Patent Application
20090179963
The present invention relates to the field of inkjet printing and in particular, inkjet printers with pagewidth printheads.
The following applications have been filed by the Applicant simultaneously with the present application:
The disclosures of these co-pending applications are incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.
The Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional reciprocating printhead designs. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute, speeds previously unattainable with conventional inkjet printers.
The high resolution and print speeds are largely due to the self cooling operation of the printheads. Excess heat does not build up in the nozzles because it is removed from the printhead with the ejected ink drops. This allows the nozzles to be closer together and the nozzle firing rate is limited only by the ink refill rate. The self cooling operation relies on low ejection energies which in turn correspond to small nozzles and low drop volumes. Another factor that assists low energy ejection is a short nozzle aperture length. The nozzles define a geometric shape (typically circular or elliptical) and the aperture length is the thickness of the structure (such as a nozzle plate) which defines the nozzle. A long nozzle aperture length has a high fluidic drag on the ink drop as it is ejected through the nozzle. The Applicant's printhead designs keep the nozzle aperture length relatively short (less than 5 microns).
The small nozzles clog easily and paper dust or dried ink on the nozzle face (the exterior surface defining the array of nozzle apertures) can cause color mixing between closely spaced nozzles of different color. The paper dust and other contaminants can be removed by wiping the nozzle face. However, contact pressure with wiper is critical for effective cleaning. Unfortunately, the pressure needed for effective cleaning can damage the delicate structures of the printhead IC.
Accordingly, the present invention provides a printhead assembly for an inkjet printer, the printhead assembly comprising:
an elongate printhead IC having a nozzle face defining an array of nozzles;
a support structure for supporting the elongate printhead IC on an external surface such that its length is transverse to a media feed direction through the printer; wherein,
the external surface being configured such that it has a section that is flush with a long side edge of the elongate printhead IC.
The invention mounts the printhead ICs so that a wiping surface is guided on to the nozzle face rather impacting on a side of the printhead IC sitting proud of the mounting surface. This allows the wiper to effectively clean the nozzle face without using a contact pressure that damages the delicate nozzle structures. The Applicant's work has found that a printhead IC mounted such that it sits proud of the external surface requires a wiper to have a high contact force for it to clean the nozzle face. However, the force is damaging to the printhead IC and in particular the edge that first contacts the wiper. Reducing the contact force causes the wiper blade to bounce off the edge of the printhead IC and bounce several times across the nozzle face. Consequently, the wiper does not contact the nozzle face at several points and hence fails to clean away contaminants.
Preferably, the printhead assembly has a plurality of elongate printhead ICs mounted end to end on the support structure such that in use the printhead assembly is a pagewidth printhead and the long side edge of each of the printhead ICs align with each other. Preferably, the support structure has an epoxy resin adjacent the long side edges of the printhead ICs, the epoxy resin being profiled such that it is flush with the nozzle faces of the printhead ICs. Preferably, the printhead ICs each have a line of wire bonds along a trailing long side edge opposite the long side edge adjacent the epoxy resin. Preferably, the epoxy resin is thixotropic prior to setting. Preferably, the wire bonds are encased in encapsulant profiled to present a surface inclined upwardly from the nozzle face. Preferably, the nozzle face is planar. In a further preferred form, the nozzle face is lithographically deposited silicon dioxide. Optionally, the nozzle face is lithographically deposited silicon nitride. Preferably, the printhead assembly is provided as a printhead cartridge for user insertion and removal from a printer.
Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:
Both the channel molding 68 and the top cover molding 72 are molded from LCP (liquid crystal polymer) because of its stiffness and coefficient of thermal expansion that closely matches that of silicon. It will be appreciated that a relatively long structure such as a pagewidth printhead should minimize any thermal expansion differences between the silicon substrate of the printhead ICs 31 and their supporting structure.
A layer of epoxy resin 130 is applied to the die attach film 66. The resin layer 130 contacts the wiper blade 138 as it moves across the exterior face of the printhead assembly. The thickness of the resin layer 130 is controlled such that it is flush with the nozzle faces of the printhead ICs 31. This essentially grouts the step created by the side of the printhead ICs 31. With the resin layer 130 guiding the wiper blade 138 onto the nozzle face, the front edges of the printhead ICs are shielded from hard impacts with the wiper. Consequently, there is less damage and wear to the printhead ICs 31 and the wiper can clean effectively using only a modest contact force. Impact with the front edge of the nozzle face can cause the wiper blade to bounce and lose contact with he printhead IC.
The printhead ICs are fabricated such that the nozzle face is planarized. A flat nozzle face cleans more easily as dust and contaminants have little to anchor to apart from the nozzle openings themselves. This process has been described in detail in the Applicant co-pending U.S. Ser. No. 11/877,667 (Our Docket No. MPN013US), the contents of which are incorporated by reference. Briefly, the nozzle structures have a layer of photo resist deposited over them which is then sealed under a nozzle face layer of silicon oxide and or silicon nitride. The relatively hard silicon nitride or silicon oxide has better wear resistance than printhead ICs with a nozzle face of polymer resist material.
For convenience, the encapsulant 132 and the epoxy resin layer 130 are the same polymer material. The polymer material should be thixotropic; that is, it should not flow under its own weight. In this way, the encapsulant 132 and the grout epoxy 130 can be accurately profiled and shaped without risk of the material flowing to a different shape.
