How should the production process of biaxially oriented polyethylene terephthalate (BOPET) film be controlled?

How should the production process of biaxially oriented polyethylene terephthalate (BOPET) film be controlled?

① Generally, for biaxially oriented films, PET resin with an intrinsic viscosity of 0.62 to 0.65 is preferred, and the minimum should not be lower than 0.57.
② Before processing the resin, it must be dried to control the moisture content below 0.005% to prevent degradation of the resin during extrusion and plasticization in the presence of trace amounts of water.
③ The extrusion temperature of the material is generally controlled below 280°C. The melt after extrusion and plasticization should be mixed through coarse and fine filters and a static mixer, and then conveyed to the die by a metering pump. The extruded thick sheet should be rapidly cooled by a cooling roller to maintain an amorphous state, facilitating stretching.
④ The preheating temperature for longitudinal stretching of the film is 85 to 95°C, the stretching temperature is 95 to 110°C, and the stretching ratio is 2.4 to 4.0 times.
⑤ The preheating temperature for transverse stretching is 95 to 100°C, the stretching temperature is 100 to 110°C, and the stretching ratio is 2.4 to 4 times.
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