Paper Supply Contract Pulp Index Pass through Clause Mechanics
Paper contract pass-through clauses must weight indices to exact furnish shares and apply deadbands to prevent unearned mill margin inflation.
Solid Bleached Board Furnish
Fibre Selection
Virgin chemical pulp composition governs the structural integrity and brightness ceiling of solid bleached board furnish. Multiple layers of pure hardwood and softwood pulps enter the stock preparation plant where refining parameters dictate drainage resistance and bulk retention. Softwood components deliver tensile and tearing strength through long cellulose chains while short hardwood fibres close the sheet surface to achieve print smoothness.
Mechanical pulps remain absent from this formulation to prevent yellowing under ultraviolet exposure and to maintain food contact compliance standards. Paper mills adjust the ratio of refined chemical pulps to balance stiffness against caliper requirements for high-end folding carton applications.
Drainage Kinetics
Stock dewatering behavior across the Fourdrinier wire dictates the formation quality and ply bonding characteristics of solid bleached board furnish. Vacuum boxes extract water at graduated suction levels to prevent structural disruption in the wet web before the pressing phase consolidates the multi-ply structure. Fine tuning the refining intensity alters the specific surface area of the cellulose fibres which directly controls porosity and coating holdout during subsequent finishing operations.
Pumping velocities and slice geometry adjustments prevent flocculation in the headbox to ensure uniform basis weight distribution across the entire web width.
Surface Readiness
Pigment coating application depends entirely on the microstructural absorption profile established by solid bleached board furnish during drying stages. Calendering nips compress the fibrous matrix to eliminate surface irregularities before mineral slurries containing calcium carbonate and kaolin seal the pores. Smoothness values measured on Parker Print Surf instruments determine whether the substrate accepts high speed offset lithography or gravure printing without picking or mottling defects.
Converting machinery relies on this controlled surface energy to achieve clean creasing lines and reliable glue adhesion on high speed packaging lines.