Electrophotography – Document handling – Copy
Reexamination Certificate
2000-03-03
2001-06-19
Grimley, Arthur T. (Department: 2852)
Electrophotography
Document handling
Copy
C399S341000
Reexamination Certificate
active
06249667
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a substrate conditioning device for an electrophotographic printing machine and, more particularly, concerns an improvement for eliminating water spills from the ends of moisturizing rolls in the conditioning device.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrophotographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, imaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and developing, all followed by transfer to paper, is done in a single revolution of the photoreceptor in so-called single pass machines, while multipass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color. The single pass architecture offers a potential for high throughput.
In order to fix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to apply pressure and elevate the temperature of the toner to a point at which the constituents of the toner material become tacky and coalesce. This action causes the toner to flow to some extent into the fibers or pores of the support medium (typically paper). Thereafter, as the toner material cools, solidification of the toner material occurs, causing the toner material to be bonded firmly to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy and pressure for fixing toner images onto a support member is old and well known.
One approach to heat and pressure fixing of electroscopic toner images onto a support has been to pass the support bearing the toner images between a pair of opposed roller members, at least one of which is internally heated. During operation of a fixing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls and thereby heated under pressure. A large quantity of heat is applied to the toner and the copy sheet bearing the toner image. This heat evaporates much of the moisture contained in the sheet. The quantity of heat applied to the front and back sides of the sheet are often not equal. This causes different moisture evaporation from the two sides of the sheet and contributes to sheet curling. One solution to this problem is set forth in U.S. Pat. No. 5,434,029, discussed below, the contents of which are hereby incorporated by reference.
A number of solutions to this problem have been advanced. One proposed solution is to use an offset press dampening system to add moisture to each sheet as it exits the copier. These systems typically rely on the generation of a pool of water at a roll interface to distribute the water evenly along the rolls. Such systems usually operate with a web paper supply and their use with a cut sheet feeder system creates some difficulties not previously contemplated or addressed.
Another proposed solution is disclosed in U.S. Pat. No. 5,937,258, issued Aug. 10, 1999 to Thomas Acquaviva et al. and titled PAPER CONDITIONER WITH ARTICULATING BACK-UP/TRANSFER ROLLS, which is incorporated herein by reference to the extent necessary to practice the present invention. This solution uses a conditioner located after the fuser and before a mechanical decurler. The function of the conditioner is to replace the moisture lost in the fusing process and thereby reduce image dependent curl. The approach taken to replace moisture is to drive a sheet between two closely spaced rollers: one roller, called the back-up roller, is rubber coated and drives the sheet forward. The second roller, called the transfer roller, rotates in the opposite direction and applies a thin film of water to the paper on the side opposite to the back-up roller. The surface of the transfer roller is “wet” by passing through a flooded nip. The film thickness deposited on the transfer roll surface is determined by the pressure between the transfer roller and a metering roller. Two sets of these rollers are required to moisturize both sides of the sheet. One of the biggest problems is preventing water leakage from the system.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,930,578 to Hwang discloses a paper conditioner to control image dependent curl in a copier/printer. The conditioner employs metering and transfer rolls which form a nip and have grooves positioned on the end portions of both rolls. Portions of both the metering and transfer rolls are located over a sump connected to a reservoir that supplies liquid to the nip. The grooves act as gutters and allow excess liquid to flow into the sump and subsequently back into the reservoir.
U.S. Pat. No. 5,434,029 to Moser describes an apparatus and method of preventing the curling of a substrate having toner images electrostatically adhered thereto which substrate has been subjected to heat for the purpose of fixing the toner images to the substrate. Simultaneous constraint of the copy substrate and the application of moisture thereto is effected by passing the substrate through the nip formed by two pressure engaged rollers, one of which is utilized for applying the water to the back side of the substrate as the substrate passes through the aforementioned nip.
U.S. Pat. No. 5,264,899 discloses a system for adding moisture to a copy sheet. The toner fixation step of electrostatographic reproduction desiccates paper, which may lead to the formation of a wave along the sheet edge. The invention uses a pair of porous rolls defining a nip to transfer additional moisture to the coy sheet as it is passed through the nip. The added moisture prevents edge wave formation.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided an apparatus for adding moisture to a sheet. The device includes a reservoir for storing a quantity of liquid, a pair of rolls in contact with one another so as to define a nip between their outer surfaces, and a metering roll associated with the reservoir and one of the pair of rolls. The metering roll forms a nip with one of the pair of rolls to direct a controlled flow of liquid from the reservoir to the nip area. Seals located at the ends of the metering roll and the roll with which it forms a nip retain excess liquid in the nip.
In accordance with another aspect of the invention there is provided a printing machine, which includes a pair of rolls aligned with one another to define a nip. A metering roll is in circumferential surface contact with one of the cylindrical rolls to form a nip and control th
Acquaviva Thomas
Schlageter Alan G.
Grimley Arthur T.
Robb Linda M.
Tran Hoan
Xerox Corporation
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