Electrode assembly for a continuous ink jet printer

Abstract: A method of making an electrode assembly for a continuous ink jet printer comprises providing on a flexible non-conductive film (1), side by side, a plurality of conductive tracks (2) each having an electrode portion (3), a conductor portion (4) and a connector portion (4'). Thereafter the film is mounted on a support block with the electrode portions of the conductive tracks disposed at an end surface of the block.

Description: The present invention relates to continuous ink jet printers, i.e. those in which a continuous stream or streams of droplets are produced, individual droplets within the stream or streams being selectively charged and then deflected to a print position as required. Continuous ink jet printers of the single nozzle type are very well known, but less common are continuous ink jet printers having plural nozzles and therefore plural continuous streams of droplets. The present invention is particularly directed to multi jet printers and in particular is directed to the construction of electrodes for use in such printers. In a multi jet continuous ink jet printer each stream of droplets requires a related charge electrode and usually a corresponding phase detector electrode (used to detect correct charging of droplets). Various techniques have been proposed for manufacturing multiple, closely-spaced, charged electrodes, see for example the US-A-4928116, US-A-4928113, and US-A-4560991. These techniques involve electro-plating the electrodes in a defined pattern onto a copper foil sheet, through a photoresist, removing the photoresist, bending the composite sheet and plated electrodes, moulding a dielectric around the electrodes and thereafter removing the copper foil sheet to expose the electrodes within the moulded dielectric. It will be appreciated that such a method is time consuming, since it involves a number of different steps in the manufacturing process, but, significantly, in practice, the yield (i.e. the percentage of usable electrode assemblies formed) is relatively low and thus manufacturing costs are high. There is a need therefore for a method of making an electrode assembly for a continuous ink jet printer which involves fewer and simpler steps and which enables a greater yield, in order to reduce manufacturing costs, whilst at the same time providing an improvement in the assembly structure (See for example US-A-4 651 163). According to the present invention there is provided 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. The invention also includes an electrode assembly for a continuous ink jet printer, the assembly comprising a flexible non-conductive film; a plurality of conductive tracks disposed side by side on the film, each having an electrode portion, a conductor portion and a connector portion; and the film being mounted on a support block with the electrode portions of said conductive tracks disposed at an end surface of the block. Preferably, the film comprises an elongate strip and the electrode portions of the tracks are disposed substantially centrally along its length, with the conductor portions extending along the strip from one end or the other of the electrode portions to connector portions at one or the other end of the strip. By this means, adjacent connector portions can be arranged at a greater spacing pitch than the electrode portions for improved connection. Alternate conductor portions may extend from opposite ends of the respective electrode portions or else alternate groups of conductor portions may extend from opposite ends of the respective electrode portions. To improve connection further, the conductor portions and connector portions may not only have a greater pitch, but may be wider than the electrode portions. It will be appreciated that by using both ends of the strip for connector portions, and thus halving the number on each side of the electrode portions, the connector and conductor portions may occupy twice the width of the electrode portions. In particular, increasing the spacing between tracks may also serve to reduce crosstalk between adjacent conductive tracks in use. The conductive tracks may be formed by electrode plating copper laminate onto a flexible substrate such as polyimide and thereafter creating a pattern of electrode, conductor and connector portions using conventional techniques such as chemical etching or by, for example laser abrasion, if a greater resolution is required. The conductive tracks are preferably thereafter coated or encapsulated over the majority of their area, leaving uncoated a central portion over the electrodes and end portions over the connector portions. The exposed portions may be further plated with other metals such as gold, for corrosion protection, if desired and/or may be coated with a dielectric material of controlled resistivity to achieve desired electric charge dissipation. Mounting the film to the support block involves folding and bonding the film onto a metal or other former in such a way that the electrode portions are placed on the outside of the fold and are located against a flat end edge of the support block. If desired, alternate conductive tracks may form shielding tracks to the conductive tracks used to provide voltages to the electrodes for charging the droplets, the shielding conductors being, if desired, of narrower width in order to reduce increases in the pitch between adjacent charging electrodes. Furthermore, if desired, a pair of charge electrode assemblies as described above, may be mounted in opposition to one another, with adjacent electrodes on the same electrode assembly being oppositely charged or being alternately charged and grounded and opposite electrodes being similarly oppositely charged or grounded. Such a technique can be used to improve charging of individual droplets and reduce crosstalk. An electrode assembly according to the present invention may also be employed as a phase detector electrode assembly or the like. One example of a charge electrode assembly according to the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a partial planar view of the assembly; Figure 2 is a further partial planar view on a greater scale; Figure 3 illustrates a laminated construction of the film from which the assembly is manufactured; Figure 4 illustrates a completed electrode assembly and, Figure 5 illustrates, diagrammatically, an electrode arrangement for reducing cross-talk. Figure 1 shows a portion, in planar view, of a non-conductive film 1 of polyimide on which are formed plural conductive tracks 2, by first electrode depositing a thin layer of copper and then etching away portions of the copper through a mask (not shown) to leave the conductive tracks 2. At a central portion of the film 1, i.e. centrally of its length, the conductive tracks form individual electrodes 3 which are disposed at the desired pitch corresponding to the pitch of the nozzles in a multi-nozzle continuous ink jet printer printhead. It can be seen that the conductive tracks extend away from the electrode portions 3 on opposite sides, in groups. This enables the conductive tracks to be of a greater width and of a greater spacing than the electrodes 3 which is useful, particularly at the ends of the film where the conductive tracks form connecting portions for connection of the electrode assembly to the charging electronics of the printer. In the example the conductive tracks are shown extending away from the electrode portions in groups, but it will be appreciated that alternative configurations are possible, for example, alternate conductive tracks extending on opposite sides. Figure 2 shows a smaller central portion of the film and conductive tracks in more detail. In the example the electrode portions of the conductive tracks have a width of 100µm, with a 100µm gap, the conductive track being deposited to a thickness of 15µm. The conductor portions 4 have a width of 200µm and a spacing of 200µm. Figure 3 shows a film 1 with conductive tracks 2 and, above and below, additional non-conductive films 5, 6, on each of which is disposed, in a grid arrangement, a plurality of copper tracks 7, 8 which, in use, are electrically grounded and form electrical shields to the conductive tracks 2, to reduce crosstalk and noise. The film 6 has a window 9 cut through it which, when the films 5 and 6 are bonded (by means of a suitable epoxy adhesive) to the film 1, lies over the electrode portions 3 of the conductive tracks 2 and the end portions of the film 6 are left free of shielding conductors 7 in order to enable the ends of the conductive tracks 2 to form connector portions 4'. Figure 4 shows the assembled electrode assembly, the assembled films 1, 5, 6, carrying the conductive tracks, being folded around and adhesively mounted to a metal support block 10, at one edge of which the exposed electrode portions 3 are disposed. The flexible nature of the films 1, 5, 6 enable the electrode assembly to be mounted as desired with connections being made remotely from the electrode assembly at the ends 11, 12 of the films carrying the conductor tracks. Figure 5 illustrates an arrangement of electrodes which may be used, where necessary, to protect individual charging electrodes from cross-talk. The Figure is a diagrammatic one and illustrates a number of charge electrodes 3 which are separated by interstitial, guard electrodes 14. It will be appreciated that these interstitial electrodes can either be on the same electrode structure as the charge electrodes or may be on an entirely separate electrode structure. They may be narrower than the charging electrodes as shown in the drawing. In operation a single "charge signal" sent to a particular charge electrode 3 is altered by suitable electronics to provide the following simultaneous signals. 1. A +V charge to the relevant charge electrode 3; 2. A -kV charge compensating opposite charge to the interstitial electrode 14 to one side of the charge electrode 3; and, 3. A -kV charge to the interstitial electrode on the other side of the charge electrode. The signals 2 and 3 thus protect neighbouring electrodes from picking up any of the charge not intended for them thus protecting neighbouring droplet streams from erroneous charging. The voltage levels can be set at a predetermined level which would be factory set to compensate for cross-talk. Since each interstitial electrode has two neighbouring charge electrodes 3, even if both jets on each side of a particular guard electrode 14 are to be charged, the interstitial electrode need only receive one charge and therefore an OR gate 15 is used on the input to each interstitial electrode so that it is appropriately charged if one or the other or both of the adjacent charge electrodes is actuated. In an alternative construction (not shown) the interstitial electrodes are disposed on the opposite side of the droplet streams to the charging electrodes.

Claims: A method of making an electrode assembly for a continuous ink jet printer, the method comprising providing a flexible non-conductive film (1); disposing on the film, side by side, a plurality of conductive tracks (2) each having an electrode portion (3), a conductor portion (4) and a connector portion (4'); and thereafter mounting the film on a support block (10) with the electrode portions (3) of said conductive tracks disposed at an end surface of the block. A method according to claim 1, wherein the film (1) comprises an elongate strip and the electrode portions (3) of the tracks are disposed substantially centrally along its length, with the conductor portions (4) extending along the strip from one end or the other of the electrode portions to connector (4') portions at one or the other end of the strip. A method according to claim 2, wherein alternate conductor portions (4) are disposed to extend from opposite ends of the respective electrode portions (3). A method according to claim 2, wherein alternate groups of conductor portions are disposed to extend from opposite ends of the respective electrode portions. A method according to any of claims 1 to 4, wherein the conductor portions (4) and connector (4') portions are disposed to be wider than the electrode portions (3). A method according to any of claims 1 to 5, wherein the conductive tracks are formed by electro-plating copper laminate onto a flexible substrate and thereafter creating a pattern of electrode (3), conductor (4) and connector (4') portions by conventional techniques. A method according to claim 6, wherein the conductive tracks (2) are thereafter coated or encapsulated over the majority of their area, leaving uncoated a central portion over the electrodes and end portions over the connector portions. A method according to claim 7, wherein the exposed portions are further plated with other metals for corrosion protection. A method according to claim 7 or 8, wherein the exposed portions are coated with a dielectric material of controlled resistivity to achieve desired electric charge dissipation. A method according to any of claims 1 to 9, wherein the film is mounted to the support block (10) by folding and bonding the film onto a metal or other former in such a way that the electrode portions are placed on the outside of the fold and are located against a flat end edge of the support block (10). An electrode assembly for a continuous ink jet printer, the assembly comprising a flexible non-conductive film (1); a plurality of conductive tracks (2) disposed side by side on the film, each having an electrode portion (3), a conductor portion (4) and a connector (4') portion; and the film being mounted on a support block (10) with the electrode portions (3) of said conductive tracks disposed at an end surface of the block. An electrode assembly according to claim 11, wherein the film comprises an elongate strip and the electrode portions (3) of the tracks (2) are disposed substantially centrally along its length, with the conductor portions (4) extending along the strip from one end or the other of the electrode portions to connector portions (4') at one or the other end of the strip. An electrode assembly according to claim 12, wherein alternate conductor portions (4) extend from opposite ends of the respective electrode portions. An electrode assembly according to claim 12, wherein alternate groups of conductor portions (4) extend from opposite ends of the respective electrode portions. An electrode assembly according to any of claims 11 to 14, wherein the conductor portions (4) and connector portions (4') are wider than the electrode portions. An electrode assembly according to any of claims 11 to 15, wherein the conductive tracks are an electro-plated copper laminate onto a flexible substrate and to form a pattern of electrode, conductor and connector portions. An electrode assembly according to claim 16, wherein the conductive tracks (2) are coated (5, 6) or encapsulated over the majority of their area, leaving uncoated a central portion over the electrodes and end portions over the connector portions. An electrode assembly according to claim 17, wherein the exposed portions are plated with other metals for corrosion protection. An electrode assembly according to claim 17 or 18, wherein the exposed portions are coated with a dielectric material of controlled resistivity to achieve desired electric charge dissipation.

Inventors: PALMER DANNY CHARLES, WALLACE CAROLINE LOUISE, ZABA JERZY MARCIN, PALMER, DANNY CHARLES, WALLACE, CAROLINE LOUISE, ZABA, JERZY MARCIN
Applicants: DOMINO PRINTING SCIENCES PLC
Application year: 1995
Main classification: B41J2
IPC codes: B41J2