curling or flatness
The curl of sheet materials depends generally on temperature and conditioning state. So multilayer materials produced by usage of materials having different coefficients of thermal expansion or unequal expansion/ shrinkage due to differing hygroscopic tendency may tend to curl caused by a kind of bi-metall effect. In addition to that excessive mechanical stress in the processing of rolls can cause curl.
small reel (if not available: film stack or hand roll without folds, kinks and contaminations)
Standardprüfungen
flatness: cross section method When materials with strong curling tendency have to be tested this method differentiates better than the methodologically similar circle method. A diagonal cross cut is made in the film, and the sample is stored. The direction of curling and the distance between the tips of the cross cut are recorded in [mm]. The measurements are carried out in standard climate at 23°C and 50% relative humidity and are well suitable for material comparisons. Measurements under varying climatic conditions are possible for an additional charge, please contact us. Norm: DIN 55403
flatness: flatness temperature This method is useful for determining the flatness temperature of multi-layer films, which are produced by usage of individual layers with different coefficients of thermal expansion. This can cause a tendency to curl in consquence of temperature variations ("bimetaleffect"). Norm: DIN 55403
flatness: circle method A circle cut with a diameter of 113 mm is stored, the direction of curling and the edge distance in [mm] is measured. The measurements are carried out in standard climate at 23°C and 50% relative humidity and are well suitable for material comparisons. Measurements under varying climatic conditions are possible for an additional charge, please contact us. Norm: DIN 55403