JP7734580B2 - powder paint - Google Patents

Description

The present invention relates to a powder coating made from a powdered thermosetting composition suitable for use in electrical components, particularly for bonding coils.

A wound coil is placed within the core space of the rotor (armature) of an electric motor, generator, or other device. The coil is fixed within the core space to prevent the coil windings from coming apart due to rotation, or to prevent the winding insulation from peeling off and causing a short circuit due to friction or collision between the windings and the teeth or between the windings themselves. Epoxy-based powder coatings have been used to fix the coils in this way (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 63-221174

The powder coating described in Patent Document 1 has good flowability when melted, allowing it to fill the core space well, but the resulting cured product (coating film) has the problem of poor heat dissipation. In recent years, therefore, the addition of various heat dissipation agents to powder coatings has been investigated, with an emphasis on heat dissipation measures to address the increase in heat generated by electric motors, generators, and other devices that are becoming more powerful and powerful.

When a heat-dissipating agent is added to a composition to improve the heat dissipation properties of the cured product, this can reduce the flow of the powder coating when melted, worsening its paintability and making it difficult to obtain a cured product with a smooth, good appearance. Increasing the amount of heat-dissipating agent added to give the cured product high heat dissipation properties not only exacerbates this tendency, but also reduces the relative proportions of other components in the composition, resulting in a decrease in various important properties of the cured product, such as heat resistance.

The present invention was made in light of the above circumstances. It aims to provide a powder coating that can impart excellent heat dissipation properties to a coating film while suppressing deterioration of paintability, and a coated object formed from the coating and equipped with a coating film that has a good appearance and excellent heat dissipation properties.

As a result of extensive research, the present inventors have found that a powder coating material that satisfies the following requirements is effective in forming a coating film that has a good appearance and excellent heat dissipation properties.
- An epoxy compound with a small molecular weight (specific epoxy compound) is used as the thermosetting compound.
The insulating inorganic filler used has a thermal conductivity of a predetermined value or more and a predetermined particle size (d ₅₀ , d ₁₀ ) (specific filler).
The blending amount of the specific filler is within a specific range.
Based on these new findings, the present inventors have completed the invention provided below and solved the above-mentioned problems.

In the following,
(A): an epoxy compound having an epoxy equivalent in the range of 200 g/eq or more and 1000 g/eq or less;
(B): a curing agent that reacts with (A);
(C): an insulating inorganic filler having a thermal conductivity of 10 W/(m·K) or more, a particle diameter (d ₅₀ ) of 10 μm or more and 60 μm or less, and a particle diameter (d ₁₀ ) of 3 μm or more and 40 μm or less;
(D): Fine particles having an average particle size of primary particles of 1 μm or less,
Let's say.

According to the present invention, there is provided a powder coating material for forming a cured product, comprising:
It is composed of a finely ground thermosetting composition,
The thermosetting composition comprises (A), (B), and (C),
The powder coating material is provided in which (C) is contained in the entire composition in an amount ranging from 72% by mass to 85% by mass.
According to the present invention, there is provided a coating film comprising a cured product formed from the above powder coating material.
According to the present invention, there is provided an object to be coated having the above coating film.
According to the present invention, there is provided the above-mentioned object to be coated, which is a coil.

The above powder coating may include the following aspects.
The mass ratio of (C) to the mixture of (A) and (B) may be 2.6 or more and 6.0 or less per 1:1.
(C) may have a maximum particle size (d _max ) in the range of 40 μm or more and 200 μm or less.
The thermosetting composition may further contain (D).
(D) may be contained in the entire composition in a range of 0.02 mass % or more and 0.5 mass % or less.

The present invention provides a powder coating that contains specific epoxy compounds and fillers (A and C), with the latter in an adjusted proportion, thereby imparting excellent heat dissipation properties to the coating film while suppressing deterioration of paintability, and a coated object such as a coil formed from the coating and equipped with a coating film that has a good appearance and excellent heat dissipation properties.

The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment. Appropriate modifications and improvements to the following embodiment based on the common knowledge of those skilled in the art are also within the scope of the present invention, provided they do not deviate from the spirit of the present invention.

1. (powder paint)
A powder coating according to one embodiment of the present invention is a powder coating for forming a cured product, and is composed of finely pulverized (powder particles) thermosetting composition. The thermosetting composition (hereinafter also referred to simply as "composition") according to one embodiment for forming the powder coating contains a thermosetting compound, (B) a curing agent, and a filler. The thermosetting compound and the filler each contain 95% by mass or more (preferably 100% by mass) of (A) a specific epoxy compound and (C) a specific insulating inorganic filler. The thermosetting compound and the filler may contain components other than (A) and (C), respectively. That is, a composition according to one embodiment contains at least (A), (B), and (C). Each component is described in detail below.

1-1. (thermosetting compound)
In a composition according to one embodiment, a specific thermosetting compound is used, specifically, (A) an epoxy compound having an epoxy equivalent in the range of 200 g/eq or more and 1000 g/eq or less.
The epoxy compound is not particularly limited as long as it can be used as a raw material in the production of powder coatings. Examples include bisphenol-type epoxy compounds (e.g., bisphenol A-type epoxy compounds, bisphenol F-type epoxy compounds, brominated bisphenol A-type epoxy compounds, hydrogenated bisphenol A-type and AD-type epoxy compounds), phenol novolac-type epoxy compounds, dicyclopentadiene-type epoxy compounds, cresol novolac-type epoxy compounds, bisphenol A novolac-type epoxy compounds, and naphthalene ring-containing epoxy compounds. Epoxy compounds also include epoxy resins, which are polymers of the above epoxy compounds. Among these, preferred epoxy compounds are bisphenol-type epoxy compounds such as bisphenol A-type epoxy resins and cresol novolac-type epoxy compounds.

The epoxy compound used has an epoxy equivalent of 200 g/eq or more and 1000 g/eq or less (i.e., (A)). By setting the epoxy equivalent of the epoxy compound within the above range, the cured product will have excellent flowability as well as toughness. In particular, by setting the epoxy equivalent to 200 g/eq or more, toughness can be imparted to the cured product, and by setting it to 1000 g/eq or less, good flowability will be achieved during coating.
The epoxy compounds may be used in combination of two or more types having different epoxy equivalents so that the epoxy equivalent falls within the range of 200 g/eq or more and 1000 g/eq or less.

The physical properties of (A) are not particularly limited, but preferably the softening point is 70° C. or higher and 120° C. or lower. By adjusting the softening point of the epoxy compound within the above range, the fluidity during application is improved. In addition, the effect of preventing blocking is also excellent.
Two or more epoxy compounds having different softening points may be used in combination so that the softening point is in the range of 70° C. to 120° C. The softening point can be measured by the ring and ball method according to JIS K 7234.
(A) may be used alone or in combination of two or more.

The content (total amount) of (A) in the composition is not particularly limited, but taking into consideration the blending balance with other components, it is preferably 10% by mass or more and 30% by mass or less relative to the total amount of all solids in the composition (100% by mass).

1-2. (Hardening agent)
The curing agent (B) used in forming the composition is not particularly limited as long as it reacts with the thermosetting compound, particularly with (A). Examples include phenol-based curing agents, diamine-based curing agents, acid anhydride-based curing agents, cyanate-based curing agents, isocyanate-based curing agents, imidazole-based compounds, organic phosphorus-based compounds, tertiary amines, and quaternary ammonium salts.
Examples of phenol-based curing agents include phenol novolac resins, phenol aralkyl resins, bisphenol A-type novolac resins, cresol novolac resins, and naphthol aralkyl resins. Examples of diamine-based curing agents include diethyldiaminodiphenylmethane and dicyandiamide (DICY). Examples of acid anhydride-based curing agents include alicyclic acid anhydrides (e.g., hexahydrophthalic anhydride (HHPA), methyltetrahydrophthalic anhydride (MTHPA)), and aromatic acid anhydrides (e.g., trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), benzophenonetetracarboxylic acid (BTDA)). Examples of cyanate-based curing agents include bisphenol A-type cyanate ester resins. Examples of the isocyanate curing agent include 4,4'-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (2,4-TDI), and 2,6-toluene diisocyanate (2,6-TDI).
(B) may be used alone or in combination of two or more.

The content of (B) in the composition is not particularly limited. In one embodiment, the equivalent ratio of (B) to (A) is preferably 0.3 or more and 2.0 or less, and more preferably 0.5 or more and 1.5 or less. In other words, the contents of (A) and (B) are preferably such that the above-mentioned equivalent ratio is satisfied. If the contents of (A) and (B) are such that the above-mentioned equivalent ratio is satisfied, the composition will have superior heat resistance and mechanical properties in the cured product. This is thought to be because the curing reaction of (A) and (B) proceeds smoothly.

1-2-1. (Curing accelerator)
The composition may contain a curing accelerator as needed. 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 include imidazole compounds, organic phosphorus compounds, tertiary amines, and quaternary ammonium salts.
The curing accelerator may be used alone or in combination of two or more.
When the composition contains a curing accelerator, the content of the curing accelerator in the composition is not particularly limited. From the viewpoint of storage stability, the mass ratio of the curing accelerator to (B):1 is, for example, 0.1 or more, preferably 0.2 or more, and for example, 10 or less, preferably 5 or less. In addition, by setting the content of the curing accelerator within the above range, the smoothness of the coating film is also improved.

1-3. (Filler)
In one embodiment, the composition uses a specific filler, specifically (C) an insulating inorganic filler having a thermal conductivity of 10 W/(m·K) or more, a particle diameter (d ₅₀ ) of 10 to 60 μm, and a particle diameter (d ₁₀ ) of 3 to 40 μm. "Insulating" refers to the property of the inorganic filler itself not to conduct current even when a voltage of several hundred to several thousand volts is applied, and is a property possessed by a large energy gap between the valence band, which has the highest energy level occupied by electrons, and the next band above it (the conduction band).
In order to impart high thermal conductivity to the coating film, it is desirable that the specific filler (C) itself has a thermal conductivity of preferably 20 W/(m·K) or more, more preferably 25 W/(m·K) or more.

(C) may have a single peak or multiple peaks when a particle size distribution curve is plotted with particle diameter on the horizontal axis and frequency on the vertical axis. (C) with multiple peaks can be constructed, for example, by combining two or more types of (C) with different particle diameters.

When (C) draws a particle size distribution curve, the particle size ( _d50 ) corresponding to the cumulative 50% from the small particle size side of the weight cumulative particle size distribution of (C) is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and preferably 60 μm or less, more preferably 55 μm or less, even more preferably 50 μm or less, from the viewpoint of the heat dissipation properties of the obtained coating film.
In addition, the particle diameter ( _d10 ) of (C) corresponding to the cumulative 10% from the small particle diameter side of the weight cumulative particle size distribution is preferably 3 μm or more, more preferably 5 μm or more, and preferably 40 μm or less, more preferably 30 μm or less, from the viewpoint of imparting a good appearance to the coating film by suppressing a decrease in flowability when the coating material melts (i.e., deterioration of coatability).
The _d50 and _d10 of (C) are both measured using a laser diffraction method, and correspond to the particle sizes at which the weight cumulative is 50% and 10%, respectively, when the weight cumulative particle size distribution curve is plotted from the smaller particle size side. Particle size distribution measurement using the laser diffraction method can be performed using a laser diffraction/scattering particle size distribution analyzer (e.g., LS230, manufactured by Beckman Coulter, Inc.).

The maximum particle size ( _dmax ) of (C) may exceed 200 μm, but from the viewpoint of the coatability and heat dissipation of the resulting coating film, it is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 90 μm or less, and preferably 40 μm or more. By using (C) with _dmax within the specified ranges in addition to _d50 and _d10 , it is possible to obtain a powder coating that can further suppress deterioration of coatability and impart better heat dissipation properties to the coating film.
The d _max of (C) can be measured, for example, by sieving (C) using a JIS standard sieve with a predetermined mesh size.

Examples of materials for (C) include alumina, magnesia, zinc oxide, beryllia, silica, boron nitride, aluminum nitride, silicon nitride, silicon carbide, boron carbide, and titanium carbide. Among these, alumina, magnesia, zinc oxide, beryllia, boron nitride, aluminum nitride, and silicon nitride are preferred because of their high thermal conductivity and electrical insulation, and alumina is particularly preferred because of its improved storage stability and packability.

(C) may be used singly or in combination of two or more. When two or more (C) having different thermal conductivities are used in combination, it is sufficient that the thermal conductivity after combination satisfies the above condition (10 W/(m·K) or more). When two or more (C) having different _d50 and _dmax are used in combination, it is sufficient that the _d50 and _dmax after combination satisfy the above condition ( _d50 is preferably 10 μm or more and 60 μm or less, and _dmax is preferably 40 μm or more and 200 μm or less).

(C) may be a commercially available product. Examples include AX35-75 (manufactured by Nippon Steel & Sumikin Materials Co., Ltd.) and DAM-45 (manufactured by Denka Co., Ltd.).

The content (total amount) of (C) in the composition is preferably 72% by mass or more, more preferably 75% by mass or more, and preferably 85% by mass or less, more preferably 83% by mass or less, based on the total amount of all solids in the composition (100% by mass). If the content of (C) is too low, the heat dissipation effect cannot be expected, while if the content of (C) is too high, the coating film loses its smoothness, which is undesirable.
The mass ratio of (C) is preferably 2.6 or more, more preferably 3.0 or more, and preferably 6.0 or less, more preferably 5.0 or less, relative to the mixture of (A) and (B) : 1. If the mass ratio of (C) is too low, the heat dissipation effect cannot be expected, while if the mass ratio of (C) is too high, the coating film loses its smoothness, which is undesirable.

1-4. (fine particles)
The composition according to one embodiment may contain fine particles as needed. When fine particles are contained in the composition, the fine particles preferably contain the specific fine particles (D) in an amount of 95% by mass or more (preferably 100% by mass).

(D) is a component that imparts fluidity (allowing air to pass through and allowing powder particles to flow uniformly when applied using the fluidized bed method), workability (making the coating smooth and non-sticky), and storage stability (preventing blocking) to the powder coating. Examples of (D) include dry-process silica (silicic anhydride), hydrophilic fumed silica, hydrophobic fumed silica, and acrylic microparticles. These may be used alone or in combination of two or more.

Commercially available products of (D) include those from Wacker Asahi Kasei Silicone Co., Ltd., Nippon Aerosil Co., Ltd., Elkem Japan Co., Ltd., DSL Japan Co., Ltd., and Tokuyama Corporation.

In one embodiment, when the composition contains (D), the content (total amount) of (D) in the composition is preferably 0.02% by mass or more, more preferably 0.05% by mass or more, and preferably 0.5% by mass or less, more preferably 0.3% by mass or less, based on the total amount of all solids in the composition (100% by mass). If the content of (D) is too low, it is not possible to expect the powder coating to be imparted with fluidity, workability, and storage stability. On the other hand, if the content of (D) is too high, the coating film will lose its smoothness, which is undesirable.

1-5. (Supplementary ingredients)
The composition constituting the powder coating can contain, as necessary, auxiliary components other than the above components ((A), (B), (C) and (D)) as long as the effects of the invention are not impaired. Examples of auxiliary components include fillers other than (C), fine particles other than (D), leveling agents, pigments, antifoaming agents, flow control agents, etc. The amount of auxiliary components to be added is determined as appropriate as long as the effects of the invention are not impaired.

2. (Example of powder coating production)
The method for producing the powder coating material according to one embodiment is not particularly limited, but it can be produced, for example, by the following method.
First, the ingredients are dry-mixed using a mixer or the like, and then melt-mixed using an extruder. The mixing temperature and mixing time are not particularly limited and are set depending on the types of raw materials, composition ratios, etc. Typically, the mixing temperature is preferably 100°C to 150°C, more preferably 105°C to 120°C. The resulting mixture is then cooled and solidified, and the solidified mixture is pulverized and classified to obtain a powder coating material.

A powder coating according to one embodiment contains at least (A), (B), and (C). Depending on the mixing conditions, partial polymerization may occur, resulting in a polymer containing structural units derived from (A).

3. (Powder coating form and characteristics)
3-1. (Volume average particle size)
The particle size of the powder coating according to one embodiment is not particularly limited, but the volume average particle size measured by a laser diffraction/scattering method (JIS Z 8825) is, for example, 20 μm or more, preferably 30 μm or more, and for example, 80 μm or less, preferably 70 μm or less. The volume average particle size can be measured using a laser diffraction particle size distribution analyzer (SYMPATEC Corporation, HELOS and PRODOS analysis software: WINDOX5). By using a powder coating having a volume average particle size within the above range, better coating film smoothness can be obtained.

3-2. (Melting horizontal flow rate)
The powder coating material according to one embodiment has a melt horizontal flow rate of, for example, 0% or more, preferably 2% or more, for example, 40% or less, preferably 30% or less. If the melt horizontal flow rate of the coating material is too small, the coating material will not flow when melted, which makes it more likely that coating defects such as small holes will occur and a smooth coating film will not be obtained. If the melt horizontal flow rate of the coating material is too large, a phenomenon known as sagging will occur during the process from melting to curing when obtaining a cured coating film, making it impossible to form the desired film thickness.
The melt horizontal flow rate indicates the melting property of a powder paint when heated, and a large value indicates that the paint has low viscosity when melted and therefore flows easily, while a small value indicates that the paint has high viscosity when melted and therefore does not flow easily. The method for measuring the melt horizontal flow rate of a paint will be described later.

3-3. (Gelation time)
The powder coating material according to one embodiment has a curing property such that the gel time at 200°C according to JIS C 2104 is, for example, 120 seconds or less, preferably 60 seconds or less. If the gel time is too long, a sufficiently cured coating film is not formed, and the desired heat resistance and mechanical properties are not obtained. On the other hand, if the gel time is too short (for example, less than 10 seconds), the coating material does not flow sufficiently when melted, and a smooth coating film cannot be formed.

4. (Powder paint application method)
The method for applying the powder coating material according to one embodiment is not particularly limited, and known coating methods can be used. Specific examples include electrostatic coating, triboelectric coating, uncharged coating, fluidized bed coating, etc. If necessary, the surface of the object to be coated can be subjected to a surface treatment in advance to improve the adhesion of the cured product.

5. (Coating film (hardened powder coating))
The thickness of the coating film (cured product) formed from the powder coating material according to one embodiment is not particularly limited, but is preferably 50 μm or more and 1 mm or less.
The thermal conductivity of the coating film (cured product) formed from the powder coating material according to one embodiment is adjusted to be 1.0 W/(m K) or more. If the thermal conductivity of the coating film is less than 1.0 W/(m K), it is insufficient from the viewpoint of heat dissipation measures due to the increase in heat generated by the recent trend toward higher performance and higher power consumption of various devices. The method for measuring the thermal conductivity of the coating film will be described later.

6. (Object to be painted)
The object to be coated according to one embodiment has the above-described coating film (a cured product of the powder coating). Examples of the object to be coated include coated coils for electrical and electronic components. To manufacture the coated coils, the powder coating is applied to the coil surface of the object to be coated, the coating is melted and impregnated into the coil, and the coating is then cured by heating. Such coated coils, which are an example of the object to be coated, are used for electrical and electronic components such as drive stators and rotor motors.

The present invention will be specifically explained below based on experimental examples (including working examples and comparative examples), but the present invention is not limited to these experimental examples. In the following description, "parts" means "parts by mass" and "%" means "% by mass."

[Constituents of the composition]
The following was prepared as A (epoxy compound).
A1: Bisphenol A type (solid) epoxy resin with an epoxy equivalent of 630 g/eq (jER1002, manufactured by Mitsubishi Chemical Corporation)
A2: Bisphenol A type (solid) epoxy resin with an epoxy equivalent of 910 g/eq (jER1004, manufactured by Mitsubishi Chemical Corporation)
A3: Cresol novolac epoxy resin with an epoxy equivalent of 210 g/eq (EPICLON N-680, manufactured by DIC Corporation)

The following was prepared as B (curing agent):
B1: Dicyandiamide (jER Cure DICY20, manufactured by Mitsubishi Chemical Corporation, solid dispersion type amine curing agent)

The following curing accelerators were prepared:
Imidazole compound 1 (Curezol 2MZ-A, manufactured by Shikoku Chemicals Corporation)
Imidazole compound 2 (Curezol 2MZ-P, manufactured by Shikoku Chemicals Corporation)

As C (insulating inorganic filler), the following was prepared.
C1: Spherical alumina 1 (thermal conductivity: 30 W/(m K))
(AX35-75, manufactured by Nippon Steel & Sumikin Materials Co., Ltd.)
C2: Spherical alumina 2 (thermal conductivity: 30 W/(m K))
(AX3-10, manufactured by Nippon Steel & Sumikin Materials Co., Ltd.)

For both C1 (AX35-75) and C2 (AX3-10), when a particle size distribution curve is drawn with particle diameter on the horizontal axis and frequency on the vertical axis, the _d50 was 37 μm for C1 and 3 μm for C2, the _d10 was 13 μm for C1 and 0.7 μm for C2, and the _dmax was 85 μm for C1 and 32 μm for C2.

The following was prepared as D (fine particles):
D1: Hydrophilic fumed silica (average particle size of primary particles: 12 nm)
(Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)

The following supplementary ingredients were prepared:
Leveling agent (Nicalite XK-21, manufactured by Nippon Carbide Industries Co., Ltd.)
- Black pigment (carbon black, manufactured by Mitsubishi Chemical Corporation)

1. Preparation of powder coatings [Experimental Examples 1 to 9]
All materials for each experimental example were dry-blended in the compounding ratios (by mass) shown in Table 1, and then kneaded in an extruder to obtain a kneaded mixture. The obtained kneaded mixture was cooled and solidified, and then finely pulverized to obtain a powder coating material.

2. Evaluation The powder coatings obtained in each experimental example were evaluated for various properties (applicability, curability) using the methods described below. In addition, the cured products (thermocured coating films) of the powder coatings obtained in each experimental example were evaluated for various properties (thermal conductivity, smoothness) using the methods described below. The results are shown in Table 1.

(2-1) Coatability The coatability of the powder coating was evaluated by measuring the horizontal flow rate.
1.0 g of the powder coating material obtained in each experimental example was placed in a tablet-forming die with an inner diameter of 16 mm, pressed under a load of 113 MPa for 60 seconds to obtain a tablet, and the diameter (a) of the tablet was measured with a vernier caliper. Next, the obtained tablet was placed on a slide glass, heated at 140°C in a hot air dryer for 10 minutes, removed, and the diameter (b) of the tablet was measured in the same manner. The increase in diameter due to heating (b-a) was then divided by the diameter (a) before heating, and this was multiplied by 100 to calculate the horizontal flow rate for each powder coating material obtained in each experimental example. The evaluation criteria are as follows:

○: Horizontal flow rate is 2% or more ×: Horizontal flow rate is less than 2%

(2-2) Curability The curability of the powder coating was evaluated by measuring the gel time.
Approximately 0.05 to 0.1 g of the powder coating obtained in each experiment was placed in the circular recess of a hot plate maintained at 200°C, and stirred with a stirring rod. The time until the strings disappeared, i.e., the time until gelation occurred (in seconds), was measured. Measurement was performed in accordance with JIS C 2104. The evaluation criteria were as follows:

○: Gelation time is 10 seconds or more and less than 60 seconds ×: Gelation time is 60 seconds or more or less than 10 seconds

(2-3) Thermal Conductivity The thermal conductivity (heat dissipation) of the cured product was evaluated by determining its thermal conductivity. Thermal conductivity (W/(m·K)) is calculated as the product of thermal diffusivity (m ² /s), density (kg/m ³ ), and specific heat (J/(kg·K)). Thermal diffusivity is also called the thermal diffusion coefficient.
The powder coating material obtained in each experimental example was molded into a thickness of 0.5 mm using a heat press and cured at 200°C for 10 minutes (cured product) to prepare a test specimen. The thermal diffusion coefficient of the test specimen was measured using a thermal diffusivity measuring device (ai-Phase Mobile 1u, manufactured by i-Phase Corporation). The density of the test specimen was measured using an electronic hydrometer (ED-120T, manufactured by Alpha Mirage). The specific heat of the test specimen was measured using a differential scanning calorimeter (EXSTAR6000 DSC6220, manufactured by Seiko Instruments Inc.).

The evaluation criteria for the thermal conductivity of each test piece are as follows:
○: Average thermal conductivity is 1.0 W/(m·K) or more ×: Average thermal conductivity is less than 1.0 W/(m·K)

(2-4) Smoothness The smoothness of the cured product was evaluated by visually inspecting the appearance of the test piece as follows.
The powder coating material obtained in each experimental example was applied to the surface of an iron plate preheated to 200°C by the fluidized bed method, and then heated at 200°C for 5 minutes to harden, forming a coating film on the surface of the iron plate to obtain a test specimen.

The evaluation criteria for smoothness are as follows:
○: No unevenness or small holes in the coating film ×: Unevenness or small holes in the coating film

3. Discussion As shown in Table 1, when (C1) was not included in the paint as (C) (Experimental Examples 6 to 8), the paint's coatability (horizontal flow rate) and the smoothness of the coating film (cured product) were not satisfactory. On the other hand, even when (C1) was included (Experimental Examples 1 to 5, 9, and 10), when the content of (C1) relative to the entire composition (paint) (100 mass%) was less than 72 mass% (Experimental Example 1) or more than 85 mass% (Experimental Example 5), one or more of the paint's coatability (horizontal flow rate), the coating film's smoothness, and the coating film's thermal conductivity were not satisfied.
In contrast, when the content of (C1) relative to the total composition was 72% by mass or more and 85% by mass or less (Experimental Examples 2 to 4, 9, and 10), the coating properties and curing properties of the coating material, as well as the thermal conductivity and smoothness of the coating film, were all satisfactory.

Claims (8)

A powder coating for forming a cured product,
It is composed of a finely ground thermosetting composition,
The thermosetting composition comprises (A), (B), and (C),
(C) is contained in the powder coating in an amount of 72% by mass or more and 85% by mass or less in the entire composition.
(A): an epoxy compound having an epoxy equivalent in the range of 200 g/eq to 1000 g/eq; (B): a curing agent that reacts with (A); (C): an insulating inorganic filler having a thermal conductivity of 10 W/m·K or more, a particle diameter (d ₅₀ ) of 10 μm to 60 μm, and a particle diameter (d ₁₀ ) of 3 μm to 40 μm. The powder coating according to claim 1, wherein the mass ratio of (C) to the mixture of (A) and (B) is 2.6 to 6.0 parts by mass. 3. The powder coating according to claim 1, wherein (C) includes particles having a maximum particle size (d _max ) in the range of 40 μm or more and 200 μm or less. The powder coating material according to any one of claims 1 to 3, wherein the thermosetting composition comprises (D).
(D): Fine particles having an average particle size of primary particles of 1 μm or less The powder coating composition according to any one of claims 1 to 4, wherein (D) is contained in an amount ranging from 0.02 mass% to 0.5 mass% of the total composition. A coating film formed from a cured product of the powder coating composition described in any one of claims 1 to 5. A coated object having the coating film according to claim 6. The object to be coated according to claim 7 is a coil.