Method for forming multilayer coating film

Abstract

To provide a method for forming a multilayer coating film, which can suppress the occurrence of dripping through dispense painting of high coating efficiency.SOLUTION: This method for forming the multilayer coating film comprises: applying a thermosetting intermediate paint composition (A) on an object to be coated; applying a thermosetting colored first clear paint composition (C1) by using a dispenser after the application of the intermediate paint composition (A); heat-hardening the intermediate paint composition (A) to acquire an intermediate coating film; heat-hardening the first clear paint composition (C1) to acquire a colored first clear coating film. The first clear paint composition (C1) is solvent-based, and low shear viscosity measured at a temperature 23°C under a condition of a shearing speed of 0.1-1 sec., is 1 Pa s-40 Pa s.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for forming a multilayer coating film.

Background Art

[0002] Conventionally, automobile bodies and parts have been spray-painted. In spray painting, the paint is atomized and flows with air to adhere to the object to be painted. Therefore, the coating efficiency of spray painting is low, generally said to be from 50% to 70%.

[0003] In view of recent environmental problems, efforts have been made to improve the coating efficiency. For example, Patent Documents 1 and 2 disclose devices capable of applying droplet-shaped paint to automobile parts.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When applying droplet-shaped paint, dripping is likely to occur. An object of the present invention is to provide a method for forming a multilayer coating film capable of suppressing the occurrence of dripping by using dispense coating.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides the following aspects. [1] Coating a thermosetting intermediate coating paint composition (A) on the object to be painted, and After applying the intermediate coating composition (A), a thermosetting and colored first clear coating composition (C1) is applied using a dispenser. The intermediate coating composition (A) is heat-cured to obtain an intermediate coating film. The first clear coating composition (C1) is heat-cured to obtain a colored first clear coating film, and it includes: The first clear coating composition (C1) is a solvent-based composition, and the low-shear viscosity LSV measured under the conditions of a temperature of 23 °C and a shear rate of 0.1 sec-1 is 1 Pa·s or more and 40 Pa·s or less. A method for forming a multilayer coating film. [2] The first clear coating composition (C1) is applied before heat-curing the intermediate coating composition (A). The heat-curing of the intermediate coating composition (A) and the first clear coating composition (C1) is carried out at once. The method for forming a multilayer coating film according to [1] above. [3] After the intermediate coating composition (A) is heat-cured to obtain an intermediate coating film, The coating of the first clear coating composition (C1) is carried out. The method for forming a multilayer coating film according to [1] above. [4] After applying the intermediate coating composition (A), before applying the first clear coating composition (C1), a base coating composition (B) is applied. The base coating composition (B) is heat-cured to obtain a base coating film, and it further includes: The method for forming a multilayer coating film according to [1] above. [5] After applying the intermediate coating composition (A), before applying the first clear coating composition (C1), a base coating composition (B) is applied. After applying the base coating composition (B), before applying the first clear coating composition (C1), a second clear coating composition (C2) is applied. The second clear coating composition (C2) is heat-cured to obtain a second clear coating film, and it further includes: The method for forming a multilayer coating film according to [1] above. [6] After applying the first clear coating composition (C1), apply the second clear coating composition (C2). The method for forming a multilayer coating film according to [1] above, further comprising heating and curing the second clear coating composition (C2) to obtain a second clear coating film. [7] The high-shear viscosity HSV measured under the conditions of a temperature of 23°C and a shear rate of 1000 sec -1 for the first clear coating composition (C1) is 0.009 Pa·s or more and 0.40 Pa·s or less. The method for forming a multilayer coating film according to [1] above. [8] The solid content concentration of the first clear coating composition (C1) is 20% by mass or more and 60% by mass or less. The method for forming a multilayer coating film according to [1] above. [9] The rate of decrease in the solid content concentration after 60 seconds from the application of the first clear coating composition (C1) is 10% by mass or less with respect to the solid content concentration of the first clear coating composition (C1). The method for forming a multilayer coating film according to [1] above.

[10] The diameter of the nozzle of the dispenser is 50 μm or more and 400 μm or less. The method for forming a multilayer coating film according to [1] above.

[11] The first clear coating composition (C1) contains at least one selected from the group consisting of a coloring pigment, a pearlescent pigment, and a dye. The method for forming a multilayer coating film according to [1] above.

[12] The first clear coating composition (C1) contains at least one selected from the group consisting of a polyamide-based binder, a cellulose-based binder, a polyolefin-based binder, a polyurea-based binder, and an organic resin fine particle binder. The method for forming a multilayer coating film according to [1] above. [Advantages of the Invention]

[0007] According to the present invention, there is provided a method for forming a multilayer coating film capable of suppressing the occurrence of sagging by using a dispenser with high coating efficiency. [Brief Description of the Drawings]

[0008]

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Mode for Carrying Out the Invention

[0009] Painting using a dispenser (hereinafter referred to as dispense painting) is a method of quantitatively discharging a liquid paint composition from a nozzle toward an object to be painted. In dispense painting, the paint composition is not atomized but is discharged as a liquid such as droplets or a liquid column. Therefore, the coating efficiency is high, and dust can be reduced compared to conventional spray painting.

[0010] In spray painting, when the paint composition becomes atomized, the solvent contained therein volatilizes, increasing the solid content concentration and the viscosity of the paint composition after discharge. Therefore, sagging is less likely to occur. On the other hand, in dispense painting, since the paint composition is discharged as a liquid, sagging is likely to occur. If the paint composition is prone to sagging, it is necessary to perform painting in multiple passes, which reduces the painting workability and causes unevenness in the film thickness, deteriorating the appearance.

[0011] In dispense painting, in order for the paint composition to be discharged from the nozzle, it is required to have a low viscosity before discharge, while in order to prevent sagging, it is required to have a high viscosity after discharge. However, in dispense painting, since the paint composition is discharged as a liquid, the solid content concentration of the paint composition hardly changes before and after discharge. That is, when the paint composition is adjusted to a solid content concentration suitable for discharge, the viscosity is low, so sagging is likely to occur.

[0012] Paints are generally non-Newtonian fluids. Non-Newtonian fluids such as paints (especially thixotropic fluids) change their viscosity depending on the shear rate applied during discharge. In the case of dispense painting where the change in the solid content concentration of the paint composition before and after discharge is small, it has been found that controlling the shear viscosity of the paint composition before discharge is important. And as the shear viscosity corresponding to the shear viscosity, by setting the low shear viscosity LSV measured under the conditions of a temperature of 23°C and a shear rate of 0.1 sec -1 to be 1 Pa·s or more and 40 Pa·s or less, it has been found that it is possible to achieve both a discharge property suitable for dispense painting and suppression of the occurrence of sagging.

[0013] In dispensing coating, usually, the paint composition is discharged from the nozzle at a shear rate higher than 0.1 sec -1 Therefore, even if the low shear viscosity LSV is increased as described above, it is difficult to affect the dischargeability.

[0014] Hereinafter, a multi-layer coating film, which is one aspect of the present disclosure, will be described in detail with reference to the illustrated embodiments. Note that the drawings include some schematic ones and may not reflect actual dimensions and ratios. The present disclosure is not limited to these embodiments.

[0015] [First Embodiment] The method for forming the multi-layer coating film of the present embodiment includes coating a thermosetting intermediate paint composition (A) on an object to be coated, and after coating the intermediate paint composition (A), coating a thermosetting and colored first clear paint composition (C1) using a dispenser, heating and curing the intermediate paint composition (A) to obtain an intermediate coating film, and heating and curing the first clear paint composition (C1) to obtain a colored first clear coating film. The first clear paint composition (C1) is coated before the intermediate paint composition (A) is heated and cured, and the heating and curing of the intermediate paint composition (A) and the first clear paint composition (C1) are performed at once (in the same step).

[0016] FIG. 1 is a flowchart showing an example of the method for forming a multi-layer coating film according to the first embodiment. First, a thermosetting and solvent-based intermediate paint composition (A) is coated on an object to be coated (S11), and pre-drying is performed (S12). Subsequently, a thermosetting and colored first clear paint composition (C1) is coated by a dispenser (S13). Thereafter, heating for curing (referred to as "heat curing" hereinafter; also referred to as "baking") is performed (S14). By one baking treatment, both the intermediate paint composition (A) (i.e., the uncured intermediate coating film) and the first clear paint composition (C1) are cured.

[0017] By the method of the first embodiment, a multilayer coating film is formed, which includes an intermediate coating film disposed on an object to be coated and a colored first clear coating film (hereinafter also referred to as "colored clear coating film") disposed on the intermediate coating film. FIG. 2 is a schematic cross-sectional view showing the multilayer coating film 10 in the first embodiment. The multilayer coating film 10 includes an intermediate coating film 12 disposed on an object to be coated 11 and a colored clear coating film 13 disposed on the intermediate coating film 12.

[0018] First, the paint compositions used in each step will be described.

[0019] Hereinafter, the weight average molecular weight Mw and the number average molecular weight Mn are measured by the polystyrene standard by the GPC (gel permeation chromatography) method.

[0020] The hydroxyl value and the acid value are determined based on the solid content mass. The hydroxyl value and the acid value can be measured by known methods described in JIS K 0070:1992. The hydroxyl value and the acid value may be calculated from the blending amount of the unsaturated monomer in the raw material monomers of the target resin.

[0021] The epoxy equivalent can be measured by known methods described in JIS K 7236:2001.

[0022] The solid content of the paint composition is all components obtained by removing volatile components (typically solvents) from the paint composition. The solid content concentration of the paint composition can be calculated from the residue when the paint composition is heated at 140 °C according to the JIS K 5601-1-2 heating residue measurement method.

[0023] The thickness of the coating film can be measured by an electromagnetic film thickness gauge (for example, SDM-miniR manufactured by SANKO). The thickness of the coating film is the average value of the thicknesses of the coating film at any five points.

[0024] (First Clear Paint Composition (C1)) The first clear paint composition (C1) is a solvent-based system. The solvent-based paint composition contains an organic solvent as a solvent.

[0025] The first clear paint composition (C1) may be a one-component paint or a multi-component paint such as a two-component paint containing a main agent and a curing agent. The main agent and the curing agent constituting the two-component paint may be supplied to the nozzle after being mixed, or may be supplied to the same nozzle and mixed while being discharged.

[0026] The low-shear viscosity LSV of the first clear paint composition (C1) is 1 Pa·s or more and 40 Pa·s or less. Thereby, the sagging of the first clear paint composition (C1) after discharge (after being applied to the object to be painted) is suppressed.

[0027] The low-shear viscosity LSV of the first clear paint composition (C1) may be 3 Pa·s or more, and may be 6 Pa·s or more. The low-shear viscosity LSV of the first clear paint composition (C1) may be 30 Pa·s or less, and may be 10 Pa·s or less.

[0028] The low-shear viscosity LSV of the first clear paint composition (C1) can also affect the leveling property along with the sagging suppression effect (hereinafter sometimes referred to as "sagging property"). When the low-shear viscosity LSV is within the above range, the leveling property of the first clear paint composition (C1) is likely to be exhibited.

[0029] The high-shear viscosity HSV of the first clear paint composition (C1) measured under the conditions of a temperature of 23°C and a shear rate of 1000 sec -1 may be 0.005 Pa·s or more and 0.40 Pa·s or less. The shear rate of 1000 sec -1 is close to the shear rate applied during discharge. By setting the high-shear viscosity HSV within the above range, the dischargeability is improved, and it becomes easier to apply evenly without unevenness. The shear rate of 1000 sec -1 is also a speed at which a stable measured value can be obtained, so it is suitable as a condition for evaluating the dischargeability.

[0030] The high-shear viscosity HSV of the first clear coating composition (C1) may be 0.008 Pa·s or more, may be 0.05 Pa·s or more, and may be 0.08 Pa·s or more. The high-shear viscosity HSV of the first clear coating composition (C1) may be 0.40 Pa·s or less, may be 0.20 or less, and may be 0.17 Pa·s or less.

[0031] In terms of being easily compatible with sag prevention and dischargeability, the low-shear viscosity LSV and the high-shear viscosity HSV may satisfy the following relationship. (a) When 0.005 Pa·s ≤ HSV < 0.11 Pa·s, 1.0 Pa·s ≤ LSV ≤ 32.0 Pa·s (b) When 0.11 Pa·s < HSV ≤ 0.5 Pa·s, 4.0 Pa·s < LSV ≤ 40 Pa·s Among them, when 0.005 Pa·s ≤ HSV < 0.11 Pa·s, (c) 1.0 Pa·s ≤ LSV ≤ 4.0 Pa·s (in particular, 1.0 Pa·s ≤ LSV < 3.0 Pa·s) may be satisfied.

[0032] In terms of being easily compatible with sag prevention and dischargeability, the index (LSV / HSV) obtained by dividing the low-shear viscosity LSV by the high-shear viscosity HSV may be 5 or more and 1200 or less. LSV / HSV may be 8 or more, and may be 10 or more. LSV / HSV may be 500 or less, may be 400 or less, and may be 350 or less.

[0033] The solid content concentration of the first clear coating composition (C1) may be 20% by mass or more and 60% by mass or less. When the solid content concentration of the first clear coating composition (C1) is 20% by mass or more, a colored clear coating film with sufficient thickness can be formed even with a small coating amount, so the coating workability is improved. In addition, the low-shear viscosity LSV is easily adjusted within the above range. When the solid content concentration of the first clear coating composition (C1) is 60% by mass or less, the high-shear viscosity HSV is easily adjusted within the above range. The solid content concentration of the first clear coating composition (C1) may be 30% by mass or more, and may be 40% by mass or more. The solid content concentration of the first clear coating composition (C1) may be 57% by mass or less, and may be 50% by mass or less.

[0034] The change amount of the solid content concentration of the first clear coating composition (C1) before and after discharge is small. For example, the reduction rate of the solid content concentration 60 seconds after the first clear coating composition (C1) is coated (discharged) may be 10% by mass or less with respect to the solid content concentration before the discharge of the first clear coating composition (C1). Thus, even when the change in the solid content concentration before and after discharge is small, the sag of the first clear coating composition (C1) is suppressed. The above reduction rate of the solid content concentration of the first clear coating composition (C1) may be 7% by mass or less, and may be 4% by mass or less. The above reduction rate of the solid content concentration of the first clear coating composition (C1) may be 0.1% by mass or more.

[0035] The solid content concentration after 60 seconds have elapsed since the first clear paint composition (C1) is applied (hereinafter, may be referred to as "immediately after application" for convenience) can be calculated as follows. On an aluminum foil whose weight has been measured in advance, the first clear paint composition (C1) is applied with a dispenser (for example, MDS 3200 manufactured by Vermes, nozzle diameter 100 μm) so that the dry film thickness becomes 15 μm. 60 seconds after application, the above aluminum foil is folded, the mass is measured while preventing drying, and then it is heated at 140 °C. The mass of only the aluminum foil is subtracted from the samples before and after heating to calculate the mass W of the first clear paint composition (C1) before heating and the mass Wh of the heat residue. Finally, the solid content concentration immediately after application of the first clear paint composition (C1) is calculated from (formula) 100 × Wh / W (mass%).

[0036] The dischargeability can be evaluated, for example, by the degree of peeling of the colored clear coating film or the scattering of the first clear paint composition (C1). The peeling of the coating film refers to the uncoated part. In dispensing coating, the peeling appears in streaks. The peeling in dispensing coating is caused by the first clear paint composition (C1) not being applied to the desired position, indicating that the straightness of the first clear paint composition (C1) after discharge is low. The straightness of the discharged first clear paint composition (C1) is affected by the shear viscosity of the first clear paint composition (C1) during discharge (corresponding to the above high shear viscosity HSV). If the high shear viscosity HSV is excessively large, the straightness will decrease. Here, when the low shear viscosity LSV of the first clear paint composition (C1) is 1 Pa·s or more and 40 Pa·s or less, slight peeling can be eliminated by the leveling of the paint composition.

[0037] Spittability can also be evaluated by the degree of scattering of the first clear coating composition (C1). The scattering of the first clear coating composition (C1) occurs when the first clear coating composition (C1) scatters in all directions from the nozzle, indicating that it has been applied to a position other than the desired one. The scattering of the first clear coating composition (C1) in dispensing coating is also affected by the shear viscosity of the first clear coating composition (C1) during ejection (corresponding to the above high shear viscosity HSV). If the high shear viscosity HSV is excessively small, the first clear coating composition (C1) is likely to scatter.

[0038] Since the first clear coating composition (C1) is excellent in spittability with little occurrence of sagging and scattering, it can be easily applied to a desired position using a dispenser. Therefore, masking is not required.

[0039] The first clear coating composition (C1) contains, for example, a film-forming resin, an organic solvent, and at least one selected from the group consisting of a coloring pigment, a pearlescent pigment, and a dye. The first clear coating composition (C1) may further contain a thickener. The first clear coating composition (C1) may further contain a surface conditioner.

[0040] 《Film-Forming Resin》 The film-forming resin is a thermosetting resin. Examples of the film-forming resin include an acrylic resin, a polyester resin, a polyurethane resin, an alkyd resin, a fluororesin, a silicone resin, an epoxy resin, a polyether resin, and a polycarbonate resin. These can be used alone or in combination of two or more. The film-forming resin has a crosslinkable functional group. Examples of the crosslinkable functional group include a carboxy group, a hydroxy group, an epoxy group, a silanol group, and a (meth)acryloyl group.

[0041] The first clear coating composition (C1) contains, as a film-forming resin, for example, a half-ester acid group-containing acrylic resin (i), a carboxy group-containing polyester resin (ii), and an acrylic resin (iii) having a hydroxyl group and an epoxy group. The above three types of polymers react with each other to progress the curing reaction. The resin composition containing the above three types of polymers is called an acid-epoxy curing type resin composition.

[0042] · Half-ester acid group-containing acrylic resin (i) The acrylic resin (i) has an acid anhydride group half-esterified by a hydroxyl group. The acrylic resin (i) can be obtained, for example, by copolymerizing an ethylenically unsaturated monomer having an acid anhydride group and other ethylenically unsaturated monomers, and then half-esterifying the acid anhydride group with a low molecular weight alcohol-based compound.

[0043] Examples of the ethylenically unsaturated monomer having an acid anhydride group include maleic anhydride, itaconic anhydride, and citraconic anhydride. These can be used alone or in combination of two or more.

[0044] Examples of other ethylenically unsaturated monomers include C1-C alkyl esters of acrylic acid or methacrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; olefins such as ethylene and propylene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated amides such as acrylamide, methacrylamide, and N-methylacrylamide; and vinyl compounds such as vinyl acetate, vinyl chloride, 2-vinylpyridine, and 4-vinylpyridine. These can be used alone or in combination of two or more. 24 Examples of other ethylenically unsaturated monomers include C1-C alkyl esters of acrylic acid or methacrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; olefins such as ethylene and propylene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated amides such as acrylamide, methacrylamide, and N-methylacrylamide; and vinyl compounds such as vinyl acetate, vinyl chloride, 2-vinylpyridine, and 4-vinylpyridine. These can be used alone or in combination of two or more.

[0045] The acrylic resin (i) may have, for example, an acid value (AV) of 50 mgKOH / g or more and 200 mgKOH / g or less, and a number average molecular weight (Mn) of 1000 or more and 10000 or less.

[0046] · Carboxy group-containing polyester resin (ii) The polyester resin (ii) is obtained, for example, by an addition reaction of a polyester polyol having 3 or more hydroxyl groups and a compound having an acid anhydride group.

[0047] The polyester resin (ii) may have, for example, an AV of 50 mgKOH / g or more and 200 mgKOH / g or less, an OHV of 5 mgKOH / or more and 50 mgKOH / g or less, and an Mn of 400 or more and 3500 or less.

[0048] · Acrylic resin (iii) having a hydroxyl group and an epoxy group The acrylic resin (iii) is obtained, for example, by copolymerizing an epoxy group-containing ethylenically unsaturated monomer and a hydroxyl group-containing ethylenically unsaturated monomer. The acrylic resin (iii) may have an average of 2 or more epoxy groups.

[0049] Examples of the epoxy group-containing ethylenically unsaturated monomer include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, and allyl glycidyl ether. These may be used alone or in combination of two or more.

[0050] Examples of the hydroxyl group-containing ethylenically unsaturated monomer include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts thereof with ε-caprolactone. These may be used alone or in combination of two or more.

[0051] The acrylic resin (iii) may have, for example, an OHV of 5 mgKOH / g or more and 100 mgKOH / g or less, an Mn of 500 or more and 10,000 or less, and an epoxy equivalent of 200 g / eq or more and 700 g / eq or less.

[0052] 《Organic solvent》 Examples of the organic solvent include ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol -t- butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as swazol, shellzol, and mineral spirit; and aromatic solvents such as xylene, toluene, Solvesso - 100 (S - 100), and Solvesso - 150 (S - 150). These can be used alone or in combination of two or more.

[0053] The organic solvent is added, for example, so that the solid content concentration of the first clear coating composition (C1) is 20% by mass or more and 60% by mass or less.

[0054] 《Pigment and dye》 The first clear coating composition (C1) contains at least one selected from the group consisting of a coloring pigment, a bright pigment, and a dye. Thereby, the obtained clear coating film becomes colored. Colored means having a color, which may be achromatic or chromatic.

[0055] Examples of the coloring pigments include organic coloring pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, dioxazine pigments, anthraquinone pigments, isoindolinone pigments, and metal complex pigments; and inorganic coloring pigments such as lead yellow, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. These may be used alone or in combination of two or more.

[0056] Examples of the lustrous pigments include aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, metal-coated mica powder, titanium dioxide-coated mica powder, and titanium dioxide-coated glass powder. These may be used alone or in combination of two or more. The lustrous pigments may be colored.

[0057] Examples of the dyes include 1:2 chromium complex black, 1:2 chromium complex yellow, and 1:2 cobalt complex yellow. These may be used alone or in combination of two or more.

[0058] Among them, the first clear coating composition (C1) may contain a black pigment (typically carbon black).

[0059] Examples of the carbon black include general furnace black and acetylene black. Specific examples include ColorBlack Fw200, ColorBlack Fw200P, ColorBlack Fw285 manufactured by Degussa; Raven5750, Raven5250, Raven5000, Raven3500 manufactured by Columbian; and Emperor 2000, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 manufactured by Cabot. These may be used alone or in combination of two or more.

[0060] The first clear paint composition (C1) may also contain an extender pigment or a matting pigment. Examples of the extender pigment include calcium carbonate, barium sulfate, clay, and talc. Examples of the matting pigment include silica. These may be used alone or in combination of two or more.

[0061] The total PWC of all pigments and dyes T may be 0.01% by mass or more and 60% by mass or less. From the viewpoint of hiding power, the PWC T may be 1.7% by mass or more and may be 14.0% by mass or more. The PWC T may be 60% by mass or less, may be 40% by mass or less, and may be 20% by mass or less.

[0062] The total PWC of coloring pigments, bright pigments, and dyes C may be 0.01% by mass or more and 50% by mass or less. From the viewpoint of hiding power, the PWC C may be 1.7% by mass or more and may be 4.0% by mass or more. The PWC C may be 50% by mass or less, may be 30% by mass or less, and may be 20% by mass or less.

[0063] PWC is the mass ratio of the total of the target pigments and dyes to the solid content mass of the paint composition.

[0064] From the viewpoint of suppressing nozzle clogging, the average particle diameter of the pigment may be less than 1 / 4 of the diameter of the nozzle. The average particle diameter of the pigment may be, for example, 50 μm or less and may be 25 μm or less. Prior to dispensing coating, the first clear paint composition (C1) may be filtered through a filter to remove particles having an average particle diameter of 1 / 4 or more of the diameter of the nozzle.

[0065] The average particle diameter of the pigment is the 50% average particle diameter (D50) in the volume-based particle size distribution measured using a particle size distribution measuring device of the laser diffraction / scattering method. The average particle diameter of the pigment may be measured using image processing software from an image of an electron microscope of the coating film. For example, from the above image, 10 pigments are arbitrarily selected, and the diameter of a circle (equivalent circle) having the same area as the area of these is regarded as the diameter of the pigment. The diameters of 10 pigments are calculated, and the average value thereof can be taken as the average particle diameter of the pigment.

[0066] When the particle diameter of the pigment is large, generally the hiding power of the coating film is improved. As described above, it is advisable to avoid using large pigments in the dispensing coating, but in the present disclosure, as long as the low-shear viscosity is within a predetermined range, the PWC of the pigment and the dye can be increased. Thereby, the hiding power of the colored clear coating film can be improved. For example, the black-and-white hiding film thickness of the colored clear coating film can be 30 μm or less, and can be 15 μm or less.

[0067] The smaller the black-and-white hiding film thickness, the better the hiding power. In other words, when the hiding power is high, the film thickness can be made thinner. Therefore, when using the first clear coating composition (C1) that can obtain a coating film with high hiding power, it can be coated under conditions where sagging is less likely to occur.

[0068] The black-and-white hiding film thickness is measured using a hiding power test paper conforming to JIS K 5600-4-1(b). A colored clear coating film is dispensed and coated on the 2×2 cm square black-and-white checkered pattern of the hiding power measurement paper so as to form a gradient of the dry film thickness, and then heat-cured. Next, visually, the coating film part where the black-and-white checkered pattern cannot be seen through is determined, and the film thickness of that part is measured. This measured film thickness is the black-and-white hiding film thickness.

[0069] 《Binder》 The first clear coating composition (C1) may contain a binder. By the binder, the low-shear viscosity of the first clear coating composition (C1) can be easily adjusted to the above range.

[0070] Examples of the adhesive include silica fine powder, mineral adhesives, polyamide adhesives, cellulose adhesives, polyolefin adhesives, polyurea adhesives, barium sulfate atomized powder, and organic resin fine particle adhesives. These can be used alone or in combination of two or more.

[0071] Among them, the adhesive may be at least one selected from the group consisting of polyamide adhesives, cellulose adhesives, polyolefin adhesives, polyurea adhesives, and organic resin fine particle adhesives. According to these adhesives, white blooming in the obtained colored clear coating film is likely to be suppressed. White blooming can occur due to the difference in optical properties between the pigment and the adhesive, which reduces the design quality.

[0072] The silica fine powder is a powder containing SiO2. Examples of the silica fine powder include clay, diatomaceous earth, white carbon, and colloidal silica. Among them, it may be colloidal silica.

[0073] Examples of the mineral adhesive include swelling layered silicates having a 2:1 type crystal structure. Specifically, smectite group clay minerals such as natural or synthetic montmorillonite, saponite, hectorite, stibnite, beidellite, nontronite, bentonite, laponite; swelling mica group clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na salt-type fluorotennantite, Li-type fluorotennantite; vermiculite; and their substituents and derivatives. Among them, it may be bentonite.

[0074] Examples of the polyamide adhesive include fatty acid amide, polyamide, acrylamide, long-chain polyaminoamide, aminoamide, and their salts (such as phosphate).

[0075] Examples of the cellulose-based adhesives include cellulose acetate butyrate (CAB), carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and cellulose nanofiber gel. These may be used alone or in combination of two or more. Among them, CAB may be used.

[0076] Examples of the polyolefin-based adhesives include polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-maleic anhydride copolymer, and propylene-maleic anhydride copolymer.

[0077] The polyurea-based adhesive is a reaction product of an isocyanate and an amine and has a plurality of urea bonds in one molecule.

[0078] The organic resin fine particle adhesive is an organic resin particle having a three-dimensional crosslinked structure inside. The organic resin fine particle adhesive swells in an organic solvent, and the swelling amount is controlled by the three-dimensional crosslinked structure.

[0079] The solid content of the adhesive is, for example, 0.1% by mass or more and 40% by mass or less with respect to the solid mass of the first clear coating composition (C1). When the content of the adhesive is within this range, it becomes easy to adjust the low-shear viscosity to a desired range.

[0080] <<Surface conditioner>> The first clear coating composition (C1) may contain a surface conditioner. The surface conditioner is added to control the surface tension of the first clear coating composition (C1). By the surface conditioner, the wettability of the first clear coating composition (C1) to the lower layer is improved. By the surface conditioner, the recoatability of the multilayer coating film can also be improved.

[0081] Examples of the surface conditioner include silicone-based, acrylic-based, vinyl-based, and fluorine-based surface conditioners. These may be used alone or in combination of two or more. Among them, at least one of silicone-based and acrylic-based surface conditioners is preferred. Examples of the silicone-based surface conditioner include polydimethylsiloxane and modified silicones obtained by modifying the same. Examples of the modified silicones include polyether-modified products, acrylic-modified products, and polyester-modified products. Examples of the acrylic-based surface conditioner include acrylic copolymers.

[0082] The solid content of the surface conditioner is, for example, 0.01% by mass or more and 10% by mass or less of the solid mass of the first clear coating composition (C1). The above content of the surface conditioner may be 0.02% by mass or more, and may be 0.04% by mass or more. The above content of the surface conditioner may be 8% by mass or less, and may be 6% by mass or less.

[0083] 《Others》 The first clear coating composition (C1) may contain various additives as required. Examples of the additives include ultraviolet absorbers, antioxidants, defoamers, dispersants, pinhole preventives, pigment derivatives, silane coupling agents, and interface control materials.

[0084] For example, the dispersant is added to enhance the dispersibility of the pigment. The dispersant is not particularly limited and is appropriately selected according to the types of the solvent and the pigment, etc. Examples of the dispersant include compounds having an acid or a base such as acrylic-based, polyester-based, and polyurethane-based compounds. These may be used alone or in combination of two or more. Among them, the dispersant may be a copolymer-based compound. The solid content of the dispersant is, for example, 0.01% by mass or more and 8% by mass or less of the solid mass of the first clear coating composition (C1). The above content of the dispersant may be 0.1% by mass or more. The above content of the dispersant may be 4.5% by mass or less.

[0085] (Intermediate coating composition (A)) The intermediate coat paint composition (A) is solvent-based. As the intermediate coat paint composition (A), a conventionally known intermediate coat paint composition can be used. The intermediate coat paint composition (A) contains, for example, a film-forming resin, a curing agent, a pigment or a dye, and an organic solvent as a solvent.

[0086] 《Film-forming resin》 Examples of the film-forming resin include an acrylic resin, a polyester resin, a polyurethane resin, an alkyd resin, a fluororesin, an epoxy resin, a polyether resin, and a polycarbonate resin. These can be used alone or in combination of two or more. The film-forming resin has a crosslinkable functional group. Examples of the crosslinkable functional group include a carboxy group, a hydroxyl group, an epoxy group, a silanol group, and a (meth)acryloyl group.

[0087] 《Curing agent》 Examples of the curing agent include a melamine resin, a blocked isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, an oxazoline compound, and metal ions. These can be used alone or in combination of two or more.

[0088] 《Pigment and dye》 Examples of the pigment and dye are the same as those exemplified in the first clear coat paint composition (C1).

[0089] 《Organic solvent》 Examples of the organic solvent are the same as those exemplified in the first clear coat paint composition (C1).

[0090] 《Others》 The intermediate coat paint composition (A) may contain various additives as necessary. Examples of the additives are the same as those exemplified in the first clear coat paint composition (C1).

[0091] Next, each step will be described.

[0092] ·Painting of the intermediate coat paint composition (A) The intermediate coating composition is applied to the object to be coated 11. The coating method may be other than dispensing coating. Examples of the coating method include air spray coating, airless spray coating, and rotary atomization coating. These methods may be combined with electrostatic coating. Among them, from the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferable. For rotary atomization electrostatic coating, for example, rotary atomization type electrostatic coating machines generally called "micro micro bell (μμ bell)", "micro bell (μ bell)", "metallic bell (meta bell)" and the like are used.

[0093] The intermediate coating composition (A) is applied so that the thickness (dry film thickness) of the intermediate coating film 12 after curing is 5 μm or more and 40 μm or less, for example.

[0094] (Object to be coated) Examples of the material of the object to be coated 11 include metal, resin, and glass. Specifically, examples of the object to be coated 11 include automobile bodies such as passenger cars, trucks, motorcycles, and buses, and parts for automobile bodies, and automobile parts such as spoilers, bumpers, mirror covers, grills, and door knobs.

[0095] Examples of the metal include iron, copper, aluminum, tin, zinc, or alloys thereof (for example, steel). Representative examples of the metal object to be coated 11 include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-based galvanized steel sheets, zinc-iron alloy-based galvanized steel sheets, zinc-magnesium alloy-based galvanized steel sheets, zinc-aluminum-magnesium alloy-based galvanized steel sheets, aluminum-based galvanized steel sheets, aluminum-silicon alloy-based galvanized steel sheets, tin-based galvanized steel sheets, and the like.

[0096] The metal object to be coated 11 may be surface-treated. Examples of the surface treatment include phosphate treatment, chromate treatment, zirconium chemical conversion treatment, and composite oxide treatment. After the surface treatment, the metal object to be coated 11 may be further coated with an electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0097] Examples of the resin include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The resin-coated object 11 may be degreased.

[0098] ·Pre-drying of the intermediate coating composition (A) After the intermediate coating composition (A) is applied, pre-drying is performed before the application of the colored first clear coating composition. In the pre-drying, at least a part of the solvent is removed. Examples of the pre-drying method include natural drying (hereinafter also referred to as "WET treatment") and heat drying (hereinafter also referred to as "PH treatment"). In natural drying, for example, the object 11 coated with the intermediate coating composition is left to stand under temperature conditions of 20°C or higher and 25°C or lower for 5 minutes or more and 15 minutes or less. Heat drying is performed under conditions where the curing reaction by the film-forming components does not proceed or at least the curing reaction is not completed. In heat drying, for example, the object 11 coated with the intermediate coating composition is heated at a temperature condition of 50°C or higher and 100°C or lower for 30 seconds or more and 30 minutes or less.

[0099] ·Coating of the first clear coating composition (C1) The first clear coating composition (C1) is further applied. The first clear coating composition (C1) is applied using a dispenser. Thereby, the coating efficiency is improved, and the desired portion can be coated without the need for masking. According to the first clear coating composition (C1) used in the present disclosure, even when dispensing coating is performed, the occurrence of sagging is suppressed.

[0100] The first clear coating composition (C1) is applied so that, for example, the thickness of the colored clear coating film after curing is 5 μm or more and 70 μm or less. The thickness of the colored clear coating film after curing may be 10 μm or more and may be 15 μm or more. According to the present disclosure, even when a large amount of the clear coating composition is applied at once, sagging is suppressed.

[0101] In dispensing coating, the first clear paint composition (C1) is discharged in a liquid state in a fixed amount from the nozzle holes toward the object to be coated 11. The first clear paint composition (C1) may be discharged in the form of droplets or in the form of a liquid column. The methods of discharging in the form of droplets and in the form of a liquid column are called so-called dust-free coating (Oversray-free Coating). In dispensing coating, for example, the paint composition is discharged from a plurality of micropores formed at a predetermined pitch in the nozzle head and is applied to the object to be coated while remaining in the form of droplets or a liquid column. Thereby, a paint film having a predetermined width is formed on the object to be coated 11. The method of discharging in the form of droplets is similar to inkjet coating. The method of discharging in the form of a liquid column is described, for example, in Japanese Patent Application Laid-Open No. 2015-196140.

[0102] The object to be coated 11 is placed, for example, on a mounting table (not shown). The object to be coated 11 may be moved together with the mounting table, the dispenser may be moved, or both the mounting table and the dispenser may be moved.

[0103] The discharge mechanism of the dispenser is not particularly limited, and examples thereof include a pneumatic type, a piezo type, a plunger type, a non-contact type, and a thermal valve type. The open / closed state of the discharge nozzle during coating may be periodic or may continue in a continuous state. Depending on the open / closed state of the discharge nozzle, the paint composition is discharged in the form of droplets or a liquid column. The number of nozzles is also not particularly limited and may be 1 or more, or may be 2 or more.

[0104] The diameter of the nozzle of the dispenser is, for example, 50 μm or more and 400 μm or less. When the diameter of the nozzle is 400 μm or less, excessive discharge is suppressed, so that the film thickness is easily controlled. When the diameter of the nozzle is 50 μm or more, nozzle clogging is easily suppressed.

[0105] · Heat curing Next, by heating, the intermediate coating composition (A) and the first clear coating composition (C1) are cured. Thereby, a multilayer coating film including an intermediate coating film 12 and a colored clear coating film 13 is obtained. According to the present embodiment, since a plurality of coating compositions can be cured by a single heating, the environmental load and the production cost are reduced.

[0106] The heating temperature is, for example, 110°C or higher and 180°C or lower. The heating temperature may be 120°C or higher. The heating temperature may be 160°C or lower. The heating time is appropriately set according to the heating temperature. When the heating temperature is 120°C or higher and 160°C or lower, the heating time may be 10 minutes or more and 60 minutes or less.

[0107] [Second Embodiment] This embodiment is different from the first embodiment in that after the first clear coating composition (C1) is applied, the second clear coating composition (C2) is applied, and then heat curing is performed. This difference will be described below. In this embodiment, since the other steps are the same as those in the first embodiment, the description thereof is omitted.

[0108] FIG. 3 is a flowchart showing an example of a method for forming a multilayer coating film according to the second embodiment. First, a thermosetting and solvent-based intermediate coating composition (A) is applied onto an object to be coated (S31), and pre-drying is performed (S32). Subsequently, a thermosetting and colored first clear coating composition (C1) is applied by a dispenser (S33). After pre-drying is performed again (S34), a thermosetting and solvent-based second clear coating composition (C2) is applied (S35). Finally, heat curing is performed to cure the intermediate coating composition (A), the first clear coating composition (C1), and the second clear coating composition (C2) at once (S36).

[0109] By the method of the second embodiment, a multilayer coating film is formed which includes a primer coating film disposed on an object to be coated, a colored clear coating film disposed on the primer coating film, and a second clear coating film disposed on the colored clear coating film. FIG. 4 is a schematic cross-sectional view showing the multilayer coating film 10A in the second embodiment. The multilayer coating film 10A includes a primer coating film 12 disposed on an object to be coated 11, a colored clear coating film 13 disposed on the primer coating film 12, and a second clear coating film 14 disposed on the colored clear coating film 13.

[0110] · Pre-drying of the first clear coating composition (C1) The pre-drying of the first clear coating composition (C1) may be carried out under the same conditions as the pre-drying of the primer coating composition (A), or may be carried out under different conditions.

[0111] · Coating of the second clear coating composition (C2) Examples of the coating method include the same method as the coating method of the primer coating composition (A). Among them, it may be rotary atomization electrostatic coating.

[0112] The second clear coating composition (C2) is coated so that, for example, the thickness of the second clear coating film 14 after curing is 1 μm or more and 50 μm or less. The second clear coating film 14 may be a single layer or a laminated coating film of two or more layers.

[0113] (The second clear coating composition (C2)) The second clear coating composition (C2) is solvent-based. As the second clear coating composition (C2), a conventionally known clear coating composition can be used. The second clear coating composition (C2) may include, for example, a film-forming resin, a curing agent, an organic solvent, and additives as necessary, similar to the primer coating composition (A). The second clear coating composition (C2) may or may not contain a coloring pigment, a pearlescent pigment, and a dye.

[0114] [Third Embodiment] This embodiment is different from the first embodiment in that heat curing is performed after the application of the intermediate coating composition (A), and an aqueous base coating composition (B) is applied after the application of the intermediate coating composition (A) and before the application of the first clear coating composition (C1), and then heat curing is performed. This difference will be explained below. In this embodiment, since the other steps are the same as those in the first embodiment, the description thereof will be omitted.

[0115] Figure 5 is a flowchart showing an example of a method for forming a multilayer coating film according to the third embodiment. First, a thermosetting and solvent-based intermediate coating composition (A) is applied onto an object to be coated (S41), and subsequently, heat curing is performed (S42). Thereafter, an aqueous base coating composition (B) is applied (S43), and pre-drying is carried out (S44). Subsequently, a thermosetting and colored first clear coating composition (C1) is applied by a dispenser (S45). Finally, heat curing is performed again (S46), and the aqueous base coating composition (B) and the first clear coating composition (C1) are cured at once.

[0116] By the method of the third embodiment, a multilayer coating film is formed which includes an intermediate coating film disposed on an object to be coated, a base coating film disposed on the intermediate coating film, and a colored clear coating film disposed on the base coating film. Figure 6 is a schematic cross-sectional view showing the multilayer coating film 10B in the third embodiment. The multilayer coating film 10B includes an intermediate coating film 12 disposed on an object to be coated 11, a base coating film 15 disposed on the intermediate coating film 12, and a colored clear coating film 13 disposed on the base coating film 15.

[0117] · Heat curing of the intermediate coating composition (A) The heat curing of the intermediate coating composition (A) may be carried out under the same conditions as the heat curing of the first clear coating composition (C1), or may be carried out under different conditions.

[0118] · Application of the aqueous base coating composition (B) As the coating method, the same method as the coating method of the intermediate coating composition (A) may be mentioned. Among them, it may be rotary atomization electrostatic coating.

[0119] The water-based base paint composition (B) is applied, for example, so that the thickness of the base paint film after curing is 2 μm or more and 30 μm or less. The base paint film may be a single layer or a laminated paint film of two or more layers.

[0120] (Water-based base paint composition (B)) As the water-based base paint composition (B), a conventionally known base coat paint composition can be used. The water-based base paint composition (B) may contain, for example, a film-forming resin, a curing agent, a pigment or a dye, a solvent containing water, and, if necessary, an additive, similar to the intermediate coat paint composition (A). In an aqueous paint, the film-forming resin can be contained as an emulsion, as a dispersion, or in a state dissolved in a solvent.

[0121] [Fourth Embodiment] This embodiment is different from the third embodiment in that the second clear paint composition (C2) is applied after the application of the water-based base paint composition (B) and before the application of the first clear paint composition (C1). This difference will be described below. In this embodiment, since the other steps are the same as those in the third embodiment, the description thereof is omitted.

[0122] FIG. 7 is a flowchart showing an example of a method for forming a multilayer paint film according to the fourth embodiment. First, a thermosetting and solvent-based intermediate coat paint composition (A) is applied onto an object to be painted (S51), and heat curing is performed (S52). Thereafter, the water-based base paint composition (B) is applied (S53), and pre-drying is carried out (S54). Subsequently, the second clear paint composition (C2) is applied (S55), and pre-drying is carried out again (S56). Next, the thermosetting and colored first clear paint composition (C1) is applied by a dispenser (S57). Finally, heat curing is performed again (S58), and the water-based base paint composition (B), the second clear paint composition (C2), and the first clear paint composition (C1) are cured at once.

[0123] By the method of the fourth embodiment, a multilayer coating film is formed that includes an intermediate coating film disposed on the object to be coated, a base coating film disposed on the intermediate coating film, a second clear coating film disposed on the base coating film, and a colored clear coating film disposed on the second clear coating film. FIG. 8 is a schematic cross-sectional view showing the multilayer coating film 10C in the fourth embodiment. The multilayer coating film 10C includes an intermediate coating film 12 disposed on the object to be coated 11, a base coating film 15 disposed on the intermediate coating film 12, a second clear coating film 14 disposed on the base coating film 15, and a colored clear coating film 13 disposed on the colored clear coating film 13.

[0124] · Pre-drying of the second clear coating composition (C2) The pre-drying of the second clear coating composition (C2) may be carried out under the same conditions as the pre-drying of the intermediate coating composition (A), or may be carried out under different conditions.

[0125] [Fifth Embodiment] This embodiment is different from the fourth embodiment in that the order of coating the first clear coating composition (C1) and the second clear coating composition (C2) is reversed. This difference will be described below. In this embodiment, since the other steps are the same as those in the fourth embodiment, the description thereof is omitted.

[0126] FIG. 9 is a flowchart showing an example of a method for forming a multilayer coating film according to the fifth embodiment. First, a thermosetting and solvent-based intermediate coating composition (A) is applied (S61) on the object to be coated, and heat curing is performed (S62). Then, an aqueous base coating composition (B) is applied (S63), and pre-drying is carried out (S64). Subsequently, a thermosetting and colored first clear coating composition (C1) is applied by a dispenser (S55), and pre-drying is carried out again (S66). Next, the second clear coating composition (C2) is applied (S67). Finally, heat curing is performed again (S68), and the aqueous base coating composition (B), the first clear coating composition (C1), and the second clear coating composition (C2) are cured at once.

[0127] By the method of the fifth embodiment, a multilayer coating film is formed which includes an intermediate coating film disposed on an object to be coated, a base coating film disposed on the intermediate coating film, a colored clear coating film disposed on the base coating film, and a second clear coating film disposed on the colored clear coating film. FIG. 10 is a schematic cross-sectional view showing the multilayer coating film 10D in the fifth embodiment. The multilayer coating film 10D includes an intermediate coating film 12 disposed on an object to be coated 11, a base coating film 15 disposed on the intermediate coating film 12, a colored clear coating film 13 disposed on the base coating film 15, and a second clear coating film 14 disposed on the colored clear coating film 13.

[0128] [Sixth Embodiment] This embodiment is different from the third embodiment in that the intermediate coating composition (A) is aqueous and pre-drying is performed instead of heat curing after the intermediate coating composition (A) is applied. This difference will be explained below. In this embodiment, since the other steps are the same as those in the third embodiment, the description thereof will be omitted.

[0129] FIG. 11 is a flowchart showing an example of a method for forming a multilayer coating film according to the sixth embodiment. First, a thermosetting and aqueous intermediate coating composition (A) is applied to an object to be coated (S71), and pre-drying is performed (S72). Then, an aqueous base coating composition (B) is applied (S73), and pre-drying is performed again (S74). Subsequently, a thermosetting and colored first clear coating composition (C1) is applied by a dispenser (S75). Finally, heat curing is performed (S76), and the intermediate coating composition (A), the aqueous base coating composition (B), and the first clear coating composition (C1) are cured at once.

[0130] By the method of the sixth embodiment, a multilayer coating film is formed which includes an intermediate coating film disposed on an object to be coated, a base coating film disposed on the intermediate coating film, and a colored clear coating film disposed on the base coating film. The multilayer coating film in the sixth embodiment has the same configuration as that in the third embodiment (FIG. 6).

[0131] The aqueous intermediate coating composition (A) contains water and, optionally, an organic solvent as a solvent. The aqueous intermediate coating composition (A) may contain, as a film-forming resin, for example, an aqueous polyester resin, an aqueous polyurethane resin, and a hydroxyl group-containing resin other than these (for example, an aqueous acrylic resin).

[0132] [Embodiment 7] This embodiment is different from the fourth embodiment in that the intermediate coating composition (A) is aqueous and pre-drying is carried out instead of heat curing after the intermediate coating composition (A) is applied. This difference will be described below. In this embodiment, since the other steps are the same as those in the fourth embodiment, the description thereof is omitted.

[0133] FIG. 12 is a flowchart showing an example of a method for forming a multilayer coating film according to the seventh embodiment. First, a thermosetting and aqueous intermediate coating composition (A) is applied onto an object to be coated (S81), and pre-drying is performed (S82). Then, an aqueous base coating composition (B) is applied (S83), and pre-drying is performed again (S84). Subsequently, a second clear coating composition (C2) is applied (S85), and pre-drying is performed three times (S86). Thereafter, a thermosetting and colored first clear coating composition (C1) is applied by a dispenser (S87). Finally, heat curing is performed (S88), and the intermediate coating composition (A), the aqueous base coating composition (B), the second clear coating composition (C2), and the first clear coating composition (C1) are cured at once.

[0134] By the method of the seventh embodiment, a multilayer coating film is formed, which includes an intermediate coating film disposed on an object to be coated, a base coating film disposed on the intermediate coating film, a second clear coating film disposed on the base coating film, and a colored clear coating film disposed on the second clear coating film. The multilayer coating film in the seventh embodiment has the same configuration as that in the fourth embodiment (FIG. 8).

[0135] [Embodiment 8] This embodiment is different from the seventh embodiment in that the order of painting the first clear paint composition (C1) and the second clear paint composition (C2) is reversed. This difference will be described below. In this embodiment, since the other steps are the same as those in the seventh embodiment, the description thereof will be omitted.

[0136] Figure 13 is a flowchart showing an example of a method for forming a multilayer coating film according to the eighth embodiment. First, a thermosetting and aqueous intermediate paint composition (A) is applied onto the object to be painted (S91), and pre-drying is performed (S92). Thereafter, an aqueous base paint composition (B) is applied (S93), and pre-drying is performed again (S94). Subsequently, the second clear paint composition (C2) is applied (S95), and pre-drying is performed three times (S96). Next, the thermosetting and colored first clear paint composition (C1) is applied by a dispenser (S97). Finally, heat curing is performed (S98), and the aqueous intermediate paint composition (A), the aqueous base paint composition (B), the first clear paint composition (C1), and the second clear paint composition (C2) are cured at once.

[0137] By the method of the eighth embodiment, a multilayer coating film is formed which includes an intermediate coating film disposed on the object to be painted, a base coating film disposed on the intermediate coating film, a colored clear coating film disposed on the base coating film, and a second clear coating film disposed on the colored clear coating film. The multilayer coating film in the eighth embodiment has the same configuration as that in the fifth embodiment (Figure 10).

[0138] Note that the present disclosure is not limited to the above-described embodiments, and design changes can be made without departing from the gist of the present disclosure. For example, any two or more of the features of the above-described embodiments may be combined.

[0139] In the above-described embodiments, the intermediate paint composition, the aqueous base paint composition, and the second clear paint composition are applied by a method other than the dispensing coating method, but the present disclosure is not limited thereto. The intermediate paint composition, the aqueous base paint composition, and the second clear paint composition may be applied by dispensing coating.

[0140] In the above-described embodiments, an aqueous base paint composition was used, but the present invention is not limited thereto. The base paint composition may be aqueous or solvent-based.

[0141] In the above-described embodiments, a solvent-based second clear paint composition was used, but the present invention is not limited thereto. The second clear paint composition may be aqueous or solvent-based.

[0142] In the above-described embodiments, the preliminary drying may be a WET treatment or a PH treatment.

Examples

[0143] The present invention will be described more specifically by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0144] The solid content concentration was calculated from the residue when the paint composition was heated at 140 °C in accordance with the JIS K 5601-1-2 heating residue measurement method.

[0145] LSV and HSV were measured using "MCR302" (manufactured by Anton Paar) as a rheometer at a measurement temperature of 23 °C, a cone plate of 25φ or 50φ, and each shear rate.

[0146] Mn was measured using "HLC8220GPC" (trade name, manufactured by Tosoh Corporation) as a GPC device and three "TSK Gel SuperMultipore HZ-M" (manufactured by TOSOH BIOSCIENCE) columns under the conditions of mobile phase: tetrahydrofuran, measurement temperature: 40 °C, flow rate: 0.35 mL / min, and detector: RI.

[0147] AV and OHV were calculated based on the acid value and hydroxyl value of the raw material monomers used.

[0148] [Preparation of Pigment Dispersion Paste] 28.6 parts of a dispersant (Disperbyk 161, manufactured by BYK), 57.1 parts of an organic solvent (Solvesso 150), and 14.3 parts of a black pigment (trade name: RAVEN 5000, carbon black, manufactured by COLUMBIAN) were premixed. Subsequently, using a paint conditioner and glass bead media, the mixture was blended at room temperature until the average particle size of the pigment became 5 μm or less. In this way, a solvent-based black pigment dispersion paste with a solid content concentration of 22.9% by mass was obtained.

[0149] [Preparation of the First Clear Paint Composition (C1-1)] 62.7 parts of the following half-ester anhydride group-containing acrylic resin (i), 20.0 parts of a carboxyl group-containing polyester resin (ii), 73.7 parts of an acrylic resin (iii) having a hydroxyl group and an epoxy group, 1 part of an ultraviolet absorber, 1 part of a light stabilizer, 0.3 part of an acrylic surface conditioner, 4.9 parts of a viscous agent a, and 1.0 part of a surface conditioner were mixed. Subsequently, 30 parts of an organic solvent and 35.7 parts of the above pigment dispersion paste were blended to obtain the first clear paint composition (C1-1).

[0150] [Preparation of the First Clear Paint Compositions (C1-2 to 13, c1-1 to 6)] As shown in Table 1, the first clear paint compositions (C1-2 to 13, c1-1 to 6) were prepared in the same manner as the first clear paint composition (C1-1), except that the compounding components and compounding amounts were changed.

[0151] The descriptions in Table 1 and Table 2 are as follows.

[0152] (Acrylic resin (i)) Half-ester anhydride group-containing acrylic resin, manufactured by Nippon Paint Automotive Coatings Co., Ltd., solid content concentration 51.5% by mass, AV: 150 mgKOH / g, Mn 2800 (Polyester resin (ii)) Carboxyl group-containing polyester resin, manufactured by Nippon Paint Automotive Coatings Co., Ltd., solid content concentration 75.0% by mass, AV: 120 mgKOH / g, Mn 2500 (Acrylic resin (iii)) Acrylic resin having a salicylic acid group and an epoxy group, manufactured by Nippon Paint Automotive Coatings Co., Ltd., solid content concentration 71.5% by mass, epoxy equivalent 400 g / eq, OHV: 50 mgKOH / g, Mn2200)

[0153] (Adhesive) a: Trade name BHEOBYK-410, manufactured by BYK, polyurethane-based adhesive, solid content concentration 52% by mass b: Trade name SETALUX 91756 VS-60YA, manufactured by Allnex, polyurethane-based adhesive c: Trade name BHEOBYK-430, manufactured by BYK, urea-modified polyamide-based adhesive d: Trade name Disparon BB102, manufactured by Kusumoto Chemicals, polyamide-based adhesive e: Trade name Disparon 6900-20X, manufactured by Kusumoto Chemicals, polyamide-based adhesive f: Trade name Disparon 4200-10, manufactured by Kusumoto Chemicals, polyolefin-based (oxidized polyethylene) adhesive g: 10% ethyl acetate solution of trade name CAB-1000 (cellulose-based adhesive, manufactured by EASTMAN CHEMICAL) h: 12% Solvesso 100 solution of trade name Pliolite AC4 (organic resin fine particle adhesive, manufactured by Eriochem)

[0154] (UV absorber) Trade name Tinuvin 928, manufactured by BASF, solid content concentration 100% (Light stabilizer) Trade name Tinuvin 123, manufactured by BASF, solid content concentration 100% (Acrylic surface conditioner) Trade name RESIFLOW LV, manufactured by Estron Chemical, solid content concentration 100% (Anti-cratering agent) Trade name Disparon OX-881, manufactured by Kusumoto Chemicals, solid content concentration 30% (Organic solvent) Mixture of ethyl 3-ethoxypropionate and Solvesso 150 mixed at a ratio of 1:1

[0155] [Table 1]

[0156] [Example 1] A multi-layer coating film having a structure similar to that shown in FIG. 6 was formed by a method similar to that of the third embodiment described above (the flow chart shown in FIG. 5).

[0157] (1) Preparation of the object to be coated A cationic electrodeposition paint (product name: Powernics 110, manufactured by Nippon Paint Co., Ltd.) was electrodeposited on a zinc phosphate-treated dull steel plate so that the dry coating film was 20 μm thick. Then, the coating was cured by heating at 160° C. for 30 minutes to form a cured electrodeposition coating film, and a coated object was obtained.

[0158] (2) Application of intermediate coating composition and heat curing Onto the cured electrodeposition coating film, the solvent-based intermediate coating composition (A-2) shown below was applied by rotary atomization electrostatic coating to a cured film thickness of 20 μm, and the coating was heat-cured at 140° C. for 30 minutes to obtain an intermediate coating film.

[0159] (3) Coating of the water-based coating composition and preliminary drying Next, the aqueous base coating composition (B) was applied by rotary atomization electrostatic coating so that the cured film thickness was 15 μm, followed by preliminary drying (PH treatment 1) as described below.

[0160] (4) Dispense coating of the first clear coating composition Next, the first clear coating composition (C1-1) was applied using a dispenser (Vermes, MDS 3200, nozzle diameter 100 μm) so as to give a cured film thickness of 15 μm.

[0161] (5) Heat curing Finally, the coating was heat-cured at 140° C. for 30 minutes to form a multi-layer coating film comprising an intermediate coating film (thickness 20 μm), a base coating film (thickness 15 μm) and a colored clear coating film (thickness 15 μm).

[0162] [Examples 2 to 13, Comparative Examples 1 to 6] A multilayer coating film including an intermediate coating film (thickness: 20 μm), a base coating film (thickness: 15 μm), and a colored clear coating film (thickness: 15 μm) was formed in the same manner as in Example 1, except that the first clear coating compositions (C1-2 to 13, c1-1 to 6) were used instead of the clear coating composition (C-1).

[0163] [Table 2]

[0164] [Examples 14 to 23] Using the same method as in Example 1, each coating composition was applied in order from the bottom to the top of Table 3 to form a multilayer coating film. Between the applications of each coating composition, pre-drying or baking was performed as shown in Table 3. After applying the last coating composition, heat curing was performed at 140°C for 30 minutes.

[0165] The descriptions in Table 3 are as follows. A-1: Aqueous intermediate coating composition, trade name: Aqua Rex AR620, manufactured by Nippon Paint Automotive Coating A-2: Solvent-based intermediate coating composition, trade name: Orga-30-P, manufactured by Nippon Paint Automotive Coating B: Aqueous base coating composition, trade name: Aqua Rex AR2000, aqueous, manufactured by Nippon Paint Automotive Coating C2: Solvent-based second clear coating composition, trade name: Mac Flow O-1820KN, manufactured by Nippon Paint Automotive Coating

[0166] WET treatment: Pre-drying, left standing at 23°C for 7 minutes PH treatment 1: Pre-drying, left standing at 23°C for 3 minutes, then heated at 80°C for 3 minutes PH treatment 2: Pre-drying, left standing at 23°C for 7 minutes, then heated at 90°C for 4 minutes Cure: Baking, left standing at 23°C for 7 minutes, then heated at 140°C for 30 minutes

[0167]

Table 3

[0168] [Example 24] A multilayer coating film was formed in the same manner as in Example 2, except that the nozzle diameter was changed to 50 μm.

[0169] [Example 25] A multilayer coating film was formed in the same manner as in Example 2, except that the nozzle diameter was changed to 400 μm.

[0170]

Table 4

[0171] [Evaluation] The following evaluations were performed on the multilayer coating film. The evaluation results are shown in Tables 2 to 4.

[0172] (1) Sagging property The multilayer coating film obtained in the same manner as in Example 1, except that the first clear paint composition was vertically applied, was visually observed and evaluated based on the following criteria. If the evaluation is C or higher, it can be evaluated that the first clear paint composition is excellent in sagging property (sagging is suppressed).

[0173] (Evaluation criteria) A: No sagging B: Intermediate between evaluation A and C, and practical. C: A pool of the paint composition was observed at the bottom, but it is practical D: A pool of the paint composition was observed at the bottom, and it is not suitable for practical use

[0174] (2) Levelling property The multilayer coating film obtained in the examples was visually observed, and whether the unevenness (streaks) extending in the scanning direction of the nozzle was levelled was evaluated based on the following criteria. If the evaluation is C or higher, it can be evaluated that the first clear paint composition is excellent in levelling property.

[0175] (Evaluation Criteria) A: No unevenness can be confirmed B: It is between Evaluation A and C and is practical C: The unevenness can be confirmed upon close inspection and is practical D: The unevenness immediately after painting remains as it is and is not suitable for practical use

[0176] (3) Straightness The multilayer coating film obtained in the example was visually observed, and the presence or absence of unpainted parts (missing parts) was evaluated based on the following criteria. If the evaluation is B or above, the first clear coating composition can be evaluated as having excellent straightness

[0177] (Evaluation Criteria) A: No missing parts can be confirmed B: Streaks that seem to be caused by missing parts are visible, but it is practical C: Clear missing parts can be confirmed and it is not suitable for practical use

[0178] (4) Spattering property The multilayer coating film obtained in the example was visually observed, and whether the first clear coating composition had spattered onto parts other than the painted part was evaluated based on the following criteria. If the evaluation is B or above, the first clear coating composition can be evaluated as having excellent spattering property (spattering is suppressed)

[0179] (Evaluation Criteria) A: No spattering can be confirmed B: A few spattered points are visible, but it is practical C: A large number of spattered points can be confirmed and it is not suitable for practical use

[0180] (5) Hiding power A hiding rate test paper (manufactured by Nippon Test Panel Co., Ltd.) compliant with JIS K 5600-4-1(b) was used. The first clear coating composition was dispensed and applied onto the 2D2 cm square black-and-white checkered pattern of the hiding rate test paper so as to form a gradient in dry film thickness, and then heat-cured. Subsequently, the film thickness at the site where the black-and-white checkered pattern was no longer visible to the naked eye was visually determined, and the film thickness at that site was measured. The measured film thickness was taken as the black-and-white hiding film thickness. Based on the following evaluation criteria, the hiding property of the colored clear coating film was evaluated from the obtained black-and-white hiding film thickness. If it is Evaluation A, it can be evaluated that the colored clear coating film is excellent in hiding property.

[0181] (Evaluation Criteria) A: The black-and-white hiding film thickness is 13 μm or less B: The black-and-white hiding film thickness exceeds 13 μm

[0182] (6) White Blurring The multilayer coating film obtained in the examples was visually observed, and the white blurring (cloudiness) of the coating film was evaluated. The evaluation was carried out with reference to the reference colored clear coating film prepared from the first clear coating composition (c1-1). Since the first clear coating composition (c1-1) does not contain a viscous agent, white blurring hardly occurs in the obtained colored clear coating film. If it is Evaluation B or higher, it can be evaluated that the colored clear coating film is less likely to cause white blurring.

[0183] (Evaluation Criteria) A: It is equivalent to the reference colored clear coating film and can be evaluated as having no white blurring B: Although white blurring is observed more than that of the reference colored clear coating film upon staring, it is practical C: White blurring can be clearly confirmed as compared with the reference colored clear coating film, and it is not suitable for practical use

[0184] This disclosure includes the following aspects. [1] Coating a thermosetting intermediate coating composition (A) on an object to be coated; After coating the intermediate coating composition (A), coating a thermosetting and colored first clear coating composition (C1) using a dispenser; Heating and curing the intermediate coating composition (A) to obtain an intermediate coating film; Heating and curing the first clear coating composition (C1) to obtain a colored first clear coating film, The first clear coating composition (C1) is a solvent-based composition, and the low-shear viscosity LSV measured under the conditions of a temperature of 23 °C and a shear rate of 0.1 sec-1 is 1 Pa·s or more and 40 Pa·s or less. A method for forming a multi-layer coating film. [2] The first clear coating composition (C1) is applied before the intermediate coating composition (A) is heated and cured. A method for forming a multi-layer coating film according to [1] above, wherein the heating and curing of the intermediate coating composition (A) and the first clear coating composition (C1) are carried out at once. [3] After heating and curing the intermediate coating composition (A) to obtain an intermediate coating film, A method for forming a multi-layer coating film according to [1] above, wherein the first clear coating composition (C1) is applied. [4] After applying the intermediate coating composition (A) and before applying the first clear coating composition (C1), applying a base coating composition (B); Further comprising heating and curing the base coating composition (B) to obtain a base coating film. A method for forming a multi-layer coating film according to any one of [1] to [3] above. [5] After applying the intermediate coating composition (A) and before applying the first clear coating composition (C1), applying a base coating composition (B); After applying the base coating composition (B) and before applying the first clear coating composition (C1), applying a second clear coating composition (C2); Further comprising heating and curing the second clear coating composition (C2) to obtain a second clear coating film. A method for forming a multi-layer coating film according to any one of [1] to [4] above. [6] After applying the first clear coating composition (C1) and applying the second clear coating composition (C2); Further comprising heating and curing the second clear coating composition (C2) to obtain a second clear coating film, the method for forming a multi-layer coating film according to any one of the above [1] to [4]. [7] The high-shear viscosity HSV measured under the conditions of a temperature of 23 ° C and a shear rate of 1000 sec of the first clear coating composition (C1) is 0.009 Pa·s or more and 0.40 Pa·s or less, the method for forming a multi-layer coating film according to any one of the above [1] to [6]. -1 [8] The solid content concentration of the first clear coating composition (C1) is 20% by mass or more and 60% by mass or less, the method for forming a multi-layer coating film according to any one of the above [1] to [7]. [9] The rate of decrease in the solid content concentration after 60 seconds from the application of the first clear coating composition (C1) is 10% by mass or less with respect to the solid content concentration of the first clear coating composition (C1), the method for forming a multi-layer coating film according to any one of the above [1] to [8].

[10] The diameter of the nozzle of the dispenser is 50 μm or more and 400 μm or less, the method for forming a multi-layer coating film according to any one of the above [1] to [9].

[11] The first clear coating composition (C1) contains at least one selected from the group consisting of a coloring pigment, a pearlescent pigment, and a dye, the method for forming a multi-layer coating film according to any one of the above [1] to

[10] .

[12] The first clear coating composition (C1) contains at least one selected from the group consisting of a polyamide-based binder, a cellulose-based binder, a polyolefin-based binder, a polyurea-based binder, and an organic resin fine particle binder, the method for forming a multi-layer coating film according to any one of the above [1] to

[11] . [Industrial Applicability]

[0185] According to the method of the present invention, a multi-layer coating film with suppressed sagging can be obtained using dispenser coating. The method of the present disclosure is particularly suitable for automobile painting. [Explanation of Symbols] ​

[0186] Multi-layer coatings 10, 10A to 10D Workpiece 11 Intermediate coating film 12 Colored first clear coating film (colored clear coating film) 13 Second clear coating film 14 Base coating film 15

Claims

1. Coating a thermosetting intermediate coating composition (A) on an object to be coated; After coating the intermediate coating composition (A), coating a thermosetting and colored first clear coating composition (C1) using a dispenser; Heat-curing the intermediate coating composition (A) to obtain an intermediate coating film; Heat-curing the first clear coating composition (C1) to obtain a colored first clear coating film, comprising: The first clear coating composition (C1) is solvent-based, and the low-shear viscosity LSV measured under the conditions of a temperature of 23 ° C and a shear rate of 0.1 sec-1 is 1 Pa·s or more and 40 Pa·s or less. A method for forming a multilayer coating film.

2. The first clear coating composition (C1) is coated before heat-curing the intermediate coating composition (A), The method for forming a multilayer coating film according to claim 1, wherein the heat-curing of the intermediate coating composition (A) and the first clear coating composition (C1) is carried out at once.

3. After heat-curing the intermediate coating composition (A) to obtain an intermediate coating film, The method for forming a multilayer coating film according to claim 1, wherein the first clear coating composition (C1) is coated.

4. After coating the intermediate coating composition (A), before coating the first clear coating composition (C1), coating a base coating composition (B); The method for forming a multilayer coating film according to claim 1, further comprising heat-curing the base coating composition (B) to obtain a base coating film.

5. After coating the intermediate coating composition (A), before coating the first clear coating composition (C1), coating a base coating composition (B); After coating the base coating composition (B), before coating the first clear coating composition (C1), coating a second clear coating composition (C2); The method for forming a multilayer coating film according to claim 1, further comprising heat-curing the second clear coating composition (C2) to obtain a second clear coating film.

6. After coating the first clear coating composition (C1), coating a second clear coating composition (C2); The method for forming a multilayer coating film according to claim 1, further comprising heat-curing the second clear coating composition (C2) to obtain a second clear coating film.

7. The high-shear viscosity HSV measured under the conditions of a temperature of 23°C and a shear rate of 1000 sec of the first clear coating composition (C1) is 0.009 Pa·s or more and 0.40 Pa·s or less. The method for forming a multilayer coating film according to claim 1. －１ ​

8. The method for forming a multilayer coating film according to claim 1, wherein the solid content concentration of the first clear coating composition (C1) is 20% by mass or more and 60% by mass or less.

9. The method for forming a multilayer coating film according to claim 1, wherein the reduction rate of the solid content concentration after 60 seconds from the application of the first clear coating composition (C1) is 10% by mass or less with respect to the solid content concentration of the first clear coating composition (C1).

10. The method for forming a multilayer coating film according to claim 1, wherein the diameter of the nozzle of the dispenser is 50 μm or more and 400 μm or less.

11. The method for forming a multilayer coating film according to claim 1, wherein the first clear coating composition (C1) contains at least one selected from the group consisting of a coloring pigment, a pearlescent pigment, and a dye.

12. The method for forming a multilayer coating film according to claim 1, wherein the first clear coating composition (C1) contains at least one selected from the group consisting of a polyamide-based binder, a cellulose-based binder, a polyolefin-based binder, a polyurea-based binder, and an organic resin fine particle binder.

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