EP0890142B1 - Electrophotographic printing process for printing a substrate - Google Patents

Description

The invention relates to an electrophotographic printing process according to claims 1 to 13 for printing on a support in which a photosensitive Layer system with an electrode layer, an insulating one Top layer and one between electrode layer and Cover layer arranged photoconductor layer by stamping an electric field of a first direction in one homogeneous initial state is brought. The photoconductor layer is through the cover layer or through the electrode layer through with pictorial structures exposed, the layer system a second electrical Field is impressed in the opposite direction, so that a charge pattern in and on the layer system corresponding to the Image structures arise. The entire photoconductor layer is then through the cover layer and / or through the electrode layer exposed evenly so that on the Surface of the top layer corresponding to the picture structures Potential picture emerges. After that, cover the top layer toner particles charged in a development step applied, which according to the potential image as a toner image deposit, which is then transferred to the carrier becomes.

The creation of the charge and potential image with the above layer system and those listed above Steps is similar to that under the name "Katsuragawa method" "Canon np process" known methods (see e.g. US 3,124,456; DE 1 497 164 or DE 1 522 567). At acquaintances This type of printing process can vary from print to print a variable picture structure can be specified. However can only print speeds with such printing processes can be achieved, which is far below that of offset printing lie. With an offset printer today there are up to 2500 Print images printable per minute. However, offset printing has the disadvantage that a print mask before printing a print image made inside or outside the offset printer must become. This results in a complex printing process only from a print run of a few hundred Print images works economically. Also a quick one Changing the image structures is not possible and usually lies at least in minutes.

US-A-4,444,859 describes electrophotographic processes explained in which after an imagewise exposure of a photosensitive layer system n-copies of the image printed without being exposed again in the meantime becomes. The layer systems, which are an upper insulating layer, a Contain photoconductor layer and a lower electrode layer, ensure that the mechanically sensitive photoconductor through the upper insulating layer during the development process is protected.

In Patent Abstracts of Japan, Volume 6, No. 195 (5.10.82), JP-A-57-105755 explains an electrophotographic copier that with a run n = 1 at a first speed and with a print run n> 1 compared with one copied to the first speed higher speed. The structure of the layer system or the influence of the layer system on the print quality is not described. Described becomes a technology of n-edition printing, in which a Toner image is fixed on the photoconductor drum.

DE-A-27 41 713 relates to a method and an apparatus to stabilize an electrostatic charge pattern, where the stabilization by choosing a suitable one Potential for generating the charge image is achieved.

US-A-5,053,304 describes a layer system for electrophotographic n-run printing without intermediate exposure explained.

US-A-3,821,931 explains a copier in which a electrophotographic printer and an offset printer combined are.

It is an object of the invention to provide a method for electrophotographic Specify n-layer print where the pictures can be printed with high print quality without re-exposure.

This task is for a method of the aforementioned Art solved in that with a print run greater than 1 the development step and the transfer step several times below Preservation of the existing inside the layer system electrical charge pattern are carried out.

The invention is based on the knowledge that electrophotographic Proven procedures, but on condition greater than 1 an insufficient printing speed have an exposure but especially with a print run larger than 1 in principle only has to be done once, since the picture structures are the same for each print of the edition. Therefore be in a printing method according to the invention in one edition greater than 1 the development step and the transfer step several times while maintaining the inside of the layer system existing charge pattern executed. In particular, not applicable imagewise exposing, even exposing and one Establishing the homogeneous initial state. This allows the Print speed is essential for a print run greater than 1 increase. In addition, the print increases with one run 1 performed with lower energy consumption because the mentioned steps are omitted. By dropping one Cleaning step in which remaining toner particles from Layer system are removed, the life increases of the layer system considerably. In the invention, the Development step and the transfer step several times executed immediately in succession. The means the development step and the transfer step consecutively without any pictorial in between Expose an even exposure and make the homogeneous initial state.

The charge pattern is located inside the layer system in one embodiment of the invention between the cover layer and photoconductor layer. The charge pattern is in deep traps localized. That means practical no lateral shifting of the load can occur. Even when using conductive substances, e.g. liquid Toner, there is no so-called image blurring. In addition, this charge pattern remains practical when exposed to light unchanged. The result is that a high limit circulation can be achieved up to which the print images of an edition are of sufficiently good quality.

To the charge pattern inside the layer system at one To be able to essentially maintain a print run greater than 1, are measures in embodiments of the invention through which the charge pattern when applying the charged toner particles in the development step and during Essentially transferring the toner image onto the carrier remains unchanged. For example, applying the Toner particles over an air gap between the top layer and a toner particle carrier for applying the toner particles be performed.

The printing method according to the invention is preferably in one High performance printer used. With a controller can between a print with edition 1 and a print with edition greater than 1 can be switched. When printing with a print run the printing speed becomes greater than 1 according to the above through an appropriate control of the printing process significantly increased.

In a further embodiment of the invention, the imagewise exposure just before or at the beginning of the imprint of the second electric field. The pictorial Exposure takes place line by line according to the Image structure controlled LED line or by an according of the image structures modulated laser beam, so that a digital Pressure is performed.

If an intermediate carrier is used as the carrier, from which the Toner image in a further transfer step sheet material, e.g. Paper that is transferred can the wear of the layer system can be reduced since the Intermediate carrier can be made from one material, which the cover layer only when transferring the toner image little mechanical attack.

There is a between the photoconductor and the electrode layer insulating intermediate layer, so the contrast and / or increases the sensitivity of the layer system during exposure be, which further increases the quality of the printed images elevated.

The invention also relates to an electrophotographic Printer with the features of claim 14. The above The effects mentioned also apply analogously to the electrographic Printer according to the invention. The electrographic Printer according to the invention combines the advantages of the known electrophotographic printing and offset printing there he without electronic mask preparation one in electronic form available print information with the edition 1 and variable Print content from page to page at the speed of one known electrographic printer print or optionally with a circulation greater than 1 with a clearly increased Print speed prints at the print speed of offset printing is comparable.

The layer system used in the invention can be a Form a plane or a curved surface. Besides, that can Layer system optionally made of a flexible or rigid Material.

Figur 1

eine Prinzipdarstellung eines elektrografischen Druckers mit wesentlichen elektronischen und mechanischen Funktionseinheiten,

Figur 2

eine schematische Darstellung eines fotoempfindlichen Schichtsystems,

Figur 3

eine schematische Darstellung des Ladungsbildes und des Potentialbildes in der fotoempfindlichen Schicht, und

Figur 4

ein Flußdiagramm des Druckverfahrens nach der Erfindung.

The invention is described below using exemplary embodiments. Show:

Figure 1

a schematic diagram of an electrographic printer with essential electronic and mechanical functional units,

Figure 2

1 shows a schematic illustration of a photosensitive layer system,

Figure 3

is a schematic representation of the charge image and the potential image in the photosensitive layer, and

Figure 4

a flowchart of the printing method according to the invention.

Figure 1 shows a schematic diagram of an electrographic Printer 10 with essential electrical and mechanical Functional units. The printer 10 has one through a motor 12 transport device 16 driven by a shaft 14, which is arranged near a transfer station 18 and endless carrier material 20 at the transfer station 18 essentially transported past according to a predetermined printing speed VD. As an alternative to the continuous carrier material 20, a change in transport also printed single sheets become.

In the transfer station 18 is on a photoconductor drum 22 applied, toner-colored charge image by means of a corona device (not shown) on the carrier material 20 transferred. The photoconductor drum 22 rotates doing so in the direction of an arrow 24. After the transfer printing any residual toner in an eraser 26 removed and a residual charge image in a photoconductor layer on the photoconductor drum 22 may be deleted. The activation of the extinguishing device 26 depends on whether the printer 10 is in a first operating state I or is in a second operating state II. In the operating state I operates the printer 10 like a known electrographic Printer in which the print image changes from print image to print image Print information can be printed. In the operating state II will be a single print specification with one edition printed larger than 1.

In operating state II, the photoconductor drum 22 is in contrast for operating status I only once per edition an exposure line 28 of LED diodes in accordance with the image exposed to a given image structure. This process is explained in more detail below with reference to FIG. 3. Subsequently the photoconductor drum is exposed evenly 22 by an exposure device, not shown. Through the two exposure steps and the one below explained influence of external electrical fields arises a potential image on the surface of the photoconductor drum 22, that corresponds to the image structures.

If the photoconductor drum 22 continues to rotate, it becomes hers Surface in both operating states I and II on one Developer station 30 passed. In the developer station 30 are loaded according to a known method Applied toner particles.

As already mentioned, in both operating states I and II then the charge image colored with toner by means of of the corona device onto the carrier material 20 in one Transfer step transmitted. Be in operating state II subsequently in contrast to operating state I without one Activate the eraser 26 and the exposure line 28 a predetermined number of printed images, e.g. 100 printed images, temporally and spatially one after the other on the carrier material 20 printed.

After the carrier material 20 is transported past the transfer station 18 , it will be in both operating states I and II fed to a fuser 32 in which the still smearable toner image in the carrier material with the help of Pressure and temperature is melted smudge-proof. In the seen by an arrow 34 indicated transport direction in front of the transfer station 18 is a first deflection unit 36 arranged which the carrier material 20 of the transfer printing station 18th feeds. A second deflection unit 38 is in the transport direction seen after the fixing station 32 arranged. This second deflection unit 38 stacks the printed carrier material 20 on a stack 40. The carrier material 20 is at the beginning the printing process from a stack 42 by the first deflection unit 36 taken. Instead of the two stacks 40 and 42 rolls are also used on which the carrier material 20 is rolled up.

The printing process is controlled by a print controller 44, which contains a microprocessor 46 and a memory 47. The microprocessor 46 operates a stored in the memory 47 Print program. The print controller 44 outputs the image structures before and transmits those belonging to these image structures Image signals via a bus system 48 to the exposure line 28. In operating state I are when printing each one Print image by the print controller 44 new image signals transfer. The motor 12 is connected via a control line 50 controlled by the pressure controller 44 so that it is one in Lower speed compared to operating mode II Has. Alternatively, the pressure control 44 can also be used With the help of a gear, not shown, the transport speed of the carrier material 20 in the operating state I be reduced.

In operating state II, the motor 12 is accordingly controlled that the carrier material 20 has a higher transport speed has as in operating state I. In addition, the Exposure line 28 in operating state II only for exposure used in the first print of the edition. The extinguishing device 26 is not used in operating state II because the charge image in the photoconductor layer of the photoconductor drum is preserved over the entire print run.

The pressure controller 44 is connected to a via data lines 52 Input / output device 54 connected, among other things, the one you want Operating state I or II specified by an operator can be.

FIG. 2 shows a photosensitive layer system 70 which is applied to the photoconductor drum 22. The layer system 70 contains an insulating cover layer 72 made of a transparent material, an underlying photoconductor layer 74, e.g. from a flexible organic photoconductor N-type (OPC), and a lower electrode layer 76 made of a sufficiently conductive material, e.g. Copper.

Is between the cover layer 72 and the photoconductor layer 74 a greatly enlarged boundary layer 78 is shown in FIG. Between the photoconductor layer 74 and the electrode layer 76, a barrier layer 80 is shown. The boundary layer 78 and the barrier layer 80 form in the respective Edge areas of the photoconductor layer 74.

Figure 3 shows a schematic representation of the charge images and the potential images in the layer system 70 during the printing process, which is used in printer 10 to generate the charge image becomes. In part a of Figure 3, the charge pattern is in and on the layer system 70 for three steps A, B and C. shown. In step A, the layer system is charged 70 carried out, in step B a reload and an imagewise exposure is carried out and in step C. uniform exposure of the layer system 70 is carried out.

In Fig. 3b the potentials on the surface of the Layer system 70 in each of steps A to C for bright and dark picture structures shown. Is on the abscissa axis the time t is ablated and is on the ordinate axis the potential P is removed.

In step A, the on the photoconductor drum is charged 22 applied layer system 70 by a not corona device shown. The layer system is thereby brought into a homogeneous initial state. In this State are on the surface of the insulating Cover layer 72 positive charge carriers that are evenly distributed are. There are opposite poles in the boundary layer 78 plus negative charge carriers, which also essentially are evenly distributed in the boundary layer. The Potential course on the surface of the cover layer 72 is such that during the time of step A, the between a time t0 and t1 is performed, a positive Potential that builds up the tension of the corona device approximates.

In step B below, a transhipment takes place and simultaneous imagewise exposure of the layer system 70 through the LEDs of the exposure line 28, with the help of a further corona device an electric field on the Layer system 70 is impressed, which is an opposite Has polarity, like the electric field in step A. An darkened areas of the layer system 70 is a transshipment complicated by the further corona device, since the photoconductor layer 74 has a high resistance in the dark.

The charge carriers present in the photoconductor layer 74 due to the photoelectric properties of the Do not leave the photoconductor layer. Through the further corona device there is nevertheless a reload into the darkened areas. Located in the electrode layer 76 positive charge carriers, the negative charge carriers in face the photoconductor layer 74, which are not positive Charge carriers on the surface of the cover layer 72 more because they are removed by the further corona charge were. These positive charge carriers can also be due to the photoelectric properties of the photoconductor layer 74 do not penetrate the photoconductor layer 74.

In the areas illuminated by exposure line 28 of the layer system 70 light rays 90 impinge. The Light rays 90 cause an altered photoelectric Behavior of the photoconductor layer 74, which becomes low-resistance. As a result, the effect caused by the further corona device Transshipment carried out entirely in the illuminated areas become. Store on the surface of the top layer 72 negative charge carriers. These negative charge carriers there are positive charge carriers in the photoconductor layer 74 opposite that from the electrode layer 76 in the Arrive photoconductor layer 74. The potential distribution at the The surface of the layer system 70 is in part b of FIG. 3 between the time t1 and a time t2. Distinguish the potentials for light and dark areas barely change in size at time t2. The bright areas have a negative potential due to the negative charges on the surface of the top layer 72 and the darkened Areas have approximately the same negative potential the surface of the cover layer 72 due to the negative Charges in the photoconductor layer 74.

In step C, the entire exposure is uniform Layer system 70 in the longitudinal axis of the photoconductor drum 22 for a streak by blasting 92. The even exposure can e.g. through another exposure line in which all LEDs are uniform Have brightness.

The entire photoconductor layer is formed by the uniform exposure 74 low impedance. In the areas already in Step B were illuminated, the charge pattern changes in the Layer system 70 does not. In the darkened in step B. Areas takes place due to the changed properties of the now there also a low-resistance photoconductor layer 74, as a result, the positive charge carriers of the electrode layer 76 penetrate into the photoconductor layer 74 and at least part of the negative there Neutralize charge carriers. The potential picture on the surface cover layer 72 is again in part b of FIG. 3 shown. The charge is balanced out of potential in the dark areas. This results in a potential difference D between light and dark areas. This potential difference causes the charged Toner particles only in the areas illuminated in step B. adhere to the surface of the cover layer 72.

In operating state II, the charge distribution remains inside of the layer system 70 via a multiplicity of printing processes, in each of which an entire print image is printed on the carrier material 20 is printed, essentially unchanged.

Figure 4 shows a flow diagram of the method according to the invention in operating state II of the printer 10. In one step 100 a printing cycle is started for a print run N, e.g. an operator via the input / output device 54 sets operating state II and inputs a start signal.

In a step 102, the microprocessor 46 Image data for image elements of a print image in the memory 47 saved. In a step 104, the operator the number of copies N is fixed, whereby in operating state II the print run N is greater than 1.

Then the corona device for charging the Layer system 70 activated according to step A (step 106). In In a step 108, the layer system 70 is reloaded and simultaneously through the exposure line 28 according to the specifications the pressure controller 44 exposed. In a step 110 by another exposure line in the direction of rotation 22 Photoconductor drum seen behind exposure line 38 one uniform exposure of the layer system 70 according to step C carried out.

Then a counter for counting the printed images of the respective edition set to zero (Step 112). By the developer device 30 Toner is applied to the photoconductor drum 22 (step 114). The transfer then takes place at the transfer printing station 18 of the toner image on the carrier material 20, which is in the fixing station 32 is fixed (step 116).

The length of a printed image in the transport direction 34 is through limits the size of the photoconductor drum 22. No later than after the photoconductor drum 22 one turn with activated Exposure line 28 has performed the corona device to charge the photoconductor according to step A, the exposure line 28 and the exposure line for uniform Exposure no longer activated. Steps 114, 116 and a step 118 can take place without the influence of the pressure control 44 are carried out when the counting process is carried out by a separate counter is carried out when a Counter reading, which corresponds to the edition N, the Pressure control 44 reactivated.

After one revolution of the photoconductor drum, the speed is reduced the photoconductor drum 22 still by the pressure control 44 significantly increased, since in particular the imagewise exposure step when printing the other print images of the edition not applicable. The extinguishing device 26 is in operating state 2 only activated if another edition is to be printed.

In a step 118 it is checked whether the counter has a value that corresponds to the edition height N. Is not this the case, the counter value is in a step 120 by the Value 1 increases and the process loops from the Steps 114 through 120 continued. If it is determined in step 118 that the counter has a counter value that matches the Edition N corresponds, i.e. all prints of the Edition has already been printed, so will the edition print ended in a step 122.

The printing method according to the invention achieves that in operating state II a printing speed of over 1000 pages per minute is reached.

Claims (14)

1. Electrophotographic printing method for printing a carrier (20),

   in which a photosensitive layer system (70), having an electrode layer (76), an insulating covering layer (72), a photoconductor layer (74) arranged between the electrode layer (76) and the covering layer (72), a blocking layer (80) arranged between the photoconductor layer (74) and the electrode layer (76) as well as an intermediate layer (78) with deep traps for charge carriers, arranged between the photoconductor layer (74) and the covering layer (72), is brought into a homogeneous initial state by means of the impression of an electric field having a first direction (step A; 106),

   the photoconductor layer (74) is exposed with predetermined image structures according to the image through the covering layer (72) or through the electrode layer (76) (step B; 108),

   a second electric field with an opposite direction being impressed on the layer system (70),

   so that a charge image corresponding to the image structures arises in and on the layer system (70),

   the entire photoconductor layer (74) is uniformly exposed through the covering layer (72) and/or through the electrode layer (76) (step C; 110), so that a potential image corresponding to the image structures arises on the surface of the covering layer (72),

   in a development step (step 114), charged toner particles are applied to the covering layer (72), which settle according to the potential image as a toner image,

   the toner image is subsequently transferred to the carrier (20) (step 116), and in which, given an edition greater than 1, the development step and the transfer step are carried out in multiple fashion while maintaining the electric charge image present in the interior of the layer system (step 114 to 120).
2. Method according to claim 1, characterized in that the development step (114) and the transfer step (116) are executed in multiple fashion in immediate chronological succession.
3. Method according to one of the preceding claims, characterized in that during the application of the toner particles the charge image in the interior of the layer system (70) remains essentially unaltered.
4. Method according to one of the preceding claims, characterized in that during the application of the toner particles an air gap is present between the covering layer (72) and a toner particle carrier for the application of the toner particles.
5. Method according to one of the preceding claims, characterized in that during the transfer of the toner image the charge image in the interior of the layer system (70) is maintained essentially unaltered.
6. Method according to one of the preceding claims, characterized in that the method is used in a high-performance printer (10).
7. Method according to one of the preceding claims, characterized in that a control unit (44) switches between a first operational state I for printing with an edition of 1 and a further operational state II for printing with an edition greater than 1.
8. Method according to claim 7, characterized in that in the operational state II a printing speed VD is essentially increased in comparison to the printing speed in the operational state I, at least given printing of the print images of a document following a first print image of the same document.
9. Method according to one of the preceding claims, characterized in that the charge image in the interior of the layer system (70) is arranged between the covering layer (72) and the photoconductor layer (74).
10. Method according to one of the preceding claims, characterized in that a liquid toner or a toner powder is used as a toner.
11. Method according to one of the preceding claims, characterized in that the exposure according to the image is carried out shortly before or at the beginning of the impression of the second electric field.
12. Method according to one of the preceding claims, characterized in that the exposure according to the image takes place in line-by-line fashion, preferably by means of an LED row (28) driven according to the image structures or by means of a laser beam modulated according to the image structures.
13. Method according to one of the preceding claims, characterized in that the carrier (20) is made of sheet-type material or that the carrier is an intermediate carrier from which the toner image is transferred onto a sheet-type material, preferably paper, in a further transfer step.
14. Electrophotographic printer for carrying out the method according to one of the claims 1 to 14,

    having a control unit (44) for controlling the printing process,

    a transport means (16) for transporting a carrier (20),

    a photosensitive layer system (70) having an electrode layer (76), an insulating covering layer (72), and having a photoconductor layer (74) arranged between the electrode layer (76) and the covering layer (72),

    a corona discharge means for producing a homogeneous initial state of the layer system (70) by impressing an electric field having a first direction,

    an exposure means for the exposure according to the image of the photoconductor layer (74) according to image structures predetermined by the control unit (44),

    a second electric field with an opposite direction being impressed on the layer system (70),

    a further exposure means for the uniform exposure of the layer system (70),

    a developer means for applying charged toner particles on the surface of the covering layer (72),

    and having a transfer printing station (18) for the transfer of a toner image formed from the toner particles onto the carrier (20), the carrier (20) being transported past the transfer printing station (18) by means of the transport system,

    characterized in that the control unit (44) optionally controls the printing process in a first operational state I with an edition equal to 1 or in a second operational state II with an edition greater than 1,

    that the transport means (16) transports the carrier with a first speed (VD) in the operational state I and with a speed exceeding the first speed (VD) in the operational state II,

    and in that the photosensitive layer system contains a blocking layer between the photoconductor layer (74) and the electrode layer (76), and contains, between the photoconductor layer (74) and the covering layer (72), an intermediate layer (78) with deep traps for charge carriers.

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