A resistance to hydrophilic liquid penetration (normally water), known as “sizing,” is an important property of paper, both in the papermaking process and in the final product. For example, the extent to which a paper is weakened by the rewetting at the size press during production is influenced by its degree of sizing. Additionally, a high level of internal sizing of a sheet contributes to the sheet's structural stability in environments where the sheet may come in contact with liquid water. Beverage and food packaging are typical examples of the use of board and paper products where a high level of sizing is desirable.
Generally, resistance to water penetration is achieved by the introduction of a sizing agent at the wet end of the papermaking process. A common sizing agent is alkenyl succinic anhydride (“ASA”). ASA-containing materials are used to impart a degree of hydrophobicity to paper fibers during production, and an overall resistance to liquid absorption to the finished paper product. A drawback to using ASA as a sizing material is that ASA is not water soluble and typically must be uniformly suspended in the pulp as an emulsion so that the ASA can make adequate contact with the cellulosic fibers and, thus, create the desired effect on the final product. A conventional sizing program is disclosed in U.S. Pat. No. 4,657,946 to Rende et al., the disclosure of which is hereby incorporated by reference in its entirety.
USPTO Backgrounds
USPTO Backgrounds