Requirements for processing multilayer coextrusion composite films

日期:2019/8/19 8:56:39 / 阅读: / 来源:本站

Requirements for processing multilayer  coextrusion composite films
Mainly considering the following aspects
1) The adhesive composite film is composed of a plurality of layers of different resins. Therefore, it is necessary to have sufficient adhesion between the layers, and the adhesion property determines the structure, polarity, and viscosity flow of the resin during processing. The bonding properties of commonly used resins are shown in Table 7-5-11.
As can be seen from Table 7-5-11, some resins have good adhesion, such as LDPE/HDPE, LDPE/EVA, etc.
Some resins do not have sufficient adhesion between them, such as PE/PA, PE/EVOH, etc., these resins must be combined and co-extruded, and a bonding layer must be added in the middle. The bonding layer usually uses a bonding resin. It has a good adhesion to two resins that cannot be bonded to each other. In addition, the adhesive resin itself has the advantages of easy heat sealing, good oil resistance, and low temperature resistance.
2) Rheology and processing conditions In the co-extrusion production, since there are two or more kinds of melts at the same time, the rheology of the selected resin and the choice of the process have a great relationship with the quality of the product.
In the coextrusion compounding, when the melt stream layer is recombined, the melt viscosities of the two resins are as similar as possible, and the solution is as follows.
1) The selected resin has the same viscosity at head temperature and shear rate, but it is often difficult to do so.
2) Select a resin with roughly the same rheological properties, or adjust the viscosity of a certain resin by changing the temperature or shear rate to achieve a more harmonic viscosity group. In actual production, the melt temperature and shear rate in the extruder can be controlled separately, but when the head meets, the temperature and shear rate values of the various melts are consistent, therefore, the rheology is selected. Resins with similar properties and proper control of process conditions are critical to ensuring the quality of coextruded products.
The difference in rheological properties of the selected resin is also related to the composite head structure used.
Resins with large differences in melt viscosity are used for coextrusion production, and it is not acceptable to adjust the extrusion temperature. One method is to improve the structure of the head so that the material is at different temperatures in the handpiece; another convenient and convenient method is to use blending techniques. If the melt viscosity of a certain resin is too large, another resin having a similar property but a small melt viscosity may be blended with it to lower its melt viscosity so that it is at the head temperature and another Kinds of resins have similar viscosities, if you want to raise some kind of tree
A similar method can be used for the melt viscosity of the grease.

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