KR20190053403A - Powder coating composition - Google Patents

Abstract

The present invention relates to a powder coating composition which comprises: at least one kind of a carboxyl group-containing polyester resin; two kinds of curing agents; an extender pigment; and a colored pigment. When the powder coating composition of the present invention is applied, good appearance characteristics are exhibited even after a diamond cutting (D/C) process of an automobile aluminum wheel, and excellent smoothness and pinhole-preventing characteristics can be secured in middle infrared ray (MIR) curing.

Description

POWDER COATING COMPOSITION [0002]

The present invention relates to a powder coating composition for automotive wheel undergarments.

The powder coating material does not contain solvents such as organic solvents and water used in general paints, and if necessary, a suitable pigment or a hardening agent is mixed, and uniformly melted and mixed powder bodies are pulverized to a predetermined particle size, Means a powdery paint.

Powder coating using powder coating is excellent in physical properties of coating film and does not require much skill of operator compared to solvent type paint and has excellent impact resistance and is widely used in various fields such as construction, home appliance, and automobile industry. The powder coating can be applied to the object to be coated by an electrostatic spray coating method, a fluid deposition method and an electrostatic fluid deposition method.

The wheels that support automobile tires are divided into iron wheels (cast iron wheels) and aluminum wheels, and aluminum wheels are mainly used now. The aluminum wheel is not only beautiful in appearance, but also light in weight, easy to handle, and high in thermal conductivity, so that heat generated in the tire can be quickly absorbed and released by friction with the ground during running, thereby preventing overheating of the tire. In addition, since the aluminum wheel has a strong strength, when the tire is touched during driving, it is not easily crushed or broken like a cast iron wheel, so that safety is high.

A prior art related to such functionally excellent powder coatings for undercoat of aluminum wheels is Korean Patent Publication No. 2014-0003283. The prior art relates to a general thermosetting powder coating composition to which a polyester resin having an acid value of 20-80, a polyester curing agent, an inorganic filler, a pigment and the like is applied in a specific range. In the conventional powder coating, when powder paint coating, liquid phase painting / curing process and D / C processing are sequentially performed to produce a diamond cutting (D / C processing) wheel, which is a wheel trend in recent years, The edge portion of the substrate is cracked, thereby causing a serious defect in the appearance. In a conventional hot air type (direct and indirect) oven, it can be applied without particular problems. However, in the middle infrared ray (MIR) curing oven, pinhole phenomenon and smoothness lowering phenomenon of the transitional membrane occur.

Therefore, it is urgently required to develop a powder coating composition having excellent D / C processability and having excellent pinhole stability even when a medium infrared (MIR) curing system is applied.

The present invention relates to a powder that can realize a smooth appearance without cracking at the edge portion of the spoke front surface after D / C processing and can realize excellent appearance and physical properties in a powder coating line of an automobile aluminum wheel to which a medium infrared (MIR) curing oven is applied Thereby providing a coating composition.

The present invention provides a powder coating composition comprising at least one carboxyl group-containing polyester resin, a curing agent, an extender pigment and a colored pigment, wherein the curing agent comprises an epoxy curing agent and an isocyanate-modified epoxy curing agent.

When powder coating material according to the present invention is used to form an undercoating film of an automobile wheel, it is possible to secure a smooth appearance on the surface of the edge portion of the wheel spokes after D / C processing, ) Can be omitted.

In addition, the powder coating composition of the present invention can prevent appearance defects (overhanging pinholes, etc.) in the powdery ground even when an oven of a medium infrared (MIR) curing system is applied as well as a hot air type oven, Properties can be implemented.

Accordingly, the powder coating composition of the present invention can be usefully used as an undercoat of an automobile wheel, for example, an automobile aluminum wheel.

Hereinafter, the present invention will be described in detail. However, it should be understood that the present invention is not limited by the following description, and that various elements may be variously modified or selectively mixed according to need. Accordingly, it is to be understood that the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

<Powder Coating Composition>

The powder coating composition of the present invention comprises at least one kind of polyester resin, two kinds of curing agents, extender pigments and colored pigments which are the subject matter, and may contain other additives commonly used in the field of powder coating as required. Hereinafter, the composition of the powder coating composition will be specifically described.

Polyester resin

The powder coating composition of the present invention uses a polyester resin as a main resin. As the polyester resin, a conventional resin known in the art can be used, and for example, a polyester resin containing a carboxyl group in a molecule can be used.

The carboxyl group-containing polyester resin may have a carboxyl group acid value of 60 to 80 mg KOH / g, and as another example, 65 to 80 mg KOH / g. When the acid value of the carboxyl group-containing polyester resin is less than 60 mg KOH / g, the reactivity is deteriorated to deteriorate the mechanical properties and the weather resistance, and the crosslinking density of the coating film becomes low and the desired coating film property can not be exhibited. When the acid value exceeds 80 mg KOH / g A pinhole may be generated due to an increase in the reaction rate upon curing, and the appearance may be deteriorated due to a sharp deterioration of the leveling.

The carboxyl group-containing polyester resin may have a melt viscosity of 10 to 40 poise (200 ° C, ICI viscometer), a glass transition temperature (Tg) of 35 to 75 ° C and a number average molecular weight (Mn) of 1,000 to 4,000. When the melt viscosity is less than 10 poise, the appearance is deteriorated. When the melt viscosity exceeds 40 poise, the leveling is lowered and the storage stability is deteriorated. If the glass transition temperature is less than 35 ° C, there is a problem that the storage stability is poor. If the glass transition temperature is more than 75 ° C, the dispersibility may be deteriorated. If the number average molecular weight is less than 1,000, the appearance of the coated film becomes poor, while if it exceeds 4,000, the mechanical properties of the coated film may be deteriorated.

In the present invention, at least one kind of the carboxyl group-containing polyester resin can be used, and for example, two kinds of them can be used in combination. At this time, the mixing ratio between the two carboxyl group-containing polyester resins is not particularly limited and can be appropriately adjusted.

The content of the carboxyl group-containing polyester resin is not particularly limited and may be, for example, 30 to 40% by weight based on the total weight of the powder coating composition. If the content of the polyester resin is smaller than the above-mentioned range, the mechanical properties of the coating film are deteriorated. If the content of the polyester resin is more than the above-mentioned content range, the workability of painting is lowered.

Hardener

The powder coating composition of the present invention is a curing agent capable of curing reaction with a polyester resin as a main resin, and an epoxy curing agent and an isocyanate-modified epoxy curing agent are mixed.

The epoxy curing agent may be a bisphenol A type epoxy resin.

The bisphenol A type epoxy resin may have an epoxy equivalent weight (EEW) of 780 to 840 g / eq. If the epoxy equivalent weight is less than 780, the storage stability may be deteriorated. If the epoxy equivalent weight exceeds 840, the appearance characteristics may be deteriorated, and salt water repellency and corrosion resistance may be deteriorated. Further, the bisphenol A type epoxy resin may have a softening point of 85 to 105 캜, and as another example, 90 to 105 캜.

The isocyanate-modified epoxy-based curing agent may be an isocyanate-modified epoxy resin obtained by modifying mono-isocyanate or di-isocyanate. As the epoxy resin, a conventional resin known in the art can be used. Non-limiting examples of usable epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, naphthalene type epoxy resins, anthracene epoxy resins, biphenyl type epoxy resins, tetramethylbiphenyl type epoxy A phenol novolak type epoxy resin, a biphenyl novolak type epoxy resin, a naphthol novolac type epoxy resin, a naphthol phenol coaxial type epoxy resin, a phenol novolak type epoxy resin, a naphthol novolak type epoxy resin, Novolac type epoxy resin, novolac type epoxy resin, novolac type epoxy resin, novolac type epoxy resin, novolac type epoxy resin, novolac type epoxy resin, novolac type epoxy resin, Epoxy resin, phenol aralkyl type epoxy resin, polyfunctional phenol resin, naphthol aral A quarternary epoxy resin, or a mixture thereof. For example, it may be an isocyanate-modified bisphenol A type epoxy resin modified with 20 to 30% by weight of the isocyanate.

The isocyanate-modified epoxy resin may have an epoxy equivalent weight (EEW) of 430 to 500 g / eq. If the epoxy equivalent is out of the above-mentioned range, the appearance characteristics may be deteriorated and salt water repellency and corrosion resistance may be deteriorated.

The content of the curing agent may be appropriately adjusted according to the content of the main resin. For example, the content of the curing agent may be 31 to 45% by weight based on the total weight of the powder coating composition. When the content of the curing agent is less than the above range, the degree of curing of the coating film is lowered and the physical properties thereof are lowered. If the content exceeds the above range, the physical properties of the coating film are lowered due to the unreacted curing agent.

For example, the epoxy-based curing agent is 30 to 40% by weight based on the total weight of the powder coating composition, and the isocyanate-modified epoxy-based curing agent may be 1 to 5% by weight based on the total weight of the powdery coating composition. If the content of the epoxy-based curing agent is less than 30 wt%, it is difficult to cure at low temperature. When the content of the epoxy-based curing agent is more than 40 wt%, the reaction progresses rapidly and mechanical properties are improved. When the content of the isocyanate-modified epoxy-based curing agent is less than 1% by weight, sufficient adhesion can not be obtained when applied to a paint, and if it exceeds 5% by weight, heat-resistant performance at high temperature is deteriorated.

The mixing ratio of the epoxy-based curing agent and the isocyanate-modified epoxy-based curing agent is not particularly limited and may be, for example, 5 to 40: 1 by weight, or 10 to 20: 1 by weight.

Extender pigment

In the powder coating composition of the present invention, extender pigments may be used without limitation as those applicable in the field of powder coatings. Non-limiting examples of the extender pigments that can be used include calcium carbonate, feldspar, barium sulfate, silica, alumina hydroxide, magnesium hydroxide, titanium dioxide, magnesium carbonate, alumina, mica, montmorollonite, Silicon nitride, boron nitride, aluminum oxide, aluminum nitride, barium sulfate, and the like. These may be used alone or in combination of two or more.

The average particle diameter of the extender pigment is not particularly limited, and may range, for example, from 1 to 20 mu m. The shape of the extender pigment may be spherical, plate-like or amorphous, and is not particularly limited to this.

The powder coating composition of the present invention may include, for example, a first extender pigment having an average particle diameter of 1 to 4 탆 and a second extender pigment having an average particle diameter of 10 to 20 탆. In this case, the mixing ratio of the first extender pigment and the second extender pigment is not particularly limited, and may be, for example, 0.5 to 2: 1 by weight. In addition to the above-mentioned extender pigments, a third extender pigment having an average particle size different from those of the third extender pigments. In this case, the average particle size of the third extender pigment is not particularly limited, and may be, for example, 5 to 9 탆.

In the present invention, the content of the extender pigment is not particularly limited and may be, for example, 20 to 30% by weight based on the total weight of the powder coating composition. If the content of the extender pigment is out of the above-mentioned range, the mechanical properties, impact resistance and adhesion of the coating film may be deteriorated.

Colored pigment

In the powder coating composition of the present invention, the colored pigment is mixed with the main resin for the purpose of expressing a desired color in the powder coating. The above-mentioned colored pigments may be organic pigments, inorganic pigments, metallic pigments, Al-paste, pearl, and the like which are conventionally used for powder coatings, and may be used alone or in combination of two or more. .

Non-limiting examples of usable pigments include azo pigments, phthalocyanine pigments, iron oxide pigments, cobalt pigments, carbonate pigments, sulfate pigments, silicate pigments, and chromate pigments. Examples of the pigments include titanium dioxide, zinc oxide, bismuth vanadate , Cyanine green, carbon black, iron oxide red, iron oxide yellow, navy blue, cyanine blue, or the like.

The content of the colored pigment may be 0.5 to 1.5% by weight based on the total weight% of the powdery coating composition. If the content of the colored pigment is out of the above-described range, the hiding power of the coating film to which the powder coating composition of the present invention is applied may not be sufficiently secured, the color representation may be insufficient, and the mechanical properties of the coating film may be deteriorated.

Hardening accelerator

The powder coating composition of the present invention may further contain a curing accelerator, if necessary. As the curing accelerator, conventional components known in the art can be used without limitation.

The curing accelerator is a substance that promotes the reaction between the polyester resin as the main resin and the two curing agents, and may be a phosphonium-based compound or an amine-based compound that is easily activated at a low temperature and is excellent in reactivity, or a mixture thereof. When a phosphonium-based curing accelerator and an amine-based curing accelerator are mixed, the mixing ratio of the phosphonium-based curing accelerator and the amine-based curing accelerator may be 1 to 5: 1 by weight.

Non-limiting examples of usable phosphonium curing accelerators include benzyltriphenylphosphonium chloride, butyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide, ethyltriphenylphosphonium acetate, ethyltriphenylphosphonium bromide, ethyl Triphenylphosphonium iodide, tetraphenylphosphonium bromide, tetraphenylphosphonium chloride or tetraphenylphosphonium iodide, and the like.

Non-limiting examples of the amine-based curing accelerator include triethylamine, triethylenediamine, tetramethyl-1,3-butanediamine, ethylmorpholine, diazabicyclo-undecene, diazabicyclo- none, and the like.

The curing accelerator may be used alone or in combination of two or more.

The content of the curing accelerator may be appropriately controlled depending on the reactivity of the main resin or the curing agent. For example, the content of the curing accelerator may be 1 to 5% by weight based on the total weight of the powder coating composition. If the content of the curing accelerator is out of the above range, the mechanical properties of the coating film may be deteriorated or the appearance may be poor.

additive

The powder coating composition of the present invention may further include additives commonly used in the powder coating field, so long as the inherent properties of the composition are not impaired.

Examples of usable additives include, but are not limited to, pinhole inhibitors, leveling agents, waxes, low stressing agents, dispersants, flow improvers, anti-cratering agents, coupling agents, gloss control agents, adhesion improvers, flame retardants, A mixture of two or more thereof, and the like. For example, at least one of a pinhole inhibitor, a flow improver, a wax, a leveling agent, and a dispersant.

The anti-pinhole agent is a substance that is added to prevent volatile substances from being released from the coating film during the curing process, to prevent occurrence of pinholes in the coating film and to improve appearance characteristics. Examples of the pinhole preventing agent include an amide-based, polypropylene-based, and stearic acid-based pinhole inhibitor. Benzoin may be used, for example.

The flow improver is used for lowering the surface tension of the coating film and realizing a flexible appearance, and conventional ones known in the art can be used. Non-limiting examples include acrylic or silicone flow improvers.

As the wax, paraffin wax, natural wax, synthetic wax or a mixture thereof may be used. Natural waxes include carnauba wax and synthetic waxes include polyethylene wax.

The leveling agent is intended to improve the appearance property of the coating film while improving the adhesion in the composition by leveling the coating composition so as to be flat and smoothly coated. Examples of usable leveling agents include acrylic type, silicone type, polyester type, and amine type leveling agent.

The dispersing agent may be any conventional one known in the art. For example, a polyacrylic dispersant adsorbed on the surface of the pigment to maximize the degassing effect may be used.

The additive may be appropriately added within the range of contents known in the art, for example, 1 to 5% by weight based on the total weight of the powder coating composition. If the content of the additive is less than 1% by weight, problems may occur in the appearance of the coating film. If the content is more than 5% by weight, the hardness of the coating film may decrease.

The powder coating composition of the present invention may comprise, for example, 30 to 40% by weight of at least one carboxyl group-containing polyester resin having an acid value of 60 to 80 mg KOH / g based on the total weight of the powder coating composition, an epoxy equivalent weight of 780 to 840 g 1 to 5% by weight of an isocyanate-modified epoxy resin having an epoxy equivalent of 430 to 500 g / eq, 1 to 5% by weight of a curing accelerator containing a phosphonium-based and amine-based epoxy resin, 20 to 30% by weight of an extender pigment, 0.5 to 1.5% by weight of a colored pigment and 1 to 5% by weight of at least one additive.

The average particle diameter of the powder constituting the above powder coating material is not particularly limited, and may be, for example, 10 to 100 占 퐉, and in another example, 20 to 80 占 퐉. When the average particle diameter of the above-mentioned powder is satisfied, the paint workability and the appearance characteristics of the coating film can be improved.

The powder coating composition according to the present invention can be prepared by a method known in the art and can be produced through processes such as metering, pre-mixing, melt dispersion and pulverization.

For example, a raw material mixture containing a polyester resin, two kinds of curing agents, a curing accelerator, an extender pigment, a coloring pigment and optionally additives is added to a container mixer to be mixed and homogeneously mixed, Followed by pulverizing them. For example, the raw material mixture is melt-dispersed at 70-130 ° C by a melt kneading apparatus such as a kneader or an extruder to produce chips with a predetermined thickness (for example, 1 to 5 mm) Thereafter, the prepared chips are pulverized in the range of 10 to 120 mu m using a pulverizer such as a high-speed mixer and classified to prepare a powder coating composition.

The classification process is not particularly limited, and may be filtered by, for example, 40 to 200 mesh, and alternatively 100 to 200 mesh. As a result, a powder coating material having an average particle size in the range of 10 to 100 mu m can be obtained.

In order to improve the flowability of the powder coating material, the surface of the powder coating material particle according to the present invention may be coated with a fine powder such as silica. As a method for carrying out such a treatment, a pulverization mixing method in which a fine powder is added while being pulverized, or a dry mixing method using a Henschel mixer or the like can be used.

The powder coating composition of the present invention can be applied as an undercoat of an automobile wheel, and the automobile wheel can be aluminum (Al) or an aluminum alloy material. The powder coating composition of the present invention can exhibit favorable appearance characteristics without defects such as cracking even if it undergoes a diamond cutting (D / C) processing step in the manufacturing process of an automobile wheel. In addition, excellent smoothness and pinhole-preventing property can be secured at the same time in the medium-infrared (MIR) curing system.

The process for manufacturing an automotive aluminum wheel using the powder coating composition according to the present invention is as follows.

1) Aluminum surface smoothing process

Aluminum wheels are manufactured through casting and the surface is partially oxidized to form rough and pitted holes. Therefore, the aluminum wheel is mechanically polished to smooth the surface of the aluminum wheel.

2) Pretreatment process

A pretreatment step is carried out in order to enhance the adhesion with the coating film formed in the undercoat powder coating or the top coating step and to smooth the surface of the aluminum wheel to improve the appearance characteristics. A pretreatment method known in the art can be used without limitation. For example, an oxide film removing process, a neutralizing process, a coating process, a water reducing process, and the like can be sequentially performed.

3) Undercoating process

The primer coating process is carried out using the powder coating composition for automobile wheel undergarment of the present invention. For example, the powder coating material of the present invention is coated on the surface of an aluminum wheel subjected to a pretreatment step by an electrostatic spraying method, followed by drying in a hot air or medium infrared (MIR) oven to form a primer film.

4) Middle painting process

The intermediate coating composition is coated on the surface of the aluminum coating surface and then thermally cured to form the intermediate coating. At this time, the liquid phase intermediate coating composition can be applied by an air spray method.

5) DIACUTING (D / C) PROCESSING PROCESS

The surface of the painted aluminum wheel is subjected to diamond cutting (D / C) processing to improve the appearance and illumination. The machining conditions and operating conditions of the diamond cutting process can be appropriately adjusted in consideration of the life of the machining tool, gloss, roughness, rotational speed of the workpiece, and the like.

6) Top painting process

The aluminum wheel having been subjected to the D / C machining step as described above is finally subjected to the upper painting step to complete all the steps. The top coating process is not particularly limited, and a transparent coating is applied to the surface of the aluminum wheel using acrylic powder or acrylic liquid paint as is known in the art. For example, an acrylic type transparent powder coating material is coated to a thickness of 80 to 120 탆 and dried to form a top coat layer.

The automobile aluminum wheel manufactured as described above exhibits excellent appearance characteristics even after the diamond cutting (D / C) process, and is excellent in corrosion resistance and abrasion resistance against salt water. In addition, since it can be applied not only to the conventional hot air curing method but also to the powder lowering line employing the medium infrared ray (MIR) curing method, mass productivity, process simplification and economical efficiency can be enhanced.

Hereinafter, the present invention will be described more specifically by way of examples. However, the following examples are provided to aid understanding of the present invention and are not intended to limit the scope of the present invention in any sense.

[ Example  1-4]

The specifications of the raw materials constituting the powder coating composition of the present invention are shown in Table 1 below. Each component was blended according to the composition shown in Table 2, and then mixed uniformly using a container mixer. The mixture was melt-mixed at 120 to 130 캜 through an extruder and a kneader extruder, and each powder coating composition of Example 1-4 having an average particle size of 35 to 42 탆 was prepared using a pulverizer. In Table 2, the usage unit of each composition is% by weight.

[ Comparative Example  1-3]

Powder coating compositions of Comparative Examples 1-3 were respectively prepared according to the compositions shown in Table 2 in the same manner as in Examples.

[ Experimental Example . Property evaluation]

The physical properties of the powder coating compositions prepared in Examples 1-4 and Comparative Examples 1-3 were measured as follows, and the results are shown in Table 3 below.

(1) Appearance (leveling)

Aluminum (chromate treated) specimens of 75 mm x 150 mm x 0.4 mm in size were prepared and electrostatically sprayed using each of the powder coating compositions (powders) to visually confirm the external appearance. Judging grade was rated as?: Excellent,?: Good,?: Normal, and X: poor.

(2) Adhesiveness

The specimens prepared in the above (1) were subjected to a tape peel test in accordance with ISO 2409, by making ten chambers at intervals of 1 mm.

(3) Die cutting (D / C) processability

Each powder coating composition was coated and cured on an aluminum wheel pretreatment material, and then a liquid phase heavy composition was painted and cured thereon. Then, after the diamond cutting (D / C) step, the degree of breakage of the front edge of the wheel spoke was confirmed. Judgment grade was evaluated as classified as occurrence of ⊚: no crack, ◯: occurrence of fine crack (less than 1 mm), Δ: slight crack (1-2 mm), and X: severe crack (3 mm or more).

(4) Salt water silent

Each powder coating composition was applied to the test specimen prepared in the above (1), and then the test was carried out for 1,000 hours, and then the one-side peel width (unit: mm) was confirmed. The smaller the peeling width, the better.

(5) Pinhole Generated Film Thickness (Pinhole Limit Film Thickness at MIR Oven Curing)

Each powder coating composition was applied to an aluminum wheel material by electrostatic spraying and cured in a mid infrared (MIR) oven, and then the pinhole generated coating thickness was determined. The larger the film thickness, the better.

As shown in Table 3, in the case of Examples 1-4 using the powder coating composition according to the present invention, it was found that all of the coating compositions were excellent in all physical properties of the coating film as compared with Comparative Example 1-3, I could.

Specifically, Comparative Example 1 and Comparative Example 2 using only one curing agent exhibited poor physical properties in at least one of appearance, D / C processability, and salt water repellency. On the other hand, in the case of Comparative Example 3 in which a polyester resin having an acid value outside the scope of the present invention was used, the D / C processability and the salt water repellency were poor, and when cured at a medium infrared (MIR) wavelength, A phenomenon has occurred.

From the above results, it was confirmed that when the powder coating material according to the present invention was used, not only the D / C processability and the salt water repellency were excellent, but also exhibited excellent appearance characteristics without causing defects even when cured at a medium infrared (MIR) wavelength .

Claims (9)

At least one carboxyl group-containing polyester resin having an acid value of 60 to 80 mg KOH / g, a curing agent, an extender pigment and a colored pigment,
Wherein the curing agent comprises an epoxy-based curing agent and an isocyanate-modified epoxy-based curing agent. The powder coating composition according to claim 1, wherein the mixing ratio of the epoxy curing agent and the isocyanate-modified epoxy curing agent is 5 to 40: 1 by weight. The powder coating composition according to claim 1, wherein the epoxy curing agent is a bisphenol A epoxy resin having an epoxy equivalent of 780 to 840 g / eq. The powder coating composition according to claim 1, wherein the isocyanate-modified epoxy curing agent is an isocyanate-modified epoxy resin having an epoxy equivalent of 430 to 500 g / eq. The powder coating composition according to claim 1, further comprising a curing accelerator. The powder coating composition according to claim 5, wherein the curing accelerator comprises a phosphonium curing accelerator and an amine curing accelerator. The powder coating composition according to claim 6, wherein the mixing ratio of the phosphonium curing accelerator to the amine curing accelerator is 1: 5: 1. The powder coating composition according to claim 1, wherein the extender pigment comprises an extender pigment having an average particle diameter of 1 to 4 占 퐉 and an extender pigment having an average particle diameter of 10 to 20 占 퐉. The composition according to claim 5, wherein 30 to 40 wt% of the carboxyl group-containing polyester resin, 31 to 45 wt% of the curing agent, 1 to 5 wt% of the curing accelerator, 20 to 30 wt% of the extender pigment, By weight based on the total weight of the powder coating composition.