Inkjet printer nozzle plate

Abstract: A nozzle apparatus for a printer having an nozzle aperture formed between a pair of cover plates (111,112), between which are disposed, transversely, a plurality of strands each formed by a corresponding land (104) of a body (102) in which are disposed a plurality of grooves (103) one disposed on each side of each land and the grooves being partially closed on one side by the cover plates (111,112), adjacent grooves defining a cell (105) and each groove having an ink inlet and outlet for supplying ink to the cell, the lands between each pair of grooves (103) in the centre of the cell (105) having ejection upstands (106) projecting outwardly of the cell (105).

Description: The present invention relates to nozzle plate for an inkjet printer having a nozzle aperture through which ink is dispensed. It is known in the field of fluid mechanics and in inkjet printing technology that, if a liquid is held in a container and that container has a hole in it with the hole below the level of the surface of the liquid, the liquid will not necessarily leak from the container depending upon the parameters of the liquid and the hole. The parameters which determine whether or not the liquid leaks from the container or not are the size of the hole, the surface tension of the liquid, the surface energy of the material in which the hole is formed, the vertical height of the liquid above the hole and the force of gravity. In inkjet printer systems, for example the so-called "BubbleJet" printers, additional means are used to control the pressure which the liquid exerts on the hole, typically in the form of an open cell foam structure. The surface tension force of the liquid acting in the capillaries of the foam at the liquid/air interface on the external surface of the foam can generate a back pressure which is able to balance the weight of the liquid in the foam. There can be occasions when it is beneficial to have a large hole or slit in an inkjet printer, but where it is not feasible to use an open cell foam structure in order to exert a back pressure. For example, WO-A-93-11866, PCT/GB95/01215 and WO-A-94-18011 all disclose printing methods where a large slit may be useful. It is desirable therefore to provide an alternative mechanism for ink retention. According to the present invention there is provided a nozzle apparatus for a printer having a nozzle aperture formed between a pair of cover plates, a dielectric body disposed therebetween, which body contains a plurality of transverse grooves, leaving interposed plate-like lands, the plurality of grooves being disposed one on each side of each plate-like land and the grooves being partially closed on one side by the cover plates, adjacent grooves defining a cell and each groove having an ink inlet and outlet for supplying ink to the cell, the plate-like lands between each pair of grooves in the centre of the cell having ejection upstands projecting outwardly of the cell. Preferably, the cover plates have a series of edge slots aligned with the grooves. A nozzle plate assembly according to the present invention will now be further described with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of an array type inkjet printhead; Figure 2 is a close-up view of the nozzle plate aperture; Figures 3 and 4 are cross-sectional views through alternative embodiments; and Figure 5 is a partial perspective view of a portion of a further printhead incorporating ejection apparatus according to the present invention. The figures illustrate printers of the type generally described in the above mentioned patent specifications. In the printhead of figures 1 to 4, the printhead 1 has a flow of ink, in this case, an ink having particles which are dispensed according to the method described in WO-A-93-11866, the ink 2 flowing around an angled path 3,4 behind nozzle plate component 5,6. The nozzle plate 6 contains a series of protruding electrodes 7 which are spaced apart from one another as seen in Figure 2 and which project from a slit-like aperture 8. Between each of the electrodes 7 are providing nylon filaments 9 which sub-divide the slit 8 between the two component parts 5, 6 of the nozzle plate into segments corresponding to each of the electrodes 7. Figure 2 shows how, under the action of the surface tension of the liquid, plural liquid menisci are formed, from which the ink is dispensed, in use, as described in the above mentioned patent specifications. The example shown in Figures 3 and 4 has a slot 8 which is partially sub-divided by walls 10 which extend part of the way across the slot. Figure 4 illustrates the internal structure of the foam 11 indicated generally in Figure 3. Between each pair of walls is an electrode 7 and in the space between the free ends of the walls 10 and the other side of the slot 8 there is provided Basotect foam 11. The foam 11 prevents the liquid from escaping and provides a plurality of strands 12 which, when taken in association with the walls, divide the slit into a plurality of apertures 13. Figure 4 illustrates the strands 12 in relation to their depth in the figure by way of the darkness of the strands, darker strands being nearer the surface of the cross-section. In a modification of this construction the foam could be replaced by individual strands of the type for example as shown in Figure 2. The above examples are described and claimed in our European Patent 0,885,129. Another example, in accordance with the present invention, is illustrated in Figure 5. Figure 5 illustrates part of an array-type printhead 101, the printhead comprising a body 102 of a dielectric material such as a synthetic plastics material or a ceramic. A series of grooves 103 are machined in the body 102, leaving interposing plate-like lands 104. The grooves 103 are each provided with a ink inlet and ink outlet (not shown, but indicated by arrows I & O) disposed at opposite ends of the grooves 103 so that fluid ink carrying a material which is to be ejected (as described in our earlier applications) can be passed into the grooves and depleted fluid passed out. Each pair of adjacent grooves 103 define a cell 105, the plate-like land or separator 104 between the pairs of grooves 103 defining an ejection location for the material and having an ejection upstand 106,106'. In the drawing two cells 105 are shown, the left-hand cell 105 having an ejection upstand 106 which is of generally triangular shape and the right-hand cell 105 having a truncated ejection upstand. Each of the cells 105 is separated by a cell separator 107 formed by one of the plate-like lands 104 and the corner of each separator 107 is shaped or chamfered as shown so as to provide a surface 108 to allow the ejection upstand to project outwardly of the cell beyond the exterior of the cell as defined by the chamfered surfaces 108. A truncated ejection upstand 106' is used in the end cell 105 to reduce end effects resulting from the electric fields which in turn result from voltages applied to ejection electrodes 109 provided as metallised surfaces on the faces of the plate-like lands 104 facing the ejection upstand 106,106' (ie. the inner faces of each cell separator). The ejection electrodes 109 extend over the side faces of the lands 104 and the bottom surfaces of the grooves 103. The precise extent of the ejection electrodes 109 will depend upon the particular design and purpose of the printer. Figure 5 illustrates two alternative forms for side covers of the printer, the first being a simple straight-edged cover 111 which closes the sides of the grooves 103 along the straight line as indicated in the top part of the figure. A second type of cover 112 is shown on the lower part of the figure, the cover still closing the grooves 103 but having a series of edge slots 113 which are aligned with the grooves. This type of cover construction may be used to enhance definition of the position of the fluid meniscus which is formed in use and the covers, of whatever form, can be used to provide surfaces onto which the ejection electrode and/or secondary or additional electrodes can be formed to enhance the ejection process. Additionally, the fingers 115 between the edge slots 113 serve to reduce the overall size of the aperture between the opposed covers 111, 112, thus acting in accordance with the invention, to sub-divide the aperture into smaller apertures. In all the examples referred to above, sub-dividing the basic aperture into plural smaller ones allows a larger basic aperture to be used (without the risk of leakage) which, in turn, allows an increased migration of material for ejection within the liquid in the device.

Claims: A nozzle apparatus for a printer having a nozzle aperture formed between a pair of cover plates (111,112), a dielectric body (102) disposed therebetween, which body (102) contains a plurality of transverse grooves (103), leaving interposed plate-like lands, the plurality of grooves (103) being disposed one on each side of each plate-like land and the grooves being partially closed on one side by the cover plates (111,112), adjacent grooves defining a cell (105) and each groove having an ink inlet and outlet for supplying ink to the cell, the plate-like lands between each pair of grooves (103) in the centre of the cell (105) having ejection upstands (106) projecting outwardly of the cell (105). A nozzle apparatus according to claim 1, wherein the cover plates have a series of edge slots (113) aligned with the grooves.

Inventors: JANSE VAN RENSBURG RICHARD WIL, NEWCOMBE GUY CHARLES FERNLEY, JANSE VAN RENSBURG, RICHARD WILHELM, NEWCOMBE, GUY CHARLES FERNLEY
Applicants: TONEJET CORP PTY LTD, TONEJET CORPORATION PTY LTD
Application year: 1997
Main classification: B41J2
IPC codes: B41J2