1. Printing quality: Check if there’s apparently a third color at the joint of two colors. The higher definition of the physical figure, the better the effect. Check if there’s drawn wire, foggy plate, plate plugging and printing omission.

2. Materials: Packaging bags need to be odorless. Bags with odor show a sense of nonconformity to the hygienic standard and might influence the normal use. Besides, bags shall also be checked if they’re evenly clear and if there’s any impurity.

3. Firmness: Firmness of the bag includes the compliance firmness and thermal wind firmness. Firmness of tin-free aluminum foil bags varies to different materials used.
A main way to differentiate them is to tear the seal by hand. It’s normally hard to tear off bags compounded with nylon and HP film, which could be used for relatively heavy things, such as stone and big-particle things. Bags made of OPP thermal seal film can be easily torn off, which can only be used for containing light things. When the bags are torn off, check the shape and structure of the section. If the bag is evenly torn off from the middle of the thermal seal, it means the bag’s thermal seal is bad and it’s easy to destroy during the production process. If it’s torn off from the seal edge, it means the seal is good. Also, the compounding firmness shall be confirmed by checking how many layers there are at the breakage and trying to separate them by hand. If the layers can be easily separated, it means they have good compounding firmness. Otherwise, it means they have poor compounding firmness. In addition, it shall also be checked to see if there are blisters or wrinkles on the surface.

4. Appearance evenness: First observe the bags’ stiffness. Normally the greater the evenness, the better the bags. For instance, nylon and HP film composite bags will show waves at the thermal seal. Also, it shall be checked if the cutting edge of the bags is even. The greater the evenness, the better the bags.

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