On Print | Inkjet for Packaging

Published: March 21, 2012, By Dr. Dene Taylor

How digital printing is entering newer markets is always of considerable interest. Will it dominate, as it has with outdoor advertising and segments of commercial printing, or will it be complementary? Our prognosis for consumer packaging is the latter, certainly for the foreseeable future. The challenges are not just the economies of run length and high volume productivity. The suitability of the imaging materials themselves can be a constraint. This is certainly the case for inkjet.

Inkjet is inherently handicapped by the requirement for inks to have low viscosity. As we all know from our desktop experiences, these inks are runny and prone to bleed. We know we must use specific papers and special films to prevent this. Uncoated bond papers of course have high absorbency, but their image appearance lacks drawing power. High impact imaging requires coated substrates. Thus to print flexible packaging films, which are inherently impervious, or folding carton stock with the types of inks that the desktop and wide format graphics markets employ, would require the use of these expensive coatings. Such additional cost is not practical. Therefore, alternative approaches, which can use current packaging substrates without modification, are called for.

There are aqueous ink solutions that we are monitoring. For example, precoating with reactive materials to cause rapid gelling and immobilizing the ink is one approach. This is practiced on Fujifilm's Jet Press 720, a sheet-fed machine for regular coated offset papers that operates like an offset press, except that it is printing with aqueous inkjet. The primer is applied only a short time before all four process inks are sequentially jetted. Its new MEMs printheads deposit very small droplets, so the total volume of water is minimized—further helping to avoid bleed between printing and drying. None of the presses in the field is producing folding carton stock, but that market will soon, as we previously predicted, be targeted. The inherent water-sensitivity of the ink would be the most obvious drawback for packaging, but matched overprint varnishes will address this.

Hewlett Packard first introduced latex inks for wide format printing on a wide range of materials including vinyl. At Fespa Digital 2012, Mimaki also offered its latex technology. Both have inks with good colors and durability suitable for outdoor use without over-coating, so they give a glimpse of future potential for aqueous inks on non-absorbent substrates. By using latex as the binder-carrier, a much greater range of binder can be incorporated, so that inks intended for specific substrates will be easier to produce. While both latex inks require active drying, in the case of Mimaki, this is only after all layers are applied. Drying will, of course, be a requirement in the design of fixed head roll-to-roll printers suitable for packaging. There are several configurations that can accomplish this. The ideal will be printing all colors wet-on-wet, which is how ultraviolet (UV)-cure inks can be applied.

Low viscosity is obtained for UV-cure inkjet inks, first through monomer selection, and secondly through processing the inks hot, as heat acts to reduce ink viscosity. UV chemistry has wide substrate latitude, and with LED lamps that run cool, the range is further increased. Therefore, the same inks can be used for a large number of applications, although their chemical composition remains a barrier to food packaging, which is the best market for short run capability. A peculiarity of UV inkjet is the structure of the ink dot, which has discernable height so the print can have an unusual appearance. This artifact is less obvious with small drops, which are desirable also because they give better ink mileage and finer detail. Therefore, we will continue to see improved small scale image quality, faster speeds, and greater width. But the throughput speed for full color inkjet useful for packaging is still rarely above 150 fpm, which is, of course, slow for gravure, offset, and flexography.

Another industrial inkjet limitation has been printer cost, particularly for custom solutions, and installations on existing process lines. The electronics and software to control the printer, deliver the image, and also interface with the original files are major cost components of any inkjet printer development program. The OEMs traditionally have done all this in-house and have had the ability to spread the cost over many units, which integrators have not. However, we are seeing new ventures providing complete hardware and software packages to the OEMs and integrators. Most of the functionality to run any of a range of printheads is embedded and selectable. Additionally, they have all the necessary functionality for optimization and operation. The time from order to start up for new machines and custom printers is being cut, and costs are coming down. Again, this bodes well for the packaging and label markets because it permits better utilization of existing equipment.

Toner-based printing is making a mark in packaging through the efforts of HP Indigo, Xerox, and Xeikon in particular. Their inherent print quality and water resistance are obvious advantages. And the coupling with finishing lines, for varnishing, die-cutting, and scoring of board for folding cartons, or laminating, coating, perforating, and slitting for flexible packaging has demonstrated the value for short-run production. However, print speed and web width are fundamental limitations.

How much penetration of the packaging market can we expect to see digital print make? Certainly not the type of transformation we have seen with commercial print—unadorned packaging by itself performs a necessary function, and print adds considerable value. And the economy of scale is still going to apply for the majority of products. Furthermore, the adoption of digital and electronic technologies for all print operations, and the remarkable developments by the flexo, gravure, and offset OEMs at reducing set up and changeover times, is a push back on digital printing claims for large economical run lengths.

Of course, while digital presses are mostly narrow and have limitations in substrates, speed, and applications, they provide capability complementary to existing capability. In the label market, all printers need access to digital presses—inkjet and toner—but not all need to own them. Perhaps Drupa 2012 will give greater insight into when that will be the rule for packaging too.

Printing expert Dene Taylor, PhD, founded Specialty Papers & Films Inc. (SPF-Inc.), New Hope, PA, in 2000 for clients seeking consultation for technical management, new product design, development, commercialization, and distribution, as well as locating/managing outsourced manufacturing. Contact him at 215-862-9434; This email address is being protected from spambots. You need JavaScript enabled to view it.; www.spf-inc.com.