Low-temperature cure conductive inks
As applications for conductive inks continue to emerge in Printed Electronics, so do the substrates that these inks are printed onto also expand. Many of these substrates such as PVDF, PVC and PC require to be processed at temperatures much lower than what a conventional Polymer Thick Film (PTF) ink can be processed.
Heat Stabilized PET has traditionally been used because of its dimensional stability at the temperatures (120°C – 140°C) required to process conventional inks. Nagase ChemteX America, LLC. (NCU) has developed a silver (CI-1095) low-temperature, curing conductive ink for Printed Electronics applications. The silver ink can be processed at 80°C for <10 minutes and achieve resistivity suitable for most Printed Electronics applications. In Figure 1, below, is a chart comparing CI-1095 processed at 80°C compared to a conventional PTF ink, CI-1036.
As can be seen in Figure 1 CI-1095 after 8 minutes at 80°C has resistivity of 0.020 ohm/sq/mil whereas the CI-1036 is 3.5x higher. This is excellent resistivity for processing at 80°C.
While the CI-1095 does process at 80°C this does NOT have a negative impact on screen life. Figure 2 shows that the CI-1095 has comparable screen life compared to CI-1036.
In testing screen life, NCU placed each material on the screen and made prints every 15 minutes for two hours. There was negligible change in dry film thickness (DFT) for the low temp ink, CI-1095, and the conventional cure ink, CI-1036. This would indicate that even with the capability to process at 80°C there is not an impact on the screen life.
While the CI-1095 can be processed at 80°C, users shouldn’t assume that being able to process at lower temperatures should equate to faster processing at conventional temperatures such as 120 – 130°C. Figure 3 demonstrates that while CI-1095 could be processed at 120°C it does not process faster. It’s the unique chemistry of the CI-1095 that allows for it to be processed at low temperature.
Adhesion is another critical factor to consider when working with substrates that must be processed at low temperatures. Table 1 shows cross-hatch adhesion testing.
Because of being able to process conductive ink at a low temperature such as 80°C this allows the potential use of substrates that couldn’t be previously used in Printed Electronics applications. Potential markets include consumer electronics, medical, automotive as well as many others.