PE protective film is a common plastic product in our days. It is produced by calendering process, extrusion process, blow molding process and other methods. The method of film blow molding is to melt and extrude the plastic material into a thin pipe through the extruder, then blow it with compressed air while it is hot, and then cool it to form a film product.

The main materials used for blow molding film are LDPE, HDPE, LLDPE, EVA, PVC, PP, PS, PA, etc.

Molding process of polyethylene blown film

After the material is plasticized and extruded, it forms a tube, and then carries out blow molding, cooling, traction and coiling.

In the process of blow molding film, there are three methods: flat blowing, up blowing and down blowing according to the different extrusion and traction directions. This is a common molding process, and there are also special blow molding methods, such as extrusion and up blowing. Let's see the differences between these methods.

1、 [flat extrusion and upward blowing method] this method is to use a right angle head, that is, the discharge direction of the head is straight with the extruder, the extrusion pipe is broken and upward, and after being pulled to a certain interval, it is clamped by a herringbone plate. The extruded tube is inflated into a bubble tube by the compressed air introduced from the bottom, and its transverse dimension is controlled by the amount of compressed air, and its longitudinal dimension is controlled by the traction speed. After the bubble tube is cooled and shaped, the blown film can be obtained. The main types of plastics suitable for the up blowing method are PVC, PE, PS and HDPE protective films.

2、 [flat extrusion and blow down method] this method uses a right angle machine head, and the process of bubble tube leading out from under the machine head is called flat extrusion and blow down method. This method is especially suitable for materials with low viscosity and plastic films requiring high transparency. Such as PP, PA, PVDC (vinylidene chloride).

3、 [flat extrusion and flat blowing method] this method uses a flat head concentric with the screw of the extruder, and the process that the bubble tube and the center line of the head are on the same horizontal plane is called flat extrusion and flat blowing method. This method is only applicable to the products of blowing small-diameter films, such as LDPE, PVC and PS films. The flat blowing method is also applicable to the production of blowing heat shortened films.

The above three processes have their own advantages and disadvantages. Now, compared with the advantages of the process flow, the defects are flat extrusion, the bubble blowing pipe is hung on the cooling pipe, the traction is stable, the floor area is small, the operation is convenient and easy to produce, the folding diameter is large, the protective film with thick thickness requires high workshop and high cost, which is not suitable for processing plastic with high fluidity, which is not conducive to the cooling of the protective film, and the production efficiency is low. Flat extrusion and blow down are conducive to the cooling of the protective film The plastic extruder with high production efficiency can process plastic with high fluidity, which is higher from the ground and inconvenient to operate. It is not suitable to produce thin protective film. The flat extrusion and flat blowing head is central, simple structure, uniform protective film thickness, convenient to operate, simple film introduction, and large expansion ratio. It is not suitable to process protective film with large relative density and large folding diameter. It covers a large area and the bubble tube cools slowly. It is not suitable to process plastic with high fluidity.