Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-08-12
2004-06-29
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C399S328000, C399S333000
Reexamination Certificate
active
06757514
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electrostatographic imaging, and more particularly, it relates to a high-speed heat and pressure belt fusing apparatus for fixing images to a final substrate that exhibits long belt life, minimal edge wear and reliable stripping.
In a typical electrophotographic copying or printing process, a charge retentive surface such as 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 selectively exposed to light to dissipate the charges thereon in areas subjected to the light. 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 one or more developer materials 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 electrostatic image on the photoconductive member. When attracted to a donor roll the toner particles are subsequently deposited on the latent electrostatic images. The toner powder image is then transferred from the photoconductive member to a final substrate. The toner particles forming the toner powder images are then subjected to a combination of heat and/or pressure to permanently affix the powder images to the copy substrate.
In order to fix permanently or fuse the toner material onto a substrate or support member such as plain paper 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 and/or into the 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 final 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 substrate to which the toner images are electrostatically adhered is moved through a nip formed between the pressure engaged 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 (i.e. conformable) by a harder pressure roll when the two rolls are pressure engaged. The length of the nip determines the dwell time or time that the toner particles remain in contact with the surface of the heated roll, the dwell time being also determinative of the fuser's speed.
The layer or layers usually comprise an abhesive (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 well for fusing color images at lower speeds since the required process conditions such as temperature, pressure and dwell can be achieved. When process speeds approach faster speeds, for example 100 pages per minute (ppm), roll fusing performance is no longer acceptable. As fusing speed increases, dwell time must be maintained above a minimum, which means an increase in nip length. Increasing the nip length can be accomplished either by increasing the fuser roll rubber thickness, and/or reducing the modulus and/or increasing 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 fuser roll deformable layer thickness is limited by the maximum temperature the material forming the layers can withstand, and the thermal gradient across the layer. The roll size also becomes a critical issue for reasons of space, weight, cost and substrate stripping therefrom.
In order to obtain much higher fusing speeds than heretofore possible for color xerography, very large or long fusing nips are necessary. One way to achieve longer fusing nips for this purpose is to use a thick deformable belt instead of a fuser roll with a thick deformable layer or layers. Due to poor thermal conductivity, however, it is necessary to heat the outer surface of a thick elastomer belt over an extended contact zone using a source of thermal energy. To create a long, nip for extending fusing dwell time, it is desired that the belt be as thick as possible. However, belt flexibility can be compromised with relatively large belt thicknesses. Additional nip length can also be obtained using an elastomeric layer or layers on a pressure roll that contact the internal surface of the thick belt. The thicknesses of the elastomers on the pressure roll and the fuser belt along with other characteristics of the elastomers such as Shore A hardness contribute to the desired characteristics of the fusing nip. The thickness and the durometer of both elastomers can be varied to obtain the desired dwell times in the fusing nip.
One problem with a belt and roll arrangement that yields the desired nip length and thus the desired higher fusing speeds is that the creep is so low that substrate stripping from the belt without a separate stripping device is impossible. Creep is defined as the % velocity difference of the fuser belt surface in the fusing nip compared to its speed outside the nip.
Therefore, it is desired to provide a combination high-speed (i.e. above 100 ppm) belt and roll fuser for fusing color toner images that exhibit high gloss with minimal edge wear and long belt life and reliable substrate stripping.
Following is a discussion of references that may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description of the present invention to follow, may provide a better understanding of the invention. The references that are discussed herein are hereby incorporated by reference in their entirety.
U.S. patent application Ser. No. 10/093,263 filed on Mar. 8, 2002, assigned to the same assignee as the present invention discloses a heat and pressure belt fuser structure having an endless belt and a pair of pressure engageable members between which the endless belt is sandwiched for forming a fusing nip through which substrates carrying toner images pass with the toner images contacting an outer surface of the endless belt, at least one of the pressure engageable members has one or more deformable layers, and the endless belt has a thickness of from about 1 to about 8 mm; and the fuser structure includes an external source of thermal energy for elevating a pre-nip area of the belt. The thick belts in combination with a deformable layer of at least one of the pressure member(s) cooperate to provide a large nip and adequate creep for intrinsic paper stripping. A creep value less than a predetermined value prevents stripping.
U.S. Pat. No. 5,890,047 granted to Rabin Moser on Mar. 30, 1999 discloses a combination belt and roll fuser has a pair of pressure engageable rolls with a belt looped or wrapped around one of the pressure engageable rolls such that the belt is sandwiched between the two rolls. The belt is deformed due to the force exerted by the pressure rolls such that it forms a single fusing nip. Substrates carrying toner images pass through the single fusing nip with the toner images contacting the outer surface of the belt. An internally heated, thermally conductive roll contacts a portion of the belt externally at a pre-nip location for elevating its temperature of the belt. The pressure engageable roll about which the
Berkes John S.
Bott Donald M.
Condello Anthony S.
Ngo Hoang
Sklar Ben
Xerox Corporation
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