Using An Impregnation (Controlled Penetration) Sizing Method for Improving the Barrier and Strength Properties of Paper and Board

摘要

Paper is a fibrous, hydrophilic substrate; it readily absorbs materials such as water, grease, and oil. Furthermore, uncoated paper allows easy passage of moisture. The main reason for this easy passage is the space between the interwoven fibers of paper that consists of countless air voids. It is these air voids and micropores within cell walls of fibers that determine the porosity of the paper. Fiber refining influences porosity. Extensive refining results in a shortening and collapsing of fiber cell walls, resulting in a more closed, i.e., less porous, sheet. Surface sizing agents such as starch, when applied to the surface of paper, further decrease the porosity of the paper by filling the air voids between the fibers and coating the micropores on the fiber walls. As a result of these treatments, many of the pores in the base paper are inaccessible to fluid flow. Starch is relatively abundant and a good film former. Its linear structure, which is similar to that of cellulose, makes it a good binder. As a result, the application of starch to paper improves the surface and internal bonding strength of paper. The amount of strength improvement and porosity reduction is" dependent upon the amount of starch applied and its distribution in the sheet. Although starch and other size press chemical treatments reduce porosity, there remain a few micropores on the surface of the paper that will allow some fluid flow. In this situation, the use of nano-pigments, in the sizing formulation, may help plug the micropores, further reducing the porosity of the paper. To study how the depth of nano-clay and starch penetration influences the physical and printing properties, and the porosity of paper, coatings of nano-clay and starch at different pigment to starch ratios were prepared and applied to one paper using both a flooded nip size press and impregnator coater. The properties of these nano-pigment coated papers were compared to a 100% starch size press and impregnation treated paper. The results showed significant differences in the properties of the two treatment processes.