Abstract:
The electrode arrangement (1) consists of a dielectric substrate (2) on which there are several electrodes (4) with terminal leads. A dielectric layer (6) extends over the electrodes (4) over which there is a screening electrode (7) with an aperture (8) for each of the electrodes (4). The arrangement is especially suitable for a contragraphy apparatus. It can be economically produced.

Description:
BACKGROUND OF THE INVENTION 
     The invention pertains to the art of printing and, more particularly, to an electrode arrangement and contragraphy instrument. 
     An example of contragraphy process is disclosed in DE-OS 34 11 948. In the contragraphy process, an electrical field is developed through the paper, between the developer surface, which transports a thin layer of electrically charged toner particles, and suitable print electrodes. The respective print electrode develops the required drawing field. If the electrical field force is strong enough at the location of the developer surface in order to overcome the adhesive power of the toner, the toner is torn off at that location and accelerated in the direction of the paper. The shape of the reproduction of the toner on paper is basically determined by the spatial shape and force of the electrical field between print electrode and developer surface. A description is given in DE-OS 34 11 948 of the utilization of one or several, vis-a-vis the developer surface, vertically oriented needles of electrically conducting material (metal). In order to ensure appropriate through-put during the contragraphy process, several print electrodes must operate simultaneously. For example, for printing of DIN A 4 format pages with a resolution of 200 dpi on a page-at-a-time printer, 1654 of such print electrodes are needed. 
     With this type of matrix of print electrodes, it is, however, difficult to guarantee accurate position of electrodes to each other. Mass production of such an array of electrodes combined with difficulty in automated contacting of individual electrodes is the reason why contragraphy printing in this form has not as yet been able to establish itself on the market. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrode arrangement for use in contragraphy printing, which can be produced at favorable costs. Said object is achieved by the combination of characteristics of the present invention. 
     In the electrode arrangement according to the present invention, methods of industrial thin layer technology are employed which permit trouble-free control of combinations of electrically conducting and electrically isolating micro-structures with a resolution of up to the μ-range. Particularly suitable as carriers for the electrode structure are thin polymer foils, which can be structurally coated by the so-called &#34;in-line-process&#34;. Normal conductor plates, which are, for example, structurally coated by the flow-solder method, can also be used. Representation of conductor paths with individual diameters of up into the μ-range is state of the art. So, preferably circularly-shaped electrodes can, from a production-engineering aspect, beneficially be electrically contacted. Contacting should preferably occur in the same plane. Available processes are, for example: wire-bonding, dye-bonding or the hot-weld process. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following are exemplary embodiments of the invention, which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, wherein: 
     FIG. 1 shows a cross-section through an electrode arrangement; 
     FIG. 2 shows a section along lines II--II in FIG. 1; 
     FIG. 3 shows a top view of the arrangement in FIG. 1; 
     FIG. 4 shows a schematic cross-section through the contragraphy instrument of the present invention; 
     FIG. 5 shows a schematic cross-section through another specific embodiment of the instrument of the present invention; 
     FIG. 6 shows another application of the electrode arrangement according to the present invention; and, 
     FIG. 7 shows a contragraphy instrument with an arrangement according to FIG. 6. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for purposes of the limiting same. 
     The electrode arrangement 1 according to FIGS. 1-3 is constructed on a dielectric carrier foil 2. Foil 2 can consist for example of a polymer, for example of polyethylene. First a thin metal layer 3 is applied to foil 2, which preferably is thinner than 10 μm. From the metal layer there is now formed a multitude of circular electrodes 4 with conductors 5 connected therewith, by removal via etching of the areas indicated in hatched fashion in FIG. 2. The remaining rest of the metal layer 3 forms a continuous screening electrode, which effectively screens off the closely arranged adjacent electrodes 4. The leaving in place of the screening electrode 3 has the added benefit that during etching only the hatched area in FIG. 2 must be removed by means of etching, in other words, only a small amount of etching solution is used. Above electrodes 4, conductor 5 and screening electrode 3 there is applied a dielectric layer 6, which also fills out the spaces between the electrodes 4 and conductors 5 and the screening electrode 3. Layer 6 preferably consists of polyethylene because of its high electrical disruptive field force of 7.5 E 7 V/m (75 million volts per meter). Above this layer 6 there is arranged a continuous metal shield grid 7, which has a circular opening 8 above each electrode 4, whose diameter is smaller than the diameter of the respective electrodes 4. As a result, requirements relative to precision of position and shape of electrodes 4 are low. Determining factors with respect to precision are only position and diameter of the openings 8 in the shield grid 7. The thickness of the shield grid can be very small, for example less than 10 μm. The shield grid 7 makes sure that electrical fields between the electrode arrangement 1 and a developer device for transfer of toner onto an information carrier, for example paper, can only be constructed via the openings 8. The electrical charge of conductors 5 has, in fact, no influence on the reproduction process. The electrical field of conductors 5 is screened off against the developer surface. The thickness of the layer 6 above the electrodes 4, conductors 5 and the screening electrode 3 is as thin as possible, preferably less than 50 μm, but it is, in any event, sufficiently thick that no reciprocal arcing-over can occur between the electrodes 4 and the shield grid 7. There may be also be arranged above the shield grid 7, a dielectric thin protective film 9, in order to protect the shield grid 7 from mechanical damage. 
     The array of electrodes 4, conductors 5 and the shield grid 7 can initially also be produced on two different carriers and subsequently, isolated by a thin polymer foil, glued together. The dielectric layer 6 below the opening 8 can be removed or omitted during the manufacturing process. FIG. 3 depicts a bird&#39;s eye view of the electrode array 1. Each conductor 5 is connected to a separate electrical line 10, for example by means of wire-bonding, dye-bonding or the hot-weld process. An additional line 11 is connected to the shield grid 7. 
     FIG. 4 depicts a possibility of using the electrode array in a contragraphy instrument 20. The electrode array I is positioned on a partially cylindrical basic body 21, which is movably transported on tracks 22. Above the electrode array I a developer device 23 is movable on other tracks 24. Tracks 24 are parallel to tracks 22. The developer device 23 and the basic body 21 are driven by a joint drive 25. Drive 25 is schematically indicated as two endless toothed belts 26, which are passed via toothed belt disks 27. Two of the disks 27 are connected with each other by means of a gear connection and with a servo-motor 29, so that the mutual position between the developer device 23 and the basic body 21 is constant. The developer device 23 has a storage chamber 30, filled with toner and a developer roll 31, which closes off the lower opening 32 of chamber 30. The opening 32 defines a print location 33 above the electrodes 4 of the electrode arrangement 1. Between the opening 32 and the electrode arrangement 1, an information carrier 34 is clamped, for example a piece of paper, which is symbolically indicated by two clamping units 35. The two clamping units 35 can be moved, for example, step by step, vertically vis-a-vis the plane depicted according to FIG. 4, whereby the instrument 20, between two forward feed steps, each time prints one line by moving across the width of the paper. Consequently, the required length of the electrode arrangement 1 and the number of targeted electrodes 4 is low. Cost of electronics for targeting of electrodes 4 can thus be reduced. On the other hand, it is also possible to provide for the length of the electrode arrangement 1 and the developer device 23 which is equal to the length of the paper. This, naturally, requires a greater cost expenditure in circuit electronics, but significantly increases the printing speed. 
     In FIG. 5, another variation of the contragraphy instrument 20&#39; is shown, whereby analog parts are identified with identical reference symbols, so that detailed description of these parts becomes unnecessary. In this specific embodiment, the developer device 23 and the basic body 21 are stationary with the electrode arrangement 1 and the paper 34 is passed along the printing location 33 by pairs of propelled rollers 40. The top side of the basic body 21 and thus of the electrode arrangement 1 is cylindrically convex and the paper 34 drags across the electrode arrangement 1. As a result, the geometry is accurately defined between the developer roller 31, the electrode arrangement 1 and the paper 34. The individual lines to the electrodes 4 can randomly be switched via electronic switches between two tensions, for example between the tension which is put on the developer roller 31 and another opposite tension which is generated by tension source 42. The shield grid 7 and the screening electrode 3 are placed at the tension of the developer roller 31. When in operation, the developer roller 31 rotates in the direction of the arrow and carries along, by means of static and/or magnetic forces, dosed by a blade 43, a thin toner layer. If one of the electrodes 4 is switched, through switching of the appropriate switch 41, from the indicated basic position, an electrical field develops between said electrode 4 and roller 31, through the respective opening 8 of the shield grid 7. Said field pulls electrically charged toner particles off the roller 31 and accelerates them toward the paper 34, on which they adhere. The pair of rollers 40, which is arranged downstream, is heated, so that the pattern printed on paper 34 becomes fixated. 
     FIGS. 6 and 7 represent another specific embodiment of the invention. In this example one single, continuous, tabular electrode 4 is arranged on carrier 2. The dielectric layer 6 covers almost the entire electrode 4, but is drawn in smaller scale in FIG. 6 because of representation. The shield grid 7 covers, in turn, almost the entire dielectric layer 6 (contrary to the representation). The openings 8 can be in form of dots or in form of lines and jointly produce a printable pattern, for example a logo, --in the represented example--the word &#34;label&#34;. The electrode arrangement 1 according to FIG. 7 is clamped on a cylindrical drum 50. The drum 50 rotates synchronous with the movement of the paper 34. If an appropriate tension is hereby put on line 10 to electrode 4, the logo is printed on paper 34 during the forward feed movement. The contragraphy instrument 20&#34; according to FIG. 7 with the electrode arrangement according to FIG. 6 has a particularly simple design and requires a minimum in circuit expenditure. 
     The invention has been described with reference to a preferred embodiment thereof. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.