JP4534679B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an image forming apparatus using, for example, an electrophotographic method, and more particularly to a fixing device including a rotatable belt member.

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

  A fixing device used in such an image forming apparatus includes a heat source inside a cylindrical metal core, and is formed by laminating a heat-resistant elastic layer on the metal core and a release layer on the outer peripheral surface thereof. The fixing roll is press-fitted to the fixing roll, and is formed by laminating a heat-resistant elastic body layer on the metal core and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on the outer peripheral surface thereof. It consists of a pressure roll. Then, the recording paper carrying the unfixed toner image is passed between the fixing roll and the pressure roll, and the unfixed toner image is heated and pressed to thereby form the toner image on the recording paper. It has become established. Such a fixing device is called a roll nip system and is generally widely used.

In recent years, with the progress of high productivity and colorization in image forming apparatuses, and the spread of double-sided printing mechanisms, it has been required that fixing apparatuses also support high speed. At that time, in the roll nip type fixing device, it is necessary to set the nip width widely in proportion to the fixing speed so that a sufficient amount of heat can be supplied to the toner and the recording paper. As a method of widening the nip width, a method of increasing the load between the fixing roll and the pressure roll, a method of increasing the thickness of the elastic layer, and a method of increasing the roll diameter are conceivable.
However, in the method of increasing the load or the method of increasing the thickness of the elastic layer, the shape of the nip width due to the deflection of the roll becomes non-uniform along the roll axis. There is a problem in image quality such as being easily generated. In addition, the method of increasing the roll diameter causes problems that the apparatus is increased in size and the time (warm-up time) until the roll is raised from room temperature to a fixable temperature is increased.

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

  In the fixing device described in Patent Document 1 (referred to as “belt nip method”), the endless belt is pressed against the fixing roll by using a pressure pad as a pressure member instead of the pressure roll in the conventional roll nip type fixing device. I am letting. By adopting such a configuration, the width of the belt nip formed by the fixing roll and the endless belt can be easily made larger than the width of the conventional roll nip between the fixing roll and the pressure roll. Since a uniform and high nip pressure can be applied to the portion, it is possible to cope with a high speed, and it is easy to reduce the size of the apparatus.

  Furthermore, since the heat capacity of the endless belt pressed against the fixing roll is small, and the pressure pad is arranged in a non-rotating state, a configuration in which heat transmitted from the fixing roll is not easily dissipated to the outside is realized. Therefore, even when the rotation of the fixing roll is started, the amount of heat taken from the fixing roll to the endless belt side is small, the thermal efficiency at the time of melting the toner can be increased, and the amount of temperature decrease at the belt nip is also small. There is also an advantage that the fixing property of the toner can be improved.

Japanese Patent No. 3298354 (pages 4-7)

  By the way, in the above-described belt nip type fixing device, when the endless belt is brought into pressure contact with the fixing roll by the pressure member, it is necessary to ensure slipperiness (reduction in sliding resistance) between the pressure member and the endless belt. . Therefore, a low friction member made of a material having a small friction coefficient is fixedly disposed between the pressure member and the endless belt, and sliding is performed while applying a lubricant to the friction surface between the low friction member and the endless belt. I am letting. In this case, the lubricant is supplied by arranging the lubricant application member upstream of the pressure member, applying the lubricant from the lubricant application member to the inner peripheral surface of the endless belt, and rotating the endless belt. This is done by conveying the lubricant to the sliding part. Furthermore, the lubricant that has passed through the sliding portion is collected again by the lubricant application member, and the circulation of the lubricant is attempted.

However, since a pressing force is applied to the sliding portion between the low friction member and the endless belt, a force that pushes out the sliding portion acts on the lubricant supplied to the sliding portion. . As a result, the lubricant leaks from both longitudinal end regions of the sliding portion, the amount of lubricant recovered by the lubricant application member decreases, and the amount of lubricant applied to the inner peripheral surface of the endless belt gradually increases. Will decrease. As a result, the amount of lubricant in the sliding portion is insufficient and the pressure member surface is thereby worn, and the sliding resistance between the pressure member and the endless belt increases. Therefore, there is a disadvantage that the endless belt loses the smoothness of rotation and the possibility of causing paper wrinkles and image misalignment increases.
In addition, the leaked lubricant infiltrates into the elastic body such as silicone rubber or fluororubber constituting the pressure member, so that the elasticity of the pressure member is gradually lost, resulting in a decrease in the nip pressure at the nip portion. There is also a new problem that image defects such as uneven gloss are likely to occur.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object thereof is to suppress leakage of lubricant from the belt member in the fixing device.

  For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording material, and includes a rotating member, a belt member rotatable while being in contact with the rotating member, A pressure member that is disposed inside the belt member and presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member; and between the belt member and the pressure member The low friction member is characterized in that a step which becomes higher toward the belt member side is formed in a region including the nip portion in the end region.

Here, a lubricant application member for applying a lubricant to the inner peripheral surface of the belt member is further provided, and the low friction member is a part of all or a part of the members disposed inside the belt member other than the lubricant application member. It can be set as the structure arrange | positioned so that it may cover. Further, the step of the low friction member may be formed so as to be inclined toward the center in the width direction of the belt member in the rotation direction of the belt member. Further, the step of the low friction member may be arranged outside the region through which the recording material passes.
In addition, a heating member for heating the rotating member or a heating member for heating the belt member can be further provided.

The fixing device of the present invention is a fixing device that fixes a toner image carried on a recording material, and includes a rotating member, a belt member that can rotate while being in contact with the rotating member, and an inner side of the belt member. A pressure member that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member, and a sliding friction between the belt member and the pressure member. A low friction member to be reduced, a lubricant application member that applies a lubricant to the inner peripheral surface of the belt member, and a belt member and a low friction member in an end region of the low friction member that includes a nip portion; And a lubricant regulating member that regulates the movement of the lubricant to the outside.
Here, the low friction member can be configured to cover all or part of the members disposed inside the belt member other than the lubricant application member. Further, the lubricant regulating member may be formed of the same material as the low friction member. Further, the lubricant regulating member may be formed by bending a part of the low friction member.

  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 a toner image formed by the toner image forming unit onto a recording material. A fixing means for fixing the toner image transferred onto the recording material to the recording material, the fixing means including a rotating member, a belt member rotatable while being in contact with the rotating member, and an inner side of the belt member And a pressure member that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member, and a lubricant is applied to the inner peripheral surface of the belt member. It is disposed so as to cover all or part of the lubricant application member and the members disposed inside the belt member other than the lubricant application member, and reduces the sliding friction between the belt member and the pressure member. A low friction member, In a region including the A and nip a part region is characterized by a step which increases towards the belt member side is formed.

  As an effect of the present invention, it is possible to form a high-quality image over a long period of time by suppressing leakage of the lubricant from the belt member in the fixing device.

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 a plurality of image forming units 1Y, 1M, 1C, and 1K on which toner images of respective color components are formed by electrophotography. The primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the superimposed toner image transferred onto the intermediate transfer belt 15. Are provided with a secondary transfer unit 20 that collectively transfers (secondary transfer) to a paper P that is a recording material (recording paper), and a fixing device 60 that fixes the secondary transferred image onto the paper P. 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 has a charger 12 that charges the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and the photosensitive drum 11. A laser exposure device 13 for writing an electrostatic latent image thereon (exposure beam is indicated by a symbol Bm in the figure), each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. A developing unit 14, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, and a drum cleaner that removes residual toner on the photosensitive drum 11. 17 and the like are sequentially arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged substantially linearly in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15. 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 to 10 ⁹ 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 on the inside. The surface resistivity is 10 ⁷ to 10 ¹⁰ Ω / □, and the hardness is set to 70 ° (Asker C), for example. 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 to 10 ⁹ 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. In response to an instruction from the control unit 40 based on the recognition of the reference signal, each image forming unit. 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 A transport roll 52 that transports the paper P fed by the roll 51, a transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and transported after being secondarily transferred by the secondary transfer roll 22. A conveyance belt 55 that conveys the paper P to be fixed to the fixing device 60 and a fixing inlet 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. After being 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 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Transcribed. More specifically, in the primary transfer portion 10, a voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (minus polarity) is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the toner image. Are sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  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 conveyed to the secondary transfer unit 20, in the paper conveyance system, the pickup roll 51 rotates in accordance with the timing at which the toner image is conveyed to the secondary transfer unit 20, so 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 in the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. .

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 a configuration of the fixing device 60 of the present embodiment. The fixing device 60 mainly includes a fixing roll 61 as an example of a rotating member, an endless belt 62 as an example of a belt member, and a pressure pad 64 as an example of a pressure member pressed from the fixing roll 61 via the endless belt 62. The part is composed.

The fixing roll 61 is a cylindrical roll configured by laminating a heat-resistant elastic body layer 612 and a release layer 613 around a metal core (cylindrical cored bar) 611, and is rotatably supported. Rotates at a predetermined surface speed.
Inside the fixing roll 61, for example, a halogen heater 66 having a rating of 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 controls the lighting of the halogen heater 66 based on the temperature measurement value by the temperature sensor 69 so that the surface temperature of the fixing roll 61 maintains a predetermined set temperature (for example, 175 ° C.). It is adjusted to.

The endless belt 62 is a seamless endless belt, and includes a pressure pad 64 disposed in the endless belt 62, an upstream belt guide member 63 a and a downstream belt guide member 63 b, and both end portions of the endless belt 62. It is rotatably supported by an edge guide member 80 (see FIG. 3 in the subsequent stage) arranged at the position. Then, it is disposed so as to be pressed against the fixing roll 61 at the nip portion N, and rotates following the fixing roll 61.
Here, FIG. 3 is a diagram illustrating a state in which the endless belt 62 is supported, and is a cross-sectional view of the end region of the fixing device 60 as viewed from the downstream side in the conveyance direction of the paper P.
As shown in FIG. 3, edge guide members 80 are disposed at both ends of the holder 65 disposed inside the endless belt 62. The edge guide member 80 is provided outside the belt traveling guide portion 801 and the belt traveling guide portion 801 having a cylindrical shape in which a notch is formed in a portion corresponding to the nip portion N and the vicinity thereof, that is, a C-shaped cross section. A flange portion 802 formed with an outer diameter larger than the inner diameter of the belt 62 and a holding portion 803 provided on the outer surface of the edge guide member 80 for positioning and fixing the edge guide member 80 to the fixing device 60 main body. It is configured.

At both ends in the width direction of the endless belt 62, the inner peripheral surface of the endless belt 62 is supported by the outer peripheral surface of the belt traveling guide portion 801 except for the nip portion N and the vicinity thereof, and the outer peripheral surface of the belt traveling guide portion 801. It is comprised so that it may rotate along. Therefore, the belt traveling guide portion 801 is formed of a material having a small friction coefficient so that the endless belt 62 can smoothly rotate, and further has low thermal conductivity so that it is difficult to remove heat from the endless belt 62. It is made of material.
Further, the flange portion 802 is disposed with an interval where the inner side surfaces of both flange portions 802 disposed so as to face each other at both ends of the holder 65 substantially coincide with the width of the endless belt 62. By arranging in this way, movement of the endless belt 62 in the width direction (belt walk) is restricted.

  In the region excluding both end portions of the endless belt 62, the endless belt 62 is supported by the pressure pad 64, the upstream belt guide member 63a, and the downstream belt guide member 63b (see also FIG. 2). Since the pressure pad 64 and the upstream belt guide member 63a and the downstream belt guide member 63b are all covered in the longitudinal direction by the low friction sheet 68 as described later, the endless belt 62 is covered. In the region excluding both ends, the inner peripheral surface of the endless belt 62 is configured to rotate while sliding on the low friction sheet 68 except in a region where a lubricant application member 67 described later is disposed. .

  Next, the pressure pad 64 is supported by a metal holder 65 inside the endless belt 62. Then, it is arranged in a state of 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 64 a for securing a wide nip portion N is disposed on the inlet side (upstream side) of the nip portion N. Further, on the outlet side (downstream side) of the nip portion N, the surface of the fixing roll 61 is locally pressed to smooth the surface of the toner image and impart image gloss, and the surface of the fixing roll 61 is distorted (dented). ) To form a down curl on the sheet P, and a separation nip member 64b for separating the sheet P from the surface of the fixing roll 61 is disposed.

Further, the fixing device 60 includes a low friction sheet 68 as an example of a low friction member formed of a material having a small friction coefficient in order to reduce the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64. Is provided.
The low friction sheet 68 is provided inside the endless belt 62 with the holder 65, the pressure pad 64 held by the holder 65, and the upstream belt guide member 63a and the downstream belt guide member 63b that support the rotating endless belt 62. And the like, so as to cover all the members disposed inside the endless belt 62 excluding the lubricant applying member 67 described later.

That is, as shown in FIG. 2, one end of the low friction sheet 68 is located on the bottom surface of the downstream belt guide member 63 b fixed to the holder 65 on the bottom surface opposite to the fixing roll 61 side. It is fixed by a sheet fixing member 75 so as to be adjacent to the side portion of the lubricant application member 67 disposed on the member 63b. The low friction sheet 68 is extended along the rotational direction of the endless belt 62 on the downstream side of the lubricant application member 67, and the other end of the low friction sheet 68 extends from the upstream side of the lubricant application member 67. It arrange | positions to the position which contacts. With such a configuration, the low friction sheet 68 covers almost all the region in the longitudinal direction along the rotational direction of the endless belt 62 by covering the members disposed inside the endless belt 62 except for the lubricant application member 67. ing. The other end portion of the low friction sheet 68 is not fixed and is set to a free end (free) state so that the low friction sheet 68 is not distorted.
The low friction sheet 68 has a sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64 under a state in which a pressing force is applied between the pressure pad 64 and the fixing roll 61 at the nip portion N. (Friction resistance) is reduced.

  Thus, the low friction sheet 68 for reducing the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64 is around the members disposed inside the endless belt 62 except for the lubricant application member 67. By covering the substantially entire area in the longitudinal direction, the inner peripheral surface of the endless belt 62 does not come into direct contact with the members disposed therein when the endless belt 62 is rotated, and the low friction sheet 68 is interposed. Can be realized. Therefore, for example, even when the paper P is jammed in the fixing device 60 and the endless belt 62 is reversely rotated when the jammed paper P is removed, the endless belt 62 and a member (for example, a downstream belt) Since the sliding with the guide member 63b) is performed smoothly, the contact state between the endless belt 62 and the member does not change. As a result, it is possible to suppress a new increase in frictional friction based on a shift in the relative position between the endless belt 62 and the member and an increase in wear on the inner peripheral surface of the endless belt 62, and smoothen the endless belt 62 and the member. It is possible to maintain the rotation.

Further, since the inner peripheral surface of the endless belt 62 to which the lubricant is applied does not directly contact these members, the lubricant does not adhere to the members, and the decrease in the lubricant can be suppressed.
Further, since the inner peripheral surface in the region excluding both ends of the endless belt 62 rotates while being supported by the low friction sheet 68, the lubricant applied to the inner peripheral surface of the endless belt 62 by the lubricant applying member 67 is The contact surface between the endless belt 62 and the low friction sheet 68 is held. As a result, a high lubricant retention capability in a state of being sandwiched between the contact surfaces can be realized, and therefore, leakage of the lubricant from both ends of the endless belt 62 hardly occurs.

  In addition to the configuration of the low friction sheet 68 of the present embodiment, if fine irregularities are formed on the inner peripheral surface of the endless belt 62, the ability of retaining the lubricant on the inner peripheral surface of the endless belt 62 is further improved. be able to. By increasing the holding ability of the lubricant on the inner peripheral surface of the endless belt 62, the holding ability of the lubricant on the contact surface between the endless belt 62 and the low friction sheet 68 can be further improved. It becomes possible to further suppress the leakage of the agent.

Next, the lubricant application member 67 is disposed across the longitudinal direction of the downstream belt guide member 63b on the bottom surface of the downstream belt guide member 63b opposite to the fixing roll 61 side. The lubricant application member 67 is not covered by the low friction sheet 68 and is disposed so as to contact the inner peripheral surface of the endless belt 62. Further, the lubricant application member 67 is impregnated with a lubricant such as amino-modified silicone oil having a viscosity of 300 cs, for example. The lubricant application member 67 always applies an appropriate amount of lubricant to the inner peripheral surface of the endless belt 62 and supplies the lubricant to the friction surface between the endless belt 62 and the low friction sheet 68 by the rotation of the endless belt 62. is doing. Thereby, the sliding resistance between the endless belt 62 and the pressure pad 64 via the low friction sheet 68 is further reduced, and the endless belt 62 is smoothly rotated.
In addition, the lubricant application member 67 also has a function of collecting the lubricant adhering to the inner peripheral surface of the endless belt 62 that has passed through the nip portion N. The lubricant application member 67 maintains the equilibrium of the lubricant application amount on the inner peripheral surface of the endless belt 62 by reapplying (recycling) the recovered lubricant.

  Note that the lubricant application member 67 of the present embodiment is configured such that the length in the longitudinal direction is slightly shorter than the width of the low friction sheet 68, and the lubricant application member 67 is not in contact with both ends of the low friction sheet 68. Is preferably provided. Since the lubricant applied from the lubricant application member 67 tends to spread outward in the width direction, by setting in this way, the lubricant is applied to both ends of the low friction sheet 68 due to the spread. Can be done. Accordingly, the amount of lubricant at both ends of the low friction sheet 68 can be set relatively low, and leakage of the lubricant from both ends of the endless belt 62 can be effectively suppressed.

  In such a configuration, the fixing roll 61 is rotated in the direction of arrow C by a drive motor (not shown), and the endless belt 62 is rotated in the same direction following the 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. 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 roll 61. In the fixing device 60 of the present embodiment, since the nip portion N can be widely configured 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 the vicinity of the downstream side of the nip portion N, the paper P peeled off from the fixing roll 61 by the peeling nip member 64b is completely separated from the fixing roll 61 and guided to the paper discharge path toward the discharge portion of the image forming apparatus. A peeling assisting member 70 is provided for this purpose. The peeling auxiliary member 70 is held by a baffle 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 formed of a cylindrical body having an outer diameter of 26 mm and a length of 350 mm formed of a metal having high thermal conductivity such as iron, aluminum, and SUS. 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.
Any material can be used for the heat-resistant elastic layer 612 as long as it is an elastic body having high heat resistance. In particular, it is preferable to use an elastic body such as rubber or elastomer having a rubber hardness of about 25 to 40 ° (JIS-A), and specific examples include silicone rubber and fluorine rubber.

  The release layer 613 is a heat-resistant resin such as a silicone resin or a fluorine resin, and a resin having a release property to the toner is used. A fluorine resin having excellent wear resistance is suitable. Yes. As the fluororesin, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), or the like can be used. The thickness of the release layer 613 is preferably 5 to 30 μm, more preferably 10 to 20 μm. If the thickness of the release layer 613 is less than 5 μm, the paper P is likely to be wrinkled due to the distortion of the fixing roll 61, while if it exceeds 30 μm, the release layer 613 becomes hard and the image has defects such as uneven gloss. This is because there is an increase in the possibility of the occurrence of both.

  The endless belt 62 is an endless belt whose original shape is formed in a cylindrical shape with a diameter of, for example, 30 mm, a base layer, and a release layer coated on the surface (outer peripheral surface) or both surfaces of the base layer on the fixing roll 61 side. It is composed of For the base layer, a polymer such as a thermosetting polyimide resin, a thermoplastic polyimide resin, a polyamideimide resin, or a polybenzimidazole resin is preferably used from the viewpoint of heat resistance, mechanical properties, and the like. Moreover, the thickness is 30-200 micrometers, Preferably it is 50-125 micrometers, More preferably, it is about 75-100 micrometers. The release layer coated on the surface of the base layer is formed of a fluororesin such as PFA, PTFE, or FEP, and has a thickness of about 5 to 100 μm, preferably about 10 to 30 μm.

As described above, the pressure pad 64 includes the pre-nip member 64a and the peeling nip member 64b, and is fixed to the holder 65. An elastic body such as silicone rubber or fluorine rubber, a leaf spring, or the like can be used for the prenip member 64 a, 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 formed of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, polyamide, or a metal such as iron, aluminum, or SUS. 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.

  The low friction sheet 68 is formed of a material having a small friction coefficient and excellent wear resistance and heat resistance so as to reduce sliding friction (sliding resistance) between the inner peripheral surface of the endless belt 62 and the pressure pad 64. Yes. Further, the low friction sheet 68 is configured so as not to be infiltrated into the lubricant (i.e., difficult to pass through) so that the lubricant does not permeate and leak from the back surface. Specifically, a glass fiber sheet is impregnated with PFA or PTFE to wrap the surface, and a porous resin fiber cloth made of fluororesin is used as a base material to wrap a PET resin sheet on the pressure pad 64 side surface. A sintered PTFE resin sheet or the like can be used.

Next, the configuration in the nip portion N of the low friction sheet 68 of the present embodiment will be described.
FIG. 4 is a perspective view showing the low friction sheet 68 mounted on the fixing device 60. As shown in FIG. 4, the low friction sheet 68 of the present embodiment has stepped portions 68 a at both ends of the nip N peripheral region. The stepped portion 68a is in close contact with and overlaps with the main body portion 68b of the low friction sheet 68, thereby forming a step that becomes higher toward the endless belt 62 side on the contact surface between the low friction sheet 68 and the endless belt 62. ing. Further, the step formed by the step portion 68 a is formed so as to be gradually inclined toward the center portion in the width direction of the endless belt 62 with respect to the rotation direction of the endless belt 62. That is, the stepped portion 68 a is formed so that the width gradually increases toward the downstream side in the rotational direction of the endless belt 62. Therefore, the edge surface (step surface) of the step portion 68a is configured to approach the center portion toward the downstream side in the rotation direction.

  Incidentally, since the pressure pad 64 is disposed so as to press the fixing roll 61 at the nip portion N, the sliding portion between the low friction sheet 68 disposed on the pressure pad 64 and the endless belt 62 is disposed at the sliding portion. A pressing force is applied. Therefore, in this sliding part, the force pushed out from the sliding part acts on the lubricant applied to the inner peripheral surface of the endless belt 62 by the lubricant application member 67. The force that pushes out the lubricant acts to push out the lubricant in all directions. Therefore, the low friction sheet 68 except for the lubricant application member 67 does not cause the endless belt 62 to move as in the fixing device 60 of the present embodiment. Even when the members arranged inside are covered over substantially the entire region in the longitudinal direction, leakage of the lubricant to the outside tends to occur at both ends in the width direction of the nip portion N.

Therefore, in the fixing device 60 of the present embodiment, the step portion 68a is formed at both ends of the peripheral region of the nip portion N in the low friction sheet 68. By forming such a step by the step portion 68a, as shown in FIG. 5 (a diagram for explaining the flow of the lubricant in the nip portion N), both end directions are caused by the pressing force of the pressure pad 64 and the fixing roll 61. When the lubricant is pushed out, the pushed-out lubricant can be blocked, and the lubricant can be restricted from being pushed out. Therefore, the leakage of the lubricant can be suppressed also in the area around the nip portion N. In this respect, the stepped portion 68a functions as a lubricant regulating member.
In addition, since the level difference due to the level difference 68a is gradually inclined toward the center in the width direction of the endless belt 62 with respect to the rotational direction of the endless belt 62, the dammed lubricant is Is returned to the central portion of the endless belt 62. As a result, the dammed lubricant is retained on the inner peripheral surface of the endless belt 62 and is collected again by the lubricant application member 67, so that the lubricant can be circulated and used, so that the inner periphery of the endless belt 62 can be used. The amount of lubricant applied to the surface can be maintained at a predetermined amount over a long period of time. Thereby, since the smooth rotation of the endless belt 62 can be maintained, it is possible to suppress the occurrence of paper wrinkles and image misalignment in the nip portion N.
Further, since the leaked lubricant can be prevented from infiltrating into an elastic body such as silicone rubber or fluorine rubber constituting the pre-nip member 64a of the pressure pad 64, the elasticity of the pressure pad 64 is lost, and the nip pressure at the nip portion N is lost. Can be prevented, and a high-quality image without uneven gloss can be maintained.

  Here, as a method of forming the stepped portion 68a in the low friction sheet 68, as shown in FIG. 6A, a triangular convex portion is formed in a portion corresponding to the nip portion N of the low friction sheet 68. In addition, it can be formed by bending the triangular protrusions inward. Further, as shown in FIG. 6B, a triangular sheet made of the same sheet material as the low friction sheet 68 is prepared separately from the low friction sheet 68. It can also comprise so that it may affix on the low friction sheet | seat 68. FIG.

  Further, as the position in the width direction of the low friction sheet 68 where the stepped portion 68a is disposed, as shown in FIG. 4, the region through which the largest size of the paper P that passes through the fixing device 60 passes. It is preferable to dispose outside (maximum paper passing area). By disposing the stepped portion 68a outside the maximum sheet passing area, the pressing force (nip pressure) at the nip portion N is uniformly distributed over the entire sheet passing area without being affected by the stepped portion 68a. Can be set.

As described above, in the fixing device 60 of this embodiment, the low friction sheet 68 for reducing the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64 is the endless except for the lubricant applying member 67. The low-friction sheet 68 is provided with step portions 68a at both ends of the peripheral region of the nip portion N. Is formed. With such a configuration, the leakage of the lubricant from the inner peripheral surface of the endless belt 62 including the peripheral region of the nip portion N can be suppressed. Therefore, since the lubricant is sufficiently collected from the inner peripheral surface of the endless belt 62, the amount of lubricant applied to the inner peripheral surface of the endless belt 62 is maintained at a predetermined amount over a long period by circulating the lubricant. Can do. As a result, since the endless belt 62 can be smoothly rotated, the occurrence of paper wrinkles and image misalignment in the nip portion N can be suppressed.
Further, by suppressing the leakage of the lubricant from the inner peripheral surface of the endless belt 62, the leaked lubricant does not infiltrate into the pressure pad 64, so that the nip pressure can be maintained at a predetermined value, and uneven glossiness can be obtained. You can also maintain no high quality images.

[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 is a fixing device using a fixing belt with a heat generation source pressed as a heating unit and a pressure roll as a pressing unit. explain. In addition, about the structure similar to Embodiment 1, the same code | symbol is used and the detailed description is abbreviate | omitted here.

FIG. 7 is a side cross-sectional view showing the configuration of the fixing device 90 in the present embodiment. As shown in FIG. 7, in the fixing device 90 of the present embodiment, a fixing belt 92 as an example of a belt member is disposed on the toner image carrying surface side of the paper P. A ceramic heater 82 which is a resistance heating element as 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.

On the other hand, a pressure roll 91 as an example of a rotating member is disposed so as to face the fixing belt 92, and is rotated in the direction of arrow D by a drive motor (not shown). It is configured as follows. 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.
The fixing belt 92 is an endless belt whose original shape is formed in a cylindrical shape, and includes a base layer made of a thermosetting polyimide resin, a thermoplastic polyimide resin, a polyamideimide resin, a polybenzimidazole resin, and the like, It is comprised with the release layer which consists of a fluororesin etc. coat | covered on the surface (outer peripheral surface) or both surfaces by the side of the pressure roll 91.
Furthermore, a peeling assisting member 70 may be disposed on the downstream side of the nip portion N of the fixing belt 92 as a peeling assisting means. The peeling assisting 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 90 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 90 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, in the fixing device 90 of the present embodiment, the low friction sheet 68 for reducing the sliding resistance between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82 is the same as that of the fixing device 60 of the first embodiment. In addition, the low friction sheet 68 is arranged so as to cover the periphery of the members disposed inside the fixing belt 92 excluding the lubricant application member 67 over substantially the entire region in the longitudinal direction. Step portions 68a are formed at both ends of the peripheral area of the portion N. With such a configuration, the leakage of the lubricant from the inner peripheral surface of the fixing belt 92 including the peripheral region of the nip portion N can be suppressed. Therefore, since the lubricant is sufficiently collected from the inner peripheral surface of the fixing belt 92, a predetermined amount of lubricant can be secured on the inner peripheral surface of the fixing belt 92 by circulating the lubricant. it can. As a result, smooth rotation of the fixing belt 92 can be maintained, so that the occurrence of paper wrinkles and image misalignment in the nip portion N 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, to 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. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. FIG. It is a figure explaining the state by which the endless belt was supported. FIG. 6 is a perspective view illustrating a low friction sheet in a state where it is mounted on a fixing device. It is a figure explaining the flow of the lubricant in a nip part. It is a figure explaining the method of forming the level | step-difference part in a low friction sheet. FIG. 4 is a side sectional view illustrating a configuration of a fixing device according to a second embodiment.

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 section, 60, 90 ... Fixing device, 61 ... Fixing roll, 62 ... Endless belt, 63a ... Upstream belt guide member, 63b ... Downstream belt guide member, 64 ... Pressure pad, 64a ... Prenip member 64b ... peeling nip member, 65 ... holder, 66 ... halogen heater, 67 ... lubricant application member, 68 ... low friction sheet, 68a ... step portion, 69 ... temperature sensor, 70 ... peeling assisting member, 80 ... edge guide member , 82 ... Ceramic heater, 91 ... Pressure roll, 92 ... Fixing belt

Claims (9)

A fixing device for fixing a toner image carried on a recording material,
A rotating member;
A belt member that is rotatable while being in contact with the rotating member;
A pressure member that is disposed inside the belt member, and that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member;
A low friction member that reduces sliding friction between the belt member and the pressure member;
The fixing device according to claim 1, wherein the low-friction member is formed with a step that increases toward the belt member side in an end region that includes the nip portion. A lubricant application member for applying a lubricant to the inner peripheral surface of the belt member;
The fixing device according to claim 1, wherein the low friction member is disposed so as to cover all or a part of members disposed inside the belt member other than the lubricant application member.   2. The fixing device according to claim 1, wherein the step of the low friction member is formed so as to be inclined toward the center in the width direction of the belt member toward the rotation direction of the belt member.   The fixing device according to claim 1, wherein the step of the low friction member is disposed outside a region through which the recording material passes.   The fixing device according to claim 1, further comprising a heating member that heats the rotating member or a heating member that heats the belt member. A fixing device for fixing a toner image carried on a recording material,
A rotating member;
A belt member that is rotatable while being in contact with the rotating member;
A pressure member that is disposed inside the belt member, and that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member;
A low friction member that reduces sliding friction between the belt member and the pressure member;
A lubricant application member for applying a lubricant to the inner peripheral surface of the belt member;
A lubricant regulating member that is disposed between the belt member and the low friction member in an end region of the low friction member and includes the nip portion, and regulates movement of the lubricant to the outside. And
The fixing device, wherein the lubricant regulating member is formed by bending a part of the low friction member .   The fixing device according to claim 6, wherein the low friction member is disposed so as to cover all or a part of members disposed inside the belt member other than the lubricant application member.   The fixing device according to claim 6, wherein the lubricant regulating member is made of the same material as the low friction member. 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 rotating member;
A belt member that is rotatable while being in contact with the rotating member;
A pressure member that is disposed inside the belt member, and that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member;
A lubricant application member for applying a lubricant to the inner peripheral surface of the belt member;
A low friction member disposed to cover all or part of the members disposed inside the belt member other than the lubricant application member and reducing sliding friction between the belt member and the pressure member And
The low-friction member is an image forming apparatus, wherein a step that is increased toward the belt member side is formed in an end region that includes the nip portion.

Images