Roller Imprinting Research Articles

Laser-assisted direct roller imprinting of large-area microstructured optical surfaces

In this study, a high-throughput fabrication method called laser-assisted direct roller imprinting (LADRI) was developed to lower the cost of nanoimprinting large-area polymer films and to address problems associated with nanoimprinting, namely, microstructural damage and precision in flatness of entire film. With LADRI, the laser directly heats the microstructured surface of the roller mold, which heats and melts the surface of a polymethyl methacrylate (PMMA) film to replicate the microstructures on the mold rapidly. In this study, the effects of laser power density, scanning speed, size of the microstructures, and contact pressure on the replication speed were investigated experimentally. The replication speed increased as the power and scanning speed increased. However, because the film required heating until it filled the entire depth of the microstructure, an appropriate replication speed was necessary. This result was supported by simulation of the temperature distribution inside the mold and the PMMA using transient heat conduction analyses. To demonstrate the applications of LADRI, two different optical surfaces were replicated: an antireflection (AR) structure with conical structures sized several hundred nanometers and a light-extraction structure with a microlens array (MLA) comprising 10 μm lenses, for display and illumination, respectively. The replication degree of the MLA was governed by the contact pressure. Polymer flow simulation indicated that the heat conduction and flow speeds of the melted PMMA surface were comparable within several tens of micrometers. In addition, the reflectivity of the AR structure decreased from 4 to 0.5%, and the light intensity of the light-extraction structure increased by a factor of 1.47.

Analysis of the roll imprint on the cross-sectional area of hot rolled wire rod by frequency spectroscopy

This work presents an approach for analysing the sensor data of an eddy-current based cross-sectional area measurement for hot rod and wire steel in an innovative manner and for approximating the influence on the forward slip by longitudinal tensile forces between the mill stands. The method is based on frequency spectroscopy of the cross-sectional area of the rolled stock. The measurement data of three sensors already implemented in two hot rolling mills is used in order to obtain information out of the roll imprint on the cross-sectional area. Since measurement data from two measuring sites and from three sensors are evaluated, this allows statements to be made about the reliability and reproducibility of the measurement and shows that the method can be used for different rolling blocks such as 3-roll and 2-roll blocks. In addition, a mathematical model is presented which allows conclusions to be drawn about possible causes for certain characteristics in the measured frequency spectrum of the cross-sectional area.

Development and Research Application of Optical Waveguide Microstructure Component Manufacturing Process for Triangle Roller Imprinting

This research integrates the stable pressuring of the flat surface of roll-to-plate (R2P) imprinting, the fast production features of roll-to-roll (R2R) imprinting, and compound layer ring-type microstructure mold cavity manufacturing technology. Using the compound multilayer method with air molecule assistance, the stability of the roller imprinting process is enhanced. In addition, with precision modulation of the triangle roll-to-plate (TR2P) system, a stable microstructure roller imprinting manufacturing process is achieved. The experimental results indicate that the developed triangle roll-to-plate system can stabilize the imprinting process of the continuous microstructure array components. Also, by modulating the angles of the roller axis and the ring, the exterior features of the microstructure can also be adjusted. Gas-molecule-assisted continuous pressuring effectively elevated the roll imprinting angle and continuous pressuring time and reached a high replication rate of 99.14%. The optical waveguide microstructure component produced by this process and the average waveguide propagation losses of approximately 1.2~1.4 dB/cm show that it has optical stability and transparency after optical testing. The research proves that the manufacturing process can effectively provide an innovative process for the equipment and application of the microstructure component.

Manufacture of Binary Nanofeatured Polymeric Films Using Nanosphere Lithography and Ultraviolet Roller Imprinting.

This paper describes the manufacture of binary nanostructured films utilizing nanosphere lithography and ultraviolet (UV) roller imprinting. To manufacture the binary nanofeatured template, polystyrene nanocolloids of two distinct dimensions (900 and 300 nm) were primarily self-assembly spun coated on a silicon substrate. A roller imprinting facility equipped with polydimethylsiloxane molds and ultraviolet radiation was employed. During the imprinting procedure, the roller was steered by a motor and compressed the ultraviolet-curable polymeric layer against the glass substrate, where the nanofeatured layer was cured by the UV light source. Binary nanofeatured films were thus obtained. The influence of distinct processing variables on the imprinting of nanofeatured films was investigated. The empirical data suggested that with appropriate processing conditions, binary nanofeatured plastic films can be satisfactorily manufactured. It also demonstrated that roller imprinting combined with ultraviolet radiation can offer an easy yet effective method to prepare binary nanofeatured films, with a miniatured processing time and enhanced part quality.

ITO and graphene-covered Ag grids embedded in PET substrate by thermal roll imprinting for flexible organic solar cells

The development of a low-resistive flexible transparent conductive film (TCF) was demonstrated by showing thermal roll imprinted and an embedded Ag grid. The Ag-embedded TCF shows excellent optical and electrical properties when the secondary layer of ITO and graphene is coated onto the flexible embedded Ag grid substrate. The TCF showed an extremely high transmittance of 77.56% with ITO and 77.73% with graphene; moreover, it showed a very low sheet resistance of 4.05 Ω/□ and 14.0 Ω/□ with ITO and graphene, respectively. This high performance is achieved by thermal imprinting of channels at 15 μm wide so that the DI-based nano silver paste filled in the narrow channels using Dr. Blade's method, thus providing the embedded pattern of Ag grid in the flexible PET substrate. The succeeding TCF performance was validated by fabrication of an OSC (organic solar cell) that exhibits excellent power conversion efficiency (PCE) of 2.649% and 2.551% for the ITO-Ag grid and graphene-Ag grid, respectively. This indicates that the hybrid flexible electrode using an intaglio method can be applied to transparent conducting electrodes for highly efficient opto-electronic devices.

Ultraviolet Beam Lithography System for Digital Fabrication of Roller Molds

This article presents a digital ultraviolet (UV) beam lithography system for fabricating microstructures of arbitrary patterns on a roller mold. This roller mold can then be used in roller imprinting for fast and large-area replication of microstructures on substrates. This digital optomechanical system consists of a UV light source, a digital micromirror device (DMD) and its electronic controller, a high-precision image lens, a fiber array integrated with microlenses on both ends, and a two-axis ( x – θ ) servo-controlled motion stage. It exposes a photoresist (PR) layer coated on the cylindrical surface of a roller with a linear array of 192 small UV spots focused by a microlens/fiber array. On the other end of the fibers, UV light is fed by DMD's micromirrors so that the UV light can be dynamically modulated. Finally, by synchronizing the electronics of DMD chip and the mechanical movement (rotation and translation) of the roller, one can achieve arbitrary UV patterning on the roller's PR layer in a digital and maskless manner. This system can successfully achieve UV patterning with a smallest linewidth of 8 μ m, a pattern resolution of 2.5 μ m, and a total patterning width of 192 mm on a roller with a diameter of 100 mm.

Mass printing of colored natural patterns on Al plate by roll imprinting and thin film deposition

Abstract Metal surfaces finished in color patterns are useful and attractive for both practical and artistic purposes. Although the surface of metals can be patterned by diverse methods including computerized-numerical-control machining, laser-direct surface structuring, and droplet printing, these serial processes are not suitable for the massive manufacturing of complex patterns with variant feature sizes. In this work, we present a continuous roll-imprinting process as a large-area, high-throughput method for producing arbitrary surface patterns on Al. The surface patterns of natural objects such as silk, leather, and paper are replicated via Ni electroplating, and the electroplated Ni replica mold is used as the imprinting roller to transfer the original natural pattern onto an Al plate. The conformity of the imprinted pattern to the original pattern is 80―85 %. Surface-patterned Al plates are also colorized by coating a metal-dielectric double layer, where the top metal layer adjusts the amount of light incident into the underlying dielectric film, strengthening the interference effect. Diverse colors are generated by varying the thicknesses of the coating layers. The colors obtained via experiments agree well with the results predicted using finite-difference time-domain simulation. This study provides a fast and scalable route for producing colored surface patterns on metals and may find various applications ranging from surface decoration and visual arts to product identification and anti-counterfeiting.

Step and scanning lithography for patterning seamless microstructures on the inner surface of a hollow roller

This paper presents a step-and-repeat photolithography method for patterning seamless microstructures on the inner cylindrical surface of a hollow roller. The purpose is for subsequent replication of the microstructures onto the surface of another mold for roller imprinting. The processes include coating of a photoresist (PR) layer, ultraviolet (UV) exposing the PR layer with a photomask, and finally PR developing to obtain patterned microstructures on the inner cylindrical surface. To achieve seamless patterning, UV exposure process is first conducted locally on a narrow and slender area and then consecutively repeated. Through efforts on precision mechanical system design and using a collimated UV light source, consecutively exposed areas can be seamlessly stitched together to form a complete UV exposed pattern on the inner cylindrical surface. Experiments have been carried out using three photomasks with hexagonal arrays of hexagons and circles. Typical feature sizes are around ten to a few tens of micrometers. Details on the experimental results as well as future perspectives on the applications of this new type of lithography for roller imprinting will be addressed.

Facile and Scalable Fabrication of Flexible Reattachable Ionomer Nanopatterns by Continuous Multidimensional Nanoinscribing and Low-temperature Roll Imprinting.

We develop a facile route to the scalable fabrication of flexible reattachable ionomer nanopatterns (RAINs) by continuous nanoinscribing and low-temperature roll imprinting, which are repeatedly attachable to and detachable from arbitrarily shaped surfaces. First, by sequentially performing continuous nanoinscribing over a polymer substrate along the multiple directions, we readily create the multidimensional nanopattern, which otherwise demands complex nanofabrication. After its transfer to an elastomer pad for use as a soft nanoimprinting stamp, we then conduct a low-temperature roll imprinting of the ionomer film to fabricate a flexible and highly transparent RAIN. Reversible loosening of ionic units in the ionomer material at the mild temperature as low as ∼60-70 °C enables the faithful nanopatterning over thermosensitive organic compounds and fragile materials under a slight pressure. The excellent adhesion purely emerging from ionic interactions uniquely realizes the conformal attachability and clean detachability of RAINs for universal targets in ambient conditions, particularly beneficial for individual wearable and mobile devices requiring the user-specific "on/off" of the nanopattern-driven functionalities. As one vivid example, we demonstrate that a single light-emitting device can be switched from the focused pointer to the widespread flashlight depending on the RAIN application upon user's purpose.

Fabrication of seamless roller mould with smooth surface microstructures by rotation lithography and reflow process

In this work, the authors conducted a versatile approach for an innovative fabrication of a seamless micro-stripes array on the roller which is as a mould for roller imprinting lithography. The major steps in the proposed fabrication method include an uniform speed PR-coating process, followed by a digital micromirrors device based maskless lithography projection and an incremental step-and-rotate exposure process. In addition to above-mentioned steps, a following thermal reflow process was performed to transform the micro-stripes into smooth surface microstructures. The study also analysed the mechanism of the reflow process by numerical simulations and experiments. The mechanism includes the gravitational effect and the definition of the four stages of the reflow process. Study results show that the reflow process on the roller is feasible and the proposed method is a promising approach for fabricating three-dimensional smooth surface microstructures on the roller with different requirements.

Development of an UV rolling system for fabrication of micro/nano structure on polymeric films using a gas-roller-sustained seamless PDMS mold

Roller imprinting is one of the most effective methods to fabricate polymeric plate components with nanostructures on the surface. In this study, a gas-bag roller is employed to increase the contact area and ensure conformity of contact between the roller mold and the substrate. The gas-bag roller has a seamless polydimethylsiloxane (PDMS) roller mold with a nano-pillar array. Most of the replicated patterns are not continuous because of roller mold with seams, therefore, the seamless roller mold was produced by PDMS and used to imprint the patterns in this research. Micro/nano-structures were fabricated by casting into the micro/nano-pores of the anodic aluminum oxide (AAO) roller. The micro/nano-pores in the AAO roller are made by a two-step anodization process from a circular aluminum tube of 99.9% purity. An UV-based imprinting facility integrating a gas-bag roller and PDMS roller mold were designed and implemented to replicate nanostructures on the surface of the polycarbonate (PC) continuously. The antireflection and the hydrophobic effects of the fabricated PC film were verified. The reflection drops from 14.7% in the bare PC film to 2% in the PC film, and the contact angle increases from 77.5° in the bare PC film to 124.1° in the PC film with nanostructures.

Double-sided UV roller imprinting of microstructures on transparent plates

UV roller imprinting is one of the most efficient mass-production processes for microstructure replication. Roller imprinting of microstructure on both top and bottom surfaces of substrate is challenging. The imprinting pressure has to remain uniform. Furthermore, it is difficult to irradiate UV light if both molds in the top and bottom are not transparent. In this study, air bearing was used to pressurize the top mold, which resulted in uniform non-contact pressure. UV light was irradiated from the lateral of the transparent substrate. An UV roller imprinting apparatus with air bearing pressing and lateral irradiating of UV light was designed and implemented. Pressure distribution measurements with pressure sensitive film proved that the air bearing provided a uniform imprinting pressure over a large area. V-groove microstructures with micrometer precision have been successfully fabricated on both sides of poly (methyl methacrylate) (PMMA) substrates over 98% replication rate. This study demonstrated lateral-irradiating, air bearing assisted UV roller imprinting has great potential for production of optical components with microstructures on both surfaces.

The Fabrication of Flexible Ag Grid Mesh Electrode by a New Thermal Roll Imprinting Process and Its Application

The Fabrication of Flexible Ag Grid Mesh Electrode by a New Thermal Roll Imprinting Process and Its Application

Constraints and optimization of the laser microwelding process of thin metal foils

Laser microwelding of thin metal foils of various materials is established in several fields of application. Within all these application fields, a sufficient and reliable welding process is required to join thin metal foils successfully. One crucial function of the weld is often a gas-tight sealing. For instance, titanium foils provide hermetic and sterile packaging of medical implants, and vacuum insulation panels and pressure sensors are assembled from stainless steel foils. Even if gas-tightness is not the aim, weld defects lower the functionality of the product. In the case of a roll imprint process in order to structure optical surfaces on films and panels, where nano-structured nickel foils serve as masters, weld imperfections lead to failures in the optical structure. Furthermore, insufficiently welded cathode foils, which are made of aluminum, cause an increasing electric resistivity. Weld defects during laser microwelding are provoked by thermally induced distortion due to small foil thickness. The distortion causes gaps between the joining partners and can lead to a partial process abortion. Hence, metal foils have to be joined in the deep welding mode, which causes less heat conduction losses than conduction welding. In addition to a defect-free weld seam, a broad process window is required for a reliable and robust process. The process window in laser microwelding is determined by the transitions from a full penetration weld to a fusion cut regime and to an incomplete penetration weld. Furthermore, the onset of humping at higher feed rates decreases the cross-sectional area of the join and, as a consequence, the tensile strength, and has to be avoided in order to achieve a high weld quality. For the purpose of considering all mentioned constraints (deep welding regime, process window broadness, and onset of humping) while designing the process with due regard to the applied material, focal diameter, laser power, and feed rate, a deeper understanding of the process is necessary. The present work gives a qualitative and quantitative overview of the occurrence of these constraints in laser microwelding and determines the ideal working range with respect to the combination of process parameters.

Study on the fabrication of transparent electrodes by using a thermal-roll imprinted Ag mesh and anATO thin film

Transparent conductive films have been widely studied because of their potential applications in optoelectronic devices such as paper displays, dye-sensitized solar cells (DSSCs), organic lighting-emitting diodes (OLEDs), organic solar cells and so on. In this paper, we report on a low-resistance, a high-transparents conductive film that can be applied as It a flexible device substrate. In order to the fabricate transparent conductive film, we used a high-resolution roll imprinting method. The following steps were performed: The design and manufacture of an electroforming stamp mold, the fabrication of high resolution roll imprinted on flexible film, and the manufacture of an Ag grid that was filled by using a doctor blade process with a nano-sized Ag paste. Then on patterned Its films, antimony tin oxide was coated with ATO sol solution by using bar the coating method. The fabricated ATO/Ag mesh electrode showed good flexibility, and It exhibited a high optical transmittance of 85.3% in the visible wavelength and a sheet resistance of 41 Ω/sq. Furthermore, the bending test for mechanical properties showed that the ATO/Ag thin film had good flexibility.

Fabrication of seamless roller mold with 3D micropatterns using inner curved surface photolithography

Continuous roller imprinting is one of the most promising means of fabricating micro/nano structures over a large area. However, the fabrication of roller molds with seamless and three-dimensional (3D) complex patterns poses a significant challenge. Accordingly, this paper presents an innovative approach for fabricating a seamless hollow roller master mold patterned with discrete or continuous 3D structures. The major steps in the proposed fabrication method include an inner pneumatic rotary photoresist (PR) coating process followed by a step-and-rotate lithography process or a continuous rotation lithography process. Having fabricated the master mold, the microstructure patterns are transferred to a roller by means of a polydimethyl-siloxane (PDMS) casting technique. The effectiveness of the proposed method is demonstrated by patterning a PDMS-casted roller mold with wavy microstructures and then using the roller mold to fabricate a diffusion optical film. The experimental results show that the diffusion film has a haze of 97.1% and a total transmittance of 91.6%.

The application of magnetic fluid bag micro-roll imprinting technology in optical anti-reflective and solar concentrator soft film replication

This study developed the magnetic fluid bag micro-roll imprinting system equipment, and compared the roll imprinting behavior of the general rigid roller and soft roller imprinting systems. Using the precision equipment system, this study developed optical anti-reflective micro Nano-structure roll imprinting replication and conducted an inspection of the optical features. The research results suggested that the proposed magnetic fluid bag micro-roll imprinting equipment and processing technology can provide even distribution of the magnetic fluid inside the bag. The magnetic force can effectively increase the imprinting contact area of the roller and substrate during the roll imprinting process, while effectively enhancing roll imprinting velocity. In addition, the experiment confirmed that the precision system equipment and processing methodology of this innovative design can successfully print optical anti-reflective film and solar concentrator (Fresnel lens micro-structure). Moreover, it has very good performance in the optical anti-reflective experiment, sunlight intensity analysis, and inspection.

Extrusion Roller Imprinting with a Variotherm Belt Mold

Although many precision fabrication techniques have demonstrated the ability to produce microstructures and micro-devices with sub 100 nm accuracy, we are yet to see a scalable manufacturing process for large-area production. One promising solution to scalable micro- and nanofabrication is thermal roller imprinting. However, existing investigations on thermal roller imprinting revealed poor pattern transfer fidelity, especially for high aspect ratio features. The standard roller imprinting process suffers from the lack of an effective holding and cooling stage so that the adverse effects from the viscoelastic nature of polymers are not managed. To rectify this problem and further improve the production rate, a new extrusion roller imprinting process with a variotherm belt mold is designed, and its prototype was established at a laboratory scale. The process testing results demonstrate that a 30 μm sawtooth pattern can be faithfully transferred to extruded polyethylene film at take-up speeds higher than 10 m/min. The results are promising in that microfeatures or even nanofeatures may be successfully replicated by a robust and scalable industrial process suitable for large-area, continuous production.

Fabrication of a metallic roll stamp with low internal stress and high hardness for large area display applications by a pulse reverse current electroforming process

With the increasing demand for large scale micro/nano components in the fields of display, energy and electrical devices, etc, the establishment of a roll imprinting process has become a priority. The fabrication of a roll stamp with high dimensional accuracy and uniformity is one of the key issues in the roll imprinting process, because the roll stamp determines the properties of the replicated micro/nano structures. In this study, a method to fabricate a metallic roll stamp with low internal stress, high flatness, and high hardness was proposed by a pulse reverse current (PRC) electroforming process. The effects of PRC electroforming processes on the internal stress, hardness, and grain size of the electroformed stamp were examined, and the optimum process conditions were suggested. As a practical example of the proposed method, various micro-patterns for electronic circuits were fabricated via the roll imprinting process using a PRC electroformed stamp.

Fabrication of a roll imprint stamp using zirconia for the UV roll imprinting process

In the present work, we have developed a new method for fabricating a roll imprint stamp containing three dimensional micro- and nanosized patterns for the ultraviolet (UV) roll imprinting process, using a flexible poly-dimethylsiloxane (PDMS) mold and a UV-curable zirconium oxide (ZrO2) nanoparticle (NP) dispersion resin. By employing the UV-curing imprinting process, the micro- and nanopatterns on the PDMS mold were successfully transferred to the ZrO2 NP dispersion resin film, attached to the surface of the roll. The obtained ZrO2 roll imprint stamp has two main advantages: a high hardness after annealing at 600 °C and a good anti-sticking surface after the surface treatment carried out using a hydrophobic self-assembled monolayer (SAM). As a result, the ZrO2 roll imprint stamp effectively transferred its micro- and nanopatterns to a large area of the flexible polymer substrate, maintaining a high quality throughout the whole UV roll imprinting process.