Co extrusion method can laminate multiple melt layers together (usually using multiple extruders to feed through the same head). This method uses melt heat to stick various plastics together in blocks, and co extrusion is very economical because it reduces the cost of material processing, raw material costs, and machine time costs. The method of using an extruder to separate the melt into two layers can also achieve good results.
For co extrusion method, how to control the thickness of each layer is often the most difficult problem for operators to solve. This problem involves the properties of each layer of raw materials, the design and processing quality of the die head, and the production rate. It requires operators and engineering technicians to jointly negotiate and find the adjustment rules. When two or more extruders are feeding simultaneously, the extruders should first be calibrated based on the ratio of yield to speed (a gear pump can be used), and then the width, thickness, and stretching speed of the product should be determined, and the yield of each raw material should be calculated separately. Determine the screw speed by combining its yield results with the calibration curve. When the design of the co material mold head is not appropriate, excessive pressure drop, high shear rate, and long retention time will occur, all of which will affect the quality of each layer of the product. Multiple extruders simultaneously transfer the melt to the die head. The transfer device, such as the extruder connector pipe, may be designed to be short or long, but in any case, the inner diameter of the pipe should be large enough to avoid excessive pressure drop, but not too large, otherwise it will increase the retention time of the melt. Require uniform temperature distribution to avoid uneven temperature distribution caused by the use of heating coils, such as local overheating or undercooling. Suggest using a low-pressure heater. The location of the thermometer is also important, as overheating in a certain area may cause the material to degrade into gas and generate high pressure.
