Protective coatings for Silicone rubber keypads.
Most users of electronic products with Silicone rubber keypads as their main interface, will have seen examples of key legends being worn away due to key use. This blog post looks at the options available for customers who want to maximise the field life of their keypad.
Once a silicone Rubber keypad has been moulded and any additional painting processes of individual keys or key legends has been completed, an optional protective coating can be applied to increase the keypads resistance to abrasion.
Diamond HMI recommend that our customers coat all Keypads with either a Clear Polyurethane or Silicon lacquer. Both coatings can be applied in either matt or gloss finish and provide protection against wear of printed surfaces.
The additional cost of adding a coating is very low considering the benefits offered. If required, we can demonstrate the improvements by testing a sample of a customer keypad during the preproduction process.
Most customers choose the Polyurethane coating due to its extended life when compared to the silicon option. Polyurethane however, has a slightly different feel to that of Silicon due to its lower friction surface which translates to a different user experience.
How are Silicone Rubber keypad coatings tested?
Coatings are tested using an abrasion wear testing machine manufactured by Norman Tool Inc USA (see pic attached) these have been widely used for surface coating testing since 1964 and set the industry standard for the leading Appliance Manufacturers, Automotive Industry as well as used to test to Military Specifications.
The test involves rubbing the surface with a coarse paper and the Silicon coating passes 20 cycles were the Polyurethane passes 100 cycles, 1 cycle equates to 8000 finger pressings and so silicon would be expected to withstand 160,000 presses and the Polyurethane 800,000 presses.
Can I add hard keytops to a rubber keypad?
For customers who require the maximum wear resistance we can also attach clear resin domes to key tops. These resin tops have a typical hardness of 70 Shore `A` and are only available in a gloss finish. They add an average additional height of 0.6mm to a key (depending on surface area), however we do not recommend this for outside applications as it is not UV resistant.
We also supply the keypads with a Polycarbonate Key Top permanently attached, these also have a clear lacquer coating in gloss or matt with a H2 hardness rating and the ink can either be printed on-surface or under-surface.