Method of making an electro-optical display

Disclosed is a method of making an electro-optical display and the display made by such method having improved optical uniformity provided by the use of one or two pressure plates having raised portions that are dimensionally adapted to press uniformly on the seal enclosing the electro-optical material in a cavity between two plates of the display or uniformly upon the seal and at least one support member disposed in the cavity as a means of providing support and improving parallelism between the plates. The method also includes embodiments of electro-optical displays in which the support members, if used in the display, comprise a plurality of graphically shaped support members that not only provide support and improve parallelism between the plates but which are also able to convey information to a viewer of the display regardless of whether the electro-optical material is in an electrically energized or an electrically unenergized state.

INTRODUCTION 
This invention relates generally to a method of making electro-optical 
displays of the type which contain an electro-optical material 
hermetically sealed within a cavity between two plates of the display and 
more particularly to a method of making such displays having only the 
hermetic seal or having the hermetic seal in combination with a plurality 
of support members disposed within the cavity as a means of providing 
support and maintaining parallelism between the plates across the cavity 
where the support members are preferably graphically shaped such that in 
combination they convey information to a viewer of the display regardless 
of whether the electro-optical material is in an electrically energized or 
an electrically unenergized state. 
BACKGROUND OF THE INVENTION 
Electro-optical displays utilizing an electro-optical material whose 
ability to block or transmit light is dependent on its ability to 
re-orient the direction of its molecular structure with respect to the 
direction of incident light as a result of its being converted from 
electrically energized state to an electrically un-energized state or vice 
versa is well known in the art. 
Such displays typically feature the electro-optical material hermetically 
sealed within a cavity between two plates of which at least one of the 
plates is made from a transparent material such as glass or quartz or 
other suitable material. In instances where both of the plates are 
transparent, the display is termed a "transmissive type" display. In 
transmissive type displays, light is able to enter into the cavity through 
one of the plates and exit from the cavity through the other plate. A 
"reflective type" display on the other hand is provided where either both 
of the plates are transparent and a reflector is disposed on the side of 
one of the plates facing away from the cavity such that the reflector is 
able to reflect light back into the cavity that has entered into the 
cavity through the other transparent plate or alternatively where one of 
the plates is itself a non-transparent reflector able to reflect light 
back into the cavity that has entered into the cavity through the other 
transparent plate. 
Electro-optical materials suitable for use in transmissive and reflective 
type displays are well known in the art and generally feature an organic 
crystalline structure alone or in combination with an organic amorphic 
medium with the crystalline structure having the ability to block or 
transmit light dependent upon the direction that incident light impinges 
upon the structure in combination with having the ability to re-orient the 
direction of its crystalline structure in response to an electrical field 
imposed thereacross and thus changing the direction of its crystalline 
structure with respect to the direction of the incident light. 
Electro-optical materials generally include materials such as liquid 
crystalline nematic materials, smectic materials and cholesteric materials 
in which in the absence of an electrical field, nematic materials feature 
the crystalline structure randomly dispersed throughout the amorphic 
medium, smectic materials feature the crystalline structure tending to lay 
in planes within the amorphic medium and cholesteric materials feature the 
crystalline structure in the form of coils within the amorphic medium. 
Most commonly in use are nematic liquid crystalline materials which 
preferably have sufficient positive dielectric anistrophy such that in the 
absence of an electrical field they tend to align substantially parallel 
to uni-directional rubbing lines provided by rubbing a suitable surfactant 
coating disposed on the surface of the plates in contact with the nematic 
liquid crystalline material and to align parallel to an electrical field 
imparted thereacross in the presence of an electrical field. Such displays 
become even more effective by rotating the direction of the rubbing lines 
on one of the plates from the direction of the rubbing lines on the other 
plate so as to impart a twist to the nematic liquid crystalline material 
and thereby increase the responsiveness of the nematic material to lower 
level electrical fields. Also in common use are cholesteric materials 
particularly when they are able to change to a nematic phase material in 
the presence of an electrical field. In addition, electro-optical 
materials commonly employ blends of two or more of liquid crystalline 
materials as well as blends of such materials with homologous nonliquid 
crystalline materials and other compatible materials such as dichroic dyes 
and the like to produce a particularly desired effect. 
In addition to the previously described electro-optical materials, such 
displays may further include polarizing films disposed on one or both of 
the sides of the plates facing away from the cavity where desired which 
may be aligned or crossed to each other depending on the particular 
optical characteristics desired. 
The electro-optical material contained within the previously described 
displays is commonly electrically energized by means of supplying 
electrical power to a transparent electrically conductive coating such as 
a coating of tin oxide or indium oxide disposed in the form of discrete 
images on the side of the plates facing toward the cavity and in contact 
with the electro-optical material such that, by selectively energizing the 
electro-optical material between a particular discrete image aligned 
between the plates, the electro-optical material contained in the cavity 
therebetween is caused to re-orient the direction of its molecular 
structure with respect to the direction of incident light so as to either 
block or transmit the image to a viewer of the display. 
Although electro-optical displays have been used for many years, a problem 
has existed, particularly with respect to larger displays, in providing 
support and maintaining parallelism between the plates across the display 
cavity. It has been observed that undesirable refraction patterns tend to 
appear in the electro-optical material in regions of the cavity where the 
plates are closer together due to the difficultly in maintaining 
parallelism between the plates across the cavity and that such refraction 
patterns tend to become more of a problem as the size of the display 
cavity is increased due to the even greater difficultly in maintaining 
parallelism between the plates of larger displays. 
Although the hermetic seal itself is generally able to provide support and 
maintain suitable parallelism for displays having smaller cavities, the 
ability of the seal to provide such support and parallelism between the 
plates is highly dependant upon the uniformity of pressure exerted on the 
seal when the plates are pressed together during the process of making the 
display. 
As a means of aiding the seal in providing support and maintaining 
parallelism between the plates, it has been common practice in the past to 
mix solid materials such as glass beads or fibers to the electro-optical 
material provided that such materials are compatible with the 
electro-optical material and are able to be used without interfering with 
the electrical properties of the display and the optical properties 
desired of the electro-optical material. Although the addition of such 
materials as glass beads and fibers has been used to advantage, the 
practice has not been altogether satisfactory in that such materials may 
tend to migrate within the electro-optical material to the extent that 
higher concentrations occur in some regions of the cavity versus other 
regions and thereby diminish the ability of such materials to maintain 
parallelism between the plates. 
More recently a support member made from glass or a flurocarbon based bead, 
such as disclosed in U.S. Pat. No. 3,990,781, has been disposed within the 
cavity such that it extends across the cavity from one plate to the other 
plate to provide support and maintain parallelism between the plates. Even 
more recently, a plurality of graphically shaped support members have been 
found to provide support and improve parallelism between the plates in 
addition to providing information to a viewer of the display regardless of 
whether the electro-optical material is in an electrically energized or 
electically un-energized state. 
Although such support members within the cavity, either singularly or in 
conjunction with materials such as glass beads or fibers, are able to 
provide support and improved parallelism between the plates, a problem (as 
in the case with the seal above) has existed in being able to press the 
plates uniformly together while pressing with substantially equal force 
upon the hermetic sealant and upon the individual support members in order 
to insure that the plates are evenly spaced across the cavity so as to 
preclude the development of the previously described undesirable 
refraction patterns in the electro-optical material and thereby improve 
the optical uniformity of the display. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an 
electro-optical display made by a method that provides the display with 
improved optical uniformity. 
It is another object of this invention to provide a method of making an 
electro-optical display that reduces or eliminates undesirable refraction 
patterns arising in the electro-optical material enclosed by a hermetic 
seal within a cavity between two plates of the display as a result of 
unequal spacing between the plates due to non-uniform pressure being 
exerted upon the plates during the process of pressing the plates 
together. 
It is yet another object of this invention to provide a method of making an 
electro-optical display having a plurality of support members disposed 
within a cavity of the display containing the electro-optical material 
enclosed by a seal by which refraction patterns are reduced or eliminated 
that might otherwise arise in the electro-optical material as a result of 
unequal pressure being exerted upon the seal and the support members 
during the process of pressing the plates together.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Shown in the FIGURE is electro-optical Display 14 in the process of being 
made by the method of the present invention. Display 14 has spaced apart 
plates 1 and 2 that for transmissive type displays are preferably made 
from transparent glass but may be made from transparent quartz or other 
transparent material that is suitable for use in such displays. In the 
event that a reflective type display is desired, display 14 may have a 
reflector (not shown) disposed adjacent the side of plate 2 facing away 
from plate 1 or, in the alternative, plate 2 may itself be a reflector 
rather than transparent provided it is not so electrically conductive as 
to electrically interfere with electrical conductive coatings 5B and 5A 
disposed respectively on the facing surfaces of plates 1 and 2. In the 
event that display 14 is a transmissive type display, coatings 5A and 5B 
are made from a transparent electrically conductive material such as tin 
oxide or indium oxide. In the event that plate 2 is itself a reflector and 
is not required to be transparent, then coating 5A is not required to be 
transparent. 
Disposed between plates 1 and 2 is hermetic seal 3. Seal 3 encloses cavity 
4 and is made from a sealant composition that is non-conductive and is 
able to bond plates 1 and 2 together so as to hermetically seal an 
electro-optical material within cavity 4 between plates 1 and 2 after they 
have been pressed together. Although the FIGURE shows the hereinafter 
described support members disposed in the cavity of the display in 
conjunction with seal 3, the method of the present invention also includes 
embodiments of optical displays that have no support members in the cavity 
containing the electro-optical material. 
Coating 5A is in the form of a plurality of discrete segments having 
separate leads 6 extending past seal 3 for connection to a source of 
electrical power. Although other suitable means may be utilized to 
transfer electrical power to plate 1, for the embodiment shown in the 
FIGURE, electrical power is transferred from plate 1 to plate 2 by means 
of lead 9 of coating 5A that electrically contacts plug 7 through seal 3 
which in turn electrically contacts coating 5B on plate 1. Plug 7 is made 
from any suitable electrically conductive material such as for example, 
silver and the like. Coating 5B is in the form of discrete patterns which, 
when aligned with coating 5A in the manner desired, is able to provide an 
electrical field therebetween and thereby electrically energize the 
electro-optical material contained within cavity 4 between the particular 
aligned portion of coating 5A and 5B and thereby impart an image of the 
particular electrically energized segment of coating 5A to a viewer of the 
display. Although coatings 5B and 5A may be respectivley disposed on 
plates 1 and 2 by any suitable manner, they are commonly disposed 
thereupon by silk-screening-etching techniques well known to those 
ordinarily skilled in the art such as where the undesired portions of 
coatings 5A and 5B are removed by a suitable etching material such as 
hydrofluoric acid. 
Support members 8 in the form of graphically shaped letters "F" and "E", 
the word "GAS" and the referenced bars are disposed in cavity 4. For the 
purposes of this invention the term "support members 8" includes support 
members that are graphically shaped such as the letters "F" and "E" and 
the word "GAS" as well as the referenced bars or other shapes (not shown) 
which in combination are only intended to provide support and improved 
parallelism between the plates and are not intended to convey information 
to a viewer of the display. Support members 8 are of substantially the 
same thickness as seal 3 which typically is in the order of about 10 
microns to about 100 microns. Although shown in the FIGURE as only being 
disposed on plate 2, seal 3 and support members 8 may also be disposed in 
a mirror image aligned relationship on the side of plate 1 facing plate 2 
with their respective thicknesses on plates 1 and 2 adjusted such that the 
desired thickness of seal 3 and support members 8 is achieved when plates 
1 and 2 are pressed together. 
Support members 8 are made from a material that is non-conductive and 
non-contaminating to the electro-optical material contained within cavity 
4 and possess the desired rigidity to provide support and maintain 
parallelism between plates 1 and 2 during and after the time they are 
pressed together in conjunction with preferably aiding seal 3 in bonding 
plate 1 to plate 2. Embodiments of optical displays made by the method of 
the present invention include those displays having at least one support 
member 8 disposed in cavity 4 that is not graphically shaped either alone 
or in conjunction with support members 8 that are graphically shaped or 
where all of the support members 8 are graphically shaped so that in 
combination they are able to convey information to a viewer of the display 
regardless of whether the electro-optical material contained in cavity 4 
is in an electrically energized state or an electrically unenergized state 
as previously described. Although not required, Seal 3 and support members 
8 are preferably made from the same material, such as for example, glass 
or where they are both made from a composition comprising a blend of a 
thermoplastic phenoxy and at least one epoxy resin that contains an amount 
of a crosslinking agent such as ethyl methyl imidizole sufficient to 
convert the composition to a thermoset by heating display 14 for 
sufficient time at a temperature high enough to convert the composition to 
a thermoset without damaging display 14. Although Seal 3 and support 
members 8 may be disposed on plate 2 or on both plates 1 and 2 by any 
suitable manner, they are preferably disposed thereupon by the previously 
described silk-screening-etching techniques well known to those ordinarily 
skilled in the art. 
Although a particular type of display is shown in the FIGURE, it is to be 
understood that any type of electro-optical display that utilizes a 
hermetic seal to contain the electro-optical material within a cavity 
between two plates of the display or that in combination with such seal 
feature support members, such as support members 8, whether or not 
graphically shaped, is considered within the scope of the invention. 
Pressure plates 10 and 13 are disposed respectively adjacent the side of 
plates 1 and 2 facing away from cavity 4. Although only one pressure plate 
may be used in practicing the method of the invention, two pressure plates 
such as plates 10 and 13 may also be used where desired. Plates 10 and 13 
are made from a material having sufficient rigidity to press plates 1 and 
2 uniformly together when an external force F is applied (such as by 
clamping or other suitable means) in such a manner as to uniformly press 
plates 10 and 13 respectively against plates 1 and 2 and urge plates 1 and 
2 together. Whether or not the electro-optical material is present in 
cavity 4 when plates 10 and 13 are pressed against plates 1 and 2 
generally depends on the type of sealant used and whether the 
electro-optical material is to be poured into cavity 4 or injected through 
seal 3 after plates 1 and 2 have been pressed together. Sufficient 
material has been removed from plates 10 and 13 in referenced areas 9 on 
the side of plates 10 and 13 facing towards plates 1 and 2 to respectively 
provide raised portions 11 and 12. There is an individual raised portion 
12 to correspond with each support member 8 and raised portion 11 
corresponds to seal 3. In cases where the display cavity does not utilize 
support members then plates 10 and 13 are only required to have raised 
portion 11. Raised portions 11 and 12 are of substantially the same height 
so that plates 10 and 13 are respectively able to press uniformly against 
plates 1 and 2. Raised portions 11 and 12 are respectively aligned with 
and dimensionally adapted to press uniformly against seal 3 and support 
members 8 when plates 1 and 2 are pressed together by plates 10 and 13 and 
thereby minimize or eliminate refraction patterns in the electro-optical 
material that might otherwise arise had plates 1 and 2 been pressed 
together in regions on plates 1 and 2 between support members 8. 
Although not required, portions 11 and 12 are respectively preferably 
substantially dimensionally equivalent images of seal 3 and support 
members 8 such that the facing dimensions of portion 11 and seal 3 are 
substantially dimensionally equivalent and the facing dimension of each 
member 12 is substantially equivalent to the facing dimensions of the 
particular support member 8 to which it respectively corresponds. 
Although plates 10 and 13 may be made from any suitable material such as 
metal from which material is removed by machining or other suitable 
techniques to provide raised portions 11 and 12, they are preferably made 
from a material such as glass, which is able to be etched by a suitable 
etching solution such as hydroflouric acid to provide raised portions 11 
and 12. The same silk-screen used in conjunction with etching to provide 
seal 3 and support members 8 on plate 2 can be conveniently used to 
provide raised portions 11 and 12 on plates 10 and 13. In cases where seal 
3 and support members 8 are made from compositions that require curing 
under heat while plates 1 and 2 are being pressed together by plates 10 
and 13, the materials from which plates 10 and 13 are made must 
necessarily be able to withstand such heat. 
Thus the invention provides a method of making an electro-optical display 
having improved optical uniformity by providing one or two pressure plates 
having at least one raised portion that is respectively aligned with and 
are dimensionally adapted to press uniformly against seal 3 or a plurality 
of raised portions adapted to press uniformly against seal 3 and support 
members 8 where present to reduce undesirable refraction patterns that 
otherwise might arise in the electro-optical material had the raised 
portions not been present on the pressure plates and the display plates 
merely pressed together in the manner commonly practiced in the past.