by Cassandra Balentine
Many years ago, digital print was a solution for limited applications. Namely, short-run work that only required “business quality” output. However, significant advancements to continuous-feed inkjet printing are disrupting the industry. At the same time, cultural shifts and demands favor shorter runs, personalization, faster turnarounds, and reduced waste are all primary benefits afforded by digital print technologies.
Today, continuous-feed production inkjet devices continue to advance in terms of speed, quality, precision, drying, and media handling and are more than capable of hitting millions of impressions every month.
Above: The KODAK PROSPER ULTRA 520 Press replicates offset quality and productivity on the most demanding high-ink coverage applications. Taking full advantage of KODAK ULTRASTREAM Inkjet Technology, PROSPER ULTRA 520 is aimed at the mid-volume market segment and printers that would have production volumes of around ten million A4 images per month.
Technologies
In the digital print space, continuous- or web-feed inkjet presses utilize drop on demand (DOD) or continuous inkjet (CIJ) technologies.
Within DOD, both thermal and piezoelectric technologies are utilized in the commercial print space. “All DOD eject an ink droplet from the printhead nozzle when needed. The advantage is that it enables better control of the ink drop placements with higher accuracy,” offers Rolando Martinez, head of HP PageWide Commercial Products and Solutions, HP Industrial Print.
Piezoelectric DOD technology handles a range of ink viscosities and compositions making it versatile for various printing applications. “Piezoelectric is typically more robust for high-volume printing environments. The initial investment may be higher, but it can be more cost effective in the long run due to lower maintenance and ink costs. The piezoelectric inkjet printheads also offer more flexibility in droplet size and can eject larger droplets at higher speeds, which is beneficial for faster printing without compromising quality,” explains Lisa Weese, senior director of marketing, Canon Solutions America, Production Print Solutions.
Both the Canon ProStream and ColorStream utilize Canon DigiDot piezoelectric DOD technologies.
Ricoh’s production inkjet portfolio also relies exclusively on piezoelectric, DOD-based technologies. “This approach provides end users with flexible, reliable solutions that are purpose built to solve their business challenges today and into the foreseeable future,” says Tim Bolton, manager, inkjet technology portfolio, Ricoh Graphic Communications.
Benefits of piezoelectric DOD include precise drop placement, dynamic variable drop size, high resolutions and frequencies, as well as industrial grade durability to support a range of applications in many different industries, such as commercial print, ceramics, textiles, wide/grand format, and additive manufacturing, according to Bolton.
HP utilizes its proprietary DOD thermal inkjet technology.
“All inkjet printing processes involve ejecting ink droplets through specially designed firing chambers with small orifices or nozzles. Over time, these nozzles can clog, which is a natural aspect of the inkjet printing process,” says Martinez.
HP’s thermal inkjet technology addresses this with cost-efficient, user-replaceable printheads. “Replacing these printheads takes only a few minutes, providing users with greater control over print quality and productivity,” says Martinez, adding that HP thermal inkjet requires no purging, significantly reducing ink waste.
CIJ is also available either as a single jet or an array system. The systems can print at very high frequencies/speeds as part of a high-speed process.
Another positive of CIJ is the drop velocity is very high and can print at a significant distance from the substrate. “This can improve the reliability of the process, which is important when printing at high speeds,” says Paul Edwards, VP, digital division, INX International Ink Co.
When comparing CIJ and DOD technology, DOD is generally slower but has the benefit of greater print resolution. “It also has the ability to print a full-color process; although it is less common in CIJ, it is possible to print full color in some systems. The printheads are suitable for UV inks and different UV technologies, as well as for water and solvent. It is also easier to build a wide DOD system than a similar width for CIJ. The throw distance for DOD heads is lower, and more care and maintenance are often required compared with CIJ,” says Edwards.
Martinez points out that the CIJ method consists of ink droplets constantly being produced and ejected, but only when the drops are needed to land on the page is when they are diverted onto the paper, otherwise they are collected again.
“Strengths include more simple ink formulation and less procedures to service the printheads’ health since there is less risk of ink drying or clogging the nozzles as they are constantly being fired, but they still degrade,” shares Martinez. “The main weaknesses is that there are higher risks of misdirection of ink drops reducing accuracy; limited redundancy when nozzles do go out; and since ink is recirculating after being in contact with air, there is a degree of contamination and evaporation that can alter the pigment-to-water ratio, which may have an impact on the color balance and print consistency.”
Ink Chemistries
A full range of ink chemistries have potential in ultra-high-volume production. Each has their benefits and limitations, shares Edwards.
“Less common are oil/glycol-based inks, which tend to only be used where the substrate is absorbent. Hence, the ink dries by absorption. The very slow drying rate is a benefit for printhead reliability but it places a limit on substrates and leads to a slower production process. This technology is mostly used in DOD systems,” explains Edwards.
Solvent-based inks have benefits related to the speed of drying and range of polymers (adhesion), which can be used in the inks. “They can be printed at high speeds with minimal drying and are especially suitable for CIJ systems as the non-printed ink is continually recirculated and ‘made up’ to control viscosity by the automatic addition of solvent fluid. Inks can be used in DOD systems but tend to be slower drying and less beneficial at higher speeds. Solvent inks can be an issue unless the emissions are controlled,” comments Edwards.
Water-based systems are somewhat in the middle of oil/glycol and solvent inks. “It is slower drying and more suitable to absorbent substrates, but also can be used on non-absorbent substrates if drying is sufficient. When used on non-absorbent substrates, the water drying time will be a factor due to speed potential and/or complexity of the equipment. Your choice of polymers in the ink is more limited with solvent, making adhesion more difficult to achieve on some substrates. Water-based inks can be used in both CIJ and DOD systems, and are viewed as more ‘green’ friendly and the safer choice,” says Edwards.
UV inks are the final class, according to Edwards, who notes that these inks dry almost instantly on exposure to UV light and can be run at high speeds if curing is sufficient. These inks will also adhere to almost any substrate. “Since they are slow to evaporate, UV inks are usually very reliable in the printheads. But they are generally used in DOD technology since they can create high-quality images and their drop spread can be controlled via the cure process. UV can be used in CIJ printhead technologies, but it is not common since viscosity constraints the formulation and ink properties.”
Both pigments and dyes can be used in DOD and CIJ ink systems. The same can be said for all the different ink chemistries. “Dyes can be more difficult to use depending on their solubility in the different chemicals, but they do provide a very bright and colorful image. Pigments can be dispersed into all chemistries and provide good color, but they do have better fade properties and images last longer in brighter lighting conditions. Dyes can be more reliable than pigments as a pigment needs to be dispersed to ensure stability, and they can become unstable over time,” notes Edwards.
Canon’s ColorStream uses water-based pigment inks while ProStream uses ColorGrip conditioning fluid and a polymer CMYK pigment ink set with InkSafe technology.
Martinez says HP spent decades inventing, developing, and perfecting ink chemistries to meet the diverse needs of high-volume commercial customers. “HP ink chemists have formulated a high-performing pigment, water-based ink that delivers a wide color gamut with rich reds and deep blues, and boosts gloss by surpassing the sheet gloss level on a variety of coated papers. HP Brilliant Ink delivers stunning print quality on standard offset coated and uncoated media, and is environmentally and workspace friendly with extremely low emissions. HP Pigment water-based inks provide high durability and permanence as well as a wide media range suitable for all commercial printing applications.”
All PROSPER Presses utilize Kodak’s CIJ technology, which provides high-quality, high-speed color printing with eco-friendly, water-based inks.
KODAK EKTACOLOR Inks are used in Stream Inkjet Technology, while KODACHROME Inks are designed for high-quality ULTRASTREAM Technology systems.
“A common feature of KODACHROME and EKTACOLOR inks is a lower level of humectants compared to competitive inks. This results in very fast drying, even with high ink coverage on coated and glossy papers. The low humectant inks, together with interstation near-infrared drying—which is adjustable depending on volume and ink coverage—are enablers for printing heavy ink coverage on coated and glossy papers at top speeds,” says Andrea Connor, worldwide marketing manager, Kodak.
Ricoh continuous-feed inkjet presses utilize aqueous inks with low water content in both dye and pigment formats. “These inks allow customers to effectively print and dry at increasing speeds and resolution. Dye inks are typically used in the RICOH Pro VC40000 based on the targeted applications of the press, but pigment and MICR options are also available. The RICOH Pro VC60000, VC70000, and VC80000 presses use pigment-based inks exclusively to achieve wide color gamut and output resolutions for more challenging applications and print quality requirements. While water-based inks are tailored almost exclusively to paper-based substrates, they also avoid many handling, environmental, or disposal concerns that often accompany other ink chemistries like UV,” shares Bolton.
Future Trends
As traditionally offset printed applications shorten in run length, digital inkjet is an appealing solution for more commercial print work.
“We anticipate growth across commercial, publishing, book printing, and packaging sectors,” notes Conner. “This growth is expected to increasingly capture market share from traditional printing methods, particularly offset printing. Factors such as cost pressures, shorter print runs, customer demands for quicker turnaround times, and a persistent shortage of skilled labor are driving this shift.”
“Commercial and book printing continue to see runs shortened as print on demand and the need to reduce waste and improve efficiencies become increasingly important,” shares Martinez.
Further, direct mail campaigns need to be more targeted and personalized to be relevant and continue to drive higher return on investment compared with pure digital campaigns. “All of these trends continue to favor digital printing, which is forecasted to continue to grow in the next few years,” says Martinez.
To capitalize on these trends, Martinez says HP is constantly innovating in the continuous-feed inkjet market with a proven track record of decades of innovations. HP plans to bring more intelligent automation to the print process with On Press profiling and Smart work cell controller technologies.
Continued advancements in versatility are expected as the market learns to leverage investments for more applications in order to diversify and capture greater share of the market and to expand into more applications. “They need their press to be versatile, flexible, scalable, and sustainable in addition to highly productive,” offers Martinez.
Bolton points out that Ricoh is investing in increased utilization and productivity of its current generation presses. Increased on-press automation, reduced reliance on operator skill set and judgement, as well as overall pressroom automation are big focus areas.
Conner feels that transitioning to continuous-feed digital printing can also help address sustainability concerns and reduce the carbon footprint of printing operations. “Our highly automated, high-speed inkjet presses and imprinting systems offer excellent solutions to these challenges, enabling consistent, high-quality production at full speeds, cost effectively.”
Sustainability will continue to play an important role in the print industry and Martinez says HP presses’ longevity provide customers with upgradable and scalable solutions. “We see that 95 percent of the presses installed since 2008 are still in use today,” he offers.
Weese confirms that the future of digital continuous-feed printing aims at higher levels of throughput and productivity. “This is evident in the Canon 2024 announcements with the ColorStream 8200 and ProStream 3180. These advances help enable print service providers to produce more prints per hour so they can take on more jobs and/or meet tight service level agreements.”
High Speeds, Impressive Quality
The digital print industry continues to mature. While the adoption of continuous- or web-fed inkjet was once limited to transactional documents and books, today the technology attracts print buyers looking for the highest quality and customization in a variety of commercial applications.
Nov2024, DPS Magazine
