Printed, flexible electionics for e-textiles

Can printed electronics (PE) and flexible hybrid electronics (FHE) offer to e-textiles a means to overcome the design, manufacturing and sustainability challenges facing the industry? The Large-Area, Organic & Printed Electronics Convention (LOPEC), an annual conference and trade show, recently was held in Munich, Germany, with 176 exhibiting companies from 28 countries and more than 2,400 visitors from 48 countries communicating about challenges, including these.

The biggest takeaway from presentations and conversations with exhibitors was how interlinked those three topics—PE, FHE and e-textiles—are, so that when finding solutions for one, progress is made with the others. From an e-textile point of view, the fiber and textile industry needs to have a greater presence to overcome PE stakeholder preconceptions.

Cooperation required

Klaus Hecker, Ph.D., is the managing director of the Organic and Printed Electronics Association (OE-A) and a key partner of LOPEC. He has seen the printed, organic and flexible electronics market grow to a global industry worth around $50 billion. It’s expected to reach $75 billion by 2032. In an interview for the OPE Journal (Organic and Printed Electronics), he acknowledged some of the unique challenges wearables face.

“Putting printed electronics into products often represents a revolution for these companies because they basically have to become an electronics manufacturer, which requires additional and completely different competencies [compared with apparel],” Hecker says in the journal.

Conversations at LOPEC also made clear the need for the electronics sector to overcome its perception of fabric as offering a “rough” substrate compared to polyurethane or paper. That certainly is true for certain applications but not all of them. In his opening remarks, LOPEC general chair Wolfgang Mildner stressed, “Printed electronics is the industry of collaboration. No one can do it alone; it needs cooperation.” Over the three-day program, many conference speakers repeated this viewpoint.

Waste and risk

“Waste is the ‘elephant in the room’ because there are no real solutions so far,” said Covestro’s Karine Benbelaid during her presentation on the opportunities in the medical sector. Like many, her company is looking at potential solutions, such as the greater use of biomaterials, as a 45%–57% biomass content can deliver a 30% carbon footprint reduction.

Bringing hospital stakeholders on board is a challenge, with attitudes varying globally. The U.K. is seen as forward-looking in this respect, driven by government policies. Benbelaid highlights the question of risk, which, from a hospital’s perspective, is regarded as part of the total cost of a product or material. Risk and financial cost are closely linked at the time of purchase. This introduces another perennial challenge for PE and e-textiles in general: the question of testing.

Standardization

Testing is a vital step toward standardization, providing data on the usability, quality and durability of PE and FHE in e-textiles. The uniqueness of use cases must be addressed, from the anticipated environmental conditions to the frequency of use and the impact of repeated use on electrical performance.

Bayflex Solutions in Alameda, Calif., manufactures equipment that tests some of the commonly faced needs for FHE and e-textiles, such as bending, folding, rolling or sliding and stretching. The Flexdata system is a control and analytics cloud platform capable of operating with passive and flexible components in both ambient and hostile environments, using a machine-learning data framework.

With 40 channels of data capture and a continuous process of taking measurements, the Flexdata system can measure resistance, voltage, temperature, humidity, torque and load cell during testing. These capture the profile of test-sample changes over repeats with specified bending parameters and time periods.

The live camera monitoring and an ActionReplay quick image compiler allow users to check “what happened” from captured images. Acknowledging that multiple stakeholders may need access to the data, cloud storage is used for remote monitoring, control and teamwork.

Rethinking the design process

The role of design when creating sustainable PE and FHE e-textiles and wearables results in stakeholders throughout the value chain engaging with the problem at an early stage. Researchers at the Technische Universität Dresden are designing both sensor and power supply together, rather than treating them as separate components of the final product. This is indicative of the change in design as engineers search for more holistic solutions at an early point in the process.

Design that extends use and identifies repair and end-of-life solutions is prominent. In Finland, the PrintoCent Pilot Factory has been established for roll-to-roll prototyping, verification, piloting, upscaling and reliability testing with a strong focus on sustainability. VTT is a partner in the Horizon Europe-funded Convert2Green project. The aim is to establish an open innovation network that specifically supports SMEs in developing circular and environmentally friendly materials.

Developments emerging from the plan include lighting foils that use recycled and bio-based substrates. Electrocardiogram skin patches are another example using fully bio-based and biodegradable substrates. Designing for end of life is particularly important for products that have limited use periods due to their functionalities. PrintoCent also has been developing smart labels using bio-based substrates that are fully energy autonomous.

Under the European Horizon 2020 funding scheme, the Swiss Federal Laboratory for Materials Science and Technology has been undertaking a life-cycle analysis to investigate the design of paper-based printed electronics for recycling as e-waste, as opposed to composting it as bio-waste at its end of life. The laboratory is using a crystalline nanocellulose-coated paper substrate printed with nano-silver (Ag) conductive tracks.

The intention is to offer a more sustainable alternative to conventional printed circuit boards. Researchers concluded that despite loss of Ag at end of life, there is a benefit when recycled materials have been used during manufacture or when material recycling can be assured at end of life. These projects highlight the interconnectedness of the whole value chain in designing for sustainability.

Growing smaller

Miniaturization is creating the demand for increasingly fine printing of conductive inks and narrow spaces between. In turn, this is driving the need for an even finer mesh for silk-screen printing where textiles offer advantages over stainless-steel mesh. PVF Mesh and Screen Technology in Germany produces a range of textile mesh that offers high physical stability and low distortion properties for this purpose.

The V-Screen NEXT textile, from Tokyo-based NBC Meshtec Inc., does not suffer plastic deformation during the tensioning or printing processes, even under high blade pressure or long print runs. Eliminating tension shifts ensures that the mesh remains in register, causing no machine downtime for readjustments. The threads used have twice the tensile strength of a comparable stainless steel.

The company’s product offers a higher light transmission and a low-light reflection so that the coating is fully exposed from the print to squeegee sides with minimal light scattering. In the end, the industry and consumers are looking to increase performance characteristics from e-textiles but with reduced visibility so that demands for this quality of mesh will continue to grow. 

Marie O’Mahony, Ph.D., is an industry consultant, author and academic. She is based in London.