PH26717A

PH26717A - Encapsulated liquid crystal and method and enhanced scattering in voltage sensitive encapsulated liquid crystal

Info

Publication number: PH26717A
Application number: PH30401A
Authority: PH
Inventors: James Lee Fergason
Original assignee: Manchester R & D Partnership
Priority date: 1983-03-21
Filing date: 1984-03-14
Publication date: 1992-09-15

Description

ae, 0

Cia oo } - IN 0 to 2 al _ er gy : ’ 1- . : Title: "Encapsulated Liquid Crystal And Method And Enhanced ~ - So le Scattering in Voltage Sensitive Encapsulated Liquid Crystal” oo | | CROSS REFERENCE TO RELATED APPLICATION i : This application is & continuation-in-part of copending, com- - monly assigned U.S. Patent Application Serial No. 302,780, filed September 16, 1981, for "Encapsulated Liquid Crystal and Method, the entire disclosure

BE of which is hereby incorporated by reference. oo

Reference additionally is made to applicant's commonly assigned

U.S. Patent Application Serial No. 477,242, filed March 21, 1983, fer -- "Encapsulated Liquid Crystal and Mathod". Such additional application also - is a continuation-in-part of Serial Mo. 302,780, and the entire disclosure of such additional application is hereby incorporated by reference. . oC TECHNICAL FIELD - ~ oC The present invention relates generally to the art of liquid

C15 crystals and more particularly, in one embodiment, to the scattering of light oC by liquid crystal material. Moreover, the invention relates to use of such - scattering in a liquid crystal display apparatus to form a& white or bright

Co . character and in optical shutter devices, e.g. to control brightness, to } : St enhancing of the light output/contrast of a liquid crystal apparatus, to : L200 especidlly of the type using encapsulated liquid crystal or liquid. crystal : ; . material held in a containment medium, such as an emulsion, and to methods - : of making and using such liquid crystal apparatus. : ;

Sr ’ Co The invention also relates, in another embodiment, to use of ‘ i } “= pleochroic dye in the liquid crystal for absorbing light incident thereon, and jo 125 "to corresponding methods of making and using same. : , BACKGROUND

Liquid crystal material currently is used in a wide variety of - | devices, including, for example, optical devices such as visual displays. A

A property of liquid crystals enabling use in visual displays is the ability to - 30 scatter and/or to absorb (especially when pleochroic dye is mixed with the ~ liquid crystal) light when the liquid crystals are in a random alignment and : so the ability to transmit light when the liquid crystals are in an ordered

Co alignment.

DOL TL een pT Ee . 3 ew ce Ce 3 LIers

Te TE 26717 - ‘ Frequently a visual display using liquid crystals displays dark .

Lob Ce characters on a gray or relatively light background. In various circum- .. = stances it would be desirable, though, using liquid erystal material to be able co to display with facility relatively bright characters or other information, 3 5 etc. on a relatively dark background. It would be desirable as well to

Cd improve the ‘effective contrast between the character displayed and the . background of the display itself. : oo oo

TE oo _.__ An example of electrically responsive liquid crystal material and use thereof is found in U.S, Patent No. 3,322,485." Certain types of liquid y 10 crystal material are responsive to temperature, changing the optical charac- }

L teristics, such as the random or ordered alignment of the liquid crystal material, in response to temperature of the liquid crystal material. Be

Currently there are three categories of liquid crystal materials, : namely cholesteric, nematic and smectic. Various principles of the inven- . 15 tion may be employed with various one or ones of the other known types of : : liquid crystal material or combinations thereof. The present invention ; "preferably uses nematic liquid crystal material or a ‘combination of nematic

De ‘ and some cholesteric type. More specifically, the liquid crystal material i oa preferably is operationally nematic, i.e. it acts as nematic material and not : . Bb "20 as the other types. “Operationally nematic means that in the absence of - 4 - external fields, structural distortion of the liquid crystal is dominated by the - i orientation of the liquid crystal at its boundaries rather than by bulk : } wt oo effects, such as very strong twists as in cholesteric material, or layering as : ’ "in smectic material. Thus, for example, chiral ingredients which induce a . x | 25 -._tendericy to twist but cannot ‘overcome the effects of boundary alignment oo . : ’ - still would be operdtionally- nematic.” Such material should have a positive : - Po | Ts dielectric anisotropy. Although various characteristics of the various liquid : . crystal materials are ‘described in the prior art, one known characteristic is oh that of reversibility. Particularly, nematic liquid crystal material is known - ! 30 to be reversible, but cholesteric material ordinarily is not reversible. 3 S Pleochroic dyes have been mixed with the liquid crystal material

Co . to form a solution therewith. The pleochroic dye generally aligns with the = o structure of the liquid crystal material. Therefore, such pleochroic dyes

Eo .

SE : oo Cae . oo will. tend to function optically in a manner similar to that of the liquid : - — - crystal material in response to a changing parameter, such as application or wo LT . non-application of an electric field. Examples of the use of pleochroic dyes o with liquid crystal material are described in U.S. Patents 3,499,702 and

Lg 3,551,026. One advantage to using pleochroic dye with the liquid crystal

Co : material is the eliminating of a need for a polarizer. However, in the nematic form a pleochroic device has relatively low contrast. In the past cholesteric material could be added to the nematic material together with .. the dye to, improve contrast ratio. See for example the White et al article : in Journal of Applied Physics, Vol. 45, No. 11, November 1974, at pages 4718- © 4723. However, although nematic material is reversible, depending on ’ whether or not an electric field is applied across the same, cholesteric i material ordinarily would not tend to its original zero field form when the electric field would be removed. Another disadvantage to use of pleochroic dye in solution with liquid crystal material is that the absorption of the dye - ] is not zero in the field-on condition; rather, absorption in the field-on - oo condition follows an ordering parameter, which relates to or is a function of . : the relative alignment of the dyes. }

FO } ~~ © Usually liquid crystal material is anisotropic both optically - : n 20 (birefringence) and, for example in the case of nematic material, electri- ol - cally. ‘The optical anisotropy is manifest by the scattering of light when the i i i .. liquid crystal material is in random alignment, and the transmission of light ~ through the liquid crystal material when it is in ordered alignment. The = 3 iE . electrical anisotropy may be a relationship between the dielectric constant : - or dielectric coefficient with respect to the alignment of the liquid crystal :

Co ER - material. 0 oo : :

Co "In the past, devices using liquid crystals, such as visual display ; | devices, have been relatively small. One reason is the fluidity of the liquid

Lo crystals; (the liquid crystal material may tend to flow creating areas of the

Co | 30 display that have different thicknesses). As a result, the optical character-

Ce istics of the display may lack uniformity, have varying contrast character- - i. istics at different portions of the display, etc.; the thickness variations in ih ~ turn cause variations or gradations in optical properties of the liquid crystal

Po

: Co | . Co -4- - - device. . Moreover, the varying thickness of the Jiquid crystal layer will : . cause corresponding variations in the electrical properties of the liquid EE i Loe crystal layer, such 8s capacitance and impedance, further reducing uni--—- ST : CL formity of & large size liquid crystal device. The varying electrical CL oo 5 . properties of the liquid crystal layer, then, also may cause & corresponding - : ; variation in the effective electric field applied across the liquid erystal -

IE material and/or in response to a constant electric “field would respond

SE differently at areas of the liquid crystal that are of different thicknesses.

To overcome such problems, the liquid erystal material should p10 : have an optimum uniform thickness. (As used herein the term "iquid } crystal" material means the liquid crystals themselves and, depending on i context, the pleochroic dye in solution therewith). There also should be an . optimum spacing of the electrodes by which the electric field is applied to . the liquid crystal material. To maintain such optimum thickness and spacing, rather close tolerances must be maintained. To maintain close k ’ tolerances, there is a limit as to the size of the ‘device using such liquid i : : Bs } crystals, for it is quite difficult to maintain close tolerances over large 3 : : 3 ~ surface areas, for example. ’ | : iB oe a _. Use of encapsulated liquid crystals disclosed in accordance with

CL ; 20 " } s applicant's invention has enabled the satisfactory use of liquid crystals in

Pe : : - relatively large size displays, Ey as billboards, ete. as is disclosed in such

So above applications; and anothet large (or small) scale use may be as an i 1 : optical shutter to control passage of light from one area into another, say at’ . ; i. | a ©. a window or window-like area of a pbuilding. The present invention relates to oo nN 25 : - improvements in such encapsulated liquid crystals and to the utilization of . — TR ,. ©. the light scattering characteristic of the liquid crystal material as opposed, - ; : . for example, to the light absorption (usually with pleochroic dye) character- : ; ) istic thereof. The invention also relates to the use of such material and ; characteristics, for example, to obtain a relatively bright character orf ‘ \ J 30 information displayed on a relatively dark or colored background in both small and large displays as an optical shutter, and so on. Such large displays i : and shutters may be about one square foot surface area or even larger. In i: ) accordance with the present invention the liquid crystal material most : . "preferably is of the encapsulated type. i

Lo

- | . se | . oo

As used herein with respect to the present invention, encapsul- oo oo - ated liquid crystal ‘material means liquid crystal material in a substantially Co - closed containment medium, such as discrete capsules or cells, and prefer- . ably may be in the form of an emulsion of the liquid crystal material and the containment medium. Such emulsion should be a stable one. Various oo . methods for making and .using encapsulated liquid erystal material and

TT apparatus associated therewith are disclosed below and in applicant's co- pending application, which is incorporated by reference. : One typical prior art display may include a support medium and . 10. liquid crystal material supported thereby. The display is relatively flat and is viewed from a viewing side from which a so-called front surface is - viewed. The back surface of the support medium may have a light : reflective coating tending to make the same appear relatively bright in ) comparison to relatively dark characters formed at areas where there-is cL 1s liquid crystal material. (Back, front, top, bottom, etc. are only for ) ; ) convenience; there is no constraint that in operation the viewing direction ", must be, for example, 8s shown from only the top, etec.). “When the liquid - crystal material is in ordered alignment incident light from the viewing . direction passes through the liquid crystal material to the light reflective

OL 20 Co coating and also where there is no liquid crystal material passes directly to

So Ce the light reflective coating; and no character is observed from the viewing. ; : CL direction. However, when the liquid crystal material is in random align- : So ment, it will absorb some and scatter some incident light thereby to form a

Po Eo ‘ relatively dark character on a relatively light color background, for example . 25 of gray or other color depending on the type of light reflective coating. In

EN + this type of display it is undesirable for the liquid erystal material to scatter

LD ; : : light because some of that scattered light will be directed back in the " ’ viewing direction thereby reducing the darkness or contrast of the character

Hf . relative to the background of the display. Pleochroic dye often is added to \ | 30 the liquid crystal material to increase absorbence and, thus, contrast when

Bf the liquid crystal material is in random alignment.

Le BRIEF SUMMARY OF INVENTION i Briefly, according to one aspect of the invention, liquid crystal

Lo | material is encapsulated; according to another aspect the encapsulated

I

- : Lo ’ . : TIE Ten WEENIE {TTT TTT OLGA eryStel material is used in liquid erystal devices, such es relatively ae - oo large size visual display devices and optical shutters; and’ according to .

A Jr.% io further aspects there are provided methods for encapsulating liquid crystal nN | CL ... material and for making a liquid crystal device using such encapsulated I 4 5 liquid crystal material. } oo So : ; In one embodiment of the invention broadly the liquid crystal B i Co scatters or absorbs light in the absence of a prescribed input, such as an oo . electric field, and in the presence of such input Scattering or absorption is . reduced. Absorption is increased in the absence of such input ‘by mixing oo Co. . 10 : pleochroic dye with the liquid crystal. : Co -

TH Co no In another embodiment, which may include but preferably does

LL oo - not include pleochroic dye; suceinetly stated, the invention relates to the : ’ g isotropic scattering of light by liquid crystal material and to the use of such =. isotropically scattered light to yield a white or bright appearance, char- : 15 acter, information, ete. especially relative to background,’ when a liquid toni ; oo - crystal material is in a field-off or distorted alignment condition and a bh

K CL i colored or dark appearance, e.g. the same as background, when a liquid . .

Bb CL crystal material is in field-on parallel or ordered alignment condition. : ol

Es oo oo Preferably ‘the liquid crystal material! is nearly completely isotropically Lo : 20 Co scattering when in distorted alignment. Isotropic scattering means that. oo : when a beam of light enters the liquid crystal material there is virtually no. i ) way to predict the exit angle of scattered light. Pleochroic dye preferably i "is not used in this embodiment because the dye would absorb light to reduce’ Co + : : .. brightness when scattering and brightening would be intended. : Lo ‘| 25 o As’ it is used herein with respect to the invention, the terms Co ; t distorted alignment, random alignment and field-off condition mean essen- -— a i} Co "tially the same thing; namely, that the directional orientation of the liquid. Lo oo crystal molecules is distorted to an’ effectively curved configuration. Such oT ; ) Nn IE distortion is effected, for example, by the wall of respective capsules. The

C30 ) particular distorted alignment of liquid crystal material in a given capsule 1 ; p . usually always will be substantially ‘the same in.the absence of an electric Co 1 Cs -field.- On thé other hand, as it is used herein with respect to the invention, © - 8 - parallel aligned, ordered alignment, and field-on condition means that the Ce do : CL ol PE

Co EE | a oo liquid crystal material in a capsule is generally aligned with respect to an . } externally applied electric field. Operationally nematic is defined above.

Co : - A capsule refers to a containment device or medium that confines a quantity of liquid erystal material, and nencapsulating medium" or "material" is that medium or material of which such capsules are formed.

An "encapsulated liquid crystal" or "encapsulated liquid crystal material” means a quantity of liquid crystal material confined or contained in discrete volumes within the encapsulating medium, for example in a solid medium as - individual capsules or dried stable emulsions.

Capsules according to this invention generally have an approxi- : mately spherical configuration (though this is not, per se, a requisite of the invention) having a diameter from about 0.3 to 100 microns, preferably 0.1 to microns, especially 3 to 15 microns, for example 5 to 15 microns. In the context of this invention, encapsulation and like terms refer not only to the 38 . formation of such articles as are generally referred to as capsules, but also to the formation of stable emulsions or dispersions of the liquid crystal material in an agent (an encapsulating medium) which results in the ) formation of stable, preferably approximately uniformly sized, particles in a uniform surrounding medium. Techniques for encapsulation, generally : : 26 referred to as microencapsulation because of the capsule size, as well known in the art (see, e.g., "Microcapsule Processing and Technology" by Asaji } : ©. Kondo, published by Marcel Dekker, Inc.) and it will be possible for one

Co skilled in the art, having regard to the disclosure herein, to determine oy suitable encapsulating agents and methods for liquid erystal materials.

Co 25 - - "A liquid erystal device is a device formed of liquid crystal . 3 : -material. In the présent invention such devices are formed of encapsulated : : liquid erystals capable of providing a function of the type typically inuring . to liquid crystal material; for example, such a liquid crystal device may be a visual display or an optical shutter that in response to application and - 20 removal of an electric field effects a selected attenuation of optical ol radiation, preferably including from far infrared through ultraviolet wave- a lengths. ” - - One method of making encapsulated liquid crystals includes mixing together liquid crystal material and an encapsulating medium in i . } . . . - : . : . - ~8- E BN which the liquid crystal material will not dissolve and permitting formation

Co oo oo of discrete capsules containing the liquid crystal material. - - . . A method of making a liquid crystal device including such : ) encapsulated liquid crystal includes, for example applying such encapsulated liquid crystal material to a substrate. Moreover, such method may include - . providing means for applying an electric field to the liquid crystal material to affect a property thereof.

According to another feature of the invention an operationally oC nematic material in which is dissolved a pleochroic dye is placed in a ’ generally spherical capsule. In the absence of an electric field, the capsule wall distorts the liquid crystal structure so it and the dye will tend to absorb light regardless of its polarization direction. When a suitable electric field is applied across such a capsule, for example across an axis thereof, the liquid crystal material will tend to align parallel to such field causing the . 15 : absorption characteristic of such material to be reduced to one assumed when the liquid crystal material is in the planar configuration. To help - oo assure that adequate electric field is applied across the liquid- erystal Co i material in the capsule, and not just across or through the encapsulating . medium, and, in fact, with a minimum voltage drop across the wall thickness

Li 20 of the respective capsules, the encapsulating material preferably has a - - dielectric constant no less than the lower dielectric constant of the liquid - - n crystal material, on the one hand, and a relatively large impedance, on the i oo other hand. Ideally, the dielectric constant of the encapsulating medium co oo should be close to the higher dielectric constant of the liquid crystal. ™ - 25 } "+ Contrast of a liquid crystal device employing encapsulated liquid

RE : ; crystals may be iniproved by selecting an encapsulating medium that has an : . index of refraction that is matched to the ordinary index of refraction of . the liquid crystal ‘material (i.e. the index of refraction parallel to the optical axis of the crystal. See, e.g. "Optics" by Borne & Wolf, or "Crystals and the

Polarizing Microscope” by Hartshorne & Stewart. The encapsulating = medium may be used not only to encapsulate liquid crystal material but also to adhere the capsules to a substrate for support thereon. Alternatively, a - further binding medium may be used to hold the liquid crystal capsules (

FIRE ES - Cs Se TET eT Ci TREE RAI PEER HEE TR ; relative to a substrate. In the latter case, though, preferably the additional ‘binding medium has an index of refraction which is matched to that of the om encapsulating medium for maintaining the improved contrast characteristic oo described above. Because the index of refraction of a material is generally strain—dependent, and. strain may be induced in, e.g. the encapsulating medium, it may be necessary to consider this effect in matching the indices -

So of refraction of the liquid erystal, encapsulating medium, and binding . medium, if present. Further, if iridescence is to be avoided, it may be

Lo . . desirable to match the indices of refraction over a range of wavelengths to oC the extent possible, rather than at just one wavelength. - Co. 7 A feature of ‘the spherical or otherwise curvilinear surfaced

Co : . capsule which confines the liquid crystal material therein in accordance oo

Co : . with the present invention is that the liquid crystal material tends to follow ) } the curvature or otherwise to align itself generally parallel with the curved DE 15 .. surfaces of such capsule. Accordingly, the liquid crystel structure tends to | Co . be forced .or distorted to a specific form, being folded back on itself ina = oo : | : - sense as it follows the capsule wall, so that the resulting optical character- i istic of a ‘given capsule containing liquid crystal material is such that =~ -

BE substantially all light delivered thereto will be affected, for example, ) Lo 20° _ scattered (when no pleochroic dye is present) or absorbed (when plebchroic «=

CT dye is present), when no electric field is applied, regardless of the ’ j } polarization direction of the incident light. Even without dye this effect Co "+ can cause scattering and thus opacity. eo a ; : oo : Another feature is the ability to control the effective thickness Co : 28 - -- of the liquid ‘crystal material contained in a capsule by controlling the - . "internal diameter of such capsule. Such diameter control may be effected : CT by a size fractionation separation process during the _ making. of the : i CL encapsulated liquid crystals using any one of a variety of conventional or : i. ~~. novel sorting techniques as‘ well as by controlling the mixing process, the ; 30 : quantities of ingredients, and/or the nature of the ingredients provided ’ ’ during mixing. By controlling such thickness parameter to relatively close Co : tolerances, then, the subsequent tolerance requirements when the final ; CL liquid crystal device is ‘made using, the encapsulated liquid ¢rystals willnot ___ + ) be ss critical as was required in the past for non-encapsulated devices. CL ; = mn me mde th ane Tan DT a eh

- : Co A rol TreERE Sm TEE = RELA EA RE SR

EE However, 8 fartiier and very significant feature of the present i oe invention is that there eppears to be no limitation on the size of a high : ) = quality liquid crystal device that can be made using the encapsulated liquid Ty ~~ crystals in accordance with the present invention. More specifically, by : - oo providing for confinement of discrete quantities of liquid crystal material, - ’ | TTR mo far example, in the described capsules, the various problems endounterad in TTT : ‘the past that prevented the use of liquid crystal material in large Size

I : Co devices are overcome, for each individual capsule in effect can still operate oo

Cb . es an independent liquid crystal device. Moreover; each capsule preferably " © has physical properties enabling it to be mounted in virtually any environ-. - oo

Leo Co ment including one containing a plurality of further such liquid crystal . i : a. capsules ‘mounted to a substrate or’ otherwise supported for use in response Lo ; [ EI to application and removal of some type of excitation source, "such gs, for = | Ce

LL no -- example, an electric or magnetic field. This feature also enables placement Co

Cl SE of the liquid crystal material on only selected areas of the optical device, Co y Co such as in large size displays (e.g. billboards), optical shutters, ete: - N Co i) ! ) oR Important considerations in accordance with the invention, ‘end : B B = the discovery of the inventor, are that an encapsulating medium having IN . ©. electrical properties matched in a prescribed way to the electrical proper- oo

A - ties of liquid erystal material encapsulated thereby and additionally prefer- - oo - Hl ably optically matched to optical properties of such liquid crystal material ~~ i EE permits efficient and high quality functioning of the liquid crystal material

Ll s ol in response to ‘excitation or non-excifation by an external source; and that TEs oo 5 _ - oo the interaction of the encapsulating medium with the liquid crystal material ) ) i Co distorts the latter in a prescribed manner changing an operational mode of i Co Co liquid crystal material, Regarding the latter, by forcing the liquid crystal - ! | ) To Co structure to distort into generally parallel or conforming alignment with the : \ . i ; capsule wall, the liquid crystals will absorb or block, rather than transmit, 1 co light when not subject to an electric” field and- will be finctional with ~~ ° oo | a 30. } ‘respect to all manners of incident light regardless of the direction of oC ; ! Co B polarization, if any, of such incident light. : : } i$ ) . Co In accordance with one aspect of the present invention, a liquid : l g Cos oT erystal display ‘can produce relatively bright or white characters, informa- : v

JT TT TET

. -11- oo : tion, etc., on a relatively dark background; the bright character is produced by liquid crystal material that is randomly aligned (preferably without } ~ pleochroic dye that would absorb and reduce scattering); the background is ) } caused, for example, by liquid crystal material that is in ordered alignment and, thus, substantially optically transparent and/or by areas of the display j where there is no liquid crystal material. When the liquid crystal material is in parallel or ordered alignment, only the relatively dark background, e.g. formed by an absorber, would appear. The foregoing is accomplished using relatively low power requirements, minimum liquid crystal material, and illumination either from the viewing side or direction or from the back or : non-viewing side of the display. The principles of the invention also may be used in an optical shutter or light control device to control brightness, for example.

Briefly, the liquid crystal apparatus includes liquid crystal mate- “rial for selectively primarily scattering or transmitting light in response to a : prescribed input and a support medium for holding therein the liquid crystal - material. In a preferred embodiment the liquid crystal material is of the : encapsulated type that will cause substantially isotropic scattering of light . : incident thereon, including the scattering of some of such light back in the 20 . : viewing direction toward, for example, the eye of an observer. More : “rs : preferably, such liquid crystal is operationally nematic, has a positive a dielectric anisotropy, and has an ordinary index of refraction that substan- 0 tially matches that of the containment or encapsulating medium therefor. . : In one embodiment, a large quantity of light that is isotropically ; 25 “scattered by the liquid crystal material is totally internally reflected by the

Co : - support medium back to the liquid crystal ‘material thereby illuminating the oo - same and causing further isotropic scattering and brightening of the a appearance of the liquid crystal material, for example to the eye of an i observer. The internal reflectance characteristic of the support medium

Lo 30 may be effected by the interface of such back surface with another medium, ' such as a solid, liquid, or gas, even including air, with the constraint that the . , index of refraction of the support medium is greater than the index of refraction of such other medium. The support medium may be comprised of oo Co -12- several components, including, for example, the containment/encapsulating © material (or that with which the liquid crystal material is in emulsion), additional quantities of such encapsulating or other material, a mounting medium, such as a plastic-like film or glass, ete., all of which will be } described in further detail below.

The back surface of the support medium may be optically

Co transmissive so that light that reaches such surface in a direction substan-

Co tially normal thereto will be transmitted. A light absorbing black or colored } material beyond such back surface can help darken or color the apparent - 10 .background on which the characters formed by liquid crystal material : appear. Ordered alignment of the liquid crystal material will at least substantially eliminate the isotropic scattering 50 that substantially all the ; . “light passing through the liquid crystal material will also pass through the : Po back surface of the support medium. . :

In an alternate embodiment, a tuned dielectric coating may be - applied, e.g. by evaporation techniques, to the back surface of the support medium to effect selective constructive and destructive optical interfer- - oo ence. The thickness of such tuned dielectric coating will be a function of } : : lambda ( A) divided by 2, lambda being the wavelength of light employed to 20 with the apparatus. Constructive interference will enhance the internal : . ’ - reflection, especially by reducing the solid angle within which light would 3 ... : . - not be totally internally reflected in the support medium; and, therefore, ) . such interference will further brighten the appearance of the liquid crystal ~ AEE _ material characters. . ! ; ©25 : ; . Incident illumination for a liquid crystal display embodying the . “invention may be from the front or viewing side. - Alternatively, incident ; illumination may’ be from the back side, preferably through a mask or : ‘ director to direct light fully transmitted by the liquid crystal material out \ of the field or angle of view at the viewing side. However, light scattered by the liquid crystal material within the viewing angle would be seen.

Moreover, a cholosteric material may be_ added to the-nematic liquid crystal material to expedite return of the latter to distorted align-

So © ment pattern following in general the configuration of the capsule or cell

. - ) . > -13- : ‘ wall when the electric field is turned off, especially when the capsules are - i } relatively large. Also, if desired, a viscosity controlling additive may be - mixed with the liquid crystal. Further, an additive to the liquid crystal may be used to help force a preferred alignment of the liquid erystal structure in a capsule. : : These and other embodiments of the invention will become apparent as the following description proceeds.

The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention, these being indica- tive, however, of but ‘a few of the various ways in which the principles of the invention may be employed. : BRIEF DESCRIPTION OF DRAWINGS

In the annexed drawings: , Fig. 1 is a schematic representation of a liquid crystal device in accordance with the present invention; ‘

Figs. 2 and 3 are enlarged schematic illustrations ‘of a liquid crystal capsule in accordance with the present invention respectively under : a no-field or field-off condition and under an applied electric field or field- on condition; : . oo 20 © Figs. 4 and 5 are schematic representations of a liquid crystal : - apparatus according to one embodiment of the invention, respectively in a . no-field condition and in an applied electrie field condition; i oo ’ Fig. 6 is a schematic representation of another embodiment of a ye liquid crystal apparatus in accordance with the present invention using an : ., © 25 - air gap to cause total internal reflection; Co ©. Figs. 7 and 8 are schematic representations of another embodi- ment of liquid crystal apparatus in accordance with the present invention : employing optical interference principles respectively under a no-field conditign and under an applied electric field condition;

Fig. 9 is an isometric view of a liquid crystal display apparatus in accordance with the present invention and which may be formed of any of the embodiments disclosed herein; -

R Lo } ) . oc _14- : Fig. 10 is a fragmentary schematic elevation view of another

Sr oo embodiment of liguid crystal apparatus using continuous layers of liquid

BE } crystal material and interrupted electrodes; } :

Fig. 1l is a schematic isometric view, partly broken away, of the embodiment of Fig. 10; : Fig. 12 is a schematic view of an approximately proportioned liquid crystal display according to the invention showing a more accurately representative size relationship of the support medium layers and encapsul- ated liquid erystal layer for the several embodiments herein;

Fig. 13 is a schematic illustration of a nematic liquid crystal - . capsule with cholosteric material additive, which may be used with the : "several embodiments herein;

Co Figs. 14 and 15 are schematic illustrations of still another oo embodiment of liquid crystal apparatus with a light control film director 1s : provided with incident illumination from the non-viewing side, respectively, - © in the field on and field off conditions; . : oo | Fig. 16 is a schematic illustration similar to Figs. 14 and 15 but } | with the light control film director cemented to the support medium;

Fig. 17 is a schematic illustration like Figs. 2 and 3 showing an .

KE 10 "alternate embodiment of encapsulated liquid erystal; and CC E }

B : BN Fig. 18 is a schematic representation of a liquid crystal device in oo accordance with the invention employing pleochroic dye in the liquid : "crystal; IE : ; | ‘ } : Fig. 19 is an enlarged fragmentary view, partly broken away, of . - S25 _a portion of the liquid crystal display device of Fig. 9, but including . - : ; pleochroic dye, for example, as in the embodiment illustrated in Fig. 18; and - } - : Fig. 20 is a schematic electric circuit diagram representation of ~ : a liquid crystal capsulé according to the invention with an applied field. + DESCRIPTION OF THE PREFERRED EMBODIMENTS : BE 30 Referring to Figs. 1, 2 and 3, encapsulated liquid crystal material

So used in accordance with the present invention is illustrated. In Fig. lis a schematic representation of a liquid érystal apparatus 10 in accordance with - the present invention. The apparatus 10 includes encapsulated liquid crystal material 11 represented by a single capsule in Figs. 1-3. Although the capsules illustrated in the drawings are shown in two dimensions and, therefore, planar form, it will be appreciated that the capsules are three } dimensional, most preferably spherical. The capsule 11 is shown mounted in a preferably transparent support medium 12 having upper and lower portions 12a, 12b which may be integral with each other. The apparatus 10 also includes a pair of electrodes 13, 14 for applying an electric field across the liquid crystal material when a switch 15 is closed to energize the electrodes from a conventional voltage source 16.

A primary feature of the present invention is that such encapsu- lated liquid crystal material will isotropically scatter light impinging thereon when in a field-off random alignment condition; and in the field-on orderly aligned condition, such material will be substantially optically transparent. 28 ~The capsule 11 may be one of many capsules that are discretely formed or, more preferably, that are formed by mixing the liquid crystal material with a so-called encapsulating material or containment medium to form an emulsion, preferably a stable one. The emulsion may be applied to or sandwiched between the support media portions 12a, 12b, and electrodes 28 13, 14, as is illustrated. If desired, the support medium 12 and the so-called - encapsulating material or containment medium may be the same material.

As a further alternative, the upper and lower support medium portions 12a, 12b, or one of them, may be a plastic-like, glass, or like, preferably ‘ transparent, mounting material. In this latter case the electrodes 13, 14 may 28 be applied to such mounting material and the encapsulated liquid crystal * material/emulsion, including many capsules ll, for example, may be sand- wiched between such mounting material 12a, 12b to form the apparatus 10, as } . will be deseribed in further detail below. i , A reflectance medium 18 forms an interface 19 with the lower support medium portion 12b to obtain the desired total internal reflection function. Due to the total internal reflection principle of operation, the liquid crystal material in the capsule 11 will be illuminated by incident light, for example represented by a light beam 17, and with light that it isotropi-

k 15 - ) . cally scatters in the apparatus 10 so that from the viewing area 20 beyond . the upper support medium portion 12a, the liquid crystal material 11 will ) N i oo ‘appear white or relatively bright when under a no-field condition, e.g. the switch 15 is open. Although such isotropic scattering (and some absorption, especially with a pleochroic dye present in the encapsulated liquid erystal material) occurs in applicant's invention disclosed in the above co-pending application Serial No. 302,780, the total internal reflection principle of the present invention enhances scattering and, thus, brightens the visual/optical oo appearance of characters formed by the encapsulated liquid crystal i material. A light absorbing layer 21 of black or colored material may be oo applied to the bottom or back surface of the reflectance medium 18 remote _ from the interface 19 to absorb light incident on the layer 21.

The electrode 13 may be vacuum deposited indium tin oxide : applied to the lower support medium portion 12b, and the electrode 14 may be électrically conductive ink applied directly to the liquid crystal material or could be like the electrode 13. Other electrode material and mounting i oo : means therefor also may be used for either electrode. Examples include tin } | oxide and antimony doped tin oxide. Preferably the electrodes are rela- tively thin, for example, about 200 angstroms thick, and transparent so that ; they do not significantly affect the optics of the liquid crystal apparatus 10. - . The encapsulated liquid erystal material 11 includes liquid crystal - 30 contained within the confines or interior volume 31 of a capsule 32. Each :

A - capsule 32 may be a discrete one or alternatively the liquid crystal 30 may

Cl } Co be contained in a stable emulsion of a containment medium or so-called ~ = -.25 ] encapsulating material 33 that tends to form a multitude of capsule-like - ) environments for containing the liquid erystal material. "For convenience of - ! 3 “illustration, the capsules 32 are shown as discrete capsules in and preferably formed of the overall quantity of containment medium or encapsulating material 33. Preferably the capsule 32 is generally spherical, and the liquid

C30 crystal 30 is nematic or operationally nematic liquid crystal material having

DL positive dielectric anisotropy. However, the principles of the invention would apply when the capsule 32 is of a shape other than spherical; such oo shape should provide the desired optical and electrical characteristics that will satisfactorily conet with the optical characteristics of the liquid crystal - material 30, e.g. index of refraction, and will permit an adequate portion of ’ the electric field to occur across the liquid erystal 30 itself for effecting desired ordered or parallel alignment of the liquid crystal when it is desired "to have a field-on condition. The shape also should tend to distort the liquid crystal material when in a field-off or random alignment condition. A particular advantage to the preferred spherical configuration of the capsule 39 is the distortion it effects on the liquid crystal 30 therein when in a field- off condition. This distortion is due, at least in part, to the relative sizes of the capsules and the pitch of the liquid erystal; they preferably are about the same or at least about the same order of magnitude. Moreover, nematic liquid crystal material has fluid-like properties that facilitate the conform- ance or the distortion thereof to the shape of the capsule wall in the } absence of an electric field. On the other hand, in the presence of an electric field such nematic material will relatively easily change to ordered - alignment with respect to such field. . }

Liquid crystal material of a type other than nematic or combina- tions of various types of liquid crystal material and/or other additives may be used with or substituted for the preferred nematic liquid crystal material as long as the encapsulated liquid crystal is operationally nematic: How- ever, cholesteric and smectic liquid crystal material generally are bulk

To driven. It is more difficult to break up the bulk structure thereof for } "conformance to capsule wall shape and energy considerations in the capsule.

Co Co : Turning to Figs. 2 and 3, a schematic representation of the single s “28 capsule 32 containing liquid crystal 30 is shown, respectively, in the field- “off and field-on conditions. The capsules 32 have a generally smooth curved - ! | interior wall surface 50 defining the boundary for the volume 31. The actunl co dimensional parameters of the wall surface 50 and of the overall capsule 32 [ are related to the quantity of liquid crystal 30 contained therein and possibly to other characteristics of the individual liquid crystal material i therein. Additionally, the capsule 32 applies a force to the liquid crystals 30 tending to pressurize or at least to maintain substantially constant the pressure within the volume 31. As a result of the foregoing, and due to the

) surface wetting nature of the liquid crystal, the liquid crystals which oo . ordinarily in free form would tend to be parallel, although perhaps randomly distributed, are distorted to curve in a direction that generally is parallel to a relatively proximate portion of the interior wall surface 50. Due to such distortion the liquid crystals store elastic energy. For simplicity of illustration, a layer 51 of liquid erystal molecules whose directional orienta- tion is represented by respective dashed lines 52 is shown in closest proximity to the interior wall surface 50. The directional orientation of the liquid crystal molecules 52 is distorted to curve in the direction that is © 10 parallel to a proximate area of the wall surface 50. The directional pattern of the liquid crystal molecules away from the boundary layer 52 within the g capsule is represented by 53. The liquid crystal molecules are directionally represented in layers, but it will be appreciated that the molecules oo themselves are not confined to such layers. Thus, the organization in an

C 1s individual capsule is predetermined by the organization of the structure 52

SC at the wall and is fixed unless acted on by outside forces, e.g. an electric field. On removal of the electric field the directional orientation would revert back to the original one, such as that shown in Fig. 2.

Co Nematic type material usually assumes a parallel configuration . 20 and usually is optical polarization direction sensitive. However, since the oo : material 52 in the encapsulated liquid crystal ll is distorted or forced to curved form in the full three dimensions of the capsule 32, such nematic

AE ~~" liquid crystal material in such capsule takes on an improved characteristic ) . : of being insensitive to the direction of optical polarization of incident light. - - ,. 25 _The inventor has discovered, moreover, that when the liquid crystal material : : : 30 in the capsule .32 has pleochroic dye dissolved therein, such dye, which - : . . ordinarily also would be expected to have optical polarization sensitivity, no ’ longer is polarization ‘sensitive because the dye tends to follow the same i kind of .curvature orientation or distortion as that of the individual liquid 4 30 crystal molecules 52.

The liquid crystal 30 in the capsule 32 has a discontinuity 55 in the generally spherical orientation thereof due to the inability of the liquid crystal to align uniformly in a manner compatible with parallel alignment

. . i -19- with the wall 50 and a requirement for minimum elastic energy. Such discontinuity is in three dimensions and is useful to effect a distorting of the liquid crystal 30 further to decrease the possibility that the liquid crystal 30 } would be sensitive to optical polarization direction of incident light. The discontinuity protrusion 55 would tend to cause scattering and absorption within the capsule, and the tangential or parallel alignment of the liquid crystal molecules with respect to portions of the interior wall surface 50 of the capsules both cause scattering and absorption within the capsule 32.

When the electric field is applied, for example, as is shown in Fig. 3, the : discontinuity will no longer exist so that such discontinuity will have a minimum effect on optical transmission when the encapsulated liquid crystal : . 11 is in a field-on or aligned condition.

Although the foregoing discussion has been in terms of a " homogeneous orientation of the liquid crystal material (parallel to the

Co capsule wall), such is not a requisite of the invention. All that is required is "that the interaction between the wall and the liquid crystal produce an orientation in the liquid crystal near that wall that is generally uniform and piecewise continuous, sO that the spatial average orientation of the liquid crystal material over the capsule volume is strongly curved and there is no

S20 i substantial parallel direction of orientation of the liquid crystal structure in “7 oT. the absence of an electric field. It is this strongly curved orientation that results in the scattering and polarization insensitivity in the field-off - oo condition, which is a feature of this invention. : In the field-on condition, or any other condition which results in ; 25 | the liquid crystal being in ordered or parallel alignment, as is shown in Fig. : - 3, the encapsulated liquid crystal 11 will transmit substantially all the light - incident thereon and will tend not to be visible in the support medium 12.

On the other hand, in the field-of[ condition when the liquid crystal is in distorted alignment, sometimes referred to herein as random alignment, for example as is shown in Fig. 2, some of the incident light will be absorbed, but also some of the incident light will tend to be scattered isotropically in the support medium 12. Using total internal reflection such isotropieatly scattered light can be redirected to the encapsulated liquid crystal 11 thus

Co oC -20- brightening the same tending to cause it to appear white to a viewer or viewing instrument. .. © The index of refraction of the encapsulating medium 32 and the a ordinary index of refraction of the liquid crystal 30 should be matched as _ much as possible when in the field-on or liquid crystal orderly aligned .. condition to avoid optical distortion due to refraction of incident light passing therethrough. However, when the liquid crystal material is in distorted or random alignment, i.e. there is no field applied, there will be a difference in the indices of refraction at the boundary of the liquid erystal 30 and wall of capsule 32; the extraordinary index of refraction of the liquid - crystal is greater than the index of refraction of the encapsulating medium.

This causes refraction at that interface or boundary of the liquid crystal p material and of the containment or encapsulating medium and, thus, further - - scattering. Light that is so further scattered will be internally reflected for further brightening in the liquid crystal appearance. Such occurrence of

Le different indices of refraction is known or birefringence. Principles of birefringence are described in Optics by Sears and in Crystals- And The ] Polarizing Microscope by Hartshorne and Stewart, the relevant disclosures of which are hereby incorporated by reference. Preferably the encap- i sulating or containment medium 32 and the support medium 12 have the same index of refraction to appear optically substantially as the same ’ material, thus avoiding a further optical interface. . : Co no As long as the ordinary index of refraction of the liquid crystal oo : inaterial is closer to the index of refraction of the so-called encapsulating . ) - 25 - medium, than is the extraordinary index of refraction, a change in scatter- : ) . h ing will result when going from field-on to ficld-off conditions, and vice- - oo versa. Maximum contrast results when the ordinary index of refraction

J ) | matches the index of refraction of the medium. The closeness of the index { matching will be dependent on the desired degree of contrast and trans- \ 30 parency in the device, but the ordinary index of refraction of the crystal and the index of the medium will preferably differ by no more than 0.1, ! preferably 0.03, more preferably 0.01, -especially 0.001. The tolerated difference will depend upon capsule size.

Desirably the electric field E shown in Fig. 3 is applied to the liquid crystal 30 in the capsule 32 for the most part rather than being dissipated or dropped substantially in the encapsulating material. There * should not be a substantial voltage drop across or through the material of which the wall 54 of the capsule 32 is formed; rather, the voltage drop should occur across the liquid erystal 30 within the volume 31 of the capsule 32.

The electrical impedance of the encapsulating medium prefer- ably should in effect be large enough relative to that of the liquid crystal in the encapsulated liquid crystal 11 that a short circuit will not occur exclusively through the wall 54, say from point A vin only the wall to point

B, bypassing the liquid crystal. Therefore, for example, the effective tee .. impedance to induced or displacement current flow through or via only the wall 54 from point A to point B should be greater than the impedance that would be encountered in a path from point A to point A' inside the interior ) wall surface 50, through the liquid crystal material 30 to point B' still within . the volume 31, ultimately to point B again. This condition will assure that there will be a potential difference between point A and point B. Such - potential difference should be large enough to produce an electric field across the liquid crystal material that will tend to align the same. It will be appreciated that due to geometrical considerations, namely the length ‘ tlirough only the wall from point A to point B, for example, such condition "still can be met even though the actual impedance of the wall material is oo . lower than that of the liquid crystal material therein. : 25 _ The dielectric constants (coefficients) of the material of which ~ “the encapsulating medium is formed and of which the liquid crystal is com- prised, and the effective capacitance values of the capsule wall 54, } particularly in a radial direction and of the liquid crystal across which the electric field E is imposed, all should be so related that the wall 54 of the capsule’ 32 does not substantially drop the magnitude of the applied electric field E. Ideally the capacitance dielectric constants (coefficients) of the entire layer 61 (Fig. 4) of encapsulated liquid crystal material should be . substantially the same for the field-on condition.

: : -22- Co ‘ . : The liquid crystal 30 will have a dielectric constant value that is - "anisotropic. It is preferable that the dielectric constant (coefficient) of the . “wall 54 be no lower than the dielectric constant (coefficient) of the oo : anisotropic liquid crystal material 30 to help meet the above conditions for optimum operation. It is desirable to have a relatively high positive dielectric anisotropy in order to reduce the voltage requirements for the electric field E. The differential between the dielectric constant (co. efficient) for the liquid erystal 30 when no electric field is applied, which } should be rather small, and the dielectric constant (coefficient) for the liquid erystal when it is aligned upon application of an electric field, which - should be relatively large, should be as large as possible. The dielectric : constants (coefficients) relationships are discussed in the concurrently filed : application, the entire disclosure of which is specifically incorporated by 3 } reference here. It should be noted, in particular, though, that the critical relationship of dielectric values and applied electric field should be such ) . that the field applied across the liquid erystal material in the capsule(s) is adequate to cause alignment of the liquid crystal structure with respect to - the field. The lower dielectric values of commonly used liquid crystals are, :

Lo . for example, from as low as about 3.5 to as high as about 8. : Co “The capsules 32 may be of various sizes: The smaller. the size, though, the higher the requirements will be for the electric field to effect . ! Co ) "alignment of the liquid crystal in the capsule. Preferably, though, the v a capsules should be of uniform size parameters so that the various character- ~ ” ! oo oo istics, such as the optical and electrical characteristics, of an apparatus,’ : 25 } such as a display, using the encapsulated liquid crystal will be substantially

Lo & “uniform. Moreover, the capsules 32 should be at least 1 micron in diameter - Co . so they appear as discrete capsules relative to an incident light beam; a . v smaller diameter ‘would result in the light beam seeing” the capsules as a - continuous homogeneous layer and would not undergo the required isotropic a © 30 scattering. Examples of capsule sizes, say from 1-30 microns diameter, and , of liquid crystal material are in the above concurrently filed application and . are hereby specifically incorporated by reference.

J A preferred liquid crystal material in accordance with the best wo "mode of the invention is that nematic material NR -8250, an ester sold by

} Atnerican Liquid Xtal Chemical Corp., Kent, Ohio, U.S.A. Other examples may be ester combinations, biphenyl and/or biphenyl combinations, and the . like.

Several other types of liquid crystal material useful nccording to the invention include the following four examples, each being a recipe for the respective liquid crystal materials. The so-called 10% material has . about 10% 4-cyano substituted materials; the 20% material has about 20% 4-cyano substituted materials, and so on. 10% Material

Pentylphenylmethoxy Benzoate 54 grams " Pentylphenylpentyloxy Benzoate 36 grams . - Cyanophenylpentyl Benzoate 2.6 grams

Cyanophenylheptyl Benzoate 3.9 grams . Cyanophenylpentyloxy Benzoate 1.2 grams : Cyanophenylheptyloxy Benzoate 1.1 grams oo Cyanophenyloctyloxy Benzoate 9.94 grams

Cyanophenylmethoxy Benzonte 0.35 grams 20% Material : . Pentylphenyimethoxy Benzoate 48 grams : Pentylphenylpentyloxy Benzoate 32 grams : no . 200 Cyanophenylpentyl Benzoate 5.17 grams

Cyanophenylheptyl Benzoate 7.75 grams oo : : Cyanophenylipentyloxy Benzoate = 2.35 grams oo Cyanophenylheptyloxy Benzoate 2.12 grams

CL ] _ + Cyanophenyloctyloxy Benzoate 1.88 grams : : : | ) 38 } ) - Cyanophenylmethoxy Benzoate 0.705 grams } . 40% Material

Co } Pentylphenylinethoxy Benzoate 36 grams / . Pentylphenylpentyloxy Benzoate ‘ 24 grams \ Cyanophenylpentyl Benzoate 10.35 grams ’ 30 Cyanophenylheptyl Benzoate 15.52 grams i Cyanophenylpentyloxy Benzoate 4.7 grams

Cyanophenylheptyloxy Benzoate 4.23 grams

. Cyanophenyloctyloxy Benzoate 3.76 grams -, Cyanophenylmethoxy Benzoate 1.41 grams ) . 40% MOD

Pentylphenylmethoxy Benzoate 36 grams 5 . Pentylphenylpentyloxy Benzoate 24 grams

Cyanophenylpentyl Benzoate 16 grams SL

Cyanophenylheptyl Benzoate 24 grams

The encapsulating medium forming respective capsules 32 should be of a type that is substantially completely unaffected by and does not . 10 affect the liquid crystal material. Various resins and/or polymers may be used as the encapsulating medium. A preferred encapsulating medium is : polyvinyl alcohol (PVA), which has a good, relatively high, dielectric constant and an index of refraction that is relatively closely matched to that of the preferred liquid crystal material. An example of preferred PVA is an about 84% hydrolized, molecular weight of at least about 1,000, resin.

CL Use of a PVA of Monsanto Company identified as Gelvatol 20/30 represents the best mode of the invention. : }

A method for making emulsified or encapsulated liquid crystals un oo may include mixing together the containment or encapsulating medium, the 20. liquid ‘crystal material, and perhaps a carrier medium, such as water. ©

Mixing may occur in a variety of mixer devices, such as a blender, a colloid ) oo mill, which is most preferred, or the like. What occurs during such mixing is the formation of an emulsion of the ingredients, which subsequently can be oo : dried eliminating the carrier medium, such as water, and satisfactorily

ST 25 curing the encapsulating medium, such as the PVA. Although the capsule 32 B ) “of each thusly made encapsulated liquid crystal 11 may not be a perfect . sphere, each capsule will be substantially spherical in configuration because a sphere is the lowest free energy state of the individual droplets, globules or capsules of the emulsion, both when originally formed and after drying and/or curing. . | The capsule size (diameter) preferably should be uniform in the ) emulsion for uniformity of operation with respect to effect on incident light : and response to electric field. Exemplary capsule size range may be from

} about 0.3 to about 100 microns, preferably 0.3 to 30 microns, especially 3 to 15 microns, for example 5 to 15 microns. -

Various techniques may be employed to form the support medium 12, which may be of the same or similar material as the encapsulating or containment medium. For example, the lower support medium 12b may be formed using a molding or casting process. The electrode 13 and liquid crystal material may be applied for support by that medium 12b. The electrode 14 may be applied, e.g. by printing. Thereafter, the upper support medium portion 12a may be poured or cast in place to complete enclosing "10 the encapsulated liquid crystal material and the electrodes. Alternatively, the support medium portions 12a, 12b may be a substantially transparent

Co plastic-like film or a plate of glass, as is described in Example 1, for example.

The reflectance medium 18, if a solid, for example, may be - 15 applied to the support medium portion 12b by a further casting or molding - technique, and a lower coating 21 of black or colored light absorbing material may be applied to the back surface of the reflectance medium 18, . i.e. the surface remote from the interface thereof with the lower support medium portion 12b. Alternatively, the reflectance medium may be an air or other fluid gap between the support mediuri portion 12b and the absorber - Co 21, or a tuned dielectric layer may be applied by conventional evaporation technique directly to the bottom surface of the lower support medium ’ portion 12b in place of the reflectance medium 18, as will be described : further below. - 25 ] ~~ The following are several examples of materials and methods for ) “making.liquid crystal display devices and operational characteristics thereof } in secordanae with the present invention.

Co © Example 1 ! . An example of the isotropically scattering material was pro- \ 30 duced by mixing about 2 grams of 8250 (an ester by American Liquid Xtal) . nematic liquid crystal with about 4 grams of a 20% solution of Airco 405 - polyvinyl alcohol (the other 80% of such solution was water). The material was mixed in a small homogenizer at low shear to form an emulsion. Using a doctor blade at about a 5 mil setting the emulsion was coated on an electrode of Intrex material already in position on a polyester film base of about 5 mils thickness. Sueh film was that known as Mylar. Another sheet of such film with such an electrode was placed on the encapsulated liquid crystal layer, thus sandwiching the latter between the respective electrodes } and films. The individual encapsulated operationally nematic liquid crystal capsules or particles were about 4 to 5 microns in diameter and the total layer of encapsulated liquid crystal material was about 20 to 30 microns thick. ; The device made according to Example 1 was tested. The resulting material scattered light in a zero electric field (hereinafter usually referred to as a zero field or field off condition) condition. In an applied field of 10 volts the scattering decreased and at 40 volts scattering stopped altogether.

Although 4 homogenizer was used, other types of mixers, blen- ‘ders, ete., may be used to perform the desired mixing.

Example 2

An example of the isotropically scattering material was pro- “duced by mixing about 2 grams of 8250 nematic liquid crystal with about 4

S20 ‘grams of a 22% solution (78% water) of Gelvatol 20/30 (by Monsanto) : polyvinyl alcohol. The material was mixed in a small homogenizer at low = shear to form an emulsion. The emulsion was coated on Intrex film

So ’ electrode and Mylar film polyester base, as in Example 1, with a doctor

So blade at a 5 mil setting ‘and the sandwich was completed as in Example 1. : The nematic capsules or particles were about 3 to 4 microns in diameter,

C- oo “. and the encapsulated liquid crystal layer was about 25 microns thick. . The device made according to Example 2 .was tested. The : resulting material scattered light in a zero or field-off electric field condition. In an applied field of 10 volts the scattering decreased and at 40 - 30 volts scattering stopped altogether. ’ Example 3

An example of the isotropically scattering material was pro- } duced by mixing about 2 grams of E-63 (a biphenyl by British Drugtlouse, a subsidiary of E. Merck of West Germany) nematic liquid crystal with about 4 grams of a 22% solution of Gelvatol 20/30 (by Monsanto) polyvinyl alcohol.

The material was mixed in a small homogenizer at low shear to form an emulsion. The emulsion was coated on Intrex film electrode and Mylar film polyester base with a doctor blade at a 5 mil setting and the sandwich was completed as above. The thickness of the encapsulated liquid crystal layer was about 25 microns; the nematic capsules or particles were about 4to5 : microns in diameter.

The device made according to Example 3 was tested. The resulting material scattered light in a zero field or field-off condition. In an applied field of 7 volts the scattering decreased and at 35 volts scattering

Co stopped altogether.

Example 4

An example of the isotropically scattering material was pro- duced by mixing about 2 grams of 8250 liquid crystal with about 4 grams of a 22% solution of Gelvatol 20/30 polyvinyl alcohol. The material was mixed = in a small homogenizer at low shear to form an emulsion. The emulsion was coated on Intrex film electrode and Mylar polyester film base with a doctor blade at a 5 mil setting and the sandwich was completed as above.” The

C20 Ts thickness of the encapsulated liquid crystal layer was about 25 microns; the : nematic capsules or particles were about 4 to 5 microns in diameter. . To improve the emulsion stability and coating uniformity 0.001%" "of GAF LO 630 non-ionic surfactant (detergent) was added before the mixing step. Improved performance instability of the emulsion” and in : coating of the emulsion onto the electrode/polyester film base were noted.

Le “The operational rests were otherwise substantially similar to those des- ca cribed above with respect to Example 1. ; : | Thus, it will be appreciated that in accordance with the inven-

J tion a surfactant, preferably a non-ionic surfactant, a detergent, or the like may be mixed with the encapsulated liquid crystal material prior to \ - depositing on the electrode coated film, as was just described above.

Example 5 i

The steps of Example 1 were followed using the same materials as in Example 1 except that 1/8 inch glass plate was substituted for the

Mylar film. Operation was substantially the same as was described with respect to Example L oo - Example 6

A mixture was formed of 8250 nematic liquid erystal and a solution of 15% ANI169 Gantrez in 85% water. Such Gantrez is poly(methyl vinyl ether/maleic anhydride), a polymaleic acid product, of GAF Corpora- tion. The mixture was of 15% liquid crystal and 85% Gantrez as the containment medium. The mixture was homogenized at low shear to form an emulsion, which was applied to an electrode/support film as above; such support film was about 1.2 mils thick. After drying of the emulsion, the resulting liquid crystal emulsion responded to an electric field generally as above, scattering when in field-off{ condition, showing a threshold of about 7 volts to begin reducing scattering, and having a saturation level of substan-- tially no scattering at about 45 volts.

Another example of an acid type containment medium useful in the invention is carbopole (carboxy polymethylene polymer by B. F. | Goodrich Chemical Company), or polyacid. i . : Other types of support media 12 that may be used include } } polyester materials; and polycarbonate material, such as Kodel film. Tedlar

Do : + film, which is very inert, also may be used if adequate adhesion of the } Co electrode can be accomplished. Such media 12 preferably should be oo ~ 25 _ substantially optically transparent. } : } ; . Several different polymer containment media that may be used ' | : are listed in Chart I below. The chart also indicates several characteristics - of the respective polymers.

CHART 1 . Temperature

Molecular &

Containment Medium Viscosity % Hydrolyzed Weight 9% Solutions 20/30 4-6 CPS 88.7 - 85.5 10,000 4% at 20°C

Gelvatol, by ; Monsanto Company 40/20 2.4-3 CPS 77-172.9 3,000 4% at 20°C

Gelvatol, by 10 . Monsanto Company 523, by 21-25 87 - 89 — 4% at 20°C © Air Products And

Chemicals, Inc. 72/60 55-60 99 - 100 — 4% at 20°C

Elvanol, by

DuPont Co. 405 9-4 CPS 80-82 — 4% at 20°C i ‘ Poval, by )

Kurashiki Cl

Other Gelvatol PVA materials that may be used include those _ designated by Monsanto as 20-90; 9000; 20-60; 6000; 3000; and 40-10. : A preferred quantity ratio of liquid crystal material to contain- ; . ment medium is about one part by weight liquid crystal material to about oo three pats by weight of containment medium. Acceptable encapsulated 5 25 liquid crystal emulsion operative according to the invention also may be : . achieved using a quantity ratio of about one part liquid crystal material to : Co i about two parts containment medium, e.g., Gelvatol PVA. Moreover, "although a 1:1 ratio also will work, generally it will not function quite as well as material in the ratio range of from about 1:2 to about 1:3. : ” . 30 Turning now to Figs. ‘4 and 5, a portion 60 of a liquid crystal { : display device in accordance with the present invention is illustrated. The portion or device 60 is a completion of the liquid crystal apparatus 10 described above with reference to Fig. 1 in that plural encapsulated liquid ] crystals 11, indeed plural layers thereof, are contained in a support medium 15 12. The sizes, thicknesses, diameters, ete., of the several parts shown in

Co -30-

Figs. 4 and 5 are not necessarily to scale; rather the sizes are such as is -, necessary to illustrate the several parts and their operation. : The electrodes 13, 14 are employed to apply a desired electric field to effect selective alignment of the liquid crystal material in the manner shown in Fig. 3, for example. Means other than electrodes may be : employed to apply some type of input to the display device 60 for the purpose of effecting ordered or random alignment of the liquid crystal. ~The encapsulated liquid crystals ll are arranged in several layers 61 within the display portion 60. The layers 61 may be divided into several . 10 portions representing the various characters or portions of characters intended to be displayed by the display 60. For example, the longer lefthand portion 61L of the layers 61 shown in Fig..4 may represent a section view through one part of a well known 7-segment display pattern, and the . relatively short righthand portion 61R of the layers 61 shown in Fig. 4 may : represent a part of another 7-segment character display. Various patterns oo of liquid crystal material may be employed in accordance with the present invention. A zone 62 of support medium 12 fills the area between the liquid } crystal layer portions 61L, 61R. Subsequent reference to layers 61 will be in the collective, i.e. referring to layer 61 as including the several levels or layers comprising the same. As an example, the composite thickness of such } : layer 61 may be from about 0.3 mils to about 10 mils; uniform thickness is ) preferred for uniform response to electric field, scattering, ete. 5 oo Such an arrangement or pattern of encapsulated liquid crystal o } material layer portions 61L and 61R separated at zone 62 by support medium : 12 or other material is facilitated, or even made possible due to’ the 27 ) . encapsulating or confining of the liquid erystal in discrete containment ; media, such as is formed by the preferred stable emulsion. Therefore,

N especially on a relatively large size device such as a display, billboard, optical shutter, ete., encapsulated liquid crystal material may be applied to

C20 the support medium 12 only where it is required to provide the selectable

Co optical characteristics. Such patterning can reduce the amount of such ) material required for a particular application. Such patterning is further - made possible due to the desired functional operation described in detail below.

"The display 60 may be used, for example, in an air environment, such air being represented by the reference numeral 63, and the air forms an interface 64 at the viewing side or from the viewing direction 20 with the support medium 12. The index of refraction N of the external medium 63 is . different from the index of refraction N' of the encapsulating medium 12, the latter usually being larger than the former. As a result, a beam of light 65, which arrives generally from the viewing direction 20, passing through the interface 64 into the support medium 12 will be bent toward the normal, which is an imaginary line 66 perpendicular to that interface 64. That light beam 65a inside the support medium 12 will be closer to normal than the incident beam 65 satisfying the equation relationship N Sine ©-= N' Sine-&}, . "wherein © is the angle of the incident light beam 65 with respect to the normal and-& is the angle of the light beam 65a with respect to normal.

Such mathematical relationship will apply at the interface 19, as follows: N' - Sine -©* = N" Sine or. To achieve the desired total internal reflection in . accordance with the invention, the index of refraction N" of the reflectance medium 18 is smaller than the index of refraction N' of the support medium 12. Accordingly, if the light beam 65a, for example, were able to and did . pass through the interface 19, it would be bent away from the normal at the interface 19 to the angle ov with respect to normal. Actually, since the . "light beam 65, 65a is not scattered off course by the liquid crystal material in layers 61, i.e., because it passes through the zone 62, it will indeed likely : exit through the interface 19. oo on In operation of a liquid crystal display 60 (Fig. 4) the operation-

Ce 25 - ally nematic liquid crystal 30 is in distorted or random alignment due to ho existence of a field-off condition. Incident light beam 70 enters the support medium 12 at the interface 64 and is bent as the light beam 70a that impinges as incident light on the layer 61 of encapsulated liquid crystal. The random or distorted encapsulated liquid crystal material will isotropically scatter the light incident thereon. Therefore, there are several possibilities of how such incident light beam 70a would tend to be scattered, as follows:

A. One possibility is that the incident light beam 70a will be directed according to the dotted line 70b toward the interface 13. The angle

- at which the light beam 70b impinges on the interface 19 is within the illustrated solid angle oX (defined in the planar direction of the drawing of

Fig. 4 by the dashed lines 71) of a so-called cone of illumination. Light falling within such solid angle &4 or cone of illumination is at too small an . 5 angle with respect to normal at the interface 19 to be totally internally reflected at that interface; therefore, the light beam 70b will pass through interface 19 while bending away from the normal to form the light beam

Co 70c. Light beam 70c passes into the reflectance medium 18 and is absorbed by layer 21. :

B. Another possibility is that the light beam 70a will be :

Lo isotropically scattered in the direction of the light beam 70d outside the cone angle oL . Total internal reflection will occur at the interface 19 causing the light beam 70d to be reflected as light beam 70e back to the _ layer 61 of encapsulated liquid crystal material where it will be treated as - another independently incident light beam thereto, just like the light beam 70a from which it was derived. Therefore, such light beam 70e will undergo isotropic scattering again as is described herein. :

C. Still another possibility is that the incident light beam 70a,

So or that derived therefrom, such as the light beam 70e, will be isotropically scattered toward the interface 64 at an angle that is so close to normal at . that interface 64 that the light beam will pass through the interface 64 into : - *_._ the "medium" 63, such as the air, to be viewed by an observer or observing . instrument. The solid angle AA ' of a cone of illumination, like the cone oo angle oA mentioned above, within which such scattered light bean 70e must

LT 25 “- fall to be emitted out through the interface 64 is represented by the single 2 dot phantom lines 72. Light beam 70f represents such a light beam that is

Co | so emitted from the display 60. It is that light, e.g. the sum of such emitted ; light beams 70f, which exits at the interface 64 that causes the layer 61 of encapsulated liquid erystals ll to give the appearance of a white or bright

CE 30 character as viewed from the viewing direction 20.

D. Still a further possibility is that the light beam 70a may be isotropically scattered in the direction of the light beam 70g. Light beam 70g is outside the solid cone angled ' and, therefore, will undergo total internal reflection at the interface 64, whereupon the reflected beam 70h © will impinge back on the layer 61 as an effectively independent incident light beam, like the beam 70e mentioned above and having a similar effect.

The index of refraction of the electrodes 13,14 usually will be higher than that (those) of the containment medium and support medium and the containment and support medias indices of refraction preferably are at least about the same. Therefore, the light passing from the containment medium into the electrode material will bend toward the normal, .and that passing from the electrode into the support medium will bend away from the ) 10 normal; the net effect of the electrode thus being nil or substantially negligible. Accordingly, the majority of total internal reflection will occur at the interfaces 19,64.

As viewed from the viewing direction 20, the zone 62 will appear dark or colored according to the composition of the absorbent layer 21. This is due to the fact that the light beam 65, 65a, 65b, representing the majority ] of light that passes through zone 62, will tend to pass through interface 64, support medium 12, the interface 19 and the reflectance medium 18, being bent toward or away from the normal, at respective interfaces as shown, ultimately being substantially absorbed by layer 21.

Briefly referring to Fig. 5, the field-on or ordered alignment condition and operation of the encapsulated liquid crystal layer 61 in the

Co display device 60 are shown. The encapsulated liquid crystals in the layer "61 of Fig. 5 are like those seen in Fig. 3. Therefore, like the light beam 65, . 65a, 65b which passes through the zone 62 and is absorbed by the layer 21, - . 25 the light beam 70, 70a, 70i will follow a similar path also being transmitted - - through the aligned and, thus, effectively . transparent or non-scattering oo layer 61. At the interface 19, the light beam 70a will be bent away from the normal and subsequently light beam 70i will be absorbed by the layer 21.

Accordingly, whatever visual appearance the light beam 65 would tend to cause with respect to an observer at the viewing location 20, so too will the light beam 70 cause the same effect when passing through the orderly i aligned encapsulated liquid crystal material. Thus, when the display 60, and .. particularly the encapsulated liquid crystal material therein, is in the

| -34- | : orderly aligned or field-on condition, the area at which the liquid erystal is ’ =~ located will have substantially the same appearance as that of the zone 62. : It is noted that if. either the incident beam 65 or 70 were to + enter the support medium 12 at the interface 64 at such a large angle with 5 respect to the normal there, and, therefore, ultimately to impinge on the interface 19 at an angle greater than one falling within the so-called cone of : light angle , such beam would be totally internally reflected at the interface 19. However, such reflected light probably would remain within . the support medium 12 due to subsequent transmission through the layer of . 10 liquid crystal material 61 and subsequent total internal reflectance at the interface 64, etc. : In Fig. 6, the preferred reflectance medium 80 air is illustrated. : In Fig. 6 primed reference numerals designate elements corresponding to - those designated by the same unprimed reference numerals in Figs. 4 and 5. 15. The display 60' has an interface 19' formed with air 80. To achieve absorbence of the light transmitted through the interface 19’ and medium 80, a black or colored absorber 81 may be positioned at a location displaced : from the interface 19'. The preferred absorber 81 is carbon black which may

Ch be mounted on a support surface positioned generally as is shown in Fig. 6. SE

The preferred liquid crystal is NM-8250; the preferred containment medium . is PVA; and the preferred support medium 12 is polyester. Moreover, it is ; > - preferred that the index of refraction of the support medium 12a, 12b and oo that of the containment medium for the liquid erystal be at least substan- : : co : tially the same; this helps to assure that the total internal reflection will - occur primarily at the interfaces 19, 64' and not very much, if at all, at the

A interface between the containment medium and support medium; this

CL _ minimizes optical distortion while maxi-mizing contrast. The display 60" / functions substantially the same as the display 60 described above with reference to Figs. 4 and 5. ; 30 Referring, now, to Figs. 7 and 8, a modified liquid erystal display 90 includes a support medium 12 with a layer of encapsulated liquid crystal material 61, as above. However, at the interface 19 there is a tuned dielectric interference layer 91. The thickness of the dielectric layer 91,

which is exaggerated in the drawings, preferably is an odd whole number

So function or multiple of lambda divided by two such as 372, 57/2, ete, wherein A is the wavelength of the light in the support display 60. The tuned dielectric interference layer 91 may be applied to the back surface of , 5 the support medium 12 by conventional evaporation technique. Such dielectric layer may be comprised of barium oxide (Ba0), lithium fluoride (LiF) or other material that provides the desired optical interference function. Preferably such layer has a smaller index of refraction than the medium 12 to obtain an interface 19 at which total internal reflection of light within cone angle will be internally reflected. A comprehensive description of optical interference is found in Optics by Born and wolf,

Fundamentals of Physics, 2nd Ed., 198], Resnick and Halliday, pgs. 731-735, and in University Physics by Sears and Zemansky, the relevant disclosures of which are hereby incorporated by reference. "In the field-off/random liquid crystal alignment condition shown : in Fig. 7 the display 90 will function substantially the same as the display 60 oo described above with respect to: (a) isotropic scattering of light by the encapsulated liquid crystal material layer 61; {b) the total internal reflection ‘of that light falling outside the solid angle cones , this due to the interface

S20 19 seen in Fig. 7, (or &X ' with respect to light isotropically scattered to the : interface 64), and; (¢) the transmitting of light, such as the light beam 70f, toward the viewing direction 20 to give the appearance of a white character

Co on a relatively dark background. . tH Co ~. By use of the tuned dielectric interference layer 91 and optical ~ 25 . - interference, in the field-off condition the illumination effected of the : a encapsulated liquid crystal layer 61 is further enhanced. Specifically, the effective cone of light angle 4 becomes reduced to the angle ¢ shown in

Fig. 7. , Generally, an incident light beam 92 impinging on the interface 64 will be’ deflected as the light beam 92a which then is incident on the layer } 30 61. If the light beam 92a were isotropically scattered as beam 92b at an angle outside the original angle <A , the total internal reflection operation . described above with reference to the display 60 will occur. However, if the light beam 92a is isotropically scattered as light beam 92c at an angle

ER -36- g falling within the cone of lighte{ but outside the cone of light q, it will : actually be reflected constructive optical interference will occur further to os enhance the illumination of the encapsulated liquid crystal layer 61.

More particularly when the light beam 92¢ enters the tuned dielectric interference layer 91, at least a portion 92d actually will be : reflected back toward the interface 19. At the interface 19, there will be } constructive interference with another incident light beam 93 increasing the effective intensity of the internally reflected resultant light beam 94, which ‘ ‘ is directed back toward the encapsulated liquid crystal layer 61 enhancing : 10 the illumination thereof. The result of such constructive interference is that the display 90 yields more light beams scattered up to or reflected up to the layer 61 than in the display 60. However, there is a disadvantage in that the viewing angle at which the display 90 will function effectively is less than the viewing angle at which the display 60 will function effectively. :

Specifically, incident light entering the support medium 12 at an angle equal : or less than the angle eA with respect to the interface 64, will tend to be totally reflected because the back or reflective surface of the tuned dielectric interference layer 81 will tend to act as a mirror so that some : contrast will be lost in the display 90. The angle , if it exists at all, in connection with the display 60 would tend to be smaller than the angle c4 of

Co the display 90.

E Co Light beams 95 and 96 (Fig. 7) that pass through the zone 62 of - oo the display 90 and light beams 92' (Fig. 8) that pass through the orderly . aligned (field-on) liquid crystal layer 61 and fall within the cone angle O will

Sa: - undergo destructive optical interference. Therefore, from the viewing area : ce © 20 thé zone 62 and the area where there is ordered field-on liquid crystal . ‘ will appear relatively dark, i.e. as a dark background relative to the white or { brightly illuminated liquid crystal layer 61 portion that is field-off and scattering. If desired, an absorber (black or colored) may be used beyond 1 30 the layer 91. Also, the color of background may be altered as a function of the thickness of the layer 31. - Turning now to Fig. 9, an example of a liquid crystal device 100 in accordance with the invention is shown in the form of a liquid crystal

-31- oo display device, which appears as a square cornered figure eight 101 within the substrate or suppoit medium 12, which in this case preferably is a plastic . ~ material, such as Mylar, or may alternatively be another material, such as glass, for example. The shaded area appearing in Fig. 9 to form the square cornered figure eight is comprised of one or more layers 61 of encapsulated liquid crystals 1 arranged in one or more layers on and adhered to the substrate 12. An enlarged fragmentary section view of a portion of the ~ figure eight 101 is illustrated in Fig. 4 as the display 60, 60' or 90 described above with reference to Figs. 4-8. Each of the seven segments of the figure . 10 eight 101 may be selectively energized or not so as to create various numeral characters. Energization here means the placing of the respective segments in a condition to appear bright relative to background. Therefore, energiza- tion means field-off or random alignment condition of, for example, segments 10la and 101b to display "1" while the other segments are in field- on, ordered alignment. : : . <0 Figs. 10 and lI illustrate, respectively in fragmentary section and fragmentary isometric-type views, an embodiment of the invention repre- senting the preferred arrangement of the liquid crystal layer 61" and . . electrodes 13", 14" in the support medium 12". In Figs. 10 and 1, double : primed reference numerals designate parts corresponding to those desig- nated by unprimed reference numerals in Figs. 4 and 5, or primed reference

Co numerals in Fig. 6. In particular, it is preferred according to the illustration ~ - of Figs. 10 and 1 that the display device 60"have the layer 61" and the oo electrode 13" substantially continuous over the entire or at least a relatively large portion of a display device. The electrode 13" may be connected, for

X - example, to a source of electrical ground potential. “The electrode 14" may be divided into a plurality of electrically isolated electrode portions, such as those represented at 14a, 14b, each of which may be selectively coupled to a source of electric potential to complete application of an electric field 20 across ‘that liquid crystal material which is between such energized elec- trode portion 14a or 14b and the other electrode 13". Therefore, for example, an electric field may be applied across the electrodes 14a, 13" causing the . encapsulated liquid crystal material falling substantially directly there-

oo RE between to be in ordered, field-on alignment and, thus, effectively optically transparent in the manner described above. At the same time, it may be that the electrode 14b is not connected to a source of electric potential so that the liquid crystal material between such electrode 14b and the electrode 13" will be in distorted or random alignment and, therefore, will appear relatively bright from the viewing direction 20". A small gap 120 } between electrodes 14a, 14b provides electric isolation therebetween to : permit the just-deseribed separate energization or not thereof.

Briefly referring to Fig. 12, the preferred embodiment and best : mode of the present invention is shown as the display 60". In Fig. 12 the various portions designated by triple primed reference numerals correspond to those portions designated by similar reference numerals, as are described above. The display device 60" is made generally in accordance with the numbered examples presented above. In particular, the lower support medium 12b™ is formed of Mylar film having an indium doped tin oxide } Co Intrex electrode 13" thereon; and the layer 61" of encapsulated liquid crystal material was applied to the electrode coated surface, as is shown. Several } electrode portions 14a™, 14b'™, etc. with a respective gap 120" therebetween, were applied either directly to the surface of the layer 61" opposite the support medium 12b™ or to the support medium 12a", and the latter was applied in the manner shown in Fig. 12 to complete a sandwich of the display - device 60". Moreover, the reflectance medium 80" was air, and a carbon’ "black absorber 21" mounted on ‘a support shown in Fig. 12 was placed opposite such air gap 80" from the support medium 12b", as can be seen in the figure. Operation of the display device 60" is according to the - “operation described pbove, for example, with reference to Figs. 4-6 and 10. - . Referring to Fig. 13, an encapsulated liquid crystal 130 of the type described in Example 7 below is schematically shown. Such capsule 130 ; includes a spherical capsule wall 131 of containment material 132, operation- ally nerhatic liquid crystal material 133 inside the capsule, and a cholosteric

J chiral additive 134. The additive 134 is generally in solution with the ! nematic material 13, although the additive is shown in Fig. 13 at a central location because its function primarily is with respect to the liquid crystal )

material remote from the capsule wall, as is described further below. The - capsule 130 is shown in field-off, distorted condition with the liquid crystal material distorted in the manner described above, for example, with reference to Fig. 2. The liquid crystal material most proximate the wall 131 tends to be forced to a shape curved like the inner boundary of that wall, and there is a discontinuity 135 analogous to the discontinuity 55 shown in

Fig. 2.

Example 7

The steps of Example 1 were followed using the same materials and steps as in Example 1 except that 3% cholesterol oleate (chiral additive), a cholosteric material, was added prior to the mixing step, and then such mixing was carried out at very low shear. The resulting capsules were somewhat larger than those produced in Example 1. The encapsulated liquid crystal material was still operationally nematic. : 15 In operation of the material formed in Example 7, it was found oo that the chiral additive improved (reduced) the response time of the operationally nematic encapsulated liquid crystal material, particularly in returning to the distorted alignment generally following the wall shape of the individual capsules, promptly after going from a field on to a field off condition. In such relatively large capsules, say about on the order of at . least 8 microns total diameter, when going to the field off condition, it is ) | the usual case that the liquid crystal material adjacent the capsule wall . © would return to the distorted alignment following the capsule wall shape or : : curvature faster than would the liquid crystal material closer to the center of the capsule; this disparity tends to slow the overall response time of the - “-material. However, the chiral additive induces a tendency for the structure oC to twist. This influence on the nematic material is most noticeable remote from the capsule wall and, thus, speeds up the return of such relatively remote material to distorted alignment, preferably influenced by the shape 20 of the capsule wall. Such chiral additive may be in the range of about 0.1% to about 8% of the liquid crystal material and a preferred range of about 2% i to about 5%. The amount may vary depending on the additive and the liquid . crystal and could even be outside the stated range as long as the capsule remains operationally nematic.

oo ’ -10- l . :

It will be appreciated that the encapsulated liquid crystal 130 of

Fig. 13 may be substituted in various embodiments of the invention described in this application in place of or in conjunction with the otherwise herein described encapsulated liquid crystal material. Operation would be gene- rally along the lines described in Example 7. i Another additive also may be used to reduce and/or otherwise to control the viscosity of the liquid crystal during manufacturing of a device 60, for example. The reduced viscosity may have a positive effect on : emulsion formation and/or on the process of applying the emulsion to an electrode covered support medium 12. An example of such an additive may be chloroform, which is water-soluble and leaves the emulsion on drying.

Example 8

An emulsion was prepared using about 15 grams of 22% (the rest was water) low viscosity, medium hydrolysis PVA; about 5 grams of 8250 liquid crystal (of American Liquid Xtal) containing about 3% (percentages oo Co are with respect to the weight of the liquid crystal) cholesterol oleate, about 0.1% of a 1% (the rest was water) solution of L.O. 630 surfactant, and 15% chloroform. . Such material was mixed at high shear for about 3 minutes. The capsules produced were about 1 to 2 microns in diameter. A layer of such encapsulated liquid crystal was applied to an electrode covered support

Co medium using a doctor blade at a gap 5 setting. The material was dried and } ’ ‘operated generally as the materials described above. . . A modified liquid crystal display device 140 in accordance with ; 25 the present invention is shown schematically in Figs. 14 and 15. In the device : a - 140 the primary source of illumination is derived from a light source 141 at the so-called back or non-viewing side 142 of the display device. More

Co specifically, the display device 140 includes a layer 61 of encapsulated liquid ; crystal between a pair of electrodes 13, 14 supported on upper and lower support media 12a, 12b generally in the manner disclosed above, for example i with reference to Fig. 12. The reflectance medium 80 is an air gap, as was ! described in connection with the preferred embodiment above.

A light control film (LCF) sold by 3-M Company is shown at 143; the one preferrd is identified by product designation LCFS-ABRO-30°-0B-

. : -4 1- v ‘ 60°-CLEAR-GLOS-.030. The light control film 143 is a thin plastic sheet preferably of black substantially light absorbing material that has black micro-louvers 144 leading therethrough from the back surface 145 toward the front surface 146 thereof. Such film or like material ‘may be used in connection with the various embodiments of the invention. Such film may in effect tend to collimate the light passing therethrough for impingement on the liquid crystal material.

The micro-louvers function like a venetian blind to direct light from the source 141, for example light beams 150, 15], into and through the 20 display device 140, and particularly through the support medium 12 and liquid crystal layer 61, at an angle that would generally be out of the viewing angle line of sight of an observer looking at the display device 140 from the viewing direction 20 - this when the liquid crystal is aligned or substantially optically transparent. Such field-on aligned condition is shown in Fig. 14 in which the light beams 150, 151 pass substantially through the display device : ‘140 out of the line of view. Moreover, light, such as light beam 152, incident on the display device 140 from the viewing direction 20 will generally pass through the support medium 12 and aligned, field-on liquid crystal layer 61 - } for absorption by the black film 143, which functions as the absorber 2" in : : connection with Fig. 12, for example. :

However, as is seen in Fig. 15, when the liquid crystal layer 61 is : in the field-off condition, i.e. the liquid crystal is distorted or randomly : "aligned, the light beams 150, 151 from the source 141 are isotropically . scattered by the layer of liquid crystal material 61 causing total internal . 25 reflection. and brightened appearance of the liquid érystal material in the : “manner described ahove. Thus, for example, the beam 151 is shown being co : isotropically scattered as beam 15la, totally internally reflected as beam 151b, and being further isotropically scattered as beam 151c which is directed out through the interface 64 toward the viewing direction 20. The display device 140 of Figs. 14, 15 is particularly useful in situations where it is desirable to provide lighting from the back or non-viewing side. However, such display device also will function in the manner described above, for : example with respect to the display device 60" of Fig. 12, even without the oo —42- : back light source 111 as long as adequnte light is provided from the viewing direction 20. Therefore, the device 140 may be used in daylight, for example, being illuminated at one or both sides by ambient light with or without the light source 141, and at night or in other circumstances. in which ambient lighting is inadequate for the desired brightness, for example, by using the illumination provided from the source 141.

A display device 160 in Fig. 16 is similar to the display device 140 except that the light control film 161 is cemented at 162 directly to, or is otherwise placed in abutment with the support medium material 12b. Total internal reflection would occur in the manner ‘described above when the display device 160 is illuininated with light from the viewing direction 20 due primarily to the interface 64 of the support medium 12a with air. There also may be some total internal reflection at the interface 162. However, since the LCF film is directly applied to the support medium 12b, a relatively large quantity of the light reaching the interface 162 will be absorbed by the black film. Therefore, in the display device 160 it is particularly desirable to supply a back lighting source 141 to assure adequate illumination of the liquid erystal material in the layer 61 for achieving the desired bright oo character display function in accordance with the invention. : 20 - Briefly referring to Fig. 17, there is shown an. alternate embodi- ment of encapsulated liquid crystal material 200, which may be substituted or for the various other embodiments of the invention disclosed herein. The . Co encapsulated liquid crystal material 200 includes operationally nematic } liquid crystal material 201 in a capsule 202 having preferably a generally . 25 spherical wall 203. In Fig. 17 the material 200 is in field-off condition, and - } in that condition the structure 204 of the liquid crystal molecules is oriented

EE to be normal or substantially normal to the wall 203 at the interface 205

Co therewith. Thus, at the interface 205 the structure 204 is generally oriented : : in a radial direction with respect to the geometry of the capsule 202.

Moving closer toward the center of the capsule 202, the orientation of the . structure 204 of at least some of the liquid crystal molecules will tend to : curve in order to utilize, i.e. to fill, the volume of the capsule 202 with 8 substantially minimum free energy arrangement of the liquid crystal in the capsule, for example, as is seen in the drawing.

Such alignment is believed to occur due to the addition of an additive to the liquid crystal material 201 which reacts with the support medium to form normally oriented steryl or alkyl groups at the inner capsule - wall. More particularly, such additive may be a chrome steryl complex or =

Werner complex that reacts with PVA of the support medium (12) that forms the capsule wall 203 to form a relatively rigid crust or wall with a steryl group or moeity tending to protrude radially into the liquid crystal material itself. Such protrusion tends to effect the noted radial or normal alignment of the liquid crystal structure. Moreover, such alignment of the liquid crystal material still complies with the above strongly curved distortion of the liquid crystal structure in field-off condition because the directional derivatives taken at right angles to the general molecular direction are non- zero.

An example of such material 200 is presented below:

EXAMPLE 9 : : To a 5 gm sample of 8250 nematic liquid crystal was added .005 gm of a 10% solution of Quilon M, a chrome steryl complex manufactured by

Co DuPont, along with 3 gm of chloroform. The resulting material was

Co homogenized at low shear with 15 gms of a 22% w/w solution of Gelvatol -- 20 ; 20/30 PVA (the remaining 78% of such Gelvatol solution was water).

The result was an encapsulated liquid crystal in which the . capsule wall reacted with the Quilon M to form an insoluble shell.

Co } By observation with polarized light it was determined that the oo capsule wall aligned the liquid crystal in a radial direction. . } A film was cast on a Mylar support medium already having an

Ce “. Intrex electrode thereon, as above, using & doctor blade with a gap setting

SL of 5 mils. The resulting film had a thickness of 1 mil on drying. An auxiliary . electrode was attached. The material began to align in the capsule at 10 volts and was fully aligned at 40 volts. Such alignment would be like that . 30 shown in Fig. 3 above. : | The invention may be used in a variety of ways to effect display of data, characters, information, pictures, etc. on both small and large scale. According to the preferred embodiment and best mode of the oo -44- ) invention, the liquid crystal material is placed in the support medium 12 at only those areas where characters, etc., are to be formed. In the alternative, the layer 61 may extend across the entire support medium 12, and only those areas where characters are to be displayed will have electrodes for controlling field-on/field-off with respect to the proximate .. portions of the liquid crystal layer 61. As an optical shutter, the invention may be used to adjust the effective and/or apparent brightness of light viewed at the viewing side. Various other designs also may be employed, as may be desired, utilizing the enhanced scattering effected by the total internal reflection arid/or optical interference principles in accordance with the present invention. - _ -

Turning now to Fig. 18, a liquid crystal device in accordance with the present invention is indicated at 310. The device 310 includes an encapsulated liquid crystal 311 which is supported by a mounting substrate 312 across which an electric field may be applied via electrodes 313, 314. oo : The electrode of 313 may be, for example, a quantity of vacuum deposited indium tin oxide applied to the substrate 312, and the electrode 314 may be, for example, electrically conductive ink. A protective layer or coating 315 may be applied over the electrode 314 for protective purposes 50 CC but such layer 315 ordinarily’ would not be necessary for supporting or confining the encapsulated liquid crystal 311 or the electrode 314. Voltage ” may be applied to the electrodes 313, 314 from an AC or DC voltage source . © 316, selectively closable switch 317, and electrical leads 318, 319 in turn to apply an electric field across the encapsulated liquid crystal 311 when the switch 317 is closed. - } - . The encapsulated liquid crystal 31 includes liquid crystal mater- ial 320 contained within the confines or interior volume 321 of a capsule 322.

BE According to the preferred embodiment and the best mode of the present [ invention, the capsule 322 is generally spherical. However, the principles of \ 30 the invention would apply when the capsule 322 is of a shape other than v : spherical. Such shape should provide the desiréd optical and electrical } characteristics that will satisfactorily coexist with the optical characteris- tics of the liquid crystal 320, e.g. index of refraction, and will permit an adequate portion of the electric field to occur across the liquid crystal material 320 itself for effecting desired alignment of the liquid crystal structure when it is desired to have a field on condition. A particular advantage to the preferred spherical configuration of the capsule 322 will be described below with respect to the distortion it effects on the liquid crystal structure.

The mounting substrate 312 and the electrodes 313, 314 as well as the protective coating 315 may be optically transmissive so that the liquid crystal device 310 is capable of controlling transmission of light there- through in response to whether or not an electric field is applied across the electrodes 313, 314 and, thus, across the encapsulated liquid crystal 31.

Alternatively, the mounting substrate 312 may be optically reflective or may have thereon an optically reflective coating so that reflection by such reflective coating of incident light received through the protective coating 315 will be a function of whether or not there is an electric field applied across the encapsulated liquid crystal 311. : - | i

According to the preferred embodiment and best mode of the invention a plurality of encapsulated liquid crystals 311 would be applied to the mounting substrate 312 in a manner such that the encapsulated liquid : 20 crystals adhere te the mounting substrate 312 or to an interface material, - such as the electrode 313, for support by the mounting substrate 312 and retention in a fixed position relative to the other encapsulated liquid "crystals 31. Most preferably the encapsulating medium of which the capsule } : i 322 is formed is also suitable for binding or otherwise adhering the capsule ‘ - ~ 25 322 to the substrate 312. Alternatively, a further binding medium (not a “shown) may be used to adhere the encapsulated liquid crystals 3ll to the substrate 312. Since the capsules 322 are adhered to the substrate 312, and since each capsule 322 provides the needed confinement for the liquid crystal material 320, a second mounting substrate, such as the additional

C20 one typically required in the prior art liquid crystel devices, ordinarily would be unnecessary. However, for the purpose of providing protection - from scarring, electrochemical deterioration, e.g. oxidation, or the like, of . the electrode 314, a protective coating 315 may be provided on the side or surface of the liquid crystal device 310 opposite the mounting substrate 312, © the latter providing the desired physical protection on its own side of the - device 310.

Since the encapsulated liquid crystals 311 are relatively securely adhered to the substrate 312 and since there ordinarily would be no need for an additional substrate, as mentioned above, the electrode 314 may be applied directly to the encapsulated liquid crystals 321. } : An enlarged fragmentary section view of a portion 332 of a liquid crystal display, for example, like the figure eight 101 and substrate 12 of Fig 9, is illustrated in Fig. 19. As is seen in Fig. 19, on the surface of the . substrate 12 (312 in Fig. 19), which may be approximately 10 .mils thick, is : deposited a 200 angstrom thick electrode layer 333 of, for example, indium tin oxide or other suitable electrode material such as gold, aluminum, tin oxide, antimony tin oxide, etc. One or more layers 334 of plural encapsul- : 15 ated liquid erystals 311 are applied and adhered directly to the electrode - layer 333. Such adherence according to the preferred embodiment and best - mode is effected by the encapsulating medium that forms respective capsules 322, although, if desired, as was mentioned above, an additional

Co adhering or binding material may be used for such adherence purposes. The oo 20 thickness of the layer 334 may, be, for example, epproximately 0.3 to 10

Co mils, preferably 0.7 to 4 mils, more preferably 0.8 to 1.2 mils, especially 1

Po i mil. Other thicknesses may also be used, depending inter alia on the ability ; i : to form a thin film and the electrical breakdown properties of the film. A

Co further electrode layer 335 is deposited on the layer 334 either directly to . _ 25 the material of which the capsules 322 are formed or, alternatively, to the ve “- additional binding material used to bind the individual encapsulated liquid - | crystals 311 to each other and to the mounting substrate 312." The electrode

Lo layer 335 may be, for example, approximately 1/2 mil thick and may be / : formed, for example, of electrically conductive ink or of the materials : 20 mentioned above for layer 333. A protective coating layer 336 for the ly purposes described above with respect to the coating 15 in Fig. 18 also may i be provided as is shown in Fig. 19.

A feature of the present invention utilizing the encapsulated liquid crystals 311 is that a versatile substrate 312 can be created to be capable of displaying virtually any desired display as a function of only the selective segments of conductive ink electrodes printed on the liquid crystal material. In this case, the entire surface 331 of the substrate 312 may be coated with electrode material 333, and even the entire surface of that electrode material may be coated substantially contiguously with layer 334 of encapsulated liquid crystals 3il. Thereafter, a prescribed pattern of electrode segments of conductive ink 335 may be printed where desired on the layer 334. A single electrical lead may attach the surface 331 to a voltage source, and respective electrical leads may couple the respective : 10 conductive ink segments via respective controlled switches to such voltage source. Alternatively, the encapsulated liquid crystals 311 and/or the . : . electrode material 333 may be applied to the surface 331 only at those areas where display segments are desired. The ability to apply encapsulated liquid crystal to only a desired area or plurality of areas such as the segments of a display by essentially conventional processes (such as e.g. silk-screening or a other printing processes) is particularly attractive, when compared with the prior art, which has the problem of containing liquid crystals between flat plates.

The encapsulated liquid crystals in the layer 334 function to : 20 attenuate or not to attenuate light incident thereon in dependence on. } whether or not an electric field is applied thereacross. Preferably a pleochroic dye is present in solution in the liquid crystal material to provide : - substantial attenuation by absorption in the "field-off" condition but to be

Co : substantially transparent in the "field-on" condition. Such an electric field

S25 _ may be, -for example, one produced as a result of the coupling of the oo “electrode layer partions 333, 335 at an individual segment, such as segment 101a, of the liquid crystal device 10' to an electrical voltage source. The magnitude of the electric field required to switch the encapsulated liquid crystals 31 from a no field (deenergized) condition to a field-on (energized) condition may be a function of several parameters, including, for example,

Co the diameter of the individual capsules and the thickness of the layer 334, - which in turn may depend on the diameter of individual capsules 322 and the : number of such capsules in the thickness direction of layer 334.

oo _43-

Importantly, it will be appreciated that since the liquid crystal material 320 a. is confined in respective capsules 322 and since the individual encapsulated } liquid crystals 311 are secured to the substrate 312, the size of the liquid crystal device 10' or any other liquid crystal device employing encapsulated liquid crystals in accordance with the present invention is virtually unlim- ited. Of course, at those areas where it is intended to effect a change in the optical properties of the encapsulated liquid crystals of such a device in response to a no field or field on condition, it would be necessary to have at "such areas electrodes or other means for applying to such liquid crystals a } 10 suitable electric field. . The electrode layer 333 may be applied to the substrate 312 by evaporation, by vacuum deposition, by sputtering, by printing or by another conventional technique. Moreover, the layer 334 of encapsulated liquid . crystals 31l may be applied, for example, by a web or gravure roller or by © 15 + reverse roller printing techniques. The electrode layer 335 also may be applied by various printing, stenciling or other techniques. If desired, the : electrode layer 333 may be prepared as a full coating of the substrate 312, such as Mylar, as described above, as part of the process in which the Mylar sheet material is manufactured, and the layer 334 also may be applied as . - 20 . part of such manufacturing process. . E CC - The inventor has discovered, moreover, that when the liquid crystal material 30 in the capsule 32 (Fig. 2) has pleochroic dye dissolved

BN therein, such dye, which ordinarily also would be expected to have optical - : polarization sensitivity, no longer is polarization sensitive because the dye

EE 25 tends to follow the same kind of curvature orientation or distortion as that

He “of the liquid crystal structure. It is noted here that in the capsule 32 the

Co discontinuity 55 further distorts the liquid crystal structure which in turn further decreases the possibility that the liquid crystal material 30 would be sensitive to the optical polarization of the incident light. With the liquid crystal ‘structure and pleochroic dye being distorted to fold in on itself generally in the manner illustrated in Fig. 5, for example, the encapsulated liquid crystal ordinarily will absorb or block light from being transmitted . therethrough when no electric field is applied across the encapsulated liquid crystal and particularly across the liquid erystal material thereof.

However, when an electric field is applied across the encapsu- lated liquid erystal in the manner illustrated in Fig. 3, the liquid erystal and any pleochroic dye in solution therewith will align in response to the electric field in the manner shown in such figure. Such alignment permits light to be transmitted through the encapsulated liquid crystal ll. i To optimize the contrast characteristics of a liquid crystal device, such as that shown at 10' in Fig. 9, comprised of encapsulated liquid crystals 1 with pleochroic dye therein, and more particularly, to avoid optical distortion, due to refraction of incident light passing from the encapsulating medium into the liquid crystal material and vice versa, the : index of refraction of the encapsulating medium and that the ordinary index of refraction of the liquid crystal material should be matched so as to be as much as possible the same. The closeness of the index matching will be dependent on the desired degree of contrast and transparency in the device, - 15 but the ordinary index of refrection of the crystal and the index of the : . medium will preferably differ by no more than 0.1, more preferably 0.01, especially 0.001. The tolerated difference will depend on capsule size and intended use of the device. The text "Optics" by Sears, published by

Addison-Wesley, contains a thorough discussion of birefringence relevant to : the foregoing, and the relevant portions of such text are incorporated herein by reference.

However, when no field is applied there will be a difference in indices of refraction at the boundary of the liquid crystal and capsule wall oo : due to the extraordinary index of refraction of the liquid crystal being © .25 ] greater than the encapsulating medium. This causes refraction at that a “interface or boundary and thus further scattering and is a reason why ) encapsulated nematic liquid crystal material in accordance with the present a invention, in particular, will function to prevent transmission of light even i without the use of pleochroic dye; with such dye, though, substantial 20 absorption of the scattered light will occur in the capsule. . Ordinarily the encapsulated liquid crystals 311 would be applied to the substrate 312 such that the individual encapsulated liquid crystals 31 are relatively randomly oriented and preferably several capsules thick to

. : . -30 ~ | . - . . | 0 i . ‘assu re an adequate quantity of liquid crystal material to thereby provide he EY : desired level of light blockage and/or transmission characteristics for, for example, a liquid crystal device 10" or the like. ‘ Co BR :

In a liquid crystal device, such as that shown in 10° in Fig. 9, - no 5 - which is comprised of liquid crystal material 320 including pleochroic dye to ’ i BE ~ . form encapsulated liquid crystals 311 according to the invention (Fig. 18), it . . Co has been discovered that the degree of optical absorbency is at Jeast about Lo i Cal the same as that of relatively free (unencapsulated) liquid crystal material : . : including pleochroie dye. It also has been discovered unexpectedly that ! : re. when the electric field is applied in the manner illustrated in Fig. 3, for : - example, the clarity or lack of opaqueness of the encapsulated liquid crystal : : no material 30 including pleochroic dye is at least about the same as that of : the ordinary. case in the prior art device 1 having dye in solution with

Lo relatively free liquid crystal material. | . BE . - | - A schematic electric circuit ‘diagram representing the: circuit . ’ n across which the electric field E of Fig. 3 is imposed is illustrated in Fig. 20." : : ) ‘The electric field is derived from the voltage source 316 when the switch 317° oo ; Cis closed. A capacitor 370 represents the capacitance of the ‘liquid erystal - -

I material 30,320 in the encapsulated liquid erystal 1, 311 when such electric . | }

Co 20. . field is applied in the ménner. illustrated in Fig. 3. The capacitor 371. - - represents ‘the capacitance of the capsule wall 54 at an ‘upper area (the

Co direction conveniently referring to the drawing but having no other partic= : : ular meaning). The capacitor 372 similarly represents the capacitance of ~ the lower portion of the capsule exposed to. the electric field E.. The oo : : magnitudes of capacitance for gach capacitor 370-372 Will be a function of oo N

Lo the dielectric constant (coefficient) of the material of which the respective Co i ... © + capacitors are formed and of the spacing of the effective plates thereof. It. ~ bi ) "is desirable that the voltage drop occurring across the respective capacitors } - 371, 372 will be less than the voltage drop across the capacitor 370; the 4 30 ) result, then, is application of a maximum portion of the electric field E ) i. Tatross the liquid crystal material 30 in thé eéncapsulated liquid crystal ll, 311757 ~~ © © ~ ’ for achieving optimized operation, i.e. alignment, of the liquid crystal i - structure thereof with & minimum total energy requirement of the voltage source 316. However, it is possible that the voltage drop in one or both capacitors 371, 372 will exceed the voltage drop across capacitor 370; this is operationally acceptable as long as the drop across the capacitor 370 (liquid crystal material) is great enough to produce an electric field that tends to align the liquid crystal material to and/or toward the field-on condition of

Fig. 3, for example. :

In connection with capacitor 371, for example, the dielectric material is that of which the wall 54 is formed relatively near the upper portion of the capsule 32,322. “The effective plates of such capacitor 371 are the exterior and interior capsule wall surfaces and the same is true for the capacitor 372 at the lower portion of the capsule. By making the wall 54 as thin as possible, while still providing adequate strength for containment of the liquid crystal material, the magnitudes of capacitors 371, 372 can be maximized, especially in comparison to the rather thick or lengthy distance between the upper and lower portions of the liquid ‘crystal material in the : Co capsule which approximately or equivalently form the plates of the same number of the capacitor 370.

The liquid crystal material 320 will have a dielectric constant

Co i value that is anisotropic; therefore, such value also is referred to as dielectric coefficient. It is preferable that the dielectric constant of the wall 54 be no lower than the lower dielectric coefficient of the anisotropic + liquid crystal material 20 to help meet the above conditions. Since a typical

Po - lower dielectric coefficient for liquid crystal material is about 8, this indicates that the dielectric constant of the encapsulating material is _ preferably at least about 6. ‘Such value can vary widely depending on the ’ liquid crystal material used, being, for example, as low as about 3.5 and as : : high as about 8 in the commonly used liquid crystals. : : The encapsulated liquid crystal 311 has features such that since i the liquid crystal structure is distorted and since the pleochroic dye \ ~ 20 similarly is distorted, absorbency or blockage of light transmission through : the encapsulated liquid crystals will be highly effective when no electric field E is applied thercacross. On the other hand, due both to the efficient application of an electric field across the liquid crystal material 320 in the encapsulated liquid crystals 311 to align the liquid crystal molecules and the dye along therewith as well as the above described preferred index of : refraction matching, i.e. of the encapsulating medium and of the liquid crystal material, so that incident light will not be refracted or bent at the = interface between the capsule wall and the liquid crystal material 320 when an electric field is applied, the encapsulated liquid crystal 3U will have a good optically transmissive characteristic. "Since a plurality of encapsulated liquid crystals 11, 311 ordinarily is required to construct a final liquid crystal device, such as the device 10' of : 10 oo Fig. 9, and since those encapsulated liquid crystals are ordinarily present in several layers, it is desirable for the liquid crystal material to have a relatively high dielectric anisotropy in order to reduce the voltage require- ments for the electric field E. More specifically, the differential between the dielectric coefficient for the liquid crystal material when no electric field is applied, which coefficient should be rather small, and the dielectric - ‘coefficient for the liquid crystal material when it is aligned upon application of an electric field, which coefficient should be relatively large, should be as large as possible consistent with the dielectric constant of the encapsul- ating medium. : : : } As was noted above, the larger the capsule size, the smaller the : electric field required to effect alignment of the liquid crystal molecules therein. However, the larger the sphere, the longer the response time. A } . person of ordinary skill in the art should have no difficulty, having regard to

IE : this disclosure, in determining a suitable or optimum capsule size for a given 85 _ application.

Co ; . The encapsulating medium forming capsules should be of a type . . that is substantially completely unaffected by and does not react with or : otherwise chemically affect the liquid crystal material or the pleochroic : dye. The dye should be soluble in the liquid crystal material and not subject to absorption by the encapsulating medium. Additionally, to achieve the tL desired relatively high impedance for the encapsulating medium, such medium should have a relatively high level of purity. Especially when the : encapsulating medium is prepared as an aqueous dispersion or by ionic polymerization, ete., it is important that the level of ionic (conductive) impurities should be as low as possible. oT

Examples of pleochroic dyes that may suitably be used in the encapsulated liquid erystals 11 in accordance with the present invention are indophenol blue, Sudan black B, Sudan 3, and Sudan 2, and D-37, D-43 and D- 85 by E. Merck identified above.

EXAMPLE 10

A .45% Sudan black B pleochroic dye was dissolved in a liquid crystal which was composed of aromatic esters. Such combined material is commercially sold under the designation NMB250 by American Liquid Xtal

Chemical Corp. of Kent, Ohio. Such material was mixed with a solution of 7% PVA, which had been purified to remove all salts. The solution also was made with ASTM-100 water. The resulting mixture was put into a colloid mill whose conegap setting was 4 mils, and the material was milled for four : 15 minutes to give a rather uniform particle suspension size. The result was a ; - stable emulsion whose suspended particle size was approximately 3 microns.

The emulsion was east on a Mylar film which was precoatd with a 200 ohm per square layer of indium tin oxide electrode purchased from Sierracin. A doctor blade was used to cast the emulsion material on the Mylar film on : 20 ’ the electrode coated side. . A 7 mil lay-down of the emulsion material was placed on such . electrode and was allowed to dry to a total thickness of 0.8 mil. A sccond ! layer of such emulsion subsequently was laid on the first with a resulting . : aggregate layer of liquid crystal droplets in a polyvinyl alcohol matrix

LL 25 - having a thickness of 1.6 mil. Preferably the encapsulated liquid crystals

The thusly formed liquid crystal device, including the layer of , Mylar, electrode, and encapsulated liquid crystals was then tested by : applying an electric field, whereupon the material changed from black to nearly clear-transparent. The material exhibited a very wide viewing angle, i.e. the angle at which light was transmitted, and the contrast ratio was 7:1 } at 50 volts of applied electric field. The switching speed was about two milliseconds on and about 4 milliseconds off.

~51- : oo : : EXAMPLE 11 ' 900 grams of 7% high viscosity fully hydrolysed polymer (SA-72 of American Liquid Xtal Chemical Corp.), 100 grams of 8250 nematic liquid crystal material also of American Liguid Xtal Chemical Corp., .45 grams of

C26510 Sudan Black B, and .15 grams of C26100 Sudan HI (the latter two ingredients being pleochroic dyes), were used. he ~olvmer was weighed out in a beaker. The liquid erystal was weighed out, was placed on a hot plate, and was heated slowly. The dye was weighed out on a balance and was added very slowly to the liquid erystal, being stirred until all the dye went . 10 into solution.

The liquid crystal and dye solution then was filtered through a standard Millipore filtering system using 8 m. filter paper. The filtered : . liquid crystal and dye solution was stirred into the polymer using a Teflon - rod. Such mixture was encapsulated by placing the same in a colloid mill . that was operated at medium shear for five minutes. The emulsion film was 3 then pulled on a conductive polyester sheet.

In operation of such example, upon the application of a 10 volt electric field, the liquid crystal structure began to align, and at 40 volts - reached saturation and maximum optical transmissivity. ’ 20° EXAMPLE 12 Co . - The procedure of Example 11 was carried out using the same oo ingredients and steps except that a 5% high viscosity fully hydrolysed : polymer, such as SA-72, was substituted for the 7% polymer of Example 2. . Operational results were the same as in Example 2. ) i = EXAMPLE 13 - } - The process of Example 11 was carried out to make an emulsion using 4 grams of 20% medium viscosity, partly hydrolysed polymer (such as 405 identified in Table I above), 2 grams of 8250 nematic liquid crystal material having 0.08% of D-37 magenta pleochroic dye (a proprietary pleochroic dye manufactured and/or sold by E. Merck of West Germany) in ; the solution with the liquid crystal.

A slide was taken using a Teflon rod, and upon inspection showed medium size capsules of about 3 to 4 microns in diameter. The material was

. filtered through a Millipore screen filter and another slide was taken; on inspection there was very little change in capsule size from the first- mentioned inspection.

The emulsion was pulled onto a conductive polyester support film as in Example 11 using a doctor blade set at a 5 mil gap. In operation, the encapsulated liquid crystal material began to align upon the application of an electric field of 10 volts and was at saturation or full on at from about 40 to 60 volts.

EXAMPLE 14

Using a glass rod cleaned and washed with deionized ASTM-100 water, 2 grams of 40% 8250 nematic liquid crystal material with 0.08% of

D-37 pleochroic dye dissolved therein was stirred into 4 grams of 405 desalted 20% by weight medium hydrolysis medium viscosity polymer very carefully for approximately 15 minutes. The material was then placed through a Millipore screen filter approximately 4 microns in size. A slide - : was taken after the bubbles had dissipated.

Thereafter, a film was pulled at a gap 5 mil setting on Intrex electrically conductive electrode film material that was placed on a polyester support of Mylar material. In operation it was evident that the : 20 liquid. crystal material began aligning upon application of a 5 volt electric field. Contrast was good and the liquid crystal material was at full on or saturation upon the application of a 40 volt electric field. oo EXAMPLE 15 | . } This example used 8 grams of D-85 pleochroic dye dissolved in E- - ~~. 25 | _ 63 biphenyl liquid crystal. Such material is sold premixed by British Drug : "House, which is a subsidiary of E. Merck of West Germany: The example

Coe also used 16 grams of 20% PVA medium viscosity medium hydrolysis polymer ; as the encapsulating medium. The liquid crystal and pleochroic dye solution was mixed carefully by hand into the polymer at a slow rate. The combined

V 20 material was then screened at a low shear. A slide was taken and on \ observation showed approximately 3 micron size capsules. A film of such emulsion was pulled onto an electrically conductive polyester sheet, as above, using a gap 5 mil setting. The film was on or began having liquid

. . ’ =56- . - crystal structure align with the electric field at approximately 6 volts and was at saturation or full on at 24 volts. Co

EXAMPLE 16 :

A mixture was formed of 8250 nematic liquid crystal with 0.08%

D-37 pleochroic dye in solution therewith and a solution of 15% ANI69 : Gantrez in 85% water. The mixture was of 15% liquid crystal and 85%

Gantrez as the containment medium. The mixture was homogenized at low shear to form an emulsion, which was applied to an electrode/support film as above; such support film was about 1.2 mils thick. After drying of the emulsion, the resulting liquid crystal emulsion responded to an electric field generally as above, Substantially absorbing or at least not substantially transmitting light when in field-off condition, showing a threshold of about 7 volts to begin transmitting, and having a saturation level of substantially : maximum transmission at about 45 volts.

In accordance with the present invention the quantities of - ingredients for making the encapsulated liquid crystals 1, for example in the manner described above, may be, as follows:

The liquid crystal material - This material may be from about :

Cs . 5% to about 20% and preferably about 50% (and in'some circumstances even

C20 "greater depending on the nature of the encapsulating material) including the

Co pleochroic dye, by 25% (when using Gelvatol as the encapsulating material) volume of the total solution delivered to the mixing apparatus, such as a : colloid mill. The actual — of liquid crystal material used should ordinarily exceed the volume quantity of encapsulating medium, e.g. PVA to 25 ' ._ optimize the capsule size. | :

SE So : The PVA - The quantity of PVA in the solution should be on the : . | : order of from about 5% to about 50%, and possibly even greater depending ; on the hydrolysis and molecular weight of the PVA, and preferably, as described above, about 22%. For example, if the PVA has too large a molecular weight, the resulting material will be like glass, especially if too much PVA is used in the solution. On the other hand, if the molecular weight is too low, use of too little PVA will result in too low a viscosity of the material, and the resulting emulsion will not hold up well, nor will the

. } : : ~57- i droplets of the emulsion solidify adequately to the desired spherical ] encapsulated liquid crystals. : Carrier medium - The remainder of the solution would be water or other, preferably volatile, carrier medium, as described above, with : which the emulsion can be made and the material laid down appropriately on gd substrate, electrode or the like.

It will be appreciated that since the uncured capsules or droplets of encapsulating medium and liquid erystal material are carried in a liquid, various conventional or other techniques may be employed to grade the capsules according to size so that the capsules can be reformed if of an undesirable size by feeding again through the mixing apparatus, for example, : and so that the finally used capsules will be of a desired uniformity for the ; reasons expressed above. . Although the encapsulation technique has been described in

Bh detail with reference to emulsification, since the fact that the encapsulant ! oo material and binder are the same makes facile the production of liquid crystal devices; the preparation of discrete capsules of the liquid crystal material may on occasion be advantageous, and the use of such discrete : capsules (with a binder) is within the contemplated scope of this invention. : Although the presently preferred invention operates in response oo to application and removal of an electric field, operation also may be effected by application and removal of a magnetic field.

Co Co STATEMENT OF INDUSTRIAL APPLICATION

Lo : * The invention may be used, inter alia, to produce a controlled optical display. . i CL

Claims

So | I" 96" 1 7 . -58- -

1. Liquid crystal apparatus comprising liquid crystal ‘means - for selectively primarily scattering light or transmitting light in response to a prescribed input, a support medium ‘means for supporting said liquid ° crystal means, and reflecting means for effecting reflection of light . scattered by said liquid crystal means. : ’ a. The apparatus of claim 1, said liquid crystal means com- prising at least one layer of encapsulated operationally nematic liquid Co crystal material in said support medium mesns, said liquid erystal material having positive dielectric anisotropy .and an ordinary index of refraction substantially matched to that of said support medium means te maximize optical transmission in the presence of an electric field and to effect : substantially isotropic scattering in the absence of an electric field.

:

3. The apparatus of claim 1, said liquid crystal means having ’ C15 oo positive dielectric anisotropy and wherein the dielectric constant of said CC . oo : support medium means’ is at least about as large as the lower dielectric ‘constant of said liquid crystal means." : : :

4. The apparatus of claims 1, 2, or 3, said support medium : “means having. a viewing side and an opposite side, respective media at said : 20 - viewing and opposite sides, and the index of refraction of said support Co medium means being greater than the index of refraction of the medium at : i ; .. one of respectively such viewing and opposite sides, said reflecting means ‘comprising an interface of such one of said sides with the medium thereat to fo - effect total internal reflection of light in said support medium means 25 incident on such interface at an angle exceeding a predetermined cone of So light angle at which ight would be transmitted through such interface. ; R ~ 5. The apparatus of claims 1, 2, 3, or 4, said liquid crystal means comprising a layer of encapsulated liquid crystal, and further : comprising electrode means positioned between said $upportrmedium means and said layer of encapsulated liquid crystal for applying an €lectric field to align said liquid crystal with respect thereto.

7 6. The apparatus of claims 1-5, said support medium means ; including a containment medium, and said liquid crystal comprising an ‘emulsion of liquid crystal material and a containment medium.

: ’ : ) -59-

7. The apparatus of claims 1-8, further comprising light } director means for directing incident light into said support medium means at said opposite side thereof, said director means comprising means for directing such incident light into said support medium means at a direction substantially out of the usual viewing line of sight from said viewing side.

8. The apparatus of elaim 7, said director means comprising a light control film having light transmitting and light absorbing portions, and means for coupling said film to said opposite side of said support medium means to form an interface therewith.

8. The apparatus of claims 1-8, said support medium means having a viewing side and an opposite side, and further comprising a tuned dielectric interference layer on said opposite side of said support medium means for effecting optical constructive interference of at least some of the light in said support medium means incident on said interference layer or the interface thereof with said support medium means at an angle exceeding a predetermined cone angle and destructive interference of light incident at an angle within such cone angle, said layer comprising means for forming an interface therewith to effect total internal reflection of light in said support medium means incident on such interface at an angle exceeding : 20 a further predetermined cone angle at which light would be transmitted through such interface, such further predetermined cone angle being larger : than such predetermined cone angle.

10. The apparatus of claims 1-9, said liquid crystal means ] comprising operationally nematic liquid crystal material, and said support . | medium means comprising containment means for containing discrete quantities of operationally nematic liquid erystal material to distort the : same when in random alignment and to permit alignment thereof in the ~~ presence of an electric field. Co

II. The apparatus of claim 10, further comprising “additive means in said operationally nematic liquid crystal material for expediting : Co such distorting and return to random alignment upon the removal of such electric field.

12. The apparatus of claim ll, said additive means comprising a chiral additive. : eT TTT TTT TT TT TTT TT TTT TTT Ts rm ee oo -60-

13. The apparatus of claims 1-12, said support medium means having a viewing side for emitting at least some light isotropically scattered : by said liquid crystal means, and said support medium means having an opposite side relative to said viewing side. :

14. The apparatus of claim 13, further comprising optical ab- oo - } sorbing means for absorbing light transmitted through said opposite side of said support medium means. :

15. The apparatus of claim 10, further comprising means Te- active with said containment medium means for tending to force at least a portion of at least some of said liquid erystal means into substantially normal alignment with the wall of such capsule-like volumes.

16. The apparatus of claims 1-15, said liquid crystal means comprising at least one layer of liquid crystal material in a containment : medium that tends to distort at least some of the liquid crystal material to : align generally with respect to a wall of such containment medium when in the absence of an electric field, and said liquid crystal material being responsive to an electric field to tend to align with respect thereto.

17. The apparatus of claims 1-16, said reflecting means com- prising means for reflecting light scattered by said liquid crystal means back "20 to said liquid crystal means to display relatively bright characters or the like on a relatively dark background. :

18. A display device comprising a liquid crystal apparatus having liquid crystal means for selectively primarily scattering light or . transmitting light in response to a prescribed input, a support medium means : for supporting said liquid crystal means, and reflecting means for effecting ) reflection of light scattered by said liquid crystal means. . - ©

19. An optical shutter comprising a liquid erystal apparatus oo having liquid crystal means for selectively primarily scattering light or Ct transmitting light in response to a prescribed input, a support medium means - 30 for supporting said liquid erystal means, and reflecting means for effecting : reflection of light scattered by said liquid crystal means.

20. Liquid crystal apparatus comprising liquid crystal material, a support medium containing said liquid crystal ‘material, and a tuned dielectric interference layer of material for effecting selective constructive and destructive optical interference.

’ .

21. Liquid crystal apparatus comprising liquid crystal means } for selectively primarily scattering light or transmitting light in response to a prescribed input, support medium means for supporting said liquid crystal means for viewing from a viewing side within a prescribed viewing angle, : and directing means for directing incident light to said liquid crystal means "at an angle at least substantially outside such viewing angle. : 22. The apparatus of claim 21, said directing means comprising a louvered light control film.

23. The apparatus of claim 2I, said directing means comprising a light control film, and further comprising means for coupling said light control film in interfacing engagement with said support medium means at a side thereof opposite said viewing side. 24, The apparatus of claim -21, further comprising reflecting means for reflecting light scattered in said support medium means by said liquid crystal means, said reflecting means comprising a gap between said support medium means and said directing means to cause a total internal reflection between said support medium means and such gap.

25. The apparatus of claims 1-24, further comprising a light source for illuminating said liquid crystal means. - 26. An operationally nematic liquid crystal material in a containment medium that tends to distort said material into alignment with . respect to a wall thereof when in generally random alignment in the absence 25° of an electric field, said liquid crystal material being responsive to an electric field to tend to align with respect thereto, and additive means in said liquid crystal material for expediting such distorting and return to random alignment upon the removal of such an electric field. : 27. The device of claim 26, said additive comprising a chiral C130 additive. ~~ - ; Co ) C. 28. A method of displaying a character or other informationon a background using liquid crystal material in a containment medium arranged in a pattern, comprising substantially isotropically scattering at De —— ce - i oo -62- : least some light incident on such liquid crystal material to form such : character or other information, and totelly internally reflecting at least some isotropically scattered light back to such liquid crystal material to brighten the same. © © 29. The method of claim 28, further comprising effecting constructive optical interference with respect to at least some of such iso- ’ tropically scattered light to direct the same incident on such liquid erystal ~~ - material. :

30.. The method of claims 28 or 29, further comprising trans- mitting some of such isotropically scattered light to a viewing area.

3l. The method of claims 28-30, further comprising illumi nating such liquid erystal material from opposite a viewing side thereof . using incident light directed at an angle ordinarily out of the viewing line of sight. : :

32. The method of claims 28-31, further comprising selectively applying an electric field to such liquid crystal material to align the same for transparency.

33. The method of claims 28-32, further comprising absorbing at least some of the light transmitted by such liquid crystal material.

34. A method of making a liquid crystal apparatus comprising : forming encapsulated liquid crystal material as operationally nematic material, and placing an encapsulated liquid crystal material in a support medium that has an optical internal reflection characteristic.

i . 35. The method of claim 34, further comprising providing a * further medium at an interface with such support medium and selecting the index of refraction of such support medium to be greater than the index of refraction of such further medium. } ) "36. The method of claim 35, said providing comprising pro- CL viding an air interface. : :

©. 30 Co ~~ 37. The method of claims 34-36, said forming comprising ’ - “forming. an emulsion.of an operationally nematic liquid crystal material and © a containment medium to provide capsule-like containment volumes of such liquid crystal material; the walls of such volumes tending to distort the structure of such liquid crystal material when generally randomly aligned in : the absence of an electric field.

38. The method of claims 34-37, further comprising mixing with such liguid crystel material an additive that expedites return to distorted random alignment upon removal of nn electric field. . 39. The method of claims 34-38, further comprising applying a tuned dielectric interference layer to a surface of such support medium opposite the surface at which such support medium ordinarily is viewed.

40. The method of claims 34-39, further comprising applying a light absorbing coating beyond such further medium for absorbing light transmitted through such further medium. :

4]. The method of claims 34-40, further comprising adding & control agent to such liquid erystal material to control the viscosity thereof. : 42. The method of claim 41, said adding comprising adding chloroform to such liquid crystal material and mixing the same.

43. The method of claims 34-42, further comprising adding a ' : surfactant to such liquid crystal material. : 44, The method of claim 43, said adding comprising adding a non-ionic surfactant. : ~~ 45, The method of claims 34-44, further comprising mixing an i aligning material with operationally nematic liquid crystal material. i 46. The method of claim 45, said mixing comprising mixing a chrome alkyl complex with such liquid erystal material. i : . - 47. An article made by the method of forming encapsulated Toes liquid crystal material as operationally nematic material, and placing an : encapsulated liquid crystal material in a support medium that has an optical internal reflection characteristic. : - 48. An emulsion of an operationally nematic liquid crystal : "material and a containment medium, further comprising a surfactant mixed : - 30 *. therein, said surfactant comprising a non-ionic surfactant. - = 49. An optical display made from an emulsion of an operation- ally nematic liquid crystal material and a containment medium, and further comprising a surfactant mixed therein, said surfactant comprising a non- onic surfactant. | :

-64- Co

50. In combination, a liquid crystal and a chrome alkyl complex in solution therewith, further comprising a containment medium means for containing discrete quantities of such solution in capsule-like volumes, said chrome alkyl complex being at least partly reactive with said containment medium means to align in relatively fixed position with respect thereto, and said chrome alkyl complex being so positioned with respect to the capsule- like walls of said volumes and with respect to said liquid crystal to align at least part of at least some of the latter substantially normal with respect to : said wall, said liquid crystal comprising operationally nematic liquid crystal material.

51. | A method of making an encapsulated liquid crystal, com- - prising mixing together a support medium material and a solution of liquid crystal material and a chrome alkyl complex.

52. Liquid erystal apparatus, comprising liquid crystal material, and encapsulating medium means for confining said liquid crystal } material in discrete volumes, said encapsulating meduim means inducing a generally non-parallel alignment of said liquid erystal material which in response to such alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or absorption. : : - 53. The invention of claim 52, further comprising substrate means for supporting a layer of said liquid crystal material and encap- sulating medium means. Se } 54. The invention of claim 53, said layer being from about 0.3 ‘mil to about 10 mils thick. ;

55. The invention of claim 54, said discrete volumes com- prising capsule-like volumes of liquid érystal material in said encapsulating medium means, said capsule-like volumes having a diameter of from about

: 0.3 micron to about 100 microns. : EB 30 Ce . 56. The invention of claim 53, said discrete volumes com- - ‘prising capsule-like Volumes of liquid crystal material in said encapsulating medium means, and said layer comprising several layers of capsule-like volumes in thickness.

: 57. The invention of claim 52, said liquid crystal material being optically anisotropic, and wherein the difference between the ordinary index of refraction of said liquid crystal material and the index of refraction of said encapsulating medium means is no more than about 0.3. :

58. The invention of claim 52, wherein said encapsulating : medium means comprises at least one component of the group consisting of gelatin, carboxy polymethylene polymer, and polymethyl vinyl ether/maleic anhydride.

59. The invention of claim 52, said encapsulating medium means comprising a solid medium forming individual capsules.

60. The invention of claim 52, said encapsulating medium means comprising a dried stable emulsion.

61. Liquid crystal apparatus, comprising liquid crystal material, and containment means for inducing a generally non-parallel alignment of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or absorption, said" liquid crystal material and containment means comprising a dispersion thereof.

62. Liquid crystal apparatus, comprising liquid crystal material, and containment means for inducing a generally non-parallel : alignment of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or absorption, said containment means forming capsule-like volumes for containing said liquid crystal material, said volumes being of a diameter of from about 0.3 oC microns to about 100 microns. oo ~ 63. The invention of claim 62, said volumes being of a dia- meter of from about 1 micron to about 39 microns. ~ -64. The invention of claim 63, said volumes being of a dia- : oo * “meter of from about 3 microns to about 15 microns.

65. The invention of claim 64, said volumes being of a dia- meter of from about 5 microns to about 15 microns. TT rl

66. The invention of claim 62, further comprising substrate means for supporting a layer of said liquid crystal material and containment : means.

67. The invention of claim 66, seid layer being from about 0.3 © mil to about 10 mils thick. oo : 68. The invention of claim 66, said layer comprising several layers of capsule-like volumes in thickness. oo © 69. The invention of claim 62, further comprising substrate means for supporting a layer of said liquid crystal material and containment

10. means, a first electrode positioned between said substrate means and said "layer, and a second electrode positioned on the opposite side of said layer relative to said substrate means.

70. The invention of claim 69, said first electrode being posi- tioned over substantially the entire surface of said substrate means where said layer is supported on the latter. : : TL. The invention of claim 70, said second electrode being positioned only over predetermined selected areas, less than the entire area, of said layer.

72. The invention of claim 69, said substrate means having a thickness of about 10 mils, said first electrode having a thickness of about : 200 Angstroms, said second electrode having a thickness of about 0.5 mil, and said layer having a thickness of from about 0.3 mil to about 10 mils.

73. The invention of claim 62 or 89, said capsule-like volumes . . oo of liquid erystal being sitk-screened for support on said substrate means. : ‘ 74. A billboard display comprising a liquid crystal apparatus, . including liquid crystal material and containment means for inducing a . generally non-parallel alignment of said liquid crystal material which in : oC response to such alignment at least one of scatters and absorbs light and Co : which in response to a prescribed input reduces the amount of such CL 30 : scattering or absorption. - = . 75. - The invention of claim 74, said liquid crystal apparatus - Co being over a substantial surface area of the billboard.” f

76. Liquid crystal apparatus, comprising liquid crystal ee me ————

material, containment means for inducing a generally non-parallel alignment ’ of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or ebsorption, and electrode means for applying an electric field as such prescribed input, said electrode means ; comprising electrically conductive ink.

"77. The invention of claim 76, said electrically conductive ink being applied to a surface of said containment means. Co

78. ‘The invention of claim 76, said electrically conductive ink being optically reflective.

79. The invention of claim 76, further comprising substrate - means for suporting said liquid crystal material in said containment means, said electrically conductive ink being applied to a surface of said contain- ment means remote from said substrate means.

80. The invention of claim 79, further comprising further } electrode means on said substrate means, both said electrode means being : positioned and coupled to apply such electric field in response to receiving an electrical input. : Co gl. The invention of claim 80, wherein said further electrode is applied over substantially the éntire sirface of said substrate means that is directly supporting said liquid crystal material and containment means, and said electrically conductive ink electrode is arranged in a pattern over 8 portion less than all of such surface of said containment means. } oo 82. Liquid crystal apparatus, comprising liquid erystal : 25 material, containment means for inducing a generally non-parallel alignment of said liquid crystal material which in response to such alignment at least . one of scatters and absorbs light and which in response to a prescribed input : reduces the amount of such scattering or absorption, and electrode means , - for applying an electric field as such prescribed input, said electrode means . SL 30 ) being applied by at least one of evaporation, vacuum deposition, sputtering, printing, web roller, gravure roller, reverse roller printing, stencilling, or © printing.

83. ‘The invention of claim 82, further comprising substrate

$ -68- means for supporting said liquid crystal material in seid containment means, I and said liquid crystal material and said containment means being applied to said substrate means by silk-screening. - g

84. Liquid crystal apparatus, comprising liquid crystal ’ : material, containment means for inducing a generally non-parallel alignment of said liquid crystal material which in response to such alignment at least 3 one of scatters and absorbs light and which in response to a prescribed input } i reduces the amount of such scattering or absorption, and substrate means - for supporting said liquid crystal material in said containment means, said substrate including reflecting means for reflecting light transmitted through said liquid crystal material in the presence of such prescribed input. : :

85. The invention of claim 84, said reflecting means com- prising a reflective coating on said substrate means.

86. Liquid crystal apparatus, comprising liquid : crystal material, containment means for inducing & generally non-parallel alignment of said liquid erystal material which in response to such alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or absorption, and substrate means } for supporting theron said containment means and liquid crystal material, said containment meens having a surface remote from said substrate means, : - said surface being substantially directly unsupported or covered by a separate substrate means. oo Co 87. The invention of claim 86, further comprising electrode means at said surface for applying an electric field to said liquid crystal 25: material as such prescribed input. :

88. The invention of claim 87; said electrode means being ~ applied by at least one of evaporation, vacuum deposition, sputtering, printing, web roller printing, gravure roller printing, reverse roller printing, : and stenciling. : ~ : 30 . "89. The invention of claim 87, said electrode means comprising Coe électrically conductive ink. . oo Co : i

‘90. The invention of claim 87, further comprising further ~~ electrode means on said substrate means, both said electrode means being ee ee mm = - ’

Co 1 . } Co } E -69- : : oo positioned and coupled to apply such electric field in response to receiving | : ; an electrical input.

9]. The invention of claim 890, wherein seid further electrode is applied over substantially the entire surface of said substrate means that is © 5 directly supporting said liquid crystal material and containment means. i

92. The invention of claim 9], said eléctrode means at said . surface being arranged in a pattern over less than all of said surface. i : 93. The invention of claim 92, said electrode means at said - - surface comprising electrically conductive ink printed on said surface in a predetermined pattern. - -

94. The invention of claim 86, said substrate meens including "reflecting means for reflecting light transmitted through said liquid crystal material in the presence of such prescribed input.

95. The invention of .claim 94, said reflecting means com- -15 prising a reflective coating on said substrate means. oo 96. The invention of claim 84 or 86, wherein said substrate . : means comprises at least one component of the group consisting of Mylar CL and glass. i oC SR 47. Liquid crystal apparatus, comprising a substrate and ‘sup- : : I said substrate a layer of liquid erystel material gnd containment oo : means for inducing a generally non-parallel ‘alignment of said liquid erystel material which in response to such alignment at least one of scatters and absorbs light and which in response toa prescribed input reduces the amount of. such scattering or absorption, said layer being from about 0.3 mil to about 10 mils thick. Co - : 98. The invention of claim 97, said layer being from about 0.7 .- milto about 4 mils thiek. : oo Co 99. The invention of claim 97, said layer being from about 0.8 Co mil to about 1.2 mils thick. Lo oo - 30 Lo - 7 100. The invention of claim 97, further comprising en electrode Co " between ‘said substrate and said layer of liquid crystal material and : So containment means. Co ’

101. The invention of claim 100, said electrode being about 200 Angstroms thick. : J . Ce ——— SS Co

: } ~70- : : oo :.

102. The invention of claim 100, said electrode comprising at least one component of the group consisting of indium tin oxide, gold, aluminum, tin oxide, and antimony tin oxide. :

103. The invention of claim 100, further comprising & further : electrode at an opposite surface of said layer away from said substrate. ;

104. The invention of claim 103, said further electrode com- : prising electrically conductive ink. oT

105. The invention of claim 97, said substrate being bout 10 : mils thick.

10 . 106. The invention of claim 97, said liquid crystal material and containment means comprising capsule-like volumes of liquid crystal } oo material, and said layer comprising plural layers of said capsule-like co volumes thick. } .

107. The invention of claim 97, said liquid crystal material Co comprising optically anisotropic liquid crystal material, and wherein the i difference between the ordinary index of refraction of said liquid crystal - material and the index of refraction of said containment means being no . greater than 0.3. : : Cd

108. The invention of claim 52 or 97, said liquid crystal material : having positive dielectric ‘anisotropy, and wherein the lower dielectric . constant of said liquid crystal material is between about 3.5 and about 8.

109. -The invention of claim 97, wherein said containment means comprises at least one component of the group consisting of gelatin, } polyvinyl alcohol, carboxy polymethylene polymer and polymethyl vinyl Co

25. ether/maleic anhydride. : oo . 110. A base stock liquid crystal apparatus, comprising a support ’ + substrate, and supported with respect to said substrate at least one layer of liquid crystal material and containment means for inducing a generally non- Co oC parallel alignment of said liquid crystal material which in response to such - 30 alignment at least one of scatters and absorbs light and which in response to a prescribed input reduces the amount of such scattering or absorption. : : 1M. The invention of claim 110, further comprising a first : oo electrode between said substrate and said layer of liquid crystal material ~ and contdinment means. ee eee ar eee eee men

“i : : 112. The invention of eclaiin Ul, said electrode being over ) substantially tie entice erea of said substrate where said layer is supported

H3. "The invention of elaim nz, further comprising a further electrode applied ta at least part of said layer to cooperate with said first . mentioned electrode to apply an electric field to selected areas of said . Co liquid crystal material as such prescribed input. oo ’ 114. Liquid crystal material and a medium for containing dis- oo "crete quantities of such liquid crystal material, said material having positive Co 10° -. dielectric anisotropy, and wherein the difference between ‘the ordinary index — -- - . - Co of réfraction of said liquid crystal material and the index of refraction of said medium being no greater than 0.03. Lo So CL ~ 15. The invention of claim nd, wherein said difference in CL indices of refraction being no greater than 0.01. Co -

16. The invention of claim 114, wherein the difference between said indices of refraction is no greater than 0.001.

U7. The invention of claim 52, 82, 75, 76, 82, 84, 86, 97, 110, or : 114, further comprising pleochroic dye mixed with said liquid crystal a material.

20 . 8. The invention of claim 52, 62, 75, 76, 82, 84, 86, 97, LI0, or - 114, wherein the invention is operative independent of polarization of light incident thereon. : . : «0 19. Liquid erystal material and a medium for containing dis- oo : crete quantities of such liquid erystal material, said inaterial having positive oo 25 dieleetric anisotropy, said medium having a dielectric constant that is no . : less than the lower dielectric constant value of said material and such lower : : oo Co dielectric constant being from about 3.5 to about 8. - or So a. o ho 120. The invention of ‘claim 52, 62, 75, 80, 90, 97, U3, or:19, Co Co ‘wherein said prescribed inputis an AC electrical field. Po 30: Ba 121. A method of making encapsulated nematic liquid erystals, Co Co - "comprising mixing at least an encapsulating medium and a ‘nematic liquid Lo ) - crystal material, and further comprising causing such liquid crystal material oo = ol N i to verfo rm substantially independently of the optical polarization : direction of incident light, ‘including confining such liquid crystal B ’ I - material in a capsule formed by such encapsulating medium that fh causes distortion of the direction of the liquid crystal molecules ’l when no electric field is applied thereto. EE i JAMES LEE FERGASON ae ’ : - Inventor -

- . illuminated from the viewing side or direction or through a louvered light ) ‘guide from the back side will appear bright or white relative to background oC when in distorted alignment, e.g. in the absence of an electric field. Incident light impinging on the liquid crystal material is isotropically . i scattered into the support medium, and using the principle of total internal © reflection and possibly also optical interference a relatively large part of the isotropically scattered light is directed back to illuminate the distorted liquid crystal material tending to brighten the same so that light it scatters back to the viewing direction out of the support medium causes the liquid oo Co : crystal material to appear relatively light o bright as compared to the } background where there is no liquid crystal material or where the liquid ’ : crystal material is in parallel alignment in field-on condition, i.e. aligned with respect to an electric field, and, thus, substantially transmissive. - Original incident light where there is no liquid crystal material, that light : which is isotropically scattered toward ‘the back or non-viewing side of the display and within a certain cone or solid angle, and that light passing : through aligned (field-on) liquid crystal material will tend not to be totally ! 20 internally reflected; such light will pass through the support medium and Co may bé absorbed by a remote black or colored material. oo | ST In ahotiter embodiment operationally nematic type liquid crystal i oe BN having pleochroic dye mixed therewith is contained in a containment

I . medium and functions to absorb light in the absence of an electric field and : 1 25 _ to redtice absorption in the presence of such field. - CL According to another aspect the encapsulated liquid crystal material is used in liquid crystal devices, such as relatively large size visual display’ devices; and according to further aspects there are provided methods for encapsulating liquid crystal material and for making a liquid crystal : 30 : device using such encapsulated liquid crystal material. :