Nils Pauler, Ole Norberg, Per Edström

Abstract
It is known that colour reproduction of inkjet comprises a range of mechanisms. It was possible to understand and explain some of these mechanisms by evaluating print tests with standard optical measurement and by calculations using algorithms of the Kubelka Munk and Murray Davies theories. The combined interaction of the substrate, the ink penetration, the optical properties of the inks and the dot size were clarified. Large colour gamut is governed by low ink penetration, low light scattering of the substrate and small dot size. The non-ideal property of process inks and the continuous tone character of colour reproduction of the studied desktop inkjets explained the observed convex shape of the colour gamut. For plain paper, dye-based and pigment-based inks were shown to follow different mechanisms, with lower penetration of the pigment-based ink. Colour gamut could be increased by a surface treatment that further reduced the penetration, but this treatment worked only for the pigment-based inks. Internal sizing of plain paper had only a very small influence on colour gamut for dye-based ink, even though the ink penetration was reduced.

Keywords: Paper, Inkjet, Colour Gamut, Simulation, Kubelka Munk, Murray Davies
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Abhay Sharma, Martin Habekost

Abstract
Digital production printing technology is gaining a strong foothold in the print industry, complementing and often rivaling offset printing. There has been rapid growth in this new printing technology with suppliers adding faster and better machines every year. It is now appropriate to begin to develop a series of test protocols and quality metrics for benchmarking of digital production color printing. This research describes a series of tests and then shows and compares results from commercial digital print systems.

This paper summarizes the efforts being made in the area of digital print certification by ISO, FOGRA, IPA and IDEAlliance. This paper reviews the applicability of ISO 12647 standards to digital printing. Test protocols exist for offset printing and single sheet inkjet color proofing, this study examines how those tolerances may be adapted for digital production printing.

Tests were conducted in regards to color and color management, sheet-to-sheet variability, and physical properties such as rub resistance, cracking, fading, and deinking properties. Digital printing is often criticized as tending to drift, unable to color manage, unable to match Pantone colors, and many fear digital output cracks during folding in areas of high coverage. The results from this series of test demonstrates that these accusations are largely unjustified and that digital printing matches, and in some cases surpasses, offset in terms of color, print quality and durability.

Keywords: Digital printing, Digital print certification, Color matching, GRACoL, SWOP, ISO 12647
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Philip Gerstner, Patrick A. C. Gane

Abstract
Rapid toner fusing and adhesion to coated paper is critical for energy efficiency and runnability in electrophotographic printing. The thermal transfer from the fusing roll to the toner layer competes with heat loss into the substrate. Whilst it is essential that the surface of the coated substrate displays a continuity of thermal conductivity to ensure uniformity at the coating-toner interface, the authors have previously shown by simulation that providing an insulating coating layer may provide advantages in terms of lower temperature fusing. To develop the concept further, two insulating constructions were formed using pre-coating layers consisting of either mica or a highly porous modified calcium carbonate (MCC). Thin top-coatings consisting of a fine narrow particle size GCC were applied to each to provide the predicted necessary surface continuity. A reference paper adopted a single coating layer having a similar coating formulation to that of the top-coatings, being predominantly carbonate-based. Adopting a method of controlling fusing roll temperature (KCL “DUPLO” apparatus), it could be shown that the onset of toner fusing and final adhesion could be developed at lower temperature for the case of the insulating pre-coat, the effect being most marked for mica. The MCC was compromised in this study due to poor binding strength of the coating layer, such that the porous MCC had to be diluted by blending with a standard broad particle size GCC, thus increasing coating density. Important differences were observed between the behaviour of full tone and half tone areas. The full tone response matched that of a tri-layer, consisting of the adhesive tape used to test the toner adhesion, the toner layer itself and the coating/base paper, in which the competition of internal cohesive development and toner-coating interface adhesion led to abrupt adhesion failure following the build of internal cohesion prior to complete establishment of fully fused adhesion. The half tone areas, by contrast, due to the absence of the thin film effect of continuous toner in the full tone case, displayed a smooth transition from adhesion failure to fully fused adhesion. Print gloss of the full tone area correlated with the transitional response, and could be used in this case to monitor toner fusing.

Keywords: Electrophotography, Thermal properties, Properties of coatings, Toner adhesion, Heat transfer in porous materials, Printability
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