PP共挤薄膜挤出温度对挤出流率的影响

Effects of the Extrusion Temperature of Co-extruded PP Films on the Extrusion Flow Rate

多层共挤薄膜生产通常采用单螺杆-熔体泵串联挤出系统,薄膜厚度的稳定性控制是决定其产品质量的重要技术难题。本文通过分析共挤聚丙烯薄膜纵向厚度波动的相关因素,得到薄膜厚度纵向波动是由挤出流率的波动引起,并研究挤出温度变化对熔体泵出口压力与挤出流率波动的影响,以确定纵向厚度稳定性较高的挤出温度。基于现有多层共挤试验线可调整与监测参数,以挤出温度为变量开展实验,将熔体泵进口压力与转速设为固定值,分析物料黏度变化引发的熔体泵出口压力与挤出流率的波动情况。结果表明,随着挤出温度升高,物料黏度下降,熔体流动性增强,螺杆转速与熔体泵出口压力波动变化趋势基本一致,螺杆转速波动幅度约为熔体泵出口压力波动幅度的2.75倍;同时熔体泵出口压力降低,熔体泵进出口压差减小,容积效率提高,挤出流率小幅增加;对比不同温度下挤出流率波动,可知试验线挤出温度设定为220℃时,波动值最小,薄膜具有较高的纵向厚度稳定性,对薄膜产品生产具有一定的指导意义。

The tandem extrusion system of single screw and melt pump is usually used in the production of multilayer co-extruded films.The stability control of film thickness is an important technical problem to determine the qualities of film products.In order to determine the extrusion temperature with higher longitudinal thickness stability,this paper analyzed the factors related to the longitudinal thickness fluctuation of co-extruded polypropylene films,found that the longitudinal thickness fluctuation was caused by the fluctuations of extrusion flow rate,and investigated the effects of extrusion temperature change on the fluctuation of melt pump outlet pressure and extrusion flow rate.To analyze the fluctuations of melt pump outlet pressure and extrusion flow rate caused by the changes of material viscosity,the existing multi-layer co-extrusion test line was used to adjust and monitor parameters.The extrusion temperature was set as the variable,and the melt pump inlet pressure and rotational speed were set as the fixed values.The experiment results show that with the increase of extrusion temperature,the viscosity of the material decreases and the fluidity of melt increases.The fluctuation trend of screw speed is basically the same as that of melt pump outlet pressure,and the fluctuation amplitude of screw speed is 2.75 times that of the melt pump outlet pressure.At the same time,when the melt pump outlet pressure decreases,the melt pump pressure difference between the inlet and outlet decreases,the volume efficiency increases,and the extrusion flow rate increases slightly.Compared the fluctuations of extrusion flow rate at different temperatures,it could be concluded that the fluctuation value is the smallest when the extrusion temperature is set at 220℃.The film has a high longitudinal thickness stability which has certain guidance for the film productions.