In relating the quality of the coated sheet to the properties of the base paper, the liquid absorbency of the base paper is a most important consideration for all coating processes.
Nor surprisingly, base sheet absorbency has received a great deal of published attention. Recently, there has been a growing appreciation that the Lucas-Washburn equation does not fully explain the penetration of aqueous fluids into paper. The shortcomings of the Lucas-Washburn equation are clearly indicated in the work described on the mechanism of the size press.
A new method of following the penetration of aqueous solutions and suspensions is presented.
Analysis of the results indicates that a wetting time exists and that the Lucas-Washburn equation is inadequate to describe the penetration of aqueous fluids into paper.
A new model for penetration is suggested, which allows for the swelling of the sheet that occurs as penetration takes place. A penetration equation is derived from this model.