Curling or flatness
The curling of sheet materials depends generally on temperature and conditioning state. So multilayer materials made of materials having different coefficients of thermal expansion or unequal expansion/shrinkage due to deviating 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 lead ot curling.
In short — AI-generated
This test determines the tendency of flexible packaging films to curl or lose their flatness. A defined sample of the material is placed on a flat surface under controlled temperature and humidity conditions to measure the extent of deformation or curvature.
The resulting value indicates how stable a material remains during processing and storage, helping to identify issues caused by internal stress or mismatched material layers. This information is used to ensure that films can be processed smoothly on packaging machines without jamming or alignment errors.
Text is AI-generated; based on test method data curated and verified by Innoform.
Standard Tests
flatness: flatness temperature
Specific Norm: DIN 55403
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").
flatness: circle method
Specific Norm: DIN 55403
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.
flatness: cross section method
Specific Norm: DIN 55403
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.
