FIXING APPARATUS AND IMAGE FORMING APPARATUS

A fixing apparatus includes a pressing unit, a belt unit disposed to be pressed by the pressing unit and including a conductive layer, and a magnetic flux generation unit configured to generate a magnetic flux that causes the conductive layer to generate heat. The conductive layer has ends that are disposed inwardly of regions of the belt unit that contact ends of the pressing unit while the pressing unit rotates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-158926, filed Jul. 31, 2013, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate to a fixing apparatus and an image forming apparatus.

BACKGROUND

There is an image forming apparatus, such as a copier or printer, having a fixing apparatus which heats a fixing belt by causing a heating layer included in the fixing belt to generate heat through electromagnetic induction heating (IH). In such a fixing apparatus, the heating layer extends to an end portion of the fixing belt in a longitudinal direction. However, the heating layer at the end portion of the fixing belt may be damaged while the fixing belt is repeatedly pressed by a pressing unit of the fixing apparatus and released from the press of the pressing unit.

DETAILED DESCRIPTION

In accordance with one embodiment, a fixing apparatus includes a pressing unit, a belt unit disposed to be pressed by the pressing unit and including a conductive layer, and a magnetic flux generation unit configured to generate a magnetic flux that causes the conductive layer to generate heat. The conductive layer has ends that are disposed inwardly of regions of the belt unit that contact ends of the pressing unit while the pressing unit rotates.

Embodiments of the present invention are described in detail below with reference to accompanying drawings ofFIG. 1-FIG.4.FIG. 1illustrates an MFP (Multi-Function Peripherals)10as an example of an image forming apparatus according to an embodiment. The MFP10comprises, for example, a scanner12, a control panel13, a paper feed cassette section16, a manual feed tray17, a printer section18, and a paper discharging section20.

The scanner12reads an original image for the printer section18to form an image. The control panel13accepts an input from, for example, a user or display information for a user.

The paper feed cassette section16comprises a paper feeding cassette16afor storing a sheet P serving as a recording medium and a pickup roller16bfor picking up a sheet P from the paper feeding cassette16a. The sheet P includes an unused sheet or a sheet for reuse (e.g. a sheet an image on which has been erased through a color erasing processing) and the like. The manual feed tray17is capable of feeding an unused sheet P or a sheet P for reuse with a pickup roller17a.

The printer section18comprises an intermediate transfer belt21. In the printer section18, the intermediate transfer belt21is supported by a backup roller40having a driving section, a driven roller41, and a tension roller42, and configured to rotate in a direction indicated by an arrow m.

The printer section18comprises Y (yellow), M (magenta), C (cyan) and K (black) image forming stations22Y,22M,22C, and22K, which are arranged in parallel along the lower side of the intermediate transfer belt21. The printer section18comprises replenishing cartridge23Y,23M,23C, and23K above the image forming stations22Y,22M,22C, and22K to store toners to be replenished, respectively.

For example, the Y (yellow) image forming station22Y includes a charger26, an exposure scanning head27, a developing apparatus28, and a photoconductor cleaner29, around a photoconductive drum24rotating in a direction indicated by an arrow n. The Y (yellow) image forming station22Y has a primary transfer roller30, which is located at a position opposite to the photoconductive drum24with the intermediate transfer belt21therebetween.

The M (magenta), C (cyan), and K (black) image forming stations22M,22C, and22K have the same configuration as that of the Y (yellow) image forming station22Y. Therefore, detailed description of the M (magenta), C (cyan), and K (black) image forming stations22M,22C, and22K is omitted.

In the image forming stations22Y,22M,22C, and22K, the photoconductive drum24, after being charged by the charger26, is exposed by the exposure scanning head27, thereby forming electrostatic latent images on the photoconductive drum24. The developing apparatus28develops the electrostatic latent images on the photoconductive drum24with a two-component developing agent including Y (yellow), M (magenta), C (cyan), and K (black) toners and a carrier. The toner for development may be, for example, a color non-erasable toner or a color erasable toner, which can be erased when heated to a given temperature, and the like.

The primary transfer roller30primarily transfers a toner image formed on the photoconductive drum24to the intermediate transfer belt21. The image forming stations20Y,20M,20C, and22K forms a color toner image on the intermediate transfer belt21by overlapping Y (yellow), M (magenta), C (cyan), and K (black) toner images with the primary transfer rollers30. The photoconductor cleaner29removes the toner left on the photoconductive drum24after the primary transfer.

The printer section18includes a secondary transfer roller32which is located at a position opposite to the backup roller40with the intermediate transfer belt21therebetween. The secondary transfer roller32secondarily transfers all the color toner images on the intermediate transfer belt21to a sheet P. The sheet P is fed from the paper feed cassette section16or the manual feed tray17along a conveyance path33in synchronization with a conveyance of the color toner image on the intermediate transfer belt21. A belt cleaner43removes the toner left on the intermediate transfer belt21after the secondary transfer.

The printer section18includes a register roller33a, a fixing apparatus34, and a paper discharging roller36along the conveyance path33. The printer section18further includes a bifurcation unit37and a reversal conveyance unit38at a position downstream with respect to the fixing apparatus34in a direction of sheet conveyance. The bifurcation section37distributes the sheet P towards the paper discharging section20or the reversal conveyance section38. In the case of a duplex printing, the reversal conveyance section38conveys the sheet P distributed from the bifurcation section37towards the register roller33a.

The intermediate transfer belt21, the image forming stations22Y,22M,22C, and22K, and the secondary transfer roller32constitute an image forming section.

With such a configuration, the MFP10forms a fixed toner image on a sheet P using the printer section18and discharges the sheet P to the paper discharging section20.

The image forming apparatus is not limited to the MFP10. The image forming apparatus is not limited to a tandem form, and no limitation is given to the number of the developing apparatuses. The image forming apparatus may transfer a toner image directly from a photoconductor to a recording medium.

Next, the fixing apparatus34is described below in detail. As shown inFIG. 2, the fixing apparatus34comprises an endless fixing belt50having a conductive layer61serving as a heating layer, a press roller51serving as a pressing unit, and an electromagnetic induction heating coil unit (hereinafter referred to as an IH coil unit for short)52serving as a generating unit.

In a space within the fixing belt50, a press pad53serving as a support unit, a magnetic shunt alloy70, and a shield71including an aluminum are disposed. Further, in the space within the fixing belt50, a temperature sensor72for detecting a temperature of the fixing belt50and a thermostat73for detecting an abnormal heating of the fixing belt50are disposed. Moreover, in the space, a frame74for supporting the press pad53is disposed. The frame74supports a support spring76which adjusts the position of the shield71.

The press pad53is located at a position opposite to the press roller51with the fixing belt50therebetween. The press pad53urges an inner peripheral surface of the fixing belt50towards the press roller51. The press roller51presses the fixing belt50urged by the press pad53to form a nip54between the fixing belt50and press roller51. The press pad53is made from, for example, heat-resistant polyphenylene sulfide resin (PPS). A sliding sheet, which is formed, for example, by coating fluororesin on the surface of glass fiber, may be arranged between the press pad53and the fixing belt50to reduce a friction resistance between the fixing belt50and the press pad53.

Magnetic characteristics of the magnetic shunt alloy70change in accordance with temperature. As permeability of the magnetic shunt alloy70decreases at a temperature higher than a Curie point temperature, density of magnetic flux passing the fixing belt50decreases, and, thus, the heat generated from the fixing belt50decreases. By reducing the heat value of the fixing belt50, the magnetic shunt alloy70can restrict the temperature rise of the fixing belt50in, for example, a non-paper passing area of the fixing belt50. When temperature is below the Curie point temperature, the magnetic shunt alloy70generates heat with the magnetic flux from the IH coil unit52and assists the fixing belt50in generating heat.

The press roller51has an elastic layer51b, such as a heat-resistant rubber layer, around a core bar51aand a release layer51cincluding fluororesin on the surface of the press roller51. The press roller51is in contact with the fixing belt50under the pressure of a press spring56. As shown inFIG. 3, in the fixing apparatus34, a motor57drives the press roller51with a gear57a, and the fixing belt50is driven by the press roller51.

A wheel58, which keeps the fixing belt50substantially in a circular shape, is arranged on the inner periphery at ends of the fixing belt50. The wheel58supports a frame shaft74awith a bearing58atherebetween. The fixing belt50that is in contact with the press roller51at the position of the press pad53is driven by the press roller51to rotate integrally with the wheel58. The fixing belt50may also be driven to rotate independently from the press roller51. When the fixing belt50is independently driven to rotate, a one-way clutch may be inserted to prevent a difference of speed between the fixing belt50and the press roller51.

The middle area of the fixing belt50in a longitudinal direction (a direction parallel to a rotation axis) is in a tension-free state. The middle area of the fixing belt50in the longitudinal direction is in contact with the press roller51at the position of the press pad53and is therefore deformed.

In the longitudinal direction, for example, a width (L1) of the fixing belt50is 368 mm, a width (L2) of the press pad53is 355 mm, and a width (L3) of the press roller50is 332 mm. For example, the width (L2) of the press pad53is slightly greater than the maximum fixing width of the fixing apparatus34.

The IH coil unit52comprises a core52bwhich covers a coil52aand the periphery of the coil52aand regulates the magnetic flux of the coil52a. In the IH coil unit52, a high-frequency current is applied to the coil52ato generate a magnetic flux in the direction of the fixing belt50. The conductive layer61of the fixing belt50generates an eddy current in accordance with the magnetic flux from the IH coil unit52, and generates heat.

The fixing belt50is a multi-layer structure including the conductive layer61. As shown inFIG. 4, the fixing belt50comprises, for example, from the inner periphery side to the outer periphery side, an endless base material60, the conductive layer61serving as a heating layer, an elastic layer62, and a toner release layer63. No limitation is given to the layer structure of the fixing belt50as long as the fixing belt50comprises the conductive layer61. The base material60is, for example, a polyimide sleeve having a thickness of 70 μm.

The conductive layer61includes, for example, a Cu layer having a thickness of 10 μm. The conductive layer61comprises a Nickel (Ni) layer66ahaving a thickness of 1 μm and a Nickel (Ni) layer66bhaving a thickness of 8 μm with the Cu layer64therebetween. As long as the conductive layer61generates heat in accordance with the magnetic flux from the IH coil unit52, then the conductive layer may be a single Fe, Nickel (Ni) or Cu layer. The elastic layer62is, for example, a Silicon (Si) rubber layer having a thickness of 200 μm, and the toner release layer63is, for example, a fluroresin (e.g., PFA resin) tube having a thickness of 30 μm. In order to enables a fast warming up, the conductive layer61is preferably reduced in thickness and heat capacity.

A width (W) of the conductive layer61in the longitudinal direction is, for example, equal to the width L3 of the press roller51. The conductive layer61does not extend to an area α outside the contact area of the press roller51and the fixing belt50, that is, the nip54, which has a width of L3. No limitation is given to the width (W) of the conductive layer61as long as the conductive layer61does not extend to a region outside the nip54(width L3) and causes no damage to the heat generation performance of the fixing belt50. As the conductive layer61does not extend to a region outside the nip area, the conductive layer61is prevented from being deformed even if the middle area of the fixing belt50, of which end parts are kept in circular shape by the wheel58, is deformed at the position of the press pad53. If the conductive layer61is formed on the surface of the base material60through deposition or plating, then the conductive layer61is formed while the areas a at two ends of the base material60are masked.

When the press roller51rotates in the direction indicated by an arrow x as shown inFIG. 2, the fixing belt50is driven to rotate in the direction indicated by an arrow y. When a portion of the area α, which is between the wheel58and the end parts of the press roller51, is in a position opposite to the press roller51, the portion of the area α51is deformed as the press contact stress generated by the end part of the press roller51is concentrated in the portion of the area α. After the fixing belt50passes through the nip54, the portion of the area α of the fixing belt50is released from the press contact stress generated by the end parts of the press roller51, and the portion of the area α stretches.

When the fixing belt50is driven to rotate in the direction indicated by the arrow y, the area α of the fixing belt50is repeatedly deformed under the press contact stress generated by the end parts of the press roller51and then stretches. However, the conductive layer61at a position within the areas a generates few cracks as the conductive layer61is little influenced by the press contact stress generated by the end parts of the press roller51. The fixing belt50more reliably generates heat even at the end part of the nip54. The fixing apparatus34can achieve an excellent fixation in the whole width of the sheet P, without generating a poor fixation at the end part of the nip54.

As a comparative example, a fixing belt formed with a conductive layer formed as far as the end part in the longitudinal direction was examined in a life test. In the comparative example, a crack occurred in the conductive layer during the period in which the end parts of the fixing belt were repeatedly deformed and stretch due to the press contact stress generated by the end parts of a press roller at the ends of the nip. Further, when the end parts of the fixing belt were deformed and stretch repeatedly, the crack generated in the conductive layer extended to a fixing area and the heat generated at the fixing belt was reduced. In the comparative example, a crack extended from a part of the conductive layer that corresponds to the end part of the press roller to the entire conductive layer, which lead to a poor fixation due to poor heat generation.

According to the embodiments described herein, the conductive layer61of the fixing belt50does not extend to the area α outside the area that will be in contact with the press roller51. The conductive layer61is less influenced by the press contact stress generated by the end parts of the press roller51even if the area α at the end parts of the fixing belt50is repeatedly deformed and stretches due to the press contact stress generated by the press roller51. The fixing belt50can prevent the generation of a crack in the conductive layer61. The fixing apparatus34prevents a poor fixation caused by the crack generated in the conductive layer61of the fixing belt50and therefore achieves an excellent fixation.

The present invention is not limited to the embodiments above which may have various variations. In the embodiments described herein, the end part of the fixing belt is kept in a circular shape by the wheel; however, the present invention is not limited to this. The fixing belt may be stretched by a plurality of rollers. Further, the press section may be in a belt shape, but is not limited to be in a roller shape.