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Integrating coating technologies

February 1st, 2013 / By: / Advanced Textiles, Feature, Technical

The coated textiles industry is currently in a state of flux as new markets are emerging and traditional processes (and partnerships) are being adapted in response.

A wide range of coating technologies and processes were showcased and explained at the 2012 International Conference on Textile Coating and Laminating (TCL) held in Valencia, Spain, in November. Discussions emphasized that while some end-use products veered far from the domain of technical textiles, they served to illustrate how techniques developed within the industry are now being exploited in other fields.

Thomas Kolbusch, vice president of Dormagen, Germany-based Coatema® Coating Machinery GmbH, for example, provided a highly detailed paper on the production of large area printed electronics as part of his company’s work with the Organic Electronics Association (OE-A).

Real connectivity

The OE-A consists of some 190 members worldwide from both industry and academic institutions, involving component and material suppliers, equipment makers, system integrators and end-use product purchasers. Its vision is based on the seemingly inevitable “Internet of things”: the next logical step in the technological revolution that now connects people anytime and anywhere is to connect inanimate objects as well. This, the OE-A believes, will drive the development of a range of potentially huge new markets.

These markets include printed organic photovoltaics, which have existed for a number of years as prototypes and limited products such as shoulder bags with integrated panels for charging consumer electronics. They are now being employed in tents and awnings as their performance becomes more reliable. Within five years, the OE-A sees their use extending, first to off-grid building facades and then to roof tops, fully connected to the grid as a viable means of supplementary power generation.

Flexible displays will move from their current employment in price labels, gimmicky greeting cards and rather rugged e-readers to use in tomorrow’s screens, as well as large information signage and in-molded displays, as color e-paper becomes cheaper and more readily available. Further down the road, roll-up OLED (organic light emitting diode) TVs are envisaged.

OLED lighting, which is currently glass-based and limited to use in interior decoration, will first progress into much thinner glass and metal constructions, allowing it to find new uses in both automotive and architectural designs. Within 10 years, it will become 3-D, flexible and transparent, for general integration into all manner of components and structures.

Similar progress over the next decade is envisaged for printed memory, as well as for printed batteries.

Roll-to-roll

All of these new products are viewed by Coatema as achievable by adapting its conventional, roll-to-roll coating machines such as the market-proven Easycoater and Click&Coat™ ranges—albeit largely in the nitrogen environment required for the production of highly moisture-sensitive electronics.

“The key to the successful production of flexible printed electronics is in bundling together a range of existing roll-to-roll technologies and integrating them in-line,” says Kolbusch. “This includes surface treatment, printing, coating, photolithography, nanoimprinting, laser patterning, soldering and pick-and-place automation.”

Major process parameters that must be considered, he adds, are operational speed, the rheology of the coating and printing inks, the substrate condition, tension and edge control, the resolution and registration accuracy of the printing/laminating systems, coating precision and curing, drying and cross-linking.

Funding frameworks
in Europe

In Europe, projects that have been funded by the European Union (EU) within its €50 billion Seventh Framework program, running between 2007–2013, have been particularly rewarding for such new developments. Coatema was involved with six partners in the successful Facess project, which ended in 2011. This project involved the coating of efficient organic solar cells and a thin-film battery onto a flexible substrate, as a fully autonomous energy source.

Dr. Joost Wille, R & D director for the Belgian coating specialist Sioen Industries, named three other EU projects with which his company has involvement: S(P)EEDKITS, AT~SEA and i-Tex.

In the €9 million S(P)EEDKITS project, Sioen and 15 partners are working to advance the contribution coated textiles play in regions affected by natural disasters such as floods and earthquakes; AT~SEA, bringing together 11 European partners, is exploring the use of advanced 3-D multi-layer textile substrates for seaweed cultivation.

The six companies involved in the three-year i-Tex project have developed coated textiles embedded with LEDs (light emitting diodes). The integration of an electronic conductor and transmitter in coated textiles is aimed at applications
in security curtains for trailers and containers and the packaging materials of valuable goods.

As a result of such collaborations, Sioen has developed a new range of conductive coatings using a technology that evenly disperses carbon nanotubes into an aqueous binder, to act as conductors and heating elements.

“People have to look further than their daily business and need to be open to innovation, because specialized potential markets and opportunities are constantly emerging within the coating sector,” says Wille. “Open innovation and joint development projects are now essential.”

Factory of the future

The biggest widespread change in coating technology is occurring in the gradual shift from solvent and water-based systems to the use of powders and hot melts, as the first stage in what Prof. Dr. Marc Van Parys, head of the textile department and Research Lab TO2C at University College, Ghent, Belgium, calls simply “the move from wet to dry.”

“The factory of the future will be based largely on dry coating technologies in order to achieve considerable savings, not just in the removal of water from systems, but in reductions in energy, chemicals and waste, as well as the elimination of VOCs,” he says. “These technologies are leading to increased production speeds, higher production capacities, greater flexibility and cheaper overall production costs.”

He identified a number of potential breakthrough technologies pioneered at TO2C that are likely to prove instrumental in this transition:

  • Hotmelt and UV coating
  • Reactive curing systems such as plasma and microwave
  • Digital coating
  • Magnetron sputtering

“Each of these has specific advantages,” Van Parys explains. “Hotmelts can be applied by slot die, reverse roll, spray or screen application techniques, and in Europe there is a significant number of reliable suppliers of the various systems such as EVA, PUR, copolyamides and copolyesters. The compact hotmelt coating systems reduce investment costs, since there is no requirement for a thermal oven or an afterburner, and allow for high-speed production and rapid product changeover times. The use of substrate-compatible hotmelts also makes the production of fully recyclable products possible.”

Atmospheric plasma systems are specifically suited to increasing the surface tension of materials and the production of self-cleaning surfaces, as well as imparting improved wetting, spreading and adhesion.

UV coating

Like hotmelt processing, UV coating technology is already in operation on an industrial scale, Van Parys says, with tremendous advantages in terms of energy consumption and, in respect of dry systems involving UV curing, the almost complete elimination of VOCs. There is further potential envisaged in UV-cured materials being digitally coated with extremely thin layers for a range of new functionalities. These, along with the new possibilities being opened up by magnetron sputtering technology, are the subject of intensive investigation at the TO2C lab.

“Magnetron sputtering is based on mechanically assisted gas discharge,” says Van Parys. “The magnets keep the gas discharge at low pressure, opening up the ability for much higher deposition rates.” A 60cm wide pilot line for the new technique has been installed at TO2C.

Nanocoating

Significant industrial take-up is also anticipated by the textile industry for nanotextiles containing fibers embedded with nano objects or structures, either directly at the extrusion stage or through coatings. Growth, however, has been more muted than anticipated, according to Dr. Dirk Hegemann, a group leader with the EMPA (Swiss Federal Research Institute, headquartered in St. Gallen, Switzerland), which has 1,000 employees at three sites carrying out research on behalf of international OEMs. This is despite the perfection of state-of-the-art processes such as the development of sol-gel coatings comprising nanoparticles for stain repellency. A bimodal, superhydrophobic surface results, with virtually no leaching of the nanoparticles due to abrasion in accelerated wear tests.

“What may be lacking to some extent is the courage by companies to invest,” Hegemann says. “The success of nanotextiles has been limited to date because many companies are simply focusing largely on just running operations and only incremental innovation. Highly qualified personnel are necessary for introducing these techniques on an industrial scale, which is why the take-up has been predominantly by companies with a focus on R & D and the introduction of novelties.”

The biggest success story so far has been in the introduction of nanosilver for antibacterial treatments, but Hegemann sees a bigger opportunity arising. “One area where nanotextiles may be able to make huge inroads is in the strengthening of natural fibers such as flax, kenaf and hemp, as the reinforcing materials for composites employed by the automotive industry,” he says.

At their current strength, natural fiber composites are employed as door panels and inserts and parcel shelves, which by 2015 will be a U.S. $72 million market, accounting for 145 million pounds of these materials. A 25 percent improvement in the strength of these natural fiber composites, however, would allow their use in both spare wheel pan covers and headliners, estimated to be a $117 million opportunity for 234 million pounds of composites.

A further $162 million opportunity representing 324 million pounds is envisaged, however, if the strength of the natural fiber reinforcements can be improved by 50 percent, allowing their use to extend to components such as bumpers and protective trims.

Wrapping up

At the 2012 TCL conference, the focus was on coating and laminating developments in Europe, but there was reassurance (if it’s needed) from Daniel R. Dwight, president and CEO of the Cooley Group, that coated textiles will continue to be invaluable to U.S. industry.

Having flown the flag with Dow Chemical during 2012 in providing the low carbon and recyclable stadium wrap fabric for the Olympic Stadium in London, Dwight noted that, among other developments, Cooley’s highly portable CoolPro 80,000-liter liquid-storage containers are to be employed in the rapidly-growing fracking industry, on which the U.S. is now staking its claim to assist with future energy independence.

Adrian Wilson is an analyst, writer and editor specializing in the technical textiles, nonwovens and composites industries. He is currently the editor of Sustainable Nonwovens (MCL Communications) and Smart Textiles and Nanotechnology (International Newsletters).

Editor’s note: For more information on the use of geotextiles in the fracking industry, see “Opportunities and challenges for geosynthetics.”

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