Photoprinting screens coating application - is carried out using venturi pumps and cyclones

摘要

Powder coatings for photosensitive printing panels are applied via a cyclone from which controlled amounts of suspended powder can be withdrawn, together with a relatively small volume of air, and discharged as a uniform coating on to a passing film base (1). The powder (C) is collected by discharge into a venturi cannon (31) which disperses and suspends the powder in a blend of jet air (A1) and entrained air (A2). The pneumatic suspension is conveyed to the cyclone (36) which exhausts most of the air in one direction (34) and discharges a relatively concentrated stream of dispersed particles at the apex (35). For coating a wide film, several cyclones may be used side by side or in a staggered pattern offset relative to the film axis. Pref. the coatings are applied at loadings of 0.005-0.5 g/m2.