Conductor for use in electro-optical displays

Disclosed is an electrical conductor for conveying electricity between electrically conductive coatings and disposed respectively on plates and of the display that are spaced-apart from each other by means of a hermetic seal enclosing a cavity between the plates for containment of the electro-optical material. The conductor is made from a thermoplastic phenoxy resin or one or more epoxy resin and mixtures thereof and an amount of conductive particles sufficient to provide the amount of conductivity desired in addition to containing an amount of an organic glycol sufficient to insure that electrical continuity is maintained between the plates when the display is subjected to temperature cycling. The material is also useful for conducting electricity at other locations on the display.

INTRODUCTION 
This invention relates generally to electro-optical displays that utilize 
an electrical current to change orientation of an electro-optical material 
contained between a pair of parallel plates of the display to provide an 
image to a viewer and more particularly to an improvement to such displays 
that utilize an electrically conductive member for transferring electrical 
current from one plate to the other. 
BACKGROUND OF THE INVENTION 
Electro-optical displays are well known in the art. Such displays typically 
feature an electro-optical material enclosed by a hermetic seal within a 
cavity between two plates of the display of which either one or both 
plates are made from a transparent material such as glass or quartz. The 
electro-optical material is generally of the class of materials whose 
ability to block or transmit light is dependent upon the direction in 
which light impinges upon its molecular structure with its ability to 
transmit or block light dependent upon whether it is an electrically 
energized or an electrically un-energized state whereby it is able to 
re-orient the direction of its molecular structure with respect to the 
direction of the incident light. The means by which the electro-optical 
material is electrically energized is commonly provided by coating the 
inside surface of the plates adjacent the electro-optical material with a 
transparent electrically conductive material such as tin oxide or indium 
oxide. The images transmitted to a viewer of the display are provided by 
forming the conductive coating into one or more discrete configurations on 
at least one of the plates so that only the electro-optical material 
between the configuration and the coating on the opposite plate is 
electrically energized when electrical power is connected to the 
particular configuration. 
Electro-optical materials suitable for use in electro-optical displays are 
well known to those ordinarily skilled in the art and have been the object 
of considerable study and development for many years. Generally, they 
comprise a unique class of organic materials having a crystalline 
structure which is able to be rotated or otherwise re-oriented by an 
electric field and, as a result of such re-orientation, effect the amount 
of light that is able to be transmitted through the material. 
Electro-optical materials in common use today are generally known as 
"liquid crystalline" materials. Liquid crystalline materials are 
classified according to their liquid crystal packing structure into 
smectic, chlosteric and nematic type materials. Generally, smectic type 
liquid crystals feature a parallel layered dispersion of the organic 
crystalline structure in an amorphic organic fluid medium whereas the 
chlosteric type features an organic crystalline structure that is in the 
form of coils and the nematic type features a uniformly disposed organic 
crystalline structure within an amorphic organic medium. 
Most commonly used today for electro-optical displays are nematic type 
liquid crystals whose polarity can be controlled by means of the location 
and type of chemical groups that are attached to the organic crystalline 
structure. By controlling polarity, nematic liquid crystalline materials 
have developed into those having positive dielectric anistrophy and those 
having negative dielectric anistrophy. Those having positive dielectric 
anistrophy tend to align parallel to the direction of an electric field 
and those having negative dielectric anistrophy tend to align at 
90.degree. to the direction of an electric field imposed across the 
material Although nematic liquid crystalline materials having positive 
dielectric anistrophy are most popular today for use in electro-optical 
displays, the invention contemplates electro-optical displays using any 
suitable electro-optical material or mixtures of such materials with or 
without additional materials such as dichroic organic dyes, colorants and 
homologous non-liquid crystalline materials and the like. 
The electrically conductive coatings on the side of the plates facing the 
electro-optical material may be electrically energized by imposing either 
a direct current or alternating current voltage between the coatings. 
Commonly, the voltage is of a positive polarity derived by trimming the 
negative polarity from an alternating current source such that a pulsed 
current of positive polarity is provided. For electro-optical displays 
utilizing twisted nematic liquid crystals, the voltage is commonly from 
about 3 to about 10 volts. 
Although the voltage may be imposed across the electro-optical material by 
attaching one of the conductive coatings to the ground side of the voltage 
source and the other conductive coating to the active side of the voltage 
source, it is preferred to attach only the active side of the voltage 
source to a particular separate conductive lead of one of the coatings of 
negligble resistance for transmission of the current to an electrical 
connecting member of controlled conductivity that extends between and 
electrically connects the conductive lead to a conductive lead of the 
conductive coating on the other plate. Although the electrical connecting 
member may have any suitable shape, it preferably has a cylindrical shape 
having its opposite ends abutting respectively against the conductive 
coating leads on the opposed spaced-apart plates of the display. The 
conductive connecting member typically has an electrical resistance 
controlled from about 1 ohm to about 10 ohms and is preferably isolated 
from the electro-optical material in order to prevent any adverse effect 
of one upon the other. Typically, the conductive connecting member extends 
between the plates either outside of the cavity or through the seal 
enclosing the electro-optical material as a means of insuring isolation 
between the conductive connecting member and the electro-optical material. 
An example of an electro-optical display utilziling an electrically 
conductive epoxy material as a conductive connector between the facing 
conductive coatings of the spaced apart plates of the display is disclosed 
in U.S. Pat. No. 3,881,809. The connector extends through the gasket 
enclosing the liquid crystalline material of the display and electrically 
connects the conductive coating on one of the plates to the conductive 
coating on the other plate of the display. 
Commonly, the highly conductive connecting member is provided by blending 
high amounts of a highly electrically conductive material such as silver 
into suitable non-electrically conductive resins such as the epoxy resins 
disclosed in U.S. Pat. No. 3,881,809. An example of the use of a 
solderable metal coating in a hole in the plates, of a liquid crystal cell 
for providing an electrical bridge between the plates is disclosed in U.S. 
Pat. No. 4,106,860. 
It has been found, however, that electro-optical displays using conductive 
connecting members of the above type are not entirely satisfactory in that 
they are not able to maintain continuous electrical contact between the 
conductive leads on the plates of the display when the display is 
subjected to temperature cycling due generally to either the inability of 
the connecting member material to withstand the stress arising from the 
changes in temperature or the inabiliy of the connecting member material 
to maintain a bond to the conductive coating on both of the plates over 
the range of temperature cycling. 
In view of the above and in order to provide electro-optical displays that 
are operable over a broad temperature range, a need exists to provide a 
material suitable for use as an electrically conductive connecting member 
for providing an electrical bridge between the respective conductive 
coating leads disposed on the plates of the display that has sufficient 
resiliency and is able to bond to and to maintain the bond to the 
respective plates and conductive coatings over a broad temperature cycling 
range. Likewise, it is also of advantage to use such material at other 
locations associated with electro-optical displays where the maintenance 
of electrical continuity over a broad temperature cycling range is 
desirable. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide electro-optical 
displays of the type utilizing an electrical conductive connecting member 
between conductive coatings on the plates of the displays that are 
operable over a broad temperature cycling range. 
It is another object of this invention to provide an improved material for 
use as a highly electrically conductive connecting member between the 
conductive coatings on plates of electro-optical displays of the type 
utilizing such connecting members that is able to bond to and maintain the 
bond to either or both the respective conductive coating and the plates 
over a broad temperature cycling range. 
It is further object of this invention to provide an improved, highly 
electrically conductive, material for use in electrical optical displays 
wherever the maintenance of electrical continuity is desired over a broad 
temperature cycling range.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an embodiment of electro-optical display 18 of the invention 
in an exploded perspective view prior to the assembly for convenience in 
referring to its parts. Display 18 comprises a pair of spaced-apart plates 
1 and 2 of which at least one plate is made from a transparent material 
such as glass. In "transmissive" type displays, both plates 1 and 2 are 
transparent in order to permit light to pass completely through with 
plates of the display. In "reflective" type displays, only the plate 
through which light enters the display is transparent with the other plate 
being either transparent with a reflective coating or in the form of a 
reflector itself which reflects light back through the display which has 
entered the display through the other plate. 
Plates 1 and 2 have respective transparent electrically conductive coatings 
5B and 5A on their facing surfaces. Coatings 5A and 5B are typically 
formed from indium or tin oxide which is deposited as a coating on the 
plates with portions etched away to provide the desired configurations on 
each plate commonly by a silk screening--etching process familiar to those 
skilled in the art. In display 18, coating 5B is in the form of a 
rectangular coating that is broader in area than the area occupied by the 
separate conductive strips of coating 5A on plate 2 shown in FIG. 1. 
Hermetic seal 3 is disposed between plates 1 and 2. Seal 3 is preferably 
made from an electricaly insulative material that will not contaminate the 
electro-optical material and is able to bond plate 1 to plate 2 when they 
are pressed together during the process of making display 18. Seal 3 is 
designed to enclose cavity 4 between plates 1 and 2 when plates 1 and 2 
are pressed together. The electro-optical material previously described is 
disposed within cavity 4 by any suitable method during the process of 
making display 18. Seal 3 has a thickness typically in the order of from 
about 8 microns to about 15 microns and is uniform in thickness so that 
plates 1 and 2 are substantially parallel when pressed together. Seal 3 
may be made from a material that undergoes a cure by baking during the 
process of making display 18 as is well known to those skilled in the art. 
Display 18 may further include a single polarizer such as polarizer 10 or 
crossed polarizers such as polarizer 10 and 11 where appropriate for a 
partcular design. Display 18 may also include a light emitting diode such 
as light bulb 12 where such is desired to add illumination to enhance the 
image to a viewer of the display. 
Coating strips 5A extend from cavity 4 past seal 3 in the form of separate 
leads that are supported by plate 2 as shown in FIG. 1. The separate leads 
of coating 5A provide a way of connecting coating strips 5A to a source of 
electrical power by the use of electrical connecting pins such as 
hereinafter described with respect to FIG. 2. Understandably displays made 
in accordance with the invention feature at least one electrical lead 
connecting the conductive coating on one of the plates within cavity 4 to 
a source of electrical power. 
Electrical lead 6 extends away from the edge of plate 2 partially past seal 
3. Lead 6 like leads 5A is made from a conductive material such as indium 
oxide or tin oxide. Lead 6 is the lead through which electrical current is 
transferred from plate 2 to plate 1. It is to be noted that lead 6 could 
extend into cavity 4 to become part of the configuration of coating 5A 
within cavity 4 where such is desired. 
Electrical connecting member 7 extends between coatings 5A and 5B through 
seal 3 and provides an electrical interconnection therebetween when plates 
1 and 2 are pressed together during the process of making display 18. 
Although it is preferred that member 7 extend between plates 1 and 2 
through seal 3, member 7 may extend between plates 1 and 2 outside of seal 
3 where such is desired. 
Connecting member 7 is made from a material that is highly electrically 
conductive and able to bond to coatings 5A and 5B. Member 7 is preferably 
also able to bond to plates 1 and 2 in the region of its contact with 
coatings 5A and 5B in order to ensure an electrical contact therebetween. 
Member 7 provides an electrical interconnection between lead 6 and coating 
5B when plates 1 and 2 are pressed together such that it is able to 
transfer an electrical current to plate 1. The voltage imposed on coating 
5B differs from the voltage on coating 5A by the amount of resistance 
associated with member 7 such that a voltage gradient is imposed across 
the electro-optical material contained within cavity 4 which, when pulsed 
between the "on" and "off" condition, is able to rotate the molecular 
structure of the electro-optical material to provide an image to a viewer 
of the display as previously described. 
Although member 7 may have any cross-sectional shape that is able to 
suitably conduct electrical current between coatings 5A and 5B, member 7 
preferably has a substantially circular cross-sectional shape such that it 
is in the form of a cylinder passing through seal 3. An example of typical 
optical display utilizing a cylindrically shaped member 7 is where the 
diameter of member 7 is about 0.025 inch and the length of member 7, which 
is the same as the thickness of seal 3, is about 10 microns. In display 18 
member 7 is disposed in an opening provided through seal 3 before plates 1 
and 2 are pressed together. Member 7 may be disposed between plates 1 and 
2 by the silk screening process where such is desired. 
Understandably display 18 will undergo some dimensional change when subject 
to temperature cycling as previously described, it is extremely important 
that member 7 maintain continuous electrical contact between coatings 5A 
and 5B during such periods of thermal cycling. In order for member 7 to 
maintain continuous electrical contact between coatings 5A and 5B, it must 
remain bonded to coatings 5A and 5B possess sufficient resiliency to 
withstand any stresses imposed upon it during such periods through 
cycling. 
Member 7 has heretofor commonly been made by blending an amount of 
conductive particles into a suitable epoxy resin sufficient to impart the 
amount of electrical resistance desired. Although tin, nickle, silver, 
conductive carbon black or other highly conductive material may be used 
for the electrically conductive particles, it is preferred to use silver. 
Typically, the conductive particles comprise from about 50% to about 95% 
and more commonly from about 75% to about 95% of the weight of the 
epoxy-resin to provide a resistance for the particular configuration of 
member 7 that is from about 1 ohm to about 10 ohms. Other resins found 
suitable for use in making member 7 are the thermoplastic phenoxy resins 
disclosed in U.S. Pat. No. 3,994,568, the disclosure of which is 
incorporated herein by reference. Such phenoxy resins may also include one 
or more epoxy resins where such is desired. 
It has been discovered however that such epoxy and phenoxy resins and 
blends thereof have not been able to maintain a continuous electrical 
connection between plates of an electro-optical display when the display 
is subjected to temperature cycling in the range if from about -30.degree. 
C. to about 80.degree. C. The desireability that electro-optical displays 
be operable over such temperature ranges readily be appreciated for 
enabling broad applications of such displays. 
It has been discovered that the defect in the use of epoxy or phenoxy or 
epoxy-phenoxy resins in member 7 can be overcome by incorporating an 
effective amount of an organic glycol into the subject resin-conductive 
particle blend. More particularly, it has been discovered that a 
phenoxy-epoxy resin blend containing from about 50% to about 95% by 
weight, and preferably from about 75% to about 95% by weight of conductive 
particles to the total weight of the phenoxy or epoxy or phenoxy-epoxy 
resin blend plus an effective amount of an organic glycol possesses good 
flexibility and has the ability to remain bonded to the conductive 
coatings on the plates of the display when the display is subjected to 
temperature cycling from about -30.degree. C. to about 80.degree. C. 
A suitable phenoxy resin for use in making member 7 is sold under grade 
type PKHJ by Union Carbide Corporation. Although other epoxy resins may be 
suitable, it has been found that epoxy resins sold under the Trademarks 
"EPON" 1001F and "EPON" 1009 are particularly suitable for making member 
7. 
Although a suitable epoxy or phenoxy resin may be used alone, it is 
preferred to add one or more epoxy resins to the phenoxy resin such that 
the epoxy resin comprises from about 1% to about 75% by weight to the 
total weight of the phenoxy-epoxy resin blend. A preferred blend in where 
the epoxy resin comprises about 20% to about 50% by weight of the total 
weight of the phenoxy-epoxy resin blend. Although other materials may be 
added to the material for making member 7 provided they do not interfer 
with the electrical conductivity desired or the ability of member 7 to 
maintain a bond to the conductive coatings when exposed to temperature 
cycling from about -30.degree. C. to about 80.degree. C., the material 
preferably comprises a blend of phenoxy resin, preferably including at 
least one epoxy resin, a suitable amount of electrically conductive 
particles such as silver, and an effective amount of an organic glycol. 
An organic glycol found particularly suitable for enabling member 7 to 
maintain continuous electrical contact between the conductive coatings on 
the plates of an electrical display during temperature cycling from about 
-30.degree. C. to about 80.degree. C. is a triple ester glycol such as 
triacetin. Triacetin is available from numerous chemical supply houses. 
The term "an effective amount" of the organic glycol as used herein means 
an amount sufficient to ensure that the phenoxy or epoxy or phenoxy-epoxy 
resin and conductive particle blend will have sufficifient flexibility and 
ability to maintain the bonded electrical interconnection between the 
conductive coatings on the plates of the electro-optical display when the 
display is subjected to temperature cycling from about 30.degree. C. to 
about 80.degree. C. Typically, the organic glycol comprises about 10% to 
about 40% by weight to the weight of the epoxy, thermoplastic phenoxy or 
phenoxy-epoxy resin blend used in the material for making member 7. An 
example of a material found particularly suitable is where 76 grams of a 
phenoxy-epoxy resin blend comprising approximately 60% by weight of Epon 
1001F and 40% by weight of Union Carbide phenoxy resin PKHJ is blended 
with about 23 grams of triacetin to which total weight of 100 grams is 
added about 90 grams of silver. The material was found to have a viscosity 
such that it could be easily deposited in the opening through the seal, 
exhibited attractive physical and electrical properties after air drying, 
and retained good flexibility and the desired electrical resistance and 
the ability to maintain a continuous electrical contact between the 
conductive coatings on the plates during temperature cycling from about 
-30.degree. C. to about 80.degree. C. after the plates of the 
electro-optical display were pressed together and the seal between the 
plates were cured for about 10 minutes at about 105.degree. C. to about 
120.degree. C. 
The material for making member 7 may also include an effective amount of at 
least one solvent when such is desired to provide the viscosity desired 
for pouring or silk screening member 7 through an opening in seal 3 or 
outside of seal 3 as previously described. A solvent found particularly 
suitable for use in selecting Union Carbide PKJH phenoxy resin and Epon 
1001F epoxy resin is diethylene either diethyl glycol. Diethylene glycol 
diethyl ether has been found to be compatible with the phenoxy and epoxy 
resins and triacetin and exhibits an evaporation rate sufficient to enable 
commercial production of electro-optical displays at an attractive rate. 
An effective amount of diethylene glycol diethyl ether for use in 
solvating Union Carbide PKJH phenoxy resin and Epon 1001F epoxy resin has 
been found to be from about 40% to about 70% by weight of the solvent to 
the weight of the phenoxy resin or phenoxy-epoxy resin mixture. 
In cases where the epoxy resin is a liquid at ambient temperature, the 
epoxy resin may itself act as solvating agent for the thermoplastic 
phenoxy resin and thus preclude the addition of one or more solvents as a 
means of eliminating the necessity of heating phenoxy resin or epoxy 
resins that are solids at ambient temperature above their respective 
softening points in order to facilitate production of electro-optical 
displays using the material of the invention. 
FIG. 2 shows an example of another use in electro-optical displays of the 
highly conductive material used to make member 7 of the display of FIG. 1. 
In FIG. 2, plate 2, conductive coating 5A, and seal 3 are the same as 
previously described for FIG. 1. Coating 5A extends past seal 3 from 
coating 4, not referenced, towards the edge of plate 2 in the form of a 
lead and is supported by plate 2 as previously described. Electrical 
connecting pin 13 is connected to electrical conductor 15 which is encased 
by electrical insulation 14. Pin 13 is "U" shaped such that it is able to 
be pressed against the edges of plate 2 and enclose both surfaces of plate 
2 as well as the particular coating 5A lead shown to connect the 5A 
coating lead to a source of electrical power. An electrical connecting pin 
such as pin 13 may also be used to connect lead 6, previously described 
for FIG. 1, to a source of electrical power. Pin 13 is dimensionally 
adapted so that a suitable amount of the highly conductive material used 
to make member 7 can be deposited on the coating 5A lead before pin 13 is 
squeezed together to secure it to plate 2 and the coating 5A lead. In FIG. 
2 the highly conductive material is shown in the form of a spherical dot 
16 which is able to flatten when pin 13 is secured to plate 2 and the 
coating 5A lead. Since most electro-optical displays have a plurality of 
leads on one of the plates which require separate connection to a source 
of electrical power, automatic dot producing devices can be employed to 
rapidly deposit each dot 16 onto respective coating leads before each 
electrical connecting pin is secured to the plate to which the leads are 
adhered. 
It has been found that the depositing of the highly conductive material 
hereinbefore described between the conductive coating leads and the 
respective pins greatly enhances the electrical contacting relationship 
between the two and, as in the case of member 7 of FIG. 1, ensures a 
continuous electrical contacting relationship when the display is 
subjected to temperature cycling from about -30.degree. C. to about 
80.degree. C. The region of the securement between pin 13 and plate 2 and 
the respective coating 5A leads may be additionally enclosed by a suitable 
protective encapsulating compound where such is desired.