Henderson, Gillespi C. (Moorestown, NJ)
Roger, Olden G. (Gwynedd, PA)

04/706835

02/23/1971

02/20/1968

Download PDF 3566110       PDF help

Click for automatic bibliography generation

250/324

361/230, 250/326

G03G15/02; B41M5/22; G03G15/00; G03G13/00

250/49.5(61) 346/74(ES) 250/49.561

3173049	Printing head in cathode ray tube face	March 1965	Benn
3370212	Corona charging apparatus	February 1968	Frank
3390266	Apparatus for charging the surface of photoelectric layers using corona discharge	June 1968	Epping
3409768	Light lock for air ionizer to shield photosensitive material	November 1968	Whitmore et al.

James, Lawrence W.

Church C. E.

Glenn, Bruestle H.

1. Apparatus for imparting an electric charge to an electrophotographic recording element disposable at a charging station in an electrophotographic printing machine, said apparatus comprising: gas charging means disposed at a location remote from said charging station for charging gas thereat; conduit means communicating between said location and said charging station, said conduit means comprising a first portion of relatively large cross-sectional area at said location for housing said gas charging means and a second tapered portion of relatively much smaller cross-sectional area formed with an elongated narrow opening adjacent said charging station; and blower means for blowing charged gas from said location through said conduit means to said charging station and upon said recording element.

2. In an electrostatic system for producing a charge-pattern on an insulating surface of a recording element, the combination of: means including an electrically conductive plate to support said recording element at a charge-pattern forming station; a corona discharge device having a pair of electrodes disposed at a location remote from said station and adapted to charge ambient air between said electrodes with an electrostatic charge of substantially one polarity when energized by a voltage of sufficient amplitude to produce a corona discharge, a conduit communicating between said electrodes and said insulating surface at a desired location substantially adjacent said station, said conduit comprising a tubular member having a first portion of relatively large cross-sectional area for housing said pair of electrodes and a second portion tapered to an elongated narrow opening adjacent said station; said plate also supporting said recording element at said location; and means to blow said charged air through said conduit to said desired location, whereby to charge said insulating surface at said desired location, and to blow said recording element into good contact with said

3. In an electrostatic printing system wherein a web of a recording element, having a relatively insulating photoconductive layer on a relatively conductive backing, is moved adjacent to the face of a cathode ray tube at a charge-pattern forming station, the improvement comprising: an electrically conductive plate adjacent to said face and adapted to contact said backing of said recording element, said photoconductive layer facing said face; a corona discharge device having a pair of electrodes remote from said station and adapted to produce a corona discharge in a gas between said electrodes to charge said gas when said device is electrically energized; a conduit communicating between said electrodes and the surface of said photoconductive layer at a location substantially adjacent said station, said conduit having a first portion for housing said pair of electrodes therein and a second tapered portion having an elongated narrow opening adjacent said location and extending transversely across said layer; said plate also supporting said recording element at said location; and a blower to blow said charged gas through said conduit to said location, whereby to charge said surface of said photoconductive layer at said location, to blow said conductive backing into good electrical contact with said plate and to provide a slight separation between said

4. In an electrostatic printing method of the type wherein a surface of a photoconductive layer of a recording element is first electrostatically charged and then exposed to a light image to produce an electrostatic latent image the improvement of applying an electrostatic charge to said surface at a desired location, comprising: charging a gas in a space of relatively large volume and cross-sectional area remote from said desired location with an electrostatic charge of a desired polarity; and blowing said charged gas while concentrating it into a narrow stream of relatively smaller cross-sectional area to said surface at said desired

5. Electrophotographic printing apparatus comprising: means for supporting an electrophotographic recording element at an exposure station; gas conduit means having a relatively large cross section at one end, and a relatively smaller cross section at the other end; a relatively large gas charging means which is larger than said relatively small cross section disposed in the lager end of said conduit means; and blower means for blowing gas charged by said charging means through said conduit means and out the smaller cross section end thereof; said conduit means being disposed with the larger end thereof together with said gas charging means remote from said exposure station and with the smaller end thereof adjacent to said exposure station, said smaller end by virtue of its relatively small size being spaced closer to said exposure station than could said relatively large charging means because of its relatively large size be spaced from said exposure station in the absence of said conduit means, whereby gas can be charged remote from said exposure station and blown through said conduit means to within close proximity of said exposure station.

This invention relates generally to electrostatic charging, and more particularly to improved apparatus for, and an improved method of, generating electrostatic charges and applying them to an insulating surface at a desired location relatively remote from the charge generating source.

In many electrostatic printing systems of the type wherein a continuous web of an electrophotographic recording element is moved simultaneously past a charging station and exposure station, it is desirable that the distance between these stations be as short as possible. Unless this were so, the electrostatic charge on the portion of the web between the charging and exposure stations would either decay to a useless value or be entirely dissipated if the printing system were shut down for some time. Since nothing can be printed on the discharged portion of the web when the system is started again, the discharged portion represents a loss of the recording element. Also, in electrostatic printing systems of the demand type, wherein it is necessary for the recording element to be available substantially instantly on demand, the aforementioned portion of the web between the charging and exposure stations may have lost enough of its original electrostatic charge during a waiting (nondemand) period so that it is not available for substantially instant exposure, again representing a waste of material and a loss of both information and time. The length of the portion of the web of recording element between the charging and exposure stations, however, is greater than usually desired because of the bulkiness of the parts in conventional, prior art, electrophotographic printing systems.

The improved electrostatic charging method and apparatus described herein provide an electrostatic charge on demand on the insulating surface of the recording element at a location immediately adjacent the exposure station, thereby eliminating or substantially reducing the aforementioned disadvantages of prior art electrostatic printing systems.

Briefly stated, the improved method of charging a surface at a desired location comprises (1) charging a gas relatively remote from the desired location, and (2) blowing the charged gas to the desired location. The improved apparatus comprises a conduit disposed between a pair of electrodes and the desired location relatively remote from the electrodes. When the electrodes are suitably energized, they produce a corona discharge in the ambient gas, charging the latter. Blower means are disposed to blow the charged gas through the conduit to the surface to be charged at the desired location.

FIG. 1 is a view of a portion of one type of electrostatic printing system, some parts being in cross section and some partly schematic, showing one embodiment of improved electrostatic charging means; and

FIG. 2 is a view of a portion of another type of electrostatic printing system, some parts being in cross section and some partly schematic, showing another embodiment of improved electrostatic charging means for charging the insulating surface of a web of a recording element at a location adjacent an exposure station provided by a cathode ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown an electrostatic printing system 10, employing one embodiment of improved electrostatic charging means 12. The electrostatic printing system 10 is of a type adapted to provide an electrostatic latent image on an insulating surface 14 of a recording element 16. The recording element 16 is a continuous web of sheet material which comprises a relatively insulating photoconductive layer 18, such as zinc oxide in a suitable binder, on a relatively conductive backing 20, such as paper.

The recording element 16 is pulled from a source of supply (not shown) past an electrostatic charging station 22, a charge-pattern forming station, hereinafter called an exposure station 24, and a developing station 25 by a pair of opposed pressure rollers 26 and 28. The roller 28 is mechanically coupled to an electric motor 30 for pulling the paper in a direction indicated by an arrow 32. The travel of the recording element 16 may be either continuous or intermittent.

A corona discharge device 34 is disposed over the recording element 16 at the charging station 22 so that a wire electrode 36 of the device 34 is disposed about one-half inch from the insulating surface 14 of the recording element 16. The corona discharge device 34 is energized by a suitable source of a unidirectional voltage whose negative terminal is connected to a negative terminal 38 of the device 34, and whose positive terminal is grounded, as is the shield 40 of the device 34. Thus, when the corona discharge device 34 is energized, a substantially uniform negative charge is deposited on the surface 14 at the charging station 22. The backing 20 of the recording element 16 rests on a grounded, electrically conductive plate 42 that extends between the charging station 22 and the exposure station 24.

Means are provided to form a charge pattern, such as a latent electrostatic image, on the previously uniformly charged insulating surface 14 at the exposure station 24. To this end, a light-image projector 44, such as a photographic enlarger, for example, is disposed over the recording element 16 at the exposure station 24 and adapted to project a series of light images successively onto the charged surface 14 as it moves past the exposure station. Thus, a series of latent electrostatic images are formed on the surface 14 as a result of discharging the previously imparted, uniform electrostatic charge selectively through the photoconductive layer 18 in proportion to the light intensities of the projected images. The latent electrostatic images may be developed at the developing station 25 by any toning and fixing means 45 known in the electrostatic printing art.

It has been observed that, in the absence of the improved charging means 12, hereinafter to be described, any electrostatic charge deposited on the insulating surface 14 between the charging station 22 and the exposure station 24 would decay rapidly and eventually disappear if the motion of the recording element 16 were stopped for even a few minutes. Hence, no satisfactory charge patterns would be formed on this discharged portion of the recording element 16 when this portion eventually passed through the exposure station 24. This portion of the recording element 16 would, therefore, be wasted every time the electrostatic printing system was stopped, in the absence of the improved charging means 12.

The improved charging means 12 is adapted to provide an electrostatic charge on the insulating surface 14 immediately adjacent the exposure station 24 so that substantially no portion of the recording element 16 would be wasted if the electrostatic printing system 10 were stopped. The improved charging means 12 comprise a pair of electrodes 50 and 52, a blower 54, and a conduit 56, such as a tubular member of insulating plastic material open at both ends. The electrode 50 comprises a piece of metallic screen material, such as a metal screen of about 40 to 60 mesh. The electrode 50 is supported within the conduit 56, by any suitable means, at a location relatively remote from the exposure station 24 and is connected to the positive output terminal of a power supply 58. The power supply 58 should provide a unidirectional output voltage of at least 6,000 volts. The electrode 52 comprises a relatively thin wire electrode connected to the negative output terminal of the power supply 58. The thin wire of the electrode 52 is adapted to produce electrical charges when employed in a corona discharge device. The polarity of the charges depend upon the polarity of the output terminal of the voltage source connected to the electrode 52.

The input terminals of the power supply 58 are connected to terminals 60 and 62 of a suitable power source through serially-connected switches 64 and 66. The blower 54 is connected in parallel with the input terminals of the power supply 58 through switches 64 and 65. The motor 30 is connected to the power source terminals 60 and 62 through the switch 66.

The electrodes 50 and 52 comprise a corona discharge device which, when energized by the power supply 58, produces a corona discharge in the gas (air) between the electrodes 50 and 52, thereby charging the ambient gas. The polarity of the charge of the charged ambient gas is predominantly that of the polarity of the onput terminal of the power supply connected to the wire electrode 52. The wire electrode 52 should be connected to the negative output terminal of the power supply 58, as shown, to charge the surface 14 of the layer 18 negatively when the layer 18 is of zinc oxide. The corona discharge device 34 can be energized either from the power supply 58 or from a separate power supply, as desired.

The blower 54 communicates with the conduit 56 and is disposed, by any suitable means, adjacent an open end of the conduit 56 above the screen electrode 50. When energized, the blower 54 is adapted to blow the air charged by the corona discharge between the energized electrodes 50 and 52, through the conduit 56 and onto the insulating surface 14 at a location immediately adjacent the exposure station 24. The conduit 56 has an elongated lower opening 68 adjacent to both the insulating surface 14 and the exposure station 24 so that the charged air can impinge upon the insulating surface 14 at this location for charging the surface 14. The opening 68 extends perpendicularly to the direction of travel of the recording element 16.

The improved charging means 12 operates in the electrostatic printing system 10 as follows: The electrostatic system 10 is started by closing the switches 64, 65, and 66. This action (1) moves the web of the recording element 16 in the direction of the arrow 32, (2) provides a corona discharge between the electrodes 50 and 52 to charge the ambient air therebetween, (3) causes the blower 54 to blow the charged air through the conduit 56 and through the opening 68 therein, (4) applies the charged air onto the insulating surface 14 at a location substantially adjacent the exposure station 24, and (5) causes the blower to force the recording element 16 into good electrical contact with the grounded plate 42. Thus, the insulating surface 14 of the recording element 16 is provided with a uniform electrostatic charge at a location where it can be exposed substantially immediately by images from the light-image projector 44. The electrodes 50 and 52 of the charging means 12 may be about 5 inches, for example, from the surface 14 of the recording element 16 to be charged.

The conventional corona discharge device 34 may be energized from its own power supply (not shown) when the motor 30 is started, and the switches 64 and 65 may be opened to deenergize the power supply 58 and the blower 54 after the insulating surface 14 of the recording element 16 that has been charged by the corona discharge device 34 has reached the exposure station 24, thereafter obviating the need for the improved charging means 12.

Thus, the electrostatic printing system 10 may be operated with the electrostatic charging provided by either the improved charging means 12 alone or the combination of the improved charging means 12 and the conventional, corona discharge device 34. The operation of the improved charging means 12 is necessary, however, to prevent waste and to provide a charged surface for substantially instant exposure every time the electrostatic printing system 10 is started.

The blower 54 may be operated independently of the power supply 58 through the switch 65. Such operation is desirable because the stream of air provided by the blower 54 also functions to force the recording element 16 into good electrical contact with the plate 42. Such action is important for the formation of good electrostatic images at the exposure station 24.

Referring now to FIG. 2, there is shown another electrophotographic printing system 70 using another embodiment of improved charging means 12a. The electrophotographic printing system 70 (FIG. 2) differs from the system 10 (FIG. 1) primarily in the charge-pattern forming means. Analogous parts with substantially similar functions in the systems 10 and 70 are designated by similar reference numerals. Where analogous parts differ in form, one is distinguished from the other by a reference letter.

The light-image projector in the electrophotographic printing system 70 is a cathode ray tube 72 having an elongated phosphor screen or face 74. The face 74 extends perpendicularly to the direction (arrow 32) of travel of the recording element 16. Light images are formed on the face 74 by an electron beam in response to signal receiving equipment (not shown) in a manner well known in the art. An exposure station 76 is adjacent the face 74 of the cathode ray tube 72. The recording element 16 in the system 70 is pulled past a charging station 78 and the exposure station 76, in the direction of the arrow 32, by any suitable drive means, such as those described, for example, for driving the recording element 16 in the system 10 in FIG. 1. The backing 20 of the recording element 16 is kept in contact with a grounded plate 80, at the exposure station 76, in a manner to be hereinafter described.

The charging means 12a in the system 70 (FIG. 2) is substantially similar to the charging means 12 in the system 10 (FIG. 1). The wire electrode 52a is connected to the negative terminal of a power supply 82 through a switch 84. The negative terminal of the power supply 82 is also connected to a wire electrode 86 of a corona discharge device 88, through a switch 89. The positive terminal of a power supply 82 is grounded, as is the screen electrode 50a of the charging means 12a.

A corona discharge device 90 is arranged to form a double corona discharge arrangement with the corona discharge device 88. A wire electrode 91 of the corona discharge device 90 is connected to the positive terminal of a power supply 92, through a switch 93. The negative terminal of the power supply 92 is grounded, as are the shields of the corona discharge devices 88 and 90. Each of the power supplies 82 and 92 is energized from a suitable input voltage source and is adapted to provide a unidirectional voltage of at least 6000 volts.

The blower 54a, in FIG. 2, is energized from the input voltage source to the power supply 82, through a switch 94. The switches 84 and 94 may be ganged for simultaneous operation of the blower 54a and energization of the electrodes 50a and 52a.

In operation, the recording element 16 is moved, either continuously or intermittently, in the direction of the arrow 32. The corona discharge devices 88 and 90 are energized by the power supplies 82 and 92 through switches 89 and 93, respectively, and the corona discharge device formed by the electrodes 50 a and 52a in the charging means 12a is energized through the switch 84. The blower 54a is started by closing the switch 94. The ambient air between the electrodes 50a and 52a is charged negatively by the resulting corona discharge and is blown by the blower 54a, through the conduit 56a and onto the insulating surface 14 at a location substantially adjacent the exposure station 76.

The charged air blown through the opening 68 at the bottom of the conduit 56a, in addition to charging the surface 14, forces the recording element 16 against the grounded plate 80. This action maintains the recording element 16 a very short distance away from the face 74 of the cathode ray tube 72, thereby preventing frictional wear on the face 74 that may otherwise be caused by the movement of the recording element 16 thereover.

After the system 70 has been rendered operative and the portion of the recording element originally between the exposure station 76 and the charging station 78 has passed the exposure station 76, the switch 84 may be opened, inactivating the electrodes 50a and 52a. Under these conditions, the surface 14 of the recording element 16 is charged by the corona discharge devices 88 and 90.

The blower 54a alone may, however, remain activated to provide a stream of air between the face 74 of the cathode ray tube 72 and the recording element 16. Thus, the stream of air provides two functions, keeping the recording element 16 in good electrical contact with the plate 80, and separating the recording element from the face 74 of the cathode ray tube 72. The first of these functions provides good electrostatic image formation at the exposure station 76, and the second of these functions prevents undue wear on the face 74 of the tube 72. The latent electrostatic images formed on the recording element 16 can be toned at the developing station 25 by any suitable developing means 45 known in the electrostatic printing art.