Charge electrode for continuous inkjet printer

Abstract

 A charge electrode 50 for a multi-jet continuous inkjet printer has a ceramic substrate 53 having a substantially rectangular cross-section and defining a pair of elongate rectangular major faces 51, 52 adjacent to one another. A plurality of conductive tracks 50 are disposed on the major faces of the substrate 53 and extend from one major 52 face over the edge and along the second major face 51. The tracks are parallel to one another and form a plurality of charge electrodes on one of the major faces 51.

Description

[0001] The present invention relates to continuous inkjet printers and, more particularly, to a charge electrode for use in a continuous inkjet (CIJ) printer.

[0002] In our European patent application EP-A-0671269 we describe and claim a method of making an electrode assembly for a continuous ink jet printer, the method comprising providing a flexible non-conductive film; disposing on the film, side by side, a plurality of conductive tracks each having an electrode portion, a conductor portion and a connector portion; and thereafter mounting the film on a support block with the electrode portions of said conductive tracks disposed at an end surface of the block.

[0003] Whilst that prior design works satisfactorily in a relatively narrow multi-jet CIJ printer, in a printer having a large number of nozzles and hence a large number of droplet streams, with the previous type of charge electrode there may be some slight curvature in the front face of the charge electrode which results in a reduction of the charge passed on to the drops.

[0004] It is also desirable to increase the length over which charging of the droplets take place and to do this in the prior design referred to above, may increase the curvature and hence reduce the charge as mentioned above.

[0005] There is therefore a need of a charge electrode design which overcomes these problems.

[0006] According to the present invention there is provided a charge electrode for a multi-jet continuous inkjet printer, the charge electrode comprising:

a ceramic substrate having a substantially rectangular cross-section and defining a pair of elongate rectangular major faces adjacent to one another and defining an edge therebetween; and

a plurality of conductive tracks disposed on the major faces of the substrate and extending from one major face over the edge and along the second major face, the tracks being parallel to one another and forming a plurality of charge electrodes on one of the major faces.

[0007] Preferably, the conductive tracks are applied using a screen-printing process.

[0008] The conductive tracks on the face which does not provide the charge electrodes are preferably wire-bonded to the conductive tracks of a flexible multi-track strip-conductor and a protective layer is applied over the wire bonds to increase durability.

[0009] One example of a charge electrode according to the present invention may now be described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic view of a continuous ink jet printer;

Figure 2 is a front (face) view of a charge electrode assembly;

Figure 3 shows the charge electrode assembly connected to a flexible multi-conductor strip; and,

Figure 4 is a sectional view through a pair of charge electrode assemblies, one according to the present invention and the other (shown on the other side for convenience) according to a prior design.

[0010] Figure 1 shows a multi-jet continuous inkjet printhead. Because Figure 1 shows the printhead sideways on, only a single stream of droplets 3 is seen in the figure. A stream of ink 3 is shown issuing from a nozzle assembly 4 and breaks up into droplets at a position substantially alongside a charge electrode assembly 5 which is constructed in accordance with the present invention.

[0011] Figure 2 shows one end of the charge electrode assembly 5 in face view, the plurality of inkjet streams shown passing in front of individual charge electrodes 50 which are formed by conductive metal tracks (of Dupont 5723 gold) screen-printed onto adjacent elongate faces 51, 52 of a ceramic substrate 53, which is formed of AD-96 Alumina. The gold tracks 50 are coated with a protective glaze.

[0012] As is conventional, the ceramic charge electrode applies charges to the individual drops of ink exiting from the drop generator nozzles and, more specifically, applies the charge at the time at which the drops break off from the stream. This is achieved by sending a charging signal to the individual electrodes. The specific charge electrode assembly shown has 260 charge electrode tracks 50, 256 of which are used for charging droplets in corresponding 256 streams 3, there being two streams 31 at each end of the droplet generator which are deflected into a gutter (not shown). These are known as guard jets and they allow the electrostatic and aerodynamic interactions for the printed lines at the extremities of the row of streams to be the same as the interactions further inward of the drop generator. Outside the guard jets at each end are a further two 2 tracks 54 which operate to maintain the guard jet interactions as close as possible to the other interactions taking place elsewhere between row of streams.

[0013] The charge electrode assembly is supported on a stainless steel mounting 55 via appropriate holes in the ceramic block and is then secured into the printhead module.

[0014] As shown in Figure 3, a multi-conductor flexible strip 60 is attached to the charge electrode assembly face 52, conventional wire bonds being used to attach each of the charge electrode conductive tracks to a corresponding track on the flexible conductor strip. A rubber grommet 61 is provided approximately midway along the strip 60 so as to provide a seal between the print module and the rest of the printhead in use. At the other end of the strip 60 from the charge electrode assembly 5 there is mounted a board 62 on which two multipin connectors 63 are provided in order to connect the tracks of the flexi to appropriate circuit boards within the printhead.

[0015] Figure 4 illustrates, on the left hand side, a charge electrode 5 according to the present invention and, on the right, a charge electrode 2 of the prior art formed in accordance with EP-A-0671269.

[0016] As can be seen, in the prior art, because the charge electrodes 20 are formed on the surface of a flexible conductor 21, they may bow and thus the distance between an ink droplet 30 in the stream 3 and the charge electrode 2 is reduced from that desired. This results in lower charge being applied to the droplet. By means of the charge electrode assembly 5 of the present invention any variation in the distance between the droplet and the corresponding charge electrode is avoided. This distance is critical and may be of the order of 20 µm, so small variations (as may occur with the prior art) can result in significantly less charge being applied to individual droplets, causing misprinting.

Claims

1. A charge electrode for a multi-jet continuous inkjet printer, the charge electrode comprising:

a ceramic substrate having a substantially rectangular cross-section and defining a pair of elongate rectangular major faces adjacent to one another and defining an edge therebetween; and

a plurality of conductive tracks disposed on the major faces of the substrate and extending from one major face over the edge and along the second major face, the tracks being parallel to one another and forming a plurality of charge electrodes on one of the major faces.

2. A charge electrode according to claim 1, wherein the conductive tracks are applied using a screen-printing process.

3. A charge electrode according to claim 1 or claim 2, wherein the conductive tracks on the face which does not provide the charge electrodes are wire-bonded to the conductive tracks of a flexible multi-track strip-conductor and a protective layer is applied over the wire bonds to increase durability.

4. A charge electrode according to claim 3, wherein a protective layer is applied over the wire bonds to increase durability.

Drawing