Optimizing Score Line Geometry for Low-Fibre-Length Recycled Substrates
Low-fibre recycled board requires widening female matrix channels to 1.8 times caliper and reducing penetration depth to prevent top-liner rupture.
CRB Substrate
Fibrous Composition
Multi-ply paperboard grades made primarily from recovered paper fibers and finished with a clay coating provide cost-effective options for dry food carton packaging. This material class, known as CRB substrate, typically consists of several layers of recycled pulp with a top liner of bleached chemical pulp or high-quality deinked fiber. The clay coating on the print side ensures a smooth, non-porous surface that accepts high-resolution offset printing without excessive ink absorption.
Mechanical Behaviour
Stiffness profiles in these multi-ply sheets depend on the thickness and the bond strength between individual layers of recovered pulp. Standard CRB substrate exhibits a high ratio of stiffness to basis weight, although its tensile strength and tearing resistance are lower than those of virgin-fiber boards. During the converting process, moisture absorption must be monitored because recycled fibers expand more than virgin wood fibers.
This expansion affects the flatness of the sheet and can cause feeding jams in high-speed folder-gluers.
Converting Limit
Die-cutting operations demand precise blade pressure settings to prevent delamination of the plies. If the moisture content of the CRB substrate falls below six percent, the creases may fracture during folding, destroying the carton structure. This material limits the complexity of the folds that can be executed.