Evonik Industries AG
Solventborne paints have demon- strated over decades that they are asy to handle and are distinguished
by a very wide processing window. The
technology is reliable and established
worldwide. However, since EC Directive
1999/13 came into force, many solvent-borne paints in European countries no
longer meet the regulations for reducing
organic volatiles.
Experience shows that, with conventional binder technology, it is not possible
to formulate high-solids paints with fewer
than 250 g/L VOC. Simply reducing the
solvent content in existing medium-solids
paints to meet legal requirements results
in a highly viscous paint which cannot be
applied. To reduce the non-volatile components (NVCs) requires major changes
in the molecular structure of the binder.
Reduction in molecular weight, improved dilutability of the resin in common solvents, and lower intermolecular
interaction are just some of the fundamental demands on innovative high-solids binders. The challenge is to increase
the NVC at working viscosity to comply
with the regulations, without impairing
drying (both dry-to-touch and complete
cure), optical appearance, or mechanical
and chemical resistance.
One way to achieve high NVC at
low-processing viscosity is with 2-pack
paints – in particular, isocyanate-curing
silicone hybrid resins. Silicone hybrid
resins combine a broad range of proper-
ties which result in high quality paints.
The polyester component enables, for
example, a high crosslinking density in
the fully cured film which delivers very
good mechanical and chemical prop-
erties. The silicone component in the
resin molecule lowers viscosity. This
effect is attributed to the free rotation
of the silicone chains ~[Si(CH3)2 – O
– Si(CH3)2] and their low tendency to
interact. The silicone component also
reduces the UV-yellowing tendency of
the polymer.
Figure 1 compares two silicone hy-
brid resins with a high-solids polyester
resin. It is obvious that the new type of
silicone hybrid resins possess a signifi-
cantly higher NVC at comparable intrin-
sic viscosities of the polymer solutions. At
approximately 7500 mPa·s the conven-
tional polyester resin solution has a NVC
of 76%, whereas the new silicone hybrid
resin has a NVC of 90%. This enormous
difference gives the paint formulator
great scope regarding other constituents
in the formulation such as rheological ad-
ditives or solvents.
Innovative Binder Technology
for High-Solids Industrial Coatings
Figure 1: Comparison of two silicone hybrid resins with a high-solids polyester resin.
Table 1: Silicone hybrid resin test formulation.
