Clear coating composition

Abstract

A clear coating composition includes a hydroxyl group-containing acrylic resin (a), a hydroxyl group-containing polyester resin (b), a polyol compound (c) other than the hydroxyl group-containing acrylic resin (a) and the hydroxyl group-containing polyester resin (b), a polyisocyanate compound (d), organic dispersed particles (e), a cellulose derivative (f), and an organic amine catalyst (g) having an amidine group. The hydroxyl group-containing acrylic resin (a) has a hydroxyl value of 90 mg KOH / g to 190 mg KOH / g, a weight average molecular weight of 4000 to 6000, and a glass transition temperature of 15°C to 100°C. The polyol compound (c) has a hydroxyl value of more than 200 mg KOH / g to 1000 mg KOH / g and a molecular weight of 100 to 1000. The cellulose derivative (f) contains at least one selected from the group consisting of cellulose ethers and cellulose esters and has a solids concentration of 50 mass% or more.

Description

Clear coating composition

[0001] This invention relates to a clear coating composition.

[0002] In the field of automotive technology, low-temperature curing properties are required for paints from an energy-saving perspective. In this regard, Patent Document 1 discloses a clear coating composition containing an organometallic catalyst consisting of a metal compound and an amidine compound. According to Patent Document 1, this clear coating composition cures at low temperatures and in a short time.

[0003] International Publication No. 2013 / 047209

[0004] Paint compositions with low-temperature curing properties tend to have shorter pot life. In addition, low-temperature curing can reduce the physical properties of the paint film, such as hardness and water resistance.

[0005] Another approach to energy conservation is the development of high-solids paints. High-solids paints can be applied using existing painting lines, eliminating the need for capital investment. High-solids paints also reduce VOCs and shorten painting time. However, increasing the solids typically increases the viscosity of the paint composition, which can reduce the smoothness (appearance) of the resulting paint film.

[0006] The present invention aims to solve the above-mentioned conventional problems and to provide a clear coating composition that is highly solid and yields a coating film with good appearance and high physical properties.

[0007] To solve the above problems, the present invention provides the following embodiments. [1] A hydroxyl group-containing acrylic resin (a), a hydroxyl group-containing polyester resin (b), a polyol compound (c) other than the hydroxyl group-containing acrylic resin (a) and the hydroxyl group-containing polyester resin (b), a polyisocyanate compound (d), organic dispersed particles (e), a cellulose derivative (f), and an organic amine catalyst having an amidine group (g), wherein the hydroxyl group-containing acrylic resin (a) has a hydroxyl value of 90 mg KOH / g or more and 190 mg KOH / g or less, a weight-average molecular weight of 4000 or more and 6000 or less, and a glass transition temperature of 15°C or more and 100°C or less, the polyol compound (c) has a hydroxyl value exceeding 200 mg KOH / g and 1000 mg KOH / g or less, and a molecular weight of 100 or more and 1000 or less, and the cellulose derivative (f) comprises at least one selected from the group consisting of cellulose ethers and cellulose esters. [1] A clear coating composition having a solid content concentration of 50% by mass or more. [2] The clear coating composition according to [1], wherein the polyol compound (c) has two hydroxyl groups and an alicyclic hydrocarbon group. [3] The clear coating composition according to [1] or [2], wherein the solid content of the polyol compound (c) is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of resin solids. [4] The clear coating composition according to any of [1] to [3], wherein the organic amine catalyst (g) has a heterocycle containing a nitrogen atom. [5] The clear coating composition according to any of [1] to [4], wherein the content of the organic amine catalyst (g) is 0.1% by mass or more and 1% by mass or less relative to the resin solids. [6] The hydroxyl group-containing polyester resin (b) has a hydroxyl value of 250 mg KOH / g or more and less than 500 mg KOH / g, and a weight-average molecular weight of 1500 or more and 2500 or less, and is a clear coating composition of any of the above [1] to [5]. [7] A clear coating composition of any of the above [1] to [6] for coating a resin substrate. [8] The average particle size of the organic dispersed particles (e) is 10 nm or more and 500 nm or less, and is a clear coating composition of any of the above [1] to [7].

[0008] According to the present invention, a clear coating composition is provided that is highly solid and yields a coating film with good appearance and high physical properties.

[0009] [Clear Coating Composition] The clear coating composition according to this embodiment comprises a hydroxyl group-containing acrylic resin (a), a hydroxyl group-containing polyester resin (b), a polyol compound other than the hydroxyl group-containing acrylic resin (a) and the hydroxyl group-containing polyester resin (b) (c), a polyisocyanate compound (d), organic dispersed particles (e), a cellulose derivative (f), and an organic amine catalyst (g).

[0010] The hydroxyl group-containing acrylic resin (a) has a hydroxyl value of 90 mg KOH / g or more and 190 mg KOH / g or less, a weight-average molecular weight of 4,000 or more and 6,000 or less, and a glass transition temperature of 15°C or more and 100°C or less. The polyol compound (c) has a hydroxyl value of more than 200 mg KOH / g and 1,000 mg KOH / g or less, and a molecular weight of 100 or more and 1,000 or less. The cellulose derivative (f) contains at least one selected from the group consisting of cellulose ethers and cellulose esters.

[0011] In this embodiment, three hydroxyl group-containing components are used as coating film-forming components, along with a polyisocyanate compound (d) which is a curing agent. In particular, it is essential to use a polyol compound (c) with a low molecular weight and high hydroxyl value as part of the hydroxyl group-containing components.

[0012] Polyol compound (c) has a low molecular weight. Therefore, polyol compound (c) controls the viscosity of the clear coating composition to an appropriate range and improves the pot life, even though the clear coating composition is a high-solids material with a solid content of 50% by mass or more. Polyol compound (c) also has a high hydroxyl value. Therefore, the crosslinking density is increased, resulting in a coating film with excellent physical properties.

[0013] The physical properties of a paint film include, for example, adhesion, water resistance, hardness, weather resistance, and tackiness. Pot life is the time (working time) during which the paint can be used after mixing the main component and hardener. When the main component and hardener are mixed, the reaction between the two begins, and the hardening of the paint composition progresses. During the hardening reaction, the viscosity of the paint composition increases, and eventually its fluidity is lost. If the pot life is short, the viscosity of the paint composition increases rapidly, and the smoothness of the resulting paint film decreases.

[0014] It is even more important to use a specific organic amine catalyst (g) as a curing catalyst in the presence of the polyol compound (c). Since the organic amine catalyst (g) does not readily exhibit catalytic activity at room temperature, the pot life of the paint composition is improved. On the other hand, the organic amine catalyst (g) exhibits excellent catalytic activity under heated conditions, improving the hardness and water resistance of the coating film. By using the polyol compound (c) and the organic amine catalyst (g) in combination, the pot life is further improved and the curing reaction proceeds more easily. As a result, even with high-solids paints, a coating film with excellent appearance and physical properties can be obtained. Since the organic amine catalyst (g) exhibits catalytic activity even at relatively low temperatures, a coating film with excellent physical properties can be obtained even when high-solids paints are cured at low temperatures, for example, below 100°C.

[0015] The clear coating composition according to this embodiment also contains a cellulose derivative (f). The cellulose derivative (f) is positioned near the surface of the coating film through interaction with hydroxyl group-containing components (a) to (c). Therefore, tack on the surface of the coating film is suppressed.

[0016] The clear coating composition according to this embodiment further includes organic dispersed particles (e). The organic dispersed particles (e) control the viscosity of the coating composition after application, suppressing appearance abnormalities such as sagging. In addition, the organic dispersed particles (e) suppress the reaction between the hydroxyl group-containing components in the coating composition and the isocyanate compound, further increasing the pot life, while interacting with the hydroxyl group-containing components (a) to (c) after application to further increase the hardness of the coating film. The hydroxyl group-containing components (a) to (c) are dissolved in the clear coating composition and do not exist as particles. In this respect, the hydroxyl group-containing components (a) to (c) and the organic dispersed particles (e) are distinguishable.

[0017] Hereinafter, hydroxyl group-containing acrylic resins (a), hydroxyl group-containing polyester resins (b), and polyol compounds (c), as well as other coating film-forming components containing hydroxyl groups (excluding curing agents), may be collectively referred to as "hydroxyl group-containing components."

[0018] The solid content concentration of the clear coating composition is 50% by mass or more. The above solid content concentration is for the clear coating composition to be used for coating. The clear coating composition to be used for coating is diluted to a viscosity suitable for coating using, for example, a diluent. According to this embodiment, even if the solid content concentration of the diluted clear coating composition to be used for coating is 50% by mass or more (high solid), the smoothness of the resulting coating film is improved.

[0019] The solid content concentration of the clear coating composition may be 55% by mass or more, or 58% by mass or more. The solid content concentration of the clear coating composition may be 70% by mass or less, or 65% by mass or less. In one embodiment, the solid content concentration of the clear coating composition is 50% by mass or more, or 70% by mass or less.

[0020] The viscosity of the clear coating composition measured by the flow cup method at 23°C is, for example, 30 seconds or less. The above viscosity is for the clear coating composition to be used for painting, immediately after preparation (specifically, within 30 minutes after the hardener and other components have been mixed). Hereinafter, the above viscosity will be referred to as the coating viscosity η. ０ This is referred to as [this]. According to this embodiment, even though the solid content concentration is 50% by mass or more, the coating viscosity of the clear coating composition is [this].０ The viscosity of the paint can be reduced. ０ The time may be 29 seconds or less, or 28 seconds or less. Coating viscosity η ０ This may be 14 seconds or more, and may be 18 seconds or more. In one embodiment, the coating viscosity η of the clear coating composition measured by the flow cup method at 23°C ０ The time is between 15 and 30 seconds.

[0021] The viscosity of the clear coating composition is measured at 23°C using a No. 4 Ford cup, in accordance with JIS K5600-2-2:1999, "3. Flow Cup Method". The viscosity is the average value of the viscosities of five different coating compositions with the same composition.

[0022] The clear coating composition of this embodiment has a long pot life, and the viscosity is maintained for a long period of time. For example, the time until the viscosity of the clear coating composition measured by the above method exceeds 30 seconds (especially 28 seconds) is 4 hours or more. Therefore, a sudden increase in viscosity during the clear coating film formation process is prevented, and a decrease in workability and smoothness is suppressed.

[0023] (a) Hydroxyl group-containing acrylic resin The hydroxyl group-containing acrylic resin (a) is a resin (film-forming component) that forms the base of the clear coating film. The hydroxyl group-containing acrylic resin (a) reacts with the polyisocyanate compound (d) to form a crosslinked structure.

[0024] The hydroxyl group-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 from among acrylic acid and its esters, and methacrylic acid and its esters.

[0025] The hydroxyl value (OHV) of the hydroxyl group-containing acrylic resin (a) is 90 mgKOH / g or more and 190 mgKOH / g or less. When the hydroxyl value of the hydroxyl group-containing acrylic resin (a) is 90 mgKOH / g or more, the crosslink density tends to be high. When the hydroxyl value of the hydroxyl group-containing acrylic resin (a) is 190 mgKOH / g or less, the hydrophilicity of the coating film is suppressed, and the water resistance of the clear coating film tends to be improved. The hydroxyl value of the hydroxyl group-containing acrylic resin (a) may be 100 mgKOH / g or more, and may be 110 mgKOH / g or more. The hydroxyl value of the hydroxyl group-containing acrylic resin (a) may be 180 mgKOH / g or less, and may be 170 mgKOH / g or less. The hydroxyl value of the hydroxyl group-containing acrylic resin (a) may be, for example, 100 mgKOH / g or more and 180 mgKOH / g or less, and may be 110 mgKOH / g or more and 170 mgKOH / g or less.

[0026] The hydroxyl value and acid value can be determined by a neutral titration method using an aqueous potassium hydroxide solution described in JIS K 0070.

[0027] The weight average molecular weight of the hydroxyl group-containing acrylic resin (a) is 4,000 or more and 6,000 or less. When the weight average molecular weight of the hydroxyl group-containing acrylic resin (a) is 4,000 or more, the hardness and weather resistance of the resulting coating film tend to be improved. When the weight average molecular weight of the hydroxyl group-containing acrylic resin (a) is 6,000 or less, an excessive increase in the viscosity of the coating composition is likely to be suppressed. The weight average molecular weight of the hydroxyl group-containing acrylic resin (a) may be 4,200 or more, and may be 4,300 or more. The weight average molecular weight of the hydroxyl group-containing acrylic resin (a) may be 5,800 or less, and may be 5,500 or less. The weight average molecular weight of the hydroxyl group-containing acrylic resin (a) may be 4,200 or more and 5,800 or less, and may be 4,300 or more and 5,500 or less.

[0028] The weight average molecular weight can be calculated based on the molecular weight of standard polystyrene from the chromatogram measured by gel permeation chromatography. As the gel permeation chromatography, for example, HLC-8200 (manufactured by Tosoh Corporation) is used. The measurement conditions using this are as follows. Column: 3 TSgel Super Multipore HZ-M Developing solvent: Tetrahydrofuran Column inlet oven: 40 °C Flow rate: 0.35 ml Detector: Differential refractive index detector (RI) Standard polystyrene: PS oligomer kit manufactured by Tosoh Corporation

[0029] The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (a) is 15 °C or higher and 100 °C or lower. When the Tg of the hydroxyl group-containing acrylic resin (a) is 15 °C or higher, the stain resistance, scratch resistance, and hardness of the resulting coating film are likely to be improved. When the Tg of the hydroxyl group-containing acrylic resin (a) is 100 °C or lower, the quick drying property of the clear coating composition is likely to be improved. The Tg of the hydroxyl group-containing acrylic resin (a) may be 18 °C or higher, and may be 20 °C or higher. The Tg of the hydroxyl group-containing acrylic resin (a) may be 95 °C or lower, and may be 90 °C or lower. The Tg of the hydroxyl group-containing acrylic resin (a) may be 18 °C or higher and 95 °C or lower, and may be 20 °C or higher and 90 °C or lower.

[0030] The glass transition temperature (Tg) is determined by the following method using a differential scanning calorimeter (DSC). For the hydroxyl group-containing acrylic resin (a), a step of heating from 20 °C to 150 °C at a heating rate of 10 °C / min (step 1), a step of cooling from 150 °C to -50 °C at a cooling rate of 10 °C / min after step 1 (step 2), and a step of heating from -50 °C to 150 °C at a heating rate of 10 °C / min after step 2 (step 3) are performed. The value obtained from the chart during the heating in step 3 is the Tg of the hydroxyl group-containing acrylic resin (a). As the DSC, for example, a thermal analyzer SSC5200 (manufactured by Seiko Electronics) is used.

[0031] The acid value (AV) of the hydroxyl group-containing acrylic resin (a) may be, for example, 2 mg KOH / g or more and 30 mg KOH / g or less. This can further improve the smoothness of the resulting coating film. Furthermore, when the coating composition is applied on another uncured coating film, the occurrence of mixed layers can be suppressed. The acid value of the hydroxyl group-containing acrylic resin (a) may be 3 mg KOH / g or more. The acid value of the hydroxyl group-containing acrylic resin (a) may be 20 mg KOH / g or less, and may be 15 mg KOH / g or less. The acid value of the hydroxyl group-containing acrylic resin (a) may be 3 mg KOH / g or more and 20 mg KOH / g or less, and may be 3 mg KOH / g or more and 15 mg KOH / g or less.

[0032] The amount of hydroxyl group-containing acrylic resin (a) relative to 100 parts by mass of the total solid content of hydroxyl group-containing components is, for example, 60 parts by mass or more. This makes it easier to improve the smoothness of the resulting coating film. The above amount of hydroxyl group-containing acrylic resin (a) may be 65 parts by mass or more, and may be 70 parts by mass or more. The above amount of hydroxyl group-containing acrylic resin (a) is, for example, 95 parts by mass or less. This makes it easier to improve the drying properties of the clear coating composition. The above amount of hydroxyl group-containing acrylic resin (a) may be 92 parts by mass or less, and may be 90 parts by mass or less. In one embodiment, the amount of hydroxyl group-containing acrylic resin (a) relative to 100 parts by mass of the total solid content of hydroxyl group-containing components is 60 parts by mass or more and 95 parts by mass or less, may be 65 parts by mass or more and 92 parts by mass or less, and may be 70 parts by mass or more and 90 parts by mass or less.

[0033] Examples of raw material monomers for the hydroxyl group-containing acrylic resin (a) include hydroxy acrylate esters such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; hydroxy methacrylate esters such as 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate. Furthermore, if necessary, acrylic acid; acrylic acid esters such as methyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and isobornyl acrylate; methacrylic acid; methacrylic acid esters such as methyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and isobornyl methacrylate; and ethylenically unsaturated monomers having an aromatic ring such as styrene may also be used. These can be used individually or in combination of two or more. Commercially available hydroxyl group-containing acrylic resin (a) may also be used.

[0034] (b) Hydroxyl group-containing polyester resin The hydroxyl group-containing polyester resin (b) is also a coating film-forming component. The hydroxyl group-containing polyester resin (b) reacts with the polyisocyanate compound (d) to form a crosslinked structure. The hydroxyl group-containing polyester resin (b) has multiple ester bonds and one or more hydroxyl groups.

[0035] The hydroxyl group-containing acrylic resin (a) tends to increase the viscosity of the clear coating composition. On the other hand, the hydroxyl group-containing polyester resin (b) generally has low viscosity and tends to increase the hydroxyl value. By using the hydroxyl group-containing polyester resin (b) in combination, it is possible to improve the crosslinking density while suppressing the increase in viscosity.

[0036] The hydroxyl value of the hydroxyl group-containing polyester resin (b) is, for example, 250 mg KOH / g or more and less than 500 mg KOH / g. If the above hydroxyl value is 250 mg KOH / g or more, the crosslinking density may be further increased. If the above hydroxyl value is less than 500 mg KOH / g, the hydrophilization of the coating film is suppressed, and the water resistance of the clear coating film may be further improved. The hydroxyl value of the hydroxyl group-containing polyester resin (b) may be 260 mg KOH / g or more, and may be 270 mg KOH / g or more. The hydroxyl value of the hydroxyl group-containing polyester resin (b) may be 480 mg KOH / g or less, and may be 450 mg KOH / g or less. The hydroxyl value of the hydroxyl group-containing polyester resin (b) may be 260 mg KOH / g or more and 480 mg KOH / g or less, and may be 270 mg KOH / g or more and 450 mg KOH / g or less.

[0037] The weight-average molecular weight of the hydroxyl group-containing polyester resin (b) is, for example, 1,500 or more and 2,500 or less. When the weight-average molecular weight is 1,500 or more, the hardness and weather resistance of the resulting coating film can be further improved. When the weight-average molecular weight is 2,500 or less, excessive viscosity increase of the coating composition is further suppressed. The weight-average molecular weight of the hydroxyl group-containing polyester resin (b) may be 1,600 or more, or 1,700 or more. The weight-average molecular weight of the hydroxyl group-containing polyester resin (b) may be 2,400 or less, or 2,300 or less. The weight-average molecular weight of the hydroxyl group-containing polyester resin (b) may be 1,600 or more and 2,400 or less, or 1,700 or more and 2,300 or less.

[0038] From the viewpoint of viscosity, the hydroxyl group-containing polyester resin (b) may have a hydroxyl value of 250 mg KOH / g or more and less than 500 mg KOH / g, and a weight-average molecular weight of 1,500 or more and 2,500 or less.

[0039] The amount of solids of the hydroxyl group-containing polyester resin (b) relative to 100 parts by mass of the total solids of the hydroxyl group-containing components is, for example, 4 parts by mass or more. This makes it easier to improve the smoothness of the resulting coating film. The amount of solids of the hydroxyl group-containing polyester resin (b) may be 7 parts by mass or more, and may be 10 parts by mass or more. The amount of solids of the hydroxyl group-containing polyester resin (b) may be, for example, 30 parts by mass or less. This makes it easier to improve the drying properties of the clear coating composition. The amount of solids of the hydroxyl group-containing polyester resin (b) may be 25 parts by mass or less, and may be 20 parts by mass or less. In one embodiment, the amount of solids of the hydroxyl group-containing polyester resin (b) relative to 100 parts by mass of the total solids of the hydroxyl group-containing components is 4 parts by mass or more and 30 parts by mass or less, may be 7 parts by mass or more and 25 parts by mass or less, and may be 10 parts by mass or more and 20 parts by mass or less.

[0040] The hydroxyl group-containing polyester resin (b) can be obtained, for example, by polycondensation (esterification reaction) of a polyhydric alcohol with a polybasic acid or its anhydride. A commercially available hydroxyl group-containing polyester resin (b) may also be used.

[0041] The polyhydric alcohols are not particularly limited and include, for example, 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 can be used individually or in combination of two or more.

[0042] Polybasic acids or their anhydrides are not particularly limited and include, for example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic 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, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid, and endo anhydride. These can be used individually or in combination of two or more.

[0043] The hydroxyl group-containing polyester resin may be modified using lactones, oils or fatty acids, melamine resin, urethane resin, etc. The oils or fatty acids are not particularly limited and include, for example, oils such as castor oil, dehydrated castor oil, coconut oil, corn oil, cottonseed oil, linseed oil, perilla oil, poppy oil, safflower oil, soybean oil, and tung oil, or fatty acids extracted from these oils.

[0044] (c) Polyol compound Polyol compound (c) is also a coating film-forming component. Polyol compound (c) reacts with polyisocyanate compound (d) to form a crosslinked structure.

[0045] Polyol compound (c) is other than hydroxyl group-containing acrylic resin (a) and hydroxyl group-containing polyester resin (b), and has two or more hydroxyl groups in one molecule. The hydroxyl value of polyol compound (c) is high, exceeding 200 mg KOH / g and being 1,000 mg KOH / g or less. Therefore, even with the addition of a small amount, the crosslinking density of the clear coating composition can be improved. In addition, the molecular weight (weight-average molecular weight in the case of a polymer) of polyol compound (c) is between 100 and 1,000, which is a low molecular weight. Therefore, the viscosity of the clear coating composition does not increase easily.

[0046] In this embodiment, a hydroxyl group-containing acrylic resin (a) and a hydroxyl group-containing polyester resin (b) are used together with a different low-molecular-weight polyol compound (c) with a high hydroxyl value. This results in a clear coating composition that is high-solid, yet has low viscosity, and can form a clear coating film with excellent smoothness and hardness.

[0047] The hydroxyl value of polyol compound (c) may be 300 mg KOH / g or more, and may be 400 mg KOH / g or more. The hydroxyl value of polyol compound (c) may be 950 mg KOH / g or less, and may be 900 mg KOH / g or less. The hydroxyl value of polyol compound (c) may be 300 mg KOH / g or more and 950 mg KOH / g or less, and may be 400 mg KOH / g or more and 900 mg KOH / g or less.

[0048] The molecular weight of polyol compound (c) may be 110 or more, or 120 or more. The molecular weight of polyol compound (c) may be 800 or less, or 500 or less, or 300 or less. The molecular weight of polyol compound (c) may be 110 or more and 800 or less, or 120 or more and 500 or less, or 120 or more and 300 or less.

[0049] The solid content of polyol compound (c) relative to 100 parts by mass of resin solids in the clear coating composition is, for example, 1 part by mass or more and 10 parts by mass or less. When the solid content of polyol compound (c) is 1 part by mass or more, the smoothness of the resulting coating film tends to improve. When the solid content of polyol compound (c) is 10 parts by mass or less, the drying properties of the clear coating composition tend to improve. The solid content of polyol compound (c) may be 3 parts by mass or more. The solid content of polyol compound (c) may be 5 parts by mass or less. The solid content of polyol compound (c) may be 3 parts by mass or more and 5 parts by mass or less.

[0050] The amount of polyol compound (c) relative to 100 parts by mass of the total solid content of hydroxyl group-containing components is, for example, 1 part by mass or more. This makes it easier to improve the smoothness of the resulting coating film. The amount of polyol compound (c) relative to 100 parts by mass or more may be 1.5 parts by mass or more, and may be 2 parts by mass or more. The amount of polyol compound (c) relative to 10 parts by mass or less is, for example. This makes it easier to improve the drying properties of the clear coating composition. The amount of polyol compound (c) relative to 100 parts by mass of the total solid content of hydroxyl group-containing components is 1 part by mass or more and 10 parts by mass or less, 1.5 parts by mass or more and 7 parts by mass or less, and 2 parts by mass or more and 5 parts by mass or less.

[0051] The solids content ratio (b / c) of the hydroxyl group-containing polyester resin (b) and the polyol compound (c), based on mass, is, for example, 90 / 10 to 50 / 50. This makes it easier to improve the physical properties of the resulting coating film while suppressing an increase in the viscosity of the clear coating composition. The solids content ratio (b / c) may be 90 / 10 to 60 / 40, or 90 / 10 to 70 / 30.

[0052] The solid content ratio (a / (b+c)) of the hydroxyl group-containing acrylic resin (a), hydroxyl group-containing polyester resin (b), and polyol compound (c), based on mass, is, for example, 90 / 10 to 60 / 40. This makes it easier to improve the physical properties of the resulting coating film while suppressing an increase in the viscosity of the clear coating composition. The mixing ratio (a / (b+c)) may be 90 / 10 to 70 / 30, or 90 / 10 to 75 / 25.

[0053] From the viewpoint of viscosity, film smoothness, and hardness, the amount of solids of the hydroxyl group-containing acrylic resin (a) relative to the total solids of the hydroxyl group-containing acrylic resin (a), hydroxyl group-containing polyester resin (b), and polyol compound (c) per 100 parts by mass may be 60 parts by mass or more and 95 parts by mass or less. Similarly, the amount of solids of the hydroxyl group-containing polyester resin (b) may be 4 parts by mass or more and 30 parts by mass or less. Similarly, the amount of solids of the polyol compound (c) may be 1 part by mass or more and 10 parts by mass or less.

[0054] The amount of solids in the hydroxyl group-containing acrylic resin (a) relative to 100 parts by mass of the solids of (a) + (b) + (c) may be 65 parts by mass or more, and may be 70 parts by mass or more. The amount of solids in the hydroxyl group-containing acrylic resin (a) relative to 100 parts by mass of the solids of (a) + (b) + (c) may be 95 parts by mass or less, and may be 90 parts by mass or less. In one embodiment, the amount of solids in the hydroxyl group-containing acrylic resin (a) relative to 100 parts by mass of the solids of (a) + (b) + (c) is 60 parts by mass or more and 95 parts by mass or less, may be 65 parts by mass or more and 95 parts by mass or less, and may be 70 parts by mass or more and 90 parts by mass or less.

[0055] The amount of solids in the hydroxyl group-containing polyester resin (b) relative to 100 parts by mass of the solids of (a) + (b) + (c) may be 7 parts by mass or more, and may be 10 parts by mass or more. The amount of solids in the hydroxyl group-containing polyester resin (b) relative to 100 parts by mass of the solids of (a) + (b) + (c) may be 25 parts by mass or less, and may be 20 parts by mass or less. In one embodiment, the amount of solids in the hydroxyl group-containing polyester resin (b) relative to 100 parts by mass of the solids of (a) + (b) + (c) is 7 parts by mass or more and 25 parts by mass or less, may be 7 parts by mass or more and 25 parts by mass or less, and may be 10 parts by mass or more and 20 parts by mass or less.

[0056] The amount of solids in polyol compound (c) relative to 100 parts by mass of the solids in (a) + (b) + (c) may be 1.5 parts by mass or more, and may be 2 parts by mass or more. The amount of solids in polyol compound (c) relative to 100 parts by mass of the solids in (a) + (b) + (c) may be 7 parts by mass or less, and may be 5 parts by mass or less. In one embodiment, the amount of solids in polyol compound (c) relative to 100 parts by mass of the solids in (a) + (b) + (c) is 1.5 parts by mass or more and 7 parts by mass or less, may be 1.5 parts by mass or more and 7 parts by mass or less, and may be 2 parts by mass or more and 5 parts by mass or less.

[0057] The polyol compound (c) is not particularly limited as long as it is other than the hydroxyl group-containing acrylic resin (a) and the hydroxyl group-containing polyester resin (b) and has two or more hydroxyl groups in one molecule. The polyol compound (c) may have alicyclic hydrocarbon groups, as this easily improves the physical properties of the resulting coating film (especially hardness and weather resistance). From a similar viewpoint, the polyol compound (c) may have two hydroxyl groups.

[0058] At least one hydroxyl group of polyol compound (c) may be directly bonded to an alicyclic hydrocarbon group or bonded via a C1 or C2 hydrocarbon group. The alicyclic hydrocarbon group may be a five-membered ring or a six-membered ring.

[0059] The polyol compound (c) may have two hydroxyl groups and an alicyclic hydrocarbon group. The two hydroxyl groups may be bonded to the alicyclic hydrocarbon group via a hydrocarbon group having one or two carbon atoms. Examples of such polyol compounds (c) include diol compounds such as cyclohexanediol, cyclohexanedimethanol, cyclohexanediethanol, and cyclopentanedimethanol. The arrangement of the two hydroxyl groups of the diol compound is not particularly limited and may be 1,1-, 1,2-, 1,3-, or 1,4-. From the viewpoint of hardness, it may be 1,4-cyclohexanedimethanol or 1,1-cyclohexanediethanol.

[0060] (Other hydroxyl group-containing components) The clear coating composition according to this embodiment may further contain, for example, at least one selected from the group consisting of polycarbonate polyol resin, polyether polyol resin, and polycaprolactone polyol resin, as other hydroxyl group-containing components.

[0061] The amount of solids of other hydroxyl group-containing components relative to 100 parts by mass of the total solids of hydroxyl group-containing components is, for example, 20 parts by mass or less, may be 15 parts by mass or less, or may be 10 parts by mass or less.

[0062] (d) Polyisocyanate compound The polyisocyanate compound (d) is a curing agent that reacts with hydroxyl group-containing components to form a crosslinked structure and cure the paint composition.

[0063] Polyisocyanate compound (d) has at least two isocyanate groups in one molecule. Examples of polyisocyanate compound (d) include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having aromatic rings not bonded to isocyanate groups in the molecule (aroliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specifically, examples include aromatic polyisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; and polymers of these, such as biuret type, nurate type, and adduct type. These can be used individually or in combination of two or more.

[0064] The equivalent ratio (NCO / OH) of the isocyanate group contained in the polyisocyanate compound (d) to the hydroxyl group contained in the hydroxyl group-containing component may be 0.7 or more, or 0.8 or more. The equivalent ratio (NCO / OH) may 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. When the equivalent ratio (NCO / OH) is within this range, a clear coating film with excellent hardness and weather resistance is easily formed. The equivalent ratio (NCO / OH) may be 0.8 or more and 1.8 or less, or 0.8 or more and 1.5 or less.

[0065] (Other curing agents) The clear coating composition according to this embodiment may further contain, as other curing agents, at least one selected from the group consisting of, for example, amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. The content of the other curing agents is appropriately set depending on the coating film forming components.

[0066] (e) Organic dispersed particles The organic dispersed particles (e) contribute to viscosity control and pot life improvement of the clear coating composition, as well as improvement of coating film hardness. The organic dispersed particles (e) are particles made of organic compounds. Because the organic dispersed particles (e) can be uniformly dispersed in particulate form even in a high-solid clear coating composition, interactions between the particles are unlikely to occur, and the viscosity of the clear coating composition does not increase significantly.

[0067] On the other hand, as the clear coating composition is applied and the solid content concentration increases further, the interactions between the organic dispersed particles (e) become stronger. As a result, the organic dispersed particles (e) function as viscosity modifiers, suppressing appearance abnormalities such as sagging. At this time, the organic dispersed particles (e) also strongly interact with the hydroxyl group-containing components. Therefore, a highly hard coating film is quickly formed from the clear coating composition. This coating film fully satisfies the performance requirements of, for example, automotive parts.

[0068] In a high-solidity clear coating composition, the reactivity between the hydroxyl group-containing component and the polyisocyanate compound (d) tends to increase. As described above, the organic dispersed particles (e) are dispersed in the clear coating composition and can easily penetrate between the hydroxyl group-containing component and the polyisocyanate compound (d), maintaining their separation. This can improve the pot life of the clear coating composition. Due to these effects, the organic dispersed particles (e) significantly contribute to the high-solidity of the coating.

[0069] The particle size of the organic dispersed particles (e) is not particularly limited. The average particle size of the organic dispersed particles (e) is, for example, 10 nm to 500 nm. The average particle size of the organic dispersed particles (e) in the clear coating composition may be 15 nm or more, or 20 nm or more. The average particle size of the organic dispersed particles (e) may be 300 nm or less, or 150 nm or less. The average particle size of the organic dispersed particles (e) is the 50% mean particle size (D50) of the primary particles in the number-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer. The average particle size of the organic dispersed particles (e) may be 15 nm to 300 nm, or 20 nm to 150 nm.

[0070] The amount of organic dispersed particles (e) per 100 parts by mass of the total solid content of the hydroxyl group-containing components is, for example, 0.1 parts by mass or more. This is expected to improve the pot life of the clear coating composition. The above amount of organic dispersed particles (e) may be 0.5 parts by mass or more, and may be 1 part by mass or more. The above amount of organic dispersed particles (e) may be, for example, 10 parts by mass or less. This makes it easier to suppress the increase in the coating viscosity of the clear coating composition. The above amount of organic dispersed particles (e) may be 7 parts by mass or less, and may be 5 parts by mass or less. In one embodiment, the amount of organic dispersed particles (e) per 100 parts by mass of the total solid content of the hydroxyl group-containing components is 0.1 parts by mass or more and 10 parts by mass or less, may be 0.5 parts by mass or more and 7 parts by mass or less, and may be 1 part by mass or more and 5 parts by mass or less.

[0071] The organic dispersed particles (e) are organic compounds and are not particularly limited as long as they are insoluble in the clear coating composition. Examples of organic dispersed particles include organic compounds having a cross-linking structure within the molecule (cross-linked dispersed particles (e1)), core-shell type organic compounds (core-shell dispersed particles (e2)), and NAD (non-aqueous dispersed particles).

[0072] The cross-linked dispersed particles (e1) are, for example, (meth)acrylic resin. "(meth)acrylic" is a concept that includes both acrylic and methacrylic.

[0073] Crosslinked dispersed particles (e1) are prepared, for example, as follows: First, an ethylenically unsaturated monomer (e11) and a crosslinkable monomer (e12) are emulsion polymerized in an aqueous solvent by a known method to obtain an emulsion containing polymer crosslinked fine particles. Then, the water contained in the emulsion is removed. This yields crosslinked dispersed particles (e1). Water removal is performed, for example, by replacing the aqueous solvent with an organic solvent, azeotropy, centrifugation, filtration, or drying. When the aqueous solvent is replaced with an organic solvent, the crosslinked dispersed particles (e1) are obtained dispersed in the organic solvent.

[0074] Typical examples of ethylenically unsaturated monomers (e11) include alkyl esters of (meth)acrylic acid. Examples of alkyl esters of (meth)acrylic acid include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These can be used individually or in combination of two or more.

[0075] As the ethylenically unsaturated monomer (e11), other monomers having an ethylenically unsaturated bond that can copolymerize with the alkyl ester of acrylic acid or methacrylic acid mentioned above may be used. Examples of other monomers include styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, and dimethylaminoethyl (meth)acrylate. These may be used individually or in combination of two or more.

[0076] Typical examples of crosslinkable monomers (e12) include monomers (e12a) having two or more radically polymerizable ethylenically unsaturated bonds within a single molecule, and combinations (e12b) of two ethylenically unsaturated group-containing monomers, each having mutually reactive groups. Monomers (e12a) and monomer combinations (e12b) can be used individually or in combination.

[0077] Examples of monomers (e12a) include polymerizable unsaturated monocarboxylic acid esters of polyhydric alcohols, polymerizable unsaturated alcohol esters of polybasic acids, and aromatic compounds having two or more vinyl groups.

[0078] As the raw material monomer for the crosslinked dispersed particles (e1), a monomer (e13) having a functional group that can react with the crosslinking agent may also be used. Typical examples of monomers (e13) include carboxyl group-containing monomers, hydroxyl group-containing monomers, and nitrogen-containing monomers.

[0079] The core-shell dispersed particles (e2) are, for example, (meth)acrylic resins. In the core-shell dispersed particles (e2), the core part contains, for example, an acrylate monomer (e21) containing a hydroxyl group or an α,β-ethylenically unsaturated monomer (e22a) having a carboxyl group, and an α,β-ethylenically unsaturated monomer (e22b) having a hydroxyl group. The hydroxyl value of the core part is, for example, 100 mgKOH / g or more and 200 mgKOH / g or less.

[0080] Examples of the acrylate monomer (e21) containing a hydroxyl group include 4-hydroxybutyl acrylate (4HBA), CH ２ =C(R)COO(CH ２ ) ２ O[CO(CH ２ ) ｍ O] ｎ H (where R is hydrogen or a lower alkyl group having 6 or less carbon atoms, and m and n are natural numbers such that the number of carbon atoms in the “(CH ２ ) ２ O[CO(CH ２ ) ｍ O] ｎ ” part is 4 or more and 12 or less).

[0081] Examples of the α,β-ethylenically unsaturated monomer (e22a) having a carboxyl group include acrylic acid, methacrylic acid, etc. Examples of the α,β-ethylenically unsaturated monomer (e22b) having a hydroxyl group include hydroxy acrylates such as 2-hydroxyethyl acrylate; hydroxy methacrylates such as 2-hydroxyethyl methacrylate;

[0082] The core part may further contain acrylic acid; acrylate esters such as methyl acrylate; methacrylic acid; methacrylate esters such as methyl methacrylate; monomers having one or two vinyl groups; monomers having an isocyanate group; monomers having an allyl group; monomers having an epoxy group; acid anhydrides having one or two vinyl groups;

[0083] In the organic dispersed particles (e), the shell portion includes, for example, a hydroxyl group-containing acrylic resin (polymer). The hydroxyl value of the shell portion is, for example, 50 mg KOH / g or more and 160 mg KOH / g or less.

[0084] Examples of raw material monomers for the shell portion include hydroxyacrylate esters such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; and hydroxy methacrylate esters such as 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate. The raw material monomers for the shell portion may further include acrylic acid; acrylic acid esters such as methyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and isoboronyl acrylate; methacrylic acid; methacrylic acid esters such as methyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and isoboronyl methacrylate; and ethylenically unsaturated monomers having an aromatic ring such as styrene.

[0085] Core-shell dispersed particles (e2) can be produced, for example, by polymerizing the constituent material (polymer) of the shell portion and the constituent material (monomer) of the core portion in a solvent in which the monomer dissolves but the polymer does not.

[0086] (f) Cellulose derivatives Cellulose derivative (f) suppresses tack of the coating film. Low tack is particularly desired for clear coating films. Tack is more likely to occur in coating films that have been cured at low temperatures. Cellulose derivative (f) can also function as a viscosity modifier.

[0087] The cellulose derivative (f) comprises at least one selected from the group consisting of cellulose ethers and cellulose esters.

[0088] Examples of cellulose esters include nitrocellulose, cellulose acetate, cellulose triacetate, cellulose acetate phthalate, cellulose acetate butyrate, cellulose butyrate, cellulose triplythyrate, cellulose propionate, cellulose triplythyrate, cellulose acetate propionate, carboxymethylcellulose acetate, carboxymethylcellulose acetate propionate, carboxymethylcellulose acetate butyrate, cellulose acetate butyrate succinate, and cellulose propionate butyrate. These can be used individually or in combination of two or more. Among these, carboxymethylcellulose acetate butyrate (CAB) is preferred from the viewpoint of solubility with resin components and the development of viscosity.

[0089] Examples of cellulose ethers include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose.

[0090] The number-average molecular weight of the cellulose derivative (f) is, for example, 10,000 or more. This makes it easier to suppress tack on the surface of the coating film. The number-average molecular weight of the cellulose derivative (f) may be 12,000 or more, or 13,000 or more. The number-average molecular weight of the cellulose derivative (f) is, for example, 40,000 or less. This further suppresses the increase in viscosity of the clear coating composition. The number-average molecular weight of the cellulose derivative (f) may be 30,000 or less, or 25,000 or less. In one embodiment, the number-average molecular weight of the cellulose derivative (f) is 10,000 or more and 40,000 or less, 12,000 or more and 30,000 or less, or 13,000 or more and 25,000 or less.

[0091] The Tg of cellulose derivative (f) is, for example, 80°C or higher. This can improve tackiness. The Tg of cellulose derivative (f) may be 82°C or higher, or 85°C or higher. The Tg of cellulose derivative (f) is, for example, 160°C or lower. This can properly maintain the viscosity of the clear coating composition. The Tg of cellulose derivative (f) may be 150°C or lower, or 130°C or lower. In one embodiment, the Tg of cellulose derivative (f) is 80°C or higher and 160°C or lower, 82°C or higher and 150°C or lower, or 85°C or higher and 130°C or lower.

[0092] From the viewpoint of viscosity, the cellulose derivative (f) may have a number-average molecular weight of 10,000 or more and 40,000 or less, and a Tg glass transition temperature of 80°C or higher.

[0093] The amount of cellulose derivative (f) blended with 100 parts by mass of the total solid content of the hydroxyl group-containing components is, for example, 0.1 parts by mass or more. This makes it easier to suppress the tack on the surface of the resulting coating film. The above amount of cellulose derivative (f) may be 0.2 parts by mass or more, and may be 0.5 parts by mass or more. The above amount of cellulose derivative (f) may be 10 parts by mass or less. This makes it easier to suppress the increase in viscosity. The above amount of cellulose derivative (f) may be 7 parts by mass or less, and may be 5 parts by mass or less. In one embodiment, the amount of cellulose derivative (f) blended with 100 parts by mass of the total solid content of the hydroxyl group-containing components is 0.1 parts by mass or more and 10 parts by mass or less, may be 0.2 parts by mass or more and 7 parts by mass or less, and may be 0.5 parts by mass or more and 5 parts by mass or less.

[0094] (Other viscosity modifiers) The clear coating composition according to this embodiment may contain other viscosity modifiers other than the organic dispersed particles (e) and the cellulose derivative (f). Other viscosity modifiers can be used insofar as they do not hinder the effects of the present invention. The amount of other viscosity modifiers blended with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing components may be 10 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less.

[0095] Other viscosity modifiers include, for example, inorganic viscous agents, urethane-associated viscous agents, polycarboxylic acid-type viscous agents, and amide-based viscous agents. These can be used individually or in combination of two or more. Examples of inorganic viscous agents include layered silicates (silicate minerals), halide minerals, oxide minerals, carbonate minerals, borate minerals, sulfate minerals, molybdate minerals, tungstate minerals, phosphate minerals, arsenate minerals, and vanadate minerals. Examples of urethane-associated viscous agents include polyurethane-based viscous agents having hydrophobic chains in their molecules, and urethane-urea-based viscous agents in which at least a portion of the main chain is a hydrophobic urethane chain.

[0096] (g) Organic amine catalyst The organic amine catalyst (g) has an amidine group. Compounds having an amidine group are a type of amine. The organic amine catalyst (g) does not contain metal atoms. The clear coating composition has a long pot life when used in combination with the organic amine catalyst (g) and the polyol compound (c). On the other hand, the organic amine catalyst (g) exhibits excellent catalytic activity under heating. In particular, the organic amine catalyst (g) shows high activity even at low temperatures (e.g., below 80°C), improving the physical properties of the resulting coating film. In addition, with the organic amine catalyst (g), the curing reaction can be completed in a short time (e.g., within 20 minutes) even at low temperatures. Therefore, post-treatment such as polishing can be performed immediately after the curing treatment.

[0097] The amidine group has a structure in which a carbon (C) atom is bonded to one nitrogen (N) atom by a double bond and to one nitrogen atom by a single bond. The general formula for the amidine group is: -C(=NR １ )-N(R ２ ) - is represented by this.

[0098] In the formula, R １ and R ２ These are, independently of each other, a hydrogen atom and a monovalent or divalent hydrocarbon group having 1 to 3 carbon atoms. １ and R ２ This means that a ring structure (a heterocycle containing an N atom) may be formed via one or more C atoms.

[0099] Examples of the above-mentioned organic amine catalyst (g) that does not have a heterocycle include N'-cyclohexyl-N,N-dimethylformamidine, N'-methyl-N,N-di-n-butylacetamidine, N'-octadecyl-N,N-dimethylformamidine, N'-cyclohexyl-N,N-dimethylvaleroamidine, 1-methyl-2-cyclohexyliminopyrrolidine, 3-butyl-3,4,5,6-tetrahydropyrimidine, N-(hexyliminomethyl)morpholine, N-(α-(decyliminoethyl)ethyl)pyrrolidine, N'-decyl-N,N-dimethylformamidine, N'-dodecyl-N,N-dimethylformamidine, and N'-cyclohexyl-N,N-acetamidine.

[0100] Examples of the above heterocycles include imidazoline rings, imidazole rings, tetrahydropyrimidine rings, dihydropyrimidine rings, and pyrimidine rings. The organic amine catalyst (g) may have an imidazole ring.

[0101] The organic amine catalyst (g) may have the above-mentioned heterocycle, or it may be a polycyclic compound having the above-mentioned heterocycle.

[0102] Examples of organic amine catalysts (g) having an imidazole ring include N-(2-hydroxyethyl)imidazole, N-(3-aminopropyl)imidazole, 4-(hydroxymethyl)imidazole, 1-(tert-butoxycarbonyl)imidazole, imidazole-4-propionic acid, 4-carboxyimidazole, 1-butylimidazole, 1-methylimidazole, 2-methyl-4-imidazolecarboxylic acid, 4-formylimidazole, 1-(ethoxycarbonyl)imidazole, reaction products of propylene oxide with imidazole and 2-methylimidazole, 1-trimethylsilylimidazole, 4-(hydroxymethyl)imidazole hydrochloride, 1H-imidazolium, 3-ethyl-1-methyl-benzoyl Examples include copolymers of 1-chloro-2,3-epoxypropane and imidazole, 1-(p-toluenesulfonyl)imidazole, 1,1-carbonylbisimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, 2-phenyl-2-imidazoline pyromelitate, 4-(hydroxymethyl)imidazole picrate, disodium salts of 2-propenoic acid and 4,5-dihydro-2-nonyl-1H-imidazole-1-ethanol and 2-heptyl-4,5-dihydro-1H-imidazole-1-ethanol, 1-(cyanoethyl)-2-undecylimidazole trimellitate, formate esters of 1-(2-hydroxypropyl)imidazole, sodium imidazole salts, and silver imidazole salts.

[0103] Examples of polycyclic organic amine catalysts (g) include 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), 1,4-diazabicyclo[3.3.0]octe-4-ene, 2-methyl-1,5-diazabicyclo[4.3.0]one-5-ene, 2,7,8-trimethyl-1,5-diazabicyclo[4.3.0]one-5-ene, 2-butyl-1,5-diazabicyclo[4.3.0]one-5-ene, and 1,9-diazabicyclo[6.5.0]tridece-8-ene.

[0104] The organic amine catalyst (g) can be used individually or in combination of two or more types.

[0105] The content of the organic amine catalyst (g) is, for example, 0.1% by mass or more and 1.0% by mass or less relative to the resin solids. This can further improve the smoothness and pot life of the resulting coating film. The content of the organic amine catalyst (g) may be 0.2% by mass or more, and may be 0.5% by mass or more. The content of the organic amine catalyst (g) may be 1.5% by mass or less, and may be 1.0% by mass or less. The content of the organic amine catalyst (g) may be 0.2% by mass or more and 1.5% by mass or less, and may be 0.5% by mass or more and 1.0% by mass or less.

[0106] (Other Catalysts) The clear coating composition according to this embodiment may contain catalysts other than the organic amine catalyst (g). Examples of other catalysts include organometallic compounds, bismuth compounds, amine compounds without an amidine group, metal (e.g., lead, tin, zinc) complexes of carboxylic acids, and boric acid compounds. These may be used individually or in combination of two or more.

[0107] Examples of organometallic compounds include organotin compounds such as diacetyltin diacetate, dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, diacetyltin dioctoate, tin octoate, dibutyltin diacetate, and dibutyltin dioctoate; organoaluminum compounds such as aluminum trimethoxide, aluminum tris(acetylacetonate), aluminum tri-n-butoxide, aluminum tris(acetacetate ethyl), aluminum diisopropoxy(acetacetate ethyl), and aluminum acetylacetonate; and titanium tetra Examples include organotitanium compounds such as (monoethyl ethoxide), titanium tetra(monoethyl ethoxide), titanium tetra(monobutyl ethoxide), titanium tetrakis(acetylacetonate), and tetran-butyl titanate; organozirconium compounds such as zirconium tetra(monomethyl ethoxide), zirconium tetra(monoethyl ethoxide), zirconium tetra(monobutyl ethoxide), zirconium-n-propylate, zirconium-n-butyrate, and zirconium tetrakis(acetylacetonate); and organozinc compounds such as zinc naphthenate.

[0108] Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, and bismuth carboxylic acid.

[0109] Examples of amine compounds that do not have an amidine group include trimethylamine, triethylamine, 2-(dimethylamino)ethyl methacrylate, 1-methylpiperidine, 1-methylpyrrolidine, pyridine, 4-dimethylaminopyridine, 4-(1-piperidyl)pyridine, N-methylimidazole, and N,N-dimethylaniline.

[0110] Examples of boric acid compounds include boric acid esters such as trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, triphenyl borate, tri(4-chlorophenyl) borate, and trihexafluoroisopropyl borate.

[0111] The content of other catalysts is, for example, less than 0.05% by mass relative to the resin solids. This may further improve the pot life. The content of other catalysts may be 0.03% by mass or less, or 0.02% by mass or less. The content of other catalysts may be 0.01% by mass or more. The content of other catalysts may be 0% by mass.

[0112] (h) Diluting component The clear coating composition according to this embodiment may contain a diluting component (h). The clear coating composition is diluted with the diluting component as appropriate, taking into consideration the coating method and the coating environment such as temperature and humidity. Examples of diluting components include water and non-aqueous solvents. The clear coating composition according to this embodiment may also contain non-aqueous solvents used in the manufacture of each component.

[0113] Non-aqueous solvents include, for example, aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, and mineral split; ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl-i-butyl ketone, methyl amyl ketone, and cyclohexanone; aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, and decalin; ester organic solvents such as methyl acetate, ethyl acetate, n-butyl acetate, and amyl acetate; cellosolve organic solvents such as methyl cellosolve, ethyl cellosolve, n-propyl cellosolve, i-propyl cellosolve, n-butyl cellosolve, i-butyl cellosolve, i-amyl cellosolve, phenyl cellosolve, and benzyl cellosolve; methyl carbitol, etc. Examples of carbitol-based organic solvents include carbitol carbitol, n-propyl carbitol, i-propyl carbitol, n-butyl carbitol, i-butyl carbitol, i-amyl carbitol, carbitol acetate, phenyl carbitol, and benzyl carbitol; and ether-based organic solvents such as ethylene glycol monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-n-butyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and dioxane. These can be used individually or in combination of two or more.

[0114] (Other Additives) The clear coating composition according to this embodiment may contain other additives commonly used in the coating field. For example, it may contain coloring pigments and / or gloss pigments, to the extent that they do not impair transparency. Furthermore, it may contain ultraviolet absorbers, hindered amine light stabilizers, antioxidants, crosslinked resin particles, surface modifiers, catalysts, etc.

[0115] [Clear Coating] A clear coating can be formed using the clear coating composition according to this embodiment. The resulting clear coating has good smoothness and physical properties.

[0116] The thickness of the clear coating is not particularly limited. From the viewpoint of scratch resistance and smoothness, the thickness of the clear coating after drying may be, for example, 15 μm or more, and may be 20 μm or more. The thickness of the clear coating may be 60 μm or less, and may be 40 μm or less. The thickness of the clear coating after drying may be, for example, 15 μm or more and 60 μm or less, and 20 μm or more and 40 μm or less. The thickness of the clear coating can be measured using an electromagnetic film thickness gauge (for example, SANKO SDM-miniR). The thickness of the clear coating is the average value of the thickness of the clear coating at any five points. The thickness of other coatings is measured and calculated in the same way.

[0117] The clear coating has high hardness. The hardness of the clear coating, measured according to JIS K-5600-5-4 scratch hardness (pencil method), is, for example, B or higher.

[0118] The clear coating has excellent smoothness. The amount of reflected light in the long-wavelength region (1200 μm to 12000 μm) is measured by a surface reflectance measuring instrument (e.g., Wave Scan-dual, manufactured by BYK). ０ ) may be 20 or less. In Wave Scan-dual, laser light is shone onto the clear coating at a 60° angle while the light source is moved, and the reflected light is measured. The measured reflected light is classified by wavelength. The above LW ０ The smaller the value, the smoother the surface. LW ０ This value was measured for the clear coating film formed by the clear coating composition immediately after preparation.

[0119] Because the clear coating composition according to this embodiment has a long pot life, for example, a clear coating film formed using the clear coating composition four hours after preparation is also smooth. ０ And the LW of the clear coating film formed using the clear coating composition four hours after preparation. １Difference from: LW １ -LW ０ For example, it may be 10 or less, 5 or less, or 1 or less.

[0120] [Method for forming a clear coating] A clear coating is formed by applying a clear coating composition to the object to be coated and then curing it. The clear coating composition can be cured by heating. The application method and curing conditions will be described later.

[0121] [Painted Article] The clear coating is usually positioned on the outermost layer so as to cover one or more other coatings formed on the object to be coated. A painted article having a clear coating comprises, for example, an object to be coated, a colored coating formed on the object to be coated, and a clear coating formed on the colored coating. The clear coating is formed by the clear coating composition according to this embodiment.

[0122] (Subject to be coated) The material of the subject to be coated is not particularly limited. Examples of subject materials include metal, resin, and glass.

[0123] The shape of the object to be painted is not particularly limited. Specifically, the objects to be painted include automobile bodies and parts for automobile bodies such as passenger cars, trucks, motorcycles, and buses, as well as automobile parts such as spoilers, bumpers, mirror covers, grilles, and door handles.

[0124] Examples of metals include iron, copper, aluminum, tin, zinc, or alloys thereof (e.g., steel). Typical examples of metals to be coated include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy plated steel sheets, zinc-aluminum-magnesium alloy plated steel sheets, aluminum plated steel sheets, aluminum-silicon alloy plated steel sheets, and tin plated steel sheets.

[0125] Metallic workpieces may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, metallic workpieces may be further coated with electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0126] Examples of resins include polyethylene resin, EVA resin, polyolefin resin (polyethylene resin, polypropylene resin, etc.), vinyl chloride resin, styrene resin, polyester resin (including PET resin, PBT resin, etc.), polycarbonate resin, acrylic resin, acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene (AS) resin, polyamide resin, acetal resin, phenolic resin, fluororesin, melamine resin, urethane resin, epoxy resin, and polyphenylene oxide (PPO). The resin-coated object may be degreased.

[0127] The clear coating composition according to this embodiment is suitable for coating resin substrates because it can be cured at low temperatures. The substrate may include both resin parts (parts formed from resin) and metal parts (parts formed from metal). The substrate may be made of resin.

[0128] (Colored coating) The colored coating may be a single layer or a laminated coating of two or more layers. The colored coating may be a so-called primer coating of one or two or more layers, a so-called base coating of one or two or more layers, or a combination thereof.

[0129] <Base Coating> The base coating is formed by a base paint composition comprising, for example, a film-forming component, a curing agent, a viscosity modifier, a diluent, and a pigment. The base paint composition may contain various additives as needed. The components contained in each base coating may be the same or different. The base paint composition may be solvent-based or water-based. Examples of film-forming components, curing agents, viscosity modifiers, and diluent components incorporated into the base paint composition include the components exemplified above as those incorporated into the clear coating composition.

[0130] The viscosity of the base coating composition, as measured by Ford Cup No. 4 at 20°C, is, for example, between 11 seconds and 25 seconds. The solid content of the base coating composition is, for example, between 15% by mass and 70% by mass. The solid content of the base coating composition is the total components of the base coating composition excluding the diluent components.

[0131] The thickness of the base coating is not particularly limited and is set appropriately according to the purpose. The thickness of one layer of the base coating is, for example, 10 μm or more, may be 15 μm or more, or may be 20 μm or more. The thickness of one layer of the base coating is, for example, 50 μm or less, may be 45 μm or less, or may be 40 μm or less. The thickness of one layer of the base coating is, for example, 10 μm or more and 50 μm or less, may be 15 μm or more and 45 μm or less, or may be 20 μm or more and 40 μm or less.

[0132] Examples of pigments include coloring pigments, luminosity pigments, and extender pigments. Examples of coloring pigments include organic coloring pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolon pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments; and inorganic coloring pigments such as lead yellow, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. These can be used individually or in combination of two or more.

[0133] Examples of luminous pigments include metal flakes (aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel-chromium, 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 can be used individually or in combination of two or more.

[0134] Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc. These can be used individually or in combination of two or more.

[0135] The total pigment concentration, i.e., the mass ratio (PWC) of the total pigment to 100% by mass of the resin solids content of the base coating composition, is preferably 0.1% by mass or more and 50% by mass or less. This improves the smoothness of the resulting coating film. The PWC of individual pigments is not particularly limited. The PWC of a lustrous pigment may be, for example, 1% by mass or more and 40% by mass or less. The PWC of a lustrous pigment is preferably 5% by mass or more. The PWC of a lustrous pigment is preferably 30% by mass or less. The PWC of a lustrous pigment is preferably 5% by mass or more and 30% by mass or less.

[0136] <Primer Coating> The primer coating is interposed between the object to be coated and the base coating. The primer coating improves the adhesion between the base coating and the object to be coated (especially resin-based objects). In addition, if the surface of the object to be coated is uneven, the primer coating makes the painted surface uniform, which helps to suppress unevenness in the base coating.

[0137] The primer coating is formed by a primer coating composition comprising, for example, a film-forming component, a material adhesion component, a viscosity modifier, a diluent, a pigment, and optionally a curing agent. The primer coating composition may optionally contain various additives. The primer coating composition may be solvent-based or water-based. Examples of the film-forming component, curing agent, viscosity modifier, diluent, and pigment include the components exemplified as being blended into the base coating composition. For example, the viscosity of a water-based primer coating composition, as measured by a B-type viscometer at 20°C, 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 the total components of the primer coating composition excluding the diluent.

[0138] The thickness of the primer film is not particularly limited. In terms of the smoothness and chipping resistance of the painted article, the thickness of the primer film may be 5 μm or more and 40 μm or less. The thickness of the primer film may be 7 μm or more. The thickness of the primer film may be 25 μm or less. The thickness of the primer film may be 7 μm or more and 25 μm or less.

[0139] [Method for Manufacturing Painted Articles] The above-mentioned painted articles are manufactured by a method comprising the steps of: applying a colored paint composition to an object to be painted to form an uncured colored coating film; curing the uncured colored coating film; applying a clear paint composition to the colored coating film to form an uncured clear coating film; and curing the uncured clear coating film.

[0140] When a clear coating is formed, the colored coating may be cured or uncured. In particular, from the viewpoint of productivity, adhesion, and water resistance, it is preferable to laminate each coating without curing it (so-called wet-on-wet coating) and then cure these multiple uncured coatings simultaneously. That is, it is preferable that the coated article be manufactured by a method comprising: applying a colored paint composition onto a workpiece to form an uncured colored coating; applying a clear paint composition onto the uncured colored coating to form an uncured clear coating; and curing the uncured colored coating and the uncured clear coating.

[0141] The following describes each step using a method for forming a base coating as a colored coating as an example. However, the method for manufacturing a painted article according to this embodiment is not limited thereto. A primer coating and a base coating may be formed as the colored coating. The primer coating can be formed in the same way as the base coating.

[0142] (I) Formation of an uncured base coating film An uncured base coating film is formed by applying the above-mentioned base coating composition to the object to be coated. The base coating composition is applied, for example, so that the thickness of the base coating film after curing is 10 μm or more and 50 μm or less.

[0143] The painting method is not particularly limited. Examples of painting methods include air spray painting, airless spray painting, and rotary atomization painting. These methods may be combined with electrostatic painting. Among these, rotary atomization electrostatic painting is preferred from the viewpoint of coating efficiency. For rotary atomization electrostatic painting, rotary atomization electrostatic painting machines commonly known as "micro-microbell (μμbell)", "microbell (μbell)", or "metallicbell (metabell)" are used.

[0144] After applying the base coating composition, pre-drying (preheating) may be performed. This suppresses the boiling of diluent components in the base coating composition during curing, making it easier to suppress the occurrence of bubbling. Furthermore, pre-drying suppresses the mixing of the uncured base coating film and the coating composition applied on top of it, making it difficult for a multiphase to form. As a result, the smoothness of the resulting coated article is easily improved.

[0145] The conditions for pre-drying are not particularly limited. Examples of pre-drying include leaving the product at room temperature for 5 to 15 minutes, or heating it at a temperature of 50°C to 80°C for 30 seconds to 5 minutes.

[0146] (II) Formation of an uncured clear coating The uncured clear coating is formed by applying the above-mentioned clear coating composition onto the colored coating. The clear coating composition is applied, for example, so that the thickness of the clear coating after curing is 15 μm or more and 60 μm or less.

[0147] The painting method is not particularly limited. For example, the painting method may be the same as that used for the base coating composition. Among these, rotary atomizing electrostatic coating is preferred from the viewpoint of coating efficiency. After painting the clear coating composition, pre-drying may be performed. The conditions for pre-drying are not particularly limited and may be the same as those for pre-drying the base coating film.

[0148] (III) Curing each of the cured and uncured coating films. Each coating film can be cured by heating. In this step, the base coating film and the clear coating film may be cured at the same time.

[0149] The heating conditions are set appropriately according to the composition of each coating composition and the material of the object to be coated. The heating temperature is, for example, 60°C to 100°C. According to the clear coating composition of this embodiment, a clear coating film with high hardness is formed even at such low temperatures. The heating temperature may be, for example, 75°C or lower, or 70°C or lower.

[0150] The heating time can be set appropriately according to the heating temperature. When the heating temperature is between 60°C and 100°C, the heating time may be, for example, between 5 minutes and 20 minutes, or between 10 minutes and 15 minutes. The heating time refers to the time during which the heating device is maintained at the target temperature, and does not take into account the time it takes to reach the target temperature. Examples of heating devices include drying ovens that utilize heat sources such as hot air, electricity, gas, and infrared radiation.

[0151] The present invention will be described below with reference to examples. However, the present invention is not limited to the examples described below.

[0152] [Examples 1-11, Comparative Examples 1-12] Each component was mixed according to the components and amounts shown in Table 1. The solid content concentration of the obtained clear coating composition was 58% by mass.

[0153] The components used in the examples and comparative examples are as follows: (a) The hydroxyl group-containing acrylic resin was manufactured as follows.

[0154] [Production of hydroxyl group-containing acrylic resin A] In a reactor equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet, and cooling tube, 57 parts of butyl acetate were charged, and the temperature was raised to 120°C under stirring while introducing nitrogen gas. To this reactor, a mixture consisting of 0.8 parts methacrylic acid, 26.8 parts 2-ethylhexyl acrylate, 33.0 parts methyl methacrylate, and 39.4 parts 2-hydroxyethyl methacrylate, and a solution of 10 parts t-butyl peroxy-2-ethylhexanate dissolved in 5 parts butyl acetate were added dropwise over 3 hours. After the dropwise addition was complete, the reactor was allowed to mature for 1 hour. Then, a solution of 0.2 parts t-butyl peroxy-2-ethylhexanate dissolved in 5 parts butyl acetate was added dropwise over 1 hour. The reactor was allowed to mature for 2 hours while maintaining the temperature at 120°C to complete the reaction and obtain a hydroxyl group-containing acrylic resin. The obtained hydroxyl-containing acrylic resin had a non-volatile content of 60%, a weight-average molecular weight of 4,500, and a glass transition temperature of 20°C. The hydroxyl value (OHV) was calculated to be 170 from the monomer composition.

[0155] [Production of hydroxyl group-containing acrylic resins B to F] Hydroxyl group-containing acrylic resins B to F were produced in the same manner as hydroxyl group-containing acrylic resin A, except that the type and amount of monomer and the amount of polymerization initiator (t-butyl peroxy-2-ethylhexanate) were as shown in Table 1.

[0156]

[0157] (b) Hydroxyl group-containing polyester resin, trade name Basonol HPE1170B, manufactured by BASF, hydroxyl value 280 mgKOH / g, weight-average molecular weight 1,800

[0158] (c) Polyol compound A: 1,4-cyclohexanedimethanol, hydroxyl value 780 mgKOH / g, molecular weight 144

[0159] B: 1,1-Cyclohexanediethanol, hydroxyl value 652 mgKOH / g, molecular weight 172

[0160] C: Polypropylene glycol diol type 2000, manufactured by Wako Pure Chemical Industries, Ltd., hydroxyl value 56 mg KOH / g, molecular weight 2,000. D: Polycarbonate diol, Duranol T-5650J, manufactured by Asahi Kasei Corporation, hydroxyl value 140 mg KOH / g, molecular weight 800.

[0161] (d) Polyisocyanate compound, trade name N3300, manufactured by Covestro, isocyanurate of hexamethylene diisocyanate.

[0162] (e) Organic dispersed particles A: Product name Setalux10-6266, manufactured by Allnex, average particle size 65 nm, cross-linked dispersed particles B: Product name AZS-797, manufactured by Nippon Paint Co., Ltd., average particle size 94 nm, cross-linked dispersed particles

[0163] (f) Cellulose derivative, trade name Eastman CAB 551-0.01, manufactured by Eastman Chemical Company, carboxymethylcellulose acetate butyrate (CAB), number average molecular weight 16,000, Tg 85℃

[0164] (g) Organic amine catalyst DBU: 1,8-diazabicyclo[5.4.0]undeca-7-ene

[0165] DBN: 1,5-diazabicyclo[4.3.0]nona-5-ene

[0166] KAT-1: 1H-Imidazolium,3-ethyl-1-methyl-,benzoate, CAS No. 150999-33-0

[0167] (h) Diluting component: N-butyl acetate

[0168] (Other viscosity modifiers) Product name: Disparon 6900, manufactured by Kusumoto Kasei Co., Ltd., amide-based viscosity modifier

[0169] (Other catalysts) Tin catalyst: Dibutyltin dilaurate, manufactured by Tokyo Chemical Industry Co., Ltd.

[0170] [Evaluation] The clear coating compositions prepared in the examples and comparative examples, or test specimens (coated articles) coated with these clear coating compositions, were evaluated as follows. The evaluation results are shown in Tables 2 and 3. The method for preparing the test specimens is as follows.

[0171] (Preparation of test specimens) An ABS resin substrate was prepared as the substrate to be coated, and it was wiped with isopropyl alcohol. Next, Nippon Paint Automotive Coatings Co., Ltd.'s high-solid base coating R-3410 #1J7 (silver) was applied to this substrate using a spray gun (Anest Iwata Corporation; W-101-134G) to a dry film thickness of 15 μm. After that, it was dried for 3 minutes in an environment with a temperature of 20 ± 5°C and a relative humidity of 78% or less to form an uncured base coating film on the ABS substrate.

[0172] Next, the freshly prepared clear coating composition was applied to the base coating using a spray gun (Anest Iwata Corporation; W-101-134G) to achieve a dry film thickness of 30 μm. The substrate was then left for 10 minutes at a temperature of 20 ± 5°C and a relative humidity of 78% or less to form an uncured clear coating. Subsequently, the substrate with these multi-layer coatings was heated in a drying oven at 70°C for 10 minutes to obtain test specimens with cured base and clear coatings.

[0173] (Paint viscosity η) ０ The viscosity of the clear coating composition within 30 minutes of preparation was measured at 23°C using a No. 4 Ford cup, in accordance with JIS K5600-2-2:1999 "3. Flow cup method". The average viscosity of five different clear coating compositions with the same composition was used to determine the coating viscosity η. ０ The viscosity of the paint was determined to be η. ０ The following criteria were used for evaluation: Good: Paint viscosity η ０ Failure if 15 seconds or more but 28 seconds or less: Paint viscosity η ０ Over 28 seconds

[0174] (Smoothness A) The smoothness A of the test specimen was evaluated using a surface measuring instrument (BYK, Wave Scan-dual). The evaluation criteria are as follows: Good: LW ０If 20 or less is defective: LW ０ over 20

[0175] (Smoothness B) The smoothness B of test specimens prepared in the same manner as above, except that a clear coating composition that had been prepared 4 hours prior was used, was measured and evaluated in the same manner as smoothness A. Good: LW １ If 20 or less is defective: LW １ over 20

[0176] (Hardness) The hardness of the test specimen was measured in accordance with JIS K-5600-5-4 scratch hardness (pencil method). The measured values ​​were evaluated according to the following criteria: Good: Measured value of "B" or higher; Poor: Measured value of "2B" or lower.

[0177] (Initial Adhesion) A single-blade cutting tool specified in JIS K-5600-5-6 was applied vertically to the coated surface of the test specimen to make cuts (parallel lines 1) that reached the substrate. Furthermore, 10 cuts parallel to these parallel lines 1 were made at equal intervals. Eleven cuts (parallel lines 2) were made at equal intervals, intersecting these 11 parallel lines 1 perpendicularly and reaching the substrate. The spacing between parallel lines 1 and between parallel lines 2 was 2 mm. In this way, a grid pattern was formed with 100 squares enclosed by four straight lines.

[0178] A transparent pressure-sensitive tape, as specified in JIS K-5600-5-6, was applied to the grid-like pattern described above, ensuring that no air bubbles were trapped between it and the painted surface. The tape was then quickly peeled off within 0.5 to 1.0 seconds, and the degree of peeling in the grid-like pattern was visually evaluated. The evaluation criteria were as follows: Good: No peeling of the paint film was observed. Poor: Peeling of the paint film was observed.

[0179] (Water Resistance) The test specimens were immersed in a water bath maintained at 40°C for 240 hours. After that, the test specimens were removed from the water and dried at room temperature for 1 hour. Next, a grid pattern was formed on the test specimens in the same manner as above, and a peel test and evaluation were performed.

[0180] (Surface Tack) Under a 23°C atmosphere, the surface of the coating on the test piece was pressed with a finger to evaluate the presence or absence of tackiness (surface tack). The evaluation criteria were as follows: Good: No tackiness was felt. Poor: Tackiness was felt.

[0181] (Weather Resistance) A 1200-hour accelerated weathering test was performed on the test specimens using a Sunshine Weatherometer S80 (Sunshine Carbon Arc type accelerated weathering tester, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS B 7753. After the test, the appearance of the test specimens was visually observed, the color difference (ΔE) before and after the test was measured, and the 60° gloss value was measured. The 60° gloss value was measured using a gloss meter GN-268Plus (manufactured by Konica Minolta Corporation). The following four items were evaluated: no peeling of the coating after the accelerated weathering test, no significant abnormalities observed in appearance, a color difference (ΔE) of 3.0 or less, and a 60° gloss value of 80 or more. Good: All of the above four items are satisfied. Acceptable: One of the above four items is not satisfied. Poor: Two or more of the above four items are not satisfied.

[0182] (Pot Life) Clear coating compositions were prepared in 500 mL poly cups under conditions of 23°C and 50% RH. The viscosity of the clear coating composition within 30 minutes after preparation and the viscosity after standing for 4 hours under conditions of 23°C and 50% RH were measured using the method described above. The difference between these was evaluated according to the following criteria: Good: Viscosity change within 5 seconds. Poor: Viscosity change exceeding 5 seconds.

[0183]

[0184]

[0185] The clear coating compositions of the examples had a high solid content, but their viscosity remained sufficiently low even after 4 hours from preparation. Examples 9 and 10, in particular, exhibited excellent pot life. The clear coating compositions of the examples yielded a coating film with good appearance and high physical properties under low-temperature, short-time curing conditions of 70°C for 10 minutes.

[0186] The clear coating compositions of Comparative Examples 1, 4, 7, and 11-12 had excessively high viscosity even within 30 minutes of preparation, making it impossible to obtain a smooth coating film. Furthermore, the clear coating compositions of Comparative Examples 1, 4, and 7 had even higher viscosity after 4 hours, making them unsuitable for application, and thus the smoothness B could not be evaluated. The clear coating compositions of Comparative Examples 2 and 5 had low viscosity immediately after preparation, but were unable to maintain low viscosity and were inferior in smoothness A. Comparative Example 5 could not be evaluated for smoothness B. Comparative Example 10 was inferior in smoothness A, B, and pot life. In Comparative Examples 3, 6, and 8-9, coating films with inferior physical properties were obtained under low-temperature, short-time curing conditions of 70°C for 10 minutes.

[0187] The clear coating composition of the present invention can be suitably used, for example, in automobile vehicles and automobile parts.

[0188] This application claims priority under Japanese Patent Application No. 2024-197935, filed in Japan on November 13, 2024, the entirety of which is incorporated herein by reference.

Claims

1. The material comprises a hydroxyl group-containing acrylic resin (a), a hydroxyl group-containing polyester resin (b), a polyol compound (c) other than the hydroxyl group-containing acrylic resin (a) and the hydroxyl group-containing polyester resin (b), a polyisocyanate compound (d), organic dispersed particles (e), a cellulose derivative (f), and an organic amine catalyst having an amidine group (g), wherein the hydroxyl group-containing acrylic resin (a) has a hydroxyl value of 90 mg KOH / g or more and 190 mg KOH / g or less, a weight-average molecular weight of 4000 or more and 6000 or less, and a glass transition temperature of 15°C or more and 100°C or less, the polyol compound (c) has a hydroxyl value exceeding 200 mg KOH / g and 1000 mg KOH / g or less, and a molecular weight of 100 or more and 1000 or less, and the cellulose derivative (f) comprises at least one selected from the group consisting of cellulose ethers and cellulose esters. A clear coating composition having a solid content concentration of 50% by mass or more.

2. The clear coating composition according to claim 1, wherein the polyol compound (c) has two hydroxyl groups and an alicyclic hydrocarbon group.

3. The clear coating composition according to claim 1 or 2, wherein the solid content of the polyol compound (c) is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of resin solids.

4. The clear coating composition according to any one of claims 1 to 3, wherein the organic amine catalyst (g) has a heterocycle containing a nitrogen atom.

5. The clear coating composition according to any one of claims 1 to 4, wherein the content of the organic amine catalyst (g) is 0.1% by mass or more and 1% by mass or less relative to the resin solids.

6. The clear coating composition according to any one of claims 1 to 5, wherein the hydroxyl group-containing polyester resin (b) has a hydroxyl value of 250 mg KOH / g or more and less than 500 mg KOH / g, and a weight-average molecular weight of 1500 or more and 2500 or less.

7. A clear coating composition according to any one of claims 1 to 6, for coating a resin substrate.

8. The clear coating composition according to any one of claims 1 to 7, wherein the average particle size of the organic dispersed particles (e) is 10 nm or more and 500 nm or less.

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