Digital Printing
Not just high tech printing Digital printing is used for a large variety of printed products.
In this article Lauri Järvinen, technical marketing manager at Metsä Board looks at both inkjet and electrophotography.
D
igital printing uses two technologies: Inkjet and Electrophotography (EP). These two technologies are totally different from each other, making the generic term ‘digital printing’ a potentially confusing one. It is essential to understand the difference between these two technologies. O Inkjet – a pigment-based ink is applied from print head nozzles to transfer an image directly onto paperboard. Paperboard absorbs the ink that is either dried or UV cured. Digital inkjet printing can use either water-based or UV inks.
O Electrophotography (EP) – a digital printing press creates an image with polymer-based ink (toner) that it transfers onto paperboard. The interaction between the toner and paperboard is adhesion – none of the toner is absorbed into the paperboard.
INKJET
Digital inkjet printing produces very good printing results onto most paperboards. It often requires the use of a pre-print primer to avoid ink spreading.
The high presence of moisture requires good dimensional stability and optimised water absorption capabilities from paperboards. The paperboard coating should have an even micro pore size and distribution to ensure evenness of ink (and pre-print primer) absorption. At the corrugated post print stage, final print quality is highly influenced by the quality of the corrugated sheet. A curled sheet would cause runnability issues and can even cause damage to sensitive inkjet heads. Washboarding on a corrugated sheet would cause unevenness of ink absorption.
UV cured inks do not share the challenge in terms of drying energy consumption, but UV inks may not always be food safe.
ELECTROPHOTOGRAPHY
Electrophotography uses two methods: dry toner and HP Indigo ElectroInk (liquid toner). On digital printing presses that use dry toner, an image is first created on photo conductor drums and subsequently transferred onto the paperboard. Dry toner transfers easily onto all surfaces. It has no issues with toner adhesion onto
paperboard and thus would not need a pre-print primer. In general, the print result is good. For paperboard, dry toner requires consistent moisture to maintain electrical resistivity at the dry toner transfer. For the same reason, the process requires a smooth paperboard surface. The sheet needs to be flat, square and precise in size to guarantee trouble-free passage through the press.
In HP Indigo digital presses, an image is first created on a photo imaging plate and subsequently transferred onto paperboard via a blanket.
All the HP Indigo digital presses produce excellent printing results. HP Indigo recommends the use of HP Indigo certified paperboards that contribute to the right surface chemistry for HP Indigo ElectroInk. Ink adhesion can be optimised by using off-line or in-line pre-print primer for non HP Indigo certified paperboards. For all the HP Indigo digital presses, the paperboard sheet needs to be flat, square and precise in size to guarantee trouble free passage through the press.
MARKETS AND TRENDS
Traditional printing methods require mechanical interfaces – printing plates or cylinders – to multiply fixed images for a desired print run. Digital printing does not need mechanical interfaces and can thus create variable images during a desired print run.
Digital printing does not have the same production efficiency as conventional printing – but does it need to? In fact, digital printing would complement the offering of a print house with high value orders of special editions, seasonal packaging, etc.
Mass production with long runs would benefit from the higher speeds of conventional printing. Although digital printing is virtually instantaneous, the full turnaround time in packaging production does not yet fully benefit from this. Die cutting, folding and gluing still needs to be completed by conventional technologies. However, there are already solutions for this issue. Kama has introduced a flexible small format die cutting machine that is ideal for digital output. Highcon has a fully digital die cutting machine that cuts with a laser and can offer a creasing tool manufacture that is integrated inside the machine using polymer made creasing tools.
DIGITAL PRINT MARKETS
In the year 2021, about 3.4% of all cartonboard and corrugated packaging was printed digitally. By the year 2026 the share of digitally printed cartonboard and corrugated packaging is estimated to increase to 6.7%.
The use of digital printing is particularly increasing for corrugated materials. In the manufacture of corrugated boxes, displays, point of sale materials, etc. digital inkjet printing is seriously challenging flexo printing. In folding carton manufacture, converters use electrophotography (EP) for short print runs and personalised cartons. A number of press manufactures are developing digital inkjet presses for folding cartons, but these developments are still awaiting their breakthrough in the packaging market.
Digital printing in paperboard packaging is opening new opportunities for packaging design and even functionality. Personalisation can make packages experiential. Packages can include promotions, advertising, and celebrity endorsements and even be used as a viral influencing tool for marketing.
Digital printing is virtually instant, enabling packages to be produced on-demand and closer to consumers. It should be understood much wider than an interesting high-tech, it holds the potential to enhance the world of printing.
Xwww.metsagroup.com/metsaboard/
20
November 2022
www.convertermag.com
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