INNO-KOM-Ost MF 110132
Textile materials are a wide-ranging alternative to printed foils. This is proven by interesting and very concrete research questions from the textile and processing industry. In particular, the flexibility and breathability of textiles can be seen as a great advantage compared to glass, plastic, foils and the like. The combination of conductive printing with textile substrates results in an attractive niche technology with application-specific and unique products even for the smallest batch sizes. A new solution for printing conductive substances on textiles has been developed as part of the project. The chromojet spray printing process is suitable for the requirements for high application quantities as well as individually designed printing pastes.
Objectives of the research project are the production of printed conductive structures on textile substrates using the chromojet spray printing technique (Fig. 1) as well as the development of suitable formulations for conductive pastes. This creates the possibility of manufacturing conductive textile substrates with constant resistances over the width and length of the conductive print. The result of the project is a technology for the production of conductive printed textile structures, which are characterised by the following properties:
1. defined electrical conductivity in the printed areas
2. textile properties such as flexibility, drapability and breathability.
In order to achieve the objective, printed conductive structures are produced in different layouts. An example of this are interdigital structures. They function as sensors, bus and heating structures or as the basis for luminous textiles. These can be individually integrated into various products and enable new solutions for the manufacture of smart textiles.
Intrinsically conductive polymers, silver in paste and powder form as well as other functional pigments were tested as printing additives. An essential feature in the selection process is the theoretically calculated, required particle size of max. 20 µm. Larger particles can clog the nozzles of the chromojet printing technology. Appropriate binders and additives were selected for the preparation of the printing pastes as well as for the pre- and post-treatment. Based on previously determined conductive substances and binder systems, polyester fabrics, knitted fabrics and nonwovens were investigated as carrier materials for printing the conductive structures. By pretreating the carrier material, impurities and preparatives were removed and appropriate hydrophilic and hydrophobic finishes were applied, either. The developed conductive structures have been defined and calculated with respect to all necessary properties, such as conductivity, required resistance, required power, spacing of electrode structures, electrode spacing and electrode thickness. These defined properties are the basis for the designs created and the digital layout for further processing on the chromojet system.
The conductive pastes developed serve as the basis for the printed conductive structures (Fig. 2). The pastes are applied to the previously selected textile materials according to the specified design. The sharpness of the print contours, the distance between the electrode structures and the layer thickness required for conductivity are taken into account. In addition to rheological and textile-physical investigations, the electrical characteristic values have also been examined.
Functional samples for sensory and actuator applications, in particular a tactile switching element and heating systems (Fig. 3), have been realised. For the safe use of the functional samples and the printed conductive structures, insulating layers were applied by means of lamination, thus preserving the textile character.
The most important target markets for textile and printed electronics include the automotive industry, microsystems technology, biomedical technology, home textiles, telecommunications and IT peripherals. New fields of application include textile interdigital structures, which are the basis for sensory applications. The advantages of such smart textiles are their flexibility, their drapability and their cost-effective production. Due to the low weight of the printed conductive textiles, energy savings can also be achieved, for example in the automotive sector. Planned areas of application for the developed conductive textile products are:
- Basis for luminous surfaces for the automotive industry and upholstery furniture
- Basis for keyboards
- Components of cleanroom clothing
- Sensors and switches
- Functionalised textiles for security personnel (military, police, etc.) and occupational health and safety.
Dipl.-Ing. (FH) Katharina Gnewuch