What is the principle of cast film forming and flat film extrusion?
The casting film forming principle is that the plastic melt is extruded through a T-die in an extruder, directly into an aqueous solution or a chill roll, and after cooling and drawing, a cast film is obtained. This processing method can fully exert the performance of the material being processed while maintaining the best dimensional accuracy. Most thermoplastic films can be produced by casting. Especially suitable for semi-crystalline thermoplastics. The forming principle of flat film extrusion is: extruding a plastic melt which has been plasticized uniformly in the extruder from a flat film head, cooling and solidifying by contact with a cooling roll, and finally cutting into a film of a certain width and winding into a film. volume. The structure of each layer of the coextruded film may be symmetrical or asymmetrical. When the adhesion between the two films is not good, it is necessary to add a thin bonding layer between the two layers to improve the heat. Sealing properties and boundary adhesion properties. There are three types of co-extrusion heads for flat and cast film, namely multi-channel co-extrusion heads, co-extrusion heads with feed blocks, and a combination of multi-flow heads and feed blocks. Extruder head. (1) Multi-channel co-extrusion head: The melt extruded by several extruders flows into the split channel of the set width and thickness from the feed end of the head with multiple channels, and the melt of each layer Composite molding in the nose of the machine. With this method, one can select a plastic material having a large difference in fluidity and melting point to obtain a composite product. However, the number of composite layers should not be too much, otherwise the co-extrusion head is too large. (2) Handpiece with coextruded feed block: The melt extruded from several extruders is fed through the feed block splitter, through which the melt flow rate is adjusted compared to the regulating valve and the thickness adjustment plug. Then merge into the hanger head extrusion molding. This method allows one to produce more layers of composite film, and the co-extrusion head is small and precise. The disadvantage is that only plastics with similar fluidity and processing temperature can be combined with each other, and the processing range is narrow. (3) Co-extrusion heads with multiple runner heads and feed block combinations. It is a co-extrusion head developed by Reifenh妘ser GmbH, Germany, which is used to process more than five layers of heat sensitive materials.
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