An investigation of heat curl in newsprint

Curl in paper sheets affects performance in printing and converting processes. Here we present a series of experiments designed to identify the cause of curl in newsprint produced from nominally the same furnish on two different paper machines. The tendency of the sheet to curl is shown to be dependent on the z-directional distribution of in-plane elastic modulus. Moreover, distribution of the MD:CD ratio of in-plane elastic modulus appears to have a greater effect on the tendency of a sheet to curl than the distribution of elastic modulus in either the CD (cross-machine direction) or the MD (machine direction) independently. Cross direction, curl, elastic stregnth, infared heating, machine direction, newsprint, paper sheets, stiffness, thickness, two sidedness, twin wire machines, z direction.