What is MI value?
MI就是熔融指数（Melt Flow index）
MI是一种表示塑胶材料加工时的流动性的数值，是美国材料与试验协会(ASTM)根据美国杜邦公司惯用的鉴定塑料特性的方法制定，用以区别各种热塑性材料在熔融状态时流动性的参数。最常使用的测试标准是ASTM D1238，该测试标准的量测仪器是熔液指数计。其测试方法是先让塑料粒在一定时间(10MIn) 内、一定温度及压力下，融化成塑料流体，然后通过一直径为2.1mm 圆管所流出的克数(g)。一般常用塑料的MI值大约介于1－25之间，其值越大，表示该塑胶材料的加工流动性越佳，反之则越差。
对同一种树脂，可以用MI（熔融指数）比较其分子量的大小，以作为生产质量控制。一般来说，对化学结构一定的树脂，其熔融指数越小，分子量就越大，则其断裂强度、硬度、韧性、耐老化稳定性等性能都有所提高。而熔融指数大，分子量就小，成型时的流动性就相应好一些。对于注塑生产过程中工艺的确认和调整有一定作用。MI (Melt Flow index) is a numerical value indicating the fluidity of plastic materials during processing. It is formulated by the American Society for testing and materials (ASTM) according to the method used by DuPont company to identify the characteristics of plastics, and is used to distinguish the fluidity of various thermoplastic materials in the molten state. The most commonly used test standard is ASTM d1238, and the measuring instrument of this test standard is melt index meter. The test method is to melt the plastic particles into plastic fluid in a certain time (10MIn), under a certain temperature and pressure, and then pass through a round pipe with a diameter of 2.1mm to deterMIne the number of grams (g). Generally, the MI value of commonly used plastics is about 1-25. The higher the value is, the better the processing fluidity of the plastic material is, and vice versa.
For the same resin, MI (melt index) can be used to compare the molecular weight of the resin for quality control. Generally speaking, for the resin with certain cheMIcal structure, the smaller the melt index is, the larger the molecular weight is, and the fracture strength, hardness, toughness, aging stability and other properties are improved. When the melt index is large, the molecular weight is small, and the fluidity is better. It plays a certain role in the confirmation and adjustment of injection molding process.
