Key points for the process operation of extrusion casting method for forming thin films:
1) When using extrusion casting method to form films for PP, PE, and PA6 resins, the temperature control of the plasticization process should gradually increase from the feeding section of the barrel. The temperature on the forming mold body should be higher at both ends than at the middle. However, attention should be paid to the impact of melt temperature on product quality: when the melt temperature is high, the surface roughness value of the formed film is small, and the transparency is high; But when the temperature of the molten material exceeds 290 ℃ (referring to PP material), the impact strength of the product tends to decrease, and the molten material is prone to decomposition.
2) The temperature control of the cooling and shaping roller should be as low as possible, which is beneficial for the surface glossiness and transparency of the product.
3) The distance between the cooling and shaping roller of the cast film and the lip of the mold should be adjusted in a timely manner when the cast film is extruded normally. The size of this distance dimension has a significant impact on the quality of film shaping and the variation of film width, and the maximum distance should not exceed 10mm.
4) The gap between the jet ports generally does not exceed 2. 5mm, if the gap is too large, it will also increase the turbidity of the film; The compressed air pressure at the jet port is controlled at 0. 4~0. Within the range of 6MPa.
5) The cast film used for printing should undergo corona treatment during the production process to ensure printing quality.
6) A certain proportion of anti-static agent or anti-static agent coated on the surface of the film should be added to the material used for automatic rapid packaging of extrusion casting formed films.
7) When the molten material of the cast film flows onto the cooling roller surface, it must be in full contact with the roller surface. There must be no gaps or air between the film surface and the roller surface, otherwise it will affect the appearance quality of the film.
8) The working surface of the cooling roller must be kept bright and clean, without any dirt or volatile substances, otherwise it will affect the surface quality of the finished film and the cooling effect of the cast film.
9) The operating speed of the cooling roller should be stable and adjustable, matching the speed of the molten material flowing from the mold mouth during operation, in order to ensure the stability of the film thickness and width size during production and operation.
10) The cooling rate has a significant impact on the quality of the cast film, such as the rapid cooling of the cast film on the cooling roller (referring to PP and PE films), which can accelerate its crystallization rate. If the crystallinity is small, the product will be soft, transparent, and the tensile strength will also be improved.