JPS5837029B2 - How to coat articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating an article with a powder material.

2. Description of the Related Art Conventionally, articles have been coated with various liquid substances at room temperature or high temperature for the purpose of electrical insulation, corrosion resistance, chemical resistance, cosmetic appearance, and the like.

However, with the aim of eliminating disasters, pollution, resource saving, and improving the work environment regarding the solvents contained in various liquid substances, as well as mechanization and labor saving in the coating process, various industries are using coating methods using powder substances. Research on coating equipment was carried out,
Some of them have already reached the stage of practical application.

Particularly in the field of paints, powder paints have been adopted in place of conventional liquid paints with the development of various coating methods and coating equipment, and it is expected that the field of application will continue to expand in the future.

Coating methods that are currently in practical use include (i) a method in which the article is heated in advance to a temperature higher than the melting point of the powder material, and then the powder material is fused and coated;

(Generally referred to as the fluidized immersion method) 2) In a fluidized bath, a high voltage is applied through an electrode, and a grounded article is placed on the upper diluted layer of the powder material being fluidized by compressed air to eliminate the electrostatic force. A method consisting of applying and covering.

(Generally called electrostatic dynamic dipping method) 3) Other methods include electrostatic spray method, rolling method, cascade method, thermal spray method, etc.

However, each of the above methods (IX2) has the following drawbacks.

■ In the fluidized dipping method, ■ it cannot be applied to articles for which it is impossible to preheat to a temperature above the melting point of the powder substance.

■The deposited film thickness per application is approximately 0. 1 mm is the limit,
When thick coating is required, coating operations are required many times depending on the required film thickness, which is extremely time-consuming.

■In articles made of composite materials, the heat dissipation rate of each material after preheating is different, so uneven coating is likely to occur due to uneven preheating temperature of the article.

(2) For articles having parts that do not need to be coated with a powder material, such as lead wires of electronic parts, it is generally necessary to pre-treat the parts that do not need to be coated, such as masking, and then immerse and fusion coat them, which is time-consuming.

(2) In the electrostatic dynamic dipping method, (1) If a large amount of powder material is deposited to obtain a thick film, the powder material may fall off or fall off the surface of the article.

In addition, with respect to articles made of composite materials, depending on the type of material, some parts may be difficult to adhere to, and uneven coating may occur.

It is also conceivable to apply intermittent shocks to the coating after it has been deposited to prevent it from falling off, but in this case localized shedding tends to occur and it is difficult to obtain a smooth coating.

■Since it is applied to the article with a thin upper layer of flowing powder material, it takes a long time to adhere if a thick film is required.

■The voltage applied to the powder substance is a high voltage (for example, D.C.
．． ．． 60 to 100 kV), making it very dangerous.

■Since a large amount of compressed air is applied to the powdered material in the fluidized fluidized tank to cause it to flow violently, a device to collect the scattered powdered material is required, and the fluidized fluidized material needs to be sealed each time it is deposited, so it takes time to open and close the fluidized material. The efficiency (productivity) for adhesion is low.

(2) In order to improve the fluidity and adhesion uniformity of the powder material in the fluidized tank, it is necessary to narrow the particle size distribution during the production of the powder material.

The inventors of the present invention have conducted intensive research to improve the various drawbacks mentioned above, and as a result, we have developed a method for pre-treating articles in a highly concentrated powder substance that is made to flow weakly with compressed air and to which a voltage is applied using electrodes. (2) By immersing the article without pretreatment, and applying continuous vibration to the article and attaching the powder substance while applying rocking, it is possible to significantly shorten the adhesion time of the powder substance. .

■ There is no uneven adhesion of powder substances, and there is high uniformity, and
Since there is no peeling or peeling phenomenon, the coating film after baking has an excellent uniform appearance and smoothness.

(Especially effective for articles made of composite materials or articles with significant unevenness.

) ■ Because the powder material flows very weakly, there is no need for special dust countermeasures such as collection of the powder material.

■ There is no need to take the trouble of narrowly adjusting the particle size distribution of powdered materials.

We have discovered an effective coating method.

Incidentally, the present inventors previously proposed in Japanese Patent Application No. 51-85188 that while continuously applying continuous vibrations to an article, compressed air flows weakly and a voltage is applied to the article by electrodes. A coating method is disclosed which is characterized in that the article is immersed in a concentrated powder substance.

The present invention further adds oscillation to the present invention.

When the article is agitated, the adhesion time is shortened, the powder material can be more closely adhered, and the uniformity of the coating film is improved.

Although the reason for this phenomenon will continue to be investigated in the future, the inventors speculate that it may be due to the fact that by shaking the article, the number of machines in which the article and the powder material come into contact further increases.

The constituent elements and purpose of the present invention will be explained.

The article is pretreated or immersed without pretreatment in a highly concentrated powder substance that is weakly fluidized by compressed air and a voltage is applied by means of electrodes, and the article is subjected to continuous vibrations continuously. The basic method is to deposit the powder substance while applying and shaking it.

First of all, the vibration referred to here is one that can continuously apply continuous vibration to the article or article support frame from the time the article is in the flowing powder substance atmosphere until uniform adhesion is obtained. However, in reality, the objective can often be achieved by continuously applying continuous vibrations only while the article is in an atmosphere of flowing powder material.

In addition, the required magnitude of vibration varies depending on the type, property, adhesion conditions, etc. of powder substances, and on the other hand, the type, size, shape, etc. of articles, so the frequency or amplitude must be adjusted over a wide range. For example, preferably the frequency is 1,000 to 10,000 times/min and the amplitude is 5 to 20 times/min.
It is within the range of 0 microns, and more preferably the frequency is 2.00-0 to 8,000 times/min and the amplitude is 10 to 100 times/min in order to balance the phenomenon of powder material falling and falling off.
The idea is to give continuous vibrations of microns.

Furthermore, since the required direction of vibration varies depending on the type, shape, etc. of the article, it can be applied horizontally or vertically as necessary.

Note that the continuous vibration referred to in the present invention is completely different from intermittent impact.

Due to this intermittent impact, it is virtually impossible to balance the phenomenon of powder material falling and the phenomenon of shedding.
Uniform adhesion cannot be obtained.

In the present invention, rocking refers to the period from when the article is in a flowing powder substance atmosphere until uniform adhesion is obtained.
This applies vibration and rocking to the article.

Also, this objective can often be achieved by applying agitation only while the article is in the flowing powder material atmosphere.

Incidentally, the rocking mentioned here does not necessarily have to be applied continuously, and may be an intermittent gentle movement.

The type of rocking is to make the movement of the article reciprocate on the same spatial plane as much as possible.

If this item is moved in such a way that it reciprocates on the same spatial plane with significant deviations,
The mechanism for imparting swing to the article becomes complicated, and the effect of imparting the swing becomes unclear.

In general, it is often possible to achieve a goal by swinging it like a pendulum.

Next, the magnitude of the vibration depends on the type, material, and shape of the article to which the powder substance is attached, or the type, property, and property of the flowing powder substance.
Although it varies depending on the adhesion conditions, for example, when adhering a powder substance such as an epoxy resin powder coating for electrical insulation to a small article such as an electronic component, the period is 0.3 with a pendulum-like oscillation.
~3 seconds, preferably when the amplitude is in the range of 10 to 300 mm, and in order to prevent the occurrence of rolling and falling phenomena of loose powder materials in a well-balanced manner, and further improve the uniformity of the coating film. More favorable results are obtained when the period is in the range of 0.5 to 2 seconds and the amplitude is in the range of 30 to 200 millimeters.

In the coating method of the present invention, the powder material can be applied to the article in a state where the flow concentration of the powder material is very high.

Furthermore, safety is improved by lowering the applied voltage for generating electrostatic force.

That is, although it goes without saying that the applied voltage differs depending on the type of powder material, usually D. C. It is preferable to charge using a relatively low voltage of 10 to 50 kV.

The coating method of the present invention is a method in which the article is immersed to the inside in a weakly fluid powder substance, and a thick film can be obtained with a single deposition operation, and since the coating method is weakly fluid, no dust is generated. No collection device is required.

This weak flow refers to the apparent volume ratio of the powder material used, which varies depending on its properties and type, but is generally 1.05.
1.5 times, more preferably 1.1 to 1.2 times.

To explain the apparent volume ratio described here, the apparent volume ratio is defined as the normal apparent volume of the powder substance being 1,
It is the increase in apparent volume when a powder substance is fluidized with compressed air.

Furthermore, in the method of the present invention, by pre-treating the article, it is possible to exhibit the effects of the present invention to a greater extent than when the article is not treated.

Pretreatment of an article as used herein refers to preheating the article, prewetting the article with a liquid substance, and using a combination of preheating and wetting the article with a liquid substance.

Preheating means that in contrast to the known fluidized dipping method that does not use static electricity, which requires preheating the article to a temperature above the melting point of the powder material, the method of the present invention does not necessarily require preheating the product to a temperature above the melting point of the powder material. Even weak preheating can further improve the effect.

The liquid substance of the present invention includes thermoplastic resins, thermosetting resins,
It includes common liquid substances such as plasticizers, solvents, inorganics, or mixtures of at least two of these.

This liquid substance is used by impregnating or applying it to the article,
It is preferably used to improve coating properties such as improved adhesion, improved water resistance, and prevention of pinholes.

Powder materials that can be used in the present invention include all powder materials that can be coated onto articles.

For example, synthetic organic compounds such as epoxy resin, acrylic resin, polyester, polyurethane, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide, ethylene vinyl acetate copolymer resin, polyvinyl butyral, phenol resin, amino resin, fluororesin, synthetic rubber, etc. , natural organic compounds such as starch and rosin, mixed compositions containing these as main components and inorganic compounds, and further inorganic compounds such as frits.

The articles to which the present invention is applied are various articles requiring a surface coating.

Examples include electronic parts, electrical parts, mechanical parts and their products, building materials, industrial products, daily necessities, and ceramic products.

Hereinafter, the present invention will be specifically explained with reference to Examples.

However, in the coating method of the present invention, after attaching the powder substance to the article, a normal post-processing operation such as heating is performed to coat the article.
Also included is obtaining a coating.

Note that the vibration and rocking may not only be applied directly to the article, but also indirectly applied to the article through a part of the device that supports the article.

Example 1 A cast iron water pipe joint with an inner diameter of 25 mm was used as an article, and continuous vibration was applied to it at a frequency of 3,600 times/minute and an amplitude of 50 microns, and the period was 1 second and the amplitude was 50 microns. gave a pendulum-like swing of 100 mm.

Heavy-duty corrosion-resistant epoxy resin powder paint (manufactured by Sumitomo Teurez) is flowing gently in a fluidized tank with compressed air making the apparent volume 1.15 times the normal apparent volume.
Both vibration and rocking were applied to the joint (Sumilite Resin PR-52000K), and the grounded joint was immersed.

D. to the powder coating. C. 3 Apply a voltage of 0 kV to charge the joint, apply powder paint to the joint for 2 seconds by electrostatic force, and then apply continuous vibration for another 1 second.
The joint was then lifted out of the powder coating while being rocked.

As a result, a joint was obtained in which no particles of the powder coating or falling off were observed, and the powder coating was uniformly adhered to all parts.

Next, the joint to which the powder coating was applied was baked in a furnace at a temperature of 180° C. for 1 hour.

As a result, the film thickness over the entire surface was approximately 0. 4 mm, there was no uneven coating, and the coating film had excellent smoothness.

Example 2 A cast iron water pipe joint with an inner diameter of 25mm was pre-treated with 100 parts by weight of a liquid epoxy resin ("Epikoat" 828, manufactured by Shell Chemical Co., Ltd.) and a liquid acid anhydride curing agent (manufactured by Hitachi Chemical Co., Ltd., methylnadic anhydride). The surface was wetted with a liquid substance consisting of 90 parts by weight of the mixed solution.

Next, a powder coating was applied by the same procedure as described in Example 1 except that the application time was changed to 1 second, and then baking was performed.

As a result, the film thickness over the entire surface was approximately 0. The coating film had a thickness of 4 mm and had very little unevenness.

In this example, compared to Example 1, the adhesion time could be shortened, there were no pinholes, and the smoothness of the coating film was extremely excellent.

Example 3 Regarding a cast iron water pipe joint with an inner diameter of 251n7IL, 60
A powder coating was applied to the joint preheated to 0.degree. C. by the same procedure as described in Example 1, and then baked.

As a result, the film thickness over the entire surface was approximately 0. The thickness was 5 mm, and the uniformity was extremely excellent.

In this example, compared to Example 1, a particular effect was observed in that the thickness of the deposited film was thicker at the same deposition time.

Example 4 Continuous vibrations with a frequency of 3,600 times/minute and an amplitude of 60 microns were continuously applied to a lead wire welding type polypropylene film capacitor element, and a pendulum-type motion with a period of 1 second and an amplitude of 60 mm was applied. A vibration consisting of

Epoxy resin powder paint for electrical insulation (manufactured by Sumitomo Durez ■, "
The element, which was subjected to both vibration and rocking and was grounded, was immersed in a Sumilight Range JPR-52102).

D. to powder coating. C. After applying a voltage of 50 kV to charge the element, and adhering the powder paint to the element for 1.5 seconds by electrostatic force, vibration was continuously applied for an additional 0.5 seconds, and rocking was applied. The device was pulled out of the powder paint.

As a result, an element was obtained in which the powder coating was uniformly adhered to all parts without any phenomenon of powder coating or falling off.

Next, the element to which the powder coating was applied was baked in an oven at a temperature of 90°C for 2 hours, and as a result, the film thickness on the entire surface was about 0. The coating thickness was 4 mm, and there was no uneven coating, and the coating film had excellent smoothness.

Reference Example Regarding a lead wire welding type polypropylene film capacitor element, while continuously applying continuous vibration to the element at a frequency of 3,600 times/min and an amplitude of 60 microns,
Epoxy resin powder paint for electrical insulation (Sumitomo Durez ■, "Sumilight Resin JPR-52102") flowing gently in a fluidized tank with compressed air making the apparent volume 1.2 times the normal apparent volume. The grounded element was immersed in the

D. to powder coating. C. 5 After applying a voltage of 0 kV to charge the element and adhering the powder paint to the element for 2 seconds by electrostatic force, the element was pulled out of the powder paint while continuously applying vibrations for an additional 0.5 seconds. .

As a result, an element was obtained on which the powder coating was evenly adhered without any phenomenon of powder coating or falling off.

Next, the element to which the powder coating was applied was baked in a furnace at a temperature of 90°C for 2 hours, but the film thickness was approximately 0.3
It had a coating film that was transparent and had little coating unevenness.

However, in this comparative example, it took a little longer than in Example 4 to deposit a powder coating of the same weight (same film thickness).

Comparative Example: A cast iron water pipe joint with an inner diameter of 25 mm was coated with a heavy-duty anti-corrosion epoxy resin powder coating (Sumitomo Teurez ■, "Sumilight Range JPR52000K") using the normal electrostatic dynamic dipping method.
．． C. A high voltage of 70 kV was applied to charge the joint, and the powder coating was applied to the joint for 15 seconds by electrostatic force.

Next, baking was performed for 1 hour in a furnace at a temperature of 180°C.

The result was a film thickness of about 0. A 3 mm powder coated water pipe joint was obtained.

However, during the adhesion operation, the upper surface becomes a thick film, and the average film thickness is about 0.3%, with a maximum of ±0.0%. 2 mm. This was not a desirable result.

In addition, due to the slight impact that occurs during the baking process after adhesion, the adhered powder coating may locally fall off, resulting in
For 6 out of 0, the coating film after baking lacked smoothness and had poor appearance.

In this comparative example, the above-mentioned falling-off phenomenon occurred due to a slight impact, but such a phenomenon did not occur in the cases of each of the above-mentioned Examples.

Furthermore, compared to Example 1, it took a long time to apply a powder coating of the same weight (same film thickness), and the coating film was inferior in smoothness.

Claims (1)

[Scope of Claims] 1. An article is immersed with or without pretreatment in a highly concentrated powder substance that is weakly fluidized by compressed air and a voltage is applied by electrodes; While continuously applying continuous vibration and rocking,
A method of coating an article, comprising applying the powder substance to the article. 2. The method of claim 1, wherein the continuous vibration is continuously applied to the article while it is in the highly concentrated powder material atmosphere until uniform adhesion is achieved. 3. A method according to claim 1, characterized in that the continuous vibration is continuously applied to the article while the article is in a highly concentrated powder material atmosphere. 4. Claim 1, characterized in that the shaking is applied to the article while the article is in a highly concentrated powder substance atmosphere.
3. The method described in Section 2, Section 2, or Section 3. 5 The vibration given to the article has a frequency of 1,000 to 10
,000 times/min and an amplitude of 5 to 200 microns. 6. The method according to claim 1 or 4, wherein the swinging motion is applied so that the article moves back and forth on the same plane in space. 7. Claims 1, 2, 3, 4, and 7, characterized in that the apparent volume of the flowing powder substance is 1.05 to 1.5 times the normal apparent volume. Section 5 or Section 6
The method described in section. 8. Claims 1, 2, 3, 4, 5, 6, or 8, characterized in that the powder substance is applied to the article after it has been wetted with a liquid substance in advance. The method described in Section 7. 9 Claims 1, 2, 3, 4, 5, and 6, characterized in that the article is pre-wetted with a liquid substance and then preheated to adhere the powder substance. or the method described in paragraph 7. 10. The method according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the powder substance is applied after preheating the article. Method. 11. Claims 1, 2, 3, 4, 5, 6, or 11, characterized in that the article is preheated, then wetted with a liquid substance, and then a powder substance is applied. The method described in Section 7.