Most thermoplastics can be blown to produce blown film. The blown film is a cylindrical film product obtained by extruding the plastic into a thin tube, then blowing the plastic with compressed air while it is hot, and then cooling and shaping. The performance of this film is between the orientation film and the casting film: the strength is better than the casting film, and the heat sealing property is worse than the casting film. There are many kinds of films produced by blow molding, such as low-density polyethylene (LDPE), polypropylene (PP), high-density polyethylene (HDPE), nylon (PA), ethylene vinyl acetate copolymer (EVA), etc. Here we will discuss the blowing production process of commonly used low-density polyethylene (LDPE) films and its common
Briefly introduce the fault.
Selection of polyethylene blown film materials
1. The selected raw materials shall be blown film grade polyethylene resin particles, containing an appropriate amount of smooth agent to ensure the opening of the film.
2. The melt index (MI) of the resin particles cannot be too large. If the melt index (MI) is too large, the viscosity of the molten resin is too small, the processing range is narrow, the processing conditions are difficult to control, the film forming property of the resin is poor, and it is not easy to process the film; In addition, the melt index (MI) is too large, the relative molecular weight distribution of the polymer is too narrow, and the strength of the film is poor. Therefore, resin raw materials with small melt index (MI) and wide relative molecular weight distribution should be selected to meet the performance requirements of the film and ensure the processing characteristics of the resin. Polyethylene raw materials with a melt index (MI) of 2-6g / 10min are generally used for blowing polyethylene films.
Key points of blow molding process control
The process flow of blown film is as follows:
Hopper feeding - material plasticization and extrusion → blowing and traction → air ring cooling → herringbone splint → traction roller traction → corona treatment → film winding
However, it is worth pointing out that the performance of blown film has a great relationship with the production process parameters. Therefore, in the process of blowing film, it is necessary to strengthen the control of the process parameters, standardize the process operation, ensure the smooth production and obtain high-quality film products.
