Flexographic Printing Research Articles

Characterization and functionalization of flexographic printing forms for an additive manufacturing process of polymer optical waveguides

To improve printing results, a printing form can be functionalized and the material transferring behavior can be adjusted. In this work, a flexographic printing form is divided into three different areas: first the elevated, material transferring structures (1); second the rising edges between the printing form substrate and the elevated structures (2); and third the transition area (3) between (1) and (2). These three areas are laser functionalized by inserting a defined micropattern. Subsequently, the printing results are investigated and categorized into groups. The groups indicate which functionalized surfaces (1, 2, and 3) have what kind of influence on the printing result. As part of a low cost and efficient approach to manufacture polymeric optical waveguides, a way is presented to show how the waviness of printed conditioning lines can be reduced significantly by laser functionalizing to improve the quality of the waveguides.

Simultaneous Wrinkle-Patterning and In Situ Foaming in Polymer Films Using Supercritical Carbon Dioxide.

Unique and random wrinkle features are desired for applications, especially in anticounterfeiting. Multifunctional wrinkled materials as well as simple wrinkling methods are desired for more applications. In this study, free-standing wrinkle-patterned porous polymer films were prepared using a modified supercritical CO2 foaming strategy. Spontaneous wrinkling was generated by applying moderate normal stress to the polymer films while foaming in situ. The wrinkle characteristics (wavelength and amplitude) were shown to be governed by the film thickness and the magnitude of the applied stress. Excessive (>5000 N) or no stress produced no obvious wrinkling or foaming whatsoever. Moreover, different morphologies of the wrinkles such as brain coral and herringbone patterns were achieved depending upon the shape of the mold used to apply the stress. Thus, the patterns show unique features for each batch process. Notwithstanding, geometric shape of the foamed wrinkle area is customizable. The reported wrinkling strategy offers the complementary advantage of patterning a foam in a polymer film and templating a PDMS stamp for different applications such as "mask-less" soft lithography, anticounterfeiting, pattern transfer, flexographic printing, and displays.

Printing accuracy tracking with 2D optical microscopy and super-resolution metamaterial-assisted 1D terahertz spectroscopy

Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices, ranging from displays to active wear. It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process. However, this process is still not being subjected to a quality control method that is both non-invasive and in situ. To address this issue, we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz (THz) waves. The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression, or expansion factor, for a pattern printed on a flexible plastic substrate. The pattern, which is carefully selected, has Babinet’s electromagnetic transmission properties in the THz frequency range. To validate our choice, we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy. Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission. Notably, under specific conditions, one-dimensional (1D) THz information from a resonant pattern can be more accurate than two-dimensional (2D) microscopy information. This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production.

Flexographic and screen printing of carboxymethyl chitosan based edible inks for food packaging applications

Abstract In this study, carboxymethyl chitosan (CMC) based edible inks were prepared and the flexographic and screen printing properties of the inks were investigated. The water soluble carboxymethyl chitosan was prepared through a one-pot, environmental-friendly method in an alkali/urea mixture. The monascus pigment was then mixed with the carboxymethyl chitosan to obtain the inks. The inks showed good printing quality (e.g. pH, scratch resistance, optical density, contact angle and chromatic value) on coated paper after flexographic and screen printing. Also, the obtained inks, with excellent antibacterial activity against E. coli and S. aureus, demonstrated great printing effect on different substrates including different foods. We believe that this water soluble chitosan based edible inks may have potential applications in different food and medical packaging fields.

Influence of Some Flexographic Printing Process Conditions on the Optical Density and Tonal Value Increase of Overprinted Plastic Films

The print quality of prints performed with flexographic printing technology is influenced by various parameters such as viscosity of the printing inks, printing substrates, plates, anilox rolls, etc. The aim of this work is to analyze the influence of ink viscosity, printing plate and printing base on selected properties of print quality, such as optical density of full tone area and the increase of tonal value (TVI). Additionally, the printed dots on 5, 15, 30, 50 and 75% of half tone area were investigated using digital microscopy. The least square fitting method in a matrix form was successfully used in order to confirm the influence of printing process parameters on print quality. The results obtained reveal the significant influence of the printing plate and printing substrate characteristics and the lesser influence of printing ink viscosity for 40–100% coverage area. The values of the optical densities of full tone areas are mainly influenced by the properties of the printing plate and the printing base. Furthermore, the optical density decreases when the value of flow time decreases, which is related to the lower thickness of dried ink film. The TVI on light tones (0 to 20%) is mainly influenced by the ink viscosity.

A precision desktop plate-to-roll apparatus for development of advanced flexographic printing processes

Flexographic printing, which involves high-speed contact of an inked stamp against a substrate, is of increasing interest for scalable manufacturing of electronics in new formats. However, the adaptation of flexography to thinner, finer features which are generally required for printed electronics requires improved understanding of stamp-substrate contact mechanics. Here, we present a desktop plate-to-roll (P2R) printing apparatus which enables the study of flexographic printing in a semi-continuous format that mimics industrial printing. In particular, we tailor the specifications of the machine to use nanoporous stamps which have been shown to enable flexographic printing of ultrathin ink features with micron-scale linewidth. Printing with nanoporous stamps requires precise control of stamp-substrate contact force (2–250 mN) and elimination of shear force at the interface among others; these are accomplished using a flexure-supported substrate, and by coordinated rotary-linear motion of the system. We detail the design and evaluation of the P2R machine and demonstrate printing of high-resolution features (<3 μm line width) with nanoporous stamps at speeds of up to 0.2 m/s.

Vertically Aligned Graphene Prepared by Photonic Annealing for Ultrasensitive Biosensors.

Graphene exhibits excellent physical, electronic, and chemical properties that are highly desirable for biosensing applications. However, most graphene biosensors are based on graphene lying flat on a substrate and therefore do not utilize its maximum specific surface area for ultrasensitive detection. Herein, we report the novel use of photonic annealing on a flexographically printed graphene-ethyl cellulose composite to produce vertically aligned graphene (VAG) biosensors for ultrasensitive detection of algal toxins in drinking water. These VAG structures, which maximized the specific surface area of graphene, were formed by partial removal of the polymeric binder upon applying intense pulsed light on the printed graphene. A label-free and low-cost VAG biosensor based on a non-faradaic electrochemical impedance spectroscopy technique was fabricated. The biosensor exhibited a limit of detection of 1.2 ng/L for microcystin-LR in local tap water. Such an ultrasensitive VAG biosensor is suitable for low-cost mass production using an integrated roll-to-roll flexographic printing with rapid photonic annealing technique.

Investigating Porous Media for Relief Printing Using Micro‐Architected Materials

Advances in printed electronics are predicated on the integration of sophisticated printing technologies with functional materials. Although scalable manufacturing methods, such as letterpress and flexographic printing, have significant history in graphic arts printing, functional applications require sophisticated control and understanding of nanoscale transfer of fluid inks. Herein, a versatile platform is introduced to study and engineer printing forms, exploiting a microscale additive manufacturing process to design micro‐architected materials with controllable porosity and deformation. Building on this technology, controlled ink transfer for submicron functional films is demonstrated. The design freedom and high‐resolution 3D control afforded by this method provide a rich framework for studying mechanics of fluid transfer for advanced manufacturing processes.

Exploitation influence on compressible polyurethane flexographic sleeve properties

Abstract Flexographic sleeves are made using various materials, including a sub-group with extremely durable polyurethane foam shock-absorbing layer. During exploitation, the sleeves are exposed to cyclic dynamic loading, and the flexographic printing process is highly sensitive to the changes in pressure. Deformation of printing elements occurs due to the almost two times higher residual strain of the exploited sleeves. Changes in the residual strain induce occurrence of the hysteresis losses, which lead to heat generation. The forces impacting the material are not strong enough to induce permanent deformation in the microstructure. Therefore, the leading cause of the change lies in the molecular structure of the parent polymer of the polyurethane foam cell walls, whose resilience is declining. The thickness of the exploited sleeves tends to be around 8 % lesser. In addition to high-frequency cyclic loads during printing, the adhesive layer of self-adhesive sleeves undergoes reduction in the share of acrylates, phthalates and rosin, thereby reducing the adhesive strength and the force needed to initiate the de-adhesion by half. The knowledge of mechanisms of change in certain characteristics of the sleeves enables predicting their service life and increasing the stability of the printing process through possible corrections of other process parameters.

Thermoforming of planar polymer optical waveguides for integrated optics in smart packaging materials

Abstract The innovations in smart packaging will open up a wide range of opportunities in the future. This work describes the processing of additive manufactured and planar integrated polymer optical waveguides for use in smart packaging products. The previously published combination of flexographic and Aerosol Jet printing is complemented by thermoforming and thus creates three-dimensional integrated multimode waveguides with optical attenuation of 1.9 dB/cm ± 0.1 dB/cm @ 638 nm. These properties will be the basis to develop smart applications in packaging materials.

Novel Paper Based Hand-Fabricated Point of Care Prothrombin Time Sensing Platform Using Pencil and Correction Pen

Cardiovascular diseases (CVDs) are reported to be the leading cause of death worldwide by World Health Organization (WHO) with an approximate of 31% of global deaths. Consequently, it has been noted that the largest sector of population which experiences coagulation or hemostatic imbalances or undergo oral anticoagulation therapy (OAT) are the major sector susceptible to the risk of mortality due to cardiovascular ailments such as atherosclerosis, deep vein thrombosis (DVT), stroke etc. These candidates are prescribed or administered using oral anticoagulation therapy (OAT) and are advised to take the Prothrombin Time (PT) test respectively. Prothrombin Time (PT) analyzers are the type of haemostasis analyzer mainly catering to the coagulation following the extrinsic pathways. Additionally, the candidates under OAT requires routine administration of the coagulation status for proper dosage of warfarin or its derivatives which shares a very narrow therapeutic window. A slight amount of imbalance in the coagulation chemistry can disrupt the cardiovascular functioning, hence a routine monitoring is strongly mandated by cardiac surgeons. It is important to realize a simplified hand held, low cost point of care solution for diagnosing hemostasis or coagulation status to cater both the rural and urban sectors resulting in lower casualties due to coagulation imbalance. The respective work proposes a handheld point of care PT sensing paper sensor using very inexpensive pencil and correction pen and Whattman filter paper. In addition the sensor has enhanced capability of carrying our sensitive detection of coagulation status compared to the existing complex and expensive sensors developed through a variety of methods like screen printing, lithography, flexography printing, wax printing, PDMS printing, stamping etc. The proposed device consists of two pencil marks as electrodes. The device is illustrated in Figure 1. The sensor monitors a change in impedance (resistance) w.r.t time. Blood being an ionic fluid whose chemistry changes with the ionic interactions during the process of coagulation results in a direct correlation of the coagulation process to the respective impedimetric signatures. The synthetic coagulation behavior and the response of the device has been measure using nail paint as an analyte. The points of maximum changes in resistance (first and second) denotes the application of the analyte to the sensor and initiation of coagulation or solidification respectively (shown in Figure 2) from which the coagulation time is further derived. Lab View has been used as an interfacing platform for processing the respective resistive data and generating corresponding coagulation status. Thus, the particular PDE-PAD (pencil drawn electrodes- paper-based analytical devices) can be considered as a promising future device for low cost sensitive detection platform for a point of care PT diagnosis. Figure 1

Printability Analysis of Compostable Films by Flexographic Water Based Ink

This research analyzed the printability of compostable films commercialized in the Thai market such as PLA/PBAT and PBAT/starch; and to comply with EN 13432 standard by using flexographic water based ink. A narrow web flexographic printing press was set up and opperated. Print quality parameters such as optical density, tone reproduction, print contrast and print uniformity were investigated. Results showed that these compostable films were hydrophobic in nature, in combination with fracture and voids of substrates’ surface. Even the substrates could be printed relatively well but showed poor ink adhesion. Surface treatment, therefore, was necessary, but having limitation. Anilox line screen 700 lpi and printing speed at 30 m/min were preferable to achieve the optimum tone reproduction and print contrast. This was based on the image resolution of 133 lpi and corona dosage at 500 watt-min/m2. Images of printed samples from SEM and SPM indicated that the fracture surface and void of films could lead to decrease their printability. It was found that starch blend gave better results as being a filler of the surface roughness of the substrate..

Determining the factors that affect the quality of test prints at flexographic printing

The intensive use of flexographic printing for packaging decoration and the increased consumer demands for it require an in-depth study of the factors that influence the prints’ quality. In this paper, we examined the test prints obtained at a flexographic proofer. Images on cardboard were printed by the environmentally friendly inks made by a Ukrainian manufacturer. The effect of the cardboard surface layer on the microgeometry of the prints created by cyan, yellow, black, and magenta inks has been shown. It has been established that the roughness parameter Ra for a two-layer coated cardboard is reduced by 3 times as compared to the uncoated cardboard. The photographs of the microstructure of the prints’ surface, their profile demonstrate a significant effect of the chalked coating on the image quality. It has been confirmed that the ink layer smooths out the micro-roughness of the print surface. However, when printed on the uncoated cardboard, the ink particles penetrate deeper into the structure and do not completely smooth out its micro-roughness. If the size of the printing element is smaller than the size of the cell on a raster roller, it falls into this cell and the ink is applied beyond the boundaries of the image. As a result, a spot of an arbitrary shape is formed on the print instead of a raster dot of a certain size, that is, the so-called "inverse tone transfer" occurs. We have measured the densitometric indicators of prints (optical density, gray balance), which significantly affect the quality of the product. Based on a Harrington's desirability function, the maximum permissible values of optical density, evenness of printing, contrast, dot gain of raster elements, and trapping, have been calculated. According to the generalized optimization criterion, a comprehensive index of the prints’ quality has been determined, which could ensure the predicted quality of a would-be run of the printed products, and would make it possible to adjust the printing process if necessary

Modal analysis of central impression cylinder based on fluid–solid coupling method

As a key component of satellite flexographic printing equipment, the vibration characteristics of the central impression cylinder have an important effect on the product quality. In order to improve dynamic characteristic of the central impression cylinder, the modal analysis on the central impression cylinder is carried out in combination with finite element software in this paper. Then, the modal properties are systematically compared between the central impression cylinder with circulating cooling water and without. The results show that the natural frequency of the central impression cylinder is greatly reduced based on the fluid–solid coupling method. Simultaneously, the natural frequencies and mode shapes of the central impression cylinder based on the finite element analysis are verified by an experimental test. The simulation results are in good agreement with the experimental results, indicating the effectiveness of the finite element model and experimental method used in this study.

Dynamic characteristics of printing cylinder with rotating dynamic load

The structural vibration of the center impression cylinder in the flexographic printing machine will bring about production quality problems such as printing ghosts. To this problem, it become an important method to analysis the dynamic characteristics of the center impression cylinder. In this paper, a three-dimensional structural model of the central impression cylinder is established, and builds the dynamic model in finite element software. The vibration modes of the central impression cylinder were studied in the simple-supported system at both ends of the static impression cylinder. In view of the real existence of the rotating dynamic load, the evolution law of the natural frequency and mode shape of the cylinder with the rotating dynamic load is discussed. It is found that as the rotation speed increases, the natural frequency undergoes two steps, and the natural frequency after each step will keep continuity with the high first-order natural frequency, and the modal shape is the same as the high-order original mode. Then, the mode shape is continuously changed, not have a step.

Parametric investigation of flexographic printing processes for R2R printed electronics

ABSTRACTRecent technological advancement in flexographic printing has allowed flexography to catch up with other R2R processes such as gravure printing in the printed electronics field. However, there are many process parameters involved in flexography that can affect the print quality. This work attempted to achieve finer line printing compared to the current 45–100 µm printed line width range of flexography by manipulating and studying these process parameters. A design of experiments was conducted to investigate the influence and interaction of various process parameters such as anilox volume, anilox force and printing force on the printed line width. After identifying the key process parameter from the design of experiments, another in-depth study of the key process parameter was conducted to further investigate how printed line width was affected. The results showed that the printing plate was elastically deformed with a range of 50–400 N printing forces. Beyond the 400-N printing force, the printing plate experienced plastic deformation.

Effect of the Common Solvents on UV-Modified Photopolymer and EPDM Flexographic Printing Plates and Printed Ink Films

The aim of this research was to analyze the influence of the solvents commonly used in flexography on photopolymer and ethylene propylene diene monomer (EPDM) flexographic printing plates and prints. EPDM plates are recommended when the reproduction process includes a higher amount of the solvents or aggressive solvents. Since additional UV treatment of flexographic printing plates could decrease the interaction between the plate and solvent, photopolymer and EPDM plates were treated with varied UV radiation and exposed to different types of solvents. Effects of the UV treatment and of the solvents on printing plate properties and on prints were analyzed. Results show that EPDM plates are more resistant to solvents in terms of the degree of swelling; however, surface properties of the plates were affected for both plate materials. In addition, the degree of swelling and increased hardness due to UV radiation were crucial for changes of the width of printed lines, and altered surface free energy affected the thickness of deposited ink film for both plate materials. Therefore, depending on the qualitative requirements of specific printed film, the duration of UV treatment can be adjusted for use with specific types of printing plate and solvent.

Printed, Highly Stable Metal Oxide Thin‐Film Transistors with Ultra‐Thin High‐κ Oxide Dielectric

AbstractLately, printed oxide electronics have advanced in the performance and low‐temperature solution processability that are required for the dawn of low‐cost flexible applications. However, some of the remaining limitations need to be surpassed without compromising the device electronic performance and operational stability. The printing of a highly stable ultra‐thin high‐κ aluminum‐oxide dielectric with a high‐throughput (50 m min−1) flexographic printing is accomplished while simultaneously demonstrating low‐temperature processing (≤200 °C). Thermal annealing is combined with low‐wavelength far‐ultraviolet exposure and the electrical, chemical, and morphological properties of the printed dielectric films are studied. The high‐κ dielectric exhibits a very low leakage‐current density (10−10 A cm−2) at 1 MV cm−1, a breakdown field higher than 1.75 MV cm−1, and a dielectric constant of 8.2 (at 1 Hz frequency). Printed indium oxide transistors are fabricated using the optimized dielectric and they achieve a mobility up to 2.83 ± 0.59 cm2 V−1 s−1, a subthreshold slope &lt;80 mV dec−1, and a current ON/OFF ratio &gt;106. The flexible devices reveal enhanced operational stability with a negligible shift in the electrical parameters after ageing, bias, and bending stresses. The present work lifts printed oxide thin film transistors a step closer to the flexible applications of future electronics.

CONSIDERATIONS ON QUALITY ASSURANCE FOR FLEXOGRAPHIC PRINT PRODUCTS

The paper presents considerations on quality assurance for products such as preformed boxes, made out of thin cardboard, created through flexographic printing. The elements specific to the technological process are analysed, followed by the setting of the levels of product conceptualisation after the analysis of its functions and the defining characteristics of its optimal quality. In addition, the paper covers some of the procedures which are specific to the quality assurance of the flexographic printing procedures which were implemented in the typography where the case study for certifying the process in compliance with SR EN ISO 9001:2015 was carried out.

Ablation and functionalization of flexographic printing forms using femtosecond lasers for additively manufactured polymer-optical waveguides

An efficient and low-cost approach to manufacture Opto-Mechatronic Interconnect Devices will be obligatory to handle the strongly increasing amount of data. The presented approach is based on a flexographic printing process. To adjust the transferred material the printing form is functionalized by means of laser-induced structures using an ultrashort-pulsed laser. The long-term goal is to adjust the printing result through microstructures in the printing form in order to create spatially resolved material transfer.In this work, first the ablation parameters are investigated at different repetition rates using a femtosecond laser. Further, a line structure is inserted in the material transferring areas of the printing form, which is consequently widened. Its influence on the printing result is presented.