US3420151A - Apparatus for electrophotographic printing - Google Patents

Description

APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed NOV. 16, 1955 Jan. 7, 1969 s. w. LEVINE ETAL Sheet mm i v w iwkmyn wzfimoowu 5 0mm M LV W P mmw %f4 1 N M H A I m W Y B APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed NOV. 16. 1965 Jan. 7, 1969 s. w. LEVINE ETAL Sheet DE 3 KAN 0 2 0L E TEv H Illlllll N E Il VO 3 u fl m1 mc U n U Q MM O A s a H J I, l R i M A 2 3 .1 m T. Wm E S 0 0 c Z/K United States Patent 3,420,151 Patented Jan. 7, 1969 ice 3,420,151 APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Samuel W. Levine, Westbury, and John S. Copeland, Stony Brook, N.Y., assignors to Fairchild Camera and Instrument Corporation, Syosset, N.Y., a corporation of New York Filed Nov. 16, 1965, Ser. No. 508,055 U.S. Cl. 355- 4 Int. Cl. G03g /00 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to apparatus for electrophotographic printing and more particularly to the continuous and automatic printing and developing of electrophotographic color images in which electrostatic forces are used to selectively deposit particulate matter directly onto the printing medium.

There is today an ever-increasing awareness by manufacturers of the advantages to be gained by the use of outdoor advertising. This is due to the ever-increasing use of automobiles and other modes of mass transportation in this country. The outdoor advertising field in its infancy relied primarily upon black and White advertisements but in the last few years these have been almost entirely surplanted by large size color panels.

The present state of the art of outdoor advertising is such that if the supply of color bulletins required is sufficiently large a set of lithographic printing plates is prepared and the required panels are then reproduced in quantity. If only a few panels are required the bulletin boards are generally individually painted by hand. In the latter case the time involved from receipt of the original art work to completion of the final product is generally a matter of months. The reason for resorting to the individual painting of bulletin boards is that it has heretofore been considered economically impractical to produce small quantities of large size color panels.

In view of the aforegoing it is a primary object of the present invention to provide apparatus for improved electrophotographic color printing.

A further object of the present invention-is to provide apparatus for electrophotographic color printing which will permit the economic production of small quantities of large size color panels.

Yet another object of the present invention is to provide improved apparatus for electrophotographic color printing which will permit rapid, continuous and automatic printing and developing of electrophotographic images.

These and further objects, features and advantages of the present invention will appear from a reading of the following detailed description of one embodiment of the invention which is to be read in conjunction with the accompanying drawings wherein like components in the several views are identified by the same reference numerals.

In the drawings:

FIGURE 1 is a vertical cross-section of apparatus for electrophotographic color printing in accordance with the present invention, only portions of the apparatus being shown for purposes of clarity;

FIGURE 2 is a cross-section taken on the lines 22 of FIGURE 1; and v FIGURE 3 is a top view of the apparatus illustrated in FIGURE 1 and illustrating the projection and printing cylinders of the present invention.

Briefly stated, the apparatus of the present invention basically consists of two cylinders that rotate synchronously thereby permitting information on separation transparencies to be enlarged and recorded by electrostatic means onto a specially coated material. The art Work to be printed is converted into a color transparency and from this original a set of color corrected screened positives are produced corresponding to the primary colors to be printed. In this manner, for example, the art work to be printed is converted into four (4) color separation records corresponding to the black portions of the original art work plus those portions containing the basic colors yellow, magenta and cyan. In the preferred form of the invention slit scan projection techniques are employed in order to product full size color panels.

The copy cylinder is transparent and is provided with a slit and a light source which projects an image through the slit as the copy cylinder rotates past the slit. The copy cylinder preferably has means for mounting the four (4) color separations in the proper sequence so that the desired registration is obtained. In this manner when the four color separations are placed end to end along the circumference of the copy cylinder they will be in register with each other. As the copy cylinder rotates pas the slit the light source projects the image through a len: onto a billboard panel which is secured to the recording cylinder. In this embodiment the copy cylinder makes 2 a quarter revolution for each full revolution of the record ing cylinder.

Located about the periphery of the recording cylinde are means for electrostatic charging, color development image fixing and if desired solvent recovery. Once thi panels have been fastened to the recording cylinder it i indexed to the start position in the same manner as th copy cylinder. When the apparatus is started both th copy cylinder and the recording cylinder rotate synchro nously, the copy cylinder preferably being slaved to th recording cylinder by a servo mechanism. As the panel on the recording cylinder pass under a corona discharg device the photo-conductive surface becomes electrostat ically charged and becomes light sensitive. Selective di: charging of the photoconductive surface takes place as function of the image projected from the copy cylindei As the cycle progresses the latent image on the panel 5 immersed in developing tanks where colored particle are selectively attracted to the charged areas. The imag which is now visible proceeds to the next station wher the material is dried and fixed.

Referring now to the drawings and particularly 1 FIGURE 1, there is illustrated in schematic form app: ratus for electrophotographic color printing in accordanc with the present invention, Although the invention wi be described with reference to the printing and processir of color images it is to be understood that the inventic is applicable as well to the printing and developing 1 black and white images.

In the application of the apparatus of the present inve: tion for printing large size color panels the original a Work is first concerted into a color transparency fro. which a set of preferably four (4) color corrected screen: positives are prepared. In this way the color image be reproduced is divided into the three basic colors pl black, that is, into cyan, magenta, yellow and black. 1 a result four different positives are obtained, one pot tive representing only the cyan portion of the image to be reproduced, one positive representing the magenta portion of the image to be reproduced, one positive representing the yellow portion of the image to be reproduced and one positive representing the black portion of the image to be reproduced.

Once the color separation is completed the result is four color separations, 10, 11, 12 and 13 consisting of the cyan, magenta, yellow and black portions of the color image to be printed. These individual color separations can be placed individually on the copy cylinder 14, or, if desired, they can be placed simultaneously on the copy cylinder 14 as illustrated in FIGURE 1 with each positive transparency occupying approximately one quarter of the periphery of the copy cylinder.

The copy cylinder 14 must be transparent or translucent and is therefore made from a material such as glass, transparent plastic or similar materials. As illustrated in FIGURE 1 a light source 15 is mounted within the copy cylinder 14. The positioning of the light source is not critical. The light source 15, however, must be so selected as to have a wave length that is compatible with the surface to be printed, that is, the spectral response of the surface to be printed must be matched with the wave length of the light source. As a typical example if a zinc oxide surface is being used as the printing medium the wave length of the light source 15 must be so selected that it is compatible with the spectral response of the zinc oxide printing surface.

A condensing lens 16 is mounted within the copy cylinder 14 in order to concentrate the light emanating from the light source 15. The presence and positioning of this lens, however, is neither critical nor essential, but is desirable. Radiant light energy which focuses in a different plane is removed with a suitable filter (not illustrated). If desired panchromatic coatings may be employed which obviate the restriction on the use of a particular light source or filter.

The copy cylinder 14 is provided with any well-known registration device so that when each succeeding separation 10, 11, 12 or 13 is projected, its images will coincide with the preceding separation. In one form, for example, a register board may be utilized which contains permaient optical register marks and a mechanical punch. The register marks on each sheet of film 10, 11, 12 or [3 are manually aligned using a microscope with the Jermanent marks on the register board. The punch is then )perated producing a set of holes in each film, the holes then being used to mount each film on the copy cylinier 14 in the proper alignment. In this manner optical 'egistration has been converted into a mechanical method )f alignment.

The copy cylinder 14 is enclosed in a light proof housng 17. The light proof housing 17 has an opening or lit- 18 on the side facing the recording cylinder 19. The vidth of the slit or opening 18 in the housing 17 is related iroportionately to the area of the image that is to be proected on the recording cylinder 19, that is if the slit .8 occupies 3% of the periphery of the copy cylinder 14, he projected image will occupy 3% of the periphery of be recording cylinder 19.

The projection lens is positioned between the copy ylinder 14 and the recording cylinder 19. The positioning f the projection lens 20 depends upon the enlargement equired and the focal length of the projection lens. n one embodiment of the invention the recording cyliner 19 has a diameter ten times greater than the diameter f the copy cylinder 14. The focal length and position- 1g of the projection lens 20 are so selected as to sharply sons the image on the periphery of the recording cylin er on a scale ten times that of the image on the copy ylinder 14.

The recording cylinder 19 is made from any material 'hich is non-reactive with the developing solution and l preferably made from stainless steel. As indicated in 4 FIGURE 3 the copy cylinder 14 and the recording cylinder 19 are both driven by a motor 21 which drives the two cylinders through a servo system 22 so that the two cylinders rotate in synchronism.

The recording cylinder 19 is belt driven directly by synchronous motor 21. This arrangement insures that recording cylinder 19 rotates at constant speed and thereby minimizes the generation of visible bands in the reproduction. Attached to the end of shaft 36, on which drum 19 is mounted, is a servo transmitter motor 39 which transmits to the servo control unit 38 information giving the instantaneous angular position of drum 19. Attached to the end of the shaft of the copy cylinder 14 is the servo motor 37. The signal for causing the rotation of servo motor 37 comes from the servo control unit 38. This servo system consisting of transmitter motor 39, control unit 38, and servo motor 37, insures that copy cylinder 19 and recording cylinder 14 rotates synchronously. The servo system may take any desired form in order to ensure that the two cylinders rotate in synchronism.

It is essential to the proper functioning of the apparatus of the present invention that some means be provided on the copy cylinder 14 for aligning the projected image on the recording cylinder. This can either be done automatically or manually when the color separations are placed on the copy cylinder. As explained above the alignment or registration is preferably accomplished by means of a register board. This assures not only registration of the positives on the copy cylinder 14 but also that the projected image is properly aligned on the recording cylinder 19.

In the operation of the invention the surface to be printed which is a flexible sheet 23 coated with a photoconductive material is in some manner affixed to the periphery of the recording cylinder 19. The printing surface 23 must have a conductive surface which is covered with a photo-conductive material. If desired, it is possible to print directly on paper provided that the paper passes through a salt solution or other solution such that the paper for a short period of time is conductive prior to being subjected to a corona discharge. The timing of such an operation, however, must be such that the conductive material such as salt is present for only a short period of time prior to development since a substance such as salt has a detrimental effect on the photoconductive surface which is coated on the paper.

As illustrated in FIGURE 1 the printing material 23 is positioned about the periphery of the recording cylinder 19 and is maintained in this position by the guide rollers 24 which maintain the printing material 23 in contact with the periphery of the recording cylinder 19. A corona discharge device 25 is positioned adjacent the periphery of the recording cylinder 19 just prior to the point that the surface 23 is subjected to the light image emanating from the copy cylinder 14. A drying and fixing station 26 is also positioned adjacent the periphery of the recording cylinder 19 at a point after the printing 23 passes through the developing tank 27. The function of the drying and fixing station 26 is to dry the development material and apply a coating over the printed material in order to fix the developing material to the printing surface 23.

Once the color separations transparencies 10, 11, 12 and 13 are affixed about the periphery of the copy cylinder 14 and properly aligned in the manner described above the printing material 23 is positioned about the periphery of the recording cylinder 19 and the motor 21 is started which causes the copy cylinder 14 to rotate in synchronism with the recording cylinder 19 by virtue of the servo system. The photoconductive surface of the printing material 23 is subjected to a corona discharge by the unit 25 and the charged surface is then subjected to the light image being projected from the copy cylinder 14. The projected light image in the usual manner selectively discharges portions of the charge on the surface 23 leaving an electrostatic positive of the image being projected. The sensitization of the printing surface 23 may be accomplished by a corona discharge device employing a continuous high voltage DC source which ionizes the atmosphere surrounding a fine wire, or any other means may be used for sensitizing the printing surface 23. As mentioned above after leaving the charging station 25 the printing sheet 23 is exposed to the light image being projected from the copy cylinder 14. Selective discharging takes place as a function of the projected image and the printing sheet 23 then contains an invisible charge image which is subsequently made visible by immersion in the developing solution contained in the developing tank 27.

In the form of the invention illustrated in FIGURE 1 the recording cylinder 19 makes one revolution for each corresponding separation projected onto it. As an example the recording cylinder 19 makes one complete revolution for every one quarter revolution of the copy cylinder 14. In this manner, for example, the color separation 10, which covers one quarter of the periphery of the copy cylinder 14, passes by the slit 18 during the time that the recording cylinder makes one complete revolution. It is to be understood, however, that the invention is equally applicable where the copy cylinder rotates at the same rate of rotation as the recording cylinder.

The developing solution 28 consists of electroscopic particles of different colors which are suspended in an insulating carrier, for example, a fluorinated hydrocarbon such as Freon T.F. The particles are selectively attracted to the charged or image areas on the surface of the printing sheet 23. The developed image then passes through the fixing station 26 where the surface of the printing material 23 is dried and the printed surface is sprayed, for example, with a resinous overlay to fix the toners and developers to the surface 23 of the printing material.

When the apparatus of the present invention is being utilized for color printing the same procedure may be utilized as described in patent application Ser. No. 445,794 which was filed on Apr. 5, 1965, and which is assigned to the same assignee as this patent application. As explained in that patent application the photoconductive surface of the printing material 23 is sequentially exposed to the cyan, magenta yellow and black portion of the image to be reproduced, these portions corresponding to the color separations '10, 11, 12 and 13. When, for example, the printing surface v23 is exposed to color separations such as corresponding to one color the developer after being deposited on the electrostatic image is fixed and subsequent layers are then placed over this image and onto the base material. The resultant multi-layer image produces the same colors as the original copy being reproduced.

In one form of the invention the developing station 29 consists of a developing tank 27, which is divided into four compartments 30, 31, 32 and 33. Rollers 34, 35, 36 and 37 are positioned above each compartment of the tank 27 and are movable vertically such that the rollers can be immersed in the developing solution 28 in each compartment. The various tanks 30, 31, 32 and 33 contain the proper developers for developing the various colors corresponding to the color separations 10, 11, 12 and 13, i.e. one compartment for black, one compartment for yellow, one compartment for magenta and one compartment for cyan. In the step illustrated in FIGURE 1 the printing surface 23 has already had applied to it an image corresponding to one color and an overlay corresponding to the second color has been applied to the surface 23 and is being developed. As the printing surface 23 passes over the guide roller 24 a sequencing means (not illustrated) is activated in order to move the roller 35 vertically downward so that it is immersed in the developer 28 in the compartment 31. In this manner, as the printing surface 23 passes over the roller 35 it also passes through the developer solution in the compartment 31. After leaving the compartment 31 the printing sheet 23 passes through to the drying and fixing station 26.

The proper tension on the printing sheet 23 is maintained by the roller 38 which is spring biased against the sheet 23 by means of the spring 39. As illustrated in FIGURE 2 when one of the rollers 34, 35, 36 or 37 is moved vertically downward into one of the compartments 30, 31, 32 or 33 the roller 33 is moved upwardly against the force of the spring 39. When the roller 35, for example, returns to its original position the roller 38 is returned to the position indicated in dotted lines by the action of the spring 39. The sequence of operation is as follows.

The color separations transparencies 10, 11, 12 and 13 are placed about the periphery of the copy cylinder 14 and are properly aligned and registered. The surface 23 to be printed is then placed about the periphery of the recording cylinder 19. The motor 21 is then started and the surface of the printing material 23 is subjected to a corona discharge by the unit 25. The light from the copy cylinder 14 impinges upon the charged surface 23 bleeding off a portion of the charge and leaving an electrostatic positive of the image being projected. The developing station 29 is then indexed such that the roller 34 is moved vertically downward to be immersed in the developing solution in the compartment 30. After all of the surface of the printing material 23 has passed through the developer in the compartment 30 and passed the fixing station 26 the surface of the printing material 23 is again subjected to a corona discharge and light from the second color separations 11. The developing station 29 is then indexed to the position illustrated in FIGURE 1 so that the printing surface 23 passes through the developer in the second compartment 31. This practice is repeated for each color separation 12 and 13 such that the surface 23 has then deposited on it a multi-layer deposit corresponding to the four images, the composite being a duplicate of the surface to be duplicated.

In one embodiment of the invention each compartment 30, 31, 32 and 33 at the developing station 29 has a perforated screen which is so positioned that it is spaced approximately 0.050 of an inch from the perimeter of the recording cylinder. This perforated screen functions as a fixed electrode and eliminates the edge effect which results when no electrode is present. If desired a floating, rather than a fixed, electrode can be used. Such a floating electrode is described in copending patent application Ser. No. 445,794 filed on Apr. 5, 1965 and assigned to the same assignee as the subject patent application.

It is to be noted that the resinous overlay is applied to the surface 23 only after the final color has been developed, i.e. after the unit has been indexed to four (4-) developing stations. It has been found that for optimum results the printing surface 23 should remain in each developing compartment 30, 31, 32 and 33 for approximately 10 to 30 seconds and that approximately 10 seconds should be allowed for drying before the surface 23 is immersed in the next compartment. These timed relationships are correct where the carrier used in Freon T.F. and the times must be adjusted for other carriers.

If desired a solvent recovery station can be provided in order to promote rapid drying and to conserve the highly volatile carrier. In addition a station may be provided for automatically replenishing the toner particles as they are consumed.

Since many of the portions of the apparatus of the present invention are light sensitive the entire apparatu: must be enclosed in a light tight enclosure. In practicr it is preferred that the entire printing and developing pro cedure be conducted in a darkroom.

What has been described is an apparatus for the con tinuous and automatic printing and developing of multi color electrophotographic images. It is to be understoot that although a preferred embodiment of the inventior has been described changes and modifications may bl made thereto without departing from the scope of the invention for which reference should be made to the appended claims.

What is claimed is:

1. Apparatus for electrophotographic color printing of a color image on a flexible printing sheet having one surface thereof coated with photoconductive material, said color image being in the form of a plurality of flexible transparent image sheets with each image sheet containing a color separation record corresponding to a primary color in said color image whereby when images from each color separation record are superimposed said color image is reproduced, said apparatus comprising a rotatable copy cylinder the surface of which is transparent to the passage of light therethrough, a light source mounted within said copy cylinder, a rotatable recording cylinder spaced from said copy cylinder, said copy cylinder being constructed to simultaneously hold said plurality of image sheets serially about its periphery to rotate therewith, said recording cylinder being constructed to hold said flexible printing sheet about its periphery to rotate therewith and with said coated surface exposed, means for electrostatically charging the coated surface of said printing sheet whereby as said copy cylinder rotates said light projects images of said color separation records onto the charged surface of said printing sheet to form electrostatic reproductions of same, means for developing said electrostatic reproductions, and motor means for driving said copy cylinder and said recording cylinder in synchronized relationship permitting superimposed printing on said printing sheet of images of said color separation records thereby reproducing said color image.

2. Apparatus in accordance with claim 1 wherein said copy cylinder is enclosed in a light tight enclosure, said enclosure having an opening therein opposite said recording cylinder through which light can pass.

3. Apparatus in accordance with claim 2 wherein servo means are used for slaving one of said cylinders to the other so that they rotate in synchronism.

4. Apparatus in accordance with claim 3 wherein said apparatus is all enclosed in a light tight enclosure.

5. Apparatus in accordance with claim 4 wherein said copy cylinder includes registration means for aligning said image sheets on the surface of said copy cylinder.

6. Apparatus in accordance with claim 5 wherein a fixing station is disposed adjacent said recording cylinder for fixing said developed electrostatic reproduction.

7. Apparatus for electrophotographic color printing of a color image on a flexible printing sheet having one surface thereof coated with photoconductive material, said color image being in the form of a plurality of flexible transparent image sheets with each image sheet containing a color separation record corresponding to a primary color in said color image whereby when images from each color separation record are superimposed said color image is reproduced, said apparatus comprising a rotatable copy cylinder the surface of which is transparent to the passage of light therethrough, a light source mounted within said copy cylinder, a rotatable recording cylinder spaced from said copy cylinder, said copy cylinder being constructed to simultaneously hold said plurality of image sheets serially about its periphery to rotate therewith, said recording cylinder being constructed to hold said flexible printing sheet about its periphery to rotate therewith and with said coated surface exposed, means for electrostatically charging tha coated surface of said printing sheet whereby as said copy cylinder rotates said light projects images of said color separation records onto the charged surface of said printing sheet to form electrostatic reproductions of same, means for developing said electrostatic reproductions, said developing means including a develop ing tank having developing solutions therein for developing the electrostatic reproduction on said printing sheet, roller means for directing said printing sheet through said developing solution after said printing sheet has had said electrostatic reproduction formed thereon, and motor means for driving said copy cylinder and said recording cylinder in synchronized relationship permitting superimposed printing on said printing sheet of images of said color separation records thereby reproducing said color lmage.

8. Apparatus in accordance with claim 7 wherein said motor means rotates said recording cylinder n times faster than said copy cylinder, where 11 corresponds to the number of said flexible transparent image sheets positioned about the periphery of said copy cylinder.

9. Apparatus in accordance with claim 8 wherein said developing tank has n departments pigmented to correspond to a primary color in said color image.

10. Apparatus in accordance with claim 9 wherein said roller means has at least n rollers, each positioned above one of said departments and adaptable to be immersed in said one department.

11. Apparatus in accordance with claim 10 wherein said roller means includes means for sequentially immersing said rollers in one of said departments after completion of one rotation of said recording cylinder.

12. Apparatus in accordance with claim 11 wherein a fixing station is disposed adjacent said recording cylinder for drying said printed sheet after it leaves said developing tank.

References Cited UNITED STATES PATENTS 2,041,153 5/1936 Shiraeif --75 3,102,045 8/1963 Metcalfe 951.7 X 3,109,355 11/ 1963 Ritzerfeld 95-l.7 3,155,022 11/1964 Schwertz 95--1.7 3,207,050 9/ 1965 Limberger 95-1.7 3,313,223 4/1967 Frantzen 95--77.5 X

JOHN M. HORAN, Primary Examiner.

U.S. Cl. X.R.

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