Causes Analysis of Delamination in Retort Pouches (Ⅱ)
1. Incompatibility between the ink, adhesive, and film.
According to adhesion theory, when the surface tension of the adhesive matches that of the substrate and their polarities are similar, the interfacial tension is minimized, resulting in maximum adhesion strength. Therefore, the surface conditions of the ink or adhesive after curing and the film surface may vary depending on the products from different manufacturers. When the surface groups of various materials cannot effectively attract each other to form intermolecular forces or chemically bond to create chemical bonds, adhesion might occur at low temperatures due to weak interactions. However, under high temperatures, these weak adhesive forces can be disrupted, leading to delamination.
2. Issues with the film
This issue mainly manifests in two aspects: First, the film treatment does not meet the requirements, or the film has not been treated at all, resulting in inadequate peeling strength and heat seal strength after sterilization. Second, certain additives in the film may migrate to the surface at high temperatures, potentially weakening adhesion. These additives can include opening agents, anti-static agents, lubricants, and other substances added to plastic films.
If delamination occurs in retort pouches after sterilization, the first step is to identify the interface where the delamination occurs and determine which two materials are involved. It is also crucial to verify whether the production process adhered to the required standards. Additionally, swapping materials for comparison experiments can help pinpoint the true cause of the delamination.
3. Issues with the retort process
①When using retort pouches, food companies should strictly control the temperature within the range specified by the manufacturer. Even a few degrees over this range can be critical, as the materials used to make the retort pouch are often already at their maximum tolerable limits. Whether the retort pouch's performance can still be guaranteed with these extra degrees becomes a key factor.
②Affected by the packed contents, the physical and chemical properties of the contents inside the packaging, along with any chemical changes or new substances that may form under high temperatures, can penetrate the layers of the retort pouch, leading to a decline in its performance, such as causing delamination.
③The impact of vacuum level. Even the vacuum level inside the retort pouch can create differences in stress between the layers of the pouch, leading to delamination between film layers with weaker adhesion.
④Back-pressure during sterilization. Under high-temperature conditions, the heat seal strength of the pouch is much lower than at room temperature. At this point, the pressure difference between the inside and outside of the retort pouch can cause excessive expansion, similar to inflating a balloon, potentially leading to rupture or leakage.
