EP0018742B1 - Procédé pour améliorer la densité maximale et l'étendue de variations des tons d'images électrographiques et copieur électrographique employant ce procédé - Google Patents

Procédé pour améliorer la densité maximale et l'étendue de variations des tons d'images électrographiques et copieur électrographique employant ce procédé Download PDF

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Publication number
EP0018742B1
EP0018742B1 EP80301189A EP80301189A EP0018742B1 EP 0018742 B1 EP0018742 B1 EP 0018742B1 EP 80301189 A EP80301189 A EP 80301189A EP 80301189 A EP80301189 A EP 80301189A EP 0018742 B1 EP0018742 B1 EP 0018742B1
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EP
European Patent Office
Prior art keywords
image
developer
layer
halftone screen
insulating layer
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Expired
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EP80301189A
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German (de)
English (en)
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EP0018742B2 (fr
EP0018742A1 (fr
Inventor
George Philip Kasper
Arthur Stanley Kroll
Michael Mosehauer
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Eastman Kodak Co
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Eastman Kodak Co
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Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Priority to AT80301189T priority Critical patent/ATE4435T1/de
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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
    • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
    • G03G15/04027—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material and forming half-tone image

Definitions

  • This invention relates to the production of electrographic images and particularly to an electrophotographic method for forming improved copies of originals which contain a wide range of image densities.
  • Electrographic copying methods commonly produce images having high contrast. These methods are very useful for producing good line copy reproductions. However, such methods have not been particularly useful in reproducing originals that contain a wide range of image densities or relatively large areas of uniform density. Frequently, adjunct means such as halftone screens are used to improve the reproduction of such images which are so difficult to reproduce. Halftone tint screens have opaque dots of uniform density.
  • Typical techniques for producing half-tone copies of continuous tone images or of large image areas of uniform density involve transforming the image into a plurality of dots or lines which can then be developed.
  • discrete charge-bearing zones discrete charge-bearing zones (dots, lines or other shapes) are formed on the surface of the element, which zones are separated by areas that bear little or no electrical charge relative to that of the discrete charge-bearing zones.
  • Such discrete charge-bearing zones are referred to herein as "charge islands”.
  • Latent electrostatic images comprising charge islands can be created by initially charging the electrographic surface in a screen pattern, by masking the original image with a halftone screen during exposure, or by uniformly exposing a charged photoconductive surface through a halftone screen before, during or after image exposure, but before development.
  • a typical method is disclosed in U.S. Patent 2,598,732.
  • the range of densities of the original which can be faithfully reproduced is referred to hereinafter as the tonal range.
  • an electrographic copying method for producing copies having increased maximum density and tonal range which method comprises:
  • Copies produced according to the present invention have greater than expected maximum densities and greatly improved tonal ranges as compared with images produced by prior art electrographic methods in which halftone screens are used. Continuous tone originals, as well as originals having alphanumeric line copy and relatively large areas of uniform density, are reproduced with greater fidelity to the original than has been obtainable with such prior art electrographic methods.
  • the method of the present invention can be used to produce continuous tone images, which method comprises:
  • the charge islands are produced on a photoconductive layer by exposure through a halftone screen which is an integral part of the photoconductive element.
  • This embodiment of the invention offers several advantages including 1) registration problems are minimised, 2) simple continuous exposure techniques can be used since the screen moves with the photoconductive layer, 3) a fixed space is maintained between the screen pattern and the photoconductive layer and 4) high frequency screen patterns may be used without significant resolution loss.
  • This invention also provides electrographic copying apparatus comprising (a) means for forming on an insulating layer a latent electrostatic image of an original; (b) means for forming a plurality of charge islands in the image area of the said insulating layer in addition to any charge islands that result from use of the means (a); and c) means for developing the latent image resulting from use of the means (a) and (b) with a dry developer composition which has a resistance of less than 10 9 ohms as measured by the test procedure described herein or obtains such a resistance by electrical breakdown during development.
  • Figs. 1 and 2 show the results of developing charge islands with two kinds of developer; a non-conductive developer having been used in the case of Fig. 1 and a conductive developer, as required for the method of this invention, having been used for Fig. 2.
  • the developed charge islands are discrete and faithfully retain the size and shape of the transparent areas of the halftone screen.
  • the developed charge islands do not retain the dimensions of the transparent areas of the halftone screen.
  • the developed charge islands of Fig. 2 appear to have expanded, making the open spaces between the islands smaller. This surprising expansion causes the maximum density of the image to be increased.
  • the maximum density obained using the method of the present invention is more than three times the predicted density. This effect, referred to herein as dot enlargement, is entirely unexpected.
  • the improvement of the tonal range of images reproduced by the method of this invention is one result of dot enlargement.
  • the present invention is broadly applicable to any electrographic method for reproducing an image which method provides a modulated latent electrostatic image, e.g., a latent electrostatic image having a range of charge intensities.
  • the photoconductive element 11 contains a transparent support 12.
  • the support provides mechanical strength to the element and makes it suitable for use in electrophotographic copying machines.
  • the support can be fabricated of almost any transparent material, and may be selected from such diverse materials as glass and plastics of various types.
  • the support can be rigid as in the case of a plate or cylinder of glass or polymethylmethacrylate, or it can be flexible as with the case of a plastic such as polyethylene or polyethylene terephthalate.
  • a transparent support is shown in Fig. 3, other types of supports can be used, especially in the circumstances where the photoconductive layer is to be exposed other than through the support.
  • a halftone screen 13 made up of a number of finely divided, alternating, opaque and transparent areas. This screen is used to form charge islands on the photoconductive layer.
  • the screen pattern of opaque and transparent areas can be a conventional dot pattern or line pattern of the type used for the fabrication of halftone plates for newspaper printing.
  • the alternating opaque and transparent areas of the screen pattern may be of almost any shape, including round dots, elliptical dots and lines.
  • the spacings of the pattern can also vary so that the pattern is regular, irregular, or random.
  • the pattern can also be varied in size from dot-to- dot or line-to-line. Since the screen is utilized only for forming charge islands, it can be either electrically conducting or insulating.
  • the halftone screen should be oriented such that after exposure through the screen, the resultant halftone pattern is at an angle of from 30° to 10° to any halftone pattern that may be present in the original which is to be copied.
  • the halftone screen When the halftone screen is used, it can be located in the film base as disclosed in U.S. Patents 3,310,401 and 3,335,003. It can be integral with the conductive layer as disclosed in Canadian Patent 577,137. It can be in the barrier layer as disclosed in U.S. Patent 3,341,326. It can be present as an overcoat layer over the photoconductive layer as disclosed in U.S. Patent 3,627,526 and it can be integral with the photoconductive layer as disclosed in U.S. Patent 3,681,071.
  • Methods for producing electrophotographic images using halftone screens are well known. Such methods are disclosed in the aforementioned patents.
  • the halftone screens can have almost any frequency. Particularly useful results are obtained with halftone screens having a frequency of 32 to 80 dots/cm and a percent tint i.e. percent opaque areas of 10 to 90%.
  • a halftone screen is not the only means for forming charge islands on the electrophotographic element.
  • Other means can also be used for this purpose.
  • charge islands can be formed by corona charge or discharge through a screen such as a grid-controlled screen or insulator screen, or by a pulsed corona charge through a longitudinal screen. They can also be formed using a patterned array of pulsed styli or wires, by discharging the photoconductive layer with a textured conducting roller, or by discharging in a voltage contrast pattern in a layer beneath the photoconductive layer.
  • Latent electrostatic images composed of charge islands according to the present invention can also be formed with a single exposure by using a scanning type exposure device such as a computer addressed light emitting diode array, cathode ray tube or laser.
  • the continuous tone image can be momentarily or permanently stored in binary form in a computer memory.
  • the proper output transducer circuits between the computer's memory and the exposure means are engaged.
  • the computer's logic controls the transducer circuits in a way to cause the cathode ray tube, laser or light emitting diode array to modulate and/or pulse on and off according to the tonal range of the continuous tone image, while scanning and thus exposing a photoconductive layer.
  • a very thin transparent conductive layer 14 which can be composed of tin oxide, nickel, cermet, or copper iodide. Methods for forming such conductive layers are well known.
  • an electrical or chemical barrier layer can be used in combination with the conducting layer 14 and the halftone screen 13.
  • the photoconductive layer 16 can be any of the photoconductive insulating layers generally used in electrophotography, and can include layers of vitreous selenium, aggregate photoconductive layers of the type disclosed in U.S. Patent 3,615,414 or any one of many other organic photoconductive layers including multilayer photoconductive elements having separate charge generating and charge transport functions.
  • the photoconductive element is first charged in darkness so that the photoconductive layer is sensitized with a generally uniform electrostatic field.
  • photoconductive layer 16 of the element is exposed in an original containing a continuous tone image by projector means thereby forming on said layer 16, a latent electrostatic image of the original. Formation of the plurality of charge islands within the latent electrostatic image is effected in this mode by a second uniform exposure of the photoconductive layer 16 through the rear of the element, and thus through the halftone screen 13.
  • the rear exposure is carried out prior to, simultaneously with, or after exposure of the photoconductive layer to the image, the only requirement being that this rear exposure be carried out after the charging step and prior to the development step.
  • This uniform exposure step is illustrated by arrows 18 in Fig. 3.
  • the uniform rear exposure of the charged photoconductive layer through screen 13 serves to discharge at least partially all areas of the photoconductive layer 16 directly opposite transparent areas of the screen. This exposure thus forms a plurality of charge islands on photoconductive layer 16.
  • the amount of exposure used to form these charge islands will vary according to a variety of factors, including the nature of the photoconductive layer, type of developer, and mode of development.
  • the number and size of the charge islands is governed by the frequency and percent tint of the halftone screen used. Assuming image exposure after rear exposure through the screen, the charge islands opposite white areas of the original image being copied are substantially completely discharged by the exposure to the original. Charge islands opposite grays in the original are partially discharged. And charge islands opposite blacks in the original retain their original charge level.
  • the charge islands are formed first and then modulated by the exposure to the original. If both front and rear exposures are made simultaneously, modulated charge islands are formed in a single step. If the image exposure is made prior to the rear exposure, the level of charge across the whole element is first modulated according to the light received from the image exposure to the subject. The resulting latent electrostatic image is then divided into charge islands by the subsequent rear exposure through the halftone screen. Regardless of which sequence is employed, the resulting charge pattern on the element is modulated by the uniform exposure through a halftone screen.
  • a photoconductive surface was used in the above described method. However, such charge islands could be formed by other means on a dielectric surface. Information about the original could be received from a computer or other data source and recorded by computer-addressed styli on a dielectric surface.
  • the charge island image is contacted with a developer which is conductive either intrinsically or as a result of electrical breakdown.
  • the resistance of an intrinsically conductive developer should be less than 10 9 ohms (52), preferably less than 10 6 ohms, when measured as described below.
  • Resistance is measured using a General Radio DC electrometer type 1230-A, 6-9 Volts, or comparable equipment, in accordance with the following procedure. For each measurement, a 15 gram quantity of developer material was used. A cylindrical bar magnet (560 Gauss North Pole) having a circular end of about 6.25 sq.cm. was used to attract the developer and hold it in the form of a brush. After formation of the brush, the bar magnet was posi-tioned with the brush carrying end approximately parallel to and about 0.5 cm. from a burnished copper plate. The resistance of the particles in the magnetic brush was then measured between the magnet and the copper plate at 21 °C and 40% relative humidity.
  • a cylindrical bar magnet (560 Gauss North Pole) having a circular end of about 6.25 sq.cm. was used to attract the developer and hold it in the form of a brush. After formation of the brush, the bar magnet was posi-tioned with the brush carrying end approximately parallel to and about 0.5 cm. from a burnished copper plate. The resistance of the particles in the magnetic brush was
  • Typical conductive developers comprise a toner and a carrier and are non-liquid.
  • the carrier may be conductive.
  • a conductive additive may be present to improve the conductivity of the developer.
  • Typical conductive developers include carriers such as iron, cobaltic oxide, stannic oxide, zinc and ferromagnesium, cupric carbonate, zinc carbonate, manganese carbonate, cupric oxide, lead acetate, zirconium, and nickel carbonate. Single component conductive developers can be used.
  • This electrical breakdown phenomenon exhibited by developers manifests itself when the resistance of the developer material is measured as a function of the electrical field across the developer.
  • the resistance is conveniently measured by 1) placing a metal electrode in the plane of the photoconductive element above an operating magnetic brush, 2) applying a known potential to the electrode, and 3) measuring the current passing through the magnetic brush. Resistance is calculated by dividing the voltage by the current. At a certain level of the applied field, called the electrical breakdown value, for a small increase in field there is a large drop in the resistance of the developer material. The developer then acts as though it has a higher conductivity.
  • Development by using the electrical breakdown phenomenon can be carried out by a) contacting a latent electrostatic image with a developer composition and b) establishing across such developer an electrical field greater than the electrical breakdown value of the developer, thereby causing the developer to undergo electrical breakdown.
  • Development by the electrical breakdown mode can be influenced by a number of factors such as: the composition of the carrier particles; the concentration of toner particles in the developer; the strength of the electric field between the surface bearing the electrostatic charge pattern and the electrode; the thickness of the developer (i.e., the distance between the surface bearing the electrostatic charge pattern and the electrode); initial photoconductor charge or charge on the support; voltage on the electrode and the choice of photoconductor thickness to govern the surface potential per unit charge. Development is accomplished by selecting one or more of the aforementioned factors such that the electric field which forms across the developer during development is greater than the electrical breakdown value of the developer under the conditions of development. Development by the electrical breakdown mode can be accomplished using liquid developers or dry developers.
  • Preferred developers are those which have relatively low electrical breakdown values. Less than 25 volts/mm is typical. Also, in order to prevent discharging of the latent electrostatic image, preferred developers are those which exhibit relatively high resistivity prior to electrical breakdown, i.e., when subjected to a low strength electrical field. A low field resistivity of at least 10 5 ohm-cm is preferred. By the term “low field resistivity” and “measured under low fields” as used herein, we mean resistance measurements made in accordance with the procedure previously described.
  • the latent image can be transferred to another support before it is developed.
  • the transfer can be made before or after the latent image is made into a charge island image.
  • any of the methods for electrostatic image transfer described in the prior art can be used. If the latent electrostatic image is transferred before the charge islands are formed, the charge islands can be formed on an insulated receiving element before, during or after the transfer. Development is carried out on the transferred latent charge island image in the same manner as described for development on photoconductive layers.
  • Development with conductive developers or via the electrical breakdown mode can be carried out using any of the conventional electrographic developing means, including cascade and magnetic brush technique.
  • a particularly useful magnetic brush technique comprises 1) moving a member bearing an electrostatic image past a development zone and 2) transporting such developer a) through a first development zone in a direction generally counter-current to the moving member and b) through a second development zone in the same direction as the moving member.
  • the development apparatus 30 comprises two magnetic brushes 31, 32 mounted at a development station along the path of an electrographic member 33.
  • the electrographic member can be a photoconductive insulating layer 34, an electrically conductive backing layer 35 and a film support 36.
  • Each of the magnetic brushes 31, 32 comprises an array of strip magnets, denoted N and S, arranged as shown around the periphery of inner cores 38 and 39, which are stationary within developer reservoir 40.
  • Each brush also includes an electrically conductive outer cylinder 41 and 42 respectively, which is non-magnetic and rotatable around the core to transport developer mixture, attracted by the magnets N and S, from the reservoir 40 into contact with the image member 33 and back into the reservoir to be replenished.
  • augers 48, 49 can be provided in the reservoir as shown.
  • the augers have a pitch which varies longitudinally to equalize the quantity of developer supplied.
  • the cylinders 41 and 42 of brushes 31 and 32 are rotated in different directions, as indicated, by drive means 43, 44 respectively, and that each cylinder has a separate electrical voltage from respective potential sources Vb, and Vb z .
  • Any electrographic apparatus which includes an image recording member having an image recording area and means for forming an electrostatic image on said area can be adapted to perform the method of the present invention.
  • Such apparatus can be modified to include means for forming, in the image recording areas of the image recording member, a plurality of charge islands and development means which includes a supply of conductive developer for applying the developer to the resulting electrostatic image.
  • Image-forming stations of a representative electrographic apparatus are presented schematically in Fig. 7.
  • the electrographic apparatus as presented, comprises a photoconductive image recording element 70 which includes the halftone screen described in Fig. 3.
  • the apparatus also includes charging means 71, imaging exposure means 72, and means 73 for uniformly exposing the imaging area of the photoconductive layer through the halftone screen. The uniform exposure through the halftone screen can be made before, during or after formation of an electrostatic image or an original.
  • development means 74 which includes a conductive developer composition as required by the present invention.
  • the method of the present invention can be used to form both monochrome and polychrome copies. Suitable colorants can be incorporated into toners according to known methods.
  • a transparent aggregate photoconductive element of the type described in Example 1 of U.S. Patent 3,615,414 was charged and exposed to a step tablet having neutral density areas of 0.09, 0.41, 0.75 and 1.05.
  • the element was given a second uniform exposure from the front side through a halftone screen having a frequency of 60 dots/cm, and a percent tint of 50 percent of its area.
  • the resulting latent charge island image was then developed with a magnetic brush and a developer composition like that of Example 7 herein having a resistance of 1.5 x 106Q measured as described hereinbefore.
  • the reflection densities of the developed image of the step tablet were compared graphically with the densities one would ordinarily expect from the use of a 50 percent tint halftone screen.
  • the expected densities were calculated assuming that the dots on each step of the step tablet were faithfully reproduced as in Fig. 1. The calculation was carried out in the following manner.
  • the density (D) of a particular image area is given by the formula
  • R represents reflectance. To a first approximation, reflectances are additive when viewed at a normal viewing distance. Hence, the total reflectance (R t ) of an area of several densities is given by in which X " is the fraction of the total area covered by reflectance R " .
  • D 1 represents the density of the solid area.
  • D 2 represents the density of the paper base. Therefore the total expected density (D t ) is The calculation is then repeated for different Dout levels, as found by developing in the absence of a halftone screen.
  • Fig. 4 The graphic comparison of the actual reflection densities and the expected densities is shown in Fig. 4.
  • the graph of Fig. 4 shows that the expected output Dmax (0.38) is about 1/3 of the actual output Dmax (1.2).
  • the tonal range of this example is also greater than that expected. More steps of the step stablet were faithfully reproduced than expected.
  • Example 1 prints were made as in Example 1 with two different developers: a dry partially conductive developer, with a resistance of a 1.5 x 10 6 ⁇ (a developer like that of Example 7 herein) and a dry developer with a resistance of 4.4 x 10 9 52.
  • Example 2 Each element was imagewise exposed substantially as in Example 1 except that the uniform screen exposure was through the halftone screen from the rear of the film.
  • a reflection original document was used as a test with areas having neutral densities of 0.09, 0.41, 0.75 and 1.05 respectively.
  • the prints were developed as in' Example 1 with a conductive developer having a resistance of 1.5 x 10652. Density measurements were made and plotted as in Example 2.
  • the prints showed smooth, uniform, neutral tones with very little mottle and edge defects.
  • the graphs describing density input vs. density output showed high Dmax, lowered image contrast and extended tonal range as in Example 1.
  • the developers used in Examples 4-8 contained toner particles comprising carbon black in a styrene-acrylate polymeric matrix and magnetic carrier particles coated with a vinylidene fluoride-fluoro-ethylene-copolymer.
  • Various carrier particle cores were used (see list below) to produce developers exhibiting a range of resistances that were measured as previously described.
  • Example 3 Copies were made as in Example 3 with a reflection original document having neutral density area (referred to as input density or Din) as indicated in Table 1.
  • input density or Din neutral density area
  • This example illustrates the use of a developer that is made conductive by the breakdown development mode.
  • the developer was similar to the developer described in Example 8 with the exception that the mean particles size of the toner was smaller (6.8 millimicrons).
  • the toner concentration was 3.1 %.
  • An integral screen photoconductive element was used similar to the element described in Examples 4-8 with the exception that the halftone screen had a frequency of 52 dots/cm. and a 40% tint.
  • the developer was run in a two-roller magnetic brush development station for 1 hour to allow the developer to come to equilibrium.
  • the photoconductive element was charged to -500 volts, exposed such that the film voltage corresponding to a 0.15 neutral density grey scale step was -150 volts, uniformly rear exposed through the screen and developed in a breakdown development mode in a two roller magnetic brush development device with 7.6 cm diameter rollers operating at brush speeds of 160 and 180 RPM.
  • the film velocity was 25 cm/second and the magnetic brush spacing from the film surface was 1.9 milli-metres with a development brush bias of -140 volts.
  • the breakdown value for this developer, as measured according to the procedure described hereinbefore was 13.6 volts per millimeter.
  • the present invention is also useful in forming reversal images.
  • Image tone reversal can be obtained by developing the discharge areas of the images (instead of the charge islands) using a highly biased magnetic brush, and then developing with a toner having the same polarity as the brush bias.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrophotography Using Other Than Carlson'S Method (AREA)
  • Dry Development In Electrophotography (AREA)
  • Combination Of More Than One Step In Electrophotography (AREA)
  • Magnetic Brush Developing In Electrophotography (AREA)
  • Thermal Transfer Or Thermal Recording In General (AREA)
  • Silver Salt Photography Or Processing Solution Therefor (AREA)
  • Photoreceptors In Electrophotography (AREA)
  • Liquid Crystal (AREA)
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  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Claims (16)

1. Procédé de reproduction électrographique qui comprend:
a) la formation, sur une couche isolante, d'une image électrostatique latente d'un original,
b) avant, pendant ou après la phase (a), la formation d'une pluralité d'ilots de charge dans la plage d'image de ladite couche isolante, qui s'ajoutent aux ilôts de charge dus à la mise en oeuvre de la phase (a) et,
c) le développement de l'image électrostatique latente obtenue par une composition révélatrice qui présente une résistance inférieure à 109 ohms, mesurée par le procédé indiqué dans la description, ou qui acquiert cette résistance pendant le développement.
2. Procédé conforme à la revendication 1, dans lequel le révélateur acquiert une résistance inférieure à 109 ohms pendant le développement par suite de l'établissement, à travers le révélateur, d'un champ électrique suprieur au seuil de claquage électrique du révélateur.
3. Procédé conforme à la revendication 2, dans lequel la composition révélatrice a un seuil de claquage inférieur à 25V/mm.
4. Procédé conforme à l'une quelconque des revendications 1 à 3, dans lequel on utilise, pour la mise en oeuvre de la phase (c), une composition révélatrice sèche.
5. Procédé conforme à la revendication 4, dans lequel le développement s'effectue à l'aide d'une brosse magnétique.
6. Procédé conforme à l'une quelconque des revendications précédentes, dans lequel, pendant la phase (a), on expose suivant une image une couche photoconductrice.
7. Procédé conforme à la revendication 6, dans lequel, pendant la phase (b), on expose uniformément la couche photoconductrice à travers un écran tramé.
8. Procédé conforme à la revendication 7, dans lequel l'écran tramé présente une linéature de 32 à 80 points par centimètre et une densité de points de 10 à 90%.
9. Procédé conforme aux revendications 7 ou 8, dans lequel l'écran tramé fait partie d'un produit photoconducteur qui comprend la couche photoconductrice.
10. Procédé conforme à la revendication 9, dans lequel l'écran tramé est placé entre un support transparent du produit et la couche photoconductrice, cette couche étant exposée suivant une image par sa face frontale et à travers l'écran tramée par sa face dorsale.
11. Procédé conforme à l'une quelconque des revendications 1 à 8, dans lequel la couche isolante fait partie d'un produit récepteur d'image.
12. Procédé conforme à l'une quelconque des revendications 1 à 6, dans lequel la couche isolante fait partie d'un produit récepteur d'image et l'image latente formée pendant la phase (a) est transférée sur la couche isolante avant la mise en oeuvre des phases (b) et (c).
13. Procédé conforme à l'une quelconque des revendications 1 à 5, dans lequel on effectue simultanément les phases (a) et (b) par exposition d'une couche photoconductrice à un dispositif d'exposition à balayage adressé par ordinateur.
14. Appareil de reproduction électrographique comprenant (a) un dispositif pour former, sur une couche isolante, une image électrostatique latente d'un original;
(b) un dispositif pour former une pluralité d'ilôts de charge dans la plage d'image de ladite couche isolante, qui s'ajoutent aux ilots de charge formés à l'aide du dispositif (a) et
(c) un dispositif pour développer l'image latente, obtenue par utilisation des dispositifs (a) et (b), avec une composition révélatrice sèche qui présente une résistance inférieure à 109 ohms, mesurée par le procédé indiqué dans la description, ou qui acquiert cette résistance par claquage électrique pendant le développement.
15. Appareil de reproduction électrographique, conforme à la revendication 14 dans lequel la couche isolante est une couche photoconductrice transparente et le dispositif (a) comprend des moyens pour charger uniformément la face frontale de la couche et des moyens pour exposer suivant une image à un rayonnement activateur cette face ainsi chargée, par cette face frontale, et le dispositif (b) comprend un écran tramé placé du côté de la face dorsale de la couche photoconductrice et des moyens pour exposer toute cette couche à un rayonnement activateur à travers cet écran tramé.
16. Appareil de reproduction électrographique conforme à la revendication 14, dans lequel les dispositifs (a) et (b) comprennent un système d'exposition à balayage adressé par ordinateur.
EP80301189A 1979-04-16 1980-04-15 Procédé pour améliorer la densité maximale et l'étendue de variations des tons d'images électrographiques et copieur électrographique employant ce procédé Expired EP0018742B2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT80301189T ATE4435T1 (de) 1979-04-16 1980-04-15 Verfahren zur verbesserung der maximalen dichte und des tonumfangs elektrographischer bilder und elektrographisches kopiergeraet zur durchfuehrung des verfahrens.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US3066879A 1979-04-16 1979-04-16
US30668 1979-04-16

Publications (3)

Publication Number Publication Date
EP0018742A1 EP0018742A1 (fr) 1980-11-12
EP0018742B1 true EP0018742B1 (fr) 1983-08-10
EP0018742B2 EP0018742B2 (fr) 1988-08-24

Family

ID=21855368

Family Applications (1)

Application Number Title Priority Date Filing Date
EP80301189A Expired EP0018742B2 (fr) 1979-04-16 1980-04-15 Procédé pour améliorer la densité maximale et l'étendue de variations des tons d'images électrographiques et copieur électrographique employant ce procédé

Country Status (7)

Country Link
EP (1) EP0018742B2 (fr)
JP (1) JPS5619067A (fr)
AT (1) ATE4435T1 (fr)
AU (1) AU536674B2 (fr)
BR (1) BR8002337A (fr)
DE (2) DE3014449C2 (fr)
FR (1) FR2454646A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL8400922A (nl) * 1984-03-23 1985-10-16 Oce Nederland Bv Werkwijze voor het vervaardigen van kopieen.

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2598732A (en) * 1949-03-09 1952-06-03 Haloid Co Electrophotography
DE1175985B (de) * 1959-11-05 1964-08-13 Agfa Ag Verfahren zur Herstellung elektro-photographischer Bilder
US3337339A (en) * 1962-10-01 1967-08-22 Xerox Corp Screen xerography
NL298605A (fr) * 1962-10-01
US3335003A (en) * 1963-10-09 1967-08-08 Xerox Corp Reflex xerographic process
US3627526A (en) * 1969-12-29 1971-12-14 Rca Corp Electrophotographic recording elements with half-tone screen coatings thereon
US3681071A (en) * 1970-01-02 1972-08-01 Rca Corp Method of pressure treating electrophotographic recording elements to change their sensitivity to light
ZA73911B (en) * 1972-03-15 1973-11-28 Minnesota Mining & Mfg Electrographic development process
US3905822A (en) * 1973-10-23 1975-09-16 Xerox Corp Compound screen for object screening
US4051536A (en) * 1975-03-14 1977-09-27 Xerox Corporation Electronic halftone imaging system
US4083632A (en) * 1976-04-05 1978-04-11 Xerox Corporation Multi-frequency screen
JPS52143826A (en) * 1976-05-26 1977-11-30 Mita Industrial Co Ltd Electric recording method
US4076857A (en) * 1976-06-28 1978-02-28 Eastman Kodak Company Process for developing electrographic images by causing electrical breakdown in the developer

Also Published As

Publication number Publication date
JPS5619067A (en) 1981-02-23
EP0018742B2 (fr) 1988-08-24
EP0018742A1 (fr) 1980-11-12
FR2454646B1 (fr) 1983-12-09
DE3014449A1 (de) 1980-10-30
FR2454646A1 (fr) 1980-11-14
BR8002337A (pt) 1980-12-02
AU5751880A (en) 1980-10-23
JPH0210954B2 (fr) 1990-03-12
DE3014449C2 (de) 1986-03-27
ATE4435T1 (de) 1983-08-15
AU536674B2 (en) 1984-05-17
DE3064518D1 (en) 1983-09-15

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