Ink Separation Research Articles

Enhancing the Performance of the Mesoporous TiO2 Film in Printed Perovskite Photovoltaics through High‐Speed Imaging and Ink Rheology Techniques

AbstractMesoscopic carbon‐based perovskite solar cells (C‐PSCs) have the potential to be manufactured at an industrial scale by utilizing screen‐printing, a simple, affordable, and commercially mature process. As such, many recent publications have focused on enhancing performance through modifying cell architecture and perovskite chemistries. This work examines how ink rheology can be tuned to optimize cell performance through reducing the occurrence of common print defects to create higher quality m‐TiO2 films. Inks with different solvent dilutions and rheological profiles are assessed using high‐speed imaging through the screen‐printing visualization (SPV) technique, to investigate the impact of the viscosity and elasticity on ink separation mechanisms. The resultant film quality and its influence on device performances are then assessed. Ink separation lengths are minimized, and the formation of filaments ceases during printing, leading to improved TiO2 film topography and homogenous infiltration of the perovskite precursor. Consequently, PCE is improved by over 10% of the original efficiency in cells and 224 cm2 active area modules due to enhanced Voc and FF. These results not only provide key insights into tailoring ink rheology, to achieve improved print homogeneity and higher performing cells, but also aid further work on enhancing the performance of other screen‐printed functional films.

The influence of carbon morphologies and concentrations on the rheology and electrical performance of screen-printed carbon pastes

Screen-printing inks containing various morphologies of carbon are used in the production of a variety of printed electronics applications. Particle morphology influences the rheology of the ink which will affect the deposition and therefore the electrical performance of a printed component. To assess the effect of both carbon morphology and concentration on print topography and conductivity, screen printable carbon inks with differing loading concentrations of graphite, carbon black and graphite nanoplatelets (GNPs) were formulated, printed and characterised, with rheological and novel print visualisation techniques used to elucidate the mechanisms responsible. Carbon morphology had significant effects on the packing of particles. The smaller carbon black particles had more interparticle interactions leading to better conductivities, but also higher ink viscosities and elasticities than the other morphologies. Increases in carbon concentration led to increases in film thickness and roughness for all morphologies. However, beyond a critical point further increases in carbon concentration led to agglomerations of particles, mesh marking and increases in surface roughness, preventing further improvements in the print conductivity. The optimal loading concentrations were identifiable using a custom-made screen-printing apparatus used with high speed imaging for all morphologies. Notable increases in filamentation during ink separation were found to occur with further increases in carbon concentration beyond the optimum. As this point could not be identified using shear rheology alone, this method combined with shear rheology could be used to optimise the carbon concentration of screen-printing inks, preventing the use of excess material which has no benefit on print quality and conductivity.

Modelling of the rheological curve and printing ink flow mechanism in rotary viscometer measuring cell clearance

The complete rheological curves of basic role printing offset inks in the temperature range 20÷60°C have been obtained. The flow models and analytical formulas are analyzed and tested tocalculate of value of the most important macro- and microrheological parameters; identified the boundaries of appearance and extinction of wall effects, the phenomenon of ink separation (generation of axial "pigment streamer"), the formation (and the reformation) of the structure of liquid layers of material in the clearance of the measuring cell of the rotary viscometer.

The Effect of Carbon Ink Rheology on Ink Separation Mechanisms in Screen-Printing

Screen-printable carbon-based inks are available in a range of carbon morphologies and concentrations, resulting in various rheological profiles. There are challenges in obtaining a good print when high loading and elasticity functional inks are used, with a trade-off often required between functionality and printability. There is a limited understanding of how ink rheology influences the ink deposition mechanism during screen-printing, which then affects the print topography and therefore electrical performance. High speed imaging was used with a screen-printing simulation apparatus to investigate the effect of viscosity of a graphite and carbon-black ink at various levels of solvent dilution on the deposition mechanisms occurring during screen-printing. With little dilution, the greater relative volume of carbon in the ink resulted in a greater tendency towards elastic behavior than at higher dilutions. During the screen-printing process this led to the ink splitting into filaments while remaining in contact with both the mesh and substrate simultaneously over a greater horizonal length. The location of separating filaments corresponded with localized film thickness increases in the print, which led to a higher surface roughness (Sz). This method could be used to make appropriate adjustments to ink rheology to overcome print defects related to poor ink separation.

De-Inking of ONP Paper by using Different Surfactants: In Dissolved Air Flotation Process

Meeting the demand of paper and paper product requirement and at the same time decreasing the availability of fibrous raw materials, keeping an eye on cost effectiveness is challenging. Thus, recycling of paper is an alternative. Corrugated box, old newspapers and office waste papers are the sources of raw materials for paper and paper product industries. Deinking is an important step for recycling of old waste writing, printing and newsprint papers. The efficiency of ink separation in the process of waste paper recycling depends on the ink properties, kind of the additives, surfactants used, age of waste papers, the printing techniques and printing conditions. In general, deinking process consumes a large amount of chemicals which makes this method expensive, pollution intensive and even quality is compromised. In this study the effectiveness of surfactants like benzene dodecyl sulphonate, lauryl benzene sulphonate and sodium carbonate for cost effective deinking process by optimizing the chemical doses has been studied. The physical strength and optical properties of the paper after deinking was also explored. The surfactant better for both physical strength properties and optical properties of paper is identified to be the sodium dodecyl benzene sulfonate.

Deinking Technology; its Modification and Recent Developments: A Review

Deinking is an important step for recycling of old waste writing, printing and newsprint papers. The demand of paper has been continuously faster than the availability of fibre from natural source. The efficiency of ink separation in the process of waste paper recycling depends on the ink properties, kind of the substrates, age of waste papers, the printing techniques and printing conditions. In general deinking process a large amount of chemical is required which makes this method expensive, pollution intensive and also not obtained a perfect quality. In the present paper a brief Journal review has been carried out on the recent developments in the deinking process and what are the better steps to obtain a standard recycle quality paper. Recycling of waste paper has been found to be more economical and eco-friendly.

Electric treatment for hydrophilic ink deinking.

Hydrophilic inks have been widely used due to higher printing speed, competitive cost and being healthy non-organic solvents. However, they cause problems in both product quality and process runnability due to their hydrophilic surface wettability, strong negative surface charge and sub-micron size. Electric treatment was shown to be able to increase the ink sizes from 60 nm to 700 nm through electrocoagulation and electrophoresis. In addition, electric treatment assisted flotation could reduce effective residual ink concentration (ERIC) by 90 ppm, compared with only 20 ppm by traditional flotation. Furthermore, the effect of electric treatment alone on ink separation was investigated by two anode materials, graphite and stainless steel. Both of them could remove hydrophilic inks with less than 1% yield loss via electroflotation and electrophoresis. But graphite is a better material as the anode because graphite reduced ERIC by an additional 100 ppm. The yield loss of flotation following electric treatment was also lower by 17% if graphite was the anode material. The difference between the two electrode materials resulted from electrocoagulation and ink redeposition during electric treatment. An electric pretreatment-flotation-hyperwashing process was conducted to understand the deinking performance in conditions similar to a paper mill, and the ERIC was reduced from 950 ppm to less than 400 ppm.

Fractionation by micro-hole pressure screening and hydrocyclone applied to deinking line rationalization and future manufacturing concept

This study pursued two objectives related to deinking. The first objective deals with the application of fractionation for deinking operations rationalization, which requires all free ink separation in one fraction and treatment in ink removal operations. Following accomplishment of the first objective, the second objective was fractions generation for stratified sheet formation. The first objective requires separation based on length, and the second requires separation by development of surface characteristics. The experimental plan was focused on selective fines separation and further valorization of fiber and fines fractions. It was shown that fractionation by a pressure screening system equipped with a smooth hole basket with 0.25mm perforations was very selective towards fines (free ink, fillers, cellulosic fines) separation in the accepts. Long fibers, as well as specks, were retained in the rejects fraction. Due to the higher selectivity of the micro-hole screen, fibers are retained on the screen basket. Hence, they are not subjected to flotation operations, thereby effectively reducing their probability of being lost during flotation. This essentially translated into a fractionation-deinking concept. It was also shown that 1-stage micro-hole fractionation and fines flotation provided higher yield than conventional direct pulp flotation, though the final residual ink content was high. A multistage fractionation process would allow further reduction in long fiber residual ink. The second objective was achieved by applying hydrocyclone fractionation on the fine and fiber fractions generated.Separation was based on fiber and fines development. This new fractionation strategy allowed production and characterization of four different fractions: well developed fibers/coarse fibers and fibrillar/flake type fines.

Handwritten text separation from annotated machine printed documents using Markov Random Fields

The convenience of search, both on the personal computer hard disk as well as on the web, is still limited mainly to machine printed text documents and images because of the poor accuracy of handwriting recognizers. The focus of research in this paper is the segmentation of handwritten text and machine printed text from annotated documents sometimes referred to as the task of "ink separation" to advance the state-of-art in realizing search of hand-annotated documents. We propose a method which contains two main steps--patch level separation and pixel level separation. In the patch level separation step, the entire document is modeled as a Markov Random Field (MRF). Three different classes (machine printed text, handwritten text and overlapped text) are initially identified using G-means based classification followed by a MRF based relabeling procedure. A MRF based classification approach is then used to separate overlapped text into machine printed text and handwritten text using pixel level features forming the second step of the method. Experimental results on a set of machine-printed documents which have been annotated by multiple writers in an office/collaborative environment show that our method is robust and provides good text separation performance.

Spectral Modeling of an n-Ink Printer via Thin Plate Spline Interpolation

Reducing metamerism is one of the main goals of spectral printing. There are three main steps in spectral printing to address:1. What is the printer gamut in spectral space (Printer Forward Model)2. Given an input spectrum, what is the closest point on the printer gamut to the input reflectance (Spectral Gamut Mapping)3. What ink density combination produces the given point on the gamut (Ink Separation)In this paper we address the first issue for printers with a large number of inks. The performance of the model is evaluated based on an 8-ink printer and is compared to the most commonly used technique. We show that the new model performs as accurately as the existing models but does not require as many as constraints to set up the model.

Geodesic Based Ink Separation for Spectral Printing

Geodesic Based Ink Separation for Spectral Printing

Acoustic microcavitation at surfaces: New results in deinking of paper

Deinking remains an important step in environmentally conscious manufacturing of paper. A novel method based on acoustic microcavitation is used for deinking xerographic ink from paper. Microcavitation evolves microimplosions, which are effective in causing deinking preferentially at ink sites. Acoustic microcavitation is brought about by low megahertz acoustic fields giving rise to micron-sized bubbles that live a few microseconds. In exposing a surface to continuous waves for a defined duration one could obtain cavitation effects in an average, overall sense; the details of nucleation, evolution of inertial events, and the precise interplay of field parameters in effecting cavitation, however, get glossed over. Studying pulsed cavitation using tone bursts at low duty cycles, instead of CW insonification, reveals interesting details of the initiation and evolution of acoustic microcavitation. Experiments indicate that the 2-D context of how a xerographic print is deinked might be useful in inferring some attributes of 3-D pulp deinking. Assuringly, the results indicate that paper fibers are entirely undamaged, and the ink separation leaves them immaculately white, and that acoustic methods for deinking are a viable, chemical free, environmentally responsible means of recycling paper.

Acoustic coaxing of microimplosions for chemical-free deinking of paper

Deinking remains an important step in environmentally conscious manufacturing of paper. A novel method based on acoustic-coaxing-induced microcavitation is presented for deinking of xerographic ink from paper. Microcavitation evolves microimplosions which are effective in deinking. Acoustic coaxing is an acoustic mediation that enables one to control the onset, intensity, and evolution of acoustic microcavitation. Acoustic microcavitation is brought about by low-megahertz acoustic fields giving rise to micron-size bubbles that live a few microseconds. Liquid-borne microparticles when exposed to strong sound fields will not, ordinarily, cause any cavitation. However, if in addition to this sound field there exists even a very weak, high-frequency auxiliary acoustic field, cavitation by the microparticles is readily facilitated. This technique of facilitating cavitation is referred to as ‘‘acoustic coaxing.’’ Acoustic-coaxing methods for deinking are a chemical-free, environmentally responsible means of recycling paper. Here, initial experimental results are presented and the technique is elaborated upon in detail for easy implementation. Preliminary results indicate that the paper fibers are entirely undamaged, and the ink separation leaves them immaculately white. The microimplosions appear to occur preferentially at the ink sites.

A novel chemistry to ink separation from mixed paper waste contaminated with flexo ink

A novel chemistry to ink separation from mixed paper waste contaminated with flexo ink

Deinking Agent for Waste Paper

Waste papers are recycled by deinking. All over the world, the flotation method is the mainstream as the deinking method because of the advantages such as higher pulp yield, less use of water, less area for installation and less total reagent cost. The flotation method is mainly consisted of pulping and flotation processes, the former for ink separation from cellulose, the latter for ink rejecting out from the system. Function to assist the mechanical separation of printing ink from cellulose is required for the deinking agent in the pulping process. In the flotation process, there are three particles, namely, ink, cellulose and bubble, and main four interaction between them in the flotation cell. The following relationship must be held to reject out the ink particles effectively. Vr0<Vr1<<Vr2<Vr3 where Vr0, Vr1, Vr2 and Vr3 are the repulsive energy between ink and ink, ink and bubble, ink and cellulose and cellulose and bubble, respectively. The deinking agent in the flotation process must be that to control the repulsive energy following the relationship as mentioned above. The deinking agent which possesses the above-mentioned function can be designed from viewpoint of surface science.