Bonding shoe soles via digital printing

Atom Lab, the research and innovation business unit of shoe machinery manufacturer Atom has presented a fully-automated process for shoe production at the Simac Tanning Tech 2018. The most technically challenging step in this process is bonding the outsole to the shoe upper. Covestro developed a solution which is based on polyurethane raw materials for adhesives. These are applied to the outsole or upper by means of digital printing. For the application, Atom Lab used a variation of the melt layer method (Fused Filament Fabrication FFF, or Fused Deposition Modeling FDM).

For digital printing of adhesives using the melt layer method (FFF) the adhesive is applied in the form of strands – so-called filaments. They are fed from a role.

This method uses strands of melt-processable adhesive filaments. The molten adhesive is applied according to a digital print layout. The sole and upper are then joined under pressure. This creates a solid, permanent adhesive bond. This application using adhesive filaments is quick and efficient. Furthermore, it is very precise and reproducible, and it is also well suited for absorbent substrates. Due to the use of solid filaments, for example, the subsequent drying process may be dispensed. The adhesive features a high initial strength. Since application takes place from the melt, the adhesive is already activated. If the open time is sufficiently long, the fabricator can dispense with prior heat activation. Thus, two process steps can be saved in total.