JP5533490B2 - 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. 13, 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. 14, 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 or more, in order to obtain a wide nip width, the roller diameter needs to be 50 mm or more. 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.

  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. Therefore, 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.

  Therefore, the present invention can obtain 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 rotator, It is an object of the present invention to provide a fixing device and an image forming apparatus that can be reduced in size by reducing the circumference and can improve warm-up performance.

  In order to achieve this object, a fixing device according to claim 1 is a heating rotating body 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 rotating body, and a heating rotation. A pressurizing member for forming a nip portion includes: a flexible fixing belt that is stretched between the body and the fixing member; and a pressure rotating body that presses and contacts the fixing member via the fixing belt to form a nip portion. And a separating means for separating the heating rotator and the fixing member from each other, and the pressure of the nip portion is controlled by the heating rotator and the pressing rotator via the fixing belt and the fixing member. It is given by the applied pressure between.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the separating means separates the pressure rotator and the fixing belt.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the separating means releases the pressing of the pressure rotator to the heating rotator for forming the nip portion, The heating rotator and the fixing member are separated from each other.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, during the warm-up operation for raising the fixing belt to a predetermined temperature, the heating rotator and the fixing member are separated by the separating means. Are separated.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the separating unit includes a pressure unit that presses the pressure rotator toward the heating rotator, and a fixing member. An urging means for urging in a direction away from the heating rotator, and in the contact state between the heating rotator and the fixed member, the pressing force by the pressing means is greater than the urging force by the urging means, and the heating rotation In the separated state of the body and the fixing member, the pressing force by the pressing means is smaller than the urging force by the urging means.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, a pressure rotator driving unit that rotates the pressure rotator and a heating rotator are rotated. A heating rotator driving means, and in a state where the heating rotator and the fixing member are separated by the separating means, the fixing belt is driven to rotate by the rotation driving of the heating rotator by the heating rotator driving means. .

  According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, the rotation speed of the heating rotator by the heating rotator driving means is such that the heating rotator is rotated by the pressure rotator driving means. The rotational speed is lower than that in the case of driven rotation via a fixing belt that is driven to rotate by a pressure rotating body.

  According to an eighth aspect of the present invention, in the fixing device according to any one of the first to seventh aspects, the heating rotator and the fixed member are in contact with each other via a rotator provided on the fixed member. It is what.

According to a ninth aspect of the present invention, in the fixing device according to any one of the first to eighth aspects, the fixing belt and the fixing member are provided on the fixing member at the nip portion inlet and / or outlet. It is in contact via a rotating body.

  According to a tenth aspect of the present invention, in the fixing device according to any one of the first to ninth aspects, the fixing member has a rotation center provided on one of the nip portion inlet side and the outlet side. The separating means separates from the heating rotator on the side having no rotation center.

  According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to tenth aspects, the heat source is an infrared heater disposed inside a heating rotator having a hollow pipe shape. is there.

  According to a twelfth aspect of the present invention, in the fixing device according to any one of the first to eleventh aspects, the heat source is an induction heating device provided inside or outside the heating rotator.

  According to a thirteenth aspect of the present invention, in the fixing device according to the twelfth aspect, a magnetic shunt alloy layer and a magnetic shielding layer are provided in this order with respect to the induction heating device.

  An image forming apparatus according to a fourteenth aspect includes the fixing device according to any one of the first to thirteenth aspects.

  According to the present invention, it is possible to obtain a nip having a wide and high surface pressure without increasing the fixing member, and it is possible to realize a reduction in size of the fixing device by shortening the circumferential length of the fixing belt, and The warm-up performance can be improved.

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. FIG. 3 is an example of a side view of a fixing device. It is explanatory drawing which shows the winding angle in a 1st state. It is explanatory drawing which shows the winding angle in a 2nd state. 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 which shows a mode that a fixing member rotates by a rotation fulcrum. FIG. 3 is a schematic configuration diagram of a fixing device in which a heating roller and a fixing member are separated from each other, and a pressure roller is in contact with the fixing member via a fixing belt. It is another example of the side view of a fixing device. 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 which shows the other 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. Apart from the roller shape, a brush or a non-contact charger may be used.

  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 25 according to this embodiment includes a heating roller 78 that is heated and rotated by a heat source 84, a fixing member 74 that is in sliding contact with a part of the outer peripheral surface of the heating roller 78, and the heating roller 78 and the fixing member 74. A fixing belt 77 having flexibility, and a pressure roller 72 that forms a nip portion in pressure contact with the fixing member 74 via the fixing belt 77, and a pressure direction for forming the nip portion. And a separating means (such as a cam 50) for separating the heating roller 78 and the fixing member 74 from each other. The pressure at the nip portion is heated via the fixing belt 77 and the fixing member 74. The pressure is applied by the pressure between the roller 78 and the pressure roller 72. In this specification, “circumferential direction” refers to the rotation direction of the heating rotator (and pressurizing rotator), and “axial direction” refers to the rotation of the heating rotator (and pressurizing rotator). Refers to the axial direction.

[During fixing operation (first state)]
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 of the fixing device shown in FIG. The fixing device shown in FIG. 2 shows a state during a fixing operation for fixing a toner image on a sheet (hereinafter, the state shown in FIG. 2 is also referred to as a first state (pressurized state)).

  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 as shown in FIG.

  Further, the thermistor 85-2 detects the surface temperature of 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 as shown in FIG.

  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.

  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 this embodiment, the pressure roller 72 is a metal pipe made of steel or the like provided with a silicone rubber layer having a thickness of 2 mm, the diameter of which is 40 mm, and the journal portions 60 at both ends are reduced to a diameter of 20 mm. Bearings 61 are provided in the journal portions 60 at both ends. The bearing 61 is pressed in the direction of the heating roller 78 by a pressure lever 82 and a compression spring 62 that are rotatably provided on the frame of the fixing device (pressure means). Then, driving from a driving means (not shown) is input to a gear (hereinafter also referred to as a pressure roller driving gear) 63 provided at the end of the pressure roller and rotates counterclockwise. As the pressure roller 72 configured as described above rotates, the fixing belt 77 in the fixing nip portion rotates.

  As the heating roller 78, an aluminum pipe (hollow pipe shape) having a good thermal conductivity and a thickness of 0.5 mm to 3 mm and having a diameter of 40 mm is used. The surface of the pressure roller 78 is subjected to alumite treatment, fluororesin treatment or the like in order to prevent wear due to contact with the fixing belt 77 or sliding contact with the fixing member 74. 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 ends of the heating roller 78 are rotatably supported by the frame 81 via bearings 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. 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 is smaller than the outer diameter of the heating roller 78 and wider than the fixing nip portion. Further, the vertical direction in the figure 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, LCP (liquid crystal polymer), PPS (polyphenylene sulfide), PAI (polyamideimide), PI (polyimide) and 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. 6, the contact portion 74-1 is configured by a rotating body such as a roller, or as shown in FIG. 7, 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 72, thereby forming 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 40 mm diameter roller pair, the curvature of the exit is small (R = 20 mm), and the paper is not easily separated naturally. 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. 6, the 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 45 mm, which has high heat resistance and has a release layer coated on a surface layer and a back layer of polyimide resin having a thickness of 0.05 to 0.2 mm. Here, the surface release layer is made of a material such as silicone rubber, fluororesin, a two-layer structure of silicone rubber and fluororesin, a mixture of silicone rubber and fluororesin, and follows the unevenness of the toner on the paper. In order to do so, it has elasticity. Further, the back release layer is subjected to fluororesin treatment in order to reduce the sliding resistance with the fixing member 74. 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 a resin, and it is also preferable to use a metal such as stainless steel, nickel, or copper, or rubber.

  The fixing belt 77 configured as described above is heated by being wound around the large-diameter heating roller 78, and the toner image on the paper P is fixed by heating and pressing the paper at the fixing nip portion.

[Warm-up operation (second state)]
Next, a state other than the fixing operation of the fixing device 25 will be described. The states other than the fixing operation include, for example, a warm-up operation, a standby time, and a power-off of the fixing device (image forming apparatus).

  Here, the “warm-up operation” refers to an operation of heating until the temperature of the fixing belt 77 reaches a temperature at which the fixing operation can be performed. The fixing belt 77 and the heating roller 78 are rotationally driven to turn on the heat source 84. The fixing belt 77 is heated uniformly. The “standby” means a state where the apparatus from the fixing operation to the next fixing operation is not used. Conventionally, the fixing belt temperature is controlled to a constant temperature during standby, but in recent years, there are many fixing devices that do not perform temperature control for energy saving. In such a fixing device, the temperature of the fixing belt decreases even during standby, so that it is necessary to perform a warm-up operation before the next fixing operation. Also, the operation of the fixing belt 77 is stopped during “standby” and “when the apparatus is turned off”.

  The fixing device according to the present embodiment includes a separating unit that releases the contact state between the heating roller 78 and the fixing member 74. The separating means is constituted by a cam 50 provided on the other end side of the pressure lever 82 of the compression spring 62. The cam 50 shown in FIG. 2 is rotated about the cam shaft 50a by a driving means (not shown), thereby weakening the pressure applied to the pressure roller 72 by the pressure means (compression spring 62 and pressure lever 82). It can be in a non-pressurized state. Hereinafter, this non-pressurized state is also referred to as a second state.

  By rotating the cam 50 180 degrees from the pressure state (first state) shown in FIG. 2 to the non-pressure state (second state), the pressure roller 72 is moved downward ( In the direction away from the heating roller 78) and away from the fixing belt 77.

  Further, as shown in FIG. 3, tension springs 51 are provided at both ends of the fixing member 74 in the axial direction, and the fixing member 74 is urged (tensed) in a direction away from the heating roller 78. Here, the urging force by the tension spring 51 is assumed to be weaker than the pressing force by the compression spring 62.

  Therefore, in the first state shown in FIG. 3, the tension spring 51 is stretched by being pressed by the pressing force of the compression spring 62. On the other hand, in the second state, the fixing member 74 is pulled downward by the tension spring 51 and thus the fixing member 74 is separated from the heating roller 78 because the compression spring 62 does not receive pressure. That is, the tension spring 51 functions as a separating unit that separates the fixing member 74 from the heating roller 78 in a non-pressurized state.

  Further, the urging force of the tension spring 51 is assumed to be equal to or greater than the force necessary for tensioning the fixing belt 77 strongly. For this reason, in the second state, the tension spring 51 tensions the fixing belt 77 more strongly than in the first state.

  As shown in FIG. 3, a gear (hereinafter also referred to as a heating roller driving gear) 52 is provided at an end portion in the axial direction of the heating roller 78, and a one-way clutch 57 is provided inside the gear 52. Is provided. Here, the heating roller driving gear 52 and the pressure roller driving gear 63 are connected to driving means (motor) (not shown), and both gears are driven simultaneously.

  As described above, in the first state, the heating roller 78 is driven and rotated by the fixing belt 77 driven and driven by the pressure roller 72. At this time, the heating roller driving gear 52 is several percent (1%) from the heating roller 78. It is designed to rotate at a slow speed. Here, the one-way clutch 57 is in a free state that is not locked in a state of “heating roller driven rotation speed> heating roller gear rotation speed”.

  On the other hand, in the second state, since the pressure roller 72 is separated from the fixing belt 77, the fixing belt 77 is not driven by the pressure roller 72. Therefore, in this case, the one-way clutch 57 is locked at the heating roller gear rotation speed, and the heating roller 78 is driven to rotate at a rotation speed several percent slower than that in the first state.

  With this configuration, the fixing belt 77 and the heating roller 78 can be driven by the pressure roller 72 in the first state, and the fixing belt 77 can be driven by the heating roller 78 in the second state.

  Here, in the first state during the fixing operation, since the paper P enters between the pressure roller 72 and the fixing belt 77, it becomes difficult for the pressure roller 72 to drive the fixing belt 77 and slip occurs. There is a fear. In particular, slipping may occur when using thick paper, coated paper, or the like.

  However, even in such a case, in the fixing device according to the present embodiment, as described above, the heating roller 78 can rotate the fixing belt 77 by the heating roller driving gear 52 at a speed that is several percent slower. The fixing belt 77 does not stop rotating. Therefore, it is possible to prevent a problem that the paper stops at the nip portion and causes jamming. Further, since the fixing belt 77 does not stop, the pressure roller 72 can be returned to the state in which the fixing belt 77 is driven as soon as slip occurs.

[Wrapping angle]
Next, the winding angle of the fixing belt 77 will be described. The winding angle refers to an angle of a portion of the circumference (360 °) of the heating roller 78 where the fixing belt 77 is in contact with (wound around) the heating roller 78. FIG. 4 is a diagram for explaining the winding angle in the first state, and FIG. 5 is a diagram for explaining the winding angle in the second state.

  In the present embodiment, the shape and the like of the fixing member 74 are set so that the winding angle a is 110 ° in the first state (FIG. 4). Here, if the winding angle is too small, the heat transfer time from the heating roller 78 to the fixing belt 77 is insufficient, so that heat cannot be transferred efficiently.

  Further, when the frictional force between the heating roller 78 and the fixing member 74 is larger than the force by which the fixing belt 77 is driven to rotate the heating roller 78, there arises a problem that the heating roller 78 is not driven to rotate. In the present embodiment, since the heating roller 78 is provided with the gear 52, there is no problem even if the heating roller 78 does not rotate in a driven manner. However, as in an embodiment (third embodiment) to be described later, the gear 52 is provided. If the configuration does not have, the heating roller 78 does not rotate, which is problematic.

  On the other hand, if the winding angle is too large, the rotational resistance of the fixing belt 77 increases, and therefore the pressure roller 72 cannot rotate the fixing belt 77 and the fixing belt 77 does not rotate. In this embodiment, since the heating roller 78 is provided with the gear 52, the fixing belt 77 rotates. However, the fixing belt 77 rotates at a speed lower than the speed when driven by the pressure roller 72. Thus, although the problem arises when the winding angle is too small or too large, according to the study by the inventors of the present application, the winding angle is 90 ° to during the fixing operation (first state). By setting the angle within a range of about 180 °, a good fixing operation can be performed.

  FIG. 5 showing the second state shows that the pressure roller 72 is moved downward by 3 mm and released from the fixing belt 77, and the fixing member 74 is pulled. This shows a state in which the fixing belt 77 is strongly stretched by being pulled 1.9 mm downward by the spring 51 and separated from the heating roller 78. For this reason, in the second state, the winding angle becomes large. In the example shown in FIG. 5, the winding angle b is 220 °.

  Further, since the nip forming surface of the fixing member 74 is convex toward the fixing member as described above, a gap is generated between the nip forming surface and the fixing belt 77 in the second state. Furthermore, since the second state is a non-pressurized state, a large pressure is not applied to the pressure roller 72, the fixing member 74, and the heating roller 78, and even when the standby state or the power-off state continues for a long time, There is no deformation of parts.

  The fixing device according to the present embodiment performs the warm-up operation in the second state. In the second state, since the winding angle is large, the fixing belt 77 can be reliably driven, and heat can be efficiently transmitted from the heating roller 78 to the fixing belt 77. Further, since the heating roller 78 and the fixing member 74 are separated from each other, heat transfer from the heating roller 78 to the fixing member 74 can be prevented. In addition, since the contact area between the fixing member 74 and the fixing belt 77 is small, useless heat transfer from the fixing belt 77 to the fixing member 74 can be prevented. Further, since the fixing belt 77 and the pressure roller 72 are separated from each other, useless heat transfer from the fixing belt 77 to the pressure roller 72 can be prevented.

  Thus, by setting the non-pressurized state (second state) during the warm-up operation, it is possible to complete the warm-up operation faster than warming up in the pressurized state (first state).

[Operation of fixing device]
An example of the operation flow of the fixing device 25 described above will be described. As described above, since temperature control is not performed during standby, the warm-up operation is performed before the image forming operation.
(Step S1) The apparatus is turned on. In this case, the state is stopped in the second state.
(Step S2) When a standby state is reached and the print command signal arrives, the process proceeds to Step S3.
(Step S3) The warm-up operation starts. That is, in the second state, the driving means (heating roller) is driven and the heat source is turned on.
(Step S4) When the fixing belt temperature reaches a predetermined temperature (for example, 140 ° C.), the state is switched to the first state.
(Step S5) Further, when the fixing belt temperature reaches a predetermined temperature (a temperature equal to or higher than the predetermined temperature in Step S4, for example, 160 ° C.), temperature control at the temperature is started. At this point, the warm-up operation ends.
(Step S6) The image forming operation starts. That is, in the first state, driving of each driving means and temperature control are performed.
(Step S7) The image forming operation ends. After the heat source is turned off and driving of the driving means is stopped, the state is switched to the second state.
(Step S8) It will be in a standby state again. Return to step S2.

  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.

  Further, in the fixing device according to the present embodiment, by setting the heating rotator and the fixing member to move away from each other, the wrapping angle of the fixing belt around the heating rotator is increased and the heating efficiency is improved. . In addition, since the fixing member and the heating roller are separated from each other, and the contact area between the fixing member and the fixing belt is also reduced, useless heat transfer to the fixing member side can be prevented, and the time required for the warm-up operation is shortened. be able to. Furthermore, since the pressure rotator moves away from the fixing belt and the nip width is reduced, wasteful heat transfer from the fixing belt to the pressure rotator can be prevented, and the time required for the warm-up operation Can be shortened. Thus, the warm-up performance can be improved.

(Second Embodiment)
Hereinafter, other embodiments of the fixing device according to the present invention will be described. Note that a description of the same points as in the first embodiment will be omitted.

  In the above embodiment, as shown in FIG. 5, the example in which the fixing member 74 is pulled downward by the tension spring 51 and is completely separated from the heating roller 78 and is not in contact with the fixing member 74 has been described. However, it may be difficult to design the position and the like of the tension spring 51 so that the fixed member 74 that is smaller than the outer diameter of the heating roller 78 and is reduced in size is translated.

  Therefore, in this embodiment, as shown in FIG. 8, the rotation fulcrum 53 pivotally supported by the frame is provided on the 74-3 side of the fixing member 74, and the 74-4 side of the fixing member 74 is attached by the tension spring 51. By urging, the fixing member 74 may be rotated around the rotation fulcrum 53. In this case, the 74-3 side of the fixing member may be in contact with the heating roller 78.

(Third embodiment)
In the above embodiment, since the pressure roller 72 is separated from the fixing belt 77 in the second state, the fixing belt 77 cannot be rotated by the pressure roller 72 in the second state. It is driven to rotate by driving means provided on the side.

  However, as shown in FIG. 9, the downward movement of the fixing member 74 is made to follow the downward movement of the pressure roller 72, for example, by making the biasing force of the tension spring 51 larger than that of the above embodiment. Although the heating roller 78 and the fixing member 74 are separated from each other, the pressure roller 72 may be in contact with the fixing member via the fixing belt 77. In the second state, unlike the first state, the pressing force necessary for fixing is not required, so the pressing force between the fixing member 74 and the pressure roller 72 is small enough to drive the fixing belt 77. It only has to be pressure.

  According to the fixing device configured as described above, since the fixing belt 77 can be driven and rotated by the pressure roller 72 even in the second state, it is not necessary to provide a driving means on the heating roller 78 side, and the device configuration It is possible to reduce the cost by simplifying.

(Fourth embodiment)
In the above embodiment, as shown in FIG. 3, the configuration including the pressure unit on the pressure roller side has been described. However, as illustrated in FIG. 10, the pressure unit is provided on the heating roller side, that is, The pressure roller 72 may be fixed to the frame 81 and pressed from the heating roller side. In the example shown in FIG. 10, the compression spring 62 is provided on the bearing 64. However, as in FIG. 2, the pressure lever 82 is provided on the heating roller 78 side, and the compression spring 62 is provided thereon. Also good. Alternatively, the fixing member 74 may be fixed and pressure may be applied from both the heating roller side and the pressure roller side.

(Fifth embodiment)
Further, as a heat source, induction heating means 89 may be used as shown in FIG. Reference numeral 54 denotes a coil. The induction heating unit 89 is arranged in a non-contact manner on the outer surface side of the fixing belt, heats the heat generating layer provided on the surface layer of the heating roller 78, and the heated heating roller 78 contacts and heats 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 means 89 in a non-contact manner on the outer 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. 11 on the inner surface side of the heating roller 78, it is possible to increase the strength and cope with a higher surface pressure.

(Sixth embodiment)
Further, when the induction heating means 89 is used as a heat source, as shown in FIG. 12, the magnetic shunt alloy layer 55 that passes the magnetic flux and stops generating heat when reaching a predetermined temperature on the inner surface side of the heating roller 78. Is preferably provided. For example, a magnetic shunt alloy (for example, Ni38, Fe62, etc.) having a Curie point at which the magnetic permeability suddenly changes around 200 ° C. is provided in contact or non-contact with the heating roller 78. In the example of FIG. 12, the gap is 0.3 mm and is not contacted. Further, in this case, it is preferable to provide a magnetic shielding layer 56 that shields magnetism on the inner surface side of the magnetic shunt alloy layer 55. The magnetic shielding layer 56 is, for example, an aluminum alloy, and is provided in a non-contact manner with respect to the magnetic shunt alloy layer 55. In the example shown in FIG. 12, the magnetic shunt alloy layer 55 is configured separately from the heating roller 78, but the magnetic shunt alloy layer 55 may be provided on the heating roller 78 and configured integrally.

  With this configuration, heat generation by the induction heating unit 89 can be suppressed at high temperatures. That is, during the fixing operation, the induction heating means 89 is controlled so that the fixing belt 77 reaches a predetermined temperature. At this time, the magnetic shunt alloy layer 55 is maintained at a temperature equal to or lower than the Curie point. The magnetic flux generated in 89 forms a loop along the magnetic shunt alloy layer 55, and the heating roller 78 can be heated by induction heating. However, for example, when a narrow sheet is passed, the heat of the non-sheet passing portion is not taken away by the sheet, and the temperature of the heating roller 78 in the non-sheet passing portion is increased. Therefore, the magnetic shunt alloy layer 55 near the heating roller 78 also rises in temperature, exceeds the Curie point temperature, and the magnetic shunt alloy layer 55 transmits the magnetic flux. The magnetic flux that has passed through the magnetic shunt alloy layer 55 reaches the aluminum alloy layer and a reverse magnetic flux is generated. Therefore, the magnetic flux in the non-sheet passing portion is reduced, and heat generation due to induction heating can be suppressed. As described above, even if a narrow sheet is passed, it is possible to prevent the temperature of the non-sheet passing portion from increasing.

  Further, by using the image forming apparatus (FIG. 1) provided with the fixing device 25 having the above-described configuration, an image forming apparatus 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.

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 50 Cam 51 Tension spring 52 Gear 53 Rotation fulcrum 54 Coil 55 Magnetic shunt alloy layer 56 Magnetic shielding layer 57 One-way clutch 60 Journal portion 61, 64 Bearing 62 Compression spring 63 Gear 68 Rib 72 Pressure roller 74 Fixing member 77 Fixing belt 78 Heating roller 81 Frame 82 Pressure lever 83 Separation claw 84, 86 Heat source 85-1 Thermopile 85-2, 87 Thermistor 88 Entrance guide 89 Induction heating means 100 Copying machine main 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 (14)

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 rotator that is in pressure contact with the fixing member via the fixing belt to form a nip portion;
Arranged in this order in the pressing direction for forming the nip portion,
And a separating means for separating the heating rotator and the fixing member,
The fixing device according to claim 1, wherein 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.   The fixing device according to claim 1, wherein the separation unit separates the pressure rotating body and the fixing belt.   The said separating means separates the said heating rotary body and the said fixing member by releasing the press to the said heating rotary body side of the said pressurization rotary body for the said nip part formation. The fixing device according to 1 or 2. During a warm-up operation for raising the fixing belt to a predetermined temperature,
The fixing device according to claim 1, wherein the heating rotator and the fixing member are separated by the separation unit. The spacing means is
Pressurizing means for pressing the pressurizing rotator toward the heating rotator;
An urging means for urging the fixing member in a direction away from the heating rotator,
In the contact state between the heating rotator and the fixing member, the pressing force by the pressing means is larger than the urging force by the urging means,
5. The fixing according to claim 1, wherein in a separated state of the heating rotator and the fixing member, a pressing force by the pressing unit is smaller than an urging force by the urging unit. apparatus. A pressure rotator driving means for rotationally driving the pressure rotator;
A heating rotator driving means for rotationally driving the heating rotator,
In the state where the heating rotating body and the fixing member are separated by the separation means,
6. The fixing device according to claim 1, wherein the fixing belt rotates following the rotation of the heating rotator by the heating rotator driving unit. The rotation speed of the heating rotator by the heating rotator driving means is:
The heating rotator has a lower speed than a rotation speed when the heating rotator is driven and rotated via the fixing belt driven and rotated by the pressure rotator driven by the pressure rotator driving unit. The fixing device according to claim 6.   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. The fixing belt and the fixing member are in contact with each other through a rotating body provided on the fixing member at the nip portion entrance and / or outlet. The fixing device according to 1. The fixing member has a center of rotation provided on one of the inlet side or the outlet side of the nip portion,
10. The fixing device according to claim 1, wherein the separation unit separates the heating rotating body on a side not having the rotation center.   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 fixing device according to claim 1, wherein the heat source is an induction heating device provided inside or outside the heating rotator. For the induction heating device,
The fixing device according to claim 12, wherein a magnetic shunt alloy layer and a magnetic shielding layer are provided in this order. An image forming apparatus comprising the fixing device according to claim 1.

Images