DE2920464A1 - ELECTROPHOTOGRAPHIC COPYING PROCEDURE AND COPYING MACHINE FOR PERFORMING THE PROCESS - Google Patents

Description

DR. -ING. DIPL.-ΙΝΘ M. "^ C. [JIPL.-Ff-Λ S. Di DIPL-PHYS. DlI ⁰ L-PHYS. DR

HÖGER - LEGAL RIGHTS - GRIcSSBACH - HAECKER BOEHMR

PATENT LAWYERS IN STUTTGART

A 43 386 b Applicant: Savin Corporation

k - 177 Columbus and Stevens Avenues

May 3, 1979 Valhalla, New York, 10595

United States

description

Electrophotographic copying process and copier for performing the Procedure

The invention relates to an electrophotographic process in which a latent electrostatic is present on a photoconductive surface Charge image of an original is generated with light and dark image areas and in which the latent charge image is developed in order to obtain a visible copy of the original, as well as a copier to carry out the process.

One of the main problems with electrophotographic copiers arises from the desire to make copies at as high a speed as possible. After a photoconductor has been electrostatically charged, however, the energy required to produce a latent image of the light and dark areas of the original with sufficient contrast to produce a usable copy is a function of the amount of light that strikes the photoconductor , as well as a function of the photosensitivity of the photoconductor. Ideally, the photoconductor should be exposed in such a way that the lightest image areas are completely discharged, while the darkest image areas of the photoconductor retain their full charge. In practice, this can never be achieved because known photoconductors have limitations with regard to their sensitivity to light. With the current state of the art for photocopiers, the energy required to operate the copier is when more than about 30 copies per minute are made.

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should be provided at about 1500 W. As the usual mains voltage in many cases is only 110 V, but this is the power output at a socket or the like is limited to about 1500 W. Accordingly, a special electrical connection is required to make satisfactory copies at a higher speed be created. This means that the copier must be set up where a connection for a higher output power or a higher mains voltage is available. Besides that the high energy requirement brings problems with regard to heat dissipation, both with regard to the photoconductor as well as with regard to the environment of the device, with the costs for the high energy consumption added. Because Given these problems, many attempts have been made to increase the sensitivity of photoconductors to light.

Earlier developments in the field of interest here are for example in US Patents 2,756,676, 3,892,481, 3,907,423, 3,912,387 and 3,994,723. In particular, US Patent 2,756,676 suggests only one single exposure process using an original to produce multiple copies of an image produced in the process. In the known method, the photoconductor is recharged after each transfer of a developed image, whereupon the recharged charge image is enhanced by illuminating it.

Furthermore, in US Pat. No. 3,892,481 there is an automatic control system for generating a bias voltage for a developer electrode.

U.S. Patent 3,907,423 describes a copier with a counter rotating Roller, which is used to remove excess liquid after developing the latent electrostatic image remove the photoconductor.

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Finally, US Patents 3,912,387 and 3,994,723 describe ways of detecting underexposed background areas and discharging them by illumination prior to developing an electrostatic latent image.

Based on the prior art, the invention is based on the object based on specifying an improved electrophotographic copying process, which with comparatively low energy consumption enables the copying speed to be accelerated.

In the case of a copying process, this task becomes the one described at the beginning Type solved according to the invention in that the latent charge image is treated with a toner in order to produce an optical To obtain shielding over the image areas of the charge image corresponding to the dark image areas of the original, that the photoconductive surface is then illuminated in order to discharge the image areas of the charge image which are the bright image areas correspond to the original, and that one then develops the charge image.

To carry out this method, a copier with a photoconductive surface, with a charging station and with Charging devices for generating an electrostatic charge on the photoconductive surface, including an exposure station Illumination devices for exposing the photoconductive surface with a light image of an original with bright and dark image areas and for generating a corresponding latent electrostatic charge image on the photoconductive Surface, with a developer station with developer devices for developing the charge image into an optically visible one Image and with devices for bringing about a relative movement between the said stations on the one hand and the photoconductive surface on the other hand, particularly proven, which is characterized in that a masking station with

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Masking devices for producing an optical shielding or masking of the dark image areas of the original corresponding areas of the latent electrostatic charge image is provided that a lighting station with lighting devices for discharging the unmasked areas of the latent electrostatic charge image by exposure to light is provided and that the masking station and the lighting station between the exposure station and the Developer station are arranged.

The present invention is therefore an improved electrophotography process which enables the "effective Speed "of a photoconductor. The characteristic The feature of xerography is the creation of an electrostatic image at one point in the process. It is best for this if a photoconductor is charged in the dark and then exposed to a light-dark image of the original creating an electrostatic latent image of the original. To get a satisfactory copy the exposure time must be chosen so that a sufficient contrast is achieved to allow the latent image to pass through Applying a developer to make visible, which from the beginning colored or from pigmented tiny charged Particles. The speed at which the copies can be made is a function of the light incident on the photoconductive surface and the conductivity of the photoconductor upon exposure. As the speed with which in a certain photoconductor discharges a previously generated surface potential under the action of light is limited, the speed can only be increased by increasing the light intensity. But this makes an increased Requires energy and leads to increased heat generation. In the method according to the invention is now a charged photoconductor is intentionally underexposed with a light image of an original in order to avoid a weak latent elec-

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to obtain a static image with a contrast which is too low to produce a satisfactory copy. The latent However, the electrostatic image is sufficiently rich in contrast to be created using a toner to allow an optical mask or shielding of the image areas. According to the invention, the masked electrostatic Charge image then fully illuminated to discharge the background areas on the photoconductor, including only one comparatively little energy is required. During this step, the optical masking prevents the Image areas are discharged, so that the contrast of the initially very weak latent charge image is increased. That amplified Charge image can now be developed by any known method in order to produce a visible image at a developer station Image.

What the copiers for carrying out the method according to the invention As far as is concerned, any known electrophotographic copier can be assumed, with devices according to the invention can be provided in order to create an optical shield for the image areas of the weak latent image and then to discharge the background areas before the now intensified charge image to the developer station of the copier got. The optical masking is carried out at a pre-developer station, where usual or special Toners is worked, which can be present either in a carrier liquid or as a dry powder. An essential one However, the feature of the copier is the facilities for applying the developer or toner material to the weak latent charge image. These devices must be biased to a potential which is higher than the potential of the background areas and is lower than the potential of the image areas. This ensures that the background areas masked while the image areas are masked or

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be provided with an optical shield.

The method according to the invention therefore has the advantage that the "effective speed" of the photoconductor is increased.

There is also the advantage that originals with low contrast can be copied well.

The advantage is also achieved that originals with image areas, which have a color to which the photoconductor is very sensitive, can be copied well.

Further details and advantages of the invention are provided below explained in more detail with reference to drawings and / or are the subject of claims for protection. Show it:

1 shows a schematic flow diagram to explain the individual steps of the method according to the invention, where the solid connecting lines for necessary steps and the dashed connecting lines apply to possibly advantageous steps of the procedure;

2 shows a schematic representation of a copier for carrying out the method according to the invention;

3 shows an idealized curve with a logarithmic scale on the ordinate and a linear scale on the abscissa, wherein the potential on the surface of the photoconductor is plotted against the amount of light which the Photoconductor has been exposed;

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4 shows a schematic representation on a logarithmic scale for the ordinate, starting with the voltage or the potential at the surface of the photoconductor
of an initial charge according to FIG. 3, after exposure to the original;

FIG. 5 shows a schematic representation corresponding to FIG. 4 for the intensified electrostatic charge image according to FIG
the masking and the full-surface illumination of the
photoconductive surface.

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As is clear from the flow graphs according to E "ir /. 1 *. ^T iru, a first step of the inventive method according to block consists first of all in that an electrostatic charge is generated on a photoconductive surface in the dark. After the charge has been generated in the dark, the photoconductive surface is then exposed to a light image or a light-dark image of the original to be copied, with an electrostatic charge image being produced on the photoconductive surface With this original exposure only a fraction, for example 5 or 10% of the amount of light which is normally required to produce a satisfactory image, ie an image in which there is sufficient contrast, is effective is present so that the dark image areas such as letters or the like are dark while the background is white However, the latent electrostatic charge image generated in the method step according to block 2 has a sufficient contrast to be provided with a toner - ie to be developed with a suitable toner, such as e.g. B. a resinous powder or, what is more favorable, with a toner which is dispersed in an insulating liquid, as is known per se. The weak electrostatic charge image is developed in the method according to the invention in accordance with block 3, with the image areas of the original to be copied corresponding to the image areas of the original to be copied over the parts of the charge image, a gap being generated which is essentially impermeable to light. When masking the charge image with a toner according to block 3, it is essential that an optical or optical shielding is generated over the image or information areas and not over the background areas. This is achieved by biasing a developer electrode or the means for applying the toner during masking to a potential which is above the potential of the background areas and below the potential of the image areas dec latent electrostatic charge images.

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In the next step of the method according to the invention, according to. Block 4 fully exposes the photoconductive surface in the area, which corresponds to the size of the copy to be generated. The electrostatic charge falls in the masked areas of the dild very little, if any, from the photoconductive surface, while the electrostatic charge in the background areas is lowered to a very low level, for example to about 50 V. Exposure of the masked charge image for discharging the unmasked background areas according to block 4, increased in the latent electrostatic charge image the charge difference between the rapid area and the background areas by a very large percentage, using only about a tenth of the energy that is normally required in order to obtain an electrostatic charge image with the required high contrast, as in accordance with the invention is achieved. The electrostatic charge image, enhanced in its contrast, can now first be cleaned according to block 5, by removing the liasque from the high-contrast charge image will. / enclosing the cleaned charge image according to block 5 or - dispensing with the method step according to Block 5 - directly into the charge image obtained in accordance with block 4 using a conventional method known per se developed or fully developed and can now easily on a carrier sheet, for example on ordinary copier paper transmit v / earth (block 7).

To carry out the explained with reference to FIG. 1 according to the invention A copier according to FIG. 2 is suitable for the method, which has a metal drum 1C with a photoconductive surface 12, for example from selenium. The drum 10 is supported by apertured disks 14 with a shaft are wedged in a rotationally fixed manner. The shaft 16, which can be grounded or connected to reference potential, is provided by means of suitable drive devices driven in such a way that the drum rotates in the direction of the arrow. The photoconductive

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Surface 12 can be charged to a voltage between 8CO and 1000 V with the help of a corona discharge. For this purpose, a positive voltage between 5000 and COOO V is applied to the corona discharge device. The elements of the corona discharge device 18 cause ionization of the surrounding atmosphere and ensure that a uniform positive charge is produced on the photoconductive surface 12, for example the selenium layer. If the method according to the invention for producing copies were applied to zinc oxide paper, then the corona discharge device 18, as is readily apparent to the person skilled in the art, would be activated in such a way that it would generate a negative charge. The photoconductive surface 12 running £ ^a Ser generation of electrostatic charge at an exposure station 20 over. There, with the aid of projection optics, which are indicated by a lens 22, a light image of the original to be copied is projected onto the photoconductive surface 12. The exposure time is extremely short in the method according to the invention. In fact, with exposure marks down to 5% of the normal exposure time, fully satisfactory copies of the originals were obtained.

The charge of a selenium photoconductor increases when exposed to an amount of light of about 3 ft-cd see

a fifth of the original charge. This is readily apparent from the diagram according to FIG. 3, v / o the potential on the surface of a selenium light guide when irradiated with an amount of light of about 2 to 3 ft-cd see from

6OG V drops to 160 V. Usually the light source supplies a photocopier provides a sufficient amount of light so that the background areas on the photoconductor have a potential about 50 to 60 V can be discharged. There is an amount of light for this. of about 5 ft-cd see required. 5% of this amount of light is about c, 25 ft-cd see, 7ms. The diagrams according to FIGS. 3 and 4 make it clear that after a short or weak exposure the potential

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the background areas D compared to the potential of the lild areas I dropped by about 100 V. If at this state of charge If the final development of the photoconductor would take place with a toner, then one would use a toner image very low contrast received. If this toner image were transferred from the drum to copy paper, then the density would be of the toner image so small that only a small amount, if any, of toner would be transferred to the copy material, so that only a very faint copy would result. /On the other hand is the low-contrast toner image after developing the latent electrostatic charge image optically sufficiently dense, so that there is a latent electrostatic charge image a mask or shield that is useful for practical use

Implementation of the method according to the invention is sufficiently tight.

In detail, the development of the latent electrostatic takes place Charge image in which there are only slight potential differences, according to FIG. 2 behind the exposure station 22 at a first developer station 29. At this developer station a tank 24 is provided, from which a developer liquid 26, in which toner particles are dispersed, which can be charged, is sucked in via a line 28 and pumped by means of a pump via a line 3 2 to a nozzle 34, which the developer sprayed onto the photoconductive surface 12 in front of a counter-rotating roller 36. If the toner particles are conductive, they can assume an induced charge when they are in the vicinity of the latent image under the action of the electric field move the same. In this case, the electrostatic charge image is first used to charge the particles, which then captured by the charge image. If the toner particles are dispersed in a liquid, then it is called a liquid an insulating liquid, such as a liquid hydrocarbon, a liquid fluorine-containing hydrocarbon or the like used, which at room temperature has a low

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gen has vapor pressure and in which the tiny toner particles are dispersed, with the help of which the electrostatic charge image made visible. It is well known that the polarity of the charged particles can be changed by the addition of certain substances to the developer liquid controlled v / ground. These act by adsorption on the surface of the particles and change their size and polarity of the charge assumed by the particles as a function of the surroundings of the particles when they are produced as well as depending on the method of their production. The toner particles must be applied by a developer electrode which is biased to a potential of the same polarity as the electrostatic latent image, the The potential of the developer electrode must be higher than the potential of the background areas and lower than the potential of the Image areas. According to the invention, when a liquid developer is used, a counter-rotating roller is preferably used as the developer electrode used. This roller 36 is made of metal and sits on a shaft 38 which, as indicated by an arrow is 'drivable in the opposite direction of rotation' like the drum 10. The counter-rotating roller 36 is opposite the earth isolated and arranged close to the surface of the photoconductor, so that there is a gap with a gap width between 0.05 and 0.1 mm. The counter-rotating roller 36 is driven by a motor, the speed of which is controlled so that it wipes off excess developer fluid from the photoconductive surface. The electrical bias of the developer electrode is critical for the method according to the invention, since it does not form a mask in the background areas may be, as will be explained in more detail below. The counter-rotating, metallic roller 36 is the surface of the charged photoconductor 12 so closely adjacent that they are floating Jas assumes the average potential of the photoconductor and thus automatically receives the correct electrical bias. Since the mean potential of the roller 36 rotating in the opposite direction is higher than the potential of the background areas of the photoconductor

Z \ JL

change the toner particles of the roller 36 instead of the background

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areas on the photoconductor. If so desired, the Roller 36, which simultaneously serves as an application and metering roller, is switched to a predetermined value by means of a suitable direct voltage source Potential are biased, which is between the potentials of the background areas and the image areas of the latent electrostatic image. The electrical bias of the counter-rotating roller serving as the developer electrode essentially prevents the deposition of masking toner particles on the background areas of the photoconductor. With the usual Developer liquids, however, the carrier liquid for the toner particles has a low boiling point, so that it evaporates slightly to ensure that the developed image, when "printed on a copy material such as paper, is transferred, results in a copy that is as dry as possible. When masking, however, can be used as a carrier liquid according to the invention a hydrocarbon with a higher boiling point that does not evaporate immediately can be used. This creates the danger environmental pollution due to the masking step avoided. If desired, a / toner can be used in place of a liquid carrier toner for the masking will. Such dry toners are known. Furthermore, US Pat. No. 3,907,423 discloses a construction for a counter-rotating roller known how it can be used according to the invention. The excess toner is returned to tank 24 during masking collected and can be used again. A wiper blade keeps the metallic counter-rotating roller 36 clean.

After in a suitable manner, for example as described above, an optical mask or shield is produced, the photoconductive surface 12 is exposed on the full area. This can be done with the help of an elongated incandescent lamp 42, which is arranged adjacent to the drum or the photoconductor carrying the masked image and transversely to the Direction of the same runs. In the case of an office copier

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Usually a quartz-halogen lamp with a power of about 500 W is used. In contrast, in the method according to the invention, a much weaker lamp can be used at the exposure station to project the image of the original. In addition, only a relatively small amount of energy is required to expose the background areas to discharge them to a residual voltage of about 50 V. As those skilled in the art know, the photoconductor is exposed to a reflected light image of the original during exposure. The light image of the original is focused on the charged photoconductor with the help of the optical system (lens 22). Since the amount of light captured by the projection optics is only a small fraction of the amount of light that is used to illuminate the original, very bright illumination of the original is required. When discharging the background areas after the optical masking of the electrostatic charge image, the photoconductor is exposed directly to the light source, so that a small amount of light is sufficient to discharge the background areas. In contrast, the image areas I are not discharged due to the masking or shielding that is generated according to the invention. The effect of discharging the background areas B while maintaining the charge in the image areas I is clear from Fig. 5 of the drawing.

It can be seen that according to the invention a contrast or a level difference of substantially 750 V is achieved between the background areas and the image areas and that this high contrast between the potentials of the areas of the electrostatic image moreover only with a tenth of the energy for the exposure of the original is achieved. This means that with a photocopier that is currently using a quartz-halogen lamp is used with a tungsten wire, which has a power of 500 W, an incandescent lamp with a power of 50 W or a fluorescent lamp can be used.

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In addition, with the currently common photocopiers only achieve a speed of about 25 copies per minute while using the method according to the invention a photocopier can be made which theoretically can easily make 150 copies per minute. In practice However, because of the inertia of the components of the photocopier to avoid extreme working conditions and to Maintaining a certain safety factor The copier working according to the invention designed for the production of about 75-100 copies per minute. This is higher Output power possible without a significant increase in the energy supply, since the only additional energy in the first Development step or when masking is required to after masking the image areas of the background areas. It goes without saying that for large-area exposure of the photoconductor, any other suitable lamp or light source can be used instead of an incandescent lamp.

In itself, large area exposure to enhance a weak latent charge image on a photoconductor is not new. For example, in US Pat. No. 2,756,676 a method is described which addresses the problem, according to a single exposure to produce multiple xerographic reproductions from an original. However, this will be the actual The speed of the photoconductor is not increased, since a first development step is carried out in the known processes, in which the full amount of toner is applied to the charge image, so that one does not need a masking step as in the present one Procedure can speak. In the known method, the charge image provided with the full amount of toner is applied a carrier material, for example a sheet of paper. The weak toner and charge image that is on the photoconductor remains, has insufficient charge differences,

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to be intensified by re-exposure or to enable the production of another copy. The weak one However, the image is not deleted in the known method; rather, the photoconductor is charged again and then a discharge of the background areas by exposure. Because the faint toner image at full exposure the image area causes a shielding of the image areas, an intensified latent charge image is obtained in this way. However, the known method lacks the crucial step of the method according to the invention, which consists in a latent step Develop an electrostatic charge image with low contrast in such a way that the background areas are free of toner stay. This is because, in the known method, the developer electrode does not have a specific bias voltage but always lies on reference potential. According to the aforementioned US Pat. No. 2,756,676, the process must be carried out in such a way that the The residual image after the first copying process is developed into a high-contrast charge image at the usual slow speed will. The copying process is not accelerated in this way.

Due to the extremely wide range in which, according to the invention a mask with sufficient optical density can be achieved, according to the invention, the exposure time and the bias voltages can be set permanently, whereby it is nevertheless guaranteed that that in any case a sharp and clear copy of any original is obtained, regardless of whether the background is snow white or mouse gray.

From the graphic representation according to Fig. 5 it becomes clear that that the potential differences between image areas and background areas are so large that there are no problems in producing a sharp and clear copy.

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After the potential in the background areas has been reduced with the aid of the incandescent lamp 42, the optical shielding of the intensified electrostatic image, which has been produced in the manner described, wiped off with the aid of a cleaning roller 44 which can consist of a rubber sponge or the like, if desired. Cleaning or wiping of the toner can use either a liquid carrier toner or a dry toner for masking take place. After cleaning, the enhanced electrostatic latent image can then be deposited in any conventional manner with the aid of a toner to be developed.

In Fig. 2 of the drawings, a toner system is shown for developing, as described, for example, in US Pat. No. 3,892,481 is. In this system, a tank 46 is provided, from which a liquid toner 48 via a line 50, a toner supply tank (not shown) and a return line 52 to the tank 46 can be circulated. There is also a developer electrode 54 is provided, the bias of which is regulated so that any residual charge in the background areas of the photoconductor is rendered ineffective. In the method according to the invention, a fixed bias voltage for the developer electrode 54 can be used this bias voltage is only slightly above the average residual charge of the background areas, since according to the invention these have been uniformly discharged to a low potential. This will help with the finished copies a clean white background is achieved without a special one Background sampling and bias control as described in U.S. Patent 3,892,481 would be required.

After developing with the liquid toner, the excess becomes Developer is removed from the developed image by a counter rotating roller 52 as described in U.S. Patent 3,907,423

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is described. The counter-rotating roller 56 is again provided with a scraper 58 and works with the one mentioned in FIG Patent specification specified speeds and in the position specified there.

On the photoconductive surface 12 is now a developed image, which is on a sheet-shaped carrier material, especially on a simple sheet of paper can. Such a paper sheet 60 is fed by means of transport rollers to a roller 64, where it is applied to the drum, whereupon the paper sheet 60 is moved past a corona discharge device 66. On the surface of the selenium drum or the photoconductor, there is still a high electrostatic charge in the image areas under the toner, which neither by the large-area exposure nor by the bias to erase the remaining background potential was discharged. For this reason, with the help of the corona discharge device 66 generates a high positive charge on the rear side of the paper sheet 60 facing away from the drum, this a high positive charge causes the toner particles to be drawn from the drum surface onto the paper. Included a pick-up 68 ensures that the paper sheet is lifted off the drum again and that the end 70 of the paper sheet, which now carries the copied image, a drying device and a collecting basket (not shown) are fed can. A cleaning roller 72 then cleans the drum of the remaining toner particles that have not been transferred, followed by a final cleaning of the photoconductive surface 12 takes place with the aid of a wiper blade 74.

When the inventive method using paper with a zinc oxide coating then remains

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the picture, of course, on the coated paper. Also understand it is that in the method according to the invention also with a dry toner made of a fusible, resinous Powder can be worked, which is thermally fixed.

Furthermore, it is clear from the above description that the extremely high-contrast charge image that can be achieved according to the invention can be developed in any suitable known manner.

A selenium photoconductor is very sensitive to blue light, so that photocopiers that work with a selenium photoconductor do not provide high-contrast copies of blue-colored originals. A selenium photoconductor therefore reacts to blue areas of the image almost like on white background areas. In the inventive Processes, on the other hand, copy blue image areas just as well as black ones.

Yellow image areas of an original are very bright in color and reflect a significant amount of light, so they do appear only faintly on the copies when working with conventional photocopiers. When working according to the invention Processes, on the other hand, also copy yellow image areas of the original perfectly due to the charge image intensification. Furthermore, the method according to the invention also ensures perfect reproduction of gray levels.

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Due to the fact that according to the invention for a broad Flawless copies can be obtained in an automatic bias control according to US Pat. No. 3,892,481, the exposure during production can be obtained of the weak charge image can be carried out before masking in such a way that the lightest background areas, i.e. H. pure white areas of the original, satisfactory on the copy can be reproduced. In this case, a charge image is initially obtained, the contrast of which is too low to immediately produce a satisfactory one To generate a copy, the contrast of which, on the other hand, is sufficient to easily perform a masking to be able to. The bias for the roller for applying the toner is high enough to meet the potential of the On the other hand, making background areas completely ineffective is sufficiently low in terms of the potential of the Image areas. This allows the image areas to be optically masked with the aid of a toner. The lighting in the image intensification can easily be regulated by ^ clie intensity the light source changed or by providing a diaphragm in the beam path of the image projection system.

From the above description it is also clear that the image intensification according to the invention in every electrophotographic Procedure can be done. For example, the enhanced electrostatic image can be applied to a dielectric sheet which is then treated with a toner to produce a visible image on this material, such as this is known.

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Claims (16)

DR.-ING. DIPL.-INC.M. SC OIPU.-PHY5 DH DIPL-PHYS. C .. '! ..- F1HYS. Cl HÖGER - LEGAL RIGHT - CAR-ESSBACH - HAECKER BOEHME PATENTANWÄLTE IN STUTTGART A 43 386 b Applicant: Savin Corporation τ_177 Columbus and Stevens Avenues' i iq7q Valhalla, New York, 10595 i ia / J USA patent claims 1. ) Electrophotographic process in which a latent electrostatic charge image of an original with light and dark image areas is first generated on a photoconductive surface and in which the latent charge image is developed in order to obtain a visible image of the original, characterized in that the treated latent charge image with a toner in order to obtain an optical shield over the image areas of the charge image corresponding to the dark image areas of the original, that the photoconductive surface is then illuminated to discharge the image areas of the charge image that correspond to the light image areas of the original, and that one then develops the charge image. 2. The method according to claim 1, characterized in that the photoconductive surface before the generation of the latent Electrostatically charges the charge image to a predetermined potential. 3. The method according to claim 2, characterized in that the charging is carried out in the dark. 4. The method according to any one of claims 1 - 3, characterized in, that the generation of the latent charge image is carried out in such a way that the bright image areas of the original corresponding image areas of the charge image discharges to a potential which is significantly higher 909941/8731 - 2 - A 43 386 b half of the
as / output potentials and that the illumination of the charged image treated with the toner is carried out in such a way that the image areas corresponding to the bright image areas of the original are discharged to a potential which is significantly lower than half the initial potential. 5. The method according to any one of claims 1 - 4, characterized in that that the development of the enhanced charge image is carried out after exposure with the aid of a toner. 6. The method according to claim 5, characterized in that this is done in the development of the enhanced charge image obtained visible image of the original is transferred to a sheet-shaped copy material. 7. The method according to any one of claims 1-6, characterized in that that the charge image of the original can be obtained by exposing the photoconductive surface to a light image of the original. 8. The method according to claim 7, characterized in that the photoconductive surface with reflected from the original Exposed to light. 9. The method according to any one of claims 1 - 8, characterized in, that the toner serving for optical shielding is carried out with the aid of a pre-tensioned voltage standing toner applicator on the latent electrostatic charge image. 10. The method according to any one of claims 1-9, characterized in that that the lighting of the partially shielded 309340/0737 - "3 - A 43 386 b k - 177 - 3 - May 3, 1979 2920A64 th charge image with direct light. 11. The method according to any one of claims 1 - 10, characterized in that that the toner, which is used for optical shielding or masking, is used after illuminating the charge image removed. 12. The method according to claim 1, characterized in that the optical shield is removed from the enhanced electrostatic charge image after exposure and that one then develops the intensified charge image with the aid of a toner. 13. Copier for carrying out the method according to one of claims 1 to 12, with a photoconductive one Surface, with a charging station and with charging devices for generating an electrostatic charge on the photoconductive surface, with an exposure station with exposure devices for exposing the photoconductive surface with a light image of an original with light and dark image areas and for Generation of a corresponding latent electrostatic charge image on the photoconductive surface, with a Developer station with developer devices for developing the charge image into an optically visible image and with devices for bringing about a relative movement between said stations on the one hand and the photoconductive surface on the other hand, characterized in that that a masking station (29) with masking devices (30-40) for generating an optical shield or Masking of the areas of the latent electrostatic charge image corresponding to the dark image areas of the original it is provided that a lighting station with 909848/073 * Λ 43 386 b k - 177 May 3, 1979 - 4 - 2920464 Illumination devices (40) for discharging the unmasked areas of the latent electrostatic charge image is provided by exposure to light and that the masking station (29) and the lighting station (42) between the Exposure station (20) and the developer station (46-54) are arranged. 14. Copier according to claim 13, characterized in that the masking devices (30-40) are designed such that that with their help on the latent electrostatic charge image a toner for masking the dark image areas areas of the latent charge image corresponding to the original can be applied. 15. Copier according to claim 12 or 13, characterized in that that the lighting devices have a light source (42) and that fastening devices for attachment of the light source (42) are provided between the masking devices (30-40) and the developing devices (46-54). 16. Copier according to one of claims 13-15, characterized in that that the masking devices have an electrically conductive element, in particular a roller (38) the aid of which a toner contained in a liquid can be applied to the latent electrostatic charge image for masking purposes is. 909848/0731