KR101149570B1 - Aqueous paint compostion having improved hardness and chipping resistance - Google Patents

Abstract

The present invention relates to a coating composition, specifically, the present invention comprises a main resin containing 45 to 70 parts by weight of polyurethane dispersion resin having a hydroxyl group and 15 to 35 parts by weight of urethane-modified polyester resin; And a curing agent containing 3 to 20 parts by weight of hexamethylene diisocyanate trimer blocked with dimethyl pyrazole and 3 to 20 parts by weight of hexamethylene diisocyanate trimer blocked with methylethylkeoxime, wherein the equivalent ratio of hydroxyl group and isocyanate is 1: It is a water-soluble coating composition which is 1.4-1: 0.5, and improves the appearance quality, hardness, and chipping resistance of a coating film.

Water-soluble intermediate paint, polyurethane, urethane modified polyester, hexamethylene diisocyanate

Description

Aqueous PAINT COMPOSTION HAVING IMPROVED HARDNESS AND CHIPPING RESISTANCE

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-soluble middle paint for automobiles, and more particularly, to water-soluble automobiles having a higher curing density and lowering baking temperature of the coating film, thereby promoting the curing speed and improving the appearance quality, hardness, and chipping resistance of the coating film. It relates to a intermediate coating composition.

In general, an oil-soluble intermediate paint for controlling the evaporation rate of a volatile mixed organic solvent, having good paintability, having good resin dissolving power and compatibility, has been used for the intermediate paint of automobiles. However, the oil-soluble intermediate paint has the advantage of having excellent gloss and appearance quality after coating and baking hardening, but more than 40% of the paint composition is a volatile organic compound, causing environmental pollution.

In recent years, the use of organic solvents and harmful heavy metals generated in automobile coatings, mainly in Europe and the United States, has been restricted by policy. Therefore, the global trend of technology for automotive paints is becoming more water-based, and there is a demand for a method for saving energy and increasing process efficiency by shortening processes required for paint drying and curing processes. In particular, researches for reducing volatile organic compounds have been actively conducted, and researches on volatile organic compounds reduction technologies have been actively conducted in Korea.

An object of the present invention is to secure a better degree of curing with respect to the temperature and time required for curing water-soluble intermediate paints in general, to reduce the energy required for curing, and to improve cold resistance and hardening of the coating film. It is to provide an intermediate coating composition.

The present invention, based on a total of 100% by weight of the following main resin components and the following curing agent components, a main containing 45 to 70% by weight polyurethane dispersion resin having a hydroxyl group and 15 to 35% by weight urethane-modified polyester resin Suzy; And a curing agent containing 3 to 20 wt% of hexamethylene diisocyanate trimer blocked with dimethyl pyrazole and 3 to 20 wt% of hexamethylene diisocyanate trimer blocked with methylethylkeoxime, wherein the equivalent ratio of hydroxyl and isocyanate is 1 It relates to a water-soluble coating composition which is from: 1.4 to 1: 0.5.

Hereinafter, the present invention will be described in detail.

The present invention provides a non-one-to-one curing method between resins and hardeners by designing multicomponent bonds between polyurethane resins and urethane-modified polyester resins and two hexamethylene diisocyanate trimer curing agents blocked with dimethyl pyrazole and methylethylkeoxime. Complementary weaknesses such as lowering of the crosslinking density that may occur during the reaction of a single curing agent, and by forming a more dense crosslinked structure of the coating film, the mechanical properties of the coating film were improved. In addition, a hexamethylene diisocyanate trimer blocked with dimethyl pyrazole and a hexamethylene diisocyanate trimer blocked with methylethylkeoxime are used as a curing agent, and a crosslinkable amino resin is optionally used as an auxiliary curing agent to increase the curing density and at the same time, The baking temperature was lowered by constructing a composition ratio.

The synthesis method of the polyurethane dispersion resin used for this invention is as follows. Add a polyester polyol, dimethyl propionic acid (DMPA), N-methyl pyrrolidine (NMP) and dibutyltin dilaurate (DBTDL) to a 2-liter three-necked flask and dissolve DMPA at 90-120 ° C until Cool down to 60 ~ 80 ℃ after holding. Hexamethylene diisocyanate (HMDI) and acetone are mixed and added for 30 minutes, and then the reaction is maintained at 50 to 80 ° C. for at least 5 hours. When the NCO content is 0.05% or less, the reaction is terminated and cooled to 40 ° C. Dimethylethanolamine (DMEA) is added for 20 minutes, water is dispersed at 100-500 rpm for 1 hour with water, and then the temperature is raised to 60-80 ° C. to remove acetone.

The polyurethane dispersion resin according to the present invention has a hydroxyl value of 50 to 200 mgKOH / g, a nonvolatile content of 20 to 60% by weight, a glass transition temperature (Tg) of -40 to 40 ° C, and a weight average molecular weight of 1,000 It is preferably from 25,000. More preferably, the hydroxyl value of polyurethane dispersion resin is 70-170 mgKOH / g, Most preferably, it is 80-150 mgKOH / g. If the hydroxyl value is less than 50 mgKOH / g, the hardness decreases, and if it exceeds 200 mgKOH / g, the impact resistance and cold resistance chipping resistance are lowered. In addition, preferably the non-volatile component of the polyurethane dispersion resin is 30 to 55% by weight, most preferably 35 to 50% by weight. If the nonvolatile component is less than 20% by weight, sagging becomes weak during vertical coating, and if it exceeds 60% by weight, leveling is caused due to deterioration in flowability. In addition, the glass transition temperature of the polyurethane dispersion resin is preferably -30 to 30 ° C, and most preferably -20 to 10 ° C. If the glass transition temperature is lower than -40 ° C, the coating film hardness is lowered. If the glass transition temperature is higher than 40 ° C, the impact resistance and cold resistance chipping resistance are lowered. In addition, the weight average molecular weight of the polyurethane is preferably 2,000 to 20,000, most preferably 5,000 to 15,000. When the weight average molecular weight is less than 1,000, the weather resistance decreases and the coating film hardness decreases, and when the weight average molecular weight exceeds 25,000,

It causes workability problems such as leveling due to weakness of wetting and deterioration of flowability.

The synthesis method of the urethane modified polyester resin used for this invention is as follows. Polyester polyol, N-methylpyrrolidine (NMP), hexamethylene diisocyanate (HMDI) and acetone are added to a 2-liter three-necked flask and held at 50-80 ° C for at least 5 hours. When the NCO content is 0.05% or less, the reaction is terminated and cooled to 40 ° C. DMEA is added for 20 minutes, water is dispersed at 100-500 rpm for 1 hour, and then the temperature is raised to 60-80 ℃ to remove acetone.

In the case of the urethane-modified polyester according to the present invention, the number average molecular weight is 100 to 4,000, the solid content is 30 to 80%, and the hydroxyl value is 5 to 100 mgKOH / g. Preferably the number average molecular weight of a urethane modified polyester resin is 200-3,000, More preferably, it is 500-2,500. If the number average molecular weight is less than 100, the weather resistance decreases and the coating film hardness decreases. If the number average molecular weight exceeds 4,000, workability problems such as leveling due to poor wettability of the base material and lowering of flowability are caused. Further, preferably the nonvolatile component of the urethane-modified polyester is 35 to 70% by weight, more preferably 40 to 65% by weight. If the nonvolatile component is less than 30% by weight, sagging property becomes weak during vertical coating, and if it exceeds 80% by weight, the leveling is lowered due to the decrease in flowability. Moreover, Preferably the hydroxyl value of urethane-modified polyester resin is 10-90 mgKOH / g, More preferably, it is 30-80 mgKOH / g. If the hydroxyl value is less than 5 mgKOH / g, the hardness is lowered, and if the hydroxyl value is more than 100 mgKOH / g, impact resistance, bending resistance, and cold resistance chipping resistance are lowered.

The main resin content used in the present invention is 30 to 60% by weight, preferably 35 to 55% by weight, and more preferably 40 to 55% by weight, based on the solids of the total composition. Less than 30% by weight results in problems of impact resistance and cold resistance chipping due to reduced flexibility, and more than 60% by weight results in reduced hardness. In addition, the main resin contains 45 to 70% by weight of polyurethane dispersion resin and 15 to 35% by weight of urethane-modified polyester resin based on 100% by weight of the total of the main resin components and the following curing agent components. If the urethane dispersion resin is less than 45% by weight or the urethane-modified polyester resin is more than 35% by weight, the appearance quality decreases due to gloss loss after baking, and the polyurethane dispersion resin is more than 70% by weight or urethane. If the modified polyester resin is less than 15% by weight, the cold resistance chipping problem occurs.

Curing agents used in the present invention are hexamethylene diisocyanate trimers blocked with dimethyl pyrazole and hexamethylene diisocyanate trimers blocked with methylethylkeoxime. Hexamethylene diisocyanate trimmers provide flexibility and resilience to coatings, providing a cushion against chipping caused by gravel or stone pavement caused by high-speed rotation of wheels during driving. As a result, hexamethylene diisocyanate trimers increase the most important chipping resistance in automotive intermediate paints.

Hexamethylene diisocyanate trimers according to the invention are blocked with dimethyl pyrazole and methylethylkeoxime. Dimethyl pyrazole has a melting point of 107 ~ 109 ℃ and a boiling point of 218 ℃, so unlike methyl ethyl keoxime (melting point 140 ~ 160 ℃, boiling point 152 ℃), dimethyl pyrazole does not volatilize during the heat drying process and remains as an inert filler in the coating film. In order to prevent the occurrence of pinholes or popping on the surface of the coating film which may appear due to volatilization of the blocking agent, it is possible to reduce thio water defects that may occur in the automotive coating process by reducing oven contamination. In addition, it is excellent in yellowing resistance, which can solve the yellowing problem caused by underestimation that may occur in the road. On the other hand, methyl ethyl cheoxime is relatively high in melting point and low in boiling point, but when used alone, pinholes or paping may occur due to volatilization of blocking agent during baking, but when used in combination with dimethyl pyrazole, dimethyl pyrazole dissociation during baking Phase hardening is possible by primary curing by secondary curing and secondary curing by dissociation of methyl ethyl keoxime, enabling the formation of a denser coating network than a single curing system, thereby obtaining excellent coating properties such as impact resistance, flex resistance and durability. have.

Preferably the curing agent is based on 100% by weight total of the main resin components and the curing agent components, 3 to 20% by weight of hexamethylene diisocyanate trimer blocked with dimethyl pyrazole and hexamethylene diisocyanate blocked with methylethylkeoxime It contains 3 to 20% by weight of the trimmer. Pinholes or paping by methylethylkeoxime volatilized during the baking if the hexamethylene diisocyanate trimer blocked with dimethyl pyrazole is less than 3% by weight or the hexamethylene diisocyanate trimer blocked with methylethylkeoxime exceeds 20% by weight. Problems arise and impact and cold chipping problems arise when the hexamethylene diisocyanate trimer blocked with dimethyl pyrazole exceeds 20% by weight or the hexamethylene diisocyanate trimer blocked with methylethylkeoxime is less than 3% by weight. .

In addition, the content of the curing agent used in the present invention is 10 to 30% by weight, preferably 15 to 30% by weight, more preferably 20 to 30% by weight based on the solids of the total composition. When less than 10% by weight hardening failure occurs, more than 30% by weight to form a fragile coating film structure results in a decrease in impact resistance and cold resistance chipping resistance.

Moreover, in order to form the dense network structure of a coating film by resin and hardening | curing agent reaction of this invention, it is preferable that the equivalence ratio of the hydroxyl of polyurethane and the isocyanate of hardening agent is 1: 1.4-1: 0.5, and it is 1: 1.3-1: 0.6. It is more preferable. If the equivalent ratio of hydroxyl group to isocyanate is less than 1: 1.4, the amount of hardener will be excessive compared to the hydroxyl group, so that popping and pinholes will occur, and if the equivalent ratio of hydroxyl group to isocyanate exceeds 1: 0.5, the amount of hardener will be As a result, the curing is poor and the coating film hardness is low.

In addition, the present invention preferably comprises an auxiliary curing agent. The auxiliary curing agent used in the present invention can be freely selected from known auxiliary curing agents so long as they do not adversely affect the degree of curing and cold resistance chipping resistance of the composition. Specifically, the auxiliary curing agent used in the present invention is not limited thereto, but for example, a crosslinkable amino resin or a melamine resin containing an imino group may be used, and preferably, completely with partial methoxy or butoxy melamine. Melamine resins selected from the group consisting of full methoxy melamine are used. Melamines that may be used in the present invention include, for example, Cymel 325, Cymel370, Cymel323, 328, Resimine717 from Cytech, Luwipal 073 from BASF, and the like. Preferably, melamine which is cured at a lower temperature than blocked isocyanates is used as auxiliary curing agent to form a dense coating structure. The amount of melamine resin to be added is in the range of 1 to 20% by weight with respect to the solid content of the composition, more preferably 5 to 20% by weight. If the amount of melamine used is less than 1% by weight with respect to the solid content of the composition, a decrease in hardness of the coating film occurs, and when it exceeds 20% by weight, the bending resistance, impact resistance, and cold resistance chipping resistance of the coating film due to excessive hardness are caused.

The water-soluble coating composition according to the present invention may further include a tin catalyst and an acid catalyst for controlling the baking temperature at the time of curing, in addition to a leveling agent, an ultraviolet absorber, an alkalizing agent as a neutralizing agent, a buffer, a solvent mixture for forming an azeotrope, Pigments and thickeners and the like. Leveling agents that can be used in the present invention include polyether modified dimethylpolysiloxane, 2,4,7,9-tetramethyl-5-dekin-4,7-diol, or modified urea mixture, the amount of which is 0.05 to 10 parts by weight And more preferably 0.1 to 5 parts by weight. If the leveling agent is used at less than 0.05 parts by weight, the high surface tension of water causes wettability and appearance deterioration, and when it is more than 10%, it causes a problem of adhesion with the top coat.

Examples of the ultraviolet absorber include benzotriazole, benzophenone, hydroxy phenyl triazine, and light stabilizer. The amount of the ultraviolet absorber is 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight. If the amount of the ultraviolet absorber is less than 0.1 parts by weight, the weather resistance is lowered. If the amount of the ultraviolet absorber is greater than 10%, the curing density of the coating film is lowered and the chipping resistance and the impact resistance are lowered.

The neutralizing agent is dimethyl ethyl amine or 2-aminomethyl-1-propanol, and the amount used is 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight. If the neutralizing agent is used in less than 0.1 parts by weight, storage problems such as paint gelation may occur, and if it exceeds 10 parts by weight, workability problems such as sagging may occur due to a decrease in paint non-volatile content due to an increase in paint viscosity.

 Examples of the buffer include barium sulphate and titanium dioxide, and the use amount is 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight. If the content of the buffer is less than 0.1 parts by weight, the chipping resistance and the sandmark hiding power is lowered. When the content of the buffer exceeds 10 parts by weight, the appearance is reduced. Solvent mixtures include butyl cellosolve, hexyl cellosolve, pennitro methyl pyrrolidone, 2-ethyl hexanol, normal butyl alcohol or normal propyl alcohol, and the amount used is 1-20 parts by weight, more preferably 5-15 Parts by weight. When the solvent is used in less than 1 part by weight, the resin dissolving power in the paint is lowered, resulting in a deterioration in appearance such as clearness or gloss of the paint, and exceeding 20 parts by weight violates VOC regulation.

Pigments include TiO ₂ white pigments, carbon black FW285, Raven Ultra 5000, Raven 3500, Blanc Fixe Micro, Hostaperm Violet RL-S, Heliogen Green L8730, Manstral Blue FNX, Sicopal Yellow L1100, Paliotan Yellow L1945, Irgazin DPP BO Alternatively, Hostaperm Red E3B and the like may be used. In addition, both organic and inorganic pigments that may be used in automotive paints may be used. The content of the pigment used is 1 to 20 parts by weight, more preferably 5 to 18 parts by weight. If the use angle is less than 1 part by weight, the undercoat concealment failure occurs, and if it exceeds 20 parts by weight, the leveling of the paint and the feeling of clearness are reduced, resulting in a drop in impact resistance chipping resistance due to brittle coating properties.

Thickeners to have the acrylic copolymer emulsion of the DML VISCALEX HV30, VISCALEX like or LO30 and the A100 SOLTHIX ^ⓡ Laponite RD Clay type may be used. The content of the thickener used in the coating composition according to the present invention is 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight. If the amount is less than 0.5 parts by weight, the control of the paint rheology becomes difficult, resulting in sagging degradation.

The undercoat which can be used together with the water-soluble coating composition according to the present invention is an electrodeposition paint used in automobile coating, and the feature of the present invention includes expandability applicable to almost all electrodeposition paints using epoxy as the main resin. Basecoat paints include acrylic acid containing carboxyl groups, acrylic resins containing hydroxy groups, and melamine curing agents or polyester resins, and polyester resins and melamine curing agents, and useful automotive paints, polyurethane dispersions and acrylic urethane dispersants. It is a water-soluble automotive paint that uses perfusion, acrylic emulsion as a main resin of single or hybrid type, and selectively uses melamine as a curing agent, and a transparent coating for top coating is thermosetting containing acrylic acid containing epoxy or carboxyl groups and hydroxyl or siloxane groups. It is a one-component automotive top transparent paint made of acrylic resin composition and blocked isocyanate as a curing agent and a two-component automotive top transparent paint using isocyanate as a curing agent.

Hereinafter, the present invention will be described using examples, but the present invention is only for understanding of the present invention, and the scope of the present invention is not limited thereto in any sense.

Examples 1-6 and Comparative Examples 1-4

According to the composition described in Table 1 below, the water-soluble intermediate coating compositions of Examples 1 to 6 and Comparative Examples 1 to 4 were prepared.

1): Polyurethane Dispersion Resin: (Hydroxy group 50 ~ 200 mgKOH / g, Nonvolatile content 20 ~ 60 wt%, Glass transition temperature (Tg) -40 ~ 40 ℃, Weight average molecular weight 1,000 ~ 25,000)

2): urethane-modified polyester resin: (number average molecular weight 100-4000, solid content 30-80%, hydroxyl value 5-100 mgKOH / g)

3): Block diisocyanate (A): Hexamethylene diisocyanate trimer blocked with dimethyl pyrazole.

4): Block diisocyanate (B): Hexamethylene diisocyanate trimer blocked with methylethylkeoxime.

5): BLANC FIXE MICRO: Propylene Glycol: Butyl Carbitol: Dispersebyk 190: Disperse Ayd W-22: Tego Foamex 830: BYK011: BYK021 "AMP 95: Sulfinol 104BC: Butyl Cellosolve: Water = 10 ~ 80: 0 ~ 10: 0 ~ 20: 0 ~ 40: 0 ~ 5: 0 ~ 1: 0 ~ 1: 0 ~ 1: 0 ~ 0.1: 0 ~ 5: 0 ~ 5: 4 ~ 25 (weight ratio)

6): TiO ₂ : Propylene glycol: Butyl carbitol: Dispersebyk 190: Disperse Ayd W-22: Tego Foamex 830: BYK011: BYK021 "AMP 95: Sulfinol 104BC: Butyl cellosolve: Water = 10 ~ 80: 0 ~ 10 : 0 ~ 20: 0 ~ 40: 0 ~ 5: 0 ~ 1: 0 ~ 1: 0 ~ 1: 0 ~ 0.1: 0 ~ 5: 0 ~ 5: 4 ~ 25 (weight ratio)

7): Carbon Black (FW 285): Propylene Glycol: Butyl Carbitol: Dispersebyk 190: Disperse Ayd W-22: Tego Foamex 830: BYK011: BYK021 "AMP 95: Sulfinol 104BC: Butyl Cellosolve: Water = 10-80 : 0 ~ 10: 0 ~ 20: 0 ~ 40: 0 ~ 5: 0 ~ 1: 0 ~ 1: 0 ~ 1: 0 ~ 0.1: 0 ~ 5: 0 ~ 5: 4 ~ 25 (weight ratio)

Test Example 1: Paint property evaluation of water-soluble paint composition (middle paint alone coating)

Medium coating is discharged by 170 ~ 250cc / min using electrostatic bell sprayer, external voltage -60kv, shaping air 0.5 ~ 1kg / cm ² , Bell rpm 40,000 ~ 55,000, Head target distance (HTD) is 200 ~ 250mm Immediately after setting for 1-2 minutes for stabilization of the coating film, and pre-drying for 3-7 minutes in a hot air section of 60 ~ 80 ℃ to evaporate water. The air pressure at this time is 3-4 kg / cm ² . Then, after baking at 150 degreeC for 20 minutes, glossiness, adhesiveness, hardness, and smoothness were evaluated by the intermediate coating material by the following method. The results are shown in Table 2.

1. Gloss: The horizontal coating was measured with a gloss.

2. Adhesion: After cross cut (2 * 2mm, 100), the adhesion of the coating film was confirmed.

Good: no drop of coating is observed

Medium: 1 to 2 coatings

Poor: 3 or more coatings

3. Hardness: The hardness of 3B, 2B, B, HB, F, H, 2H, 3H was measured with a pencil that does not damage the coating film.

4. Smoothness: The smoothness of the coating film was measured by the Wave scan D.O.I. It was confirmed by the long wave value (good: less than 7, medium: 7 to 10, poor: more than 10).

Test Example 2: Paint property evaluation of the water-soluble coating composition (base coat and clear coat coating)

Pre-drying process for evaporating water in hot air section at 80 ℃ after setting process for stabilization of coating film for 2 minutes after application of ordinary water-soluble base coat (metallic or solid color) on the cured middle coating film Was done. Thereafter, a clear coat was applied, set for 5 to 10 minutes, and cured for about 25 minutes in an oven at 150 ° C. to form a dry coating film.

1. Appearance: The horizontal coating was measured by Wave Scan DOI, and the CF value was confirmed.

2. Water resistance: After dipping the coating film in hot water at 40 ° C. for 240 hours, discoloration, component noise, blister generation, and adhesion abnormalities were measured.

3. Acid resistance: 2 cc of sulfuric acid PH1, 2 and PH 1,2 solution of phosphoric acid were added dropwise onto the coating film, and then the coating film damage was judged after 30 minutes of holding at 50 ° C, 60 ° C and 70 ° C, respectively.

4. Cold resistance chipping: Chipping test was performed after standing at -40 ℃ X 3 hours.

5. Solvent resistance: According to the time course (10 minutes or more) at the time of xylene spot test, it investigated whether the nail hardness of the coating film by xylene was abnormal.

6. Scratch resistance: 20˚ after 10 round trips with CAR WASH SCRATCH TSET facility with reduced automatic car wash Gloss was measured and the gloss retention was checked before and after the test (good: above 60%, normal: 50-60%, poor: below 50%).

7. Solin resistance: Softening, swelling, and discoloration of the coating film were examined during the 1 hour deposition test of the automobile gasoline spot.

8. Impact resistance: Using the Dupont Tester, 50g weight was dropped at 20, 30, 40, 50 cm to measure the height at which the coating film was broken (good: 30 cm or more, normal: 20 cm ~ 30 cm, poor: 20 less than cm).

9. Hardness: The hardness was measured according to the method described in "3. Hardness" of Test Example 1.

10. Obbaking adhesiveness: The presence or absence of the coating film after the cross cut was determined according to the adhesion criteria of Test Example 1.

11. Brake oil resistance: There should be no softening, swelling or discoloration of the coating film during 1 hour deposition test of automobile brake oil spot.

Water-soluble intermediate coating composition for automobiles according to the present invention has the effect of providing a stable curing behavior and excellent cold resistance chipping resistance for the same temperature, time and improved mechanical properties by increasing the degree of curing of the coating film.

Claims (5)

Based on a total of 100% by weight of the following main resin components and the following curing agent components: Main resin containing 45 to 70 weight% of polyurethane dispersion resin which has a hydroxyl group, and 15 to 35 weight% of urethane modified polyester resin; And Curing agent containing 3 to 20% by weight of hexamethylene diisocyanate trimer blocked with dimethyl pyrazole and 3 to 20% by weight of hexamethylene diisocyanate trimer blocked with methylethylkeoxime; And a water-soluble coating composition having an equivalent ratio of hydroxyl group and isocyanate 1: 1.4 to 1: 0.5. The hydroxyl value of the polyurethane dispersion resin is 50 to 200 mgKOH / g, non-volatile content 20 to 60% by weight, glass transition temperature (Tg) is -40 ~ 40 ℃, weight average molecular weight The water-soluble coating composition which is 1,000-25,000. The water-soluble coating composition according to claim 1, wherein the urethane-modified polyester resin has a number average molecular weight of 100 to 4,000, a solid content of 30 to 80%, and a hydroxyl value of 5 to 100 mgKOH / g. The composition according to claim 1, wherein the content of main resin is 30 to 60% by weight based on the solids content of the composition. The composition according to claim 1, wherein the content of the curing agent is 10 to 30% by weight based on the solids content of the composition.