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.
Calendering
Mechanical Compaction
High pressure application between rotating steel rolls determines the final density and surface smoothness of paper substrates. Calendering forces individual fibres closer together to collapse voids within the sheet structure. This operation directly influences the ink holdout and print gloss of a finished packaging board.
Surface Alignment
Heavy iron nips apply force across the width of the moving web to remove irregularities created during the initial drying phase. Calendering manages the target caliper by controlling the gap between rolls or the intensity of the hydraulic loading. Variations in moisture content or base sheet formation produce uneven results under these extreme pressures.
Operators maintain consistency by monitoring the crown of the rolls and the temperature of the internal heating systems. High speeds increase the risk of crushing the fibres if the sheet enters the unit with excess moisture.
Production Outcome
Achieving uniform thickness allows a converted carton to pass through high speed folding and filling machinery without jamming or inconsistent seal formation. Precise control over this mechanical deformation ensures that coatings apply evenly to the surface later in the manufacturing sequence. Substrates requiring high opacity often undergo a lighter nip treatment to avoid reducing the bulk of the sheet too drastically.
Uniform caliper distribution represents the physical foundation for successful register during offset printing.