WO2000030858A1

WO2000030858A1 - Direct printing method with improved control function

Info

Publication number: WO2000030858A1
Application number: PCT/SE1998/002142
Authority: WO
Inventors: Bengt Bern; Anders Ingelhag; Karin Bergman
Original assignee: Array Ab (Publ)
Priority date: 1998-11-26
Filing date: 1998-11-26
Publication date: 2000-06-02
Also published as: AU2079599A

Abstract

A method for producing a printhead structure (130) forming a part of an image recording device (100) for recording an image on an image receiving medium (200). The printhead structure comprises a first surface (131), a second surface (132) facing the image receiving medium, and control electrodes (133). The method comprises the following steps. Covering at least one of the first surface (131) or the second surface (132) with a first conducting layer (310). Etching a circuit pattern (160) on the first conducting layer forming feed lines for the control electrodes (133). Applying a second conducting layer (340) onto areas of the first conducting layer, which areas are to constitute the control electrodes, so that the second conducting material layer partly overlaps the etched circuit pattern. Forming the apertures (134) in the printhead structure (130), thereby also cutting through the second conducting layer where it covers said apertures. And finally, forming the control electrodes by removing selected areas of the second conductive layer.

Description

DIRECT PRINTING METHOD WITH IMPROVED CONTROL FUNCTION

TECHNICAL FIELD:

The present invention relates to the field of direct electrostatic printing, preferably performed in consecutive print cycles, where an apertured printhead structure is brought into cooperation with a toner particle source to modulate a stream of toner particles from the particle source through the apertured printhead structure. The invention further relates to an apertured printhead structure.

BACKGROUND OF THE INVENTION:

Of the various electrostatic printing techniques, the most familiar and widely utilised is that of xerography wherein latent electrostatic images formed on a charged retentive surface are developed by a suitable toner material to render the images visible, the images being subsequently transferred to plain paper.

Another form of electrostatic printing is one that has come to be known as direct electrostatic printing (DEP) . This form of printing differs from the above mentioned xerographic form in that toner is deposited in image configuration directly onto an image receiving medium. The novel feature of DEP printing is to allow simultaneous field imaging and toner transport. Thus, a visible image is produced on an image- receiving medium directly from computer generated signals, without the need for those signals to be intermediately converted to another form of energy such as light energy, as is required in electrophotographic printing.

A direct electrostatic printing device and method was

CONFIRMATION introduced in U.S. Patent No. 5,036,341, granted to Larson. Larson discloses a direct electrostatic printing device and method to produce text and pictures using toner particles on an image receiving medium directly from computer generated signals.

One intermittent phenomenon possibly associated with this printing device and printing technique is the occurrence on the printed surface of lighter stripes substantially in the direction of travel of the image-receiving medium. When present, these stripes substantially degrade the appearance of the printed image. The stripes are usually most pronounced when printing more solid black areas, but may be visible in all types of printouts, also less densely printed areas.

SUMMARY OF THE INVENTION:

The present invention is advantageously applied to a direct electrostatic printing method, in which a stream of computer generated signals, defining an image information, is converted to a pattern of electrostatic fields on control electrodes arranged on a printhead structure. The pattern selectively permits or restricts the transport of charged toner particles through the printhead structure, e.g. from a particle source toward a back electrode, and controls the deposition of the charged toner particles in an image configuration onto an image-receiving medium.

A main object of the invention is thus to provide an improved method for manufacturing a device for direct printing.

This objective is accomplished with a method for producing a printhead structure comprising laser forming the apertures and the control electrodes. Laser forming allows considerably better tolerances and a smaller conductive pattern width on the printhead structure, compared to known methods of forming the electrode pattern and the aperture holes. The control electrodes may be preformed using conventional etching techniques, but will get their final shape as a result of the laser working operation.

The printhead structure preferably forms a part of an image- recording device for recording an image on an image-receiving medium. The image-recording device further comprises a toner particle source, a voltage source, and a back electrode. The toner particle source provides electrically charged toner particles. The printhead structure is intended to be arranged between the toner particle source and the image-receiving medium. The image-receiving medium is intended to be arranged between the back electrode and the printhead structure. The voltage source is connected to the toner particle source and the back electrode to create an electrical field for transporting toner particles from the toner particle source toward the image-receiving medium. The printhead structure further comprises a first surface facing the toner particle source, a second surface facing the image-receiving medium, and control electrodes. A plurality of apertures is arranged through the printhead structure from the first surface to the second surface. The control electrodes enable a selective electrostatic opening or closing of the plurality of apertures. The transport of toner particles is thus permitted or restricted to regulate the amount of toner particles transported through the plurality of apertures in order to thereby enable the formation of a toner particle image on the image-receiving medium.

The method further advantageously comprises the following steps. Covering at least one of the first surface or the second surface with a first conducting layer. Etching a connecting lead pattern on the first conducting layer, thus forming an outline for the control electrodes. Performing the forming of the apertures in the printhead structure, and performing the forming of the control electrodes by removing selected areas of the first conductive layer. In this way, the conventional technique of wet etching is combined with the more precise technique of laser forming.

Alternatively, the method further comprises the following steps. Covering at least one of the first surface or the second surface with a first conducting layer. Etching a circuit pattern on the first conducting layer, thus forming feed lines for the control electrodes. Applying a second conducting layer onto areas of the first conducting layer, which areas are to constitute the control electrodes. The second conducting material layer should partly overlap the etched circuit pattern. Performing the forming of the apertures in the printhead structure, thereby also cutting through the second conducting layer where it covers the apertures. Performing the forming of the control electrodes by removing selected areas of the second conductive layer. Using this method, the actual electrode area of the printhead structure may be made of a relatively thin conducting layer, which is easier to laser form thus resulting in even better tolerances.

The second layer of conducting material is advantageously applied using a thin film technique to achieve the required thin conductive layer.

The first conducting layer is advantageously a layer of metal, preferably copper or aluminium.

The second conducting layer is advantageously a layer of metal, such as copper or aluminium, or a layer of semiconducting material .

The method may further advantageously comprise the step of applying a layer of an electrically insulating material to the first conductive layer after the step of forming the control electrodes. In this way, the overlap of neighbouring electrodes from different rows may be reduced, and the space necessary between the apertures may be decreased, without risk of spark-over between the apertures and any conductor (control electrode) to the toner carrier.

The electrically insulating material layer is advantageously a layer of Parylene (TM) .

The step of forming the apertures is advantageously performed so that the resulting apertures have an oblong shape with a major axis and a minor axis. The major axis is preferably substantially parallel to a travelling direction of the image-receiving medium. The oblong shape of the apertures enables an even further close packing of apertures per length unit of each row of the printhead structure, thus increasing the print resolution of the printing device, whilst the problem of lighter lines mentioned earlier is mitigated by the apertures being relatively more narrow. The orientation of the apertures optimises the print control and printing result .

A further objective of the invention is to still further increase the print resolution.

This is achieved by a method further comprising the step of etching a circuit pattern on a third conductive layer covering at least one of the first surface and the second surface. The circuit pattern will constitute deflection electrodes for controlling the amount of deflection of the toner particles in a direction substantially perpendicular to the travelling direction of the image-receiving medium.

Another objective of the invention is to provide an improved device for direct printing as well as an improved printhead structure for direct printing devices. This is achieved as a result of using the methods according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS:

The invention will be described in greater detail in the following with reference to the accompanying drawings, in which

Fig. 1 is a schematic side view of an image recording device according to the invention,

Fig. 2 is an elevational side view of a pair of apertures in a printhead structure according to the invention,

Fig. 3 is a schematic top view of a pair of aperture rows in a printhead structure according to the invention,

Fig. 4 is a schematic side view of a printhead structure and its geometrical relationship to the toner particle source, according to the invention,

Fig. 5a is a schematic top view of a first aperture shape according to the invention,

Fig. 5b is a schematic top view of a second aperture shape according to the invention,

Fig. 5c is a schematic top view of a third aperture shape according to the invention,

Fig. 6 is a schematic elevational side view of an aperture according to the invention,

Fig. 7 is a schematic bottom view of the aperture in Fig. Fig. 8 is a schematic top view of a pair of apertures with the associated control electrode circuits and the required pattern geometry thereof,

Figs. 9a to 9d are schematic top views of a method of manufacturing apertures and control electrodes on a printhead structure, according to the invention,

Figs. 10a to lOf are schematic top views of another embodiment of a method of manufacturing apertures and control electrodes on a printhead structure, according to the invention,

Fig. 11 is a flow diagram showing a method of manufacturing apertures and control electrodes on a printhead structure, according to the invention, as described in Figs. 9a to 9d,

Fig. 12 is a flow diagram showing a method of manufacturing apertures and control electrodes on a printhead structure, according to the invention, as described in Figs. 10a to lOf,

Fig. 13 is a flow diagram showing a method of laser working a printhead structure, according to the invention, and

Fig. 14 is a schematic top view of a method of manufacturing deflection electrodes on a printhead structure, according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: Although the examples shown in the accompanying drawings illustrate toner particles having a negative charge polarity, particles having positive charge polarity may be used without departing from the scope of the present invention. In this case, all potential values will have the opposite sign.

In Fig. 1, an image-recording device 100 for recording an image on an image receiving medium 200 is shown. The image- recording device 100 comprises a toner particle source 110, for providing electrically charged toner particles, a voltage source 120, a printhead structure 130, and a back electrode 140. The printhead structure 130 is arranged between the toner particle source 110 and the image-receiving medium 200. The image-receiving medium 200 is arranged between the back electrode 140 and the printhead structure 130. The image- receiving medium 200 may be a belt, a paper or a drum, depending upon the technique used to transfer the toner particle image. The voltage source 120 is connected to the toner particle source 110 and the back electrode 140 to create an electrical field for transporting toner particles from the toner particle source toward the image-receiving medium. The image-recording device 100 further typically comprises a housing (not shown) for protecting the device, control means (not shown) for regulating the printing process and an image-receiving medium feeding mechanism (not shown) for displacing the image-receiving medium 200 relative to the printhead structure 130. The voltage source 120 is further connected to the printhead structure 130 to supply control voltages, which will be described in detail later.

A uniform electric field is produced between the back electrode 140 and the toner particle source 110, e.g. a developer sleeve coated with charged toner particles, thus attracting the toner particles toward the back electrode. The printhead structure 130 is interposed in the electric field and utilised to produce a pattern of electrostatic fields.

A printhead structure 130 for use in direct electrostatic printing devices may take on many designs, for example a lattice of intersecting wires arranged in rows and columns, or a screen-shaped and apertured printed circuit. Generally, the matrix is formed of a thin, flexible carrier of electrically insulating material, such as polyimid, provided with a plurality of apertures and overlaid with a printed circuit of control electrodes arranged adjacent the apertures, so that each aperture is surrounded by an individually addressable control electrode. In order to ensure complete coverage of the print area, the apertures are generally aligned in several parallel rows where each row is displaced sideways compared to the adjacent rows. Each aperture thus corresponds to a specific addressable area of the print receiving medium, seen in a direction perpendicular to the travelling direction of the image-receiving medium.

As is shown in Fig. 2, the printhead structure 130 comprises a flexible carrier 400, a first surface 131 facing the toner particle source and a second surface 132 facing the image- receiving medium. The printhead structure 130 further comprises a plurality of control electrodes 133 and a plurality of first apertures 134. The first apertures 134 are arranged through the printhead structure, from the first surface 131 to the second surface 132. The control electrodes 133 are used to selectively open or close each individual first aperture 134, to thus permit or restrict the transport of toner particles through the aperture. Thus, the amount of toner particles transported through the plurality of first apertures 134 is controlled in order to thereby enable the formation of a toner particle image on the image receiving medium 200. The particle stream is thus modulated by the voltage source, which applies an electric potential to selected individual control electrodes to create electrostatic fields, which thus either permit or restrict the toner particle transport through the apertures of the printhead structure. The modulated stream of toner particles allowed to pass through the opened passages impinges upon the image receiving medium, such as paper, interposed between the printhead structure and the back electrode, to provide line- by-line scan printing to form a visible image.

As shown in Fig. 3, the first apertures 134, together with the corresponding control electrodes 133, may be arranged in one or more substantially straight rows across the printhead structure 130. Each row has a longitudinal axis 137, which is substantially perpendicular to the travelling direction of the image-receiving medium. The rows are furthermore substantially parallel to each other.

The first apertures 134 are advantageously arranged in one single substantially straight row (as shown in Fig. 2) for applications requiring a normal print resolution. This simplifies the adjustment of the printhead structure 130 visa-vis the toner particle source.

For applications requiring a larger print resolution, the first apertures 134 may be arranged in two, or more, substantially straight rows, as shown in Fig. 3.

A multiple row printhead structure is shown in Fig. 4. The printhead structure has a first row 1 of apertures and a second row 2 of apertures. The distance from the first row 1 to the toner particle source 110 is designated l_Kι, and the distance from the second row 2 to the toner particle source 110 is designated l_κ . It is essential that the distances l_Kι and 1_K2 are kept as equal as possible to facilitate the printing control and to enhance the printing result. Typically, the distances l_κι and lκ₂ are between 30 and 50 μm. The toner particle source has a radius R, which is large compared to the distances l_κι and 1_K2. According to the invention, because the oblong shape of the apertures enables them to be spaced closer together, a fewer number of aperture rows is needed to achieve a certain print resolution, compared to other printhead structures .

A consideration associated with printhead structures having multiple transverse rows of apertures, is thus that the distance, known as l_κ, between each row of apertures and the surface of the toner supply, usually a rotating toner drum, should be substantially equal for each row of apertures. If the distance lκ differs enough from row to row in the printhead, the effect is possible non-uniform printing and increased difficulty in regulating the printing. The positioning of the, by comparison, large printhead structure relative to the toner supply becomes increasingly difficult when a printhead structure having more than two rows of apertures is used. It is thus advantageous to use a printhead structure having as few rows of apertures as possible.

The control electrode for each aperture is disposed around the aperture and encompasses an area greater than the aperture. When active, the control electrode has a release area, defined as the area in which toner is drawn from the toner carrier. Because the control electrode is disposed around the aperture, the release area is larger than the aperture area.

When printing a solid black surface the amount of toner available decreases from row to row of apertures. When the release area of the individual apertures is sufficiently large, release areas of consecutive apertures will overlap. This will result in dots printed downstream, as seen in the travelling direction of the toner particle feeding system

(toner particle source) , having a lower density as a result of an insufficient amount of toner being available for the downstream row of apertures. This phenomenon can be referred to as "toner starvation", and causes a degradation in the print uniformity because the printed dot image density will be dependent on which row of apertures is actually printing the individual dots. The result of toner starvation is seen on the printed surface as lighter stripes substantially in the direction of travel of the image-receiving medium.

Thus, to prevent toner starvation, there is a need to optimise the release areas of the apertures to provide a uniform toner supply to consecutive rows of apertures.

Another requirement of printing images on an image-receiving medium is the ever-increasing demand for higher resolutions, often measured in dots printed per inch of medium, dpi. Previously, 300 dpi was considered sufficient, but the quest for better image reproduction has led to a de facto minimum requirement of 600 dpi in today's printing applications. Using known techniques for the manufacturing of apertured printhead structures, where the control electrode is etched in a metallic copper layer on a carrier and the apertures drilled using round drill bits, imposes certain dimensional limitations on the design.

Referring to Fig. 8, a minimum aperture 138 hole diameter 520 of approximately 100 μm can be safely drilled or laser cut and not cause toner clogging when used, i.e. toner particles staying in and obstructing the aperture opening. Mass- produced etched circuit boards are limited to 30/30 dimensions, i.e. 30 μm of conductor pattern width 500 and 30 μm of space 530 between the conductor patterns. The aperture 138 also requires an insulation area 510 between itself and any conductor (control electrode 133) to prevent spark-over therebetween or spark-over to the toner carrier. The resulting pattern of an aperture 138 surrounded by a control electrode 133 will thus have the following typical minimum width dimensions: 30 μm of space 530 between conductors added to 30 μm of conductor pattern width 500 (control electrode 133) together with 15 μm of insulation area 510. Furthermore, 100 μm of aperture width 520 and a second 15 μm of insulation area 510 together with 30 μm of a further conductor pattern width 500, which adds up to 220 μm of total transverse space required on the carrier, per aperture 138.

To reduce toner starvation, the release areas of the apertures on the toner particle source will have to be limited in the transverse direction to the travel direction of the image-receiving medium. Simultaneously, the aperture dimension in the transverse direction has to be kept sufficiently large not to cause clogging of the aperture with toner particles.

According to the invention, the first apertures 134 advantageously have an oblong shape with a major axis 135 and a minor axis 136, as is shown in Fig. 2. The major axis is advantageously substantially parallel to the travelling direction of the image-receiving medium. By using oblong apertures, it is possible to combine a saturated print, no clogging of the aperture and substantially reduced striping of the print. The release area on the toner particle source, for example a developer roll, is narrowed at the same time as the aperture area is sufficiently large to prevent clogging and also to give a sufficiently black print (optical density above 1.4). The smallest total area of an aperture is decided by factors such as avoiding clogging and required printed dot size and density. Tests have shown that the printed dot is substantially round even if printed through an aperture, which is almost twice as long as it is wide. Also, the smaller the aperture opening area, the more scattered and/or weak is the resulting dot image.

The apertures 134, 134', 134" may have different cross- sectional shapes, as is shown in Figs. 5a to 5c, as long as the general shape is oblong. The general shape of the control electrodes 133, 133', 133" corresponds to the shape of the apertures 134, 134', 134". For instance, the first aperture 134 of a substantially oval shape may be employed (shown in Fig. 5a) . Alternatively, a second aperture 134' of a substantially rectangular shape (shown in Fig. 5b), with or without rounded corners may be used. Finally, a third aperture 134" of a substantially egg shaped cross-section (shown in Fig. 5c), with the narrow end advantageously pointing in the travelling direction of the image receiving medium.

As shown in Figs. 6 and 7, the printhead structure may further comprise deflection electrodes 150, connected to the voltage source. The deflection electrodes 150 are used to control the amount of deflection of the toner particles, in a direction at an angle to the travelling direction of the image-receiving medium. The actual angle value depends on the speed of the image-receiving medium, the dot printing speed and how many deflection dots that are to be printed when printing non-symmetrical print resolutions. For symmetrical print resolutions, i.e. when the distance between printed dots are the same within a row as the distance between adjacent dots of different rows, the angle will only vary depending on the number of dots that are to be printed. Typically, the angle is between 5 and 85 degrees, preferably between 10 and 25 degrees and most preferably around 18 degrees .

The above described method of increasing the resolution capacity of a direct electrostatic printing printhead structure, so called dot deflection control, consists of performing several development steps during each print cycle to increase print resolution. A print cycle is, in this context, the printing of one row of dots on the image- receiving medium. For each development step, the symmetry of the electrostatic field is modified in a specific direction, thereby influencing the transport trajectories of toner particles toward the image-receiving medium. This allows several dots to be printed through each single aperture during the same print cycle, each deflection direction corresponding to a new dot location. The electrostatic field is modified using dot deflection electrodes arranged on the carrier.

Practically, two or more, for example three, different discrete dots may be generated by one single aperture using dot deflection control. Thus, an aperture density of 200 apertures per inch would produce a dot density of 600 dpi. The space available for each aperture/control electrode pattern is thus 127 μm for an aperture density of 200 dpi. The minimum total transverse space required on the carrier per aperture was 220 μm, as calculated above, thus a new technique is necessary to arrive at a printhead structure capable of printing a dot density of 600 dpi, unless the apertures are arranged in several rows. As described above, when printing with several rows of apertures, toner starvation may be a problem, resulting in poor printing quality.

One limitation to lower the number of rows used is connected to the size of the apertures and electrode patterns of the printhead structure. The manufacturing processes set these limitations to the aperture and electrode pattern dimensions. Thus, certain minimum dimensions are required for the aperture dimensions and the electrode pattern width and its associated insulation space widths.

The traditional method of producing the above described printhead structures involves masking and etching a circuit board blank to form the electrode pattern. Thereafter, the apertures are drilled. This technique has several limitations. One is the fineness of the pattern, which can be achieved, and another is the precision with which the pattern and the apertures may be formed. The finer the pattern required, the higher the precision will have to be, when placing the masks and when forming the apertures, in order to avoid mismatching the pattern and the aperture holes. Any mismatch would result in rejection of the part and thereby decreased yield of the production process.

The different steps of a method of manufacturing a printhead structure according to the invention are shown in Figs. 9a to 9d and Fig. 11. The initial material used may be any standard flexible printed circuit board material (PCB) , such as a polyimid board. A first board 170 is covered with a first conducting layer 310, for example a copper layer, either on one side or on both sides of the board. Fig. 9a shows a part of the first board 170 after a first etching operation, wherein the first conducting layer 310 is etched to form connecting lead patterns 300. In Fig. 9b, a part of the first board 170 is shown after the apertures 134 have been formed, using laser cutting, milling, drilling or a similar technique. As shown in Fig. 9c, after the apertures are formed, the final shaping of the control electrodes 133 is performed by laser cutting passages 320 in the first conducting layer between the apertures 134.

The laser is used for vaporising the unwanted substance of the printhead structure, either the conducting layer (forming electrodes) or the carrier itself (forming apertures) . The same laser may be used for both operations, for example using different size masks for the opening of the laser. Alternatively, two different lasers may be employed, each optimised for its particular operation, but this is more expensive than using one laser. The fluence and wavelength of the laser light is advantageously optimised for any material that is to be vaporised. Thus, the thermal load of the laser may be regulated depending upon the wanted precision of the cutting operation. If an excimer laser is used, the light will be pulsed, i.e. switched on-off-on-off and so on, to reach the desired thermal load.

A mask having a plurality of openings is advantageously used to work on several areas of the printhead structure simultaneously. Also, as shown in Fig. 13, several different masks having holes with different pitch are advantageously used to compensate for variations between individual printhead structures having pre-processed patterns, for example pre-formed outlines for control electrodes or deflection electrodes. Thus, a test is performed on the printhead structure before laser working, as to the actual distance between different pattern objects. A suitable mask is then selected which will shorten the actual time needed to perform the laser working operation.

Using a laser to cut apertures and electrode patterns has the advantage that smaller width cuts may be performed, compared to conventional etching techniques. For etching, the minimum conducting pattern that can be achieved is around 15 μm, and the minimum non-conductive space that can be etched is around 25-30 μm. A laser can cut patterns 10 μm in width. Conventional drilling limits the aperture diameter to around 100 μm, a smaller diameter hole would cause clogging of the toner particles. A laser can cut a hole with a cross-section dimension of approximately 60 μm, but with a maintained cross-sectional area, thus avoiding toner particle clogging in the aperture.

To reduce the overlap of neighbouring electrodes from different rows, and decrease the space necessary between the apertures, a very efficient insulating material may be applied onto the printhead structure. A material having a high electrical breakdown voltage is required, such as Parylene™ (having a breakdown strength of approximately 2.5 kV/5 μm) . As is shown in Fig. 9d, a very thin insulating layer 190 of this material is advantageously applied over the entire first board 170 or only over a printing area P as insulation for the electrodes, typically a layer approximately 5-7 μm thick. Parylene™ may advantageously be applied using a known atomary vacuum deposition method. In this way, the distance between the aperture and the electrodes can be minimised. Using Parylene™, the distance between neighbouring electrodes may be 10 μm without the risk of electrical breakdown. Such small structures are possible to accomplish using laser removal techniques. Thus, a laser is used to create a surface pattern with very high precision. The insulating layer is advantageously applied after the apertures 134, 134', 134" have been formed, making it possible to have the apertures the same size as the inside dimension of the electrode. This further decreases the circuit pattern width requirements for an aperture and its associated electrode (compare Fig. 8) . All the critical manufacturing processes are thus handled by laser machining, which results in a product having a closer aperture packing without increased errors during manufacturing and thus higher yield compared to traditional manufacturing processes.

The method further advantageously comprises the step of etching a circuit pattern on a third conductive layer (350) covering at least one of the first surface (131) and the second surface (132) . The circuit pattern constitutes deflection electrodes (150) for controlling the amount of deflection of the toner particles in a direction at an angle to the travelling direction (A) of the image receiving medium (200) .

Another method of manufacturing a printhead structure according to the invention is shown in Figs. 10a to lOf and Fig. 12. The initial material used may be any flexible printed circuit board material (PCB) as described in connection with Figs. 9a to 9d. Fig. 10a shows a part of such a second board 180 with a first conductive layer 310. Fig. 10b shows a part of the second board 180 after a first etching operation, wherein the first conducting layer 310 (as described in connection with Figs. 9a to 9d) is etched to form separate connecting leads 330 surrounding a printing area on the board. The printing area is designated P. In Fig. 10c, a part of the second board 180 is shown after a second conducting layer 340 has been applied on the printing area P of the board. The second conducting layer 340 may be applied using plasma vapour deposition (PVD, for example sputtering or evaporation) , chemical vapour deposition (CVD) , plasmaspraying, electrodeposition, chemical deposition or other techniques which result in the formation of a relatively thin conducting layer on the board. Typically, the second conducting layer has a thickness of 0.1 to 0.3 μm. Advantageous materials to use for forming the second conducting layer are metals, such as copper or aluminium, or a semi-conducting material. Thereafter and as shown in Fig. lOd, the apertures 134 are formed, using laser cutting, drilling or a similar technique. After the apertures are formed, the final shaping of the control electrodes 133 is performed by laser cutting passages 320 in the second conducting layer 340 between the apertures 134, as shown in Fig. lOe. A thin insulating layer 190 is advantageously applied over the entire second board or only over the printing area P, as shown in Fig. lOf in analogy with Fig. 9d.

A normal, simple and cheap etch process is used to form all the electrode parts outside the print zone of the printhead structure. In the print zone, either the first metal layer is left unetched or it is etched away and a second metal layer is applied, for example a thin layer of aluminium is sputtered onto the print zone. The apertures are then preferably made with laser cutting techniques and the electrodes separated by removing the metal layer between them, by using laser cutting.

The connecting leads 330 are shown as double conductors from each aperture 134, but may be designed as only one conductor per aperture. The single conductor may then exit either all conductors towards the same direction on the printhead structure or every other conductor to alternating sides of the printhead structure.

The advantages of the invention are thus cheaper manufacture of the printhead structure because a cheaper traditional etching technique may be used for forming non-critical electrode patterns together with laser working for the high precision machining. The yield is increased substantially compared to using only traditional higher precision etching technique, which in any case would not give the same high precision end result. An elimination or radically reduced striping of the print is obtained due to minimised toner starvation. The demands on the alignment of the printhead structure vis-a-vis the toner particle source are reduced when using a printhead structure having a single row of apertures or, possibly, two rows of apertures. This makes it possible to employ a simpler mechanical attachment of the printhead structure in the image-recording device.

The invention is not limited to the descriptions above nor to the examples shown on the drawings, but may be varied within the scope of the appended claims.

Claims

1. A method for producing a printhead structure (130), where the finished printhead structure has a first surface (131) and a second surface (132), the printhead structure further comprising a carrier (400) , at least one conductive layer (310, 340) on one or both of the first surface and the second surface, and a plurality of apertures (134, 134', 134") arranged through the printhead structure from the first surface to the second surface, and a plurality of control electrodes (133) for selectively and electrostatically opening or closing the plurality of apertures for passing or not passing charged toner particles through the plurality of apertures, c h a r a c t e r i z e d i n that the method comprises laser forming the apertures (134, 134' , 134") and the control electrodes (133) wherein a laser is used for vaporising the unwanted substance of the printhead structure, either the conducting layer (310, 340) when forming the control electrodes or the carrier (400) when forming apertures .

2. The method for producing a printhead structure (130) according to claim 1, c h a r a c t e r i z e d i n that the method further comprises the steps of covering at least one of the first surface (131) or the second surface (132) with a first conducting layer (310) , etching a connecting lead pattern (300) on the first conducting layer, thus forming an outline for the control electrodes (133) in a printing area (P) , performing the forming of the apertures (134) in the printhead structure (130), and performing the forming of the control electrodes by removing selected areas of the first conductive layer (310) .

3. The method for producing a printhead structure (130) according to claim 1, c h a r a c t e r i z e d i n that the method further comprises the steps of covering at least one of the first surface (131) or the second surface (132) with a first conducting layer (310) , etching a circuit pattern (160) on the first conducting layer, thus forming feed lines for the control electrodes (133), applying a second conducting layer (340) onto areas of the first conducting layer (310) , which areas are to constitute the control electrodes (133) in the printing area

(P) , so that the second conducting layer (340) partly overlaps the etched circuit pattern (160), performing the forming of the apertures (134) in the printhead structure (130), thereby also cutting through the second conducting layer (340) where it covers the apertures (134), and performing the forming of the control electrodes

(133) by removing selected areas of the second conductive layer (340) .

4. The method according to any of the claims 1 to 3, c h a r a c t e r i z e d i n that the second conducting layer (340) is applied using a thin film technique.

5. The method according to any of the claims 1 to 4, c h a r a c t e r i z e d i n that the first conducting layer (310) is a layer of copper metal.

6. The method according to any of the claims 1 to 4, c h a r a c t e r i z e d i n that the first conducting layer (310) is a layer of aluminium metal.

7. The method according to any of claims 3 to 6, c h a r a c t e r i z e d i n that the second conducting layer (340) is a layer of copper metal.

8. The method according to any of claims 3 to 6, c h a r a c t e r i z e d i n that the second conducting layer (340) is a layer of aluminium metal .

9. The method according to any of claims 3 to 6, c h a r a c t e r i z e d i n that the second conducting layer (340) is a layer of semi^¬ conducting material.

10. The method according to any of claims 2 to 9, c h a r a c t e r i z e d i n that the method further comprises the step of applying a layer of an electrically insulating material (190) to the first conductive layer (310) after the step of forming the control electrodes (133) .

11. The method according to claim 10, c h a r a c t e r i z e d i n that the electrically insulating material layer (190) comprises a layer of Parylene (TM) .

12. The method according to any of claims 1 to 11, c h a r a c t e r i z e d i n that the step of forming the apertures (134, 134', 134") is performed so that the apertures have an oblong shape with a major axis (135) and a minor axis (136) and where the major axis is substantially parallel to a travelling direction (A) of an image-receiving medium (200) .

13. The method according to any of claims 1 to 12, c h a r a c t e r i z e d i n that the method further comprises the step of etching a circuit pattern on a third conductive layer (350) covering at least one of the first surface (131) and the second surface (132), where the circuit pattern constitutes deflection electrodes (150) for controlling the amount of deflection of the toner particles in a direction at an angle to the travelling direction (A) of the image receiving medium (200) .

14. The method according to any of claims 1 to 13, c h a r a c t e r i z e d i n that the method further comprises utilising a laser mask having a plurality of openings to enable laser working on several areas of the printhead structure (130) simultaneously.

15. The method according to claim 14, c h a r a c t e r i z e d i n that the method further comprises using several different laser masks having holes with different pitch to compensate for variations between individual printhead structures (130) having pre-processed patterns, wherein the method further comprises the steps performing a test on the printhead structure

(130) before laser working, to determine the actual distance between different pattern objects, selecting a suitable mask to perform the laser working on that particular printhead structure (130), which will shorten the actual time needed to perform the laser working operation.

16. A printhead structure (130) having a first surface (131] and a second surface (132), the printhead structure further comprising a carrier (400) , at least one conductive layer (310, 340) on one or both of the first surface and the second surface, and a plurality of apertures (134, 134', 134") arranged through the printhead structure (130) from the first surface to the second surface, produced according to the method of any of claims 1 to 15.

17. An image-recording device (100) comprising a printhead structure (130), for recording an image on an image-receiving medium (200) , the image-recording device further comprising a toner particle source (110) for providing electrically charged toner particles, a voltage source (120), and a back electrode (140), and the finished printhead structure having a first surface (131) and a second surface (132), the printhead structure further comprising a carrier (400) , at least one conductive layer (310, 340) on one or both of the first surface and the second surface, and a plurality of apertures (134, 134', 134") arranged through the printhead structure (130) from the first surface to the second surface, and where the printhead structure (130) is arranged between the toner particle source (110) and the image-receiving medium

(200) , and the image-receiving medium is arranged between the back electrode (140) and the printhead structure (130), and the voltage source (120) is connected to the toner particle source (110) and the back electrode (140) to create an electrical field for transporting toner particles from the toner particle source (110) toward the image-receiving medium (200) to thus permit or restrict the transport of toner particles to control the amount of toner particles transported through the plurality of apertures (134, 134', 134") in order to thereby enable the formation of a toner particle image on the image-receiving medium (200) , wherein the printhead structure (130) is produced according to the method of any of claims 1 to 15.

18. A method for producing a printhead structure (130), where the finished printhead structure has a first surface (131) and a second surface (132), the printhead structure further comprising a carrier (400) , at least one conductive layer (310, 340) on one or both of the first surface and the second surface, and a plurality of apertures (134, 134', 134") arranged through the printhead structure (130) from the first surface to the second surface, c h a r a c t e r i z e d i n that the method comprises the steps of covering at least one of the first surface (131) or the second surface (132) with a first conducting layer (310) , etching a connecting lead pattern (300) on the first conducting layer, thus forming an outline for the control electrodes (133), forming the apertures (134) in the printhead structure (130), and forming the control electrodes (133) by removing selected areas of the first conductive layer (310) , wherein a laser is used for vaporising the unwanted substance of the printhead structure (130), either the first conducting layer (310) when forming the control electrodes (133) or the carrier (400) when forming apertures.

19. A method for producing a printhead structure (130), where the finished printhead structure has a first surface (131) and a second surface (132) , the printhead structure further comprising a carrier ( 400 ) , at least one conductive layer (310, 340) on one or both of the first surface and the second surface, and a plurality of apertures (134, 134', 134") arranged through the printhead structure (130) from the first surface to the second surface, c h a r a c t e r i z e d i n that the method comprises the steps of covering at least one of the first surface (131) or the second surface (132) with a first conducting layer (310), etching a circuit pattern (160) on the first conducting layer, thus forming feed lines for the control electrodes (133), applying a second conducting layer (340) onto areas of the first conducting layer (310) , which areas are to constitute the control electrodes (133), so that the second conducting layer (340) partly overlaps the etched circuit pattern (160) , forming the apertures (134) in the printhead structure (130), thereby also cutting through the second conducting layer (340) where it covers the apertures, and forming the control electrodes (133) by removing selected areas of the second conductive layer (340) , wherein a laser is used for vaporising the unwanted substance of the printhead structure (130) , either the conducting layer

(310, 340) when forming the control electrodes or the carrier

(400) when forming apertures.