DE1497086C3 - Method and apparatus for electrophotographic image reproduction - Google Patents

Description

The invention relates to a method for electrophotographic image reproduction, in which the to reproducing image on an electrical control grid provided with a photoconductive layer is optically mapped, and free charge carriers are generated, which with the help of the control grid in image-wise distribution are applied to an insulating image carrier, as well as a device for Implementation of this procedure.

In the usual electrophotographic image reproduction processes is generally a reusable electrophotographic plate that includes a photoconductive layer on an electrically conductive surface

ίο has, initially evenly charged, then with an optical image that corresponds to the original to be reproduced, exposed and then with Toner particles developed. The image developed in this way is then normally transferred to another Carrier, e.g. paper, is transferred, after which the electrophotographic plate is cleaned and reinserted a process cycle is used.

Another method is also known, which is one-time use electrophotography Plate is made, for example, of paper with a layer of a photoconductive Material and a coating consists of an insulating binder. In this process, the electrophotographic plate directly as the final image support. It does not apply to this procedure separate transfer process.

From the DT-AS 11 56 308 is already a electrophotographic image reproduction process known in which an image is not immediately on one photoelectric image carrier can be formed. According to the known method, a electrically conductive grid on which a photoconductive layer is applied, in a specially designed one provided device first uniformly charged in the dark with electrostatic charges and then exposed imagewise with the image to be reproduced, whereby in the exposed areas the applied electrostatic charges flow away, while only in the unexposed areas the electrostatic charges are retained. After this imagewise exposure of the control grid this used in the actual image reproduction device in such a way that the control grid in one predetermined distance to the image carrier material is arranged on which the image to be reproduced should be trained. This process must be carried out in complete darkness, otherwise the electrostatic latent image present on the control grid would be distorted. A copy of the too reproducing image is then produced in that at a distance from the control electrode a Device for generating charged toner particles is arranged. These are generated in that a cloud of toner powder is blown into a space charge of free charge carriers, whereby the add free charge carriers to toner powder particles. The clinging this way with Toner powder particles with charge carriers then either pass through the earth's gravity field Generation of an electric field between the device for generating these toner powder particles and the image carrier through the control electrode onto the image carrier. As a result of the different exposure caused by the When charging the control device, toner powder particles are preferred in such areas of the control grid, in which the electrostatic charges of the control grid due to the exposure have flowed away. This then results on the image carrier

an image corresponding to the original to be reproduced from toner particles which are known to be on the Image carrier material can be fixed. However, the known method is relatively time consuming because first an intermediate image must be produced by first placing the control grid in a separate Process is electrostatically charged and exposed. Only when this intermediate image is on the control grid is available, the actual image can be produced. So that at all a picture with relatively good resolution and contrast can be achieved, a photoconductor material must be used on the one hand the highest possible dark resistance and on the other hand a possible has a long after-effect time or recovery time, since the conductive state of the exposed areas during the entire imaging process must be maintained. The photoconductive materials that make up this Meet conditions, but generally have a relatively low photosensitivity. Because of the required long recovery time of the photoconductor material still cannot be used for images be carried out in quick succession. The fact also stands for such a procedural sequence contrary to the fact that the control grid is cleaned of adhering toner powder particles after each imaging process must be, but this is relatively cumbersome and difficult.

From the French patent specification 12 13 493 there was already an electrostatic imaging process known on a dielectric image carrier layer, in which opposite the image carrier layer an arrangement is provided for generating free charge carriers, for example in the form of a corona discharge device. Between the device for generating free charge carriers and the image carrier become one of the free ones Charge carrier accelerating towards the image carrier control electrode as well as one on a predetermined one Potential held stencil electrode provided. The template electrode indicates the one to be reproduced Image corresponding passage openings, while the remaining parts of the electrode for the free Load carriers are impermeable. The charge carriers that hit these parts of the template electrode Are derived from the electrode. This known method allows the production of relatively high charge density electrostatic latent images, but are only images possible in black and white without halftone transitions. There is a particularly significant disadvantage furthermore that a special stencil electrode is made for each image and inserted into the relevant arrangement must be used before a corresponding image can be generated. A mapping of any images to be reproduced in quick succession is therefore included this device is not possible.

A common electrophotographic reproduction process is also already disclosed in US Pat. No. 2,8 03,177 known in which an electrophotographic plate is initially charged evenly and then imagewise exposed to the image to be reproduced. The process of charging and the imagewise exposure can also be carried out at the same time.

From the DT-AS 10 93 384 there is already a modification of the general electrophotographic Method has become known in which an electrophotographic plate using a. Corona discharge is charged while simultaneously holding the electrophotographic plate with the reproduced image is imagewise exposed. During the charging of the plate, toner particles are simultaneously in the Charging current is blown in, so that the free charges attach to the toner particles and these in the deposit essentially in the exposed areas of the electrophotographic plate.

It is an object of the present invention to provide an electrophotographic imaging method and to specify a device for its implementation, with the of any templates in images can be generated directly on an electrically insulating copy material in a rapid sequence be able.

Based on a method of the type mentioned at the outset, this object is achieved according to the invention solved that the free charge carriers simultaneously during the optical imaging of the reproduced Image generated on the control grid and without adhering developer particles in the form of an electrostatic, latent image are applied to the image carrier, and that the electrostatic, latent image is subsequently developed.

The invention makes it possible to display images from any templates directly in quick succession to produce an electrically insulating copier material without the need for a special transfer step the developed image from an electrophotographic plate onto the copy material. In contrast to the method known from DT-AS 11 56 308 eliminates the need for the control grid after a Illustration by cleaning, electrostatic charge and exposure for the next illustration prepare. At the same time it was surprisingly found that now a photoconductor material! With relatively low dark resistance can be used, which has hitherto generally been the case with the usual electrophotographic imaging processes had to be disregarded. Precisely such photoconductor materials but generally have an increased sensitivity to light. Furthermore, there is a improved resolution and contrast with improved halftone reproduction at the same time.

In the following, the invention will be described in more detail with reference to preferred exemplary embodiments shown in the drawing explained. In the drawing shows

F i g. 1 shows the image reproduction on a flexible, translucent belt in schematic form;

2 shows an example of a device for generating an electrostatic charge pattern a dielectric surface in schematic form;

F i g. 3 shows a modified embodiment for the generation of an electrostatic charge pattern;

4 shows an image development for a thermoplastic Body. . ■

The in Fig. 1 includes embodiment shown the various components of a system for reproducing a document 1 on a tape 2.

The belt 2 and another endless belt 3 are moved in the direction of the arrows by means of conventional drives. A motor Mi, which is connected to a roller ti, and a motor M2 to which a roller 5 is coupled, for example, can be used for this purpose. In the exemplary embodiment, the two

5 6

the drives for the belt 3 and the belt 2 to those of the belt 2 with an electrically grounded layer

same linear speed synchronized The tape is deposited. A transparent conductive layer can be used for this purpose

2 runs from a roller 4 and is made of tin oxide, tin chloride, copper iodide or the like by means of rollers 6, 10, 9.

11 passed through various process stations. serve as shown in Fig.l. In the one shown

The document! That is to be reproduced is 5 embodiment, the tape 2 is flexible; the

placed on the tape 3, which it through a projection stage components of the apparatus can but in the frame

tion 7 transported, where it is illuminated by a lamp 8 professional action also modified in this way

will. The light reflected from the document will be used to create an image on a rigid body

with the help of the mirror S and 14 and a lens system.

15 shown on a control screen 12. io The potential threshold for the corona discharge is

The projection station 7 shown is suitable as a function of the diameter of the electrode 17. It

mainly for opaque documents; However, it has proven to be beneficial to use the corona equipment

in their place also other projection devices device 18 with a potential slightly above the

to operate the image of the original on the control screen 12 threshold value. This leads to unfavorable

usable. For example, the light can be influenced by a non-uniformity of the electrode

Microfilm slide or the like guided and effectively reduced on the screen 12 and the charge can be more easily

to be bundled for illustration. steer. See one as particularly advantageous

The control screen 12 includes a conductive screen of electrical potential of approximately 6500 to 7500 volts

21 made of, for example, interwoven conductive strands, for an electrode diameter of approximately 0.089 mm

a copper grid, a metallic sieve or the like. 20, but values are in another

At least one side of the screen is useful with one area.

photoconductive semiconductor layer 22 coated. After the latent electrostatic image of the screen 21 has been produced, a perforated metal plate or document, a metal grate or a sieve can also be used. The tape 2 is passed through a development station 30 and photoconductor layer 22 can be directed onto the control screen 25. At this development station the latent will be deposited by oxidizing one side of the conductive image by means of an electrophotographic screen 21 and visibly depositing a coating of selenium or art on another photoconductor. Made at this one. For example, a two-component design, better control is achieved, the winder, which consists of finely divided plastic toner parts, if the screen 12 with the semiconductor layer 22 is not mixed with larger carrier beads, is placed facing the tape. ; Since the in Fig.l let trickle down onto the surface of the belt 2. The device shown is intended for continuous operation of the toner particles following electrical attraction, is ^ a photoconductor layer with strong adherence to the band 2 in the image configuration and deliver • reduced 'signs of fatigue, especially a: faithful' reproduction of the original -1.
desirable. Thus, for example, a according to FIG. 35 It is optional to fix the visible toner image on US Pat. No. 3,077,386 treated selenium in a melting chamber 31 with better results in order to obtain a glassy, more stable image than that otherwise used in xerography . Selenium in the melting chamber. 31, the toner image is exposed to vapors, which simultaneously with the projection of an optical solvent for the plastic particles and an image onto the control screen 12, the corona discharge 40 will soften them and allow them to flow together. After the electrode 17 'from an energy source 24 leaves the melting chamber 31, the synthetic corona device 518 on the corona discharge material hardens again and adheres firmly to the band 2. Other known potentials brought. As shown in Fig. 1, the conductive fusing process, such as heat fusing, shielding 25 is preferably grounded, as can be used if desired.
transparent conductive layer 9 of the strip 2. In the embodiment shown with the device in FIG 17 viewing screen can be thrown>. ; Is the included. The illustrated single-electrode device control screen 12, as shown, on which the image is only used for illustration, with no other corona devices 50 known in the art, then the tape 2 must be transparent in order to exclude want. The projection of the optical image onto the control under the influence of the optical image is made possible by the screen 12. However, the method described semiconductor layer 22 in the areas struck by the light is not selectively more conductive due to the use of transparent areas. This causes the image carrier to be restricted

Deposition of the electrical charge on the belt 2 55 Fig.2 illustrates an embodiment at

is controlled in such a way that on this a latent dem the transparency and flexibility of the

electrostatic image does not play a role in the configuration of the document-image carrier for image reproduction,

mentes! is created. In this example, the image carrier 35 can be transparent,

The tape 2 can be any suitable material, translucent or opaque. At least

Retention of an electrostatic charge pattern on 60 a surface of the image carrier 35 must be sufficient

included on its surface. Such materials are highly insulating to an electrostatic charge: in

about plastics, cellulose acetate, polyethylene tere- image configuration to be able to hold. Like Fig. 2

phthalate and the like, but it can also be shown to others when the image carrier 35 is located during the production of the

Materials having at least one non-conductive electrostatic image on a conductive plate 36, the

Surface layer are equipped as unpigmented 65 is grounded.

tes paper with a coating of non-conductive. In a modified form, the image carrier 35

Plastic. For the sake of sufficient- also be electrically conductive and non-conductive

The charge accumulation is the image-bearing surface having an image-forming surface. Then could

the image carrier 35 itself could be grounded and the conductivity of the plate 36 could consequently be bypassed will.

Materials suitable for the image carrier 35 include glass, paper, cellulose acetate, Mylar polyester film, Paper with a thin coating of insulating material such as methyl styrene and the like shown example, the light from the original to be reproduced is not directly on the control

Energy source dispensed with. The electrode 17 of the corona device is partially covered by a conductive shield 25 surrounded, which is provided with a window 26. This is preferably made of glass with a conductive Overlay windows allow an optical image to be projected from the projector 40 onto the Control screen 12. In this embodiment, control screen 12 is connected to grounded conductive screen 25 attached and thus works at zero potential. the

screen, but the light is previously reflected in the contrast of the charge, although it is reflected a little down on the image carrier. The surface of the image tray can, however, be used with this device. The light must therefore be reflected. Otherwise,
if the image carrier 35 is transparent, this can be the
Figure on the control screen causing light
instead be reflected from plate 36.

The electrode 17 comprises a fine wire or needle, which (the) with the energy source 24 through a line 37 is connected. The line 37 can

create developable electrostatic images.

As in connection with Fig. 2 already explained, the light is transmitted from the image carrier 35 onto the control screen 12 reflected according to the optical image. To this

also serve as a holder for the electrode, which in

In this way, the photoconductor layer 22 is made relatively conductive at selective locations. This changes the potential of the control screen from point to point under the influence of the photoconductive layer 22

a cylindrical conductive shield 38 in 20 projected or reflected light. This gives a

Axial direction is arranged vertically. The control screen 12 is provided with a bias voltage by an energy source 27.
It consists of a conductive screen 21, one of which

Control of the accumulation of charges on the image carrier.

One can therefore expect a more effective charge control when working with reflection Devices of FIGS. 2 and 3 of the control screen 12

Side has a photoconductive layer 22. Is arranged by 25 as close as possible to the image carrier 35,

1.6mm or

at a distance

projecting an optical image to a projector 40, then
forms on the image carrier 35 on the dark ones
Areas corresponding to the optical image
an electric charge. The accumulation of charges in
If a latent electrostatic image is correspondingly significantly smaller or negligibly small, the areas that correspond to the bright image areas are produced. On the original projected by the projector 40, in this way a is created on the image carrier 35
developable, corresponding to the optical image,
electrostatic charge pattern. Will be with the
Setting up not copies in a sequence but in 35 A transparent image carrier 35 and a form of individual copies are made, so the question of transparent plate 36, for example made of glass, plays with fatigue (one based on a previous one
Exposure longer lasting change in resistivity) of the photoconductive layer only
a minor role. In this case the 4 ° is needed
photoconductive layer 22 in Figs. 2 and 3 are not off
a specially treated photoconductor material
exist. Rather, the photoconductor materials customary in the electrophotographic technology can be used
be used.

Successful control of charge accumulation
can be on the image carrier 35 by applying
different electrical potentials to the control screen 12 of FIG. 2 achieve. Does the control screen 12
a distance of approximately 1.6 mm from image carrier 35, 5 ° image can be generated on an image carrier 35, which then shows a bias voltage of 100 to 150 volts the deformable plastic, such as diethylene glycol ester of greatest charge contrast between the exposed and hydrogenated rosin, polystyrene plastics the unexposed areas. As an experiment, od. The like. Has. The latent image is then applied to about 6500 to 7000 volts through the electrode 17 and a softening process is developed, be it by exposure to the control screen 12 changing potentials between solvent vapors or heat, such as zero and a few hundred volts. The control screen Fig.4 shows.

consisted of a copper grid with about 60 lines per figure. 4 is below the image carrier 35

cm (about 26 Ψο free area) and an about 80 micron electrical heating element 43 is arranged. If the thick selenium layer 22. It resulted in a charge con- Image carrier 35 is softened, the image-bearing is retained trast, who for the xerographic development of the 6 ° surface the ability under the influence of on her electrostatic images was sufficient, with the attacking electrostatic forces flowing. Contrast peak was in the indicated potential range. The image carrier 35 forms a microscopic one

If, in an application, the charge contrast of a non-uniform surface with a wrinkled appearance is sufficient even with a bias voltage of zero, this can be done in an image configuration. The resulting image also removes the energy source that supplies the bias voltage. ⁶ 5 has sufficient light scattering to either allow the control screen to be simply grounded. directly or by means of a suitable projector

In Fig. 3 shows a further exemplary embodiment. to be looked at. This example is entirely based on the prestressing

1 sheet of drawings 609 545/365

preferably
fewer.

The reflection from the image carrier 35 then changes the conductivity of the layer 22 and on the image carrier

Of course, the embodiments of FIGS. 2 and 3 are redesigned in such a way that instead of direct projection is used for reflection.

a thin tin oxide coating or the like, and the projector 40 is not on the shown but on the other side of the image carrier 35 is arranged.

There are various options for converting the latent electrostatic image into a visible image Procedure available. In addition to the at F i g. 1 are also other cascade developments Techniques for applying an electroscopic toner are known. With a suitable choice of materials It is also possible to use other development processes than applying toner to make the images visible apply. For example, with the method just described, a latent electrostatic

Claims (8)

Patent claims: 1. Process for electrophotographic image reproduction in which the image to be reproduced is based on an electrical control grid provided with a photoconductive layer is optically imaged, and free charge carriers are generated, which are distributed in an image-wise manner with the aid of the control grid are applied to an insulating image carrier, characterized in that the free Charge carriers simultaneously during the optical imaging of the image to be reproduced on the Control grid generated and without adhering developer particles in the form of an electrostatic, latent Image are applied to the image carrier, and that the electrostatic, latent image thus produced is then developed. 2. Apparatus for performing the method according to claim 1 for direct electrophotographic Image reproduction on an insulating image carrier, with a corona discharge device for generating free charge carriers which can be moved against the image carrier, with a device by the the image to be reproduced onto an electrically conductive layer provided with a photoconductive layer Control grid can be exposed, and with an image developing device, characterized in that that image carrier (2, 35), control grid (12), corona discharge device (18), exposure device (7,40) and image developing device (30) are arranged so that during exposure the generated free charge carrier, moved through the control grid and on the image carrier as latent Charge image are applied and then the charge image is developed. 3. Apparatus according to claim 2, characterized in that the control electrode (12) has a Bias can be applied. 4. Device according to one of claims 2 or 3, characterized in that the photoconductive Layer of the control grid (12) is image-wise exposable through the image carrier (2). 5. Apparatus according to claim 2 or 3, characterized in that the photoconductive layer (22) of the control grid (12) can be exposed imagewise via a reflection on the image carrier layer (2). 6. Device according to one of claims 2, 3 or 5, characterized in that the corona discharge device (18) a screen (25) with an optically transparent window (26) for the passage of the projection light of the to be reproduced Image has. 7. Apparatus according to claim 6, characterized in that the control screen (12) is contiguous is formed with the shield (25). 8. Device according to one of claims 2 to 7, characterized in that the distance between the control electrode (12) and the image carrier (2) is 1.6 mm or less.