paint 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-containing polyester resin and / or a hydroxyl-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 be applied by so-called wet-on-wet coating 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 using these metals, plastics, and foams. The substrate may have a cured electrodeposition coating formed on the surface. The cured electrodeposition coating is formed by electrodeposition coating an electrodeposition paint on the substrate and curing the paint by heating. 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 normally used for electrodeposition coating of automobile bodies. The method for forming a multilayer coating film (lustrous 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] As the clear coating composition used in the present disclosure, a coating composition known as a clear coating composition for automobile bodies can be used. Such a clear coating composition can be, for example, one that contains a clear coating film-forming resin, and a curing agent and other additives as necessary, in a state dispersed or dissolved in a medium. 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 viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin with an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid-epoxy curing system. For example, the clear coating composition contains a predetermined amount of an ultraviolet absorber and a light stabilizer together with the above resin components, thereby improving adhesion to the anticorrosive coating film. In addition, the use of such a clear coating composition is preferable in that it can prevent corrosion even when used in areas prone to salt damage.

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

[0151] The thickness of the second base coating is from 1 μm to 20 μm, for example, from 2 μm to less than 15 μm. In another embodiment, the thickness of the second base coating is from 3 μm to 7 μm. By setting the thickness of the second base coating film within this range, a multi-layer coating film having excellent sagging prevention properties and excellent design can be formed. Note that the above-mentioned thickness is the thickness after heat curing.

[0152] For example, the thickness (t1) of the first base coating film formed from the first base coating composition and cured by heating and the thickness (t2) of the second base coating film formed from the second base coating composition and cured by heating have a relationship of (t1) ≧ (t2). By having such a relationship, a multilayer coating film having a better metallic feel can be formed, and furthermore, a multilayer coating film having excellent physical properties such as chipping resistance and excellent base transferability as painting workability can be formed. Furthermore, a multilayer coating film having excellent water resistance and high temperature water resistance can be formed. The obtained thin film has excellent gloss and high flip-flop properties (so-called FF properties), and is a metallic coating film that has a dense feel without any graininess (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, brush, roller, roll coater, air spray, airless spray, curtain flow coater, roller curtain coater, and die coater. These can be appropriately selected according to the object to be coated. For example, the aqueous coating composition may be applied by an electrostatic coater. In addition, conditions such as the amount of discharge of the coating film can be appropriately set according to the required thickness of the coating film.

[0154] After the base coating composition is applied, it is preferable to carry out a step of volatilizing water at 40°C to 100°C for 1 to 10 minutes. By setting the curing temperature after the 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. EXAMPLES

[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 weight 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 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 dimethylethanolamine 10% by weight aqueous solution (3) 28.3 parts of water-soluble acrylic resin manufactured by Nippon Paint Co., Ltd. (non-volatile content 30%, solid acid value 40 mgKOH / g, hydroxyl value 50 mgKOH / g) (4) Sanyo Chemical Industries, Ltd. "Primepol PX-1000" (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%) 8.6 parts (5) Mitsui Chemicals "Cymel 204" (mixed alkylated melamine resin, 100% non-volatile content) 21.5 parts (6) Avecia "Neolet's R-9603" (polycarbonate urethane emulsion) hmm, Non-volatile content 33%) 26 parts (7) Lauryl acid phosphate 0.2 parts (8) 60 parts of 2-ethylhexanol (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 mass of the main resin) was 100 parts by mass.

[0157] <Preparation of first base coating composition> The above resin composition 1 was mixed with the components shown below 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 luster material, and the PWC of the first inorganic brightening agent were calculated according to the following formula. Non-volatile content (NV1) = [(mass of the first base coating composition after drying) / (mass of the first base coating composition before drying)] × 100 (%)

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

[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 weight per 100 parts by weight of solid content of main resin)

[0163] <Preparation of second base coating composition> The above resin composition 1 was mixed with the components shown below 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 (manufactured by 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 (Manufacturer) 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 (polyether adduct of an acetylenic diol compound).

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

[0171] The first base coating composition of each of the Examples and Comparative Examples was applied onto the obtained substrate using a Cartridge Bell (a rotary atomizing coater manufactured by ABB) so as to achieve 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 coater 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 clear paint "Macflow O-1820 Clear" (manufactured by Nippon Paint Co., Ltd., epoxy curing acrylic resin paint) was applied wet-on-wet using a rotary atomizing electrostatic coater so that the dry film thickness was 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 has been observed. △: Pigments have settled slightly and the supernatant is cloudy. ×: Pigments have settled and the supernatant liquid is transparent

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

[0175] (Saggy) The first base coating composition and the second base coating composition obtained were applied to a coated plate having an electrocoating film and an undercoat coating film (formed from Orga P-30) with a hole of 5 mm diameter drilled therein using a cartridge bell (a rotary atomizing coater manufactured by ABB Corporation) to the dry film thicknesses 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 sagging length at the bottom of 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 (×). In addition, (△) means that even when the same coating composition was used, there were cases where the sagging property was good and cases where the sagging property was NG.

[0176] (Hiding ability of second base coating composition) The obtained second base coating composition was applied to a black and white hiding test paper using a Cartridge Bell (ABB, rotary atomizing coating machine) to the dry film thickness shown in the table below. After preheating at 80°C for 3 minutes, heat curing was performed at 140°C for 30 minutes. The hiding power of the obtained sample was evaluated visually. Those that were completely concealed were marked with (O), and those where the base was visible were marked with (X). In addition, the symbol (◎) for the hiding power means that even higher hiding power is exhibited. Moreover, the hiding power of (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 was formed on the substrate (formed from Orga P-30), and the intermediate coating film of the obtained coated plate was water-sanded with #800 water-sanding sandpaper until the gloss of 60 degrees was 50%. Next, based on the same procedure as in the above-mentioned coating film manufacturing example, a first base coating film, a second base coating film, and a clear coating film were formed to form a composite coating film. Then, the transfer of the grinding marks was visually confirmed. The evaluation criteria are as follows: ○: No grinding marks △: Slight grinding marks were observed ×: Grinding marks were observed over the entire surface.

[0178] (Metallic feel) An electrodeposition coating film and an undercoat coating film were formed on the substrate. A multi-layer coating film having a first base coating film, a second base coating film and a clear coating film was further formed on the electrodeposition coating film. The obtained multi-layer coating film was i " (BYK-Gardner) was used to measure the FI value (flip-flop property) and G value (graininess) 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 is less than 15 or G value is 4.0 or more

[0179] (Water-resistant adhesion) An electrodeposition coating film and an intermediate coating film were formed on the substrate. A multi-layer coating film having a first base coating film, a second base coating film, and a clear coating film was further formed on the electrodeposition coating film. The obtained test piece was immersed in water at 40°C for 240 hours, after which the appearance of the coating film was visually observed and an adhesion test described later 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 the substrate. A multi-layer coating film having a first base coating film, a second base coating film, and a clear coating film was further formed on the electrodeposition coating film. The obtained test piece was immersed in water at 80°C for 120 hours, after which the appearance of the coating film was visually observed and an adhesion test described later was carried out. The evaluation criteria were as follows.

[0181] (Adhesion test) The coating of the test piece is cut with a cutter into 10 vertical and horizontal lines at 1 mm intervals, and then coated with cellophane tape. (登録商標) (manufactured by Nichiban Co., Ltd.) was applied to the surface, which was then peeled off, and the number of peeled squares out of 100 squares was counted (also called the cross-cut test). This test was used to confirm whether the coating had peeled off or not. 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%, which means that 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. A multi-layer coating film was then formed on the electrodeposition coating film, which had a first base coating film, a second base coating film, and a clear coating film formed from the base coating composition of each Example and Comparative Example. The obtained test plate was subjected to a stone chipping test under the following conditions using a Grarove tester KSS-1 (manufactured by Suga Test Instruments Co., Ltd.) (assuming an automobile hood). <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 ×: 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 having 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 paint 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 base transferability in terms of painting 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 having excellent design properties, particularly an excellent metallic feel, and 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, and the environmental burden can be reduced.

[0188] On the other hand, in Comparative Example 1, since the second inorganic viscosity agent according to the present disclosure is not included, the second coating composition has poor sedimentation properties and poor dispersion stability. Moreover, the water resistance (40°C) and high-temperature water resistance (80°C) of the obtained coating film were both insufficient. In Comparative Example 2, since the second hydrophobic association type viscous agent according to the present disclosure is not included, the sedimentation property of the second coating composition is poor and the dispersion stability is 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 gloss agent was not contained, the G value did not satisfy the standard value, and the multilayer coating film had a poor metallic feel. [Industrial Applicability]

[0189] The aqueous coating composition set for forming a multi-layer coating film according to the present disclosure improves the orientation of the glittering pigment. Therefore, it is possible to suppress diffuse reflection of light and form an excellent metallic coating film having sufficient highlight brightness. Furthermore, the aqueous coating composition set for forming a multi-layer coating film according to the present disclosure can form a coating film having excellent physical properties such as good chipping resistance and excellent base transferability as 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 method for forming a multi-layer coating film using an aqueous paint 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 method for forming the multi-layer coating film comprises the steps of: A step of applying the first base coating composition onto a substrate to form an uncured first base coating film; A step of applying the 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 on the uncured second base coating film to form an uncured clear coating film; and The uncured first base coating film, the uncured second base coating film, and the uncured clear coating film are simultaneously baked and cured 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, The first base coating composition comprises a first film-forming resin, a first curing agent, a first inorganic gloss agent, and a first hydrophobic association type viscous 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 includes 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 viscous agent includes 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 method for forming a multi-layer coating film, wherein the non-volatile content NV1 and the non-volatile content NV2 satisfy the relationship NV1>NV2.

2. The method for forming a multi-layer coating film according to claim 1, wherein 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 have a relationship of (t1) ≧ (t2).

3. A method for forming a multi-layer coating film as described in claim 1 or 2, wherein the second luster material includes a surface-treated luster material.

4. A method for forming a multi-layer coating film described in any one of claims 1 to 3, wherein the second luster material has a scale-like shape and includes a luster material having an aspect ratio of 5 to 2000.

5. The second base coating composition contains the second inorganic viscous agent in an amount of 1 part by mass or more and 7 parts by mass or less per 100 parts by mass of a total resin solid content of the second coating film-forming resin and the second curing agent, The method for forming a multilayer coating film according to any one of claims 1 to 4, 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.

6. 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 solid content 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 solid content of the second coating film-forming resin and the second curing agent, 6. The method for forming a multilayer coating film according to claim 1, wherein the ratio of Am1 to Am2, (Am1) / (Am2), is 2.0 or more.

7. A method for forming a multilayer coating film described in any one of claims 1 to 6, wherein the first base paint composition further contains at least one of a first lustrous material and a first inorganic viscous agent.

8. A method for forming a multilayer coating film described in any one of claims 1 to 7, wherein the second coating film forming resin includes at least one selected from an acrylic-based resin, a urethane-based resin, and a polyester-based resin.

9. A method for forming a multilayer coating film described in any one of claims 1 to 8, wherein the second inorganic viscous agent includes a silicate layered compound.

10. A method for forming a multi-layer coating film described in any one of claims 1 to 9, 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.

11. The first base coating composition further comprises a first dispersant, 11. The method for forming a 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.

12. A method for forming a multi-layer coating film described in any one of claims 1 to 11, wherein the first inorganic gloss agent includes an inorganic gloss agent having a positively charged surface.

13. A method for forming a multi-layer coating film as described in claim 6, wherein the second inorganic gloss agent includes an inorganic gloss agent having a positively charged surface.

14. A method for forming a multi-layer coating film as described in claim 7, wherein the thickness of the first inorganic viscous agent is 100 nm or less.

15. A method for forming a multilayer coating film described in any one of claims 1 to 14, wherein the thickness of the second inorganic viscous agent is 100 nm or less.

Images