Multi-component clear coating composition and method for manufacturing coated articles

Abstract

The present invention provides a multi-component clear coating composition that yields a clear coating film with excellent car wash resistance, polishability, and stain resistance. [Solution] A multi-component clear coating composition comprising a first liquid containing a hydroxyl group-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C), and a second liquid containing a polyisocyanate compound (D), wherein the glass transition temperature of the hydroxyl group-containing acrylic resin (A) is greater than 10°C, the weight-average molecular weight of the melamine resin (C) is 400 or more and less than 4000, the content of the polycarbonate polyol (B) is 6 to 17 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), and the content of the melamine resin (C) is 1 part by mass or more and less than 10 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C).

Description

[Technical Field]

[0001] The present invention relates to a multi-component clear coating composition and a method for manufacturing a coated article. [Background technology]

[0002] A clear coat is typically applied as the outermost layer on the body of an automobile. This clear coat requires resistance to car washes to prevent scratches.

[0003] Patent documents 1 to 3 disclose paint compositions containing melamine resin (C) that can form a coating film with high car wash resistance (scratch resistance). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6869753 [Patent Document 2] Patent No. 7187483 [Patent Document 3] International Publication No. 2022 / 030536 [Overview of the project] [Problems that the invention aims to solve]

[0005] In automotive paint lines, there is a polishing process where the clear paint composition is applied and then polished with sandpaper. Paint films with high car wash resistance tend to have reduced polishing properties and also tend to have poor stain resistance.

[0006] The object of the present invention is to provide a multi-component clear coating composition that yields a clear coating film with excellent car wash resistance, polishability, and stain resistance, and a method for manufacturing a coated article using this multi-component clear coating composition. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides the following aspects. [1] A first liquid containing a hydroxyl group-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C), and a second liquid containing a polyisocyanate compound (D), where the glass transition temperature of the hydroxyl group-containing acrylic resin (A) exceeds 10°C, the weight average molecular weight of the melamine resin (C) is 400 or more and less than 4000, the content of the polycarbonate polyol (B) is 6 to 17 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), the content of the melamine resin (C) is 1 part by mass or more and less than 10 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), a multi-liquid type clear paint composition. [2] The multi-liquid type clear paint composition according to [1] above, wherein the solid content mass ratio (C / B) of the polycarbonate polyol (B) to the melamine resin (C) is 0.3 to 0.95. [3] The multi-liquid type clear paint composition according to [1] or [2] above, wherein the polycarbonate polyol (B) has a number average molecular weight of 300 to 2000. [4] The multi-liquid type clear paint composition according to [1] or [2] above, wherein the melamine resin (C) has an average value of the total number of imino groups and methylol groups per triazine ring of 0.3 to 3.1, and a solubility parameter of 9.5 or more. [5] The melamine resin (C) has an alkyl ether group bonded to a nitrogen atom, and the multi-liquid type clear paint composition according to [1] or [2] above, wherein the number ratio (methyl group: butyl group) of the methyl group to the butyl group contained in the alkyl ether group is 100:0 to 20:80. [6] Applying a base paint composition onto an object to be coated to form an uncured base coating film; Applying the two-component clear paint composition of [1] onto the uncured base coating film to form an uncured clear coating film; Simultaneously curing the uncured base coating film and the uncured clear coating film, a method for manufacturing a coated article comprising the above. [7] The method for manufacturing a coated article according to [6] above, wherein the solid content concentration during the application of the two-component clear paint composition is 40 to 60% by mass. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a two-component clear paint composition capable of obtaining a clear coating film excellent in abrasion resistance, antifouling property, and car wash resistance. According to the present invention, furthermore, a method for manufacturing a coated article using this two-component clear paint composition can be provided. [Embodiments for Carrying Out the Invention]

[0009] Car wash resistance refers to the performance that the lightness is difficult to decrease after washing with a car washing machine. If the surface of the coating film is damaged, the lightness may decrease. A coating film with high car wash resistance has the property that the surface is difficult to be destroyed and scratched by the brush of the car washing machine. A coating film with high car wash resistance can be said to have the performance of relaxing the force applied from the brush of the car washing machine by deforming it, or the performance of self-repairing even if the surface is damaged by the force applied from the brush of the car washing machine.

[0010] Abrasion resistance indicates the ease of performing a polishing operation after the formation of the coating film. High abrasion resistance means that the polishing operation can be completed in a short time. Alternatively, a coating film with high abrasion resistance can be said to have the property that the surface of the coating film is easily destroyed by polishing. That is, high car wash resistance and high abrasion resistance are mutually contradictory performances.

[0011] Stain resistance refers to the ability to easily wipe away dirt from the surface of a paint film. Higher hardness generally correlates with higher stain resistance. Paint films with high stain resistance are easier to wipe clean. High car wash resistance and high stain resistance are contradictory properties.

[0012] The multi-component clear coating composition according to this disclosure comprises a polycarbonate polyol (B) in the main component (corresponding to the first component of this disclosure). The polycarbonate polyol (B) imparts flexibility to the cross-linked structure, thereby improving car wash resistance.

[0013] Furthermore, this disclosure incorporates melamine resin (C) as the main component. Melamine resin (C) is generally used as a curing agent for hydroxyl group-containing resins. However, in this disclosure, melamine resin (C) is used together with hydroxyl group-containing acrylic resin (A) and polycarbonate polyol (B) as a substance that reacts with a polyisocyanate compound. The melamine resin (C) imparts hardness to the crosslinked structure, thereby improving stain resistance.

[0014] In addition, this disclosure incorporates a hydroxyl group-containing acrylic resin (A) with a glass transition temperature (Tg) of over 10°C. This makes the clear coating less prone to deformation and makes the surface easier to polish, thus improving polishability. It may also improve stain resistance.

[0015] To achieve both high car wash resistance and polishability, the blending ratio of polycarbonate polyol (B) and melamine resin (C) is important. The content of polycarbonate polyol (B) is 6 to 17 parts by mass per 100 parts by mass of the total amount of hydroxyl group-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C). The content of melamine resin (C) is 5 parts by mass or more and less than 10 parts by mass per 100 parts by mass of the total amount of hydroxyl group-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C).

[0016] The glass transition temperature (Tg) may be calculated from the type and amount of raw material monomers in the resin. Tg may also be measured using a differential scanning calorimeter (DSC).

[0017] The weight-average molecular weight (Mw) is determined by the GPC method using polystyrene as the standard.

[0018] The hydroxyl value and acid value are determined based on the solid content mass. The hydroxyl value and acid value can be measured by known methods described in JIS K 0070:1992. The hydroxyl value and acid value may also be calculated from the amount of unsaturated monomers in the raw material monomers of the resin (for example, hydroxyl group-containing acrylic resin (A)).

[0019] Acrylic resins containing hydroxyl groups (A), polycarbonate polyols (B), and other coating film-forming components containing hydroxyl groups may be collectively referred to as hydroxyl group-containing resins.

[0020] [Multi-component clear coating composition] The clear coating composition is a multi-component type containing a first and a second component. The multi-component clear coating composition (hereinafter sometimes simply referred to as the clear coating composition) may further contain a third component containing other components.

[0021] Clear coating compositions are prepared using methods commonly used by those skilled in the art. A clear coating composition can be prepared by mixing a first liquid and a second liquid. In another embodiment, a clear coating composition can be prepared by mixing the first liquid, the second liquid, and a third liquid. Mixing methods include kneading and mixing using a kneader or roll, and dispersion and mixing using a sand grind mill or disperser.

[0022] Clear coating compositions may be water-based or solvent-based. Clear coating compositions may be solvent-based. Water-based coating compositions contain water as a solvent. In clear coating compositions, the proportion of water in the solvent may be 50% by mass or more, 70% by mass or more, or 100% by mass. Solvent-based coating compositions contain an organic solvent (also called a non-aqueous solvent) as a solvent. In solvent-based coating compositions, the proportion of the organic solvent in the solvent may be 50% by mass or more, 70% by mass or more, or 100% by mass.

[0023] The solid content concentration of the clear coating composition during application is, for example, 40-60% by mass or more. Even with such a high solid content concentration, the clear coating composition has low viscosity during application because the melamine resin (C) has a low molecular weight. Therefore, the clear coating film has an excellent appearance.

[0024] The solid content concentration C1 of the clear coating composition at the time of application is the solid content concentration of the clear coating composition immediately after mixing the first liquid and the second liquid (within 10 minutes after mixing) and immediately before application (within 10 minutes before application). The solid content concentration C1 of the clear coating composition at the time of application is determined by measuring the mass of the residue (also called the heated residue) after heating the clear coating composition, which is heated at 140°C for 30 minutes, within 10 minutes after mixing the first liquid and the second liquid.

[0025] The solid content concentration C1 of the clear coating composition during application can be calculated specifically as follows: First, measure the mass (initial mass W0) of an aluminum cup of appropriate size. Next, pour the clear coating composition, which has been mixed with the first and second liquids within 10 minutes, into this aluminum cup, and measure the mass (W1) within 10 minutes after pouring.

[0026] Next, the aluminum cup is heated at 140°C for 30 minutes, and its mass (W2) is measured again. W2 is the total mass of the solids (residue after heating) of the clear coating composition and the aluminum cup. Finally, the solids concentration C1 of the clear coating composition at the time of application is determined using the following formula. (W1-W0) represents the total mass of solvent and solids remaining in the clear coating composition immediately after application. (W2-W0) represents the mass of solids only in the clear coating composition. Solid concentration C1(%)=100×(W2-W0) / (W1-W0)

[0027] The viscosity of the clear coating composition during application can be considered as the viscosity of the clear coating composition immediately before application. The solid content concentration C1 of the clear coating composition during application may be 45% by mass or more, 50% by mass or more, or 53% by mass or more. The solid content concentration C1 of the clear coating composition may be 59% by mass or less, or 58% by mass or less.

[0028] ·1st liquid The first solution contains a hydroxyl group-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C).

[0029] (A) Acrylic resin containing hydroxyl groups The hydroxyl group-containing acrylic resin (A) is the base resin (film-forming component) for the clear coating. The hydroxyl group-containing acrylic resin (A) reacts with the polyisocyanate compound (D) to form a crosslinked structure.

[0030] The hydroxyl group-containing acrylic resin (A) has multiple (meth)acryloyl groups and one or more (typically two or more) hydroxyl groups (-OH) within one molecule.

[0031] The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A) is greater than 10°C. When the above Tg is greater than 10°C, the clear coating film is given high polishability. In addition, the antifouling properties may be improved. The above Tg may be 15°C or higher, or 18°C ​​or higher. The above Tg may be 130°C or lower. When the above Tg is 130°C or lower, the quick-drying properties of the clear coating composition tend to be improved. The above Tg may be 110°C or lower, 100°C or lower, 90°C or lower, or 70°C or lower. The above Tg may be greater than 10°C and 130°C or lower, 15 to 110°C, 15 to 100°C, 18 to 90°C, or 18 to 70°C.

[0032] The hydroxyl value (OHV) of the hydroxyl group-containing acrylic resin (A) is, for example, 90 to 180 mgKOH / g. When the above OHV is 90 mgKOH / g or higher, the crosslinking density tends to be high. When the above OHV is 180 mgKOH / g or lower, the hydrophilization of the coating film is suppressed, and the water resistance of the clear coating film tends to improve. The above OHV may be 100 mgKOH / g or higher, or 110 mgKOH / g or higher. The above OHV may be 180 mgKOH / g or lower, or 170 mgKOH / g or lower. The above OHV may be 100 to 180 mgKOH / g, or 110 to 170 mgKOH / g.

[0033] The weight-average molecular weight (Mw) of the hydroxyl group-containing acrylic resin (A) is, for example, 4,000 to 12,000. When the above Mw is 4,000 or more, the hardness and weather resistance of the resulting coating film tend to improve. When the above Mw is 12,000 or less, excessive viscosity increase of the paint composition tends to be suppressed. The above Mw may be 4,500 or more, or 4,800 or more. The above Mw may be 10,000 or less, or 9,000 or less, or 8,500 or less. The above Mw may be 4,500 to 10,000, or 4,800 to 9,000.

[0034] From the standpoint of hardness, the hydroxyl group-containing acrylic resin (A) may have a hydroxyl value of 90 to 180 mgKOH / g, a weight-average molecular weight of 4,000 to 12,000, and a Tg of 10 to 100°C.

[0035] The hydroxyl group-containing acrylic resin (A) can be prepared by polymerizing a hydroxyl group-containing α,β-ethylenically unsaturated monomer with another α,β-ethylenically unsaturated monomer using a known method. The hydroxyl group-containing acrylic resin (A) can be prepared, for example, by solution polymerization. A commercially available hydroxyl group-containing acrylic resin (A) may also be used.

[0036] Examples of hydroxyl-containing α,β-ethylenically unsaturated monomers include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts of these with ε-caprolactone. These can be used individually or in combination of two or more.

[0037] Examples of α,β-ethylenically unsaturated monomers other than those mentioned above include polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds. These can be used individually or in combination of two or more.

[0038] (B) Polycarbonate polyol Polycarbonate polyol (B) is also a coating film-forming component. Polycarbonate polyol (B) reacts with polyisocyanate compound (D) to form a crosslinked structure.

[0039] Polycarbonate polyol (B) has two or more carbonate bonds (-O-(C=O)-O-) and two or more hydroxyl groups. The hydroxyl groups may be located at both ends of the molecular chain. Polycarbonate polyol (B) imparts high car wash resistance to the clear coating film.

[0040] The polycarbonate polyol (B) content is 6 to 17 parts by mass per 100 parts by mass of the total amount of hydroxyl group-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C). This provides high car wash resistance from the polycarbonate polyol (B), high stain resistance from the melamine resin (C), and high polishability from the hydroxyl group-containing acrylic resin (A).

[0041] The above content of polycarbonate polyol (B) may be 1 part by mass or more, or 5 parts by mass or more. The above content may be 30 parts by mass or less, or 20 parts by mass or less. The above content may be 1 to 30 parts by mass, or 5 to 20 parts by mass.

[0042] The number-average molecular weight (Mn) of polycarbonate polyol (B) is, for example, 300 to 2,000. This further improves car wash resistance. The above Mn may be 400 or more, or 450 or more. The above Mn may be 1,750 or less, or 1,500 or less, or 1,300 or less. The above Mw may be 400 to 1,500, or 450 to 1,300.

[0043] The hydroxyl value (OHV) of polycarbonate polyol (B) is, for example, 50 to 500 mgKOH / g. The above OHV may be 50 to 250 mgKOH / g or 100 to 250 mgKOH / g.

[0044] Polycarbonate polyols (B) can be obtained, for example, by the reaction of a polyol with a polycarbonate such as alkylene carbonate. Examples of polyols include ethylene glycol, glycerin, trimethylolpropane, propylene glycol, tetramethylene glycol, and pentaerythritol. These can be used individually or in combination of two or more.

[0045] Examples of the polycarbonate polyol (B) include polyhexamethylene carbonate diol and polyethylene carbonate diol. These may be used alone or in combination of two or more.

[0046] Examples of commercially available polycarbonate polyols include Duranol T5650E (manufactured by Asahi Kasei Corporation), C-590 (manufactured by Kuraray Co., Ltd.), and ETERNACOLL PH-50 (manufactured by Ube Industries, Ltd.).

[0047] (C) Melamine resin The melamine resin (C) is a component for forming a coating film. As described above, the melamine resin (C) reacts with the hydrophilic polyisocyanate compound (D) and is incorporated into the crosslinked structure between the hydroxyl group-containing resin (A) and the hydrophilic polyisocyanate compound (D), thereby imparting high car wash resistance to the coating film.

[0048] The melamine resin (C) has a structure in which six substituents R 1 ~N 3 are bonded via three nitrogen atoms N 1 ~R 6 to the periphery of the triazine ring (triazine nucleus) (-N 1 (R 1 )(R 2 ), -N 2 (R 3 )(R 4 ), -N 3 (R 5 )(R 6 )).

[0049] The melamine resin (C) is, for example, represented by the following general formula (1):

[0050]

Chemical formula

[0051] Alkyl ether (-CH2-OR 7 ) constitutes an alkyl group (R 7 The number of carbon atoms in ) may be 1 to 8, or 1 to 4. 7 It may be linear or branched. 7 This may be a methyl group, an ethyl group, a propyl group, or a butyl group.

[0052] Melamine resin (C) is generally composed of a polynuclear body in which multiple triazine rings are bonded together. Melamine resin (C) may also be a mononuclear body consisting of a single triazine ring.

[0053] For example, melamine resin (C) is -N(-CH2-OR 7 Methylol group having (-CH2OH); -N(-CH2-OR 7 Imino group having )(H);-N(-CH2-OR 7 )(-CH2OH) and -N(-CH2-OR 7 Examples include methylol / imino groups having (H).

[0054] Substituent R 1 ~R 6 At least one of these may be a methylol group or an imino group. This can improve both car wash resistance and polishability. The melamine resin (C) may be methylol-based, imino-based, or methylol / imino-based.

[0055] The average value of the total number of imino groups and methylol groups per triazine ring (hereinafter sometimes simply referred to as the average number of functional groups) is, for example, 0.3 to 3.1. This makes it easier for the melamine resin (C) to be incorporated into the crosslinked structure, resulting in a hard coating film. The average number of functional groups may be 0.5 or more, or 1.0 or more. The average number of functional groups may be 2.8 or less, or 2.5 or less. The average number of functional groups may be 0.5 to 2.8, or 1.0 to 2.5.

[0056] Substituent R1 ~R 6 At least one of them is an alkyl ether group (-CH2-OR 7 ) is acceptable. R 7 The group may be a methyl group or a butyl group. The number ratio of methyl groups to butyl groups (methyl group:butyl group) is, for example, 100:0 to 20:80. The number ratio (methyl group:butyl group) may be 90:10 to 30:70, or 80:20 to 40:60. By using the above melamine resin, in addition to obtaining good stain resistance, the viscosity of the paint composition can be adjusted to a suitable range, and a good coating film appearance can be achieved.

[0057] Melamine resin (C) is dissolved or finely dispersed in the clear coating composition. The solubility parameter (SP value) of melamine resin (C) can be measured by the diaphragm method. Acetone (HSP value δg of 9.77 as measured by Hansen) is used as a good solvent, and hexane (SP value δpl of 7.24) and deionized water (SP value δph of 23.50) are used as poor solvents. The SP value of melamine resin (C) measured by the diaphragm method using these good and poor solvents may be 9.5 or higher. The above SP value may be 10.0 or higher, or 11.0 or higher. The above SP value may be 14.8 or lower, or 14.5 or lower. The above SP value may be between 9.5 and 14.8, between 10.0 and 14.8, or between 11.0 and 14.5.

[0058] The SP value of melamine resin (C) can be determined by dissolving the melamine resin (C) in a good solvent with a known SP value and titrating the turbidity with a poor solvent with a higher SP value than the good solvent and a poor solvent with a lower SP value. For information on how to determine the SP value, please refer to Reference 1: CMHansen J.Paint.Tech., 39

[0505] , 104 (1967) and Reference 2: Kobayashi Toshikatsu, Colorants, 77[4], 188-192 (2004).

[0059] The SP value of melamine resin (C) is determined specifically as follows: Measurement temperature: 20℃ Good solvent: Acetone (HSP value δg = 9.77) Poor solvents: Hexane (SP value δpl = 7.24), deionized water (SP value δph = 23.50) Sample: Weigh 0.5 g of melamine resin (C) into a 100 ml beaker, add 10 ml of good solvent using a volumetric pipette, and dissolve using a magnetic stirrer.

[0060] (Turbidity measurement) When hexane is added dropwise to the sample, the volume fraction φ of hexane at the point where turbidity occurs is determined. pl Next, calculate the SP value δ of melamine resin (C) when hexane is used as a poor solvent using the following formula. ml We seek.

[0061]

number

[0062] Separately, deionized water was added dropwise to a similarly prepared sample, and the volume fraction φ of the deionized water at the point where turbidity occurred was determined. ph Next, calculate the SP value δ of melamine resin (C) when deionized water is used as a poor solvent using the following formula. mh We seek.

[0063]

number

[0064] SP value (δ) of melamine resin (C) poly ) is δ ml and δ mh It is an intermediate value and is calculated by the following formula.

[0065]

number

[0066] The melamine resin (C) may have an average total number of imino groups and methylol groups per triazine ring of 0.3 to 3.1, and a solubility parameter of 9.5 or higher. This further improves its stain resistance.

[0067] The weight-average molecular weight (Mw) of melamine resin (C) is 400 or more and less than 4000. This provides a good balance of stain resistance, car wash resistance, and polishability. The above Mw may be 3,500 or less, or 3,000 or less. The above Mw may be 450 or more, or 500 or more. The above Mw may be between 450 and 3,500, or between 500 and 3,000.

[0068] The melamine resin (C) content is 1 part by mass or more and less than 10 parts by mass per 100 parts by mass of the total amount of hydroxyl group-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C). This allows for high polishability due to the polycarbonate polyol (B), high car wash resistance due to the melamine resin (C), and high stain resistance due to the hydroxyl group-containing acrylic resin (A).

[0069] The above content of melamine resin (C) may be 2 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more. The above content may be 9 parts by mass or less, or 8 parts by mass or less. The above content may be 2 to 9 parts by mass, 4 to 9 parts by mass, or 5 to 8 parts by mass.

[0070] The solid content mass ratio (C / B) of polycarbonate polyol (B) to melamine resin (C) is, for example, 0.3 to 0.95. This further improves the balance between stain resistance and car wash resistance. C / B may be 0.7 or less, or 0.6 or less. C / B may be 0.32 or more, or 0.4 or more, or 0.5 or more. C / B may be 0.32 to 0.7, or 0.32 to 0.7, or 0.4 to 0.6, or 0.5 to 0.7.

[0071] (Other hydroxyl group-containing resins) The first liquid may contain other hydroxyl group-containing resins. Examples of other hydroxyl group-containing resins include polyether polyol resins, hydroxyl group-containing urethane resins, and polyester polyol resins. These can be used individually or in combination of two or more.

[0072] The solid content of the other hydroxyl group-containing components is, for example, 10 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less, based on 100 parts by mass of the total amount of hydroxyl group-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C).

[0073] (solvent) The first solution may contain a solvent. The solvent may be water or a non-aqueous solvent.

[0074] Non-aqueous solvents include, for example, aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, and mineral splits; ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl-i-butyl ketone, methyl amyl ketone, and cyclohexanone; aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, and decalin; methyl acetate, ethyl acetate, butyl acetate, amyl acetate, ethyl propionate, propio Ester-based organic solvents such as methyl phosphate and ethyl 3-ethoxypropionate; cellosolve-based organic solvents such as methyl cellosolve, ethyl cellosolve, n-propyl cellosolve, i-propyl cellosolve, n-butyl cellosolve, i-butyl cellosolve, i-amyl cellosolve, phenyl cellosolve, and benzyl cellosolve; carbitol-based organic solvents such as methyl carbitol, ethyl carbitol, n-propyl carbitol, i-propyl carbitol, n-butyl carbitol, i-butyl carbitol, i-amyl carbitol, carbitol acetate, phenyl carbitol, and benzyl carbitol;Ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene glycol di-n-butyl ether, propylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol Glycol ether-based organic solvents such as diisobutyl ether, dipropylene glycol diallyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n-butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, 2-butoxyethyl tetraethoxyethyl ether, etc.; acetate-based organic solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate, etc.;Examples of alcohol-based solvents include methanol, ethanol, propanol, isopropyl alcohol, butanol, and isobutyl alcohol. These can be used individually or in combination of two or more.

[0075] (Preparation method) The first liquid can be prepared by mixing the above components by a method known to those skilled in the art. The mixing method is the same as that used for preparing the clear coating composition.

[0076] ·Second liquid The second solution contains a polyisocyanate compound (D).

[0077] (D) Polyisocyanate compounds Polyisocyanate compound (D) is a curing agent that reacts with hydroxyl group-containing resin and melamine resin (C) to form a crosslinked structure and cure the multi-component clear coating composition. Polyisocyanate compound (D) has at least two isocyanate groups in one molecule.

[0078] In this specification, "isocyanate group" means an unblocked free isocyanate group. The unblocked isocyanate group allows for curing at low temperatures, for example.

[0079] Examples of polyisocyanate compounds (D) include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having aromatic rings not bonded to isocyanate groups in the molecule (aroliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specifically, examples include aromatic polyisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; and polymers of these, such as biuret type, nurate type, and adduct type. These can be used individually or in combination of two or more.

[0080] The equivalent ratio (NCO / OH) of isocyanate groups in the polyisocyanate compound (D) to hydroxyl groups in the hydroxyl group-containing resin may be 0.7 or higher, or 0.8 or higher. The equivalent ratio (NCO / OH) may be 2.0 or lower, 1.8 or lower, or 1.5 or lower. In one embodiment, the equivalent ratio (NCO / OH) is 0.7 or higher and 2.0 or lower. When the equivalent ratio (NCO / OH) is within this range, a clear coating film with excellent hardness and weather resistance is easily formed.

[0081] (Other hardening agents) The multi-component clear coating composition may contain curing agents other than the polyisocyanate compound (D). Examples of other curing agents include amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. These may be used individually or in combination of two or more. The content of the other curing agents is appropriately set depending on the hydroxyl group-containing resin.

[0082] The second liquid may contain melamine resin (including melamine resin (C)) as a curing agent. However, from the viewpoint of storage stability, it is desirable to have less melamine resin in the second liquid. The ratio of the mass of melamine resin to 100 parts by mass of the solid content of polyisocyanate compound (D) (melamine resin / polyisocyanate compound (D)) may be 0.2 parts by mass or less, 0.1 parts by mass or less, or 0 parts by mass.

[0083] (solvent) The second solution may contain a solvent that does not have hydroxyl groups. Examples of such solvents include the glycol ether-based organic solvents, acetate-based organic solvents, ketone-based organic solvents, and ester-based organic solvents mentioned above. These can be used individually or in combination of two or more.

[0084] (Preparation method) The second liquid can be prepared by mixing the above components by a method known to those skilled in the art. The mixing method is the same as that used to prepare the first liquid.

[0085] (Other ingredients) Clear coating compositions may contain additives commonly used in the coatings field. Additives may be added to any of the first, second, or third components. Examples of additives include pigments, UV absorbers, hindered amine light stabilizers, antioxidants, crosslinked resin particles, leveling agents, defoamers, curing accelerators, and viscosity modifiers.

[0086] [Painted items] A painted article can be obtained using the clear coating composition according to this disclosure. The painted article comprises, for example, an object to be coated and a multilayer coating including a base coating and a clear coating. The clear coating is formed by the clear coating composition according to this disclosure. Therefore, the painted article has excellent colorfastness and appearance.

[0087] The base coating is positioned between the workpiece and the clear coating. The multi-layer coating may further include an intermediate coating positioned between the workpiece and the base coating. That is, a painted article may comprise a workpiece and a multi-layer coating in which an intermediate coating, a base coating, and a clear coating are laminated in that order.

[0088] If the object to be coated is made of resin, the multilayer coating may further include a primer coating placed between the object to be coated and the base coating. That is, the coated article may include the object to be coated and a multilayer coating in which a primer coating, a base coating, and a clear coating are laminated in that order.

[0089] (subject to be coated) Examples of materials to be coated include metal, resin, and glass. Specifically, examples of materials to be coated include automobile bodies and parts for automobile bodies such as passenger cars, trucks, motorcycles, and buses, as well as automobile parts such as spoilers, bumpers, mirror covers, grilles, and door handles.

[0090] Examples of metals include iron, copper, aluminum, tin, zinc, or alloys thereof (e.g., steel). Typical examples of metals to be coated include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy plated steel sheets, zinc-aluminum-magnesium alloy plated steel sheets, aluminum plated steel sheets, aluminum-silicon alloy plated steel sheets, and tin plated steel sheets.

[0091] Metallic workpieces may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, metallic workpieces may be further coated with electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0092] Examples of resins include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The resin-coated object may be degreased. The resin-coated object may be surface-treated.

[0093] (Intermediate coating film) The intermediate coating film is formed by the intermediate coating paint composition. The intermediate coating paint composition will be described later. The cured film thickness (dry film thickness) of the intermediate coating film is, for example, 5 μm or more and 80 μm or less. The dry film thickness of the intermediate coating film may be 10 μm or more. The dry film thickness of the intermediate coating film may be 50 μm or less.

[0094] The thickness of the coating can be measured using an electromagnetic film thickness gauge (for example, SANKO's SDM-miniR). The coating thickness is the average value of the coating thickness at any five points.

[0095] (Primer coating) The primer film is interposed between the object to be coated and the base coating. The primer film improves the adhesion between the base coating and the object to be coated (especially resin-based objects). Furthermore, if the surface of the object to be coated is uneven, the primer coating helps to make the painted surface uniform, which helps to suppress unevenness in the base coating.

[0096] The primer coating is formed by a primer paint composition comprising, for example, a film-forming component, a material adhesion component, a viscosity modifier, a diluent, a pigment, and optionally a curing agent. The primer paint composition may optionally contain various of the above additives. The primer paint composition may be solvent-based or water-based.

[0097] Examples of film-forming components, curing agents, viscosity modifiers, diluents, and pigments include those exemplified as being incorporated into the base paint composition described later. The viscosity of the water-based primer paint composition, as measured by a Type B viscometer at 20°C, is, for example, 500 cps / 6 rpm to 6,000 cps / 6 rpm. The solid content of the primer paint composition is, for example, 30% by mass to 50% by mass. The solid content of the primer paint composition is the total components of the primer paint composition excluding the diluents.

[0098] The thickness of the primer coating is not particularly limited. In terms of smoothness and chipping resistance of the painted article, the primer coating thickness may be 5 μm or more and 40 μm or less. The primer coating thickness may be 7 μm or more. The primer coating thickness may be 25 μm or less.

[0099] (Base coating) The base coating is formed by a base paint composition. The base paint composition will be described later. The base coating may be a single layer or a laminated coating of two or more layers. The base coating imparts aesthetic appeal to the coated article. The dry film thickness per layer of the base coating is, for example, 5 μm or more and 35 μm or less. The dry film thickness per layer of the base coating may be 7 μm or more. The dry film thickness per layer of the base coating may be 30 μm or less.

[0100] (Clear coating) The clear coating is formed by the multi-component clear coating composition according to this disclosure. The dry film thickness of the clear coating is, for example, 10 μm or more and 80 μm or less. The dry film thickness of the clear coating may be 20 μm or more. The dry film thickness of the clear coating may be 60 μm or less.

[0101] [Method for manufacturing painted articles] The above-mentioned painted article is manufactured, for example, by a method comprising: applying a base coating composition onto an object to be coated to form an uncured base coating film; applying the clear coating composition according to the present disclosure to the uncured base coating film to form an uncured clear coating film; and simultaneously curing the uncured base coating film and the uncured clear coating film.

[0102] Before applying the base coating composition, an intermediate coating composition (or primer coating composition; the same applies hereinafter) may be applied to the object to be coated. When the base coating composition is applied, the intermediate coating film (or primer coating film; the same applies hereinafter) may be cured or not. When the base coating composition is applied, the intermediate coating film may be cured.

[0103] In other words, the painted article may be manufactured by a method (two-coat, one-bake method) comprising: applying an intermediate coating composition to the object to be coated, then curing it to form a cured intermediate coating film; sequentially applying a base coating composition and a clear coating composition onto the cured intermediate coating film to form an uncured base coating film and a clear coating film in that order; and simultaneously curing the uncured base coating film and the clear coating film.

[0104] The painted article may also be manufactured by a method (3-coat 1-bake method) comprising sequentially applying an intermediate coating composition, a base coating composition, and a clear coating composition onto the object to be coated to form an uncured intermediate coating film, a base coating film, and a clear coating film in that order, and simultaneously curing the uncured intermediate coating film, base coating film, and clear coating film.

[0105] The following describes each step using the example of manufacturing a painted article having a multi-layer coating in which an intermediate coating, a base coating, and a clear coating are laminated in that order using the two-coat, one-bake method. However, the manufacturing method of the painted article is not limited to this.

[0106] (I) Formation of a hardened intermediate coating film First, the intermediate coating composition is applied to the object to be coated to form an uncured intermediate coating film. The intermediate coating film improves the adhesion between the base coating film and the object to be coated. In addition, the intermediate coating makes the painted surface more uniform, which helps to suppress unevenness in the base coating film.

[0107] Examples of coating methods include the roll coater method, air spray coating, airless spray coating, and rotary atomization coating. These methods may be combined with electrostatic coating. Among these, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. For rotary atomization electrostatic coating, rotary atomization electrostatic coating machines commonly known as "micro-microbell (μμbell)", "microbell (μbell)", or "metallicbell (metabell)" may be used.

[0108] Next, the uncured intermediate coating film is cured. The intermediate coating composition can be cured by heating. The curing (heating) conditions are set appropriately according to the composition of the intermediate coating composition and the material of the object to be coated. The heating temperature is, for example, 100°C to 180°C, and may be 120°C to 160°C. The heating time can be set appropriately according to the heating temperature. When the heating temperature is 100°C to 180°C, the heating time is, for example, 10 minutes to 60 minutes, and may be 10 minutes to 30 minutes. The heating time refers to the time during which the heating device reaches the target temperature and the object to be coated is maintained at the target temperature; the time it takes to reach the target temperature is not considered. Examples of heating devices include drying ovens that utilize heat sources such as hot air, electricity, gas, and infrared rays.

[0109] (Intermediate coating paint composition) The intermediate coating composition may be water-based or solvent-based.

[0110] The intermediate coating composition includes, in addition to various solvents, for example, resins, pigments, and various additives. Examples of resins include acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluororesins, epoxy resins, and polyether resins. These can be used individually or in combination of two or more. The intermediate coating composition may further contain the curing agent described above.

[0111] (II) Formation of an uncured base coating An uncured base coating is formed by applying a base coating composition onto a cured intermediate coating. Two or more layers of uncured base coating can be formed by applying the same or different base coating composition two or more times. An interval of several minutes may be provided between the application of the nth base coating composition and the application of the (n+1)th base coating composition.

[0112] As for the painting method, for example, a method similar to the painting method for the intermediate coating paint composition can be used.

[0113] After applying the base coating composition, pre-drying (also called preheating) may be performed before applying the clear coating composition. This suppresses the boiling of diluent components in the base coating composition during the curing process, making it easier to suppress the occurrence of bubbling. Furthermore, pre-drying suppresses the mixing of the uncured base coating film and the clear coating composition, making it difficult for a mixed layer to form. As a result, the smoothness of the resulting coated article can be further improved.

[0114] Pre-drying methods include, for example, leaving the product at a temperature of 20°C to 25°C for 5 to 15 minutes, or heating it at a temperature of 50°C to 80°C for 30 seconds to 10 minutes.

[0115] (Base paint composition) The base coating composition may be water-based or solvent-based. A water-based base coating composition may include, for example, an acrylic resin emulsion, a water-soluble acrylic resin, a curing agent (typically melamine resin), and a polyether polyol resin. The base coating composition usually includes at least one of a coloring pigment and a glossy pigment. The base coating composition may further include various additives.

[0116] (III) Formation of an uncured clear coating The clear coating composition according to this disclosure is applied to an uncured base coating to form an uncured clear coating.

[0117] The painting method is not particularly limited. For example, a painting method similar to that used for the intermediate coating composition can be used. Among these, rotary atomizing electrostatic coating is preferred from the viewpoint of coating efficiency. After applying the clear coating composition, pre-drying may be performed in the same manner as described above.

[0118] (IV) Hardening The uncured base coat and clear coat are cured simultaneously. Each coat can be cured by heating.

[0119] The heating temperature is, for example, 80 to 160°C. The heating temperature may be 85°C or higher, or 90°C or higher. The heating temperature may be 150°C or lower, or 145°C or lower. The heating temperature may be 85 to 150°C, or 90 to 145°C.

[0120] The heating time should be set appropriately according to the heating temperature. When the heating temperature is between 80 and 160°C, the heating time may be, for example, 10 minutes to 60 minutes, or 15 minutes to 45 minutes. [Examples]

[0121] The present invention will be further described in detail by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" refer to the mass of resin solids unless otherwise specified.

[0122] [Manufacturing Example 1-1] Manufacturing of hydroxyl group-containing acrylic resin (A-1) In a container equipped with a stirrer, temperature control device, reflux condenser, and dropping funnel, 24.2 parts by mass of butyl acetate was charged and the temperature was raised to 120°C. A monomer solution (a mixture consisting of 20 parts by mass of styrene, 15.8 parts by mass of n-butyl acrylate, 21.8 parts by mass of n-butyl methacrylate, 41.1 parts by mass of 2-hydroxypropyl methacrylate, and 1.3 parts by mass of acrylic acid) and a mixed solution of 11.0 parts by mass of tert-butyl peroxy-2-ethylhexanoate and 5 parts by mass of butyl acetate were simultaneously added dropwise to the container over a period of 3 hours.

[0123] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butylperoxy-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. The reaction was then continued for 1 hour at 120°C, after which 7 parts by mass of butyl acetate was added. This yielded a varnish with a solid content of 64% by mass containing a hydroxyl group-containing acrylic resin (A-1) with Mw 8,200, hydroxyl value 160 mgKOH / g, acid value 10 mgKOH / g, and Tg 20°C.

[0124] [Manufacturing Example 1-2] Manufacturing of hydroxyl group-containing acrylic resin (A-2) In a container equipped with a stirrer, temperature control device, reflux condenser, and dropping funnel, 24.2 parts by mass of butyl acetate was charged and the temperature was raised to 120°C. A monomer solution (a mixture consisting of 20 parts by mass of styrene, 27 parts by mass of n-butyl acrylate, 9.3 parts by mass of n-butyl methacrylate, 41.1 parts by mass of 2-hydroxypropyl methacrylate, and 2.6 parts by mass of acrylic acid) and a mixed solution of 11.0 parts by mass of tert-butyl peroxy-2-ethylhexanoate and 5 parts by mass of butyl acetate were simultaneously added dropwise to the container over a period of 3 hours.

[0125] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butylperoxy-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. The reaction was then continued for 1 hour at 120°C, after which 7 parts by mass of butyl acetate was added. This yielded a varnish with a solid content of 64% by mass containing a hydroxyl group-containing acrylic resin (A-2) with Mw 7,800, hydroxyl value 160 mgKOH / g, acid value 20 mgKOH / g, and Tg 10°C.

[0126] [Manufacturing Example 1-3] Manufacturing of hydroxyl group-containing acrylic resin (A-3) In a container equipped with a stirrer, temperature control device, reflux condenser, and dropping funnel, 40 parts by mass of Solvesso 100 and 13 parts by mass of butanol were charged and the temperature was raised to 120°C. A monomer solution (a mixture consisting of 30 parts by mass of styrene, 13 parts by mass of 2-ethylhexyl acrylate, 4 parts by mass of n-butyl methacrylate, 12 parts by mass of Acryester SL (manufactured by Mitsubishi Chemical Corporation, a mixture of lauryl methacrylate / tridecyl methacrylate in a mass ratio of 4 / 6), 18 parts by mass of 2-hydroxypropyl acrylate, 2 parts by mass of acrylic acid, and 21 parts by mass of Praxel FM2D) and a mixed solution of 11.0 parts by mass of tert-butyl peroxy-2-ethylhexanoate and 5 parts by mass of butyl acetate were simultaneously added dropwise over 3 hours.

[0127] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butylperoxy-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. The reaction was then continued for 1 hour at 120°C, after which 7 parts by mass of butyl acetate was added. This yielded a varnish with a solid content of 60% by mass containing a hydroxyl group-containing acrylic resin (A-3) with Mw 14,000, hydroxyl value 120 mgKOH / g, acid value 15 mgKOH / g, and Tg -8°C.

[0128] [Polycarbonate polyol (B)] (B-1): Product name "Duranole T5650E", manufactured by Asahi Kasei Chemicals, polycarbonate diol, hydroxyl value 225 mg KOH / g, average number of hydroxyl groups 2, Mn 500 (B-2): Product name "Duranole T5651", manufactured by Asahi Kasei Chemicals, polycarbonate diol, hydroxyl value 110 mg KOH / g, average hydroxyl group count 110, Mn 1000

[0129] [Melamine resin (C)] A melamine resin (C) having the physical properties shown in Table 1 was used.

[0130] [Table 1]

[0131] [Example 1] (1) Preparation of the first solution In a 1L metal container, 80 parts of the above-mentioned hydroxyl group-containing acrylic resin (A-1), 15 parts of polycarbonate polyol (B-1), 5 parts of melamine resin (C-1), 1.4 parts of ultraviolet absorber (product name "Chinubin 384", manufactured by BASF Japan), 1.4 parts of light stabilizer (product name "Chinubin 123", manufactured by BASF Japan), 1.4 parts of acrylic surface modifier, 57.0 parts of methyl amyl ketone, and 22.0 parts of DBE (manufactured by Shoei Chemical Co., Ltd.) were sequentially added, and the mixture was thoroughly stirred with a disperser to obtain the first liquid.

[0132] (2) Preparation of the second solution Separately, 40.0 parts of polyisocyanate compound (D) (product name "Dismodule N-3300", manufactured by Sumitomo Bayer Urethane Co., Ltd., NCO active ingredient 22%) and 2-ethylethoxypropanol were sequentially added to a metal container and thoroughly stirred to obtain the second solution.

[0133] (3) Preparation of multi-component clear coating composition The first and second liquids were mixed to obtain a multi-component clear coating composition. The solid content concentration C1 of the multi-component clear coating composition measured as described above was 55% by mass.

[0134] (4) Manufacturing of painted articles A 150 x 300 x 0.8 mm dull steel plate treated with zinc phosphate was coated with Powernix 1010 (manufactured by Nippon Paint Automotive Coatings Co., Ltd., cationic electrodeposition paint) and Olga P-30 (manufactured by Nippon Paint Automotive Coatings Co., Ltd., intermediate coating paint) to achieve dry film thicknesses of 20 μm and 40 μm, respectively.

[0135] Next, AR-3020 Black (a water-based base coat manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was air-sprayed to a dry film thickness of 15 μm, and dried at 80°C for 5 minutes to form an uncured base coat.

[0136] Each of the above clear coating compositions was diluted with a thinner consisting of n-butyl acetate / ethyl 3-ethoxypropionate = 1 / 2 (by mass ratio) in a No. 4 Ford cup for 30 seconds at 20°C.

[0137] A diluted clear coating composition was air-sprayed to form an uncured clear coating film with a dry film thickness of 40 μm. After setting for 7 minutes, it was baked and cured at 140°C for 25 minutes to form a multi-layer coating film. In this way, a coated article was obtained.

[0138] [Examples 2-10 and Comparative Examples 1-10] A multi-component clear coating composition was prepared and a coated article was obtained by the same procedure as in Example 1, except that the types and amounts of the components were changed as shown in Tables 2 and 3.

[0139] [evaluation] The above-mentioned painted items were used as test panels, and the following evaluations were conducted. The evaluation results are shown in Tables 2 and 3.

[0140] (1) Car wash resistance The tests were conducted using a car wash testing machine, following a test method compliant with ISO 20566. First, the brightness of the surface of the test plate before the evaluation test was measured using a variable-angle colorimeter (manufactured by Suga Test Instruments Co., Ltd.) to determine L0. For brightness measurement, the incident light was perpendicular to the coating surface, and the receiving angle of the reflected light was set to a point 10 degrees away from the incident light.

[0141] A test solution (including JIS Z8901 test powders, type 8) was applied to the test plate. The surface of the test plate was brushed while running water through a car wash machine. After repeating this process 50 times, the surface of the test plate was wiped with alcohol. Subsequently, it was washed with water and air-blown. After that, the brightness L1 was measured in the same manner as above, and the difference from the initial value L0 (△L1 = L0 - L1) was calculated. The smaller this difference, the better the car wash scratch resistance (scratch resistance). △L was evaluated according to the following criteria.

[0142] [Evaluation Criteria] A:△L1<5 B: 5 ≤ △L1 ≤ 10 C:10<△L1

[0143] (2) Polishability The test plate was polished according to the following procedure. A portion of the test plate was wet-sanded using #3000 grit waterproof sandpaper. Then, the area was polished with a coarse polishing compound using a coarse buffing pad to remove the sandpaper scratches. Next, the area was polished with a secondary polishing compound using a secondary polishing pad to remove the scratches from the coarse buffing pad. Finally, the area was polished with a finishing compound using a finishing buffing pad, and a halogen lamp was shone perpendicularly to the paint film. The polishing was performed until the polished and unpolished areas appeared to be of similar surface quality to the naked eye. The above procedure was performed at three locations on the same test plate, and the total time required for polishing at the three locations (total time) was evaluated according to the following evaluation criteria.

[0144] [Evaluation Criteria] A: Total time less than 150 seconds B: Total time between 150 and 180 seconds C: Total time is 180 seconds or more

[0145] (3) Stain resistance A mixture of eight test powders specified in JIS Z8901:2006, JSTM pigment carbon black, and JSTM pigment synthetic yellow ochre was applied to the surface of the test plate using an air spray. The plate was then dried in an oven. This process was repeated eight times. Following this, a steam jet was applied, and the dirt was wiped off with a flannel cloth while running water over the surface.

[0146] Subsequently, the brightness L2 was measured in the same manner as described above, and the difference from the initial value L0 (△L = L0 - L2) was calculated. The smaller this difference, the more effectively the dirt has been wiped away, indicating better stain resistance. △L2 was evaluated according to the following criteria.

[0147] [Evaluation Criteria] A:△L2<0.5 B: 0.5 ≤ △L2 ≤ 1.0 C:1.0<△L

[0148] (4) Thermal cycle test After leaving the test plate at a temperature of 23±2℃ (room temperature) for 2 hours, the following procedure (i) to (iv) was repeated 10 times, with each cycle consisting of these steps. Then, the test plate was left undisturbed in the laboratory for 2 hours.

[0149] (i) Heat in a constant temperature chamber at -90±2℃ and humidity of 20% or less for 4 hours. (ii) Leave at room temperature for 30 minutes, then cool at -40±2℃ for 1.5 hours. (iii) After leaving at room temperature for 30 minutes, heat in a constant temperature chamber at a temperature of -70±2℃ and humidity of 95% or higher for 3 hours. (iv) Leave at room temperature for 30 minutes, then cool at -40±2℃ for 1.5 hours, and then leave at room temperature for 30 minutes.

[0150] Next, the test panels were visually inspected for cracks and blisters in the coating. The results were evaluated according to the following criteria.

[0151] [Evaluation Criteria] A: No cracks were observed. B: A few minute cracks are visible, which can be seen using a magnifying glass. C: Cracks are visible to the naked eye. D: A clear crack is visible to the naked eye.

[0152] (5) Storage stability The viscosity of the first and second components of the clear coating composition was measured according to the following procedure. Immediately after preparation (within 10 minutes of preparation), each of the first and second solutions was placed in a 250 mL container up to three-quarters of its capacity, and the viscosity (viscosity at the time of preparation) was measured at 23°C and a rotation speed of 60 rpm using a B-type viscometer (VISCOMETER TVB-10; manufactured by Toki Sangyo Co., Ltd.).

[0153] After viscosity measurement, the container was left sealed at 23°C for 2 hours, and the viscosity after standing (viscosity after standing) was measured. The viscosity change rate was calculated using the following formula and evaluated according to the following criteria. Viscosity change rate [%] = 100 × (Viscosity after storage stability test - Viscosity during preparation) / Initial viscosity

[0154] [Evaluation Criteria] A: The viscosity change rate is 150% or less. B: Viscosity change rate exceeds 150%

[0155] (6) Exterior The Long Wave (LW) value (measurement wavelength: 1,300~12,000 μm) was measured using Wave-Scan DOI (product name, manufactured by BYK-Gardner) and evaluated according to the following criteria. A smaller LW value indicates higher coating film smoothness.

[0156] [Evaluation Criteria] A: LW ≤ 2.0 B:2.0 <LW≦4.0 C:4.0 <LW

[0157] [Table 2]

[0158] [Table 3]

[0159] The clear coatings formed by the multi-component clear coating compositions of the examples all exhibited excellent car wash resistance, as well as superior polishability and stain resistance.

[0160] Comparative Example 1 had poor polishability and also poor stain resistance because the Mw of the melamine resin (C) was over 4000. Comparative Example 2 had poor stain resistance because the Tg of the hydroxyl group-containing acrylic resin (A) was 10°C or lower. Comparative Example 3, a hydroxyl group-containing acrylic resin (A), had a lower Tg than Comparative Example 2, resulting in inferiority not only in stain resistance but also in polishability. Comparative Example 4 had inferior stain resistance because the first liquid did not contain melamine resin (C). Comparative Example 5 had poor polishing properties because it contained an excessive amount of melamine resin (C). Comparative Example 6, lacking polycarbonate polyol (B), exhibited inferior car wash resistance. Comparative Example 7 had poor car wash resistance because it contained less polycarbonate polyol (B). Comparative Examples 8 and 9 contained an excess of polycarbonate polyol (B), resulting in poor polishability and stain resistance. Comparative Example 10 had inferior stain resistance because it used polyester polyol instead of polycarbonate polyol (B).

[0161] This disclosure includes the following aspects. [1] A first liquid comprising a hydroxyl group-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C), A second liquid containing a polyisocyanate compound (D), and The glass transition temperature of the hydroxyl group-containing acrylic resin (A) is greater than 10°C. The weight-average molecular weight of the melamine resin (C) is 400 or more and less than 4000. The content of the polycarbonate polyol (B) is 6 to 17 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C). A multi-component clear coating composition in which the content of the melamine resin (C) is 1 part by mass or more and less than 10 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C). [2] The multi-component clear coating composition according to [1] above, wherein the solid content mass ratio (C / B) of the polycarbonate polyol (B) to the melamine resin (C) is 0.3 to 0.95. [3] The polycarbonate polyol (B) is a multi-component clear coating composition according to [1] or [2] above, wherein the polycarbonate polyol (B) has a number average molecular weight of 300 to 2000. [4] The melamine resin (C) is a multi-component clear coating composition according to any of the above [1] to [3], wherein the average total number of imino groups and methylol groups per triazine ring is 0.3 to 3.1, and the solubility parameter is 9.5 or higher. [5] The melamine resin (C) has an alkyl ether group bonded to a nitrogen atom, A multi-component clear coating composition according to any of the above [1] to [4], wherein the number ratio of methyl groups to butyl groups (methyl group:butyl group) contained in the alkyl ether group is 100:0 to 20:80. [6] Applying a base coating composition to the object to be coated to form an uncured base coating film, The uncured base coating film is coated with one of the multi-component clear coating compositions [1] to [5] above to form an uncured clear coating film. A method for manufacturing a painted article, comprising simultaneously curing the uncured base coating and the uncured clear coating. [7] A method for producing the coated article according to [6], wherein the solid content concentration of the multi-component clear coating composition at the time of application is 40 to 60% by mass. [Industrial applicability]

[0162] The multi-component clear coating composition of the present invention is a multi-component clear coating composition that provides a clear coating film with excellent car wash resistance, polishability, and stain resistance. Therefore, it is suitably used for forming various clear coating films, particularly clear coating films for automobiles.

Claims

1. A first liquid comprising a hydroxyl group-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C), A second liquid containing a polyisocyanate compound (D), and The glass transition temperature of the hydroxyl group-containing acrylic resin (A) is greater than 10°C. The weight-average molecular weight of the melamine resin (C) is 400 or more and less than 4000. The content of the polycarbonate polyol (B) is 6 to 17 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C). A multi-component clear coating composition in which the content of the melamine resin (C) is 1 part by mass or more and less than 10 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C).

2. The multi-component clear coating composition according to claim 1, wherein the solid content mass ratio (C / B) of the polycarbonate polyol (B) to the melamine resin (C) is 0.3 to 0.

95.

3. The polycarbonate polyol (B) has a number average molecular weight of 300 to 2000, as described in claim 1 or 2, for the multi-component clear coating composition.

4. The melamine resin (C) has an average total number of imino groups and methylol groups per triazine ring of 0.3 to 3.1, and a solubility parameter of 9.5 or higher, as described in claim 1 or 2.

5. The melamine resin (C) has an alkyl ether group bonded to a nitrogen atom, The multi-component clear coating composition according to claim 1 or 2, wherein the number ratio (methyl group:butyl group) of methyl groups to butyl groups contained in the alkyl ether group is 100:0 to 20:

80.

6. Applying a base coating composition to the object to be coated to form an uncured base coating film, The uncured base coating film is coated with the multi-component clear coating composition described in claim 1 to form an uncured clear coating film. A method for manufacturing a painted article, comprising simultaneously curing the uncured base coating and the uncured clear coating.

7. The method for manufacturing a painted article according to claim 6, wherein the solid content concentration of the multi-component clear coating composition at the time of application is 40 to 60% by mass.

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