JP2018180568A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that requires a short warm-up time and first print time, and prevents the occurrence of a fixing failure and a stationary member having a reinforcement member in pressure contact therewith from falling even when the device is accelerated, and an image forming apparatus.SOLUTION: When the length of a nip part in a conveyance direction is A and the length from an upstream-side contact part to a downstream-side contact part at each of which a stationary member 26 and a reinforcement member 23 are in contact with each other is B, the relationship A<B is established, and the fixing device is formed to have the range (A) of the nip part included in the range (B) from the upstream-side contact part to the downstream-side contact part.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction peripheral thereof, and a fixing device installed therein.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, there is known a fixing device which has a short warm-up time and a first printing time, and is less likely to cause a fixing failure even when the speed is increased (for example, Patent Document 1).

Specifically, the fixing device described in FIG. 2 and FIG. 4 of Patent Document 1 has a fixing belt (symbol 21) and a pipe-like fixing fixed so as to face the inner peripheral surface of the fixing belt except for the nip portion. A heating member (code 22), a heater (code 25) provided internally to the heating member to heat the heating member, and a pressure belt (code 31) via a fixing belt to form a nip portion A fixing member (symbol 26) installed inside the fixing belt, and a substantially plate-like reinforcing member (symbol 23) that abuts on the fixing member to reinforce the fixing member, and the like. The substantially plate-like reinforcing member is formed to have a relatively narrow width (which is the length in the transport direction) so as to abut on a part of the surface of the fixing member.
Then, the fixing belt is heated by the pipe-shaped heating member heated by the heater, and the toner image on the recording medium conveyed toward the nip portion receives heat and pressure at the nip portion to be placed on the recording medium It will be fixed.

  Since the fixing device of Patent Document 1 described above is installed so that the fixing member is fitted into the recess of the pipe-shaped heating member, the contact area (contact width) of the reinforcing member in contact with the fixing member is narrow. Even if the balance of the force received by the fixing member from the reinforcing member is deteriorated, it does not cause the fixing member to fall down.

On the other hand, in the fixing device of Patent Document 1, etc., the pipe-shaped heating member is removed and the pipe-shaped heating member is interposed for the purpose of further improving the heating efficiency of the fixing belt and reducing the cost and size of the device. Instead, it is conceivable to adopt a configuration in which the fixing belt is directly heated by the heating means.
However, in this case, since the heating member (recessed portion) for preventing the fixing member from falling is eliminated, the fixing member in a state in which the reinforcing member is in pressure contact can not be held in a well-balanced manner. There is. Then, if the fixing member falls down like that, a desired nip can not be formed, so that a fixing failure occurs in the output image or a conveyance failure of the recording medium occurs.

  The present invention has been made to solve the above-mentioned problems, and it is possible to shorten the warm-up time and the first printing time, and prevent a fixing failure or the like from occurring even when the speed of the apparatus is increased. It is an object of the present invention to provide a fixing device and an image forming apparatus in which the fixing member in a pressure-contacted state does not fall.

  A fixing device according to a first aspect of the present invention comprises an endless fixing belt having flexibility, and is fixed on the inner peripheral surface side of the fixing belt, and pressure rotation is performed via the fixing belt. A fixing member forming a nip portion for conveying a recording medium in pressure contact with a body, a heating source for heating the fixing belt directly opposite to at least a part of the fixing belt other than the nip portion; A reinforcing member is disposed between the fixing member and the heat source on the inner circumferential surface side of the belt and has an opposing surface that abuts on the fixing member to reinforce the fixing member, and both ends of the fixing belt in the width direction A pair of holding members for holding a portion, and assuming that the length of the nip portion in the recording medium conveyance direction is A, the upstream side contact between the fixing member and the reinforcing member on the upstream side in the conveyance direction From the contact part And B. When the length to the downstream contact portion where the fixing member and the reinforcing member abut on the downstream side of the direction is B, the relationship of A <B is established, and the nip with respect to the transport direction The range of the portion is formed to be included in the range from the upstream side abutment portion to the downstream side abutment portion, and the pair of holding members have an insertion portion to be inserted into the inner peripheral surface of the fixing belt. The insertion portions are spaced apart inside the fixing belt.

  In the present application, the state in which the fixing member and the reinforcing member are “fixed” is defined as a state in which the fixing member and the reinforcing member are held in a non-rotational manner without being rotationally driven. Therefore, for example, even when the fixing member is biased toward the nip portion by the biasing means such as a spring, the fixing member is “fixed” as long as the fixing member is held by non-rotation. It becomes a state.

Further, in the present application, the “conveying direction” of the recording medium is the same direction as the tangential direction of the nip portion when the fixing belt or the pressure rotating body is brought into contact without deformation in the nip portion while drawing an ideal arc. Defined as
Further, in the present application, the “width direction” is defined as a direction orthogonal to the transport direction and the same direction as the rotation axis direction of the fixing belt and the pressure rotating body.
Further, in the present application, the “nip portion” is defined as a portion where the pressure roller is in contact with the fixing belt.

  The present invention optimizes the relationship between the length of the nip portion and the length of the contact portion between the fixing member and the reinforcing member with respect to the transport direction, and the relationship between the ranges thereof. As a result, the warm-up time and the first print time are short, and even when the apparatus is speeded up, fixing failure does not occur, and the fixing member in a state in which the reinforcing member is in pressure contact does not fall down. An apparatus and an image forming apparatus can be provided.

FIG. 1 is an overall configuration diagram showing an image forming apparatus in Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a fixing device. FIG. 2 is a side view of the fixing device in the width direction. It is an enlarged view which shows the vicinity of a nip part. FIG. 6 is a cross-sectional side view showing the fixing belt held by a holding member. FIG. 7 is a schematic front view showing a state in which the fixing belt and the reinforcing member are held by the holding member. FIG. 7 is a configuration diagram showing a fixing device in Embodiment 2 of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the redundant description will be appropriately simplified or omitted.

Embodiment 1
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus 1 according to the first embodiment is a tandem color printer. Four toner bottles 102Y, 102M, 102C, 102K corresponding to the respective colors (yellow, magenta, cyan, black) are detachably (replaceably) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle storage unit 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are juxtaposed so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. In addition, around the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge removing unit (not shown), and the like are disposed, respectively. Then, on each of the photosensitive drums 5Y, 5M, 5C, and 5K, an imaging process (charging step, exposing step, developing step, transferring step, cleaning step) is performed to form each photosensitive drum 5Y, 5M, 5C, An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven clockwise in FIG. 1 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (charging step).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and an electrostatic latent image corresponding to each color is formed by exposure scanning at this position. (Exposure step).

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, where the electrostatic latent image is developed to form toner images of the respective colors (developing process) Is).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach opposing positions of the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and the photosensitive drums 5Y and 5M at this position. , 5C, and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a slight amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, 5K reach the position facing the cleaning unit 77, and the untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, 5K at this position is the cleaning unit It is mechanically recovered by the cleaning blade 77 (cleaning step).
Finally, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the discharging unit (not shown), and the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. Ru.
Thus, a series of imaging processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K are completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the development process are superimposed and transferred onto the intermediate transfer belt 78. Thus, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc. The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84, and is endlessly moved in the arrow direction in FIG. 1 by the rotational drive of one roller 82.

The four primary transfer bias rollers 79Y, 79M, 79C and 79K respectively sandwich the intermediate transfer belt 78 between the photosensitive drums 5Y, 5M, 5C and 5K to form a primary transfer nip. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the arrow direction and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. Thus, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are superimposed on the intermediate transfer belt 78 and primarily transferred.

Thereafter, the intermediate transfer belt 78 on which the toner images of the respective colors are transferred in an overlapping manner reaches the position opposite to the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 with the secondary transfer roller 89 to form a secondary transfer nip. Then, the four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner which has not been transferred to the recording medium P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 are completed.

Here, the recording medium P conveyed to the position of the secondary transfer nip is fed from the paper feed unit 12 disposed below the apparatus main body 1 to the paper feed roller 97, the registration roller pair 98 (timing roller pair), etc. It was transported via.
In more detail, the paper feed unit 12 stores a plurality of recording media P such as transfer paper in an overlapping manner. Then, when the feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the top recording medium P is fed toward the space between the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 whose rotational drive has been stopped. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. Thus, the desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred on the surface is fixed on the recording medium P by the heat and pressure of the fixing belt 21 and the pressure roller 31.
Thereafter, the recording medium P passes between the rollers of the discharge roller pair 99 and is discharged to the outside of the apparatus. The recording medium P discharged to the outside of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus are completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
Referring to FIGS. 2 to 4, the fixing device 20 includes a fixing belt 21 (belt member) as a fixing member, a fixing member 26 (nip portion forming member), a reinforcing member 23, a heater 25 as a heating unit (heat source , A pressure roller 31 as a pressure rotating body, a temperature sensor 40, a reflecting member 27, a sheet-like member 22, a screw 24, a plate-like member 28 (fixed plate), and the like.

Here, the fixing belt 21 is a thin and flexible endless belt, and rotates (travels) in the arrow direction (counterclockwise direction) in FIG. The fixing belt 21 has a base material layer, an elastic layer, and a releasing layer sequentially laminated from the inner peripheral surface 21a (a sliding contact surface with the fixing member 26) side, and the total thickness is 1 mm or less It is set to.
The base material layer of the fixing belt 21 has a layer thickness of 30 to 50 μm, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.
The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm, and is formed of a rubber material such as silicone rubber, foamable silicone rubber, fluorine rubber, or the like. By providing the elastic layer, fine unevenness on the surface of the fixing belt 21 in the nip portion is not formed, heat is uniformly transmitted to the toner image T on the recording medium P, and generation of a dull skin image is suppressed.
The releasing layer of the fixing belt 21 has a layer thickness of 10 to 50 μm and is made of PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( It is formed of materials such as polyether sulfide) and the like. By providing the release layer, the releasability (peelability) to the toner T (toner image) is secured.

The diameter of the fixing belt 21 is set to 15 to 120 mm. In the first embodiment, the inner diameter of the fixing belt 21 is set to 30 mm.
Inside the fixing belt 21 (inner peripheral surface side), a fixing member 26, a heater (heating means), a reinforcing member 23, a reflecting member 27, a sheet-like member 22, a screw 24, a plate-like member 28 (fixing plate), etc. Is fixed.
Here, the fixing member 26 is fixed in sliding contact with the inner circumferential surface 21 a of the fixing belt 21. Then, the fixing member 26 is in pressure contact with the pressure roller 31 via the fixing belt 21 to form a nip portion for conveying the recording medium P. Referring to FIGS. 3 and 5, both ends in the width direction of the fixing member 26 are held by the flange 29 (holding member) fixed and supported by the side plate 43 of the fixing device 20. Further, both ends in the width direction of the fixing belt 21 are rotatably held by the flange 29. The configurations of the fixing member 26 and the flange 29 will be described in more detail later.
The fixing belt 21 is directly heated by the radiant heat of the heater 25 (heating means) installed therein.

The heater 25 as a heating means is a halogen heater (or a carbon heater), and both ends thereof are fixed to the side plate 43 of the fixing device 20 (refer to FIG. 3). Then, the radiation heat of the heater 25 (heating means) whose output is controlled by the power supply unit of the apparatus body 1 mainly heats the portion of the fixing belt 21 excluding the nip portion. Further, heat is applied to the toner image T on the recording medium P from the heated surface of the fixing belt 21. The output control of the heater 25 is performed based on the detection result of the belt surface temperature by the temperature sensor 40 such as a thermistor facing the surface of the fixing belt 21. Further, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature by such output control of the heater 25.
In the first embodiment, one heater 25 is installed on the inner peripheral surface side of the fixing belt 21, but a plurality of heaters can also be installed on the inner peripheral surface side of the fixing belt 21.

Thus, in the fixing device 20 according to the first embodiment, not only a part of the fixing belt 21 is locally heated but the fixing belt 21 is heated over a relatively wide range in the circumferential direction. Therefore, even if the speed of the apparatus is increased, the fixing belt 21 can be sufficiently heated to suppress the occurrence of the fixing failure. That is, since the fixing belt 21 can be efficiently heated with a relatively simple configuration, the warm-up time and the first print time can be shortened, and the apparatus can be miniaturized.
In particular, the fixing device 20 according to the first embodiment is configured such that the fixing belt 21 is directly heated by the heater 25 (heating means), so that the heating efficiency of the fixing belt 21 is further improved. The fixing device 21 can be further reduced in cost and size.

Here, referring to FIGS. 5 and 6, two flanges 29 as holding members are formed of a heat resistant resin material or the like, and are fitted into side plates 43 of both end portions in the width direction of fixing device 20, respectively. There is. On the flange 29, there are a guide portion 29a for holding the fixing belt 21 while maintaining the circular posture of the fixing belt 21, a stopper portion 29b for restricting the movement of the fixing belt 21 in the width direction (belt shift), etc. Is provided.
Further, on the inner peripheral surface 21 a of the fixing belt 21, sliding portions with the guide portion 29 a of the flange 29 (circled by a broken line in FIG. 5) at both ends in the width direction (the left and right direction in FIG. Low friction portion 21a1 for reducing the sliding resistance in the Specifically, the low friction portion 21a1 is formed by coating a low friction material such as a fluorine resin on the surface of the base material layer. With such a configuration, even if the fixing belt 21 and the flange 29 (guide portion 29a) are in sliding contact with each other due to the rotation (traveling) of the fixing belt 21, the fixing belt 21 and the flange 29 (guide portion 29a) are less likely to wear and deteriorate. .
In the first embodiment, the members in contact with the inner peripheral surface 21a of the fixing belt 21 are only the flanges 29 at both ends in the width direction and the fixing member 26, and in addition, they are in contact with the inner peripheral surface 21a. There is no member (belt guide) that guides the rotation of the fixing belt 21.

Here, in the first embodiment, the reinforcing member 23 for reinforcing the strength of the fixing member 26 forming the nip portion is fixed on the inner peripheral surface side of the fixing belt 21. Referring to FIG. 3, reinforcing member 23 is formed such that the length in the width direction is equal to that of fixing member 26, and both widthwise end portions thereof are held by flange 29 (holding member) of fixing device 20. It is done. Specifically, the reinforcing member 23 is positioned between the flange 29 and the fixing member 26 so as to be positioned.
Then, the reinforcing member 23 abuts against the pressure roller 31 via the fixing member 26 and the fixing belt 21 so that the problem that the fixing member 26 receives large pressure from the pressure roller 31 and is largely deformed in the nip portion is suppressed. ing. In the first embodiment, the reinforcing member 23 is a substantially U-shaped plate-like member formed such that the recess is opposed to the side where the heater 25 is located. The reinforcing member 23 is preferably formed of a metal material having high mechanical strength, such as stainless steel or iron, in order to satisfy the above-described function.
The configuration of the reinforcing member 23 will be described in more detail later.

In the first embodiment, the reflecting member 27 (reflecting plate) is fixed on the side of the reinforcing member 23 facing the heater 25. As a result, the heat (heat for heating the reinforcing member 23) from the heater 25 toward the reinforcing member 23 is reflected by the reflecting member 27 and used for heating the fixing belt 21, so that the heating efficiency of the fixing belt 21 is increased. It will be further improved.
The same effect can be obtained even when mirror processing or heat insulation is provided on part or all of the surface of the reinforcing member 23 facing the heater 25.

  Referring to FIG. 2, pressure roller 31 as a pressure rotating body, which is in contact with the outer peripheral surface of fixing belt 21 at the position of the nip portion, has a diameter of 30 mm and an elastic layer on hollow core 32. 33 is formed. The elastic layer 33 of the pressure roller 31 (pressure roller) is formed of a material such as foamable silicone rubber, silicone rubber, or fluoro rubber. A thin release layer made of PFA, PTFE or the like may be provided on the surface layer of the elastic layer 33. The pressure roller 31 is in pressure contact with the fixing belt 21 to form a desired nip between the two members. Further, referring to FIG. 3, the pressure roller 31 is provided with a gear 45 engaged with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is in the direction of the arrow in FIG. It is rotationally driven. Further, both ends in the width direction of the pressure roller 31 are rotatably supported by the side plate 43 of the fixing device 20 via a bearing 42. A heat source such as a halogen heater may be provided inside the pressure roller 31.

When the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip can be reduced, so the load generated on the fixing member 16 can be reduced. It can be reduced. Furthermore, the heat insulation of the pressure roller 31 is enhanced, and the heat of the fixing belt 21 is less likely to move to the pressure roller 31 side, so the heating efficiency of the fixing belt 21 is improved.
Further, in the first embodiment, the diameter of the fixing belt 21 is formed to be substantially equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 is smaller than the diameter of the pressure roller 31. It can also be formed. In that case, since the curvature of the fixing belt 21 at the nip portion is smaller than the curvature of the pressure roller 31, the recording medium P delivered from the nip portion is easily separated from the fixing belt 21.

Referring to FIG. 4, fixing member 26 in sliding contact with inner circumferential surface 21 a of fixing belt 21 is concave so that the surface (sliding surface) opposite to pressure roller 31 follows the curvature of pressure roller 31. Is formed. As a result, since the recording medium P is sent out from the nip portion so as to conform to the curvature of the pressure roller 31, the problem that the recording medium P after the fixing process is not attracted to the fixing belt 21 and separated does not occur. be able to.
In the first embodiment, the shape of the fixing member 26 forming the nip portion is formed in a concave shape, but the shape of the fixing member 26 forming the nip portion can also be formed in a planar shape. That is, the sliding contact surface (the surface facing the pressure roller 31) of the fixing member 26 can be formed in a planar shape. As a result, the shape of the nip portion becomes substantially parallel to the image surface of the recording medium P, and the adhesion between the fixing belt 21 and the recording medium P is enhanced, whereby the fixing property is improved. Furthermore, since the curvature of the fixing belt 21 at the exit side of the nip portion becomes large, the recording medium P delivered from the nip portion can be easily separated from the fixing belt 21.

Further, as a material for forming the fixing member 26, a material having a certain degree of rigidity (for example, heat resistance such as liquid crystal polymer or the like) so as not to be largely bent even under the pressure applied by the pressure roller 31. It is made of a resin material having properties and heat insulation, an elastic material of high hardness, and the like.
Further, in order to reduce the sliding resistance with the fixing belt 21, a sheet-like member 22 made of a low friction material such as PTFE is covered on the fixing member 26. Specifically, the sheet-like member 22 is interposed in the width direction between the fixing member 26 and the fixing belt 21 at the position of the nip portion, so that the fixing member 26 is fixed around the periphery (in a cross section as shown in FIG. And the periphery of the member 26). The sheet-like member 22 in the first embodiment is formed of a fiber material (a cloth member made of PTFE) impregnated with a lubricant such as silicone oil. As a result, the lubricant is held on the surface where the fixing member 26 and the fixing belt 21 abut. Therefore, the problem that the members 21 and 26 wear due to the sliding contact between the fixing member 26 and the fixing belt 21 is reduced.

Referring to FIG. 4, the sheet-like member 22 is formed with a plurality of holes which are fitted to the upstream protrusion 26 a and the downstream protrusion 26 b. And the sheet-like member 22 is installed so that it may closely_contact | adhere to the fixing member 26 along the circumferential direction in the position except two protrusion part 26a, 26b.
Specifically, the sheet-like member 22 has a rectangular shape when expanded as a single part. Then, on both ends of the rectangular sheet-like member 22, a plurality of holes (holes for fitting to the protrusions 26a and 26b) and holes for screws (screws of the screws 24 are inserted). And the hole for the
And when the sheet-like member 22 is covered by the fixing member 26, both ends of the rectangle are folded between the upstream side projecting portion 26a and the downstream side projecting portion 26b to form a superposed portion. Then, the plate-like member 28 is fixed to the fixing member 26 by a plurality of screws 24 (a plurality of which are installed in the width direction) so as to sandwich the overlapping portion of the sheet-like member 22. Specifically, the plate-like member 28 is placed on the fixing member 26 via the overlapping portion so as to sandwich the overlapping portion of the sheet-like member 22, and the screw hole of the plate-like member 28 and the screw for the sheet-like member 22 The screw portion of the screw 24 is screwed into the female screw portion of the fixing member 26 by inserting the hole portion. Here, the screw 24 is formed such that the height of its screw head does not contact the reinforcing member 23 beyond the height of the protrusions 26a and 26b.

In the first embodiment, the reinforcing member 23 (and the reflecting member 27) is installed to isolate the space between the fixing member 26 and the heater 25 (heating means).
In the first embodiment, the heater 25 is disposed to face the relatively wide range in the circumferential direction of the fixing belt 21 (inner peripheral surface 21 a), so fixing is performed even during heating standby (print operation standby). The belt 21 can be heated in the circumferential direction without temperature unevenness. Therefore, the printing operation can be performed promptly after receiving the printing request. At this time, in the conventional on-demand type fixing device (see, for example, Japanese Patent No. 2884714), if heat is applied while the pressure roller is being deformed at the heating standby time in the nip portion, the rubber of the pressure roller Depending on the material, the life of the pressure roller may be shortened due to thermal degradation, or compression set may be generated on the pressure roller. (The compression set of the rubber may cause the deformation of the rubber to be heated. Increase by adding.). Then, when compression permanent strain occurs in the pressure roller, a part of the pressure roller is in a recessed state, and a desired nip width can not be obtained, so that fixing failure occurs or abnormal noise occurs during rotation. Do.
On the other hand, in the first embodiment, since the reinforcing member 23 (and the reflection member 27) is disposed between the fixing member 26 and the heater 25 so as to block the heat of the heater 25, heating is performed. Heat is less likely to reach the fixing member 26 during standby. Therefore, it is possible to reduce the problem that the high temperature heating is performed in the state where the pressure roller 31 is deformed during the heating standby, and to suppress the occurrence of the above-mentioned problems.

Further, the lubricant applied between the two members in order to reduce the frictional resistance between the fixing member 26 and the fixing belt 21 is deteriorated by the use under the high temperature condition in addition to the high pressure condition in the nip portion. There is a possibility that problems such as slip may occur.
On the other hand, in the first embodiment, since the reinforcing member 23 (and the reflection member 27) is disposed between the fixing member 26 and the heater 25 so as to block the heat of the heater 25, the heater It becomes difficult for the heat of 25 to reach the lubricant at the nip. Therefore, the high temperature deterioration of the lubricant can be mitigated to prevent the problems described above from occurring.

  Further, in the first embodiment, since the reinforcing member 23 (and the reflecting member 27) is disposed between the fixing member 26 and the heater 25 so as to interrupt the heat of the heater 25, the fixing member 26 is The heat is insulated, and the fixing belt 21 is not positively heated at the nip portion. Therefore, the temperature of the recording medium P fed into the nip portion is lowered when it is fed out from the nip portion. That is, at the exit of the nip portion, the temperature of the toner image fixed on the recording medium P is lowered, the viscosity of the toner is lowered, and the toner adhesion to the fixing belt 21 is decreased. It is separated from the fixing belt 21. Therefore, the recording medium P immediately after the fixing process is prevented from being wound around the fixing belt 21 and jamming is prevented, and the toner fixing to the fixing belt 21 is also suppressed.

Hereinafter, the normal operation of the fixing device 20 configured as described above will be briefly described.
When the power switch of the apparatus main body 1 is turned on, the electric power is supplied to the heater 25 and the rotational driving of the pressure roller 31 in the direction of the arrow in FIG. 2 is started. As a result, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31 at the nip portion.
Thereafter, the recording medium P is fed from the paper feeding unit 12, and the unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the pressure roller 31 in pressure contact with each other. It is fed into the nip.
Then, the toner image T is fixed on the surface of the recording medium P by the heating by the fixing belt 21 heated by the heater 25 and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 31. . Thereafter, the recording medium P delivered from the nip portion is conveyed in the direction of the arrow Y11.

Hereinafter, the characteristic configuration and operation of the fixing device 20 according to the first embodiment will be described in detail.
As described above, the fixing device 20 according to the first embodiment is fixed on the inner peripheral surface side of the fixing belt 21 and is in pressure contact with the pressure roller 31 via the fixing belt 21 to form a nip portion. A fixing member 26 and a reinforcing member 23 fixed on the inner circumferential surface side of the fixing belt 21 and abutted against the fixing member 26 from the inside of the fixing belt 21 to reinforce the fixing member 26 are provided.
Here, in the first embodiment, as shown in FIG. 4, assuming that the length (nip width) of the nip portion in the recording medium conveyance direction is A, the fixing member 26 and the reinforcing member 23 are on the upstream side in the conveyance direction. Assuming that the length from the upstream contact portion in contact to the downstream contact portion in which the fixing member 26 and the reinforcing member 23 contact on the downstream side in the transport direction is B,
A <B
The following relationship is established.
Furthermore, the range of the nip portion (the range of A in FIG. 4) with respect to the transport direction is the range from the upstream contact portion to the downstream contact portion (the range of B in FIG. 4). It is formed to be included in.
In other words, the range of the nip width is included in the range of the conveyance direction (the vertical direction in FIG. 4) of the fixing member 26 in contact with the reinforcing member 23.

With such a configuration, the fixing member 26 in a state in which the reinforcing member 23 is in pressure contact is held in a well-balanced manner even when the pipe-like heating member for fixing the fixing member 26 in is not installed. Thus, the problem of falling down at 26 is suppressed. Then, a desired nip is formed with high accuracy, and a fixing failure occurs in an output image, a conveyance failure of a recording medium occurs, and a defect is prevented.
That is, when the above-described condition is not achieved, the fixing member 26 which has received the pressure contact force at the nip portion is likely to rotate clockwise or counterclockwise in FIG. 4 with the contact portion with the reinforcing member 23 as a fulcrum It is easy to fall). On the other hand, when the above-described conditions are achieved, the fixing member 26 which receives the pressing force at the nip portion is supported by the reinforcing member 23 in a well-balanced manner. As a result, the fixing member 26 is less likely to fall down.

Furthermore, in the first embodiment, as shown in FIG. 4, when the length of the facing surface 23 a of the reinforcing member 23 facing the fixing member 26 in the transport direction is C,
A <B <C
The following relationship is established.
Further, the range from the upstream contact portion to the downstream contact portion in the transport direction (the range of B in FIG. 4) is the range of the facing surface 23a of the reinforcing member 23 (C in FIG. 4). Is included in the scope).
In other words, the range in the transport direction of the fixing member 26 in contact with the reinforcing member 23 is included in the range in the transport direction of the opposing surface 23 a of the reinforcing member 23.
With such a configuration, the fixing member 26 which has received a pressure contact force at the nip portion is more easily supported by the reinforcing member 23 in a well-balanced manner, and the falling of the fixing member 26 is further less likely to occur.

In the first embodiment, referring to FIG. 4, the fixing member 26 and the reinforcing member 23 respectively pass through the center in the conveyance direction in the nip portion when viewed in a cross section orthogonal to the width direction, and the conveyance direction It is formed to be line symmetrical with respect to an imaginary straight line (which is a straight line indicated by an alternate long and short dash line in FIG. 4) orthogonal to the angle.
With such a configuration, the fixing member 26 which has received a pressure contact force at the nip portion is more easily supported by the reinforcing member 23 in a well-balanced manner, and the falling of the fixing member 26 is further less likely to occur.

In particular, in the reinforcing member 23 in the first embodiment, rising portions 23c, which stand up with the same length H in the direction away from the facing surface 23a, are respectively formed on the upstream side and the downstream side in the transport direction. Then, the end surface (reference surface 23b) of the two rising portions 23c abuts on the holding portion 29c (refer to FIG. 6) of the flange 29 so that the reinforcing member 23 is held.
With such a configuration, the fixing member 26 which has received a pressure contact force at the nip portion is more easily supported by the reinforcing member 23 in a well-balanced manner, and the falling of the fixing member 26 is further less likely to occur.
The reinforcing member 23 can be held in contact with the side plate 43 instead of the holding portion 29 c of the flange 29.

Further, referring to FIG. 4, fixing member 26 in the first embodiment projects upstream side protruding toward opposing surface 23 a of reinforcing member 23 to form an upstream side contact portion with reinforcing member 23. A portion 26 a and a downstream protrusion 26 b projecting toward the opposing surface 23 a of the reinforcing member 23 to form a downstream contact portion with the reinforcing member 23 are provided. That is, in the fixing member 26, two protrusions 26a and 26b (the distance between the upstream end and the downstream end is set to B) which are separated in the transport direction on the side facing the reinforcing member 23. These two projections 26a and 26b are in surface contact with the opposing surface 23a of the reinforcing member 23, respectively.
With such a configuration, compared to the case where the fixing member 26 is formed so as to be one flat surface from the upstream contact portion with the reinforcing member 23 to the downstream contact portion, the reinforcing member 23 and the fixing member 26 Since the contact area can be reduced, heat is less likely to be transmitted to the fixing member 26. That is, the heat transmitted from fixing belt 21 through fixing member 26 toward reinforcing member 26 in the nip portion can be reduced (the amount of heat escaping from fixing belt 21 through reinforcing member 26 toward reinforcing member 23) Can be reduced). In particular, when the thickness of the fixing belt 21 is reduced (for example, when the thickness is set to 160 μm or less) or when the nip width is set wide, heat is easily transferred from the fixing belt 21 to the fixing member 26. Therefore, a configuration in which the contact area between the reinforcing member 23 and the fixing member 26 is reduced as in the first embodiment is useful.
In the first embodiment, the two projecting portions 26a and 26b are configured to be in surface contact with the facing surface 23a of the reinforcing member 23, respectively. However, in order to further ensure the effects described above, the two projecting portions 26a and 26b may be configured to be in line contact with (or in close proximity to) the facing surfaces 23a of the reinforcing members 23, respectively.

  As described above, in the first embodiment, the relationship between the length A of the nip portion and the length B of the contact portion between the fixing member 26 and the reinforcing member 23 in the transport direction, or the like The relationship of the range is made appropriate. As a result, the warm-up time and the first print time are short, and even when the apparatus is speeded up, fixing defects and the like do not occur, and the problem that the fixing member 26 in a state in which the reinforcing member 23 is in pressure contact is prevented from falling can do.

  In the first embodiment, the fixing belt 21 having a multilayer structure is used as the fixing belt, but an endless fixing film made of polyimide, polyamide, fluorocarbon resin, metal or the like may be used as the fixing belt. Also in this case, the same effect as that of the first embodiment can be obtained.

Second Embodiment
Second Embodiment A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is a block diagram showing the fixing device in the second embodiment, which corresponds to FIG. 2 in the first embodiment. The fixing device in the second embodiment is different from that in the first embodiment in that the fixing belt 21 is heated by electromagnetic induction.

As shown in FIG. 7, similarly to the fixing device 20 of the first embodiment, the fixing device 20 in the second embodiment also includes the fixing belt 21 (belt member), the fixing member 26, the reinforcing member 23, and the pressure roller 31 ( It comprises the heating rotating body), the temperature sensor 40 and the like.
Also in the second embodiment, as in the first embodiment, the range of the nip width is within the range of the conveyance direction (the vertical direction in FIG. 7) of the fixing member 26 in contact with the reinforcing member 23. It is included. Further, the range in the transport direction of the fixing member 26 in contact with the reinforcing member 23 is included in the range in the transport direction of the facing surface 23 a of the reinforcing member 23.

  Here, in the fixing device 20 according to the second embodiment, an induction heating unit 50 is provided instead of the heater 25 as a heating unit. The fixing belt 21 in the second embodiment is heated by electromagnetic induction by the induction heating unit 50 unlike the first embodiment in which the fixing belt 21 is heated by radiant heat of the heater 25.

The induction heating unit 50 includes an excitation coil, a core, a coil guide, and the like. The exciting coil is formed by extending a litz wire obtained by bundling fine wires in the width direction (the direction perpendicular to the sheet of FIG. 7) so as to cover a part of the fixing belt 21. The coil guide is made of a highly heat-resistant resin material or the like, and holds the exciting coil and the core. The core is a semi-cylindrical member made of a ferromagnetic material (having a relative permeability of about 1000 to 3000) such as ferrite, and a center core or a core for forming an efficient magnetic flux toward the fixing belt 21. A side core is provided. The core is disposed to face the exciting coil extended in the width direction.
On the other hand, the fixing belt 21 includes a heat generating layer (e.g., an elastic layer and a releasing layer) which is heated by the induction heating unit 50 separately from the base material layer, the elastic layer and the releasing layer described in the first embodiment. It can be formed between the layers, and the substrate layer can be used as a heat generating layer). As a material of the heat generating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of metals of these, and the like can be used.

The fixing device 20 configured as described above operates as follows.
When the fixing belt 21 is rotationally driven in the arrow direction in FIG. 7, the fixing belt 21 is heated at a position facing the induction heating unit 50. More specifically, magnetic flux lines are alternately switched in both directions alternately around the fixing belt 21 by supplying high frequency alternating current to the exciting coil. At this time, an eddy current is generated on the surface of the heat generating layer of the fixing belt 21 and Joule heat is generated due to the electric resistance of the heat generating layer itself. The heat generation layer is electromagnetically heated by the Joule heat to heat the fixing belt 21.
In order to efficiently heat the fixing belt 21 by electromagnetic induction, it is preferable that the induction heating unit 50 be configured to face the entire circumferential direction of the fixing belt 21.

  As described above, also in the second embodiment, as in the above embodiments, the length A of the nip portion in the transport direction and the length of the contact portion between the fixing member 26 and the reinforcing member 23 The relationship between B and B and their range are optimized. As a result, the warm-up time and the first print time are short, and even when the apparatus is speeded up, fixing defects and the like do not occur, and the problem that the fixing member 26 in a state in which the reinforcing member 23 is in pressure contact is prevented from falling can do.

In the second embodiment, the fixing belt 21 is heated by electromagnetic induction heating, but the fixing belt 21 can also be heated by the heat of the resistance heating element. Specifically, the resistance heating element is brought into contact with part or all of the inner peripheral surface or the outer peripheral surface of the fixing belt 21. The resistance heating element is a planar heating element such as a ceramic heater, and a power supply unit is connected to both ends thereof. Then, when a current flows through the resistance heating element, the resistance heating element is heated by the electric resistance of the resistance heating element itself, and the fixing belt 21 in contact is heated.
Even in such a case, the relationship between the length A of the nip portion, the length B of the contact portion between the fixing member 26 and the reinforcing member 23, and the length C of the opposing surface 23a of the reinforcing member 23 By optimizing the relationship, the same effect as that of the second embodiment can be obtained.

  The present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be appropriately modified in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape and the like of the component members are not limited to those of the above-described embodiments, and the number, position, shape and the like suitable for practicing the present invention can be employed.

Appendix (Supplementary Note 1)
An endless fixing belt having flexibility while traveling in a predetermined direction to heat and melt the toner image;
A fixing member fixed on the inner peripheral surface side of the fixing belt and forming a nip portion in which a recording medium is conveyed by being in pressure contact with a pressure rotating body via the fixing belt;
A reinforcing member fixed on the inner peripheral surface side of the fixing belt and abutted against the fixing member from the inside of the fixing belt to reinforce the fixing member;
Equipped with
Assuming that the length of the nip portion with respect to the conveyance direction of the recording medium is A, the fixation member at the downstream side of the conveyance direction from the upstream contact portion where the fixing member and the reinforcing member abut on the upstream side of the conveyance direction. When the length to the downstream side contact part where the part and the reinforcing member abut is B,
A <B
Relationship is established,
The fixing device is characterized in that the range of the nip portion with respect to the conveyance direction is included in the range from the upstream contact portion to the downstream contact portion.
(Supplementary Note 2)
When the length of the opposing surface of the reinforcing member facing the fixing member in the transport direction is C,
B <C
Relationship is established,
The range from the upstream side contact portion to the downstream side contact portion with respect to the transport direction is formed so as to be included in the range of the opposing surface of the reinforcing member. Fixing device.
(Supplementary Note 3)
The fixing member includes an upstream protrusion projecting toward the opposite surface of the reinforcing member to form the upstream contact portion, and the fixing member configured to form the downstream contact portion. The fixing device according to claim 1 or 2, further comprising: a downstream side protruding portion that protrudes toward the opposite surface.
(Supplementary Note 4)
Each of the fixing member and the reinforcing member is axisymmetrical to a virtual straight line passing through the center of the conveyance direction at the nip portion and orthogonal to the conveyance direction when viewed in a cross section orthogonal to the width direction The fixing device according to any one of appendices 1 to 3, characterized in that
(Supplementary Note 5)
A holding member for holding both widthwise end portions of the fixing belt;
A heating unit that heats the fixing belt by facing or in contact with the fixing belt;
And further
In the reinforcing member, rising portions rising in the same length in the direction away from the opposing surface are formed on the upstream side and the downstream side in the transport direction, and the two rising portions correspond to the holding member. The fixing device according to any one of appendices 1 to 4, characterized in that the reinforcing member is held in contact.
(Supplementary Note 6)
An image forming apparatus comprising the fixing device according to any one of supplementary notes 1 to 5.

1 Image forming apparatus main body (apparatus main body),
20 fixing devices,
21 Fixing belt (fixing member),
23 reinforcement members,
23a facing surface, 23b reference surface, 23c rising portion,
25 heater (heating means),
26 fixed members,
26a upstream projection, 26b downstream projection,
29 flange (holding member),
31 Pressure roller (pressure roller).

Patent No. 2010-96782

A fixing device according to a first aspect of the present invention comprises an endless fixing belt having flexibility, and is fixed on the inner peripheral surface side of the fixing belt, and pressure rotation is performed via the fixing belt. A fixing member forming a nip portion for conveying a recording medium in pressure contact with a body, a heating source for heating the fixing belt directly opposite to at least a part of the fixing belt other than the nip portion; A reinforcing member is disposed between the fixing member and the heat source on the inner circumferential surface side of the belt and has an opposing surface that abuts on the fixing member to reinforce the fixing member, and both ends of the fixing belt in the width direction A pair of holding members for holding the recording medium, and the fixing member on the downstream side in the conveying direction from an upstream contact portion on which the fixing member and the reinforcing member abut on the upstream side in the conveying direction of the recording medium With the reinforcing member Up to a length of the downstream-side abutting portion abuts and is B, the length of the facing surfaces of the facing the fixed member of the reinforcing member with respect to the transport direction when the C, B <C the relationship is established When the fixing member and the reinforcing member are viewed in a cross section substantially orthogonal to the width direction, the fixing member contacts at two places, and the pair of holding members are inserted into the inner peripheral surface of the fixing belt. The insertion portions are spaced apart inside the fixing belt.

Claims (10)

A flexible endless fixing belt,
A fixing member fixed on the inner peripheral surface side of the fixing belt and forming a nip portion in which a recording medium is conveyed by being in pressure contact with a pressure rotating body via the fixing belt;
A heating source that heats the fixing belt directly opposite to at least a portion of the fixing belt other than the nip portion;
A reinforcing member disposed between the fixing member and the heating source on the inner circumferential surface side of the fixing belt and having an opposing surface that abuts on the fixing member to reinforce the fixing member;
A pair of holding members for holding both widthwise end portions of the fixing belt;
Equipped with
Assuming that the length of the nip portion with respect to the conveyance direction of the recording medium is A, the fixation member at the downstream side of the conveyance direction from the upstream contact portion where the fixing member and the reinforcing member abut on the upstream side of the conveyance direction. When the length to the downstream side contact part where the part and the reinforcing member abut is B,
A <B
Relationship is established,
The range of the nip portion with respect to the transport direction is formed to be included in the range from the upstream contact portion to the downstream contact portion.
The pair of holding members has an insertion portion inserted into the inner peripheral surface of the fixing belt,
The fixing device is characterized in that the insertion portions are respectively separated in the fixing belt.   The reinforcing member is an upstream side wall portion provided on the upstream side with respect to the facing surface and substantially perpendicular to the direction opposite to the fixing member, and the fixing member on the downstream side with respect to the facing surface 2. The fixing device according to claim 1, further comprising: a downstream side wall portion provided substantially perpendicular to the opposite direction to the upstream side wall portion and opposed to the upstream side wall portion. When the length of the opposing surface of the reinforcing member facing the fixing member in the transport direction is C,
B <C
Relationship is established,
The range from the said upstream contact part to the said downstream contact part with respect to the said conveyance direction was formed so that the range of the said opposing surface of the said reinforcement member may be included. The fixing device according to Item 2.   The fixing device according to any one of claims 1 to 3, wherein the heating source is an induction heating device.   The fixing device according to any one of claims 1 to 3, wherein the heating source is a resistance heating element.   Each of the fixing member and the reinforcing member is axisymmetrical to a virtual straight line passing through the center of the conveyance direction at the nip portion and orthogonal to the conveyance direction when viewed in a cross section orthogonal to the width direction The fixing device according to any one of claims 1 to 5, wherein the fixing device is formed in   The fixing device according to claim 6, wherein the heating source is disposed at a position on the imaginary straight line when viewed in a cross section orthogonal to the width direction. The heating source is a heater,
The fixing device according to any one of claims 1 to 3, wherein a reflecting member is provided between the reinforcing member and the heat source.   The fixing device according to any one of claims 1 to 8, further comprising: a sheet-like member impregnated with a lubricant and covering the width direction of the fixing member.   An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

Images