8 structural types of commonly used films

　　1. Single film:

　　It is required to be transparent, non-toxic, impermeable, with good heat sealing and bag making properties, heat and cold resistance, mechanical strength, grease resistance, chemical resistance and adhesion resistance. It can be prepared by extrusion blowing, extrusion tape casting, calendering, solvent tape casting and other methods.

　　The heat sealing performance of the monolayer film is not only related to the relative molecular weight distribution and molecular disproportionation of the resin, but also related to the process conditions during film preparation, such as temperature, cooling rate, blowing ratio, etc.

　　2. Aluminum foil:

　　99.5% pure electrolytic aluminum is melted and pressed into foil by calender, which is ideal as the base material for soft plastic packaging. It has good gas barrier, water vapor barrier, light shielding, thermal conductivity and shielding.

　　3. Vacuum evaporation aluminum film:

　　Under high vacuum, the metal with low boiling point, such as aluminum, is melted, vaporized and stacked on the plastic film on the cooling drum to form an aluminized film with good metallic luster. When the aluminum plating thickness reaches certain requirements, the oxygen resistance and moisture resistance of the substrate can be greatly improved. The substrate shall be corona treated and coated with sol.

　　4. Silicon coating:

　　It is also called ceramic coating. No matter how high the temperature and humidity are, the performance will not change. It is suitable for making high-temperature cooking bags. There are two kinds of coatings: one is silicon oxide SiOx, the smaller the X is, the better the barrier is; The second is Al2O3. The coating methods include physical evaporation and chemical evaporation.

　　5. Gluing (dry/wet) composite film:

　　Single layer films have certain advantages as well as inherent disadvantages. They are often difficult to meet a variety of packaging performance requirements. Multiple layers of different substrates can complement each other and give full play to their comprehensive advantages.

　　6. Extrusion coating composite film:

　　On an extruder, thermoplastic is streamed on the paper, foil, and plastic substrate to be covered through a T-shaped die, or the extruded resin is used as the intermediate binder, and other film substrates are pressed together while hot to form a sandwich type composite film.

　　In order to improve the composite fastness, it is necessary to conduct corona treatment and apply anchor paint. The extruded composite film can be reverse printed, the thickness of each layer can be precisely controlled, the residual amount of solvent is small, and the price is cheap.

　　7. Co extruded composite film:

　　Two or three extruders are used to use a common composite die to laminated several compatible thermoplastics to produce multilayer films or sheets. Co extruded composite film can only be printed on the front, not on the back.

　　It is difficult to control the thickness of each layer compared with dry composite film and extruded cast film. No adhesive and anchor paint are used, which is pollution-free and sanitary. Co extruded composite membrane has the lowest cost.

　　8. High barrier film:

　　It is a multilayer structure film. It can effectively prevent the infiltration of oxygen and other gases, thus causing the propagation of microorganisms; Prevent the wrapped articles from oxidation; Prevent the outflow of fragrance, solvent, etc.

　　The commonly called high barrier and high-strength materials, such as EVAL, PVDC, PET, PAN, self PA, can be made into packaging films, which can significantly extend the shelf life of food, or replace the traditional rigid packaging materials with good barrier performance.

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