JP2025148037A - Epoxy resin powder coating - Google Patents

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

The present invention relates to an epoxy resin powder coating. In particular, it relates to an epoxy resin powder coating in which the decrease in elastic modulus of the cured coating film at high temperatures is effectively suppressed.

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 such as capacitors and transistors to provide heat resistance and electrical insulation, and as coatings for automotive components such as starters and wipers to provide electrical insulation and moisture resistance.

Known methods for painting with epoxy resin powder paint include electrostatic painting, preheated electrostatic painting, fluidized bed dipping, and hot spraying.

Examples of coating films formed on the surface of objects using epoxy resin powder paint include those that cover and insulate grooves in the rotor core of electric motors. Because the inside of motors can reach high temperatures (over 150°C) depending on the operating environment, coating films must be heat-resistant and have high mechanical strength.

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.

Japanese Patent Application Laid-Open No. 2020-169314

When conventional epoxy resin powder paints are used to form coatings in the grooves in 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. One approach to improving heat resistance would be to raise the glass transition temperature of the epoxy resin powder paint so that the coating would remain strong even at high temperatures, but this has the drawback of creating a hard, brittle coating (cured product) that is weak against deformation and fracture. On the other hand, if an epoxy resin powder paint has a good elastic modulus, it will have good mechanical strength, but conventional epoxy resin powder paints have the problem of a significant drop in elastic modulus at high temperatures.

The present invention was developed with the above points in mind, and aims to provide an epoxy resin powder coating in which the decrease in elastic modulus of the cured coating film at high temperatures is effectively suppressed.

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 material 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), containing 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.

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.

1 is a graph showing the relationship between storage modulus and temperature in Examples and Comparative Examples.

The following describes an epoxy resin powder coating according to an embodiment of the present invention, but the present invention should not be construed as being limited to this description. Various changes, modifications, and improvements may 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.

In this specification, the term "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.

(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) 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) Layered silicate compounds.

The following describes each component contained in the epoxy resin powder coating according to an embodiment of the present invention.

<(A) Bisphenol A Epoxy Resin>
Powder coatings containing bisphenol A epoxy resins exhibit excellent mechanical properties, chemical resistance, electrical properties, and moisture resistance in the coating film that forms a cured product after application. 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, excellent 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.
The bisphenol A type epoxy resin may be used in combination of two or more types having different epoxy equivalents so that the epoxy equivalent falls within the range of 500 to 2400 g/eq.
Commercially available products of the bisphenol A epoxy resin (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 D.E.R. 671, D.E.R. 662E, D.E.R. 664UE, and D.E.R. 667E (all manufactured by Olien Corporation).

<(B) Novolac-type epoxy resin>
Powder coatings containing novolac epoxy resins provide coating films, which are cured products formed after application, 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.
The novolac epoxy resin may be used in combination of two or more types having different epoxy equivalents 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.).

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

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, more preferably 0.1 to 0.5.
In this specification, unless otherwise specified, the "mixing ratio" refers to the mass ratio.

<(C) Curing Agent>
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.

Hydrazide compounds have a structure in which the hydroxyl groups of an acid are replaced with hydrazino groups. They have advantages such as high reactivity, low-temperature curing, and use as latent curing agents with high melting points. The crosslink density can be adjusted by adjusting the number of functional groups, and the cured product has excellent adhesive properties. Examples of hydrazide compounds include adipic acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, and dodecanediohydrazide. Of these, isophthalic acid dihydrazide is preferred because it can be cured at a lower temperature.

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 formed into a cured film after application.

Examples of the amine-based curing agent include aliphatic amines, alicyclic amines, aromatic amines, modified amines, polyamidoamines, etc. Two or more types of amine-based curing agents may be used in combination.
Examples of the aliphatic amine 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-xylenediamine.
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 and Fujicure (registered trademark) FXR-1030 (both manufactured by T&K TOKA Corporation), Amicure (registered trademark) PN-23, and Amicure (registered trademark) MY-24 (both manufactured by Ajinomoto Fine-Techno Co., Ltd.).
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.

Examples of phenolic curing agents include bisphenol A-type phenolic resin curing agents and bisphenol F-type phenolic resin curing agents. Two or more types of phenolic curing agents may be used in combination.

Examples of imidazole-based 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-based curing agents may be used in combination.

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

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. However, 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.

<(D) Layered Silicate Compound>
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 volconzcoite), 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.

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 layered silicate compound (D) in the epoxy resin powder coating according to an embodiment of the present invention is preferably an average major axis of 20 to 170 μm, more preferably 20 to 130 μm, and even more preferably 20 to 90 μm. The average minor axis is preferably 10 to 70 μm, more preferably 10 to 65 μm, and even more preferably 10 to 60 μm. In addition, the ratio of the average major axis to the average minor axis, calculated by dividing the average major axis of the layered silicate compound (D) in the epoxy resin powder coating according to an embodiment of the present invention 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 the major and minor diameters of 10 or more particles are randomly selected as measurement targets, and the obtained measurements 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, as measured with an electron microscope, fall within the above ranges.

The layered silicate compound (D) is contained in an amount of 35 to 95 parts by mass when the total amount of epoxy resin is 100 parts by mass. When the layered silicate compound (D) is contained in an amount of 35 parts by mass or more when the total amount of epoxy resin is 100 parts by mass, 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 when the total amount of epoxy resin is 100 parts by mass, 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.

<(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.

If an epoxy resin powder coating contains too much layered silicate compound (D), the melt viscosity of the epoxy resin powder coating will increase too much. By using the acicular silicate compound (D') in combination, the layered silicate compound (D)'s function of increasing the elastic modulus is fulfilled. 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.

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 decrease in the elastic modulus at high temperatures of the coating film formed by curing the epoxy resin powder coating can be prevented. 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, and even more preferably 0.3 to 1.0.

Although the layered silicate compound (D) and the acicular silicate compound (D') described above function as fillers, the epoxy resin powder coating according to an embodiment of the present invention may also contain (D") other fillers. The (D") other fillers 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).

<(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).

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-xylenediamine.
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 and Fujicure (registered trademark) FXR-1030 (both manufactured by T&K TOKA Corporation), Amicure (registered trademark) PN-23, and Amicure (registered trademark) MY-24 (both manufactured by Ajinomoto Fine-Techno Co., Ltd.).

<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.

<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. Because 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.

<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.

(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.

(Method for manufacturing 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, if necessary, further adding (D') acicular silicate compound, (E) curing accelerator, and conventional auxiliary components such as surface conditioners other than the above-mentioned components, 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) when the total amount of the epoxy resin is 100 parts by mass.
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.

The following examples of the present invention are provided to provide a better understanding of the present invention and its advantages, and are not intended to limit the invention.

1. Preparation of epoxy resin powder coatings <Examples 1 to 8, Comparative Example 1>
A composition was prepared by mixing all materials for each experimental example in the blending ratio (mass ratio) shown in Table 1. The raw materials for each component shown in Table 1 are as follows. The average particle size D50 of the filler (D'') was measured using a laser diffraction particle size distribution analyzer.

(A) Bisphenol A type epoxy resin (a1) 625 g/eq bisphenol A type solid epoxy resin (a2) 938 g/eq bisphenol A type solid epoxy resin (B) Cresol novolac type epoxy resin (b1) 225 g/eq cresol novolac type epoxy resin (b2) 200 g/eq cresol novolac type 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 = 30 μm, 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

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

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

<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.

<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 (length 60 mm, width 60 mm, thickness 3.2 mm) 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 cause problems in practical use.
d: There are irregularities and small holes.

3. Discussion The samples according to Examples 1 to 8 were epoxy resin powder coatings containing (A) a bisphenol A type epoxy resin having an epoxy equivalent of 500 to 2400 g/eq, (B) a novolac type epoxy resin having 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 the epoxy resin was taken as 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 (filler) (D). 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, thereby 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 to 8.

Claims (3)

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