Replication and Comparison of Concave and Convex Microlens Arrays of Light Guide Plate for Liquid Crystal Display in Injection Molding

Abstract

A back light unit (BLU) is a key module of a thin-film transistor liquid crystal display (TFT-LCD), frequently utilized in various mobile displays. In this study, we experimentally characterize transcription and optical properties of concave and convex microlens arrays (MLAs) of light guide plate (LGP) fabricated by injection molding with polycarbonate as a LGP substrate material. Nickel mold inserts were manufactured by electroforming on the MLA, which was fabricated by the thermal reflow of photoresist microstructures patterned by UV-photolithography. For the case of convex microlens, the height of replicated microlens was less than that of the mold insert while maintaining almost the same microlens diameter of the mold insert as the location of the microlens is far from the gate. In contrast, for the concave microlens, the diameter of replicated microlens was larger than that of mold insert, while showing almost the same microlens height as the mold insert. From the optical examination of replicated convex and concave MLAs, it was found that a higher luminance of the LGP was achieved by the concave MLAs compared to the convex MLAs with the same number density of microlenses (about 30% enhancement in this case) due to the utilization of a larger amount of light provided by the light sources. POLYM. ENG. SCI., 50:1696-1704, 2010. (C) 2010 Society of Plastics Engineers