Even after considering all the factors in the installation of 3-D UV curing and the presentation of the part through the UV curing zone, there may be areas that cannot be reached by sufficient UV to ensure an adequately cured coating.
This does not detract from all the advantages for UV curing, and in most applications does not represent a major hurdle. The issue is being addressed by the use of hybrid UV/thermal coatings, where a secondary cure mechanism, which may be accelerated by heat, is used to ensure complete cure even in shadow areas.
The hybrid systems being developed require much lower bake temperatures – and for shorter periods – than their 100% thermal counterparts. In addition, the part may be touch-dry in all areas after the UV exposure, thus retaining the advantage of less risk of contamination. The hybrid systems retain all the improved performance characteristics of 100% UV curable coatings in terms of improved scratch, chip, scuff resistance, etc.
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