JP5760610B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus. More specifically, the present invention relates to a fixing device suitable for an electrophotographic color image forming apparatus capable of high-speed printing.

  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). Also, the image is formed by being transferred onto the image and fixed by a fixing device.

  Various types of fixing devices have been proposed. For example, a roller fixing type fixing device is known. For example, as shown in FIG. 11, the roller fixing method includes a fixing roller 91 and a pressure roller 92. Rubber layers 95 and 96 are provided on the surface layers of the metal pipes 93 and 94, respectively, and halogen heaters 97 and 98 are provided on the inner side. It has. In such a roller fixing type fixing device, since the rubber layer becomes a thermal resistance, if the surface is controlled at a constant temperature, the interface temperature between the metal pipe and the rubber layer becomes high and 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 fixing roller and the pressure roller with a thin rubber layer is small, and the roller fixing method cannot cope with a high speed machine that requires a wide nip.

  Further, for example, in Patent Document 1, as shown in FIG. 12, a heating rotator 78, a fixing member (rotating body) 74, a fixing belt 77 stretched between the heating rotator 78 and the fixing member 74, and fixing. There is disclosed a belt fixing type fixing device including a pressure rotating body 72 that is in pressure contact with a fixing member 74 via a belt 77. In this fixing device, the fixing member 74 and the pressure rotator 72 are pressurized, and the heating rotator 78 is driven and rotated while being in close contact with the fixing belt 77.

  According to the fixing device of the belt fixing method described in Patent Document 1, the rubber layer of the fixing roller can be made thicker than that of the roller fixing method, and a wide nip can be obtained. However, for example, in a high-speed machine of 50 ppm (Page Per Minute) or more, the roller diameter needs to be 50 mm or more in order to obtain a wide nip width. Since such a large-diameter roller has a small curvature (the degree of bending is loose), the paper at the nip exit portion winds around the roller (cannot be naturally separated). For this reason, forced separation by the separation claw 83 in contact with the belt surface at the nip exit portion is necessary, but there is a problem in that a wear scratch due to the separation claw 83 in contact with the belt surface is transferred to the image.

  Patent Document 2 discloses a fixing device in which a fixing member is a fixing member and an auxiliary roller is added to the fixing member in the belt fixing method. In this fixing device, a fixing member (fixing member) and a pressure rotator are pressurized, and the heating rotator is driven to rotate while being in close contact with the fixing belt.

  According to the fixing device described in Patent Document 2, it is easy to obtain a wide nip width in a space-saving manner by using the fixing member as a fixing member. At this time, the fixing belt and the fixing member may slide, but by adding an auxiliary roller, sliding reduction is realized. Further, depending on the shape of the fixing member, the curvature of the nip exit portion is increased (the degree of bending is tight) and the paper separation property is improved (natural separation is possible). However, since the fixing member is small, it cannot withstand high pressure. That is, there is a problem that the uniform nip cannot be secured due to bending.

  Patent Document 3 discloses a fixing device in which a fixing member is a fixed member and a rotating body in a belt fixing method. In this fixing device, the fixing member (fixing member and rotating body) and the pressure rotating body are pressurized, and the heating rotating body is driven to rotate while being in close contact with the fixing belt.

  According to the fixing device described in Patent Document 3, it is easy to obtain a wide nip width in a small space by using the fixing member as a fixed member and a rotating body. At this time, there is a drawback that the fixing belt and the fixing member slide, but the rotation is reduced by the rotating member. Further, since the rotating member of the fixing member has a small diameter, the curvature of the nip exit portion is increased to improve the paper separation property (natural separation is possible). However, like the above-mentioned Patent Document 2, there is a problem that the fixing member is small and cannot withstand high pressure.

  Patent Document 4 discloses a fixing device including a fixed cylindrical heating member, a heating member, a fixing belt, and a pressure rotating body that is in pressure contact with the heating member via the fixing belt. ing. In this fixing device, the heating member and the pressure rotator are pressurized, the heating member is fixed, and the fixing belt slides and rotates while maintaining contact with the heating member or a minute clearance.

  According to the fixing device described in Patent Document 4, the warm-up time and the first print time can be shortened as compared with the belt fixing type fixing device disclosed in Patent Documents 1 to 3. However, in the technique described in Patent Document 4, the fixing belt and the heating member slide. Here, in order to improve the heat transfer performance from the heating member to the fixing belt, it is necessary to make the clearance between the heating member and the fixing belt close to 0 and increase the contact area, but the sliding resistance increases. Further, in order to maintain the running performance of the fixing belt, it is necessary to widen the clearance between the heating member and the fixing belt and reduce the sliding resistance, but the heat transfer performance is deteriorated. Further, since the portion where the clearance occurs is heat transfer by convection or radiation, the temperature of the heating member becomes higher than that of the fixing belt, and thermal expansion, thermal deformation, and thermal deterioration of the heating member become a problem.

In recent years, image forming apparatuses have been developed in color, high image quality, and high speed. In order to fix a color image with high image quality, the time during which the recording paper is in contact with the nip (hereinafter referred to as nip time) needs to be 40 to 60 msec, and the pressure at the nip portion needs to be 7 N / cm ² or more. is there. In particular, in a high-speed machine of 50 PPM (A4 size) or higher, the recording paper conveyance speed is high, so that a nip width of 10 mm or more is necessary to ensure the nip time, and a surface pressure of 7 N / cm ² or more. Need. Also, coated paper (resin-coated paper) that is frequently used in high-speed machines tends to cause toner image disturbance due to water vapor while passing through the nip, and therefore requires a higher surface pressure (12 N / cm ² or more).

  In order to improve the image quality, the recording paper needs to be naturally separated at the nip exit, and the shape of the nip, the roller curvature of the nip exit, and the guide member are devised. Although there is a method of forcibly separating the recording paper by bringing a separation claw or the like into contact with the roller, there is a possibility that the abrasion damage of the roller is transferred to the image and the image is deteriorated.

  In such a high-speed image forming apparatus, a belt fixing apparatus as in Patent Document 1 that easily secures a nip width is often used. However, in order to obtain a wide nip width of 10 mm or more and a high surface pressure, a high pressing force is required between the fixing roller and the pressure roller. In order to obtain the width, a large-diameter roller having a high strength and a diameter of 50 mm or more is required.

  In addition, the belt fixing device for large-diameter rollers has a problem that the device itself becomes large and the cost of parts increases. In addition, since the roller curvature at the nip exit becomes small and the recording paper is not easily separated naturally, for example, the recording paper is wound around the fixing belt due to the adhesive force of the melted toner. Further, if forced separation is performed by the separation claw, the image may be deteriorated.

  Further, in the fixing devices as described in Patent Documents 2 and 3 using the fixing member as a fixing member, the fixing belt and the fixing member slide by using the fixing member as the fixing member. However, in Patent Documents 2 and 3, a roller is provided on the fixed member to reduce sliding resistance, or each member is deteriorated. However, since the fixing member is small compared to the large-diameter roller, the strength is insufficient. For this reason, there is a problem that high surface pressure cannot be obtained and it is difficult to improve image quality.

  Further, in the fixing device of Patent Document 4, it is possible to cope with a high surface pressure by increasing the diameter of the heating member and enlarging the reinforcing member, and a wide nip can be obtained depending on the shape of the nip portion. When the diameter of the heating member is increased, the roller curvature at the nip exit becomes small as in the belt fixing device of Patent Document 1, so that the recording paper is not easily separated naturally, and the recording paper is applied to the fixing belt by the adhesive force of the melted toner. There was a problem of wrapping around. In addition, it is difficult to achieve both heat transfer performance and belt running performance, and it has been difficult to employ in a high-speed image forming apparatus.

  In order to solve the above problems, the present invention obtains a nip having a wide and high surface pressure without enlarging the fixing member by receiving the pressure of the nip portion not only by the fixing member but also using a heating rotating body. The present invention provides a fixing device and an image forming apparatus that can be reduced in size by shortening the circumferential length of the fixing belt.

  Furthermore, it has been found that the above configuration may cause slippage of the fixing belt and / or the heating rotator. Here, if the fixing belt slips, the paper may not be conveyed accurately. If the heating rotator slips, it becomes difficult to transfer the heat of the heating rotator to the fixing belt and the sliding resistance of the fixing belt. In some cases, the fixing belt slips.

  Therefore, the present invention can obtain a wide and high surface pressure nip without enlarging the fixing member by receiving the pressure of the nip portion not only by the fixing member but also using a heating rotating body, and fixing. A fixing device and an image forming apparatus that can be reduced in size by shortening the belt circumference and that can reliably rotate the fixing belt and the heating rotator in response to the driving of the pressure rotator. It is intended to do.

  In order to achieve such an object, a fixing device according to the present invention includes a heating rotator that is heated and rotated by a heat source, a fixing member that is in sliding contact with a part of the outer peripheral surface of the heating rotator, a heating rotator, A flexible fixing belt that is stretched over a fixing member, and a pressure rotator that rotates and rotates the fixing belt by driving and rotating to form a nip portion in pressure contact with the fixing member via the fixing belt. Are arranged in this order in the pressing direction for forming the nip portion, and the pressure of the nip portion is between the heating rotator and the pressure rotator via the fixing belt and the fixing member. The contact width B between the fixing member and the heating rotator is narrower than the contact width A between the fixing belt and the heating rotator in the axial direction of the heating rotator. , Between the fixing belt and the heating rotor Ri is intended with a slip prevention means for preventing.

  According to the present invention, it is possible to obtain a nip having a wide and high surface pressure without increasing the size of the fixing member, and it is possible to reduce the size of the fixing device by shortening the circumferential length of the fixing belt and to apply pressure. The fixing belt and the heating rotator can be reliably driven and rotated with respect to the driving of the rotator.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram illustrating an example of a fixing device according to the present invention. 3 is an example of a side cross-sectional view of a fixing device. FIG. It is a schematic diagram of the fixing member which has a roller. It is a schematic diagram of the fixing member which has a protrusion shape. It is a schematic diagram of the pressure roller which used the axial direction outer side part as the high friction coefficient member. FIG. 6 is a schematic diagram of a fixing belt having an axially outer portion as a high friction coefficient member. It is a schematic diagram of the heating roller to which the rough surface processing was performed. It is a schematic diagram of a heating roller and a fixing belt having a fitting shape. It is a schematic block diagram which shows an example of the fixing device using the induction heating means as a heat source. It is a schematic block diagram of a conventional roller fixing type fixing device. It is a schematic block diagram of the conventional fixing device of a belt fixing system.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Image forming device)
FIG. 1 shows an overall schematic configuration of a color copying machine as a position embodiment of an image forming apparatus provided with a fixing device according to the present invention. Reference numeral 100 in the drawing denotes a copying machine main body. In the copying machine main body 100, an endless belt-like intermediate transfer member 10 is wound around a driving roller 14, a first driven roller 15 and a second driven roller 16 in the illustrated example, and rotates clockwise in the drawing. Provide for transport. Of course, it may be hung around four or more rollers, such as hung around a roller for adjusting the offset of the intermediate transfer member 10 separately. The intermediate transfer member 10 is stretched almost horizontally in the illustrated example, but may be stretched obliquely instead of horizontally.

  In this illustrated example, although not illustrated, a belt cleaning device is provided in the vicinity of the second driven roller 16 to remove residual toner remaining on the intermediate transfer member 10 after image transfer.

  Further, on the intermediate transfer member 10 stretched between the driving roller 14 and the second driven roller 16, four monochrome image forming means 18 of black, yellow, magenta, and cyan are laterally arranged along the conveying direction. A tandem imaging device 20 is provided side by side. An exposure device 21 is further provided on the tandem image forming device 20.

  On the other hand, a secondary transfer device 22 using a roller is provided below the stretched area of the intermediate transfer body 10. The secondary transfer device 22 is pressed against the first driven roller 15 to transfer the image on the intermediate transfer body 10 to the recording medium P. In the illustrated example, a conveying belt 24 that is an endless belt is provided between the secondary transfer device 22 and the two rollers 23. A fixing device 25 that fixes a transfer image on the recording medium P is provided beside the conveyance belt 24.

  The secondary transfer device 22 described above 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 arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this medium conveying function together.

  Below the secondary transfer device 22, the conveyance belt 24, and the fixing device 25, a medium storage cassette 28 that stores a recording medium P such as paper and an OHP film is provided.

  By the way, when making a copy using this color copying machine, the original G is set on the original table 30 of the scanner 200 and pressed by an original presser (not shown). When a start switch (not shown) is pressed, the scanner 200 can be driven to read the document content. That is, the original G is irradiated with a light source 31 such as a halogen lamp, the reflected light is reflected by a mirror 32, condensed through a lens 33, and put into a CCD 34 to convert an image into an electrical signal.

  When a start switch (not shown) is pressed, the drive roller 14 is rotated by a drive motor (not shown) and the driven rollers 15 and 16 are driven to rotate, and the intermediate transfer body 10 is rotated and conveyed. At the same time, the individual image forming means 18 rotates the image carrier 40 to form black, yellow, magenta, and cyan monochrome images on each image carrier 40. Then, along with the conveyance of the intermediate transfer member 10, the single color images are sequentially superimposed and primary transferred to form a composite color image on the intermediate transfer member 10.

  On the other hand, when a start switch (not shown) is pressed, the paper feed roller 35 is rotated, the recording medium P is fed out from the medium storage cassette 28, put into the paper feed path 36 and abutted against the registration roller 37 and stopped.

  Then, the registration roller 37 is rotated in synchronization with the composite color image on the intermediate transfer member 10, and the recording medium P is sent between the intermediate transfer member 10 and the secondary transfer device 22. The composite color image on the transfer body 10 is secondarily transferred together to form a color image on the recording medium P.

  The recording medium P after the image transfer is transported by the transport belt 24 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image, and then is stacked on the paper discharge tray 38. .

  On the other hand, the intermediate transfer member 10 after the image transfer is removed by a belt cleaning device (not shown) to remove residual toner remaining on the intermediate transfer member 10 after the image transfer, and prepares for another image formation by the tandem image forming device 20.

  In the tandem image forming apparatus 20 described above, each monochromatic image forming means 18 is more specifically arranged around a drum-shaped image carrier 40, a charging device 41, a developing device 42, a primary transfer device 43, and a cleaning device 44. And a static elimination device (not shown).

  Although not shown in the drawing, a process cartridge may be formed by all or part of the parts constituting the monochromatic image forming means 18 so as to be detachable from the copying machine main body 100 in a lump to improve maintainability. .

  Of the portions constituting the monochromatic image forming means 18, the charging device 41 uses a charging roller in the illustrated example, and charges the image carrier 40 by contacting the image carrier 40 and applying a voltage.

  In the illustrated example, the developing device 42 uses a two-component developer composed of a magnetic carrier and a non-magnetic toner.

  The primary transfer device 43 is formed in a roller shape and is pressed against the image carrier 40 with the intermediate transfer member 10 interposed therebetween. The shape is not limited to a roller, and may be a brush or a non-contact charger.

  The cleaning device 44 is in contact with the image carrier 40 and includes a cleaning member such as a cleaning blade and a cleaning brush, and the residual toner on the image carrier 40 is removed by the cleaning member.

  The static eliminator (not shown) is, for example, a lamp, and initializes the surface potential of the image carrier 40 by irradiating light.

  Then, along with the rotation of the image carrier 40, the surface of the image carrier 40 is first uniformly charged by the charging device 41, and then writing by a laser, LED, or the like is performed in the above-described exposure device 21 according to the reading content of the scanner 200. The light L is reflected by the polygon mirror 47, further reflected by the mirror 48, and applied to the image carrier 40 to form an electrostatic latent image on the image carrier 40.

  Thereafter, toner is attached by the developing device 42 to visualize the electrostatic latent image, 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 residual toner with a cleaning device 44 and is discharged with a static eliminator to prepare for another image formation.

(Fixing device)
The fixing device according to the present invention includes a heating rotator (heating roller 78) that is heated and rotated by a heat source (heat source 84), and a fixing member (fixing member 74) that is in sliding contact with a part of the outer peripheral surface of the heating rotator. ), A flexible fixing belt (fixing belt 77) that is stretched between the heating rotator and the fixing member, and press-contacting with the fixing member via the fixing belt to form a nip portion, which is driven to rotate. In the fixing device, the pressure rotator (pressure roller 72) that rotates the fixing belt following the rotation of the fixing belt is arranged in this order in the pressing direction for forming the nip portion. The fixing member is heated by the pressing force between the heating rotator and the pressurizing rotator via the fixing member, and the fixing member is heated more than the contact width A between the fixing belt and the heating rotator in the axial direction of the heating rotator. The contact width B with the rotating body is Ku, in the outer portion of the contact width B, and those with a slip preventing means (pressing roller 70, etc.) to prevent slippage of the fixing belt and the heating rotating body. In the present specification, “circumferential direction” refers to the rotation direction of the heating rotator, and “axial direction” refers to the rotation axis direction of the heating rotator.

  FIG. 2 is a schematic configuration diagram (front view) of the fixing device according to the present embodiment. FIG. 3 is a right side view (cross section) of the fixing device shown in FIG.

  The fixing device 25 includes a heating roller 78 rotatably supported by the frame, a fixing member 74 that is in sliding contact with the outer peripheral portion of the heating roller 78 and is fixed so as to be movable only in the vertical direction in the figure, The heating roller 78 and the fixing member 74 are composed of a flexible fixing belt 77 that is wound around in an elliptical shape and a pressure roller 72, and is fixed to the fixing member 74 via the fixing belt 77. The pressure roller 72 is pressed to form a fixing nip portion (referring to a contact portion between the fixing belt 77 and the pressure roller 72).

  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) is generated to return to a circular shape.

  The pressing roller 72 is given an upward pressing force in the figure, and this pressing force is transmitted to the fixing belt 77, the fixing member 74 and the heating roller 78. Accordingly, pressure is generated at 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.

  On the exit side of the fixing nip portion of the fixing belt 77, a separation plate 83 that assists in separating the paper P from the fixing belt 77 is installed so that the tip portion does not contact the fixing belt 77. Here, the separation plate 83 has a rotation fulcrum on the downstream side in the conveyance direction, and a positioning portion (located outside the sheet width in the axial direction) near the tip of the separation plate is attached to the fixing belt 77 with a spring member or the like. Thus, the separation plate tip and the fixing belt 77 form a minute gap. Therefore, the sheet P naturally separated on the exit side of the fixing nip portion is guided by the separation plate 83 and does not wrap around the fixing belt 77.

  The heating roller 78 includes a heat source 84 inside. The heat source is, for example, a halogen heater, an infrared heater, or the like, and induction heating means, thermal resistance, or the like may be used.

  The thermopile 85-1 detects the surface temperature at a position after the fixing belt 77 that has been wound around the heating roller 78 has been wound. The thermopile 85-1 is arranged in a non-contact manner with the fixing belt 77 and is provided within the paper width in the axial direction. It is provided at a position corresponding to the dotted line portion (fixing belt surface) shown in FIG. Further, a thermistor 85-2 (not shown in FIG. 3) is provided to detect the surface temperature at the portion of the fixing belt 77 that is wound around the heating roller 78. The thermistor 85-2 is disposed in contact with the fixing belt 77, and is provided outside the paper width in the axial direction and at a position different from slip prevention means described later.

  The heat source 84 is turned on and off by a controller (not shown) based on the detected temperature of the thermistor 85-2 while the fixing belt is stopped, and based on the detected temperature of the thermopile 85-1 while the fixing belt is running. Hold at temperature.

  Similarly, the pressure roller 72 includes a heat source 86 such as a halogen heater inside, and similarly, a thermistor 87 is pressed against the peripheral surface. Then, the heat source 86 is on / off controlled by a controller (not shown) based on the temperature detected by the thermistor 87, and the pressure roller 72 is similarly held at a predetermined temperature. Note that the pressure roller 72 is not necessarily provided with the heat source 86.

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

  The members that are in contact with the surface of the fixing belt 77 are the abutting portions of the thermistor 85-2 and the separating plate 83, but both are disposed outside the paper width, so that the fixing belt 77 within the paper width is attached to the fixing belt 77. Without causing the wear scar, image degradation due to the transfer of the wear scar to the toner image on the paper P does not occur.

In the present embodiment, as the pressure roller 72, a silicone rubber layer having a thickness of 2 mm is provided on a metal pipe such as steel, and a fluororesin tube having a thickness of 30 μm is provided on the surface thereof, and the diameter is 50 mm. The journal portion 60 of which the diameter is reduced to 25 mm is used.
The journal portions 60 at both ends are provided with bearings 61, and the bearings 61 are pressed in the direction of the heating roller 78 by a pressure lever 82 and a spring 62 provided rotatably on the frame (pressure mechanism portion). Then, driving from a driving means (not shown) is input to the gear 63 provided at the end of the pressure roller and rotates counterclockwise. When the pressure roller 72 configured as described above rotates, the fixing belt 77 in the fixing nip portion is driven to rotate by frictional force.

  As the heating roller 78, for example, an aluminum pipe (hollow pipe shape) having a thermal conductivity of 0.5 mm to 3 mm in thickness and having a diameter of 50 mm is used. The heating roller 78 is driven to rotate by a frictional force by a fixing belt 77 wound around the heating roller 78. The surface of the heating roller 78 is subjected to processing to be described later. In addition, heat-resistant black coating is applied to the inner surface to make it easier to absorb heat from the heat source 84.

  Further, both end portions of the heating roller 78 are fixedly supported by the frame 81 via a bearing 64 so as to be rotatable. 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. It should be noted that the heating roller 78 has a rigidity that hardly bends even when it receives a pressure contact force from the pressure roller 72.

  The fixing member 74 has an upper surface in sliding contact with the heating roller 78 and a lower surface in sliding contact with the fixing belt 77. The horizontal dimension in the drawing (FIG. 2) is smaller than the outer diameter of the heating roller 78 and wider than the fixing nip portion. In the drawing (FIG. 2), the vertical direction is such that the fixing belt 77 is loosely stretched by both the heating roller 78 and the fixing member 74.

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

  Further, the surface facing the fixing belt 77 is partly made of a heat-resistant elastic body 74-2 such as silicone rubber, so that the adhesion between the fixing belt 77 and the paper P can be improved and the image quality can be improved. Moreover, it is preferable to reduce sliding resistance by coating the sliding surface of the fixing member 74 with a fluororesin or by interposing a fluororesin sheet.

  Further, the surface facing the heating roller 78 is in sliding contact with the heating roller 78 at two contact portions 74-1 in the circumferential direction. It is preferable that the heating roller facing surface has a configuration in which sliding resistance with the heating roller 78 is small and heat transfer is difficult. For example, as shown in FIG. 4, the contact portion 74-1 is constituted by a rotating body such as a roller, or as shown in FIG. 5, a large number of semicircular protrusions are formed on the contact surface with the heating roller 78. By forming with 74-5 and reducing the contact area, sliding resistance can be reduced and heat transfer can be prevented.

  Further, the surface facing the fixing belt 77 is formed by a curved surface in the same direction as the outer surface of the pressure roller 78 to form a fixing nip. In such a nip shape convex toward the fixed member side, the paper P is discharged along the pressure roller side, so that the paper P is less likely to wind around the fixing belt 77. The nip shape is not limited to this, and for example, a flat nip shape may be formed by flattening the surface facing the fixing belt 77. The flat fixing nip shape provides good transportability of the paper P and is less likely to cause paper transport failures such as wrinkles.

  In addition, the fixing belt entry portion (entrance portion) 74-3 and / or the exit portion 74-4 on the left and right of the surface facing the fixing belt 77 have 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 come into contact with the two R portions. In the fixing nip with a 50 mm diameter roller pair, the curvature of the exit portion is small (R = 25 mm) and the paper is not easily separated naturally. In this configuration, the curvature of the exit portion is set to be large (R = 8 mm). The paper has a feature that it can be easily separated.

  In addition, since the fixing belt entrance portion 74-3 and the exit portion 74-4 are in sliding contact with the fixing belt 77, it is preferable that the sliding resistance is reduced. For example, as shown in FIG. 4, sliding resistance can be reduced by configuring the contact portion with a rotating body such as a roller.

  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 of a polyimide resin having a high heat resistance and a thickness of 0.05 to 0.2 mm. Here, the release layer has a two-layer structure of silicone rubber (inner side) and fluororesin (front side). Due to the elasticity of the silicone rubber layer, the surface of the fixing belt can follow the unevenness of the toner on the paper, and the toner can be fixed uniformly. Moreover, the process mentioned later is given to the back surface. The base material of the fixing belt 77 is not limited to a resin, and it is also preferable to use a metal such as stainless steel, nickel, or copper, or rubber.

  A pressing roller 70 as a slip prevention unit is provided on the surface side of the fixing belt 77, and the pressing roller 70 presses the fixing belt 77 toward the heating roller 78 by a spring 71. The slip prevention means will be described later.

(Each contact surface)
Next, the configuration of the contact surface of each member constituting the fixing device 25 will be described with reference to FIG. The frictional force F on the contact surface is expressed by the following equation (1).
F = coefficient of friction μ × normal force N (1)
Therefore, in order to control the friction force F, it is necessary to pay attention to the friction coefficient μ and the normal force N.

  As shown in FIG. 3, the contact width A indicates the axial width of the contact portion between the back surface (inner peripheral surface) of the fixing belt 77 and the heating roller 78, and the contact width B indicates the back surface of the fixing belt 77 and the fixing member. 74 is a contact portion (also a contact portion between the heating roller 78 and the fixing member 74). Further, the contact width C indicates a sheet passing range, and the contact width D is a contact portion between the pressure roller 72 and the surface (outer peripheral surface) of the fixing belt 77. Details will be described below.

  In the fixing device 25, the axial length of the body portion of the pressure roller 72 is shorter than the axial length of the fixing belt 77. Accordingly, the contact portion (contact width D) between the pressure roller 72 and the surface of the fixing belt 77 is the same as the axial length of the body portion of the pressure roller 72.

  The pressure roller 72 is pressed upward in the figure, and the pressure applied at this time is applied to the heating roller 78 through a certain range (contact width B) of the fixing member 74. Therefore, the contact width D is the same as the contact width B.

  In the fixing device 25 configured as described above, when the pressure roller 72 is driven and rotated, the fixing belt 77 is driven and rotated by the frictional force at the contact portion.

  Here, at the contact portion (contact width D) between the pressure roller 72 and the surface of the fixing belt 77, the pressure force of the pressure roller 72 becomes the vertical drag N, and the contact portion between the back surface of the fixing belt 77 and the fixing member 74. The same normal force N is generated even at (contact width B).

Therefore, in order for the fixing belt 77 to rotate following the rotational driving of the pressure roller 72,
The friction coefficient of the contact portion (contact width D) between the pressure roller 72 and the surface of the fixing belt 77 is μ1, and the friction coefficient between the back surface of the fixing belt 77 and the contact portion (contact width B) of the fixing member 74 is μ2.
Then, the following formula (2) needs to be satisfied.
μ1> μ2 (2)

  Further, as described above, a release layer is provided on the surface of the pressure roller 72 and the surface of the fixing belt 77 to prevent toner and paper dust on the paper from adhering. Since the fluororesin used for the release layer is a low friction member, the friction coefficient μ1 of the contact portion (contact width D) between the pressure roller 72 and the surface of the fixing belt 77 is small.

On the other hand, if the outer portion of the sheet passing range C that does not require a release layer ( contact width D— the portion corresponding to the sheet passing range C ) is a high friction coefficient member, the surfaces of the pressure roller 72 and the fixing belt 77 The friction coefficient μ1 of the contact portion (contact width D) can be increased.

  That is, for example, as shown in FIG. 6, the fluorocarbon resin layer 90 is not provided in the portion corresponding to the outer portion of the paper passing range C in the pressure roller 72, and the silicone rubber 91 of the base material is the surface of the pressure roller 72. It is intended to be exposed. In this embodiment, the contact width D of the pressure roller 72 is longer by 15 mm on one side than the sheet passing width C, and the high friction member (silicone rubber 91) is pressed so as not to interfere with the sheet passing width C. Both ends of the roller 72 are provided at 10 mm.

  Further, for example, as shown in FIG. 7, the fluororesin layer 90 is not provided in a portion corresponding to the outer portion of the sheet passing range C in the fixing belt 77, and at least a portion in sliding contact with the pressure roller 72. The base silicone rubber 91 is exposed on the surface of the pressure roller 72.

  Since the silicone rubber is a member having a higher coefficient of friction than that of the fluororesin, the contact portion (contact width D) between the pressure roller 72 and the surface of the fixing belt 77 can be set as shown in FIG. 6 or FIG. The friction coefficient μ 1 can be increased, and the fixing belt 77 can be reliably driven to rotate with respect to the rotational drive of the pressure roller 72.

  The fixing member 74 is disposed 15 mm longer than the sheet passing range C at both ends in the axial direction (that is, the length of B). The fixing member 74 is in contact with the fixing belt 77 on its lower surface side, and is in contact with the heating roller 78 on its upper surface side. As shown in FIGS. 4 and 5, it is also preferable that the heating roller surface side has a configuration in which contact portions are scattered within the contact width B.

  At both ends in the axial direction of the fixing member 74, there are receiving portions 74-6 having a thin shape so as not to come into contact with the fixing belt 77 and the heating roller 78 in a region other than the contact width B. 74-6 is supported by a stopper 79. The stopper 79 is provided so as to be able to reciprocate by a predetermined amount (several millimeters) only in the vertical direction in FIG. 3, and the fixing member 74 can also be reciprocated by a predetermined amount only in the vertical direction in FIG. Further, the fixing member 74 is pressed toward the heating roller 77 by the pressure of the pressure roller 72.

  The stopper 79 supports the fixing member 74 and restricts the movement of the fixing belt 77 in the axial direction (preventing fixing belt deviation). Further, the portion where the end face of the fixing belt 77 contacts is coated with grease so that the rotation resistance of the fixing belt 77 does not occur.

  In the fixing device 25, it is preferable that the contact portion between the back surface of the fixing belt 77 and the fixing member 74 and the contact portion between the heating roller 78 and the fixing member 74 are slidable.

  For this reason, the contact surface between the fixing member 74 and the back surface of the fixing belt 77 is configured to have low friction as described above. The back surface of the fixing belt 77 is coated with a fluororesin having a low friction coefficient. Furthermore, it is also preferable to apply a lubricant such as fluorine grease. In addition, the contact portion between the heating roller 78 and the fixing member 74 is also configured to have low friction as described above. Further, the surface of the heating roller 78 is coated with a fluororesin having a low friction coefficient. Furthermore, in the range of the contact width B, it is also preferable to apply a lubricant such as fluorine grease.

In the fixing device 25 configured as described above, the fixing belt 77 driven and rotated by the pressure roller 72 further rotates the heating roller 78. Here, the frictional force F1 by which the fixing belt 77 drives the heating roller 78 can be expressed by the following equation (3).
F1 = [Friction coefficient between the back surface of the fixing belt and the heating roller] × Tensioning belt tension (3)

Further, since the heating roller 78 slides with the fixing member 74, the sliding resistance force F2 can be expressed by the following equation (4).
F2 = [Friction coefficient between the back surface of the fixing belt and the fixing member] × Pressure roller pressure (4)

  Therefore, in order for the heating roller 78 to be driven and rotated, it is necessary to satisfy F1> F2. Here, since the fixing belt tension is smaller than the pressure applied by the pressure roller, it is necessary to increase [the friction coefficient between the back surface of the fixing belt and the heating roller].

  However, as described above, since the friction coefficient of the back surface of the fixing belt 77 and the heating roller 78 is reduced in the range of the contact width B, [the friction coefficient of the back surface of the fixing belt and the heating roller] is increased. Contradicts.

(Slip prevention means)
Therefore, in the fixing device 25 according to the present embodiment, the contact width A is set longer than the contact width B by a predetermined amount (in the example of FIG. 3, 30 mm on each side), and the range of contact width A−contact width B on both sides is set. In addition, a means (slip prevention means) for driving the heating roller 78 without sliding as the fixing belt 77 rotates is provided. Hereinafter, a plurality of configuration examples of the slip prevention means will be described.

<Slip prevention means (1)>
The first configuration example of the slip prevention means is to assist the vertical drag due to the fixing belt tension. That is, as shown in FIG. 2 and FIG. 3, a pressing roller 70 is provided on the surface side of the fixing belt 77 spanned by the heating roller 78, and this pressing roller 70 causes the fixing belt 77 to be heated by the spring 71. The pressure is applied to the 78 side. In the example shown in FIG. 3, one pressing roller 70 is provided in the circumferential direction on both sides of the fixing belt 77 in the axial direction (range of contact width A−contact width B). Instead, it is more preferable to provide at a plurality of locations in the circumferential direction.

  As described above, by applying an external force by the pressing roller 70 from the outer peripheral surface side of the fixing belt 77 at the axially outer portion of the fixing member 74, the frictional force between the fixing belt 77 and the heating roller 78 is increased, and the fixing belt 77. Thus, the driven rotation of the heating roller 78 can be reliably performed.

  Although the pressing roller 70 can be provided in any range in the contact width A, the pressing roller 70 is provided in the contact width B region because the friction coefficient between the back surface of the fixing belt 77 and the heating roller 78 is small. Even if the vertical drag is assisted, the effect is small. In addition, in the sheet passing area C, due to the sheet passing, toner and paper dust stains adhere to the pressing roller 70, or the heat of the fixing belt moves to the pressing roller 70, and the heating efficiency of the sheet decreases. This is not preferable because there is a possibility that problems such as the above may occur. From the above, it is preferable that the installation position of the pressing roller 70 in the axial direction is in the range of contact width A−contact width B.

<Slip prevention means (2)>
In the second configuration example of the slip prevention means, the surface of the heating roller 78 and / or the back surface of the fixing belt 77 is a high friction coefficient member in the range of the outside of the contact width B (contact width A−contact width B). That is. As a result, the frictional force between the fixing belt 77 and the heating roller 78 is increased, and the driven rotation of the heating roller 78 by the fixing belt 77 can be reliably performed.

  In the example shown in FIG. 8, both ends 25 mm of the heating roller 78 have a high friction coefficient as the roughened surface portion 92 by sandblasting or the like. Here, the roughened surface portion 92 has a margin so as not to be in the range of the contact width B where slidability is required.

  Further, instead of (or in combination with) the rough surface processing portion 92 shown in FIG. 8, the same rough surface processing may be performed on the back surface of the fixing belt 77. Further, a high friction coefficient may be obtained by a method such as coating the fixing belt 77 with rubber.

<Slip prevention means (3)>
The third configuration example of the slip prevention means includes a shape (fitting portion) for fixing the fixing belt 77 and the heating roller 78 to each other instead of friction driving the driving of the heating roller 78 by the fixing belt 77. The driving of the heating roller 78 by the fixing belt 77 is a fitting drive. Accordingly, the fixing belt 77 and the heating roller 78 are fitted and driven, and the driven rotation of the heating roller 78 by the fixing belt 77 can be reliably performed.

  The shape in which the fixing belt 77 is fitted to the heating roller 78 is not particularly limited. For example, as shown in FIG. 9, a plurality of hemispherical projections 93 are provided in the circumferential direction on the heating roller 78 to fix the fixing belt 77. A plurality of round holes 94 that fit into the protrusions 93 may be provided in the belt 77 in the circumferential direction. By making the pitch of the projections 93 and the round holes 94 the same, the fixing belt 77 can reliably drive the heating roller 78 without slipping.

  In addition, it is also preferable to implement each structural example of said slip prevention means in combination. Thereby, the heating roller 78 can be reliably rotated by the fixing belt 77 without causing the fixing belt 77 and the heating roller 78 to slip.

  The fixing belt 77 configured in this manner is wound around the heating roller 78 and heated, and the toner image on the paper P is fixed by heating and pressing the paper at the fixing nip portion.

  As described above, the fixing device according to the present embodiment receives not only the fixing member but also the heating rotator, so that the fixing member is not enlarged (increases the strength). A wide and high surface pressure nip can be obtained, and high-speed and high-quality images can be handled. Further, since the fixing member is small and is in contact with the heating rotator, the circumference of the fixing belt can be shortened, and the apparatus can be miniaturized. Further, the fixing belt curvature at the nip exit can be increased depending on the shape of the fixing member, and the separation performance is excellent and natural separation is possible. Further, since the heating rotator is in contact with the fixing belt while rotating, the heat transfer efficiency from the heating rotator to the fixing belt can be excellent.

  Furthermore, since the fixing belt is configured to drive the heating rotator, the inner peripheral surface of the fixing belt and the outer peripheral surface of the heating rotator have a low coefficient of friction in order to reduce sliding resistance with the fixed member. The contact pressure between the fixing belt, the heating rotator, the fixing member, and the pressure rotator is less than the contact pressure between the fixing rotator and the heating rotator. The surface is configured as described above, and the slip resistance between the fixing member and the fixing belt, and the fixing member and the heating rotator is increased by providing the anti-slip means on the outer side in the axial direction of the heating rotator (fixing belt). Accordingly, the heating rotator can be reliably rotated by the fixing belt, and the fixing belt and the heating roller can be reliably rotated with respect to the rotational driving of the pressure rotator.

  By using the image forming apparatus (FIG. 1) including the fixing device 25 having the configuration described above, an image forming apparatus including the fixing device that functions as described above can be configured.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  For example, induction heating means 89 may be used as the heat source as shown in FIG. The induction heating unit 89 is disposed in a non-contact manner on the outer peripheral surface side of the fixing belt and heats a heat generating layer provided in the layer of the fixing belt 77. Note that the induction heating unit 89 may be disposed on the inner surface side of the heating roller, and the fixing roller 77 may be indirectly heated by heating the heating roller 78.

  By using the induction heating unit 89 in a non-contact manner on the outer peripheral surface side of the fixing belt, it is not necessary to provide a heat source inside the heating roller 78. Therefore, for example, by providing the rib 68 shown in FIG. 10 on the inner surface side of the heating roller 78, it is possible to increase the strength and cope with a higher surface pressure.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 14 Drive roller 15 1st driven roller 16 2nd driven roller 18 Monochromatic 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
35 Paper feeding roller 36 Paper feeding path 37 Registration roller 38 Paper discharge tray 40 Image carrier 41 Charging device 42 Developing device 43 Primary transfer device 44 Cleaning device 47 Polygon mirror 48 Mirror 60 Journal portion 61, 64 Bearing 62 Spring 63 Gear 68 Rib 70 Pressure roller 71 Spring 72 Pressure roller 74 Fixing member 77 Fixing belt 78 Heating roller 79 Stopper 81 Frame 82 Pressure lever 83 Separation claw 84, 86 Heat source 85-1 Thermopile 85-2, 87 Thermistor 88 Inlet guide 89 Induction heating Means 90 Fluororesin layer 91 Silicone rubber 92 Rough surface processing portion 93 Protrusion portion 94 Round hole 100 Copier body 200 Scanner G Document L Writing light P Recording medium (paper)

JP-A-4-50883 JP 2004-252354 A JP 2004-198556 A JP 2007-334205 A

Claims (10)

A heating rotator that is heated and rotated by a heat source;
A fixing member that is in sliding contact with a part of the outer peripheral surface of the heating rotator,
A flexible fixing belt spanning the heating rotator and the fixing member;
A pressure rotating body that pressurizes and contacts the fixing member via the fixing belt to form a nip portion, and drives and rotates the fixing belt to rotate the fixing belt. In the fixing device arranged in this order,
The pressure of the nip portion is applied by a pressing force between the heating rotator and the pressure rotator via the fixing belt and the fixing member,
In the axial direction of the heating rotator, the contact width B between the fixing member and the heating rotator is narrower than the contact width A between the fixing belt and the heating rotator. A fixing device comprising slip prevention means for preventing slippage between the fixing belt and the heating rotator.   The fixing device according to claim 1, wherein the slip prevention means is a pressing roller provided on an outer peripheral surface side of the fixing belt, and presses the fixing belt toward the heating rotator by the pressing roller. .   The fixing device according to claim 2, wherein a plurality of the pressing rollers are provided in a circumferential direction of the heating rotator.   The slip prevention means is that the inner peripheral surface of the fixing belt and / or the outer peripheral surface of the heating rotator is formed of a member having a higher coefficient of friction than other portions of the respective members. The fixing device according to claim 1, wherein the fixing device is a fixing device.   5. The fixing according to claim 1, wherein the slip prevention means is a fitting portion provided on an inner peripheral surface side of the fixing belt and an outer peripheral surface side of the heating rotator. apparatus.   The fixing device according to claim 1, wherein the heat source is an infrared heater disposed inside a heating rotator having a hollow pipe shape. The heat source, a fixing device according to claim 1, wherein an induction heating apparatus provided inside or outside of the heating rotator to 5.   The fixing device according to claim 1, wherein the heating rotator and the fixing member are in contact with each other via a rotator provided on the fixing member. 9. The fixing belt and the fixing member are in contact with each other via a rotating body provided on the fixing member at the nip entrance and / or the outlet. A fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1.

Images