Differential Expansion
Material deformation occurs when two layers with distinct thermal or hygroscopic expansion coefficients are joined and subjected to environmental changes. Bimetallic bending curvature is a concept adapted from thermodynamics to describe how paper and plastic laminates warp. A change in humidity causes the cellulose fibres to expand while the synthetic layer remains stable.
Such a reaction creates a predictable arc.
Lamination Strain
When a moisture sensitive paperboard is bonded to a metal foil or polymer film, any subsequent drying or wetting forces the composite to deviate from a flat plane. The bimetallic bending curvature is quantified by the radius of the resulting bend. Thinner layers generally result in tighter curves because the internal resistance to the bending moment is lower.
Industrial Control
Managing this effect requires matching the stiffness of the carrier to the expansion potential of the coating. Converters adjust tension or apply moisture to the reverse side to counteract the force. High precision packaging lines rely on these adjustments to prevent jams.
Bimetallic bending curvature remains a primary cause of feed failure in high speed inkjet printing where heat is applied. The resulting curl often exceeds the tolerance of the vacuum transport system. This leads to costly downtime and wasted stock.
