Substrate Core Thermal Expansion Limits in High Speed Sheetfed Converting Operations
Substrate core thermal expansion limits dictate sheet dimensional stability, requiring precise thermal control to prevent misregister and bimetallic warp.
Inter-Pass Dwell Time
Drying Duration
Temporal intervals between successive coating or printing applications determine the extent of ink absorption and the degree of surface drying achieved by the substrate. The inter-pass dwell time represents the seconds or milliseconds a sheet spends traveling between one station and the next. Sufficient duration allows the solvent or water to migrate into the board or evaporate into the air.
Short durations lead to ink set-off or smearing on the impression cylinder.
Absorption Rate
Press speed directly influences this duration by changing the distance-to-time ratio between the printing units. Increasing the inter-pass dwell time gives the ink more time to set into the surface pores of the paper. This is especially useful when using heavy ink weights or slow-drying metallic pigments.
If the press runs too fast, the second ink color may mix with the first, causing a muddy appearance. Fans and heaters are often installed between units to compensate for short travel distances.
Coating Quality
Extended dwell times are necessary for heavy ink coverage on non-porous boards. This interval allows the chemistry of the ink to stabilize before the next layer is applied. Proper adjustment of the press speed ensures the highest level of print clarity.