Patent Publication Number: US-3876937-A

Title: Layer transfer imaging system

Description:
United States Patent 1191 Kamola Apr. 8, 1975 [54] LAYER TRANSFER IMAGING SYSTEM 3.234.019 2/1966 Hall 96/1 R 3.394.002 7/1968 Brickmore 96/ l R [75] Invent North 3.438.772 4/l969 Gundlach 96/13 x 3.707368 12/1972 Van Dorn 96/1 R [73] Assignee: Xerox Corporation, Rochester. NY. F d J 29 73 Primary E.\&#39;aminerRobert P. Greiner 1 e an.  
 [2H Appl. No.: 327,35l [57] ABSTRACT R a s Appncation Data A layer transfer imaging system for generating hard [62] Division of 763.290 Sept 1968 copy output from optical mput. The umt generates imabundone ages on paper, plastlc coated paper, metal fo1ls, metal paper and metal plastic laminates utilizing a layer [521 US. Cl. 355/3 R; 96/ L3 transfer imaging System comprising a cohesively weak [5]] Int CL 603g 15/00; 003g 15 /22 imaging layer sandwiched between a donor sheet and 5 Fi of Search 355/3 R, 17. 9 /1 R, L3 a receiver sheet. Separation Of the dOl&#39;lOl&#39; and receiver (m/L4; 1 17/175 sheets provides a negative image on one of the sheets and a positive image on the other. Inputs maybe from [56] References cued a cathode ray tube, document light reflection, or any UNITED STATES PATENTS other suitable optical scan transfer system. 2.951.443 9/1960 Byrne 96/l.4 16 Claims, 7 Drawing Figures PATENTEDAPR 8|9T5 spam 3 or e PATENTEDAPR 8mm 4 $876,937  
 SEiiETSHFgS PATENTEDAPR 8I975 876,937 slzimsm g LAYER TRANSFER IMAGING SYSTEM This is a division of application Ser. No. 763,290, filed Sept. 27, 1968 now abandoned.  
 BACKGROUND Prior art image recording apparatus include, for example, the xerographic and the photographic type of recording. vIn the xerographic type of recording, an image is first recorded on a photoreceptive surface to form a latent image thereon. Toner is cascaded across the xerographic surface to develop the recorded image. Transfer to a printout record sheet or other substrate is made including image fixation by any of the known prior art manners. This xerographic technique has been profitable and advantageous for typewritten and other types of image sources but the system remains excessively complicated due to the image transfer, cascading of toner, etc.  
  The photographic method of image recording has been advantageously used in the prior art, but it also has its limitationsoFor example, the ordinary photographic camera must have the film removed and developed for subsequent printing. The instant picture cameras have their use in graphic display reproduction but are not automated to allow for continuous and automatic operation. Copending application Serial No. 452,641 describes an imaging system utilizing a manifold recording set comprising a photoresponsive material between a pair of insulating sheets. In this imaging system, an imageable plate is prepared by coating a layer of cohesively weak photoresponsive imaging material onto a substrate. This coated substrate is called the donar. In preparation for the imaging operation, the imaging layer is usually activated by treating it with a swelling agent or partial solvent for the material, or by heating. Once the imaging layer is activated, a receiving sheet is laid over its surface. An electrical field is then applied across this manifold set while it is exposed to a pattern of light and shadow representative of the image to be reproduced. Upon separation of the donor substrate or sheet and receiving sheet, the imaging layer fractures along the lines defined by the pattern of light and shadow to which the imaging layer has been exposed, withpart of the imaging layer being transferred to the receiving sheet while the remainder is retained on the donor sheet. Thus, a positive image, that is, a duplicate of the original, is produced on one sheet while a negative image is produced on the other.  
  Either the donor sheet or receiver sheet must be at least partially transparent to permit exposure of the imaging material to the image to be reproduced. The imaging layer serves a dual function of imparting light sensitivity to the system while at the same time acting as colorant for the final image produced. In one form, the imaging layer comprises a photosensitive material such as a metal free phthalocyanine dispersed in a cohesively weak insulating binder.  
 OBJECTS It is, accordingly, an object of the present invention to provide an improved imaging system.  
  It is another object of the present invention to provide an improved graphic imaging system utilizing the formation of images by layer transfer in image configuration. 7  
 BRIEF SUMMARY OF THE INVENTION In accomplishing the above and other desired aspects of the present invention, applicants have invented improved apparatus for producing images in a graphic imaging system by the use of layer transfer in an image configuration. In one embodiment, an activator applicator roll deposits activator onto a continuous roll of donor web material. The readout copy material is fed into the system and by means of a sandwich roll the copy is guided into contact with the donor web with the activator thereon. The donor-copy sandwich moves past a pair of charge rolls where it is charged and then continues on to the exposure station to receive the input image. After exposure, the donor supply roll turns in the opposite direction which moves the copy down&#39;to the charge rolls where an abrupt change in web direction coupled with the inherent stiffness of the copy material causes the copy to leave the web and proceed into output guides to guide the copy material past a fusing apparatus for delivery from the system.  
  The above embodiment utilizes the activation of the donor material followed by a reversal of the original direction of the donor material to cause separation of the copy material from the donor. Further embodiments include the copy material being activated with other operations remaining essentially the same. Another embodiment includes the continuous one-directional movement of the donor supply roll with copy material or donor activation, with copy material and donor supply separation taking place at the output of the exposure station. A further embodiment would utilize a web of material for receiving the image transfer from the donor, with subsequent image transfer to the output copy material.  
 DESCRIPTION OF THE DRAWINGS For a more complete understanding of the invention, reference may be had to the following detailed description in conjunction with the drawings wherein:  
  FIG. 1 is a side sectional view of a photosensitive imaging member for use in the present invention;  
  FIG. 2 is a side sectional view diagrammatically illustrating the steps in forming an image by utilizing the transfer process;  
  FIG. 3 is one embodiment of the present invention utilizing a forward and reverse moving donor with donor activation;  
  FIG. 4 is another embodiment of the present invention utilizing a forward and reverse moving donor with receiver activation;  
  FIG. 5 is another embodiment of the present invention utilizing a straight-through, one-way moving donor with receiver activation;  
  FIG. 6 is one embodiment showing the structure of a system utilizing the present invention; and  
  FIG. 7 is another embodiment showing a selected placement of apparatus utilizing the present invention.  
 DETAILED DESCRIPTION OF THE INVENTION In copending application Ser. No. 609,057, there is disclosed a process of forming an image by means of layer transfer. In FIG. 1 of the present application, taken from said copending application, imaging layer 2 comprising photosensitive particles 4 dispersed in binder 3, is deposited on aninsulating donor substrate sheet 5. The image receivingportion of the manifold set comprises an insulating receiver sheet 6. Sheets 5 and 6 are preferably insulating materials so that they will hold a charge placed on their surface.  
  Referring now to FIG. 2, also similar to that in application Ser. No. 609,057, the first step in the imaging process is the activation step. Although the activator may be applied by any suitable technique such as with a brush, with a smooth or rough surface roller, by flow coating, by vapor condensation or the like, HO. 2 which diagrammatically illustrates the steps of the layer transfer imaging process shows the activator fluid 23 being sprayed onto image layer 12 of the manifold set from a container 24. Following the deposition of this activator fluid, the set is closed by a roller 26 which also serves to squeeze out any excess activator fluid which may have been deposited. The activator reduces the cohesive strength of imaging layer 12. In certain instances the first two steps of the imaging process as diagrammatically illustrated in FIG. 2 may be omitted; thus, for example, a manifold set which is preactivated during manufacture may be supplied wherein imaging layer 12 is initially fabricated to have a low enough cohesive strength so that activation may be omitted and receiving layer 16 may be adhered to the surface of imaging layer 12 at the time when that layer is coated on substrate 17. It is considered preferable, however, to include an activation step in the process because stronger and more permanent imaging layers may then be provided which can withstand storage and transportation prior to imaging.  
  Once the proper physical properties have been imparted to imaging layer 12 and the receiving sheet 16 has been placed on layer 12, an electrical field is applied across the manifold set through electrodes 18 and 21 which are connected to potential source 28 and resistor 30. Although FIG. 2 shows the manifold sandwich not coming in contact with either electrode 18 or 21, since the receiver sheet and the donor sheet are preferably insulating materials they may contact one or both of the electrodes during the charging operation. Preferably, the sandwich will contact one electrode to serve as a guide and to be spaced one to three thousandths of an inch from the other electrode to prevent binding. Alternatively, the charging electrode may be a corona discharge apparatus, a roller, wherein roller 26 could be conductive for example, and be used to charge in place of electrode 18, a sharp edge or a friction charging device such as a fur covered roller.  
  The sign of the charge as shown on electrodes 18 and 21 may also be reversed, electrode 18 being made the negative electrode and electrode 21 being made the positive electrode. The charge bearing manifold set then moves into transparent plate 27 where it is exposed to light image 29. Light image 29 may be light projected through a transparency, light information projected from an opaque subject, such as a document or from the face of a cathode ray tube as to be more fully hereinafter described. In a continuous operation the light image may be projected through a slit in such a manner that there is little or no relative movement between the projected light image and the manifold set. The manifold sandwich then passes roller 32 which acts as a guide for the manifold sandwich and as a bearing point for the strippingapart of the receiver and the donor sheets. Alternatively, roller 32 may be a sharp edge, a rod, or a wire. Upon separation of substrate 17 and receiving sheet 16, imaging layer 12 fractures along the edge of exposed areas and at the surface where it had adhered to substrate 17. Accordingly, once separation is complete, exposed portions of imaging layer 12 are retained on one of sheets 17 and 16 while unexposed portions are retained on the other sheet which provide a positive image on one sheet and a negative image on the other sheet.  
  In copending application Ser. No. 609,057, there is fully set forth representative compounds and materials which can be used in the layer transfer imaging process. For purposes of example, the following materials are representative. The electrodes may consist of any suitable conductive material, such as aluminum, brass, stainless steel, copper, nickel, zinc, and other mixtures thereof. The donor substrate and the receiving sheet may preferably consist of a suitable insulating material. Typical insulating materials include polyethylene, polyethylene terephthalate, cellulose acetate, paper, plastic coated paper, such as polyethylene coated paper, and mixtures thereof. Suitable activating fluids may include any material which will reduce the cohesive strength of the imaging layer. Typical materials include kerosene, carbon tetrachloride, petroleum ether, silicon oils, etc. The imaging layer may comprise any typical photoresponsive material in a binder. Typical photoresponsive materials include photoconductors such as substituted and unsubstituted phthalocyanine; quinacridones; zinc oxide, mercuric sulfide, etc. Binder materials may include insulating resins such as polyethylene, polyproplylene, etc. For more complete information on the above compounds and materials, reference is made to the aforementioned copending application Ser. No. 452,641.  
  FIG. 3 shows one embodiment of the imaging system utilizing the layer transfer process. The donor supply roll 301 supplies a continuous donor web 302 along a path of movement to the activator applicator 303, the sandwich rolls 305, the charge rolls 307, the exposure station 309 to the donor takeup roll 31]. A sheet of record paper material or other substrate 313 would be fed into the apparatus through guide rollers 315. The guide rollers 315 would be driven by a motor not shown in order to feed sheet 313 at a uniform rate into the system. As the sheet 313 moves into the system, the donor roll 301 begins to move in the direction of the arrow shown, advancing the donor web 302 past the activator applicator where it is uniformly coated with the activator. The sandwich rollers 305 grip the donor web 302 and the sheet 313 at the beginning of the area that has been applied with activator. The sandwich rollers 305.  
 move the sandwich formed of the donor supply web 302, the activator, and the copy sheet 313 to the area occupied by the charge rollers 307. The charge rollers 307 uniformly charge the sandwich to the desired static potential in addition to driving the sandwich to the exposure station 309. At this point, the exposure of the sandwich is made by any of the known techniques as hereinbefore set forth, such as by cathode ray tube, reflection from a document or other source, or image through a transparency, through appropriate lens systerns.  
  After exposure the donor supply roll becomes the takeup roll and moves in a direction opposite the arrows shown. This causes the sandwich to move back along the path originally traveled from the time the sheet of copy material was originally fed into the machine. Now, however, as the sandwich reaches the area of the charge rollers 307, the sharp turn thereat without an additional roller to aid the sandwich in making the turn, causes the copy paper due to its inherent stiffness to continue toward heater-fuser 314 while the donor web is rewound. Heater-fuser 314 is utilized to fix the image formed on the sheet of copy material at the charge roller area 307 when the copy sheet 313 is separated from the donor web 302. The heater-fuser 314 is exemplary only as any form of apparatus for permanently fixing the image to the sheet of copy paper may be utilized. Bin 317 is used for collecting the output documents.  
  Referring now to FIG. 4, a different embodiment is shown wherein the solvent is applied to the copy sheet material rather than the donor supply web. All other aspects of the invention are the same. Thus, the donor supply roll 401 supplies the donor web 402 in the direction of the arrow as shown. The donor web 402 travels around the roller 403 which is the stripping point between the sandwich and the copy sheet. From roller 403 the donor web passes charge rollers 405, exposure station 407 to donor takeup roll 409.  
  When a copy is to be made, a copy sheet 411 is drawn off the supply 413 by any feeding apparatus known in the art. The copy sheet 411 is fed into the web drive apparatus 415 which only touches the edges of the document 411 so as not to disturb the activator application to the copy sheet in any manner. By pressure between the web 415 and wheel 417, the document 411 is driven to the charge rollers 405 past the activator applicator 419. Clearly in FIG. 4 can be seen the application of the activator to the copy sheet 411 rather than the donor supply web 401. At the rollers 405 the copy sheet 411 meets the donor web 402 to form a sandwich which proceeds to the exposure station 407. The image rays are impinged upon the sandwich which have been charged by charge rollers 405 to form the image on the sandwich. Subsequently to the exposure of the sandwich, the donor supply roll 401 becomes the takeup roll and moves in a direction opposite to the arrows shown in the figure. This causes the sandwich to travel back along the path that it originally traveled in the generation of the sandwich. Due to the large turn made by the donor supply web 402 at point 403, the stiffness of the copy sheet 411 causes the sheet to come away from the donor web, thereby generating the positive and negative images as hereinbefore described. The donor web 402 continues to be taken up by supply roll 401 while sheet 411 now moves by means of web 421 past the heater unit 423 into the output document bin 425.  
  In FIG. 5, is shown a straight-through, one-way donor with receiver activation. Equally as well, the donor could be activated in a similar manner as shown in FIG. 3. In this embodiment then, donor supply roll 501 supplies the donor web in the direction of the arrow as shown past the sandwich rollers 503, the charge rollers 505, the exposure station 507, to sandwich rollers 509 to the donor takeup roll 511. The copy sheet 513 is drawn off the paper supply 515 between the felt web 517 and drive roller 519. Again, the copy sheet is touched by the web 517 only by the edges as the activator is applied to the sheet by solvent applicator 521.  
  At the sandwich rolls 503, the copy sheet 513 and the web 502 come into contact to form the sandwich. The chargingrolls 505 charge the sandwich to the desired potential prior to exposure at the exposure station 507.  
 After the exposure by the image rays at station 507, the donor 502 moves along the path to the takeup roll 511 while the copy sheet is stripped off at sandwich rolls 509 for traveling along web 523 past heater-fuser 525 to document bin 527.  
  It can be seen, however, that the single path of the donor web 502 would cause a large waste of donor web material due to the movement of the web through the system. The previous figures show embodiments wherein the donor web is conserved by the reverse movement of the donor web prior to separation of the copy material from the donor web. Because of the fact that in FIG. 5 there is no reversal of the direction of movement of the donor supply web 502, a second copy sheet from paper supply 515 would be fed into the system past the solvent applicator 521 to the point of the first sandwich rolls 503. After exposure of the first copy sheet and the exiting thereof from the system, the second sheet is advanced to the exposure station. If the second sheet is exposed within a predetermined time period, the operation continues as hereinabove set forth. If, however, exposure does not come within such predetermined time period, either the charge rolls 505 may be moved to recharge the sandwich of the second copy sheet and the donor web, or the second sheet may be discarded from the system and a new sheet supplied to the system in the above manner.  
  FIG. 6 shows an additional embodiment wherein the activator is applied to a receiver web or belt rather than the donor web or the receiver sheet. In a manner similar to that for the above figures, donor supply roll 601 supplies the web 602 past roller 603, the charge rollers 605, the exposure station 607, the roller 609 to the donor takeup roll 611.  
  Here, however, the receiver web or belt 613 is utilized to form the sandwich for the necessary layer transfer. The receiver web 613 is applied with activator from the activator applicator 615 prior to the entrance of the donor supply web 602 to the exposure area 607. A record sheet would be advanced into the system, either manually or by any of the known mechanical advance devices, through guides 617 and rollers 619 to contact the receiver web 613 at the transfer rolls 621. At this point, the transfer between the receiver web 613 and the copy sheet is made subsequent to the separation of the donor and receiver web at roller 609. The  
 copy sheet advances past the transfer rolls 621 to the heater-fuser 623 for permanent retention of the image, and by means of the feedout rollers 625, the document is advanced to the output bin 627. In order to utilize the receiver web 613 for additional documents, a cleaning web 629 is utilized which moves in the direction of the arrows shown to clean the receiver web 613 at roller 631. Roll 633 stores the used cleaning web 629.  
  Also shown in FIG. 6 is a lens system which may be used for imaging from, for instance, a cathode ray tube which would be situated along the same plane of the exposure station 607 but adjacent the apparatus as shown in the figure. A twomirror system 635 would be utilized to reflect the image from the cathode ray tube onto the mirror system and into the exposure station of the apparatus shown in the figure. Lens 637 would be utilized for focusing.  
  FIG. 7 shows an actual embodiment of an imaging mechanism which operates in accordance with the principals of the present invention. When a copy is to be made, a continuous torque is supplied to the donor supply roll 701 and the donor takeup roll 703 through slip clutches, not shown, in the directions shown by the arrow. At the same time the activator applicator roller 705 begins turning at a fixed speed. The copy sheet material would be fed into the input chute 707 which trips the start microswitch 709 on its way to the feed rollers 711. The start switch 709 starts the feed roller 711 turning, the donor drive roll 713 turning, brings the activator applicator roller 715 into contact with the donor web 702, and energizes the charge rollers 717. The activator applicator is withdrawn from the donor web 702 as the trailing edge of the copy sheet leaves the start switch 709.  
  The distance from the start switch to the sandwich rollers 719 is approximately equal to that of the activator applicator 705 to the sandwich rollers 719 such that the activator is applied to the donor web 702 only in the area which would come into contact with the copy sheet material. The purpose of the sandwich rollers is to guide the copy material into contact with the activator wetted donor web 702. A fixed gap of about 0.010 inches exists between the sandwich rollers 719 and the donor web 702. This is to prevent solvent and used donor material from coming in contact with it and offsetting the copy material. An alternate method for forming the sandwich would be to remove the sandwich rollers and extend the lower plate of the copy guide chute 721 such that it would function to guide the leading edge of the copy sheet into contact with the wetted donor web 702. Once in contact with the wetted web, the copy sheet is held against the web 702 by the adhesive force of surface tension.  
  The donor-copy sandwich moves past the charge rollers 717 where it is charged and continues to the exposure station 723 where it stops, as the leading edge of the sandwich is sensed by sandwich stop switch 725. A gap also exists between the web and the negative charge roller, as shown, for the same purpose mentioned above under the sandwich rollers 719. The sandwich stop switch 725 also de-energizes the charge rollers 717 and actuates the exposure mechanism. After exposure the donor drive roll 701 is turned in the opposite direction. This moves the copy down to the charge rollers 717 where the abrupt change in donor web direction coupled with the stiffness of the copy sheet material causes the copy to leave the web and proceed into the wire guides 727 which guide it past the heaterfuser 729 into the feedout rollers 73]. The feedout rollers 731 deliver the fused copy into the output tray 733.  
  The fuser, which could be of the quartz infrared type, for example, is turned on at the end of exposure and turns off as the copy leaves the feedout rollers 731. The used portion of the donor supply web 701 is returned to a position about one inch ahead of the solvent applicator 705 and the machine is ready for the next copy.  
  There has been described methods and apparatus for generating hard copy outputs from image inputs. While the invention has been described in conjunction with specific substances for use with the activator, image transfer layer, etc., it is apparent that any substances that meet the system requirements may be substituted. In addition, the invention has been described with a continuous donor supply roll and discrete sheets of receiver material but this was for ease of illustration only as the donor and receiver material could be cut sheets, continuous webs, or any combination thereof. It is further understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. Moreover. many modifications may be made to adapt a particular situation to the principles of the invention without departing from its essential teachings.  
 What is claimed is:  
  1. An imaging apparatus for layer transfer imaging wherein an electrically photosensitive imaging layer, structurally fracturable in response to the combined effects of an applied electric field and exposure to electromagnetic radiation to which said layer is sensitive, residing on a continuous donor web substrate is subjected to an electric field and to said electromagnetic radiation while sandwiched between said web and a continuous web receiver and wherein said layer is fractured in imagewise configuration by the separation of said webs to provide a positive image on one of said webs and a negative image on the other comprising;  
 a reversibly driven donor feeding and takeup means;  
 a reversibly driven endless belt receiver web means;  
 a charging means to subject said imaging layer to an electric field;  
 means to bring said receiver web into contact with said imaging layer in a first direction of said webs in a path of travel to said exposure means and out of contact in a second direction of said webs, said second direction being substantially reverse to said first direction;  
 an exposure means to expose said imaging layer to said electromagnetic radiation while said layer is sandwiched between said webs and subjected to said field;  
 means to bring a record sheet into contact with at least one of said images and to transfer said image from said web to said record sheet during travel in said second direction; and,  
 cleaning means associated with said receiver web to remove imaging material therefrom.  
  2. The apparatus of claim 1 wherein said cleaning means comprises a continuous web.  
  3. The apparatus of claim 1 wherein the exposure means includes at least one mirror.  
  4. The apparatus as set forth in claim 1 further including activator applicator means for applying an activator to said receiver sheet means.  
  5. The apparatus as set forth in claim 1 wherein said electrical charging means comprises roller means which further drive said sandwich along said first direction path.  
 6. The apparatus as set forth in claim 1 further including means for fixing or fusing the image produced on said receiver sheet means.  
  7. An imaging apparatus for layer transfer imaging wherein an electrically photosensitive imaging layer, structurally fracturable in response to the combined effects of an applied electric field and exposure to electromagnetic radiation to which said layer is sensitive, residing on a continuous donor web substrate is subjected to an electric field and said electromagnetic radiation while sandwiched between said web and a rigid receiver sheet and wherein said layer is fractured in imagewise configuration by the separation of said web and receiver providing a positive image on one of said web and receiver and a negative image on the other, comprising;  
 a reversibly driven donor feeding and takeup means;  
 a receiver sheet feeding means to bring said receiver into contact with said imaging layer in a first direction in a path of travel bringing said layer to said exposure means;  
 a charging means to subject said imaging layer to an electric field;  
 an exposure means to expose said imaging layer to said electromagnetic radiation;  
 drive means to drive said web and receiver together in a second direction including a means to turn said donor web sharply away from said receiver so as to allow said rigid receiver to continue said second direction due to its rigidity thereby separating said receiver from said web and fracturing said imaging layer providing a positive image on one of said web and receiver and a negative image on the other.  
  8. The apparatus of claim 7 further including means for fixing the image produced on said receiver.  
  9. The apparatus of claim 7 further including activator applicator means for applying activator to said imaging layer.  
  10. The apparatus of claim 7 further including activator applicator means for applying an activator to said receiver.  
  11. The apparatus of claim 7 wherein said charging means comprises a pair of charging rollers positioned adjacent said sandwich composed of said donor web, imaging layer and receiver.  
  12. The apparatus of claim 11 further including switch means to control the charging rollers at the end of travel of said sandwich to said first direction.  
  13. An imaging apparatus for layer transfer imaging wherein an electrically photosensitive imaging layer, structurally fracturable in response to the combined effects of an applied electric field and exposure to electromagnetic radiation to which said layer is sensitive,  
 residing on a continuous donor web substrate is subjected to an electric field and to said electromagnetic radiation while sandwiched between said web and a continuous web receiver and wherein said layer is fractured in imagewise configuration by the separation of said webs to provide a positive image on one of said webs and a negative image on the other comprising;  
 a reversibly driven donor feeding and takeup means;  
 a reversibly driven receiver web means;  
 a charging means to subject said imaging layer to an electric field;  
 means to bring said receiver web into contact with said imaging layer in a first direction in a path of travel to said exposure means;  
 an exposure means to expose said imaging layer to said electromagnetic radiation while said layer is sandwiched between said webs and subjected to said field;  
 means to turn said donor web sharply in said first path of travel so as to allow said receiver to continue said first said path of travel due to its rigidity thereby separating said donor web and receiver and fracturing said imaging layer providing a positive image on one of said web and receiver and a negative image on the other;  
 and, means to drive said donor web in a second direction, substantially in reverse to said first direction.  
  14. The apparatus of claim 13 wherein said charging means comprises a pair of charging rollers positioned adjacent said sandwich composed of said donor web, imaging layer and receiver.  
  15. The apparatus of claim 13 further including an activator applicator means for applying an activator to said receiver.  
 16. The apparatus of claim 13 further including means for fixing the image produced on said receiver.