EP0713155A2 - Anisotropic printing device and method - Google Patents

Abstract

The printing device uses a recording component, e.g. a roller (12), with a dielectric outer surface (12a) having a matrix of conductivity points (42). A cooperating printing head (14) positioned adjacent the dielectric surface is used for generating variable electrical charges at the dielectric surface representing parts of a recorded image, in response to voltages applied across sets of voltage supply points within the printing head. Pref. the conductivity points are embedded in the dielectric layer, with a conductive underlying layer coupled to each of these points via couplings with a resistance which is less than that of the dielectric.

Description

Cross Reference to Related Applications This application is a partial extension of U.S. Application Serial No. 08 / 342,135, filed November 18, 1994.

Field of invention

The invention relates to an apparatus and method for printing, more particularly to an apparatus and method for electrophoretic and dielectrophoretic printing.

Background of the Invention (Prior Art)

Digital systems for producing print media have become widespread in the field of graphic printing. The systems typically work with a digital database, based on the printing forms, and either on a plate that is then mounted in a press or deposited on the press roll of a press. In both cases, the print information can be recorded in the form of binary signals, which together represent the "signature image". These plates or rollers are always separated according to the main color components of the original image, e.g. cyan, magenta, yellow and black. The color components can be obtained sequentially or simultaneously with parallel recording heads. The recording heads used in prior art devices are characterized by: 1) several laser beams which travel across the plate or cylinder line by line at high speed, 2) several laser diodes which spiral through the recording medium when writing several lines, or 3) groups (arrays) of light-emitting diodes (LEDs) for the serial recording of a spiral-shaped pattern, which represents a single-color sheet.

According to the prior art, the recording medium is light-sensitive in each case, and this always requires a light-tight recording and pressure chamber in order to prior art devices to prevent accidental exposure of the recording medium. The first method uses a waterless method for picking up offset ink and then transferring it to the printing substrate.

The second method uses a special, liquid electrostatic toner made of charged particles, and these particles are electrostatically deposited on the printing component and from there on an offset cloth, which in turn transfers the toner electrostatically to a sheet of paper or other printing medium.

In the third method, dry toner is xerographically deposited on the photosensitive printing component, from where the toner is transferred directly to the printing medium using a standard xerographic method.

The aforementioned systems according to the prior art have various shortcomings. They are primarily designed for simple printed matter in small editions. The quality of the color image reproductions in these systems varies greatly in terms of color type, resolution and degree of blackening. Also, prior art devices typically have significant speed limitations.

In particular, the relatively slow recording, writing and printing speeds interfere with these devices. In addition, the set-up times for these systems are considerably shorter than for classic graphics systems, but the sheet-cost factors are considerably higher.

Finally, systems that use charged toner typically require relatively large toner particles, i.e. above or at least equal to 5 microns so that the toner particles can carry a uniform charge.

Without a uniform charge, it would be difficult to control the toner particles and dust problems would arise.

Printing devices are also known which operate with a printing roller which acts both as an electrode and as a dielectric signal storage component works. The platen has a heated, dielectric, low color phobic recording surface in rolling contact with a platen that can carry a print medium such as paper. Beneath this dielectric surface is a conductive layer that acts as an electrode when an image is written or recorded on the platen. Arranged around the printing roller is a writing station with a printhead, an inking station via which different-colored thermoplastic printing inks can be dispensed, and an ink transfer station, which is actually the gap between the two rollers. At the writing station, a printhead responsive to incoming data is stored on the platen while successive revolutions of the same emit electronic latent images representing the color components or signatures of an original image, and each such image consists of a pattern of electrostatic charge areas or dots, the field strengths of which correspond to Gray or color values vary. When the printing roller rotates, this charge pattern is transported to the application station, at which a heated application head presents the surface of the plate cylinder with successive revolutions of the cylinder, special thermoplastic printing inks, the actual colors of which, as a rule, but not necessarily, match the colors of the surface mentioned images recorded on the printhead. These colors usually include cyan, magenta, yellow and black in subtractive color printing.

When a recorded area on the platen surface passes the application station, the field lines from the electrostatic charge areas or pixels that make up the latent image cause "pieces" of the melted ink to be removed from the application head. The field lines can change briefly as they pass under the application head or not, depending on the presence of earthed or pre-stressed components of the application head. The quantities The color elements are directly proportional to the field strengths of the charge areas. Thus, if the surface of the printing roller, in spite of its color-phobic nature, receives variable amounts of color at these image points, which are related to the field strengths at these points, the latent image on this surface is effectively obtained. The color is held on this surface by electrostatic forces when the developed images are transported to the ink transfer station.

At the ink transfer station, the colors - still in the molten state on the printing roller - and the relatively cool paper on the paper roller are rotated through the gap between the two rollers. At the line of contact, the ink changes phase so that the color changes from a liquid state to a solid state, so that the ink is immediately transferred to the paper. This adhesion and the color-phobic nature of the roller surface overcome the electrical forces that hold the ink on the plate cylinder, so that essentially complete transfer of the ink takes place where the ink touches the paper. As a result, the image printed on the paper of the paper roll corresponds exactly to the latent image embossed on the plate cylinder.

A printing device of the above type is described, for example, in U.S. Patent 5,325,120, the content of which is hereby incorporated by reference.

Most recently, Dr. Manfred R. Kuehnle at IMX Corporation, Billerica, MA, developed a completely new printing technique based on dielectrophoresis. According to this technique, electrostatic images can be recorded on a platen or other printing component with a printhead similar to that described in the above patent.

In this case, however, the printing component has an anisotropic recording surface, so that the electrostatic charge areas generated on this surface by the print head are uniform or result in inhomogeneous electrostatic fields at the location of each picture element (pixel), with a field beyond the surface of the printing component. If these charged areas of the printing component are moved against the development medium, ie dielectric printing ink or toner, the field induces an electrical dipole moment in the medium in question by dielectric polarization. The polarized medium obtained is drawn through the field gradient to the area of maximum field strength. In other words, the polarization charge at one end of the medium in the stronger field is pulled more towards the stronger field, while the opposite and equal polarization charge at the other end of the medium is pushed back less strongly in the other direction because the field there is weaker. The development medium thus migrates to the areas of the pressure component in which the fields are strongest and adheres there.

Dielectrophoretic printing therefore enables electrostatic printing without the need for charged ink or charged toner particles. This means that while the development medium is polarized because the positive and negative charges are located on the medium due to the presence of a uniform electrostatic field, the net charge on the medium is zero. In contrast to the usual charged printing inks or toner particles, such an uncharged medium is not bound to the surface by image charge attraction or by interactions with a charge-induced polarization of the dielectric printing roller. For this reason, it is easier to obtain a clean, fog-free developed image on the printing roller than is possible with the images developed using electrically charged printing inks or toner particles.

A uniform electric field on the dielectric surface of a printing component, such as a printing roller, can be applied to various Because of being won. For example, as the Dr. Kuehnle provides for writing on the surface with a wire on which there is a periodically varying voltage, for example alternating voltage or rectified alternating voltage (direct voltage), the amplitude of the voltage varying in accordance with the digital input signal on the printing device.

Alternatively, the uniform field for the printing component can be brought about by the structure of the printing component itself. More specifically, the printing component can be provided with a dielectric surface that is anisotropic in that it contains a pattern of conductive paths that extend from the surface of the dielectric layer to a ground plane below that layer. One way to obtain these grounded areas or field endpoints on the dielectric layer is to form the layer so that it contains many crystallites with so-called grain boundaries, the electrical conductivity of which is considerably greater than that within the crystallites themselves. These interface zones between the crystallites result in a periodic pattern of low resistance paths through the dielectric layer to the ground plane, whereby anisotropy of the dielectric layer is achieved. If electrical charges are then brought to the surface, for example by the microtunnel write head described in the above patent, the charges on the surface of the printing component are arranged in such a way that a maximum field strength is achieved around each grounding point with a steep drop in the field strength between the grounding points .

However, a pressure component such as that described would be desirable, the anisotropy of which does not depend on the morphology or molecular structure of the dielectric layer.

In areas other than direct printing, dielectric surfaces have been applied to a metal roller to aid in the transfer of uniform amounts of charged toner. For example, U.S. Patent No. 5,315,061 describes a donor or development roller for transferring a charged toner onto a photoconductor belt for developing a latent image on the photoconductor belt. The donor roller is made of metal and small dielectric bodies are distributed over the surface. When friction is charged on the entire surface of the donor roller, electrostatic fields are formed between the dielectric bodies and the metal surface. Small closed electric fields - so-called "microfields" - are thus formed on the surface of the donor roller. These microfields help attract the charged toner to the surface of the donor roller. A squeegee then sets the toner to a uniform thickness.

The donor roller of U.S. Patent 5, 315,061 provides a homogeneous and uniform amount of charged toner to allow development of an image on a photoconductor belt. No images are written directly on the donor roller, rather the images are written on the photoconductor tape.

Also, U.S. Patent No. 3,739,748 shows a donor roller for transferring charged toner onto a xerographic drum. The donor roller has a dielectric surface which is contacted by pins connected to a voltage source.

The pens cannot write images on the donor roller, but rather only facilitate the gray value reproduction of the image which is written on the xerographic drum by an exposure device.

Neither of these two donor rollers and no related devices cause inhomogeneous microfields over the surface of a printing component.

SUMMARY OF THE INVENTION The present invention accordingly aims to provide an optoelectric printing device, the printing component of which has an anisotropic dielectric recording layer. Another purpose of the invention is the indication of such a device that is relatively easy to manufacture.

Another purpose of the invention is to provide such a device in which strong inhomogeneous fields can be maintained over the surface of the pressure component.

Another purpose of the invention is to provide a device with a printing component on which electronic images can be recorded with very good resolution.

Another purpose of this invention is to provide effective write heads in conjunction with a dielectric surface that can record electronic images with very good resolution.

Other purposes are likely to be apparent in part and will be apparent in part from the following.

Accordingly, the invention included features of construction, combination of elements, and arrangement of parts, as will be exemplified from the following detailed description, and the scope of the invention is defined in the claims.

The printing component includes a substrate that supports a thin layer of dielectric material, the resistivity of which is very high, for example about 1015 ohms / cm, to prevent premature discharge. A conductive layer can be provided in the middle between the substrate and the dielectric layer. This conductive layer can be grounded or can remain ungrounded, as will be described below in connection with the various embodiments. A pattern of minute conductive areas or dots may be present on the work surface or within the dielectric layer. If present, the dots are preferably arranged periodically with a period at least equal to or smaller than the size of a resolution element or picture element (pixel) of the electronic image that is to be recorded on the printing component. The conductive dots are made of a material with a smaller resistivity than that of the dielectric preferably of a metallic type, but in certain applications can also be electrically connected to the conductive level below the dielectric layer. In addition, in many applications, an adhesive coating covers the surfaces of the dielectric layer and the conductive dots, so that the recording surface of the printing component is slightly ink-phobic. The cross sections of the points can be circular, but various other shapes are also possible, including rectangular or toroidal.

In some applications, electrical charges can be applied to the recording surface of the print component by a microtunnel type print or write head as described in U.S. Patent No. 5,325,120. Typically, these charges represent an image recorded on the print component. These charges result in uniform electric fields that are strongest around the conductive dots. The mean voltage around each point is also a monotonous function of the gray value at the relevant point in the electronic image.

An important aspect is that the uniform fields generated by the conductive dots on the dielectric surface of the recording component extend beyond the surface. Thus, when this surface is placed against a source of a dielectric development medium such as ink or toner, the electric fields induce an electric dipole moment in the medium by dielectric polarization, and the medium becomes proportional to the strengths of the charged surfaces of the recording surface by dielectrophoresis Charges pulled. The development medium thus accumulates around each conductive point in an amount that increases monotonically with the field strength at the location in question, thereby developing the electronic image recorded on the printing component.

Similar non-uniform fields can be obtained on a print component whose conductive dots are not grounded, using a print or write head, as will be described later, which has multiple electrical contacts that carry image-dependent voltages. In this case, the relatively strong fields around the points decrease steeply with increasing distance from the points. Such an electrical contact print or write head can also be used to generate positive and negative charges that charge the dielectric surface, as will be described later.

Uneven fields can also be obtained by writing directly to a dielectric surface with or without dots using a write head similar to the electrical contact write head, but using alternating current instead of direct current. In this write head, an ungrounded conductive layer can be provided below the dielectric layer, as will be described later.

If there are conductive dots, the dots and any paths or other connections to the ground plane in the dielectric position of the pressure component can be formed using methods of conventional circuit board technology. The printing components can thus be manufactured relatively inexpensively in large numbers.

As a result, printing components such as the described are likely to find widespread use in feeding and other printing devices for dielectrophoretic and electrophoretic printing.

Brief description of the drawings

• FIG. 1 eine isometrische (dreidimensionale) Ansicht des Druckgeräts, einschließlich einer Druckwalze, entsprechend der Erfindung;
• FIG. 2 eine teilweise Schnittansicht in weit größerem Maßstab entlang der Linie 2-2 von FIG. 1;
• FIG. 3 eine entsprechende Ansicht für eine zweite Druckwalzen-Ausführung;
• FIG. 4 eine Unteransicht eines Druckkopfes für das Gerät nach FIG. 1, einschließlich der Druckwalze nach FIG. 3;
• FIG. 4a eine Seitenansicht eines Druckkopfes ähnlich dem Druckkopf von FIG. 4, in Interaktion mit einer Druckwalze;
• FIG. 4b die Mikrofelder, die sich an der Oberfläche der Aufzeichnungskomponente bilden;
• FIG. 5 eine Schnittansicht in viel größerem Maßstab entlang der Linie 5-5 von FIG. 4 und
• FIG. 6 eine Ansicht ähnlich FIG. 3 für eine weitere Ausführung der Druckwalze;
• FIG. 7 eine schematische Darstellung eines Schreibkopfes mit Sätzen von Anlegungspunkten für das Anlegen einer Spannung parallel zu einer Bewegungsrichtung einer dielektrischen Oberfläche;
• FIG. 8 eine schematische Darstellung eines Schreibkopfes mit Sätzen von Anlegungspunkten zum Anlegen einer Spannung senkrecht zu einer Bewegungsrichtung einer dielektrischen Oberfläche;
• FIG. 9 eine dielektrische Oberfläche mit langen rechteckigen Punkten;
• FIG. 10 eine weitere Ausführungsart der Aufzeichnungskomponente zum Gebrauch mit einem Wechselstrom-Schreibkopf.

For a better understanding of the nature and purposes of the invention, the following detailed description will be used, reference being made to the accompanying drawings. Show it:

• FIG. 1 is an isometric (three-dimensional) view of the printing device, including a printing roller, according to the invention;
• FIG. 2 is a partial sectional view on a much larger scale along the line 2-2 of FIG. 1;
• FIG. 3 shows a corresponding view for a second pressure roller embodiment;
• FIG. 4 is a bottom view of a print head for the device according to FIG. 1, including the pressure roller according to FIG. 3;
• FIG. 4a is a side view of a printhead similar to the printhead of FIG. 4, interacting with a platen roller;
• FIG. 4b the microfields that form on the surface of the recording component;
• FIG. 5 is a sectional view on a much larger scale along line 5-5 of FIG. 4 and
• FIG. 6 is a view similar to FIG. 3 for a further execution of the pressure roller;
• FIG. 7 shows a schematic illustration of a write head with sets of application points for the application of a voltage parallel to a direction of movement of a dielectric surface;
• FIG. 8 shows a schematic illustration of a write head with sets of application points for applying a voltage perpendicular to a direction of movement of a dielectric surface;
• FIG. 9 a dielectric surface with long rectangular dots;
• FIG. Figure 10 shows another embodiment of the recording component for use with an AC write head.

Description of the preferred embodiments

As the FIG. 1 of the drawing sheets shows, the printing device according to the invention includes a rotary roller 10 for holding a printing medium such as the paper web W. A printing roller 12 is arranged parallel to the roller 10 in such a way that its cylindrical surface just touches the web W. Around the pressure roller 12 are provided: an electronic print or write head 14, an ink application head 16, which offers the plate roller a dielectric, electrically uncharged ink, an ink transfer station 18 formed by the nip, and an erase head 22, all of which functions are controlled by a control device 24 .

The control device 24 receives input signals in the form of a digital data stream for the gray or color values of an image to be reproduced. In the case of a color press, FIG. 1 a single printing unit for printing a single color component or signature of an original document, e.g. Cyan component. In a color press, three further printing units are arranged behind the roller 12 for printing the other color components, namely magenta, yellow and black, as shown, for example, in U.S. Patent 4,792,860, the content of which is hereby incorporated by reference.

Alternatively, the device according to FIG. 1 print all four color signatures as modified for a multi-color application station, as described, for example, in U.S. Patent 5,325,120.

The data representing the different color components of a color original are fed to the device in the form of successive streams (chains). For example, the system can receive the data in the order of cyan, magenta, yellow, and black. A mass storage device 24a is preferably used in connection with the control device 24 for storing the relatively large amounts of data that are required to operate the device.

To print on the web W, the control device 24 controls the print head 14 such that when the print roller 12 rotates, the print head records electrostatic images on the roller surface 12a in accordance with at least one of the color components, as shown in the incoming data stream. The printhead can be a microtunnel head as specified in U.S. Patent 5,325,120.

The application head 16 can be constructed like that described in the patent specification 4,792,860 or 5,325,120. It provides a melted thermoplastic ink made from pigment particles in one of the four inks dispersed in a binder. The platen surface 12a is preferably weakly color phobic so that the ink does not tend to adhere to the surface of the platen except at the locations charged by the printhead 14. If, for example, a cyan image is written on the printing roller 12, the application head 16 supplies cyan ink.

Then, when the electrostatic image on the roller surface 12a has passed the application head 16, cyan ink is picked up by the head 16 at the charged areas of this image, and thereby a cyan image is developed on the platen surface 12a. As described in the aforementioned patents, the roller 12 is heated so that the ink remains melted on the surface 12a and adheres to the surface of the charged areas mentioned.

As will be described in more detail later, the amounts of ink picked up or detected by the charged areas on the roller surface 12a increase monotonically with the field strengths emanating from these charged areas. This variation of field strengths across the image on the printing roller surface 12a facilitates the reproduction of the complete gray scale area.

If the roller 26 rotates further, the developed area of the image is transported on the surface 12a to the application station 18, which consists of the gap between the rollers or cylinders 10 and 12. The control device 24 controls the position of the image on the roller 12 so that after this image has been developed and transported through the nip, the image developed thereon is transferred to the correct position on the web W. There is complete transfer of the ink from the roller surface 12a to the web W at the transfer station 18 because of the transfer thermodynamically takes place by phase transformation of the printing ink, which changes from a hot, molten liquid state to a solid state at the contact line with the relatively cool web W.

The charged areas of the roller surface 12a, which now no longer have any printing ink, can be transported past the erasing station 22. This station can be funds, e.g. an ultraviolet lamp 22a is included to render the roller surface 12a conductive so that the charges thereon are dissipated.

Thus, when the roller surface 12a leaves the station 22, it is completely unloaded and ready for further "imaging" by the write head 14 during the next or a later rotation of the roller 12. In the meantime, an image of a certain color component, e.g. the cyan component of the original image has been printed on the web W.

The device according to FIG. 1 differs from the devices described in the above patents in that its platen roller 12 has an anisotropic recording surface so that the electrical charges caused by the printhead 16 during a write operation are unevenly distributed on the platen surface 12a to thereby produce uneven electric fields that extend beyond the surface of the roller.

Thus, when the platen roller 12 is rotated so that these unevenly charged areas face the applicator head 16, the charged areas pick up ink from the applicator head by dielectrophoresis. This means that the ink particles are polarized by the unevenly charged roller surface 12a where the fields are strongest in amounts that increase monotonically with the field strengths in these charged areas.

As best seen in FIGURES 1 and 2, roller 12 includes a rigid core 32, which may be made of steel or aluminum, and this core is preferably slotted as shown to reduce its weight and thereby allow air to cool through the core can circulate. A sleeve 34 is arranged around the core 32, for example made of a material such as ceramic material, which is thermally and electrically well insulated. There is a layer 36 of a conductive material such as metallic copper on the surface of the sleeve 34. This conductive layer serves as a ground plane for the printing roller 12.

Around the layer 36 is a thin layer 38 - e.g. 1 µm thick - provided, which consists of a dielectric, such as silicon nitride or sapphire with a very high specific resistance. Anisotropy of layer 38 is achieved by providing a pattern of conductive points 42 in layer 38 that are electrically connected to conductive layer 36. The grounded dots can be formed, for example, by forming a pattern of minute through holes in the layer 38 in the thickness direction and filling the holes with conductive material such as metal or polysilicon. For better illustration, these points 42 in the figures of the drawings are shown relatively large and at a large distance. In reality, however, the points can never have a diameter of less than 1 µm and are only a few µm apart. As the FIG. 1 shows, the dots 42 in the roller 12 are arranged in columns and rows at right angles, e.g. 10 x 10 dots per picture element (pixel).

However, it is obvious that other patterns can also be used. The dot pattern for each picture element (pixel) should be periodic for best results.

The roller 12 is preferably also provided with a very thin outer coating 44 made of an adhesive material such as polytetrafluoroethylene (Teflon) or others that are color phobic. This surface adhesion coating prevents ink from adhering to uncharged areas of roller surface 12a and also minimizes ink smear on that surface.

During a writer action after the device according to FIG. 1 is set up and running, generated the group of microtunnels of the printhead 14 weakest rays of positively charged ions as described in the aforementioned U.S. Patent 5,325,120.

The ions tend to migrate through the openings of the microtunnels and are attracted there by the electrically grounded layer 36 of the pressure roller 12. The incoming positive charges accumulate on the recording surface 12a of the roller 12 so that areas of charge are applied, each of which has a specific Coulomb charge density corresponding to the bias of the control electrode, if any, in connection with the corresponding micro tunnel.

The plasma in the microtunnels can be caused to "exit" at the end of the microtunnels by appropriately increasing the tunnel currents. The plasma can be thought of as a gaseous "wire" that charges the dielectric surface to the plasma potential.

As described in the '120 patent, these bias levels can be digitally adjusted so that the individual microtunnels are separately activated and controlled by the controller so that electrostatic images are generated from imagewise patterns of the charge on the roller surface 12a.

A feature of this invention, however, is that when roller 12 is written to by printhead 14, the surface of sheet 38 is passed unevenly through each micro-tunnel of the printhead. In particular, the presence of the grounded points 42 causes the surface tension of the roller to periodically decrease to zero volts.

There is thus a strong field around each point 42, since the surface potential on the roller must increase in an extremely short way to the average voltage that has been applied to the dielectric by printhead charging. Thus, in the illustrated device, each picture element (pixel) of the electronic image on the platen 12 consists of a microscopic pattern of unevenly distributed charge areas, the uneven electric fields cause - so-called micro-fields - which extend outward from the roller surface 12a; but these charges are averaged across the picture element (pixel), so that macroscopically the charge is proportional to the gray or color value for the picture element (pixel) in question.

Thus, when the charged areas of roller 12 are rotated relative to applicator head 16, the non-uniform electric field at each spot polarizes the development medium and causes ink particles to be drawn to roller surface 12a by dielectrophoresis in an amount that is monotonous with the charge of each Point increases. Printing ink does not adhere to uncharged areas of the roller surface 12a, in particular not because the adhesive layer 44 is present.

Writing heads other than the micro tunnel writing head described above can also be used to apply charges to the dielectric surface, but the micro tunnel writing head is preferred when the dots are grounded, as shown in FIG. 2 shown.

Note that the grounded points of FIG. 2 do not have to be directly grounded, rather it is sufficient to connect to the ground plane through materials with a lower resistance than the dielectric. The dots could also be embedded in the dielectric, as long as defined areas are formed on the recording surface, the potential of which is closer to the ground potential.

In a departure from the embodiment described above, in which ions or charges are applied to the dielectric surface and then migrate to earthed points, there is also the possibility of directly charging ungrounded points, preferably with the aid of direct wire contacts. In a particular embodiment, a grounded layer can be provided beneath the dielectric material so that the dielectric material can be charged between the charged point and the grounded layer and how a capacitor works. The dot retains much of its charge when the printhead moves away from it. The dielectric material on the surface around the point remains approximately uncharged or only very weakly charged. Microfields are thus formed between the charged point and the uncharged dielectric on the surface.

The FIG. 3 shows such a pressure roller 52. Just like roller 12, roller 52 has a core 32, a ceramic sleeve 34 and a conductive layer or ground plane 36. On this layer 36, a dielectric layer 54 is formed with a pattern of conductive areas or points 56 on her. These points are not connected to the conductive layer 36. Alternatively, the dots may be embedded on the dielectric material 54 or, less preferably, entirely provided therein, but the recording surface should have areas with a higher conductivity than that of the normal dielectric layer 54, which can still retain a charge when the Printhead moves away. The roller 52 can also have an outer adhesive coating 60, the surface of which represents the recording surface 52a of the roller 52. In this embodiment, however, it is preferred that the points or defined areas with higher conductivity can be connected directly to contacts of the write head.

An electronic image can be written directly on the recording surface 52a of the platen roller 52 with sliding contacts. FIGS. 4 and 5 show a print head 72 with a linear group of wire-like contacts or voltage feed points 74, which can run over the entire width of the printing roller. The contacts or voltage feed points 74 are "scratched" and the printhead 72 may be arranged so that the contacts resiliently abut the recording surface 52a of the platen 52 at locations of the conductive dots 56 thereon. Image-dependent voltages are then applied to the various contacts 74 when they face the conductive dots 56 so that the dots are charged. Each contact 74 can be quite small, for example several contacts within the width of a picture element (pixel), because only the corresponding point 56 has to be contacted very briefly (order of magnitude nanoseconds) in order for the conductive point to be fully charged to the full potential of the corresponding contact becomes.

The contact can also be as wide as a picture element (pixel), and a single contact can also make contact with more than a single point.

Conductive point 56 thus serves as one plate of a capacitor, ground plane 36 as the other. The dielectric between the point and the ground plane can thus be charged by the write head. When the write head moves away from the point, the dielectric material under the point and the connection point retain a charge, and thus field lines extend across the charged points and the substantially uncharged surrounding dielectric. In this way, microfields are formed that attract ink around the dots. The effectiveness of the printing roller is considerably increased by the presence of the points, because stronger fields can be generated than with wire-like contacts on a flat dielectric surface. In general, it can be roughly assumed that practically no charge remains on the non-metallized dielectric when using narrow contacts. The potential around each point is closer to the ground potential (desirable for creating strong cross fields) the thinner the dielectric layer 54 is.

The roller 52 thus operates more or less the same as the roller 12 with regard to the detection of a pattern of electrical charge areas with microscopic periodic variation, but macroscopic image dependency. The charge areas thus produce non-uniform image-dependent electric fields that can and may extend from the roller surface 52a polarize a development medium and pull it onto this surface.

The write head 72 with its "scratched" contacts 74 can be produced using the methods of conventional printed circuit board technology. The in FIG. 5 includes a substrate 76 made of an insulating material such as ceramic or glass, which extends over the full width of the printing roller 52. A selectively etchable insulating layer 78 made of silicon dioxide or the like is deposited on the substrate. A conductive metal layer 82 is deposited above this layer. The deposited metal can be patterned (i.e., etched after photoresist is applied) so that a contact 74 is present approximately every 50 µm with suitable width / spacing dimensions. The distance can be, for example, one half of the metal width or can be chosen as desired. At one end of the contacts, "terminal pads" 74a can be used to connect the contacts to the pressure source, i.e. a wire charging component can be provided. These paths can be shifted from one another, as shown, to provide enough space for wire bonding or to provide contact areas for a removable contact assembly (not shown).

To "claw out" the working ends of the contacts 74, the layer 78 of insulating material at the bottom of the substrate 76 next to the contact working ends can be etched away so that the contact ends are free of the substrate and "float" as schematically shown in FIG. 4 shown. If desired, the conductive layer 82 can be formed as a bimetal layer, so that when detached the metal bends like a bimetal spring, so that the contacts 74 are in good elastic sliding contact with the roller surface 52 a.

By forming a write head as described, accurate spacing between contacts 74 of the write head is achieved. Various modifications are possible if desired. For example, the ends of the contacts 74 can be made thicker for better wear resistance. You can also use these ends split to form a brush for better elasticity and better contact with the conductive dots on the platen.

Each voltage feed point 74 can also be formed in the form of a plurality of smallest electrical fingers, as shown in FIG. 4a. In FIG. 4a, the points 56 are embedded in the dielectric layer 54.

The electrical fingers of a single feed point 74 are all charged to an equal (similar) voltage, but have a very high resistivity in a direction parallel to a line immediately across the width of the recording surface.

The control device for the write head can be set to the voltage of each feed point individually, as described above. Due to manufacturing tolerances, contact 74 may often touch not only the point but also part of the dielectric, as shown in FIG. 4a. But due to the larger difference and the lack of a conductive point that facilitates the feeding of the electrical charge, the charge on the dielectric on the surface is minimal. Thus, when voltage contact 74 moves away from the point, micro-fields arise between point 56, which remains charged, and the dielectric surface, which remains largely uncharged.

It is also possible that the in FIG. 4 points shown contact the ground plane via resistors or ohmic connectors with a smaller specific resistance than that of the dielectric.

If the feed points move away from the points, the point remains charged for a certain time, even if its discharge rate is higher than if there were no resistors. The optimal specific resistance between the point and the ground plane depends on various factors, including the speed of the printing roller, tension limits, desired ink strength and others. The specific resistance can also be via the Composition, depth and size of the points can be influenced.

When contacting with metal wires, the dots are preferably made from a hard metal connection, e.g. TiN, ZrN or zirconium oxide.

The FIG. 4b shows, by way of illustration, microfields MF located on the surface 52a between the points and the substantially uncharged dielectric material as the points 56 move away from the contacts 74. The microfields MF then attract ink from the application station as described above.

The FIG. 6 illustrates another embodiment of a pressure roller, generally designated 92, but having a slightly different anisotropic dielectric layer 94 on the conductive layer 38. The layer 94 also bears a pattern of conductive points 96. The points 96 are alternately connected to the ground plane 36 by conductive paths 98. The conductive paths 98 can be formed by "pinholes" filled with conductive material, by plated paths, or even by minute wires. If desired, conductive paths 98 may be made of a semiconductor material, e.g. Polysilicon, so that there is a relatively high resistance. In this way, somewhat higher transverse electric fields are achieved over the recording surface 92 of the roller 92 when the roller is written with the write head 72.

More specifically, even the polysilicon connection can be used directly as the conductive point 96; Covering with another, more conductive metal is not necessary because, from an electrostatic point of view, only very low conductances are required for points 96. The same applies to the points 42 on the roller 12 (FIG. 2).

Another embodiment shown eliminates the need for a ground plane in the pressure roller because unearthed adjacent points of the dot pattern are charged in opposite directions. In FIG. 3, for example, points 56 can be made via the roller odd numbers are positively charged, even numbered dots 56 having a corresponding negative potential using the contact write head 72 as shown in FIGURES 5 and 6. This causes field lines across the space between the two sets of dots so that ink is drawn between the dots.

The various methods for charging such a surface without a ground plane can be better understood with reference to the schematically drawn write heads of FIGS. 7 and 8. In FIG. 7 shows a write head 172 which has a multiplicity of sets S1, S2, S3 etc. of two feed points with a parallel arrangement to the direction of movement of a dielectric recording surface. The recording surface may be a simple dielectric surface, preferably one with dots or areas of higher conductivity on the surface as described above. In this embodiment, the write head can be independently set to a voltage difference for each set S1, S2, etc. based on electronic data representing the image to be recorded on a dielectric recording surface. Thus, successive lines of the image are written with the write head across the entire width of the recording surface as it traverses the recording surface.

The voltage difference preferably varies between zero and a maximum of 30 to 200 volts, so that the ink is attracted variably in accordance with the voltage difference.

As shown schematically in FIG. 8, it is also possible to arrange the sets of voltage feeding points of the write head 172 in a direction perpendicular to the moving direction of the recording surface.

The grouping can be done as for the write head of FIG. 4 and 5.

In the schematically shown embodiments of the two FIGURES 7 and 8 there are also more than two Infeed points per set possible, e.g. three infeed points for one set with voltages V1, V2, V1. In the embodiment according to FIG. 8 For example, in the next set the voltages V1, V3, V1 can be such that the voltages of the feed points in the sets next to one another are equal. This helps to avoid microfields between two adjacent sets if desired.

The recording surface for this embodiment can be a simple dielectric surface, and dots as described above can also be present. As the FIG. 9, dots 156 may be rectangles with the full size of a picture element (pixel), e.g. 50 microns.

In the embodiments according to FIGURES 7 and 8, it should be ensured that the plus and minus contacts do not touch the same point at the same time. If this happens, the two contacts will most likely cancel each other, even with a current-limited supply or with high resistance contacts, and little or no charge will be generated on the platen.

In all of the embodiments described above, the varying voltages can be supplied by a DC voltage source.

However, alternating voltage sources can also be used, the voltage amplitude being variable.

When using an AC voltage source, there is also the possibility of grounding the underlying layer of FIG. 3 as shown in FIG. 10 shown. The layer 136 is an ungrounded conductive layer which receives an approximately constant voltage equal to the mean value of the varying AC voltage when the pressure roller rotates. The varying voltage of the contact points on surface 52a can then be used to charge the dielectric since the voltage on layer 136 remains approximately constant.

It should also be noted that in all types of construction with an underlying grounded position the Instead, it is possible to provide a layer with constant voltage instead of an earthed layer.

A printing component with a charged anisotropic surface, as described in the above embodiments, can interact with a dielectric development medium or any other dielectric material with a dielectric constant greater than one. We have described the invention here for use in printing equipment with a dispensing station that dispenses thermoplastic inks, but the printing components described can also be used to hold solid, uncharged dielectric dyes and uncharged toners. When used in the application, the term "printing ink" is therefore intended to generally refer to a dielectric development medium in which the dielectric constant is greater than one, and is not restricted to liquid printing inks.

Instead of uncharged toners or printing inks, charged ones can also be used in connection with the embodiments described above, but the resulting desired attraction of the color and the thicknesses must then be modified taking into account the stronger attraction.

It should also be noted that other types of contact points may be used when charging the points or more conductive areas, instead of the wire contact points as shown in FIG. 4. The write head can also comprise a plasma charging component and charge via individual plasma introduction points, similar to the microtunnel plasma device described above. The print head can also have a gas charging device and charge the points via the gas delivery points. The contact wires of the embodiment shown in FIG. 4 can, for example, be designed such that there is no real contact with the recording surface, but rather the charges are conveyed via the air.

It can thus be seen that the purposes described above are effectively achieved together with those arising from the above description. Certain changes can of course also be made to the above designs without departing from the scope of the invention.

It is further assumed that the following claims are intended to cover all general and special features of the invention described here.

Claims (24)

A recording device comprising:
a recording component having an outer region made of a dielectric material and a plurality of dots;
with the outside area and the dots arranged so
that there is an outer recording surface with areas of different conductivity, and
a write head close to the recording surface for generating variable electric charges on the recording surface, the variable charges corresponding to a part of an image to be recorded. Apparatus according to claim 1, characterized in that the points are outside. Device according to claim 1, characterized in that the points are embedded in the outer area. Apparatus according to claim 1, characterized in that the recording component additionally has an underlying layer below the outer region, the dots communicating with the underlying layer in such a way that there is better conductivity than in the outer region. Apparatus according to claim 4, with additional connectors between each point and the underlying layer, the connectors having a resistance which is less than that of the dielectric. Apparatus according to claim 1, characterized in that the write head comprises a plurality of voltage feed points, the write head being able to independently determine the voltage of each feed point. Apparatus according to claim 6, characterized in that the feed points consist of a plurality of electrical "fingers". Apparatus according to claim 1, characterized in that the write head applies a variable voltage to the recording surface, the upper limit of the voltage being between 30 and 200 volts. Device according to claim 1, characterized in that the dots are made of metal. Apparatus according to claim 1, characterized in that the write head comprises a wire charging component, the wire charging component delivering charges to the recording surface via wire contacts. Apparatus according to claim 1, characterized in that the write head comprises a gas charging component, the gas charging component delivering charges to the recording surface via a gaseous medium. Apparatus according to claim 1, characterized in that the write head comprises a plasma charging component, the plasma charging component delivering charges to the recording surface via a plasma medium. Apparatus according to claim 1, characterized in that the write head has a plurality of sets of at least two feed points, the feed points of each set supplying a voltage so that the dielectric material is charged between two adjacent points and the write head is the voltage between the feed points each set regardless of the tension of other sets. Apparatus according to claim 13, characterized in that the recording surface has a direction of movement and the feed points of each set are arranged parallel to the direction of movement. Apparatus according to claim 13, characterized in that the recording surface has a direction of movement and the feed points of each set are arranged perpendicular to the direction of movement. The apparatus of claim 1, further comprising an application station close to the recording surface for applying ink to the recording surface. The apparatus of claim 1, further comprising a thin color phobic layer on the recording surface. Apparatus according to claim 1, characterized in that the write head works with a DC voltage source. Apparatus according to claim 1, characterized in that the write head contains an AC voltage source. A recording device comprising:
a recording component having a dielectric recording surface comprising a plurality of relatively conductive defined areas and a writing head in the vicinity of the recording surface for discharging charges corresponding to a part of an image to be recorded on the recording surface, the writing head having a plurality of Has voltage injection points that are arranged across the width of the recording surface to produce micro-fields around the defined areas. Apparatus according to claim 20, characterized in that the recording component additionally comprises an underlying layer under the recording surface, the defined areas with the Interact underlying layer so that relative conductivity is achieved. Apparatus according to claim 20, characterized in that the feed points are arranged in the form of sets of at least two feed points, each set of feed points providing a voltage between adjacent defined areas. A method of recording an image on a recording component having an outer recording surface with areas of different conductivity, the method comprising the steps of:
Generate electronic data according to the image to be recorded and
Form microfields that extend beyond the recording surface and lie between regions of different conductivity by delivering charges to the outer recording surface based on the electronic data. The method of claim 23, further comprising applying an uncharged ink to the recording surface.

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