Extrusion & Post
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PPA reduces the film breakage rate in BOPP film
Problembeschreibung
During the machine direction orientation (MDO) process of BOPP biaxially oriented film, film breaks occur frequently, with the film breakage rate reaching 8% (normal <2%), and the capacity loss caused by shutdown cleaning and re-threading of the film is serious.
Ursachenanalyse
Insufficient PPA addition causes microscopic defects (microcracks/uneven thickness) on the sheet surface at the die exit to become the starting points of stress concentration during stretching; the dispersion of PPA in the PP resin is insufficient so that some areas have no coating protection; the machine direction orientation temperature (110-130°C) does not match the thermal stability of the PPA fluoropolymer coating, leading to failure; the sheet edge effect is intensified.
Lösung
Increase the PPA addition to 0.04-0.06% and ensure sufficient pre-dispersion in the extruder; select a high-temperature-resistant PPA (service temperature >250°C) to ensure the coating is effective at the machine direction orientation temperature; optimize the extruder temperature distribution to help PPA coat the metal surface earlier; install heating devices on the sheet edges to reduce edge stress concentration.
Wichtigste Erkenntnis
An effective PPA coating is the key to ensuring uniform stretching of the BOPP sheet and reducing the film breakage rate.
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