Ply Adhesion
The controlled deposition of uncooked starch slurry between the wet plies of a multi-ply paperboard during the forming process enhances the internal bond strength of the finished sheet. Mill operators utilize starch spray application to apply a uniform layer of adhesive directly onto the fiber web before the plies are consolidated in the press section. This chemical addition is critical for preventing delamination during subsequent converting and printing.
Starch Gelatinization
As the wet board passes through the heated dryer section of the paper machine, the sprayed starch granules absorb moisture and gelatinize under the high temperatures. This thermal activation causes the starch molecules to flow and form a strong adhesive matrix that bridges the fiber networks of the adjacent plies. Proper starch spray application ensures that the bond remains strong across the entire width of the sheet, even when the pulp has a high recycled fiber content.
If the spray is applied unevenly, the resulting weak zones can lead to localized blistering or peeling on the press.
Process Parameter
Technical crews monitor the spray nozzle pressure and slurry concentration to avoid over-saturating the sheet. Too much water can disrupt the forming web and cause wet spots that delay drying. This precise control maintains production speed while ensuring the board meets the required internal bond standards.
