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PE protective film is a common plastic product in our life. It is produced by calendering process, extrusion process, blow molding process, etc. The method of film blow molding is to melt and extrude the raw material through an extruder. The thin tube is then inflated with compressed air while it is still hot, and then cooled and shaped into a film product.
The main materials used for blow molding film are: LDPE, HDPE, LLDPE, EVA, PVC, PP, PS, PA, etc.
Polyethylene blown film forming process
After the material is extruded through plasticization, it is formed into a tube shape and then inflated, cooled, pulled and coiled.
In the blown film forming process, there are three methods of flat blowing, top blowing and bottom blowing according to the different extrusion and pulling directions. This is a commonly used forming process and there are also special blow molding methods, such as the top extrusion and top blow method. Let's take a look. See how these methods differ.
1. [Flat extrusion and blowing method] This method is to use a right-angle head, that is, the discharge direction of the head is straight with the extruder, and the extrusion tube is broken upward. The compressed air introduced from the bottom of the tube will inflate it into a bubble tube, and its lateral dimension is controlled by the amount of compressed air, and its longitudinal dimension is controlled by the pulling speed. After the bubble tube is cooled and shaped, a blown film can be obtained. The main types of plastics suitable for the blow-up method are PVC, PE, PS, HDPE protective films.
2. [Flat extrusion down blowing method] This method uses a right-angle head, and the process in which the bubble tube is drawn from the bottom of the head is called flat extrusion down blowing method. This method is especially suitable for materials with low viscosity and plastic films that require high transparency. Such as PP, PA, PVDC (vinylidene chloride).
3. [Flat extrusion and flat blowing method] This method uses a straight head that is concentric with the extruder screw. The process in which the bubble tube and the center line of the head are on the same level is called the flat extrusion and flat blowing method. This method is only suitable for blowing small For products of caliber film, such as LDPE, PVC, PS film, the flat blowing method is also suitable for the production of blown thermally shortened film.
The above three technological processes have their own advantages and disadvantages. Now comparing the advantages and disadvantages of the above-mentioned technological process The film requires high workshop and high cost. It is not suitable for processing plastics with high fluidity. It is not conducive to the cooling of the protective film. High, and inconvenient to operate, it is not suitable to produce thinner protective films. The flat extrusion and blowing head is a central type, with a simple structure, and the thickness of the protective film is relatively uniform. The protective film with large diameter covers a large area and the cooling of the bubble tube is slow, which is not suitable for processing plastics with high fluidity.
