JP2019028274A - Fixation device - Google Patents

Abstract

To provide a fixation device that has a reduced contact pressure of a stationary member with a fixation belt inner face, has reduced oscillation resistance, and is long-lived.SOLUTION: A fixation device has: an endless fixation belt; two heating rollers that hang the fixation belt up; a pressure member that rotates while facing the fixation belt; and a stationary member that internally backs up the fixation belt, in which the pressure member and the stationary member are put into pressing-contact with each other via the fixation belt to form a fixation nip. During a print standby, a contact pressure of the fixation belt with the stationary member is reduced.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device that can be mounted on an image forming apparatus such as a multifunction peripheral, a copier, a printer, or a fax machine.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing member is slidably contacted with an inner peripheral surface of an endless belt member, and the fixing member is pressed against a rotating body via the belt member to rotate with the belt member. 2. Description of the Related Art A fixing device is used that forms a nip portion with a body, conveys a recording medium to the nip portion, and fixes a toner image on the recording medium.

  The fixing device proposed in Patent Document 1 employs a configuration in which a fixing belt is stretched by a first support roll and a second support roll, and a nip is formed by the fixing roll and a fixing member via the fixing belt. The tension by the first support roll can be made variable. Since it has a mechanism that makes the tension variable, it is possible to suppress the occurrence of indentation of the belt by relaxing the tension during non-printing.

JP 2006-235573 A

  However, as in Patent Document 1, in the fixing device that slides the fixing member and the fixing belt, it is a durability problem that the sliding member is worn at the nip portion.

  It is possible to lower the nip pressure by separating the pressure roller during standby and driving the upper belt with the support roller, but there is still contact pressure between the inner surface of the fixing belt and the fixing member. Even if printing is not performed, there is a problem that wear progresses at the sliding portion as the standby time elapses.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device having a long service life in which the contact pressure between the fixing member and the inner surface of the fixing belt is lowered, the sliding resistance is reduced.

  In order to achieve the above object, a fixing device according to the present invention includes an endless fixing belt, two heating rollers that stretch the fixing belt, a pressure member that rotates to face the fixing belt, A fixing member for backing up the fixing belt from the inner surface, and forming a fixing nip by press-contacting the pressure member and the fixing member via the fixing belt. The contact pressure between the fixing belt and the fixing member is lowered.

  According to the present invention, the contact pressure between the fixing member and the inner surface of the fixing belt is lowered, the sliding resistance is reduced, and a long-life fixing device can be provided.

Schematic diagram of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention Schematic diagram of a fixing device according to an embodiment of the present invention Schematic diagram of fixing belt Schematic diagram of fixing member displacement means Durability test flow in the first embodiment Schematic diagram when the fixed member is displaced by the fixed member displacement means The figure which showed transition of the torque about a comparative example and 1st Embodiment The figure explaining the relationship between the displacement of the fixed member and the contact pressure Diagram explaining the relationship between contact pressure and life Schematic diagram of the fixing device in the second embodiment Durability test flow in the second embodiment Schematic diagram of the fixing device when the biasing force of the spring is not changed in the second embodiment

<Image forming apparatus>
FIG. 1 is a schematic diagram of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a color electrophotographic printer as an example, and is a cross-sectional view along a sheet conveyance direction. In this embodiment, the color electrophotographic printer is simply referred to as “printer”.

  The printer shown in FIG. 1 includes an image forming unit 10 for each color of Y (yellow), M (magenta), C (cyan), and Bk (black). The photosensitive drum 11 is charged in advance by a charger 12. Thereafter, a latent image is formed on the photosensitive drum 11 by the laser scanner 13. The latent image becomes a toner image by the developing device 14. The toner image on the photosensitive drum 11 is sequentially transferred by the primary transfer blade 17 to, for example, an intermediate transfer belt 31 that is an image carrier. After the transfer, the toner remaining on the photosensitive drum 11 is removed by the cleaner 15. As a result, the surface of the photosensitive drum 11 becomes clean and prepares for the next image formation.

  On the other hand, the sheets P are sent one by one from the paper feed cassette 20 or the multi paper feed tray 25 and sent to the registration roller pair 23. The registration roller pair 23 receives the sheet P once, and straightens it when the sheet is skewed. The registration roller pair 23 feeds the sheet between the intermediate transfer belt 31 and the secondary transfer roller 35 in synchronization with the toner image on the intermediate transfer belt 31. The color toner image on the intermediate transfer belt is transferred onto the sheet P by, for example, a secondary transfer roller 35 which is a transfer body. Thereafter, the toner image on the sheet is fixed to the sheet by heating and pressing the sheet by the fixing device 40.

<Fixing device>
The fixing device 40 used in this embodiment will be described with reference to FIG. The fixing belt 41 is an endless annular belt and has an outer diameter of 300 mm. FIG. 3 shows the layer structure. The base material 42 uses a heat-resistant resin made of polyimide having a thickness of 100 μm, and an elastic layer 43 having a thickness of 400 μm is provided on the outer periphery of the base material. A heat-resistant silicone rubber can be used for the elastic layer 43. Further, a release layer 44 is provided on the outer periphery, and a PFA tube having a thickness of 40 μm is covered.

  The fixing member 50 is a member that backs up the fixing belt 41, and is composed of a SUS plate having a thickness of 2 mm. A halogen heater 51 is incorporated inside the fixing member 50, and the temperature of the fixing belt 41 is suppressed from lowering during continuous paper feeding by warming the fixing member during warm-up and standby.

  A sliding sheet 52 is put on the outside of the fixed member 50. The sliding sheet 52 is made of a fluororesin, and can reduce sliding resistance (frictional force) with the inner surface of the fixing belt 41. The sliding sheet 52 has a two-layer structure, and a 10 μm PTFE layer and a 10 μm polyimide layer are laminated in order from the sliding surface with the fixing belt 41.

  The first heating roller 60 and the second heating roller 61 have the same configuration. In particular, when the first and second are not distinguished, they are called heating rollers. The heating roller 60 is a hollow roller having an outer diameter of 40 mm, and has a configuration in which 10 μm of PFA is coated as a surface layer 63 on the outer periphery of a pipe-shaped aluminum core metal 62 having a thickness of 2 mm.

  The heating rollers 60 and 61 are flanged at both ends, and the heating roller is rotated by a DC motor via a gear. The fixing belt 41 rotates by rotating the heating roller. The heating roller 60 incorporates a halogen heater 63 inside the metal core 62. The halogen heater 63 generates radiant heat when a voltage is applied from a power supply device (not shown), and heats the heating roller 60 from the inside.

  A plurality of halogen heaters 63 can be arranged for each of the first heating roller 60 and the second heating roller 61. By arranging heaters with different heat generation widths in the longitudinal direction, it is possible to handle media of various sizes.

  A contact-type thermistor 65 is provided on the surface of the first heating roller 60 as temperature detection means for the heating roller. Similarly, a contact-type thermistor 66 is also provided on the surface of the second heating roller 61, and the temperature is controlled by temperature control means.

  The pressure roller 70 is a roller having an outer diameter of 40 mm. A 4 mm-thick elastic layer 72 is provided on the outer periphery of the cored bar 71 made of iron. A heat-resistant silicone rubber can be used as the material of the elastic layer 72. A release layer 73 is provided on the outer periphery of the elastic layer 72 and is covered with a PFA tube having a thickness of 50 μm.

  One end side and the other end side of the metal core 71 of the pressure roller 70 are rotatably supported by bearings, and are driven to rotate by a DC motor (not shown). The pressure roller 70 is separated from the fixing member 50 during warm-up and standby, and is pressed toward the fixing member during printing. In this embodiment, pressure is applied with a load of 500 N during printing.

  Next, the fixing member displacing means 80 that is a feature of the present embodiment will be described. As shown in FIG. 4, the fixed member displacing means 80 includes a solenoid 81 and a movable core 82. The movable core 82 is joined to the sliding side with the fixing belt 41 at both ends in the longitudinal direction of the fixed member 50. When power is supplied to the solenoid 81, the position of the fixing member 50 can be displaced by a predetermined distance to the side opposite to the pressing member. The amount of displacement can be designed as appropriate. In this embodiment, an experiment was performed on the amount of displacement of 0 to 15 mm.

<Durability test>
In order to examine the effect of this embodiment, intermittent paper passing durability was performed. As a method for evaluating durability, a torque meter was attached to a DC motor that is a driving source of the fixing device, and the transition of the torque value was monitored. When the friction coefficient of the sliding portion increases due to wear, the torque increases. Therefore, the wear of the sliding portion can be predicted by monitoring the torque.

  Paper passing conditions were 100 ppm, 500 mm / s, fixing belt surface temperature set at 180 ° C., basis weight 80 g paper, 23 ° C. and 50% environment. Assuming the print mode that is actually used, the test was repeated 100 sheets and 5 minutes standby.

  FIG. 5 shows the execution flow of this test. A feature of the present embodiment is that, when shifting from the print state to the standby state, the fixing member 50 is displaced to the side opposite to the pressure member after separating the pressure roller. It is a feature of this embodiment that the contact pressure between the fixing belt 41 and the fixing member 50 during standby is lowered by this operation.

  The initial position of the fixing member 50 is set to a position where the fixing belt 41 is strongly stretched in order to improve separation, and the contact pressure between the fixing belt 41 and the fixing member 50 is high. With respect to this position, the contact pressure is lowered by displacing the fixing member 50 during standby, thereby reducing the sliding resistance.

  The durability was judged as NG when the torque value exceeded 2.0 N · cm with respect to a torque value of about 1.0 N · cm during normal use. Since the torque suddenly increases as it nears the end of its life, it is sufficient that the number of the sheets can be roughly determined.

  FIG. 6 shows the transition of torque in the durability test. As a comparative example, the case where the position of the fixing member 50 is not changed during standby is shown, and the case where the position of the fixing member 50 is displaced by 5 mm in the opposite direction to the pressure member during standby is shown as this embodiment. When the position of the fixing member 50 is not changed, the durability becomes NG at 800k sheets, whereas when the fixing member 50 is displaced by 5 mm as in this embodiment, the durability becomes OK up to 1500k sheets. . As described above, the durability can be improved by displacing the fixing member 50 during standby and reducing the contact pressure between the fixing member 50 and the fixing belt 41.

  Next, an experiment was conducted on how the lifetime changes when the displacement amount of the fixing member 50 is changed and the contact pressure between the fixing member 50 and the fixing belt 41 is changed. FIG. 7 shows a change in the contact pressure between the fixing member 50 and the fixing belt 41 with respect to the displacement amount of the fixing member 50. The pressure is measured using a surface pressure distribution measurement system I-SCAN (NITTA Corporation).

  When the fixing member 50 was not displaced at all as in Comparative Example 1, the contact pressure was 0.06 MPa, and when the fixing member 50 was displaced 5 mm as in the present embodiment, it was 0.03 MPa. As the amount of displacement was further increased, the contact pressure was about 15 mm, that is, the fixing member 50 and the fixing belt 41 were not in contact with each other.

  Further, when the amount of displacement was set to 12 mm, the driving of the fixing belt became unstable during standby. This is because the driving force of the fixing belt 41 becomes very small because the tension between the first heating roller and the second heating roller and the fixing belt 41 is weakened.

  Next, the change in the life when the displacement amount of the fixing member 50 was changed was examined. FIG. 9 is a graph showing the relationship of life to contact pressure. The displacement is converted into contact pressure using the relationship shown in FIG. It has been found that the contact pressure can be lowered and the life can be extended by displacing the fixing member 50.

  In order to obtain a sufficient effect when the present invention is implemented, it is desirable to reduce the contact pressure to 80% or less as shown in FIG. Since the wear of the sliding portion contributes both during printing and during standby, it is desirable to reduce the contact pressure to a region where the effect of lowering sliding resistance during standby can be seen.

  Further, as described above, if the displacement amount of the fixing member 50 is excessively large, the driving of the fixing belt 41 may become unstable. Therefore, the displacement amount is set as small as possible within the range in which the lifetime improvement effect can be obtained. It is desirable to do. Since the position of the fixing member that can be stably driven varies depending on the diameter of the fixing belt 41 and the positional relationship between the two heating rollers 60, the amount of displacement of the fixing member 50 may be appropriately determined at the time of design.

  Thus, a fixing device having a long life can be provided by displacing the fixing member 50 during standby.

(Second Embodiment)
FIG. 10 is a schematic diagram of a fixing device according to the second embodiment. The positions of the first heating roller 60 and the second heating roller 61 are not fixed, and each is biased by a spring 64 and the fixing belt 41 is stretched. The force applied from the spring 64 is 2N each.

  The spring 64 is provided with adjusting means 65 that can weaken the urging force. The biasing force applied to the heating roller 60 can be weakened by moving the fixed end of the spring to the side opposite to the biasing force direction by the adjusting means 65.

  In the fixing device having this configuration, an experiment was conducted to determine whether the effect of reducing the contact pressure between the fixing member 50 and the fixing belt 41 can be obtained as in the first embodiment.

  FIG. 11 shows the test flow of this embodiment. The difference from the first embodiment is that the fixing member 50 is displaced and the urging force of the spring 64 is weakened.

  In the first embodiment, since the heating roller 60 is fixed, the position of the heating roller 60 does not change even when the fixing member 50 is displaced. However, in this embodiment, when the tension of the fixing belt 41 is weakened, the pressure roller 60. Will be displaced in the biasing direction of the spring 64.

  FIG. 12 shows a case where the force of the biasing spring is not weakened. When the fixing member 50 is displaced in the opposite direction to the pressure member 60 during standby, the heating roller 60 is displaced. If the heating roller is displaced in this way, the fixing belt 41 does not loosen, and the contact pressure between the fixing belt 41 and the fixing member 50 is unlikely to decrease. Therefore, it is necessary to adjust the urging force of the spring 64 so that the heating roller 60 does not move. In the case of carrying out this embodiment, if the urging force is lowered from 2.0 N to 1.5 N when the fixing member 50 is displaced, only the fixing member 50 can be displaced without changing the position of the heating roller 60. It was.

  Thus, by weakening the force of the biasing spring during standby, the fixing member 50 can be displaced while the position of the heating roller 60 is fixed, as in the first embodiment. Therefore, even in a fixing device configured to bias the heating roller with a spring, sliding resistance during standby can be lowered by displacing the fixing member, and a long-life fixing device can be provided.

10: image forming unit 11: photosensitive drum 12: charger 13: laser scanner 14: developing device 15: cleaner 17: primary transfer blade 20: paper feed cassette 25: multi paper feed tray 23: registration roller pair 31: intermediate transfer belt 35: secondary transfer roller 40: fixing device 41: fixing belt 50: fixing member 60: heating roller 70: pressure roller 80: fixing member displacement means

Claims (4)

An endless fixing belt,
Two heating rollers for stretching the fixing belt;
A pressure member that rotates to face the fixing belt;
A fixing member for backing up the fixing belt from the inner surface;
A fixing device that forms a fixing nip by press-contacting the pressure member and the fixing member via the fixing belt,
A fixing device in which contact pressure between the fixing belt and the fixing member is reduced during printing standby. A fixing member displacing means for displacing the fixing member to the side opposite to the pressure member;
The fixing device according to claim 1, wherein the fixing member displacing unit is displaced in a direction opposite to the pressing member during printing standby, and a distance between the pressing member and the fixing member is increased.   The fixing device according to claim 2, wherein a position of the heating roller is fixed.   A tension is applied to the fixing belt by applying a force from a spring to the heating roller, and when the fixing member is displaced in a direction opposite to the pressure member, the position of the heating roller is the original position. The fixing device according to claim 2, wherein the fixing device is held as it is.