US3711196A

US3711196A - Image transfer

Info

Publication number: US3711196A
Application number: US00879962A
Authority: US
Inventors: V Tulagin; L Carreira; I Stein
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1966-04-12
Filing date: 1969-12-04
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16
Also published as: CH482230A; DE1572384A1; BE696853A; SE332754B; ES339049A1; NL6705032A; DE1572384B2; GB1185931A

Abstract

Apparatus for electrostatically transferring images formed by photoelectrophoresis. The color balance of the images which are made up of electrically photosensitive particles on a transparent conductive substrate are modified during electrostatic transfer by exposure to electromagnetic radiation to which at least a portion of the particles are sensitive.

Description

United States Patent 1 Carreira et a].

[541 IMAGE TRANSFER [75] Inventors: Leonard M. Carreira, Webstemlra S. Stein; Vsevolod Tulagin, both of 4 Rochester, all of N.Y. [73] Assignee: Xerox Corporation, Rochester, NY. 22 Filed: Dec. 4, 1969 [21] Appl.No.: 879,962

Related US. Application Data [62] Division of Ser. No. 542,050, April 12, 1966, Pat.

[52] Cl. ..355/16, 96/l.2, 355/4 [51] Int. Cl. ..-.G03g 15/00 [58] Field of Search ....355/l6, 3, 4; 96/1, 1.2, 1.3, 96/l.4

[451" Jan. 16,1973

[56] References Cited UNITED STATES PATENTS 2,968,552 l/l96l Gundlach ..3s5/3x Primary ExarninerSamuel S. Matthews Assistant Exa r'ninerRichard L. Moses AttorneyStanley Z. Cole, James J. Ralabate and Ronald Zibelli I [5 7] ABSTRACT Apparatus for electrostatically transferring images formed by photoelectrophoresi's. The color balance of the images which are made up of electrically photosensitive particles on a transparent conductive substrate are modified during electrostatic transfer by exposure to electromagnetic radiation to which at least a portion of the particles are sensitive.

12 Claims, 4 Drawing Figures PATENTEDJAH 16 I975 3 71 l 196 SHEET 1 [IF 2 IMAGE TRANSFER CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION This invention relates in general to imaging systems and more specifically to a photoelectrophoretic imaging system.

In photoelectrophoretic imaging, the imaging particles which are generally intensely colored are suspended in an insulating carrier liquid. This suspension is then placed between a pair of electrodes, subjected to a potential difference and exposed to an image to be reproduced. Ordinarily, when carrying out the process, the imaging suspension is placed on a transparent electrically conductive plate in the form of a thin film and exposure is made through the bottom of this plate while a second electrode is brought into contact with the top of the suspension, while a potential is applied across the twoelectrodes. The particles are believed to bear an initial charge when suspended in the liquid which causes them to be attracted to the transparent base electrode and to change polarity by exchanging charge with this base electrode upon exposure so that the exposed particles migrate across to the upper electrode to form an image on the base electrode by particle subtraction. This image is clearly and easily visible on the base electrode after the upper electrode carrying the particles which are not used to form part of the image is separated from the base electrode. The system may be used to produce monochromatic images by using a single color of particles in the suspension or a number of differently colored particles in the suspension which respond to the light exposure. In polychromatic systems, mixtures of two or more differently colored particles which are each sensitive only to light of a specific different wavelength or narrow range of wavelengths are used. Thus, for example, a full color image may be produced by using a mixture of cyan,

magenta and yellow particles which respond to red,

green and blue light respectivelysAn extensive and.

detailed description of a photoelectrophoretic imaging technique of the type described above is found in copending application Ser. No. 384,737, now US. Pat. No. 3,384,565 filed July 23, 1964, which is incorporated herein by reference.

Although the electrophoretic imaging technique generally described above has been found to be capable of producing excellent quality images in both monochromatic and polychromatic systems, it is frequently undesirable to leave the final image on the transparent base electrode. Thus, for example, when a very high quality optically flat reusable electrode is employed, the use of a new electrode each time the imaging process is carried out might, make the process prohibitively expensive for Another problem is that the electrode may not have any physical properties most desired as the final imaging substrate so that if the image is made on a conductive transparent glass substrate, it must be transferred to some other surface if a flexible print is to be produced. Although transfer of the image may be accertain applications.

complished by bringing an adhesive into contact with it and stripping it away, such adhesive materials are relatively expensive and frequently difficult and messy to work with. In addition to the aforementioned problems it has also been found that there is sometimes left behind on the electrode some unwanted imaging particles that tend to form a dirty background on the final image, and in other instances where a polychromatic color system is involved the color balance of the image as formed on the electrode needs corrections because one or more of the particles in the system responds to the imaging steps either more or less vigorously than it should to form a perfect color image of the original.

SUMMARY OF THE INVENTION Further objects will become apparent to those skilled in the art'as the disclosure is more fully made.

I The above and still further objects may be accomplished in accordance with the present invention by transfer of the image after it has been formed on one of the imaging electrodes by bringing a transfer substrate into close proximity with the formed image and applying an electrical field across the image in such a direction as to transfer it (i.e., the image) to the transfer substrate. Any suitable technique may be employed for applying the electrical field including, for example, bringing a roller, plate or other conductive elements connected to a high potential source closely adjacent to the back of the transfer substrate or applying a high potential corona discharge to the back of the transfer substrate while bringing it into proximity with the image. Since it is believed that the particles, remaining after the imaging electrode has passed over the imaging suspension, have a non-uniform charge distribution, that is, some are positively charged and some are negatively charged, the polarity of the applied field can be either positive or negative. In its preferred form however, the polarity of the applied field will be opposite to the polarity applied to the imaging electrode;

thus, if the imaging electrode is negatively charged, the

transfer electrode is positively charged, and vice versa. This is so because it is believed that the majority of the particles constituting the particle image are charged the same as the charge on the imaging electrode. Such ing the transfer step to improve, alter or otherwise modify transfer. Ithas been found, forexample, that 1 transfer from the base electrode onto the transfer substrate is more efficient when exposure of the image to the original being reproduced is continued during the transfer step. Transfer can also be effectedwhen the image is illuminated uniformly with white light during the transfer step. In another modification of the. process, filtered light of selected wavelengths may be used to expose the image during transfer for color correction or partial image transfer of polychromatic images using imaging particles of two or more colors.

BRIEF DESCRIPTION OF THE DRAWINGS glass 12 overcoated with a thin optically transparent layer 13 of tin oxide. Tin oxide coated glass is commer cially available under the tradename NESA glass from the Pittsburgh Plate Glass Company of Pittsburgh, Pennsylvania. This base electrode 'will be referred to hereinafter as the injecting electrode. Coated on the upper surface of electrode 11 is a thin layer 14 of finely divided photosensitive particles dispersed in an insulatthe formed particle image and applying an electric field ing carrier liquid. This suspension may also contain binders for the particles whichare dissolved or suspended along with the particles in the carrier liquid. Adjacent electrode 11 is a roller electrode generally designated 16 mounted for rotation on a rigid plate 18. The electrode 16 is connected in this instance to the negative side of a potential source 20 with the opposite side of the source being connected .to ground. Since the tin oxide layer of injecting electrode 11 is also connected to ground, an electric field is applied across the liquid suspension when electrode 16 rolls across the surface of electrode 11 in the direction indicated by the arrow 22in the drawing. Electrode 16 is made up of a central core 24 which is preferably of fairly high electrical con- .ductivity and this core is covered with a layer of a blocking electrode material 26, which may, for example, consist of Baryta paper (a paper coated with a gelatin suspension of barium sulphate). An image projector made up of a light source 28, atransparency 30, and a lens 32 is provided to expose suspension 14 to a light image of the original transparency 30 'to be reproduced. This electrode surface 26 collects unwanted (i.e. exposed) particles from suspension 14 as it rolls across electrode 11 during exposure,as explained in copending application Ser. No.'384,737, now US. Pat. No. 3,384,565 and leaves a particle image corresponding to the transparency to be reproduced on reused. It has been found that the particle image can be efficiently transferred to a more desirable surface by across the image in such a direction so as to transfer it to the transfer substrate.

Referring back to FIG. 1,- there is seen a third electrode generally designated 34 which is, in this instance, also mounted for rotation on rigid plate 18. This electrode 34 will be referred to hereinafter as the transfer electrode. Transfer electrode 34 is, in this embodiment, similar in constructionto electrode 16; that is, electrode 34 is made up of a conductive core 36 covered with a transfer surface 38, such as Baryta paper sleeve,

regular bond paper or onion skin paper. Conductive core 36 is connected by any suitable means to a potential source 40. The potential applied to conductive core 36 is, in this embodiment, of opposite polarity to the potential applied to electrode 16;

Accordingly, electrode 34 is connected to the positive side of potential source 40 with the opposite side of the source being connected to ground. Since the tin oxide layer 13 on injecting electrode 11 is also con-' nected to ground, an electric field is applied across liquid suspension 14 when electrode 34 rolls across the surface of electrode '11 in the direction indicated by arrow 22in the Figure. In this manner, the particle image is cleanly transferred to transfer electrode 34. If transfer electrode 34 is covered with a: removable transfer surface, such as Baryta paper sleeve, for'example, as previously disclosed, the complete image is transferred to surface 38, which can then be removed and replaced with a new sleeve for use in subsequent transfers. After

electrodes

16 and 34 have traveled across liquid suspension 14 in the directionindicated by arrow 22, they are raised slightly and returned to their initial position along the path indicated by arrow 42. Y

F IG. 2 shows an alternate embodimentof' the structure of transfer electrode 34. In this 1 embodiment, transfer electrode 34 is made up'of a continuous web 44 of a conductive material having a'suitable transfer surface 45. Web 44 carried, by plate 18 in the form of by any suitable means, such as by a set of conductive rollers 50."The electric field applied to the back of web' 44 is, once again, of opposite polarity to that of 'elec{ trode 16 so that the particles left behind during the passage of electrode 16 are attracted to web 44.

FIG. 3 shows'an alternate embodiment of the manner in which the field is applied across the imaging suspension. In this Figure,like numerals have been used to identifyparts of the apparatus which are identical to 2. The embodiment shown here in FIG. 3 is the same as the FIG. 2 embodiment except for the'distinctions hereinafter noted, including the fact that the potential is applied to the back of transfer web 44 by means of high potential corona discharge device 52. Such a' device is more fully described in 1 US. Pat. No. 2,588,699. Rollers 54'are used to keep the transfer web surface under tension sufficient to maintain the transfer surface in a flat condition, whereby its entire applicable surface is placed in direct contact with liquidsuspension 14 during the transfer step. Each

potential source

20 and 40 is individuallygrounded rather than having their opposite poles connected and then grounded as in FIG. 2 Here, as distinguished from FIGS. 1 and 2, the polarity of the potential applied to electrode 34 is the same as the polarity of the potential applied to electrode 16. As has previously been set forth, since it is believed that the particles, remaining after the imaging electrode has passed over the imaging suspension, have a nonuniform charge distribution, that is, some are positively charged and some are negatively charged, the polarity of the applied field can be either positive or negative. In this particular embodiment an imaging apparatus isshown wherein the polarity of the field applied to the transfer electrode is negative (i.e., the same polarity as is applied to the imaging electrode).

FIG. 4 represents a side sectional view of an embodiment of the invention after imaging electrode 16 has rolled over the exposed photosensitive suspension. In this instance, imaging electrode 16 is of the tractor type having aconductive inner web 56 covered with a layer of blocking electrode material 58, such as Baryta paper. Electrode 16 is connected to the negative side of a potential source 20 by means of roller contacts 60 and plate contact 62. The roller contacts also perform the auxiliary function of holding surface 58 under tension sufficient to maintain that surface in a flat condition, thereby enabling the entire applicable surface to be placed in direct contact with exposed suspension 14 as electrode 16 rolls thereover during the imaging operation. In this embodiment of the invention, electrode 16 has been caused to roll across the top surface of injecting electrode 11 during the period of image exposure. This light exposure causes the exposed particles originally attracted to electrode 11 to migrate throughthe suspension and adhere to surface 58 of electrode 16, leaving behind a particle image 14' on the injecting electrode surface which is a duplicate of original-transparency 30. Passage of transfer electrode 34 over injecting electrode 11 during application of an electric field across the image 14 will cause the image to adhere to transfer surface 44, thereby resulting in a duplicate of original transparency on transfer surface 44.

Asexplained in Ser. No. 384,737, now U.S. Pat. No. 3,384,565 the system can produce monochromatic or polychromatic images depending upon the type and number of particles suspended in the liquid carrier and the color of light to which the suspension is exposed in the'process.

In addition to transferring image 14 from the surface of injecting electrode 1 l to transfer

surface

38 or 44 by applying an electric field across the particle image, it has now been found, quite unexpectedly, that exposure to actinic electromagnetic radiation during the transfer operation enhances the transfer of the final image. In one aspect of this illumination, exposure through transparency 30 is continued during the passage of electrode 34 over the surface of injecting electrode. This imagewise exposure has been found to result in a more efficient transfer of particle image 14 than when transfer is accomplished in the absence of additional actinic electromagnetic radiation.

In another aspect, it has been found that transfer may be aided by flooding particle image 14' uniformly with white light during transfer. This can be accomplished by rotating original transparency 30 around pivot 64 (see FIG. 4) so that it is out of the path of the white light emanating from source 28.

It is also contemplated that transfer can be effected by electrode 34 while image 14 is subject to actinic electromagnetic radiation having a single wavelength or a selected band of wavelengths, which can be accomplished by any suitable means, for example, by rotating transparency 30 about pivot 64 out of the path of illumination from light source 28 and moving filter 66, also pivoted about point 64 for convenience into said illumination path. In the event that more than one type of photosensitive particle is used in the imaging suspension, each type being responsive to a different (or overlapping) portion of the visible spectrum, it has been found that an excellent transfer occurs when the particle image is flooded uniformly with actinic electromagnetic radiation having a wavelength (or a selected band of wavelengths) at which the particles in suspension 14 are equally responsive or as nearly equally responsive as nature permits. For example, where the suspension comprises a dispersion of phthalocyanine, Algol Yellow, andWatchung Red in a liquid carrier, (as described in Ser. No. 384,737 now U.S. Pat. No. 3,384,565), effective transfer occurs when the particle image is flooded with blue light of approximately 400 m.p.. wavelength. Thus, it has been found that a relatively low intensity light of correct wavelength is far more effective than white light (whose absolute intensity made the orders of magnitude greater, yet produces less than complete transfer). It is also contemplated that transfer can be effected by electrode 34 while image 14' is subjected to actinic electromagnetic radiation which is passed through both transparency 30 and filter 66, thereby resulting in imagewise illumination of a particular wavelength (or a selected band of wavelengths only).

With respect to the production of color images (that is, where suspension 14 contains two or more photosensitive particles which are responsive to different wavelengths in the visible portion of the spectrum) it has been found that proper illumination, as hereinafter described, during transfer will aid in color correction of the final image (i.e., the image transferred to electrode 34), should a color imbalance exist in the image 14' as it is viewed on electrode 11 prior to transfer. For purposes of illustration, this aspect of the invention will be described with reference to a suspension having three photosensitive particles; namely,

- cyan, yellow and magenta therein.

After image 14' is formed by the passage of electrode 16 over the surface of injecting electrode 11, the image may look to be off color (i.e., imbalanced) because of an unexpected photoresponse in one or more of the particles in suspension 14. For example, if the image is viewed in white light and it appears to be too red, this is because the cyan particles responded too readily to the original exposure so that there are not enough cyan I particles left behind in image 14' to filter out the proper amount of red light from the white light source. To remedy this color imbalance, it will be necessary to transfer magenta and yellow particles to the transfer electrode 34 at a relatively lower rate than cyan particles are transferred. It has been found that this color correction can be achieved by illuminating image 14 with a light source which is deficient in the color (or 7 colors) cotresponding to the particle (particles) which an analgous manner, if the image appears to betoo blue when viewed in white light, transfer is conducted while the image is subjected to illumination from a light source which is deficient in blue light (e.g., by passing white light through a yellow filter) and if the image appears to be too green, then transfer is conducted'while the image is illuminated with a light source which is deficient in green light (e.g., by passing white light through a magenta filter). Passage of electrode 34 over image 14' during such illumination, while under a potential of opposite polarity to the potential applied to the imaging electrode, will result in the transfer of an image, in proper color balance, to the surface of the transfer electrode. Y

C onvers' e'ly, an imbalanced color image can be color corrected by selectively transferring, at a relatively greater rate, the remaining photosensitive particles corsystem are reversed, electrode 11 will preferably be capable of accepting injected holes from bound particles upon exposure tolight and electrode 16 would preferably be a blocking electrode incapable of injecting holes into the particles at more than a very slow rate when they come into contact with the surface of this 7 electrode. In this preferred embodiment, electrode ll may be composed not only of conventional conductive materials such as'tin oxide, copper, copper iodide, gold or the like, but may also include many semiconductive materials such as raw'cellophane which are not ordina'rily thought of asconductors, but which are. stilltcapable of accepting injected charge carriers of thebecause charge which leaves the particles initially responding to the particle (or particles) which has (have) exhibited the unexpected photoresponse. It has been found that this can be achieved by illuminating image 14' with a light source which is richer in light corresponding to the particle which has exhibitedthe unexpected photoresponse. I

1 For example, if the particle mixprevi'ously disclosed is,"once again, too re'd, this selective transfer with the resultant color correction of the final image can be achieved by exposing image 14 during transfer to illumination which, is rich in red light (e.g., by passing a the transfer of an image, in proper color balance, to the surface of the -transfer electrode. In this manner, more cyan particleswill be transferred (in a relative nature) than yellow particles or magenta particles and, in so do-,

bound on this surface upon exposure to light can merely move out of the particles and remain on the insulating surface therebyallowing the exposed particles to migrate. However, the use of the more conductive materials is preferred because it allows for cleaner charge separation in that charge leaving the particles upon exposure can move into the underlying surface and away from the particle in which it originated. This also prevents'possible charge build-up on the electrode which might tend to diminish the inter-electrode field;

Onthe other hand, the preferredembodiment of the blocking electrode 16 isselectedso as to prevent or greatly retard the injection of electrons (or holes, depending upon the initial polarity of charge on the particle) into a bound particle when it reaches the surface of this electrode. Accordingly, the surface of this electrode facing suspension 14 in the preferredembodiment may be either an insulator or a semiconductor I which will not allow for the passage of sufficient charge mg, image '14 will be brought back into color balance. 7

ln an analogous manner, if the imageappearsto be too 7 ,blue or green'when viewed in white light transfer is conducted while the image is subjected to illumination from alight source which is rich in blue or green light the transfer electrode-as it'passes over image 14, is

I under'a potential of the'same polarity .as the potentia originallyappliedto the imaging electrode.

As 'should be clear at this pointin the disclosure,

respectively. This corrective exposure is made while there are certain preferred properties for e lectrode's l 1.

carriers under the influence of the applied field to discharge the particles finally bound to it, thereby preventingparticle oscillationIin the system. Even if this blocking electrode will allow for the passage of some charge carriers through it to the particles, will still be considered to come within the class of preferred materials if it does not allow for the passage of sufficient carriers to recharge the particles to the opposite polarity because even a discharge particle will tend to adhere to this blocking electrode by Van Der Waals forces. Here again materials not coming within the preferred class may be employed but they tend to lead to particle oscillation in the system, resulting in lower image density, poor image-resolution, image reversal and similar deficiencies, with the degree of these de ficiencies, in most instances, depending upon h owfarthe material employed deviates from the preferred class of I i 1 materials infits electrical characteristics.

suspension 14 when it (i.e., the particle) is exposed to.

blocking electrode which is incapable of injecting elec' trons into such a bound particle at more than a very.

slow rate when it comes into contact with the surface of the electrode 16. Obviously, if all polarities in the Baryta paper and other suitable "materials may be I employed to surface the blockingelectrode and maybe wet on their'back surfaces with electrically conductive materials.

Although this invention has been-described for the most-part in connection with a- Baryta paper covered imaging electrode 116 and transfer electrode 34, any

suitable material having aresistivity of about l0 ohm cm. or greater may be. employed, as a preferred. material- Typical materials in thisr'esistivity range -inwill not adversely affect the transfer of the particle image to the transfer electrode.

Applicable carrier liquids and photosensitive imaging particles, and the preparation and composition of the imaging suspension have already been described in Ser. No. 384,737, now US. Pat. No. 3,384,565 and that copending application should be referred to for such additional disclosure. A more detailed listing of applicable photosensitive particles can be found in copending application, Ser. No. 518,041, now US. Pat. No. 3,383,993 filed Jan. 3,- 1966, which list is incorporated herein by reference. This latter list is of greatest interest where color originals are being reproduced and, of course, is of particular'interest with respect to the manner in which a suspension of a plurality of different photosensitive particles is color corrected for an imbalance in image 14 as heretofore set forth.

It should be understood that the heretofore described processes are applicable to a repetitive or cyclic process, that is, where all or some of the following steps are performed, completely removing the imaging suspension from its supporting electrode after imaging and transfer (e.g., by cleaning the electrode of residual particles that may remain after transfer), applying a new imaging suspension to the electrode, and

repeating the imaging and transfer operations at least one additional time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The followingexamples are given to enable those skilled in the art to more clearly understand and practice the invention. They should not be considered as a limitation upon the scope of the invention,-but merely as being illustrative thereof.

EXAMPLES roughly 3 inches square and is exposed as described in each particular example.

EXAMPLEl A suspension including 1.5 grams of Watchung Red B, a barium salt of 1-(4'-methyl-5-chloro-azobenzene- 2-sulfonic acid )-2-hydroxy-3-naphthoic a'cid, C.l. No. 15865, available from DuPont; 2 grams Algol Yellow o.c., l,2,5,6-di(C,C-diphenyl)-thiazole-anthraquinone, C.l. No. 67300, available from General Dyestuffs; and 1.5 grams Monolite Fast Blue G.S., the alpha form of metal-free phthalocyanine, C.l. No. 74100, available from Arnold Hoffman Co.; is made up in 50 milliliters of Sohio Odorless Solvent 3440 (a kerosene fraction available from Standard Oil Company of Ohio). These particles are magenta, yellow, and cyan respectively. This mixture, known as tri-mix, is coated on a NESA glass substrate and exposed with a light intensity of 1,800 foot candles. A Kodachrome color transparency is placed between the light source and the NESA glass substrate so that a colored image is projected onto this tri-mix as the imaging electrode moves across the surface of the glass. The imaging electrode has a polyvinylidene fluoride covering thereon and the roller is held at a negative potential of 2,500 volts with respect to the glass substrate. After the imaging electrode passes over the substrate, an excellent quality subtractive threecolor image corresponding to the Kodachrome transparency is left behind on the glass. A Baryta paper covered transfer electrode which is employed is held at a positive potential of 2,500 volts with respect to the glass substrate. After the transfer electrode passes over the remaining particle image left behind on the glass, a

good quality image is obtained on the surface of the Baryta paper.

EXAMPLE ll The procedure of Example I is repeated including exposure of the particle image during transfer to uniform white light from the 1,800 foot candle light source. A

fair quality image is obtained on the Baryta paper transfer surface.

EXAMPLE III quality image is now obtained on the Baryta paper transfer surface.

EXAMPLE IV The procedure of Example I is repeated except that the Baryta paper covered transfer electrode is held at a negative potential of 2,500 volts with respect to the glass substrate. The poor quality image is obtained on the transfer surface.

EXAMPLE V The procedure of Example IV is repeated including exposure of the particle image during transfer to uniform white light from the 1,800 foot candle light source. A good quality image is obtained on the transfer surface.

EXAMPLE VI 3,000 volts, and the transfer electrode is held at a posi-.

tive potential of 3,000 volts. After the imaging elec-' trode passes over the substrate, an excellent quality three-color image is left behind on the NESA glass, and after the transfer electrode passes over the particle image, a good quality image is obtained on the Baryta paper transfer surface.

EXAMPLE vu The procedureof Example V1 is followed with the further step of exposing the particle image during transfer to uniform white light from the800 foot candle light source. A good quality image is obtained on the Baryta paper transfer surface.

EXAMPLE V111 The procedure of Example V1 is followed with the additional operation of exposing the particle image during transfer 'to light which has passed through the original Kodachrome color transparency. A superior quality image is obtained on the surface of the Baryta paper transfer paper.

EXAMPLE IX The procedure of Example V1 is followed except that approximately 2 mol percent 2,4,7-trinitro-9- fluorenone sensitizer is added to the tri-mix suspension.

A good quality image is obtained on the NESA glass substrate when a light source of 250 foot candles is vused. A good quality image is also obtained on the Baryta paper transfer surface when the particle image is exposed to the 250 foot candle light source during transfer.

EXAMPLE X A suspension including equal amountsof Watchung Red B, Algol Yellow GC and Monolite Fast Blue GS is 7 made up in Sohio solvent with total particle concentrationapproximately percent by weight. This mixture is coated on a NESA glass substrate and exposed with a light intensity'of 1,800 foot candles. A Kodachrome color transparency is passed between the light source thereon and is held at a negative potential of 2,500

volts with respect to the glass substrate. After the imaging electrode passes over the substrate, a good quality subtractive three-color image corresponding to the Kodachrome transparency is produced on the glass; however, the image when viewed in white light appears too green. A Baryta paper covering transfer electrode which is employed is held ata positive potential of 2,500 volts with respect to the glass substrate. During the passage of the transfer electrode over the colorv EXAMPLEXI A suspension including 1.0 grams of Watchung Red B, 1.5 grams of the yellow particle of Example V and 1.25 grams Monolite Fast Blue 0.8. is made up in 50 milliliters Sohio Odorless Solvent 3440. Theprocedure of Example X is followed except that the Baryta paper covering transfer electrode is held at a negative potential of 2,500 volts with respect tothe glass substrate. After theimaging electrode passes over the substrate, a

good quality subtractive three-color image corresponding to the Kodachrome transparency, except that the image when viewed in white light appears to be too red, is left behind on the glass. During the passage of the transfer electrode over the remaining particle image left behind on the glass substrate, the image is exposed to visible light which is more intense in the red portion of the visible spectrum than in other portions. This is achieved by passing the white light from the 1,800 foot candle source through a Wratton red filter. A good quality color corrected image is obtained on the surface of the transfer electrode.

EXAMPLE Xll The procedure of Example V1 is followed with the further step of exposing the particle image during transfer to blue light of approximately, 400 m.p.. wavelength. This exposure is achieved by passing white light from the 800 foot candle source through a Wra't ten blue filter. A superior quality image is obtained on the Baryta paper transfer surface. v

While the invention has been described ,with reference to preferred embodiments thereof, it will be understood by ,those skilled in the art that various changes in form and details may be made without departing from the true spiritand scope of the invention.

It should be understood that the present invention is not dependent upon the exact nature of the photose nsitive particles employed, rather any suitable particle composition (either in pure form or admixed with other. photosensitive or non-photosensitive materials) or structure may be employed,provided the advantageous results of this invention are not adversely affected.

Further, as will be apparent to those skilled in-the art, additional operations may be performed to achieve the herein disclosed results or, in certain circumstances, certain operations may be deleted. The apparatus herein disclosed may be modified in numerous ways to, once again, achieve the effective transfer heretofore set forth. All such additions, deletions, modifications, etc. are considered to be within the scope of the present invention.-

What is claimed is:

l. A photoelectrophoretic imaging apparatus comprising a smooth optically transparent first electrode for supporting a layer of an imaging suspension comprising electrically photosensitive particles in an insulating carrier liquid, a second electrode for uniformly contacting the free surface of an imaging suspension on said first electrode, means for applying a potential difference between said first and said second electrodes, means for exposing a suspension on said first electrode through said first electrode to radiation to which at least a portion of the particles in the imaging suspension are responsive until an image is formed on said first electrode, a transfer member for contacting an image on said first electrode, means for applying a potential difference between said transfer member and said first electrode, means for exposing an image on said first electrode to only a portion of the wavelengths in the visible light spectrum while said transfer member is in contact with the image.

2. The apparatus of claim 1 wherein said transfer member is in the form of-a roller.

3. The apparatus of claim 1 wherein said transfer member is in the form of a continuous web.

4. The apparatus of claim 1 wherein said transfer member comprises a conductive support having an insulated covering thereon.

5. The apparatus of claim 1 wherein said transfer member comprises a conductive support having a semiconductive covering thereon.

6. The apparatus of claim 1 wherein said means for applying a potential difference between'said transfer member and said first electrode is a corona discharge unit.

7. A photoelectrophoretic imaging apparatus com prising a smooth optically transparent first electrode for supporting a layer of an imaging suspension comprising electrically photosensitive particles in an insulating carrier liquid, a second electrode for uniformly contacting the free surface of an imaging suspension on said first electrode, means for applying a potential difference between said first and said second electrodes, means for exposing a suspension on said first electrode through said first electrode to radiation to which at least a portion of the particles in the imaging suspension are responsive until an image is formed on said first electrode, a transfer member for contacting an image on said first electrode, means for exposing an image on said first electrode to visible light which is less intense in at least one portion of the visible spectrum while said transfer member is in contact with the image.

8. The apparatus of claim 7 wherein said transfer member is in the form of a roller.

9. The apparatus of claim 7 wherein said transfer member is in the form of a continuous web.

10. The apparatus of claim 7 wherein said transfer member comprises a conductive support having an insulated covering thereon.

11. The apparatus of claim 7 wherein said transfer member comprises a conductive support having a semiconductive covering thereon.

12. The apparatus of claim 7 wherein said means for applying a potential difference between said transfer member and said first electrode is a corona discharge unit.

Claims

2. The apparatus of claim 1 wherein said transfer member is in the form of a roller.
3. The apparatus of claim 1 wherein said transfer member is in the form of a continuous web.
4. The apparatus of claim 1 wherein said transfer member comprises a conductive support having an insulated covering thereon.
5. The apparatus of claim 1 wherein said transfer member comprises a conductive support having a semi-conductive covering thereon.
6. The apparatus of claim 1 wherein said means for applying a potential difference between said transfer member and said first electrode is a corona discharge unit.
7. A photoelectrophoretic imaging apparatus comprising a smooth optically transparent first electrode for supporting a layer of an imaging suspension comprising electrically photosensitive particles in an insulating carrier liquid, a second electrode for uniformly contacting the free surface of an imaging suspension on said first electrode, means for applying a potential difference between said first and said second electrodes, means for exposing a suspension on said first electrode through said first electrode to radiation to which at least a portion of the particles in the imaging suspension are responsive until an image is formed on said first electrode, a transfer member for contacting an image on said first electrode, means for exposing an image on said first electrode to visible light which is less intense in at least one portion of the visible spectrum while said transfer member is in contact with the image.
8. The apparatus of claim 7 wherein said transfer member is in the form of a roller.
9. The apparatus of claim 7 wherein said transfer member is in the form of a continuous web.
10. The apparatus of claim 7 wherein said transfer member comprises a conductive support having an insulated covering thereon.
11. The apparatus of claim 7 wherein said transfer member comprises a conductive support having a semi-conductive covering thereon.
12. The apparatus of claim 7 wherein said means for applying a potential difference between said transfer member and said first electrode is a corona discharge unit.