US3551145A - Method of reproducing a toner image carried by an electrophotographic plate - Google Patents

Description

29, 1970 w. TRACHTENBERG 3,551,145

METHOD REPRODUCING A TONER IMAGE CARRIED BY AN ELECTROPHOTOGRAPHIC PLATE I Filed Aug. 2l, 1967 V 2 Sheets-Sheet 1 7'0 same average ground To same average ground -TTT -TT? I 24 Conductive Support 23 4- M III-m 25 Pnatoconduotive Layer conductive support- Fram same average ground Conduct/x1e Support 43 Pnotoconduotive Layer 54 Conductive Support 54 53 Toned image Pnatoc'onductive Layer Conductive Support 50 Transparent 52 Original) Uniform I iiuminatio n WILL/AM TEACH TE/VBERG INVENTOR.

AGE/VT As-ZZ' 304 conductive Support 40 7 32/ I g 4/ D c. 9, 1970 w., TRACHTENBERG 3,551,145

METHOD OF REPRODUCING A TONER IMAGE CARRIED BY AN ELECTROPHOTOGRAPHI C PLATE Filed Aug, 21; 1967 2 Sheets-Sheet 2 Copy Material Developing WILL/AM m4 021 TE/VBE/PG INVENTQR.

United States Patent 3,551,145 METHOD OF REPRODUCING A TONER IMAGE CARRIED BY AN ELECTROPHOTOGRAPHIC PLATE William Trachtenberg, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Aug. 21, 1967, Ser. No. 662,049 Int. Cl. G03g 13/22 US. Cl. 96-1 Claims ABSTRACT OF THE DISCLOSURE A method of reproducing a fully developed and visual image carried by a xerographic plate comprising a photo.- conductive insulating layer overlying a transparent, conductive backing support as a latent electrostatic image on an unexposed xerographic plate. In order to eliminate any possibility of secondary discharge effects, a uniform electrostatic charge of the same polarity is applied to a surface of the photoconductive layer carrying the image and to the photoconductive layer of the unexposed xerographic plate before the charge surfaces are positioned in intimate contact for exposure through the image-carrying xerographic plate.

FIELD OF THE INVENTION This invention relates to electrophotographic reproduction and more particularly to an improved method for reproducing a fully developed image, which is carried by a xerographic plate, as a latent electrostatic image on another Xerographic plate whereby there is little, if any, loss of image sharpness or resolution.

DESCRIPTION OF THE PRIOR ART The text Electrophotography by R. M. Schaffert (Focal Press), chapter VI, pages 87-96, discloses various techniques for accomplishing the transfer of latent electrostatic images that are referred to as TESI Processes, the name TESI being derived from Transfer of Electro- Static Images. In each of the disclosed processes an electrostatic image is formed on the surface of a dielectric material either by inducing a charge pattern on the surface of the dielectric material or by actual transfer of the charges from the surface of one dielectric material to another. In the TESI Technique No. 3, an electrostatic image is formed on a xerographic plate by conventional methods and a charged dielectric film with a conductive base is placed on top of the electrostatic image on the plate surface. Both electrodes are then brought to ground potential and since the potential difference between the conductive substrates is zero, the voltage across the air gap in the image area is determined by the combined potentials of the positively charged image and the negatively charged dielectric. The surfaces are then separated and the image transfer takes place during separation. In this process it is noted that the provision is made to bring both electrodes to ground potential so that no secondary discharge effect occurs between the surfaces upon separation.

It is well known that a discharge occurs between charged contacting photoconductive layers when they are brought into contact or separated, because air between the layers undergoes a dielectric breakdown. This breakdown is caused by the close proximity of the charged photoconductive surfaces and the high electric fields. Unless the potential gradients that exist between the surfaces can be reduced or eliminated, the secondary discharge effects that occur upon bringing the surfaces into contact or upon separation of the surfaces manifest themselves during development as a distinct pattern.

Patented Dec. 29, 1970 One object of the invention is to provide an improved electrophotographic reproduction system in which a visible image on a xerographic plate can be reproduced or duplicated on another xerographic plate.

Another object of the invention is to provide an im proved electrophotographic reproduction method by which secondary discharge effects between the contacting surfaces of two insulating materials are substantially eliminated upon separation of the surfaces.

Yet another object of the invention is to provide an improved electrophotographic reproduction method by which surface discharge patterns are eliminated from the surface of a photoconductive insulating material bearing a latent electrostatic image.

Other objects and advantages of the invention will be apparent to those skilled in the art by the more detailed description and examples set forth hereinbelow.

The above objects of the invention are attained by a method of reproducing a fully developed and visual image carried by a xerographic plate (original) comprising a photoconductive insulating layer overlying a transparent, conductive backing support as a latent electrostatic image on an unexposed xerographic plate (copy). In order to eliminate any possibility of secondary discharge effects, a uniform electrostatic charge is applied to a surface of the photoconductive layer of the xerographic plate. A uniform electrostatic charge of the same polarity and potential is also applied to the photoconductive surface of the second xerographic plate. The charged surfaces (original and copy) are then positioned in intimate contact and the photoconductive layer of the second xerographic plate is exposed through the xerographic plate (original) to a source of uniform actinic illumination. With exposure of the photoconductive layer on the second xerographic plate, the charges in the light or transparent area's are substantially neutralized and the charges remain in the dark or unexposed areas, the latter being the toned areas on the original xerographic plate. As a result, the potential gradient between the facing surfaces in both the image and non-image areas is reduced to a level of potential such that no dielectric breakdown of air can occur upon separation of the facing surfaces of the original and copy. The second xerographic plate is then separated from the first xerographic plate and the electrostatic image thereon is then developed by any known xerographic method. Since the electrostatic image is formed on the surface that is in contact with, or in close proximity to, the duplicated image, it is identical to the original image with little, if any. loss in sharpness or resolution.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying drawings wherein like reference numerals designate like parts and wherein:

FIG. 1 is a schematic representation of two xerographic plates having the photoconductive layers in close proximity and showing the manner in which discharge patterns are formed;

FIG. 2 is a schematic representation similar to that shown in FIG. 1 showing the manner in which discharge patterns are formed when the conductive backing support of one of the xerographic plates is connected to ground;

FIG. 3 is a schematic representation similar to that shown in FIG. 1 showing the manner in which the field lines are formed when a bias voltage is applied to the conductive hacking support of one of the xerographic plates without exposure to subsequent illumination;

FIG. 4 is a schematic representation similar to that shown in FIG. 1 in which the photoconductive layer of each xerographic plate is charged to the same polarity and to substantially the same level of potential and showing that no external fields exist to form any discharge pattern;

FIGS. and 6 are schematic representations of a xerographic plate havin a fully developed and visual image thereon and a xerographic plate for receiving a duplicate image, FIG. 5 showing the charge formation prior to illumination and FIG. 6 showing the charge configuration relative to the image after illumination; and

FIG. 7 is a schematic arrangement of an apparatus for practicing the invention as a continuous method.

DESCRIPTION OF THE PREFERRED EMBODIMENT Before describing the invention it is believed that the invention will be best understood if the factors to be overcome by the invention are first described. As noted above, the problem of secondary discharge effects arises when a photoconductive duplicating material bearing a surface charge is brought into contact with a photoconductive original or separated therefrom. The effect of various biases applied to the conductive backing support is disclosed in the description of the following examples.

EXAMPLE I (FIG. 1)

With reference to FIG. 1 a xerographic plate 10 comprises a photoconductive insulating layer 11 overlying a conductive backing support 12.. A second xerographic plate 13 comprises a photoconductive layer 14 and a conductive backing support 15. The surface of layer 14 was first charged negatively to a potential of 1000 volts. The plate 13 was then placed with its photoconductive layer 14 in contact with the photoconductive insulating layer 11 of plate 10. The conductive backing support of each plate was allowed to float, that is, was not intentionally grounded, and there was no exposure step. Since the support 12 is conductive, it contains both positive and negative charges that may move about freely. When the charged surface of layer 14 is brought into contact with layer 11, some of the positive charges in layer 12 will be drawn by the induced electrical field toward negative charges on layer 14. On the other hand, some of the negative charges in layer 12 and some of the positive charges in layer 15 are drawn to the extremity of their respective layer. The arrows 16 indicate the electrical field existing between the photoconductive layers 11, 14 and in which areas secondary discharge effects occur due to such induced charges. After the plate 13 was separated from the plate 10, each of the plates was developed with a liquid developer using a facing electrode. Upon development, it was noted that surface discharge patterns were visible on the surface of each of the photoconductive layers 11 and 14. A control material was charged and developed in the same manner without being placed in contact with another surface and showed a uniform deposit of toner particles with no discharge patterns.

EXAMPLE II (FIG. 2)

A xerographic plate 20 comprising a conductive backing support 21 and a photoconductive layer 22 had its conductive support 21 connected to ground. A second xerographic plate 23 comprises a conductive backing support 24 and a photoconductive layer 25. The surface of layer 25 was charged negatively to a potential of 1000 volts and then placed in contact with the surface of layer 22. Upon separation and development of each of plates 20 and 23, discharge patterns were again evident on each of the surfaces of layers 22. and 25.

As in Example I, the arrows 26 indicate the electrical field existing between the photoconductive layers 22, 25 and in which areas secondary discharge effects occur due to the induced charges. In this case, however, the negative charges in layer 21 leak off because the layer 21 is connected to ground.

4 EXAMPLE 111 (FIG. 3)

A xerographic plate 30 comprising a photoconductive layer 31 overlying a conductive backing support 32 had a negative bias of 1000 v. connected to the conductive support 32. A xerographic plate 33 comprises a conductive backing support 34 and a photoconductive layer 35. The surface of layer 35 was charged negatively to 1000 v. and the photoconductive layer 35 was then placed in contact with the layer 31 of xerographic plate 30. Upon separation and subsequent development of the plates 30 and 33 no discharge patterns were observed on the surfaces of layers 31 and 35. In this example it is believed that biasing the plate 30 to a potential of the same polarity as that of the plate 33, in effect, neutralizes any electrical field that may exist between photoconductive layers 31, 35 so that the plates can be separated without any transfer of charge or secondary discharge effects. However, even with the application of a bias to support 32, secondary discharge effects are obtained upon subsequent illumination through support 32 and separation of layers 31, 35.

EXAMPLE IV (FIG. 4)

In this example, a xerographic plate 40 comprising a conductive backing support 41 and a photoconductive layer 42 and a xerographic plate 43 comprising a conductive backing support 44 and a photoconductive layer 45 were charged in the same manner as the previous examples to the same negative voltage (1000 volts). The plates 40 and 43 were then placed photoconductive layer to photoconductive layer in accordance with the present invention. After separation, each plate was developed and no discharge patterns were evident on either plate. When the plate 43 was charged to a negative 500 volts surface potential and the plate 40 was charged to a negative 1000 volts surface potential and then positioned in the same relationship as described above, the developed images showed some secondary discharge effects which were less than with no charging of the layer 42, but more than with equal charging.

EXAMPLE V FIGS. 5 and 6 disclose the invention as practiced with substantially no secondary discharge effects. An original or xerographic plate 50 comprising a photoconductive layer 51 overlying a backing support 52 carries a toned image '53. The toned image 53 is one which has been formed by well known xerographic methods and is therefore a fully visible imageQA copy material 54 can comprise a xerographic plate with a photoconductive layer 55 overlying a conductive backing support 56. The photoconductive layers 51 and 55 were charged negatively to a surface potential 1000 v. and then placed in intimate contact. The conductive support 52 must be transparent in order to permit uniform illumination through the original 50. The illumination therefore is through the original and the light incident on the photoconductive surface 55 renders the exposed areas conductive so that the charges in these areas are substantially neutralized. Since the toned image 53 prevents light from reaching the corresponding areas of the surface of layer 55 the charge remains in the image areas. Upon separation, electric fields exist only in the image areas and are not sufficient to cause dielectric breakdown when the plates 50 and 54 are separated one from the other. The latent electrostatic image on the original, that is, on the surface of the toner, is formed because of the toner thickness, and under proper charging conditions the two latent electrostatic images can be identical. The extent to which the original and photoconductive copy material should be charged is a function of the relative dielectric constants, the thickness of the toner deposit on the original and the thickness of the photoconductive layers, the secondary discharge effects being caused by the capacitive arrange ment of the photoconductive layers, the air gap and the conductive backing supports.

Reference is now made to FIG. 7 in which a schematic apparatus is disclosed for practicing the invention on a continuous basis. The original material 70 is shown as a web comprising a xerographic material which would contain a number of longitudinally spaced visible images. The copy material 71 is a xerographic material having a photoconductive layer overlying a conductive support as described above. The two materials are brought together at a point determined by a pair of rolls 72, 73 which are connected to ground. The image surface on the original is positioned so as to be brought into contact with the photoconductive layer of the copy material. A corona charging means 74 is arranged between the copy and original material and connected to a DC. source of potential 75. The source can provide either positive or negative potential to the corona wire 76 which charges the materials with either a or charge in accordance with the requirement. Either one or a pair of spaced corona shields 77 which are connected to ground can be used to direct the spray of ions to the surfaces of the original and copy materials. Between the rolls 72,73 and a pair of rolls 78, 79, the copy material is subjected to uniform actinic illumination by means of a lamp 80 and a condenser lens system 81. The copy material 71 and original 70 are separated at rolls 78, 79, the original being taken up in the form of a roll 82 and the copy material being moved through a developing means 83, a fusing means 84 and then wound up on roll 85. Obviously, the image in the copy material 71, after being developed, can be transferred to another material in a known manner to provide a paper copy, in which case the copy material 71 would then be wound onto roll 85 and the transfer material would be moved into and through the fusing station 84. As noted above, if the original material 70 is a xerographic material bearing visual images, it must be provided with a transparent conductive backing support in order to permit illumination through the material to provide the necessary neutralization of the charge in the non-image areas.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A method of reproducing a fully developed image on a first member, said image being carried by a photoconductive insulating layer overlying a transparent, conductive backing support, as a latent electrostatic image on a second member comprising a photoconductive insulating layer overlying a conductive backing support, said method comprising the steps of:

applying a uniform electrostatic charge to the surface of the photoconductive insulating layer of said first member; applying a uniform electrostatic charge of the same polarity as applied to said first member to the surface of the photoconductive layer of said second member, the level 'of potential being dependent on the relative capacitance of said first and second members;

positioning said first member relative to said second memberwith the respective charged surfaces in intimate contact and with substantially no potential gradient existing between said surfaces; and

exposing, through said first member while in contact with said second member, the photoconductive layer of said second member to a source of uniform actinic illumination, whereby an electrostatic image is formed on the facing surfaces of each of said members in accordance with said visible image and the potential gradient between said facing surfaces in both the image and non-image areas is maintained at a level of potential at which substantially no dielectric breakdown of air can occur upon separation of sail members.

2. The method in accordance with claim 1 including the step of separating said members one from the other.

3. The method in accordance with claim 2 including the step of xerographically developing the electrostatic image on said second member.

4. The method in accordance with claim 1 wherein a uniform negative electrostatic charge of about 200 to 1500 volts is applied to the surface of the respective photoconductive insulating layers.

5. The method in accordance with claim 1 wherein a a uniform positive electrostatic charge of about 200 to 1500 volts is applied to the surface of the respective photoconductive insulating layers.

References Cited UNITED STATES PATENTS 2,982,647 5/ 1961 Carlson et al 96-1 3,015,304 1/1962 Carlson et al. 118-637 3,147,679 9/1964 Schaffert 1.7 3,169,062 2/ 1965 Klupfel 96-1 3,442,645 5/ 1969 Olden 961.4 3,464,818 9/1969 Waly 96-l.3

CHARLES E. VAN HORN, Primary Examiner J. C. COOP-ER III, Assistant Examiner US. Cl. XR. 117l7.5

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