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. Morton Powder
Coatings [800-842-1994] and others 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 probably 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.
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