KR20220136819A - Clear coat composition for low temperature curing - Google Patents

Abstract

The present invention relates to a clear coat composition for low temperature curing, which includes an acrylic resin, a first polyester resin, a second polyester resin and an isocyanate-based curing agent. The first polyester resin has a hydroxyl value of 240 to 320 mgKOH/g, and the second polyester resin has a hydroxyl value of 100 to 180 mgKOH/g. The present invention is to provide a clear paint composition capable of producing a coating film having excellent mechanical properties while being curable at a low temperature of 120 ℃ or less.

Description

Low temperature curing type clear coat composition {CLEAR COAT COMPOSITION FOR LOW TEMPERATURE CURING}

The present invention relates to a low-temperature curing type clear coat composition that can be cured at a low temperature, so that the manufacturing cost is low and the appearance characteristics of the prepared coating film are excellent.

In general, the exterior plate of a vehicle body should not cause deterioration and rust of the coating film, and should have durability to maintain the luster or color of the coating film. Therefore, in the vehicle painting process, after electrodeposition painting of the vehicle body that has undergone the pretreatment process, intermediate painting is performed to improve adhesion and smoothness, and base painting is performed on the intermediately painted vehicle body for the aesthetics of the vehicle body. Thereafter, it is common to apply a clear coating film to protect the color of the base coating film, to improve the appearance, and to protect the base coating film from the outside.

Conventionally, as a clear paint for automobiles, a thermosetting coating composition of a resin containing a hydroxyl group and an amino resin is widely used. However, when using a conventional thermosetting coating composition, parts made of plastic materials such as bumpers and rearview mirrors may deform or distort the appearance of parts when cured under high temperature curing conditions. There was trouble. In addition, there was a disadvantage in that the color of the plastic material part separated from the body and painted separately and the color of the body were different. Accordingly, a low-temperature curing type clear paint composition in which the curing temperature is lowered so that the plastic material parts can be integrally combined with the vehicle body and the painting process can be performed is attracting attention.

As an alternative to this, Korean Patent Registration No. 1,655,621 (Patent Document 1) discloses a clear paint composition comprising two types of acrylic polyol resin, polyester polyol resin, reactive silicone additive and isocyanate curing agent. However, the conventional low-temperature curing type clear paint composition, such as the clear paint composition of Patent Document 1, has insufficient mechanical properties of the coating film prepared therefrom, so it can be applied only for repair or painting of parts, and is limited in application for body painting. there was

Therefore, there is a need for research and development on a clear paint composition suitable for application to car body painting because it can be cured at a low temperature of 120° C. or less and has excellent mechanical properties of a coating film prepared therefrom.

Korean Patent Registration No. 1,655,621 (published on: 2016. 6. 28.)

An object of the present invention is to provide a clear paint composition capable of producing a coating film having excellent mechanical properties while being curable at a low temperature of 120° C. or less.

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

The first polyester resin has a hydroxyl value of 240 to 320 mgKOH / g,

The second polyester resin provides a low-temperature curable clear coat composition having a hydroxyl value of 100 to 180 mgKOH/g.

The clear paint composition according to the present invention can be cured at a low temperature of 120° C. or less, so it is possible to reduce the cost of the painting process, which is economical. The problem of different colors 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. Furthermore, 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.

As used herein, "weight average molecular weight" and "number average molecular weight" are measured by a conventional method known in the art, and may be measured by, for example, a gel permeation chromatograph (GPC) method.

In addition, the "glass transition temperature" is measured by a conventional method known in the art, for example, it can be measured by differential scanning calorimetry (DSC).

Functional groups such as "acid value" and "hydroxyl value" may be measured by a method well known in the art, for example, may represent a value measured by a method of titration.

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

The low-temperature curable clear coat composition according to the present invention includes an acrylic resin, a first polyester resin, a second polyester resin, and an isocyanate-based curing agent.

acrylic resin

The acrylic resin serves to impart coating film formation and mechanical properties to the composition.

The acrylic resin may be directly synthesized according to a known method, or a commercially available product may be used. For example, the acrylic resin may be prepared by polymerizing at least one of a vinyl-based monomer and a (meth)acrylate-based monomer.

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

The (meth)acrylate-based monomer may include at least one selected from the group consisting of a hydroxyl group-free (meth)acrylate-based monomer and a hydroxyl group-containing (meth)acrylate monomer.

The hydroxyl group-free (meth) acrylate monomer is, for example, (meth) acrylic acid, methyl (meth) acrylic acid, (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl ( Meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate , heptyl (meth) acrylate, isooctyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, decyl (meth) acrylate, dodecyl It may include at least one selected from the group consisting of (meth)acrylate, isobornyl (meth)acrylate, and lauryl (meth)acrylate.

The hydroxyl group-containing (meth)acrylate monomer may be, for example, a hydroxyalkyl-containing (meth)acrylate, specifically, 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate ) may include at least one selected from the group consisting of acrylate, 2-hydroxypropyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate.

For example, the acrylic resin can be prepared using a radical polymerization method, and the physical properties, i.e., weight average molecular weight (Mw), hydroxyl value (OHv), acid value (Av), etc. can be adjusted according to the initiator and polymerization time. have.

The acrylic resin may have a weight average molecular weight (Mw) of 10,000 to 40,000 g/mol, 15,000 to 35,000 g/mol, or 20,000 to 30,000 g/mol. When the weight average molecular weight of the acrylic resin is within the above range, the hardness of the prepared coating film may be excellent. In addition, when the weight average molecular weight of the acrylic resin is less than the above range, the water resistance and chemical resistance of the prepared coating film are insufficient due to the small molecular weight, and when the weight average molecular weight of the acrylic resin is higher than the above range, the viscosity is increased according to the increase of the molecular weight. Since workability is poor and leveling property is also poor, it may be difficult to manufacture a coating film having an excellent appearance.

In addition, the acrylic resin may have a hydroxyl value (OHv) of 100 to 200 mgKOH/g, or 145 to 170 mgKOH/g. When the hydroxyl value of the acrylic resin is within the above range, there is an effect of improving the weather resistance of the coating film. In addition, when the hydroxyl value of the acrylic resin is less than the above range, the coating film formation by the crosslinking reaction with the curing agent is insufficient, and the hardness and water resistance of the coating film are reduced. ), resulting in poor elasticity, and deterioration of the appearance and weather resistance of the prepared coating film.

The acrylic resin may have an acid value (Av) of 5 to 15 mgKOH/g, or 8 to 11 mgKOH/g. When the acid value of the acrylic resin is within the above range, water dispersibility and storage stability of the coating composition are improved, and water resistance is improved. In addition, when the acid value of the acrylic resin is less than the above range, there is a problem that the curing reaction rate is lowered, so that the appearance of the prepared coating film and the water dispersion stability of the resin are lowered. There may be a problem in that the water resistance and water resistance of the coating film are poor.

In addition, the acrylic resin may have a glass transition temperature (Tg) of 20 to 100 °C, 40 to 70 °C, or 52 to 58 °C. When the glass transition temperature of the acrylic resin is within the above range, there is an effect of improving the coating film formation and defoaming properties of the composition, and the gloss properties of the coating film. In addition, when the glass transition temperature of the 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, thereby reducing the impact resistance and water resistance of the prepared coating film. Brittle), the appearance and hardness of the coating film may deteriorate.

The acrylic resin may have a solid content (NV) of 60 to 80 wt%, 65 to 75 wt%, or 68 to 73 wt%, based on the total weight of the resin. When the solid content of the acrylic resin is within the above range, storage stability of the resin and storage stability of the coating composition may be improved, and workability may be excellent. In addition, when the solid content of the acrylic resin is less than the above range, there is a problem that the viscosity is too low and the workability of the coating composition including the same is insufficient. falls, and dispersion stability deteriorates, and agglomeration may occur over time.

In addition, the acrylic resin may be included in an amount of 15 to 35% by weight, or 20 to 30% by weight based on the total weight of the coating composition. When the acrylic resin is included within the content range, there is an effect of improving adhesion and impact resistance of the coating film. In addition, when the content of the acrylic resin is less than the above range, the dryness may be lowered, so that the adhesion and durability of the coating film may be reduced. can be

first polyester resin

The first polyester resin serves to form the appearance characteristics and mechanical properties of the coating film prepared through chemical bonding with an isocyanate-based curing agent.

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

In this case, the first carboxylic acid is, for example, adipic acid (AA), isophthalic acid (IPA), trimmaletic anhydride (TMA), alicyclic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, It may be at least one selected from the group consisting of fumaric acid, maleic anhydride, tetrahydrophthalic anhydride (HHPA), hexahydrophthalic anhydride, and derivatives thereof.

The first polyol is, for example, methoxypolyethylene glycol, 1,6-hexanediol (1,6-HD), neopentyl glycol (NPG), trimethylol propane (TMP), ethylene glycol, propylene glycol, diethylene It may be at least one selected from the group consisting of glycol, butanediol 1,4-hexanediol, and 3-methylpentanediol.

The first polyester resin may have a hydroxyl value (OHv) of 240 to 320 mgKOH/g, or 260 to 290 mgKOH/g. When the hydroxyl value of the first polyester resin is within the above range, there is an effect of improving the spreadability of the coating film and improving the chemical resistance by the urethane reaction. In addition, when the hydroxyl value of the first polyester resin is less than the above range, there is a problem that the durability and chemical resistance of the prepared coating film are reduced due to insufficient crosslinking density with the isocyanate-based curing agent. The coating film may be brittle, resulting in deterioration of impact resistance and cold chipping resistance.

In addition, the first polyester resin may have a number average molecular weight (Mn) of 100 to 1,000 g/mol, 200 to 900 g/mol, or 300 to 800 g/mol. When the number average molecular weight of the first polyester resin is within the above range, there is an effect of forming a smooth and soft (SOFT) coating film of the coating material. When the number average molecular weight of the first polyester resin is less than the above range, the molecular weight is small and there is a problem in that the mechanical properties of the prepared coating film are reduced. There may be problems in which cold chipping resistance and impact resistance are deteriorated due to being brittle.

The first polyester resin may have an acid value (Av) of 5 to 35 mgKOH/g, or 15 to 25 mgKOH/g. When the acid value of the first polyester resin is within the above range, rapid hardening by heat treatment is prevented, thereby preventing poor appearance of the coating film and reducing the occurrence of popping. When the acid value of the first polyester resin is less than the above range, there is a problem that the curing reaction rate is lowered and the hardness and appearance characteristics of the prepared coating film are lowered, and when it exceeds the above range, the water resistance is lowered as the hydrophilicity is improved. may occur.

In addition, the first polyester resin may have a solid content (NV) of 50 to 80% by weight, or 60 to 70% by weight, based on the total weight of the resin. When the solid content of the first polyester resin is within the above range, there is an effect of reducing the content of total volatile organic compounds (TVOC) due to the high solid content. When the solid content of the first polyester resin is less than the above range, there is a problem that the curing reactivity is lowered due to a decrease in the solid content of the composition, and when it exceeds the above range, the workability of the prepared paint is inferior and the appearance is deteriorated. can occur

In addition, the first polyester resin may be included in an amount of 5 to 15% by weight, or 8 to 12% by weight based on the total weight of the coating composition. When the first polyester resin is included within the content range, there is an effect of improving the appearance, scratch resistance and smoothness of the coating film. When the content of the first polyester resin in the composition is less than the above range, there is a problem that the crosslinking density is lowered and mechanical properties and appearance are deteriorated. There may be problems with degradation.

The composition may include the first polyester resin and the second polyester resin in a weight ratio of 1.5:1 to 2.5:1, or 1.8:1 to 2.2:1. When the mixing weight ratio of the first polyester resin and the second polyester resin is within the above range, durability and scratch resistance of the prepared coating film are improved. When the mixing weight ratio of the first polyester resin and the second polyester resin is less than the above range, there is a problem in that the crosslinking density of the prepared coating film is lowered to lower durability and scratch resistance, and when it exceeds the above range, the viscosity of the composition This may cause a problem in that the mechanical properties of the prepared coating film are deteriorated due to the decrease in dryness and curing reactivity.

Second polyester resin

The second polyester resin serves to increase the solid content of the composition and improve the appearance, smoothness, scratch resistance and slip properties of the prepared coating film.

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

In this case, the second carboxylic acid is, for example, adipic acid (AA), isophthalic acid (IPA), trimmaletic anhydride (TMA), cycloaliphatic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, It may be at least one selected from the group consisting of fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (HHPA), isononanoic acid (INA), and derivatives thereof.

The second polyol is 1,6-hexanediol (1,6-HD), pentaerythritol, sorbitol, methoxy polyethylene glycol, neopentyl glycol (NPG), trimethylol propane (TMP), ethylene It may be at least one selected from the group consisting of glycol, propylene glycol, diethylene glycol, butanediol 1,4-hexanediol and 3-methylpentanediol.

The second polyester resin may have a hydroxyl value (OHv) of 100 to 180 mgKOH/g, or 130 to 150 mgKOH/g. When the hydroxyl value of the second polyester resin is within the above range, there is an effect of improving the spreadability of the coating film and improving the chemical resistance due to the urethane reaction. In addition, when the hydroxyl value of the second polyester resin is less than the above range, the crosslinking density with the isocyanate-based curing agent is insufficient, and there is a problem in that the appearance, durability and chemical resistance of the prepared coating film are lowered. This may cause a problem in that the coating film becomes brittle and the coating workability and cold-resistant chipping properties are deteriorated.

In addition, the second polyester resin may have a number average molecular weight (Mn) of 1,200 to 5,000 g/mol, 1,300 to 4,500 g/mol, or 1,500 to 4,000 g/mol. When the number average molecular weight of the second polyester resin is within the above range, there is an effect of forming a smooth and soft (SOFT) coating film of the paint. When the number average molecular weight of the second polyester resin is less than the above range, the molecular weight is small and there is a problem that the mechanical properties of the prepared coating film are reduced. This may cause a problem of deterioration of cold chipping resistance due to hardening.

In addition, the second polyester resin may have an acid value (Av) of 10 to 40 mgKOH/g, or 20 to 30 mgKOH/g. When the acid value of the second polyester resin is within the above range, rapid hardening by heat treatment is prevented, thereby preventing poor appearance of the coating film and reducing the occurrence of popping. When the acid value of the second polyester resin is less than the above range, there is a problem that the curing reaction rate is lowered and the hardness and appearance characteristics of the prepared coating film are lowered, and when it exceeds the above range, the water resistance is lowered as the hydrophilicity is improved. may occur.

The second polyester resin may have a solid content (NV) of 60 to 80% by weight, or 65 to 75% by weight, based on the total weight of the resin. When the solid content of the second polyester resin is within the above range, there is an effect of reducing the content of total volatile organic compounds (TVOC) due to the high solid content. When the solid content of the second polyester resin is less than the above range, there is a problem in that the solid content of the composition is lowered and the curing reactivity is lowered to lower the mechanical properties of the prepared coating film, and when it exceeds the above range, the workability of the prepared paint This deterioration may cause a problem in that the appearance characteristics of the coating film are deteriorated.

In addition, the second polyester resin may be included in the composition in an amount of 1 to 10% by weight, or 3 to 7% by weight based on the total weight of the coating composition. When the second polyester resin is included within the content range, there is an effect of improving the appearance, scratch resistance and smoothness of the coating film. When the content of the second polyester resin in the composition is less than the above range, there is a problem in that the crosslinking density of the coating film is lowered to lower the cold chipping resistance and scratch resistance, and when it exceeds the above range, the viscosity of the composition becomes excessively high There may be a problem that the appearance is deteriorated due to deterioration of properties and drying properties.

Isocyanate-based curing agent

The isocyanate-based curing agent acts to form a coating film by reacting with the hydroxyl group of the resin as described above to form a urethane bond to cure the composition.

The type of the isocyanate-based curing agent is not particularly limited, and may include, for example, an aliphatic polyisocyanate compound without yellowing. Specifically, the isocyanate-based curing agent may include hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl methane diisocyanate, tetramethyl xylene diisocyanate, or a mixture thereof.

In addition, the isocyanate-based curing agent may have a content of unreacted isocyanate groups (NCO%) of 15 to 30% by weight, or 19 to 24% by weight, based on the total weight of the curing agent. When the NCO% of the isocyanate-based curing agent is less than the above range, there is a problem in that the crosslinking density of the coating film is lowered and the impact resistance, water resistance and cold chipping resistance of the coating film are lowered. As a result, the appearance characteristics, gloss, and mechanical properties of the coating film may be deteriorated.

The isocyanate-based curing agent may be included in the composition in an amount of 20 to 35% by weight, or 24 to 29% by weight based on the total weight of the coating composition. When the content of the isocyanate-based curing agent is less than the above range, there is a problem in that the crosslinking density is lowered and mechanical properties are lowered due to insufficient reactivity of the composition. And workability may be deteriorated.

The clear coat composition may further include a solvent.

solvent

The solvent controls the viscosity of the composition, improves dryness, and serves to improve the appearance characteristics and spreadability of the prepared coating film.

The solvent is not particularly limited as long as it is commonly used in the clear coat composition, and may include, for example, at least one selected from the group consisting of aromatics, acetates, alcohols, and propionates. Specifically, the solvent is an aromatic solvent such as toluene and xylene; 1-Methoxy-2-propyl acetate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl glutarate, methyl succinate, methyl adipate, dimethyl glutarate, dimethyl succinate, dimethyl adipate acetate-based solvents such as pate, propylene glycol methyl ether acetate (PMA), butyl carbitol acetate, and butyl cellosolve acetate; alcohol solvents such as n-butanol, propanol, 1-methoxy-2-propanol, and 2-butoxyethanol; ketones such as acetone, methyl ethyl ketone, methyl butyl ketone and methyl isobutyl ketone; and propionate solvents such as ethyl ethoxypropionate; and the like. Moreover, Cocosol #100, Cocosol #150, etc. are mentioned as a commercial item of the said aromatic solvent.

In addition, the solvent may be included in the composition in an amount of 15 to 45% by weight, or 25 to 35% by weight based on the total weight of the coating composition. When the solvent is included within the above range, the viscosity of the composition is appropriately adjusted to improve workability and dryness.

additive

The clear coat composition according to the present invention may further include additives such as a curing catalyst, a UV absorber, a surface smoothing agent, and a flow control agent. In this case, the additive is not particularly limited as long as it can be added to the coating composition in general.

In addition, the content of the additive is not particularly limited as long as it can be included in the clear coat composition. For example, the additive may be included in the composition in an amount of 1 to 10% by weight, or 3 to 7% by weight, based on the total weight of the coating composition.

Two-component paint composition

The clear paint composition may be a two-component paint composition including a main part and a curing agent part. For example, the clear paint composition may include a main part including an acrylic resin, a first polyester resin, a second polyester resin, a solvent, and an additive; and a curing agent unit including an isocyanate-based curing agent. In addition, the clear paint composition may be used after mixing the main part and the curing agent part before application.

The clear paint composition may have a solid content of 40 to 60% by weight, or 45 to 55% by weight. When the solid content of the clear coating composition is within the above range, there is an advantage in that the coating workability of the composition is appropriate.

The clear paint composition may be cured at 60°C to 120°C, 70°C to 110°C, or 80°C to 110°C. 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, or 50 to 60 seconds based on Pod Cup No. 4 at 25°C. When the viscosity at 25° C. of the clear paint composition is less than the above range, problems such as vertical flow down may occur. A load may be applied to the machine 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 120° C. or less, thereby reducing the cost required during 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 one painting process, it is possible to reduce the hassle or cost of the process. Furthermore, 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 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 15 and Comparative Examples 1 to 7. Preparation of clear coat composition

A clear coat composition having a viscosity at 25°C of 55 seconds based on Podcup No. 4 was prepared by mixing the components in the content shown in Tables 1 to 3.

Composition (wt%) Example One 2 3 4 5 6 7 acrylic resin 25 25 25 25 25 25 25 First polyester resin-1 9.8 - - 9.8 9.8 8 12 First polyester resin-2 - 9.8 - - - - - 1st polyester resin-3 - - 9.8 - - - - 1st polyester resin-4 - - - - - - - 1st polyester resin-5 - - - - - - - Second polyester resin-1 4.8 4.8 4.8 - - 4.8 4.8 Second polyester resin-2 - - - 4.8 - - - 2nd polyester resin-3 - - - - 4.8 - - 2nd polyester resin-4 - - - - - - - 2nd polyester resin-5 - - - - - - - Isocyanate-based curing agent 26 26 26 26 26 26 26 curing catalyst 0.1 0.1 0.1 0.1 0.1 0.1 0.1 UV absorber 1.6 1.6 1.6 1.6 1.6 1.6 1.6 surface leveling agent 0.5 0.5 0.5 0.5 0.5 0.5 0.5 flow regulator 2.9 2.9 2.9 2.9 2.9 2.9 2.9 solvent 29.3 29.3 29.3 29.3 29.3 31.1 27.1 total 100 100 100 100 100 100 100

Composition (wt%) Example 8 9 10 11 12 13 14 15 acrylic resin 25 25 25 25 17 33 12 38 First polyester resin-1 6 13 3 18 9.8 9.8 9.8 9.8 First polyester resin-2 - - - - - - - - First polyester resin-3 - - - - - - - - 1st polyester resin-4 - - - - - - - - 1st polyester resin-5 - - - - - - - - Second polyester resin-1 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 Second polyester resin-2 - - - - - - - - 2nd polyester resin-3 - - - - - - - - 2nd polyester resin-4 - - - - - - - - 2nd polyester resin-5 - - - - - - - - Isocyanate-based curing agent 26 26 26 26 26 26 26 26 curing catalyst 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 UV absorber 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 surface leveling agent 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 flow regulator 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.9 solvent 33.1 26.1 36.1 21.1 37.3 21.3 42.3 16.3 total 100 100 100 100 100 100 100 100

Composition (wt%) comparative example One 2 3 4 5 6 7 acrylic resin 25 25 25 25 - 25 25 First polyester resin-1 - - 9.8 9.8 15 - 9.8 First polyester resin-2 - - - - - - - First polyester resin-3 - - - - - - - 1st polyester resin-4 9.8 - - - - - - 1st polyester resin-5 9.8 - - - - - Second polyester resin-1 4.8 4.8 - - 7 4.8 - Second polyester resin-2 - - - - - - - 2nd polyester resin-3 - - 4.8 - - - - 2nd polyester resin-4 - - 4.8 - - - 2nd polyester resin-5 - - - - - - - Isocyanate-based curing agent 26 26 26 26 29 26 26 curing catalyst 0.1 0.1 0.1 0.1 0.1 0.1 0.1 UV absorber 1.6 1.6 1.6 1.6 1.6 1.6 1.6 surface leveling agent 0.5 0.5 0.5 0.5 0.5 0.5 0.5 flow regulator 2.9 2.9 2.9 2.9 2.9 2.9 2.9 solvent 29.3 29.3 29.3 29.3 43.9 39.1 34.1 total 100 100 100 100 100 100 100

Hereinafter, the manufacturers and product names, or component names, etc. of each component used in Comparative Examples and Examples are shown in Table 4.

composition Manufacturer and product name, physical property or compound name acrylic resin Mw: 25,000 g/mol, OHv: 155 mgKOH/g, Av: 9 mgKOH/g, Tg: 56°C, NV: 70 wt% First polyester resin-1 Mn: 500 g/mol, OHv: 275 mgKOH/g, Av: 20 mgKOH/g, NV: 65 weight First polyester resin-2 Mn: 500 g/mol, OHv: 250 mgKOH/g, Av: 20 mgKOH/g, NV: 65 weight 1st polyester resin-3 Mn: 500 g/mol, OHv: 310 mgKOH/g, Av: 20 mgKOH/g, NV: 65 weight 1st polyester resin-4 Mn: 500 g/mol, OHv: 228 mgKOH/g, Av: 20 mgKOH/g, NV: 65 weight 1st polyester resin-5 Mn: 500 g/mol, OHv: 330 mgKOH/g, Av: 20 mgKOH/g, NV: 65 weight Second polyester resin-1 Mn: 1,950 g/mol, OHv: 135 mgKOH/g, Av: 25 mgKOH/g, NV: 69 weight Second polyester resin-2 Mn: 1,950 g/mol, OHv: 115 mgKOH/g, Av: 25 mgKOH/g, NV: 69 weight 2nd polyester resin-3 Mn: 1,950 g/mol, OHv: 170 mgKOH/g, Av: 25 mgKOH/g, NV: 69 weight 2nd polyester resin-4 Mn: 1,950 g/mol, OHv: 91 mgKOH/g, Av: 25 mgKOH/g, NV: 69 wt. 2nd polyester resin-5 Mn: 1,950 g/mol, OHv: 187 mgKOH/g, Av: 25 mgKOH/g, NV: 69 weight Isocyanate-based curing agent NCO content: 22% by weight, curing catalyst dibutyltin dilaurate UV absorber Manufacturer: BASF, product name: Tinuvin 384 surface leveling agent Manufacturer: BASF, Product Name: BYK-325 flow regulator Manufacturer: Akzo Nobel, product name: Setalux 81198 SS-55 solvent Cocosol #100, xylene, and butyl acetate are mixed in a weight ratio of 1:1:1

experimental example. Characteristic evaluation of coating film

A top coat (manufacturer: KCC, product name: WT3090) was applied to the specimen and dried to form a top coat with a thickness of 15 µm. Thereafter, the clear paint compositions prepared in Examples and Comparative Examples were coated on the top coat and cured at 100° C. for 25 minutes to form a clear coat having a thickness of 40 μm to prepare a final coat. The physical properties of the specimens were measured in the following manner, and the results are shown in Table 5.

Specifically, the clear coating film uses a handgun spray (nozzle diameter: 1.5mm, air pressure: keep constant around 4.5kgf/cm2), and horizontally 40~ while maintaining a constant distance between the nozzle inlet and the specimen at 30cm 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 manufactured final coating film, and comprehensive appearance evaluation values using the measured properties (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 checkered method, 100 squares of 2 mm in width and 2 mm in length were made on the surface of the clear coating film with a knife, and then the square was removed using a tape to measure adhesion. At this time, the measured adhesion is 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 and 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 final coating film 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 on the lower part of the hole. The thickness (μm) of the coating film at the starting point at which flow generation was observed was recorded as the flow limiting 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 the painted specimen of size 150mmX70mm at -20±3°C for 3 hours, the 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° at a pressure of 4 bar on the final coating. 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 (×).

stamp
Workability Exterior Polish Repainting Adhesion impact resistance water resistance seven flow Cold-resistant chipping resistance Example One ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 2 ◎ ◎ ◎ ◎ ○ ○ ◎ ○ 3 ◎ ○ ○ ◎ ○ ◎ ◎ ○ 4 ◎ ○ ◎ ◎ ○ ○ ◎ ○ 5 ○ ○ ○ ◎ ◎ ◎ ◎ ○ 6 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 7 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 8 ◎ ○ ◎ ◎ ○ ○ ◎ ○ 9 ○ ○ ○ ◎ ◎ ◎ ○ ◎ 10 ◎ △ ○ ◎ △ △ ◎ △ 11 △ △ △ ○ ◎ ◎ △ ◎ 12 ◎ ○ ◎ ○ ○ ○ ◎ ○ 13 ○ ◎ ◎ ◎ ◎ ○ ○ ◎ 14 ◎ △ ◎ △ △ △ ◎ △ 15 △ ○ ○ ◎ ◎ △ △ ◎ comparative example One ◎ ○ ○ ◎ X X ◎ X 2 ◎ X X ○ X ○ ○ X 3 ◎ X ◎ ◎ X X ◎ X 4 X X X ◎ ○ ◎ ○ X 5 △ X △ X X X ○ X 6 ○ X △ ○ X ○ X X 7 ○ △ X ○ X X △ X

As can be seen in Table 5, the composition of Examples is superior to the composition of Comparative Example in paint workability and paint flow, and the coating film prepared from the composition of Example has appearance, gloss, repainting adhesion, impact resistance and better than the coating film of Comparative Example. It was found that the cold chipping resistance was excellent.

On the other hand, the coating film of Comparative Example 1 including the first polyester resin-4 having a low hydroxyl value and Comparative Example 3 including the second polyester resin-4 having a low hydroxyl value lacks impact resistance, water resistance and cold chipping resistance. did. In particular, the coating film of Comparative Example 3 was also poor in appearance characteristics.

In addition, the coating film of Comparative Example 2 containing the first polyester resin-5 having a high hydroxyl value and Comparative Example 4 containing the second polyester resin-5 having a high hydroxyl value lacked appearance characteristics, gloss and cold chipping resistance. did. In particular, the coating film of Comparative Example 2 was also poor in impact resistance, and the composition of Comparative Example 4 was also poor in coating workability.

The coating film of Comparative Example 5 which did not contain the acrylic resin was poor in appearance characteristics, repainting adhesion, impact resistance, water resistance and cold chipping resistance.

In addition, the composition of Comparative Example 6 including only one kind of second polyester resin without the first polyester resin lacks chill flow properties, and the coating film prepared therefrom has excellent appearance characteristics, impact resistance and cold chipping resistance. lacked

The coating film of Comparative Example 7 including only one kind of the first polyester resin without the second polyester resin lacked gloss, impact resistance, water resistance and cold chipping resistance.

Claims (6)

An acrylic resin, a first polyester resin, a second polyester resin, and an isocyanate-based curing agent,
The first polyester resin has a hydroxyl value of 240 to 320 mgKOH / g,
The second polyester resin has a hydroxyl value of 100 to 180 mgKOH/g, a low temperature curable clear coat composition. The method according to claim 1,
The acrylic resin has a weight average molecular weight of 10,000 to 40,000 g/mol, a hydroxyl value of 100 to 200 mgKOH/g, an acid value of 5 to 15 mgKOH/g, and a glass transition temperature of 20 to 100° C., a low-temperature curing type clear coat composition. The method according to claim 1,
The first polyester resin has a number average molecular weight of 100 to 1,000 g / mol,
The second polyester resin has a number average molecular weight of 1,200 to 5,000 g/mol, a low temperature curable clear coat composition. The method according to claim 1,
A low temperature curable clear coat composition comprising the first polyester resin and the second polyester resin in a weight ratio of 1.5:1 to 2.5:1. The method according to claim 1,
The low-temperature curable clear coat composition, wherein the isocyanate-based curing agent has an unreacted isocyanate group content of 15 to 30% by weight based on the total weight of the curing agent. The method according to claim 1,
Based on the total weight of the coating composition, 15 to 35% by weight of an acrylic resin, 5 to 15% by weight of a first polyester resin, 1 to 10% by weight of a second polyester resin, and 20 to 35% by weight of an isocyanate-based curing agent comprising , a low-temperature curing type clear coat composition.