Digital printing technologies support this fast-growing segment of textile printing.

By Dr. Lisa Parrillo Chapman, Technical Editor

For the first time, InPrint — the premier exhibition for industrial printing technologies — will be held in the United States. The show is collocated with ICE USA 2017, the International Converting Exhibition (ICE), which will highlight machinery, technology and manufacturing processes for nonwovens and other flexible based materials.
The exhibitions in Orlando, Fla., April 25-27, 2017, will be of high interest to textile manufacturers involved in, or wishing to learn more about, industrial inkjet printing for textiles in market sectors such as automotive, furnishing and interior décor, labels, and packaging.

Industrial Digital Printing And The U.S. Market

Industrial digital printing can be 2-D or 3-D printing for decorative or functional purposes. Unlike decorative digital printing, which typically occurs as a roll-to-roll process before the product is made, industrial printing is integrated into the production line as a continuous process. For this reason, industrial printed products tend to require a highly specialized system.

The specialization is justified though because the benefits of digital printing are significant. In the print world, consumer demand calls for an increase in the color and image complexity, image quality, and variety of prints. Digital printing supports these customer demands by allowing for small production runs, shorter lead times and improved design aesthetics such as increased number of colors, fine line detail, gradients and photographic type imagery. The print-on-demand production ability of digital printing supports customized designs, leads to a decrease in time to market, and offers cost reduction and higher consumer satisfaction.

Consumer demand is forcing change within all manufacturing industries. Consumers are demanding higher transparency in the goods and services used to manufacture their products, assured safety, higher quality, increased functional attributes, and a wide variety of products delivered to them with lightning speed. The development of industrial digital textile printing technologies increases opportunities for U.S. job growth by creating new markets and better supporting established market segments. These new markets likely would come from an array of new products that cannot be made as cost effectively using traditional printing technologies. Examples include those products that may require multiple colorways, customizable imagery or text, the ability to print to shape, or where precise registration or placement of ink is required.

Conductive Printing

Considerable research and development currently is being conducted on printed electronics in flexible circuitry. Conductive printing would support consumer products for wearables and interior e-textiles designed for health and fitness monitoring, self-cleaning, and communication. England-based IDTechEx, a market analysis firm specializing in electronics, suggests that the highest compound annual growth rate of e-textile markets will be in the home textiles sector. As well as providing new functional attributes to the consumer, conductive digital printing provides improved manufacturing capability. For example, printed radio frequency identification labeling has a broad application range such as for material tracking in the supply chain process. Alternatively, a microchip could be embedded into the product to relay information throughout the supply chain or to provide to consumer care instructions. This information could be read and updated throughout the manufacturing, distribution and consumer stages.

Mass Customization

Digital printing enables mass customization and provides a competitive advantage for those companies wishing to manufacture closer to the point of sale. Because print designs are stored in a digital format and can be printed on demand, digital printing enables highly customizable products that can be made further down the supply chain and closer to the consumer. The shortened lead-times for domestic production will provide the U.S. customer with access to a quality, customizable product, at a low price in the dot com and retail markets. In addition, retailers can provide a more cohesive brand of products. For example, digital printing enables a retailer to provide a color and pattern coordinated range of products including wall covering, floor tiles, carpeting, bedding, stationary, tableware, and personal electronics. The labeling and packaging also may remain highly consistent.

The Luxury Market

The global luxury market generated more than $1 trillion in revenue in 2015 with the personal luxury sector making up about 13 percent of the total. Apparel products comprised approximately 25 percent of the personal luxury market, and brought in over $253 billion in revenue, according to consultancy.uk. Worth Global Style Network reports that the top three ways to attract future luxury consumers was through “exclusive collaborations with relevant partners (78%), secret and exclusive brand experiences (59%) and personalized online experiences (e.g. notifications) (53%).”

In a 2013 article published by Boston-based Bain & Co., Elizabeth Spaulding and Christopher Perry stated that allowing customers to create or add to their own specific product has “elevated customer loyalty and engagement” boosting sales by increasing the perceived value. Customers are willing to pay upwards of 20-percent more when customization options are available. Spaulding & Perry further stated that brands gain further benefits by being able to “gain insights from customized designs and fine tuning products in a feedback loop.” This consumer preference data allows brands to utilize important information in new product development and marketing campaigns.

In its “Post-drupa Technology Forecast for Print and Printed Packaging to 2026” market report, England-based Smithers Pira lists enhanced luxury packaging processes as one of six key technology developments that will fuel revenue and new businesses. The report from Smithers Pira states there is “a new interest in enhanced ranges of print embellishment products and processes, to add luxury appearance and better tactile effects to printed products.”

Industrial printing processes enable brands to more easily and and cost effectively manufacture customizable products, limited edition designs, and unique and higher quality packaging all while engaging the consumer with a more interactive shopping experience by allowing the customer to co-design.

InPrint Highlights

At InPrint, digital printing machinery and chemistries will be shown from leaders in the digital textile printing arena including Italy-based EFI Reggiani and Fujifilm.

EFI Reggiani’s array of digital textile printers enables highly efficient industrial manufacturing to support personalization and quick response for home interior and apparel products. Complementary technologies, such as EFI’s newly acquired Optitex 3-D design technology, bring yet another essential layer of time-savings and automation to industrial manufacturing. The Optitex 3-D design software for industrial fabrics and upholstery reduces fabrics wastage, cuts labor cost and maximizes productivity using automatic nesting software and enables product developers to visualize designs as true-to-life, photorealistic 3-D images. These digital technologies can cut back on lead times, make it practical to generate lower and variable volumes, and cater for different world demographics and trends. EFI states that none of these criteria were possible with analogue methods that are geared for long runs that cannot be easily adapted to changing market needs once production is underway. The old model of industrial analog printing leads inevitably to overstocking and, often, to loss-making heavy discounts on manufactured goods.

Robust printhead technology is needed to support the high-speed printing required for industrial digital printing, as color shifts and print defects will occur if the nozzles are clogged. Stability of colorant is usually most problematic with pigments , but can be an issue with dye-based colorants as well.

The Fujifilm Samba printheads incorporate a recirculating ink channel system that prevents ink clogging. The SAMBA™ piezo MEMS printhead platform is facilitating the creation of families of sophisticated printheads for jetting a wide range of inks for decorative and functional applications, and is installed in a number of different types of industrial printing machines. Fujifilm also will demonstrate water-based and ultraviolet (UV) inks. Fujifilm Imaging Colorants is a global leader in the development and supply of high-performance dye and pigment-based colorants and inks for aqueous ink-jet digital printing applications.

Fujifilm also was responsible for commercializing the UV-cured inkjet inks that fueled the world’s first UV flatbed inkjet printers. A key factor in the growth of inkjet in the wide format, packaging and industrial markets has been the ability to print with UV-curable inks.Pigments developed for inkjet printing typically have a smaller printable range of colors or color gamut, and lower wash and wet and dry crockfastness than dyes, but have increased UV resistance and save time and money because they do not require a post-washing step.

Future Outlook

As industrial printing companies find that established markets related to office and advertising mature and decline, textile markets offer potential for high growth. Boston-based I.T. Strategies estimates the U.S. analog and digital print market at $31.5 billion with textiles comprising one of the largest print categories. By 2020, I.T. Strategies predicts an 18-percent growth in printed textile vendor and retail revenues. Traditionally, textile coloration processes such as textile dyeing, screen-printing and fabric graphics were created in other countries because of high labor costs and environmental regulations in the United States. Industrial digital textile printing technology has lower labor requirements and offers the potential to have lower environmental impacts in areas such as chemical, water, energy and material usage. More importantly, industrial digital printing encourages U.S. market growth by enabling new product innovations such as conductive printed textiles, increased speed-to-market for customized products, and improved print aesthetics to support the decorative and luxury markets.

January/February 2017

SPNano has developed a low-cost method for creating conductive polyester yarns with tunable resistance.

By Dr. Konstantin Press, Dr. Asa Eitan, Dr. Leonid Melekhov and Dr. Amnon Wolf

Natural or man-made textiles act predominantly as insulators. Conductive textiles are created by either coating a nonconductive substrate with electrically conductive elements or by embedding the conductive material within the substrate. These textiles are then used in antistatic applications, for electromagnetic interference shielding and infrared absorption, or in protective clothing for people working with explosives, among other applications. Wearable electronics bring a new application for conductive textiles, which can be found in sports and healthcare sectors where body conditions are monitored to provide health information. The wearable device market is predicted to reach $20.6 billion by 2018.

Most commonly, metal wires are drawn, woven or knitted into the textile to create a conductive fabric (See Figure 1). These techniques form 85 percent of the market. There are significant disadvantages in using these techniques however as noted in Table 1:

• the metal filaments — typically made from brass, stainless steel, aluminum, copper or nickel — are heavy and less flexible than polymer-based textile fibers, which are not favorable characteristics for wearable textiles;
• the filaments also are very fragile and easily broken, which leads to breaks in electrical continuity; and
• the textiles are not biodegradable and therefore are not environmentally friendly, which is an important factor to consider for post-consumption.

Other less popular methods for producing conductive yarns and fabrics include printing/depositing conductive polymers, printing metallic inks on the surface, plasma deposition on the threads, and electroless plating.

New Developments

Researchers at Israel-based SPNano Ltd. have developed a new technology for electroless copper coating of polyester (PET)-based textiles. The technology is based on nanometric dispersion of carbon black (CB) and palladium salt nanoparticles using a recombinant protein called SP1. Coating the yarn with the SP1/CB/Pd⁺² complex followed by a reduction step to form SP1/CB/Pd⁰ allows efficient copper deposition on the polyester’s surface. The technology has been demonstrated in industrial settings using several fibers including polyester, nylon and Kevlar®.

According to SPNano, the copper-coated textile combines the electronic characteristics of metals with the engineering properties of polymers. The benefits of SPNano’s coated conductive yarn process include:

• The ability to tune the final resistance from 10 ohms/meter (Ω/m) up to 1 mega Ω/m with good uniformity;
• The ability to produce a lightweight, flexible conductive PET yarn that might be biodegradable;
• Cost — the most expensive ingredient in the process is palladium, which is used in small amounts, making the final product affordable;
• Ease of application — the SPNano process is conducted using industrial yarn batch dyeing machines in just a few hours, and is easily scalable;
• The conductive coating layer is stable and does not oxidize under normal conditions; and
• The yarn is protected from abrasion by a polymeric coating.

The SP1 Solution

SP1 is an exceptionally stable protein originally isolated from poplar plants. The sp1 gene was cloned and the protein now is expressed in bacteria by means of fermentation. The protein forms a ring-shape homo-dodecameric particle with the 12 N-termini facing the central cavity. The protein’s exceptional stability allows development of an inexpensive production procedure for industrial applications. Genetic engineering was used to fuse material specific peptides to SP1. Display of twelve copies of such peptides confers the high binding ability of the protein to a variety of materials. The same principle was applied to construct a modified SP1 variant, capable of forming reversible and non-covalent molecular associations with carbon-based nanoparticles (CNPs) — such as carbon nanotubes (CNT), CB and graphene nanoparticles. When SP1 forms a stable nanometric CNP dispersions it can bind to polymer fibers such as polyester.

Sonication was used to make a stable SP1/CB dispersion by applying sound energy to N326 carbon black with the L3SP1 protein. The maximum SP1/CNP dry weight/weight ratio was 1:7, and the maximum SP1/CB concentration was 14.5 percent. Stability upon centrifugation was used as a quantifiable measurement of dispersion quality. The supernatant fraction of CNP remaining upon centrifugation was greater than 70 percent. The dispersion was stable for several months at room temperature. Figure 2A shows a high-resolution scanning electron microscope (SEM) image of the nanometric SP1/CB dispersion.

The polyester yarn was coated with the nanometric SP1/CB dispersion using a yarn batch dyeing machine in water-based solutions under mild pH and temperature. Screening for optimal coating was conducted using a coating machine from Italy-based Ugolini S.r.l. featuring 100 gram bobbins. The SP1/CNP loading was controlled by the number of binding cycles. Figure 2B shows a high-resolution SEM image of the polyester yarn coated with the SP1/CB dispersion. Coating with the SP1/CB dispersion dramatically increases the yarn surface area and its reactivity with palladium ion.

Electroless Plating

Electroless or chemical plating is a metal deposition method that does not involve the use of external electric energy. It involves a chemical reduction oxidation reaction in an aqueous solution for metal deposition on a non-conductive substrate. A high-performance polymer filament such as PET was used as the substrate for copper coating, which results in an electroconductive, yet flexible polymer/metal hybrid yarn. In this case, the yarn is activated by introduction of a palladium seed, followed by the copper deposition by using a commercial copper salt solution. One of the major drawbacks of this method is the high cost of palladium — at least $15,000 per kilogram (kg). For commercialization, the amount of palladium should be as low as possible using a cost-effective application method.

All steps in SPNano’s process are conducted using a batch yarn dyeing machines. First yarns are coated with the SP1/CB complex, followed by its immersion in a Pd+2 solution. A reduction step converts Pd⁺² salt to form the active catalyst Pd⁰, leaving Pd nanoparticles on the surface of the yarn. Upon addition of the copper solution, the Pd nanoparticles initiate the electroless copper deposition reaction. The role of the coated SP1/CB coating is to provide Pd binding sites because pristine yarns or protein-treated yarns do not allow electroless coating under these conditions (See Figure 3). Since palladium is the most expensive part of the electroless copper process, it was important to reduce its quantity without affecting the yarn quality, particularly with respect to plating coverage. During the research, it was demonstrated that SP1/CB coated yarns display a high affinity for Pd.

Using an industrial yarn dying machine and low concentrations of palladium salt Na₂PdCl₄ (1mM, 7 millimoles/kg yarn) achieves high-resistance yarns without any loss in coverage. Application of lower palladium concentrations leads to higher electrical resistance but also uneven copper deposition. In addition, mixing other divalent solutions such as copper (II) chloride with palladium ions leads to higher electrical resistance, indicating competition on limited binding sites.

To further thicken the copper coating layer and improve uniformity, PET yarns were coated repeatedly, allowing more copper to attach to the fiber’s surface. However, there is a limitation on improving the resistance because a thick conductive copper coating above 3 microns reduces the flexibility of the yarn and leads to the creation of copper flakes. Figure 4 shows the electroless copper coating method in more detail using a 1,100 decitex * 3 yarn with high twist.

Factors that dictate resistance are:

• Yarn decitex and twist — with equal copper deposition levels per kilogram, high decitex yarns display lower resistance compared to a low decitex yarn and high twist results in lower resistance compared to a low twist yarn. Conversely, high twist levels limit the copper’s penetration into the yarn resulting in uneven coating in comparison with low twist yarn.
• The amount of SP1/CB loaded on the yarn — approximately 2 grams of CB per kilogram were loaded onto the yarn because coating lower CB loadings lead to uneven copper deposition.
• The amount of copper deposited on the yarn before rewinding is important for uniform coating.
• The amount of copper deposited on the yarn after rewinding.

New Possibilities

Metal-coated textiles are breathable and lightweight compared to metal wires. The new production method allows efficient copper deposition on the polyester surface using a low-cost production process, and SPNano’s technology was demonstrated using an industrial dyeing machine.

A hybrid metal-polymer filament may replace copper wire in signal wiring. Coating thickness and evenness affect the electrical properties of the coated yarn, where a thicker coating layer typically leads to lower resistance.

Editor’s Note: Senior Scientists Dr. Konstantin Press, Dr. Asa Eitan, Dr. Leonid Melekhov; and Chief Technology Officer Dr. Amnon Wolf work for Israel-based SP Nano Ltd.

January/February 2017