Multi-liquid type clear coating composition and method for manufacturing coated article

Abstract

This invention provides a multi-component transparent coating composition that yields a transparent coating film with excellent car wash resistance, polishability, and stain resistance. The multi-component transparent coating composition comprises a first liquid containing a hydroxyl-containing acrylic resin (A), a polycarbonate polyol (B), and a melamine resin (C), and a second liquid containing a polyisocyanate compound (D). The hydroxyl-containing acrylic resin (A) has a glass transition temperature exceeding 10°C, and the melamine resin (C) has a weight-average molecular weight of 400 or more and less than 4000. Relative to 100 parts by weight of the total solids of the hydroxyl-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), the content of the polycarbonate polyol (B) is 6 to 17 parts by weight, and the content of the melamine resin (C) is 1 part by weight or more and less than 10 parts by weight.

Description

Technical Field

[0001] This invention relates to a multi-component transparent coating composition and a method for manufacturing coated articles. Background Technology

[0002] As the outermost layer of a car body, it is usually coated with a transparent film. For transparent coatings, it is required to be resistant to car wash damage from car wash machines.

[0003] Patent documents 1-3 disclose a coating composition comprising melamine resin (C) that can form a coating film with high car wash resistance (scratch resistance).

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6869753 Patent Document 2: Japanese Patent No. 7187483 Patent Document 3: International Publication No. 2022 / 030536. Summary of the Invention

[0005] The problem that the invention aims to solve On automotive painting lines, this includes a polishing process after the application of a clear coat composition, where the paint is sanded. Coatings with high wash resistance tend to have reduced polishability and poor stain resistance.

[0006] The object of the present invention is to provide: a multi-component transparent coating composition that yields a transparent coating film with excellent car wash resistance, polishability, and stain resistance; and a method for manufacturing coated articles using the multi-component transparent coating composition.

[0007] Methods for solving problems To address the aforementioned problem, the present invention provides the following solution.

[0008] [1] A multi-component transparent coating composition comprising: A first liquid containing hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C); and The second liquid contains polyisocyanate compound (D). The glass transition temperature of the hydroxyl-containing acrylic resin (A) exceeds 10°C. The melamine resin (C) has a weight-average molecular weight of 400 or more and less than 4000. Relative to 100 parts by weight of the total solids of the hydroxyl-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), the content of the polycarbonate polyol (B) is 6 to 17 parts by weight. The content of melamine resin (C) is more than 1 part by mass and less than 10 parts by mass relative to the total solid content of the hydroxyl-containing acrylic resin (A), the polycarbonate polyol (B) and the melamine resin (C).

[0009] [2] The multi-component transparent coating composition of [1] above, wherein the solid component mass ratio (C / B) of the polycarbonate polyol (B) to the melamine resin (C) is 0.3 to 0.95.

[0010] [3] The multi-liquid transparent coating composition of [1] or [2] above, wherein the number average molecular weight of the polycarbonate polyol (B) is 300 to 2000.

[0011] [4] The multi-liquid transparent coating composition of [1] or [2] above, wherein the melamine resin (C) has an average total number of imino groups and hydroxymethyl groups per triazine ring of 0.3 to 3.1, and the melamine resin (C) has a solubility parameter of 9.5 or higher.

[0012] [5] The multi-component transparent coating composition of [1] or [2] above, wherein the melamine resin (C) has an alkyl ether group bonded to a nitrogen atom, The ratio of methyl to butyl groups in the alkyl ether group (methyl:butyl) is 100:0 to 20:80.

[0013] [6] A method for manufacturing coated articles, comprising: A base coating composition is applied to the substrate to form an uncured base coating film. The above-described [1] multi-component transparent coating composition is applied to the uncured base coating film to form an uncured transparent coating film; and The uncured base coating and the uncured transparent coating are cured simultaneously.

[0014] [7] The method for manufacturing coated articles described in [6] above, wherein the concentration of solid components in the multi-component transparent coating composition during coating is 40 to 60% by mass.

[0015] Invention Effects According to the present invention, a multi-component transparent coating composition is provided, which yields a transparent coating film with excellent wash resistance, polishability, and stain resistance. According to the present invention, a method for manufacturing coated articles using the multi-component transparent coating composition is also provided. Detailed Implementation

[0016] Car wash resistance refers to the property of a coating's gloss not easily diminishing after being washed with a car wash machine. If the coating surface is damaged, the gloss will decrease. A highly wash-resistant coating has the property of being difficult to damage by car wash machine brushes. A highly wash-resistant coating can be said to have the property of mitigating deformation caused by the force applied by the car wash machine brushes, or the property of self-repairing even if the surface is damaged by the force applied by the car wash machine brushes.

[0017] Polishability refers to the ease with which a polishing (buffing) operation can be performed after the coating has formed. High polishability can be described as the ability to complete the polishing operation in a short time. Alternatively, a coating with high polishability can be described as having a surface that is not easily damaged by abrasion. In other words, high car wash resistance and high polishability are opposite properties.

[0018] Stain resistance refers to the ease with which dirt can be wiped off the surface of a coating. Higher hardness generally translates to higher stain resistance. Coatings with high stain resistance are easier to wipe off. High car wash resistance and high stain resistance are opposite properties.

[0019] The multi-component transparent coating composition disclosed herein incorporates polycarbonate polyol (B) into the main agent (corresponding to the first liquid of this disclosure). The polycarbonate polyol (B) imparts flexibility to the cross-linked structure, thereby improving car wash resistance.

[0020] Furthermore, in this disclosure, melamine resin (C) is incorporated into the main agent. Melamine resin (C) is typically used as a curing agent for hydroxyl-containing resins. However, in this disclosure, melamine resin (C), together with hydroxyl-containing acrylic resin (A) and polycarbonate polyol (B), is used as a substance that reacts with polyisocyanate compounds. The melamine resin (C) imparts hardness to the crosslinked structure, thereby improving stain resistance.

[0021] Furthermore, in this disclosure, a hydroxyl-containing acrylic resin (A) with a glass transition temperature (Tg) exceeding 10°C is incorporated. This makes deformation of the transparent coating less likely, and the surface is easier to polish, thus improving polishability. Additionally, it also improves stain resistance.

[0022] To achieve a balance between high washability and polishability, the blending ratio of polycarbonate polyol (B) and melamine resin (C) is crucial. The content of polycarbonate polyol (B) should be 6-17 parts by weight relative to 100 parts by weight of the total volume of hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C). The content of melamine resin (C) should be 1 part by weight or more but less than 10 parts by weight relative to 100 parts by weight of the total volume of hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C).

[0023] The glass transition temperature (Tg) can be calculated based on the type and amount of monomers used in the resin. Tg can be measured using a differential scanning calorimeter (DSC).

[0024] The weight-average molecular weight (Mw) was determined using the GPC method based on polystyrene.

[0025] Hydroxyl value and acid value are determined based on the mass of the solid components. Hydroxyl value and acid value can be determined by known methods described in JIS K 0070:1992. Hydroxyl value and acid value can also be calculated based on the amount of unsaturated monomers blended in the raw material monomers of the resin (e.g., hydroxyl-containing acrylic resin (A)).

[0026] Sometimes, hydroxyl-containing acrylic resins (A), polycarbonate polyols (B), and other coating-forming components containing hydroxyl groups are collectively referred to as hydroxyl-containing resins.

[0027] [Multi-component transparent coating composition] The transparent coating composition is a multi-liquid type comprising a first liquid and a second liquid. The multi-liquid transparent coating composition (hereinafter, sometimes simply referred to as transparent coating composition) may further comprise a third liquid containing other components.

[0028] The transparent coating composition is prepared using methods commonly employed by those skilled in the art. The transparent coating composition can be prepared by mixing a first liquid and a second liquid. In another embodiment, the transparent coating composition can be prepared by mixing a first liquid, a second liquid, and subsequently a third liquid. Examples of mixing methods include: kneading mixing using a kneader or rollers, and dispersion mixing using a mill or disperser.

[0029] Transparent coating compositions can be either water-based or solvent-based. Water-based coating compositions contain water as a solvent. In transparent coating compositions, the proportion of water in the solvent can be 50% by mass or more, 70% by mass or more, or 100% by mass. Solvent-based coating compositions contain an organic solvent (also known as a non-aqueous solvent) as a solvent. In solvent-based coating compositions, the proportion of organic solvent in the solvent can be 50% by mass or more, 70% by mass or more, or 100% by mass.

[0030] The solids concentration of the transparent coating composition during application is, for example, 40-60% by mass. Even with such a high solids concentration, the transparent coating composition has a low viscosity during application because melamine resin (C) has a low molecular weight. Therefore, the transparent coating film has an excellent appearance.

[0031] The solids concentration C1 of the transparent coating composition during application is the solids concentration of the transparent coating composition immediately after the first and second liquids are mixed (within 10 minutes of mixing) and just before application (within 10 minutes of application). The solids concentration C1 of the transparent coating composition during application is determined as follows: the transparent coating composition within 10 minutes of mixing the first and second liquids is heated at 140°C for 30 minutes, and the mass of the residue after heating (also known as the heating residue) is measured.

[0032] Specifically, the solid component concentration C1 during the application of the transparent coating composition can be calculated as follows. First, the mass of an appropriately sized aluminum cup (initial mass W0) is measured. Next, the transparent coating composition, in which the first and second liquids are mixed, is added to the aluminum cup within 10 minutes, and the mass (W1) is measured within 10 minutes of addition.

[0033] Next, the aluminum cup was heated at 140°C for 30 minutes, and its mass (W2) was measured again. W2 is the total mass of the solids (residual after heating) of the transparent coating composition and the aluminum cup. Finally, the concentration of the solids C1 of the transparent coating composition during application was calculated using the following formula: (W1-W0) represents the total mass of the solvent and solids remaining in the transparent coating composition immediately after application. (W2-W0) represents the mass of the solids only of the transparent coating composition.

[0034] Solid component concentration C1 (%) = 100 × (W2 - W0) / (W1 - W0) The viscosity of the transparent coating composition during application can be considered as the viscosity of the transparent coating composition before application. The solids concentration C1 of the transparent coating composition during application can be 45% by mass or more, 50% by mass or more, or 53% by mass or more. The solids concentration C1 of the transparent coating composition can be 59% by mass or less, or 58% by mass or less.

[0035] First Liquid The first liquid contains: hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C).

[0036] (A) Hydroxyl-containing acrylic resin Hydroxyl-containing acrylic resin (A) is the base resin (film-forming component) for transparent coatings. Hydroxyl-containing acrylic resin (A) reacts with polyisocyanate compounds (D) to form a cross-linked structure.

[0037] Hydroxyl-containing acrylic resin (A) has multiple (meth)acryloyl groups and one or more (typically two or more) hydroxyl groups (-OH) within one molecule.

[0038] The glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A) exceeds 10°C. If the Tg exceeds 10°C, it imparts high polishability to the transparent coating. Furthermore, it improves stain resistance. The Tg can be 15°C or higher, or 18°C ​​or higher. The Tg can be 130°C or lower. If the Tg is 130°C or lower, the quick-drying properties of the transparent coating composition are easily improved. The Tg can be 110°C or lower, 100°C or lower, 90°C or lower, or 70°C or lower. The Tg can be above 10°C and below 130°C, or it can be 15~110°C, 15~100°C, 18~90°C, or 18~70°C.

[0039] The hydroxyl value (OHV) of the hydroxyl-containing acrylic resin (A) is, for example, 90~180 mgKOH / g. If the OHV is above 90 mgKOH / g, the crosslinking density tends to be higher. If the OHV is below 180 mgKOH / g, hydrophilicity of the coating film can be suppressed, easily improving the water resistance of the transparent coating film. The OHV can be above 100 mgKOH / g or above 110 mgKOH / g. The OHV can be below 180 mgKOH / g or below 170 mgKOH / g. The OHV can be between 100~180 mgKOH / g or between 110~170 mgKOH / g.

[0040] The weight-average molecular weight (Mw) of the hydroxyl-containing acrylic resin (A) is, for example, 4,000 to 12,000. If the Mw is 4,000 or higher, the hardness and weather resistance of the resulting coating film are easily improved. If the Mw is 12,000 or lower, excessive viscosity increase in the coating composition is easily suppressed. The Mw can be 4,500 or higher, or 4,800 or higher. The Mw can be 10,000 or lower, 9,000 or lower, or 8,500 or lower. The Mw can be 4,500 to 10,000, or 4,800 to 9,000.

[0041] From the perspective of hardness, the hydroxyl-containing acrylic resin (A) has a hydroxyl value of 90~180mgKOH / g, a weight-average molecular weight of 4,000~12,000, and a Tg of 10~100℃.

[0042] Hydroxyl-containing acrylic resin (A) can be formulated by polymerizing a hydroxyl-containing α,β-ene unsaturated monomer with other α,β-ene unsaturated monomers using known methods. Hydroxyl-containing acrylic resin (A) can be formulated, for example, by solution polymerization. Commercially available hydroxyl-containing acrylic resin (A) can also be used.

[0043] Examples of hydroxyl-containing α,β-ene unsaturated monomers include: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methylallyl alcohol, and their adducts with ε-caprolactone. They can be used alone or in combination of two or more.

[0044] Examples of α,β-ene unsaturated monomers other than those mentioned above include: polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable epoxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds. They can be used alone or in combination of two or more.

[0045] (B) Polycarbonate polyols Polycarbonate polyol (B) is also a film-forming component. Polycarbonate polyol (B) reacts with polyisocyanate compound (D) to form a cross-linked structure.

[0046] Polycarbonate polyols (B) have two or more carbonate bonds (-O-(C=O)-O-) and two or more hydroxyl groups. The hydroxyl groups can be located at both ends of the molecular chain. Polycarbonate polyols (B) impart high car wash resistance to transparent coatings.

[0047] The content of polycarbonate polyol (B) is 6 to 17 parts by mass relative to the total mass of 100 parts by mass of hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C). This allows for the utilization of the high car wash resistance based on polycarbonate polyol (B), the high stain resistance based on melamine resin (C), and the high polishability based on hydroxyl-containing acrylic resin (A).

[0048] The content of polycarbonate polyol (B) can be more than 1 part by mass or more than 5 parts by mass. The content can be less than 30 parts by mass or less than 20 parts by mass. The content can be 1 to 30 parts by mass or 5 to 20 parts by mass.

[0049] The number-average molecular weight (Mn) of the polycarbonate polyol (B) is, for example, 300 to 2,000. This further improves its resistance to car washes. The aforementioned Mn can be 400 or higher, or 450 or higher. The aforementioned Mn can be 1,750 or lower, 1,500 or lower, or 1,300 or lower. The aforementioned Mn can be 400 to 1,500, or 450 to 1,300.

[0050] The hydroxyl value (OHV) of the polycarbonate polyol (B) is, for example, 50~500 mgKOH / g. The above-mentioned OHV can be 50~250 mgKOH / g or 100~250 mgKOH / g.

[0051] Polycarbonate polyols (B) are obtained, for example, by reacting a polyol with a polycarbonate such as an alkylene dicarbonate. Examples of polyols include ethylene glycol, glycerol, trimethylolpropane, propylene glycol, tetramethylene glycol, and pentaerythritol. They can be used alone or in combination of two or more.

[0052] Examples of polycarbonate polyols (B) include polyhexamethylene carbonate diol and polyethylene carbonate diol. They can be used alone or in combination of two or more.

[0053] Commercially available polycarbonate polyols include, for example: DURANOL T5650E (manufactured by Asahi Kasei Corporation), C-590 (manufactured by Kuraray Corporation), and ETERNACOLL PH-50 (manufactured by Ube Industries, Ltd.).

[0054] (C) Melamine resin Melamine resin (C) is the film-forming component. As described above, melamine resin (C) reacts with hydrophilic polyisocyanate compound (D) and is incorporated into the cross-linked structure of hydroxyl-containing resin (A) and hydrophilic polyisocyanate compound (D), thereby imparting high car wash resistance to the coating.

[0055] Melamine resin (C) contains: 6 substituents R 1 ~R 6 Through 3 nitrogen atoms N 1 ~N 3 The structure (-N) bonded around the triazine ring (triazine nucleus) 1 (R 1 (R) 2 ), -N 2 (R 3 (R) 4 ), -N 3 (R 5 (R) 6 )).

[0056] Melamine resin (C) is represented, for example, by the following general formula (1): In the formula, the substituent R 1 ~R 6 Each can independently represent a hydrogen atom, an alkyl ether group, a hydroxymethyl group, or a bonded portion of another triazine ring.

[0057] Constituting alkyl ethers (-CH2-OR) 7 ) alkyl (R 7 The number of carbon atoms in R can be 1 to 8, or 1 to 4. 7 It can be linear or branched. R 7 It can be methyl, ethyl, propyl, or butyl.

[0058] Melamine resin (C) is typically composed of a polynuclear structure consisting of multiple triazine rings bonded together. Melamine resin (C) can also be a mononuclear structure consisting of a single triazine ring.

[0059] Examples of melamine resins (C) include those with -N(-CH2-OR) 7 )(-CH2OH) hydroxymethyl type; having -N(-CH2-OR 7 (H) imino form; possessing -N(-CH2-OR) 7 (-CH2OH) and -N(-CH2-OR) 7 )(H) hydroxymethyl / imino type.

[0060] Substituent R 1 ~R 6 At least one of the components can be hydroxymethyl or imino. This improves both wash resistance and polishability. The melamine resin (C) can be hydroxymethyl, imino, or a hydroxymethyl / imino type.

[0061] The average total number of imino groups and hydroxymethyl groups in each triazine ring (hereinafter sometimes simply referred to as the average functional group number) is, for example, 0.3 to 3.1. As a result, melamine resin (C) is readily absorbed into the aforementioned crosslinking structure, and the coating becomes rigid. The average functional group number can be 0.5 or more, or 1.0 or more. The average functional group number can be 2.8 or less, or 2.5 or less. The average functional group number can be 0.5 to 2.8, or 1.0 to 2.5.

[0062] Substituent R 1 ~R 6 At least one of them can be an alkyl ether group (-CH2-OR) 7 R 7 It can be methyl or butyl. The ratio of methyl to butyl (methyl:butyl) is, for example, 100:0 to 20:80. The ratio (methyl:butyl) can be 90:10 to 30:70, or 80:20 to 40:60. By using the above-mentioned melamine resin, in addition to obtaining good antifouling properties, the viscosity of the coating composition can be adjusted to an appropriate range, which has the advantage of achieving a good coating appearance.

[0063] Melamine resin (C) is dissolved or micro-dispersed in transparent coating compositions. The solubility parameter (SP value) of melamine resin (C) can be determined by the cloud point method. Acetone is used as a good solvent (based on the HSP value determined by Hansen). d g (SP value is 9.77), hexane is a poor solvent (SP value). d pl (SP value is 7.24) and deionized water (SP value) d ph (23.50). The SP value of melamine resin (C) based on the cloud point method using these good and bad solvents can be 9.5 or higher. The above SP value can be 10.0 or higher, or 11.0 or higher. The above SP value can be 14.8 or lower, or 14.5 or lower. The above SP value can be 9.5 to 14.8, 10.0 to 14.8, or 11.0 to 14.5.

[0064] The SP value of melamine resin (C) can be determined by dissolving melamine resin (C) in a good solvent with a known SP value and performing turbidity titration with a poor solvent with a higher SP value than the good solvent and a poor solvent with a lower SP value than the good solvent. For the method of determining the SP value, see reference 1: CM Hansen J. Paint. Tech., 39

[505] , 104 (1967) and reference 2: Kobayashi Toshikatsu Color Materials, 77 [4], 188-192 (2004)).

[0065] The SP value of melamine resin (C) can be determined as follows.

[0066] Measurement temperature: 20℃ Good solvent: Acetone (HSP value) d g =9.77) Unsuitable solvent: Hexane (SP value) d pl =7.24), deionized water (SP value) d ph =23.50) Sample: Weigh 0.5g of melamine resin (C) into a 100ml beaker, add 10ml of good solvent using a full-volume pipette, and dissolve with a magnetic stirrer.

[0067] (Turbidity Measurement) Add hexane dropwise to the sample and calculate the volume fraction of hexane at the point that produces turbidity. f pl Next, the SP value of melamine resin (C) when using hexane as a poor solvent is calculated according to the following formula. dml .

[0068] [Mathematical Expression 1] In addition, deionized water was added dropwise to the same prepared sample, and the volume fraction of deionized water at the points that produced turbidity was calculated. f ph Next, the SP value of melamine resin (C) when using deionized water as a poor solvent is calculated according to the following formula. d mh .

[0069] [Mathematical Expression 2] The SP value of melamine resin (C) d poly )for d ml and d mh The intermediate value is calculated by the following formula.

[0070] [Mathematical Expression 3] In melamine resin (C), the average total number of imino groups and hydroxymethyl groups per triazine ring is 0.3 to 3.1, and the solubility parameter can be above 9.5. This further improves the antifouling properties.

[0071] The weight-average molecular weight (Mw) of melamine resin (C) is 400 or higher and less than 4000. This provides a good balance of antifouling, wash resistance, and polishing properties. The aforementioned Mw can be below 3,500 or below 3,000. Alternatively, the aforementioned Mw can be above 450 or above 500. Or, the aforementioned Mw can be between 450 and 3,500, or between 500 and 3,000.

[0072] Of 100 parts by mass of the total components of hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C), the content of melamine resin (C) is 1 part by mass or more but less than 10 parts by mass. This allows for the utilization of the high polishability based on polycarbonate polyol (B), the high car wash resistance based on melamine resin (C), and the high stain resistance based on hydroxyl-containing acrylic resin (A).

[0073] The content of melamine resin (C) can be 2 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more. The content can be 9 parts by mass or less, or 8 parts by mass or less. The content can be 2 to 9 parts by mass, 4 to 9 parts by mass, or 5 to 8 parts by mass.

[0074] The solid content mass ratio (C / B) of polycarbonate polyol (B) to melamine resin (C) is, for example, 0.3 to 0.95. This results in a better balance between stain resistance and washability. C / B can be below 0.7 or below 0.6. C / B can be above 0.32, above 0.4, or above 0.5. C / B can be between 0.32 and 0.7, between 0.32 and 0.7, between 0.4 and 0.6, or between 0.5 and 0.7.

[0075] (Other hydroxyl-containing resins) The first liquid may contain other hydroxyl-containing resins. Examples of other hydroxyl-containing resins include: polyether polyol resins, hydroxyl-containing polyurethane resins, and polyester polyol resins. They may be used alone or in combination of two or more.

[0076] Compared to the total amount of 100 parts by mass of hydroxyl-containing acrylic resin (A), polycarbonate polyol (B) and melamine resin (C), the amount of other hydroxyl-containing solid components is, for example, 10 parts by mass or less, or 5 parts by mass or less, or 3 parts by mass or less.

[0077] (solvent) The first liquid may contain a solvent. The solvent may be water or a non-aqueous solvent.

[0078] Examples of non-aqueous solvents include: aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, and mineral spirit; ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl isobutyl ketone, methyl pentyl ketone, and cyclohexanone; aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, propylbenzene, tert-butylbenzene, o-xylene, m-xylene, p-xylene, tetrahydronaphthalene, and decahydronaphthalene; ester organic solvents such as methyl acetate, ethyl acetate, butyl acetate, amyl acetate, ethyl propionate, methyl propionate, and ethyl 3-ethoxypropionate; and methyl cellosolves, ethyl cellosolves, n-propyl cellosolves, and isopropyl cellosolves. Solvents such as n-butyl, isobutyl, isopentyl, phenyl, and benzyl are organic solvents; carbitols such as methyl carbitol, ethyl carbitol, n-propyl carbitol, isopropyl carbitol, n-butyl carbitol, isobutyl carbitol, isopentyl carbitol, carbitol acetate, phenyl carbitol, and benzyl carbitol are carbitol-based organic solvents; and diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, and diethylene glycol butyl methyl ether are also available. Diethyl 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 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, butanediol Dimethyl ether, butanediol diethyl ether, butanediol di-n-butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, 2-butoxyethyl tetraethoxyethyl ether, and other glycol ether-based organic solvents; 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, and other acetate-based organic solvents; methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and other alcohol-based solvents. These can be used individually or in combination of two or more.

[0079] (Modulation method) The first liquid can be prepared by mixing the above-mentioned components using methods known to those skilled in the art. Examples of such mixing methods include those used for preparing transparent coating compositions.

[0080] ·Second liquid The second liquid contains a polyisocyanate compound (D).

[0081] (D) Polyisocyanate compounds The polyisocyanate compound (D) is a curing agent that reacts with hydroxyl-containing resins and melamine resins (C) to form a cross-linked structure, thereby curing the multi-component transparent coating composition. The polyisocyanate compound (D) has at least two isocyanate groups in one molecule.

[0082] In this specification, "isocyanate group" refers to an unblocked free isocyanate group. Because the isocyanate group is not blocked, it can be cured, for example, in low-temperature regions.

[0083] Examples of polyisocyanate compounds (D) include: aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having an aromatic ring in the molecule that is not bonded to an isocyanate group (aromatic aliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specifically, examples include: aromatic polyisocyanates such as toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, phenylenediamine diisocyanate, and isophthalic diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; and polymers of these polyisocyanates in biuret, ureate, or adduct forms. They can be used alone or in combination of two or more.

[0084] The equivalent ratio (NCO / OH) of the isocyanate groups in the polyisocyanate compound (D) to the hydroxyl groups in the hydroxyl-containing resin can be 0.7 or more, or 0.8 or more. The equivalent ratio (NCO / OH) can be 2.0 or less, 1.8 or less, or 1.5 or less. In one embodiment, the equivalent ratio (NCO / OH) is 0.7 or more and 2.0 or less. If the equivalent ratio (NCO / OH) is within this range, a transparent coating film with excellent hardness and weather resistance can be easily formed.

[0085] (Other curing agents) Multi-component transparent coating compositions may contain curing agents other than polyisocyanate compounds (D). Examples of other curing agents include, for instance, amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. They may be used alone or in combination of two or more. The content of other curing agents is appropriately determined based on the hydroxyl-containing resin.

[0086] The second solution may contain melamine resin (including melamine resin (C)) as a curing agent. From the viewpoint of storage stability, the less melamine resin contained in the second solution, the better. The mass ratio of melamine resin to polyisocyanate compound (D) solids (melamine resin / polyisocyanate compound (D)) can be less than 0.2 parts by mass, less than 0.1 parts by mass, or even 0 parts by mass.

[0087] (solvent) The second liquid may contain a solvent that does not have a hydroxyl group. Examples of such solvents include: the glycol ether-based organic solvents described above; the acetate-based organic solvents described above; the ketone-based organic solvents described above; and the ester-based organic solvents described above. They may be used alone or in combination of two or more.

[0088] (Modulation method) The second liquid can be prepared by mixing the above-mentioned components using methods known to those skilled in the art. Examples of such mixing methods include the same method used for preparing the first liquid.

[0089] (Other ingredients) Transparent coating compositions may contain additives commonly used in the coatings industry. These additives may be added to any of the first, second, and third liquids. Examples of additives include, for instance, pigments, UV absorbers, hindered amine light stabilizers, antioxidants, crosslinking resin particles, leveling agents, defoamers, curing accelerators, and viscosity modifiers.

[0090] [Painted Items] A coated article is obtained using the transparent coating composition disclosed herein. The coated article includes, for example, a substrate; and a multilayer coating comprising a base coating and a transparent coating. The transparent coating is formed from the transparent coating composition disclosed herein. Therefore, the coated article exhibits excellent colorfastness and appearance.

[0091] A base coat is disposed between the substrate and the clear coat. A multilayer coating may further include an intermediate coat disposed between the substrate and the base coat. That is, the coated article may include: a substrate; and a multilayer coating consisting of an intermediate coat, a base coat, and a clear coat layered sequentially.

[0092] When the object to be coated is made of resin, the multilayer coating may further include a primer film disposed between the object to be coated and the base coating. That is, the coated article may include: an object to be coated; and a multilayer coating consisting of a primer film, a base coating, and a clear coat layered sequentially.

[0093] (Object to be painted) Materials that can be coated include, for example, metal, resin, and glass. More specifically, examples of objects that can be coated include: car bodies and parts used in cars, trucks, motorcycles, buses, etc., such as spoilers, bumpers, rearview mirror covers, grilles, and door handles.

[0094] Examples of metals include iron, copper, aluminum, tin, zinc, or their alloys (e.g., steel). Representative examples of metal coatings include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy steel sheets, zinc-iron alloy steel sheets, zinc-magnesium alloy steel sheets, zinc-aluminum-magnesium alloy steel sheets, aluminized steel sheets, aluminized-silicon alloy steel sheets, tin-plated steel sheets, and so on.

[0095] Metallic substrates can also undergo surface treatment. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium formation treatment, and composite oxide treatment. After surface treatment, metallic substrates can be further coated with electrodeposited coatings. Electrodeposited coatings can be cationic or anionic.

[0096] Examples of resins include: polypropylene resin, polycarbonate resin, polyurethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. Resin-coated substrates can be degreased. Resin-coated substrates can also undergo surface treatment.

[0097] (Intermediate coating) The intermediate coating film is formed from the intermediate coating composition. The intermediate coating 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 dried film thickness of the intermediate coating film can be 10 μm or more. The dried film thickness of the intermediate coating film can be 50 μm or less.

[0098] The coating thickness can be measured using an electromagnetic thickness gauge (e.g., the SDM-miniR manufactured by SANKO). The coating thickness is the average of the coating thickness at any 5 points.

[0099] (Primer coating) A primer film is sandwiched between the substrate and the base coat. The primer film improves the adhesion between the base coat and the substrate (especially resin-based substrates). Furthermore, in cases where the substrate surface is uneven, the primer application helps to create a more uniform coating surface and effectively suppresses unevenness in the base coat.

[0100] A primer coating film is formed, for example, from a primer coating composition comprising film-forming components, raw material adhesion components, viscosity modifiers, diluents, pigments, and, if necessary, a curing agent. The primer coating composition may contain various of the aforementioned additives, if desired. The primer coating composition may be solvent-based or water-based.

[0101] Examples of components that can be included as film-forming agents, curing agents, viscosity modifiers, diluents, and pigments in the base coating composition described below are: The viscosity of the water-based primer coating composition, measured at 20°C using a type B viscometer, is, for example, 500 cps / 6 rpm or more and 6,000 cps / 6 rpm or less. The solids content of the primer coating composition is, for example, 30% by mass or more and 50% by mass or less. The solids content of the primer coating composition is all the components remaining after removing the diluent from the primer coating composition.

[0102] There are no specific limitations on the thickness of the primer film. Considering the smoothness and chip resistance of the coated item, the primer film thickness can be 5μm or more but less than 40μm. The primer film thickness can be 7μm or more. The primer film thickness can be less than 25μm.

[0103] (Basic coating) The base coating is formed from a base paint composition. The base paint composition will be described later. The base coating can be a single layer or a multilayer film of two or more layers. The base coating imparts design characteristics to the coated article. The dried film thickness of each base coating layer is, for example, 5 μm or more and 35 μm or less. The dried film thickness of each base coating layer can be 7 μm or more. The dried film thickness of each base coating layer can be 30 μm or less.

[0104] (Transparent coating) The transparent coating film is formed from the multi-component transparent coating composition disclosed herein. The dried film thickness of the transparent coating film is, for example, 10 μm or more and 80 μm or less. The dried film thickness of the transparent coating film may be 20 μm or more. The dried film thickness of the transparent coating film may be 60 μm or less.

[0105] [Manufacturing Method for Painted Items] The aforementioned coated articles can be manufactured, for example, by the following method, which includes: applying a base coating composition to a substrate to form an uncured base coating film; applying the transparent coating composition disclosed herein to the uncured base coating film to form an uncured transparent coating film; and simultaneously curing the uncured base coating film and the uncured transparent coating film.

[0106] Before applying the base coating composition, a mid-coat composition (or primer composition, hereinafter the same) may be applied to the substrate. When applying the base coating composition, the mid-coat film (or primer film, hereinafter the same) may or may not be cured. The mid-coat film may be cured when applying the base coating composition.

[0107] That is, the coated article can be manufactured by the following method (two-coat-one-bake method), the method comprising: applying a mid-coat paint composition to the object to be coated, and then curing it to form a cured mid-coat film; sequentially applying a base paint composition and a clear paint composition to the cured mid-coat film to form an uncured base paint film and a clear paint film in sequence; and simultaneously curing the uncured base paint film and the clear paint film.

[0108] Alternatively, coated articles can be manufactured by the following method (three-coat-one-bake method), which includes: sequentially applying a mid-coat paint composition, a base paint composition, and a clear paint composition to a workpiece to sequentially form an uncured mid-coat film, a base paint film, and a clear paint film; and simultaneously curing the uncured mid-coat film, the base paint film, and the clear paint film.

[0109] The following example illustrates the process of manufacturing a coated article with a multi-layered coating consisting of a mid-coat, a base coat, and a clear coat, using a two-coat, one-bake method. However, the manufacturing method for the coated article is not limited to this.

[0110] (I) Formation of a cured intermediate coating film First, a mid-coat paint composition is applied to the substrate to form an uncured mid-coat film. This mid-coat film improves the adhesion between the base coat and the substrate. Furthermore, the mid-coat application makes the coating surface more uniform, easily suppressing unevenness in the base coat.

[0111] Examples of coating methods include roller coating, air spray coating, airless spray coating, and rotary atomization coating. These methods can also be combined with electrostatic coating. From the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferred. In rotary atomization electrostatic coating, for example, rotary atomization electrostatic coating machines commonly referred to as "Micro·Micro Bell (μμBell)," "Micro Bell (μBell)," or "Metallic Bell (MetaBell)" can be used.

[0112] Next, the uncured intermediate coating film is cured. The intermediate coating composition can be cured by heating. The curing (heating) conditions are appropriately set according to the composition of the intermediate coating composition or the material of the object being coated. The heating temperature is, for example, 100°C or higher and 180°C or lower, or 120°C or higher and 160°C or lower. The heating time can be appropriately set according to the heating temperature. When the heating temperature is 100°C or higher and 180°C or lower, the heating time is, for example, 10 minutes or higher and 60 minutes or lower, or 10 minutes or higher and 30 minutes or lower. The heating time refers to the time during which the target temperature is reached in the heating device and the object being coated is held at the target temperature, excluding the time before the target temperature is reached. Examples of heating devices include, for example, a drying oven that uses a heating source such as hot air, electricity, gas, or infrared radiation.

[0113] (Intermediate Coating Composition) The intermediate coating composition can be water-based or solvent-based.

[0114] In addition to various solvents, the intermediate coating composition also includes, for example, resins, pigments, and various additives. Examples of resins include: acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluoropolymers, epoxy resins, and polyether resins. These can be used alone or in combination of two or more. The intermediate coating composition may further include the aforementioned curing agents.

[0115] (II) Formation of an uncured base coating A base coating composition is applied over a cured intermediate coating to form an uncured base coating. Two or more uncured base coatings can be formed by applying the same or different base coating compositions twice or more. A few minutes' interval can be set between the application of the nth base coating composition and the (n+1)th base coating composition.

[0116] As a coating method, for example, the same method as the coating method for intermediate coating compositions can be cited.

[0117] Pre-drying (also known as preheating) can be performed after applying the base coating composition and before applying the clear coat composition. This suppresses the sudden boiling of diluents in the base coating composition during the curing process, thus easily inhibiting foaming. Furthermore, pre-drying prevents the uncured base coating from mixing with the clear coat composition, making it difficult to form mixed layers. Therefore, the smoothness of the resulting coated article can be further improved.

[0118] As a pre-drying process, examples include: placing the product at a temperature of 20°C or higher and 25°C or lower for 5 to 15 minutes; or heating it at a temperature of 50°C or higher and 80°C or lower for 30 to 10 minutes.

[0119] (Base coating composition) The base coating composition can be water-based or solvent-based. Water-based base coating compositions may include, for example, acrylic resin emulsions, water-soluble acrylic resins, curing agents (typically melamine resins), and polyether polyol resins. Base coating compositions typically contain at least one of coloring pigments and gloss pigments. Base coating compositions may further contain various additives.

[0120] (III) Formation of an uncured transparent coating The transparent coating composition disclosed herein is applied onto an uncured base coating to form an uncured transparent coating.

[0121] There are no particular limitations on the coating method. For example, a method similar to the method used for coating the intermediate coat composition can be cited. From the viewpoint of coating efficiency, rotary atomizing electrostatic coating is preferred. After applying the clear coat composition, pre-drying can also be performed in the same manner as described above.

[0122] (IV) Curing This process allows both the uncured base coat and the clear coat to cure in one step. Each coat can be cured by heating.

[0123] The heating temperature can be, for example, 80~160℃. The heating temperature can be above 85℃ or above 90℃. The heating temperature can be below 150℃ or below 145℃. The heating temperature can be 85~150℃ or 90~145℃.

[0124] The heating time can be set appropriately according to the heating temperature. When the heating temperature is 80~160℃, the heating time can be, for example, more than 10 minutes and less than 60 minutes, or more than 15 minutes and less than 45 minutes. Example

[0125] The invention is illustrated in more detail by means of the following examples, but the invention is not limited thereto. In the examples, unless otherwise stated, "parts" and "%" refer to the mass of the resin solids component.

[0126] [Manufacturing Example 1-1] Manufacturing of Hydroxyl Acrylic Resin (A-1) 24.2 parts by mass of butyl acetate were added to a container equipped with a stirrer, temperature control device, reflux cooler, and dropping funnel, and the temperature was raised to 120°C. Over 3 hours, a monomer solution (a mixture 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 mixture of 11.0 parts by mass of tert-butyl peroxide and 5 parts by mass of butyl acetate were added dropwise to the container.

[0127] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butyl peroxide and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. Then, after reacting at 120°C for 1 hour, 7 parts by mass of butyl acetate were added. This yielded a varnish with a solid content of 64% by mass of hydroxyl-containing acrylic resin (A-1), containing Mw 8,200, hydroxyl value 160 mg KOH / g, acid value 10 mg KOH / g, and Tg 20°C.

[0128] [Manufacturing Examples 1-2] Manufacturing of Hydroxyl Acrylic Resin (A-2) 24.2 parts by mass of butyl acetate were added to a container equipped with a stirrer, temperature control device, reflux cooler, and dropping funnel, and the temperature was raised to 120°C. Over 3 hours, a monomer solution (a mixture 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 mixture of 11.0 parts by mass of tert-butyl peroxide and 5 parts by mass of butyl acetate were added dropwise to the container.

[0129] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butyl peroxide-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. Then, after reacting at 120°C for 1 hour, 7 parts by mass of butyl acetate were added. This yielded a varnish with a solid content of 64% by mass of hydroxyl-containing acrylic resin (A-2), comprising Mw 7,800, hydroxyl value 160 mg KOH / g, acid value 20 mg KOH / g, and Tg 10°C.

[0130] [Manufacturing Examples 1-3] Manufacturing of Hydroxyl Acrylic Resin (A-3) 40 parts by weight of SOLVESSO 100 and 13 parts by weight of butanol were added to a container equipped with a stirrer, temperature control device, reflux cooler and dropping funnel, and the temperature was raised to 120°C. Over 3 hours, a monomer solution (a mixture of 30 parts by weight of styrene, 13 parts by weight of 2-ethylhexyl acrylate, 4 parts by weight of n-butyl methacrylate, 12 parts by weight of ACRYESTER SL (manufactured by Mitsubishi Chemical Corporation, with a lauryl methacrylate / tridecyl methacrylate mixing ratio (by mass) of 4 / 6), 18 parts by weight of 2-hydroxypropyl acrylate, 2 parts by weight of acrylic acid and 21 parts by weight of PLACEL FM2D) and a mixed solution of 11.0 parts by weight of tert-butyl peroxide and 5 parts by weight of butyl acetate were added dropwise to the container.

[0131] After standing for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butyl peroxide-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. Then, after reacting at 120°C for 1 hour, 7 parts by mass of butyl acetate were added. This yielded a varnish with a solid content of 60% by mass of hydroxyl-containing acrylic resin (A-3), containing Mw 14,000, hydroxyl value 120 mg KOH / g, acid value 15 mg KOH / g, and Tg -8°C.

[0132] [Polycarbonate polyol (B)] (B-1): Trade name "DURANOL T5650E", manufactured by Asahi Kasei Chemicals Co., Ltd., polycarbonate glycol, hydroxyl value 225 mgKOH / g, average hydroxyl number 2, Mn 500 (B-2): Trade name "DURANOL T5651", manufactured by Asahi Kasei Chemicals Co., Ltd., polycarbonate diol, hydroxyl value 110mgKOH / g, average number of hydroxyl groups 110, Mn 1000.

[0133] [Melamine resin (C)] Use melamine resin (C) with the properties shown in Table 1.

[0134] [Example 1] (1) Preparation of the first liquid 80 parts of the above-mentioned hydroxyl-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 (trade name "Tinuvin 384", manufactured by BASF Japan), 1.4 parts of light stabilizer (trade name "Tinuvin 123", manufactured by BASF Japan), 1.4 parts of acrylic surface conditioner, 57.0 parts of methyl amyl ketone and 22.0 parts of DBE (manufactured by Showa Chemical Co., Ltd.) were added sequentially to a 1L metal container and stirred thoroughly using a disperser to obtain the first liquid.

[0135] (2) Preparation of the second liquid In addition, 40.0 parts of polyisocyanate compound (D) (trade name "Desmodur N-3300", manufactured by Sumitomo Bayer Urethane, NCO active ingredient 22%) and 2-ethylethoxypropanol were added sequentially to a metal container and stirred thoroughly to obtain a second liquid.

[0136] (3) Preparation of multi-component transparent coating composition The first and second liquids were mixed to obtain a multi-liquid transparent coating composition. The solid content C1 of the multi-liquid transparent coating composition, as determined above, was 55% by mass during application.

[0137] (4) Production of painted items On a 150×300×0.8mm matte steel plate treated with zinc phosphate, POWERNICS 1010 (a cationic electrodeposition coating manufactured by Nippon Paint Automotive Coatings) and ORGA P-30 (a mid-coat coating manufactured by Nippon Paint Automotive Coatings) were applied to achieve dry film thicknesses of 20μm and 40μm, respectively.

[0138] Next, AR-3020 Black (manufactured by NipponPaint Automotive Coatings, a water-based base coating) was applied by air spray to achieve a dry film thickness of 15 μm and dried at 80°C for 5 minutes to form an uncured base coating film.

[0139] The above transparent coating composition was diluted separately in a Ford cup No. 4 with a diluent consisting of n-butyl acetate / ethyl 3-ethoxypropionate = 1 / 2 (mass ratio) to achieve 30 seconds / 20°C.

[0140] A diluted transparent coating composition was applied by air spraying to achieve a dry film thickness of 40 μm, forming an uncured transparent coating film. After standing for 7 minutes, it was sintered and cured at 140°C for 25 minutes to form a multilayer coating film. This process yielded a coated article.

[0141] [Examples 2-10 and Comparative Examples 1-10] Except for changing the type and amount of the blending components as shown in Tables 2 and 3, a multi-component transparent coating composition was prepared using the same procedure as in Example 1 to obtain coated articles.

[0142] [evaluate] The coated items described above were used as test panels, and the following evaluation was conducted. The evaluation results are shown in Tables 2 and 3.

[0143] (1) Car wash resistance The car wash test machine was used to conduct the test according to the test method of ISO 20566.

[0144] First, the brightness of the test panel surface before the evaluation test was measured using a variable light difference meter (manufactured by Suga Test Instruments Co., Ltd.), and L0 was calculated. In the brightness measurement, the incident light was set to be perpendicular to the coating measurement surface, and the angle of reception (acceptance angle) of the reflected light was set to be 10 degrees away from the incident light.

[0145] A test solution (containing 8 types of JIS Z8901 test powders) was applied to the test panel. The surface of the test panel was washed with running water using a car wash test machine. After repeating this operation 50 times, the surface of the test panel was wiped with alcohol. Then, it was washed with water and blown with air. Afterward, the brightness L1 was measured in the same manner as above, and the difference from the initial value L0 was calculated (ΔL1 = L0 - L1). The smaller this difference, the better the car wash scratch resistance (scratch resistance). ΔL1 was evaluated according to the following criteria.

[0146] [Evaluation Criteria] A: △L1<5 B: 5 ≤ △L1 ≤ 10 C: 10 < △L1.

[0147] (2) Polishability For the test plate, perform the polishing operation according to the following guidelines.

[0148] use ＃A portion of the test panel was wet-polished using 3000 g / m² water-resistant abrasive paper. Next, a coarse polishing wheel and a coarse polishing compound were used to polish this portion, removing the paper scratches caused by the water-resistant abrasive paper. Then, a secondary polishing wheel and a secondary polishing compound were used to polish this portion, removing the scratches caused by the coarse polishing wheel. Finally, a finishing wheel and a finishing compound were used, with halogen lamp light incident vertically onto the coating, to perform finishing polishing until the surface finish of the polished and unpolished areas reached the same level visually.

[0149] The above operations were performed at three locations on the same test plate, and the total time required for polishing operations at the three locations (total time) was evaluated using the following evaluation criteria.

[0150] [Evaluation Criteria] A: The total time is less than 150 seconds. B: Total time is 150 seconds or more but less than 180 seconds. C: The total time is more than 180 seconds.

[0151] (3) Anti-fouling properties A mixture of eight test powders as shown in JIS Z8901:2006, JSTM pigment carbon black, and JSTM pigment synthetic loess was applied to the surface of a test panel via air spraying. It was then dried in an oven. This process was repeated eight times. Following steam spraying, any contaminants were wiped off with flannel while running water.

[0152] Next, measure the brightness L2 in the same manner as above, and calculate the difference between it and the initial value L0 (ΔL = L0 - L2). The smaller this difference, the better it can be said that the dirt has been wiped away and the better the stain resistance. Evaluate ΔL2 according to the following criteria.

[0153] [Evaluation Criteria] A: △L2<0.5 B: 0.5 ≤ △L² ≤ 1.0 C: 1.0 < △L2.

[0154] (4) Thermal cycling test After placing the test plate at 23±2℃ (room temperature) for 2 hours, repeat the operation of (i) to (iv) below 10 times as one cycle, and then let the test plate stand in the test chamber for 2 hours.

[0155] (i) Heat in a thermostat at -90±2℃ and below 20% humidity for 4 hours. (ii) After being placed at room temperature for 30 minutes, cool at -40±2℃ for 1.5 hours. (iii) After being placed at room temperature for 30 minutes, it is heated for 3 hours in a thermostat with a temperature of -70±2℃ and a humidity of 95% or higher. (iv) After being placed at room temperature for 30 minutes, cool at -40±2℃ for 1.5 hours, and then place at room temperature for 30 minutes.

[0156] Next, visually inspect the coating on the test panel for cracks and bulges. Evaluate the results according to the following criteria.

[0157] [Evaluation Criteria] A: No cracks (fissures) were observed. B: Fine cracks were observed and could be confirmed with a magnifying glass. C: Cracks observed visually D: Obvious cracks were observed visually.

[0158] (5) Storage stability The thickening rates of the first and second liquids of the transparent coating composition were determined using the following procedure.

[0159] The first and second liquids, freshly prepared (within 10 minutes of preparation), were each poured into a 250mL container, filling it to three-quarters full. The viscosity (viscosity at preparation) was measured at 23°C and 60rpm using a Type B viscometer (VISCOMETER TVB-10; manufactured by Toki Sangyo Co., Ltd.).

[0160] After measuring the viscosity, place the container in a sealed state at 23°C and measure the viscosity after 2 hours (viscosity after storage). Calculate the viscosity change rate using the following formula and evaluate it according to the following standards.

[0161] Viscosity change rate [%] = 100 × (viscosity after storage stability test - viscosity at the time of preparation) / initial viscosity [Evaluation Criteria] A: Viscosity change rate is below 150% B: Viscosity change rate exceeds 150%.

[0162] (6) Appearance The long wave (LW) value (measurement wavelength: 1,300~12,000 μm) was measured using a Wave-Scan DOI (trade name, manufactured by BYK-Gardner) and evaluated according to the following criteria. The smaller the LW value, the smoother the coating.

[0163] [Evaluation Criteria] A: LW≤2.0 B: 2.0 < LW ≤ 4.0 C: 4.0 < LW.

[0164] The transparent coatings formed from the multi-liquid transparent coating compositions of the embodiments all exhibit excellent wash resistance, as well as polishability and stain resistance.

[0165] In Comparative Example 1, the melamine resin (C) had poor polishability and poor stain resistance because its Mw exceeded 4000.

[0166] In Comparative Example 2, the Tg of the hydroxyl-containing acrylic resin (A) is below 10°C, resulting in poor antifouling properties.

[0167] In Comparative Example 3, the Tg of the hydroxyl-containing acrylic resin (A) was lower than that of Comparative Example 2, and its anti-fouling and polishing properties were both poor.

[0168] In Comparative Example 4, the first liquid does not contain melamine resin (C), so its antifouling properties are poor.

[0169] In Comparative Example 5, the polishability was poor due to the excessive presence of melamine resin (C).

[0170] In Comparative Example 6, since it does not contain polycarbonate polyol (B), it has poor car wash resistance.

[0171] In Comparative Example 7, the car wash resistance was poor due to the low content of polycarbonate polyol (B).

[0172] In Comparative Examples 8 and 9, the polishability and stain resistance were poor due to the excessive content of polycarbonate polyol (B).

[0173] In Comparative Example 10, the stain resistance was poor because a polyester polyol was used instead of polycarbonate polyol (B).

[0174] This disclosure includes the following schemes.

[0175] [1] A multi-component transparent coating composition comprising: A first liquid containing hydroxyl-containing acrylic resin (A), polycarbonate polyol (B), and melamine resin (C); and The second liquid contains polyisocyanate compound (D). The glass transition temperature of the hydroxyl-containing acrylic resin (A) exceeds 10°C. The melamine resin (C) has a weight-average molecular weight of 400 or more and less than 4000. Relative to 100 parts by weight of the total solids of the hydroxyl-containing acrylic resin (A), the polycarbonate polyol (B), and the melamine resin (C), the content of the polycarbonate polyol (B) is 6 to 17 parts by weight. The content of melamine resin (C) is more than 1 part by mass and less than 10 parts by mass relative to the total solid content of the hydroxyl-containing acrylic resin (A), the polycarbonate polyol (B) and the melamine resin (C).

[0176] [2] The multi-component transparent coating composition of [1] above, wherein the solid component mass ratio (C / B) of the polycarbonate polyol (B) to the melamine resin (C) is 0.3 to 0.95.

[0177] [3] The multi-liquid transparent coating composition of [1] or [2] above, wherein the number average molecular weight of the polycarbonate polyol (B) is 300 to 2000.

[0178] [4] The multi-liquid transparent coating composition of any one of [1] to [3] above, wherein the average total number of imino groups and hydroxymethyl groups of each triazine ring in the melamine resin (C) is 0.3 to 3.1, and the solubility parameter of the melamine resin (C) is 9.5 or higher.

[0179] [5] A multi-component transparent coating composition of any one of [1] to [4] above, wherein the melamine resin (C) has an alkyl ether group bonded to a nitrogen atom. The ratio of methyl to butyl groups in the alkyl ether group (methyl:butyl) is 100:0 to 20:80.

[0180] [6] A method for manufacturing a coated article, comprising: A base coating composition is applied to the substrate to form an uncured base coating film. Applying any one of the above [1] to [5] multi-liquid transparent coating compositions onto the uncured base coating film to form an uncured transparent coating film; and The uncured base coating and the uncured transparent coating are cured simultaneously.

[0181] [7] The method for manufacturing coated articles described in [6] above, wherein the concentration of solid components in the multi-component transparent coating composition during coating is 40 to 60% by mass.

[0182] Industrial applicability The multi-component transparent coating composition of the present invention is a multi-component transparent coating composition that yields a transparent coating film with excellent car wash resistance, polishability, and stain resistance. Therefore, it is suitable for forming various transparent coating films, especially automotive transparent coating films.

Claims

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

2. The multi-liquid transparent 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 multi-component transparent coating composition according to claim 1 or 2, wherein, The number average molecular weight of the polycarbonate polyol (B) is 300-2000.

4. The multi-component transparent coating composition according to claim 1 or 2, wherein, In the melamine resin (C), the average total number of imino groups and hydroxymethyl groups in each triazine ring is 0.3 to 3.1, and the solubility parameter of the melamine resin (C) is 9.5 or higher.

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

80.

6. A method for manufacturing a coated article, comprising: A base coating composition is applied to the substrate to form an uncured base coating film. Applying the multi-component transparent coating composition according to claim 1 onto the uncured base coating film to form an uncured transparent coating film; and The uncured base coating and the uncured transparent coating are cured simultaneously.

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

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