Currently, the bonding of the sole to the upper in footwear and the bonding of leather goods materials are principally carried out using solvent based adhesives whose application, as well as prolonging process times, carry a potential risk for the environment and for the health of the workforce. These adhesives also pose serious storage and disposal problems.
In the last few years alternative solvent-free products have been studied, such as water based adhesives and moisture-curable solid adhesives. Nevertheless, it has been proved that they are not an adequate answer due to their lack of versatility and difficult application procedures. Solid adhesives in filmic form developed previously in the CRAFT CR-1463 Project provide good characteristics for bonding the sole to the upper in the footwear industry, offering the same guarantees of bonding stability as the solvent based adhesives currently used for this task. These adhesives have also shown themselves to be very efficient for the bonding of materials used in the fabrication of other leather goods.
These solid adhesives are cleanly and quickly applied in filmic form and they are activated with heat, eliminating waiting time for the removal of solvents and without the need for curing. This results in a clean technology which could contribute to a notable increase in productivity in the footwear and leather goods industry, favouring its diversification and the creation of employment.
The objective of this project was the optimization of the application of solid thermoplastic adhesives in filmic form in different types of shoe and leather goods production. For the implementation it was necessary to optimize the prototypes and application systems, to validate the procedures within the industry and to disseminate the results among companies in the footwear and leather goods sector.
The implementation of this new bonding technology was expected to produce the following benefits in the footwear-leather goods sector:
- reduction of the fabrication process time by about 35%
- increase in the quality of the finished product since it avoids the spotting of the product and the subsequent repair operations.
- increase in productivity of about 30%
- optimization of the consumption of adhesive resulting in a greater profitability of the process.
- elimination of the risks which solvents pose for the environment and for the health of the workforce.
It was also hoped that when current legislation concerning the restriction of the use of solvents takes effect, the demand for the technology will undergo a rapid increase.