KR102517108B1 - Powder coating composition - Google Patents

Abstract

The present invention relates to a powder coating composition excellent in smoothness, pinhole prevention and weather resistance.

Description

Powder coating composition

The present invention relates to a powder coating composition excellent in smoothness, pinhole prevention and weather resistance.

Metals such as aluminum, titanium, and copper are used as main materials for parts of buildings, automobiles, and aircraft, and the surfaces of the metals are painted with a paint composition to protect them from harsh external environments. The paint composition requires various physical properties such as weather resistance, corrosion resistance, acid resistance, alkali resistance, gloss, and adhesion. , gloss, adhesion, etc. are important.

For this reason, research on a paint composition with excellent weather resistance has been conducted. For example, Korean Patent Publication No. 10-2013-0082191 discloses a powder paint composition for a roof rack of an automobile made of aluminum. The powder coating composition includes a polyester resin and an epoxy curing agent, and has a disadvantage in that long-term weatherability is poor because the epoxy resin is applied. In order to solve this problem, a paint composition using triglycidyl isocyanurate resin as a curing agent instead of epoxy resin has been developed, but there is a problem that triglycidyl isocyanurate resin can be harmful to workers' health. .

The present invention provides a powder coating composition excellent in smoothness, pinhole prevention and weather resistance.

The present invention provides a powder coating composition comprising two or more carboxyl group-containing polyester resins and a hydroxyalkyl amide-based curing agent.

The present invention provides a powder coating composition excellent in smoothness, pinhole prevention and weather resistance. In particular, the powder coating composition according to the present invention has excellent long-term weather resistance and corrosion resistance, and is suitable for application as various industrial paints exposed to the outdoors for a long period of time. In addition, the powder coating composition according to the present invention can realize stable semi-glossy or matte, and secure pinhole stability to realize excellent appearance. In addition, the powder coating composition of the present invention is eco-friendly because it does not use a triglycidyl isocyanurate curing agent.

Hereinafter, the present invention will be described. However, it is not limited only by the following contents, and each component may be variously modified or selectively mixed as needed. Therefore, it should be understood to include all modifications, equivalents or substitutes included in the spirit and scope of the present invention.

The "weight average molecular weight" used herein is measured by a conventional method known in the art, and can be measured, for example, by a gel permeation chromatograph (GPC) method. Functional groups such as "acid value" and "hydroxyl value" can be measured by methods well known in the art, and can be measured, for example, by titration. "Viscosity" can be measured by methods well known in the art, for example using a Brookfield viscometer.

The powder coating composition according to the present invention includes at least two carboxyl group-containing polyester resins and a hydroxyalkyl amide-based curing agent. In addition, the powder coating composition of the present invention may further include additives commonly used in the powder coating field, if necessary.

Carboxyl group-containing polyester resin

The powder coating composition according to the present invention includes a polyester resin containing a carboxyl group as a main resin. The carboxyl group-containing polyester resin serves to secure weather resistance and mechanical properties when applied to paint.

The carboxyl group-containing polyester resin may be a carboxyl group-containing polyester resin having a carboxyl group at a polymer resin terminal. The carboxyl group-containing polyester resin has a crosslinked structure introduced therein, and is prepared by polymerizing at least one of monomers and polymers having a hydroxyl group as a terminal functional group and at least one of monomers and polymers having a carboxyl group as a terminal functional group in the presence of a catalyst. it could be

The monomer having the hydroxyl group as a terminal functional group may include a polyfunctional alcohol, and the polyfunctional alcohol may be a difunctional or higher functional alcohol, for example, a 2 to 4 functional alcohol. The type of polyfunctional alcohol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and trimethylol propane. propane), methyl propanediol, pentaethylene glycol, tripropylene glycol, cyclohexanedimethanol, 1,2-butylene glycol , Neopentyl glycol, 1,6-hexanediol, and glycerol, or a mixture thereof may be used.

The polymer having the hydroxyl group as a terminal functional group may be prepared by polymerizing a monomer having the hydroxyl group as a terminal functional group. The type of the polymer having the hydroxyl group as a terminal functional group is not particularly limited, and for example, one or a mixture thereof selected from the group consisting of polyethylene glycol and polypropylene glycol may be used.

The monomer having the carboxyl group as a terminal functional group may include a polyfunctional acid, and the polyfunctional acid may be a bifunctional or higher functional acid, for example, a bifunctional to tetrafunctional acid. The type of the polyfunctional acid is not particularly limited, and examples thereof include terephthalic acid, isophthalic acid, 1,4-cyclohexane dicarboxylic acid, and adipic acid. Adipic acid, Sebacic acid, Phthalic anhydride, Trimellitic anhydride, Benzoic acid, Tetrahydrophthalic anhydride, Hexahydrophthalic anhydride ) One or a mixture thereof selected from the group consisting of may be used.

For example, the polyfunctional acid may include isophthalic acid. Isophthalic acid has excellent heat stability, and when applied in a large amount, it can implement a matte effect with excellent weather resistance. The isophthalic acid may be included in an amount of 80% by weight or more based on the total weight of the polyfunctional acid. When 80% by weight or more of isophthalic acid is included, excellent weatherability and matte appearance can be secured.

As another example, the polyfunctional acid may include terephthalic acid. When a large amount of terephthalic acid is applied, an excellent appearance can be secured as the cross-linking ability is improved. The terephthalic acid may be included in an amount of 80% by weight or more based on the total weight of the polyfunctional acid. When terephthalic acid is included in an amount of 80% by weight or more, a coating film having excellent appearance such as leveling property and pinhole prevention property can be obtained.

The polymer having the carboxyl group as a terminal functional group may be prepared by polymerizing a monomer having the carboxyl group as a terminal functional group.

In the present invention, the carboxyl group-containing polyester resin includes two or more carboxyl group-containing polyester resins. For example, the carboxyl group-containing polyester resin includes a first carboxyl group-containing polyester resin having excellent weather resistance and a second carboxyl group-containing polyester resin having excellent mechanical properties.

The first carboxyl group-containing polyester resin is prepared by polymerizing at least one of a monomer and a polymer having a hydroxyl group as a terminal functional group and a polyfunctional acid containing isophthalic acid and not containing terephthalic acid, and the second carboxyl group-containing polyester resin may be prepared by polymerizing at least one of monomers and polymers having a hydroxyl group as a terminal functional group and a polyfunctional acid including terephthalic acid. For example, the first carboxyl group-containing polyester resin is prepared by polymerizing a polyfunctional alcohol containing neopentyl glycol and a polyfunctional acid containing isophthalic acid and not containing terephthalic acid, and the second carboxyl group-containing polyester resin is It may be prepared by polymerizing a polyfunctional alcohol including neopentyl glycol and a polyfunctional acid including terephthalic acid.

For example, the first carboxyl group-containing polyester resin may have an acid value of 25 to 40 mgKOH/g, for example, 30 to 36 mgKOH/g, and the second carboxyl group-containing polyester resin may have an acid value of 25 to 40 mgKOH/g. g, for example 30 to 35 mgKOH/g. When the acid values of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin exceed the above range, the high acid value may limit the implementation of matte gloss or may cause moisture generation due to a condensation reaction that reacts with surrounding hydroxyl groups. Pinhole phenomenon can be severe. On the other hand, when the acid value is less than the above range, the degree of curing is reduced, and cross-linking strength and mechanical properties are lowered, and weather resistance and corrosion resistance are lowered.

The first carboxyl group-containing polyester resin may have a weight average molecular weight (Mw) of 5,000 to 12,000 g/mol, for example, 8,500 to 11,000 g/mol, and the second carboxyl group-containing polyester resin may have a weight average molecular weight (Mw). ) may be 5,000 to 20,000 g/mol, for example 9,000 to 15,000 g/mol. When the weight average molecular weights of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin are out of the above range, the paint may not be formed uniformly, resulting in poor appearance.

The first carboxyl group-containing polyester resin may have a melt viscosity (200 ° C., Brookfield viscometer) of 3,000 to 7,000 mPa.s, for example, 3,000 to 5,000 mPa.s, and the second carboxyl group-containing polyester resin has a melt viscosity (200 °C, Brookfield viscometer) may be 3,000 to 8,000 mPa.s, for example 3,000 to 6,000 mPa.s. When the melt viscosity of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin have excessively high or low viscosities out of the above range, painting workability may be deteriorated.

As described above, by mixing and using the first carboxyl group-containing polyester resin with excellent weather resistance and the second carboxyl group-containing polyester resin with excellent mechanical properties, not only excellent weather resistance is imparted to the coating film, but also the effect of improving mechanical properties such as impact resistance can exert

The first carboxyl group-containing polyester resin may be included in an amount of 20 to 40% by weight, for example, 25 to 37% by weight based on the total weight of the powder coating composition. When the content of the first carboxyl group-containing polyester resin is less than the above-mentioned range, it may be difficult to implement a matte effect, and when it exceeds the above-mentioned range, craters or pinholes may occur, resulting in degraded appearance.

The second carboxyl group-containing polyester resin may be included in an amount of 20 to 40% by weight, for example, 25 to 35% by weight based on the total weight of the powder coating composition. When the content of the second carboxyl group-containing polyester resin is less than the above range, salt spray resistance may be deteriorated, and when it exceeds the above range, weather resistance may be deteriorated, such as a decrease in gloss retention or an increase in color difference value.

For example, the mixing ratio of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin may be 1: 0.5 to 2, or 1: 0.7 to 1.3 in weight ratio. When the two kinds of carboxyl group-containing polyester resins are mixed and used within the above-mentioned range, characteristics such as weather resistance, gloss, and mechanical properties of the coating film can be further improved. Specifically, when the content of the second carboxyl group-containing polyester resin relative to the first carboxyl group-containing polyester resin is less than the above range, the content of the second carboxyl group-containing polyester resin having excellent mechanical properties is small, so that salt water spray resistance is lowered and pinhole The generation thickness becomes thin and the arrival efficiency may decrease. On the other hand, when the content of the second carboxyl group-containing polyester resin with respect to the first carboxyl group-containing polyester resin exceeds the above-described range, the content of the first carboxyl group resin having excellent weather resistance is small, so that the gloss retention rate is lowered or the color difference value is increased. Weatherability may be reduced.

curing agent

The powder coating composition according to the present invention includes a hydroxyalkyl amide-based curing agent as a curing agent.

The curing agent may have a hydroxyl value of 500 to 800 mgKOH/g, for example, 600 to 700 mgKOH/g. When the hydroxyl value of the curing agent is out of the above-mentioned range, the curing speed may be affected and the external appearance and weather resistance may be deteriorated.

The hydrogen equivalent weight (HEW) of the curing agent may be 60 to 110 g/eq, for example, 75 to 95 g/eq. When the hydrogen equivalent of the curing agent is less than the above range, pinholes may occur, and when it exceeds the above range, it may be difficult to implement a matte effect.

The curing agent may be included in an amount of 0.5 to 15% by weight, for example, 1 to 5% by weight based on the total weight of the powder coating composition. When the content of the curing agent is within the above range, long-term weatherability, adhesion, leveling, and the like of the coating film may be improved.

additive

The powder coating composition of the present invention may optionally further include additives commonly used in the powder coating field within a range that does not impair the inherent characteristics of the composition. Non-limiting examples of the additives usable in the present invention include a leveling agent, a matting agent, a pinhole inhibitor, and an ultraviolet absorber, which may be used alone or in combination of two or more.

The leveling agent is for leveling the coating composition so that it is coated flatly and smoothly, thereby enhancing the adhesion within the composition and improving the appearance properties of the coating film. The leveling agent may be at least one selected from acrylic, silicone, polyester, and amine leveling agents, and may be, for example, an acrylic leveling agent. Non-limiting examples of the acrylic leveling agent include polyacrylate polymers, polymethacrylate polymers, polyethylacrylates, polybutylacrylates, poly-2-ethylhexyl acrylate, and the like.

The matting agent serves to lose or reduce the gloss of the coating film. Non-limiting examples of the matting agent include polyolefin wax, mercaptobenzothiazole, acrylic acid, and acrylic acid copolymer resin, which may be used alone or in combination of two or more. When two or more of the matting agents are mixed and used, an excellent glossiness can be realized. For example, the matting agent may be a mixture of polyethylene wax and acrylic acid or a mixture of mercaptobenzothiazole and acrylic acid. The mercaptobenzothiazole may be a metal salt-containing mercaptobenzothiazole.

The pinhole inhibitor may release volatile substances from the coating film during the curing process, thereby preventing the occurrence of pinholes in the coating film and improving appearance characteristics. Non-limiting examples of the pinhole inhibitor include amide-based (eg, ceraflour 960, BYK Co.), polypropylene-based, and stearic acid-based pinhole inhibitors. For example, the pinhole inhibitor may be benzoin or a mixture of benzoin and an amide-based pinhole inhibitor.

UV absorbers can improve external durability after painting. Non-limiting examples of UV absorbers include benzotriazole-based, benzylidenehydant-based, benzophenone-based, benzoguanine-based, and the like, which may be used alone or in combination of two or more.

The additives may be appropriately added within a content range known in the art, for example, 0.01 to 10% by weight based on the total weight of the powder coating composition.

pigment

The powder coating composition of the present invention may further include pigments commonly used in the paint field, such as extender pigments, colored pigments, or mixtures thereof, within a range that does not impair the inherent properties of the composition.

The extender pigment fills pores in the coating film, supplements the formation of the coating film, and serves to impart salinity or mechanical properties to the coating film. Therefore, when an extender pigment is included, a good coating film appearance can be obtained and hardness, impact resistance and rust prevention can be improved.

As the extender pigment, those commonly used in powder coating compositions may be used without limitation, and non-limiting examples include barium sulfate, calcium carbonate, clay, talc, magnesium silicate, kaolin, mica, silica, aluminum silicate, and aluminum hydroxide. side, etc. The above components may be used alone or in combination of two or more.

For example, barium sulfate having a particle size of 10 μm or more, for example, 10 to 20 μm may be used as the extender pigment. If the particle size of the extender pigment is less than 10 μm, the matting effect and pinhole covering power may be reduced, and if it exceeds 20 μm, smoothness may be deteriorated, excessive staining may occur in the coating film, or transfer efficiency may be reduced.

The extender pigment may be included in an amount of 15 to 45% by weight, for example, 18 to 40% by weight, based on the total weight of the powder coating composition. When the content of the extender pigment is within the above range, mechanical properties, impact resistance, adhesion, and the like of the coating film may be improved.

Colored pigments may be used to express a desired color in a paint or to increase the strength or gloss of a paint film. As such colored pigments, organic pigments, inorganic pigments, metallic pigments, aluminum-paste, pearls, etc. commonly used in paints may be used without limitation, and these may be used alone or in combination of two or more. can Non-limiting examples of usable color pigments include azo-based, phthalocyanine-based, iron oxide-based, cobalt-based, carbonate-based, sulfate-based, silicate-based, and chromate-based pigments, such as titanium dioxide, zinc oxide, bismuth banana date, cyanine green, carbon black, red iron oxide, iron oxide sulfur, navy blue, cyanine blue, and mixtures of two or more thereof. Inorganic pigments such as titanium dioxide and zinc oxide described above may be colored white when used alone. As another example, the inorganic pigment may be mixed with other colored pigments to match a specific color.

The color pigment may be included in an amount of 0.1 to 20% by weight, for example, 3.5 to 10% by weight, based on the total weight of the powder coating composition. When the content of the pigment is in the above range, the color expression of the coating film is excellent, and the mechanical properties and impact resistance of the coating film may be improved.

The powder coating composition according to the present invention can be prepared by a method known in the art, and for example, it can be prepared through processes such as basis weight of raw materials, dry preliminary mixing, dispersion and coarse grinding, grinding and classification. For example, a raw material mixture containing a carboxyl group-containing polyester resin, a curing agent, a matting agent, a pigment, and other additives may be introduced into a container mixer, uniformly mixed, melt-mixed, and then pulverized. there is. For example, the raw material mixture is melt-dispersed at 70 to 130 ° C. by a melt kneading device such as a kneader or an extruder to prepare chips with a predetermined thickness (eg, 1 to 5 mm). Afterwards, the prepared chips may be pulverized into a range of 40 to 80 μm using a pulverizing device such as a high-speed mixer, and then classified to prepare a powder coating composition.

The classification process is not particularly limited, and may be filtered with, for example, 80 to 200 mesh. Accordingly, a powder coating having an average particle size in the range of 20 to 80 μm can be obtained. The average particle diameter of the powder is not particularly limited, but when the above range is satisfied, painting workability and appearance characteristics of the coating film may be improved.

In order to improve the fluidity of the powder coating, the surface of the powder coating particles according to the present invention may be coated with fine powder such as polyethylene-based wax or fumed silica. As a method for performing such a treatment, a pulverization and mixing method in which fine powder is added while mixing during pulverization or a dry mixing method using a Henschel mixer or the like can be used.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are only for facilitating the understanding of the present invention, and the scope of the present invention is not limited to the examples in any sense.

[Example 1-7]

According to the composition shown in Table 1 below, each component was put into a mixing tank and premixed, and then melted and dispersed at 100 ° C. in a disperser to prepare chips. The prepared chips were pulverized with a high-speed mixer to prepare powder coating compositions of Examples 1-7 having an average particle size of 25 to 55 μm. The usage unit of each component in Table 1 below is % by weight.

[Comparative Example 1-8]

Powder coating compositions of Comparative Examples 1-8 were prepared in the same manner as in Examples, except for the compositions described in Table 2 below. The usage unit of each component in Table 2 below is % by weight.

Resin 1-1: carboxyl group-containing polyester (AV: 30 mgKOH/g, Mw: 9,000 g/mol, melt viscosity (200°C): 4,000 mPa.s, main monomer: isophthalic acid (IPA)/neopentyl glycol (NPG) ))

Resin 1-2: Carboxyl group-containing polyester (AV: 33 mgKOH/g, Mw: 11,000 g/mol, melt viscosity (200°C): 3,000 mPa.s, main monomer: isophthalic acid (IPA), adipic acid (AA) )/neopentylglycol (NPG))

Resin 1-3: carboxyl group-containing polyester (AV: 50 mgKOH/g, Mw: 13,000 g/mol, melt viscosity (200°C): 3,000 mPa.s, main monomer: isophthalic acid (IPA), trimellitic anhydride ( TMA) / ethylene glycol (EG), diethylene glycol (DEG), neopentyl glycol (NPG))

Resin 2-1: carboxyl group-containing polyester (AV: 33 mgKOH/g, Mw: 10,000 g/mol, melt viscosity (200°C): 3,200 mPa.s, main monomers: terephthalic acid (TPA), isophthalic acid (IPA), Adipic acid (AA)/neopentylglycol (NPG))

Resin 2-2: Carboxyl group-containing polyester (AV: 31 mgKOH/g, Mw: 12,000 g/mol, melt viscosity (200°C): 5,200 mPa.s, main monomers: terephthalic acid (TPA), isophthalic acid (IPA), Cyclohexanedicarboxylic acid (1,4-CHDA)/neopentylglycol (NPG))

Resin 2-3: carboxyl group-containing polyester (AV: 30 mgKOH/g, Mw: 11,000 g/mol, melt viscosity (200°C): 4,000 mPa.s, main monomer: adipic acid (AA), sebacic acid) acid), terephthalic acid (TPA)/neopentyl glycol (NPG))

Curing agent 1: hydroxyalkyl amide (HEW 82-86 g/eq, OHv 620-700 mgKOH/g, EMS, primid XL-552)

Curing agent 2: hydroxyalkyl amide (HEW 92-95 g/eq, OHv 550-650 mgKOH/g, EMS, QM-1260)

Curing agent 3: glycidyl ester (EEW 141-154 g/eq, Huntsman)

Curing agent 4: triglycidyl isocyanurate (HEW 105 g/eq)

Additive 1: Leveling agent (Estron)

Additive 2: Matting agent (Paraffin wax, EMS)

Additive 3: Degassing agent (Benzoin, Miwon Special Chemical)

Additive 4: Dispersing additive (Micronized modified amide wax, BYK)

Additive 5: light stabilizer (Hindered Amine, BASF)

Additive 6: UV Absorber (BASF)

Additive 7: Post additive (Fumed silica, KCC)

Additive 8: Post additive (Polyethylene wax, Lubrizol)

White pigment: TIO ₂

Black pigment: Carbon black (Columbian)

Blue pigment: Cyanine blue (BASF)

Extender pigment 1: Barium sulfate (Particle size 10-13 ㎛)

Extender pigment 2: Barium sulfate (Particle size 5-7 ㎛)

Indigenous pigment 3: Barium sulfate (Particle size 1-2 ㎛)

[Experimental Example-Evaluation of physical properties]

The physical properties of the powder coating compositions prepared in each Example and Comparative Example were measured as follows, and the results are shown in Tables 3 and 4 below.

specimen preparation

The powder coating composition according to each Example and Comparative Example was electrostatically sprayed on 75 mm × 150 mm × 0.4 mm aluminum (chromate treatment), and then cured to prepare a specimen having a dry film thickness of 70 μm.

Appearance (Leveling)

The appearance state of each specimen was visually observed to confirm pinholes and cratering.

Polish

Using a gloss meter (BYK Gardner), the gloss of each specimen was measured under a 60 degree light source.

salt spray resistance

After the salt spray test was performed for 1,000 hours on each specimen, the peel width on one side was measured.

Thickness of film with pinhole occurrence

The powder coating composition according to each Example and Comparative Example was electrostatically sprayed on aluminum (chromate treatment) having a size of 75 mm × 150 mm × 0.4 mm, and then the pinhole generation limit coating thickness was measured under overcuring conditions (220 ° C) did

weatherability

Each specimen was put into an accelerated weathering test apparatus maintained in accordance with ISO 16474-2 standards, and after 1,000 hours, the gloss retention rate and color difference of the coating film were confirmed.

arrival efficiency

After coating 100 g of the powder coating composition according to each Example and Comparative Example on 40 cm Х 50 cm aluminum (chromate treatment) (coating voltage: 60 KV, discharge pressure: 1 BAR. Distance between specimen and paint gun: 15 cm), and the weight of the coating film was checked to evaluate the transfer efficiency (film weight/100g, %).

As shown in Tables 3 and 4, the coating films formed of the powder coating compositions of Examples according to the present invention were generally superior in physical properties compared to the coating films formed of the powder coating compositions of Comparative Examples. Specifically, the coating films formed from the powder coating compositions of Examples according to the present invention showed excellent physical properties in all measurement items such as appearance, salt spray resistance, pinhole generation thickness, weather resistance, and coating efficiency.

On the other hand, in the case of the powder coating compositions of Comparative Example 1 and Comparative Example 2 using extender pigments having a particle size outside the range of the present invention, the appearance (leveling property) was deteriorated, the matte effect was less, and the gloss retention rate was poor. appear.

In addition, in the case of Comparative Example 3 using only one type of the second carboxyl group-containing polyester resin, the pinhole generation thickness was thin, and the salt spray resistance and weather resistance were poor. On the other hand, in the case of Comparative Example 4 using only one type of first carboxyl group-containing polyester resin, pinholes occurred and the appearance deteriorated, it was difficult to implement the quenching effect, and the salt spray resistance and the transfer efficiency decreased. In addition, in the case of Comparative Example 5 in which the two first polyesters were mixed, pinholes occurred and the appearance deteriorated, it was difficult to implement the quenching effect, and the salt spray resistance and the transfer efficiency decreased. On the other hand, in the case of Comparative Example 6 in which the two second polyesters were mixed, the pinhole generation thickness was thinner and the weather resistance was poor.

On the other hand, in Comparative Examples 7 and 8 in which a different curing agent was applied instead of the hydroxyalkyl amide curing agent according to the present invention, the pinhole generation thickness was reduced, and the salt spray resistance and weather resistance were deteriorated.

Claims (5)

A powder coating composition comprising a first carboxyl group-containing polyester resin, a second carboxyl group-containing polyester resin, a hydroxyalkyl amide-based curing agent, and an extender pigment,
The first carboxyl group-containing polyester resin is prepared by polymerizing at least one of monomers and polymers having a hydroxyl group as a terminal functional group and a polyfunctional acid containing isophthalic acid and not containing terephthalic acid,
The weight average molecular weight (Mw) of the first carboxyl group-containing polyester resin is 8,500 to 11,000 g / mol, and the melt viscosity (200 ℃, Brookfield viscometer) is 3,000 to 5,000 mPa.s,
The second carboxyl group-containing polyester resin is prepared by polymerizing at least one of a monomer and a polymer having a hydroxyl group as a terminal functional group and a polyfunctional acid including terephthalic acid,
The weight average molecular weight (Mw) of the second carboxyl group-containing polyester resin is 9,000 to 15,000 g / mol, and the melt viscosity (200 ℃, Brookfield viscometer) is 3,000 to 6,000 mPa.s,
The compounding ratio of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin is 1: a weight ratio of 0.5 to 2,
The curing agent has a hydroxyl value of 500 to 800 mgKOH / g, and a hydrogen equivalent weight (HEW) of 60 to 110 g / eq,
The extender pigment has a particle size of 10 μm or more. delete delete The powder coating composition according to claim 1, wherein the extender pigment is barium sulfate. According to claim 1, based on the total weight of the powder coating composition, the first carboxyl group-containing polyester resin 20 to 40% by weight, the second carboxyl group-containing polyester resin 20 to 40% by weight, the hydroxyalkyl amide-based curing agent A powder coating composition comprising 0.5 to 15% by weight and 15 to 45% by weight of the extender pigment.