JP4655848B2 - 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, image formation is performed as follows. First, for example, the surface of a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged by a charging device. The charged photosensitive drum is scanned and exposed with light controlled based on the image information, and an electrostatic latent image is formed on the surface thereof. Subsequently, the electrostatic latent image formed on the photosensitive drum is made a visible image (toner image) by the developing device, and then the toner image is conveyed to the transfer unit along with the rotation of the photosensitive drum to be recorded. Electrostatic transfer on paper. The toner image carried on the recording paper is subjected to a fixing process by a fixing device to complete the toner image.

  As a fixing device used in such an image forming apparatus, a configuration called a two-roll system has been widely used in general. The two-roll fixing device includes a fixing roll formed by laminating a heat-resistant elastic layer and a release layer on the surface of a cylindrical metal core having a heat source (heater) disposed therein, A pressure roll formed by laminating a heat-resistant elastic layer and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on a metal core is configured to be in pressure contact with each other. Then, the recording paper carrying the unfixed toner image is passed through the pressure contact area (nip portion) between the fixing roll and the pressure roll, and the toner image is heated and pressed against the unfixed toner image. Is firmly established.

By the way, in recent years, high productivity and colorization have rapidly progressed in image forming apparatuses, and many apparatuses having a double-sided printing mechanism have become widespread. Therefore, it is necessary to further cope with the high speed in the fixing device mounted on the image forming apparatus.
However, the conventional two-roll type fixing device has a problem that it is difficult to perform a sufficient fixing process on a large number of recording sheets continuously fed at a high speed. That is, in the two-roll type fixing device, a core metal constituting the fixing roll, an elastic layer made of silicone rubber coated on the core metal, or the like acts as a thermal resistor. Therefore, in the two-roll type fixing device, it is structurally difficult to supply the heat corresponding to the amount of heat taken by the recording paper from the surface of the fixing roll promptly and sufficiently from the heater arranged inside the fixing roll. .
As a result, when the recording paper is continuously fed to the two-roll type fixing device at a high speed, the surface temperature of the fixing roll gradually decreases and the fixing performance gradually decreases. In addition, when the image forming apparatus starts up, a so-called “temperature droop phenomenon” in which the surface temperature of the fixing roll temporarily drops tends to occur. In particular, when thick paper with a large heat capacity is used as recording paper, the amount of heat taken away from the surface of the fixing roll increases, so that the fixing performance decreases and the temperature droop increases, resulting in image quality deterioration due to poor fixing. Will be generated.

Under such circumstances, a technique has been developed that solves the above-described problems that occur when a two-roll type fixing device is used, and realizes a fixing device that can cope with higher speed of the image forming apparatus. For example, there is a technique related to a fixing device in which a heating member that heats recording paper is configured by a film-like belt member (fixing belt) stretched by a plurality of stretching rolls (see, for example, Patent Document 1).
In such a fixing device using a fixing belt, the fixing belt is sufficiently heated by a heater provided in advance in the stretching roll before entering the nip portion, and the fixing belt heated in the nip portion is heated. The toner image is fixed by applying heat to the recording paper and the toner image. Therefore, even if the fixing belt is deprived of heat by the recording paper during the fixing process, since the heat capacity of the fixing belt itself is small, the fixing belt is recovered to a predetermined fixing temperature in a short time by the heater in the stretching roll. It is possible to make it. Accordingly, in the fixing device using the fixing belt as the heating member, it becomes easy to maintain the temperature of the fixing belt when entering the nip portion at a predetermined value, and even if the image forming apparatus is speeded up, It is possible to supply a sufficient amount of heat.

  However, even in a fixing device using a fixing belt, since a toner image is carried on the surface of the recording paper, when the toner image is melted by the heat of the fixing belt, the toner image becomes an adhesive and becomes a recording paper. Adhesive force acts between the toner and the fixing belt. Therefore, it is necessary to provide a mechanism for peeling the recording paper from the surface of the fixing belt as in the conventional two-roll type fixing device. In particular, when the speed of the image forming apparatus is increased, if a separation failure occurs once in the fixing device and a paper jam occurs, the number of subsequent recording papers damaged by the influence increases. For this reason, it is necessary to stably and reliably peel the recording paper that has passed through the nip portion at a high speed from the fixing belt side.

  As a mechanism for separating the recording paper from the surface of the fixing belt, as described in Patent Document 1 described above, a structure in which a separation claw is disposed in contact with the fixing belt on the downstream side of the nip portion is conventionally used. Yes. In a fixing device having a configuration in which a pressure roll is disposed in pressure contact with a fixing belt stretched between a fixing roll and a heating roll, a position corresponding to an outlet portion (the most downstream portion) of the nip portion A fixing member for setting a large curvature of the fixing belt at the outlet is provided inside the fixing belt, and the recording paper is peeled off by changing the curvature of the fixing belt (see, for example, Patent Document 2). .

  However, in a fixing device using a fixing belt, when a separation claw is used as a mechanism for separating the recording paper from the surface of the fixing belt, the separation claw is attached to the fixing belt in order to stably peel the recording paper from the fixing belt side. It is necessary to be disposed in contact with the. Therefore, when the separation claw is used, the surface of the fixing belt is easily worn by the separation claw. If wear due to the separation claw occurs on the surface of the fixing belt, fixing unevenness corresponding to the wear mark on the surface of the fixing belt may occur on the fixed image, which may deteriorate the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Furthermore, when the surface of the fixing belt progresses, the thin-layer fixing belt eventually breaks, and the function of the fixing device may be impaired. Therefore, in a fixing device using a fixing belt, a separation mechanism based on curvature separation that does not require a contact member such as a separation claw is optimal.

JP-A-3-133871 (page 4, FIG. 3) Japanese Patent Laying-Open No. 2003-5566 (page 6-8, FIG. 4)

However, when using the curvature separation as a mechanism for peeling the recording paper from the surface of the fixing belt, as described above, it is necessary to provide a peeling member on the outlet side of the nip portion for largely bending the curvature of the fixing belt. It becomes. As a result, a wide area is formed where the fixing belt wraps the pressure roll, so that heat can be sufficiently supplied to the recording paper, but a large amount of heat is transmitted from the fixing belt to the pressure roll. Become. Therefore, there arises a problem that the temperature of the pressure roll is likely to rise.
When the surface temperature of the pressure roll becomes higher than necessary due to the heat from the fixing belt, the recording paper passing through the nip portion is excessively heated by both the fixing belt side and the pressure roll side. Therefore, there is a case where moisture in the recording paper is vaporized into water vapor or a phenomenon in which the air is thermally expanded to cause blistering (paper blister) on the recording paper. When such a paper blister occurs, a significant image defect such as an image shift occurs.
In addition, particularly when small-size paper is passed, the width direction end portion side of the pressure roll is always in direct contact with the fixing belt. Therefore, in the axial direction of the pressure roll, there is a difference in the amount of thermal expansion between the center portion and the end portion, and a large outer diameter difference occurs in the pressure roll in the axial direction. As a result, such an outer diameter difference is repeatedly generated for each image forming operation due to long-term use, and the surface of the pressure roll is likely to be wrinkled, cracked or even damaged. For this reason, an image defect occurs, and in some cases, the fixing function may be significantly impaired.

Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to stably separate the recording paper from the belt member in the fixing device using the belt member. There is.
Another object is to provide a fixing device capable of obtaining a high-quality fixed image over a long period of time.

  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 heats the fixing roll, a belt member stretched around the fixing roll, and the belt member. In addition, a tension roll that stretches the belt member, and a pressure member that is disposed so as to press the fixing roll and that forms a nip portion through which the recording material passes between the belt member that is stretched on the fixing roll. A peeling member arranged to press the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member, and a cooling member for cooling the pressure member. It is characterized by that.

Here, the cooling member may be arranged on the downstream side of the nip portion. In addition, the cooling member may include a heat-absorbing roll member having high thermal conductivity that is in contact with the surface of the pressure member along the axial direction. In particular, the cooling member can be characterized in that the endothermic roll member is a Peltier element.
Further, the cooling member may be characterized in that the cooling belt member stretched around the roll member is disposed so as to contact the pressure member. Further, the cooling member may be configured to cool the inside of the pressure member. In addition, the cooling member may include a cooling belt member stretched so as to wrap the surface of the pressure member.
Further, the pressing member may be characterized in that the dent amount is larger than the dent amount of the fixing roll at the press contact portion between the fixing roll and the pressing member.

  The fixing device of the present invention is a fixing device that fixes a toner image carried on a recording material, and includes a heat source, a fixing roller formed of a rigid body, and stretched between the fixing roller. A belt member, a belt member that heats the belt member, a tension roll that stretches the belt member, a pressure member that is arranged to press the fixing roll, and that is covered with an elastic layer, and a fixing roll A peeling member disposed so as to press the outer surface of the belt member against the pressure member near the downstream side of the pressure contact portion with the pressure member, and the pressure member has a temperature lower than the temperature of the fixing roll It is characterized by being controlled within a predetermined range.

Here, the fixing roll can be characterized by being heated to a temperature lower than the temperature of the belt member by a heat source.
Further, the peeling member can be characterized in that it is composed of a block member having a substantially arc-shaped cross section. Further, the peeling member can be characterized in that the side surface located on the side opposite to the fixing roll side is formed in a shape that changes the bending direction of the fixing belt. In addition, the peeling member is disposed in a wedge-shaped region defined by the fixing roll and the pressure member at the upstream end of the surface that presses the pressure member via the belt member. You can also.

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. A fixing unit that fixes the toner image transferred onto the recording material to the recording material. The fixing unit heats the belt member, a fixing roll formed of a rigid body, a belt member stretched around the fixing roll, And a downstream side of the pressure contact portion between the fixing roll and the pressure member, the tension roll that stretches the belt member, the pressure member that is arranged to press the fixing roller, and is covered with the elastic layer In the vicinity, a peeling member disposed so as to press the outer surface of the belt member against the pressure member and a cooling member for cooling the pressure member are provided. Lower than temperature It is being controlled in a constant range.
Here, the fixing means has a nip pressure in a region extending from the most downstream portion of the pressure contact portion between the fixing roll and the pressure member to the most downstream portion of the pressure contact portion between the pressure member and the peeling member in the traveling direction of the belt member. It can be characterized by being set so as to monotonously decrease.

  According to the present invention, the recording paper can be stably peeled from the belt member even when the speed of the image forming apparatus is increased. Further, high fixing performance can be stably maintained, and high quality images can be provided over a long period of time.

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 17 that removes residual toner on the photosensitive drum 11. , Etc. 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 of arrow 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 extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the intermediate 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 secondary transfer unit 20. The backup roll 25 and a cleaning backup roll 34 provided in a cleaning unit that scrapes residual toner on the intermediate transfer belt 15 are disposed.

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 body 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 that the toner images superimposed on the intermediate transfer belt 15 are formed.

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. And it forms so that the surface resistivity may be 10 < ⁷ > -10 < ¹⁰ > (omega | ohm) / square, and hardness is set to 70 degrees (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 body 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. 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 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 Y, M, C, and K colors by the developing devices 14 of 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 unit 10, a voltage (primary transfer bias) having a reverse polarity (plus polarity) to the charging polarity of the toner 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 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, if a voltage (secondary transfer bias) having the same polarity (negative polarity) as the charging polarity of the toner 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 transport belt 55 transports the paper P to the fixing device 60 at an optimal transport speed in accordance with the transport speed of 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 fixing processing 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 mounting portion (not shown) provided in the discharge portion of the image forming apparatus.
On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed along with the rotation of the intermediate transfer belt 15 and is intermediately transferred by the cleaning backup roll 34 and the intermediate transfer belt cleaner 35. It is removed from the 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 schematic configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing belt module 61 as an example of a heating member and a pressure roll 62 as an example of a pressure member disposed in pressure contact with the fixing belt module 61. Yes.
The fixing belt module 61 includes a fixing belt 610 as an example of a belt member, a fixing roll 611 that rotates while the fixing belt 610 is stretched, a tension roll 612 that stretches the fixing belt 610 from the inside, and a fixing belt 610 from the outside. A tension roll 613 that stretches the belt, a posture correction roll 614 that corrects the posture of the fixing belt 610 between the fixing roll 611 and the tension roll 612, and a region where the fixing belt module 61 and the pressure roll 62 are in pressure contact with each other. A peeling pad 64 as an example of a peeling member disposed in the vicinity of the fixing roll 611 in a downstream area in the nip portion N, and a tension roll 615 that stretches the fixing belt 610 on the downstream side of the nip portion N. The main part is composed.

  The fixing belt 610 is a flexible endless belt having a circumferential length of 314 mm and a width of 340 mm. Then, a base layer made of polyimide resin having a thickness of 80 μm, an elastic layer made of 200 μm thick silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, and further covering the elastic layer And a release layer comprising a 30 μm thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube. Here, the elastic layer is provided in order to improve the image quality especially for color images. The configuration of the fixing belt 610 can be appropriately selected in terms of material, thickness, hardness, and the like according to device design conditions such as the purpose of use and use conditions.

The fixing roll 611 is a hard roll formed of a cylindrical roll made of aluminum having an outer diameter of 65 mm, a length of 360 mm, and a thickness of 10 mm. The fixing roll 611 is formed with high rigidity so as to satisfy the relationship of “the depression amount of the pressure roll 62> the depression amount of the fixing roll 611” described later. The fixing roll 611 rotates in the arrow C direction at a surface speed of 440 mm / s in response to a driving force from a driving motor (not shown).
In addition, a halogen heater 616 a rated at 900 W is provided as a heat source inside the fixing roll 611, and based on the measured value of the temperature sensor 617 a arranged so as to contact the surface of the fixing roll 611, The controller 40 (see FIG. 1) controls the surface temperature of the fixing roll 611 to 180 ° C.

The tension roll 612 is a cylindrical roll formed of aluminum having an outer diameter of 30 mm, a wall thickness of 2 mm, and a length of 360 mm. A halogen heater 616b rated at 1000 W is disposed as a heat source inside the tension roll 612, and the surface temperature is controlled to 210 ° C. by the temperature sensor 617b and the control unit 40 (see FIG. 1). Yes. Therefore, the tension roll 612 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the inner peripheral surface side.
In addition, spring members (not shown) that press the fixing belt 610 outward are disposed at both ends of the tension roll 612, and the tension of the entire fixing belt 610 is set to 15 kgf. At that time, in order to make the tension of the fixing belt 610 uniform in the width direction and to suppress the displacement of the fixing belt 610 in the axial direction as much as possible, the tension roll 612 has an outer diameter at the center portion rather than the end portion. It is formed in a so-called crown shape that is larger by 100 μm.

The tension roll 613 is a cylindrical roll formed of aluminum having an outer diameter of 25 mm, a thickness of 2 mm, and a length of 360 mm. Further, a release layer made of PFA having a thickness of 20 μm is formed on the surface of the tension roll 613. This release layer is formed to prevent slight offset toner and paper powder from the outer peripheral surface of the fixing belt 610 from accumulating on the stretching roll 613. Similarly to the tension roll 612, the tension roll 613 has a crown shape in which the outer diameter is larger by 100 μm at the center than at the end. Note that not only the tension roll 612 and the tension roll 613 are both formed in a crown shape, but only one of the tension roll 612 and the tension roll 613 may be formed in a crown shape.
Inside the tension roll 613, a halogen heater 616c rated at 1000 W as a heat source is disposed, and the surface temperature is controlled to 210 ° C. by the temperature sensor 617c and the control unit 40 (see FIG. 1). Yes. Accordingly, the tension roll 613 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the outer peripheral surface side. Therefore, in this embodiment, a configuration in which the fixing belt 610 is heated by the fixing roll 611, the stretching roll 612, and the stretching roll 613 is employed.

  The posture correction roll 614 is a cylindrical roll formed of aluminum having an outer diameter of 15 mm and a length of 360 mm. A belt edge position detection mechanism (not shown) that detects the edge position of the fixing belt 610 is disposed in the vicinity of the posture correction roll 614. The posture correction roll 614 is provided with an axis displacement mechanism that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism, and performs meandering (belt walk) of the fixing belt 610. Configured to control.

The peeling pad 64 is a block member having a substantially arc shape in cross section formed of a rigid body such as SUS metal or resin. Then, the entire area in the axial direction of the fixing roll 611 is located in the vicinity of the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 (see “roll nip portion N1”: FIG. 3 in the subsequent stage). Are fixedly arranged. Further, the peeling pad 64 allows the pressure roll 62 to be uniformly applied with a predetermined load (for example, 10 kgf) over a predetermined width region (for example, a width of 5 mm along the traveling direction of the fixing belt 610) via the fixing belt 610. The “peeling pad nip portion N2” (see FIG. 3 in the subsequent stage) described later is formed.
The tension roll 615 is a cylindrical roll formed of aluminum having an outer diameter of 12 mm and a length of 360 mm. The fixing belt 610 that has passed through the peeling pad 64 is disposed in the vicinity of the downstream side of the fixing pad 610 in the traveling direction of the fixing belt 610 so that the fixing belt 610 smoothly rotates toward the fixing roll 611.

  Next, the pressure roll 62 is made of silicone rubber having a rubber hardness of 30 ° (JIS-A) in order from the base side, with a cylindrical roll 621 made of aluminum having an outer diameter of 45 mm, a length of 360 mm, and a thickness of 10 mm as a base. A soft roll formed by laminating a 10 mm thick elastic layer 622 and a release layer 623 made of a 100 μm thick PFA tube. The pressure roll 62 is installed so as to be pressed against the fixing belt module 61. As the fixing roll 611 of the fixing belt module 61 rotates in the direction of arrow C, the pressure roll 62 follows the fixing roll 611 and moves in the direction of arrow E. To turn. The traveling speed is 440 mm / s, which is the same as the surface speed of the fixing roll 611.

Further, the pressure roll 62 is disposed outside the nip portion N of the pressure roll 62 as a cooling member for cooling the pressure roll 62, and first cooling for cooling the pressure roll 62 from the outside. A member 90 and a second cooling member 100 that is disposed inside the nip portion N of the pressure roll 62 and that cools the pressure roll 62 from the inside are disposed.
The first cooling member 90 absorbs heat from the pressure roll 62 and also has endothermic rolls 91 and 92, an endothermic roll 91 as an example of heat absorption means for making the temperature difference in the axial direction of the pressure roll 62 uniform. The cooling fan 93 cools the surfaces of the 92 and the pressure rolls 62, and the duct 94 guides the air blown from the cooling fan 93 to the heat absorbing rolls 91 and 92 and the surfaces of the pressure rolls 62. Here, the endothermic rolls 91 and 92 are cylindrical rolls formed of a metal having a high thermal conductivity such as copper or aluminum. And it arrange | positions so that it may contact | abut over the axial direction whole region of the pressure roll 62, and it is comprised so that it may follow with rotation of the pressure roll 62. FIG.
In addition, the second cooling member 100 is a duct that guides air from one pressure roll 62 end opening toward the other end opening along the inner peripheral surface of the nip N downstream side region of the pressure roll 62. 101, a cooling fan 102 that sends air from one end opening of the pressure roll 62 to the duct 101.

Next, the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
FIG. 3 is a schematic cross-sectional view showing the vicinity of the nip N. As shown in FIG. As shown in FIG. 3, in the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other, the fixing belt 610 is wound (wrapped) in the region (wrapped region) around the fixing roll 611. , The pressure roll 62 is arranged so as to be in pressure contact with the outer peripheral surface of the fixing belt 610, whereby a roll nip portion (first nip portion) N1 is formed.

Here, in the fixing device 60 of the present embodiment, as described above, the fixing roll 611, which is one of the rolls forming the roll nip portion N1, covers the surface of the core roll made of aluminum with a heat insulating layer made of a fluororesin. The fixing roll 611 is not covered with an elastic layer. The pressure roll 62, which is the other roll forming the roll nip portion N1, is a soft roll coated with an elastic layer 622.
With such a configuration of the fixing roll 611 and the pressure roll 62, the roll nip portion N1 is formed by the deformation of the elastic layer 622 of the pressure roll 62 in the roll nip portion N1 of the present embodiment. The roll 62 side functions as a roll (NIP Forming Pressure Roll) that forms a nip. That is, in the roll nip portion N1, the fixing roll 611 is hardly dented, and only the surface of the pressure roll 62 is largely dented (the amount of depression of the pressure roll 62> the amount of depression of the fixing roll 611). Thus, a nip region having a predetermined width in the traveling direction of the fixing belt 610 is created.
As described above, in the fixing device 60 of the present embodiment, the fixing roll 611 on the side where the fixing belt 610 is wrapped in the roll nip portion N1 is hardly deformed, and the cylindrical shape is maintained. Therefore, the fixing belt 610 rotates along the circumferential surface of the surface of the fixing roll 611, and the rotation radius does not change. Therefore, the fixing belt 610 can pass through the roll nip portion N1 while maintaining a constant traveling speed. it can. Accordingly, even when the fixing belt 610 passes through the roll nip portion N1, wrinkles and distortions (so-called “waves”) hardly occur in the fixing belt 610. As a result, the occurrence of image disturbance in the fixed image is suppressed, and a high-quality fixed image can be stably provided. In the fixing device 60 of the present embodiment, the roll nip portion N1 is set to a width of 15 mm along the traveling direction of the fixing belt 610.

Further, a peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1, and the peeling pad 64 presses the fixing belt 610 against the surface of the pressure roll 62. Accordingly, a peeling pad nip portion (second nip portion) N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed downstream of the roll nip portion N1.
As shown in FIG. 3, the peeling pad 64 that forms the peeling pad nip portion N2 has a substantially arc-shaped cross section, and is disposed along the axial direction of the fixing roll 611 in the vicinity of the downstream side of the roll nip portion N1. Yes. Then, the fixing belt 610 after passing through the peeling pad nip portion N <b> 2 rotates following the side surface of the peeling pad 64. Accordingly, the advancing direction of the fixing belt 610 is rapidly changed so as to be bent in the direction of the tension roll 615 by the peeling pad 64. Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 cannot follow the change in the advancing direction of the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the paper P is fixed by its so-called “koshi”. The belt 610 is peeled off. In this way, the curvature separation with respect to the paper P is stably performed at the exit portion of the peeling pad nip portion N2. In the fixing device 60 of the present embodiment, the peeling pad nip portion N2 is set to a width of 5 mm along the traveling direction of the fixing belt 610.

Next, the peeling pad 64 and the peeling pad nip portion N2 formed by the peeling pad 64 will be described in detail.
As described above, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. Accordingly, in the nip portion N including the roll nip portion N1 and the peeling pad nip portion N2, the most downstream side of the peeling pad nip portion N2 from the position where the nip pressure peaks in the roll nip portion N1 (see FIGS. 4 and 5 in the subsequent stage). In the region up to the position, the generation of a valley region where the nip pressure drops below a predetermined value is suppressed, and the nip pressure can be set to continuously and monotonously decrease. Therefore, the fixing device 60 according to the present embodiment can realize stable sheet separation and provide a high-quality fixed image without image defects such as image unevenness. Here, the peeling pad 64 disposed in the vicinity of the downstream side of the roll nip portion N1 suppresses the generation of a valley region where the nip pressure drops below a predetermined value, and the nip pressure is continuously increased in the nip portion N. The point set so as to monotonously decrease will be described.

In the fixing device 60 of the present embodiment, a fixing belt module 61 is used in which a fixing belt 610 is stretched by a plurality of rolls including a fixing roll 611 as a heating member. Such a configuration using the fixing belt module 61 can always maintain a predetermined fixing temperature in the fixing device 60 even when the speed of the image forming apparatus is increased, as will be described later. Further, it has an excellent feature that it is possible to suppress the occurrence of a so-called “temperature droop phenomenon” in which the fixing temperature drops at the start of the high-speed fixing operation.
However, also in the fixing device 60 using the fixing belt module 61, since the toner image is carried on the surface of the paper P, when the toner image is melted by the heat of the fixing belt 610, the toner image is bonded to the adhesive. Thus, an adhesive force acts between the paper P and the fixing belt 610. For this reason, it is necessary to provide a mechanism for peeling the paper P from the surface of the fixing belt 610 as in the conventional fixing device. In particular, when the speed of the image forming apparatus is increased, if a separation failure occurs once in the fixing device 60 and a paper jam occurs, the number of subsequent sheets P that are damaged by the influence increases. Therefore, the sheet P that has passed through the nip portion N at a high speed needs to be stably and reliably peeled from the fixing belt 610 side.

At this time, if a conventional separation claw is used as a mechanism for separating the paper P from the surface of the fixing belt 610, the separation claw is applied to the fixing belt 610 in order to stably peel the paper P from the fixing belt 610 side. It is necessary to arrange it in contact. Therefore, when the separation claw is used, the surface of the fixing belt 610 is easily worn by the separation claw, and the following problems are likely to occur. In other words, wear marks due to the separation claws are generated on the surface of the fixing belt 610, and fixing unevenness corresponding to the wear marks on the surface of the fixing belt 610 may occur on the fixed image, thereby reducing the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Furthermore, when the surface of the fixing belt 610 is worn, the thin-layer fixing belt 610 eventually breaks, and the function of the fixing device 60 may be impaired. For this reason, as described above, the separation mechanism based on the curvature separation that does not require the contact member such as the separation claw is optimal for performing the sheet separation in the fixing belt module 61 using the fixing belt 610.
Therefore, in the fixing belt module 61 of the present embodiment, a member that changes the traveling direction of the fixing belt 610 abruptly, that is, a peeling pad 64 is disposed in the downstream portion of the nip portion N.

However, when the peeling pad 64 is provided to form the peeling pad nip portion N2 continuously to the roll nip portion N1, the region in the peeling pad nip portion N2 where the peeling pad 64 is provided (the peeling pad 64 and the pressure roll). In the boundary region N2S (see FIG. 3) located on the side of the roll nip N1 from N2T, there is no member that directly presses the fixing belt 610 to either the fixing roll 611 or the pressure roll 62. Therefore, the boundary region N2S is pressed against the pressure roll 62 only by the tension of the fixing belt 610, and the nip pressure in the boundary region N2S (hereinafter, the nip pressure in the boundary region N2S is referred to as Pn). It is formed only by the tension of the fixing belt 610. For this reason, when the peeling pad 64 is arranged at a predetermined distance or more away from the downstream end N1E (see FIG. 3) of the roll nip portion N1, the nip pressure Pn in the boundary region N2S is separated from the nip pressure of the roll nip portion N1. A region between the nip pressure in the region N2T in which the pad 64 is disposed is formed as a region of a valley where the nip pressure Pn falls below a predetermined value (hereinafter referred to as Pn1). The nip pressure Pn in the boundary region N2S is relatively lower than the nip pressure in the roll nip portion N1 and the nip pressure in the region N2T in which the peeling pad 64 is disposed.
Here, FIG. 4 shows the nip pressure distribution of the nip portion N (the roll nip portion N1 and the peeling pad nip portion N2) when the peeling pad 64 is spaced apart from the downstream end N1E of the roll nip portion N1 by a predetermined distance or more. FIG. As shown in FIG. 4, in this case, in the peeling pad nip portion N2, a valley region where the nip pressure Pn falls below a predetermined value Pn1 is formed in the boundary region N2S with the roll nip portion N1.

By the way, in the fixing process by the fixing device 60 of the present embodiment, the paper P carrying the toner image is heated and pressed in the roll nip portion N1, and the toner is melt-pressed. At that time, the water in the paper P vaporizes from the paper P and the toner that have received heat in the roll nip portion N1 to generate water vapor, or the air in the toner tends to thermally expand. However, since a high nip pressure is applied at the roll nip portion N1, an air gap (bubbles) due to water vapor or expanded air does not occur between the fixing belt 610 and the pressure roll 62.
However, when the nip pressure Pn in the boundary region N2S with the roll nip portion N1 in the peeling pad nip portion N2 is formed in a low state below a predetermined value Pn1, bubbles that have been suppressed in the roll nip portion N1 are generated in the boundary region N2S. Will occur without being suppressed. Then, when the paper P enters the high nip pressure region N2T where the peeling pad 64 is disposed in a state where bubbles are generated, the bubbles generated in the boundary region N2S move around on the surface of the paper P due to the high nip pressure. . As a result, the toner image on the paper P is immediately after passing through the roll nip portion N1, and the melted toner is not yet completely solidified. Arise. As a result, a situation in which an image defect such as unevenness occurs in the fixed image is caused.

Therefore, in the fixing device 60 of the present embodiment, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. By installing the peeling pad 64 in this way, the width of the boundary region N2S between the roll nip portion N1 and the region N2T in which the peeling pad 64 is disposed in the peeling pad nip portion N2 can be set as narrow as possible. Become. As a result, the area pressed against the pressure roll 62 only by the tension of the fixing belt 610 is narrowed. Therefore, as shown in FIG. 5 (a diagram showing an outline of the nip pressure distribution when the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1), the nip pressure Pn is larger than the predetermined value Pn1 in the boundary region N2S. It is also possible to suppress the generation of a valley region that falls. The nip pressure can be set so as to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 in the nip portion N to the most downstream position of the peeling pad nip portion N2. Become.
Thus, since the nip pressure Pn in the boundary region N2S can be set higher than the predetermined Pn1, the generation of bubbles in the boundary region N2S can be suppressed. Further, by setting the nip pressure continuously and monotonically from the position where the nip pressure reaches a peak in the roll nip portion N1 to the most downstream position of the peeling pad nip portion N2, a high nip is obtained in the roll nip portion N1. The water vapor or air that is about to expand due to the pressure is gradually released along the path until it passes through the peeling pad nip portion N2, thereby suppressing the phenomenon of bubbles moving around as described above. Is possible. Therefore, the toner image that has not been completely solidified is hardly disturbed, and it is possible to suppress the occurrence of image defects such as image unevenness in the fixed image.

Here, in order to suppress the generation of bubbles in the boundary region N2S, the pressure (nip pressure) Pn in the boundary region N2S needs to satisfy the following expression (1).
Pn ≧ Po × (Tn / To−1) (1)
That is, the predetermined value Pn1 of the nip pressure Pn in the boundary region N2S described above is
Pn1 = Po × (Tn / To−1)
It becomes.
Tn is the absolute temperature of the fixing belt 610, To is the absolute temperature of air (environment temperature) at a position sufficiently away from the fixing roll 611, and Po is atmospheric pressure.

Equation (1) is derived as follows. First, the equation of state of the ideal gas is expressed by the following equation (2).
PV = nRT (2)
In addition, P is a pressure, V is a volume, n is the number of moles, R is a gas constant, and T is an absolute temperature.
Therefore, the following equations (3) and (4) are derived.
(Po + Pn) × Vn = nRTn (3)
PoVo = nRTo (4)
Vn is the volume of bubbles in the boundary region N2S, and Vo is the volume of bubbles under atmospheric pressure. In order to suppress the generation of bubbles in the boundary region N2S, the condition Vn ≦ Vo may be satisfied. Therefore, the following equation (5) is derived from the equations (3) and (4).
Tn / (Po + Pn) ≦ To / Po (5)
Further, when the equation (5) is modified, the above equation (1) is derived.
The peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1 so that a sufficiently narrow boundary region N2S that satisfies the nip pressure Pn satisfying the expression (1) is formed.

Next, the shape of the peeling pad 64 that can be disposed in the vicinity of the downstream side of the roll nip portion N1 will be described.
FIG. 6 is a schematic cross-sectional view showing the periphery of a region where the peeling pad 64 is disposed. As shown in FIG. 6, the peeling pad 64 mainly includes an inner surface 64a facing the fixing roll 611 side, an outer surface 64b that rapidly changes the advancing direction of the fixing belt 610 that has passed through the peeling pad nip portion N2, and fixing. A pressing surface 64 c that presses the belt 610 against the pressing roll 62 is formed.
The inner surface 64a of the peeling pad 64 is arranged around the fixing roll 611 in order to place the peeling pad 64 as close as possible to the fixing roll 611 side (for example, the gap between the peeling pad 64 and the fixing roll 611 is 0.5 mm). It is formed with a curved surface following the surface. That is, in order to set the boundary region N2S shown in FIG. 6 as narrow as possible, it is defined by the fixing roll 611 and the pressure roll 62 in the vicinity of the downstream side of the roll nip portion N1 (see also FIG. 3). In the wedge-shaped region Q, it is necessary to arrange the peeling pad 64 so as to press the surface of the pressure roll 62. Therefore, the upstream end portion (upstream end portion of the pressing surface 64c) 64p of the inner surface 64a is located near the downstream end portion N1E of the roll nip portion N1, that is, the position close to the fixing roll 611 in the wedge-shaped region Q described above. The inner side surface 64 a is formed in a curved surface that follows the peripheral surface of the fixing roll 611. In the peeling pad 64 of the present embodiment, the inner side surface 64a is formed by a substantially circumferential surface having a curvature radius of 33 mm. The inner side surface 64a is not limited to a curved surface such as a substantially circumferential surface as long as it is a curved surface that follows the circumferential surface of the fixing roll 611, and can be formed by bending a plurality of planes stepwise.
In addition, in order to allow the upstream end 64p of the inner surface 64a to be installed at a position close to the fixing roll 611 in the wedge-shaped region Q, and to ensure the strength and rigidity of the upstream end 64p portion, The angle θ1 formed by the side surface 64a and the pressing surface 64c is preferably set to 20 to 50 °.

The pressing surface 64 c of the peeling pad 64 is a surface that presses the fixing belt 610 against the pressure roll 62 and presses against the surface of the pressure roll 62. Therefore, the pressing surface 64 c is formed as a flat surface so that the fixing belt 610 is uniformly pressed against the pressure roll 62. Furthermore, the pressing surface 64c can also be formed as a concave curved surface that follows the circumferential surface of the pressure roll 62, whereby the pressing force can be made more uniform.
Further, as described above, the upstream end 64p of the pressing surface 64c is disposed at a position close to the fixing roll 611 in order to reduce the width of the boundary region N2S as much as possible. It is also possible to arrange the portion 64p so as to contact the fixing roll 611. By setting in this way, the boundary region N2S can be almost eliminated, and almost the entire area of the peeling pad nip portion N2 can be formed by the pressure contact portion N2T between the peeling pad 64 and the pressure roll 62. In addition, since the upstream end portion 64p of the pressing surface 64c can simultaneously receive the pressing force from the fixing roll 611, a sufficient nip pressure can be formed in the entire area of the peeling pad nip portion N2.

FIG. 7 is a view showing a configuration in which the upstream end portion 64p of the pressing surface 64c is set in contact with the fixing roll 611 and receives the pressing force from the fixing roll 611 at the same time. As shown in FIG. 7, in this case, the upstream end portion 64p of the pressing surface 64c is formed in a wedge shape so as to fill the deepest portion of the wedge-shaped region Q. Thus, by forming the upstream end portion 64p of the pressing surface 64c in a wedge shape, it is possible to stably receive the pressing force from the fixing roll 611, and at the same time, even if it rubs against the fixing roll 611, Wear is unlikely to occur on the contact surface of the upstream end portion 64p with the fixing roll 611 and the surface of the fixing roll 611. Therefore, it is possible to maintain the function of the peeling pad 64 over a long period of time.
The pressing surface 64c rubs against the fixing belt 610 and the fixing roll 611, so that the fixing belt 610 advances smoothly, and the friction coefficient is applied to the surface of the pressing surface 64c in order to reduce wear on the fixing roll 611. For example, it is preferable to have a structure that is small and excellent in wear resistance, such as Teflon (registered trademark).

The outer side surface 64b is a surface from which the sheet P is peeled off from the fixing belt 610 by guiding the fixing belt 610 in cooperation with the stretching roll 615 and the fixing roll 611 and rapidly changing the traveling direction thereof. Therefore, in order to stably peel the sheet P from the fixing belt 610, in the upstream end region (region where the fixing belt 610 is separated from the pressure roll 62) R of the outer surface 64b, The angle θ2 (see FIGS. 6 and 7) formed by the tangent to the outer side surface 64b is set to be 40 ° or more. Further, in the upstream end region R, the outer side surface 64b is formed as a curved surface so that the fixing belt 610 can be smoothly moved in the upstream end region R that is bent sharply.
Further, the outer surface 64b is formed by a plane inclined toward the stretching roll 615 so that the fixing belt 610 moves smoothly in the direction of the stretching roll 615 and the fixing roll 611 after being separated from the pressure roll 62. Has been. In this case, the outer side surface 64b can be formed as a curved surface that curves toward the outer side (the fixing belt 610 side). Since the outer surface 64b also rubs against the fixing belt 610 in the same manner as the pressing surface 64c, the surface of the fixing belt 610 has a small friction coefficient and excellent wear resistance. It is preferable that the structure is coated with Teflon (registered trademark) or the like.

As described above, in the fixing device 60 according to the present embodiment, the nip portion N including the roll nip portion N1 and the peeling pad nip portion N2 is formed in the region where the fixing belt module 61 and the pressure roll 62 are pressed. . The release pad 64 that forms the release pad nip portion N2 is disposed in the vicinity of the downstream side of the roll nip portion N1, and the release pad 64 is set to press the pressure roll 62. Therefore, it is possible to suppress the generation of a valley region where the nip pressure falls in the nip portion N, and it is possible to form the nip pressure Pn that satisfies the above-described expression (1) also in the boundary region N2S. Accordingly, the nip pressure is set to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 in the nip portion N to the most downstream position of the peeling pad nip portion N2. Is possible.
Therefore, by setting a predetermined nip pressure Pn in the boundary region N2S, the generation of bubbles in the boundary region N2S can be suppressed. Furthermore, by setting the nip pressure so as to continuously decrease monotonously, the water vapor or air to be thermally expanded that has been suppressed by the high nip pressure in the roll nip portion N1 is allowed to pass through the peeling pad nip portion N2. It becomes possible to gradually open the route. As a result, it is possible to suppress the phenomenon that water vapor or thermally expanded air becomes bubbles and move around in the nip, so that the toner image that has not yet been completely solidified is hardly disturbed and fixed. It is possible to suppress the occurrence of image defects such as image unevenness in the image.

  Further, since the cross section of the peeling pad 64 forming the peeling pad nip portion N2 is formed in a substantially arc shape, the fixing belt 610 that has passed through the peeling pad nip portion N2 is rapidly changed so that the traveling direction thereof is bent. It is done. Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 is peeled from the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the curvature separation from the paper P can be performed.

Next, a fixing operation in the fixing device 60 of the present embodiment will be described.
The sheet P on which the unfixed toner image is electrostatically transferred in the secondary transfer unit 20 (see FIG. 1) of the image forming apparatus is directed toward the nip N of the fixing device 60 by the conveyance belt 55 and the fixing inlet guide 56 ( See FIG. 2: arrow F direction). The unfixed toner image on the surface of the paper P passing through the nip portion N is fixed on the paper P mainly by pressure and heat acting on the roll nip portion N1.

  At this time, in the fixing device 60 of the present embodiment, heat acting on the nip portion N is supplied by the fixing belt 610. The fixing belt 610 mainly includes heat supplied from the halogen heater 616b disposed inside the tension roll 612 through the tension roll 612, and from the halogen heater 616c disposed inside the tension roll 613 to the tension roll 613. It is comprised so that it may be heated with the heat supplied through. When the fixing belt 610 is conveyed to the nip portion N, heat energy has already been supplied from the stretching roll 612 and the stretching roll 613 sufficiently and quickly. Even at a high speed of 440 mm / s, a sufficient amount of heat can be applied to the paper P.

  That is, the fixing belt 610 functioning as a direct heating member is a thin layer belt member and has a very small heat capacity. In addition, the fixing belt 610 is configured to contact the tension roll 612 and the tension roll 613 that are main heat supply members with a wide lap area (large wrap angle). Accordingly, since a sufficient amount of heat is supplied from the stretching roll 612 and the stretching roll 613 during a short period in which the fixing belt 610 rotates once, the fixing belt after finishing the fixing process after passing through the nip portion N. It becomes possible to return 610 to a necessary fixing temperature in a short time.

Therefore, in the fixing device 60 of the present embodiment, the fixing temperature can be maintained substantially constant even during continuous high-speed paper feeding. In addition, it is possible to suppress the occurrence of a temperature droop phenomenon in which the fixing temperature drops at the start of the high-speed fixing operation. In particular, even when fixing on thick paper having a large heat capacity, it is possible to maintain the fixing temperature and suppress the occurrence of temperature droop. In addition, since the fixing belt 610 is configured to come into contact with the stretching roll 612 and the stretching roll 613 with a wide lap area, heat utilization efficiency can be improved and warm-up can be shortened. It becomes possible.
Further, when it is necessary to switch the fixing temperature in the middle (including both fixing temperature up and down) corresponding to the paper type, the fixing belt 610 has a small heat capacity, so the halogen heater 616b and / or By adjusting the output of the halogen heater 616c, it is possible to easily and quickly switch to a desired temperature.

  By the way, the fixing roll 611 of the present embodiment does not have a function of actively supplying thermal energy to the fixing belt 610 to raise the temperature of the fixing belt 610. That is, the halogen heater 616a disposed inside the fixing roll 611 is set to maintain a temperature at which the fixing roll 611 does not take heat from the fixing belt 610 at the roll nip portion N1. Specifically, the temperature of the fixing roll 611 is set to maintain a predetermined value (for example, 180 ° C.) lower than the temperature (for example, 210 ° C.) of the fixing belt 610 at the nip portion N.

The reason why the temperature of the fixing roll 611 is set lower than the temperature of the fixing belt 610 is based on the following reason.
As described above, in the fixing device 60 of the present embodiment, the nip portion N is widely formed by the roll nip portion N1 and the peeling pad nip portion N2. Therefore, a sufficient amount of heat can be supplied from the fixing belt 610 to the paper P that passes through the nip portion N, and stable fixing performance can be exhibited even on the paper P that is continuously passed at high speed.
However, the fixing belt 610 is in direct contact with the pressure roll 62 at an interval between sheets. For example, when small-size paper is continuously passed, both end regions of the pressure roll 62 or one end region are in direct contact with the pressure roll 62 over a long period of time. . Therefore, the temperature of the pressure roll 62 tends to gradually increase.
In addition, the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 at the roll nip portion N1. Therefore, when the temperature of the fixing roll 611 made of aluminum and having a large heat capacity is set to be equal to or higher than that of the fixing belt 610, the temperature of the pressure roll 62 rises to substantially the same temperature as the fixing roll 611. Will be. Then, at the nip portion N, the paper P is excessively heated from both the fixing belt 610 side and the pressure roll 62 side. As a result, a phenomenon occurs in which water vaporizes and water vapor is generated in the paper P, or the air thermally expands, and the paper P does not occur when heated only from one side ( Paper blisters) are likely to occur.

  Further, the fixing belt 610 and the pressure roll 62 are always in direct contact with each other, particularly on the side in the width direction when small-size paper is passed. As a result, a difference in thermal expansion occurs in the axial direction of the pressure roll 62, and a large outer diameter difference in the axial direction occurs in the pressure roll 62 every image forming operation cycle. As a result, in the pressure roll 62, the occurrence of a difference in outer diameter for each image forming operation is repeated due to long-term use, so that the surface of the pressure roll 62 is likely to be wrinkled, cracked, or even damaged. For this reason, an image defect occurs, and in some cases, the fixing function may be significantly impaired.

  Accordingly, the surface temperature of the fixing roll 611 of the present embodiment is set to a predetermined temperature lower than the temperature of the fixing belt 610 at the nip portion N. Accordingly, it is possible to suppress an excessive temperature rise in the pressure roll 62 as much as possible by suppressing heat from being transmitted from the fixing roll 611 to the pressure roll 62 more than necessary via the fixing belt 610 in the roll nip portion N1. It is configured as follows.

  In the fixing device 60 according to the present embodiment, in addition to the temperature setting of the fixing roll 611, the pressure roll 62 is actively used as a further means for suppressing an excessive temperature rise in the pressure roll 62. The 1st cooling member 90 and the 2nd cooling member 100 as an example of the cooling member cooled automatically are arrange | positioned. In a high-speed image forming apparatus, due to the nature of the apparatus, a large amount of printing is often performed at one time, and the operation time is often long. In addition, the image forming apparatus may be used in an environment where the temperature is high. Therefore, it may be assumed that setting the temperature of the fixing roll 611 lower than the temperature of the fixing belt 610 is insufficient to suppress an excessive temperature rise of the pressure roll 62. Therefore, the pressure roller 62 is provided with the first cooling member 90 and the second cooling member 100, and the temperature of the pressure roller 62 is controlled within a predetermined range.

The first cooling member 90 is provided outside the pressure roll 62 and cools the pressure roll 62 from the outer surface of the pressure roll 62. The endothermic rolls 91 and 92 of the first cooling member 90 are columnar or cylindrical roll members formed of a metal having a high thermal conductivity such as copper or aluminum. Therefore, the pressure roll 62 is disposed so as to be in contact with the entire area in the axial direction, and is driven by the rotation of the pressure roll 62, thereby effectively absorbing heat from the pressure roll 62. Furthermore, for example, it also functions to relieve the temperature difference between the end region and the center region of the pressure roll 62 that occurs when small-size paper is continuously fed.
The air blown from the cooling fan 93 is guided by the duct 94 to the surface of the pressure roll 62 in the peripheral region where the heat absorption rolls 91 and 92 and the heat absorption rolls 91 and 92 are disposed. Thereby, the cooling fan 93 cools the pressure roll 62 indirectly through the heat absorbing rolls 91 and 92 and also directly cools the surface of the pressure roll 62.

  On the other hand, the second cooling member 100 is provided inside the pressure roll 62 and cools the pressure roll 62 from the cylindrical roll 621 side of the pressure roll 62. Inside the cylindrical roll 621, a duct 101 for guiding air to move along the inner peripheral surface of the cylindrical roll 621 on the downstream side of the nip portion N is disposed. And it guide | induces so that the air sent from the cooling fan 102 arrange | positioned in the one edge part opening (end part of the pressure roll 62) vicinity of the duct 101 may be exhausted from the other edge part opening. Therefore, the pressure roll 62 is cooled (air cooled) from the cylindrical roll 621 side by the air passing through the duct 101.

  Here, the first cooling member 90 and the second cooling member 100 are located downstream of the nip portion N (downstream in the rotation direction of the pressure roll 62 from the line m connecting the nip portion N and the rotation axis of the pressure roll 62. Area), that is, the pressure roll 62 immediately after passing through the nip portion N is set to be cooled. With such a configuration, it is possible to prevent the fixing belt 610 from being cooled before the air blown from the cooling fan 93 enters the nip portion N. Further, by cooling immediately after passing through the nip portion N, diffusion of heat into the pressure roll 62 can be suppressed, so that effective cooling can be performed.

Moreover, ON / OFF control of both or either of the cooling fan 93 and the cooling fan 102 can be performed based on an output from a sensor (not shown) that detects the surface temperature of the pressure roll 62. Specifically, when the output from the sensor indicates a predetermined temperature value or more, the cooling fan 93 and / or the cooling fan 102 can be turned on. In addition, when the sensor is disposed at the axial center and both ends of the pressure roll 62 and the temperature difference between the axial center and both ends exceeds a predetermined value, the cooling fan 93 and / or cooling The fan 102 can also be turned on.
Further, ON / OFF control can be performed based on a paper type selection instruction signal from the operation panel (not shown) of the image forming apparatus by the user. For example, when the user selects a predetermined paper P (for example, thick paper), the cooling fan 93 and / or the cooling fan 102 can be set to be turned on. In addition, the ON / OFF control can be performed based on the use status of the apparatus such as the number of prints and the drive time of the apparatus, and external factors such as the use environment temperature of the apparatus.

Moreover, in the 1st cooling member 90 and / or the 2nd cooling member 100, it can also be set as the setting which raises the cooling performance to the axial direction both ends of the pressure roll 62, or any one edge part. Specifically, both of the cooling fan 93 and the cooling fan 102, or any one of them, has an air flow rate to both ends in the axial direction of the pressure roll 62 or one of the end portions, which is higher than the air flow rate to the center portion. It can also be configured to increase. As a result, the amount of thermal expansion in the axial direction of the pressure roll 62 is enhanced by enhancing the cooling effect at both ends of the pressure roll 62 in the axial direction when one of the small-size papers is continuously passed. Generation | occurrence | production of a difference can be relieve | moderated and the damage to the pressurization roll 62 surface can be suppressed further smaller.
Furthermore, in the fixing device 60 of the present embodiment, the first cooling member 90 and the second cooling member 100 are disposed, but only one of the first cooling member 90 and the second cooling member 100 is disposed. You may set up.
In the first cooling member 90, Peltier elements can be used as the heat absorbing rolls 91 and 92. In that case, the cooling fan 93 and the duct 94 are configured to cool the heat dissipation portion of the Peltier element.
Furthermore, the endothermic rolls 91 and 92 can be configured by only one of the endothermic roll 91 and the endothermic roll 92. Also, three or more endothermic rolls can be provided.

  By the way, the temperature of the pressure roll 62 cooled by the first cooling member 90 and / or the second cooling member 100 is 70 to 160 ° C., more preferably 90 to 160 ° C. when the fixing belt 610 is set to 210 ° C. It is preferred that the temperature be controlled to maintain 140 ° C. This is because when the temperature of the pressure roll 62 becomes lower than 70 ° C., the temperature of the fixing belt 610 at the nip portion N is significantly reduced, so that the fixing performance is lowered and temperature droop is likely to occur. . On the other hand, when the temperature of the pressure roll 62 is higher than 160 ° C., the generation rate of paper blisters is increased, which is not preferable.

Here, using the fixing device 60 of the present embodiment, the occurrence of fixing failure and the presence or absence of paper blisters were evaluated. As the paper P, so-called thick paper, specifically, mirror coated platinum paper manufactured by Oji Paper Co., Ltd. with a basis weight of 256 (g / cm) is used, and continuous 10,000 sheets are fed by SEF (Short Edge Feed) feeding. Went. As a result, it was confirmed that neither fixing failure nor paper blister occurred.
Moreover, as a result of monitoring the temperature of the pressure roll 62 during the evaluation test, it was confirmed that the temperature of the pressure roll 62 could be controlled to 100 to 160 ° C. It was also confirmed that the temperature difference in the axial direction of the pressure roll 62 was suppressed to 50 ° C. or less.

Subsequently, the fixing operation after passing through the roll nip portion N1 will be described.
After passing through the roll nip portion N1, the paper P is conveyed to the peeling pad nip portion N2. The peeling pad nip portion N <b> 2 is formed such that the peeling pad 64 is pressed against the pressure roll 62 and the fixing belt 610 comes into pressure contact with the pressure roll 62. Therefore, as shown in FIG. 3, the roll nip portion N1 has a curved shape that is convex downward due to the curvature of the fixing roll 611, whereas the peeling pad nip portion N2 is convex upward due to the curvature of the pressure roll 62. It has a certain curved shape.
Therefore, the traveling direction of the paper P heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 is changed to the curvature directed in the opposite direction by the pressure roll 62 in the peeling pad nip portion N2. At that time, a minute micro slip occurs between the toner image on the paper P and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and a state is formed in which the paper P is easily peeled off from the fixing belt 610. As described above, the peeling pad nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

Since the fixing belt 610 is conveyed so as to be wound around the peeling pad 64 at the exit of the peeling pad nip portion N2, the conveyance direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface 64b of the peeling pad 64, the bending of the fixing belt 610 becomes large. For this reason, the paper P whose adhesion to the fixing belt 610 has been weakened in advance in the peeling pad nip portion N2 is self-striped from the fixing belt 610 by the stiffness of the paper that the paper P itself has.
Then, the paper P separated from the fixing belt 610 is guided in its traveling direction by a peeling guide plate 83 as an example of a peeling auxiliary member disposed on the downstream side of the peeling pad nip portion N2. The paper P guided by the peeling guide plate 83 is then discharged out of the apparatus by the paper discharge guide 65 and the paper discharge roll 66 (see FIG. 2), and the fixing process is completed.

  As described above, the fixing device 60 of the present embodiment uses the fixing belt module 61 in which the fixing belt 610 is stretched by a plurality of rolls including the fixing roll 611 as a heating member. Even if the speed of the forming apparatus is increased, a predetermined fixing temperature can always be maintained in the fixing device 60. Furthermore, it is possible to suppress the occurrence of a temperature droop phenomenon in which the fixing temperature drops at the start of the high-speed fixing operation. For this reason, it is possible to provide a large amount of high-quality fixed images in a short time.

At the same time, the nip portion N includes a roll nip portion N1 and a peeling pad nip portion N2 formed downstream of the roll nip portion N1 and continuously to the roll nip portion N1. The peeling pad 64 that forms the peeling pad nip portion N2 is disposed in the vicinity of the downstream side of the roll nip portion N1, and the peeling pad 64 is set to press the pressure roll 62. Accordingly, by setting the nip pressure Pn satisfying the above-described expression (1) in the boundary region N2S, the generation of a valley region where the nip pressure falls is suppressed, and the generation of bubbles in the boundary region N2S is suppressed. can do. Furthermore, it is possible to set the nip pressure to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 to the most downstream position of the peeling pad nip portion N2.
As described above, in the fixing device 60 according to the present embodiment, the generation of bubbles in the boundary region N2S is suppressed, and the nip pressure is set so as to continuously and monotonously decrease, whereby a high nip pressure is obtained in the roll nip portion N1. It is possible to gradually release the water vapor or the air that is about to be thermally expanded that has been held in by the path until it passes through the peeling pad nip portion N2, and the water vapor or the thermally expanded air becomes bubbles and moves around in the nip. Occurrence of the phenomenon can be suppressed. Therefore, the toner image that has not been completely solidified is hardly disturbed, and it is possible to suppress the occurrence of image defects such as image unevenness in the fixed image.

  In the fixing device 60 of the present embodiment, the first cooling member 90 and the second cooling member 100 for actively cooling the pressure roll 62 are provided. Thereby, even when the operation time is long for a high-speed image forming apparatus, it is possible to suppress an excessive temperature rise of the pressure roll 62. Thereby, it is possible to suppress the occurrence of paper blisters. It is also possible to suppress the occurrence of wrinkles, cracks, and damage on the surface of the pressure roll 62.

  Further, since the cross section of the peeling pad 64 forming the peeling pad nip portion N2 is formed in a substantially arc shape, the fixing belt 610 that has passed through the peeling pad nip N2 is rapidly changed so that the traveling direction thereof is bent. . Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 is peeled from the fixing belt 610 when it leaves the peeling pad nip portion N2, and it becomes possible to perform curvature separation with respect to the paper P.

[Embodiment 2]
In the first embodiment, in the fixing device 60 mounted on the image forming apparatus, the heat absorbing rolls 91 and 92 are the outer surfaces of the pressure roll 62 as an example of a pressure member cooling unit that actively cools the pressure roll 62. The structure provided with the 1st cooling member 90 arrange | positioned in contact with 2nd and the 2nd cooling member 100 arrange | positioned inside the pressure roll 62 was demonstrated. In the second embodiment, a configuration in which the pressure roll 62 is cooled by a belt member disposed so as to come into contact with the outer surface of the pressure roll 62 will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

FIG. 8 is a side sectional view showing the configuration of the fixing device 200 according to the present embodiment. In the fixing device 200 of the present embodiment, the fixing of the first embodiment is different except that the third cooling member 110 is provided as an example of a cooling member that actively cools the pressure roll 62. Similar to the device 60.
The third cooling member 110 is external to the cooling belt 111 disposed so as to be in contact with the outer surface of the pressure roll 62, the two stretching rolls 112 and 113 that stretch the cooling belt 111, and the cooling belt 111. The cooling fan 114 that blows air from the inside, the duct 115 that guides the air blown from the cooling fan 114 to the outer surface of the cooling belt 111, and the cooling fan 116 that blows air from the inside to the cooling belt 111.

The cooling belt 111 is an endless belt member whose original shape is formed in a cylindrical shape, and is a metal film such as SUS having a high thermal conductivity, a thermosetting polyimide resin, a thermoplastic polyimide resin, a polyamideimide resin, a polybenzo It is composed of a heat resistant resin such as an imidazole resin. Further, the cooling belt 111 is rotatably stretched by stretch rolls 112 and 113 which are cylindrical roll members made of metal such as SUS or aluminum having high thermal conductivity.
The tension rolls 112 and 113 are pressed against the pressure roll 62 while the cooling belt 111 is stretched, so that the cooling belt 111 and the tension rolls 112 and 113 are pressed against the pressure roll 62. Thereby, the cooling belt 111 is rotated by following the pressure roll 62 while being in contact with the pressure roll 62.

With such a configuration, the heat of the pressure roll 62 is absorbed by the cooling belt 111 and the stretching rolls 112 and 113, and the pressure roll 62 is cooled. The heated cooling belt 111 is cooled from the outer surface side by air blown from the cooling fan 114 by the duct 115. Further, the air is cooled from the inner surface side by the air blow from the cooling fan 116.
On the other hand, the stretching rolls 112 and 113 are formed of cylindrical rolls, and fans 117 and 118 are disposed outside the end portions thereof. Therefore, the heated tension rolls 112 and 113 are cooled from the inside by being blown by the fans 117 and 118 from one end portion toward the other.
The arrangement position of the third cooling member 110, the control of the fans 114, 116, 117, and 118 can be set in the same manner as in the first embodiment.

As described above, also in the fixing device 200 of the present embodiment, the heat of the pressure roll 62 is cooled by the cooling belt 111 and the stretching rolls 112 and 113 constituting the third cooling member 110. Accordingly, as in the first embodiment, the temperature of the pressure roll 62 is maintained in the temperature range of 70 to 160 ° C., more preferably 90 to 140 ° C. when the fixing belt 610 is set to 210 ° C. Can be controlled.
In particular, in the fixing device 200 of the present embodiment, the cooling belt 111 can contact the pressure roll 62 in a wide area, so that the heat of the pressure roll 62 can be absorbed more efficiently and high cooling can be achieved. It is possible to demonstrate performance.
Therefore, even when the operation time is long for a high-speed image forming apparatus, an excessive temperature rise of the pressure roll 62 can be suppressed. Thereby, it is possible to suppress the occurrence of paper blisters. In addition, it is possible to suppress the occurrence of wrinkles, cracks, and damage on the surface of the pressure roll 62.

[Embodiment 3]
In the first embodiment, as an example of a cooling member that actively cools the pressure roll 62 in the fixing device 60 mounted on the image forming apparatus, the heat absorbing rolls 91 and 92 abut on the outer surface of the pressure roll 62. The structure provided with the 1st cooling member 90 arrange | positioned and the 2nd cooling member 100 arrange | positioned inside the pressurization roll 62 was demonstrated. In the third embodiment, a configuration in which the pressure roll 62 is cooled by a belt member stretched so as to wrap the outer surface of the pressure roll 62 will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

FIG. 9 is a side cross-sectional view showing the configuration of the fixing device 300 according to the present embodiment. In the fixing device 300 of the present embodiment, the fixing of the first embodiment is different except that the fourth cooling member 120 is provided as an example of a cooling member that actively cools the pressure roll 62. Similar to the device 60.
The fourth cooling member 120 is disposed inside the cooling belt 121 that is stretched so as to wrap the outer surface of the pressure roll 62, the stretching roll 122 that stretches the other of the cooling belt 121, and the inside of the cooling belt 121. The fan 123 that blows air, the duct 124 that guides the blown air from the fan 123 to the inner peripheral surface of the cooling belt 121, and one end of the tension roll 122, and blows air into the tension roll 122. The fan 125 is configured.

The cooling belt 121 is an endless belt member whose original shape is formed in a cylindrical shape, and is a metal film such as SUS having a high thermal conductivity, a thermosetting polyimide resin, a thermoplastic polyimide resin, a polyamideimide resin, a polybenzo It is composed of a heat resistant resin such as an imidazole resin.
The tension roll 122 is a cylindrical roll made of metal such as SUS or aluminum having a high thermal conductivity, and rotates following the pressure roll 62 while applying a predetermined tension to the cooling belt 121.

The cooling belt 121 cools the pressure roll 62 by absorbing heat from the pressure roll 62 in a lap region with the pressure roll 62 while being rotated by the pressure roll 62. The heated cooling belt 121 is cooled from the inner surface side by air blown from the cooling fan 123 by the duct 124. On the other hand, the tension roll 122 is cooled from the inside by being blown from one end to the other by the fan 125 disposed at the end. As a result, the cooling belt 121 is also cooled by the tension roll 122.
The arrangement position of the fourth cooling member 120 (the stretching roll 122), the control of the fans 123 and 125, and the like can be set in the same manner as in the first embodiment.

Here, if the heat capacity of the cooling belt 121 is configured to be about the same as the heat capacity of the fixing belt 610, a thermal equilibrium between the cooling belt 121 and the fixing belt 610 can be formed, and the excessive temperature of the pressure roll 62 is increased. It is effective in suppressing the rise.
That is, the heat of the fixing belt 610 heated by the tension roll 612 and the tension roll 613 is used for the fixing process in the nip portion N, but the heat not used for the fixing process is applied to the fixing belt 610. Remain. This heats the pressure roll 62. However, if the heat capacity of the cooling belt 121 and the heat capacity of the fixing belt 610 are approximately the same, the residual heat of the fixing belt 610 has a characteristic that it easily moves to the cooling belt 121. Therefore, by configuring the cooling belt 121 and the fixing belt 610 to have similar heat capacities, the fixing process for the toner is performed, and at the same time, the residual heat of the fixing belt 610 is easily transferred to the cooling belt 121 at the nip portion N. be able to. And it can comprise so that it may be cooled in the 4th cooling member 120 (specifically, the fan 123 and the tension roll 122). For this reason, since the residual heat of the fixing belt 610 can be absorbed by the cooling belt 121 before it is transferred to the pressure roll 62, an excessive temperature rise of the pressure roll 62 can be effectively suppressed.

Thus, also in the present embodiment, the heat of the pressure roll 62 is cooled by the cooling belt 121 and the stretching roll 122 that constitute the fourth cooling member 120. Accordingly, as in the first embodiment, the temperature of the pressure roll 62 is maintained in the temperature range of 70 to 160 ° C., more preferably 90 to 140 ° C. when the fixing belt 610 is set to 210 ° C. Can be controlled.
In particular, in the fixing device 300 of the present embodiment, the cooling belt 121 is cooled before the residual heat that has not been subjected to the fixing process of the fixing belt 610 is transferred to the pressure roll 62 in the lap region with the pressure roll 62. Since heat can be absorbed by the belt 121, higher cooling performance can be exhibited.
Therefore, even when the operation time is long for a high-speed image forming apparatus, an excessive temperature rise of the pressure roll 62 can be suppressed. Thereby, it is possible to suppress the occurrence of paper blisters. Further, it is possible to suppress the occurrence of wrinkles, cracks, and damage on the surface of the pressure roll 62.

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. 2 is a side cross-sectional view illustrating a schematic configuration of a fixing device according to Embodiment 1. FIG. It is a schematic sectional drawing showing the vicinity area | region of a nip part. It is the figure which showed the outline of the nip pressure distribution of a nip part when a peeling pad is spaced apart and arrange | positioned more than predetermined distance from a roll nip part. It is the figure which showed the outline of nip pressure distribution at the time of arrange | positioning a peeling pad in the downstream vicinity of a roll nip part. It is a schematic sectional drawing showing the periphery of the area | region where the peeling pad is arrange | positioned. It is a schematic sectional drawing showing the periphery of the area | region where the peeling pad is arrange | positioned. FIG. 4 is a side sectional view showing a schematic configuration of a fixing device according to a second embodiment. FIG. 6 is a side sectional view showing a schematic configuration of a fixing device according to a third 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 part, 60, 200, 300 ... fixing device, 61 ... fixing belt module, 62 ... pressure roll, 64 ... peeling pad, 610 ... fixing belt, 611 ... fixing roll, 616a, 616b, 616c ... Halogen heater, 112, 113, 122, 612, 613, 615 ... tension roll, 90 ... first cooling member, 91, 92 ... endothermic roll, 93, 102, 114, 116, 117, 118, 123, 125 ... fan 94, 101, 115, 124 ... duct, 100 ... second cooling member, 110 ... third cooling member, 111, 121 ... cooling belt, 120 ... fourth cooling member

Claims (14)

A fixing device for fixing a toner image carried on a recording material,
A fixing roll;
A belt member stretched around the fixing roll;
A heating roll that heats the belt member and stretches the belt member;
A pressure member that is arranged to press the fixing roll and forms a nip portion through which the recording material passes between the belt member and the belt member stretched around the fixing roll;
The pressure contact portion between the fixing roll and the pressure member is disposed near the downstream side of the pressure contact portion between the fixing roll and the pressure member so as to press the outer surface of the belt member against the pressure member. A peeling member that sets the nip pressure in the region from the most downstream part to the most downstream part of the pressure contact part between the pressure member and itself so as to monotonously decrease toward the traveling direction of the belt member ;
A fixing device comprising: a cooling member that cools the pressure member.   The fixing device according to claim 1, wherein the cooling member is disposed downstream of the nip portion.   The fixing device according to claim 1, wherein the cooling member includes a heat-absorbing roll member having high thermal conductivity that abuts the surface of the pressure member along the axial direction.   The fixing device according to claim 3, wherein the heat absorbing roll member of the cooling member is a Peltier element.   The fixing device according to claim 1, wherein the cooling member is disposed such that a cooling belt member stretched around a roll member contacts the pressure member.   The fixing device according to claim 1, wherein the cooling member is configured to cool an inside of the pressure member.   The fixing device according to claim 1, wherein the cooling member includes a cooling belt member stretched so as to wrap the surface of the pressure member.   The fixing device according to claim 1, wherein the pressing member has a dent amount larger than a dent amount of the fixing roll at a pressure contact portion between the fixing roll and the pressure member. A fixing device for fixing a toner image carried on a recording material,
A fixing roll formed of a rigid body with a heat source;
A belt member stretched around the fixing roll;
A heating roll that heats the belt member and stretches the belt member;
A pressure member arranged to press the fixing roll and covered with an elastic layer;
A peeling member arranged to press the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member ;
A cooling member for cooling the pressure member ,
The pressure member is controlled within a predetermined range in which the temperature is lower than the temperature of the fixing roll by the cooling member, and the pressure member and the pressure member from the most downstream portion of the pressure contact portion between the fixing roll and the pressure member. A fixing device , wherein a nip pressure in a region reaching a most downstream portion of a pressure contact portion with a peeling member is set so as to monotonously decrease toward a traveling direction of the belt member .   The fixing device according to claim 9, wherein the fixing roll is heated to a temperature lower than a temperature of the belt member by the heat generation source.   The fixing device according to claim 9, wherein the peeling member is formed of a block member having a substantially arc-shaped cross section.   The fixing device according to claim 9, wherein the peeling member is formed in a shape in which a side surface located on the side opposite to the fixing roll side is changed so as to bend the traveling direction of the belt member.   The peeling member is disposed in a wedge-shaped region defined by the fixing roll and the pressure member at an upstream end of a surface that presses the pressure member via the belt member. The fixing device according to claim 9. 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 fixing roll formed of a rigid body;
A belt member stretched around the fixing roll;
A heating roll that heats the belt member and stretches the belt member;
A pressure member arranged to press the fixing roll and covered with an elastic layer;
A peeling member arranged to press the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member;
A cooling member for cooling the pressure member,
The pressure member is controlled within a predetermined range in which the temperature is lower than the temperature of the fixing roll by the cooling member, and the pressure member and the pressure member from the most downstream portion of the pressure contact portion between the fixing roll and the pressure member. An image forming apparatus , wherein a nip pressure in a region reaching a most downstream portion of a pressure contact portion with a peeling member is set so as to monotonously decrease toward a traveling direction of the belt member .

Images