In the present study, replication of flow-through microfilters in the newly developed microfluidic lab-on-a-chip for blood typing by microinjection molding process was experimentally investigated. As a precise replication of the microfilters was required in order to effectively filter out agglutinated red blood cells, the effects of important processing conditions on the replication of the flow-through microfilters were investigated. By using a mold insert fabricated by a nickel electroplating process and a newly designed mold base, microinjection molding experiments were carried out. A three-dimensional solid model reconstruction method was proposed with the help of specific features characterizing the geometry of microfilters, and accordingly, the feature values of the replicated microfilters were measured by a noncontact optical measurement system. So reconstructed solid modeling result was then used to investigate the effects of various processing conditions, such as a flow rate, a mold temperature, and a packing pressure. Amongst the processing conditions investigated in the present study, the flow rate was found to be the most important one.

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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. © 2010 Society of Plastics Engineers

Microchannel is a fundamental structure in various microfluidic systems. Precise reproduction of microchannel is required to achieve reliable efficiency of microfluidic systems. In this paper, we present the parametric sensitivity study of the replication of a cross microchannel by injection molding with a nickel mold insert which was fabricated by the UV-LIGA process. The effects of processing parameters of the injection molding on the transcription properties of cross-sectional geometry of the microchannel were quantitatively characterized by means of design of experiments based on the Taguchi method by varying mold temperature, melt temperature, injection speed and packing pressure. To quantitatively characterize the transcription properties, a measure, relative error between the size of mold insert and that of injection molded microchannel was newly suggested. From the sensitivity analysis of the experimental results based on the relative error, it was identified that mold temperature is the most sensitive processing parameter in this study. And also, the important processing parameter was found to become mold temperature, injection speed, packing pressure and melt temperature in the order of sensitivity. The optimal and worst processing conditions were also found in this study.