聚丙烯/超临界氮气微孔注塑充模过程工艺参数研究

Study on process parameters for filling process of polypropylene microcellular injection molding under supercritical N

以聚丙烯(PP)为原料,超临界氮气(N_(2))为发泡剂,通过自行设计的一种扁平螺旋线形流道模具探究了注塑制品充模长度与减重比、泡孔结构之间的关系,并设计正交试验研究了注气压差、注气时间、注射压力和注射速率对制品充模长度的影响。结果表明,在一定范围内,熔体背压越高,制品充模长度越长,且随着充模长度增加,制品的减重比呈先缓慢增大后急剧增大的趋势;在靠近浇口位置的泡孔少,整体呈扁平的椭球形结构;在中间位置泡孔增多且分布均匀,整体呈现为较为规整的球形结构;在远离浇口位置泡孔十分致密,但泡孔合并以及破裂现象较严重,整体尺寸分布不均匀;正交试验表明注气压差、注气时间、注射压力和注射速率的增大均会使制品的充模长度增大。

Employing polypropylene as a raw material and supercritical nitrogen gas as a foaming agent,a flat spiral linear runner mold was designed,and the mold filling length and weight loss ratio of the molded part and the relationship between the cell structures were investigated.An orthogonal experiment was designed to study the effects of gas injection pressure difference,gas injection time,injection pressure,and injection speed on the mold filling length.The results indicated that in a certain range,a higher melt back pressure resulted in a longer filling length for the injection-molded part.The weight loss ratio of the part increased slowly at first and then rose drastically with an increase in filling length.Meanwhile,the number of bubbles was less near the gate,and these bubbles presented a flat ellipsoidal structure.In the middle position,the number of bubbles increased along with a uniform distribution.Their overall appearance presented a relatively regular spherical structure.At the location far from the gate,the cells are very dense.However,the cell merge and rupture phenomenon are serious,and the overall size distribution is ununiform.Based on the orthogonal experiment,the filling length of the part was found to increase with an increase in gas injection pressure difference,injection time,injection pressure,and injection speed.