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In the “dry” state, pigment particles are held together by attraction forces of various physical chemical natures including the van der Waals force and the “liquid bridge” force. These attraction forces must be overcome in order to disperse pigment particles into liquid media. Dispersion machinery is designed to generate energy required to overcome, to various extents, such attraction forces. On the other hand, the efficiency of dispersion operation is significantly dependent upon the effectiveness of the transfer of energy from the dispersion tools/dispersion charges to the oversized pigment particles, as a result of the presence of the adhesion and cohesion within the dispersion system. This paper explores the nature and the significance of various forces between pigment particles and of the adhesion and cohesion phenomena associated with pigment dispersion, from a practical point of view. Principles relevant to improving the efficiency of pigment dispersion via minimisation of the adhesion between pigment particles and via maximisation of the adhesion and cohesion within the dispersion system are also discussed.

In this present study, electrophotographic printing is made on papers which are subjected to different recycling numbers, and this paper aims to examine the colour changes of this printing type.

Four-colour electrophotographic printing is carried out on adhering to the INGEDE 11p standard recycled papers four times under the same conditions. Colour measurements are made by means of electrophotographic printed colour scales printed on these recycled papers. Colour measurements are made with the X-Rite eXact spectrophotometer according to the ISO 13655:2017 standard. As a result of colour measurements, colour differences (ΔL′, ΔH′, ΔC′, ΔE₀₀) of recycled papers are determined using some formulas.

According to the values obtained after four recycling, the highest ΔL′ value is found to be 4.80 yellow and the lowest 1.92 black. Again, according to the measurement results, it is determined that the highest ΔE00 is yellow colour with a value of 5.66, and lowest ΔE₀₀ is black colour with a value of 1.98. In ΔH′, black colour is the highest value of 12.61, the lowest value with −2.05 is obtained in magenta colour. It was observed that the highest ΔC′ value is 2.98 in yellow, and the lowest value is −0.28 in black.

In the printing industry, sometimes customers want to monitor the colour differences in the printing by taking the L′a′b′ obtained values as a result of printing from the printing houses. If the colour differences exceed the tolerance values, then they can interfere with the printing. As a result of the calculations, colour changes in electrophotographic printing are observed with many parameters. This study can be a pioneer for the studies that can be done on this subject.

This paper aims to develop and then evaluate a novel consolidation and powder transfer mechanism for electrophotographic 3D printing, designed to overcome two longstanding limitations of electrophotographic 3D printing: fringing and a build height limitation.

Analysis of the electric field generated within electrophotographic printing was used to identify the underlying causes of the fringing and build height limitations. A prototype machine was then designed and manufactured to overcome these limitations, and a number of print runs were carried out as proof of concept studies.

The analysis suggested that a machine design which separated the electrostatic powder deposition of the print engine from the layer transfer and consolidation steps is required to overcome fringing and build height limitations. A machine with this build architecture was developed and proof of concept studies showed that the build height and fringing effects were no longer evident.

Electrophotography (EP) was initially seen as a promising technology for 3D printing, largely because the potential for multi-material printing at high speed. As these limitations can now be overcome, there is still potential for EP to deliver a high-speed 3D printing system which can build parts consisting of multiple materials.

The analysis of EP, the new method for the transfer and consolidation of layers and the proof of concept study are all original and provide new information on how EP can be adopted for 3D printing.

A solid freeform fabrication (SFF) technique is described where powder is deposited layer‐by‐layer using electrophotographic printing. In the electrophotography process, powder is picked up and deposited using an electrostatically charged surface. A test bed was designed and constructed to study the application of electrophotography to SFF. It can precisely deposit powder in the desired shape on each layer. A polymer toner powder was used to build small components by thermally fusing each layer of printed powder using a hot compaction plate. The feasibility of 3D printing using this approach was also studied by printing a binder powder using electrophotography on to a part powder bed.

This study aims to determine the ink removal efficiency of papers with different recycling numbers and to examine some electrophotographic printing properties.

The base papers prepared according to the INGEDE 11p standard are subjected to six recycling stages (RS) under equal conditions. The physical-optical properties of the papers obtained at the end of each RS are measured and CMYK (cyan, magenta, yellow, key) color measurement scales are printed on each paper with electrophotographic printing. Color measurements of the printed papers are measured using the X-Rite eXact spectrophotometer, adhering to the ISO 13655:2017 standard. According to the measurement results of the optical properties, the ink removal efficiency of each recycling step is determined as a percentage (%) using some formulas.

As general, according to DEMLab and IERIC data, it is determined that the ink removal efficiency increased as the recycling repetition increased. In DEMf factor values, the highest deinking efficiency is obtained after the fourth RS. There is no significant difference between the printing properties of the samples.

It has been a matter of curiosity that papers lose their properties after how many RS. Many studies have been carried out on this subject and it has been presented by experimental methods that the printability properties of papers increase or decrease after which RS. This study can be a pioneer for future studies.

A method for rapid prototyping based on electrophotographic powder deposition was investigated to study its potentials and to identify design and implementation challenges. This technique is referred to here as the electrophotographic rapid prototyping (ERP). In this technique, powder is printed layer‐by‐layer in the shape of the cross‐sections of the part using electrophotography a very widely used non‐impact printing method. Each layer of powder is consolidated by fusing before the next layer of powder is printed. A fully automated test bed was constructed that consists of a printing system, fusing/heating plate, build platform that has two‐degrees of freedom as well as software that drives the system.

This paper aims to report on production of the colour digital printing toners cyan, magenta and yellow. Colour digital electrophotographic printing is currently in high demand. The provision of a large colour gamut depends on appropriate selection of precise colourants to produce toner capable of producing a thin layer on paper.

Printing toners were synthesised by the emulsion aggregation method, and then evaluated for chemical constitution and effects of the colourant substituents.

Results demonstrated that increasing the polarity of a pigment produced better dispersion and lower particle size with narrower distribution and even better colour reproduction. While, changing a pigment’s characteristics did not affect the toner shape or its thermal properties.

The developed method provides a simple way to synthesise colour printing toner.

Emulsion aggregation toners provide less hazardous materials during printing.

Evaluations of the influence of solid-state parameters and physicochemical properties of the pigments on printing toner characteristics were done for the first time.

Printing toners are polymer composites accountable for transmission of digital images onto target substrates. Bearing in mind the ever increasing demand for high quality digital printing, modification and/or integration of existing techniques for manufacturing toners with favourable morphological and colour characteristics appears of vital importance. The present study aims to uncover the significance of in-situ polymerisation method, i.e. suspension, emulsion and mini-emulsion to control the microstructure of toner particles (particle size, particle size distribution and sphereness) while keeping the energy required for polymerisation along with reaction conversion at a reasonable level.

Assessment of particle size, particle size distribution and reaction conversion visualised the potential of suspension, emulsion and mini-emulsion polymerisation techniques to control microstructure, and colour characteristics of synthesized toners as well.

The results provided support for the fact that either the emulsion or mini-emulsion polymerisation routes will result in toners having an acceptable particle size and particle size distribution in the presence of a redox precursor. The higher monomer conversion at low temperature, as compared to the suspension polymerisation, was noticeable.

Analysing the glass transition temperature and colour characteristics of the resulting toners elucidated the superiority of mini-emulsion with respect to the other two cases which ranks this method on account of application.

For the first time, mini-emulsion route was put into practice and toners with acceptable colour and microstructure features were synthesised. In spite of lower polymerisation temperature and higher conversion of mini-emulsion compared to suspension and emulsion polymerisation techniques, further investigations are required to fine-tuning the properties of toners produced through this method.

This paper aims to report an experimental study of how surface defects evolve in EP3D printing as more layers are accumulated and proposes a simulation model for the process.

A series of measurements on the surface roughness were taken layer-by-layer for two 30-layer samples. A model of the process was constructed based on dynamic system modeling, system identification techniques and the analysis of the measurements from the samples.

The transient response of the fuser has a significant impact on the surface of the print. The surface of the EP3D printed part depends heavily on the compliance of the interface. The model developed is able to approximate the behavior of the surface as more layers are deposited.

The model requires tuning multiple parameters, especially the compliance threshold for the interface; similar experiments/measurements are needed for any change in the system.

The simulation model provides a way to evaluate different process parameters and conditions that otherwise would be difficult and expensive to test.

This work provides better understanding into the limitations of EP3D printing process and provides a tool to find countermeasures to achieve successful EP3D prints.

Polymer-particle composites, which have demonstrated wide applications ranging from energy harvesting and storage, biomedical applications, electronics and environmental sensing to aerospace applications, have been investigated for decades. However, fabricating polymer-particle composites with controlled distribution of particles in polymer continues to be a fundamental challenge. As to date, a few additive manufacturing (AM) technologies can fabricate composites, however, with a limited choice of materials or limited dispersion control. Against this background, this research investigated a hybrid polymer-particle composite manufacturing process, projection electro-stereolithography (PES) process, which integrates electrostatic deposition and projection based stereolithography (SL) technologies.

In PES process, a photoconductive film collects charged particles in the regions illuminated by light. Then, collected particles are transferred from the film to a polymer layer with defined patterns. Lastly, a digital mask is used to pattern the light irradiation of the digital micromirror device chip, selectively curing the photopolymer liquid resin and particles of that layer. By transferring particles from the photoconductive film to the photopolymer in a projection-based SL system, multi-material composites with locally controlled dispersions could be produced. A proof-of-concept PES testbed was developed. Various test cases have been performed to verify the feasibility and effectiveness of the developed approach.

Challenges in this novel AM process, including process design, particle patterning and transferring, are addressed in this paper. It is found that particles can be transferred to a layer of partially cured resin completely and accurately, by using the stamping approach. The transferring rate is related to stamping force and degree of conversion of the recipient layer. The developed hybrid process can fabricate polymer-particle composites with arbitrary dispersion pattern, unlimited printable height and complicated geometries.

Although an electrostatic deposition process has been investigated as a 3D printing technology for many years, it is the first attempt to integrate it with projection SL for fabricating multi-material polymer composite components. The novel hybrid process offers unique benefits including local dispersion control, arbitrary filling patterns, wide range of materials, unlimited printable height and arbitrary complicated geometries.