Patent Application
20120230743
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2011-051293 and 2011-199253, filed on Mar. 9 and Sep. 13, 2011, respectively, in the Japanese Patent Office, the entire disclosures of which are hereby incorporated by reference herein.
1. Field of the Invention
This invention relates to a fixing device and an image formation apparatus, such as a copier, a printer, a facsimile, or a multifunctional apparatus having several of these capabilities, etc., with the fixing device capable of fixing an unfixed toner image using electrophotography.
2. Description of the Related Art
A fixing device employing an electromagnetic induction heating system is widely known, which reduces a startup time period needed in an imaging formation apparatus, such as a copier, a printer, etc., to save energy. For example, a fixing device of the Japanese Patent Application No. 2006-350054 (JP-2006-350054-A) employs an electromagnetic induction heating system and mainly consists of a supporting roller (e.g. a heating roller) as a heater, an auxiliary fixing roller (e.g. a fixing roller), a fixing belt stretched by the supporting roller and the auxiliary fixing roller therearound, an induction heating unit (e.g. an induction heating device) opposed to the supporting roller via the fixing belt, and a pressing roller contacting the auxiliary fixing roller via the fixing belt, etc. The induction heating unit mainly consists of a coil unit (e.g., an excitation coil) wound in a longitudinal direction and a core (e.g., an excitation coil core) opposed to the coil unit.
The fixing belt is heated at a position opposite an induction heating unit and heats and fixes a toner image on a recording medium conveyed to a position between the auxiliary fixing roller and the pressing roller. Specifically, by supplying an alternating high-frequency current to a coil unit and thereby forming an alternating magnetic field therearound, an eddy current is generated near a surface of the supporting roller. When the eddy current is generated, the supporting roller generates Joule heat by its own electrical resistance as a heater. Due to the Joule heat, the fixing belt wound around the supporting roller is heated. Since the heater is directly activated by the electromagnetic induction, it is known that the fixing device with an electromagnetic induction heating system like this has a higher thermal effectiveness and is capable of increasing a surface temperature (i.e., a fixing temperature) of a fixing belt to a prescribed level achieving quick startup with less energy than a conventional system with a halogen heater or the like.
A coil unit used in the induction heating system mainly consists of an excitation coil and a core for guiding an alternating magnetic field arising from the excitation coil.
Further, in the fixing device described above, a pair of side cores 26b is arranged parallel to each other or parallel to a secondary hold unit 20 that functions as a part of a housing of the fixing device 19. However, the side core 26b is not extended along a radial line drawn from an axis of the supporting roller 23 in a radius direction. In addition, an end face of the side core 26b placed opposite an outer circumferential surface of the supporting roller 23 is not perpendicular to the radial line. Accordingly, leakage of magnetic flux occurs, and accordingly heat generation effectiveness deteriorates due to the presence of a magnetic flux not passing through the supporting roller.
As described later in detail with reference to
Japanese Patent Application Publication No. 2000-056603 (JP-2000-056603-A) discloses a technology in which an opposed surface of a ferromagnetic core opposite a fixing roller as a heater is molded to a prescribed shape almost parallel to a fixing roller to increase an area of the opposed surface thereof. A magnetic flux caused by an excitation coil concentrates within a space between leading ends of protruding portions of the ferromagnetic core, so that leakage of the magnetic field outside of a magnetic circuit, which mainly consists of the ferromagnetic core and a conductive layer on a fixing roller, is decreased. However, forming the opposed surface opposite the magnetic core made of ferrite in parallel to the fixing roller is generally difficult and costly. For molding the ferrite core itself, a method of baking and hardening ferrite powder in a mold is usually employed. However, a problem caused by this manufacturing method is that the core shrinks during a sintering process, and accordingly its dimensional accuracy is degraded.
In addition, highly accurate dimensioning is needed for locating a surface of the core opposite the fixing roller due to the shape of the fixing roller, and as a result, the fixing unit cannot be assembled when the dimensional accuracy is poor. To avoid this problem, the surface of the core opposite the fixing roller must undergo additional processing, such as cutting, etc., thereby increasing manufacturing cost.
Accordingly, the present invention provides a novel fixing device comprising a fixing member having a heat generation layer, an excitation coil disposed opposite an outer circumferential surface of the fixing member to cause the fixing member to induce electromagnetic heat, and a magnetic core to form a continuous magnetic path guiding a magnetic flux generated by the excitation coil to the fixing member. A holder is provided to accommodate and hold the excitation coil and the magnetic core. A first core included in the magnetic core and is arranged opposite the outer circumferential surface of the fixing member not via the excitation coil along a line extended from an axis of the fixing member in a radius direction. An end face of the first core arranged opposite the outer circumferential surface of the fixing member is substantially perpendicular to the line.
In another aspect, a second core having a curved end face at its one end is provided to contact the first core. The magnetic core covers most of the above-mentioned excitation coil.
In yet another aspect, the first core has a substantially rectangular parallelepiped shape.
In yet another aspect, a pair of first cores contacts the second core and is not arranged parallel to each other in the holder.
In yet another aspect, a spacer is provided between the holder and the first core to position the first core.
In yet another aspect, the spacer is constituted by a rib integrally molded with the holder.
In yet another aspect, the fixing device is a belt type and includes a heating roller as the fixing member, an auxiliary fixing roller, a fixing belt stretched by the heating roller and the auxiliary fixing roller, and a pressing roller pressing against the auxiliary fixing roller through the fixing belt.
In yet another aspect, the fixing member is a roller type and includes a heating roller as the fixing member, and a pressing roller pressing against the fixing roller.
In yet another aspect, an image forming apparatus forming an image comprises an image formation device to form a toner image and a fixing system to fix the toner image. The fixing system includes a fixing member having a heat generation layer, an excitation coil disposed opposite an outer circumferential surface of the fixing member to cause the fixing member to induce electromagnetic heat, and a magnetic core to form a continuous magnetic path guiding a magnetic flux generated by the excitation coil to the fixing member. The fixing system also includes a holder to accommodate and hold the excitation coil and the magnetic core and a first core included in the magnetic core. The first core is arranged opposite the outer circumferential surface of the fixing member not via the excitation coil along a line extended from an axis of the fixing member in a radius direction. An end face of the first core arranged opposite the outer circumferential surface of the fixing member is substantially perpendicular to the line.
A more complete appreciation of the present invention 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 when considered in connection with the accompanying drawings, wherein:
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof and in particular to
Each photoconductor drum, 1Y, 1M, 1C, or 1Bk of the image formation unit 10Y, 10M, 10C, or 10Bk contacts a surface of the conveyor belt 20. A paper sheet is electrostatically attracted to a surface of the conveyor belt 20. These four image formation units 10M, 10Y, 10C, and 10Bk have substantially the identical structure with each other. Therefore, the image formation unit 10Y arranged upstream most in a sheet transport orientation is typically explained hereinafter, and specific descriptions of the remaining image formation units 10M, 10C, and 10Bk are omitted while the same signs are added to corresponding devices.
The image formation unit 10Y includes a photoreceptor drum 1Y rotated contacting the conveyor belt 20 at its almost central position. Around the photoconductor drum 1Y, there are provided a charge device 2Y for charging a surface of the photoconductor drum 1Y with a certain potential, an exposure device 3Y to execute exposure based on an image signal obtained by col separation onto a surface of a drum previously charged, a developing device 4Y for supplying yellow toner to an electrostatic latent image formed on a surface of the drum to develop the electrostatic latent image, a transfer roller 5Y as a transfer device to transfer the developed toner image onto a paper sheet conveyed via the conveyor belt 20, a cleaner 6Y to remove residual toner remaining on the drum surface not transferred therefrom, and a charge removing lamp, not shown, to remove an electrical charge remaining on the photoconductor drum 1Y in this order in a rotation direction thereof.
On the right-lower side of the conveyor belt 20 in the drawing, a paper sheet feeding mechanism 30 is provided to feed a paper sheet onto a conveyor belt 20. On the left side of the conveyor belt 20 in the drawing, a fixing device 40 of the present invention described later is disposed. The paper sheet transported by the conveyor belt 20 is further transported onto a conveyance path continuously extended from the conveyor belt 20 through the fixing device 40 and passes through the fixing device 40.
The fixing device 40 applies heat and pressure onto the thus conveyed paper sheet bearing the toner image of each color on its surface. The fixing device 40 then fuses the toner image of the each color so that the toner image penetrates the paper sheet and is fixed. The paper sheet is then ejected downstream of the fixing device 40 on the conveyance path.
Now, the fixing device 40 according to one embodiment of the present invention is described with reference to
The heating roller 51 can be made of metal, such as stainless steel, aluminum, iron, etc., to have a prescribed thickness and a stiffness (rigidity) to withstand a load imposed when the belt fixing 53 is stretched. Further, a metal core layer can be made of material having insulating and non-magnetic properties, such as ceramic, etc., to be isolated from the electromagnetic induction heating. The thickness of the metal core layer is preferably from about 0.2 mm to about 1 mm.
In this first embodiment, the heating roller 51 is made of non-magnetic stainless steel (SUS) and includes a metal core layer having a thickness of from approx. 0.2 mm to approx. 1 mm. A heat generation layer made of copper (Cu) having a thickness of about 3 μm to about 15 μm is formed on a surface of the metal core to increase heat generation effectiveness. In this situation, nickel plating may be preferably applied to the Cu surface layer for the purpose of rust prevention.
Magnetic shunt alloy having a curie point of from about 160 degree Celsius to about 220 degree Celsius can be used instead of the stainless steel as another example. In this situation, the magnetic shunt alloy can be used as a heat generation layer. Copper having a thickness of from about 3 μm to about 15 μm may be formed on the magnetic shunt alloy as a heat generation layer. By disposing aluminum in the interior of the magnetic shunt alloy, temperature can be stopped increasing near the curie point without a particular control mechanism.
The auxiliary fixing roller 52 is constituted by a metal core 52a made of stainless steel, carbon steel, etc., and an elastic member 52b made of silicone rubber or the like with heat resistance wrapped around the metal core 52a in a solid or foam state. The auxiliary fixing roller 52 thus forms a contact (i.e., a fixing nip section N) having a prescribed width between the pressing roller 55 and the auxiliary fixing roller 52 under pressure applied from the pressing roller 55. The auxiliary fixing roller 52 preferably has an outer diameter of from approx. 30 mm to approx. 40 mm, a thickness of from approx. 3 mm to approx. 10 mm, and a hardness of from about 10 degree to about 50 degree (JIS-A).
Now, one example of a fixing belt 53 is described in greater detail with reference to
The elastic layer 32 is employed to give flexibility to a belt surface and thereby obtaining a uniform image without uneven glossiness. The elastic layer 32 is thus desirably made of elastomer material with a hardness of from about 5 degree to about 50 degree (JIS-A) and a thickness of from about 50 μm to about 500 μm. Further, silicone and fluorosilicone rubbers or the like are preferably used as material of the elastic layer 32 from a view point of heat-resistance under a fixing temperature.
As the material of the mold releasing layer 33, fluorine resin, such as tetrafluoride ethylene resin (PTFE), tetrafluoride ethylene-Perfluoroalkyl vinylether copolymer resin (PFA), and tetrafluoride ethylene- hexafluoride propylene copolymer (FEP), etc., or these resin mixture, or heat-resistant resin with these dispersions is exemplified.
By coating the mold releasing layer 33 with the elastic layer 32, prescribed releasing performance of toner can be obtained preventing paper dust sticking without using silicone oil, thereby realizing an oil-less system. However, these resins with the mold releasing performance do not have elasticity like rubber material in general. Thus, when a thick mold releasing layer 33 is formed on the elastic layer 32, flexibility of the belt surface is lost by some degree causing uneven glossiness. To obtain both the flexibility and the mold releasing performance, a thickness of the mold releasing layer 33 preferably ranges from about 5 μm to about 50 μm, and more desirably from about 10 μm to about 30 μm. Further, a primer layer may be preferably placed between each of the layers as needed.
A durable layer is also disposed on an inner surface of the substrate to improve durability under a sliding condition. Further, a heat generation layer may be preferably disposed on the substrate 31. For example, a cu-layer having a thickness of from about 3 μm to about 15 μm is formed on a base layer made of polyimide, etc., to be used as a heat generation layer.
The pressing roller 55 is mainly consists of a cylindrical metal core 55a, a high heat-resistant elastic layer 55b, and a m0old releasing layer 55c, and form a fixing nip N by pressing against the auxiliary fixing roller 52 through the fixing belt 53. An outer diameter of the pressing roller 55 is from approx. 30 mm to approx. 40 mm. A thickness of the elastic layer is from approx. 0.3 mm to approx. 5 mm having a hardness of from about 20 degree to about 50 degree (Asker hardness). Since a prescribed heat resistance is needed, silicone rubber is preferably used as an elastic layer 55b. Further, a mold releasing layer 55c made of fluorine resin with a thickness of from about 10 μm to about 100 μm is formed on the elastic layer 4b to further increase the mold releasing performance for a two-sided printing operation.
With a harder elastic layer 55b of the pressing roller 55 than that of the auxiliary fixing roller 52, the pressing roller 55 digs into the auxiliary fixing roller 52 and the fixing belt 53. With this digging, the fixing belt 53 has a curvature impossible for a recording medium to go along the surface thereof at an exit of the fixing nip N. Thus, a releasing performance of a recording medium releasing from a pressing roller 55 can be improved thereby capable of preventing a problem, such as sheet jam, etc., beforehand.
Now, an induction heating coil 54 formed in a coil unit is described with reference to
Now, a magnetic core is described in greater detail. The ferromagnetic core almost encircles an excitation coil 41 and mainly consists of an arch core 42 as a second core located at a position behind the excitation coil 41 and opposite an outer surface of the heating roller 51, a side core 44 as a first core disposed opposite the outer surface of the heating roller 51 not via the excitation coil 41 nearer the heating roller 51 than the arch core 42, and a center core 43. The ferromagnetic core forms a continuous magnetic path to concentrate a magnetic flux arising from the coil unit 42 on the heating roller 51. The side core 44 is placed on a side of the casing 5. The center core 43 is placed at a center of the casing 45. The arch core 42 engages the side core 44.
The arch core 42 has multiple pieces disposed in a longitudinal direction of the heating roller 51 (i.e., front and rear sides in
Since the ferrite core is molded and sintered using ferrite powder under compression, a problem, such as ferrite core shrinkage, etc., occurs during the sintering as mentioned above resulting in low dimensional accuracy of the ferrite core.
Then, in the first embodiment, the side core 44 and the center core 43 each has an I-letter shape (i.e., a rectangular parallelepiped core) to substantially equally receive pressure when powder is molded under compression and ensure prescribed dimensional accuracy thereof. As shown in
Now, the excitation coil 41 is described. The excitation coil 41 is prepared by winding up litz wires from 5 times to 15 times, each of which is obtained by twisting from about 50 pieces to about 500 pieces of conductive lines each having a diameter of from approx. 0.05 mm to approx. 0.2 mm with an insulation coat. A fusion layer is provided on a surface of a litz wire, and is stiffened by applying heat either by means of supplying power or in a thermostatic oven, so that a shape of the wound coil can be maintained. Instead of this, a coil can be prepared by winding litz wires without fusion layers, but are subjected to press molding to provide the shape thereto. Since the litz wire needs a prescribed heat-resistance higher than a fixing temperature, prescribed resin, such as polyamide-imide, polyimide, etc., having insulation performance and heat resistance at the same time is used for wire insulation coat.
The excitation coil 41 thus formed is glued to the casing 45 using silicone glue or the like. Since the heat resistance higher than a fixing temperature is needed for resin of the casing 45, liquid crystal polymers or polyethylene terephthalate (PET) and the like having a high heat-resistance is used.
Now, a configuration of the excitation coil 41 of the first embodiment is described in greater detail with reference to
Now, a behavior of the fixing device 40 configured as described above is described. The fixing belt 53 rotates in a direction as shown by arrow X in
With thus improved performance of the induction heating, temperature of the surface of the fixing belt 53 quickly increases, and startup performance may be significantly improved as well. The startup performance represents a temperature rising time required for the fixing belt 53 to fix a toner image T. Thus, the shorter the temperature rising time, the better the user friendliness when using an image formation apparatus.
Now, a first embodiment is described in detail. In the first embodiment, the side core 44 is disposed along a line extended from an axis of the heating roller 51 in a radius direction. By placing an end face 44a of the side core 44 opposite the outer circumferential surface of the heating roller 51 almost perpendicular to the line, an area of the side core opposite the outer circumferential surface of the heating roller 51 increases, so that leakage of flux not passing through the heating roller 51 is reduced, thereby upgrading heat generation effectiveness. Now, reasons for upgrading the heat generation effectiveness is described based on comparison between various embodiments of the present invention and conventional examples.
First,
Whereas,
Hence, the magnetic flux B, which is diffused while separating away from the core drawing the parabola almost passes through the heating roller 51. When the magnetic flux B passes through the heating roller 51, current is induced and flown into a metal heat generation layer constituting the heating roller 51, and the heating roller 51 thereby generates heat as Joule heat. Percentage of the magnetic flux successfully passing through the heating roller 51 to the leakage, i.e., heat generation effectiveness, is dependent on a distance of the gap between the side core 44 and the heating roller 51. Thus, when the distance between the side core 44 and the heating roller 51 in this embodiment is the same to that in a conventional system, this embodiment can allow much more magnetic flux B to pass through the heating roller 51 thereby capable of improving effectiveness of heat generation than the conventional system.
Hence, the area of the side core opposite the heating roller is easily increased by using the I-shape side core capable of obtaining prescribed dimensional accuracy, so that leakage of the magnetic flux not passing through the heating roller is reduced, thereby capable of increasing the heat generation effectiveness.
Now, startup performance of the fixing device of this embodiment is described with reference to
In the experiment, a time period from a time when power is supplied to the fixing belt 53 to a time when surface temperature thereof reaches a prescribed fixing setting temperature of 170 degree Celsius is measured. As shown by a temperature curve (b), a conventional fixing device using the side core of the first example has started up in 30 seconds. Whereas the fixing device with the side core of this first embodiment has started up in 25 seconds as shown by temperature curve (a). Thus, it is found that the fixing device of this first embodiment has started up 5 seconds earlier than the conventional fixing device, while leaked magnetic flux not passing through the heating roller 51 decreases, so that heat generation effectiveness is improved. Hence, a fixing device having a preferable startup performance is realized in this first embodiment with a simple configuration.
Now, with reference to
Now, a modification of the side core 44 is described with reference to
Now, yet another modification of the side core 44 is described with reference to
Now, a modification of the arch core 42 is described with reference to
Then, in this embodiment of the present invention, since the side core 44 is diagonally disposed, specifically, along the line extended from the axis of the heating roller in the radius direction while the end face 44a of the side core 44 opposed to an outer circumferential surface of the heating roller 51 is arranged almost perpendicular to this liner line, a contact area between the arch core 42 and the side core 44 significantly varies in accordance with a variation in shape of the arch core 42. In other words, the contact area becomes smaller if the arch core and the side core make line contact therebetween. Whereas, the contact area increases when contact surfaces of the side core and the arch core become parallel to each other making surface contact therebetween in accordance with an opening condition of the arch core.
In this respect, end faces of the both ends of the arch core 42 are curved to make surface contact with the side cores 44 in a large uniform area as much as possible as shown in the right upper and lower columns of
As shown in the left upper column, an arch core is formed as intended with its both ends not opened outwardly. Thus, when these both ends of the arch core are flat as conventional, the arch core 42 and the side core 44 make line contact each other. Whereas in the left lower column, an arch core is formed with its both ends being opened outwardly. Thus, when these both ends of the arch core are flat as conventional, the arch core 42 and the side core 44 make surface contact each other. Further, the arch core 42 and the side core 44 sometimes completely or partially contact each other also in the longitudinal direction (i.e., perpendicular to a sheet plane). Such a contacting condition largely changes when these ends of the arch core 42 are widely opened outwardly (as in the left lower column) than when not widely opened (as in the left upper column). Therefore, due to a variation in opening angle of the arch core between its both ends, temperature of the heat generation-layer greatly changes at portions opposite the opening (i.e., both ends).
On the other hand, according to one embodiment of the present invention, when the arch core has curved end faces at its both ends, the arch core 42 contacts the side core 44 via the curved end faces as shown in the right upper and lower columns. As a result, the contacting condition is stabilized regardless of a variation in opening angle between these ends of the arch core. Accordingly, temperature uniformity of the heating roller in the longitudinal direction is not lost by the variation in opening angle between these ends of the arch core.
In addition, an arch core can be obtained at low cost by providing curved end faces to both ends thereof. Because, when the arch core has at flat end faces at its both ends, a tolerance of the opening angle needs to be strictly managed to obtain a constant contact condition resulting in increasing cost due to degrading of yielding thereof. Hence, heat uniformity can be obtained preventing the degrading of yielding without applying the strict tolerance to the opening portion according to one embodiment of this invention due to the curved end faces at both ends.
Now, various heat experiments executed based on first and second comparative examples and second and third embodiments are described.
A shape of end face is the same as a side face of a cylinder having a parallel axis to a rotation axis of a heating roller 51. Thus, by forming the end face 42a of the arch core 42 at both ends in a curved state, the arch core 42 always contact the side core 44 via the curvature even if these ends of the arch core are opened. Accordingly, temperature of the heating roller can be substantially the same in its longitudinal direction eliminating variations in contact condition in a longitudinal direction without precisely selecting the arch cores 42 having small and large openings.
Now, a third embodiment is described. An arch core of this embodiment is prepared having a height, a width, a thickness, and a curvature R at an end face of about 25 mm, about 60 mm, about 2.5 mm, and about 5 mm, respectively, to confirm an impact when the curvature is small and the arch core and the side core contact each other almost in a plane. Then, an induction heating coil 54 is produced under substantially the same condition as the second embodiment other than the curvature.
Now, a first comparative example is described. As a first comparative example, an induction heating coil is configured to be equivalent to that of the second embodiment using an arch core having a plane end face. Specifically, to produce the induction heating coil, arch cores having a relatively large opening angle between both ends are arranged within a range of ±30 mm from the center while other arch cores having a small opening angle therebetween are arranged in the remaining range.
Now, a second comparative example is described. Contrary to the first comparative example, a prescribed cutting process is applied to end faces of both ends as finishing. Then, arch cores with its both ends contacting the side core making surface contact are arranged within a range of ±30 mm from the center, thereby preparing an induction heating coil for the second comparative example. This is to confirm an impact when an accurate arch core is mixed.
Now, evaluation result is described. Specifically, heating experiments are executed using a fixing device with induction heating coils of the second and third embodiments and the first and second comparative examples prepared in the above-described manner. More specifically, Ricoh Imagio C5000 (TM) manufactured by Ricoh Co, Ltd., is prepared. Subsequently, an induction heating coil installed in a body of Ricoh Imagio C5000 is replaced with above-described various induction heating coils while providing a thermocouple (not shown) for measuring a surface temperature of a fixing belt in the vicinity of an inlet of a fixing nip.
Now, a result of comparison of an impact of a dimensional difference in curvature R of the end face between the second and third embodiments to a startup performance is described with reference to
Hence, according to this invention, it is proved that temperature uniformity in the longitudinal direction of the fixing belt is obtained without fail by disposing the side core 44 along a line extended from an axis of the heating roller 51 in a radius direction, and locating an end face 44a of the side core 44 opposite an outer circumferential surface of the heating roller 51 perpendicular to the line while forming the end faces of both ends of the arch core into a curved shape. Further, by increasing the dimension R of the end faces of the arch core at both ends thereof in an acceptable range, heat generation effectiveness can be further improved.
Now, fourth embodiment is described. This embodiment is only different from other embodiments in that an induction heating coil 54 mainly consists of a casing 45, an excitation coil 41, and multiple ferromagnetic cores 42, 43, and 44 is applied to a roller type fixing device 40, and other configurations are substantially identical.
As shown, the induction heating coil 54 is disposed opposite an outer circumferential surface of the fixing roller 61 and causes induction heating in a heat generation layer 61c thereby heating the fixing roller 61. Further, the side core 44 is placed along a line (a radial line) extended from an axis of the heating roller 51. The end face 44a of the side core 44 opposed to an outer circumferential surface of the heating roller 51 is arranged almost perpendicular to this line. Accordingly, almost all of magnetic flux diffused drawing a parabolic as parting from the core passes through the fixing roller 61. Hence, by increasing an area of the side core opposite the fixing roller 61, heat generation effectiveness can be improved.
The above-described fixing roller 61 has a multi-layer structure and is mainly composed of a metal core 61a, an elastic layer 61b, and the heat generation layer 61c in this order from an inside thereof as laminate. Specifically, the fixing roller 61 has a diameter of approx. from 30 mm to approx.40 mm and is configured by stacking the elastic layer 61b, the heat generation layer 61c, and a mold releasing layer (not shown) or the like on the metal core 61a as laminate.
The mold releasing layer (not shown) is formed on the fixing roller 61 as an outmost layer. The mold releasing layer may be made of fluorocarbon resin, such as polytetrafluoride ethylene resin (PTFE), polytetrafluoride ethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polytetrafluoride ethylene-hexafluoride propylene copolymer (FEP), etc., or these resin mixture, or heat-resistant resin with dispersion of these fluorocarbon resins. Such a mold releasing layer has a thickness of from about 5 μmm to about 50 μmm (preferably, from about 10 μmm to about 30 μmm). Hence, prescribed mold releasing performance of toner borne on the fixing roller 61 is assured and flexibility of the fixing roller 61 is maintained at the same time.
The heat generation layer 61c is made of material having a low electrical resistance. As metal suitable for induction heating, a high resistance one is generally known. However, by thinning high-conductivity material, a substantial resistance of a heat generation layer 61c may be optionally obtained, thereby capable of improving a heat generation amount. In this fourth embodiment, a copper layer having a thickness of about 10 μm is used as the heat generation layer 61c. Since the heat generation layer is suitable if having a preferable conductivity, metal, such as aluminum, silver, magnesium, nickel of magnet, etc., is employed.
Further, fluorine rubber, silicone and fluorosilicone rubbers, and other material are available as an elastic layer 61b. By employing an elastic layer 61b on the fixing roller 61 and allowing the fixing roller 61 to deform thereby increasing a width of a nip region, while lowering a roller hardness of the fixing roller 61 than that of the pressing roller 55, sheet ejection and separation performance can be improved.
By including elastic sponge rubber, the elastic layer 61b can remain insulated from heat of the heat generation layer 61c. For the same reason, the elastic layer 61b and the mold releasing layer disposed on a front surface side of the fixing roller is quickly heated and the surface thereof quickly reaches a prescribed temperature necessary for fixing. At the same time, a recording medium can be promptly supplied with heat even when the recording medium has taken the heat. Depending on the above-described configuration, a preferable nip region is formed. Insulation from heat of the heat generation layer 61c is kept. In addition, heat transfer to an inside of the fixing roller can be suppressed.
Now, a fourth embodiment is described, in which a foam silicone rubber halving a thickness of about 9 mm is used as an elastic layer 61b. Heat is not easily flown from the heat generation layer 61c positioned on the front surface of the fixing roller 61 into an interior of the fixing roller, thereby capable of heating effectively.
The metal core layer 61a is provided to give a prescribed amount of rigidity capable of withstanding load, which is put on the fixing roller 61 to form a nip region thereon. Further, with insulation and non-magnetic material, such as ceramic, etc., the core metal layer 61a can employ material not providing an impact on induction heating. In the fourth embodiment, the core metal layer is made of aluminum and has an outer diameter of about 22 mm and a thickness of about 2 mm. Such a thickness provides a prescribed amount of stiffness to withstand a prescribed amount of load, which is put on the fixing roller 61 to form a nip region thereon.
Accordingly, as shown in the drawing, a pair of center cores 43 and a pair of arch cores 42 respectively divided as two parts are provided in the induction heating coil 54. Further, each end face of the arch core 42 is curved and only contacts the side core 44. Whereas, the other end of the arch core 42 contacts the center core 43. By providing a curved end face to the arch core 42 contacting the side core 44, temperature uniformity in a longitudinal direction of the fixing roller 61 can be absolutely obtained.
According to one embodiment of the present invention, by placing an end face 44a of the side core 44 opposite the outer circumferential surface of the heating roller 51 almost perpendicular to the line, an area of the end face opposite the outer circumferential surface of the heating roller 51 can be increased and leakage of flux not passing through the heating roller 51 can be reduced while upgrading heat generation effectiveness. Further, by making the end face of the second core contacting the first core into a curved state, a contact area between of the first and second cores can be constant and a stable temperature distribution in the longitudinal direction of the fixing member can be obtained with a simple configuration even if the first core is disposed in this way. Further, a preferable fixing device and an image forming apparatus with the fixing device capable of quickly starting up can be obtained.
Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-051293 | Mar 2011 | JP | national |
| 2011-199253 | Sep 2011 | JP | national |
