JP2005165098A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of processing also a printing medium for frameless printing and quickly and stably performing separation processing, when separating the printing medium from the fixing device, after fixing processing because a fixing device capable of processing frameless printing is required recently for an image forming apparatus. <P>SOLUTION: A fixing belt 5 is stretched between a heat roller 4 to be heated by an eddy current formed by a magnetic field generating coil 3 and a core 2 and a pressurizing member 6, a pressure roller 7 is rotatably arranged on a position forming a nip part 9 in press-contact with the pressurizing member 6 via the fixing belt 5, and an are of about 2mm radius is formed on the terminal part of the nip part 9 of the pressurizing member 6. Consequently, a printing paper 10 to which fixing processing is applied can be separated smoothly from the fixing belt 5 on the terminal part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer, a copying machine, and a facsimile, and more particularly to a structure of a fixing device that heats and fixes a recording material on a print medium.

Conventionally, as a fixing device in an image forming apparatus such as a copying machine, a printer, or a facsimile, when a toner image carried on a printing medium passes through a nip between a fixing roller and a pressure roller, In order to prevent the print medium from the nip from sticking to the surface of the fixing roller due to the adhesive force, for example, in order to separate the print medium from the nip from the surface of the fixing member in the vicinity of the exit of the nip. Some fixing member-side separating means (for example, a sheet-like separating member) is arranged with respect to the surface of the fixing member (for example, see Patent Document 1).
Japanese Unexamined Patent Publication No. 2003-107947 (page 6, FIG. 2)

  However, in the above-described fixing device, at least the front end portion of the print medium needs to be naturally separated from the fixing roller. For this reason, a predetermined blank portion (a region where printing is not performed) must be provided at the front end of the print medium. . For this reason, there is a problem in that printing cannot be performed on the tip portion and the recent needs for borderless printing cannot be met.

  An object of the present invention is to provide a fixing device that can suppress the margin width necessary for separation after fixing at the leading end in the conveyance direction of the printing medium to a width that can meet the recent needs for borderless printing. There is to do.

The fixing device according to the present invention includes:
A belt that moves along a predetermined path, and belt support means that stretches and supports the belt;
Heat generating means for supplying heat to the belt, and a rotating body that presses the belt supporting means through the belt and forms a nip portion that sandwiches the belt together with the belt supporting means,
The belt support means includes a facing surface that faces the rotating body, and a curved portion formed at a downstream end portion of the facing surface in the moving direction of the belt, and the belt support of the nip portion. The nip surface of the means is formed so as to include the facing surface and the curved portion.

  Furthermore, an image forming apparatus according to the present invention includes the above-described fixing device, and the fixing device is supplied with a printing medium onto which a toner image is transferred and fixed.

  According to the present invention, the width of the margin (the portion where printing is not performed) provided at the front end portion of the print medium necessary for separating the print medium from the belt of the fixing device after fixing is extremely small. Since the print medium is not heated by the belt after fixing, the print medium can be smoothly separated from the belt, and the fixing device and image formation suitable for high-speed printing are also possible. An apparatus can be provided.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing a main configuration of an image forming apparatus 50 including a fixing device according to the present invention.

  The printing paper 10 loaded on the paper feed tray 61 of the paper feed unit 51 is fed by the paper feed roller 62 and conveyed to the image forming unit 52 along the conveyance path 60. The printing paper 10 conveyed to the image forming unit 52 is conveyed on the photosensitive drum 56 by an unillustrated developer (hereinafter referred to as toner) and an unillustrated developing means while being conveyed by the conveying belt 55. The electrostatic latent image that has been visualized is transferred by the transfer roller 65. For example, four developing devices including the pair of photosensitive drums 56 and the transfer roller 65 are disposed along the conveyance path 60, and the toner images of the respective colors of yellow, magenta, cyan, and black are sequentially printed from the upstream side to the printing paper 10. Sequentially formed on top.

  The printing paper 10 to which the toner image is transferred passes through the image forming unit 52 and is conveyed to the fixing device 1. The toner on the printing paper 10 conveyed to the fixing device 1 is heated and pressurized by the fixing belt 5 and the pressure roller 7 (FIG. 2) that are rotated while being pressed against each other as will be described later. Melted and fixed. The printing paper 10 on which the toner image has been fixed is conveyed to the paper discharge section 54 and discharged to the paper stacker section 58 at the top of the apparatus by the paper discharge roller 57.

  FIG. 2 is a configuration diagram illustrating a main configuration of the fixing device 1 according to the first embodiment of the present invention. As described above, the fixing device 1 is provided in the image forming apparatus 50 and is disposed on the downstream side of the image forming unit 52.

  In the figure, a heating roller 4 formed of a metallic pipe made of aluminum, iron, stainless steel or the like is rotatably held in the fixing device 1 by holding means (not shown), and further rotated in the direction of arrow A by a driving means (not shown). Driven. The heating roller 4 includes a core 2 and a magnetic field generating coil 3 wound around the core 2. The core 2 is made of a ferromagnetic material having high electrical resistance, such as ferrite, and converges the magnetic flux generated by the magnetic field generating coil 3.

  The pressure member 6 is made of a highly heat-resistant and heat-insulating material such as silicon, fluorine-based, highly heat-resistant resin such as PI (poly imide) or PAI (poly amide imide), or a sintered body such as alumina or glass. And fixedly arranged at a predetermined position in the fixing device 1. A fixing belt 5 is stretched between the pressure member 6 and the heating roller 4.

  The fixing belt 5 is configured so that the heat capacity does not become too large, and an elastic layer 5b is provided on a base 5a as shown in FIG. 4 which is a partially enlarged view thereof. As the thin base 5a of the fixing belt 5, for example, in the case of a base made of nickel or pyrimido, a thickness of about 30 to 150 μm is appropriate, and as the elastic layer 5b, a silicon rubber having a thickness of about 50 to 300 μm, Alternatively, a fluorine resin system having a thickness of about 10 to 50 μm is preferable, and it is formed as thin as possible to improve the thermal response.

  As shown in FIG. 5 showing the internal structure of the pressure roller 7, the pressure roller 7 is composed of a pipe-shaped cored bar 7a and an elastic layer 7b formed therearound. The cored bar 7a includes aluminum, iron, and stainless steel. Metal pipes such as are used. Then, as shown in FIG. 2, at a position where the nip portion 9 is formed by being pressed against the pressure member 6 via the fixing belt 5, it is rotatably held by a holding means (not shown). The nip portion 9 here is a portion where the fixing belt 5 is sandwiched between the pressure member 6 and the pressure roller 7. The pressure member 6 and the heating roller 4 correspond to a first support member and a second support member, respectively, of the belt support means, and the pressure roller 7 corresponds to a rotating body that forms a nip portion.

  3 is an enlarged view for explaining the shape of the pressure member 6. As shown in FIG. 3, the pressure member 6 has at least a bottom surface 6b facing the pressure roller 7 (FIG. 2). In the present embodiment, a radius R of curvature (R) is provided at the downstream end 6a of the printing paper 10 in the conveyance direction (indicated by arrow D). 0.0mm or less is set.

  When the nip portion 9 (FIG. 2) is formed, the nip surface on the pressure member 6 side that forms the nip portion 9 is added to the flat bottom surface 6b facing the pressure roller 7, and the R is It is comprised so that it may reach even part of the formed front-end | tip part 6a.

  In FIG. 2, the fixing belt 5 moves in the direction of arrow B by the rotation of the heating roller 4 in the direction of arrow A, as will be described later. During this time, the fixing belt 5 is instantaneously heated by contact with the heating roller 4. The nip portion 9 is desired to have a temperature characteristic that the surface is cooled instantaneously. On the other hand, however, the fixing belt 5 is designed to have a heat capacity necessary to sufficiently melt and fix the toner transferred on the printing paper 10 at the pressure portion between the fixing belt 5 and the pressure roller 7. It must be done. Therefore, the thickness of the fixing belt 5 is set in a range that satisfies both of these requirements.

  The operation of the above configuration will be described below with reference mainly to FIG.

  When a drive current is supplied to the magnetic field generating coil 3 by a drive power supply (not shown), the core 2 converges the magnetic flux generated thereby, and an eddy current is generated in the heating roller 4. The heating roller 4 generates heat due to Joule heat at this time. Therefore, the magnetic field generating coil 3, the core 2, the driving power source (not shown), and the heating roller 4 correspond to heat generating means.

  The heating roller 4 rotates in a direction indicated by an arrow A while being heated by a driving unit (not shown) and generates heat. By this rotation, the fixing belt 5 heated by heat transfer moves in a direction indicated by an arrow B. The heated fixing belt 5 and the pressure member 6 slide, and the pressure roller 7 that forms the pressure member 6 and the nip portion 9 sandwiching the fixing belt 5 is moved by the arrow with the rotation of the fixing belt 5. Rotate in C direction.

  In this state, the printing paper 10 onto which the toner image has been transferred by the image forming unit 52 (FIG. 1) is conveyed to the nip 9 formed by the pressure member 6 and the pressure roller 7 with the fixing belt 5 interposed therebetween. Then, while passing through the nip portion 9, sufficient heat and pressure are applied and fixing is performed.

  At this time, the fixing belt 5 is partially released because the fixing belt 5 is released from the pressure contact state at the leading end 6a (FIG. 3) where the radius of curvature R of the pressing member 6 is formed, and the moving direction is suddenly changed. Pulls strongly to cause distortion. The recording paper 10 that is slightly adhered to the fixing belt 5 due to the adhesive force of the toner generated by the fixing is separated from the fixing belt 5 due to distortion such as elongation of the fixing belt 5 at this time, and proceeds straight as it is. It is discharged from the fixing device 1.

  However, a thinner printing paper 10 is used, and the radius of curvature R of the tip 6a (FIG. 3) of the pressure member 6 is relatively large. Further, as shown in FIG. ), The recording paper 10 is not separated from the fixing belt 5 due to the adhesive force of the toner generated by the fixing, or does not move straight ahead. May be bent and not discharged from the fixing device 1.

  In the grab shown in FIG. 7, the printing paper 10 is normally separated from the fixing belt 5 when the printing paper 10 is fixed by the fixing device 1 including the pressure member 6 having a radius R of curvature at the leading end 6a. The relationship between the minimum necessary separable margin width a ′ and the radius of curvature R to be performed is plotted by experiment. This experiment was conducted on 32 (lb), 24 (lb), and 17 (lb) A4 size printing papers as typical of thick paper, plain paper, and thin paper. Further, as an experimental condition, a toner image is formed on the entire surface of printing paper of 100% cyan, 100% magenta, and 100% yellow, which has the maximum print density under normal use.

  As can be understood from the graph, the minimum required separable margin width as the radius of curvature R of the tip 6a (FIG. 3) of the pressing member 6 increases and the thickness of the printing paper decreases. On the contrary, by setting the radius of curvature R to be small, the minimum required separable margin width a ′ can be reduced even in the case of thin printing paper with the worst separation. For example, when the radius of curvature R is 2 mm, the detachable margin width a ′ required for normal separation can be set to about 0.5 mm even for thin printing paper.

  On the other hand, even if the curvature radius R is made as small as possible, the separable margin width a ′ has a limit and cannot be made any smaller. This is because of the flexibility of the fixing belt 5, for example, even if the radius of curvature R is 0 mm, the radius of curvature of the surface of the fixing belt 5 does not become zero. The minimum radius of curvature R measured in the experiment is 0.1 mm as shown in the graph of FIG. 7 because the radius of curvature of the surface of the fixing belt 5 is not limited even if the radius of curvature R is further reduced. This is because it was determined that there is no meaning because it does not become small and also causes deterioration of slidability.

  In recent image forming apparatuses, the need for borderless printing such as photographs and posters has been increasing due to higher image quality. Therefore, the margin width “a” at the leading end is reduced to about 0.5 mm even in a normal printing medium. However, it is possible to satisfy this requirement by setting the radius of curvature R of the tip 6a of the pressure member 6 to 2 mm or less.

  In the present embodiment, the configuration of the fixing belt 5 has been described as a two-layer structure of the base body 5a and the elastic layer 5b as shown in FIG. 4, but is not limited to this. For example, FIG. As shown in a), the release layer 5c may be formed on the upper layer of the elastic layer 5b. Furthermore, as shown in FIG. 5B, the release layer 5c may be directly formed on the substrate 5a. good. In the pressure roller 7 as well, the elastic layer 7b is provided with a releasability as required, or a release layer is formed on the elastic layer 7b in the fixing belt 5 as in FIG. 8A. It may be formed.

  As described above, according to the fixing device 1 of the present embodiment, the recording sheet 10 that is slightly adhered to the fixing belt 5 by the adhesive force of the toner generated by the fixing is the terminal portion of the nip portion 9. Is separated from the fixing belt 5 by distortion such as elongation of the fixing belt 5 that occurs at the tip portion 6a where the rounded portion of the pressure member 6 corresponding to is formed. In addition, the printing paper 10 separated from the fixing belt 5 at the end portion of the nip portion 9 is not heated again in contact with the fixing belt 5, so that the winding around the fixing belt 5 is avoided. Can do.

  Further, by setting the radius of curvature R of the end portion 6a of the pressure member 6 to 2.0 mm or less, the margin width a of the front end portion of the printing paper 10 can be reduced to 0.5 mm or less, and there is no edge. The printing needs can be almost satisfied. Furthermore, since the separation of the printing paper 10 and the fixing belt 5 can be performed reliably and stably, it is possible to cope with high-speed printing.

Embodiment 2. FIG.
FIG. 9 is a configuration diagram showing a main configuration of the fixing device 11 according to the second embodiment of the present invention.

  As shown in this block diagram, the fixing device 11 of the present embodiment is mainly different from the fixing device 1 of Embodiment 1 (see FIG. 2) in that the core 12 and the magnetic field generating coil 13 are different. However, a tension compensation roller 15 that is integrated with the pressure member 14 and presses the fixing belt 5 is newly provided. Accordingly, in the fixing device 11 shown in FIG. 9, parts that are the same as those of the fixing device 1 of the first embodiment shown in FIG. Will be explained with emphasis.

  The shape of the portion of the pressure member 14 forming the pressure roller 7 and the nip portion 9 is exactly the same as that of the pressure member 6 shown in FIG. 2 described in the first embodiment. The description on the configuration of the part concerned is omitted here in order to avoid duplication.

  The core 12 and the magnetic field generating coil 13 wound around the core 12 are integrally formed on the pressing member 14, and the core 2 made of a ferromagnetic material such as ferrite having a high electric resistance has a magnetic field The magnetic flux generated by the generating coil 3 is converged.

  The tension compensating roller 15 is rotatably supported in the fixing device 11 by a support member (not shown), and is further pressed by an urging means (not shown) from the outside of the fixing belt 5 in the direction of arrow E. Rotate with 5 The tension compensating roller 15 is not particularly limited in size and material, and may not rotate. The roller surface may be covered with felt, silicon sponge, or the like.

  The operation of the above configuration will be described with reference to FIG.

  When a drive current is supplied to the magnetic field generating coil 13 by a drive power supply (not shown), the core 12 converges the magnetic flux generated thereby, and an eddy current is generated in the heating roller 4. The heating roller 4 generates heat due to Joule heat at this time. The heating roller 4 rotates in a direction indicated by an arrow A while being heated by a driving unit (not shown) and generates heat. By this rotation, the fixing belt 5 heated by heat transfer moves in a direction indicated by an arrow B. The heated fixing belt 5 and the pressure member 14 slide, and the pressure roller 7 which forms the pressure member 14 and the nip portion 9 with the fixing belt 5 interposed therebetween is moved by an arrow with the fixing belt 5. The tension compensation roller 15 rotates in the direction C, and rotates while pressing the fixing belt 5 from the outside of the fixing belt 5.

  In this state, the printing paper 10 onto which the toner image has been transferred by the image forming unit 52 (FIG. 1) is conveyed to the nip 9 formed by the pressure member 14 and the pressure roller 7 with the fixing belt 5 interposed therebetween. Then, while passing through the nip portion 9, sufficient heat and pressure are applied to perform fixing. At this time, the process of separating the printing paper 10 from the fixing belt 5 is exactly the same as that in the first embodiment, and a description thereof is omitted here.

  As described above, according to the fixing device 11 of the present embodiment, in addition to the effects of the first embodiment, the number of parts can be reduced by integrating the core 12, the magnetic field generating coil 13, and the pressing member 14. Can be reduced. Further, the tension compensating roller 15 reduces distortion such as elongation of the fixing belt 5 generated at the front end portion 6a of the pressure member 6 corresponding to the end portion of the nip portion 9 due to the elongation of the fixing belt 5 with time. As a result, the separation effect of the printing paper 10 can be maintained for a long time. Further, when the surface of the tension compensating roller 15 is covered with felt, silicon sponge, or the like, the toner adhering to the surface of the fixing belt 5 can be scraped off, and the surface can be kept clean.

Embodiment 3 FIG.
FIG. 10 is a configuration diagram showing a main configuration of the fixing device 21 according to the third embodiment of the present invention.

  As shown in this configuration diagram, the fixing device 21 of the present embodiment is mainly different from the fixing device 1 of the first embodiment (see FIG. 2) in that the core 22 and the magnetic field generating coil 33 are different. Is a point disposed around the heating roller 4. Therefore, the fixing device 21 shown in FIG. 10 is different from the fixing device 21 of the first embodiment shown in FIG. Will be explained with emphasis.

  The core 22 and the magnetic field generating coil 23 wound around the core 22 are fixed and held at predetermined positions near the periphery of the heating roller 4 in the fixing device 21 by holding means (not shown).

  In the above configuration, when a driving current is supplied to the magnetic field generating coil 23 by a driving power supply (not shown), the magnetic flux generated thereby is converged by the core 22 and an eddy current is generated in the heating roller 4. The heating roller 4 generates heat due to Joule heat at this time. Since other operations are the same as those in the first embodiment, the description thereof is omitted here.

  As described above, according to the fixing device 21 of the present embodiment, in addition to the effects of the first embodiment, the core 22 and the magnetic field generating coil 23 are disposed outside the heating roller 4 and the fixing belt 5. Therefore, it is possible to increase the heat dissipation effect, and the heat generation efficiency with respect to the input power due to the increase in electrical resistance due to heating of the magnetic field generating coil 23 in continuous printing or the decrease in magnetic characteristics due to the heating of the core 22. Can be prevented.

Embodiment 4 FIG.
FIG. 11 is a configuration diagram showing a main configuration of the fixing device 31 according to the fourth embodiment of the present invention.

  As shown in this configuration diagram, the fixing device 31 of the present embodiment is mainly different from the fixing device 1 of the first embodiment (see FIG. 2) in that a halogen heater 33 is used as a heat generating means. A heating member 32 that is not rotationally driven is provided in place of the heating roller 4 (FIG. 2). Therefore, in the fixing device 31 shown in FIG. 11, parts that are the same as those of the fixing device 1 of the first embodiment shown in FIG. Will be explained with emphasis.

  The heating member 32 is a substantially semi-cylindrical member fixedly disposed at a predetermined position in the fixing device 31 and is formed of a metallic member such as aluminum, iron, or stainless steel. A fixing belt 5 is stretched between the outer peripheral surface of the heating member 32 and the pressure member 6, and a halogen heater 33 is disposed at a predetermined position in an inner region surrounded by the fixing belt 5. As shown in the figure, the pressure roller 7 is rotatably held at a position where the nip portion 9 is formed by being pressed against the pressure member 6 via the fixing belt 5, and is further arrowed by a driving means (not shown). It is rotationally driven in the C direction. Accordingly, the fixing belt 5 moves in the direction of the arrow B by the rotation with the pressure roller 7. In the fixing device 31, the pressure member 6 and the heating member 32 correspond to belt support means, and the halogen heater 33 corresponds to a heating element.

  The operation of the above configuration will be described with reference to FIG.

  When the halogen heater 33 is turned on by a power source (not shown), the energy radiated from the halogen heater 33 heats the heating member 32 and further heats the fixing belt 5 directly. The fixing belt 5 heated directly or by heat transfer moves in the direction of arrow B and slides on the pressure member 6. The pressure member 6 forms a pressure roller 7 and a nip portion 9 with the fixing belt 5 interposed therebetween. To do.

  In this state, the printing paper 10 onto which the toner image has been transferred by the image forming unit 52 (FIG. 1) is conveyed to the nip 9 formed by the pressure member 6 and the pressure roller 7 with the fixing belt 5 interposed therebetween. Then, while passing through the nip portion 9, sufficient heat and pressure are applied and fixing is performed. At this time, the process of separating the printing paper 10 from the fixing belt 5 is exactly the same as that in the first embodiment, and a description thereof is omitted here.

  As described above, according to the fixing device 31 of the present embodiment, since the halogen heater is used as the heating element, the configuration can be simplified as compared with the respective embodiments using the magnetic field generating coil and the core. Both the member and the drive power supply can reduce the cost. Moreover, since the heating member 32 can be fixedly arranged because it is not rotationally driven, the configuration can be similarly simplified and the cost can be reduced.

Embodiment 5 FIG.
FIG. 12 is a configuration diagram showing a main configuration of the fixing device 41 according to the fifth embodiment of the present invention.

  As shown in this configuration diagram, the fixing device 41 according to the present embodiment is mainly different from the fixing device 31 according to the fourth embodiment (see FIG. 11) in that the heating members 42 and 43 are arranged in two places. And a point where the upper surface of the pressure member 41 is mirror-finished with a circular arc cross section. Therefore, the fixing device 41 shown in FIG. 12 has the same reference numerals as those in the fixing device 1 of the first embodiment shown in FIG. 2 and the fixing device 31 shown in the fourth embodiment shown in FIG. Or, omitting the drawings and omitting the description, the different points will be mainly described.

  The heating members 42 and 43 are substantially 1/4 cylindrical members that are fixedly arranged at important points in the fixing device 31 that determine the moving path of the fixing belt 5, and are metallic members such as aluminum, iron, and stainless steel. Is formed. The fixing belt 5 is stretched between the outer peripheral surfaces of the heating members 42 and 43 and the lower surface 44b of the pressure member 44, and the halogen heater 33 is disposed at a predetermined position in the inner region surrounded by the fixing belt 5. ing. Here, the shape of the portion of the pressure member 44 that is in sliding contact with the fixing belt 5 is exactly the same as the shape of the same portion of the pressure member 6 described in the first embodiment.

  As shown in the figure, the pressure roller 7 is rotatably held at a position where the nip portion 9 is formed by being pressed against the pressure member 44 via the fixing belt 5 and is further moved by an arrow (not shown) by a driving means. It is rotationally driven in the C direction. Accordingly, the fixing belt 5 moves in the direction of the arrow B by the rotation with the pressure roller 7.

  The inner peripheral surfaces 42a and 43a of the heating members 42 and 43 and the upper surface 44c having a circular arc shape of the pressing member 44 are mirror-finished or mirror-coated, respectively. Accordingly, each of these mirror-finished or mirror-coated surfaces reflects and converges the energy radiated from the halogen heater 33 and heats the fixing belt 5 positioned at the reflection destination. For this reason, it is necessary to consider the shape and arrangement of the heating members 42 and 43 and the pressure member 44 so that the energy reflected on each surface that is mirror-finished or mirror-coated reaches the fixing belt 5 as much as possible.

  The operation of the above configuration will be described with reference to FIG.

  When the halogen heater 33 is turned on by a power source (not shown), the fixing belt 5 is heated directly or after the energy radiated from the halogen heater 33 is reflected. As a result, the heated fixing belt 5 moves in the direction of arrow B and slides with the pressure member 44, and the pressure member 44 forms the pressure roller 7 and the nip portion 9 with the fixing belt 5 interposed therebetween.

  In this state, the printing paper 10 onto which the toner image has been transferred by the image forming unit 52 (FIG. 1) is conveyed to the nip 9 formed by the pressure member 44 and the pressure roller 7 with the fixing belt 5 interposed therebetween. Then, while passing through the nip portion 9, sufficient heat and pressure are applied and fixing is performed. At this time, the process of separating the printing paper 10 from the fixing belt 5 is exactly the same as that in the first embodiment, and a description thereof is omitted here.

  As described above, according to the fixing device 41 of the present embodiment, in addition to the same effects as those of the fourth embodiment described above, the energy reflected by the mirror-finished or mirror-coated surface is efficiently fixed on the fixing belt. The heating efficiency with respect to the input power can be further increased.

FIG. 2 is a configuration diagram illustrating a main configuration of an image forming apparatus 50 including a fixing device according to the present invention. 1 is a configuration diagram illustrating a main configuration of a fixing device 1 according to a first embodiment of the present invention. It is an enlarged view for demonstrating the shape of the pressurization member 6. FIG. 4 is a partially enlarged view for explaining the configuration of the fixing belt 5. FIG. FIG. 3 is a configuration diagram for explaining a configuration of a pressure roller 7. 4 is an explanatory diagram for explaining a margin width a which is an unprinted portion at a leading end portion of the printing paper 10. FIG. 6 is a graph in which a relationship between a minimum separable margin width a ′ required for separation of the printing paper 10 from the fixing belt 5 and a radius of curvature R is plotted by experiment. (A), (b) is a figure where it uses for description of the other structural example of the fixing belt 5. FIG. It is a block diagram which shows the principal part structure of the fixing device 11 of Embodiment 2 by this invention. It is a block diagram which shows the principal part structure of the fixing device 21 of Embodiment 3 by this invention. It is a block diagram which shows the principal part structure of the fixing device 31 of Embodiment 4 by this invention. It is a block diagram which shows the principal part structure of the fixing device 41 of Embodiment 5 by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Fixing device, 2 Core, 3 Magnetic field generating coil, 4 Heating roller, 5 Fixing belt, 5a Base body, 5b Elastic layer, 6 Pressure member, 6a Tip part, 6b Bottom surface, 7 Pressure roller, 7a Core metal, 7b Elastic layer, 9 nip, 10 printing paper, 10a tip, 11 fixing device, 12 core, 13 magnetic field generating coil, 14 pressure member, 15 tension compensating roller, 21 fixing device, 22 core, 23 for generating magnetic field Coil, 31 fixing device, 32 heating member, 33 halogen heater, 41 fixing device, 42 heating member, 42a inner peripheral surface, 43 heating member, 43a inner peripheral surface, 44 pressure member, 44c upper surface, 50 image forming device, 51 Paper feed unit, 52 Image forming unit, 54 Paper discharge unit, 55 Conveyor belt, 56 Photoconductor Ram, 57 discharge roller, 58 paper stacker unit, 60 conveyance path 61 feed tray, 62 paper feed roller, 65 a transfer roller.

Claims (11)

A belt that moves along a predetermined path;
Belt support means for stretching and supporting the belt;
Heat generating means for supplying heat to the belt;
A rotating body that presses against the belt support means via the belt and forms a nip portion that sandwiches the belt together with the belt support means,
The belt support means includes a facing surface that faces the rotating body, and a curved portion formed at a downstream end portion of the facing surface in the moving direction of the belt, and the belt support of the nip portion. The fixing device is characterized in that a nip surface of the means includes the facing surface and the curved portion. The belt support means includes a first support member that has the nip surface and presses against the rotating body via the belt, and a roller-shaped second support member that is rotatably disposed. The fixing device according to claim 1. The fixing device according to claim 2, wherein the heat generating unit includes a magnetic field generating unit and a magnetic flux converging unit for generating heat by generating an eddy current in the second support member. The fixing device according to claim 3, wherein the magnetic field generating unit and the magnetic flux converging unit are disposed inside the second support member. The fixing device according to claim 3, wherein the magnetic field generating unit and the magnetic flux converging unit are disposed in the vicinity of the second support member. The fixing device according to claim 3, wherein the magnetic field generating unit and the magnetic flux converging unit are formed integrally with the first support member. The fixing device according to claim 1, wherein the heat generating unit includes a heating element that is disposed in an inner region of the belt and heats the belt or the belt and the belt support unit. 8. The fixing device according to claim 7, wherein a surface of the belt supporting unit facing the heating element is mirror-finished or mirror-coated, and heat reflected by the mirror surface reaches the belt. The fixing device according to claim 1, further comprising a tension compensation unit that presses the belt to increase a tension of the belt. 10. The fixing device according to claim 1, wherein a radius of curvature of 2.0 mm or less is formed as the curved portion. An image forming apparatus comprising: the fixing device according to claim 1, wherein a printing medium having a toner image transferred thereto is supplied to the fixing device and fixed.

Images