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David Collander
Coating Solutions Co.
davidrcollander@hotmail.com
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.
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.
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.
A company in San Diego called Advanced Coating Solutions has a
"Water Based Conductive Primer" which is remarkable. The liquid gray primer is sprayed onto the piece to be powder coated and allowed to dry (or force dried at 150 to 200 deg F). Now the part is conductive as if it were a piece of metal. One client recently coated a piece of structural foam, and another coated a plastic bezel. As long as a part being coated can withstand a powder coat cure cycle (low to mid 300s for ten minutes), then it can be powder coated after application of the conductive primer.
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