The flexibility of packaging bags at low temperatures can increase their applicability

Under low temperature conditions, the molecular chain activity inside the polymer material of flexible packaging bags decreases, and the ability to resist external deformation decreases. On the macro level, it is manifested as a weakened impact resistance, resulting in a decrease in flexibility and an increase in brittleness of the flexible packaging. When subjected to external force impact, it is easy to cause problems such as bag breakage and air leakage.

So how to improve the flexibility of packaging bags at low temperatures and reduce damage rates?

Firstly, packaging materials should be reasonably selected based on the characteristics of the content and cost control. For example, OPP/LDPE materials are commonly used as low-temperature materials due to their moisture resistance, cold resistance, good low-temperature heat sealing strength, and cost-effectiveness; PA/LDPE has good cold resistance, impact resistance, and puncture resistance, and is suitable for packaging products with relatively hard content, but the cost is relatively high. In addition, materials such as PE, PET/PE, BOPP/PE, BOPP/CPP, etc. can also be selected according to actual needs.

Secondly, monitor the cold resistance of packaging materials. Cold resistance is an important performance indicator of flexible plastic packaging materials, which assesses the physical performance of packaging materials in terms of flexibility changes under low temperature conditions. It is a key indicator that should be paid attention to for product packaging circulating in low temperature environments. If the packaging bag manufacturer fails to meet the requirements for cold resistance of the material, and the material cannot maintain its original physical properties at low temperatures, causing the packaging bag to break and crack, which cannot meet the protective effect on the content. By selecting appropriate resin raw materials, improving the processing technology of packaging materials, adding an appropriate amount of plasticizer, and selecting packaging materials with good low-temperature resistance, measures can effectively improve the cold resistance of packaging bags and prevent an increase in the rate of packaging bag damage in low-temperature environments.

The cold resistance can be tested using the pendulum impact test. The testing method is to compare the pendulum impact energy tested under standard environmental conditions and low temperature environments (mostly -18 ℃). The cold resistance should not be less than a fixed percentage ratio, as specified in QB/T1871-93 "Biaxial Stretch Nylon (BOPA) Low Density Polyethylene (LDPE) Composite Film and Bag". The cold resistance of the material should not be less than 60%, and the testing method is as follows:

After placing the sample at -18 ℃ for 2 hours, measure the resistance to pendulum impact energy of the film according to GB8809, and calculate the cold resistance according to the following formula, taking two significant digits.

In addition, do not neglect the comprehensive physical performance testing of packaging bags. For example, testing for tensile performance and packaging puncture resistance. Soft packaging materials used for frozen food should have a certain degree of flexibility. If the material has poor flexibility and low elongation at room temperature, and there is air pressure inside the finished product packaging, the packaging material can easily form resistance, leading to bag body rupture. Moreover, frozen food is relatively hard, and during transportation and storage, the product is compressed. Packaging bag manufacturers must have good puncture performance to resist the puncture force from the content of the packaging material. Therefore, the testing of comprehensive physical properties such as tensile properties and puncture resistance of frozen food packaging materials should not be ignored.

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