| High performance multilayer composite film has been widely used in medicine,food,industry,agriculture,daily chemical and other fields,has an extremely broad development prospects.However,the conventional polymer film self-reinforcing technology often has some disadvantages,such as complicated steps,difficult continuous production,and unfavorable to industrialization and promotion.In the forming process,the interface between melts is prone to be unstable,uneven,and easy to cross layers.Moreover,the transverse mechanical properties of the film products are weak,and the transverse and longitudinal mechanical properties are different.How to achieve low-cost enhancement of multilayer composite films has become an urgent problem to be solved.Based on this situation,the research group independently developed the reverse rotation blow molding mold for internal and external molds in the early stage,and successfully realized the self-strengthening of multi-layer co-extruded composite films.In this paper,through the establishment of inner and outer mold body reverse rotation mold based multilayer melt evenly distributed in the process of the melt in extrusion theory and interlayer orientation theory,the interlayer mixed orientation of autofrettage composite film blowing molding technology to provide theoretical guidance for further development and perfection,promotes the industrialization of this technology,has important scientific academic value and practical significance.On the basis of reasonable assumptions,the uniform distribution theoretical model and interweaving orientation model of multi-layer melt co-extrusion process in the die of inner and outer die reverse rotation were established.Through the mathematical physics model theoretically for the first time reveals the mold all structure parameters of the flow and processing parameters on the interface between layers of the melt layer development,melt the thickness distribution of each layer,each layer melt velocity uniformity and the influence law of string layer phenomenon,and each layer of multilayer melt orientation direction distribution and the distribution of the degree of orientation of the law,It provides theoretical basis and guidance for practical production.Furthermore,the theoretical model is verified by simulation and film blowing experiment,and the results show that the experiment is in good agreement with the theory.Based on the discussion of melt uniform distribution in each layer of die,a melt uniform distribution model was established,and the influence of various structural parameters and processing parameters in the flow passage on the pressure uniformity of melt distribution in each layer and the development of melt interface between layers was discussed.Theoretical and simulation results show that the die structure and die rotation can promote the uniform distribution of single-sided feed melt in the ring,and the higher the rotation speed,the better the uniformity,which effectively solves the cross-layer problem in the process of multi-layer melt co-extrusion.Based on the melt interweave orientation principle under the combined flow field of rotary drag and extrusion pressure,a multilayer melt interweave orientation model was established.The concepts of orientation angle,orientation twist angle,normal interweave curvature and orientation deformation ratio were put forward in turn to describe the interweave orientation characteristics.The influence of various structural parameters and processing parameters in the flow channel on the above interweave orientation characteristics was discussed.According to the theory and simulation results,the optimization strategy of the three-layer composite film is obtained based on the uniform distribution of the interlaced orientation characteristics of each layer of melt in the melt thickness direction.The effects of different process conditions on melt distribution in multi-layer melt coextrusion were studied.By comparing the effects of the rotational speed,traction ratio and blowing ratio on the thickness uniformity of the film in the transverse and longitudinal directions,the effects of the reverse rotation die of the inner and outer mold on the uniform distribution of the multi-layer melt in the annular direction were verified.The results show that appropriate phantom rotational speed,blowing ratio and traction ratio can improve the thickness uniformity of the film in both transverse and longitudinal directions,and the optimal phantom rotational speed is around 7-8 rpm.At the same time,through the observation of the film cross section,it is found that with the increase of the rotational speed of the phantom,the uniformity of the film interface becomes better,and the cross-layer phenomenon is more difficult to appear.The effects of different processing conditions on the microstructure and properties of the films were studied.The results show that the transverse orientation of the films can be increased by increasing the rotational speed of the phantom and the blowing ratio,and the longitudinal orientation of the films can be increased by increasing the pulling ratio.Mold rotation can induce grain refinement,improve grain arrangement regularity and change grain arrangement direction.The rotation of the phantom can also effectively enhance the thermal shrinkage of the films.Finally,the mechanical properties of the three-layer composite films are self enhanced,and the mechanical properties in both horizontal and vertical directions are basically consistent with the thermal shrinkage properties.Use inside and outside the die body reverse rotation mold to achieve the autofrettage mixed orientation of multilayer composite films,changed the traditional way of distribution of melt blown film technology,through the role of the rotating die body inside and outside layers is implemented,a total of extrusion film thickness and good uniform distribution of each layer interface,and gives the film transverse,longitudinal mechanical properties of mixed orientation characteristic of good balance.. |
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