By Melissa Donovan
The process of printing textiles, whether screen or digital, has always had its share of challenges involving color. Part of the reason for this is the majority of methods involve many steps—washing, drying, steaming—and each step is an additional variable that influences the final color.
Managing that color means many things, whether it’s as simple as monitoring environmental conditions or working with hardware and software that help to dial into the exact hue required. Then of course there is the need for consistent color—lot to lot, roll to roll. Print service providers (PSPs) rely on trusted tools to maintain consistency.
Above: AVA Colour extends color matching benefits from the digital design and production environment all the way through to conventionally printed bulk production.
Presented with Obstacles
Color management for textile-based applications—digitally printed, either direct or transfer methods—are challenging compared to other substrates. Two reasons for this are the multi-step process of decorating the fabric and the fabric itself.
“Textiles are always a process and in many textile-based applications like dye-sub, the finishing or heat pressing/calendaring is part of the printing portion. There is an extra step but also different textiles receive ink differently, which means that the fine tuning needed for each material used can create a lengthy process in just the profiling stage,” explains Jeremy Pilcher, textiles solutions architect, HP Inc.
Nick Langford, CEO, AVA CAD/CAM, points out that unlike their counterparts in non-textile decorative printing, “textile printers tend to use a greater variety of substrates, which multiplies the scale of challenges faced.”
The substrate range necessitates different inks to complete the final product. According to Fabio Santoro, color engineer, Rekordata BDM color engineering business unit, Alwan Color Expertise, reactive and acid for example not only involve printing onto the textile, cotton and polyamide, respectively, but also require steaming, washing, and drying. To manage color during steaming and drying, time and temperature need to monitored. During washing, water temperature and soap quantity should be controlled. “We have different inks, materials, and depth of ink penetration inside the substrate that needs to be controlled and managed,” continues Santoro.
This makes it so “textile printing can be more challenging to color manage as there are additional steps in the printing process that can affect the final color results. Print materials, substrates, print settings, and heat transfer parameters need to be controlled in a proper functioning color management system,” agrees Tim Check, senior product manager, Professional Imaging, Epson America.
Curing or pressing the image introduces what Tony Simmering, product manager, Mutoh America, Inc. refers to as variability. “Heat press time duuring direct and transfer and pressure for transfer can change the outcome from one color profiling chart to the next. When it comes time for production, those variabilities will create slight differences from order to order.”
The second reason color management is challenging is the fabric itself. “Textiles are generally woven, textured materials—with this matrix of fibers that interlock at a micro level to create a seemingly flat surface at the macro level. So when it comes to measuring color—which is a process that uses light—you have some funny things that happen as a result of the physical make up of the fabric itself,” explains Chris Des Biens, business unit manager – Americas, Ergosoft.
He provides the following analogy for the principles at work when trying to accurately measure color in fabric. “Think about looking at the world through a cardboard paper towel tube. If you hold it up to your eye, and close the other eye, you actually can’t see very much of the world. But then, if you took a Pringles container, and cut the bottom out and looked through that you would be able to see much more of the bigger picture.”
Two issues that Santoro believes should be addressed include choosing the right instrument for color measurement and identifying a standard illuminant. The first point, about the instrument, is because textiles are not smooth and can sometimes be textured, which leads to challenges.
“Getting accurate measurement results on textiles is a bigger challenge than on rigid surfaces. A way to overcome this is to measure multiple times and widen the patch—and aperture size,” continues Dries Hublin, inkjet application specialist, Agfa.
“Surface texture can negatively influence how accurately a typical color measurement device will work. A large aperture measurement device can help to overcome this issue by sampling a larger area and better averaging out the texture influence,” adds Eric Dalton, director of sales, West Region, GMG Americas.
Michael Dreher, strategic and technical partnership director, Caldera, notes that the RIP software used is important here as well. “Despite the fact that the RIP software is computing the data read from the spectrophotometer, it needs to be flexible enough to optimize as much of the printed colors as possible.”
Santoro’s second point, about a standard illuminant, involves textiles versus traditional industry requirements. “The standard illuminant in textiles is D65/10° geometry while most profilers and color management software use graphics industry standard D50/2° geometry. Color conversion from D65 to D50—or vice versa—cannot be done with ∆E.”
Color accuracy with textile-based applications is particularly challenging because standards have not been set, says Jonathan Rogers, international marketing manager, Onyx Graphics, Inc. “iccMAX profiles, for example, is just one standard that is recommended by the International Color Consortium (ICC) for all wide format print applications including soft signage and textile that is beginning to gain adherence in the textile market.”
Dye-sub transfer printing presents added obstacles, since the fabric isn’t printed to directly. Color management must occur not only for the final output but on the sublimation paper in between.
“Transfer printing is certainly more challenging than direct printing as it requires additional specific controls,” explains Santoro. Although, he notes that as aforementioned, direct printing technologies have their own parts of the process that impact color consistency like washing, steaming, and drying.
The challenge is in the sublimation process. “The color needs to be transferred from the paper to the textile. This needs the correct temperature, drum pressure, and time. To find out these settings, some time needs to be spent on it,” notes Hublin.
The heat press should be monitored. “Is the temperature of the transfer press stable and even across the platen? Presses are notorious for having poor temperature gauges and often have an area that is stronger/weaker than the rest of the press. This needs to be closely tracked,” says Liz Quinlisk, business unit manager, X-Rite, Incorporated.
“Different fabrics may have different settings for optimal sublimation and material handling. Noting these heat press settings and profiling around those is critical as changes to this post-profile can lead to large variances in color,” agrees Mike Syverson, textile manager, Durst North America.
Environmental variables must also be managed. “Transfer printing is more challenging from a color management perspective because it adds another step to the process that, itself, needs to be managed to be consistent. Humidity and ambient temperature of the operating plant may influence the sublimation/transfer process and need to be managed properly for the final color output to be consistent. When using a dye-sub process, it is imperative that adjustments be made to both regulate the process temperature and speed during different seasons, and/or develop working process adjustments to accommodate different conditions,” shares Dalton.
On the flip side, John Ingraham, senior marketing specialist, dye-sub, Canon Solutions America, argues that “most print shops prefer transfer printing because it’s easier to print on paper than fabrics with different levels of stretch. Printing mistakes on transfer paper also incurs lower waste costs than on direct printed fabric.”
Langford says it is “considerably easier to obtain consistent production color management for transfer printing than for direct printing. The transfer process itself from paper to textile tends to be pretty consistent and rarely causes color management problems.”
The correct transfer paper offers a level of control. “Utilizing good transfer paper provides very consistent print results from batch to batch. After the ink is printed to it, the water in the ink evaporates, which greatly reduces color variation from moisture in the heat transfer process,” notes Check.
Print providers need to ensure color remains consistent order after order in regards to textiles. There are both software and hardware tools that help to achieve this.
Consistency can be thought of in two ways. One, from sampling to production runs. “The key to this is to build color management into the design and coloring process right from the start—rather than trying to add it on at the end. This can be achieved by using an integrated design/color/print solution such as the one offered by AVA. Color control on complex designs can be greatly facilitated by color separation during the design process,” says Langford.
Another type of consistency is lot to lot or run to run. “Once a product is designed, sampled, and production printed for the first time, the key to accurate repeatability is to store all of the relevant digital print settings within the design file itself,” suggests Langford.
In explaining how to ensure consistency, Santoro groups two categories—a long and a short process. “With washing and drying, some processes can be very long, we have to wait a long time to get the printed material back, which makes profiling and color management nearly impossible. The common method here is to color manage these jobs the same way screenprinting is, in the ink kitchen, by editing manually the recipe for the color channels before the final print.”
With the shorter process, final color appearance is quickly obtained and color management technologies can be used. Alwan HydraFix enables a small color strip reading to quickly compensate for the printing process color drift. DevStudio ColorTable software allows for printing the spot colors of the channels and measures the printed result in order to correct the file color values and minimize ∆E.
“Print shops can run production color control strips and monitor changes in density or Lab while printing to check that the ink laydown remains the same over one or multiple jobs. For checking color accuracy, color charts can be printed and heat transferred for measurement with a spectrophotometer,” says Ingraham.
A spectrophotometer is an important tool for calibration and profiling, admits Sharon Donovich, senior marketing manager, Kornit Digital.
These tools can be separate or even included on the printer. The HP STITCH printers use an onboard spectrophotometer. “This is to create a calibration or a known repeatable state, then we can use it to continually bring the printers back to that state as needed. This can reduce the time needed to color manage and reduce the extra cost for add ons,” explains Pilcher.
Quinlisk recommends a spectrophotometer and color profiling software combined. X-Rite offers i1Pro 3 Plus, which includes a larger aperture device—an eight millimeter (mm) aperture compared to 4.5 mm on a standard device—specifically developed for textiles and other unique substrates.
“It comes with i1Profiler software, which provides all the necessary features to create custom printer profiles and includes a workflow for transparent materials. In addition, i1Profiler provides a quality check to ensure that even after you have a color proven workflow it remains consistent over time from batch to batch,” explains Quinlisk.
A light booth or visual color matching system are key products in achieving consistent manufacturing and reliable quality control processes to meet high demand for quality textile products, according to Brian Wolfenden, field marketing manager, GTI Graphic Technology Inc.
“Light booths are required to visually check the quality printed fabric samples against the proof and from piece to piece. Textile manufacturers also need to be concerned about metamerism with the fabrics. Metamerism occurs when two colored objects appear to match under one light source and do not match under a different light source. A multi-source light booth is a practical way to evaluate for this phenomenon. A light booth equipped with a UV light source is also a good way to check for optical brighteners in material,” continues Wolfenden.
Color management tools integrated within actual RIP software are helpful. “Print businesses may want to look for specific feature sets that help them achieve accurate, consistent color output across devices for all print applications not just textile that also conform to color standards around the world. As part of this search tools such ICC profiling with iccMAX, integrated G7 verification, and reporting and tests for standards matching such as G7 and Fogra can help ensure color output accuracy and consistency over time,” says Rogers.
“Measurement tools need to be linked to software, like a RIP software to drive, measure, analyze, and appropriately correct. Caldera RIP software will automatically make the adjustment to meet your color expectations,” Dreher.
Another example, Ergosoft offers certain features like a module referred to as Color Quality Production Control or QPC, which allows a shop to objectively measure for drift and recalibrate if necessary. A newer module is Color Equalizer, which helps with matching color output across machines of the same and different makes and models.
Donovich suggests “using RIP systems that are tailored for a printing system and include color look up tables, spot libraries, color profiles, and color management, keeping the systems always calibrated and well maintained. Also color matching between systems is required.”
Calibration—or recalibration—is a means to achieve consistency. “Recalibration is the process of setting a printing system back to its original condition so that it can produce the same color. The best approach to recalibration is using a tool that recalibrates the entire color space, such as GMG SmartProfiler, which is included with GMG ColorServer. A three-dimensional recalibration tool recovers the entire set of printing colors and insures that the next print looks like the first,” explains Dalton.
Quality materials and consistent practices are tried-and-true methods to ensure color consistency for textiles, batch to batch, production to production. “Good quality transfer papers have tight tolerances on coating quality to help reduce variation from lot to lot. Fabrics can have a lot of variability from batch to batch as well, which premium digital textile fabric suppliers will control through additional quality control checks. The printer also needs to have consistency, with a quality permanent printhead a must,” suggests Check.
“Ensure that printers and presses are properly maintained and calibrated; ask questions like is the foam padding on my heat press wearing out? A maintenance issue such as that will definitely cause variability,” summarizes Simmering.
Achieve Correct Color
In terms of textiles, print providers should be aware that color management is a bit challenging. Not only the fabric itself but the many parts of the decoration process present sometimes unpredictable variables that may make it difficult to achieve correct color.
When properly utilized, tools like spectrophotometers, RIP software, and more can help ensure critical color needs are met.
May2022, Digital Output