Patent Grant
8011773
The present invention relates to the field of printers and particularly inkjet printheads. It has been developed primarily to improve print quality and reliability in high resolution printheads.
The following applications have been filed by the Applicant simultaneously with this application:
The disclosures of these co-pending applications are incorporated herein by reference.
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
Supplying ink from an ink reservoir to many thousand densely packed nozzles is a particular challenge in high-resolution pagewidth printing. One problem is avoiding ink pressure surges when a nozzle stops printing. During printing, each nozzle acts like a pump so that each nozzle chamber is refilled with ink almost instantaneously. Forming the nozzle chambers from hydrophilic materials (e.g. silicon nitride, silicon dioxide etc.) facilitates refilling of nozzle chambers during printing.
However, when printing ceases, it is equally important that ink does not flood out from nozzle openings and onto the printhead face. Flooding of this nature has a deleterious effect on print quality and may require frequent cleaning by a printhead maintenance station. Flooding is a particular problem in high-speed pagewidth printheads, where a relatively large mass of ink moves towards each nozzle of the printhead during printing. This moving mass of ink has an associated inertia, which may cause ink to continue leaking from nozzles even when printing ceases. The greater the momentum of ink in the ink supply system, the higher the risk of flooding.
To this end, pressure dampening structures have been proposed in the ink supply system, which absorb the pressure wave of ink being supplied to the nozzles. Hitherto, the Applicant has described air boxes in fluid communication with ink supply lines, which have a dampening effect on ink pressure waves. For a full discussion of ink pressure dampening, reference is made to [INSERT CROSSREF], the contents of which is herein incorporated by cross-reference. Essentially, it is desirable to allow some ‘give’ in the ink supply system, so that the pressure wave associated with a moving body of ink can be absorbed when printing ceases.
However, the use of air to absorb pressure surges is not wholly satisfactory. Outgassing of ink is a particular problem with air-dampening structures. Outgassing is undesirable, because air bubbles in the ink can lead to blockages in ink supply lines, and even initiate catastrophic printhead depriming. Furthermore, air-dampening structures are usually incorporated into ink supply systems a relatively long distance upstream of the inkjet nozzles—typically in a molded ink manifolds to which a MEMS printheads is mounted. Any ink downstream of such air-dampening structures will still carry a significant momentum that will not be absorbed by the air-dampening structures. Again, this problem is exacerbated in pagewidth printheads, which carry a large volume of ink compared to traditional scanning printheads.
It would be desirable to provide improved dampening structures, which are capable of absorbing pressure surges in ink supplied to inkjet nozzles. In view of the problems of outgassing, it would desirable to avoid air dampening as a means for dampening pressure surges. It would be further desirable to minimize the mass of ink between the dampening structures and the inkjet nozzles so as to improve the efficacy of any dampening system.
In a first aspect the present invention provides an inkjet printhead comprising:
Optional embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
The present invention may be used with any type of printhead. The present Applicant has previously described a plethora of inkjet printheads. It is not necessary to describe all such printheads here for an understanding of the present invention. However, the present invention will now be described in connection with a thermal bubble-forming inkjet printhead. For the avoidance of doubt, all references herein to “ink” should be construed to mean any ejectable printing fluid and includes, for example, traditional inks, invisible inks, fixatives and other printable fluids.
Printheads Having Sidewall Nozzle Chamber Inlets
Hitherto, we have described a thermal bubble-forming inkjet printhead, in which ink is supplied to a nozzle chamber from an ink conduit via a sidewall of the nozzle chamber. Such a printhead was described, for example, in our earlier US Publication No. 2007/0081044, the contents of which is herein incorporated by reference.
Referring to
Each nozzle assembly comprises a nozzle chamber 24 formed by MEMS fabrication techniques on a silicon wafer substrate 2. The nozzle chamber 24 is defined by a roof 21 and sidewalls 22 which extend from the roof 21 to the silicon substrate 2. As shown in
Returning to the details of the nozzle chamber 24, it will be seen that a nozzle opening 26 is defined in a roof of each nozzle chamber 24. Each nozzle opening 26 is generally elliptical and has an associated nozzle rim 25. The nozzle rim 25 assists with drop directionality during printing as well as reducing, at least to some extent, ink flooding from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 positioned beneath the nozzle opening 26 and suspended across a pit 8. Current is supplied to the heater element 29 via electrodes 9 connected to drive circuitry in underlying CMOS layers 5 of the substrate 2. When a current is passed through the heater element 29, it rapidly superheats surrounding ink to form a gas bubble, which forces ink through the nozzle opening. By suspending the heater element 29, it is completely immersed in ink when the nozzle chamber 24 is primed. This improves printhead efficiency, because less heat dissipates into the underlying substrate 2 and more input energy is used to generate a bubble.
As seen most clearly in
Hitherto, we have also described how the nozzle plate 56 of the printhead 1 may be coated with a layer of hydrophobic material, such as polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE). This hydrophobic exterior layer provides the printhead 1 with superior properties for printhead maintenance, as well as reducing the risk of flooding across the nozzle plate. Such a printhead and the fabrication thereof was described in detail in our earlier U.S. patent application Ser. No. 11/685,084 filed on Mar. 12, 2007, the contents of which is herein incorporated by reference. Further improvements in the manufacture of this hydrophobically-coated printhead were described in our earlier U.S. patent application Ser. No. 11/740,925 filed on Apr. 27, 2007, the contents of which is herein incorporated by cross-reference.
Printheads Incorporating Pressure-Dampening Structures
A manufacturing process for a printhead incorporating pressure-dampening structures will now be described. A partially-fabricated inkjet nozzle assembly, at the stage of fabrication shown in
As shown in
Referring to
In the process described in US Publication No. 2007/0081044, the next stage of fabrication defines an elliptical nozzle aperture 26 by etching through the remaining roof material 20 bounded by the nozzle rim 25. However, in the present invention, a vent 60 is etched simultaneously with the nozzle aperture 26. As shown in
Referring to
This polymeric material 100 may be resistant to ashing in an oxidizing plasma to facilitate late-stage ashing of the photoresist. However, as described in Applicant's U.S. application Ser. No. 11/740,925 filed on Apr. 27, 2007, any incompatibility of the polymer 100 with the ashing process may be circumvented by employing metal film protection of the polymer 100.
The polymer 100 should have some degree of flexibility or elasticity. Optionally, the polymer 100 has a relatively low stiffness. Optionally, the polymer 100 has a Young's modulus of less than 1000 MPa, and typically of the order of about 500 MPa. Optionally, the polymer 100 should also be relatively hydrophobic. The Applicant has identified a family of polymeric materials which meet the above-mentioned requirements of being hydrophobic, being resistant to ashing and having a low stiffness. These materials are typically polymerized siloxanes or fluorinated polyolefins. More specifically, polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE) have both been shown to be particularly advantageous. PDMS is a preferred material. A further advantage of these materials is that they have excellent adhesion to ceramics, such as silicon dioxide and silicon nitride of which the nozzle plate 56 is typically formed. A further advantage of these materials is that they are photopatternable, which makes them particularly suitable for use in a MEMS process. For example, PDMS is curable with UV light, whereby unexposed regions of PDMS can be removed relatively easily.
After deposition of the polymer 100, and with reference now to
Accordingly, as shown in
The printhead 200 shown in
Moreover, the dampening structures 70 are positioned adjacent each nozzle chamber 24. Optionally, each dampening structure is within less than 100 microns, optionally within less than 50 microns, or optionally within less than 25 microns of a nozzle assembly or a nozzle aperture 26. Hence, the volume of ink between the dampening structure 70 and the nozzle aperture 26 is relatively small compared to prior art dampening structures. This provides improved dampening efficacy and minimizes ink flooding due to pressure surges.
Moreover, since the dampening structures 70 are formed by the MEMS fabrication process, a large number of these structures can be provided on a single printhead. This large-scale multiplication of dampening structures 70 on the printead improves the effectiveness of pressure dampening compared to prior art designs, where far fewer dampening structures are typically included further upstream of the nozzle chambers 24. The Applicant's pagewidth printheads typically have an areal nozzle density of at least 10,000 nozzles per square cm of printhead surface. In accordance with the present invention, printheads may have at least 100, at least 500 or at least 1000 dampening structures per square cm of printhead surface (or nozzle plate).
A further advantage of printheads according to the present invention is that they maintain all the advantages of having a hydrophobic printhead face. Moreover, the hydrophobicity of the printhead face combined with the pressure-dampening structures 70 synergistically minimize printhead face flooding. On the one hand, the pressure-dampening structures 70 minimize pressure surges experienced at the nozzle aperture 26; on the other hand, the hydrophobicity of the printhead face compared with the hydrophilic walls of the nozzle chambers 24 minimizes ink leakages from the nozzle aperture 26, even if a pressure surge reaches the nozzle aperture 26. It will be appreciated that this synergism provided by the printhead according the present invention is particularly effective in minimizing printhead face flooding.
Self-evidently, printheads described herein may be used in inkjet printers.
It will be appreciated by ordinary workers in this field that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.
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