Thermal Measurement
Scaling of material dimensions per degree of temperature change defines the rate at which substrates and tooling expand or contract. Knowing the coefficient of thermal expansion is essential when running polymer films, metal plates, and foil laminates through heated drying tunnels or chilled rollers. Different materials react at widely varying rates under identical temperature shifts.
Material Behaviour
Polymer films generally display much higher rates of expansion than paperboards or steel cylinders. When a composite web consisting of paper and polyester is heated, the mismatched thermal rates generate internal shear forces that can lead to wrinkling or delamination. For example, a polyester layer will expand more rapidly than the supporting paper board, creating a dimensional imbalance that disrupts web tension and spoils the winding process.
In high speed printing, this disparity is particularly troublesome because the paper absorbs heat from drying units while the polyester layer retains it.
Production Tolerance
Maintaining a stable temperature profile across the entire print line ensures that materials with different thermal properties remain stable. High-speed lines utilize cooled backup rollers to dissipate heat from drying lamps before it can trigger unwanted substrate expansion. Operators adjust the tension settings on the unwinds and rewinds to counteract the minute dimensional shifts that occur as the web travels through different temperature zones.
