Abstract: An improvement is disclosed over conventional internal sizing of stock furnish for papermaking, wherein alum is added to the thick paper stock and the long retention time permits complete reaction with the fibers. The invention process permits successfully adding novel aluminum rosinate size composition unconventionally in thin stock furnish, where retention times are on the order of less that 1 minute. The highly charged aluminum rosinate size is able to be quickly adsorbed onto the fiber surfaces to permit surprisingly efficient sizing in thin stock. The quick sizing avoids concern with rising pH over time (in conventional thick stock application) and increases sizing efficiency.

Abstract: The present invention comprises an alum/rosin composition for internally sizing paper which is useful in any papermaking furnish with moderate to high hardness, as well as methods for preparing such alum/rosin composition. Employing the invention alum/rosin composition of an alum to rosin ratio of 1-3:1, respectively, and of a mean particle diameter of no greater than 10 microns, results in sizing of improved efficiency. In the preparation of the invention sizing composition, the pre-reacting of either neat or solutions of alum and rosin before introducing the mixture into the papermaking furnish, allows the alum to be free to react with the rosin size without any competition from other cations in the furnish.