Shoe gluing process: problems and solutions

In the different operations for the production of footwear and manufactures, the use of adhesives is essential to achieve the union of materials and parts. For this reason, it is very important to choose the correct adhesive, with regard to the characteristics of the materials to be bonded, and above all to prepare them properly, following the corresponding process.

Among the main problems that may arise, we can establish the following and their possible causes.

Lack of adhesion in the upper or sole

• Improper sanding or roughing
• Lack of compatibility between the adhesive and the substrate (unsuitable adhesive)
• Excess oil or plasticizer in the substrate
• Insufficient removal of dirt, dust, ink, etc.
• Insufficient adhesive penetration
• Inadequate surface preparation

Superficial or total rupture of the substrates

• Low resistance of the substrate structure
• Surface penetration of the adhesive
• Excessive solvent or halogen attack on the surface of the substrate
• Excessive sanding or roughing

Lack of cohesion of the adhesive

• Insufficient drying time
• Migration of oils or plasticizers to the glue line
• Insufficient crystallization time
• Incorrect reactivation temperature

Lack of bonding of the adhesive films

• Contamination of the film with dirt, dust, oils, humidity, etc.
• Insufficient reactivation
• Insufficient pressing
• Adhesive film in an advanced state of crystallization

​Selecting the correct adhesive

Several factors must be observed in choosing the appropriate adhesive, depending on the operations in which it will be used, and the characteristics it must provide.

For preparation and backstitch

• Long open time
• Relatively fast drying
• Medium initial resistance

For assembly

• Fast dry
• High initial resistance
• High heat resistance

For gluing soles, welts and others

• Fast dry
• High initial, final and heat resistance

Care in the use of adhesives

• Store the adhesives in a suitable space: dry, with good ventilation and without large variations in temperature
• Observe the validity period of the lot, using the oldest ones first and not letting the final period expire
• Homogenize the adhesives before use
• After reactivation, the surfaces must be joined immediately, to proceed to pressing
• Containers must be kept closed
• Carry out the “press bed” test to verify the pressing conditions
• When all the adhesive is consumed, empty the container without leaving residues
• Do not mix adhesive residue with metallic waste
• Empty containers must be compacted with manual or hydraulic equipment. Or send them to an industrial waste landfill

​RELATED ARTICLE:
- Adhesives for EVA: features and usage

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