Structural Component
Manufacturing of multi-layered board involves bringing together different fibre types in a headbox to create a finished sheet with specific mechanical traits. The configuration of folding boxboard plies usually consists of a top layer of bleached chemical pulp followed by multiple layers of mechanical pulp in the center. This arrangement produces a stiff but light material with a high quality printing surface.
Matrix Mechanics
Strength increases significantly when chemical pulp is also used for the bottom layer to sandwich the more voluminous mechanical core. Adjusting the thickness of the folding boxboard plies allows mills to hit target stiffness values while keeping the overall grammage as low as possible. These individual layers fuse during the pressing stage to create a single sheet that resists splitting when die cut.
Mechanical pulp provides the internal bulk that separates the stronger outer faces.
Converting Performance
Flexibility during the folding process depends on the specific moisture content and fibre alignment found in the internal sections of the sheet. If the folding boxboard plies are too stiff or dry, the surface is likely to crack when deep creases are applied in the packaging plant. Proper layer adhesion prevents the board from delaminating during high speed glue applications on the tray assembly line.
Balance between bulk and bond strength determines the runability.
