Embossing of the Paperboard and the Effect of Polymer Coating on Local Deformation

Embossing is used in packaging solutions as an additional tool to improve the appearance of the product but can also be used to increase product safety by improving functionality and identifiability of packages. Especially in food packaging, there is a risk that the local stresses caused by embossing will break the structure of the board, thereby losing its barrier properties. The object of the study was to investigate effects of the elevated mould temperature, material thickness and polymer coating layer on the embossing process. A heated precision tool that embosses a pattern similar to ones often placed on the bottom or on the walls of the packages was manufactured. Selected pattern is demanding from material's point of view because it has almost vertical edges and a large maximum depth. Local strains up to 27% are needed to form this pattern. The test material for forming experiments was a three-layer sbs-board, typically used in the production of food packages. The embossed samples were visually analysed by means of microscopy and topography. In addition to the degree of damage to sample materials, material thinning during processing was investigated. The results of the study show that despite the local stretching and thinning of the test materials, tightness properties were maintained with PET-coated samples. Thus, the plastic coating functioned ideally for the barrier properties, otherwise its effect on the shape of the pattern was found to be small. Correspondingly, the results proved that the tool made for the experiments works as desired with several different material grammages. The female mould temperature has an evident effect on both the height of the pattern and the thinning of the material, which in practice makes it possible to reduce the material springback by means of a higher tool temperature.