KR102261877B1 - Powder Coating Composition - Google Patents

Abstract

The present invention relates to a powder coating composition having excellent heat resistance and boiling water resistance.

Description

Powder Coating Composition

The present invention relates to a powder coating composition having excellent heat resistance and boiling water resistance.

Epoxy resin powder coating has a high glass transition temperature, so it not only has excellent thermal properties, but also excellent adhesive strength, chemical resistance, mechanical strength and electrical insulation, preventing corrosion and improving durability of steel pipes or pipelines buried underground or under the sea. is used for the purpose of However, as the burial environment of the pipe becomes increasingly harsh, the conventional epoxy resin powder coating having a glass transition temperature of about 100 ° C. could not obtain a sufficient effect to protect the pipe from corrosion. Accordingly, improvement of thermal, chemical, and physical properties of the epoxy coating is required, and studies on coatings that satisfy these properties are continuing.

For example, US Patent No. 9,617,413 describes a powder coating composition using a divinylarene dioxide resin and a dicyandiamide curing agent. In addition, Japanese Patent No. 6,342,696 describes a powder coating composition comprising a trifunctional or higher epoxy resin, and at least one curing agent selected from a guanidine compound and an imidazole compound. However, even in the case of the powder coating composition, there is a problem in that the boiling water resistance and adhesion properties required in a high temperature environment are not sufficient.

The present invention provides a powder coating composition having excellent heat resistance and boiling water resistance.

The present invention provides a powder coating composition comprising at least one of a urethane-modified epoxy resin and a bisphenol A-type epoxy resin, a curing agent, and an extender pigment.

The powder coating composition according to the present invention has excellent heat resistance, boiling water resistance, and cathode peeling resistance, and can reduce the bubble generation rate, thereby improving adhesion and appearance characteristics due to bubbles generated during coating film formation. In addition, the powder coating composition of the present invention has excellent impact resistance and flex resistance, while ensuring constant workability and a glass transition temperature of 120° C. or higher, so that it can be effectively protected when applied to a steel pipe.

epoxy resin

In the powder coating composition according to the present invention, the epoxy resin includes at least one of a urethane-modified epoxy resin and a bisphenol-A epoxy resin as a main resin.

Non-limiting examples of the urethane-modified epoxy resin that can be used include a urethane-modified novolac epoxy resin, a urethane-modified bisphenol epoxy resin, a urethane-modified cresol epoxy resin, or a mixture thereof. For example, the urethane-modified epoxy resin may include a urethane-modified novolac epoxy resin.

The urethane-modified epoxy resin may be an epoxy resin obtained from a reaction between a urethane prepolymer and an epoxy resin. The urethane prepolymer may be prepared by reacting a polyol with an isocyanate compound.

The type of the polyol is not particularly limited, but for example, one selected from the group consisting of polyester polyol, polyoxypropylene glycol, polybutadiene, bisphenol A, diethylene glycol, dipropylene glycol, polycaprolactone and polycaprolactam. more can be used. The type of the isocyanate compound is not particularly limited, but for example, 2,4-toluene diisocyanate, 4,4-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, and 4 One or more selected from the group consisting of ,4-biphenyl diisocyanate may be used.

The isocyanate modification rate of the urethane-modified epoxy resin is not particularly limited, but may be, for example, 10% to 40%, or 15% to 30% as another example.

The epoxy equivalent weight (EEW) and softening point of the urethane-modified epoxy resin are not particularly limited, but the epoxy equivalent weight (EEW) may be 250 to 700 g/eq, for example 400 to 650 g/eq, and the softening point is 100 ℃ to 130 °C, for example 105 °C to 120 °C. When the urethane-modified epoxy resin has an epoxy equivalent weight and a softening point in the above ranges, the dispersibility of the coating film may be excellent.

The viscosity and glass transition temperature of the urethane-modified epoxy resin are not particularly limited, but the viscosity (175° C., ICI viscometer) may be 1,000 to 3,500 cps, for example 1,500 to 3,000 cps, and the glass transition temperature is 50 to 65° C. , for example, may be 52 to 60 °C. When the urethane-modified epoxy resin has a viscosity and a glass transition temperature in the above-described ranges, chemical resistance may be improved.

Bisphenol-A epoxy resin is an epoxy resin obtained from the reaction of bisphenol A (BPA) and epichlorohydrin. As the bisphenol A-type epoxy resin, a conventional epoxy resin known in the art may be used without particular limitation.

The epoxy equivalent weight (EEW) and softening point of the bisphenol A-type epoxy resin are not particularly limited, but the epoxy equivalent weight may be 700 to 1,500 g/eq, for example, 1,000 to 1,300 g/eq, and the softening point may be 100 to 130 ° C. have. When the bisphenol-A epoxy resin has an epoxy equivalent weight and a softening point in the above-described ranges, storage stability may be improved.

The viscosity and glass transition temperature of the bisphenol A-type epoxy resin are not particularly limited, but the viscosity (200° C., ICI viscometer) may be 1,000 to 5,000 cps, for example, 1,500 to 4,500 cps, and the glass transition temperature is 50 to 80° C. , for example, may be 60 to 70 °C. When the bisphenol-A epoxy resin has a viscosity and a glass transition temperature in the above-described ranges, the appearance characteristics and flexibility of the coating film of the composition are improved, thereby minimizing the occurrence of cracks in the coating film.

The powder coating composition of the present invention may include the urethane-modified epoxy resin and bisphenol-A epoxy resin as an epoxy resin. The mixing ratio of the urethane-modified epoxy resin and the bisphenol A-type epoxy resin is not particularly limited, but may be in a weight ratio of 1 to 5:1, for example, 1 to 3:1. When the two types of epoxy resins are mixed and used in the above-mentioned range, heat resistance and boiling water resistance of the powder coating composition can be improved.

The epoxy resin may be in an amount of 45 to 90% by weight, for example, 60 to 80% by weight, or 65 to 75% by weight, based on the total weight of the powder coating composition. If the content of the epoxy resin is less than 45% by weight, a heat resistance problem may occur due to a decrease in the glass transition temperature of the coating film, and if it exceeds 90% by weight, mechanical properties may be poor.

hardener

The powder coating composition of the present invention may include at least one of an amine-based curing agent and a phenol-based curing agent as a curing agent.

The amine-based curing agent is not particularly limited as long as it is an amine-based curing agent capable of curing reaction with an epoxy resin. For example, there are an aliphatic amine-based curing agent, an alicyclic amine-based curing agent, an aromatic amine-based curing agent, and the like, and these may be used alone or in combination of two or more.

The amine value of the amine-based curing agent is not particularly limited, and may be, for example, 15 to 30 mgKOH/g. When the amine value of the amine-based curing agent satisfies the above-described range, excellent corrosion resistance may be secured.

As the phenol-based curing agent, those commonly used in the field of powder coatings may be used without limitation. Non-limiting examples of the phenol-based curing agent that can be used include a resol-type phenol-based resin, a novolak-type phenol-based resin, and a polyhydroxystyrene resin. Examples of the resol-type phenol-based resin include aniline-modified resol resin, melamine-modified resol resin, and the like. Examples of the novolak-type phenolic resin include phenol novolak resin, cresol novolak resin, tert-butylphenol novolak resin, nonylphenol novolak resin, naphthol novolac resin, dicyclopentadiene-modified phenol resin, terpene-modified phenol. resins, triphenol-methane type resins, and naphthol aralkyl resins. Examples of the polyhydroxystyrene resin include poly(p-hydroxystyrene) and the like.

The hydroxyl equivalent of the phenol-based curing agent is not particularly limited, and may be, for example, 200 to 300 g/eq.

The curing agent may be included in an amount of 0.1 to 5% by weight, for example, 0.1 to 3% by weight based on the total weight of the powder coating composition. When the content of the curing agent is within the above-mentioned range, the degree of curing of the coating film is high, so that the physical properties of the coating film may be improved.

extender pigment

The powder coating composition of the present invention may further include an extender pigment commonly used in the powder coating field within a range that does not impair the intrinsic properties of the composition. The extender pigment can further improve the high temperature/high pressure chemical resistance of the paint.

Non-limiting examples of extender pigments that can be used include calcium carbonate, barium sulfate, feldspar, kaolin, alumina hydroxide, magnesium hydroxide, titanium dioxide, magnesium carbonate, alumina, mica, montmorolonite, olastonite, talc, aluminum nitride, There are silicon nitride, boron nitride, aluminum oxide, aluminum nitride, and the like, and these may be used alone or in combination of two or more.

The extender pigment may include at least one extender pigment selected from the group of inorganic pigments including calcium carbonate, barium sulfate, feldspar and kaolin.

For example, the extender pigment may include barium sulfate and feldspar. The mixing ratio of barium sulfate and feldspar is not particularly limited, but may be 1:0.5 to 5, for example, 1:0.8 to 2.5 by weight. When the extender pigment contains barium sulfate and feldspar in the above-mentioned mixing ratio range, excellent corrosion resistance can be secured by improving boiling water resistance and long-term cathodic peeling resistance of the coating film.

The shape of the extender may be spherical or amorphous, but is not particularly limited thereto. In addition, the average particle diameter of the extender is not particularly limited, and may be, for example, 1 to 20 μm.

The amount of the extender pigment may be 5 to 45% by weight, in another example 15 to 40% by weight, based on the total weight of the powder coating composition. When the content of the extender pigment is within the aforementioned range, mechanical properties, impact resistance, adhesion, and the like of the coating film may be improved.

colored pigment

The powder coating composition of the present invention may further include a colored pigment commonly used in the powder coating field within a range that does not impair the inherent properties of the composition.

Colored pigments can be mixed with an epoxy resin to express a desired color (colored) in a powder coating or to increase the strength or gloss of a coating film. As these colored pigments, organic pigments, inorganic pigments, metallic pigments, aluminum-paste, pearls, etc. commonly used in powder coatings may be used without limitation, and these may be used alone or in combination of two or more. can do. Non-limiting examples of usable colored pigments include azo-based, phthalocyanine-based, iron oxide-based, cobalt-based, carbonate-based, sulfate-based, silicate-based, chromate-based pigments, and the like, for example, titanium dioxide, zinc oxide, bismuth bar or the like. date, cyanine green, carbon black, iron oxide, iron sulfur oxide, navy blue, cyanine blue, and mixtures of two or more thereof.

In the present invention, the content of the colored pigment is not particularly limited, and may be, for example, 0.1 to 15% by weight, for example, 0.1 to 10% by weight, based on the total weight of the powder coating composition. When the content of the colored pigment is within the above-mentioned range, the color expression of the coating film to which the powder coating composition of the present invention is applied may be excellent, and the hiding property and mechanical properties of the coating film may be improved.

catalyst

The powder coating composition of the present invention may further include a catalyst commonly used in the powder coating field within a range that does not impair the intrinsic properties of the composition.

The catalyst is a material that promotes the reaction between the main resin, the epoxy resin, and the curing agent, for example, there are imidazole-based catalysts, phosphonium-based catalysts, amine-based catalysts, metal-based catalysts, etc., these are used alone or two or more can be mixed and used.

Non-limiting examples of the imidazole-based catalyst include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-decylimidazole, 2-hexylimidazole, and 2-isopropyl imida. Sol, 2-undecylimidazole, 2-heptanedecylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl -2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1 -Cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecyl-imidazole trimellitate, 1-cyanoethyl-2 -Phenylimidazole trimellitate, 2,4-diamino-6-(2'-methylimidazole-(1')-ethyl-s-triazine, 2-pecyl-4,5-dihydroxy Methylimidazole, 2-pecyl-4-methyl-5-hydroxymethylimidazole, 2-pecyl-4-benzyl-5-hydroxymethylimidazole, 4,4'-methylene-bis- (2 -Ethyl-5-methylimidazole), 2-aminoethyl-2-methyl imidazole, 1-cyanoethyl-2-phenyl-4,5-di (cyanoethoxymethyl) imidazole, 1-dode sil-2-methyl-3-benzylimidazolinium chloride, imidazole-containing polyamide, and the like.

Non-limiting examples of the phosphonium-based catalyst include benzyltriphenyl phosphonium chloride, butyltriphenyl phosphonium chloride, butyltriphenyl phosphonium bromide, ethyltriphenyl phosphonium acetate, ethyltriphenyl phosphonium bromide, ethyltriphenyl phosphonium phonium iodide, tetraphenyl phosphonium bromide, tetraphenyl phosphonium chloride or tetraphenyl phosphonium iodide.

Non-limiting examples of the amine-based catalyst include triethylamine, triethylenediamine, tetramethyl-1,3-butanediamine, ethylmorpholine, diazabicycloundecene, diazabicyclononene, and the like.

Examples of the metal-based catalyst include organometallic complexes or organometallic salts such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Examples of the organometallic complex include organocobalt complexes such as cobalt(II) acetylacetonate and cobalt(III) acetylacetonate, organocopper complexes such as copper(II) acetylacetonate, zinc(II) acetylacetonate, and the like. an organic zinc complex of , an organic iron complex such as iron (III) acetylacetonate, an organic nickel complex such as nickel (II) acetylacetonate, and an organic manganese complex such as manganese (II) acetylacetonate. not limited Examples of the organometallic salt include, but are not limited to, zinc octylate, tin octylate, zinc naphthenate, cobalt naphthenate, tin stearate, zinc stearate, and the like.

In the present invention, the content of the catalyst may be appropriately adjusted according to the reactivity of the epoxy resin and the curing agent. For example, the content of the catalyst may be 0.01 to 2% by weight, for example 0.01 to 1% by weight, based on the total weight of the powder coating composition. If the content of the catalyst is out of the above range, mechanical properties of the coating film may be deteriorated.

additive

The powder coating composition of the present invention may further include additives commonly used in the powder coating field within a range that does not impair the intrinsic properties of the composition.

Non-limiting examples of additives usable in the present invention include leveling agents, pinhole inhibitors, dispersants, adhesion promoters, fluidity additives, flowability enhancers, low-stressing agents, anti-cratering agents, coupling agents, gloss control agents, flame retardants, matting agents , an auxiliary curing agent, and a light absorber, and these may be used alone or in combination of two or more.

The leveling agent is to improve the appearance characteristics of the coating film while enhancing adhesion in the composition by leveling the coating composition so that it is coated evenly and smoothly. For example, there are acrylic, silicone, polyester, amine-based leveling agents, and the like, but is not particularly limited thereto.

The pinhole inhibitor may cause volatile substances to be released from the coating film during the curing process, thereby preventing pinholes in the coating film and improving the appearance characteristics. Non-limiting examples of pinhole inhibitors include amide-based agents (eg, ceraflour 960 (BYK)), 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.

As the dispersant, a conventional dispersant known in the art may be used without limitation, and for example, a polyacrylic dispersant that is adsorbed on the surface of a colored pigment to maximize a degassing effect may be used.

The adhesion promoter is a material for enhancing the adhesion of the coating film, and a silane-based adhesion promoter or the like may be used. Non-limiting examples of the adhesion promoter include mercaptoalkylakoxysilane, gamma glidoxypropyltrimethoxysilane, and the like, for example, the adhesion promoter is a mercaptoalkylalkoxysilane having a molecular weight of 150 to 300 g/mol. can be

Fluidity additives are used to maximize the fluidity effect, and long-term fluidity can be secured while improving the adhesion of the paint. As the fluidity additive, waxes, silica, and the like may be used. Non-limiting examples of the rheological additive that can be used include paraffin wax, natural wax (eg, carnauba wax, etc.), synthetic wax (eg, polyethylene wax, etc.), silica, etc., which are used alone or in combination of two or more types. and can be used In addition, waxes may be mixed with silica. The fluidity additive may be used as a post-addition component added after the chips are made.

The flowability improving agent is used to lower the surface tension of the coating film and implement a flexible appearance, and a conventional one known in the art may be used. Non-limiting examples include acrylic or silicone-based flowability improvers.

Such additives may be appropriately added within a content range known in the art, for example, 0.01 to 15% by weight, for example, 0.1 to 5% by weight based on the total weight of the powder coating composition. When the content of the additive is within the above-described range, the appearance and hardness of the coating film may be improved.

The powder coating composition according to the present invention may be prepared by a method known in the art, and for example, may be prepared through processes such as raw material basis weight, dry pre-mixing, dispersion and coarse pulverization, pulverization and classification, and the like.

For example, a raw material mixture containing an epoxy resin, a curing agent, an extender pigment, a colored pigment, a catalyst, and optionally an additive, etc. is put into a container mixer and uniformly mixed, and the mixed composition is melted and mixed and then pulverized. can be For example, the raw material mixture is melt-dispersed at 85 to 120° C. by a melt-kneading device such as a kneader or an extruder to produce chips with a predetermined thickness (eg, 1 to 5 mm). Thereafter, the manufactured chips are pulverized to a range of 30 to 100 μm using a grinding device such as a high-speed mixer, and then classified to prepare a powder coating composition.

The classification process is not particularly limited, and, for example, may be filtered with 80 to 120 mesh. Accordingly, it is possible to obtain a powder coating having an average particle size in the range of 30 to 100 μm. The average particle diameter of the powder is not particularly limited, but when it satisfies the above-described range, coating 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 a fine powder such as silica. As a method of performing such a treatment, a pulverizing mixing method in which fine powder is added while mixing, 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 provided to help the understanding of the present invention, and the scope of the present invention is not limited to the examples in any sense.

[Examples 1-12 and Comparative Examples 1-3]

After mixing each component according to the composition shown in Tables 1 to 3 below, it was uniformly mixed using a container mixer (CM6). The uniformly mixed composition was melt-mixed at 85 to 120° C. through a kneader (PLK-46, Booth Co.), then pulverized using a pulverizer, and classified into an average particle size of 30 to 100 microns in Examples 1-12 And the powder coating composition of Comparative Examples 1-3 was prepared. The units used in Tables 1 to 3 below are weight %.

Epoxy resin 1: Urethane-modified epoxy resin (epoxy equivalent 465 g/eq, softening point 115 ° C, viscosity (175 ° C, ICI viscometer) 2,250 cps, glass transition temperature 57 ° C, isocyanate modification rate: 25% )

Epoxy resin 2: Urethane-modified epoxy resin (epoxy equivalent 400 g/eq, softening point 105 ° C, viscosity (175 ° C, ICI viscometer) 1,500 cps, glass transition temperature 52 ° C, isocyanate modification rate 15%)

Epoxy resin 3: Urethane-modified epoxy resin (epoxy equivalent 600 g/eq, softening point 120 ° C, viscosity (175 ° C, ICI viscometer) 3,000 cps, glass transition temperature 60 ° C, isocyanate modification rate 30%)

Epoxy resin 4: Urethane-modified epoxy resin (epoxy equivalent 900 g/eq, softening point 90 ℃, viscosity (175 ℃, ICI viscometer) 1,000 cps, glass transition temperature 45 ℃)

Epoxy resin 5: Bisphenol-A epoxy resin (epoxy equivalent 1,150 g/eq, softening point 120 ℃, viscosity (200 ℃, ICI viscometer) 2,300 cps, glass transition temperature 65 ℃)

Epoxy resin 6: Bisphenol A type epoxy resin (epoxy equivalent 1,000 g/eq, softening point 115 ℃, viscosity (200 ℃, ICI viscometer) 1,500 cps, glass transition temperature 60 ℃)

Epoxy resin 7: Bisphenol-A epoxy resin (epoxy equivalent 1,300 g/eq, softening point 125 ℃, viscosity (200 ℃, ICI viscometer) 4,500 cps, glass transition temperature 70 ℃)

Epoxy resin 8: Bisphenol A type epoxy resin (epoxy equivalent 650 g/eq, softening point 130 ℃, viscosity (200 ℃, ICI viscometer) 3,000 cps, glass transition temperature 45 ℃)

Hardener: dicyandiamide (dicyanex 1400F, Air Products, amine value 21 mgKOH/g)

extender pigment 1: barium sulfate

Extender Pigment 2: Feldspar

Colored Pigments: Iron Oxide

Catalyst: imidazole-based catalyst (Curesol, Shikoku)

Additive 1: Acrylic polymer (Reciflow P-67, Estron Chemical, leveling agent)

Additive 2: Trisamino (adhesion promoter)

Additive 3: Amide (Auxiliary Hardener)

Additive 4: Liquid Silane (Adhesive Enhancer)

[Experimental Example - Evaluation of Physical Properties]

Specimen preparation

The powder coating compositions prepared according to Examples 1-12 and Comparative Examples 1-3 were electrostatically sprayed on a specimen preheated at 230° C. for 1 hour, and coated to a thickness of 400 μm. Thereafter, heat was applied at 230° C. for 5 minutes, followed by immersion cooling with water to prepare a coating film, and the physical properties were measured as follows, and the results are shown in Tables 4 to 6 below.

coagulation time

The solidification time was measured at a temperature of 204 ° C. through a geltime tester.

glass transition temperature

It was measured using a differential scanning calorimeter (Differential Scanning Calorimeter).

flexibility

According to the CSA Z245.20 standard, the angle and temperature of the specimen are set to 3° (5°C), 3.75° (10°C), and 5.5° (25°C). Cracking was measured.

impact

According to the CSA Z245.20 standard, the temperature of the specimen was set to 25℃, and after applying an impact of 4 J/g, damage due to the impact was checked through a holiday tester.

bubble generation rate

According to the CSA Z245.20 standard, after forcibly separating the coated object and the coating film from the specimen, the adhesive part was observed with a stereo microscope (SZX16).

boiling water resistance

The specimen was immersed in a constant temperature water bath at 75° C. and taken out after 28 days to evaluate the adhesion. For adhesion, after cooling the sample taken out to room temperature for 1 hour, scrape a 15 mm wide and 30 mm rectangular shape with a knife until the base is exposed, and press the knife between the coating film and the base around the exposed part of the base with a lever. After measuring the adhesion according to the principle of , the peeling area was evaluated. The evaluation criteria are as follows.

Grade 1: No peeling off of the coating

Grade 2: 50% peeling

Grade 3: 75% peel

Grade 4: 100% peeling

Grade 5: Failure to maintain film adhesion

cathodic peel resistance

After drilling a hole with a diameter of 3 mm in the center of the specimen, a 3% concentration of brine was applied to the surface of the coating film to abut the surface, and after stopping evaporation using a container, a 1.5 V voltage was applied to the substrate at 65 ° C. for 30 days, and from the hole The peeling distance of was measured twice. If the peeling distance was 20 mm or less, it was evaluated as pass, and if it exceeded 20 mm, it was evaluated as fail.

As shown in Tables 4 to 6 above, the coating film formed of the powder coating composition of Examples 1-12 according to the present invention was generally superior in physical properties to the coating film formed of the powder coating composition of Comparative Examples 1-3. In particular, it was confirmed that the coating film formed of the powder coating composition of Examples 1-12 had excellent boiling water resistance and cathode peeling resistance, and improved the bubble generation rate to ensure excellent adhesion.

Claims (7)

It contains a urethane-modified epoxy resin, a bisphenol A-type epoxy resin, a curing agent, and two or more kinds of extender pigments,
The mixing ratio of the urethane-modified epoxy resin and the bisphenol A-type epoxy resin is 1 to 3 : 1 by weight,
The epoxy equivalent of the urethane-modified epoxy resin is 400 to 650 g / eq, the softening point is 105 to 120 ℃, the viscosity (175 ℃, ICI viscometer) is 1,500 to 3,000 cps, the glass transition temperature is 52 to 60 ℃,
The bisphenol A-type epoxy resin has an epoxy equivalent of 1,000 to 1,300 g/eq, a softening point of 100 to 130 ℃, a viscosity (200 ℃, ICI viscometer) of 1,500 to 4,500 cps, and a glass transition temperature of 60 to 70 ℃ powder paint composition. delete delete delete The powder coating composition of claim 1, wherein the extender pigment comprises at least one selected from the group consisting of calcium carbonate, barium sulfate, feldspar and kaolin. The powder coating composition according to claim 1, wherein the extender pigment includes barium sulfate and feldspar, and the mixing ratio of barium sulfate and feldspar is 1:0.5 to 5 by weight. The powder coating composition according to claim 1, comprising 45 to 90% by weight of a urethane-modified epoxy resin and a bisphenol A-type epoxy resin, 0.1 to 5% by weight of a curing agent, and 5 to 45% by weight of an extender pigment based on the total weight of the powder coating composition.