High print quality printhead

Details High print quality printhead High print quality printhead

1999-08-30

2002-12-10

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S062000, C347S064000, C347S058000

Reexamination Certificate

active

06491377

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to inkjet printing devices, and more particularly to a print cartridge providing high quality print output and adapted for use in inkjet printing devices. The present disclosure may contain material related to the inventions disclosed in U.S. Pat. No. 6,123,419 entitled “Segmented Resistor Drop Generator For inkJet Printing”, U.S. patent application No. 09/386,548 entitled “Redundant Input Signal Paths For An InkJet Print Head”, U.S. Pat. No. 6,132,033 entitled “InkJet Printhead With Flow Control Manifold And Columnar Structures”, U.S. patent application No. 09/386,580 entitled “Asymmetric Ink Emitting Orifices For Improved Inkjet Drop Formation”, U.S. Pat. No. 6,139,131 entitled “High Drop Generator Density PrintHead”, U.S. Pat. No. 6,234,598 entitled “Shared Multiple Terminal Ground Returns For An Inkjet Printhead”, U.S. patent application No. 09/385,297 entitled “High Thermal Efficiency InkJet Printhead”, and U.S. Pat. No. 6,270,201 entitled “Ink Jet Drop Generator And Ink Composition Printing System For Producing Low Ink Drop Weight With High Frequency Operation”, filed on even date herewith and assigned to the assignee of the present invention.
The art of inkjet printing technology is relatively well developed. However, users of inkjet printing products expect a perfect or near-perfect rendition of characters and images, in both black and color, as a hard copy output from their printing device. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines successfully employ inkjet technology for producing the hard copy printed output. The basics of the technology has been disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No.1 (February 1994) editions. Inkjet devices have also been described by W. J. Lloyd and H. T. Taub in Output Hardcopy Devices (R. C. Durbeck and S. Sherr, ed., Academic Press, San Diego, 1988, chapter 13). The technology for improved print quality often is realized in the mechanism-the print cartridge-that delivers ink to the medium to be printed upon.
A thermal inkjet printer for inkjet printing typically includes one or more translationally reciprocating print cartridges in which small drops of ink are ejected by a drop generator towards a medium upon which it is desired to place alphanumeric characters, graphics, or images. Such cartridges typically include a printhead having an orifice member or plate that has a plurality of small nozzles through which the ink drops are ejected. Beneath the nozzles are ink firing chambers, enclosures in which ink resides prior to ejection by an ink ejector through a nozzle. Ink is supplied to the ink firing chambers through ink channels that are in fluid communication with an ink reservoir, which may be contained in a reservoir portion of the print cartridge or in a separate ink container spaced apart from the printhead.
Ejection of an ink drop through a nozzle employed in a thermal inkjet printer is accomplished by quickly heating the volume of ink residing within the ink firing chamber with a selectively energizing electrical pulse to a heater resistor ink ejector positioned in the ink firing chamber. At the commencement of the heat energy output from the heater resistor, an ink vapor bubble nucleates at sites on the surface of the heater resistor or its protective layers. The rapid expansion of the ink vapor bubble forces the liquid ink through the nozzle. Once the electrical pulse ends and an ink drop is ejected, the ink firing chamber refills with ink from the ink channel and ink reservoir.
The minimum electrical energy required to eject an ink drop of a reliable volume is referred to as “turn-on energy”. The turn-on energy is a sufficient amount of energy to overcome thermal and mechanical inefficiencies of the ejection process and to form a vapor bubble having sufficient size to eject an amount of ink (generally determined by the design parameters of the firing chamber) from the printhead nozzle. Conventional thermal inkjet printheads operate at a firing energy slightly greater than the turn-on energy to assure that drops of a uniform size are ejected. Adding substantially more energy than the turn-on energy generally does not increase drop size but does deposit excess heat in the printhead.
Following removal of electrical power from the heater resistor, the vapor bubble collapses in the firing chamber in a small but violent way. Components within the printhead in the vicinity of the vapor bubble collapse are susceptible to fluid mechanical stresses (cavitation) as the vapor bubble collapses, thereby allowing ink to crash into the ink firing chamber components. The heater resistor is particularly susceptible to damage from cavitation. One or more protective layers are typically disposed over the resistor and adjacent structures to protect the resistor from cavitation and from chemical attack by the ink. One protective layer in contact with the ink is a mechanically hard cavitation layer that provides protection from the cavitation wear of the collapsing ink. Another layer, a passivation layer, is typically placed between the cavitation layer and the heater resistor and its associated structures to provide protection from chemical attack. Thermal inkjet ink-is chemically reactive, and prolonged exposure of the heater resistor and-its-electrical interconnections to the ink will result in a degradation and failure of the heater resistor and electrical conductors. The foregoing protection layers, however, tend to increase the inherent turn-on energy of the heater resistor required for ejecting ink drops due to the insulating properties of the layers.
Some of the energy that is deposited by the heater resistors is not removed by the ejected ink drop as momentum or increased drop temperature, but remains as heat in the printhead or the remaining ink. As the temperature increases, the ink drop size can change and at some temperature, the printhead will no longer eject ink. Therefore it is imp to control the amount of heat that is generated and that remains in the printhead during a printing-operation As more resistors are activated with higher frequencies of activation and are packed with greater density in the printhead, significantly more heat is retained by the printhead. Consequently, there must be a reduction in the amount of energy input to the printhead for higher frequencies and greater drop generator densities to be realized.
The heater resistors of a conventional inkjet printhead comprise a thin film resistive material disposed on an oxide layer of a semiconductor substrate. Electrical conductors are patterned onto the oxide layer and provide an electrical path to and from each thin film heater resistor. Since the number of electrical conductors can become large when a large number of heater resistors are employed in a high density (high DPI—dots per inch) printhead, various multiplexing techniques have been introduced to reduce the number of conductors needed to connect the heater resistors to circuitry disposed in the printer. See, for example, U.S. Pat. No. 5,541,629 “Printhead with Reduced Interconnections to a Printer” and U.S. Pat. No. 5,134,425, “Ohmic Heating Matrix”. Each electrical conductor, despite its good conductivity, imparts an undesirable amount of resistance in the path of the heater resistor. This undesirable parasitic resistance uselessly dissipates a portion of the electrical energy which otherwise would be available to the heater resistor thereby contributing to the heat gain of the printhead. If the heater resistance is low, the magnitude of the current drawn to nucleate the ink vapor bubble will be relatively large resulting in the amount of energy wasted in the parasitic resistance of the electrical conductors being significant relative to that provided to the heater resistor. That is, if the

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