Research On Injection Molding And In-mold Bonding Microfluidic Chip

Abstract:With the deepening of research on microfluidic chip, demand on low-cost, high-volume, single-use chips is increasingly urgent.polymer microfluidic chips have become a main research direction of industrialization and commercialization in mini portable analytical instruments. Currently, one-piece or small quantities manufacturing of chips for laboratory studies have been able to achieve, but how to achieve a polymer microfluidic chips efficient, low-cost manufacturing is a critical challenges for industrialization. This paper presents a new technology on injection molding and bonding polymer microfluidic chip,to achieve effective integration of injection molding and thermal bonding. With numerical simulation and experimental study, the key technologies were studied on the process of injection molding and in-mold bonding polymer microfluidic chip to improve molding quality, which can provide a new idea for industrialization of microfluidic chip.Basing on analysis of the traditional polymer microfluidic chip manufacturing process and in-mold assembly technology, the processes of molding, alignment and bonding of the substrate and cover sheet were integrated in an injection mold. It was compared and analyzed on the design of gating system, core pulling cylinders and temperature control system to achieve effective integration molding, aligning, in-mold bonding polymer microfluidic chip ultimately.In the injection molding process, the microfluidic chip warpage was investigated experimentally. The pressure distribution in the substrate and the cover sheet filling process was analyzed by mold flow analysis software. The influence of process parameters on the warpage was revealed, and a preliminary process optimization for the injection molding molding was achieved. Based on preliminary optimization, the single factor injection molding experiments were carried out to research the influence of process parameters on the degree of replication of transverse and longitudinal micro-channel. The uniform micro-channel morphology can be got by increasing mold temperature and melt temperature appropriately. The requirements for high mold temperature and melt temperature can be reduced by increasing injection speed in micro-injection molding. And the optimal combination of process parameters was obtained. Mold temperature of90?, melt temperature of245?, injection speed of 35cm3/s, holding pressure of140MPa, dwell time of3s, ensure warpage small and micro-channel morphology uniform.Based on polymer mechanics theory, deformation mechanism of microfluidic chip microchannel was analyzed in in-mold bonding process. The mechanical performance test of PMMA at high temperature was carried out to obtain its parameters of mechanical properties. At the vicinity of the glass transition temperature, PMMA materials exhibit significant viscoelastic properties. Simulation was carried out by finite element analysis software to analyze the microchannel deformation of PMMA microfluidic chip in in-mold bonding process. Combined with experimental results, the influence of bonding temperature, bonding pressure and bonding time on the micro-channel deformation was obtained. With bonding temperature, bonding pressure and bonding time increasing, the deformation of chip microchannel increases, and bonding temperature and bonding pressure are the main influence on microchannel deformation. In the process of in-mold bonding, the top and side walls of microchannel could be adhered, which had a great influence on the micro-channel deformation, mainly reflected in the top width and height direction. Generalized Maxwell material model could be used to simulate the microchannel deformation of polymer microfluidic chip in the process of in-mold bonding.The formation mechanism of bonding strength was analyzed in the process of in-mold bonding basing on adsorption theory and diffusion theory. A molecular dynamics software was used to simulate for bonding process of PMMA chip. In-mold bonding experiments and bonding strength test experiments were also carried out to study and verify the influence of process parameters on the formation of the bonding strength. The results show that the formation of bonding strength is results of diffusion and adsorption of interface moleculars. An appropriate increase in pressure can significantly improve the bonding strength and shorten the bonding time. With the bonding temperature and bonding time increasing, the mutual diffusion of interface molecules is increased to improve the interface force, thereby to increase the bonding strength.Considering the microchannel deformation and bonding strength in in-mold bonding process, the bonding temperature of102?, pressure of1.8MPa bonding and bonding time of240s were selected as the optimal process parameters. Under the optimal process parameters, the experiments of in-mold bonding was carried out. The bonding strength of microfluidic chip was350KPa, its micro-channel networks was sealed well, and the deformation of chip micro-channel is small, the height of36?m, the top width of85?m, width at the bottom of38?m. The maximum deformation was not more than10%, meeting the requirements of application.