EP1438639B1 - Method and device for cleaning support elements in printers or copiers by means of magnetic fields - Google Patents

Description

The invention relates to an electrophotographic printing or copying device, in which a Toneranlagerungseinheit attached electrically charged toner particles on the surface of a first carrier element. At least part of the deposited toner particles is transferred from the first carrier element to a second carrier element. A cleaning unit removes residual toner particles from the first support member. A further aspect of the invention relates to an apparatus for cleaning a roll of toner particles in an electrophotographic printer or copier on the surface of which a particle mixture of electrically charged toner particles and ferromagnetic carrier particles is conveyed. Furthermore, methods for operating an electrophotographic printer or copier and for cleaning a roller in an electrophotographic printer or copier are given.

Electrophotographic printers or copiers use image development techniques that include electrostatic charge images on surfaces, e.g. Charge images on a photoconductor, develop over an air gap or in direct contact with triboelectrically charged toner, which is located on the surface of an applicator element. Such an applicator element may e.g. be designed as a roller or as an endless belt. The toner particles are triboelectrically charged prior to transfer to the applicator element. In known printers or copiers, a two-component mixture of toner particles and ferromagnetic carrier particles is produced. The bicomponent mixture is mixed in the printer or copier so that the toner particles rub against the carrier particles, whereby they are charged triboelectrically.

It is a common art to color surfaces with toner particles that are in a two component blend are included. A magnet roll arrangement transports the two-component mixture into an area with a small distance between the magnet roller arrangement and the surface to be inked, wherein a magnetic field of a magnetic element acts on the two-component mixture. In this area, a magnetic brush is formed containing carrier particles and toner particles, only the latter being transferred to the surface to be inked. The carrier particles are retained due to the magnetic field.

The transfer of the toner particles from the magnetic roller assembly to the applicator element occurs in other known printers or copiers via an air gap between the magnetic roller and the applicator element, which is not completely bridged by the accumulation of the two-component mixture. The transfer of the toner particles onto the applicator element surface can be assisted by a transfer auxiliary voltage, ie by a potential difference between magnet roller and applicator element. During an image development process, the toner is transferred in accordance with a charge distribution of a charge latent image from the applicator element surface via an air gap or by direct contact with the charge image bearing surface, eg, the surface of a photoconductor drum or photoconductor belt. According to the latent charge image, toner particles remain on the surface of the applicator element in the form of an image negative of the developed charge image. Before re-applying a closed homogeneous toner layer to the applicator element, the toner particles remaining on the applicator element must be removed from the applicator element. The unprinted area of a printed page with text averages about 95% of the total area. Thus, when printing such an average print page, about 95% of the toner particle deposited on the applicator element must be removed therefrom. Depending on the type of printed image to be inked From 0 to 100% of the toner particle quantity must be removed again from the applicator element.

In printing systems with high printing speed, the cleaning of the applicator element by means of known cleaning devices is insufficient. After several times depositing toner particles on the applicator element and after incomplete cleaning of the toner particles remaining on the applicator element after the staining of the latent charge image, these form an unevenly thick layer on the applicator element. The varying thickness of the inhomogeneous toner layer can cause print image disturbances, e.g. the so-called memory effect. When memory effect is in the inked areas of the printed image, the previous print image visible due to the inhomogeneous toner layer on the applicator, which is transmitted as a print image on a medium to be crushed. For a high quality print, therefore, prior to re-depositing toner on the applicator element, complete removal of the remaining toner particles is required.

In the case of a photoconductive drum, when the latent charge image is developed, i. colored in accordance with the charge distribution with toner particles, and when the toner image is transferred to a carrier material, some remnants of the toner image remain on the surface of the photoconductor drum. These toner residues must be removed from the photoconductor drum prior to re-application of a latent charge image.

Also, in printing or copying machines, it is necessary to remove toner particles from photoconductor belts, transfer belts and magnetic rollers so as not to impair the electrophotographic process and to ensure high print quality.

In known printing or copying machines, cleaning, i. removal of the toner remnants, photoconductor drums with the aid of plastic brushes which are in direct contact with the surface of the photoconductor drum. In this case, wear occurs both on the plastic brushes themselves and on the photoconductive drum. Furthermore, the toner particles to be removed are subjected to a considerable mechanical stress during the cleaning process with such brushes, thereby adversely changing the physical properties of the toner particles.

From the publication US 4,383,497 An arrangement for cleaning an applicator element is known in which the toner particles are mechanically stripped off from the applicator element with the aid of a doctor blade which is in direct contact with the surface of the applicator element. The toner particles are mechanically stressed, ie high mechanical pressure and shear forces are exerted on the toner particles. The mechanical stress on the toner particles leads to a negative change in the physical properties or even a loss of function of the toner material, which can occur when re-use of these toner particles for developing subsequent printed images print defects. Such blades are made of plastic, metal or ceramic-coated metal, for example. The direct contact between the blade and applicator causes a high level of wear, especially with the blade. The wear is different in areas of the blade, which results in a worn blade uneven cleaning of the applicator. For high-performance printing systems, this blade must be replaced frequently. Due to the mechanical friction between blade and applicator also the surface of the applicator element can be damaged. Such damage may affect the overall function of the applicator element.

From the document DE 41 05 261 A1 For example, an image forming device having two identical image forming units is known. A first image forming unit is disposed in a developing position and operates as a developing unit. The second image forming unit is disposed in a cleaning position and operates as a cleaning unit.
The image forming units are alternatively and repeatedly brought into the development position and the cleaning position. As a result, the particle mixture contained in an image-forming device is used for application of toner material and at another time for cleaning.

From the document US 4,141,165 An electrostatic copier is known in which magnetic brushes are used for coloring a charge image of a photoconductor drum and removing residual toner from the photoconductor drum. For application and cleaning a roller is used, which contains stationary magnets inside. With the help of magnets, the magnetic brush is generated. With the aid of doctor blades, the edge of which scrapes on the surface of the roll, a mixture of particles is removed from the surface of the roll.

From the document DE 32 46 940 A1 a magnetic brush cleaning device for a copying machine is known. By means of a magnetic brush device it is achieved that a mixture of a magnetic carrier and the toner glides over the surface of a photoconductor and decreases on the photoconductor surface adhering toner residues. The cleaned toner is supplied by means of a toner recovery device containing a plurality of rollers. Toner material adhering to the rolls of the toner recovery device is removed therefrom by means of doctor blades scraping on these rolls.

From the document DE 32 41 819 C2 a magnetic brush cleaning device is known in which a cleaning roller is provided, provided in the interior of stationary magnets are that produce magnetic brushes. The magnetic brush touches the surface of a photoconductor drum and cleans residual toner therefrom, which remains on the photoconductor drum after the toner image has been rewritten. The cleaned toner material is transferred from the magnetic roller to a second roller. By means of a scraper, which rests against the surface of the second roller, the toner material is scraped off the surface of the second roller.

From the document JP 2000267397 A Magnetic rollers are known, which are used for coloring a charge image of a photoconductor drum and for cleaning residual toner from the photoconductor drum. Two abutting magnetic elements, which are arranged opposite to the surface of the photoconductor drum, the contact of the magnetic brush is prevented with the surface of the photoconductor drum. The magnets of the magnetic roller rotate with the magnetic roller.

From the document DE 32 49 767 For example, a cleaning apparatus for removing developer particles from an imaging surface of a movable photoconductive belt in an electrophotographic copying machine is known. With the help of this cleaning device and the back of the tape is cleaned of any toner residues and dust deposits. With the aid of a scraper, the belt is pressed against a cleaning roller. The scraper is pressed by means of a plate of a magnetizable material arranged in the cleaning roller magnets against the cleaning roller.

From the document DE 39 40 079 C2 For example, a method of removing a thin layer from a photoconductive movable member of an image forming apparatus is known. In this case, toner material located on a roll surface is removed by means of a scraper scraping the toner material from the roll surface.

The object of the invention is to provide electrophotographic printing or copying devices and methods for operating electrophotographic printing or copying devices, in which a high print quality is achieved, wherein a low stress of the particle mixture of ferromagnetic carrier particles and electrically charged toner particles takes place. Furthermore, devices and methods for cleaning a roller in an electrophotographic printer or copier are provided, which ensure a maintenance-free operation of the devices for cleaning.

From the document JP-A-63281186 An arrangement is known with a magnetic roller for transporting a particle mixture of toner particles and carrier particles on their surface. Inside the roller, two magnetic elements are arranged side by side, the adjacent poles facing the particle mixture are similar. The magnetic field generated by the magnetic elements, the mixture of particles in the region of these magnetic elements is lifted from the roll surface and the toner particles mixed with the carrier particles, so that the toner concentration is distributed uniformly in the radial direction to the magnetic roller. By lifting a cleaning effect of the roll surface is achieved. Furthermore, a doctor for limiting the applied layer height is known.

From the document JP-A-58055960 An arrangement is known with a toner adsorption unit for depositing toner material on a photoconductor drum and with a cleaning unit for cleaning the photoconductor drum. A particle mixture of carrier particles and toner particles is used to deposit the toner material on the photoconductor drum and is then transported to the cleaning unit and used for cleaning.

This object is achieved for an electrophotographic printing or copying device having the features of patent claim 1 solved. Advantageous developments of the invention are specified in the dependent claims.

With the aid of a device according to the invention, toner particles deposited on the surface of a roll of an electrophotographic printer or copier are reliably removed with little effort. In the interior of the roller two magnetic elements are fixedly arranged, one pole of which is directed towards the roller surface so that they act approximately in the same direction The magnetic elements are arranged at a distance from one another in the direction of rotation of the roller such that the carrier particles The cleaning device reliably removes the toner particles adhering to its surface and does not require any additional space in the electrophotographic printer or copier, since the magnetic elements are fixed to the magnetic elements and form raised aggregates, so-called magnetic brushes, with the carrier particles rubbing on their surface as the roller rotates are arranged inside the roller.

The device works wear-free and causes an additional triboelectric charging of the toner. To operate the device auxiliary power is not required. Furthermore, the device is for different sub-mixtures made of toner particles and carrier particles. The cleaning is also reliable when changing the physical properties of a particle mixture used in a printing or copying device. With increasing useful life, such changes occur due to mechanical stress on the toner particles. The adjacent poles of the two magnetic elements facing the particle mixture are similar, ie the magnetic fields of these poles act approximately in the same direction, so that a small field strength is present between the magnetic elements on the roll surface. The field vectors of the magnetic fields have in this area on the roll surface an opposite sense of direction, so that there is no resulting field strength at approximately similar magnetic elements. At the magnetic elements, the mixture of particles remains on the surface of the roll and forms raised accumulations in which, during a rotational movement of the roll, a rotating cylindrical movement is generated within the particle mixture. During this movement, the particle mixture rubs off the toner particles adhering to the roll surface.

In an advantageous embodiment of the device, the magnetic elements are arranged such that at least a portion of the carrier particles is dissolved in a portion between the two magnetic elements by the magnetic fields of the magnetic elements acting on the carrier particles forces from the roll surface, wherein the particle mixture in the region of the magnetic elements in a Rotary movement of the roller is particularly well swirled. This ensures that toner particles, which are located on the roll surface, are released from this and completely abraded, wherein the mechanical stress of the particle mixture is low. The physical properties of the particle mixture remain the same. The toner particles electrostatically deposited on the outer peripheral surface of the roller can be particularly effectively removed in this embodiment. As the roller rotates, carrier particles are introduced into the areas on the roller surface nachgefördert, whereby also a part of the remaining in these areas particle mixture is transported. With this particle mixture and the abraded toner particles are removed, so that an exchange of the persisting particle mixture takes place.

It is also advantageous to align the axes of the poles of the magnetic elements radially with respect to the axis of rotation, since thereby a maximum field effect of the inside of the roller static, i. stationary, arranged magnetic elements is achieved on the carrier particles.

In another embodiment of the invention, in addition to the magnetic elements, a doctor blade is arranged at a predetermined distance from the roll surface. It is advantageous to arrange the doctor in the direction of rotation of the roller after the first and second magnetic element in the vicinity of the second magnetic element. It is also advantageous to arrange the doctor blade in the lower half of the roll. The swirling of the particle mixture for abrading the toner particles from the surface of the roller and the separation of the particle mixture from the roller surface by the placement of the doctor blade effectively and with little design effort.

In another advantageous embodiment, the outer peripheral surface of the roll has a roughness in the range of 1 to 5000 microns. The roughness of the roll surface can be inexpensively produced by high quality flame spraying to produce a layer containing aluminum, chromium, nickel, copper, conductive plastic and / or a plastic having a conductive layer. As a result, the surface of the roller can be subjected to a set potential in order, for example, to support the transfer of toner particles onto this roller or from this roller. Also, rollers and surfaces made of these materials can be produced easily and inexpensively.

To be particularly advantageous, it has been found to arrange the adjacent edges of the two magnetic elements at a distance in the range of 0.01 to 10mm, since at this distance a particularly thorough cleaning. However, this distance range depends on the field strength of the magnetic elements used, on the circumferential speed of the roller, on the particle mixture used, especially on the carrier particles used, and on the distance between the magnetic element and the outer peripheral surface of the roller. The cleaning device can be easily adapted to the operating conditions of the printer or copier by varying the distance between the magnetic elements and / or by using magnetic elements with other field strengths.

The roller used in this cleaning device may contain other magnetic elements for generating raised on the roller surface particle accumulations of so-called magnetic brushes. The magnetic elements are permanent magnets in further advantageous embodiments. This is particularly advantageous since, in contrast to electromagnets, no auxiliary energy is required for permanent magnets.

By a method according to the invention for cleaning a roller in an electrophotographic printer or copier, a thorough and wear-free cleaning of the roller takes place. For cleaning, no additional accessories are required, whereby no additional space for the cleaning device is required for cleaning. The toner particles are also charged triboelectrically by the cleaning process. The roller is cleaned almost wear-free.

A second aspect of the invention relates to an electrophotographic printing or copying device and to a method according to the invention for operating an electrophotographic printing or copying device toned with toner, said carrier element is subsequently cleaned of toner residues by means of a roller assembly of a cleaning unit. The toner residues are removed from this roller assembly by means of a doctor-magnet element arrangement. This prevents toner particles from being permanently attached to the surface of the roller assembly and forming a crusted layer which hinders electrostatic effects and thus interferes with the electrophotographic process. The electrophotographic printing or copying operation can be carried out in the apparatus according to the invention and in the method according to the invention in high quality and at high speed. Such an electrophotographic printing or copying device can be produced inexpensively by the simple compact design.

According to a third aspect of the invention, there is provided an apparatus for cleaning a roller in an electrophotographic printer or copier. This device has a doctor blade which is arranged at a distance from the surface of a roll, on the roll surface of which a particle mixture of ferromagnetic carrier particles and electrically charged toner particles is conveyed. A magnetic element is static in the area of the doctor blade, ie stationary with respect to the doctor blade, arranged in the interior of the roller such that the carrier particles in the region in the direction of rotation of the roller seen in front of the doctor form a raised on the roll surface accumulation, ie a magnetic brush. The carrier particles of the collection rub on a rotating movement of the roller on the surface thereof. By this device, it is easily possible to achieve a high degree of cleaning of the roller to be cleaned. Such a device is simple and inexpensive to manufacture. The wear of the cleaning elements and the roller has been significantly reduced compared to known roller cleaning devices.

In another embodiment of the invention, the squeegee strips off at least part of the sub-mixture located on the roller. The magnetic field of the magnetic element keeps parts of the particle mixture stiffened by the doctor blade in the area in front of the doctor blade. Due to the rotational movement of the roller and the fixedly positioned doctor blade, the particle mixture is vortexed in the area in front of the doctor blade. This ensures that even toner particles that are located directly on the roll surface, are mechanically rubbed off the surface of the roller by the turbulence of the particle mixture in the blade, especially by the turbulence of the carrier particles. The abraded toner particles are taken up by the particle mixture in the area in front of the doctor blade. As a result, toner particles, which are located directly on the surface of the roller, are released therefrom and can thus be eliminated. The negative changing of physical properties of the roller by a crust-like layer of toner particles on the roller surface is thus easily and inexpensively prevented. A layer of toner particles on the roll surface has an electrical insulation effect and limits the effect of a potential difference between the roll surface and other elements, such as the surface of the roll. other rollers and ribbons of the printer or copier, or prevents this effect. Such potential differences are e.g. used to transfer electrically charged toner particles in printers or copiers.

It is also advantageous to align the axis of the poles of the magnetic element radially to the axis of rotation of the roller assembly. As a result, areas of high magnetic field strength are formed on the roll surface, in which areas of toner particles and carrier particles, so-called magnetic brushes, form on the surface of the roll. It is also advantageous to arrange a plurality of magnetic elements in the interior of the roller stationary. The axes of the poles are each radially aligned, wherein the poles of adjacent magnetic elements are aligned approximately opposite. This will achieve in that a strong magnetic field is formed between adjacent magnetic elements.

In another embodiment, when the squeegee is placed in the lower half of the roll, the particle mixture on the squeegee can simply fall down. The removal of the particle mixture on the doctor blade is thus easily possible. The falling particle mixture may e.g. collected in a container arranged under the roller or fall directly into a so-called mixed sump of the printer or copier, in which the two-component mixture is, and then fed back to the electrophotographic printing or copying process.

In another embodiment, the outer peripheral surface of the roll has a roughness in the range 1 to 5000 microns. This ensures that the particle mixture to be transported on the roll surface has sufficient adhesion for transport and that the particle mixture can be removed from the surface again by simple means. Additionally or alternatively, the roller surface may be profiled to reduce slippage of the particulate mixture on the roller surface and to ensure continuous transport of the particulate mixture upon rotational movement of the roller.

It is advantageous to produce the surface of the roll by means of a flame spraying process. With the aid of the flame spraying method, it is possible to produce a surface of the roll with a suitable roughness simply and inexpensively. If the roll surface and / or at least part of the rotating hollow roll made of aluminum, chromium, nickel, copper, conductive plastic and / or a plastic with a conductive layer, so the surface of the roll can be acted upon by a set potential, for example To support the transfer of toner particles on this roller or from this roller. Also can be Producing rolls from these materials easily and inexpensively.

The distance between doctor blade and roll surface is set in an advantageous development of the invention in the range of 0.05 to 6 mm. Such spacing ensures low blade and roller wear and reliable cleaning of the roller from toner particles set on the roller surface.

By an inventive method for cleaning a roller in an electrophotographic printer or copier is achieved that the cleaning of the roller is done thoroughly with little effort. Additional auxiliary power is not needed. With the help of the method, a compact design of the printer or copier is also possible, wherein the method by the distance between the doctor blade and roll surface for the roller and the doctor blade is almost wear-free feasible. This method of cleaning the roll can be used for various particle mixtures of toner particles and carrier particles. The cleaning effect of such an arrangement also remains if the physical properties of the particle mixture change.

A fourth aspect of the invention relates to an electrophotographic printing or copying apparatus in which a toner attaching unit deposits electrically charged toner particles on the surface of a first support member. At least a part of the toner particles is transferred from the first carrier element to a second carrier element. A cleaning unit removes the toner particles left on the first support member after being transferred from the first support member. The cleaning unit includes a roller which is arranged at a distance from the first carrier element. Inside the roller at least two magnetic elements are arranged stationary. On the surface of the roller becomes a particle mixture containing electrically charged toner particles and ferromagnetic carrier particles. The particle-mixture facing adjacent poles of the two magnetic elements are similar and viewed in the direction of rotation of the roller at a distance from each other arranged so that the carrier particles on the surface of the roller to the magnetic elements at least one accumulation forms whose carrier particles in a rotational movement of the roller on the surface rub.

With the aid of the electrophotographic printing or copying device according to the invention and in a method for operating this electrophotographic printing or copying device, it is possible with little effort to produce high-quality printed images in a simple manner, wherein the mechanical stress of the toner is relatively low. By cleaning the first support member and the used for cleaning roller assembly a high quality print image is guaranteed even with prolonged use of the printing or copying device, wherein toner particles adhere to the surface of the roller from this by a magnetic element arrangement of the particle mixture on the surface of the Roller to be rubbed off. This prevents toner particles from being permanently deposited on the surface of the roller, obstructing electrostatic operations and thus adversely affecting the electrographic process. The physical properties of the roller assembly and the toner mixture can be kept constant by the apparatus or method over a long period of time.

In an advantageous development, a doctor blade is arranged at a predetermined distance to the roll surface in the region of the second magnetic element or in the direction of rotation of the roll after the two magnetic elements fixed. The roller-shaped movement within the particle mixture of carrier particles and toner particles in the region of the magnetic elements on the roll surface is reinforced by the doctor blade, wherein in the region in front of the doctor blade at least parts of the Toner particles that have settled on the roll surface, are abraded by this and detached.

A fifth aspect of the invention relates to an electrophotographic printing or copying apparatus and a method of operating such an electrophotographic printing or copying apparatus. The electrophotographic printing or copying device has a toner attaching unit which transfers toner particles to a first support member by means of a particle mixture of electrically charged toner particles and ferromagnetic carrier particles. The particle mixture is fed to a cleaning unit after transfer of at least a portion of the toner particles of the particle mixture to a second support member. The cleaning unit absorbs the toner particles present on the first carrier element with the aid of the added particle mixture.

In one development of the invention, an applicator element is used as the first carrier element and a photoconductor as the second carrier element. As a result, it is achieved that the applicator element is colored with toner particles by means of the toner adsorption unit, whereby a part of the toner particles are transferred from the applicator element to the photoconductor in accordance with the latent charge image on the photoconductor and the toner particles remaining on the applicator element are removed therefrom. The combination of the applicator element and the photoconductor ensures a uniform layer thickness of the toner particles of the printed image, as a result of which high-quality homogeneous printed images having a uniform print intensity are produced.

In another development of the invention, the first carrier element is a photoconductor and the second carrier element is a carrier material to be printed or a transfer element. The photoconductor is colored according to its latent charge image with toner particles, and the toner image is on printed substrate or transfer element umgedruckt. The toner particles remaining on the photoconductor after transfer printing are removed from the photoconductor by means of the cleaning unit. This ensures that the photoconductor is completely cleaned of toner particles after a printing or copying before another printing or copying process and memory effects are avoided in the subsequent printed image.

In a further embodiment of the invention, the direction of rotation of the roller is equal to the direction of rotation of the first carrier element. Opposite an opposite direction of rotation of the roller to the direction of movement of the first support member, the cleaning effect is increased, since with the aid of the roller more ferromagnetic carrier particles for receiving toner particles are passed to the first support member which touch the surface of the first support member and remove the adhesive on her toner. Together with the roller, the carrier particles, which are located on the surface, rotated and thus transported by the rotational movement of the roller in the circumferential direction. A rough and / or structured roller surface favors this transport of the carrier particles.

In an advantageous embodiment of the invention, the axes of the poles of the magnetic element are aligned radially to the axis of rotation of the roller. This ensures that the magnetic field of the magnetic element exerts a particularly large force on the ferromagnetic carrier particles in the region in that the peripheral surface of the roller facing pole of the magnetic element has a small distance from the roll surface. By this force, the carrier particles are aligned with the field lines of the magnetic element and at least partially held temporarily in this area, so that by the concentration of the carrier particles and their orientation a raised accumulation, a so-called magnetic brush, is formed. The distance between the carrier element and the roller is preferably less than or equal to the height of the magnetic brush on the roller. The distance between the roller and the first carrier element is preferably set in the range between 0.1 and 7 mm.

It is also possible in another example of the invention that the amount of ferromagnetic carrier particles carried on the surface of the roller contains a predetermined amount of toner particles, whereby a particle mixture of carrier particles and toner particles is used to clean the roller. Thus, particle mixtures of carrier particles and toner particles can also be used for cleaning, which have been previously described e.g. have been used for coloring a support element. The toner attaching unit transfers toner particles of a two-component mixture of electrically charged toner particles and ferromagnetic carrier particles to the first carrier member. This two-component mixture is fed to the roller of the cleaning unit after transferring at least a portion of the toner particles to the first support member. The particle mixture fed to the cleaning unit absorbs the toner particles remaining on the first support element. This ensures that the particle mixture must be processed only once in the electrophotographic printing or copying device. It is used first for toner application and then for cleaning.

In another embodiment, the particle mixture is transferred from the Tonanlagerungseinheit to the cleaning unit by means of a magnetic field of at least one magnetic element. The force of the magnetic field on the ferromagnetic carrier particles, together with the toner particles located on the ferromagnetic carrier particles, transports them from the toner attachment unit to the cleaning unit.

Alternatively or additionally, the transfer of the particle mixture from the toner attachment unit to the cleaning unit may be carried out by means of an intermediary between the toner attachment unit and the cleaning unit arranged guide element done. Such a guide element may for example be a guide plate or a conveyor, such as a conveyor belt or a screw conveyor. This ensures that the particle mixture is transferred continuously from the toner attachment unit to the cleaning unit.

If permanent magnets are used as magnetic elements, no supply energy is required for the magnetic elements. Furthermore, permanent magnets are inexpensive and can be produced in almost any shape. The side of the magnetic elements facing the surface of the roller can thereby be e.g. be executed curved, so that the design of the roller assembly can be made even more compact. If a plurality of magnetic elements are arranged in the interior of the roller, whose poles are each aligned approximately radially to the axis of rotation, so a plurality of magnetic brushes with the aid of these magnetic elements can be formed on the surface of the roller. The transfer of toner and / or carrier particles can thus be done easily, inexpensively and wear-free in the printing or copying device.

In another advantageous development of the invention, a first potential difference and / or a second potential difference between the cleaning unit and the first carrier element are generated between the toner accumulation unit and the first carrier element. It is thereby achieved that the transfer of the toner particles from the toner attachment unit to the first carrier element or from the first carrier element to the cleaning unit takes place with simple means. With the help of the potential differences, a simple transfer of the toner particles between different elements with little design effort is cost possible. By this potential difference, the removal of the toner particles is supported by the first support member, whereby all toner particles are completely removed from the support element.

In a method according to the invention for operating an electrophotographic printing or copying device, the production of high-quality printed images is simple and inexpensive. The application of the toner particles to carrier elements and the cleaning of the carrier elements with the aid of magnetic rollers takes place according to the method of the invention almost without wear.

Figur 1

eine Anordnung zum Anlagern und Entfernen von Toner an bzw. von einer Applikatorelementoberfläche, wobei zum Anlagern und zum Entfernen ein Teilchengemisch aus ferromagnetischen Trägerteilchen und elektrisch geladenen Tonerteilchen dient;

Figur 2

eine weitere Anordnung zum Anlagern und Entfernen von Toner ähnlich der in Figur 1 gezeigten Anordnung;

Figur 3

die Anordnung aus Figur 1, wobei elektrische Potentiale der Walzenoberflächen dargestellt sind;

Figur 4

eine Anordnung zum Reinigen eines Applikatorelementes mit Hilfe einer Magnetwalzenanordnung, wobei zum Reinigen der Magnetwalzenanordnung eine Rakel-Magnetelement-Vorrichtung dient;

Figur 5

eine Anordnung zum Entwickeln eines latenten Ladungsbildes auf einer Fotoleitertrommel mit Hilfe einer Magnetwalzenanordnung sowie eine Rakel-Magnetelement-Vorrichtung zum Reinigen der Magnetwalzenanordnung;

Figur 6

ein Ausführungsbeispiel für die Konfiguration des Magnetstators und der Rakel, bei der die Oberfläche der Magnetwalzenanordnung von Tonerteilchen gereinigt wird;

Figur 7

die Bewegungen innerhalb des Teilchengemisches im Bereich der Magnetwalze bei der in Figur 5 gezeigten Anordnung;

Figur 8

eine Anordnung zum Entfernen der Tonerteilchen von einer Magnetwalze mit Hilfe einer Magnetanordnung aus zwei Magnetelementen, wobei die Magnetwalze zum Entfernen einer homogenen Tonerschicht auf eine Applikatorwalze dient;

Figur 9

eine Anordnung zum Entfernen der Tonerteilchen von einer Magnetwalze mit Hilfe einer Magnetanordnung aus zwei Magnetelementen, wobei die Magnetwalze zum Entwickeln eines latenten Ladungsbildes auf einem Fotoleiter dient;

Figur 10

ein Ausführungsbeispiel für die Konfiguration des Magnetstators des Walzensystems aus Figur 9 zum Erzielen des Reinigungseffektes auf der Walzenoberfläche;

Figur 11

das Ausbilden von Magnetbürsten an den Magnetelementen sowie die Bewegungen innerhalb des Teilchengemisches auf der Walzenoberfläche, die durch die Pfeile neben dem Gemisch angedeutet sind;

Figur 12

die Feldverteilung im magnetischen Nahfeld direkt auf der Walzenoberfläche des in Figur 10 gezeigten Magnetwalzensystems; und

Figur 13

die Feldverteilung im magnetischen Fernfeld im Abstand von ca. 9 mm von der Walzenoberfläche des in Figur 10 gezeigten Magnetwalzensystems.

For a better understanding of the present invention, reference will now be made to the preferred embodiments illustrated in the drawings, which are described in terms of specific terminology. It should be understood, however, that the scope of the invention should not be so limited since such changes and other modifications to the illustrated devices and / or method, as well as such other uses of the invention as heretofore, are to be considered as present and contemplated Expertise of a competent expert. The figures show embodiments of the invention, namely:

FIG. 1

an arrangement for attaching and removing toner to an applicator element surface, a particle mixture of ferromagnetic carrier particles and electrically charged toner particles serving for deposition and removal;

FIG. 2

another arrangement for attaching and removing toner similar to that in FIG. 1 shown arrangement;

FIG. 3

the arrangement FIG. 1 showing electrical potentials of the roll surfaces;

FIG. 4

an arrangement for cleaning an applicator element by means of a magnetic roller assembly, wherein for cleaning the magnetic roller assembly, a squeegee-magnetic element device is used;

FIG. 5

an arrangement for developing a charge latent image on a photoconductive drum by means of a magnetic roller assembly, and a doctor blade magnetic element device for cleaning the magnetic roller assembly;

FIG. 6

an embodiment of the configuration of the magnetic stator and the doctor blade, wherein the surface of the magnetic roller assembly is cleaned of toner particles;

FIG. 7

the movements within the particle mixture in the area of the magnetic roller at the in FIG. 5 shown arrangement;

FIG. 8

an arrangement for removing the toner particles from a magnetic roller by means of a magnet arrangement of two magnetic elements, the magnetic roller serving to remove a homogeneous toner layer on an applicator roller;

FIG. 9

an arrangement for removing the toner particles from a magnetic roller by means of a magnet arrangement of two magnetic elements, the magnetic roller serving to develop a charge latent image on a photoconductor;

FIG. 10

an embodiment of the configuration of the magnetic stator of the roller system FIG. 9 to achieve the cleaning effect on the roll surface;

FIG. 11

the formation of magnetic brushes on the magnetic elements as well as the movements within the particle mixture on the roller surface, indicated by the arrows next to the mixture;

FIG. 12

the field distribution in the magnetic near field directly on the roll surface of in FIG. 10 shown magnetic roller system; and

FIG. 13

the field distribution in the magnetic far field at a distance of about 9 mm from the roll surface of in FIG. 10 shown magnetic roller system.

In FIG. 1 For example, an array 10 for toner deposition to an applicator roller 12 is shown by means of a first magnetic roller assembly 14 wherein a particle mixture of electrically charged toner particles and ferromagnetic carrier particles, a so-called bicomponent mixture, is used to attach the toner to the applicator roller 12. Such an applicator roller 12 is used in a printer or copier for transporting toner particles. In the following, the toner particles are also generally referred to as toners. Applicator rollers are used in particular for developing a latent charge image on a photoconductor element with toner, wherein the surface of the applicator roller is provided with a uniform toner layer. The uniform toner layer is guided past the charge latent image of the photoconductor element, wherein in the areas to be inked of the charge latent image the toner layer is transferred from the applicator roller to the photoconductor element.

For transferring toner particles onto the surface of the applicator roller 12, a so-called magnetic brush is formed between the first magnetic roller assembly 14 and the applicator roller 12 from the two-component mixture. Inside a rotatable, hollow roller 24 of the arrangement 14 are on a stator 26 elongated magnetic elements 28, 20, 32, 34, the outwardly directed poles seen in the circumferential direction alternate. The ferromagnetic carrier particles are arranged and aligned on each magnetic element 28, 20, 32, 34 by the force of the magnetic field along the magnetic field lines, wherein on the surface of the roller 24 in the region of the outwardly facing poles of the magnetic elements 28 to 34 projecting from the roll surface 24 accumulation of Carrier particles and the toner particles adhering to them are formed. Such a protruding collection of carrier particles is called a magnetic brush due to the brush-like shape.

The first magnetic roller assembly 14 is supplied in the region 20, a treated two-component mixture having a predetermined weight fraction of toner particles, wherein the toner particles are charged triboelectrically. The weight fraction of the toner is typically in the range of 2% to 8%. The feeding of the two-component mixture is e.g. by a Schaufelradanordnung not shown. A metering blade 22 arranged at a predetermined distance from the first magnetic roller arrangement 14 produces a uniform layer of the two-component mixture 20 on the outer surface of the roller 24.

The first magnetic roller assembly 14 includes, as mentioned, the one rotating hollow roller 24, in the interior of which a magnetic roller stator 26 is arranged, which contains the magnetic elements 28, 30, 32, 34. The longitudinal axes of the magnetic elements 28, 30, 32, 34 are aligned in the radial direction, with north pole N and south pole S side by side magnetic elements 28, 30, 32, 34 each seen in the circumferential direction follow each other. The magnetic elements 28, 30, 32, 34 are rod-shaped permanent magnets and extend over the entire roll width. In this embodiment, the distance between each of the permanent magnets 28, 30, 32, 34 and the inner surface of the roller 24 is set in the range of 0.2 to 1 mm, between each of the permanent magnets 28, 30, 32, 34 and the outer circumferential surface of the roller 24 gives a distance in the range of 1.2 mm to 3 mm. Around Magnetic brush 18 is ideally a constant toner supply in the two-component mixture. The toner particles on the carrier particles of the magnetic brush 18 deposit on the surface of the applicator roller 12 as a uniform toner layer 36. An electric field generated by a potential difference between the surfaces of the applicator roller 12 and the roller 24 exerts a force on the electrically charged toner particles, by which the toner particles are released from the carrier particles and deposited on the applicator roller 12. These electrostatic processes will be explained in more detail later.

The applicator roller 12 is guided past a photoconductor, not shown. Corresponding to the latent charge image of the photoconductor, areas of the toner layer 36 are transferred thereto via an air gap or in direct contact between the applicator roller 12 and the photoconductor. The non-photoconductive regions 38, 40, 42 of the toner layer 36 form the image negative to the latent image and must be removed from the applicator roll 12. The cleaning is effected by a second magnet roller arrangement 16.

This second magnet roller assembly 16, like the first magnet roller assembly 14, has a rotating hollow roller 44 and a magnet roller stator 46 that includes rod-shaped magnet members 48, 50, 52 that are permanent magnets and radially aligned. The direction of rotation of the applicator roller 12 is indicated by the arrow P1, the direction of rotation of the roller 24 with the arrow P2 and the direction of rotation roller 44 with the arrow P3. The bicomponent mixture is transferred in the region 54 from the surface of the roller 24 to the surface of the roller 44 by means of the magnetic field of the magnetic elements 34 and 48. The ferromagnetic carrier particles become with them electrostatically adhering toner particles upon rotation of the roller 24 in the resulting magnetic Field between the south pole S of the permanent magnet 34 and the north pole N of the permanent magnet 48 transported.

The proportion by weight of the toner particles in the two-component mixture in the area 54 is reduced compared to the prepared two-component mixture fed in the area 20 as a result of the toner transfer to the applicator roller 12. This two-component mixture with reduced toner content is transported on the surface of the roller 44 to the area 56 on.

The effective magnetic field of the magnetic element 50 in the region 56 generates a magnetic brush. In the area 56, the distance between roller 44 and applicator roller 12 is relatively small. The magnetic brush in region 56 contains the two-component mixture with reduced toner content. The toner residues 38, 40, 42 are due to the potential difference between the surfaces of the roller 44 and the applicator 12 and electrostatically by rubbing the magnetic brush on the surface of the applicator 12 of this dissolved and transported in the direction of the roller 44. The two-component mixture of the magnetic brush 56 touches the surface of the applicator roller 12 and additionally rubs the toner particles from the surface of the applicator roller 12. On the magnetic element 52 of the second magnetic roller assembly 16 and the magnetic element 30 of the first magnetic roller assembly 14 further magnetic brushes 58, 60 are formed. After cleaning the surface of the applicator roller 12 by means of the magnetic brush in the area 56, the two-component mixture is transported on the surface of the roller 44 and dissolved in the area 62 of the roller 44 of the second magnetic roller assembly 16 and then collected in a collecting device, not shown, and the electrophotographic process the printer or copier supplied, in which the assembly 10 is included. In other embodiments, the particle mixture falls directly into a so-called mixed sump in which the two-component mixture is recycled.

In FIG. 2 is an arrangement 64 similar to the arrangement 10 of FIG. 1 shown. Like elements have the same reference numerals. In contrast to the arrangement 10 off FIG. 1 For example, a guide element 66 is used to transfer the two-component mixture in region 54. Such a guide element 66 is formed, for example, as a guide plate. The axis of rotation 68 of the first magnet roller arrangement 14 is arranged above the axis of rotation 70 of the second magnet roller arrangement 16 as viewed in the vertical direction. The guide member 66 is disposed obliquely so that the two-component mixture can slide or slip from the first magnet roller assembly 14 to the second magnet roller assembly 16 on an inclined plane. For larger roller distances or in a horizontal arrangement of the axes of rotation 68, 70, it may be advantageous, instead of a guide member 66 and a conveyor, such as a conveyor belt or a paddle wheel, between the first magnetic roller assembly 14 and the second magnetic roller assembly 16 provide.

In FIG. 3 is the in FIG. 1 shown arrangement 10 with the set in the operating state electrical potentials of the roll surfaces. The surface of the applicator roller 12 has a potential difference DC1 from a ground potential as a reference potential, the outer surface of the roller 24 has a potential difference DC2 from the ground potential, and the outer surface of the roller 44 has a potential difference DC3 from the ground potential. At the in FIG. 3 As shown, a negative toner system is used. Taking into account the sign in the case of a negative toner system, the potential difference DC1 is smaller than the potential difference DC2 and the potential difference DC3 is greater than the potential difference DC1.

In contrast, in another embodiment, a positive toner system in the in FIG. 3 used arrangement, taking into account the sign is the Potential difference DC1 smaller than the potential difference DC2 and the potential difference DC3 smaller than the potential difference DC1 set.

In the arrangement according to FIG. 3 With a negative toner system, the potential differences to the reference potential are set to DC1 = 500 volts, DC2 = 100 volts and DC3 = 700 volts. The potential differences are generated by DC voltage sources 72, 74, 76. However, in other embodiments it is also possible to set one of these potentials DC1, DC2, DC3 to reference potential and to select the voltage of the other two DC voltage sources accordingly. Also, negative voltages are possible with respect to the ground potential. In other embodiments, other set potentials DC1, DC2, DC3 of the surfaces of the rollers 12, 24, 44 with respect to the reference potential are possible. The potentials to be set depend, above all, on the composition of the toner material, on the distances between the rollers 12, 24, 44 and on the roller materials. The electrostatic processes which are achieved by the set potentials DC1, DC2, DC3 are mainly due to the potential difference (DC1-DC2) resulting from the potentials DC1, DC2, DC3 between the surfaces of the applicator roller 12 and the magnet roller arrangement 14 and of FIG the potential difference (DC1 - DC3) between the surfaces of the applicator roller 12 and the magnetic roller assembly 16 in consideration of the sign depends.

With one in the FIGS. 1 to 3 As shown, it is possible to produce a virtually wear-free system for applying and cleaning toner on or from rollers 12 simply and inexpensively. The roller 12 to be cleaned, for example an applicator roller or a photoconductor roller, is not mechanically stressed during the cleaning process or only to a very small extent. This is achieved above all by the direct absorption of the toner 38, 40, 42 into the two-component mixture. The mechanical stress of the toner is due to the direct absorption of the toner particles in the two-component mixture low or absent. Also occurs in the application and / or cleaning only a very small heat generation. In a printer or copier with an arrangement according to the FIGS. 1 to 3 It is possible to use particle mixtures of toner particles and carrier particles with different physical properties, ie with different toner parameters, which makes possible a large operating range with regard to these parameters of the particle mixture. Also, no special additives for the cleaning device are required, as they are required for example in cleaning systems with blades in which the toner additional waxes must be added.

At one in the FIGS. 1 to 3 As shown, not only does the inking of the applicator roller surface take place electrostatically with the aid of a magnet roller arrangement 14, but also its cleaning. The in the description of FIG. 3 illustrated electrical potentials DC1, DC2, DC3 and the resulting therefrom between the surfaces of the applicator roller 12 and the roller 44 potential difference generates an electric field between the rollers 12, 44, whose force on the toner particles in the direction of the roller 44 and in the direction the two-component mixture acts on the roll surface. The toner can be removed from the applicator roller 12 in direct contact with the two-component mixture or transferred to the two-component mixture on the surface of the magnet roller arrangement 16 via an air gap between the applicator roller 12 and the magnet roller arrangement 16.

In FIG. 4 an arrangement for cleaning an applicator roller 78 by means of a magnetic roller system 80 with a rotating hollow roller 81 is shown. This arrangement also includes a cleaning device with magnetic elements 96, 98 and a squeegee 82 for cleaning the outer surface of the roller 81. On the surface of an applicator roller 78th The magnetic roller system 80 is disposed at a predetermined distance from the applicator roller 78 and has a Magnetwalzenstator 84, are arranged on the permanent magnets 86 to 100 equidistant from each other on a circular path about the axis of rotation 127 of the magnetic roller system 80. The axis of the poles N, S of each individual permanent magnet 86 to 100 is aligned radially with respect to the rotation axis 127, ie, the north pole N or the south pole S of each permanent magnet 86 to 100 faces the surface of the roller 81 of the magnetic roller system 80.

In the region 102, the roller 81 is supplied with ferromagnetic carrier particles as pure carrier particles or with the aid of a particle mixture of carrier particles and toner particles. This supply of carrier particles can be effected, for example, by a second roller system (not shown) for depositing toner onto the applicator element 78, as is already the case with the Figures 1 and 2 has been explained. However, in other embodiments, these carrier particles may also be supplied to the magnetic roller system 80 from a reservoir.

The magnetic fields of the stationary permanent magnets 88, 90, 92, 94 form on the surface of the roller 81 magnetic brushes 104, 106, 108, 110, 112 of carrier particles. The permanent magnet 90 is arranged in the area with the smallest distance between applicator roller 78 and magnetic roller system 80. The magnetic brush 106 formed on the surface of the roller 81 rubs on the surface of the applicator roller 78, whereby the toner particles 79 to be removed are abraded. The toner particles 79 are attached to the carrier particles of the magnetic brush 106. The detachment of the toner particles 79 from the surface of the applicator roller 78 and the attachment of these toner particles to the carrier particles of the magnetic brush 106 is further affected by the force of an electric field on the toner particles 79 and the particles rubbing on the surface of the applicator roller 12. This electric field arises due to the potential difference DC between the surfaces of the applicator roller 78 and the roller 81, which is adjusted by means of a DC voltage source 116.

The directions of rotation of the applicator roller 78 and the roller 81 are the same, as indicated by the arrows P4 and P5. It is thus achieved that a large amount of ferromagnetic carrier particles is guided past the applicator roller 12 in the area of the magnetic brush 106 on the applicator roller 78, with the aid of the magnetic brush 106 also a mechanical brushing action being exerted on the surface of the applicator roller 78 by the toner particles are rubbed off the surface. The peripheral speeds of the applicator roller 78 and the magnetic roller system 80 are approximately equal.

In other embodiments, the peripheral speed of the magnetic roller system 80 is less than or greater than the peripheral speed of the applicator roller 78. In other embodiments, the directions of rotation of the applicator roller 78 and the magnetic roller system 80 are opposite to each other such that e.g. the direction of rotation of the magnetic roller system 80 is directed opposite to the direction of rotation according to the arrow P5. This ensures that the mechanical stress of the carrier particles and toner particles in the region of the magnetic brush 106 is further reduced. In an opposite direction arrangement to the arrow P5, the elements of the arrangement, i. the region 102 and the doctor blade 82 on the line through the two axes of rotation of the applicator roll 78 and the magnetic roller system 80 to arrange mirrored. The further magnetic brushes 104, 108, 110, 112 then likewise form on the permanent magnets 92, 88, 86, 100 mirrored on this straight line.

The toner particles removed from the applicator roller 78 in the area of the magnetic brush 106 are picked up by the carrier particles of this magnetic brush and in the direction of rotation of the magnetic roller system 80 transported away. The permanent magnet 96 is arranged in the direction of rotation P5 of the magnetic roller system 80 just before the doctor blade 82. The blade of the squeegee 82 is disposed at a predetermined distance from the surface of the roller 81, whereby a portion of the particle mixture of carrier particles and toner particles is stripped from the surface of the magnetic roller system 80 during rotational movement of the magnetic roller system 80.

Due to the force acting on the ferromagnetic carrier particles of the particle mixture by the magnetic field of the permanent magnet 96 not only a magnetic brush forms directly on the north pole N of the permanent magnet 96 on the surface of the roller 81, but it additionally with the help of the doctor blade 82 stripped carrier particles in the area 112th held, so that a cluster of carrier particles and toner particles in the area in front of the squeegee 82 forms. This grape is also called a standing particle mixture. The force effect on the carrier particles decreases as the distance from the permanent magnet 96 increases, as a result of which parts of the two-component mixture in the lower region 114 of the grape fall into a collecting container (not shown) for reprocessing of the particle mixture. Upon rotation of the hollow roller 81, the carrier particles and toner particles in the region 112 are mixed and fluidized so that the particle mixture rubs on its surface upon rotation of the roller 81, whereby toner particles adhered directly to the surface of the roller 81 are abraded therefrom become. The movement processes within the grape, ie in the area 112, are related below FIG. 7 explained in more detail. In other embodiments, the particle mixture falls directly into a so-called mixed sump in which the two-component mixture is treated.

In FIG. 5 is essentially the arrangement FIG. 4 however, which here serves to develop a latent charge image formed on the surface of a photoconductor drum 77 is located. On the surface of the photoconductor drum, a toner layer 118 is applied or deposited in the areas to be inked. The construction of in FIG. 5 The arrangement shown is similar to that in FIG FIG. 4 shown arrangement for cleaning the applicator roller 78. The same elements have the same reference numerals.

In area 120, the magnetic roller system is fed with a two-component mixture, ie a particle mixture of carrier particles and toner particles, in which the toner particles have a weight fraction in the range from 2% to 8% of the particle mixture. As already related to FIG. 4 described, is formed in the region 106 by the permanent magnet 90, a magnetic brush. This magnetic brush touches the surface of the photoconductive drum 77. As already mentioned, a latent charge image is present on this surface. The surfaces of the photoconductive drum 77 have a potential difference DC generated by the DC power source 122 through the charge image in the areas to be inked to the roller 81.

In the case of a negative toner system, ie negatively charged toner particles, the potential of the areas of the photoconductive drum 77 to be inked is to be set positively relative to the potential of the surface of the roller 81. In the case of a positive toner system, on the other hand, the potential of the areas of the photoconductive drum 77 to be inked is to be set negative relative to the potential of the surface of the roller 81. The potential difference between the areas of the photoconductive drum 77 and roller 81 to be inked causes electrostatic attachment of toner particles 118 on the surface of the photoconductive drum 77 in the areas to be inked. In the non-inking areas of the photoconductive drum 77, the so-called background area, an opposite potential difference must be set with respect to the areas to be inked, whereby a force is exerted on the toner particles in the direction of the roller 81 and thus in the background area no toner particles are deposited. The force effects on the toner particles due to the potential differences were already in the description of the figures FIG. 3 explained. In the FIG. 5 Squeegee-magnet element arrangement shown for cleaning the magnetic roller surface is already in connection with FIG. 4 been described.

In FIG. 6 the magnetic roller system 80 is shown enlarged, which in the in the FIGS. 4 and 5 shown arrangements is used. The distance between the cutting edge of the doctor blade 82 and the outer surface of the roller 81 is designated by A1. This distance A1 is set in the range of 0.05 to 6 mm depending on the physical properties of the particle mixture. In the illustrated embodiment, the distance A1 is set in the range of 0.1 mm to 4 mm. The longitudinal axis 123 of the permanent magnet 96 arranged on the magnet roller stator 84 is arranged in front of the cutting edge of the doctor blade 82 at a predetermined distance A2 in the direction of rotation of the roller 81. This distance A2 is set depending on the physical properties of the particle mixture and the peripheral velocity in the range of 0.01 to 10 mm. A particularly effective cleaning effect could be achieved at a distance in the range of 4 mm to 6 mm.

The longitudinal axes 123, 124, 125, 126 of the permanent magnets 86 to 100, represented by dash-dotted lines, pass through the axis of rotation 127, ie the centers of the north pole N and the south pole S of the permanent magnets 86 to 100 are approximately on the lines 123 to 126. The straight lines 123 to 126 have an angular distance of 45 ° from one another, ie the permanent magnets 86 to 100 are arranged at the same angular distance from one another on a circular path about the axis of rotation 127. Between the permanent magnets 86 to 100 and the inner surface of the roller 81, a distance in the range of 0.2 mm to 1.5 mm is set in each case. The distance between the permanent magnets 86 to 100 and the outer surface the roller 81 results according to the material thickness of the roller 81 and is in the range of 2.3 mm and 3.5 mm.

Particularly favorable is a distance between the side of the permanent magnets 86 to 100 facing the roller 81 and the inner surface of the roller 81 in the range of 0.2 mm to 1 mm and the outer surface of the roller 81 in the range of 2 mm to 3 mm proved. At these intervals, not only suitable magnetic brushes are formed, but also a grape-like accumulation of the particle mixture in the region 112, as in the FIGS. 4 and 5 is shown. However, the distance between the permanent magnets 86 to 100 and the surface of the roller 81 is dependent on the field strength of the magnetic elements 86 to 100 used, the printing speed of the printing or copying device, especially the peripheral speed of the outer roller surface, of the physical properties the used toner and especially the physical properties of the carrier particles.

As the carrier particle material, e.g. Ferrite and iron, in particular, the magnetic saturation of the carrier particle material is significant. Furthermore, the distance depends on the overall arrangement of the printing or copying device. Thus, it is also possible to set clearances which are outside the stated ranges, if the circumferential speed is increased, if other toner material is used, if other carrier particle materials are used and / or a modified overall arrangement of the printing or copying device is used.

In FIG. 7 a section of the magnetic roller system 80 is shown together with the doctor blade 82, wherein the movements within the particle mixture, which result in a rotational movement of the roller 81 in the direction of the arrow P5, with the aid of arrows P6, P7, P8, P9 are shown. Also, the arrangement of the particle mixture in the area 112 opposite the representations of the FIGS. 4 and 5 shown in more detail. At the north pole N of the permanent magnet 96, a magnetic brush 128 is formed by its magnetic field. In front of the cutting edge of the doctor blade 82, an accumulation of the particle mixture of toner particles and carrier particles, which are held in this region by the magnetic field of the permanent magnet 96, is formed in the form of a grape.

Between the magnetic brushes in the regions 110 and 128, the particle mixture is transported on the roll surface approximately at the peripheral speed of the roll 81, as indicated by arrow P6. From the magnetic brush in the region 128, the particle mixture in the direction of arrow P7 is further transported to the grape-like accumulation of the particle mixture in front of the doctor blade 82. As already explained, part of the particle mixture is held in front of the doctor blade 82 in the region 130 in the direction of rotation of the roller 81 by the field forces of the permanent magnets 96, 98. Due to the rotational movement of the hollow roller 81 and the associated feeding of further particle mixture, a rotating roller-shaped movement within the particle mixture forms in front of the doctor blade 82, which is indicated by means of the arrow P8.

The particle mixture is circulated in the region 130 in front of the doctor blade 82, whereby it rubs against the surface of the roller 81. It rubs especially the carrier particles, whereby toner particles are rubbed off the roll surface, which adhere directly to this. The formation of an electrically insulating crust-like layer and electrically insulating regions of toner particles on the magnetic roller surface is effectively prevented by rubbing the toner particles from this surface. Electrostatic processes, such as the transfer of toner particles from or to the roller 81 are thus not affected. Depending on the field forces of the permanent magnets 96, 98, a more or less large grape-like accumulation 130 forms in front of the doctor blade 82. This accumulation 130 is also called a standing particle mixture.

In the lower region of the grape-like accumulation 130, the forces acting on the carrier particles of the magnetic fields of the permanent magnets 96, 98 are lower than at the roll surface, so that parts 114 of the particle mixture fall in the direction of arrow P9 in a collecting container, not shown, down. The distance A2 to be set between the permanent magnet 96 and the edge of the doctor blade 82 depends on the peripheral speed of the roller 81, the surface roughness of the roller 81, the toner used, the carrier particle material used, the speed of the printing or copying device, and the overall arrangement the printing or copying device.

The surface of the roller 81 is electrically conductive. It may contain, for example, aluminum, copper, nickel, conductive plastic or a compound of these materials, for example an alloy. In other embodiments, the poles N, S of the magnetic elements 86 to 100 may vary in shape, shape and field strength. Thus, the shape of the magnetic elements 86 to 100 may not be rod-shaped, so that only the roller surface facing pole N, S acts in the direction of the normal. Also, the magnetic elements 86 to 100 may have different field strengths. Between the poles N, S juxtaposed permanent magnets 86 to 100 with opposite orientation, for example between the south pole S of the permanent magnet 94 and the north pole N of the permanent magnet 96, a resulting magnetic field is formed, resulting from an addition of the field vectors of the magnetic fields , At the field lines of the resulting magnetic field, the ferromagnetic carrier particles of the two-component mixture align. The transport of the continuously applied particle mixture on the surface of the roller 81 is effected by the rotation thereof.

The roller 81 has a roughness in the range of 1 micron to 5000 microns. It has proved to be particularly favorable to adjust the roughness in the range from 10 μm to 3000 μm. With this roughness, a safe transport of the particle mixture is ensured, and the detachment of toner particles is not hindered by the roll surface. The distance A1 between the surfaces of the doctor blade 82 and the roller 81 is preferably less than the thickness of the layer of the particle mixture in front of the doctor blade 82. The thickness of the layer of the particle mixture remaining after the doctor blade 82 is limited by the distance A1 between roller surface and doctor blade can be adjusted by changing the distance A1.

The portion of the particle mixture blocked by the doctor blade 82 forms the standing particle mixture on the surface thereof relative to the roller 81. The force with which the ferromagnetic particle mixture of toner particles and carrier particles adhere to the surface of the roller 81 is dependent on the ferromagnetic properties of the carrier particle material, the magnetic field strength of the magnetic elements 86 to 100, and above all the field strength of the permanent magnets 96, 98 and the distance between the surface of the roller 81 and the respective permanent magnet 86 to 100 dependent.

The standing particle mixture in the region 112 or 130 in front of the doctor blade 82 rubs on the outer surface of the roller 81 during a rotational movement of the roller 81 in the direction of arrow P5. This friction abrades the toner adhering to the surface of the roller 81 and again through the particle mixture taken, wherein the abraded toner particles adhere to the carrier particles electrostatically. This ensures that a permanent toner particle layer on the surface of the roller 81 is prevented and the electrostatic process in the printer or copier is not impaired.

The portions of the particle mixture passing through the squeegee 82 remain on the surface of the roller 81. In others Embodiments, these can also be separated by a corresponding structural design of the magnet stator 136 of the roll surface and a collecting device, such as the mixture sump of the printer or copier, fed or transferred to an adjacent magnetic roller system.

In order to reduce the mechanical energy required to perform the cleaning process, it is possible, in other embodiments, to provide the outer surface of the roller 81 with a coating that has a very low surface energy. Such a coating may e.g. be made with the help of Teflon. Also, the entire roller 81 may be made of such a material. However, in order not to adversely affect the electrostatic process, such a coating should have no electrically insulating properties, but should be correspondingly conductive for charge transport to and from the roller 81.

Embodiments are also possible in which the high-surface-area low energy insulating material is applied only in the recesses of a rough surface of the roller 81. The remaining conductive areas ensure the required charge flow. The arrangement for cleaning requires no additional auxiliary power. Furthermore, during the cleaning, the toner is additionally charged triboelectrically by the friction processes.

The arrangement for cleaning the surface of magnetic roller systems contains no wearing parts. Due to the simple structure and a compact design of the cleaning device and the entire printing or copying device is possible. It is also suitable for different particle mixtures with different toner parameters. The magnetic roller system 80 can both remove toner particles from applicator rollers 78 and photoconductors, as well as develop latent charge images on photoconductors and color applicator rollers 78. Instead of an applicator roller 78, in other embodiments Applicator tapes or transfer tapes are used. In further embodiments, other magnetic elements, such as electromagnets are used instead of the permanent magnets. The in the FIGS. 4 and 5 For example, arrangements can also be shown in an arrangement according to the FIGS. 1 and 2 be used.

In FIG. 8 an arrangement for cleaning the surface of an applicator roller 132 is shown. This arrangement serves to remove a toner layer 133 and toner debris from the surface of the applicator roller 132 and includes a magnetic roller assembly 134 having a magnetic roller stator 136 having permanent magnets 138, 140, 142, 144 and a rotating hollow roller 162 connected to a drive unit, not shown is driven in the direction of rotation P11.

The toner particles of the toner layer 133 adhere electrostatically to the surface of the applicator roller 132. A drive unit, not shown, drives the applicator roller 132 in the direction of rotation of the arrow P10. A DC power source 160 generates a potential difference DC between the surfaces of the applicator roller 132 and the roller 162. The force of the electric field generated by the potential difference DC on the toner particles of the toner layer 133 is directed toward the surface of the roller 162.

In region 146, ferromagnetic carrier particles are fed to the magnetic roller system 134 by means of a device (not shown). In other embodiments, the magnetic roller system 134 in region 146 may also be supplied with a particle mixture of electrically charged toner particles and ferromagnetic carrier particles.

The orientation of the poles N, S of the magnetic element 138, as well as the alignment of the poles of the magnetic elements 140, 142, 144, radial to the axis of rotation 164, ie that each of the north pole N or the south pole S of a magnetic element 138, 140, 142, 144 faces the inner surface of the roller 162. Magnetic element 140 is disposed in the region of least distance between applicator roller 132 and roller 162. When the poles N, S are regarded as points, the poles N, S of the magnetic element 140 lie approximately on a line 166 shown as a dashed-dotted line, which intersects the axes of rotation 164, 165 of the magnetic roller system 134 and the applicator roller 132.

The longitudinal axis of the magnetic element 138, which intersects the axis of rotation 164, is rotated relative to the straight line 166 by approximately 50 ° counter to the direction of rotation P11 of the roller 162. The longitudinal axis of the magnetic element 142 is about 50 ° relative to the straight line 166 and the longitudinal axis of the magnetic element 144 is rotated relative to the straight line 166 by approximately 100 ° in the direction of rotation P11 of the roller 162. The longitudinal axes of the magnetic elements 142 and 144 extend through the axis of rotation 164 of the magnetic roller system 134.

On the outer surface of the roller 162 form in the areas 148, 150, 152, 154 by the magnetic fields of the magnetic elements 138 to 144 magnetic brushes. The distance between the outer surfaces of the roller 162 and the applicator roller 132 is set so that the magnetic brush formed by the magnetic field of the magnetic member 140 contacts the roller surface of the applicator roller 132 in the region 150. The toner particles of the layer 133 are removed from the surface of the applicator roller 132 and adhere to the ferromagnetic carrier particles of the magnetic brush 150. As already described, this process is assisted by the potential difference DC between the surfaces of the applicator roller 132 and the roller 162 of the magnetic roller system 134 is generated by the DC voltage source 160. The set potential difference DC is, as already in connection with FIG. 7 described, depending on the toner system used.

The transport of the carrier particles between the magnetic members 138 and 140 occurs on the surface of the roller 162. Between the magnetic member 140 and the magnetic member 142, the particle mixture of ferromagnetic carrier particles and the toner particles removed from the surface of the applicator roller 132 is rotated by the rotational movement of the roller 162 transported by the arrow P11.

The magnetic fields of the magnetic elements 142, 144 act in substantially the same direction, with the north poles N of the magnetic elements 142, 144 directed toward the surface of the roller 162. The particle-mixture facing adjacent poles N, N of the two magnetic elements 142, 144 are characterized by the same. The adjacent edges of these magnetic elements 142, 144 are arranged in the direction of rotation at a distance in the range of 0.01 to 10 mm to each other, wherein the order between the adjacent edges need not be constant. The magnetic fields of the magnetic elements 142, 144 are superimposed, with the resulting magnetic field in each point of the space being the resultant vector of addition of the field vectors generated by the magnetic elements 142, 144. In the area between the magnetic elements 142, 144 on the surface of the roller 162, the field vectors have approximately the same magnitude and are directed approximately opposite, so that the resulting magnetic field strength in this area is small, at a distance from about 5 mm to the surface of the roller 162, the field vectors are the same amount, but the directions are not nearly opposite, and there is an area at 5 mm to 15 mm from the surface of the roller 162 at an axis of symmetry between the axes of the poles N, S of the magnetic elements 142, 144 high magnetic field strength and high magnetic flux density, which is also referred to as magnetic far field.

The ferromagnetic carrier particles are pulled in the direction of high magnetic field strengths. This means that the carrier particles correspond to the resulting magnetic field strength be pulled into the region 156 with high magnetic field strength at a distance between 5 mm and 15 mm to the surface of the roller 162. During a rotational movement of the roller 162, carrier particles are subsequently conveyed into the region 152, then pushed into the region 156 and subsequently supplied to the magnetic brush in the region 154, wherein they have a distance to the surface of the roller 162 in the region 156 due to the resulting magnetic field. From the magnetic brush 154, the particle mixture of carrier particles and toner particles falls in the region 158 down into a collecting container, not shown, for example, in a so-called mixed sump of the printer or copier, for the reprocessing of the particle mixture. During the entire cleaning process, toner particles adhere to the carrier particles. The toner particles abraded from the roller surface also adhere to the carrier particles and are transported together with them.

At the in FIG. 8 As shown arrangement is achieved by the arrangement of the magnetic elements 138 to 144, a self-cleaning effect of the conductive surface of the roller 162. This self-cleaning effect is based on the fact that in the two adjacent magnetic elements 142, 144, the north and south poles N, S are aligned approximately in the same direction, whereby on the surface of the roller 162 in the areas 152, 154 respectively a stationary particle mixture is produced rubs on the surface and dissolves toner particles from this. The resulting magnetic field has a low resultant field strength between the magnetic elements 142, 144 on the surface of the roller 162. The transport of the particle mixture during the rotation of the roller 162 takes place in the region 156 at a distance from the surface of the roller 162. The particle mixture remains in the region of the magnetic brush 152, whereby the mixture transport is inhibited. The force with which the particle mixture of ferromagnetic carrier particles and electrically charged toner particles adhere to the surface of the roller 162 is directly dependent on the magnetic field strength of the magnetic field Magnetic elements of Magnetwalzenstators 136 dependent, especially of the magnetic element 142nd

The standing particle mixture adhering to the surface of the roller 162 rubs in the areas 152, 154 the toner particles adhering to the surface of the roller 162. The abraded toner particles adhere to the carrier particles and fall down with them in region 158. The thus cleaned surface of the roller 162 ensures that the continuous electrostatic process in the printer or copier is not affected. Due to the friction between carrier particles and toner particles, a triboelectric charging of the toner particles partially discharged by the preceding electrophotographic process continues to take place.

In the magnetic far field, the north poles N of the magnetic elements 142, 144 can be regarded as a common north pole. The particle mixture is drawn in the direction of the far field from the surface of the roller 162 in the region of high magnetic field strength, which is, however, lower than the field strength on the roll surface at the poles. As a result, the particle mixture remains on the roll surface in the regions at the poles N, N of the magnetic elements 142, 144 and forms accumulations there. In these aggregates, a portion of the particulate mixture is forced away from the roll surface by post-conveyed particulate mixture. The magnetic field strength decreases with the distance to the magnetic element. The formation of the magnet roll stator 136 and the arrangement of the magnetic elements 138-144 on this stator 136 cause the region 158 to form the resulting magnetic field on the surface of the roll 162 so that the mixture of particles moves past falls down.

In other embodiments, arrangements of the magnetic elements are provided which further transport on the roller 162 or a transfer of the particle mixture to an adjacent Magnetic roller system allow. The resulting distance of the particle mixture to the surface of the roller 162 in the region 156 is mainly due to the magnetic field strength of the magnetic elements 142, 144, the distance between the north poles N of these magnetic elements 142, 144 and the outer surface of the roller 162, the thickness and the Material of the roller 162, the roughness of the roller 162 and the peripheral speed of the roller 162 dependent.

The falling of the particle mixture in the region 158 takes place when the centrifugal force tangential to the roller 162, which is caused by the rotation of the roller 162, outweighs the radially acting magnetic force on the particle mixture. A transfer to an adjacent magnetic roller system takes place when the magnetic configuration produces a sufficiently large magnetic flux between the adjacent roller system and the magnetic roller system 134.

The stationary particle mixture at the north poles N of the magnetic elements 142, 144, which act in approximately the same direction, is replaced by a newly introduced particle mixture during a rotary movement of the rollers 132, 162 and thus constantly exchanged. A continuous enrichment of the stationary particle mixture with toner does not occur. To reduce the required mechanical energy acting on the particle mixture during the cleaning process, the roller 162 may be provided with a coating having a very low surface energy, e.g. with Teflon. However, a closed coating should not be used which is electrically insulating so as not to hinder the electrostatic process. For charge transport from and to the roller 162, its surface must be electrically conductive.

In alternative embodiments, low surface energy, highly insulating materials may also be incorporated in the wells of a rough surface structure of the roller 162 become. The remaining conductive areas of the roller 162 then ensure the required charge flow. At the in FIG. 8 arrangement shown no additional devices for removing toner residues on the roller 162 are required. Thus, a very compact structure of the overall system is possible. Additional power to clean the roller 162 is not required. The arrangement has consumables still consumables are needed. This makes it low maintenance. This arrangement can be used for different types of toners that have different toner parameters. In another embodiment, the in FIG. 8 used arrangement for cleaning a magnetic roller 162, which is used for coloring a surface. In the particle mixture for coloring may be included incorrectly charged toner particles. Due to the force acting on these toner particles by a potential difference, these toner particles are not transported to the surface to be inked, but adhere to the surface of the magnetic roller 162 by this force on which they then form an electrically insulating layer. The inventive cleaning of this magnetic roller 162 prevents the formation of such a layer.

In FIG. 9 An arrangement for coloring a latent image on a photoconductor drum 168 in an electrophotographic printer or copier is illustrated. The arrangement is essentially the same as in FIG. 8 shown assembly for cleaning the applicator roller 132 constructed. Like elements have the same reference numerals. The photoconductor drum 168 is moved in the direction of arrow P10 and is spaced from a magnetic roller system 134. The structure of the magnetic roller system 134 has already been described in connection with FIG. 8 described.

At the in FIG. 9 In the arrangement shown in the region 172, a two-component mixture, ie a mixture of particles Toner particles and carrier particles, which has a high proportion by weight of toner particles in the range of 2% to 8%. In region 150, the magnetic field of the magnetic element 140 forms a magnetic brush of the two-component mixture which contacts the surface of the photoconductive drum 168. On this surface of the photoconductor drum 168 there is a latent charge image in which the areas to be inked with toner have a high potential difference DC to the surface of the roller 162. By this potential difference DC, the toner particles are released from the surface of the roller 162 and deposited on the surface of the photoconductor drum 168.

A portion of the toner particles of the bicomponent mixture supplied to the array in area 172 is deposited directly on the surface of the roller 162 and forms a toner layer on the surface of the roller 162. Further, toner particles are imparted to the toner particles by the already described force effects of electric fields. eg in the background area and with incorrectly charged toner particles, deposited on the surface of the roller 162. The standing particulate mixture in the regions 152, 154 rubs on the surface of the roller 162 by roller-shaped rotating motions within the particle mixture. The toner particles on the surface are abraded, as already described in connection with FIG FIG. 8 described. The formation of the stationary particle mixture, the transport and the falling of the particle mixture in the region 158 likewise take place as in FIG FIG. 8 illustrated arrangement. At the in FIG. 9 In particular, such embodiments are possible, already in connection with FIG. 8 have been described. The so-called memory effect is reflected in an electrophotographic printer or copier with an arrangement FIG. 9 effectively avoided by cleaning the roller 162.

In FIG. 10 is the magnetic roller system 134 after the FIGS. 8 and 9 shown in an enlarged view. They are the indicated between the axes 174 to 177 of the poles N, S of the magnetic elements 138 to 144 enclosed angle. The axes 174 to 177 of the magnetic elements 138 to 144 each have an angular distance of about 50 ° from each other. When setting the angular distance between the axes 176, 177 of the poles N, S of the same aligned magnetic elements 142, 144, the magnetic field strength of the magnetic elements 142, 144, the size of the magnetic elements 142, 144 and the absolute distance between the two magnetic elements 142, 144th to take into account. Accordingly, in other embodiments, the angle to be set may also have a value deviating from 50 °, for example, this angle may be in the range between 10 ° and 100 °.

In FIG. 11 FIG. 12 shows a section of the magnetic roller system 134 together with the particle mixture of toner particles and carrier particles during a rotational movement of the roller 162. The movements of the particle mixture can be recognized by the arrows P12 to P16. The particle mixture is transported from the south pole S of the magnetic element 140 to the north pole N of the magnetic element 142 in the arrow direction of the arrow P12 on the surface of the roller 162 by the rotational movement thereof. As already described, as a result of the north poles N of the magnetic elements 142, 144, which point approximately in the same direction, the stationary particle mixture in the region of the north pole N of the magnetic element 142 on the surface of the roller 162 occurs.

As a result of the quantity of the particle mixture subsequently conveyed in the direction of the arrow P12 on the surface of the roller 162 and its rotational movement, a rotating roller-shaped movement and a roller-shaped turbulence and mixing within the stationary particle mixture are produced in the stationary particle mixture on the surface of the roller 162 in the region 152. The movement of the particle mixture in the region 152 can be recognized by the arrow P13. The parts of the standing particle mixture, which are in the far magnetic field in the outer region 152 of the magnetic brush by the increasing accumulation of the magnetic particle Particle mixtures are pushed and pulled, as already described, in the direction of arrow P14 in the common magnetic far field of the magnetic elements 142, 144, have in the region 156 at a distance from the surface of the roller 162, wherein the particle mixture by the continuous Nachfördern in the area 152 is transported in the direction of the arrow P14 through the area 156 toward the area 154.

A portion of the particle mixture is supplied to the region 154 in front of the north pole N of the magnetic element 144 at a distance from the surface of the roller 162 in the region 156 corresponding to the arrow P15. The remaining part falls directly into a collecting container, not shown, e.g. into a mixed sump of the printer or copier. The magnetic field of the magnetic element 144 also generates a stationary mixture of particles on the surface of the roller 162 in the area 154, wherein there is also a rotating cylindrical movement in the particle mixture through which toner particles are rubbed off the surface of the roller 162. This rotating movement within the standing particle mixture is represented by the arrow P16.

Continuous delivery of the particulate mixture into region 154 causes an accumulation of particles in this region 154. In this process, particles are forced outward into regions of low magnetic field strength, i. away from the roll surface. The force of the magnetic field decreases with increasing distance to the magnetic element 144, and a part of the particle mixture in the outer region 154 of the magnetic brush falls downwards due to gravity. The falling particle mixture is shown in the region 158.

In an alternative embodiment, the north and south poles N, S of the magnetic elements 142, 144 are opposite to those in FIG FIG. 11 arranged orientation, ie, the south poles S of the magnetic elements 142, 144 act in approximately the same direction and are facing the surface of the roller 162. The arrangements according to FIGS. 1 to 11 are sectional views of roller assemblies. The magnetic elements shown therein are preferably arranged on the entire width of the respective magnetic roller. The width of the magnetic roller is preferably greater than or equal to the possible printing width of the printer or copier. Also, the magnetic elements may be composed of a plurality of individual magnets. As the longitudinal axis of the magnetic elements, the axis is denoted by the poles N, S of the magnetic elements in the figure descriptions. In further embodiments, the counter poles N, S of the particle mixture facing poles N, S act by the structural design of the magnetic elements not in the opposite direction. By this constructive design, the shape of the raised accumulations of the particle mixture, ie the magnetic brushes and the stationary particle mixtures, can be influenced. In this embodiment, the poles N, N act approximately in the radial direction.

In FIG. 12 For example, the field distribution in the near-field magnetic field is shown directly on the surface of the roller 162 of the magnetic roller system 134 in a polar coordinate system. On the axis of the polar coordinate system, the magnetic flux density is plotted. The numerical values given from 0 to 1 when multiplied by 2000 indicate the magnetic flux density in Gauss. When multiplied by 0.2, these numbers indicate the magnetic flux density in Tesla. The longitudinal axis through the magnetic element 140 is in the diagram the 90 ° axis. The orientation of the resulting magnetic field, which produces the magnetic flux density, is characterized by the letters N and S arranged next to the curves in the diagram. The flux density is directly proportional to the magnetic field strength, the magnetic flux density being the product of absolute permeability and magnetic field strength. In area 152, the in FIG. 11 illustrated magnetic element 142 on the surface of the roller 162 has a maximum magnetic flux density of 1800 Gauss. This also generates on the surface of the roller 162 in FIG. 11 shown magnetic element 144 has a maximum flux density of about 1780 Gauss. In region 156, a minimum resultant flux density of about 100 Gauss is obtained.

In FIG. 13 the field distribution in the far-field magnetic field is shown at a distance of about 9 mm from the surface of the roller 162. The scale graduation agrees with the graduation of the scale FIG. 12 shown diagram. In the in FIG. 13 As shown in the diagram, the magnetic far field in the area 156 between the magnetic elements 142, 144 at a distance of about 9 mm to the surface of the roller 162 has a relatively high magnetic flux density of up to 950 Gauss. The maximum difference in magnetic flux density in region 156 between the surface and a region 9 mm apart from the surface is 850 Gauss. The magnetic field is thus at a distance of 9 mm in the region 156 many times greater than at the surface of the roller 162. Due to the strong magnetic far field, as described, the detachment of the particle mixture from the surface of the roller 162 in the area 156 and the stationary Particle mixtures in the areas 152, 154.

In addition, the in the FIGS. 8 and 9 described arrangement may be provided in other embodiments with a squeegee, which is arranged, for example, at a predetermined distance in the direction of rotation of the roller 162 after the magnetic element 144. Thus, in further embodiments, the in FIG. 8 and 9 shown arrangements with elements of the in FIGS. 4 and 5 arrangements are shown combined. All magnetic elements can be designed depending on the requirements of the field strength and the embodiment as electromagnets or permanent magnets. Also in the FIGS. 4 and 5 8 and 9 are used to apply toner and to clean surfaces in arrangements similar to those shown in Figs FIGS. 1 and 2 constructed arrangements are constructed.

In all embodiments, it is possible to superimpose the potential differences DC generated by the DC voltage sources with potential differences generated by AC voltage sources. If a plurality of DC voltage sources are provided in one embodiment, only individual potential differences generated by these DC voltage sources can be superimposed on the potential difference generated by one or more AC voltage sources. The potential difference generated by the AC voltage source causes a movement and thereby a loosening of the toner particle accumulation in the two-component mixture.

Although in the drawings and in the foregoing description preferred embodiments have been shown and described in detail, this should be considered as purely exemplary and non-limitative of the application. It is to be understood that only the preferred embodiments are shown and described and all changes and modifications as presently and in the future within the scope of the invention are intended to be protected.

LIST OF REFERENCE NUMBERS

10

roll arrangement

12

applicator

14

first magnetic roller assembly

16

second magnetic roller assembly

18

magnetic brush

20

prepared two-component mixture

22

metering blade

24

rotating hollow roller

26

Magnetwalzenstator

28, 30, 32, 34

permanent magnet

36

toner layer

38, 40, 42

toner,

44

rotating hollow roller

46

Magnetwalzenstator

48, 50, 52

permanent magnets

54

Range of transmission of the particle mixture

56, 58, 60

Area with magnetic brush

62

down falling particle mixture

64

roll arrangement

66

guide element

68, 70

axis of rotation

72, 74, 76

DC voltage sources

77

Photoconductor drum

78

applicator

79

toner layer

80

Magnetic roller system

81

rotating hollow roller

82

doctor

84

Magnetwalzenstator

86, 88, 90, 92, 94, 96, 98,

100 permanent magnet

102

fed particle mixture

104, 106, 108, 110

Area with magnetic brush

112

standing particle mixture

114

sloping particle mixture

116

DC voltage source

118

toner particle

120

fed particle mixture

122

DC voltage source

123, 124, 125, 126

Normal through poles

127

axis of rotation

128

Area with magnetic brush

130

standing particle mixture

132

applicator

133

toner layer

134

Magnetic roller system

136

Magnetwalzenstator

138, 140, 142, 144

magnetic element

146

supplied carrier particles

148, 150, 152, 154

Area with magnetic brush

156

Area with lifted from the roll surface particle mixture

158

discarded particle mixture

160

DC voltage source

162

rotating hollow roller

164, 165

axis of rotation

166

Normal through poles

168

Photoconductor drum

169

colored area of the latent charge image

170

DC voltage source

172

Area for feeding the particle mixture

174, 175, 176, 177

Longitudinal axis of the magnetic element

P1 to P16

directional arrows

Claims (43)

1. A device for cleaning a roller in an electrophotographic printer or copier,
   in which inside of the roller (134) at least two magnet elements (142, 144) are arranged stationarily,
   on the surface of the roller (134) a particle mixture is conveyed which includes electrically charged toner particles and ferromagnetic carrier particles,
   and in which adjacent poles (N, N) of both magnet elements (142, 144) facing the particle mixture are identical and, viewed in the rotation direction of the roller (134), are arranged at a distance from one another such that the particle mixture on the surface of the roller (134) forms at the magnet elements (142, 144) at least one raised accumulation,
   characterized in that the distance between the magnet elements (142, 144), the roughness of the surface of the roller (134), the distance of the magnet elements to the surface of the roller (134) and the field strength of the magnet elements (142, 144) are dimensioned such that in an area of the accumulation given a rotation motion of the roller (134) movements are generated in the particle mixture, by which the carrier particles abrade on the surface of the roller (134) and in doing so remove at least a part of the toner particles present on the surface of the roller (134) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (134) after the magnet elements (142, 144).
2. The device according to claim 1, characterized in that the forces acting on the carrier particles by the resulting magnetic field of the two magnet elements (142, 144) detach at least a part of the particle mixture in a partial area between the magnet elements (142, 144) from the roller surface (162), and that the particle mixture in the area of the magnet elements (142, 144) is moved such given a rotation motion of the roller (134) that the carrier particles abrade on the surface of the roller (134).
3. The device according to claim 2, characterized in that by way of the motion of the particle mixture at least a part of the toner particles that are electrostatically attached to the outer circumferential surface of the roller (134) are abraded from this surface.
4. The device according to one of the preceding claims, characterized in that the further magnet elements (38, 140) whose poles (N, S) are respectively aligned radially relative to the roller are arranged inside the roller (134).
5. The device according to one of the preceding claims, characterized in that a doctor blade (82) is arranged at a distance (A1) in the range of 0.1 to 0.4 mm from the roller surface (162).
6. The device according to claim 5, characterized in that, when viewed in rotation direction (P11) of the roller (134), the first and second magnet element (142, 144) are arranged in front of the doctor blade (82) in proximity thereto.
7. The device according to claim 5 or 6, characterized in that the doctor blade (82) is arranged in the lower roller half.
8. The device according to one of the preceding claims, characterized in that the outer circumferential surface of the roller (134) has a roughness in the range of 1 to 5000 µm.
9. The device according to one of the preceding claims, characterized in that the roller surface (162) comprises aluminium, chromium, nickel, copper, conductive plastic and/or a plastic with a conductive layer.
10. The device according to one of the preceding claims, characterized in that the surface of the roller (134) is a flame-spraying-method-formed surface.
11. The device according to one of the preceding claims, characterized in that the magnet elements (138 to 144) are permanent magnets.
12. The device according to one of the preceding claims, characterized in that the two magnet elements (142, 144) have at the adjacent poles N, N facing towards the particle mixture a separation of adjacent edges in the range of 0.01 to 10 mm from one another, viewed in the rotation direction of the roller.
13. A method for cleaning a roller in an electrophotographic printer or copier,
    in which at least two magnet elements (142, 144) are arranged stationarily inside a roller (134),
    on the surface of the roller (134) a particle mixture is conveyed, that comprises electrically charged toner particles and ferromagnetic carrier particles,
    and in which adjacent poles (N, N) of both magnet elements (142, 144) facing the particle mixture are identical and, viewed in the rotation direction of the roller (134), are arranged at a distance from one another such that at the magnet elements (142, 144) on the surface of the roller (134) at least one raised accumulation is formed that contains carrier particles, characterized in that by measurement of the distance between the magnet elements (142, 144), the roughness of the surface of the roller (134), the distance of the magnet elements to the surface of the roller (134) and the field strength of the magnet elements (142, 144) in an area of the accumulation given a rotation motion of the roller (134) movements are generated in the particle mixture, by which the carrier particles abrade on the surface of the roller (134) and in doing so remove at least a part of the toner particles present on the surface of the roller (134) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (134) after the magnet elements (142, 144).
14. An electrophotographic printing or copying device,
    in which a toner application unit (14) applies electrically charged toner particles to the surface of a first carrier element (12),
    at least a part of the toner particles is transferred from the first carrier element (12) to a second carrier element,
    a cleaning unit (16) which removes from the first carrier element (12) toner particles remaining on the first carrier element after the transfer,
    the cleaning unit includes a roller (81) which is arranged at a distance from the first carrier element (12),
    at least one magnet element (96) is arranged stationarily inside a roller (81),
    on the surface of the roller (81) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    a doctor blade (82) is arranged at a distance to the roller surface,
    the magnet element (96) is arranged in front of the doctor blade (82) in proximity thereto viewed in rotation direction of the roller (81),
    the doctor blade (82) strips off at least a part of the particle mixture present on the roller surface,
    the magnetic field of the magnet element (96) keeps parts of the particle mixture stripped off by the doctor blade (82) in the area of the doctor blade (82) so that the particle mixture forms a raised accumulation on the surface of the roller (81),
    and in which in the area of the doctor blade (82), by the rotation motion of the roller (81) and by the fixedly positioned doctor blade (82) movements are generated in the particle mixture by which the carrier particles abrade on the surface of the roller (81) and thus remove at least a part of the toner particles present on the surface of the roller (81) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (81) after the magnet element (96) on the doctor blade (82).
15. A method for operating an electrophotographic printing or copying device,
    in which with the aid of a toner application unit (14) electrically charged toner particles are applied to the surface of a first carrier element (12),
    at least a part of the toner particles is transferred from the first carrier element (12) to a second carrier element,
    with the aid of a cleaning unit (16) the toner particles (38 to 42) remaining on the first carrier element (12) after the transfer are removed from the first carrier element (12),
    the cleaning unit (16) includes a roller (81) which is arranged at a distance from the first carrier element (12),
    at least one magnet element (96) is arranged stationarily inside a roller (81),
    on the surface of the roller (81) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    a doctor blade (82) is arranged at a distance to the roller surface,
    the magnet element (96) is arranged in front of the doctor blade (82) in proximity thereto viewed in the rotation direction of the roller (81),
    by the doctor blade (82) at least a part of the particle mixture present on the roller surface is stripped off,
    by the magnetic field of the magnet element (96) parts of the particle mixture stripped off by the doctor blade (82) are kept in the area of the doctor blade (82) so that the particle mixture forms a raised accumulation on the surface of the roller (81),
    and in which in the area of the doctor blade (82) by the rotation motion of the roller (81) and by the fixedly positioned doctor blade (82) movements are generated in the particle mixture by which the carrier particles abrade on the surface of the roller (81) and thus remove at least a part of the toner particles present on the surface of the roller (81) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (81) after the magnet element (96) on the doctor blade (82).
16. An electrophotographic printing or copying device,
    in which a toner application unit (14) applies electrically charged toner particles to the surface of a first carrier element (12),
    at least a part of the toner particles is transferred from the first carrier element (12) to a second carrier element,
    a cleaning unit (16) which removes from the first carrier element (12) the toner particles remaining on the first carrier element (12) after the transfer,
    the cleaning unit (16) includes a roller (134) which is arranged at a distance from the first carrier element (12),
    at least two magnet elements (142, 144) are arranged stationarily inside the roller (134),
    on the surface of the roller (134) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    and in which adjacent poles (N, N) of both magnet elements (142, 144) facing the particle mixture are identical and, viewed in the rotation direction of the roller (134), are arranged at a distance from one another such that the particle mixture on the surface of the roller (134) forms at the magnet elements (142, 144) at least one raised accumulation,
    characterized in that the distance between the magnet elements (142, 144), the roughness of the surface of the roller (134), the distance of the magnet elements to the surface of the roller (134) and the field strength of the magnet elements (142, 144) are dimensioned such that in an area of the accumulation given a rotation motion of the roller (134) movements are generated in the particle mixture, by which the carrier particles abrade on the surface of the roller (134) and in doing so remove at least a part of the toner particles present on the surface of the roller (134) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (134) after the magnet elements (142, 144).
17. The device according to claim 16, characterized in that a doctor blade (82) is arranged at a distance from the roller surface.
18. The device according to claim 17, characterized in that, viewed in the rotation direction of the roller, the first and second magnet elements (142, 144) are arranged in front of the doctor blade (82) in proximity to it.
19. The device according to one of the claims 16 to 18, characterized in that the first and/or second carrier element (12) is a roller or a band.
20. The device according to one of the claims 16 to 19, characterized in that the first carrier element (12) is an application element and the second carrier element is a photoconductor.
21. The device according to one of the claims 16 to 19, characterized in that the first carrier element (12) is a photoconductor and the second carrier element is a carrier material to be printed or a transfer element.
22. The device according to one of the claims 16 to 21, characterized in that the rotation direction of the roller (134) of the cleaning unit (16) is identical with the rotation direction of the first carrier element (12).
23. The device according to claim 22, characterized in that a magnet element (50) is arranged stationarily inside the roller at the position having the smallest distance between the first carrier element (12) and roller (44), and that the axis of the poles (N, S) of the magnet element (50) runs radially to the roller (44).
24. The device according to one of the claims 16 to 23, characterized in that the amount of ferromagnetic carrier particles conveyed on the roller surface of the cleaning unit (16) includes a predetermined portion of toner particles.
25. The device according to one of the claims 16 to 24, characterized in that the transfer of the particle mixture from the toner application unit (14) to the cleaning unit (16) takes place with the aid of the magnetic field of at least one magnet element (34, 48).
26. The device according to one of the claims 16 to 25, characterized in that the transfer of the particle mixture from the toner application unit (14) to the cleaning unit (16) takes place with the aid of a guide element (66) arranged between toner application unit (14) and cleaning unit (16).
27. The device according to claim 26, characterized in that the guide element (66) is a guide sheet.
28. The device according to one of the claims 23 to 27, characterized in that several magnet elements (28 to 34, 48 to 52) are arranged inside the roller (24, 44), the axis of the poles (N, S) of each magnet element (28 to 34, 48 to 52) being oriented radially to the rotation axis.
29. The device according to one of the claims 23 to 27, characterized in that the magnet element or the magnet elements (28 to 34, 48 to 52) are permanent magnets.
30. The device according to one of the claims 16 to 29, characterized in that between the toner application unit (14) and the first carrier element (12) a first potential difference (DC1-DC2) and/or that between the cleaning unit (16) and the first carrier element (12) a second potential difference (DC1-DC3) is present.
31. The device according to claim 30, characterized in that the electrostatically charged toner particles are electrically negatively charged, that the potential of the first carrier element (12) is positive relative to the potential of the toner application unit (24) and negative relative to the potential of the cleaning unit (44).
32. The device according to claim 30, characterized in that the electrostatically charged toner particles are electrically positively charged, that the potential of the first carrier element (12) is negative relative to the potential of the toner application unit (24) and positive relative to the potential of the cleaning unit (44).
33. A method for operating an electrophotographic printing or copying device,
    in which with the aid of a toner application unit (14) electrically charged toner particles are applied to the surface of a first carrier element (12),
    at least a part of the toner particles is transferred from the first carrier element (12) to a second carrier element,
    with the aid of a cleaning unit (16) the toner particles remaining on the first carrier element (12) after the transfer are removed from the first carrier element (12),
    the cleaning unit (16) includes a roller (134) which is arranged at a distance from the first carrier element (12),
    at least two magnet elements (142, 144) are arranged stationarily inside the roller,
    on the surface of the roller (134) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    and in which adjacent poles (N, N) of both magnet elements (142, 144) facing the particle mixture are identical and, viewed in the rotation direction of the roller (134), are arranged at a distance from one another such that on the surface of the roller (134) at the magnet elements (142, 144) at least one raised accumulation is formed that contains carrier particles,
    characterized in that the distance between the magnet elements (142, 144), the roughness of the surface of the roller (134), the distance of the magnet elements to the surface of the roller (134) and the field strength of the magnet elements (142, 144) are dimensioned such that in an area of the accumulation given a rotation motion of the roller (81) movements are generated in the particle mixture, by which the carrier particles abrade on the surface of the roller (81) and in doing so remove at least a part of the toner particles present on the surface of the roller (134) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (134) after the magnet elements (142, 144).
34. A device for cleaning a roller in an electrophotographic printing or copying device,
    in which inside the roller (81) at least one magnet element (96) is stationarily arranged,
    on the surface of the roller (81) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    a doctor blade (82) is arranged at a distance to the roller surface,
    the magnet element (96) is arranged in the rotation direction of the roller (81) in front of the doctor blade (82) in proximity to it,
    the doctor blade (82) strips off at least a part of the particle mixture present on the roller surface,
    the magnetic field of the magnet element (96) keeps parts of the particle mixture stripped off by the doctor blade (82) in the area of the doctor blade (82) so that the particle mixture forms a raised accumulation on the surface of the roller (81),
    and in which in the area of the doctor blade (82) by the rotation motion of the roller (81) and by the fixedly positioned doctor blade (82) movements are generated in the particle mixture by which the carrier particles abrade on the surface of the roller (81) and thus remove at least one part of the toner particles present on the surface of the roller (81) from the surface, and that at least one part of the particle mixture is removed viewed in the rotation direction of the roller (81) after the magnet element (96) on the doctor blade (82).
35. The device according to claim 34, characterized in that the axes of the poles (N, S) of the magnet element (96) are oriented radially to the rotation axis of the roller (81).
36. The device according to claim 34 or 35, characterized in that several magnet elements (86 to 100) are arranged inside the roller (81) and the axes of the poles (N, S) are each oriented radially to the roller (81), the poles (N, S) of adjacent magnet elements (86 to 100) having opposite effective directions.
37. The device according to one of the claims 34 to 36, characterized in that the doctor blade (82) is arranged in the lower half of the roller.
38. The device according to one of the claims 34 to 37, characterized in that the outer circumferential surface of the roller (81) has a roughness in the range of 1 to 5000 µm.
39. The device according to one of the claims 34 to 38, characterized in that the roller surface comprises aluminium, chromium, nickel, copper, conductive plastic and/or a plastic with a conductive layer.
40. The device according to one of the claims 34 to 39, characterized in that the surface of the roller (81) is a flame-spraying-method-formed surface.
41. The device according to one of the claims 34 to 40, characterized in that the magnet element (96) or the magnet elements (86 to 100) are permanent magnets.
42. The device according to one of the claims 34 to 41, characterized in that between the doctor blade (82) and roller surface a distance (A1) is set in the range of 0.1 to 0.4 mm.
43. A method for cleaning a roller in an electrophotographic printing or copying device,
    in which inside the roller (81) at least one magnet element (96) is stationarily arranged,
    on the surface of the roller (81) a particle mixture is conveyed that comprises electrically charged toner particles and ferromagnetic carrier particles,
    a doctor blade (82) is arranged at a distance to the roller surface,
    the magnet element (96) is arranged in the rotation direction of the roller (81) in front of the doctor blade (82) in proximity to it,
    with the aid of the doctor blade (82) at least a part of the particle mixture present on the roller surface is stripped off,
    parts of the particle mixture stripped off by the doctor blade (82) are kept by the magnetic field of the magnet element (96) in the area of the doctor blade (82),
    so that a raised accumulation is formed by the particle mixture on the surface of the roller,
    and in which in the area of the doctor blade (82) by the rotation motion of the roller (81) and by the fixedly positioned doctor blade (82) movements are generated in the particle mixture by which the carrier particles abrade on the surface of the roller (81) and thus remove at least a part of the toner particles present on the surface of the roller (81) from the surface, and that at least a part of the particle mixture is removed viewed in the rotation direction of the roller (81) after the magnet element (96) on the doctor blade (82).

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