Graphic Overlay Materials

The issues to be considered when specifying polycarbonate are texture, scratch resistance, outdoor use, thickness, and fire ratings. You can find technical information about polycarbonate, and related overlay materials in this pdf file: GE Lexan, HP Lexan, FR Lexan, Valox PTX (heat-stabilized polyester), and Ultem (high-temperature film).

• Texture: Textured polycarbonate is frequently specified if the overlay is expected to be used indoors, and viewable transparent windows are not required for LCD or other types of display. Textures are available from fine matte’s to course velvets depending on the visual effect desired. General Electric’s “Lexan” brand sets the industry standard for polycarbonate film textures with identities such as 8b35, 8a35, 8a35f, etc.
• Scratch resistance: Hard coated polycarbonate: Polycarbonate is a relatively soft material and therefore, will easily scratch if not treated with a hard coat material. Scratches are not readily viewable when they occur on textured polycarbonate films. However, if the application requires a clear window, a hard-coated polycarbonate is nearly always appropriate. Hard coatings are available with various gloss levels depending on the application’s need for glare attenuation.
• Outdoor use: Polycarbonates formulated for UV resistance are essential if the overlay will be used outdoors. If the polycarbonate overlay is used with exposure to UV light, yellowing will occur if the polycarbonate is not outdoor rated.
• Thickness: Polycarbonate is available from .005” to .156” (and thicker)
• Fire ratings

Polycarbonate Limitations: In keypad applications, polycarbonate will fatigue and crack after approximately 100,000 key cycles.

Sabic (formerly GE) is the leading supplier of polycarbonate. Learn more.

Polyester

Polyester is the preferred overlay material in membrane switches. Autotype is the leading supplier of polyester for such applications. It is available in textured, scratch-resistant glass, and outdoor-rated options.

• Fatigue Resistance: Polyester offers superior fatigue resistance (to 1,000,000 cycles).
• Chemical Resistance: Polyester is somewhat more resistant to chemical attack than polycarbonate.
• Textures: Less extensive range of options than with polycarbonate.
• Thickness: .008” and thinner
• Fire Rating: Primarily due to their thin gauge, fire ratings are limited or non-existent (although usually unnecessary).
• Scratch resistance: Available with scratch resistance hard coats essential in clear window applications.

Polyester Limitations: the range of thicknesses, fire ratings, and textures are less extensive than polycarbonate.

Autotype is a leading supplier of polyester. Learn more.

Adhesives

Selecting the appropriate adhesive for an overlay application depends

• The second surface printed ink on the backside of the overlay,
• The surface to which the overlay will be attached,
• Environmental factors,
• Spacer stack-up requirements.

Melrose can assist you in making the proper adhesive selection if you advise us of these factors.

3m is the leading supplier of adhesives. Learn more.