Note: Descriptions are shown in the official language in which they were submitted.
11~L70~2
¦ BACKGROUND OF THE INVENTION
5 , Thi~ invention relates to displays made from electro-
chromic materials, and more particularly to such displays having
an ion-conducting medium for ion transfer disposed between spaced
layers of electrochromic material.
The term "electrochromic material" as used herein is
defined in the literature, and is understood in the art to mean
or to refer to a material responsive to the application o~ an
electric field of a given polarity to change from a first stable
persistent state in which it is essentially non-absorbtive of
electromagnetic radiation in a given wave length region, and hence
clear or substantially colorless, to a second stable persistent
~tate in which it is absorbtive o~` electromagnetic radiation in
the given wave length region, and hence co~ored. Once in said
second stable state, it is respon~ive to the re-application of
! an electric field of the opposite polarity to return to its ~irst
20 iistable state. A~ is well known in this ar*, the phenomenon is
evidenced by a change in color, ~or example, the change in color
I from essentially clear to blue, and back to clear, obtained by
¦ electrically reducing thin ~ilms of tungsten (VI~ oxides in a sul-
'furic acid electrolyte, as described in Journal of the American
Chemic~l Society (Yol. 73, p~. 5427-5732, Nov. 1951) at p. 5429
I
in an article by Brimm et al. entitled "Sodium Potassium Tungsten
Bronzes" .
There are numerous examples in the art to which the
present invention relates Or fabrication of devices incorporat-
3o ing electrochromic materials. For example, devices in which one
~7~
~ er o~ electrochromic material is sandwiched with or without
a~ ion-conducting material, such as an electrolyte, between two
conductive electrode surfaces are sho~n in Talmey U.S. Patents
2,173,141`, issued September 19, 1939; 2,281,013, issued April 28,
1942 ; and 2,319,765, issued May 18, 1943;. Deb et al U.S.
3,521,941, issued July 28, 1970 and Deb U.S. 3,829,196, issued
August 13, 1974. Devices incorporating two layers of electro-
chromic materials between two electrodes and separated by an
ion conducting medium are shown in Brimm et al supra, Giglia
et al U.S. 3,827,784, issued August 6, 1974; Witzke et al U.S.
3,840,287, issued October 8, 1974; Bruesch et al U.S. 3,971,624,
issued July 27, 1976; Giglia U.S. 3,9?3,829, issued August 10,
1976 and Leibowitz U.S. 4,012,831, issued March 22, 1977.
Prior art devices which incorporate crystalline or
solid state ion conducting media, for example, Deb et al U.S.
3,521,941,Bruesch et al U.S. 3,971,624, Jasinski U.S. 3,995,943,
issued December 7, 1976 and Ka~ai U.S. 4,009,936, issued March 1,
1977, exhibit switching speeds from clear to colored to
. clear state~, whicb are too slow ~or many display applications,
ror example, timepiece displays. Moreover~ prior art deYice~
~hich utilize concentrated acids in liquid or semi-solid form, for
example,`sul~uric acids as sho~n in ~itzke~ et al, U~S. 3,840,287,
al~o exhibit the same defec~s, and a~ well addi.tional defects in
that (1) the concentrated acid promotes the migration o~ anions
~rom one layer o~ electrochr~mic material-to another, and (2) the
. eohcentrated acid attacks, and ultimat81y destroy~, conYentional
~eal~ o~ the de~ice.
Furthermore, when the insoluble form o~ cationic ion
i;excha~ge re~in-~ is ut~li2ed, a3 disclosed in Bruesch et al. U.S.
3 3,971J624 (at col. 4,- line 27-~9), as an ion conductive material
betweer two layers of solid electrochromic ~aterials, additional
problems are encountered. For example, proper operation o~ the
display requires continual u~iform contact between both layers
. Or electrochromic material and the catioDic ion exchange resin.
Cationic ion exchange resin~ disclosed for thi~ purpo~e in the
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prior art, for example in Bruesch et al supra,
and Kissa U.S. 3,453,038, issued July 1, 1969 (at col. 5,
lines 18-34), are in the form of insoluble
~heet~ or in~oluble powder~. The sheet form i~ thick, and ulti-
i~ately exhibits discont~nultie~ i~ contact between t~o ~olid lay-
¦er~ o~ electrochromiC ~aterial, as well a~ exhibiting expansion
';when chemically wetted. Such sheet materials when chemically wet-
! ~ed expand signi~icantly in volume causing physical separation
of the ~ubstrates of the fabricated device, and consequent leak-
;age o~ fluids contained therein. Resins fabricated i~ powderform are difficult to work with from a manufacturing standpoint,
5since the insoluble powder must first be dispersed in a binder
be~ore being placed between two layer9 of electrochromic material.
It is, thererore, the purpose o~ the present invention
to proYide a display device, incorporating spaced layers of solid
electrochromiO material, which is significantly less subject to
degradation than prior de~ices, because no liquid electrolyte is
employed, thereby obtaining improved Reali~g of the display con-
~truction, and having improved ionic transfer between the eleo-
trochromic laye~s due to the mobility Or hydrated hydrogen ionsand haring improved switching speeds due to the blocking of paq-
sage of anions through the ion transferring mediumO
SUM~5ARY OF THE INYENTION
-
Electrochromic displays o~ the kind described according
to the pre~ent invent~on in~orporate a soluble cationic ion ex-
¦change resir e g a membrane Or the acid for~ of a soluble poly-
~tyrene Rulfonic acid polymer chemically wetted with ~ater, or a
membrane Or the acid form of a soluble perfluorosulfonic acid
polymer chemically wetted with water, located bet~ee~ the solid
electrochro~ic layers o~ the display, o~e Or which ~s an electro-
chromic counterelectrode o~ the ~ind disclo~ed in my U.S. Patent
,~1 ,
1 ' ' `, :
11471~4Z
4,012,831- By utilizing the soluble cationic ion exchange reYin
as the electrolyte-separator layer, the function of the electro-
lyte c~n be accomplished without any ~ree acid being present in
I the di~play as is required in present dlsplay~ which utilize acid
! electrolytes.
The electrolyte-separator layer of the present invention
may be ~ormed directly on one of the solid electrochromic material
layers by castin~, spraying, or the like. The soluble cationic
ion exchasge resin provides the necessary conductivity for opera-
tion of the display, it is believed, by enhancing the mobility ofhydrated hydrogen ions through the resin layer. Acid groups,
which are normally free when a liquid sulfuric acid is employed,
do not move; it i~ therefore believed that the corrosive and deg-
radative effects on the display's seal and switching speed, which
are normally encountered, are eliminated or at least vastly mini- ;-
mized with display~ accoring to the present invention.
A~ disclosed in Kissa U.S. 3,453,038 (at aol. 5, lines
59-63), Giglia U.S. 3,892,4~2, issued July 1, 1975 and Leibowitz
U.S. 3,944,333, issued March 16, 1976, greater contras~ of the
display can be effected if piyments are incorporated into the
separator, or if the pigment is held in place by the separator
between one electrochromic layer and the separator.
Preferred soluble polystyrene sulfonic acid polymer cat-t
ionic ion exchange resins are known to those skilled in the art,
¦ and particularly preferred are the family of soluble polystyrene
i qulfonates marketed by National Starch and Chemical Corporatio~ I
¦under the ~.S. Re~istered tradenark VERSA-TL, e.g. VERSA-TL 71,
~YERSA-TL 20 serie~, Y~RSA-TL 70 series, VERSA-TL 400 series, VERSA-
!TL 500 serLes, YERSA-TL 700 series, and the like~
¦ The utilization o~ a soluble acid polymer cationic lon
texchange resin, e~g. 9 soluble polystyrene sul~onic acid polymer
I ~ -5-
'' ~L1~7{)42 ` ` '.
cationic ion exchange resin, a~ the electrolyte-separator in dis-
~-play devices according to the present invention eliminates the
presence of a liquid or semi-solid acid electrolyte and thus the
. . .
j need for the presence of significant amounts of sulfuric or other
5 ~,~trong acids, which previously were utilized as electrolytes.
This minimizes the difficulties of sealing the display initially
iand o~ deterioration o~ the seal over a period of time. It espe-
cially prevents or greatly minimizes the passage of anions from
the counterelectrode electrochromic material through the electro-
lyte-separator to the display electrode electrochromic material,
thereby dramatically improving the display's switching speedO
While the present invention eliminates the presence of
electrolyte in liquid form, in order to activate the electrolyte-
aeparator member, it must be "ohemically wet" with water. It
~is not necessary nor desirable that flowable liquid be p~resent
in the membrane after chemically wetting it.
The soluble polystyrene sulfoni~,acid polymer membrane
is especially pre~erred because it iq very selectively permeable
i to positively charged ions and impermeable to negatively charged
ions, and extremely inert, being comprised of a polymer chain 9
jhaving attached thereto negatively charged and essentially immo-
¦bile sulfonic acid groups. Such polymer combines extremely good
ionic selectively with low resistance to cationic ~low, ease o~
~application, and high physical strength.
Thus the electrolyte-separator of the present invention ¦
i~ comprised o~ a membrane o~ a soluble acid polymer cationic ion
exchange r~sin, e.g~ 9 a soluble polystyrene sul~onic acid polymer
~ationic ion exchange resin, which i5 permeable to positively
jcharged ions or cations~ but essentially impermeable to negativelyl
3o charged ions or anions~ ¦
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This cati~nic ion exchange resin allows preferential
migration Or hydrated hydrogen ions and prevents electroph~retic
di~fusion Or colloidal partieles from the ele~tr~chromic counter-
. electrode to the electrochromic ~isplay electrode.
More particularly, there is provided:
' an electrochro~ic display de~ice ~omprisin~ in
layered Sorm, a ~irst transparent ~ubstrate with a ~electi~ely
actuatable transparent electrode thereon and a rirst electrochro-
mic layer on said transparent electrode, a counterelectrode haY-
ing a second electrochro~ic layer thereon, with an electrolyte-
~eparator layer bet~een said electrochromic layers9 where~n the
i~provement comprises a-solid electrolyte-separator comprised o~
a soluble acid-polymer cationic ion exchange resin in the acid
form, chemically wetted.
In an electrochromic variable light modulating
device having an arrangement comprising a light transmitting
substrate with a persistent electrochromic material as a
light modulating material and a counter-electrode separated
from said substrate by an i~n conducting medium, an improved
ion conducting medium comprising a polymeric ion exchange
membrane layer wetted with an electrolyte solution, the
said ion exchange membrane layer consisting of a soluble resin
of the polystyrene sulfonic acid type.
BRIEF DESCRIPTION OF THE DRAWING
--
In the accompanying drawin~ which ~orms a part o~ the
speci~ication:
FIG~.1 is an exploded perspective ~iew Or a typical
electr~chro~ic display ineorp~rating the present inventivn, and,
FIG. 2 is an enlarged oross sectional,view taken throu6~.
30 aD assembled display Or the kind shown ~n FIG~ 1.
DETAILED DESCRIP~ION OF ~HE INVE~TION
ReferrinB nou tc~ FIG, 1 of' the drawings, the display
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. . .. . .. . ....
~47~2
de~ice i9 shown as a sandwich construction oompris~ng a rirst
transparent substrate 2 and a econd spaced substrate or section
4, ~hich need no~ be transparent, a~d a separator-electrolyte lay-
er 2~ made from a s~luble acid pDlymer catioric ion exchan~e res-
in, e.g., soluble polystyrene sulfonic acld polymer, bet~eeD tbe
elements 2 and 4
The preqent inventioD is concerned primarily ~ith this
separator-electrol~te layer in co~binat~on ~it~ the electr~chro~ic
counterelectrode d~clo~ed 1D Leibo~itz U.S. ~,~12,831, and the
improved display~ resulting from thi~ co~binatlon, although, when
the separatsr-electrolyte layer which i~ described in detail belo
is employed iD other display~ of the ~ind described above, the.
operation and life o~ such other displays are improYed.
A3 depicted in FIG~ 1, substrate 2 has a conductiYe pat
tern Or transparent electrodes on the underside thereof in the
~orm of a pattern such as -~egme~ts 6, 8 comprised of segment~
which can be selectively actuated to form digits or other optical
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.. . . . . .
71D42
atterns via conductive leads 10, 12 leading to terminals 14, 16~
Sub9trate 2 may be of trahsparent ~las~ or plastic with
the transparent electrode~ 6, 8 thereon formed of a clear, con-
i ductive material ~uch a~ t~ oxide, applied usin~ known method~.
I! The pattern for exa~ple ~ay be etched on the substrate
by using a commercially available material such as NESA (a trade-
mark of Pittsburgh Plate Class Co. used to designate a glass sheet
having a conductive coating thereon of, e.g., tin or indium oxide)
and then removing the conductive coating except for electrodes 6, 8.
T~e second ~ection 4 has a conducti~e counterelectrode
18 thereon. Section 4 may be Or glass, cera~ic or plastic, coated
; with a conductive layer 18 connected to terminal 29.
Formed on the transparent electrode se~ments 69 8 and
al~o on the conductive layer 18 are layers o~ electrochromic ma-
terial indicated a-~i 22, 24, 26. The electrochro~ic material lay-
ers 22t 24 on segments 6, 8 respectively are applied by suitable
ma~king techniques to cover a smaller area than the electrodes,
30 a~ to giYe good edge definition.
There are many suitable solid electrochromic materials
which change their colors according to the particular oxide state 9
~or example, tungsten (VI) oxide, disclosed by Brimm et al. The
suitable materia~s are well known to tho3e skilled in the art and
i there is no need to list in detail the many materials which car be
! used in the practice of this invention~ Merely by way o~ example,
¦ a large number of conventional materi~ls, which can be used, are
identified in the U.SO Patents to Talmey, supra. I prefer to em-
ploy tunssten (VI) oxide as the electrochromic material ~or layers
22, 24. Tungsten (VI) oxide is prererably deposited o~ segment~
~, 8 by vacuum evaporation, or other conventional proce~se~. The
electrochromic counterelectrode layer 26 i-~, however, formed i~
accordance with the method taught i~ my patent U.S. 4,012,831,
issued March 22, 1977.
The electrochromic material~26 formed thereby is brown in color,
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~7~39LZ
.
i~ stable in air, and contains substantially more capacity to col-
or the front electrochromic layers 22, 24 than the blue counter-
electrode disclosed in Witzke et al. U.S. 3,840,287, or than the
,;partially electrioally charged or partially "blued" counterelec-
!' trode disclosed in Giglia U S 3,973,829~
Referring to FIG. 2 o~ the drawing, an assembled display
according to the present invention is shown in cross section. The
elements 2 and 4 are bound to one another by an adhesive 30 such
a~ epoxy which serves to hold the assembly together and to seal
the inner layers around the periphery of the sandwich structure
between the elements 2 and 4.
Illustrated in the drawing are conventional circuit and
conductors for aotuatin~ the display element for applying an elec-
tric charge from the battery 32 to, for example1 selected segment
8 to a terminal 16 and the counterelectrode 18 at terminal 20.
The polarity of the applied voll;age may be reversed to erase the
image formed, by the actuation of the two-pole double-throw switch
34.
The electrochromic material of layers 22 and 24 may
range in thickness from 0.1 to 100 microns, however, a thickness
of approximately 1 to 10 microns or less is preferred; the thick- ,
ness of the electrochromic material layer 26 is about 25 microns. i
The separator 28 which sPrves as the solid electrolyte
¦,for the display device is usually on the order of 25 to 75 microns
Iin thickness. The solid electrolyte-separator utilized in this
invention i5 a soluble, selectively permeable cationic ion exchange
resin made for example from a soluble polystyrene sulfonic acid
polymer. It has a high degree of perferential transportability
¦for cations as opposed to anions, and also for hydrogen ions as
¦opposed to other cations. Optionally, as disclosed for example
_9_
.. . . ~ . , . ~
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~1~7~3~2
in Kissa U.S. 3~453,0381 Giglia U.S. 3,892,472, and Leibowitz U.S.
3,944,333, an opacifier or a contrast enhancing opaque pigment,
uch as titanium dioxide, can be incorporated in the separator-
,electrolyte material to conceal the counterelectrode 18, 26 from5 !Ithe ~ield of view o~ the optical patterns formed by segments 6,
8. The separator 28 preferably comprises a membrane formed di-
rectly on the electrochromic layers 22, 24 or 26 by spraying,
casting and t~e like.
Before or after assembly, the separator-electrolyte is
chemically wet with water, or a water solution o~ the soluble
acid polymer cationic ion exchange resin incorporated in the sep-
arator e.g., a water solution of polystyrene sulfonic acid poly-
mer. For best results in the form of stability of the electro-
chromic layers, no liquid excess moisture should be present, i.e.,
the cationic ion exchange resin layer should only be chemically
wet and no more.
While the invention has been exp~ained by a detailed
description of certain speci~ic embodiments, it is to be under-
stood that various modifications and substitutions can be made
in any of them within the scope of the a~pended claims whi`ch are
'intended also to include equivalents of such e~bodiments.
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