JP3258256B2 - Powder coating suitable for electrostatic fluidized immersion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention uses the electrostatic fluidized-bed coating
A because of powder coatings, particularly suitable for thin film powder coating to an object to be coated of compact insulating coating film is required. Here, small objects to be coated include small motor cores and magnets, various machine tools, vehicles, ships, airplanes, home appliances,
Small parts such as office equipment, electric and electronic parts, and the like. Examples of the material of the object to be coated include various conductive metals.

[0002]

2. Description of the Related Art It is well known that powder coatings have less volatile components and odors than solvent coatings and are very useful in terms of pollution control and environmental regulations. Conventionally, the powder coating for insulating coating used in the electrostatic flow immersion method has a volume average particle diameter of about 30 to 40 μm, is not strictly classified, and has a particle diameter of 25 μm or more. Particle volume ratio of 4
About 0 to 90%, the number ratio of particles having a particle diameter of 5 μm or less was about 60 to 80%. In the case of a powder coating for insulating coating, the flowability of the powder coating melted during the heat treatment is reduced by the following method in order to enhance the coverage of the edge portion of the object to be coated. A thickener of inorganic fine particles is added. Immediately after being melted, it is cured using a curing agent having a high curing speed. Combine with. Therefore, the conventional powder coating has a large volume average particle diameter and poor flowability at the time of melting, so that the unevenness of the coating after heat treatment becomes large. Therefore, in powder coating of a thin film having an average film thickness of about 40 μm, pinholes and extremely thin portions are easily generated, and it has been difficult to obtain a film having good insulating properties. For this reason, in many cases, the formation of a thin film that requires insulating properties is performed by solvent coating.

[0003]

In the conventional powder coating for insulating coating, in order to form a film having good insulating properties, it is necessary to apply a thick coating having an average film thickness of about 100 μm. It was unsuitable for coating on small parts requiring thin film coating. Also, powder coatings for insulating coating require uniform formation of fine details, but it is not preferable to enhance the flowability at the time of melting in consideration of the covering properties of the edges of the object to be coated. Therefore, in order to enable thin film coating, it is preferable to reduce the volume average particle diameter of the particles of the powder coating. However, the mere pulverization of the powder coating deteriorates the fluidity of the powder coating, making it impossible to bring the powder coating into a fluidized state in the fluidizing tank of the coating machine. Therefore, a film cannot be formed on the object to be coated.
An object of the present invention is to solve the above-mentioned problems of the conventional powder coating and to provide a powder coating capable of obtaining a thin film having excellent insulation properties by an electrostatic flow immersion method.

[0004]

As a result of investigations to improve the above-mentioned problems, when powder coating is performed by an electrostatic fluidized immersion method using a powder coating for insulating coating, the following is required. Having a particle diameter, and (a) a volume average particle diameter of 10 to 20 μm.
m, (b) the volume ratio of particles of 25 μm or more in all particles is 25% or less, (c) the number ratio of particles of 5 μm or less in all particles is 45% or less, and the silica fine particles are powder particles. The powder particles adhere to the surface of the binder tree
50 to 150 parts by weight of hydroxide
It has been found that the powder coating to which luminium or calcium carbonate is added becomes a uniform fluidized state in a fluidizing tank of a coating machine and can form a thin film having good insulating properties.

First, an electrostatic flow immersion method using the powder coating of the present invention will be described with reference to FIG. In the electrostatic flow immersion method, a fluidized tank 1 in which a perforated plate 2 is provided on the bottom surface is used.
The powder paint 3 in the fluidized tank is put into a fluidized state when the powder paint 3 in the fluidizing tank is put into the fluidized state by the fluidized air 5 which is ionized negatively in the charging zone 4 and is jetted from the porous plate 2. It is negatively charged. By dipping the object 6 to which the ground is attached into the cloud of the powdered coating material 3 in the fluidized state, the charged powder coating material 3 is electrically attracted on the surface of the coating object 6. To adhere.
As the electrostatic fluid immersion method, there is a method in which a charging zone is provided in a perforated plate in addition to the method described with reference to FIG. 1, but the electrostatic fluid immersion method using the powder coating of the present invention employs a charging zone. It is not limited by the difference in the method.

Hereinafter, the powder coating of the present invention will be described in detail. Since the powder coating of the present invention is a powder coating for components that require insulation such as home appliances and electric / electronic devices, the powder coating may be thermosetting so as to withstand heat generated when electricity is conducted. Preferably, at least one comprising a binder resin and a curing agent is suitable. Examples of the binder resin include an epoxy resin and a phenol resin. Examples of the curing agent include amide, acid dihydrazide, acid anhydride, imidazole and the like, and a phenol resin may be used as a curing agent for the epoxy resin. And the curing agent is
They can be used alone or in combination of two or more.
In the powder coating of the present invention, which is a powder coating for insulating coating, the flowability of the powder coating melted during the heat treatment is reduced for the purpose of enhancing the coverage of the edge portion of the object to be coated. Is important and is used by any of the following approaches:
Can be A thickener composed of inorganic fine particles is added. Immediately after being melted, it is cured using a curing agent having a high curing speed. Combine with. Field of the powder coating of the present invention
If, as it is the inorganic fine particles used is aluminum hydroxide or calcium carbonate, 50 to 150 parts by weight per 100 parts by weight of the binder resin as the addition amount thereof, and more preferably is added 75-125 parts by weight. Also, acid anhydrides as fast hardeners hardening rate, that Re et imidazole and the like <br/>. Also, titanium oxide in powder coating of the present invention, carbon black, iron oxide, copper phthalocyanine, azo pigments, condensed polycyclic various colorants such as pigments, an acrylic oligomer, leveling agents such as silicone, foam benzoin such Various additives such as an inhibitor, a coupling agent, an antioxidant, and a wax may be appropriately added.

In the present invention, the powder coating composition composed of the above materials is dry-mixed using a mixer or a blender, and then melt-kneaded by a kneader and cooled. Then, after pulverizing using a mechanical or air-flow type pulverizer, powder particles are obtained by classifying using a pneumatic-type classifier. Then, the powder coating of the present invention can be obtained by attaching silica fine particles described below to the surfaces of the powder particles. The production of the powder particles is not limited to the above-mentioned method, but may be, for example, a spray-dry method.

In the present invention, the volume average particle diameter and the particle diameter distribution of the powder coating material having silica particles adhered to the surface of the powder particles must satisfy the following conditions. (B) The volume average particle diameter is 10 to 20 μm. (B) The volume ratio of particles of 25 μm or more in all particles is 25% or less. (C) The number ratio of particles of 5 μm or less in all particles is 45% or less. When the volume average particle diameter is larger than 20 μm, in a thin film coating having an average film thickness of about 40 μm, the unevenness of the surface of the powder particle adhesion layer on the object to be coated becomes large. Therefore, unevenness of the surface of the film after the heat treatment becomes large, and pinholes or portions having an extremely small thickness are easily formed, and the insulating property of the film is unfavorably reduced. On the other hand, when the volume average particle diameter is less than 10 μm, the interparticle force such as van der Waals force increases due to an increase in the specific surface area of the particles of the powder coating, and the particles are easily aggregated. Is reduced. For this reason, the powder coating cannot be fluidized in the fluidizing tank of the coating machine, and a film cannot be formed on the object to be coated. Further, in this case, even if silica fine particles as a fluidity imparting agent described below are added,
It is difficult to uniformly fluidize the powder coating in a fluidized tank.

The powder coating of the present invention has a particle diameter of 25.
The volume fraction of particles that are greater than or equal to μm must be less than or equal to 25%. If the volume ratio of the particles having a particle diameter of 25 μm or more exceeds 25%, the unevenness of the surface of the powder particle adhesion layer on the object to be coated becomes large. As a result, the unevenness of the film after the heat treatment becomes large, and in the case of the thin film coating having an average film thickness of about 40 μm, an extremely thin portion is easily formed, and the insulating property of the film is deteriorated. For this reason, when a thin film is applied, the volume ratio of particles having a particle size of 25 μm or more is 25%.
%.

The powder coating of the present invention has a particle diameter of 5 μm.
The number proportion of particles less than m must be less than 45%. Particles having a particle diameter of 5 μm or less tend to agglomerate with each other for the same reason as in the case where the volume average particle diameter is less than 10 μm, and lower the fluidity of the powder coating. Therefore, fluidization of the powder coating in the fluidizing tank of the coating machine is impeded. Further, particles having a particle size of 5 μm or less have a small surface area of each particle and are difficult to be charged, so that they are difficult to adhere to the object to be coated. Therefore, when the number ratio is large, the coating efficiency of the powder coating decreases. For these reasons, when the number ratio of particles having a particle diameter of 5 μm or less exceeds 45%, the fluidity and adhesion of the powder coating deteriorate, and a uniform thin film is formed on the object to be coated. It is difficult to form.

In the present invention, the particle size is determined by using a Coulter Multisizer II manufactured by Coulter Electronics Co., Ltd. to prepare a powder coating in water to which a surfactant is added.
After sufficiently dispersing using an ultrasonic disperser, the concentration of the powder coating was adjusted to 5 to 10%, and the mixture was stirred with a small screw to prevent sedimentation of the powder coating.
This is a measurement value measured using a μm aperture.

As described above, in the powder coating of the present invention, the silica fine particles must adhere to the surface of the powder particles. By adhering the silica fine particles to the surface of the powder particles, the powder coating is hardly agglomerated, its flowability is improved, and the powder coating is easily made to be in a uniform fluidized state in the fluidizing tank of the coating machine. . The silica fine particles are powder particles 100
It is preferable to adhere to the surface at a ratio of 0.2 to 0.8 parts by weight with respect to parts by weight. When the added amount of silica fine particles is 0.2
When the amount is less than part by weight, the effect of imparting fluidity is insufficient, and the powder coating may not be fluidized uniformly in the fluidizing tank of the coating machine. On the other hand, when the addition amount of the silica fine particles is more than 0.8 parts by weight, the fluidity of the powder coating material becomes too high, so that the filling density of the powder coating material deposited in the fluidizing tank of the coating machine becomes high. In addition, the gap between the particles becomes very small. As a result, the fluidized air ejected from the perforated plate at the bottom of the fluidized tank does not evenly spread to the gap between the particles, and the fluidized air that has lost its place forms a straw-shaped airway vertically in the powder paint deposition layer Then, it escapes to the surface of the deposited layer of the powder coating. Therefore, the powder coating may not be in a fluidized state.

The average particle diameter of the primary particles of the silica fine particles is preferably 50 nm or less. When the average particle diameter of the primary particles of the silica fine particles is larger than 50 nm,
Due to the agglomerated powder and coarse powder of the silica fine particles, the surface of the film after the heat treatment tends to have a pit (convex). At this time, the convex portion is not preferable because the insulating property is lower than other portions of the film. This is because electricity flows from the surface of the object to be coated to the surface of the film through the surface of the agglomerated powder and coarse powder of silica in the film, and is caused by the fact that the surface resistivity is lower than the volume resistivity. The silica fine particles may be made of either a silane coupling agent or a hydrophobic silica that has been subjected to a hydrophobic treatment with a coupling agent such as a titanium coupling agent, or a hydrophilic silica that has not been subjected to a surface treatment. May be used.

In order to attach the above-mentioned silica fine particles to the surface of the powder particles, a blender or a mixer is used.
The powder particles and the silica fine particles may be dry-blended, or the silica fine particles may be added to the powder coating kneaded material before pulverization by dry blending and then pulverized.

The addition amount of the silica fine particles can be measured by using an EDX (energy dispersive X-ray microanalyzer), and the particle size of the silica fine particles can be measured by using an electron microscope. it can.

[0016]

EXAMPLES The powder coating of the present invention will be described below based on examples and comparative examples. However, the scope of the present invention is not limited to these. <Examples and Comparative Examples> Production of powder particles ・ Epoxy resin 49.5% by weight (product name: Epicoat 1004 manufactured by Yuka Shell Epoxy) ・ Curing agent (dicyandiamide) 1.3% by weight ・ Curing accelerator (Imidazole) 0.2% by weight-Flow-off agent (acrylic copolymer) 0.7% by weight-Antifoaming agent (benzoin) 0.3% by weight-Colorant (titanium dioxide) 11.0% by weight-Increase Viscous agent (aluminum hydroxide) 37.0% by weight After the raw materials having the above mixing ratios were mixed with a super mixer, the mixture was melt-kneaded with a kneader at a temperature of 120 ° C., cooled and then cooled. Was crushed using a crusher. Thereafter, powder particles A to G having different volume average particle diameters and particle diameter distributions were obtained using an airflow classifier.

Production of Powder Coating A hydrophilic silica (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 200, average particle diameter of primary particles: 12 nm) was added to the above powder particles A to G by 100 weight of the powder particles. Parts by weight of 0.2 parts by weight, 0.4 parts by weight, 0.6 parts by weight, and 0.8 parts by weight by dry blending using a Henschel mixer. A body paint was obtained. In addition, a comparative powder coating to which the hydrophilic silica was not attached was used as a comparative powder coating. The volume average particle size and the particle size distribution of each powder coating after the silica fine particles were adhered were measured using a Coulter Multisizer II, and the measurement results are shown in Table 1.

[0018]

[Table 1]

Next, each of the powder coating materials shown in Table 1 was applied to ELECTROSTATIC TECHNOLOGY having the structure shown in FIG.
INC. Electrostatic Flow Immersion Coating Machine (trade name: C-3)
0) was charged into the fluidizing tank of (0), and the fluidizing air flow rate was 40 L / min. , And allowed to stand for 1 hour. Then, the fluidized state of the powder coating in the fluidizing tank of the coating machine was observed, and the state is shown in Table 2. The evaluation criteria for the fluidization test of the powder coating are as follows. ：: Uniform fluidized state ×: Not partially or completely fluidized Note that the fluidized air flow rate was 40 L / min. To 80 L / min. Did not result in a uniform fluidized state. In addition, the powder coating material that could be in a uniform fluidized state in the fluidizing tank of the coating machine was 10 m
A jig also serving as an earth was attached to one end of an iron prism of mW × 10 mmH × 40 mmL, and the applied voltage was 60 KV.
Coating was performed so that the average film thickness of the flat portion after the heat treatment became 40 μm. Then, the object to be coated is placed in a hot air drying oven for 1 hour.
Heat treatment was carried out at 80 ° C. for 20 minutes to cure the powder coating to obtain a film. After the object to be coated was allowed to stand at room temperature for 24 hours, the insulating property of the obtained film was evaluated by the following test method. A test lead of a pressure resistance tester (manufactured by Kikusui Electronics Co., Ltd., trade name: TOS-5030) is applied to a portion where the coating of the object is not formed (a portion where a jig also serving as an earth was attached at the time of coating). Black) was attached, and a test lead (red) was brought into contact with the four flat portions of the side surface of the prism and the edge portions of the four sides of the side surface to scan 30 mm, and the insulation of the coating was evaluated. It was shown to. In this test, the applied voltage was 50
The measurement was performed at 0 V, and the buzzer was set when a current of 0.5 mA or more flowed. The evaluation criteria for the insulation test of the film are as follows. ○: No conductive part ×: Conductive part-: Powder coating does not flow in the fluidizing tank, so film formation is not possible

[0020]

[Table 2]

As is clear from Tables 1 and 2, in order to make the small particle size powder coating for thin film coating into a uniform fluidized state in the fluidizing tank of the coating machine, the particles of the powder coating are agglomerated. It is necessary that there be a gap between the particles so that the fluidizing air can be distributed evenly within the layer of the particles of the powder coating, and the powder coating of the present invention satisfies these conditions. ing. From Table 2, using the powder coating of the present invention,
The thin film formed by the electrostatic flow immersion method
It can be seen that both edges have good insulating properties.

Further, using the powder coating of D-3, the above-mentioned object 30
After continuous coating on 0 pieces, the powder coating in the fluidizing tank of the coating machine was taken out, and the volume average particle diameter and the particle diameter distribution were measured. As a result, the volume average particle diameter was 14.9 μm, and 25 μm in all particles. The volume ratio of the above particles was 15.0%, and the number ratio of particles of 5 μm or less to all particles was 32.0%.
%Met. As described above, the volume average particle size and the particle size distribution of the powder coating D-3 hardly change between the start and the end of the continuous coating. This means that there is almost no selective adhesion of particles of the powder coating during electrostatic powder coating.That is, by having both a sharp particle size distribution and appropriate fluidity, coating can be performed during continuous coating. This proves that a stable film can be formed without problems such as a decrease in deposition efficiency.

[0023]

By using the powder coating material of the present invention in the electrostatic fluidization immersion method, it has become possible to form a thin film, which has conventionally been considered difficult, requiring an insulating property by powder coating. became. In addition, the powder coating of the present invention hardly causes selective adhesion to an object to be coated, which is a drawback of electrostatic powder coating, and there is almost no change in the particle size distribution of the powder coating in a fluidized tank due to continuous coating. Therefore, there is no deterioration in paintability such as a decrease in coating efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an electrostatic flow immersion method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fluid tank 2 Perforated plate 3 Powder coating material 4 Charging zone 5 Fluidized air 6 Workpiece

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C09D 5/03

Claims (3)

(57) [Claims] 1. A is a powder coating for insulation coating by electrostatic fluidized-bed coating, have a particle size below (b) the volume average particle diameter of 10 to 20 [mu] m, the total particles (b) 25 μm
Volume fraction of particles larger than 25% or less, (c) the number ratio of 5μm or smaller particles in the total particles 45% or less, and the silica fine particles are adhered to the surface of the powder particles, the
The powder particles are 50 to 15 parts by weight based on 100 parts by weight of the binder resin.
0 parts by weight of aluminum hydroxide or calcium carbonate
Powder coating, characterized in der Rukoto those pressure. 2. The powder coating according to claim 1, wherein the silica fine particles are attached at a ratio of 0.2 to 0.8 parts by weight based on 100 parts by weight of the powder particles. 3. The powder coating according to claim 1, wherein the primary particle of the silica fine particles has an average particle diameter of 50 nm or less.