Key points of blown film process

日期:2021/10/11 8:32:16 / 阅读: / 来源:本站

Key points of blown film process

      After the raw materials are determined, as long as the processing temperature, die gap, film cooling, expansion ratio, traction ratio and other parameters are well controlled, the production can be stabilized and qualified films can be obtained.
      1. Low-density polyethylene blown film process control
      The processing temperature of low-density polyethylene blown film is the core of process control. According to the common temperature setting principle, the temperature in the feeding section of the screw cannot be lower than the softening point of polyethylene, but not too high. Excessive heat conduction will cause the resin to be heated at the feeding port. Soften and block the feed inlet, so that the material cannot enter. The temperature of the compression section should be controlled above the melting temperature of the resin to make the material fully melted and plasticized. The temperature of the homogenization section can be equal to or lower than the temperature of the compression section to ensure that the material is homogenized in this section. The temperature of the tee is the same as or slightly higher than that of the homogenization section, and the temperature of the die head should be slightly lower than that of the homogenization section, which can increase the internal pressure of the extruder and make the material dense.
     2. Process control of high-density polyethylene blown film
      (1) Blow molding grade high-density polyethylene resin is divided into two types: one is ultra-high molecular weight high-density polyethylene (HMWHDPE) with a melt flow rate of about 0.05g/min, and the film has high vertical and horizontal strength. The other is high-density polyethylene (HDPE) for general use. The melt flow rate is about 1g/10min. The lateral strength of the film is relatively low. At present, manufacturers use linear low-density polyethylene resin to blend and use. The strength of the film is significantly improved.
     (2) The processing temperature of high-density polyethylene is relatively higher than that of low-density polyethylene, and the temperature of the extrusion molding process adopts a flat curve type.
     (3) Because the production of high-density polyethylene film has a high cold-setting line, a large blow-up ratio, and poor bubble stability, it is necessary to have a suitable bubble stabilization device to obtain qualified products. The foam stabilizing device can be divided into an external foam stabilizing ring and an internal foam stabilizing rod. At present, the internal stabilizing foam rod is usually used. The internal foam stabilizing rod is shown in Figure 3-8. The material of the cylinder can be washed with aluminum alloy or steel, etc., and a layer of coarse cloth is wrapped around the cylinder.

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