What are the reasons for poor heat sealing strength during the production process of vacuum packaging bags?

The sealing performance of vacuum packaging bags is a prerequisite for their performance. There is a term in the industry called "heat sealing degree", which is an important factor in whether the sealing degree of vacuum packaging bags is qualified. Seals with strong heat sealing degree will be stronger. So, what are the reasons for poor heat sealing strength during the production process of vacuum packaging bags?

Reason 1: Different types of heat sealing materials result in varying heat sealing strengths, such as inconsistent heat sealing strengths for PP, PE, and EVA; Products with the same film but different polymerization methods have different heat sealing strengths; The thickness and uniformity of the material can also affect the heat sealing strength; Different processing methods for heat sealing, such as blow molding, cast film, etc., all affect the heat sealing strength. The storage time of the film is too long, resulting in an increase in precipitates and poor heat sealing strength after corona treatment. Moisture absorbing materials absorb moisture, causing delamination of the hot cover and a decrease in peel strength.

Reason 2: Poor temperature resistance of printing ink or inappropriate additives in the ink, resulting in delamination of the printing layer and a decrease in heat sealing strength at high bag making temperatures. Hot sealed edges should be designed as free of patterns as possible. The selection of adhesive is also important in the composite process, and the rationality of parameters such as adhesive ratio and viscosity will affect the sealing strength. In the extrusion composite or coating process, high processing temperature leads to a high degree of surface oxidation of the material, an increase in carboxyl group generation, and is not conducive to heat sealing.

Reason 3: Insufficient cooling and shaping of the edge after heat sealing cannot eliminate internal stress, affecting strength and appearance. It should be checked in a timely manner and the cooling water circulation system should be strengthened. The more heat sealing times, the higher the heat sealing strength. The number of longitudinal heat seals depends on the ratio of the effective length of the longitudinal welding knife to the bag length; The number of horizontal heat sealing cycles is determined by the combination of horizontal heat sealing devices on the machine. Good heat sealing requires at least two heat sealing cycles.

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