CH638061A5 - COLOR ELECTROSTATIC PRINTING PROCESS AND APPARATUS FOR CARRYING OUT SAID METHOD. - Google Patents

Description

The invention also provides an apparatus for implementing this method, for making one or more colored copies of a colored original, electrostatically, comprising a rotary electrophotographic element, drive means for said element. electrophotographic following in a cycle by a series of processing stations arranged along its periphery, said processing stations comprising, in order, a charging station, an exposure station, a development station and a processing station image transfer, means for applying a uniform electrostatic charge on a part of the electrophotographic element to the charge station, characterized by:

5

10

is

20

25

30

35

40

45

50

55

60

65

638,061

4

A. means for sequentially forming a plurality of latent electrostatic images on said electrophotographic element at the exposure station during the rotation of said electrophotographic element, each of said electrostatic images corresponding to a color image different from the components of the colored original and each image being formed during a respective cycle,

B. a developing device adapted to move in the developing station along a path which is generally tangential to said rotating electrophotographic element, said developing device comprising a plurality of developing units arranged in a row and arranged in a manner to pass through the development station successively, each development unit having a tack development material, the color of which corresponds to the component of the colored image of one of the latent electrostatic images,

C. drive means for driving said development device step by step along its tangential trajectory through said development station in time relation with the formation of the corresponding colored latent images and bringing the development units in relation to application of a tacker to the electrophotographic element in series when each unit is in said station, said drive means operating so as to advance step by step each development unit in said development station, and then to maintain this during a sufficiently long downtime, then advancing said development unit step by step out of the development station while simultaneously bringing the next unit into the station, the part of the electrophotographic element having a color corresponding to the latent image of each development unit fully traversing the development station during the downtime that their respective development unit marks in said station, and

D. a transfer device at said transfer station for transferring each developed image onto a sheet of superimposed support material when each developed image passes through said transfer station during its respective cycle, the number of cycles corresponding to that colors and that of the prints on each sheet.

The drawing represents, by way of example, an embodiment of the subject of the invention.

The single figure is partly a perspective view and partly a block diagram of an apparatus for producing colored images from colored originals, certain details being more or less symbolic or schematic.

The apparatus shown in the drawing for electrophotographic copying is generally designated by 11.

An original to be copied is placed on a flat bed observation device 13 where its image is rapidly observed and converted into three or four digital color separation information. The flat bed observation device 13 can comprise a white light source, an optical observation unit, red, green and blue filtration units, to form the three color separations, and a converter. analog / digital to convert analog information into digital information. The three or four color separations can be formed simultaneously by directing the images of the original through the three filters at the same time. A special filter or observation system can be used for black pigments.

The digital data thus obtained are sent to a computer 15 where they are stored either permanently or temporarily, and then processed subsequently. Further processing includes converting the digital values of red, green, blue and black, respectively, to values of cyanide, magenta, yellow and black. Subsequent processing can also include operations such as reduction or increase in scale, change in density, gamma change, color balance, color inversion, application of legends, etc.

A graphic display device 17 which is connected to the computer 15 allows the images stored in the computer to be viewed at all times.

A laser system 19 for writing the images using the digital values is also connected to the computer 15. The laser system 19 can comprise an observation prism, a laser and an acousto-optical modulator for modulating the output beam of the laser in function of digital information. The laser system 19 is arranged to observe at a particular angle. Instead of a single laser, the laser system 19 may include a plurality of lasers, each being arranged to observe a portion of the particular angle.

The apparatus comprises an electrophotographic element constituted by a rotary electrophotographic drum 21 mounted on an axis 23 which can rotate on a support frame 25, in the direction shown by the arrows. The support frame 25 is cut and the trunnion and support bearings have not been shown in order to simplify the drawing. The drum 21 is driven by a motor 27 whose output shaft is mechanically connected, as indicated at 22, to the axis 23. The peripheral surface of the drum 21 comprises a photoconductive coating on a conductive substrate. The conductive substrate can be constituted either by a sleeve mounted on the drum 21, or by an integral part of the drum 21. Thus, it can comprise a metallic substrate provided with a photoconductive coating on its surface or be constituted by an insulating sheet having an ohmic layer interposed between the sheet material and the photoconductive coating. In both cases, the metal substrate or the ohmic layer must be electrically connected to a charging circuit comprising a corona voltage source. Photoconductive coating is one of those by which latent electrostatic images can be formed by laser writing at very high speed and then developed to provide prints of high quality and high resolution. An example of such a coating is the coating described in US Patent No. 4,025,339.

There are, placed around the peripheral surface of the drum 21, and in the following order: a charging station 31, an exposure station 33, a development station 35, a transfer station 37 and a cleaning station 39 ultrasonic or other. As can be seen, the development station 35 is located just under the drum 21.

The charging station 31 comprises a charging device 41 applying a uniform electrostatic charge to the photoconductive surface of the drum 21. The charging device may comprise one or a series of corona wires connected to a switchable corona voltage source 42 by a suitable connection 40. The wire or wires, not shown, of the device 41 can move back and forth or rotate to produce a uniform load.

When the part of the surface charged to the charging station 31 passes through the exposure station 33, a latent electrostatic image corresponding to one of the four components of the colored image of the original (i.e. say cyanide, magenta, yellow or black) is written on the surface by the laser beams 20 coming from the laser system 19 (the beam (s) are illustrated only symbolically in the drawing).

When the latent electrostatic image is moved through the development station 35, it is developed with its corresponding colored development material (tacker) in a development device 43.

The development device 43 comprises four individual development units 45, 47, 49 and 51 arranged in a row on a frame 53. Each development unit comprises a tray comprising a quantity of development material consisting of a differently colored liquid indicator, a tack applicator roller being partially submerged in each tray. The color of the liquid indicator in each tray corresponds to one of the four colors

10

is

20

25

30

35

40

45

50

55

60

65

5

638,061

their image components of the original. Thus the colors of the tackers in the four bins will be cyanide, magenta, yellow and black respectively.

The chassis 53 is mounted on a rigid sub-carriage 54 which is guided on tracks 55 for a tangential step-by-step movement relative to the drum 21, movement during which it brings the development units 45, 47, 49 and 51 successively in the development station 35. The chassis 53 and the sub-carriage 54 are driven by a screw and nut device comprising a programmed stepping motor 57 whose shaft is connected to the screw 59, which cooperates with a mounted nut on the sub-carriage 54. The nut may consist of a threaded cleat 61 fixed to the sub-carriage 54. The motor 57 can be mounted on a block 62 in which the screw 59 will be pivoted and which will be connected to the support 25. These electrical connections have not been shown in the drawing.

The development units 45, 47, 49 and 51 are arranged on the carriage 53 in the order in which it is desired to transfer the four images developed on the receiver to the transfer station 37.

Thus, if the developed images are transferred in the order cyanide, magenta, yellow and black, this order will be adopted for the colors of tack in the tanks of the development units 45, 47, 49 and 51, respectively, it being admitted that the sub-carriage 54 moves to the left. (See the double-headed arrow which indicates the directions of movement of the carriage 53-54.)

In operation, when a multi-color image is to be reproduced, the apparatus is synchronized and programmed so that the carriage 53 advances step by step to the left, causing the tacker applicator roller of the developing unit 45 to cooperate with the base of the electrophotographic drum 21 a short time before the arrival of the leading edge of the first latent image applied to the exposure station 33. This gives the applicator roller of the unit 45 sufficient time to allow it to start to take the colored tacker from its tray to ensure good development. Alternatively, the applicator rollers can be driven slowly and in rotation, continuously, to keep the tacker flowing on the surfaces of the rollers. A friction drive capable of being overcome can be used to drive the applicator rollers.

The carriage 53 maintains the developing unit applicator roller 45 in engagement with the drum 21 for a period of rest until the complete applied latent image of the particular color of the unit 45 has been provided with a tacker. The rotation of the drum produces or accompanies the rotation of the applicator roller. In the blank areas between the latent images, for a fraction of a turn of the drum 21, the carriage 53 is advanced one step to the left of the figure, then bringing the applicator roller of the second developing unit 47 into engagement with the base of the drum 21. The applicator roller of the development unit 45 is then free, having moved to the left of the development station. This development unit 47 will apply the magenta tacker from its tank to the drum 21 at the development station to provide the second latent image applied by the laser system with tackers. It remains in position for the same stop time as previously.

The first image provided with cyanide tacker is brought by the drum 21 to the transfer station 37 where it is transferred to the receiving sheet S carried by the transfer roller 65. Any tacker remaining on the surface of the drum 21 is removed from the station 39 by a cleaning device 67 such as a vacuum device or an ultrasonic device so that the photoconductive coating on the drum 21 is ready for the next image, to be produced during the next rotation. Thus, when the carriage 53 and the sub-carriage 54 are moved one step to the left to bring the applicator roller of the developing unit 47 into engagement with the base of the roller 21, there may still be a portion of the image previously provided with a tacker turning towards the transfer station 37 to the left of the roller 21, and the following image can already be partially applied in latent form on the right part of the drum 21 and be moved towards the development station 35 .

In this way, the carriage 53 advances step by step to the left and stops once for each revolution of the drum 21 until it has brought the four development stations 45, 47, 49 and 51 into engagement with the drum 21 and that the four developed images have been transferred to the paper S.

This can be considered as a complete cycle made of four steps and four stops since the complete multicolored image was thus produced. One revolution of the transfer roller 65 can be used to eliminate the receiving element S while the drum 21 rotates freely released from the development station. At this time, the motor 57 can be programmed to reverse the direction of rotation of the screw 59 to return the sub-carriage 54 to its initial position, to the right of the drawing. It does not need to be done step by step. Preferably, contact and / or transfer of tack between the applicator rollers of the developing units 45, 47, 49 and 51 and the drum 21 is avoided during the return stroke. For example, the entire carriage 53 may be mounted on springs which, in turn, will rest on the sub-carriage 54 directly driven by the screw 59. A simple cam, a relay, a lever or the like can pull the carriage 53 slightly down towards the sub-carriage 54 and hold the latter while the sub-carriage 54 moves to the right, during the return stroke to its initial position, by releasing it afterwards.

Alternatively, the drum 21 and the transfer roller 65 may be moved slightly upward during the return movement.

Another variant would consist in allowing contact of the applicator rollers with the drum 21 during the return and in providing means such as 63 for cleaning the drum 21 from any tacker which could be brought to the virgin part of the drum 21 during its movement. Another variant, but which is not preferred, consists in reversing the order of transfer of the colored images on sheets of paper S. Thus, the laser system 19 would be controlled by the computer 15 to reverse the order of writing of the colored images and the latent images would be developed in the order 51, 49, 47 and 45 during the return stroke of the sub-carriage 54 and of the carriage 53, from left to right, step by step.

In any event, the various components must be synchronized, in motion and in operation, in such a way that, when a particular color image is written by the laser system 19 on the drum 21, it reaches the development station 35 at the moment when the applicator roller of the development unit of this same color is in contact with the base of the drum 21. Thus, each latent electrostatic image is developed with its own colored marker and in the correct order.

After the latent electrostatic image has been developed at the development station, an excess of tacker is removed from the surface of the drum 21 when the developed image is brought into the transfer station 37 by a vacuum knife 63 disposed along of the trajectory between these two stations. At the transfer station 37, the developed image is transferred onto a sheet of support material S such as paper from a reserve of such sheets indicated at 64.

A transfer roller 65 is located at the transfer station 37 and is mounted to rotate in the direction indicated by the arrows and is in any suitable manner driven at the same linear surface speed as the drum 21. A sheet of material of support S is brought on guides 67 by a supplying mechanism whose suction cups are represented at 68 and is brought into contact with the transfer roller 65. By any known means, such as electrostatic attraction, the sheet S is wound and is held firmly on the peripheral surface of the transfer roller 65 while the latter is rotated.

After each developed image has been transferred to the receiver or S sheet wrapped around the transfer roller 65, the drum surface 21 moves clockwise through the area which is designated as the station from s

10

15

20

25

30

35

40

45

50

55

60

65

638,061

6

cleaning 39. At this station, an excess of tack which can remain on the surface of the drum 21 after the transfer is eliminated by the cleaning device 67 which, as mentioned above, can be constituted by vacuum pipes or by an ultrasonic device which eliminates and / or dissipates the remaining vireur.

Charging, imaging, developing, transferring and cleaning are repeated for each of the colored images. If there are three, the total number of images transferred to the receiving sheet is three. If there are four colored images, the total number of transferred images is four. These images must be in perfect coincidence, which can be easily obtained with this device. The mixing of the colors, in order to obtain the reproduction by the use of toners of different basic colors such as cyanide, magenta, yellow and black, must be carried out by considering their transparency and perhaps other characteristics which , of course, are known to those skilled in the art. Obviously, the character of the tacker must be taken into account in order to obtain the most realistic results.

When the final composite colored image has been produced, the individual colored images being formed on the receiving sheet by a series of consecutive transfers of the various multiple colors, the rollers 21 and 65 rotate together at the same speed. These rollers are of the same diameter. Therefore, the number of turns of each of them in order to produce a single composite colored image on the receiver S is equal and consists in the number of colors producing the final composite colored image. Normally, this number is four and the receiving sheet S is held in place at the periphery of the roll while this is being done.

When the composite image has been completed and all the colors which produce it have been transferred to the sheet S, the image is for example of a series of four images provided with a tacker, but not fixed, superimposed. At this point of machine operation,

either before the sheet S is released from the transfer roller 65, or immediately thereafter, the composite colored image provided with a tacker is fixed to the sheet by passing it through a fixing device 69. This can be a heating or other suitable means of attachment. For example, instead of applying heat, the device 69 can roll or spray a protective coating layer, made of glassy resin, on the finished composite image. There are different forms of material which are transparent and relatively resistant to abrasion and which are used for the protection of inked or tacked images and which can be applied for this purpose. Preferably, a glossy finish is desired to give the resulting image a certain appearance of depth. The finished sheet S is brought to the left in the drawing and deposited in an outlet hopper 73.

s After the development device 43 has been returned to the right, in its initial position, which is illustrated in the drawing, the apparatus 11 has completed its complete cycle and is ready to make another composite copy with the same information from computer memory or by means of different information contained in said memory.

Additional tacker for the development units can be stored in tanks 75, 77, 79 and 81 mounted at the bottom of the frame 25 which can be fitted with pumps and flexible hoses to allow the transfer to the respective tanks of the development units. 15 ment.

Although the invention has been described with reference to making colored copies or colored originals, it should be noted that the apparatus can also be used, if desired, to make black and white copies from black and white originals or to make black and white copies of colored originals.

During the operation of the apparatus 11, the programming of the functions of the various components can be carried out by suitable programming means such as banks or relays, shafts, cams or the like. Preferably, the operation is programmed by the computer with suitable control and / or trigger signals which are transmitted on the lines 100 to the various motors and drive devices, etc., of the apparatus.

The achievement of the coincidence of the images superimposed on the paper element S depends on a precise construction and on the synchronization of the mobile elements of the apparatus 11, but adjustments can be made either by mechanical means controlled manually, or by automatic observer devices, laser pattern adjustment and / or a combination of all of these.

In the claims, reference is made to a cycle, which generally means a revolution of the drum 21 and the transfer roller 65 during which a colored print is produced and is transferred. For a complete four-color composite image, four such cycles will be required, the complete process or complete cycle being completed after the sheet S has been released, its composite image, fixed and / or coated, deposited in the output hopper , the developing device returned to its initial position and the device made ready for the next series of cycles or rotations.

25

30

35

R

1 drawing sheet

Claims (22)

638,061 1. Method for electrostatic color printing in which the individual colors of a colored composite image are stored digitally in a computer and are capable of being called up separately for laser writing on an electrophotographic element, comprising the use of a rotating electrophotographic drum and a transfer roller arranged to carry an element of receiving material pressed against the rotating electrophotographic drum, charging the drum, exposing the charged drum to a color image of the element composite, to provide the image with a tacker and to transfer the image provided with a tacker to the element of receiving material, characterized in that the exposure consists in calling up and writing with the laser said image and in carrying out said operations all during a single revolution of the drum flowing during a single and simultaneous rotation of the transfer roller, and by the fact that the loading operations e, writing, applying the transfer and transfer for each color of the composite element are repeated during each subsequent revolution of the drum and the transfer roller until all the colors have been transferred on top of the element of receiving material, the latter being then removed from the transfer roller and replaced by another in order to allow the repetition of the process on said replacement element. 2. Method according to claim 1, characterized in that each latent electrostatic image corresponding to one of the components of the colored image of the colored original is formed during one revolution of the rotary element, each latent electrostatic image thus formed being developed with a material whose color corresponds to the color of the image component of the latent electrostatic image by moving a plurality of developing units each containing a material of different color opposite said electrophotographic element in succession and in a controlled timing sequence, such that each developing unit independently develops a respective latent electrostatic image during its revolution and that each image is transferred so as to apply in sequence to a sheet of support material in relation superimposed as much colors that the rotating element makes of turns. 2 3 638,061 3. Method according to one of claims 1 or 2, characterized in that the plurality of latent electrostatic images are formed by charging said electrophotographic element and then writing the latent electrostatic images thereon in succession using a laser modulated by digital information derived from the colored original. 4. Method according to any one of claims 1 to 3, characterized in that each of the latent electrostatic images is developed by application of a liquid indicator. 5 5. Method according to claim 1, characterized in that said plurality of latent electrostatic images comprise at least three latent electrostatic images, each being arranged to produce a developed image of a different color. 6. Apparatus for carrying out the method according to any one of claims 1 to 5, for making one or more colored copies of a colored original, electrostatically, comprising a rotating electrophotographic element, means for driving for said electrophotographic element following itself in a cycle by a series of processing stations arranged along its periphery, said processing stations comprising, in order, a charging station, an exposure station, a processing station developing and an image transfer station, means for applying a uniform electrostatic charge on a part of the electrophotographic element to the charging station, characterized by: A. means for sequentially forming a plurality of latent electrostatic images on said electrophotographic element at the exposure station during the rotation of said electrophotographic element, each of said electrostatic images corresponding to a color image different from the components of the colored original and each image being formed during a respective cycle, B. a developing device capable of moving in the developing station along a path which is generally tangential to said rotating electrophotographic element, said developing device comprising a plurality of developing units arranged in a row and arranged in a manner to pass through the development station successively, each development unit having a tack development material, the color of which corresponds to the component of the colored image of one of the latent electrostatic images, C. drive means for driving said development device step by step along its tangential trajectory through said development station in time relation with the formation of the corresponding colored latent images and bringing the development units in relation to application of a tacker to the electrophotographic element in series when each unit is in said station, said drive means operating so as to advance step by step each development unit in said development station, and then to maintain this during a sufficiently long downtime, then advancing said development unit step by step out of the development station while simultaneously bringing the next unit into the station, the part of the electrophotographic element having a color corresponding to the latent image of each development unit fully traversing the development station during the downtime that their respective development unit marks in said station, and D. a transfer device at said transfer station for transferring each developed image onto a sheet of superimposed support material when each developed image passes through said transfer station during its respective cycle, the number of cycles corresponding to that colors and that of the prints on each sheet. 7. Apparatus according to claim 6, characterized in that it comprises a coding converter transforming the original color into digital color coded information and a laser having an output modulated as a function of said digital information for writing each of said plurality latent electrostatic images on said electrophotographic element. 8. Apparatus according to one of claims 6 or 7, characterized in that each development unit comprises a tray and a tack applicator in transfer relationship with the electrophotographic element, the development material whose color corresponds to the image color component of said electrostatic image being a liquid toner disposed in the container in contact with the applicator. 9. Apparatus according to claim 8, characterized in that the applicator is a roller. 10 10. Apparatus according to one of claims 6 to 9, characterized in that it comprises three development units each for a different color. 11. Apparatus according to one of claims 6 to 10, characterized in that the development device comprises a carriage arranged on a track and a stepping motor connected to said carriage to move the latter along said track. 12. Apparatus according to claim 11, characterized in that the developing device is moved step by step in one direction on said tangential path while said cycles are executed, and by the fact that said carriage is brought back in its opposite direction. initial position after the execution of said cycles for each fully developed image so that the carriage is ready to move step by step in said first direction for the next series of cycles. 13. Apparatus according to one of claims 6 to 12, characterized in that said tangential path is rectilinear. 14. Apparatus according to one of claims 6 to 13, characterized in that the transfer device comprises a rotary transfer cylinder. 15. Apparatus according to claim 14, characterized in that the transfer cylinder comprises means for selectively holding and releasing the sheet of paper material to move the latter along a path away from said transfer cylinder. 15 16. Apparatus according to one of claims 14 or 15, characterized in that the rotary electrophotographic element and the rotary transfer cylinder are in close contact along an axial line of the surface of each of them, are of the same diameter and are driven at the same speed. 17. Apparatus according to one of claims 6 to 16, characterized in that it comprises a cleaning station arranged so as to remove the residual tack from said electrophotographic element after the image developed on said electrophotographic element has passed through said image transfer station, this cleaning station also being located along the periphery of said electrophotographic element between said image transfer station and said exposure station. 18. Apparatus according to claim 17, characterized in that said cleaning station comprises an ultrasonic cleaner. 19. Apparatus according to claim 15, characterized in that it comprises a fixing station arranged so as to fix the images developed on said sheet of support material after all the developed images of a complete series of prints have been applied to said sheet. 20. Apparatus according to claim 19, characterized in that the fixing station is adjacent to the path of said sheet after it has been released. 20 25 30 35 40 45 50 55 60 65 21. Apparatus according to claim 19, characterized in that the fixing station comprises a coating device applying a protective coating to said developed images. 22. Apparatus according to claim 19, characterized in that it comprises a coating station adjacent to the fixing station for applying a coating layer to said sheet after it has passed through said fixing station. Known methods and apparatuses for making color copies of color originals by electrostatic techniques include the operations of optically projecting the color images of the original onto a single charged electrophotographic element or onto a plurality of charged electrophotographic elements, one for each color, to form corresponding latent electrostatic images, to develop each of the latent electrostatic images with its own color and then to fix each image in superposition. The images projected onto the electrophotographic elements are obtained by projecting an image of the original onto said electrophotographic element by a plurality of color separation filters, one per color to be reproduced. Depending on the system employed, the final composite image was either formed directly on a single electrophotographic element, or transferred from one or more electrophotographic elements onto a sheet of support material such as paper. Although several different types of electrostatic systems have been proposed or produced, these systems have proved unsatisfactory. Some of the reasons are that the resulting apparatus is too large in size, too complicated in its construction, too expensive to manufacture and operate, insecure and / or not capable of producing images having a quality of resolution compatible with copies. made by photographic and / or lithographic techniques. In addition, these systems are not capable of effecting changes in color, size or shade of the final color if such changes are either desired or required, if not by means of very complicated and costly arrangements involving changes in the process . An electrophotographic film is now available, it has qualities and properties making it very superior to all the electrophotographic films known previously. This electrophotographic film has a photoconductive coating which is fully inorganic, micro-crystalline, electrically anisotropic which does not exhibit reciprocal or intermittent effects, operates at low voltage, has very high sensitivity and can produce gunshot images. exceptionally high quality from either analog or digital information. This electrophotographic film is particularly suitable for making high resolution color copies of color originals by means of electrostatic techniques and, in fact, has properties which allow its use for this purpose in a manner which, until now , could not be obtained with other types of electrophotographic elements. Due to the high response speed of said coating (capable of being exposed in nanoseconds), the device may include a high speed machine. Among the suggestions made previously, the following USA patents belong to the field of the invention: LUSHER 3,399,611 SMITH 3,690,756 NAGAMATSU et al 3,832,170 KATAYAMA et al 4,095,879 WATANABE et al 4,120,577 BARASCH 4,124,286 It does not appear that the above-mentioned documents are not relevant to the invention, that the devices they describe are analogous to that of the invention and that the invention is the equivalent of what is described in none of them. Accordingly, the invention provides a method for electrostatic color printing in which the individual colors of a colored composite image are stored digitally in a computer and are capable of being called up separately for laser writing on an electrophotographic element. , comprising using a rotating electrophotographic drum and a transfer roller arranged to carry an element of receiving material pressed against the rotating electrophotographic drum, loading this drum, exposing the loaded drum to an image of '' a color of the composite element, of providing the image with a tacker and of transferring the image provided of a tacker onto the element of receiving material, characterized in that the exposure consists in calling up and writing by laser said image and to carry out said operations all during a single revolution of the drum flowing during a single and simultaneous rotation of the transfer roller, and by the fact that the operations of loading, writing, application of tack and transfer for each color of the composite element are repeated during each subsequent revolution of the drum and of the transfer roller until all the colors have been transferred superimposed on the receiving material element, the latter being then removed from the transfer roller and replaced by another in order to allow the repetition of the process on said replacement element.