Sizing
Also: sizing, internal sizing, surface sizing
The treatment that makes paper resistant to water and aqueous inks. Internal sizing is added to the furnish; surface sizing is applied to the dry sheet.
Internal sizing is added to the pulp slurry to make paper water-resistant. Alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) are the dominant neutral-pH sizing agents. Rosin sizing was the historical standard but required acid pH and has been largely replaced.
Surface sizing applies a starch or synthetic polymer film to the dry sheet, improving surface strength, print receptivity, and water resistance. Most office paper and most printing grades use both internal and surface sizing.
Related
- AKD (alkyl ketene dimer). A wax-like internal sizing agent that reacts with cellulose to create a water-repellent fiber surface. Works at neutral pH.
- Starch. A polysaccharide used as internal strength additive, surface sizing polymer, and adhesive in coatings and corrugated bonding.