Why do plastic bags tear?

Damage to plastic packaging bags during production, transportation, and storage is a common quality issue for businesses. Shunxingyuan Packaging, a professional flexible packaging manufacturer, has specially compiled The following situations where damage is most likely to occur:

1. Damage caused by the automatic packaging process: During automatic packaging, the filling material strongly impacts the bottom of the bag. If the bottom of the bag cannot withstand the impact force, it will crack.

2. Damage caused during transportation and product stacking: Flexible packaging bags cannot withstand the increased internal pressure caused by the stacking of goods and friction during transportation, resulting in bag breakage.

3. Damage caused by the vacuum packaging process: If the packaging bag is too thin, it will shrink during vacuuming. If the contents contain hard objects, sharp corners, or the vacuum machine contains hard objects (dirt), it can puncture the packaging bag, causing damage.

4. High-temperature sterilization bags may be damaged during vacuuming or high-temperature and high-pressure sterilization due to insufficient pressure and high-temperature resistance of the material.

5. Frozen packaging bags become hard and brittle due to low temperatures, and poor freeze-resistance and puncture resistance can cause the packaging bag to break.

Causes of Damage

1. Causes of packaging bag damage during automatic packaging

Generally, heat sealing strength refers to the bonding strength after two films are bonded together by heat sealing and completely cooled. However, on automatic packaging production lines, the two layers of packaging materials do not get sufficient cooling time, so the heat sealing strength of the packaging materials is not suitable for judging the heat sealing performance here. At this time, the heat adhesion, that is, the peeling force when the heat-sealed part of the material has not yet cooled, should be used as the basis for selecting the heat-sealing material, so that it can meet the heat-sealing strength requirements during filling.

To achieve the best heat adhesion of the film material, there is an optimal temperature point. When the heat sealing temperature exceeds this temperature point, the heat adhesion will show a downward trend. On the filling production line, the heat sealing of the flexible packaging bag and the filling of the contents are almost synchronized. Therefore, when filling the contents, the heat-sealed part at the bottom of the bag has not yet completely cooled, and the impact force it can withstand will be greatly reduced.

The impact force of the contents on the bottom of the flexible packaging bag during filling can be tested using a heat adhesion tensile tester. By adjusting the heat sealing temperature, heat sealing pressure, and heat sealing time, a heat adhesion curve can be drawn to select the optimal combination of heat sealing parameters for the production line.

2. Causes of bag breakage during storage and transportation

Items packaged in flexible packaging bags may cause an increase in gas pressure inside the bag due to stacking during storage and transportation, which can cause the flexible packaging bag to break. Since the breakage often occurs at the heat-sealed position between the materials, which is the weakest point of the heat seal of the flexible packaging bag, bag breakage can be avoided by testing the heat sealing strength of the packaging heat seal edge, changing the material, or adjusting the heat sealing process parameters.

The heat sealing strength of the material can be roughly divided into tensile heat sealing strength and expansion heat sealing strength according to the detection method. The tensile heat sealing strength, which can be tested using a tensile tester, is the ability of the heat-sealed part to resist separation when the force is consistent and uniform in the direction of force. It is particularly suitable for evaluating the opening performance of flexible packaging bags, but not for solving the problem of bag breakage, because the direction and magnitude of the internal pressure causing bag breakage are uncertain, and the material near the heat seal may deform due to bearing part of the pressure, causing pressure damage to the flexible packaging bag.

The detection of expansion heat sealing strength requires the use of a leakage and sealing strength tester, which requires pressurizing the flexible packaging bag, and can detect the weakest and most vulnerable position in the entire package (not limited to the heat-sealed part). Since the expansion heat sealing strength does not represent the average strength of the heat seal, there is no correlation between the expansion heat sealing strength and the tensile heat sealing strength. The expansion heat sealing strength is related to the size, geometric shape, and materials used in the flexible packaging bag.

3. Causes of damage to vacuum-packed food packaging

Mainly due to two aspects: food vacuum packaging design and external vacuum packaging materials:

（ 1) In terms of food vacuum packaging design, if the net content or volume of the contents exceeds the bearing capacity of the flexible packaging material used, it will cause bag breakage and cracking problems with slight external force during transportation or sales. Generally, the thickness of the material used as the heat-sealed layer of the vacuum packaging bag should not be less than 50μm.

（ 2) Quality problems with food vacuum packaging materials lead to sealing cracks in finished packaging, generally focusing on the following aspects:

（ A) Physical and mechanical properties of food packaging—such as tensile strength and elongation at break, puncture resistance, impact resistance, peel strength, etc., can comprehensively judge whether the toughness, puncture resistance, and impact resistance of the packaging bag meet the requirements of packaging, storage stacking, and transportation. (Related to the contents, size of the packaging bag, transportation distance, and packaging method)

（ B) Sealability of food packaging—such as burst pressure testing, can determine the location of bag breakage and the weak points of mechanical strength. Heat sealing strength testing can determine whether the heat sealing strength meets the requirements of the food contents and determine the location of poor heat sealing and the uniformity of the heat sealing effect. For example, damage to vacuum-packed chicken feet is caused by the fact that when chicken feet are cut, some broken chicken feet bones are cut very sharply, and when boiled, the skin shrinks, so the bones are exposed, and the bag is easily punctured during transportation. Therefore, the puncture resistance of the packaging bag should be a key consideration for the packaging material combination.

The leakage and sealing strength tester can not only detect the maximum breaking force of the flexible packaging bag, but also test the breaking time of the packaging bag by setting the applied pressure. Based on the test data, the stacking structure can be designed, the parameters of the heat sealing process can be further adjusted to improve the packaging effect, or the problems in the packaging structure can be analyzed based on the location of the breakage of the flexible packaging bag.