Date of Award
Doctor of Philosophy (PhD)
Kevin W. Kelly
Injection molding and hot embossing proved to be suitable for use to reproduce layouts of micropatterns manufactured by LIGA. The research work was based on two commercially available machines. Preliminary experiments with both machines indicated that several modifications and additions were necessary to adapt the injection machine and the embossing press for microreplication. For the injection machine, a mold geometry was designed to ensure minimal pressure loss upstream from the entrance into the mold cavity, and optimal shape for molding and demolding. For the hot embossing press, a vacuum chamber was designed containing the embossing sandwich, with the temperatures of the mold insert and of the substrate controlled through the press' heating/cooling system. Experiments were performed to identify the important process parameters in injection molding of HARMs. It was established that mold insert temperature is of primary importance for the process, followed by melt flow rate. In hot embossing, it was argued that temperature of the polymer has most evident effects on the process, followed by variations in embossing force and embossing time. It was shown that the embossing time should preferably be long, to allow for relaxation of the macromolecular chains resulting in stress-free moldings. Compared to HDPE, it was shown that PMMA is heat-sensitive, and that it requires special care including drying before dosage, and dosage under controlled temperature and shear conditions. When used in hot embossing, PMMA is advantageous compared with polycarbonate-PC, because it allows embossing at lower temperatures. Three micro heat exchanger geometries were molded (and fabricated for testing), one stacked pattern and two cross flow patterns. Also, several DNA sequencing chips were microreplicated, using both injection molding and hot embossing. Also, a test pattern was designed for comparison between molding techniques. Molding was performed into two inserts of different heights (200 and 500 microns) using the same material (PMMA). An overall mean value of 1.25% was reported for shrinkage of the plastic compared to the mold insert. Qualitative interpretation of the molding results showed differences in the demolding success rate between the two molding techniques combined with the two mold insert heights.
Despa, Mircea Stefan, "Molding Large Area Plastic Parts Covered With HARMs." (2001). LSU Historical Dissertations and Theses. 277.