Production and compounding of the most fire-resist

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Production of impermeable plastic packaging film

generally, impermeable materials are not used alone due to the limitations of their own characteristics or price factors. In order to meet the requirements of different commodities for impermeability, soft plastic packaging has developed from the production of single-layer film to multi variety and multi-functional composite packaging film. At present, there are four kinds of composite technologies of impermeable plastic packaging film used most commonly: dry composite method, coating composite method, coextrusion composite method and evaporation composite method. The dry compounding method uses various sheets or films as the base material, and it starts in front of others. The gravure roller is coated with a layer of adhesive on the surface of the base material, and then pasted on the compounding roller after drying and tacking. This is the most commonly used production method of composite membrane in China at present. The characteristic of dry compounding is that the foam granulator has a wide range of adaptability, and the proper adhesive is selected. Any sheet or film material can be compounded, such as PE film, PP film, PET film, PA film, etc., and the compounding strength is high and the compounding speed is fast. However, among these methods, dry compounding has the highest cost. In addition, due to the use of adhesives, there are solvent residues and environmental pollution problems

the process of coating and compounding is relatively simple. Coating and compounding can be used for barrier resins that are difficult to be processed into films alone, such as PVA, PVDC, etc. The melting temperature of PVA is 220 ℃ ~ 240 ℃, and the decomposition temperature is 200 ℃. To process into a film, plasticizers and stabilizers need to be added to increase the thermal decomposition temperature and reduce the melting temperature

the equipment and technology for producing PVA series polymer films are very expensive. For the same reason, PVDC is difficult to form film alone. Therefore, at present, the more mature technology for the use of PVA and PVDC is the coating process. PVA is water-soluble. In practice, a mixture of water and ethanol is used as solvent to coat a layer of PVA on PE or PP film. Due to the poor water resistance of PVA, the method of adding crosslinking agent to PVA solution can be adopted to improve its water resistance, and at the same time, the adhesion between PVA and PE, PP can be improved, so the primer is omitted. For the convenience of bag making, PE or PP film coated with PVA can be dry compounded with other films to form a composite film coated with PVA/PE (or PP)/LDPE structure. Next, let's take a look at the specific installation steps of the fixture of the tensile testing machine. This film has good permeability resistance, better vacuum pumping effect and lower cost than p LDPE. PVDC used for coating is a copolymer of vinylidene chloride and acrylate monomer through lotion polymerization. After adding appropriate solvents and additives, it is coated on cellophane, BOPP, nylon and polyester to make it have good moisture and gas resistance and heat sealing performance. The biggest problem of PVDC is its safety and hygiene

coextrusion compounding method is a technology that uses multiple extruders to produce multilayer composite films through a compounding head with multiple channels. This method has high requirements for equipment, especially for head design and process control. In recent years, with the maturity of machining and manufacturing technology, coextrusion composite method has developed rapidly, and it can be produced from the earliest two-layer to the present nine layer composite film. According to the functional needs, different materials can be selected, such as the last typical 7-layer composite film, whose core layer is EVOH, sandwiched between two layers of nylon film, which improves the barrier performance and reduces the thickness of the film. The outer layer uses adhesive compound PE or EVA as the heat sealing layer, which ensures the need of packaging and reduces the cost. According to relevant investigations, coextrusion packaging films in developed countries account for 40% of the whole flexible plastic packaging materials, while China accounts for only 6%. Therefore, multi-layer coextrusion technology will have great application space in China. With the development of film surface printing inks and the improvement of surface printing technology, it is expected that the coextrusion composite technology will get greater development. In terms of technology, coextrusion composite includes coextrusion film blowing and coextrusion tape casting

according to the introduction of W H company, the blown film production line used to produce multi-layer (3-layer, 5-layer, 7-layer) barrier composite films has a maximum output of 1000kg/h. Under the condition of meeting the functional needs, the ultra-thin film saves resources, reduces packaging waste, and meets the requirements of environmental protection. Thanks to the new technology, the bubbles are more stable and the control of film thickness deviation is more accurate. At present, China has also developed a 5-layer co extrusion barrier film blowing equipment, but its products are generally suitable for the needs of the low-end market. Another process of coextrusion composite method is coextrusion casting. The cast film is a kind of non stretching flat extruded film produced by the sudden cooling of polymer melt on the cooling roller through T-type slotted die. The production of cast film in China began with the introduction of single-layer cast production lines from Japan and Germany in the 1980s, and three layers were introduced in the mid-1990s, an increase of 10% over the same period in 2017 (2) 1%; It is estimated that the net profit attributable to the parent company after deducting extraordinary profits and losses is 7.5 million yuan (0.13 million yuan) or 5-layer co extrusion casting equipment. Production lines with 7-layer and 9-layer film structures have appeared abroad. At present, there are nearly 50 casting film production lines in China. In recent years, due to the rapid development of multi-layer coextrusion blown film, the demand for cast film is relatively weak. However, with the development of new materials and the use of new equipment, the production efficiency has been improved, the types of products have been increased, and new application fields have been continuously expanded. The manufacturing of cast film is entering a new round of investment boom

evaporation composite method is a technology that takes organic plastic film as the substrate and combines with inorganic materials. The dense inorganic layer can give the material excellent barrier performance. The most typical evaporation composite is vacuum aluminum plating technology. Under the condition of high vacuum, the aluminum wire is melted and evaporated at high temperature, and the aluminum vapor precipitation is concentrated on the surface of the plastic film to form a barrier layer with a thickness of about 35 ~ 40nm. The plastic as the base material can be PE, PP, pet, PA, PVC, etc. Vacuum aluminized film has excellent impermeability. Under the condition of not requiring transparent packaging, aluminized film is the best choice. Although the aluminized layer is very thin, its impermeability reaches 0.1g/MH moisture permeability and 0.1cm oxygen permeability M for 24h, its impermeability is not affected by humidity. The aluminized film has good fragrance retention, metallic luster and beautiful decoration, but it is opaque, the contents of the package are not intuitive, and the bending resistance is poor. It is easy to produce pinholes or cracks after kneading, thus affecting the permeability resistance. In order to improve the shortcomings of aluminum coating, one of the latest technologies is to coat silicon oxide (SiOx) on plastic film, in which SiOx is a mixture of Si, O and Si O. physical deposition method and chemical deposition method can be used in the process. The inorganic layer coated with silicon oxide film is dense, with a thickness of only 0.05 ~ 0.061 u m, and its permeability resistance is better than that of common coextrusion film and PVDC coating film. In addition, it also has good transparency, kneading resistance, acid and alkaline resistance, excellent printability, and is suitable for use in microwave ovens, with little residue from combustion treatment. In addition to SiOx, MgO, TiO and other raw materials can be used for evaporation

nanotechnology also plays a unique role in the research of new barrier plastic packaging materials. Bayer of Germany and Nan ℃ ol of the United States dispersed nano-sized modified silicate clay in PA matrix to make a film material with good barrier property. Using microcrystalline coating process, nano wollastonite and silicon dioxide were coated on the surface of BOPP, pet and PA films, and high resistance and permeability films with excellent properties were developed

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