Structural Bulk
High-bulk retention in the middle layer of folding boxboard ensures structural integrity while reducing total weight. The bctmp core preservation maintains the thickness of bleached chemi-thermomechanical pulp through the wet end and pressing stages. This retention provides the required bending stiffness for cartons.
Mechanical Protection
Mechanical pulp fibres offer high stiffness per unit of weight compared to chemical pulps. When board goes through the press section, moisture and pressure threaten to crush these spring-like fibres. Using wide-nip or shoe presses prevents the collapse of the bulky structure.
This protection allows a converter to use a lighter board that performs like a heavier grade. Low-density fibres require careful temperature management in the drying section to prevent thermal degradation of the bulk. The mill adjusts the nip pressure to a specific limit to avoid permanent compaction.
Protecting the hollow nature of these fibres ensures the board remains rigid enough for high-speed filling lines.
Economic Yield
Cost savings arise from using fewer tonnes of fibre to cover the same surface area. Low density in the centre of the sheet keeps the outer layers far apart, which is the physical basis of stiffness. Maintaining this gap during drying and calendering preserves the protective qualities of the packaging.
Higher yield per reel results from successful preservation.
