Outer Facing
Flat paperboard sheets forming the outer and inner facing surfaces of corrugated fiberboard panels supply structural rigidity and print surfaces for shipping containers. Standard production of linerboard utilizes unbleached softwood kraft pulp or recycled containerboard stock to achieve high tensile and burst strength. Multiple plies are formed on multi-wire paper machines to optimize surface smoothness on the top layer and strength on the bottom layer.
High tear resistance and stiffness protect internal fluting and box contents from external impact. Sizing chemicals added to the pulp slurry resist moisture absorption during transportation. The definition excludes internal corrugated fluting media, solid bleaching boxboard, and uncombined single-face web rolls.
Structural Layering
Unbleached kraft pulps furnish long softwood fibers that interlock during wet-end sheet formation. Multi-ply headboxes place clean white virgin fiber on the top surface while utilizing recycled linerboard stock for internal plies. Calendering increases sheet smoothness to improve printing ink holdout on outer container facings.
Print Substrate
Flexographic printing on box facings demands uniform ink absorption across the web width. Selecting coated linerboard options combines starch or clay coatings with bleached top plies to enhance graphic print quality. Tensile stiffness in the machine direction prevents web stretching during high-speed printing and corrugating operations.
Scoreline cracking occurs when dry linerboard suffers excessive tensile strain during box folding operations. Moisture control at the paper mill preserves fiber elasticity and reduces scoring failures during carton conversion.
