Direct-write printing process of conductive paste on fiber bulks for wearable textile heaters

• Published in: Smart materials and structures 2020-08, Vol.29 (8), p.85018
• Main Authors: Shahariar, Hasan, Kim, Inhwan, Bhakta, Raj, Jur, Jesse S
• Format: Article
• Language: English
• Subjects: conductive paste; direct-write printing; e-textiles; flexible electronics; porous substrates
• ISSN: 0964-1726; 1361-665X
• DOI: 10.1088/1361-665X/ab8c25

In the printing of electronic materials for electronic textiles (e-textiles), reliability and durability of devices are of critical importance. A unique capability of a direct-write (DW) printing process is introduced that takes advantage of ink penetration in fiber bulks, owed in part to the capillary action phenomena of conductive inks on the textile. As a result of the penetration, the durability of the printed patterns improved in deformability and washability. To understand this phenomenon, the ink-to-substrate interaction of the Ag-based conductive ink on thermoplastic polyurethane (TPU) films, polyethylene terephthalate (PET) nonwoven textiles, and nylon-PET nonwoven (Evolon®) textiles are studied. Substrate properties such as surface roughness and porosity show a significant impact on the flow properties of the ink. The penetration of the conductive ink into the fiber bulk created a unique fiber-ink composite structure that is structurally more stable under mechanical deformation. Due to the high porosity and penetration to the cross-sectional direction, the patterns on the PET nonwoven textiles showed less ink spreading on the surface and higher resistance compared to a densely structured Evolon® textiles. The printed patterns were demonstrated as wearable textile heaters and showed reliable performance during mechanical deformation, wash, and cyclic heating tests. Finally, a printed heater wrap was demonstrated on the human body to explain a use case scenario for the DW process for wearable electronics.