JP2024092990A - Coating composition and coated article - Google Patents

Abstract

To provide a coating composition from which a clear coating film excellent in non-sand recoating property can be obtained.SOLUTION: A coating composition contains a hydroxyl group-containing acrylic resin (a), polycarbonate diol (b), a cellulose derivative (c), and an isocyanurate compound (d) having three or more isocyanate groups, wherein a number average molecular weight of the cellulose derivative (c) is 10,000 or more and 40,000 or less, and a content of the polycarbonate diol (b) to the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b) is 1 to 19 mass%.SELECTED DRAWING: None

Description

The present invention relates to a coating composition and a coated article.

When there are defects in the paint on plastic parts used in automobiles (e.g., bumpers, plastic fenders, and plastic tailgates), they are repainted to cover the defects. In order to reduce the process load, the plastic parts with defects are usually repainted without pretreatment such as polishing. This type of painting is called non-sand recoating. Patent Document 1 discloses a paint composition with high recoatability.

In Patent Document 1, the surface free energy of a film containing hardened inorganic particles is controlled to improve recoatability. The present invention aims to provide a coating composition that has a different structure from that of the above Patent Document and that can provide a coating film that is excellent in appearance and non-sand recoatability.

Patent Document 2 discloses a two-liquid paint composition that contains a base agent that contains acrylic polyol and polycarbonate diol, and a curing agent that contains polyisocyanate, and that limits the content of polycarbonate diol. This type of paint composition is intended to more efficiently fill in irregularities present on the surface of carbon fiber reinforced plastic (CFRP) molded products and the like, to obtain a smooth painted surface, but no consideration has been given to recoatability.

JP 2021-172688 A JP 2022-65832 A

The present invention aims to provide a coating composition that produces a coating film with excellent appearance and non-sandricating properties.

The present invention provides a coating composition comprising:
The composition comprises a hydroxyl group-containing acrylic resin (a), a polycarbonate diol (b), a cellulose derivative (c), and an isocyanurate compound (d) having three or more isocyanate groups,
The number average molecular weight of the cellulose derivative (c) is 10,000 or more and 40,000 or less,
The coating composition is characterized in that the content of the polycarbonate diol (b) is 1 to 19% by mass based on the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b).

The polycarbonate diol preferably has a number average molecular weight of 500 to 1,000 and a hydroxyl value of 100 to 300 mgKOH/g.
The cellulose derivative (c) preferably has a glass transition temperature of 85° C. or higher and a hydroxyl value of 1.0 to 2.0 mgKOH/g.
The cellulose derivative is preferably carboxymethyl cellulose acetate butyrate (CAB).

The hydroxyl-containing acrylic resin (a) preferably has a hydroxyl value of 90 mgKOH/g or more and 190 mgKOH/g or less, a weight average molecular weight of 3,500 or more and 8,000 or less, and a glass transition temperature of 10°C or more and 70°C or less.
The coating composition further comprises a hydroxyl group-containing polyester resin (e),
The amount of the hydroxyl-containing polyester resin (e) to be blended per 100 parts by mass of the solid content of the hydroxyl-containing acrylic resin (a) is preferably 0.1 parts by mass or more and 25 parts by mass or less.
The above-mentioned coating composition preferably further contains organic nanoparticles.
In the above-mentioned coating composition, the content of the cellulose derivative (c) relative to the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b) is preferably 0.5 to 5 mass %.

The present invention also relates to a coated article having a substrate, a base coating film, and a coating film formed from the above-mentioned coating composition.
The coated article may further have a primer coating.

The present invention provides a coating composition that produces a clear coating film with excellent non-sandricating properties.

The present invention will be described in detail below.
Painting after removing the existing coating by grinding is called a repair. In a repair, the existing coating is removed, so adhesion of the new coating is usually not an issue.

On the other hand, as mentioned above, in non-sandric coating, the paint film around the defect is not usually removed. Therefore, in non-sandric coating, the adhesion between the existing paint film and the paint film formed by repainting is important. Hereinafter, the adhesion between the existing paint film and the new paint film will be referred to as non-sandric coating properties. Excellent non-sandric coating properties refer to high adhesion between the existing paint film and the new paint film.

The existing coating film and the coating film formed by repainting are often formed from paints of the same composition, but this is not limited to this. Adhesion between coating films of different compositions is particularly likely to decrease. Non-sandricating properties are particularly related to the physical properties of the clear coating film that is placed on the outermost side of the existing coating film.

Two-component paints composed of an isocyanate compound and a hydroxyl-containing resin cure by the reaction between the isocyanate group and the hydroxyl group. However, this reaction does not usually proceed entirely during the coating film curing process, but continues to progress over time even after curing. This tendency is particularly pronounced when curing is performed under low-temperature, short-time conditions. Non-sandric coating is often performed a certain amount of time after the existing coating film has been formed. If the above-mentioned reaction progresses over time before non-sandric coating and the number of unreacted isocyanate groups and hydroxyl groups decreases, the non-sandric coating properties are likely to decrease. Furthermore, if the isocyanate group reacts with moisture in the air before non-sandric coating, urea bonds are formed on the surface of the existing coating film, which can also decrease the non-sandric coating properties.

The present invention has discovered that the combination of a specific cellulose derivative and a polycarbonate diol can significantly improve non-sandric coating properties.

The coating film obtained from the coating composition of the present invention has excellent adhesion to newly applied coatings. Therefore, the coating composition of the present invention is particularly suitable as a coating for the clear coating film that is formed on the outermost part of the composite coating film that is first formed on the substrate.

Hereinafter, the hydroxyl-containing acrylic resin (a) and other coating film-forming components that contain hydroxyl groups (typically the hydroxyl-containing polyester resin (e) described below, excluding the curing agent) will be collectively referred to as the hydroxyl-containing resin.

(a) Hydroxyl-containing acrylic resin The hydroxyl-containing acrylic resin (a) is a resin (film-forming component) that serves as the base of the coating film. The hydroxyl-containing acrylic resin (a) reacts with the isocyanurate compound (d) to form a crosslinked structure.

The hydroxyl-containing acrylic resin (a) has multiple acryloyl groups and one or more (typically two or more) hydroxyl groups in one molecule. The acrylic resin is obtained by polymerizing at least one monomer selected from the group consisting of acrylic acid and its esters, and methacrylic acid and its esters.

The hydroxyl value of the hydroxyl-containing acrylic resin (a) is, for example, 70 mgKOH/g or more. This makes it easy to increase the crosslink density. The hydroxyl value of the hydroxyl-containing acrylic resin (a) may be 100 mgKOH/g or more, or 110 mgKOH/g or more. The hydroxyl value of the hydroxyl-containing acrylic resin (a) is, for example, 190 mgKOH/g or less. This makes it easy to suppress hydrophilization of the coating film and improve the water resistance of the coating film. The hydroxyl value of the hydroxyl-containing acrylic resin (a) may be 180 mgKOH/g or less, or 170 mgKOH/g or less. In one embodiment, the hydroxyl value of the hydroxyl-containing acrylic resin (a) is 70 mgKOH/g or more and 170 mgKOH/g or less.

The hydroxyl value can be determined by the neutralization titration method using an aqueous potassium hydroxide solution as described in JIS K 0070.

The weight average molecular weight of the hydroxyl-containing acrylic resin (a) is, for example, 3,000 or more. This makes it easier to improve the hardness and weather resistance of the resulting coating film. The weight average molecular weight of the hydroxyl-containing acrylic resin (a) may be 4,000 or more. The weight average molecular weight of the hydroxyl-containing acrylic resin (a) is, for example, 7,000 or less. This makes it easier to suppress excessive viscosity increase of the coating composition. In one embodiment, the weight average molecular weight of the hydroxyl-containing acrylic resin (a) is 3,000 or more and 7,000 or less.

The weight average molecular weight can be calculated from a chromatogram measured by a gel permeation chromatograph, based on the molecular weight of standard polystyrene. For example, an HLC-8200 (manufactured by Tosoh Corporation) is used as the gel permeation chromatograph. The measurement conditions using this are as follows.
Column: TSgel Super Multipore HZ-M (3 columns) Developing solvent: Tetrahydrofuran Column inlet oven: 40°C
Flow rate: 0.35ml
Detector: Refractive index detector (RI)
Standard polystyrene: PS oligomer kit manufactured by Tosoh Corporation

The glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (a) is, for example, 8°C or higher. This tends to improve the stain resistance, scratch resistance, and hardness of the resulting coating film. The Tg of the hydroxyl-containing acrylic resin (a) may be 10°C or higher. The Tg of the hydroxyl-containing acrylic resin (a) is, for example, 70°C or lower. This tends to improve the quick-drying property of the clear coating composition. The Tg of the hydroxyl-containing acrylic resin (a) may be 60°C or lower, or 55°C or lower. In one embodiment, the Tg of the hydroxyl-containing acrylic resin (a) is 10°C or higher and 70°C or lower.

The glass transition temperature (Tg) is determined by the following method using a differential scanning calorimeter (DSC). The hydroxyl-containing acrylic resin (a) is subjected to the following steps (step 1): heating from 20°C to 150°C at a heating rate of 10°C/min; after step 1, cooling from 150°C to -50°C at a heating rate of 10°C/min (step 2); and after step 2, heating from -50°C to 150°C at a heating rate of 10°C/min (step 3). The value obtained from the chart during heating in step 3 is the Tg of the hydroxyl-containing acrylic resin (a). For example, a thermal analyzer SSC5200 (manufactured by Seiko Electronics) is used as the DSC.

From the viewpoint of hardness, it is preferable that the hydroxyl group-containing acrylic resin (a) has a hydroxyl value of 90 mgKOH/g or more and 190 mgKOH/g or less, a weight average molecular weight of 3,500 or more and 8,000 or less, and a Tg of 10°C or more and 70°C or less.

The acid value (AV) of the hydroxyl-containing acrylic resin (a) may be 2 mgKOH/g or more and 30 mgKOH/g or less. This tends to improve the smoothness of the resulting coating film. Furthermore, when the coating composition is applied onto another uncured coating film, the occurrence of mixed phases is likely to be suppressed. The acid value of the hydroxyl-containing acrylic resin (a) may be 3 mgKOH/g or more. The acid value of the hydroxyl-containing acrylic resin (a) may be 20 mgKOH/g or less, or 15 mgKOH/g or less. The acid value can be determined by the same method as the hydroxyl value.

The solid content of the hydroxyl-containing acrylic resin (a) in 100 parts by mass of the solid content of the coating composition is, for example, 60 parts by mass or more. This makes it easier to improve the appearance (particularly smoothness) of the resulting coating film. The solid content of the hydroxyl-containing acrylic resin (a) may be 65 parts by mass or more, or 70 parts by mass or more. The solid content of the hydroxyl-containing acrylic resin (a) is, for example, 95 parts by mass or less. This makes it easier to improve the drying properties of the coating composition. The solid content of the hydroxyl-containing acrylic resin (a) may be 90 parts by mass or less, or 85 parts by mass or less. In one embodiment, the solid content of the hydroxyl-containing acrylic resin (a) in 100 parts by mass of the solid content of the coating composition is 60 parts by mass or more and 95 parts by mass or less.

The raw material monomers for the hydroxyl group-containing acrylic resin (a) include, for example, acrylic acid hydroxy esters such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; methacrylic acid hydroxy esters such as 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate; and the like. Furthermore, if necessary, acrylic acid; acrylic acid esters such as methyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isobornyl acrylate; methacrylic acid; methacrylic acid esters such as methyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, isobornyl methacrylate; and ethylenically unsaturated monomers having aromatic rings such as styrene. These may be used alone or in combination of two or more. Commercially available hydroxyl group-containing acrylic resin (a) may also be used.

(b) Polycarbonate diol Polycarbonate diol is a compound having multiple polycarbonate bonds (-OCOO-) and two hydroxyl groups, and it is preferable that both ends are hydroxyl groups. By blending polycarbonate diol, adhesion to a substrate such as CFRP can be ensured. In addition, when a design layer is applied as a top coat on the coating film obtained by the coating composition according to the present invention, adhesion to the design layer can also be ensured.

In the coating composition of the present invention, it is preferable that the number average molecular weight of the polycarbonate diol is 400 to 1000 and the hydroxyl value of the polycarbonate diol is 100 to 300 mgKOH/g. The number average molecular weight is more preferably 500 to 1000. If the number average molecular weight of the polycarbonate diol is less than 500, sufficient adhesion may not be obtained. If the number average molecular weight of the polycarbonate diol exceeds 1000, the paintability may decrease. If the hydroxyl value of the polycarbonate diol is less than 100 mgKOH/g, the drying property may be poor. If the hydroxyl value of the polycarbonate diol exceeds 300 mgKOH/g, the adhesion may decrease.

In this specification, the number average molecular weight is a value calculated as a styrene homopolymer, measured by gel permeation chromatography.
The hydroxyl value of the polycarbonate diol refers to a hydroxyl value based on 100% by mass of the solid content of the polycarbonate diol.

In the coating composition of the present invention, the content of the polycarbonate diol (b) relative to the total mass of the hydroxyl-containing acrylic resin (a) and the polycarbonate diol (b) is 1 to 19% by mass. If the content is less than 1% by mass, the adhesion to the substrate or top coat may be poor. If it exceeds 19% by mass, the drying properties may be poor. The content of the polycarbonate diol (b) is preferably 2 to 15% by mass, more preferably 5 to 10% by mass, relative to the total mass of the hydroxyl-containing acrylic resin (a) and the polycarbonate diol (b).

(c) Cellulose derivatives: An appropriate amount of cellulose derivatives improves non-sandric coating properties. Cellulose derivatives tend to be unevenly distributed on the surface of the coating film, and can increase the cohesive force of the surface of the coating film. Therefore, the existing coating film containing cellulose derivatives has high adhesion to the new coating film (i.e., non-sandric coating properties).

The amount of cellulose derivative (c) is preferably 0.1 parts by mass or more per 100 parts by mass of the total solid content of the hydroxyl-containing resins contained in the paint composition. This improves the non-sandricating properties of the resulting coating film. The amount of cellulose derivative (c) may be 1 part by mass or more, or 2 parts by mass or more. Regardless of the viscosity of cellulose derivative (c), the amount of cellulose derivative (c) is preferably 0.1 parts by mass or more.

On the other hand, it is preferable that the upper limit of the blending amount of the cellulose derivative (c) is set so that the coating viscosity does not exceed 35 seconds, taking into consideration the viscosity of the cellulose derivative (c) and other blending components. For example, the blending amount of the cellulose derivative (c) having a viscosity of 0.005 seconds or more and less than 0.5 seconds measured by the method described in ASTM-D-1343 (standard test method for viscosity of cellulose derivatives by ball drop method) is, for example, 10 parts by mass or less, and may be 7 parts by mass or less. The blending amount of the cellulose derivative (c) having a viscosity of 0.5 seconds or more and less than 5 seconds is, for example, less than 5 parts by mass, and may be 3 parts by mass or less. The blending amount of the cellulose derivative (c) having a viscosity of 5 seconds or more is less than 3 parts by mass, and may be 1 part by mass or less.

In the coating composition of the present invention, the content of the cellulose derivative (c) relative to the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b) is preferably 0.5 to 5 mass%.

The number average molecular weight of the cellulose derivative (c) is, for example, 10,000 or more. This can further improve the non-sandric coating property. The number average molecular weight of the cellulose derivative (c) may be 12,000 or more, or 15,000 or more. The number average molecular weight of the cellulose derivative (c) is, for example, 40,000 or less. This can suppress the increase in viscosity of the coating composition. The number average molecular weight of the cellulose derivative (c) may be 30,000 or less, or 25,000 or less. In one embodiment, the number average molecular weight of the cellulose derivative (c) is 10,000 or more and 40,000 or less.

The Tg of the cellulose derivative (c) is, for example, 85°C or higher. This improves the cohesive force when the clear coating composition forms a film, and further improves adhesion. The Tg of the cellulose derivative (f) is, for example, 130°C or lower. This makes it easier to maintain the above-mentioned viscosity of the clear coating composition at 35 seconds or less. In one embodiment, the Tg of the cellulose derivative (f) is 85°C or higher and 130°C or lower. In this case, the non-sandricating property is further improved, and the viscosity is easily maintained at 20 seconds or higher and 35 seconds or lower.

Similarly, from the viewpoint of achieving both non-sandric coating properties and optimized paint viscosity, it is preferable that the cellulose derivative (c) has a number average molecular weight of 10,000 or more and 40,000 or less, and a glass transition temperature of 85°C or more.

The cellulose derivative (c) is not particularly limited. Representative examples of the cellulose derivative (c) include cellulose ether and cellulose ester. The cellulose derivative (c) may contain at least one selected from the group consisting of cellulose ether and cellulose ester, and may contain at least cellulose ester.

Specific examples of cellulose esters include nitrocellulose, cellulose acetate, cellulose triacetate, cellulose acetate phthalate, cellulose acetate butyrate, cellulose butyrate, cellulose tributyrate, cellulose propionate, cellulose tripropionate, cellulose acetate propionate, carboxymethylcellulose acetate, carboxymethylcellulose acetate propionate, carboxymethylcellulose acetate butyrate, cellulose acetate butyrate succinate, and cellulose propionate butyrate. These may be used alone or in combination of two or more. Among these, carboxymethylcellulose acetate butyrate (CAB) is preferred from the viewpoints of solubility with the resin component and expression of viscosity.

Examples of cellulose ethers include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose.

(d) Isocyanurate Compound The isocyanurate compound (d) is a curing agent that reacts with the hydroxyl group-containing resin to form a crosslinked structure, thereby curing the coating composition.

The isocyanurate compound (d) has at least three isocyanate groups and a triazinetrione ring in one molecule. The isocyanurate compound (d) may have three isocyanate groups in one molecule. The isocyanurate compound (d) is typically a trimer of a polyisocyanate compound.

Examples of polyisocyanate compounds include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having aromatic rings in the molecule that are not bonded to isocyanate groups (araliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specific examples include aromatic polyisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and meta-xylylene diisocyanate; aliphatic polyisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, undecane diisocyanate-(1,11), and lysine ester diisocyanate; and alicyclic polyisocyanates such as isophorone diisocyanate. In particular, the isocyanurate compound (d) may be a trimer of an aliphatic polyisocyanate having 3 to 24 carbon atoms, or a trimer of an aliphatic polyisocyanate having 5 to 18 carbon atoms.

The equivalent ratio NCO/OH between the isocyanate group contained in the isocyanurate compound (d) and the hydroxyl group contained in the hydroxyl group-containing resin may be 0.8 or more, 0.9 or more, or 1.0 or more. When the equivalent ratio is in this range, the cohesive force of the resulting coating film is likely to be increased, and the non-sandric coating property may also be improved. The equivalent ratio NCO/OH may be 2.0 or less, 1.8 or less, or 1.5 or less. When the equivalent ratio is in this range, the formation of urethane bonds is suppressed, and therefore, the non-sandric coating property can be expected to be improved. In one embodiment, the equivalent ratio NCO/OH is 0.8 or more and 2.0 or less. According to the coating composition of the present invention, excellent non-sandric coating property can be achieved even when the reaction rate changes over time within the above-mentioned equivalent ratio NCO/OH range.

(Other hardeners)
The coating composition according to the present invention may further contain, as another curing agent, a polyisocyanate compound other than the isocyanurate compound (d). The other polyisocyanate compound may be at least one selected from the group consisting of polyisocyanate compounds such as uretdione, iminooxadiazinedione, biuret, and adduct derived from bifunctional isocyanate, amino resin, epoxy compound, aziridine compound, carbodiimide compound, and oxazoline compound. The content of the other curing agent is appropriately set according to the coating film forming components.

(e) Hydroxyl-containing polyester resin The coating composition according to the present invention may further contain a hydroxyl-containing polyester resin (e). The hydroxyl-containing polyester resin (e) is also a coating film-forming component, and reacts with the isocyanurate compound (d) to form a crosslinked structure. The hydroxyl-containing polyester resin (e) has a plurality of ester bonds and one or more hydroxyl groups.

Hydroxyl-containing acrylic resin (a) tends to increase the viscosity of the coating composition. On the other hand, hydroxyl-containing polyester resin (e) generally has a low viscosity and tends to increase the hydroxyl value. By using hydroxyl-containing polyester resin (e) in combination, it is possible to improve the crosslink density while suppressing the increase in viscosity.

The hydroxyl value of the hydroxyl-containing polyester resin (e) is, for example, 80 mgKOH/g or more. This makes it easy to increase the crosslink density of the coating film. The hydroxyl value of the hydroxyl-containing polyester resin (e) may be 100 mgKOH/g or more. The hydroxyl value of the hydroxyl-containing polyester resin (e) is, for example, 500 mgKOH/g or less. This makes it easy to suppress hydrophilization of the coating film and improve the water resistance of the coating film. The hydroxyl value of the hydroxyl-containing polyester resin (e) may be 480 mgKOH/g or less, or 450 mgKOH/g or less. In one embodiment, the hydroxyl value of the hydroxyl-containing acrylic resin (a) is 80 mgKOH/g or more and 500 mgKOH/g or less.

The number average molecular weight of the hydroxyl-containing polyester resin (e) is, for example, 700 or more. This makes it easier to improve the hardness and weather resistance of the resulting coating film. The number average molecular weight of the hydroxyl-containing polyester resin (e) may be 900 or more. The number average molecular weight of the hydroxyl-containing polyester resin (e) is, for example, 2,500 or less. This makes it easier to suppress excessive viscosity increase of the coating composition. The number average molecular weight of the hydroxyl-containing polyester resin (e) may be 2,000 or less. In one embodiment, the number average molecular weight of the hydroxyl-containing polyester resin (e) is 700 or more and 2,000 or less.

From the viewpoint of viscosity, it is preferable that the hydroxyl group-containing polyester resin (e) has a hydroxyl value of 80 mgKOH/g or more and 500 mgKOH/g or less, and a number average molecular weight of 700 or more and 2,000 or less.

The amount of hydroxyl-containing polyester resin (e) per 100 parts by mass of the solid content of hydroxyl-containing acrylic resin (a) is, for example, 0.1 parts by mass or more in terms of solid content. This makes it easy to increase the crosslink density of the coating film. The amount of hydroxyl-containing polyester resin (e) per 100 parts by mass of the solid content of hydroxyl-containing acrylic resin (a) is, for example, 25 parts by mass or less in terms of solid content. This makes it easy to improve the water resistance of the coating film. In one embodiment, the amount of hydroxyl-containing polyester resin (e) per 100 parts by mass of the solid content of hydroxyl-containing acrylic resin (a) is, for example, 0.1 parts by mass or more and 25 parts by mass or less in terms of solid content.

The hydroxyl group-containing polyester resin (e) can be obtained, for example, by polycondensation (ester reaction) of a polyhydric alcohol with a polybasic acid or its anhydride. Commercially available hydroxyl group-containing polyester resins may also be used.

The polyhydric alcohol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl- Examples include 3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, N,N-bis-(2-hydroxyethyl)dimethylhydantoin, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, and tris-(hydroxyethyl)isocyanate. These may be used alone or in combination of two or more.

The polybasic acid or anhydride is not particularly limited, and examples thereof include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, himic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, lactic acid, dodecenylsuccinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-dicarboxylic acid, and endo acid anhydride. These may be used alone or in combination of two or more.

The hydroxyl group-containing polyester resin may be modified with lactone, fats and oils or fatty acids, melamine resin, urethane resin, etc. The fats and oils or fatty acids are not particularly limited, and examples include fats and oils such as castor oil, dehydrated castor oil, coconut oil, corn oil, cottonseed oil, linseed oil, perilla oil, poppy seed oil, safflower oil, soybean oil, and tung oil, or fatty acids extracted from these fats and oils.

(Other hydroxyl-containing resins)
The coating composition according to the present invention may further contain, as another hydroxyl-containing resin other than the hydroxyl-containing acrylic resin (a) and the hydroxyl-containing polyester resin (e), for example, at least one selected from the group consisting of polycarbonate polyol resins, polyether polyol resins, and polycaprolactone polyol resins.

The solid content of the other hydroxyl-containing resins per 100 parts by mass of the total solid content of the hydroxyl-containing resins is, for example, 10 parts by mass or less, and 5 parts by mass or less.

(f) Dilution component The coating composition according to the present invention may contain a dilution component (f). The coating composition is appropriately diluted with a dilution component, taking into consideration the coating method and the coating environment such as temperature and humidity. Examples of the dilution component include water and non-aqueous solvents. The coating composition according to the present invention may also contain non-aqueous solvents used in the production of each component.

The non-aqueous solvent may, for example, be an aliphatic or alicyclic hydrocarbon solvent such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, or mineral split; a ketone organic solvent such as acetone, acetylacetone, methyl ethyl ketone, methyl-i-butyl ketone, methyl amyl ketone, or cyclohexanone; an aromatic hydrocarbon organic solvent such as benzene, toluene, ethylbenzene, propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, or decalin; an ester organic solvent such as methyl acetate, ethyl acetate, n-butyl acetate, or aluminum acetate; an ester-ether organic solvent such as monomethyl ether acetate or propylene glycol monoethyl ether acetate; or an ether organic solvent such as dioxane. These may be used alone or in combination of two or more.

(Viscosity adjuster)
The coating composition according to the present invention may contain a viscosity modifier. The viscosity modifier can be used within a range that does not impair the effects of the present invention. The amount of the other viscosity modifier to be blended relative to 100 parts by mass of the total solid content of the hydroxyl group-containing resin may be 5 parts by mass or less, or 3 parts by mass or less.

Other viscosity modifiers include, for example, inorganic viscosity agents, urethane association type viscosity agents, polycarboxylic acid type viscosity agents, and amide type viscosity agents. These may be used alone or in combination of two or more. Examples of inorganic viscosity agents include layered silicates (silicate minerals), halide minerals, oxide minerals, carbonate minerals, borates, sulfate minerals, molybdate minerals, tungstate minerals, phosphate minerals, arsenate minerals, and vanadate minerals. Examples of urethane association type viscosity agents include polyurethane type viscosity agents having hydrophobic chains in the molecule, and urethane-urea type viscosity agents in which at least a portion of the main chain is a hydrophobic urethane chain.

As the viscosity modifier, commercially available products such as "AZS-522" and "AZS-607" (manufactured by Nippon Paint Co., Ltd.) can also be used. Of these, it is preferable to use "AZS-607" (organic nanoparticles, manufactured by Nippon Paint Co., Ltd.).

(Other additives)
The coating composition of the present invention may contain other additives commonly used in the coating field. For example, it may contain color pigments and/or luster pigments to the extent that transparency is not impaired. In addition, it may contain ultraviolet absorbers, hindered amine light stabilizers, antioxidants, surface conditioners, catalysts, etc.

The solid content concentration of the coating composition of the present invention is not particularly limited. From the viewpoint of low VOC and shortening the process, the solid content concentration of the coating composition is preferably, for example, 45 mass% or more and 60 mass% or less. As described above, the above solid content concentration is that of the coating composition to be applied. The solid content concentration of the coating composition may be 48 mass% or more, or may be 50 mass% or more. The solid content concentration of the coating composition may be 58 mass% or less, or may be 57 mass% or less. The solid content of the coating composition is all components excluding diluting components such as non-aqueous solvents.

The coating composition of the present invention is suitable for forming a clear coating film. A clear coating film is usually disposed on the outermost side so as to cover one or more other coating films (typically, a base coating film) formed on the substrate. When the coating composition of the present invention is used to form the outermost clear coating film, it is easy to exhibit non-sandricating properties.

[Coating film]
A coating film is formed using the coating composition according to the present invention. The obtained coating film has excellent appearance and non-sandricating properties. The coating film according to the present invention may be a coating film laminated on an existing coating film, or may be a coating film formed first on a substrate.

The thickness of the coating film is not particularly limited. From the viewpoint of scratch resistance and smoothness, the thickness of the coating film after drying may be, for example, 15 μm or more, and 20 μm or more. The thickness of the coating film may be 50 μm or less, and 40 μm or less. The thickness of the coating film can be measured with an electromagnetic film thickness meter (for example, SDM-miniR manufactured by SANKO Corporation). The thickness of the coating film is the average value of the thickness of the coating film at any five points.

The coating film according to the present invention has excellent non-sandricating properties. For example, even if a coating film equivalent to an existing coating film is formed on an object using the paint composition according to the present invention and then left at room temperature for a long period of time (e.g., 10 days at 25°C), and then another coating film is formed on the coating film, peeling between the existing coating film and the new coating film is unlikely to occur. In particular, when the existing coating film and the new coating film have the same composition, the non-sandricating properties are further improved.

For example, a method based on JIS K-5600-5-6 is used to evaluate the adhesion of a coating. A single-blade cutting tool as specified in JIS K-5600-5-6 is placed perpendicularly on the coated surface of the test piece, and cuts (parallel lines 1) are made that reach the base material (substrate). In addition, 10 cuts parallel to the parallel lines 1 are made at equal intervals. Eleven cuts (parallel lines 2) are made at equal intervals that intersect perpendicularly with the eleven parallel lines 1 and reach the base material. The distance between parallel lines 1 and between parallel lines 2 is 2 mm. In this way, a grid section is formed with 100 squares surrounded by four straight lines.

A transparent pressure-sensitive tape as specified in JIS K-5600-5-6 is adhered to the above grid area so that no air bubbles are trapped between the tape and the coating surface. The tape is then peeled off in one go within 0.5 to 1.0 seconds, and the peeling state of the grid area is evaluated visually. Peeling of the coating film can occur between the existing coating film and the new coating film, and between the existing coating film and the substrate. If peeling occurs in either case, the coating film is evaluated as peeling. If no peeling is observed in either case, the coating film obtained using the coating composition of the present invention can be evaluated as having excellent adhesion to the substrate and excellent non-sandric coating properties.

[Method of forming coating film]
The coating film is formed by applying the coating composition to an object and then curing the composition. The coating composition can be cured by heating. The coating method and curing conditions are described below.

[Painted items]
The coated article comprises a substrate and a coating film formed on the substrate and formed at least from the coating composition according to the present invention. The coated article may be provided with a primer and a base coating film in advance. In this case, the coating composition according to the present invention may be used to form a clear coating film. Such a coated article also constitutes the present invention.
The following describes the case where the coating composition according to the present invention is used to form a clear coating film, although the use of the coating composition according to the present invention is not limited thereto.

[Substrate]
The material of the object to be coated is not particularly limited. Examples of the material of the object to be coated include metal, resin, and glass. The shape of the object to be coated is also not particularly limited. Specific examples of the object to be coated include automobile bodies such as passenger cars, trucks, motorcycles, and buses, and parts for automobile bodies, and automobile parts such as spoilers, bumpers, mirror covers, grilles, and door knobs.

Examples of metals include iron, copper, aluminum, tin, zinc, and alloys thereof (e.g., steel). Representative examples of metallic substrates include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrolytic 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.

The metallic substrate may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, the metallic substrate may be further coated with an electrocoating paint. The electrocoating paint may be of the cationic type or the anionic type.

Examples of resins include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, polyvinyl chloride resin, and polyamide resin. It is preferable that the resin substrate has been degreased.

(Primer coating)
The primer coating is interposed between the substrate and the base coating. The primer coating improves adhesion between the base coating and the substrate (especially a resin substrate). In addition, when the substrate has an uneven surface, the primer coating makes the coated surface uniform, making it easier to suppress unevenness in the base coating.

The primer coating film is formed by a primer coating composition containing, for example, a coating film-forming component, a material adhesion component, a viscosity modifier, a dilution component, a pigment, and, if necessary, a curing agent. The primer coating composition may contain various of the above-mentioned additives as necessary. The primer coating composition may be solvent-based or water-based. The coating film-forming component, the curing agent, the viscosity modifier, the dilution component, and the pigment may be the components exemplified as those to be blended in the base coating composition. For example, the viscosity of the water-based primer coating composition measured at 20°C with a B-type viscometer is 500 cps/6 rpm or more and 6,000 cps/6 rpm or less. The solid content of the primer coating composition is, for example, 30% by mass or more and 50% by mass or less. The solid content of the primer coating composition is all the components of the primer coating composition excluding the dilution component.

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

(Base coating)
The base coating may be one layer or a laminated coating of two or more layers. The base coating may be, for example, one or more so-called base coating layers.

The base coating film is formed, for example, by a base paint composition containing a coating film-forming component, a curing agent, a viscosity modifier, a diluent component, and a pigment. The base paint composition may contain various of the above-mentioned additives as necessary. The components contained in each base coating film may be the same or different. The base paint composition may be solvent-based or water-based. The coating film-forming component, curing agent, viscosity modifier, and diluent component blended into the base paint composition may include each of the components exemplified as those blended into the above-mentioned paint composition.

The viscosity of the base paint composition measured at 20°C using a Brookfield viscometer is, for example, 500 cps/6 rpm to 6,000 cps/6 rpm in the case of an aqueous paint. The solids content of the base paint composition is, for example, 30% by mass to 70% by mass. The solids content of the base paint composition is all components of the base paint composition excluding dilution components.

The thickness of the base coating film is not particularly limited and is set appropriately depending on the purpose. The thickness of each layer of the base coating film may be, for example, 10 μm or more, and may be 15 μm or more. The thickness of each layer of the base coating film may be, for example, 45 μm or less, and may be 30 μm or less.

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

Examples of photoluminescent pigments include metal flakes (aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel chrome, stainless steel, etc.), metal oxide flakes, pearl pigments, glass flakes coated with metal or metal oxide, silica flakes coated with metal oxide, graphite, holographic pigments, and cholesteric liquid crystal polymers. These may be used alone or in combination of two or more.

Examples of extender pigments include calcium carbonate, barium sulfate, clay and talc. These may be used alone or in combination of two or more.

The concentration of the total pigments, i.e., the mass ratio (PWC) of the total pigments to 100 mass% of the resin solids of the base paint composition, is preferably 0.1 mass% or more and 50 mass% or less. This improves the smoothness of the resulting coating film. The PWC of each pigment is not particularly limited. The PWC of the luster pigment may be, for example, 1 mass% or more and 40 mass% or less. The PWC of the luster pigment is preferably 5 mass% or more. The PWC of the luster pigment is preferably 30 mass% or less.

[Method of manufacturing coated articles]
The above-mentioned coated article is produced by a method comprising the steps of applying a base coating composition onto a substrate to form an uncured base coating film, curing the uncured base coating film, applying a clear coating composition onto the base coating film to form an uncured clear coating film, and curing the uncured clear coating film.

The above-mentioned coated article may also be produced by a method comprising the steps of applying a primer coating composition onto a substrate to form an uncured primer coating film, curing the uncured primer coating film, applying a base coating composition to form an uncured base coating film, curing the uncured base coating film, applying a clear coating composition onto the base coating film to form an uncured clear coating film, and curing the uncured clear coating film.

When the clear coating film is formed, the primer coating film and the base coating film may be cured or uncured. In particular, from the viewpoints of productivity, adhesion, and water resistance, it is preferable to laminate each coating film without curing it (so-called wet-on-wet coating), and then simultaneously cure these multiple uncured coating films. In other words, it is preferable that the coated article is manufactured by a method including a step of applying a primer coating composition and a base coating composition onto a substrate to form an uncured primer coating film and a base coating film, a step of applying a clear coating composition onto the uncured base coating film to form an uncured clear coating film, and a step of curing the uncured primer coating film, the base coating film, and the uncured clear coating film.

Below, each step will be explained using an example of producing a painted article having a primer coating, a base coating, and a clear coating by wet-on-wet painting. However, the method of producing a painted article according to the present invention is not limited to this.

(I) Step of forming uncured primer coating film The uncured primer coating film is formed by applying the above-mentioned primer coating composition to a substrate. The primer coating composition is applied so that the thickness of the primer coating film after curing is, for example, 5 μm to 40 μm.

The coating method is not particularly limited. Examples of coating methods include air spray coating, airless spray coating, and rotary atomization coating. These methods may be combined with electrostatic coating. Among them, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. For rotary atomization electrostatic coating, for example, rotary atomization electrostatic coating machines commonly known as "micro-microbell (μμbell)", "microbell (μbell)", "metallicbell (metabell)", etc. are used.

After applying the primer coating composition, pre-drying (also called pre-heating) may be performed. This prevents the diluting components contained in the primer coating composition from bumping during the curing process, making it easier to prevent popping. Furthermore, pre-drying prevents the uncured primer coating from mixing with the coating composition to be applied thereon, making it harder for a mixed phase to form. This makes it easier to improve the smoothness of the resulting coated article.

The conditions for pre-drying are not particularly limited. Examples of pre-drying include leaving the material at a temperature of 20°C to 25°C for 5 to 15 minutes, and heating the material at a temperature of 50°C to 80°C for 30 seconds to 10 minutes.

(II) Step of forming uncured base coating film The uncured base coating film is formed by applying the above-mentioned base coating composition to a substrate. The base coating composition is applied so that the thickness of the base coating film after curing is 10 μm or more and 45 μm or less.

The coating method is not particularly limited. For example, the coating method may be the same as the coating method for the primer coating composition.

From the same viewpoint as above, after applying the base coating composition, pre-drying (also called pre-heating) may be performed in the same manner as the primer. The conditions for pre-drying are not particularly limited. The conditions for pre-drying are not particularly limited and may be the same as the pre-drying of the primer coating film.

(III) Step of forming uncured clear coating film The uncured clear coating film is formed by applying the coating composition according to the present invention (hereinafter, sometimes referred to as the clear coating composition) onto the base coating film. The clear coating composition is applied so that the thickness of the clear coating film after curing is 15 μm or more and 50 μm or less.

The coating method is not particularly limited. Examples of coating methods include methods similar to those used for coating the primer coating composition. Among these, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. After coating the clear coating composition, preliminary drying may be performed. The conditions for preliminary drying are not particularly limited and may be the same as those for preliminary drying of the primer coating film or base coating film.

(IV) Curing step: Each uncured coating film is cured. Each coating film may be cured by heating. In this step, the primer coating film, the base coating film, and the clear coating film may be cured at the same time.

The heating conditions are set appropriately depending on the composition of each paint composition and the material of the object to be coated. The heating temperature is, for example, 60°C or higher and 120°C or lower, and may be 65°C or higher and 90°C or lower. With the clear paint composition of the present invention, even at such low temperatures, a clear coating film with high hardness is ultimately formed.

The heating time may be set appropriately depending on the heating temperature. When the heating temperature is 60°C or higher and 120°C or lower, the heating time may be, for example, 10 minutes or more and 60 minutes or less, or 15 minutes or more and 45 minutes or less. The heating time means the time during which the inside of the heating device reaches the target temperature and the coated object is maintained at the target temperature, and does not take into account the time until the target temperature is reached. Examples of heating devices include drying furnaces that use heat sources such as hot air, electricity, gas, and infrared rays.

The present invention will be described below with reference to examples. In the examples, parts and percentages in the compounding ratios mean parts by mass and percentages by mass unless otherwise specified. The present invention is not limited to the examples shown below.

Example 1
(Preparation of Base Agent)
The main component was 37 parts by mass of acrylic polyol (acrylic resin manufactured by Nippon Paint Co., Ltd.; weight average molecular weight 6000, hydroxyl value 151 mgKOH/g, solid content concentration 50% by mass, Tg 10°C), 7 parts by mass of polycarbonate diol (Duranol T5650E manufactured by Asahi Kasei Corporation; number average molecular weight 500, hydroxyl value 200 to 250 mgKOH/g, solid content concentration 100% by mass), and cellulose derivative (CAB-551-0.2 Eastman Chemical: number average molecular weight 30,000, hydroxyl value 1.8 mgKOH/g, solids concentration 100% by mass, Tg 101°C) 1 part by mass, Microgel (Nippon Paint Co., Ltd. product AZS-607, gelling particles) 0.7 parts by mass, UV absorber (Tinuvin 384, BASF Corporation) 0.7 parts by mass, light stabilizer (Tinuvin 292, BASF Corporation) 0.3 parts by mass, leveling agent (BYK-310, BYK Corporation) 0.1 parts by mass, butyl acetate 20 parts by mass, xylene 33.19 parts by mass, and curing catalyst (dibutyltin dilaurate, Tokyo Chemical Industry Co., Ltd., solids concentration 100% by mass) 0.01 parts by mass were blended. In the base resin, the content of the polycarbonate diol relative to the total mass of the acrylic polyol and the polycarbonate diol (represented as the polycarbonate diol content in the table) was 16 mass%.

(Preparation of Coating Composition)
100 parts by mass of the obtained base agent was mixed with 30 parts by mass of a polyisocyanate (Coronate HX, Toso) as a curing agent and 30 parts by mass of a dilution solvent (T-507HCL, Nippon Paint Co., Ltd.) to prepare a coating composition.
The solids concentration of this coating composition was 43.6% by mass.

(Formation of painted product)
The resulting coating composition was spray-coated on a coated plate having a surface of a PP material (length 150 mm, width 100 mm, thickness 3 mm) coated with a PP primer (RB-170CD primer: manufactured by Nippon Paint) and a color base (R-303 base: manufactured by Nippon Paint), and then dried at 80°C for 30 minutes under Keep (clear coating thickness: 25 to 35 µm) to obtain a coated product.
The coated plates for evaluating recoat adhesion were prepared by spraying primer/base/clear onto the coated plates obtained above, drying at 70°C for 30 minutes and keeping for coating product A, drying at 70°C for 90 minutes and keeping for coating product B, and drying at 90°C for 120 minutes and keeping for coating product C.

(Recoat adhesion evaluation)
A single-blade cutting tool as specified in JIS K-5600-5-6 was placed perpendicularly on the coated surface of the above-mentioned coated product, and cuts (parallel lines 1) were made that reached the base material (substrate). Furthermore, 10 cuts parallel to the parallel lines 1 were made at equal intervals. Eleven cuts (parallel lines 2) were made at equal intervals that intersected perpendicularly with the eleven parallel lines 1 and reached the base material. The intervals between the parallel lines 1 and between the parallel lines 2 were each 2 mm. In this way, a grid section having 100 squares surrounded by four straight lines was formed.
A transparent pressure-sensitive tape as specified in JIS K-5600-5-6 was adhered to the grid portion so that no air bubbles were trapped between the tape and the coating surface. The tape was then peeled off in one go within 0.5 to 1.0 seconds, and the peeling state of the grid portion was visually evaluated. The evaluation criteria are as follows. If the evaluation is "◎" or "◯", there is no problem in practical use.
◎: No peeling of the coating film was observed after 24 hours and 72 hours for Coated Product A, Coated Product B, and Coated Product C. ○: No peeling of the coating film was observed after 24 hours and 72 hours for Coated Product A and Coated Product B, but peeling of the coating film was observed after 24 hours and 72 hours for Coated Product C. ×: Peeling of the coating film was observed after 24 hours and 72 hours for Coated Product A, Coated Product B, and Coated Product C.

Example 2 and Comparative Example 1
A coated article was obtained in the same manner as in Example 1, except that the composition of the coating composition was changed to that shown in Table 1.

The results in Table 1 show that adding a cellulose derivative ensures recoatability 24 hours after baking at 70°C for 90 minutes. It was also shown that increasing the amount of cellulose derivative ensures recoatability 72 hours after baking at 90°C for 120 minutes.

The coating composition of the present invention can be suitably used, for example, in automobile vehicles and automobile parts.

The present invention provides a coating composition comprising:
The composition comprises a hydroxyl group-containing acrylic resin (a), a polycarbonate diol (b), a cellulose derivative (c), and an isocyanurate compound (d) having three or more isocyanate groups,
The number average molecular weight of the polycarbonate diol (b) is less than 1,000,
The number average molecular weight of the cellulose derivative (c) is 10,000 or more and 40,000 or less,
The coating composition is characterized in that the content of the polycarbonate diol (b) is 1 to 19% by mass based on the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b).

The polycarbonate diol preferably has a number average molecular weight of from 500 to less than 1,000 and a hydroxyl value of from 100 to 300 mgKOH/g.
The cellulose derivative (c) preferably has a glass transition temperature of 85° C. or higher and a hydroxyl value of 1.0 to 2.0 mgKOH/g.
The cellulose derivative is preferably carboxymethyl cellulose acetate butyrate (CAB).

Claims (10)

A coating composition comprising:
The composition comprises a hydroxyl group-containing acrylic resin (a), a polycarbonate diol (b), a cellulose derivative (c), and an isocyanurate compound (d) having three or more isocyanate groups,
The number average molecular weight of the cellulose derivative (c) is 10,000 or more and 40,000 or less,
A coating composition, characterized in that the content of the polycarbonate diol (b) is 1 to 19 mass% based on the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b). The coating composition according to claim 1, wherein the polycarbonate diol has a number average molecular weight of 500 to 1000 and a hydroxyl value of 100 to 300 mgKOH/g. The coating composition according to claim 1 or 2, wherein the cellulose derivative (c) has a glass transition temperature of 85°C or higher and a hydroxyl value of 1.0 to 2.0 mgKOH/g. The coating composition according to claim 1 or 2, wherein the cellulose derivative is carboxymethyl cellulose acetate butyrate (CAB). The coating composition according to claim 1 or 2, wherein the hydroxyl-containing acrylic resin (a) has a hydroxyl value of 90 mgKOH/g or more and 190 mgKOH/g or less, a weight average molecular weight of 3,500 or more and 8,000 or less, and a glass transition temperature of 10°C or more and 70°C or less. Further, the composition contains a hydroxyl group-containing polyester resin (e),
3. The coating composition according to claim 1, wherein the amount of the hydroxyl-containing polyester resin (e) is 0.1 parts by mass or more and 25 parts by mass or less based on 100 parts by mass of the solid content of the hydroxyl-containing acrylic resin (a). The coating composition according to claim 1 or 2, further comprising organic nanoparticles. The coating composition according to claim 1 or 2, wherein the content of the cellulose derivative (c) relative to the total mass of the hydroxyl group-containing acrylic resin (a) and the polycarbonate diol (b) is 0.5 to 5 mass%. A coated article having a substrate, a base coating film, and a coating film formed from the coating composition according to claim 1 or 2. The coated article according to claim 9, further comprising a primer coating.