US3271145A

US3271145A - Process for producing an electrostatic charge image

Info

Publication number: US3271145A
Application number: US332695A
Authority: US
Inventors: Gene H Robinson
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1963-12-23
Filing date: 1963-12-23
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06
Also published as: GB1092813A; DE1472937B2; BE657150A; DE1472937A1

Description

PROCESS FOR PRODUCING AN ELECTROSTATIC CHARGE IMAGE Filed DeC. 23, 1963 GENE H. ROB/NSOA/ INVENTOR.

Ar TOR/VEYS United States Patent Filed Dec. 23, 1963, Ser. No. 332,695 2 Claims. (Cl. 96-1) The present invention relates to xerography and xeroprinting and more particularly to a process and apparatus for charging xerographic and Xeroprinting plates.

Various systems for electrostatically charging xerographic and xeroprinting plates, hereinafter referred to as xero plates, are known. The most common systems employ fine wires held at corona-producing potentials. Other systems employ materials of intermediate conductivity bridging the space between an electrode and surface of the plate to be charged. All such systems require means for moving the charger and the plate to be charged relative to each other to achieve uniformity of charging. Such relative movement is customarily achieved by sweeping the charging device over the surface to be charged.

It is the primary object of the present invention to provide a simple method for applying in a uniform manner an electrostatic charge to the entire surface of a xero plate without requiring any relative movement between the charging device and the xero plate.

It is another object of the invention to provide a simple method of electrostatically charging a xerographic plate which is particularly adapted for use with reflex printing.

It is a still further object of the invention to provide a method of electrostatically charging a xerographic plate in which the charging step itself effects reflex exposure of the plate.

It is another object of the invention to provide a method and apparatus for electrostatically charging a xerographic sheet while it is in contact with a document to be reproduced.

These objects are accomplished by the following invention. The process of the invention comprises placing a sheet of paper, or material of similar conductivity, in contact with a xero plate, sandwiching the sheet and the plate between parallel, plate electrodes, and applying a potential difference of about 1500 volts between the electrodes for approximately one second. In one embodiment the sheet is the document to be reproduced, and by having the appropriate electrode transparent, a reflextype of exposure is made without disassembling the sandwich. In a species of this embodiment, prolonged charging itself effects simultaneous reflex exposure of the xerographic sheet.

These and other objects of the invention will be more fully understood from the following description, when read in connection with the accompanying drawing, in which:

FIG. 1 is a cross-sectional view through a xerographic plate and a document sandwiched between a pair of plate electrodes;

FIG. 2 is a cross-sectional view through a xerographic plate and a layer of cellophane sandwiched between a pair of plate electrodes;

FIG. 3 is a diagrammatic view of an apparatus for electrically charging and reflex exposing successive portions of a xerographic sheet according to the present invention; and

FIG. 4 is a cross-sectional view through a xeroprinting plate and a sheet of paper sandwiched between a pair of plate electrodes.

FIG. 1 shows a xerographic plate 1 which may consist of a support 3 such as paper, coated with a zinc-oxide-inresin-binder photoconductive layer 5. The plate 1 is 3,2713% Farmed Sept. 6, tees ICC placed in contact with a document 7, to be reproduced. The xerographic plate 1 'and the document 7 are sandwiched between the plate electrodes 9 and 11. A voltage source 13 and a switch 15 are connected between the electrodes 9 and 11. The electrode 9 is connected to the negative terminal of the voltage source 13 and the posi tive terminal and the electrode 11 are connected to ground. In addition to charging the xerographic plate 1, the arrangement shown in FIG. 1 is also adapted to permit reflex exposure of the xerographic plate 1. By having the appropriate electrode, in this case the electrode 11, transparent, the xerographic plate 1 can be reflex exposed, for example by means of a light source 17, after or during and after charging, without having to disassemble the sandwich. The sandwich can then be disassembled for xerographic development of the electrostatic image on the xerographic plate 1, by any of the known methods, such as cascade, magnetic brush, etc.

FIG. 2 shows a xerographic plate 2% consisting for example of a paper support 22 having a photoconductive layer 24, such as Zinc-oxide-in-resin binder, coated thereon. The photoconductive side of the plate 20 is placed in contact with a transparent sheet 26 of material having the appropriate conductivity. The plate 20 and the sheet 26 are sandwiched between an upper plate electrode 28 and a lower plate electrode 30. A voltage source 32 and a switch 34 are connected across the

plate electrodes

28 and 30. The positive terminal of the voltage source 32 is connected to the upper electrode 28 and to ground and the negative terminal is connected to the lower electrode 30. By having the lower electrode 30 transparent, the photoconductive layer 24 can be projection exposed, after charging, without disassembling the sandwich, by means of a lamp 36, a transparency 38, and a lens 40. The sandwich can then be disassembled and the electrostatic image xerographically developed.

nected to the electrode 54 and the positive terminal of the voltage source 58 and the electrode 56 and connected to ground. A document 62 to be reproduced is sandwiched between the

electrodes

54 and 60 with the image surface in contact with the xerographic sheet 50. By having the lower electrode 56 transparent, the xerographic sheet 50 can be reflex exposed by means of a light source 64. After the charging and exposing steps, the xerographic sheet 50 is advanced through the sandwhich to position a new area of the xerographic sheet 56 for charging and exposing. As the sheet 50 is advanced, the previ ously charged and exposed areas of the xerographic sheet 50 are fed through a station 66 for subsequent operations. For example, the electrostatic image is first developed and the toner particles either fixed to the sheet 50 or transferred to a permanent record medium and fixed thereto. These subsequent operations are well known in the art, and since they form no part of the present invention they will not be described in detail. The xerographic sheet 50 can be advanced through the sandwhich as many times as is necessary to produce the required number of copies of any given document 62, without requiring the sandwich to be disassembled. The upper electrode 54 is made easily removable, for example, by hinging one side thereof, to

provide for simple replacement of documents to be reproduced. The arrangement shown in FIG. 3 for continuous operation without disassembling the sandwhich is also be between about 10 and ohms.

3 useful in the embodiment described with reference to FIG. 2.

According to the present invention the auxiliary sheet, such as the sheet 26 of FIG. 2, should have a resistance per unit area lying between that of metal on one hand, and a good insulator on the other hand. The resistance between the upper and lower surfaces of an area of the auxiliary sheet of one square centimeter should preferably Too low resistance leads to non-uniform charging and provides the xero plate with no protection against localized or arc breakdown.

Too high resistance leads to insufficient charging or a very I low rate of charging.

A large variety of paper grades and thicknesses have been used; all worked well. Plastic films of appropriate conductivity, for example, cellophane, gelatin, or glassine, can be used, especially when transparency is required in the auxiliary sheet. Fabrics such as cotton, wool, linen, and viscose rayon have been successfully employed. Various types of exposure, e.g., reflex, projection, and contact, have been successfully employed in combination with the charging method of the present invention.

Two unexpected results arose from the practice of the invention with xerographic sheets having zinc-oxide-inresin-binder photoconductive layers. First, it was found that uniform sandwhich charging could be accomplished only when the pigment-to-binder ratio is 3:1 or lower. Such photoconductive layers having a higher pigment content would not charge uniformly and they displayed a mottled appearance when developed. Second, it was found that if charging times were extended to approximately 30 seconds under the conditions described below in Example 1 for reflex exposing, the discharge occurring between the photoconductive layer and the document not only serves to charge the photoconductive layer but also serves as a light source supplying enough energy in the visible and ultraviolet region of the spectrum to cause reflex exposure of the photoconductive layer. A possible explanation for this phenomenon is that the long exposure required induces in the photoconductive layer a state of fatigue; 21 state in which the layer is less able to store charge.

Another unexpected result was associated with the use of printed documents as the auxiliary or buffer sheets. It was expected that the printed matter would interfere with uniform charging of the photoconductive layer. However, over a wide range of charging times and electrode potentials no such interference was found.

FIG. 4 shows a xeroprinting plate 70, which may consist, for example, of a metal plate 71 having a pattern 72 of insulating resin. The plate 70 is placed in contact with a sheet 73 0f paper or other material of similar conductivity. The plate 70 and the sheet 73 are sandwiched ,between

plate electrodes

74 and 75. A voltage source 76 and a switch 77 are connected between the

electrodes

74 and 75.

The present invention is further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention.

Example N0. 1

A zinc-oxide-in-resin-binder xerographic layer with a pigment-to-binder ratio of 3:1 and an original document were placed between a pair of plate electrodes (one of trodes.

A zinc-oxide-in-resin-binder xerographic sheet with a pigment-to-binder ratio of 3:1 was placed between a pair of plate electrodes, one of which was transparent and had between itself and the xerographic layer a layer of cellophane, see FIG. 2. Cellophane has a resistivity of the same order of magnitude as that of paper. A potential difference of 2500 volts was applied to the elec- With the sandwich still assembled, the xerographic sheet was exposed by projection through the transparent electrode and the cellophane. The sandwich was then diassembled and the electrostatic image on the xerographic sheet was developed with an electroscopic powder which was then fused thereon to produce a permanent copy.

Example N0. 3

A zinc-oxide-in-resin-binder xerographic sheet was placed between a pair of plate electrodes as in Example No. 1, with a piece of paper used in place of the document. A potential difference of 1500 volts was applied across the electrodes as in Example No. 1 and the sandwich was then disassembled for contact exposure. The electrostatic image on the xerographic sheet was then developed with an electrostatic powder and the powder was then fused thereon to produce a permanent copy.

Example N0. 4

Kodak Photo Resist was used to produce a pattern of insulating resin on a metal plate. The metal plate was then place-d between a pair of electrodes as shown in FIG. 4 with a sheet of paper. A potential difference of 1500 volts was applied across the electrodes. The sandwich was disassembled and the charged resist pattern was developed with an electroscopic powder. The powder was then electrostatically transferred to bond paper and fused thereto to produce a permanent copy.

Example N0. 6

A dispersion of photoconductive zinc cadmium sulfide (No. 2225, The New Jersey Zinc Company) in a binder (Plaskon ST-856, a silicone-alkyd resin, Barrett Division, Allied Chemical Corporation) Was coated on Nesa glass and placed between a pair of electrodes as in Example No. 1 with a piece of paper used in place of the document. A potential difference of 1500 volts was applied across the electrodes and the coated Nesa glass was subsequently processed as in Example No. 3 to produce a permanent print.

Although the invention has been described in detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as' defined in the appended claims.

I claim:

1. A process for producing an electrostatic charge image, corresponding to an image on a document to be recorded, on a xerographic sheet comprising a photoconductive insulating layer on a conductive backing, comprising the steps of:

(a) positioning said document in facing, virtual contact with said sheet, said document and said sheet being separated by a minute air gap, with said image of said document in contact with said layer,

(b) sandwiching said document and said sheet between and in contact with two plate electrodes,

(c) applying a voltage across said electrodes of a value sufiicient to ionize the air in said air gap whereby ions of one polarity deposit on and therefore charge said layer, and

(d) continuing said voltage application for a time sufficient to allow the light produced by said ionization to reflex expose said layer, whereby an electrostatic charge image, corresponding to said image to be recorded on said document, is produced on said layer without the necessity for a separate, additional exposure step from an external source of actin-ic radiation.

2. The process according to claim 1 in which said document comprises a material of intermediate conductivity having a resistance of between about 10 and 10 ohm/cmfl, in which said photoconductive insulating 6 layer comprises zinc oxide in resin binder with a pigment to binder ratio no greater than 3:1, in which said applying step comprises applying about 1500 volts across said electrodes, and in which said continuing step comprises continuing said voltage application for about 30 seconds.

References Cited by the Examiner NOR-MAN G. TORC HIN, Primary Examiner.

20 C. E. VAN H'ORN, Assistant Examiner.

Claims

1. A PROCESS FOR PRODUCING AN ELECTROSTATIC CHARGE IMAGE, CORRESPONDING TO AN IMAGE ON A DOCUMENT TO BE RECORDED, ON A XEROGRAPHIC SHEET COMPRISING A PHOTOCONDUCTIVE INSULATING LAYER ON A CONDUCTIVE BACKING, COMPRISING THE STEPS OF: (A) POSITIONING SAID DOCUMENT IN FACING, VIRTUAL CONTACT WITH SAID SHEET, SAID DOCUMENT AND SAID SHEET BEING SEPARATED BY A MINUTE AIR GAP, WITH SAID IMAGE OF SAID DOCUMENT IN CONTACT WITH SAID LAYER, (B) SANDWICHING SAID DOCUMENT AND SAID SHEET BETWEEN AND IN CONTACT WITH TWO PLATE ELECTRODES,