KR20220135423A - Single-liquid type clear coat composition for low temperature curing - Google Patents

Abstract

The present invention relates to a one-component type clear coat composition for low temperature curing, which contains a first acrylic resin, a second acrylic resin, a block 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. An object of the present invention is to provide the one-component type clear coating composition capable of preparing a coating film having excellent mechanical properties while being curable at a low temperature of 130℃ or less.

Description

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

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

A vehicle body is subjected to multiple coating processes, such as electrodeposition painting, intermediate painting, base painting, and clear painting, in order to improve the appearance characteristics and protect the surface from the external environment. Specifically, it is common to apply and cure an electrodeposition paint to a vehicle body, apply and cure an intermediate paint, and then continuously apply a base coat and a clear coat on the intermediate coat layer, followed by drying and curing. As described above, for the base coat and the clear coat, the clear coat composition is applied after the base coat composition is applied and dried, and the clear coat and the base coat are cured together at 140 to 150° C. However, in order to reduce the cost of the coating process, the demand for a clear coating composition that can be cured at a shorter temperature and at a low temperature has recently increased.

As an alternative to this, various clear coat compositions have been proposed, which can be used under low-temperature baking conditions, particularly under heat curing conditions of 140° C. or less. Specifically, Korean Patent Application Laid-Open No. 2016-01201110 (Patent Document 1) discloses an acrylic resin having a double bond oligomer and a hydroxyl group at the same time; a thermal radical initiator for crosslinking through the polymerization reaction of the double bond; a thermosetting agent for crosslinking the hydroxyl group; and additives; a low-temperature curing one-component clear coat composition for automobiles is disclosed. Conventional clear coat compositions that can be baked at low temperatures such as Patent Document 1 do not have sufficient mechanical properties of the manufactured coating film, so there is a limit to their application as a paint for car body.

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

Korean Patent Application Laid-Open No. 2016-01201110 (Published date: 2016.10.17.)

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

The present invention comprises 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, and provides 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 less, thereby reducing the cost required during the painting process, and thus is economical, and can paint the car body and the material parts connected thereto in one piece. It is possible to avoid the problem that the color of the rear parts and the body are different. In addition, since both the car body and the parts can be painted in one painting process, it is possible to reduce the hassle or cost of the process. 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 thus can be usefully used for car body painting.

Hereinafter, the present invention will be described in detail.

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

In addition, in the present invention, the "glass transition temperature (Tg)" of the resin or the like is measured by methods such as DSC (Differential Scanning Calorimetry), DTA (Differential Thermal Analysis), Mechanicla Methods, Volume Methods, which are methods well known in the art. It can be, for example, it can represent the value measured by the method of DSC (Differential Scanning Calorimetry).

In the present invention, functional groups such as "acid value", "hydroxyl value" and "unreacted NCO group content" can be measured by a method well known in the art, for example, a value measured by titration, etc. can

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

The low-temperature curable one-component clear paint 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 greater hydroxyl value and a weight average molecular weight than the second acrylic resin. . As described above, when two types of acrylic resins having different hydroxyl values and weight average molecular weights are used, there is an effect of improving the appearance characteristics and mechanical properties of the coating film by controlling the drying rate and crosslinking density of the coating film.

first acrylic resin

The first acrylic resin serves to improve 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)acryl and C _1-12 alkyl (meth)acrylic acid esters.

The hydroxyl group-containing (meth)acrylic monomer is, for example, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cadura acrylate, Cadura methacrylate, caprolactone acrylate, caprolactone methacrylate, 2,3-dihydroxypropyl acryl, 2,3-dihydroxypropyl methacrylate, polypropylene modified acrylate, polypropylene modified methacrylate , 4-hydroxymethylcyclohexyl-methyl acrylate and 4-hydroxymethylcyclo-methyl methacrylate may be at least one selected from the group consisting of.

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, it is possible to improve the initial hardness of the prepared coating film. In addition, when the glass transition temperature of the first acrylic resin is less than the above range, there is a problem in that the drying rate and crosslinking density of the coating film are lowered, so that hardness and water resistance are lowered. The appearance and chipping resistance may be deteriorated.

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 the 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 is lowered and mechanical properties are lowered. 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 appearance characteristics of the coating film prepared therefrom may be improved by controlling the reactivity of the composition including the same. 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 prepared coating film is deteriorated. There may be a problem of deterioration in performance and storage at room temperature.

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, if the weight average molecular weight of the first acrylic resin is less than the above range, the molecular weight is small, and the acid resistance, water resistance and cold chipping resistance of the prepared coating film may be deteriorated. This may cause a problem in that appearance and mechanical properties are deteriorated due to deterioration of properties.

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

When a resin having a higher hydroxyl value than that of the second acrylic resin is used as the first acrylic resin, mechanical properties are increased by increasing the crosslinking density, and the difference in hydroxyl values between the first acrylic resin and the second acrylic resin is within the above range If it is less than, there is a problem that the crosslinking density is lowered and the appearance of the prepared coating film is lowered. can occur

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

When a resin having a higher weight average molecular weight than 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 reduced. When it is less than the above range, there is a problem in that the appearance and mechanical properties of the prepared coating film are reduced due to increased reactivity, and when it exceeds the above range, the reactivity and crosslinking density are lowered, and water resistance and chemical resistance are lowered.

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 coating 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 including the same are lowered. As it progresses, the coating workability and coating flowability of the composition may be insufficient, which may cause a problem in that the appearance of the coating film and the cold chipping resistance are deteriorated.

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 by weight. When the weight ratio of the first acrylic resin to the second acrylic resin is less than the above range, that is, when a small amount of the first acrylic resin is included, the crosslinking density may be lowered to cause a problem in that water resistance and chemical resistance are lowered, exceeding the above range In the case of , that is, when an excessive amount of the first acrylic resin is included, the viscosity of the composition increases and the coating workability and paint flowability of the composition are insufficient, so that a problem may occur as long as the appearance and mechanical properties of the coating film are deteriorated.

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)acryl and C _1-12 alkyl (meth)acrylic acid esters.

The hydroxyl group-containing (meth)acrylic monomer is, for example, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cadura acrylate, Cadura methacrylate, caprolactone acrylate, caprolactone methacrylate, 2,3-dihydroxypropyl acryl, 2,3-dihydroxypropyl methacrylate, polypropylene modified acrylate, polypropylene modified methacrylate , 4-hydroxymethylcyclohexyl-methyl acrylate and 4-hydroxymethylcyclo-methyl methacrylate may be at least one selected from the group consisting of.

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 controlling the flowability of the 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 that the crosslinking density is lowered and the appearance characteristics and gloss of the prepared coating film are lowered. There may be problems in that elasticity is lowered, and water resistance and weather resistance of the composition are lowered.

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 controlling 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. This lowering problem may occur.

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 prepared 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 there may be a problem that the appearance is deteriorated. This lowering problem may occur.

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 in that the acid resistance and chemical resistance of the coating film prepared due to the small molecular weight are lowered. This may cause a problem in that appearance and mechanical properties are deteriorated.

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 coating composition. When the content of the second acrylic resin is less than the above range, there is a problem in that the dryness is lowered and the gloss and water resistance of the coating film prepared from the coating composition containing the same is lowered. There may be problems in which the paint workability, paint flowability and appearance of the paint are deteriorated.

Block isocyanate curing agent

The block isocyanate-based curing agent serves to form a coating film by curing the composition by cross-linking with the components in the composition. In this case, the block isocyanate-based curing agent means that the isocyanate group (NCO group) at the terminal is treated with a blocking agent to control reactivity.

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 one in which the terminal isocyanate group is blocked with one or more blocking agents 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 (for example, 100 to 130 ° C, the curing temperature of the coating composition), so that the curing agent plays its original role can make it work.

Due to the blocking agent, the coating composition of the present invention can exhibit stable storage and curing reactivity even in a one-component type, thereby 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 has 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 in that flowability is lowered and the appearance and mechanical properties of the prepared coating film are lowered, and when it exceeds the above range, there is a problem that the coating workability is lowered can occur

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 content of unreacted NCO groups in the block isocyanate-based curing agent is less than the above range, there is a problem in that the crosslinking density is lowered to lower the impact resistance, water resistance and cold resistance of the coating film, and when it exceeds the above range, the curing rate is increased and the resin is agglomerated, which may cause a problem in that the appearance characteristics, gloss, and mechanical properties of the coating film are deteriorated.

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, and there is a problem that the appearance and mechanical properties are lowered. Difficulty in control and painting workability may cause a problem in which mechanical properties are deteriorated.

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 crosslinking density of the prepared coating film is lowered due to insufficient reactivity of the composition, resulting in a problem in that mechanical properties are lowered. This may cause a problem in that the appearance, adhesion and cold resistance of the coating film are deteriorated.

solvent

The solvent serves to improve the workability of the composition by adjusting the viscosity of the coating 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 is an aromatic hydrocarbon solvent such as toluene and xylene; 1-Methoxy-2-propyl acetate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, dimethyl glutarate, dimethyl succinate, dimethyl adipate, methyl glutarate, methyl succinate, methyl adipate acetate-based solvents such as paint; alcohol solvents such as n-butanol, propanol and 1-methoxy-2-propanol; and the like. Moreover, as a commercial item of the said aromatic hydrocarbon type solvent, Cocosol #100, Cocosol #150, etc. are mentioned. Furthermore, as a commercial item of the said acetate-type solvent, Rhodiasolv RPD by Solvay, etc. are mentioned.

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 coating. When the content of the solvent is less than the above range, the viscosity of the composition is high and workability is insufficient.

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 coating composition.

The UV absorber absorbs UV rays to prevent discoloration of the coating composition, and serves to prevent swelling, delamination, and loss of gloss of a coating film prepared from the coating composition. In addition, the ultraviolet absorber may be used without any particular limitation as long as it is a conventional material that can be used in the coating composition, and for example, a benzotriazole type such as hydroxyphenyl benzotriazole may be mentioned. Moreover, as a commercial item of the said ultraviolet absorber, BASF's Tinuvin 384 and Tinuvin 5151 are mentioned.

The curing catalyst serves to prevent incomplete curing of the coating composition and improve mechanical properties of the coating film prepared therefrom. In addition, examples of the curing catalyst 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 characteristics of the coating film prepared therefrom. In addition, the leveling agent may be used without particular limitation as long as it is a conventional material that can be used in the coating composition, for example, ether-modified polysiloxane may be mentioned.

The antifoaming agent serves to suppress the generation of bubbles generated during the preparation of the coating composition and to suppress or remove phenomena such as pinholes or popping caused during the formation of the coating film. The antifoaming agent may be used without particular limitation as long as it is a conventional material that can be used in the paint composition, for example, BYK-011, BYK-015, BYK-072 and BYKETOL-OK by BYK, DF-21 by Air Product as commercially available products. , agitan 281 manufactured by Munzing and Foamster-324 manufactured by Sannovko.

One-component paint composition

The clear coating composition is a one-component coating composition comprising two types 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 coating composition is within the above range, the coating workability of the composition may be improved.

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

The clear paint composition may have a viscosity of 40 to 70 seconds, 45 to 65 seconds, or 50 to 60 seconds based on Pod Cup No. 4. If the viscosity of the clear paint composition is less than the above range, problems such as vertical flow down may occur. It may catch and cause a failure of 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, thereby reducing the cost required for the painting process, and thus is economical, and the vehicle body and the material parts coupled thereto can be integrally painted. It is possible to avoid the problem that the color of the rear parts and the body are different. In addition, since both the car body and the parts can be painted in a single painting process, it is possible to reduce the hassle and cost of the process. Furthermore, the coating film prepared from the clear paint composition has excellent mechanical properties such as appearance characteristics, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, and thus can be usefully used for car 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

Each component was stirred and mixed in the composition as shown in Tables 1 to 3 to prepare a clear paint composition with a duration of 55 seconds using Podcup No. 4.

Composition (wt%) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 1st acrylic resin-1 46 37 52 26 63 46 46 No. 1 Acrylic Resin-2 - - - - - - - No. 1 Acrylic Resin-3 - - - - - - - No. 1 Acrylic Resin-4 - - - - - - - No. 1 Acrylic Resin-5 - - - - - - - 2nd acrylic resin-1 9.4 9.4 9.4 9.4 9.4 4 14 2nd acrylic resin-2 - - - - - - - 2nd acrylic resin-3 - - - - - - - 2nd acrylic resin-4 - - - - - - - 2nd 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 first 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 third 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 (wt%) Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 1st acrylic resin-1 46 46 46 46 46 46 No. 1 Acrylic Resin-2 - - - - - - No. 1 Acrylic Resin-3 - - - - - - No. 1 Acrylic Resin-4 - - - - - - No. 1 Acrylic Resin-5 - - - - - - 2nd acrylic resin-1 0.5 22 9.4 9.4 9.4 9.4 2nd acrylic resin-2 - - - - - - 2nd acrylic resin-3 - - - - - - 2nd acrylic resin-4 - - - - - - 2nd 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 first solvent 5.6 1.6 3.6 3.6 5.6 1.6 second solvent 4 One 3 3 5 1.1 third 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 (wt%) 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 1st acrylic resin-1 55.4 - - - - - 46 46 46 46 No. 1 Acrylic Resin-2 - - 46 - - - - - - - No. 1 Acrylic Resin-3 - - - 46 - - - - - - No. 1 Acrylic Resin-4 - - - - 46 - - - - - No. 1 Acrylic Resin-5 - - - - - 46 - - - - 2nd acrylic resin-1 - 55.4 9.4 9.4 9.4 9.4 - - - - 2nd acrylic resin-2 - - - - - - 9.4 - - - 2nd acrylic resin-3 - - - - - - - 9.4 - - 2nd acrylic resin-4 - - - - - - - - 9.4 - 2nd 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 first 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 third 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, manufacturers and product names, and physical properties of each component used in Comparative Examples and Examples are as follows.

composition note 1st acrylic resin-1 Av: 2 mgKOH/g, OHv: 185 mgKOH/g, Tg: 52° C., solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol No. 1 Acrylic Resin-2 Av: 2 mgKOH/g, OHv: 155 mgKOH/g, Tg: 52°C, solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol No. 1 Acrylic Resin-3 Av: 2 mgKOH/g, OHv: 257 mgKOH/g, Tg: 52° C., solid content: 65% by weight,
Viscosity at 25°C: 5,200 cps, Mw: 20,000 g/mol No. 1 Acrylic Resin-4 Av: 2 mgKOH/g, OHv: 185 mgKOH/g, Tg: 52° C., solid content: 65% by weight,
Viscosity at 25°C: 4,500 cps, Mw: 13,800 g/mol No. 1 Acrylic Resin-5 Av: 2 mgKOH/g, OHv: 185 mgKOH/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: 3 mgKOH/g, OHv: 140 mgKOH/g, solid content: 54 wt%,
Viscosity at 25°C: 4,100 cps, Mw: 8,700 g/mol, Tg: 50°C 2nd acrylic resin-2 Av: 3 mgKOH/g, OHv: 89 mgKOH/g, solid content: 54 wt%,
Viscosity at 25°C: 4,100 cps, Mw: 8,700 g/mol, Tg: 50°C 2nd acrylic resin-3 Av: 3 mgKOH/g, OHv: 157 mgKOH/g, solid content: 54 wt%,
Viscosity at 25°C: 4,100 cps, Mw: 8,700 g/mol, Tg: 50°C 2nd acrylic resin-4 Av: 3 mgKOH/g, OHv: 140 mgKOH/g, solid content: 54 wt%,
Viscosity at 25°C: 2,900 cps, Mw: 4,600 g/mol, Tg: 50°C 2nd acrylic resin-5 Av: 3 mgKOH/g, OHv: 140 mgKOH/g, solid content: 54 wt%,
Viscosity at 25°C: 4,900 cps, Mw: 11,000 g/mol, Tg: 50°C Block isocyanate curing agent Curing agent in which terminal isocyanate groups are blocked with polyethylene glycol
(Solid content: 70 wt%, viscosity at 25 °C: 7,600 cps,
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 first solvent n-Butyl Acetate second solvent n-butanol (N-butanol) third solvent Manufacturer: Solvay, product name: RHODIASOLV RPD 4th solvent Kocosol #100 (Kocosol #100)

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

A top coat (manufacturer: KCC, product name: WT3900) was bell-coated on the specimen to a dry film thickness of 15 μm, and then hot air was blown at 80° C. for 3 minutes to evaporate the remaining water in the paint to form a top coat. Thereafter, the clear paint compositions of Examples and Comparative Examples were coated on the top coat and cured at 120° C. for 25 minutes to form a clear coat 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 handgun spray (nozzle diameter: 1.5 mm, air pressure: keep constant around 4.5 kgf/cm 2 ), and horizontally 40 while maintaining a constant distance between the nozzle inlet and the specimen at 30 cm It was painted while moving at a speed of ~50 cm/sec.

(1) Painting workability

At the time of discharging the paint by handgun spray, the clear paint compositions of Examples and Comparative Examples were coated twice reciprocally to compare the degree of atomization, the degree of smoothness and the rise of the paint film during painting.

Specifically, visually good skin spreadability on the surface and excellent spreadability is excellent (◎), visually good riseability but insufficient paint spreadability is good (○), and visual riseability and spreadability are insufficient. And if the foreign coating was less than 3 points, it was evaluated as normal (Δ), and if the foreign coating was 3 or more points and cratering occurred, it was evaluated as bad (×).

(2) Appearance

Gloss (LU), sharpness (SH), and orange peel (OP) were measured using Wave Scan DOI (BYK Gardner), an automobile exterior measuring instrument, on the painted specimens. 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 (◎), when it was 60 or more and less than 65, it was good (○), when it was 55 or more and less than 60, it was evaluated as normal (Δ), and when it was less than 55, it was evaluated as bad (×).

(3) gloss

The gloss of 20° was measured using a gloss meter on the coated specimen. If the 20° gloss was 90 or higher, excellent (◎), 85 or more and less than 90 good (○), and 80 to less than 85 average ( △), less than 80 was evaluated as bad (×).

(4) Repainting adhesion

After removing both the top coat and the clear coat, the top coat and the clear paint composition were coated in the same manner as described above, and then repainting adhesion was evaluated by a checkerboard method.

Specifically, in the checkerboard 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 excellent (◎) when 100 squares are 100% completely attached, good (○) when the remaining squares are 70% or more and less than 100%, good (○) when 50% or more and less than 70%, normal (△), 50% If less than, it was evaluated as defective (×).

(5) Impact resistance

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

(6) water resistance

After 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, adhesion evaluation was performed in the same manner as in item (4).

(7) Chill flow

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

Specifically, it was observed that paint was formed at the bottom of the hole, and the thickness (㎛) of the coating film at the starting point where the flow generation was observed was recorded as the flow limit film thickness. At this time, it was determined that the flowability was insufficient as the numerical value of the measured flow limit film thickness was lower. At this time, if the flow limit film thickness is 40㎛ or more, it is evaluated as excellent (◎), if it is 35㎛ or more and less than 40㎛, it is good (○), if it is 30㎛ or more and less than 35㎛, it is evaluated as normal (Δ), and if it is less than 30㎛, it is evaluated as bad (Х) did.

(8) Cold-resistant chipping resistance

After leaving a specimen of size 150mmX70mm at -20±3° C. for 3 hours, cold chipping resistance was measured using a chipping resistance tester (manufacturer: Grebrometa, model name: SAE J 400).

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

evaluation item stamp
Workability Exterior Polish Repainting Adhesion impact resistance water resistance seven flow Cold-resistant 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 Examples has excellent paint workability, and the coating film prepared from the composition is excellent in appearance, gloss, repainting adhesion, impact resistance, water resistance, paint flow and cold chipping resistance. did.

On the other hand, Comparative Examples 1 and 2 including only one type of acrylic resin lacked gloss and water resistance of the prepared coating film. 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 was also poor in 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 lacked impact resistance and water resistance. Furthermore, in Comparative Example 4, the coating workability of the composition was also insufficient, and the cold chipping resistance of the prepared coating film was also insufficient.

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 was also poor in repainting adhesion. Furthermore, Comparative Example 6 was also poor in appearance and coating flowability of the coating film.

In addition, Comparative Example 7 containing the second acrylic resin-2 having a low hydroxyl value and Comparative Example 8 containing the second acrylic resin-3 having a high hydroxyl value lacked the appearance characteristics of the coating film. Furthermore, Comparative Example 7 lacks gloss and paint flow, and Comparative Example 8 lacks coating workability of the composition and also lacks impact resistance, water resistance and cold chipping resistance of the prepared 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 lacked appearance, water resistance and cold chipping resistance. Moreover, Comparative Example 9 was also insufficient in impact resistance, and Comparative Example 10 was also insufficient in coating workability and coating flowability.

Claims (5)

A first acrylic resin, a second acrylic resin, comprising 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, a low temperature curable one-component clear paint composition. The method according to claim 1,
The first acrylic resin has a glass transition temperature of 40 to 70 ℃,
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 according to 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 paint composition . The method according to claim 1,
The block isocyanate-based curing agent is an active methylene-based compound, a polyalkylene polyol compound, and one or more blocking agents selected from the group consisting of a pyrazole-based compound, wherein the terminal isocyanate group is blocked, a low-temperature curable one-component clear paint composition. The method according to claim 1,
Based on the total weight of the coating composition, 30 to 60% by weight of the first acrylic resin, 1 to 20% by weight of the second acrylic resin, 10 to 30% by weight of a block isocyanate-based curing agent, and 10 to 45% by weight of a solvent. A curable one-component clear paint composition.