The "flower blooming phenomenon" is known simply as "blooming" or "flower spots". For information on this phenomenon and remedies, please refer to the "Guidebook of Coating Film Defects and Remedies" (3,000 Yen), published by the Coating Equipment Manufacturers Association of Japan. This guidebook contains information on more than 90 types of coating defects and their remedies. It is also available on CD-ROM (18,000 Yen). Please contact the secretariat of the association to purchase the guidebook or the CD-ROM.
(Reply from: Asahi Sunac Corporation)
The term spattering means "to splash coating material here and there". This method of coating can be used to create a variety of different patterns by spattering paint particles on the surface of the coating object. By changing paint particle sizes and colors, many types of patterns can be sprayed, thus allowing for a high degree of creativity. The coating equipment used to perform spatter coating has been adapted with inspiration from bell-shaped spray equipment. Spray gun type spatter coating equipment has also been developed.
(Reply from: Asahi Sunac Corporation)
The different kinds of coating methods available can be generally classified according to: (1) coating equipment; and (2) type of coating material.
"Transfer efficiency" is utilized as a means of evaluating coating equipment, in terms of environmental safety.
A variety of measures are available to allow compliance with stricter environmental regulations, depending upon the particular area involved, such as water quality, atmospheric pollution, noise and the work environment. However, Japan currently lags in the development of countermeasures and stringent regulations to address the release of VOCs and CO2, which are the major causes of global warming. All parties involved with the coating industry or the manufacture and usage of coating materials should begin implementation of the PRTR system, as was enacted in April of this year and should also comply with ISO14001 guidelines.
(Reply from: Nippon Paint Plant Engineering)
Powder coating involves charging a resin-based paint powder, made of polyester or epoxy, with an electrostatic charge. When this charged paint powder is then sprayed toward a coating object that has been electrically grounded, the electrostatic forces of attraction cause the paint particles to adhere to the object.
The paint-coated object is then baked for 15 - 20 minutes at a temperature of 160 - 180 °C, which fuses the powder, producing a durable film of paint.
Two methods may be used to generate an electrostatic charge (to charge the paint particles with static electricity). In one method, a voltage of 60 - 100 kV (usually of negative potential) is applied to a needle-like electrode, resulting in an electrical discharge (corona discharge). This discharge generates ions (negative ions for a negative potential, or positive ions for a positive potential), which then charge the paint powder with electricity.
Another method of charging paint powder uses a static electricity generator, which creates a charge from the friction between two electrically dissimilar substances that are rubbed together.
In general, by forcing the paint powder to rush through a Teflon "charger" pipe, friction occurs between the powder and the internal Teflon walls, causing the paint powder to gain a positive charge. Therefore, every particle of paint powder contains an electrostatic charge and is attracted to the coating object. This attractive force causes the paint powder to adhere strongly to the coating object, until the powder is fused into a durable film by the baking process.
As the paint powder is composed 100% of resin (including pigment), only a miniscule amount of chemical substances are released into the atmosphere during the coating operation and the baking process. As well, excess paint overspray that did not adhere to the coating object can be easily recovered for reuse. For these reasons, powder coating is attracting much attention as a coating method that "conserves resources and energy" as well as being both "environmentally-friendly and human-friendly".
Please refer to the "Handbook of New Coating Operations - Introduction" (published by the Coating Equipment Manufacturers Association of Japan) as it contains both detailed and general-purpose information about coating. Please contact the secretariat of the association to purchase this publication.
(Reply from: Parker Engineering Co., Ltd.)
Powder coating requires the application of electrostatic charges in order for the paint powder to be attracted and adhere to the coating object. Therefore, even though only a minute amount of electrostatic charge is required (2 - 20 mA), if no such charge is present, then coating cannot be performed. However, many non-metal substances can also be made to conduct a small amount of electricity, by adjusting the moisture content within the substance or by properly conditioning the surface. Therefore, in certain cases, powder coating can be performed on objects made of plastic, glass, wood, paper, concrete and rubber.
Therefore, the answer to whether powder coating can be performed on non-metals is a definite "Yes". However, the most important determining factor is actually whether the object to be coated can withstand the temperatures at which paint powder must be baked.
Furthermore, defects in the coating film may occur on objects made of concrete and wood, due to the water vapor that escapes from the object during the baking process. Therefore, this issue must be addressed prior to initiating coating operations. For non-metal materials, powder coating equipment can still be utilized for "charged electrostatic dispersion", in order to facilitate the application of a coating material that does not require baking.
(Reply from: Nihon Parkerizing Co., Ltd.)
The greatest advantage of the powder coating process is that it allows excess paint overspray to be easily recovered and reused. If this paint overspray is not recovered (i.e. blown away and not reused), although dependent upon the number of guns, the color change process is relatively easy to perform by merely replacing the paint hoppers and cleaning the gun hoses.
When preparing for a color change operation, select an economical system that is easy to operate, by carefully considering the number of colors and frequency of change operations required.
Each color has its own separate booth, coating equipment and recovery system, which is used only for that particular color. Other colors may be used and then discarded.
[Examples]
In this method, two booths are utilized alternately for each color change operation.
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While booth 1 is in operation, remove booth 2 from the line to perform the color change. As soon as the color change operation has been completed, place the booth back onto the line. Follow the same procedure, in turn, for booth 1. |
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Using power and a free conveyor system to exchange booth 1 and booth 2 |
A fully automatic color change system is available.
(Reply from: Nordson Corporation)
Any number of colors can be changed by setting the recovery equipment to cyclone powder collection.
(Reply from: Nordson Corporation)
These factors all depend upon the size of the change operation. For example, when using 1 booth and 6 - 8 guns;
(Reply from: Nordson Corporation)
The powder coating process is an environmentally friendly method of coating that uses no organic solvents, unlike liquid coating processes. As implied by its name, the coating material itself is a powdered paint. This paint powder is electrostatically charged and adheres strongly to the coating object after application. The adhering powder coating is then baked, fusing the powder to form an attractive and durable film. Powder coating allows excess paint powder overspray to be easily recovered for reuse, thus wasting very little coating material. Furthermore, in contrast to liquid coatings, a smooth, thick film can be obtained with only a single coating and without any special level of skill, thus making it relatively easy to set up a powder coating process with automatic coating systems.
| Area of Usage | Coating of objects |
|---|---|
| Home Appliances | Refrigerators, microwave ovens, washing machines, air conditioning equipment for outdoor exposure, light fixtures |
| Roads / Building Materials | Fences, balls, guard rails |
| Automobile Parts | Springs, undercarriage components, wiper arms, wheels |
| Electrical Equipment | Switchboards, distribution boards, cubicles, cable racks |
| Water Supply Materials | Couplings, tubing of varying diameters, valves, cast iron pipes |
| Metal Furniture | Chairs, beds, display stands, lockers, bookshelves |
| Other Uses | Pipes, reinforcing rods, multi-story parking areas, automated warehouse parts, agricultural implements |
This method of electrifying the powder coating generally utilizes a high voltage generator within the gun to produce a corona discharge from an electrode located at the gun tip. Paint powder receives an electrostatic charge as it passes through this corona discharge.
Paint powder is carried to the coating object, where it adheres, due to both the flow of air spray and the creation of an electric field. Unlike triboelectrification, corona charging actually forces the coating material to accept an electrostatic charge, thus enabling the use of the electrostatic coating process, regardless of the particular type of coating material or its physical properties. For this reason, corona charging has been widely utilized up until recent times.
However, many free ions are produced as a result of the corona discharge, thus creating electrical lines of force. These lines of force tend to concentrate at the edges of the coating object, thus the coating material that flows along these lines of force also tends to adhere to the edges of the coating object, resulting in uneven film thickness. Furthermore, as the electrical lines of force do not readily enter recessed areas on the coating object (Faraday cage effect), the interiors of these areas often do not receive uniform coatings. In order to compensate for this shortcoming, corona charging is often utilized in conjunction with additional equipment that removes free ions.
With triboelectrification, as the paint powder passes through the inside of the gun, it comes into contact with the internal walls of the gun, acquiring an electrostatic charge.
In this case, the physical properties of the internal walls of the gun and the particular type of resin powder used (Triboelectrification series) greatly affects the electrification efficiency (refer to the "Handbook of New Coating Operations" for more details of "Triboelectrification series"). Therefore, the use of triboelectrification results in a more limited selection of potential coating materials. For this reason, corona charging has traditionally been the most widely utilized electrostatic spray application. However, in recent years, coating materials have been greatly improved and high performance coating materials for use with triboelectrification have become popular. In addition, additives have been developed that improve electrification efficiency. These new developments are causing triboelectrification to rapidly increase in popularity.
(Reply from: Matsuo Sangyo Co., Ltd.)
Metallic paint powders possess enhanced coating performance and better weather resistance, which allows the coating film to adhere more strongly. These improvements have been achieved through the application of a resin coating and a special surface treatment to the aluminum powder.
As paint powders do not contain solvents, the usage of the electrostatic coating method does not allow a horizontal orientation to be achieved, as it can be with liquid metallic paint. Moreover, metallic paint powder appears blacker than liquid metallic paint and has somewhat less of a metallic appearance than that of the liquid metallic paint.
Conventionally, paint powders are manufactured using a method called dry blend, through the following procedure: paint powder that does not contain aluminum powder is first produced using the melt/blend/grind method and then aluminum powder is subsequently blended into this paint powder.
However, this method of manufacture contains several shortcomings, as listed below:
Recently, new metallic paint powders are being sold, which improve upon the abovementioned shortcomings. These new paint powders are manufactured using a special technique called the "bonding method." This method bonds the aluminum particles directly to the particles of paint powder, in order to eliminate any separation of the paint from the aluminum powder during the coating application.
As for coating equipment, in order to prevent the powder from adhering to the corona pin at the gun tip, metallic paint-compatible guns, such as those that employ air washing, are available on the market.
(Reply from: Nordson Corporation)
The baking process that occurs immediately subsequent to electrostatic powder coating causes the coated surface to become electrically insulated. Therefore, recoating must be performed while both the applied voltage and the electric current are being reduced. However, recent electrostatic powder coating gun models do incorporate a recoat mode, which makes recoating operations relatively easy.
(Reply from: Nordson Corporation)
Theoretically, it is possible to perform color mixing with paint powders.
However, when a primary red color is mixed with a primary white color, a solvent-based paint would appear pink, yet such a paint powder mixture would appear as a mix of red and white dots.
This difference occurs because of the ability of the human eye to discriminate among objects with sizes similar to those of paint particles.
When red and white solvent-based paints are mixed, the human eyes detect a pink color, as the sizes of the individual color particles are extremely minute. However, as paint powders use particles of much larger sizes, which are individually detectable by the human eye, the dot pattern of the mixed paint powder becomes visible.
Therefore, in order to make color mixing viable for paint powder, the particle sizes must be made extremely small, on par with those of solvent-based paints.
In recent years, such paint powders have been under development.
One actual example of this kind of powder is the toner used in color copying machines.
(Reply from: Dai Nippon Toryo)
As depicted in the figure below, the following phenomenon is referred to as reverse electrolytic dissociation: when there is an increase in the electric current that flows to the powder coated layer on the surface of the object being coated (mainly free ions that do not charge the paint), a significant drop occurs in the potential at the powder coated layer, thus causing dielectric breakdown during the powder coating operation. This phenomenon can be represented by the formula: Ed = ρ×Id, where Ed is the electric field strength of the powder coated layer, ρ is the electrical resistivity of the paint powder layer and Id is the current density of the electric current that flows to the paint powder layer. Reverse electrolytic dissociation occurs if Ed exceeds Edb, which represents the field strength at dielectric breakdown of the paint powder layer. Therefore, in order to prevent the occurrence of reverse electrolytic dissociation, the current density Id that flows to the paint powder layer must be reduced, i.e., the electric current that flows from the gun tip to the object being coated (primarily a current of free ions) must be limited.
Once the field strength at dielectric breakdown has been exceeded, minute spark discharges will occur within the powder coated layer and an ionic current having reverse polarity will begin to flow from the powder coated layer back toward the gun. At this stage, the paint particles charged with electricity by the gun now become discharged by the reverse-polarized ions, thus reducing transfer efficiency, creating craters at the locations where spark discharges have occurred and causing an orange peel-like roughening of the coated surface.
reverse electrolytic dissociation
(Reply from: Japan Parker IONICS)
Electrostatic coating is a coating method in which the grounded coating object is considered to act as an anode (+) and the electrostatic coating equipment acts as a cathode (-). A negative voltage (usually DC 60 kV or 90 kV) is applied across these two electrodes, causing an electrical field to be created between them. The sprayed paint particles are negatively charged, thus they are attracted toward and adhere to the coating object, which is the oppositely charged electrode.
When using water-borne paint, the water, which functions as the solvent, is electrically conductive and therefore results in a significant weaker electrostatic effect. In other words, the high negative voltage applied through the electrostatic coating equipment will leak away through electrical conduction by the paint supply system, resulting in a poor or nonexistent electrostatic effect. In order to solve this problem, the paint supply must be electrically isolated (the system is isolated from the ground by electrical insulators), usually by insulating the complete paint supply system.
To isolate the paint supply system, the paint tank is placed on an insulated stand and all of the paint supply equipment located between the stand and the electrostatic spray apparatus is insulated. However, this insulation method does have some drawbacks. Safety can be an issue, as there are more locations where static electricity may tend to build up. Furthermore, operational problems may occur, such as not being able to perform "color changes" or "coating material refills" unless the coating line is first stopped. In order to address these drawbacks, a different method of insulation has been developed, in which the paint pathway between the paint tank and the electrostatic spray equipment is electrically isolated, with the paint tank being electrically grounded (this method is generally known as voltage block isolation).
In addition, electrostatic spray equipment is now available that employs an external electrode. This equipment has become widely used for the application of water-borne paints to automobile bodies. This spray equipment contains a needle-like electrode that is positioned outside of the spray equipment. A high voltage is applied to this electrode in order to provide an indirect electrical charge to the paint particles. Although this method can be utilized without insulating the paint supply system, the transfer efficiency is lower than that of the aforementioned insulation method.
(Reply from: Ransburg Industrial Finishing K.K.)
Yes, as long as certain precautions are taken.
There are two methods that may be used to perform electrostatic coating with water-borne paints.
When this method is employed, the paint supply system must be electrically insulated from the ground, in order to prevent the electrostatic charge from leaking away. A robotic coating applicator possesses several axes of motion, thus can perform complex movements more efficiently than can a reciprocator unit that operates in only 1 or 2 axes. However, since the main body of the robotic coating applicator is grounded, the paint supply system is much more difficult to insulate. Therefore, the usage of paints that require such insulating procedures will inevitably entail greater restrictions upon operational conditions, than paints for which such electrical insulation is not required.
Furthermore, another method exists, in which the paint supply tube is made thicker in order to increase its electrical insulation value. However, this additional thickness may increase the stiffness of the tube and thus restrict the robot applicator's range of motion.
This method does not require insulation of the paint supply system, as described in the above section (1). However, this type of coating equipment tends to be more susceptible to contamination by dirt or foreign material, which can cause high voltage leakage. For this reason, it is important to perform teaching to ensure that the coating applicator and peripheral equipment do not become dirty, and that booth conditions are carefully managed (temperature and humidity, wind direction and wind velocity).
(Reply from: Ransburg Industrial Finishing K.K.)
Basically, the color mixing of water-borne paints is possible, just as with solvent-based paints.
However, color mixing is only effective when the same primary colors (pigments) of water-borne paints are utilized, as those for the solvent-based paints currently being used.
In certain cases when special colors are used, such as deep colors, metallic colors and pearl colors, water-borne paints will not have the same primary color variations as those of solvent-based paints, thus the same colors may not be reproduced exactly. (Although in these cases, the colors will be very similar. This is referred to as metamerism. Metamerism is a phenomenon in which two different colors appear to be the same under a certain light source, yet appear colored differently under a different light source.)
In the event that a more exact color match is required, it may be necessary to send a color sample to the paint manufacturer for color confirmation.
(Reply from: Rock Paint)
