Du Pont

Mylar

Mylar is a type of polyester film (specifically BoPET: biaxially-oriented polyethylene terephthalate), originally developed by DuPont, Imperial Chemical Industries and Hoechst in the 1950s. In the keyboard industry, Mylar found a use as a suitable material for membranes in keyboards of that type.

Products confirmed to use Mylar include:

• Datanetics DC-50 discrete switches
• Micro Switch SC Series capacitive membrane keyboards
• Cherry solid state capacitive (metallised Mylar pads)
• NMB membrane keyboards

The patent for General Instrument S700 Series also suggests metallised Mylar for the foil covering on the foam pads.

Kapton

Kapton is polyimide film, also developed by DuPont, in the late 1960s. Kapton was specified for the spacer sheets in Datanetics batch-fabricated array keyboards. It was also used for the membrane layers of prototype Datanetics DC-50 switches, before Datanetics changed to Mylar. Mylar is also confirmed for Cherry’s membrane production line in the UK, although only for the centre spacer sheet.

Silver ink

Cherry used an off-the-shelf silver-loaded ink from DuPont in their UK membrane production line. Conductive inks are still part of DuPont’s product range.

Documentation

All documents scanned by Bitsavers unless otherwise noted.

• Mylar advertisement, Electronics, Vol. 36 No. 17, April 26 1963