Effect of bending velocity on time-dependent release behavior of creased white-coated paperboard

Abstract

This work deals with time-dependent creasing characteristics of coated paperboard. The knowledge of dynamic bending moment (resistance) acting on a hinge which is folded onto a creased line, is important in order to adjust a few of boxing condition. The correlation between the dynamic bending resistance and several primary problems such as the time-dependent residual strains on actual processing phenomenon was not sufficiently discussed in the past. It is difficult to estimate various time-dependent responses from a quasi-static initial stiffness of a creased part, such as the maximum peak bending moment and the gradient of bending moment. Therefore, a prototype Crease Stress Tester (CST) has been applied to seek the dynamic bending moment and its residual deformation. In order to reveal the relaxation characteristics of bending angle during the folding and returning back motion from a tracking angle of 90°, a white-coated paperboard of 0.3 mm thickness was scored with a creaser knife and a grooved face counter plate under a specified feed velocity, and then the bending and release test was carried out up to the second round folding under a couple of indentation depth of crease forming (nominal shear strain). Through this work, the followings were found: (1) The release response of folded angle during returning back was characterized and approximated by a logarithmic function of elapsed time; (2) The release of folded angle depends on the bending rotation velocity.