Paperboard Grammage and Caliper Fundamentals for Sourcing Specialists
Paperboard grammage and caliper dictate sheet yield, bending stiffness, and converting performance, making exact testing under ISO standards essential for sourcing.
Crease Torque
Rotational Resistance
Physical force required to fold a pre-scored paperboard sample to a specific angle. Crease torque measures the internal resistance of the board as the fibres and internal layers deform during the folding process. This value is necessary for the setup of automated packaging machinery.
Proper creasing reduces the torque to a level that allows clean, square folds.
Machine Interaction
Automated cartoning lines rely on consistent resistance levels to ensure that glue flaps stay in position. High crease torque causes the board to spring back, which leads to open flaps or jammed equipment. When the torque is too low, the carton lacks the structural integrity to hold its shape during filling.
Friction between the board and the mechanical folders also influences the actual energy required. Every machine adjustment must account for these forces to prevent damage to the substrate.
Material Property
Delamination of the internal plies of the board occurs during the scoring process to facilitate the fold. Crease torque reflects how well this internal structure has been broken down by the creasing rule and matrix. A thicker board generally requires a more aggressive score to achieve a low torque value.
Factors such as moisture content and fibre orientation greatly impact the measurement. Testing involves a specialized instrument that records the peak force as the board moves through a ninety degree arc.