Powder Coatings---Properties & Selection

andrewfei

Epoxy powders: can be formulated to give high gloss
and smooth coatings with excellent adhesion, flexibility
and hardness as well as solvent and chemical resistance.
The main deficiencies are their poor tolerance to heat
and light as well as their pronounced tendency to
yellow at elevated temperatures and exposure to
diffused day light.
Acrylic powders: are widely used in surface coatings.
They have good gloss and colour retention on exterior
exposure as well as heat and alkali resistance.
Polyester powders: general performance can be
categorised between epoxy and acrylic powders. They
have excellent durability and a high resistance to
yellowing under ultra-violet light. Most coatings used
on buildings today are based on linear polyesters crosslinked
with TGIC. Today modern polyester powders
are TGIC-free
Epoxy polyester hybrid powders: are epoxy powders
by origin containing a high percentage of special
polyester resin (sometimes exceeding 50%). These
hybrids have properties similar to those of epoxy
powders, however, their additional advantage is that
they have improved resistance to overbake yellowing
and improved weatherability. Hybrid powders are now
regarded as the main backbone of the powder coatings
industry.
Polyurethane powders: provide good all-round
physical and chemical properties as well as giving good
exterior durability.

Table 1: Main Properties of Different Types of Thermosetting Powder Coatings
Properties of Thermosetting Powder Coatings
Property Epoxy Acrylic Polyester Hybrid Polyurethane
Weatherability Poor Excellent Excellent Fair-Poor Good
Corrosion Resistance Excellent Good Very Good Excellent - Very Good Very Good
Chemical Resistance Excellent Very good Very Good - Good Very Good Very Good
Heat Resistance Very Good Good Good Very Good - Good Very Good
Impact Resistance Excellent - Very Good Good-Fair Good Very Good Very Good
Hardness HB-5H HB-4H HB-4H HB-2H HB-3H
Flexibility Excellent - Very Good Good-Fair Very Good Very Good Very Good
Adhesion Excellent Good-Fair Excellent Excellent Very Good