Precautions during the co-extrusion casting process of the wound film

日期:2019/8/12 8:55:18 / 阅读: / 来源:本站

Precautions during the co-extrusion casting process of the wound film
LLDPE has high melt viscosity and poor fluidity. The extrusion cooling process is prone to film shrinkage, and the film has more crystal points during processing. These problems directly affect the quality of the product. After analysis and testing, the following methods can be used.
(1) Film shrinkage phenomenon.
1 Check whether the temperature of the quenching setting roller is suitable. If the temperature is too low, the shrinkage will be aggravated. If it is too high, the cooling effect will be poor.
2 Check the position, direction and outlet uniformity of the air knife.
3 Increase the pressure of the pinch roller and the tension of the flattening roller so that the film is in close contact with the chill roll.
(2) Film crystal point.
1 The cylinder temperature is low or too high is unfavorable. The temperature is low, the resin cannot be completely plasticized; the temperature is too high, the melt pressure is small, and the shearing force is small, which is unfavorable for the plasticization of the LDPE resin, so the appropriate barrel processing temperature is determined according to the resin grade.
2 The number of mesh layers and the number of meshes can be appropriately increased to solve the problem that the shear pressure is small and the plasticization is poor due to low melt pressure.
3 The screw speed is low and the shearing force is not enough. For the shear-sensitive LLDPE resin, the plasticizing phenomenon is easy to occur, and the screw speed should be appropriately increased.
(3) Processing technology and film self-adhesive. The self-adhesiveness of the film directly affects the performance of the product, and the problem of poor self-adhesion in production can be solved by the following methods.
1 In the flat film coextrusion flow process, the self-adhesiveness and flexibility of the LDPE stretch film is not caused by the addition of a tackifier, but by the quenching of the quenching setting roll to make the film self-adhesive, so the quenching temperature is extremely critical.
2 The thickness of the film also has a certain influence on the viscosity, such as too large thickness, insufficient self-adhesiveness and waste; the thickness is too small, the film strength is poor, the puncture resistance is reduced, and it is difficult to wrap the package, so the film thickness is controlled at 18um-22um. It is appropriate.
3 increase the distance between the die and the cooling roller, can also increase the viscosity of the film.
4 In order to ensure the viscosity and tightness of the film, the contact pressure of the winding and the characteristic tension ratio of the winding and take-up traction are appropriately adjusted.


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