Electrostatic spray coatings have the advantage of less paint consumption compared to conventional non-electrostatic spray-coating methods.
Some special products are required to enhance the electrostatic paint performances and avoid problems from batch to batch. These are better known as Conductivity Agents or Conductivity Improvers.
Electrostatic Spraying: Resistivity and Conductivity
The electrostatic spray application consists of creating an electrostatic field with the help of high voltage source
. It enables wrapping up complex objects with a paint layer. Thanks to this field, the paint is forced-orientated following the electrostatic lines and is able to cover even the shadow parts.
Due to this forced orientation, the electrostatic spray application offers better yields (around 30% more) than common air spray techniques.
Combined with an airless application, it can also significantly reduce the solvent mist and as a consequence the VOC emission.
In order to be charged and electrostatically attracted to the substrate, the paint must have a defined conductivity / Resistivity. These two parameters can be defined as follow:
Electrical Resistivity (ρ)
Resistivity is a measure of how strongly a material opposes the flow of electric current
. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm meter (Ω.m)
Electrical Conductivity (σ)
Conductivity is the reciprocal quantity, and measures a material ability to conduct an electric current
The SI unit is Siemens per meter (S.m−1). The relation between the electrical Resistivity and Conductivity is:
An electrostatic liquid paint has generally a resistivity between 1 and 50 MΩ.cm.
- 1 MΩ.cm could cause electrical short circuit
- 50 MΩ.cm reduces the charge of the particles and the paint ability to cover properly the pieces