Electrochromic device having a self-cleaning hydrophilic coating

• US 6,193,378 B1
• Filed: 11/05/1999
• Issued: 02/27/2001
• Est. Priority Date: 06/25/1999
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Cammenga, David J., Tonar, William L., Anderson, John S.
• Primary Examiner(s): SIKDER, MOHAMMAD YUNUS
• Application Number:
  US09/435,266
• Time in Patent Office: 480 Days
• Field of Search: 359/603, 359/604, 359/586, 359/587, 359/589, 359/883, 359/884, 359/265, 359/512, 428/325, 428/428
• US Class Current: 359/603
• 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 1/105 Protective coatings
• 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:

a variable reflectance mirror element having a reflectivity that varies 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 mirror element,

wherein said rearview mirror exhibits a reflectance of less than 20 percent in said low reflectance state, and

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

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 hydrophilic optical coating includes an outermost hydrophilic enhancement layer having a thickness of less than about 800 Å

.

6. The rearview mirror as defined in claim 5, wherein said hydrophilic enhancement layer is made of silicon dioxide.

7. The rearview mirror as defined in claim 5, wherein said hydrophilic optical coating includes a photocatalytic layer immediately underlying said outermost hydrophilic layer.

8. The rearview mirror as defined in claim 7, wherein said photocatalytic layer is made of primarily titanium dioxide.

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

10. 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

.

11. 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 immnediately behind said outermost layer.

12. 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.

13. The rearview mirror as defined in claim 12, wherein said first layer includes titanium dioxide.

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

15. The rearview mirror as defined in claim 12, wherein said second layer includes silicon dioxide.

16. The rearview mirror as defined in claim 13, wherein said fourth layer has a thickness of less than about 800 Å

.

17. The rearview mirror as defined in claim 13, wherein said fourth layer has a thickness of less than about 500 Å

.

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

19. 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.

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

21. The rearview mirror as defined in claim 20, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 800 Å

.

22. The rearview mirror as defined in claim 20, 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 1, wherein said variable reflectance mirror element is an electrochromic mirror.

23. A rearview mirror for a vehicle comprising:

a variable reflectance mirror element having a reflectivity that varies 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 mirror element,

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

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 ot less than about 30°

.

24. The rearview mirror as defined in claim 23, wherein said hydrophilic optical coating includes an outermost hydrophilic layer having a thickness of less than about 800 Å

.

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

.

26. The rearview mirror as defined in claim 23, 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. The rearview mirror as defined in claim 23, wherein said variable reflectance mirror element is an electrochromic mirror.

29. An electrochromic device comprising an electrochromic element having a transmittance that varies 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, wherein said electrochromic device exhibits a C* value less than about 20 in both high and low transmittance states and wherein said hydrophilic coating is sufficiently hydrophilic such that water droplets on a front surface of said hydrophilic coating exhibit a contact angle of less than about 30°

.