Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-03-08
2004-08-24
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S333000
Reexamination Certificate
active
06782233
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to an electrostatographic, including digital, apparatus, and more particularly, it relates to heat and pressure fusing members for fixing images to a final substrate. In embodiments, the invention relates to fuser and pressure members useful in a high-speed color xerographic apparatus.
In a typical electrophotographic copying or 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 selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. 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 either to a donor roll or to a latent image on the photoconductive member. The toner attracted to a donor roll is then deposited as latent electrostatic images on a charge-retentive photoconductive surface, such as a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support member or otherwise upon the surface thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through a nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. In a Nip Forming Fuser Roll (NFFR), the heated fuser roll is provided with a layer or layers that are deformable by a harder pressure roll when the two rolls are pressure engaged. The length of the nip and process speed determines the dwell time or time that the toner particles remain in contact with the surface of the heated roll.
The heated fuser roll is usually the roll that contacts the toner images on a substrate such as plain paper. In any event, the roll contacting the toner images is usually provided with an adhesive (low surface energy) material for preventing toner offset to the fuser member. Three materials, which are commonly used for such purposes, are fluoropolymers, fluoroelastomers and silicone rubber.
Roll fusers work very well for fusing color images at low speeds since the required process conditions such as temperature, pressure and dwell can easily be achieved. When process speeds approach 100 pages per minute (ppm), roll fusing performance starts to falter. As fusing speed increases, dwell time must remain constant, which means an increase in nip width. Increasing the nip width can be accomplished by either increasing the fuser roll rubber thickness, and/or reducing the modulus and/or the outside diameter of the roll. However, each of these solutions reach their maximum effectiveness at about 100 ppm. Specifically, for an internally heated fuser roll, the rubber thickness is limited by the maximum temperature the rubber can withstand, and the thermal gradient across the elastomer layer. The roll size also becomes a critical issue for reasons of space, weight, cost and stripping.
Following is a discussion of references, the disclosures each of which are hereby incorporated by reference in their entirety.
U.S. Pat. No. 4,242,566 discloses a heat and pressure fusing apparatus that exhibits high thermal efficiency. The fusing apparatus comprises at least one pair of first and second oppositely driven pressure fixing feed rollers, each of the rollers having an outer layer of a thermal insulating material; first and second idler rollers, a first flexible endless belt disposed about the first idler roller and each of the first pressure feed rollers and a second flexible endless belt disposed about the second idler roller and each of the second pressure feed rollers, at least one of the belts having an outer surface formed of a thermal conductive material, wherein there is defined an area of contact between the outer surfaces of the first and second belts located between the first and second pressure feed rollers for passing the copy sheet between the two belts under pressure; and means spaced relative to the belt whose outer surface comprises the thermal conductive material for heating the outer surface thereof, whereby when an unfused copy sheet is passed through the area of contact between the two belts it is subject to sufficient heat and pressure to fuse developed toner images thereon.
U.S. Pat. No. 4,582,416 discloses a heat and pressure fusing apparatus for fixing toner images. The fusing apparatus is characterized by the separation of the heat and pressure functions such that the heat and pressure are effected at different locations on a thin flexible belt forming the toner-contacting surface. A pressure roll cooperates with a stationary mandrel to form a nip through which the belt and copy substrates pass simultaneously. The belt is heated such that by the time it passes through the nip its temperature together with the applied pressure is sufficient for fusing the toner images passing through.
U.S. Pat. No. 4,992,304 discloses a fuser belt for a reproduction machine. The belt may have one of several configurations which all include ridges and interstices on the outer surface which contacts the print media. These interstices are formed between regularly spaced ridges, between randomly spaced particles, between knit threads. These interstices allow the free escape of steam from the media during high-temperature fusing of the reproduction process. As the steam escapes freely, the steam does not accumulate in the media causing media deformations and copy quality deterioration. Additionally, media handling is improved because the ridges and interstices reduce the unwanted but unavoidable introduction of thermal energy into the copy media.
U.S. Pat. No. 5,250,998 discloses a toner image fixing device wherein there is provided an endless belt looped up around a heating roller and a conveyance roller, a pressure roller for pressing a sheet having a toner image onto the heating roller with the endless belt intervening between the pressure roller and the heating roller. A sensor is disposed inside the loop of the belt so as to come in contact with the heating roller, for detecting the temperature of the heating roller. The fixing temperature for the toner image is controlled on the basis of the temperature of the heating roller detected by the sensor. A first nip region is formed on a pressing portion located between the heating roller and the fixing roller. A second nip region is formed between the belt and the fixing roller, continuing from the first nip region but without contacting the heating roller.
U.S. Pat. No. 5,349,424 discloses a heated, thick-walled, belt fuser for an electrophotographic printing machine. The belt is rotatably supported between a pair of rolls. One of the spans of the belt is in contact with a heating roll in the form of an aluminum roll with an internal heat source such as a quartz lamp. The belt is able to wrap a relatively large portion of t
Amico Mark S.
Berkes John S.
Bott Donald M.
Condello Anthony S.
Vaughan Derek E.
Bade Annette L.
Braun Fred L.
Xerox Corporation
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