12th ANNUAL EUROPEAN INK JET PRINTING CONFERENCE
October 20-22 2004, Barcelona, Spain
Report by David J. Tyler
Ink Jet printing is a fast-moving discipline that provides a stimulating mix of fundamental research, applications technology, colour science, ink chemistry, market research and financial appraisal. Interdisciplinary skills are essential and conferences help to develop these skills. Applications of digital printing in the areas of textiles and clothing are but a small part of the total activity, and this report majors on areas that are of most interest to putting ink on to textile substrates. A complete listing of contents is here.
Directions in Ink Jet Technology
Mike Willis, Managing Director of Pivotal Resources Limited.
Developments in Desk-top and industrial printers were reviewed. Many of the new industrial machines appear to be designed for solvent and UV cure inks, so this is the growth market. Always, there is interest in higher printing speeds. Ink jet patents in 2003 numbered 2,771, led by Hewlett-Packard with 522. The level of patent activity has been fairly constant over the past 3 years. Contemporary print heads give drop sizes down to a few picolitres, but there is great interest in higher resolution printers with drop sizes measured in femtolitres. This is to use the heads for printed electronics and other advanced fabrication systems (see Hudd's presentation).
European End-User Market Research
Stewart Partridge, Web Consulting Ltd.
The market was analysed in three sectors: Wide and Grand Format Graphics (60%), Textiles (~20%) and Speciality Applications (~20%). Solvent-based inks are by far the most widely used inks in screen printing and is a growth area in digital printing. However, their are environmental issues with these inks, particularly when CFCs are used. Environmental legislation from the EU has become effective this year and these will affect inkjet as well as screen printers. Growth in solvent inks is being paralleled by growth in UV curables in the Wide Format market.
Digital Garment Printing - opportunities and solutions
Ofer Ben-Zur, CEO of Kornit Digital Ltd.
A snapshot of the U.S. screen-printing sector is provided by a report in Impressions Magazine (A new beginning, Shannon Wilder, November 2002). Over 70% of the business is custom rather than contract, and the majority of substrates are T-shirts. This is the market perceived as an opportunity for textile digital printing by Kornit Digital. The company has developed the machinery and ink to offer a solution to the screen printing trade. Benefits are perceived as: shorter lead times, reduced labour costs, enhanced flexibility, and the potential to print photo-realistic images. The digital images are soft touch, and this is also seen as a quality enhancement.
Two machines have been produced: the Kornit 930 (with one one pallet system, offering 100 pieces/hour) and the Kornit 931 (with two pallet systems offering 200 pieces/hour). Print resolution is quoted as up to 630 dpi.
The ink has been specially developed for the fabrics and applications found in the screen printing market sector. A solvent-based ink is used (carrying a resin and pigments). After printing, the ink is dried and cured as a second stage to the process - making use of equipment already possessed by the screen printers. The technology challenges that have been addressed here have been to make the ink low bleeding, with good adhesion, high fastness to light and washing, and a soft handle.
FastJet. High Speed Digital Printing for the Corrugated Market
Stefan Slembrouck, Product Director Europe for SunChemical.
|Digital printing has always been perceived as slow in comparison with conventional techniques. A partnership between a machinery builder (Inca Digital) and an ink manufacturer (SunChemical) led to the appearance of FastJet at the Drupa exhibition in June 2004. The machine has a print resolution of 300 dpi (matching flexo print quality), a linear speed of 100 metres/minute and a real output of 2000 square metres per hour.|
SunChemical claims to be the world's largest producer of printing inks and related products/services. It is strong in waterbased inks for flexoprinting on corrugated sheet packaging. This initiative illustrates the importance of partnerships in developing new technologies for digital printing: a collaboration of print head manufacturers, machinery developers, ink producers and integrators. The next step is to involve a supplier of processing equipment to the corrugated packaging industry. The next development machine has the real output target of 4000 square metres per hour.
The machine uses UV curable inks and curing takes place in an atmosphere of nitrogen to obtain the best results.
The Power and the Glory; the full inkjet story
Alan Hudd, President of Xennia Technology Ltd
The theme of this presentation was innovation. Inkjet solutions have emerged for a variety of challenging problems, and Xennia Technology's role is to provide specialist expertise in the area of ink chemistry.
The first example was solar panel manufacture, where commercial exploitation
has been limited by the cost of the panels. Inkjet has been incorporated into
the manufacturing process by Pacific Solar (now CSG) and comercial units will
become available in 2006. CSG refers to Crystaline Silicon
on Glass, which has been found to be rugged, durable,
reduced cost and having a higher efficiency. The surface of the substrate is
then printed with an aggressive ink, creating craters (by etching) and dimples
within the thin films on the glass substrate. These are precisely controlled
in terms of spacing, size and depth - an inkjet technologies can deliver this
ldegree of accuracy. A paper on the technology is by Paul A. Basore, Large-area
Deposition for Crystalline Silicon on Glass Modules (Presented at the 3rd
World Conference on Photovoltaic Energy Conversion, Osaka, May 2003).
The solar panel example is just one of a whole range of direct etch manufacturing processes, including PCB components, visual display units, and various forms of sensors.
A notable example of developments affecting engineering structures with a precision sub-50 nm comes from Molecular Imprints, Inc. This company have pioneered step-and-flash imprint lithography (S-FIL) that uses a precise piezo-driven dispense head to dispense a silicon-rich, low-viscosity, photocurable, monomer solution onto a substrate. A mould is used to constrain the shape of the monomer and after UV curing, the surface has a precise topography at a nanometre scale. Further details of the process are in S-FIL for sub-80nm contact hole patterning (Solid State Technology Magazine. February 2004. Vol 47, Issue 2.).
Another case discussed by Hudd concerned printing a conducting metal later onto a substrate, to open the doot to all sorts of benefits, including cost-reduction, compactness, improved quality and enhanced performance. Xennia have developed a technique involving a receiving layer that has an open sponge-like structure for holding the metal and to ensure good conductivity. This layer can be anything from 50 nm to 6 microns thick, but many layers can be superimposed if required, with no loss of performance. This innovation has led to the setting up of a joint venture company CIT Ltd (Conductive Inkjet Technology). See also the Xennia page on this. One application of interest to the textiles/clothing community concerns low-cost RFID tags, where there is talk of the price coming down to 5 cents/tag.
Although not discussed in the lecture, Xennia have an interest in textile digital printing, and have a joint venture company called Lumenia Ltd. One major interest is in security and the web page has this overview: "Lumenia is developing a number of breakthrough covert color-change materials that offer new design opportunities in a range of applications, such as document security, brand protection and food protection. Lumenia's unique photo-chromic, thermo-chromic and pressure sensitive materials are opening the door for design of novel security features."
More generally, the web page claims: "Lumenia probably leads the world in developing novel inks for inkjet printing onto textiles. Over the past 2 years, we have made giant strides towards achieving the textiles "holy grail" - the ability to inkjet print, reliably and cost effectively, sharp, bright and wash-fast images onto a range of fabrics, including cotton, wool and polyester, onto dark backgrounds as well as white. Lumenia's materials science, synthesis and processing expertise are the perfect complement to Xennia's inkjet applications capabilities. We therefore have the capability to develop a complete textile inkjet technology package, including inks and printing system."
Colour Technologies for Inkjet Devices
D. de Baer, Agfa Monotype Corp.
Agfa's interest in digital printing took a major leap when, in January 2004,
Agfa acquired the Belgian based company dotrix. Since then, dotrix has launched
a digital colour press for short - medium run industrial printing using UV curable
Due to the broad nature of Agfa's business, colour management issues have been addressed in both digital photography and in commercial printing. Traditionally, colour management has been about the control of individual colours in images and documents to achieve predictability, accuracy and consistency. It has not been thought to include image enhancement (contrast, colour cast, red-eye removal, etc.). However, the case was made in this presentation that colour management should include image enhancement. As evidence of this, it was pointed out that the work of amateur photographers is routinely enhanced by mini-labs to address common faults and to give customers improved results.
Problems of colour management arise because devices have different colour gamuts. It is necessary to create profiles for each device and to develop appropriate ways of converting between devices or to a standardised colour space. Injet colours vary with ink type, the substrate used, and with the lighting conditions. For example, printing on glossy paper will give different results when compared with matt paper. Another example concerns fluorescence: paper brighteners can have different effects under different lighting conditions. Each combination of ink and substrate requires its own profile.
The presentation went on to consider specific issues arising when moving from digital camera images to offset printing and to inkjet printing. Conventional techniques make conversions via LAB colour space, but this loses context information linked to the source device. The case was made for a smart colour module that is informed about input devices, output devices and is able to optimise gamut mapping. Such an approach was described as a third generation colour management workflow. Further on Agfa's colour management interests is here.
New Developments in UV Inkjet Inks
Carole Noutary, Sericol Imaging
Whilst UV curables have been used in traditional printing for over 25 years, it is only more recently that it has taken off as an inkjet technique. It is gaining market share from solvent-based inks, which have more environmental issues and they are volatile and flammable. Sericol consider them to have several properties that make them superior to solvent inks for inkjet: they give reduced nozzle failure, they can be dry instantly, they give printing that is highly resistant to solvents and the energy requirements are lower.
However, there are significant challenges. Most notably, the printed material shrinks when it is polymerised and this makes the film pull away from the substrate. The result is poor adhesion, poor flexibility, poor durability and cracking. The chemists have been looking for a highly flexible UV inkjet product that avoids these difficulties. The background to the problem was explained: UV curable inks are based on acrylate chemistry that give up to 25% shrinkage on polymerisation. There are avenues to explore in modifying the acrylate materials used, there are alternatives using vinyl ether monomers with acrylates, and there are cationic UV curing technologies based on epoxy resins. Sericol has patents in these areas - and demonstrable improvements in ink performance.
Inkjet Printing with Nitrogen Inerting - All Hot Air?
Peter Walshe, Business Development Manager, SunJet.
This presentation complemented the previous overview of UV curable inks. The big problem is that oxygen inhibits the curing process and may result in an incomplete cure. The danger of ink migration is real, leading to a loss of definition. The effect is most severe in low viscosity ink systems - which applies to inkjet formulations. An overview of the inerting process and the benefits obtained is here.
The technical background for the nitrogen inerting used in the FastJet machine was reviewed, demonstrating that commercial solutions are viable.
|Department of Clothing Design & Technology, Manchester
Prepared: 29 October 2004
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