Partially submerged bead monolayer

• US 20080037261A1
• Filed: 08/10/2006
• Published: 02/14/2008
• Est. Priority Date: 08/10/2006
• Status: Abandoned Application

• Current Assignee: Rohm and Haas Denmark Finance A/S
• Original Assignee: Eastman Kodak Company
• Inventors: Lander, Charles W., Chari, Krishnan, Lee, Junwon, Wang, Jin-Shan
• Application Number:
  US11/502,565
• Publication Number:
  US 20080037261A1
• Time in Patent Office: Days
• US Class Current: 362/326
• CPC Class Codes: G02B 5/021 the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
• CPC Class Codes: G02B 5/0268 characterized by the fabrication or manufacturing method
• CPC Class Codes: G02B 5/0284 used in reflection
• CPC Class Codes: G02B 5/128 transparent spheres being embedded in matrix
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members

Abstract

The invention provides a certain type of optical film, processes for making the film, and a backlight device containing the film. The film includes a substantially monolayer arrangement of beads partially submerged in a binder.

Claims

1. A process for forming an optical film comprising the steps of:

(a) applying to a transparent substrate a coating comprising (1) a carrier (2) an aqueous dispersible or soluble polymeric binder and (3) a bead population of desired refractive index and low polydispersity, wherein the binder is selected to have a refractive index that substantially matches that of the beads upon removal of the carrier, and wherein the relative proportions of the coating components is sufficient to provide a substantially mono layer arrangement of the beads that is partially submerged in the binder upon removal of the carrier; and

(b) removing the carrier from the coating to provide a substrate coated with a substantially mono layer arrangement of the beads that is partially submerged in the binder.

2. The process of claim 1 wherein the weight % binder is selected so as to obtain a desired degree of submersion whereby a desired angular light distribution can be obtained.

3. The process of claim 1 wherein the proportions are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 15 to 80%.

4. The process of claim 1 wherein the proportions are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 20 to 70%.

5. The process of claim 1 wherein the proportions are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 25 to 60%.

6. The process of claim 1 wherein the binder is selected to provide a sol-gel transition temperature below 30°

C.

7. The process of claim 1 wherein the binder is selected to provide a sol-gel transition temperature below 20°

C.

8. The process of claim 1 wherein the binder is selected to provide a sol/gel transition temperature below 10°

C.

9. The process of claim 1 wherein the binder comprises a gelatin.

10. The process of claim 1 wherein the binder comprises a gelatin derived from a marine species.

11. The process of claim 1 wherein the binder comprises fish gelatin.

12. The process of claim 1 wherein the refractive index of the bead is within 0.2 of that of the binder after carrier removal.

13. The process of claim 1 wherein the beads have a coefficient of variation of less than 0.2.

14. The process of claim 1 wherein the beads have a coefficient of variation of less than 0.15.

15. The process of claim 1 wherein the carrier is water.

16. The process of claim 1 wherein the binder is subjected to a crosslinking step.

17. The process of claim 1 wherein the carrier is removed by drying in air and the surface tension at the air/coating interface is at least 25 dynes/cm.

18. The process of claim 1 wherein the refractive index of the beads and the binder is at least 1.2.

19. A light redirecting device comprising in order:

(a) a light source and

(b) an optical film which comprises, in the direction of light travel, a transparent substrate bearing a layer containing a bead population of desired refractive index and low polydispersity disposed in an aqueous dispersible or soluble polymeric binder, wherein;

the bead refractive index is matched to the binder,

the bead population is present in a substantially monolayer arrangement of the beads with the beads partially submerged in the binder; and

(c) a transparent medium exhibiting a refractive index at least 0.2 less than that of the bead population.

20. The device of claim 19 wherein the binder comprises gelatin.

21. The device of claim 19 wherein the binder comprises gelatin having a sol-gel temperature less than 30°

C.

22. The device of claim 19 wherein the binder comprises gelatin having a sol-gel temperature less than 20°

C.

23. The device of claim 19 wherein the binder comprises gelatin having a sol-gel temperature less than 10°

C.

24. The device of claim 19 wherein the binder comprises fish gelatin.

25. The device of claim 19 wherein the binder is a gelatin that comprises an imino content of less than 20% by weight.

26. The device of claim 19 wherein the beads have an average diameter of from 1 to 20 μ

m.

27. The device of claim 19 wherein the proportions of bead and binder are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 15 to 80%.

28. The device of claim 19 wherein the proportions of bead and binder are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 20 to 70%.

29. The device of claim 19 wherein the proportions of bead and binder are selected to provide a substantially mono-layer arrangement of the beads that is partially submerged in the binder so that the weight % binder is from 25 to 60%.

30. The device of claim 19 wherein the beads are ellipsoidal.

31. The device of claim 19 wherein the beads are spherical.

32. The device of claim 19 wherein the beads contain a polymer or copolymer based on one selected from styrene, acrylate, methacrylate, and vinylidene chloride.

33. The device of claim 19 wherein the beads are made by the process of “

limited coalescence”

.

34. The device of claim 19 wherein a diffusive component providing uniform illumination and hiding the light source appearance is located between the light source (a) and the optical film (b),

35. The device of claim 34 additionally comprising a reflective polarizer.

36. The device of claim 19 wherein a component (d) comprises a pixelated light-gating device creating images.

37. An optical film which comprises a transparent substrate bearing a layer containing a bead population of desired refractive index and low polydispersity disposed in an aqueous dispersible or soluble polymeric binder, wherein:

the bead refractive index is matched to the binder,

the bead population is present in a substantially monolayer arrangement of the beads with the beads partially submerged in the binder.

38. A process for forming an optical film comprising the steps of:

(a) applying to a substrate a coating comprising a polymer in a solvent;

(b) drying the coating in a humid atmosphere to create a micro-voided polymer film;

(c) coating a curable composition over the micro-voided polymer film;

(d) curing the curable composition by heat or by radiation; and

(e) separating the cured optical film composition from the micro-voided polymer film.