Optimizing the Use of Synthetic Surface Sizes on Alkaline Basestock, 1991 Papermakers Conference Proceedings

The use of synthetic surface sizes on alkaline basestock have assisted papermakers in solving many problems associated with the alkaline process. Most of these concerns are inherent in the alkaline process and result directly from the use of alkaline sizing and filler additives. High addition levels of internal alkaline size, precipitated calcium carbonate, retention aids, and internal starches result in major papermaking concerns such as:

* Increased number of holes and breaks

* Deposits

* Increased slipperiness of the sheet

* Liming and dusting

* Ink feathering

These concerns can be eliminated, to a degree, by the reduction of additives used. However, some of the additives, such as PCC, which provided the economic incentive to convert to an alkaline system, cannot be reduced efficiently. By using synthetic surface sizes in combination with the alkaline sizes, many of the benefits of alkaline papermaking can be maintained. Combination sizing is most commonly used on tablet, forms bond, envelope, xerographic, duplicator, and ink jet grades.

Surface sizes studied in this paper include an anionic polyurethane dispersion and an ammonium salt of a styrene maleic anhydride copolymer. This study was conducted to determine the optimum conditions necessary to maintain sizing of the paper by using combination sizing. All data obtained for this presentation is supported from pilot paper machine studies and commercial evaluations. The pilot paper machine study was based on a statistical experimental design called a Hadamard Matrix.

It was concluded that synthetic surface sizes significantly improve HST, contact angle, Gurley porosity, and static and kinetic coefficient of friction. Minimizing internal size and maximizing the sizing at the surface improves the surface properties of the paper, such as ink feathering and ink jet printing. These synthetic surface sizes also help seal the sheet and minimize the amount of linting and dusting in printing operations.