JP2008111907A - Fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of lessening the waviness of transfer material caused by the inverted crown shape of a fixing means, and to provide an image forming apparatus using the same. <P>SOLUTION: The fixing device is equipped with: the fixing means T comprising a heating rotating body 172 having a heating element H and a pressure rotating body 173 opposed to the heating rotating body 172 to form a nip part, at least either of which has the inverted crown shape; and a post-fixing roller 11 provided on the downstream side of the heating rotating body 172 and the pressure rotating body 173. The post-fixing roller 11 has stronger conveying force on both end sides than at a center part in a width direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In particular, the present invention relates to a fixing device for preventing a transfer material from undulating immediately after a toner image is thermally fixed on a sheet, and an image forming apparatus using the same.

  In general, an electrophotographic toner image forming unit includes a photosensitive member as an image bearing member having a photosensitive layer on an outer peripheral surface, a charging unit that uniformly charges the outer peripheral surface of the photosensitive member, and a uniform charging unit using the charging unit. An exposure unit that selectively exposes the outer peripheral surface charged to form an electrostatic latent image, and a toner as a developer is applied to the electrostatic latent image formed by the exposure unit to form a visible image ( Developing means for forming a toner image).

  As a rotary type image forming apparatus for forming a color image, the toner image forming means as described above is arranged on the intermediate transfer belt. The toner images on the photoconductor by these toner image forming means are sequentially transferred to an intermediate transfer belt, and a plurality of toner images (for example, yellow, cyan, magenta, black (black)) are superimposed on the intermediate transfer belt, There is an intermediate transfer belt type that obtains a color image on an intermediate transfer belt.

  As the fixing device of the image forming apparatus having the above-described configuration, the recording material guide member passes through the nip portion between the fixing roller and the pressure roller, and is closer to the pressure roller than the straight normal line connecting the centers of the fixing roller and the pressure roller. Depending on the recording material, the opposite side of the recording material guide member is opened, so that there is no wavy wrinkles in the recording material or curling becomes large, and jamming can be easily performed (Patent Document 1). reference).

In addition, a paper discharge means for discharging the paper fixed and conveyed between the reverse crown-shaped heating roller and the pressure roller having a uniform diameter to the downstream side is used to convey the paper at the center of the paper width at the end of the paper. In order to apply a relatively strong tension in the direction, (1) the peripheral speed of the central driving roller is made faster than that of the side driving roller, and (2) the force pressing the driven roller against the driving roller is made stronger at the central portion. (3) By arranging the central driving roller to be denser than the side driving roller, vertical wrinkles can be generated by the reverse crown-shaped heating roller, and (1), (2) or (3) Can prevent rib-like wrinkles and undulations that occur in the lateral direction of the paper (see Patent Document 2).
Japanese Patent Laid-Open No. 5-6117 JP-A-5-40428

  However, in the invention described in Patent Document 1, since there is no roller after fixing, the recording paper and the guide are always in a state of being rubbed, and the print is scratched due to uneven gloss (gloss) and toner adhesion to the guide. There is a risk. Further, since a large amount of paper dust is generated, there is a possibility that a lump of toner and paper dust adheres to the recording paper or accumulates on a thermistor and a detection temperature shift occurs.

  Further, in the invention described in Patent Document 2, if the fixing roller paper conveyance force is made larger than the post-fixing roller conveyance force in order to compensate for the conveyance force that is insufficient at the center portion of the reverse crown roller, an extreme setting is required. As a result, there is a possibility that extreme wear of the roller after fixing or unevenness in gloss (gloss) of the printed image may occur.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the prior art, and its object is to fix a wave of a transfer material due to an inverted crown shape of a fixing roller, and an image forming apparatus using the same. Is to provide.

  The fixing device of the present invention that achieves the above object comprises a heating rotator having a heating element and a pressure rotator that forms a nip portion facing the heating rotator, at least one of which has a reverse crown shape. And a post-fixing roller provided downstream of the heating rotator and the pressure rotator, and the post-fixing roller has a conveying force at both ends in the width direction larger than that at the center. Therefore, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing roller.

  In addition, the post-fixing roller has a both-end side post-fixing roller disposed on both ends in the width direction and a central post-fixing roller disposed on the center in the width direction, and the interval between the both-end side post-fixing rollers However, since it is smaller than the interval between the rollers after fixing at the central portion, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing means.

  In addition, the post-fixing roller has both end-side post-fixing rollers disposed at both ends in the width direction and a central post-fixing roller disposed at the center in the width direction. Since the diameter is larger than the outer diameter of the post-fixing roller at the center, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing means.

  Further, the post-fixing roller has both end-side post-fixing rollers disposed at both ends in the width direction and a center post-fixing roller disposed at the center in the width direction, and the friction between the both-end-side post-fixing rollers. Since the force is larger than the frictional force of the post-fixing roller at the central portion, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing means.

  Further, the post-fixing roller has a both-end-side post-fixing roller disposed at both ends in the width direction and a center-post-fixing roller disposed at the center in the width direction, and a nip between the both-end-side post-fixing rollers. Since the pressure is larger than the nip pressure of the post-fixing roller at the central portion, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing means.

  Furthermore, an image forming apparatus using the fixing device of the present invention includes an image carrier, a developer carrier that develops a latent image on the image carrier, and the image carrier developed by the developer carrier. An intermediate transfer member that transfers the image on the image, a secondary transfer unit that transfers the image on the intermediate transfer member to a transfer material, and the fixing device that fixes the image on the transfer material. Therefore, it is possible to reduce the waviness of the transfer material due to the reverse crown shape of the fixing unit.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the first embodiment, the end-side driving and fixing rollers 12b are densely arranged in a larger number than the central driving and fixing rollers 12a. FIG. 1 is a perspective view of a fixing device according to a first embodiment of the present invention, FIG. 2 is a perspective view of the fixing device according to the first embodiment in an operation state with a sheet S interposed therebetween, and FIG. FIG. 2 shows a front view and a cross-sectional view of the fixing device according to the first embodiment. In the figure, 1 is a fixing device, 11 is a post-fixing roller, 12 is a post-fixing roller, 12a is a central driving post-fixing roller, 12b is an end side driving post-fixing roller, 13 is a driven post-fixing roller, and 13a is a central roller. Part driven post-fixing roller, 13b post-end side driven fixing roller, T fixing roller as fixing means, 172 heating roller as heating rotator, H heater as heating element, 173 as pressure rotator The pressure roller S is a sheet as a transfer material.

  As shown in FIG. 1, the fixing device 1 includes a heating roller 172, a pressure roller 173, and the like. The heating roller 172 incorporates a heater H and is supported rotatably at both ends. The pressure roller 173 is installed in parallel with the heating roller 172, has an inverted crown shape in which the outer dimensions of both end portions are larger than the central portion, and both end portions are rotatably supported. The sheet S on which the toner image is heat-fixed by the heating roller 172 and sent out while being sandwiched between the heating roller 172 and the pressure roller 173 is discharged further downstream by the post-fixing roller 11.

  The post-fixing roller 11 includes a driving post-fixing roller 12 provided on one side of the paper S, a driven post-fixing roller 13 provided on the other side of the paper S, and a post-fixing roller (not shown). Drive means.

  The four post-fixing rollers 12 have four first ends in total, each having two central post-fixing rollers 12a provided at the central portion in the width direction, and two rollers disposed at a distance shorter than the central portion at both ends in the width direction. It is composed of a part-side driving post-fixing roller 12b and a second end-side driving post-fixing roller 12c, and is integrally driven by a post-fixing roller driving means (not shown). The driven post-fixing rollers 13 are provided with four first end portions, each having two central post-fixing rollers 13a provided at the central portion in the width direction, and two rollers arranged at a distance shorter than the central portion at both ends in the width direction. It comprises a part-side driven post-fixing roller 13b and a second end-side driven post-fixing roller 13c, which are respectively provided to face the driving post-fixing roller 12, pressed against the driving post-fixing roller 12 side, and driven post-fixing roller 12 Follow and rotate.

  As shown in FIGS. 2 and 3, in the fixing device arranged in this way, first, after the fixing, the heating roller 172 is heated by the heater H and the sheet S is sandwiched between the pressing roller 173. Transport to roller 11. At this time, due to the reverse crown shape of the pressure roller 173, the sheet S has a small amount of conveyance at the center in the width direction and a large amount of conveyance at both ends. Due to the difference in the transport amount, the sheet S is loosened at both ends on the downstream side of the pressure roller 173, and wrinkles are likely to occur.

  Subsequently, as shown in FIGS. 2 and 3, the sheet S is sandwiched between the post-fixing roller 12 and the driven post-fixing roller 13 of the post-fixing roller 11 and conveyed. At this time, as shown in FIG. 3A, the distance between the two rollers, the first end side driving post-fixing roller 12b and the second end side driving post-fixing roller 12c of the post-fixing roller 12, respectively, The distance between the two rollers of the end side driven post-fixing roller 13b and the second end side driven post-fixing roller 13c of the driven post-fixing roller 13 is shorter than that of the central portion. It tends to be pulled from the part side to the both end parts side. Accordingly, it is possible to reduce the looseness of the sheet S on the both end sides generated between the heating roller 172 and the pressure roller 173 and the post-fixing roller 11.

  FIG. 4 shows an example in which the arrangement of the first embodiment is compared with another arrangement. 4A shows a case where four post-fixing rollers 11 are arranged at equal intervals, FIG. 4B shows a case where six post-fixing rollers 11 are arranged at equal intervals, and FIG. This is a case of arrangement as in one embodiment. Table 1 shows the results of examining the wavy state of each paper edge.

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  Here, the post-fixing roller conveying force indicates a force required when the paper S is sandwiched between the post-fixing roller 11 and the paper S is pulled out by a tension gauge.

  In this way, the speed and conveying force of each post-fixing roller 11 are the same, but as shown in FIG. 4C, the number is denser at both end portions than the central portion of the post-fixing roller 11. By arranging in this way, the waviness at the edge of the paper S is reduced.

  Next, a second embodiment will be described. In the second embodiment, the outer diameter of the end portion driving post-fixing roller 32b is larger than that of the central portion driving post-fixing roller 32a. FIG. 5 is a perspective view of the fixing device according to the second embodiment of the present invention, FIG. 6 is a perspective view of the fixing device according to the second embodiment in a state where the paper S is sandwiched, and FIG. FIG. 5 is a plan view of a fixing device according to a second embodiment. In the figure, 21 is a roller after fixing, 22 is a roller after driving and fixing, 22a is a roller after driving and fixing at the center, 22b is a roller after driving and fixing at the end, 23 is a roller after driven fixing, and 23a is a roller after driven fixing at the center. , 23b is an end side driven post-fixing roller, T is a fixing roller, 172 is a heating roller, H is a heater, and 173 is a pressure roller.

  The heating roller 172 incorporates a heater H and is supported rotatably at both ends. The pressure roller 173 is installed in parallel with the heating roller 172, has an inverted crown shape in which the outer dimensions of both end portions are larger than the central portion, and both end portions are rotatably supported. The sheet S on which the toner image is thermally fixed by the heating roller 172 and is sent out while being sandwiched between the heating roller 172 and the pressure roller 173 is discharged further downstream by the post-fixing roller 21.

  The post-fixing roller 21 includes a driving post-fixing roller 22 provided on one side of the paper S, a driven post-fixing roller 23 provided on the other side of the paper S opposite to the driving post-fixing roller 22, and a post-fixing roller (not shown). Drive means, and is composed of an elastic body.

  Two post-fixing rollers 22 are provided at the center in the width direction, and two post-fixing rollers 22a are provided at the both ends of the width direction. And is integrally driven by a post-fixing roller driving means (not shown). The outer diameter of the end portion driving post-fixing roller 22b is larger than the outer diameter of the central portion driving post-fixing roller 22a.

  The driven post-fixing roller 23 includes two central driven post-fixing rollers 23a provided at the central portion in the width direction, and two end-side driven post-fixing rollers 23b provided one on each side in the width direction. It is pressed to the post-fixing roller 22 side by a pressing means such as a spring (not shown), and is driven to rotate by the post-fixing roller 22.

  In the fixing device configured as described above, as shown in FIGS. 6 and 7, first, after the fixing, the heating roller 172 is heated by the heater H and the sheet S is sandwiched between the pressing roller 173. Transport to roller 11. At this time, due to the reverse crown shape of the pressure roller 173, the sheet S has a small amount of conveyance at the center in the width direction and a large amount of conveyance at both ends. Due to the difference in the transport amount, the sheet S is loosened at both ends on the downstream side of the pressure roller 173, and wrinkles are likely to occur.

  Subsequently, the paper S is sandwiched between the post-fixing roller 22 and the driven post-fixing roller 23 of the post-fixing roller 21 and conveyed. At this time, the outer diameter of the end side driving post-fixing roller 22b of the post-fixing roller 22 is larger than the outer diameter of the center driving post-fixing roller 22a. Is larger than the sheet conveyance amount of the post-fixing roller 22a at the center. Accordingly, it is possible to reduce the looseness of the sheet S generated between the heating roller 172 and the pressure roller 173 and the post-fixing roller 21.

  Table 2 shows the wavy state at the edge of the sheet S with respect to the speed difference between the center driving post-fixing roller 22a and the end side driving post-fixing roller 22b.

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  Here, the gloss unevenness at the center will be described. Usually, since the post-fixing roller 21 is faster than the fixing roller T, slip occurs between the post-fixing roller 21 and the paper S. As a result, gloss unevenness is likely to occur in the printed image, particularly on the post-fixing drive roller 22 side, which is the printing contact side during double-sided printing. In the standby state (printing standby state), heat escapes from the both ends of the fixing roller T to the bearing and the frame. Therefore, the temperature distribution in the axial direction of the fixing roller T is usually high at the center and low at both ends. The axial temperature distribution of the fixing roller T immediately after the start of printing is also high at the center. As a result, gloss unevenness is likely to occur at the center.

  As shown in Table 2, by giving a speed difference between the center driving post-fixing roller 22a and the end side driving post-fixing roller 22b, the waviness at the end of the sheet S is reduced. In particular, preferably, when the difference in speed between the center driving post-fixing roller 22a and the end side driving post-fixing roller 22b is about 2% to 3%, wear and gloss unevenness are also reduced.

  In this embodiment, the outer diameter of the end-side drive fixing roller 22b is merely made larger than that of the center-side drive fixing roller 22a. However, after the end-side drive fixing roller 22b and the end-side driven fixing, The outer diameter of at least one of the rollers 23b may be larger than the center driven post-fixing roller 22a and the center driven post-fixing roller 23a.

  Next, a third embodiment will be described. In the third embodiment, the conveying force such as the frictional force and nip pressure of the end side driving post-fixing roller 32b is made larger than that of the central driving post-fixing roller 32a. 8 is a perspective view of the fixing device according to the third embodiment of the present invention, FIG. 9 is a perspective view of the fixing device according to the third embodiment in a state where the paper S is sandwiched, and FIG. 10 is a state where the paper S is sandwiched. The front view and sectional drawing of the fixing device which concern on 3rd Embodiment are shown. In the figure, 31 is a roller after fixing, 32 is a roller after driving and fixing, 32a is a roller after driving and fixing at the center, 32b is a roller after driving and fixing at the end, 33 is a roller after driven fixing, and 33a is a roller after driven fixing at the center. , 33b are end-side driven post-fixing rollers, T is a fixing roller, 172 is a heating roller, H is a heater, and 173 is a pressure roller.

  The heating roller 172 incorporates a heater H and is supported rotatably at both ends. The pressure roller 173 is installed in parallel with the heating roller 172, has an inverted crown shape in which the outer dimensions of both end portions are larger than the central portion, and both end portions are rotatably supported. The sheet S on which the toner image is thermally fixed by the heating roller 172 and is sent out while being sandwiched between the heating roller 172 and the pressure roller 173 is discharged further downstream by the post-fixing roller 31.

  The post-fixing roller 31 includes a driving post-fixing roller 32 provided on one side of the paper S, a driven post-fixing roller 33 provided on the other side of the paper S, and a post-fixing roller (not shown). Drive means.

  Two post-fixing rollers 32 are provided at the center in the width direction, and two post-fixing rollers 32a are provided at the both ends of the width direction. And is integrally driven by a post-fixing roller driving means (not shown). The conveying force of the end side driving post-fixing roller 32b is larger than the conveying force of the center driving post-fixing roller 32a.

  The driven post-fixing roller 33 includes two central driven post-fixing rollers 33a provided at the central portion in the width direction, and two end side driven post-fixing rollers 33b provided at the both ends in the width direction. It is pressed to the post-fixing roller 32 side by a pressing means such as a spring (not shown), and is rotated by being driven by the post-fixing roller 32.

  In the fixing device configured as described above, as shown in FIGS. 9 and 10, first, after the fixing, the heating roller 172 is heated by the heater H and the sheet S is sandwiched between the pressure roller 173. Transport to roller 31. At this time, due to the reverse crown shape of the pressure roller 173, the sheet S has a small amount of conveyance at the center in the width direction and a large amount of conveyance at both ends. Due to the difference in the transport amount, the sheet S is loosened at both ends on the downstream side of the pressure roller 173, and wrinkles are likely to occur.

  Subsequently, the sheet S is sandwiched between the post-fixing roller 32 and the driven post-fixing roller 33 of the post-fixing roller 31 and conveyed. At this time, since the conveying force of the post-fixing roller 32b on the end portion side of the post-fixing roller 2 is larger than that of the post-fixing roller 32a on the central portion, the sheet S has a large conveying amount on both ends. Become. Accordingly, it is possible to reduce looseness of the sheet S generated between the heating roller 172 and the pressure roller 173 and the post-fixing roller 1.

  Table 3 shows the corrugated state of the edge of the sheet S with respect to the conveying force of the center driving post-fixing roller 32a and the end side driving post-fixing roller 32b.

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  Here, the conveyance stability of the narrow paper indicates the stability of the paper conveyance only by the center driving post-fixing roller 32a.

  In this way, the wavy state at the end of the sheet S can be reduced by weakening the conveying force of the post-fixing roller 32a at the center portion relative to the post-fixing roller 32b at the end portion side.

  In the present embodiment, the conveying force of the end side driving post-fixing roller 32b is merely made larger than that of the center driving post-fixing roller 32a, but after the end side driving post-fixing roller 32b and the end side driven fixing. The conveying force of at least one of the rollers 33b may be greater than that of the center driven post-fixing roller 32a and the center driven post-fixing roller 33a.

  Next, a fourth embodiment will be described. The fourth embodiment is a combination of the first to third embodiments. 11 is a perspective view of the fixing device according to the fourth embodiment of the present invention, FIG. 12 is a perspective view of the fixing device according to the fourth embodiment in a state where the paper S is sandwiched, and FIG. 13 is a state where the paper S is sandwiched. FIG. 9 is a plan view of a fixing device according to a fourth embodiment. In the figure, reference numeral 41 is a post-fixing roller, 42 is a post-fixing roller, 42a is a central driving post-fixing roller, 42b is an end side driving post-fixing roller, 43 is a driven fixing roller, and 43a is a central driven post-fixing roller. 43b are end side driven post-fixing rollers, T is a fixing roller, 172 is a heating roller, H is a heater, and 173 is a pressure roller.

  The heating roller 172 incorporates a heater H and is supported rotatably at both ends. The pressure roller 173 is installed in parallel with the heating roller 172, has an inverted crown shape in which the outer dimensions of both end portions are larger than the central portion, and both end portions are rotatably supported. The sheet S on which the toner image is thermally fixed by the heating roller 172 and is sent out while being sandwiched between the heating roller 172 and the pressure roller 173 is discharged further downstream by the post-fixing roller 41.

  The post-fixing roller 41 includes a driving post-fixing roller 42 provided on one side of the paper S, a driven post-fixing roller 43 provided on the other side of the paper S opposite to the driving post-fixing roller 42, and a post-fixing roller (not shown). Drive means.

  Two post-fixing rollers 42 are provided at the central portion in the width direction, and the post-fixing rollers 42a are provided at the center, and four post-fixing rollers 42b are provided at the both ends in the width direction. And is integrally driven by a post-fixing roller driving means (not shown). The outer diameter and frictional force of the end side driving post-fixing roller 42b are larger than the outer diameter and frictional force of the central driving post-fixing roller 42a.

  The driven post-fixing rollers 43 include two central post-fixing rollers 43a provided at the central portion in the width direction, and four end-side driven post-fixing rollers 43b provided at the both ends in the width direction. It is pressed to the post-fixing roller 32 side by a pressing means such as a spring (not shown), and is rotated by being driven by the post-fixing roller 42. The frictional force of the end side driven post-fixing roller 43b is larger than the frictional force of the central part driven post-fixing roller 43a.

  In the fixing device configured as described above, as shown in FIGS. 12 and 13, first, after the fixing, the heating roller 172 is heated by the heater H and the sheet S is sandwiched between the pressure roller 173. Transport to roller 41. At this time, due to the reverse crown shape of the pressure roller 173, the sheet S has a small amount of conveyance at the center in the width direction and a large amount of conveyance at both ends. Due to the difference in the transport amount, the sheet S is loosened at both ends on the downstream side of the pressure roller 173, and wrinkles are likely to occur.

  Subsequently, the sheet S is sandwiched between the post-fixing roller 32 and the driven post-fixing roller 43 of the post-fixing roller 41 and conveyed. At this time, the frictional force of the end side driving post-fixing roller 42b of the post-fixing roller 42 is larger than the frictional force of the central driving post-fixing roller 42a, and the end side driven post-fixing roller 43 of the post-fixing roller 43 is driven. Since the frictional force 43b is larger than the frictional force of the roller 43a after the center driven fixing, the sheet S has a large conveyance amount on both ends. Accordingly, it is possible to reduce the looseness of the sheet S generated between the heating roller 172 and the pressure roller 173 and the post-fixing roller 41.

  In the present embodiment, the outer diameter and the conveying force of the end side driving post-fixing roller 42b are merely made larger than those of the center side driving post-fixing roller 42a, but the end side driving post-fixing roller 42b and the end side The outer diameter and conveying force of at least one of the driven post-fixing roller 43b may be larger than the central driven post-fixing roller 42a and the central driven post-fixing roller 43a.

  Moreover, although this embodiment combines 1st Embodiment thru | or 3rd Embodiment, you may select and combine two each. Further, the present invention is not limited to this embodiment, as long as the conveyance amount of the end side driving and fixing roller is larger than that of the center driving and fixing roller 42a.

  FIG. 14 is a vertical side view of an image forming apparatus to which the present invention is applied. In FIG. 14, the image forming apparatus 160 includes, as main constituent members, a rotary developing device 161, a photosensitive drum 165 functioning as an image carrier, and an image writing means (line head) 167 provided with an organic EL array. An intermediate transfer belt 169 as an intermediate transfer member, a sheet S conveyance path 174, a heating roller 172 of a fixing device, and a paper feed tray 178 are provided.

  In the developing device 161, the developing rotary 161a rotates in the arrow A direction about the shaft 161b. The inside of the development rotary 161a is divided into four, and image forming units for four colors of yellow (Y), cyan (C), magenta (M), and black (K) are provided. Reference numerals 162a to 162d are arranged in the image forming units of the four colors, and developing rollers as toner carriers that rotate in the direction of arrow B, and 163a to 163d are toner supply rollers that rotate in the direction of arrow C. is there. Reference numerals 164a to 164d are regulating blades that regulate the toner to a predetermined thickness.

  The photosensitive drum 165 is driven in the direction of arrow D opposite to the developing roller 162a by a drive motor (not shown), for example, a step motor. The intermediate transfer belt 169 is stretched between the driven roller 170b and the drive roller 170a, and the drive roller 170a is connected to the drive motor of the photosensitive drum 165 to transmit power to the intermediate transfer belt 169. By driving the drive motor, the drive roller 170 a of the intermediate transfer belt 169 is rotated in the arrow E direction opposite to the photosensitive drum 165.

  The operation from the image forming apparatus 160 developing apparatus 161 having such a structure to the intermediate transfer belt 169 will be described. First, toner is supplied from the toner supply roller 163 to the developing roller 162. At this time, the toner amount is adjusted by the regulating blade 164. The developing roller 162 develops the latent image on the photosensitive drum 165 formed by the line head 167 or the like. The image on the photosensitive drum 165 is transferred to the intermediate transfer belt 169.

  The sheet S conveyance path 174 is provided with a plurality of conveyance rollers and paper discharge roller pairs 176 and conveys the sheet S. An image (toner image) on one side carried on the intermediate transfer belt 169 is transferred to one side of the paper S at the position of the secondary transfer roller 171. The secondary transfer roller 171 is brought into contact with and separated from the intermediate transfer belt 169 by a clutch, and is brought into contact with the intermediate transfer belt 169 when the clutch is turned on, so that an image is transferred onto the sheet S.

  The sheet S on which the image has been transferred as described above is then subjected to a fixing process by the fixing device 1 having the heater H described above. The fixing device 1 is provided with a heating roller 172 and an inverted crown-shaped pressure roller 173. The sheet S after the fixing process is discharged to the downstream side by the post-fixing roller 5, is drawn into the paper discharge roller pair 176, and proceeds in the arrow F direction. When the paper discharge roller pair 176 rotates in the opposite direction from this state, the paper S reverses its direction and advances in the double-sided printing conveyance path (double-sided conveyance path) 175 in the arrow G direction. Reference numeral 183 denotes a first double-sided roller, and 184 denotes a second double-sided roller. Reference numeral 177 denotes an electrical component box, 178 denotes a paper feed tray for storing the paper S, and 179 denotes a pickup roller provided at the outlet of the paper feed tray 178. An exhaust fan 191 is provided in the housing case 190. An opening / closing door 190a for pulling out the paper S at the time of jamming is provided on the side of the paper S conveyance path 174 of the housing case 190.

  A feed roller 181 is provided in the single-sided sheet S conveyance path 174 on the downstream side when viewed from the sheet S conveyance direction of the pickup roller 179. A gate roller 180 is disposed on the upstream side of the secondary transfer roller 171. In the example of FIG. 14, a line head that uses a light emitting element as an exposure unit is provided. However, a scanning optical system that uses laser light as a light source may be provided.

  Thus, the fixing device of the present embodiment and the image forming apparatus using the fixing device can reduce the waviness of the transfer material due to the reverse crown shape of the fixing roller.

The above description has been made with respect to a heat roller fixing method using a heating roller 172 and a pressure roller 173. However, when a belt is used as at least one of, for example, a heating device and a pressure device of another contact heat fixing method as a fixing device. It is obvious that the same effect can be obtained.

  The fixing device and the image forming apparatus using the fixing device according to the embodiments of the present invention have been described above. However, the present invention is not limited to these embodiments, and various modifications can be made.

1 is a perspective view of a fixing device according to a first embodiment. FIG. 3 is an operation diagram of the fixing device according to the first embodiment. 2A and 2B are a plan view and a cross-sectional view of the fixing device according to the first embodiment. It is a comparison figure of arrangement | positioning of 1st Embodiment, and other arrangement | positioning. FIG. 6 is a perspective view of a fixing device according to a second embodiment. FIG. 6 is an operation diagram of a fixing device according to a second embodiment. FIG. 6 is a plan view of a fixing device according to a second embodiment. FIG. 10 is a perspective view of a fixing device according to a third embodiment. FIG. 9 is an operation diagram of a fixing device according to a third embodiment. FIG. 9 is a plan view of a fixing device according to a third embodiment. FIG. 10 is a perspective view of a fixing device according to a fourth embodiment. It is an operation | movement figure of the fixing device of 4th Embodiment. FIG. 10 is a plan view of a fixing device according to a fourth embodiment. 1 is a longitudinal side view illustrating an image forming apparatus according to an exemplary embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fixing device, 11 ... Roller after fixing, 12 ... Roller after driving and fixing, 12a ... Roller after center driving and fixing, 12b ... Roller after end side driving and fixing, 13 ... Roller after driven fixing, 13a ... Roller after driven fixing Rear roller, 13b ... End side driven post-fixing roller, S ... Paper (transfer material), 160 ... Image forming device, 161 ... Developing device, 165 ... Photosensitive drum, 169 ... Intermediate transfer belt, 171 ... Secondary transfer roller 172 ... Heating roller (heating rotator), H ... Heater (heating element), 173 ... Pressure roller (pressure rotator), T ... Fixing roller (fixing means)

Claims (6)

  A fixing unit including a heating rotator having a heating element and a pressure rotator that forms a nip portion facing the heating rotator, at least one of which has an inverted crown shape, the heating rotator, and the pressure rotation And a post-fixing roller provided downstream of the body, wherein the post-fixing roller has a conveying force at both ends in the width direction larger than that at the center.   The post-fixing roller has a both-end-side post-fixing roller disposed on both ends in the width direction, and a central-fixing post-roller disposed on the center in the width direction. The fixing device according to claim 1, wherein the fixing device is smaller than an interval between the rollers after fixing at the center.   The post-fixing roller has a both-end-side post-fixing roller disposed on both ends in the width direction and a center-fixing post-roller disposed on the center in the width direction. The fixing device according to claim 1, wherein the fixing device is larger than an outer diameter of the center post-fixing roller.   The post-fixing roller has a both-end-side post-fixing roller disposed at both ends in the width direction and a center-post-fixing roller disposed at the center in the width direction, and the friction force of the both-end-side post-fixing rollers is The fixing device according to claim 1, wherein the fixing device is larger than a frictional force of the center post-fixing roller.   The post-fixing roller includes a both-end side post-fixing roller disposed on both ends in the width direction and a center-post-fixing roller disposed on the center in the width direction, and the nip pressure of the both-end side post-fixing roller is The fixing device according to claim 1, wherein the fixing device has a nip pressure greater than a nip pressure of the post-fixing roller at the center.   An image carrier, a developer carrier that develops a latent image on the image carrier, an intermediate transfer member that transfers an image on the image carrier developed by the developer carrier, and the intermediate transfer member 6. The fixing according to claim 1, further comprising: a secondary transfer portion that transfers the image on the transfer material; and the fixing device that fixes the image on the transfer material. An image forming apparatus using the apparatus.

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