JP6520258B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus.

  In an electrophotographic image forming apparatus such as a copying machine or a laser printer, an electrostatic latent image formed on an image carrier is developed by a developing device, and the toner image is recorded on a recording medium (paper, fixing material, recording material And the image is formed by fixing by a fixing device.

Various fixing methods have been proposed as this fixing device, and for example, a fixing device of a roller fixing method or a fixing device of a belt fixing method is known.
The fixing device of the roller fixing type includes, for example, a heating roller and a pressure roller, and a rubber layer is provided on the surface layer of the metal pipe, and a halogen heater is provided inside. In such a roller fixing type fixing device, since the rubber layer has a thermal resistance, when the surface is controlled to a constant temperature, the interface temperature between the metal pipe and the rubber layer becomes high, which exceeds the heat resistance temperature of the rubber. Therefore, it is necessary to make the rubber layer thin (about 0.5 to 2 mm). However, the nip width obtained from the thin rubber layer fixing roller and the pressure roller is small, and a high speed machine requiring a wide nip can not be coped with by the roller fixing method.
The fixing device of the belt fixing type includes, for example, a heating roller, a fixing member, a fixing belt stretched by the heating roller and the fixing member, and a pressure roller brought into pressure contact with the fixing member through the fixing belt. . By using the fixing member as a fixing member, it becomes easy to obtain a wide nip width with space saving (see, for example, Patent Documents 1 and 2).

In recent years, colorization, high image quality, and speeding up of image forming apparatuses have been advanced. In order to fix a color image with high image quality, the time for which the recording paper is in contact with the nip (hereinafter, nip time) needs 40 to 60 msec, and the pressure at the nip needs to be 7 N / cm ² or more. is there. In particular, the 50PPM (A4 size) or more high-speed machines, since the conveyance speed of the recording paper is fast, in order to secure the nip time, the nip width is required a wide, not less than 10 mm, and 7N / cm ² or more surface pressure Need. Further, coated paper (resin-coated paper) frequently used in high-speed machines is likely to cause toner image disturbance due to water vapor while passing through the nip, and therefore requires a further high surface pressure (12 N / cm ² or more).

  Further, in order to improve the image quality, the recording sheet needs to be separated naturally at the exit of the nip, and the shape of the nip, the roller curvature of the exit of the nip, and the guide member are devised. There is also a method of forcibly separating the recording sheet by bringing a separation claw or the like into contact with the roller, but there is a possibility that the abrasion damage of the roller may be transferred to the image to deteriorate the image.

  On the other hand, the fixing device described in Patent Document 1 prevents the deformation (deflection) of the fixing member by receiving the pressure of the nip portion not only by the fixing member but also by using the heating rotating body, and widening and high surface pressure It is possible to obtain a natural nip and to make the natural separation of the recording paper possible by reducing the fixing belt radius of curvature at the exit of the nip portion by the shape of the fixing member. The rubber layer of the fixing roller can be thickened and a wide nip can be obtained as compared with the fixing device by the roller fixing method.

  However, for example, in a high speed machine of 50 ppm or more, in order to obtain a wide nip width, the diameter of the roller needs to be 50 mm or more. Since such a large diameter roller has a small curvature (less bending), the sheet at the exit of the nip is wound around the roller (it can not be separated naturally). Therefore, in the fixing device described in Patent Document 1, although the forced separation by the separation claw contacting the belt surface at the nip exit portion is necessary, the defect that the wear scratch by the separation claw contacting the belt surface is transferred to the image There is a problem that will occur.

  For example, in the fixing device as shown in FIG. 7A, the radius of curvature of the fixing belt at the exit of the nip portion can be reduced by the shape of the fixing member, and natural separation of the sheet is enabled. On the other hand, as shown in FIG. 7B, when the position of the heating roller is shifted to the upstream side in the sheet conveying direction, the traveling direction of the fixing belt at the exit of the nip portion makes an angle with the nip surface. (Θ1 <θ2), it is possible to improve the separation ability of the sheet.

  In the fixing devices of Patent Documents 1 and 2 as shown in FIG. 7A, a pressure roller, a normal line (vertical direction line) Na to a contact surface Sa with a fixing member via a fixing belt, and a heating roller The normal (vertical direction line) Nb with respect to the contact surface Sb with the fixing member is arranged in the same straight line. In this configuration, when the position of the heating roller is shifted to the upstream side in the sheet conveyance direction as shown in FIG. 7B in order to improve the sheet separation capability, the normals Na and Nb become parallel.

When the normal lines Na and Nb are in parallel, the force in the rotational direction indicated by M in the figure is determined by the force (Na direction) applied from the pressure roller to the fixing member and the force applied from the heating roller to the fixing member (Nb direction). As a result, a pressure deviation occurs in the nip area. Specifically, when the position of the heating roller is shifted to the upstream side in the sheet conveyance direction, the pressure on the inlet side of the nip is high, and the pressure on the outlet side of the nip is low.
In such a state, the range in which the necessary pressure can be secured in the nip portion is reduced, and there is a problem that the toner image can not be sufficiently fixed on the sheet.

  Therefore, in view of the above problems, the present invention can obtain a wide and high contact pressure nip without increasing the size of the fixing member, and can realize downsizing of the apparatus, and shift the position of the heating rotator. An object of the present invention is to provide a fixing device capable of obtaining uniform and sufficient pressure at the nip portion even when the separation performance is improved.

  In order to achieve the above object, the fixing device according to the present invention comprises a heating rotating body heated and rotated by a heat source, and a fixing member having a contact portion in sliding contact with a part of the outer peripheral surface of the heating rotating body. A fixing belt that spans the heating rotating body and the fixing member, and a nip portion that is brought into pressure contact with the fixing member via the fixing belt to form a nip portion through which the recording medium is conveyed; And a pressing rotating body for rotating the fixing belt in the pressing direction for forming the nip portion in this order, and the pressure of the nip portion is the heating rotating body via the fixing belt and the fixing member. In the fixing device applied by pressure between the pressure roller and the pressure roller, the straight line connecting the rotation center of the heating roller and the rotation center of the pressure roller is the conveyance of the recording medium in the nip portion. The surface normal at the center position of the surface of the heating rotator facing the fixed member and the surface normal at the center position of the facing surface of the pressure rotator against the fixing member. And intersect at a region where the fixing member is provided.

  According to the present invention, a wide and high contact pressure nip can be obtained without increasing the size of the fixing member, and downsizing of the apparatus can be realized, and the position of the heating rotator is shifted to improve separation performance. It is possible to provide a fixing device capable of obtaining uniform and sufficient pressure at the nip portion even in the case where the fixing is performed.

FIG. 1 is a schematic configuration view showing an example of an image forming apparatus according to the present embodiment. FIG. 2 is a schematic configuration view showing an example of a fixing device according to the present embodiment. FIG. 2 is a side view showing an example of a fixing device according to the present embodiment. FIG. 2 is a side view showing an example of a fixing device according to the present embodiment. It is a schematic diagram of the rotation mechanism part of a heating roller and a pressure roller. It is a schematic block diagram which shows an example of the fixing device which used the induction heating means as a heat source. FIG. 6A is a schematic diagram showing the configuration of a fixing device and FIG. 4B is a diagram schematically showing pressure distribution in the nip area, wherein FIG. 6A shows an example of a conventional fixing device, and FIG. And (C) show examples of the fixing device according to the present embodiment. It is a perspective view which shows the fulcrum part of a fixing member.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to embodiment shown below, It can change in the range which those skilled in the art could concidentize, such as other embodiment, addition, correction, deletion, and any aspect Even within the scope of the present invention, as long as the functions and effects of the present invention can be achieved.

(Image forming device)
FIG. 1 shows an overall schematic configuration of a color copying machine which is an embodiment of an image forming apparatus provided with a fixing device according to the present invention. In the figure, reference numeral 100 denotes a color copying machine main body.
At the center of the color copying machine main body 100, an endless belt-like intermediate transfer member 10 is provided. The intermediate transfer member 10 is wound around the driving roller 14, the first driven roller 15 and the second driven roller 16, and is provided so as to be rotatable and conveyed clockwise.
The intermediate transfer body 10 is not limited to the mode shown in FIG. 1, and may be wound around four or more rollers including other rollers such as, for example, a roller for adjusting the offset. In addition, it may be stretched diagonally instead of horizontal.

In the vicinity of the second driven roller 16, a belt cleaning device may be provided to remove the toner remaining on the intermediate transfer member 10 after image transfer.
Further, on the intermediate transfer member 10 stretched between the drive roller 14 and the second driven roller 16, four single-color image forming means 18 of black, yellow, magenta and cyan are arranged along the transport direction. A tandem imaging device 20 is provided.
An exposure device 21 is provided above the tandem imaging device 20.

On the other hand, below the spanning area of the intermediate transfer member 10, a secondary transfer device 22 using a roller is provided. The secondary transfer device 22 presses the first driven roller 15 to transfer the image on the intermediate transfer member 10 to the recording medium P.
A conveyor belt 24, which is an endless belt, is stretched between two rollers 23 beside the secondary transfer device 22. A fixing device 25 according to the present invention for fixing a transferred image on a recording medium (hereinafter, also referred to as “paper”) P is provided beside the conveyance belt 24.

  The secondary transfer device 22 is also provided with a medium transport function for transporting the recording medium P after image transfer. Of course, a non-contact charger may be disposed as the secondary transfer device 22. However, when a non-contact charger is arranged, it is difficult to provide a medium transport function together.

  Below the secondary transfer device 22, the conveyance belt 24, and the fixing device 25, a medium storage cassette 28 for storing the recording medium P is provided. As the recording medium P, in addition to paper, an OHP film etc. may be mentioned.

  When copying is performed using this color copying machine, the document G is set on the document table 30 of the scanner 200 and pressed by the document holder. When the start switch is pressed, the scanner 200 is driven to read the document content. Specifically, the document G is illuminated by a light source 31 such as a halogen lamp, the reflected light is reflected by a mirror 32, transmitted through a lens 33, collected and input to a CCD 34, and an image is converted into an electrical signal. Ru.

  Further, when the start switch is pressed, the drive roller 14 is driven to rotate by the drive motor, and the driven rollers 15 and 16 are driven to rotate, whereby the intermediate transfer member 10 is rotationally conveyed. At the same time, the image carrier 40 is rotated in the four single-color image forming means 18, and black, yellow, magenta and cyan single-color images are formed on the respective image carriers 40. Then, the single-color images are sequentially superimposed as the intermediate transfer member 10 is transported, and primary transfer is performed to form a composite color image on the intermediate transfer member 10.

  When the start switch is pressed, the paper feed roller 35 is rotated, and the recording medium P is fed out from the medium storage cassette 28. After the recording medium P is conveyed to the paper feeding path 36, it strikes the registration roller 37 and stops.

  Then, the registration roller 37 rotates with timing to the composite color image on the intermediate transfer member 10, and the recording medium P is fed between the intermediate transfer member 10 and the secondary transfer device 22, and the secondary transfer device 22 The composite color image on the intermediate transfer member 10 is secondarily transferred collectively and a color image is formed on the recording medium P.

  The recording medium P on which the image has been transferred is conveyed by the conveyance belt 24 and fed to the fixing device 25. The heat and pressure are applied by the fixing device 25, and the recording medium P on which the transfer image is fixed is stacked on the discharge tray 38.

  After transfer of the image, the intermediate transfer member 10 has a residual toner removed by a belt cleaning device, and is prepared for another image formation by the tandem imaging device 20.

Each single-color image forming unit 18 of the tandem image forming apparatus 20 includes a charging device 41, a developing device 42, a primary transfer device 43, a cleaning device 44, a charge removing device, and the like around a drum-shaped image carrier 40. .
Maintainability can be improved by forming a process cartridge by all or a part of the apparatus constituting the single-color image forming means 18 and making the process cartridge removable with respect to the copying machine main body 100 collectively.

For example, a charging roller can be used as the charging device 41 constituting the single-color image forming means 18. The charging device 41 charges the image carrier 40 by contacting the image carrier 40 and applying a voltage.
The developing device 42 uses, for example, a two-component developer composed of a magnetic carrier and a nonmagnetic toner.
In the example of FIG. 1, in the primary transfer device 43, a roller-shaped member is pressed against the image carrier 40 with the intermediate transfer member 10 interposed therebetween, but the invention is not limited thereto. It may be a charger.
The cleaning device 44 includes a cleaning member such as a cleaning blade or a cleaning brush that contacts the image carrier 40, and removes residual toner on the image carrier 40.
The static eliminator is, for example, a lamp, which emits light to initialize the surface potential of the image carrier 40.

As the image carrier 40 rotates, the charging device 41 uniformly charges the surface of the image carrier 40. Next, according to the reading contents of the scanner 200, the writing light L by a laser, LED, etc. is reflected by the polygon mirror 47 in the exposure device 21 and further reflected by the mirror 48 and irradiated on the image carrier 40. Form an electrostatic latent image on the
Thereafter, toner is attached by the developing device 42 to make the electrostatic latent image visible, and the visible image is transferred onto the intermediate transfer member 10 by the primary transfer device 43. The surface of the image carrier 40 after the image transfer is cleaned by removing the residual toner by the cleaning device 44, and removed by the charge removing device to prepare for the image formation again.

(Fixing device)
First Embodiment
The fixing device according to the present embodiment includes a heating rotating body heated and rotated by a heat source, a fixing member having a contact portion in sliding contact with a part of the outer peripheral surface of the heating rotating body, the heating rotary body and the heating rotatable body A fixing belt is stretched over a fixing member, and a nip portion is formed in pressure contact with the fixing member via the fixing belt to convey the recording medium, and the fixing belt is driven to rotate by driving rotation. A pressure rotating body is provided in this order in the pressing direction for forming the nip portion, and the pressure in the nip portion is determined by the heating rotating body and the pressure rotating body via the fixing belt and the fixing member. In the fixing device applied by the pressure between them, the straight line connecting the rotation center of the heating rotating body and the rotation center of the pressure rotating body is disposed so as not to be orthogonal to the conveyance direction of the recording medium in the nip portion. And the surface normal at the center position of the surface of the heating rotator facing the fixing member, and the surface normal at the center position of the pressing rotator facing the fixing member are the fixing member. It crosses in the provided area.
In the present specification, the “circumferential direction” refers to the rotational direction of the heating rotator, and the “axial direction” refers to the rotational axis direction of the heating rotator.

  2 and 3 show schematic configurations of the fixing device according to the present embodiment. 2 is a sectional view, and FIG. 3 is a right side view of the fixing position shown in FIG. The fixing device shown in FIG. 2 shows a state at the time of a fixing operation for fixing a toner image on a sheet. Hereinafter, the state shown in FIG. 2 is also referred to as a “pressure state”.

  The fixing device 25 is in sliding contact with the heating rotating body (hereinafter referred to as “heating roller”) 78 rotatably supported by the frame 81 and the outer peripheral portion of the heating roller 78, and moves only in the vertical direction in FIG. A fixing member 74 supported rotatably, a fixing belt 77 having flexibility which is elliptically wound on the outside of the heating roller 78 and the fixing member 74, and a pressure rotating body (hereinafter referred to The pressure roller 72 is pressed against the fixing member 74 via the fixing belt 77 to form a nip portion (hereinafter referred to as a “fixing nip portion”). The fixing nip portion refers to a portion where the fixing belt 77 and the pressure roller 72 are in contact.

The position of the heating roller 78 is shifted upstream in the sheet conveyance direction. The shift in this case means that a straight line connecting the rotation center of the heating roller 78 and the rotation center of the pressure roller 72 is disposed so as not to be orthogonal to the conveyance direction of the recording medium in the nip portion.
That is, with respect to the arrangement of the heating roller 78 in which the straight line connecting the rotation center of the heating roller 78 and the rotation center of the pressure roller 72 is orthogonal to the conveyance direction of the recording medium (horizontal direction in the drawing). It is arranged to be inclined (with an angle). In other words, with respect to the center of the nip portion of the fixing member 74, the rotation center of the heating roller 78 is offset to the upstream side in the conveyance direction of the recording medium.
With such an arrangement, the traveling direction of the fixing belt at the exit portion of the fixing nip portion is oriented at an angle with respect to the nip surface, and the sheet separating ability is improved.

The fixing member 74 has contact portions 74 a and 74 b in sliding contact with a part of the outer peripheral surface of the heating roller 78.
The contact portions 74 a and 74 b of the fixing member 74 are provided on both sides of the fixing nip portion in the circumferential direction of the heating roller 78. The facing surface Sb of the heating roller 78 with the fixing member 74 is an outer circumferential surface partitioned by the contact portions 74a and 74b.
The opposing surface Sa of the pressure roller 72 with the fixing member 74 is a sliding contact surface with the fixing member 74, and is an area corresponding to the fixing nip portion.
In the case where the contact surfaces Sa and Sb do not have a uniform planar shape, they can be considered as being approximated to a planar shape.

  As shown in FIG. 2, in the fixing device of the present embodiment, the surface normal Nb at the center position of the opposing surface Sb of the heating roller 78 with the fixing member 74 and the opposing surface Sa of the pressure roller 72 with the fixing member 74. The surface normal Na at the central position of the cross intersects in the region where the fixing member 74 is provided.

FIG. 8 shows a partially enlarged view of the longitudinal end of the fixing member 74. Although FIG. 8 shows one end, the other end has the same shape.
The fixing member 74 includes a fulcrum 74c serving as a rotation fulcrum, as well as the contact portions 74a and 74b in sliding contact with the outer peripheral surface of the heating roller.
The fixing member 74 is rotatably supported about a fulcrum 74c. That is, the fixing member 74 can rotate (swing) in the direction substantially perpendicular to the facing surfaces Sa and Sb.

As shown in FIG. 2, in the fixing device of this embodiment, the tangent Tb of the surface Sb of the heating roller 78 facing the fixing member 74 and the tangent Ta of the surface Sa of the pressing roller 72 against the fixing member 74 , And intersect in a region where the fulcrum portion 74c of the fixing member 74 is disposed.
The tangent of the contact surfaces Sa and Sb can be considered as an extension of the surfaces when the contact surfaces Sa and Sb are approximated to a planar shape.

  By setting the heating roller 78, the fixing member 74, and the pressure roller 72 as described above, a wide and high surface pressure nip can be obtained without enlarging the fixing member, and the apparatus can be miniaturized. In addition, uniform and sufficient pressure can be obtained at the nip portion.

  The fixing belt 77 is in close contact with the fixing member 74 by the pressure roller 72, and the fixing belt 77 is in close contact with the heating roller 78 because a force (tension) to return to a circular shape is generated.

  The pressing roller 72 is given a pressing force upward in the vertical direction (normal Na direction) of the fixing nip portion (facing surface Sa). The pressure is transmitted to the fixing belt 77, the fixing member 74 and the heating roller 78. As a result, the fixing nip portion, the contact portion between the fixing member 74 and the fixing belt 77, and the contact portion between the fixing member 74 and the heating roller 78. Pressure is generated.

Since the fixing member 74 is configured to be able to swing in the normal Na direction and the normal Nb direction as described above, the fixing member 74 is configured to move between the fixing roller 77 and the heating roller 78 via the fixing belt 77. There is a uniform pressure between them.
Further, although a pressing force is generated on the fixing member 74 in the normal Na direction and the normal Nb direction, the intersection point between the normal Na direction and the normal Nb direction is located in the region of the fixing member 74. As shown in FIG. 7 (B), a rotational force (a force indicated by M in the figure) does not occur in 74, and the pressure becomes uniform as shown in FIG. 7 (C).

A separation plate 83 for assisting the separation of the sheet P from the fixing belt 77 is installed on the exit side of the fixing nip portion of the fixing belt 77 so that the tip end does not contact the fixing belt 77.
The separating plate 83 has a rotation fulcrum on the downstream side in the sheet conveying direction, and biases the positioning portion (located in the axial direction and outside the sheet width) in the vicinity of the front end of the separating plate There is a minute gap between the fixing belt 77 and the fixing belt 77. As a result, the sheet P naturally separated at the exit side of the fixing nip portion is guided by the separating plate 83 and prevented from being wound around the fixing belt 77.

  The heating roller 78 is internally provided with a heat source 84. The heat source is, for example, a halogen heater, an infrared heater, or the like, and an induction heating unit, a thermal resistance, or the like may be used.

  The thermopile 85 a detects the surface temperature at the position after the completion of the winding of the fixing belt 77 wound around the heating roller 78. The thermopile 85a is disposed in non-contact with the fixing belt 77, and as shown in FIG. 3, is provided within the sheet width in the axial direction.

  The thermistor 85 b also detects the surface temperature of the fixing belt 77 wound around the heating roller 78. The thermistor 85 b is disposed in contact with the fixing belt 77 and, as shown in FIG. 3, is provided outside the sheet width in the axial direction.

  Then, while the fixing belt is stopped, the heat source 84 is on / off controlled by the controller based on the detected temperature of the thermistor 85b based on the detected temperature of the thermistor 85b and the heating roller 78 is maintained at a predetermined temperature.

  Similarly, the pressure roller 72 is internally provided with a heat source 86 such as a halogen heater, and the thermistor 87 is pressed against the circumferential surface. Then, the heat source 86 is on / off controlled by the controller based on the temperature detected by the thermistor 87, and the pressure roller 72 is also maintained at a predetermined temperature.

  An inlet guide 88 is provided on the inlet side of the fixing device 25 so as to guide the sheet P to the fixing nip portion.

  The members in contact with the surface of the fixing belt 77 are the abutting portions of the thermistor 85 b and the separating plate 83, but since both are disposed outside the sheet width, the fixing belt 77 in the sheet width is worn away There is no possibility of image degradation due to the abrasion damage being transferred to the toner image of the sheet P without causing

In this embodiment, as the pressure roller 72, a metal pipe made of steel or the like is provided with a silicone rubber layer having a thickness of 2 mm, and the diameter is 50 mm, and journals 60 at both ends are narrowed to a diameter of 20 mm.
Bearings 61 are provided on the journals 60 at both ends, and the pressure levers 82 and springs 62 rotatably provided on the frame 81 press the bearings 61 in the direction of the heating roller 78 (pressure mechanism portion).
Then, the drive from the drive means is input to the gear 63 provided at the end of the pressure roller, and rotates counterclockwise.
The rotation of the pressure roller 72 configured as described above causes the fixing belt 77 of the fixing nip portion to rotate in a driven manner.

As the heating roller 78, for example, an aluminum pipe (hollow pipe shape) having a thickness of 0.5 mm to 3 mm, which has a good thermal conductivity, and which has a diameter of 50 mm is used.
The surface of the pressure roller 72 is subjected to an alumite treatment, a fluorine resin treatment, or the like in order to prevent the abrasion with the fixing belt 77 and the sliding contact with the fixing member 74. In addition, a heat resistant black coating is applied to the inner surface to make it easy to absorb the heat from the heat source 84.

  Further, both ends of the heating roller 78 are rotatably fixed to and supported by a frame 81 via a bearing 64. The heating roller 78 configured in this manner heats the fixing belt 77 while being driven to rotate by the rotation of the fixing belt 77. The heating roller 78 has a rigidity that hardly bends even when it receives a pressure contact force from the pressure roller 72.

  The upper surface of the fixing member 74 is in sliding contact with the heating roller 78, and the lower surface is in sliding contact with the fixing belt 77. The dimension in the left-right direction in the drawing is smaller than the outer diameter of the heating roller 78 and wider than the fixing nip portion. The fixing member 74 is shaped so that the fixing belt 77 can be loosely stretched on both the heating roller 78 and the fixing member 74.

  As a material of the fixing member 74, it is preferable to use a heat-resistant resin which is good in heat resistance and slidability and causes little heat transfer from the heating roller 78. For example, PPS (polyphenylene sulfide), PAI (polyamide imide), PI (polyimide) or the like can be used.

  The sliding surface of the fixing member 74 is preferably made of a fluorocarbon resin coating or a fluorocarbon resin sheet to reduce the sliding resistance.

  When the load on the contact portions 74a and 74b is large on the sliding surface with the heating roller 78 and the fixing member 74 is worn, as shown in FIG. 7C, the upper surface is the outer peripheral surface of the heating roller 78. It is also possible to disperse the load as a curved surface shape along

The sliding surface with the fixing belt 77 is formed in a flat surface to form a flat fixing nip. With the flat fixing nip shape, the transportability of the sheet P is good and a sheet transport failure such as wrinkles is less likely to occur.
The shape of the fixing nip is not limited to this, and for example, the surface facing the fixing belt 77 may be formed as a loose curved surface in the same direction as the outer surface of the pressure roller 72. In the case of such a nip shape having a convex shape on the fixing member side, the sheet P is discharged along the pressure roller side, so that the sheet P is unlikely to be wound around the fixing belt 77.

  The fixing belt entry portion (inlet portion) 74c and / or the outlet portion 74d on the left and right of the surface facing the fixing belt 77 has a small R shape in the same direction as the outer surface of the heating roller. The fixing belt 77 is stretched so as to be in contact with the two R portions. At the fixing nip with a 50 mm diameter roller pair, the curvature of the exit is small (R = 25 mm), and the paper is not easily separated naturally, but the curvature of the exit is set large (R = 8 mm) in this configuration. , There is a feature that the paper is easy to separate naturally.

  As apparent from comparison with the conventional fixing device shown in FIG. 7A, in the fixing device (FIG. 7C) of the present embodiment, the heating roller 78 is on the sheet entrance side (upstream side in the sheet conveying direction) Since the offset is performed, the traveling direction of the fixing belt at the exit of the nip portion is oriented at an angle with respect to the nip surface (θ1 <θ2), and the sheet separation capability is improved.

  The fixing belt 77 is, for example, a belt having a diameter of 58 mm, in which a release layer is coated on the surface layer and the back layer of a highly heat resistant polyimide resin having a thickness of 0.05 to 0.2 mm. Here, the surface release layer is made of, for example, a material such as silicone rubber, fluorocarbon resin, a two-layer structure of silicone rubber and fluorocarbon resin, a mixture of silicone rubber and fluorocarbon resin, and the like, and follows the unevenness of toner on paper. It has elasticity in order to In addition, in order to reduce the sliding resistance with the fixing member 74, the backing layer is treated with a fluorine resin. Furthermore, it is also preferable to apply a lubricant such as fluorine grease. The base material of the fixing belt 77 is not limited to the resin, and for example, it is preferable to use a metal such as stainless steel, nickel, copper or the like, or to use rubber or the like.

  The fixing belt 77 configured as described above is wound around and heated by the heating roller 78 having a large diameter, and heats and presses the sheet at the fixing nip portion, thereby fixing the toner image on the sheet P.

As described above, the fixing device of the present embodiment receives the pressure of the nip portion not only by the fixing member 74 but also by using the heating roller 78, so the fixing member 74 can be increased in size without increasing its size ), A wide and high contact pressure nip can be obtained, and high-speed and high-quality image correspondence can be achieved.
Further, since the fixing member 74 is small and in contact with the heating roller 78, the circumferential length of the fixing belt 77 can be shortened, and the apparatus can be miniaturized.
Furthermore, the fixing belt curvature at the exit of the nip can be increased by the shape of the fixing member 74, the separation performance is excellent, and natural separation is possible.
Since the heating roller 78 is in contact with the fixing belt 77 while rotating, the heat transfer efficiency from the heating roller 78 to the fixing belt 77 can be made excellent.

Second Embodiment
A side view of the fixing device of the present embodiment is shown in FIG.
In the first embodiment described above, the pressure mechanism portion is provided on the pressure roller 72 side, but as in the fixing device of the present embodiment, the pressure mechanism portion can be provided on the heat roller 78 side. . That is, the pressure roller 72 can be fixed to the frame 81, and pressure can be applied from the heating roller 78 side.
Alternatively, the fixing member 74 may be fixed, and pressure may be applied from both the heating roller 78 side and the pressure roller 72 side.

Third Embodiment
A partially enlarged view of the side view of the fixing device of the present embodiment is shown in FIG.
Since the heating roller 78 is driven to rotate by the fixing belt 77, no difference in speed occurs between the respective members, and wear and deterioration of the respective members can be prevented.
However, since the heating roller 78 rotates while sliding with the fixing member 74, there is a problem that the heating roller 78 does not rotate if the sliding resistance with the fixing member 74 becomes larger than the heating roller driving force by the fixing belt 77. It occurs. If the heating roller 78 does not rotate, not only the heating efficiency of the fixing belt 77 is deteriorated, but also there is a possibility that the fixing belt 77 does not rotate due to the rotational resistance of the fixing belt 77.
In order to prevent this, the fixing device of the present embodiment is provided with a rotation mechanism shown in FIG.

As shown in FIG. 5, the rotation mechanism unit gears the pressure roller 72 and the heating roller 78 by gears 65 and 66, and provides a one-way clutch 67 between the heating roller 78 and the gear 65.
The heating roller 78 is driven to rotate by the fixing belt 77, and the gear 65 is rotated at a speed that is a few percent (about 1 to 5%) slower than the heating roller 78.

Therefore, although the one-way clutch 67 is in the free state in the state of (heat roller rotation speed)> (heat roller gear rotation speed), when the heat roller rotation speed decreases due to slip etc., (heat roller rotation speed) = (heat roller gear) Locking is performed at the rotational speed, and the heating roller 78 is driven to rotate at a several percent slow rotational speed.
As described above, in the fixing device according to the present embodiment, even when a slip occurs between the fixing belt 77 and the heating roller 78, the fixing belt 77 is rotated by driving the heating roller 78. It is possible to prevent the rotation stop by the slip.

Fourth Embodiment
The fixing belt 77 is rotated by a pressure roller 72. However, since the fixing belt 77 rotates while sliding with the fixing member 74, there is a problem that the fixing belt 77 does not rotate if the sliding resistance with the fixing member 74 is larger than the driving force of the fixing belt by the pressure roller 72. Occur. In particular, since the sheet P is present between the pressure roller 72 and the fixing belt 77 during sheet conveyance in the fixing nip portion, the fixing belt driving force by the pressure roller 72 is reduced. That is, if the fixing belt 77 does not rotate, the sheet P can not be conveyed.
Therefore, as in the third embodiment shown in FIG. 5, it is preferable that the heating roller 78 and the pressure roller 72 be connected by a gear 65 and a gear 66 so that the heating roller 78 is also rotationally driven.

  The speed of the heating roller 78 is set to be approximately the same as the driving speed of the fixing belt 77 by the pressure roller 72 (± 1%) or to increase in the range of ̃10%.

  The inner surface of the fixing belt 77 is subjected to the fluorine resin treatment as described above and is coated with a lubricant, so that the inner surface of the fixing belt 77 is easily slipped at the contact surface with the heating roller 78. Therefore, even if the heating roller 78 is rotated at a speed different from that of the fixing belt 77, the rotation driving state of the fixing belt 77 is maintained because the sheet stably slips and rotates.

  While the conveyed sheet passes through the nip portion, the fixing belt driving force by the pressure roller 72 is reduced, but the fixing belt driving force by the heating roller 78 prevents the fixing belt 77 from rotating. it can. Furthermore, since the heating roller 78 is driven to rotate, the problem that the heating roller 78 does not rotate due to the slip between the fixing belt 77 and the heating roller 78 as described above does not occur.

  Although it is possible to rotate the heating roller 78 slower than the speed of the fixing belt 77, the heating roller 78 serves as a rotational resistance of the fixing belt, and the fixing belt at the exit of the nip is slackened to separate the sheets. May become unstable. Therefore, it is preferable that the heating roller 78 be rotated at a constant velocity (± 1%) or at a speed of 10% or more with the fixing belt.

Fifth Embodiment
In the fixing device of the present embodiment, the heat source can be induction heating means provided inside or outside of the heating roller 78.
For example, as shown in FIG. 6, an induction heating unit 89 may be provided as a heat source of the heating roller 78.

  In the example of FIG. 6, the induction heating means 89 is disposed on the outer surface side of the fixing belt 77 in a noncontact manner, and heats a heat generating layer provided in the layer of the fixing belt 77. The induction heating unit 89 may be disposed on the inner surface side of the heating roller, and the heating roller 78 may be heated to indirectly heat the fixing belt 77.

  By providing the noncontact induction heating means 89 on the outer surface side of the fixing belt 77, it is not necessary to provide a heat source inside the heating roller 78. Therefore, by providing the ribs 68 on the inner surface side of the heating roller 78, it is possible to increase the strength and to cope with higher surface pressure.

  By using the image forming apparatus (FIG. 1) provided with the fixing device 25 of the present invention configured as described above, an image forming apparatus that functions as described above can be configured.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 14 Drive roller 15 First driven roller 16 Second driven roller 18 Single-color image forming means 20 Tandem image forming device 21 Exposure device 22 Secondary transfer device 23 Roller 24 Conveying belt 25 Fixing device 28 Medium storage cassette 30 Document table 31 Light source 32 Mirror 33 Lens 34 CCD
Reference Signs List 35 paper feed roller 36 paper feed path 37 registration roller 38 paper discharge tray 40 image carrier 41 charging device 42 developing device 43 primary transfer device 44 primary transfer device 44 cleaning device 47 polygon mirror 48 mirror 60 journal portion 61, 64 bearing 62 spring 63, 65 , 66 Gear 67 one-way clutch 68 rib 72 pressure roller (pressure rotor)
74 Fixing members 74a and 74b Contact portion 74c Rotational fulcrum 77 Fixing belt 78 Heating roller (heating rotating body)
81 frame 82 pressing lever 83 separating claw 84, 86 heat source 85a thermopile 85b, 87 thermistor 88 entrance guide 89 induction heating means 100 copying machine main body 200 scanner L writing light G original P recording medium (paper)
S Counterface N Normal T Tangent

Patent No. 5640405 gazette JP 2012-242550 A

Claims (7)

A heating rotating body heated and rotated by a heat source,
A fixing member having a contact portion in sliding contact with a part of the outer peripheral surface of the heating rotator;
A fixing belt that spans the heating rotating body and the fixing member;
Forming a nip portion in which the recording medium is conveyed by pressure contact with the fixing member via the fixing belt, and forming a nip and rotating the fixing belt by rotating the fixing belt by driving and rotating; In this order in the pressure direction for the image forming, the pressure in the nip portion is fixed by the pressure between the heating rotating body and the pressure rotating body via the fixing belt and the fixing member. In the device
The straight line connecting the rotation center of the heating rotator and the rotation center of the pressure rotator is disposed so as not to be orthogonal to the conveyance direction of the recording medium at the nip portion.
The fixing member is provided with a surface normal at a central position of a surface of the heating rotating body facing the fixing member, and a surface normal at a central position of the pressing rotating body facing the fixing member. A fixing device characterized in that it intersects in a narrow area. The contact portions of the fixing member are provided on both sides of the nip portion in the circumferential direction of the heating rotator.
The fixing device according to claim 1, wherein a surface of the heating rotating body facing the fixing member is an outer peripheral surface divided by the contact portion.   The fixing device according to claim 1, wherein a surface of the pressure rotating body facing the fixing member is a sliding contact surface with the fixing member.   The fixing device according to any one of claims 1 to 3, further comprising: a fulcrum portion serving as a rotation fulcrum of the fixing member, wherein the fixing member is rotatably supported around the fulcrum portion. The fixing device according to any one of claims 1 to 4 , wherein the heat source is an infrared heater disposed inside a heating rotary body having a hollow pipe shape. The fixing device according to any one of claims 1 to 4 , wherein the heat source is an induction heating unit provided inside or outside of the heating rotating body. An image forming apparatus comprising the fixing device according to any one of claims 1 to 6 .

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