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High Solid Polyurethane/Polyurea System
Traditional solventborne polyurethane systems are typically formulated at a solid
level of 30-40 percent, which would be equivalent to the volatile
organic compounds (VOC) level of 5 lb/gal or above. With more stringent
emission levels regulations, demand for low VOC coating systems have
increased. This demand has led to the need for lower viscosity resins,
both in the polyol and polyisocyanate components. Bayer supplies high
solids polyol components, such as polyesters, polyacrylates and polyaspartic
esters, as well as low viscosity polyisocyanates for the formulation
of high solids coatings.
To accommodate the market's drive for a high solid system and to overcome the limitation of the traditional co-reactants, Bayer developed a new class of co-reactants, namely polyamino co-reactants (PACs).
In the past, the extremely high reactivity of primary aminesq has
prevented their use as a viable co-reactant in coating's application.
However, the significantly reduced reactivity of hindered or blocked
amine such as polyaspartic esters and aldimines (see Table
1 for structures) has made PACs a whole new family of co-reactants
available to polyurethane formulators. The systems based on these
polyamino co-reactants can be formulated with solid levels in excess
of 60-70 percent, resulting in a system with VOC level of 2 lbs/gal
or below. Table 1
also lists the advantages of polyaspartic esters and aldimines. The
availability of various aspartic esters with vastly different reactivities
and viscosity made it a more versatile co-reactant for formulators
(Table 2). One can blend
two or more polyaspartic esters to achieve a wide range of application
viscosity and potlife. One significant characteristic of the coatings
based on PAC is that they offer extremely high hardness, balanced
with a reasonable flexibility. In addition, both aldimines and polyaspartic
esters are compatible with several traditional polyester or polyacrylic
resins. One can easily blend PAC and polyesters or polyacrylics to
achieve the desired solid level/VOC, hardness, viscosity and cost.
For additional information including technical papers, please visit our literature request section.
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