Multi-Layer Packaging Substrate
Multi-ply paperboard grades composed primarily of recovered paper fibres and finished on one or both sides with mineral pigment coatings provide rigid, print-receptive stock for secondary retail packaging. Known widely in international paper sourcing as recycled coated board, the substrate incorporates bleached chemical pulp outer liners, mixed mechanical and deinked waste paper middle plies, and recovered kraft or newsprint backing layers. Pigment coatings composed of calcium carbonate, clay, and latex binders provide surface smoothness and ink holdout necessary for multi-colour offset, flexographic, or gravure printing.
Its industrial domain spans folding cartons for dry foods, household goods, consumer hardware, and secondary pharmaceuticals.
Fibre Architecture And Structural Performance
Sheet formation relies on multi-fourdrinier or cylinder former paper machines that deposit distinct fibre slurries in successive layers. Short, recycled fibres in the core plies yield bulk and thickness at lower raw material costs, but they provide lower tensile and tear strength than virgin sulphate pulps. Top layers utilize virgin or high-grade deinked pulp to prevent recycled grey or brown undertones from degrading print brightness.
Mineral coating formulations seal microscopic surface voids, eliminating ink strike-through and optimizing print gloss. Because recycled pulp retains fragmented fibres, residual starch, and mineral fillers, internal bond strength, measured by the Scott bond test, is lower than in solid bleached grades. This reduced delamination resistance requires converting plants to adjust creasing rule depths, die-cutting knives, and blanket release tensions to prevent ply delamination during printing and scoring.
Converting Trade-Off Limits
Converting operations adjust creasing matrix geometries to accommodate the weaker internal shear strength of recycled plies. Creasing dies that are too narrow crush the board, rupturing the top coating layer and leaving visible white fractures across dark printed inks. Moisture sensitivity is higher in recycled grades, meaning ambient humidity shifts cause sheet curling and feed misregistration more readily than in virgin boards.
Carton design must incorporate heavier calipers, ranging from three hundred and fifty to seven hundred micrometres, to match the stacking strength delivered by lighter virgin boards. Clean cut edges require sharp die knives to prevent fibre flaking from contaminating printing plates.
