Multilayer injection molding of high‐profile convex lens

ABSTRACT The use of injection molding to produce a convex lens of a high thickness and a high proportion of the component thickness requires not only a long cooling time but also results in a low production efficiency and a low yield. In particular, the heat concentration in thick regions can create high shrinkage and create poor surface geometry in these lenses. Multilayer injection molding (MIM) has reduced the cycle time and also improved the geometrical accuracy of thick parts, and thus it has drawn attention in recent years. This study evaluated the feasibility of MIM to produce a convex lens having a high thickness and a high thickness ratio, in which a thick optical lens would be made of a plurality of thin layers. In this study, conventional injection molding (CIM), two‐layer IM, and three‐layer IM were evaluated empirically to explore the effects of various molding combinations on surface contours accuracy, cycle time, residual stress, and lens transmittance. In the comparison, the three‐layer IM significantly reduced the surface profile error to 0.015 mm (CIM was 0.1 mm) and reduced the surface profile error to 30%. Moreover, uniformity of the shrinkage distribution and good surface profile accuracy can be obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48600.