CA1054247A - Seal for electro-optical device - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In an electro-optical device having a liquid layer between elec-trodes, and which also comprises a light modulating or imaging layer, e.g.
electrochromic or liquid crystal devices, or the like, a hole for access of the liquid layer has to be provided in a back plate of the device. Sealing of the hole is accomplished by a layer of adhesive, e.g. epoxide or silane adhesive around the hole with an impervious plate covering the hole and pressed in contact with the adhesive. The system for sealing the hole rep-resents an improvement over known techniques.

Description

lOS~Z47 This invention relates to electro-optical devices whose electro-magnetic radiation absorption characteristics can be selectively altered by influence of a suitable controlled electric field. More particularly, this invention is directed to a sandwich type cell in which there is a fluid layer, and an electrochromic or liquid crystal material for example so that sealing against leakage and against exposure to the atmosphere is necessary.
In U.S. Patents 3,521,941 which issued July 28, 1970 to Deb and Shaw, 3,578,843 which issued May 18, 1971 to Castellion, 3,704,057 which issued November 28, 1972 to Beagle and 3,708,220 which issued January 2, 1973 to Meyers and Augurt, there are described electro-optical devices exhibiting a phenomenon known as persistent electrochromism wherein electromagnetic radiation absorption characteristic of a persistent electrochromic material is altered under the influence of an electric field. Such devices were em-ployed in sandwich arrangement between two electrodes. Coloration was induced by charging the electrochromic film negativo with respoct to tho counter-electrode, employing an external potential. Ihe 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.
Other electro-optical devices make use of materials in solution which color under electric current, such as those described in U.S. Patents 3,626,410 which issued December 7, 1971 to deKoster and 3,283,656 which lssued November 8, 1966 to Jones and Friedrich or to the use of electro-phoretic materials as in U.S. Patent 3,540,209 which issued November 17, 1970 to Zatsky and Keeler; or to devices making use of liquid crystals as in U.S.
Patent 3,613,351 which issued October 19, 1971 to Walton.

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~054Z~7 All of these devices require seals at ~he cell edges which are adequate to prevent fluid leakage, i.e. liquid out of the cell, or atmospheric gas into the cell.
It is therefore an object of this invention to provide a seal for an electrooptic device which is fluid impervious.
This and other objects of the invention will become apparent as the description thereof proceeds.
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION
The performance of certain electrooptic devices is adversely affected by leakage of gaseous or li~uid components out of the device and/or by contamination from without the device by other materials leaking in. Devices such as liquid crystal and electrochromic types normally take the form of a relatively thin sandwich structure requiring a peripheral, edge seal. Satisfactory edge seals are known which employ glass frit or epoxy but the sealing materials normally require high temperature curing which would damage one or more components of the completed device. Therefore, it is common practice in assembly to make the peripheral seal before adding the temper-ature sensitive component. Another reason to complete an edge seal before addition of all components is illustrated in the case of a liquid crystal display in which addition of the liquid before sealing could interfere with the curing of the edge seal (in the case of epoxy). Normally a hole or holes are left in one of the faces to permit filling after the edge seal is completed. The filling holes are normally sealed with a low temperature curing or setting material which becomes the weak link in the device seal. By the invention herein dis-closed, the deficiency of the filling hole seal is overcome by the use of an impervious cap over the hole which results in a great increase in the length of the leakage path without 105~247 significantly increasing the cost or the thickness of the overall structure.
Previous seals as applied to electrochromic devices resulted in shorter service life. The disclosed seal design can tolerate limited numbers of voids in the sealant under cap but because of the relatively high area covered the overall result under normal manufacturing conditions can be expected to be high in quality.
The invention relates to the use of an impervious layer over fill-ing holes in an electrooptic device so as to improve the quality of the seal at those points by producing a very thin, extended leakag0 path without appreciably increasing the cost or the thickness of the device.
Thus, according to the invention, there is provided in an electro-optical device comprising a transparent face plate and a back plate, and a fluid contained thorebetween a filling hole through one of said plates for addin8 said fluid, and means around the periphory to contain said fluid;
means to soal said filling holo comprising a layor of adhesiva arotJnd said filling hole and an impervious layer pressed in contact with s~id udhesive over the entire area of the plate having said filling hole.
DETAILED DESCRIPTION OF ~IE INVENTION
_ The present invention will be illustratecl as used in the construc-tion of an electrochromic cell, e.g. as described in U.S. Patent 3,708,220.
Such a cell consists of a sandwich construction of a transparent substrate with a conductive electrode coated thereon; an electrochromic layer on the electrode, an ion conducting layer (e.g. an acid electrolyte), and a counter-electrode deposited on a conductive surface. The edges of the device are sealed to contain the electrolyte and keep out the atmosphere.
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 persistent 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 radi-ation in a given wavelength region, and once in said second state, is respon-sive to the application of an electric field of the opposite polarity to return to its first .~ -3-~ 054247 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 or non-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 MATERIALS
The materials which form the electrochromic materials of the device in general are electrical insulators or semicon-ductors. Thus are excluded those metals, metal alloys, and other metal-containing compounds which are relatively good electrical conductors, as described in United States Patent Number 3,704,057.
These include materials containing a transition metal element ~including Lanthanide and Actinide series ele-ments), and materials containing non-alkali metal elements such as copper. Preferred materials of this class are films of transition metal compounds in whicll the transition metal may exist in any oxidation state from +2 to +8. Examples of these are: transition metal oxides, transition metal oxysul-fides, transition metal halides, selenides, tellurides, chro-mates, molybdates, tungstates, vanadates, niobates, tantalates, titanates, stannates, and the like.
A particularly advantageous aspect of the present invention is in the use of two separate layers of identical electrochromic materials one layer being employed as the counter-electrode for the other layer. A preferred embodiment consists of tungsten oxide as the electrochromlc color elec-trode and tungsten oxide and graphite as the counter-electrode.
When the persistent electrochromic materials are employed as films, thickness desirably will be in the range 1054Z~7 of from about 0.1-100 microns. However, since a small poten-tial 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 com-pound and film-forming method may place physical (e.g., non-uniform film surface) and economic limitations on manufacture o~ the devices.
The films may be laid down on any substrate which, relative to the film, is electrically conducting. The elec-trically conductive material may be coated on another suit-able substrate material including glass, wood, paper, plastics, plaster, and the like, including transparent, translucent, opaque or other optical quality material~. A p~eferred em bodiment 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 persistent electro-chromic 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 appear-ance. Prior to the application of the electric field, the electrochromic imaging layer was essentially non-absorbent and thus transparent.
ELECTROLYTE
A fluid layer containing an acid may also be used as disclosed in United States Patent Number 3,704,057. A pre-ferred embodiment employs H2SO4.

~(?S~Z9~7 SEALANTS
Various sealants or adhesives may be used such as an epoxide, a silane, a glass frit, and the like.
COUNTER-ELECTRODE
Suitable counter-electrode materials are disclosed in United States Patent Numbers 3,704,057 and 3,844,636 which issued October 29, 1974 to Maricle and Giglia. A particularly good counter-electrode material is pal-ladium. The counter-electrode may also be an electrochromic material as dis-closed in U.S. Patent Numbers 3,847,468 which issued October 12, 1974 to Clasen and Giglia and 3,827,784 which issued August 6, 1974 to Clasen and Giglia.
The invention may be further understood by reference to the drawing in which:
I`he ~igure is a cross-section of an olectrochromic display devico showing the lnventive seal means.
As shown in the Pigure, the light modulating device consists of a front plate 1, consisting of a transparent or translucent matorial 2 such as glass or plastic, with a light transmitting layer 3, which is electrica11y conductive, e.g. tin oxide. The structure of 2 and 3 is available commercial-ly as NESA* glass which is a glass plate with a conductive coating on atleast one surface. As shown, a layer of tungsten oxide 4 is deposited upon the tin oxide 3. The back of the cell is made up of a stainless steel plate 5 and on this a layer of tungsten oxide and graphite 6 as a counter-electrode.
A space 7 is provided to contain an acid electrolyte. A filling hole 8 is provided in plato 5, for adding electrolyte.
The edges of the cell are closed by a teflon spacer 9 around the periphery of the cell, and an adhesive seal 10 over spacer 9. After space 7 has been filled with electrolyte through hole 8, an adhesive is applied to the hole to close it. In the present case, the adhesive is spread over the entire outside surface of plate 5, as a layer ll, a second plate 12, of stain-less steel or other suitable inert material is applied to the adhesive layer ll. Thus, without materially increasing * trade mark the thickness of the device, the leakage path through adhesive layer 11 has been lengthened laterally. The electrodes 3 and 5 are connected by electrical leads 13 and 14 respectively to a source of direct current, and switching means not shown to provide current in either direction to color or erase layer 3.
As shown in the Figure, adhesive layer 11 covers the entire back of layer 5, as does plate 12. This is practical where the device is small, such as a display in a wristwatch or small electronic calculator. In larger devices, it would be sufficient to form adhesive layer 11 over an area surrounding filling hole 8, e.g. for one-quarter to one-half inch radius from the hole for example, and provide plate 12 of approxi-mately the same area.
An information display device could be fabricated with the structure of this invention, if the tungsten oxide layer is in the form of discrete dotq and segments with the required electrical circuitry and logic means.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an electrooptical device comprising a transparent face plate and a back plate, and a fluid contained therebetween a filling hole through one of said plates for adding said fluid, and means around the periphery to contain said fluid; means to seal said filling hole comprising a layer of adhesive around said filling hole and an impervious layer pressed in contact with said adhesive over the entire area of the plate having said filling hole.

2. The device of claim 1 wherein said device includes an electro-chromic material as an electrooptical material.

3. The device of claim 1 wherein said device includes a liquid cry-stal material as an electrooptical material.

4. The device of claim 1 wherein said adhesive is an epoxide adhesive.

5. The device of claim 1 wherein said adhesive is a silane adhesive.