US3413063A

US3413063A - Electrophotographic apparatus

Info

Publication number: US3413063A
Application number: US537964A
Authority: US
Inventors: Charles J Young
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1966-03-28
Filing date: 1966-03-28
Publication date: 1968-11-26
Anticipated expiration: 1985-11-26

Description

NOV. 26, 1968 Q L YOUNG v 3,413,063

ELECTROPHOTOGRAPHIC APPARATUS Filed March 28, 1966 ra Wel/0M 911g? i064 @u goo fm IN VE N TOR. ('/MxzfsJ )fw/ v6 BLLMM United States Patent O 3,413,063 ELECTROPHOTOGRAPHIC APPARATUS Charles J. Young, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Mar. 28, 1966, Ser. No. 537,964 3 Claims. (Cl. 355-14) ABSTRACT F THE DISCLOSURE Apparatus for making a plurality of visible copies of an electrostatic latent image on an insulating surface of a recording element comprises means to move the recording element along a predetermined path and a plurality of developing stations and copy transfer stations disposed sequentially along the path. The original latent image is redeveloped for each transfer copy (in addition to the first copy desired).

This invention relates generally to electrophotography, and more particularly to improved apparatus for making multiple, visible, transfer copies from an electrostatic charge pattern. Th-e improved apparatus is particularly useful for making a plurality of copies of output data from computers whose outputs can be converted to electrostatic charge patterns.

In an electrophotographic process of the type described in RCA Review, vol. XV, p. 469, December 1954, for example, an electrophotographic recording element, comprising a layer of photoconductive zinc oxide dispersed in a resin binder on a backing of suitable conductivity, is charged negatively so that the photoconductive layer carries a uniform electrostatic charge over its surface. The recording element is exposed to a light image to discharge its surface in accordance with the light intensity falling on it and to leave thereon an electrostatic latent image. The latent image is developed by applying a finely divided electrically attractable toner, such as from an electroscopic mixture of fusible toner palticles and iron tiling-s, thereon. The developed image may be fixed to the recording element by applying heat to the toner particles to fuse them on the recording element.

Previously, multiple electrostatic prints of an original have been made by exposing successively a plurality of uniformly charged, electrophotographic recording elements to the same light image of the original and developing each recording element separately. Such apparatus for making a plurality of copies of the light image, however, requires the same light image to be available for each of the multiple exposures. In certain types of apparatus, as, for example, in computers where ouptut data is presented on the face of a cathode ray tube, the data is usually presented for a time sufficient to make only one copy thereof, thereby rendering the aforementioned prior-art apparatus unsuitable for providing multiple copies here.

In some other prior-art apparatus for making multiple copies, a number of transfer copies are made from a single, untixed, developed original. Since only the amount of toner used to develop the original is available to produce all of the transfer copies, each succeeding copy usually has less contrast than the former.

It has also been proposed to provide apparatus for making a plurality of transfer copies that utilizes only a single combination of a developing station and a copy transfer station, but such an arrangement usually involves the use of reciprocating or recycling means that complicate the apparatus unduly.

It is an object of the present invention to provide improved apparatus for making a plurality of developed` transfer copies of information that can be presented as an electrostatic image on a surface.

Another object of the present invention is to provide improved apparatus for making multiple copies of an image, utilizing only a single exposure of the image.

Still another object of the present invention is to provide improved apparatus for making a plurality of transfer copies of controllable and/or uniform contrast.

Briefly, the improved apparatus for making a plurality of developed transfer copies of an image comprises means to move along a predetermined path an insulator member having an electrostatic charge pattern of the image on a surface thereof. A plurality of developing and transfer stations, a separate transfer station being associated with each developing station, are disposed successively along the path. Developing means are disposed at each developing station to apply toner to the charge pattern to develop it, and transfer means are disposed at each transfer station to transfer toner from the developed charge pattern to a transfer material, whereby to provide a transfer copy of the image on the transfer material. A transfer voltage may be provided at each transfer station, if necessary, to aid in transferring toner from the developed charge pattern to the transfer material. Each successive transfer voltage may vary in amplitude to control the amount of toner transferred and to insure uniform contrast in each transfer copy, if so desired. Erasing means may be provided to remove any remaining toner from the charge pattern after all of the transfer copies have been made so that the insulating surface may be reused.

The improved apparatus will now be described in detail with reference to the accompanying drawing, the single ligure of which is a schematic elevation of the improved electrophotographic apparatus.

Referring now to the drawing, there is shown improved electrophotographic apparatus 10 for producing a plurality of developed, transfer copies from a charge pattern on an insulating surface 12 of a recording element 14. The recording element 14 may comprise a backing of suitable conductivity, such as paper, having a moisture -content of about 546%, and the insulating surface 12 may be that of a photoconductive layer of zinc oxide, as described in the aforementioned RCA Review. The recording element 14 is preferably in the form of an elongated web and is moved, by any suitable means, as by a motor 16 and suitable coupling means, along a predetermined path from a supply roll 18 to a take-up roll 20. Thus, the recording element 14 is unwound from the supply roll 18, and moved sequentially between rollers 22 and 24, around rollers 26 and 28, between

rollers

30 and 32, and onto the take-up roll 20. The arrows associated with the aforementioned components indicate the directions of their movements.

A charging station 34 and an exposure station 36 are disposed along the path of travel of the recording element 14 between the rollers 24 and 26. Three developing and transfer stations 40, 42, and 44 are disposed along the path of travel between the rollers 26 and 28, and erasing apparatus 46 is disposed at an erasing station 47 between the

rollers

28 and 30. In a typical example of operation of the .apparatus 10, the recording element 14 may be advanced along its predetermined path at a rate of about 1,000 inches per minute.

The recording element 14 is charged uniformly as it passes through the charging station 34. A negative corona discharge device S0 is disposed adjacent to one major surface of the recording element 14, preferably the zinc oxide insulating surface 12, and a positive corona discharge device 52 is disposed adjacent to the other major surface of the recording element 14. The corona discharge devices 50 and 52 comprise a double corona discharge device known in the art. When terminals 54 and 56 of the negative and positive discharge devices 50 and 52 are connected to the negative and positive terminals of a suitable power supply (about 6,000 volts, not shown) the insulating surface 12 will be charged negatively with respect to the conductive backing.

A charge pattern, that is, a latent electrostatic image, of information to be copied is formed at the exposure station 36 with the aid of a thin-window cathode ray tube 58 of the type described in RCA Review, vol. XXII, No. 3, p. 582, September 1961. Briefly, the tube 58 is one in which information is provided on a transparent thin window 60 when a stream of electrons within the tube 58 impinges upon a phosphor on the window 60. The output of the tube 58, that is, the image to be recorded, is determined by a character generator 62 electrically connected to the tube 58 in a manner well known in the art, and as explained in the aforementioned RCA Review. The character generator 62 may be a part of a computer (not shown) for presenting information (images) to be reproduced by the apparatus 10. Thus, as the uniformly charged recording element 14 is moved across the thinwindow 60 of the tube 58, the zinc oxide insulating surface 12 is rendered conductive by the light images on the thin-window screen 60, whereby to produce charge patterns, i.e. electrostatic latent images, on the insulating surface 12. The relative speed of the recording element 14 with respect to the exposure time at the exposure station 36 is relatively slow so that the recording element 14 can be exposed while it is in motion Without producing blurred images.

The electrostatic latent image is developed and transferred to a transfer material for each transfer copy desired. In the apparatus 10, as illustrated herein, three developing and transfer stations 40, 42, and 44 are shown disposed along the path of travel of the charge pattern between the rollers 26 and 2S. Although only three developing and transfer stations 40, 42, and 44 are shown herein, merely for illustrative purposes, additional developing and transfer stations may be included.

The combination of apparatus at the developing and transfer station 40 is substantially similar in structure and function to that at each of the developing and transfer stations 42 and 44. Hence, only the apparatus at the developing and transfer station 40 will be described in detail, and the corresponding parts of the apparatus at the developing and transfer stations 42 and 44 will be designated with the same reference numeral plus the additional letters a and b, respectively.

A combination of developing apparatus 70 and transfer apparatus 72 is disposed at the developing and transfer station 40. The developing apparatus 70 comprises a rotatable brush 74, such as a cylindrical brush of velour, disposed for rotation, by any suitable means, in a trough 76 filled with developer 78, such as a triboelectric mixture of toner particles and iron filings. A wide belt 80, disposed between rollers 82 and 84, serves to replenish the developer 78 with toner particles 86 from `a hopper 88 as toner is consumed in developing the latent electrostatic image. A vibrating mechanism 90 is mechanically coupled to the hopper 88 to shake it and to cause the toner particles 86 to fall onto the belt 80.

The belt 80 is rotated by any suitable means connected to either one of the rollers 82 or 84. The belt 80 is disposed to contact the brush 74 which, in turn, develops the latent image on the insulating surface 12 of the recording element 14 by applying the toner particles from the developer 78 to it. Any magnetic particles, such as the iron lings of the developer 78, that may adhere to the insulating surface 12, after development, are removed by a magnetic system comprising iron rollers 92, 94, and a magnet 96, such as an electromagnet. The rollers 92 and 94 are rotated by any suitable means. Since the rollers 92 and 94 are disposed closer to the insulating surface 12 than the magnet 96, magnetic particles are attracted to the rollers 92 and 94, are carried out of the magnetic field as these rollers turn, and drop onto the brush 94 or the belt 80 for eventual return to the developer 78 in the trough 76.

After development of the latent electrostatic image, the unxed, developed image is transferred to a transfer material by the transfer apparatus 72. The transfer apparatus 72 comprises two electrically conducting rollers 98 and disposed on opposite sides of the recording element 14 along its path of travel. The roller 100 is connected to a common connection, such as ground, and the roller 98 is connected to one terminal 102 of a transfer voltage source (not shown), the other terminal of the transfer voltage source also being connected to the common connection, ground.

If development of a direct charge pattern (latent electrostatic image) of a light image on the insulating surface 12 is desired, the roller 98 is connected to the negative terminal of the transfer voltage source. To develop a reverse image, the roller 98 is connected to the positive terminal of the transfer voltage source. If, for example, a page comprising black letters (image) on a white background is to be copied, a direct charge pattern of the image on the surface 12 is here defined as one which is formed by discharging the charge in the image area (letters). A reverse charge pattern of the image is one which is formed by discharging the charge in the image area, and retaining the charge in the background area.

The

rollers

100 and 102 are also mechanically biased toward each other, by any suitable means, as by springs (not shown) to apply pressure between the recording element 14 and a transfer material, such as a transfer sheet 104. At least one of the

rollers

98 and 100 may be of conductive rubber for good pressure contact. The transfer sheet 104 may be in the form of an elongated web taken from a supply roll 106 and wound around the roller 98 so that it can come in contact with the unxed developed latent image on the insulating surface 12 of the recording element 14. The motor 16 is mechanically coupled to the roller 100 which, in turn, may be coupled to the roller 98 for moving the sheet 104 at the same rate of speed as the recording element 14. (The motor 16 is also coupled to the rollers 100a and 100b). Thus, a portion of the unlixed toner from the unixed, developed latent image is transferred to the transfer sheet 104 to provide a first copy of the image. The image on the transfer sheet 104 may be fixed, as by heat rays 108 from any suitable source of heat.

The amount of electroscopic toner that may be transferred from an unfixed developed latent image on the insulating surface 12 to the transfer sheet 104 may be controlled by a transfer voltage of suitable amplitude and polarity applied between the

rollers

98 and 100, that is, across the transfer sheet 104 and the recording element 14. Thus, if the electroscopic toner that is responsible for the development of the latent electrostatic image is negative, the greater the :positive voltage applied to the roller 98 with respect to ground the greater will be the transfer of negative toner particles from the insulating surface 12 to the transfer sheet 104.

Additional transfer copies can be made on transfer sheets 104g and 104b by redevoloping the charge pattern (latent electrostatic image) on the insulating surface 12 with developing apparatus 70a and 70b, and transferring toner from the unfixed redeveloped electrostatic images to the transfer sheets 104a and 104b, respectively.

Since the charge of the latent electrostatic image on the insulating surface 12 tends to decay with time, uniformity of contrast of the images on the transfer sheets 104a and 104b are assured by suitable transfer voltages applied to the terminals 102a and 102b. In practice, where similar developer 78 is used for each transfer copy, it has been found that the transfer voltage for each additional transfer copy should be increased to provide transfer copies of uniform contrast. Thus, if the transfer voltage applied to the terminal 102 is 600 volts, the voltages applied to the terminals 102a and 102b may be in the order of 650 volts and 750 volts, respectively.

While only three developing and transfer stations 40,

42, and 44 are illustrated in the apparatus 10 merely for illustrative purposes, additional developing and transfer stations may be disposed along the path of travel of the recording element 14, if so desired. Six transfer copies of substantially uniform contrast, for example, have been made easily from a single latent electrostatic image, utilizing apparatus similar to the apparatus but having six developing and transfer stations instead of the three shown.

After the required number of transfer copies have been made, all of the toner on the insulating surface 12 may be removed by the erasing apparatus 46. The erasing apparatus 46 comprises substantially a vacuum cleaner having a plurality of brushes 110, 112, 114 and 116 rotated by any suitable means in a hood 118 connected to any suitable Vacuum system. The cleaned recording element 14 is wound on the take-up roller 20 and may be reused.

From the foregoing description, it will be apparent that there has been provided improved apparatus for making a plurality of visible transfer copies from a single charge pattern on an insulating surface. While the improved apparatus has been illustrated with developing apparatus carried out by electroscopic powder developer, variations of the apparatus, all coming within the spirit of this invention, will, no doubt, suggest themselves to those skilled in the art. For example, liquid developing means for applying a liquid developer instead of a powder developer may be used to develop the latent electrostatic image by any suitable means known in the art. Hence, it is desired that the foregoing description shall be considered as merely illustrative and not in a limiting sense.

What is claimed is:

1. In apparatus of the type wherein an electrostatic charge pattern of an image is formed on an insulating surface, improved means for making a plurality of visible, transfer copies of said image comprising:

means to move said insulating surface along a predetermined path,

a plurality of image developing and image transfer combinations stationed successively along said path, and

each of said combinations comprising developing means to apply toner to said charge pattern to develop it and transfer means to bring a transfer material momentarily into contact with the developed charge pattern to transfer at least a portion of said toner to said transfer material,

said transfer means comprising a pair of electrically conductive rollers, said transfer material comprising a sheet of paper, said insulating surface comprising the surface of a web of a recording element, said -path being between said pair `of rollers, and a transfer voltage applied between said pair of rollers, the transfer voltage in each successive combination along said path being greater than that in the previous combination.

2. In apparatus Vof the type wherein an electrostatic charge pattern of an image on an insulating surface is developed by a toner, and at least a portion of the toner of the developed image is transferred to a first transfer material at a transfer station to provide a first transfer copy, improved means for making a plurality of additional transfer copies of said image comprising:

a plurality of developing and transfer combinations,

means to move said insulating surface from said transfer station past each of said combinations in succession,

each of said combinations comprising developing means to redevelop said electrostatic charge pattern with a toner, and transfer means to transfer at least a portion of the toner from the redeveloped charge pattern to an additional transfer material,

said transfer means comprising a pair of electrically conductive rollers to press momentarily said addiditional transfer material against the redeveloped charge pattern and to apply a transfer voltage to said toner to attract said toner from said surface to said transfer material.

3. Apparatus for making a plurality of visible copies of a latent electrostatic image on an insulating surface of a photoconductive layer of a recording element, said apparatus comprising, in combination:

means to move said recording element along a predetermined path,

a charging station, an exposure station, a plurality of image developing and image transfer stations, and an erasing station disposed sequentially along said path,

a double corona charging device comprising a negative corona discharge device and a positive corona discharge device disposed on opposite sides of said recording element to charge said insulating surface uniformly at said charging station,

a cathode ray tube having a screen for displaying information disposed adjacent to said insulating surface at said exposure station to expose said surface with a light image, whereby to form said latent electrostatic image,

a plurality of image developing and image transfer combinations disposed at said plurality of image developing and image transfer stations, respectively, each of said combinations comprising developing means to apply toner to said latent electrostatic image on said surface to develop it, and image transfer means to press momentarily a transfer material against the developed image, whereby to transfer at least a portion of the toner from said surface to said transfer material, said transfer means comprising a pair of electrically conductive rollers disposed to receive said recording element and said transfer material therebetween,

means connected to said rollers to apply a voltage therebetween to aid in transferring said toner from said insulating surface to said transfer material, the transfer voltage in each successive combination being greater than that in the previous combination, and

cleaning means disposed at said erasing station to remove toner from said insulating surface, whereby said recording element may be reused.

References Cited UNITED STATES PATENTS 3,115,814 12/1963 Kaprelian 95-1.7 3,128,683 4/1964 Rubin 95-1.7 3,267,840 8/1966 Honma 95-1.7 X

JOHN M. HORAN, Primary Examiner.