First and foremost, we should always define the colors of the silicone rubber keypads by the process; molded colors or printed colors. The natural color of the silicone material is translucent; the colors of the finished products can be defined by adding color pigments, and/or by printing. PANTONE and RAL are two color standards generally use.
There are several processes for molded colors: inserted buttons, color bleeding buttons and combination.
Picture 1 and 2 show the inserted button keypads. The colors of the buttons are defined individually. Colored key top molded by auxiliary mold and separated in advance, then co-molding the colored key tops with the main mold (or rubber base). This process is good for bezel-less applications.
Inserted Button Color Rubber Keypads
Molding Process is good for bezel-less applications
Picture 3 below shows color bleeding method. Simply mounted different colors at targeted areas, then compression molded. This is a less cost solution but must go with a housing to hide the bleed from one to the next.
Almost all keypad graphics, either positive or negative image, are surface printed using a special silicone ink that is actually bonded to the keypad. Graphics are permanently applied to the top surfaces of rubber switches by curing in high-temperature ovens after printing. Special attention must be given to key top design if negative-image graphics are desired due to the complexities of printing on concave or convex key tops. Each graphic color requires its own individual screen, and represents an additional step in the manufacturing process. Pantone numbers are normally used for specifying graphic colors, and color chips can be matched if Pantone/RAL numbers are not suitable/available for a given application.
If the keypad graphics are going to be exposed to conditions more severe than normal abrasion (i.e.: operator wearing gloves) or subjected to an excessive number of actuations, they can be coated with translucent ink (matte or shiny finish) to enhance legend life. Over coating typically doubles the life of silk-screened graphics and two overcoats of translucent ink can be applied if necessary. However, over coating does increase the actuation force of keypad because the web area is covered with layers of coating ink. The most common coating is Silicone, PU (Polyurethane) or Epoxy (Resin) Coating.
General measurement method: a solution widely adopted in the field of rubber keypads so called: Norman Tool Continuous paper tape with 175 gram loading cell.
Printing: approx. 5 cycles
Overcoat Silicone = 10 cycles
Overcoat PU = 100 cycles
Another popular process is laser etched graphic keypad, see picture below. This is normally for keypads which require backlight features. It provides a very durable finish as well.
Do you use rubber keypads for your applications or do you prefer membrane switches or touch screens? If you use rubber keypads, what do you experience with rubber keypads when selecting colors?