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Favorable Flatbed Inks

UV Expands Possibilities for Flatbed Printing

By Amber E. Watson

Flatbed ink sets are known for the ability to print directly to a variety of media. Many jobs are created on flatbed printers, including billboards, point of purchase (POP), trade show graphics, outdoor advertising, banners, posters, and in-store displays. The possibilities, of course, do not stop there.


While it is possible for flatbeds to print with latex, water-based, solvent, and eco-solvent ink sets, UV is the most common one. Benefits include optimum media compatibility, instant curing, and the elimination of lamination as graphics are printed directly to the substrate. UV technology also provides a new range of applications for print service providers (PSPs) due to durability, color gamut, flexibility, and cost.


UV Popularity

Flatbed printers using UV-curable and UV LED ink offer high media compatibility, with the ability to print on practically any rigid material.


Success of UV ink with wide format flatbed printers derives from the ink’s capability to cure instantly as it solidifies upon exposure to the UV light within the printer, and the adhesion bonding to many different surfaces without embedding through a coating, solvent, or heat process. Since heat is required for curing non-UV inks, many substrates run the risk of warping, buckling, or burning. The result is that UV devices allow PSPs to print onto all different types of thicknesses, including thinner materials, used in packaging.


Erez Shoshani, GM, Bordeaux Digital Printink, explains that all UV inks contain photoinitiators, which initiate a chemical reaction causing the ink to harden on the surface and create durability. The immediate curing and high durability of UV inks enable printing on almost any surface.


Instant drying/curing time means that prints are ready to stack without offsetting, and may be finished, packaged, shipped, and invoiced immediately. There is also less waste.


“Prints that need to dry are more vulnerable to damage from anything contacting the wet ink, and potentially from any extra human handling. Also, in the drying process non-UV inks need to evaporate the solvent component leaving the pigment component behind. This solvent component is a major portion of the overall ink volume,” explains Randy Paar, display graphics marketing manager, Océ North America.


“Instead, UV printers cure the entire amount of ink jetted onto the media. This means that one liter of UV ink typically yields greater coverage than a similar volume of non-UV ink,” he continues.


While the use of latex, solvent, or aqueous inks in a flatbed printer is possible, it is not as practical. The primary limitation with other ink types is application range. “Latex and water-based inks are primarily for indoors with limited UV protection and short-term use. Solvent and eco-solvent are being phased out for volatile organic compounds and health reasons, where UV does not have the same volatility as solvent-based inks,” notes Jim Cain, director of sales, digital, Polytype America Corporation.


“Unlike solvent inks that adhere via a mechanical bond, UV inks stay on the surface of the media and produce a chemical bond with the substrate to achieve adhesion. LED inks are formulated to cure at a specific UV wavelength, which is different from conventional UV inks,” notes John Kaiser, product marketing manager, inkjet inks, Fujifilm North America Corporation.


Another benefit of UV is the capability of printing at higher speeds without the need for extensive drying systems. Hiroshi Ono, group product manager, Roland DGA Corporation, explains that PSPs with non-UV flatbed printers must install an infrared heater above the surface, which is used to heat the material, and in turn, heats the printer, its electronics, and the surrounding area.


“In order to keep up with production speed, specific drying systems result in an increased footprint of the machine, as well as significant increase in electricity consumption,” adds Kobi Markvitch, CTO, MTL Print Ltd.


Cater to New Markets

The main advantage of UV flatbeds is the ability to print directly to a variety of rigid media, which saves time and money by eliminating the need to laminate a printed flexible material onto a piece of rigid stock. “This makes the process popular for POP and packaging applications where rigid media is dominant,” notes Markvitch.


Along with traditional applications, such as signs and banners, David Cich, VP of sales and marketing, CET Color, Inc., notices a number of unique applications created with UV-curable and UV LED ink on flatbed printers, such as mirrors, furniture, wood flooring, ornaments, guitar picks, packaging, picture frames, ice sculptures, concrete sculptures, tiles, pool floats, marble, and glass. 


Paul McGovern, national sales manager, industrial products, Mimaki USA, Inc., also notices growth in industrial markets, such as graphic overlay printing—membrane switches, home furnishings, architectural glass printing, promotional products, and sporting product color decoration. “LED lamps and UV-curing ink technology allows flatbed printers to enter markets with heat-sensitive substrate requirements. The increase in digital UV-curable inkjet printing over conventional screenprinting methods make it possible to offer variable information along with color printing without the time-consuming screen setup procedures, cleaning, and post-processing workflow challenges of traditional screenprinting,” he says. This reduces time, increases productivity, and saves money overall in manufacturing costs.


UV Limitations

While many applications are achieved with UV, some are better suited than others. Vehicle wraps, for instance, have remained predominantly solvent based. “Solvent inks are better suited for vehicle wraps for two main reasons,” explains Paar. “First, solvent inks are inherently more flexible than UV inks. Due to the tight corners and stretching that a wrap is typically subjected to during installation, UV inks may crack. Secondly, UV inks are also not as resistant to physical abrasion as they cure on the surface of the substrate rather than penetrating into the material like solvent ink.”


Another application where UV inks require special consideration is in food packaging, unless the ink is certified safe by the Food and Drug Administration or other responsible party. “Food packaging printed with UV inks requires a barrier film or coating between the substrate and the contents within it to prevent any migration of the inks into the food,” shares Paar.


Otherwise, most flatbed applications are produced with UV inks due to the increased quality of UV printers, the ink sets, and instant dry time. Still, it is best to perform a cost-benefit analysis, taking factors such as speed and quantity into consideration. “In sign and graphics markets it comes down to whether a screenprinting process was used before, and if the substrates require the same image repeatedly several hundred times. In this scenario, the cost of ownership of screenprinting inks and methods is more cost effective. For instance, if a restaurant requires the same window film image for thousands of stores, screenprinting is currently the most viable printing solution for high-volume, mono-image jobs,” recommends McGovern.


The Greatest Number

Unlike conventional screenprinting in which the PSP chooses ink specifically formulated for the substrate and/or application, digital UV inks are formulated to work on as many substrates as possible. However, as Paar points out, this one-size-fits-all approach does not come without occasional compromises ranging from image quality, jet-ability to image artifacts, and printhead performance to physical limitations such as poor adhesion, chipping, cracking, and marring.


Many ink manufacturers agree the greatest challenge for flatbed inks is developing an ink formulation that adheres to a variety of media with different chemical composition. For instance, ink developed to work well with vinyl may not print well on other media utilized in a shop. These challenges reflect on the ink compositions and the choice of ingredients such as oligomers and monomers—influencing adhesion, flexibility, and other mechanical properties—and the pigments that affect the color gamut and durability. With PSPs printing on traditional and untraditional substrates, ink that works for a range of options is an important issue.


“When considering key performance characteristics such as adhesion, color gamut, drying time, durability, and flexibility, the challenge of producing an ink set that performs well in all categories can be daunting,” shares Kevin M. Sykes, founder/SVP, sales, Novus Imaging, Inc. “This is why so many inks target a specific group of materials, but coming up with an across-the-board solution is difficult without certain limitations and sacrifices.”


Eyal Duzy, marketing segment manager, Scitex Industrial Solutions, Hewlett Packard (HP), explains that UV-curable ink is essentially a dispersion of pigment particles in UV-curable materials. As such, these inks are prone to sedimentation, pigment aggregation, and viscosity build up. Another challenge is achieving the correct curing speed, as it impacts ink film properties such as flexibility and scratch resistance.


The good news is that several improvements have been made in a relatively short time. “UV inks now offer a wider adhesion profile compared to just a few years ago. Substrates are also available with higher dyne levels or special surface treatments to allow for increased ink adhesion,” shares Kaiser.


Many manufacturers offer different types of UV ink products to satisfy the varying needs of print providers. For example, Bordeaux offers three types. PLSF is used in hybrid printers printing flatbed and roll to roll with high flexibility. PLFD is suitable for the newest LED technology and PLFX is found in most conventional UV applications.


New UV-curable inks, such as HP FB225 Scitex Inks for the HP Scitex FB7600 Industrial Printer, deliver high flexibility ideal for printing on corrugated cardboard without cracking on the folds. In regards to sustainability, HP FB225 Scitex Inks are also Greenguard certified and meet increasing end user and print provider demands for environmentally conscious printing options.


Roland also offers multiple UV ink formulations for flatbed printing. ECO-UV, a fast drying ink available in CMYK, white, and clear formulations, is highly flexible and cures instantly on materials used in commercial printing, signage, and specialty graphics, including vinyl, film, paper, foil, shrink wrap, fabric, board stock, and leather. ECO-UV S is available in CMYK and white. It offers greater flexibility for thermoforming and other applications that require inks to stretch around sharp corners, curves, and other complex shapes without cracking or compromising image quality.


Accommodating Hybrids

When printing with a hybrid device, ink must be flexible enough to handle diverse materials. Most hybrids use the same inks as true flatbeds. For instance, the inks in CET Color’s hybrids and flatbeds are the same, and adhere well to all porous substrates and many non-porous.


Sykes explains that there is no difference in terms of ink formulation required for hybrid printing with the exception of printing on pressure-sensitive vinyl used for vehicle wraps. “For this application, increased ink flexibility is an additional requirement,” he explains.


“Since hybrid printers print on both rigid and rolled substrates, inks must remain flexible and stretch to conform to curved surfaces and sharp corners after curing, so the ink formulation is typically different from printers that are designed to print exclusively on rigid substrates,” says Ono.


Larry Salomon, VP, wide format, Agfa Graphics, points out that ink advancements with flexibility open the doors to using UV-curable for vehicle graphics and other applications where the end use is a contour or curve.


EFI offers two sets of inks for the EFI Wide Format T1000 series—one for flexible and the other for rigid. While the flexible inks address substrates such as vinyl, foam core, pressure-sensitive adhesives, backlit material, and canvas, the other ink set designed for rigid materials trades flexibility for enhanced adhesion on materials such as coated and uncoated metals, acrylics, ceramics, glass, plastics, and specialty rigid substrates. The flexible ink set is the same product used in the EFI Wide Format H series of hybrid printers.


Media Compatibility

The potential range of applications for flatbed printers is virtually unlimited due to recent advancements in UV LED technology. The low-heat LED lamps used to cure UV inks even enable printing on heat-sensitive media, including shrink wrap and packaging materials. “Due to the unique properties of UV inks, which are typically used with flatbed technology, shops are able to print on anything they can fit in the printer—and there are many businesses doing just that,” says Ono.


Media is categorized into two distinctive classifications, porous—absorbent materials such as paper, foams, textiles, and ceramics; and non-porous—most plastics, some metals, glass, and other low surface energy synthetic materials. “The inkjet UV-curable inks formulated for either LED or quartz lamp technologies vary according to material makeup—either rigid/hard substrates, or flexible properties, such as bending, thermoforming, creasing, or folding, to determine which ink works best for a specific application,” explains McGovern.


It is important to note that many inks are developed with target applications or specific properties in mind. “There is not a universal standard for UV inks with respect to media compatibility, however, most UV ink sets developed for wide format devices are formulated to work well with plastic and paper-based products,” says Ono.


Manufacturers agree that UV-curable ink sticks well to paper-based media or media with a high surface energy/tension, measured by dyne level, in which the ink anchors to the fibers. Depending on the specific ink formulation, a range of substrates work well with UV inks even beyond paper and plastic, such as metal, wood, acrylic, and glass. A key factor effecting ink adhesion is the surface tension of the substrate relative to the surface tension of the ink.


Some substrates, either hard or flexible, may require a pre-coat treatment preparation prior to printing with UV ink, or liquid primer applications to ensure a good adhesion bond of the printed inks. “Media with too low a surface tension such as aging fluted polypropylene, may not work well without some additional process such as corona treatment, or use of a chemical adhesion promoter or receptive coating. Surface roughness is also a factor in determining how well the ink sticks. For instance, paper works better than glass,” adds Paar.


Sykes explains that while most UV inks perform well in terms of adhesion to common substrates like vinyl and paper, they are typically less likely to adhere well to substrates with higher surface energy like glass, acrylic, and ceramic tile. “This is because many ink manufacturers develop inks to work well on the broadest array of substrates,” he says. “Since the surface energy or dyne level of the more common substrates is lower, the inks struggle with substrates at the higher end of the dyne spectrum.” This is limiting for the PSP.


The chemical composition of the ink influences factors like adhesion, flexibility, and durability. For this reason, ink composition differences are dependent on the properties needed for the intended application. “For flatbeds, and especially hybrids, the ink’s mechanical characteristics should be able to support both flexible substrates of the roll feeding and the rigid substrates used in the flatbed configuration,” explains Shoshani. “The main challenge is providing unified inks that maintain the best adhesion for both types of substrates.”


A Work in Progress

With new ink formulations constantly introduced, finding the perfect balance is a gradual process. As Cich points out, no matter what claims are made, the “holy grail” of ink sets has yet to be created. This is why printers are forced to carry different ink sets.


Kaiser explains that the ink performance, whether conventional UV or LED cured, is a deciding factor in selecting a printer and ink for specific print applications. “Generally speaking, most conventional UV curing systems print at higher speeds compared to LED systems. LED systems, however, generate less heat and are therefore more suitable for printing thin substrates that may be distorted when exposed to high heat,” he shares.


In Salomon’s opinion, trying to apply a Swiss Army knife approach to a tool compromises certain features and benefits, and affects the final outcome. “Evolution of ink technology leads to ink sets that bridge larger application requirements, however, for most shops, it is best to have multiple print platforms designed for intended applications,” he says.


While there are variations on the best ink, media, and print method for every job, PSPs continue to enjoy expanded possibilities with UV-curable and UV LED inks on flatbed devices.


Dec2012, Digital Output

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