The development of novel polyisocyanates has the principal objective to make coating processes more efficient while meeting evver more stringent ecological and quality requirements. The main objectives are:
There is a particular focus on the development of polyisocyanates with even more reduced viscosity. Examples of newly developed crosslinkers of this type are shown in Fig. 10. These crosslinkers allow the formulation of so-called "Very High Solid" coatings with solid contents of more than 90 %. This makes it possible to achieve high coating thicknesses in one single operation, a particular economic advantage in thick or multilayered systems, e.g. in corrosion protection.
- The reduction in the number of working steps, e.g. by reducing the number of coats or in the "wet-on-wet" process,
- The ongoing reduction in solvent emissions, and
- The ongoing improvement in mechanical and chemical resistance
Also, low-viscosity polyisocyanates – in addition to hydrophilized polyisocyanates – can be incorporated as crosslinkers into water-thinnable two-component polyurethane coatings as well.
More on waterbased polyurethane coatings systems
More on waterbased polyurethane adhesive systems
Fig. 10: Selection of low-viscosity HDI polyisocyanates (*viscosity at 23°C)
The extremely strong growth of precisely these modern low-viscosity polyisocyanates demonstrates that the development of polyurethane coatings is still ongoing, even 50 years after the introduction of the first coating polyisocyanates.
 DRP 728981 (1937) I. G. Farben; O. Bayer, Angew. Chem. 59, 257 (1947)
 D. Dieterich, Chemie in unserer Zeit, 24, 135 (1990)
 H. J. Laas, R. Halpaap and J. Pedain, J. Prakt. Chem./Chem. Ztg. 336, 185 (1994)
 www.aktuelle-wochenschau.de/woche12/woche12.html: Fig. 8 and Fig. 5 (german)
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