An electrostatic paint spray system is a highly efficient technology for the application of paint to specific workpieces. Negatively charged atomized paint particles and a grounded workpiece create an electrostatic field that draws the paint particle to the workpiece, minimizing overspray.
 

For this technology, an ionizing electrode, typically located at the paint gun atomizer tip, causes paint particles to pick up additional electrons and become negatively charged. As the coating is deposited on the workpiece, the charge dissipates through the ground and returns to the power supply, completing the circuit. The electrostatic field influences the path of the paint particles. Because the charged particles are attracted to the grounded workpiece, overspray is significantly reduced. Paint particles that pass a workpiece can be attracted to and deposited on the back of the piece. This phenomena is known as "wrap".
 

The transfer efficiency is the percent of sprayed paint that is applied to the workpiece. Paint that is not applied to a workpiece is captured in the paint spray booth's emission control system and ultimately disposed as waste. The typical transfer efficiency for an electrostatic paint spray systems is 75%.
 

In conventional paint spray systems, paint atomization occurs via high velocity air jets forcing paint through small air holes in the paint gun face caps. Air pressures used in these systems range from 40 to 80 psi, with air volumes of 8 to 30 standard cubic feet per minute (scfm). The atomized paint particles travel at high velocities and have a greater tendency to bounce off the object being painted, as compared to electrostatic systems. Transfer efficiencies of 50% are typical for conventional painting systems.
 

No new wastes are generated when a conventional paint spray system is converted to an electrostatic paint spray system. Significant reductions in waste generation are achieved due to the electrostatic systems increased transfer efficiency.
 

A potential drawback to electrostatic finishing, particularly for coating complicated surfaces, is the Faraday cage effect: a tendency for charged coating particles to deposit around entrances of cavities. The Faraday cage effect allows electric charges on a conductor to reside on the outer surface of the conductor. In the case of coating complicated surfaces, the electric charge resides on the entrances of cavities. High particle momentum can help overcome Faraday cage effects, since particles with greater momentum (larger particles or particles traveling at higher speeds) are influenced less by the electrostatic forces. However, high particle momentum also lowers efficiency.
 

Electrostatic paint equipment is available in three basic types: air atomized, airless, and rotating discs and bells. High-speed discs atomize the coating more finely than air atomization and direct more paint to the target. This technology is particularly efficient for the application of difficult to disperse, high-solids paints. However, the Faraday cage effect is generally greater with rotary atomizers than with air or airless types. Rotary atomizers, therefore, may not provide adequate coverage for complicated surfaces.
 

Materials Compatibility:
 

Any material that can be atomized can accept an electrostatic charge, regardless of the coating conductivity. The workpiece must be groundable. Metal and some wooden pieces can be painted electrostatically, but plastic, rubber, ceramic, and glass can not.
 

Safety and Health:
 

Electrostatic paint spray systems operate at high voltages (30 to 150 kV). Hence, operator safety is a major concern. All items in the work area must be grounded, including the operators, the paint booth, the application equipment (unless applying conductive coatings), and conveyors. Ungrounded items should be removed from the work area. Removing paint buildup from the paint booth helps assure that workpieces are grounded. Workers should never wear rubber- or corked-soled shoes (special shoe-grounding devices are available.). Adequate skin contact is required when using hand-held guns. Painters should grasp the gun with bare hands or use gloves with finger tips and palms cut out.
 

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.
 

Benefits:
 

• Higher transfer efficiencies results in a significant reduction in the generation of waste and reduction in paint usage.
• Less maintenance is required for pollution control equipment serving the paint booth.

Disadvantages:
 

• High capital cost and more spray equipment maintenance is required.
• The electric charges tend to repel on complicated surfaces.
• Faraday Cage Effect
• Surface imperfections are possible due to air molecules becoming trapped in the coating surface