The Research For Injection Molding And Hot-embossing Process Of Plastic Microreactor

Microfluidic chip has the functions of material separation, cell culture and analysis, which makes it widely used in the fields of chemical analysis, cell analysis, energy and so on. Due to its high efficiency and high precision of structure, micro injection molding has become one of the most important methods for microfluidic chip. However, due to the effect of residual stress, the micro plastic parts appear defects such as shrinkage and warpage, which reduces the quality of the surface topography (flatness and waviness). At the bonding and adhesive stage of plastic parts, the above problem will lead to leakage and low detection accuracy because of poor sealing performance and difficulty of bonding, which affects the normal capabilities of the devices. In this paper, a plastic microreactor was studied to improve the problems. On the base of optimizing the injection molding process parameters, an isothermally hot-embossing methodology for flattening the plastic microreactor was simulated and analyzed. The flattened plastic parts was used to assemble the micro reactor by adhesive. The contact angle measurement was carried out to analyze the droplet wettability and make sure the location of droplet. The study is beneficial to improve the precision of flat plastic microparts. It mainly included the following aspects:A micro injection mold with ejection mechanism was designed and the orthogonal experiment was carried out to optimize the process parameters of PC material. Under the conditions of melt temperature 250?, mold temperature 95?, injection pressure 90MPa, packing pressure 25Mpa, packing time 5s, the width and depth replication accuracy of micro structure were 99.2% and 98.7%.To solve the warping, the performance of the micro device was tested. Then, an isothermally hot-embossing methodology was proposed and applied to flatten the plastic microreactor. The flattening mechanism of PMMA micro plastic parts was studied, and an elastic-plastic model was established to describe the deformation process. The influences of temperature and pressure on the flattening of plastic microparts were quantitatively analyzed by ANSYS. The result indicated that the deformations at the ends of microreactor were much larger than the middle chamber owing to the larger contact area, the influence of thermal load on flattening degree was more obvious than the external pressure. The changing rate of temperature about waviness could achieve to 4.70e-5/? at inlet surface on the condition of pressure 20kgf, temperature 60?80?.The results provided the theoretical basis for the next experiment.Hot-embossing platform was established to carry out the experiment and analyze the effect of key process parameters on flatness, waviness and micro structure accuracy. The result indicated that the influence of temperature on flattening degree was more obvious than the pressure, which coincided with the simulation. Under the condition of pressure 20kgf, temperature 70?, the PMMA plastic parts had the optimal surface morphology. Flatness was 7.297?m and changing rate was 72.7%. The changing rates of waviness at inlet and cavity were 40.1% and 9.69%. The changing rates of the depth and width about microstructure were 0.64% and 0.55%.The flattened plastic parts was used to assemble the micro reactor by adhesive. To solve the adhesive pollution (connection and filling) problem caused by the change of adhesive position, contact angle measurement was carried out under different conditions and the infiltration spreading process of droplets on the plate was numerical simulated to ensure the spreading distance and droplet location. The result indicated that contact angle decreased with the solidification of glue droplets. Contact angle on PMMA decreased at a rate of 64.53%, which was larger than PC. The spreading distance of droplet on PC was 0.272mm, which was the 0.05mm radius of 5.44 times. The spreading distance of droplet on PMMA was 0.405mm. The microreactor without pollution problems was acquired on the base of the optimized adhesive position.