紙のカール Ｉ カール形状の新しい評価方法

Abstract

A general method for evaluating complex curl shapes of paper has been proposed, and underlying geometrical significance and the determination method have been examined in detail.Various curl shapes which paper exhibits in its end use, such as cylindrical curl and diagonal curl, are fully described in terms of three curvature components, i.e., k1 bending curvature in CD, k2 bending curvature in MD, and k3 twisting curvature. By using these curvatures, an apparent curl shape observed from an arbitrary direction can be predicted and characteristic quantities of curved surface including the orientation of curl axis (principal direction) and principal curvatures can be calculated with Eqs. (3) and (4).The curvatures k1 and k2 were measured in cross machine and machine direction for a narrow strip of paper, and the twisting curvature k3 was determined from k1, k2, and k (45), curvature in the direction of 45 degrees to MD, by use of Eq. (6) which was derived from curvature transformation equations.It was demonstrated that an apparent curl shape is not always same as a latent curl shape which is predicted from measured curvature values for a narrow paper strip, because of geometrical and mechanical stability of curl shape. Rational evaluation of curl shapes presented in this paper gave us detailed information on heredity effects of curl behavior and CD curl profile in paper machine.