Switchable glass, also known as smart glass or privacy glass, is a technology that allows glass unit to switch between its transparent and opaque states. This effect is achieved by sandwiching laser structured PLDC (Polymer Dispersed Liquid Crystal) or SPD (Suspended Particle Devices) foil between two glass panes. In the following we explain the working principle of these foils and laser processes that are used to structure them.
PDLC and SPD Foils
PDLC and SPD foils consist of two PET films coated with ITO (Indium Tin Oxide) and an active material that changes its optical properties in response to the external electrical field.
Each PET/ITO pair constitute an electrode. When external voltage is applied, the molecules of the active material re-orient themselves in response to the electrical field. The foil becomes transparent. When voltage is removed, molecules of the active material relax and obtain random orientations. The foil becomes opaque.
For this technology to work, smart foils must be structured and cut very carefully. We use following laser processes for that:
- Ablation (or scribing)
- Full-cut and kiss-cut
Ablation Process
Ablation process is used to create insulating lines on the ITO layer. Using accurate laser focus control, we can target desired ITO layer and create insulating regions on it. When smart film is energized, these insulated regions will not switch, thus allowing selective opacity of the foil. Ablated lines are barely visible to the naked eye and measure below 40 µm under the microscope.
Full-Cut and Kiss-Cut
Full-cut refers to cut of the foil through its entire thickness. It is used to create external contour of the foil. When making full-cut, we ensure that:
- the function of the film is not compromised, e.g. two PET layers do not melt together
- the contour precisely meets desired dimensions
- is aesthetic
Kiss-cut refers to partial cut of the foil.
Kiss cut is used to create PET/ITO electrode pair. When doing kiss-cut, it is crucial that the depth of the cut is carefully controlled, so that lower ITO layer is not affected. In case lower ITO layer is damaged, smart foil will not work! When making kiss-cut, we verify and compensate height variations of the foil to ensure that kiss-cut is precise as it should be.
Application in Switchable Glass
In switchable glass, these processes are used to create patterns and sections that can independently switch between opaque and transparent states. The ability to control specific areas without damaging the conductive ITO layers ensures reliable and efficient operation of the switchable glass. This technology is widely used in privacy windows, projection screens, and energy-saving building designs.
Watch our video on the switchable glass here:
