The quality achieved by inkjet printing is limited by various factors, including the nozzle–substrate throw distance, the substrate velocity, and the occurrence of satellite droplets. Under certain conditions, particularly for large throw distances, unacceptable inaccuracies and defects in drop placement occur. In this paper, a new technique based on high-speed imaging and laser optics is presented that allows the visualization of air currents and droplet movement patterns beneath and in the proximity of a printhead and a moving substrate. The images obtained with this technique provide better temporal and spatial resolution than those obtained in previous studies. Tests with two different commercial printheads show that the entrained airflow depends on the interaction with the stream of printed droplets. The formation of unsteady eddies, particularly between nozzle rows, can result in serious errors in drop placement.
Spectral printing aims to achieve an illuminant-invariant match between the original and the reproduction. Due to limited printer spectral gamuts, an errorless spectral reproduction is mostly impossible, and spectral gamut mapping is required to reduce perceptual errors. The recently proposed paramer-mismatch-based spectral gamut mapping (PMSGM) strategy minimizes such errors. However, due to its pixel-wise processing, it may result in severely different tonal values for spectrally similar adjacent pixels, causing unwanted edges (banding) in the final printout. While the addition of some noise to the a* and b* channels of the colorimetric (e.g., CIELAB) image—rendered for the first illuminant—prior to gamut mapping solves the banding problem, it adversely increases the image graininess. In this article, the authors combine the PMSGM strategy with subsequent spectral separation, considering the spatial neighborhood within the tonal-value space and the illuminant-dependent perceptual spaces to directly compute tonal values. Their results show significant improvements to the PMSGM method in terms of avoiding banding artifacts.
Industrial continuous inkjet printers are typically used in production lines for printing directly on various types of products such as cans, bottles, and packages. To enable their application to higher speed production lines, their print quality needs to be improved. Print distortion results from aerodynamic and electric interference among the ink particles during their flight from the nozzle to the print target. An ink-particle flight simulation method that enables the trajectories of ink particles and the airflow around them to be calculated simultaneously has been developed for use in identifying the mechanism of print distortion. Simulated printing of multiple-dot lines revealed that the lines were distorted when they hit the print target. This was because the trajectories of the charged particles in the lines were distorted by electric and aerodynamic interference during flight. Simulation showed that the appropriate insertion of dummy particles reduces the print distortion.
In many real-world commercial applications, such as electrophotographic printing, the adsorption of water on critical surfaces has an overwhelming but poorly understood effect on the desired materials performance. This work is focussed to better understand the effect of water on the triboelectric charge transfer between surfaces in xerography.
Molecular mechanics was used to find the most probably water adsorption sites for isolated polymethylmethacryate (PMMA) and isolated silica models, and for intermolecular complexes between PMMA and silica which are responsible for triboelectric charge transfer. Density functional theory (DFT) was used calculate the local energy minima, the adsorption of water molecules on different surface functional groups, and the analysis of the frontier orbitals, to quantitatively compare the energy gap differences for electronic charge transfer, and thus the effect of the hydration site on PMMA and silica on electronic charge transfer.
Four ways were found for surface water adsorption to affect the electronic charge transfer between PMMA and silica: (1) adsorption of a water molecule on the carbonyl group of PMMA decreases the energy level of the highest occupied molecular orbital (HOMO) on PMMA, thus making electron charge transfer more difficult because of the transfer barrier increase; (2) a water molecule acts as part of the electron accepter when adsorbed at the active site of the lowest unoccupied molecular orbital (LUMO) on silica, which lowers the LUMO and thus lowers the charge transfer barrier, but at the same time creates a charge dissipation pathway as a part of the charge transfer is now to water, rather than to silica; (3) a water molecule acts as a spacer between PMMA and silica, which increases the energy gap for charge transfer and thus decreases the charge transfer; and (4) water molecules can act as a charge carrier, dissipating electrons by accepting charge when adsorbed on silica and then donating back charge when adsorbed on PMMA.
This work provides a detailed mechanistic understanding of the effects of water on the surface electronic structure of amorphous silica and PMMA that are critical to electrophotographic applications, and no doubt to other applications where the surface electronic structure is relevant.
In this research, computer generated reproductions of colors from a color test chart were analyzed considering type of virtual light, illumination settings, gamma values and background color. In the introduction and theoretical part, a review of relevant research is presented and the importance of testing conditions, 3D illumination and rendering process is explained. In the experimental part, two types of light (standard and photometric) with variations of light intensity were used within mental ray® settings in 3ds Max software. Gamma values varied from 1.8 to 2.2 and illumination settings were adapted to light type. Background color systematically changed from R = G = B = 0 to R = G = B = 255 with a step of 50 units. The color test chart was reproduced in a simple scene and defined with texture mapping. In the results, optimal conditions for color test chart reproduction within the computer generated scenes are presented and discussed, pointing out some interesting phenomena in deviations of lightness, saturation and hue between the original and the reproduced colors which occur in dependence on simultaneous changes of light intensity, gamma value and background color.