Electrostatic Powder Coating

What is electrostatic powder coating?

Electrostatic powder coating is a coating method that uses electrostatic charges tattract charged solid particles to the surface of a workpiece. Since the 1960s, the powder electrostatic spraying process has been widely used in the world.

It includes preparing the powder, charging it, spraying it, depositing it on the workpiece, and then curing it as needed. Compared with wet paint, this technology ensures coating quality, corrosion resistance, environmental protection, efficient and uniform coating.

What is the principle of electrostatic powder coating?

The principle of powder electrostatic spraying is tuse the principle of high-voltage electrostatic corona electric field. The metal guide cup at the head of the spray gun is connected ta high-voltage negative charge, and the workpiece tbe coated is grounded to form a positive electrode, thereby forming a strong electrostatic field between the spray gun and the workpiece.

What is the process of powder coating using electric charges?

During the electrostatic powder spraying process, the powder particles need tbe charged. Once the powder particles are charged, these particles will be attracted tthe workpiece, that is, the surface tbe painted.

So, how does the charge play a role in this process?

First of all, electrostatic spraying can use positive or negative charges, depending on your needs. At the same time, the piece you need tcoat may have an opposite charge, attracting the charged powder. It makes sense - opposites attract.

Powder electrostatic spraying process

Spraying process

Get your spray gun and gloves ready, let's start electrostatic powder spraying!

1. Powder preparation: Mix solid powder with air or other gas for delivery.
2. Workpiece pretreatment: Increase the bonding strength between the workpiece and the coating
3. Charging: Charge the powder particles by friction or electric field.
4. Spraying: Use a spray gun tpoint the charged powder tthe workpiece.
5. Deposition: The charged powder is attracted tthe surface of the workpiece and covers it evenly.
6. Solidification: As needed, the powder is melted or solidified tform the final coating.

Metal material pretreatment

Before powder spraying, it is generally necessary tpretreat the workpiece tincrease the bonding strength between the workpiece and the coating.

The pretreatment of powder coating generally includes processes such as rust removal, degreasing, chemical phosphating or passivation.

Powder coating defects and pretreatment

Most powder coating defects such as foreign matter, stains, discoloration, oil marks, pinholes, etc. are caused by negligence in the pretreatment process, such as incomplete degreasing, incomplete rust removal or improper phosphating. Tsolve these problems, the following measures are recommended:

• Thorough pretreatment: Ensure that all oil, rust and other foreign matter are thoroughly removed before painting.
• Correct phosphating: Control the amount of phosphating film attached and ensure thorough drying after pretreatment.
• Regular inspection: Regularly inspect the pretreatment equipment and process tensure that it operates as required.
• Training and supervision: Properly train operators and supervise them tfollow the correct pretreatment procedures.

What factors affect the effect of electrostatic spraying

In addition tthe spraying process, the factors that affect the performance of the coating in the powder electrostatic spraying process are alsrelated tthe powder coating.

Powder particle size

Changes in particle size will affect the fluidity, coating, tendency tbe blown away, clogging of the spray gun and film thickness of the powder.

• Fluidity: As the particle size decreases, the fluidity gradually deteriorates.
• Coating: Coating ranges from difficult teasy as particle size decreases.
• Blow-off tendency: Blow-off tendency ranges from difficult teasy as particle size decreases.
• Spray gun clogging: Smooth tclogging as particle size decreases.
• Film thickness: Film thickness ranges from thick tthin as particle size decreases.

Summary:It is critical tselect the appropriate particle size tbalance these conflicting properties.

Conductivity of powder coatings

The optimal range of conductivity of powder coatings is 10¹⁰–10¹⁴ Ω·cm. Keeping the volume resistivity within this range ensures good construction performance and coating thickness.

• Below 10⁹ Ω·cm: easy trelease charge, powder particles are easy tfall off.
• 10¹⁰–10¹⁴ Ω·cm: good construction performance and thick coating can be obtained.
• Above 10¹⁵ Ω·cm: particle charge is not easy trelease, charge accumulates on the workpiece surface, and thick coating cannot be obtained.

Spraying distance

The change in spraying distance affects the electric field strength, which in turn affects the coating thickness and powder deposition efficiency. When the spraying distance is 250 mm, the deposition efficiency is the highest.

• 250 mm: deposition efficiency 100%.
• 300 mm: deposition efficiency 91%.
• 400 mm: deposition efficiency 56%.

Spraying voltage

Increasing the spraying voltage increases the amount of powder deposited, but the rate of increase in the amount of deposited decreases when it exceeds 90 kV. It is recommended that the spraying voltage be controlled between 60–90 kV tbalance the amount of deposited and film thickness while avoiding breakdown.

• Film thickness: As the voltage increases, the initial film thickness growth rate increases, but as time goes by, the effect of voltage on film thickness decreases.
• Spraying distance: As the spraying distance increases, the effect of voltage on film thickness decreases.
• Risk: Tohigh a voltage (over 90 kV) may cause powder breakdown, affecting quality.

Gas supply pressure

Increasing the gas supply pressure of the powder feeder will cause a decrease in deposition efficiency. A lower gas supply pressure (4.9 Pa) can maintain a higher deposition efficiency.

• 4.9 Pa: 100% deposition efficiency.
• 6.89 Pa: 97% deposition efficiency.
• 9.8 Pa: 9% deposition efficiency.
• 14.7 Pa: 88% deposition efficiency.
• 19.6 Pa: deposition efficiency 84%.

Electrostatic spraying of paints and powder coating

Powder spraying has obvious advantages in environmental friendliness, durability, coating efficiency, safety and appearance quality, and is especially suitable for large-scale, high-demand industrial coating.

Paint spraying has advantages in flexibility, applicable material range, maintenance convenience and initial investment, and is suitable for small-scale, multi-variety coating needs.

Environmental friendliness

Powder coating

• Advantages: Powder coatings dnot contain volatile organic compounds (VOCs) and have less impact on the environment.
• Disadvantages: If the powder recovery system is not perfect, dust pollution may be generated.

Paint spraying

• Disadvantages: Paints usually contain high VOCs, which have a greater impact on the environment and human health.
• Advantages: Some paint types (such as water-based paints) have lower VOC content, but their performance may not be as good as powder coatings.

Durability and adhesion

Powder coating

Powder coatings have excellent wear resistance, chemical resistance and adhesion, and are suitable for high-demand industrial applications.

Paint spraying

• Disad vantages: Paints are generally not as abrasion-resistant and adhere better than powder coatings, especially in harsh environments.
• Advantages: Certain specialty paints can provide good chemical resistance, but may be more expensive.

Coating thickness and uniformity

Powder coating

• Advantages: Electrostatic spraying can achieve more uniform coating thickness and reduce coating defects.
• Disadvantages: Tothick a coating may cause sagging or orange peel effect, but this can be avoided by controlling spraying parameters.

Paint spraying

• Disadvantages: Paint spraying is difficult tcontrol thickness and is prone tunevenness and defects.
• Advantages: Thicker coatings can be achieved through multiple spraying and drying, but it takes longer.

Coating efficiency and cost

Powder coating

• Advantages: High powder recycling rate, reduced material waste, and lower costs in the long run.
• Disadvantages: High initial equipment investment, requiring specialized spraying and curing equipment.

Paint spraying

• Advantages: Low initial investment, relatively simple equipment.
• Disadvantages: Paint material costs are high, and the cost of handling and recycling unused paint is high.

Coating speed and flexibility

Powder coating

• Disadvantages: The spraying and curing process takes a certain amount of time, especially for large or complex-shaped workpieces.
• Advantages: Once set up, multiple workpieces can be sprayed quickly, suitable for mass production.

Paint spraying

• Advantages: Fast spraying speed, suitable for fast painting needs.
• Disadvantages: Long drying time, affecting production efficiency.

Safety and health

Powder coating

• Advantages: Nsolvent, reduced risk of fire and explosion, less impact on the health of operators.
• Disadvantages: Inhalation of powder may be harmful thealth, requiring appropriate respiratory protection.

Paint spraying

• Disadvantages: Contains solvents, has fire and explosion risks, and has a greater impact on the health of operators.
• Advantages: The use of appropriate ventilation and protective measures can reduce the risk, but the overall risk is still higher than powder spraying.

Color and appearance

Powder coating

• Advantages: High gloss and uniform color can be achieved, and the appearance quality is high.
• Disadvantages: Color changes require thorough cleaning of the spraying equipment, suitable for large-scale single-color production.

Paint spraying

• Advantages: Easy color change, suitable for small-scale multi-color production.
• Disadvantages: Color uniformity and gloss may not be as good as powder spraying.

Applicable materials

Powder coating

• Advantages: Applicable ta variety of metal and non-metal materials, especially conductive materials.
• Disadvantages: Non-conductive materials require special treatment tbe charged.

Paint spraying

• Advantages: Suitable for almost all materials, including non-metallic and porous materials.
• Disadvantages: Some materials may require special primers or treatments tensure adhesion.

Repair and recoating

Powder coating

• Disadvantages: Repair and recoating are difficult, and the entire area needs tbe re-sprayed.
• Advantages: Once the coating is completed, the coating film is very durable, reducing the need for repairs.

Paint spraying

• Advantages: Repair and recoating are relatively easy, and local repairs can be made.
• Disadvantages: Recoating may require the removal of old paint, which increases the workload.

Equipment and maintenance

Powder coating

• Advantages: Equipment maintenance is relatively simple, mainly involving cleaning of the spray gun and recovery system.
• Disadvantages: The electrostatic system needs tbe calibrated and maintained regularly tensure performance.

Paint spraying

The equipment is relatively simple and easy tmaintain.

Scope of application

• ‌Electrostatic powder spraying‌: Suitable for large-scale industrial production, especially for workpieces with complex shapes and large sizes, such as automobiles, electrical appliances, furniture and other industries.
• ‌Spray painting‌: Suitable for small batch, multi-variety production and some hand-made and maintenance operations, such as home decoration, car repair, artistic creation, etc.

Paint composition

I have introduced the composition of powder spray coating in the best aluminum paint. Powder electrostatic spray coating is often composed of resin, pigment, curing agent, additives, etc. Depending on the type of resin, the coating can alsbe called magic powder coating, polyester powder coating, epoxy powder coating

Paint spray coatings usually include acrylic paint, epoxy powder paint, Polyester (PE) paint, water-based paint, PVDF paint.

E-Coating VS Powder Coating

Electrophoretic coating, alsknown as electrodeposition coating, is a coating method that deposits charged paint particles on the surface of a conductive workpiece through an electric field.

Coating form

• Electrophoretic coating: Liquid water-based paint is used, and the paint particles are dispersed and charged in water.
• Powder spraying: Dry powder paint is used, and the powder particles are charged and attached tthe surface of the workpiece through electrostatic action.

Coating process

• Electrophoretic coating: The workpiece is immersed in a charged paint solution, and the paint particles are deposited on the surface of the workpiece through the electric field.
• Powder spraying: Dry powder paint is sprayed onta grounded workpiece through an electrostatic spray gun, and the powder particles adhere tthe surface of the workpiece under the action of the electric field.

Coating film characteristics

• Electrophoretic coating: The coating film is uniform and can penetrate intthe concave and convex parts of the workpiece tform a uniform and dense protective layer.
• Powder coating: The coating film thickness is controllable and the surface is smooth, but the coverage ability of complex shapes is slightly inferior telectrophoretic coating.

Application range

• Electrophoretic coating: suitable for metal products, especially workpieces with complex shapes such as automobile bodies and home appliance shells.
• Powder coating: suitable for various metal and non-metal materials, widely used in furniture, electrical appliances, construction and other fields.

Environmental protection

• Electrophoretic coating: high coating utilization rate, relatively simple wastewater treatment, but the coating contains a small amount of organic solvents.
• Powder coating: almost nsolvent, high coating recycling rate, more environmentally friendly.

Cost

• Electrophoretic coating: high initial investment, but low long-term operating costs.
• Powder coating: relatively low initial investment, but high equipment maintenance and consumables costs.

Electrostatic powder coating vs powder coating

At first glance, the twterms seem similar, but the differences are worth a closer look.

First, powder coating is a coating technique in which a dry powder coating is applied tthe surface of the object tbe coated by spraying and then cured by heating tform a coating film.

What role does electrostatics play in this? The word "electrostatic" implies the use of an electrical charge. In electrostatic powder spraying, the powder particles are given an electrical charge, and the object tbe coated is grounded.

Conventional powder spraying, on the other hand, does not involve electrostatic technology, or uses non-electrostatic methods. This means that the adhesion of the powder may rely on other factors, such as physical contact or mechanical retention of the powder tthe surface of the object, rather than electrostatic attraction.

Electrostatic powder coating vs roller coating

Roller coating is a technology that uses a rotating roller tevenly apply liquid paint tthe surface of an object.

Coating method

• Electrostatic powder coating: Use charged dry powder particles tspray onta grounded object through electrostatics.
• Roller coating: Use a rotating roller to apply liquid paint tthe surface of an object.

Coating film characteristics

• Electrostatic powder coating: The coating film is uniform and has strong adhesion, which is suitable for coating of complex shapes.
• Roller coating: The coating film thickness is controllable, but it may not be as uniform as powder spraying, which is suitable for flat coating.

Applicable scenarios

• Electrostatic powder coating: Suitable for industrial products that require high coating quality and complex shape coating, such as furniture, home appliances, automotive parts, etc.
• Roller coating: Suitable for large-scale production of flat or coiled materials, such as color steel plates for construction, furniture boards, etc.

Environmental protection

• Electrostatic powder coating: Almost no solvent, the powder can be recycled, which is more environmentally friendly.
• Roller coating: Using liquid paint, it may contain solvents, which has a certain impact on the environment and the health of operators.

Key points of electrostatic powder spraying

Distance between spray gun and workpiece

The distance between the workpiece and the nozzle should be between 150-300mm. If the distance is toclose, it is easy to short-circuit, resulting in a breakdown point in the coating, while if the distance is tofar, it is not easy tspray powder on the surface of the workpiece.

Angle and movement of spray gun

The spray gun and the workpiece should always be kept vertical, and the arc movement of the spray gun should be avoided. The moving speed should be kept uniform, otherwise it will affect the final spraying effect, resulting in waste of paint or the formation of "orange peel" phenomenon.

Control of air pressure

If the air pressure is tohigh, it will offset the electrostatic attraction, sthat the powder attached tthe workpiece will be blown off, reducing the powdering rate; if the air pressure is tolow, it may cause problems such as poor powder atomization and insufficient powder output. Generally, the input air pressure should be kept constant between 0.4MPa-0.7MPa.

Spray gun maintenance

Cleaning the spray gun

Disassemble the spray gun regularly to remove the powder residue and scale inside tprevent blockage from affecting the spraying effect. You can use a special cleaning agent or compressed air for purging.

Check the wear of parts

Check whether the nozzle, guide ring, electrode needle and other parts of the spray gun are worn. If worn, they should be replaced in time tensure the normal operation of the spray gun and the spraying quality.

Maintain the powder supply system

Keep the powder in the powder supply barrel fluidized evenly, and clean the powder supply pipe and powder pump regularly to prevent blockage. At the same time, check whether the sealing rubber ring of the powder pump is damaged. If damaged, it should be replaced in time.

Why choose electrostatic powder coating?

• A variety of colors, precise matching
• Better durability and adhesion
• Uniform coating
• High coating efficiency
• High coating thickness, from 20µm t200 µm
• Safety and environmental protection
• Low cost