Electrochromic device having a self-cleaning hydrophilic coating

• US 20030048538A1
• Filed: 09/09/2002
• Published: 03/13/2003
• Est. Priority Date: 06/25/1999
• Status: Active Grant

• Current Assignee: David J. Cammenga, John S. Anderson, William L. Tonar
• Original Assignee: David J. Cammenga, John S. Anderson, William L. Tonar
• Inventors: Cammenga, David J., Tonar, William L., Anderson, John S.
• Granted Patent: US 6,789,906 B2
• Time in Patent Office: Days
• US Class Current: 359/604
• CPC Class Codes: B60R 1/0602 comprising means for cleaning or deicing
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G02B 1/18 Coatings for keeping optical surfaces clean, e.g. hydrophobic or photo-catalytic films G02B1/16 takes precedence
• CPC Class Codes: G02B 27/0006 with means to keep optical surfaces clean, e.g. by preventing or removing dirt, stains, contamination, condensation G02B1/18 takes precedence; cleaning in general B08B
• CPC Class Codes: G02F 1/157 Structural association of cells with optical devices, e.g. reflectors or illuminating devices

Abstract

An electrochromic device is disclosed having a self-cleaning, hydrophilic optical coating. The electrochromic device preferably forms an external rearview mirror for a vehicle The coating preferably includes alternating layers of a photocatalytic material having a high index of refraction and a hydrophilic material having a low refractive index More specifically, the coating includes a first layer having a high refractive index, a second layer having a low refractive index, a third layer of titanium dioxide, and a fourth layer of silicon dioxide provided as an outermost layer. The disclosed optical coating exhibits a reflectance at the front surface of the reflective element that is less than about 20 percent, and has sufficient hydrophilic properties such that water droplets on a front surface of the optical coating exhibit a contact angle of less than about 20°.

Claims

1. A rearview mirror for a vehicle comprising:

an electrochromic mirror element having a reflectivity that may he varied in response to an applied voltage so as to exhibit at least a high reflectance state and a low reflectance state, and

a hydrophilic optical coating applied to a front surface of said electrochromic mirror element,

wherein said rearview mirror exhibits a spectral reflectance of less than 20 percent in said low reflectance state.

2. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating is sufficiently hydrophilic such that water droplets on a front surface of said optical coating exhibit a contact angle of less than about 30°

.

3. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating is sufficiently hydrophilic such that water droplets on a front surface of said optical coating exhibit a contact angle of less than about 20°

.

4. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating is sufficiently hydrophilic such that water droplets on a front surface of said optical coating exhibit a contact angle of less than about 10°

.

5. The rearview mirror as defined in claim 1, wherein said rearview mirror exhibits a C* value less than about 20 in both said high and low reflectance stales

6. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating includes an outermost hydrophilic enhancement layer having a thickness of less than about 800 Å

.

7. The rearview mirror as defined in claim 6, wherein said hydrophilic enhancement layer is made of silicon dioxide.

8. The rearview mirror as defined in claim 6, wherein said hydrophilic optical coating includes a photocatalytic layer immediately underlying said outermost hydrophilic layer.

9. The rearview mirror as defined in claim 8, wherein said photocatalytic layer is made of primarily titanium dioxide.

10. The rearview mirror as defined in claim 9, wherein said hydrophilic layer is made of primarily silicon dioxide.

11. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating includes an outermost hydrophilic enhancement layer having a thickness of less than about 500 Å

.

12. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating includes an outermost layer of silicon dioxide and a titanium dioxide layer disposed immediately behind said outermost layer

13. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating includes

a first layer having a high refractive index disposed on a front surface of reflective element,

a second layer having a low refractive index disposed on said first layer,

a third layer of titanium dioxide disposed on said second layer;

and

a fourth layer of silicon dioxide disposed on said third layer.

14. The rearview mirror as defined in claim 13, wherein said first layer includes titanium dioxide.

15. The rearview mirror as defined in claim 14, wherein said second layer includes silicon dioxide.

16. The rearview mirror as defined in claim 13, wherein said second layer includes silicon dioxide.

17. The rearview mirror as defined in claim 14, wherein said fourth layer has a thickness of less than about 800 Å

.

18. The rearview mirror as defined in claim 14, wherein said fourth layer has a thickness of less than about 500 Å

.

19. The rearview mirror as defined in claim 1, wherein said rearview mirror exhibits a spectral reflectance of less than 15 percent in said low reflectance state.

20. The rearview mirror as defined in claim 1, wherein said hydrophilic optical coating is sufficiently hydrophilic such that water droplets on a front surface of said optical coating exhibit a contact angle of less than about 20°

, and said rearview mirror exhibits a C* value less than about 20 in both said high and low reflectance states.

21. The rearview mirror as defined in claim 20, wherein said rearview mirror exhibits a spectral reflectance of less than 15 percent in said low reflectance state

22. The rearview mirror as defined in claim 21, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 800 Å

.

23. The rearview mirror as defined in claim 21, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 500 Å

24. A rearview mirror for a vehicle comprising:

an electrochromic mirror element having a reflectivity that may he varied in response to an applied voltage so as to exhibit at least a high reflectance state and a low reflectance state, and

a hydrophilic optical coating applied to a front surface of said electrochromic mirror element,

wherein said rearview mirror exhibits a C* value less than about 20 in both said high and low reflectance states.

25. The rearview mirror as defined in claim 24, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 800 Å

.

26. The rearview mirror as defined in claim 24, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 500 Å

.

27. The rearview mirror as defined in claim 24, wherein said hydrophilic optical coating is sufficiently hydrophilic such that water droplets on a front surface of said hydrophilic optical coating exhibit a contact angle of less than about 20°

.

28. An electro-optic device comprising:

an electro-optic element having a variable transmittance, said electro-optic element having a front surface and a rear surface; and

a hydrophilic optical coating comprising in sequence.

a first layer having a high refractive index.

a second layer having a low refractive index,

a third layer of titanium dioxide, and

a fourth layer of silicon dioxide provided as an outermost layer

29. The electro-optic device as defined in claim 28, wherein said first layer of said hydrophilic optical coating includes titanium dioxide.

30. The electro-optic device as defined in claim 29, wherein said second layer of said hydrophilic optical coating includes silicon dioxide.

31. The electro-optic device as defined in claim 28, wherein said second layer of said hydrophilic optical coating includes silicon dioxide.

32. The electro-optic device as defined in claim 28, wherein said electro optic element is an electrochromic element including a reflective surface so as to function as an electrochromic mirror

33. The electro-optic device as defined in claim 32, wherein said electrochromic element includes an electrochromic medium having a color that it is less absorbing of green light than other colors of light when the electrochromic element is activated.

34. The electro-optic device as defined in claim 28, wherein said electro-optic device exhibits a C* value of less than about 20

35. The electro-optic device as defined in claim 28, wherein said electro-optic device has a C* value less than about 15.

36. The electro-optic device as defined in claim 28, wherein said electro-optic device has a C* value less than about 10.

37. An electro-optic device comprising:

an electro-optic element having a variable transmittance, said electro-optic element having a front surface and a rear surface; and

a self-cleaning hydrophilic optical coating disposed on one of the front and rear surfaces of said electro-optic element, said hydrophilic optical coating comprising alternating layers of a photocatalytic material having a high index of refraction and a hydrophilic material having a low refractive index.

38. The electro-optic device as defined in claim 37, wherein said photocatalytic material is titanium dioxide.

39. The electro-optic device as defined in claim 38, wherein said hydrophilic material is silicon dioxide

40. The electro optic device as defined in claim 37, wherein said hydrophilic material is silicon dioxide.

41. The electro-optic device as defined in claim 37, wherein a first layer of said coating adjacent the finest surface of the electro-optic element is made of said photocatalytic material

42. The electro-optic device as defined in claim 37, wherein said electro-optic element includes:

front and rear substrates sealably bonded together to form a chamber, each substrate including a front and a rear surface, the front surface of said front substrate serving as the front surface of said electrochromic element;

an electrochromic medium contained in said chamber;

a transparent first electrode carried on one of the front surface of said rear substrate and said rear surface of said front substrate; and

a second electrode carried on the front surface of said rear substrate

43. The electro-optic device as defined in claim 42, wherein said electro-optic element further includes a reflector carried on the rear surface of said rear substrate.

44. The electro-optic device as defined in claim 42 wherein aid second electrode is reflective

45. The electro optic device as defined in claim 42, wherein said electrochromic medium is a solution-phase electrochromic medium.

46. An external electrochromic rearview mirror for a vehicle comprising:

front and rear elements each having front and rear surfaces and being sealably bonded in spaced-apart relation to form a chamber;

a transparent first electrode carried on one of said front surface of said rear element and said rear surface of said front element;

a second electrode carried on one of said front surface of said rear element and said rear surface of said front element, wherein either said second electrode is reflective or a separate reflector is provided on a surface of said rear element;

an electrochromic medium contained in said chamber in electrical contact with said first and second electrodes;

a first layer having a high refractive index disposed in front of said front surface of said front element;

a second layer having a low refractive index disposed on said first layer;

a third layer of a photocatalytic material disposed on said second layer, and

a fourth layer of a hydrophilic material disposed on said third layer

47. The external electrochromic rearview mirror as defined in claim 46, wherein said third layer includes titanium dioxide.

48. The external electrochromic rearview mirror as defined in claim 47, wherein said fourth layer includes silicon dioxide

49. The external electrochromic rearview mirror as defined in claim 46, wherein said fourth layer includes silicon dioxide

50. The external electrochromic rearview mirror as defined in claim 46, wherein said first layer includes titanium dioxide.

51. The external electrochromic rearview mirror as defined in claim 50, wherein said second layer includes silicon dioxide.

52. The external electrochromic rearview mirror as defined in claim 46, wherein said second layer includes silicon dioxide

53. The external electrochromic rearview mirror as defined in claim 46, wherein said fourth layer has a thickness of less than about 800 Å

.

54. The external electrochromic rearview mirror as defined in claim 46, wherein said rearview mirror is non-planar.

55. A non-planar rearview mirror for a vehicle comprising:

a non-planar mirror element including at least one bent glass element; and

a hydrophilic sol-gel coating on said bent glass element, wherein said hydrophilic sol-gel coating is applied just prior to bending of the glass element and is fired in the process of bending the glass element.

56. A method of making a non-planar rearview mirror for a vehicle comprising the steps of:

applying a hydrophilic sol-gel coating on a glass element; and

heating and bending the coated glass element.

57. A non-planar rearview mirror made using the method defined in claim 56.

58. An electrochromic device comprising an electrochromic element having a transmittance that may be varied in response to an applied voltage, said electrochromic element including a glass substrate having a rear surface coated in a transparent conductive material, and a front surface having a color suppression coating formed thereon for suppressing color imparted to the device by the transparent conductive material.

59. The electrochromic device as defined in claim 58, wherein said electrochromic element further comprises a reflective layer so as to function as a mirror having variable reflectivity.

60. The electrochromic device as defined in claim 58, wherein said color suppression coating is hydrophilic.

61. An electrochromic device comprising an electrochromic element having a transmittance that may be varied in response to an applied voltage, said electrochromic element including a glass substrate having a rear surface coated in a transparent conductive material, and a front surface having a hydrophilic coating formed thereon, wherein the thickness of said transparent conductive coating is selected for suppressing color imparted to the device by said hydrophilic coating.