Imaging system

BACKGROUND OF THE INVENTION

This invention relates to imaging systems, and more specifically, to an imaging system wherein the imaging member comprises a liquid crystalline material.

Liquid crystalline substances exhibit physical characteristics some of which are typically associated with liquids and others which are typically unique to solid crystals. The name “liquid crystals” has become generic to substances exhibiting these dual properties. Liquid crystals are known to appear in three different forms: the smectic, nematic, and cholesteric forms. These structural forms are sometimes referred to as mesophases, thereby indicating they are states of matter intermediate between the liquid and crystalline states. The three mesophase forms of liquid crystals mentioned above are characterized by different structures wherein the molecules of the compound are arranged in a molecular structure which is unique to each of three mesomorphic structures. Each of these structures is well known in the liquid crystal art.

Liquid crystals have been found to be sensitive or responsive to temperature, pressure, foreign chemical compounds, and to electric and magnetic fields, as disclosed in copending applications Ser. No. 646,532, filed June 16, 1967, Ser. No. 821,565, filed May 5, 1969, Fergason et al. Pat. 3,144,838, French Pat. 1,484,584, and Fergason Pat. 3,409,404.

Various types of imaging systems are already known and to date electrostatographic imaging systems and image reproduction systems have been among the most successful imaging systems. The xerographic imaging system, as first described in Carlson Pat. 2,297,691, is an outstanding example of electrostatographic imaging systems. Generally, the xerographic process is performed upon a xerographic plate comprising a layer of photoconductive insulating material upon a conductive backing. The surface of the plate is typically uniformly charged and then exposed to a light and shadow image pattern. The photoconductive plate discharges in the exposed areas proportionally to the intensity of the radiation reaching the exposed areas, thereby creating an electrostatic latent image on the surface of the photoconductive layer corresponding to the light and shadow image pattern projected upon the plate. The electrostatic latent image is then typically developed by contact with an electroscopic marking material called “toner.” The elec5 trostatic latent image which has been developed by contact with toner is then referred to as the “toner image” or “developed image.” This developed image may be fixed on the xerographic plate itself, or it may be transferred to paper or other material, and the transferred 10 image may be fixed on said other material.

Various other techniques for developing electrostatic latent images in xerography and other electrostatographic imaging systems are known, including, for example, liquid development techniques as described in 15 U.S. Pats. 3,068,115, 3,076,722, and 3,096,198. However, the aforementioned imaging and development systems are typically directed to either “transfer xerography” or to systems wherein the image is fixed directly on the plate; rather than systems producing visible ²⁰ images on imaging members that are immediately reusable.

Xerographic plates and photoconductors are known to have been used with overcoatings, for example such as those described in Duebner Pat. 2,860,048, Dessauer et ²⁵ al. Pat. 2,901,348, and Owens Pat. 2,886,434. Similarly, liquid crystalline materials such as those described above, have been used in systems wherein the liquid crystalline material was sandwiched between thin films or overcoated with various protective materials as dis³⁰ closed in Waterman Pat. 3,439,525, Fergason et al. Pat.

3,401,262, and Bishop, “A Procedure for Applying a Protected Layer of Liquid Crystals,” Sandia Laboratories, Albuquerque, N. Mex., U.S. Department of Commerce, National Bureau of Standards, PB 183838, November 1968.

There is a continuing need for immediately reusable electrostatographic development systems, and in new and growing areas of technology such as liquid crystalline 4Q imaging systems, new methods, apparatus, compositions, and articles of manufacture are often discovered for the application of the new technology in a new mode. The present invention relates to a new and advantageous system wherein liquid crystalline materials are used in such _4g electrostatographic imaging processes.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to satisfy the above-noted needs, and to provide a novel imaging ₅₀ system.

It is another object of this invention to provide a novel liquid crystal imaging system.

It is another object of this invention to provide a system for the development of electrostatic latent images 55 on electrostatic latent image support surface or other electrostatographic surfaces.

It is yet another object of this invention to provide a new and immediately reusable electrostatographic imaging system.

It is yet another object of this invention to provide liquid crystalline imaging systems wherein a cholesteric liquid crystalline material in a field-induced texture state or imaged to such a state is returned to its original texture state, or thereby erased.

It is another object of this invention to provide an erasable liquid crystalline imaging system.

It is another object of this system to provide an erasable and immediately reusable electrostatographic imaging system.

The foregoing objects and others are accomplished in accordance with this invention by a system wherein a layer of liquid crystalline imaging material on a photo3,671,231 conductive layer is provided with a suitable overcoating, imaged by providing an electrical latent image on the above described imaging member, and erased, and thereby made immediately reusable, by uniformly electrically charging overcoated surface of the imaging member.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed disclosure of the preferred embodiments of the invention taken in conjuction with the accompanying drawings thereof, wherein:

FIG. 1 is a partially schematic cross-sectional view of the imaging member of the present invention.

FIG. 2 illustrates the advantageous process steps of the present invention is partially schematic cross-sectional views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 a preferred embodiment of the advantageous overcoated liquid crystalline imaging member 10 is illustrated in a partially schematic cross-sectional view wherein a xerographic plate comprising photoconductive layer 12 upon substrate 11, which is typically a conductive substrate, supports on the free surface of the photoconductive layer a gasket member 13 wherein liquid crystalline imaging material 14 is contained, and the liquid crystalline imaging material 14 is overcoated with a transparent protective layer 15.

Xerographic plates such as the one described above are well-known in the electrostatographic imaging arts and in the xerographic art in particular. For example, such xerographic plates are described in Bixby Pat. 2,970,906, and in Middleton adn Reynolds Pat. 3,121,006. Photoconductive materials suitable for use in such xerographic plates include selenium, selenium sulfur mixtures, selenium-tellurium alloys, zinc oxide, phthalocyanine, and many others and mixtures thereof. Any suitable photoconductor may be used in the photoconductive layers in the present invention. The xerographic plate having a photoconductive layer comprising vitreous selenium in a preferred photoconductive insulating layer in reusable xerography, and the photoconductive layer comprising vitreous selenium is also a particularly preferred photoconductor in the advantageous system of the present invention.

The gasket or spacer 13 in FIG. 1, which contains the liquid crystalline imaking material 14 on the surface of the photoconductive insulating layer 12 is typically chemically inert, substantially electrically insulating, and may be transparent in various embodiments. Materials suitable for use in such gaskets include cellulose-acetate, cellulose-triacetate, cellulose-acetate-butyrate, polyurethane-elastomers, polyethylene, poly-propylene, polyesters, polystyrene, polycarbonates, polyvinylfluoride, polytetrafloroethylene, polyethylene terephthalate and mixtures thereof. Such spacers, which also approximately define the thickness of the layer of liquid crystalline imaging material, are preferably of a thickness in the range between about 0.5 and about 100 microns.

In other embodiments of the advantageous imaging system and members of the present invention, the advantageous protective overlayer 15 may be adhered to liquid crystalline material layer 14 by simply coating photoconductive insulating layer 12 with a thin film of the liquid crystalline imaging material and placing the advantageous protective layer 15 directly onto the exposed surface of the liquid crystalline imaging material. In such an embodiment, no gasket or spacing member 13 is necessary, and the surface tension forces between the surface of the protective overlayer 15 and the photoconductive insulating layer 12 act to contain the liquid crystalline imaging member between the protective overlayer and the photoconductor. In still another embodiment, the gasket or spacer 13 may be replaced with or itself comprise a layer of adhesive which seals the edges of the surfaces of the photoconductor and the protective overlayer 15.

Any suitable cholesteric liquid crystalline material 14, mixture or composition comprising cholesteric liquid crystals, or composition having cholesteric liquid crystalline characteristics may be used in the imaging system of the present invention. Cholesteric liquid crystals suitable as imaging materials in present invention include derivatives from reactions of cholesterol and inorganic acids; for example, cholesteryl chloride, cholesteryl bromide, cholesteryl iodide, cholesteryl fluoride, cholesteryl nitrate; esters derived from reactions of cholesterol and carboxylic acids; for example, cholesteryl crotonate; cholesteryl nonanoate, cholesteryl hexanoate; cholesteryl formate; cholesteryl docosonoate; cholesteryl chloroformate; cholesteryl propionate; cholesteryl acetate; cholesteryl valerate; cholesteryl vacconate; cholesteryl linolate; cholesteryl linolenate; cholesteryl oleate; cholesteryl erucate; cholesteryl butyrate; cholesteryl caproate; cholesteryl laurate; cholesteryl myristate; cholesteryl clupanodonate; ethers of cholesterol such as cholesteryl decyl ether; cholesteryl lauryl ether; cholesteryl oleyl ether; cholesteryl dodecyl ether; carbamates and carbonates of cholesterol such as cholesteryl decyl carbonate; cholesteryl oleyl carbonate; cholesteryl methyl carbonate; cholesteryl ethyl carbonate; cholesteryl butyl carbonate; cholesteryl docosonyl carbontate; cholesteryl cetyl carbonate; cholesteryl-p-nonylphenyl carbonate; cholesteryl-2-(2-ethoxy ethoxy) ethyl carbonate; cholesteryl-2-(2-butoxyethoxy) ethyl carbonate; cholesteryl-2-(2 - methoxyethoxy)ethyl carbonate; cholesteryl geranyl carbonate; cholesteryl heptyl carbamate; and alkyl amides and aliphatic secondary amines derived from 3/J-amino-A-5-cholestene and mixtures thereof; peptides such as poly-7-benzyl-X-glutamate; derivatives of beta sitosterol such as sitosteryl chloride; and amyl ester of cyano benzylidene amino cinnamate. The alkyl groups in said compounds are typically saturated or unsaturated fatty acids, or alcohols, having less than about 25 carbon atoms, and unsaturated chains of less than about 5 double-bonded olefinic groups. Aryl groups in the above compounds typically comprise simply substituted benzene ring compounds. Any of the above compounds and mixtures thereof may be suitable for cholesteric liquid crystaline materials in the advantageous system of the present invention.

Smectic liquid crystalline materials are also suitable for use in combination with cholesteric liquid crystalline materials in the present invention and such smectic materials include n-propyl-4'-ethoxy biphenyl-4-carboxylate; 5-chloro-6-n-heptyloxy-2-naphthoic acid at temperatures in the range of about 166-176° C.; lower temperature mesophases of cholesteryl octanoate, cholesteryl nonanoate, and other open-chain aliphatic esters of cholesterol with chain length of 7 or greater; cholesteryl oleate; sitosteryl oleate; cholesteryl decanoate; cholesteryl laurate; cholesteryl myristate; cholesteryl palmitate; cholesteryl stearate; 4'-nalkoxy-3'-nitrobiphenyl-4-carboxylic acids; ethyl-p-azoxybenzoate; potassium oleate; ammonium oleate; p-n-octyloxybenzoic acid; the low temperature mesophase of 2-p-nalkoxybenzylideneaminofluorenones with chain length of 7 or greater; the low temperature mesophase of p-(nheptyl) oxybenzoic acid; anhydrous sodium stearate; thallium (I) stearate; mixtures thereof and others.

Nematic liquid crystalline materials suitable for use in combination with cholesteric liquid crystalline materials in the advantageous system of the present invention include: p-azoxyanisole, p-ozoxyanisole, p-azoxyphenetole, p-butoxybenzoic acid, p-methoxy-cinnamic acid, butylp-anisylidene-p'-aminocinnamate, anisylidene para-aminophenylacetate, p - ethoxy-benzalamino-a-methyl-cinnamic acid 1,4-bis (p-ethoxy benzylidene) cyclohexanone, 4,4'dihexyloxybenzene, 4,4' - diheptyloxybenzene, anisal-pamino-azobenzene, anisaldazine, a-benzeneazo- (anisala - naphthylamine), anisylidene-p-n-butylaniline, n,n'3,671,231 nonoxybenzeltoluidine, mixtures of the above and many others.

The above lists of suitable liquid crystalline imaging materials is intended to encompass mixtures of any of the above. The list is representative of suitable materials, and is in no way intended to be exhaustive or limiting. Although any liquid crystalline composition having cholesteric liquid crystalline characteristics is suitable for use in the present invention, compositions comprising cholesteryl oleyl carbonate have been found particulary useful in the inventive system. Various concentrations of cholesteryl oleyl carbonate may be used to control the viscosity Of the imaging composition and to stabilize the composition against crystallization.

The liquid crystalline imaging materials may be prepared by dissolving the liquid crystals or mixtures thereof in any suitable solvent, for example, organic solvents such as chloroform, trichloroethylene, tetrachloroethylene, petroleum ether, methyl-ethyl ketone, and others. The solution containing the liquid crystal material is then typically poured, sprayed or otherwise applied to the supporting substrate. After evaporation of the solvent, a thin layer of liquid crystals remains on the substrate. Alternatively, the individual liquid crystals of the liquid crystalline mixture can be combined and applied directly by heating the mixed components above their isotropic transition temperatures. The imaging composition films comprising cholesteric liquid crystals in the present invention are preferably of a thickness in the range between about 0.5 and about 100 microns.

Preferably, imaging is conducted at or near room temperature; therefore, it is preferred to use liquid crystalline materials which have a liquid crystal state at room temperature. More broadly, the liquid crystalline material preferably has a liquid crystal state at the desired operational temperature.

The advantageous protective overlayer 15 is designed to protect the liquid crystalline imaging material 15, which is typically tacky, soft, viscous, or liquid, from foreign matter such as dust, insects, etc., and this overlayer is typically transparent to allow viewing of the imaged liquid crystalline materials. Because the electrical mechanism or a model for the advantageous system of the present invention is not completely understood, the electrical characteristics of the advantageous overlayer 15 are not completely understood. However, it is clear that the protective overlayer 15 possesses the physical and electrical properties which allow the entire composite imaging member 10 to be electrically latently imaged and cyclically reused in the advantageous system of the present invention, and the overlayer 15 in no way impairs the imaging of the photoconductive layer in the preferred chargeexpose mode. Electrically insulating materials will typically perform this function, and some partially conductive materials may perform this function satisfactorily. Materials suitable for use as the advantageous overlayer include Tedlar, a polyvinylfluoride, available from Du Pont; polyethylene film; polyvinylchloride film; Mylar, a polyester resin film available from Du Pont; mixtures thereof, and others. The overlayer 15 is typically a thin transparent film, and preferably of thickness not greater than about 2 mils. Optimum results are achieved using overlayer thicknesses in the range between about and about 1 mil.

FIG. 2 illustrates the steps of the advantageous system of the present invention in partially schematic crosssectional views. In FIG. 2A, the imaging member 10 is illustrated being electrically charged, here by an electrostatic corona charging device 16. The electrical charging of the imaging member is typically enhanced by grounding the conductive substrate 11, or where the substrate is electrically insulating, by placing the substrate 11 on a grounded conductive plate, or by charging both sides of the member to opposite polarities. In this way the imaging member is uniformly electrically charged as illustrated at

18. Although the imaging member is shown being positively charged in FIG. 2A, it will be understood that either positive or negative charges may be placed upon the imaging member and the imaging system of the present 5 invention performs equally satisfactorily when charged to either polarity. The imaging members of the present invention are typically electrically charged to surface potentials in the range between about 100 and about 1000 volts.

In FIG. 2B, the substantially uniformly electrically charged imaging member 10 is shown being exposed to an imagewise pattern of activating electromagnetic radiation thereby forming an electrically latent image on the imaging member 10. As shown in FIG. 2B, one method of 15 imagewise exposing the imaging member is to expose said member through a lens system 21 which focuses light from source 20 reflected from original image 19 onto the imaging member 10. The electrical latent image on imaging member 10 typically comprises areas having differing ₂Q surface potentials, and said areas of differing potential typically correspond to or are complementary to the relative exposure of the various areas of the imaging member to activating electromagnetic radiation, where the optimum charge-expose imaging mode is used. Exposure 25 levels used in commercial xerography are typically suitable for use in the present invention.

Although the electrical latent image referred to above is formed as disclosed above, a visible image is typically formed in the liquid crystalline imaging material layer 14 30 in response to the electrical latent image formed on the imaging member. In this way, a visible image is produced in response to the electrical latent image on the image member. Surprisingly, the presence of advantageous protective layer 15 does not impair the visible imaging of ₃5 the liquid crystalline imaging material.

It is pointed out that the electrical latent image, which in some embodiments is an electrostatic latent image, in response to which a visible image is formed on the advantageous imaging member of the present invention, may 40 be produced by any suitable means in addition to the preferred mode of charging and exposing a xerographic plate. Other modes include charging or sensitizing in an image configuration through the use of a mask or stencil, or first forming such a charge pattern on a separate photoconductive insulating layer according to conventional ⁴⁵ xerographic techniques, and then transferring this charge pattern to the surface of the imaging member by bringing the two into very close proximity and utilizing breakdown techniques as described, for example, in Carlson ₅₀ Pat. 2,982,647, and Walkup Pats. 2,825,814 and 2,937,943. In addition, charge patterns conforming to selected shaped electrodes or combinations of electrodes may be formed on a support surface by the “TESI” discharge technique, as more fully described in Schwertz Pats. 55 3,023,731 and 2,919,967, or by the charging techniques described in Walkup Pats. 3,001,848 and 3,001,849, as well as by electron beam recording techniques, as described for example in Glenn Pat. 3,113,179. The electron beam recording technique may be particularly suited for ₆₀ use in a system wherein an image may be visibly produced from stored electronic data, for example a computer print-out might be brought into visible form for the desired length of time on the advantageous imaging member of the present invention, and then erased by the 55 advantageous system of the present invention, so that the imaging member may be used to display other desired portions of data from the same or any other desired electronic input source.

In FIG. 2C, a top view of the imaged liquid crystalline 70 imaging member of the present invention illustrates that the visibly imaged member may be erased by the one step process illustrated in FIG. 2D, comprising substantially uniformly electrically charging the overcoated surface of the imaging member. In FIG. 2D the erasure step 75 is shown being performed by an electrostatic corona

3,671.

charging device 23, like that described above in conjunction with FIG. 2A, and it will be appreciated that the substantially uniformly electrically charging step illustrated in FIG. 2D prepares the imaging member for immediate re-imaging, at the same time that it erases or 5 destroys the visible image previously displayed on the imaging member as illustrated in FIG. 2C. The uniform electrical re-charging or erasure step illustrated in FIG. 2D may be performed in the presence of activating electromagnetic radiation, and the image in the imaging com- 10 position will thereby be erased.

The liquid crystalline imaging member in the present invention is believed to be imaged by the action of imagewise electrical fields across the liquid crystalline film in an imagewise pattern corresponding to the electrical latent 15 image. The electrical fields across the liquid crystalline film cause an electrical field-induced texture transition to occur, wherein a liquid crystalline material comprising cholesteric liquid crystalline material initially in its predominately Grandjean or “disturbed” texture is largely 20 transformed into its predominately focal-conic or “undisturbed” texture in the charged areas. Where the imaging member is uniformly charged and imagewise exposed, the exposed areas typically have low surface potentials, or low magnitude electrical fields across the liquid crystalline 25 layer, and in such exposed areas the texture transformed liquid crystalline composition typically re-transforms from the predominately focal-conic texture state back into the predominately Grandjean texture state, thereby producing visible contrast between image and background areas in 30 the liquid crystalline imaging composition.

The texture change liquid crystalline imaging system described herein is fully described in copending application Ser. No. 867,593, filed Oct. 20, 1969, all of which is hereby incorporated by reference in the present specifi- 35 cation. The visible imaging produced by the texture change transition in the advantageous system of the present invention is typically exhibited by a change in the translucency of the liquid crystalline imaging material, by a change of color of the imaged areas in the imaging mate- 40 rial, or by a change in the optical characteristics, such as birefringence, optical activity, and circular dichroism, of the imaging composition. The imaging member in the inventive system is suited for viewing, typically with reflected light; however, where substrate 11 and photoconductive insulating layer 12 can be provided in a substan- ^atially transparent form, the imaging member of the present invention may be suitable for use in modes where the images are viewed using transmitted light.

The following examples further specifically define the ₅θ present invention with respect to the liquid crystalline imaging system having a liquid crystalline imaging member which is quickly erasable and immediately reusable. The parts and percentages are by weight less otherwise indicated. The examples below are intended to illustrate 55 various preferred embodiments of the novel erasable overcoated liquid crystalline imaging system.

Example I

A liquid crystalline imaging member is provided by ⁶⁰using a xerographic plate from a Model “D” Processor, available from the Xerox Corporation, Rochester, New York, which comprises a photoconductive coating of vitreous selenium on a conductive sheet. The exposed surface of the photoconductor is framed in a spacer gasket ^Jcomprising an about Vz inch wide strip of Mylar film, a polyester resin available from DuPont. The area of the surface of the photoconductor framed by the spacing gasket is coated with an imaging composition comprising γθ cholesteric liquid crystalline material, here a mixture of about 20% cholesteryl oleyl carbonate, about 28% cholesteryl chloride, and about 52% cholesteryl nonanoate. The liquid crystalline composition is then overcoated with an about Vz mil thick film of transparent 75

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Tedlar, a polyvinylfluoride resin film available from DuPont.

This imaging member is then substantially uniformly electrostatically charged to a surface potential of about 700 volts and imagewise exposed to an image pattern of activating electromagnetic radiation, here light, in the Model “D” Processor. Upon charging and exposing an image corresponding to the original image from which the imagewise pattern of activating electromagnetic radiation was derived appears on the above described imaging member. The liquid crystalline composition exhibits green image areas on a substantially colorless background, which exhibits the color of the xerographic plate itself in the background areas.

The imaged member is then again uniformly electrostatically charged to a surface potential of about 700 volts in the Model “D” Processor, which destroys the image produced by the previous imaging steps, and the imaging member is then ready to be reimaged by the above recited process.

Example II

The imaging process of Example I is performed using an imaging member as described in Example I with an imaging composition comprising cholesteric liquid crystalline material comprising a mixture of about 16% cholesteryl oleyl carbonate, about 30% cholesteryl chloride, and about 54% cholesteryl nonanoate. The imaging composition is overcoated with an about Vx mil thick film of transparent Mylar, a polyester resin film available from DuPont. When imaged by the process of Example I, this composition exhibits red image areas. This imaged member is also uniformly electrostatically charged whereby the image is destroyed or erased, thereby providing the imaging member in condition for re-use.

Example III

The imaging and erasing process of Example I is performed using the imaging member and apparatus of Example I with an imaging composition comprising cholesteric liquid crystalline material here comprising a mixture of about 25% cholesteryl oleyl carbonate, about 26.3% cholesteryl chloride, and about 48.7% cholesteryl nonanoate. This imaging member is imaged by charging and exposing, and then erased by recharging, as described in Example I.

Example IV

The imaging and erasing process of Example I is performed using the imaging member and apparatus of Example I with an imaging composition comprising cholesteric liquid crystalline material here comprising a mixture of about 10% cholesteryl oleyl carbonate, about 52% cholesteryl nonanoate, about 28% cholesteryl chloride, and about 10% anisylidene-p-n-butylaniline. This imaging member is imaged by charging and exposing, and then erased by recharging, as described in Example I.

Although specific components and proportions have been stated in the above description of the preferred embodiments of the erasable, overcoated liquid crystalline imaging system of the present invention, other suitable materials and variations in the various steps in the system as listed herein, may be used with satisfactory results and various degrees of quality. In addition, other materials and steps may be added to those used herein and variations may be made in the process to synergize enhance, or otherwise modify the properties of the invention. For example, various other mixtures of liquid crystals which undergo the inventive texture transition may be discovered and used in the system of the present invention, and such mixtures may require somewhat different imaging conditions for preferred results. Likewise, various other means for creating the electrical image to address the inventive imaging member may be used with satisfactory results in the inventive system.

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It will be understood that various other changes in the details, materials, steps, and arrangements of elements which have been herein described and illustrated in order to obtain the nature of the invention, will occur to and may be made by those skilled in the art, upon a reading of this disclosure, and such changes are intended to be included within the principle and scope of this invention.