JP4288109B2 - Fixing apparatus and image forming apparatus having the fixing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device for fixing a toner image on a recording medium and an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, and a facsimile machine having the fixing device.
[0002]
[Prior art]
[Patent Document 1]
JP-A-2002-123111 [Patent Document 2]
In a fixing device of an image forming apparatus, conventionally, heat roller fixing in which a fixing roller and a pressure roller are combined has been mainstream. However, as described in JP-A-2002-123111, in recent years, Many fixing devices using belts can be seen. As the heating means used in the fixing device, a heating element such as a halogen lamp built in the fixing roller is often used, but the induction heating method described in Japanese Patent Laid-Open No. 8-137306 is beginning to be adopted. As described above, the biggest factor of using the fixing belt or adopting the induction heating method is that the rise time of the fixing device can be shortened.
[0003]
FIG. 5 is an explanatory diagram showing an induction heating type fixing device 100 using a conventional fixing belt.
In FIG. 5, reference numeral 101 denotes an endless heating belt, and the heating belt 101 is wound around a heating roller 102 and a driven roller 103. A pressure roller 104 is pressed against the heating roller 102 via a heating belt 101, and a recording medium P carrying a toner image in a nip formed by the pressure roller 104 and the heating roller 102 via the heating belt 101. Is sent. The heating belt 101 and the heating roller 102 are magnetic materials, and are made of, for example, stainless steel, iron, nickel, cobalt, or the like. Reference numeral 105 denotes a coil disposed in opposition to the running side of the heating belt 101, and reference numeral 106 denotes a coil built in the heating roller 102. In the coils 105 and 106, current flows through the heating belt 101 and the heating roller 102, which are magnetic bodies, in accordance with the change in the magnetic field generated by the coil when a high-frequency current is passed, and Joule heat is generated by the change in current. The heating roller 102 is heated.
[0004]
The heating belt 101 may be provided with an elastic layer (for uniformly fixing) and a release layer (for preventing toner from sticking) on a magnetic belt substrate. The driven roller 103 is made of a nonmagnetic metal such as aluminum. Reference numeral 107 denotes a tension roller that applies tension to the heating belt 31.
[0005]
In the fixing device 100 configured as described above, for example, when the heating roller 102 is driven in the direction of an arrow by a driving device (not shown), the driven roller 103 and the pressure roller 104 rotate in the direction of the arrow, respectively, and the heating belt 101. Also run in the direction of the arrow. Here, when the recording medium P carrying the toner image is sent to the fixing device 100, it is sandwiched between the heating roller 102 and the pressure roller 104 and heated and pressurized. At this time, since the heating belt 101 and the heating roller 102 are heated, the toner image is reliably fixed to the recording medium P by passing through the nip between the heating roller 102 and the pressure roller 104.
[0006]
[Problems to be solved by the invention]
In this type of fixing device, in order to apply tension to the heating belt 101, a tension member that contacts the heating belt 101 is provided. In the example of FIG. 4, a tension roller 107 that is pressed against the running side of the heating belt 101 is provided. Yes. However, when the tension roller 107 is provided, part of the heat of the heating belt 101 and the heating roller 102 is transmitted to the tension roller 107 and escapes. For this reason, there has been a problem that the rise time of the fixing device is not shortened as much as expected, and heating must be performed including escape.
[0007]
An object of the present invention is to provide a fixing device capable of improving the escape of heat from the tension member described above.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an endless fixing belt that is wound around at least a heating roller and an outlet roller, a pressure roller that is in pressure contact with the heating roller via the fixing belt, and the fixing roller. A heating unit that heats the belt, and a bias unit that applies a bias for adsorbing the recording medium to the fixing belt, and the recording medium carrying the toner image is pressed against the heating roller via the fixing belt. In a fixing device in which a toner image is fixed to a recording medium while being held between rollers and adsorbed to a fixing belt and conveyed from the heating roller to an exit roller, tension is applied from the inside of the fixing belt. the in across the fixing belt oppositely disposed coil made of a magnetic material to generate Joule heat by passing a high frequency current heating Heating tension member having provided, the heating tension member is arranged in the region where the recording medium is conveyed while being attracted to the fixing belt, the convex its belt contact face is viewed from one end side in the belt width direction A fixing device is proposed which is a formed tension plate .
[0013]
The present invention is effective when the heating tension member is made of a magnetic shunt alloy.
In order to achieve another object of the present invention, in the image forming apparatus of the present invention, an image forming means for forming a toner image on a recording medium, and a toner image formed on the recording medium by the image forming means The fixing device according to claim 1 or 2 for fixing.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram illustrating an embodiment of an image forming apparatus. The image forming apparatus includes an image forming unit that forms a toner image on a recording medium and a fixing device 1 that fixes the toner image on the recording medium. First, an outline of the image forming means will be described.
[0015]
The image forming means in FIG. 1 has a drum-shaped photoconductor 1, and the photoconductor 1 is driven to rotate clockwise in FIG. 1, and at this time, the surface is uniformly charged to a predetermined polarity by a charging roller 2. Next, the charged surface is irradiated with a light-modulated laser beam L emitted from the laser writing device 7. As a result, an electrostatic latent image is formed on the photosensitive member 1, and the electrostatic latent image is visualized as a toner image by the developing device 3.
[0016]
On the other hand, a recording medium P made of, for example, transfer paper is fed from a paper feeding device 10 provided on the lower side of the apparatus main body, and the recording medium P is interposed between the photoreceptor 1 and the transfer roller 4 via a registration roller 11. It is sent. A voltage having a polarity opposite to that of the toner on the photoreceptor 1 is applied to the transfer roller 4, whereby the toner image on the photoreceptor 1 is transferred onto the recording medium P. The transfer residual toner that is not transferred to the recording medium P and remains on the photosensitive member 1 is removed by the cleaning device 5, and further, the residual charge remaining on the photosensitive member 1 is removed by the charge eliminating device 6.
[0017]
The recording medium P on which the toner image is formed is sent to the fixing device 20 via the conveyance belt 12. At this time, the toner image is fixed on the recording medium P, and the recording medium P after the fixing is discharged on the paper discharge tray 13. Discharged to the top. As described above, the image forming apparatus illustrated in FIG. 1 fixes the image forming unit and the toner image formed on the recording medium P by the image forming unit.
[0018]
As shown in FIG. 2, the fixing device 20 according to the present invention includes a heating roller 22 and an outlet roller 23 which are two members that are parallel to each other, and an endless fixing belt 21 is provided between the heating roller 22 and the outlet roller 23. Is wrapped around. The heating roller 22 is a cylindrical member made of a magnetic material such as stainless steel, iron, nickel, cobalt, and the like, and a coil 25 is provided therein. The exit roller 23 is made of a non-magnetic metal such as aluminum. The belt base material of the fixing belt 21 may be either a magnetic material or a non-magnetic material, and an elastic layer for uniformly fixing the surface of the fixing belt 21 and a release layer for preventing toner from sticking to the surface. It is advantageous.
[0019]
A pressure roller 24, which is an opposing member, is pressed against the heating roller 22 via the fixing belt 21. The heating roller 22, the exit roller 23, and the pressure roller 24 are rotatably supported by a frame (not shown) of the fixing device 20, and the heating roller 22 or the heating roller 22 and the pressure roller 24 are respectively driven by a driving device (not shown). It is rotationally driven in the direction of the arrow. As a result, the fixing belt 21 rotates in the clockwise direction in FIG. 2, and the exit roller 23 is driven to rotate in the same direction. The pressure roller 24 may also be provided with a heating means.
[0020]
A bias roller 26 serving as a bias applying unit for electrostatically attracting the recording medium P is provided on the surface of the fixing belt 21 so as to contact the fixing belt 21. The recording medium P is attracted to the fixing belt 21. Further, a tension roller 27 as a tension member is pressed against the surface of the fixing belt 21, and the fixing belt 21 is always kept in a tensioned state by the tension roller 27. The adsorption of the recording medium P to the fixing belt 21 is between the heating roller 22 and the pressure roller 24 via the fixing belt 21 from the nip to the exit roller, and thus the bias roller 26 is connected to the heating roller 22 and the pressure roller. It is preferably arranged in the vicinity of the upstream side of the nip 24, and in the example of FIG. The tension roller 27 is provided on the traveling side of the fixing belt 22. The tension roller 27 in this example is in pressure contact with the outer peripheral surface of the fixing belt 21, and the recording medium P is attracted to the fixing belt 21 on the lower traveling side. Therefore, the tension roller 27 is provided on the upper running side of the fixing belt 22.
[0021]
In the fixing device 20 configured as described above, when a high frequency current is passed through the coil 25, a current flows through the heating roller 22 that is a magnetic body in accordance with a change in the magnetic field generated by the coil, and Joule heat is generated by the change in the current. The heating roller 22 is heated. When the heat of the heating roller 22 is transmitted to the fixing belt 21 and the fixing belt 21 reaches a predetermined temperature, the fixing is possible. Here, when the recording medium P carrying the toner image T formed by the image forming means is conveyed to the fixing device 20, the recording medium P is nipped between the heating roller 22 and the pressure roller 24 via the fixing belt 21. The toner image T is fed into contact with the fixing belt 21. The recording medium P is heated and pressurized as it passes through the nip between the heating roller 22 and the pressure roller 24, and is attracted to the fixing belt 21 to which a bias is applied via the bias roller 26. When the recording medium P attracted to the fixing belt 21 is conveyed to the exit roller 23, it cannot follow the curvature of the exit roller 23 and is separated from the fixing belt 21.
[0022]
By the way, in a conventional fixing device using a fixing belt, if a tension member is provided, the heat of the fixing belt is taken away by the tension member, and therefore the fixing belt must be heated by a heating roller.
[0023]
Therefore, in the fixing device 20 of this example shown in FIG. 2, the tension roller 27 has a heating function. The tension roller 27 of this example employs an induction heating method, similar to the heating roller 22. For example, a cylindrical heat generating portion made of a magnetic material such as stainless steel, iron, nickel, cobalt, etc. Is provided. When a high-frequency current is passed through the coil 28, a current flows through the tension roller 27, which is a magnetic body, with a change in the magnetic field generated by the coil. Joule heat is generated by the change in the current, and the tension roller 22 is heated.
[0024]
In this way, the tension roller 27 is provided with a heating function, and the tension roller 27 heats the fixing belt 21, so that the heat of the fixing belt 21 is reliably prevented from being taken away by the tension roller 27. In addition, since the fixing belt 21 is warmed by the tension roller 27, an effect that the rise time to the fixing temperature in the fixing device can be shortened is also obtained.
[0025]
In the fixing device 20 shown in FIG. 2, a tension roller 27 that applies tension and heats the fixing belt 21 is disposed on the upper running side of the fixing belt 21, but the fixing belt 21 holds the recording medium P on the lower running side. When the tension member directly heats the lower traveling side for adsorption and conveyance from the heating roller 22 to the exit roller 23, the recording medium P can be heated through the fixing belt 21, which is advantageous in terms of thermal efficiency.
[0026]
Therefore, in another embodiment of the present invention shown in FIG. 3, a tension plate 37 as a tension member is disposed so as to contact the lower running side from the inside of the fixing belt 21. The other configuration of the fixing device 20 shown in FIG. 3 is the same as that of the fixing device of FIG. 2, and the same members are denoted by the same reference numerals.
[0027]
The tension plate 37 itself is a heat generating part made of a magnetic material such as stainless steel, iron, nickel, cobalt, etc., and its shape is a convex shape with a gentle curvature in a direction substantially perpendicular to the running direction of the belt. Is formed. That is, as is apparent from FIG. 3, the tension plate 37 is formed in a convex shape having a gentle curvature when viewed from one end side in the belt width direction. The tension plate 37 is configured to always apply tension to the fixing belt 21 by pressing a convex surface with a gentle curvature against the fixing belt 21. Below the tension plate 37, a coil 38 is disposed at a position slightly away from the surface of the fixing belt 21, and the fixing belt 21 is made of a nonmagnetic material.
[0028]
In the fixing device configured as described above, when a high frequency current is passed through the coil 38, the fixing belt 21 is a non-magnetic material, and the coil 38 is disposed close to the tension plate 37. As the current changes, current flows through the tension plate 37, which is a magnetic material, Joule heat is generated by the change in current, and the tension plate 37 is heated. That is, if the fixing belt 21 is a nonmagnetic material, the tension plate 37 is heated through the belt. Further, when the heating roller 22 is heated and the fixing belt 21 reaches a predetermined temperature, the recording medium P carrying the toner image T is conveyed from the image forming unit. The recording medium P is sent to the nip between the heating roller 22 and the pressure roller 24 via the fixing belt 21 so that the toner image T is in contact with the fixing belt 21, and the recording medium P is transferred between the heating roller 22 and the pressure roller 24. When passing through the nip, it is heated and pressurized, and is attracted to the fixing belt 21 to which a bias is applied via the bias roller 26. The recording medium P adsorbed by the fixing belt 21 is conveyed toward the exit roller 23, heated between them by the tension plate 37, and when it reaches the exit roller 23, it can not follow the curvature of the exit roller 23 and is fixed. Separated from the belt 21.
[0029]
Since the fixing device 20 configured as described above is provided with the tension plate 37 that heats the lower running side of the fixing belt 21 that sucks and conveys the storage medium P, it assists the heating of the heating roller 22 and fixes it. The storage medium P is directly heated with the belt 21 interposed therebetween. Therefore, compared with the embodiment shown in FIG. 2 in which the upper running side of the fixing belt 21 is heated, the efficiency can be transmitted to the recording medium P.
[0030]
Since the fixing belt 21 is in sliding contact with the tension plate 37 of this embodiment, the corners are rounded so that the fixing belt 21 is not caught and bent. Further, the curvature of the tension plate 37 is a gentle curved surface so that the fixing belt 21 can be easily along, and the radius of curvature is several times larger than that of the heating roller. Furthermore, since the tension plate 37 does not rotate, a friction reducing layer having a smaller frictional force may be provided on the surface on the belt side in order to reduce friction with the fixing belt 21. The coil 38 is formed in a curved shape so that the gap with the tension plate 37 is substantially constant, but it may be formed in a flat plate shape that is easier to make. Further, the tension plate 37 can be moved in the vertical direction in FIG. 2 by a mechanism (not shown). With this configuration, the fixing belt 21 can be appropriately tensioned or loosened.
[0031]
Still another embodiment of the present invention shown in FIG. 4 is an example of a fixing device 20 in which a toner image is formed on the lower surface of the recording medium P by the image forming means, and the toner image is fixed to the recording medium P. Compared with the fixing device of FIG. 3, the fixing device 20 of this example has a pressure roller 24 pressed against the upper portion of the heating roller 22 via the fixing belt 21, and a rotatable bias roller below the heating roller 22. 27 is different in arrangement relation. Further, a tension roller 47 as a tension member is arranged on the fixing belt 21 so as to push up the upper running side of the fixing belt 21. The tension roller 47 itself is a heat generating portion made of a magnetic material such as stainless steel, iron, nickel, cobalt, and the like, and a coil 48 is provided above the tension roller 47. When a high-frequency current is passed through the coil 48, the fixing belt 21 is a non-magnetic material. Therefore, a current flows through the tension roller 47, which is a magnetic material, with the change in the magnetic field generated by the coil, and Joule heat is generated due to the change in current. Then, the tension roller 47 is heated.
[0032]
Also in the fixing device configured as described above, the heat generated by the tension roller 47 assists the heating roller 22 and the storage medium P can be directly heated with the fixing belt 21 interposed therebetween.
[0033]
As described above, by providing the tension member with a heating function, heat does not escape from the tension member, and heating of the heating roller 22 can be assisted.
[0034]
By the way, in the above-mentioned embodiment, since the induction heating method is adopted for the tension member, it is preferable to use a magnetic shunt alloy for the magnetic material used here. Since the magnetic shunt alloy loses magnetism when it reaches a certain temperature, even if the device runs out of control and keeps heating, the tension member will not be heated above a certain temperature. It is safer than when it is not a magnetic alloy. Of course, since the heating roller 22 of the above embodiment also employs the induction heating method, a magnetic shunt alloy may be used for the magnetic body.
[0035]
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited only to the said embodiment, Various modifications can be carried out.
For example, in the above embodiment, the induction heating method is used as the tension member heating means, but the heating method is not limited to induction heating, and other heating methods such as a heater may be used. Similarly, the heating method of the fixing device is not limited to the induction heating method, and various other heating methods can be used.
[0036]
Furthermore, the present invention can be applied to various types of fixing devices, even if the fixing device does not attract the recording medium to the fixing belt, as long as the fixing belt is used and tension is applied to the belt.
[0037]
【The invention's effect】
According to the present invention, since the tension member for applying tension to the belt and heating the belt is provided, it is possible to improve the escape of heat from the tension member.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an image forming apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing an embodiment of a fixing device of the present invention.
FIG. 3 is an explanatory diagram showing another embodiment of the fixing device of the present invention.
FIG. 4 is an explanatory view showing still another embodiment of the fixing device of the present invention.
FIG. 5 is an explanatory diagram of a fixing device using a conventional fixing belt.
[Explanation of symbols]
20 fixing device 21 fixing belt 22 heating roller 23 outlet roller 24 pressure roller 25 coil 27 tension roller 28 coil 37 tension plate 38 coil 47 tension roller 48 coil P recording medium

Claims (3)

An endless fixing belt that is wound around at least a heating roller and an exit roller, a pressure roller that is in pressure contact with the heating roller via the fixing belt, a heating unit that heats the fixing belt, and the fixing belt Bias means for applying a bias for adsorbing the recording medium, and the recording medium carrying the toner image is sandwiched between a heating roller and a pressure roller via the fixing belt, and adsorbed to the fixing belt. In the fixing device in which the toner image is fixed to the recording medium while being conveyed from the heating roller to the exit roller,
A heating tension member having a heat generating portion made of a magnetic material that generates Joule heat by flowing high-frequency current through coils arranged opposite to each other across the fixing belt while being in contact from the inside of the fixing belt is provided,
The heating tension member is a tension plate that is disposed in a region where the recording medium is attracted and conveyed by the fixing belt, and whose belt pressure contact surface is formed in a convex shape when viewed from one end side in the belt width direction. A fixing device characterized by the above.   The fixing device according to claim 1, wherein the heating tension member is made of a magnetic shunt alloy.   An image comprising image forming means for forming a toner image on a recording medium, and the fixing device according to claim 1 or 2 for fixing the toner image formed on the recording medium by the image forming means. Forming equipment.

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