In a world increasingly conscious of the environmental impact of manufacturing, there is clearly a great need for the textile dyeing and finishing industry to make substantial savings in its consumption of water, chemicals and energy. According to Femke Zijlstra, Head of Sustainable Development at DyeCoo of Weesp, The Netherlands, the industry needs an average of 100–150 l of water to dye 1 kg of textile, with approximately 28 billion kg of textiles being dyed annually.
Several companies have now developed commercial technologies for dyeing, finishing and coating textiles that offer tremendous savings, often achieved by applying only the required amount of dye and/or chemical finish to the surface of the fabric via the use of the latest sensor-based controllers.
Pioneering Baldwin Technology
One leader in this field is Baldwin Technology(1), which has its global headquarters in St Louis, Missouri, USA, and its product and technology centre in Arlöv, Sweden. Baldwin, which is owned by the multi-billion-dollar global manufacturing and engineering consultancy Barry-Wehmiller of St Louis, is a major manufacturer and supplier of process automation equipment, and related consumables for printing, packaging, converting and film extrusion, as well as textiles.
During ITMA 2019, held in Barcelona, Spain, on 20–26 June 2019(2), the company introduced its latest non-contact spray model (TexCoat G4) and championed the technology’s numerous advantages compared with conventional methods of applying finishes. TexCoat G4 uniformly distributes chemicals across the textile’s surface and applies them only where required, on one or both sides simultaneously, claims Baldwin. Localised application is beneficial when working with water- repellents on fabrics intended for lamination, for instance, because it greatly reduces the problem of the finishes affecting the quality of the adhesion layer.
In addition, the non-contact technology lessens the dilution of chemicals in wet-on-wet processes and, with no contamination of the baths used in conventional finishing processes, which then require cleaning, the downtime between different production runs is kept short.
With the TexCoat G4, only small amounts of chemicals need be applied to the fabric for a given effect and any that are lost (“over sprayed”) are collected in a trough for recycling. As a result, compared with traditional bath-based applications, the volumes of chemicals required for full coverage of the textiles are halved.
Complete tracking and control of the process provides consistent quality. The TexCoat G4’s recipe management allows for precise selection of the coverage, and automated delivery of chemicals and adjustment of speed. In addition, algorithms attempt to compensate for the bowing and skewing caused by slight changes in tension as the fabric runs through, by adjusting the amount of finish being applied (so-called “fabric-width compensation”).
Although limited to using low-viscosity liquids, the system can process a wide range of water-based chemicals, such as flame-retardants, water- and oil-repellents, softeners and antimicrobial agents.
Immediately upon demonstrating TexCoat G4 during ITMA 2019, Baldwin won major orders and deliveries have continued throughout 2020, despite the disruption caused by the covid-19 pandemic. In one busy period, the company reports it was able to complete six installations in just 60 days(3), thanks to the close collaboration of onsite engineers and local agents, together with remote support from Sweden.
A newly formed Swedish company, Limhamn-based imogo, also introduced its spray-dyeing technology (Dye-Max) at ITMA 2019(4), and has subsequently gained considerable attention by promising its use can slash the consumption of fresh water, energy and chemicals, as well as reducing waste water, by as much as 90%, when compared with conventional jet-dyeing processes.
Dye-Max’s application unit is a closed chamber containing a series of spray cassettes with precision nozzles for accurate and consistent coverage, each nozzle in combination with a patented valve that controls the volume of chemical applied. The chamber also has an exhaust system and droplet separator to ensure that the environment around the unit is kept clean.
“The spray cassettes are a key part in the Dye-Max line,” explains imogo’s Founding Partner Per Stenflo(5). “There is one set for each of the three separate dye-dispersion feed lines and they can be easily exchanged without the need for tools in less than one minute. This allows extremely fast changeovers between colours, because the operator simply needs to insert a new cassette.” Unlike existing processes, there is no need for a lengthy, thorough cleaning of the chamber each time and, because the spray cassettes are interchangeable, all maintenance on them can be performed off-line, he adds.
In addition, the technology requires an extremely low liquor ratio of 0.5 l.kg–1, resulting in substantial savings in the amounts of treatment water and auxiliary chemicals used. Nearly all the dye is used during each run and so the process consumes only a modest amount of water to rinse the chamber of the little that does escape. As well as keeping the generation of waste water low, the reduction in the amount of liquid applied helps keep down the energy needed for fixation.
Two German companies – RotaSpray from Hohenlohe and Weitmann & Konrad GmbH & Co KG (Weko) of Leinfelden-Echterdingen – are independently developing application technologies based on the use of rotating atomisers to generate the sprays.
RotaSpray and Dystar
Both of RotaSpray’s patented systems (RotoDyer and RotoCoater) can be retrofitted on existing production lines to eliminate the need to repeatedly run yarns, tows and fabrics through large vats of dyes. In addition, their use precludes the need for manufacturers to prepare and often discard significant quantities of chemicals and dyes.
Working with Singapore-based chemical specialist Dystar, RotaSpray has developed a process (PS2) for dyeing denim yarns and fabrics, which combines the use of the RotoDyer with a range of Dystar’s dyes and process auxiliaries. PS2 has already been successfully adopted by a number of major denim manufacturers, including: Artistic Fabric Mills and Nishat Mills in Pakistan; Arvind in India; Mou Fung in China; Orta in Turkey.
A common problem with denim-dyeing is the limitation of conventional indigo-dyeing machines with respect to the mixtures of other dyes that can be combined successfully with indigo and sulfur dyes to provide specific shades and effects. The co-developers claim PS2 overcomes these limitations and allows a previously unachievable variety of colours in the continuous dyeing of warp yarns, particularly for small lots that are typically prone to inconsistent dyeing when processed in traditional, larger-scale equipment. Now, mixtures of indigo, sulfur and vat dyes can be applied in a single step, without fear of the differences in affinity and exhaustion behaviour of the dyes leading to a non-uniform finish.
In addition, when using reactive and vat dyes, the contactless application of the process prevents contamination, which otherwise can result in undesirable hydrolysis, and removes the need for an intermediate drying stage.
As with Baldwin, Weko introduced its latest non-contact precision application system (Weko-Neo) at ITMA 2019. One year before, the company had launched the Weko-ProTec for the functional finishing of technical textiles and nonwovens.
Weko-Neo is designed for installation at the entrance or exit of a stenter frame and used for denim processes, such as fixation, resin and flat finishing, lustre or brilliance enhancement, softening, tinting and over-dyeing. In common with RotaSpray’s systems, chemicals are supplied to rapidly rotating discs and dispersed by centrifugal forces to form a uniform ultra-ﬁne aerosol, which falls on the material. Common functional finishes applied by the system include flame-protection agents, hydrophilic/hydrophobic finishes, antimicrobial treatments and silicones, as well as more traditional ones such as softeners.
During 2020, Weko has worked with Polygiene of Malmö, Sweden, to meet the demand for a dedicated technology and process to apply the anti-viral finish, ViralOff, a durable protective finish claimed to effective against the SARS-CoV-2 virus.
Technologies from two other companies allow dyeing and finishing without using any water at all.
Developed over 20 years by DyeCoo, the first example is a closed-loop process that replaces water with reclaimed carbon dioxide (CO2) as the dyeing medium. Heating and pressurising the CO2 makes it supercritical, a state between a liquid and a gas with a very high solvent power, meaning the medium can carry the dye easily and deeply into the fibres. The resulting textiles have vibrant colours.
The technology has been adopted by suppliers to major retail brands such as adidas, IKEA and Nike, and there are now nine DyeCoo machines in operation in Thailand and Taiwan, while three new machines are being installed in Vietnam for dyeing polyester (PES), the material to which the system is best suited.
More recently, Alchemie Technology, based in Cambridge, UK, introduced its waterless dyeing system (Endeavour), and while eager to promote its environmental benefits, has yet to divulge the process behind it(6).
The immediate benefits of these technologies seem clear, but, despite some successes in the market, the developers believe far greater potential exists for their adoption. Representatives from Alchemie Technology, DyeCoo, imogo, RotaSpray and Weko, as well as the textile consultancy StepChange Innovations of Kandern, Germany, debated these issues during an online discussion held on the 24 October 2020(7).
Prior to the covid-19 pandemic, many more companies were focusing on sustainability in their production and investment planning, but there remains a barrier to changing the outlook of many others unwilling to take risks and accept the initial costs in return for the long-term benefits, according to Weko’s Sales Director Tobias Schurr. Stenflo agreed that the “textile industry is quite conservative”, adding that following the onset of the pandemic, it has adopted a survival mentality: “It is not the time to be a visionary. Day-to-day business is about staying alive—that’s the reality for many of our customers.”
In any case, any investment is a risk, according to Stenflo, who called on retail brands to put pressure on their suppliers to be more sustainable. Governments also have a role to play, in providing incentives for producers to adapt. ”Sustainability alone will never cut it, there has to be a business case or it won’t happen.”
Zijlstra echoed the sentiments of conservatism, noting that the industry is familiar with using water. The processes “date back almost 200 years,” she said, adding that there are other water-intensive steps required before and after the dyeing, such as pre-washing, desizing and mercerising. She also raised the issue of the difficulties to be faced of scaling-up new technologies to meet the demands for significant volumes.
However, RotaSpray’s Business Manager Rainer Tüxen noted that companies are increasingly streamlining their ranges, which has created a trend for batch sizes to become smaller. He described this as “a definite opportunity” for the emerging technologies, because producers operating lines designed for high volume are dramatically increasing their costs for small-batch production. As well as their advantages in terms of sustainable production, the newer technologies are suitable for smaller lot sizes, and provide more production flexibility.
Pressure on manufacturers will come automatically as orders tend to becoming smaller, which will be a real problem for many companies in the near future: “If they don’t change, they’ll lose,” Tüxen said. The return of manufacturing to regions, such as Europe, in order to be closer to customers could also exert a positive influence for change, he concluded.
“We believe our technology could work in Europe,” said Zijlstra, while acknowledging the PES supply chain is still based in Asia and driven by high-volume economics. Nevertheless, the emergence of different ways of collaborating and the substantial interest shown by brands in the recycling of PES are changing the business landscape. Currently, producers are taking a hard look at their business and sourcing models.
In conclusion, the participants agreed that, despite the advantages of their respective technologies, it will be hard to convince an industry under pressure in the current climate to pursue long-term goals. Longer-term, however, many factors work in their favour, not least pressures that will continue to come from the brands, ever-tightening regulations and, ultimately, consumers. In the meantime, Tüxen observed: “Investment in textile machinery is always cyclical and the companies who invest against this cycle of highs and lows are usually the most successful. They use the [quiet] time to change, because they have the resources and the people available to develop new things, which is quite difficult in times of peak production.”