Patent Application
20100215405
Liquid electro-photographic (LEP) printing, sometimes also referred to as liquid electrostatic printing, uses liquid toner to form images on paper or other print media. Liquid toner used in LEP is commonly referred to as ink. LEP is often used for large scale commercial printing. The basic LEP printing process involves placing a uniform electrostatic charge on a photoconductor, the photoconductive surface on a rotating drum for example, and exposing the photoconductor to light in the pattern of the desired printed image to dissipate the charge on the areas of the photoconductor exposed to the light. The resulting latent electrostatic image on the photoconductor is developed by applying a thin layer of ink to the photoconductor. The ink generally consists of charged toner particles dispersed in a carrier liquid. The charged toner particles adhere to the discharged areas on the photoconductor (discharged area development DAD) or to the charged areas (charged area development CAD), depending on the charge of the toner particles, to form the desired image on the photoconductor. The image is transferred from the photoconductor to an intermediate transfer member and then from the intermediate transfer member to the paper or other print medium.
a-c illustrate exemplary cleaning, systems which may be provided in an embodiment of an SOP ink development unit.
Exemplary squeegee on a PIP (photo imaging plate) (or “SOP”) ink development unit are disclosed which may be implemented in stand-alone printer systems, such as liquid electro photography (LEP) printers. In exemplary embodiments, one or more SOP ink development units may be provided (e.g., one SOP ink development unit for each color). The SOP ink development unit includes an ink dispenser which dispenses ink onto a compliant surface of a developer roller during a printing operation. It is noted that the ink dispenser may take any suitable form, including the ink “jet” shown in the drawings, ink “pan” (not shown), and the like. The developer roller rotates against the PIP with a contact force sufficient to serve as a squeegee to remove excess ink. Thus, the SOP ink development unit transfers a more compacted ink layer with higher solids concentration onto an image area of the PIP for development. Also, embodiments of the new SOP ink development unit may simplify the ink development process by bringing the ink directly to the developer roller near the nip between the developer roller and the PIP, instead of first having to develop the ink on another roller and then having to transport the ink to the developer roller. This simplification results in an ink development unit (the SOP ink development unit) which may be easier to manufacture and less expensive than traditional development units.
Further advantages may also be realized, for example, because there are no gaps which need to be set as there are between the various rollers in a traditional ink development unit, such as the gap between the developer roller and the PIP. In addition, the surface quality of the developer roller is not as large a factor as it is in a traditional ink development unit because in the SOP ink development unit the ink is applied directly to a compliant surface of the developer roller. The compliant surface of the developer roller deforms as it is compressed against the PIP drum to maintain a force at the nip sufficient to squeeze “excess” ink out of the nip. Thus, quality control standards during the manufacturing process may be relaxed, reducing manufacture time and costs. In addition, the compacted ink layer helps more completely transfer to the image area on the PIP even when manufacturing defects are present on the compliant surface of the developer roller, or as surface quality deteriorates over time.
The latent image on PIP 12 is developed through the application of the ink which adheres to the discharged areas of PIP 12 in a uniform layer of ink on PIP 12, developing the latent electrostatic image into an ink image. The ink image is transferred from PIP 12 to an intermediate transfer member (ITM) 20 and then from intermediate transfer member 20 to print medium 22 as medium 22 passes through a nip 23 between intermediate transfer member 20 and a pressure roller 24. Print medium 22 represents generally any suitable print medium and may be delivered to print engine 10 as a continuous web dispensed from a roll or as individual sheets. Pressure roller 24 is commonly referred to as an impression cylinder (IMP). An LED lamp or other suitable discharging device 26 removes residual charge from PIP 12 and toner residue is removed at a cleaning station 28 in preparation for developing the next image or for applying the next toner color plane.
In an exemplary embodiment, the SOP ink development unit 110 serves as an ink tray 115 to collect excess ink, while also housing a developer roller 120 and ink dispenser 130. The ink dispenser 130 is positioned in the SOP ink development unit 110 such that ink is delivered directly onto a compliant surface 122 of the developer roller 120 during a printing operation (see, e.g.,
The developer roller 120 may be manufactured as a hollow cylindrical roller having a conductive core. The core may be manufactured of any conductive material, such as, e.g., metal, plastic with one or more conductive layer, and the like. In an exemplary embodiment, the core is formed from one or more of aluminum, stainless steel, cold drawn steels with a coating, etc., and/or combinations thereof The core may also be covered with a layer of a conductive polymeric material. An example is polymeric material incorporating additives such as metal particles, ionic charged particles, carbon black, graphite, etc., and/or combinations thereof In an exemplary embodiment, this layer is formed from a conductive urethane material.
The developer roller 120 may also include a suitable shaft and gear system which may be operatively associated with a drive assembly (not shown) of the printer system. Generally, the drive assembly includes mating gears to effect rotational movement (e.g., in the direction of arrow 121) of the developer roller 120 during a printing operation in which the PIP is also rotated (e.g., in the direction of arrow 141), as is well understood in the printer arts.
Notably missing in the SOP ink development unit 10 are the separate electrode and ink-compacting roller that would otherwise be present in a traditional developer unit. Instead, the developer roller 120 serves both of these functions, and therefore a separate electrode and ink-compacting roller are not necessary. Eliminating these components in the SOP ink development unit 110 reduces part count and the associated cost and failure points, while also increasing the speed at which print jobs may be completed (i.e., by reducing the path from ink dispenser 130 to the imaging surface of the PIP 140).
Before continuing, it is noted that the systems and methods described herein are not limited to any particular printer system.
During a printing operation, the ink dispenser 130 uniformly feeds ink 131 onto the compliant surface 122 of the developer roller 120. The ink travels toward the nip 150 formed between the developer roller 120 and the PIP 140 so that the ink 131 is applied onto the PIP 120. Excess ink 131 is simultaneously squeegeed by the interaction between the developer roller 120 and the PIP 140. Thus, the developer roller 120 regulates the solids ratio in the ink on the PIP 140. Ink develops on the PIP 140 only where the PIP has a discharged image area (e.g., as illustrated in
a-c illustrate exemplary cleaning systems which may be provided in an embodiment of an SOP ink development unit. The cleaning system may include one or more secondary rollers, sponge rollers, wipers or scrapers, and or any combination thereof.
The exemplary cleaning system shown in
This cleaning process, in many instances, may substantially minimize sludge buildup on developer roller 120. In each of these embodiments, the excess ink 135 may collect in the ink reservoir 115 of the SOP ink development unit 110 for recycling, remixing, reuse, or disposal. Thus, contamination of other parts of the printer system by the excess ink is reduced or altogether eliminated.
The exemplary embodiments shown and described herein are provided for purposes of illustration and are not intended to be limiting. By way of example, the cleaning systems are not limited to the particular configurations shown and described herein. It is also noted that the placement of the roller(s) in the SOP ink development unit 110 may also be varied depending on design considerations. Exemplary design considerations include, but are not limited to the cost and size of components, printer throughput, type of ink being used, and so forth.
