US3804618A

US3804618A - Liquid crystal imaging system

Info

Publication number: US3804618A
Application number: US00646532A
Authority: US
Inventors: E Forest; C Keller
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1967-06-16
Filing date: 1967-06-16
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: DE1772672A1; GB1235552A; FR1572784A

Abstract

An imaging system wherein a liquid crystal composition is placed in an imagewise field. Molecular orientation within the liquid crystal in areas of field provides a visible image.

Description

United States Patent [1 1 Forest et a1.

1 1 LIQUID CRYSTAL IMAGING SYSTEM [75] Inventors: Edward Forest; Carol K. Keller,

both of Rochester, NY.

[73] Assignee: Xerox Corporation, Rochester, N.Y.

[22] Filed: June 16, 1967 [21] Appl. No.: 646,532

[52] US. Cl 96/1 R, 252/408, 350/160 LC [51] Int. Cl. G03g 13/22, G02f 1/16 {58] Field of Search 96/1, 1.1, 1.5; 117/37 LX; 252/501 [56] References Cited UNITED STATES PATENTS 3,484,162 12/1969 Clark 355/3 3,627,408 12/1971 Fergason 350/160 X 3,410,999 11/1968 Fergason et a1. 250/435 3,167,607 l/1965 Marks et a1 88/61 3,322,485 5/1967 Williams 350/160 FOREIGN PATENTS OR APPLICATIONS 1,484,584 6/1966 France OTHER PUBLICATIONS Zocher, H. and Birstein, J. Beitrage zur Kenntnis Der Mesophasen, .l. uber Die Beeinflussung durch Das Elecktrische und Magnetische Feld Zeitschrift fur Physikalishe Chemie, Vol. 142, pt. A, (1929), pp. 186-194.

Vistin, L. K., and Kapustin, A. P., Domains in Liquid Crystals of Smectic Type," Soviet Physics-Crystalog- 1 Apr. 16, 1974 raphy, Vol. 13, No. 2, SeptemberOctober, 1968, pp. 284-286. I

158th American Chemical Society Annual Meeting, N.Y., N.Y., September 7-12, 1969, Abstract of Pa pers, Craftsman Press, Inc., Bladensburg, Md., C011, 72. Liquid Crystals IV, Electro-Optic Effects in P-Alkyloxybenzilidene-p-Amin0a1kylphenones and Related Compounds.

Les Etats Mesomorphes de la Matiere, Friedel, Ann. de Phys. Le Serie, t XVIII (1922) pp. 273-474. Jones et al., Investigation of LargeArea Display Screen Using Liquid Crystals, Westinghouse Research Lab., 12/65, pp. 4, 7, 9, 15, 99, 101, 119.

Harper, Voltage Effects in Caolesteric Liquid Crystals, Westinghouse Research Labs, 1966, pp. 325-332. Transient Behavior of Domains in Liquid Crystals George H. I-Ieilmeher Journal of Chemical Physics, Vol. 44, No. 2, l/15/66.

Domains in Liquid Crystals Richard Williams Journal of Chemical Physics, Vol. 39, No. 1, 7/15/63.

Primary Examiner-Charles E. Van Horn Attorney, Agent, or Firm-James .l. Ralabate; David C. Petre; Richard A. Tomlin [57] ABSTRACT An imaging system wherein a liquid crystal composition is placed in an imagewise field. Molecular orientation within the liquid crystal in areas of field provides a visible image.

17 Claims, 1 Drawing Figure PATENTEDAPR 1 19 3804.6 1 8 INVENTORS EDWARD FOREST BY CAROL K. KELLER Err ORNE Y LIQUID CRYSTAL IMAGING SYSTEM BACKGROUND OF THE INVENTION This invention relates in general to imaging and in particular to a xerographic system.

In the art of xerography according to Carlson, US. Pat. No. 2,297,691, it is usual to employ the simultaneous application of electric field and a pattern of activating radiation on a photoconductive insulating memher to form an electrostatic charge pattern otherwise known as an electrostatic latent image. This electrostatic latent image then is capable of being utilized such as, for example, developed by the deposition of electroscopic material thereon to form a visible image. Customarily, deposition of the electroscopic material is accomplished by cascading the electrostatic image with an electroscopic powder and a granular carrier as described in US. Pat. No. 2,638,416 to Walkup and Wise.

Development by means of depositing electroscopic powders on the surface of photoconductive members has a disadvantage in that the softer photoconductors, particularly those based on selenium, are abraded by the action of the powders on the photoeonductor surface. The abrasive action occurs at two stages of conventional xerography: first, during the initial cascading, and second, when the powder is removed by brushing the photoconductive member prior to the members reuse. In a display system, that is, where the developed image is viewed directly or where light information from the developed image is projected onto a screen or a fast developing film, the abrasion problem is more severe. In conventional xerography almost all of the electroscopic powder in the developed image is transferred to paper before the insulating surface is cleaned. In a display system, however, all of the electroscopic powder remains on the insulating surface until the cleaning step resulting in greatly increased abrasion.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a system for developing electrostatic images which overcome the above noted disadvantages.

It is another object of this invention to provide a system for developing an electrostatic image which does not require physical contact between the developer and the photoconductive member.

It is another object of this invention to provide a system for developing an electrostatic image which comparatively does not abrade the photoconductive insulating member.

It is another object of this invention to provide a system for developing an electrostatic image which does not require the deposition of the electroscopic powders.

It is another object of this invention to provide a system for developing an electrostatic image which does not require a cleaning step.

The foregoing objects and others are accomplished in accordance with this invention by a system comprising placing a liquid crystalline substance in the field generated between an electrostatic latent image and a conductor, or in a field generated by a source of potential connected to shaped electrodes whereby the liquid crystalline substance is strained by the imagewise field in image configuration providing a visible image.

Liquid crystalline substances are those liquids whose molecules, instead of being randomly distributed such as a gas, are regularly oriented similar to the distribution of molecules in a crystalline solid. Normally, substances which exhibit liquid crystalline characteristics do so only in a relatively narrow temperature range; below this temperature range they are solids, above the range they are liquids. Customarily, liquid crystalline substances are divided into three classes: smectic, nematie and cholesteric. Mechanically, these substances resemble liquids having viscosities ranging from runny glue to solid glass. Optically, they behave like crystals, for example, a typical cholesteric liquid crystal substance scatters light in symmetrical patterns and refleets different colors depending on the angle from which it is viewed. The light refraction properties of liquid crystals are also sensitive to the temperature of the liquid crystal. US. Pat. No. 3,114,836 to Fergason, Vogl and Garbuny, for example, utilizes the temperature sensitivity of liquid crystals in a thermal imaging device. For further information see The Mesomorphic State Liquid Crystals in Chemical Reviews, Vol. 57, No. 6, December 1957, p. 1049, by G. H. Brown and W. G. Shaw.

By strained is meant that the oriented molecules in the liquid crystal are reoriented. A visual difference between the field strained and the un-strained liquid crystals provides an image. This difference may be a difference in hue such as red, green, blue, etc. or in lightness, i.e., different shades of grays. The visible image may also result from a difference in reflectance, refraction, or transparency. Alternatively, light information from the visible image may be projected onto a screen or onto a fast developing film. This invention would be particularly useful in a rapid recording and display system such as that disclosed in US. Pat. 3,1 15,075 to Alexander. The insulating member is then removed from the system, solvent washed to remove any liquid crystal adhering to it, air-dried, and stored for later use. Preferably, the liquid crystal is separated from the insulating member by a thin walled, opaque, insulating film, thereby preventing contact between the liquid crystal and the insulating member. This eliminates the requirement of solvent washing the insulating member followed by air-drying.

It is also possible to effect reversal imaging, that is, to develop uncharged areas of the electrostatic latent image. Reversal imaging may be accomplished by charging the conductive member to the same potential as is present on the charged areas of the electrostatic latent image. In this embodiment the resultant field is present only between the conductive member and the uncharged areas of the electrostatic image resulting in straining of the liquid crystalline material above uncharged areas of the electrostatic image providing a visible image which is the reverse of the electrostatic latent image.

The electrostatic latent image may be forrned on either an insulating or photoconductive insulating surface. If a photoconductive insulating surface is to be used, care must be taken not to discharge the electrostatic latent image during display. That is, actinic radiation impinging on the surface of the photoconductive layer may discharge the electrostatic latent image before it has been developed and displayed. It may be necessary, therefore, to use light conditions during development and display which will not render the photoconductive layer conductive. For example, red light would be suitable for selenium photoconductive layers since selenium is not affected by red light. Suitable lighting conditions for various photoconductive layers which will not render the photoconductor conductive, may be determined by referring to graphs of the relative energy of response of photoconductors as a function of the wavelength of light used, avoiding wavelengths which result in photoconductor response. See, for example, Xerography and Related Processes by Dessauer and Clark, Focal Press Ltd, 1965. Preferably, however, the insulating film which is placed between the liquid crystal and the insulating member is opaque thereby eliminating the requirement of special lighting during development and display.

It should be understood that for the purposes of this disclosure, the term insulating when used in reference to the surface bearing the electrostatic image is intended to include photoconductive insulating materials.

Any suitable insulating member may be used. Typical photoconductive insulating materials include inorganic photoconductors such as zinc oxide; cadmium sulfide; zinc sulfide; lead sulfide; cadmium selenide; selenium; lead iodide and lead chromate; organic photoconductors such as triphenyl amine; 2,4-bis (4,4'-diethylaminophenyl)-l,3,4-oxadiazol; N-isopropyl carbazole; triphenyl pyrrol; 4,5-diphenylimid-azolidinone; 1,4-dicyanonaphthalene; Z-mercapto-benzthiazole, 2,4-diphenylquinazoline; S-benzideaminoacenaphthalene; and mixtures thereof. These materials may be used as the photoconductive layer by themselves as a one phase photoconductor or in a suitable binder. Typical binders are polystyrene resins, silicone resins, acrylic and methacrylic polymers and copolymers and mixtures thereof. Selenium is preferred because it has excellent sensitivity and the ability to receive and retain an electrostatic image with comparatively low dark decay.

Typical non-photoconductive insulating materials known in the art are: non-self-supporting or selfsupporting films of organic resins, plastics, binders including cellulose, cellulosic materials, and insulating resins such as lacquer coatings, and resin films and layers including urea and melamine-type resins, acrylic resins and mixtures thereof.

Any suitable liquid crystal or mixture of liquid crystals may be used. Typical liquid crystals are cholesteric liquid crystals, such as reaction products of cholesterol and inorganic acids such as cholesteryl chloride; cholesteryl nitrate; etc., organic esters of cholesterol such as cholesteryl crotonate, cholesteryl nonanoate; chlesteryl chloroformate; cholesteryl linolate; cholesteryl linolenate; cholesteryl oleate; cholesteryl erucate; cholesteryl butyrate; cholesteryl caprate; cholesteryl laurate; cholesteryl myristate; and cholesteryl clupanodonate; etc.; ethers of cholesterol such as cholesteryl decyl ether; cholesteryl lauryl ether; cholesteryl oleyl ether; etc.; carbamates and carbonates of cholesterol such as cholesteryl decyl carbonate; cholesteryl oleyl carbonate; cholesteryl heptyl carbamate etc., alkyl amides and aliphatic secondary amines derived from 33- amino-A -cholestene and mixtures thereof; nematic liquid crystals, such as anisaldazine; p-azoxyphenetole; p-butoxybenzoic acid; p-methoxycinnamic acid; pazoxyanisole and mixtures thereof. A mixture comprising cholesteryl butyrate and cholesteryl myristate is preferred because of its high color sensitivity to an electric field and because it exhibits liquid crystal characteristics at a comparatively low temperature.

Any suitable transparent conductive electrode may be used. Typical transparent conductive materials include:

conductively coated glass such as tin or indium oxide coated glass, and aluminum coated glass, etc., and similar coatings on transparent plastic substrates. NESA (a tin oxide coated glass available from the Pittsburgh Plate Glass Company) is preferred because it is highly transparent and is readily available.

The thin film which is placed between the liquid crystal and the insulating member may be of any insulating material. Typical insulating materials are: cellulose acetate, cellulose triacetate, cellulose acetate butyrate, polyurethane elastomers, polyethylene, polypropylene, polyesters, polystyrene, polycarbonates, and mixtures thereof. Pigmented Type 30 Tedlar, a polyvinylfluoride available from DuPont, is preferred because it is readily available in thin films and because it is opaque and has good insulation qualities.

BRIEF DESCRIPTION OF THE DRAWING The advantages of this improved method of developing an electrostatic image will become apparent upon consideration of the detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawing wherein:

The FIGURE shows a sectional side view of a simple exemplary system for carrying out the process of this invention wherein the liquid crystalline material has been placed between a photoconductive insulating member and a grounded transparent electrode.

Referring now to the FIGURE, a NESA glass plate 1 is prepared by placing on its surface an inert gasket 2. The shallow cup formed by plate 1 and inert gasket 2 is filled with a liquid crystalline material 3. The depth of this cup, i.e., the depth of the liquid crystalline material 3 used is a function of the composition of the liquid crystal, the temperature of the liquid crystal, the potential of the electrostatic latent image and the thickness and insulating properties of thin film 4. Insulating film 4 is placed in contact with liquid crystal 3 and inert gasket 2. Xerographic plate 7 comprising a layer 5 of photoconductive material on a conductive substrate 6 is sensitized by corona charging. Plate 7 is then exposed to a pattern of light and shadow which causes the charge to drain away from those areas on which light impinges. The remaining surface charge is an electrostatic latent image. Xerographic plate 7 is brought into contact with film 4. The molecules in liquid crystal 3 are strained in field areas providing a visible image viewable through NESA glass plate 1.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples further specifically illustrate the present invention. The examples below are intended to illustrate various preferred embodiments of the improved development method. The parts and percentages are by weight unless otherwise indicated.

In the following examples the charge density of the latent image is such that a field of about 2,000 to 4,000 volts is developed across the liquid crystalline layer.

EXAMPLE I A 2 inch square by /8 inch thick NESA glass plate is prepared by placing on its surface a Teflon (polytetrafluoroethylene available from E. I. du Pont de Nemours & Company, Inc.) gasket having overall dimensions about 2 inches square and a cross sectional dimension about 0.l millimeter. The NESA glass plate is then grounded. The NESA plate and Teflon gasket are then heated to a temperature of about 130C. and maintained at about that temperature throughout the experiment by an electrical radiant energy heater. The about 0.1 millimeter deep cup formed by the Teflon gasket and NESA glass electrode is filled with a mixture of about 55 percent cholesteryl benzoate and about 45 percent cholesteryl acetate which is prepared as follows: The mixture of liquid crystals are placed in an oven and heated to a temperature of about 137C. The mixture is then removed from the oven and allowed to cool to a temperature of about 130C. The mixture is then poured onto the NESA glass plate. An approximately 0.05 millimeter thick film of Pigmented Type Tedlar is placed in contact with the liquid crystalline material and the Teflon gasket.

A 2 inch square by 7 8 inch thick Teflon member is corona charged through a grounded metal stencil in image configuration resulting in an electrostatic latent image on the surface of the insulating member. The Teflon member containing the electrostatic latent image is then placed in contact with the insulating film. The image is then viewed through the NESA plate. This experiment may be carried out under ordinary incandescent light conditions because the Teflon member is not photoconductive, hence will not discharge an electrostatic image in the presence of ordinary light conditions.

EXAMPLE II A 2 inch square by 7 9 inch thick NESA glass plate is prepared by placing on its surface a Teflon (polytetrafluoroethyle ne available from E. I. du Pont de Nemours & Company, Inc.) gasket having overall dimensions about 2 inches square and a cross sectional dimension about 0.1 millimeter. The NESA glass plate is then grounded. The NESA plate and Teflon gasket are then maintained at a temperature of about 24C. throughout the experiment. The about 0.1 millimeter deep cup formed by the Teflon gasket and NESA glass electrode is filled with a mixture of about 30 percent cholesteryl butyrate and about 70 percent cholesteryl myristate which is prepared as follows: the mixture of liquid crystals are placed in an oven and heated to a temperature of about 45C. The mixture is then removed from the oven, poured onto the NESA glass plate, and allowed to cool to a temperature of about 24C. An approximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar (DuPont) is placed in contact with the liquid crystalline material and the Teflon gasket.

A 2 inch square by rt; inch thick selenium xerographic plate comprising an 80 micron selenium photoconductive layer on an aluminum substrate is sensitized by corona charging. The xerographic plate is then exposed to a pattern of light and shadow which causes the charge to drain away from those areas on which light impinges. The remaining surface charge is an electrostatic latent image. The xerographic member containing the electrostatic image is placed under red light conditions in contact with the film. The image is then viewed through the NESA glass plate under conventional incandescent light conditions.

EXAMPLE III A liquid crystalline substance made of a mixture of about one part cholesteryl crotonate and about one part cholesteryl oleate is dissolved in chloroform to make a free flowing solution. This solution is poured onto the NESA glass plate Teflon gasket arrangement used in Example I except that in this experiment all components are at about room temperature. The chloroform is allowed to evaporate in air leaving a viscous liquid crystal material on the surface of the NESA glass plate. The insulating film of Example I is placed in contact with the liquid crystal and the Teflon gasket. The NESA glass plate is then grounded. The xerographic member of Example II containing an electrostatic latent image is then under red light conditions placed in contact with the insulating film. No heating device need be utilized in this Example since the liquid crystal used in this Example exhibits liquid crystal characteristics at or near room temperature. The image is then viewed through the NESA glass plate under conventional incandescent light conditions.

EXAMPLE IV A 2 inch square by A; inch thick polycarbonate member made from the phosgenation of bisphenol A (4,4- dihydroxydiphenyl-2-2-propane) is corona charged through a grounded metal stencil in image configuration resulting in an electrostatic latent image on the surface of the insulating polycarbonate member. A Teflon gasket having overall dimensions about 2 inches square by about 0.1 millimeter in cross section is placed over an about 2 inch square by Vs inch thick NESA glass plate. A mixture of approximately 30 percent cholesteryl butyrate and about percent cholesteryl myristate is dissolved in chloroform to provide a free-flowing solution. The solution is then poured into the about 0.1 millimeter deep cup formed by the NESA plate and Teflon gasket. The chloroform is allowed to evaporate in air. The insulating film of Example II is then placed in contact with the liquid crystal and Teflon gasket. The NESA plate is then grounded. The polycarbonate member containing the electrostatic latent image is then placed in contact with the insulating film. The image is then viewed through the NESA plate. No heating device need be utilized in this Example since the liquid crystal used in this Example exhibits liquid crystal characteristics at room temperature. This experiment may be carried out under ordinary incandescent light conditions because the polycarbonate member is not photoconductive, hence, will not discharge an electrostatic image in the presence of ordinary light conditions.

EXAMPLE V A 2 inch square by :4; inch thick NESA glass plate is prepared by placing on its surface a Teflon (polytetrafluoroethylene available from E. I. du Pont de Nemours & Company, Inc.) gasket having overall dimensions about 2 inches square and a cross sectional dimension about 0.1 millimeter. The NESA glass plate is then grounded. The NESA plate and Teflon gasket are then heated to a temperature of about C. and maintained at about that temperature throughout the experiment by an electrical radiant energy heater. The about 0.1 millimeter deep cup formed by the Teflon gasket and NESA glass electrode is filled with p-azoxyanisole which is prepared as follows: the crystals are placed in an oven and heated to a temperature of 140C. The liquid is then removed from the oven and poured onto the NESA glass plate. The liquid is then allowed to cool to the temperature of the NESA glass plate. An approximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar is placed in contact with the liquid crystalline material and the Teflon gasket.

A 2 inch square by /8 inch thick polycarbonate member is corona charged through a grounded metal stencil in image configuration resulting in an electrostatic latent image on the surface of the insulating member. This polycarbonate member containing the electrostatic latent image is then placed in contact with the insulating film. The image is then viewed through the NESA plate. This experiment may be carried out under ordinary incandescent light conditions because the polycarbonate member is not photoconductive, hence, will not discharge an electrostatic image in the presence of ordinary light conditions.

EXAMPLE VI A 2 inch square by Vs inch thick NESA glass plate is coated with p-azoxyanisole as in Example V. An approximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar is placed in contact with the liquid crystalline material and the Teflon gasket. A shaped electrode is made by vacuum depositing aluminum in image configuration on the surface of a 2 inch square by /8 inch thick piece of molded polycarbonate made from the phosgenation of bisphenol A(4,4- dihydroxydiphenyl-2-2'-propane). The aluminum image is continuous so that current will flow to all parts of the image. The polycarbonate member is then placed on the Tedlar so that the aluminum image contacts the Tedlar film. The conductive surface of the NESA plate is connected to the negative terminal of a potential source of 3,000 volts DC and ground. The aluminum image is connected to the positive terminal of the potential source. The image is then viewed through the NESA plate.

EXAMPLE VII A 2 inch square by /4; inch thick NESA glass plate is coated with p-azoxyanisole as in Example V. An approximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar is placed in contact with the liquid crystalline material and the Teflon gasket. A second 2 inch square by Vs inch thick NESA glass plate is prepared by placing Kodak Photoresist insulator (available from the Eastman Kodak Company of Rochester, New York and described generally as the cinnamate esters of polyvinyl alcohol and of cellulose) on it in image configuration. The Photoresist coated surface of the NESA plate is placed in contact with the Tedlar. The liquid crystal coated NESA plate is connected to the negative terminal of a 2,000 volt DC potential source and ground. The other NESA plate is connected to the positive terminal of the potential source. The image is viewed through the liquid crystal coated NESA plate.

Although specific components and proportions have been stated in the above description of preferred embodiments of the invention, other typical materials as listed above if suitable may be used with similar results. In addition, other materials may be added to the mixture to synergize, enhance or otherwise modify the properties of the liquid crystals, electrodes, light sources, and the photoconductive layers. For example, the photoconductive layer may be modified so that ordinary incandescent light will not discharge the electrostatic latent image formed on the photoconductive layer.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An imaging process comprising:

providing a layer of an imaging composition comprising a material having a cholesteric liquid crystalline phase, and

providing an imagewise electrical field across said layer while said material is in the cholesterie liquid crystalline phase to cause an imagewise change in the appearance of image portions of said composition layer, while the background portions of said composition layer retain an appearance substantially distinguishable from the appearance of the image portions of said layer.

2. The process of claim 1 wherein said imaging composition comprises a mixture of cholesteryl benzoate and cholesteryl acetate.

3. The process of claim 1 wherein said imaging composition comprises a mixture of cholesteryl oleate and cholesteryl crotonate.

4. The process of claim 1 wherein said imaging composition comprises a mixture of cholesteryl myristate and cholesteryl butyrate.

5. The process of claim 1 wherein said composition comprises a mixture of cholesteric liquid crystalline material and nematic liquid crystalline material.

6. The imaging process of claim 1 comprising the steps of:

a. providing a pair of conductive electrode members in spaced relationship at least one of said members being sufficiently transparent to transmit a change in the appearance of an imaging composition placed between said members;

b. placing between said members an imaging composition comprising a material having a cholesteric liquid crystalline phase; and

c. applying an electrical field between said conductive electrode members while said material is in the cholesteric liquid crystalline phase to cause a change in the appearance of said composition in an imagewise configuration.

7. The process of claim 6 wherein at least one of said conductive members has an insulating material in image configuration on at least its surface.

8. The process of claim 6 wherein there is additionally a gasket of substantially electrically insulating material containing the imaging composition between the conductive members.

9. The process of claim 6 wherein at least one of said conductive electrode members is shaped in an image configuration.

10. The process of claim 9 wherein there is additionally a substantially electrically insulating layer between the conductive mmember in image configuration and the layer of imaging composition.

11. The process of claim 1 comprising:

providing a surface of a photoconductive member having an electrostatic latent image thereon; and

15. The process of claim 11 wherein the photoconductive member comprises phthalocyanine dispersed in a binder.

16. The process of claim 11 wherein the photoconductive member comprises zinc oxide dispersed in a binder.

17. The process of claim 11 wherein said composition comprises a mixture of cholesteric liquid crystalline material and nematic liquid crystalline material.

Claims

2. The process of claim 1 wherein said imaging composition comprises a mixture of cholesteryl benzoate and cholesteryl acetate.
3. The process of claim 1 wherein said imaging composition comprises a mixture of cholesteryl oleate and cholesteryl crotonate.
4. The process of claim 1 wherein said imaging compositIon comprises a mixture of cholesteryl myristate and cholesteryl butyrate.
5. The process of claim 1 wherein said composition comprises a mixture of cholesteric liquid crystalline material and nematic liquid crystalline material.
6. The imaging process of claim 1 comprising the steps of: a. providing a pair of conductive electrode members in spaced relationship at least one of said members being sufficiently transparent to transmit a change in the appearance of an imaging composition placed between said members; b. placing between said members an imaging composition comprising a material having a cholesteric liquid crystalline phase; and c. applying an electrical field between said conductive electrode members while said material is in the cholesteric liquid crystalline phase to cause a change in the appearance of said composition in an imagewise configuration.
7. The process of claim 6 wherein at least one of said conductive members has an insulating material in image configuration on at least its surface.
8. The process of claim 6 wherein there is additionally a gasket of substantially electrically insulating material containing the imaging composition between the conductive members.
9. The process of claim 6 wherein at least one of said conductive electrode members is shaped in an image configuration.
10. The process of claim 9 wherein there is additionally a substantially electrically insulating layer between the conductive mmember in image configuration and the layer of imaging composition.
11. The process of claim 1 comprising: providing a surface of a photoconductive member having an electrostatic latent image thereon; and providing a layer of an imaging composition comprising a material having a cholesteric liquid crystalline phase, on or adjacent said surface.
12. The process of claim 11 wherein a substantially insulating layer is present between the photoconductive member and the imaging composition.
13. The process of claim 11 wherein the photoconductive member comprises vitreous selenium.
14. The process of claim 11 wherein the photoconductive member comprises phthalocyanine.
15. The process of claim 11 wherein the photoconductive member comprises phthalocyanine dispersed in a binder.
16. The process of claim 11 wherein the photoconductive member comprises zinc oxide dispersed in a binder.
17. The process of claim 11 wherein said composition comprises a mixture of cholesteric liquid crystalline material and nematic liquid crystalline material.