JP2005140889A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device restraining occurrence of temperature droop phenomenon by coping with enhancement in speed in an image forming apparatus. <P>SOLUTION: A fixing belt 614 is stretched by a fixing roller 610 and a stretching roller 615. At the same time, a fixing belt 614 is constituted to be heated by the fixing roller 610 where a halogen heater 613 is arranged and the stretching roller 615 where a halogen heater 615 is arranged. Furthermore, a pressurization belt 620 abuts on the outer periphery surface of a fixing belt 614 and a nip part N is formed between the belt 620 and the fixing belt 614, in a region of the fixing roller 610 where the fixing belt 614 is wound around. Moreover, the fixing belt 614 is constituted to have higher heat conductivity than the pressurization belt 620. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

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

  In a fixing device used in such an image forming apparatus, as shown in FIG. 6, a heating source 113 is provided inside a cylindrical metal core 111, and a release layer 112 is formed on the outer peripheral surface of the metal core 111. The fixing roll 110 and the fixing roll 110 are pressed against each other, and a heat-resistant elastic layer 122 and a release layer 123 made of a heat-resistant resin film or a heat-resistant rubber film are formed on the outer peripheral surface of the core metal 121. It is comprised with the pressure roll 120. Then, the recording paper carrying the unfixed toner image is passed between the fixing roll 110 and the pressure roll 120, and the unfixed toner image is heated and pressed to thereby apply the toner to the recording paper. The image is fixed. Such a fixing device is called a heating roll method and is generally widely used.

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

  Therefore, in order to solve these problems and realize a fixing device corresponding to the speedup of the image forming apparatus, the applicant of the present invention has a tension roll formed by a fixing roll whose surface is covered with an elastic body and a plurality of support rolls. The endless belt is wound around the fixing roll by a predetermined angle so as to form a nip area between the endless belt and the fixing roll, and at the exit of the nip area from other parts of the nip area. Has also proposed a technique related to a fixing device configured to generate a strain on an elastic body on the surface of a fixing roll by applying a large pressure locally (see, for example, Patent Document 1).

  Furthermore, the present applicant has a rotatable fixing roll whose surface is elastically deformed, an endless belt that can run while being in contact with the fixing roll, and a pressure pad that is arranged in a non-rotating state inside the endless belt. The endless belt is pressed against the fixing roll so that a contact surface with the fixing roll is formed by the pressure pad, and a belt nip is provided so that the sheet can pass between the endless belt and the fixing roll. At the same time, a technique related to a fixing device configured to locally elastically deform the exit side of the sheet on the surface of the fixing roll is proposed (for example, see Patent Document 2).

In the technique described in Patent Document 1, an endless belt stretched by a plurality of rolls is contacted to form a belt nip. In the technique described in Patent Document 2, a belt nip is formed by pressing an endless belt against a fixing roll using a pressure pad. By adopting such a configuration, the width of the belt nip formed by the fixing roll and the endless belt can be easily made larger than the width of the roll nip between the conventional fixing roll and the pressure roll. It is easy to reduce the size of the apparatus.
In particular, since the heat capacity of the endless belt brought into pressure contact with the fixing roll is small, the heat transmitted from the fixing roll is also difficult to dissipate. Therefore, even when the rotation of the fixing roll is started, the amount of heat taken from the fixing roll to the endless belt side is relatively small, and the efficiency of using the heat for melting the toner is increased. Has the advantage of being able to

Japanese Patent No. 3084692 (pages 5-8) Japanese Patent No. 3298354 (pages 4-7)

However, in the fixing devices described in Patent Document 1 and Patent Document 2 (collectively referred to as “belt nip method”), a wide nip can be formed, but the image forming apparatus can be further increased in speed. Therefore, when a fixing process is performed on a large number of recording sheets fed continuously in a short time, the so-called “temperature droop” phenomenon in which the surface temperature of the fixing roll temporarily decreases is unavoidable. It becomes. In particular, the temperature droop becomes large in thick paper having a large heat capacity. When such a temperature droop phenomenon occurs, a fixing failure may occur in a certain number of recording sheets until the surface temperature of the fixing roll recovers.
By the way, this temperature droop phenomenon is caused even when a sufficient amount of heat is supplied from the inside of the fixing roll by the elastic layer made of silicone rubber or the like coated on the core metal of the fixing roll acting as a thermal resistor. This is because heat is not quickly transferred to the surface of the fixing roll. Therefore, although a wide nip can be formed with the belt nip type fixing device, there is a situation in which a sufficient amount of heat cannot be temporarily supplied to the recording paper in order to further increase the speed. In some cases, the merits of the belt nip method cannot be fully utilized.

  For this temperature droop phenomenon, a method may be considered in which an external heating roll is placed in contact with the fixing roll and heat is supplied to the surface of the fixing roll from the outside. Therefore, it is difficult to sufficiently transmit the heat energy from the external heating roll to the fixing roll, and it is difficult to obtain a satisfactory effect. Further, the amount of heat released from the external heating roll to the external environment is large, and it cannot be said to be an appropriate method from the viewpoint of energy use efficiency.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to suppress the occurrence of the temperature droop phenomenon corresponding to the speeding up of the image forming apparatus. It is an object of the present invention to provide a fixing device capable of achieving the above.

For this purpose, the fixing device of the present invention is configured such that the fixing belt is stretched by the fixing roll and the stretching member, and the fixing belt is heated by the heating member. In the region where the belt is wound, the pressure belt is in contact with the outer peripheral surface of the fixing belt and forms a nip portion with the fixing belt. Furthermore, the fixing belt has a higher thermal conductivity than the pressure belt.
Here, the fixing belt may be characterized in that the heat conductivity in the thickness direction is higher than that of the pressure belt. Further, the heating member can be disposed inside the tension member. Further, the heating member can be configured to heat the fixing belt by electromagnetic induction.
In addition, a nip portion formed between the fixing belt and the pressure belt may further include a pressing member that presses the pressure belt toward the fixing roll.

In addition, the fixing device of the present invention has a first belt member that is rotatable, a heating member that heats the first belt member, and a thickness that is larger than the first belt member. A second belt member having low thermal conductivity in the direction.
Here, a pressing member that presses the contact portion between the first belt member and the second belt member may be further provided. Moreover, the 1st belt member can take the structure stretched by the heating member. Furthermore, the second belt member can be stretched around a plurality of rolls. In particular, the second belt member may be configured to be stretched by at least one roll formed with a heat insulating layer. Here, the base material of the belt itself may have the performance, and in the case of a multilayer structure, the heat insulating layer may be formed in any layer.

  Furthermore, the fixing device of the present invention is stretched between a fixing roll having a heating source, at least one tension roll, a fixing roll and a tension roll, and has a high heat transmission rate in the thickness direction. A rotatable fixing belt, a heating member that heats the fixing belt, and an abutment surface of the fixing belt in a region around which the fixing belt is wound to form a nip portion between the fixing belt and the fixing belt; A pressure belt having a low heat transfer rate in the thickness direction, and a pressing member that presses the pressure belt toward the fixing roll at a nip formed between the fixing belt and the pressure belt. Yes.

Here, it is preferable that the heat passage rate in the thickness direction of the fixing belt is set to 700 to 25000 (W / m ² · k). Moreover, it is preferable to set the heat passage rate with respect to the thickness direction of the pressure belt to 5000 (W / m ² · k) or less. Further, the fixing belt can include a metal layer. In particular, the fixing belt preferably includes a metal layer made of stainless steel. On the other hand, the pressure belt can be configured to include a resin layer.
In addition, the fixing belt and / or the pressure belt can include an elastic layer.
Further, the fixing roll may be configured to have a region where the fixing belt of the fixing roll is wound, and a region where the pressure belt does not contact the upstream side of the nip portion in the rotation direction of the fixing roll. . The fixing roll may be made of a metal.

Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording material. Fixing means for fixing the toner image transferred onto the recording material to the recording material. The fixing means includes a fixing roll, a fixing belt stretched over the fixing roll, and a tension for stretching the fixing belt. A bridge member, a heating member that heats the fixing belt, and a pressure belt that contacts the outer peripheral surface of the fixing belt in a region where the fixing belt of the fixing roll is wound and forms a nip portion with the fixing belt; The fixing belt is characterized in that it has a higher thermal conductivity than the pressure belt.
Here, the fixing unit may further include a pressing member that presses the pressure belt toward the fixing roll at a nip portion formed between the fixing belt and the pressure belt.

  As an effect of the present invention, it is possible to suppress the occurrence of the temperature droop phenomenon in the fixing device corresponding to the speeding up of the image forming apparatus.

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

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

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

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

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

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

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

  Further, in the image forming apparatus according to the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup 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 an image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After being applied, the image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In IPS, the input reflectance data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. Is done. The image data that has undergone image processing is converted into color material gradation data of four colors, Y, M, C, and K, and is output to the laser exposure unit 13.

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

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

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

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

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

Next, the fixing device 60 used in the image forming apparatus of the present embodiment will be described.
FIG. 2 is a side sectional view showing a configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing belt module 61 and a pressure belt module 62 that constitute a main part.
The fixing belt module 61 includes a fixing roll 610 that rotates in the direction of arrow A, a tension roll 615 as an example of a tension member in which a halogen heater 616 as a heating member is disposed, a fixing roll 610, and a tension roll 615. And a fixing belt (first belt member) 614 that is stretched around and rotated in the direction of arrow D.
The fixing roll 610 is a soft roll having an outer diameter of 65 mmφ and a length of 350 mm, which is formed by covering the surface of a cored bar 611 made of aluminum having a thickness of 5 mm with an elastic layer 612 having a thickness of 1.5 mm. . For the elastic layer 612, LSR (Liquid Silicone Rubber) having a hardness of 25 to 45 ° (JIS-A) is used. In addition, a halogen heater 613 rated at 1000 W is provided as a heating member inside the fixing roll 610. A temperature sensor 617a is disposed so as to contact the surface of the fixing roll 610, and the control unit 40 (see FIG. 1) of the image forming apparatus sets the surface temperature of the fixing roll 610 to 160 ° C. based on the measured value of the temperature sensor 617a. Is controlling. Further, the fixing roll 610 rotates in the arrow A direction at a surface speed of 400 mm / s.
The material of the elastic layer 612 is not limited to silicone rubber, and various conventionally known materials such as fluorine rubber can be used, and a plurality of laminated elastic layers made of silicone rubber and fluorine rubber can be used. 612 may be used. Further, when a so-called hard roll having no elastic layer 612 is used as the fixing roll 610, the heat supply from the fixing roll 610 to the fixing belt 614 is further improved, and the high-speed aptitude having a smaller temperature droop is excellent. A fixing device 60 is obtained.

The fixing belt 614 is stretched by a fixing roll 610 and a tension roll 615 with a tension of 10 kg. The fixing belt 614 is formed of a flexible endless belt having a circumferential length of 330 mm and a width of 340 mm.
In particular, the fixing belt 614 has a high thermal conductivity in the thickness direction. Specifically, the fixing belt 614 has a base layer made of stainless steel having a thickness of 50 μm, and a silicone rubber having a hardness of 20 ° (JIS-A) and a thickness of 200 μm is formed on the surface (outer peripheral surface side) of the base layer. And an endless belt having a multilayer structure in which a surface layer of tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA) having a thickness of 30 μm is further coated thereon as an elastic layer. As the base layer, stainless steel is excellent from the viewpoint of ease of manufacture, but metals and alloys such as aluminum, copper, and silver having high thermal conductivity, and carbon fibers can also be used. Further, as the release layer, a silicone rubber or fluororubber layer can be used, and the surface layer can be used in combination with a device that applies silicone oil or fluorine oil as a release agent.
Here, the elastic layer made of silicone rubber is provided particularly for improving the image quality of color images. Further, the configuration of the fixing belt 614 is not limited to the above-described one, and the conditions such as the material, the thickness, and the hardness are set so as to correspond to the use conditions and the like and to obtain sufficiently high thermal conductivity. It only has to be selected.

The tension roll 615 is made of a stainless steel pipe roll having an outer diameter of 23 mmφ, a wall thickness of 2 mm, and a length of 350 mm, and the outer surface thereof is coated with PFA having a thickness of 20 μm as a release layer. This release layer has a function of preventing a slight amount of offset toner and paper powder from the surface of the fixing belt 614 from being accumulated.
Inside the tension roll 615, a halogen heater 616 rated at 800 W is disposed as a heating member. The surface temperature of the tension roll 615 is set to 200 ° C. by the temperature sensor 617b and the control unit 40 (see FIG. 1). It is controlled. Therefore, the tension roll 615 has both a function of stretching the fixing belt 614 and a function of heating the fixing belt 614.
Further, for the purpose of making the displacement of the fixing belt 614 in the rotation axis direction (direction perpendicular to the moving direction) as small as possible and making the tension of the fixing belt 614 uniform, the tension roll 615 has an outer diameter. Is formed in a so-called drum shape in which the central portion is larger than the end portion by 100 μm.
The tension roll 615 includes a belt edge position detection mechanism of the fixing belt 614 and an axis displacement mechanism that displaces the contact position in the axial direction of the fixing belt 614 according to the detection result of the belt edge position detection mechanism. It is also possible to configure such that the meandering of the fixing belt 614 is controlled.

On the other hand, the pressure belt module 62 includes a pressure belt (second belt member) 620 stretched by three rolls of a lead roll 621, a pressure roll 622, and a tension roll 623, and a pressure belt 620. The main part is constituted by a pressure pad (pressing member) 63 pressed against the fixing roll 610. The pressure belt 620 rotates in the direction of arrow B following the fixing roll 610 as the fixing roll 610 of the fixing belt module 61 rotates in the direction of arrow A. The traveling speed is 400 mm / s which is the same as the surface speed of the fixing roll 610.
The pressure belt 620 is in contact with the outer peripheral surface of the fixing belt 614 to form a nip portion N in a region where the fixing belt 614 is wound (wrapped) around the fixing roll 610. Further, in this nip portion N, a pressure pad (pressing member) 63 is disposed inside the pressure belt 620 in a state of being urged toward the fixing roll 610 via the pressure belt 620. Therefore, when the paper P carrying the toner image passes through the nip portion N, the paper P is heated and pressurized in the nip portion N, and the toner image is fixed on the paper P.
In the fixing device 60 of the present embodiment, the nip portion N is formed as a band-like region extending over 45 ° as the central angle with respect to the rotation axis of the fixing roll 610 (hereinafter, this central angle is referred to as “wrapping angle”). ing. In this case, the nip width is 26 mm.

Further, the pressure belt 620 is configured to have low thermal conductivity in the thickness direction. The pressure belt 620 includes a base layer and a release layer coated on the surface thereof (the surface on the fixing roll 610 side or both surfaces). The base layer has a low thermal conductivity and a heat resistance strength. For example, polyimide, polyamide, polyamideimide and the like are suitable. The thickness of the base layer is, for example, 50 to 125 μm, and it is sufficient that the conditions such as the material and the thickness are selected so as to correspond to the use conditions and the like and to obtain sufficiently low thermal conductivity. As the release layer formed on the surface of the base layer, a layer in which a fluororesin such as PFA is coated with a thickness of 5 to 20 μm is preferable. Furthermore, the structure which laminated | stacked the elastic layer on the base layer and formed the heat insulation layer can also be taken.
In the fixing device 60 of the present embodiment, as the pressure belt 620, a base layer of a polyimide film having a thickness of 75 μm, a width of 300 mm, and a circumferential length of 288 mm, an elastic layer made of silicone rubber having a thickness of 200 μm, and further thereon Further, a multilayer structure in which a surface layer of PFA having a thickness of 30 μm is coated is formed.

The pressure belt 620 is stretched with a tension of 10 kg by three rolls, that is, a lead roll 621, a pressure roll 622, and a tension roll 623. Each roll has a diameter of 22 mm, 20 mm, and 20 mm, and is configured by covering a stainless steel core metal with a PFA resin tube as a heat insulating layer to suppress the outflow of heat from the pressure belt 620 to each roll. Yes. In addition, a halogen heater 625 for raising the pressure belt 620 to a predetermined temperature in advance is disposed inside the lead roll 621.
Further, any one of the lead roll 621, the pressure roll 622, and the tension roll 623 is pressurized according to the detection result of the belt edge position detection mechanism of the pressure belt 620 and the belt edge position detection mechanism. An axial displacement mechanism for displacing the contact position of the belt 620 in the axial direction may be provided to control the meandering of the pressure belt 620.

Next, the pressure pad 63 as a pressing member includes an elastic member for securing a wide nip portion N, and a low friction provided on the surface where the elastic member contacts the inner peripheral surface of the pressure belt 620. And is held by a holder made of metal or the like. The elastic member having the low friction layer on the surface is formed in a concave shape in which the fixing roll 610 side substantially follows the outer peripheral surface of the fixing roll 610, and is pressed against the fixing roll 610.
As the elastic member, an elastic body having high heat resistance such as silicone rubber or fluorine rubber, a leaf spring, or the like can be used. The low friction layer formed on the elastic member is provided to reduce the sliding resistance between the inner peripheral surface of the pressure belt 620 and the pressure pad 63, and is a material having a low friction coefficient and wear resistance. It is desirable. Specifically, a glass fiber sheet impregnated with Teflon (trade name), a fluororesin sheet, a fluororesin coating film, or the like can be used.
The pressure pad 63 may be, for example, a roll-shaped one in addition to the pad-shaped one as in the present embodiment, and may be a fixing roll 610 via a pressure belt 620. The surface may be urged and driven to rotate. However, the pressure pad 63 molded in the shape of a pad as in the present embodiment can apply a nip pressure more widely and uniformly over the entire nip portion N in contact.

A pressure roll 622 disposed downstream of the pressure pad 63 in the paper P conveyance direction (arrow C direction) is provided with a pressure belt 620 and a fixing belt by a compression coil spring (not shown) as pressure means. It is biased toward the central axis of the fixing roll 610 via 614, and a certain amount of distortion is generated at the contact portion between the fixing roll 610 and the fixing belt 614. That is, the elastic layer 612 and the fixing belt 614 on the surface of the fixing roll 610 are elastically deformed and distorted. At the exit of the nip portion N, the sheet P is fixed by the distortion of the fixing roll 610 and the fixing belt 614. And peeled from the fixing belt 614 side.
In order to efficiently apply distortion of the fixing roll 610 and the fixing belt 614 with a low load, it is desirable that the pressure roll 622 has a smaller diameter than the fixing roll 610 and the surface thereof is hard.

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 ( It is conveyed (in the direction of arrow C). The unfixed toner image on the surface of the paper P passing through the nip portion N is fixed on the paper P by pressure and heat acting on the nip portion N. In the fixing device 60 of the present embodiment, as described above, the nip portion N can be set wide by the configuration in which the fixing roll 610 wrapped with the fixing belt 614 and the pressure belt 620 are brought into contact with each other. Stable fixing performance can be ensured.
At this time, heat acting on the nip portion N is mainly supplied by the fixing belt 614. The fixing belt 614 is supplied from the halogen heater 613 disposed inside the fixing roll 610 through the fixing roll 610 and from the halogen heater 616 disposed inside the stretching roll 615 through the stretching roll 615. It is configured to be heated by heat. Therefore, even when the heat energy is insufficient with only the fixing roll 610, the heat energy can be replenished appropriately and quickly from the stretching roll 615. Therefore, in the nip portion N, the process speed is 400 mm / s. A sufficient amount of heat can be secured even at high speeds.

  Note that the paper P that has passed through the nip N is removed from the fixing belt 614 due to distortion of the fixing roll 610 and the fixing belt 614 that are formed when the pressure roll 622 is pressed against the fixing roll 610 at the exit of the nip N. It is peeled off. Then, the sheet is separated by a peeling guide plate 626 disposed in the nip portion N downstream of the fixing roll 610 in the rotation direction A and in the vicinity of the surface of the fixing roll 610. The separated paper P is guided by a discharge guide 628, conveyed by a discharge roll 629 to a paper discharge placement portion (not shown) provided in a discharge portion of the image forming apparatus, and placed.

Here, heat transfer to the paper P through the fixing belt 614 will be described in detail.
When the process speed is as high as 400 mm / s as in the image forming apparatus of the present embodiment, when continuous fixing is performed in which the paper P is successively conveyed to the nip portion N of the fixing device 60, The sheet P and the unfixed toner image are deprived of heat, and the amount of heat released from the pressure belt module 62 is also increased. Therefore, if the pressure belt 620 is simply wound around the fixing roll 610, the fixing roll 610 is used. The surface temperature of the glass tends to decrease. Further, when only the heat energy is supplied from the inside of the fixing roll 610 by the halogen heater 613, the fixing roll 610 itself has a thickness, so that a time lag is caused until the heat reaches the surface.
In order to keep the surface temperature of the fixing roll 610 at a necessary temperature, it is necessary to heat from the inside at an extremely high temperature if only the configuration of the fixing roll 610 is used. In such a method, energy loss is large and the load on the apparatus itself is also large. Further, since the surface temperature becomes higher than necessary after the end of continuous fixing, the surface of the fixing roll 610 is damaged, and there is a concern that a fixing failure may occur in the next image forming cycle.
As a countermeasure, a method of arranging an external heating device such as an external heating roll so as to directly contact the surface of the fixing roll 610 and auxiliary heating the surface of the fixing roll 610 from the outside can be considered. Since it is difficult to set a large contact width with the surface of the fixing roll 610, it is difficult to supply a sufficient amount of heat to the surface of the fixing roll 610 after all.

On the other hand, in the fixing device 60 according to the present embodiment, a tension roll 615 having a halogen heater 616 disposed therein is arranged in parallel with the fixing roll 610 with respect to a general belt nip type fixing device. In addition, an endless fixing belt 614 is stretched between a tension roll 615 and a fixing roll 610. In such a configuration, the fixing belt 614 functions as a direct heating member that heats the paper P, and both the fixing roll 610 and the stretching roll 615 function as a heat supply source that supplies heat to the fixing belt 614. Yes. However, since the fixing roll 610 is in contact with the paper P via the fixing belt 614, a part of the fixing roll 610 also has a function of directly heating the paper P.
In the fixing belt 614, as described above, the fixing belt 614 is configured to have high thermal conductivity in the thickness direction. With this configuration, the fixing belt 614 can efficiently receive heat from the fixing roll 610 and the stretching roll 615 and can efficiently transfer heat to the paper P in the nip portion N. it can. Furthermore, the flow rate of heat supplied from the fixing roll 610 directly to the paper P via the fixing belt 614 can be increased.
On the other hand, the pressure belt 620 is configured to have low thermal conductivity in the thickness direction. With this configuration, the pressure belt 620 does not easily take heat from the paper P, and even if heat once flows into the pressure belt 620, it is difficult for the heat to flow out. Therefore, it is possible to improve the heat utilization efficiency.

Here, the thermal conductivities of the fixing belt 614 and the pressure belt 620 can be grasped as heat passing rates. The heat transfer rate K (W / m ² · k) is Q when the amount of heat flowing is Q and the temperature gradient is ΔT,
Q = KΔT
Where the layer thickness in the direction of heat flow is δ _i (m), and the thermal conductivity of the layer is λ _i (W / m · k),
K = 1 / Σ (δ _i / λ _i )
It is expressed.
In the fixing belt 614, it is preferable to set the heat transmission rate K to 700 to 25000 (W / m ² · k). If the heat transfer rate K of the fixing belt 614 is smaller than 700 (W / m ² · k), it is not sufficient to realize the ease of heat flow to the extent that temperature droop described below is suppressed.
On the other hand, it is generally effective that the heat transfer rate K of the fixing belt 614 is as large as possible to suppress temperature droop. In order to increase the heat transfer rate K, the fixing belt 614 may be formed in a thin layer. Necessary. On the other hand, the mechanical strength of the fixing belt 614 needs to be maintained at a certain level or more, and for this purpose, the layer thickness needs to be set to a predetermined thickness or more. Therefore, as a configuration in which the heat transmission rate K is set as large as possible and the mechanical strength of the limit capable of realizing the function as the fixing belt 614 can be secured, the heat transmission rate K is 25000 (W / m ² · k) or less. It is preferable to do this.

Further, in the pressure belt 620, it is preferable to set the heat passage rate K to 5000 (W / m ² · k) or less. If the heat transfer rate K of the pressure belt 620 is greater than 5000 (W / m ² · k), the heat outflow from the paper P becomes large at the nip portion N, and temperature droop is likely to occur. Further, heat loss to the member in contact with the pressure belt 620 is also generated, and the amount of heat released from the pressure belt module 62 is increased, which is not preferable.
On the other hand, the heat transfer rate K of the pressure belt 620 is desirably as low as possible. However, the pressure belt 620 needs to select a material due to structural restrictions such as ensuring flexibility. Therefore, the lower limit value of the heat transfer rate K of the pressure belt 620 is determined from this configuration.

  In such a configuration, the fixing belt 614 that is a direct heating member has an extremely small heat capacity as compared with the fixing roll 610 that is a heating member. In the case where only the fixing roll 610 is used as a heating member as in a conventional belt nip type fixing device, the surface layer of the fixing roll 610 passes through a region where it contacts the paper P and then again. Since it was necessary to return the fixing roll 610 having a large heat capacity to a predetermined fixing temperature during one rotation until returning to the area in contact with the sheet P, when the speed of the image forming apparatus is increased, the predetermined roll temperature is increased. In some cases, the return to the fixing temperature may not be in time for one rotation of the fixing roll 610. However, the fixing belt 614 has an extremely small heat capacity. In addition, both the fixing roll 610 and the tension roll 615 that are heat supply sources can be in contact with each other with a wide wrap area (a large winding angle). Since the heat conductivity in the thickness direction is high, the fixing belt 614 can be returned to a necessary fixing temperature while the fixing belt 614 rotates once.

As described above, in the fixing device 60 of the present embodiment, the fixing belt 614 having an extremely small heat capacity is in contact with both the fixing roll 610 and the tension roll 615 that are heat supply sources with a wide wrap area (large winding angle). Furthermore, since the heat conductivity in the thickness direction of the fixing belt 614 is high, heat transfer from the fixing roll 610 and the stretching roll 615 to the fixing belt 614 is performed quickly and sufficiently. Thus, the fixing belt 614 can be returned to the necessary fixing temperature in a short time during which the fixing belt 614 rotates once. Further, since the heat conductivity in the thickness direction of the pressure belt 620 is low, the flow rate of heat from the paper P to the pressure belt 620 becomes extremely small. Therefore, at the nip portion N, a predetermined fixing temperature can always be maintained even if the speed of the fixing device 60 is increased.
As a result, it is possible to suppress the occurrence of temperature droop (a phenomenon in which the surface temperature of the fixing roll temporarily decreases), which is a major problem during high-speed fixing. In particular, the occurrence of temperature droop can be suppressed even when fixing thick paper having a large heat capacity. Also, when it is necessary to switch the fixing temperature in the middle of the paper type (including both fixing temperature up and down), the fixing belt 614 has a small heat capacity, and the fixing belt 614 has a thickness direction. Since the thermal conductivity is high, switching to a desired temperature is easy and can be performed quickly by adjusting the outputs of the halogen heater 613 and the halogen heater 616.

  Further, since the heat conductivity in the thickness direction of the fixing belt 614 is high in the nip portion N, it is possible to efficiently supply heat from the fixing belt 614 to the paper P. Further, since the heat conductivity in the thickness direction of the pressure belt 620 is low, the flow rate of heat from the paper P to the pressure belt 620 becomes extremely small, and heat once flows into the pressure belt 620. However, since this heat hardly flows out to the outside, the heat radiation amount from the pressure belt module 62 can be kept low. Therefore, even if the fixing device 60 is speeded up, in the nip portion N, it is possible to simultaneously supply heat to the paper P and suppress leakage of heat from the paper P at the same time. Fixing performance can be realized.

In addition, in the fixing device 60 of the present embodiment, the outer periphery of the fixing belt 614 is only in the region where the pressure belt 620 of the pressure belt module 62 is wound around the surface of the fixing roll 610. The nip portion N is formed so as to be in contact with the surface. That is, in the nip portion N, the fixing roll 610 is located over the entire area on the inner peripheral surface side of the fixing belt 614. Accordingly, the contact between the fixing belt 614 and the pressure belt 620 is formed so as to be stably supported by the surface of the fixing roll 610, so that the contact can be made uniformly in the entire nip portion N. Due to the good adhesion between the fixing belt 614 and the pressure belt 620, heat conduction from the fixing belt 614 to the paper P can be performed more efficiently, and the occurrence of temperature droop is more effectively suppressed. be able to.
Further, due to the configuration of the nip portion N, an area where the fixing belt 614 contacts only the fixing roll 610 is formed upstream of the fixing belt 614 on the inlet side of the nip portion N. Therefore, when the fixing belt 614 passes through this region, wrinkles generated in the fixing belt 614 during rotation are corrected. Accordingly, since the nip portion N can be brought into contact with the unfixed toner image on the paper P in a smooth state, a high-quality fixed image can be obtained.

  Further, in the nip portion N, water in the paper P and the unfixed toner image is rapidly heated to become water vapor. Therefore, when the nip pressure is low such that only the belts are in contact with each other and the contact is not uniform, the water vapor pressure cannot be suppressed, and the heated and melted unfixed toner image is disturbed by the water vapor, causing image defects ( Image disturbance). On the other hand, in the fixing device 60 of the present embodiment, the fixing belt 614 and the pressure belt 620 are in close contact with the fixing roll 610 and the pressure pad 63 in the entire nip portion N. Therefore, since the water vapor pressure can be suppressed, the occurrence of image defects can be suppressed.

Here, the surface of the fixing belt 614 when the sheet P on which the unfixed toner image is formed is continuously fixed using the fixing device 60 of the present embodiment and the conventional belt nip type fixing device. An experiment was conducted to compare the temperature and the transition of the surface temperature of the fixing roll 610. FIG. 3 is a diagram showing the results.
In this experiment, as the fixing roll 610, an outer diameter formed by covering the surface of a cored bar 611 made of aluminum having a thickness of 5 mm with an elastic layer 612 made of LSR having a thickness of 1.5 mm. Using a soft roll of 65 mmφ and 350 mm in length, as the fixing belt 614, the base layer is made of a 50 μm-thick stainless steel, a 200 μm-thick silicone rubber elastic layer, and a 30 μm-thick PFA release layer in multiple layers A flexible endless belt having a circumferential length of 330 mm and a width of 340 mm and having a heat transmission rate of 1800 (W / m ² · k) is used. Further, as the pressure belt 620, a base layer of a polyimide film having a thickness of 75 μm, a width of 300 mm, and a peripheral length of 288 mm, an elastic layer made of 200 μm thick silicone rubber, and a surface layer of PFA having a thickness of 30 μm are multilayered. What is comprised and the heat passage rate is 1230 (W / m < ² > * k) is used. The process speed was set to 400 mm / s.
As a conventional belt nip type fixing device for comparison, a heating source is arranged so as to be in direct contact with the halogen heater in the fixing roll and the outer peripheral surface of the fixing roll, and from the outer surface to the fixing roll. The one provided with an external heating roll for auxiliary heating was used. Various conditions of the apparatus and paper are the same as those of the fixing apparatus 60 of the present embodiment except for the configuration in which the fixing belt 614 is provided.

  As shown in FIG. 3, in the conventional belt nip type fixing device, even if auxiliary heating is performed by an external heating roll, the surface temperature of the fixing roll decreases with the lapse of printing time from the start of printing, and the set fixing is performed. It was confirmed that a temperature droop phenomenon that decreases by 10 to 15 ° C. from the temperature (190 ° C.) occurred. Here, the temperature droop phenomenon in which the temperature once drops during continuous printing and then recovers, the elastic layer coated on the fixing roll acts as a thermal resistance, so that heat is deprived to the paper P at the beginning of printing. This is a phenomenon that occurs because the supply of heat from the halogen heater disposed inside is not in time. Further, at the beginning of printing, various rolls disposed in the pressure belt module 62 become a heat load, and taking a lot of heat from the fixing roll is also a factor for increasing the temperature droop. As the printing is continued thereafter, the heat from the halogen heater is sufficiently supplied to the entire fixing roll, so that the surface temperature is recovered and the temperature droop is eliminated.

In contrast to the conventional belt nip type fixing device, in the fixing device 60 of the present embodiment, the surface temperature of the fixing belt 614 does not significantly decrease even when the printing time has elapsed from the start of printing, and the temperature droop phenomenon occurs. Was minor. Also, no influence on the fixing performance of the fixing device 60 immediately after the start of printing was observed. This is because the fixing belt 614 of the fixing device 60 has an extremely small heat capacity, and both the fixing roll 610 and the tension roll 615 that are heat supply sources can be in contact with each other with a wide lap area, and the thickness of the fixing belt 614 is further reduced. Since the heat conductivity in the direction is high, sufficient heat can be supplied during one rotation of the fixing belt 614, and further, the heat conductivity in the thickness direction of the pressure belt 620 is low. Therefore, the flow rate of heat from the paper P to the pressure belt 620 is extremely small.
As described above, it was confirmed from the results shown in FIG. 3 that the temperature droop can be greatly improved even in the high-speed fixing according to the fixing device 60 of the present embodiment.

As described above, in the fixing device 60 of the present embodiment, the tension roll 615 in which the halogen heater 616 that is a heating member is disposed is disposed in parallel with the fixing roll 610. A configuration in which the fixing roll 610 is stretched by an endless fixing belt 614 is employed. The fixing belt 614 functions as a main heating member for heating the paper P, and both the fixing roll 610 and the stretching roll 615 function as a heat supply source for supplying heat to the fixing belt 614. Therefore, the fixing belt 614 can be configured with an extremely small heat capacity, and both the fixing roll 610 and the stretching roll 615 that are heat supply sources can be in contact with each other with a wide lap area. Furthermore, by setting the heat conductivity in the thickness direction of the fixing belt 614 high, the fixing belt 614 can efficiently receive heat from the fixing roll 610 and the stretching roll 615. Furthermore, by setting the thermal conductivity in the thickness direction of the pressure belt 620 to be low, the pressure belt 620 hardly takes heat from the paper P. As a result, in the nip portion N, even if the fixing device 60 is speeded up, a predetermined fixing temperature can be always maintained, so that the occurrence of temperature droop can be suppressed.
In addition, since the pressure belt 620 is configured to contact the outer peripheral surface of the fixing belt 614 only in the region where the fixing belt 614 is wound around the surface of the fixing roll 610, the nip portion N is formed. A good adhesion state between the fixing belt 614 and the pressure belt 620 can be formed. Therefore, heat conduction from the fixing belt 614 to the paper P can be performed more efficiently, and the occurrence of temperature droop can be more effectively suppressed.

[Embodiment 2]
In the first embodiment, a tension roll 615 in which a halogen heater 616 that is a heating member is disposed in parallel with the fixing roll 610, and the tension roll 615 and the fixing roll 610 are connected to an endless fixing belt. The image forming apparatus in which the fixing device 60 configured to be stretched at 614 is mounted has been described. The second embodiment is a fixing device mounted on the image forming apparatus shown in FIG. 1, in which two tension rolls 615 are arranged, and one newly arranged tension roll attaches the fixing belt 614 to the outer surface. Next, the fixing device 70 that comes into contact with the head will be described. In addition, about the structure similar to Embodiment 1, the same code | symbol is used and the detailed description is abbreviate | omitted here.

FIG. 4 is a side sectional view showing the configuration of the fixing device 70 according to the present embodiment. The fixing device 70 of the present exemplary embodiment is the same as the fixing device 60 of the first exemplary embodiment except that the fixing belt module 61 is different from the fixing roll 615 in that a stretching roll 618 is disposed. It is.
In the fixing device 70 of the present embodiment, the fixing belt module 61 includes a fixing roll 610 that rotates in the direction of arrow A, a tension roll 615 in which a halogen heater 616 serving as a heating member is disposed, and similarly heats inside. A tension roll 618 provided with a halogen heater 619 as a member, a fixing roll 610, a tension roll 615, and a fixing belt 614 that is stretched around the tension roll 618 and is driven to rotate in the direction of arrow D. .

  The fixing belt 614 is stretched between the fixing roll 610, the tension roll 615, and the tension roll 618 with a tension of 10 kg. Specifically, the fixing belt 614 in the first embodiment is stretched by the fixing roll 610 and the stretching roll 615, whereas in the fixing device 70 of the present embodiment, the stretching roll 618 is provided there. A predetermined wound region (in the present embodiment, a winding angle of 80 ° and a winding width of 16 mm) is formed by being biased from the outer peripheral surface of 614. Accordingly, the fixing roll 610 and the stretching roll 615 are in contact with the inner peripheral surface of the fixing belt 614, and the stretching roll 618 is in contact with the outer peripheral surface of the fixing belt 614 to stretch the fixing belt 614. In the present embodiment, the winding angle of the fixing belt 614 in the tension roll 615 is also larger than that in the first embodiment due to the urging of the tension roll 618 (in this embodiment, a specific example) (The winding angle is 230 ° and the winding width is 46 mm.)

The tension roll 618 has a stainless steel pipe roll having an outer diameter of 23 mm, a wall thickness of 2 mm, and a length of 350 mm as a base, and a release layer is formed by coating PFA with a thickness of 20 μm on the surface. This release layer is formed in order to prevent a slight amount of offset toner and paper powder from the outer peripheral surface of the fixing belt 614 from accumulating on the tension roll 618.
Inside the tension roll 618, a halogen heater 619 having a rating of 800 W is disposed as a heating member, and the surface temperature is controlled to 200 ° C. by the temperature sensor 617c and the control unit 40 (see FIG. 1). Therefore, the tension roll 618 has both a function of stretching the fixing belt 614 and a function of heating the fixing belt 614. Accordingly, since the halogen heater 616 as a heating member is also provided inside the tension roll 615, in this embodiment, the fixing belt 614 is auxiliary heated by both the tension roll 615 and the tension roll 618. It is the composition to do.
The tension roll 618 also has a function as a pressing roll that applies a load so that the entire fixing belt 614 has a tension of 10 kg.

  In the fixing device 70 of the present embodiment, the tension roll 615 that is in contact with the inner peripheral surface heats the fixing belt 614 from the inner peripheral surface side of the fixing belt 614 and is in contact with the outer peripheral surface. Reference numeral 618 heats the fixing belt 614 from the outer peripheral surface side of the fixing belt 614. As described above, according to the present embodiment, the fixing belt 614 is heated from both the outer peripheral surface and the inner peripheral surface, so that a larger amount of heat can be stably supplied.

As described above, also in the fixing device 70 of the present embodiment, the tension roll 615 in which the halogen heater 616 serving as the heating member is disposed in parallel with the fixing roll 610 and the halogen heater 619 serving as the heating member in the inside. A tension roll 618 provided with a tension roll 618 is disposed, and the tension roll 615, the tension roll 618, and the fixing roll 610 stretch the endless fixing belt 614. The fixing belt 614 functions as a main heating member that heats the paper P, and the fixing roll 610, the tension roll 615, and the tension roll 618 function as a heat supply source that supplies heat to the fixing belt 614. Yes. Therefore, the fixing belt 614 can be configured with an extremely small heat capacity, and the fixing roll 610, the tension roll 615, and the tension roll 618, which are heat supply sources, can be in contact with each other with a wide lap area. Further, by setting the heat conductivity in the thickness direction of the fixing belt 614 high, the fixing belt 614 can efficiently receive heat from the fixing roll 610, the tension roll 615, and the tension roll 618. Furthermore, by setting the thermal conductivity in the thickness direction of the pressure belt 620 to be low, the pressure belt 620 hardly takes heat from the paper P. Therefore, in the nip portion N, even if the fixing device 70 is speeded up, a predetermined fixing temperature can always be maintained, and the occurrence of temperature droop can be suppressed.
In addition, since the pressure belt 620 is configured to contact the outer peripheral surface of the fixing belt 614 only in the region where the fixing belt 614 is wound around the surface of the fixing roll 610, the nip portion N is formed. A good adhesion state between the fixing belt 614 and the pressure belt 620 can be formed. Therefore, heat conduction from the fixing belt 614 to the paper P can be performed more efficiently, and the occurrence of temperature droop can be more effectively suppressed.

In the fixing device 70 of the present embodiment, the tension roll 618 is disposed in contact with the outer peripheral surface of the fixing belt 614, and the fixing belt 614 is also heated from the outer peripheral surface side of the fixing belt 614 by the tension roll 618. However, the fixing belt 614 may be configured to be induction-heated by disposing an electromagnet as an AC magnetic field generating unit in the vicinity of the inner peripheral surface side or the outer peripheral surface side of the fixing belt 614. is there. In this configuration, a material in which a metal such as iron, cobalt, nickel, copper, and chromium is formed with a thickness of about 30 to 80 μm is used so that the base layer of the fixing belt 614 forms an electromagnetic induction heat generating layer.
Also with this configuration, the fixing belt 614 is heated from the inner peripheral surface by the tension roll 615 and is entirely heated by the electromagnet, so that a larger amount of heat can be supplied more stably. It becomes possible and generation | occurrence | production of temperature droop can be suppressed more effectively.
Further, the generation of temperature droop can also be improved by a configuration in which the halogen heater 616 is not disposed on the stretching roll 618 and only induction heating is performed by an electromagnet.

[Embodiment 3]
In the first embodiment, as the pressure belt module 62, a fixing device 60 having a configuration using a pressure belt 620 stretched by three rolls of a lead roll 621, a pressure roll 622, and a tension roll 623 is mounted. The image forming apparatus thus described has been described. In the second embodiment, the fixing device is mounted on the image forming apparatus shown in FIG. 1, and the pressure belt module 62 is connected to the fixing roll by a pressure pad arranged in a non-rotating state inside the endless belt. A fixing device 80 in which an endless belt is pressed against a fixing roll so that a contact surface is formed will be described. In addition, about the structure similar to Embodiment 1, the same code | symbol is used and the detailed description is abbreviate | omitted here.

FIG. 5 is a side sectional view showing the configuration of the fixing device 80 according to the present embodiment. The fixing device 80 according to the present embodiment has a configuration in which the endless belt 82 rotates in a free state without being stretched around a roll in the pressure belt module 62 (in particular, referred to as a free belt nip method). Except for this, it is the same as the fixing device 60 of the first embodiment.
The main part of the pressure belt module 62 includes an endless belt 82 and a pressure pad 84 pressed from the fixing roll 610 via the endless belt 82.
The endless belt 82 is rotatably supported by a pressure pad 84 and a belt traveling guide 83. In the nip portion N, it is placed in pressure contact with the fixing roll 610.
The pressure pad 84 is disposed inside the endless belt 82 so as to be pressed against the fixing roll 610 via the endless belt 82, and forms a nip portion N with the fixing roll 610. In the pressure pad 84, a pre-nip member 84a for securing a wide nip portion N is disposed on the inlet side of the nip portion N, and a peeling nip member 84b for distorting the fixing roll 610 is disposed on the outlet side of the nip portion N. Is arranged. Further, in order to reduce the sliding resistance between the inner peripheral surface of the endless belt 82 and the pressure pad 84, a low friction sheet 88 is provided on the surface of the pre-nip member 84a and the peeling nip member 84b in contact with the endless belt 82. The pressure pad 84 and the low friction sheet 88 are held by a metal holder 85.

  Further, a belt traveling guide 83 is attached to the holder 85 so that the endless belt 82 can smoothly rotate. That is, the belt running guide 83 is formed of a material having a small static friction coefficient in order to rub against the inner peripheral surface of the endless belt 82. Further, the belt traveling guide 83 is formed of a material having low thermal conductivity so that it is difficult to take heat away from the endless belt 82.

  The fixing roll 610 is rotated in the direction of arrow A by a drive motor (not shown), and the endless belt 82 is also rotated by this rotation. The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided by the fixing inlet guide 56 and conveyed to the nip N. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the fixing belt 614. In the fixing device 80 of the present embodiment, since the nip portion N can be widely configured by the concave pre-nip member 84a that substantially follows the outer peripheral surface of the fixing roll 610, stable fixing performance can be ensured.

  In addition, in the fixing device 80 according to the present embodiment, the separation nip member 84b is disposed so as to protrude from the outer peripheral surface of the fixation roll 610, so that the fixing roll 610 and The fixing belt 614 may be configured so that distortion is locally increased. If the separation nip member 84b is arranged in this manner, the sheet P after fixing passes through the locally formed distortion when passing through the separation nip portion. Therefore, the fixing roll 610 and the fixing belt are used. The sheet P that does not wind around the 614 can be effectively peeled off.

Next, each member constituting the pressure belt module 62 will be described in detail. The endless belt 82 is configured to have low thermal conductivity in the thickness direction. The endless belt 82 is composed of a base layer and a release layer coated on its surface (the surface on the fixing roll 610 side or both surfaces). The base layer has a low thermal conductivity and a high heat resistance. For example, polyimide, polyamide, polyamideimide or the like is suitable. The thickness of the base layer is, for example, 50 to 125 μm, and it is sufficient that the conditions such as the material and the thickness are selected so as to correspond to the use conditions and the like and to obtain sufficiently low thermal conductivity. As the release layer formed on the surface of the base layer, a layer in which a fluororesin such as PFA is coated with a thickness of 5 to 20 μm is preferable. Furthermore, the structure which laminated | stacked the elastic layer on the base layer and formed the heat insulation layer can also be taken.
In the fixing device 80 of the present embodiment, the pressure belt 620 is a multilayer structure in which a base layer of a polyimide film having a thickness of 75 μm, a width of 300 mm, and a peripheral length of 78 mm is coated with a PFA surface layer having a thickness of 30 μm. It is configured.

As described above, the pressure pad 84 includes the pre-nip member 84a and the peeling nip member 84b and is supported by the holder 85. An elastic body such as silicone rubber or fluororubber, a leaf spring, or the like can be used for the prenip member 84 a, and the surface on the fixing roll 610 side is formed in a concave shape that substantially follows the outer peripheral surface of the fixing roll 610.
The peeling nip member 84b is formed of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, polyamide, or a metal such as iron, aluminum, or SUS. As the shape of the peeling nip member 84b, the outer surface shape in the nip portion N is formed in a convex curved surface shape having a constant radius of curvature.

  The low friction sheet 88 is provided to reduce the sliding resistance (friction resistance) between the inner peripheral surface of the endless belt 82 and the pressure pad 84, and a material having a small friction coefficient and excellent wear resistance and heat resistance is suitable. ing. Specifically, a sintered molded PTFE resin sheet, a glass fiber sheet impregnated with Teflon, or the like can be used. The low friction sheet 88 may be configured separately from the prenip member 84a and the peeling nip member 84b, or may be configured integrally with the prenip member 84a and the peeling nip member 84b.

Further, as described above, the belt traveling guide 83 is made of a material having a low coefficient of friction and a low thermal conductivity so that heat is not easily taken from the endless belt 82 because it slides on the inner peripheral surface of the endless belt 82. A heat resistant resin such as PFA or PPS is used.
A lubricant application member 87 is disposed in the belt traveling guide 83 along the longitudinal direction of the fixing device 80. The lubricant application member 87 is disposed so as to be in contact with the inner peripheral surface of the endless belt 82 and supplies an appropriate amount of lubricant such as amine-modified silicone oil. As a result, the lubricant is supplied to the sliding portion between the endless belt 82 and the low friction sheet 88, and the sliding resistance between the endless belt 82 and the pressure pad 84 via the low friction sheet 88 is further reduced. 82 is smoothly rotated.
In addition, in order to ensure stable travel of the endless belt 82 at both ends of the belt travel guide 83, it is preferable to provide a belt edge guide that restricts the displacement of the rotation shaft of the endless belt 82 in the axial direction.

  In addition to this configuration, in the fixing device 80 of the present embodiment, a tension roll 615 having a halogen heater 616 as a heating member disposed therein is disposed in parallel with the fixing roll 610. A configuration in which an endless fixing belt 614 is stretched between the fixing roll 610 and the fixing roll 610 is employed. The fixing belt 614 functions as a main heating member that heats the paper P, and the fixing roll 610 and the stretching roll 615 function as a heat supply source that supplies heat to the fixing belt 614. Therefore, the fixing belt 614 can be configured with a very small heat capacity, and the fixing roll 610 and the stretching roll 615 that are heat supply sources can be in contact with each other with a wide lap area. Furthermore, by setting the heat conductivity in the thickness direction of the fixing belt 614 high, the fixing belt 614 can efficiently receive heat from the fixing roll 610 and the stretching roll 615. Furthermore, by setting the thermal conductivity in the thickness direction of the endless belt 82 low, it becomes difficult for the endless belt 82 to remove heat from the paper P. Therefore, in the nip portion N, even if the fixing device 70 is speeded up, a predetermined fixing temperature can always be maintained, and the occurrence of temperature droop can be suppressed.

In addition, since the endless belt 82 is configured to contact the outer peripheral surface of the fixing belt 614 only in the region where the fixing belt 614 is wound around the surface of the fixing roll 610, the nip portion N is formed. A good contact state between the fixing belt 614 and the endless belt 82 can be formed. Therefore, heat conduction from the fixing belt 614 to the paper P can be performed more efficiently, and the occurrence of temperature droop can be more effectively suppressed.
In particular, by adopting a free belt nip configuration, the endless belt 82 does not require a tension roll, and therefore the tension roll does not take heat away from the endless belt 82, so that the generation of temperature droop is more effective. Can be suppressed.

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

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. FIG. FIG. 6 is a diagram showing a change in the surface temperature of the fixing roll. FIG. 4 is a side sectional view illustrating a configuration of a fixing device according to a second embodiment. FIG. 6 is a side cross-sectional view illustrating a configuration of a fixing device according to a third embodiment. FIG. 10 is a side sectional view showing a configuration of a conventional fixing device.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developing device, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... Secondary transfer section, 60, 70, 80 ... Fixing device, 61 ... Fixing belt module, 62 ... Pressure belt module, 63, 84 ... Pressure pad, 82 ... Endless belt, 83 ... Belt running guide, 87 ... Lubricant application member, 88 ... low friction sheet, 614 ... fixing belt, 613, 616, 619 ... halogen heater, 615, 618 ... tension roll, 620 ... pressure belt, 621 ... lead roll, 622 ... pressure roll, 623 ... tension roll

Claims (21)

A fixing roll;
A fixing belt stretched around the fixing roll;
A tension member that stretches the fixing belt;
A heating member for heating the fixing belt;
A pressure belt that contacts the outer peripheral surface of the fixing belt in a region where the fixing belt of the fixing roll is wound and forms a nip portion with the fixing belt;
The fixing device, wherein the fixing belt is configured to have higher thermal conductivity than the pressure belt.   The fixing device according to claim 1, wherein the fixing belt has a higher thermal conductivity in the thickness direction than the pressure belt.   The fixing device according to claim 1, wherein the heating member is disposed inside the stretching member.   The fixing device according to claim 1, wherein the heating member heats the fixing belt by electromagnetic induction.   The fixing device according to claim 1, further comprising a pressing member that presses the pressure belt toward the fixing roll at a nip portion formed between the fixing belt and the pressure belt. A rotatable first belt member;
A heating member for heating the first belt member;
A fixing device comprising: a second belt member that contacts the first belt member and has lower thermal conductivity in the thickness direction than the first belt member.   The fixing device according to claim 6, further comprising a pressing member that presses a contact portion between the first belt member and the second belt member.   The fixing device according to claim 6, wherein the first belt member is stretched by the heating member.   The fixing device according to claim 6, wherein the second belt member is stretched around a plurality of rolls.   The fixing device according to claim 9, wherein the second belt member is stretched by at least one roll formed with a heat insulating layer. A fixing roll having a heating source;
At least one tension roll;
A rotatable fixing belt stretched between the fixing roll and the stretching roll and having a high heat transmission rate in the thickness direction;
A heating member for heating the fixing belt;
In the region where the fixing belt of the fixing roll is wound, an abutment is formed between the fixing belt and the outer peripheral surface of the fixing belt, and a nip portion is formed between the fixing belt and the fixing belt. A pressure belt;
A fixing device, comprising: a nip portion formed between the fixing belt and the pressure belt; and a pressing member that presses the pressure belt toward the fixing roll. The fixing device according to claim 11, wherein a heat passage rate in the thickness direction of the fixing belt is 700 to 25000 (W / m ² · k). The fixing device according to claim 11, wherein a heat passage rate in the thickness direction of the pressure belt is 5000 (W / m ² · k) or less.   The fixing device according to claim 11, wherein the fixing belt includes a metal layer.   The fixing device according to claim 14, wherein the fixing belt includes a metal layer made of stainless steel.   The fixing device according to claim 11, wherein the pressure belt includes a resin layer.   The fixing device according to claim 11, wherein the fixing belt and / or the pressure belt includes an elastic layer.   The fixing roll is a region where the fixing belt of the fixing roll is wound, and has a region where the pressure belt does not contact the upstream side of the nip portion in the rotation direction of the fixing roll. The fixing device according to claim 11.   The fixing device according to claim 11, wherein the fixing roll is made of metal. 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;
A fixing belt stretched around the fixing roll;
A tension member that stretches the fixing belt;
A heating member for heating the fixing belt;
A pressure belt that contacts the outer peripheral surface of the fixing belt in a region where the fixing belt of the fixing roll is wound and forms a nip portion with the fixing belt;
The image forming apparatus, wherein the fixing belt is configured to have higher thermal conductivity than the pressure belt.   21. The fixing unit further includes a pressing member that presses the pressure belt toward the fixing roll at a nip portion formed between the fixing belt and the pressure belt. The image forming apparatus described.

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