NC State researchers report team of textile expert say fabric printed to resemble denim was a good match for the real thing.

By Laura Oleniacz

Drop by drop, researchers from North Carolina State University printed ink on cotton fabric to make “digital” denim fabric resembling six different styles of jeans. When they asked a team of textile experts, they found that overall, the samples made with the computer and printer were a good match on average for denim made using traditional, more labor-intensive methods.

However, in the Journal of Imaging, Science and Technology, the researchers reported that certain styles of jeans were easier to replicate using inkjet printing than others, and certain features, like color, were more easily replicated. With further study, researchers said they expect digital printing will be a viable method for making new jean products in the future, with less waste.

Writer Laura Oleniacz recently spoke with study co-author Lisa Chapman, associate professor of textile and apparel technology and management at NC State, Raleigh, N.C., and lead author Ming Wang, a former graduate student at NC State, about the study.

Oleniacz: Why were you interested in printing jeans digitally?

Chapman: Denim is a staple of our wardrobe. Almost everybody has several pairs of jeans in their closet. It’s a really popular item. It’s also one of those garments that’s sold worldwide. But the process for making denim is water-intensive. One of the things the industry is looking at is: How do you reduce the amount of water that’s used for denim?

Wang: To make jeans, the cotton yarn is dyed, and then there are finishing and washing processes that give jeans a certain look. Those processes can have a lot of negative environmental impacts such as water pollution and energy consumption. I wanted to explore another way to produce the same look of the denim that is more environmentally friendly.

Oleniacz: What is inkjet printing? Why is it used in textile manufacturing?

Chapman: Inkjet printing is really similar to your inkjet printer at home in that it’s going to jet droplets of ink onto the fabric. But in this case, it’s dropping textile colorant onto the surface of the fabric.

We consider it an emerging technology in that it’s still fairly small market share in textiles. But it has potential mainly because it uses less water, it uses less energy and it’s a print-on-demand process. So you’re eliminating some of the steps in the coloration process, and you have unlimited colors. To print using the traditional process, as you increase the number of colors, you increase the cost of the design. Inkjet printing is not like that; 200 colors is the same as two colors in cost.

At one point in the history of apparel, and in home furnishings, we had a lot of the same products. We would print lots of yards of the same design. Now we’ve moved to a consumer group that demands a lot of variety. When you have a lot of variety, you have more prints and you have smaller production runs and costs of the screen can be really expensive. Inkjet printing becomes more cost effective.

Oleniacz: In your experiment, how did you create the digital denim?

Wang: I used a high-resolution scanner to scan a very high-resolution image of the jean samples, then transferred it to a computer file that can contain the color and transparency information. Then I chose a pre-treated fabric that has the same weight and texture as the traditional jean samples. In the digital print lab, I had access to four different inkjet printers. After struggling to find the right ink and printer, I chose the latex printer, which is more environmentally friendly. I chose six different denim types that have different washing effects. We found digital printing can reproduce all of those effects.

Oleniacz: What did the expert panel say about the digital denim quality?

Wang: We found 12 experts from the textile industry who have a lot of experience, especially on denim and color matching. We asked them to compare the digital denim and the traditional jean samples. For color, the traditional and digital denim were very close. On a scale from one to five, with one as the greatest difference, five means there is no difference, the average score for color was around three or above three. Which means we had a good match for color.

Besides color, we also evaluated the line quality, the texture, the lightness, and overall match. What we found is that it’s very hard to achieve the line quality and texture. We think the reason might be that the traditional dyeing has high ink penetration. But for digital printing, it’s printing on the surface of the fabric, and it’s not penetrating that much into the fabric. That could cause the difference in line quality and texture.

Oleniacz: What is the future of digital denim?

Wang: If someone could solve the ink penetration problem, I think we could mass produce denim products with a high-speed printer. It could bring the cost of production down. However, since mass production is not quite realistic yet, we could use digital printing for high-end denim products like for home textiles or apparel. For kids, they are growing every day, so you could have something that looks like jeans.

Chapman: It may be difficult to replace traditional denim, but there are other markets where this could do a much better job. Jeggings is a great example. In addition to infant wear, there are situations where you want the denim look, but you want a higher drape and a softer fabric, like dress shirts or women’s dresses.

Oleniacz: What is the future of digital printing for textiles?

Chapman: While there is a pretty high learning curve for digital printing, there are also advantages with reduced energy use, chemicals, and water waste when we’re comparing digital printing to screen printing. The dot-com market is also going to drive digital printing. We’ll be looking at new technologies that speed up the production cycle to get goods to consumers faster.

Editor’s Note: Laura Oleniacz is Public Communications Specialist at NC State News Services.

November/December 2021

Digital printing developments in various dye classes present challenges to adoption by traditional textile printers.

TW Special Report

From its introduction in the early 1990s, the promise of digital textile printing was enticing, but slow to develop. Initially, digital printing became a sample and development tool for designers in a preproduction environment. The technology was expensive, but found a niche in commercial printing for banners and signage.

Development Of Digital Printing

Printing speeds for early jet technologies were relatively slow compared to traditional printing methods and this hampered adoption by the textile industry. But printhead development brought speed into the equation; dyes, inks and substrates improved; and the color gamut available to the printer increased. Scanning technology and computational power also expanded capabilities.

Easing The Transition

For some textile printers, the transition from traditional to digital printing involves only minor changes to established processes, and offers great savings in the engraving and storage of traditional screens and other pre-print necessities and design constraints.

A traditional reactive printer adopting digital reactive printing will face fewer challenges than those printers trying to adopt a new dye class with significant processing changes.

Conventional And Digital Mix

Data provided by long time printing technology supplier Austria-based Zimmer Austria points to a 97 to 3 percent traditional to digital printing product mix, with 45 percent of the traditional printing achieved using pigments and 57 percent of the digital printing performed using a sublimation — transfer paper — process. Conventional printers also produce 27 percent of their output using reactive dyes, while digital printers use 36 percent reactive.

This presents an interesting contrast into the penetration of digital printing into the traditional market and the challenge for traditional pigment printers to adopt new dye class processing technologies.

Conventional Dyestuff Selection Criteria

When adopting digital printing for textiles, dye selection has not really changed regardless of the system. The addition of pre- and post- fabric coating options in digital printing can enhance the digitally printed fabric’s appearance and performance, which is a bonus for digital processes.

Reactive, pigment, vat, acid, and disperse dye classes, or inks, all retain the performance achieved through the years of traditional printing development.

Printheads and processes, including dye circulation, have evolved. For instance, reactive and acid dyes don’t require circulation in the digital print process, while pre-metalized dyes benefit from dye circulation. Disperse, pigment and vat dyes must be circulated.

These developments have reached a point where digital printing can meet the needs of the printer’s final product performance and where each dye class performs at its best.

Where Pigments Shine

There are many reasons why pigment printing holds a 45-percent share of the conventional printing market. Pigment printing is versatile in that it has few substrate constraints so one printing and processing system can print on many different fabrics — unlike for many of the other dye classes. It is also a fairly uncomplicated printing system, whether a conventional or digital printing platform is used. “What you see is what you get,” unlike the mysteries of other dye classes as they go through sometimes complex finishing processes to reveal the final color.

There also is the benefit of little wastewater, no solvents and low energy consumption combined with low initial investment and ability to achieve low print costs when using pigments.

End Uses

According to Zimmer, pigment-printed fabrics are suitable for applications in:

• home textiles;
• bed-Linen;
• upholstery;
• cushions;
• window fashions;
• outdoor fabrics; and
• print on panels.

Although there are many digital printing technology developers and suppliers in the evolving textile space, Zimmer Austria stands out with the development of its Colaris technology.

As a printing systems manufacturer, the company builds on more than 140 years in the textile printing industry and 45 years in digital printing with a deep knowledge of the complete textile and print process.

Zimmer’s Digital Path

In 1986, Zimmer offered the CHROMOJET 16 dpi for carpet printing, and introduced the high resolution 76 dpi printer for carpet in 2006 and towel printing in 2007.

In 2009, Zimmer developed the CHROMOJET 76 dpi with process color printing.

The following year, COLARIS entered the market targeting applications in home textiles, fashion, and flags and banners. The Colaris technology introductions continued with new products for narrow fabrics, digital carpet printing and more.

Digital Printhead Solution

The Colaris digital printing technology utilizes the Fujifilm Dimatix StarFire™ industrial printhead. Originally developed for the ceramics industry, the head features 1,024 nozzles per head, the RediJet™ ink circulation system and an integrated heating system. The printhead’s modular design makes it repairable with the changing of individual components. In order to add value and extend the system’s useful life, Zimmer opened the Colaris Printhead Reconditioning Center offering a repair service for a nominal fee.

Interestingly, Zimmer’s technology features an “open ink system,” which allows the printing company to choose its ink or dye supplier. Zimmer does test inks and dyes for performance in its printheads and system and can make recommendations to Colaris users.

Colaris Pigment Printers

The StarFire industrial printhead currently is the centerpiece of a family of seven Colaris pigment printers. The models range from print widths of 74 millimeters (mm) up to 3,400 mm, and feature square meter per hour (sqm/h) performance at 400 X 800 dpi from 140 up to 1,060 sqm/h. The Colaris family features six-color machines with a maximum 2 to 16 heads per color, depending on the model.

A Digital Future

As the promise of digital textile printing technology seemingly rounds the corner from a sample and development tool for designers in a preproduction environment to a full blown production process offering speed, quality and efficiency — digital print adoption by traditional printers is looked upon with optimism.

Solutions for conventional pigment printers to adopt digital solutions utilizing familiar finishing processes are available. Certainly costs matter and will the process transition savings — like screen engraving, rotary screen storage and management, repeat design constraints, and a smaller manufacturing footprint offset the costs of digital inks and maintenance? Those analyses are underway in many places and a digital future may happen sooner than expected.

November/December 2021

The family-owned textile dyeing machinery company continues to innovate to meet today’s dyeing industry challenges.

TW Special Report

Thies GmbH & Co. KG is a family-owned and -run custom textile dyeing machinery company established in 1892. Currently, the fifth generation — siblings Verena, Christiane and Alexander Thies — manage the export-oriented business. Thies’ production facility in Coesfeld, Germany, produces its dyeing machines using components made by subsidiary companies based in Poland and Slovenia. “With a qualitatively and quantitatively strong team of young and experienced employees, we strive to develop innovative and sustainable solutions for practical use,” said Verena Thies. The company also promises a customer partnership with investment security and strong service. “We have built up a comprehensive network of dedicated service technicians, salespeople and agencies over the past six decades,” Thies added. “Hence, customers are optimally looked after locally, in their time zone and language.”

Modern Machines, Intelligent Controls

Thies strives to build dyeing machines that consume extremely low amounts of water and energy and feature efficient control technologies. It’s state-of-the-art iMaster series embodies these concepts in a modern dyeing machine. Chemical consumption, primarily measured in grams per liter (g/L) is largely dependent on the water consumption. In 1980, the complete dyeing cycle — including washing, dyeing and rinsing — required approximately 105 liters of water per kilogram of fabric. Today, the Thies iMaster series can achieve on average 28 L/kg on medium shades, which represents a reduction of 73 percent.

Sustainable Technologies

Sustainability is the driver for change. With this in mind, Thies has developed a new machine series — the Signature Series.

According to the company, the Signature Series not only achieves a further reduction in water consumption, but also lowers dye consumption and significantly reduces the amount of total dissolved solids (TDS) when processing cotton fabrics. Solids production as well as their treatment in wastewater treatment systems is very complex and ties up many resources.

Thies emphasizes that when talking about sustainability goals, the entire finishing process must be considered. “Fabric preparation — consisting of scouring and/or bleaching — and after-treatment processes often are not considered and sustainability efforts are limited to one process part — the dyeing,” Verena Thies noted.

Digital measurement and analyses of dyeing processes are key to process optimization, according to Thies. The company offers several tools for this purpose that optimize the recipes and dye curves. DyeControl, for example, is an automated system for more water-efficient dyeing and rinsing. This is achieved by individually adapting the required amount of water during the wet finishing process. Rinsing, washing and dye baths are measured and analyzed online. The visual representation of the process curves enables both a control of the turbidity and a determination of the dye extract from the liquor.

Heat Recovery Systems

According to Hardy Sullivan, sales, Thies Corp., Rock Hill, S.C., heat recovery systems are often not used in U.S. dye houses or they are undersized based on the needs of the plant. This is because they weren’t promoted initially when dye houses were purchasing equipment. However, today this is a technology included from the beginning when investing in new dye house equipment.

The Thies heat recovery system uses hot wastewater to heat up cold, fresh water needed for dyeing processes. According to the company, the level of benefit increases depending on the temperature difference, ∆t, between the hot wastewater and cold water. For example, a machine with a dyeing capacity of 500 kg dyeing three batches of cotton per day can save up to 80 percent of the steam needed with the consistent use of a heat recovery system. This results in a significant reduction in production costs as well as carbon dioxide emissions.

“It’s easy for dye houses without heat recovery systems to add one,” Sullivan said. “The Thies system is scalable for increased production. The closest installations of Thies heat recovery systems are in Central America, but several North American companies are showing interest, in part because of the savings in carbon dioxide emissions.”

Automation

The demand for automated machinery continues to grow. The advantages of automation are diverse — productivity rates can be increased and stabilized by the reduction of unproductive waiting times; automation increases occupational safety and the attractiveness of the work itself; and automation also may be used to counteract an ever-increasing shortage of skilled workers.

In yarn dyeing, bobbins are placed on the spindles of the bobbin carrier, which in the case of a 500 kg yarn carrier and a package weight of 1 kg, means 500 yarn bobbins must be loaded and unloaded. Thies offers robotics that can take on this time-consuming and physically demanding work, as well as locking/releasing the locking devices. The robotics can be programmed to avoid waiting times for the machines, and the bobbins and locking devices are damaged less frequently as a result of the automatic unloading. The prepared carriers can also be automatically loaded and unloaded into a horizontal yarn dyeing machine.

Thies also offers Multi Product Supply (MPS) systems for automated dye and chemical storage, weighing and dispensing. The system comprises MPS-L for liquids; MPS-D for dissolving dyes; MPS-S for solids; the gravimetric MPS-G; and at the highest level, the MPS-Colourmatic, which controls the entire path of the dyes from the warehouse to the dyeing system including storage, weighing, dissolving and provision in an automatic cycle.

According to the company, some of the advantages of the MPS systems include:

• Reduced occupational safety hazards for employees who less frequently or no longer come into contact with dyes and chemicals;
• No danger of spills, thus preventing plant damage;
• Automatically managed stock levels and auto-generated order proposals if stock falls below a predetermined level; and
• Increased productivity and reproduction rates.

Thies MPS system is a modular concept that can be implemented in small or large dye houses. The system can also be implemented gradually, making the investment economical. The systems also create a more transparent dyeing process, according to Thies. All additions are documented, and incorrect measurements and product mix-ups are prevented thus maximizing reproducibility. Down time also is avoided because the systems can prepare the dyes, chemicals and auxiliaries in advance. The synchronized system and production sequence ensures each product is available in the right quantity at the right time at the right machine.

The delivery precision of Thies’ liquid dispensing system is automatically checked, monitored and optimized. Therefore, recurring calibration is not necessary. The measurement of the supplied chemical quantities is performed volumetrically with the help of a magnetic-inductive measuring system. With integrated small quantity measurement, small amounts as little as 5 millimeters can be precisely supplied.

Sullivan reports that a relatively new manufacturer, American Merchant, Bristol, Va., has recently adopted Thies’ dye dissolver and chemical dispensing equipment. The terry towel manufacturer operates under the philosophy of supporting local farmers and workers by producing all-American made towels. American Merchant took over an abandoned factory space and invested a significant amount to bring in all new looms and other machinery including the Thies equipment. Its brand, American Choice Textiles, provides products direct to the consumer, and the company also supplies high-quality bath linens to retailers of all sizes.

Today And Tomorrow

It is clear that this established firm is dedicated to developing innovative and sustainable solutions for practical use. That being said, a company with five generations of institutional knowledge reaching back to 1892 definitely takes its craft seriously. But it’s the blend of history and ability to focus on the future that makes a difference — automation, sustainable technologies and modern machines featuring intelligent controls — that is Thies’ story today.

November/December 2021