Water-based printing ink drying test: solving speed and quality problems in inkjet printing!
Water is essential to sustaining life and is essential for the latest inkjet printers, but as every offset printer knows, water can be a hassle. There are many reasons why the inkjet printing industry wants to use water-based printing inks - cost, quality and sustainability. Alternatives such as UV or solvents cannot meet the demands of high-speed commercial printing on high-quality paper and book printing applications, they can be too expensive and unsustainable. Even the packaging and labeling industry, once comfortable with UV or EB curing, is turning to water-based inks.
But the moisture in water-based inks has to be removed somehow. The faster the press runs, the less time it takes to dry; higher resolution may mean more ink droplets on the paper, and as the transition from offset to inkjet printing accelerates, ink weight increases, and water disturbances can turn into water problems.
Years ago, catalogue printing buyers were often heard complaining about the advent of web offset presses to replace gravure printing to print long-run orders, which they saw as a finer process. They would say: "You unfold the paper, soak it in a solvent-based ink, then cook it to remove the solvent, then freeze it to lower the temperature of the paper, then soak it again to replace the lost humidity. Do you want to end up with a high-quality print?" Who knows what she will make with inkjet printing.
In the initial stages of inkjet development, when trading statements (perhaps books) were printed on uncoated paper, drying techniques were not a big problem, even though there were multiple different methods. As the requirements of the application became higher, faster, and the ink coverage became wider, this method also changed.
It culminates in new press designs such as HP PageWide Advantage, as well as new drying methods that were evident at Hunkeler's Innovation Day earlier this year. The drying technology used on inkjet printers for printing books, direct mail, and transactional documents is not sufficient for inkjet printing on paper developed for offset printing. The ink must be applied quickly, the water must be removed almost immediately, and the results must last.
Vendors are using hot air, heating rollers, near-infrared heaters, heating belts, long paper tracks, or a combination of the above. This suggests that this is still a developing market with no consistent solution, as sheetfed offset printing has used a combination of infrared and hot air for many years, while web offset printing requires long ovens to evaporate. Solvents used to fuel ovens have been standard for as long as thermosetting web offset printing is present.
The challenges facing the Ricoh Z75 B2 sheetfed inkjet press are also evident. It uses water-based inks to print one side of the paper and then dries it before printing the reverse side of the paper. After drying, it does not change the size of the paper and does not create registration problems or binding problems - especially when using PUR adhesives.
Ricoh gave no details on how to do this, how to prevent or compensate for paper shrinkage, other than to say that a new dryer design had been developed, and the answer may be clear when the machine finally hits the market.
This was a challenge for Landa Digital Printing, which sidestepped the main challenge by removing moisture before the ink reached the paper through the heated tape, but still had to maintain dimensional stability and draw high-humidity air out of the press. It prints water-based inks onto the heated tape, forming an image that is held together by a hot-melt adhesive-like substance. By the time the image is transferred onto the paper, the water in the ink has disappeared and the paper is not affected by any water.
Canon has had a longer history in inkjet printing than most companies, with the JetStream model giving way to ColorStream as well as, more recently, ProStream. The JetStream was a design borrowed from Miyazu so that Ossie could start replacing laser presses before Canon acquired the business. It was launched in 2008. Three years later, Canon introduced ColorStream, its own design, for which Canon also developed inks. It began introducing presses into book presses, again replacing or alongside toner technology.
Then in 2019, Canon launched ProStream, a press that can use new inks for commercial printing jobs on coatings, and a new drying system (unlike a thermosetting web press) to cope with the high ink coverage on these papers: short commercial prints.
This year's lessons have been incorporated into the ProStream 3000. Keeping the Kyocera nozzle at a temperature of 32 ° C helps control the viscosity of the ink as it is ejected on the company's ColorGrip primer, providing an even surface regardless of the paper underneath. The ink formula itself has been modified to carry higher pigment loads. It also contains some VOC solvents, presumably to aid in the dispersion of polymer-coated pigment particles. The polymer is designed to melt and reformulate as a protective latex-type layer around the pigment during processing. Canon says the ink can support 400% TAC.
The hot air drying system is retained, but the first part is shorter than the part used to dry the second side. The temperature within the drying system is set to 130 ° C and fans are provided on both sides of the net to distribute the heat evenly. This both evaporates the water and solvent and holds the polymer to the paper. A certain temperature is required to remove the moisture and trigger the process of melting the polymer shell around the pigment and cause it to flow together, turning solid when cooled and trapping the pigment.
Before printing and drying the second side and exiting the press, the web passes through a series of cooling rollers that reduce the temperature to 60 ° C, with the goal of minimizing stress and deformation of the paper during printing. Canon also says that the ProStream 3000 uses less energy than before, which may be due to increased water and solvent content. However, like other suppliers, it does not publish energy consumption data to allow for any type of quick comparison between suppliers. Hot air and solvents are vented to the cooling unit, which recovers the solvent for reuse.
The HP Advantage 2200 is another product that showcases new thinking based on the drying experience. The Pagewide T200 series of machines has evolved over several generations, using different dryer configurations, from a single dryer that prints in monochrome only on uncoated paper, to multiple dryers that are placed on the press as much as possible as ink coverage increases. When users find themselves limited by a large amount of ink coverage, the only solution is to slow down the print to increase the dwell time per page for drying.
This is one of the problems Advantage is trying to solve. Rather than offering a single solution for all occasions, HP offers three models with one, two or three drying modules, depending on the amount of ink and the application to be dried. HP uses a thermal inkjet process and is therefore fully committed to water-based inks. Inks are constantly evolving, improving adhesion, drying and resolution.
HP says Advantage enables the ink to adhere to any type of paper by means of an adhesive. Equivalent to commercial printing, three drying system versions are required. Drying uses shock or forced flow of hot air through the paper web. Since the drying paths are longer on the two and three module versions, cooling sections with four cooling rollers are used to lower the coil temperature for printing on the second side.https://www.risedongsheng.com/
In the process, HP took full advantage of the improved energy efficiency as well as the beneficial impact on costs, which was not paramount in the early stages of developing its specifications. Four-fifths of the hot air is recycled inside the press to reduce energy consumption, resulting in a 40% reduction in energy costs for printing a page compared to the T250. According to HP, users can change the settings, which many do, in an attempt to minimize energy consumption per page, thereby controlling the running costs of inkjet presses.
Kodak will also change the drying capabilities of the Prosper Ultra 520 to suit paper and applications. The P version of the Prosper is designed to publish applications, books and journals with limited color coverage, while the C version is for commercial color, so has additional drying capabilities. The company has been using near-infrared drying technology on several generations of inkjet printers, with a history dating back to Versamark.
Kodak's inkjet technology is continuous inkjet, which the company says means less moisturizer is needed in the ink to keep the nozzles open and prevent clogging caused by dry ink. The ink needs to react to an electric charge in order to deflect the ink into the recycling tank when it doesn't need to reach the paper.
Once on the paper, the near-infrared dryer starts working. Kodak uniquely places the dryer after each color is placed, a configuration more common on sheet-fed presses with UV lights between the printing units. Other inkjet presses keep the nozzle array close together to ensure alignment with the dryer after all ink is applied.https://www.risedongsheng.com/
Near-infrared technology uses a limited range of radiant energy to excite water molecules and efficiently evaporate them without transferring heat to the paper. This property has attracted companies that use water-based inkjet for flexible packaging that runs on different non-porous substrates that other hot air dryers may generate excessive heat in the substrate to keep it stable.
Like Hewlett-Packard and Canon, Kodak continues to work on ink formulations. The formulation developed for the Ultra 520 is the fourth generation, further reducing the use of ethylene glycol and adjusted to work with the latest generation of Adphos NIR dryers. "Our inks do not contain the moisturizers required by other companies, and the low levels of moisturizers make the ink easier to dry," said Randy van Dagliff, senior vice president of Kodak. "This level is in the single digits compared to the 20% -30% required for piezoelectric inks."
The dryer is digitally controlled and provides measured energy to process the amount of ink and save the settings for repeated jobs. This is of interest to users who understand energy costs and want to keep them under control. Netscreen is also using a NIR drying system on its Truepress Jet 520, which similarly matches the inks developed for the press. The Japanese company has been keen to use only single-fluid inks, rather than applying them to the undercoat.
The printing press itself has changed little since its introduction 12 years ago. However, the ink has undergone several transformations, and there are signs of more to come, perhaps with new press designs. A version has been developed to print on barrier paper for packaging applications that require high-energy and water-based inks.https://www.risedongsheng.com/
The commercial printing market employs NIR-compatible SC Plus inks, which provide a higher pigment load to expand the color gamut. Working this way, there is no need for pre-coatings and no need for any type of post-print protective coating. Pre-coatings can be applied, resulting in a higher gloss on the right paper, but without the need for good results on embossed paper. Screen's TruePressJet was at one point virtually indistinguishable from Ricoh's continuous-feed inkjet presses, due to the joint venture that existed between Screen and IBM prior to Ricoh's acquisition of the US company's printing interests.
As the target market has moved from trading and direct mail to books, and now to commercial colour printing, the approach has also changed. Previous heated surfaces are no longer good enough. Ricoh's solution is to combine large heated rollers with multiple smaller rollers on which paper is wound and emits heat to dry the paper, while keeping it under tension. This approach first appeared on the VC70000, a model aimed at higher ink coverage applications and commercial printing. The company has developed an extended gamut ink kit for printing presses that protects the printed surface without the need for pre-coating or post-coating. However, these are available if required.
For the latest version, the VC70000E primer has returned, which perhaps reflects some field experience from the initial version and represents a modification rather than a return to the drawing board approach. However, the heated drum technology has not yet been transferred to the upcoming B2 sheetfed press Pro Z75. The machine is currently undergoing beta testing at Heeters in the United States, with a dry section up to 12 meters long. Ricoh has not discussed what is inside and how exactly the paper dries, at least not until it receives a full commercial release. The way the water-based inks are dried can obviously gain a commercial advantage.https://www.risedongsheng.com/