Tribological investigation of thin polyester substrates for displays

Thin polyester films are currently used as substrates in thin flexible displays, touch-screens and flat panel displays. The advantages of using such films in various display technologies include excellent optical transparency, mechanical flexibility and they are light weight and low cost. However, little research has been reported to date on the tribological properties of such top-sheet display components. Nano-scale wear and friction experiments have been conducted in the past, mainly on polyethylene terepthalate (PET) in biaxially oriented thin solid films. The aim of this paper is to investigate the unlubricated tribologicall response of biaxially oriented PET and polyethylene napthalate (PEN) films developed for use in display device assemblies. Tests were conducted under a relatively high normal load for up to a few thousand sliding cycles. Counterfor-mal contact under pure dry sliding conditions is used by means of a pin-on-disc wear testing apparatus, with a steel ball on thin polyester rotating flat. Wear track depths were measured, after testing, with a contact-mode stylus profilometer. Ex situ microscopical studies were performed on virgin and worn surfaces using scanning electron microscopy, SEM, optical microscopy and contact-mode atomic force microscopy (AFM). The results such as values of friction coefficient and wear rates, can help the understanding of the tribological behaviour of the polymer film particularly in demanding display applications. Examples of such applications include electronic touch-drawing pads, where a stylus is repeatedly in contact, for at least a few hundred thousand cycles, with the polyester top-sheet surface, and flexible electronic touch-maps where top-surface handling conditions can be severe in some cases. (C) 2007 Elsevier B.V. All rights reserved.