MECHANICAL CONSEQUENCES OF COATING PENETRATION

Light weight coated papers were evaluated by dynamic mechanical analys is. In addition, water treated papers were studied to separate the con tribution from the wetting-drying cycle on the response and thickness of the sheet. Measurements in three-point bending were performed in bo th the glassy and rubbery regions of the binder. The influence of coat ing penetration on bending stiffness was determined. At low coat weigh ts, the bending stiffness of the base paper increased linearly. This w as attributed to the sandwich structure achieved. As the coat weights continued to increase, then began to decrease. The decrease in bending stiffness was determined to be caused by the influences of coating wa ter in the base paper. At higher coat weights, sufficient coating wate r was present to interfere with fiber-to-fiber bonds and release dried in strains. Variations in coating penetration and coating layer thick ness were studied by electron microscopy. The results show the possibi lity of using dynamic mechanical testing to monitor the depth of coati ng penetration and thickness of the coating layer.