WO2024196019A1 - Powder coating composition - Google Patents

Abstract

The present invention relates to a powder coating composition having excellent heat resistance, water resistance, and long-term corrosion resistance whilst also ensuring a high glass transition temperature.

Description

Powder coating composition

The present invention relates to a powder coating composition having excellent heat resistance, water resistance, and long-term corrosion resistance while securing a high glass transition temperature.

Pipes used for oil mining, transportation, etc. are coated on the inside and outside of the pipes to prevent corrosion of the pipes due to harsh conditions such as microcurrent and moisture in buried environments such as above ground, underground, and underwater. Long-term property management standards for coating materials required in the relevant industries are gradually being strengthened. In particular, as mining in harsh environments becomes more frequent due to the depletion of underground resources, mining depths are increasing and buried environments are becoming harsher, there is a continuous demand for improvements in the thermal, chemical, and mechanical properties of pipe coating paints to protect pipes from corrosion under high-temperature conditions, and research on paints that satisfy these properties is also ongoing. For example, U.S. Patent No. 5,407,978 discloses a powder coating for pipes comprising a diglycidyl ether of an aromatic bisphenol, a trifunctional polyglycidyl ether of an aliphatic polyol, a co-reactant, and a curing accelerator.

Conventional powder coatings have a glass transition temperature of 100℃ or lower, so they are not heat-resistant enough to be applied to pipes transporting high-temperature fluids, and their water resistance and long-term corrosion resistance are also insufficient for application in harsh environments. Accordingly, there is a need for the development of a powder coating composition that secures a high glass transition temperature while also having excellent heat resistance, water resistance, and long-term corrosion resistance.

The present invention provides a powder coating composition having excellent heat resistance, water resistance, and long-term corrosion resistance while securing a high glass transition temperature.

The present invention provides a powder coating composition comprising an isocyanate-modified epoxy resin, a bisphenol A epoxy resin, a silicone resin, and a curing agent.

The present invention provides a powder coating composition having excellent heat resistance, water resistance, and long-term corrosion resistance while securing a high glass transition temperature (e.g., 120° C. or higher). The powder coating composition of the present invention can be applied to coating pipes for high-temperature fluid transport.

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

The “glass transition temperature” used herein is measured by a conventional method known in the art, and can be measured, for example, by thermomechanical analysis (TMA) or differential scanning calorimetry (DSC). The “viscosity” is measured by a conventional method known in the art, and can be measured, for example, using a Brookfield viscometer at room temperature (25°C). The “softening point” is measured by a conventional method known in the art, and can be measured, for example, by a dropping point system calorimetry DP70 from Mettler Toledo.

A powder coating composition according to the present invention comprises an isocyanate-modified epoxy resin, a bisphenol A epoxy resin, a silicone resin, and a curing agent.

The above isocyanate-modified epoxy resin and bisphenol A type epoxy resin are main resins that form a coating film of the paint and can affect the basic physical properties, and can affect the glass transition temperature of the cured coating film. The above isocyanate-modified epoxy resin has an advantage of high crosslinking density because it has a network structure in its resin structure, but has a disadvantage of reduced mechanical properties, and the above bisphenol A type epoxy resin has an advantage of excellent mechanical properties because it has a symmetrical structure and is stable to external stimuli, but has a disadvantage of limitations in increasing the crosslinking density because it has a linear form. In the present invention, by mixing the above isocyanate-modified epoxy resin and the above bisphenol A type epoxy resin, a paint composition having high crosslinking density and excellent mechanical properties is provided.

Meanwhile, epoxy resin can form a hard coating film due to the characteristics of the resin itself, which can form a dense network structure with a hardener and has a high glass transition temperature, but organic resin containing carbon and carbon bonds can easily break the bond when heat is applied. In the present invention, silicone resin is mixed to compensate for this. The silicone resin contains a Si-O bond with higher bond energy than the organic resin, so decomposition occurs at a higher temperature, thereby increasing heat resistance.

The powder coating composition of the present invention may further contain a novolac-type epoxy resin, and, if necessary, may further contain additives commonly used in the relevant technical field, such as a filler pigment, a color pigment, a rust-preventive pigment, a catalyst, a surface conditioner, and an adhesion promoter.

Isocyanate modified epoxy resin

The powder coating composition according to the present invention comprises an isocyanate-modified epoxy resin. The isocyanate-modified epoxy resin is a main resin and serves to impart a high glass transition temperature and heat resistance.

Isocyanate-modified epoxy resin is a polymer in which an epoxy resin is modified with an isocyanate compound, and contains an oxazolidone ring in the main chain skeleton of the epoxy resin and a glycidyl group at the terminal. Such isocyanate-modified epoxy resin can be produced by reacting an epoxy resin with an isocyanate compound in the presence of a catalyst.

As the above epoxy resin, any epoxy resin known in the relevant technical field can be used without any special restrictions.

As the above isocyanate compound, monoisocyanate or diisocyanate can be used. Non-limiting examples of the above monoisocyanate include p-toluenesulfonyl isocyanate, 4-phenoxyphenyl isocyanate, 4-cyanophenyl isocyanate, and the like. Non-limiting examples of the above diisocyanates include methane diisocyanate, butane-1,1-diisocyanate, ethane-1,2-diisocyanate, butane-1,2-diisocyanate, transvinyline diisocyanate, heptane-1,7-diisocyanate, 2,2-dimethyl-pentane-1,5-diisocyanate, hexane-1,6-diisocyanate, octane-1,8-diisocyanate, nonane-1,9-diisocyanate, dimethylsilane diisocyanate, diphenylsilane diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene There are diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, trans-1,4-cyclohexane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, etc. These may be used alone or in combination of two or more. The content of the isocyanate compound may be about 1 to 40 parts by weight per 100 parts by weight of the epoxy resin.

As the above catalyst, bases, amines, hydrogen compounds, imidazoles, phosphonium salts and derivatives thereof can be used, but are not limited thereto. These can be used alone or in combination of two or more. The content of the catalyst can be about 0.01 to 0.5 parts by weight based on 100 parts by weight of the isocyanate compound.

The epoxy equivalent of the above isocyanate-modified epoxy resin may be 200 to 600 g/eq, for example, 400 to 500 g/eq. If the epoxy equivalent of the above isocyanate-modified epoxy resin is less than the above-mentioned range, the reactivity with the hardener may be fast, so that the coating may be cured before the film is formed, thereby deteriorating the overall physical properties. If it exceeds the above-mentioned range, the viscosity may be high, making it difficult to paint, so that the appearance may deteriorate.

In addition, the viscosity (150° C.) of the isocyanate-modified epoxy resin may be 10,000 to 30,000 CPS, for example, 15,000 to 25,000 CPS, the softening point may be 100 to 125° C., for example, 105 to 115° C., and the isocyanate modification ratio may be 20 to 30 wt%. When the viscosity of the isocyanate-modified epoxy resin is less than the above-mentioned range, the mechanical properties may deteriorate, and when it exceeds the above-mentioned range, an appropriate crosslinking density may not be formed. When the softening point of the isocyanate-modified epoxy resin is less than the above-mentioned range, the storability and dispersibility may deteriorate, and when it exceeds the above-mentioned range, the crosslinking density and dispersibility may deteriorate. If the isocyanate modification rate of the above isocyanate-modified epoxy resin is below the above-mentioned range, the crosslinking density of the coating film may be reduced, and if it exceeds the above-mentioned range, the mechanical properties may be reduced.

Bisphenol A epoxy resin

The powder coating composition according to the present invention includes bisphenol A epoxy resin. Bisphenol A epoxy resin has a symmetrical structure and thus plays a role in supplementing physical properties such as rust prevention.

The epoxy equivalent (EEW) of the above bisphenol A type epoxy resin may be 900 to 1,300 g/eq, for example, 1,100 to 1,200 g/eq. When the epoxy equivalent of the above bisphenol A type epoxy resin is less than the above-mentioned range, the mechanical properties may deteriorate, and when it exceeds the above-mentioned range, the appearance and dispersibility may deteriorate.

In addition, the viscosity (200° C.) of the bisphenol A type epoxy resin may be 1,800 to 2,800 cps, for example, 2,000 to 2,600 cps, and the softening point may be 100 to 130° C., for example, 110 to 125° C. When the viscosity of the bisphenol A type epoxy resin is less than the aforementioned range, low-temperature flexibility may deteriorate, and when it exceeds the aforementioned range, appearance and dispersibility may deteriorate. When the softening point of the bisphenol A type epoxy resin is less than the aforementioned range, storage properties and mechanical properties may deteriorate, and when it exceeds the aforementioned range, dispersibility may deteriorate.

The above isocyanate-modified epoxy resin and the bisphenol A type epoxy resin can be mixed in a weight ratio of 0.8 to 1.8: 1. The isocyanate-modified epoxy resin has a structure that is advantageous for forming crosslinks, and the bisphenol A type epoxy resin has a structure that is advantageous for improving mechanical properties. When these are mixed in the above-mentioned weight ratio, excellent properties can be imparted to the paint composition. When the content of the isocyanate-modified epoxy resin with respect to the bisphenol A epoxy resin is less than the above-mentioned range, the crosslinking density decreases and becomes lower than the required glass transition temperature, which may lower the heat resistance of the coating film. When it exceeds the above-mentioned range, mechanical properties such as water resistance may deteriorate.

silicone resin

The powder coating composition according to the present invention includes a silicone resin. The silicone resin is a resin manufactured by synthesizing silicon, and has excellent heat resistance and water repellency due to the inherent properties of silicone, thereby playing a role in improving the heat resistance and water repellency of the coating composition.

Since the bonding energy of silicon and oxygen (Si-O) of silicone resin is higher than the bonding energy of carbon and carbon (C-C) of organic synthetic resin, silicone resin is strong against heat and is not easily decomposed by heat, so it exhibits excellent heat resistance. The silicone resin includes a polyalkylphenylsiloxane resin. In the polyalkylphenylsiloxane resin, the alkyl group (R) may be an alkyl group having 1 to 3 carbon atoms. For example, the polyalkylphenylsiloxane resin may include a silanol at a terminal.

The above polyalkylphenylsiloxane resin is a siloxane resin containing both an alkyl group and a phenyl group. The phenyl group is a stable form of aromatic hydrocarbon in which a double bond of a sigma bond and a pi bond coexists, and since the bond energy is high compared to a molecular structure consisting of only a single bond, chemical decomposition does not occur easily even when heated, so the heat resistance of the coating can be improved. As the content of the phenyl group increases, the molecular weight of the silicone resin increases, and the silicone resin with a high molecular weight can improve the hardness and mechanical strength of the formed coating. In addition, the phenyl group is a type of hydrocarbon derivative and can affect the compatibility with other organic components constituting the paint, such as an epoxy resin, and the higher the content, the better the compatibility can be. Meanwhile, the alkyl group has a structure capable of forming a crosslink, so it can form a smooth crosslink with the surroundings and provide stable adhesion to the paint.

By adjusting the ratio of phenyl groups and alkyl groups in the above polyalkylphenylsiloxane-based resin to a specific range, excellent physical properties can be provided to the paint composition. For example, the ratio of phenyl groups to alkyl groups (P/R ratio) in the polyalkylphenylsiloxane-based resin may be 0.5 to 1.5. If the ratio of phenyl groups to alkyl groups is less than the above-mentioned range, the content of phenyl groups is low, so the heat resistance of the coating film may be reduced, and compatibility with epoxy resin, which is an organic resin, may be reduced. On the other hand, if the ratio of phenyl groups to alkyl groups exceeds the above-mentioned range, the content of phenyl groups is high, so the heat resistance is excellent, but the adhesion may be reduced due to a decrease in the content of alkyl groups participating in crosslinking.

In the above polyalkylphenylsiloxane resin, the hydroxyl group content may be greater than 0 wt% and less than or equal to 7 wt%. If the hydroxyl group content exceeds the above-mentioned range, appearance deterioration due to bubble generation may occur.

The weight average molecular weight of the polyalkylphenylsiloxane-based resin may be 1,000 to 4,500 g/mol, for example, 1,000 to 4,000 g/mol. If the weight average molecular weight of the polyalkylphenylsiloxane-based resin is less than the above-mentioned range, the gloss may be reduced, and if it exceeds the above-mentioned range, the appearance may be deteriorated due to bubble generation.

The degree of substitution of the polyalkylphenylsiloxane-based resin, i.e., the average number of organic substituents per silicon atom (R/Si), may be 0.8 to 2, for example, 1 to 2, or in another example, 1 to 1.5. The degree of substitution of the polyalkylphenylsiloxane-based resin affects the degree of crosslinking, and when the degree of substitution is less than the above-mentioned range, the adhesion may be reduced, and when it exceeds the above-mentioned range, the degree of crosslinking may be reduced, resulting in reduced flexibility.

The silicone resin may be included in an amount of 0.1 to 1 part by weight relative to 100 parts by weight of the total of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin. If the content of the silicone resin is less than the above-mentioned range, water resistance may be reduced, and if it exceeds the above-mentioned range, corrosion resistance may be reduced and compatibility with the epoxy resin may be reduced.

The above-mentioned isocyanate-modified epoxy resin and bisphenol A-type epoxy resin have high crosslinking density, but when the epoxy resin is applied alone, water resistance may be reduced. On the other hand, the silicone resin has excellent water resistance, but when it is applied alone, high-temperature corrosion resistance may be poor. In the present invention, by mixing the isocyanate-modified epoxy resin, bisphenol A-type epoxy resin, and the silicone resin, it is possible to implement a suitable crosslinking density and provide excellent water resistance at the same time.

Novolac type epoxy resin

The powder coating composition according to the present invention may further include a novolac-type epoxy resin. The novolac-type epoxy resin is a multifunctional epoxy resin and has more epoxide rings than other types of epoxy resins, so that it can increase the crosslinking density when forming a coating film, thereby improving the durability, corrosion resistance, and chemical resistance of the coating film. As the novolac-type epoxy resin, phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, bisphenol A novolac-type epoxy resin, bisphenol S novolac-type epoxy resin, biphenyl novolac-type epoxy resin, naphthol novolac-type epoxy resin, or the like can be used. Preferably, the novolac-type epoxy resin may include a cresol novolac-type resin.

The epoxy equivalent of the novolac-type epoxy resin may be 100 to 400 g/eq, for example, 200 to 210 g/eq. When the epoxy equivalent of the novolac-type epoxy resin is less than the above-mentioned range, the mechanical properties may deteriorate, and when it exceeds the above-mentioned range, the crosslinking density may deteriorate. In addition, the viscosity (150° C.) of the novolac-type epoxy resin may be 2,000 to 5,000 cps, for example, 3,000 to 4,500 cps, and the softening point may be 100 to 125° C., for example, 110 to 125° C. When the viscosity of the novolac-type epoxy resin is less than the above-mentioned range, the mechanical properties may deteriorate, and when it exceeds the above-mentioned range, the crosslinking density may deteriorate. If the softening point of the above novolac-type epoxy resin is below the above-mentioned range, the mechanical properties may deteriorate, and if it exceeds the above-mentioned range, the crosslinking density may deteriorate.

With respect to the total of 100 parts by weight of the above isocyanate-modified epoxy resin and the above bisphenol A epoxy resin, 0.5 to 2 parts by weight of the above novolac-type epoxy resin may be included. If the content of the above novolac-type epoxy resin is less than the above-mentioned range, heat resistance may be deteriorated, and if it exceeds the above-mentioned range, mechanical properties may be deteriorated.

Hardener

The powder coating composition of the present invention includes a curing agent. The curing agent is not particularly limited as long as it is a curing agent capable of curing reaction with an epoxy resin, and an aliphatic amine curing agent, an alicyclic amine curing agent, an aromatic amine curing agent, etc. can be used. These can be used alone or as a mixture of two or more. For example, 4,4'-diamino diphenyl sulfone, 4,4'-diamino diphenyl methane, dicyandiamide, etc. can be used.

The amine value of the above-mentioned curing agent may be 10 to 40 mgKOH/g, for example, 15 to 25 mgKOH/g. If the amine value of the above-mentioned curing agent is less than the above-mentioned range, the mechanical properties may deteriorate, and if it exceeds the above-mentioned range, the water resistance may deteriorate.

The curing agent may be included in an amount of 1.6 to 3.3 parts by weight based on 100 parts by weight of the total of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin. When the content of the curing agent satisfies the above-mentioned range, the degree of curing of the coating film may be increased, thereby improving the physical properties of the coating film.

Pigment

The powder coating composition of the present invention may further include at least one of a filler pigment, a color pigment, and a rust-preventive pigment commonly used in the powder coating field, within a range that does not impair the inherent characteristics of the coating composition.

The extender pigment plays a role in supplementing water resistance and corrosion resistance. As the extender pigment, olastonite, calcium carbonate, feldspar, barium sulfate, silica, alumina hydroxide, magnesium hydroxide, titanium dioxide, magnesium carbonate, alumina, mica, montmorillonite, talc, aluminum nitride, silicon nitride, boron nitride, aluminum oxide, aluminum nitride, barium sulfate, etc. can be used, and these can be used alone or as a mixture of two or more. With respect to the total 100 parts by weight of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin, 20 to 50 parts by weight of the extender pigment can be included. When the content of the extender pigment satisfies the above-mentioned range, the mechanical properties, impact resistance, adhesion, etc. of the coating film can be improved.

Color pigments are used to implement a desired color in powder coating. As color pigments, organic pigments, metallic pigments, aluminum paste, pearl, etc. can be used without limitation, and these can be used alone or in combination of two or more. Non-limiting examples of color pigments that can be used include azo pigments, phthalocyanine pigments, iron oxide pigments, cobalt pigments, silicate pigments, chromate pigments, etc., and for example, titanium dioxide, zinc oxide, bismuth vanadate, cyanine green, carbon black, iron oxide red, iron oxide sulfur, navy blue, cyanine blue, and mixtures of two or more thereof. With respect to a total of 100 parts by weight of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin, 1 to 5 parts by weight of the color pigment can be included. When the content of the color pigment satisfies the above-mentioned range, the color expression of the coating film is excellent and the hiding property of the coating film can be improved.

The anti-rust pigment plays a role in supplementing corrosion resistance. As the anti-rust pigment, zinc phosphate, etc. can be used. 1 to 3 parts by weight of the anti-rust pigment may be included relative to 100 parts by weight of the total of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin. When the content of the anti-rust pigment satisfies the above-mentioned range, the corrosion resistance of the coating film can be improved.

Additives

The powder coating composition of the present invention may further include additives commonly used in the relevant field, such as a catalyst, a surface conditioner, and an adhesion promoter, within a range that does not impair the inherent characteristics of the coating composition.

As a substance that promotes the reaction between the above catalyst epoxy resin and the hardener, there are, for example, imidazole-based, phosphonium-based, amine-based, and metal-based catalysts, and these can be used alone or in combination of two or more.

The above surface conditioner is intended to improve the appearance properties of the coating film by leveling the paint composition so that it is coated evenly and smoothly, thereby increasing the adhesion within the composition. For example, acrylic, silicone, polyester, and amine leveling agents can be used, but are not limited thereto.

The above adhesion promoter is a substance that improves the adhesion of the coating film and supplements corrosion resistance, and an amino-based or silane-based adhesion promoter can be used.

The above additives may be appropriately added within a content range known in the relevant technical field, and for example, may be included in an amount of 0.1 to 10 parts by weight, respectively, with respect to 100 parts by weight of the total of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin.

The powder coating composition according to the present invention can be manufactured by a method known in the art, and for example, can be manufactured through processes such as metering, pre-mixing, melt dispersion, and grinding. For example, a raw material mixture containing an isocyanate-modified epoxy resin, a bisphenol A epoxy resin, a silicone resin, a curing agent, and, if necessary, a novolak-type epoxy resin, an extender pigment, a color pigment, a rust-preventive pigment, a catalyst, a surface conditioner, and an adhesion promoter is placed in a container mixer, mixed uniformly, the mixed composition is melt-mixed, and then ground, so as to be manufactured. For example, the raw material mixture is melt-dispersed at 70 to 130° C. by a melt mixing device such as a kneader or an extruder to manufacture chips with a predetermined thickness (e.g., 1 to 5 mm), and then the manufactured chips are ground to a size of 40 to 80 μm by using a grinding device such as a high-speed mixer and then classified, so as to manufacture a powder coating composition.

The above classification process is not particularly limited, and can be filtered with, for example, 40 to 80 mesh. Accordingly, a powder coating having an average particle size in the range of 40 to 80 ㎛ can be obtained. The average particle size of the powder is not particularly limited, but when it satisfies the above-mentioned range, the coating workability and the appearance characteristics of the coating film can 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 silica. As a method for performing this treatment, a grinding mixing method in which fine powder is added and mixed during grinding, or a dry mixing method using a Henschel mixer, etc., may be used.

Hereinafter, the present invention will be described more specifically through examples. However, the following examples are only intended to help understand the present invention and do not limit the scope of the present invention in any way to the examples.

[Example 1-13]

According to the compositions described in Tables 1 and 2 below, each component was placed in a mixing tank, pre-mixed, and then melted and dispersed at 100° C. in a disperser to produce chips. The produced chips were pulverized in a high-speed mixer to produce powder coating compositions of each example having an average particle size of 40 μm.

[Comparative Example 1-3]

Except for the compositions described in Table 3 below, powder coating compositions of each comparative example were prepared in the same manner as in the examples.

Isocyanate modified epoxy resin 1: Epoxy equivalent 465 g/eq, viscosity (150 ℃) 21,000 cps, softening point 110 ℃, NCO modification rate 25 wt%

Isocyanate modified epoxy resin 2: Epoxy equivalent 400 g/eq, viscosity (150 ℃) 15,000 cps, softening point 105 ℃, NCO modification rate 20 wt%

Isocyanate modified epoxy resin 3: Epoxy equivalent 500 g/eq, viscosity (150 ℃) 25,000 cps, softening point 115 ℃, NCO modification rate 30 wt%

Bisphenol A epoxy resin 1: Epoxy equivalent 1,150 g/eq, viscosity (200 ℃) 2,300 cps, softening point 118.5 ℃

Bisphenol A epoxy resin 2: Epoxy equivalent 1,100 g/eq, viscosity (200 ℃) 2,000 cps, softening point 110 ℃

Bisphenol A epoxy resin 3: Epoxy equivalent 1,200 g/eq, viscosity (200 ℃) 2,600 cps, softening point 125 ℃

Silicone Resin 1: SILANOL FUNCTIONAL METHYLPHENYL SILICONE RESIN (Mw 2,600 g/mol, substitution degree 0.8, P/R ratio 1.3)

Silicone Resin 2: SILANOL FUNCTIONAL METHYLPHENYL SILICONE RESIN (Mw 2,000 g/mol, substitution rate 1.1, P/R ratio 1)

Silicone Resin 3: SILANOL FUNCTIONAL METHYLPHENYL SILICONE RESIN (Mw 4,000 g/mol, substitution rate 1.5, P/R ratio 1.5)

Novolac type epoxy resin: Epoxy equivalent 205 g/eq, viscosity (150 ℃) 3,750 cP, softening point 115 ℃

Hardener: Dicyandiamide (Evonik, AHEW 21)

Auxiliary curing agent: Amino alcohol amine-adduct

Catalyst: 2-Methyl-imidazole

Adhesion promoter: Adhesion promoter(KCC)

Coloring pigment: Iron oxide (BAYFERROX 130M)

Constitution pigment: Wollastonite (NYCO)

Anti-rust pigment: Zinc phosphate (Hanchang Industry)

[Property Evaluation]

The properties of the powder coating compositions manufactured in each example and comparative example were measured as follows, and the results are shown in Table 4-6 below.

Psalm production

After preparing short specimens (100 mm × 100 mm × 6 mm), the specimens were preheated at a temperature of 230°C for more than 30 minutes, and then each powder coating composition was painted on the preheated specimens using a paint gun (film thickness: 562 μm).

Flexibility

The bending property (2˚ Bending) of each specimen was measured at -30℃ using a bending tester.

[metewand]

Excellent (◎): No cracking, Defective (X): Cracking

cathodic peeling

After testing for 28 days at 65°C and 95°C under 1.5 V conditions, the peeling distance of the coating was confirmed using a cathodic peeling tester.

[Evaluation criteria at 65℃]

Excellent (◎): 5.0 mm or less, Good (○): Over 5.0 mm and under 6.0 mm, Average (β: Over 6.0 mm and under 7.0 mm, Poor (X): Over 7.0 mm

[Evaluation criteria at 95℃]

Excellent (◎): 6.0 mm or less, Good (○): Over 6.0 mm and under 7.0 mm, Average (△): Over 7.0 mm and under 8.0 mm, Poor (X): Over 7.0 mm

Boiling water

After immersion in water at 75°C for 28 days, the adhesion of the coating was checked and evaluated as Rating 1 to 5 according to the following criteria.

Rating 1: Almost no peeling of the coating

Rating 2: Less than 50% peeling

Rating 3: Resistance to peeling and levering action of 50% or more

Rating 4: The coating peels off easily in pieces.

Rating 5: 100% peeling

[metewand]

Excellent (◎: Rating 1, Good (○): Rating 2-3, Average (β: Rating 4, Poor (X): Rating 5

Shock

Using a Dupont impact tester, an impact was applied to each specimen with a 1 kg weight from a height of 30 cm to check for cracks in the coating.

[metewand]

Excellent (◎): No cracking, Defective (X): Cracking

Porosity

The coating of each specimen was removed, and the degree of porosity on the bottom and side surfaces of the coating was measured under a microscope at 40x magnification, and evaluated as Rate 1 to 5 according to CSA Z245.20:22.

[metewand]

Excellent (◎): Rate 1, Good (○): Rate 2-3, Average (β: Rate 4, Bad (X): Rate 5

Glass transition temperature of the film

According to the CSA Z245.20 standard, 9-11 mg of paint was placed in the cell of the DSC instrument and heated according to the specified cycle to determine the glass transition temperature.

[metewand]

Excellent (◎): 120 ℃ or higher, Good (○): 110 ℃ or higher but less than 120 ℃, Average (β: 100 ℃ or higher but less than 110 ℃, Bad (X): less than 100 ℃

As shown in Table 4-6, the paint compositions of the examples exhibited excellent properties across the measured items. On the other hand, the paint composition of Comparative Example 1, which did not contain bisphenol A type epoxy resin, exhibited poor bendability, cathodic peeling, boiling water resistance, and porosity, and a low glass transition temperature, the paint composition of Comparative Example 2, which did not contain isocyanate-modified epoxy resin, exhibited poor cathodic peeling, boiling water resistance, and porosity, and the paint composition of Comparative Example 3, which did not contain silicone resin, exhibited poor bendability, cathodic peeling, boiling water resistance, impact resistance, and porosity.

The present invention provides a powder coating composition having excellent heat resistance, water resistance, and long-term corrosion resistance while securing a high glass transition temperature (e.g., 120° C. or higher). The powder coating composition of the present invention can be applied to coating pipes for high-temperature fluid transport.

Claims (7)

A powder coating composition comprising an isocyanate-modified epoxy resin, a bisphenol A epoxy resin, a silicone resin and a curing agent. A powder coating composition in claim 1, wherein the mixing ratio of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin is 0.8 to 1.8:1 in weight ratio. A powder coating composition in claim 1, wherein the isocyanate-modified epoxy resin has an epoxy equivalent of 200 to 600 g/eq, a viscosity (150°C) of 10,000 to 30,000 CPS, a softening point of 100 to 125°C, and an isocyanate modification ratio of 20 to 30 wt%. A powder coating composition in claim 1, wherein the bisphenol A type epoxy resin has an epoxy equivalent weight (EEW) of 900 to 1,300 g/eq, a viscosity (200°C) of 1,800 to 2,800 CPS, and a softening point of 100 to 130°C. A powder coating composition in claim 1, wherein the silicone resin is a polyalkylphenylsiloxane-based resin, and the ratio of phenyl groups/alkyl groups (P/R ratio) in the polyalkylphenylsiloxane-based resin is 0.5 to 1.5. In the first paragraph, a novolac-type epoxy resin is further included, A powder coating composition having an epoxy equivalent of the above novolac-type epoxy resin of 100 to 400 g/eq, a viscosity (150°C) of 2,000 to 5,000 cps, and a softening point of 100 to 125°C. In claim 6, a powder coating composition comprising 0.1 to 1 part by weight of the silicone resin, 0.5 to 2 parts by weight of the novolac-type epoxy resin, and 1.6 to 3.3 parts by weight of the curing agent, relative to 100 parts by weight of the total of the isocyanate-modified epoxy resin and the bisphenol A epoxy resin.