US3308731A - Electrostatic printing - Google Patents

Description

United States Patent f 3,308,731 ELECTROSTATIC PRINTING Roger George Olden, Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Original application Mar. 22, 1961, Ser. No. 97,611, now Patent No. 3,210,185. Divided and this application Jan. 7, 1965, Ser. No. 424,101 1 Claim. (Cl. 951.7)

This is a division of application Ser. No. 97,611, filed Mar. 22, 1961, and issued as US. Patent No. 3,210,185 on Simultaneous Identical Electrostatic Image Recording on Multiple Recording Elements.

This invention relates generally to electrostatic printing, and more particularly to novel apparatus for exposing a plurality of electrophotographic recording elements simultaneously. The novel apparatus of the present invention is particularly useful for making duplicate copies of an image by electrophotographic means.

Previously, duplicate electrostatic prints have been made by exposing a plurality of uniformly charged, electrophotographic recording elements to the same light image successively and developing each recording element separately. Data read-out time in electronic computers, for example, is at a premium. Therefore, successive read-out for making duplicate copies of computer data is not desirable. Heretofore, if duplicate electrostatic prints were desired in a period of time less than that required to produce these prints successively in one automatic processing machine, duplicate machines had to be employed. Since machines for automatically producing electrostatic prints are expensive, the use of duplicate apparatus to speed production may be prohibitive in many instances. Accordingly, it is an object of the present invention to provide improved means for producing electrostatic prints faster and more economically than is possible by prior art methods and apparatus.

Another object of the present invention is to provide improved automatic apparatus for making a plurality of electrostatic prints in substantially the same amount of time required to process a single electrostatic print. Still another object of the present invention is to provide improved apparatus for making a plurality of electrostatic prints by employing novel means to expose a plurality of uniformly charged electrophotographic recording elements simultaneously.

A further object of the present invention is to provide improved means for making simultaneously a plurality of electrostatic prints, including a master print useful in making reproduction by another reproductive process.

Briefly, a preferredembodiment of the improved apparatus of the present invention comprises automatic means for processing a plurality of recording elements simultaneously. In each of the embodiments of the apparatus described herein, a plurality of recording elements are exposed simultaneously. In one embodiment of the present invention, all of the recording elements are oriented similarly so that the backing sheet of one recording element is in contact with the photoconductive layer of an adjacent recording element during the exposure step in the process. In another embodiment of the present invention, two recording elements are arranged so that their photoconductive layers contact each other during the exposure step, there-by providing for a mirror-image master print that may be used in other reproductive processes.

Other novel features of the present invention, both as to its organization and methods of operation, as well as additional objects and advantages thereof, will be described in greater detail by reference to the accompanying drawings, in which similar reference characters designate similar parts throughout, and in which:

FIGS. 1A, 1B, and 1C show three electrophotographic ice Patented Mar. 14, 1967 recording elements undergoing successive steps of charging, exposing, and developing, respectively, in the process of electrostatic printing, in accordance with the present invention;

FIG. 2 is a schematic diagram of one embodiment of improved apparatus, employing a thin-window cathode ray tube, for exposing a plurality of electrophotographic recording elements simultaneously in the process of making duplicate electrostatic prints, in accordance with the present invention;

FIG. 3 is a schematic diagram of another embodiment of improved apparatus, employing light means, for exposing a plurality of electrophotographic recording elements simultaneously, in accordance with the present invention; and

FIG. 4 is a schema-tic diagram of still another embodiment of improved apparatus, employing a thin-window cathode ray tube, for exposing a plurality of electrophotographic recording elements simultaneously in a manner to produce one master copy for use in another reproductive process, in accordance with the present invention.

Referring now to FIGS. 1A, 1B, and 1C, there are shown three electrophotographic recording elements 10, 12, and 14 in some of the steps of the process of electrophotographic printing, in accordance with the present invention. The recording elements 10, 12, and 14 comprise backing sheets 10a, 12a, and 14a having photoconductive layers 1%, 12b, and 14b on their upper surfaces, respectively. The backing sheets 10a, 12a, and 14a may comprise any suitable translucent material, such as paper and the like, and the photoconductive layers 10b, 12b, and 1412 may comprise photoconductive zinc oxide embedded in a. resin binder. The photoconductive layers 10b, 12b, and 14b may also contain different amounts of dyes mixed r in the binder for the purpose of rendering each successive layer more sensitive to electromagnetic radiation, for the purpose hereinafter appearing.

Referring now to FIG. 1A, the recording elements 10, 12, and 14 are shown in the process of receiving a uniform electrostatic charge. The recording elements 10, 12, and 14 are placed on a sheet 16 of electrically conducting material so that their respective backing sheets 10a, 12a, and 14a are in contact with the sheet 16. The sheet 16 is grounded. A corona discharge device, that is, a charging unit 18 is connected to a source (not shown) of relatively high unidirectional voltage (about 6,000 volts) for producing a corona discharge from wires 20 of the charging unit. The charging unit 18 is moved over the photoconductive layers 10b, 12b, and 14b of recording elements so as to deposit a uniform negative electrostatic charge on the photoconductive layers.

In the next step, the uniformly charged recording elements 10, 12, and 14 are arranged one behind the other, front to back, so that the backing sheet of one recording element is in contact with the photoconductive layer of an adjacent recording element, as shown in FIG. 1B. When so arranged, the recording elements 10, 12, and 14 are exposed simultaneously by an image of electromagnetic radiation directed onto one recording element, the recording element 10, for example, with an intensity sufficient to penetrate this and other translucent recording elements and to permit a latent electrostatic image to be formed on each of the photoconductive layers 10b, 12b, and 14b of the recording elements. The image of elec tromagnetic radiation is directed preferably perpendicularly to the photoconductive layers, as illustrated by the arrows 22 in FIG. 1B. The image of electromagnetic radiation may be formed with visible light, infra red radiation, and X-rays, for example. The recording element that is farthest from the source of electromagnetic radiation need not be transparent because its photoconductive layer can be exposed through the translucent elements in front of it. If, for example, the photoconductive layers 1%, 12b, and 14b were sensitized with fluorescein, rose bengal and methylene blue, respectively, each of the stacked recording elements 10, 12, and 14 would be sensitive to electromagnetic radiations in a different spectral range. Thus, differently sensitized recording elements may be exposed simultaneously by a colored image, in cluding light in all the spectral ranges, to produce separation prints useful in some color printing methods.

After the simultaneous exposure of the recording elements 10, 12, and 14, they are separated from each other and developed separately, as shown in FIG. 1C. To this end, each of the recording elements 10, 12, and 14 is brushed with a developing mixture 24 of tribe-electrically charged particles, comprising, for example, a powdered dye material mixed with iron filings. The developing mixture 24 is applied to the latent images by means of a magnet 26, as described, for example, in U.S. Patent 2,874,063 to H. G. Greig.

Referring now to FIG. 2, there is shown schematically apparatus 30 for making two electrostatic prints simultaneously. One web of a continuous recording element 32, stored on a roll 34, is pulled past the window 35 of a thin-window cathode ray tube 37 by means of a pair of drive rollers 36 and 38, and guide rollers 39 and 40. The drive rollers 36 and 38 are driven by any suitable means (not shown). Another web of a continuous recording element 42, stored on a roll 44, is pulled over the recording element 32 at the site where the recording element 32 comes in contact with the window 35, by means of a pair of drive rollers 46 and 48, and guide rollers 49 and 50. The recording element 42 is directly behind, and in contact with, the recording element 32 at the window 35, the exposure station. The drive rollers 46 and 48 are driven by any suitable means (not shown). The recording elements 32 and 42 are similar to the recording elements 10, 12, and 14, previously described, and they have photoconductive layers 32a and 42a, respectively, on the sides that face the window 35 of the tube 37.

The recording element 32 is pulled past a developer trough 52 and a fuser 54 by means of a pair of drive rollers 56 and 58, and a guide roller 60. The developer trough 52, as well as other developer apparatus described herein, may comprise the apparatus described by A. Stavrakis et 'al. in U.S. Patent No. 2,910,964. The recording element 42 is pulled past a developer trough 62 and a fuser 64 by means of a pair of drive rollers 66 and 68. A charging unit 70, with voltage applied to its elements as indicated, is disposed about the webs of the recording elements 32 and 42 to charge the photoconductive layers 32a and 42a negatively, in a manner well known in the art. The charging unit 70 is located between the guide rollers 39 and 40 and between the guide rollers 49 and 50.

The thin-window cathode ray tube 37 comprises means to write on a phosphor screen with an electron beam in accordance with the principles well known in the television art, as described, for example, in RCA Review, September 1957, vol. XVIII, No. 3, at pages 343 to 350. The electronic circuitry for operating the tube 37 is not shown because it forms no part of the instant invention. The cathode ray tube 37 is formed with a relatively thin window 35 which is elongated in one direction (perpendicular to the direction of travel of the recording elements). It will be understood that when the phosphor screen (not shown) on the window 35 is caused to luminesce by an electron beam impinging on it, the image of the light from the phosphor screen will expose the recording elements 32 and 42. In order to prevent excessive wear of the window 35 due to friction, a web 72 of transparent plastic material, such as a clear, tough plastic material sold under the trademark Mylar, is caused to move between the window 35 and the recording element 32.

To this end, the web 72, stored on a roll 74, is pulled over the window 35 by a takeup roller 76, by any suitable means known in the art. In practice, the web 72 is pulled over the window 35 at a relatively much slower rate than the recording elements 32 and 42.

The operation of the apparatus 30, in accordance with the present invention, will now be described. The photoconductive layers 32a and 42a of the recording elements 32 and 42 are charged negatively by the charging unit 70 and moved into contact with each other and with the web 72 over the window 35 of the tube 37. When in contact with each other, the recording elements 32 and 42 are exposed simultaneously by light from the fluorescent Window 35. The light is of suflicient intensity to expose the photoconductive layers 32a and 42a of both of the recording elements 32 and 42. After exposure, the recording elements 32 and 42 move through the developer troughs 52 and 62 where they are developed. From the developer troughs 52 and 62, the recording elements 32 and 42 pass through the fusers 54 and 64 where the developer mixture is fused onto the recording elements, and the electrostatic print is finished.

Referring now to FIG. 3, there is shown apparatus for exposing a plurality of recording elements simultaneously to visible light in the process of electrostatic printing according to the present invention. A recording ele ment 81, wound on a roll 82, is pulled past a grounded platen 83, a developer trough 84, and a fuser by means of drive rollers 86 and 87, and guide rollers 88, 89, and 90. The drive rollers 86 and 87 are driven by any suitable means, such as an electric motor (not shown). A continuous recording element 91, stored on a roll 92, is pulled over the recording element 81 at the site of the platen 83, through a developer trough 94, and a fuser by means of drive rollers 96 and 97 and guide rollers 98 and 99. The drive rollers 96 and 97 are driven by any suitable means (not shown). A pair of corona discharge units 100, 102 are disposed to charge the photoconductive lay ers 81a and 91a of the recording elements 81 and 91, respectively, with a uniform negative charge. The photoconductive layers 81a and 91a are separated from each other by the backing sheet of the recording element 91, and the backing sheet of the recording element 81 is in contact with the grounded platen 83.

Means are provided to expose the recording elements 81 and 91 simultaneously. To this end, electromagnetic radiation, such as light from a light source 104, is directed onto the platen 83, the exposure station, by means of an optical projector 106. A transparency 108, such as a photographic negative, for example, disposed between the light source 104 and the projector 106, produces a light image on the photoconductive surface 91a of recording element 91. In accordance with the present invention, the light image is of suflicient intensity to penetrate the translucent recording element 91 and to expose the photo conductive layer 81a of the recording element 81. After the simultaneous exposure of the recording elements 81. and 91, the recording elements are developed .and fused in the manner described for the apparatus 30 of FIG. 2.

Referring now to FIG. 4, there is shown apparatus for exposing two recording elements simultaneously in a manner to produce a normal electrostatic print and a master print from which other prints may be made. A recording element 112, stored on a roll 113, is pulled across the window 35 of the thin-window cathode ray tube 37 and then successively through a first developer trough 114, a second developer trough 115, and a fuser 116 by means of suitably driven drive rollers 117 and 11 8, and guide rollers 119, 120, '121, and 122. A recording element 123, stored on a roll 124, is pulled over the recording element 112 at the window 35 of the tube 37, and then successively through a developer trough 125, and a fuser 126 by means of suitably driven drive rollers 127 and 128, and guide rollers 129, 130, 131, 132, and 133. A corona discharge unit is disposed about the recording elements 112 and 123 in a manner to charge adjacent photoconductive layers 112w and 123a, respectively, with a negative charge. It will be noted that in the embodiment of the apparatus shown in FIG. 4, the photoconductive layers 112a and 123a of the recording elements 112 and 123, respectively, are adjacent to each other, face to face.

In operation, the uniformly charged recording elements 112 and 123 are exposed simultaneously by means of writing on the phosphor screen (not shown )on the window 35, as explained heretofore for the apparatus 30 of FIG. 2. After exposure, the recording elements are separated. The recording element 123 is developed in the developer trough 125, and the developed image is fused in the fuser 126.

Since the recording element 112 was exposed with radiant energy that first had to penetrate the backing sheet of the recording element 112, the latent image produced on the photoconductive layer 112a of the recording element 112 is a mirror image of the true image. This mirror image is developed in the developer tank 114. By means of a pair of opposed pressure rollers 136 and 138, a uniformly, negatively charged Web of uncoated paper 140 can be pressed against the developed image on the photoconductive layer 112a of the recording element 112 to cause the unfused developed image on the recording element 112 to be transferred to the paper 140.

The web of paper 140, stored on a roll 142, is pulled past a charging unit 144, between the rollers 136 and 138, and through a fuser 146 by means of suitably driven drive rollers 148 and 150, and a guide roller 152. Thus, the unfused powdered image transferred to the charged paper 140 can be fused in the fuser 146. After the transfer process, the recording element 112 may be developed once more in the developer tank 115 and fused in the fuser 116. The developed image appearing upon the recording element 112 is a mirror image of the images appearing on the recording element 123 and on the paper 140*. Because the image on the recording element 112 is a mirror image, the developed recording element 112 can be used in other recording processes, such as by transfer to a multilith master for the multilith process of reproduction.

From the foregoing description, it will be apparent that there has been provided improved means for making duplicate electrostatic prints. By means of the apparatus shown and described, a plurality of recording elements, superimposed on each other at an exposure station, are exposed simultaneously with electromagnetic radiation of sufficient intensity to penetrate all of the recording elements. While the apparatus has been illustrated in schematic form, variations in the apparatus coming within the spirit of this invention will, no doubt, readily suggest themselves to those skilled in the art. For example, a greater number of recording elements may be exposed simultaneously than the number described and illustrated. Hence, it is desired that the foregoing description shall be considered merely as illustrative and not in a limiting sense.

What is claimed is:

Apparatus for processing two electrophotographic recording elements simultaneously to provide an original copy and a mirror-imaged master copy of an image, said master copy comprising means from which additional copies of said image may subsequently be made, each of said elements comprising a backing sheet and a photoconductive layer thereon, said apparatus comprising means to charge each of said elements electrostatically, an exposure station, means to guide said elements through said charging means to said exposure station so that said photoconductive layers of said two elements are in contact with each other at said exposure station, means to direct an image of electromagnetic radiation through said elements to expose said photoconductive layers simultaneously and to produce electrostatic images thereon, the layer of one said elements being exposed through its backing whereby the electrostatic image produced on said one element is the mirror image of that produced on the other of said elements, first means to develop said electrostatic image on said one element, means to guide said one element through said first means to develop said electrostatic image thereon; sheet material, means to press said sheet material against said developed image on said one element to transfer at least part of said developed image from said one element to said sheet material to produce a mirror image of said developed image on said sheet material, second means to redevelop said one element to restore said developed image thereon, means to guide said one element through said second means to redevelop and to restore said developed image whereby to provide said master copy from which other copies may subsequently be made, third means to develop said other of said elements, and means to guide said other of said elements through said third means to develop the electrostatic image thereon whereby to provide said original copy.

References Cited by the Examiner UNITED STATES PATENTS 2,182,142 12/1939 Ball l2.20 2,749,792 6/1956 Kelly 95-l2.20 2,952,796 9/1960 Crews 954.5 X 2,962,374 11/1960 Dessauer 95--1.7 X 3,057,275 10/1962 Walkup 95- 17 3,145,632 8/1964 McNaney 95-1.7

JOHN M. HORAN, Primary Examiner.

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