KR102524077B1 - Powder coating composition - Google Patents

Abstract

The present invention relates to a powder coating composition that realizes a clear structure pattern and has excellent pinhole prevention and heat resistance.

Description

Powder coating composition

The present invention relates to a powder coating composition that realizes a clear structure pattern and has excellent pinhole prevention and heat resistance.

Metals such as aluminum, titanium, and copper are used as main materials for buildings, automobiles, and industrial devices, and the surfaces of the metals are painted with paint compositions to protect them from harsh external environments. The paint composition requires various physical properties such as heat resistance, corrosion resistance, weather resistance, acid resistance, alkali resistance, gloss, and adhesion, and in particular, for various industrial devices (eg, cooking devices such as BBQ grills) repeatedly exposed to high-temperature heat for a long period of time. In the case of a paint composition applied as a coating composition, it is important to secure excellent heat resistance, corrosion resistance and transient film pinhole stability, and to secure physical properties capable of implementing a stable structure pattern.

For this reason, various studies on paint compositions with excellent heat resistance have been conducted. For example, Patent Publication No. 10-2014-0003283 is based on a polyester resin having a specific acid value range, and isocyanurate-based, glycol A powder coating composition in which at least one of cydyl ester and isocyanate is applied as a curing agent is disclosed. However, the powder coating does not exhibit sufficient physical properties to be used as a paint for cooking appliances requiring high heat resistance, since a pinhole phenomenon and a decrease in heat resistance occur at high temperatures.

On the other hand, Patent Registration No. 10-2047889 discloses a heat-dissipating powder coating to which fired-processed aluminum silicate is applied as a thermally conductive filler in order to realize heat resistance performance. However, when aluminum silicate is applied, workability and appearance are poor, and there are disadvantages in that it exhibits insufficient physical properties to be applied as a pattern paint.

The present invention provides a powder coating composition that implements a clear structure pattern and has excellent pinhole prevention and heat resistance.

The present invention provides a powder coating composition comprising three or more carboxyl group-containing polyester resins having different acid values, triglycidyl isocyanurate (TGIC), and bisphenol A glycidyl ether type epoxy resin.

The present invention provides a powder coating composition that implements a clear structure pattern and has excellent pinhole prevention and heat resistance. In particular, the powder coating composition according to the present invention has excellent heat resistance, corrosion resistance, and transient film pinhole stability, and can implement a stable structure pattern, so that various industrial devices (eg, BBQ grills, etc.) repeatedly exposed to high-temperature heat for a long period of time It is suitable for application for cooking equipment).

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.

As used herein, "viscosity" is measured by a conventional method known in the art, and can be measured using, for example, a Brookfield viscometer. "Weight average molecular weight" is measured by a conventional method known in the art, and can be measured, for example, by a gel permeation chromatograph (GPC) method. In addition, a functional group such as "acid value" can be measured by a conventional method known in the art. It is measured by a method, and can be measured by, for example, a titration method.

The powder coating composition according to the present invention includes three or more carboxyl group-containing polyester resins having different acid values, triglycidyl isocyanurate (TGIC), and bisphenol A glycidyl ether type epoxy resin. 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 plays a role in securing weather resistance and mechanical properties when applying 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.

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 three or more carboxyl group-containing polyester resins having different acid values. By mixing three or more types of carboxyl group-containing polyester resins having different acid values, a difference in curing speed may occur, resulting in improved pattern formation. When only one type of carboxyl group-containing polyester resin is used or two types of carboxyl group-containing polyester resins having different acid values are applied, pattern formation may be difficult or heat resistance, pinhole resistance, and corrosion resistance may be deteriorated.

In the present invention, the carboxyl group-containing polyester resin includes a first carboxyl group-containing polyester resin having excellent heat resistance, a second carboxyl group-containing polyester resin having excellent pinhole resistance, and a third carboxyl group having excellent mechanical properties, corrosion resistance and structure pattern formation. contains polyester resins.

The first carboxyl group-containing polyester resin may have an acid value of 28 to 36 mgKOH/g. When the acid value of the first carboxyl group-containing polyester resin satisfies the above range, excellent heat resistance and adhesiveness can be secured. When the acid value of the first carboxyl-containing polyester resin is less than the above range, heat resistance and adhesion may be deteriorated, and when the acid value exceeds the above range, impact resistance, scratch resistance, and structure pattern formation may be deteriorated. can

The first carboxyl group-containing polyester resin may have a viscosity of 800 to 1,000 Poise (165 ℃). When the viscosity of the first carboxyl group-containing polyester resin satisfies the above range, excellent paint workability and structure pattern formation may be secured. When the viscosity of the first carboxyl group-containing polyester resin is less than the above range, electrostatic painting may not be performed smoothly during paint work, so that the paint film may be unevenly coated, and sagging defects may occur during curing after painting. On the other hand, when the viscosity exceeds the above range, structure pattern formation may be deteriorated.

The weight average molecular weight of the first carboxyl group-containing polyester resin may be 6,000 to 12,000 g/mol. When the weight average molecular weight of the first carboxyl-containing polyester resin satisfies the above range, a coating film is smoothly formed and excellent smoothness can be secured. When the weight average molecular weight of the first carboxyl-containing polyester resin is less than the above range, even if the same amount is applied, the coating film may be formed shallowly and the appearance may be deteriorated, and when the weight average molecular weight is out of the above range, the coating film is excessively formed Pinhole resistance and pattern formation may be deteriorated.

The second carboxyl group-containing polyester resin may have an acid value of 15 to 21 mgKOH/g. When the acid value of the second carboxyl group-containing polyester resin satisfies the above range, excellent heat resistance and particularly excellent high-temperature yellowing property may be secured. When the acid value of the second carboxyl group-containing polyester resin is less than the above range, heat resistance, particularly high-temperature yellowing may be reduced, and when the acid value exceeds the above range, structure pattern formation may be deteriorated.

The second carboxyl group-containing polyester resin may have a viscosity of 60 to 85 Poise (200 ° C). When the viscosity of the second carboxyl group-containing polyester resin satisfies the above range, excellent structure pattern formation may be secured. When the viscosity of the second carboxyl group-containing polyester resin is out of the above range, electrostatic coating may not be smoothly performed during paint work, and thus the coating film may be painted non-uniformly, and as a result, structure pattern formation may be deteriorated.

In addition, the second carboxyl group-containing polyester resin may have a weight average molecular weight of 5,000 to 10,000 g/mol. When the weight average molecular weight of the second carboxyl-containing polyester resin satisfies the above range, a coating film may be smoothly formed and excellent hardness may be secured. When the weight average molecular weight of the second carboxyl-containing polyester resin is less than the above range, the coating film is formed shallowly and the appearance may be deteriorated, and when the weight average molecular weight is out of the above range, the coating film is excessively formed, resulting in pinhole resistance and pattern formation may be lowered

The third carboxyl group-containing polyester resin may have an acid value of 68 to 76 mgKOH/g. When the acid value of the third carboxyl group-containing polyester resin satisfies the above range, the curing speed is faster than that of the first carboxyl-containing polyester resin and the second carboxyl-containing polyester resin, so that a pattern can be formed well, and an excellent coating film can be formed. Corrosion resistance can be secured. When the acid value of the third carboxyl-containing polyester resin is less than the above range, corrosion resistance and adhesion may be deteriorated, and when the acid value exceeds the above range, the coating film may be excessively crosslinked, resulting in a decrease in hardness and impact resistance. .

The third carboxyl group-containing polyester resin may have a viscosity of 20 to 50 Poise (200 ℃). When the viscosity of the third carboxyl group-containing polyester resin satisfies the above range, it is smoothly coated and excellent corrosion resistance can be secured. When the viscosity of the third carboxyl group-containing polyester resin is out of the above range, electrostatic painting may not be performed smoothly during paint work, so that the paint film may be painted non-uniformly, and as a result, structure pattern formation may be deteriorated.

The third carboxyl group-containing polyester resin may have a weight average molecular weight of 6,000 to 8,000 g/mol. When the weight average molecular weight of the third carboxyl-containing polyester resin satisfies the above range, a coating film may be smoothly formed and a structure pattern may be formed. When the weight average molecular weight of the third carboxyl-containing polyester resin is less than the above range, the coating film is formed shallowly and adhesion may be deteriorated, and when the weight average molecular weight is out of the above range, the coating film is excessively formed, resulting in pinhole resistance and pattern formation this may deteriorate.

The carboxyl group-containing polyester resin may be included in an amount of 55 to 65% by weight based on the total weight of the powder coating composition.

The first carboxyl group-containing polyester resin may be included in an amount of 5 to 30% by weight, for example, 10 to 20% by weight based on the total weight of the powder coating composition. When the content of the first carboxyl group-containing polyester resin satisfies the above range, excellent heat resistance, adhesion and pattern formation may be secured. When the content of the first carboxyl group-containing polyester resin is less than the above range, heat resistance and adhesion may be deteriorated, and when it exceeds the above range, pattern formation may be deteriorated.

The second carboxyl group-containing polyester resin may be included in an amount of 5 to 40% by weight, for example, 20 to 30% by weight based on the total weight of the powder coating composition. When the content of the second carboxyl group-containing polyester resin satisfies the above range, excellent heat resistance and particularly excellent high-temperature yellowing property may be secured. When the content of the second carboxyl group-containing polyester resin is less than the above range, heat resistance, particularly high-temperature yellowing may be deteriorated, and when it exceeds the above range, structure pattern formation may be poor.

The third carboxyl group-containing polyester resin may be included in an amount of 5 to 35% by weight, for example, 15 to 25% by weight based on the total weight of the powder coating composition. When the content of the third carboxyl group-containing polyester resin satisfies the above range, excellent pattern formation and corrosion resistance may be secured. When the content of the third carboxyl group-containing polyester resin is less than the above range, pattern formation and corrosion resistance may be poor, and when it exceeds the above range, the hardness of the coating film may be reduced.

For example, the weight ratio of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin may be 1:0.5 to 3.5, for example 1:1 to 3. When the weight ratio of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin is out of the above range, heat resistance and structure pattern formation may be deteriorated.

For example, the weight ratio of the first carboxyl group-containing polyester resin and the third carboxyl group-containing polyester resin may be 1:0.3 to 3.5, for example, 1:0.5 to 2.5. When the weight ratio of the first carboxyl group-containing polyester resin and the third carboxyl group-containing polyester resin is out of the above range, pattern formation, corrosion resistance and hardness may be deteriorated.

curing agent

The powder coating composition according to the present invention includes a polyester curing agent and a bisphenol A glycidyl ether type epoxy resin as a curing agent. By adjusting the curing speed of the coating film by mixing two types of curing agents having different structures and epoxy equivalents, excellent pattern formation, salt spray resistance and smoothness can be secured.

As the polyester curing agent, one having an epoxy equivalent of 100 to 120 g/eq may be used. When the equivalent weight of the polyester curing agent is less than the above range, dispersibility and salt water spray resistance may be deteriorated, and when it exceeds the above range, curing property may be deteriorated.

Non-limiting examples of the polyester curing agent include isocyanurate-based curing agents, such as triglycidyl isocyanurate (TGIC); Glycidyl ester-based curing agents, such as diglycidylterephthalate (DGT), triglycidyltrimellitate (TML); Alkylamide-based curing agents, such as bis (N, N'- Dihydroxyethyl)-adipamide) (Bis(N,N'-dihydroxyethyl)-Adipamide); isocyanate-based curing agents such as ε-Caprolactam blocked Isophorone Diisocyanate; or mixtures thereof.

The polyester curing agent may be included in an amount of 1 to 10% by weight, for example, 4 to 6% by weight based on the total weight of the powder coating composition. When the content of the polyester curing agent is less than the above-mentioned range, it is impossible to cure and thus it may be difficult to form a coating film, and when it exceeds the above-mentioned range, the coating film may be easily broken.

The bisphenol A-type glycidyl ether-type epoxy resin is used as an auxiliary curing agent, and by mixing it, excellent smoothness and interlayer adhesion to liquid medium as well as excellent corrosion resistance can be secured.

As the bisphenol A glycidyl ether type epoxy resin, one having an epoxy equivalent of 700 to 900 g/eq, for example, 780 to 840 g/eq may be used. When the epoxy equivalent is less than the above-mentioned range, flexibility may be deteriorated due to a decrease in viscosity and storage properties of the paint may be deteriorated. On the other hand, when the epoxy equivalent exceeds the above range, the viscosity of the paint increases due to the increase in the viscosity of the resin, and the wetting property and impact resistance may be lowered, and the adhesion may be lowered.

The bisphenol A-type glycidyl ether-type epoxy resin may be included in an amount of 1 to 10% by weight, for example, 2 to 4% by weight based on the total weight of the powder coating composition. When the content of the bisphenol A-type epoxy resin is less than the above range, interlayer adhesion with the liquid medium may be deteriorated, and smoothness and corrosion resistance may be deteriorated. On the other hand, when the above range is exceeded, the glass transition temperature of the coating film may be lowered.

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 characteristics 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, as the extender pigment, a particle size of 10 μm or more, for example, 10 to 25 μm, and another example, 15 to 25 μm may be used. If the particle size of the extender pigment is less than the above-mentioned range, the matting effect and pinhole coverage may be reduced, and if it exceeds the above-mentioned range, 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, 25 to 35% 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 10% 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 colored pigment is within the above range, the color expression of the coating film is excellent, and mechanical properties, impact resistance, and the like 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 1-16]

According to the composition shown in Tables 1 and 2 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 each example having an average particle size of 25 to 55 μm.

[Comparative Example 1-14]

Powder coating compositions of each Comparative Example were prepared in the same manner as in Examples, except for the compositions described in Tables 3 to 4 below.

Polyester 1-1: carboxyl group polyester (AV 32 mgKOH/g, Vis 912 poise (165 ° C), Mw 9,050 g/mol)

Polyester 1-2: carboxyl group polyester (AV 28 mgKOH/g, Vis 804 poise (165 ℃), Mw 6,280 g/mol)

Polyester 1-3: Carboxyl group polyester (AV 36 mgKOH/g, Vis 992 poise (165 ° C), Mw 11,400 g/mol)

Polyester 1-4: carboxyl group polyester (AV 26 mgKOH/g, Vis 881 poise (165 ℃), Mw 9,600g/mol)

Polyester 1-5: carboxyl group polyester (AV 38 mgKOH/g, Vis 897 poise (165 ℃), Mw 9,300 g/mol)

Polyester 2-1: carboxyl group polyester (AV 18 mgKOH/g, Vis 70 poise (200 ℃), Mw 7,560 g/mol)

Polyester 2-2: carboxyl group polyester (AV 15 mgKOH/g, Vis 60.5 poise (200 ℃), Mw 5,210 g/mol)

Polyester 2-3: carboxyl group polyester (AV 21 mgKOH/g, Vis 84.2 poise (200 ℃), Mw 9,720 g/mol)

Polyester 2-4: Carboxyl group polyester (AV 13 mgKOH/g, Vis 71 poise (200 ℃), Mw 7,200 g/mol)

Polyester 2-5: carboxyl group polyester (AV 23 mgKOH/g, Vis 73 poise (200 ℃), Mw 7,070 g/mol)

Polyester 3-1: carboxyl group polyester (AV 72 mgKOH/g, Vis 33 poise (200 ℃), Mw 7,300 g/mol)

Polyester 3-2: carboxyl group polyester (AV 68 mgKOH/g, Vis 21 poise (200 ℃), Mw 6,020 g/mol)

Polyester 3-3: carboxyl group polyester (AV 76 mgKOH/g, Vis 47 poise (200 ℃), Mw 7,910 g/mol)

Polyester 3-4: carboxyl group polyester (AV 66 mgKOH/g, Vis 37 poise (200 ℃), Mw 7,500 g/mol)

Polyester 3-5: carboxyl group polyester (AV 78 mgKOH/g, Vis 36 poise (200 ℃), Mw 7,260 g/mol)

Curing agent 1-1: triglycidyl isocyanurate (EEW 110 g/eq, CIBA)

Curing agent 2-1: bisphenol-A type glycidyl ether (EEW 780 g/eq)

Curing agent 2-2: bisphenol-A type glycidyl ether (EEW 810 g/eq)

Curing agent 2-3: bisphenol-A type glycidyl ether (EEW 840 g/eq)

Additive 1: polyethylene wax (Lubrizol)

Additive 2: Acrylic Copolymer (DSM)

Additive 3: aluminum oxide (Evonik)

Black Pigment: Carbon Black (Columbian)

Extender pigment 1: calcium carbonate (particle size: 15-18 μm)

Extender pigment 2: calcium carbonate (particle size: 4-6 μm)

[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 5 to 8 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 (pattern)

The appearance state of each specimen was observed with the naked eye, and the degree of clarity of the pattern (structure) was evaluated.

[Criteria]

◎: very clear pattern formation, ○: clear pattern formation, △: disordered pattern formation, X: no pattern formation

adhesiveness

According to ISO 2409, a tape peel test was conducted by making 10 cells at intervals of 1 mm in each specimen.

impact

After dropping a weight of 500 g on each specimen from a height of 50 cm using a Dupont impact tester, it was confirmed whether cracks occurred in the coating film.

salt spray resistance

After conducting a salt spray test for 1,000 hours for each specimen, the peel width on one side was measured. It is excellent, so that peeling width|variety is small.

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 The thicker the coating film, the better.

Heat Resistant Cycle

After performing a heat resistance cycle test (curing at 280 ° C for 1 hour and then reaching room temperature (23 ° C) 10 times), the color difference and adhesion (ISO 2409) of the coating film were evaluated.

As confirmed from the results of Tables 5 and 6, when the coating compositions of Examples 1-16 according to the present invention were applied, the appearance (pattern), adhesion, impact resistance, salt spray resistance, pinhole prevention and heat resistance were improved. All turned out great. On the other hand, as confirmed from the results of Tables 7 and 8, when the paint composition of Comparative Examples 1-14 outside the composition according to the present invention was applied, the physical properties of the measured items were generally poor compared to the paints of Examples.

Specifically, when the paint composition of Comparative Example 1 not containing the first polyester resin according to the present invention was applied, adhesion and heat resistance were poor, and Comparative Example not containing the second polyester resin according to the present invention was applied. When the coating composition of 2 was applied, salt spray resistance and pinhole prevention were poor, and when the coating composition of Comparative Example 3 not containing the third polyester resin according to the present invention was applied, the appearance (pattern) and heat resistance were poor. appeared

When the coating compositions of Comparative Examples 4 to 5 using only one of the curing agents according to the present invention were applied, salt spray resistance and impact resistance were poor.

Although three kinds of polyester resins were applied, when the paint compositions of Comparative Examples 6 to 11 using polyester resins outside the acid value range according to the present invention were applied, adhesion, impact resistance, heat resistance, appearance (pattern formation), etc. showed up fiercely. In addition, when the coating compositions of Comparative Examples 12 to 14 using only one of the polyester resins according to the present invention were applied, the measured physical properties were all poor.

Claims (7)

Including three or more carboxyl group-containing polyester resins, a polyester curing agent and a bisphenol A glycidyl ether type epoxy resin,
The first carboxyl group-containing polyester resin having an acid value of 28 to 36 mgKOH / g, the second carboxyl group-containing polyester resin having an acid value of 15 to 21 mgKOH / g, and an acid value of 68 to 76 mgKOH / g A powder coating composition comprising a third carboxyl group-containing polyester resin. The method of claim 1, wherein the viscosity of the first carboxyl group-containing polyester resin is 800 to 1,000 Poise (165 ℃), and the weight average molecular weight is 6,000 to 12,000 g / mol,
The second carboxyl group-containing polyester resin has a viscosity of 60 to 85 Poise (200 ° C), a weight average molecular weight of 5,000 to 10,000 g / mol,
A powder coating composition wherein the third carboxyl group-containing polyester resin has a viscosity of 20 to 50 Poise (200 ° C) and a weight average molecular weight of 6,000 to 8,000 g / mol. According to claim 1, wherein the weight ratio of the first carboxyl group-containing polyester resin and the second carboxyl group-containing polyester resin is 1: 0.5 to 3.5, the first carboxyl group-containing polyester resin and the third carboxyl group-containing polyester resin The weight ratio of 1: 0.3 to 3.5 of the powder coating composition. The powder coating composition according to claim 1, wherein the epoxy equivalent of the polyester curing agent is 100 to 120 g/eq. The powder coating composition according to claim 1, wherein the epoxy equivalent of the bisphenol A glycidyl ether type epoxy resin is 700 to 900 g/eq. The powder coating composition according to claim 1, further comprising an extender pigment having a particle size of 10 to 25 μm. According to claim 1, based on the total weight of the powder coating composition, the first carboxyl group-containing polyester resin 5 to 30% by weight, the second carboxyl group-containing polyester resin 5 to 40% by weight, the third carboxyl group-containing polyester A powder coating composition comprising 5 to 35% by weight of resin, 1 to 10% by weight of the polyester curing agent, and 1 to 10% by weight of the bisphenol A glycidyl ether type epoxy resin.