High solids content calcium stearate dispersions

Aqueous calcium stearate dispersions have long been used as additives in paper coating formulation, the calcium stearate imparting lubricating, leveling, and anti-dusting properties to the coating formulation. Since it is preferable in the paper-making industry to use as many pre-dispersed starting materials as possible to prepare various coating formulations, it is advantageous to provide aqueous calcium stearate dispersions with as high a solids content as possible. Such advantages include lower shipping costs and less water in the coating formulation. It is reported that conventional aqueous calcium stearate dispersions containing much above 50 to 55 weight percent of solids do not retain desirable rheological properties, i.e., they are pretty dense and difficult to handle and meter. Therefore, Efforts have been directed at preparing aqueous calcium stearate dispersions with a high solids content, i.e., higher than 55 percent. Some such high solids content calcium stearate compositions having workable viscosities are reported in U.S. Pat. No. 4,659,489 and 4,676,836. U.S. Pat. No. 4,659,489 discloses high solids content, i.e., 50 to 75 weight percent, aqueous dispersions containing calcium stearate, dispersing agent, non-ionic lubricant, and urea. U.S. Pat. No. 4,676,836 describes similar compositions, except that anionic lubricant is used in place of the non-ionic oil of U.S. Pat—no. 4,659,489. Copending, commonly owned U.S. application Serial No. 07/448,787, filed Dec. 11, 1989, also discloses high solids content, i.e., 60 to 80 weight percent, aqueous calcium stearate dispersions containing calcium stearate, urea, and starch syrup. A possible disadvantage to such urea containing high solids calcium stearate dispersions is that urea, in an aqueous solution, slowly hydrolyzes to ammonium carbamate.

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