Metered Size Press Coating Formulation Design for Fiber Reduction

A major driving force in paper technology development is the reduction in cost of paper production. A primary material cost in the paper production process is wood fiber, the cost of which is increasing rapidly. Reducing fiber usage is difficult, as paper properties are tightly coupled to the amount of fiber. Advances in coating formulation design have begun to show how coatings may be designed for fiber replacement without sacrificing paper properties. Both pigment and binder influence coating mechanical properties. Pigment shapes and sizes, and binder types and amounts are all relevant variables. We report here on combinations of these variables investigated at laboratory and pilot scales. Variations in average coating pigment shape are achieved by varying the ratio between GCC and kaolin, and by varying the platiness of the kaolin. Platier average pigment shape tended to improve stiffness. Many size press binder formulations consist of a sole starch component. Laboratory and pilot scale experiments show synergistic interactions between starch and protein, leading to reduced binder migration into the substrate. Results demonstrate that stiffness and other mechanical and optical properties can be moved above the cubic basis weight dependence on fiber amount with significant potential economic advantages.