Backlighting lightpipes for display applications

• US 5,881,201 A
• Filed: 03/11/1997
• Issued: 03/09/1999
• Est. Priority Date: 03/11/1997
• Status: Expired due to Fees

• Current Assignee: CNA Holdings Incorporated (Celanese Corporation)
• Original Assignee: Hoechst Celanese Corporation (Sanofi )
• Inventors: Khanarian, Garo
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US08/815,172
• Time in Patent Office: 728 Days
• Field of Search: 385/140-146, 385/2, 385/121, 359/245, 600/182, 600/212, 600/245, 600/249, 606/13, 606/15, 250/227.31, 250/330, 250/395, 250/458.1, 250/495.1, 349/62, 349/9, 349/64, 349/96
• US Class Current: 385/146
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0041 provided in the bulk of the light guide
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity

Abstract

This invention discloses improved lightpipes for backlighting applications in liquid crystal display devices. The lightpipes comprise transparent polymers with scattering centers. A preferred composition for such lightpipes comprises a cycloolefin polymer containing scattering centers from suitable elastomers and inorganic fillers. The inventive lightpipes offer superior scattering efficiency as well as spatial uniformity of scattering and uniformity of scattering across a wide wavelength range.

Claims

1. A light guiding device suitable for display applications comprising:

(a) a light source and (b) a light guide having an entry edge for light to enter and an exit surface for light to exit, with said light source positioned at said entry edge, wherein said light guide comprises a transparent polymer and a light scattering material with said light scattering material having refractive index different from that of said transparent polymer, and wherein light from said light source scatters substantially internally within said light guide prior to exiting through said exit surface, with said scattering occurring substantially uniform over the wavelength range 400-740 nm, further wherein said light exiting through said exit surface is substantially uniform in brightness and still further wherein said light guide has an impact resistance of at least 0.5 ft-lb per inch.

2. The device of claim 1, wherein said polymer is selected from the group consisting of polyester, polycarbonate, polyacrylate, polystyrene, styrene-acrylonitrile copolymer, and polyolefin.

3. The device of claim 2, wherein said polyolefin is a polymer comprising a cycloolefin moiety.

4. The device of claim 3, wherein said polymer is a cycloolefin copolymer.

5. The composition of claim 4, wherein said copolymer is a copolymer of a cycloolefin with one or more acyclic olefins.

6. The composition of claim 5, wherein said cycloolefin is selected from the group consisting of norbornene, tetracyclododecene, bicyclo 2,2,1!hept-2-ene, 1-methylbicyclo 2,2,1!hept-2-ene, hexacyclo 6,6,1,1³,6,1¹⁰,13,0²,7,0⁹,14 !-4-heptadecene, and mixtures thereof.

7. The composition of claim 4, wherein said acyclic olefin is selected from the group consisting of ethylene, propylene, butylene, pentene and combinations thereof.

8. The device of claim 2, wherein said polymer is a polyester.

9. The device of claim 8, wherein said polyester is polyethylene terephthalate.

10. The device of claim 8, wherein said polyester is further modified with a different polyester.

11. The device of claim 1, wherein said scattering material is organic, inorganic or mixtures thereof.

12. The device of claim 11, wherein said inorganic scattering material is selected from the group consisting of alumina, silica, titanium dioxide, silicate, glass fiber and beads, mica, magnesium titanate, calcium titanate, strontium titanate, barium neodymium titanate, barium strontium titanate, magnesium zirconate and combinations thereof.

13. The device of claim 11, wherein said organic scattering material is selected from the group consisting of polyacrylate, polyester, polycarbonate, polystyrene, polystyrene acrylonitrile and polyolefin.

14. The device of claim 1, wherein said transparent polymer and said light scattering material are present in said light wave in a 85:

15 weight ratio.

15. The device of claim 1, wherein said transparent polymer and said light scattering material are present in said light wave in a 95:

5 weight ratio.

16. The device of claim 1, wherein said transparent polymer and said light scattering material are present in said light wave in a 99.99:

0.01 weight ratio.

17. The device of claim 1, wherein said scattering material has particle size in the range 0.01-10 μ

m.

18. The device of claim 1, wherein said scattering material has particle size in the range 0.04-5 μ

m.

19. The device of claim 1, wherein said scattering material has particle size in the range 1-3 μ

m.

20. The device of claim 1, wherein said light guide is molded from said transparent polymer and said scattering material.

21. The device of claim 1, wherein said light guide is extruded from said transparent polymer and said scattering material.

22. The device of claims 1, wherein said scattering material is substantially uniformly distributed within said transparent polymer in said light guide.

23. The device of claim 1, wherein said scattering material varies in distribution within said transparent polymer in said light guide.

24. The device of claim 1, wherein said light guide is a parallel faced slab lightpipe.

25. The device of claim 1, wherein said light guide is a wedge shaped lightpipe.

26. The device of claim 25, wherein said light guide further comprises a second wedge shaped light pipe in intimate contact therewith.

27. The device of claim 25, wherein said wedge shaped light pipe is thicker at its end closer to said light source and thinner at the end farther removed from said light source.

28. The device of claim 26, wherein one wedge shaped light pipe contains light scattering particles, and the other wedge shaped light pipe lacks scattering particles.