Patent Application
20250100282
This disclosure relates generally to devices that produce ink images on media, and more particularly, to the preservation of inkjet operational status during long periods of printer inactivity.
Inkjet imaging devices, also known as inkjet printers, eject liquid ink from printheads to form images on an image receiving surface. The printheads include a plurality of inkjets that are arranged in an array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead controller. The printhead controller generates firing signals that correspond to digital data content that define the images. The actuators in the printheads respond to the firing signals by expanding into an ink chamber fluidly connected to a nozzle to eject ink drops from the nozzle onto an image receiving surface to form an ink image that corresponds to the digital image content used to generate the firing signals. The image receiving surface is usually a continuous web of media material or a series of media sheets.
Inkjet printers used for producing color images typically include multiple printhead modules. Each printhead module includes one or more printheads that typically eject a single color of ink. In a typical inkjet color printer, four printhead modules are positioned in a process direction with each printhead module ejecting a different color of ink. The four ink colors most frequently used are cyan, magenta, yellow, and black. The common nomenclature for such printers is CMYK color printers. Some CMYK color printers have two printhead modules that print each color of ink. The printhead modules that print the same color of ink are offset from each other by one-half of the distance between adjacent inkjets in the cross-process direction to double the number of pixels per inch to increase the density of a line of the color of ink ejected by the printheads in the two modules. As used in this document, the term “process direction” means the direction of movement of the image receiving surface as it passes the printheads in the printer and the term “cross-process direction” means a direction that is perpendicular to the process direction in the plane of the image receiving surface.
Inkjets, especially those in printheads that eject aqueous inks, need to fire regularly to help prevent the ink in the nozzles from drying. Sometimes the nozzles in a printhead dry because the inkjets have ejected a substantial amount of ink to form high coverage areas in an ink image. The operation of a high proportion of inkjets in a portion of the faceplate on the printhead to print a high coverage area can produce a large number of satellite drops that tend to adhere to the faceplate. Satellite drops are small ink drops that separate from the larger drops that travel from the nozzles to the image receiving substrates. The buildup of these satellite drops on a faceplate can clog nozzles in the faceplate. Additionally, if the inkjets in a printhead are not operated frequently enough, such as when low ink area coverage image portions are printed, then the ink within an inkjet can dry and render the inkjet inoperative. To maintain the operational status of the inkjets, the printhead modules are moved from positions opposite the path of the image receiving substrates to printhead maintenance stations where the printheads are purged. Purging a printhead means a pressurized gas or liquid is applied to the ink supply chambers within a printhead to force ink from the chamber into the nozzles where the ink is emitted from the nozzles onto the faceplate. One or more wipers are then moved across the faceplate to remove the purged ink from the faceplate into a waste ink receptacle.
During long periods of printer inactivity, such as overnight or weekend shutdowns, some inks deteriorate in the nozzles and contaminate a printhead by producing buildup on rock screens, manifolds, piezoelectric tiles, and nozzles within the printheads. This contamination results in streaks in ink images produced when the printer is returned to service, lower ink drop mass, vent line failures, intermittent firing, missing, or mis-directional ink drops from the inkjets, and eventually unrecoverable inkjets, even after purging.
Contamination appears to occur due to chemical and physical stresses in the inkjet stack of the printhead that increase pigment particle size and viscosity of the ink. This contamination may lead to irreversible printhead damage. While reformulation of the inks may remedy the contamination issues, that process is an expensive and lengthy endeavor. Additionally, changes in the ink composition may adversely affect image quality. Thus, inkjet printers would benefit from being able to stabilize ink properties during long periods of printer inactivity without changing ink compositions.
A printhead maintenance station for a color inkjet printer is configured to stabilize ink properties during long periods of printer inactivity without changing ink compositions. The printhead maintenance station includes a printhead cap configured to cover a face of a printhead; an opening in the printhead cap; a printhead vent blocking member configured to block manifold vents in the printhead when the printhead is moved to engage the printhead vent blocking member; and a valve configured to open and close, the valve being positioned within the printhead cap to enable the printhead cap to hold a volume of high pH fluid entering the printhead cap through the opening in the printhead cap when the valve is closed and to enable egress of the high pH fluid from the printhead cap when the valve is opened.
A method of operating a printhead maintenance station stabilizes ink properties during long periods of printer inactivity without changing ink compositions. The method includes filling a printhead cap having a manifold vent blocking member with the high pH liquid; lowering a printhead onto the printhead cap to block manifold vents in the printhead and contact the nozzle plate of the printhead with the high pH fluid; and applying a vacuum to an ink supply line of the printhead to pull the high pH fluid into the printhead.
An inkjet printer includes a printhead maintenance station that is configured to stabilize ink properties during long periods of printer inactivity without changing ink compositions. The inkjet printer includes at least one printhead module configured with at least one printhead; a printhead maintenance module having a printhead cap with a manifold vent blocking member, an opening in the printhead cap, a printhead vent blocking member configured to block manifold vents in the printhead when the at least one printhead is moved to engage the printhead vent blocking member, and a valve configured to open and close, the valve being positioned within the printhead cap to enable the printhead cap to hold a volume of high pH fluid entering the printhead cap through the opening in the printhead cap when the valve is closed and to enable egress of the high pH fluid from the printhead cap when the valve is opened; and a controller operatively connected to the at least one printhead module and the printhead maintenance station. The controller is configured to: fill the printhead cap with the high pH liquid; lower the at least one printhead onto the printhead cap to block manifold vents in the printhead and contact the nozzle plate of the printhead with the high pH fluid; and apply a vacuum to an ink supply line of the printhead to pull the high pH fluid into the printhead.
A high pH fluid has been developed that is useful for preserving printheads during periods of inactivity of at least two hours. The high pH fluid includes a fluid; and a base added to the fluid that raises the pH level of the fluid to at least 8.
The foregoing aspects and other features of a printhead maintenance station and printhead maintenance station operational method so the printer stabilizes ink properties during long periods of printer inactivity without changing ink compositions are explained in the following description, taken in connection with the accompanying drawings.
For a general understanding of the environment for the printhead maintenance station and the printhead maintenance station operational method disclosed herein as well as the details for the printhead maintenance station and the printhead maintenance station operational method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. As used herein, the word “printer” encompasses any apparatus that ejects ink drops onto different types of media to form ink images.
The print zone PZ in the printer 10 of
With further reference to
Controller 80 operates at least one of the actuators 40 to rotate a pivoting member at position 88 to either direct a sheet to receptacle 56 or to return path 72. A sheet S is moved by the rotation of rollers along the return path 72 in a direction opposite to the direction of movement in the process direction past the printheads. Pivoting member 82 is operated by the controller 80 to either direct the sheet along a curved portion of the return path 72 into inverter 76 so the sheet is turned over for duplex printing or along the straight portion of the return path 72. When the sheet follows the straight portion, the inverter 76 is bypassed and the side of the sheet previously printed can be printed again. The controller operates one of the actuators 40 to move the pivoting member 82 clockwise to direct a sheet into the inverter 76 and counterclockwise to bypass the inverter. Regardless of whether the substrate is inverted or not, it merges into the job stream being carried by the media transport 42 when controller 80 operates another actuator 40 to rotate pivoting member 86 to provide ingress of a sheet S from return path 72 to the job stream entering the print zone PZ.
As further shown in
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80 is operatively connected to the components of the printhead modules 34A-34D (and thus the printheads), the actuators 40, and the dryer 30. The ESS or controller 80, for example, is a self-contained computer having a central processor unit (CPU) with electronic data storage, and a display or user interface (UI) 50. The ESS or controller 80, for example, includes a sensor input and control circuit as well as a pixel placement and control circuit. In addition, the CPU reads, captures, prepares, and manages the image data flow between image input sources, such as a scanning system or an online or a work station connection (not shown), and the printhead modules 34A-34D. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the printing process.
The controller 80 can be implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions can be stored in non-transitory computer readable medium associated with the processors or controllers. The processors, their memories, and interface circuitry configure the controllers to perform the operations described below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in very large scale integrated (VLSI) circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits.
In operation, image content data for an image to be produced are sent to the controller 80 from either a scanning system or an online or work station connection for processing and generation of the printhead control signals output to the printhead modules 34A-34D. Along with the image content data, the controller receives print job parameters that identify the media weight, media dimensions, print speed, media type, ink area coverage to be produced on each side of each sheet, location of the image to be produced on each side of each sheet, media color, media fiber orientation for fibrous media, print zone temperature and humidity, media moisture content, and media manufacturer. As used in this document, the term “print job parameters” means non-image content data for a print job and the term “image content data” means digital data that identifies an ink image to be printed on a media sheet.
A side view of a printhead maintenance station 32 and its interaction with a printhead 204 to inject a high pH liquid is shown in
The high pH fluid can be made from an ink used in the printer that has been buffered to a pH of 8 or more by adding a base such as triethanolamine, triethylamine, diethylamine, dimethylethanolamine, KOH, or NaOH. Alternatively, a known printhead cleaning/flushing solution, such as KF200 or CL67 available from Nippon Kayaku, is buffered to a pH of 8 or more by adding one of the bases identified above. In another embodiment, the high pH fluid is a solution consisting of water, propylene glycol, hexanediol, butane diol, glycol ethers, glycerol, surfactants and bases like triethylamine, hydrazine, dimethylethanolamine, KOH, NaOH, or the like. As used in this document, the term “high pH fluid” means a liquid having a pH of at least 8 and not more than 12.
A process 500 for operating the printhead maintenance station that injects high pH fluid into the printheads of an inkjet printer is shown in
The process 500 of
It will be appreciated that variants of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.
