Technology Interchange: Polyester Powder Coatings: TGIC vs. HAA
Posted on Friday, July 8, 2016
By: Kevin Biller
Polyester powders are ubiquitous regardless of what
part of the world you live. These are the mainstay of the
outdoor durable powder market and represent anywhere
from 32 to 45 percent of powders sold, depending on
global region and who you’re talking to.
This technology has been around since the mid-1970s
and continues to dominate the outdoor durable finishing
world. Here is a review of the prevailing technologies and
Polyester powder coatings fall
into two broad categories
based on what material is
used to crosslink these polymers.
Common vernacular describes
polyesters as “TGIC” and “TGICfree.”
In addition, some folks call
the non-TGIC containing polyesters
HAA-polyester or even “Primid®
polyesters.” TGIC refers to the curing
agent triglycidyl isocyanurate whereas
HAA describes β-hydroxyl-alkyl
amide, an alternate curing agent.
Primid® is the registered tradename of
EMS-Griltech, the original supplier of
HAA curing agent. In this Technology
Interchange, I present a comparison
of properties of these closely related
powder coating types. For the sake of
this discussion, I will use the terms
TGIC-polyester and HAA-polyester.
One important issue I will not
be covering is toxicity. Volumes of
information are available that discuss
the handling issues associated
with TGIC. Regulations for handling
TGIC vary by jurisdiction and global
regions. The European Union and
Australian regulatory agency require
strict labeling for TGIC-containing
products. Consultation with the
appropriate regulating agencies will
provide more insight into whether
TGIC-based powders can be used in
Both types of
polyester powders use strikingly
similar polymers. The backbones are
comprised mainly of terephthalic and
isophthalic acids with neo-pentyl
glycol. Other monomers are used to
alter melt viscosity, flexibility and
coating physical properties. And both
polyester types have reactive carboxyl
groups for crosslinking.
Curing Agents and Cure Mechanism.
TGIC is a compact
molecule based on a heterocyclic ring
with three pendant epoxide groups.
These epoxide (aka glycidyl) groups
react with the carboxyl groups on the
polyester resin. HAA is another rather
compact molecule that contains four
fairly reactive hydroxyl groups that
crosslink with the carboxyl functionality
on the polyester resin.
The reactive glycidyl groups on
the TGIC molecule chemically bond
with the carboxyls on the polyester
resin in an additive fashion. That is,
there is no condensate or volatile
emitted during cure. Alternately the
HAA-carboxyl reaction produces
water as a condensate which evolves
from the coating film during cure.
of a coating is predicated on a
number of formulation variables. The
UV resistance of the primary polymer,
in this case a polyester resin, has the
most significant influence on durability.
Hence, the choice of specific polyester
resin will dictate the expected weathering resistance in a polyester
irrespective of whether it is cured
with TGIC or HAA. The use of TGIC
or HAA is weathering neutral as both
materials inherently provide good
Both standard durable and “superdurable”
versions of TGIC and HAA
polyester powders are available to the
coating user. Standard durable polyesters
withstand about 18 months
south Florida exposure before exhibiting
signs of degradation. Superdurable
polyesters typically endure up to 5 years exposure in south Florida
before they degrade.
Other formulation variables affect
outdoor durability. Non-durable
pigments and additives can reduce
weathering resistance, whereas
ultraviolet (UV) absorbers and light
stabilizers can enhance UV durability—especially
in clear coats. These
variables are independent of the
crosslinker used in the formula (e.g.,
HAA vs. TGIC).
properties such as impact resistance,
flexibility, hardness and abrasion
resistance are generally equal between
TGIC and HAA polyester powder
coatings. Formulation approaches can
influence these properties, but neither
polyester chemistry is inherently better
than the other for basic physical
polyesters typically have slightly
better chemical resistance than their
HAA polyester counterparts. The
HAA curing mechanism emits water
during the reaction which makes the
resultant coating slightly more water
soluble than a TGIC cured polyester.
Consequently, the alkali and acid resistance
of HAA polyesters is slightly
less than TGIC polyesters.
the potential for residual H2O from
the cure mechanism, HAA polyesters
are somewhat less corrosion resistant
than TGIC polyesters. Of course
formulation conventions affect the
ultimate corrosion resistance but
a straight-up comparison demonstrates
a slight advantage to the
TGIC coating variants.
Processing Issues: Manufacture,
formulas are easier to manufacture
because TGIC melts in the extrusion
process whereas HAA, having a
higher melt point, is more difficult
to process. This requires a more
closely managed powder coating
manufacturing process with particular
attention to extrusion conditions.
Conversely, HAA polyester powders typically apply better than
TGIC powders. HAA based powders
tend to possess higher first pass
transfer efficiency than TGIC types
and therefore create less reclaim and
better overall electrostatic deposition.
Most HAA polyester users
claim this technology penetrates
cavities and tight corners better than
Interestingly TGIC has the advantage
in low temperature cure capability.
Powder coatings cured with
TGIC can be cured at temperatures
as low as 266°F (130°C) but more
practically around 293°F (145°C).
HAA-based polyesters can be cured
no lower than 311°F (155°C) but in
practice are cured about 20°F higher
TGIC polyester powders can
be applied at a wide range of film
thickness. Typically, the low coating
threshold is around 1.5 mils (38
microns) but consistent films of up
to 10 mils (250 microns) are possible.
HAA powders emit water during
cure which can create pinhole
defects at thick films. Consequently,
the high thickness threshold is
around 3.5 to 4.0 mils (90 to 100
microns) for these products.
Color stability of TGIC based
powders is considered the best for
main stream powder coating technology.
Very little color drift is observed
over a large cure temperature
(and time) range. Alternately HAA
based powders tend to yellow with
overbake conditions. More stable
versions of HAA are available but
more expensive than standard grade
HAA. In addition, antioxidants can
be used to reduce oven yellowing of
Both of these coating types are relatively
economical and demonstrate high
performance. Outdoor durability is
very good to excellent (1 to 5 yrs.
Florida). Film performance exhibits
a very good balance of flexibility,
hardness and abrasion resistance.
TGIC polyesters are more forgiving
to process variables in powder manufacture
and curing. HAA powders
have an advantage in electrostatic
behavior and transfer efficiency.
Neither product is cost prohibitive
and both provide good overall value
to the coating user.
One final note, handling issues,
specifically toxicity, tilt the decision
making choice to HAA polyester
powders, however in most markets
outside of Europe and Australia,
TGIC polyester powders can be easily
handled with the proper personal
protective equipment (PPE) and
Kevin Biller is technical editor of
Powder Coated Tough magazine and president
of The Powder Coating Research Group.
He can be reached via email at