US3615392A

US3615392A - Electrophotographic reproduction of originals containing both multicolor and line areas

Info

Publication number: US3615392A
Application number: US820019A
Authority: US
Inventors: Satoru Honjo
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1968-05-02
Filing date: 1969-04-28
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26

Abstract

A multicolor imaging process is disclosed whereby an original document comprising both multicolor areas and monochrome or black and white line areas may be reliably reproduced.

Description

Inventor Satoru Honjo Snitama, Japan Appl. No. 820,019 Filed Apr. 28, 1969 Patented Oct. 26, I971 Assignee Xerox Corporation Rochester, NY. Priority May 2, 1968 Japan 43/294114 ELECTIROPIIOTOGIRAPHIC REPRODUCTION OF ORIGINALS CONTAINING BOTH MULTICOLOR AND LINE AREAS 3 Claims, No Drawings 11.s.c1 96/l.2, 915/1, 117/175, 96/41, 96/43, 252/621 1m. (:1 G03g 13/22 OTHER REFERENCES Industrial Photography, Nov. 1961, pages 19 and 74 Primary Examiner-George F Lesmes Asristanl Examiner.lohn C. Cooper, 111

Attorneys-James .I. Ralabate, Albert A. Mahassel and Donald C. Kolasch ABSTRACT: A multicolor imaging process is disclosed whereby an original document comprising both multicolor areas and monochrome or black and white line areas may be reliably reproduced.

ELEC'IIROPIIOTOGRAIHIC REPRODUCTION OF ORIGINALS CONTAINING BO'II-I MIJL'IICOLOR AND LINE AREAS BACKGROUND OF THE INVENTION This invention relates to an electrophotographic copying process and more specifically to a multicolor imaging system.

Conventionally a document which includes multicolored areas, for example, a page of a book containing pictures or figures comprising differently colored curves or lines accompanied with a sentence explanation of the figures, is generally photographically reproduced or converted to a black and white or monochromatic image. This is true in cases such an electrophotographic imaging referred to as xerography, and diffusion transfer methods utilizing light sensitive silver halide emulsions are employed. Recently, the utilization of multicolored figures and drawings in books and business documents has rapidly increased to the point such that the demand for faithful reproduction of the colors in the final print is an ever increasing one. When an entire area of a document is occupied with a multicolored picture one may employ as a copying material color photographic material commercially available based upon multilayer coated silver halide emulsions used in conjunction with color forming development. Similarly, several methods are known whereby multicolored pictures may be produced from the application of electrophotography. One such method consists in the formation of three separate colored images on a respective photoconductive insulating plate and the transfer thereof, one by one onto a suitable transfer material in registration. However, in a practical, everyday business use one generally encounters such documents or printed materials which comprise relatively restricted, multicolored areas with the remaining printed area being black and white such as line images constituting sentences, titles or numerical tables. It should also be noted that the former areas usually constitute closed, island or isolated regions surrounded by the latter.

High-speed reproduction of multicolored originals of the nature herein dealt with may be carried out by electrophotography, but, because of the nature of the system a single electrophotographic cycle will reproduce only one color. Therefore, multicolor reproduction can be accomplished as mentioned above through repeated cycles of charging, imagewise exposure and development, in strict registration. It should be again noted that most common documents mainly consist of black and white line image areas. Accordingly, if such a document is reproduced by three differently colored toners, such as yellow, magenta and cyan toners which are the three principal colors in a subtractive system, the line image area must comprise a superposition of the same three different toner images to produce a black image. Obviously, this is not a desirable approach inasmuch as a very slight discrepancy of registration between each image will render the resulting image difficult to read especially in situations when the original includes many small characters such as Chinese characters in the line image areas.

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 color electrophotographic imaging process which with a high degree of reliability will reproduce in an uncomplicated manner a multicolor image.

Still a further object of this invention is to provide a novel color electrophotographic imaging process.

SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with the present invention generally speaking by providing an original document including a multicolored area and a black and white line image area. The beforesaid original is placed in an exposure position of an electrophotographic copying apparatus with an opaque mask placed over the multicolor area which will reflect light. An electrophotographic recording member is uniformly charged and exposed to a light image of the arranged original with the resulting electrostatic latent image develop with electroscopic marking particles otherwise referred to as toner material which produces a developed image of a sufficiently low surface resistivity so as to render the developed area substantially incapable of holding an electrostatic charge. The opaque mask, generally white, is removed form the original and the entire process repeated with the electrophotographic member being recharged and exposed to a light image of the entire original utilizing the proper filter system which will permit a limited region of light in the visible spectrum to be transmitted thereby producing an electrostatic latent image corresponding to the particular color image which is to be reproduced. The resulting image is developed with a colored toner which will absorb the transmitted light. This imaging step is repeated until the entire copy image is reproduced.

It has been determined that by initially developing those areas of an original corresponding to a black and white line image area with a relatively high electrically conductive toner that the image and immediate surrounding area will in subsequent imaging steps except a very low surface potential during charging and that potential which does exist, if any, rapidly leaks away under dark conditions so that the toner deposition on these areas will be negligible during the subsequent development steps.

Any suitable development developer material may be used which will deliver the required conductivity of the present invention. Developer material which makes the developed area and the immediately surrounding areas substantially incapable of retaining electrostatic charges thereon is desired. The conductivity of the developer material should be suitable adjusted so that the electroscopic marking particles or toner are such that although not retaining charge it still will develop the initial electrostatic latent image it has been determined that a preferable rage of conductivity of the toner material is such to exhibit a surface resistivity of from about 10 to 10 ohms-cm. A practical example of a toner formulation is a mixture of carbon black and a relatively small amount of insulating resinous component. In addition to carbon black other typical conducted pigments include graphite, aluminum powder, bronze powders, zinc dust, lead powder, gold, silver as well as mixtures and alloy powders of these materials. The hue of these conductive toners is generally preferred to be of a black to deeply colored nature for example dark blue, dark green, a dark bluish green, to various shades of gray. Thus, powdered dyes may be used to render a specific hue such as the use of nigrosene dye to give a dark-colored powder.

Procedures subsequent to the first development step are quite similar to conventional over-print color electrophotographic processes; the electrophotographic recording member bearing the developed line image thereon is uniformly charged, exposed to the entire original, minus the mask, with the use of a filter which transmits only a limited region of the visible spectrum. Development is carried out by applying to the exposed member a toner which can absorb the transmitted light. The developed image area produced in this development will exhibit an electrical insulating property so as to hold electrostatic charges along with the remaining surface of the elec trophotographic member, excluding the initially developed image with the conductive toner. The process steps are repeated with various filters and their corresponding colored toners. A conductive or insulating toner may be used in the final development step. Registration of the colored images is again considered important, however, requirement for its accuracy can be relieved since the line image portion of the reproduction, which has been separately reproduced, is not effected by the possible shift between each color toner image development step. Any suitable color developer material may be used in conjunction with the process of the present invention such as disclosed in U.S. Pat. No. 3,345,293. As stated above the toner material utilized with each development step is such that it will absorb the light transmitted during exposure.

Any suitable photoconductive insulating material may be used in the course of the present invention. Typical such photoconductive materials are disclosed in US. Pat. Nos. 3,12l,007 and 3,121,006. Typical photoconductive materials include selenium, sulfur, anthracene, inorganic photoconductive pigments such as zinc oxide, lead oxide, cadmium sulfide, and cadmium sulfoselenide dispersed in binder resins, organic photoconductive pigments such as phthalocyanine and sensitized polyvinylcarbazole, halogen doped selenium and arsenic-selenium alloy compositions as disclosed in U.S. Pat. Nos. 2,803,542 and 3,312,548. The conductive support material is utilized in conjunction with the photoreceptors are those which present the desire of conductivity for their specific use. Generally it is preferred that the backing material have an electrical resistance less than that of the photoconductive layer such that it will act as a ground when the electrostatically charged coating is exposed to light. Typical conductive materials include aluminum, brass, copper, zinc, conductive paper and any suitable plastic substrate having the necessary conductivity properties.

PREFERRED EMBODIMENTS 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. Tl'le examples are also intended to illustrate various preferred embodiments of the present invention.

EXAMPLE 1 A zinc oxide photoconductive plate is uniformly electrostatically charged with a negative potential. The zinc oxide plate is dye sensitized with three sensitizers, fluorescein, eosin and tetrabromophenol blue, so as to exhibit a panchromatic response to light. The original to be reproduced consists of one page of an encyclopedia including a multicolor printed figure and a large portion of printed Japanese'letters containing Chinese characters. Prior to the first exposure, a sheet of white, opaque paper having the same size as the multicolor figure is superimposed on the figure. A light image is reflected from this masked original and projected onto the charged photoconductive layer through a suitable optical system. During this exposure a filter is not employed. Liquid development is carried out on the resulting latent image utilizing a dispersion comprising about 1 gram of a commercially available offset ink purchased under the trade name Zipset Process T Set Black from Tokyo lnk Company, Ltd. dispersed in a mixture comprising about 600 milliliters of cyclohexane and about 400 milliliters of kerosene. Following development the sheet is rinsed with mineral spirit then dried in the dark. The surface resistivity of the area developed by the black toner is about ohms-cm.

The developed sheet is again charged. A blue filter is superimposed on the original after the white, opaque mask is removed. THe charged sheet is exposed to the original in register with the first image. A liquid developer prepared by dispersing a commercially available yellow offset printing ink in a mixture of cyclohexane and kerosene is applied to the surface of the exposed plate. Development occurs only in the area where the light image from the multicolored areas has impinged. The sheet is again rinsed with mineral spirit and dried in the dark. Similar operations are repeated with a blue filter being substituted with a red and green filter respectively nd the yellow ink substituted with a cyan and magenta offset ink respectively. The three liquid developers include toners of positive polarity. The reproduced image finally obtained is composed of a line image area comprising the black toner, and a multicolored figure comprising the three colored toners developed in registration.

EXAMPLE ii EXAMPLE Ill A parallel line resolution test chart is prepared by drawing lines having the same length on a transparent film in such a manner that the series of lines have different line widths and are arranged such that the line width gradually decreases. Each line is separated one from the other by the same distance of its own width. A sheet of zinc oxide electrophotographic recording material is uniformly charged, exposed to light with superposition of the test chart and then developed with the black developer employed in the above example 1. A faithful reproduction of the charge image is produced with very low background. Following drying in the dark the developed sheet is again charged and immediately dipped in a cyan developer similar to that utilized in example 1 without exposing to light. The cyan toner deposited uniformly on the background area but not on the black lines or adjacent to the areas of these lines. A similar result is obtained when the cyan developer is replaced by the magenta and yellow developers. This example illustrates the property effect of the conductive developer which is desirable for the process of the present invention.

Although the present examples were specific in terms of conditions and materials used any of the above listed typical materials may be substituted when suitable in the above examples with similar results. in addition to the steps used to prepare the color print of the present invention other steps or modifications may be used if desirable. Furthermore, other materials may be incorporated in the developers and the electrophotographic plate which will enhance, synergize or otherwise desirably effect their properties for the present invention.

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

What is claimed is:

1. ln electrophotographic multicolor imaging process com prising exposing a uniformly charged electrophotographic member selectively to an original document comprising a multicolored area in conjunction with a monochromatic line image area, said multicolored image area of said original being masked with a light reflecting material, developing the resulting latent image on said electrophotographic member with a electrically conductive toner material having a resistivity of from about 10 to 10 ohms-cm, removing said mask, repeating said charging and exposure steps to a light image of the entire original utilizing the proper filter system with respect to each remaining color in the original and developing each subsequently formed electrophotographic image with a colored toner material which will absorb light transmitted during each exposure step.

2. The process as disclosed in claim 1 wherein said mask is a white opaque mask.

3. The process as disclosed in claim 1 wherein said conductive toner material comprises a mixture of carbon black and an insulating resinous component.

Claims

2. The process as disclosed in claim 1 wherein said mask is a white opaque mask.
3. The process as disclosed in claim 1 wherein said conductive toner material comprises a mixture of carbon black and an insulating resinous component.