It is common for adhesive leather shoe uppers and soles to loosen due to poor adhesion. There are many reasons for this, mainly due to improper selection of raw materials and process control in the factory.
Rubber soles and leather can be bonded using neoprene adhesive, while imitation leather soles and polyurethane soles with high resin content are difficult to work. It is necessary to use polyurethane finger glue or other adhesives to adhere firmly, as one adhesive is not suitable for any material
Before bonding, the sole and upper of the shoe need to be polished and fluffed, brushed multiple times with glue and baked, and then pressed with a press machine to firmly adhere. The bonding quality of leather shoes is controlled by the peel strength index, which needs to be measured using a peel tester.