Multi-liquid type clear coating composition

Abstract

To provide a clear coating composition which enables formation of a coating film that is excellent in pot life property while curable at low temperature, and has excellent scratch resistance and bird dropping resistance.SOLUTION: A multi-liquid type clear coating composition contains a first liquid containing a hydroxyl group-containing acrylic resin, polyester polyol (B), an organic metal catalyst (C) and an acid (D), and a second liquid containing a polyisocyanate compound (E), wherein the polyester polyol (B) contains at least one kind selected from the group consisting of polyester polyol (B1), polyester polyol (B2), polyester polyol (B3), polyester polyol (B4), and polyester polyol (B5) which is a reactant of linear or branched polyhydric alcohol having three or more hydroxyl groups, linear or branched alkandiol, and a linear or branched alkanedicarboxylic acid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a multi-component clear coating composition.

Background Art

[0002] In recent years, in the technical field of automobiles and the like, shortening of the coating process has been demanded from the viewpoints of energy saving and reduction of carbon dioxide emissions. Patent Document 1 discloses a two-component coating material containing a) a specific polyisocyanate, b) a hydroxy-functional poly(meth)acrylate polyol, c) a Lewis base, d) an organic solvent, etc., and it is disclosed that the above coating material may contain a polyester polyol.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The two-component coating material of Patent Document 1 can be cured at low temperature. Usually, in order to achieve curing at low temperature, many catalysts for promoting the reaction of the crosslinking component are blended. Therefore, the pot life tends to be short. That is, the pot life property deteriorates. In addition, the coating film obtained by low-temperature curing may not have sufficient scratch resistance and bird droppings resistance.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a clear coating composition that can be cured at low temperature, has excellent pot life property, and can form a coating film having excellent scratch resistance and bird droppings resistance.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides the following aspects. [1] A first liquid containing a hydroxyl group-containing acrylic resin (A), a polyester polyol (B), an organometallic catalyst (C), and an acid (D), and a second liquid containing a polyisocyanate compound (E), wherein the polyester polyol (B) is at least one selected from the group consisting of a polyester polyol (B1) represented by the following formula (1), a polyester polyol (B2) represented by the following formula (2), a polyester polyol (B3) represented by the following formula (3), a polyester polyol (B4) represented by the following formula (4), and a polyester polyol (B5) which is a reaction product of a linear or branched polyhydric alcohol having three or more hydroxyl groups, a linear or branched alkanediol, and a linear or branched alkanedicarboxylic acid, Formula (1):

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0007] According to the present invention, there is provided a clear coating composition capable of forming a coating film having excellent pot life properties, excellent scratch resistance and excellent bird droppings resistance while being curable at low temperature. [Embodiments for Carrying Out the Invention]

[0008] [Clear Coating Composition] The clear coating composition according to the present disclosure includes a first liquid containing a hydroxyl group-containing acrylic resin (A), a polyester polyol (B), an organometallic catalyst (C), and an acid (D), and a second liquid containing a polyisocyanate compound (E).

[0009] The polyester polyol (B) contains at least one selected from the group consisting of polyester polyols (B1) to (B4) represented by the following formulas (1) to (4), and a polyester polyol (B5) which is a reaction product of a linear or branched polyhydric alcohol having three or more hydroxyl groups, a linear or branched alkanediol, and a linear or branched alkanedicarboxylic acid.

[0010] Formula (1):

Chemical formula

[0011] Formula (2):

Chemical formula

[0012] Formula (3):

Chemical formula

[0013] Formula (4):

Chemical formula

[0014] The reasons why the coating film obtained by low-temperature curing does not have sufficient scratch resistance are considered as follows. Usually, in a clear coating composition for the purpose of low-temperature curing, components capable of forming a three-dimensional crosslinked structure are often blended so that sufficient hardness can be obtained even at low temperature curing. A coating film having a three-dimensional crosslinked structure generally has high hardness. On the other hand, such a coating film tends to be brittle and the scratch resistance tends to decrease.

[0015] The polyester polyol (B) used in the present disclosure has a hydroxyl group only at the terminal, and the hydroxyl group is bonded to a linear hydrocarbon group (a hydrocarbon group that is not a cyclic structure). Therefore, by the reaction of the polyester polyol (B) and the polyisocyanate compound (E), a linear portion (linear portion) is formed in the clear coating film. As a result, the stress relaxation property of the entire coating film is enhanced and the scratch resistance is improved.

[0016] By using the polyester polyol (B), it has been found that the resistance to bird droppings is further improved. The resistance to bird droppings means that after removing the adhered bird droppings, the change in the surface state of the coating film is small. The reason for the change in the surface state of the coating film even after removing the bird droppings is not clear, but the following can be considered. When the bird droppings containing moisture dry, the protein contained in the bird droppings shrinks. At this time, the part of the coating film where the bird droppings adhere and the surrounding coating film may shrink or crack along with the shrinkage of the protein even after the bird droppings are removed. As a result, the surface state of the coating film changes.

[0017] Such a change in the surface state of the coating film is also suppressed by increasing the stress relaxation property of the entire coating film.

[0018] The organometallic catalyst (C) is blended to promote the reaction between the hydroxyl group-containing resin typified by the hydroxyl group-containing acrylic resin (A) and the polyester polyol (B) and the polyisocyanate compound (E). Usually, more organometallic catalyst (C) is blended to achieve curing at low temperature. However, the more the blending amount of the organometallic catalyst (C) increases, the shorter the pot life becomes. The pot life is the time during which it is possible to use the mixture as a paint after mixing the first liquid and the second liquid. The coating composition beyond the pot life has an excessively high viscosity, so the performance and appearance of the coating film obtained using it may deteriorate. Hereinafter, the property of being able to maintain a long pot life is referred to as excellent pot life property, and the increase in the pot life is referred to as the improvement of the pot life property.

[0019] In the multi-component clear coating composition according to the present disclosure (hereinafter sometimes simply referred to as the clear coating composition), an acid (D) is blended together with an organometallic catalyst (C). The acid (D) further coordinates or chemically bonds to the central metal of the organometallic catalyst (C) to reduce its catalytic activity. As a result, the promotion of the reaction between the hydroxyl group-containing resin and the polyisocyanate compound (E) is inhibited, and the pot life property is improved. On the other hand, by heating performed for curing, the acid (D) decomposes or becomes a gas and is discharged out of the reaction system. Thereby, the catalytic function of the organometallic catalyst (C) is reactivated again, and a rapid curing reaction occurs even at a low temperature.

[0020] The clear coating composition may be aqueous or solvent-based. The clear coating composition may be solvent-based. The aqueous coating composition contains water as a solvent. In the aqueous coating composition, the proportion of water in the solvent may be 50% by mass or more, may be 70% by mass or more, or may be 100% by mass. The solvent-based coating composition contains an organic solvent (also referred to as a non-aqueous solvent) as a solvent. In the solvent-based coating composition, the proportion of the organic solvent in the solvent may be 50% by mass or more, may be 70% by mass or more, or may be 100% by mass.

[0021] The clear coating composition is a multi-component type containing a first liquid and a second liquid. The clear coating composition may further contain a third liquid containing other components. The clear coating composition is prepared using a method commonly used by those skilled in the art. The clear coating composition can be prepared by mixing the first liquid, the second liquid, and further the third liquid. Examples of the mixing method include a kneading and mixing method using a kneader or a roll, and a dispersion mixing method using a sand grinder mill or a disper.

[0022] The clear coating composition can be cured at a low temperature. The clear coating composition can be cured, for example, at a temperature of 60°C or higher and 120°C or lower. The curing temperature may be 65°C or higher, or may be 70°C or higher. The curing temperature may be 95°C or lower, or may be 90°C or lower.

[0023] (First Liquid) The first liquid contains a hydroxyl group-containing acrylic resin (A), a polyester polyol (B), an organometallic catalyst (C), and an acid (D).

[0024] (A) Hydroxyl group-containing acrylic resin The hydroxyl group-containing acrylic resin (A) is a resin (coating film-forming component) that serves as the base of the clear coating film. The hydroxyl group-containing acrylic resin (A) reacts with the polyisocyanate compound (E) to form a crosslinked structure.

[0025] The hydroxyl group-containing acrylic resin (A) has a plurality of 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 of acrylic acid and its esters, methacrylic acid and its esters.

[0026] The hydroxyl value (OHV) of the hydroxyl group-containing acrylic resin (A) is, for example, 90 mgKOH / g or more and 180 mgKOH / g or less. When the hydroxyl value of the hydroxyl group-containing acrylic resin (A) is 90 mgKOH / g or more, the crosslinking density tends to be high. When the hydroxyl value of the hydroxyl group-containing acrylic resin (A) is 180 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.

[0027] The hydroxyl value can be determined in accordance with the Standard Oil Analysis Test Method 2.3.6.2-1996 established by the Japan Oil Chemists' Society, a public interest incorporated association.

[0028] The weight average molecular weight (Mw) of the hydroxyl group-containing acrylic resin (A) is, for example, 4,000 or more and 8,000 or less. When the Mw of the hydroxyl group-containing acrylic resin (A) is 4,000 or more, the hardness and weather resistance of the resulting coating film are likely to be improved. When the Mw of the hydroxyl group-containing acrylic resin (A) is 8,000 or less, an excessive increase in the viscosity of the coating composition is likely to be suppressed. The Mw of the hydroxyl group-containing acrylic resin (A) may be 4,500 or more, and may be 4,800 or more. The Mw of the hydroxyl group-containing acrylic resin (A) may be 7,500 or less, and may be 7,000 or less.

[0029] Mw is determined by the GPC method using polystyrene as a standard.

[0030] The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A) is, for example, 5°C or more and 100°C or less. When the Tg of the hydroxyl group-containing acrylic resin (A) is 5°C or more, 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 less, 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 8°C or more, and may be 10°C or more. The Tg of the hydroxyl group-containing acrylic resin (A) may be 90°C or less, may be 70°C or less, and may be 50°C or less.

[0031] Tg may be determined by calculation from the types and amounts of the raw material monomers of the resin. Tg may also be measured by a differential scanning calorimeter (DSC).

[0032] From the viewpoint of hardness, the hydroxyl group-containing acrylic resin (A) may have a hydroxyl value of 90 mgKOH / g or more and 180 mgKOH / g or less, a weight average molecular weight of 4,000 or more and 8,000 or less, and a Tg of 5°C or more and 100°C or less.

[0033] The hydroxyl group-containing acrylic resin (A) may contain a hydroxyl group-containing acrylic resin (A1) having an acid value (AV) of 10 mgKOH / g or more and 50 mgKOH / g or less. Thereby, the chemical resistance and hardness of the resulting coating film are likely to be improved. The acid value of the hydroxyl group-containing acrylic resin (A1) may be 15 mgKOH / g or more, and may be 18 mgKOH / g or more. The acid value of the hydroxyl group-containing acrylic resin (A) may be 40 mgKOH / g or less, may be 30 mgKOH / g or less, and may be 25 mgKOH / g or less. The hydroxyl value, Mw, and Tg of the hydroxyl group-containing acrylic resin (A1) may be the same as those of the hydroxyl group-containing acrylic resin (A).

[0034] The acid value can be determined in accordance with the Standard Oil Analysis Test Method 2.3.1-2013 established by the Japan Oil Chemists' Society, a public interest incorporated association.

[0035] The solid content ratio of the hydroxyl group-containing acrylic resin (A) in the total solid content of 100% by mass of the hydroxyl group-containing components (typically, the hydroxyl group-containing acrylic resin (A) and the polyester polyol (B)) is, for example, 60% by mass or more and 95% by mass or less. When the solid content ratio of the hydroxyl group-containing acrylic resin (A) is 60% by mass or more, the smoothness of the resulting coating film is likely to be improved. When the solid content ratio of the hydroxyl group-containing acrylic resin (A) is 95% by mass or less, the drying property of the clear coating composition is likely to be improved. The solid content ratio of the hydroxyl group-containing acrylic resin (A) may be 65% by mass or more, and may be 70% by mass or more. The solid content ratio of the hydroxyl group-containing acrylic resin (A) may be 92% by mass or less, and may be 90% by mass or less.

[0036] The solid content ratio of the hydroxyl group-containing acrylic resin (A1) in 100% by mass of the solid content of the hydroxyl group-containing acrylic resin (A) is, for example, 15% by mass or more and 100% by mass or less. When the solid content ratio of the hydroxyl group-containing acrylic resin (A1) is 20% by mass or more, the hardness of the resulting coating film can be further improved. The solid content ratio of the hydroxyl group-containing acrylic resin (A1) may be 20% by mass or more, may be 30% by mass or more, and may be 40% by mass or more. The solid content ratio of the hydroxyl group-containing acrylic resin (A) may be 90% by mass or less, may be 85% by mass or less, and may be 80% by mass or less.

[0037] The hydroxyl group-containing acrylic resin (A) can be prepared by polymerizing a hydroxyl group-containing α,β-ethylenically unsaturated monomer and other α,β-ethylenically unsaturated monomers by a known method. The hydroxyl group-containing acrylic resin (A) is, for example, prepared by solution polymerization. A commercially available hydroxyl group-containing acrylic resin (A) may also be used.

[0038] Examples of the hydroxyl group-containing α,β-ethylenically unsaturated monomer include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts of these with ε-caprolactone.

[0039] Examples of the α,β-ethylenically unsaturated monomers other than those described above include polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds.

[0040] (B) Polyester polyol The polyester polyol (B) is also a component for forming a coating film. The polyester polyol (B) reacts with the polyisocyanate compound (E) to form a crosslinked structure. The polyester polyol (B) has two or more ester bonds and two or more hydroxyl groups.

[0041] The acrylic resin (A) containing a hydroxyl group tends to increase the viscosity of the clear coating composition. On the other hand, the polyester polyol (B) generally has a low viscosity and is easy to increase the hydroxyl value. By using the polyester polyol (B) in combination with the acrylic resin (A) containing a hydroxyl group, the crosslink density can be improved while suppressing the increase in viscosity.

[0042] In addition, the polyester polyol (B) used in the clear coating composition according to the present disclosure has two or more hydroxyl groups, and all the hydroxyl groups are at the ends of the molecular chain. Therefore, a linear portion is formed in the clear coating film by the reaction of the polyester polyol (B) and the polyisocyanate compound (E). As a result, the stress relaxation property of the entire coating film is enhanced, and the scratch resistance and bird droppings resistance are improved.

[0043] Examples of the polyester polyol (B) having two or more hydroxyl groups and all the hydroxyl groups at the ends of the molecular chain include at least one selected from the group consisting of the following polyester polyols (B1) to (B5). The polyester polyols (B1) to (B4) are represented by formulas (1) to (4), respectively.

[0044] In formulas (1) to (4), the linear alkylene group is a divalent aliphatic hydrocarbon group represented by -(C n H 2n )-. The number of carbon atoms n is, for example, from 1 to 20, and may be from 2 to 12. Examples of the linear alkylene group include methylene, ethylene, n-propylene, n-butylene, n-pentylene, n-hexylene, n-heptylene, n-octylene, n-nonylene, and n-decylene.

[0045] In formulas (1) to (4), the branched alkylene group branched at a position other than the α-position and the β-position is a divalent aliphatic hydrocarbon group represented by -C α H2-C β H2-R-C β H2-C α H2-. C α and C βrepresent the carbon atoms at the α-position and the β-position, respectively. The carbon atom at the α-position is the carbon atom bonded to the hydroxyl group (-OH). The carbon atom at the β-position is the carbon atom bonded to the carbon atom to which the hydroxyl group (-OH) is bonded. R represents an alkylene group which may be branched. The number of carbon atoms in R is, for example, from 1 to 20, and may be from 2 to 12.

[0046] Examples of the branched alkylene group include 3-methyl-n-pentylene group, 3-ethyl-n-pentylene group, 3,4-dimethyl-n-hexylene group, and neopentylene group.

[0047] The hydrocarbon group is a group containing carbon and hydrogen, and is a group obtained by detaching one or more hydrogen atoms from a hydrocarbon. The saturated hydrocarbon group is a hydrocarbon group having no carbon-carbon unsaturated bond (for example, -C=C-, -C≡C-). Specific examples of the saturated hydrocarbon group include aliphatic hydrocarbon groups. The aliphatic hydrocarbon group may be linear, branched or cyclic, and may be either linear or branched. The saturated hydrocarbon group may have one or more N, O, S, Si, amide, sulfonyl, siloxane, carbonyl, carbonyloxy, etc. at its terminal or in the molecular chain. The hydrogen atoms of the saturated hydrocarbon group may be substituted by one or more substituents other than the hydroxyl group.

[0048] (B1) Polyester polyol The polyester polyol (B1) is represented by the following formula (1):

Chemical formula

[0049] a may be an integer from 3 to 50, and may be an integer from 5 to 30.

[0050] R 11 may be a linear alkylene group or a branched alkylene group. R 11 Specifically, examples include linear or branched alkylene groups having 3 to 12 carbon atoms.

[0051] R 12 and R 13 Specifically, examples include linear or branched alkylene groups having 3 to 12 carbon atoms. In two or more repeating units, a plurality of R 12 may be the same. R 12 and R 13 may be the same.

[0052] R 11 is a linear alkylene group having 3 to 12 carbon atoms, R 12 is a linear or branched alkylene group having 3 to 12 carbon atoms, and R 13 may be a linear or branched alkylene group having 3 to 12 carbon atoms. R 11 and R 12 and R 13 may be the same.

[0053] The polyester polyol (B1) is obtained, for example, by an esterification reaction or a transesterification reaction of a specific dicarboxylic acid and a specific diol. In the esterification reaction or the transesterification reaction, the specific dicarboxylic acid and the diol are mixed and heated to 180 to 250°C in the presence of a catalyst.

[0054] Specific examples of the specific dicarboxylic acid include succinic acid, malonic acid, adipic acid, sebacic acid, azelaic acid, or derivatives thereof such as their lower alkyl esters (for example, C1 to C4 alkyl esters) or their acid anhydrides, acyl halides, etc. These may be used alone or in combination of two or more.

[0055] Examples of specific diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 1,9-nonanediol. These can be used individually or in combination of two or more. These can be used individually or in combination of two or more.

[0056] (B2) Polyester polyol The polyester polyol (B2) is represented by the following formula (2):

Chemical formula

[0057] j and k may each be an integer from 1 to 50, and may each be an integer from 2 to 30. j + k may be 2 or more. j + k may be 50 or less, may be 30 or less, and may be 20 or less.

[0058] R 21 may be a linear, branched or alicyclic alkylene group. R 21 Specific examples of R 21 include a linear alkylene group having 2 to 12 carbon atoms, a branched alkylene group having 3 to 12 carbon atoms, and an alicyclic alkylene group having 5 to 12 carbon atoms. R

[0059] R 22 and R23 Specific examples include linear alkylene groups having 2 to 12 carbon atoms and branched alkylene groups having 3 to 12 carbon atoms. R 22 and R 23 may particularly be linear alkylene groups having 2 to 12 carbon atoms, may be linear alkylene groups having 3 to 10 carbon atoms, or may be linear alkylene groups having 4 to 8 carbon atoms. In two or more repeating units, a plurality of R 22 may be the same. In two or more repeating units, a plurality of R 23 may be the same. R 22 and R 23 may be the same.

[0060] R 21 is an alicyclic alkylene group having 5 to 10 carbon atoms, R 22 is a linear alkylene group having 4 to 8 carbon atoms, and R 23 may be a linear alkylene group having 4 to 8 carbon atoms.

[0061] The polyester polyol (B2) is obtained, for example, by a ring-opening polymerization reaction of a lactone compound. In the ring-opening polymerization reaction of the lactone compound, the lactone compound and a diol as an initiator are mixed and heated to 130 to 220°C in the presence of a catalyst.

[0062] Examples of the lactone compound include ε-caprolactone, δ-valerolactone, γ-butyrolactone, β-propiolactone, α-acetolactone, and cyclic esters of these and lactide.

[0063] Examples of the diol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 1,2-propanediol, 1,3-butanediol, 1,2-butanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,8-octanediol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, and 2,4-diethyl-1,5-pentanediol.

[0064] (B3) Polyester polyol The polyester polyol (B3) is represented by the following formula (3):

Chemical formula

[0065] p, q, and r may each be an integer from 3 to 50, or may be an integer from 5 to 30. p + q + r is 3 or more, may be 5 or more, and may be 6 or more. p + q + r may be 50 or less, may be 30 or less, and may be 20 or less.

[0066] R 31 may be a linear or branched trivalent aliphatic hydrocarbon group. R 31Specific examples include branched trivalent aliphatic hydrocarbon groups having 3 to 10 carbon atoms.

[0067] R 32 、R 33 or R 34 Specific examples include linear alkylene groups having 2 to 12 carbon atoms and branched alkylene groups having 3 to 12 carbon atoms. R 32 、R 33 or R 34 may particularly be a linear alkylene group having 2 to 12 carbon atoms, may be a linear alkylene group having 3 to 10 carbon atoms, or may be a linear alkylene group having 4 to 8 carbon atoms. In two or more repeating units, a plurality of R 32 may be the same. In two or more repeating units, a plurality of R 33 may be the same. In two or more repeating units, a plurality of R 34 may be the same. R 32 and R 33 and R 34 may be the same.

[0068] R 31 is a branched trivalent aliphatic hydrocarbon group having 3 to 10 carbon atoms, and R 32 、R 33 and R 34 may all be linear alkylene groups having 4 to 8 carbon atoms.

[0069] The polyester polyol (B3) can be obtained, for example, by a procedure similar to the ring-opening polymerization reaction of the lactone compound of the polyester polyol (B2), except that the above diol is changed to a trihydric alcohol.

[0070] Examples of the trivalent alcohol include glycerin, trioxyisobutane, 1,2,3 - butanetriol, 1,2,3 - pentanetriol, 2 - methyl - 1,2,3 - propanetriol, 2 - methyl - 2,3,4 - butanetriol, 2 - ethyl - 1,2,3 - butanetriol, 2,3,4 - pentanetriol, 2,3,4 - hexanetriol, 4 - propyl - 3,4,5 - heptanetriol, 2,4 - dimethyl - 2,3,4 - pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4 - butanetriol, 1,2,4 - pentanetriol, trimethylolethane, and trimethylolpropane.

[0071] (B4) Polyester polyol The polyester polyol (B4) is represented by the following formula (4): [Chemical formula] (In the formula, w, x, y, and z are each an integer from 1 to 100, and R 41 represents a saturated hydrocarbon group having four bonds, and R 42 , R 43 , R 44 and R 45 each independently represent a linear alkylene group or a branched alkylene group branched at a position other than the α - position and the β - position. ) It is represented by

[0072] w, x, y, and z may each be an integer from 3 to 50, and may be an integer from 5 to 30. w + x + y + z is 4 or more, and may be 5 or more, and may be 6 or more. w + x + y + z may be 50 or less, may be 30 or less, and may be 20 or less.

[0073] R 41 may be a linear or branched tetravalent aliphatic hydrocarbon group. Specifically, as R 41 , a branched tetravalent aliphatic hydrocarbon group having 3 to 10 carbon atoms can be mentioned.

[0074] R 42 、R 43 、R 44 and R 45 and, specifically, examples thereof include linear alkylene groups having 2 to 12 carbon atoms and branched alkylene groups having 3 to 12 carbon atoms. R 42 、R 43 、R 44 and R 45 In a more preferred embodiment of R 42 、R 43 、R 44 、R 45 、linear alkylene groups having 3 to 10 carbon atoms are included, and in a more preferred embodiment, linear alkylene groups having 4 to 8 carbon atoms are included. In two or more repeating units, a plurality of R 42 may be the same. In two or more repeating units, a plurality of R 43 may be the same. In two or more repeating units, a plurality of R 44 may be the same. In two or more repeating units, a plurality of R 45 may be the same. R

[0075] R 41 is a branched tetravalent aliphatic hydrocarbon group having 3 to 10 carbon atoms, R 42 is a linear alkylene group having 4 to 8 carbon atoms, R 43 is a linear alkylene group having 4 to 8 carbon atoms, R 44 is a linear alkylene group having 4 to 8 carbon atoms, and R 45 may be a linear alkylene group having 4 to 8 carbon atoms.

[0076] The polyester polyol (B4) is obtained, for example, by the same procedure as the ring-opening polymerization reaction of the lactone compound of the above polyester polyol (B2), except that the above diol is changed to a tetravalent alcohol.

[0077] Examples of the tetravalent alcohol include pentaerythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerin, sorbitan, and the like.

[0078] (B5) Polyester polyol The polyester polyol (B5) is a reaction product of a linear or branched polyhydric alcohol having three or more hydroxyl groups, a linear or branched alkanediol, and a linear or branched alkanedicarboxylic acid. That is, the polyester polyol (B5) does not have a cyclic structure such as an alicyclic hydrocarbon group and an aromatic hydrocarbon group.

[0079] Examples of the linear or branched polyhydric alcohol having three or more hydroxyl groups include trivalent alcohols such as glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, trimethylolethane, and trimethylolpropane; tetravalent alcohols such as pentaerythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerin, and sorbitan; pentavalent alcohols such as adonitol, arabinitol, xylitol, and triglycerin; and hexavalent alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, dulcitol, talose, and allose. These can be used alone or in combination of two or more.

[0080] Examples of the linear or branched alkanediols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol. These can be used alone or in combination of two or more.

[0081] Examples of the linear or branched alkanedicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These can be used alone or in combination of two or more.

[0082] The polyester polyol (B5) is obtained by mixing the above components and heating, for example, to 180°C or higher and 250°C or lower in the presence of a catalyst.

[0083] The polyester polyol (B) may contain at least one selected from the group consisting of polyester polyols (B1), (B2), and (B5). The polyester polyol (B) may contain the polyester polyol (B2).

[0084] The hydroxyl value of the polyester polyol (B) is, for example, 50 mgKOH / g or higher and 600 mgKOH / g or lower. When the hydroxyl value of the polyester polyol (B) is 50 mgKOH / g or higher, the crosslinking density tends to be high. When the hydroxyl value of the polyester polyol (B) is 600 mgKOH / g or lower, 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 polyester polyol (B) may be 75 mgKOH / g or higher, and may be 500 mgKOH / g or higher. The hydroxyl value of the polyester polyol (B) may be 100 mgKOH / g or lower, and may be 400 mgKOH / g or lower.

[0085] The hydroxyl value of at least one polyester polyol (B) selected from the group consisting of polyester polyols (B1) to (B5) contained in the clear coating composition may be within the above range.

[0086] The Mw (or molecular weight) of the polyester polyol (B) is, for example, 250 or more and 150,000 or less. When the Mw of the polyester polyol (B) is 250 or more, the hardness and weather resistance of the resulting coating film are likely to be improved. The Mw of the polyester polyol (B) may be 300 or more, and may be 350 or more. The Mw of the polyester polyol (B) may be 120,000 or less, and may be 100,000 or less.

[0087] The weight average molecular weight of at least one polyester polyol (B) selected from the group consisting of polyester polyols (B1) to (B5) contained in the clear coating composition may be within the above range.

[0088] The content of the polyester polyol (B) may be, for example, 10 parts by mass or more, 12 parts by mass or more, 15 parts by mass or more, or 18 parts by mass or more with respect to 100 parts by mass of the hydroxyl group-containing acrylic resin (A). Thereby, the stress relaxation performance in the coating film is likely to be exhibited. The content of the polyester polyol (B) may be, for example, 50 parts by mass or less, 40 parts by mass or less, or 35 parts by mass or less with respect to 100 parts by mass of the hydroxyl group-containing acrylic resin (A). In one aspect, the content of the polyester polyol (B) is 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the hydroxyl group-containing acrylic resin (A).

[0089] ≪Other Hydroxyl Group-Containing Components≫ The clear coating composition according to the present embodiment may further contain at least one selected from the group consisting of, for example, a polycarbonate polyol resin, a polyether polyol resin, and a polycaprolactone polyol resin as other hydroxyl group-containing components.

[0090] The solid content ratio of other hydroxyl group-containing components in the total solid content of 100% by mass of the hydroxyl group-containing components is, for example, 20% by mass or less, may be 15% by mass or less, and may be 10% by mass or less.

[0091] (C) Organometallic catalyst The organometallic catalyst (C) promotes the reaction between the hydroxyl group-containing resin (typically, the hydroxyl group-containing acrylic resin (A) and the polyester polyol (B)) and the polyisocyanate compound (E).

[0092] The metal M constituting the organometallic catalyst (C) may contain at least one selected from the group consisting of zinc, bismuth, and tin. Thereby, the above reaction can be further promoted.

[0093] The organometallic catalyst (C) contains, for example, at least one selected from the group consisting of an acylate compound, an alkoxide compound, and a chelate compound of the above metal M. The organometallic catalyst (C) may contain, for example, an oxide compound of the above metal M. Among them, the organometallic catalyst (C) may contain an acylate compound of at least one metal selected from the group consisting of zinc, bismuth, and tin.

[0094] The acylate compound of zinc is, for example, represented by the following general formula (C11): Zn-(O-C(=O)-R c11 )2(C11) (In the formula, R c11 represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms.) It is represented by.

[0095] The number of carbon atoms of R c11 may be 3 or more, may be 4 or more, and may be 5 or more. The number of carbon atoms of R c11 may be 9 or less, may be 8 or less, and may be 7 or less. R c11 may be a linear, branched, or cyclic aliphatic hydrocarbon group, and may be a linear or branched aliphatic hydrocarbon group.

[0096] The acylates of bismuth are, for example, represented by the following general formula (C12): Bi-(O-C(=O)-R c12 )3(C12) (wherein R c12 represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms.) It is represented by

[0097] R c12 may have 3 or more carbon atoms, may have 4 or more carbon atoms, and may have 5 or more carbon atoms. R c12 may have 9 or fewer carbon atoms, may have 8 or fewer carbon atoms, and may have 7 or fewer carbon atoms. R c12 may be a linear, branched or cyclic aliphatic hydrocarbon group, and may be a linear or branched aliphatic hydrocarbon group.

[0098] The acylates of tin are, for example, represented by the following general formula (C13): Sn-(O-C(=O)-R c13 )2(C13) (wherein R c13 represents an aliphatic hydrocarbon group having 1 to 12 carbon atoms.) It is represented by

[0099] R c13 may have 3 or more carbon atoms, may have 4 or more carbon atoms, and may have 5 or more carbon atoms. R c13 may have 11 or fewer carbon atoms, and may have 10 or fewer carbon atoms. R c13 may be a linear, branched or cyclic aliphatic hydrocarbon group, and may be a linear or branched aliphatic hydrocarbon group.

[0100] The alkoxide compound of metal M is, for example, represented by the following general formula (C2): M(ОR c2 ) s (C2) (wherein R c2 each independently represents an aliphatic hydrocarbon group having 1 to 12 carbon atoms, and s represents the valence of metal M.) It is represented by

[0101] R c2 The carbon number of may be 2 or more, may be 3 or more, and may be 4 or more. R c2 The carbon number of may be 11 or less, may be 10 or less, and may be 9 or less. R c2 R may be a linear, branched or cyclic aliphatic hydrocarbon group, and may be a linear or branched aliphatic hydrocarbon group.

[0102] The chelate compound of metal M is, for example, represented by the following general formula (C3): M(R c3 ) t (C3) (In the formula, R c3 represents an acetylacetonato group, an ethylacetoacetonato group, a propylacetoacetonato group, an isopropylacetoacetonato group, a butylacetoacetonato group, a propionylacetoacetonato group or a propionylacetoacetonato group, t represents the coordination number of metal M.) It is represented by

[0103] When metal M is tin, the organotin oxide compound is, for example, represented by the following general formula (C4): Sn(=O)-(-R c14 )2(C4) (In the formula, R c13 represents an aliphatic hydrocarbon group having 1 to 12 carbon atoms.) It is represented by

[0104] The organometallic catalyst (C) may optionally have an additional ligand different from the above. Examples of the additional ligand include linear, branched or cyclic aliphatic hydrocarbon groups. The additional ligand may be an aliphatic hydrocarbon group having 1 to 12 carbon atoms.

[0105] The mass ratio of the organometallic catalyst (C) to 100% by mass of the hydroxyl group-containing resin may be 0.01% by mass or more and 1% by mass or less. The above mass ratio of the organometallic catalyst (C) may be 0.02% by mass or more, and may be 0.03% by mass or more. The above mass ratio of the organometallic catalyst (C) may be 0.5% by mass or less, may be 0.4% by mass or less, and may be 0.3% by mass or less.

[0106] (D) Acid In the clear coating composition, the acid (D) coordinates or chemically bonds to the central metal of the organometallic catalyst (C) to reduce its catalytic activity. As a result, the pot life property is improved. On the other hand, during curing, the acid (D) decomposes or becomes a gas and is discharged out of the reaction system, and the organometallic catalyst (C) is reactivated again.

[0107] The acid (D) may contain a carboxylic acid having an acid dissociation constant pKa of 2 or more and 7 or less. The larger the acid dissociation constant pKa, the easier it is to coordinate or chemically bond to the central metal of the organometallic catalyst (C), which can contribute to the improvement of the pot life property. On the other hand, if the acid dissociation constant pKa is excessively large, the reactivation of the organometallic catalyst (C) may not be sufficient. The acid dissociation constant pKa of the carboxylic acid may be 2.5 or more, and may be 3.0 or more. The acid dissociation constant pKa of the carboxylic acid may be 6.0 or less, and may be 5.0 or less.

[0108] The acid (D) may contain a monocarboxylic acid having 7 or less carbon atoms. The monocarboxylic acid having 7 or less carbon atoms is easily decomposed or volatilized by heating performed for curing. The monocarboxylic acid having 7 or less carbon atoms is represented by, for example, R d -COOH (R d represents a hydrocarbon group having 1 to 7 carbon atoms.). The above hydrocarbon group may be linear or branched. The above hydrocarbon group may be a saturated hydrocarbon group.

[0109] The acid dissociation constant pKa is 2 or more and 7 or less, and examples of monocarboxylic acids having 7 or less carbon atoms include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, n-caprylic acid, 2-ethylhexanoic acid, pivalic acid, 3-methylbutanoic acid, lactic acid, and octylic acid.

[0110] The acid (D) may be formulated in the multi-liquid clear coating composition in an amount greater than the equivalent number of organic compounds capable of binding or coordinating to the central metal of the organometallic catalyst (C). When the acid (D) is present in excess, during storage, the acid (D) can bind or coordinate to the central metal of the organometallic catalyst (C) to an extent that can inhibit its activity.

[0111] For example, when the organometallic catalyst (C) contains a zinc acyl compound, the content of the acid (D) may be more than 2 equivalents and 700 equivalents or less per 1 equivalent of the metal of the zinc acyl compound. The above content of the acid (D) may be 3 equivalents or more, 100 equivalents or more, 200 equivalents or more, or 300 equivalents or more. The above content of the acid (D) may be 600 equivalents or less or 500 equivalents or less.

[0112] When the organometallic catalyst (C) contains a bismuth acyl compound, the content of the acid (D) may be more than 3 equivalents and 700 equivalents or less per 1 equivalent of the metal of the bismuth acyl compound. The above content of the acid (D) may be 4 equivalents or more or 5 equivalents or more. The above content of the acid (D) may be 600 equivalents or less or 500 equivalents or less.

[0113] When the organometallic catalyst (C) contains a tin acyl compound, the content of the acid (D) may be more than 2 equivalents and 700 equivalents or less per 1 equivalent of the metal of the tin acyl compound. The above content of the acid (D) may be 3 equivalents or more or 4 equivalents or more. The above content of the acid (D) may be 600 equivalents or less or 500 equivalents or less.

[0114] ≪Solvent≫ The first liquid may contain a solvent. The solvent may be water or a non-aqueous solvent.

[0115] Examples of the non-aqueous solvent include aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, and mineral spirits; ketone-based organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl-i-butyl ketone, methyl amyl ketone, and cyclohexanone; aromatic hydrocarbon-based organic solvents such as benzene, toluene, ethylbenzene, propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, and decalin; ester-based organic solvents such as methyl acetate, ethyl acetate, butyl acetate, amyl acetate, ethyl propionate, methyl propionate, and ethyl 3-ethoxypropionate; cellosolve-based organic solvents such as methyl cellosolve, ethyl cellosolve, n-propyl cellosolve, i-propyl cellosolve, n-butyl cellosolve, i-butyl cellosolve, i-amyl cellosolve, phenyl cellosolve, and benzyl cellosolve; carbitol-based organic solvents such as methyl carbitol, ethyl carbitol, n-propyl carbitol, i-propyl carbitol, n-butyl carbitol, i-butyl carbitol, i-amyl carbitol, carbitol acetate, phenyl carbitol, and benzyl carbitol;Glycol ether-based organic solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene glycol di-n-butyl ether, propylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, dipropylene glycol diallyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n-butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, 2-butoxyethyl tetraethoxyethyl ether; acetate-based organic solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate;Examples of the alcohol solvents include methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, etc. These can be used alone or in combination of two or more.

[0116] ≪Preparation Method≫ The first liquid can be prepared by mixing the above components by a method known to those skilled in the art. Examples of the mixing method include the same method as for preparing a clear paint composition.

[0117] (Second Liquid) The second liquid contains a polyisocyanate compound (E).

[0118] (E) Polyisocyanate Compound The polyisocyanate compound (E) is a curing agent, which reacts with the hydroxyl group-containing resin to form a crosslinked structure and cure the clear paint composition.

[0119] The polyisocyanate compound (E) has at least two isocyanate groups in one molecule. Examples of the polyisocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having an aromatic ring not bonded to the isocyanate group in the molecule (araliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. Specifically, 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 multimers such as their biuret type, nurate type, and adduct type. These can be used alone or in combination of two or more.

[0120] The equivalent ratio (NCO / OH) of the isocyanate groups contained in the polyisocyanate compound (E) to the hydroxyl groups contained in the hydroxyl group-containing resin may be 0.7 or more, and may be 0.8 or more. The equivalent ratio (NCO / OH) may be 2.0 or less, may be 1.8 or less, and may be 1.5 or less. In one aspect, 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 having excellent hardness and weather resistance is likely to be formed.

[0121] ≪Other curing agents≫ The clear coating composition may contain other curing agents other than the polyisocyanate compound (E). Examples of other curing agents include amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. These may be used alone or in combination of two or more. The content of other curing agents is appropriately set according to the hydroxyl group-containing resin.

[0122] ≪Solvents≫ The second liquid may contain a solvent having no hydroxyl groups. Examples of such solvents include the above glycol ether-based organic solvents; the above acetate-based organic solvents; the above ketone-based organic solvents; the above ester-based organic solvents. These may be used alone or in combination of two or more.

[0123] ≪Preparation method≫ The second liquid can be prepared by mixing the above components by a method known to those skilled in the art. Examples of the mixing method include the same method as the preparation of the first liquid.

[0124] (Other components) The clear coating composition may contain additives commonly used in the paint field. The additives may be added to any of the first liquid, the second liquid, and the third liquid. Examples of the additives include pigments, ultraviolet absorbers, hindered amine light stabilizers, antioxidants, crosslinked resin particles, leveling agents, defoamers, curing accelerators, and viscosity modifiers.

[0125] [Coated article] A coated article is obtained by the clear coating composition according to the present disclosure. The coated article includes, for example, an object to be coated and a multilayer coating film including a base coating film and a clear coating film. The clear coating film is formed by the clear coating composition according to the present disclosure. Therefore, the coated article has excellent color fastness and appearance.

[0126] The base coating film is disposed between the object to be coated and the clear coating film. The multilayer coating film may further include an intermediate coating film disposed between the object to be coated and the base coating film. That is, the coated article may include an object to be coated and a multilayer coating film in which the intermediate coating film, the base coating film, and the clear coating film are laminated in this order.

[0127] When the object to be coated is made of resin, the multilayer coating film may further include a primer coating film disposed between the object to be coated and the base coating film. That is, the coated article may include an object to be coated and a multilayer coating film in which the primer coating film, the base coating film, and the clear coating film are laminated in this order.

[0128] [Object to be coated] Examples of the material of the object to be coated include metal, resin, and glass. 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, grills, and door knobs.

[0129] Examples of the metal include iron, copper, aluminum, tin, zinc, or alloys thereof (e.g., steel). Representative examples of the metal object to be coated include steel sheets such as cold-rolled steel sheets, hot-rolled steel sheets, stainless steels, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-coated steel sheets, zinc-iron alloy-coated steel sheets, zinc-magnesium alloy-coated steel sheets, zinc-aluminum-magnesium alloy-coated steel sheets, aluminum-coated steel sheets, aluminum-silicon alloy-coated steel sheets, and tin-coated steel sheets.

[0130] The metal object to be coated may be surface-treated. Examples of the surface treatment include phosphate treatment, chromate treatment, zirconium chemical conversion treatment, and composite oxide treatment. After the surface treatment, the metal object to be coated may be further coated with an electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[0131] Examples of the resin include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The resin object to be coated may be degreased. The resin object to be coated may be surface-treated.

[0132] (Intermediate coating film) The intermediate coating film is formed by an intermediate coating composition, which will be described later. The film thickness (dry film thickness) of the intermediate coating film after curing is, for example, 5 μm or more and 80 μm or less. The dry film thickness of the intermediate coating film may be 10 μm or more. The dry film thickness of the intermediate coating film may be 50 μm or less.

[0133] The thickness of the coating film can be measured by an electromagnetic film thickness gauge (e.g., SDM-miniR manufactured by SANKO). The thickness of the coating film is the average value of the coating film thicknesses at any five points.

[0134] (Primer coating film) The primer coating film is interposed between the object to be coated and the base coating film. The primer coating film improves the adhesion between the base coating film and the object to be coated (especially the resin object to be coated). Also, when the surface of the object to be coated is uneven, the primer coating makes the coating surface uniform, and it becomes easier to suppress the unevenness of the base coating film.

[0135] The primer coating film is formed, for example, by a primer coating composition containing a film-forming component, a material adhesion component, a viscosity modifier, a diluent component, a pigment, and, if necessary, a curing agent. The primer coating composition may contain various additives as necessary. The primer coating composition may be solvent-based or water-based.

[0136] Examples of the film-forming component, curing agent, viscosity modifier, diluting component, and pigment include the respective components exemplified as those to be incorporated into the base paint composition described later. The viscosity of the aqueous primer paint composition measured with a B-type viscometer at 20°C is, for example, 500 cps / 6 rpm or more and 6,000 cps / 6 rpm or less. The solid content ratio of the primer paint composition is, for example, 30% by mass or more and 50% by mass or less. The solid content of the primer paint composition is all the components excluding the diluting component from the primer paint composition.

[0137] The thickness of the primer coating film is not particularly limited. In terms of the smoothness and chipping resistance of the painted article, the thickness of the primer coating film may be 5 μm or more and 40 μm or less. The thickness of the primer coating film may be 7 μm or more. The thickness of the primer coating film may be 25 μm or less.

[0138] (Base coating film) The base coating film is formed by the base paint composition. The base paint composition will be described later. The base coating film may be a single layer or a laminated coating film of two or more layers. The dry film thickness per layer of the base coating film is, for example, 5 μm or more and 35 μm or less. The dry film thickness per layer of the base coating film may be 7 μm or more. The dry film thickness per layer of the base coating film may be 30 μm or less.

[0139] (Clear coating film) The clear coating film is formed by the multi-component clear paint composition according to the present disclosure. The dry film thickness of the clear coating film is, for example, 10 μm or more and 80 μm or less. The dry film thickness of the clear coating film may be 20 μm or more. The dry film thickness of the clear coating film may be 60 μm or less.

[0140] [Method for manufacturing a painted article] The above-mentioned coated article is manufactured, for example, by a method comprising a step of coating a base paint composition on an object to be coated to form an uncured base paint film, a step of coating the uncured base paint film with the clear paint composition according to the present disclosure to form an uncured clear paint film, and a step of curing the uncured base paint film and the uncured clear paint film simultaneously.

[0141] Before the step of coating the base paint composition, a step of coating the object to be coated with an intermediate paint composition (or a primer paint composition; the same shall apply hereinafter) may be performed. When the base paint composition is coated, the intermediate paint film (or the primer paint film; the same shall apply hereinafter) may be cured or uncured. When the base paint composition is coated, the intermediate paint film may be cured.

[0142] That is, the coated article may be manufactured by a method (two-coat one-bake method) comprising a step of coating the object to be coated with the intermediate paint composition, then curing it to form a cured intermediate paint film, a step of sequentially coating the cured intermediate paint film with the base paint composition and the clear paint composition to form an uncured base paint film and a clear paint film in this order, and a step of curing the uncured base paint film and the clear paint film at once.

[0143] The coated article may also be manufactured by a method (three-coat one-bake method) comprising a step of sequentially coating the object to be coated with the intermediate paint composition, the base paint composition and the clear paint composition to form an uncured intermediate paint film, a base paint film and a clear paint film in this order, and a step of curing the uncured intermediate paint film, the base paint film and the clear paint film at once.

[0144] Hereinafter, each step will be described by taking as an example the case of manufacturing a coated article having a multilayer paint film in which an intermediate paint film, a base paint film and a clear paint film are laminated in this order by the two-coat one-bake method. However, the manufacturing method of the coated article is not limited thereto.

[0145] (I) Step of forming a cured intermediate paint film First, apply the intermediate coating composition onto the object to be coated to form an uncured intermediate coating film. The intermediate coating film improves the adhesion between the base coating film and the object to be coated. Also, the intermediate coating makes the coating surface uniform, making it easier to suppress the unevenness of the base coating film.

[0146] Examples of the coating method include the roll coater method, air spray coating, airless spray coating, and rotary atomization coating. These methods may be combined with electrostatic coating. Among them, from the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferred. For rotary atomization electrostatic coating, for example, a rotary atomization type electrostatic coating machine generally called "micro-micro bell (μμ bell)", "micro bell (μ bell)", "metallic bell (meta bell)", etc. may be used.

[0147] Next, cure the uncured intermediate coating film. The intermediate coating composition can be cured by heating. The curing (heating) conditions are appropriately set according to the composition of the intermediate coating composition, the material of the object to be coated, etc. The heating temperature is, for example, 100°C or higher and 180°C or lower, and may be 120°C or higher and 160°C or lower. The heating time can be appropriately set according to the heating temperature. When the heating temperature is 100°C or higher and 180°C or lower, the heating time is, for example, 10 minutes or longer and 60 minutes or shorter, and may be 10 minutes or longer and 30 minutes or shorter. The heating time means the time when the inside of the heating device reaches the target temperature and the object to be coated is maintained at the target temperature, and the time until it reaches the target temperature is not considered. Examples of the heating device include a drying furnace using a heat source such as hot air, electricity, gas, or infrared rays.

[0148] (Intermediate coating composition) The intermediate coating composition may be aqueous or solvent-based.

[0149] The primer coating composition contains, in addition to various solvents, for example, resins, pigments, and various additives. Examples of the resins include acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluororesins, epoxy resins, and polyether resins. These may be used alone or in combination of two or more. The primer coating composition may further contain the curing agent described above.

[0150] (II) Step of forming an uncured base coating film The base coating composition is applied onto the cured primer coating film to form an uncured base coating film. Two or more layers of uncured base coating films can be formed by applying the same or different base coating compositions two or more times. An interval of several minutes may be provided between the n-th application of the base coating composition and the (n + 1)-th application of the base coating composition.

[0151] Examples of the coating method include the same method as the coating method of the primer coating composition.

[0152] After applying the base coating composition and before applying the clear coating composition, pre-drying (also referred to as pre-heating) may be performed. Thereby, the dilution component contained in the base coating composition is suppressed from boiling over in the curing process, and the generation of blisters is likely to be suppressed. Further, pre-drying suppresses the uncured base coating film and the clear coating composition from mixing with each other, and it becomes difficult to form a mixed layer. Therefore, the smoothness of the obtained coated article can be further improved.

[0153] Examples of the pre-drying include a method of leaving it for 5 minutes or more and 15 minutes or less under temperature conditions of 20°C or more and 25°C or less, and a method of heating it for 30 seconds or more and 10 minutes or less under temperature conditions of 50°C or more and 80°C or less.

[0154] (Base coating composition) The base paint composition may be water-based or solvent-based. The base paint composition may be water-based. The water-based base paint composition contains, for example, an acrylic resin emulsion, a water-soluble acrylic resin, a curing agent (typically, a melamine resin), and a polyether polyol resin. The base paint composition may further contain a pigment and various additives.

[0155] (III) Step of forming an uncured clear coating film The clear paint composition according to the present disclosure is applied onto an uncured base coating film to form an uncured clear coating film.

[0156] The coating method is not particularly limited. Examples of the coating method include the same methods as those for the coating method of the intermediate coat paint composition. Among them, from the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferable. After applying the clear paint composition, preliminary drying may be performed in the same manner as above.

[0157] (IV) Curing step The uncured base coating film and the clear coating film are cured at once. Each coating film can be cured by heating.

[0158] The heating temperature is, for example, 60°C or higher and 120°C or lower. The heating temperature may be 65°C or higher, and may be 70°C or higher. The heating temperature may be 95°C or lower, and may be 90°C or lower. According to the multi-component clear paint composition of the present disclosure, a clear coating film having high hardness is formed even at such a low temperature.

[0159] The heating time may be appropriately set according to the heating temperature. When the heating temperature is 60°C or higher and 120°C or lower, the heating time is, for example, 10 minutes or longer and 60 minutes or shorter, and may be 15 minutes or longer and 45 minutes or shorter.

Examples

[0160] The present invention will be described more specifically by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on the mass of the solid content unless otherwise specified.

[0161] The acid value was measured in accordance with the Standard Oil Analysis Test Method 2.3.1 - 2013 established by the Japan Oil Chemists' Society, a public interest incorporated association. The hydroxyl value was measured in accordance with the Standard Oil Analysis Test Method 2.3.6.2 - 1996 established by the Japan Oil Chemists' Society, a public interest incorporated association.

[0162] [Production Example 1 - 1] Production of Hydroxyl - containing Acrylic Resin (A - 1) 24.2 parts of butyl acetate was charged into an autoclave equipped with a stirrer, a temperature controller, a reflux condenser, a nitrogen inlet tube, and a liquid feed pump, and the temperature was raised to 170°C. Into the above - mentioned autoclave, a monomer solution (a mixed solution consisting of 20.00 parts of styrene, 22.27 parts of n - butyl acrylate, 14.05 parts of 2 - ethylhexyl methacrylate, 41.12 parts of 2 - hydroxypropyl methacrylate, and 2.57 parts of acrylic acid), and a mixed solution of 1.65 parts of di - tert - amyl peroxide and 7.74 parts of butyl acetate were dropped over 3 hours by a liquid feed pump.

[0163] After completion of the dropping, the temperature was maintained at 170°C for 30 minutes and then cooled to 120°C over 30 minutes. Subsequently, a mixed solution of 0.2 part of di - tert - amyl peroxyoctoate and 2.0 parts of butyl acetate was dropped over 30 minutes by a liquid feed pump.

[0164] Next, after continuing the reaction at 120°C for 1 hour, 6.4 parts of butyl acetate was added. Thereby, a varnish with a non - volatile content of 70.0% containing a hydroxyl - containing acrylic resin (A - 1) with Mw 6000, a hydroxyl value of 160 mg KOH / g, an acid value of 20 mg KOH / g, and Tg 10°C was obtained.

[0165] [Production Example 1 - 2] Production of Hydroxyl - containing Acrylic Resin (A - 2) A varnish with a non-volatile content of 70% containing a hydroxyl group-containing acrylic resin (A-2) with Mw 6000, a hydroxyl value of 160 mg KOH / g, an acid value of 10 mg KOH / g, and a Tg of 20 °C was obtained in the same manner as in Production Example 1-1, except that a mixture consisting of 20.00 parts of styrene, 4.76 parts of n-butyl acrylate, 32.84 parts of 2-ethylhexyl methacrylate, 41.12 parts of 2-hydroxypropyl methacrylate, and 1.28 parts of acrylic acid was used as the monomer solution.

[0166] [Production Example 1-3] Production of Hydroxyl Group-Containing Acrylic Resin (A-3) A varnish with a non-volatile content of 70% containing a hydroxyl group-containing acrylic resin (A-3) with Mw 6000, a hydroxyl value of 150 mg KOH / g, an acid value of 6.5 mg KOH / g, and a Tg of 10 °C was obtained in the same manner as in Production Example 1-1, except that a mixture consisting of 20.00 parts of styrene, 18.40 parts of n-butyl acrylate, 22.21 parts of 2-ethylhexyl methacrylate, 38.55 parts of 2-hydroxypropyl methacrylate, and 0.83 parts of acrylic acid was used as the monomer solution.

[0167] [Production Example 1-4] Production of Hydroxyl Group-Containing Acrylic Resin (A-4) A varnish with a non-volatile content of 70.0% containing a hydroxyl group-containing acrylic resin (A-4) with Mw 6000, a hydroxyl value of 170 mg KOH / g, an acid value of 6.5 mg KOH / g, and a Tg of 10 °C was obtained in the same manner as in Production Example 1-1, except that a mixture consisting of 20.00 parts of styrene, 21.48 parts of n-butyl acrylate, 14.00 parts of 2-ethylhexyl methacrylate, 43.69 parts of 2-hydroxypropyl methacrylate, and 0.83 parts of acrylic acid was used as the monomer solution.

[0168] [Production Example 2-1] Production of Polyester Polyol (B-5) 20 parts (1 mol equivalent) of trimethylolpropane and 62 parts (2 mol equivalents) of sebacic acid were charged into a reactor, and methyl isobutyl ketone was added to adjust the viscosity. Subsequently, a dehydration catalyst was added, and the reaction was carried out at 170 °C for 4 hours. Subsequently, 18 parts (1.5 mol equivalents) of 1,3-propanediol were added to the above reactor and the reaction was further carried out at 170 °C.

[0169] When the acid value became less than 0.5 mg·KOH / g, the degree of vacuum was gradually increased by a vacuum pump to terminate the reaction. Thereby, a polyester polyol (B-5) represented by the formula (5) was obtained. The hydroxyl value of the polyester polyol (B-5) was 193 mgKOH / g, the acid value was less than 0.1 mgKOH / g, and Mw was 100,000.

[0170] [Production Example 2-2] Polyester polyol (b-1) Into a reaction vessel equipped with a thermometer, a stirrer, a condenser tube and a nitrogen inlet tube, 8.85 parts by weight of pentaerythritol, 57.5 parts by weight of Placcel M (trade name, manufactured by Daicel Corporation, ε-caprolactone monomer), 33.92 parts by weight of Rica Sid HH-A (trade name, manufactured by Shin Nippon Rika Co., Ltd., hexahydrophthalic anhydride) and 0.1 part of dibutyltin oxide were charged, and the temperature was raised to 150 °C.

[0171] After holding at 150 °C for 2 hours, 6.16 parts of hexahydrophthalic anhydride dissolved therein were added to the above reaction vessel. After further holding at 150 °C for 1 hour, it was cooled. Subsequently, 33.4 parts of 3-ethoxyethyl propionate were added to the above reaction vessel for dilution.

[0172] Thereby, a varnish having a non-volatile content of 75% containing polyester polyol (b-1) was obtained. The polyester polyol (b-1) had a hydroxyl value of 20 mgKOH / g and an acid value of 120 mgKOH / g. The polyester polyol (b-1) has a hydroxyl group bonded to an alicyclic hydrocarbon group and does not correspond to any of the above polyester polyols (B1) to (B5).

[0173] [Production Example 2-3] Polyester polyol (b-2) Into a reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen inlet pipe, a water separator, and a rectification column, 11.85 parts of trimethylolpropane, 38.29 parts of neopentyl glycol, 30.23 parts of adipic acid, 34.36 parts of isophthalic acid, and 3 parts of dibutyltin oxide were charged and heated. When the raw materials melted and stirring became possible, stirring was started and the temperature of the reaction vessel was set to 210°C. At that time, the temperature was raised at a constant rate from 150°C to 210°C over 3 hours. When 210°C was reached, heat was retained and the condensation reaction was continued. The condensed water produced was distilled out of the system. Cooling was started when the acid value of the polymer reached 5.0. Thereafter, 38.24 parts of butyl acetate were added.

[0174] Thereby, polyester polyol (b-2) was obtained. The hydroxyl value of the polyester polyol (b-2) was 100 mgKOH / g, and the acid value was less than 5 mgKOH / g. The polyester polyol (b-2) has hydroxyl groups only in the side chain and does not correspond to any of the above polyester polyols (B1) to (B5).

[0175] [Production Example 2-4] Polyester polyol (b-3) Synthesis was carried out in the same manner as in Production Example 2-3, except that the monomers used were changed to 36.07 parts of trimethylolpropane, 17.09 parts of neopentyl glycol, 28.39 parts of adipic acid, and 32.27 parts of hexahydrophthalic anhydride.

[0176] Thereby, polyester polyol (b-3) was obtained. The hydroxyl value of the polyester polyol (b-3) was 210 mgKOH / g, and the acid value was less than 5 mgKOH / g. The polyester polyol (b-3) has hydroxyl groups bonded to alicyclic hydrocarbon groups and does not correspond to any of the above polyester polyols (B1) to (B5).

[0177] Details of other polyester polyols are as follows. · Polyester polyol (B-1) The compound represented by formula (2), trade name: PCL205H, manufactured by Daicel Corporation, molecular weight 530, hydroxyl value 213.4 mg KOH / g, acid value 0.1 mg KOH / g · Polyester polyol (B-2) The compound represented by formula (3), trade name: PCL305, manufactured by Daicel Corporation, molecular weight 550, hydroxyl value 305.6 mg KOH / g, acid value 0.5 mg KOH / g · Polyester polyol (B-3) The compound represented by formula (1), trade name: P-1010, manufactured by Kuraray Co., Ltd., molecular weight 1,000, hydroxyl value 112 mg KOH / g, acid value ≒ 0 mg KOH / g · Polyester polyol (B-4) The compound represented by formula (5), trade name: F-1010, manufactured by Kuraray Co., Ltd., molecular weight 1,000, hydroxyl value 168 mg KOH / g, acid value ≒ 0 mg KOH / g

[0178] [Example 1] (1) Preparation of the first liquid In a 1 L metal container, 30 parts of a hydroxyl group-containing acrylic resin (A-1), 20 parts of a hydroxyl group-containing acrylic resin (A-4), 10 parts of a polyester polyol (B-1), 0.1 part of an organometallic catalyst (C-1) (dibutyltin dilaurate), and an acid (D-1) (acetic acid, pKa 4.76) in an amount of 500 equivalents per 1 equivalent of the metal of the organometallic catalyst (C-1), 2.0 parts of an ultraviolet absorber (Tinuvin 384, manufactured by BASF), 1.0 part of a light stabilizer (Tinuvin 123, manufactured by BASF), 1.0 part of an acrylic surface conditioner, 18 parts of butyl acetate, and 13 parts of DBE dibasic ester (organic solvent, a mixture of dimethyl succinate, dimethyl glutarate, and dimethyl adipate, manufactured by Shouei Chemical Co., Ltd., CAS No. 95481-62-2) were sequentially added and thoroughly stirred with a disper to obtain the first liquid.

[0179] (2) Preparation of the second liquid To another metal container, 35 parts of polyisocyanate compound (E-1) (uretdione form of hexamethylene diisocyanate, trade name: Desmodur N-3400, manufactured by Sumitomo Covestro Urethane Co., Ltd., solid content concentration 100%), 5 parts of polyisocyanate compound (E-2) (isocyanurate form of hexamethylene diisocyanate, trade name: Desmodur N-3300, manufactured by Sumitomo Covestro Urethane Co., Ltd., solid content concentration 100%), and 18 parts of butyl acetate were sequentially added and stirred to obtain a second liquid.

[0180] (3) Preparation of clear paint composition The first liquid and the second liquid were mixed to obtain a clear paint composition.

[0181] [Examples 2 to 20 and Comparative Examples 1 to 6] A clear paint composition was prepared in the same procedure as in Example 1, except that the types and amounts of the compounding ingredients, the solid content at the time of painting, etc. were changed as shown in Tables 1 to 3.

[0182] The polyisocyanate compound (E-3) shown in Tables 1 to 3 is an isocyanurate form of hexamethylene diisocyanate, trade name: Desmodur N-3800, manufactured by Sumitomo Covestro Urethane Co., Ltd., and has a solid content concentration of 100%. The acid (D-2) is octylic acid (2-ethylhexanoic acid, pKa 4.89).

[0183] [Evaluation] Using the clear paint compositions prepared in the above Examples and Comparative Examples, the following evaluations were carried out. The scratch resistance, appearance, bird dropping resistance, and water resistance were evaluated using test panel A or B having a metal or resin substrate, an intermediate coating film, a base coating film, and a clear coating film formed from the clear paint compositions of the Examples and Comparative Examples. The evaluation results are shown in Tables 1 to 3.

[0184] The clear paint composition of Comparative Example 6 did not cure sufficiently at 80°C, and neither of the following test panels A and B could be obtained.

[0185] · Manufacture of test panel A (metal substrate) On a zinc phosphate-treated mild steel plate with a thickness of 0.8 mm, a length of 30 cm, and a width of 40 cm, "Power Top U-50)" (manufactured by Nippon Paint Automotive Coatings Co., Ltd.), which is a cationic electrodeposition coating composition, was electrodeposition coated so that the dry film thickness became 20 μm. Subsequently, it was baked at 160°C for 30 minutes to obtain a metallic object to be coated.

[0186] Next, a polyester-melamine-based paint (product name: OP-30P Middle Gray, manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was diluted so that the viscosity at 20°C using a No. 4 Ford cup became 25 seconds to prepare an intermediate coat paint composition. This intermediate coat paint composition was applied to the metallic object to be coated using an air spray gun (W-101-132G manufactured by Anest Iwata Co., Ltd.) so that the dry film thickness became 35 μm. Subsequently, it was baked and cured at 140°C for 30 minutes to form an intermediate coat film.

[0187] An aqueous base paint composition (product name: AR-3020, manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was applied to the obtained intermediate coat film using a spray gun (W-101-134G manufactured by Anest Iwata Co., Ltd.) so that the dry film thickness became 15 μm. Subsequently, preheating was performed at 80°C for 5 minutes to form an uncured base coat film.

[0188] On the uncured base coat film, the clear paint compositions prepared in the examples and comparative examples and diluted with butyl acetate were applied using a spray gun (W-101-134G manufactured by Anest Iwata Co., Ltd.) so that the dry film thickness became 35 μm. Then, it was left standing for 10 minutes in a painting environment at a temperature of 20 ± 5°C and a relative humidity of 78% or less. Subsequently, using a dryer, the temperature of the substrate was raised until it reached 80°C, and it was dried and heated at 80°C for 30 minutes. Thereby, test panel A having a multilayer coating film was obtained.

[0189] · Manufacture of Test Panel B (Resin Object to be Coated) An alloy resin substrate of polyphenylene ether resin / polyamide resin (trade name: NPRYL GTX (trademark) 973, manufactured by SABIC-SHPP Japan) was frame-treated using a frame treatment machine FTM101DR manufactured by Arcotec to obtain a resin-coated object.

[0190] An aqueous primer paint (trade name: WB-1200CD-5, manufactured by Nippon Paint Automotive Coatings) was applied to the resin-coated object using a spray gun (W-101-134G manufactured by Anest Iwata) so that the dry film thickness was 7 μm. Then, after leaving it for 1 minute in an environment of 20 ± 5°C and a relative humidity of 78% or less, it was dried in an electric oven at 60°C for 5 minutes.

[0191] Next, after confirming that the surface temperature of the coated object had reached 30°C or lower, an aqueous base paint composition (trade name: AR-3020, manufactured by Nippon Paint Automotive Coatings) was applied using a spray gun (W-101-134G manufactured by Anest Iwata) so that the dry film thickness was 15 μm. Then, it was left for 1 minute in an environment of 20 ± 5°C and a relative humidity of 78% or less. Subsequently, preheating was carried out in an electric oven at 80°C for 5 minutes to form an uncured primer coating film and base coating film.

[0192] On the uncured base coating film, a clear paint composition prepared in Examples and Comparative Examples and diluted with butyl acetate was applied using a spray gun (W-101-134G manufactured by Anest Iwata) so that the dry film thickness was 35 μm. After leaving it for 10 minutes in a coating environment of 20 ± 5°C and a relative humidity of 78% or less, a dryer was used to raise the temperature of the substrate to 80°C and it was dried and heated at 80°C for 30 minutes. Thereby, a test plate B having a multilayer coating film was obtained.

[0193] (1) Scratch resistance A flat abrasion tester manufactured by Dai-ichi Kagaku Seiki Co., Ltd. was used. A metal cylindrical jig with a tip diameter of 16 mm, which is horizontal with respect to the surface of the abraded object (test plate A), was attached to the flat abrasion tester. Felt and abrasive paper (manufactured by 3M, 281Q, WETORDRY PRODUCTION POLISHING PAPER 9μGRADE) were fixed to the tip of the jig in the order of jig tip, felt, and abrasive paper. While applying a load of 900 g to the surface of the abrasive paper fixed to the jig, the surface of the coating film of test plate A was rubbed 10 reciprocations at a speed of 40 reciprocations per minute with a stroke length of 10 cm.

[0194] For the rubbed part and the non-rubbed part, the 20° gloss value was measured with a gloss meter (Micro Tri Gloss, manufactured by BYK-Chemie). The gloss retention rate was obtained by dividing the 20° gloss value of the rubbed part by the 20° gloss value of the non-rubbed part. The higher the gloss retention rate, the better the scratch resistance. The measured values were evaluated according to the following criteria.

[0195] (Evaluation Criteria) A: Gloss retention rate is 80% or more B: Gloss retention rate is 70% or more and less than 80% C: Gloss retention rate is 60% or more and less than 70% D: Gloss retention rate is less than 60%

[0196] (2) Appearance The 60° glossiness of test plate A was measured in accordance with JIS K-5600-4-7 using a gloss meter (Micro Tri Gloss, manufactured by BYK-Chemie). The measured values were evaluated according to the following criteria. The higher the 60° glossiness, the better the appearance.

[0197] (Evaluation Criteria) A: 60° glossiness is 85 or more, and no coating film surface abnormalities such as swelling, cracking, pinholes, and orange peel are observed B: 60° glossiness is less than 85, or at least one coating film surface abnormality such as swelling, cracking, pinholes, and orange peel is observed

[0198] (3) Bird droppings resistance 0.2 ml of 3% aqueous albumin solution was dropped onto the coating film surface of Test Panel B and allowed to stand for 1 hour under the conditions of 50 ± 1°C and 30 ± 5% RH. Then, Test Panel B was washed with water, the water droplets were wiped off, and it was allowed to stand at room temperature for 24 hours. Subsequently, the surface state of the coating film was visually observed and evaluated according to the following criteria. The lower the grade, the better the resistance to bird droppings.

[0199] (Evaluation Criteria) Grade 0: No change Grade 1: Swelling Grade 2: Wrinkling Grade 3: Cracking

[0200] (4) Pot life The first liquid and the second liquid were mixed and stirred with a disperser for 1 minute, and then allowed to stand at 23°C. At the same time as the end of stirring, the stopwatch was started to measure the time, and the time required until the fluidity of the mixture of the first liquid and the second liquid (coating composition) completely disappeared was measured and taken as the gelling time. The gelling time was evaluated according to the following criteria. The longer the gelling time, the better the pot life.

[0201] (Evaluation Criteria) A: Gelling time is 3 minutes or more B: Gelling time is less than 3 minutes C: Gelation occurred at the end of stirring

[0202] (5) Water resistance Test Panel A was immersed in warm water at 40°C for 240 hours. Then, it was taken out of the water and dried at room temperature for 1 hour. The appearance of the coating film after drying was visually observed, and abnormalities (wrinkles, cracks, swelling, peeling, gloss reduction, and discoloration) were evaluated according to the following criteria.

[0203] (Evaluation Criteria) A: No abnormalities B: Some abnormalities C: Most parts have abnormalities

[0204] [Table 1]

[0205] [Table 2]

[0206] [Table 3]

[0207] The present disclosure includes the following aspects. [1] A first liquid containing a hydroxyl group-containing acrylic resin (A), a polyester polyol (B), an organometallic catalyst (C), and an acid (D), and a second liquid containing a polyisocyanate compound (E), wherein the polyester polyol (B) is at least one selected from the group consisting of a polyester polyol (B1) represented by the following formula (1), a polyester polyol (B2) represented by the following formula (2), a polyester polyol (B3) represented by the following formula (3), a polyester polyol (B4) represented by the following formula (4), and a polyester polyol (B5) which is a reaction product of a linear or branched polyhydric alcohol having three or more hydroxyl groups, a linear or branched alkanediol, and a linear or branched alkanedicarboxylic acid, Formula (1): [Chemical formula] (In the formula, a is an integer from 1 to 100, R 11 represents a saturated hydrocarbon group having two bonds, independently for each repeating unit, R 12 and R 13 each independently represent a linear alkylene group or a branched alkylene group branched at a position other than the α-position and the β-position.) Formula (2): [Chemical formula] (wherein j and k are each an integer from 0 to 100, satisfying j + k ≥ 1, R 21 represents a saturated hydrocarbon group having two bonds, R 22 and R 23 each independently represent a linear alkylene group or a branched alkylene group branched at a position other than the α- and β-positions. ) Formula (3): [Chemical formula] (wherein p, q, and r are each an integer from 1 to 100, R 31 represents a saturated hydrocarbon group having three bonds, R 32 , R 33 and R 34 each independently represent a linear alkylene group or a branched alkylene group branched at a position other than the α- and β-positions. ) Formula (4): [Chemical formula] (wherein w, x, y, and z are each an integer from 1 to 100, R 41 represents a saturated hydrocarbon group having four bonds, R 42 , R 43 , R 44 and R 45 each independently represent a linear alkylene group or a branched alkylene group branched at a position other than the α- and β-positions. ) [2] The hydroxyl group-containing acrylic resin (A) contains a hydroxyl group-containing acrylic resin (A1) having an acid value of 10 mgKOH / g or more and 50 mgKOH / g or less, and is the multi-component clear coating composition described in [1] above. [3] The multi-component clear coating composition according to [1] or [2] above, wherein the acid (D) includes a carboxylic acid having an acid dissociation constant pKa of 2 or more and 7 or less. [4] The multi-component clear coating composition according to any one of [1] to [3] above, wherein the acid (D) includes a monocarboxylic acid having 7 or less carbon atoms. [5] The multi-component clear coating composition according to any one of [1] to [4] above, wherein the metal constituting the organometallic catalyst (C) includes at least one selected from the group consisting of zinc, bismuth, and tin. [6] The organometallic catalyst (C) includes an acyl compound of at least one metal selected from the group consisting of zinc, bismuth, and tin. The content of the acid (D) satisfies the following conditions: When the organometallic catalyst (C) includes a zinc acyl compound, it is more than 2 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the zinc acyl compound. When the organometallic catalyst (C) includes a bismuth acyl compound, it is more than 3 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the bismuth acyl compound. When the organometallic catalyst (C) includes a tin acyl compound, it is more than 2 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the tin acyl compound. The multi-component clear coating composition according to any one of [1] to [5] above, satisfying at least one of the above. [7] The multi-component clear coating composition according to any one of [1] to [6] above, wherein the content of the polyester polyol (B) is 15 parts by mass or more with respect to 100 parts by mass of the hydroxyl group-containing acrylic resin (A).

Industrial Applicability

[0208] According to the clear coating composition of the present invention, it is possible to form a coating film that can be cured at a low temperature, has excellent pot life properties, and has excellent scratch resistance and bird droppings resistance. Therefore, it is suitably used for forming various clear coating films, particularly clear coating films for automobiles.

Claims

1. A first liquid containing a hydroxyl group-containing acrylic resin (A), a polyester polyol (B), an organometallic catalyst (C), and an acid (D), and a second liquid containing a polyisocyanate compound (E), wherein the polyester polyol (B) is a polyester polyol (B1) represented by the following formula (1), a polyester polyol (B2) represented by the following formula (2), a polyester polyol (B3) represented by the following formula (3), a polyester polyol (B4) represented by the following formula (4), and at least one selected from the group consisting of a polyester polyol (B5) which is a reaction product of a linear or branched polyhydric alcohol having three or more hydroxyl groups, a linear or branched alkanediol, and a linear or branched alkanedicarboxylic acid, a multi-component clear coating composition. Formula (1): 【Chemical 1】 (In the formula, a is an integer from 1 to 100, R １１ represents, independently for each repeating unit, a saturated hydrocarbon group having two bonds R １２ and R １３ each independently represents a linear alkylene group or a branched alkylene group branched at a position other than the α-position and the β-position, for each repeating unit. Formula (2): 【Chemical 2】 (In the formula, j and k are each an integer from 0 to 100, and j + k ≧ 1 is satisfied, R ２１ represents a saturated hydrocarbon group having two linking hands, R ２２ and R ２３ each independently represents a linear alkylene group or a branched alkylene group branched at a position other than the α-position and the β-position, for each repeating unit. Formula (3): [Chemical Formula 3] (In the formula, p, q, and r are each an integer from 1 to 100, R ３１ represents a saturated hydrocarbon group having three linking hands, R ３２ 、 R ３３ and R ３４ each independently represents a linear alkylene group or a branched alkylene group branched at a position other than the α- and β-positions, on a per repeating unit basis. Formula (4): 【Chemical Formula 4】 (In the formula, w, x, y, and z are each an integer from 1 to 100, R ４１ represents a saturated hydrocarbon group having four linking hands, R ４２ , R ４３ , R ４４ and R ４５ each independently represents a linear alkylene group or a branched alkylene group branched at a position other than the α-position and the β-position, for each repeating unit, and for each other. )

2. The multi-component clear coating composition according to claim 1, wherein the hydroxyl group-containing acrylic resin (A) contains a hydroxyl group-containing acrylic resin (A1) having an acid value of 10 mgKOH / g or more and 50 mgKOH / g or less.

3. The multi-component clear coating composition according to claim 1 or 2, wherein the acid (D) contains a carboxylic acid having an acid dissociation constant pKa of 2 or more and 7 or less.

4. The multi-component clear coating composition according to claim 1 or 2, wherein the acid (D) contains a monocarboxylic acid having 7 or less carbon atoms.

5. The multi-component clear coating composition according to claim 1 or 2, wherein the metal constituting the organometallic catalyst (C) contains at least one selected from the group consisting of zinc, bismuth, and tin.

6. The organometallic catalyst (C) contains an acylate compound of at least one metal selected from the group consisting of zinc, bismuth, and tin, and the content of the acid (D) satisfies the following conditions: When the organometallic catalyst (C) contains a zinc acylate compound, it is more than 2 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the zinc acylate compound; When the organometallic catalyst (C) contains a bismuth acylate compound, it is more than 3 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the bismuth acylate compound; When the organometallic catalyst (C) contains a stannous acyl compound, it is more than 2 equivalents and 700 equivalents or less with respect to 1 equivalent of the metal of the stannous acyl compound; The two-component clear coating composition according to claim 1 or 2, satisfying at least one of the following:

7. The content of the polyester polyol (B) is 15 parts by mass or more with respect to 100 parts by mass of the hydroxyl group-containing acrylic resin (A). The two-component clear coating composition according to claim 1 or 2.

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