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Qingdao Advanmatch Packaging’s multi-layer co-extruded composite film is generally divided into base layer, functional layer and adhesive layer according to the function of each layer of the film regardless of the number of layers.
Base layer: Generally, the inner and outer layers of the composite film which should have good physical and mechanical properties, molding and processing properties and thermal sealing layer. It has good heat-sealing performance and heat welding performance with relatively low cost. Meanwhile, it also has good support and retention effect on the functional layer and the highest proportion in the composite membrane which determines the overall rigidity of the composite membrane. The base material is mainly PE, PP, EVA, PET and PS.
Functional layer: The coextrusion functional layer of packaging film is mostly barrier layer, which is generally the middle of multi-layer composite film. It mainly uses barrier resins such as EVOH, PVDC, PVA, PA, PET, etc. Among them, the most commonly used high barrier materials are EVOH and PVDC, and the common PA and PET have similar barrier properties, belonging to medium barrier materials.
Ethylene-vinyl alcohol copolymer is a kind of polymer material that integrates the processability of ethylene polymer and the gas barrier of ethylene alcohol polymer. It is highly transparent and has good gloss. EVOH has excellent barrier against gas and oil. Its mechanical strength, flexibility, wear resistance, cold resistance and surface strength are excellent and it has excellent processing performance. The barrier property of EVOH depends on the content of ethylene. Products packed with EVOH materials include condiments, dairy products, meat products, cheese products, etc.
Polyvinylidene chloride is a polymer of vinylidene chloride (1,1-dichloroethylene). The decomposition temperature of homopolymer polyvinylidene chloride is lower than its melting point, so it is difficult to melt. Therefore, PVDC as a packaging material is a copolymer of vinylidene chloride and vinyl chloride which has good gas tightness, corrosion resistance, good printing and heat-sealing characteristics. At the beginning, it was mainly used for military packaging. But it began to be used as food preservation film in the 1950s. Especially the quick-freezing and fresh-keeping packaging which was developed in large quantities with the acceleration of modern packaging technology and the pace of modern people's life, the revolution of microwave cookers and the extension of the shelf life of food and medicine which made the application of PVDC more popular. PVDC can be made into extremely thin film, thus reducing the amount of raw materials and packaging costs, It still prevails today.
Due to the poor affinity of some base resins and functional layer resins, it is necessary to place some adhesive layers between these two layers to play the role of glue, so as to form an "integrated" composite film. The adhesive layer uses adhesive resin, commonly used are maleic anhydride grafted polyolefin and ethylene-vinyl acetate copolymer (EVA).
Multi-layer co-extruded film characteristics:
1. High barrier property: The use of multilayer polymer instead of monolayer polymerization can greatly improve the barrier property of the film and achieve the high barrier effect of oxygen, water, carbon dioxide, odor, etc. Especially when EVOH and PVDC are selected as barrier materials, their oxygen transmission and water vapor transmission are obviously very low.
2. Strong function: Due to the wide selectivity of multilayer film in the application of materials, a variety of resins can be selected according to the application of useful materials are fully reflecting the functions of different levels, so as to enhance the functionality of co-extrusion film, such as oil resistance, moisture resistance, high temperature cooking resistance, low temperature cold freezing resistance. It can be used for vacuum packaging, sterile packaging and inflatable packaging.
3. Low cost: Compared with glass packaging, aluminum foil packaging and other plastic packaging are able to achieve the same barrier effect. At the same time, co-extruded film has greater advantages in cost. For example, in order to achieve the same barrier effect, the seven-layer co-extruded film has greater advantages in cost than the five-layer co-extruded film. Due to its simple fabrication, the cost of the film products produced can be reduced by 10-20% compared with the cost of dry composite film and other composite films.
4. Flexible structure design: adopt different structure design to meet the quality assurance requirements of different products.