Embossing Process Research Articles

Fabrication of superhydrophobic surfaces on a glass substrate via hot embossing

This study developed a new hot pressing process to prepare superhydrophobic surfaces with controllable shape and size on a glass substrate. Microstructures were fabricated on tungsten carbide mold via picosecond laser processing. Microgroove structures were reproduced on glass during the hot embossing process and SiO2 nanoparticles laid on the mold were also embedded into the glass surface under the action of heat and pressure to provide nanostructures. The contact angle of the superhydrophobic glass surface reached up to 161.8°, and the sliding angle was only 3°. The structures and chemical composition of superhydrophobic glass surface were identified by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), and Fourier transformed infrared (FTIR) spectroscopy. The 3D laser scanning microscopy result showed the height (20 μm) of the microgroove structures, while white light interferometry revealed the surface roughness (Ra 2.725 μm). The superhydrophobic glass surface demonstrated satisfactory temperature resistance and chemical stability through temperature and acid and alkali solution immersion tests. The surface exhibited certain mechanical stability by friction and wear test. This work provides a new hot embossing method for solving the problem of structural consistency and mass production of superhydrophobic glass, and will have great application prospects in the engineering field.

Study on soft hot embossing process for making microstructures in a cyclo-olefin polymeric (COP) film

Thermoplastic polymers are the primary materials for fabricating commercial microfluidic devices. Despite many excellent properties, the low thermal conductivity is a common limiting factor in speeding up temperature-dependent biological processes, particularly for polymerase chain reactions. There is a need to develop a fabrication process to create thin-film microfluidic devices that can have a small thermal mass and a short microchannel-to-surface distance. This type of device requires the depth of micropatterns to be very close to the film thickness, which can encounter serious fractures during the demolding process. To overcome this challenge, we develop a soft hot embossing process to create micropatterns in a 188 µm thick cyclo-olefin polymeric (COP) film with a high embossing-depth to film-thickness ratio. The advantage of using a soft master is it can easily be peeled off from the molded film without causing a fracture from micropatterns. Polydimethylsiloxane (PDMS) is used as the soft silicone master, and four different 110 µm high micropatterns are studied, including ribs, grooves, and circular columns and cavities. PDMS masters for creating a 110 µm deep microchannel with different arrays of 70 µm deep microwells are also investigated. The heights of these one-layer and two-layer PDMS masters are 58.8% and 95.7% of the film thickness. Experimental findings show that less than 3% height variation can be achieved using a single-layer PDMS master with a low aspect ratio. For the two-layer micropatterns, it was found that a dense array with a smaller gap between microwells can have a better pattern transfer. In summary, this study demonstrates the feasibility of using a soft master to create deep or tall micropatterns in a COP film. The possibility of using a soft hot embossing process to create micropatterns for thin-film microfluidic devices is verified.

AAO Mould for Fabricating Anti-Reflective Polymer Nanopillar Array on Large Area

Anti-reflective polystyrene nanopillar arrays were fabricated by the process of hot embossing where it utilizes the nickel coated anodised aluminium oxide template. Electroless plating being a catalytic method of plating uniformly coats the membrane which increases its strength. The supporting layer of nickel makes AAO template suitable to be used as a mould multiple times. Highly conformal nanopillars of average diameter 400nm and length 30 μm to 50μm were fabricated on the area of ⁓5cm2. Hot embossing process ensures repeatability with precision and high throughput. The enhanced light entrapping is attributed to the multiple internal reflection in the nanopillars of high aspect ratio.

Modified polymer nanopillars array for enhanced light trapping on large area

ABSTRACT Electroless plating is used to enhance the strength of anodised aluminium oxide (AAO) which can be further utilised as a mould to fabricate the structures on large area of polymer for anti-reflection properties. Nanopillars of high aspect ratio are fabricated on polymer (polystyrene) sheet by hot embossing process which has ensured repeatability with precision and high throughput. The height of nanopillars matches the depth of the mould cavity. The enhanced light trapping performance is attributed to the high aspect ratio nanopillars with cup-shaped top surface.

Investigation on ultrasonic-assisted embossing process of micro-features with variable curvature as functional surface using ultra-thin sheet of 5052 aluminum alloy

Investigation on ultrasonic-assisted embossing process of micro-features with variable curvature as functional surface using ultra-thin sheet of 5052 aluminum alloy

Parametric optimization of two-photon direct laser writing process for manufacturing polymeric microneedles

Laser-based additive manufacturing methods have been rapidly developed in recent years and it is anticipated that this new generation of microfabrication tools will dominate the market in the near future. Three-dimensional (3D) microprinting based on two-photon polymerization allows manufacturing of complex microstructures with a resolution down to hundreds of nanometers. In recent years, the technology has been used for the manufacturing of a variety of nano- and micro-sized features such as microfluidic devices, photonics, micro-optics, and microneedle arrays. Microneedles have been mainly studied for transdermal drug delivery of therapeutic agents across the skin and withdrawing bio samples for point-of-care (POC) diagnostics. With significant development being made, it is now possible to 3D print complex microneedle structures directly from computer-aided design (CAD) models by the two-photon direct laser writing technique. However, selecting the optimal parameters and investigating the possible arrangement for the print process often involves intensive optimization process and testing. Herein we report on fabrication of highly detailed microneedles using the two-photon direct laser writing process with a discussion of optimization and parameter selection for microprinting tall microneedles with side-channels and other complex designs. Due to the long printing time, this manufacturing process is currently best suited to print master microneedles. Therefore, we further demonstrate the replication capabilities of the master microneedles by the soft embossing process. Additionally, the mechanical characteristics and insertion force of the microneedle replicas are investigated.

Fabrication of High Precision Silicon Spherical Microlens Arrays by Hot Embossing Process.

In this paper, a high-precision, low-cost, batch processing nanoimprint method is proposed to process a spherical microlens array (MLA). The nanoimprint mold with high surface precision and low surface roughness was fabricated by single-point diamond turning. The anti-sticking treatment of the mold was carried out by perfluorooctyl phosphoric acid (PFOPA) liquid deposition. Through the orthogonal experiment of hot embossing with the treated mold and subsequent inductively coupled plasma (ICP) etching, the microstructure of MLA was transferred to the silicon substrate, with a root mean square error of 17.7 nm and a roughness of 12.1 nm Sa. The average fitted radius of the microlens array units is 406.145 µm, which is 1.54% different from the design radius.

Blends Based on Poly(ε-Caprolactone) with Addition of Poly(Lactic Acid) and Coconut Fibers: Thermal Analysis, Ageing Behavior and Application for Embossing Process.

In this research a biodegradable blend of poly(ɛ-caprolactone) (PCL) and poly(lactic acid) (PLA) is proposed as a new material for the production of a relief printing plate used for special applications on packaging materials, i.e., the embossing process. Coconut fibers (CFs) were added as a natural filler to PCL/PLA blends to improve the functional properties of the prepared blends. Thermal, mechanical and surface analyses were performed on the unaged and artificially aged blends. The results showed that CF has been proven to optimize the hardness of the blend, which is crucial for the production of relief plate for embossing applications. The lowest hardness was measured on neat PCL (53.30° Sh D) and the highest value on PCL/PLA/CF 70/30/3.0 blend (60.13° Sh D). Stronger interfacial interactions were present at the PLA/CF interface because the interfacial free energy is closer to zero and the work of adhesion and spreading coefficient are higher than for the PCL/CF interface. The results of thermal analysis of unaged and aged blends showed that ageing for 3 weeks resulted in significantly lower thermal stability, especially for neat PCL and PCL/PLA 80/20 blends. Blends with a higher content of PLA and CF showed a slightly increased ageing resistance, which is attributed to the increased crystallinity of PLA after ageing due to the addition of CF showed in the DSC diagrams.

NUMERICAL AND EXPERIMENTAL INVESTIGATIONS ON GFRP AND AA 6061 LAMINATE COMPOSITES FOR DEEP-DRAWING APPLICATIONS

Fibre-metal laminates (FMLs) are a multi-layered prominent class of hybrid composites gaining keen attention among researchers due to the combined advantages of the products used for aerospace and lightweight applications. This work involves one such investigation of hybrid sandwich laminate composites of aluminium sheets and a glass-fibre-reinforced thermoplastic (GFRP) core. FRPs can be conjoined with other lightweight materials to enhance the weight-to-strength forming performance and reduce manufacturing costs. However, the thickness reduction of the components for lightweight products makes the FRP-to-metal amalgamation a great challenge. The process of warm embossing is imposed to enhance the quality of single-lap adhesive bonding in FRPs and AA 6061 thin sheets. In this investigation, the formability of a FML made of AA 6061 and GFRP is predicted based on its deformation and wrinkle formation when it is processed during deep drawing. This research paper deals with analytical and experimental results regarding the prediction of deformation cause and effect in fabricated composite laminates with orientation angles of (90°; 0°; 60°; 30°; –45°; 45°). The method of evaluation combines the usage of ANSYS PrepPost with an explicit-dynamics module that bolsters designing, drafting and analysis.

Study on Filling Capacity of Optical Glass in a Novel Rapid Hot Embossing Process

This paper aims to present a novel rapid hot embossing approach and to study filling capacity of optical glass in the hot embossing process. Firstly, a novel rapid hot embossing device is developed, which consists of a rapid heating module and a precision loading module. Particularly, the rapid heating module allows a maximum temperature of 800 °C and a heating rate of 300 °C/min, with decent temperature control accuracy and uniform temperature distribution. In hot embossing process, by incompletely filling the microhole of silicon carbide mold, a microlens would be formed on the surface of glass disc, and the filling capacity of glass is quantified by the maximum height of the microlens. The tailor-made hot embossing device was exploited to conduct a series of experiments for evaluating effects of process parameters on the filling capacity of N-BK7 glass. Experimental results indicate that the filling capacity of glass could be enhanced by increasing the embossing force, the embossing temperature, the soaking time but decreasing the annealing rate. Furthermore, compared to soaking time and annealing rate, embossing force and embossing temperature have more significant influence on the filling capacity of N-BK7 glass. Therefore, the novel rapid hot embossing is a practical and promising technology for fabricating microstructures on glass materials with high softening points.

Fabrication of microstructured polymers by a simple biotemplate embossing method and their characterization

AbstractIn this work, microstructures were developed on a polymer surface using an embossing process by utilizing the transverse section of a wood as a biotemplate/mold. Microstructured polymers obtained by the proposed practical method were characterized by optical microscope for rough imaging, by scanning electron microscope for morphological properties and by Fourier transform infrared spectroscopy for surface chemistry. Utilization of a fluoropolymer eliminates the anti-stick surface pre-treatment and facilitates intact demolding of polymer structures from micro-voids of the wood. The height of the polymer microstructures was measured as 4 to 6 μm. Dimensions of the wood micro-voids can be tuned via acid/base treatment process. A drastic increase in heights of polymer microstructures (26 μm) was observed for the sample stamped by the acid/base treated biotemplate. The proposed method, which delivers well-organized microstructure patterns on fluoropolymer surfaces, can be utilized in the production of specialty surfaces, such as antibacterial, stick/anti-stick and water repellent.

Low‐Cost, Large‐Area, Multifunctional Stretchable E‐Tattoos Inspired by Dough Figurines for Wearable Human‐Machine Interfaces

AbstractNoninvasive electronic tattoo (e‐tattoo) attached to human skin surface for accurately obtaining various physiological information, has been widely used in wearable human‐machine interfaces (HMIs) for medical care, sports training, and artificial intelligence. The existing preparation technologies of e‐tattoos are difficult to satisfy the requirement of commercial mass production due to their high cost and low time efficiency. Here, inspired by the Chinese folk craftsmanship of dough figurines, a set of one‐step forming embossing process and a thermal‐mismatch‐induced transfer method are proposed for high‐efficient manufacture of low‐cost, large‐area, and multifunctional stretchable e‐tattoos. Benefited from the excellent flexibility and stretchability, the fabricated e‐tattoos can conformably follow the deformation of skin and collect high‐quality bioelectrical signals. Moreover, it can maintain good mechanical and electrical properties even when stretched to 40%. As a proof‐of‐concept, the 5‐µm‐thick e‐tattoo electrodes with hollow‐out and serpentine design are fabricated and demonstrated for the wearable HMI applications of electrocardiogram, electromyogram, brain training, epidermal heating, and flexible interconnection. Therefore, this cost‐effective and high‐fidelity e‐tattoo provides a potential path for the wearable HMI of widespread, non‐irritating, and multifunctional.

Water-repellent hierarchical microstructured PTFE films via micro powder hot embossing

The preparation of hierarchical microstructured surfaces to obtain different wettability has been studied in both academy and industry. Polytetrafluoroethylene (PTFE) is an ideal material for preparing superhydrophobic surface due to its ultra-low surface energy. However, it is still a challenge to prepare hierarchical structure on the surface of PTFE. In this paper, PTFE films with hierarchical structure were successfully prepared by micro powder hot embossing (mPHE) process. Through characterization, the maximum contact angle and minimum sliding angle can reach up to 164° and 5.3° respectively. The influence of processing parameters and particle size on forming qualities was discussed. A dimensionless indicator was proposed to successfully describe the hierarchical character and characterize the relationship between wetting states and forming quality. Finally, a series of mechanical and chemical durability tests were carried out, verifying the practical application value of the prepared PTFE films.

Fast tool machining and hot embossing for the manufacture of diffractive structured surfaces

Nowadays, highly functional optical elements are part of day-to-day use by most of us, whether in form of camera systems in mobile phones or as security features on banknotes and identification documents. The conventional production of diffractive optical elements is mainly covered by lithographic processes. Nevertheless, due to long production times, this process is very expensive when it comes to mass production and the structuring of large areas. For this reason, a novel manufacturing process for structured moulds was developed by the Leibniz Institute for Materials Engineering (IWT). This involves a diamond turning process in combination with a high frequency nano Fast Tool Servo (nFTS) to generate the negative diffractive structure on a metal surface. Afterwards, the structured surface can be replicated in large numbers in a hot embossing process and thus increase market share. In recent work, this process has been investigated in cooperation with Karlsruhe Institute of Technology. The surfaces reproduced in this process meet the highest requirements in terms of precision and shape accuracy of the structure elements. Moreover, the optical functionality of such structures applied as security holograms was successfully demonstrated.

Material Modeling of PMMA Film for Hot Embossing Process.

This study provides an analysis of the hot embossing process with poly methyl methacrylate (PMMA) film. The hot embossing process engraves a fine pattern on a flexible film using a stamp, applied heat and pressure. As the quality of the embossing pattern varies according to various process variables, the mechanism of making the embossed shape is complicated and difficult to analyze. Therefore, analysis takes much time and cost because it usually has to perform a lot of experiments to find an appropriate process condition. In this paper, the hot embossing process was analyzed using a computational analysis method to quickly find the optimal process. To do this, we analyzed the embossing phenomenon using the finite element method (FEM) and arbitrary Lagrangian–Eulerian (ALE) re-mesh technique. For this purpose, we developed a constitutive model considering the strain, strain rate, temperature-dependent stress and softening of the flexible film. Work hardening, strain softening, and temperature-softening behavior of PMMA materials were well described by the proposed method. The developed constitutive model were applied in the embossing analysis via user-subroutine. This proposed method allowed a precise analysis of the phenomenon of film change during the hot embossing process.

Cover Picture: Materials and Corrosion. 10/2021

Cover:The influence of an embossing process on the microstructure and corrosion behavior of Al—1.1 wt%Mn strips used in the manufacturing of high‐frequency welded microfin tubes was studied. The optical and electron microscopic images, X‐ray tomography and FIB cross‐sectional analysis on the cover page present an overall view of deformation asymmetry caused by embossing and its influence on different corrosion behaviors at each side of the corroded embossed fins.More detailed information can be found in: Giorgio Giovanni Battista Zaffaroni, Visweswara Chakravarthy Gudla, Simone Laganá, Carsten Gundlach, Bjorn Olsson, Rouhollah Yazdi, Jan Halvor Nordlien, Rajan Ambat, Microstructure—Dependent Corrosion of Herringbone Grooved Embossed Al‐1.1 wt%Mn Strips for Heat Exchanger Tubes, Materials and Corrosion 2021, 72, 1582.

Improvement of Sheet Metal Properties by Inducing Residual Stresses into Sheet Metal Components by Embossing and Reforming

In sheet metal forming, combination of embossing and reforming allows the mechanical properties of sheet metal materials to be specifically improved. Here, local property modification is achieved by the residual stresses induced as a result of the one-sided embossing process followed by a reforming step. The residual stresses induced in this specific way can lead to a significantly increase in the fatigue strength of processed sheet metal components. However, in order to ensure this kind of component optimization in continuous operation, the induced stresses have to be homogeneous. In this respect, the main objective of the study reported about in this paper was to identify a forming strategy, consisting of the process steps embossing and reforming, that generates preferably homogeneous residual stress distributions into sheet metal blanks. For this, numerical and experimental investigations were carried out with samples of the stainless steel (X6Cr17) having a thickness of 1.5 mm. It was found that embossing and reforming, integrated into a conventional forming process, is a novel approach to specifically induce very localized homogeneous compressive residual stresses in sheet metal materials. This eliminates the need for costly post-processing by means of surface treatment.

Thermo-Physics characterization of polypropylene/multi-walled carbon nanotube nanocomposites for rapid replication using hot embossing process

This study presents a comprehensive review of the thermophysical, rheological, and mechanical characteristics of nanocomposites reinforced with carbon nanotubes (CNTs). The high-loaded polypropylene (PP) nanocomposites with multi-walled carbon nanotube loadings ranging from 0.01 wt.% to 5 wt.% were elaborated via high-shear mixing using a twin-screw mixer. The structural and rheological properties of the neat polypropylene in the molten state and those of the elaborated composites were determined. The thermophysical properties of the nanocomposites were investigated via differential scanning calorimetry and thermogravimetric analysis. The mechanical properties were determined through quasi-static tensile testing at room temperature. The results clearly indicate that the incorporation of CNTs in a thermoplastic polymer matrix significantly improves the final thermophysical and mechanical properties of the nanocomposites, through excellent dispersion of CNTs in the thermoplastic matrix and an improvement in interfacial interaction. The produced nanocomposites were granulated and used in a hot embossing process to manufacture micro-structured components. These micro-shapes on the surface of a metal mould were successfully transferred to a CNTs/PP nanocomposite substrate.

An anchoring array assembly method for enhancing the electrical conductivity of composites of polypropylene and hybrid fillers

Constructing an interconnected filler-filler network in a polymer matrix is essential for enhancing the electrical conductivity of polymer composites. This work describes an Anchoring Array Assembly method for distribution of copper particles (CP) and carbon fibers (CF) in a polypropylene (PP) matrix. Constrained by a predesigned array anchoring template, the CP distribution achieved a high packing density in the PP matrix during compression molding which is key for filling the gaps between CFs, as well as for forming an interconnected hybrid filler network. Using the fixed array anchoring design, the dispersion and flow behavior of the conductive fillers and the polymer matrix are critical. When the inclination angle between the groove of the anchor mold and the horizontal plane is greater than 11.5°, the migration of CP in the molten PP in the anchor mold during the hot embossing process is restricted. The most conductive composites were obtained when the CPs were densely arranged in a triangular format. The conductive filler network was determined by the preset dense triangular “island-bridge” structure of the customized microarray mold. The conductivity of the composites prepared by the anchoring array assembly method (CF content 18 vol.% and CP content 2 vol.%) reached 137.70 S/m, 52 times higher than that prepared by traditional hot embossing methods with the same filler loading.

Hot embossing of moth eye-like nanostructure array on transparent glass with enhanced antireflection for solar cells

Antireflection (AR) silicon and glass surfaces are necessarily required for solar cells, because a reflective silicon solar cell with a glass covering will reflect a percentage of sunlight. In this work, we demonstrate a universal and scalable net-shape nanofabrication method for broadband nanostructured AR surface on transparent glass, intended for solar cell applications. Moth eye-like glass nanopillars with various diameters were successfully fabricated by a combination of precision hot embossing and ultrasonic vibration demolding process. The morphologies of nanopillars were detected to characterize different profiles formed by glass flow at elevated temperatures. Facile optical experiments were designed and conducted to measure the AR performance at varying wavelengths and angle of incidences and the proposed nanostructures exhibit excellent AR property. Additionally, a feasible optical modeling is developed and compared with the measurement to evaluate the theoretical optical behaviors of glass nanostructures based on their embossed shapes. The inexpensive and environmental hot embossing method with ultrasonic vibration demolding is expected to create AR glass nanostructured surfaces for widespread applications such as solar cells, displays and laser systems.