JP2004205560A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fixing device that fixes toner images formed on both sides of a recording medium from causing deterioration of the image quality of the toner images after fixing, by steadily conveying the recording medium, thereby avoiding disturbance of the toner images held on the recording medium. <P>SOLUTION: The recording medium P with the toner images T held on both its sides is passed through a nip N between a fixing belt 27 rotated while wrapped round first and second support rollers 25 and 26 and a fixing roller 28 disposed in pressure contact with the fixing belt 27. At the time, heat and pressure are applied to the toner images T, thereby fixing the toner images T to the recording medium, and also the recording medium P before entering the nip N is conveyed while attracted to the surface of the fixing belt 27 charged electrostatically. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device for fixing toner images formed on both sides of a recording medium to the recording medium, and an image forming apparatus having the fixing device.
[0002]
[Prior art]
2. Description of the Related Art An image forming apparatus in which toner images are formed on both sides of a recording medium and each of the toner images is fixed by a fixing device is conventionally known. In this type of image forming apparatus, it is necessary to feed the recording medium to the fixing device in a stable state so that the toner images formed on the respective surfaces are not disturbed, and the image quality of the toner image after fixing is prevented from deteriorating. .
[0003]
Therefore, an image forming apparatus has been proposed in which a spur is provided on a conveyance path for conveying the recording medium to a fixing device after transferring the toner image to both sides of the recording medium, and the spur is used to guide the recording medium (Patent Document 1). reference). According to the image forming apparatus of this type, the recording medium can be guided by the spur projections, so that the toner image carried on the recording medium conveyed to the fixing device can be prevented from being disturbed. However, when a spur is provided, the spur may be stained with toner over time, and the toner may be transferred to a recording medium, thereby deteriorating image quality.
[0004]
[Patent Document 1]
JP-A-10-142869 (paragraph [0050], FIG. 3)
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a fixing device capable of transporting a recording medium in a stable state without causing the above-described inconveniences and preventing an unfixed toner image from being disturbed, and an image forming apparatus having the fixing device. Is to do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention sends a recording medium carrying an unfixed toner image on both sides between a fixing belt and its mating fixing member, and the toner image is transferred between the fixing belt and the mating fixing member. When passing, in a fixing device that applies heat and pressure to the toner image to fix the toner image on a recording medium, the recording medium before entering between the fixing belt and a mating fixing member is placed on the surface of the fixing belt. There is proposed a fixing device provided with a charging unit for charging the recording medium in order to electrostatically attract the recording medium.
[0007]
At this time, it is advantageous that the angle between the surface of the belt contacting the recording medium and the surface of the recording medium immediately before contacting the surface is 60 ° or less (claim 2).
[0008]
Further, in the fixing device according to the first or second aspect, it is advantageous that the charging unit includes a power supply that applies a voltage to the counterpart fixing member (claim 3).
[0009]
In order to achieve the above object, the present invention proposes an image forming apparatus including an image forming means for forming toner images on both sides of a recording medium, and the fixing device according to any one of claims 1 to 3. (Claim 4).
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 is a schematic sectional view showing an example of an image forming apparatus for forming an image on both sides of a recording medium. The image forming apparatus shown here includes an image forming means 1 for forming a toner image on both sides of a recording medium, a sheet feeding device 2 for feeding the recording medium to the image forming means 1, and both sides of the recording medium by the image forming means 1. And a fixing device 3 for fixing the toner image formed on the recording medium. First, the configuration and operation of the image forming means 1 will be described.
[0012]
The image forming means 1 has a drum-shaped photoconductor 4 as an example of a first image carrier, and an endless belt-shaped intermediate transfer belt 5 as an example of a second image carrier. The intermediate transfer belt 5 is wound around a plurality of rollers 6, 7, 8, and 9 and is driven to rotate in the direction of arrow A. The photoconductor 4 contacts the intermediate transfer belt 5 and is driven to rotate in the direction of arrow B. . A first transfer device 10 including a transfer roller is disposed at a position facing the photoconductor 4 with the intermediate transfer belt 5 interposed therebetween. A second transfer device 11 composed of a corona discharger and a belt cleaning device 12 for cleaning the intermediate transfer belt 5 are disposed outside the intermediate transfer belt 5, and a cooling device 13 is disposed inside the intermediate transfer belt 5. Is provided. The belt cleaning device 12 includes a cleaning roller 14 that is supported so as to be able to contact and separate from the surface of the intermediate transfer belt 5, a blade 15 that removes toner attached to the peripheral surface of the cleaning roller 14, and a toner that has been removed. And a toner conveying member 16 for conveying the toner to the outside of the cleaning case. The cleaning roller 14 is made of, for example, a metal roller having a surface roughness of 5 μm, and the intermediate transfer belt 5 is made of a heat-resistant belt capable of transferring toner, for example, a belt made of polyimide. The surface roughness of the intermediate transfer belt 5 is, for example, about 3.4 μm.
[0013]
When the photoconductor 4 rotates in the direction of arrow B, its surface is charged to a predetermined polarity by the charging device 17, and the charged surface is irradiated with the laser beam L emitted from the exposure device 18, so that the electrostatic latent An image is formed, and the latent image is visualized as a toner image by the developing device 19. If this toner image is referred to as a first toner image as needed, the first toner image rotates in the direction of arrow A in synchronization with the photoconductor 4 by the operation of the first transfer device 10. The image is transferred to the surface of the intermediate transfer belt 5. The surface of the photoconductor after the transfer of the toner image is cleaned by the cleaning device 20. The photoconductor 4, the charging device 17, the developing device 19, the cleaning device 20, and the like may be unitized as a process cartridge so that the process cartridge can be replaced when its life has expired.
[0014]
The first toner image transferred to the intermediate transfer belt 5 is carried on the intermediate transfer belt 5 and moves together with the intermediate transfer belt 5 in the direction of arrow A. This toner image passes through the second transfer device 11. Then, the transfer device 11 does not operate, and when the first toner image passes through the cleaning roller 14 of the belt cleaning device 12, the cleaning roller 14 is separated from the surface of the intermediate transfer belt 5. In this way, the problem that the first toner image on the intermediate transfer belt 5 is disturbed is prevented.
[0015]
When the first toner image on the intermediate transfer belt 5 moves to a predetermined position, the next toner image starts to be formed on the photoconductor 4 by charging, exposure, and development in the same manner as described above. This toner image and a second toner image as needed.
[0016]
On the other hand, the paper feeding device 2 includes a paper feeding cassette 21 containing a recording medium P made of, for example, transfer paper, a paper feeding roller 22 for feeding out the uppermost recording medium, and a registration roller pair 23. The recording medium P sent out in the direction of arrow C from 21 is fed between the photoconductor 4 and the intermediate transfer belt 5 at a predetermined timing by the rotation of the registration roller pair 23, and one surface of the recording medium P is Then, the second toner image on the photoconductor 4 is transferred by the operation of the first transfer device 10. At this time, the other surface of the recording medium P moves together with the first toner image on the intermediate transfer belt 5, and when the recording medium P passes through the second transfer device 11, a transfer voltage is applied to the transfer device 11. Then, the first toner image on the intermediate transfer belt is transferred to the other surface of the recording medium P.
[0017]
As described above, the recording medium P having the toner images transferred to one and the other surface thereof respectively passes through the fixing device 3, whereby the respective toner images are fixed to the respective surfaces of the recording medium P. The recording medium P that has passed through the fixing device 3 is discharged to the paper discharge unit 24.
[0018]
The surface of the photoreceptor after the transfer of the second toner image is cleaned by the cleaning device 20, and the surface of the intermediate transfer belt 5 after the transfer of the first toner image is cleaned by the cleaning roller 14 of the belt cleaning device 12 in contact with the surface. Will be cleaned by When the cleaned intermediate transfer belt 5 passes through the cooling device 13, the intermediate transfer belt 5 is cooled. Although the cooling device 13 illustrated in FIG. 1 is configured by a heat pipe, a device that cools the intermediate transfer belt 5 by blowing cold air to the intermediate transfer belt 5 can also be used. At this time, when the first toner image on the intermediate transfer belt 5 passes through the cooling device of the cool air system, the first toner image is prevented from being blown to the intermediate transfer belt 5 so as to prevent the toner image from being disturbed. It is preferable to configure.
[0019]
When the first toner image is formed on the photoconductor 4, the image is controlled to be a normal image, and when the second toner image is formed on the photoconductor 4, the image is controlled to be an inverted image.
[0020]
A mode in which the toner image formed on the photoconductor 4 is directly transferred to one surface of the recording medium P fed from the paper feeding device 2 can be selected. In this case, the second transfer device 11 Does not work. This toner image is also fixed on the recording medium by the fixing device 3, and the recording medium is discharged to the paper discharge unit 24 with the image facing downward.
[0021]
Next, the fixing device 3 will be described. As shown in an enlarged manner in FIG. 2, the fixing device 3 includes a fixing belt 27 wound around a plurality of support rollers, in this example, first and second two support rollers 25 and 26, and a fixing belt 27. And a fixing roller 28 which is an example of a mating fixing member. Heaters 29 and 30 are disposed inside the fixing roller 28 and the second support roller 26, respectively, and the heaters 29 and 30 generate heat, thereby fixing the fixing roller 28 and the fixing belt 27 to fix a toner image. Heat to a suitable temperature. The first support roller 25 and the fixing roller 28 are pressed against each other via the fixing belt 27, whereby the fixing belt 27 is pressed against the surface of the fixing roller 28, and a nip N is formed therebetween. The first and second support rollers 25 and 26 rotate in the directions of the arrows, respectively, and the fixing belt 27 rotates in the direction of the arrow D. Further, the fixing roller 28 rotates in the direction of arrow E, and the fixing belt 27 and the fixing roller 28 move in the same direction at the nip N. Instead of using the fixing roller 28 as the mating fixing member of the fixing belt 27, for example, similarly to the fixing belt 27, a mating fixing member composed of an endless belt that is wound around a plurality of supporting rollers and rotates can be used.
[0022]
As described above, the toner image is formed on the recording medium by the image forming means 1 shown in FIG. 1, and the recording medium P carrying the unfixed toner image T on both sides as shown in FIG. As described above, the fixing belt 27 is fed between the fixing belt 27 and the fixing roller 28 which is an example of the fixing member. When the toner image T carried on the recording medium P passes between the fixing belt 27 and the fixing roller 28, heat and pressure are applied to the toner image, and the toner image T is formed by the action of the heat and pressure. Is fixed on each side of At this time, the fixing device 3 is disposed close to the intermediate transfer belt 5, and the recording medium P that has left the intermediate transfer belt 5 forms a flat fixing belt portion between the first and second support rollers 25 and 26. 27A, and enters between the fixing belt 27 and the fixing roller 28 while moving with the fixing belt 27. At this time, the surface of the fixing belt 27 is charged by a charging unit described later, whereby the recording medium P before entering the nip N between the fixing belt 27 and the fixing roller 28 is charged by the fixing belt 27. It is electrostatically attracted and adheres to the surface (the flat belt portion 27A in the illustrated example). As described above, the recording medium P before entering the nip N between the fixing belt 27 and the fixing roller 28 is brought into close contact with the surface of the fixing belt 27, so that the recording medium P does not shift on the fixing belt 27. In addition, the recording medium P can be smoothly transported to the nip N in a stable state. For this reason, the toner image T carried on the recording medium surface on the side in close contact with the surface of the fixing belt 27 is not disturbed, and the problem that the image quality of the toner image fixed by the fixing device 3 is deteriorated can be prevented. . In addition, since there is no need to provide a spur unlike the related art, no problem occurs when the spur is provided.
[0023]
As described above, the recording medium P before entering the space between the fixing belt 27 and the mating fixing member (the fixing roller 28 in the illustrated example) is electrostatically attracted to the surface of the fixing belt 27 so as to be electrostatically attracted. By providing the charging means for charging the recording medium P, the conventional defect can be eliminated.
[0024]
The angle θ between the surface of the fixing belt 27 with which the recording medium P contacts as described above, that is, the fixing belt portion 27A, and the surface of the recording medium P immediately before contacting the surface is adjusted to be 60 ° or less. When the fixing belt 27 is disposed, the recording medium P starts to smoothly come into contact with the surface of the fixing belt 27, and the occurrence of the disturbance of the toner image T can be more reliably prevented. At this time, the fixing belt 27 and the intermediate transfer belt 5 are brought close to each other, and the conveyance speed at which the recording medium P is conveyed by the fixing belt 27 and the fixing roller 28 and the conveyance speed at which the recording medium P is conveyed by the intermediate transfer belt 5 are almost equal. If the speed is set to be the same, the impact applied to the recording medium P can be reduced, the recording medium P can be conveyed in a more stable state, and the effect of preventing the occurrence of disturbance of the toner image can be enhanced. Alternatively, the conveyance speed of the recording medium P by the fixing belt 27 and the fixing roller 28 is slightly lower than the conveyance speed of the recording medium P by the intermediate transfer belt 5 (5% at the maximum), so that the toner image It is also advantageous that the correct transfer operation is not hindered.
[0025]
As a charging unit for charging the fixing belt 27, a device having a power supply and a voltage applying member such as a brush or a roller to which a voltage is applied by the power supply is used, and the voltage applying member is brought into contact with the surface of the fixing belt 27. Alternatively, a voltage applying member composed of a corona discharger to which a voltage is applied may be arranged to face the fixing belt 27, and the fixing belt 27 may be charged by the discharging action. However, such a charging unit has a drawback that the cost is increased since it has a voltage applying member.
[0026]
Therefore, in the fixing device 3 shown in FIG. 2, a power supply 31 is connected to the fixing roller 28 that comes into contact with the fixing belt 27, and the power supply 31 applies a direct current or a voltage obtained by superimposing a direct current to a direct current to the fixing roller 28. Thus, the fixing belt 27 is configured to be charged. The charging means includes a power supply for applying a voltage to a mating fixing member of the fixing belt.
[0027]
According to the above-described configuration, since the fixing roller 28 functions as a voltage applying member, an independent voltage applying member can be omitted, and simplification of the configuration and reduction in cost can be achieved. Further, if an independent voltage applying member is used, it is necessary to provide a means for preventing the voltage applying member from being stained with toner. However, according to the above configuration, such a stain preventing means is not required.
[0028]
When employing a configuration in which the fixing belt 27 is charged via the fixing roller 28, it is preferable to use a conductive fixing roller 28. For example, the fixing roller 28 is configured by a metal core, a conductive primer on the surface, a conductive rubber layer on the surface, and a conductive resin layer coated on the surface. . A voltage is applied to the core of the fixing roller 28 by the power supply 31 to charge the fixing belt 27. At this time, when the first support roller 25 disposed inside the fixing belt 27 is an insulating roller, for example, a conductive belt base material and an insulating surface layer coated on the surface thereof are used. The surface layer of the fixing belt 27 can be charged by grounding the belt base material to the main body of the image forming apparatus using the fixing belt 27 having More specifically, a fixing belt 27 is used in which an insulating fluororesin having a thickness of 40 μm is coated on a surface of a base made of Ni having a thickness of 40 μm and conductive Si rubber having a thickness of 200 μm. When a conductive roller is used as the first support roller 25, by fixing the first support roller 25 to ground, the fixing belt 27 having an insulating single-layer structure can be used. The surface of the fixing belt 27 is charged via a conductive fixing roller 28.
[0029]
The present invention is also applicable to an image forming apparatus that forms a full-color image on each surface of a recording medium and a fixing device thereof.
[0030]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the present invention, while a recording medium having a toner image formed on both sides is conveyed in a stable state, the toner image can be fixed to the recording medium, and the occurrence of image quality deterioration due to the disturbance of the toner image can be prevented. can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of an image forming apparatus.
FIG. 2 is an enlarged view of the fixing device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming means 3 Fixing device 31 Power supply P Recording medium T Toner image

Claims (4)

A recording medium carrying an unfixed toner image on both surfaces is fed between the fixing belt and the mating fixing member. When the toner image passes between the fixing belt and the mating fixing member, heat and pressure are applied to the toner image. In addition, in a fixing device for fixing the toner image on a recording medium, the recording medium before entering between the fixing belt and a mating fixing member is electrostatically attracted to the surface of the fixing belt. A fixing device for charging the fixing device. 2. The fixing device according to claim 1, wherein an angle between a surface of the fixing belt contacting the recording medium and a surface of the recording medium immediately before contacting the surface is 60 ° or less. The fixing device according to claim 1, wherein the charging unit includes a power supply that applies a voltage to the mating fixing member. An image forming apparatus comprising: an image forming unit that forms a toner image on both sides of a recording medium; and the fixing device according to claim 1.

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