Patent Application
20140241764
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2013-035610, filed on Feb. 26, 2013, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
1. Technical Field
Embodiments of this disclosure generally relate to a fixing device to fix an unfixed toner image onto a recording medium by electromagnetic induction heating, and to an electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine having two or more of copying, printing, and facsimile capabilities, incorporating the fixing device.
2. Related Art
Image forming apparatuses may incorporate a fixing device employing an electromagnetic induction heating method to reduce startup time of the image forming apparatuses, thereby enhancing energy efficiency. Such a fixing device employing the electromagnetic induction heating method includes, e.g., a heating roller serving as a heat generator, a fixing roller, an endless fixing belt stretched over the heating roller and the fixing roller, an induction heater facing the heating roller via the fixing belt, and a pressing roller to contact the fixing roller via the fixing belt. The induction heater includes, e.g., an excitation coil wound in a longitudinal direction of the induction heater, cores to direct alternating magnetic flux arising from the excitation coil to the heat generator, and a holder (or coil guide) to hold the excitation coil and the cores.
The induction heater faces and heats the fixing belt. The heated fixing belt heats and fixes a toner image formed on a recording medium conveyed between the fixing roller and the pressing roller. Specifically, a high-frequency alternating current supplied to the excitation coil forms an alternating magnetic field around the excitation coil, which generates eddy currents on a surface of the heating roller. When the eddy currents are generated around the heating roller serving as a heat generator, the electrical resistance of the heating roller leads to Joule heating of the heating roller, thereby heating the fixing belt stretched over the heating roller.
In such a fixing device employing the electromagnetic induction heating method, the heat generator is directly heated by electromagnetic induction. Accordingly, compared to a typical fixing device using a halogen heater, the fixing device employing the electromagnetic induction heating method has a higher heat-exchange efficiency and therefore the surface temperature of the fixing belt can be increased to a desired fixing temperature more efficiently, that is, with less energy and a shorter startup time.
Toner includes wax to enhance fixing performance at a low temperature, and to facilitate separation of recording media from a fixing member (fixing belt or fixing roller) and a pressing member (pressing roller or pressing belt). When such toner including wax is used for a fixing operation employing the induction heating method, the wax may cause fixing failures, e.g., the wax may adhere to a recording medium during fixing of an image formed on the recording medium. Specifically, the wax is evaporated when the toner is heated in the fixing nip. The evaporated wax floats and moves by rotation of the fixing member, and consequently adheres to the holder (or coil guide) of the induction heater that is disposed facing the fixing member, particularly to a surface that faces the fixing member. As the wax adhering to the holder accumulates, it eventually fills a small gap between the induction heater and the fixing member, and some of the wax adheres to the fixing member. The wax adhering to the fixing member is fused again and adheres to the recording medium in the fixing nip, thereby causing a fixing failure in that the wax adheres to the recording medium during fixing of the image formed on the recording medium.
As one approach to such fixing failure, JP-2009-288578-A provides a passage for drainage on a surface of an induction heater facing the fixing member to drain off any wax adhering to the surface. Yet the wax may still accumulate without being drained, depending on how the induction heater is oriented. Moreover, the drainage passage is provided in a holder (or coil guide) made of resin, and because the resin has good heat resistance, the accumulated wax is easily fused again upon absorbing heat from the fixing member. Consequently, the wax adheres to a recording medium during fixing of an image formed on the recording medium.
This specification describes below an improved fixing device. In one embodiment of this disclosure, the fixing device includes a fixing member including a heat generator and an induction heater to heat the fixing member by electromagnetic induction. The induction heater includes an excitation coil, a ferromagnetic core to form a magnetic path to direct magnetic flux arising from the excitation coil to the fixing member, and a holder to hold the excitation coil and the ferromagnetic core. The holder has a surface facing the heat generator. The surface has a plurality of slits extending parallel to a direction of rotation of the fixing member. The ferromagnetic core is coupled to the holder and covers an open bottom portion of each slit of the plurality of slits to form a plurality of bottomed grooves.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be more readily obtained as the same becomes better understood by reference to the following detailed description of embodiments when considered in connection with the accompanying drawings, wherein:
The accompanying drawings are intended to depict embodiments of this disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve similar results.
Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable to the present invention.
In a later-described comparative example, embodiment, and exemplary variation, for the sake of simplicity like reference numerals will be given to identical or corresponding constituent elements such as parts and materials having the same functions, and redundant descriptions thereof will be omitted unless otherwise required.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of this disclosure are described below.
Initially with reference to
It is to be noted that, in the following description, suffixes Y, M, C, and Bk denote colors yellow, magenta, cyan, and black, respectively.
The image forming apparatus 100, herein serving as a printer, includes four imaging stations 10Y, 10M, 10C, and 10Bk. The imaging stations 10Y, 10M, 10C, and 10Bk include photoconductive drums 1Y, 1M, 1C, and 1Bk, and form toner images of yellow, magenta, cyan, and black on surfaces of the photoconductive drums 1Y, 1M, 1C, and 1Bk, respectively. A conveyance belt 20 is disposed below the imaging stations 10Y, 10M, 10C, and 10Bk to convey a sheet P serving as a recording medium through the imaging stations 10Y, 10M, 10C and 10Bk.
The photoconductive drums 1Y, 1M, 1C, and 1Bk of the respective imaging stations 10Y, 10M, 10C and 10Bk are disposed to rotatably contact the conveyance belt 20. The sheet P electrostatically adheres to a surface of the conveyance belt 20. It is to be noted that the four imaging stations 10Y, 10M, 10C, and 10Bk have the same configurations, differing only in the color of toner employed. Hence, a description is herein given only of the imaging station 10Y employing the yellow color, which is disposed at a most upstream end in a direction in which the sheet P is conveyed, as a representative example of the imaging stations 10M, 10C, and 10Bk. Detailed descriptions of the imaging stations 10M, 10C and 10Bk are herein omitted, unless otherwise required.
The imaging station 10Y includes the photoconductive drum 1Y disposed substantially at a center of the imaging station 10Y. The photoconductive drum 1Y rotatably contacts the conveyance belt 20. The photoconductive drum 1Y is surrounded by various pieces of imaging equipment, such as a charging device 2Y, an exposure device 3Y, a developing device 4Y, a transfer roller 5Y, a drum cleaner 6Y, and a charge neutralizing device, disposed sequentially along a direction of rotation of the photoconductive drum 1Y. The charging device 2Y charges the surface of the photoconductive drum 1Y so that a predetermined electric potential is created on the surface of the photoconductive drum 1Y. The exposure device 3Y directs light to the charged surface of the photoconductive drum 1Y according to an image signal after color separation to form an electrostatic latent image on the surface of the photoconductive drum 1Y. The developing device 4Y develops the electrostatic latent image thus formed on the surface of the photoconductive drum 1Y with toner of yellow, thereby forming a visible image, also known as a toner image, in this case of the color yellow. The transfer roller 5Y serving as a transfer device transfers the toner image thus developed onto the sheet P conveyed by the conveyance belt 20. The drum cleaner 6Y removes residual toner remaining on the surface of the photoconductive drum 1Y after a transfer process. The charge neutralizing device removes residual charge from the surface of the photoconductive drum 1Y.
A sheet-feeding unit 30 is disposed to the right of the conveyance belt 20, at a bottom right in
Referring now to
The fixing device 40 includes, e.g., a heating roller 41, a fixing roller 43, a fixing belt 44 stretched over the heating roller 41 and the fixing roller 43, an induction heater 45 facing the heating roller 41 via the fixing belt 44, and a pressing roller 42 configured to contact the fixing roller 43 via the fixing belt 44, that is, to contact the outer surface of the fixing belt 44, opposite the fixing roller 43, with the fixing belt 44 sandwiched therebetween.
The heating roller 41 serving as a heat generator is a stainless steel roller having a thickness of about 0.2 mm to about 1 mm. The heating roller 41 may be covered by a copper (CU) layer having a thickness of about 3 μm to about 20 μm to enhance the efficiency of heat generation. In such a case, preferably, the copper (Cu) layer may be nickel-plated to prevent rust. A ferrite core may be disposed inside the heating roller 41 to enhance the efficiency of heat generation.
Alternatively, the heating roller 41 may be made of a magnetic shunt alloy having a Curie point of about 160° C. to about 220° C. An aluminum member may be disposed inside the magnetic shunt alloy to stop a temperature rise around the Curie point. The heating roller 41 made of the magnetic shunt alloy may be covered by a nickel-plated copper (Cu) layer to enhance the efficiency of heat generation.
The fixing roller 43 is constructed of a metal core 43a and an elastic member 43b. The metal core 43a is, e.g., stainless steel or carbon steel. The elastic member 42b is, e.g., solid or foam heat-resistant silicone rubber, and coats the metal core 43a. The fixing roller 43 and the pressing roller 42 contact each other with pressure applied by the pressing roller 42, thereby forming an area of contact herein called a fixing nip N having a predetermined width. The fixing roller 43 has an outer diameter of about 30 mm to about 40 mm. The elastic member 43b has a thickness of about 3 mm to about 10 mm and a JIS-A hardness of about 10° to about 50°.
Referring now to
The fixing belt 44 is constructed of a substrate 44a, an elastic layer 44b and a release layer 44c. As illustrated in
By coating the elastic layer 44b with the release layer 44c, toner releasability can be enhanced without using silicone oil, thereby preventing paper dust from sticking to the fixing belt 44 and realizing an oil-less system. However, the resin having good releasability does not typically have elasticity like that of a rubber material. Accordingly, if a thick release layer 44c is formed on the elastic layer 44b, the flexibility of the surface of the fixing belt 44 might be lost to an extent, causing uneven glossiness. To strike a good balance between flexibility and releasability, the release layer 44c has a thickness of about 5 μm to about 50 μm, and preferably about 10 μm to about 30 μm.
Optionally, a primer layer may be provided between the foregoing layers. A durable layer may be provided on an inner surface of the substrate 44a to enhance sliding durability against the heating roller 41 and the fixing roller 43. Preferably, a heat generation layer may be formed on the substrate 44a. For example, a copper (Cu) layer having a thickness of about 3 μm to about 15 μm may be formed on a base layer of, e.g., polyimide to be used as a heat generation layer.
Returning to
The pressing roller 42 is configured to be harder than the fixing roller 43 so that the pressing roller 42 presses and is engaged with the fixing roller 43 via the fixing belt 44. Such an engagement gives a curvature to the sheet P sufficient to prevent the sheet P from hugging the surface of the fixing belt 44 when the sheet P exits the fixing nip N. Thus, the releasability of the sheet P can be enhanced.
Referring now to
The induction heater 45 includes a case 45a serving as a coil holder, an excitation coil 45b wound in a longitudinal direction of the induction heater 45, and ferromagnetic cores. The ferromagnetic cores include arch cores 45c, side cores 45d and end cores 45e. The ferromagnetic cores, namely, the arch cores 45c, the side cores 45d and the end cores 45e, are disposed to encompass the excitation coil 45b, thereby forming a magnetic path to direct magnetic flux arising from the excitation coil 45b to the heating roller 41.
The excitation coil 45b is prepared by 5-20 windings of a Litz wire. The Litz wire is constructed of about 50 to about 500 conductive wire strands, individually insulated and twisted together. Each conductive wire strand has a diameter of about 0.05 mm to about 0.2 mm. A fusion layer is provided on a surface of the Litz wire. The fusion layer is stiffened by applying heat either by means of supplying power or in a thermostatic oven. Accordingly, a winding shape of the excitation coil 45b can be maintained. Alternatively, the excitation coil 45b may be prepared by winding a Litz wire without a fusion layer, and press-molding the wound Litz wire to reliably maintain the shape of the excitation coil 45b. To provide the Litz wire with heat resistance at a fixing temperature or higher, resin having insulation performance and heat resistance, such as polyamide-imide or polyimide, may be used as an insulation material to coat the Litz wire.
The windings of the excitation coil 45b are glued to the case 45a with an adhesive, e.g., silicone glue. The case 45a is disposed to cover part of an outer circumferential surface of the heating roller 41 with a slight gap therebetween. To ensure heat resistance at a fixing temperature or higher, the case 45a is made of a high heat-resistant resin material such as polyethylene terephthalate (PET) or liquid crystal polymers.
Each of the ferromagnetic cores, namely, the arch cores 45c, the side cores 45d and the end cores 45e, is made of a ferrite material such as a manganese-zinc (Mn—Zn) ferrite material or a nickel-zinc (Ni—Zn) ferrite material. A plurality of side cores 45d are arranged in a rotational axis direction of the heating roller 41 to minimize warping of the side cores 45d during a sintering process that contracts the ferrite material. The end cores 45e are disposed at each end of the excitation coil 45b to increase the temperature of each end, thereby preventing the temperature of each end of the sheet P from decreasing in the fixing nip N. If the temperature is sufficiently uniform in the fixing nip N, the end cores 45e may be omitted.
Referring now to
According to the embodiments of this disclosure, a ferromagnetic core is formed as an integral part of a case, which serves as a holder or coil guide, and exposed at slits formed in a surface of the case facing a heat generator. For example, as illustrated in
The side core 45d is coupled to the portion A in which the slits 45f are formed so as to partially cover a bottom side of each of the slits 45f. Each of the slits 45f has a partial bottom, with an open bottom portion covered by the side core 45d. Thus, the side core 45d and the slits 45f together define bottomed grooves 45g. Taking into account the formability of resin used for the case 45a, each of the bottomed grooves 45g preferably has a depth of about 0.2 mm to about 3 mm, and a width of about 0.5 mm to about 5 mm. In addition, the bottomed grooves 45g are preferably disposed at intervals of about 0.5 mm to about 5 mm. The side core 45d thus coupled to the slits 45f to cover the open bottom portion of the slits 45f is exposed at the slits 45f. The side core 45d made of a ferrite material has a higher heat conductivity and a larger heat capacity than a resin material. Accordingly, if wax adheres to the surface 45a1 of the case 45a, the wax adheres to the side core 45d through the slits 45f. Accordingly, the temperature of the wax hardly increases when the wax is heated by the heating roller 41 serving as a heat generator, and therefore, the wax is hardly fused again.
Referring now to Table 1, a description is given of a comparison of the heat conductivity of some specific materials. As is apparent from Table 1, ferrite material has about ten times the heat conductivity and about twice the heat capacity of liquid crystal polymers. The ferrite material thus having a relatively high heat conductivity can quickly absorb heat that is received by the wax. In addition, the ferrite material thus having a larger heat capacity can absorb a larger amount of heat than the liquid crystal polymers. With such a high heat conductivity and a heat capacity, a relatively large amount of heat from the wax is quickly absorbed by the side core 45d, thereby preventing a temperature rise and re-fusion of the wax, and thus further preventing the wax from adhering to the sheet P during fixing of an image formed on the sheet P.
Alternatively, the induction heater 45 installed in the fixing device 40 of
It is to be noted that, in the fixing device 40A according to the second embodiment, a fixing roller 43 having a heat generation layer 43c is inductively heated by an induction heater 45, instead of the heating roller 41 that is inductively heated by the induction heater 45 incorporated in the fixing device 40 according to the first embodiment. In other words, the fixing roller 43 serves as a fixing member and a heat generator. The heat generation layer 43c is constructed of, e.g., a base layer, a main heat generation layer, an elastic layer, and a release layer resting in this order from an inner circumference side of the heat generation layer 43c. The base layer of the heat generation layer 43c is made of nickel and has a thickness of about 3 μm to about 15 μm. The main heat generation layer is made of copper and has a thickness not greater than 5 μm. The elastic layer is made of silicone rubber and has a thickness of about 100 μm to about 500 μm. The release layer is made of a fluorine compound such as PFA and has a thickness of about 10 μm to about 100 μm. In the fixing device 40A according to the second embodiment, a distance between the induction heater 45 and a fixing nip N is shorter than a distance between the induction heater 45 and the fixing nip N in the fixing device 40 according to the first embodiment. Hence, wax is more likely to adhere to a ferromagnetic core and therefore fixing failures are more likely occur. Accordingly, the fixing device 40A according to the second embodiment has a greater advantage of adapting the induction heater 45 that incorporates the case 45a in which the side core 45d is exposed at the slits 45f to prevent such fixing failures.
Instead of the foregoing arrangements illustrated in
Referring now to
In each of the fixing devices 40′ and 40A′ according to the third and fourth embodiments, respectively, a case 45a of an induction heater 45 is inclined such that a surface 45a1 of the case 45a is closer to an entry side from which a sheet P enters a fixing nip N. The sheet P is conveyed upward, and the induction heater 45 faces upward. The induction heater 45 serving as a heat source thus disposed closer to the fixing nip N can enhance heat efficiency. Specifically, in the fixing device 40′ according to the third embodiment, heat release can be reduced while a portion of a fixing belt 44 that is heated by the induction heater 45 via a heating roller 41 reaches the fixing nip N, thereby enhancing heat efficiency. In the fixing device 40A′ according to the fourth embodiment, heat release can be reduced while a portion of fixing roller 43 that is heated by the induction heater 45 reaches the fixing nip N, thereby enhancing heat efficiency. It is to be noted that the fixing device 40′ according to the third embodiment has the same configuration as the fixing device 40 according to the first embodiment, differing only in the arrangement of the induction heater 45. The fixing device 40A′ according to the fourth embodiment has the same configuration as the fixing device 40A according to the second embodiment, differing only in the arrangement of the induction heater 45. Hence, detailed descriptions of the configurations of the fixing devices 40′ and 40A′ according to the third and fourth embodiments, respectively, are herein omitted.
In such arrangement of the induction heater 45 as illustrated in
Referring now to
In the foregoing embodiments, the slits 45f are formed in the bottom area of the surface 45a1, that is, the area located on the downstream side in the direction of rotation of a fixing member (e.g., fixing belt 44). In addition to the bottom area, the case 45a′ has slits 45f in a top area, that is, an area located on an upstream side in the direction of rotation of the fixing member. In other words, the slits 45f are formed in areas located on the entry side from which the sheet P enters the fixing nip N and on an exit side toward which the sheet P exits the fixing nip N. The slits 45f and accordingly bottomed grooves 45g are symmetrically arranged in a cross-section of the case 45a′, thereby reducing warping in a longitudinal direction of the induction heater 45 upon molding. Accordingly, a uniform gap is created between the induction heater 45 and a heat generator (e.g., heating roller 41) in the longitudinal direction, thereby uniformly preventing wax from adhering to the sheet P in the longitudinal direction during fixing of an image formed on the sheet P.
As described above, each of the slits 45f formed in the surface 45a1 has a partial bottom, with an open bottom portion covered by the side core 45d, thereby defining the bottomed grooves 45g. The partial bottom is thin and might have a hole due to filling failures upon molding. To prevent creation of such a hole, slits 45f′ are formed as illustrated in
Although the slits 45f′ are herein illustrated such that the slits 45f′ are formed in the top and bottom areas of the surface 45a1′ in the case 45a′ illustrated in
As described above, slits (e.g., 45f) are formed in a surface (e.g., surface 45a1′) facing a heat generator (e.g., heating roller 41) of a holder (e.g., case 45a′). The slits extend in a direction of rotation of a fixing member (fixing belt 44). The slits and a ferromagnetic core (e.g., side core 45d′) that is formed as an integral part of the holder define bottomed grooves. Thus, the ferromagnetic core is exposed at the slits as seen from the heat generator. In such a configuration, if wax is evaporated from toner and adheres to the bottomed grooves, the wax contact the ferromagnetic core having a larger heat capacity than the holder. Accordingly, the wax is hardly fused again, thereby preventing the wax from adhering to a recording medium (e.g., sheet P) during fixing operation, regardless of how an induction heater (e.g., induction heater 45) is oriented.
This disclosure has been described above with reference to specific exemplary embodiments. It is to be noted that this disclosure is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the scope of the invention. It is therefore to be understood that this disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this invention. The number of constituent elements and their locations, shapes, and so forth are not limited to any of the structure for performing the methodology illustrated in the drawings.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-035610 | Feb 2013 | JP | national |
