FUSER ROLLS

Abstract: A quick-start fuser has a hollow, relatively-thin, fiber-wound cylinder (48) supporting a resistance wire, heating foil, or printed circuit (52) secured on the outside surface of the cylinder or embedded in the surface of the cylinder. The interior of the cylindrical tube is filled with air, and the wire, heating foil or printed circuit is connected to electrical leads extending through caps (49) on the ends of the cylinder. The fuser roll is fabricated from the cylinder outward to the final step of applying a release agent on the outer surface.

Description: This invention relates to fuser apparatus, and more particularly to a filament wound foil fusing system. In order to fuse electroscopic toner material permanently onto a support surface by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner materials coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become firmly bonded to the support member. The use of thermal energy for fixing toner images onto a support member is well known. Several approaches to thermal fusing of electroscopic toner images are known. These methods include providing the application of heat and pressure substantially concurrently by various means, for example, a roll pair maintained in pressure contact, a flat or curved plate member in pressure contact with a roll, and a belt member in pressure contact with a roll. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time is provided. Typically, in such direct contact systems, the roller surface may be dry, i.e. no application of a release agent to the surface of the roller as described, for example, in US-A-3,498,596 and 3,666,247. Alternatively, the fuser roll surface may be wetted with a release agent such as a silicone oil as described in US-A-3,268,351 and 3,256,002. It is also known to fuse toner images by the use of a flash fusing process, for example, as disclosed in US-A-3,874,892. In such a process, a flash lamp is generally pulsed on for a very short period. It can be appreciated that since the lamp is pulsed or flashed for short period, a large amount of power must be used to fuse the toner particles. Another method for fusing toner images to a substrate is radiant fusing. Radiant fusing differs from flash fusing in that, in radiant fusing, the radiant energy source, typically an infrared quartz lamp, is turned on during the entire fusing step rather than pulsed for a short period as in flash fusing. Examples of radiant fuser apparatus are shown in US-A-3,898,424 and 3,953,709. Such known radiant fusers are generally of heavy metallic construction, which requires the constant use of a heating element to maintain the apparatus at standby temperature. US-A- 3,471,683 shows a heater roll with a printed circuit heating element. However, the heater roll is relatively thick and the adhesive material not suitable for relatively high temperature operation. Such known fusing systems have been effective in providing the fusing of many copies in relatively large, fast duplicating machines, in which the use of standby heating elements to maintain the machine at or near its operating temperature can be justified. However, there is a continuing need for an instant-ready fuser which requires no standby power for maintaining it at a temperature above ambient. It is known to use a positive characteristic thermistor having a self temperature controlling property as a heater for a heating roller. The roller is regulated to a prescribed temperature by a heating control temperature detection element. It is known to employ radiation absorbing materials for the fuser roll construction to effect faster warm-up time as described in US-A-3,669,706. It is also known as disclosed in US-A-3,948,214 to use a cylindrical member having a first layer made of elastomeric material for transporting radiant energy, a second layer for absorbing radiant energy, and a third layer covering the second layer to affect a good release characteristic on the fuser roll surface. The fuser roll layers are relatively thin and have an instant-start capability. US-A-4,395,109 discloses an instant-ready fuser having a core of metal or ceramic supporting a fuser roller, and including a heat insulating layer, an electrically insulating layer and a protective layer formed on the outer circumference of the core. A difficulty with the known fusing systems is that they are often relatively complex and expensive to construct and/or the mass of the system is relatively large to preclude an instant-start fusing capability. Another difficulty is that known fuser rolls are not always easily adapted to provide sufficient mechanical strength depending upon the size of paper to be fused or able to be tailored to selectively fuse different size copy sheets. It is an object of the present invention, therefore, to provide an improved instant-ready fusing apparatus. Accordingly the present invention provides a fuser roll which is as claimed in the appended claims. For a better understanding of the present invention, reference is made to the accompanying drawings, which show an embodiment thereof, and wherein: Figure 1 is an illustration of a copier incorporating the fuser roll of the present invention; Figure 2 is an isometric view of one form of fuser apparatus incorporated in Figure 1; Figure 3 is a cross-sectional view of the apparatus of Figure 2; Figure 4 is an illustration of the fiber weave of a fuser cylinder, and Figures 5A and 5B illustrate a segmented heating element to fuse different-sized copy sheets selectively. Referring now to Figure 1, there is shown by way of example an automatic xerographic reproducing machine 10 including an image recording drum 12, its outer periphery coated with suitable photoconductive material 13. The drum 12 is suitably journaled for rotation within a machine frame (not shown) by means of shaft 14 and rotates in the direction indicated by arrow 15 to bring the image-bearing surface 13 thereon past a plurality of xerographic processing stations. Suitable drive means (not shown) are provided to power and coordinate the motion of the various cooperating machine components whereby a faithful reproduction of the original input information is recorded upon a sheet of final support material or copy sheet 16. Initially, the drum 12 moves the photoconductive surface 13 through a charging station 17 providing an electrostatic charge uniformly over the photoconductive surface 13 in known manner preparatory to imaging. Thereafter, the drum 12 is rotated to exposure station 18 and the charged photoconductive surface 13 is exposed to a light image of the original document to be reproduced. The charge is selectively dissipated in the light-exposed regions to record the original document in the form of an electrostatic latent image. After exposure, drum 12 rotates the electrostatic latent image recorded on the photoconductive surface 13 to development station 19 wherein a conventional developer mix is applied to the photoconductive surface 13 of the drum 12, rendering the latent image visible. Typically, a suitable development station could include a magnetic brush development system utilizing a magnetizable developer mix having coarse ferromagnetic carrier granules and toner colorant particles. The copy sheets 16 of the final support material are supported in a stack arrangement on an elevating stack support tray 20. With the stack at its elevated position, a sheet separator 21 feeds individual sheets therefrom to the registration system 22. The sheet is then forwarded to the transfer station 23 in proper registration with the image on the drum. The developed image on the photoconductive surface 13 is brought into contact with the sheet 16 of final support material within the transfer station 23 and the toner image is transferred from the photoconductive surface 13 to the contacting side of the final support sheet 16. After the toner image has been transferred to the sheet of final support material or copy sheet 16, the copy sheet 16 with the image is advanced to fusing station 24 for coalescing the transferred powder image to the support material. After the fusing process, the copy sheet 16 is advanced to a suitable output device such as tray 25. Although a preponderance of toner powder is transferred to the copy sheet 16, invariably some residual toner remains on the photoconductive surface 13. Such residual toner particles are removed from the drum 12 as it moves through a cleaning station 26. The toner particles may be mechanically cleaned from the photoconductive surface 13 by any conventional means, as for example, by the use of a cleaning blade. Normally, when the copier is operated in a conventional mode, the original document to be reproduced is placed image side down upon a horizontal transparent platen 27, and the stationary original then scanned by means of a moving optical system. The scanning system includes a stationary lens 30 and a pair of cooperating movable scanning mirrors, half-rate mirror 31 and full-rate mirror 32 supported upon suitable carriages. A document handler 33 can also be provided, including registration assist roll 35 and switch 37. When a document is inserted, switch 37 activates registration assist roll 35 and the document is fed forward and aligned against a rear edge guide of the document handler 33. The pinch rolls 38 are activated to feed a document around 180° curved guides onto the platen 27 for copying. The document is driven by a platen belt transport including platen belt 39. After copying, the platen belt 39 is activated and the document is driven off the platen by the output pinch roll 41 into the document catch tray 43. The fusing station 24 includes a heated fuser roll 45 and a back-up or pressure roll 47 forming a nip through which the copy sheets to be fused are advanced. The copy sheet is stripped from the fuser rolls by suitable (not shown) stripper fingers. The pressure roll 47 comprises a rotating member suitably journaled for rotation about a shaft and covered with an elastomeric layer of silicone rubber, PFA, or any other suitable material. The fuser roll 45 comprises a rotary cylindrical member 48 mounted on a pair of end caps 49, as seen in Figures 2 and 3. To be instant-ready, a fuser should achieve operating temperatures in a time shorter than the arrival time of the paper at the fuser, at machine start-up, approximately a 5-10 second warm-up time. That is, assume a copy sheet 16 takes from 5-10 seconds to be transported from the support tray 20 to the transfer station 23 to fuser 24 after a 'start print' or 'start copy' button is pushed. It is usually then necessary for the fuser to be elevated at least 120°C. Raising the temperature of a rigid structure by approximately 120° -160°C in five seconds, using reasonable power levels, for example, 700 watts, requires the mass to be heated to be small. In accordance with the present invention, the cylindrical member 48 is a hollow cylinder of fiber glass, carbon graphite, or boron carbide fibers or any other suitable fiber material of suitable mechanical strength. Preferably, the radial thickness of the cylindrical member 48 wall is approximately 0.5 to 1.0 mm. With reference to Figures 2 and 3, preferably supported on the filament wound cylindrical member 48 is a poly adhesive securing fiber glass backing 50. Supported on the fiber glass backing 50 is a suitable heating wire, printed circuit or photo-etched circuit pattern 52. A suitable release agent 54, such as PFA or rubber, covers the heating element. It should also be noted that a suitable high temperature adhesive may secure the fiber glass backing 50 to the cylindrical member 48. Any method of attaching the heating element to the fiber wound cylindrical member is suitable. According to another aspect of the present invention, it is important for the fuser roll to have sufficient mechanical strength, including hoop strength and beam strength. The hoop strength is the property of the fuser roll core material to resist inward radial pressure, and beam strength is the property of the fuser roll core material to resist bending. With reference to Figure 4, there is illustrated a filament wound tube or cylinder with the fibers wound at approximately 50° with respect to the longitudinal axis to provide sufficient mechanical strength. It should be noted that it is within the scope of the invention to weave fiber glass, carbon graphite, boron carbide, or any other fiber at a suitable angle to achieve sufficient mechanical strength. In general, the higher the diameter of the cylindrical member 48, the larger a nip that can be formed and the slower the rotational speed. This allows a greater dwell time of the copy sheet in the nip of the fuser formed by the fuser roll 45 and pressure roll 47, dwell time being a function of surface speed plus the size or area of the nip. Higher diameter also means there is more recovery time, that is, the heat is held longer on the outside surface of the fuser roll and there is more time allowed for reheating. A difficulty, however, with a large-diameter fuser roll or cylindrical member is the need for sufficient mechanical strength. In accordance with another aspect of the present invention, using a suitable choice of a fiber in the filament wound cylinder, plus appropriate angle of fiber weave and suitable epoxy, cylindrical diameters of 75 to 100 mm are easily obtainable. Wall thicknesses are preferably less than 1.25 mm. In one embodiment, with a wall thickness less than 1.0 mm, fuser roll diameters of up to 100 mm have been used with fuser roll lengths up to 1.2 m. To fabricate the fuser roll or cylindrical member of the present invention, it is necessary to start with a filament-wound cylinder or tube. The remaining portions of the roll are fabricated from the tube outward. The filament core structure can be wound on a mandrel using standard winding machines. The machine computers could be set or tailored to give proper winding angles (47° to 59°) to obtain the maximum mechanical strength. Each cylinder would be wound until a desired wall thickness is obtained, preferably 0.5 to 1.0 mm. At this point, fabrication would vary with the size of the roll, length, and production quantity. For short-run large rolls, it is possible to consider winding a helical heating element directly on the surface of the filament-wound core. An additional layer of filament winding would be wound directly over the filament and the entire structure cured. After curing, the composite structure would be ground to obtain a smooth outer surface for finishing. Assuming standard xerographic fuser rolls are of 25 to 50 mm in diameter and approximately 400 mm long, high speed continuous filament winding can be considered. With this type of fabrication, the core or cylindrical member would be wound to a desired wall thickness and continuously fed down its mandrel to be cured, ground, and cut to length. With this technique, a heater foil could be wrapped on the outside surface of the core and finished in the second operation. It is known to use a layer of metal on a fuser roll to distribute the heat energy. It is contemplated that, using the filament-wound roll, there would be the option of eliminating the metal layer energy distributor altogether, or adding a minimum conductive layer by plating, spraying or any other cost-effective technique. In accordance with another aspect of the present invention, with reference to Figure 5aA and 5B, there is illustrated a selective fuser heating roll control. During the fabrication of the fuser roll, the heating element 58 can be laid down in separate sections, such as illustrated in sections A, B1, and B2, and C1 and C2. Therefore, depending upon the size of the copy sheet to be fused, the appropriate heating element could be selectively activated by the control 60. For small copy sheets, only element A of the heating element would be activated. For larger size copy sheets, elements B1 and B2 along with A would be activated. Finally, for large size copy sheets, elements C1 and C2 along with A and B1, B2 would be selectively energized.

Claims: A quick-start fuser roll for a xerographic copying machine, comprising: a hollow, relatively-thin, rotary cylinder (48) wound from filaments (50) of heat-resistant material; a pair of end caps (49) for supporting the cylinder, and an electrical heater-element (52) affixed to the external surface of the cylinder. The fuser roll of Claim 1, wherein the cylinder has a core of air. The fuser roll of Claim 1 or 2, wherein the radial thickness of the cylinder is less than 1.25 mm. The fuser roll of any preceding claim, wherein the filaments are of glass, carbon graphite or boron carbide. The fuser roll of any preceding claim wherein the heater element is a wire or other conductor embedded in the cylinder. The fuser roll of any of claims 1 to 4, in which the heater element is secured to the cylindrical surface by a high-temperature resistant adhesive. The fuser roll of any preceding claim wherein the heater element is partitioned into several segments, and in which each segment is adapted to be electrically connected to an external control (60). The fuser roll as claimed in any preceding claim, in which the heater element is covered with a layer of elastomeric material.

Inventors: MARTIN, ROBERT G., SWANTON, PAUL C.
Applicants: XEROX CORPORATION
Application year: 1987
Main classification: G03G15
IPC codes: G03G15, H05B3