Tzu-Chien Huang

Fabrication of plastic microlens arrays using hybrid extrusion rolling embossing with a metallic cylinder mold fabricated using dry film resist

This paper reports a novel and effective method to fabricate microlens arrays on polycarbonate films by hybrid extrusion rolling embossing. The metallic cylinder mold bearing an array of micro-holes is fabricated using photolithography with dry film resist. During the extrusion rolling embossing process, the extruded PC film is immediately pressed against the surface of the roller mold. Under the influence of the rolling pressure and surface tension, an array of convex microlenses is formed. The uniformity and optical properties have been verified. An efficient continuous mass production technique has been demonstrated.

Fabrication of large area resin microlens arrays using gas-assisted ultraviolet embossing

Large-area microlens arrays are becoming important components in many applications such as LCD-TV diffusers. This paper reports a uniform pressure, low temperature process for their fabrication. The process integrates gas-assisted embossing and UV-curing embossing. During the process, the 230mm x 203mm PMMA substrate is pressed against the stainless-steel stamper coated with UV-curable resin. Under the gas pressuring and UV irradiating, a large array of microlens can be formed. By using this process, high embossing temperature and high embossing pressure can be avoided. Little residual stress is observed in the embossed PMMA substrate. The uniformity of large-area fabrication and optical properties of fabricated resin microlens array have been verified. This study has successfully shown the potential of this gas-assisted UV embossing process for the replication of large-area microstructures.

Fast fabrication of integrated surface-relief and particle-diffusing plastic diffuser by use of a hybrid extrusion roller embossing process.

Most plastic diffusers are either of surface-relief or particle-diffusing types, based on different principles and fabrication methods. This paper reports an innovative extrusion roller embossing process, which enables the fabrication of diffusers with both surface-relief and particle-diffusing functions. An extruder with die is employed to fabricate the thin film of PC/bead composite; the roller micro-embossing process is used to replicate the microstructure onto the surface of PC composite film. A metallic roller mold with microstructures is fabricated using turning process. During the extrusion rolling embossing process, the extruded film of PC with diffusion beads is immediately pressed against the surface of the roller mold. Under the proper processing parameters, the plastic diffusers integrating surface-relief and particle-diffusing functions have been successfully fabricated. The shape, uniformity, and optical properties of fabricated diffuser have been verified. This method shows the great potential for continuous fabrication of high-performance plastic diffusers integrating surface-relief and particle-diffusing functions with high throughput.

Direct fabrication of rigid microstructures on a metallic roller using a dry film resist

This paper presents a novel method to fabricate a metallic roller mold with microstructures on its surface using a dry film resist (DFR). The DFR is laminated uniformly onto the curvy surface of a copper roller. After that, the micro-scale photoresist on the surface of the roller can be patterned by non-planar lithography using a flexible film photomask, followed by ferric chloride wet etching to obtain the desired microstructures. This method overcomes the uniformity issue of photoresist coating on rollers, and solves the molds sliding problem during the embossing process because the microstructures are fabricated directly on the roller surface. Furthermore, the rigid metallic roller mold has excellent strength durability and temperature endurance, which can be used in roller hot embossing with a high embossing pressure. The fabricated microstructure roller mold is used as a mold in the hybrid extrusion roller embossing process and successfully fabricates uniform micro-scale prominent line arrays on PC films. This result proves that the roller fabricated by this method can be successfully used in roller embossing for microstructure mass production. The excellent flatness of dry film resist laminating is the key in this fabrication process. The flexible film photomask can be easily designed using CAD software; this roller fabrication method enhances the design flexibility and reduces the cost and time.

Fabrication of microlens arrays using a CO2-assisted embossing technique

This paper reports a method to fabricate microlens arrays with a low processing temperature and a low pressure. The method is based on embossing a softened polymeric substrate over a mold with micro-hole arrays. Due to the effect of capillary and surface tension, microlens arrays can be formed. The embossing medium is CO2 gas, which supplies a uniform pressing pressure so that large-area microlens arrays can be fabricated. CO2 gas also acts as a solvent to plasticize the polymer substrates. With the special dissolving ability and isotropic pressing capacity of CO2 gas, microlens arrays can be fabricated at a low temperature (lower than Tg) and free of thermal-induced residual stress. Such a combined mechanism of dissolving and embossing with CO2 gas makes the fabrication of microlens arrays direct with complex processes, and is more compatible for optical usage. In the study, it is also found that the sag height of microlens changes when different CO2 dissolving pressure and time are used. This makes it easy to fabricate microlens arrays of different geometries without using different molds. The quality, uniformity and optical property of the fabricated microlens arrays have been verified with measurements of the dimensions, surface smoothness, focal length, transmittance and light intensity through the fabricated microlens arrays.

CO2-assisted embossing for the fabrication of PMMA components under low temperature and with low pressure

Gas-assisted pressurizing has been proven to provide a uniform pressure distribution over a large-area substrate. This paper reports an innovative embossing technique, which makes use of the unique combination of plasticizing and isotropic pressurizing poly(methyl methacrylate) substrates possible with CO2 gas. CO2 serves as a plasticizer and as a pressurizer of a substrate during gas-assisted embossing. As a result, CO2-assisted embossing can be performed under lower temperatures and with lower pressure, and enhances the replication quality by reducing the residual stress in the substrates. In this paper, the process parameters and the quality of the CO2-assisted embossed substrates with V-grooves are shown and discussed. Results show that the processing temperature, embossing pressure and residual stress in substrates are significantly lower with CO2-assisted embossing.

Bubble-free replication of large area microstructures using gas-assisted UV embossing with modified reversal imprinting and gap-retained vacuuming

Air bubble defects have been regarded as a critical problem in ultraviolet (UV)-based imprinting/embossing processes, especially in large area fabrication. This paper reports a gas-assisted UV embossing process for bubble-free replication of large area microstructures. This gas-assisted pressurizing process provides uniform embossing pressure over the whole large area, while UV curing enables the process to be performed at room temperature and low pressure. To overcome the problem of air bubble entrapments in the large area UV embossing process, the mechanisms of modified reversal imprinting and gap-retained vacuuming have been developed and used. Experimental results show that the microstructures have been successfully transferred from the stamper to the polymethylmethacrylate substrate with the size of 230 × 203 mm2 inducing no air bubble defects.

Improving Flow Balance during Filling a Multi-cavity Mold with Modified Runner Systems

Abstract Multi-cavity injection molding has been regarded as low cost mass-production method for producing plastic products such as optical elements. However, the flow imbalance during filling a multi-cavity mold using symmetrical runner system is a serious problem. This paper is devoted to improving the flow balance by modifying the runner system design. For this purpose, four eight-cavity molds with four modified symmetrical runner systems are designed, constructed and tested. They are tapering H-type runners, pinned H-type runners, curved A runners, and curved B runners. The flow imbalance in each runner system is observed and measured with the aid of short-shot experiments. The experimental results indicate that the tapering H-type runner system can improve flow balance. The pinned H-type runner system fails to improve flow balance. The curved A and B runner system can reverse the imbalance trend, but the stability of the curved systems is poor at high melt temperature.