Waveguide materials for optical touch screens
This invention relates to polymeric optical materials suitable for use in waveguide-based optical touch screen sensors. In particular, the materials should have a glass transition temperature (Tg) below a minimum operating temperature of the touch screen device. Preferably, waveguides composed of the materials are fabricated on polymer substrates, so that the waveguide assembly is flexible. In this case, the materials should have Tg below a Tg of the polymer substrate.
1. An optical waveguide when used as a component of an optical touch screen sensor, the waveguide comprising a light guiding portion on a substantially flexible substrate, wherein the light guiding portion is composed of a polymer with Tg below an operating temperature of the optical touch screen sensor.
2. An optical waveguide according to claim 1 wherein the operating temperature of the optical touch screen sensor is in the range 0° C. - 50° C.
3. An optical waveguide according to claim 2 wherein the operating temperature of the optical touch screen sensor is in the range 0° C. -35° C.
4. An optical waveguide according to claim 1 wherein the light guiding portion is composed of a polymer with Tg below 100° C., preferably below 50° C., more preferably below 25° C., and most preferably below 10° C.
5. An optical waveguide according to claim 1 wherein the optical waveguide can be bent repeatedly and reversibly through 180° with a radius of curvature that is less than 100 cm, preferably less than 10 cm, more preferably less than 1cm, and most preferably less than 2 mm.
6. An optical waveguide according to claim 1 wherein the substrate is a polymer substrate.
7. An optical waveguide according to claim 6 wherein the light guiding portion is composed of a polymer with Tg lower than a Tg of the polymer substrate.
8. An optical waveguide according to claim 6 wherein the polymer substrate has a Tg above 80° C., preferably above 150° C. and most preferably above 350° C.
9. An optical waveguide according to claim 1 wherein the light guiding portion is formed by depositing a curable liquid polymer material onto the substrate, and curing it to form a cross-linked polymer material.
10. An optical waveguide according to claim 9 wherein the curable liquid polymer material is substantially non-volatile.
11. An optical waveguide according to claim 10 wherein the curable liquid polymer material does not contain any solvent.
12. An optical waveguide according to claim 9 wherein the curable liquid polymer material is cured by a UV initiated free radical polymerisation.
13. An optical waveguide according to claim 9 wherein the curable liquid polymer material is processed by a method selected from the group consisting of UV lithography/wet etching and moulding.
14. An optical waveguide according to claim 1 wherein the polymer light guiding portion is 0.5 μm to 250 μm in thickness, preferably 3 μm to 50 μm in thickness and most preferably 5 μm to 25 μm in thickness.
15. An optical waveguide according to claim 1 wherein the substrate is 25 μm to 1 mm in thickness, preferably 75 μm to 250 μm in thickness, and most preferably about 175 μm in thickness.
16. An optical waveguide according to claim 1 further comprising a lower cladding between said polymer light guiding portion and said substrate.
17. An optical waveguide according to claim 1 further comprising an upper cladding in contact with at least a portion of said polymer light guiding portion.
18. An optical waveguide when used as a component of an optical touch screen sensor, the waveguide comprising a light guiding portion on a substantially flexible substrate, wherein the light guiding portion is composed of a polymer with Tg below an operating temperature of the optical touch screen sensor and wherein the light guiding portion is formed by depositing a substantially non-volatile curable liquid siloxane polymer onto the substrate, and curing it to form a cross-linked siloxane polymer.
19. An optical waveguide according to claim 18 wherein the light guiding portion is composed of a polymer with Tg below 50° C., more preferably below 25° C., and most preferably below 10° C.