Electrostatic powder coating technology achieves efficient coating through high-voltage electrostatic adsorption. Its core process is as follows: compressed air delivers powder coating material to the electrostatic spray gun, where a high-voltage generator at the gun nozzle generates an 80-100kV electrostatic field to induce corona discharge, charging the atomized powder; the charged particles are adsorbed directionally onto the surface of the grounded workpiece under the influence of electric field force, forming charge accumulation as the coating thickens, and autonomously regulating the uniformity of film thickness through electrostatic repulsion of the same sign; finally, high-temperature curing forms a dense coating film, completing the full industrial application process from powder adsorption to coating formation.
Workflow Processes
1. Preprocessing
Purpose:
Remove contaminants from the surface of the workpiece, forming a rust-proof and adhesion-enhancing phosphate coating
Detailed steps:
① Degreasing: Remove oil and grease with acidic degreaser (sulfuric acid/hydrochloric acid)
② Rust removal: Remove the oxide layer through acid pickling or mechanical grinding
③ Phosphating: Generating a gray phosphate crystalline film (2-4g/m²)
④ Passivation: Sealing the pores of the phosphate coating to enhance corrosion resistance
2. Electrostatic spraying
Purpose:
Achieve uniform adsorption and efficient recovery of powder coatings
Detailed steps:
① Electrostatic generation: Spray gun loaded with 60-100kV negative high voltage
② Powder atomization: Disperse powder with compressed air (0.4-0.6MPa)
③ Electric field adsorption: directional deposition of charged powder onto the surface of the workpiece
④ Recycling and processing: Cyclone + filter cartridge secondary recycling (95% utilization rate)
3. High-temperature curing
Purpose:
Complete powder melting, leveling, and crosslinking curing reaction
Detailed steps:
① Temperature rise stage: increase to 185℃ at a rate of 10℃/min
② Isothermal curing: Maintain at 185±5℃ for 15 minutes
③ Cooling stage: Natural cooling to below 50℃
④ Quality inspection: hardness/adhesion/appearance inspection
4. Decorative treatment
Purpose:
Achieve special appearance effects (wood grain/pattern/high gloss, etc.)
Detailed steps:
① Glazing treatment: spraying transparent powder/UV coating to enhance gloss
② Thermal transfer printing: Replicating textures through transfer film (150-200℃)
③ Water transfer printing: Impregnate and activate the film to form 3D patterns
④ Local fine adjustment: manually re-spraying special effect paint
Working Principle
During work, the spray gun or spray cup part of electrostatic spraying is connected to the negative pole, while the workpiece is connected to the positive pole and grounded. Under the high voltage of the high-voltage electrostatic generator, an electrostatic field is formed between the end of the spray gun (or spray disc, spray cup) and the workpiece. The electric field force experienced by the paint particles is proportional to the sum of the voltage of the electrostatic field and the charge on the paint particles, and inversely proportional to the distance between the spray gun and the workpiece. When the voltage is high enough, an air ionization zone forms near the end of the spray gun, where the air is intensely ionized and heated, causing a dark red halo to form around the sharp edges of the spray gun end or the needle. This halo is clearly visible in the dark, indicating that strong corona discharge occurs in the air.
The film-forming substances in coatings, namely resins and pigments, are mostly composed of high molecular organic compounds, often becoming conductive dielectrics. Solvent-based coatings, in addition to film-forming substances, also contain organic solvents, co-solvents, curing agents, electrostatic diluents, and other various additives. Except for benzene, xylene, and solvent gasoline, most of these solvent-based substances are polar materials with low resistivity and certain conductivity, which can improve the charging performance of coatings.
The molecular structure of dielectrics can be divided into two types: polar molecules and non-polar molecules. Dielectrics composed of polar molecules exhibit electrical properties when subjected to an external electric field; dielectrics composed of non-polar molecules exhibit electric polarity under the influence of an external electric field, thereby exerting an affinity for external conductive charges, enabling the outer surface of the dielectric to become locally charged in the external electric field.
The paint is atomized through a nozzle and sprayed out. The atomized paint particles become charged when they pass through the contact with the needle at the gun's mouth or the edges of the spray disc or cup. As they pass through the gas ionization zone generated by corona discharge, their surface charge density is further increased. Under the electrostatic field of these negatively charged paint particles, they move towards the workpiece surface with a guiding polarity and are deposited on the workpiece surface to form a uniform coating film.
Advantages of powder coating
Excellent environmental protection: no solvent volatilization, powder recovery and utilization rate > 95%, in line with RoHS environmental standards.
Outstanding performance: The coating hardness reaches 2H-3H, with salt spray resistance exceeding 500 hours, and adhesion reaching Level 0 (Cross Cut Method).
Significant efficiency: Single film formation of 60-120μm, curing in just 15-20 minutes, and an automation spraying efficiency increase of 40%.
Strong decorative appeal: Customizable wood grain/metal/3D texture, with gloss levels ranging from matte to mirror finish.
Disadvantages of powder coating
Thickness limitations: Coating processes with ultra-thin (<40μm) or ultra-thick (>200μm) layers exhibit poor stability.
Difficulty in color change: Color change requires thorough cleaning of the equipment, resulting in a 30%-50% increase in cost for small batches of multi-color orders.
Substrate restrictions: Applicable only to metal parts with a temperature resistance of >180℃. Plastic/wood requires special treatment.
High energy consumption: The energy consumption of the curing oven accounts for 65% of the total process power consumption, and the carbon emissions from gas heating are 20% higher than those from traditional painting.
