What is the production process of ordinary polyethylene film?

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What is the production process of ordinary polyethylene film?

(1)Production process. The flat extrusion blowing process is adopted, and the process is shown in Figure 6- As shown in Figure 30, polyethylene resin is added into the hopper of the extruder, and the tube blank is extruded by the die of the machine head through screw plasticization. After blowing and air cooling, it enters the traction roller through the splint, then take it up after passing through several guide rollers.

(2)Production process. Ordinary polyethylene film is produced by flat extrusion and blowing.

(3)Key points of process operation.

① temperature. Temperature control is the key in film production, which directly affects product quality. There are two kinds of temperature control conditions. One is that the temperature gradually rises from the feeding section of the machine body to the outlet of the Machine Head; The other is the highest temperature in the middle and front sections of the fuselage, and the temperature of the nose is lower. If ordinary polyethylene film is produced by an extruder with Beat 5mm, length-diameter ratio 20:1 and compression ratio 3:1, the extrusion temperature is controlled as follows: 140- 150 ℃, middle 170- 180 ℃, front section 180 ~ 190 ℃, head 180 ℃ or so.

② blowing and traction of membrane tube. The molten material is extruded from the die to form a tube blank, which should be blown up immediately, stretched transversely, and stretched longitudinally under the action of the traction roller, therefore, the molecular chain has orientation effect in vertical and horizontal directions, and the orientation degree has a significant influence on the strength of the film, with high orientation degree and high strength; The degree of orientation is low and the intensity is small. In order to prepare films with equal longitudinal and transverse strength, the transverse blowing ratio ( Ratio of film tube diameter to die diameter after blowing)Compared with longitudinal drafting ( The ratio of the linear velocity of the traction membrane pipe to the linear velocity of the untraction extruded membrane pipe) It is better to be the same. In actual production, the head die of the same specification is usually used to make films with different thicknesses and widths by adjusting the blowing ratio and drawing ratio. The inflation ratio is usually controlled (1. 5-3): 1, the blowing ratio is too small, the lateral strength is low; The inflation ratio is too large, the film tube is unstable, and the film diameter and thickness are uneven. Drafting ratio is generally controlled (3-7) : 1, the drafting ratio is too small, the physical and mechanical properties are poor, and the drafting ratio is too large, and the membrane tube is easy to be broken.

③ cooling and setting. After the film is extruded from the nose, it is immediately cooled by air. If the cooling effect is not good, the film is sticky and cannot be lifted, so cooling and setting is an important link. In order to improve the output, double air ring cooling method can be adopted, while the more advanced cooling method is film internal cooling method.