By Olivia Cahoon
Several methods exist for digitally printing fabrics and textiles including dye-sublimation (dye-sub). Print service providers (PSPs) select dye-sub printers partly because of the process. It uses inks that sublimate, turning into gas when exposed to heat, essentially fusing with textiles, and becoming part of the fabric. This enables images to sustain washing and wear and tear.
Dye-sub printers include two categories—transfer and direct. Dye-sub transfer printing entails printing output onto transfer paper, which is then run through a separate heat press and sublimated onto the fabric. Unlike direct dye-sub printing, the transfer method requires additional steps but also comes with its own advantages like higher resolution and greater detail.
Above: SCG Digital’s dye-sub transfer printers are used in the manufacturing of tote bags.
Transfer Printing
Compared to direct dye-sub printing, transfer methods offer a wider substrate versatility by allowing users to transfer images onto fabrics or rigid substrates in a variety of sizes, weights, and features. Direct dye-sub printers are limited in media options due to the need for coated fabrics and complications with direct printing onto velour and materials with less than 50 percent polyester composition.
“You don’t need to use a coated fabric for dye-sub transfer applications, while fabrics must be coated for direct dye-sub,” explains Lily Hunter, product manager, textiles and consumables, Roland DGA Corporation. Direct dye-sub requires a fabric with an ink receptive coating, which is applied by the fabric manufacturer, otherwise, the ink will bleed.
According to Hunter, direct dye-sub is traditionally used for printing flags because the higher saturation allows the flag to be viewed from both sides. Dye-sub transfer typically yields better results for printing graphics with fine lines and greater detail.
Matt Gusse, VP of sales and marketing, Advanced Color Solutions, agrees and says that a transfer printing method controls quality easier and expands the color gamut. Transfer sublimation allows for a variety of applications besides fabrics that includes metal, plastic, wood, and stone.
Gusse says this method also permits paper features like the ability for lower ink consumption, drying additives, ability to stick or be tacky when pressed, a variety of available fabrics, minimum waste, and help for controlling costs. “Clients making mugs/drinkware, license plates, ceramic tiles, photos on metal, key chains, wood tables, phone cases, or pre-sewn wearables are all paper sublimation candidates,” he offers.
Additionally, dye-sub transfer printers generally offer a lower investment than direct dye-sub printing. According to Gusse, direct dye-sub devices can range between $40K and $150K while wide format transfer devices are available for under $20K for 44-inch wide solutions. Desktop and small format dye-sub transfer printers are available as well.
Users that benefit the most from a dye-sub transfer printer handle a variety of apparel, banners, promotional products, and trade show signage. Specialty materials unavailable in large rolls or too expensive for purchase in high quantities are usually suited for dye-sub transfer printing as well.
“Shops that intend to explore a wider range of polyester substrates will likely adopt transfer,” says Kevin Currier, business development manager, digital products, Novus Imaging, an M&R Company. This includes materials that are difficult, wrinkle prone, or stretchy.
Currier believes many shops welcome the workflow of dye-sub transfer because it allows color management based on the transfer paper and applied to multiple substrates. He offers, “in transfer printing, the paper becomes the known factor and all the settings and quirks of running the paper through the system are then easily managed by the operators. The issues introduced by the fabric are then dealt with at the heat press, which is often easier to handle,” he admits.
Learning Curves
There are challenges throughout the dye-sub transfer process. Dye-sub doesn’t have a high light fastness rating, and as a result, outdoor applications are limited. To make dye-sub transfer printing more durable for outdoor use, Hunter says substrate manufacturers are working to create special coatings that prolong the outdoor durability of sublimated prints and goods.
The sublimation process is also sensitive to the environment in which the process takes place. “If the temperature or humidity level is too high or too low, that will negatively affect the output,” explains Hunter. Moisture in the substrate or transfer paper can cause bleeding, color shifting, and uneven transfer.
Shauna Malgieri, product specialist, S-One Holdings Corporation, agrees and believes environment and understanding the sublimation chemistry is one of the most considerable challenges of implementing dye-sub transfer printing. To achieve optimal conditions for quality prints, she recommends keeping accurate records of the testing process.
Additionally, Malgieri suggests PSPs consider the types of products they intend to sublimate to. “If it is fabrics, the sublimation is limited to high polyester content-based fabrics. If they want to sublimate to other products, they need to consider the investment in finishing equipment as well as the production space needed for the equipment,” she explains.
Paper selection is also an important factor for achieving desired image quality. Robin Kavanagh, public relations manager, Sawgrass Inc., believes the paper chosen depends on the end product and that it’s important for PSPs to choose a paper that provides consistent quality. “As is the case with ink, choosing paper simply because it is cheaper can result in greater expenses because of the generation of unacceptable finished materials and other associated wastes,” she explains.
Finishing equipment includes heating presses and sewing machines. Dye-sub transfer printers require a calender device to heat the transferred image onto the application whether that be t-shirts, mugs, or any other fabric or rigid substrate. This requires a more significant amount of space than an inline calender dye-sub system.
According to Greg Lamb, CEO, Global Imaging, a calender is around 25 percent larger than a printer. “If a print shop is considering a three-meter width, there is a significant space requirement for the two pieces of equipment,” he says. This also increases the electrical requirements and costs for operating the printer and heating press.
Before selecting a dye-sub transfer printer, PSPs should consider their target width capacity. For wide format applications, printers are available as wide as 130 inches. Additionally, heat transfer units should be explored to ensure the entire dye-sub transfer printing process is efficient.
“Flat heat presses limit the size and throughput for dye-sub, so those who do mostly fabric will opt for a calender unit,” suggests Randy Anderson, product marketing manager, ValueJet Printers, Mutoh America, Inc. Calender units are available in two basic designs—a heated chamber or a heated oil drum.
According to Anderson, the chamber unit typically uses a quartz heater to heat the air in a chamber that the fabric and paper are exposed to. “Since the heater heats air, these can vary in temperature depending on how long the fabric and paper need to be exposed to sublimate and the capacity of the heat to maintain air temperature,” he explains.
Heated oil drums use hot oil with buffering properties that allow them to maintain steady temperatures under varying conditions. Anderson says a good oil drum feeds more than one printer and is available in a variety of drum diameters.
“If a PSP chooses a dye-sub printer and an appropriate oil drum calender and its demands increase so that additional capacity is needed, then only additional printers are needed as drum calenders run much faster than a single printer, allowing two or more printers per drum calender,” offers Anderson.
Advancements
Some of the newest advancements for dye-sub transfer printers are influenced by the need for longer operation with little to no intervention. According to Currier, the optimum usage of dye-sub transfer printing entails the user loading the printer with a substantial quantity of paper and print files that are printed with little to no supervision.
“This is difficult in situations where only minimal rolls can be loaded, or the transfer paper is difficult to manage, specifically if wrinkles occur or the paper itself walks left or right,” explains Currier. He suggests PSPs seek systems designed to handle large rolls around 400 lbs to allow for several shifts worth of material. Once combined with a printer that has a print queue, large ink tanks, and reliable printheads, PSPs have a solution where printing can occur unattended.
In addition to longer and uninterrupted operation, dye-sub transfer printers are also becoming faster. For high-speed printing, Jacky Shi, partner, SCG Digital America Inc., says the first step is to ensure the ink can dry immediately before it gets reeled into the take up. It’s also important that the roll paper exhibits the ideal amount of tension.
“A take-up reel that sits in the back of the printer ensures that the image has enough time to dry during high-speed printing,” says Shi. Additionally, dual air compression rollers provide efficient media feeding. To help ensure precision feeding during high-speed printing, tension control systems provide sensors that monitor efficiency and speed.
Some companies increase production speed by implementing more printheads into the dye-sub printer. Although it does increase maximum print speed, Tim Check, product manager, professional imaging, Epson, warns that each printhead increases the cost, lowers the reliability, and increases the challenge to keep multiple printheads producing identical output.
As an alternative for faster textile printing, Check says advancements in hyper-accurate paper feed systems and MPO technology can reduce the number of printhead passes used by 50 percent.
Output Quality
Features like paper tension control, fabric head wipers, take-up reels, and high-capacity ink tanks are important to the overall output produced by dye-sub transfer printers. For example, high-capacity tanks allow unattended runs to keep printing without interruption and provide notifications when ink is low.
Larry D’Amico, director of sales, large format, Durst US, says the printer controls for roll-to-roll media are critical for efficiently using dye-sub transfer printers.
Additionally, the ability to handle a variety of popular stretch media and make adjustments automatically during printing allows PSPs to operate unattended. “This provides a significant labor savings, especially in the last shift when you can essentially run with the lights off and no one is present,” shares D’Amico.
Built-in technologies and processes help ensure consistent quality output. This includes printhead gap height, waveform control, and nozzle check and recovery. Tommy Martin, product manager, textiles and apparel business development and marketing, Mimaki USA, Inc., says a high printhead gap enables high-quality printing on thin transfer paper without concerns for cockling. Cockling can produce uneven results or even cause a printhead strike. Waveform control is a manufacturer-specific technology that improves visible quality and dot gain.
Nozzle check and recovery work together to enable continuous and unattended printing by ensuring clogged nozzles don’t reduce image quality. Martin explains that before printing, nozzle check automatically checks for and cleans clogged nozzles. It also enables mapping of unrecoverable nozzles, so printing can continue.
For higher capacity runs that utilize larger machines, Martin shares that media handling systems are available to apply calibrated tension to the paper to maintain stable and precise media feed. “Systems such as these also help reduce telescoping of media during take up and eliminate the potential for buckling or creasing during the calender transfer process thereby accommodating long-run, full-roll transfers.”
Transfer Printing
Using a variety of substrates, dye-sub transfer printers offer high definition and vibrant colors for indoor signage, home décor, and fabrics. Before selecting a dye-sub transfer device, PSPs should consider if the transfer printing method best suits their targeted offering. In addition, the work environment should maintain low humidity and controlled temperatures as well as fit a heat press.
Feb2018, Digital Output
