Micromold filling behavior studies of polymer materials

The micromolding process is a key enabling technology in realization of wide industrial applications of microsystems because the process enables mass production of disposable polymer microcomponents at a high automation level. Micromold cavity filling is an important step in successful molding of polymer microcomponents. To fill microcavities, polymer materials with low viscosity are desired. However, there are also stringent requirements on mechanical and other application properties of the polymer materials used. There are, therefore, limitations for many of the commercial polymer materials used in the conventional molding process to be used successfully in micromolding applications. In the present paper, the micromold filling behavior of polymer materials with different rheological properties is studied. Both commercialized materials and blends developed through the compounding process are used. A micromolding machine with a maximum injection capacity of 1 cm3 is used in the study. It has been found that the viscosity of a polymer material affects the injection pressure required to fill up a microcavity and the final dimensions of the molded component. In the micromolding process, only a narrow cavity pressure curve is usually built up as the melt cools down quickly in the flow channels. The injection pressure applied to the injection plunger is mainly consumed to overcome friction force and to push melt flow through the runner and gate system. Polymer blends compounded with a small amount of processing aids (up to 2 wt-%) greatly reduce the blend viscosity and therefore, are very good for micromolding applications.