Delamination of a dual density shoe sole

Description:

Insufficient adhesion between mid and outsole with different densities.

Affected Foam Parts:

Polyester shoe soles with two different densities.

What causes it:

The reason for delamination of two PU layers can be over application of release agent on the dummy last. Too fast curing of outer sole or machine downtime between the two injections will result in insufficient bonding between the two PU-layers. The use of an unsuitable release agent can also negatively affect the adhesion between mid and outsole.

• Over application of release agent on dummy last (first layer)
• Too fast curing of first PU-layer
• Stop of the machine between 1st and 2nd injection/too long time between injections-> outsole is already fully cured
• Improper mould release agent
• Contamination of dummy last

Solutions:

To improve the quality and adhesion of polyurethane dual density shoe soles, the release agent used must be tested sufficiently. Once this has been identified as suitable, it is important to monitor the quantity and dilution ratio (if applicable).

In addition, it is crucial to maintain the standard process time between the first and second shot and to actively control process parameters such as temperature, pressure and dosage. Adjusting reactivity through proper PU-formulation also helps to prevent delamination.

• Adjust sprayed amount of Release Agent
• Adjust pressures
• Check dilution ratio (if applicable)
• Change Release Agent
• Before break, “run out” moulds which remain between 1st and 2nd layer/ Keep the standard time of process (between 1st and 2nd shot)
• Check polyurethane-process parameters
• Adjust reactivity of PU-system

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