Inkjet ink formulators have expanded sign printers’ opportunities over the past two decades with continuous improvement of their offerings. They have met customer requirements for inkjet ink reliability by providing degassed inks to prevent jet-outs, improved outdoor durability, adhesion to substrates and color vibrancy. They have reduced the hazards of high-solvent-based inks with their introductions of low-solvent, eco-solvent, aqueous-pigmented, aqueous dye sublimation transfer and direct-disperse dye, aqueous latex, aqueous UV, mercury bulb UV curable, LED UV, and UVgel inkjet ink solutions described below.
• Sublimation dye inkjet inks print heat transfers for decorating flexible polyester and other sublimation receptive fabrics and materials. Dye sub transfers provide an effective means for decorating flexible signage, as well as dye-receptive polymer coated substrates, such as metal sign blanks. Sublimation dye is a type of disperse dye. Both narrow and wide-format inkjet printers are available for printing sublimation transfers.
• Direct inkjet print disperse dye inks are directly jetted onto receptive fabrics such as polyester and fabrics with a high-polyester content without first printing to transfer paper and heat transferring their designs. Sublimation and disperse dye prints typically fade in a relatively short period of time if kept outdoors in direct sunlight, but they can provide vibrant colors for indoor and short-term outdoor applications. Since the dye becomes part of the fabric, prints do not have a feel that is different from the unprinted parts. Properly processed disperse dyes and dye sub inks exhibit virtually no crocking. If the fabric is to be worn, washing after printing and fixation is recommended to remove any residual dye that has not penetrated the fabric’s fibers. South Korean inkjet printer manufacturer d.gen was an early provider of signmaking solutions for direct-inkjet printing of disperse dye (direct dye-sub). The company also offers water-based inks that meet European REACH requirements and regulations.
• Water-based latex inks. HP developed these inks for use with its line of Latex thermal inkjet (TIJ) printers. HP touts its water-based Latex ink for its image quality and durability, as well as being appropriate for use on signs used at sensitive indoor locations, such as healthcare facilities, where solvent ink signs would not be acceptable. HP notes that its Latex inks do not require special ventilation during printing and processing, do not need hazard warning labels, and are certified by UL ECOLOGO for reduced environ-mental impact and UL GREENGUARD Gold for low-chemical emissions. HP Latex inks also meet AgBB criteria for health-related evaluation of VOC emissions for indoor use.
Third-party ink suppliers like STS Inks (Boca Raton, FL), provide its latex inks for older and many of the current HP Latex printers. Mimaki also provides a latex ink, LX101, for its JV400LX piezo inkjet (PIJ) printer models. LX101 ink is also UL Greenguard Gold certified. The Mimaki LX101 ink, like HP’s, offers hexachrome expanded gamut ink colors and also a white ink. Inkjet print latex inks provide both indoor and outdoor durability for sign applications, including billboards, banners, POP or POS posters and product displays, print-and-cut vehicle wraps, floor and window graphics, backlit signs, textile flexible signage, and decorative wallpapers and coverings.
• Aqueous-based inks. The main attraction of aqueous-based inks is their generally non-toxic nature that will not expose workers, customers and the environment to VOC hazards. TIJ printers primarily use aqueous inks due to their penetration into absorbent substrates, such as most papers and textiles. They are suitable for indoor applications, with some formulations also usable outdoors. For example, IIMAK’s newly developed ResinJet ink is used in wide-format inkjet printers with TIJ printheads. IIMAK’s proprietary outdoor-durable ResinJet polymers encapsulate its ink pigments and attach them to the substrate in a polymeric film.
• Solvent-based inks. Solvent-based inkjet inks offer several advantages for signmakers. They are very fast-drying, pigmented inks that offer excellent adhesion to a common sign substrate: PVC. They can provide resistance to abrasion and offer long-lasting, weather-resistant vivid color. Typically, solvent inks disperse pigment in an organic solvent.
However, they can expose sign printers who use them to solvent vapors and thus require continuous ventilation when printing with them. But all solvent-based inkjet inks are not equally hazardous. High-solvent inks can perform well outdoors, but are not designed for indoor use. Ink manufacturers have developed solvent inks that emit less hazardous vapor. For example, Mimaki’s SS21 and BS4 solvent-based inkjet inks have achieved UL Greenguard Gold certification for low-chemical emissions. The company has also developed a solvent UV-curable ink that resists drying in nozzles and cures with in-line UV exposure. Finally, Roland’s EJ INK for its SOLJET EJ-640 printer is also Greenguard Gold certified.
Recently, I visited with Wayne Driscoll, owner of Custom Sign Studio in Waynesboro, PA. Driscoll inkjet prints SS21 inks for both indoor and outdoor signage. He uses them for vinyl banners and signs, but also in combination with other processes for specialty signs. During my visit, he was assembling a two-sided hanging sign composed of SS21 solvent inkjet ink printed PVC, designed to look like natural wood, laminated to a shaped synthetic wood board, onto which he was mounting plasma-cut metal signs.
• Eco-solvent-based inks suspend their pigments in a mild biodegradable solvent with minimal VOCs and odor. They have been available for almost two decades and were developed as an alternative to high-solvent inks. While not as free of hazards as most aqueous inks, many eco-solvent inks have earned Greenguard Gold certification, are generally considered safe for indoor signage and can be operated in shop environments with standard office ventilation. They are less aggressive than high-solvent inks, resulting in longer printhead life. They typically are not as outdoor durable and require more heat to dry than high-solvent inks, which can restrict their use on temperature-sensitive substrates.
Roland has championed eco-solvent printer solutions, offering a number of eco-solvent machines and inks. Sun Chemical has developed and formulated its Sun Streamline inks for use with Roland’s eco-solvent inkjet printers. Mimaki’s eco-solvent ES3 ink is relatively fast drying and scratch resistant. Mutoh and Epson also offer eco-solvent inkjet printers and inks. Epson’s SureColor S-series with eco-solvent inks have reduced the time needed to off-gas before lamination.
• Solvent UV combines the durability of solvent inks with the speed of UV curing. Mimaki introduced solvent UV in 2013 with its SU100 inkjet ink. Mimaki reports that its solvent UV pigments adhere with its solvent evaporating and dry quickly in-line with UV exposure. SU100 enables lamination without wait time. The ink provides a gloss finish with improved abrasion resistance.
• UV curable and LED UV curable inks. UV curable pigmented inks do not use VOCs, provide instant curing, scratch resistance, high print quality, rich color, and light fastness. UV inks use either mercury bulb UV lamps or LED UV lamps. The mercury bulb lamps are more intense and cover a broad range of UV wavelengths. LED lamps, on the other hand, concentrate their energy around one wavelength to activate the inks’ photo-initiators that are matched to the LED lamp.
While UV curing can deliver instant ink drying of UV inkjet inks, it does not typically produce total polymerization of the ink and can leave a small percentage of its photo-initiators not encapsulated, which can lead to initiator migration from the print. As a consequence, UV curable inks are typically not used where the printed ink will come in direct contact with food. But for production signmakers, UV and LED inkjet inks can provide high-performance solutions. UV curable inks are available to decorate a range of flexible and rigid substrates: PVC, polycarbonate (PC), polystyrene (PS) acrylic, MDF, aluminum, stainless steel, brass, glass and ceramic. PIJ printheads deposit almost all of the currently used UV curable and LED UV inkjet inks. UV LED inks are the fastest growing inkjet ink type.
• UVgel ink. Canon-Océ introduced its UVgel ink for its roll-to-roll Océ Colorado 1640 in 2017. The company indicates that its UVgel is a high-viscosity liquid that stores as a gel. For printing, it is fed through ink lines to heated PIJ printheads that reduce the viscosity of the ink for jetting. The ink cools on contact with its substrate and reverts to a gel, thus pinning the deposited dot and reducing dot spread, ensuring print image sharpness. Canon-Océ claims that its UVgel ink provides outdoor durability and scratch resistance.
Signmakers have adopted digital inkjet printing as a way to create colorful and durable signage, and photographic images from one to thousands, profitably. Improvements in inkjet inks are driving the growth in print quality and performance as well as market adoption of inkjet produced signage. The research and consulting firm Research and Markets forecasts that the digital ink market will grow from $2.71 billion in 2018 sales to $4.17 billion in 2023 for a compound annual growth rate of 9.1% for the period.
More inkjet ink innovations are on their way. Stay tuned.