US3512967A - Electrophotographic method and member for contact printing of relatively opaque documents - Google Patents

Electrophotographic method and member for contact printing of relatively opaque documents Download PDF

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Publication number
US3512967A
US3512967A US593051A US3512967DA US3512967A US 3512967 A US3512967 A US 3512967A US 593051 A US593051 A US 593051A US 3512967D A US3512967D A US 3512967DA US 3512967 A US3512967 A US 3512967A
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United States
Prior art keywords
light
document
image
photoconductive
photoconductor
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Expired - Lifetime
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US593051A
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English (en)
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Clifford E Herrick Jr
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International Business Machines Corp
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International Business Machines Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/22—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20
    • G03G15/225—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 using contact-printing
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/02—Charge-receiving layers
    • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
    • G03G5/06—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being organic
    • G03G5/07—Polymeric photoconductive materials
    • G03G5/071—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • G03G5/072—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising pending monoamine groups
    • G03G5/073—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising pending monoamine groups comprising pending carbazole groups
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/10—Bases for charge-receiving or other layers
    • G03G5/102—Bases for charge-receiving or other layers consisting of or comprising metals
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/142—Inert intermediate layers
    • G03G5/144—Inert intermediate layers comprising inorganic material

Definitions

  • ABSTRACT OF THE DISCLOSURE A contact printing electrophotographic method in which an opaque document such as bond paper is brought into face-to-face contact with a photoconductive layer on a highly light reflective backing, followed by uniformly exposing the photoconductive member through the back of the document. The exposing light is reflected back and forth between the highly light reflecting backing of the photoconductive member and the nonimage face surface of said document with only a per tion of the light being absorbed by the photoconductive layer during each passage of light, thereby enhancing the image contrast of the resultant copy of the document.
  • This invention relates to an electrophotographic method and member and, more specifically, relates to the exposure of the electrophotographic member.
  • a photoconductive member In the method of electrophotography, commonly known as xerography, a photoconductive member is given a uniform electrostatic charge over its surface and is then exposed to an opaque document to be reproduced by a conventional projection technique, such as scanning an illuminated document with a photographic copying camera having a linear optical system. An image of the document to be reproduced is reflected from the document as a light image which is transmitted through an objective lens and onto the photoconductive surface. The areas of the photoconductive member exposed to the light image are discharged and an electrostatic latent image is created. Development of this electrostatic latent image is then achieved with an electrostatically charged material, such as electroscopic powder which is brought into surface contact with the photoconductive member and is held thereon electrostatically in a pattern corresponding to the electrostatic image. Thereafter, the developed electrostatic image is transferred to a surface, such as paper, to which it may be fixed by heating or any other suitable means.
  • a surface such as paper
  • Exposure of the photoconductive member by the projection system is disadvantageous for a number of reasons. For example, lenses of good optical quality are expensive and their elimination can result in appreciable savings. Moreover, due to the photographic speed of present day photoconductors, projection exposures in most cases require exposures of a few seconds up to 20 or 30 seconds. Further, with a projection exposure system, the document must be positioned away from the photoconductive member at a distance determined by the focal length of the lens system, thereby increasing the space requirements and, consequently, the flexibility of the design of the electrophotographic apparatus.
  • An alternative exposure system in which the photoconductive member is exposed Without a lens system is contact printing.
  • the photoconductive member is brought into contact with the document to be reproduced and is exposed to a light source through the document.
  • One of the principal advantages of contact printing is that it is many times more efficient in it utilization of light than a projections system and, hence, is much better suited for high speed operation.
  • the document in order to obtain a good quality reproduction by this system with photoconductors such as selenium, the document must be transparent or translucent to the exposing radiation and carry a dense, high contrast image. Otherwise, the contrast ratio of the image to nonimage areas will not be suflicient to provide a developable el'ectrostatic image of good quality.
  • Still another object of the present invention is to provide a new and improved electrophotographic apparatus which is inexpensive, compact in size, and capable of operating at a high rate of speed.
  • an electrophotographic method in which an opaque document is brought into face-to-face contact with a photoconductive member comprising a photoconductive film and with a highly reflecting backing, and exposing through the back of the document to light which is only weakly absorbed by the photoconductive film and to which the photoconductive film is substantially transparent.
  • FIG. 1 represents an electrophotographic apparatus embodying the exposure system of the present invention.
  • FIG. 2 is an enlarged fragmentary cross-section of the photoconductive member of the exposure system of FIG. 1.
  • FIGS. 3, 4, and 5 are graphs to be utilized in explaining the mechanism of the exposure technique of the present invention.
  • FIGS. 6, 7 and 8 are graphs to be utilized to show the improvements in image contrast with the photoconductive member of the present invention.
  • the electrophotographic apparatus shown in FIG. 1 embodying the exposure system of the present invention comprises a rotatable drum 1 carrying around its periphery an electrophotographic photoconductive member 2 having situated adjacent its periphery a corona unit 3 for electrostatically charging the surface of the drum.
  • the drum 1 rotates in a clockwise direction and after its surface is electrostatically charged by the corona unit 3, a document 5 carrying an image 6 to be reproduced is fed into virtual contact with the electrostatically charged surface past the exposure station 7 wherein the photoconductive member 2 is illuminated through theback 8 of the document 5 by a light source 9 having an exposure slit 10.
  • the electrostatic charges on the area of the photoconductive member 2 corresponding to the nonimage areas of the document 5 are dissipated to a greater degree than the electrostatic charges on the areas of the photoconductive drum corresponding to the image areas, thereby forming a developable electrostatic image.
  • the document 5 is separated from the drum 1 and the drum passes a development station 11 at which a toner-carrier mixture 12 is gravity fed across the electrostatic image on the surface of the photoconductive member 2.
  • the toner having a charge opposite from the polarity of the electrostatic image is attracted to the image rendering it visible.
  • an endless conveyor belt 13 carries the toner-carrier mixture to a position for gravity feeding it across the surface of the photoconductive member.
  • a copy paper 14 is fed into contact with the developed electrostatic image.
  • a corona unit 15 is disposed beneath the paper at the area of contact and with a polarity opposite that of the toner, thereby attracting the toner to the copy paper.
  • the paper 14 is separated from the drum and fed past a fusing element 20 to permanently fix the toner to the paper.
  • the drum 1 continues to rotate past a cleaning brush 16 which wipes the surface of the photoconductive member so as to remove any excess toner. This completes a cycle of the drum.
  • the photoconductive member comprises a film of weakly light absorbing photoconductive material being substantially transparent to light and with a highly reflecting backing so that, in being exposed through an opaque document, the light penetrating the document passes through the photoconductive film and is reflected between the highly reflecting backing and the reflective nonimage areas of the document, two portions of the light being absorbed by the photoconductive material during each reflection cycle.
  • the image areas however, the light reflected from the backing of the photoconductive material is absorbed rather than being reflected by the image. Therefore, there is a substantial increase in the ratio of light absorbed in the nonimage areas to the light radiation absorbed in the image areas as compared to the ratio achieved with a strongly absorbing photoconductive material.
  • the photoconductive member 2 comprises a photoconductive film 17 and a backing 18, both of which are carried on the drum 1.
  • the exposing light as shown by the arows 19, strike the back of the opaque document and a portion of the light rays are reflected off of the document depending upon the reflectivity, R,, of the back surface 8 of the document.
  • the remainder of the light rays pass through the document with a portion being absorbed depending upon the transmission density, D,,, of the document.
  • the exposure contrast, C i.e.the ratio of light absorbed in the photoconductive material in the nonimage areas to the light absorbed in the image areas
  • a weakly absorbing photoconductive material or one which only absorbs a fraction of the light striking its surface is employed.
  • C becomes dependent on the fractional light absorption, A, of the photoconductive material; the reflectivity, R of the backing of the photoconductive material; and the reflectivity, R,,', of the face surface in the nonimage areas of the document. That is, in the process of the present invention, the initial light striking the photoconductor which is not absorbed by it passes through the photoconductor and is reflected back from the backing of the photoconductor. Again, a portion of the light is absorbed and the remaining portion passes out of the photoconductor.
  • This portion depending on whether an image or nonimage areas is adjacent the photoconductor, either is reflected back from the surface of the nonimage area of the document or is substantially absorbed by the image.
  • the document reflected light passes through the photoconductor, with a portion being absorbed, and is reflected back oif of the backing of the photoconductor. Also, a portion of this light is absorbed by the photoconductor as it travels back toward the document.
  • G is the ratio of exposure contrast of the contact exposure method of the present invention to the exposure contrast of a contact printing method with a strongly absorbing photoconductor.
  • FIG. 3 there is shown a graph, based on the above expression, plotting contrast gain, G versus the fractional light absorption of the photoconductor for a document having an image transmission density, D of 1.0.
  • the curves are plotted for different products of reflectivity, R R ranging from 0.30 to 0.85.
  • the lower of these two reflectivity products is representative of a low reflective document, such as vellum, and the higher numbered reflectivity product represents an opaque highly reflective document.
  • the contrast gain increases as the fractional absorption of light of the photoconductor decreases and the product of reflectivity increases. This is also shown to be the case when the image transmission density is low, such as 0.2, as shown in the graph of FIG. 4.
  • FIG. 5 a graph is shown in which the contrast gain, 6,, is plotted versus the image transmission density for a photoconductor having a 5% light absorption.
  • This graph illustrates that the contrast gain, G,, is constant over a wide range of image densities.
  • FIG. 5 also amplifies the influence of the reflectivity product on the gain, but it will be noted that, even with low reflective documents (the 0.30 curve), such as vellum, there is an image contrast gain over the use of a strongly light absorbing photoconductor.
  • the backing of the photoconductive film must provide a smooth surface at the interface of the photoconductive film and the backing so as to be highly reflective.
  • the reflectivity, R of the backing must be sufliciently high so that the reflectivity product, R R approaches the reflectivity, R of the document.
  • the material forming the backing of photoconductive layer should have a surface capable of reflecting greater than of the light in the wavelength range absorbed by the photoconductor. Ninety percent or greater is more preferred.
  • Suitable materials for the backing of the photoconductive member of the present invention are aluminum, gold, silver, copper, magnesium, calcium, and rhodium, which may be coated, preferably by evaporation, on a suitable substrate of plastic, metal, or paper.
  • Other reflective materials can be found on pages 6-104 through 6-110 of the American Institute of Physics Handbook (1957).
  • the reflective backing material be specular reflecting as well as highly conductive.
  • the backing material herein is aluminum deposited on a substrate of polyethylene terephthalate. If desired, however, a low conductive or nonconductive backing material can be employed in conjunction with the dual corona device of U.S. Pat. 2,922,883.
  • the reflectivity, R of the nonimage areas of the document is also important, but can vary over a wide range from transparent up to extremely highly opaque documents.
  • the reflectivity, R ,.of the nonimage areas of the document is such that the reflectivity product, R R is greater than 0.25.
  • the documents should reflect greater than 70% of the light in the nonimage areas. If, however, very low reflective documents are to be copied, a highly opaque sheet may be placed in back of the document to form a composite which has a greater reflectivity thanthe document itself and provides a reflectivity product, R R greater than 0.25.
  • the photoconductive material of the photoconductive member must only weakly absorb the light to which it is exposed.
  • the photoconductive material should only weakly absorb light Within the Wavelength range of 4000-6500 A., which is the wavelength range of the preferred light source.
  • weakly absorbing it meant that the photoconductive material preferably should absorb less than 30% of the light each time the light passes through the photoconductive film.
  • the photoconductive material should be nonlight scattering so that totally internally reflected light rays will not be generated within the photoconductive film.
  • organic photoconductors are the preferred materials for use in the present invention and include what are termed small molecule photoconductors dispersed or dissolved in an essentially transparent binder and polymeric photoconductors which can be self-supporting.
  • the mode of operation in which the photoconductive member is employed is one in which the conductive image in the photoconductive material should not persist after exposure, suchv as is the case with conventional xerography
  • the activators should be selected from the quinones, ketones, and aldehydes listed in the above-referenced patents. If, however, the photoconductive member of the present invention is to be used in a persistent electrophotographic mode in which the conductive image should persist after exposure because, for example, it is exposed prior to charging, then the photoconductive materials of the referenced copending applications are preferred.
  • the following examples will include a comparison 7 of the image quality of copies prepared using a strongly light absorbing photoconductor and the photoconductive member of the present invention in which the photoconductor is only weakly light absorbing.
  • the examples will also show the voltage change (Av.) in the exposed areas of a strongly light absorbing photoconductor and the photoconductive member of the present invention.
  • EXAMPLE I Three photoconductive compositions were prepared and coated on the aluminum side of three separate films of aluminized polyethylene terephthalate.
  • One composition contained 1:1 molar ratio of poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone and is described in copending application, Ser. No. 556,983, filed June 13, 1966.
  • the other compositions contained 40:1 molar ratio and :1 molar ratio of poly-N-vinylcarbazole and 2,4,7-trinitro-9- fluorenone.
  • the reflectivity of the aluminum surface for all three photoconductive members was about 92% or greater of the incident light in the visible range of the electromagnetic spectrum. Using a laboratory contact printing device, the prepared photoconductive members were individually tested.
  • the device comprised an electrostatic charging station having a corona unit and a contact exposure station having a l5-watt white fluorescent light source positioned to be 1 /2 inches from the document as it passed by the exposure station. Also, the device included a toning station for developing the electrostatic image by conventional cascade development.
  • the exposure setting was optimized for each sample because they varied in light sensitivity.
  • the 1:1 molar sample it was necessary to employ a 1:1 neutral density filter over the exposure aperture to limit the light intensity in order to achieve the optimum exposure.
  • an orange filter was placed over the aperture to block wavelengths below about 5000 A. because these wavelengths are more strongly absorbed.
  • the 1:1 molar, 40:1 molar and 100:1 molar samples absorbed approximately 92%, 29%, and 20%, respectively, of the light. (Wavelength range of 4000-6500 A. for the 1:1 molar sample and 5000-6500 A. for the other two samples.)
  • the document to which the samples were exposed was a composite of three different documents, one being highly opaque and the other two of low opacity.
  • the print density on the three separate documents forming the composite also varied, with the greatest print density being on the highly opaque document.
  • EXAMPLE II Using the 1:1 molar and the 40:1 molar samples of Example I, plus a sample comprising a 150:1 molar ratio of poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone, the three samples were individually exposed through a gray scale step Wedge prepared on black developing diazo paper. Using the same densitometer of Example I, the absorption of the 15021 molar sample was measured and found to be approximately (Wavelength range of 5000-6500 A.). Each sample was exposed at exposure settings ranging from 3.2 to mm. and again the orange filter was used for the 40:1 molar ratio and the 150:1 molar sample, but not the 1:1 molar sample, the neutral density being used for the latter. Prior to each exposure of the 1:1 molar sample, the sample was charged to 600 volts and prior to each exposure of the other two samples, those samples were charged to 700 volts. The reason for this voltage difference was that the 1:1 molar sample was a slightly thinner sample
  • FIG. '6 is the graph for the measurements of the 1:1 molar sample.
  • FIG. 7 is the graph for the measurements of the 40:1 molar sample.
  • FIG. 8 is the graph for the measurements of the 150.1 molar sample.
  • the contact exposure method and member of the present invention may be employed in persistent electrophotographic methods, such as that disclosed in US. Pat. 2,845,- 348 or any other method where the photoconductor is exposed b'efore charging.
  • the contact exposure method and member of the present invention can be used in conjunction with the charge transfer technique disclosed in US. Pat. 2,825,814.
  • opaque document is a document permitting less transmisson of light than that of a vellum document, such as bond paper.
  • the term opaque document does not mean one through which no visible light can be transmitted.
  • a photoconductive member comprising a photoconductive layer and a light reflecting backing having a reflectivity greater than 0.80, the reflectivity of the surface of the-document being such that the reflectivity product of the light reflective backing and the surface of the document is greater than 0.25, and
US593051A 1966-11-09 1966-11-09 Electrophotographic method and member for contact printing of relatively opaque documents Expired - Lifetime US3512967A (en)

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US59305166A 1966-11-09 1966-11-09

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US (1) US3512967A (fr)
JP (1) JPS5116776B1 (fr)
BE (1) BE703530A (fr)
CH (1) CH455521A (fr)
DE (1) DE1597856C3 (fr)
ES (1) ES346909A1 (fr)
FR (1) FR1542891A (fr)
GB (1) GB1203255A (fr)
NL (1) NL6712490A (fr)
SE (1) SE316080B (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3663291A (en) * 1969-10-14 1972-05-16 Xerox Corp Cascade development
US20070273941A1 (en) * 2006-05-23 2007-11-29 Fuji Xerox Co., Ltd. Image forming apparatus and image forming method

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3227294A1 (de) * 1982-07-21 1984-01-26 Siemens AG, 1000 Berlin und 8000 München Roentgenelektrofotografisches aufzeichnungsmaterial und verfahren zur erzeugung eines elektrischen ladungsbildes

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2689179A (en) * 1951-03-02 1954-09-14 Haloid Co Xerographic contact copying device
US3037861A (en) * 1957-09-07 1962-06-05 Kalle Ag Electrophotographic reproduction material
US3094910A (en) * 1960-07-05 1963-06-25 Xerox Corp Reflex xerographic apparatus
US3102026A (en) * 1957-12-24 1963-08-27 Metcalfe Kenneth Archibald Electrophotographic reflex and contact printing
US3131060A (en) * 1959-02-26 1964-04-28 Gevaert Photo Prod Nv Electrophotographic material
US3158475A (en) * 1960-03-31 1964-11-24 Gevaert Photo Prod Nv Electrophotographic material
US3288605A (en) * 1965-11-17 1966-11-29 Equipment Dev Corp Electrophotographic printing method
US3335003A (en) * 1963-10-09 1967-08-08 Xerox Corp Reflex xerographic process

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2689179A (en) * 1951-03-02 1954-09-14 Haloid Co Xerographic contact copying device
US3037861A (en) * 1957-09-07 1962-06-05 Kalle Ag Electrophotographic reproduction material
US3102026A (en) * 1957-12-24 1963-08-27 Metcalfe Kenneth Archibald Electrophotographic reflex and contact printing
US3131060A (en) * 1959-02-26 1964-04-28 Gevaert Photo Prod Nv Electrophotographic material
US3158475A (en) * 1960-03-31 1964-11-24 Gevaert Photo Prod Nv Electrophotographic material
US3094910A (en) * 1960-07-05 1963-06-25 Xerox Corp Reflex xerographic apparatus
US3335003A (en) * 1963-10-09 1967-08-08 Xerox Corp Reflex xerographic process
US3288605A (en) * 1965-11-17 1966-11-29 Equipment Dev Corp Electrophotographic printing method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3663291A (en) * 1969-10-14 1972-05-16 Xerox Corp Cascade development
US20070273941A1 (en) * 2006-05-23 2007-11-29 Fuji Xerox Co., Ltd. Image forming apparatus and image forming method
US7835028B2 (en) * 2006-05-23 2010-11-16 Fuji Xerox Co., Ltd. Image forming apparatus with color forming information applying unit that transmits light through image holding member and method thereof

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Publication number Publication date
SE316080B (fr) 1969-10-13
DE1597856C3 (de) 1973-11-15
FR1542891A (fr)
DE1597856B2 (de) 1973-04-05
ES346909A1 (es) 1969-01-16
BE703530A (fr) 1968-02-01
DE1597856A1 (de) 1970-08-13
GB1203255A (en) 1970-08-26
CH455521A (de) 1968-07-15
JPS5116776B1 (fr) 1976-05-27
NL6712490A (fr) 1968-05-10

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