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Powder coatings have obtained a wide acceptance in the industrial coating market.
Whereas the total industrial coating market is only growing 1-2% a year, the volume of
powder coating is expected to grow 5-8% annually the next five years [1]. This will result
in an increase of the share for powder in the total industrial coating market from 11 % in
1993 to 16% in 2000 [2]. Since the introduction of powder coating, some 30 years ago,
there has been a continuous strive for lower temperature cure. Reduction of the necessary
cure temperature of polyester-TGIC systems from 200-220°C to 160°C with acceptable
levelling has been reached. This solved the curing problem of aluminium extrusions with
plastic inserts while at the same time a 20-25% reduction of thermal energy was obtained
[3]. However, for certain applications in the automotive industry, even a cure temperature
of 160°C is too high [4,5].
The application of powder coating on heat sensitive substrates such as plastics and wood
demands for cure temperatures well below 150°C and in most cases even below 100°C.
The main problem is the finding of a system with a good balance between storage
stability, melting, flow and cure. Since the thermally activated crosslinking reaction is
governed by Arrhenius constraints, it will be almost impossible to develop a system that
is stable during conventional extrusion at eg. 100°C and gives a smooth coating with full
conversion at eg. 120°C [6]. One of the approaches to solving this "impossible" problem
is the use of radiation-activated crosslinking instead of a thermally activated reaction.
