Touch Panels

Capacitive touch is now the mainstream technology in smartphones and tablets as well as other human-machine interfaces (HMIs) of electronic devices. Capacitive touch technology with Clevios™ PEDOT conductive polymers, helps the next generation touch displays to be more flexible, foldable, curved, 3D-shapeable, wearable technology.

Touch Panels

Most film-based capacitive touch sensors are still made from ITO (indium tin oxide) film that is produced by a vacuum sputtering process, a mature but energy- and capital-intensive manufacturing process.

ITO film also lacks flexibility and easily cracks from mechanical stress such as bending (Figure 1).

Clevios™ conductive polymers offer the following benefits:

  • Economic R2R wet-coating process
  • Wide choice of substrate material, e.g. PET, PC, PI etc.
  • Better stability and flexibility against mechanical stress, e.g., stylus pen or bending
  • Lower light reflection due to low refractive index, and good index matching with plastic substrates (Figure 2)
  • Lower sheet resistances, as low as 15 Ohm/sq with Clevios™ HYE hybrid materials

Together with our long-standing partners we have developed an entire value chain for Clevios™ based touch panels, from Clevios™ dispersion, via coated films, to fully functional touch panels (Figure 3).

Hiding the pattern

Conductive film requires patterning to produce capacitive touch sensors. This can either be accomplished by laser or by a wet process.

Pattern visibility is a challenge for all conductive materials such as ITO, AgNW, metal-mesh or CNT. The different optical properties of patterned (etched) and unpatterned (unetched) areas are difficult to conceal. Transmission-, color-, haze-, and refractive index-differences cause visibility which can only be concealed by adding steps to the manufacturing process. Even then, slight visibility often remains.

Cutting out the steps

Heraeus has developed a special technology to pattern Clevios™ coatings by a wet process (Figure 5). The generated patterns are invisible or hardly visible to the human eye, so there is no need for additional steps to conceal them, keeping costs lower. A masked Clevios™ film is immersed in a solution of Clevios™ Etch, which does not physically remove (etch) the layer but deactivates the conductivity while leaving the optical properties unchanged (Figure 6).

Masking can be done by an economic screen-, gravure-, or flex-printing process, or for finer structures by photoresist. An application guide is available.

During production, optical inspection by CCD is made possible by a special analytical detection method that can easily be implemented.

Clevios™ for Touch Panels

In Clevios™ PH 1000, Heraeus offers the world’s highest conductive PEDOT:PSS dispersion, boasting up to 1000 S/cm. It yields sheet resistance levels in coating formulations as low as 150 Ohm/sq with high transmission suitable for touch panel applications.

Clevios™ F 100T is a special stabilized PEDOT:PSS dispersion for formulations and coatings with improved stability in harsh environmental tests, e.g., 60/90 or 85/85.

Clevios™ F ET is one of the ready to use coating formulations that yields SR below 200 Ohm/sq at 12 micron wet film thickness.

Clevios™ F DX2 / Clevios™ XL is a new two-component coating formulation with better hardness and resistance to solvents.

Clevios™ Etch and Clevios™ Set S3 are auxiliary materials to pattern Clevios™ coated films. Clevios™ Etch is a water-soluble powder, and Clevios™ Set S3 is a printable mask (screen printing).

Lower sheet resistance

For touch sensors that require lower sheet resistances (SR) such as for larger displays, Heraeus offers Clevios™ HY E, hybrid materials of silver nanowires (AgNW) and PEDOT:PSS. Clevios™ HY E is a ready-to-use coating formulation. A top coat to protect the silver nanowires from oxidation, Clevios™ OC 1, is also offered. Clevios™ HY E can be patterned in the same way as PEDOT:PSS only based Clevios™ coatings. Read more this topic here .

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