Jet Coating Technology for High Quality Board, 2002 Coating Conference Proceedings

S. Kuni and M. Lares  

Jet coating technology with both short and long dwell times has been compared to the traditional roll application method in top-side double coating and back-side single coating of MG treated Scandinavian-type folding boxboard. Jet application was found to produce a surface that is smoother and has a lower degree of flock-scale roughness structure than roll application. This is explained by the relatively high hydrodynamic pressure pulse on application, which causes a pressure dewatering through the stock-sized top ply into the unsized middle ply. A burn-out test verified that color distribution and hold-out properties were improved with jet application. On the more porous back side of the board, a long dwell time jet application gave the best fiber coverage and smoothness due to the more homogenous filter cake that is produced by capillary dewatering. Long and short dwell time jet application resulted in the same flock scale roughness, while the negative effect of roll application pressure dewatering produced a clearly higher flock scale roughness.