Ask Joe Powder, Jan/Feb 2015
Posted on Sunday, February 1, 2015
Hope you are fine. What is your recommendation to guarantee an adhesion of powder apint for surface "hot-dip zinc coating"?
Ozlem E., Turkey
Life is good lately, thanks! Your question is a difficult
one. One of the biggest issues is the variability in the
quality of the HDG. It can be very inconsistent—not
only from batch-to-batch of HDG, but also on different
sections of the same sheet of HDG. What I recommend
is first careful cleaning of the surface. This can be an
alkaline cleaner followed by a good quality rinse. You
may also want to consider media blasting as well,
however this adds cost to the process.
As for adhesion, some powder coatings work better
than others. A good quality epoxy will adhere better
to HDG than a polyester powder. Hybrids (epoxypolyester)
fall somewhere in between. If this is for an
outdoor durable application you need to either use
a zinc phosphate pretreatment with the polyester or
the combination of an epoxy primer followed by the
Also it is important to de-gas the HDG prior to
applying the powder coating. Otherwise, you may
observe pinholes in the coating. De-gassing involves
preheating the HDG and applying the powder to the
warm substrate. Preheating to 302 to 347°F (150 to
175°C) usually suffices.
I hope that this helps answer your question. And I
wish you and your family a healthy and prosperous
– Joe Powder
A Stinky Situation
Q- Hi Joe,
I have a problem with a functional powder coating we use to electrically insulate electric motor armatures. It's a Bis A/ECN (Bis-phenol A/Epoxy Cresol Novolac) resin system, calcium carbonate filled and Dicy (Dicyandiamide) cured.
When cure temperature gets above about 410 degrees Fahrenheit (210 Celsius) there is an odor given off that a customer is complaining about. My question is do you have experience with odor maskers or absorbers that might help us out of this one?
Definitely appreciate your help,
A- Hi John,
I really don’t have much experience in odor masking
agents. I think that you may have three or four approaches,
1. Identify and eliminate the source of the odor. This would
involve a compositional change; however, it may be as
simple as comparing different grades and suppliers of the
2. Consuming the odor-causing species. It probably involves
volatile, low molecular weight fragments and it may be
possible to react or adsorb these compounds to render them
less or non-volatile.
3. Masking. This would involve introducing a fragrant
compound that would overwhelm the odor caused by the
formula. It would be important to find something that would
perform at the relatively high temperature.
4. Bonus approach. Replacing the current product with a lower
temperature cure formula might minimize the evolution
That’s what I can think of off the top of my head. Let me
know if you have any questions or comments.
– Joe Powder
Joe Powder is our technical editor, Kevin Biller. Please
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