Evaluation and control of coated paper stiffness

For coated paper, Young's modulus of the coating layer affects the stiffnes s of the whole coated paper considerably because the external layer undergo es a larger strain during bending than the internal layer. A method to calc ulate Young's modulus of coating of a one-side coated sh ect according to f undamental material mechanics is presented here. An interpretation of the C lark stiffness formula allows its to calculate Young's modulus of the coati ng layer from Clark stiffness of the whole coated paper. To achieve this, c oating on an impervious film is required for avoiding swelling and rougheni ng problems. Pure bending stiffness meriting constant curvature along the s pan was also applied. A well-known fact that the introduction of starch int o a latex bound coating increases its stiffness is verified. Application of a starch-rich coating to the outside is found to be advantageous. Small-si zed plastic pigment provides a level of stiffness close to that of calcium carbonate.