US2934650A - Charging apparatus - Google Patents

Description

April 26, 1960 R. N. DE WITT CHARGING APPARATUS Filed April 10, 1957 INVENTOR. RICHARD N. DEWITT BY F "g Arman CHARGING APPARATUS Richard N. De Witt, Columbus, Ohio, assignor, by mesne assignments, to Haloid Xerox Inc.

Application April 10, 1957, Serial No. 651,979 6 Claims. (Cl. 250--49.5)

This invention relates in general to xerography and in particular to the sensitization of xerographic plates.

In xerography as described, for example, in Carlson US. Patent 2,297,691, an electrostatic charge pattern is formed on an insulating photoconductive surface of a plate member by applying a uniform electrostatic charge to the surface of the photoconductive insulating layer to sensitize the plate and then byexposing the sensitized plate to a pattern of light and shadow of light rays or other activating radiation to be recorded. The charge pattern may then be developed with finely divided, electrostatically charged particles or liquid droplets, or the pattern may be otherwise utilized, and if developed the developed image may be allowed to remain on the surface of the plate, or it may be transferred, photographed, or the like as is well-known in the art.

This invention is concerned with the application of uniform electrostatic charge to surfaces used in xerography and has particular applicability in connection with the sensitization of xerographic plates through the application of a uniform electrostatic charge to the surface of the photoconductive insulating layer.

Additional objects and adavantages of the present invention will be more readily apparent in view of the following disclosure and description, especially when read in conjunction with the accompanying drawing wherein an embodiment of charging according to this invention is illustrated.

In the drawing there is shown for illustrative purposes a xerographic plate 1% comprising a photoconductive insulating layer 12 overlying a conductive backing member 11 positioned on support and guide rails 13. Plate is moved at a uniform rate of speed by motor 32 driving sprocket 33 interlocked into chain links of drive chain 35. Extending from drive chain 35 at spaced intervals are arms 37 positioned to contact plate 10 when plate 10 is positioned on guide and support rails 13 and adapted to transmit movement to the plate from motor Preferably, motor 32 is a variable speed motor, as is wellknown in the art, to allow varying the speed of movement of plate 10. Drive chain 35 extends over freely rotating sprocket 36 which is positioned and disposed to maintain drive chain 35 in an extended position and without much play. Connected to guide and support rails 13. are braces 15 supporting roller member 16 at its axle 20 and supporting also bar 33. In this embodiment bar 38 comprises an insulating member such as, for example, insulating rubber, plastic, or the like in which there is positioned and disposed a number of charging needles 22. Charging needles 22 are connected together by connector 23 such as an electrically conductive wire, conductive metal plate, or the like, and connector 23 is electrically attached to lead 25 terminating in variable tap 30. Roller 16 comprises a covering layer 17 and an inner conductive core 18. Conductive core 18 is connected to lead 26 terminating in variable tap 3 1. Taps 30 and 31 are across resistor 28, which is supplied with potential from power supply 27. As illustrated in this embodiment, the

United States Patent 0 ICC lower end of resistor 28 is at ground potential and, accordingly, in this embodiment needles 22 are being supplied with high potential from power supply 27, and core 18 of roller 16 is being held at ground potential. Also in this embodiment, conductive backing member 11 of plate 10 is grounded through physical contact with guide rails 13 which are, as illustrated, held at ground potential.

In operation a plate 16) to be charged is positioned on guide and support rails 13 and against arm 37. The motor is energized as through a switch or the like to cause movement of the plate member as, for example, in the direction indicated by the arrows. Roller 16 is mounted to rotate freely in braces 15 and is also positioned and disposed to contact the upper surface of plate 1%. Accordingly, 'as plate 10 moves beneath and in contact with roller 16, roller 16 is frictionally driven by moving plate It] and rotates against the plate surface. The potential supplied from power supply 27 to needles 22 is in the order of several thousand volts and is suiiicient to produce corona discharge at the lower ends of the needles which are, preferably, quite fine or pointed. The discharge created from the needle tips is attracted to the surface of roller 16 by the field created between the grounded core 18 of roller 16 and the ions themselves as well as the lines of force extending to needles 22. Thus, during operation of the embodiment illustrated in the drawing charge is flowed from needles 22 to roller 16 and roller 16 is then rolled into contact with the surface to be charged and charge is deposited on the photoconductive insulating layer 12 of plate 16. As is illustrated in this embodiment, plate 10 being charged is formed with the backing member 11 extending beyond the photoconductive insulating layer 12. This is the usually available plate in xerography, and the margin area is generally sufiicient in operation of the present device to contact the uncharged areas of roller 16 and to cause to be presented to the photoconductive insulating layer 12 charged areas of roller 16. If a plate, for example, without a margin area is being sensitized, provisions may be made to bring about a half turn of roller lid prior to its contact with the photoconductive insulating layer as through manual manipulation, for example, through the use of a crank or through automatic features, to delay plate movement until roller rotation has taken place to a suflicient extent.

It is to be realized that, although particular elements and a particular mode of operation have been described in; connection with the drawing, there is no intention to be limited thereto, but, instead, it is intended to include within the scope of this invention various equivalents as well as various modifications in the elements and the mode of operation, as is well-known to the art, to accomplish charing according to this invention. For example, there is illustrated in the drawing charging needles 22. It is Well-known in the art that charging wires as Well as modified charging devices, for example, as shown and described in Walkup US. Patents 2,777,957 and 2,774,921, may be used and such other charging techniques and devices are intended to be incorporated herein. Also, although the backing member 11 of plate It) is illustrated as grounded through support rails 13, charging may be and has been accomplished according to this invention by positioning the plate member on a wooden table. However, in order to assure a more uniform field through the photoconductive insulating layer 12, it is generally preferred that the plate backing member 11 be maintained at ground potential. Clearly also, there is no'intention to limit this invention to movement only of the plate member but, instead, movement of the plate member in the drawing has been used to illustrate that relative movement between roller 16 and plate to sensitize plate 10 according to this invention is desirable and necessary and, accordingly, modifications including movement of roller 16 across a stationary plate 16 are also intended to be included herein as, for example, manually rolling roller 16 across a stationary plate positioned and disposed on a support such as a table or the like.

Variable tap 3% allows for the control of the potential applied to charging needles 22 and allows for regulation of charge or discharge created in the air surrounding needles 22. In addition, if desired, the present invention may be operated with needles 22 de-energized as, for example, by moving tap 30 to ground or through the use of a switch or the like in lead 25. With needles 22 deenergized, charging may be accomplished by applying potential to the surface of roller 16 through the application of a raised potential to core 18 of roller 16 by moving tap 31 to a higher point along resistor 28. The surface of roller 16 attains a raised potential which is dependent upon the potential applied to core 18, the thickness and resistive or dielectric characteristics of covering layer 17, whether or not backing member 11 of plate 10 is at a ground potential, and the like and, depending upon the potential at the surface of roller 16, charge of a particular amount is deposited across the surface of photoconductive insulating layer 12.

Outer covering layer 17 comprises as a minimum a resistive material and may comprise insulating material. Functionally, the material should be sufficiently resistive to restrain flow therethrough as well as to prevent, or substantially so, lateral conductivity along its outer surface. It is to be realized that plates are likely to have localized spots of high conductivity through the photoconductive insulator. If too low a resistive outer covering layer is used on roller 16 and the line of contact of the roller with the plate includes a spot of high conductivity in the photoconductor, the current through the photoconductor at this point will be so high as to cause serious plate damage and, in addition, the roller surface potential across the remaining areas of the line of contact will be reduced substantially resulting in the deposit on the photoconductor of substantially no charge along the line or area of contact. In addition, functionally, this layer should be of suflicient resistivity to restrain charge from laterally flowing along its surface. Specifically, it is pointed out that electrodes along the line at which they are closest, which in the embodiment of the drawing will be along the line of contact, in a constant potential system will be the area of highest capacitance and that energy tends to move to such a lower energy region. Accordingly, any charges on the surface of roller 16 around the line of contact will tend to move to the line of contact. At present, although the underlying theory of the present invention is not completely understood, it is believed that charges which move from the roller to the plate surface move from the roller along an area of the roller spaced from the surface being charged. Possibly also, charges move from the roller along the line of contact. However, the movement of charges across a gap, either the gap as that portion of the roller rolls into the line of contact or the gap which follows that area of the roller as it moves out of the line of contact, is believed to be highly important in connection with the present invention to bring about uniform and rapid charging of the surface of the plate. In addition, charging across a gap, it is presently believed and experiments tend to prove, results in a self-limiting system and is, accordingly, valuable in preventing overcharging of plates as well as uniformly charged plates even where uniformity in relative motion and the like are lacking. Accordingly, the resistive outer covering layer of roller 16 should be of sufficient resistivity to inhibit lateral flow of charges and, thus, prevent the charges from moving to the line of contact and out of the area Where a gap separates the roller surface from the plate.

Various resistive materials have been used for the covering layer. Generally, their resistivities have been above about 10 ohm-centimeters. Using materials of low resistivity, that is, in the order of 10 to 10 ohmcentimeters, and using the embodiment illustrated in the drawing, it is desirable to apply a raised potential to the core of roller 16 and apply a field from the core through the photoconductive insulating layer. In addition, when using these low resistivity materials it is desirable to deenergize the charging needles or other charging grid. In experiments carried out in connection with this invention in which the potential was placed on the outer surface of roller 16 through the application of a raised potential to the core some of the best results have been obtained using a covering layer having a resistivity in the order of 10 ohm-centimeters and having a thickness of inch. The particular material used was rubber, and the actual resistance between the core of roller 16 and a metal plate placed against it was 200 megohrns. The roller was moved manually over the photoconductive insulating layer which, in the particular experiments carried out, comprised selenium at a velocity of approximately one centimeter per second, and the plate began to be charged up following the application of a potential difference of more than about 200 volts between the core of the roller and the backing member of the plate. Using about 600 volts potential difference applied and passing the roller over the selenium surface a number of times resulted in a charge deposition measurable on the seleniurn surface of 400 volts. The use of a number of passes of the roller across the plate surface was found valuable in creating a uniform charge density across the surface and the amount of potential applied will, as a general proposition, depend on such factors as the amount of charge desired on the plate surface, the dielectric and resistivity of the outer covering layer, and the like. Generally, it may be stated, however, that the potential difference desired between the charged surface of the photoconductive insulating layer and its backing member may be controlled by creating on the surface of the outer layer of roller 16 a potential in the order of 200 to 400 volts greater than the amount of measurable potential desiredon the surface of the photoconductive insulating layer. This potential on the surface of roller 16 may be created as through the application of a potential through its core where the covering layer is of a low enough resistivity to allow the outer surface to attain a raised potential and to continue its supply of charge through flow through the covering layer and from the core, or it may be obtained where the covering layer is a sufficient insulator and will not allow charge flow to the core through the deposition of charge as from needles 22 illustrated in the drawing. In experiments carried out in which the needles have deposited charge on the covering layer and in which uniform charging of the plate has resulted fibrous materials, for example, have been used.

Preferably, this covering layer should be a resilient material so that, if particles are present between roller 16 and the surface being charged, they become temporarily imbedded in the covering layer and are not rigidly forced into the photoconductive insulating layer and, thus, damage to the plate member is prevented. Although there should be sufficient force used to press the roller against the surface being charged, force is not critical unless it is varied and then it causes a nonuniform charge to be deposited.

Various known photoconductive insulating materials such as anthracene, selenium, and the like have been charged using the device according to this invention. A particular advantage of this invention is in charging of flexible xerographic plates or other flexible members. For example, xerographic plates backed by paper or foil instead of rigid metallic members sometime tend to curl, and the use of corona discharge or the like, as is (gem.- monly employed in the art and as is illustrated in one of the aforementioned Walkup patents, will tend to create a nonuniform charge on the surface of the flexible xerographic plate unless steps are taken to hold the plate completely flat during the charging operation. Now in accordance with the present invention, the roller is pressed and rolled against the surface and as long as the thickness of the plate member is substantially uniform throughout (as is the case where reasonable quality is desired) uniform contact with the surface to be charged will be made and a uniform charge will be deposited thereon.

In addition to the various materials mentioned throughout which may be used as a covering or outer layer for the core of roller 16, there may also be used various vinyl plastics, other plastic materials, and other nonfibrous materials commonly known to the art having a sufficient resistivity to carry out this invention.

The size of roller 16 is not presently believed to be critical. Various sizes ranging from A2 inch to 3 /2 inches have been employed successfully and, from the work that has been done, it is presently believed that rollers with larger diameters tend to give best results.

While the present invention as to objects and advantages as has been described herein has been carried out in a specific embodiment thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. Xerographic charging apparatus to place a substantially uniform electrostatic charge for Xerographic image reproduction on a first surface of a Xerographic plate including a photoconductive insulating surface layer at said first surface, said apparatus comprising in combination support means to support the Xerographic plate, a xerographic plate on said support means, a cylindrical mem ber rotatably mounted with respect to said support means to contact the first surface of the Xerographic plate along a line of contact while said plate is supported by said support means, said cylindrical member comprising a core of electrically conductive material surrounded by and in electrical contact with an outer resilient covering layer of substantially uniform thickness and having a substantially uniform electrical resistivity above about ohm-centimeters, electrical means operatively connected to said cylindrical member to apply a substantially uniform charging electric potential to the outer surface of said cylindrical member and operatively adapted to maintain the second surface, opposite to said first surface, of the Xerographic plate at a uniform electric potential at least in the area opposite the line of contact, and moving means to cause a rolling contact between the cylindrical element and the first surface of the Xerographic plate while the plate is supported by said support means thereby advancing the line of contact between said plate and said cylindrical element across said photoconductive insulating layer, said electrical means being adapted to apply a sensitizing potential difference to the photoconductive insulating layer of said plate through the deposition of a uniform charge on said photoconductive insulating layer as said cylindrical member moves thereacross which on exposure of said plate results in a developable Xerographic image.

2. Xerographic charging apparatus to place a substan tially uniform electrostatic charge for Xerographic image reproduction on a first surface of a Xerographic plate including a photoconductive insulating surface layer at said first surface, said apparatus comprising in combination electrically conductive support means to support the xerographic plate, a Xerographic plate on said support means, a cylindrical member rotatably mounted with respect to said support means to contact the first surface of the xerographic plate along a line of contact while said plate is supported by said support means, said cylindrical member comprising a core of electrically conductive material surrounded by and in electrical contact with an outer resilient covering layer of substantially uniform thickness and having a substantially uniform electrical resistivity above about 10 ohm-centimeters, electrical means operatively connected to said cylindrical member to apply a substantially uniform charging electric potential to the outer surface of said cylindrical member and operatively connected to said support means to maintain the second surface, opposite to said first surface, of the Xerographic plate at a uniform electric potential at least in the area opposite the line of contact, and moving means to cause a rolling contact between said cylindrical element and the first surface of the Xerographic plate while the plate is supported by the support means thereby advancing the line of contact between the plate and the cylindrical clement across the photoconductive insulating layer, said electrical means being adapted to apply a sensitizing potential difference to the photoconductive insulating layer of said plate through the deposition of a uniform charge on said photoconductive insulating layer as said cylindrical member moves thereacross which on exposure of said plate results in a developable image.

3. Xerographic charging apparatus to place a substantially uniform electrostatic charge for Xerographic image reproduction on a first surface of a Xerographic plate including a photoconductive insulating surface layer at said first surface, said apparatus comprising in combination support means to support the Xerographic plate, a xerographic plate on said support means including a flexible paper layer bearing the photoconductive insulating layer, a cylindrical member rotatably mounted with respect to said support means to contact the first surface of the Xerographic plate along a line of contact while said plate is supported by said support means, said cylindrical member comprising a core of electrically conductive material surrounded by and in electrical contact with an outer resilient covering layer of substantially uniform thickness and having a substantially uniform electrical resistivity above about 10 ohm-centimeters, electrical means operatively connected to said cylindrical member to apply a substantially uniform charging electric potential to the outer surface of said cylindrical member and operatively adapted to maintain the second surface, opposite to said first surface, of the Xerographic plate at a uniform electric potential at least in the area opposite the line of contact, and moving means to cause a rolling contact between the cylindrical element and the first surface of the Xerographic plate while the plate is supported by the support means thereby advancing the line of contact between the plate and the cylindrical element across the photoconductive insulating layer, said electrical means being adapted to apply a sensitizing potential difference to the photoconductive insulating layer of said plate through thedeposition of uniform charge on said photoconductive insulating layer as said cylindrical member moves thereacross, charging of said photoconductive insulating layer taking place at least as said cylindrical member rolls into and rolls out of contact around the line of contact at said first surface which on exposure of said plate results in a developable Xerographic image.

4. The method of uniformly electrostatically charging a Xerographic plate including a photoconductive insulating layer to form a sensitive Xerographic plate which on exposure forms a developable Xerographic image comprising positioning a rotatable cylindrical charging electrode in line contact with the surface of a Xerographic plate to be charged, said cylindrical electrode having a conductive core and a uniformly electrically resistant uniformly thick covering layer surrounding said conductive core and in electrical contact therewith while in line contact with the Xerographic plate to be charged, said covering layer being sufficiently resistant to prevent lateral flow of charge along its surface, applying an electric potential to the outer surface of said cylindricalelectrode and an electric field between said cylindrical electrode and said plate, and rolling said cylindrical electrode across the surface of said Xerographic plate while maintaining a line of contact between said plate and said member, said cylindrical member charging said plate at least while said member rolls 'into and while said member rolls out of contact around the line of contact as said member moves relative to said plate.

5. The method of claim 4 in which the Xerographic plate comprises a flexible xerographic plate and in which the applied potential to the outer surface of said cylindrical member is in excess ofthe potential desired on the surface of the xerographic plate.

6. The method of claim 4 in which the xerographic plate comprises photoconductive insulating selenium overlying a metallic backing member and in which the electric field between said cylindrical electrode and said plate is maintained between said cylindrical electrode and said metallic backing member.

References Cited in the file of this patent UNITED STATES PATENTS Hooper Aug. 29, 1950 2,558,900 Hooper July 3, 1951 2,807,233 Fitch Sept. 24, 1957

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