Electrostatic Painting

ELECTROSTATIC PAINTING

Electrostatic painting employs the basic principle of electrostatic (opposites attract) to achieve durable and strong finish on metals and other materials. The most notable advantage of electrostatic painting over conventional liquid paints is that it leaves no runs, drips, bubbles or sags. The operating principle of this painting method involves dry powder, made of resins and pigments, being pneumatically supplied from a reservoir directed to a spray gun. The surface to be painted is grounded while the paint powder is charged with a high voltage at low amperage at exiting the spraying gun. On reaching the surface to be painted the powder particles are attracted to the grounded surface and firmly held there. The material is then taken into a curing oven where the powder is melted and fused to give a smooth coat.

Electrostatic painting machines are classified into three categories namely; airless type; air atomized types and rotating discs and bells type. The discs type employs high speed discs to atomize the coating resulting in a more fine coating and the paint particles are well directed to the grounded surface. This type is the most suitable for applying paints that are difficult to disperse and paints with high solids. Electrostatic painting is disadvantaged by the faraday cage effect. This effect involves the tendency of the charged particles to get deposited around cavities entrances.

HOW IT WORKS...

The principle of electrostatics is analogous to magnetism. An electrically charged object produces an electrostatic field and two objects with opposite charges will attract each other. An object with more electrons than the surrounding is taken to be negatively charged while the one with fewer electrons than its surrounding is positively charged. This forms the scientific basis on which electrostatic painting operates.

An atomizing electrode is located at the spraying tip. It is here the paint particles receive extra electrons and become negatively charged. During spraying the charges are dissipated through the ground and return to the power supply completing the electric circuit. The path of the paint particles is influenced by the electrostatic field. Over spray is drastically reduced since the charged paint particles are directly directed to the grounded surface of the item being painted. A phenomenon known as wrap allows the sprayed particles to be deposited to the back of the item.

PAINTING
After setting up is done, the object is grounded and the paint formulation is positively charged, the painting starts. The positively charged powder paint formulation is sprayed on the grounded item. The item being oppositely charged draws the paint towards it surface and the attraction if so strong that the paint is pulled across to coat the whole surface. The process is safe and no protection gear is required. However, some unpleasant odors may be produced during painting process and it is thus recommended that it should be carried out on the outdoors.
This method of painting uses no solvent and makes it environmentally friendly. Electrostatic painting is durable and there is a range of formulations such as urethane, polyester, epoxy or a hybrid of two of these. The choice of the best formulation is dictated by the intended use of the item to be painted. Epoxy formulation is the best choice for chemical and corrosion protection and for resistance to solvents. Polyester and urethane are chosen where a superior exterior durability is called for.


Polarizable solvents are used to formulate all paints, primers and coatings sprayed by electrostatic painting. Materials such as plastic, ceramics, glass and rubber cannot be painted electrostatically since it is not possible to ground them electrically. There is a whole spectrum of color glosses, antiques and metallic effects available for electrostatic painting. The mixing of the powder paint formulation and the catalyst compounds should be carried out by the manufacturer. Computerized matching techniques allow the manufacturer to come up with a specific mix depending on your taste. This may take time and may cost your extra.

BENEFITS OF ELECTROSTATIC PAINTING
There is a high transfer efficiency achieved by electrostatic painting. This high transfer efficiency reduces the volume of paint used. Further benefits of electrostatic painting include reduced emissions of volatile organic compounds used as solvents in conventional paints, reduced hazardous air pollutants emissions, reduced waste generation and reduced exposure during application. Less maintenance is called for the pain reservoir for pollution control. electrostatic painting requires high capital cost and regular maintenance of the spraying equipment is needed.