Waterborne Polyurethane
Coatings
The traditional solventborne
polyurethanes have long set the standard for high performance
coatings systems. Under the twin demands for high performance
coatings and more environmentally favorable alternatives, the
development of waterborne polyurethane coating technologies has
offered new solutions to the coatings formulator. Bayer offers
various waterborne coating technologies to meet the performance
demands of many industrial coatings applications.
Bayer research has demonstrated
that two-component waterborne polyurethane coatings, when properly
formulated with the wide variety of waterborne polyols available,
have film characteristics similar to those of solventborne coatings.
These properties include high gloss and DOI, good balance of flexibility
and hardness, good abrasion and chemical resistance, and good
outdoor weatherability.
You
can find this information and accompanying illustrations in the
Bayer publication, “The Chemistry of Polyurethane Coatings” by
clicking
here.
Additionally,
learn more about waterborne coatings by browsing and downloading
our collection of technical
papers.
Application Areas for
Two-Component Waterborne Coatings
- General Industrial Finishing - The general
industrial finishing market was the first to accept two-component
waterborne polyurethane coating as an answer to VOC and HAPs
regulations. The reduction in VOCs is a key benefit in this
market.
- Floor Coatings - Unlike other market areas
where regulations governing VOC are the driving force in solvent
reduction, the driving force in flooring coatings is the elimination
of solvent odor. Two-component waterborne polyurethane coatings
with virtually no cosolvent in the formulation solve the odor
problem of polyurethanes in the flooring market.
- Wood - Two-component waterborne polyurethane
coatings have been developed which meet the stringent performance
requirements of this market while releasing virtually no organic
solvents in the workplace or to the atmosphere.
- Automotive - Two-component waterborne polyurethane
coatings are growing in the demanding automotive OEM market.
They are being used for plastic coatings, including soft-feel
coatings, exterior clearcoats, primer/surfacers, and basecoats.
- Military - Though solventborne coatings have
been the traditional solution in demanding military applications,
waterborne coatings are increasingly of interest due their lower
environmental impact.
Bayhydrol®
Polyurethane Dispersions
An aqueous polyurethane
dispersion is a colloidal system in which particles of polyurethane
are dispersed in a continuous phase (water). Bayer can produce
polyurethane dispersions by various technologies.
Having a choice of production
technologies means that Bayer can select the dispersion compositions
that will optimize the polymer performance properties for the
application rather than one which is limited by a production capability.
A key benefit of Bayer's process capabilities is the ability to
produce n-methylpyrrolidone free as well as completely cosolvent
free dispersions.
A
key benefit of Bayer's process capabilities is the ability to
produce
n-methylpyrrolidone
free as well as completely cosolvent free dispersions.
Bayer markets a wide
range of polyurethane dispersions for applications in coatings
including: rigid and flexible plastics; automotive interior and
exteriors; metal primers and exterior building panels; interior
maintenance and architectural applicators; wood furniture; flooring
and paneling. These include both non-functional and functional
dispersions.
Two-Component
Waterborne Coatings (2K Coatings)
Bayer offers hydroxyl
functional polyurethane, polyacrylic and polyester dispersions
for use in two component waterborne polyurethane coatings. Bayhydrol®
dispersions are also available containing: fatty acid modification
with oxidative drying capability; carboxyl functionality; and
unsaturation with radiation curing capability. Bayer thus offers
Bayhydrol dispersions capable of further crosslinking by: hydrophylically
modified Bayhydur polyisocyanates; substituted melamines; polycarbodimides;
polyaziridines; UV and EB radiation (Bayhydrol UV dispersions).
Bayer further markets
polyurethane dispersions for textile intermediates under the trademark
Impranil®,
and for glass fiber sizings under the Baybond®
trademark.
Water
Dispersible Polyisocyanates
In order to optimize
the application and performance properties of two component waterborne
polyurethane coatings, it is necessary to develop polyisocyanate
curing agents that are more easily dispersible in water. Under
the trademark Bayhydur®,
Bayer markets hydrophylically modified polyisocyanates based on
HDI and IPDI that can be readily dispersed into a water-based
polyol to give a true two-component polyurethane coating. Just
as in the case of the Bayhydrol dispersions, the evolution of
the Bayhydur product family results in a continuous development
of technical product alternatives. In the standard product of
today, a hydrophilic polyether segment is reacted with the hydrophobic
polyisocyanate. This reaction takes place readily and can dramatically
improve the water dispersibility of the polyisocyanate, but inevitably
results in some reduction of isocyanate functionality. Bayer offers
a wide range of water dispersible polyisocyanate products, including
Bayhydur 302 and 303.
One new approach in
development takes advantage of the potential to react an isocyanate
with a urethane group to form an allophanate. This synthesis can
start with the same basic HDI polyisocyanurate as above but results
in a hydrophylically modified polyisocyanate of higher NCO functionality.
Development products based on this chemistry are being marketing
as Bayhydur VP LS 2319 and Bayhydur VP LS 2336 polyisocyanates.
The Bayhydur product
family development continues to grow to support the new application
demands for two component waterborne polyurethane coatings.
In
addition, under the trademark Bayhydur BL, Bayer markets water
dispersible blocked polyisocyanates for one component polyurethane
coatings.
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