Non-Contact Liquid Printing

Abstract

A perforate element (101) for use in a print head for non-contact liquid printing comprises: at least one ejection element (103) including an outlet (103a), configured to eject a bulk flow (F) of printing liquid (L) out of the print head; and a liquid residence element (107), arranged to provide a layer of liquid over the outlet (103a) which extends laterally of the outlet (103a) and through which the bulk flow (F) is ejected.

Claims

1-27. (canceled)

28. A print head for a non-contact liquid printer, comprising: a perforate plate or membrane comprising at least one ejection element including an outlet configured to eject a bulk flow of printing liquid out of the print head; and a bending mode actuator arranged to vibrate the at least one ejection element in order to eject the bulk flow, wherein a region of an external surface of the perforate plate or membrane extends laterally of a longitudinal axis of the at least one ejection element and is adapted to retain a layer of liquid over the outlet, such that in use the bulk flow of the printing liquid is ejected through the layer of liquid.

29. A print head according to claim 28, wherein the adapted region of the external surface of the perforate plate or membrane comprises a recess in the external surface, the recess having a depth in the direction of the longitudinal axis and a lateral width in a direction normal to the longitudinal axis.

30. A print head according to claim 29, wherein the recess has a ratio of lateral width to depth of between about 1 and 100.

31. A print head according to claim 30, wherein the recess has a ratio of lateral width to depth of about 8.

32. A print head according to claim 29, wherein the recess has depth of about 3 to 50 microns.

33. A print head according to claim 32, wherein the recess has depth of about 25 microns.

34. A print head according to claim 29, wherein the recess has a lateral width of about 40 to 2,000 microns.

35. A print head according to claim 34, wherein the recess has a lateral width of about 200 microns.

36. A print head according to claim 29, wherein the recess extends laterally of the outlet by about 15 to 920 microns.

37. A print head according to claim 36, wherein the recess extends laterally of the outlet by about 40 microns.

38. A print head according to claim 29, wherein the ratio of the lateral width of the recess to the lateral width of the outlet is about 1.7:1.

39. A print head according to claim 29, wherein the outlet has a diameter or lateral width of about 10 to 160 microns.

40. A print head according to claim 39, wherein the outlet has a diameter or lateral width of about 120 microns.

41. A print head according to claim 28, wherein the adapted region of the external surface of the perforate plate or membrane comprises an hydrophilic coating.

42. A print head according to claim 28, wherein the adapted region of the external surface of the perforate plate or membrane comprises an hydrophobic coating.

43. A print head according to claim 28, wherein the perforate plate or membrane comprises a plurality of the ejection elements and respective adapted regions of the external surface.

44. A print head according to claim 28, wherein the at least one ejection element comprises a nozzle.

45. A method of non-contact liquid printing using a print head according to claim 28, the method comprising: providing a layer of liquid at the adapted region of the external surface of the perforate plate or membrane; providing a printing liquid to the at least one ejection element; and operating the bending mode actuator, in order to vibrate the at least one ejection element so as to eject a bulk flow of the printing liquid through the layer of liquid.

46. A method according to claim 45, wherein the layer of liquid comprises printing liquid which is similar in type to the printing liquid of the bulk flow.

47. A method according to claim 45, wherein the layer of liquid comprises a liquid which is different in type to the printing liquid of the bulk flow.

Description

[0028] Embodiments will now be described, by way of example, with reference to the accompanying figures in which:

[0029] FIGS. 1a and 1b are schematic depictions of a known, non-contact printing apparatus;

[0030] FIGS. 2a and 2b are schematic depictions showing respective sectional- and plan-views of a portion of a perforate element for a non-contact printer, in accordance with an embodiment of the invention; and

[0031] FIGS. 3a and 3b show the portion of the perforate element of FIGS. 2a and 2b in an operative condition.

[0032] Referring to FIGS. 2a and 2b, a perforate element, or membrane, or nozzle plate 101, for a non-contact liquid printer, for example of the type shown in FIGS. 1a and 1b, comprises a plurality of ejection elements, or nozzles 103 (only one of which is shown), each comprising an outlet 103a. In this exemplary embodiment, the nozzle 103 is a generally convergent-type nozzle 103 having a longitudinal axis Z, and is in fluid communication with a liquid reservoir 105, which is arranged to feed all of the nozzles with a printing liquid L, in this embodiment a reagent including biological cells.

[0033] Also in this embodiment, a liquid residence element comprises a shallow, circular recess 107 which is formed in an external surface 101a of the nozzle plate 101 around the nozzle outlet 103a. The recess 107 includes a generally flat base portion 107a, which extends laterally of the outlet 103a, in a plane substantially normal to the longitudinal axis Z of the nozzle 103, and a peripheral shoulder portion 107b, which extends between the base portion 107a and the external surface 101a of the nozzle plate 101, in the direction of the longitudinal axis Z. In this exemplary embodiment, the outlet 103a has a lateral width, or diameter d, of about 120 microns, while the recess 107 has a depth D of about 25 microns and a diameter, or lateral width W, of about 200 microns. Accordingly, in this embodiment, the lateral distance between the edge of the outlet 103a and the shoulder portion 107b is about 40 microns.

[0034] Referring in particular to FIG. 2b, in this embodiment, a region of the external surface 101a of the nozzle plate 101 comprises a hydrophobic coating, which tends to repel the printing liquid L, and the base and shoulder portions 107a, 107b of the recess 107 comprise a hydrophilic coating, which tends to attract the printing liquid L.

[0035] The operation of the nozzle plate 101 will now be described, with particular reference to FIGS. 3a and 3b. For convenience, the operation will be presented in terms of only one nozzle 103 of the plurality of similar nozzles which comprise the nozzle plate 101; however it will be understood that the principle of operation is the same for all of the nozzles.

[0036] Firstly, the nozzle plate 101 is primed for printing operations. Priming is performed by vibrating the nozzle plate 101, for example as described in WO-93/10910, in order to cause a portion of the stored printing liquid L to flow through the nozzle 103 and to be expelled from the outlet 103a. As the flow emerges, the printing liquid L spreads radially outwards of the outlet 103a, across the base portion 107a of the recess 107, and outwardly with respect to the shoulder portion 107b, so as to fill the recess 107. The printing liquid L is retained, or captured, in the recess 107 due to the containing-barrier formed by the shoulder portion 107b, and also the combined hydrophilic/hydrophobic effect of the coatings on the external surface 101a and portions of the recess 107, in addition to the adhesive forces acting at the interface between the printing liquid L and the wetted surfaces of the recess 107.

[0037] Alternatively, a separate priming liquid, different to the printing liquid L, may be used for priming. An example priming liquid is glycerol. Also, irrespective of the liquid type, the recess may be filled manually from its external, open side, rather than via the nozzle. In that case, any excess liquid left on the external surface 101a of the nozzle plate 101 after filling may be wiped away.

[0038] Priming waveforms which have found to be appropriate include exciting head resonances over −60 kHz with a continuous sine-wave, or exciting several resonances together using a Sinc function. At moderate voltages these waveforms have the described effect of causing the printing liquid L to move out of the nozzle outlet 103a, laterally across the base portion 107a of the recess 107, until it reaches the edges of the recess 107, at which point the printing liquid L then pins at the sharp edges of the recess shoulder portion 107b in a new, stable equilibrium state. At lower frequencies, say −20 kHz or less, instead of spreading sideways, the tendency is for the printing liquid L to jet straight out from the nozzle 103, or form a hemispherical bulge which projects upwards to form a drop, instead of moving laterally into the recess.

[0039] Once the recess 107 has been filled with the printing liquid L (or different priming liquid) and has achieved a stable condition, the printing process may be commenced, as follows.

[0040] The nozzle plate 101 is vibrated at an appropriate rate so that droplets of the printing liquid L may be ejected from the nozzle plate 101 onto, for example, a test substrate. Accordingly, as the nozzle plate 101 is activated, a bulk flow component F of the printing liquid L is passed through the nozzle 103 and out of the outlet 103a, where it encounters the layer of liquid in the recess 107. The vibration of the nozzle plate 101 is sufficiently great that the bulk flow F is driven through the liquid layer in the recess 107, such that droplets of the printing liquid L will be expelled from the nozzle plate 101 onto the test substrate.

[0041] As the printing process goes on, any portion or component of the thin layer of liquid, residing or retained in the recess 107, which is displaced by the bulk flow F as it emerges from the outlet 103a, is effectively replaced by some portion of the bulk flow F, such that there remains at all times a layer of liquid in the recess 107 through which the bulk flow F will pass. (In the case that the recess 107 was filled with a separate liquid during priming, e.g. glycerol, that liquid will tend to be displaced by the printing liquid L from the bulk flow F, so that eventually the recess 107 will be filled entirely, or almost entirely, by the printing liquid F). Accordingly, for as long as the nozzle plate 101 is being vibrated, droplets of the printing liquid L are continually ejected, through an ever-present layer of liquid, onto the test substrate. In this way, droplet ejection is substantially unaffected by meniscus- and edge-effects, which are normally associated with contact between the nozzle outlet and the flowing liquid, thereby providing a significant improvement in print stability and reliability.

[0042] It will be understood that the invention has been described in relation to its preferred embodiments and may be modified in many different ways without departing from the scope of the invention as defined by the accompanying claims.