Stretchable Electronics
EPTATECH has combined Printed Electronics and textile printing to offer new conductive and protective inks for printing stretchable electronics on fabric
ELECTRICAL PERFORMANCES UNDER STRAIN
Inks
EPTATECH provides an assorted range of materials for “Stretchable Electronics” applications, such as:
- Silver Based (micrometric flakes) Conductive Inks
- Protective/Encapsulating Inks
- Adhesive inks for Transfer Printing
All the Inks are:
- Water-based
- Screen printable
- Highly stretchable (tested up to 100% of elongation)
Protective/ encapsulating inks are used in synergy with conductive inks. Their functions are:
- Structural support/mechanical stress absorption
- Barrier to water (for washing resistance)
- Electrical insulation
Printing Technology
No elastic (TPU) membranes are used as printing substrate to be further laminated on the final product surface:
- In case of textile applications (smart-garments, wearable technology type of applications) the transfer printing technology is used to transfer, by heat and pressure, the ink layer set from a sacrificial substrate to the final fabric
- In case of other applications the printed stack of inks can be peeled-off from the sacrificial substrate for further handling
The transfer printing process is explained in the picture below.
Figure 1. – Process in the case of final application on fabric
- Ink layers and a thermoplastic glue are screen printed on a sacrificial substrate
- The ink layer set is transferred, using a heat press, by activating the thermoplastic glue (current parameters are: 180°C/4 bar/15 sec)
- The sacrificial substrate is peeled-off
- Final curing is performed (5 min at 150°C for best performances)
The adopted technology has a few advantages:
- Reliable printing on a smooth and stable (sacrificial) substrate
- Full additive and simpler process. No membrane laser cutting-out is required as the printing substrate is totally removed after the transfer of the ink stack onto the final substrate
- Better “look and feel” and comfort. No permanent intermediate substrate is left on the fabric.
Electrical performances under strain
There is no standard to evaluate stretchable conductive Inks. We test our inks with single elongations, up to 100%, and repeated cycles (typically 1000) of 0-20% elongations.
Initial sheet resistivity is <30 mOhm/square@25micron (after curing of the ink at 150°C for 5min). The below graphs show the typical resistance behavior under strain.
Figure 2. – Single stretch
Figure 3. – Continuous cycles
The above performances relate to a straight line conductive trace 150mm long/4mm wide
According to our experience many factors affect performances under strain:
- Ink silver flakes characteristics, concentration and mix
- Protective inks. Protective inks more resistant to washing exhibit a lower elasticity. This affects the overall electrical performance, especially under repeated strains
- Final fabric, in particular the weave more than the raw material
- Trace shape. Straight lines and corners are not the best performer
EPTATECH has developed base conductive inks and a few protective inks which can be customized for the specific application.
Please contact us (info@eptatech.com) to evaluate ink performances against your requirements
The offering
EPTATECH can provide either the inks or the printed layer set ready to be transferred to the final fabric. The second option is recommended for initial tests or quick feasibility studies.
The inks are sold directly by EPTATECH and are not available through our Dealer Network. In that way EPTATECH can provide direct assistance to Clients in the fine tuning of the printing processes, in the assessment of performances and in the evaluation of possible ink customizations.