Thermal Retention
Trapping of heat within a tightly wound roll or a high pile of paperboard after hot converting processes can cause serious physical and chemical changes in the material. This rewind stack heat accumulation occurs because paper and board are excellent thermal insulators, meaning that heat from extrusion coating or hot drying cannot escape quickly from the centre of the roll. The temperature in the core can remain elevated for several days after winding.
This sustained heat can activate heat-seal coatings or soften polymer layers, causing adjacent plies of board to stick together in a defect known as blocking.
Pressure Compression
High winding tension increases the localized pressure inside the roll, which combines with the retained thermal energy to accelerate the fusion of adjacent layers. Heavy paperboard rolls can weigh several tons, creating immense compressive stress at the core that forces the warm, softened polymer layers into intimate contact with the paper fibres on the reverse side. This can result in fibre tear or ink transfer when the roll is eventually unwound.
Material Preservation
Cooling the web before it reaches the rewinder is the standard method used to prevent this thermal build-up. In-line cooling cylinders use chilled water to lower the sheet temperature to a safe level. This ensures that the material can be stored and transported without risking structural damage.
