U.S. patent application number 09/765986 was filed with the patent office on 2001-09-13 for electrochromic device having a self-cleaning hydrophilic coating.
Invention is credited to Anderson, John S., Cammenga, David J., Tonar, William L..
Application Number | 20010021066 09/765986 |
Document ID | / |
Family ID | 26838775 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021066 |
Kind Code |
A1 |
Tonar, William L. ; et
al. |
September 13, 2001 |
Electrochromic device having a self-cleaning hydrophilic
coating
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.degree..
Inventors: |
Tonar, William L.; (Holland,
MI) ; Anderson, John S.; (Holland, MI) ;
Cammenga, David J.; (Zeeland, MI) |
Correspondence
Address: |
FACTOR & PARTNERS, LLC
1327 W. WASHINGTON BLVD.
SUITE 5G/H
CHICAGO
IL
60607
US
|
Family ID: |
26838775 |
Appl. No.: |
09/765986 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09765986 |
Jan 19, 2001 |
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09435266 |
Nov 5, 1999 |
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6193378 |
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60141080 |
Jun 25, 1999 |
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Current U.S.
Class: |
359/604 ;
359/265; 359/601 |
Current CPC
Class: |
B60R 1/088 20130101;
G02B 27/0006 20130101; B60R 1/0602 20130101; G02F 1/157 20130101;
G02B 1/18 20150115 |
Class at
Publication: |
359/604 ;
359/601; 359/265 |
International
Class: |
G02F 001/15 |
Claims
The invention claimed is:
1. A rearview mirror for a vehicle comprising: an electrochromic
mirror element having a reflectivity that may be 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.degree..
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.degree..
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.degree..
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 states.
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
.ANG..
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
.ANG..
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 .ANG..
18. The rearview mirror as defined in claim 14, wherein said fourth
layer has a thickness of less than about 500 .ANG..
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.degree., 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 .ANG..
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 .ANG..
24. A rearview mirror for a vehicle comprising: an electrochromic
mirror element having a reflectivity that may be 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 .ANG..
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 .ANG..
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.degree..
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 front 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 said
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 .ANG..
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) on U.S. Provisional Patent Application No. 60/141,080,
entitled "AN ELECTROCHROMIC DEVICE HAVING A SELF-CLEANING
HYDROPHILIC COATING," and filed on Jun. 25, 1999, the entire
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to electrochromic
devices, and more specifically relates to electrochromic rearview
mirrors of a vehicle.
[0003] To enable water droplets and mist to be readily removed from
the windows of a vehicle, the windows are typically coated with a
hydrophobic material that causes the water droplets to bead up on
the outer surface of the window. These water beads are then either
swept away by windshield wipers or are blown off the window as the
vehicle moves.
[0004] It is equally desirable to clear external rearview mirrors
of water. However, if a hydrophobic coating is applied to the
external mirrors, the water beads formed on their surfaces cannot
be effectively blown off since such mirrors are relatively shielded
from direct airflow resulting from vehicle movement. Thus, water
droplets or beads that are allowed to form on the surface of the
mirrors remain on the mirror until they evaporate or grow in size
until they fall from their own weight. These water droplets act as
small lenses and distort the image reflected to the driver.
Further, when the water droplets evaporate, water spots are left on
the mirror, which are nearly as distracting as the water droplets
that left the spots. In fog or high humidity, mist forms on the
surfaces of the external mirrors. Such a mist can be so dense that
it effectively renders the mirrors virtually unusable.
[0005] In an attempt to overcome the above-noted problems, mirror
manufacturers have provided a hydrophilic coating on the outer
surface of the external mirrors. See U.S. Pat. No. 5,594,585. One
such hydrophilic coating includes a single layer of silicon dioxide
(SiO.sub.2). The SiO.sub.2 layer is relatively porous. Water on the
mirror is absorbed uniformly across the surface of the mirror into
the pores of the SiO.sub.2 layer and subsequently evaporates
leaving no water spots. One problem with such single layer coatings
of SiO.sub.2 is that oil, grease, and other contaminants can also
fill the pores of the SiO.sub.2 layer. Many such contaminants,
particularly hydrocarbons like oil and grease, do not readily
evaporate and hence clog the pores of the SiO.sub.2 layer. When the
pores of the SiO.sub.2 layer become clogged with car wax, oil, and
grease, the mirror surface becomes hydrophobic and hence the water
on the mirror tends to bead leading to the problems noted
above.
[0006] A solution to the above problem pertaining to hydrophilic
layers is to form the coating of a relatively thick layer (e.g.,
about 1000-3000 .ANG. or more) of titanium dioxide (TiO.sub.2). See
European Patent Application Publication No. EPO 816 466 A1. This
coating exhibits photocatalytic properties when exposed to
ultraviolet (UV) radiation. More specifically, the coating absorbs
UV photons and, in the presence of water, generates highly reactive
hydroxyl radicals that tend to oxidize organic materials that have
collected in its pores or on its surface. Consequently,
hydrocarbons, such as oil and grease, that have collected on the
mirror are converted to carbon dioxide (CO.sub.2) and hence is
eventually removed from the mirror whenever UV radiation impinges
upon the mirror surface. This particular coating is thus a
self-cleaning hydrophilic coating.
[0007] One measure of the hydrophilicity of a particular coating is
to measure the contact angle that the sides of a water drop form
with the surface of the coating. An acceptable level of
hydrophilicity is present in a mirror when the contact angle is
less than about 30.degree., and more preferably, the hydrophilicity
is less than about 20.degree.. The above self-cleaning hydrophilic
coating exhibits contact angles that decrease when exposed to UV
radiation as a result of the self-cleaning action and the
hydrophilic effect of the coating. The hydrophilic effect of this
coating, however, tends to reverse over time when the mirror is not
exposed to UV radiation.
[0008] The above self-cleaning hydrophilic coating can be improved
by providing a film of about 150 to 1000 .ANG. of SiO.sub.2 on top
of the relatively thick TiO.sub.2 layer. See U.S. Pat. No.
5,854,708. This seems to enhance the self-cleaning nature of the
TiO.sub.2 layer by reducing the dosage of UV radiation required and
by maintaining the hydrophilic effect of the mirror over a longer
period of time after the mirror is no longer exposed to UV
radiation.
[0009] While the above hydrophilic coatings work well on
conventional rearview mirrors having a chrome or silver layer on
the rear surface of a glass substrate, they have not been
considered for use on electrochromic mirrors for several reasons. A
first reason is that many of the above-noted hydrophilic coatings
introduce colored double images and increase the low-end
reflectivity of the electrochromic mirror. For example,
commercially available, outside electrochromic mirrors exist that
have a low-end reflectivity of about 10 percent and a high-end
reflectivity of about 50 to 65 percent. By providing a hydrophilic
coating including a material such as TiO.sub.2, which has a high
index of refraction, on a glass surface of the mirror, a
significant amount of the incident light is reflected at the
glass/TiO.sub.2 layer interface regardless of the variable
reflectivity level of the mirror. Thus, the low-end reflectivity
would be increased accordingly. Such a higher low-end reflectivity
obviously significantly reduces the range of variable reflectance
the mirror exhibits and thus reduces the effectiveness of the
mirror in reducing annoying glare from the headlights of rearward
vehicles.
[0010] Another reason that the prior hydrophilic coatings have not
been considered for use on electrochromic elements is that they
impart significant coloration problems. Coatings such as those
having a 1000 .ANG. layer of TiO.sub.2 covered with a 150 .ANG.
layer of SiO.sub.2, exhibit a very purple hue. When used in a
conventional mirror having chrome or silver applied to the rear
surface of a glass element, such coloration is effectively reduced
by the highly reflective chrome or silver layer, since the color
neutral reflections from the highly reflective layer overwhelm the
coloration of the lower reflectivity, hydrophilic coating layer.
However, if used on an electrochromic element, such a hydrophilic
coating would impart a very objectionable coloration, which is made
worse by other components in the electrochromic element that can
also introduce color.
[0011] Due to the problems associated with providing a hydrophilic
coating made of TiO.sub.2 on an electrochromic mirror,
manufacturers of such mirrors have opted to not use such
hydrophilic coatings. As a result, electrochromic mirrors suffer
from the above-noted adverse consequences caused by water drops and
mist.
SUMMARY OF THE INVENTION
[0012] Accordingly, it is an aspect of the present invention to
solve the above problems by providing a hydrophilic coating
suitable for use on an electrochromic device, particularly for an
electrochromic mirror. To achieve these and other aspects and
advantages, a rearview mirror according to the present invention
comprises an electrochromic mirror element having a reflectivity
that may be varied in response to an applied voltage so as to
exhibit at least a high reflectance state and low reflectance
state, and a hydrophilic optical coating applied to a front surface
of the electrochromic mirror element. The rearview mirror
preferably exhibits a spectral reflectance of less than 20 percent
in said low reflectance state, and also preferably exhibits a C*
value less than about 20 in both said high and low reflectance
states so as to exhibit substantial color neutrality.
[0013] These and other features, advantages, and objects of the
present invention will be further understood and appreciated by
those skilled in the art by reference to the following
specification, claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings:
[0015] FIG. 1 is a front perspective view of an external
electrochromic rearview mirror assembly constructed in accordance
with the present invention; and
[0016] FIG. 2 is a cross section of the external electrochromic
rearview mirror assembly shown in FIG. 1 along line II-II.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIG. 1 shows an external electrochromic rearview mirror
assembly 10 constructed in accordance with the present invention.
As shown, mirror assembly 10 generally includes a housing 15 and a
mirror 20 movably mounted in housing 15. Housing 15 may have any
conventional structure suitably adapted for mounting assembly 10 to
the exterior of a vehicle.
[0018] FIG. 2 shows an exemplary construction of mirror 20. As
broadly described herein, mirror 20 includes a reflective element
100 having a reflectivity that may be varied in response to an
applied voltage and an optical coating 130 applied to a front
surface 112a of reflective element 100. Reflective element 100
preferably includes a first (or front) element 112 and a second (or
rear) element 114 sealably bonded in spaced-apart relation to
define a chamber. Front element 112 has a front surface 112a and a
rear surface 112b, and rear element 114 has a front surface 114a
and a rear surface 114b. For purposes of further reference, front
surface 112a of front element 112 shall be referred to as the first
surface, rear surface 112b of front element 112 shall be referred
to as the second surface, front surface 114a of rear element 114
shall be referred to as the third surface, and rear surface 114b of
rear element 114 shall be referred to as the fourth surface of
reflective element 100. Preferably, both elements 112 and 114 are
transparent and are sealably bonded by means of a seal member
116.
[0019] Reflective element 100 also includes a transparent first
electrode 118 carried on one of second surface 112b and third
surface 114a, and a second electrode 120 carried on one of second
surface 112b and third surface 114a. Second electrode 120 may be
reflective or transflective, or a separate reflector 122 may be
provided on fourth surface 114b of mirror 100 in which case
electrode 120 would be transparent. Preferably, however, second
electrode 120 is reflective or transflective and the layer
referenced by numeral 122 is an opaque layer or omitted entirely.
Reflective element 100 also includes an electrochromic medium 124
contained in the chamber in electrical contact with first and
second electrodes 118 and 120.
[0020] Electrochromic medium 124 includes electrochromic anodic and
cathodic materials that can be grouped into the following
categories:
[0021] (i) Single layer--the electrochromic medium is a single
layer of material which may include small nonhomogeneous regions
and includes solution-phase devices where a material is contained
in solution in the ionically conducting electrolyte and remains in
solution in the electrolyte when electrochemically oxidized or
reduced. Solution-phase electroactive materials may be contained in
the continuous solution phase of a cross-linked polymer matrix in
accordance with the teachings of U.S. patent application Ser. No.
08/616,967, entitled "IMPROVED ELECTROCHROMIC LAYER AND DEVICES
COMPRISING SAME" or International Patent Application No.
PCT/US98/05570 entitled "ELECTROCHROMIC POLYMERIC SOLID FILMS,
MANUFACTURING ELECTROCHROMIC DEVICES USING SUCH SOLID FILMS, AND
PROCESSES FOR MAKING SUCH SOLID FILMS AND DEVICES."
[0022] At least three electroactive materials, at least two of
which are electrochromic, can be combined to give a pre-selected
color as described in U.S. patent application Ser. No. 08/832,596
entitled "AN IMPROVED ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A
PRE-SELECTED COLOR."
[0023] The anodic and cathodic materials can be combined or linked
by a bridging unit as described in International Application No.
PCT/WO97/EP498 entitled "ELECTROCHROMIC SYSTEM." It is also
possible to link anodic materials or cathodic materials by similar
methods. The concepts described in these applications can further
be combined to yield a variety of electrochromic materials that are
linked.
[0024] Additionally, a single layer medium includes the medium
where the anodic and cathodic materials can be incorporated into
the polymer matrix as described in International Application No.
PCT/WO98/EP3862 entitled "ELECTROCHROMIC POLYMER SYSTEM" or
International Patent Application No. PCT/US98/05570 entitled
"ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURING ELECTROCHROMIC
DEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR MAKING SUCH SOLID
FILMS AND DEVICES."
[0025] Also included is a medium where one or more materials in the
medium undergoes a change in phase during the operation of the
device, for example, a deposition system where a material contained
in solution in the ionically conducting electrolyte, which forms a
layer or partial layer on the electronically conducting electrode
when electrochemically oxidized or reduced.
[0026] (ii) Multilayer--the medium is made up in layers and
includes at least one material attached directly to an
electronically conducting electrode or confined in close proximity
thereto, which remains attached or confined when electrochemically
oxidized or reduced. Examples of this type of electrochromic medium
are the metal oxide films, such as tungsten oxide, iridium oxide,
nickel oxide, and vanadium oxide. A medium, which contains one or
more organic electrochromic layers, such as polythiophene,
polyaniline, or polypyrrole attached to the electrode, would also
be considered a multilayer medium.
[0027] In addition, the electrochromic medium may also contain
other materials, such as light absorbers, light stabilizers,
thermal stabilizers, antioxidants, thickeners, or viscosity
modifiers.
[0028] Because reflective element 100 may have essentially any
structure, the details of such -structures are not further
described. Examples of preferred electrochromic mirror
constructions are disclosed in U.S. Pat. No. 4,902,108, entitled
"SINGLECOMPARTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC
DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOF," issued Feb.
20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled
"AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES," issued
May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799,
entitled "VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR," issued Jul.
7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled
"ELECTRO-OPTIC DEVICE," issued Apr. 13, 1993, to H. J. Byker et
al.; U.S. Pat. No. 5,204,778, entitled "CONTROL SYSTEM FOR
AUTOMATIC REARVIEW MIRRORS," issued Apr. 20, 1993, to J. H.
Bechtel; U.S. Pat. No. 5,278,693, entitled "TINTED SOLUTION-PHASE
ELECTROCHROMIC MIRRORS," issued Jan. 11, 1994, to D. A. Theiste et
al.; U.S. Pat. No. 5,280,380, entitled "UV-STABILIZED COMPOSITIONS
AND METHODS," issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No.
5,282,077, entitled "VARIABLE REFLECTANCE MIRROR," issued Jan. 25,
1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled
"BIPYRIDINIUM SALT SOLUTIONS," issued Mar. 15, 1994, to H. J.
Byker; U.S. Pat. No. 5,336,448, entitled "ELECTROCHROMIC DEVICES
WITH BIPYRIDINIUM SALT SOLUTIONS," issued Aug. 9, 1994, to H. J.
Byker; U.S. Pat. No. 5,434,407, entitled "AUTOMATIC REARVIEW MIRROR
INCORPORATING LIGHT PIPE," issued Jan. 18, 1995, to F. T. Bauer et
al.; U.S. Pat. No. 5,448,397, entitled "OUTSIDE AUTOMATIC REARVIEW
MIRROR FOR AUTOMOTIVE VEHICLES," issued Sep. 5, 1995, to W. L.
Tonar; U.S. Pat. No. 5,451,822, entitled "ELECTRONIC CONTROL
SYSTEM," issued Sep. 19, 1995, to J. H. Bechtel et al.; U.S. Pat.
No. 5,818,625, entitled "ELECTROCHROMIC REARVIEW MIRROR
INCORPORATING A THIRD SURFACE METAL REFLECTOR," by Jeffrey A.
Forgette et al. ; and U.S. patent application Ser. No. 09/158,423,
entitled "IMPROVED SEAL FOR ELECTROCHROMIC DEVICES," filed on Sep.
21, 1998. Each of these patents and the patent application are
commonly assigned with the present invention and the disclosures of
each, including the references contained therein, are hereby
incorporated herein in their entirety by reference.
[0029] If the mirror assembly includes a signal light, display, or
other indicia behind the reflective electrode or reflective layer
of reflective element 100, reflective element 100 is preferably
constructed as disclosed in commonly assigned U.S. patent
application Ser. No. 09/311,955, entitled "ELECTROCHROMIC REARVIEW
MIRROR INCORPORATING A THIRD SURFACE METAL REFLECTOR AND A
DISPLAY/SIGNAL LIGHT," filed on May 14, 1999, by W. L. Tonar et
al., the disclosure of which is incorporated herein by reference.
If reflective element 100 is convex or aspheric, as is common for
passenger-side external rearview mirrors as well as external
driver-side rearview mirrors of cars in Japan and Europe,
reflective element 100 may be made using thinner elements 112 and
114 while using a polymer matrix in the chamber formed therebetween
as is disclosed in commonly assigned U.S. patent application Ser.
No. 08/834,783 entitled "AN ELECTROCHROMIC MIRROR WITH TWO THIN
GLASS ELEMENTS AND A GELLED ELECTROCHROMIC MEDIUM," filed on Apr.
2, 1997. The entire disclosure, including the references contained
therein, of this U.S. patent application is incorporated herein by
reference. The addition of the combined reflector/electrode 120
onto third surface 114a of reflective element 100 further helps
remove any residual double imaging resulting from the two glass
elements being out of parallel. The electrochromic element of the
present invention is preferably color neutral. In a color neutral
electrochromic element, the element darkens to a gray color, which
is more ascetically pleasing than any other color when used in an
electrochromic mirror. U.S. patent application Ser. No. 08/832,596,
entitled "AN IMPROVED ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A
PRE-SELECTED COLOR" discloses electrochromic media that are
perceived to be gray throughout their normal range of operation.
The entire disclosure of this application is hereby incorporated
herein by reference. U.S. patent application Ser. No. 09/311,955
entitled "ELECTROCHROMIC REARVIEW MIRROR INCORPORATING A THIRD
SURFACE METAL REFLECTOR AND A DISPLAY/SIGNAL LIGHT" discloses
additional electrochromic mirrors that exhibit substantial color
neutrality while enabling displays to be positioned behind the
reflective surface of the electrochromic mirror. The entire
disclosure of this application is hereby incorporated herein by
reference.
[0030] In addition to reflective element 100, mirror 20 further
includes an optical coating 130. Optical coating 130 is a
self-cleaning hydrophilic optical coating. Optical coating 130
preferably exhibits a reflectance at first surface 112a of
reflective element 100 that is less than about 20 percent. If the
reflectance at first surface 112a is greater than about 20 percent,
noticeable double-imaging results, and the range of variable
reflectance of reflective element 100 is significantly reduced. The
electrochromic mirror as a unit should have a reflectance of less
than about 20 percent in its lowest reflectance state, and more
preferably should have a reflectance of less than about 10
percent.
[0031] Optical coating 130 also is preferably sufficiently
hydrophilic such that water droplets on a front surface of coating
130 exhibit a contact angle of less than about 30.degree., more
preferably less than about 20.degree., and most preferably less
than about 10.degree.. If the contact angle is greater than about
30.degree., the coating 130 exhibits insufficient hydrophilic
properties to prevent distracting water beads from forming. Optical
coating 130 should also exhibit self-cleaning properties whereby
the hydrophilic properties may be restored following exposure to UV
radiation.
[0032] In one embodiment, optical coating 130 includes at least
four layers of alternating high and low refractive index.
Specifically, as shown in FIG. 2, optical coating 130 includes, in
sequence, a first layer 132 having a high refractive index, a
second layer 134 having a low refractive index, a third layer 136
having a high refractive index, and a fourth layer 138 having a low
refractive index. Preferably, third layer 136 is made of a
photocatalytic material, and fourth layer 138 is made of a material
that will enhance the hydrophilic properties of the photocatalytic
layer 136 by generating hydroxyl groups on its surface. Suitable
hydrophilic enhancement materials include SiO.sub.2 and
Al.sub.2O.sub.3, with SiO.sub.2 being most preferred. Suitable
photocatalytic materials include TiO.sub.2, ZnO, ZnO.sub.2,
SnO.sub.2, ZnS, CdS, CdSe, Nb.sub.2O.sub.5, KTaNbO.sub.3,
KTaO.sub.3, SrTiO.sub.3, WO.sub.3, Bi2O.sub.3, Fe2O.sub.3, and GaP,
with TiO.sub.2 being most preferred. By making the outermost layers
TiO.sub.2 and SiO.sub.2, coating 130 exhibits good self-cleaning
hydrophilic properties similar to those obtained by the prior art
hydrophilic coatings applied to conventional mirrors having a
reflector provided on the rear surface of a single front glass
element. Preferably, the thickness of the SiO.sub.2 outer layer is
less than about 800 .ANG.. If the SiO.sub.2 outer layer is too
thick (e.g., more than about 1000 .ANG.), the underlying
photocatalytic layer will not be able to "clean" the SiO.sub.2
hydrophilic outer layer, at least not within a short time period.
The two additional layers (layers 132 and 134) are provided to
reduce the undesirable reflectance levels at the front surface of
reflective element 100. Preferably, layer 132 is made of a
photocatalytic material and second layer 134 is made of a
hydrophilic enhancement material so as to contribute to the
hydrophilic and photocatalytic properties of the coating. Thus,
layer 132 may be made of any one of the photocatalytic materials
described above or mixtures thereof, and layer 134 may be made of
any of the hydrophilic enhancement materials described above or
mixtures thereof. Preferably layer 132 is made of TiO.sub.2, and
layer 134 is made of SiO.sub.2.
[0033] An alternative technique to using a high index layer and low
index layer between the glass and the layer that is primarily
comprised of photocatalytic metal oxide (i.e., layer 136) to obtain
all of the desired properties while maintaining a minimum top layer
thickness of primarily silica is to use a layer, or layers, of
intermediate index. This layer(s) could be a single material such
as tin oxide or a mixture of materials such as a blend of titania
and silica. Among the materials that have been modeled as
potentially useful are blends of titania and silica, which can be
obtained through sol-gel deposition as well as other means, and tin
oxide. One can use a graded index between the glass and layer
primarily composed of photocatalytic material as well.
Additionally, one can obtain roughly the same color and reflectance
properties with a thinner top layer or possibly no top layer
containing primarily silica if the index of the photocatalytic
layer is lowered somewhat by blending materials, as would be the
case, for example, for a titania and silica mixture deposited by
sol-gel. The lower index of the titania and silica blend layer
imparts less reflectivity, requires less compensation optically,
and therefore allows for a thinner top layer. This thinner top
layer should allow for more of the photocatalytic effect to reach
surface contaminants.
[0034] The index of refraction of a titania film obtained from a
given coating system can vary substantially with the choice of
coating conditions and could be chosen to give the lowest index
possible while maintaining sufficient amounts of anatase or rutile
form in the film and demonstrating adequate abrasion resistance and
physical durability. The lower index obtained in this fashion would
yield similar advantages to lowering the index by mixing titania
with a lower index material. Ron Willey, in his book "Practical
Design and Production of Optical Thin Films," Marcel Dekker, 1996,
cites an experiment where temperature of the substrate, partial
pressure of oxygen, and speed of deposition vary the index of
refraction of the titania deposited from about n=2.1 to n=2.4.
[0035] Materials used for transparent second surface conductors are
typically materials whose index of refraction is about 1.9 or
greater and have their color minimized by using half wave thickness
multiples or by using the thinnest layer possible for the
application or by the use of one of several "non-iridescent glass
structures." These non-iridescent structures will typically use
either a high and low index layer under the high index conductive
coating (see, for example, U.S. Pat. No. 4,377,613 and U.S. Pat.
No. 4,419,386 by Roy Gordon), or an intermediate index layer (see
U.S. Pat. No. 4,308,316 by Roy Gordon) or graded index layer (see
U.S. Pat. No. 4,440,822 by Roy Gordon).
[0036] Fluorine doped tin oxide conductors using a non-iridescent
structure are commercially available from Libbey-Owens-Ford and are
used as the second surface transparent conductors in most inside
automotive electrochromic mirrors produced at the present time. The
dark state color of devices using this second surface coating stack
is superior to that of elements using optical half wave thickness
indium tin oxide (ITO) when it is used as a second surface
conductive coating. Drawbacks of this non-iridescent coating are
mentioned elsewhere in this document. Hydrophilic and
photocatalytic coating stacks with less than about 800 .ANG. silica
top layer, such as 1000 .ANG. titania 500 .ANG. silica, would still
impart unacceptable color and/or reflectivity when used as a first
surface coating stack in conjunction with this non-iridescent
second surface conductor and other non-iridescent second surface
structures, per the previous paragraph, that are not designed to
compensate for the color of hydrophilic coating stacks on the
opposing surface. Techniques would still need to be applied per the
present embodiment at the first surface to reduce C* of the system
in the dark state if these coatings were used on the second
surface.
[0037] ITO layers typically used are either very thin
(approximately 200-250 .ANG.), which minimizes the optical effect
of the material by making it as thin as possible while maintaining
sheet resistances adequate for many display devices, or multiples
of half wave optical thickness (about 1400 .ANG.), which minimizes
the overall reflectivity of the coating. In either case, the
addition of photocatalytic hydrophilic coating stacks on opposing
surfaces per the previous paragraph would create unacceptable color
and/or reflectivity in conjunction with the use of these layer
thicknesses of ITO used as the second surface conductor. Again,
techniques would need to be applied per the present embodiment at
the first surface to reduce the C* of the system in the dark
state.
[0038] In somewhat analogous fashion, for modification of the first
surface-coating stack to optimize the color and reflectivity of the
system containing both first and second surface coatings, one can
modify the second surface-coating stack to optimize the color of
the system. One would do this by essentially creating a
compensating color at the second surface in order to make
reflectance of the system more uniform across the visible spectrum,
while still maintaining relatively low overall reflectance. For
example, the 1000 .ANG. titania 500 .ANG. silica stack discussed in
several places within this document has a reddish-purple color due
to having somewhat higher reflectance in both the violet and red
portions of the spectrum than it has in the green. A second surface
coating with green color, such as 3/4 wave optical thickness ITO,
will result in a lower C* value for the dark state system than a
system with a more standard thickness of ITO of half wave optical
thickness, which is not green in color. Additionally, one can
modify thicknesses of layers or choose materials with somewhat
different indices in the non-iridescent structures mentioned in
order to create a compensating color second surface as well.
[0039] Another method of color compensating the first surface is
through pre-selecting the color of the electrochromic medium in the
dark state in accordance with the teachings of commonly assigned
U.S. patent application Ser. No. 08/832,596, entitled "AN IMPROVED
ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A PRE-SELECTED COLOR."
Again, by using first surface coatings of 1000 .ANG. titania
followed by 500 .ANG. silica as an example, the following
modification would assist in lowering the C* value of an
electrochromic mirror when activated. If, in that case, the color
of the electrochromic medium was selected so that it was less
absorbing in the green region when activated, the higher reflection
of green wavelengths of light from the third or fourth surface
reflector of the element would help balance the reflection of the
unit in the dark state.
[0040] Combinations of the aforementioned concepts for the first,
second surface, and electrochromic medium are also potentially
advantageous for the design.
[0041] It is known that the optical properties for a deposited film
vary depending on deposition conditions that include partial
pressure of oxygen gas, temperature of the substrate speed of
deposition, and the like. In particular, the index of refraction
for a particular set of parameters on a particular system will
affect the optimum layer thicknesses for obtaining the optical
properties being discussed.
[0042] The discussions regarding the photocatalytic and hydrophilic
properties of titania and like photocatalytic materials and silica
and like hydrophilic materials are generally applicable to layers
of mixed materials as long as the mixtures retain the basic
properties of photocatalytic activity and/or hydrophilicity.
Abrasion resistance is also a major consideration in the outermost
layer. EP 0816466A1 describes an abrasion resistant,
photocatalytic, hydrophilic layer of silica blended titania, as
well as a layer of tin oxide blended titania with similar
properties. U.S. Pat. No. 5,755,867 describes photocatalytic blends
of silica and titania obtained through use of these mixtures. These
coatings would likely require modifications to change their optical
properties suitable for use on an electrochromic device. The
potential advantages of these optical property modifications to
this invention are discussed further below.
[0043] In some variations of this invention, it may be preferable
to include a layer of material between the substrate, especially if
it is soda lime glass, and the photocatalytic layer(s) to serve as
a barrier against sodium leaching in particular. If this layer is
close to the index of refraction of the substrate, such as silica
on soda lime glass, it will not affect the optical properties of
the system greatly and should not be considered as circumventing
the spirit of the invention with regards to contrasting optical
properties between layers.
[0044] To expedite the evaporation of water on the mirror and
prevent the freezing of thin films of water on the mirror, a
heating element 122 may optionally be provided on the fourth
surface 114b of reflective element 100. Alternatively, one of the
transparent front surface films could be formed of an electrically
conductive material and hence function as a heater.
[0045] To illustrate the properties and advantages of the present
invention, an example is provided below. The following illustrative
example is not intended to limit the scope of the present invention
but to illustrate its application and use. In this example,
references are made to the spectral properties of an electrochromic
mirror constructed in accordance with the parameters specified in
the example. In discussing colors, it is useful to refer to the
Commission Internationale de I'Eclairage's (CIE) 1976 CIELAB
Chromaticity Diagram (commonly referred to as the L*a*b* chart).
The technology of color is relatively complex, but a fairly
comprehensive discussion is given by F. W. Billmeyer and M.
Saltzman in Principles of Color Technology, 2nd Edition, J. Wiley
and Sons Inc. (1981), and the present disclosure, as it relates to
color technology and terminology, generally follows that
discussion. On the L*a*b* chart, L* defines lightness, a* denotes
the red/green value, and b* denotes the yellow/blue value. Each of
the electrochromic media has an absorption spectra at each
particular voltage that may be converted to a three-number
designation, their L*a*b* values. To calculate a set of color
coordinates, such as L*a*b* values, from the spectral transmission
or reflectance, two additional items are required. One is the
spectral power distribution of the source or illuminant. The
present disclosure uses CIE Standard Illuminant D.sub.65. The
second item needed is the spectral response of the observer. The
present disclosure uses the 2-degree CIE standard observer. The
illuminant/observer combination used is represented as D.sub.65/2
degree. Many of the examples below refer to a value Y from the 1931
CIE Standard since it corresponds more closely to the spectral
reflectance than L*. The value C*, which is also described below,
is equal to the square root of (a*).sup.2+(b*).sup.2, and hence,
provides a measure for quantifying color neutrality. To obtain an
electrochromic mirror having relative color neutrality, the C*
value of the mirror should be less than 20. Preferably, the C*
value is less than 15, and more preferably is less than about
10.
EXAMPLE
[0046] Two identical electrochromic mirrors were constructed having
a rear element made with 2.2 mm thick glass with a layer of chrome
applied to the front surface of the rear element and a layer of
rhodium applied on top of the layer of chrome using vacuum
deposition. Both mirrors included a front transparent element made
of 1.1 mm thick glass, which was coated on its rear surface with a
transparent conductive ITO coating of 1/2 wave optical thickness.
The front surfaces of the front transparent elements were covered
by a coating that included a first layer of 200 .ANG. thick
TiO.sub.2, a second layer of 250 .ANG. thick SiO.sub.2, a third
layer of 1000 .ANG. TiO.sub.2, and a fourth layer of 500 .ANG.
thick SiO.sub.2. For each mirror, an epoxy seal was laid about the
perimeter of the two coated glass substrates except for a small
port used to vacuum fill the cell with electrochromic solution. The
seal had a thickness of about 137 microns maintained by glass
spacer beads. The elements were filled with an electrochromic
solution including propylene carbonate containing 3 percent by
weight polymethylmethacrylate, 30 mM Tinuvin P (UV absorber), 38 mM
N,N'-dioctyl-4, 4'bipyridinium bis(tetrafluoroborate), 27 mM
5,10-dihydrodimethylphenazine and the ports were then plugged with
a UV curable adhesive. Electrical contact buss clips were
electrically coupled to the transparent conductors.
[0047] In the high reflectance state (with no potential applied to
the contact buss clips), the electrochromic mirrors had the
following averaged values: L*=78.26, a*=-2.96, b*=4.25, C*=5.18,
and Y=53.7. In the lowest reflectance state (with a potential of
1.2 V applied), the electrochromic mirrors had the following
averaged values: L*=36.86, a*=6.59, b*=-3.51, C*=7.5, and Y=9.46.
The average contact angle that a drop of water formed on the
surfaces of the electrochromic mirrors after it was cleaned was
7.degree..
[0048] For purposes of comparison, two similar electrochromic
mirrors were constructed, but without any first surface coating.
These two mirrors had identical construction. In the high
reflectance state, the electrochromic mirrors had the following
averaged values: L*=78.93, a*=-2.37, b*=2.55, C*=3.48, and Y=54.81.
In the lowest reflectance state, the electrochromic mirrors had the
following averaged values: L*=29.46, a*=0.55, b*=-16.28, C*=16.29,
and Y=6.02. As this comparison shows, the electrochromic mirrors
having the inventive hydrophilic coating unexpectedly and
surprisingly had better color neutrality than similarly constructed
electrochromic mirrors not having such a hydrophilic coating.
Additionally, the comparison shows that the addition of the
hydrophilic coating does not appreciably increase the low-end
spectral reflectance of the mirrors.
[0049] The present invention thus provides a hydrophilic coating
that not only is suitable for an electrochromic device, but
actually improves the color neutrality of the device.
[0050] Although the example cited above uses a vacuum deposition
technique to apply the coating, these coatings can also be applied
by conventional sol-gel techniques. In this approach, the glass is
coated with a metal alkoxide made from precursors such as tetra
isopropyl titanate, tetra ethyl ortho silicate, or the like. These
metal alkoxides can be blended or mixed in various proportions and
coated onto glass usually from an alcohol solution after being
partially hydrolyzed and condensed to increase the molecular weight
by forming metal oxygen metal bonds. These coating solutions of
metal alkoxides can be applied to glass substrates by a number of
means such as dip coating, spin coating, or spray coating. These
coatings are then fired to convert the metal alkoxide to a metal
oxide typically at temperatures above 450.degree. C. Very uniform
and durable thin film can be formed using this method. Since a
vacuum process is not involved, these films are relatively
inexpensive to produce. Multiple films with different compositions
can be built up prior to firing by coating and drying between
applications. This approach can be very useful to produce
inexpensive hydrophilic coatings on glass for mirrors, especially
convex or aspheric mirrors that are made from bent glass. In order
to bend the glass, the glass must be heated to temperatures above
550.degree. C. If the sol-gel coatings are applied to the flat
glass substrate before bending (typically on what will be the
convex surface of the finished mirror), the coatings will fire to a
durable metal oxide during the bending process. Thus, a hydrophilic
coating can be applied to bent glass substrates for little
additional cost. Since the majority of outside mirrors used in the
world today are made from bent glass, this approach has major cost
benefits. It should be noted that some or all of the coatings could
be applied by this sol-gel process with the remainder of the
coating(s) applied by a vacuum process, such as sputtering or
E-beam deposition. For example, the first high index layer and low
index layer of, for instance, TiO.sub.2 and SiO.sub.2, could be
applied by a sol-gel technique and then the top TiO.sub.2 and
SiO.sub.2 layer applied by sputtering. This would simplify the
requirements of the coating equipment and yield cost savings. It is
desirable to prevent migration of ions, such as sodium, from soda
lime glass substrates into the photocatalytic layer. The sodium ion
migration rate is temperature dependent and occurs more rapidly at
high glass bending temperatures. A sol-gel formed silica or doped
silica layer, for instance phosphorous doped silica, is effective
in reducing sodium migration. This barrier underlayer can be
applied using a sol-gel process. This silica layer could be applied
first to the base glass or incorporated into the hydrophilic stack
between the photocatalytic layer and the glass.
[0051] In general, the present invention is applicable to any
electrochromic element including architectural windows and
skylights, automobile windows, rearview mirrors, and sunroofs. With
respect to rearview mirrors, the present invention is primarily
intended for outside mirrors due to the increased likelihood that
they will become foggy or covered with mist. Inside and outside
rearview mirrors may be slightly different in configuration. For
example, the shape of the front glass element of an inside mirror
is generally longer and narrower than outside mirrors. There are
also some different performance standards placed on an inside
mirror compared with outside mirrors. For example, an inside mirror
generally, when fully cleared, should have a reflectance value of
about 70 percent to about 85 percent or higher, whereas the outside
mirrors often have a reflectance of about 50 percent to about 65
percent. Also, in the United States (as supplied by the automobile
manufacturers), the passenger-side mirror typically has a
non-planar spherically bent or convex shape, whereas the
driver-side mirror 111a and inside mirror 110 presently must be
flat. In Europe, the driver-side mirror 111a is commonly flat or
aspheric, whereas the passenger-side mirror 111b has a convex
shape. In Japan, both outside mirrors have a non-planar convex
shape.
[0052] The fact that outside rearview mirrors are often non-planar
raises additional limitations on their design. For example, the
transparent conductive layer applied to the rear surface of a
non-planar front element is typically not made of fluorine-doped
tin oxide, which is commonly used in planar mirrors, because the
tin oxide coating can complicate the bending process and it is not
commercially available on glass thinner than 2.3 mm. Thus, such
bent mirrors typically utilize a layer of ITO as the front
transparent conductor. ITO, however, is slightly colored and
adversely introduces blue coloration into the reflected image as
viewed by the driver. The color introduced by an ITO layer applied
to the second surface of the element may be neutralized by
utilizing an optical coating on the first surface of the
electrochromic element. To illustrate this effect, a glass element
coated with a half wave thick ITO layer was constructed as was a
glass element coated with a half wave thick ITO layer on one side
and the hydrophilic coating described in the above example on the
other side. The ITO-coated glass without the hydrophilic coating
had the following properties: L*=37.09, a*=8.52, b*=-21.12,
C*=22.82, and a first/second surface spectral reflectance of
Y=9.58. By contrast, the ITO-coated glass that included the
inventive hydrophilic coating of the above-described example
exhibited the following properties: L*=42.02, a*=2.34, b*=-8.12,
C*=8.51, and a first/second surface spectral reflectance of
Y=12.51. As evidenced by the significantly reduced C* value, the
hydrophilic coating serves as a color suppression coating by
noticeably improving the coloration of a glass element coated with
ITO. Because outside rearview mirrors are often bent and include
ITO as a transparent conductor, the ability to improve the color of
the front coated element by adding a color suppression coating to
the opposite side of the bent glass provides many manufacturing
advantages.
[0053] Other light attenuating devices, such as scattered particle
displays (such as those discussed in aaa, bbb, ccc, patents) or
liquid crystal displays (such as those discussed ddd, eee, fff
patents), can also benefit from the application of these
principles. In devices where the light attenuating layer is between
two pieces of glass or plastic, the same basic constraints and
solutions to those constraints will apply. The color and
reflectivity of a first surface hydrophilic layer or layer stack
can impart substantial color and reflectivity to the device in the
darkened state even when this first surface layer stack does not
appreciably affect the bright state characteristics. Adjustments to
the first surface layer stack similar to those discussed for an
electrochromic device will, therefore, affect the color and/or
reflectivity of the darkened device advantageously. The same will
apply to adjustments made to the second surface of the device or to
the color of the darkening layer itself.
[0054] These principles can also be applied to devices such as
insulated windows where the light attenuating device may be
contained within a structure having, for example, an additional
outer and inner pane of glass for insulation purposes. The
hydrophilic coating would, in this case, need to be on the outside
of the multilayer structure, but would affect the color of the
darkened device similarly. The techniques discussed could be
advantageously applied in this structure. Those familiar with the
art can see that coatings could or would be transferred to a
different surface or surfaces of the device because of the
additional surfaces either available or interposing within the
device.
[0055] The above description is considered that of the preferred
embodiments only. Modifications of the invention will occur to
those skilled in the art and to those who make or use the
invention. Therefore, it is understood that the embodiments shown
in the drawings and described above are merely for illustrative
purposes and not intended to limit the scope of the invention,
which is defined by the following claims as interpreted according
to the principles of patent law, including the Doctrine of
Equivalents.
* * * * *