Powder Coating on Wood, Plastic and Glass

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Powder coating wood, plastic and glass is a little different from powder coating metal.  Here is an explanation of the differences.

Several powder coat manufacturers have worked extensively on developing systems for powder coating wood, especially MDF (medium density fiberboard), for use in furniture and shelving. One concern is the retained moisture in the wood. If you have the time and patience, you can preheat the wood, spray hot (250°F or so), cure at an elevated temperature (say 350°). The moisture in the wood will blister out and show as blow holes in the coating. You could then sand the coating and repeat the operation. The second coat should come out okay. If not, repeat.

Some powder coating manufacturers have developed a low temperature cure powder for wood coatings. As I understand it, you first must sign a non-disclosure agreement with Morton promising your first born child if you reveal what you are about to be told. It is hard to fool the laws of physics, so I don’t believe they are doing anything that radical. This may be a combination of pre-heat (possibly with infra-red) and low temperature cure powders. They do make powders which will cross link at close to the boiling point of water, but these tend to be quite touchy at room temperature, and during transit.

The same questions apply to the powder coating of plastic. Since plastics tend to be non-conductive, the electrostatic charge will not be transferred to ground, and the powder will tend to not stick to the plastic unless it is preheated. The softening point of the plastic will be the constraint on doing this. If it is an engineering plastic, it may take a 300°+ preheat and post heat. If it is a commercial molded product, it probably won’t. I spoke with a coater a few days ago who is coating cast pewter parts. The pewter tends to melt at the standard 400° oven temp. Since the part was dense and solid, I guessed that it would not do any flexing after being coated, and the coater could get by on less than a full cure. He will try coating at 275° to 300°. The only down side is poor impact resistance, but he said that should not be a problem.

So, wood and plastic can be coated, but  not with a standard procedure and cure schedule.

Glass should not be a problem as long as the coater can get the powder on the part. Armstrong Powder Coatings (since purchased by Morton) used to produce a flat black epoxy which was used on a Tequila bottle. One coater I know said he would put a “grounding rod” down the center of glass lamp bases to enhance electrostatic attraction. Others routinely spray hot to get the powder to adhere to the glass, then do a conventional cure. It may take two coats for complete coverage. After the first coat is applied and melted (not cured), it is easier to get the second coat to stick to the first.

David Collander
Coating Solutions Co.

Powder Coating on Wood, Plastic and Glass