EP0967529B1 - Process for printing on both sides of a belt-shaped final image carrier - Google Patents

Description

The invention relates to a method for double-sided printing a ribbon-shaped final image carrier.

In the following, a color separation is understood to be a toner image applied by a single developer station has been. A multicolored toner image is therefore created by the overlay of several color separations.

In one from the European published application Printer known from EP 0 659 569 A1, becomes the first by the first printing unit single color toner image (color separation) fixed before the second also monochrome toner image on the already fixed first Toner image is applied. A perfectly fitting multi-color print is not possible with the known printer because it is not guaranteed can be that the two toner images exactly on the same surface section of the substrate to be printed. As a result, the picture elements of the first toner image and the second toner image are not exact aligned with each other. The result is that it is too unwanted overlays or spaces between picture elements different toner images come up (registration error). Ultimately, high quality color printing is not possible.

Color falsifications occur with graded flat color printing and color fringes. Furthermore, when printing Lines and characters are blurred and / or falsified Image details in the area of lines and characters.

In addition, the printer is according to the aforementioned disclosure to adapt to different printing tasks inflexible. Should e.g. can only be printed with one color, this is the second printer according to the aforementioned publication superfluous. You can also use the printer EP 0 659 569 A1 when printing only from a color palette of four preset colors can be selected.

A multi-color printer is disclosed in DE 41 10 348 A1 explained, the four printing units with each contains a photoconductor. The toner containers of the printing units are detachably connected to the printer. Against is a Loosen the printing units even when used as intended not intended for the printer.

Reference is also made to US-A-5,258,809, which is a process for double-sided printing of a final image carrier, where an intermediate carrier is used.

The object of the invention is to provide a method which a multi-color print with a relatively simple effort Quality enables.

This task is accomplished by a process with the characteristics of Claim 1 solved.

The first shot and the next shot have an example after the Invention essentially the same structure. By the same Structure of the recordings ensures that printer units can be interchanged, and that depending on required print quality an appropriate number of print units be used in the recordings. An adjustment of further developed or newly developed printing units is possible when designing these printing units on it care is taken that they are used in the recordings can.

In one embodiment of the invention, at least one of the printing units releasably inserted into one of the recordings, i.e. this printing unit can easily be included in the respective recording used or removed from this recording. This includes all measures known to the person skilled in the art, such as e.g. Lock or lock the respective printing unit in the recording. This measure ensures that the Printer according to the invention quickly, i.e. in a few simple steps, can be adapted to different printing tasks can be removed or inserted by removing the releasable printing unit is or is exchanged for another printing unit. In addition, an exchange of developer stations in the Printing unit, refilling toner and performing of maintenance work facilitated by a printing unit for the respective activity taken from the assembly and after Completion of the activity is reinstated.

In indirect printing according to the invention is a Intermediate carrier used to transfer the toner images before they are finally transferred to the final image carrier become. The Layering the toner images of different printing units can be done more precisely. This increases the registration accuracy, because photoconductors and intermediate supports are better too synchronize, as photoconductor and final image carrier. In addition, the intermediate carrier consists of a Interaction between photoconductor and intermediate carrier in Selected with regard to abrasion and chemical influence Material. This makes the photoconductor less and more uniform worn out when interacting with a Final image carrier e.g. made of paper. Furthermore concerns an embodiment of the invention a printer, which is suitable for double-sided printing.

In further exemplary embodiments of the invention, a Method with the features of claims 4 and 5 used. In these embodiments, a only exposure device in the printing unit of the photoconductor Exposed imagewise only once per toner image. This ensures that the picture elements of the Color separations of the same printing unit as opposed to one Two or more imagewise exposure no positional deviation to each other (accurate registration). With several Image-wise exposure steps are positional deviations (Registration error) between the toner images e.g. owing to not completely avoidable synchronism errors between Photoconductor and final image carrier or between photoconductor and Intermediate image carrier always available.

The printing unit used in the embodiment can Print more than two or more than three colors in one Toner image can be expanded by adding another total exposure unit for lowering the potential surface elements of the surface not yet covered with color particles Photoconductor is used and then by color particles an additional color can be applied. This The process is repeated for each additional color to be applied. With this measure it is possible to start with the first Toner image Color particles at least three or at least four to arrange different colors side by side on the toner image. A variety of subtractive coloring effects can in addition to the additive color effects within a single printing unit with the help of the second or further Printing units can be realized. By expanding the Printing units and by adding additional printing units can the color printing quality up to full color printing to the Printing task, e.g. Line and character printing, Business graphics or high quality full color printing.

In one embodiment, the photoconductor contains the Invention only an electrode layer carrying a predetermined potential and an approximately parallel photoconductor layer, which results in a simple structure.

In another embodiment of the invention the colors from a number of possible colors of a color palette selected by the pressure control. Every single color The color palette is one of the development stations Assigned printing units, their toner images to the front or back of the final image carrier directly or indirectly be transmitted. This makes it possible that after the Specifications of an operator and / or by an automatic Print order control for the respective purpose suitable colors can be selected without an or several developer stations can be exchanged manually have to. For example, in addition to the basic colors mentioned, optional additional spot colors such as gold or silver printed become.

In a further embodiment of the invention, the Developer stations can be used releasably, i.e. the developer stations can easily in the printing units used or removed from the printing units become. Is by the pressure control instead of at least one of the developer stations optionally an additional one Developer station for applying color particles additional color activated, other mixed colors are activated generated. In this way, the printable color space can be transferred to the Printing task to be adjusted. If a larger number, e.g. 10 to 20 specified colors in developer stations outside of the printer are available in a few simple steps the printing units can be used and with the help of Print control can be selected, so is the printer to a variety of printing tasks quickly and easily customizable. For many applications, such as Business graphics, is a number exceeding the number mentioned Number of different colors is not necessary. Become printing units used in which only toner particles of one polarity can be used, so the developer stations can be interchanged with each other as they are the same Way work.

In the latter two embodiments of recognized that for many color printing applications, such as. Business graphics, the printing of a few, e.g. from two, three or four color separations to sufficiently good ones Color quality leads and that in these printing applications Registration accuracy of the color separations the print quality goal decisively determined. These printing applications are called Business color printing. The desired This will make business color printing a print quality goal achieved that a print image from only a single printing unit with e.g. two, three or four developer stations becomes. By replacing the developer stations with Developer stations with other toner colors can be the printable one Color range quickly and easily to different Print targets are adjusted. In any case arise printed images without registration errors with predominantly additive Color mixing. When replacing the developer stations are only the stations of the same toner polarity are interchangeable.

In the latter two embodiments also based on the knowledge that for full color printing with high color quality subtractive color mixtures of the primary colors yellow, magenta, cyan are required, whereby the mixed colors red, blue, green by overprinting two of the primary colors are created. The overprint the toner images of two primary colors require that these of Developer units of different printing units generated are transferred to an image carrier one after the other become.

In one embodiment of the invention, the fixing process takes place the toner images only after the toner images were overlaid and possibly on both sides of the Carrier material was applied a multi-color print image. This measure makes it possible to ensure the accuracy of fit Layering the toner images increases because of the backing material not due to the fixation of solid paint particles occurring heat is affected. Also eliminated additional fuser stations, so that the printer is easy to set up is and consumes considerably less energy.

The invention can be used with a dry toner that is only solid Contains color particles, or executed with a liquid toner in which e.g. the color particles in a carrier liquid are included.

Figur 1

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

Figur 2

eine Druckeinheitenaufnahme mit einer Druckeinheit, zwei Druckeinheiten bzw. drei Druckeinheiten,

Figur 3

eine zweite Druckeinheitenaufnahme mit einer Druckeinheit, zwei Druckeinheiten bzw. drei Druckeinheiten sowie mit einem Zwischenträger,

Figur 4

die wesentlichen funktionellen Komponenten einer Druckeinheit,

Figur 5

den Potentialverlauf auf dem Fotoleiter bei einem Belichtungsschritt und zwei Tonerpolaritäten,

Figur 6

ein Ausführungsbeispiel eines Druckers nach der Erfindung mit zwei Druckeinheitenaufnahmen,

Figur 7

ein weiteres Ausführungsbeispiel eines Druckers nach der Erfindung mit zwei Druckeinheitenaufnahmen sowie mit Zwischenträger, und

Figur 8

zwei Möglichkeiten des Repetierdrucks in einem weiteren Ausführungsbeispiel eines Druckers nach der Erfindung.

The invention is described below with the aid of examples, FIG. 7 showing the method according to the invention. The other figures serve to explain various components. Show:

Figure 1

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

Figure 2

a printing unit holder with one printing unit, two printing units or three printing units,

Figure 3

a second printing unit holder with one printing unit, two printing units or three printing units and with an intermediate carrier,

Figure 4

the essential functional components of a printing unit,

Figure 5

the potential curve on the photoconductor in one exposure step and two toner polarities,

Figure 6

an embodiment of a printer according to the invention with two printing unit receptacles,

Figure 7

a further embodiment of a printer according to the invention with two printing unit receptacles and with intermediate carrier, and

Figure 8

two possibilities of repetitive printing in a further embodiment of a printer according to the invention.

Figure 1 shows a schematic diagram of an electrophotographic Printer 10 for multi-color printing with essential electrical and mechanical functional units. The printer 10 has one driven by a motor 12 via a shaft 14 Transport device 16 for transporting a carrier material 18 past a printing unit receptacle 20 essentially according to a predetermined printing speed VD. Alternatively to the endless support material 18 can be changed Transport also single sheets, fabric (e.g. T-shirt), Printed on plastic films or sheet metal (e.g. for beverage cans) become.

In the printing unit receptacle 20, depending on the printing requirements regarding the quality of the printed image and the number of colors to be printed in printing unit inserts I to III printing units added in the by an arrow 22 clarified transport direction arranged one behind the other become. The construction of a printing unit is shown below explained with reference to Figure 4. The printing units can be on simple way, e.g. in a few simple steps, into the printing unit slots I to III used or from these be removed.

A printing unit in the printing unit insert I generates an first toner image, which is made using a transfer printing corona device (cf. part a of FIG. 2) onto the carrier material 18 is transmitted. Print units in the print units II or III possibly generate a second or third toner image, which is also using the printing units assigned transfer printing corona devices (see Part b and part c of FIG. 2) transferred to the carrier material 18 becomes. The second toner image is immediately above the first Toner image applied and the third toner image becomes immediate applied over the second toner image so that the Overlay toner images to the printed image.

After the carrier material 18 on the printing unit holder 20 has been transported past, it becomes a fixing station 24 supplied, in which the still smearable toner images with the Backing material 18 with the help of pressure and temperature smudge-proof to be merged. Seen in the transport direction 22 in front of the printing unit receptacle 20 is a first deflection unit 26 arranged, the carrier material 18 of the printing unit receptacle 20 passes. Another deflection unit 28 stacks the printed carrier material 18 on a stack 30. The substrate 18 is at the beginning of the printing process removed from a stack 32 by the first deflection unit 26. Instead of the two stacks 30 and 32 there are also rolls used, on which the carrier material 18 is rolled up.

The printing process is controlled by a print controller 34, the at least one microprocessor 36 and a memory 38 contains. The microprocessor 36 works in the memory 38 stored print program and controls the printing process. In addition, the pressure controller 34 also prepares Memory 38 stored image data and transfers the processed image data via control and data buses 40, 42 or 44 to the printing units in the printing units I, II and III. The motor 12 is connected via a control line 46 controlled by the pressure controller 34 so that depending on the printing units in the printing unit receptacle 20 the carrier material 18 an optimal transport speed has that with a respective optimal printing speed VD essentially matches.

The pressure controller 34 is connected to a via data lines 48 Input / output device 50 connected, among other things, certain Colors can be determined from a color palette for printing.

FIG. 2 shows the printing unit receptacle 20 with a printing unit, two printing units or three printing units. Part A FIG. 2 shows the printing unit receptacle 20 with a Printing unit 60 in the printing unit insert I. The mode of operation the printing unit 60 is continued with the aid of FIG. 4 explained in detail below. Located in the printing unit 60 a photoconductor 62 made of a flexible material exists and like a conveyor belt around two pulleys 64 is guided within the printing unit 60. The printing unit 60 is of a chassis 66 made of a stable material surround. The chassis 66 has an opening 68 at which the Photoconductor 62 passed inside the printing unit 60 becomes. Outside of the printing unit 60 is the carrier material 18 guided past the opening 68. Opposite opening 68 a transfer printing corona device 70 is arranged, with a toner image on the photoconductor 62 onto the Carrier material 18 can be transferred.

The printing unit 60 can be directed into the pressure receptacle 20 an arrow 72 are inserted until they are not in one the snap-in shown. The printing unit 60 can be done by releasing the catch and moving in the direction an arrow 74 removed from the pressure receptacle 20 to e.g. Refill toner of a certain color Changing colors or repairs in the printing unit 60 perform.

The variant of the pressure absorption shown in part a of FIG. 2 20 with a printing unit 60 represents a basic variant, through the one already in the manufacture of the printer 10 later expansion or adaptation to more developed ones Printing units is enabled. With just one Printing unit 60 results in a variety of color combination options. For example, next to black toner particles also toner particles of one or more other colors onto the photoconductor 62 and then onto the carrier material 18 are applied as the first toner image. For one Black and white printing only produces black toner particles applied to the photoconductor 62 by the print controller 34 only one developer station for black toner particles is activated. The printing speed VD is effective regardless of how many developer stations are switched.

The developer stations are individually in the printing unit 60 can be used or removed, which means that the Printing unit 60 certain colors depending on printing requirements can be provided in the printing unit 60. The Print controller 34 switches the printing required for printing Developer stations effective. Are in the printing unit Contain 60 more developer stations than at the same time can be activated, so the variability increased again because the pressure control 34 depending on the print specification other developer stations when printing different toner images can switch effectively. Can e.g. a maximum of three Developer stations in the printing unit 60 activated are and are five developer stations in the printing unit 60 available, so when printing a toner image each three developer stations selected by the print controller 34 of the five existing developer stations at the same time be activated.

With such a printer configuration, e.g. already documentation, manuals or annual reports in of a quality that matches that of such printed products set requirements fully meet.

With the printing unit 60 according to the variant of part a of Figure 2 can be seen using three colors, one below the other have sufficient distances in the color space, e.g. Red, Green and blue through additive color mixing these side by side printed colors a large number of mixed colors to be printed. A register-accurate pressure is achieved.

Part b of FIG. 2 also shows the printing unit receptacle 20 two printing units in the printing unit slots I and II. The printing unit 60 is located in the printing unit insert I. and in the printing unit drawer II, which is like the printing unit drawer I is constructed, there is a printing unit 76, which is constructed essentially like the printing unit 60.

Of course, printing unit 76 can use other toner colors included as the printing unit 60. The printing unit 76 is assigned a transfer printing corona device 78, which a toner image formed on the carrier by the printing unit 76 18 transmits. With the variant according to part b it is possible to in addition to an additive color mix, also a subtractive one Perform color mixing. When using glazing Toners - which do not completely absorb incident light, so that it hits an underlying toner layer - Full color printing can be carried out. However In this case, the print controller 34 must use the standard printer languages such as. Postscript or HP-PCL, given Convert color information so that the printing units 60 and 76 colors are generated that match the desired Colors come close.

Part c of FIG. 2 also shows the printing unit receptacle 20 the two printing units 60 and 76 and another in the printing unit insert III inserted printing unit 80, which is also essentially the same as the printing unit 60 is constructed. The printing unit 80 is also a transfer printing corona device 82 assigned. The variant according to part c enables full color printing without special treatment of the Color information of the printer language through the print control 34. The basic colors, e.g. Yellow, magenta or cyan are like this distributed to the printing units 60, 76 and 80 that in each Printing unit 60, 76 or 80 each one of the above-mentioned primary colors is included. Contains one of the printing units 60, 76 or 80 black toner particles, so the print quality increase again because pure black is not in practice sufficiently composed from the basic colors mentioned can be. Additional toner particles certain Spot colors such as Silver or gold can still be on free developer stations in the three printing units 60, 76 or 80 can be distributed.

Figure 3 shows in parts a, b and c, a second printing unit holder 100 with printing unit inserts I ', II' and III 'which, in contrast to printing unit inserts I, II and III printing units 60 '; 60 ', 76' or 60 ', 76', 80 'included. The printing units 60 ', 76' and 80 'make toner images generated, not on the carrier material 18, but are transferred to an intermediate carrier material 102, so that there is indirect pressure. The intermediate carrier material 102 consists of a flexible material that is like a endless belt around two pulleys 104 is guided. The Print modules 60 ', 76' and 80 'are essentially like that Print modules 60, 76 and 80 built.

Part a of FIG. 3 also shows the printing unit receptacle 100 a printing unit 60 'in the printing unit slot I, the one Toner image generated with a transfer printing corona device 106 is transferred to the intermediate carrier 102. The intermediate carrier material 102 is transported in the direction of arrow 108. If the toner image reaches a transfer printing point 110, then the toner image at transfer location 110 on the carrier material 18 transferred, which also transports past the transfer printing station 110 becomes. Regarding the color combinations to be printed what has been said with reference to part a of FIG. 2 applies.

Part b of FIG. 3 also shows the printing unit receptacle 100 two printing units 60 'and 76' in the printing units I 'and II'. The intermediate carrier material 102 is related to selected its carrier properties so that the toner images with high accuracy on the intermediate carrier material 102 can be applied and the positional deviations of the Image elements of different toner images from target positions are very low. By using the intermediate carrier material the quality of multi-color printing increases. The printing unit 76 'is associated with a corona device 112 which a by the printing unit 76 'produces a toner image on the intermediate carrier transmits and that generated in the printing unit 60 ' Toner image overlaid. Regarding the colors to be printed applies what has been said with regard to part b of FIG. 2.

Part c of FIG. 3 also shows the printing unit holder 100 three printing units 60 ', 76' and 80 'in the printing units I ', II' and III '. The printing unit 80 'is one Transfer printing corona device 114 for transmitting the through the Printing unit: 80 'generated toner image on the intermediate material 102 assigned. The following applies with regard to the possible printing inks what has been said with reference to part c of FIG. 2.

Figure 4 shows the essential functional components of the Printing unit 60. The photoconductor 62 consists of a zero potential leading electrode layer 120 and one approximately parallel therefor arranged photoconductor layer 122, which with the Electrode layer 120 over a large area in electrical and mechanical Contact is there. The photoconductor 62 is by the Deflection rollers 64 moved in the direction of an arrow 124. there becomes a surface strip lying transversely to the transport direction of the photoconductor 62 in succession on a charging device 126, a character generator 128, a developer station 130 for applying positively charged toner particles, a developer station 132 for applying negatively charged toner particles, a charger 134, a total exposure unit 136, a developer station 138 for applying negatively charged toner particles, a transfer station 140, the Corona device 70, an eraser 142 and at one Cleaning device 144 passed.

The charging device 126 contains a transverse to the transport direction 124 arranged corona device, each one surface strips of the transverse to the direction of transport 124 Photoconductor 62, which is in the immediate vicinity of the charging device 126 is so charged that an initial potential VA of approximately -1200 V on the surface of the photoconductor layer arises in the area of the area strip (see FIG 5, step S1).

The character generator 128 contains one transverse to the direction of transport arranged row of light emitting diodes, each one Area of the photoconductor lying transversely to the transport direction 124 62 illuminate. The character generator 128 is replaced by the Pressure controller 34 controlled so that each image signals Picture elements of a line of the printed image simultaneously in Light signals from the LEDs are implemented. By the Exposing the photoconductor 62 increases the potential exposed surface elements of the photoconductor 62, since the Conducts photoconductor 62 better in the exposed areas, whereby charge carriers from the photoconductor layer 122 to Electrode layer 120 in the area of the exposed surface elements can drain off. Surface elements on which black Toner particles to be applied are not exposed, Area elements on which no toner particles are applied are to be exposed with a first light energy; Surface elements on which red toner particles are applied compared to the first light energy exposed to higher second light energy and surface elements, applied to the later blue toner particles should be compared to the second light energy exposed to higher third light energy. The exposure with different light energies is achieved that the light emitting diodes have essentially the same luminosity emit light over different periods of time. With increasing exposure time, i.e. with increasing light energy the potential increases on the respective surface elements (see FIG. 5, step S2).

The developer station 130 brings positively charged color particles of the color black K using an auxiliary electrode 160 with a potential VBIAS3 on surface elements that were not exposed. The exact mechanism of action will explained below with reference to FIG. 5 (step S3).

Developer station 132 brings negatively charged toner particles the color blue B with the help of an auxiliary electrode 162 a potential VBIAS4 on surface elements that match the third light energy were exposed. The exact mode of action developer station 132 is also below explained with reference to Figure 5 (step S4).

By applying the negatively charged blue toner particles the potential on the surface elements with the third light energy were exposed, lowered again. Around further reduce the potential on these surface elements, the photoconductor 62 is guided past the charging device 134. With the loading device arranged transversely to the transport direction 134 becomes the one partially covered with toner particles Photoconductor 62 in the surface elements covered with toner particles charged to a potential VB5 that is slightly larger than the potential on the surface elements, which with the second light energy were exposed (see FIG. 5, step S5).

The strip of photoconductor 62 under consideration then turns on passed the total exposure unit 136. The total exposure unit 136 contains a laser diode that crosses into a glass fiber array arranged for the transport direction of the photoconductor 62 Light energy shines in. The glass fiber array is like this trained that essentially over its entire length same light energy is emitted. The light of the total exposure unit 136 can not by already applied black or blue toner particles emit because of the Toner particles is absorbed. Strikes the light of the total exposure unit 136, however, on surface elements of the photoconductor 62, which are not yet covered with toner particles, so the potential on these surface elements is increased (cf. Figure 5, step S6).

Developer station 138 brings negatively charged toner particles the color red to the one with the second light energy exposed surface elements of the photoconductor 62. there an auxiliary electrode 164 with the potential VBIAS7 is used. The exact mode of action of applying the red Toner particles are also shown in FIG. 5 below explained (step S7).

The positively charged black are in the transfer station 140 Reloaded toner particles so that all on the photoconductor 62 applied toner particles are negatively charged (cf. Figure 5, step S8). This measure ensures that transferring the toner image from the photoconductor 62 to the Carrier material 18 with the help of the corona device 70 safely is carried out.

After the transfer of the toner image, the Color particles essentially free photoconductor 62 in one step on the extinguishing device 142, not shown passed by. The eraser 142 includes a corona device 146 and an exposure unit 148 through which Any remaining charges on the photoconductor are removed.

Toner particles left after the toner image is transferred remain on the photoconductor 62 are in the cleaning device 144 with the help of a brush 150 from the photoconductor 62 removed. After being transported past the cleaning facility 144 is the considered strip of the Photoconductor 62 again in a clean initial state and has roughly the same potential at all points.

The chassis 66 has on its backing facing away from the carrier material 18 Side one. Handle 152 with which the printing unit 60 is convenient removed from the printing unit slot I or into the printing unit slot I can be used.

Figure 5 shows the potential on the surface of the observed Strip of photoconductor 62 in an exposure step and two toner polarities. On the abscissa axis is the Time removed in nine consecutive time steps S1 to S9 is divided. That is on the ordinate axis Potential on the surface of the photoconductor 62 with respect to the Potential is shown on the electrode layer 120.

In step S1, the potential on the surface of the Photoconductor 62 by acting on the field of the charging device 126 lowered to the initial potential VA, which like already mentioned has the value of -1200 V.

Step S2 shows the potential profile on the surface of the photoconductor 62 during imagewise exposure using the Character generator 128. Area elements that later with black toner particles should not be covered exposed. The potential VA increases on these surface elements in the course of step S2 only slightly by a Self-discharge of the photoconductor 62 which cannot be suppressed to a value VK2. The potential on the surface elements, that are exposed with the first light energy rises a value VW2 of approximately -800 V. The potential on the surface elements, which exposes with the second light energy were increased to a potential value in the course of step S2 VR2 of around -400 V. The potential on the surface elements, that were exposed with the third light energy increases in step S2 to a potential value VB2 about -100 V. The light energies during exposure are dimensioned so that taking into account the nonlinear photoelectric Properties of the photoconductor 62, the potentials VK2, VW2, VR2 and VB2 are approximately 400 V apart.

In step S3, the black toner particles are replaced by the Developer station 130 applied. The auxiliary electrode 160 in the immediate vicinity of the photoconductor 62 has the auxiliary potential VBIAS3 of about -900 V. Located on the auxiliary electrode 160 the positively charged black toner particles. Since that Potential VBIAS3 lower than the potentials VW2, VR2 and VB2 is, these potentials are related to the potential VBIAS3 positive. The positively charged black toner particles can however, only be applied to a surface that is related to a of the potential VBIAS3 has lower potential. The only applies to surface elements that are not in step S2 were exposed and at the beginning of step S3 the potential VK2 have. As a result, these are the surface elements black toner particles applied. By applying the positively charged toner particles increase the potential the respective surface elements covered with toner particles to a potential value VK3. Through the mentioned not too avoiding self-discharge of the photoconductor 62 increase the potentials VW2, VR2 or VB2 slightly to the potential values VW3, VR3 or VB3.

In step S4, the blue toner particles are replaced by the Developer station 132 applied. The auxiliary electrode 162 in the immediate vicinity of the photoconductor 62 has the auxiliary potential VBIAS4 of about -390V. Located on the auxiliary electrode 162 negatively charged blue toner particles. Because the potential VBIAS4 is higher than the potentials VK3, VW3 and VR3 these potentials with respect to the potential VBIAS4 negative. The however, negatively charged blue toner particles can only show up an area can be applied which is a with respect to the potential VBIAS4 has higher potential. This only applies to surface elements to the third light energy in step S2 were exposed and at the beginning of step S4 Have potential VB3. As a result, these surface elements applied the blue toner particles. By applying of the negatively charged blue toner particles the potential on the respective with blue toner particles covered surface elements to a potential value VB4. The self-discharge of the photoconductor 62 increases the Potentials VK3, VW3 or VR3 slightly on the potential values VK4, VW4 or VR4.

In step S5, the potential VB4 on the surface of the surface elements covered with blue toner particles with the help charger 134 is reduced to about -390 V. Through the Self-discharge of the photoconductor 62 increases the potential VK4, VW4 or VR4 in step S5 to the potentials VK5, VW5 or VR5.

In step S6 by the total exposure unit 136 emitted light, the potentials VW5 and VR5 the surface elements not covered with toner particles in each case increased by about 400 V to the potentials VW6 or VR6. The potential on surface elements, which in step S2 with the second light energy have been exposed, is through the further Exposure in step S6 to the highest potential of all Area elements in step S6. The potentials VK5 and VB5 increase slightly due to the self-discharge of the Photoconductor 62 to the potentials VK6 and VB6. Between Potentials VR6 and VB6 have a difference of approximately 400 V, so that in the following step S7 similar to step S4 toner particles are applied to the surface elements can, which is exposed in step S2 with the second light energy were.

In step S7, the red toner particles are passed through the developer station 138 applied. The auxiliary electrode 164 in the immediate vicinity of the photoconductor 62 has the auxiliary potential VBIAS7 of about -370 V. Located on the auxiliary electrode 164 the negatively charged red toner particles. Analog to the electrical conditions described in step S4 the negative toner particles are applied to the surface elements, which is exposed in step S2 with the second light energy were. The potentials VK6, VW6 and VB6 increase due to the self-discharge of the photoconductor 62 to the potential values VK7, VW7 or VB7.

In step S8, the strip of the photoconductor under consideration 62 passed the transfer station 140. In the transfer station 140 includes a corona device that a Has a saturation potential value of about -1200 V. When transporting past the potentials on all surface elements significantly reduced, the polarity of the black Toner particles changes.

In step S9, the toner particles are replaced with toner particles covered surface elements essentially while maintaining their position to each other transferred to the carrier material 18. The potential on the surface elements of the increases Photoconductor 62 to about -400 V. The remaining charge on the photoconductor 62 is by the eraser 142 removed so that the photoconductor 62 on its surface a potential value after passing the quenching device 142 of about 0 V.

The method according to the invention explained with reference to FIG. 5 can be modified so that all Polarities are exchanged or that only toner particles polarity. In the latter case there is no need the step S3. Depending on the required number of colors for Printing of the printed image is different in step S2 Light energy radiated onto the respective surface elements. By repeating steps S5, S6 and S7 n times step S8, toner particles of n different additional colors applied to assigned surface elements become. Here n is an integer, e.g. one two, three etc.

Figure 6 shows an embodiment of a printer without an intermediate carrier with two printing unit receptacles 180 and 182, the are each constructed as the printing unit receptacle 20. Due to the arrangement shown in Figure 6, a bilateral Printing of the carrier material 18 take place. A printer with two printing unit receptacles 180, 182 according to FIG. 6 to a wide range of customer requirements and print qualities be adjusted. For example, with three delivered printing units all three printing units in the printing unit holder 180 or inserted in the printing unit holder 182 become. Alternatively, the three printing units for the double-sided printing also on the two print receptacles 180 and 182 can be distributed. But double-sided printing is also possible without the print unit holder 182 if the carrier material 18 turned over after a first print and again is guided past the printing unit receptacle 180.

FIG. 7 shows a further exemplary embodiment for the method according to the invention with two printing unit receptacles 190 and 192. Printing unit receptacles 190 and 192 are respectively similar to the printing unit receptacle 20. The difference for Figure 6 is that in Figure 7, toner images from the printing units not to the carrier material 18 directly, but via intermediate carrier materials 200 or 202 are transferred to the carrier material 18. With the in figure 7 variant is therefore a double-sided print possible without the carrier material 18 with the photoconductors the printing units come into contact. A wear of the Photoconductor through the carrier material 18 is thus avoided.

Figure 8 shows two possibilities of the so-called "Repeat printing". Instead of two or three printing units, that work in parallel with one print unit toner images in two or three printing steps generated that successively on the carrier material 18th or printed onto an intermediate carrier material 210.

Part a of Figure 8 shows the repeating pressure at which the Toner images directly superimposed on the carrier material 18 become. With the help of a printing unit 212, which is in a Printing unit receptacle 214 is located in a first Printing step a first toner image on the in the printing unit 212 existing photoconductor applied. With the help of a Corona device 216 is the first toner image on the in Transfer carrier material 18 moved in the direction of an arrow 218. The printing unit 212 is essentially like the printing unit 60 built. When printing the first toner image become one or more developer stations by the pressure controller 34 activated, the color particles of the desired Apply colors to the photoconductor.

After the transfer of the first toner image onto the carrier material 18 this is done by the transport device 16 in Direction of an arrow 220 against the transport direction 218 transported back when transferring the toner images. In Further printing steps become more of the first toner image Toner images superimposed, with the print controller 34 each other developer stations in printing unit 212 activated.

Part b of FIG. 8 shows the repetitive pressure on the intermediate carrier material 210 with a printing unit 212 '. A return transport of the carrier material 18 can be omitted and is by Stopping the carrier material 18 replaced. The intermediate carrier material is guided and runs by two deflection rollers 222 in the manner of a conveyor belt. With every circulation of the Intermediate substrate 210 may have a toner image on it for the location provided for the printed image can be applied. are all toner images applied, the transfer takes place overlaid toner images using a corona device 224 onto the carrier material 18. For this purpose, the carrier material 18 synchronously for the duration of an intermediate carrier material circulation moved to the intermediate carrier material.

The printing unit 212 is located in a printing unit holder 214 and the printing unit 212 'is in one Pressure unit receptacle 214 '. Are additional printing units in the printing unit receptacle 214 or 214 'inserted, see above is by the pressure control 34 from repeating pressure to parallel Pressure switched.

By using another pressure unit holder a double-sided repeating print is also provided.

Claims (8)

1. Method for printing on both sides of a final image carrier (18), in the form of a web, having the following features:

   stopping of the final image carrier (18),

   production of toner images on a photoconductor of a printing unit (212') associated with the front face of the final image carrier (18),

   production of toner images on a photoconductor of a printing unit associated with the rear face of the final image carrier (18),

   transfer of the toner images on the front-face printing unit (212') successively in time to a point provided for a printed image, on an intermediate carrier (200) which is associated with the front face, in order to produce a superimposed, front-face toner image,

   transfer of the toner images on the rear-face printing unit successively in time to a point, which is provided for a printed image, on an intermediate carrier (202) associated with the rear face, in order to produce a superimposed, rear-face toner image,

   simultaneous transfer of the front-face toner image and of the rear-face toner image to the final image carrier (18), with the final image carrier (18) being moved in synchronism with the intermediate carriers.
2. Method according to Claim 1, characterized by joint fixing of the front-face and rear-face toner image in a fixing station which is downstream in the transport direction of the final image carrier (18).
3. Method according to Claim 1 or 2, characterized in that one assembly is in each case used for holding the respective printing units in a respective holder, with the holders essentially having the same design, and in that the printing units can be detachably inserted into the respective assembly with few actions.
4. Method according to one of the preceding claims, characterized in that the following items are contained in at least one of the printing units:

   a charging apparatus (126), which is arranged close to a photoconductor (62), for producing an electrical charge, of at least one part of the photoconductor (62),

   an exposure device (128) for image exposure of the photoconductor (62),

   a first developer station (130) for applying the colour particles of the first colour (K) with a first polarity to a first area element of the photoconductor (62),

   a second developer station (132) for applying the colour particles of the second colour (B) with a second polarity to a second area element of the photoconductor (62),

   at least one total exposure unit (136) for uniform exposure of the photoconductor (62),

   and at least one further developer station (138) for applying the colour particles of a further colour (R) with the second polarity to an associated further area element of the photoconductor (62).
5. Method according to one of the preceding Claims 1 to 3, characterized in that the following items are contained in at least one of the printing units (60, 212):

   a charging apparatus (126), which is arranged close to a photoconductor (62), for producing an electrical charge, of at least one part of the photoconductor (62),

   an exposure device (128) for image exposure of the photoconductor layer,

   a first developer station for applying the colour particles of the first colour with a selected polarity to an associated first area element of the photoconductor (62),

   at least one total exposure unit (136) for uniform exposure of the photoconductor (62),

   and at least one further developer station for applying the colour particles of a further colour with the selected polarity to a further area element of the photoconductor (62).
6. Method according to Claim 4 or 5, characterized in that the photoconductor (62) contains an electrode layer (120) which is at a predetermined potential, and a photoconductor layer (122) arranged approximately parallel to it.
7. Method according to one of the preceding claims, characterized in that the colours are selected by a printing controller (34) from a colour range with a large number of predetermined colours, with each individual colour in the colour range being associated with one developer station from one of the printing units,

   in that the printing controller (34) switches developer stations to apply the selected colours effectively,

   and in that at least one additional developer station is in a rest state during printing, in which state no colour particles are applied by means of the additional developer station.
8. Method according to one of the preceding claims, characterized in that at least one developer station (130, 132, 138) is inserted detachably into the printing units.

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