US3326709A

US3326709A - Electrostatic printing

Info

Publication number: US3326709A
Application number: US317201A
Authority: US
Inventors: Nelson R Nail
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1963-10-18
Filing date: 1963-10-18
Publication date: 1967-06-20
Anticipated expiration: 1984-06-20
Also published as: DE1297988B; BE654431A; GB1088857A

Description

June 20, 1967 N. R. NAIL ELECTROSTATIC PRINTING Filed Oct. 18.1963

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FIG. 4A

Will/III; F I6 54 NELSON R. IVA/L INVENTOR u Arromvsrs Patented June 20, 1967 New Jersey Filed Oct. 18, 1963, Ser. No. 317,201 2 Claims. (Cl. 117-17.5)

This invention relates to electrostatic printing and more particularly to a method of making a succession of prints from a printing master. The invention involves forming an electrostatic image on an insulating sheet overlying a printing master and xerographically developing the image to produce a visible print.

The printing process of this invention is a fast, inexpensive, and simple way of producing copies. Further, the process employs a printing master which is inexpenslve and which can be easily produced. For example, this process can use certain xerographic or photoconductographic prints as the printing master. Some xerographic processes, for example, use a copy sheet consisting of a photoconductive insulating layer overlying a flexible, conductive support, and such a sheet must be used for each print. However, by the printing process of the present invention, a single print made on such a sheet can be used as a printing master to produce additional copies on regular paper, at considerable saving in cost.

A process of electrostatic printing from an insulating photoconductive layer carried on an electrically conducting support and having an image of electrically conducting material is known, see the Jarvis patent US. 2,972,304. However, in that process the photoconductive layer is charged and developed and the toner particles transferred to a sheet of paper. An advantage of the process of the present invention is that the electrostatic image is produced and developed on the receiving sheet. This eliminates the transfer step of the above-identified patent. Further, after several printing operations from the same printing master are carried out according to the process of the patent, it may be desirable to clean the printing master to remove any toner particles which may have deposited on the background areas. Such a problem does not arise in the present invention since no toner particles are ever required to come into contact with the printing master.

The electrostatic printing process of the present invention relates to electrophotography insofar as it can employ certain xerographic or photoconductographic prints as printing masters. As described below, any document having certain characteristics can be employed in the process of this invention as a printing master.

It is an object of this invention to provide a fast, inexpensive, and simple method of electrostatic printing.

It is another object of this invention to provide an electrostatic printing process which can use a xerographic or photoconductographic print as the printing master.

Any document having conductive image areas and nonconductive background areas, or vice versa, can be used as the printing master in the present invention. Such documents can be made in various ways; the two preferred systems are xerography and photoconductography.

According to the invention, such a printing master is used by placing over the master and in contact therewith, an insulating sheet, and by corona charging the insulating sheet to produce thereon an electrostatic image. This electrostatic image can be developed by any of the usual electrostatic toning methods such as magnetic brush, liquid development, etc. The toner particles which form the visible image on the insulating sheet can be fixed thereto or transferred to a permanent record medium, thus allowing the insulating sheet to be reused for making additional prints.

As will be described in more detail below, certain xerographic and photoconductographic prints which consist of a visible image on a photoconductive layer overlying a conductive support are particularly well suited for use as the printing master in the present invention. This is true for several reasons. First, such prints are relatively inexpensive documents in and of themselves, and are particularly inexpensive as far as printing masters go, for example, as compared to the letter press plates and type characters used in electroprinting. Second, since the top layer of the print is photoconductive, it can be used as an insulator in the subject process, or it can be exposed to actinic radiation and used as the conductor in the subject process. Thus, by forming the toned image areas on the electrophotographic print with either insulating or conducting particles, and by proper use of the photoconductor as either an insulator or a conductor, the electrophotographic print can be readily used as the printing master in this invention.

The invention will be more fully understood from the following description when read in connection with the accompanying drawings in which:

FIGS. lA-lC constitute a flow chart of the electrostatic printing process of the present invention;

FIG. 2 illustrates an explanation of the mechanism resulting in the production of the electrostatic image on the insulating sheet;

FIG. 3 illustrates the developing step in a preferred embodiment of the process shown in FIGS. lA-IC to be used instead of the step shown in FIG. 1B;

FIGS. 4A and 4B illustrate two steps in a modification of the process shown in FIGS. lA-lC;

FIGS. 5A-5C constitute a flow chart of one method for preparing a photoconductographic print to be used as a printing master according to the present invention;

FIGS. 6A6D constitute a flow chart of one method of preparing a xerographic print to be used as a printing master according to the present invention; and

FIGS. 7 and 8 illustrate variations in the process shown in FIGS. lA-IC.

The electrostatic printing process of the invention is shown in FIGS. lA-lC. A printing master 10 having electrically conductive image areas 12 and electrically insulating background areas 14 is positioned on a conductive support 16. The conductive support 16 can be an integral part of the printing master 10 or separate therefrom. An insulating sheet 18 is positioned in overlying contact with the printing master 10 and corona charged, for example, by means of a voltage source 20, a switch 22, and corona charging element 24. The element 24 is shown connected to the negative terminal of the voltage source 20, and the conductive support 16 and the positive terminal of the voltage source 20 are connected to ground. This charging step produces an electrostatic image on the insulating sheet 18.

An explanation of the probable mechanism for the production of this electrostatic image will now be given with reference to FIG. 2. A photoconductor 30 is shown having a conducting area 32 and an insulating area 34. Because of the conductivity of conductive area 32, electrical chargescan move freely to its upper surface from a conducting support 36, in contrast to the situation regarding the insulating area 34. When an insulating sheet 38 is placed over the printing master 30 and corona charged, its area directly over the conducting area 32 becomes part of'a high capacitance system in which the insulating sheet 38 is the dielectric. The area of the insulating sheet 38 over the insulating area 34 becomes part of a low capacitance system whose dielectric is composed of the insulating sheet 38 and the insulating area 34 in series. Consequently, during charging the part of the insulating sheet 38 over the conducting area 32 ac- J cumulates a higher density of charge than the remaining part of the insulating sheet 38, due to the fact that the sheet 38 will tend to be charged to a uniform potential. This results in a xerographically developable difference between the two areas. 7 I

Returning now to the description of the process of the invention shown in FIGS. lAlC: FIG. 1B shows the xerographic development of the electrostatic image produced on the insulating sheet 18. This image may be developed by any of the usual electrostatic toning methods. FIG. 1B shows the image being cascade-developed by means of a hopper 4t developer powder 42 and a collection bin Q4. The toner particles are then fixed in place, by any of the known fixing methods, and the insulating sheet stripped from the printing master to produce a final print 46, as shown in FIG. 1C. I

Various modifications of the above-described process are possible. For example, after an electrostatic image is produced on the insulating sheet 18 by the step shown in FIG. 1A, the insulating sheet 18 can be stripped from the printing master it) and placed on a grounded plate 48-, during development, as shown in FIG. 3. It has been found that this grounded plate system yields slightly better prints than does the process shown in FIGS. 1A1C.

In another variation of the process shown in FIGS. lA1C, after the electrostatic image on the insulating sheet 18 has been developed, the toner particles may be transferred to another sheet such as sheet 50, as shown in FIGS. 4A and 4B, which is to be the final record medium. The toner particles are then fixed to sheet 50 by any of the known methods, to produce the final print on sheet 50 as shown in FIG. 4B.

As stated earlier, any document having conducting image areas and nonconducting background areas, or vice versa, can be used as the printing master in the present invention. Various methods of producing such a printing master are possible. However, in the preferred method of the invention, such printing masters are conveniently produced by xerography or photoconductography.

According to the photoconductographic embodiment of the invention, a print is produced for use as the printing master which has metallic image areas such as those deposited from solutions containing ions of heavy metals such as silver, nickel, iron, etc. Various photoconductographic processes for producing such a print are known. FIGS. A5C illustrate one such method. In FIG. 5A, a photoconductive sheet 60 on a conductive support 62 is exposed through a negative transparency 64 by means of a light source 66 and a lens 68, to produce an imagewise conductivity pattern in the photoconductive sheet 60. The sheet 60 is electrolytically developed, for example, by means of a viscose sponge 70 wetted with a developer solutiton, as shown in FIG. 5B. The sponge 70 is held at a positive potential with respect to the support 62 by means of a voltage source 72. The resulting photoconductographic print 74 shown in FIG. 5C can be used as the printing master in the process shown in FIGS. lA-lC.

FIGS. 6A6C illustrate one method for the production of a xerographic print useful as a printing master in this invention. A xerographic sheet consisting of a photoconductive layer 80, such as zinc oxide in a resinous binder, on a conductive support 82, such as aluminum foil, is given a negative, uniform electrostatic charge by means of, for example, a corona charger 84, switch 86, and a voltage source 88. The conductive support 82 and the positive terminal of the voltage source 88 are connected to ground. The xerographic sheet is then exposed to actinic radiation through a transparency 90 by means of a light source 92 and a lens 94 to produce a corresponding electrostatic image on the xerogr-aphic sheet, as shown in FIG. 6B. This image may then be developed by any of the known xerographic methods. One such method is shown in FIG. 6C. A hopper 96 is used to cascade a developer composition 98 across the xerographic sheet from which the excess developer flows into a collection bin 100. The toner particles are then fixed to the xerographic sheet to form the final print 99, shown in FIG. 6D.

In the photoconductographic print the visible image consists of conducting particles. In the xerog-raphic embodiments, however, the image areas can be either conducting or insulating.

An example of a process for preparing a photoconductographic print is as follows:

Example 1 A sheet having a layer of dye-sensitized photoconductive zinc oxide in a resin binder on an aluminum foil backing as normally used in photoconductographc processes was exposed for 10 seconds to 400 ft.c. of tungsten radiation incident upon a high contrast, line-copy, negative transparency contacting the zinc oxide surface. Upon termination of exposure, the imagewise conductivity pattern induced by the exposure to light was electrolytically developed with a viscose sponge wetted with an aqueous solution of the formulation:

Solution A.-l4.62 g. of Z-hydroxyethylamino oligoethylene sulfide (n=l.42) dissolved in 500 cc. of distilled WEII'EEI'.

Solution B.17.0 g. of silver nitrate dissolved in 500 cc. distilled water.

Solution B was slowly added to Solution A with rapid stirring. Int-o this was then dissolved 50 g. of magnesium acetate tetrahydrate and 5 cc. of glacial acetic acid and the pH of the final solution was raised to 6.7 by the dropwise addition of Z-diethyl-aminoethanol.

The sponge carrying this developer was held at a potential of 60 volt positive, with respect to the aluminum foil backing of the photoconductive layer. After development, the print surface was blotted dry with a photographic blotter, rinsed several seconds with distilled water, and then again blotted dry.

With this developer, the electrolytic deposition on the conductive areas of the zinc oxide surface consists of visible image material of metallic silver and/or silver sulfide.

A photoconductographic print having conducting image areas and made by a process such as described above is employed as the printing master in the printing process of the present invention as described in the following examples.

ExampleZ An insulating sheet of 0.001-inch polyester film, alcohol-treated to remove spurious charges, was placed over the print, and the polyester side of the sandwich was placed under a 9 kv. corona discharge for 8 seconds. While still in the dark the polyester surface was cascadedeveloped with Xerox N-l developer, which has a positive charge on the particles. The visible image was then fixed by the spray lacquer Fixatif (Eagle Pencil Company, Danbury, Conn.).

Example 3 The printing process of Example 2 was repeated except that the polyester sheet was removed from the master and placed on a grounded plate during development. Prints of slightly better quality were thus produced.

Example 4 The printing process of Example 2 was repeated except that the toner particles were transferred before fixing, by the use of pressure rollers, to a sheet of plain paper and fixed thereto. The polyester sheet, after slight cleaning, was used to make another print by the same printing process.

Example5 The printing process of Example 2 was repeated except that an insulating sheet of 0.0075-inch cellulose acetate was used in place of the 0.0Ul-inch polyester film. Prints of similar quality were produced.

Example 6 The printing process of Example 2 was repeated except that an insulating sheet of 0.0035-inch crazed polystyrene was used in place of the polyester sheet. Prints of similar quality were produced.

I have found that prints of improved quality over those produced by the processes of the above examples can be produced by treating the photoconductive layer to increase the difference between the conductivities of the image areas and the non-image areas. The photoconductive layer can be treated by dark-adapting it for a period of about 24 hours to decrease the conductivity of the photoconductor in the background areas. FIG. 7 shows another method of treating the photoconductive layer of a photoconductographic print. An electrical resistance heater 119 connected to a battery 112 by a switch 111 is used to heat the photoconductive layer 113 in the dark. Results are produced by this method of treatment which are similar to those produced by the dark-adapting treatment. A still further method of treatment is shown in FIG. 8. By means of a corona charger 120 connected to a voltage source 122 by a switch 121, the photoconductive layer 123 of a print is electrostatically charged with the polarity of charge that is later used to charge the insulating sheet. This corona-charging treatment can be used in addition to the dark-adapting and the heating treatment, or if the charging is prolonged for a few seconds, it is s'ufiicient treatment in and of itself.

The following examples illustrate two methods of preparing and using xerographic prints as printing masters in the present invention.

Example 7 A xerographic sheet comprising a layer of zinc-oxidein-resin binder (of the type normally used in xerography) coated on a conductive support was charged under a -9 Kv. corona discharge and exposed through a negative line-copy transparency. The electrostatic image was developed in a liquid developer containing negatively charged toner particles (Sleight and Hellmuth Tri Dim A lithographic ink) dispersed in cyclohexane. During development, a conducting electrode behind the photoconductor was biased positively with respect to a grounded facing electrode, causing a patternwise deposition of toner. The toner deposit appeared to render the underlying portion of the zinc oxide layer conducting. The resulting print was used as the printing master in a printing process similar to that of Examples 2-6. Positive prints were produced.

Example 8 A xerographic sheet comprising a zinc-oXide-in-resinbinder coating on a conducting backing was charged under a 9 kv. corona discharge and exposed through a negative line-copy transparency. The electrostatic image was developed with a dispersion of positively charged toner par- 6 ti-cles (Sleight and Hellmuth Yellow No. 3046 lithographic ink) in cyclohexane to yield a toner deposit corresponding to the charge pattern. This toner deposit appeared to render the underlying portion of the zinc oxide layer insulating.

This Xerographic print was then used in a printing process similar to that of Examples 2-6, except that the operation was carried out in roomlight. In this case the background areas had been rendered insulating while the image areas had become conducting through exposure to roomlight. Positive prints were obtained.

The xerographic masters can be prepared with photoconductors other than zinc oxide, e.g., selenium, sulfur, and anthracene.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. I11 a process of electrostatic printing on an electrically insulating receiving sheet from a printing master comprising a photoconductive layer on an electrically conductive support, said photoconductive layer having relatively electrically conductive and relatively electrically insulating areas which form an image, the steps comprising:

positioning said receiving sheet with one surface thereof in overlying contact with said photo-conductive layer;

electrostatically charging said receiving sheet from the other surface thereof to a uniform potential to produce thereon an electrostatic image;

transferring said receiving sheet, after said charging step,

to a surface of an electrically conductive grounded plate; and

xerographically applying toner particles to said electrostatic image on said receiving sheet to produce a visible image.

2. The process according to claim 1 including the step of treating said photoconductive layer prior to the step of positioning said receiving sheet, to increase the electrostatic contrast between said electrically conductive and electrically insulating areas.

References Cited UNITED STATES PATENTS 2,297,691 10/ 1942 Carlson. 2,357,809 9/1944 Carlson. 2,647,464 8/ 1953 Ebert. 2,972,304 2/ 1961 Jarvis. 3,145,655 8/1964 Hope et al. 3,194,674 7/ 1965 Sakurai.

DAVID KLEIN, Primary Examiner.

Claims

1. IN A PROCESS OF ELECTROSTATIC PRINTING ON AN ELECTRICALLY INSULATING RECEIVING SHEET FROM A PRINTING MASTER COMPRISING A PHOTOCONDUCTIVE LAYER ON AN ELECTRICALLY CONDUCTIVE SUPPORT, SAID PHOTOCONDUCTIVE LAYER HAVING RELATIVELY ELECTRICALLY CONDUCTIVE AND RELATIVELY ELECTRICALLY INSULATING AREAS WHICH FORM AN IMAGE, THE STEPS COMPRISING: POSITIONING SAID RECEIVING SHEET WITH ONE SURFACE THEREOF IN OVERLYING CONTACT WITH SAID PHOTO-CONDUCTIVE LAYER; ELECTROSTATICALLY CHARGING SAID RECEIVING SHEET FROM THE OTHER SURFACE THEREOF TO A UNIFORM POTENTIAL TO PRODUCE THEREON AN ELECTROSTATIC IMAGE; TRANSFERRING SAID RECEIVING SHEET, AFTER SAID CHARGING STEP, TO A SURFACE OF AN ELECTRICALLY CONDUCTIVE GROUNDED PLATE; AND XEROGRAPHICALLY APPLYING TONER PARTICLES TO SAID ELECTROSTATIC IMAGE ON SAID RECEIVING SHEET TO PRODUCE A VISIBLE IMAGE.