Patent Application
20100124448
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1. Field of the Invention
The present disclosure relates generally to a fusing member suitable for use in electrophotography for fusing toner on a recording medium, and more particularly to a hot roll fuser member employing resistive heating.
2. Description of the Related Art
Currently, there are two types of fusers used for color laser printers: lamp-heated hot roll fusers and belt fusers. In general color hot roll fusers may provide better fusing quality than belt fusers at a lower cost. However, such hot roll fusers take a relatively long time to heat up, often more than one to several minutes. The lamp-heated roll fuser may be kept hot (above 150° C.) as it waits for the next printing job, however, it is then constantly consuming electrical energy. Conversely, a color belt fuser may heat up very quickly (about 15 seconds). However its design may be more complex and may use more components and cost more to produce. The belt fuser may also have a relatively short life, due to the short life of the steel-rubber belt typically employed by such fusers.
A resistance-heated fuser roll for electrophotographic devices is provided, comprising a non-metallic core, which may be either solid or hollow. The core may comprise, for instance, quartz, fused silica, ceramic, or a combination thereof. A resistive heating element is disposed on at least a portion of the outer surface of the core and may take different forms such as, for instance, a spiral, an alternating pattern of swept traces, or as bands around the core. The resistive heating element may be formed on the core, for example, by screen-printing or plating or deposition processes, and may comprise, for example, metal, semiconductor material, a blend of metallic particles and high temperature polymers, or a combination thereof.
In one embodiment, the resistive heating element comprises a patterned element. A layer of insulative material (e.g., silicone rubber or other suitable material) may cover at least a portion of the resistive heating element to provide electrical insulation, and a toner release layer may cover at least a portion of the insulative layer. A current transmitter is provided for transmitting a current to the resistive heating element, and in one example embodiment includes a current supplying member and a current receiving member. In one such case, the current receiving member is in electrical contact with said resistive heating element and arranged at both ends of the core, and the current supply member is in sliding contact with said current receiving member. In another such case, the current receiving member comprises a metallic journal fitted to the end of the core and in electrical contact with the resistive heating element. In another such case, the current supply member comprises carbon brushes held in contact with the current receiving member by spring force. In another such case, the current receiving member comprises a metallic end-cap having a concave surface fitted to the end of the core and connected to the resistive heating element using spring force, and the current supplying member comprises carbon brushes in contact with the concave surface of said end-cap.
In another embodiment, the insulation layer comprises an elastomeric layer having a thickness of about 0.1 to 1.5 millimeters. In another specific embodiment, the toner release layer comprises a fluoropolymer material with a thickness of less than or equal to 65 microns. In one such case, the fluoropolymer material may have a thickness of about 5 to 65 microns, including all values and increments therein in 1 micron increments. The toner release layer can be formed, for example, by sleeve, spray coating, dip coating, or a combination thereof. The fuser roll may be installed, for example, in a printer (e.g. color laser printer).
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
A resistance-heated hot roll fuser 10 is illustrated in cross-section in
Quartz, fused silica, ceramic, plastic, or a combination thereof may be used as materials for the core 12 (which may also be referred to as a substrate roller). Quartz has the advantages of lower thermal conductivity and higher thermal shock resistance. The selection of wall thickness and material for the core 12 may depend on the size of the hot roll 10 and certain material properties, such as thermal conductivity, thermal shock resistance, material strength, and thermal expansion coefficient. To reduce hot roll warm-up time, quartz tube may be used as a core 12 since it has much lower thermal conductivity, higher thermal shock resistance, and much less thermal expansion than ceramic tube. To increase heating element 14 durability, a ceramic tube may be preferred over quartz tube for core 12, because ceramic tube has a higher thermal expansion coefficient than quartz tube and may provide a better match of thermal expansion between heating element 14 and core 12.
The wall thickness of the tubular core 12 may be varied, for example, from about 1 to about 2.5 millimeters, including all values and increments between 1 to 2.5 millimeters. If the wall is too thin, the core may not have sufficient mechanical strength to sustain the force required for toner fusing. If the wall is too thick, the result may be a longer warm-up time due to a larger thermal mass. In one specific embodiment, a quartz tube having a diameter of 30 millimeters and a wall thickness of 1.5 millimeters is used.
The resistance heating element 14 may be provided, for example, in substantially continuous contact with the surface of a non-metallic core 12. This may be accomplished by applying a heating circuit directly to the outer surface of the core 12. In one such embodiment, the resistance heating circuit comprises a thick film resistor that may be screen-printed onto the outer surface of the core 12 using resistive ink, paint, or paste. The heating element 14 may be implemented, for example, with metal, semiconductor material, or a blend of metallic particles and high temperature polymers, or a combination thereof. In some embodiments, the circuit 14 may comprise silver, silver-palladium, or other types of suitable resistive paste. The thickness of such resistive pastes may be about 10 to about 100 microns depending on the resistance of pastes. In other embodiments, resistive heating element 14 can be implemented with a foil circuit, or a thin film deposition of suitable resistive film materials. The resistive heating circuit 14 may be a serial or parallel circuit depending on the resistance of material.
The heating element 14 may be applied to have a variety of different patterns, such as a spiral or alternating pattern of swept traces as shown in
As previously explained, the insulation layer 16 provides electrical insulation, and may improve temperature uniformity across the surface of the hot roll 10 and ensure print quality. The insulation layer 16 may be an elastomeric layer that functions as a flexible compliant layer. In one example embodiment, insulation layer 16 is implemented with a silicone rubber layer of about 0.1 to 2 millimeters in thickness, or even more specifically, about 0.5 to 1.5 millimeters in thickness. This silicone rubber layer may be applied, for example, over the heating element 14 and on the outer surface of the core 12. Color electrophotographic toner systems may require improved contact between the fusing member surface and the toner in order to obtain better fusing quality, such as uniform fuse grade and gloss. Silicone rubber is a suitable material because it is soft, has adequate thermal stability, may be made relatively thermally conductive for a polymer. In one embodiment, the silicone layer 16 comprises a thermally conductive silicone rubber having a thickness of about 500 microns.
A toner release layer 18 is provided over the insulation layer 16. The release layer 18, which generally forms the outer surface of the fuser roll 10, may contact the recording medium as the recording medium passes the fusing nip area (not shown). The release layer 18 may be implemented, for example and in accordance with one particular embodiment, with a fluoropolymer layer having a thickness 65 microns or less, including all values and increments therein, in 1 micron steps. For example, a thickness in the range of about 5 microns to about 60 microns, or 6 microns to 60 microns, or 7 microns to 60 microns, or 8 microns to 60 microns, or 5 microns to 59 microns, or 6 microns to 59 microns, etc.
The fluoropolymer (which may be understood as those polymers containing C—F type bonding within a polymer backbone) may be designed to substantially reduce any tendency of the recording medium and toner to adhere to the fuser roll 10 as the recording medium passes the fusing nip area. In one example embodiment, the release layer 18 comprises a relatively low surface energy polymer with high temperature stability, such as a polytetrafluoroethylene or a polyperfluoroalkoxy coating composition. For instance, the release layer 18 may comprise a polytetrafluoroethylene coating with a thickness of about 8 to about 30 microns, or a polytetrafluoroethylene sleeve with a thickness of about 20 to about 30 microns. In some embodiments, the thickness is as thin as possible to improve thermal response, but thick enough to maintain release for the life of the fuser roll. The release layer can be formed, for example, by one of a sleeve (e.g., form-fit, wrap, or shrink-wrap), spray coating, dip coating, or other such suitable forming processes.
A current transmitter 23, as shown in
In a second example embodiment, as shown in
As indicated in
As a specific example configured in accordance with one embodiment, a resistive heating hot roll fuser 10 was constructed using a quartz tube 12 painted with a resistive circuit 14 on its outside surface. The quartz tube 12 has 1.5 millimeters in wall thickness, and is 30 millimeters in diameter, and 279.4 millimeters in length. The serial resistive circuit 14 was painted on the outer surface of the quartz core 12 using a silver paste. The resistive heating circuit 14 pattern is shown in
Testing was carried out to assess the ability of the roll surface to achieve a printing temperature of 170° C. Using a hot roll having a 1.5-millimeter quartz core constructed as described above, the temperature response using various thicknesses of silicone rubber applied for the insulative layer 16 was evaluated. The average heating power during warm-up was 1000 watts. The warm-up times from room temperature (about 20° C.) to a desired print temperature of 170° C. are summarized in Table 1.
As can be seen, even at a thickness of 1.5 millimeters of silicone, the warm-up time achieved was comparable to known belt fusers.
The mechanical strength of the quartz core for the resistive heating hot roll was also tested. To generate enough nip pressure for achieving the desired fusing quality, about 30-lb. force may be applied at each side of hot roll or backup roll. Therefore, and in accordance with some embodiments, the thickness of a quartz roll must be sufficient to sustain a total 60-lb. force, yet be thin enough to minimize hot roll warm-up time.
To test the mechanical strength of the quartz tube having a 1.5-millimeter thickness, the quartz tube was fixed on the test fixture mounted in an Instron mechanical strength tester. A force was applied to a sliding steel bar to force a backup roll into contact with the quartz tube. The test indicated that a quartz tube having a 1.5-millimeter thickness could sustain greater than 200-lb. force without breaking. Since the quartz tube at 1.5-millimeter thickness is generally much stronger than required, it will be appreciated that the thickness of the tube may be reduced to further reduce the warm-up time due to less thermal mass.
Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.
