U.S. patent number 3,617,374 [Application Number 04/815,966] was granted by the patent office on 1971-11-02 for display device.
This patent grant is currently assigned to The National Cash Register Company. Invention is credited to Theodore L. Hodson, Joe W. Jones, John G. Whitaker.
United States Patent |
3,617,374 |
Hodson , et al. |
November 2, 1971 |
DISPLAY DEVICE
Abstract
The present disclosure is directed to articles of manufacture,
e.g., display devices, having self-contained controlled resistor
means for generation of heat upon electrical activation, which
means can be formed in any desired configuration and thickness, and
an encapsulated liquid crystal layer responsive to variations in
heat to present a display, which can be polychromatic. The resistor
is comprised of conductive ink deposited on one major surface
(usually the lower surface) of an opaque, substantially
electrically nonconductive layer having a layer of encapsulated
cholesteric liquid crystals in direct contact with at least a
portion of the other major (e.g., upper) surface of the opaque
layer. Heating due to the resistor produces reversible color
changes in the encapsulated liquid crystals resulting in the
display.
Inventors: |
Hodson; Theodore L. (Bellbrook,
OH), Whitaker; John G. (Englewood, OH), Jones; Joe W.
(Dayton, OH) |
Assignee: |
The National Cash Register
Company (DAyton, OH)
|
Family
ID: |
25219306 |
Appl.
No.: |
04/815,966 |
Filed: |
April 14, 1969 |
Current U.S.
Class: |
349/19;
252/299.7; 374/162; 428/321.3; 428/1.6 |
Current CPC
Class: |
G02F
1/1334 (20130101); G02F 1/132 (20130101); G01D
7/005 (20130101); Y10T 428/1086 (20150115); Y10T
428/249996 (20150401); C09K 2323/06 (20200801) |
Current International
Class: |
G02F
1/1334 (20060101); G02F 1/13 (20060101); G02F
1/133 (20060101); G01k 011/16 (); G01k 011/20 ();
B44d 011/8 () |
Field of
Search: |
;117/212,215,217,226
;73/356 ;161/410 ;252/408 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leavitt; Alfred L.
Assistant Examiner: Grimaldi; Alan
Claims
What is claimed is:
1. A display article having a self-contained controlled means for
generation of heat upon electrical activation comprising an opaque,
electrically nonconductive layer, a layer of encapsulated
cholesteric liquid crystals on and in direct contact with at least
a portion of one major surface of said opaque layer and a layer of
electrically conductive ink in direct contact with at least a
portion of the other major surface of said opaque layer and wherein
the configuration of the display is substantially the same as at
least a portion of the configuration of either the encapsulated
liquid crystal layer or the conductive ink layer.
2. A display article as in claim 1 wherein the display
configuration is substantially the same as at least a portion of
the configuration of the conductive ink layer.
3. A display article as in claim 1 wherein the display
configuration is substantially the same as at least a portion of
the configuration of the encapsulated liquid crystal layer.
4. A display article as in claim 1 wherein said opaque layer is
black.
5. A display article as in claim 1 wherein said encapsulated liquid
crystal layer contains encapsulated liquid crystals having
different color-temperature responses.
6. A display article as in claim 1 wherein encapsulated liquid
crystals having different color-temperature responses are employed
in different areas of said encapsulated liquid crystal layer.
7. A display article as in claim 1 wherein said encapsulated liquid
crystal layer has a substantially smooth, essentially transparent,
display brightness-improving top layer.
8. A display article as in claim 2 wherein said conductive ink
layer is comprises of a plurality of unconnected portions at least
some of which function independently from a remaining portion when
electrically activated to generate heat.
9. A display article as in claim 2 wherein said conductive ink
contains carbon black.
10. A display article as in claim 3 wherein said encapsulated
liquid crystal layer is comprised of a plurality of unconnected
portions.
Description
The display configuration can be determined by either the
configuration of the encapsulated liquid crystal layer or the
conductive ink layer. In the former case, the opaque film is heated
over the entire extent of the conductive ink layer, but the color
effects are observable only where the encapsulated liquid crystals
are present. In the latter case, the heating occurs only in that
portion of the opaque layer which overlies the configuration of the
conductive ink layer. Thus, only a portion of the opaque layer is
heated and this portion is then translated into color effects by
the portion(s) of the encapsulated liquid crystal layer in
thermally responsive contact therewith.
Provision can be made at desired sequential times for operating
partial displays by using various portions of either the conductive
ink layer, the encapsulated liquid crystal layer, or both. For
example, by providing separate leads to various unconnected
portions of the conductive ink configuration, these unconnected
portions can be sequentially switched on and off to sequentially
thermally generate sequential color effects in the overlying
portions of the encapsulated liquid crystal layer. On the other
hand, by utilizing portions of the encapsulated liquid crystal
configuration (connected or unconnected portions) having different
color advent temperatures (or ranged thereof) and color-temperature
responses, sequential mono- and polychromatic displays can be
achieved. Sequential color effects can also be produced by
supplying more heat via varying the current to the conductive ink
layer. Moreover, sequential polychromatic color effects and
displays can be achieved by a combination of switching to various
elements defining the configuration of the conductive ink layer and
the use of different encapsulated liquid crystal compounds and
mixtures for various portions of the encapsulated liquid crystal
layer configurations, viz, using encapsulated liquid crystal
formulations having different color advent (and response)
temperatures to achieve different color effects in different areas
of the encapsulated liquid crystal layer.
In accordance with this invention, a low-cost display is provided
which is capable of almost infinite variation from one article to
the next because of the adaptability of the encapsulated liquid
crystals to deposition procedures enabling use of a high resolution
and complex definition, e.g. silk screen and related printing
procedures. In like manner, the conductive ink resistors can be
printed in complex configurations by silk screening and related
procedures thereby ensuring a highly variable display of portable
nature, low unit price and high resolution.
The invention will be discussed in greater detail in conjunction
with the drawings. All six figures of the drawings are
cross-sectional views illustrating the various component layers
contained in these articles of manufacture. The articles of FIGS.
2, 3, 4 and 6 have a smooth, essentially transparent
brightness-enhancing top layer contiguous with the encapsulated
liquid crystal layer and of similar index of refraction with
respect to the capsular wall material and binder therein. The
articles of FIGS. 3 and 4 are formed by inverse coating, viz,
coating of the various layers on a transparent substrate which is
then inverted for viewing of the display. The articles of FIGS. 2
and 6 are formed by top coating procedures, and the substrate need
not be transparent. The articles of FIGS. 1 and 5 have no such top
layer and likewise can use nontransparent substrates.
As shown in FIG. 1, base or substrate 1, which need not be
transparent, has deposited thereon various conductive ink elements
2 to define a pattern or configuration. An opaque substantially
nonconductive layer 3 is located on and in direct contact with
electroconductive ink elements 2 and overlying encapsulated liquid
crystal layer 4 which, in turn, is comprised of encapsulated liquid
crystals a and binder b. FIG. 2 is like FIG. 1 with the addition of
a top layer 5 deposited by a top-coating procedure. FIG. 5 is like
FIG. 1 except that in the article of FIG. 5 the configuration of
the display is determined by the configuration of the various
elements 4 of the encapsulated liquid crystal layer, the conductive
ink layer 2 being coated over substantially the entire other major
surface of opaque layer 3. In FIG. 1, the configuration of the
display is determined largely by the configuration of the
conductive ink elements 2 defining the conductive ink layer with
the encapsulated liquid crystal layer 4 being deposited over a
substantially larger portion of opaque layer 3. FIG. 6 is like FIG.
5 but it contains a smooth transparent top layer (deposited by top
coating) over each portion 4 of the encapsulated liquid crystal
layer pattern or configuration.
In the article of FIG. 3, the transparent top layer 5 also serves
as a forming support for depositing the encapsulated liquid crystal
layer 4 followed by the opaque nonconductive layer 3; and the
configuration of the conductive ink layer is defined by conductive
ink portions 2. Upon deposition of all the aforementioned layers,
the article is inverted so that the display can be viewed by the
observer through the transparent, brightness-improving layer 5.
Such articles are referred to herein as "inverse coated" due to the
aforementioned inversion prior to use. FIG. 4 is prepared by
inverse coating as in FIG. 3 but the encapsulated liquid crystal
layer 4 is placed thereon in selected areas thereof to define a
pattern instead of covering substantially the entire surface of
transparent top layer 5, as in FIG. 3.
The article of the present invention offers great flexibility in
that the color response in the liquid crystal capsules can be
varied by varying the resistance of the conductive ink elements.
The resistance of the conductive ink elements can be controlled in
any one, more or all of the following manners: (1) by controlling
the thickness of the conductive ink coating itself, (2) by
controlling the total area of the coating, and (3) by varying the
very composition of the conductive ink layer, e.g., by diluting the
conductive ink with solvent (thinner) thereby reducing the
intensity of the conductive pigments, and/or by introduction of
adjuvant materials, such as plasticizers, in varying
concentrations. Also, the chromatic display effects can be varied
by controlling the power input to the respective elements defining
the conductive ink layer thereby varying the extent of thermal
excitation. This latter factor can be utilized to produce a
selective color response in an encapsulated liquid crystal capsular
layer containing a profusion of capsules having liquid crystal
compounds and mixtures possessing varying color response
temperatures, thus exhibiting varying colors at the color advent
temperatures and at temperatures above said advent temperatures.
The composite articles of this invention can operate at low power
input, can product display characters and images of high visual
resolution, and possess the ability of controlled color response
achievable via a variety of readily controlled easily variable
approaches.
As noted above, substrate 1 can be transparent of opaque as
desired. Additionally, it can be of an electrically insulating
material such as plastic, paper, wood or any similar materials. Of
course, instead of paper or organic plastics, inorganic materials
such as glass (e.g., conventional soda-lime-silica glass), etc. can
be employed.
LIQUID CRYSTAL MATERIALS
The term "liquid crystal," as used herein, is employed in the
generic, art-recognized sense to mean the state of matter often
referred to as a mesophase, wherein the material exhibits flow
properties associated with a liquid state but demonstrates
long-range ordering characteristics of a crystal. The term
"cholesteric liquid crystal" refers to a particular type of
mesophase most often demonstrated by esters of cholesterol. Many of
the cholesteric liquid crystals exhibit a reflective scattering of
light giving them an iridescent appearance. In addition to using
individual liquid crystal compounds, the encapsulated cholesteric
liquid crystalline layer can be and usually is comprised of a
mixture of two or more such compounds. The encapsulated cholesteric
liquid crystal layer, itself, can be composed of a plurality (and
usually a profusion) of capsules containing the same or different
cholesteric liquid crystal compositions. Suitable individual
cholesteric liquid crystal materials and mixtures which exhibit
chromatic response to varying temperatures include, but are not
limited to, the following cholesteryl nonanoate; cholesteryl
chloride, cholesteryl nonanoate and cholesteryl chloride,
cholesteryl nonanoate and cholesteryl bromide; cholesteryl
nonanoate, cholesteryl bromide and cholesteryl cinnamate;
cholesteryl nonanoate, cholesteryl iodide and cholesteryl
cinnamate; cholesteryl nonanoate, cholesteryl iodide and
cholesteryl benzoate; cholesteryl nonanoate, cholesteryl chloride
and oleyl cholesteryl carbonate; cholesteryl nonanoate, cholesteryl
chloride, oleyl cholesteryl carbonate and cholesteryl bromide;
oleyl cholesteryl carbonate and cholesteryl iodide; oleyl
cholesteryl carbonate and cholesteryl p-chloro benzoate; etc.
Also, it should be understood that included within the term
cholesteric liquid crystalline mixtures are mixtures of two or more
individual materials, one or more of which individually does not
form a cholesteric liquid crystal phase but which in admixture
exhibit a cholesteric liquid crystal phase. Hence, one or more
materials which individually are not cholesteric liquid crystals
can be employed in accordance with this invention if, when in
admixture, they do exhibit cholesteric liquid crystal behavior,
viz, they form a mesophase which demonstrates the property of
reflection (light scattering). One such mixture is cholesteryl
nonanoate, oleyl cholesteryl carbonate and cholesterol. The matter
material, by itself, does not form a cholesteric liquid crystalline
phase; but cholesterol does form a chromatically responsive
mesophase in combination with the other materials.
ENCAPSULATION PROCEDURES
A wide variety of procedures can be employed to adequately prepare
capsules and liquid crystalline layers containing the encapsulated
liquid crystals. The capsule diameters can vary from about 2 to
about 1,000 microns or more; but usually capsule diameters range in
size from about 5 to about 500 microns and preferably from about 15
to 30 microns for screen printing purposes. The 20- to 25-microns
size capsules are more preferred due to their uniform coatability,
color properties and resolution characteristics. One satisfactory
method of preparing capsules suitable for containing liquid crystal
materials is disclosed in U.S. Pat. No. 2,800,457 issued on July
23, 1957, to Barrett K. Green and Lowell Schleicher. While the
aforementioned capsules preparation system is sometimes preferred,
it should be understood that the capsules employed in this
invention can be obtained by any of the many later-developed
encapsulation procedures which are capable of the dimensions
required for a given use. The final form of the capsular material
to be coated is preferably 20 to 25 microns in diameter; but it has
been found that virtually any size of capsules can be successfully
utilized; the larger capsules showing a somewhat decreased extent
of visual resolution when used, e.g., in a data display system.
While U.S. Pat. No. 2,800,457 discloses a pioneer invention
concerning encapsulation on a minute scale, reference is also made
to application Ser. No. 591,023 filed Oct. 31, 1966 now U.S. Pat.
No. 3,341,466, which is a continuation of application Ser. No.
137,992 filed Sept. 14, 1961, by Carl Brynko et al., now abandoned,
which application discloses a procedure for making larger than
microscopic capsules. The entire disclosures of these applications
are incorporated herein by reference as illustrative in the area of
making large capsules. This same procedure is also discussed in the
corresponding British Pat. No. 935,312. While the foregoing
encapsulation procedures are chemical in nature, it should be
realized that mechanical encapsulation procedures (as well as other
chemical procedures) can be used to make the liquid crystal
capsules. Further details concerning satisfactory procedures can be
obtained in "Microencapsulation" by Anderson et al., published by
Management Reports, Boston, Mass. (1963), the entire disclosure of
which is incorporated herein by reference.
Another feature of the incorporation of encapsulated cholesteric
liquid crystalline materials into a sensing or display system is
the utilization of a mixture of capsules, as to size and content,
for indicating and/or displaying a wide range of specific levels of
temperature. Such a system, in one case, can comprise a plurality
of layers, or areas in the same layer, each comprising one, two or
more types of capsules having different mixtures of chromatically
responsive cholesteric liquid crystalline materials. These devices
can be tailor-made to accomplish a desired task by adjustment of
characteristics imparted thereto by any one or more of the
following variables: (a) temperature response range of the
encapsulated liquid crystal material used; (b) size of the liquid
crystal core; (c) type and thickness of the capsules cell wall
material; (d) specific composition of the liquid crystalline
material, and the like, all to the purpose of choosing a response
suitable for a given proposed use or product.
In accordance with this invention, capsules can be prepared which
contain from about 50 to about 99 weight percent of internal phase
payload (cholesteric liquid crystal material) with the remainder
being cell wall material. Usually, however, the internal phase
represents from about 70 to 95 weight percent of the total capsule
weight.
It is also within the purview of this invention to employ a
coloring material to tint the capsules cell wall color. The capsule
cell walls thus colored serve not only as liquid crystal contains
but also as color filters for the light traveling to and from the
encapsulated cholesteric liquid crystalline materials. Capsules
cell walls are easily tinted by any stain capable of coloring the
gelatin-gum arabic or other cell wall material selected for use.
Such a controlled system finds use in display devices and other
devices in cases where a broad spectrum iridescent effect (that
obtained from the incident light emanating from an encapsulated
cholesteric liquid crystalline member) is objectionable for certain
uses.
A wide variety of encapsulating (external phase) materials can be
employed to encapsulate the cholesteric liquid crystals in
accordance with this invention. Such suitable materials include
those referred to hereinabove in said Green et al. U.S. Pat., said
Brynko et al. patent applications, said British Pat. and the
Microencapsulation report. Usually the encapsulating material is
one or a combination of the following: a gelatin-gum arabic system
(with or without aldehydic cross-linking agents), a polyvinyl
alcohol-based system, a zein-based system, or phenol-plast or
amino-plast condensates, e.g., phenol-formaldehyde,
resorcinol-formaldehyde, urea-formaldehyde-based systems, etc.
BINDER MATERIALS FOR LIQUID CRYSTAL LAYER
Various natural and synthetic polymeric materials can be employed
to constitute the polymeric binder matrix of the encapsulated
cholesteric liquid crystal layer. Any transparent or substantially
transparent polymeric material can be used. Usually such binder has
an index of refraction in the range of about 1.40 to about 1.70.
Suitable polymeric materials for this purpose include, but are not
limited to, the following: acrylates poly alkyl acrylates and
methacrylates, e.g., poly methyl acrylate, poly ethyl acrylate,
poly n-butyl acrylate, poly methyl methacrylate, poly n-butyl
methacrylate, etc.; poly vinyl alcohol; gelatin; latex (natural
rubber and synthetic rubber latexes); zein, poly ethylene homo- and
copolymers; poly propylene homo- and copolymers; and any of the
materials mentioned hereinbelow as suitable top layer materials.
The encapsulated cholesteric liquid crystals can be associated
intimately with the polymer binder in a variety of ways. For
example, the capsule-binder mixture can be deposited onto a polymer
film, e.g., as a coating simply by spraying from a dispersion or
emulsion of the encapsulated liquid crystal in a binder or by
screen printing thereof.
OPAQUE BACKGROUND LAYER
The opaque background layer, which can be a preformed opaque film
or an opaque coating, e.g., black coating, is substantially
nonconductive. Black nonconductive paint can suffice for this
purpose. The function of this opaque background layer is to aid in
viewing the chromatic effects produced in the encapsulated liquid
crystal layer due to the heat generated by the conductive ink
resistor elements. Since the observable color effects produced due
to the change in temperature on the liquid crystals are observable
by reflection of incident light; an opaque background is usually
necessary to enable the human eye to accurately observe the
display.
CONDUCTIVE INK LAYER
The conductive ink layer, 2, can be any material which is
electroconductive and is preferably readily deposited upon a
substrate by coating procedures affording good definition. In cases
where the article is produced by inverse coating (as in FIGS. 3 and
4), the conductive ink layer in the form of patterned elements 2
thereof can be coated onto the nonconductive opaque layer 3.
Moreover, the area encompassed by the conductive ink can be
coextensive with that of opaque layer 3 in such inverse coated
articles. On the other hand, when the articles are made by a
top-coating procedure, the conductive ink elements are usually
coated upon the substrate 1 and an overlying opaque coating, e.g.,
of nonconductive black paint, is coated thereon prior to deposition
of encapsulated liquid crystal layer, e.g., as indicated in FIGS.
1, 2, 5 and 6. The conductive ink layer 2 characteristically
contains a conductive pigment (or other finely divided conductive
material colored or uncolored), a binder, a plasticizer (optional
depending upon the flexibility desired) and a liquid coating
carrier.
TOP LAYER (OPTIONAL, BUT PREFERRED)
As noted in FIGS. 2, 3, 4 and 6, the composite articles of this
invention can contain a brightness-improving, substantially smooth,
essentially transparent top layer 5. This top layer enhances the
color purity, color contrast and visual resolution characteristics
of the color effects produced in the encapsulated liquid crystal
layer. The top layer is essentially transparent and has an index of
refraction which approximates that of both the capsule cell wall
material and any polymeric or other binder employed in the
encapsulated liquid crystal layer. Moreover, it will be observed
that the top layer is in direct contact with the underlying
encapsulated liquid crystal layer throughout substantially the
entire extent of said encapsulated liquid crystal layer (or the
disconnected individual portions thereof which define the
configuration of the encapsulated liquid crystal layer). Also, the
outer surface, that is, the portion closest to the observer, is
substantially smooth. The term "smooth" as used herein means that
the average ratio of the horizontal distances or lengths between
crests (high points) on the outermost (exterior) surface of the top
layer divided by the vertical distances between said crests and
troughs (low points on the outermost surface of the top layer) is
at least 4.0, viz, said average lengths divided by said average
vertical distances are equal to 4.0 plus. When the articles of this
invention are formed by top-coating procedures, some of the crests
can be the tops of capsules which protrude through the polymer top
layer whereas other crests can be the polymer top layer material,
itself, as it overlies capsules therebeneath. Usually the depth of
surface irregularities is small in comparison to the size
(diameter) of the capsules, and the undulations are generally
continuously variable rather than sharply discontinuous, e.g., as
is the experience when no top layer is present and when a capsule
layer (encapsulated liquid crystal plus a binder) constitutes the
outermost surface.
When the top layer is plastic, it can be produced from a wide
variety of essentially transparent natural and synthetic organic
materials, such as polyolefins, e.g., polyethylene, polypropylene,
polybutylenes, polyesters, e.g., polyethylene glycol terephthalate,
acrylic resins, e.g., polyalkyl acrylates and methacrylates, such
as polymethylacrylate, polyethylacrylate, polymethylmethacrylate,
polybutylmethacrylate, polystyrene, polyvinylidene chloride homo-
and copolymers, e.g., "Saran" materials, nylons and other
polyamides, polyvinyl aldehydes, e.g., polyvinyl formaldehyde,
polyvinyl butyraldehyde; copolymers of mono-olefinically
unsaturated monomers with vinyl esters, such as ethylene-vinyl
acetate copolymers; cellulosic plastics, e.g., cellulose acetate,
ethyl cellulose; polycarbonates; polyurethanes; silicone resins,
poly alkyl siloxanes, e.g., poly methyl siloxane; alkyd resins and
varnishes; shellac; and other polymers and resins usually in the
form of sheets, films or coated layers.
Under certain circumstances, it is preferable to employ a polymer
which can be deposited, e.g., cast from an organic,
water-immiscible solvent since the presence of water could
partially dissolve the capsular cell wall and impair the quality
thereof, viz, with respect to the encapsulated cholesteric liquid
crystal member. In any event, when depositing the transparent,
smooth-surfaced film, 5, especially while employing water or a
water-miscible solvent; care should be exercised to avoid exposure
of the capsules for extended periods of time to a solvent which is
also a solvent for a capsule wall material.
While organic plastic materials, e.g., polymeric materials, have
been mentioned hereinabove for use in conjunction with the
transparent, smooth top layer 5, other materials, e.g., inorganic
materials such as glass, e.g., conventional soda-lime-silica
glasses (in the form of sheets), alkali metal silicates such as
sodium silicate, potassium silicate, etc., (in the form of coating
compositions) can be employed.
Instead of forming the top layer by overcoating the encapsulated
liquid crystal layer (as shown in FIGS. 2 and 6); preformed films,
layers or sheets of organic or inorganic material can be used via
inverse coating to constitute top layer 5, e.g., as noted in
conjunction with the description of the articles of FIGS. 3 and 4.
The thickness of top layer 5 can be varied widely from
approximately 10 microns to one-eighth inch or greater, esp., in
the case of sheets of polished plate glass where a one-eighth inch
thickness has been utilized quite satisfactorily.
As previously noted, the index of refraction of the
smooth-surfaced, transparent top layer is usually close to that of
the material employed to form the capsules cell wall and also that
of the polymer or other material employed to serve as binder in the
encapsulated liquid crystal layer. Usually the index of refraction
of the top layer, binder and cell wall ranges from about 1.40 to
1.70. More usually, the index of refraction of the top layer ranges
from about 1.45 to about 1.60, preferably from about 1.48 to 1.59
and more preferably between about 1.50 and 1.54.
While it will be observed that in all cases as shown in the
drawings, the encapsulated liquid crystal layer and the conductive
ink layer (and a top layer where one is utilized) are separate and
distinct; both the encapsulated liquid crystal layer and the
conductive ink layer can be deposited in any desired configuration,
pattern or design, both linear and nonlinear (curved), e.g., by
stencilling, screen printing, gravure roll printing, or any other
equivalent deposition procedure. It will be observed that when a
top layer is employed; the top layer is in direct contact with the
encapsulated liquid crystal layer throughout substantially the
entire extent thereof. However, this can mean only a portion of the
entire upper surface of the display article, viz, as where the
encapsulated liquid crystal layer is printed thereon in a
pattern.
Also, it will be realized that an additional insulating layer (not
shown), e.g., one of plastic, can be employed in conjunction with
the articles shown in FIGS. 3 and 4. Such insulating layers would
in fact serve the same purpose as the substrates 1 shown in FIGS.
1, 2, 5 and 6 with respect to providing insulation for conductive
ink elements 2.
The present invention will be illustrated in great detail in the
following examples. Since these examples are included to illustrate
the invention, they should not be construed as limiting thereon. In
the examples, all percentages and parts are by weight unless
indicated otherwise.
EXAMPLE I
This example illustrates formation of an inverse-coated article
having a polyester top layer, a capsular layer coated over the
entire surface thereof, and a patterned printed coating of
conductive ink, e.g., as shown in FIG. 3 of the drawings.
A liquid crystal mixture having the below-indicated composition is
encapsulated in a conventional manner using a standard two-way
gelatin coacervation.
---------------------------------------------------------------------------
TABLE
Liquid Crystal Component Concentration (weight percent)
__________________________________________________________________________
Cholesteryl Pelargonate 63.8 Cholesteryl Chloride 4.8 Oleyl
Cholesteryl Carbonate 31.4
__________________________________________________________________________
The encapsulation is conducted specifically as follows: into an
aqueous solution of 1 weight part of acid-extracted pigskin gelatin
(having a Bloom strength of 285 to 305 grams and an isoelectric
point of pH 8 to 9) in 8.09 weight parts of distilled water at
55.degree. C., there are placed 14.0 weight parts of said liquid
crystal melt. The liquid crystal melt is milled with a shear
agitator until the desired particle size is achieved, viz, from 15
to 30 microns. While the milling progresses, an aqueous solution of
1 weight part gum arabic in 93.0 weight parts of distilled water is
prepared in a separate container and maintained at a temperature of
55.degree. C. When the desired particle size is achieved, the
gelatin-liquid crystal emulsion is added slowly to the gum-arabic
solution. The pH is adjusted to 4.85 and the coacervate is
permitted to cool to 27.degree. C. over a period of 21/4 hours. The
resultant capsules are cooled to below 15.degree. C. and hardened
with 0.5 weight parts of a 25 weight percent aqueous solution of
glutaraldehyde for 12 to 15 hours. The resulting capsular slurry is
then concentrated by filtration to a slurry having approximately 40
to 45 weight percent capsular solids.
Upon completion of encapsulation and subsequent concentration of
the slurry, approximately 75 weight parts of the thus-concentrated
slurry is mixed with 25 weight parts of a 10 weight percent
solution of commercially available polyvinyl alcohol ("duPont
72-60") in water as a binder for the coating mixture forming the
encapsulated cholesteric liquid crystal layer.
The above-formulated liquid crystal capsules are then coated onto a
"Cronar" sheet using No. 12 nylon printing screen using two passes.
"Cronar" is a commercially available transparent polyester film
marketed by E. I. duPont de Nemours and Co. When the capsular layer
is dry, a coating of opaque, nonconductive "Zephyr R-M" black ink
is applied to the capsular layer using a No. 12 nylon screen and
the opaque background is allowed to dry. Then a conductive ink
pattern is printed on the dried opaque background layer using a No.
20 nylon printing screen. The conductive ink utilized is a
commercially available black conductive ink ("Conductive Ink EL
796" marketed by the Excello Color and Chemical Division of Advance
Supply Company) having carbon black and titanium dioxide conductive
particles in a conventional binder.
The printing operations are conducted at ambient room temperatures,
which range from about 24.degree. to 28.degree. C. by screen
printing in the following manner. The "Cronar" transparent support
is laid on a flat surface. A nylon screen mounted on a soft white
pine wood frame is positioned over the substrate. A supply of the
aforementioned encapsulated liquid crystal material is then poured
onto the screen and a neoprene rubber squeegee is used to pull the
supply of encapsulated liquid crystal coating formulation across
the screen, at the same time pressing it through the open mesh of
the screen. The screen is then lifted from the substrate leaving
the encapsulated liquid crystals affixed to the "Cronar." The
deposition of the black background ink and the electroconductive
ink is done in similar fashion after the encapsulated liquid
crystal layer dries. The electroconductive ink is deposited upon
the dried opaque background layer in a pattern configuration of
lines having a length of 4 inches, a width of one-sixteenth inch
and a thickness of 0.0005 inch.
Upon drying of the conductive ink layer, the article is inverted
thereby allowing a viewer to observe color changes occurring in the
encapsulated liquid crystal layer when viewed by incident white
light through the transparent "Cronar" top layer. The transparent
"Cronar" layer originally serving as a transparent support for the
deposition of the respective coatings, then serves as a
brightness-enhancing and spectral purity (for color intensity)
improving top layer in the manner noted hereinabove.
The thus-prepared display article having the integral conductive
ink resistor means is then connected to a supply of electric power,
and the voltage is adjusted until color is produced in the area of
the encapsulated liquid crystal layer which is thermally activated
by the printed conductive ink pattern. At a potential of 40 volts,
the entire area overlying the printed conductive ink line is violet
indicating maximum color response at a low current input of less
than 1 milliampere.
Another electroconductive display article containing encapsulated
liquid crystals and electroconductive ink is produced in
essentially the same manner except that the printed
electroconductive ink lines have a length of 4 inches, a width of
one-eighth inch and a thickness of 0.0005 inch. At a voltage of 25
to 30 volts, the area overlying the line appears violet at a noted
current of between 1 and 2 milliamperes. Further articles were
prepared by inverse coating wherein the display configuration was
printed by use of encapsulated liquid crystal images and conductive
ink images, respectively.
EXAMPLE II
This example illustrates a composite article prepared by top
coating, e.g., as in FIG. 1.
Using the same encapsulated liquid crystal formulation as described
above in example 1, a conductive ink coated article having a
nontransparent substrate is prepared by a top-coating procedure in
the following manner. A paper substrate (commercial Star Sapphire
paper having a dull white enamel finish and a basis weight of 80
pounds per ream-- one ream being equal to 500 sheets, each of which
has a length of 38 inches and a width of 25 inches) is provided
with a printed line one-eighth inch wide by 4 inches long utilizing
the conductive ink formulation of example 1 printed via a No. 20
nylon screen at ambient room temperature in the manner indicated in
example 1. When this coating is dried; an opaque, nonconductive
black ink, "Zephyr R-M" ink, is applied thereto (by nylon screen
printing) and dried. Then an encapsulated liquid crystal layer
having the same composition as given in example 1 is printed over
substantially the entire surface of the opaque-coated article
utilizing two passes with a No. 12 nylon screen in accordance with
example 1. Upon drying of the encapsulated liquid crystal layer,
electric leads are attached to the conductive ink resistor to
thermally activate portions of the encapsulated liquid crystal
layer overlying said line. A violet color is readily observable by
the naked eye during such thermal excitation. As the electric
current is switched off, the color rapidly disappears and the
display article returns to an overall black color.
EXAMPLE III
This example illustrates preparation of an article as shown in FIG.
2. The procedure of example II is followed using a Star Sapphire
opaque paper substrate, a screen-printed conductive ink pattern, an
opaque top-coated layer deposited over substantially the entire
surface of the paper-conductive ink assembly, and the
aforementioned encapsulated liquid crystal layer covering the
entire surface of the opaque layer.
Upon drying of the encapsulated liquid crystal layer, a
substantially smooth, essentially transparent top layer is
deposited by top coating the encapsulated liquid crystal layer. The
transparent top layer applied is a mineral spirits solution
containing 40 weight percent "Acryloid B-67," an acrylic resin,
which is screen printed over the capsular layer resulting in the
formation of a substantially smooth, essentially transparent top
layer. "Acryloid B-67" is a commercially available acrylic resin
marketed by Rohm & Haas Co. Upon thermal excitation of the
conductive ink pattern, the chromatic effects are readily
observable in the areas of the encapsulated liquid crystal film
immediately overlying the conductive ink. The observable color
effects of the article produced in this example appear brighter and
clearer to the naked eye than those observed in respect of the
articles of example 2. Thus, it is readily apparent that the
utilization of a substantially smooth, essentially transparent top
layer aids in forming an improved display article.
EXAMPLE IV
This example illustrates varying the resistance of the conductive
ink layer by compositional variation thereof. Thus, the resistance
can be varied readily by use of a plasticizer(s), thinner(s) and
combinations thereof as will be illustrated by the data tabulated
hereinbelow. The data is obtained by preparing samples in
accordance with the procedures of example I utilizing conductive
ink strips approximately 4 inches long by one-eighth inch wide and
0.0005 inch thick. The basic conductive ink formulation given in
example I is varied in some cases by use of a thinner, viz, ethyl
acetate; in other cases, by introduction of varying amounts of a
plasticizer, viz, dibutyl phthalate; and in other cases by
introduction of varying amounts of both the thinner and the
plasticizer. Fourteen comparisons are conducted to illustrate
control of resistance from 2,600 ohms to approximately 16,000 ohms.
All resistance measurements are taken with a vacuum tube volt meter
after allowing the conductive ink to dry for a period of 2 days
after deposition. The observed data are measured at an ambient room
temperature of 26.degree. C. and are tabulated hereinbelow:
---------------------------------------------------------------------------
Run No. Composition of Conductive Ink Resistance (ohms) Component
Weight percent
__________________________________________________________________________
1 Conductive Ink (as 100 2,600 given in Example I) 2 Conductive Ink
95 3,200 Dibutyl Phthalate 5 12 Conductive Ink 93 4,600 Dibutyl
Phthalate 7 13 Conductive Ink 91 7,500 Dibutyl Phthalate 9 3
Conductive Ink 90 11,000 Dibutyl Phthalate 10 4 Conductive Ink 95
2,600 Thinner 5 5 Conductive Ink 90 3,200 Thinner 10 14 Conductive
Ink 92 4,200 Dibutyl Phthalate 5 Thinner 3 6 Conductive Ink 90
5,200 Dibutyl Phthalate 5 Thinner 5 7 Conductive Ink 85 6,200
Dibutyl Phthalate 5 Thinner 10 10 Conductive Ink 89 8,500 Dibutyl
Phthalate 10 Thinner 1 11 Conductive Ink 87 10,000 Dibutyl
Phthalate 10 Thinner 3 8 Conductive Ink 85 16,000 Dibutyl Phthalate
10 Thinner 5 9 Conductive Ink 80 16,000 Dibutyl Phthalate 10
Thinner 10
__________________________________________________________________________
* * * * *