The retort pouch is a composite plastic film pouch that can be heat treated. It is divided into a water resistant pouch (≤100°C), a retort pouch (121-125°C) and a high temperature retort pouch (≥135°C depending on the temperature resistance). ). After about 30 minutes of high temperature sterilization, the retort pouch can greatly extend the shelf life of the food, and the production of the retort pouch has been rapidly developed. The delamination of the retort pouch refers to the delamination that occurs after the food is cooked. This problem has certain latency, and hidden dangers have been buried in printing, compounding and curing. However, the problem generally occurs when food enterprises use retort pouches, which often causes significant losses to enterprises. The structure of the retort pouch is generally: (inner layer) film (glue/ink/nylon film (outer layer) such as CPP, delamination may occur between the interfaces of any two materials mentioned above, and there are three interfaces, namely the inner layer Film/glue, glue/ink, ink/outer film. When the delamination phenomenon is slight, it appears as a stripe-like detachment in the force-receiving part of the package, or it is easily peeled off by hand, and in serious cases, it is naturally detached after being cooked.
The reasons for delamination of the retort pouch are as follows:
1. Insufficient wet heat bonding strength of ink or glue
The ink or glue used in the retort pouch is generally made of a urethane resin, whether it is a two-component or a single-component. The moisture-resistance of the ink or the glue is mainly determined by the moist heat resistance of the urethane resin. As far as the properties of the urethane resin itself are concerned, since the groups such as the ester bond and the urethane bond in the urethane resin have strong polarity, it is susceptible to moisture attack and hydrolysis under moist heat conditions, and the urethane resin and the surface of the substrate The formed hydrogen bonds are easily destroyed by moist heat, so that the bonding strength is lowered, and even the adhesive layer is peeled off. Ink or glue manufacturers should technically change the chemical structure of the polyurethane resin and use additives to increase the adhesion strength of the cooking ink after high temperature cooking.
2, flexible packaging manufacturers have problems with the use of ink or glue operation
The main points are as follows: First, the amount of curing agent does not meet the requirements. According to the requirements, it can not be used less or less. If the dosage is small, the degree of crosslinking between the curing agent and the resin is insufficient, and the adhesion strength, heat resistance and hydrolysis resistance of the ink layer are reduced; Excessive cross-linking occurs, which affects the crystallization and micro-phase separation between the polymers, which may impair the cohesive strength of the adhesive layer, increase the internal stress, and excessively shrink the ink layer, causing delamination. Second, the curing time is not up to the requirement. If the time is short, the crosslinking is insufficient, and the ink layer is resistant to temperature and hydrolysis. Third, the ink or glue activity is not enough, or the excess of expired residue is mixed. If the ink or glue activity is insufficient before printing or compounding, the number of groups that can be used to join the substrate is small, and thus the adhesion is not strong.
3, the compatibility between ink, glue and film does not match
According to the adhesion theory, when the surface tension of the adhesive and the adherend are equal and the polarity is the same, the interfacial tension is the smallest and the adhesion strength is the highest. Therefore, the surface of the film after curing of the ink and the glue and the surface of the film may vary depending on the product of different manufacturers, because the groups of various surfaces are not well attracted to form intermolecular forces or chemical reactions are formed. Chemical bonds, even if they have a certain effect at low temperatures, form adhesion, but at high temperatures, weak connections of surface groups may be destroyed and delamination occurs.
4, the film problem
It is manifested in the following two aspects: First, the degree of film processing is not up to standard, or it is not processed at all. Operators often do not find this problem, so that the adhesion fastness after printing, after compounding, and after curing is not high, and the problem is discovered after delamination after cooking. In production practice, I have found several such cases. Second, some additives in the film accelerate to the surface at high temperatures, which may cause a decrease in adhesion. Such as an opening agent, an antistatic agent, a slip agent, and the like added to a plastic film.
After the delamination accident occurs in the retort pouch , the enterprise must first carefully identify which interface the delamination occurs between, find out which two materials are involved, and check whether the production process is in accordance with the requirements, and at the same time change the materials for comparison test, so as to check The real reason for delamination.
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Following is some introduction about color sorter for your reference.
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