In the first of our three-part technical series on what it takes to print packaging, we will focus on the corrugated market, peeking into application and technology options. This is topic close to the heart of both the author, Mark Bale, and Insight Partner Mary Schilling since working together on Inca Digital’s first single-pass box printer called FastJet in 2009.
Early Printers and UV
As the first globally successful industrial application, wide-format graphics (WFG) grew by replacing screen printing in a range of applications, mostly on the back of advertising printing such as indoor poster prints and outdoor displays. Driven by the rising popularity in shelf-ready packaging and point-of-purchase (POP, POS) it was clear that there was a market for short-run printing of higher-value graphic content on corrugated boards. At a similar time, UV ink started to be used, replacing the original solvent ink in many of the larger WFG printers. Digital printing of corrugated was made possible by the ability of the UV ink to print onto a range of different surfaces.
One of the first printers, CorrJet, came from Scitex in Israel, then Durst jumping into the mix with a paper and board offering called the Rhopac, each offering around 150sqm/hr. By the time HP launched the FB7000 series, thus taking corrugated box “production” to the next level, Inca was selling Onset S70. Both used full-width print head arrays with scanning beds, permitting 100’s of square metres per hour (1000s sqft/hr) offering larger runs in full colour digital.
Clear from the beginning, was the corrugated industry required a spectrum of liner options. Uncoated stock’s issue was simply the absorption which could result in a residual odour if the UV ink penetrated before getting cured. Formulating a lower odour ink could help mitigate the smell but leaving uncured material in the paper was not ideal. For this reason, the CorrJet had a spray primer station. A primer station was also designed into the Beta version of FastJet, the first fullwidth single-pass inkjet printer that shared technology with the Inca Onset S70. Although, ultimately too expensive for early adopters, FastJet was the first corrugated board printer to run routinely >2000 m2/hour.
In comparison, coated boards used filler different materials that had a big influence on the inkjet droplet behaviour. It wasn’t so important for multiple-pass printers, but the poor ink wetting caused issues with streakiness and coalescence when printing single-pass. Formulating the primer correctly also helped solve this too, as shown in the pictures below, taken from some old R&D samples on different liner materials printed at 50-100m/min single pass.
Since 2008 there have been several UV printers launched, notably the Barberan JetMaster and EFI Nozomi. Both primers were housed in separate stations from the main digital unit, allowing for primers to be added only where needed. It also permits the analogue processes to be controlled independently from the inkjet technology.
Like the label printers we wrote about last year, both these printers use newer, 360dpi grayscale heads to improve the apparent resolution versus the 300dpi binary FastJet, but the ability to provide primer has remained an important option to maximising the quality of the output.
Back to Water-Based
The colour and glossy appearance means the printed image can pop amazingly well for UV, but one of the main limitations in packaging is migration of ink components after cure. Although some mitigation is possible with primer and formulations that are compliant to positive lists, there has always been a desire to use water-based (AQ) inks. Combining this constraint with continuing drive for sustainability at the corporate level has driven the development of a whole new swath of water-based inkjet printers.
The main challenge for corrugated is the rough handling often received by the package, thus requiring the ink to have good end-use rub resistance. This requires state-of-the art inkjet formulations to achieve the desired properties whilst keeping the heads reliable, a development goal made more achievable by the latest generation of recirculating print heads.
The Low-cost printer provider, Xanté made use of the Memjet print engine but experienced the issue of ink absorption described above for UV, was also a problem for AQ when colour fidelity was desired.
Integrating Priming and Solutions
Durst with their SPC-130, took a similar approach to the UV printers by integrating an inline priming station, like the CorruJet from Koenig & Bauer. Macarbox advertises an optional inline priming and varnishing units, reinforcing the importance of a modular design approach we discussed above about UV.
In contrast Sun Automation, used 600dpi Kyocera module from GraphTec and focussed on using ink as the solution; analogous to some, the ink technology was used on coated paper for production print. The printer from Chinese supplier Hanway is seemingly similar in this respect, offering compatibility with different substrates without primer.
HP also derived their printing technology for corrugated from the commercial printing side (web-press), including the pre-printed primer that prevents the ink penetration issue. Most recently, Inca Digital has announced a paper and board printer called SpeedSet. Although intended mostly for micro-flute corrugated and carton board (the subject of a future post in this series) they have described using an inkjet primer for maximising print quality.
Beyond sheet-fed “post-print” there is a new generation of ultra-fast web printers to do “pre-print”. In addition to well-known HP, beta testing for the BHS/Screen printer has recently been announced, useing 2 rows of Samba print heads to reach 300m/min, as well as offering a digital varnish.
In all these high-speed machines using AQ, the drying of the primers and inkjet inks is crucial. Paper is quite resilient to the use of infrared (IR) or near-infrared (NIR) driers, which are combined with hot air to maximise the efficient evaporation and removal of the water vapor. Careful balancing of the ink formulation is still critical for achieving head maintenance (drying speed in the nozzle), as discussed in our previous post on ink matters. For this reason, UV printers continue to sell well.
Join us for our next post in this “what it takes” series as we will be looking at the substrate challenges of applying inkjet processes to the flexible packaging segment. Until then, check our previous webinar on print heads to understand more about the technology mentioned above and look out for the next webinar in our print head series, where we explain DPI and speed specifications for print quality.
Until then, print on.