KR102340545B1 - Composition for clear coat - Google Patents

Abstract

The present invention includes a silane-modified acrylic resin, a first polyester polyol resin, a second polyester polyol resin, a melamine resin, and a urethane resin, and the number average molecular weight of the first polyester polyol resin is that of the second polyester polyol resin. It relates to a clear coating composition having a greater than number average molecular weight.

Description

Clear paint composition {COMPOSITION FOR CLEAR COAT}

The present invention relates to a clear coating composition having excellent appearance characteristics, chipping resistance and scratch resistance of the prepared coating film.

BACKGROUND ART [0002] A car body of an automobile is generally subjected to a multi-coating process such as electrodeposition painting, intermediate painting, top painting and clear painting in order to protect the surface from the exterior and the external environment. Specifically, it is a common automotive painting process to apply and harden an intermediate coat after electrodeposition painting on a car body, and continuously apply a top coat and a clear paint on the intermediate coat layer, followed by drying and curing. This automobile painting process is generally performed by a three-coat, two-bake (3C2B) painting method in which primary curing is performed after intermediate painting, and secondary curing is performed after clear paint painting.

As a clear paint for automobiles, an acrylic resin containing a hydroxyl group or a thermosetting coating composition containing an amino resin is widely used. For example, a conventional composition for a clear paint includes an acrylic resin and a melamine resin, and it is common for the melamine resin to react with a hydroxyl group included in the acrylic resin to form a chemical bond to form a coating film. However, the conventional composition for a clear paint as described above has a limitation in that the prepared coating film lacks mechanical properties, in particular, surface tension and flexibility, and thus lacks scratch resistance.

As an alternative to overcoming the limitations of such conventional clear paints, Korean Patent Registration No. 1,115,869 (Patent Document 1) discloses an acrylic resin, a melamine resin, a silane-modified block isocyanate resin, and a fluidity control resin for improved scratch resistance for automobiles. A liquid clearcoat composition is disclosed. However, the clear coat composition of Patent Document 1 has a limitation in being applied as a paint for a vehicle body because the appearance characteristics of the prepared coating film are deteriorated.

Therefore, there is a need for research and development on a clear paint composition in which the prepared coating film has excellent appearance characteristics and mechanical properties, particularly scratch resistance, flexibility, and hardness.

Korean Patent Registration No. 1,115,869 (published on: 2012.01.11.)

The present invention provides a clear paint composition excellent in scratch resistance and chipping resistance by strengthening the surface tension and flexibility of the prepared coating film.

The present invention includes a silane-modified acrylic resin, a first polyester polyol resin, a second polyester polyol resin, a melamine resin and a urethane resin,

The number average molecular weight of the first polyester polyol resin is greater than the number average molecular weight of the second polyester polyol resin, and there is provided a clear coating composition.

The clear paint composition according to the present invention has excellent scratch resistance by strengthening the surface tension and flexibility of a coating film prepared by using a combination of an organic resin and an inorganic resin. In addition, the clear paint composition has excellent flexibility and resilience of the coating film prepared by including the polyester resin of low molecular weight, and the appearance characteristics, flexibility, chipping resistance and resistance of the coating film prepared including the two types of polyester resins. Excellent scratch resistance.

Hereinafter, the present invention will be described in detail.

As used herein, "weight average molecular weight" and "number average molecular weight" are measured by a conventional method known in the art, and may be measured by, for example, a gel permeation chromatograph (GPC) method. Furthermore, the "glass transition temperature" is measured by a conventional method known in the art, for example, it can be measured by differential scanning calorimetry (DSC). In addition, functional groups such as "acid value" and "hydroxyl value" may be measured by a method well known in the art, for example, may represent a value measured by a method of titration.

In addition, in this specification, "(meth)acrylate" means acrylate and/or methacrylate.

The clear paint composition according to the present invention includes a silane-modified acrylic resin, a first polyester polyol resin, a second polyester polyol resin, a melamine resin, and a urethane resin.

Silane-modified acrylic resin

The silane-modified acrylic resin serves to improve physical properties such as hardness, acid resistance and scratch resistance of the coating film.

The silane-modified acrylic resin may be directly synthesized according to a known method, or a commercially available product may be used. In this case, the silane-modified acrylic resin may be, for example, an acrylic resin prepared by polymerizing at least one selected from the group consisting of a vinyl monomer and a (meth)acrylate monomer, modified with a silane monomer.

The type of the vinyl monomer is not particularly limited, but for example, styrene, methylstyrene, dimethylstyrene, fluorostyrene, ethoxystyrene, methoxystyrene, phenylene vinyl ketone, vinyl t-butylbenzoate, vinyl cyclohexano At least one selected from ester, vinyl acetate, vinyl pyrrolidone, vinyl chloride, vinyl alcohol, acetoxystyrene, t-butylstyrene and vinyltoluene may be used.

In addition, as the (meth)acrylate monomer, for example, 2-hydroxypropyl methacrylate, propyl methacrylate, t-butylaminoethyl methacrylate, dicyclopentenyl oxyethyl methacrylate, acrylic acid dimer, hexanediol diacrylate, butyl acrylate, triisopropylsilyl acrylate, benzyl methacrylate, 2-hydroxyethyl methacrylate, trimethylolpropane triacrylate, tripropylene glycol diacrylate, ethyl methacrylate, Isobutyl methacrylate, hydroxyisopropyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, triisopropyl silyl methacrylate, isobornyl acrylate, t-butylcyclohexyl methacrylate, trimethylcyclo hexyl methacrylate, methyl methacrylate, acrylic acid, t-butyl methacrylate, isobornyl methacrylate, methacrylonitrile, methacrylic acid, acrylamide, methacrylamide, chlorostyrene, cyclohexylvinylether One or more types may be used.

The silane monomer may be an alkoxy group-containing silane monomer. For example, the silane monomer may be gamma-glycidoxypropyl triethoxy silane, gamma-glycidoxypropyl trimethoxy silane, gamma-glycidoxypropyl methyldiethoxy silane, gamma-glycidoxypropyl triethoxy Silane, 3-mercaptopropyl trimethoxy silane, vinyltrimethoxysilane, vinyltriethoxy silane, gamma-methacryloxypropyl trimethoxy silane, gamma-methacryloxypropyl triethoxy silane, gamma-aminopropyl Trimethoxy silane, gamma-aminopropyl triethoxy silane, 3-isocyanatopropyl triethoxy silane, gamma-acetoacetatepropyl trimethoxysilane, gamma-acetoacetatepropyl triethoxy silane, beta-cyano acetyl trimethoxy silane, beta-cyanoacetyl triethoxy silane, acetoxyaceto trimethoxy silane, and the like.

The silane-modified acrylic resin has a glass transition temperature of 30 to 50 °C, 35 to 48 °C, or 40 to 45 °C, and a weight average molecular weight of 5,500 to 8,500 g/mol, 6,000 to 8,000 g/mol, or 6,500 to 7,500 g /mol, and may have a viscosity at 25°C of 500 to 2,500 cps, 700 to 2,000 cps, or 900 to 1,800 cps. When the glass transition temperature of the silane-modified acrylic resin is within the above range, storage stability is good and appropriate coating properties can be secured, and when the weight average molecular weight is within the above range, long-term physical properties such as durability and weather resistance of the prepared coating film To improve, when the viscosity at 25 ℃ is within the above range, there is an effect that the workability of the composition is easy.

In addition, the silane-modified acrylic resin has a hydroxyl value (OHv) of 80 to 90 mgKOH/g, or 82 to 88 mgKOH/g, and an acid value (Av) of 5 mgKOH/g or less, 4 mgKOH/g or less, or 1 to 3 mgKOH/g. When the hydroxyl value of the silane-modified acrylic resin is within the above range, the curability of the composition is improved to ensure impact resistance, water resistance, adhesion, and cold chipping resistance, and when the acid value is within the above range, the reactivity of the composition is controlled by There is an effect that the appearance characteristics are improved.

The silane-modified acrylic resin may be included in an amount of 1 to 20 parts by weight, 5 to 15 parts by weight, or 7 to 13 parts by weight based on 1 to 20 parts by weight of the first polyester polyol resin. When the content of the silane-modified acrylic resin is within the above range, it is possible to prevent a problem in that the gloss of a coating film prepared from a coating composition including the same, and a problem in which the appearance characteristics and curing density of the coating film are deteriorated.

First polyester polyol resin

The first polyester polyol resin serves to improve the appearance characteristics and flexibility of the prepared coating film.

The first polyester polyol resin may be directly synthesized according to a known method, or a commercially available product may be used. For example, the first polyester polyol resin may be prepared by reacting a carboxylic acid with a polyol.

In this case, the carboxylic acid is isononanoic acid, adipic acid (AA), isophthalic acid (IPA), trimmaletic anhydride (TMA), alicyclic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, fumaric acid , maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (HHPA), and may be at least one selected from the group consisting of derivatives thereof. In addition, the polyol is methoxy polyethylene glycol, 1,6-hexanediol (1,6-HD), neopentyl glycol (NPG), trimethylol propane (TMP), ethylene glycol, propylene glycol, diethylene glycol, butanediol 1 It may be at least one selected from the group consisting of ,4-hexanediol and 3-methylpentanediol.

In addition, the first polyester polyol resin has a hydroxyl value (OHv) of 100 to 180 mgKOH/g, 120 to 150 mgKOH/g, or 130 to 145 mgKOH/g, and an acid value (Av) of 10 to 50 mgKOH/g , 15 to 35 mgKOH/g, or 20 to 25 mgKOH/g. When the hydroxyl value of the first polyester polyol resin is within the above range, the composition has good water dispersibility and coating properties, and when the acid value is within the above range, storage stability and crosslinking density are improved, and cold chipping resistance is good. .

Furthermore, the number average molecular weight of the first polyester polyol resin is greater than the number average molecular weight of the second polyester polyol resin. For example, the first polyester polyol resin may have a number average molecular weight (Mn) of 1,300 to 2,500 g/mol, 1,400 to 2,300 g/mol, or 1,500 to 2,000 g/mol.

In addition, the first polyester polyol resin may have a viscosity at 25° C. of 1,000 to 3,500 cps, 1,500 to 3,000 cps, or 1,800 to 2,700 cps. When the viscosity at 25° C. of the first polyester polyol resin is within the above range, there is an effect of easy workability.

The first polyester polyol resin may be included in an amount of 1 to 20 parts by weight, 5 to 15 parts by weight, or 7 to 13 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the first polyester polyol resin is within the above range, the appearance, impact resistance and cold chipping resistance of the prepared coating film are good.

Second polyester polyol resin

The second polyester polyol resin serves to improve chipping resistance and scratch resistance by increasing the solid content and reactivity of the composition, and improving flexibility and restoring force of the prepared coating film.

In this case, the second polyester polyol resin may be directly synthesized according to a known method, or a commercially available product may be used. For example, the second polyester polyol resin may be prepared by reacting caprolactone with a polyol. In this case, the polyol may include, but is not limited to, cyclohexanedimethanol (CHDM).

In addition, the second polyester polyol resin may have a hydroxyl value (OHv) of 200 to 400 mgKOH/g, 230 to 350 mgKOH/g, or 250 to 300 mgKOH/g. When the hydroxyl value of the second polyester polyol resin is within the above range, the crosslinking density with the curing agent is improved, thereby improving the durability of the prepared coating film.

The number average molecular weight (Mn) of the second polyester polyol resin is smaller than the number average molecular weight (Mn) of the first polyester polyol resin. For example, the second polyester polyol resin may have a number average molecular weight of 500 to 1,000 g/mol, 550 to 900 g/mol, or 600 to 800 g/mol.

In addition, the second polyester polyol resin may have a viscosity at 25° C. of 700 to 2,500 cps, 800 to 2,400 cps, or 850 to 2,300 cps. When the viscosity at 25° C. of the second polyester polyol resin is within the above range, workability is easy and the appearance is excellent.

The second polyester polyol resin may be included in an amount of 1 to 20 parts by weight, 5 to 15 parts by weight, or 7 to 13 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the second polyester polyol resin is within the above range, there is a good effect in impact resistance and cold chipping resistance of the prepared coating film.

The clear paint composition includes the first polyester polyol resin and the second polyester polyol resin in a weight ratio of 1:0.1 to 1:5, a weight ratio of 1:0.2 to 1:3, or a weight ratio of 1:0.5 to 1:2 can be included as When the mixing weight ratio of the first polyester polyol resin and the second polyester polyol resin is within the above range, durability, cold chipping resistance, and appearance of the prepared coating film may be improved.

melamine resin

Melamine resin, as a curing agent, functions to cure the composition by crosslinking reaction with each component of the clear paint composition.

The melamine resin may be directly synthesized according to a known method, or a commercially available product may be used. For example, the melamine resin includes methoxy methyl melamine, methyl melamine, butyl melamine, isobutoxy melamine, butoxy melamine, hexamethylol melamine, hexamethoxy methyl melamine, hexabutoxy methyl melamine, hexamethoxybutoxy methyl. At least one selected from the group consisting of melamine and iminomethoxy methyl melamine may be used.

In addition, the melamine resin has a weight average molecular weight (Mw) of 100 to 5,000 g/mol, 500 to 4,500 g/mol or 1,000 to 4,000 g/mol, and a viscosity at 25°C of 400 to 1,200 cps, 500 to 1,100 cps , or 600 to 1,000 cps. When the weight average molecular weight of the melamine resin is within the above range, the crosslinking density is improved to improve the adhesion and hardness of the prepared coating film, and when the viscosity at 25°C is within the above range, excellent gloss and appearance are obtained. have.

The melamine resin may be included in an amount of 15 to 35 parts by weight, 16 to 30 parts by weight, or 17 to 27 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the melamine resin is within the above range, there is an effect of improving the adhesion and hardness of the prepared coating film by improving the crosslinking density.

urethane resin

The urethane resin serves to improve workability of the clear coat composition and improve the appearance characteristics of a coating film prepared from the composition.

The urethane resin may be directly synthesized according to a known method, or a commercially available product may be used. For example, the urethane resin may be prepared by reacting alcohol with diisocyanate.

In this case, the alcohol is cyclohexanol, ethylhexanol, butanol, 1,6-hexanediol, ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, trimethylol propane, butanediol, 1,4- It may be at least one selected from the group consisting of hexanediol and 3-methylpentanediol.

In addition, the diisocyanate is, for example, isophorone diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylene diisocyanate, 2,3-dimethyl Ethylene diisocyanate, 1-methyl trimethylene diisocyanate, 1,3-cyclopentene diisocyanate, 1,4-cyclopentene diisocyanate, 1,2-cyclopentene diisocyanate, 1,3-phenylene diisocyanate, 1,4 -Phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4-diphenylpropane diisocyanate, xylene diisocyanate and 1,1,6,6-tetramethylhexamethylene diisocyanate It may be at least one selected from the group consisting of.

The urethane resin may not include an unreacted NCO group. When a urethane resin that does not contain unreacted NCO groups is used, the appearance of the prepared coating film is excellent.

In addition, the urethane resin has a weight average molecular weight (Mw) of 8,000 to 13,000 g/mol, 9,000 to 12,500 g/mol, or 10,000 to 12,000 g/mol, and a solid content of 60 to 80 wt%, 65 to 75 wt% , or 67 to 73% by weight. When the weight average molecular weight of the urethane resin is within the above range, there is an effect of excellent gloss and appearance characteristics of the coating film, and when the solid content is within the above range, the workability of the composition is excellent.

The urethane resin may be included in an amount of 1 to 10 parts by weight, 2 to 9 parts by weight, or 3 to 8 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the urethane resin is within the above range, there is an excellent effect in flexibility and appearance characteristics of the prepared coating film.

solvent

The clear paint composition may further include a solvent. In this case, the solvent controls the viscosity of the clear paint composition and controls the quick-drying properties of the composition, and a conventional solvent used in the clear paint composition may be used.

The solvent, for example, may include at least one selected from the group consisting of acetate-based, alkylbenzene-based, ketone-based and carbonate-based. In another example, the solvent may include a non-polar solvent such as n-heptane, toluene, xylene, petroleum compounds and n-hexane; Ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol monoethyl ether acetate, dibasic esters, 3-methoxy butyl acetate, amyl acetate, butyl glycol acetate, methyl ethyl ketone, methyl isobutyl ketone, acetone, diiso polar solvents such as butyl ketone, isophorone and cyclohexanone; and a mixture of the non-polar solvent and the polar solvent, and may be appropriately selected and used according to the characteristics or volatilization rate of the resin contained in the composition.

In addition, the solvent may be included in an amount of 5 to 30 parts by weight, 10 to 25 parts by weight, or 12 to 23 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the solvent is within the above range, it is possible to prevent problems such as defects in the coating film, such as pinholes in the coating film, and occurrence of stains.

additive

The clear paint composition may further include at least one additive selected from the group consisting of a dispersant, a moisture absorbent, a leveling agent, a flow inhibitor, and an ultraviolet absorber.

The additive may be included in an amount of 20 to 40 parts by weight, 23 to 37 parts by weight, or 25 to 35 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin. When the content of the additive is out of the above range, the appearance characteristics of the prepared coating film may be deteriorated.

The dispersant serves to improve the storability of the composition. Furthermore, the dispersant may be used without any particular limitation as long as it is a conventional material that can be used in the coating composition, and may be, for example, benzene propanoic acid. In addition, the dispersant may be included in an amount of 0.1 to 3 parts by weight, 0.2 to 2 parts by weight, or 0.3 to 1 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin.

The water absorbent serves to improve the stain resistance of the prepared coating film. The moisture absorbent may be used without any particular limitation as long as it is a conventional material that can be used in the coating composition, and may be, for example, an ortho-ester-based compound. The ortho-ester moisture absorbent is, for example, formidine acetate, 2-methoxy-1,3-dioxolane, 1,1,3,3-tetramethoxypropane, triethyl-O-acetate , triethyl-O-formate, triethyl-O-propynate, triisopropyl-O-formate, trimethyl-O-acetate and trimethyl-O-formate. Furthermore, the moisture absorbent may be included in an amount of 1 to 10 parts by weight, 2 to 9 parts by weight, or 3 to 8 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin.

The leveling agent serves to impart leveling properties and wettability to the prepared coating film. In addition, the leveling agent may be used without any particular limitation as long as it is a conventional material that can be used in the coating composition, for example, polyether-modified polysiloxane-based. In addition, the leveling agent may be included in an amount of 0.1 to 2 parts by weight, 0.2 to 1.5 parts by weight, or 0.5 to 1 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin.

The anti-flow agent serves to improve the workability of the composition by controlling the sagging of the composition. In addition, the anti-flow agent may be used without any particular limitation as long as it is a conventional material that can be used in the coating composition, for example, a polyester resin having a diurea group may be mentioned. Furthermore, the flow inhibitor may be included in an amount of 10 to 30 parts by weight, 15 to 25 parts by weight, or 17 to 23 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin.

The UV absorber blocks UV rays reaching the prepared coating film and improves the weather resistance of the final coating film. The ultraviolet absorber may be a benzotriazole-based ultraviolet absorber. In addition, the ultraviolet absorber may be included in an amount of 1 to 5 parts by weight, 1 to 4 parts by weight, or 1 to 3 parts by weight based on 1 to 20 parts by weight of the silane-modified acrylic resin.

As described above, the clear paint composition according to the present invention has excellent scratch resistance by strengthening the surface tension and flexibility of a coating film prepared by using a combination of an organic resin and an inorganic resin. In addition, the clear paint composition has excellent flexibility and resilience of the coating film prepared by including low molecular weight polyester, and the appearance characteristics, flexibility, chipping resistance and scratch resistance of the coating film prepared including two types of polyester resins. castle is excellent

Hereinafter, the present invention will be described in more detail through examples.

However, these examples are only for helping the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

[Example]

Examples 1 to 9, and Comparative Examples 1 to 4. Preparation of clear paint composition

A clear paint composition was prepared by mixing a silane-modified acrylic resin, a first polyester polyol resin, a second polyester polyol resin, a melamine resin, a urethane resin, a solvent, and an additive according to the contents of Tables 1 and 2.

Ingredients (parts by weight) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Silane-modified acrylic resin 11 13 7 15 11 11 First polyester polyol resin 10.5 10.5 13 10.5 14 10.5 Second polyester polyol resin 10 7 10 9 9 15 melamine resin 24 24 24 22 22 20 urethane resin 5 5 5 5 5 5 additive dispersant 0.3 0.3 0.3 0.3 0.3 0.3 moisture absorbent 3 3 3 3 3 3 leveling agent 0.7 0.7 0.7 0.7 0.7 0.7 flow inhibitor 20 20 20 20 20 20 UV absorber 2 2 2 2 2 2 solvent 13.5 14.5 15 12.5 13 12.5 total amount 100 100 100 100 100 100

Ingredients (parts by weight) Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Silane-modified acrylic resin 22 9 8 - 13 13 13 First polyester polyol resin 9.5 21 9 13 - 12 12 Second polyester polyol resin 9 8 22 12 12 - 11 melamine resin 17 18 18 27 27 27 20 urethane resin 4 4 4 4 4 4 - additive dispersant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 moisture absorbent 3 3 3 3 3 3 3 leveling agent 0.7 0.7 0.7 0.7 0.7 0.7 0.7 flow inhibitor 20 20 20 20 20 20 20 UV absorber 2 2 2 2 2 2 2 solvent 12.5 14 13 18 18 18 18 total amount 100 100 100 100 100 100 100

The components and product names of each component used in the following Examples and Comparative Examples are shown in Table 3.

composition note Silane-modified acrylic resin Solid content: 70% by weight, Tg: 42°C, viscosity at 25°C: 1,500 cps, Mw: 7,000 g/mol,
Av: 2 mgKOH/g, OHv: 85 mgKOH/g, hydroxyl group content: 2.5 wt% First polyester polyol resin Solids: 70 wt%, Viscosity at 25°C: 2,300 cps, Mn: 1,700 g/mol,
OHv: 135 mgKOH/g, Av: 23 mgKOH/g Second polyester polyol resin Solid content: 86% by weight, viscosity at 25°C: 1,200 cps, Mn: 700 g/mol,
OHv: 282mgKOH/g melamine resin Solids: 58 wt %, Viscosity at 25°C: 800 cps, Mw: 2,500 g/mol urethane resin Solid content: 70% by weight, Mw: 11,000 g/mol dispersant Benzene propanoic acid moisture absorbent Trimethyl orthoacetate leveling agent Polyether-modified polydimethylsiloxane
(Polyether modified polydimethylsiloxane) flow inhibitor Polyester resin having a hydroxyl group and a diurea group
(Manufacturer: Nuplex, Product Name: SETAL91715SS-55) UV absorber Manufacturer: BASF, product name: TINUVIN5151 solvent butyl acetate

Test Example: Evaluation of the properties of the prepared coating film

A primer coat composition (manufacturer: KCC, product name: FU2270, oily) was bell-coated to a thickness of 35 μm on the electrodeposition-coated specimen, and first cured at 140° C. for 25 minutes. Thereafter, the base coat composition (manufacturer: KCC, product name: TT663, water-based) was bell-coated to a thickness of 15 μm, and the water remaining in the paint was evaporated (drying) in a drying furnace at 80° C. for 3 minutes. After cooling to room temperature for 2 minutes, the clear coat compositions (oil-based) of Examples and Comparative Examples were bell-coated to a thickness of 40 μm, followed by secondary curing at 140° C. for 25 minutes to form a final coating film. The appearance characteristics and physical properties of the final coating film were measured in the following way, and the results are shown in Table 4.

(1) Appearance of the coating film

For the final coating film, the CF value was measured using Wave Scan DOI (BYK Gardner), an automobile exterior measuring instrument, and it was determined that the higher the CF value, the better the appearance characteristics of the coating film. Specifically, when the CF value was 70 or more, excellent (◎), 65 or more and less than 70, good (○), 60 or more and less than 65, normal (Δ), and less than 60, bad (×).

(2) hardness

The hardness of the clear coating film was measured by the pencil hardness method. Specifically, the maximum hardness that does not damage the clear coating film was measured using each of 3B, 2B, B, HB, F, H, 2H, and 3H pencils (3B, 2B, B, HB, F, H, 2H). , 3H: inferior ⇔ excellent).

(3) Adhesiveness

After the specimen was heat-treated and left at room temperature for 24 hours, adhesion was evaluated using a checkerboard method.

Specifically, in the checkered method, 100 squares of 2 mm in width and 2 mm in length were made on the surface of the clear coating film with a knife, and then the square was removed using a tape to measure adhesion. At this time, the measured adhesion is M-1 (very good) when 100 squares are 100% completely attached, M-2 (excellent) when the remaining squares are 70% or more and less than 100%, and M- when 50% or more and less than 70% 3 (moderate), 30% or more and less than 50% M-4 (bad), and less than 30% M-5 (very bad).

In addition, the heat treatment was repeated for 1 cycle, a total of 3 cycles, in which the heat treatment was performed at 150° C. for 20 minutes and then left at room temperature for 20 minutes.

(4) water resistance

After the specimen was immersed in a constant temperature water bath at 40° C. for 240 hours and left at room temperature for 1 hour, a peeling test was performed in the same manner as in item (3).

(5) acid resistance

After 0.2 ml of 0.1N sulfuric acid was added dropwise to the surface of the coating film of the specimen, it was treated in an oven preheated to 40° C. or higher for 150 minutes. At this time, by visually observing whether or not etching, staining, or swelling occurred in the portion where sulfuric acid was dropped on the specimen, the highest temperature at which damage to the specimen did not occur was determined as the acid-resistant temperature.

(6) scratch resistance

The 20° gloss of the specimen was measured (initial gloss measurement), and the 20° gloss was measured after reciprocating the surface of the specimen 10 times using a car wash resistance tester (manufactured by Amtec Kistler). Thereafter, gloss retention was calculated using Equation 1 below for initial gloss and gloss after surface treatment.

[Equation 1]

Gloss retention rate = gloss after surface treatment / initial gloss × 100

(7) Solvent resistance

After putting a cotton cloth soaked in xylene on the coating film of the specimen, it was scraped 4 times with a force of 2 kg every 1 minute to record the time when the lower coating surface appeared.

film exterior Hardness adherence water resistance acid resistance initial gloss scratch resistance solvent resistance Example 1 ◎ F M-1 M-1 45℃ 91% 87% 10 minutes Example 2 ◎ F M-1 M-1 44℃ 92% 87% 10 minutes Example 3 ◎ F M-1 M-1 45℃ 90% 85% 10 minutes Example 4 ○ HB M-1 M-2 41℃ 86% 81% 9 minutes Example 5 ○ HB M-1 M-1 40℃ 87% 80% 9 minutes Example 6 ○ HB M-1 M-2 42℃ 85% 81% 9 minutes Example 7 △ B M-1 M-2 39℃ 84% 78% 8 minutes Example 8 ○ B M-2 M-2 38℃ 86% 79% 8 minutes Example 9 △ B M-1 M-2 39℃ 87% 77% 8 minutes Comparative Example 1 X 2B M-2 M-4 36℃ 78% 64% 5 minutes Comparative Example 2 △ 2B M-3 M-3 35℃ 77% 62% 4 minutes Comparative Example 3 X B M-3 M-4 34℃ 79% 62% 5 minutes Comparative Example 4 △ 2B M-3 M-3 35℃ 75% 63% 5 minutes

As shown in Table 4, the coating films prepared from the clear coating compositions of Examples 1 to 9 were excellent in appearance characteristics, hardness, adhesion, acid resistance, solvent resistance, and scratch resistance.

On the other hand, the coating films prepared from the compositions of Comparative Examples 1 to 4 lacked physical properties such as appearance characteristics, adhesion, water resistance, acid resistance, scratch resistance and solvent resistance.

Claims (6)

a silane-modified acrylic resin, a first polyester polyol resin, a second polyester polyol resin, a melamine resin, and a urethane resin,
The number average molecular weight of the first polyester polyol resin is greater than the number average molecular weight of the second polyester polyol resin,
The second polyester polyol resin has a hydroxyl value of 200 to 400 mgKOH/g and a number average molecular weight of 500 to 1,000 g/mol, a clear paint composition. The method according to claim 1,
The silane-modified acrylic resin has a glass transition temperature of 30 to 50° C., a hydroxyl value of 80 to 90 mgKOH/g, and an acid value of 5 mgKOH/g or less, a clear paint composition. The method according to claim 1,
The first polyester polyol resin has a hydroxyl value of 100 to 180 mgKOH/g, an acid value of 10 to 50 mgKOH/g, and a number average molecular weight of 1,300 to 2,500 g/mol, a clear paint composition. delete The method according to claim 1,
A mixing ratio of the first polyester polyol resin and the second polyester polyol resin is in a weight ratio of 1:0.1 to 1:5. The method according to claim 1,
The composition comprises 1 to 20 parts by weight of the silane-modified acrylic resin, 1 to 20 parts by weight of the first polyester polyol resin, 1 to 20 parts by weight of the second polyester polyol resin, 15 to 35 parts by weight of the melamine resin, and 1 to 10 parts by weight A clear paint composition comprising a urethane resin.