Epoxy resin powder coating

Abstract

To provide an epoxy resin powder coating that can obtain excellent coating appearance by a generally used coating condition, and, can obtain basic coating physical properties such as corrosion resistance, mechanical characteristics, hygiene and so on, furthermore, does not cause peeling of the coating by following even to deformation of a coated product due to external pressure.SOLUTION: An epoxy resin powder coating contains a bisphenol type epoxy resin, a curing agent, and a pigment, characterized by that relative to 100 pts.mass of the bisphenol type epoxy resin, the curing agent is contained in the range of 0.1 to 10 pts.mass, the pigment is contained in the range of 30 to 100 pts.mass, an epoxy group purity of the bisphenol type epoxy resin is 75 mol% or larger.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin powder coating. Specifically, the present invention relates to a powder coating that can provide a coating film with excellent corrosion resistance and mechanical strength. Even more specifically, the present invention relates to an epoxy resin powder coating that can provide a coating film with excellent corrosion resistance and mechanical strength, and that can maintain adhesion to the substrate and follow deformation even when the substrate is subjected to external impact or pressure that causes deformation. [Background technology]

[0002] Epoxy resin powder coatings currently in industrial use are applied to protect metal substrates by providing rust and corrosion resistance to the substrate. They are also used for similar purposes on structures such as bridges and buried pipes (Patent Document 1).

[0003] Epoxy powder paints are used for such purposes, but when external pressure is applied to the coated object due to the collision of flying objects caused by strong winds and rain, or an earthquake, the coating may break down or peel off from the coated object, even if it does not lead to the destruction of the structure or pipe. This can lead to corrosion and deterioration of the base material. Furthermore, there are many cases where paint peels off or breaks due to external shocks caused by unavoidable circumstances during the manufacturing and transportation processes of structural components and pipes, and during the production process of the final structure, which has been an issue.

[0004] Patent Document 2 discloses an epoxy powder coating composition containing an epoxy resin, a curing agent, and an inorganic filler as essential ingredients, where the epoxy resin is a bisphenol F-type epoxy resin obtained by direct synthesis of bisphenol F with a dinuclear purity of 90-95% and having a specified epoxy equivalent, melt viscosity, and glass transition temperature. However, it only broadly discloses the inorganic filler, and in the examples, the amount of inorganic filler used is small, resulting in low fracture toughness of the cured coating and the risk of peeling of the coating film due to external pressure. Patent Document 3 discloses an epoxy resin powder coating composition containing a bisphenol F-type solid epoxy resin and a curing agent, in which bisphenol F with a dinuclear purity of 70 to 95 area % is used as a raw material. However, because the epoxy group purity of the bisphenol F-type solid epoxy resin is 30 to 70 mol %, the fracture toughness of the cured coating material is low, and there is a risk of the coating film peeling off due to external pressure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-45620 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-2792 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-37917 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an epoxy resin powder coating that can obtain a good coating film appearance under commonly used coating conditions, and that can obtain basic coating film properties such as corrosion resistance, mechanical properties, and hygiene, and that can also follow deformation of the coated object due to external pressure and does not cause peeling of the coating film. [Means for solving the problem]

[0007] The inventors discovered the optimum paint properties that can maintain high fracture toughness of the cured coating film by using the properties of the epoxy resin that can solve the problem and the blending ratio of the pigment contained in the powder paint, and thus invented the epoxy resin powder paint.

[0008] That is, the present invention provides: The epoxy resin powder coating contains a bisphenol-type epoxy resin, a curing agent, and a pigment, and is characterized in that the curing agent is contained in the range of 0.1 to 10 parts by mass and the pigment is contained in the range of 40 to 100 parts by mass per 100 parts by mass of the bisphenol-type epoxy resin, and the epoxy group purity of the bisphenol-type epoxy resin is 75 mol% or more.

[0009] The fracture toughness of the cured epoxy resin powder coating is 2.0 MPa m 0.5 It is preferable that this is equal to or greater than this.

[0010] The epoxy equivalent of the bisphenol type epoxy resin is preferably 700 to 2500 g / eq., and the softening point is preferably 70 to 120°C.

[0011] The bisphenol type epoxy resin is preferably at least one selected from bisphenol F type epoxy resin, tetramethylbisphenol F type epoxy resin, bisphenol A type epoxy resin, and tetramethylbisphenol A type epoxy resin.

[0012] The curing agent is preferably an imidazoline derivative and / or an imidazole derivative.

[0013] The pigment is preferably at least one selected from iron oxide, yellow iron oxide, silica powder, quartz powder, titanium oxide, calcium carbonate, barium sulfate, and carbon black. [Effects of the Invention]

[0014] The epoxy resin powder coating of the present invention comprises a bisphenol-type epoxy resin having a specific epoxy group purity, a curing agent, and a pigment, and is capable of providing basic coating film properties such as corrosion resistance, mechanical properties, and hygiene, and is capable of maintaining adhesion to the substrate and following deformation even when the substrate is subjected to external impact or pressure accompanied by deformation. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be specifically described below. The epoxy resin powder coating of the present invention contains a bisphenol type epoxy resin, a curing agent, and a pigment as essential components.

[0016] The bisphenol epoxy resin contained in the present invention has an epoxy group purity of 75 mol% or more, preferably 80 mol% or more, and more preferably 85 mol% or more. If the epoxy group purity of the bisphenol epoxy resin used in the epoxy resin powder coating is less than this value, even if the epoxy resin powder coating is formulated, the fracture toughness of the cured product will be low, the strength of the coating film (impact resistance, flex resistance, etc.) will be deteriorated, and there is a risk of the coating film peeling off due to external pressure.

[0017] Bisphenol-type epoxy resins are generally broadly classified into one-stage epoxy resins obtained by the condensation polymerization reaction of bisphenols and epihalohydrin, and two-stage epoxy resins obtained by addition polymerization of one-stage epoxy resins obtained by the condensation reaction of bisphenols and a large excess of epihalohydrin with bisphenols. Both epoxy resins have terminal groups consisting of epoxy groups, hydrolyzable chlorine groups, α-glycol groups, and phenolic hydroxyl groups. By standardizing the unit of content of each of these functional groups to "meq. / 100g," the epoxy group purity can be calculated using the following formula: Epoxy group purity (mol%) = (epoxy group content × 100) / (epoxy group content + hydrolyzable chlorine content + α-glycol group content + phenolic hydroxyl group content)

[0018] The fracture toughness of the cured product of the epoxy resin powder coating of the present invention is 2.0 MPa m 0.5 More than 2.1 MPa m is preferable. 0.5 If the fracture toughness value of the cured product is equal to or greater than this value, the physical properties such as strength of the coating film will be sufficient, and the coating film will be able to follow deformation of the substrate due to external pressure and will not peel off.

[0019] The epoxy equivalent (g / eq.) of the bisphenol-type epoxy resin used in the present invention is preferably in the range of 700 to 2500, more preferably 900 to 2400, and even more preferably 1000 to 2300. A low epoxy equivalent may result in poor storage stability when used as a powder coating, potentially causing blocking during long-term storage and rendering the coating unusable. Furthermore, even if the gel time is adjusted, the melt viscosity during the curing process after application may be low, making it difficult to prevent sagging of the coating surface. A high epoxy equivalent may result in high melt viscosity, which may result in poor flowability when used as a powder coating, even if the gel time is adjusted, resulting in a loss of coating surface smoothness. If the epoxy equivalent is within the preferred range, a powder coating with no storage stability issues can be obtained, and a coating with good coating appearance and basic physical properties such as mechanical properties and corrosion resistance can be obtained.

[0020] The softening point of the bisphenol epoxy resin is preferably in the range of 70 to 120°C, more preferably in the range of 90 to 120°C, and even more preferably in the range of 95 to 115°C. If the softening point is low, the blocking properties of the powder coating may be poor, and if the softening point is high, when the powder coating is made, the gel time may be short and the fluidity of the coating may be poor, and even if the gel time is adjusted, the fluidity may be poor and the smoothness of the coating surface may be impaired. If the softening point is in the preferred range, when the powder coating is made, a powder coating with no blocking problems can be obtained, and a coating film with good coating appearance and basic physical properties such as mechanical properties and corrosion resistance can be obtained.

[0021] The bisphenol-type epoxy resin used in the present invention can be either a one-step epoxy resin or a two-step epoxy resin. Since the epoxy group purity of the one-step epoxy resin is relatively low and that of the two-step epoxy resin is relatively high, the epoxy group purity may be adjusted by combining the two.

[0022] The bisphenol-type epoxy resin used in the present invention is not particularly limited as long as it is solid, but may have a substituent. The substituent is preferably an alkyl group, a phenyl group, or an α-methylbenzyl group, more preferably a methyl group or an α-methylbenzyl group. The number of substituents is preferably one or two per phenol ring. Specific examples of bisphenol-type epoxy resins include bisphenol F-type epoxy resins, tetramethylbisphenol F-type epoxy resins, bisphenol A-type epoxy resins, and tetramethylbisphenol A-type epoxy resins. Among these, bisphenol F-type epoxy resins are preferred.

[0023] To apply an epoxy resin powder coating to a substrate and obtain a good cured coating film, the gel time at the preheating temperature is preferably in the range of 20 to 80 seconds, more preferably 30 to 60 seconds, and even more preferably 40 to 50 seconds. If the gel time at the preheating temperature is too short, the coating film may harden before it melts and becomes smooth, losing its fluidity and resulting in an uneven or rough coating film appearance. If the gel time is too long, curing may be insufficient if post-heating is not performed after painting, and sufficient coating properties may not be achieved. If the gel time at the preheating temperature is within the preferred range, a coating film with good appearance and basic physical properties such as mechanical properties and corrosion resistance can be obtained, even without post-heating. It can also be used in a method in which the substrate is electrostatically coated without preheating and then heat-cured.

[0024] Next, the curing agent will be described. The curing agent used in the present invention is preferably an imidazoline derivative, an imidazole derivative, or a mixture thereof. Examples of imidazoline derivatives include methylimidazoline and 2-phenylimidazoline. Examples of imidazole derivatives include methylimidazole, dodecyl imidazole, phenylimidazole, quaternary salts such as 1-dodecyl-2-methyl-3-benzylimidazolium chloride, an isocyanuric acid adduct of 2-methylimidazole, and triazine ring-containing compounds such as 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine.

[0025] Among these, 2-phenylimidazoline is particularly preferred as the imidazoline derivative, and 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine or 2-phenylimidazole is particularly preferred as the imidazole derivative. When these curing agents are used in powder coatings, the specific gel time can be easily adjusted to a range within which the effect is obtained, resulting in a coating film with good appearance and also good basic physical properties such as mechanical properties and corrosion resistance.

[0026] Furthermore, organic acid hydrazides, modified aromatic amine adducts, and acid anhydrides mainly composed of trimellitic acid and ethylene glycol may be used in combination as long as the properties are not impaired.

[0027] The amount of curing agent is in the range of 0.1 to 10 parts by mass, preferably 0.5 to 8 parts by mass, and more preferably 1 to 6 parts by mass, per 100 parts by mass of bisphenol-type epoxy resin. If the amount is too small, the gel time of the powder coating may be delayed, resulting in an insufficiently cured coating film. If the amount is too large, the gel time of the powder coating may be rapid, resulting in poor appearance of the resulting coating film, such as wrinkles and roughness, and poor storage stability. If the amount of curing agent is within the above range, the gel time of the powder coating will be within an appropriate range, resulting in a powder coating with satisfactory storage stability. Furthermore, a coating film with good basic physical properties, such as mechanical properties and corrosion resistance, can be obtained. Two or more curing agents can be mixed to adjust the gel time of the powder coating and the melt viscosity during curing.

[0028] Next, the pigment will be described. As the pigment, color pigments, extender pigments, luster pigments, anti-rust pigments, etc., which are commonly used in powder coatings, can be used. These pigments can be used alone, or two or more pigments of the same type can be used in combination, or pigments of different types can be used in combination. Preferably, the pigment is a combination of an extender pigment and a color pigment that determines the hue, and these are blended in predetermined amounts.

[0029] Examples of color pigments include inorganic pigments such as titanium oxide, yellow iron oxide, titanium yellow, red iron oxide, lithopone, and antimony oxide, and organic pigments such as Hansa Yellow 5G, Permanent Yellow FGL, Cyanine Blue, Phthalocyanine Blue, Indanthrene Blue RS, Permanent Red F5RK, Brilliant Fast Scarlet G, Cyanine Green, carbazole, quinacridone red, and carbon black.

[0030] Examples of extender pigments include inorganic pigments such as barium sulfate, barium carbonate, calcium carbonate, clay, silica powder, quartz powder, diatomaceous earth, zinc oxide, talc, basic magnesium carbonate, and alumina, as well as plastic pigments such as resin beads having a porous, hollow, or crosslinked internal structure.

[0031] Examples of luster pigments include aluminum powder, nickel powder, stainless steel powder, copper powder, bronze powder, gold powder, silver powder, mica, graphite, glass flakes, metal-coated glass powder, metal-coated mica powder, metal-coated plastic powder, flaked plastic powder, and flaky iron oxide.

[0032] Examples of anti-rust pigments include condensed calcium phosphate, aluminum phosphate, condensed aluminum phosphate, zinc phosphate, aluminum phosphite, zinc phosphite, calcium phosphite, zinc molybdate, calcium molybdate, and manganese molybdate.

[0033] Of these pigments, iron oxide, yellow iron oxide, silica powder, quartz powder, titanium oxide, calcium carbonate, barium sulfate and carbon black are preferred, and quartz powder, titanium oxide and carbon black are more preferred.

[0034] The amount of pigment to be added is in the range of 40 to 100 parts by mass, preferably 40 to 80 parts by mass, more preferably 45 to 70 parts by mass, and particularly preferably 45 to 60 parts by mass, per 100 parts by mass of bisphenol-type epoxy resin. If the amount is too small, the fracture toughness of the cured coating may be poor. If the amount is too large, the fluidity of the coating may be poor, making it difficult to obtain a smooth coating film, and further, it may become difficult to prevent poor coating appearance, such as the occurrence of pinholes. If the amount of pigment added is within the above range, a coating film with good flat coating appearance and good basic physical properties, such as mechanical properties including fracture toughness, and corrosion resistance, may be obtained.

[0035] The epoxy resin powder coating of the present invention may optionally contain general coating additives such as plasticizers, curing accelerators, crosslinking catalysts, UV absorbers, light stabilizers, anti-sagging agents, antioxidants, surface conditioners, flow control agents, and defoamers, as long as they do not impair the objectives of the present invention. Examples of antioxidants include phenolic antioxidants such as pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate, and phosphorus-based antioxidants such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. Examples of flow control agents and surface conditioners include acrylic polymers. For example, they can be added in an amount of up to 5 parts by weight, preferably 0.5 to 2 parts by weight, per 100 parts by weight of epoxy resin.

[0036] The epoxy resin powder coating of the present invention is suitable for coating the inner surface of buried pipes or other pipes, for example, by a rotary coating method in which the pipe or pipe is preheated to about 200°C and then sprayed onto the inner surface while rotating, or by a method in which the pipe is placed in a coating booth after preheating and then the inner surface is painted with a hand sprayer, and then allowed to cool to obtain a cured coating film.It is also suitable for general coating methods, such as electrostatically coating structural components at room temperature and then sufficiently heating and curing in a heating furnace at about 160 to 200°C to obtain a cured coating film. The epoxy resin powder coating of the present invention has basic coating film properties such as smoothness and corrosion resistance, and can provide a good coating film appearance without the occurrence of pinholes, etc., and can also provide a coating film that does not peel or crack even when subjected to external pressure. [Example]

[0037] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are based on mass unless otherwise specified. The unit of epoxy equivalent is "g / eq."

[0038] The methods for measuring the physical properties of the bisphenol-type epoxy resins used in the synthesis examples of the present invention are described below.

[0039] (1) The epoxy equivalent was measured in accordance with JIS K 7236.

[0040] (2) The softening point was measured in accordance with JIS K 7234 "Ring and Ball Method."

[0041] (3) The hydrolyzable chlorine content was measured in accordance with JIS K 7243-2 "Easily Saponifiable Chlorine."

[0042] (4) The α-glycol content was measured in accordance with JIS K 7146 "1,2-glycol content."

[0043] (5) The phenolic hydroxyl group content is determined by reacting tetramethylammonium with the phenolic hydroxyl groups in a mixed solution of 96% tetrahydrofuran and 4% methanol to produce a color, measuring the absorbance using a spectrophotometer, and converting it from a calibration curve prepared in advance using the bisphenols used as raw materials as standards.

[0044] The methods for evaluating the powder coatings obtained in the examples and comparative examples of the present invention will be described below.

[0045] (1) Fracture toughness was measured in accordance with ASTM E 399. The test specimens were prepared by pouring the powder coating into a mold preheated to 200°C, pressing the mold at 200°C for 10 minutes, and then removing the mold and notching the specimens.

[0046] (2) The gel time was measured by placing 0.1 g of powder coating on a hot plate heated to 200°C, stirring it with a fluororesin rod, and measuring the time it took for the coating to gel.

[0047] (3) MEK rubbing test To confirm the curability, an MEK rubbing test (1 kg load, 10 strokes) was conducted and evaluated according to the following criteria: The MEK rubbing test involves rubbing the coating surface 10 times with gauze soaked in MEK to determine the condition of the coating. No paint film attached: ○, Paint film attached: ×

[0048] (4) The impact resistance test was conducted in accordance with JIS K 5600-5-3 "Resistance to falling weights," in which a 500g weight with a radius of 1 / 4 inch was dropped from a height of 50cm onto the back of the coating film. No cracks or peeling: ○, Cracks or peeling: ×

[0049] (5) The bending resistance test was conducted in accordance with Type 1 measurement of JIS K 5600-5-1 "Cylindrical Mandrel Method" using a cylindrical mandrel with a diameter of 2 mm. No cracks or peeling: ○, Cracks or peeling: ×

[0050] Synthesis Example 1 A reactor equipped with a stirrer, nitrogen inlet tube, side temperature resistor, dropping device, and cooling condenser was charged with 104 parts of epichlorohydrin and 200 parts of bisphenol F. The system temperature was controlled at 40°C and stirred to dissolve. Next, 217 parts of a 20% aqueous solution of caustic soda was added via the dropping device. After the addition, the system temperature was controlled at 92°C and the reaction was carried out for 2 hours. After the reaction was completed, 330 parts of methyl isobutyl ketone was added, stirred for 15 minutes, and then allowed to stand to remove the water in the lower layer. The mixture was then neutralized with phosphoric acid and washed with water. The aqueous layer was removed, filtered, and the methyl isobutyl ketone was distilled off to obtain epoxy resin (A1). The epoxy equivalent was 1350, the softening point was 95°C, the α-glycol content was 15 meq. / 100g, the phenolic hydroxyl group content was 2000 ppm, the hydrolyzable chlorine content was 50 ppm, and the epoxy group purity was 83 mol%.

[0051] Synthesis Example 2 Epoxy resin (A2) was obtained using the same apparatus and operation as in Synthesis Example 1, except that 100.8 parts of epichlorohydrin and 237 parts of a 20% aqueous caustic soda solution were used. The epoxy equivalent was 2000, the softening point was 100°C, the α-glycol content was 15 meq. / 100 g, the phenolic hydroxyl group content was 5000 ppm, the hydrolyzable chlorine content was 100 ppm, and the epoxy group purity was 72 mol%.

[0052] Synthesis Example 3 Bisphenol F was added in portions to 180 parts of a bisphenol F liquid resin with an epoxy equivalent of 169, and the reaction was carried out for 6 hours at a resin temperature of 180°C using the same apparatus as in Synthesis Example 1, to obtain epoxy resin (A3).The epoxy equivalent was 1500, the softening point was 100°C, the α-glycol content was 2.3 meq. / 100g, the phenolic hydroxyl group content was 2000 ppm, the hydrolyzable chlorine content was 70 ppm, and the epoxy group purity was 97 mol%.

[0053] Synthesis Example 4 Bisphenol F was added in portions to 140 parts of a bisphenol F liquid resin with an epoxy equivalent of 169, and the reaction was carried out for 6 hours at a resin temperature of 180°C in the same apparatus as in Synthesis Example 1 to obtain epoxy resin (A4). The epoxy equivalent was 2300, the softening point was 110°C, the α-glycol content was 2.0 meq. / 100g, the phenolic hydroxyl group content was 1800 ppm, the hydrolyzable chlorine content was 50 ppm, and the epoxy group purity was 90 mol%.

[0054] Synthesis Example 5 Epoxy resin (A5) was obtained using the same apparatus and operation as in Synthesis Example 1, except that 100.4 parts of epichlorohydrin, 200 parts of bisphenol A, and 233 parts of a 20% aqueous solution of caustic soda were used. The epoxy equivalent was 950, the softening point was 95°C, the α-glycol content was 16 meq. / 100 g, the phenolic hydroxyl group content was 800 ppm, the hydrolyzable chlorine content was 50 ppm, and the epoxy group purity was 86 mol%.

[0055] Synthesis Example 6 Epoxy resin (A6) was obtained using the same apparatus and operation as in Synthesis Example 1, except that 138.8 parts of epichlorohydrin and 375 parts of a 20% aqueous caustic soda solution were used. The epoxy equivalent was 800, the softening point was 79°C, the α-glycol content was 17 meq. / 100 g, the phenolic hydroxyl group content was 4000 ppm, the hydrolyzable chlorine content was 80 ppm, and the epoxy group purity was 86 mol%.

[0056] The abbreviations used in the examples and comparative examples are as follows:

[0057] [Epoxy resin] Epoxy resins (A1) to (A6) obtained in Synthesis Examples 1 to 6

[0058] [Hardening agent] 2PZL: 2-phenylimidazoline (Curesol 2PZL, manufactured by Shikoku Chemicals Corporation) 2MZ-A: 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine (Curesol 2MZ-A, manufactured by Shikoku Chemicals Corporation) 2PZ: 2-phenylimidazole (Curezol 2PZ, manufactured by Shikoku Chemicals Corporation)

[0059] [Pigment] Silica powder: extender pigment (Marusen Mining Co., Ltd., Silica Powder A) Titanium oxide: Color pigment (Teika Corporation, JR-301) Carbon black: Color pigment (Mitsubishi Chemical Corporation, MA-100)

[0060] Example 1 100 parts of epoxy resin (A1) as the epoxy resin, 1.0 part of 2PZL, 0.5 parts of 2MZ-A, and 0.5 parts of 2PZ as the hardener, and silica powder as the pigment. 30 12 parts of titanium dioxide and 0.3 parts of carbon black were mixed. The mixture was dry-blended in a Henschel mixer (Mitsui Miike Chemical Engineering Co., Ltd., Model 10B), while 0.8 parts of an acrylic polymer was added as an additive (surface conditioner). Next, using an extruder (Ikegai Iron Works Co., Ltd., PCM-30), the mixture was melt-kneaded at 100°C, flaked to a thickness of 3 to 5 mm with a cooling roll, cooled to room temperature, finely pulverized, and classified to obtain a powder coating with an average particle size (d50) of 50 μm.

[0061] A 2.0 mm x 70 mm x 150 mm SPCC-SB steel plate was preheated for 30 minutes in a 200°C hot air circulating oven. After preheating, it was removed, hung vertically, and placed in a coating booth. It was then painted with a paint gun, moving up and down once and a half times to a thickness of 300 μm. After painting, the plate was allowed to cool to room temperature, yielding test plates for MEK rubbing tests, impact resistance tests, and flex resistance tests. The coating and coating properties are shown in Table 1.

[0062] Examples 2 to 8, Comparative Examples 1 to 3 Powder coatings were obtained by compounding the ingredients in the amounts (parts) shown in Table 1 and by the same procedures and using the same equipment as in Example 1. Tests similar to those in Example 1 were carried out, and the results are shown in Table 1. In Examples 1 to 8, normal coating films were formed and there were no problems with hygiene. Examples 4 and 5, in which the epoxy resins obtained in Synthesis Examples 3 and 4 were used, are reference examples.

[0063]

Table 1

Claims

1. An epoxy resin powder coating comprising a bisphenol-type epoxy resin, a curing agent, and a pigment, wherein the bisphenol-type epoxy resin is an epoxy resin obtained by a one-stage method, the curing agent is contained in a range of 0.5 to 6 parts by mass and the pigment is contained in a range of 40 to 100 parts by mass per 100 parts by mass of the bisphenol-type epoxy resin, the epoxy group purity of the bisphenol-type epoxy resin is 75 mol% or more (excluding epoxy group purities of 90% or more), the curing agent essentially comprises an imidazoline derivative and an imidazole derivative, and the epoxy resin powder coating does not contain a polycarboxylic acid compound.

2. The fracture toughness of the cured product is 2.0 MPa m ０．５ 2. The epoxy resin powder coating according to claim 1, wherein the above-mentioned

3. 3. The epoxy resin powder coating according to claim 1, wherein the bisphenol type epoxy resin has an epoxy equivalent of 700 to 2500 g / eq. and a softening point of 70 to 120°C.

4. 4. The epoxy resin powder coating according to claim 1, wherein the bisphenol type epoxy resin is at least one selected from the group consisting of bisphenol F type epoxy resin, tetramethylbisphenol F type epoxy resin, bisphenol A type epoxy resin, and tetramethylbisphenol A type epoxy resin.

5. The epoxy resin powder coating according to any one of claims 1 to 4, wherein the imidazoline derivative is methylimidazoline and / or 2-phenylimidazoline, and the imidazole derivative is at least one selected from methylimidazole, dodecyl imidazole, phenylimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, an isocyanuric acid adduct of 2-methylimidazole, and 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine.

6. 6. The epoxy resin powder coating according to any one of claims 1 to 5, wherein the pigment is at least one selected from the group consisting of iron oxide, yellow iron oxide, silica powder, quartz powder, titanium oxide, calcium carbonate, barium sulfate, and carbon black.

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