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News

Coming soon to coatings for wood and plastics

Bayer MaterialScience AG : 19 April, 2004  (Company News)
There has been a sharp increase in the use of powder coatings in recent years. Thanks to their favorable property profile, the solvent-free coating systems have proven themselves primarily for the coating of heat-stable substrates, especially metal surfaces.
At the same time, interest is growing in powder coatings that cure at temperatures lower than 150 °C. The objective is to expand the range of applications to include temperature-sensitive substrates such as wood and plastics, for example. Bayer Polymers LLC has for the first time developed a solid crosslinker based on diethyl malonate (DEM)-blocked isocyanates, which enables a significant reduction in the curing temperature of powder coatings formulated with it.

“A further advantage is the crosslinker’s greater reactivity compared to standard crosslinkers. This makes it possible to significantly increase the curing rate and thus the productivity of the coating process. DEM-blocked isocyanate crosslinkers therefore have enormous potential in powder coatings applications,” says Dr. Thomas Fäcke, powder coatings expert at Bayer Polymers LLC.

DEM-blocked isocyanates are well known as crosslinkers in liquid coatings. There they initiate curing at temperatures as low as approximately 80 °C. The blocking reaction is not directly transferable to powder coatings, but a synthesis path was ultimately found after detailed studies of the blocking mechanism. Curing with the new type of crosslinker also proceeds differently than with the thermal unblocking known from “classic” blocking agents such as e-Caprolactam or dimethylpryazole. Instead, the curing of DEM-blocked isocyanates with polyols is a transesterification process.

The new crosslinker can be easily incorporated into conventional hybrid or TGIC (triglycidylisocyanurate) powder coating formulations as a fortifier. A whole range of formulations were studied and cured at various temperatures. In each case, a temperature range of 120-140 °C proved optimal for crosslinking. The coating surfaces thus achieved exhibited significantly improved chemical resistance and mechanical properties.
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