Thin electrochromic display

A thin electrochromic display suitable for manufacture in a continuous process on a backing tape which becomes part of the display. The display is a sandwich structure comprised of a transparent substrate, transparent electrodes having persistent electrochromic material thereon, a solid cationic ion exchange resin electrolyte in contact with the electrochromic material, a conductive metal foil member with electroreactive layer thereon, and an impervious adhesive backing tape adhered to the substrate around the foil member and also covering and adhered to the foil member to seal the display and having an aperture therein for permitting electrical contact to be made with the foil member.

BACKGROUND OF THE INVENTION 
This invention relates generally to electrooptic displays of the 
electrochromic type, wherein a persistent electrochromic material 
undergoes reversible and stable color changes upon the application of an 
electric field. More particularly, the invention relates to a thin 
electrochromic display suitable for manufacture in a continuous process. 
Electrochromic displays are well known in the art, examples being shown in 
U.S. Pat. No. 4,012,831 issued Mar. 22, 1977 to Leibowitz and assigned to 
the present assignee, which describes a process for making an 
electroreactive layer on the rear electrode used in an electrochromic 
display by surface oxidizing and subsequently heat treating in hydrogen a 
tungsten metal layer on a ceramic base. When the ceramic base is used as a 
substrate, this substantially adds to the thickness of the display. 
Electrochromic displays built up in layers from the front substrate are 
known in the art using solid or crystalline electrolytes as ion carriers 
to enable alternately darkening or bleaching the electrochromic material 
when a field is applied across the electrolyte. Examples of such displays 
may be seen in U.S. Pat. No. 4,009,936 issued to Kasai or Mar. 1, 1977, 
U.S. Pat. No. 3,995,943 issued to Jasinski or Dec. 7, 1976 and U.S. Pat. 
No. 3,971,624 issued to Bruesch et at on July 27, 1976. The Jasinski and 
Kasai patents utilize a sealant layer of thermosetting plastic or epoxy 
resin to enclose a layer of metallic silver and the solid electrolyte, and 
require extension of the silver layer or an external electrode passing 
through the sealant to make electrical contact. The Bruesch et al patent 
utilizes a thin exposed metal layer applied on top of an electrochromic 
material. 
The foregoing Jasinski, Kasai, and Bruesch et al patents, while having 
possibilities for reducing the thickness of electrochromic displays from 
the older more bulky displays using two substrate members, nevertheless 
are built up in layers from the single transparent substrate and do not 
readily lend themselves to mass production or to continuous processing. 
Also the layer thickness and processes require great care to achieve 
uniform results. 
Accordingly, one object of the present invention is to provide an improved 
thin electrochromic display which is adapted for continuous process 
manufacture. 
Another object of the invention is to provide an improved construction for 
a thin electrochromic display of uniform and consistent quality.

SUMMARY OF THE INVENTION 
Briefly stated, the invention is practiced by providing an electrochromic 
display having a transparent substrate with transparent electrodes and 
electrochromic material thereon, a semi-solid or solid cationic ion 
exchange resin electrolyte in contact with the electrochromic material, a 
conductive foil member having an electroreactive layer thereon in contact 
with the electrolyte, and an impervious adhesive tape member adhered to 
the substrate around the foil member and also covering and adhered to the 
foil member, the tape member having an aperture therein for permitting 
electrical contact to be made with the foil member. 
The process includes providing an impervious adhesive backing tape with 
apertures, positioning the foil member with electrolyte coating thereon 
over an aperture, positioning the substrate over the coated foil with the 
electrochromic material in contact with the electrolyte and adhering the 
tape to the foil and substrate. If the tape member is continuous with 
spaced apertures, a subsequent step includes severing the tape between 
substrates. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 of the drawing, an electrochromic display shown in 
cross section comprises a transparent substrate 1, such as glass having 
transparent conductive electrodes 2 thereon. Electrodes 2 may be arranged 
in any desired pattern and provided with conductive leads 3 to contact 
terminals 4 on the edge of the substrate, each of the electrodes being 
provided with such a terminal so that it can be selectively actuated by 
application of a current source (not shown). The electrodes 2, may be 
formed by etching from a conductive tin oxide coating in any desired 
pattern, using commercially available material known as NESA glass, 
removing the conductive coating except for the segments and their 
connecting leads. 
The display shown in the drawings of FIGS. 1 and 2 is simplified to provide 
only a single digit indicated by reference numeral 5, but several such 
digits may be employed on a single display. Also the invention is 
applicable to the use of several digits on the substrate and several 
electrically isolated rear electrodes as taught in the copending 
application of Marshall Leibowitz, Ser. No. 676,030 filed Apr. 12, 1976 
and assigned to the present assignee. 
Disposed on electrodes 2 are thin layers of persistent electrochromic 
material 6. Tungsten oxide is the preferred material, but there are a 
large number of electrochromic materials referred to, for example, in U.S. 
Pat. No. 3,521,941--Deb et al as well as the materials referred to in the 
aforementioned Bruesch et al patent. The electrochromic material may be 
applied by vacuum evaporation and deposition using masks. 
Disposed in intimate contact with the electrochromic material 6 is a 
semisolid electrolyte 7, of cationic ion exchange resin in the acid form. 
This is in the form of a chemically wetted paste of putty-like consistency 
previously applied to a foil later to be described. The preferred 
electrolyte is a commercially available soluble form of polystyrene 
sulfonic acid. However, insoluble polystyrene sulfonic acid commercially 
available in powder form in a suitable binder is also useful. A color 
contrasting pigment such as titanium oxide is mixed with the electrolyte. 
In accordance with one aspect of the present invention, a foil member 8 is 
positioned with an electroreactive layer disposed in contact with the 
solid electrolyte. This foil is preferably prepared from a tungsten metal 
foil treated in the manner described in assignee's aforementioned U.S. 
Pat. No. 4,012,831. over the surface. A foil prepared in this manner 
serves as the conductive back electrode and provides requisite capacity 
enhancing the flow of cations to darken the electrochromic material 6 when 
the electrodes 2 are negative with respect to the back electrode (or foil 
8). 
Covering and adhered to the backside of the foil and also adhered to the 
substrate 1 around the outside of the foil is an insulating impervious 
film or backing tape 9 having adhesive on one side thereof. Several 
suitable tapes are commercially available. One is a contact tape number Y 
8019 produced by Minnesota Mining & Manufacturing Company. Another is an 
aluminized Mylar tape prepared with a clear silicone contact adhesive 
Number 1158 manufactured by Custom Coating & Laminating Corp., Worcester, 
Mass. 
An important feature of the present invention is the provision of an 
aperture 10 in the tape 9 exposing the foil 8, so that an electrical 
contact can be made with the back side of the foil through the aperture. 
The aperture 10 is preferably located at a place not directly over a 
segment of the digit, otherwise excessive contact pressure on the foil 
might change the spacing and affect the performance of the display. 
A peripheral void or open space 11 is left between the electrolyte 7 and 
the interface between tape and substrate, since the electrolyte, which is 
acidic, might otherwise react adversly with the tape and the adhesive over 
a long period of time. 
The tape 9 is narrower than the substrate width and is applied to the 
underside of the substrate, as shown in FIG. 2 to leave the contact 
terminals 4 exposed. The tape serves to completely seal around the foil 
and also to the surface of the foil to prevent moisture from leaving the 
electrolyte and also to prevent external contamination to the cell. 
FIGS. 3a, 3b, and 3c show in plan view, and FIGS. 4a, 4b, and 4c in 
elevation view, a continuous processing method in symbolic form for 
manufacturing the thin electrochromic display of the present invention. 
The tape 9 is shown in FIG. 3a and provided with spaced apertures 10, with 
the adhesive side up. FIG. 4a shows the corresponding elevation view. 
In FIG. 3b, and corresponding FIG. 4b, the foil members 8, previously 
oxidized and reduced as described, and having a semisolid electrolyte 
previously applied as a coating thereon, are positioned over the apertures 
10, with the electrolyte 7 facing up. The electroreactive layer on the 
foil and the subsequent coating of electrolyte are applied separately in 
advance under controlled conditions. 
In FIG. 3c, the substrates 1 with the prepared segment patterns of 
transparent electrodes 2 and electrochromic materials 6 thereon are 
positioned face down, so that the foil members 8 register with the segment 
patterns 5 on the substrates 1. 
FIG. 4c, illustrates in cross section, a suitable tool 12 compressing the 
foil and electrolyte in the central portion of the display to provide 
proper spacing, compressing the edges for adhering the tape to the 
substrate and foil, and severing the tape. The foregoing process steps may 
be undertaken manually, or by automated continuous process. 
Referring to FIG. 5 of the drawing, a construction is shown which is 
adapted to a thin electrochromic display suitable for multiplexing, i.e. 
adding a plurality of separate or electrically insulated back electrode 
members, similar to the aforementioned pending application in the name of 
Leibowitz, Ser. No. 676,030. 
A transparent substrate 15, transparent electrodes 16 with electrochromic 
materials 17 thereon are formed as previously. Two separate foil members 
18,19 prepared as before, with semisolid electrolyte films 20,21 adapted 
to cooperate with separate sets of electrodes on the substrate 15. The 
single tape member 22 is employed with an aperture 23 exposing foil 18, 
and an aperture 24 exposing foil 19. Each isolated back electrode requires 
an opening in the adhesive sealant tape to make electrical contact to each 
isolated back electrode. However the tape is not severed between sections 
but is adhered to the substrate around both display sections and also 
between display sections as indicated at 25. 
Thus there has been disclosed an improved construction for a thin 
electrochromic display, and method of making the same, which facilitates 
uniform and consistent preparation using tapes and foils rather than 
build-ups of layered materials. Therefore better quality control is 
possible and the process is adaptable to continuous automated manufacture. 
While there has been shown what is considered to be the preferred 
embodiment of the invention and one modification thereof, it is of course 
understood that various other modifications may be made therein, and it is 
intended to cover in the appended claims all such modifications as fall 
within the true spirit and scope of the invention.