US3519818A - Method of preparing a negative xerographic reproduction from a positive line copy image - Google Patents

Description

y 7, 70. L. F. BEAN 3,519,818

METHOD OF PREPARING A NEGATIVE XEROGRAPHIC REPRODUCTION FROM A POSITIVE LINE COPY IMAGE Filed July 20, 1966 FIG. 5

INVENTOR. LLOYD F. BEAN w%-Quwm ATTORNEY "United States Patent US. Cl. 250-495 14 Claims ABSTRACT OF THE DISCLOSURE An imaging process is disclosed whereby a negative xerographic reproduction may be prepared from a positive line copy image. A visible toner image is electrostatically formed on a support substrate and contacted with the surface of a donor member having dusted on its surface a uniform layer of pigmented developer material. At least one of the exposed surfaces of the resulting configuration is charged ot a predetermined potential so as to effectively bring about the exchange of the toner particles between the interface of the contacted surfaces thereby producing a negative reproduction of the original positive image input.

This invention relates to an imaging system and more specifically to electrophotographic imaging.

In conventional xerography, an electrostatic latent image is formed on an insulating surface, such as generally a photoconductive insulating layer, by the combined action of electric field and a pattern of activating radiation, such as light. The xerographic latent image is generally made visible by the deposition on the electrostatic image bearing surface of finely divided electroscopic marking particles. These particles adhere to the areas where the electrostatic charges remain forming an image pattern comprising areas of image body and areas of background. The powder image may then be transferred to a sheet of transfer material resulting in a reproduction of the original copy. Alternatively, where the base plate is relatively inexpensive, as a paper, it may be desirable to fix the powder image directly to the plate itself.

It has also been found for many purposes, and particularly for continuous tone imaging where it is desirable to reproduce varying shades of gray in a xerographic print, or otherwise obtain good solid area coverage, that the xerographic image may advantageously be developed by the deposition of powder in conjunciton with a very closely spaced counterelectrode during development so as to reduce or eliminate distortion in the electric field associated with the xerographic latent image. As a result of the presence of this development or counter-electrode it has been possible to reproduce continuous tone images.

Although the use of the development or auxiliary electrode has generally enhanced the tone, density and contiuity of images where the gradations of continuous tone photography at brought into the xerographic process, it has been determined that there are inherent disadvantages to the system. One disadvantage, for example, is that the input is not faithfully reproduced due to an increase in image density at the edges of the characters and/or lines. A second disadvantage to this system is that it is generally necessary to maintain the development electrode at ice an extremely close spacing during the development operation. Such spacing requirements obviously create problems in mechanical operation, since it is necessary to operate under extremely close dimensional limitations and also keep the working surfaces which are closely adjacent to one another substantially clean.

Therefore, it is an object of this invention to provide an imaging system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a novel imaging system utilizing electrophotographic development.

Another object of this invention is to provide a method of transforming an electrostatic latent image into a useful continuous tone visible image.

A further object of this invention is to provide a novel method of preparing a negative photographic reproduction.

Yet still a further object of this invention is to provide a method of using a negative reproduction of a line copy image prepared according to a novel imaging system.

The foregoing objects and others are accomplished in accordance with this invention, generally speaking by developing an electrostatic latent line copy image on the surface of a support substrate, such as photoconductive paper according to conventional xerographic techniques as disclosed in US. Pat. 2,297,691. An intermediate donor surface, such as a polyethylene terephthalate sheet, is dusted with a pigmented toner or developer composition, the latter developer being charged to a potential opposite in polarity to that on the developer of the positive line copy image. The charge on the toner developer of the donor sheet may be upgraded if necessary so as to increase its total potential. The dusted surface of the intermediate sheet is then brought into contact with the surface supporting the xerographically formed line copy image and a charge similar in polarity to that of the donor developer applied to the exposed side of the donor sheet. The charged donor particles on the intermediate surface are repelled to the face of the sheet bearing the positively developed line copy image while in turn attracting from the face of the line copy image bearing surface the already present electroscopic particles forming the positive image, thereby producing a negative reproduction of the original document on the surface of the respective sheet. This image may then be fixed in place or transferred to a receiving substrate by any suitable technique, such as electrostatically, where it may then be made permanent.

Alternatively, if expedient, the transferring charge may be applied to the exposed surface of the sheet bearing the positive image thereby producing a. similar transfer effect as discussed above. In this instance, however, the polarity of the charge applied to the back side of the positive image bearing surface is the same as the polarity on the toner material used to develop the positive image. As a result of this similarity in potential the toner particles are repelled to take their place on the surface of the donor sheet while in turn attracting to the background or non-image areas the pigmented toner material supported on the donor surface which has been charged to a polarity opposite in sense to that of the applied voltage thereby producing the desired negative reproducion. Still another embodiment of the present invention involves the transferring of the positively developed toner image to the surface of the desired receiving sheet prior to the preparation of the negative reproduction. The receiving sheet now bearing the positive image may be then placed in contact with the dusted surface of the intermediate donor sheet and the proper charge both as to magnitude and polarity applied to either the exposed surface of the receiving sheet or the exposed surface of the donor sheet to produce the negative image on the face of the receiving sheet. When used in the course of the present invention, the terms positive and negative image are meant to be interpreted in the photographic sense.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a diagramatic perspective view of a developed electrostatic latent image;

FIG. 2 is a magnified side view of a donor sheet supporting pigmented developer material;

FIG. 3 is a magnified side view illustrating the transfer step of the development process of the present invention;

FIG. 4 is a diagramatic perspective view showing partial separation of the final negative image bearing substrate from the donor sheet;

FIG. 5 is a diagramatic perspective view of the negative xerographic reproduction of the line copy image of FIG. 1.

Returning now to FIG. 1 there is seen a mounted receiving substrate .1, such as paper or polyethylene terephthalate, upon which has been developed according to conventional xerographic techniques a non-pigmented toner image. For purposes of the present illustration the toner particles have been charged so as to retain a potential with a positive polarity. In FIG. 2 is seen an intermediate donor substrate 3 the surface of which has been coated with a substantial amount of pigmented developer material 4 which has been charged to a potential significantly greater than and opposite in polarity to the toner material representing the positive line copy image 2 of FIG. 1. During the development phase of the process, as illustrated by FIG. 3, a charging unit generally designated is passed behind the exposed surface of the intermediate donor sheet 3. The charging unit 10 comprising a corona discharge wire 12 surrounded by conductive metal shield 13 is connected to a source of high DC potential of the same polarity as that retained on the developer particles of the donor sheet. In the case of the charging unit 10, the voltage source 14 is pre-selected to be of such a magnitude that it will produce a corona discharge substantially great enough to repel the pigmented donor particles 4 from the surface of the donor sheet 3 to the surface of the receiving substrate 1 so as to produce a negative reproduction 15 of the original line copy image 2. correspondingly, the potential supplied to the system is such that it produces a net effect at the interface between the donor particles 4 and the line copy image 2 so as to effectively attract the positively charged donor particles 2 from the receiving substrate 1. Although the resulting effect is to substantially remove the bulk of the toner particles representing the positive image, inasmuch as the original line copy image has been formed with an unpigmented toner any residual toner particles remaining on the surface of the receiving substrate Will not inhibit subsequent use of the negative reproduction.

FIG. 4 represents the separation phase of the process whereby the receiving substrate 1 is separated from the donor sheet 3 retaining thereon the negative reproduction 15 of the line copy image 2, the transfer of the respective toner materials having elfectively been achieved. FIG. 5 represents the final negative xerographic reproduction of the line copy image illustrated in FIG. 1 consisting of the receiving substrate 1 with the negatively reproduced image 15 supported on the surface thereof.

During the development of the positive line copy image of the present invention utilizing conventional xero-' graphic procedures any suitable photoconductive material may be used. Typical inorganic photoconductive materials are sulfur, selenium, zinc sulfide, zinc oxide, cadmium selenide, cadmium sulfide, cadmium sulfoselenide, and mixtures thereof. Typical organic photoconductors are:

triphenylamine;

N-isopropylcarbazole;

2,4-'bis(4,4 diethyl-aminophenyl)-l,3,4-oxadiazol; triphenylpyrrol;

4,5 -diphenyl-imidazolidinone;

4,5 -bis( 4 -amino-phenyl) -imidazolidinone; 1,5-dicyanonaphthalene; 1,4-dicyanonaphthalene; aminophthalodinitrile;

nitrothalidinitrile; 6-hydroxy-2,3-di(p-methoxy-phenyl)benzofurane; 4-dimethylamino-benzylidene-benzhydrazide; 3-benzylidene-amino-carbazole;

polyvinyl carbazole;

( Z-nitro-benzylidene)-p-bromo-aniline; 2,4-diphenyl-quinazoline;

1,2,4-triazine;

1,5-diphenyl-3-methyl pyrazoline; 3-aminocarbazole;

phthalocyanine;

and mixtures thereof.

When desirable any suitable binder material may be incorporated with the photoconductive materials of the present invention. Typical binder materials are similar to those disclosed in U.S. Pats. 3,121,006 and 3,121,007. The specific binder materials chosen will be dependent upon the nature of the photoconductive pigment utilized to prepare the photoconductive plate used in conjunction with the present invention. When necessary, the binder material employed with the photoconductive compound is such that it is an insulator to the extent that an electrostatic charge placed on the photoconductive layer is not conducted by the binder, at least in the absence of illumination, at a rate to prevent the formation and retention of an electrostatic latent image thereon. When the binder material is photoconductive, it is preferred that the specific resistivity of the binder be at least about 10 ohms-cm. to satisfactorily fulfill the requirements of the resulting photoconductive plate. When used, the binder material adheres tightly to the base of the support substrate for the photoconductive layer and provides an efficient dispersing medium for the photoconductive pigment. Furthermore, the binder material should be selected so as to be relatively inert when in the presence of the photoconductive compound. Typical non-photoconductive organic binders are: polystyrene, silicon resins, such as DC-801, DC-804 and DC996 commercially available from the Dow Corning Co., acrylic and methacrylic polyesters such as Acryloid A-10, and Acryloid B-72, polymerized ester derivatives of acrylic and alpha acrylic acids all commercially available from Rohm & Haas Co., Lucite, a polymerized butylmethacrylate commercially available from E. I. du Pont de Nemours & Co., and vinyl polymers and copolyrners such as polyvinylchloride and polyvinylacetate. Typical photoconductive binders are selenium, anthracene, and sulfur. Mixtures of the above mentioned binder materials may also be employed.

Any suitable backing material for the xerographic plate may be used in the course of this invention. Generally, the preferred backing material should have an electrical resistance less than the photoconductive composition so that it will act as a ground when the electrostatically charged coating is exposed to light. Typical materials are alumi num, brass, steel, copper, nickel, zinc, and both conductive and non-conductive paper. Other materials having electrical resistances similar to the aforementioned can also be used as a backing material to receive the photoconductive layer thereon. Other non-conductive materials such as thermoplastics may be used as the backing of the xerographic plate. When used, however, it is necessary to charge both sides of the xerographic plate according to the process set out in U.S. Pat. 2,922,883.

As mentioned above, the negative reproduction may be formed on the surface of the photoconductive plate upon which the original positive line copy image is formed and developed. When desirable the negative reproduction, however, may be subsequently transferred to the surface of a preferred substrate following development or the original positive line copy image may be initially transferred to the preferred substrate prior to being contacted with the intermediate donor member so that the finally developed negative image will be formed directly on the preferred substrate. The transfer, when made, may be carried out by any suitable technique such as by adhesive transfer or by electrostatic transfer. When the transfer is made prior to producing the negative image, the particular receiving sheet selected should be of such a nature that the toner particles which are transferred to it will retain their potentials so as to satisfy the requirements of the subsequent transfer phase of the present development process. Typical materials which may be used as the receiving substrate are ordinary bond paper; polyethylene terephthalate (Mylar); styrene polymers, such as Velsicol, commercially available from the Velsicol Chemical Corp. and Piccolastic resins, available from the Pennsylvania Industrial Chemical Corp.; ethylcellulose; cellulose acetate; polycarbonates such as Plestar, commercially available from General Aniline and Film Co.; polyethylene; polypropylene; polymeric materials such as casein and Parlon, the latter a chlorinated natural rubber commercially available from the Hercules Powder Co.; Staybelite resins, a family of thermoplastic synthetic resins prepared from hydrogenated rosin and commercially available from the Hercules Powder Co.; phenol formaldehyde; urea formaldehyde; epoxy resins; silicone resins; VYNS, a vinyl chlorideacetate thermoplastic resin commercially available from Union Carbide Co.; polyvinylchloride; Nevillac, an alkyl hydroxy resin commercially available from Neville Chemical Co.; Tedlar, a polyvinyl fluoride resin commercially available from E. I. du Pont de Nemours & Co.; cellulose acetate butyrate; fiuorocarbons such as polychlorotrifluoroethylene and polytetrafiuoroethylene; styrene-acrylonitrile copolymers; polyurethane; polyvinylidenefluoride; chlorinated polyethers; polyamide resins; phenoxy resins; vinyl and vinylidene chloride polymers and copolymers. In addition to the above suggested materials, other substrates may be used such as aluminum, steel, copper, nickel and zinc as well as other conductive materials such as aluminized Mylar. The surface upon which the final negative xerographic reproduction is to be formed may therefore be a controlled or uncontrolled substrate, whether it is the surface upon which the original positive image is developed or the support to which the negative developed image is subsequently transferred. For example, if it is desirable to use the negative reproduction as a display system then it would be expedient to form the final negative image on the surface of a substantially transparent support member, such as the suggested polyethylene terephthalate. If it is preferred that the process of the present invention be used to prepare a print-out mechanism then the negative image developed may be transferred in the final phase of the process to the surface of a silk screen support or any other suitable porous member providing printing capabilities.

The intermediate donor sheet, which serves as the source and support for the developing toner particles, will be similar in nature to the above mentioned materials suitable for use as the receiving substrate.

Any suitable toner developer material may be used in the course of this invention both to develop the positive xerographic image and to serve as the developer particles on the surface of the intermediate donor sheet for subsequent formation of the negative xerographic reproduction.

Typical toner materials are disclosed in US. Pats. 2,788,- 288, 3,079,342 and Reissue Pat. 25,136. Specific examples are styrene polymers, including substituted styrene, such as the Piccolastic resins; Staybelite; rosin modified phenol formaldehyde; and methacrylate polymers, as well as other resins having similar properties. The developer powder or electroscopic marking particles are generally blended with a pigmented material, such as carbon black. However, in the case of the toner used to develop the positive xerographic line copy image it is preferred that the electroscopic particles be unpigmented so as to reduce any loss in resolution which may result due to an incomplete transfer or exchange during the development phase of the process.

Any suitable development means may be used in the development of the positive line copy image of the present invention, such as cascade development more fully described in US. Pat. 2,618,551 and 2,618,552, powder cloud development more fully described in US. Pats. 2,725,305 and 2,918,910 and magnetic brush development more fully described in US. Pats. 2,791,949 and 3,015,- 30-5.

When fixing the developed negative xerographic reproduction to the surface of its final support any suitable means may be used, such as vapor fusing, or treatment of the developed image with a regulated amount of heat. The image may alos be fixed by applying or spraying the toner image with an adhesive film forming over-coating.

To further define the specifics of the present invention, the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated. The examples are also intended to illustrate various preferred embodiments of the present invention.

EXAMPLE I A sheet of commercial zinc oxide paper available from Charles Bruning Company is charged to about -400 volts by means of a laboratory corotron unit powered by a high voltage power supply. The charging current is about 0.1 of a milliamp at about 7500 volts. The charged Zinc oxide photoconductive paper is then selectively exposed to a light source through a transparent positive image with a 75 watt photoflood lamp. An exposure of about 20 foot-candle-seconds is required for the zinc oxide paper. The electrostatic latent image produced is then developed with an unpigmented toner material comprising polystyrene in the presence of a carrier by cascading the toner composition across the surface of the imaged zinc oxide paper. A second intermediate donor sheet comprising Mylar is dusted with a pigmented toner material comprising polystyrene and charged to a negative potential by using a tone tray with a 600 volt negative bias applied to the electrode. The dusted intermediate sheet is then placed in contact with the xerographic line copy image on the zinc oxide paper and a negative charge applied using 29 micro ampere bare plate current in a Xerox Model D charging unit to the exposed surface of the Mylar donor sheet. There is thereby produced a negative, in the photographic sense, reproduction of the original document, on the zinc oxide paper. The developed negative xerographic reproduction is then subjected to a. heat source thereby fixing the image to the surface of the paper.

EXAMPLE III The process of Example I is repeated up to and including the formation of the negative reproduction on the surface of the Zinc oxide paper. At this stage of the process the Zinc oxide paper bearing the negative image is contacted with a substantially transparent acetate sheet and the toner image electrostatically transferred to the acetate subsrate. The electrostatic transfer is thus completed and the negatvie image now on the surface of the acetate sheet is fixed by the application of heat. There is thus produced a substantially transparent substrate with a negative reproduction of the original document thereon. The negative xerographic reproduction is positioned on a display mechanism comprising a light source and lens system provided to project the image onto the surface of a display screen thereby illustrating its utility as a display device.

EXAMPLE III The procedure of Example I is repeated up to and including the step whereby the donor sheet and the positive image bearing zinc oxide paper are placed in close proximity one to the other. At this stage of the process, a positive charge is applied to the exposed surface of the imaged zinc oxide paper by a Xerox Model D charging unit operated at a charging current of about 3.5 microamps-sec./in. A negative xerographic reproduction develops on the surface of the zinc oxide receiving sheet while the positive image is in turn transferred to the surface of the Mylar donor sheet.

EXAMPLE IV The process of Example I is repeated up to and including the formation of the negative reproduction on the surface of the zinc oxide paper. At this stage of the process the zinc oxide paper bearing the negative image is contacted with a silk screen support and the toner image adhesively transferred upon contact to the surface of the silk screen. The negative image now on the surface of the silk screen support is heat treated thereby bonding the negative image to the intersticies of the silk screen. The resulting imaged screen will then serve as a stencil-like master.

Although the present examples were specific in terms of conditions and materials used, any of the above typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used in the imaging system of the present invention, other steps or modifications may be used if desirable. For example, the initial dusting of the intermediate donor sheet may be made onto the surface of a 'bare plate and electrostatically transferred to the desired intermediate donor surface. In addition, other materials may be incorporated in the photo conductive material, developer, donor support, or receiving substrate which will enhance, synergize, or otherwise desirably effect the properties of the present system. For example, the spectrosensitivity of the photoconductive plate used in accordance with the present invention may be modified by incorporating photosensitizing dyes therein.

Anyone skilled in the art will have other modifications occur to him based on the teaching of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A method of forming a negative reproduction of a light pattern comprising placing the surface of an intermediate donor sheet in contact with the imaged surface of a positive image bearing plate so as to form a sandwich configuration, said donor sheet comprising a support base having uniformly dusted on the surface adjacent to said plate charged, pigmented electroscopic particles, said image bearing plate comprising a support substrate having toner particles developed thereon in a positive imagewise configuration, said toner particles retaining a charge opposite in polarity to the charge on the donor sheet particles and applying a potential to at least one of the exposed surfaces of said sandwich configuration.

2. The process as described in claim 1 wherein said potential is applied to the exposed surface of the donor substrate, said potential having a charge similar in polarity to that of the donor sheet particles.

3. The process as described in claim 1 wherein said potential is applied to the exposed surface of the positive image bearing plate, said potential having a polarity opposite to that of the donor sheet particles.

4. A process of preparing a negative image from a positive light pattern comprising:

(a) developing electrostatically a positive non-pigmented toner image on the surface of a support substrate,

(b) uniformly dusting an intermediate donor sheet with a layer of charged, pigmented toner particles,

(c) contacting the dusted surface of the intermediate donor sheet with the surface supporting the electrostatically formed positive toner image to form a sandwich configuration,

(d) charging at least one of the exposed surfaces of said sandwich configuration to a potential so as to effect an exchange of toner particles between the interface of the contacted surfaces whereby a negative image comprising pigmented particles is formed on the surface of said support substrate, and

(e) fixing the thus transferred pigmented particles to the respective transfer surface.

5. The process as described in claim 4 wherein said potential is applied to the exposed surface of the donor substrate, said potential having a charge similar in polarity to that of the donor sheet particles.

6. A process as described in claim 4 wherein said potential is applied to the exposed surface of the positive image bearing substrate, said potential having a polarity opposite to that of the donor sheet particles.

7. A process of preparing a negative image from a positive light pattern comprising:

(a) developing electrostatically a positive non-pigmented toner image on the surface of a support substrate,

(b) transferring said image to the surface of a receiving substrate,

(c) uniformly dusting an intermediate donor sheet with a layer of charged pigmented toner particles,

((1) contacting the dusted surface of the intermediate donor sheet with the surface of said receiving substrate supporting the electrostatically formed positive toner image thereby forming a sandwich configuration,

(e) charging at least one of the exposed surfaces of the said sandwich configuration to a potential so as to effect an exchange of toner particles between the interface of the contacted surfaces whereby a negative toner image is formed on the surface of said support substrate, and

(f) fixing the thus transferred pigmented particles to the respective transfer surface.

8. The process as defined in claim 7 wherein said receiving substrate comprises a substantially transparent substrate.

9. The process as defined in claim 7 wherein said receiving substrate comprises a substantially porous substrate.

10. The process as described in claim 7 wherein said potential is applied to the exposed surface of said donor substrate, said potential having a charge similar in polarity to that of the donor sheet particles.

'11. The process as defined in claim 10 wherein said receiving substrate comprises a substantially transparent substrate.

12. The process as defined in claim 10 wherein said receiving substrate comprises a substantially porous substrate.

13. The process as described in claim 7 wherein said potential is applied to the exposed surface of said receiving substrate, said potential having a polarity opposite to that of the donor sheet particles.

14. A process of preparing a negative image from a positive light pattern comprising:

(a) developing electrostatically a positive non-pigmented toner image on the surface of a support substrate,

(b) uniformly dusting an intermediate donor sheet with a layer of charged, pigmented toner particles,

(c) contacting the dusted surface of the intermediate donor sheet with the surface supporting the electrostatically formed positive toner image to form a sandwich configuration,

(d) charging at least one of the exposed surfaces of said sandwich configuration to a potential so as to effect an exchange of toner particles between the interface of the contacted surfaces thereby producing a negative image on the surface of said support substrate,

(e) transferring said negative image to the surface of a receiving substrate, and

6/1958 Moncrieff-Yeates 25049.5 4/1963 McNaney 250-49.5

RALPH G. N ILSON, Primary Examiner A. L. BIRCH, Assistant Examiner US. Cl. XR.

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