WO2022186049A1 - Clear coating composition and method for forming multilayer coating film - Google Patents

Abstract

The present invention provides a clear coating composition which forms a clear coating film serving as as an outermost layer of a multilayer coating film that is formed on the surface of an automobile, and which provides a clear coating film that has high chemical resistance, dry scratch resistance, high car wash scratch resistance and high recoat adhesion.　The present invention provides a clear coating composition which contains a hydroxyl group-containing acrylic resin (A), a hydroxyl group-containing acrylic resin (B), a multifunctional isocyanate compound (C) and an aminoplast resin (D), wherein: the hydroxyl group-containing acrylic resin (A) has a glass transition temperature of 20°C to 35°C, a hydroxyl value of 100 mgKOH/g to 200 mgKOH/g, and a solubility parameter of 9.5 to 11.5, while containing 20% by mass to 40% by mass of an alicyclic (meth)acrylate relative to the total solid content of the hydroxyl group-containing acrylic resin (A); the hydroxyl group-containing acrylic resin (B) has a glass transition temperature of 15°C to 30°C, a hydroxyl value of 150 mgKOH/g to 250 mgKOH/g, and a solubility parameter of 10.5 to 12.5; the solubility parameter of the hydroxyl group-containing acrylic resin (A) is lower than the solubility parameter of the hydroxyl group-containing acrylic resin (B), and the difference therebetween is 0.5 or more; and the addition amounts of the components (C) and (D) are further controlled.

Description

Clear coating composition and method for forming multi-layer coating

The present invention relates to a clear coating composition, particularly a clear coating composition suitable for application to the surface of automobiles, and a method for forming a multi-layer coating film using the clear coating composition.

On the surface of automobiles, etc., a colored coating film is formed in order to impart a high degree of designability, and a clear coating is further applied thereon to make the colored coating film deeper. there is

The clear coating film formed on the colored coating film also has the function of protecting the colored coating film, and must have properties such as high chemical resistance and dry scratch resistance. In addition, recently, automobiles are often washed with a car wash machine, and a performance to prevent scratching by a car wash machine, which is called car wash abrasion resistance by a car wash machine, is also required. Furthermore, if there is a defect in the automotive coating, after polishing the coating, a multi-layer coating of the same color is formed on it, but the clear coating is formed on top to repair the defect. Adhesion (also called "recoat adhesion") to multi-layered coating films for commercial applications must also be enhanced. It is very difficult to satisfy all these performances.

Regarding clear paint, many patent applications have been filed, including Patent Document 1 (WO2013/031977). A two-part curing type clear paint that uses a hydroxyl group-containing acrylic resin as the basic resin and is crosslinked with a crosslinking agent such as a polyisocyanate compound. Although many compositions have been proposed and used in practice, none have yet been provided that are excellent in all of the above properties.

WO2013/031977

The present invention is a clear coating composition that provides a clear coating film as the uppermost layer of a multi-layer coating film formed on the surface of an automobile, which has high chemical resistance, dry scratch resistance, and high car wash scratch resistance. and to provide a product having high recoat adhesion.

Specifically, the present invention provides the following aspects:
[1]
A clear coating composition containing a hydroxyl group-containing acrylic resin (A), a hydroxyl group-containing acrylic resin (B), a polyfunctional isocyanate compound (C) and an aminoplast resin (D),
The hydroxyl group-containing acrylic resin (A) has a glass transition temperature of 20 to 35 ° C., a hydroxyl value of 100 to 200 mgKOH / g, a solubility parameter of 9.5 to 11.5 and an alicyclic (meth) acrylate hydroxyl group-containing acrylic resin ( A) in an amount of 20 to 40% by mass relative to the total solid content,
The hydroxyl-containing acrylic resin (B) has a glass transition temperature of 15 to 30° C., a hydroxyl value of 150 to 250 mgKOH/g and a solubility parameter of 10.5 to 12.5,
The solubility parameter of the hydroxyl group-containing acrylic resin (A) is lower than the solubility parameter of the hydroxyl group-containing acrylic resin (B), and the difference is 0.5 or more,
The ratio of the hydroxyl group equivalent (α) of all the hydroxyl group-containing resins (X) other than the aminoplast resin (D) and the isocyanate equivalent (β) of the polyfunctional isocyanate compound (C) is expressed by the following formula (1)
1.20>β/α>0.80: Formula (1)
and
The solid content mass ratio (Mc, Md) of the polyfunctional isocyanate compound (C) and the aminoplast resin (D) is represented by the following formula (2)
8.0>Mc/Md>1.0: Formula (2)
A clear coating composition characterized by satisfying
[2]
The clear coating composition according to [1], wherein the clear coating composition further contains inorganic fine particles having an average particle size of 2 to 500 nm.
[3]
The hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B) are 20 to 50% by mass of the hydroxyl group-containing acrylic resin (A) with respect to the total 100 parts by mass of the resin solid content of the clear coating composition. and the hydroxyl group-containing acrylic resin (B) is contained in an amount of 5 to 35% by mass, [1] or [2].
[4]
The clear paint according to any one of [1] to [3], wherein the polyfunctional isocyanate compound (C) is contained in an amount of 25 to 45% by mass with respect to 100 parts by mass of the resin component of the clear paint composition. Composition.
[5]
The clear coating composition according to any one of [1] to [4], wherein the aminoplast resin (D) is contained in an amount of 1 to 25% by mass with respect to 100 parts by mass of the resin component of the clear coating composition. .
[6]
After applying an intermediate coating composition to an object to be coated, and further coating a base coating composition on the resulting uncured intermediate coating film to obtain a base uncured coating film, [1] to obtain a clear uncured coating film by applying the clear coating composition according to any one of [5],
A method for forming a multi-layer coating film, wherein the uncured intermediate coating film, the uncured base coating film, and the uncured clear coating film are simultaneously heated and cured.

In the present invention, the composition of the clear coating composition, in particular, two types of hydroxyl-containing acrylic resins, which are basic resins for coating film formation, are used to control their properties (in particular, the solubility parameter) so that the clear coating film can be formed at the time of coating. Separates into two layers inside, forming a layer with excellent chemical resistance and dry scratch resistance on the upper layer of the coating film (opposite side of the coated object), and a layer with excellent car wash scratch resistance on the lower layer (on the coated object side) and both layers have excellent recoat adhesion, improving the performance of the clear coating film.

The clear coating composition of the present invention uses two types of hydroxyl group-containing acrylic resin (A) and hydroxyl group-containing acrylic resin (B), which are combined with two types of cross-linking agents (specifically, polyfunctional isocyanate compound (C) and aminoplast resin (D)). Each component and the properties of each component are described.

In this specification, "a to b" (both a and b are numbers) means a range from a to b.

[Hydroxyl group-containing acrylic resin (A) and (B)]
A hydroxyl group-containing acrylic resin is an acrylic resin that contains a hydroxyl group. In the present invention, two types of hydroxyl group-containing acrylic resins, that is, hydroxyl group-containing acrylic resin (A) and hydroxyl group-containing acrylic resin (B) are distinguished and described. After describing the resin, the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B) will be described individually.

In the present invention, "acrylic resin" refers to a polymer obtained by polymerizing a monomer composition containing at least one monomer of acrylic acid and its esters, methacrylic acid and its esters.

Monomers constituting the hydroxyl group-containing acrylic resin according to the present invention include, for example, hydroxyl group-containing acrylic acid esters such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; 2-hydroxyethyl methacrylate, methacrylic acid; hydroxy-containing methacrylic acid hydroxy esters such as 4-hydroxybutyl acid; and optionally acrylic acid; methyl acrylate, butyl acrylate, isobutyl acrylate, acrylic acid acrylic acid esters such as t-butyl, 2-ethylhexyl acrylate, lauryl acrylate, isobornyl acrylate; methacrylic acid; methyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, Aliphatic alkyl methacrylates such as lauryl methacrylate and isobornyl methacrylate; alicyclic (meth) acrylates such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and dicyclopentanyl (meth) acrylate; an ethylenically unsaturated monomer; and the like. The composition of the monomer is appropriately adjusted according to various physical properties required for the hydroxyl group-containing acrylic resin. Alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate

The hydroxyl group-containing acrylic resin can be polymerized using a solvent such as butyl acetate. Polymerization conditions such as the type of solvent, the concentration of monomers during polymerization, the type and amount of polymerization initiator, polymerization temperature and polymerization time can be appropriately adjusted according to the various physical properties required for the hydroxyl group-containing acrylic resin. Therefore, the method for producing the hydroxyl group-containing acrylic resin of the present invention is not particularly limited, and commercially available hydroxyl group-containing acrylic resins may be used.

In the present invention, the hydroxyl-containing acrylic resin (A) has a glass transition temperature of 20 to 35° C., a hydroxyl value of 100 to 200 mgKOH/g, a solubility parameter of 9.5 to 11.5, and an alicyclic (meth)acrylate containing hydroxyl groups. It is contained in an amount of 20 to 40% by mass based on the total solid content of the acrylic resin (A).
In the present invention, the hydroxyl-containing acrylic resin (B) has a glass transition temperature of 15-30° C., a hydroxyl value of 150-250 mgKOH/g and a solubility parameter of 10.5-12.5.
In the present invention, it is necessary that the solubility parameter of the hydroxyl-containing acrylic resin (A) is lower than the solubility parameter of the hydroxyl-containing acrylic resin (B), and that the difference therebetween be 0.5 or more.

The glass transition temperature of the hydroxyl group-containing acrylic resin (A) is 25°C or higher and 35°C or lower. By keeping the glass transition temperature within such a range, the clear coating film can have excellent stain resistance, scratch resistance, and hardness. improves. Moreover, it can have an excellent appearance.

The glass transition temperature of the hydroxyl group-containing acrylic resin (B) is 15°C or higher and 30°C or lower. By keeping the glass transition temperature within such a range, the clear coating film can have excellent stain resistance, scratch resistance, and hardness. improves. Moreover, it can have an excellent appearance.

For the glass transition temperature in this specification, the value measured by the following steps with a differential scanning calorimeter (DSC) (thermal analyzer SSC5200 (manufactured by Seiko Electronics)) was used. Specifically, the step of raising the temperature from 20 ° C. to 150 ° C. at a temperature increase rate of 10 ° C./min (step 1), and the step of lowering the temperature from 150 ° C. to −50 ° C. at a temperature decrease rate of 10 ° C./min (step 2 ), and in the step of raising the temperature from −50° C. to 150° C. at a heating rate of 10° C./min (Step 3), the value obtained from the chart during the temperature rise in Step 3 was taken as the glass transition temperature.

The difference in glass transition temperature between the hydroxyl-containing acrylic resin (A) and the hydroxyl-containing acrylic resin (B) is the glass transition temperature (Agt) of the hydroxyl-containing acrylic resin (A) - the glass transition temperature of the hydroxyl-containing acrylic resin (B) ( Bgt) is 0-20°C, preferably 5-20°C. The glass transition temperature is a factor that contributes to scratch resistance and hardness, but the upper layer of the clear coating (on the side opposite to the coated object) is expected to have a low glass transition temperature and be resistant to impact.

The hydroxyl group-containing acrylic resin (A) has a hydroxyl value of 100 mgKOH/g or more and 200 mgKOH/g or less. When the hydroxyl value is within such a range, a good crosslink density can be imparted to the clear coating film. Furthermore, hydrophilization of the coating film can be suppressed, and clear coating films and multi-layer coating films can have excellent water resistance and moisture resistance.

The hydroxyl group-containing acrylic resin (B) has a hydroxyl value of 150 mgKOH/g or more and 250 mgKOH/g or less. When the hydroxyl value is within such a range, a good crosslink density can be imparted to the clear coating film. Furthermore, hydrophilization of the coating film can be suppressed, and clear coating films and multi-layer coating films can have excellent water resistance and moisture resistance.

In the present invention, the hydroxyl value can be determined by the neutralization titration method using an aqueous potassium hydroxide solution described in JIS K 0070.

The difference in hydroxyl value between the hydroxyl-containing acrylic resin (A) and the hydroxyl-containing acrylic resin (B) is the hydroxyl value (Ahv) of the hydroxyl-containing acrylic resin (A) - the hydroxyl value (Bhv) of the hydroxyl-containing acrylic resin (B). , in the range of 0-150, preferably in the range of 50-100. The hydroxyl value is an active group that contributes to the cross-linking reaction. Material side) is better for car wash scratch resistance if it is somewhat soft.

The solubility parameter (SP) of the hydroxyl group-containing acrylic resin (A) is 9.5 or more and 11.5 or less.

The solubility parameter (SP) of the hydroxyl group-containing acrylic resin (B) is 9.5 or more and 11.5 or less.

In the present invention, the solubility parameter (Asp) of the hydroxyl-containing acrylic resin (A) is lower than the solubility parameter (Bsp) of the hydroxyl-containing acrylic resin (B), and the difference (Bsp-Asp) is 0.5. Above, preferably 0.6 or more is required. Also, the upper limit of Bsp-Asp is 3.0. Due to the difference in the SP value, the clear coating film is separated into layers, and different performance can be given to the upper layer (opposite side of the object to be coated) and the lower layer (to the coated object side) within the clear coating film, and each performance contributes to chemical resistance, dry mar, car wash mar and recoat adhesion. If the SP value difference is too large, separation will occur within the coating film, resulting in poor appearance.

The solubility parameter (SP) in this specification can be actually measured by the following method [Reference: SUH, CLARKE, J. Am. P. S. A-1, 5, 1671-1681 (1967)].
Measurement temperature: 20°C
Sample: 0.5 g of resin is weighed into a 100 mL beaker, 10 mL of a good solvent is added using a whole pipette, and dissolved with a magnetic stirrer.
solvent:
Good solvent: dioxane, acetone, etc. Poor solvent: n-hexane, ion-exchanged water, etc. Turbidity point measurement: A poor solvent is added dropwise using a 50 mL burette, and the point at which turbidity occurs is defined as the drop amount.
The SP value δ is given by the following equation.
δ=( _Vml1 / _2δml + _Vmh1 / _2δmh )/( _Vml1 / ² + _Vmh1 / ² )
V _m =V ₁ V ₂ /(φ ₁ V ₂ +φ ₂ V ₁ )
δ _m = φ ₁ δ ₁ + φ ₂ δ ₂
V _i : Molecular volume of solvent (mL/mol)
φ _i : volume fraction of each solvent at turbid point δ _i : SP value of solvent ml: low SP poor solvent mixture mh: high SP poor solvent mixture

Furthermore, the hydroxyl group-containing acrylic resin (A) is synthesized by using an alicyclic (meth)acrylate as a monomer in an amount of 20 to 40% by mass based on the total solid content of the monomers of the hydroxyl group-containing acrylic resin (A). must be included. Cycloaliphatic (meth)acrylates are described in the description of the monomers above. By including an alicyclic (meth)acrylate, the advantage of improving spot resistance can be imparted. The content of the alicyclic (meth)acrylate is preferably 20-40% by mass, more preferably 30-40% by mass.

The weight average molecular weight of the hydroxyl group-containing acrylic resin (A) is 5000 or more and 7000 or less. By having the weight average molecular weight within such a range, the clear coating film has the advantage of being able to achieve both durability and appearance.

The weight average molecular weight of the hydroxyl group-containing acrylic resin (B) is 5000 or more and 7000 or less. By having the weight average molecular weight within such a range, the clear coating film has the advantage of being able to achieve both durability and appearance.

The weight average molecular weight in this specification is a value measured by gel permeation chromatography using HLC-8200 manufactured by Tosoh Corporation. The measurement conditions are as follows.
Column TSgel Super Multipore HZ-M 3 Developing solvent Tetrahydrofuran Column inlet oven 40°C
Flow rate 0.35ml
Detector RI
Standard polystyrene PS oligomer kit manufactured by Tosoh Corporation

The amount of the hydroxyl group-containing acrylic resin (A) blended into the clear coating composition is as follows: the hydroxyl group-containing acrylic resin (A), the hydroxyl group-containing acrylic resin (B), the polyfunctional isocyanate compound (C), and the aminoplast resin ( It is preferably 20% by mass or more and 50% by mass or less, and preferably 30% by mass or more and 40% by mass or less with respect to the total 100 parts by mass of the resin solid content of the clear coating composition containing D). more preferred. With such an amount, the smoothness of the clear coating film can be maintained satisfactorily. In addition, the clear coating composition is excellent in drying property, and the clear coating composition can have good handleability.

The amount of the hydroxyl group-containing acrylic resin (B) blended into the clear coating composition is as follows: the hydroxyl group-containing acrylic resin (A), the hydroxyl group-containing acrylic resin (B), the polyfunctional isocyanate compound (C), and the aminoplast resin ( It is preferably 5% by mass or more and 35% by mass or less, and preferably 10% by mass or more and 30% by mass or less, relative to the total 100 parts by mass of the resin solid content of the clear coating composition containing D). more preferred. With such an amount, the smoothness of the clear coating film can be maintained satisfactorily. In addition, the clear coating composition is excellent in drying property, and the clear coating composition can have good handleability.

[Polyfunctional isocyanate compound (C)]
The clear coating composition of the present invention reacts with the polyfunctional isocyanate compound (C) and cures to form a cured coating film.

The polyfunctional isocyanate compound (C) is not particularly limited, and examples thereof include aliphatic, alicyclic, aromatic group-containing aliphatic or aromatic diisocyanates, diisocyanate dimers, diisocyanate trimers (preferably isocyanate Polyfunctional isocyanate compounds such as nurate-type isocyanates (so-called isocyanurates) may be used.

Diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, undecane diisocyanate-(1,11), lysine ester diisocyanate, cyclohexane-1,3- and 1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate: IPDI), 4,4′-diisocyanatodicyclomethane, ω,ω′-di Propyl ether diisocyanate, thiodipropyl diisocyanate, cyclohexyl-1,4-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-trimethyl -2,4-bis(ω-isocyanatoethyl)-benzene, 1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene, 1,3,5-triethyl-2,4-bis( isocyanatomethyl)benzene, dicyclohexyldimethylmethane-4,4'-diisocyanate and the like. Also, aromatic diisocyanates such as 2,4-diisocyanatotoluene and/or 2,6-diisocyanatotoluene, 4,4'-diisocyanatodiphenylmethane, 1,4-diisocyanatoisopropylbenzene can be used. can be done. Examples of the isocyanurate-type isocyanate include trimers of the diisocyanates described above.

Two or more of the polyfunctional isocyanate compounds (C) may be used in combination.
The content of the polyfunctional isocyanate compound (C) is not particularly limited, but from the viewpoint of promoting the curing reaction more appropriately, the number of moles of isocyanate groups in the isocyanate compound (C) with respect to the number of moles of hydroxyl groups in the hydroxyl group-containing acrylic resin (B). The number ratio (NCO/OH) may be 0.6 or more and 1.4 or less, preferably 0.8 or more and 1.2 or less.

The amount of the polyfunctional isocyanate compound (C) to be added to the clear coating composition is not particularly limited, but is 25 parts by mass with respect to 100 parts by mass of the resin component of the clear coating composition so that the curing reaction can be carried out more appropriately. % or more and 45 mass % or less, preferably 30 mass % or more and 40 mass % or less. If it is less than 25% by mass, the curing becomes insufficient, and even if it exceeds 45% by mass, the effect of addition of the polyfunctional isocyanate compound (C) does not change, and on the contrary, the car wash scratch resistance becomes worse.

[Aminoplast resin (D)]
The clear coating composition of the present invention contains an aminoplast resin (D) in addition to the polyfunctional isocyanate compound (C).

Aminoplast resin is a general term for thermosetting resins produced by the reaction of amines or amide compounds with aldehydes, and includes urea resins, aniline-formaldehyde resins, melamine resins, guanamine resins, thiourea resins, and the like. Formaldehyde is mainly used as the aldehyde. Formaldehyde is added to nitrogen atom by reaction of amino compound or amide compound with formaldehyde to form methylol compound (hydroxymethyl compound).

The content of the aminoplast resin (D) is not particularly limited, but from the viewpoint of promoting the curing reaction more appropriately, from the viewpoint of recoat adhesion and chemical resistance, it is added to 100 parts by mass of the resin solid content of the clear coating composition. On the other hand, it may be 1% by mass or more and 25% by mass or less, preferably 5% by mass or more and 15% by mass or less. If it is less than 1% by mass, recoat adhesion and chemical resistance, which are the effects of the addition of the aminoplast resin (D), cannot be obtained. is not observed, and on the contrary, the car wash scratch resistance is deteriorated.

In the present invention, the relationship between the equivalent amounts of the polyfunctional isocyanate compound (C) and the aminoplast resin (D) and the hydroxyl group-containing acrylic resins (A) and (B) contributes to the performance of the clear coating film. . Specifically, the ratio of the hydroxyl group equivalent (α) of the all hydroxyl group-containing acrylic resin (X) other than the aminoplast resin (D) to the isocyanate equivalent (β) of the polyfunctional isocyanate compound (C) is determined by the following formula ( 1)
1.20>β/α>0.80: Formula (1)
and
The solid content mass ratio (Mc, Md) of the polyfunctional isocyanate compound (C) and the aminoplast resin (D) is represented by the following formula (2)
8.0>Mc/Md>1.0: Formula (2)
needs to be satisfied.

In the above, the hydroxyl group-containing acrylic resin (X) means the sum of the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B), and (α) in the formula is the total amount of hydroxyl group equivalents. .

In the above formula (1), the isocyanate equivalent (β)/hydroxy group equivalent (α) is 0.80 to 1.2, indicating that almost the same equivalent is used. The isocyanate equivalent (β)/hydroxy equivalent (α) is preferably 0.90 to 1.10. If the equivalent ratio is out of the above range, the curing is not sufficient, and the appearance, dry scratch resistance, etc. are not bad.

In the above formula (2), the solid content mass (Mc) of the polyfunctional isocyanate compound/solid content mass (Md) of the aminoplast resin is 1.0 to 8.0, and the polyfunctional isocyanate compound (C) It means that the blended mass is about the same as or considerably greater than the blended mass of the aminoplast resin (D). The solid content mass (Mc) of the polyfunctional isocyanate compound/solid content mass (Md) of the aminoplast resin is preferably 1.0 to 3.0, and the solid content mass (Mc) of the polyfunctional isocyanate compound is the aminoplast resin. If it is less than the solid content mass (Md) of , the recoat adhesion will be poor. Conversely, when the solid content mass (Mc) of the polyfunctional isocyanate compound is more than 8 times the solid content mass (Md) of the aminoplast resin, the performance such as chemical resistance is deteriorated.

[Clear paint composition]
The clear coating composition may be water-based or organic solvent-based.
Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, and methyl propionate; tetrahydrofuran, dioxane, and dimethoxy. Ethers such as ethane; Glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; Aromatic hydrocarbons, aliphatic hydrocarbons, etc. is mentioned.
Water and an organic solvent may be used in combination, or two or more organic solvents may be used. The water is not particularly limited, and may be ion-exchanged water or the like.

By blending inorganic fine particles into the clear coating composition of the present invention, the scratch resistance and impact resistance of the surface are improved. It is preferable that the inorganic fine particles are present in the upper layer (on the side opposite to the object to be coated) of the clear coating film, because the abrasion resistance is further improved. For this reason, the inorganic fine particles preferably have an average particle size of 2 to 500 nm, and are surface-modified with a silane coupling agent, an organic resin, or the like so as to easily migrate to the upper layer.

The clear coating composition of the present invention may optionally contain a curing catalyst, a viscosity modifier, an antifoaming agent, an ultraviolet absorber, a light stabilizer (e.g., hindered amine), an antioxidant, a surface modifier, and a film-forming aid. agents, rust inhibitors, pigments, antistatic agents, and the like.

The method for producing the clear coating composition is not particularly limited, and a method known in the art such as stirring, kneading or dispersing the above materials using a disper, homogenizer, roll, sand grind mill or kneader can be used. can be done.

The clear paint composition may be a one-component paint or a multi-component paint such as a two-component paint. When using an unblocked polyfunctional isocyanate compound (C), from the viewpoint of storage stability, a main agent containing hydroxyl group-containing acrylic resins (A) and (B), a polyfunctional isocyanate compound (C) and an amino It is preferable to prepare a two-component paint containing the plasto resin (D) and mix the two immediately before use.

[Clear coating]
A clear coating film according to an embodiment of the present invention is formed from the clear coating composition according to an embodiment of the present invention. In this clear coating film, silica particles are more present near the coating film surface than inside the coating film. As a result, the resurface hardness of the coating film increases, and excellent scratch resistance is exhibited.

The distribution of silica particles inside the coating film and near the surface of the coating film can be observed, for example, with a transmission electron microscope in a cross section perpendicular to the plane direction of the clear coating film.

The method of forming the clear coating film according to the embodiment of the present invention is not particularly limited, and may be formed, for example, by the method described later.

[Painted article]
A coated article according to an embodiment of the present invention includes a clear coating film according to an embodiment of the present invention on its outermost surface.

In one embodiment, the coated article comprises an intermediate coating film or a primer coating film provided on the article to be coated, a base coating film provided on the intermediate coating film or the primer coating film, and on the base coating film A multi-layer coating comprising a clear coating according to embodiments of the present invention provided.

(1) Object to be coated The object to be coated is not particularly limited, and examples thereof include metal substrates, plastic substrates and foams thereof.

Examples of metal substrates include metals such as iron, steel, copper, aluminum, tin, and zinc, and alloys containing these metals. Specific examples of metal substrates include automobile bodies such as passenger cars, trucks, motorcycles and buses, and parts for automobile bodies. It is preferable that an electrodeposition coating film is formed in advance on such a metal substrate. In addition, before forming the electrodeposition coating film, chemical conversion treatment (for example, zinc phosphate chemical conversion treatment, zirconium chemical conversion treatment, etc.) may be performed as necessary.

Examples of plastic substrates include polypropylene resins, polycarbonate resins, urethane resins, polyester resins, polystyrene resins, ABS resins, vinyl chloride resins, and polyamide resins. Specific examples of plastic substrates include automobile parts such as spoilers, bumpers, mirror covers, grilles, and doorknobs. These plastic substrates are preferably washed with pure water and/or a neutral detergent.

(2) Intermediate coating film, primer coating film When the object to be coated is a metal substrate, an intermediate coating film may be provided on the metal substrate on which the electrodeposition coating is formed. Moreover, when the article to be coated is a plastic substrate, a primer coating film may be provided on the plastic substrate.
The intermediate coating film and the primer coating film are not particularly limited, and may be formed using, for example, an intermediate coating composition or a primer coating composition containing a coating film-forming resin and, if necessary, a curing agent and the like.

(3) Base coating film A base coating film may be provided on the intermediate coating film or the primer coating film. The base coating film is not particularly limited, and may be formed using a base coating composition containing a pigment, a coating film-forming resin and, if necessary, a curing agent and the like. Forms of the base coating composition include solvent-based and water-based

Examples of base paint compositions include those containing pigments, hydroxyl-containing acrylic resins and/or polyester resins as coating film-forming resins, and melamine resins as curing agents.

The base paint composition may contain a viscosity control agent. Viscosity control agents include, for example, crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide-based fatty acids, polyamides such as phosphates of long-chain polyaminoamides, colloidal swelling dispersions of polyethylene oxide, and the like. and organic acid smectite clay, organic bentonite-based ones such as montmorillonite, and the like.

In one embodiment, a first base coating film formed from a base coating composition containing a colored pigment and a second base coating film formed from a base coating composition containing a scale-like pigment are used in combination to provide flip-flop properties. An applied multi-layer coating may be formed.

The manufacturing method of the coated article is not particularly limited, and for example, it may be manufactured by the manufacturing method according to the embodiment of the present invention described below.

[Manufacturing method of coated article]
A method for manufacturing a coated article according to an embodiment of the present invention includes:
A step of applying an intermediate coating composition onto an object to be coated to form an uncured intermediate coating film, or coating a primer coating composition to form an uncured primer coating film;
A step of applying a base coating composition onto an uncured primer coating film or an uncured intermediate coating film to form an uncured base coating film;
A step of applying a clear coating composition according to an embodiment of the present invention onto an uncured base coating film to form an uncured clear coating film, and an uncured primer coating film or an uncured intermediate coating film. and a step of heating and curing the uncured base coating film and the uncured clear coating film to form a multi-layer coating film.

(1) Step of forming an uncured intermediate coating film or an uncured primer coating film The above intermediate coating composition or primer coating composition is applied to an object to be coated, and an uncured intermediate coating film or Forms an uncured primer coating. At that time, if necessary, for example, a preheating step may be performed at a temperature of 40° C. or higher and 80° C. or lower for 1 minute or longer and 10 minutes or shorter.
When an uncured intermediate coating film or primer coating film is formed, the dry film thickness may be, for example, 8 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

(2) Step of forming an uncured base coating film The base coating composition is applied to an uncured intermediate coating film or an uncured primer coating film to form an uncured base coating film. At that time, if necessary, for example, a preheating step may be performed at a temperature of 40° C. or higher and 80° C. or lower for 1 minute or longer and 10 minutes or shorter.
The dry film thickness of the uncured base coating film is preferably, for example, 10 μm or more and 30 μm or less.

(3) Step of forming an uncured clear coating film The clear coating composition according to the embodiment of the present invention is applied to an uncured base coating film to form an uncured clear coating film.
The dry film thickness of the uncured clear coating film may be, for example, 10 μm or more and 80 μm or less, and may be 20 μm or more and 50 μm or less.

(4) A step of heating and curing an uncured coating film to form a multilayer coating film Uncured coating film, that is, an uncured intermediate coating film or an uncured primer coating film and an uncured base coating A multi-layer coating film is formed by heating and curing the film and the uncured clear coating film. The heat-curing temperature may be, for example, 80° C. or higher and 150° C. or lower, and the heat-curing time may be appropriately adjusted within a range of, for example, 20 minutes or longer and 40 minutes or shorter.

The coating method of the intermediate coating composition, the primer coating composition, the base coating composition, and the clear coating composition according to the embodiment of the present invention is not particularly limited. Depending on the type of object to be coated, for example, air spray coating, bell coating, multi-stage coating by air electrostatic spray coating or one-stage coating, or electrostatic air spray coating and a rotary atomization system called metallic bell. A coating method generally used in the coating field may be used, such as a coating method in combination with an electrostatic coating machine.

A heating device used to heat and cure an uncured coating film includes, for example, a drying furnace that uses a heat source such as hot air, electricity, gas, or infrared rays. Moreover, it is preferable to use a drying furnace using two or more of these heat sources in combination, because the drying time is shortened.

According to the method for manufacturing a coated article according to the embodiment of the present invention, the upper layer coating film is sequentially formed on the uncured coating film, and the plurality of undried coating films are collectively heat-cured, thereby shortening the process. It is preferable from an economic and environmental point of view.
The coated article according to the embodiment of the present invention can also be produced by heating and curing the coating film each time the coating composition is applied, and sequentially forming the upper coating film.

The present invention will be described in more detail below using examples, but the present invention is not limited by the examples. In the examples, "parts" and "%" are based on mass unless otherwise specified.

Production Example 1 Production of hydroxyl group-containing acrylic resin (a) 42.8 g of propylene glycol methyl ether acetate was charged into a vessel equipped with a stirrer, a temperature controller and a reflux condenser, and heated to 120°C. Next, a monomer mixture having the following composition (4.5 parts of styrene, 42.3 parts of ethylhexyl methacrylate, 20.0 parts of isobornyl methacrylate, 9 parts of S-lauryl methacrylate, 23.2 parts of hydroxyethyl methacrylate and methacrylic acid 1.0 parts), and 9.4 parts of Kayaester O and 9.0 parts of propylene glycol methyl ether acetate were added dropwise in parallel over 3 hours and allowed to stand for 30 minutes. Part of the solution was added dropwise over 1 hour, and the reaction solution was stirred for 30 minutes to increase the rate of conversion to a resin, and then the reaction was terminated. A hydroxyl group-containing acrylic resin (a) having KOH, an acid value of 6.5 mg/KOH, an SP value of 9.6 and a Tg of 20° C. was obtained.

Production Example 2 Production of hydroxyl group-containing acrylic resin (b) The composition of the monomer mixture was 31.0 parts of styrene, 2.6 parts of ethylhexyl methacrylate, 20.0 parts of isobornyl methacrylate, and 22.2 parts of S-lauryl methacrylate. , 23.2 parts of hydroxyethyl methacrylate and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, acid value A hydroxyl group-containing acrylic resin (b) having a viscosity of 6.5 mg/KOH, an SP value of 9.6 and a Tg of 35° C. was obtained.

Production Example 3 Production of hydroxyl group-containing acrylic resin (c) The composition of the monomer mixture was 2.5 parts of styrene, 16.9 parts of ethyl acrylate, 8.2 parts of ethylhexyl acrylate, and 20.0 parts of isobornyl methacrylate. , 51.4 parts of hydroxypropyl methacrylate and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 200 mg / KOH, acid value A hydroxyl group-containing acrylic resin (c) having a viscosity of 6.5 mg/KOH, an SP value of 11.1 and a Tg of 20° C. was obtained.

Production Example 4 Production of hydroxyl group-containing acrylic resin (d) The composition of the monomer mixture was 14.0 parts of styrene, 18.0 parts of ethyl acrylate, 20.0 parts of isobornyl acrylate, 4.6 parts of methyl methacrylate, and 4.6 parts of acrylic resin. The procedure was carried out in the same manner as in Production Example 1 except that 41.4 parts of ethylhexyl acetate and 2.0 parts of methacrylic acid were used. 0 mg/KOH, SP value of 11.5 and Tg of 20°C, a hydroxyl group-containing acrylic resin (d) was obtained.

Production Example 5 Production of hydroxyl group-containing acrylic resin (e) The composition of the monomer mixture was 15.0 parts of styrene, 14.5 parts of ethylhexyl acrylate, 40.0 parts of isobornyl acrylate, and 6.46 parts of lauryl methacrylate. , 23.2 parts of hydroxypropyl acrylate and 0.84 parts of acrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, acid value A hydroxyl group-containing acrylic resin (e) having a 6.5 mg/KOH, an SP value of 9.5 and a Tg of 20° C. was obtained.

Production Example 6 Production of hydroxyl group-containing acrylic resin (f) The composition of the monomer mixture was 7.5 parts of styrene, 35.0 parts of n-butyl acrylate, 3.3 parts of ethylhexyl acrylate, and 30 parts of isobornyl methacrylate. 0 parts, 23.2 parts of hydroxyethyl methacrylate, and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, A hydroxyl group-containing acrylic resin (f) having an acid value of 6.5 mg/KOH, an SP value of 10.0 and a Tg of 15°C was obtained.

Production Example 7 Production of hydroxyl group-containing acrylic resin (g) Composition of monomer mixture: 7.5 parts of styrene, 28.62 parts of n-butyl acrylate, 1.2 parts of ethyl methacrylate, and 30.0 parts of isobornyl methacrylate , 20.88 parts of hydroxyethyl methacrylate and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 90 mg / KOH, acid value A hydroxyl group-containing acrylic resin (g) having a Tg of 30° C. and an SP value of 10.4 was obtained.

Production Example 8 Production of hydroxyl group-containing acrylic resin (h) The composition of the monomer mixture was 5.5 parts of styrene, 12.49 parts of tert-butyl methacrylate, 26.0 parts of lauryl methacrylate, and 30.0 parts of isobornyl acrylate. , 25.7 parts of hydroxypropyl methacrylate and 0.31 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, acid value A hydroxyl group-containing acrylic resin (h) having a value of 2.0 mg/KOH, an SP value of 9.4 and a Tg of 20° C. was obtained.

Production Example 9 Production of hydroxyl-containing acrylic resin (i) The composition of the monomer mixture was 9.5 parts of ethyl acrylate, 33.8 parts of tert-butyl methacrylate, 17.5 parts of lauryl methacrylate, and 15 parts of isobornyl acrylate. 0 parts, 23.2 parts of hydroxypropyl acrylate, and 1.00 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, A hydroxyl group-containing acrylic resin (i) having an acid value of 6.5 mg/KOH, an SP value of 10.0 and a Tg of 20° C. was obtained.

Production Example 10 Production of hydroxyl group-containing acrylic resin (j) The composition of the monomer mixture was 25.5 parts of ethyl acrylate, 5.5 parts of ethylhexyl acrylate, 14.8 parts of methyl methacrylate, and 30 parts of isobornyl methacrylate. 0 parts, 23.2 parts of hydroxyethyl methacrylate, and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 100 mg / KOH, A hydroxyl group-containing acrylic resin (j) having an acid value of 6.5 mg/KOH, an SP value of 10.5 and a Tg of 40° C. was obtained.

Production Example 13 Production of hydroxyl group-containing acrylic resin (k) The composition of the monomer mixture was 14.3 parts of styrene, 11.24 parts of lauryl methacrylate, 30.0 parts of isobornyl methacrylate, 43.46 parts of hydroxyethyl acrylate, The procedure was carried out in the same manner as in Production Example 1 except that methacrylic acid was changed to 1.0 part, solid content 62.4%, number average molecular weight 2500, hydroxyl value 210 mg/KOH, acid value 6.5 mg/KOH, SP value 10. 9, a hydroxyl group-containing acrylic resin (k) having a Tg of 20°C was obtained.

Production Example 12 Production of hydroxyl group-containing acrylic resin (l) The composition of the monomer mixture was 2.0 parts of ethyl acrylate, 29.5 parts of methyl methacrylate, 20.0 parts of isobornyl methacrylate, and 6.1 parts of lauryl methacrylate. , 41.4 parts of hydroxyethyl acrylate and 1.0 parts of methacrylic acid were carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 200 mg / KOH, acid value A hydroxyl group-containing acrylic resin (l) having 6.5 mg/KOH, an SP value of 11.6 and a Tg of 30° C. was obtained.

Production Example 13 Production of hydroxyl group-containing acrylic resin (m) The composition of the monomer mixture was 1.0 parts of ethyl acrylate, 19.05 parts of lauryl methacrylate, 45.0 parts of isobornyl acrylate, and 34.8 parts of hydroxyethyl methacrylate. Part, methacrylic acid was changed to 0.15 part, carried out in the same manner as in Production Example 1, solid content 62.4%, number average molecular weight 2500, hydroxyl value 150 mg / KOH, acid value 1.0 mg / KOH, SP value A hydroxyl group-containing acrylic resin (m) having a viscosity of 9.9 and a Tg of 35° C. was obtained.

Production Example 14 Production of hydroxyl group-containing acrylic resin (n) The composition of the monomer mixture was 15 parts of styrene, 0.95 parts of ethylhexyl acrylate, 30.3 parts of methyl methacrylate, 51.75 parts of hydroxyethyl acrylate and The procedure was carried out in the same manner as in Production Example 1 except that 2.0 parts of methacrylic acid was used. 41 and a Tg of 30°C, a hydroxyl group-containing acrylic resin (n) was obtained.

Production Example 15 Production of hydroxyl group-containing acrylic resin (o) The composition of the monomer mixture was 5.5 parts of styrene, 14.1 parts of ethyl acrylate, 27.65 parts of The procedure was carried out in the same manner as in Production Example 15 except that methacrylic acid was changed to 1.0 part, solid content 62.4%, number average molecular weight 3000, hydroxyl value 250 mg/KOH, acid value 6.5 mg/KOH, SP value 12.5 mg/KOH. 5, a hydroxyl group-containing acrylic resin (o) having a Tg of 15°C was obtained.

Production Example 16 Production of hydroxyl group-containing acrylic resin (p) The procedure was carried out in the same manner as in Production Example 15, except that methacrylic acid was changed to 1.0 parts. 3, A hydroxyl group-containing acrylic resin (p) having a Tg of 30°C was obtained.

Production Example 17 Production of hydroxyl group-containing acrylic resin (q) The composition of the monomer mixture was 4.0 parts of styrene, 36.0 parts of tert-butyl methacrylate, 24.2 parts of lauryl methacrylate, and 34.8 parts of hydroxyethyl methacrylate. Part and 1.0 part of methacrylic acid were carried out in the same manner as in Production Example 15, solid content 62.4%, number average molecular weight 3000, hydroxyl value 150 mg / KOH, acid value 6.5 mg / KOH, SP value 10.5 and a Tg of 30°C, a hydroxyl group-containing acrylic resin (p) was obtained.

Production Example 18 Production of hydroxyl group-containing acrylic resin (r) The composition of the monomer mixture was 5.5 parts of styrene, 18.6 parts of ethyl acrylate, 23.1 parts of methyl methacrylate, The procedure was carried out in the same manner as in Production Example 15 except that methacrylic acid was changed to 1.0 parts, solid content 62.4%, number average molecular weight 3000, hydroxyl value 250 mg/KOH, acid value 6.5 mg/KOH, SP value 12.5 mg/KOH. 5, a hydroxyl group-containing acrylic resin (r) having a Tg of 10°C was obtained.

Production Example 19 Production of hydroxyl group-containing acrylic resin (s) The composition of the monomer mixture was 33.3 parts of ethyl acrylate, 32.06 parts of methyl methacrylate, 33.64 parts of hydroxypropyl acrylate, and 1.0 part of methacrylic acid. Solid content 62.4%, number average molecular weight 3000, hydroxyl value 145 mg / KOH, acid value 6.5 mg / KOH, SP value 11.6, Tg 15 ° C. , to obtain a hydroxyl group-containing acrylic resin (s).

Production Example 20 Production of hydroxyl group-containing acrylic resin (t) The composition of the monomer mixture was changed to 33.67 parts of styrene, 25.72 parts of lauryl methacrylate, 38.56 parts of hydroxypropyl methacrylate, and 2.0 parts of methacrylic acid. The procedure was carried out in the same manner as in Production Example 15 except that the hydroxyl group had a solid content of 62.4%, a number average molecular weight of 3000, a hydroxyl value of 150 mg/KOH, an acid value of 13.0 mg/KOH, an SP value of 10.3, and a Tg of 15°C. A contained acrylic resin (t) was obtained.

Production Example 21 Production of hydroxyl-containing acrylic resin (u) The composition of the monomer mixture was changed to 35.35 parts of styrene, 24.05 parts of ethyl acrylate, 38.56 parts of hydroxypropyl methacrylate, and 2.0 parts of methacrylic acid. The procedure was carried out in the same manner as in Production Example 15 except that the solid content was 62.4%, the number average molecular weight was 3000, the hydroxyl value was 150 mg/KOH, the acid value was 13.0 mg/KOH, the SP value was 10.9, and Tg was 35°C. Containing acrylic resin (u) was obtained.

Production Example 22 Production of hydroxyl group-containing acrylic resin (v) The composition of the monomer mixture was 31.85 parts of methyl methacrylate, 8.0 parts of lauryl methacrylate, 59.15 parts of hydroxypropyl acrylate, and 1.0 part of methacrylic acid. Solid content 62.4%, number average molecular weight 3000, hydroxyl value 255 mg / KOH, acid value 6.5 mg / KOH, SP value 12.1, Tg 15 ° C. , to obtain a hydroxyl group-containing acrylic resin (v).

Production Example 23 Production of hydroxyl group-containing acrylic resin (w) The composition of the monomer mixture was 9.8 parts of ethyl acrylate, 20.0 parts of methyl methacrylate, 16.8 parts of ethyl methacrylate, and 51.75 parts of hydroxyethyl acrylate. part, acrylic acid 1.67 parts, solid content 62.4%, number average molecular weight 3000, hydroxyl value 250 mg / KOH, acid value 13.0 mg / KOH, SP value 12.6 and a Tg of 15°C, a hydroxyl group-containing acrylic resin (w) was obtained.

Example 1
Preparation of Clear Coating Composition Into a 1 L metal container, 60.0 parts of the hydroxyl group-containing acrylic resin (a) of Production Example 1 (in terms of resin solid content) and 2 parts of the hydroxyl group-containing acrylic resin (n) of Production Example 14 (in terms of solid content) were added. part, aminoplast resin LUWIPAL 018 (commercially available from BASF) in terms of solid content 10 parts, Ciba Geigy UV absorber "Tinuvin 384" 1.4 parts, Ciba Geigy light stabilizer "Tinuvin 123" 1.4 parts, acrylic 1.4 parts of a system surface conditioner, 57.0 parts of methyl amyl ketone, 22.0 parts of dibutyl ether (manufactured by Shoei Chemical Co., Ltd.), and 1.8 parts of inorganic fine particles are sequentially added, and thoroughly stirred with a disper to form a second liquid. A main component of a clear coating composition was obtained.

Into another metal container, 40.0 parts in solid content of "Dismodur N-3300" (NCO active ingredient: 22%) manufactured by Sumitomo Bayer Urethane Co., Ltd. and 2-ethylethoxypropanol were sequentially added, thoroughly stirred, and liquid 2 was obtained. A curing agent for a mold clear coating composition was obtained.

Coating film formation Powernics 1010 (cationic electrodeposition paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) and Orga P-30 (Nippon Paint Automotive Coatings Co., Ltd.) were applied to dull steel plates of 150 x 300 x 0.8 mm treated with zinc phosphate. AR-3020 black (water-based base paint manufactured by Nippon Paint Automotive Coatings) is applied to a test plate coated with a dry film thickness of 20 μm and 40 μm, respectively, so that the dry film thickness is 15 μm. An uncured base coating was formed by air spray coating and drying at 80°C for 5 minutes.

On top of that, the mixture obtained by mixing the clear main agent and the curing agent was diluted with a thinner consisting of n-butyl acetate/ethyl 3-ethoxypropionate = 1/2 (mass ratio). Dilute to 30 sec/20°C with 4 Ford cups. The two-liquid mixed clear paint composition prepared in this way is air-sprayed so that the dry film thickness is 40 μm to form an uncured clear paint film, which is set for 7 minutes and cured by baking at 140° C. for 25 minutes. to form a multilayer coating film.

For each test coating film obtained, the following evaluations (water spot resistance, resin liquid resistance, dry scratch resistance, car wash scratch resistance, and recoat adhesion) were performed. The results are listed in Table 1. Table 1 shows the classification of hydroxyl group-containing acrylic resins A and B, the glass transition temperature, hydroxyl value, solubility parameter of each hydroxyl group-containing acrylic resin, and alicyclic (meth)acrylate for hydroxyl group-containing acrylic resin (A). and the difference between the solubility parameter (Bsh) of the hydroxyl group-containing acrylic resin (B) and the solubility parameter (Ash) of the hydroxyl group-containing acrylic resin (A) (Bsh-Ash), polyfunctional isocyanate Ratio (β/α) of isocyanate equivalent (β) of compound/hydroxy equivalent (α) of all hydroxyl group-containing resin (X) other than aminoplast resin (D), solid content mass (Md) of aminoplast resin (D) and the solid content mass (Mc) ratio (Mc/Md) of the isocyanate compound (C), and the presence or absence of blending of inorganic fine particles are also described. Table 1 also shows the results of performance evaluation.

<Water spot resistance>
The water spot resistance is evaluated as follows after a coating film is formed on an electrodeposited plate having a long side of 500 mm and cured for 72 hours. 250 μL of deionized water (DIW) (≦0, 9 μS/cm) is dropped onto the coating film at intervals of 2 cm. The coating is placed in a gradient oven (2615/2610 BYK-Gardner) set at 37-81° C. with a temperature gradient of 1° C./1 cm for 30 minutes. After curing for 24 hours, it is visually confirmed whether spots are generated, and the temperature at which the spots are generated is evaluated. The temperature at this time is determined from the place of installation in the gradient oven.

⊚ (Very good water spot resistance): No spots at 81°C.
○ (Good water spot resistance): Very thin spots are generated only at 81 ° C.
(triangle|delta) (water spot resistance is generally favorable): A spot arises clearly at 81 degreeC.
x (weak water spot resistance): Spots occur even at temperatures below 81°C.

<Resin liquid resistance>
The test and evaluation of the resin liquid resistance are performed in the same manner as the water spot resistance. However, instead of DIW, 25 μL of a resin solution (manufactured by Procurementsource, Axalta, or Worwag) was added dropwise, and when taken out from the gradient oven, the resin solution was washed away with cold water and cured.

⊚ (very good resin liquid resistance): No spots at 75°C.
○ (Good resin liquid resistance): Spots are generated at 75 ° C.
Δ (Resin liquid resistance is generally good): Spots occur at 65°C.
x (weak resin liquid resistance): Spots occur even at temperatures below 65°C.

<Dry scratch resistance>
The evaluation of the scratch resistance (scratch resistance) of the obtained coating film was carried out using a flat surface abrasion tester manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd. The jig tip was horizontal to the surface of the object to be worn. A cylindrical jig is attached, and felt and abrasive paper (3M 281Q, WETORDRY PRODUCTION POLISHING PAPER 9μGRADE) are fixed to the tip of the jig in this order, and the abrasive paper fixed to the jig. A load was applied so that a total load of 900 g was applied to the surface, and the surface of the obtained coating film was abraded 10 times with a stroke length of 10 cm at a speed of 40 times per minute.

Measure the gloss at an angle of 20° with respect to the coating film surface of the test site and the untested site with Micro Trigloss (gloss meter manufactured by BYK Chemie), and the percentage of the quotient of the untested site to the test site is the gloss by the abrasion test. The scratch resistance was evaluated as the retention rate. Table 1 shows the results.

⊚ (Very good scratch resistance): Gloss retention is 80% or more.
Good (scratch resistance is good): Gloss retention is 70% or more and less than 80%.
Δ (scratch resistance is generally good): Gloss retention is 60% or more and less than 70%.
x (weak scratch resistance): Gloss retention rate is less than 60%.

<Car wash scratch resistance>
After spraying water at 23° C. from a nozzle with a diameter of 3 mm from a height of 100 mm at a pressure of 80 kg/cm ² , the scratch resistance was evaluated in the same manner as the dry scratch resistance. Table 1 shows the results.

⊚ (Very good scratch resistance): Gloss retention is 80% or more.
Good (scratch resistance is good): Gloss retention is 70% or more and less than 80%.
Δ (scratch resistance is generally good): Gloss retention is 60% or more and less than 70%.
x (weak scratch resistance): Gloss retention rate is less than 60%.

<Recoat Adhesion>
A cationic electrodeposition paint "Power Top U-50" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. was applied to a phosphoric acid-treated steel plate so that the dry film thickness was 25 μm, and then cured by heating. Aqueous paint "Aquarex AR-800" (trade name) manufactured by Paint Automotive Coatings Co., Ltd. is applied so that the dry film thickness is 20 μm, and then water-based paint "Aqualex AR-2000" manufactured by Nippon Paint Automotive Coatings Co., Ltd. is applied. (trade name) black was applied so that the dry film thickness was 10 μm, and dried at 80° C. for 5 minutes. The above clear coating composition was applied thereon in a wet-on-wet manner so as to give a dry film thickness of 40 μm, and baked and dried at 150° C. for 60 minutes to prepare a first coat coating film. Furthermore, a water-based paint "Aquarex AR-800" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. was applied on the obtained first coat coating film so that the dry film thickness was 20 μm, and then Nippon Paint Automotive. Aqueous paint "Aquarex AR-2000" (trade name) black color manufactured by Coatings Co., Ltd. was applied so that the dry film thickness was 10 μm, and dried at 80° C. for 5 minutes. The above clear coating composition was applied thereon in a wet-on-wet manner so as to give a dry film thickness of 40 μm, and baked and dried at 140° C. for 30 minutes to prepare a recoated coating film.

The cutting edge of the cutter (NT Cutter (trade name) S type, A type or equivalent) is held at about 30 degrees to the coating surface of the recoated coating film obtained, and a 2 mm checkerboard that reaches the substrate. A mesh was formed, and an adhesive tape (CELLOTAPE (registered trademark) manufactured by Nichiban Co., Ltd.) was evenly pressed with fingertips so as not to leave air bubbles. Immediately, one end of the adhesive tape was held and rapidly pulled perpendicularly to the coated surface to remove the adhesive tape from the test piece. At this time, [the number of peeled squares]/[the number of squares in the grid=100] was visually measured, and the recoat adhesion was evaluated according to the following criteria. Table 1 shows the results.

○: 0/100
△: 1/100 to 25/100
×: 26/100 to 100/100

Examples 2-8
Example 1 except that the types of the hydroxyl group-containing acrylic resins (a) to (w) used were shown in Table 1 as the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B). A two-liquid type clear coating composition was prepared in the same manner as above.
A coating film was formed in the same procedure as in Example 1 using the obtained clear coating composition. In Table 1, the same numerical values and performance evaluation as in Example 1 are described.

Comparative Examples 1-14
A two-component clear coating composition was prepared in the same manner as in Example 1, except that the hydroxyl group-containing acrylic resins (a) to (w) obtained in Production Examples were used in the combinations shown in Table 2. Incidentally, in Comparative Examples 11 and 14, no inorganic fine particles were blended.
A coating film was formed in the same procedure as in Example 1 using the obtained clear coating composition. In Table 2, the same numerical values and performance evaluation as in Example 1 are described.

As is clear from the results of Examples in Table 1 above, when hydroxyl group-containing acrylic resins (A) and (B), polyfunctional isocyanate compound (C) and aminoplast resin (D) satisfy all requirements has excellent water spot resistance, resin liquid resistance, dry scratch resistance, car wash scratch resistance and recoat adhesion. On the other hand, Table 2 shows the results of Comparative Examples, and Comparative Examples 1 to 4 are the glass transition temperature, hydroxyl value, solubility parameter and alicyclic (meth)acrylate value of the hydroxyl group-containing acrylic resin (A). is the case where it deviates from the minimum value in each range, and Comparative Examples 5 to 8 deviate from the maximum value of each value of the hydroxyl group-containing acrylic resin (A). Comparative Examples 10 and 11 are cases where the glass transition temperature, hydroxyl value and solubility parameter of the hydroxyl group-containing acrylic resin (B) deviate from the respective minimum values, and Comparative Examples 12 and 14 are cases where the hydroxyl group-containing acrylic resin ( This is the case where the maximum value of each value of B) is deviated. Comparative Examples 7 and 8 are cases where β/α is less than 0.8, and Comparative Examples 11 and 12 are cases where β/α is higher than 1.2. Furthermore, Comparative Examples 7 and 11 are cases where the value of Mc/Md is zero. In the case of the comparative example, the performance is bad in some respects.

Claims (6)

A clear coating composition containing a hydroxyl group-containing acrylic resin (A), a hydroxyl group-containing acrylic resin (B), a polyfunctional isocyanate compound (C) and an aminoplast resin (D),
The hydroxyl group-containing acrylic resin (A) has a glass transition temperature of 20 to 35 ° C., a hydroxyl value of 100 to 200 mgKOH / g, a solubility parameter of 9.5 to 11.5 and an alicyclic (meth) acrylate hydroxyl group-containing acrylic resin ( A) in an amount of 20 to 40% by mass relative to the total solid content,
The hydroxyl-containing acrylic resin (B) has a glass transition temperature of 15 to 30° C., a hydroxyl value of 150 to 250 mgKOH/g and a solubility parameter of 10.5 to 12.5,
The solubility parameter of the hydroxyl group-containing acrylic resin (A) is lower than the solubility parameter of the hydroxyl group-containing acrylic resin (B), and the difference is 0.5 or more,
The ratio of the hydroxyl group equivalent (α) of all the hydroxyl group-containing resins (X) other than the aminoplast resin (D) and the isocyanate equivalent (β) of the polyfunctional isocyanate compound (C) is expressed by the following formula (1)
1.20>β/α>0.80: Formula (1)
and
The solid content mass ratio (Mc, Md) of the polyfunctional isocyanate compound (C) and the aminoplast resin (D) is represented by the following formula (2)
8.0>Mc/Md>1.0: Formula (2)
A clear coating composition characterized by satisfying The clear coating composition according to claim 1, further comprising inorganic fine particles having an average particle size of 2 to 500 nm. The hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B) are 20 to 50% by mass of the hydroxyl group-containing acrylic resin (A) with respect to the total 100 parts by mass of the resin solid content of the clear coating composition. and the hydroxyl group-containing acrylic resin (B) is contained in an amount of 5 to 35% by mass. The clear paint according to any one of claims 1 to 3, wherein the polyfunctional isocyanate compound (C) is contained in an amount of 25 to 45% by mass with respect to 100 parts by mass of the resin component of the clear paint composition. Composition. The clear coating composition according to any one of claims 1 to 4, wherein the aminoplast resin (D) is contained in an amount of 1 to 25% by mass with respect to 100 parts by mass of the resin component of the clear coating composition. . After applying the intermediate coating composition to the object to be coated, and further coating the base coating composition on the resulting intermediate uncured coating film to obtain the base uncured coating film, claim 1 to obtain a clear uncured coating film by applying the clear coating composition according to any one of items 1 to 5;
A method for forming a multi-layer coating film, wherein the uncured intermediate coating film, the uncured base coating film, and the uncured clear coating film are simultaneously heated and cured.