JP2005077872A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an image of high quality by stabilizing the transport capability for recording paper in a fixing device and then suppressing paper wrinkling, image deviation, etc., over a long period. <P>SOLUTION: Provided are a fixing roll 61 which can rotate, a fixing belt 62 which can move in contact with the fixing roll 61, and a pressure pad 65 which is arranged in the inside of the fixing belt 62 and makes the fixing belt 62 press against a rotating member to form a nip part N, where a form P pass between the fixing roll 61 and fixing belt 62, and further a low-friction sheet 68 which reduces the slide friction between the endless belt 62 and pressure pad 64. Further, provided is a step member (low-friction sheet extension part) 68a, having steps 681k and 682k which abut against the inner peripheral surface of the endless belt 62 and are formed from an end to the center part of the endless belt 62 from upstream to downstream in the moving direction of the endless belt 62. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device and the like, and more particularly to a fixing device used in an image forming apparatus using an electrophotographic system.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic method, for example, a photosensitive member formed in a drum shape is uniformly charged, and the photosensitive member is exposed to light controlled based on image information. An electrostatic latent image is formed on the photoreceptor. The electrostatic latent image is converted into a visible image (toner image) with toner, and the toner image is further transferred onto a recording sheet and fixed by a fixing device to form an image.

  In the fixing device used in such an image forming apparatus, as shown in FIG. 9, a heating source 213 is provided inside a cylindrical metal core 211, and a release layer 212 is formed on the outer peripheral surface of the metal core 211. The fixing roll 210 and the fixing roll 210 were pressed against each other, and a heat-resistant elastic body layer 222 and a release layer 223 made of a heat-resistant resin film or a heat-resistant rubber film were formed on the outer peripheral surface of the cored bar 221. It is composed of a pressure roll 220. Then, a recording paper carrying an unfixed toner image is passed between the fixing roll 210 and the pressure roll 220, and the unfixed toner image is heated and pressed to thereby apply toner to the recording paper. The image is fixed. Such a fixing device is called a heating roll method and is generally widely used.

By the way, when it is intended to increase the speed of the heating roll type fixing device, it is necessary to widen the nip width in proportion to the fixing speed in order to supply a sufficient amount of heat to the toner and the recording paper. As a method of widening the nip width, there are a method of increasing the load between the fixing roll and the pressure roll, a method of increasing the thickness of the elastic body, and a method of increasing the roll diameter.
However, in the method of increasing the load and the method of increasing the thickness of the elastic body, the uneven nip width and paper wrinkle occur because the shape of the nip width due to the deflection of the roll becomes non-uniform along the roll axis. This causes image quality problems such as Further, the method of increasing the roll diameter has problems that the apparatus is increased in size and that the time until the roll is raised from room temperature to the fixable temperature (warm-up time) becomes longer.

  Therefore, in order to solve these problems and realize a fixing device corresponding to the speedup of the image forming apparatus, the applicant of the present invention has a rotatable heating roll whose surface is elastically deformed and remains in contact with the heating roll. A travelable endless belt and a pressure pad arranged in a non-rotating state inside the endless belt. The pressure pad presses the endless belt against the heating roll so that a contact surface with the heating roll is formed. And a belt nip so that the sheet can pass between the endless belt and the heating roll, and a fixing device configured to locally elastically deform the exit side of the sheet on the surface of the heating roll The technique regarding this is proposed (for example, refer patent document 1).

  In the technique described in Patent Document 1, the endless belt is pressed against the heating roll using a pressure pad in place of the pressure roll in the conventional heating roll type fixing device. By adopting such a configuration, the width of the belt nip formed by the heating roll and the endless belt can be easily made larger than the width of the conventional roll nip between the heating roll and the pressure roll. It is easy to reduce the size of the apparatus.

  In particular, the heat capacity of the endless belt brought into pressure contact with the heating roll is small, and furthermore, the heat transmitted from the heating roll is hardly dissipated because the pressure pad is arranged in a non-rotating state. Therefore, even if rotation of the heating roll is started, the amount of heat taken away from the heating roll to the endless belt side is small, the efficiency of using heat for melting the toner is increased, and the amount of temperature decrease at the belt nip is also small. There is an advantage that the fixing property of the toner can be improved.

Japanese Patent No. 3298354 (pages 4-7)

By the way, in the fixing device of the type in which the endless belt is pressed against the roll using the pressure pad, in order to ensure the slipperiness between the pressure pad and the endless belt when the endless belt is pressed against the roll by the pressure pad, A low friction member is interposed between the two, and a lubricant is applied to the sliding surface of the low friction member.
However, since pressure is applied between the pressure pad and the endless belt, the sliding portion between the endless belt and the low friction member has a force to push the applied lubricant from the sliding portion. As the endless belt moves, the lubricant gradually moves to both sides of the sliding portion, and it is difficult to stably hold the lubricant over the entire sliding portion. Therefore, the contact resistance (sliding resistance) between the pressure pad and the endless belt tends to increase. In that case, the movement of the endless belt becomes difficult to correspond to the heating roll, and accordingly, the recording paper is not conveyed well, and image defects such as paper wrinkles and image misalignment may occur.

  Accordingly, the present invention has been made to solve the technical problems as described above. The object of the present invention is to stabilize the recording paper conveyance capability in the fixing device, and thereby to make the paper wrinkle over a long period of time. In other words, it is possible to form a high quality image while suppressing occurrence of image misalignment and the like.

  For this purpose, the fixing device of the present invention is provided with a rotatable rotating member, an endless belt that can move while contacting the rotating member, and an inner end of the endless belt. A pressure member that forms a nip portion through which the recording material passes between the rotating member and the endless belt, and a sliding member that reduces the frictional resistance between the endless belt and the pressure member. And a step member that is in contact with the inner peripheral surface of the endless belt and has a step formed from the end of the endless belt toward the center from the upstream side to the downstream side in the moving direction of the endless belt. It is characterized by.

Here, the step member may be arranged downstream of the nip portion in the moving direction of the endless belt. Further, a pair of step members can be arranged symmetrically in the width direction of the endless belt. Further, the step member may be characterized in that the step is formed to 20 to 120 μm.
In addition, the sliding member and the step member may be characterized by having a low absorbability with respect to the lubricant.

  In addition, the fixing device of the present invention is disposed inside the endless belt, the endless belt that can be moved while being in contact with the rotating member, and the endless belt is pressed against the rotating member. A pressure member that forms a nip portion through which the recording material passes between the rotating member and the endless belt, and a sliding member that reduces the frictional resistance between the endless belt and the pressure member. The moving member is in contact with the inner peripheral surface of the endless belt on the downstream side of the nip portion, and a step is formed from the end portion of the endless belt toward the central portion from the upstream side to the downstream side in the moving direction of the endless belt. It is characterized by that.

The fixing device of the present invention has a pressure roll that is elastically deformed and connected to a driving source and is rotatable, a fixing belt that has a heat source and can be driven while contacting the pressure roll, A pressure member that is disposed inside the fixing belt, presses the fixing belt against the pressure roll to form a nip portion through which the recording material passes between the fixing belt and the pressure roll, and the fixing belt and the pressure member. And a sliding member for reducing the frictional resistance between the fixing belt and the pressure member while interposing a lubricant, and further, the lubricant attached to the inner peripheral surface of the fixing belt is removed from the fixing belt. It is characterized by having a lubricant collecting member gathered to the central part.
Here, the fixing belt may be configured such that the heat generation source is an electromagnetic induction heating body or a resistance heating body. Further, the pressure member can be constituted by a heat source provided on the fixing belt.

In addition, the fixing device of the present invention has a heat generating source, a rotatable fixing roll whose surface is elastically deformed, an endless belt movable while contacting the fixing roll, and an endless belt disposed inside the endless belt. Is pressed between the endless belt and the fixing roll so as to form a nip portion through which the recording material passes, and the endless belt is provided between the endless belt and the pressure member. And a sliding member for reducing the frictional resistance between the pressure member and the lubricant collecting member for collecting the lubricant adhering to the inner peripheral surface of the endless belt to the central portion of the endless belt. It is characterized by that.
Here, the pressure member can be characterized in that it locally elastically deforms the downstream side of the surface of the fixing roll in the recording material conveyance direction.

Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material. Fixing means for fixing the toner image transferred on the recording material to the recording material, the fixing means comprising: a rotatable rotating member; an endless belt movable while contacting the rotating member; A pressure member that is disposed inside the endless belt and presses the endless belt against the rotating member to form a nip portion through which the recording material passes between the rotating member and the endless belt; and between the endless belt and the pressure member And a sliding member that reduces the frictional resistance of the endless belt, abuts against the inner peripheral surface of the endless belt, and moves from the upstream side toward the downstream side in the moving direction of the endless belt. It is characterized in that from the ends of the belt with the step member a step is formed toward the central portion.
Here, the step member can be composed of the same member as the sliding member. Further, the step member may be characterized in that the step is formed to 20 to 120 μm.

  As an effect of the present invention, it is possible to provide an image forming apparatus capable of forming a high-quality image while suppressing the occurrence of paper wrinkles and image misalignment over a long period of time by stabilizing the recording paper conveyance capability in the fixing device. It became possible to do.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type, and includes a plurality of image forming units 1Y, 1M, 1C, on which toner images of respective color components are formed by electrophotography. 1K, a primary transfer unit 10 for sequentially transferring (primary transfer) each color component toner image formed by each image forming unit 1Y, 1M, 1C, 1K to the intermediate transfer belt 15, and a superimposition transferred on the intermediate transfer belt 15 A secondary transfer unit 20 that batch-transfers (secondary transfer) toner images to a sheet P that is a recording material (recording sheet), and a fixing device 60 that fixes the secondary-transferred image on the sheet P are provided. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the present embodiment, each of the image forming units 1Y, 1M, 1C, and 1K includes a charger 12 and a photosensitive drum around which the photosensitive drum 11 is charged around the photosensitive drum 11 that rotates in the arrow A direction. A laser exposure device 13 (an exposure beam is indicated by a symbol Bm in the drawing) in which an electrostatic latent image is written on the image 11, each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. Developing unit 14, primary transfer roll 16 for transferring each color component toner image formed on photosensitive drum 11 to intermediate transfer belt 15 in primary transfer unit 10, and residual toner on photosensitive drum 11 are removed. Electrophotographic devices such as a drum cleaner 17 are sequentially arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 15 in the order of yellow (Y), magenta (M), cyan (C), and black (K). Has been.

The intermediate transfer belt 15 as an intermediate transfer member is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. And the volume resistivity is formed so that it may become 10 < ⁶ > -10 < ¹⁴ > (omega | ohm) cm, The thickness is comprised by about 0.1 mm, for example. The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction B shown in FIG. 1 by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) having excellent constant speed and rotates the intermediate transfer belt 15, and an intermediate that extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents meandering of the intermediate transfer belt 15, and a backup provided in the secondary transfer unit 20. A cleaning backup roll 34 provided in a cleaning unit for scraping off residual toner on the roll 25 and the intermediate transfer belt 15 is provided.

The primary transfer unit 10 includes a primary transfer roll 16 that is disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The primary transfer roll 16 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ^7.5 to 10 ^8.5 Ωcm. The primary transfer roll 16 is placed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 in between, and the primary transfer roll 16 has a voltage (with negative polarity; the same applies hereinafter) having a polarity opposite to that of the toner. (Primary transfer bias) is applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15 so as to form superimposed toner images on the intermediate transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 25. The backup roll 25 is composed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and EPDM rubber inside. And it is formed so that the surface resistivity may be 10 ⁷ to 10 ¹⁰ Ω / □, and the hardness is set to, for example, 70 ° (Asker C: manufactured by Kobunshi Keiki Co., Ltd., the same shall apply hereinafter). The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact with the backup roll 25. ing.

On the other hand, the secondary transfer roll 22 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ^7.5 to 10 ^8.5 Ωcm. The secondary transfer roll 22 is disposed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween. Further, the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the secondary transfer roll 22 and the backup roll 25. The toner image is secondarily transferred onto the paper P conveyed to the transfer unit 20.

  Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided so as to be able to contact and separate. On the other hand, on the upstream side of the yellow image forming unit 1Y, a reference sensor (home position sensor) 42 that generates a reference signal serving as a reference for taking image forming timings in the image forming units 1Y, 1M, 1C, and 1K. It is arranged. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Each image forming unit is instructed by an instruction from the control unit 40 based on the recognition of the reference signal. 1Y, 1M, 1C, and 1K are configured to start image formation.

  Further, in the image forming apparatus according to the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup After secondary transfer is performed by the transport roll 52 that transports the paper P fed by the roll 51, the transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and the secondary transfer roll 22. A conveyance belt 55 that conveys the conveyed paper P to the fixing device 60 and a fixing entrance guide 56 that guides the paper P to the fixing device 60 are provided.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. Is applied, the image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In IPS, the input reflectance data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. Is done. The image data that has undergone image processing is converted into color material gradation data of four colors, Y, M, C, and K, and is output to the laser exposure unit 13.

  The laser exposure unit 13 irradiates the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, for example, with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. Yes. In each of the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent images are developed as toner images of respective colors Y, M, C, and K by the respective image forming units 1Y, 1M, 1C, and 1K.

  The toner images formed on the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 15 at the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Is transcribed. More specifically, in the primary transfer unit 10, a voltage (primary transfer bias) having a polarity opposite to the charging polarity (minus polarity) of the toner is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16. Primary transfer is performed by sequentially superimposing images on the surface of the intermediate transfer belt 15.

  After the toner images are sequentially primary transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. When the toner image is transported to the secondary transfer unit 20, in the paper transport system, the pick-up roll 51 rotates in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and the paper of a predetermined size is transferred from the paper tray 50. P is supplied. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is carried. And the position of the toner image are aligned.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, when a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 26, a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Is done. The unfixed toner image carried on the intermediate transfer belt 15 is collectively electrostatically transferred onto the paper P by the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. The

Thereafter, the sheet P on which the toner image has been electrostatically transferred is transported as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22, and transported downstream of the secondary transfer roll 22 in the sheet transport direction. It is conveyed to the belt 55. The conveyance belt 55 conveys the paper P to the fixing device 60 in accordance with the optimum conveyance speed in the fixing device 60. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge placement unit provided in a discharge unit of the image forming apparatus.
On the other hand, after the transfer onto the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. Is removed from the intermediate transfer belt 15.

  Next, the fixing device 60 used in the image forming apparatus of the present embodiment will be described. FIG. 2 is a side sectional view showing the configuration of the fixing device 60 in the present embodiment. As shown in FIG. 2, in the fixing device 60 of the present embodiment, as an example of a pressure roller pressed from the fixing roll 61 via the fixing roll 61, the endless belt 62, and the endless belt 62 as an example of a rotating member. The main portion is constituted by the pressure pad 64.

The fixing roll 61 is configured by laminating a heat-resistant elastic layer 612 and a release layer 613 around a metal core (cylindrical core) 611.
Inside the fixing roll 61, a halogen heater 66 (for example, rated 600 W) is disposed as a heat source. On the other hand, a temperature sensor 69 is disposed in contact with the surface of the fixing roll 61. The control unit 40 of the image forming apparatus shown in FIG. 1 controls the lighting of the halogen heater 66 based on the temperature measurement value by the temperature sensor 69, and the surface temperature of the fixing roll 61 is a predetermined set temperature (for example, 170 ° C.). ) Is maintained.
The endless belt 62 is supported by the pressure pad 64 and the belt traveling guide 63 so that the endless belt 62 is not deformed more than necessary and can be rotated while maintaining a smooth, substantially circular shape. The nip portion N is disposed in pressure contact with the fixing roll 61.

The pressure pad 64 is disposed inside the endless belt 62 while being pressed against the fixing roll 61 via the endless belt 62, and forms a nip portion N with the fixing roll 61. In the pressure pad 64, a pre-nip member 64a for securing a wide nip portion N is disposed on the inlet side of the nip portion N, and a peeling nip member 64b for distorting the surface of the fixing roll 61 is provided in the nip portion N. Located on the exit side.
Further, in order to reduce the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64, the surface of the pre-nip member 64a and the peeling nip member 64b contacting the endless belt 62 has a low friction as an example of a sliding member. A sheet 68 is provided. The low friction sheet 68 may be configured separately from the pressure pad 64 or may be configured integrally with the pressure pad 64.
The pressure pad 64 and the low friction sheet 68 are held by a metal pressure pad fixing member 65, and a compression coil spring (not shown) is interposed between the pressure pad 64 and the pressure pad fixing member 65. The endless belt 62 is pressed against the fixing roll 61 by the pressure pad 64.

  Further, a belt running guide 63 is attached to the pressure pad fixing member 65 so that the endless belt 62 can smoothly rotate. That is, the belt running guide 63 is made of a material having a small friction coefficient in order to rub against the inner peripheral surface of the endless belt 62. Further, the belt running guide 63 is formed of a material having low thermal conductivity so that it is difficult to remove heat from the endless belt 62.

  The fixing roll 61 is rotated in the direction of arrow C by a drive motor (not shown), and the endless belt 62 is also rotated by this rotation. The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided by the fixing inlet guide 56 and conveyed to the nip N. Then, when the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure (nip pressure) acting on the nip portion N and the heat supplied from the fixing roll 61. In the fixing device 60 of the present embodiment, since the nip portion N can be configured widely by the concave pre-nip member 64a that substantially follows the outer peripheral surface of the fixing roll 61, stable fixing performance can be ensured. In particular, by applying a high nip pressure by the pre-nip member 64a, a plurality of melted color toner images are mixed and colored, or the toner is embedded in the fibers of the paper P, thereby improving the fixing property. .

In addition, in the fixing device 60 of the present embodiment, the surface of the fixing roll 61 is provided in the exit region (peeling nip portion) of the nip portion N by disposing the separation nip member 64b so as to protrude from the outer peripheral surface of the fixing roll 61. It is also possible to configure so that the distortion of the is locally increased. If the separation nip member 64b is arranged in this way, the fixed paper P passes through the locally formed distortion when passing through the separation nip portion, and therefore is wound around the fixing roll 61. This makes it possible to more effectively peel off the paper P.
In particular, by locally increasing the distortion of the fixing roll 61, it is possible to obtain high peeling performance with a small amount of distortion. Therefore, even when a thin heat-resistant resin is used as the release layer 613 of the fixing roll 61, the occurrence of paper wrinkles on the paper P can be suppressed. Further, peeling between the heat-resistant elastic layer 612 and the release layer 613 hardly occurs, and the reliability of the component performance over a long period can be improved together with maintaining the peeling performance.

Furthermore, since the amount of strain on the surface of the fixing roll 61 can be reduced, the heat-resistant elastic body layer 612 of the fixing roll 61 can be thinned. Therefore, since the heat capacity of the fixing roll 61 can be reduced, the warm-up time can be shortened and the power consumption can be reduced. Further, since the heat-resistant elastic body layer 612 having a low thermal conductivity can be thinned, the thermal resistance between the inner surface and the outer surface of the fixing roll 61 can be reduced and the thermal responsiveness can be improved. It is also suitable for conversion.
Note that a peeling member 70 may be disposed on the downstream side of the nip portion N of the fixing roll 61 as an auxiliary means for peeling. The peeling member 70 is held by a holder 72 in a state in which the peeling baffle 71 is close to the fixing roll 61 in a direction (counter direction) opposite to the rotation direction of the fixing roll 61.

Next, each member constituting the fixing device 60 will be described in detail. First, in the fixing roll 61, the core 611 is a cylindrical body made of a material having excellent mechanical strength and high thermal conductivity. For example, a metal or alloy such as iron, aluminum, SUS, or brass, further ceramic, It is comprised by FRM etc. The outer diameter and thickness of the core 611 can be reduced in diameter and thickness because the pressing force of the pressure pad 64 is small in the fixing device 60 of the present embodiment. In the fixing device 60 of the present embodiment, an iron core 611 having an outer diameter of 30 mm, a wall thickness of 0.35 mm, and a length of 360 mm is used.
As the heat-resistant elastic layer 612, any material can be used as long as it is an elastic body having high heat resistance, and examples thereof include silicone rubber and fluorine rubber. Among these materials, silicone rubber is preferable from the viewpoint of low surface tension and excellent elasticity and thermal stability. Examples of such silicone rubber include RTV silicone rubber and HTV silicone rubber. Specifically, polydimethyl silicone rubber (MQ), methylphenyl silicone rubber (PMQ), methyl vinyl silicone rubber (VMQ), fluorosilicone rubber ( FVMQ) and the like. The thickness of the heat resistant elastic layer 612 is usually set to 3 mm or less, preferably 0.5 to 1.5 mm. In fixing device 60 of the present embodiment, HTV silicone rubber having a hardness of 45 ° (JIS-A) is coated to a thickness of 0.5 mm.
As a method for coating the heat-resistant elastic layer 612 on the core 611, for example, a known coating method such as kneader coating, bar coating, curtain coating, spin coating, dip coating, or the like can be used.

  The release layer 613 is not particularly limited as long as it is a resin having heat resistance and releasability from the viewpoint of suppressing the offset of the toner image. For example, silicone resin, fluororesin, silicone rubber, fluororubber, or the like is used. However, a fluororesin particularly excellent in releasability and wear resistance is suitable. As the fluororesin, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) and the like can be used. The thickness of the release layer 613 is preferably 30 to 50 μm. Although there is no restriction | limiting in particular as a method of coat | covering the release layer 613 to the heat resistant elastic body layer 612, For example, the coating method mentioned above can be used. In the fixing device 60 of the present embodiment, as the release layer 613, PFA having a thickness of 30 μm is coated by dip coating to form a surface close to a mirror surface.

The endless belt 62 is an endless belt whose original shape is formed in a cylindrical shape. The endless belt 62 includes a base layer and a release layer coated on the surface or both surfaces of the base layer on the fixing roll 61 side. The base layer is formed of a polymer such as thermosetting polyimide, thermoplastic polyimide, polyamide, polyimide amide, or a metal such as SUS, nickel, copper, etc. Among them, it has excellent heat resistance, wear resistance, chemical resistance, etc. In this respect, thermosetting polyimide is preferable. The thickness is set to about 30 to 200 μm, preferably about 50 to 125 μm. The release layer coated on the surface of the base layer is formed of a fluororesin such as PFA, PTFE, or FEP, and the thickness is set to about 5 to 100 μm, preferably about 10 to 50 μm. In the fixing device 60 according to the present embodiment, a base layer having a peripheral length of 94 mm, a width of 320 mm, a thermosetting polyimide having a thickness of 75 μm, and a release layer having a dip coating of PFA having a thickness of 30 μm is used.
The layer configuration of the endless belt 62 is not limited to this, and a configuration in which an elastic layer is provided on the base layer or a configuration in which a layer for further reducing sliding resistance is provided on the inner peripheral surface can also be adopted. .

As described above, the pressure pad 64 may be formed of a single member or a plurality of members having different functions. However, in the fixing device 60 of the present embodiment, the pre-nip member 64a and the peeling nip are arranged. It is comprised by the member 64b. The prenip member 64 a can use an elastic body such as silicone rubber or fluororubber, a leaf spring, or the like, and the surface on the fixing roll 61 side is formed in a concave shape that substantially follows the outer peripheral surface of the fixing roll 61.
The peeling nip member 64b is made of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, or polyamide, or a metal such as iron, aluminum, or SUS, or a ceramic. As the shape of the peeling nip member 64b, the outer surface shape in the nip portion N is formed in a convex curved surface shape having a constant radius of curvature.
In the fixing device 60 of the present embodiment, the pressure pad 64 includes a pre-nip member 64a made of silicone rubber having a width of 10 mm, an overall length of 320 mm, and an average thickness of 5 mm, and a peeling nip member 64b made of aluminum.

Further, as described above, the belt running guide 63 is made of a material having a low coefficient of friction and a low thermal conductivity so that heat is not easily taken from the endless belt 62 because it slides on the inner peripheral surface of the endless belt 62. A heat resistant resin such as PFA or PPS is used. In particular, ribs are formed on the surface of the belt running guide 63 on the endless belt 62 side in the moving direction of the endless belt 62 to reduce the contact area with the inner peripheral surface of the endless belt 62, thereby further increasing the sliding resistance. Reduced and reduced heat conduction.
Further, edge guides (not shown) having flanges are provided at both ends of the belt traveling guide 63 in the axial direction, and movement of the endless belt 62 in the axial direction (belt walk) is restricted.

A lubricant application member 67 is disposed in the belt traveling guide 63 along the longitudinal direction of the fixing device 60. The lubricant application member 67 is formed of a porous material so that the lubricant can be held. A porous material refers to a material that has a hole and can hold a lubricant, such as a substance having a large number of pores or a substance having a structure in which fine fibers are entangled. Specifically, a sponge or foam Resins, felts, woven fabrics, films made porous by stretching, and the like are included. The lubricant application member 67 supplies an appropriate amount of lubricant such as silicone oil to the inner peripheral surface of the endless belt 62.
As the lubricant, in addition to liquids such as silicone oil and fluorine oil, grease in which a solid substance and a liquid are mixed can be used, or a combination thereof can be used. In the fixing device 60 of the present embodiment, silicone oil is used from the viewpoint of safety. Examples of the silicone oil include dimethyl silicone oil, amino-modified silicone oil, carboxy-modified silicone oil, silanol-modified silicone oil, sulfonic acid-modified silicone oil, and the like. Oil is preferred.

  Here, in the fixing device 60 according to the present embodiment, the low friction sheet 68 is configured to extend from the nip portion N to the downstream side in the moving direction of the endless belt 62, and a portion (extension portion) 68a extending to the downstream side. Step portions are formed on both sides of the rubbing surface side of the endless belt 62 for collecting the lubricant to the central portion in the width direction of the endless belt 62, and the extending portion 68 a is connected to the inner periphery of the endless belt 62. It is comprised so that it may contact | abut to a surface. With this configuration, the lubricant that has shifted toward the both ends in the width direction of the endless belt 62 due to the nip pressure when passing through the nip portion N can be gathered to the central portion, so that the lubricant can be collected in the endless belt 62. It is possible to hold a sufficient amount of lubricant on the inner peripheral surface of the endless belt 62 by suppressing the leakage from the both end portions to the outside. As a result, the slidability between the endless belt 62 and the low friction sheet 68 can be stabilized, and the endless belt 62 can be smoothly rotated, so that the paper P can be stably conveyed at a constant speed with the fixing roll 61. Therefore, the occurrence of image misalignment and paper wrinkles on the paper P can be suppressed.

As described above, the paper P on which the toner image has been electrostatically transferred passes through the nip portion N of the fixing device 60, whereby the toner image is fixed to the paper P, but when the paper P passes through the nip portion N. Is received from the fixing roller 61 on the driving side. That is, the paper P is conveyed by receiving a frictional force from the fixing roll 61 as the fixing roll 61 rotates.
On the other hand, in a state where the sheet P is not conveyed to the nip portion N, the driven endless belt 62 is also rotated by receiving a frictional force from the fixing roll 61 as the fixing roll 61 rotates. However, when the paper P is conveyed to the nip portion N and the paper P is nipped by the nip portion N, the endless belt 62 receives the conveying force from the fixing roll 61 via the paper P. Accordingly, when viewed from the sheet P side, when the sheet P passes through the nip portion N, the sheet P receives a conveying force from the fixing roll 61 and a force in the direction opposite to the conveying direction from the endless belt 62 side. (Reverse conveying force) will act.

By the way, since the pressure pad 64 is pressed in the nip portion N of the endless belt 62, a force in the direction opposite to the rotation direction acts as a sliding resistance from the pressure pad 64. Therefore, as described above, the low friction sheet 68 is interposed between the endless belt 62 and the pressure pad 64, and a lubricant is applied to the sliding surface of the low friction sheet 68 so that the endless belt 62 and the pressure pad are applied. 64 is configured to reduce sliding resistance with 64 as much as possible.
Therefore, in the normal state, the endless belt 62 receives a very small sliding resistance from the pressure pad 64 and can rotate smoothly. Therefore, the endless belt 62 can rotate at the same speed as the paper P. . In this case, the reverse conveying force received by the paper P is small enough to be ignored because of the sliding resistance from the pressure pad 64 via the endless belt 62. Therefore, the paper P is stably conveyed at the same speed as the fixing roll 61.

However, since a pressing force acts between the endless belt 62 and the pressure pad 64, the applied lubricant is pushed out from the sliding portion at the sliding portion between the endless belt 62 and the low friction sheet 68. Since the force acts, as the endless belt 62 continues to move, the lubricant leaks from both ends in the width direction of the endless belt 62, and the amount of lubricant gradually decreases at the sliding portion. When the amount of lubricant at the sliding portion decreases, the sliding resistance between the endless belt 62 and the low friction sheet 68, that is, the sliding resistance between the endless belt 62 and the pressure pad 64 increases.
When the sliding resistance between the endless belt 62 and the pressure pad 64 increases, the reverse conveying force that the sheet P receives from the pressure pad 64 via the endless belt 62 when the sheet P is conveyed through the nip portion N also increases. . Furthermore, if the sliding resistance between the endless belt 62 and the pressure pad 64 becomes excessive, the reverse conveyance force acting on the paper P becomes so large that it cannot be ignored, and the conveyance of the paper P cannot follow the rotation of the fixing roll 61. A slip occurs between the paper P and the fixing roll 61. Therefore, the smooth conveyance of the paper P is hindered, causing image shift and paper wrinkles on the paper P.

  In particular, the nip portion N has a so-called reverse crown shape in which the outer diameter of the fixing roll 61 is increased from the central portion to both ends, or the pressing force between the pre-nip member 64a and the fixing roll 61 is increased from the central portion to both ends. It is set so as to increase over the part. By setting in this way, a force is always applied in the width direction from the central portion toward both ends of the nip portion N entrance side of the paper P to prevent the paper P from wrinkling. Yes. Such a balance of subtle forces acting in the width direction of the paper P increases the sliding resistance between the endless belt 62 and the pressure pad 64, so that the paper P cannot follow the conveyance of the fixing roll 61. As a result, the sheet P collapses, and a paper wrinkle is generated on the paper P or an image shift occurs.

  Therefore, in the fixing device 60 of the present embodiment, the low friction sheet 68 is configured to extend downstream from the nip portion N in the moving direction of the endless belt 62, and the sliding surface of the extending portion 68a with the endless belt 62 is configured. On both side portions on the side, step portions for collecting the lubricant to the central portion in the width direction of the endless belt 62 are formed. Then, by bringing the extending portion 68a into contact with the inner peripheral surface of the endless belt 62, the lubricant is gathered to the central portion, and the lubricant is prevented from leaking outside from both end portions of the endless belt 62, The slidability between the endless belt 62 and the low friction sheet 68 is stabilized.

  Specifically, the configuration of the low friction sheet 68 will be described. The basic structure of the low friction sheet 68 is a fluororesin sheet such as Teflon (trade name) from the viewpoint of heat resistance and low friction, and unevenness on the rubbing surface side of the fluororesin sheet for the purpose of reducing the contact area. Processed, glass fiber sheet impregnated with fluorinated resin against a nip pressure and with a strength that does not crush unevenness, and glass fiber sheet with a fluororesin sheet such as Teflon (trade name) Adhered ones are used. In the fixing device 60 of the present embodiment, a low-friction sheet 68 is used in which a glass fiber sheet having a thickness of 50 μm is used as a base and a Teflon (trade name) sheet having a thickness of 20 μm is bonded to the sliding surface side of the glass fiber sheet. ing.

The structure of the low friction sheet 68 will be described with reference to FIG. FIG. 3A is a plan view showing the extending portion 68a side of the low friction sheet 68, and FIG. 3B is a sectional view taken along line XX ′ of the extending portion 68a of the low friction sheet 68. As shown in FIG. 3A, the low friction sheet 68 is formed in a rectangular shape, and the length in the direction orthogonal to the moving direction of the endless belt 62 is approximately the same as or slightly longer than the width of the endless belt 62. Is formed. The length of the endless belt 62 in the moving direction is set so as to have a portion (extending portion 68a) that extends to the downstream side of the nip portion N (see also FIG. 2). The length of the extending portion 68a in the moving direction of the endless belt 62 can be set as appropriate, but is long enough to press the extending portion 68a against the inner peripheral surface of the endless belt 62 by the stiffness of the low friction sheet 68 itself. Can be set. In addition, the extension part 68a can be set longer, and in that case, a pressing member (not shown) that presses from the back surface of the extension part 68a toward the inner peripheral surface of the endless belt 62 is disposed. To do.
In the fixing device 60 of the present embodiment, the length of the low friction sheet 68 in the direction orthogonal to the moving direction of the endless belt 62 is 320 mm, and the length of the extending portion 68a in the moving direction of the endless belt 62 is 25 mm. A low friction sheet 68 is used.

  In the extended portion 68a of the low friction sheet 68, step portions 681 and 682 are formed on both sides of the friction surface side with the endless belt 62, as shown in FIGS. 3 (a) and 3 (b). The step portions 681 and 682 are formed of a flat plate member having a certain thickness. And each level | step-difference part 681,682 has the side surface (step | difference) 681k, 682k which goes to the center part from the edge part of the low friction sheet | seat 68 toward the downstream from the upstream of the moving direction of the endless belt 62. Yes. That is, the side surface 681k and the side surface 682k are formed in a “C” shape toward the moving direction of the endless belt 62. Therefore, the width of the concave portion 683 sandwiched between the step portions 681 and 682 on both sides is formed to become narrower toward the downstream side in the moving direction of the endless belt 62. An opening 684 sandwiched between the stepped portion 681 and the stepped portion 682 is provided in the most downstream portion of the extending portion 68a.

  By providing the step portions 681 and 682 having such a configuration, when the endless belt 62 and the low friction sheet 68 pass through the sliding portion (nip portion N), both end sides in the width direction of the endless belt 62 are caused by the nip pressure. The lubricant that has been biased to the center can be gathered to the center by the side surface 681k and the side surface 682k. Therefore, even if the endless belt 62 repeatedly moves, it is possible to prevent the lubricant from leaking out from both ends in the width direction of the endless belt 62, and the amount of lubricant in the sliding portion can be stably held over the entire sliding portion. It is possible to keep. As a result, the slidability between the endless belt 62 and the low friction sheet 68 is stabilized, so that the endless belt 62 rotates smoothly, and the paper P can be stably conveyed at a constant speed with the fixing roll 61. Thus, the occurrence of image misalignment and paper wrinkles on the paper P can be suppressed.

As a specific configuration of the extending portion 68a in the low friction sheet 68, the stepped portions 681 and 682 are laminated on the glass fiber serving as a base, and the glass fiber is laminated, and the rubbing surface including the stepped portions 681 and 682 is formed. A Teflon (trade name) sheet is bonded to the entire surface.
In addition, by covering the entire surface of the rubbing surface with a material that hardly absorbs the lubricant, the amount of the lubricant in the sliding portion due to the infiltration of the lubricant into the low friction sheet 68, and further, When the lubricant comes into contact with the pre-nip member 64a formed of silicone rubber or the like, the gelation increases and the viscosity becomes high, and it is possible to suppress the disadvantage that the lubricant is mixed into the sliding portion and increases the sliding resistance. Therefore, it is preferable that the rubbing surface of the low friction sheet 68 is made of a material such as the above-described Teflon (trade name) sheet that has low absorbability with respect to the lubricant.

Further, the heights of the side surfaces (steps) 681k and 682k of the step portions 681 and 682 in the extending portion 68a are set to 20 to 120 μm, preferably 40 to 70 μm. This is because if the level difference is lower than 20 μm, the height for gathering the lubricant is insufficient, and the lubricant leaks. On the other hand, if it is higher than 120 μm, the lubricant adheres to the low friction sheet 68 side, which causes a decrease in the amount of lubricant on the endless belt 62 side. In the fixing device 60 of the present embodiment, the height of the side surfaces 681k and 682k is set to 50 μm, but it is sufficient to block the lubricant and change the moving direction, and slips through the step portions 681 and 682. Almost no lubricant was observed. In addition, since the thickness of the low friction sheet 68 itself is 70 μm, the extension portion 68 a is also about 120 μm. Therefore, there is no problem such as an influence on the rotation of the endless belt 62.
Here, the step portions 681 and 682 may be formed of a flat plate-like member having a constant thickness, or may be formed in a wedge shape in which the plate thickness increases toward the downstream side in the moving direction of the endless belt 62. Good. Moreover, as long as it has the side surfaces 681k and 682k which go to the center part from the edge part of the low friction sheet | seat 68, the planar shape can be formed in what kind of shape.
Further, the angle θ (see FIG. 3) formed between the side surfaces 681k and 682k of the step portions 681 and 682 and the width direction of the low friction sheet 68 can be set as appropriate, but is set to 5 ° in the present embodiment.

  In the fixing device 60 of the present embodiment, the low friction sheet 68 is configured to extend from the nip portion N to the downstream side in the moving direction of the endless belt 62, and a portion (extending portion) 68a extending to the downstream side is provided. A step member (lubricant collecting member) was used. Then, stepped portions for collecting the lubricant to the central portion in the width direction of the endless belt 62 are formed on both sides of the extending portion 68a on the rubbing surface side with the endless belt 62. In addition to such a configuration, a step member (lubricant collecting member) in which a step portion for collecting the lubricant at the central portion in the width direction of the endless belt 62 is formed separately from the low friction sheet 68. The endless belt 62 may be disposed downstream of the nip portion N in the moving direction.

Here, in the fixing device 60 of the present embodiment in which the low friction sheet 68 is disposed, an experiment is performed to measure a change with time of the driving torque of the fixing roll 61 when continuous driving is performed, and the endless belt 62 and the low friction sheet 68 are reduced. The change in sliding resistance with the friction sheet 68 was measured. As a comparative example, an experiment under the same conditions was performed for a conventional low friction sheet in which the extending portion 68a is not disposed. As described above, the driven endless belt 62 is rotated by receiving a frictional force from the fixing roll 61 as the driving side fixing roll 61 rotates. This is based on the fact that the sliding resistance with the sheet 68 can be grasped as the driving torque of the fixing roll 61.
In this experiment, the fixing roller 61 was continuously driven at a process speed of 194 mm / s while controlling the fixing temperature of the fixing roller 61 at 170 ° C., and the driving torque of the fixing roller 61 was measured. Here, an amino-modified silicone oil having a viscosity of 300 cs (normal temperature) was used as the lubricant.

FIG. 4 is a diagram showing the change over time in the driving torque of the fixing roll 61 when the low friction sheet 68 of the present embodiment is used and when the conventional low friction sheet is used. As shown in FIG. 4, in the case of using a conventional low friction sheet, the driving torque was 0.30 N · m in the initial state (0 hour), but 0.65 N · m at the time of continuous driving 100 hours. rise to m. On the other hand, when the low friction sheet 68 of the present embodiment is used, the driving torque (0.35 N · m) is almost the same as in the initial state even at 100 hours, and the driving torque almost increases. There wasn't.
When observing the fixing device 60 at that time, when a conventional low friction sheet is used, leakage of silicone oil is observed from the endless belt 62 during continuous driving, and the silicone oil wraps around the surface side of the endless belt 62, Furthermore, the movement of silicone oil from the surface of the endless belt 62 to the surface of the fixing roll 61 was also confirmed. Further, after 100 hours of continuous driving, the presence of silicone oil was hardly observed in the sliding portion between the endless belt 62 and the low friction sheet. On the other hand, when the low friction sheet 68 of the present embodiment is used, leakage of silicone oil from the endless belt 62 during continuous driving is not recognized, and even after 100 hours of continuous driving, the low friction sheet 68 is low. It was confirmed that silicone oil was present in the sliding portion with the friction sheet 68 in substantially the same amount as in the initial state.
As described above, this experiment confirmed the superiority of the fixing device 60 using the low friction sheet 68 of the present embodiment.

As described above, in the fixing device 60 of the present embodiment, the low friction sheet 68 is configured to extend from the nip portion N to the downstream side in the moving direction of the endless belt 62, and the endless belt 62 of the extending portion 68a. Steps 681 and 682 are formed on both sides of the rubbing surface with the endless belt 62 so as to gather the lubricant to the central portion in the width direction, and the extended portion 68a contacts the inner peripheral surface of the endless belt 62. Touching. With this configuration, the lubricant that has shifted toward the both ends in the width direction of the endless belt 62 due to the nip pressure when passing through the nip portion N can be gathered to the central portion, so that the lubricant can be collected in the endless belt 62. It is possible to suppress leakage from the both ends of the belt to the outside, and to maintain a sufficient amount of lubricant on the inner peripheral surface of the endless belt 62. As a result, the slidability between the endless belt 62 and the low friction sheet 68 can be stabilized, and the state in which the endless belt 62 can be smoothly rotated can be maintained. As a result, the paper P can be stably conveyed at a constant speed with the fixing roll 61, and the occurrence of image misalignment and paper wrinkles on the paper P can be suppressed.
Further, since the endless belt 62 can be smoothly rotated, an increase in the driving torque of the fixing roll 61 can be suppressed. Therefore, it is possible to suppress the breakage of the transmission gear that transmits the driving force to the fixing roll 61 and to reduce the torque of the driving motor. It is also possible to save power.

[Embodiment 2]
In the first embodiment, the image forming apparatus is described in which the fixing roll 61 having a heat source is used as the heating unit and the fixing device 60 using the endless belt 62 with the pressure pad 64 pressed as the pressing unit is mounted. In the second embodiment, a fixing device mounted on the image forming apparatus shown in FIG. 1, which uses a fixing belt that is electromagnetically heated as a heating unit and uses a pressure roll as a pressing unit, will be described. To do. In addition, about the structure similar to Embodiment 1, the same code | symbol is used and the detailed description is abbreviate | omitted here.

  The fixing device 101 used in the image forming apparatus of the present embodiment will be described. FIG. 5 is a side sectional view showing the configuration of the fixing device 101 in the present embodiment. As shown in FIG. 5, the fixing device 101 is arranged such that an electromagnet 80 as an example of a magnetic field generating member that generates an alternating magnetic field is disposed close to the outer peripheral surface, and faces the fixing belt 92. A main part is configured by a pressure roll 91 as an example of the rotated member and a pressure pad 64 as an example of a pressure member pressed from the pressure roll 91 via the fixing belt 92.

First, the fixing belt 92 is an endless belt, for example, having a diameter of φ30 mm, whose original shape is formed in a cylindrical shape. As shown in FIG. 6, the layer structure of the fixing belt 92 is a base material layer 921 made of a sheet member having high heat resistance, a conductive layer 922 laminated on the base material layer 921, and the uppermost layer. The surface release layer 923 is basically composed of at least three layers.
The base material layer 921 of the fixing belt 92 is formed of a sheet having a high heat resistance with a thickness of 10 to 100 μm, more preferably 50 to 100 μm (for example, 75 μm). For example, polyester, polyethylene terephthalate, polyethersulfone, polyether What consists of synthetic resins with high heat resistance, such as a ketone, polysulfone, a polyimide, a polyimide amide, polyamide, can be used.
In order to restrict meandering (belt walk) in the width direction of the fixing belt 92, edge guides (not shown) are provided at both ends of the fixing belt 92, but both ends of the fixing belt 92 are edge guides. In order to ensure a rigidity that does not cause buckling even when it hits the substrate, and to maintain a circular shape of φ30 mm in a region other than the nip portion N, as the base material layer 921, for example, a polyimide sheet with a thickness of 80 μm Is used.

The conductive layer 922 of the fixing belt 92 is an electromagnetic induction heating element layer that induces and generates heat by the electromagnetic induction action of an alternating magnetic field generated by the electromagnet 80, and has a thickness of about 1 to 50 μm of a metal such as iron, cobalt, nickel, copper, and chromium. What was formed in is used. Here, since the fixing belt 92 needs to be deformed so as to follow the nip portion N in the nip portion N formed by the pressure pad 64 and the pressure roll 91 and in the vicinity of the nip portion N, the fixing is performed. Since the belt 92 as a whole needs flexibility, it is preferable to form the conductive layer 922 as thin as possible.
In the fixing device 101 of this embodiment, copper having high conductivity is formed as the conductive layer 922 so as to have a thickness of about 5 μm so as to increase the heat generation efficiency, and is plated on the base material layer 921 made of polyimide. -The one formed by vapor deposition or the like is used.

Further, since the surface release layer 923 of the fixing belt 92 is a layer that is in direct contact with the unfixed toner image carried on the paper P, it is necessary to use a material having good releasability. Examples of the material constituting the surface release layer 923 include PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), silicone copolymer, or a composite layer thereof. . The surface release layer 923 is provided on the uppermost layer of the fixing belt 92 by appropriately selecting one of these materials with a thickness of 1 to 50 μm.
If the thickness of the surface release layer 923 is too thin, it is not sufficient in terms of wear resistance, and the life of the fixing belt 92 is shortened. On the other hand, if it is too thick, the heat capacity of the fixing belt 92 becomes too large and the warm-up time becomes long. In view of this, in the fixing device 101 of the present embodiment, PFA having a thickness of 10 μm is used as the surface release layer 923 in consideration of the balance between wear resistance and heat capacity.

  Note that an elastic layer may be provided between the conductive layer 922 and the surface release layer 923 of the fixing belt 92. In this case, since the elastic layer is formed of an elastic material such as silicone rubber, the fixing belt 92 can be deformed so as to follow the unevenness of the toner image carried on the paper P. Heat can be supplied to the entire toner image on the paper P more evenly.

Next, the pressure pad 64 includes an elastic member 641 that is pressed from the pressure roll 91 via the fixing belt 92 to form the nip portion N, and a pad support member 642 that supports the elastic member 641 (see FIG. 5). The elastic member 641 is formed of an elastic body such as silicone rubber or fluorine rubber, and the surface on the pressure roll 91 side is formed substantially flat. Then, the sheet P that has passed through the nip portion N is peeled off from the fixing belt 92 by the change in the curvature of the fixing belt 92 in the exit region (peeling nip portion) of the nip portion N. In the fixing device 101 of this embodiment, a silicone rubber having a rubber hardness of 35 ° (JIS-A) is used as the elastic member 641.
The pad support member 642 is made of a plate material having a thickness of about 1 to 2 mm and made of a metal such as SUS or iron, a synthetic resin having a high heat resistance, and the like, and improves handling properties. The pressure pad 64 is fixed to the pressure pad fixing member 65 through the pad support member 642.
Here, as an auxiliary means for peeling by the pressure pad 64, a peeling member 70 can be disposed on the downstream side of the nip portion N of the fixing belt 92. The peeling member 70 is held by the holder 72 in a state where the peeling baffle 71 is close to the fixing belt 92 in a direction (counter direction) opposite to the rotation direction of the fixing belt 92.

The pressure pad fixing member 65 that supports the pressure pad 64 has a deflection amount of a certain amount or less so that the pressure pad 64 can uniformly receive the pressing force from the pressure roll 91 in the longitudinal direction. A material having a certain level of rigidity or higher is required. Furthermore, since the fixing device 101 of the present embodiment employs a configuration in which the fixing belt 92 is heated using electromagnetic induction, it is a material that does not affect or is unlikely to affect the induced magnetic field. The material must be unaffected or difficult to be affected by the induced magnetic field. Therefore, for example, a heat-resistant resin such as glass-mixed PPS (polyphenylene sulfide), a nonmagnetic metal such as aluminum, and the like are arranged as far as possible from the electromagnet 80.
A compression coil spring (not shown) is disposed between the pressure pad 64 and the pressure pad fixing member 65, and the fixing belt 92 is pressed against the pressure roll 91 by the pressure pad 64.

A low friction sheet 68 as an example of a rubbing member is disposed between the pressure pad 64 and the fixing belt 92 in order to reduce sliding resistance between the inner peripheral surface of the fixing belt 92 and the pressure pad 64. Has been. The low friction sheet 68 may be configured separately from the pressure pad 64 or may be configured integrally with the pressure pad 64. In the fixing device 101 of the present embodiment, the low friction sheet 68 is configured separately from the pressure pad 64, one end is fixed to the pressure pad fixing member 65, and is sandwiched between the pressure pad 64 and the fixing belt 92. It is constituted so that.
In addition, a lubricant is applied in advance to the sliding surface of the low friction sheet 68 with the inner peripheral surface of the fixing belt 92, but an appropriate amount of lubricant such as silicone oil is supplied to the inner peripheral surface of the endless belt 62. A lubricant application member may be provided.

Next, the pressure roll 91 is disposed so as to face the fixing belt 92, and is rotated in a direction indicated by an arrow D by a drive motor (not shown) at a process speed of, for example, 140 mm / s. Is configured to do. Then, the fixing belt 92 is held between the pressure roll 91 and the pressure pad 64 to form a nip portion N, and the paper P carrying an unfixed toner image is passed through the nip portion N. The unfixed toner image is fixed on the paper P by applying heat and pressure.
The pressure roll 61 includes, for example, a solid iron core (cylindrical core) 911 having a diameter of 18 mm, a heat-resistant elastic body layer 912 such as a 5 mm-thick silicone sponge coated on the outer peripheral surface of the core 911, and For example, a release layer 913 with a heat-resistant resin coating such as PFA having a thickness of 50 μm or a heat-resistant rubber coating is laminated.

Further, a temperature equalizing roll 96 made of a metal such as aluminum or stainless steel having a good thermal conductivity is disposed so as to be able to contact and separate from the surface of the pressure roll 91. The temperature equalizing roll 96 is located away from the pressure roll 91 when the temperature of the fixing belt 92 and the pressure roll 91 is cold, such as immediately after the energization of the fixing device 101 is started. When a temperature difference along the axial direction occurs in the fixing belt 92 or the pressure roll 91, for example, when a small size paper P is continuously fixed, the temperature equalizing roll 96 is changed to the pressure roll 91. It is comprised so that it may contact | abut. As the temperature equalizing roll 96 abuts on the pressure roll 91 in this way, the temperature equalizing roll 96 follows the pressure roll 91 and uniformizes the temperature distribution in the axial direction of the pressure roll 91. The temperature distribution in the axial direction of the fixing belt 92 is made uniform.
In the fixing device 101 of the present embodiment, a solid aluminum roll having a diameter of 10 mm is used as the temperature equalizing roll 96. Note that a release layer such as PFA may be formed on the surface of the temperature uniformizing roll 96, for example. Further, the temperature equalizing roll 96 may be in constant contact with the pressure roll 91.

Next, an electromagnet 80 that performs electromagnetic induction heating by applying an AC magnetic field to the conductive layer 922 of the fixing belt 92 will be described. The electromagnet 80 is formed in a round shape with a cross section that follows the shape of the fixing belt 92, and is installed with a clearance of about 0.5 to 2 mm from the outer peripheral surface of the fixing belt 92 that is a heated member (see FIG. 5). Further, the electromagnet 80 is formed in a rectangular shape extending over the entire width of the fixing belt 92 with the direction orthogonal to the moving direction of the fixing belt 92 as a longitudinal direction. The electromagnet 80 may be installed inside the fixing belt 92.
FIG. 7 is a schematic cross-sectional view for explaining the configuration and operation of the electromagnet 80. In FIG. 7, the configuration is schematically expressed for easy understanding. As shown in FIG. 7, the electromagnet 80 includes an exciting coil 801 that generates a magnetic field, a coil support member 802 that holds the exciting coil 801, an exciting circuit 803 that supplies current to the exciting coil 801, and an exciting coil 801. The magnetic field shielding member 804 provided on the opposite side of the fixing belt 92 and the core member 805 provided in the central portion of the exciting coil 801 are configured.

As the exciting coil 801, for example, a coil in which 16 litz wires having a diameter of 0.5 mm that are insulated from each other are wound in a closed loop shape such as an ellipse, an ellipse, or a rectangle is used. The exciting coil 801 is hardened with an adhesive and maintains its shape.
An alternating current having a predetermined frequency is applied to the excitation coil 801 by an excitation circuit 803. As a result, an alternating magnetic field H is generated around the exciting coil 801. When the AC magnetic field H crosses the conductive layer 922 of the fixing belt 92, an eddy current I is generated in the conductive layer 922 so as to generate a magnetic field that prevents the change of the AC magnetic field H by electromagnetic induction. The frequency of the alternating current applied to the exciting coil 801 is set to 10 to 50 kHz, for example, but is set to 30 kHz in the present embodiment.
In this way, when the eddy current I flows through the conductive layer 922 of the fixing belt 92, Joule heat is generated by the electric power W (W = I ² R) proportional to the resistance value R of the conductive layer 922, and the fixing belt 92. Heat.

The coil support member 802 is preferably made of a heat-resistant non-magnetic material. For example, heat-resistant glass, polycarbonate, polyethersulfone, PPS (polyphenylene sulfide), or the like, or glass fiber is used for these. A mixed heat resistant resin is used.
The core member 805 is disposed at the center of the coil support member 802 and is made of a ferromagnetic material such as ferrite. The core member 805 can efficiently concentrate the magnetic flux generated in the exciting coil 801 and increase the heating efficiency of the fixing belt 92. Therefore, the frequency of the exciting circuit 803 for applying an alternating current to the exciting coil 801 can be set low. In addition, the number of turns of the exciting coil 801 can be reduced. Therefore, there is an advantage that the power supply can be downsized, the excitation circuit 803 can be downsized, and these can be manufactured at low cost.
The magnetic field shielding member 804 is made of a magnetic material such as iron, cobalt, nickel, or ferrite. The magnetic field shielding member 804 collects magnetic flux leaked to the outside from the exciting coil 801 to form a magnetic path, enables efficient heating, and the magnetic flux leaks out of the fixing device 101 and is a peripheral member. Suppresses unintentional heating.

  As described above, in the fixing device 101 of the present embodiment, the fixing belt 92 can be directly heated by electromagnetic induction by the electromagnet 80, so that a sufficient amount of heat for toner fixing is instantly supplied from the fixing belt 92 at the nip portion N. It becomes possible to supply to. Further, the contact with the fixing belt 92 at the nip portion N is only the pressure pad 64 via the low friction sheet 68 inside the fixing belt 92 and only the pressure roll 91 outside the fixing belt 92. Since both are made of silicone rubber or silicone sponge having low thermal conductivity, heat does not easily flow out, and there is an advantage that the supplied energy can be used effectively for fixing processing. For this reason, the warm-up time can be shortened, and it is not necessary to set a standby mode or a low power mode for giving preheating, which is extremely excellent from the viewpoint of energy saving.

  The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided to the nip N of the fixing device 101 by the fixing inlet guide 56. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the fixing belt 92. Also in the fixing device 101 of the present embodiment, since the nip portion N can be configured widely between the pressure roll 91 and the pressure pad 64, stable fixing performance can be ensured.

Here, in the fixing device 101 of the present embodiment, as in the case of the first embodiment, the low friction sheet 68 is extended to the downstream side in the moving direction of the fixing belt 92 from the nip portion N, and this extension is performed. Step portions 681 and 682 for gathering the lubricant to the central portion in the width direction of the fixing belt 92 are formed on both sides of the protruding portion 68a on the rubbing surface side with the fixing belt 92, and the extending portion 68a is used as the fixing belt. It is made to contact | abut to the internal peripheral surface of 92.
With such a configuration, when the nip portion N passes through the nip portion N, the lubricant that has shifted to both ends in the width direction of the fixing belt 92 due to the nip pressure is gathered to the center portion, so that the lubricant is collected at both end portions of the fixing belt 92. Therefore, it is possible to maintain a sufficient amount of lubricant on the inner peripheral surface of the fixing belt 92. As a result, the slidability between the fixing belt 92 and the low friction sheet 68 can be stabilized, and the state in which the fixing belt 92 can be smoothly rotated can be maintained. As a result, the paper P can be stably conveyed at a constant speed with the pressure roll 91, and the occurrence of image misalignment and paper wrinkles on the paper P can be suppressed.

[Embodiment 3]
In the second embodiment, the image forming apparatus in which the fixing device 92 using the fixing belt 92 that is heated by electromagnetic induction as the heating unit and the pressure roll 91 as the pressing unit is mounted has been described. In Embodiment 3, a fixing device mounted on the image forming apparatus shown in FIG. 1 and using a fixing belt with a heat generation source pressed as a heating unit will be described. In addition, about the structure similar to Embodiment 2, the same code | symbol is used and the detailed description is abbreviate | omitted here.

FIG. 8 is a side sectional view showing a configuration of the fixing device 102 in the present embodiment. As shown in FIG. 8, in the fixing device 102 of the present embodiment, the fixing belt 92 is disposed on the toner image carrying surface side of the paper P. A ceramic heater 82 which is a resistance heating element as an example of a heat source is disposed inside the fixing belt 92, and heat is supplied from the ceramic heater 82 to the nip portion N.
The ceramic heater 82 has a substantially flat surface on the pressure roll 91 side. Then, it is arranged in a state of being pressed against the pressure roll 91 via the fixing belt 92 and forms a nip portion N. Therefore, the ceramic heater 82 also functions as a pressure member. The sheet P that has passed through the nip portion N is peeled off from the fixing belt 92 by the change in the curvature of the fixing belt 92 in the exit region (peeling nip portion) of the nip portion N.
Further, in order to reduce the sliding resistance between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82 between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82, a low friction sheet 68 as an example of a rubbing member. Is arranged. The low friction sheet 68 may be configured separately from the ceramic heater 82 or may be configured integrally with the ceramic heater 82.

On the other hand, the pressure roll 91 is disposed so as to face the fixing belt 92, and is configured to rotate in the direction of arrow D by a drive motor (not shown), so that the fixing belt 92 is driven to rotate. The pressure roll 91 includes a core (cylindrical cored bar) 911, a heat-resistant elastic body layer 912 coated on the outer peripheral surface of the core 911, and a release layer 913 made of a heat-resistant resin coating or a heat-resistant rubber coating. Has been configured. In the fixing device 102 of the present embodiment, the fixing belt 92 is an endless belt whose original shape is formed in a cylindrical shape, and is coated on the base layer and the surface or both surfaces of the base layer on the pressure roll 91 side. And a release layer.
Further, a peeling member 70 can be disposed on the downstream side of the nip portion N of the fixing belt 92 as an auxiliary means for peeling. The peeling member 70 is held by the holder 72 in a state where the peeling baffle 71 is close to the fixing belt 92 in a direction (counter direction) opposite to the rotation direction of the fixing belt 92.

  The paper P on which the toner image has been electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided to the nip N of the fixing device 102 by the fixing inlet guide 56. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the ceramic heater 82 on the fixing belt 92 side. Also in the fixing device 102 of the present embodiment, since the nip portion N can be configured widely between the pressure roll 91 and the ceramic heater 82, stable fixing performance can be ensured.

Here, also in the fixing device 102 of the present embodiment, the low friction sheet 68 is extended from the nip portion N to the downstream side in the moving direction of the fixing belt 92 as in the case of the first embodiment. Step portions 681 and 682 for gathering the lubricant to the central portion in the width direction of the fixing belt 92 are formed on both sides of the protruding portion 68a on the rubbing surface side with the fixing belt 92, and the extending portion 68a is used as the fixing belt. It is made to contact | abut to the internal peripheral surface of 92.
With such a configuration, when the nip portion N passes through the nip portion N, the lubricant that has shifted to both ends in the width direction of the fixing belt 92 due to the nip pressure is gathered to the center portion, so that the lubricant is collected at both end portions of the fixing belt 92. Therefore, it is possible to maintain a sufficient amount of lubricant on the inner peripheral surface of the fixing belt 92. As a result, the slidability between the fixing belt 92 and the low friction sheet 68 can be stabilized, and the state in which the fixing belt 92 can be smoothly rotated can be maintained. As a result, the paper P can be stably conveyed at a constant speed with the pressure roll 91, and the occurrence of image misalignment and paper wrinkles on the paper P can be suppressed.

  As an application example of the present invention, application to an image forming apparatus such as a copying machine or a printer using an electrophotographic method, for example, application to a fixing apparatus that fixes an unfixed toner image carried on a recording paper (paper). is there. Further, there is application to an image forming apparatus such as a copying machine or a printer using an ink jet method, for example, a fixing device that dries an undried ink image carried on a recording paper (paper).

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. FIG. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. It is a figure explaining the structure of a low friction sheet, (a) is the top view which showed the extension part side of the low friction sheet, (b) is XX 'sectional drawing in the extension part of a low friction sheet. . FIG. 6 is a diagram showing a change with time of driving torque of the fixing roll. FIG. 6 is a side cross-sectional view illustrating a configuration of a fixing device according to a second embodiment. 2 is a cross-sectional view illustrating a layer structure of a fixing belt. FIG. It is a schematic sectional drawing explaining the structure and effect | action of an electromagnet. 6 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 3. FIG. FIG. 10 is a side sectional view showing a configuration of a conventional fixing device.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developing device, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... secondary transfer part, 60, 101, 102 ... fixing device, 61 ... fixing roll, 62 ... endless belt, 63 ... belt running guide, 64 ... pressure pad, 64a ... pre-nip member, 64b ... peeling nip member, 65 DESCRIPTION OF SYMBOLS ... Pressure pad fixing member, 66 ... Halogen heater, 67 ... Lubricant application member, 68 ... Low friction sheet, 69 ... Temperature sensor, 70 ... Release member, 80 ... Electromagnet, 82 ... Ceramic heater, 91 ... Pressure roll, 92 ... Fixing belt, 96 ... Temperature equalizing roll, 681,682 ... Step part

Claims (14)

A pivotable pivot member;
An endless belt movable while contacting the rotating member;
A pressure member that is disposed inside the endless belt, presses the endless belt against the rotating member, and forms a nip portion through which the recording material passes between the rotating member and the endless belt;
A sliding member that reduces a sliding resistance between the endless belt and the pressure member;
And a step member that is in contact with the inner peripheral surface of the endless belt and has a step formed from the end of the endless belt toward the center from the upstream side to the downstream side in the moving direction of the endless belt. A fixing device characterized by the above.   The fixing device according to claim 1, wherein the step member is disposed downstream of the nip portion in the moving direction of the endless belt.   The fixing device according to claim 1, wherein a pair of the step members are arranged symmetrically in the width direction of the endless belt.   The fixing device according to claim 1, wherein the step member is formed to have a step of 20 to 120 μm.   The fixing device according to claim 1, wherein the sliding member and the step member have poor absorbability with respect to a lubricant. A pivotable pivot member;
An endless belt movable while contacting the rotating member;
A pressure member that is disposed inside the endless belt, presses the endless belt against the rotating member, and forms a nip portion through which the recording material passes between the rotating member and the endless belt;
A sliding member for reducing a sliding resistance between the endless belt and the pressure member;
The sliding member is in contact with the inner peripheral surface of the endless belt on the downstream side of the nip portion, and from the end portion of the endless belt toward the downstream side in the moving direction of the endless belt. A fixing device in which a step toward the head is formed. A pressure roll that is elastically deformed and is connected to a drive source and rotatable;
A fixing belt that has a heat source and can be driven while in contact with the pressure roll;
A pressure member that is disposed inside the fixing belt and that presses the fixing belt against the pressure roll to form a nip portion through which a recording material passes between the fixing belt and the pressure roll;
A sliding member that is provided between the fixing belt and the pressure member and reduces a frictional resistance between the fixing belt and the pressure member while interposing a lubricant;
And a lubricant collecting member for collecting the lubricant adhering to the inner peripheral surface of the fixing belt to a central portion of the fixing belt.   The fixing device according to claim 7, wherein the heat generation source of the fixing belt is an electromagnetic induction heating body or a resistance heating body.   The fixing device according to claim 7, wherein the pressure member includes a heat source disposed on the fixing belt. A rotatable fixing roll having a heat source and elastically deforming the surface;
An endless belt movable while contacting the fixing roll;
A pressure member disposed inside the endless belt, and press-contacting the endless belt to the fixing roll to form a nip portion through which a recording material passes between the endless belt and the fixing roll;
A sliding member which is provided between the endless belt and the pressure member and reduces the frictional resistance between the endless belt and the pressure member while interposing a lubricant;
And a lubricant collecting member that collects the lubricant adhering to the inner peripheral surface of the endless belt to the central portion of the endless belt.   The fixing device according to claim 10, wherein the pressure member locally elastically deforms a downstream side of the surface of the fixing roll in the conveyance direction of the recording material. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material,
The fixing means is
A pivotable pivot member;
An endless belt movable while contacting the rotating member;
A pressure member that is disposed inside the endless belt, presses the endless belt against the rotating member, and forms a nip portion through which the recording material passes between the rotating member and the endless belt;
A sliding member that reduces a sliding resistance between the endless belt and the pressure member;
And a step member that is in contact with the inner peripheral surface of the endless belt and has a step formed from the end of the endless belt toward the center from the upstream side to the downstream side in the moving direction of the endless belt. An image forming apparatus.   The image forming apparatus according to claim 12, wherein the step member is made of the same member as the sliding member.   The image forming apparatus according to claim 12, wherein the stepped member is formed with a height of 20 to 120 μm.

Images