Anti-(fill in the blank) Material for Interfaces

Anti-glare • Anti-fingerprints • Anti-scratch • Anti-smudge

Is it possible to have them all? The simple answer, no, HOWEVER, there are things suppliers can do to get you pretty darn close.

First, determine what is more important on your membrane switch:

• Having a crystal clear display?
• Anti-glare surface?
• Survival in sunlight (if used outdoors)?

Crystal clear display vs. anti-glare surfaces:

Many companies want a material that is crystal clear while also being anti-glare. To ensure the display is anti-glare, a .007” thick anti-glare polyester graphic material is often used, the downside: it has a slightly matte appearance, which, as you guessed it…reduces the clarity.

There are fine and velvet (a slightly coarser texture) graphic materials, these have a textured hard coat that help resist fingerprints and smudges. If the part has a display window, a window ‘clarifier’ can be printed, this flattens the texture and gives the window a glossy finish. However, this window ‘clarifier’ does not make for a perfect display window – the ‘clarifier’ does not actually eliminate the textured surface, it just fills in the grooves in the texture, and adds a smooth, glossy look. The light passing through is still somewhat distorted by the original textured surface.

The preferred material for a graphic with a display window is polyester with a glossy hard coat. A textured hard coat can be selectively printed, leaving the window clear. This provides a much clearer window, while the printed texture hard coat helps resist fingerprints and smudges, however, it is not completely anti-glare.

Survival in sunlight: 

One other thing to consider, is whether the part will be used indoors or outdoors. Parts used outdoors must survive UV light exposure from the sun. Long exposure to sun light will degrade the polyester substrate, turning it yellow and making it brittle. The only material meant to survive UV light outdoors comes with either a fine or velvet textured hard coat. So, if the outdoor part has a need for a non-textured display window, the only option is printing the window clarifier meant for outdoor use. As mentioned above, this does not create a perfect window.

All of the materials used for graphic overlays can have a hard coat to make the front surface scratch-resistant. If a selective texture is printed, that also acts as a hard coat.

How are these issues addressed for capacitive touch sensors?

Anti-scratch:

If glass is desired – regular soda lime and borosilicate (glass) can be scratched, Gorilla Glass® is more scratch resistant however, it can still be scratched.

Standard acrylic can be scratched but there is an abrasion resistant version available. Xymox has yet to identify a distributor producing a AR (abrasion resistant) coated, 1.5mm thick acrylic sheet, as a standard product, so in the meantime, Xymox is producing 3mm thick acrylic lenses with an AR coating to customers that require it.

Crystal-clear display:

Kodak HCF material can be used for applications needing crystal-clear displays. Xymox processes Kodak HCF film coated with Heraeus PEDOT:PSS clear conductive polymer to produce a durable, flexible and transparent PCAP sensor.

Anti-glare & survival in sunlight:

Anti-glare and UV inhibitors can be coated directly onto the overlay material (ex: glass or acrylic), however, these can have a slight impact on clarity.