How to reduce damage and delamination of packaging film

With more and more enterprises using high-speed automatic packaging machines, quality problems such as bag breakage, cracking, delamination, weak heat sealing, and sealing contamination that often occur in the high-speed automatic packaging process of flexible packaging film have gradually become key process issues that enterprises need to control.

When producing roll film for high-speed automatic packaging machines, flexible packaging enterprises should pay attention to the following points:

Strict material selection

1. Material requirements for each layer of rolled film
Due to the different equipment structure of the high-speed automatic packaging machine compared to other bag making machines, its pressure only relies on the force of two rollers or hot pressing strips squeezing each other to achieve heat sealing, and there is no cooling device. The printing layer film directly contacts the heat sealing device without the protection of insulation cloth. Therefore, the selection of materials for each layer of the high-speed printing drum is particularly important.

2. The other properties of the material must comply with:
1) Balance of film thickness
The thickness, average thickness, and average thickness tolerance of plastic film ultimately depend on the thickness balance of the entire film. In the production process, the thickness uniformity of the film should be controlled well, otherwise the produced product is not a good product. A good product should have a balanced thickness in both the longitudinal and transverse directions. Because different types of films have different effects, their average thickness and average thickness tolerance are also different. The thickness difference between the left and right sides of high-speed automatic packaging film is generally not more than 15um.

2) Optical properties of thin films
Refers to the haze, transparency, and light transmittance of a thin film.
Therefore, there are special requirements and controls for the selection and amount of masterbatch additives in film rolling, as well as good transparency. At the same time, the opening and smoothness of the film should also be considered. The opening amount should be based on the principle of facilitating the winding and unwinding of the film and preventing adhesion between the films. If the amount is added too much, it will affect the increase in haze of the film. The transparency should generally reach 92% or more.

3) Friction coefficient
The coefficient of friction is divided into static friction and dynamic friction systems. For automatic packaging roll products, in addition to testing the friction coefficient under normal conditions, the friction coefficient between the film and the stainless steel plate should also be tested. As the heat sealing layer of the automatic packaging film is in direct contact with the automatic packaging molding machine, its dynamic friction coefficient should be less than 0.4u.

4) Add dosage
Generally, it should be controlled within 300-500PPm. If it is too small, it will affect the functionality of the film such as opening, and if it is too large, it will damage the composite strength. And it is necessary to prevent a large amount of migration or penetration of additives during use. When the dosage is between 500-800ppm, it should be used with caution. If the dosage exceeds 800ppm, it is generally not used.

5) Synchronous and asynchronous shrinkage of composite film
Non synchronous shrinkage is reflected in the changes of material curling and warping. Non synchronous shrinkage has two forms of expression: "inward curling" or "outward curling" of the bag opening. This state shows that there is still asynchronous shrinkage inside the composite film in addition to synchronous shrinkage (with different sizes and directions of thermal stress or shrinkage rate). Therefore, when purchasing thin films, it is necessary to conduct thermal (wet heat) shrinkage longitudinal and transverse tests on various composite materials under the same conditions, and the difference between the two should not be too much, preferably about 0.5%.

Reasons for Damage and Control Techniques

1. The effect of heat sealing temperature on heat sealing strength is the most direct

The melting temperature of various materials directly determines the minimum heat sealing temperature of composite bags.
During the production process, due to various factors such as heat sealing pressure, bag making speed, and the thickness of the composite substrate, the actual heat sealing temperature used is often higher than the melting temperature of the heat sealing material. High speed automatic packaging machine, with lower heat sealing pressure, requires higher heat sealing temperature; The faster the machine speed, the thicker the surface material of the composite film, and the higher the required heat sealing temperature.

2. Thermal adhesion curve of bonding strength

In automatic packaging, the filled contents will have a strong impact on the bottom of the bag. If the bottom of the bag cannot withstand the impact force, it will crack.

The general heat sealing strength refers to the bonding strength after two thin films are bonded together by heat sealing and completely cooled. However, on the automatic packaging production line, the two-layer packaging material did not receive sufficient cooling time, so the heat sealing strength of the packaging material is not suitable for evaluating the heat sealing performance of the material here. Instead, thermal adhesion, which refers to the peeling force of the material's heat sealed part before cooling, should be used as the basis for selecting the heat sealing material, so as to meet the requirements of the material's heat sealing strength during filling.
There is an optimal temperature point for achieving the best thermal adhesion of thin film materials, and when the heat sealing temperature exceeds this temperature point, the thermal adhesion will show a decreasing trend. On the automatic packaging production line, the production of flexible packaging bags is almost synchronized with the filling of the contents. Therefore, when filling the contents, the heat sealed part at the bottom of the bag is not completely cooled, and the impact force it can withstand is greatly reduced.

When filling the contents, for the impact force at the bottom of the flexible packaging bag, a thermal adhesion tester can be used to draw the thermal adhesion curve by adjusting the heat sealing temperature, heat sealing pressure, and heat sealing time, and select the optimal combination of heat sealing parameters for the production line.
When packaging heavy packaged or powdered items such as salt, laundry detergent, etc., after filling these items and before heat sealing, the air inside the bag should be discharged to reduce the stress on the packaging bag wall, allowing the solid material to be directly stressed to reduce bag damage. In the post-processing process, special attention should be paid to whether the puncture resistance, pressure resistance, drop rupture resistance, temperature resistance, temperature medium resistance, and food safety and hygiene performance meet the requirements.