Variation of Paper Curl due to Fiber Orientation

Transverse deviations from the ideal flat surface in paper, or curl, can be a serious problem in the paper industry. The manufacturing of paper materials results in the material being orthotropic and laminar. Moreover, the dominant fiber orientation in a paper sheet can vary through the thickness of the sheet. Many paper structures are produced by lamination of paper plies. In these products directions of symmetry of the elastic properties, and coefficients of moisture and temperature expansion/contraction, consequently differ through the thickness of the laminated material. When subjected to humidity changes, the top and bottom portions of a paper laminate therefore expand or contract different amounts, causing the structure to curl. Paper products that curl are difficult to convert in packaging applications and print or copy in automated feeding mechanisms, leading to large costs for companies. It can become impossible to machine process and dispense paper products (such as stamps) that have curled. The present research involves determining the moisture induced curl in [0/15] and [0/45] Whatman paper laminates using a full-field 3-D laser scanner.