Nowadays, fresh milk, soy milk and many fruit juice drinks, condiments and other fresh drinks are packaged in vacuum bags. These vacuum bags are mainly made of polyethylene (PE) co-extruded film, which must meet the requirements of packaging, printing, processing, storage, transportation and hygiene. From the appearance and performance of the membrane, it can be divided into three categories: soft milky white PE film, black-white co-extruded PE film and hard high temperature cooking PE film. Soft milky white PE plastic film packaging is mainly used in milk, soy sauce, vinegar and other simple liquid packaging, co-extrusion blown film masterbatch is composed of LDPE, LLDPE and milky white material. The plastic film packaging in performance, barrier performance is poor, sterilization temperature does not exceed 90 C, short shelf life; generally used in manual or low-speed filling equipment.
Beautiful designs add color to vacuum bag packaging, among which vacuum bag printing technology contributes a lot. Vacuum bags for food packaging have very strict requirements on hygiene and temperature, and also have special requirements for vacuum bag printing, which are mainly embodied in the following three aspects:
1. Prepress treatment. The surface of plastic film should be treated by electric spark or flame. At present, the solid degree of the free-treatment plastic ink sold in the market has been improved after printing, but the firm degree of the printed product has decreased after 1-2 months.
2. Post-processing. Natural air drying is slow and takes up a lot of space. If a self-made conveyor belt of drying device is available, the efficiency and quality can be greatly improved.
3. Selection of printing materials. Different types of plastics, using different inks. Although all of them are plastic inks, if the wrong type is chosen, the ink of the prints will fall off easily. For example, soft polyethylene ink, soft polypropylene ink, soft polyvinyl chloride ink, etc., the first problem is to identify the type of plastic.
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