There are three common problems with stand up bags: bag leakage during use, uneven bag shape and asymmetric bottom seal during bag making.

The leakage of stand up bag is mainly caused by the selection of composite materials and heat sealing strength.

(1) Selection of materials

The material selection of stand up bag is very important to prevent leakage. The purpose is to increase the peel strength between the outer layer and the middle barrier layer, between the barrier layer and the heat sealing layer and the heat sealing strength of the bag. Therefore, the surface tension of the composite surface of the film is required to be greater than 38 dyn / cm; The low-temperature heat sealing performance of the inner heat sealing film is better, and the surface tension of the heat sealing surface is less than 34dyn / cm; In addition, we should choose the ink with good connection performance and the adhesive with high solid content and low viscosity.

(2) Heat sealing strength

Low heat sealing strength is also one of the important factors affecting the leakage of stand up bags. During heat sealing, the matching relationship between heat sealing temperature, heat sealing pressure and heat sealing time shall be adjusted. It is mainly necessary to explore the heat sealing temperature of bags with different structures. Due to the different melting points of different kinds of plastic films, the heat sealing temperature is also different; The heat sealing pressure should not be too large, and the heat sealing time should not be too long to avoid macromolecular degradation. The heat sealing layer is cut by the heat sealing knife in the state of high-temperature melting, so as to reduce the sealing strength. In addition, the four-layer sealing part at the bottom of the stand up bag is the key part. The heat sealing temperature, heat sealing pressure and heat sealing time can be determined only after full test and verification.

In the actual production process, the stand up bag shall be tested for leakage according to the different requirements of its contents. The simple and practical method is to fill some air into the bag, heat seal the bag mouth, put it into the basin containing water, and squeeze different parts of the bag by hand. If no bubbles escape, it indicates that the sealing tightness of the bag is good; Otherwise, the heat sealing temperature and pressure of the air leakage part shall be adjusted in time. The stand up bag containing liquid should be treated with caution. The method of extrusion and drop can be used to detect whether it leaks liquid. For example, fill some amount of water in the bag and seal the mouth.

1. The stand up bag shape is uneven

Flatness is one of the indicators to measure the appearance quality of packaging bags. In addition to material factors, the flatness of stand up bags is also related to heat sealing temperature, heat sealing pressure, heat sealing time and cooling effect. High heat sealing temperature, high heat sealing pressure and long heat sealing time will cause shrinkage and deformation of composite film. Insufficient cooling will result in insufficient setting after heat sealing, which can not eliminate the internal stress and wrinkle the bag. Therefore, the process parameters should be adjusted and the cooling water circulation system should work normally.

2. Poor symmetry of stand up bag

Symmetry not only affects the appearance of stand up bags, but also affects their sealing performance. The common asymmetry of stand up bags is often reflected in the bottom material. Due to the improper control of the bottom material tension, the round hole on the bottom surface will be deformed or wrinkled due to the mismatch with the main material tension, and the heat sealing strength will be reduced. When the round hole of the bottom material is deformed, the discharge tension shall be properly reduced, and the waiting time shall be increased for correction during heat sealing, so as to fully heat seal the intersection of the four layers at the bottom of the bag. In addition, the asymmetry of bag shape is also related to photoelectric tracking, feeding, cursor design, rubber roller balance, stepping motor or servo motor synchronization and other factors. This problem should be solved in specific operation according to different products and different bag making equipment.