Powder Coatings for
Polyurethanes, Polyesters and Hybrid Epoxy Coatings
Solid
blocked polyisocyanates are available which can be used in the
formulation of storage stable thermoset powder coatings. These
solid supply form blocked polyisocyanate hardeners or curing agents
are primarily used with solid, hydroxyl-functional polyesters
or polyacrylates in the formulation of polyurethane powder coatings.
They are also used for supplemental crosslinking in epoxy/polyester
hybrid and TGIC/polyester thermoset powder coatings. Bayer MaterialScience
markets polyisocyanate powder curing agents under the Crelan®
trademark.
[Bayer MaterialScience
provides a broad range of high-quality powder coating resins and
crosslinkers to the powder coatings industry. Click
here to find a downloadable brochure about these products
(registration required) .]
Crosslinkers
for Polyurethane Powder Coatings
- Crelan®
NI 2 -
Caprolactam blocked IPDI prepolymers
- Crelan®
NW 5 - Caprolactam blocked Desmodur® W prepolymers for increased
flexibility
- Crelan®
VP LS 2256 -
Caprolactam blocked IPDI isocyanurate for increased chemical
resistance
- Crelan®
EF 403 - Emission-free crosslinker based on an IPDI uretdione
Another
class of hardeners for polyurethane powder coatings are based
on the 4 membered uretdione ring. The uretdione linkage can be
thermally cleaved to regenerate the active isocyanate groups.
An
oligomeric uretdione of low free monomer content can be thermally
cleaved and
the liberated polyisocyanate groups then reacted with a solid
polyol to form a crosslinked polyurethane powder coating without
any blocking agent emissions. Such curing agents are primarily
used with hydroxylfunctional polyesters or polyacrylates but also
in epoxy/polyester hybrid and TGIC/polyester powder coating formulations.
Bayer markets a cycloaliphatic polyuretdione hardener for polyurethane
powder coatings under the trademark Crelan® EF 403.
Crekat
XP 2571, a catalyst for low-temperature uretdione crosslinking,
can be used with Crelan EF 403 to reduce crosslinking activation
temperature from 180°C to 120°C.
Rucote®
Polyesters
A
wide variety of solid grade hydroxyl functional polyester and
carboxyl functional resins are marketed by Bayer under the Rucote®
trademark. They are formulated to the glass transition temperature
range necessary for the production of storage stable polyurethane
powder coatings.
Rucote
100 polyesters are available in a range of OH content, functionality,
reactivity and outdoor durability so that a wide range of coating
performance properties can be achieved. Paint formulations made
with Rucote 100 resins are especially valued for producing very
high gloss, smooth and chemically resistant coatings.
Rucote
500 series carboxyl functional resins are for hybrid powder coatings.
Bayer supplies polyesters suitable for all common epoxy/polyester
ratios. The Rucote 500 series make hybrid powder coatings popular
for their cost effectiveness and corrosion protection.
Rucote
900 series carboxyl functional resins are for TGIC/polyester powder
coatings. TGIC powder coatings provide good chemical resistance
and mechanics. Resins developed for outstanding overbake stability,
excellent outdoor weatherability and low-temperature applications
are available. Several resins in the Rucote 900 series are for
use with HAAM (B-hydroxy alkylamide) crosslinkers.
[You
can find this information and accompanying illustrations in the
Bayer publication, “The Chemistry of Polyurethane Coatings” by
clicking
here.]
What are Powder Coatings?
Often referred to as "dry painting" due to powder coatings' lack of liquid, solvent or water in their formula. It is applied "dry" directly to a surface in a fine powder form. A powder coating is made of 4 key ingredients: resins , pigments, curing agents and additives. A powder coating manufacturer mixes these ingredients according to its formula. The mixture is then fed into an extruder, which melt blends the materials. After it cools, the material is chipped and ground into a fine powder. The charged powder is spray-applied to an electrically grounded surface. Finally, the coated piece is heated so that the powder coating is fused into a smooth finish. Powder coatings are used in a wide variety of applications from automobiles to lawn furniture.
Because they don't use solvents in their formula, powder coatings release little to zero volatile organic compounds (VOC) into the atmosphere. This not only helps our environment, but it also reduces costs for finishers because they no longer have to purchase and maintain expensive pollution control equipment. In addition, most powder coating over spray that does not adhere to the substrate can be reclaimed for future use. As a result, finishers utilize nearly 100 percent of their coating material leaving little waste and less clean-up.
As a leader in the coating industry, Bayer is dedicated to the powder coating market and is committed to offering its customers the best possible service. This includes a wide selection of coating materials with the ease of utilizing one supplier. Bayer also has a worldwide technical support network with agencies located in over 150 countries.
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