Ask Joe Powder
Posted on Sunday, June 1, 2014
Those Are The Brakes
I have some brake calipers that I
powder coated, and I would like to
add lettering and then add a clear
powder coat and put in the oven and
bake it. I would like to know of any
material (vinyl, decal or anything)
that can withstand 400°F to be powder
This is a tricky proposition. First of all,
PVC (vinyl) decals will not take 400°F, so
they’re out. There are a number of materials
used to make decals, and the table below provides
type and heat resistance.
For your application, I would consider PET or
polymide as the decal polymer. PET may be borderline
for heat resistance; however, you should
be able to use a clear powder coating that can cure
around 350°F and avoid exceeding its heat resistance
Otherwise you will have to use a polyimide-based decal, which easily outperforms all other
decal materials for heat resistance. Polyimide tapes
are regularly used as masking for powder coated
articles, so I can attest to their resistance to typical
powder curing temperatures.
Preparing the surface for the decal and choosing
a powder coating are also important considerations
for the success of your project. The surface should
be wiped clean with a good solvent. I recommend
either denatured alcohol or acetone. Both are readily
available at your house paint store or DIY.
I would recommend a low-temperature cure
polyester powder coating as your clear coat. Epoxies
discolor with heat, and polyurethanes have a
tendency to outgas at thick films. Polyesters capable
of low temperature (i.e., around 325° to 340°F)
are commonly available. These products have good
heat resistance and can be applied at relatively
thick films to give a high gloss with excellent distinctness
of image. Please ensure that the coating
is fully cured to make certain that it provides full
Please let me know if you need anything more.
Seeing the Light
Dear Joe Powder
I carry out jobbing, currently doing
batch oven curing. I understand that
UV powder coating materials are
different, but what will be the temperature
required for the first stage
of melt? After this, can the parts be
touched before transferring to the UV
curing? Are UV powders more expensive
than normal epoxy powders?
How about the energy costs?
Can you give some insights about
UV cured powder coatings. How is
this process carried out?
Indeed the powder must be melted, and
it cures best at an elevated temperature. The
melt phase can be accomplished by any source
of heat—convection, infrared or a combination
of both. This can take anywhere from a
few seconds to a minute or two, depending on
the source and the intensity of heat.
The melt temperature depends on the
formulation and can range from about 212° to
257°F (100° up to 125°C). The parts can be
touched; however, the coating should not be
UV powders are generally more expensive
than epoxies, but not outrageously more. Energy
costs are quite low, however the process
is more complex. Heating a substrate to 110°C
instead of 180 to 200°C obviously saves cost.
The UV process requires high energy but it is
very compact saving floor space and capital
UV cure is “line of sight,” meaning the
UV energy must penetrate the coating. Shadows
and unexposed spots do not cure. The
UV curing typically takes seconds—very few
seconds. Too long and the coating will burn.
In addition, it is important that the coating is
warm and relatively fluid when exposed to the
UV energy. This allows for better molecular mobility
and more complete cure.
Any substrate that can be powder coated can
most probably be coated and cured with a UV powder.
The key is to melt the powder without damaging
the substrate. Metals substrates are relatively
easy to finish with UV powders. More difficult are
plastics especially those possessing low heat distortion
Joe Powder is our technical editor, Kevin Biller. Please send your questions and comments to Joe Powder at email@example.com