Biaxially oriented polypropylene film

Take biaxially stretched polypropylene film as an example.

Biaxially stretched polypropylene film (BOPP) has the advantages of light weight, transparency, non-toxicity, moisture resistance and water resistance, and has good thermal stability, chemical stability and electrical properties, so it is widely used in food, candy, cigarettes, tea, medicine , fruit juice, milk, textiles and other packaging, as well as the production of electrical adhesive tapes are widely used. In recent years, the production of BOPP adopts a new seven-layer co-extrusion technology, so that BOPP can be evenly distributed inside the central gas barrier layer with acrylonitrile-butadiene copolymer, effectively blocking carbon dioxide, water vapor and other corrosive substances The entry of BOPP film greatly increases the anti-corrosion ability of the packaged objects and prolongs the storage period of the items. Therefore, people give this BOPP film with a gas barrier layer the reputation of "Packaging Queen".

1. main raw material

BOPP film is made of isotactic PP as the main raw material, and is made with additive masterbatch with a mass fraction of 3% to 5% according to different products and uses. The raw material should be film-grade PP homopolymer, and should have the following characteristics: ①The melt flow rate is 1.5g/10min~4.0g/10min; ②The isotacticity is 95%~98%; ③Moisture content<0.03%; ④Ash <0.2x10. Additives are auxiliary components for film formation. Generally, erucamide type lubricants, ethylenediamine type antistatic agents and antifreeze agents containing silica particles are used to improve the surface properties of the product.

2. Main equipment and basic process flow

The equipment is mainly manufactured by professional companies with BOPP automatic production lines. Companies that can provide complete sets of BOPP equipment technology include Mitsubishi Heavy Industries (MIT-SUBISHI) and TOSHIIBA in Japan; CELLIER in France; BRUCKNER in Germany, LENZING in Germany and MARSALL in the United States, etc. . Among these competitive technologies, the technologies of Mitsubishi Heavy Industries and Bruckner are more advanced. The technology of Mitsubishi Heavy Industries is characterized by serial twin-screw extrusion and multi-roller cooling molding; Bruckner is famous for multi-machine co-extrusion, twin-cylinder filtration, large-roller water bath chilling, and reasonable use of additives. Mitsubishi Heavy Industries’ tandem twin-screw extrusion has good PP plasticization, uniform and stable pressure, small lateral shrinkage of thick sheets, and good tolerance of thick sheets, but the multi-roll cooling process conditions are narrow, slow cooling, and large-scale high-speed production is limited. Bruckner's multi-machine co-extrusion, using different extruder combinations and matching die heads, can produce glossy film and multi-layer film; adopts double-cylinder filter device, can replace the filter while producing; adopts large roller internal cooling Add water bath for external cooling, so that the molten material can quickly pass through the crystallization temperature zone and be quenched to room temperature, which is conducive to high-speed large-scale production; the additive is used to adjust the formula, the product variability is large, and the film performance is good. However, the rapid cooling in the water bath causes shrinkage on both sides of the thick sheet, and the product tolerance is affected. The technologies of Mitsubishi Heavy Industries and Bruckner represent two different forming processes that coexist and develop today. But no matter which company's technology, the production of BOPP film is carried out according to the following basic process flow, that is, PP→extrusion-filtration-die forming→quick cooling cast sheet→thick sheet thickness measurement→longitudinal stretching→horizontal stretching → Trimming → Film thickness measurement → Corona treatment → Winding → Aging treatment → Slitting and packaging.