Meaning
A structural failure mode consists of microscopic openings or cracks that form in thin barrier layers during the processing of multi-layer films. In packaging materials, pinhole micro-fissure defects allow gases and moisture to bypass the protective layer and compromise the shelf life of the product.
Mechanical Failure
These failures typically occur when the polymer film is subjected to high tensile stresses during drawing or thermoforming. When pinhole micro-fissure defects develop, they are often located in regions where the barrier layer is thinnest or where the melt temperature was too low to ensure proper elongation of the material. This mechanical failure can be aggravated by the presence of hard gel particles in the melt.
Process Control
Moulders must control the temperature and speed of the orientation process to prevent the creation of these microscopic channels. If pinhole micro-fissure defects are left unchecked, they can lead to a rise in the oxygen transmission rate of the film, which causes the packaged food to spoil prematurely. This issue is particularly critical when working with rigid barrier materials like polyamide.
Defect Mitigation
Adding plasticizers to the barrier resin can improve its flexibility and resistance to cracking during processing. Reducing the draw ratio also helps minimize the risk of developing pinhole micro-fissure defects in high-speed production lines.
