Comparison of conductive polymer PEDOT:PSS,
which is the base for Denatron, with other materials by application
Transparent touchscreens, which are used in devices such as smartphones and tablets, have become familiar and common. Devices “that you just touch to control” are continuously spreading; for example, sophisticated flat touch switches have been adopted for the operation of automobile audio equipment recently.
Sensor electrodes are distributed across and laid on touch panels and touch switches (patterning) so that these devices can sense when a human finger touches them.
Sensor electrodes need to be made of conductive material whose transparency is high enough for invisibility. We’ll summarize typical materials used for such applications.
| Sputtered ITO film (indium tin oxide) |
Silver nanowire film | Silver mesh | PEDOT:PSS film | |
|---|---|---|---|---|
| Conductivity | good | good | excellent | good |
| Transparency | good / Yellow |
acceptable - good / Silver |
good | acceptable - good / Blue |
| Haze | good | acceptable | acceptable | good |
| Durability | excellent | good | excellent | acceptable → excellent |
| Flexibility | poor | good | good | good |
| Flatness | acceptable | acceptable | poor | good → excellent |
| Processing | Sputtering | Coating or printing | puttering or printing | Coating or printing |
| Firing temperature | High temperature (firing) | High temperature or application of pressure |
High temperature | Low temperature （drying/curing） |
| Patterning | Photolithography | Printing or Photolithography |
Photolithography | Printing or Photolithography |
| Productivity | acceptable | excellent | acceptable | excellent |
| Ability to be used on larger areas and various shapes |
acceptable | good | excellent | good → excellent |
| Stable supply of raw materials |
acceptable | excellent | excellent | excellent |
| Usability with different substrates |
acceptable | good | good | acceptable → good |
| Sputtered ITO film (indium tin oxide) |
Silver nanowire film | Silver mesh | PEDOT:PSS film |
“→” means that it can be improved with our formulation techniques.
ITO is widely used in touchscreens on smartphones because of its high transparency and superior durability. Specialized sputtering equipment is required to form conductive film, which increases manufacturing costs. In addition, ITO is not suitable for curved surfaces as it cracks if bent.
There is a concern about future supplies of the material as ITO contains the rare metal indium. Therefore, the development of alternative materials is in progress.
Applications for silver nanowire are expanding because of its good conductivity and flexibility, which allows the material to be used for more applications besides flat surfaces.
High-temperature processing and the application of pressure are required to make dispersed wires stick together.
The wire tips are sharp, which may damage films if the overlaid film is thin.
Sliver mesh is an extremely conductive and highly durable material.
But, the thickness of the mesh can be visible on the surface, which makes silver mesh inferior in flatness to other materials.
PEDOT:PSS is superior in flatness and haze, flexible, and easy to make into a conductive film with wet process.
The desired conductivity can be achieved just by vaporizing the solvent. Therefore, PEDOT:PSS can also be applied to films that can withstand temperatures of only 70°C or so. It is eco/human-friendly as it is a water-based material and is biocompatible.
Static electricity is fatal at manufacturing sites for TV/smartphone displays and other electronic devices. Static electricity can damage the products and make dust stick to the products. Static electricity is nothing but a headache.
Static electricity is caused by instantly discharging an electric charge that has been imbalanced (charged) on some surfaces by making two distinct materials contact and separate.
To prevent static electricity, conductive materials are coated on surfaces, which prevents electricity from becoming imbalanced (charged).
Here is a table to summarize typical materials for antistatic applications.
| Surfactants | Polypyrrole, polyaniline | PEDOT:PSS (polythiophene) | |
|---|---|---|---|
| Conductivity | acceptable | good | excellent |
| Transparency | excellent | acceptable | excellent |
| Durability | acceptable | poor → acceptable | acceptable → good |
| Contamination on contact surface |
Somewhat high | Low | Extremely low |
| Stability in a low-humidity environment |
poor, Ionic conduction | excellent, Electronic conduction | excellent, Electronic conduction |
| Processing | Coating Kneading |
Coating Kneading |
Coating |
| Necessary quantity | High | High | Low |
| Material cost | excellent | good | acceptable |
| Main solvent | Water-based or solvent-based |
Solvent-based | Water-based |
| Usability with different substrates |
acceptable → excellent | acceptable → excellent | acceptable → excellent |
| Surfactants | Polypyrrole, polyaniline | PEDOT:PSS (polythiophene) |
“→” means that it can be improved with our formulation techniques.
These are less expensive and widely used. But, they may not work well in a cleanroom where humidity is low because their mechanism for discharging electricity relies on ionic conduction through the absorption of water (moisture) near the surface of the material.
These are a kind of conductive polymer and possess conductivity by themselves, which enables them to stably function under a low-humidity environment.
As for their disadvantages, they are easily colored to some extent and are not so durable.
This is a polythiophene-based conductive coating material, superior in conductivity and transparency. Its feature is that it stably functions even in a low-humidity environment.
Although the cost of PEDOT:PSS is relatively high compared to other materials, the necessary quantity is low, and a film with a thickness of 0.03 μm is good enough to maintain its conductivity.
