Retort pouch breakage rate too high? Catch these 3 culprits

Bag breakage High breakage rate is one of the main quality problems that often occur in high-temperature retort pouches. High breakage rate is closely related to three aspects: material structure, unstable adhesive application, and bag-making process. Below, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will explain the specific reasons for you.

Factors Affecting High Breakage Rate

1. Material Structure

The thermal stability of the surface material of the high-temperature retort pouch after retorting is very important, especially the dimensional stability after retorting and cooling. Poor thermal stability easily leads to delamination and peeling after retorting and cooling, resulting in bag breakage.

2. Unstable Adhesive Application

High-temperature retort packaging generally uses dry lamination, and usually uses a polyurethane adhesive composed of two components: a main agent and a curing agent. For high-temperature retort resistance, it is usually a high-solid-content aliphatic two-component polyurethane adhesive. To obtain higher water and heat resistance, a coupling agent of about 1% can be added to the adhesive. If the glue concentration is too high, it is easy to block the dots of the glue coating screen, causing the amount of glue applied to decrease; if the glue concentration is too low, the glue is not easy to transfer to the material. Usually, the main agent and curing agent are mixed in a prescribed ratio and diluted with a solvent to a working solid content of about 30%.

3. Bag-Making Process

Three factors in the bag-making process affect the heat sealing strength and sealing performance of the packaging bag: the temperature, pressure, and speed of the heat sealing knife. Table below shows the bag-making process parameters and test data for a PET12/AL7/NY15/CPP70 structure. As can be seen from the table:

Bag-Making Process Parameters and Test Data

Reasonable matching of heat sealing temperature, pressure, and speed is a necessary guarantee for heat sealing quality.

If the weld after heat sealing is not cooled properly, it will not only affect the appearance flatness of the weld, but also affect the heat sealing strength. The cooling process is a process of shaping and eliminating stress concentration at a lower temperature under a certain pressure for the weld that has just been melted and heat-sealed. Therefore, insufficient pressure, poor cooling water circulation, insufficient circulation volume, too high water temperature, or untimely cooling will all lead to poor cooling, heat-sealed edges warping, and reduced heat-sealing strength.

The more heat sealing times, the higher the heat sealing strength. The number of longitudinal heat sealing times depends on the effective length of the longitudinal welding rod and the bag length; the number of transverse heat sealing times is determined by the number of sets of the transverse heat sealing device of the machine. Good heat sealing requires at least two heat sealing times. General bag-making machines have 2 sets of hot knives, and the higher the degree of overlap of the hot knife positions, the better the hot air effect.

For composite films with the same structure and thickness, the higher the interlayer peeling strength of the composite layer, the greater the heat sealing strength. For products with low composite peeling strength, the weld failure is often the interlayer peeling of the composite film at the weld first, causing the inner heat sealing layer to independently bear the destructive tensile force, and the surface material loses its reinforcing effect, greatly reducing the heat sealing strength of the weld. If the composite strength is large, interlayer peeling will not occur at the weld, and the actual heat sealing strength measured will be much greater.