KR102567440B1 - Single-liquid type clear coat composition for low temperature curing - Google Patents

Abstract

The present invention includes a first acrylic resin, a second acrylic resin, a blocked isocyanate-based curing agent and a solvent, wherein the first acrylic resin has a hydroxyl value of 160 to 250 mgKOH/g and a weight average molecular weight of 15,000 to 60,000 g/mol And, the second acrylic resin has a hydroxyl value of 100 to 150 mgKOH/g and a weight average molecular weight of 5,000 to 10,000 g/mol, and relates to a low-temperature curable one-component clear coating composition.

Description

Low-temperature curable one-component clear coating composition {SINGLE-LIQUID TYPE CLEAR COAT COMPOSITION FOR LOW TEMPERATURE CURING}

The present invention relates to a one-component clear coating composition that can be cured at a low temperature of 130°C or less.

A plurality of coating processes such as electrodeposition painting, intermediate painting, base painting, and clear painting are performed on the body of an automobile to improve exterior characteristics and protect the surface from the external environment. Specifically, after coating and curing of electrodeposition paint and coating and curing of intermediate paint on a car body, it is common to continuously paint a base coat and a clear coat on the intermediate coating layer, followed by drying and curing. As described above, it is common for the base coat and the clear coat to be coated with the clear coat composition after application and drying of the base coat composition, and to cure the clear coat and the base coat together at 140 to 150 °C. However, in order to reduce the cost of the painting process, there is an increasing demand for a clear paint composition curable at a low temperature and shortening the process.

As an alternative to this, various clear coat compositions have been proposed that can be used under low-temperature baking conditions, particularly heat curing conditions of 140° C. or less. Specifically, Korean Patent Publication No. 2016-0120110 (Patent Document 1) includes an acrylic resin having a double bond oligomer and a hydroxyl group at the same time; a thermal radical initiator for crosslinking through polymerization of the double bond; A heat curing agent for crosslinking the hydroxyl group; A low-temperature curing one-component clear coat composition for automobiles comprising; and an additive is disclosed. Conventional low-temperature bakeable clear coat compositions such as Patent Document 1 have limitations in their application as vehicle body paints because the mechanical properties of the produced coating film are not sufficient.

Therefore, there is a need for research and development on a one-component clear paint composition that can be cured at a low temperature of 130° C. or less and has excellent mechanical properties of a coating film prepared therefrom, so that it is suitable for application to vehicle body painting.

Korean Patent Publication No. 2016-0120110 (published date: 2016.10.17.)

Accordingly, an object of the present invention is to provide a one-component clear coating composition capable of preparing a coating film having excellent mechanical properties while being curable at a low temperature of 130° C. or less.

The present invention includes a first acrylic resin, a second acrylic resin, a block isocyanate-based curing agent and a solvent,

The first acrylic resin has a hydroxyl value of 160 to 250 mgKOH / g, and a weight average molecular weight of 15,000 to 60,000 g / mol,

The second acrylic resin has a hydroxyl value of 100 to 150 mgKOH/g and a weight average molecular weight of 5,000 to 10,000 g/mol, providing a low-temperature curable one-component clear paint composition.

The low-temperature curable one-component clear paint composition according to the present invention can be cured at a low temperature of 130 ° C or lower, so it is economical to reduce the cost required for the painting process, and it is possible to paint the vehicle body and the material parts combined therewith as one body. It is possible to prevent a problem in which the color of the rear part and the car body are different. In addition, since both the vehicle body and parts can be painted in one painting process, troublesome process or cost loss can be reduced. In addition, the coating film prepared from the clear paint composition has excellent mechanical properties such as hardness, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, and can be usefully used for vehicle body painting.

Hereinafter, the present invention will be described in detail.

In the present invention, the "weight average molecular weight" of the resin may be measured by a method well known in the art, and may indicate, for example, a value measured by a gel permeation chromatograph (GPC) method.

In addition, in the present invention, the "glass transition temperature (Tg)" of the resin or the like is measured by methods well known in the art such as Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), Mechanicla Methods, and Volume Methods. and, for example, a value measured by a differential scanning calorimetry (DSC) method.

In the present invention, functional groups such as "acid value", "hydroxyl value" and "unreacted NCO group content" can be measured by methods well known in the art, for example, values measured by titration or the like can

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

The low-temperature curable one-component clear coating composition according to the present invention includes a first acrylic resin, a second acrylic resin, a block isocyanate-based curing agent and a solvent, and the first acrylic resin has a higher hydroxyl value and weight average molecular weight than the second acrylic resin. . As described above, when two kinds of acrylic resins having different hydroxyl values and weight average molecular weights are used, there is an effect of improving the external appearance and mechanical properties of the coating by controlling the drying rate and crosslinking density of the coating.

First acrylic resin

The first acrylic resin serves to improve the low-temperature curability of the composition.

The first acrylic resin may include a repeating unit derived from an ethylenically unsaturated monomer and a repeating unit derived from a hydroxyl group-containing (meth)acrylic monomer. That is, the first acrylic resin may be prepared from an ethylenically unsaturated monomer and a hydroxyl group-containing (meth)acrylic monomer. For example, the first acrylic resin may be prepared from an alkyl group-containing (meth)acrylic monomer and a hydroxyl group-containing (meth)acrylate monomer.

The ethylenically unsaturated monomer may be at least one selected from the group consisting of styrene and derivatives thereof, butadiene, C _1-12 alkyl (meth)acrylic acid and C _1-12 alkyl (meth)acrylic acid ester.

The hydroxyl group-containing (meth)acrylic monomer is, for example, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cardura acrylate, Cardura methacrylate, caprolactone acrylate, caprolactone methacrylate, 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, polypropylene-modified acrylate, polypropylene-modified methacrylate , 4-hydroxymethylcyclohexyl-methylacrylate and 4-hydroxymethylcyclo-methylmethacrylate.

The first acrylic resin may have a glass transition temperature (Tg) of 40 to 70 °C, 45 to 65 °C, or 50 to 60 °C. When the glass transition temperature of the first acrylic resin is within the above range, the initial hardness of the prepared coating film may be improved. In addition, when the glass transition temperature of the first acrylic resin is less than the above range, the drying rate and crosslinking density of the coating film are reduced, resulting in a decrease in hardness and water resistance. A problem of deterioration in appearance and chipping resistance may occur.

In addition, the first acrylic resin may have a hydroxyl value (OHv) of 160 to 250 mgKOH/g, 170 to 200 mgKOH/g, or 175 to 195 mgKOH/g. When the hydroxyl value of the first acrylic resin is within the above range, the curability of a composition including the same may be improved. In addition, when the hydroxyl group of the first acrylic resin is less than the above range, the crosslinking density decreases and mechanical properties deteriorate, and when it exceeds the above range, the coating film is brittle due to overcuring, resulting in poor elasticity, The water resistance and weather resistance of the product may be insufficient, and the viscosity may increase, resulting in a decrease in workability.

The first acrylic resin may have an acid value (Av) of 7 mgKOH/g or less, 0.5 to 7 mgKOH/g, or 1 to 5 mgKOH/g. When the acid value of the first acrylic resin is within the above range, the reactivity of a composition containing the first acrylic resin may be adjusted to improve the appearance characteristics of a coating film prepared therefrom. In addition, when the acid value of the first acrylic resin is less than the above range, the curing reaction rate is lowered and the appearance of the produced coating film deteriorates. A problem of deterioration of shelf life and shelf life may occur.

In addition, the first acrylic resin may have a weight average molecular weight of 15,000 to 60,000 g/mol, 15,000 to 55,000 g/mol, or 15,000 to 30,000 g/mol. When the weight average molecular weight of the first acrylic resin is within the above range, the appearance characteristics and physical properties of the prepared coating film are appropriate. In addition, when the weight average molecular weight of the first acrylic resin is less than the above range, the molecular weight is small, and thus acid resistance, water resistance, and cold chipping resistance of the prepared coating film may deteriorate, and when it exceeds the above range, the flow according to the molecular weight increase This may result in deterioration of the appearance and mechanical properties.

The first acrylic resin has a higher hydroxyl value than the second acrylic resin described below. For example, the first acrylic resin may have a hydroxyl value higher than that of the second acrylic resin by 30 to 60 mgKOH/g.

When a resin having a higher hydroxyl value than the second acrylic resin is used as the first acrylic resin, the crosslinking density increases to increase mechanical properties, and the difference in hydroxyl value between the first acrylic resin and the second acrylic resin is within the above range. If it is less than this, there is a problem that the crosslinking density is lowered and the appearance of the prepared coating film is deteriorated, and if it exceeds the above range, the coating film is brittle due to overcuring, resulting in a decrease in elasticity, and a problem in that water resistance and weather resistance of the composition are deteriorated. can happen

In addition, the weight average molecular weight of the first acrylic resin is higher than that of the second acrylic resin. For example, the weight average molecular weight of the first acrylic resin may be higher than that of the second acrylic resin by 10,000 to 30,000 g/mol.

When a resin having a weight average molecular weight higher than that of the second acrylic resin is used as the first acrylic resin, the crosslinking density is increased to increase mechanical properties, and the difference in weight average molecular weight between the first acrylic resin and the second acrylic resin is increased. If it is less than the above range, there is a problem in that the reactivity increases and the appearance and mechanical properties of the prepared coating film are deteriorated, and if it exceeds the above range, the reactivity and crosslinking density decrease, so that water resistance and chemical resistance may deteriorate.

In addition, the first acrylic resin may be included in an amount of 30 to 60% by weight, 35 to 55% by weight, or 40 to 50% by weight based on the total weight of the paint composition. When the content of the first acrylic resin is less than the above range, there is a problem in that the drying property is lowered and the gloss, water resistance and impact resistance of the coating film prepared from the coating composition containing it is lowered, and when it exceeds the above range, drying is fast As the coating progresses, the paint workability and flowability of the composition may be insufficient, resulting in a decrease in the coating film appearance and cold chipping resistance.

The first acrylic resin and the second acrylic resin may be included in the composition in a weight ratio of 2 to 7:1 or 3 to 6:1. When the weight ratio of the first acrylic resin and the second acrylic resin is less than the above range, that is, when a small amount of the first acrylic resin is included, a problem in which water resistance and chemical resistance are lowered due to a decrease in crosslinking density may occur, exceeding the above range , that is, when an excessive amount of the first acrylic resin is included, a problem may occur as long as the viscosity of the composition increases and the coating workability and flowability of the composition are insufficient, thereby deteriorating the appearance and mechanical properties of the coating film.

2nd acrylic resin

The second acrylic resin serves to control the flowability of the composition.

The second acrylic resin may include a repeating unit derived from an ethylenically unsaturated monomer and a repeating unit derived from a hydroxyl group-containing (meth)acrylic monomer. That is, the second acrylic resin may be prepared from an ethylenically unsaturated monomer and a hydroxyl group-containing (meth)acrylic monomer. For example, the second acrylic resin may be prepared from an alkyl group-containing (meth)acrylic monomer and a hydroxyl group-containing (meth)acrylate monomer.

As another example, it may be prepared by reacting an ethylenically unsaturated monomer, a hydroxyl group-containing (meth)acrylic monomer, and benzyl amine, and may have a chemical structure in which a needle-shaped diurea group exists.

The ethylenically unsaturated monomer may be at least one selected from the group consisting of styrene and derivatives thereof, butadiene, C _1-12 alkyl (meth)acrylic acid and C _1-12 alkyl (meth)acrylic acid ester.

The hydroxyl group-containing (meth)acrylic monomer is, for example, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cardura acrylate, Cardura methacrylate, caprolactone acrylate, caprolactone methacrylate, 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, polypropylene-modified acrylate, polypropylene-modified methacrylate , 4-hydroxymethylcyclohexyl-methylacrylate and 4-hydroxymethylcyclo-methylmethacrylate.

The second acrylic resin may have a hydroxyl value (OHv) of 100 to 150 mgKOH/g, 120 to 150 mgKOH/g, or 130 to 150 mgKOH/g. When the hydroxyl value of the second acrylic resin is within the above range, workability may be improved by adjusting the flowability of a composition including the same. In addition, when the hydroxyl group of the second acrylic resin is less than the above range, there is a problem in that the crosslinking density is lowered and the appearance characteristics and gloss of the prepared coating film are lowered, and when it exceeds the above range, the coating film is brittle due to overcuring Problems such as poor elasticity and poor water resistance and weather resistance of the composition may occur.

In addition, the second acrylic resin may have an acid value (Av) of 5 mgKOH/g or less, 0.5 to 4.5 mgKOH/g, or 1 to 4 mgKOH/g. When the acid value of the second acrylic resin is within the above range, workability may be improved by adjusting the flowability of the composition including the same. In addition, when the acid value of the second acrylic resin is less than the above range, there is a problem that the curing reaction rate is lowered and the appearance of the prepared coating film is lowered, and when it is above the above range, the viscosity of the composition increases, resulting in workability and flowability This degradation may cause problems.

The second acrylic resin may have a glass transition temperature (Tg) of 30 to 70 °C, 35 to 65 °C, or 40 to 60 °C. When the glass transition temperature of the second acrylic resin is within the above range, the appearance and hardness of the produced coating film may be improved. In addition, when the glass transition temperature of the second acrylic resin is less than the above range, the drying rate of the paint is delayed and the appearance may deteriorate, and when it exceeds the above range, the coating film becomes brittle, resulting in This degradation may cause problems.

In addition, the second acrylic resin may have a weight average molecular weight (Mw) of 5,000 to 10,000 g/mol, 6,000 to 9,500 g/mol, or 7,000 to 9,000 g/mol. When the weight average molecular weight of the second acrylic resin is within the above range, the appearance characteristics and physical properties of the prepared coating film are appropriate. In addition, when the weight average molecular weight of the second acrylic resin is less than the above range, there is a problem that the acid resistance and chemical resistance of the prepared coating film are reduced because the molecular weight is small, and when it exceeds the above range, the flowability and leveling property according to the increase in molecular weight are reduced. Deterioration may cause a problem of deterioration of appearance and mechanical properties.

The second acrylic resin may be included in an amount of 1 to 20% by weight, 3 to 15% by weight, or 5 to 13% by weight based on the total weight of the paint composition. When the content of the second acrylic resin is less than the above range, there is a problem in that the drying property is lowered and the gloss and water resistance of the coating film prepared from the coating composition containing the same is lowered. Paint workability, coating flowability, and appearance may be deteriorated.

Block isocyanate curing agent

The block isocyanate-based curing agent serves to form a coating film by curing the composition through a cross-linking reaction with components in the composition. At this time, the block isocyanate-based curing agent means that the reactivity is controlled by treating the terminal isocyanate group (NCO group) with a blocking agent.

The blocking agent may include, for example, at least one selected from the group consisting of an active methylene-based compound, a polyalkylene polyol compound, and a pyrazole-based compound. That is, the blocked isocyanate-based curing agent may be a terminal isocyanate group blocked by at least one blocking agent selected from the group consisting of an active methylene-based compound, a polyalkylene polyol compound, and a pyrazole-based compound.

The blocking agent blocks the isocyanate group at the end of the isocyanate curing agent to block the curing reaction, and then dissociates from the isocyanate group in a certain temperature range (eg, 100 to 130 ° C., which is the curing temperature of the paint composition), so that the curing agent plays its original role can make it do.

Due to the blocking agent, the coating composition of the present invention can exhibit stable storability and curing reactivity even in a one-component type, and thus has an effect of improving workability of the coating composition.

The block isocyanate-based curing agent has a viscosity at 25 ° C. of 5,000 to 10,000 cps, 6,000 to 9,000 cps, or 7,000 to 8,000 cps, and a solid content of 60 to 80% by weight or 65 to 75% by weight based on the total weight of the curing agent. can be When the viscosity at 25 ° C. of the block isocyanate-based curing agent is less than the above range, there is a problem that the flowability is lowered and the appearance and mechanical properties of the produced coating film are lowered, and when it exceeds the above range, the painting workability is lowered can happen

In addition, the block isocyanate-based curing agent may have an unreacted NCO group content of 5 to 10% by weight, 6 to 9% by weight, or 6.5 to 8.5% by weight based on the total weight of the curing agent. When the unreacted NCO group content of the block isocyanate-based curing agent is less than the above range, the crosslinking density is lowered, resulting in a decrease in the impact resistance, water resistance and cold chipping resistance of the coating film, and when it exceeds the above range, the curing speed is increased and the resin may cause a problem of deterioration of the appearance characteristics, gloss and mechanical properties of the coating film due to aggregation.

The block isocyanate-based curing agent may have a weight average molecular weight (Mw) of 1,500 to 4,000 g/mol, 2,000 to 3,500 g/mol, or 2,000 to 3,000 g/mol. When the weight average molecular weight of the block isocyanate-based curing agent is less than the above range, the molecular weight is small and the reactivity of the composition is insufficient, resulting in a decrease in appearance and mechanical properties. It is difficult to control and paint workability, and a problem of deterioration of mechanical properties may occur.

In addition, the block isocyanate-based curing agent may be included in an amount of 10 to 30% by weight, 10 to 25% by weight, or 13 to 23% by weight based on the total weight of the coating composition. When the content of the block isocyanate-based curing agent is less than the above range, the reactivity of the composition is insufficient and the crosslinking density of the prepared coating film decreases, resulting in a decrease in mechanical properties, and when it exceeds the above range, unreacted substances in the coating film after curing This may cause a problem in that the appearance, adhesion, and cold chipping resistance of the coating film are deteriorated.

solvent

The solvent serves to improve the workability of the composition by adjusting the viscosity of the paint composition.

The solvent may include at least one selected from the group consisting of a hydrocarbon-based solvent, an acetate-based solvent, an alcohol-based solvent, and a carboxylic acid-based solvent. For example, the solvent may be an aromatic hydrocarbon-based solvent such as toluene and xylene; 1-methoxy-2-propylacetate, methylacetate, ethylacetate, n-propylacetate, n-butylacetate, dimethyl glutarate, dimethyl succinate, dimethyl adipate, methyl glutarate, methyl succinate, methyl adipate acetate solvents such as paint; alcoholic solvents such as n-butanol, propanol and 1-methoxy-2-propanol; etc. can be mentioned. In addition, commercially available products of the aromatic hydrocarbon-based solvent include Kokosol #100 and Kokosol #150. Further, commercially available products of the acetate-based solvent include Solvay's Rhodiasolv RPD and the like.

The solvent may be included in an amount of 10 to 45% by weight, 13 to 30% by weight, or 15 to 20% by weight based on the total weight of the coating composition. When the solvent is included within the above content range, the coating composition including the solvent has an effect of having excellent workability during manufacturing and painting. When the content of the solvent is less than the above range, the viscosity of the composition is high and workability is insufficient, and when it exceeds the above range, a problem in that it takes a long time to remove the solvent during curing may occur.

additive

The clear paint composition may further include at least one additive selected from the group consisting of a UV absorber, a curing catalyst, a leveling agent, and an antifoaming agent.

The additive may be included in an amount of 1 to 10% by weight or 2 to 6% by weight based on the total weight of the paint composition.

The ultraviolet absorber serves to prevent discoloration of the paint composition by absorbing ultraviolet rays, and to prevent swelling, delamination, and loss of gloss of the paint film prepared from the paint composition. In addition, the UV absorber may be used without particular limitation, as long as it is conventional for use in paint compositions, and examples thereof include benzotriazoles such as hydroxyphenyl benzotriazole. In addition, commercially available products of the ultraviolet absorber include Tinuvin 384 and Tinuvin 5151 manufactured by BASF.

The curing catalyst prevents incomplete curing of the coating composition and improves mechanical properties of the coating film prepared therefrom. In addition, the curing catalyst may include dibutyltin dilaurate, triethylamine, diethylenetriamine, bismuth carboxylate, zirconium chelate, dinonylnaphthalene disulfonic acid, and the like.

The leveling agent serves to suppress the occurrence of orange peel by imparting smoothness to the coating composition and improving the appearance properties of the coating film prepared therefrom. In addition, the leveling agent may be used without particular limitation as long as it is a conventional one that can be used in the paint composition, and examples thereof include ether-modified polysiloxane.

The antifoaming agent serves to suppress the generation of bubbles generated during the preparation of the coating composition and suppress or eliminate phenomena such as pinholes or popping caused during the formation of a coating film. As long as the antifoaming agent is conventional, it can be used without particular limitation, as long as it can be used in the paint composition. For example, commercially available products include BYK-011, BYK-015, BYK-072 and BYKETOL-OK, and DF-21 from Air Products. , agitan 281 from Munzing and Foamster-324 from Sanofco.

One-component coating composition

The clear paint composition is a one-component paint composition containing two kinds of acrylic resins and a block isocyanate-based curing agent.

The clear paint composition may have a solid content (NV) of 40 to 65% by weight, 45 to 60% by weight, or 40 to 55% by weight. When the solid content of the clear paint composition is within the above range, painting workability of the composition may be improved.

The clear paint composition may be cured at 100 to 130 °C, 105 to 125 °C, or 110 to 120 °C. Since the clear paint composition can be cured within the above temperature range, it is economical to reduce the cost required for the painting process, and it is possible to paint the car body and the material parts coupled thereto integrally, so that the color of the parts and the car body after painting can be changed. Different problems can be avoided. In addition, since both the vehicle body and parts can be painted in one painting process, troublesome process or cost loss can be reduced.

The clear paint composition may have a viscosity of 40 to 70 seconds, 45 to 65 seconds, or 50 to 60 seconds based on Ford Cup No. 4. If the viscosity of the clear paint composition is less than the above range, problems such as dripping down on a vertical surface may occur, and if it exceeds the above range, the viscosity of the composition is high, deteriorating the appearance characteristics of the coating film prepared therefrom or causing a load on the painting machine. It may get caught and cause damage to the sprayer.

As described above, the clear paint composition according to the present invention can be cured at a low temperature of 130 ° C or less, so it is economical to reduce the cost required for the painting process, and it is possible to paint the vehicle body and the material parts coupled thereto integrally. It is possible to prevent a problem in which the color of the rear part and the car body are different. In addition, since both the vehicle body and parts can be painted in one painting process, troublesome process or cost loss can be reduced. Furthermore, the coating film prepared from the clear paint composition has excellent mechanical properties such as appearance, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, so that it can be usefully used for vehicle body painting.

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 13 and Comparative Examples 1 to 10. Preparation of clear paint composition

A 55-second clear paint composition was prepared with Ford Cup No. 4 by stirring and mixing each component in the composition as shown in Tables 1 to 3 below.

Composition (% by weight) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 First Acrylic Resin-1 46 37 52 26 63 46 46 First acrylic resin-2 - - - - - - - First acrylic resin-3 - - - - - - - First acrylic resin-4 - - - - - - - First Acrylic Resin-5 - - - - - - - 2nd acrylic resin-1 9.4 9.4 9.4 9.4 9.4 4 14 2nd acrylic resin-2 - - - - - - - The second acrylic resin-3 - - - - - - - Second Acrylic Resin-4 - - - - - - - Second Acrylic Resin-5 - - - - - - - Block isocyanate curing agent 20 20 20 20 20 20 20 UV absorber One One One One One One One curing catalyst 1.2 1.2 1.2 1.2 1.2 1.2 1.2 leveling agent One One One One One One One antifoam One One One One One One One primary solvent 3.6 3.6 3.6 3.6 0.9 3.6 2.6 second solvent 3 3 3 4 0.7 3 2 tertiary solvent 3.8 3.8 3.8 3.8 0.6 3.8 2.8 4th solvent 10 19 4 29 1.2 15.4 8.4 total 100 100 100 100 100 100 100

Composition (% by weight) Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 First Acrylic Resin-1 46 46 46 46 46 46 First acrylic resin-2 - - - - - - First acrylic resin-3 - - - - - - First acrylic resin-4 - - - - - - First Acrylic Resin-5 - - - - - - 2nd acrylic resin-1 0.5 22 9.4 9.4 9.4 9.4 2nd acrylic resin-2 - - - - - - The second acrylic resin-3 - - - - - - Second Acrylic Resin-4 - - - - - - Second Acrylic Resin-5 - - - - - - Block isocyanate curing agent 20 20 12 25 7 32 UV absorber One One One One One One curing catalyst 1.2 1.2 1.2 1.2 1.2 1.2 leveling agent One One One One One One antifoam One One One One One One primary solvent 5.6 1.6 3.6 3.6 5.6 1.6 second solvent 4 One 3 3 5 1.1 tertiary solvent 3.8 1.4 3.8 3.8 5.8 1.7 4th solvent 15.9 3.8 18 5 17 4 total 100 100 100 100 100 100

Composition (% by weight) Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 First acrylic resin-1 55.4 - - - - - 46 46 46 46 First acrylic resin-2 - - 46 - - - - - - - First acrylic resin-3 - - - 46 - - - - - - First acrylic resin-4 - - - - 46 - - - - - First Acrylic Resin-5 - - - - - 46 - - - - 2nd acrylic resin-1 - 55.4 9.4 9.4 9.4 9.4 - - - - 2nd acrylic resin-2 - - - - - - 9.4 - - - The second acrylic resin-3 - - - - - - - 9.4 - - Second Acrylic Resin-4 - - - - - - - - 9.4 - Second Acrylic Resin-5 - - - - - - - - - 9.4 Block isocyanate curing agent 20 20 20 20 20 20 20 20 20 20 UV absorber One One One One One One One One One One curing catalyst 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 leveling agent One One One One One One One One One One antifoam One One One One One One One One One One primary solvent 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 second solvent 3 3 3 3 3 3 3 3 3 3 tertiary solvent 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 4th solvent 10 10 10 10 10 10 10 10 10 10 total 100 100 100 100 100 100 100 100 100 100

Hereinafter, the manufacturer, product name, and physical properties of each component used in Comparative Examples and Examples are as follows.

composition note First Acrylic Resin-1 Av: 2mgKOH/g, OHv: 185mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol First acrylic resin-2 Av: 2mgKOH/g, OHv: 155mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol First acrylic resin-3 Av: 2mgKOH/g, OHv: 257mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol First acrylic resin-4 Av: 2mgKOH/g, OHv: 185mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 4,500 cps, Mw: 13,800 g/mol First Acrylic Resin-5 Av: 2mgKOH/g, OHv: 185mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 7,500 cps, Mw: 61,000 g/mol 2nd acrylic resin-1 Av: 3mgKOH/g, OHv: 140mgKOH/g, solid content: 54% by weight,
Viscosity at 25°C: 4,100cps, Mw: 8,700g/mol, Tg: 50°C 2nd acrylic resin-2 Av: 3mgKOH/g, OHv: 89mgKOH/g, solid content: 54% by weight,
Viscosity at 25°C: 4,100cps, Mw: 8,700g/mol, Tg: 50°C The second acrylic resin-3 Av: 3mgKOH/g, OHv: 157mgKOH/g, solid content: 54% by weight,
Viscosity at 25°C: 4,100cps, Mw: 8,700g/mol, Tg: 50°C Second Acrylic Resin-4 Av: 3mgKOH/g, OHv: 140mgKOH/g, solid content: 54% by weight,
Viscosity at 25°C: 2,900cps, Mw: 4,600g/mol, Tg: 50°C Second Acrylic Resin-5 Av: 3mgKOH/g, OHv: 140mgKOH/g, solid content: 54% by weight,
Viscosity at 25°C: 4,900cps, Mw: 11,000g/mol, Tg: 50°C Block isocyanate curing agent A curing agent in which terminal isocyanate groups are blocked with polyethylene glycol
(Solid content: 70% by weight, viscosity at 25 ° C.: 7,600cps,
Unreacted NCO content: 7.3% by weight, Mw: 2,735 g/mol) UV absorber Manufacturer: BASF, product name: TINUVIN 5151 curing catalyst Dinonylnaphthalene Disulfonic Acid leveling agent Manufacturer: BYK, product name: BYK-325 antifoam Manufacturer: BYK, product name: BYKETOL-OK primary solvent n-Butyl Acetate second solvent n-butanol (N-butanol) tertiary solvent Manufacturer: Solvay, product name: RHODIASOLV RPD 4th solvent Kocosol #100

Test Example: Measurement of physical properties of a coating film prepared from a coating composition

After applying top coat (manufacturer: KCC, product name: WT3900) to a dry film thickness of 15 μm, hot air was blown at 80 ° C. for 3 minutes to evaporate the water remaining in the paint to form a top coat. Thereafter, the clear coating composition of Examples and Comparative Examples was coated on the top coat film, and cured at 120° C. for 25 minutes to form a clear coating film having a thickness of 40 μm.

The physical properties of the specimens coated as described above were measured in the following manner, and the results are shown in Table 5.

Specifically, the clear paint composition uses a hand gun spray (nozzle diameter: 1.5 mm, air pressure: maintained constant at around 4.5 kgf / cm 2), and maintains a constant distance between the nozzle inlet and the specimen at 30 cm, horizontally at 40 cm. It was painted while moving at a speed of ~50 cm/sec.

(1) Painting workability

When the paint was discharged with a hand gun spray, the clear paint compositions of Examples and Comparative Examples were coated twice reciprocally to compare the degree of atomization, smoothness, and lightness of the paint film during painting.

Specifically, when the spreadability in the surface is good and the spreadability is excellent visually, it is excellent (◎), when the spreadability is good, but the spreadability is poor, it is good (○), and when the spreadability and spreadability are poor visually When there were less than 3 points of paint foreign matter, it was evaluated as normal (△), and when there were more than 3 points of paint foreign matter and cratering occurred, it was evaluated as defective (×).

(2) Appearance

Gloss (LU), sharpness (SH), and orange peel (OP) were measured using Wave Scan DOI (BYK Gardner), an automotive exterior measuring instrument, for the painted specimens, and comprehensive exterior evaluation values ( CF) was calculated by Equation 1 below.

[Equation 1]

CF = LU x 0.15 + SH x 0.35 + OP x 0.5

At this time, CF was measured and calculated horizontally and vertically.

When the calculated CF was 65 or more, it was evaluated as excellent (◎), 60 or more and less than 65 as good (○), 55 or more and less than 60 as normal (Δ), and less than 55 as poor (×).

(3) gloss

The 20° gloss was measured using a gloss meter for the coated specimens. If the 20° gloss was 90 or more, it was excellent (◎), if it was 85 or more and less than 90, it was good (○), and if it was 80 or more and less than 85, it was normal ( △), if less than 80, it was evaluated as defective (×).

(4) Overcoating adhesion

After removing both the top coat film and the clear coat film and coating the top coat and clear paint composition in the same manner as described above, repaint adhesion was evaluated by a checkerboard method.

Specifically, in the check mark method, after making 100 squares of 2 mm in width and 2 mm in length with a knife on the surface of the clear coating film, the squares were removed using a tape to measure adhesion. At this time, the measured adhesion is excellent (◎) when 100 squares are fully attached (◎), good (○) when the remaining squares are 70% or more and less than 100%, normal (△), 50% when 50% or more and less than 70% If less than, it was evaluated as defective (×).

(5) Impact resistance

The impact resistance of the coated specimens was evaluated according to ASTM D2794. At this time, a DuPont impact tester was used, and the appearance of the coating film was observed when a 500g weight was dropped on the specimen while changing the drop height of the weight from 30cm to 50cm. As a result of the observation, when no cracks or peeling occurred in the top coat film at the height of 50 cm of weight fall, excellent (◎), 40 cm or more and less than 50 cm, good (○), 30 cm or more and less than 40 cm, normal (△), 30 cm If less than, it was evaluated as defective (×).

(6) water resistance

The coated specimen was immersed in a constant temperature water bath at 40 ° C for 240 hours and left at room temperature for 1 hour, and then adhesion was evaluated by the same method as the check mark method in item (4), and the same evaluation criteria were applied.

(7) Flowability

A specimen with a top coat film was vertically hung on a steel plate with a hole of 5 mm in diameter, and the clear paint compositions of Examples and Comparative Examples were coated in the same manner as described above, dried and cured, and then the surface of the prepared film was observed to coat the composition. Flowability was evaluated.

Specifically, the formation of paint on the lower end of the hole was observed, and the thickness (μm) of the coating film at the starting point where flow was observed was recorded as the flow limit film thickness. At this time, it was determined that the coating flowability was insufficient as the value of the measured flow limit film thickness was lower. At this time, when the flow limit film thickness is 40㎛ or more, it is evaluated as excellent (◎), 35㎛ or more and less than 40㎛ as good (○), 30㎛ or more and less than 35㎛ as normal (△), and less than 30㎛ as poor (Х) did

(8) Cold chipping resistance

A specimen having a size of 150 mmX70 mm was left at -20 ± 3 ° C for 3 hours, and then the chipping resistance was measured using a chipping tester (manufacturer: Grebrometer, model name: SAE J 400).

Specifically, 50 g of a chipping stone (diameter: 4 mm) was sprayed at an angle of 45° at a pressure of 4 bar on the clear coating film. Thereafter, the specimen was taken out and foreign substances such as peeled off coating film remaining on the coating film were removed with cellophane adhesive tape. At this time, if the damaged area of the final coating is less than 1 mm, it is excellent (◎), if it is more than 1 mm and less than 2 mm, it is good (○), if it is more than 2 mm and less than 3 mm, it is normal (△), if it is more than 3 mm, it is evaluated as bad (×).

evaluation item stamp
Workability Exterior Polish Overcoating adhesion impact resistance water resistance Paint flow Cold chipping resistance Example 1 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Example 2 ◎ ◎ ○ ◎ ○ ○ ◎ ◎ Example 3 ○ ○ ○ ◎ ◎ ◎ ○ ○ Example 4 ◎ ○ △ ◎ △ △ ◎ ◎ Example 5 △ △ ○ ◎ ◎ ◎ △ △ Example 6 ◎ ◎ ○ ◎ ◎ ○ ○ ◎ Example 7 ○ ○ ◎ ◎ ◎ ◎ ○ ◎ Example 8 ◎ ○ △ ◎ ◎ △ △ ◎ Example 9 △ △ ◎ ◎ ◎ ◎ △ ○ Example 10 ◎ ◎ ◎ ◎ ○ ○ ◎ ○ Example 11 ◎ ○ ◎ ○ ◎ ◎ ◎ ○ Example 12 ◎ ○ ◎ ◎ △ △ ◎ △ Example 13 ◎ △ ◎ △ ◎ ◎ ◎ △ Comparative Example 1 △ ○ X ◎ ○ X ○ ○ Comparative Example 2 ◎ ○ X ○ X X ○ X Comparative Example 3 ◎ ○ ○ ○ X X ○ ○ Comparative Example 4 X ○ ○ ○ X X ○ X Comparative Example 5 ○ ○ ○ X ○ X ○ X Comparative Example 6 ○ X ○ ○ ○ X X X Comparative Example 7 ○ X X ○ ○ ○ X ○ Comparative Example 8 X X ○ ○ X X ○ X Comparative Example 9 ○ X ○ ○ X X ○ X Comparative Example 10 X X ○ ○ ○ X X X

As shown in Table 5, the clear paint composition of the examples has excellent painting workability, and the coating film prepared from the composition has excellent appearance, gloss, repainting adhesion, impact resistance, water resistance, application flowability and cold chipping resistance. did.

On the other hand, Comparative Examples 1 and 2 containing only one type of acrylic resin lacked gloss and water resistance of the prepared coating films. In particular, Comparative Example 1 containing only the first acrylic resin was also poor in painting workability. In addition, Comparative Example 2 containing only the second acrylic resin had poor impact resistance and cold chipping resistance.

In addition, Comparative Example 3 containing the first acrylic resin-2 having a low hydroxyl value and Comparative Example 4 containing the first acrylic resin-3 having a high hydroxyl value were poor in impact resistance and water resistance. Further, in Comparative Example 4, the painting workability of the composition was also poor, and the cold chipping resistance of the produced coating film was also poor.

Comparative Example 5 including the first acrylic resin-4 having a low weight average molecular weight and Comparative Example 6 including the first acrylic resin-5 having a high weight average molecular weight lacked water resistance and cold chipping resistance. In addition, Comparative Example 5 also lacked repaint adhesion. Further, in Comparative Example 6, the appearance of the coating film and the coating flowability were also poor.

Further, Comparative Example 7 including the second acrylic resin-2 having a low hydroxyl value and Comparative Example 8 including the second acrylic resin-3 having a high hydroxyl value were poor in appearance characteristics of the coating film. Furthermore, Comparative Example 7 lacked gloss and paint flowability, and Comparative Example 8 lacked painting workability of the composition and also lacked impact resistance, water resistance, and cold chipping resistance of the produced coating film.

Furthermore, Comparative Example 9 including the second acrylic resin-4 having a low weight average molecular weight and Comparative Example 10 including the second acrylic resin-5 having a high weight average molecular weight were poor in appearance, water resistance and cold chipping resistance. Further, Comparative Example 9 was also poor in impact resistance, and Comparative Example 10 was also poor in painting workability and flowability.

Claims (5)

Including a first acrylic resin, a second acrylic resin, a block isocyanate-based curing agent and a solvent,
The first acrylic resin has a hydroxyl value of 175 to 195 mgKOH / g, and a weight average molecular weight of 15,000 to 55,000 g / mol,
The second acrylic resin has a hydroxyl value of 130 to 150 mgKOH / g, and a weight average molecular weight of 7,000 to 9,000 g / mol,
The first acrylic resin has a hydroxyl value higher than that of the second acrylic resin by 30 to 60 mgKOH/g,
The first acrylic resin has a weight average molecular weight higher than that of the second acrylic resin by 10,000 to 30,000 g/mol,
Based on the total weight of the coating composition, 40 to 50% by weight of the first acrylic resin, 5 to 13% by weight of the second acrylic resin, 13 to 23% by weight of a block isocyanate-based curing agent and 15 to 20% by weight of a solvent, low temperature A curable one-component clear coating composition. The method of claim 1,
The first acrylic resin has a glass transition temperature of 40 to 70 ° C,
The second acrylic resin has a glass transition temperature of 30 to 70 ° C., a low-temperature curable one-component clear paint composition. The method of claim 1,
The block isocyanate-based curing agent has a viscosity at 25 ° C. of 5,000 to 10,000 cps, an unreacted NCO group content of 5 to 10% by weight, and a weight average molecular weight of 1,500 to 4,000 g / mol, a low-temperature curable one-component clear coating composition. . The method of claim 1,
The blocked isocyanate-based curing agent is a low-temperature curable one-component clear coating composition in which an isocyanate group at the terminal is blocked with at least one blocking agent selected from the group consisting of an active methylene-based compound, a polyalkylene polyol compound, and a pyrazole-based compound. delete