This work deals with the time-dependent creasing characteristics of coated paperboard. The correlation between the bending strength (resistance) and time-dependent problems on the actual processing phenomenon has not been sufficiently discussed in the past. In this study, therefore, a prototype testing apparatus has been applied to investigate about the dynamic relaxation of bending moment. In order to reveal the relaxation characteristics of the bending resistance during the folding motion from an initial position up to a specified tracking angle, a white-coated paperboard of 0.3 mm thickness was scored with a creasing rule and then the bending test was carried out by varying the number of folding repetitions. Through this work, the followings were obtained: (1) The relaxation of the bending resistance was characterized by an exponential coefficient which was independent to the nominal shear strain while it varied with respect to the number of folding repetitions; (2) The relaxation coefficients of logarithmic approximation with the elapsed time are linearly characterized by the nominal shear strain and the number of folding repetitions; (3) The relaxation depends on the bending velocity.

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.

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