Structural Composition
Multi-ply paperboard engineered with specific mechanical properties is the primary material used for manufacturing lightweight consumer packaging. This material, known as folding cartonboard, usually consists of several layers of chemical and mechanical pulp designed to maximize strength. The outer layers are made of bleached chemical pulp to provide a smooth printing surface, while the inner plies utilize mechanical pulp to build thickness.
This construction yields a stiff sheet that can withstand the die-cutting and folding processes.
Stiffness Performance
Bending resistance is the primary performance metric that prevents the package from bulging under the weight of its contents. The thick middle ply of folding cartonboard acts as a spacer between the outer tensile layers, acting like an I-beam to resist bending forces. Maintaining high stiffness at a lower basis weight is a primary objective for board mills, as it reduces shipping costs and material consumption.
This property is measured in both the machine direction and the cross direction to ensure uniform carton performance.
Printability Requirement
Processing through high-speed packaging lines requires a surface that accepts adhesives and inks readily. The clay-coated surface of folding cartonboard must be uniform to ensure consistent ink coverage. High internal bond strength is also required to prevent the plies from separating during the creasing and folding steps.
