Research/ Review Paper | Textile Articles

Green Future of Digital Textile Printing – A Fast Growing Area for Textile Decoration

Published: January 15, 2020

Author: TEXTILE VALUE CHAIN

Introduction

Digital textile printing is described as ink based method of printing colorants onto the fabric. Digital textile printing is referred to when identifying printing smaller designs onto garments and printing larger designs onto large format rolls of textile. Digital textile printing was started in the late 1980s as a possible replacement for analog screen printing. With the development of a dye-sublimation printer in the early 1990s, it became possible to print with low energy sublimation inks and high energy disperse direct inks directly onto textile media, as opposed to print dye-sublimation inks on a transfer paper and, in a separate process using a heat press, transfer it to the fabric. Digital textile printing is an excellent reflection with a right blend of classic and elegant view. Also known as direct to garment printing, the process prints designs on fabrics from the computer without any other sources like designing on paper and printing. It enables for changes in color and design easily, and quickly prior to printing. This technology offers faster production technology, cost effective print runs, and provides majority of the worlds printed textiles. This process consumes less water, and dyes, thereby proving to be environmentally friendly. Consumers of today are more demanding with specific choices relating to style, design, and color combinations. This business enables quick turn-around, economic and flexible, efficient set-up and speed. Main advantage of this process is color applications through latest printers, and software applications. Recent concepts of shimmering, shadow, reflection, blurring, layering, and superimposing is also possible through digital fabric printing. The art of digital printing has influenced both the style and process of textile printing. For decades, digital printing for the textile, fashion, décor, industrial, and graphics industry was relegated to sampling and short run printing. With the aid and advantages of innovative inkjet technology, the industry is now addressing the demand for environmentally responsible output, innovative designs, and the need to improve supply chain operation.

Textile Digital Printing Transformation

The textile printing market has been changing to adopt new innovative technologies aimed at addressing a new generation of consumers, brands, as well as the supply chain. This massive industry, with over a trillion and a half dollars in annual business value in the apparel and accessories sector, is undergoing a transformation. Brands must adjust to appeal to a new generation of consumers who shop in both brick-and-mortar stores as well as through online retailers. With the digital age now an economic certainty, brands as well as textile mills must adapt. Many of these changes have evolved in the past decade as early high-speed production digital textile solutions emerged.

Product Life Cycle Management (PLM)

When brands plan their next season, they usually resort to the use of a Product Life Cycle Management system (PLM). These tools are aggregators of all the components needed to usher in a new successful season. From managing resources (ERP), design components, collection and ensembles, to patterns and product photography, these collaborative platforms enable all the functions and processes in the creation of next season’s products – a coordinated effort from brands, designers, textile mills, and cut & sew operations to the logistics that move products to shelves or ship them out in packages.

Just-in-time Manufacturing (JIT)

While just-in-time (JIT) manufacturing has technically been a term that has existed since the 1960s, it has grown in applicability in recent decades. JIT manufacturing allows new businesses to get their product lines to market in days or weeks, rather than months. For larger organizations, it can mean rapid response to the fashion industry needs to meet seasonal demand. Seasonal variations can be on shelves on time, giving textile companies better ability to please their customers.

Reduction in Overstock and Warehousing

The shift toward digital printing can also mean improved inventory planning, resulting in less overstock and warehousing needs. As textile service providers move away from longer runs and shift toward short, varied, targeted production – they have been better able to match product to client need. Clothing can now be made as needed rather than in bulk order, letting companies spend less on inventory that may or may not sell. These capabilities ushered in a new type of fabric suppliers – On Demand manufacturers. These companies use a Purchase Activated Manufacturing business model, whereby production commence only once an order was received and paid for in advance. There are no finished goods in the warehouse just blank raw materials.

Mass Customization

With the supply chain being shortened using innovative print technology and continued advancements in workflow, new players have been entering the space over the last several years, empowered by easy online tools that make it simple to start selling customized clothing commercially. These fit into the growing uses of e-commerce in the apparel industry at large, where continued growth will drive estimated revenues up to $145 Billion by 2023 according to Statista 2018 digital market Outlook. Several suppliers epitomize this trend, pointing out to the need for customization for a community of like-minded people and, on a larger scale, addressing the needs of the masses with diverse customized products.

Advancement in Digital Textile Printing

Performance of Printheads

The component at the heart of the printing system is the inkjet printheads, and development of improved printheads is a highly important factor enabling industrial printing. The major factors in printhead performance are maximum jetting frequency, number of nozzles, drop volume, jetting straightness and uniformity, operating window and cost. For many years piezo drop-on-demand printheads have given the best compromise in speed, quality, robustness and range of ink types that can be used, and are used in almost all textile applications. Other possible technologies include continuous inkjet, which has been used in the past and maintains some interest, and thermal drop-on-demand, which may yet show some promise in textiles.The rise of digital textile machines to industrial applicability has almost entirely been dependent on one printhead up to now. The combination of high speed, aqueous compatibility, large nozzle count and greyscale capability with a suitable range of drop sizes for textile printing meant that successful printers could be built around it. These range from scanning machines with one printhead per colour, up to single pass machines with several hundred printheads in total. Increasingly alternative printheads are becoming available to system manufacturers, often based on silicon (Si) MEMS (micro-electro-mechanical systems) construction that has become a popular approach to building industrial piezo printheads. The advent of single pass printer architectures has generated a need for printheads with higher nozzle counts, tighter packing densities and smaller drop sizes. This need for miniaturisation fits well with precise feature size control inherent in the photolithographic and micromachining techniques used in MEMS processes. Silicon and silicon oxide provide excellent chemical compatibility with most ink families used in inkjet textile printing. Careful selection of upstream construction materials and bonding epoxies help to push the envelope for applications requiring compatibility with complex crosslinking inks, functional materials and aggressive maintenance fluids. Finally, silicon MEMS manufacturing holds the promise of enjoying the economies of scale so important in the semiconductor industry. As the total number of units shipped grows and printhead manufacturers learn how to take advantage of this, the high fixed cost of operating a MEMS fab can be spread across a larger number of units, lowering the per unit cost of manufacture (and potentially therefore the per nozzle cost of printheads when purchased by system manufacturers). It remains to be seen how rapidly, and with what effect, the adoption of Si-MEMS printheads will progress in the textile market, but it remains a very promising technology.

Supply of Ink Jet System

While often treated as a secondary item, the ink supply system that ensures the ink is delivered to the printheads is vital in ensuring reliability in an industrial production context. While simple in principle, the ink supply is often a source of problems that can be extremely difficult to track down. The ink supply has to maintain the correct ink temperature, pressure and flow rate under varying external conditions, while also preventing particles and other contaminants from reaching the printhead and avoiding chemical interaction and other reliability problems. Importantly, it also needs to be easy to use and refill under production conditions.Inks are complex chemical fluids with a wide range of possible constituents, including particulates and binder resins in the case of pigmented inks. This makes it very difficult to find materials for the parts of the ink system in contact with the ink that will not interact with that ink chemically. Piping in scanning systems has to be carefully designed to avoid pressure fluctuations that lead to banding in the printed result. It is only continued learning and development of ink supply systems and components that has allowed inkjet printing systems to gain sufficient reliability to be a realistic option for production textile printing.

Automated Maintenance of Nozzle

As the nozzle/printhead count in systems increases and the requirement for uptime in production limits the time available for nozzle maintenance, the need for fast, automated maintenance configurations becomes more pressing. In fact in many large systems, manual nozzle maintenance is simply impossible as many of them are inaccessible. Nozzles become compromised due to satellite ink and misting collecting on the printhead faceplate, debris being trapped in non-printing nozzles, vibration leading to ink seepage, dust and fibres from the substrate and other contaminants from the printing environment, air bubbles either being drawn into the nozzle or in suspension in the ink, and ink drying in the nozzle. All of these can cause jetting to be compromised or stopped altogether.

Many systems in production today in textile mills rely on manual nozzle maintenance, and the development of reliable and fast automated maintenance is a significant factor in the continued adoption of inkjet into production textile printing.

Substrate Handling and Motion Systems

Motion systems are required to move the substrate or printheads, or both, in order to scan the entire textile and produce the printed result. An industrial motion system for digital printing, no matter what the configuration, needs to have smoothness and consistency of motion, accuracy of positioning, handling of substrates to ensure dimensional stability during printing, and the suppression of vibrations that can lead to visible print artefacts. There are a number of specific problems faced by motion system designers, as systematic errors in dot placement are highly visible to the human eye and generally undesirable. A combination of sound mechanical design and (in some cases) compensation for issues using software is required for optimum print quality.While promoting dimensional stability of textile substrates using ‘sticky rollers’ has been known for many years, the requirement and challenges are more testing for digital printing. The rotary screens in conventional printing act to hold the textile in place, while with inkjet the non-contact nature of the printing provides an additional challenge, which becomes ever more difficult as printing speeds increase. Again, significant development has been required to give good textile handling performance for production, and new and more difficult problems needed to be solved for single pass systems.

Single Pass Printing Systems

Single pass printing systems, where the printheads remain stationary in a complete line across the textile roll and the substrate moves beneath them in a continuous manner, allow for greatly increased throughput from a single printing system. Single pass printing systems have productivities that rival rotary screen systems for the first time, with the trade-off of greatly increased cost over scanning systems. A potential issue with single pass printing is the fact that there is no opportunity to use interlacing of multiple print swathes, as is commonly used in scanning printers, to help in masking print defects. Another factor to consider is that with single pass printing there is no opportunity to perform nozzle spitting during a print run – a process that is commonly used in scanning printers to ensure all nozzles continue working correctly. These factors mean that single pass print production is at a higher risk of rejection due to print defects, with the high printing speeds also meaning these print defects can extend over large areas before being recognised.

For these reasons, single pass printing has not been adopted widely so far in production textile printing, with many textile mills choosing to add productivity to their factories by ordering additional scanning machines rather than going down the single pass route. However, some of the largest textile mills have been using single pass systems successfully for several years, and the introduction of new entrants into this market suggests that single pass systems may show larger market penetration from now on.

Development in Software and Electronics

Another important area is the printing software that manages the printing system and controls the supply of data to the printheads. Development of powerful and easy to use software is a significant factor in adoption of industrial printers, especially in a production environment like a textile mill. A good user interface allows easy access to the most important controls, while enabling more detailed changes to be made by qualified users. Meanwhile the image pipeline is responsible for converting an input image file into the data that determines when each nozzle fires as the textile is being printed. This involves a number of steps including colour management (to ensure the printed colours are as expected), screening (to reproduce continuous tonal variations in the best possible way using a matrix of dots), and splitting (deciding which data to send to each printhead depending on the printer configuration). Single pass systems again make huge demands on electronics and software to handle the large data throughputs required and development in this area has been crucial to allow single pass systems to be successful.Textile-specific software is needed to handle textile design images, including flat and continuous tone designs and separation files. Also required are the acceptance of a wide variety of image file formats from CAD design and screen separation programs, handling of very large image files, support for spot and process colours with expanded process colour sets, colourway variations of designs, real time image repeating, and many more functions. Screen simulation features bridge the gap between digital and screen-printed fabrics, especially if both techniques are still to be used. Several software vendors have incorporated features useful in simulating and matching to screen printed production fabric, such as simulating screen resolution/mesh size, colour mixing and overprinting, colour trapping, and incorporating gradation curves for tonal separations. Another area where software has a part to play is in the automated recognition and compensation of print defects. Advanced vision and analysis systems have the potential to be able to recognise a wide variety of print defects (much of this work still relies on the human eye in many printing applications, including textiles). Automation of defect recognition promises to be faster, more objective and more reliable, while also enabling rapid response to the defect by triggering maintenance action, reprinting a job and even using nozzle compensation schemes where a neighbouring or backup nozzle is pressed into service to replace or hide a missing nozzle.

Conclusion

As digital technologies improve, more and more traditional textile printing companies are looking at the benefits of digital printing, which include shorter lead times, customization options, improved design aesthetics, workflow efficiencies and cost reduction. The advancements in digital printing provide innovative solutions for increased flexibility and speed to textile printing products. Applications such as home textiles, soft signage, automotive & fashion are moving in the new technology. People basically use reactive ink for cotton fabric, direct disperse for polyester Fabric or Dye sublimation is used as it’s more familiar to print on paper and then transfer on under percent polyester fabric and then we have acid that is usually use for silk and wool fabric. Pigment is the real innovation because pigment is the only one inks can be used for all the substrate. The future is to develop a complete green process, so not only green inks but a full completely green process for a greener future of the textiles.

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