While print service providers (PSPs) may take multiple features for granted, a lot goes into creating a flatbed device. Some look for speed; others compromise efficiency and productivity for high color gamut and finished quality. Ink is an essential factor that cannot be ignored. Adhesion characteristics must be considered, as well as usage and compatibility with printheads and the overall printer.
Flatbeds are complex. Their ink sets are touted as adhering to a wide variety of media—both traditional and untraditional. Additionally, if a hybrid, there is also the consideration of flexible media and its ink compatibility. Vendors have a lot of pieces to place together when developing successful ink for flatbeds. The sets in these machines adhere to target media, work well with the printhead, and provide the best possible final print.
Crafty Criteria
What goes through a developer’s mind when creating an ink set? Steve Igoe, sales manager, North America, Bordeaux Digital PrintInk Ltd., provides a laundry list including, “functional compatibility with the printhead, color gamut, flexibility, gloss, adhesion, rate of cure, weathering resistance, and storage and transportation stability.” Many factors play a part but based on a survey from vendors the biggest are intended application, printhead and other components of the hardware, eco-friendliness, and media versatility.
Application
With the range of applications available, it’s important for developers to look at what is being printed. “Although inks should be designed for the equipment, the final application is most critical to the end user,” explains Rich Nickols, digital product manager UV products, Nazdar.
Elements to take into account include the length of an application, the environment, the media, and whether any protective coatings—film or laminate—will be used. Increasingly, the ink sets created must handle multiple applications.
“You can develop the best ink set in the world, but if you don’t have it suited to application properties that the end user intended, then the ink will fail. All good ink development starts with the properties needed for the intended application,” confirms Mike Mills, CTO/senior VP engineering, Novus Imaging, Inc.
Ryan Buy, director of sales Americas, Teckwin International LLC, agrees. “Ultimately, the determining factor is based on the customer’s end product.”
Printhead and Other Mechanics
All of the parts that make up a printer must work together effortlessly with the ink. If they don’t, equipment failures occur. “We design an ink set based on the requirements of the selected printhead to ensure the desired jetting performance, print speed, and dot gain,” shares Stephen Emery, senior director, ink business, EFI.
Sandy Gramley, Scitex aftermarket supplies manager, Americas, Hewlett-Packard (HP), agrees with Emery and outlines various situations that could lead to trouble if the ink doesn’t match the hardware. We paraphrase her thoughts here.
The selection of ink components and their purity is essential to reliable printer operation. Contamination by metal ions can cause pigments to precipitate out of the ink. This may clog ink supply tubes and the microscopic ink passages inside printheads, leading to printer failure and the expense of downtime and new parts.
Interaction between the ink and all system components is also important—and often overlooked. Inks touch plastic, metal, adhesive, and elastic materials that are used in the delivery system, printheads, and printhead service stations. Every component of the materials coming into contact with the ink must be selected and designed to work together. Adverse ink material reactions can cause corrosion of metal parts and soften or dissolve plastics, adhesives, and elastomers.
Media Versatility and Eco-Friendliness
Interestingly, those that develop an ink set for media versatility also believe in a need for a sustainable product. As previously cited, as more applications come to market, printers must be able to offer the versatility to output on one device; saving on footprint and overall hardware costs. As this rises, coincidentally so does the continued perception of a volatile organic compound-free work environment.
“One of the most critical criteria for developing our ink sets is to provide customers with the ability to print on a range of media substrates for various applications with great color quality and durability. Graphics One, LLC (GO) and Sepiax are committed to producing an eco-friendly ‘green’ product to minimize harm to the environment,” explains Christian Lord Sam, marketing director, GO.
Mutoh America, Inc’s MP Ink is 60 percent bio-based and contains no hazardous air pollutants. “Hybrid ink needs to be versatile and used on multiple types of media while still maintaining vivid colors and great adhesion and abrasion characteristics. We also strive to make our ink eco-friendly so it lessens our carbon footprint and makes working environments better for customers,” adds Michelle Pugh, marketing coordinator, Mutoh.
Development Secrets
Each flatbed ink is composed of minute chemical molecules that take years of scientific research to get just right. Once these molecules join together, they provide such characteristics as adhesion, flexibility, durability, elongation, and saturation. Each vendor shares what they look for when developing an ink set for the consumer.
“There are always tradeoffs with characteristics. Inks that stick best to rigid media will not work as well for flexible applications,” admits Larry Salomon, VP, wide format, Agfa Graphics.
The unique requirements of flatbed printers necessitate inks with excellent adhesion. Bordeaux’s Igoe adds that in addition to adhesion, proper wetting and drying enable a printed rigid board to retain its edge integrity.
“We see adhesion and color vibrancy as the most important characteristics when developing an ink set,” explains Jack Skidmore, director of sales eastern U.S. and Latin America, CET Color.
EFI’s focus is tri-fold. First, careful consideration goes into the selection of pigments and grinding of pigments to get the best and brightest color control, durability, and lightfastness. For UV hybrid ink, the company places special attention on flexibility and elongation. Lastly, the purity of the ink is studied.
Fujifilm North America Corporation looks to factors such as machine reliability and usability—jetting performance, color, adhesion, print quality, finishing, and standards compliance. It is also focused on the drying or curing of the ink.
GO’s Sepiax ink is formulated to produce a wide color gamut with the ability to adhere onto any substrate that holds high-resolution details with little or no dot gain.
HP’s characteristics for developing flatbed ink are varied. These include cost per copy, image quality, media versatility, durability, permanence, color gamut and saturation, elongation and flexibility, and environmental and health safety.
When developing ink, the key is to understand the entire lifecycle of the product the ink will be used for. “It is important to consider the printhead, the many substrates the target industry will use, and the finished requirements of the printed material,” recognizes Karla Witte, VP, product development, INX Digital International Co. The main INX Digital formula for flatbeds is a multiflex that offers faster cure; greater adhesion; and no peeling, cracking, or chipping when finished.
“Flexible formulations work on most substrates and mediums using a plasticizer or polymer-based material and most plastic-based rigid substrates except for metals, glass, and some harder exotic plastics may be exceptions,” advises Paul McGovern, business development manager, Mimaki USA, Inc.
Mutoh focuses on the hybrid printer, which means the ink needs to be versatile and used on multiple types of media while still maintaining vivid color and great adhesion and abrasion characteristics.
For Nazdar, the functionality and cross link density are primary formulation factors that influence the properties of the finished coating. The choice of pigment also affects durability and color gamut.
Novus’ Mills cites that when developing ink for a pure flatbed printer, the desired result is extra durable adhesion. In addition, desired image is essential.
“All characteristics are important. The challenge is often that improvements made to one characteristic can negatively impact another. There is also the short- and long-term impact that certain ink components may have on the life of the printheads, ink lines, and pumps,” adds Randy Paar, display graphics marketing manager, Océ North America.
Teckwin utilizes specialized particle pigmentation to choose a color gamut that offers strong colors for logo printing and Pantone prints. For the company’s Aurorateck MULTI UV ink set, a combination of multi-functional monomers offer a fast cure and rigidity. Aurorateck STRETCH is composed of multi-functional monomers for a flexible, soft ink used in vacuum-form applications.
In summary, it isn’t just one overwhelming characteristic that goes into developing flatbed ink, but multiple factors that inherently play off of each other.
The Essential Component
Media versatility is in high demand. To achieve this, a perfect synergy between each ink component must be conducted. “It’s finding the proper balance of oligomers, monomers, polymers, and photo-initiators working in harmony with the printer speed, ink viscosity, drop size, surface tension of common substrates, and the wavelength and energy of the curing system,” shares Paar.
Flatbed ink sets that provide variety include water-based and UV products; as their chemical make ups provide this ability. A water-based resin ink technology, such as Sepiax, adheres to mostly all coated and uncoated materials for both flat and rigid substrates. The majority of the ink is composed of water, which makes it eco-friendly and above all provides the adhesion power and characteristics of a traditional UV ink.
For a UV-curable ink, the choice of monomers, oligomers, and adhesion promoters is vital to media versatility.
“The colorant is contained in a layer that durably binds to the surface of the print. Since the ink does not dry by evaporation, all of it remains on the substrate. The ink hardens instantly when polymerized by intense UV light. It then forms a mechanical bond to the surface for durability, and rapid curing minimizes the ink spread and feathering for sharp lines and edges and highly saturated colors,” explains Gramley.
Of course there are outside factors that lead to media versatility. Drying is one. “The most critical piece of the printing puzzle is the cure. If the ink and media interface don’t receive the proper cure, the entire construction crumbles. The most common issues with printers are the use of low power output UV systems and too much ink deposit,” says Nazdar’s Nickols.
For example UV LED means a faster dry time and the elimination of common errors associated with quick drying such as media curling. Deformed media must be avoided. Mills says print manufacturers create a variety of media hold down methods to counteract this effect.
Other innovations involve heating elements. In GO’s case, to implement Sepiax ink, the company specifically designed and modified its hybrid flatbed printer with high-performance heating elements distributed in different printing stages to cure the inks onto the media surface. Like any current flatbed printer technology there is a slight compromise in order to achieve this process. The curing on some substrates can decrease the printer’s speed.
Additionally, the environment influences drying. Agfa’s Salomon explains, “it’s ideal to have a clean, low static, 72 degrees and 50 percent humidity environment. While this example is the best case scenario, some range from this is acceptable.”
Pre-treatment is another consideration. Primers and other methods expand media offerings, especially to help achieve adhesion on high-surface tension substrates. Mimaki’s McGovern believes media manufacturers who apply pre-treatment receptor coatings allow UV inks to adhere better.
Unfortunately, while new flatbed ink sets are touted as able to print to anything and everything—the real question and concern, as brought up by Witte, is “will it stick?”
