Surface Mechanics
Folding boxboard designated as gc1 board provides a triple coated printing side bonded to a cream back containing mechanical pulp layers. Solid bleached sulphate furnishes the top and bottom plies while mechanical pulp sits inside the middle layers to deliver stiffness at a lower weight. Cylinder machines deposit these fibrous suspensions successively during formation before pressing moisture downward through heavy felts.
Calender stacks compress the dried web to reach exact caliper boundaries demanded by high speed cartoning machinery. Converting plants rely on this layered construction for pharmaceutical packaging because smooth surfaces accept fine halftone screens while bulky interiors maintain erected carton angles.
Coating Composition
Pigment slurries applied via blade coaters create the printing face through successive layers of calcium carbonate and china clay bound by synthetic latex. Top coating weights hover near twenty grams per square metre to seal porosity and stop ink absorption beneath halftone dots. Optical brightening agents mix into the final coat to raise reflectance readings measured under ultraviolet filters.
Mineral pigments fill microscopic depressions left by underlying fibres so varnishes sit evenly across printed areas without dulling. Blade pressure variations alter coat weight across the web width and mills reject reels exhibiting thickness deviations exceeding micrometres.
Bending Resistance
Mechanical pulp proportion inside the central layers governs stiffness characteristics tested via Taber bending moments in both machine and cross directions. Flexural rigidity allows folding cartons to resist bulging forces exerted by dry contents settling against interior walls during transport. Creasing channels must match caliper dimensions precisely because incorrect groove widths fracture the top coating during die cutting operations.
Environmental humidity softens the internal mechanical pulp plies and reduces overall carton compression strength under prolonged warehouse stacking loads.
