1. The choice of composite materials
Due to the higher requirements for various mechanical properties of the material, the upright bag generally adopts multi-layer composite film.
1. Outer layer
The outer layer is the printing material. At present, the stand-up bag printing materials commonly used in the market are not only slitting ordinary OPP, but also high-strength and high-barrier materials such as PET and PA, which can be selected according to the situation. If it is used to package dried fruit solid products, ordinary materials such as BOPP and matting BOPP can be used. If packaging liquid products, PET or PA materials are generally used.
2. The middle layer
The middle layer generally chooses materials with high strength and high barrier properties, such as PET, PA, VMPET, aluminum foil, etc. Moreover, RFID requires the surface tension of the intermediate layer material to meet the composite requirements, and it must have a good affinity with the adhesive.
3. Inner layer
The inner layer is the heat-sealing layer. Generally, PE, CPE, CPP and other materials with strong low-temperature heat-sealing performance are used. The surface tension of the composite surface is required to meet the composite requirements, but the surface tension of the hot cover must be less than 34mN/m, and it must have good anti-pollution, antistatic and heat-sealability.
2. Requirements for bag making process
1. Heat sealing temperature
The factors that need to be considered when setting the heat-sealing temperature are the characteristics of the heat-sealing material; the second is the film thickness; the third is the number of heat-sealing and pressing and the size of the heat-sealing area. Under normal circumstances, when the same part is pressed more frequently, the heat sealing temperature can be appropriately set lower.
2. Heat sealing pressure
Appropriate pressure must be applied during heat sealing to promote the adhesion of the heat cover material. However, if the pressure is too large, the molten material will be squeezed out, which will not only affect the analysis and troubleshooting of the flatness of the bag, but also affect the heat sealing effect of the bag and reduce the heat sealing strength.
3. Heat sealing time
The heat-sealing time is not only related to the heat-sealing temperature and heat-sealing pressure, but also related to factors such as the performance of the heat-sealing material and the heating method. The specific operation should be adjusted during the actual test machine according to different equipment and materials.
4. Heating method
The heating method of the heat-sealing knife during bag making can be divided into two types: single-side heating and two-side heating. Obviously, the two-side heating method is more efficient and practical than the one-side heating method.
There are many problems in the actual production of upright bags, but there are mainly two outstanding problems: one is leakage or air leakage when containing goods; the other is the unevenness of the bag shape and asymmetric bottom seal during the bag making process. Therefore, how to make a good choice of materials and adopt the best process and operation method plays a decisive role in improving the overall quality of the upright bag.