By Cassandra Balentine
Every printable substrate comes with a unique set of features that must be considered when printing to them. Textiles are no exception, and the method of printing—direct or transfer—make an impact on the final product. Further, the print process typically dictates the substrate options and pretreatment requirements.
A few considerations come to mind when dealing with textile printing for signage applications—image sharpness, dry time, color vibrancy, and washability and/or durability.
Direct Printing to Textiles
When specifically looking at direct print the textile itself plays a significant role. “Initially, end users have concerns as to where to source the fabric, whether the fabric needs to be prepared or pretreated for direct printing, and what types of fabric can their process print onto. There are also equipment compatibility requirements such as feeding, winding, and drying at production speeds,” shares Scott Donovan, Americas sales and global key accounts, DuPont Artistri Digital Inks.
Simon Daplyn, product and marketing manager, Sun Chemical, points out that for textile signage applications, the fabric is typically polyester and printed with either sublimation or direct disperse inks. “A key concern for signage print providers is the outdoor integrity of the print and its water fastness.”
“If printing with standard transfer sublimation or direct disperse ink, there is often a need to wash the fabric after fixation to avoid any migration of unfixed dye or colored chemicals that may be in the base formula of the ink and to remove any residual pretreatment. If a specifically designed sublimation ink for direct printing is used, this issue is resolved in the formula and no post-wash process is required,” explains Daplyn.
Specific to direct printing, “the process offers the advantage of increased ink penetration, which is a key consideration when trying to get color to show through on the reverse side of a fabric or when trying to eliminate ‘white grin’ on stretch fabrics where the ribbed design is challenging for a transfer printing process,” says Daplyn.
Direct printing is also dependent on the ink set and amount of ink. “Too much ink or an ink not optimized for direct printing can lead to excessive bleeding of the image and a lack of sharpness to the print,” cautions Mike Syverson, textile manager, North America, Durst US.
Marco Zanella, global business development director, inkjet, Europe, INX International Ink Co., points to color brightness and yield as top concerns for direct printing to textiles for signage applications. The achievable gamut, reliability, and cost are additional considerations.
Another concern is drying speed. Daplyn explains that digital inks use humectants to stop the fluids from drying in the printhead and require maintenance intervention. However, this must be balanced as the ink is required to dry on the fabric with a small drying unit to stop any ink offsetting when the fabric is wound onto the uptake roller. “Achieving the balance of drying is key to a high-performing direct print process for backlit polyester and signage fabrics.”
Mark Krzywicki, product manager, Professional Imaging, Epson America, Inc., says workflow and color consistency are top priorities for print providers producing textile signage applications. “The act of printing is only one of several steps required to print directly onto textiles. There are many variables to consider including pre- and post-treatment recipes as well as additional steps and equipment required for fixation of the inks to the fabric. Each fabric is also unique—with different print quality, hand feel, and fastness properties.”
Equipment considerations for direct textile printing might include whether or not a printer is able to handle the media size and weight, and print directly onto fabric without bleeding, adds Lily Hunter, senior product manager, Roland DGA Corporation.
Transfer Printing to Textiles
Similarly, there are specific concerns that stand out when indirect or transfer printing to textiles.
Indirect/transfer printing requires printing first to a transfer paper and utilizing a heat press to transfer the image to the fabric. Added steps often leave more room for error.
There are also considerations like transfer consumable cost, performance, and availability when utilizing transfer dye-sublimation (dye-sub) for textile printing, adds Donovan.
For dye-sub transfer, Zanella sees some of the same concerns as direct printing to textiles, but these also include the metrics of transferring as much ink as possible from paper to fabric, minimizing dye waste, and maximizing efficiency.
Syverson says transfer printing can actually be simpler in terms of the overall ink usage, “as you are generally limited to the maximum ink the paper will physically accept before media handling issues arise,” he offers.
Daplyn notes that when printing to a transfer paper, not all of the ink printed on the paper will transfer to the fabric when fixed, leaving some waste ink as well as the wastepaper from the process. “Getting the best transfer rate or consuming less ink are key value adds for print providers.”
In recent years, Daplyn shares trends like lower grammage papers, saving waste, and increasing the amount of paper on a jumbo roll. “While the paper technology has evolved and offers excellent quality, it is important to match the ink to ensure best results. Inks may interact differently on certain papers, which provides variability. Print providers should look for a solution that allows them to select materials for different print jobs without compromising on quality.”
Ink sets are continually developed to combat issues like bleeding and blurring when printing direct to textiles.
Therefore, many digital inks for direct printing to textiles are formulated to control the penetration rate of the ink. “This is partly to increase the concentration of color close to the surface of the fabric, increasing the apparent strength and vibrancy. Controlling the penetration also helps to control the wetting behavior of the ink so that the dot gain is managed and limits the sideways spread of the liquid on the porous fibers. Inks are also tuned to be compatible between colors. The surface tensions are closely matched to prevent bleeding from one color into another,” explains Daplyn.
Pretreatments are essential in textile printing, particularly for direct processes. “Most direct print inks are designed to be used with some sort of pretreatment that helps the ink not wick out and adhere to the textile. The properties designed into the ink are jettability, surface tension, drying speed, and pigment load. All need to be balanced for a sharp, clear print,” says Donovan.
Zanella feels there is actually little to be done when looking at the ink itself. “A pretreatment primer is often used to maximize yield and sharpness and reduce bleed, but that is usually adopted reluctantly since it adds a process phase and cost. UV-curable inks suffer less of a bleeding issue, but they are also subject to other concerns such as the considerable ink film thickness and the presence of materials either banned by regulations or are difficult to control,” he offers.
Krzywicki agrees, noting that properly pretreating the fabric before printing helps combat issues like bleeding and blurring when printing directly onto textiles. “The pretreatment helps control the spreading of the ink onto the fabric to improve printing definition. A uniform application of pretreatment using a padding system can help with consistency.”
When printing with eco-solvent inks, Hunter says coated fabrics—which are made specifically for printing with these types of inks—are needed to combat bleeding and blurring, whereas resin and UV inks can print onto uncoated fabrics. “Resin inks require the creation of custom profiles for each fabric to ensure that the correct amount of optimizer is used for the specific material. Typically, generic profiles work well with UV inks,” she offers.
As for transfer printing, the challenges are similar but focus more on the ink and paper interaction.
The same types of properties are designed into dye-sub transfer inks, shares Donovan, such as jettability, surface tension, drying, and pigment load.
“The weight of the paper, in combination with whether the transfer paper selected is coated or uncoated, typically has a role in the behavior of the ink on the surface,” says Daplyn. He explains that sublimation inks contain specific additives to control the drop spread. “The more concentrated the color of the ink, typically less liquid is needed to achieve the same color. If you can print less ink down, you are better able to control wet-on-wet color bleed and any wrinkle or cockling of the paper as it becomes saturated.”
The current generation of printers tend to have ink sets designed for both direct and indirect/transfer printing. “They have been formulated to minimize bleeding and blurring on direct printing, while keeping the existing qualities that transfer paper printing has been known for,” notes Syverson.
Proper profiling to ensure that there isn’t too much ink load is also recommended. “Most polyester fabrics do not typically require heavy ink loads, except when they’re used for backlit signage applications. Too much ink will cause bleeding,” suggests Hunter.
Inks for Textiles
Textiles are an excellent durable and lightweight option for a variety of signage applications. Whether direct or transfer printing is utilized there are several considerations to address up front that will ensure a successful print.
Sep2023, Digital Output