JP2005037678A - Thermal fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal fixing device of which the dimensional accuracy of parts is easily improved and which provides stable quality. <P>SOLUTION: At least one of a pair of members includes an endless belt 510, and the shape of the endless belt 510 is kept by a belt-inside supporting member 512 provided inside the belt. The belt-inside supporting member 512 is formed by extruding or drawing a metallic material, so that the dimensional accuracy of the member 512 is excellent as compared with that of a structure formed by bending and welding a metal plate. Though the dimensional accuracy of the belt inside supporting member 512 is important for obtaining a stable nip, the extruded material or the drawn material of the metallic material unnecessitates finish working for obtaining the dimensional accuracy or a part to be finish-worked is reduced even if the finish working is necessitated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image fixing device used in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, and more specifically, between a heat fixing roll and an endless belt. The present invention relates to a heat fixing apparatus that performs heat fixing by sandwiching a sheet having an unfixed toner image.

  2. Description of the Related Art Conventionally, a heat fixing device (Free Belt Nip Fuser; hereinafter referred to as FBNF) that performs heat fixing by sandwiching a sheet having an unfixed toner image between a heat fixing roll and an endless belt is disclosed in, for example, Patent Documents. 1 and the like.

In the conventional heat fixing device having the above-described configuration, a steel plate is used as an inner support member of the endless belt (belt support frame 7 described in FIGS. 15 and 17 of Patent Document 1). Thus, the strength is ensured, the shape of the endless belt is maintained, and the fixing nip is configured.
JP 2002-148984 A

  However, as a drawback of the above conventional method, it is very difficult to secure the processing accuracy (bending accuracy and welding accuracy) of the sheet metal, and it is necessary to correct by hand work to ensure accuracy, so that the accuracy of parts is extremely secured. It was difficult.

  Therefore, since it is such a part, it has a structure in which the fixing nip is likely to vary, and it takes a long time to adjust the nip. In some cases, the adjustment inspection value does not become a desired value, and the part itself cannot be used. There was also.

Against this background, this configuration has a problem in that the quality of the FBNF is not stable, and has a disadvantage that it varies from product to product.
There is a problem.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a heat fixing device that can easily improve the dimensional accuracy of parts and can obtain stable quality.

  According to a first aspect of the present invention, there is provided a thermal fixing device that sandwiches and conveys a recording sheet holding an unfixed toner image between a pair of rotatable members while being heated, and is provided on at least one of the pair of members. An endless belt, a belt inner support member that is provided inside the endless belt and formed by extrusion or drawing of a metal material, and maintains the shape of the endless belt, and between one of the pair of members and the other And a first heat source provided on at least one of the pair of members so as to form a nip.

  Next, the operation of the thermal fixing apparatus according to claim 1 will be described.

  In the heat fixing apparatus according to claim 1, the recording sheet holding the unfixed toner image is nipped and conveyed while being heated by a first heat source between a pair of rotatable members, thereby fixing the image. .

  At least one of the pair of members includes an endless belt, and the shape of the endless belt is maintained by a belt inner support member provided inside.

  Since the belt inner support member is formed by extrusion or drawing of a metal material, the dimensional accuracy is better than that of a structure in which a metal plate is bent and welded.

  In order to obtain a stable nip, the dimensional accuracy of the belt inner support member is important. However, the extruded material of metal material or the drawn material does not require finishing processing to achieve dimensional accuracy, or there was finishing processing. However, there are few processing parts.

  According to a second aspect of the present invention, in the thermal fixing device according to the first aspect, the belt inner support member has a first pad that makes the nip pressure uniform in the axial direction. Yes.

  Next, the operation of the heat fixing device according to claim 2 will be described.

  Generally, when the axial length of a rotatable member is long or when the nip pressure is large, the member is bent and the nip pressure at the center of the member is reduced compared to both sides in the axial direction. However, in the thermal fixing device according to claim 2, the first pad can make the nip pressure uniform in the axial direction. As a result, the conveying force can be made uniform in the axial direction.

  According to a third aspect of the present invention, in the heat fixing device according to the second aspect, the belt inner support member is more upstream than the first pad in the rotation direction of the endless belt than the first pad. And the second pad made of an elastomer that urges the endless belt toward the nip side.

  Next, the operation of the heat fixing apparatus according to claim 3 will be described.

  In the heat fixing device according to the third aspect, the second pad disposed upstream of the first pad in the rotation direction of the endless belt can brake the rotation of the endless belt. In the heat fixing device according to the second aspect, the conveying force is made uniform in the axial direction. However, by providing the second pad, the conveying force can be changed in the axial direction.

  According to a fourth aspect of the present invention, in the thermal fixing device according to the third aspect, the second pad has an urging force at an axially central portion larger than an urging force at both axial ends. Yes.

  Next, the operation of the thermal fixing apparatus according to the fourth aspect will be described.

  When the urging force at the axial center is greater than the urging force at both axial ends, the braking force at the axial central portion is greater than at both axial ends. As a result, the conveying force is axial at both axial ends. It becomes larger than the central part.

  According to a fifth aspect of the present invention, in the heat fixing device according to any one of the first to fourth aspects, the endless belt and the belt inner support member are formed of a material having a small friction coefficient. The sliding member to be operated is arranged.

  Next, the operation of the heat fixing apparatus according to claim 5 will be described.

  By disposing a sliding member made of a material having a small friction coefficient between the endless belt and the belt inner support member, the endless belt can rotate with little resistance.

  According to a sixth aspect of the present invention, in the heat fixing device according to any one of the first to fifth aspects, a second heat source is provided inside the belt inner support member.

  Next, the operation of the thermal fixing apparatus according to the sixth aspect will be described.

  By heating the belt inner support member with the second heat source, the endless belt disposed on the outer periphery thereof can be heated uniformly throughout. Therefore, since the endless belt can be heated in advance before entering the nip portion, the fixing speed can be increased.

  As described above, according to the present invention, it is possible to easily improve the dimensional accuracy of the parts of the thermal fixing device and to obtain a stable quality.

Hereinafter, preferred embodiments of the present invention will be specifically described based on examples.
[First Embodiment]
FIG. 1 shows a tandem type full color printer (image forming apparatus) according to a first embodiment of the present invention.

  FIG. 2 shows a main part of image formation of the full-color printer (image forming apparatus) shown in FIG.

  The full-color printer 1 is roughly composed of an image forming unit, an intermediate transfer device, a final transfer roll 40, a fixing device 500, and a paper feeding unit.

  The image forming unit includes four image forming units (image forming units) 1Y to 1K for yellow (Y), magenta (M), cyan (C), and black (K), and an exposure device 15. Composed.

  Further, each of the image forming units 1Y to K includes four photosensitive drums (image bearing members) 10Y to K, and charging rolls (contact type charging members) 11Y to K that are in contact with the photosensitive drums 10Y to 10K, respectively. The developing devices 12Y to 12K are respectively opposed to the photosensitive drums 10Y to 10K, and the photosensitive brush rolls 13Y to 13K are respectively in contact with the photosensitive drums 10Y to 10K.

  Here, regarding the arrangement of each member around the photosensitive drum 10, the charging roll 11, the developing device 12 (developing device) are centered on each photosensitive drum 10 from the upstream side to the downstream side in the rotation direction of the photosensitive drum 10. Development sleeve), a first intermediate transfer roll (to be described later), and a photoreceptor brush roll 13 are disposed.

  The photoreceptor brush roll 13 is configured by winding a conductive resinous flocking tape around a metal (stainless) roll-shaped base material in a spiral shape.

  The photosensitive drums 10Y to 10K are applied with a DC voltage of about −900V by the charging rolls 11Y to K, and are thereby uniformly charged to about −380V, and an electrostatic latent image is written by the exposure device 15. In this case, the surface potential is neutralized to about -70V.

  The developing devices 12Y to 12K are developing devices of a magnetic brush contact type two-component developing system including a developing roll, a developer amount regulating member, a developer conveying member, and an auger that conveys and stirs the developer.

The developer amount regulated by the developer amount regulating member and conveyed to the developing unit is about 30 to 40 g / m ^2. At this time, the charge amount of the toner existing on the developing roll is about −20 to −40 μC / m ^2. It is about g.

  The developing devices 12Y to 12K are developed by applying a developing voltage of AC + DC. The developing voltage is 4 kHz for AC, 1.6 kVpp, and about −300 V for DC.

  The intermediate transfer device includes a first upstream intermediate transfer roll (first upstream intermediate transfer member) 20a that contacts the photosensitive drums 10Y and 10M at the primary transfer position, and a photosensitive drum 10C and 10K at the primary transfer position. A first intermediate transfer roller (first upstream intermediate transfer roller) 20b in contact with the second intermediate transfer roller 20b and the second intermediate transfer roller 20a and 20b, which are in contact with each other at the secondary transfer position, respectively. A toner sensor 8 is provided for optically detecting the presence and density of the toner image on the roll 30 and the second intermediate transfer roll 30 in a non-contact manner.

  Further, the first upstream intermediate transfer roll 20a includes a cleaning device (cleaning means) 21a.

  The first upstream cleaning device 21a includes a metal (stainless) cleaning roll (downstream cleaning roll) 210a that contacts the first upstream intermediate transfer roll 20a and a metal (stainless steel) that contacts the cleaning roll 210a. ) Made of a cleaning blade 211a, a screw auger (conveying mechanism) 214a that conveys residual toner scraped off by the cleaning blade 211a to a toner collection box (not shown) outside the upstream cleaning device 21a, and a cleaning roller 210a. An intermediate transfer brush roll (downstream cleaning brush) 213a that contacts the intermediate transfer roll 20a in the vicinity of the upstream side in the rotation direction of the upstream intermediate transfer roll 20a, the cleaning roll 210a, and a cleaning blade 211a, a screw auger 214a, and a cleaner housing (container) 212a for accommodating the intermediate transfer brush roll 213a.

  The intermediate transfer brush roll 213a is configured by winding a conductive resinous flocking tape in a spiral shape around a metal (stainless steel) roll-shaped substrate.

  Similarly, the first downstream intermediate transfer roll 20b includes a cleaning device (cleaning means) 21b.

  The first downstream cleaning device 21b includes a metal (stainless) cleaning roll (downstream cleaning roll) 210b that contacts the first downstream intermediate transfer roll 20b, and a metal (stainless steel) that contacts the cleaning roll 210b. ) Made of a cleaning blade 211b, a screw auger (conveying mechanism) 214b that conveys residual toner scraped off by the cleaning blade 211b to a toner collection box (not shown) outside the upstream side cleaning device 21b, and a cleaning roller 210b. The intermediate transfer brush roll 213b that contacts the intermediate transfer roll 20b in the vicinity of the upstream side in the rotation direction of the downstream intermediate transfer roll 20b, the cleaning roll 210b, the cleaning blade 211b, and the screw auger 21 b, and a cleaner housing (container) 212b for accommodating the intermediate transfer brush roll 213b.

  The intermediate transfer brush roll 213b is configured by winding a conductive resinous flocking tape around a metal (stainless steel) roll-shaped base material in a spiral shape.

  The second intermediate transfer roll 30 is provided with a cleaning device (cleaning means) 31.

  The second cleaning device 32 includes a metal (stainless) cleaning roll (upstream cleaning roll) 310 that contacts the second intermediate transfer roll 30 and a metal (stainless) cleaning blade that contacts the cleaning roll 310. 311, the screw auger (conveying mechanism) 314 that conveys residual toner scraped off by the cleaning blade 311 to a toner collection box (not shown) outside the upstream cleaning device 31, and the second intermediate transfer roll 30 than the cleaning roll 310. An intermediate transfer brush roll (upstream cleaning brush) 313 that contacts the intermediate transfer roll 30 in the vicinity of the downstream side in the rotation direction, the cleaning roll 310, the cleaning blade 311, the screw auger 314, and the intermediate transfer brush roll And a cleaner housing (container) 312 that accommodates the Le 313.

  The intermediate transfer brush roll 313 is configured by winding a conductive resinous flocking tape around a metal (stainless) roll-shaped base material in a spiral shape.

  Here, the arrangement of the peripheral members of the first upstream intermediate transfer roll 20a is centered on the first upstream intermediate transfer roll 20a and is downstream from the upstream side in the rotation direction of the first upstream intermediate transfer roll 20a. A photosensitive drum 10M, a photosensitive drum 10Y, a second intermediate transfer roll 30, an intermediate transfer brush roll 213a, and a cleaning roll 210a are disposed on the side.

  The arrangement of the peripheral members of the first downstream intermediate transfer roll 20b is centered on the first downstream intermediate transfer roll 20b and from the upstream side to the downstream side in the rotation direction of the first downstream intermediate transfer roll 20b. The photosensitive drum 10K, the photosensitive drum 10C, the second intermediate transfer roll 30, the intermediate transfer brush roll 213b, and the cleaning roll 210b are disposed.

  Further, the arrangement of the peripheral members of the second intermediate transfer roll 30 is such that the first upstream is centered on the second intermediate transfer roll 30 from the upstream side to the downstream side in the rotation direction of the second intermediate transfer roll 30. A side intermediate transfer roll 20a, a first downstream intermediate transfer roll 20b, a toner sensor 8, a final transfer roll 40, a cleaning roll 310, and an intermediate transfer brush roll 313 are provided.

  In the first intermediate transfer rolls 20a and 20b, a silicone rubber layer (conductive elastic layer) is provided on a metal pipe, and a high release layer (a resistance layer having a higher electrical resistance than the conductive elastic layer) is provided thereon. The resistance value is usually in the range of 105 to 109 Ω, but here it is about 108 Ω.

  The surface potential required to transfer the toner image from the photoreceptors 10Y to 10K to the first intermediate transfer rolls 20a and 20b is usually in the range of about +250 to 500V, and the charged state of the toner and the ambient temperature The optimum value can be set according to humidity and the like.

  Similarly to the first intermediate transfer rolls 20a and 20b, the second intermediate transfer roll 30 is also provided with a silicone rubber layer (conductive elastic layer) on the metal pipe, and further a high release layer (conductive). A resistance layer having a higher electrical resistance than the elastic elastic layer), and a resistance value in the range of 108 to 1012 Ω can be normally used, but here it is about 1011 Ω (ie, The first intermediate transfer rolls 20a and 20b are configured to have a higher resistance).

  The surface potential required to transfer the toner image from the first intermediate transfer rolls 20a and 20b to the second intermediate transfer roll 30 is usually in the range of about +600 to 1200 V, and the charged state of the toner. The optimum value can be set according to the ambient temperature, humidity, and the like.

  The final transfer roll (final transfer body) 40 is in contact with the second intermediate transfer roll 30 at the final transfer position, a urethane rubber layer is provided on the metal pipe, and a resin coating is further provided thereon. As for the resistance value, a resistance in the range of 106 to 109 Ω can be used normally, but here, it is about 108 Ω (that is, lower resistance than that of the second intermediate transfer roll 30).

  The transfer voltage applied to the final transfer roll 40 to transfer the toner image from the second intermediate transfer roll 30 onto the paper (recording sheet) S is usually in the range of about +1200 to 5000 V, and the ambient temperature The optimum value is set according to the humidity, the type of the paper S (resistance value, etc.), but here, a constant current method is applied and approximately +6 μA is applied in a normal temperature and humidity environment to obtain an almost appropriate final transfer voltage. + 1600-2000V is obtained.

  The final transfer roll 40 is not in contact with a cleaning roll (cleaning body) (unlike the first intermediate transfer rolls 20a and 20b and the second intermediate transfer roll 30).

  Furthermore, the final transfer roll 40 is in contact with the second intermediate transfer roll 30 (except for when the image forming unit is replaced, including in the image forming mode, in the process control mode, and in the cleaning mode). There is no mechanism.

  The surface roughness (Rz) of the final transfer roll 40 can be 20 [μm (Rz)] or less, for example, 10 [μm (Rz)], and the first and second intermediate transfer rolls 20a and 20b. , 30 can be 10 [μm (Rz)] or less, for example, 1 [μm (Rz)].

Furthermore, the final transfer roll 40 has a rougher surface circle roughness (Rz) than the first and second intermediate transfer rolls 20a, 20b, 30. These surface roughnesses (Rz) are preferably equal to or less than the average particle diameter of the toner constituting the toner image.
(Configuration of fixing device)
As shown in FIG. 5, the fixing device 500 includes a heating roll 502, a belt rotating body 504, and a case 506 that is a synthetic resin molded product, and is unitized.

  As shown in FIG. 6, the heating roll 502 is configured such that a halogen lamp 508 as a heat source is disposed in a metal pipe 507 having a constant diameter, and the surface of the heating roll 502 is heated to a predetermined fixing temperature during fixing. ing.

  The heating roll 502 is rotatably provided on the case 506, and rotates by obtaining a driving force from a motor (not shown).

  As shown in FIGS. 6 to 8, the belt rotating body 504 includes an endless belt 510, a belt inner support member 512, a hard pad 514, a soft pad 516, a sliding member 518, a guide member 520, a felt pad 522, and a mounting bracket 524. It has.

  The endless belt 510 of this embodiment is formed of a polyimide resin in a cylindrical shape, and the surface is coated with a fluororesin.

  The belt inner support member 512 of this embodiment is an aluminum hollow extruded product.

  The belt inner support member 512 includes a first groove 526, a second groove 528, and a third groove 530 that extend in the axial direction.

  The vicinity of both ends of the groove wall 528A of the second groove 528 and the vicinity of both ends of the groove wall 530A of the third groove 530 are each milled, and the milled portion is a groove wall 526A of the first groove 526, which will be described later, and the groove. The wall 526B is used as a reference surface when milling.

  The groove wall 526A and the groove wall 526B of the first groove 526 are milled as a whole with reference to the milled portion to have a flatness of 0.1 mm or less, and the wall surface 526A and the groove wall are formed by milling. A squareness with 526B is provided.

  A hard pad 514 is disposed in the first groove 526. The hard pad 514 is a synthetic resin molded product with high dimensional accuracy.

  The hard pad 514 includes a first plate-like portion 532 that contacts the groove wall 526A of the belt inner support member 512, and a second plate-like portion 534 that contacts the groove wall 526B of the belt inner support member 512. The cross section perpendicular to the longitudinal direction has a substantially L shape.

  When the hard pad 514 is viewed in a cross section perpendicular to the longitudinal direction, the distal end portion of the first plate-like portion 532 is formed in an arc shape.

  The first plate-like portion 532 has a maximum width H in the central portion in the axial direction, and gradually decreases toward the both ends in the axial direction. The first plate-like portion 532 is curved in the axial direction (the shape in front view is a substantially arc shape). (In fact, it looks almost straight). In this embodiment, the length of the hard pad 514 is 342 mm, and the width H of the first plate-like portion 532 is 8.8 mm at the central portion in the axial direction and 7.51 mm at both end portions in the axial direction.

  A groove 536 is formed in the second plate-like portion 534 of the hard pad 514 along the longitudinal direction.

  The second plate-like portion 534 has a maximum thickness in the axial center portion in the groove portion, and is gradually formed thinner toward both axial end portions, and an arc-curved surface in which the groove bottom surface is curved in the axial direction. (In reality, it looks almost flat.)

  The thickness of the groove portion of the second plate-like portion 534 is 3.05 mm at the central portion in the axial direction and 1.99 mm at both end portions in the axial direction.

  A soft pad 516 is disposed in the groove 536 of the hard pad 514.

  The soft pad 516 includes a long base plate 538 made of an aluminum plate having a constant thickness, and a long pad body 540 made of silicone rubber that is fixed to the base plate 538 and contains oil.

  The pad main body 540 has a substantially trapezoidal cross section and is formed in a long shape. This pad main body 540 is also a molded product and has high dimensional accuracy.

  Here, a plurality of protrusions 542 (see FIG. 6) are formed in the second plate-like portion 534 of the hard pad 514 along the longitudinal direction.

  The sliding member 518 is a cloth-like long sheet made of a fluororesin (for example, PTFE) fiber, and a plurality of locking holes 544 are formed along the longitudinal direction. The sliding friction coefficient of the sliding member 518 is about 0.05 to 0.07.

  The sliding member 518 is locked to the hard pad 514 by inserting the protrusion 542 into the locking hole 544.

  The sliding member 518 is disposed between the hard pad 514 and the soft pad 516 and the endless belt 510, and the hard pad 514 and the soft pad 516 are not in direct contact with the endless belt 510.

  The guide member 520 is disposed on both ends of the belt inner support member 512 in the longitudinal direction.

  The guide member 520 is a synthetic resin molded product with high dimensional accuracy, and an engaging portion 546 that engages with an end portion of the belt inner support member 512 is formed on one surface on the belt inner support member side.

  A first protrusion 548 for positioning and a second protrusion 550 are integrally formed on one surface of the guide member 520 on the side opposite to the belt inner support member.

  The guide member 520 has a first hole 552 and a second hole 554.

  A felt pad 522 is fixed to the third groove 530 of the belt inner support member 512.

  A mounting member 524 that is a press-formed product of a steel plate is disposed on the side of the guide member 520 opposite to the belt inner support member.

  A first positioning hole 556 and a second positioning hole 558 are accurately formed in the mounting bracket 524, and the first protrusion 548 is inserted into the first positioning hole 556, and the second protrusion 550 is formed. Inserted into the second positioning hole 558, the mounting bracket 524 is accurately arranged at a predetermined position of the belt inner support member 512.

  The guide member 520 and the mounting bracket 524 are fixed to the belt inner support member 512 with screws 560.

  A bearing hole 562 and a lever portion 564 are formed in the mounting bracket 524.

  A shaft 566 provided in the case 506 shown in FIG. 5 is inserted into the bearing hole 562, and the belt rotating body 504 can swing around the shaft 566.

  The case 506 is provided with a spring 568, and the spring 568 presses the lever portion 564 of the mounting bracket 524 so as to bias the belt rotating body 504 toward the heating roll 502.

  5 and 6, the heating roll 502 is rotated by a motor (not shown).

  By energizing the belt rotator 504 by the spring 568, the endless belt 510 of the belt rotator 504 is pressed against the heating roll 502 to form a fixing nip N (see FIG. 6), and the direction of the heating roll 502 in the direction of arrow CW Following the rotation (see FIGS. 5 and 6), the endless belt 510 rotates in the arrow CCW direction.

  As shown in FIG. 6, the first plate-like portion 532 of the hard pad 514 and the pad body 540 made of silicone rubber of the soft pad 516 press the endless belt 510 against the heating roll 502 via the sliding member 518. Yes.

  As shown in FIG. 1, fixing discharge roll pairs 63 a and 63 b are disposed on the downstream side in the transport direction of the sheet S with respect to the heating roll 502 and the belt rotating body 504.

  The paper feed unit is formed along a transport path (indicated by a dotted line) P of the paper S from the paper feed tray 50 to the discharge tray 70. A plurality of sheets S are accommodated in the paper feed tray 50. From the paper feed tray 50 to the downstream side of the transport path, a roll pair of a pick-up roll 51a and a retard roll 51b, and transport rolls 52a and 52b are sequentially arranged. , A pair of resist rolls 53a and 53b (through the final transfer roll 40 and the fixing device 500), and a pair of discharge rolls 54a and 54b.

  FIG. 3 is a block diagram for explaining the potential control system of the full-color printer 1.

  Based on the situation of the full-color printer 1, that is, the print mode (image forming mode), the process control mode, and the cleaning mode, the potential control unit (potential gradient forming means) 9 includes the charging rolls 11, the photoreceptor brush rolls 13, Control the voltage applied to one intermediate transfer roll 20a, 20b, cleaning roll 210, intermediate transfer brush roll 213, second intermediate transfer roll 30, cleaning roll 310, intermediate transfer brush roll 313, and final transfer roll 40; As a result, an appropriate potential gradient according to the situation of the full-color printer 1 is applied to each of these charging rolls 11, the photoreceptor brush rolls 13, the first intermediate transfer rolls 20a and 20b, the cleaning roll 210, the intermediate transfer brush roll 213, and the second. Intermediate transfer roll 30 and cleaning roll 31 , An intermediate transfer brush roll 313, is formed between the final transfer roll 40.

In this embodiment, by using a Zener diode, a bias voltage supplied from the same power source is applied to a plurality of members as appropriate bias voltages.
(Function)
Hereinafter, the operation of the full-color printer 1 will be described.

表１は、プリントモードにおいて、本実施例において電位制御部９が各帯電ロール１１、クリーニングロール２１０、中間転写ブラシロール２１３、クリーニングロール３１０、中間転写ブラシロール３１３、最終転写ロール４０に印加するバイアス電圧をまとめたものである。

Table 1 shows biases that the potential control unit 9 applies to each charging roll 11, cleaning roll 210, intermediate transfer brush roll 213, cleaning roll 310, intermediate transfer brush roll 313, and final transfer roll 40 in the print mode in this embodiment. The voltage is summarized.

  FIG. 4 illustrates the movement status of the toner image as the output image.

  A solid line arrow in the figure indicates a moving path of a toner image as an output image.

  The toner used in this embodiment is a negatively charged toner.

  That is, the positive toner is negatively charged and the reverse toner is positively charged.

  The image forming units 1Y to 1K respectively form yellow, magenta, cyan, and black toner images on the photosensitive drums 10Y to 10K.

  That is, the surface of each photosensitive drum 10 is uniformly charged by the charging roll 11, and the exposed laser beam R corresponding to the output image is irradiated from the exposure device 15 to the surface of the photosensitive drum 10 after being charged. An electrostatic latent image is formed on the photosensitive drum 10 due to a potential difference from the unexposed portion.

  The developing device 12 selectively applies toner to the electrostatic latent image, and a toner image is formed on the photosensitive drum 10.

  First, a magenta toner image is primarily transferred from the magenta photosensitive drum 10M to the first upstream intermediate transfer roll 20a.

  Next, the yellow toner image is primarily transferred from the yellow photosensitive drum 10Y to the first upstream intermediate transfer roll 20a, and is superimposed on the magenta toner image.

  Similarly, a black toner image is primarily transferred from the black photosensitive drum 10K to the first downstream intermediate transfer roll 20b.

  Next, the cyan toner image is primarily transferred from the cyan photosensitive drum 10C to the first downstream intermediate transfer roll 20b.

  The primary-transferred magenta and yellow toner images are secondarily transferred to the second intermediate transfer roll 30.

  On the other hand, the black and cyan toner images that have been primarily transferred are also secondarily transferred to the second intermediate transfer roll 30, where the magenta and yellow toner images that have been secondarily transferred first, the cyan toner image, And a full-color toner image is formed on the second intermediate transfer roll 30.

  The full-color toner image and the black toner image that are secondarily transferred reach the nip portion between the second intermediate transfer roll 30 and the final transfer roll 40.

  In synchronization with the timing, the sheet S as a recording sheet is conveyed from the registration roll pair 53a, 53b (see FIG. 1) to the nip portion, and the full-color toner image and the black toner image are tertiary-transferred onto the sheet S (final). Transferred).

  Thereafter, the sheet S passes through the fixing nip N formed by the heating roll 502 and the belt rotating body 504 of the fixing device 500 (see FIGS. 1 and 6).

  At that time, the full-color toner image and the black toner image are fixed on the paper S by the action of heat and pressure applied from the heating roll 502 and the belt rotating body 504 to form a permanent image.

  In the fixing device 500, the endless belt 510 is sandwiched between the first plate-like portion 532 and the heating roll 502, so that a rotational force, that is, a conveyance force of the paper S is generated in the endless belt 510. Further, the conveyance force is proportional to the clamping force between the first plate-like portion 532 and the heating roll 502.

  Here, when the belt rotating body 504 is biased to the heating roll 502, the heating roll 502 bends. However, in the present embodiment, the first plate-like portion 532 of the hard pad 514 is curved in the axial direction. The clamping force between the first plate-like portion 532 and the heating roll 502 can be made uniform over the entire length in the axial direction, and thus the conveying force can be made uniform in the axial direction.

  On the other hand, the soft pad 516 receives the reaction force from the heating roll 502, the silicone rubber pad body 540 is compressed, and the base plate 538 is pressed against the groove bottom surface of the groove 536 of the hard pad 514.

  The pad main body 540 is located on the upstream side in the rotation direction of the endless belt 510 with respect to the first plate-like portion 532 that generates the conveying force, and plays a role of a brake with respect to the endless belt 510.

  Since the groove bottom surface of the groove 536 of the hard pad 514 where the soft pad 516 is disposed is curved in the axial direction, the base plate 538 receiving the pressing force is curved in the same manner as the groove bottom surface of the groove 536 (center in the axial direction). The pad main body 540 has a compressive force (pressing force with respect to the heating roll 502) at the central portion in the axial direction larger than that at the both end portions.

  For this reason, in this embodiment, the pad main body 540 has a braking force at the central portion in the axial direction larger than the braking force at both end portions.

  On the hard pad 514 side, a uniform conveying force is generated in the axial direction, but on the soft pad 516 side, the braking force at the central portion in the axial direction is larger than the braking force at both end portions, so the paper S is conveyed. The final transport force for this purpose is large on both sides in the axial direction with respect to the central portion in the axial direction, and the paper S can be transported stably without causing wrinkles.

  The oil that oozes out from the pad body 540 made of silicone rubber passes through the sliding member 518 having a small friction coefficient and is applied to the inner surface of the endless belt 510 in a small amount, so that the endless belt 510 is stabilized with a small amount of resistance. Can be rotated.

  Thereafter, the sheet S on which the image has been fixed is discharged to the discharge tray 70 by the discharge roll pair 54a and 54b, and the full-color image formation is completed.

  In the fixing device 500 of the present embodiment, since the belt inner support member 512 is an aluminum extruded product, the dimensional accuracy is better than that of a structure in which a steel plate is bent and welded.

  In this embodiment, the belt inner support member 512 is partially milled. However, since the material is an aluminum that is easy to process, and the dimensional accuracy before processing is good, the amount to be cut is small, and compared with the conventional case. This eliminates the need for processing and does not require correction, and can provide extremely high dimensional accuracy.

  In addition, since the conventional product used a thin steel plate (for example, 1.6 mm thickness) for weight reduction, when milling was performed, chattering occurred and accurate processing could not be performed.

In addition, since the accuracy of each component is high in the fixing device 500 of this embodiment, the alignment between the heating roll 502 and the belt rotating body 504 can be ensured with high accuracy, and a very stable nip can be formed.
[Other Embodiments]
In the above embodiment, the halogen lamp 508 is built in the heating roll 502. However, since the belt inner support member 512 has a hollow structure, the halogen lamp 508 may be further added to the belt inner support member 512.

  By heating the belt inner support member 512 with the halogen lamp 508, the endless belt 510 disposed on the outer periphery thereof can be heated uniformly throughout. Since the endless belt 510 can be heated in advance before entering the fixing nip N, the fixing speed can be further increased.

1 is a schematic cross-sectional view of a full-color printer. 3 is a cross-sectional view of a main part of a full-color printer. It is a block diagram explaining the electric potential gradient control system of a full-color printer. FIG. 6 is an explanatory diagram illustrating a movement state of a toner image as an output image in a full-color printer. FIG. 3 is a cross-sectional view of a fixing device. It is sectional drawing of a heating roll and a belt rotary body. It is a perspective view of a belt rotating body. It is a disassembled perspective view of a belt rotary body.

Explanation of symbols

500 Fixing device (thermal fixing device)
502 Heating roll 504 Belt rotating body
S paper (recording sheet)
508 Halogen lamp (first heat source, second heat source)
510 Endless Belt 512 Belt Inner Support Member 514 Hard Pad (First Pad)
516 Soft pad (second pad)
518 Sliding member 524 Mounting bracket (holding member)

Claims (6)

A thermal fixing device for nipping and conveying a recording sheet holding an unfixed toner image between a pair of rotatable members,
An endless belt provided on at least one of the pair of members;
A belt inner support member provided inside the endless belt, formed by extrusion or drawing of a metal material, and retaining the shape of the endless belt;
A holding member that keeps the pair of members at a constant interval so as to form a nip between one of the pair of members and the other;
A first heat source provided on at least one of the pair of members;
A thermal fixing device comprising:   The thermal fixing device according to claim 1, wherein the belt inner support member has a first pad that makes the nip pressure uniform in the axial direction.   The belt inner support member has a larger coefficient of friction than the first pad on the upstream side in the rotation direction of the endless belt relative to the first pad, and is made of an elastomer that urges the endless belt toward the nip side. The thermal fixing device according to claim 2, further comprising two pads.   4. The thermal fixing device according to claim 3, wherein the second pad has an urging force at an axially central portion larger than an urging force at both axial ends. 5.   The sliding member formed from a material with a small friction coefficient is arrange | positioned between the said endless belt and the said belt inner side support member, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. The heat fixing apparatus as described.   The heat fixing apparatus according to claim 1, further comprising a second heat source inside the belt inner support member.

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