U.S. patent number RE30,835 [Application Number 05/736,022] was granted by the patent office on 1981-12-29 for self-supporting pigment layers for electrochromic display.
This patent grant is currently assigned to American Cyanamid Company. Invention is credited to Robert D. Giglia.
United States Patent |
RE30,835 |
Giglia |
December 29, 1981 |
Self-supporting pigment layers for electrochromic display
Abstract
An electrochromic data display and imaging device which may be
formed by sandwich arrangement of the imaging area and the
counter-electrode area, with a suitable self-supporting
ion-conductive layer between.
Inventors: |
Giglia; Robert D. (Rye,
NY) |
Assignee: |
American Cyanamid Company
(Stamford, CT)
|
Family
ID: |
27027828 |
Appl.
No.: |
05/736,022 |
Filed: |
October 27, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
428563 |
Dec 26, 1973 |
03892472 |
Jul 1, 1975 |
|
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Current U.S.
Class: |
359/270; 359/274;
359/273 |
Current CPC
Class: |
G02F
1/1523 (20130101); G02F 1/157 (20130101) |
Current International
Class: |
G02F
1/15 (20060101); G02F 1/01 (20060101); G02F
001/17 () |
Field of
Search: |
;350/357 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sikes; William L.
Attorney, Agent or Firm: Feltovic; Robert J. Hart; Gordon
L.
Claims
I claim:
1. A varaible light transmission device which comprises light
transmitting substrate having a persistent electrochromic material
as a light modulating material, a counter-electrode, and a
.[.self-supporting.]. .Iadd.porous separator .Iaddend.layer
comprising a pigment and an ion-conducting material .Iadd.in a
binding medium .Iaddend.in contact with said .Iadd.light modulating
.Iaddend.material and counter-electrode.
2. A variable light transmission device as in claim 1, which
comprises two layers, one with said electrochromic material, and
the other of said counter-electrode separated by said
.[.self-supporting.]. .Iadd.porous separator .Iaddend.layer,
disposed between a pair of conductive electrodes.
3. The device of claim 2, wherein said counter-electrode is the
type of the persistent electrochromic material.
4. The device of claim 3, wherein the electrochromic materials in
each said layer are identical.
5. The device of claim 2, wherein at least one of the electrodes is
substantially transparent.
6. The device of claim 4, wherein said electrochromic materials are
WO.sub.3.
7. A device of claim 1, wherein said .[.self-supporting.].
.Iadd.porous separator .Iaddend.layer contains a color pigment.
8. The device of claim 1, wherein said .[.self-supporting.].
.Iadd.porous separator .Iaddend.layer is a porous sheet saturated
with an electrolyte. .Iadd. 9. The device of claim 1 wherein said
porous separator layer is self-supporting. .Iaddend..Iadd. 10. The
device of claim 9 wherein the self-supporting porous layer is a
separate pre-cut element. .Iaddend. .Iadd. 11. In an electrochromic
display of the type having a first substrate with selectively
actuatable transparent electrodes and first electrochromic layers
thereon, and also having a second substrate with counter-electrode
and second electrochromic layer thereon, the improvement
comprising:
porous separator means applied as a layer and uniformly and closely
spacing said first and second substrate members, the pores of said
separator means being filled with liquid electrolyte, and
pigment means held by said separator means and selected to provide
contrast with said first electrochromic layers and disposed to hide
said second electrochromic layer. .Iaddend..Iadd. 12. The
combination according to claim 11, wherein said porous separator
means comprises porous polypropylene. .Iaddend..Iadd. 13. The
combination according to claim 11, wherein said pigment means is
premixed in said separator means. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to electro-optical devices whose
electromagnetic radiation absorption characteristics can be
selectively altered by influence of a suitably controlled electric
field. More particularly, this invention is directed to a sandwich
type cell in which two layers of electrochromic material are
separated by a self-supporting ion conducting medium.
In commonly assigned, copending U.S. applications, Ser. No. 41,153
.Iadd.now abandoned, .Iaddend.Ser. No. 41,154 .Iadd.now abandoned
.Iaddend.and Ser. No. 41,155 .Iadd.now U.S. Pat. 3,708,220,
.Iaddend.all filed May 25, 1970, and U.S. Pat. Nos. 3,521,941 and
3,578,843.[.; Ser. No. 41,153, abandoned and refiled as Ser. No.
211,857, Dec. 23, 1971, abandoned and refiled as Ser. No. 361,760,
May 18, 1973, now copending; Ser. No. 41,154, abandoned and
refiled, now pending; Ser. No. 41,155, now U.S. Pat. No.
3,708,220;.]..Iadd., .Iaddend.there are described electro-optical
devices exhibiting a phenomenon known as persistent electrochromism
wherein electromagnetic radiation absorption characteristic of a
persistent electrochromic (EC) material is altered under the
influence of an electric field. Such devices were employed in
sandwich arrangement between two electrodes. Coloration was induced
by charging the electrochromic film negative with respect to the
counter-electrode, employing an external potential. The
counter-electrode can be the same as the persistent electrochromic
material or different.
By reversing the original polarity of the field or by applying a
new field, it was also possible to cancel, erase or bleach the
visible coloration.
These steps of color induction and erasure are defined as
cycling.
The devices described in the prior applications are effective to
change their electromagnetic radiation transmitting properties
under the influence of an electric field, and have extremely good
visibility over a wide range of lighting conditions, including high
ambient light. However, these EC displays normally feature a light
color background which consists of a thin layer of pigment mixed
with a liquid electrolyte to form an ion conducting layer. This
layer serves to hide the black counter-electrode and to provide
good contrast with the blue-black EC film. It has been found that
EC displays when stored for long periods of time, especially when
stored on edge, develop a problem of separation of the pigment
background. This appears as a black crack in the light background
due to the carbon counter-electrode showing through. Efforts to
cope with this problem by providing thickened, gel-like electrolyte
pastes resulted in slowing the switching speed as the thickened
electrolyte reduced the mobility of ions between the
electrodes.
It is, therefore, an object of this invention to provide an
ion-conducting medium having a color pigment incorporated which
will retain a homogeneous consistency under varying physical
conditions, over a long period of time.
This and other objects of the invention will become apparent as the
description thereof proceeds.
SUMMARY OF THE INVENTION
The image display device is formed in a sandwich arrangement of an
electrochromic layer as an imaging area and a counter-electrode
with a spacing of an ion-conducting medium, e.g. an electrolyte,
between the areas. Means are provided for supplying electric
current to the counter-electrode layer. Any conventional means is
suitable. A particularly advantageous means for electrical
connection is to deposit the electrochromic imaging layer and
counter-electrode on a conductive surface, such as NESA glass. It
is particularly advantageous to incorporate a pigment material with
the electrolyte for greater contrast and for masking the
counter-electrode.
The present invention discloses methods of preventing the pigment
from separating in one area and compacting in another by binding
the pigment in a self-supporting structure. Another advantage
provided is that the self-supporting pigment structure acts as a
separator preventing electrical shorting of the EC and
counter-electrodes. The methods used to prepare the pigment layer
result in porous structures which do not restrict ion flow and
thereby maintain good switching speed.
DETAILED DESCRIPTION OF INVENTION
As used herein, a "persistent electrochromic material" is defined
as a material responsive to the application of an electric field of
a given polarity to change from a first presistent state in which
it is essentially non-absorptive of electromagnetic radiation in a
given wavelength region, to a second persistent state in which it
is absorptive of electromagnetic radiation in the given wavelength
region, and once in said second state, is responsive to the
application of an electric field of the opposite polarity to return
to its first state. Certain of such materials can also be
responsive to a short circuiting condition, in the absence of an
electric field so as to return to the initial state.
By "persistent" is meant the ability of the material to remain in
the absorptive state to which it is changed, after removal of the
electric field, as distinguished from a substantially instantaneous
reversion to the initial state, as in the case of the Franz-Keldysh
effect.
Electrochromic Material
The materials which form the electrochromic materials of the device
in general are electrical insulators or semiconductors. Thus are
excluded those metals, metal alloys, and other metal-containing
compounds which are relatively good electrical conductors.
The persistent electrochromic materials are further characterized
as inorganic substances which are solid under the conditions of
use, whether as pure elements, alloys, or chemical compounds,
containing at least one element of variable oxidation state, that
is, at least one element of the Periodic System which can exist in
more than one oxidation state in addition to zero. The term
"oxidation state" as employed herein is defined in "Inorganic
Chemistry," T. Moeller, John Wiley & Sons, Inc., New York,
1952.
These include materials containing a transition metal element
(including Lanthanide and Actinide series elements), and materials
containing non-alkali metal elements such as copper. Preferred
materials of this class are films of transition metal compounds in
which the transition metal may exist in any oxidation state from +2
to +8. Examples of these are: transition metal oxides, transition
metal oxysulfides, transition methalides, selenides, tellurides,
chromates, molybdates, tungstates, vanadates, niobates, tantalates,
titanates, stannates, and the like. Particularly preferred are
films of metal stannates, oxides and sulfides of the metals of
Group (IV)B, (V)B and (VI)B of the Period System, and Lanthanide
series metal oxides and sulfides. Examples of such are copper
stannate, tungsten oxide, cerium oxide, cobalt tungstate, metal
molybdates, metal titanates, metal niobates, and the like.
Additional examples of such compounds are the following oxides: MO
oxides, e.g. MnO, NiO, CoO, etc.; M.sub.2 O.sub.3 oxides, e.g.,
Cr.sub.2 O.sub.3, Fe.sub.2 O.sub.3, Y.sub.2 O.sub.3, Yb.sub.2
O.sub.3, V.sub.2 O.sub.3, Ti.sub.2 O.sub.3, Mn.sub.2 O.sub.3, etc.;
MO.sub.2 oxides, e.g., TiO.sub.2, MnO.sub.2, ThO.sub.2, etc.;
M.sub.3 O.sub.4 oxides, e.g., Co.sub.3 O.sub.4, Mn.sub.3 O.sub.4,
Fe.sub.3 O.sub.4, etc.; MO.sub.3 oxides, e.g., CrO.sub.3, UO.sub.3,
etc.; M.sub.2 O.sub.5 oxides, e.g., V.sub.2 O.sub.5 etc., Nb.sub.2
O.sub.5, Ta.sub.2 O.sub.5 etc.; M.sub.4 O.sub.6 oxides; M.sub.2
O.sub.7 oxides such as M.sub.2 O.sub.7 ; complex oxides such as
those of the formula XYO.sub.2 (X and Y being different metals),
e.g., LiNiO.sub.2, etc.; XYO.sub.3 oxides, e.g., LiMnO.sub.3,
FeTiO.sub.3, MnTiO.sub.3, CoTiO.sub.3, NiTiO.sub.3, LiNbO.sub.3,
LiTaO.sub.3, NaWO.sub.3, etc.; XYO.sub.4 oxides, e.g., MgWO.sub.4,
CdWO.sub.4, NiWO.sub.4, etc.; XY.sub.2 O.sub.6, e.g., CaNb.sub.2
O.sub.6 ("Niobite" oxides); X.sub.2 Y.sub.2 O.sub.6, e.g., Na.sub.2
Nb.sub.2 O.sub.6 : Spinel structure oxides, i.e., of the formula
X.sub.2 YO.sub.4, e.g., Na.sub.2 MoO.sub.4, NaWO.sub.4, Ag.sub.2
MoO.sub.4, Cu.sub.2 MoO.sub.4, Li.sub.2 MoO.sub.4, Li.sub.2
WO.sub.4, Sr.sub.2 TiO.sub.4, Ca.sub.2 MnO.sub.4, etc.; XY.sub.2
O.sub.4, e.g., FeCr.sub.2 O.sub.4, TiZn.sub.2 O.sub.4, etc.;
X.sub.2 YO.sub.5 oxides, e.g., Fe.sub.2 TiO.sub.5, Al.sub.2
TiO.sub.5, etc.; and X.sub.3 Y.sub.3 O (ternary) oxides, e.g.,
Mo.sub.3 Fe.sub.3 O, W.sub.3 Fe.sub.3 O, X.sub.3 Ti.sub.3 O (where
X is Mn, Fe, Co, etc.). For a discussion of some complex oxides,
see Advanced Inorganic Chemistry, Cotten and Wilkinson, p. 51,
(1966), Interscience Publishers, Inc., New York and Progress in
Inorganic Chem., Vol. 1, 465 (1959) Interscience Publishers, Inc.,
New York. Also included are nitrides, and the sulfides
corresponding to the above oxides. Hydrates of certain metal oxides
may also be used, e.g., WO.sub.3.H.sub.2 O, WO.sub.3.2H.sub.2 O,
MoO.sub.3.H.sub.2 O and MoO.sub.3.2H.sub.2 O.
A particularly advantageous aspect in the present invention is the
use of two separate layers of identical electrochromic materials
one layer being employed in the counterelectrode for the other
layer. A preferred embodiment consists of tungsten oxide as the
electrochromic color electrode and tungsten oxide and graphite as
the counter-electrode.
While the general mechanism of persistent electrochromism is
unknown, the coloration is observed to occur at the negatively
charged electrochromic layer. Generally, the phenomenon of
persistent electrochromism is believed to involve cation transport
such as hydrogen or lithium ions to the negative electrode where
color centers form in the electrochromic image layer as a result of
charge compensating electron flow.
When the persistent electrochromic materials are employed as films,
thickness desirably will be in the range of from about 0.1-100
microns. However, since a small potential will provide an enormous
field strength across very thin films the latter, i.e., 0.1-10
microns, are preferred over thicker ones. Optimum thickness will
also be determined by the nature of the particular compound being
laid down as a film and by the film-forming method since the
particular compound and film-forming method may place physical
(e.g., non-uniform film surface) and economic limitations on
manufacture of the devices.
The films may be laid down on any substrate which, relative to the
film, is electrically conducting. The electrically conductive
material may be coated on another suitable substrate material
including glass, wood, paper, plastics, plaster, and the like,
including transparent, translucent, opaque or other optical quality
materials. A preferred embodiment in the instant device would
employ at least one transparent electrode.
When tungsten oxide is employed as the electrochromic imaging
material and an electric field is applied between the electrodes, a
blue coloration of the previously transparent electrochromic layer
occurs, i.e., the presistent electrochromic layer becomes
absorptive of electromagnetic radiation over a band initially
encompassing the red end of the visible spectrum, thereby rendering
the imaging layer blue in appearance. Prior to the application of
the electric field, the electrochromic imaging layer was
essentially non-absorbent and thus transparent.
Counter Electrode
As previously indicated, the counter-electrode may be any
electrically conductive material. Particularly advantageous is a
layer of electrochromic material, as described previously. It is
also advantageous to use the same electrochromic material for the
imaging area and counter-electrode. A mixture of graphite and an
electrochromic material, or graphite alone may be used as the
counter-electrode. Other metallic counter-electrodes are disclosed
in copending application, Ser. No. 41,154 .
The invention may be further understood by reference to the
drawings in which
FIG. 1 is a cross section of the electrochromic display device,
FIG. 2 is a front view of a single digital segment in an
electrochromic digital display,
FIG. 3 is a cross sectional view of the segment of FIG. 2, taken
along the lines A--A,
FIG. 4 is a front view of a linear digital display according to the
invention.
As shown in FIG. 1, a conventional EC information display having
transparent EC electrode 1, light colored, pigmented ion conducting
medium layer 2 and opaque counter-electrode 3. Layer 2 may be a
porous self-supporting layer incorporating a pigment, or other
desired materials, and soaked in an electrolyte, e.g. sulfuric
acid, or the like as disclosed in commonly assigned application
Ser. No. 41,154, filed May 25, 1970. The EC electrode 1 forms the
viewing surface and has a transparent or translucent substrate 5,
e.g. glass, with a conductive layer 6, e.g. tin oxide, and an
electrochromic layer 7. The counter-electrode 3 is also a composite
of a conductive layer 8 on a substrate 9, and a counter-electrode
material 10 such as carbon, tungsten oxide, or a mixture thereof. A
suitable substrate for the viewing area and counter-electrode is
NESA glass, which is glass having a thin transparent layer of tin
oxide.
When battery 11 is connected to make counter-electrode 3 negative,
EC electrode layer 7 colors. When the connections are reversed, EC
layer 7 erases (or bleaches).
In FIGS. 2, 3 and 4 are shown electrochromic devices with the EC
layer 7 in the form of a plurality of segments which may be
selectively activated to show numbers. FIG. 2 shows the number
4.
The invention should be usefully applied in EC displays for
watches, clocks, calculators, telephone displays, automotive
dashboards, instrument indicators and advertising displays.
EXAMPLE 1
Method For Preparing A Counter-Electrode
A counter-electrode was prepared as follows: Dixon Crucible Co.
Graphokote No. 120 was brushed on a clean substrate on NESA glass.
While the Graphokote 120 film was still wet, WO.sub.3 powder was
sprinkled onto the surface. Air drying for 1/2 hour at 25.degree.
C. and baking at 300.degree. C. for 1/2 hour followed. The WO.sub.3
particles became embedded in the graphite film as the electrode was
air dried at 25.degree. C. The electrode was cooled to 25.degree.
C. and soaked in a solution of glycerin-sulfuric acid 10:1 by
volume for 24 hours minimum, rinsed with acetone and baked at
90.degree. C. for 1/2 hour to dry. The resulting deposit was
composed of approximately 0.5 gm/cm.sup.2 WO.sub.3 on 2.0
mg./cm.sup.2 Graphokote 120.
EXAMPLE 2
Method For Preparing Pigmented Spacing Ion-Conducting Layers
Type I pigment layers employ adhesive binders to hold the pigment
powder in a self-supporting, porous film. Examples of Type I are:
(a) Mix the ratio 1 gm of Sun Yellow C pigment to 1 cc part A and 1
cc part B Peterson Clear Epoxy with 1 cc Peterson Epoxy Thinner.
The mix is sprayed onto Teflon sheet, cured for 1 hour at
65.degree. C. and stripped from the Teflon film. The pigmented
film. The pigmented film can be cut to size for insertion into the
EC device. (b) Beginning with Rohm and Haas Latex AC-34, mix 1 part
to 9 parts (by volume) water. Add 1.5 cc of this mix to 1 gram of
Sun Yellow C pigment and brush onto a microporous polypropylene
film, Celanese Plastics Company Celgard No. 2400 W. Room
temperature dry for 1/2 hour then bake at 60.degree. C. for 15
minutes. Cut the pigment on polypropylene film to size and assemble
into the device.
Type II pigment layers feature a non-adhesive method of bonding of
the pigment particles into a self-supporting layer. In one example
20 grams of BaSO.sub.4 powder was mixed with a dispersion
containing 2 grams solids of Dupont TFE Dispersion 30B and water.
The loose mix was blended in a Waring Blender for several minutes
and heated in an oven at 120.degree. C. to drive off the water. Ten
grams of glycerin was added and stirred into the mix. The mix was
placed between sheets of Teflon film and squeezed to a thin film in
a power roll. This rolling operation fibrillates the Teflon 30B and
traps the pigment in the structure. The rolled film was stripped
from the Teflon sheets and the glycerin was extracted in an
overnight water wash leaving a porous pigment film. The film was
over dried and cut to size for assembly into an EC display.
Type III pigment layers are prepared by the paper-making process.
In one example 3 grams of BaSO.sub.4 powder, 3 grams of Sun Yellow
C pigment and 1 gram (solids) of acrylic fiber pulp were mixed with
300 cc of water and blended for 15 seconds. One cc of Cyanamid
M560C flocculant was hand stirred into the mix until the water
cleared. The sheet was formed using a common 6 inch diameter,
paper-making machine. The sheet was roll sized and dried on a
rotating drum drier for 1 minute at 120.degree. C. A sheet 0.015
inch thick resulted which could be cut and assembled into an EC
display.
EXAMPLE 3
An electrochromic device was constructed from two NESA glass
plates. One conductive NESA plate was coated with a 0.5 micron
thick evaporated film of tungsten oxide. The other NESA plate was a
counter-electrode as in Example 1. The glass plate so formed were
pressed together with the electrochromic and graphite films facing
each other but separated by a spacing layer as described in Example
2, the layer having been saturated with a 1:10 ratio of
concentrated sulfuric acid and glycerin. This device was cycled
from color to clear and back to color at an applied potential of
1.1 volts D.C. with half cycles of 100 milliseconds. The device
underwent 5,000,000 cycles of switching at 60 cycles per minute
without observable deterioration.
Previous methods attempting to correct the pigment separation
problem resulted in slowing the switching speed. This invention
eliminates the problem without slowing the switching speed of the
display. The invention also makes possible a variety of cosmetic
effects not previously possible, allowing for improvements in
appearance of these background films. For example, the good
insulating properties of these films may permit the addition of
reflecting metal particles to add "sparkle" to the display
background.
The invention is expected to be useful in applications which
include information displays, indicators and others where the
display is used in the reflective mode. It is particularly useful
in applications involving large area display or applications in
which shock and vibration is present, such as in automobile
dashboard displays, and the like.
* * * * *