Touchscreen with carbon nanotube conductive layers

Abstract

The present invention is directed to a touchscreen comprising touch side electrode and device side electrode wherein each electrode comprises an insulating substrate and an exposed electrically conductive layer, wherein said exposed electrically conductive layers are adjacent and separated by dielectric spacers, and wherein only one of the exposed electrically conductive layers comprises carbon nanotubes.

Description

FIELD OF THE INVENTION[0001]The present invention relates in general to touchscreens for electronic devices. In particular the invention provides a touchscreen comprising touch side and device side electrodes wherein each electrode comprises in order an insulating substrate, an exposed electrically conductive layer, wherein said exposed electrically conductive layers are adjacent and separated by dielectric spacers, and wherein said exposed electrically conductive layers comprise single wall carbon nanotubes and wherein said carbon nanotubes comprise covalently attached hydrophilic species.BACKGROUND OF THE INVENTION[0002]Devices such as flat-panel displays typically contain a substrate provided with an indium tin oxide (ITO) layer as a transparent electrode. The coating of ITO is carried out by vacuum sputtering methods, which involve high substrate temperature conditions up to 250° C., and therefore, glass substrates are generally used. The high cost of the fabrication methods and...

AI Technical Summary

Problems solved by technology

The high cost of the fabrication methods and the low flexibility of such electrodes, due to the brittleness of the inorganic ITO layer as well as the glass substrate, limit the range of potential applications.

However, ITO tends to crack under stress and with the result that the conductivity of the electrodes, especially for the touch side electrode, is diminished and the performance of the touchscreen degraded.

More flexible conductive polymer-containing layers have also been considered for this application, but these conductive polymers are softer and less physically durable than ITO and therefore such conductive layers tend to degrade after repeated contacts.

However, these end caps may be removed via appropriate processing techniques leaving uncapped tubules.

Thus, SWCNTs have been extremely difficult to process for various uses.

This method is limited to melt extrusion which can limit opportunities for patterning or device making.

The chemically bonded polymers identified typically have high molecular weights and could interfere with some material properties of the SWCNTs (e.g. electronic or thermal transport) via wrapping around the SWCNTs and preventing tube-tube contacts.

The conductivities achieved in these polymer composites are several orders of magnitude too low for use in most electronic devices as electronic conductors or EMI shields.

Additionally, the organic solvents used are toxic, costly and pose problems in processing.

Moreover, the polymers used or polymerized are not conductive and can impede tube-tube contact further increasing the resistivity of the composite.

This method is problematic, as it needs extremely large levels of surfactant to solubilize the SWCNTs.

The surfactant is insulating and impedes conductivity of a film deposited from this composition.

The surfactant may be washed from the film but this step adds complexity and may decrease efficiency in processing.

These materials do not provide a highly transparent and highly conductive (low sheet resistance, RS) layer.

Moreover, the chemical transformations needed to add these functional groups to the end points of the SWCNTs require additional processing steps and chemicals which can be hazardous and costly.

The method discloses functionalization of the tubule ends with various functionalization groups (acyl, aryl, aralkyl, halogen, alkyl, amino, halogen, thiol) but the end functionalization alone may not be enough to produce viable dispersions via solubilization.

The chemical transformations needed to add these functional groups to the end points of the SWCNTs require additional processing steps and chemicals which can be hazardous and costly.

PANI is a highly colored conductive polymer and may result in a conductive composite with unsatisfactory displays.

The dispersion concentrations used in these methods make it very difficult to produce images via direct deposition (inkjet etc.) techniques.

Further, such high solvent loads due to the low solids dispersions create long process times and difficulties handling the excess solvent.

In addition, these patterning methods are subtractive processes, which unnecessarily waste the SWCNT material via additional removal steps thereby incurring cost and process time.

However, the stringent requirements of high transparency, low sheet resistance, flexibility, and robustness under repeated contacts demanded by modern display devices and, especially, touchscreens is extremely difficult to attain with the TCL compositions described in the prior art.

Images