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Preferred Film Orientation for Edge-Lit LED Applications

IP.com Disclosure Number: IPCOM000237546D
Publication Date: 2014-Jun-23
Document File: 2 page(s) / 28K

Publishing Venue

The IP.com Prior Art Database

Abstract

This paper describes an approach to reducing warp in certain edge-lit displays. The key finding is that transversely stretched polyethylene terephthalate (PET) films can improve resistance to warp when the transverse direction of the film (the direction with low coefficient of thermal expansion) is perpendicular to the direction of the thermal gradient.

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Preferred Film Orientation for Edge-Lit LED Applications

Optical films with orthotropic thermal expansion properties can reduce warp in certain edge-lit displays. Edge-lit displays that are lit from opposite sides (for example, left and right edges) create thermal gradients that propagate from those sides but have minimal effect in the perpendicular direction. An optical film made from polyethylene terephthalate (PET) that has been stretched in the transverse direction has a low coefficient of thermal expansion in that direction. Consequently, it warps less than polycarbonate (PC) or biaxially-stretched PET based films when the low thermal expansion direction of the transversely stretched PET is perpendicular to the direction of the thermal gradient in the display.

Thin optical films used in LCD televisions can be very sensitive to thermal gradients that television lighting and electronic systems produce. Controlling the stability of the film to avoid warp and buckling is important in controlling light output uniformity from the display. As LCD television sets evolve, manufacturers are beginning to develop light guide panel technology similar to notebook monitor design where the edge of the display is lit by LED solid-state lighting. Figure 1 shows displays illuminated from all four sides, from just the top and bottom, or from just the two sides. This figure illustrates the thermal gradients that develop. Temperatures are highest near the LEDs and decrease stead...