Total bag breakage during retort sterilization? Pay attention to these 2 points!

During high-temperature sterilization of retort pouches, the residual gas inside the pouch expands, the volume of the contents increases, and the pressure inside the pouch rises. When the internal pressure exceeds the pouch's capacity, the pouch will burst if the pressure in the retort is lower. To ensure that the retort pouch does not break during sterilization, Shunxingyuan Packaging, a professional flexible packaging manufacturer, believes that the following measures should generally be taken.

1. Use pressure sterilization and pressure cooling

After the retort pouch enters the sterilizer, the temperature at which air pressure is applied depends on the initial temperature of the retort pouch, the amount of filling, and the amount of residual air. Generally, pressurization begins at 90 degrees. If pressurization is too early, the heating time is prolonged; if pressurization is too late, bag breakage is likely to occur.

The choice of sterilizing medium during sterilization is also closely related to bag breakage. Common sterilizing media include high-pressure hot water, high-pressure steam, and steam-air mixtures, each with its own advantages.

Studies have shown that high-pressure hot water heats more evenly than the latter two during sterilization. Its disadvantage is that it consumes a lot of heat during heating and sometimes causes deformation or contamination of the packaging container. The latter two methods almost have no such disadvantages. For soft cans, the steam-air mixed medium seems to be the most ideal, but the ratio of air mixed in should be appropriate. If it is too much, the heat transfer performance of the container is poor, and the sterilization effect is reduced; conversely, if it is too little, the bag may break due to slight pressure changes.

The relationship between the ratio of steam to air and bag breakage varies with the size of the bag, the amount of filling, the amount of residual air (i.e., vacuum degree), and the sterilization temperature.

2. Packaging Strength Testing

This includes testing of peel strength, seal strength, burst strength, hydrostatic strength, puncture strength, and drop strength.

Seal strength reflects the firmness of the heat-sealed portion of the retort pouch; peel strength (or composite strength) reflects the reliability of the lamination between layers of the retort pouch; burst strength reflects the ability to withstand internal pressure; hydrostatic strength (external pressure strength) reflects the strength of a filled retort pouch to withstand external static pressure; puncture strength reflects the strength of the retort pouch to withstand sharp object pressure; drop strength reflects the allowable drop height of a sealed retort pouch filled with contents during loading and unloading.

To ensure seal strength, it is crucial to avoid contaminating the seal area of the retort pouch during filling. If there is juice, water droplets, etc., attached to the inner side of the seal area, the seal area cannot be sealed.

The evenness of the seal area of the pouch during sealing is also a factor affecting seal quality. To keep the seal area of the pouch flat and wrinkle-free after sealing, the following points should be noted: the mouth of the retort pouch must be flat and the two sides must be of equal length; the sealing machine mold must be flat and parallel, and the fixture must be good; the content blocks cannot be too large, the filling amount cannot be too much, and the total thickness of the bag cannot exceed the limit.

The sealing temperature, pressure, and time should be determined based on the constituent materials of the retort pouch, the melting temperature of the film, and the thickness of the seal. Within a certain sealing time, a temperature that is too low will result in incomplete melting and poor adhesion, while a temperature that is too high will cause excessive melting of the film, changing its physicochemical properties and resulting in a weak seal.

Similarly, too low pressure will result in insufficient bonding of the melted film, while too high pressure may cause extrusion of the melted film material, resulting in a weak seal. The sealing time determines the production capacity. Under the premise of ensuring sealing quality, the sealing time determines the size of production capacity, and vice versa. Generally, the sealing temperature, pressure, and time should be tested.

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