Grade Substitution Shipped under an Unchanged Product Name
Unannounced paper grade substitution alters structural fiber bonding and surface chemistry, demanding dockside physical and chemical testing before press loading.
Oxidized Starch Surface Sizing
Surface Sizing
Chemical modification of natural starches using sodium hypochlorite introduces carboxyl and carbonyl groups to prevent starch retrogradation and control solution viscosity. Paper mills apply oxidized starch surface sizing at the size press to improve paper surface strength and printability. The oxidized polymer film coats surface fibers, filling surface pores and binding loose fibers to the sheet matrix.
Surface sizing enhances surface pick resistance during high-speed printing operations.
Viscosity Control
Hypochlorite oxidation breaks alpha-D-glucan polymer chains into smaller fragments, reducing solution viscosity at high solids concentrations. Reduced viscosity allows paper machines to apply size press formulations at higher speeds without film splitting and uneven coat distribution. Carboxyl groups introduced during oxidation impart negative electrostatic charges that stabilize starch molecules in aqueous solution.
Paper mills monitor cooking temperatures and chemical addition rates to achieve precise viscosity specifications for size press application.
Printability Enhancement
Surface application of degraded starch films restricts printing ink vehicle penetration, resulting in enhanced print sharpness and color density. The continuous starch film prevents dusting and linting on offset printing blankets by anchoring surface fibers tightly into the fiber structure. Uncoated graphic papers and containerboard liners treated with oxidized starch surface sizing exhibit higher Dennison wax pick values and improved Cobb water absorption resistance.
Proper size press execution yields a smooth, uniform printing surface that reduces ink consumption while maintaining high image fidelity across offset and flexographic printing runs. Surface sizing remains a critical process step in producing high quality printing and packaging substrates.