Optimizing Multi-Ply Folding Boxboard Caliper for Carton Performance
Optimizing multi-ply boxboard caliper requires balancing mechanical core thickness against chemical skin elastic modulus to maximize bending stiffness per unit weight.
Core Bulk
Material Volume
Physical thickness relative to basis weight defines the spatial occupancy of the internal layers of a multi ply board. While the surface plies provide smoothness for printing, core bulk determines the overall stiffness and yield of the final product. This property is expressed as the ratio of micrometers to grams per square meter.
It allows converters to achieve a specific caliper while using less total fibre.
Manufacturing Process
Mechanical pulping techniques create stiff, resilient fibres that occupy more space than chemically treated alternatives. When a mill incorporates high yield chemithermomechanical pulp into the middle of the sheet, core bulk increases markedly without a proportional rise in weight. This layer acts like the central member of an I beam.
It keeps the outer liners apart to maximize the moment of inertia. Refining the pulp too much reduces this volume by collapsing the hollow centres of the fibres.
Performance Impact
Higher yields per tonne of raw material lower the environmental footprint of the production run. If core bulk is insufficient, the board will feel flimsy and fail to meet the requirements of high speed packaging lines. Maintaining a consistent thickness across the width of the machine ensures that glue application remains uniform during laminating.