Nano graphene platelet-based conductive inks

Abstract

A nano graphene platelet-based conductive ink comprising: (a) nano graphene platelets (preferably un-oxidized or pristine graphene), and (b) a liquid medium in which the nano graphene platelets are dispersed, wherein the nano graphene platelets occupy a proportion of at least 0.001% by volume based on the total ink volume. The ink can also contain a binder or matrix material and/or a surfactant. The ink may further comprise other fillers, such as carbon nanotubes, carbon nano-fibers, metal nano particles, carbon black, conductive organic species, etc. The graphene platelets preferably have an average thickness no greater than 10 nm and more preferably no greater than 1 nm. These inks can be printed to form a range of electrically or thermally conductive components.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to the field of conductive inks, and more particularly to nano graphene platelet-based inks that are electrically and thermally conductive.BACKGROUND OF THE INVENTION[0002]Conductive inks, particularly carbon-based inks, have been widely used in the manufacture of conducting elements in printed circuits and sensor electrodes. Other major markets for conductive inks include emerging applications, such as displays, backplanes, radio frequency identification (RFID), photovoltaics, lighting, disposable electronics, and memory sensors, as well as traditional thick film applications in which screen printing is used in the creation of PCBs, automobile heaters, EMI shielding, and membrane switches. There is tremendous interest in the field of RFID and printed electronics. This is because major retailers and institutions need to be able to more accurately and efficiently track inventory, and RFID and printed electronics are ...

AI Technical Summary

Benefits of technology

[0027]The presently invented conductive ink is preferably inkjet printable since inkjet printing is a cost-effective way to achieve patterns of various materials on both rigid and flexible substrates. Inkjet printing of electrically conductive nano particle-based inks offer a very practical platform for generating electrical components, such as electrodes and interconnects. More preferably, inkjet printing is conducted using a conventional, inexpensive printhead in a common desk-top printer. This type of printer typically requires the viscosity of the ink to be in the range of 3-30 mPa·S (centi-poise or cP). It is of significance to note that the viscosity of a CNT-based ink can not be in this useful range unless the CNT proportion is exceedingly low. For instance, the CNT concentration of the ink used by Song, et al. [Ref. 1] was as low as 20 μg/mL (approximately 0.002% by weight of CNTs in water). With such a low concentration, it would take several repeated printing passes (overwrites) to achieve a desired CNT amount, thickness, or property; e.g., it took 8 overwrites to achieve a sheet resistivity of 20 μΩm [FIG. 5 in Ref. 1]. By contrast, with the presently invented NGP-based ink that can carry a high NGP proportion, yet still maintaining a relatively low viscosity, one or two printing passes are sufficient to attain the same desired properties achieved with 5-20 overwrites using CNT-based inks. This implies that the printing speed of NGP-based inks would be much higher. This is on top of the fact that CNTs are extremely expensive.

[0028]Currently, certain type of specialty printer can print an ink with a solution viscosity up to 150 mPa·S and some experimental printers that are still under development can work with a viscosity up to 500 mPa·S. Even with these high-viscosity printers one would still find it difficult, if not impossible, to print CNT-based inks with a CNT content greater than 0.2% by weight since their viscosity will be greater than 1 Pa·S or 1,000 mPa·S. This is

Problems solved by technology

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