Electrostatic powder paint

Today, powder paint is applied by electrostatic spraying..

The spraying process takes place in the way: the powder in the gun becomes electrically charged and the coated object is grounded. This electrostatic force is sufficient to keep the charged powder dry on the product until the polymerization process.

Powder paint is charged in one of the following ways:

● Normal (corona) electrostatic charging occurs by paint passing through a high voltage electrostatic field.

● frictional (tribo) charging occurs during the friction of the paint on the dielectric.

Normal (corona) electrostatic charging

At the outlet of the sprayer a high voltage  concentrated of 40-100kV. It causes the ionization of air that passes through the nozzle. Paint passes through ionized air to receive a negative charge.

The combination of charged powder particles and free ions is called space charge.

Corona charging has more advantages over friction:

● high level of charge of paint;

● low sensitivity to air humidity;

● More reliable and productive equipment.

But corona charging also has disadvantages: the difficulty of applying paint in the corners and in deep recesses in the products.

Friction (tribo) charging

During rapid friction of paint particles on a dielectric material charging occurs along the gun barrel. At the same time, we get positively charged particles of paint and some uncharged particles at the output (then we reuse them).

 

Triboelectric series – lined materials that are classified by how easily they perceive electrons.

At the top of the row there are materials that are most easily donated by electrons (donors).

And those materials that most easily accept electrons (acceptors) are at the bottom of the row.

 

One of the best acceptors in the triboelectric series is polytetrafluoroethylene (Teflon).

Comparison of conventional and frictional charging