Electrochromic device having a self-cleaning hydrophilic coating

• US 6,447,123 B2
• Filed: 01/19/2001
• Issued: 09/10/2002
• 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:
  US09/765,986
• Publication Number:
  US 20010021066A1
• Time in Patent Office: 599 Days
• Field of Search: 359/604, 359/602, 359/603, 359/601, 359/265, 359/266, 359/267, 359/272, 359/275, 359/582, 359/586
• 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. 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.

2. The electro-optic device as defined in claim 1, wherein said photocatalytic material is titanium dioxide.

3. The electro-optic device as defined in claim 2, wherein said hydrophilic material is silicon dioxide.

4. The electro-optic device as defined in claim 1, wherein said hydrophilic material is silicon dioxide.

5. The electro-optic device as defined in claim 1, wherein a first layer of said coating adjacent the front surface of the electro-optic element is made of said photocatalytic material.

6. The electro-optic device as defined in claim 1, 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.

7. The electro-optic device as defined in claim 6, wherein said electro-optic element further includes a reflector carried on the rear surface of said rear substrate.

8. The electro-optic device as defined in claim 6, wherein said second electrode is reflective.

9. The electro-optic device as defined in claim 6, wherein said electrochromic medium is a solution-phase electrochromic medium.

10. 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.

11. The external electrochromic rearview mirror as defined in claim 10, wherein said third layer includes titanium dioxide.

12. The external electrochromic rearview mirror as defined in claim 11, wherein said fourth layer includes silicon dioxide.

13. The external electrochromic rearview mirror as defined in claim 10, wherein said fourth layer includes silicon dioxide.

14. The external electrochromic rearview mirror as defined in claim 10, wherein said first layer includes titanium dioxide.

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

16. The external electrochromic rearview mirror as defined in claim 10, wherein said second layer includes silicon dioxide.

17. The external electrochromic rearview mirror as defined in claim 10, wherein said fourth layer has a thickness of less than about 800 Å

.

18. The external electrochromic rearview mirror as defined in claim 10, wherein said rearview mirror is non-planar.