Whilst laminating reels of paper together to form sheets of corrugated board may sound simple, technically the process is complex with many potential pitfalls. Imagine an orchestra playing a classical symphony with just one of the musicians playing out of tune – the result is a discordant noise that is out of harmony and sounds dreadful! Similarly, if one of the many linked processes on a corrugated board manufacturing machine (corrugator) is not working in a synchronised manner with the others, the result is a substandard product, which is then less compatible for digital print and downstream manufacture.
Digital print platforms come in a multitude of formats, with varying ink systems, costs, and qualities, but the common factor for all of them is the requirement for consistently good quality corrugated board to achieve the best production efficiency and print results.
An acceptance from corrugated manufacturers that more dependable precision was required in the quality of sheet-board was not embraced in the early days of digital. On the contrary the pervasive viewpoint was that corrugated manufacture had limitations and digital OEMs needed to accept the foibles of corrugated and design their machines to compensate for its inconsistency. The precise nature and progress of digital print was therefore constrained by unreliable corrugated board, and it needed collaboration to drive a new era for corrugated that required a different approach.
Digital OEMs such as HP and EFI have done an amazing job of marketing the diverse opportunities that digital print on corrugated brings to emerging markets such as versioning, e-commerce, short run etc. However, many of the physical digital printing challenges were associated with inconsistent board quality – upwarp, downwarp, RH variation, irregular surface, etc. I personally visited many machine demos in the early days of sheet fed single pass digital technology and noted that much of the downtime incurred was as a direct result of poor-quality materials. Downtime could just as easily be caused by bad board causing feed, transfer, or stacker issues as it could by a print head issue. Digital print machines don’t like being idle; they run best without stop–start interruptions. Critically, progress of digital printing innovation was being suppressed by proud corrugating companies who did not see a need for change in their process, rather a need for digital companies to accept what could be offered from established corrugating technology. Quite simply, it needed corrugated producers to focus on manufacturing quality sheet by adopting a more sympathetic approach to production, and understanding exactly what digital OEMs required of corrugated to maximise the opportunities that this print technology brings to evolving markets. The starting point for these step-changes was the very papers that make up corrugated board.
Corrugated board is renowned for its strength, durability, printability, cost effectiveness, versatility, and sustainable nature. Traditionally an industrial material, it has changed very little over the last hundred years or so, but more recently, innovation in print technologies such as flexography and offset have driven marked improvements in paper qualities. Similarly, digital print as a non-contact process has further advanced paper construction to enhance sheet and consequently, print quality. Digital OEMs, paper, and corrugated companies recognised the need for collaboration to evolve new papers and manufacturing techniques to accelerate progress now that there was a common understanding with shared goals. As a result, it is now possible to engage intelligently with material suppliers who understand the digital print process, so development costs are reduced, and solutions can be found far more quickly. Leading the way with sheet-board for digital print, companies such as Smurfit Kappa have partnered with the likes of HP to develop new boards that are commercially available in the market, Smurfit Kappa’s Digiflute® being an example of where collaboration has proven its worth.
Paper innovation has also dramatically improved the image quality of all print technologies; SAICA’s Infinite Coated and Infinite Innova range of papers being a great example of this company heavily investing to meet the rising demand for superior papers that enhance the quality of digital (and analogue) print.
Corrugated material is a “living” product by nature. Like all paper-based materials, its shape can change with humidity and temperature variation after manufacture. Even after focusing on the most stringent disciplines in the material manufacturing process for digital materials, there must be an acceptance for a workable tolerance. HP has focused heavily on minimising downtime caused through material shape issues. Their innovative top feed system, developed specifically for their single-pass sheet fed platforms (C500 & C550), allows for the printing of a wider range of substrates to include thinner flutes and, being top-feed, it does not have to fight with the weight of the stack on top of the sheet being fed – this challenge is inherent with bottom feed systems. Their ‘Stack Topography Alignment’ looks at the pallet of board in the stacker using a series of cameras. The stacker can then adjust the topography of the board to allow more consistent feeding. This innovation tolerates a degree of change in board shape throughout the run.
Primers facilitate key benefits for print and product quality by providing an enhanced surface for ink adhesion and drying. The primer also has an important role in controlling how the ink interacts with the substrate once the jetted ink droplet lands on the surface. Primer controls the absorption rate of the ink into the substrate to avoid both too much absorption (dot gain), or not enough absorption where the ink appears too frugal. A consistent coverage of primer regulates absorption and maximises colour whilst reducing ink use. Other considerations for primer use are the print finish that is required (gloss, matte or satin) and whether water based, or UV inks are to be used. Once again, the collaboration between paper companies and digital OEMs is important here, because different papers need different primers, but it is prudent to operate with one primer for efficiency reasons. Adhesion between ink and the substrate is also fundamental to pack performance as it provides rub resistance which can be critical in downstream processes such as packing and transport. Such is the advancement of paper manufacture; some papers do not require primers as their surface layers are consistent and designed specifically for enhanced digital print results.
Paper is a sustainable solution and therefore, surely, we need to ensure that the inks we are using are aligned with the same principles, particularly on packaging products. Consumers expect excellent print quality when their goods arrive, and digital print delivers this. But what about the sustainability of the inks that are used? UV inks are carcinogenic as a liquid, but once cured, their molecular structure changes to a solid and they can be recycled in packaging waste streams, whereas water-based inks are harmless and do not carry the same health concerns. Potential legislation on de-inking packaging during recycling is likely to favour water-based systems.
Both UV and water-based inks have their place in the digital print world, but packaging is more legislatively controlled than point-of-sale display, as it is more likely to come into consumer contact. This being the case, water-based inks are arguably the best option for packaging to help ensure consumer safety. Coupled with the already strong credentials of paper-based packaging, I believe that technological advancement and sustainability of water-based inks is most likely to prevail over UV.
Corrugated board manufacture for digital applications has dramatically improved in quality since a more collaborative approach with digital OEMs, paper makers and corrugated board manufacturers. Digital OEMs themselves have developed innovative ways to deal with a degree of warped material caused after manufacture, so, whether a machine platform is installed in an arid country or a humid country, it can tolerate a degree of material variance. Most exciting of all, as historical challenges with corrugated are overcome, single pass technologies are just going to get better and better!
Nick Kirby is a 44-year veteran of the corrugated packaging industry, the last 22 years as CEO of Swanline Group. A strong believer in challenging convention, working collaboratively, and protecting value, Nick has led many initiatives in the industry including the early adoption of digital print technologies for corrugated packaging. Having sold Swanline Group to Zeus Packaging in 2022, Nick still takes an active role in pushing the boundaries for sustainability, innovation in corrugated packaging and display production.
You can reach Nick under LinkedIn