Letter 11023

Effect of Paint Resistivity on Electrostatic Transfer Efficiency  

I'm looking for any "Hard Data" that shows impact of paint resistivity on electrostatic transfer efficiency - particularly with bell spray. I don't seem to be getting any data from bell suppliers.

Gerald Goodell
- Troy, Michigan

What is impact of lesser or higher paint resistivity than specified range ,affects transfer efficiency, finish,wrap-a-round effect on the surface to be painted using electrostatic hand gun?

Satyajit Vasant Pandit
- Pune, Maharashtra, India

The paint resistivity is not a main factor in efficiency. But rather the charge to mass that you achieve on the droplets after or during atomization. If you use a water soluble coating and isolate so that the extreme conductivity does not cause high current flow to ground you can achieve high efficiency. More important is how you handle the following.
1. Current to ground.
a. The current reduces the voltage, which lowers the charge to mass ratio achievable. following.
2. The conductive charge, or contact with the charged tool. following.
3. The ion field, generated off the edge of the tool, sharper is better for ion field. following.
4. The droplet distribution, the largest most uniform droplets which provide the desired film formation will achieve the best charge to mass and have the best attraction to the field. following.
5. The field generated to the workpiece, proper distance etc. following.
6. The lowest droplet velocity which achieves the desired film formation. following.
Also critical are the conditions of the booth air flow.

Anthony Brajdich
- Lapeer, Michigan

If you have a paint that is adjusted to the range of resistance of the electrostatic pistol but still does not give the desired transfer to the metal, are any solvent o resin or any type of additive that improves that conduction?

Diana Gutierrez
R&D - Antioquia, Colombia

The resistivity recommended by the finishing tool is not the gating factor for efficiency. Generally it will be set so that the equipment is in a good range for current draw and will have a low limit which keeps it in the safety range of what ever rating it has. The metal in the fluid stream as well as the material before ground must be considered in the calculation for capacitance and power.
The resistivity to use is the material manufacturers, this may need to tested for given many materials are made and tested for appearance and durability with conventional airspray. Another consideration is the type of meter you use, there are three measurements I am aware of in use. There are conversions to move from one to the other.
1. Kilohm per centimeter
2. Megohm per square centimeter
3. Megohm per cubic centimeter
The main issue with changing the solvent diluent or other additives is that this may well affect the final appearance or desired characteristics of the material, it is best to do this with the material suppliers support.

Anthony Brajdich, again
Hunter Associates - Lapeer, Michigan