Thermal Exchange
The rapid reduction of temperature in a moving polymer web using a water-circulated steel drum forms the primary method of solidifying extruded coatings on paperboard. This chill roller cooling process is used in extrusion lines to transition molten resin to a solid, stable film. It prevents the polymer from sticking to the machinery.
Crystalline Structure
Heat extraction rates affect both the crystallinity and the density of the applied barrier layer. Faster heat extraction results in a more amorphous structure, which improves the toughness and heat-sealing properties of the coating. In contrast, slower cooling allows the polymer chains to organize into a more crystalline arrangement, increasing the stiffness and chemical resistance of the barrier.
The temperature of the circulating water must be kept within a narrow range to maintain consistent barrier performance.
Surface Finish
Tension and contact pressure against the cooled steel surface determine the efficiency of the heat transfer across the web. Modern extrusion lines use a pressure roll to force the molten polymer against the polished or textured face of the drum, which directly replicates the roller texture onto the finished product. Inadequate chill roller cooling can lead to uneven release of the coated board, causing localized stretching or surface tearing.
Maintaining a clean drum surface and a uniform water flow prevents localized hot spots that could compromise the surface finish of the packaging material.
