US3601483A - Imaging apparatus - Google Patents

Abstract

Imaging apparatus for making photoelectrophoretic images by placing a photoelectrophoretic suspension between two or more electrodes while exposing the suspension to activating electromagnetic radiation and an electric field. An electric field may be generated electrostatically either before or during imaging in any manner such as by a corona discharge device or by frictionally rubbing the surface of one of the electrodes.

Description

United States Patent Inventors Leonard M. Carreira l 56] References Ci'ed Penfield; UNITED STATES PATENTS Vsevolod Tulagin, Rochester, both of, 3,442,781 5/1969 Weinberger 96/1 PP 825,256 3,474,019 10/1969 Krieger et al. 96/] Filed May 16, 1969 Division ofSer. No. 561587, June 29, 1966, 'f Matthews Assistant Exammer- Robert P. Grelner 3477934 Altorne 8 Jam .1 R l b B J K 1 Patented M1814 1971 y es a a ate, arry esse man and David C. Petre Assignee Xerox Corporation Rochester, N.Y.

P' APPAFATPS ABSTRACT: Imaging apparatus for making photoelec- 8 Chums 7 Drawing Flgs trophoretic images by placing a photoelectrophoretic suspen- U.S. Cl 355/3, sion between two or more electrodes while exposing the 355/4 suspension to activating electromagnetic radiation and an Int. Cl G03g 15/02, electric field. An electric field may be generated electrostati- G03g l5/00 cally either before or during imaging in any manner such as by Field of Search 355/3, 4, a corona discharge device or by frictionally rubbing the surl7; 96/1 face of one of the electrodes.

1 20 I is, 1/ x l8 4 J Fg I PATENTEu Auswsn SHEET 1 BF 4 3501.483

INVENTOR. LEONARD M. CARREIRA VSEVOLOD TULAGIN Zl/Z'V IMAGING APPARATUS This is a division of application, Ser. No. 561,587, filed June 29, 1966 now U.S. Pat. No. 3,477,934.

This invention relates in general to imaging systems and, more specifically, to an improved electrophoretic imaging system.

There has been recently developed an electrophoretic imaging system capable of producing color images which utilizes electrically photosensitive particles. This process is described in detail and claim in US. Pat. Nos. 3,384,448; 3,384,566 and 3,383,993 all issued on May 21, 1968. In such an imaging system, variously colored light absorbing particles are suspended in a nonconductive liquid carrier. The suspension is placed between electrodes, one of which is at least partially transparent, and subjected to a potential difference while the suspension is exposed to an image through partially transparent electrode. As these steps are completed, selective particle migration takes place in image configuration providing a visible image at one or both of the electrodes. Where the positive image is formed on a conductive transparent electrode, ordinarily the image must be transferred to a receiving sheet so that the relatively expensive conductive transparent electrode may be reused. An essential component of the system is the suspended particles which must be electrically photosensitive and which apparently undergo a net change in charge polarity upon exposure to activating electromagnetic radiation, through interaction with one of the electrodes. In a monochromatic system, particles of a single color are used, producing a single colored image similar to conventional black and white photograph. In a polychromatic system, the images are produced in natural color because mixtures of particles of two or more different colors which are each sensitive to light of a specific wavelength or narrow range of wavelengths are used. Particles used in this system should have both intense pure colors and be highly photosensitive.

After the exposure and particle migration steps are completed, the electrodes are separated and the carrier liquid is allowed to evaporate. This leaves images on one or both of the electrodes made up of selectively deposited particles. Since these electrodes may consist of relatively expensive materials or may be integral parts of the imaging apparatus, it is generally required that the images be transferred to a receiving sheet, fixed thereon for later viewing use. This permits the original electrodes to be reused immediately to produce further images.

in order to produce an electric field across the suspension during the imaging process, the transparent electrode generally has a conductive surface, such astin oxide and the other electrode has a relatively insulating surface behind which is a second conductive electrode. This process is capable of producing excellent color images. However, it would be desirable to simplify the process by eliminating the need to transfer images produced from an electrode to a receiving sheet. But, it is not generally possible to fix a formed image directly on the conductive transparent electrode since these materials are expensive and must be reused to provide reasonable economy in the imaging process. Also, these material, e.g., tin oxide coated glass,are often not suitable for later handling and use even if it is possible to fix an image to the surface thereof. Also, in a reusable system, there are problems in balancing the requirements of conductivity and transparency in an electrode. Often, materials which impart conductivity to the electrode impair transparency. Thus, there is a continuing need for improved electrode materials for use in electrophoretic imaging processes of the sort described above.

In some instances it may be preferable to transfer the reformed image from the electrode. surface to a receiving sheet. For example, where the electrode upon which the image is formed is transparent, it may be desirable to transfer the formed image to an opaque viewing sheet such as paper. The preferred method of transferring the images is to do so electrophoretically. In this transfer process, immediately after the imaging process, the electrodes are separated and a receiving sheet is brought into contact with the imaged electrode. The imaging surface is illuminated with white light, causing an electrophoretic migration of the image particles to the receiving sheet. The receiving sheet is then stripped away, carrying with it the image. Where the transfer step is carried out immediately after the imaging step, effective transfer of the image to the receiving sheet is obtained. Where there is a delay of more than a few seconds, however, even with the application of additional carrier liquid to the image, the quality of the transferred image is drastically reduced. Density and color balance are degraded and irregularities or blotches are observed in the image areas.

Any time variation between image formation and image transfer introduces variations into the quality of the final image. Simple nonautomated copying devices where the various steps are carried out more or less by hand, the timing of the imaging and transfer steps will inherently vary. Thus, there is a continuing need for an improved method of transferring electrophoretic images to receiving sheet at varying times after image formation while maintaining uniform image quality.

It is, therefore, an object of this invention to provide an electrophoretic imaging system overcoming the above-noted disadvantages.

It is another object of this invention to provide an electrophoretic imaging system capable of producing final images of uniform high quality.

It is another object of this invention to provide an improved method of transferring electrophoretic images to receiving sheets.

It is another object of this invention to improve the uniformity of final images produced in an electrophoretic imaging system.

It is still another object of this invention to provide an electrophoretic imaging system which does not require conductive transparent electrodes.

It is still another object of this invention to provide an extremely simple, noncomplex electrophoretic imaging system.

The foregoing objects and others are accomplished in accordance with this invention by providing in an electrophoretic imaging process wherein the layer of suspension is subjected to an applied electric field between two electrodes, at least one of which is transparent, while an image is projected onto the suspension through said transparent electrodes to form an image on one of said electrodes, the step of electrostatically charging at least one of said elements, namely an electrode, the suspension, or the formed image.

In one embodiment of this invention, neither of the two electrodes is conductive and the electrostatic charging step is performed on one of the electrodes immediately before the suspension is placed between the electrodes. The second electrode is held at a potential opposite in sign to that of the electrostatic charge placed on the first electrode while an image is projected on the suspension through the transparent electrode. The electric field between the charged first electrode and the second electrode in combination with the photosensitive particles in the suspension enables an electrophoretic migration to take place in image configuration. The image formed on one electrode consists of particles loosely bonded to the surface. This image may be fixed by any conventional method. This imaged electrode may be removed from the system for later use or viewing. Since this electrode may be any suitable insulating material, it may be easily and quickly replaced with a fresh sheet and the imaging steps repeated.

in another embodiment of this invention, an electrophoretic image is formed on the injecting electrode, the formed image surface is electrostatically charged, and the image is transferred electrophoretically to a receiving sheet. Where the formed image is electrostatically charged before the transfer step, the quality of the transferred image is consistently high despite varying or extended periods between the image formation and the image transfer steps.

In a further embodiment of this invention, the particle suspension is coated onto one electrode and the suspension is electrostatically charged just before the second electrode is brought into contact with the suspension and during the imaging step. The second electrode is held at a potential opposite in sign to that of the electrostatic charge imposed on the suspension. This charging step has been found to increase image density and uniformity.

In a further embodiment of this invention, the two electrodes are brought into contact with the particle suspension before electrophoretic imaging. The surface of the blocking electrode not in contact with the suspension is then electrostatically charged. This eliminates the requirement for a power supply to impose a constant potential on the back of blocking electrode during imaging. This simplifies the equipment necessary for electrophoretic imaging without lowering image quality.

The uniform electrostatic charging of one or more elements of the electrophoretic imaging system as described in the different embodiments above, may be performed by any conventional means. Charging by corona discharge is preferred since a uniform charge of the desired potential may be simply and easily laid down on a surface without physical contact with said surface. Charging by corona discharge is described in detail by Carlson in U.S. Pat. No. 2,588,699 and Walkup in U.S. Pat. No. 2,777,557. Any other suitable charging methods may be used where desired. For example, where a surface such as the injecting or blocking electrode will not be harmed by physical contact therewith, the surface may be charged by rubbing a triboelectrically suitable material there against, as described by Carlson in U.S. Pat. No. 2,297,691.

Images may be formed by the above-described processes from suspensions of any suitable photosensitive particles. The photosensitive particles may, for example, comprise the materials disclosed in U.S. Pat. No. 3,383,993 issued on May 21, 1968. Where a monochromatic image is to be formed, the particles will be of a single color. Where polychromatic images are to be formed, particles of two or more colors may be used. For example, for subtractive color formation, the particles will ordinarily be magenta, cyan and yellow. Any suitable insulating liquid may be used as the carrier for the photosensitive particles and the imaging suspension. Typical insulating carrier liquids include: decane, dodecane, molten paraffin, molten beeswax or other molten thermoplastic materials, Sohio Odorless solvent 3440 (a Kerosene extraction available from Standard Oil Company of Ohio), Isopar G (a long-chain saturated aliphatic hydrocarbon available from Humble Oil Company of New Jersey) and mixtures thereof. The blocking electrode, the surface of the transfer rollers, and the injecting electrode as shown in FIG. 3 may comprise any suitable insulating material. Typical materials having suitable insulating properties include: Baryta paper (paper coated with barium sulfate in a gelatin binder), cellulose acetate or polyethylene coated papers, polyethylene terephthalate, polytetrafluoroethylene, polystyrene, polyamides, etc. In an embodiment such as that shown in FIG. 5, the blocking electrode may be transparent and the imaging suspension may be exposed through the blocking electrode rather than through the injecting electrode.

The advantages of utilizing uniform electrostatic charging in an electrophoretic imaging system will become further apparent upon consideration of the following detailed disclosure of the invention; especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows a simple schematic representation of an electrophoretic imaging system which does not include the electrostatic charging movement of this invention;

FIG. 2 shows an exemplary electrophoretic imaging system in which the suspension is electrostatically charged before imaging;

FIG. 3 shows an exemplary electrophoretic imaging system in which an insulating injecting electrode is uniformly electrostatically charged before imaging;

FIG. 4 shows an alternative method'of uniformly electrostatically charging the injecting electrode as in FIG. 3;

. blocking electrode in the configuration shown in FIG. 5; and

FIG. 7 shows an exemplary method for transferring an electrophoretic image wherein the formed image is electrostatically charged before transfer.

The same numbers are used to designate similar elements throughout the various figures.

Referring now to FIG. 1, there is shown an exemplary em bodiment of a system for forming a photoelectrophoretic image on one of the imaging electrodes and then transferring the formed image to a receiving sheet. In FIG. 1 there is shown a transparent electrode generally designated 1, which, in this exemplary instance, is made up of a layer of optically transparent glass 2 overcoated with a thin, optically transparent layer 3 of tin oxide, commercially available under the name NESA glass. This electrode shall hereafter be referred to as the injecting electrode. Coated on the surface of injecting electrode 1 is a thin layer 4 of finely divided photosensitive particles, dispersed in an insulating liquid carrier. The term photosensitive for the purposes of this application refers to the properties of a particle which once attracted to the injecting electrode, will migrate away from it under the influence of an applied electric field when it is exposed to actinic electromagnetic radiation. For a detailed theoretical explanation of the apparent mechanism of operation of the imaging process, see the above-mentioned U.S. Pat. Nos. 3,384,488; 3,384,566 and 3,383,993; the disclosure of which are incorporated herein by reference. Adjacent to the liquid suspension 4 is a second electrode 5, hereinafter called the blocking electrode, which is connected to one side of. a potential source 6 through a switch 7. The opposite side of potential source 6 is connected to ground, as is injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes 1 and 5.

During the imaging operation, blocking electrode 5 is moved across the surface of injecting electrode 1. An image projector made up of a light source 8, a transparency 9, and a lens 10 is provided to expose the liquid suspension 4 to a light image of the original transparency 9 to be reproduced. Electrode 5 is made in the form of a roller having a conductive central core 11 connected to the potential source 6. The core is covered with a layer of a blocking electrode material 12 which may be Baryta paper or other suitable material. An image is formed from the particle suspension by exposing the particle suspension to the image to be produced while a potential is applied across the blocking and injecting electrodes by closing switch 7. Roller 5 is caused to roll across the top surface of injecting electrode 1 with switch 7 closed during the period of image exposure. The light exposure causes particles originally attracted to electrode 1 to migrate through the carrier liquid and adhere to the surface of the blocking electrode 5, leaving behind a pigment image on the injecting electrode surface which is a duplicate of the original transparency 9. Preferably, the particulate image formed on the surface of injecting electrode 1 is transferred to a receiving sheet and fixed thereon for further use and viewing. As described in copending application, Ser. No. 542,050 filed Apr. 2, 1966, a transfer roller may be utilized to receive the image from the injecting electrode surface. Such a transfer roller is shown at 13. Transfer roller 13 has the same general structure as blocking electrode 5. A conductive core 14 is connected to ground through a potential source 15 and switch 16. The surface of the transfer roller comprises any suitable material 17, such as Baryta paper, for'receiving the image. The potential imposed on the transfer roller is opposite in sign to that used on the blocking electrode during the imaging step. While transfer roller 13 is passing across the surface of injecting electrode 1,

the image areas are light exposed, either to white light,

suitably filtered white light or to the original image projected through transparency 9. Where desired, the surface of the particulate image on the injecting electrode may be moistened with additional carrier liquid to improve the transfer step. Where transfer roller 13 is passed across the surface of injecting electrode 1 immediately after the image is formed, effective transfer of a good quality image to the surface of roller 13 is accomplished. However, if an appreciable delay of more than a few seconds occurs between the imaging and the transfer steps, the quality of the transferred image decreases.

Images produced by systems of the sort schematically shown in FIG. 1 are generally of excellent quality. However, the system as shown in FIG. 1 requires a conductive transparent injecting electrode which is generally rather fragile and expensive and, thus, necessitates the transfer of the image to a receiving sheet for further use in viewing. Also, image transfer must be accomplished immediately after image formation in order to obtain a good image on the receiving sheet. This imaging system may be substantially improved by the use of electrostatic charging of various elements of the system during the imaging and transfer operation. FIGS. 2-7 show various embodiments of this improved electrophoretic imaging system. Y

Referring now to FIG. 2, there is shown a modification of the system of FIG. 1 in which an image of improved density and color balance is formed on the injecting electrode surface. In this instance, however, a corona discharge unit 18 is arranged to pass across the surface of the injecting electrode immediately prior to the imaging step. The corona head 18 is connected to ground through potential source 19 and switch 20. Since injecting electrode 1 is also grounded, as corona unit 18 passes across the surface of the injecting electrode with switch closed, a uniform electrostatic charge is deposited on the surface of suspension 4. This electrostatic charge is of the same sign as the potential imposed on the blocking electrode when it passes across suspension 4 during the imaging step. It appears that this preliminary electrostatic charge enhances the ability of light-struck particles to migrate, thus resulting in an image of improved density and color balance.

FIG. 3 shows a further embodiment of the use of uniform electrostatic charging in photoelectrophoretic imaging systems. This embodiment differs from that shown in FIG. 1 in that the formed image is fixed directly onto a removable injecting electrode, thus eliminating the requirement for a transfer roller 13. In this embodiment, the injecting electrode 1 includes a sheet of insulating material 21 which is uniformly electrostatically charged as by corona unit 18 immediately before the imaging operation. Insulating sheet 21 may comprise any partially transparent insulating material, such as Mylar (polyethylene terephthalate, available from DuPont). The electrostatic charge placed on the surface of sheet 21 is opposite in sign to that imposed on the conductive center of blocking electrode 5. In the system shown in FIG. 3, the particulate suspension 4 is shown as coated on the surface of blocking electrode 5. While this is often convenient, the suspension may be coated on the surface of sheet 21 immediately after its surface has been charged by corona means 18. During the imaging step, as blocking electrode 5 passes across the surface of sheet 21, a positive image corresponding to transparency 9 is formed on the surface of sheet 21. This image may be fixed by any convenient means, such as by a binder included in the particle carrier liquid, by laminating a second sheet over the formed image, by spraying with a suitable lacquer, or by a thermoadhesive layer on the surface of sheet 21 such as is described in copending application, Ser. No. 459,860, filed June 28, l965. The embodiment shown in FIG. 3 has the distinct advantage over that shown in FIG. 1 in that the image need not be transferred to a receiving sheet. Any transfer step necessarily involves some loss of image quality. Also, this system lends itself to rapid production of multiple copies in that one need only replace imaged sheet 21 with another sheet and recoat suspension 4 onto electrode 5 to be ready for subsequent imaging.

FIG. 4 shows the embodiment of FIG. 3 with an alternative method of charging the insulating injecting electrode surface. Here, the insulating sheet 21 is charged by means of a rotating fur brush 22 which is passed across the surface of sheet 21 immediately before imaging. Such triboelectric charging is described in detail by Carlson in U.S. Patent No. 2,297,691.

The sheet 21 and brush 22 materials are selected so as to triboelectrically charge the surface of sheet 21 to a potential having a sign opposite to that imposed on the core of blocking electrode 5. This alternative has the advantage in simplifying the system by eliminating the need for corona head 18, power supply 19, and switch 20.

FIG. 5 shows a further embodiment of electrophoretic imaging utilizing electrostatic charging in which the blocking electrode material 12 as shown in FIG. 1 is placed in direct contact with the particles suspension 4 and power supply 6 connected to conductive backing is replaced with uniform electrostatic charging of the upper surface of the blocking electrode. In this embodiment, the particle suspension 4 is coated on the surface of injecting electrode 1 as in the embodiment of FIG. 1. A projection system comprising lamp 8, transparency 9 and lens 10 is positioned so as to project an image of suspension 4. In this embodiment a sheet of blocking electrode material 23 is placed over the suspension 4 and the upper surface of sheet 23 is uniformly electrostatically charged by means of corona head 18 supplied with a potential by power supply 19 through switch 20. An electric field is imposed on the suspension since the injecting electrode is grounded.

Sheet 23 may comprise any suitable insulating material, such as Baryta paper, Mylar (polyethylene terephthalate) etc. In this system the back of sheet 23 is charged, and the suspension is exposed to an image. Sheet 23 is then removed, leaving a positive image conforming to the original on the surface of the injecting electrode. When it is desired to transfer this image to a receiving sheet, a second insulating sheet 23 is placed over the formed image and corona means 18 is again passed across the back of sheet 23 to uniformly electrostatically charge itQI-Iowever, for the transfer operation the sign of the electrostatic charge placed on 23 is opposite to that used during the imaging step. When this second sheet 23 is stripped from injecting electrode 1, the formed image will be found to have transferred to sheet 23 and may be fixed thereon by any suitable method. This embodiment is a simplification of that shown in FIG. 1 in that the multilayered roller electrode 5 is replaced by a single sheet 23 and a corona discharge unit.

FIG. 6 shows an embodiment generally similar to that of FIG. 5 in which the back of sheet 23 is charged triboelectrically by means of a rotating fur brush 22 instead of the corona discharge unit. Where a second transfer step is desired as described above in the description of the embodiment of FIG. 5, it may be desirable to select the fur brushes used during the imaging step and during the transfer step so as to triboelectrically charge the surface of sheet 23 to potentials of opposite sign during imaging and transfer steps. This system is a further simplification of that shown in FIG. 5 in that corona charging unit 18, power supply 19, and switch 20 are replaced by a simple rotating fur brush.

FIG. 7 shows an embodiment of the system shown in FIG. 1 in which transfer of a formed electrophoretic image is improved. The system as used in this embodiment is generally the same as that shown in FIG. 1, except that a corona discharge unit comprising a corona head 18, potential source 19 and switch 20 is positioned between the blocking electrode roller 5 and the transfer roller 13. After blocking electrode roller 5 has passed across the surface of the injecting electrode during the image forming step, corona head 18 is passed across the formed image to electrostatically charge the surface of the formed image to a potential opposite to that imposed on the transfer roller. Where transfer takes place within a few seconds after imaging the electrostatic charging of the formed image results in somewhat improved density in the transferred image, i.e., more complete transfer of particles from the surface of the injecting electrode 1 to transfer roller 13. Where there is delay of more than a few seconds between imaging and transfer, the image quality falls off drastically where the formed image is not electrostatically charged before transfer. However, where the formed image is charged before transfer, quality of the transferred image remains high despite substantial delays between imaging and transfer. Where there is appreciable delay between image formation and transfer, it may be desirable to moisten the surface of the formed image with a small amount of the carrier liquid.

Good quality images may be produced with voltages imposed on the blocking electrode and on the transfer roller in the range from about 300 to 5,000 volts in the various embodiments of this invention. Images of high quality may be produced with potentials of about 2,000-4,000 volts without danger of undesirable air ionization. Therefore, a potential of about 3,000 volts is preferred. A corona discharge voltage may be in the range from about 4,000 to 8,000 volts. A

. preferred corona voltage is about 6,000 volts since this results in most effective image formation and transfer. Where the various elements are charged triboelectrically, the charging member may comprise any suitable material which is spaced from the material to be charged on the triboelectric series such as to produce a charge on the element of the desired sign.

The following examples further specifically define the present invention with respect to the use of uniform electrostatic charging in electrophoretic imaging systems. Parts and percentages are by weight unless otherwise indicated. Examples below are intended to illustrate various preferred embodiments of the invention and of the different embodiments described above.

All the following examples are carried out in apparatus of the general type illustrated in the various figures. Where blocking electrodes in roller form or transfer rollers are used, the rollers are approximately 2%inches in diameter and are moved across the plate surface of about 1.5 centimeters per second. In each case, the injecting electrode surface employed is roughly 3 inches square and is exposed with a light intensity of about 8,000-foot candles as measured on the uncoated injecting electrode surface. Where a monochromatic image is to be produced, the suspension is exposed to an image by means of a conventional black and white transparency. Where a polychromatic image is to be produced, the suspension is exposed to an image by means of a Color transparency. All pigments which have a relatively large particle size as received commercially or as made are ground in a ball mill for about 48 hours to reduce their size to provide a more stable dispersion and to improve the resolution of final images.

EXAMPLE I This example is performed with an imaging system of the sort shown in FIG. 1. About eight parts of 2, 4, 6-tris (3 pyrenylazo) phloroglucinol, prepared as described in U.S. Pat. No. 3,384,632 issued on May 21, 1968 is mixed with about 100 parts Sohio Odorless Solvent 3440, a kerosene fraction available from The Standard Oil Company of Ohio. This dispersion is coated onto the NESA glass substrate. A negative potential of about 2,500 volts is imposed on the roller electrode during exposure. After exposure, an image corresponding to the original is seen on the NESA surface. Immediately after image formation a transfer roller having a Baryta paper surface and subjected to a positive potential of about 2,000 volts is passed across the NESA glass while the original image is projected onto the NESA surface. The image is transferred to this roller surface from the NESA electrode. The black-onwhite image produced is of good quality. A small proportion of the black particles remain on the NESA surface must be cleaned therefrom before subsequent imaging operations.

EXAMPLE [I The imaging and transfer steps of example I are repeated except that immediately prior to imaging a corona discharge unit is passed across the particle suspension, depositing a uniform positive charge of about 6,000 volts on the suspension. The imaging and transfer steps are then performed as in example I.

The resulting image is of excellent quality and somewhat greater density than that produced in example I.

EXAMPLE m The imaging and transfer steps of example I are repeated, except that the particle suspension comprises about three parts Algol yellow GC, 1,2,5 ,6-di(c,c'-diphenyl)thiazoleanthraquinone, C.I. No. 67,300, available from General Dye Stuffs; about three parts of a magenta pigment, Watchung Red B, 1(4'-methyl-5'-chloroazo benzene-2'-sulfonic acid)-2- hydroxy-S-napthoic acid, C. I. No. 15,865, available from E. I. duPont de Nemours; and about three parts of a Cyan pigment, Monolight Fast Blue GS, a mixture of alpha and beta metalfree phthalocyanine, available from the Arnold Hoffman Co. The image produced is of good quality with good color balance.

EXAMPLE IV An image is formed as in example III except that a corona discharge unit is passed across the suspension immediately before the image forming step to deposit a uniform electrostatic charge having a negative potential of about 6,000 volts on the suspension. The image is then formed and transferred to a receiving sheet as in example III. The image is of excellent quality with density and color balance improved over the image formed in example lII.

EXAMPLE V This example uses an electrophoretic imaging system such as is shown in FIG. 3. A IO-micron sheet of Mylar, a polyethylene terephthalate film available from E. I. duPont de Nemours is placed in contact with the conductive surface of the injecting electrode. A suspension is formed comprising about seven parts of 2,4,6-tris(3'-pyrenylazo)-phloroglucino1, in about parts Isopar G, a long chain saturated aliphatic hydrocarbon available from The Humble Oil Company of New Jersey. This suspension is coated onto the blocking electrode surface to a thickness of about 5 microns. A corona charging unit is then passed across the Mylar sheet uniformly electrostatically charging the sheet to a negative potential of about 4,000 volts. Immediately thereafter the coated blocking electrode is passed across the Mylar sheet while subjected to a positive potential of about 2,500 volts. After the blocking electrode has passed across the Mylar sheet an image is seen on the Mylar sheet corresponding to the original. This image is of good quality, approximately equal to that produced in example I.

EXAMPLE VI The imaging steps of example V are repeated except that the Mylar sheet is charged by a fur brush such as is shown in FIG. IV instead of by corona discharge. The surface electrostatic potential imposed on the Mylar sheet is negative and about 3,000 volts. The image is then formed as in example V. An image of good quality corresponding to the original results on the Mylar sheet.

EXAMPLE VII The imaging steps of example V are repeated except that the pigment suspension comprises about three parts of a yellow pigment, 8,13-dioxodinaphtho-( 1,2-2',3 )-furan-6-carbon- 4"-methoxy anilide, prepared as described in copending application, Ser. No. 421,377, filed Dec. 28, 1964; about three parts of a magenta pigment, Napthyl Red B, 1-(2-methoxy- Snitrophenylazo)-2 hydroxy-3"-nitro-3-naphthanilide, C.I. No. 12,355, available from Collway Colors; and about three parts of a Cyan pigment, Cyan Blue GTNF, the beta form of copper phthalocyanine C. I. No. 74,160, available from Coll way Colors dispersed in about 100 parts Sohio Odorless Solvent 3440. This suspension is coated onto the blocking electrode surface, the Mylar sheet is corona charged and the quality corresponding to the original is formed on the surface Ser. No. 445,240, filed Apr. 2, 1965; and about three parts of a-Cyan pigment, Diane Blue, 3,3'-methoxy-4,4'-diphenyl-bis (l"-azo-2"-hydroxy-3"-naphthanilide, C]. No. 21,180, available from Harmon Colors, dispersed in about 100 parts Sohio Odorless Solvent 3440. This mixture is coated onto the Baryta surface of the blocking electrode, the surface of the injecting'electrode is corona charged to a negative potential of about 4,000 volts, and the blocking electrode is passed across the Lucite sheet under a positive potential of about 2,500 volts as in example VII. A full color image conforming to the original is left on the surface of the Lucite sheet. A 5-micron sheet of Mylar film is laminated over the image surface to fix the image. The imaged sheet is then removed and replaced with a fresh Lucite film. The imaging mix is recoated on the blocking electrode surface and another image is produced as described above.

EXAMPLE VIII This example is performed with an electrophoretic imaging system of the sort shown in FIG. 5. A pigment suspension comprising of about seven parts of Monolite Fast Blue GS, dispersed in about 100 parts Sohio Odorless Solvent 3440 is coated onto the injecting electrode surface to a thickness of about 5 microns. A l-micron Mylar sheet is then placed over the suspension in intimate contact therewith. The free surface of the Mylar sheet is then chargedv by corona to a negative potential of about 4,000 voltsfA black and white image is projected onto the suspension through the injecting, electrode. The Mylar sheet is then stripped from the suspension leaving an image on the injecting electrode corresponding to the original of satisfactory quality.

EXAMPLE ix This example uses an electrophoretic imaging system such as is shown in FIG. 5. A pigment suspension is prepared comprising about three parts of a yellow pigment, Indofast Yellow Toner, flavanthrone, C.I. No. 70,600, available from Harmon Colors; about three parts of a magenta pigment, Quindo Magenta RV-6803, a substituted quinacridone available from Harmon Colors; and about three parts of a Cyan pigment, Monolite Fast Blue GS, a mixture of the alpha and beta forms of metal-free phthalocyanine, available from theArnold Hoffman Company, dispersed in about 1001 parts Sohio Odorless Solvent 3440. This suspension is coated onto the injecting electrode surface to a thickness of about microns. A sheet of Baryta paper is then placed over the suspension. with the coated paper surface in contact with the suspension. The back of the Baryta paper is then uniformly electrostatically charged to a negative potential of about 2,000- volts by a corona discharge means. The suspension is then exposed to a full color image and the Baryta paper is stripped away. A full color image corresponding to the original remains on the injecting electrode surface. A second sheet of Baryta paper is then placed over the formed image and the back of the sheet is charged to a positive potential of about 2,000 volts while the image is again projected onto the injecting electrode surface. When the Baryta paper is stripped away it is found thatthe image has transferred to the Baryta paper surface.

EXAMPLE X The imaging steps of example VIII are repeated, except that the back of the Mylar sheet is uniformly electrostatically charged by means of a rotating fur bmsh instead of by corona discharge. The triboelectric charging is to a negative potential of about 3,000 volts. The image is then formed and the electrodes separated as in example VIII. An image of good quality corresponding to the original results.

EXAMPLE XI This example uses an electrophoretic imaging system such as is shown in FIG. 7. About eight parts of 2,4,6-tris (3'- pyrenylazo) phloroglucinol is mixed with about parts Sohio Odorless Solvent 3440 and the suspension is coated onto the NESA glass substrate to a thickness of about 5 microns, A negative potential of about 2,500 volts is imposed on the blocking electrode during exposure. After exposure, an image corresponding to the original is seen on the NESA surface. Immediately after image formation a second roller having a Baryta paper surface and subjected to a positive potential of about 2,000 volts is passed across the NESA surface while the original image is projected onto the NESA surface. The image is transferred to this roller surface from the NESA electrode. The black-on-white image produced is of good quality and corresponds to the original. A small amount of the black particles remain on the NESA surface and must be cleaned therefrom before subsequent imaging operations.

EXAMPLE XII The NESA electrode is coated, charged, and imaged as in example XI. However, here immediately before the transfer roller passes across the NESA surface, a corona discharge means is passed across said surface under a negative potential of about 6,000 volts. The image produced on the transfer roller is of higher density than in example X1 and fewer pigment particles are left on the NESA glass electrode.

EXAMPLE XIII A dispersion is coated onto the NESA electrode and an image is produced on said electrode as in'example XI. About 5 minutes after the image is formed, the image is moistened with Sohio Odorless Solvent 3440 and the transfer roller is passed across the NESA electrode. Only a small proportion of the image particles transfer to the transfer electrode. The image transferred is of low density and very poor quality.

EXAMPLE XIV The NESA electrode is coated, charged and imaged as in example XIII. I-Iere, however, a corona discharge means is passed across the NESA electrode just before the transfer roller. The corona discharge means deposits a uniform negative potential of about 5,000 volts. The image transferred is of excellent quality, comparable to that produced in example XI.

EXAMPLE XV About three parts of a yellow pigment, Algol Yellow GC, about three parts of a magenta pigment, Watchung Red B, and about three parts of a Cyan pigment, Monolite Fast Blue GS are dispersed in about 100 parts Sohio Odorless Solvent 3440. This dispersion is coated onto the NESA electrode and an image is formed as in example XI. About 5 minutes after the image is formed, the formed image is moistened with Sohio Odorless Solvent 3440 and a transfer roller is passed across the image under a positive potential of about 2,500 volts. The image transferred to the roller is of poor quality, of low density, and very poor color balance.

EXAMPLE XVI A dispersion is formed, coated onto the NESA ELEC- TRODE and an image is formed as in example XV. About 5 minutes after the image is formed, the image is moistened with Sohio Odorless Solvent 3440 and a corona discharge means is passed across the formed image depositing a uniform negative potential of about 4,000 volts on the formed image. Im-

mediately thereafter the transfer roller is passed across the formed image under a positive potential of about 2,500 volts. The image transferred to the transfer roller is of excellent quality, with much higher density and better color balance than that produced in example XV.

Although specific components and proportions have been described in the above examples relating to various electrophoretic imaging systems utilizing uniform electrostatic charging of one element of the system, any of the materials as listed above may be used with similar results. In addition, other materials may be added to the particle suspension or to the various electrodes to synergize, enhance, or otherwise modify their properties.

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

What we claim is:

1 An imaging apparatus for forming an image from a photoelectrophoretic suspension including a first electrode,

a second electrode adapted to contact said first electrode through the photoelectrophoretic suspension appliable between said electrodes,

illumination means to expose the suspension between said electrodes to activating electromagnetic radiation,

electric field generating means for providing an electric field across the suspension between the electrodes during the exposure of the suspension to the activating radiation, and

electrostatic charge generating means in close operative proximity to at least one of said first and second electrodes for depositing a uniform charge thereon.

2. The apparatus of claim 1 wherein said electrostatic charge generating means is a corona generating device.

3. The apparatus of claim 2 wherein said corona generating device is a corotron.

4. .The apparatus of claim 1 wherein said electrostatic charge generating means includes a material for depositing a charge on one of the electrodes with which it makes friction contact to improve imaging.

5. The apparatus of claim 1 wherein said first and second electrodes have insulating layers thereon.

6. The apparatus of claim 5 wherein said electrostatic charging generating means is positioned to operate on one of said electrodes prior to the application of the suspension to one of said electrodes.

7. The apparatus of claim 5 wherein said electrostatic charge generating means deposits a charge on one of said electrodes opposite to the potential of the field supplied by the electric field generating means.

8. The apparatus of claim 1 wherein the electrodes are flat members having the suspension coated therebetween and said electric field generating means includes an electrostatic charge generating means.

Claims (7)

1. 2. The apparatus of claim 1 wherein said electrostatic charge generating means is a corona generating device.
2. 3. The apparatus of claim 2 wherein said corona generating device is a corotron.
3. 4. The apparatus of claim 1 wherein said electrostatic charge generating means includes a material for depositing a charge on one of the electrodes with which it makes friction contact to improve imaging.
4. 5. The apparatus of claim 1 wherein said first and second electrodes have insulating layers thereon.
5. 6. The apparatus of claim 5 wherein said electrostatic charging generating means is positioned to operate on one of said electrodes prior to the application of the suspension to one of said electrodes.
6. 7. The apparatus of claim 5 wherein said electrostatic charge generating means deposits a charge on one of said electrodes opposite to the potential of the field supplied by the electric field generating means.
7. 8. The apparatus of claim 1 wherein the electrodes are flat members having the suspension coated therebetween and said electric field generating means includes an electrostatic charge generating means.

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