With the progress of society and the continuous growth of human needs, various functional and environmentally friendly packaging films continue to appear. For example, water-soluble polyvinyl alcohol film, which is environmentally safe, completely degradable, and has good heat-sealing performance, is being developed not only as a single-layer packaging material, but also as an inner layer film. So what are the types of raw materials used in the composite plastic packaging bags we have seen?
LDPE, LLDPE resins and films
my country's composite film started in the late 1970s. From the early to mid-1980s, my country began to introduce some extruders, blown film machines and printing machines to produce simple two-layer or three-layer composite materials. Such as extrusion composite BOPP/PE, paper/PE, pp/PE; dry composite BOPP/PE, PET/PE, BOPP/AL/PE, PET/AL/PE, etc., among which LDPE resin and film, often A certain proportion of LLDPE is blended to enhance its strength and stiffness. It is mainly used in the packaging of instant noodles, biscuits, mustard and other foods. General coating grade LDPE resins include: IC7A, L420, 19N430, 7500, etc.; blown film grade LDPE resins include: Q200, Q281, F210-6, 0274, etc.; LLDPE resins include: 218w, 218F, FD21H, etc.
CPP film, CPE film
From the late 1980s to the early 1990s, with the introduction of a new generation of flexible packaging equipment and casting equipment, the scope of packaging contents was further expanded. Some puffed food, oatmeal and other packaging bags require high transparency, while boiling, high temperature, etc. Sterilization products have come to the market one after another, and the requirements for packaging materials have also increased accordingly. The inner layer materials mainly based on LDPE and LLDPE can no longer meet the requirements of the above products. Produced by casting method has good heat sealability. CPP with oil resistance, transparency, fragrance retention, and special low-humidity heat-sealing and high-temperature cooking properties are widely used in packaging. The aluminum-coated CPP developed on this basis is rapidly and widely used because of its metallic luster, aesthetics, and barrier properties. And the CPE film produced by the casting method is being further used because of its one-way easy tearability, low temperature heat sealing, and good transparency.
MLLDPE resin
With the continuous development and changes of the packaging market, there are more and more special requirements for packaging. DOW Chemical Company of the United States produced metallocene polyethylene MLLDPE by metallocene-catalyzed polymerization. Such as APFINITY, POP1880, 1881, 1840, 1450 and other resins. Then Exxon in the United States. Mitsui in Japan and Philips in the United States have also successively produced MLLDPE. Such as EX-CEED350D60, 350D65 of Exxon, E-VOLVE SP0540, SP2520 of Mitsui Petrochemical, MPACT D143 and D139 of Philips, etc. Because MLLDPE has good blending and easy processability with LDPE and LLDPE, MLLDPE can be mixed in film blowing or casting processing, and the mixing ratio can be from 20% to 70%. This kind of film has good tensile strength, impact strength, good transparency, good low-temperature heat sealing and anti-pollution properties. The composite material with it as the inner layer is widely used in frozen, refrigerated food, shampoo, Oil, vinegar, soy sauce, detergent, etc. It can solve the packaging speed, broken package, leaked package, penetration, etc. of the above-mentioned products in the process of packaging production and transportation.
Inner layer material
Packaging cups for jelly, juice, yogurt, fruit milk, soup and other liquids. Bottle, its main material is HDPE. PP, PS, etc. The cover film of this package should not only consider the shelf life, but also consider the heat seal strength between the cover film and the cup, and also consider the convenience of consumers-ease of tearing. To achieve this particularity, the inner layer material can only form an interface bonding strength with the cup sun, but cannot completely penetrate and fuse together. Generally, modified EVA resin is used. Such as the United States DuPont APPEEL53007. TOPCO L-3388 from Toyo Japan, LOTRYL 20MA 08 from France, WT231 from HIRO.DINE from Japan, etc. Its structure can be: PET/PE/HM, BOPA/PE/HM, PET/VMPET/PE/HM, PET/AL/PE/HM, paper/PE/AL/PE/HM. For the requirement that the cover film and the bottom cup should be firmly covered without tearing, it is generally required that the material of the bottom cup is consistent with the inner material of the cover film, so that the two materials can be completely fused when heat-sealed. For example, for HDPE cups, the inner material of the cover film is: LDPE or EAA; for PP cups, the inner layer of the cover film is CPP film; for PET bottles, we have found a modified PET film as the heat-sealing layer. Capping pesticide PET bottles has achieved satisfactory results.
Co-extruded film
Films produced by blending single-layer LDPE or LDPE with other resins have single performance and cannot meet the packaging requirements of modern article development. Therefore, co-extrusion films produced by co-extrusion blown film or co-extrusion casting equipment have improved overall performance. . For example, the comprehensive performance of the film such as mechanical strength, heat sealing performance, heat sealing temperature, barrier property, opening property, and anti-pollution property is improved, and its processing cost is reduced, so it is widely used. Such as H-layer co-extrusion blown film hot melt adhesive film: PE/HM, cable film PE/EAA, low-temperature heat-sealing film of MLLDPE, EVA cover film, antistatic film, and slippery film. H-layer co-extruded co-extruded CPP, non-modified PP/heat-sealable PP, etc. Three-layer and five-layer nylon co-extruded films, five-layer and seven-layer EVOH and PVDC high barrier films are also being developed and widely used.
The development of the inner layer film of composite flexible packaging materials, from the extensive use of LDPE, LLDPE, CPP, MLLDPE, and co-extruded films, basically realizes the functionalization and individualization of packaging, and meets the quality assurance, processing performance, transportation and storage conditions of the packaging contents. With the continuous introduction of new materials and the improvement of inner film production technology and equipment, the inner film of composite flexible packaging materials will surely develop rapidly and promote food.