Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2002-08-09
2004-09-28
Lee, Susan (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C219S216000, C399S067000, C399S069000
Reexamination Certificate
active
06799000
ABSTRACT:
FIELD OF THE INVENTION
The invention relates in general to the fuser used electrostatographic printing process, and in particular to the control of temperature of roller fusing members.
BACKGROUND OF THE INVENTION
In electrostatographic imaging and recording processes such as electrophotographic reproduction, an electrostatic latent image is formed on a primary image-forming member such as a photoconductive surface and is developed with a thermoplastic toner powder to form a toner image. The toner image is thereafter transferred to a receiver, e.g., a sheet of paper or plastic, and the toner image is subsequently fused to the receiver in a fusing station using heat or pressure, or both heat and pressure. The fuser station can include a roller, belt, or any surface having a suitable shape for fixing thermoplastic toner powder to the receiver.
The fusing step in a roller fuser commonly consists of passing the toned receiver between a pair of engaged rollers that produce an area of pressure contact known as a fusing nip. In order to form the fusing nip, at least one of the rollers typically has a compliant or conformable layer on its surface. Heat is transferred from at least one of the rollers to the toner in the fusing nip, causing the toner to partially melt and attach to the receiver. In the case where the fuser member is a heated roller, a resilient compliant layer having a smooth surface is typically used which is bonded either directly or indirectly to the core of the roller. Where the fuser member is in the form of a belt, e.g., a flexible endless belt that passes around the heated roller, it typically has a smooth, hardened outer surface.
Most roller fusers, known as simplex fusers, attach toner to only one side of the receiver at a time. In this type of fuser, the roller that contacts the unfused toner is commonly known as the fuser roller and is usually the heated roller. The roller that contacts the other side of the receiver is known as the pressure roller and is usually unheated. Either or both rollers can have a compliant layer on or near the surface. In most fusing stations having a fuser roller and an engaged pressure roller, it is common for only one of the two rollers to be driven rotatably by an external source. The other roller is then driven rotatably by frictional contact.
In a duplex fusing station, which is less common, two toner images are simultaneously attached, one to each side of a receiver passing through a fusing nip. In such a duplex fusing station there is no real distinction between fuser roller and pressure roller, both rollers performing similar functions, i.e., providing heat and pressure.
Two basic types of simplex heated roller fusers have evolved. One uses a conformable or compliant pressure roller to form the fusing nip against a hard fuser roller, such as in a DocuTech 135 machine made by the Xerox Corporation. The other uses a compliant fuser roller to form the nip against a hard or relatively non-conformable pressure roller, such as in a Digimaster 9110 machine made by Heidelberg Digital L.L.C. A fuser roller designated herein as compliant typically includes a conformable layer having a thickness greater than about 2 mm and in some cases exceeding 25 mm. A fuser roller designated herein as hard includes a rigid cylinder, which may have a relatively thin polymeric or conformable elastomeric coating, typically less than about 1.25 mm thick. A compliant fuser roller used in conjunction with a hard pressure roller tends to provide easier release of a receiver from the heated fuser roller, because the distorted shape of the compliant surface in the nip tends to bend the receiver towards the relatively non-conformable pressure roller and away from the much more conformable fuser roller.
A conventional toner fuser roller includes a cylindrical core member, often metallic such as aluminum, coated with one or more synthetic layers, which typically include polymeric materials made from elastomers.
One common type of fuser roller is internally heated, i.e., a source of heat for fusing is provided within the roller for fusing. Such a fuser roller normally has a hollow core, inside of which is located a heating source, usually a lamp. Surrounding the core is an elastomeric layer through which heat is conducted from the core to the surface, and the elastomeric layer typically contains fillers for enhanced thermal conductivity. A different kind of fuser roller which is internally heated near its surface is disclosed by Lee et al. in U.S. Pat. No. 4,791,275, which describes a fuser roller including two polyimide Kapton RTM sheets (sold by DuPont® and Nemours) having a flexible ohmic heating element disposed between the sheets. The polyimide sheets surround a conformable polyimide foam layer attached to a core member. According to J. H. DuBois and F. W. John, Eds., in Plastics, 5th Edition, Van Nostrand and Rheinhold, 1974, polyimide at room temperature is fairly stiff with a Young's modulus of about 3.5 GPa-5.5 GPa (1 GPa=1 GigaPascal=10.sup.9 Newton/m.sup.2), but the Young's modulus of the polyimide sheets can be expected to be considerably lower at the stated high operational fusing temperature of the roller of at least 450 degrees F.
An externally heated fuser roller is used, for example, in an Image Source 120 copier, and is heated by surface contact between the fuser roller and one or more external heating rollers. Externally heated fuser rollers are also disclosed by O'Leary, U.S. Pat. No. 5,450,183, and by Derimiggio et al., U.S. Pat. No. 4,984,027.
A compliant fuser roller may include a conformable layer of any useful material, such as for example a substantially incompressible elastomer, i.e., having a Poisson's ratio approaching 0.5. A substantially incompressible conformable layer including a poly(dimethyl siloxane) elastomer has been disclosed by Chen et al., in the commonly assigned U.S. patent application Ser. No. 08/879,896, now U.S. Pat. No. 6,224,978, which is hereby incorporated by reference. Alternatively, the conformable layer may include a relatively compressible foam having a value of Poisson's ratio much lower than 0.5. A conformable polyimide foam layer is disclosed by Lee in U.S. Pat. No. 4,791,275 and a lithographic printing blanket are disclosed by Goosen et al. in U.S. Pat. No. 3,983,287, including a conformable layer containing a vast number of frangible rigid-walled tiny bubbles which are mechanically ruptured to produce a closed cell foam having a smooth surface.
Receivers remove the majority of heat during fusing. Since receivers may have a narrower length measured parallel to the fuser roller axis than the fuser roller length, heat may be removed differentially, causing areas of higher temperature or lower temperature along the fuser roller surface parallel to the roller axis. Higher or lower temperatures can cause excessive toner offset (i.e., toner powder transfer to the fuser roller) in roller fusers. However, if differential heat can be transferred axially along the fuser roller by layers within the fuser roller having high thermal conductivity, the effect of differential heating can be reduced.
Improved heat transfer from the core to the surface of an internally heated roller fuser will reduce the temperature of the core as well as that of mounting hardware and bearings that are attached to the core. Similarly, improved heat transfer to the surface of an externally heated fuser roller from external heating rollers will reduce the temperature of the external heating rollers as well as the mounting hardware and bearings attached to the external heating rollers.
In the fusing of the toner image to the receiver, the area of contact of a conformable fuser roller with the toner-bearing surface of a receiver sheet as it passes through the fusing nip is determined by the amount pressure exerted by the pressure roller and by the characteristics of the resilient conformable layer. The extent of the contact area helps establish the length of time that any given portion of the toner ima
Aslam Muhammed
Shifley James Douglas
Wu Fangsheng
Kessler Lawrence P.
Lee Susan
NexPress Solutions LLC
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