JP2010139879A - Belt fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing device that eliminates a risk for becoming a cause of faults by simplifying its configuration while preventing excessive application of a release agent to a pressure roller, and to provide an image forming apparatus. <P>SOLUTION: A fixing belt 46 is extended around a roller section provided with a fixing roller 41 and a heat roller 42. A pressure roller 45 forming a fixing nip N by being brought into press contact with the fixing roller 41 across the fixing belt 46 is provided so as to move forward or backward in relation to the fixing roller 41. A releasing-agent application roller 491 impregnated with a release agent is provided so as to be in outer contact with the pressure roller 45 at the same time when the fixing nip N is formed by moving the pressure roller 45 forward. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a belt fixing device used in an electrophotographic image forming apparatus and an image forming apparatus including the same.

  2. Description of the Related Art Conventionally, as a belt fixing device incorporated in an electrophotographic image forming apparatus, for example, there is one in which a minute amount of oil (release agent) application roller is always in contact with a pressure roller so as to be driven. According to this, the surface of the fixing belt is charged and the phenomenon of attracting toner from the transfer paper (so-called electrostatic offset) can be suppressed, and the toner and paper powder can be prevented from sticking to the pressure roller. (For example, refer to Patent Document 1).

As other fixing devices, there are a pressure rotating body contact / separation mechanism that contacts and separates the pressure roller from the fixing roller, and a contact / separation mechanism that contacts and separates the release agent application roller from the fixing member (fixing roller and fixing belt). In some cases, the contact / separation mechanism separates the release agent application roller from the fixing roller in conjunction with the movement or pressure reduction of the pressure roller by the pressure rotating body contact / separation mechanism.
According to this fixing device, even when the fixing member is heated and rotated during standby, the surface of the fixing member is prevented from being worn out by pressure contact with the pressure roller, and the life of the fixing member is prevented from being reduced. It is a suitable thing which can also prevent that it apply | coats excessively etc. (for example, refer patent document 2).
JP 2006-201640 A JP 2005-326524 A

Since the belt fixing device of Patent Document 1 has a configuration in which a minute amount of oil application roller is always in contact with a pressure roller so as to be driven, a release agent is applied to the pressure roller too much.
The belt fixing device disclosed in Patent Document 2 is provided with a contact / separation mechanism that contacts and separates a release agent application roller from a fixing member (a fixing roller or a fixing belt) to realize an appropriate amount of application of the release agent. Since the structure is independent of the pressure rotating body contacting / separating mechanism that contacts and separates the pressure roller from the roller, the apparatus may be complicated and cause a failure.

  SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a belt fixing device capable of simplifying the configuration and wiping out the possibility of causing a failure while preventing excessive application of a release agent to a pressure roller. An object of the present invention is to provide an image forming apparatus.

In order to achieve the above technical problem, the present invention has taken the following technical means.
The invention according to claim 1 is a pressure roller that hangs a fixing belt on a roller portion including a fixing roller and a heating roller, and presses against the fixing roller with the fixing belt interposed therebetween to form a fixing nip. A release agent application member impregnated with a release agent, which is provided so as to be able to move forward and backward with respect to the fixing roller, moves forward with the pressure roller so as to circumscribe the pressure roller simultaneously with the formation of the fixing nip. The belt fixing device is provided.
According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image forming unit that forms the toner image and transfers the toner image onto the transfer paper; and the belt fixing device according to the first aspect. To do.

  According to the present invention, the release agent application member is provided so that the pressure roller is in pressure contact with the fixing roller and is in contact with the pressure roller at the same time. It is possible to prevent the release agent from being overcoated, simplify the configuration, and eliminate the possibility of causing a failure.

  An embodiment of the present invention will be described. The main part of the present invention is a belt fixing device. Before describing the main part in detail, an outline of the image forming apparatus according to the present embodiment will be described.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment is a color image forming apparatus that can form a full-color image using a tandem method, and includes four image forming units 10 (Y (Yellow), M (Magenta), C (Cyan), Bk (Black)) travels over the endless intermediate transfer belt 20 that is stretched around a plurality of rollers 21, 22, 23, 25, 32, 33. It is juxtaposed along the side.

  Each image forming unit 10 has the same configuration except for the color of the toner to be handled. In FIG. 1, only the leftmost yellow image forming unit 10Y has a reference numeral attached to a device constituting the unit. .

  The image forming unit 10 is opposed to a photosensitive drum 11 as an image carrier, a charging unit 12, a developing device 13, a cleaning device 14, and a photosensitive drum 11 disposed around the photosensitive drum 11. Thus, a transfer roller (transfer member) 15 constituting a primary transfer portion is provided inside the intermediate transfer belt 20. In addition, the image forming apparatus 1 according to the present embodiment includes an exposure unit for each image forming unit 10. For example, an exposure unit 16 such as an LED is disposed between the charging unit 12 and the developing device 13. Has been. In addition, as an exposure means, it is also possible to use an exposure apparatus common to each image forming unit 10, for example, a laser writing apparatus.

In the image forming apparatus 1, a transfer roller 31 that is a second transfer unit is disposed opposite to a transfer counter roller 32 that is one of the support rollers of the intermediate transfer belt 20. The transfer roller 31 is provided with a pair of registration rollers 54 on the right side in the drawing and an endless conveying belt 55 on the left side in the drawing.
On the left side of the conveyance belt 55 in the figure, a belt fixing device 40 that is a main part of the present invention is provided. Details will be described later.

  A paper feed tray 50 for storing a bundle of transfer papers P is disposed in the lower part of the image forming apparatus 1, and has a pickup roller 51 and a separation feed roller 52 as paper feeding means. Further, in FIG. 1, a transport roller 53 is disposed at an appropriate position in the transfer paper transport path indicated by a one-dot chain line. Although not shown, a transfer paper guide is appropriately provided. In addition, a manual paper feed unit and a transfer paper reversing unit can be provided as necessary. It is also possible to mount an image reading device (scanner), an automatic document feeder (ADF), or the like.

Next, an image forming operation of the image forming apparatus 1 according to the present embodiment will be briefly described.
The photosensitive drum 11 of the image forming unit 10 is rotationally driven counterclockwise in the figure by a driving unit (not shown), and the surface of the photosensitive drum 11 is uniformly charged to a predetermined polarity by the charging unit 12. The charged photosensitive member surface is irradiated with scanning light from the exposure unit 16, thereby forming an electrostatic latent image on the photosensitive drum 11 surface. At this time, the image information exposed to each photosensitive drum 11 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device 13 to the electrostatic latent image formed in this manner, and visualized as a toner image.

Further, the intermediate transfer belt 20 is driven to run in the clockwise direction in the drawing, and the respective color toner images are sequentially transferred from the photosensitive drum 11 to the intermediate transfer belt 20 by the action of the primary transfer roller 15 in each image forming unit 10. In this way, the intermediate transfer belt 20 carries a full-color toner image on its surface. Note that a single color image can be formed using any one of the image forming units 10, or a two-color or three-color image can be formed using a plurality of image forming units. In the case of monochrome printing, image formation is performed using the rightmost black unit 10Bk in the drawing among the four image forming units.
The residual toner adhering to the surface of the photosensitive drum 11 after transferring the toner image is removed from the surface of the photosensitive drum by the cleaning device 14, and then the surface is subjected to the action of a static eliminator (not shown) so that the surface potential is initially set. To prepare for the next image formation.

  On the other hand, the transfer paper P is fed from the paper feed tray 50 and is sent out toward the secondary transfer position by the registration roller pair 54 in timing with the toner image carried on the intermediate transfer belt 20. The toner image on the surface of the intermediate transfer belt is collectively transferred onto the transfer paper P by the transfer roller 31 as the second transfer means. The transfer paper P onto which the toner image has been transferred is sent to the belt fixing device 40 by the transport belt 55, and when passing through the belt fixing device 40, the toner image is fused and fixed to the transfer paper P by heat and pressure. The transfer paper P on which the toner image is fixed is discharged to a paper discharge tray (not shown).

Next, the belt fixing device 40 which is a main part of the present invention will be described in detail.
The belt fixing device 40 includes a fixing unit, a pressure roller 45, a pressure adjusting unit, a release agent applying unit, and a control unit (not shown).

  The fixing unit includes a fixing roller 41, a heating roller 42, a heating roller support unit, and a fixing belt 46.

  The fixing roller 41 includes a cored bar 411 made of a round shaft-shaped metal with a support shaft portion 41a having a reduced diameter at both ends and a foamed silicone coated on a body portion that is a portion excluding the support shaft portion 41a. The rubber 412 and the foamed silicone rubber 412 coated on the body part are formed in a disk shape with the same outer diameter, and the outer peripheral edge part 41b is chamfered, and is provided at both ends of the body part so as to be pivotable. An idle ring 413 to be suppressed is provided, and is supported by a machine frame m of the belt fixing device 40 via a bearing 414.

Since the above-mentioned foamed silicone rubber 412 has high heat insulation properties, it is difficult to lower the temperature of the surface of the fixing belt 46 described later, and the rise time can be shortened. Further, since the foam is rich in elastic deformation, the fixing roller 41 can be compressed with a low load, and the length of the fixing nip N can be formed to a desired length. In other words, the passage time of the transfer paper P in the fixing nip N can be easily secured.
As an example of the fixing roller 41, the diameter of the body portion is about 52 mm, and the foamed silicone has a thickness of about 14 mm and an on-axis hardness of 25 to 50 Hs (Asuka C).

The heating roller 42 is a metal material having a high thermal conductivity such as aluminum whose surface is anodized in order to improve the corrosion resistance. (Not shown) is formed into a hollow round shaft with a built-in interior. The heating roller 42 is formed in a disk shape with the same outer diameter as the foamed silicone rubber 412 coated on the body portion, and an outer peripheral edge portion 42b is chamfered, and is provided rotatably at both ends of the body portion. The idling ring 421 (substantially the same as the idling ring 413 for the fixing roller 41 described above) is provided, and is pivotally supported by a pressurizing force adjusting unit described later at a predetermined interval from the fixing roller 41.
In the present embodiment, the idling rings 413 and 421 described above are provided on both the fixing roller 41 and the heating roller 42, but either one may be used.
As an example of this heating roller 42, the diameter of its body is about 38 mm.

  The heating roller support portion pivotally supports the support shaft portion 42a of the heating roller 42 via a heat insulating bush 431 made of resin and a bearing 432, and the upper portion is pivotally attached to the machine frame m of the belt fixing device 40. A disc-shaped tension plate 43 swingably provided on m, one end hooked to the lower part of the tension plate 43, and the other end hooked to the machine frame m of the belt fixing device 40, the heating roller 42 And a tension coil spring 44a that elastically urges in a direction away from the fixing roller 41. In addition, this heating roller support part is provided in the both ends of the heating roller 42, and the tension plate 43 mentioned above is comprised by a pair of selfishness.

  In the present embodiment, the above-described fixing roller 41 and the heating roller 42 constitute a roller unit that hangs the fixing belt 46, but instead of the above-described heating roller support unit, the fixing belt 46 is moved outward or A roller portion may be configured by adding a tension roller for inwardly urging and energizing.

  The fixing belt 46 is formed in an endless shape using polyimide as a base material, and as shown in FIG. 4, a belt detent guide 46 a that engages with the outer peripheral edge portion 41 b (chamfered portion) of the idling ring 413 is provided as a belt. It protrudes from both ends of the back surface, and is rotatably suspended on the heating roller 42 and the fixing roller 41.

The fixing belt 46 is always stretched outward because the heating roller 42 is pivotally attached to the above-described heating roller support. The reason is that the fixing roller 41 expands by heating, but the fixing belt Since 46 is made of polyimide as a base material, it does not expand and the circumference of the belt does not change. Therefore, the change in the interaxial distance between the fixing roller 41 and the heating roller 42 caused by the expansion of the fixing roller 41 This is because it absorbs by urging and energizing in the direction away from the fixing roller 41 and maintains an appropriate tension.
The fixing unit includes a means (not shown) for detecting the temperature of the surface of the fixing belt 46 and a temperature control means (not shown), and can be controlled to a set temperature. .

  The pressure roller 45 includes a cored bar 451, a solid rubber 452 thinly coated on the cored bar 451 (having higher hardness than the foamed silicone rubber 412 that is the surface layer of the fixing roller 41), and the solid rubber 452. And a release layer (not shown) for preventing toner sticking, and is supported by a pressurizing pressure adjusting unit (to be described later) so as to face the lowest outer peripheral surface of the fixing roller 41 with the fixing belt 46 interposed therebetween. Has been.

In this way, a pair of elongated members (the depth length is set to be larger than the width of the transfer paper P in FIG. 2) between the fixing portion and the pressure roller 45 with the fixing belt 46 interposed therebetween. , The pressure roller 45 is hardly compressed, only the surface layer of the fixing roller 41 is compressed, and the transfer paper P carrying an unfixed toner image is passed through. The fixing nip N is formed downward.
As an example of the pressure roller 45, the body portion has a diameter of about 50 mm and an on-axis hardness of about 83 Hs (Asuka C), which is higher in hardness than the foamed silicone rubber 412 that is the surface layer of the fixing roller 41 described above. It has become.

The pressure roller 45 includes detection means (not shown) for detecting the roller surface temperature and control means (not shown) for controlling the roller surface temperature. A heater (not shown) is provided inside the pressure roller 45. 2) or external heating means for heating from the outside of the pressure roller 45 (not shown), the temperature can be controlled by the pressure roller 45 alone.
In the vicinity of the fixing nip N exit, a separation plate (not shown) for reliably separating the transfer paper P is disposed in a non-contact manner with the belt.

  The pressure adjusting unit pivotally supports the support shaft portion 45a of the pressure roller 45 via the bearing 471, and one end side (left end side in FIG. 2) is connected to the machine frame m of the belt fixing device 40 via the pin 472. A plate-like support plate 47 that is swingably provided on the machine frame m and a rotation shaft 482 of a drive motor 481 that is attached to the machine frame m of the belt fixing device and that can control the rotation angle. One end is hooked on the plate cam 48 that is fitted and slidably contacted with the lower surface on the other end side of the support plate 47 (the lower surface on the right end side in FIG. 2), and the other side surface (the right end side surface in FIG. 2). The other end of the belt fixing device 40 is hooked to the machine frame m, and a tension coil spring 44b is provided that elastically biases the support plate 47 in the direction of the plate cam 48. In addition, this pressurization adjustment part is provided in the both ends of the pressure roller 45, and the support plate 47 mentioned above is comprised by a pair of selfishness.

The pressurizing force adjusting unit configured in this manner is configured such that the support plate 47 is moved in the vertical direction around the pin 472 provided on one end side of the support plate 47 by rotating the plate cam 48 by the drive motor 481. Swing (back and forth). As a result, the pressure roller 45 pivotally attached to the support plate 47 presses against the fixing portion to form the fixing nip N or is separated from the fixing portion.
The pressing force adjusting unit controls the rotation angle of the plate cam 48 to adjust the cam lift amount, thereby pressing the pressing roller 45 to the fixing unit (the pressing roller 45 is fixed to the fixing roller 41 by the pressing force adjusting unit). The length of the fixing nip N is adjusted to a desired length, and the passage time of the transfer paper P in the fixing nip N can be varied.
In addition, when the member of each above-mentioned Example is used, the amount of press contact in which a predetermined nip width is obtained is about 3 mm.

  When the load is continuously applied to the fixing roller 41 using the foamed silicone rubber 412, the foamed portion of the foamed silicone rubber 412 breaks (breaks bubbles) and causes a decrease in hardness. Finally, the roller itself may be broken. Therefore, when the sheet is not fed, the pressure contact amount is reduced by the above-described pressure adjusting unit, or the pressure roller 45 is separated from the fixing unit.

Further, when a heat source is provided inside the pressure roller 45, it is preferable that the amount of compression is about 0.5 mm when paper is not passed. This means that when the compression amount is completely zero, the pressure roller 45 is separated from the fixing belt 46, and the temperature rise rate is high after the image forming apparatus is turned on or returned from the energy saving mode. This is because heat cannot be acquired from the belt surface, and the temperature rise of the pressure roller 45 surface is delayed, which may cause a fixing failure.
On the other hand, when the pressure roller 45 is heated from the outside, the above-mentioned problem does not occur because the temperature rise rate of the surface of the pressure roller 45 is high even when the pressure roller 45 is separated from the compression amount of 0 when no paper is passed. For this reason, the compression amount may be 0 when the paper is not passed.

As shown in FIGS. 2 and 3, the release agent application section includes a release agent application roller 491 and a cleaning roller 492.
The release agent application roller 491 includes a foam coated on a metal core and impregnated with a release agent, and a moisture permeable waterproof film (eg, Gore-Tex (trademark), which is covered with the foam and has numerous fine holes. The pressure roller 45 is in pressure contact with the fixing portion to form the fixing nip N, and at the same time can be externally connected to the pressure roller 45 in the longitudinal direction of the shaft, and the pressure roller 45 is fixed. It is pivotally mounted at a required position in the vicinity of the pin 472, which is the center of rotation of the support plate 47, so as to release the circumscribed part or to separate the pressure roller 45 from the pressure roller 45 at the same time.
The release agent application roller 491 configured in this manner is driven to rotate in contact with the pressure roller 45 during the fixing operation, and applies the release agent ejected in a minute amount from the surface of the moisture permeable waterproof film to the pressure roller 45. To do.
As an example of the release agent application roller 491, the diameter of the body portion is about 16 mm, and the foam impregnated with the release agent has a thickness of about 5 mm.

The cleaning roller 492 is provided with a foam rubber layer capable of adhering toner or paper powder on the surface of the core metal, and is arranged in parallel with the release agent application roller 491 so as to be able to rotate following the rotation of the release agent application roller 491. Yes. The cleaning roller 492 only needs to be able to adsorb the toner and paper dust attached to the outer peripheral surface of the release agent application roller 491, and the mode thereof is not particularly limited, such as a one in which a pile brush is wound around a core metal.
The control unit (not shown) is assumed to replace the operation description of the belt fixing device according to the present embodiment shown below.

A series of operations of the belt fixing device configured as described above will be described. The description of the operation relating to image formation has been described above, and will be omitted.
As shown in FIG. 2, when the image forming apparatus is turned off, in the energy saving mode, when the temperature rises, or the like, the cam lift amount is 0 and the pressure roller 45 is not pushed up by the support plate 47, so the fixing roller 41 prevents the foamed portion of the silicone rubber 41 from breaking (breaking) and causing a decrease in hardness, and prevents the fixing roller 41 from decreasing in hardness. Further, since the release agent application roller 491 and the pressure roller 45 are separated from each other, there is no fear that the release agent is applied to the pressure roller 45.

The plate cam 48 is rotated to maximize the cam lift amount by using a signal transmitted when the image forming start switch of the image forming apparatus is pushed, the registration roller pair 54 starts to rotate, and the like. Push up. The state is shown in FIG.
Only the surface layer of the fixing roller 41 is compressed by the pressure roller 45, and a fixing nip N through which the transfer paper P carrying an unfixed toner image passes is formed downward. Note that the size of the fixing nip N can be adjusted with an arbitrary cam lift amount.

Simultaneously with the formation of the fixing nip N, the pressure roller 45 circumscribes the release agent application roller 491, starts application of the release agent to the pressure roller 45, and is released to the fixing unit via the pressure roller 45. Application of the mold begins.
After the release agent reaches the pressure roller 45 and the fixing unit, the transfer paper P carrying an unfixed toner image passes through the fixing nip N from the image forming apparatus main body side.
At the same time as the power-off of the image forming apparatus and the shift to the energy saving mode, the belt fixing apparatus according to the present embodiment shifts to the standby state shown in FIG.

  As described above, in the belt fixing device according to the present embodiment, the pressure roller 45 can be moved forward and backward with respect to the fixing belt 46 with the fixing belt 46 interposed therebetween. In addition to preventing the surface of the fixing belt 46 from being worn out due to the pressure contact with the roller 45 and reducing the service life, the release agent application roller 491 is brought into contact with the pressure roller 45 at the same time as the pressure roller 45 is in pressure contact with the fixing roller 41. This prevents the excessive application of the release agent to the pressure roller 45 and eliminates the need for a mechanism for operating the release agent application roller 491, thus simplifying the configuration. Can eliminate the cause of fear.

  Although the present embodiment has been described above, the above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto and does not depart from the gist thereof. Various modifications can be made within the range.

1 is a longitudinal front view schematically showing an image forming apparatus according to an embodiment. FIG. 2 is a simplified longitudinal sectional front view of a belt fixing device as a main part. FIG. 3 is a partial cross-sectional plan view taken along line X1-X1 of FIG. FIG. 3 is a partial cross-sectional plan view taken along line X2-X2 of FIG. FIG. 3 is a longitudinal front view in an operation state following FIG. 2.

Explanation of symbols

40 Belt fixing device 41 Fixing roller 411 Core 41a Support shaft portion 41b, 42b Outer peripheral edge portion 412 Foamed silicone rubber 413, 421 Idling ring 414, 432, 471 Bearing 42 Heating roller 42a Support shaft portion 43 Tension plate 431 Thermal insulation bush 44a, 44b Tension coil spring 45 Pressure roller 451 Core bar 45a Support shaft portion 452 Solid rubber 46 Fixing belt 46a Belt offset guide 47 Support plate 472 Pin 48 Plate cam 481 Drive motor 482 Rotating shaft 491 Release agent application roller 492 Cleaning roller P Transfer Paper N Fixing nip m Machine frame

Claims (2)

  A fixing belt is hung on a roller portion provided with a fixing roller and a heating roller, and a pressure roller that presses against the fixing roller and forms a fixing nip with the fixing belt interposed therebetween is moved forward and backward with respect to the fixing roller. And a release agent application member impregnated with a release agent, which is provided so as to contact the pressure roller simultaneously with the formation of the fixing nip by moving the pressure roller forward. Fixing device.   An image forming apparatus comprising: an image forming unit that forms the toner image and transfers the toner image onto the transfer paper; and the belt fixing device according to claim 1.

Images