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I'm attempting to create an electrostatic painting process for small plastic parts. The material is ABS and is about 4 inches by 6 inches by 1 inch high. I'm somewhat familiar with electrostatic painting of metal objects, but I am dismissive, perhaps uneducatedly so, of the necessity of the objects to be metallic.

To help the matter, I will be using a painting system that allows the paint droplets to be extremely small -- an airbrush.

I'm hypothesizing that I can connect the negative side of a high-voltage low-current source to the tip of the airbrush, through which the paint flows, while I connect the positive side of the high-voltage source to the plastic part to be painted and mist the paint over the highly-contoured part as it is attracted to the surface.

Will this work?

Chetan Bhargava
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Jordan
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3 Answers3

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The object you paint needs to be electrically conductive, which in most practical situations means it needs to be metallic.

Electrostatic painting works by charging up each tiny droplet of paint, and then setting up a E field so that the electrostatic force on the charged particles pushes them towards the object you want to paint. Car companies have used this process for a long time now. It not only saves on paint and reduces particulates in the air, but does a better job of coating the surface evenly with the paint.

It can even somewhat paint the back sides of small objects. The sprayer only needs to be roughly aimed, and each particle will find its way to the charged target surface. However, they are small particles, so the air appears quite thick to them. Some get pushed around to the back side by the air flow, with the electrostatic force then eventually pulling them towards the object.

The paint is generally not conductive. This means that opposite charge builds up on the surface of the object as the paint builds up. This attracts less new paint particles, thereby automatically evening out the paint thickness somewhat.

However, all this works by keeping the underlying object at a significantly different potential than the paint gun nozzle (and thereby the paint particles). The object needs to be conductive to do this. First, it needs to be conductive to establish the potential all along its surface in the first place. Second it needs to be conductive to counter act at least the initial opposite charge of the first layer of droplets which touch the conductive material directly. The charged paint droplets moving from the nozzle to the object is essentially a electrical current. If you can't drain that current from the object, then even a little paint will rapidly charge it up to the reverse polarity.

Olin Lathrop
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It will work if you use the standard method --- which is to metalize the surface first. Metalization can be done by vacuum deposition (used for very fine/small objects), or by electroplating (used for objects that are not very fine/small), or by flame deposition (used for objects that are coarse/large).

Electroplating is a three step process that also requires an intermediate metal surface, and that surface is done by deposition plating on to an etched ionic surface. The first step is surface etching, which exposes an ionic surface, then deposition plating, then electroplating.

This suggests two options: You could use electrostatic painting after the deposition stage. That will probably work.

Or you could try electrostic painting after the first, etching stage. You can probably find examples of dust deposition onto an ionic surface around your house. The process is very slow, and requires very fine particles with very low surface tension. If you work on it, you may be able to get a paint and a process to make it work for you. Don't expect it to be easy.

david
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As you say, this attempt is reasonable, and it is even done for things like painting aircraft.

Lufthansa says they like this process because more of the expensive paint ends up being on the aircraft and not in the hangar.

However, make sure that there is no danger of igniting your paint with sparks caused by electro-static discharge.

I guess if you use a metal object behind your plastic parts to be painted, you could still achieve good results.

zebonaut
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  • if it was a hollow object, maybe something like steel wool could be wadded inside it .. though the paint would probably end up thicker were the plastic piece is thinner, and vice versa. I.e., results will be uneven at best. – JustJeff Jun 23 '13 at 02:24
  • "*Lufthansa says they like this process ...". Their planes are metallic so wouldn't they use the plane as one electrode? – Transistor Jun 27 '19 at 11:49