The effect of the impingement air drying on print mottle and other coated paper properties

The objective of this work is to study the influence of effective initial impingement drying (one-sided high intensity air impingement drying) on the quality of blade-coated paper and to compare it with IR (infrared) drying. A specially designed 1.31 m-long impingement air dryer unit was installed 2 m downstream of the coating station of the pilot coater for more efficient paper drying. Different drying strategies using different combinations of three impingement temperatures (300, 450 and 550 °C) and three impingement velocities (25, 40 and 60 m/s) were tested in the impingement dryer unit to determine the influence of drying on paper quality. Drying effects are compared with those obtained with two rows of an electrical IR at same position. The results of the investigation indicate that backtrap (BT) mottle was reduced with increasing drying power of the impingement dryer. The paper quality parameters, gloss and smoothness of the coated samples were better with air-drying than IR drying. The interesting finding of this study is the improvement of mottle with a high drying rate in the consolidation phase for coated WF (wood-free) paper. Drying section configuration with effective impingement drying unit directly after the coating station showed good performance and is proposed as a possible solution for the future dryer designs.