Decorating: New Way to Apply Touch Sensors to Plastic Parts

New roll-on technology for applying touchscreen sensors to plastic parts will be presented at the K 2019 show in Düsseldorf Oct. 16-23. Leonhard Kurz will apply sensors to a washing-machine control panel using the company’s patented Functional Foil Bonding (FFB) process. FFB was presented for the first time at the Fakuma 2018 show in Germany, but a new semi-rotary variant will be displayed for the first time at K.

In all FFB applications to date, touch sensors have been applied by vertical stamping. But this transfer technique is not suitable, according to Kurz, for larger touchscreen sensors such as the 8-in. version to be demonstrated at K. Kurz therefore developed a new roll-on technology that can transfer large-area sensors without air entrapment. This was achieved by replacing the previous dispensing roller with a half-round silicone segment. This latest development of the roll-on process also led to reduced cycle times.

In the demonstration at K, the touch sensors are transported into the FFB machine, detected by a camera inspection system, and positioned precisely on the plastic panel by a robotic handling system. The system uses cleanroom technology and can be adapted to automated inline production.

The touch sensors were developed by Kurz subsidiary PolyIC and comprise silver-based metallic grid structures (metal mesh) on a PET carrier film. Both conductive and transparent, they are also flexible and can be applied to both flat and slightly 3D parts. The application at K will be backlit.

Kurz notes that touchscreens previously were applied with adhesive lamination in a relatively costly process. Alternating-climate tests reportedly have shown a risk of bubble formation due to outgassing of the plastic. Besides being more cost-effective, the FFB process reportedly does not show such defects in alternating-climate tests.