Epoxy resin powder coating

Abstract

To provide an epoxy resin powder coating that effectively suppresses a decrease in elastic modulus of a cured coating film at high temperature.SOLUTION: This epoxy resin powder coating comprises (A) a bisphenol A-type epoxy resin having an epoxy equivalent of 500-2400 g / eq, (B) a novolac-type epoxy resin having an epoxy equivalent of 80-250 g / eq, (C) a curing agent, and (D) a layered silicate compound. When the total amount of the epoxy resins is 100 pts.mass, component (D) is contained in an amount of 35-95 pts.mass.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin powder coating, and more particularly to an epoxy resin powder coating in which the decrease in elastic modulus of the cured coating film at high temperatures is effectively suppressed. [Background technology]

[0002] Epoxy resins have excellent mechanical properties, chemical resistance, electrical properties, and moisture resistance, and are widely used as powder coatings. Powder coatings using epoxy resins (epoxy resin powder coatings) have excellent electrical properties and moisture resistance, and are used in fields such as processed steel materials like bus bars and steel pipes. They are also used as encapsulants for electronic components like capacitors and transistors to provide heat resistance and electrical insulation, and as coatings for automotive components like starters and wipers to provide electrical insulation and moisture resistance.

[0003] Known methods for coating with epoxy resin powder paint include electrostatic coating, preheated electrostatic coating, fluidized bed dipping, and hot spray coating.

[0004] The coating film formed on the surface of the object using epoxy resin powder paint includes a coating that covers and insulates the grooves in the rotor core of the rotor installed inside an electric motor. Because the inside of a motor can reach high temperatures (over 150°C) depending on the operating environment, the coating film must be heat resistant and have high mechanical strength.

[0005] Patent Document 1 discloses an epoxy resin powder coating containing a specified epoxy resin and a specified curing agent in order to improve heat resistance, and also discloses adding calcium carbonate or the like as a filler to the epoxy resin powder coating in order to improve mechanical strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-169314 Summary of the Invention [Problem to be solved by the invention]

[0007] When conventional epoxy resin powder coatings are used to form coatings in the grooves of the rotor core of a motor's rotor, the coating softens due to the high temperatures inside the motor, causing the windings to bite into the coating. While one approach to improving heat resistance would be to raise the glass transition temperature of the epoxy resin powder coating so that the coating would remain strong even at high temperatures, this has the drawback of creating a hard, brittle coating (cured product) that is weak against deformation and fracture. While epoxy resin powder coatings with a good elastic modulus offer good mechanical strength, conventional epoxy resin powder coatings suffer from a significant drop in elastic modulus at high temperatures.

[0008] The present invention has been made in view of the above points, and has as its object to provide an epoxy resin powder coating in which the decrease in the elastic modulus of the cured coating film at high temperatures is effectively suppressed. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention is specified as follows (1) to (3). (1) (A) a bisphenol A type epoxy resin having an epoxy equivalent of 500 to 2400 g / eq; (B) a novolac epoxy resin having an epoxy equivalent of 80 to 250 g / eq; (C) a curing agent; (D) a layered silicate compound; Including, An epoxy resin powder coating containing 35 to 95 parts by mass of (D) when the total amount of epoxy resins is 100 parts by mass. (2) The epoxy resin powder coating according to (1) above, further comprising (D') an acicular silicate compound. (3) The epoxy resin powder coating according to (2) above, which contains the layered silicate compound (D) and the needle-shaped silicate compound (D') in a blending ratio (mass of (D') / mass of (D)) of 0.1 to 1.0. [Effects of the Invention]

[0010] According to an embodiment of the present invention, an epoxy resin powder coating can be provided in which the decrease in the elastic modulus of the cured coating film at high temperatures is effectively suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between storage modulus and temperature in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] Below, we will explain the epoxy resin powder coating according to an embodiment of the present invention, but the present invention should not be interpreted as being limited to this, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art as long as they do not deviate from the scope of the present invention.

[0013] In this specification, the symbol "to" indicating a range of values ​​indicates a range that includes the values ​​stated as the upper and lower limits. When a unit is stated only for the upper limit of a range of values, this means that the lower limit is expressed in the same unit as the upper limit. In the numerical ranges described in stages in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0014] (epoxy resin powder coating) The epoxy resin powder coating according to an embodiment of the present invention is an epoxy resin powder coating for forming a cured product, and contains the following (A), (B), (C), and (D). (A) Bisphenol A epoxy resin with an epoxy equivalent of 500 to 2400 g / eq, (B) a novolac epoxy resin having an epoxy equivalent of 80 to 250 g / eq; (C) a curing agent, (D) Layered silicate compounds.

[0015] Hereinafter, each component contained in the epoxy resin powder coating according to an embodiment of the present invention will be described.

[0016] <(A) Bisphenol A epoxy resin> Powder coatings containing bisphenol A epoxy resins provide coating films, which are cured products formed after coating, with excellent mechanical properties, chemical resistance, electrical properties, and moisture resistance. The bisphenol A epoxy resin (A) has an epoxy equivalent of 500 to 2400 g / eq. By setting the epoxy equivalent of the bisphenol A epoxy resin to 500 g / eq or more, it is possible to prevent the melt viscosity of the powder coating from decreasing too much, thereby preventing problems such as dripping of the molten powder coating when applying the powder coating. Furthermore, by setting the epoxy equivalent to 2400 g / eq or less, good curing reactivity can be obtained. The epoxy equivalent of the bisphenol A epoxy resin (A) is more preferably 500 to 1800 g / eq, and even more preferably 500 to 980 g / eq. Two or more types of bisphenol A type epoxy resins having different epoxy equivalents may be used in combination so that the epoxy equivalent falls within the range of 500 to 2400 g / eq. Commercially available bisphenol A epoxy resins (A) include Epotohto (registered trademark) YD-011, Epotohto (registered trademark) YD-012, Epotohto (registered trademark) YD-014, and Epotohto (registered trademark) YD-017 (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), GESR-901, GESR-902, GESR-904, and GESR-907 (all manufactured by Epoxy Base Electronic Material Corporation Limited), and DER671, DER662E, DER664UE, and DER667E (all manufactured by Olien Corporation).

[0017] <(B) Novolac-type epoxy resin> Powder coatings containing novolac epoxy resins provide a coating film, which is a cured product formed after coating, with good heat resistance. The novolac epoxy resin (B) has an epoxy equivalent of 80 to 250 g / eq. By setting the epoxy equivalent of the novolac epoxy resin to 80 g / eq or more, a decrease in toughness is suppressed and good mechanical strength is obtained. Furthermore, by setting it to 250 g / eq or less, good heat resistance is obtained. The epoxy equivalent of the novolac epoxy resin (B) is more preferably 150 to 230 g / eq. Two or more novolac epoxy resins with different epoxy equivalents may be used in combination so that the epoxy equivalent falls within the range of 80 to 250 g / eq. Examples of the novolac epoxy resin (B) include phenol novolac epoxy resin, cresol novolac epoxy resin, etc. Among these, cresol novolac epoxy resin is preferred from the viewpoint of heat resistance. Commercially available cresol novolac epoxy resins include EPICLON (registered trademark) N-660, EPICLON (registered trademark) N-665, EPICLON (registered trademark) N-670, EPICLON (registered trademark) N-673, and EPICLON (registered trademark) N-695 (all manufactured by DIC Corporation), and EOCN-1020, EOCN-102S, and EOCN-104S (all manufactured by Nippon Kayaku Co., Ltd.).

[0018] The epoxy resin powder coating according to an embodiment of the present invention contains two types of epoxy resins, namely (A) bisphenol A type epoxy resin and (B) novolac type epoxy resin, and thus can suppress the decrease in elastic modulus at high temperatures.

[0019] From the viewpoint of suppressing a decrease in the elastic modulus at high temperatures, the compounding ratio (B) / (A) of the bisphenol A epoxy resin (A) to the novolac epoxy resin (B) is preferably 0.05 to 1.0, and more preferably 0.1 to 0.5. In this specification, unless otherwise specified, the "mixing ratio" refers to the mass ratio.

[0020] <(C) Hardener> As the curing agent (C), for example, hydrazide compounds, dicyandiamide, amine-based curing agents, phenol-based curing agents, imidazole-based curing agents, acid anhydride-based curing agents, etc. can be used alone or in combination.

[0021] Hydrazide compounds are compounds having a structure in which the hydroxyl groups of an acid are replaced with hydrazino groups, and have advantages such as high reactivity, ability to cure at low temperatures, and use as latent curing agents with high melting points, the ability to adjust the crosslink density by the number of functional groups, and excellent adhesive properties of the cured product. Examples of hydrazide compounds include adipic acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, and dodecanediohydrazide. Among these, it is preferable to use isophthalic acid dihydrazide because it can be cured at a lower temperature.

[0022] Dicyandiamide is an excellent latent curing agent with a high curing temperature. When used alone, it generates a large amount of heat during curing, so it is often used in combination with a curing accelerator. Powder paints containing dicyandiamide have good mechanical properties when the coating film is cured after application.

[0023] Examples of the amine curing agent include aliphatic amines, alicyclic amines, aromatic amines, modified amines, polyamidoamines, etc. Two or more types of amine curing agents may be used in combination. Examples of aliphatic amines include ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, dipropylenetriamine, N,N-dimethyl-1,3-propanediamine, cyclohexylamine, cyclohexylamine, and N,N-dimethylcyclohexylamine. Examples of alicyclic amines include 1,3-cyclopentanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 1-amino-1-methyl-4-aminomethylcyclohexane, 1-amino-1-methyl-3-aminomethylcyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(3-methyl-cyclohexylamine), methyl-2,3-cyclohexanediamine, methyl-2,4-cyclohexanediamine, methyl-2,6-cyclohexanediamine, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane. Examples of aromatic amines include 4,4'-diaminodiphenylmethane, phenylenediamine, diaminodiphenylsulfone, ortho-toluidine, N,N-dimethylbenzylamine, and meta-xylylenediamine. Examples of modified amines include epoxy compound-added polyamines, Michael addition polyamines, Mannich addition polyamines, thiourea addition polyamines, ketone-blocked polyamines, dicyandiamide, guanidine, organic acid hydrazides, diaminomaleonitrile, amine imide compounds, boron trifluoride piperidine, boron trifluoride monoethylamine, etc. Commercially available modified amines include Fujicure (registered trademark) FXR-1020, Fujicure (registered trademark) FXR-1030 (both manufactured by T&K TOKA Corporation), Amicure (registered trademark) PN-23, Amicure (registered trademark) MY-24 (both manufactured by Ajinomoto Fine-Techno Co., Ltd.), etc. Polyamidoamines are mainly produced by condensation of dimer acid and polyamine, and include those having reactive primary and secondary amino groups in the molecule. The molecular weight, viscosity, amine value, etc. of polyamidoamines vary depending on the molar ratio of dimer acid to polyamine, the ratio of monomer acid, dimer acid, and trimer acid in the fatty acid composition, the type of polymer, the number of functional groups, etc.

[0024] Examples of phenolic curing agents include bisphenol A type phenolic resin curing agents, bisphenol F type phenolic resin curing agents, etc. Two or more types of phenolic curing agents may be used in combination.

[0025] Examples of imidazole curing agents include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and triazine compounds having an imidazole ring. Examples of triazine compounds having an imidazole ring include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Two or more imidazole curing agents may be used in combination.

[0026] Examples of acid anhydride curing agents include phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, benzene-1,2,4,5-tetracarboxylic anhydride, etc. Two or more types of acid anhydride curing agents may be used in combination.

[0027] The amount of curing agent (C) in the epoxy resin powder coating according to an embodiment of the present invention is not particularly limited as long as it is within a range that does not impair the effects of this embodiment, but when the epoxy equivalent relative to the total amount of epoxy resin is taken as 1, the ratio of the reactive group equivalent of the curing agent is preferably in the range of 0.5 to 1.5, and more preferably in the range of 0.7 to 1.3.

[0028] <(D) Layered silicate compounds> The layered silicate compound (D) in the epoxy resin powder coating according to an embodiment of the present invention is a particle of a silicate compound having a single-layer or multi-layer structure, and examples thereof include mica, talc, smectites (bentonite, organic bentonite, montmorillonite, beidellite, nontronite, saponite, hectorite, and volconescoite), vermiculite, pyrophyllite, sericite, kaolins (kaolinite, halloysite, and dickite), and sepiolite. Of these, mica and talc are preferred. Two or more types of layered silicate compounds may be used in combination. If necessary, the layered silicate compound may be pulverized alone when producing the epoxy resin powder coating.

[0029] The average particle size of the layered silicate compound (D) in the epoxy resin powder coating according to an embodiment of the present invention is, from the viewpoint of suppressing a decrease in the elastic modulus of the cured coating film at high temperatures, preferably 20 to 170 μm, more preferably 20 to 130 μm, and even more preferably 20 to 90 μm, in terms of average major axis. The average minor axis is preferably 10 to 70 μm, more preferably 10 to 65 μm, and even more preferably 10 to 60 μm. Additionally, the ratio of the average major axis to the average minor axis of the layered silicate compound (D) in the epoxy resin powder coating according to an embodiment of the present invention, calculated by dividing the average major axis by the average minor axis, is preferably 1 to 3, more preferably 1 to 2.8, and even more preferably 1 to 2.6. The average particle size of the layered silicate compound (D) is the average value of particle sizes measured using a scanning electron microscope. In the image taken with the scanning electron microscope, the particle surfaces are observed, and 10 or more particles are randomly selected as measurement targets, their major and minor diameters are measured, and the measured values ​​are averaged. This gives the average major and minor diameters. The average major axis and the average minor axis of the layered silicate compound (D) can be controlled by using, as a raw material, a layered silicate compound whose average major axis and average minor axis measured with an electron microscope fall within the above ranges.

[0030] The layered silicate compound (D) is contained in an amount of 35 to 95 parts by mass per 100 parts by mass of the total epoxy resin. When the layered silicate compound (D) is contained in an amount of 35 parts by mass or more per 100 parts by mass of the total epoxy resin, it is uniformly dispersed in the epoxy resin powder coating, and a decrease in the elastic modulus at high temperatures of the coating film formed by curing the epoxy resin powder coating can be effectively suppressed. When the layered silicate compound (D) is contained in an amount of 95 parts by mass or less per 100 parts by mass of the total epoxy resin, an excessive increase in the melt viscosity of the epoxy resin powder coating can be suppressed. The layered silicate compound (D) is contained in an amount of preferably 40 to 90 parts by mass, and more preferably 45 to 85 parts by mass, based on 100 parts by mass of the total amount of the epoxy resin.

[0031] <(D') Acicular silicate compound> The epoxy resin powder coating according to an embodiment of the present invention preferably further comprises (D') an acicular silicate compound. The acicular silicate compound (D') is a silicate compound having a needle-like shape, and examples thereof include wollastonite, silica, halloysite, imogolite, sepiolite, and palygorskite. Of these, wollastonite is preferred. Two or more acicular silicate compounds may be used in combination. The acicular silicate compound (D') in the epoxy resin powder coating according to an embodiment of the present invention preferably has an aspect ratio (average major axis / average minor axis), which is the ratio of the average major axis to the average minor axis, of 15 to 25, and more preferably 10 to 20, from the viewpoint of suppressing a decrease in the elastic modulus of the cured coating film at high temperatures. The average particle size of the acicular silicate compound (D') can be the average value of particle sizes measured using a laser diffraction particle size distribution measuring device or the like.

[0032] If an epoxy resin powder coating contains too much layered silicate compound (D), the melt viscosity of the epoxy resin powder coating will become too high. The use of an acicular silicate compound (D') in combination with the layered silicate compound (D) fulfills the function of increasing the elastic modulus of the layered silicate compound (D). This prevents the epoxy resin powder coating from containing too much layered silicate compound (D), which would increase the viscosity, while also preventing the cured coating film from losing its elastic modulus at high temperatures.

[0033] The epoxy resin powder coating according to an embodiment of the present invention preferably contains the layered silicate compound (D) and the acicular silicate compound (D') in a blending ratio (mass of (D') / mass of (D)) of 0.1 to 1.0. When the blending ratio (mass of (D') / mass of (D)) is 0.1 or more, the blending amount of the layered silicate compound (D) can be reduced, thereby preventing an excessive increase in the melt viscosity of the epoxy resin powder coating. When the blending ratio (mass of (D') / mass of (D)) is 1.0 or less, the layered silicate compound (D) is uniformly dispersed in the epoxy resin powder coating, and the coating film formed by curing the epoxy resin powder coating can be prevented from decreasing in the modulus of elasticity at high temperatures. The epoxy resin powder coating according to an embodiment of the present invention preferably contains the layered silicate compound (D) and the acicular silicate compound (D') in a blending ratio (mass of (D') / mass of (D)) of 0.2 to 1.0, more preferably 0.3 to 1.0.

[0034] Although the layered silicate compound (D) and the acicular silicate compound (D') described above function as fillers, the epoxy resin powder coating material according to an embodiment of the present invention may also contain other fillers (D"). The other fillers (D") may be either inorganic or organic. Examples of inorganic fillers include oxides such as alumina, magnesium oxide, zinc oxide, iron oxide, and silicon dioxide, calcium sulfate, barium sulfate, calcium carbonate, aluminum sulfate, aluminum hydroxide, magnesium hydroxide, calcium silicate, magnesium silicate, kaolinite, montmorillonite, and bentonite, as well as compounds containing these as components. Examples of organic fillers include acrylic resins, silicone resins, butadiene rubber, polyesters, polyurethanes, polyvinyl butyral, polyarylate, polymethyl methacrylate, acrylic rubber, polystyrene, acrylonitrile butadiene rubber, styrene butadiene rubber, and silicone-modified resins, as well as organic fine particles of copolymers containing these as components. The amount of the (D'') other filler to be blended can be 200% by mass or less relative to the layered silicate compound (D).

[0035] <(E) Curing accelerator> The epoxy resin powder coating according to the embodiment of the present invention preferably contains a curing accelerator (E). The type of curing accelerator that can be used is not particularly limited, and an appropriate one can be selected from the viewpoints of reaction rate, reaction temperature, storage stability, etc. Examples of the curing accelerator (E) include heterocyclic amines and their derivatives, amine compounds, etc. Examples of heterocyclic amines and derivatives thereof include 1,8-diazabicyclo[5.4.0]undecene-7, imidazole, imidazoline, piperidine, piperazine, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazoline, 2,4-dimethylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine, etc. Two or more types of heterocyclic amines and derivatives thereof may be used in combination. Commercially available heterocyclic amines and derivatives thereof include DBU (registered trademark) (manufactured by San-Apro Co., Ltd.), Curesol (registered trademark) 2MZ-H, and Curesol (registered trademark) 2MZ-A (all manufactured by Shikoku Chemicals Corporation).

[0036] Examples of the amine compound include aliphatic amines, aromatic amines, and modified amines. Examples of the aliphatic amine include ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, dipropylenetriamine, N,N-dimethyl-1,3-propanediamine, cyclohexylamine, and N,N-dimethylcyclohexylamine. Examples of aromatic amines include 4,4'-diaminodiphenylmethane, phenylenediamine, diaminodiphenylsulfone, ortho-toluidine, N,N-dimethylbenzylamine, and meta-xylylenediamine. Examples of modified amines include epoxy compound-added polyamines, Michael addition polyamines, Mannich addition polyamines, thiourea addition polyamines, ketone-blocked polyamines, dicyandiamide, guanidine, organic acid hydrazides, diaminomaleonitrile, amine imide compounds, boron trifluoride piperidine, boron trifluoride monoethylamine, etc. Commercially available modified amines include Fujicure (registered trademark) FXR-1020, Fujicure (registered trademark) FXR-1030 (both manufactured by T&K TOKA Corporation), Amicure (registered trademark) PN-23, Amicure (registered trademark) MY-24 (both manufactured by Ajinomoto Fine-Techno Co., Ltd.), etc.

[0037] <Other ingredients> The epoxy resin powder coating according to the embodiment of the present invention may contain, as appropriate, conventional auxiliary components other than those described above, such as a surface conditioner, a flame retardant, a colorant, a thixotropic agent, an anti-settling agent, a coupling agent, an anti-foaming agent, a release agent, and a flowability adjuster, provided that the effects of the embodiment are not impaired. Examples of the surface conditioner include a mixture of a fatty acid glyceride and an acrylic copolymer, an acrylic acid alkyl ester polymer, a methacrylic acid alkyl ester polymer, and a copolymer of an acrylic acid alkyl ester and a methacrylic acid alkyl ester. Examples of the flame retardant include phosphorus compounds, halogen compounds, antimony compounds such as antimony trioxide, and metal hydroxides. Examples of colorants include titanium dioxide, ferric oxide, carbon black, and phthalocyanine blue.

[0038] <Storage modulus> The epoxy resin powder coating according to an embodiment of the present invention has a storage modulus at 50°C of 3.8 to 5.2 GPa, preferably 4.0 to 5.0 GPa. The storage modulus at 180°C is 0.05 to 0.13 GPa, preferably 0.06 to 0.11 GPa. Since the decrease in storage modulus at high temperatures is effectively suppressed in this manner, the cured product (coating film) of the epoxy resin powder coating has good mechanical strength at high temperatures, and softening of the coating film can be suppressed. The method for measuring the storage modulus will be described later.

[0039] <Uses and effects> The epoxy resin powder coating according to the embodiment of the present invention, like general epoxy resin powder coatings, can be used as a coating that imparts insulation, chemical resistance, moisture resistance, and the like to the surfaces of processed steel materials such as bus bars and steel pipes, electronic components, and the like. In particular, the epoxy resin powder coating according to the embodiment of the present invention can be used as an epoxy resin powder coating in which the decrease in elastic modulus of the cured coating film at high temperatures is effectively suppressed. For example, a coating formed using the epoxy resin powder coating according to the embodiment of the present invention in a groove in a rotor core of a motor rotor softens when the temperature inside the motor rises above the glass transition temperature, but the decrease in elastic modulus is suppressed, thereby effectively suppressing the winding from penetrating the coating film. This maintains the insulation between the winding and the rotor core within the motor, preventing motor failure.

[0040] (Painting method using epoxy resin powder paint) The method for applying the epoxy resin powder coating according to the embodiment of the present invention is not particularly limited, and known coating methods can be applied, such as fluidized bed coating, electrostatic coating, preheated electrostatic coating, and hot spray coating. Since the epoxy resin powder coating according to the embodiment of the present invention can be cured at low temperature in a short time, it is particularly preferable to use a coating method using a fluidized bed method. A specific example of the fluidized bed method is to immerse a preheated object to be coated in a fluidized bed of the coating, and melt the epoxy resin powder coating adhering to the surface of the object to be coated. The molten epoxy resin powder coating is then cured by heating in a curing oven or the like, to form a coating film on the surface of the object to be coated.

[0041] (Manufacturing method of epoxy resin powder coating) The epoxy resin powder coating according to an embodiment of the present invention can be produced, for example, by the following method. First, a composition is prepared by blending the above-mentioned (A) bisphenol A epoxy resin, (B) novolac epoxy resin, (C) curing agent, and (D) layered silicate compound, and optionally adding (D') acicular silicate compound, (E) curing accelerator, and conventional auxiliary ingredients such as surface conditioners other than the above, flame retardants, colorants, thixotropic agents, anti-settling agents, coupling agents, antifoaming agents, mold release agents, and flowability modifiers. This composition contains 35 to 95 parts by mass of the layered silicate compound (D) per 100 parts by mass of the total epoxy resin. Next, the composition is melt-kneaded, which is preferably completed in a short time using an extruder or the like. Thereafter, the obtained mixture is cooled and solidified, and the solidified mixture (melt-kneaded product) is pulverized to obtain the epoxy resin powder coating material according to an embodiment of the present invention. [Example]

[0042] Examples of the present invention are given below, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0043] 1. Preparation of Epoxy Resin Powder Coating <Examples 1 to 8, Comparative Example 1> A composition was prepared for each experimental example by mixing all materials in the blending ratio (mass ratio) shown in Table 1. The raw materials for each component shown in Table 1 are listed below. The average particle size D50 of the filler (D'') was measured using a laser diffraction particle size distribution analyzer.

[0044] (A) Bisphenol A epoxy resin (a1) 625g / eq bisphenol A type solid epoxy resin (a2) 938g / eq bisphenol A type solid epoxy resin (B) Cresol novolac epoxy resin (b1) 225g / eq cresol novolac epoxy resin (b2) 200g / eq cresol novolac epoxy resin (C) Hardener (c1) Isophthalic acid dihydrazide (c2) Dicyandiamide (D) Layered silicate compound (filler) (d1) Mica (average major axis = 40 μm, average minor axis = 25 μm, average major axis / average minor axis = 1.6, layered) (d2) Mica (average major axis = 45 μm, average minor axis = 30 μm, average major axis / average minor axis = 1.5, layered) (D') Acicular silicate compound (filler) (d3) Wollastonite (aspect ratio = 10, needle-shaped) (D'') Others (fillers) (d4) Silica (average particle size D50=30μm, spherical) (d5) Calcium carbonate (average particle size D50 = 2.5 μm, irregular shape) (E) Curing accelerator (e1) 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine

[0045] Next, each composition was melt-kneaded using an extruder. Thereafter, the obtained mixture was cooled and solidified, and the solidified mixture (melt-kneaded product) was pulverized to obtain an epoxy resin powder coating material.

[0046] 2. Evaluation The properties of the epoxy resin powder coating samples obtained in each experimental example were evaluated by the methods described below.

[0047] <1-1: Storage modulus> The storage modulus of the cured epoxy resin powder coating material obtained in each experimental example was measured using a dynamic viscoelasticity measuring device (MCR102e, manufactured by Anton Paar) at a temperature range of 20 to 220°C, a heating rate of 2°C / min, a strain of 0.02%, and a frequency of 10 Hz. The evaluation results are shown in Table 1. A graph showing the relationship between storage modulus and temperature for Examples 1, 2, and 7 and Comparative Example 1 is shown in Figure 1.

[0048] <1-2: Appearance of cured coating film> The appearance of the cured coating film of the epoxy resin powder coating obtained in each experimental example was evaluated as follows. A mild steel plate (60 mm long, 60 mm wide, 3.2 mm thick) preheated to 150°C was immersed in a fluidized bath of the epoxy resin powder coating obtained in each experimental example, and allowed to adhere to the surface of the substrate. The epoxy resin powder coating melted on the surface of the substrate was then heated in a curing oven or the like to harden, forming a coating film. The appearance of the coating film was then visually observed. The evaluation criteria were as follows. The evaluation results are shown in Table 1. a: A smooth coating film is formed. b: There are slight irregularities, but this does not pose a problem for practical use. c: There are irregularities or small holes, which may cause problems in practical use. d: There are unevenness and small holes.

[0049] [Table 1]

[0050] 3. Discussion The samples of Examples 1 to 8 were epoxy resin powder coatings containing (A) a bisphenol A type epoxy resin with an epoxy equivalent of 500 to 2400 g / eq, (B) a novolac type epoxy resin with an epoxy equivalent of 80 to 250 g / eq, (C) a curing agent, and (D) a layered silicate compound, and the amount of (D) was 35 to 95 parts by mass when the total amount of epoxy resin was 100 parts by mass. Therefore, it was found that the decrease in elastic modulus at high temperatures was well suppressed. Furthermore, as shown in the graph of FIG. 1, which shows the relationship between storage modulus and temperature obtained in Examples 1, 2, and 7, the storage modulus at 50°C decreased with increasing temperature up to 180°C, but the decrease was small. Furthermore, the temperatures at which the modulus of elasticity began to decrease were higher in Examples 1 and 2 than in Example 7. This is thought to be due to the amount of layered silicate compound (D) (filler) blended. A higher temperature at which the modulus of elasticity began to decrease is preferable because the modulus of elasticity is maintained up to a higher temperature, improving heat resistance. The sample of Comparative Example 1 did not contain the layered silicate compound (D) but contained calcium carbonate as a filler instead, and therefore showed a greater decrease in elastic modulus at high temperatures than Examples 1-8.

Claims

1. (A) a bisphenol A type epoxy resin having an epoxy equivalent of 500 to 2400 g / eq; (B) a novolac epoxy resin having an epoxy equivalent of 80 to 250 g / eq; (C) a curing agent; (D) a layered silicate compound; Including, An epoxy resin powder coating material containing 35 to 95 parts by mass of (D) when the total amount of epoxy resins is 100 parts by mass.

2. 2. The epoxy resin powder coating according to claim 1, further comprising (D') an acicular silicate compound.

3. 3. The epoxy resin powder coating according to claim 2, comprising the layered silicate compound (D) and the needle-shaped silicate compound (D') in a blending ratio (mass of (D') / mass of (D)) of 0.1 to 1.0.

Images