Co-Injection Compression Molding of Double-sided Microlens Array

This study is devoted to the co-injection compression molding of polycarbonate double-sided microlens array. Compared with the conventional injection molding, the pressure of injection compression molding can be reduced. The uniform compression pressure over the whole projection area can improve the transcription rate. In addition, the residual stress in the product can be lowered, and the optical quality can be improved . First, the co-injection compression molding process was simulated with Moldex3D software. The experimental design using L_9 table of Taguchi method was used. The effects of four molding parameters, including the compression speed, compression stroke, mold temperature, and starting point of compression were investigated. It was found that the compression speed and mold temperature are the most significant parameters as far as the precision of diameter and height of microlens are concerned. The optimal combination of processing parameters was identified. Furthermore, a mold for co-injection compression of double-sided microlens array was designed and constructed. Co-injection compression moldings were performed using the same combinations of process parameters used in simulation. The dimensional quality of the co-injection compression molding shows the same trend as the simulation. The quality of co-injection compression molded microlens array using the optimal combination of process parameters is better than what obtained using other combination of process parameters. The transcription rate of microlens diameter is 96.3 % for the convex and concave surface of microlens, while the transcription rate of microlens height is 98.15 %. In addition, the residual stress of the molded microlens array was comparatively lower than those molded with conventional injection molding process. The optical properties, including the effective focal length (EFL) and spot size, of the injection compression molded microlens were further characterized. The average EFL was 1.5228 mm with a standard deviation of 0.0152 mm. The average spot size of the original light source of 1.2 mm diameter was focused to 50 μm diameter. The co-injection molding process can fabricate uniform precise microlens array. This research proves the potential and capability of co-injection compression molding process for the fabrication of double-sided microlens array.