After the raw materials are determined, as long as the processing temperature, die gap, film cooling, inflation ratio, traction ratio and other parameters are controlled well, the production can be more stable and qualified films can be obtained.
- Process control of low-density polyethylene blown film
The processing temperature of low-density polyethylene blown film is the core of process control. According to the general temperature setting principle, the temperature of the screw feeding section cannot be lower than the softening point of polyethylene, but not too high. If it is too high, it will cause heat conduction and cause the resin at the feeding port to soften and block the feeding port, preventing the material from entering. The temperature of the compression section should be controlled above the melting temperature of the resin to fully melt and plasticize the material. The temperature of the homogenization section can be equal to or lower than that of the compression section to ensure that the material is homogenized in this section. The temperature of the three-way valve should be the same or slightly higher than that of the homogenization section, and the head temperature should be slightly lower than that of the homogenization section. This can increase the internal pressure of the extruder and make the material denser. - Process control of high-density polyethylene blown film
(1) Blow molded high-density polyethylene resin is divided into two types: one is ultra-high molecular weight high-density polyethylene (HMWHDPE), which has a melt flow rate of about 0.05g/min and high longitudinal and transverse strength when made into thin films. Another type is commonly used high-density polyethylene (HDPE), with a melt flow rate of about 1g/10min, resulting in relatively low transverse strength of the film. Currently, manufacturers use linear low-density polyethylene resin to blend and significantly improve the strength of the film.
(2) The processing temperature of high-density polyethylene is relatively higher than that of low-density polyethylene, and the extrusion molding process temperature adopts a flat curve.
(3) Due to the high cold curing line, high inflation ratio, and poor foam stability in the production of high-density polyethylene film, it is necessary to have a corresponding foam stabilization device in order to obtain qualified products. The foam stabilization device can be divided into an outer foam stabilization ring and an inner foam stabilization rod. Currently, the inner foam stabilization rod is commonly used, as shown in Figure 3-8. The foam stabilization rod is a metal cylinder connected to the core rod, and the material of the cylinder can be washed with aluminum alloy or steel. A layer of coarse cloth is wrapped around the cylinder.
