等规聚丙烯微注塑制品结晶和取向的模拟与实验

发布时间：2018-03-17 08:28

本文选题：微注塑成型　切入点：等规聚丙烯　出处：《郑州大学》2017年硕士论文　论文类型：学位论文

【摘要】：微注塑成型可以一次成型形状复杂、尺寸精确的热塑性聚合物微制品,是适合大规模生产的最有效的工艺之一。由于其尺寸微小,在熔体充填型腔的过程中经历着复杂的剪切和热历史,这些行为会影响制品厚度方向的结晶结构及取向。本文选用等规聚丙烯为原料,采用模拟和实验的研究方法,对不同成型工艺下制品的相对结晶度、厚度方向的结晶取向因子和晶粒尺寸进行模拟分析。本文的主要工作内容和结论如下:1.微注塑制品结晶形态的模拟。运用Moldflow软件,模拟流动场中不同工艺条件下制品的平均相对结晶度、结晶取向因子、最终平均晶粒大小。研究结果表明,制品越薄,冷却越快;平均相对结晶度在制品冷却结束之前已经达到制品最大相对结晶度值,且模温和熔温越高,结晶速率越慢。平均结晶取向因子和最终平均晶粒大小受尺寸的影响较大,制品厚度越大晶粒尺寸越大,结晶取向因子的数值越小。另外,相比熔体温度与注射速度,模具温度对最终平均晶粒尺寸的影响比较大。2.工艺参数对微制品厚度方向结晶度和取向度的影响。参照模拟工艺条件,利用显微红外设备,在制品厚度方向的不同位置分别测量出平行于流动方向和垂直于流动方向的红外光谱图,利用公式计算出晶区分子链的取向、非晶区分子链的取向和分子链的平均取向以及结晶度值。检测结果表明,对于等规聚丙烯这种材料,分子链的取向主要表现为晶区分子链的取向,取向度沿着厚度方向呈现出规律的变化趋势,晶区分子链的取向受尺寸的影响因素比较大。对于1.0mm和0.2mm的制品在厚度方向结晶度值的变化表现出完全相反的变化趋势:1.0mm的制品表现为靠近制品表面的结晶度数值低,靠近制品中心处的结晶度值相对较高;0.2mm制品则是靠近制品表面的结晶度值比较高,而制品中心处的结晶度值相对较小。3.工艺参数对微注塑制品结晶形态和晶型的影响。采用广角X射线衍射研究工艺条件对制品的晶型和晶粒尺寸的影响。对于1.0mm和0.5mm的制品,其晶体类型主要表现为α晶,在特殊的工艺条件下会出现β晶。对于0.2mm的制品,在不同模具温度和不同注射速度下都会出现β晶,但β晶的含量变化很小,说明尺寸越小,越有利于β晶的生成。晶粒尺寸受模具温度的影响比较大,模具温度越高,晶粒尺寸值越大。
[Abstract]:Microinjection molding is one of the most effective processes for mass production because of its complex shape and precise size. In the process of filling the cavity with melt, there is a complicated shear and thermal history, which will affect the crystal structure and orientation in the thickness direction of the product. In this paper, isotactic polypropylene is used as the raw material, and the simulation and experimental research methods are used. The relative crystallinity, thickness orientation factor and grain size of products in different molding processes are simulated and analyzed. The main contents and conclusions of this paper are as follows: 1. Simulation of crystalline morphology of microinjection molded products. Moldflow software is used. The average relative crystallinity, crystal orientation factor and final average grain size of the products were simulated under different technological conditions in the flow field. The results showed that the thinner the products were, the faster the cooling rate was. The average relative crystallinity has reached the maximum relative crystallinity before the end of the product cooling, and the higher the mold temperature, the slower the crystallization rate. The average orientation factor and the final average grain size are greatly affected by the size. The larger the thickness of the product, the larger the grain size, the smaller the value of the orientation factor. In addition, compared with the melt temperature and the injection rate, The effect of mold temperature on the final average grain size is relatively large. 2. The effect of process parameters on the crystallinity and orientation degree in the thickness direction of microproducts. According to the simulation process conditions, the microinfrared equipment is used. The infrared spectra parallel to the flow direction and perpendicular to the flow direction were measured at different positions in the thickness direction of the WIP, and the orientation of the molecular chain in the crystal region was calculated by using the formula. The orientation of amorphous chain, the average orientation of molecular chain and the degree of crystallinity. The results show that for isotactic polypropylene, the orientation of molecular chain is mainly the orientation of crystalline chain. Orientation shows a regular trend along the thickness direction. The orientation of the molecular chain in the crystal region is greatly affected by the size. For the products with 1.0 mm and 0.2 mm in the thickness direction, the change of crystallinity values in the thickness direction shows a completely opposite trend. The products with 1.0 mm and 1.0 mm exhibit low crystallinity values near the surface of the products. Near the center of the product, the crystallinity value of 0.2mm product is relatively high, and the crystallinity value near the surface of the product is relatively high. The crystallinity value at the center of the product is relatively small. 3. The effect of process parameters on the crystalline morphology and crystal form of microinjection molded products. The effects of processing conditions on the crystal shape and grain size of the products are studied by wide angle X-ray diffraction. For the products with 1.0 mm and 0.5 mm, The crystal type is mainly 伪 crystal, 尾 crystal will appear under special technological conditions. For 0.2mm product, 尾 crystal will appear at different mold temperature and different injection speed, but the content of 尾 crystal will change very little, which means the smaller the size, the smaller the size of 尾 crystal is. The higher the mold temperature, the larger the grain size.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ325.14

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