Paperboard materials achieve high recycling rates due to widespread recycling infrastructures worldwide. This makes them an attractive alternative to packaging materials made of fossil raw materials and thus they are increasingly being used in the food sector. Nevertheless, these materials pose major challenges: On the one hand, the processing behavior of fiber-based materials differs fundamentally from that of plastics; for example, their elongation behavior is greatly reduced compared to thermoplastics. On the other hand, these materials have no relevant barrier properties without additional coating, which is why fiber materials alone cannot be used for sensitive foods. The thin barrier layers applied to the paper web for this purpose can be damaged by the high process and frictional forces, which are particularly prevalent in the compression drawing and press forming processes, and then lose their barrier effect. In hydroforming or thermoforming, the aim is to make the best possible use of the elongation capacity by using fluids, but only low degrees of deformation can be achieved as a result.
The aim of the project is to use a combination of compression molding and hydroforming or thermoforming to improve the forming process and protect the thin barrier layer at the same time. For this purpose, fiber materials with optimized stretching properties are pneumatically pre-stretched over the forming surface or only in partial areas in a first process step. Subsequently, a stamping tool, corresponding to press forming, is used to turn the material over in the direction of the die, whereby the fiber material rolls on the stamping tool and thus causes no sliding on the material surface. Furthermore, an increase in the achievable sharpness of contour elements compared to hydroforming is expected. The project result is intended to provide a proof-of-concept with regard to the general applicability of the process.