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One of the potential aspects of the degradation of digitally printed images is their sensitivity to elevated humidity. Inkjet prints in particular have been shown to exhibit humid bleed. Studies into the humidity stability of inkjet prints have led to the development of an ISO standard to test humidity fastness, published as ISO 18946:2011. This paper details the use of this methodology to examine the humidity sensitivity of a number of contemporary ink-media combinations in use ca. 2000-2010. Two environmental exposure conditions were used: 25 degrees Celsius, 85% RH and 40 degrees Celsius, 80% RH. We find that the extent of humid bleed varies widely depending on the ink-media combinations and the environ-mental exposure conditions. In particular, swellable papers printed with dye-based inks are found to exhibit pro-nounced humid bleed, while plain and archival papers are found to be less susceptible to conditions of elevated humidity. However colorimetric measurements indicate that both pigment and dye-based inks show some colour change when printed on the latter papers. This work provides valuable information regarding the comparative stability of inkjet prints, many of which make their way into heritage collections and archives.

Humidity sensitivity is one of the potential degradation routes of digitally printed images. An ISO Working Group has been developing a test method for this sensitivity that is presently being published as ISO 18946. This work describes some practical experience in using the test method together with a treatment of errors from the results. The paper first reviews some previously published work in this field as background to the development of this standard. It will then go on to illustrate some practical experience of the use of this method to test humidity sensitivity in a number of print / media combinations. The paper gives details of the changes that result from humidity sensitivity of a number of print and media combinations, predominantly from inkjet printing. Combinations utilising a number of dye and pigment based inkjet inks and media types are used to illustrate the work. This paper also compares and contrasts the results from the different test conditions described in ISO 18946 and the differences in humidity sensitivity of various areas of the proposed test target. The results are presented in both colorimetric (numeric) terms and as photomicrographs.

Increasing numbers of galleries, museums and archives are including ink jet printed materials into their collections, and therefore displays. There is evidence that the instability of these prints is such that images can suffer deterioration in print quality or in extreme cases, a loss of information over an extended period of time. This is shorter than the period typically required for perceptible deterioration to occur in many other paper-based artworks. The image stability of prints is affected by a number of factors some of which have already been studied. However the role played by the ink solvent in the loss of image quality has yet to be explored. This paper will outline research being undertaken to investigate the effects of solvent content which may increase/promote the loss in image quality of the hard copy prints when stored or displayed under a range of temperature and humidity conditions.

The purpose of this paper is to explore the previously unreported phenomenon in which changes occur to the particle size distributions of calcium carbonate fillers, used in papermaking, when exposed to high intensity ultrasound. Commercial paper pulps sonicated at a frequency of 20kHz are found to produce aggregates of their mineral filler constituents. The effects of sonication on isolated long and short fibre, and ground and precipitated calcium carbonate filler systems are also investigated both with and without the presence of dispersants. The findings are supported by particle size analysis and scanning electron microscopy of the sonicated systems. It is clearly shown that exposure to high intensity ultrasound induces filler aggregation. However, the effect only occurs when paper fibres and fillers coexist and is not apparent for suspensions of filler only or fibre only slurries. Furthermore, the treatment overrides the effect of dispersants used to keep filler in suspension during the manufacturing process. An accompanying fall in pH with increasing sonication times is also noted and is linked to these changes. It is proposed that radical species produced in the slurries during sonication may explain the observed phenomenon. The role of pH is not clearly understood and needs further study. The findings may be of interest in paper manufacture where uniform dispersal of fillers throughout the pulp is of significant importance. The phenomenon described in this paper has not previously been reported or explored. Further studies may add to knowledge of filler dispersions and their behaviour in papermaking. Abstract: Purpose – The purpose of this paper is to explore the previously unreported phenomenon in which changes occur to the particle size distributions of calcium carbonate fillers, used in papermaking, when exposed to high intensity ultrasound. Design/methodology/approach – Commercial paper pulps sonicated at a frequency of 20?kHz are found to produce aggrega

This paper details both the conventional processes used for effective ink removal during the recycling of printed papers and more novel treatments. Particular attention was paid to methods employed to deal with papers printed with ‘difficult to deink’ inks such as toners from photocopiers, UV-cured ink films and liquid toner suspensions or ElectroInks®. High intensity ultrasound was applied to pulps derived from papers printed with these newer inks in order to evaluate its effectiveness in detaching the inks from paper and establishing the resultant ink particle size distributions. In all cases, it was found that the application of ultrasound at a frequency of 20kHz had a significant effect on the resulting ink particle size distributions. In the case of toners, it was found that particle disintegration was more effective at temperatures below the ink softening point. This was attributed to the increased brittleness of the toner at this temperature. ElectroInks® can be effectively de-inked by exposure to ultrasound coupled with washing under neutral conditions. For all the inks, the size distribution of the resultant detached ink particles was such that they could be removed using standard flotation and washing techniques.

This paper presents the original work carried out into the novel application of high intensity ultrasound to the de-inking of waste papers printed with digitally printed inks. These inks include fused toners, Indigo inks (ElectroInks) and UV cured coatings. They were previously considered to be ‘difficult to de-ink’ when present in conventional recycling de-inking plants because they are difficult both to detach from paper fibres and to break down into particle sizes that can be removed by conventional flotation techniques. The significance of this work is that for all the systems investigated it was possible to both detach and reduce the size of ink particles down to a desired flotatable size range of between 20 to 120 microns. Thus digitally printed papers that had been seen as presenting a treat to effective paper recycling can be recycled using the techniques described. Temperature was found to play a role in heat fusible toner printed materials. De-inking of the tough films produced by UV curing inks showed no temperature dependence. Indigo ink that had been feared to present problems to the recycling industry was found to be relatively easy to de-ink using these techniques. The general conclusions are that the application of ultrasound can be used to aid the de-inking of waste paper and reduce the number of chemicals used. The paper was an invited presentation for the Non-impact Printing Conference (NIP 23) held in Anchorage, Alaska during September 2007. The NIP conference is organised the Society for Imaging Science and Technology (IS&T) with assistance from the Imaging Society of Japan and is considered to be the premiere event in evaluating the latest research developments in digital printing, attracting world class researchers from Japan and the USA.

This paper investigated the use of ultrasound to deink papers printed using Indigo’s liquid toner, Electroink. In recent years, concerns have been expressed over the difficulty of deinking waste paper produced using the Indigo printing process. Among other problems it was found that the ink particles were too large to be removed using conventional deinking methods. High-intensity ultrasound was applied to investigate the possibility of fragmenting the ink particles to a size where they could be removed by flotation methods. The effect of temperature and sonication power on the particle size distribution was also studied. Tests were performed on two substrates, a typical paper used with Indigo presses and Indigo’s Sapphire coated paper, treated to help the Electroink bond to the paper. Handsheets were formed from the sonicated pulp and analysed to obtain a particle distribution. The findings from this work revealed that Indigo inks are not as hard to remove as was previously thought, and the application of ultrasound improves the number of particles removed. Variations in power input and temperature were found to have a significant effect on the results, with most effective cleaning occurring at a higher power and lower temperature.

Two exhibitions resulted from investigations into the de-inking of digitally printed papers using high intensity ultrasound. The exhibitions consisted of photomicrographs taken using either an optical or electron microscope. In ‘Ink, Paper, Sound’ the fourteen micrographs illustrate the process of ink fragmentation during the de-inking process and as well as being of scientific value they are visually arresting. The exhibition was a visual exploration of the relationship between the paper, the ink and the effects produced by exposure to ultrasound. A variety of novel lighting conditions were employed in capturing the images and some images were enhanced using image analysis techniques. In ‘Paper Topographies’, the second exhibition, the images were from handsheets prepared from repulped paper that had been printed with solid black print using the Indigo liquid toner technology known as ElectroInk®. Images were also captured from virgin paper fibre and paper filler samples such as Ground and Precipitated Calcium Carbonate. Image capture was performed using a Scanning Electron Microscope (SEM) using either a secondary or backscattered electron detector. With several of the specimens it was necessary to sputter-coat them with gold prior to imaging. A range of working distances, accelerating voltages and magnifications were employed to achieve a complete set of images for analysis and display.