JP2008170539A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of defects in an image after heating and pressurizing. <P>SOLUTION: The secondary fixing device 7 has: a first cooling member 81 and a second cooling member 82 cooling a fixing belt 70 tightly stuck with an image on a recording medium. The first cooling member 81 and the second cooling member 82 are heat sinks each formed of a metal such as aluminum or copper having high thermal conductivity. In the first cooling member 81 and the second cooling member 82, the lengths in the circumferential movement direction of the fixing belt 70 are different, and, the heat capacity of the first cooling member 81 is lower than that of the second cooling member 82. When the fixing belt 70 is circumferentially moved, at first, the fixing belt 70 is cooled by the first cooling member 81 in such a manner that the temperature of the fixing belt 70 enters a prescribed temperature range, and is cooled by the second cooling member 82 in such a manner that the temperature of an image tightly stuck to the fixing belt 70 reaches the one at which the image is solidified. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus.

  As a fixing device for fixing an image formed of a color material (toner) on a recording medium, there is a belt-type fixing device (see, for example, Patent Documents 1 to 4). This belt-type fixing device heats and presses an image on a recording medium together with an endless belt that circulates in close contact with the endless belt, cools the image and the endless belt whose temperature has been increased by heating, and then removes the recording medium. Peel from the endless belt. Since the color material on the recording medium is smoothed by the surface of the endless belt, the image becomes a glossy image when the recording medium is peeled off from the endless belt.

JP-A-5-119648 JP 2003-270987 A JP-A-5-165350 JP 2005-292578 A

  An object of the present invention is to prevent uneven glossiness from occurring in an image after heating and pressurization, as compared with the case where the shrinkage amount of the fixing belt is not controlled.

In order to solve the above-described problem, in the invention described in claim 1, a heating member that heats a recording medium on which an image of a color material has been transferred, and a heating member that is disposed to face the heating member, are pressed against the heating member. A pressure member applied thereto, and an endless fixing belt which conveys the recording medium supplied between the heating member and the pressure member in the direction of the circular movement by being circulated around the heating member. The fixing belt is wound around and is disposed between a peeling member for peeling the recording medium conveyed by the fixing belt from the fixing belt, and between the peeling member and the heating member. And a cooling unit that cools the fixing belt so that the shrinkage amount of the fixing belt per 1 mm in the moving direction of the fixing belt is 5 × 10 ⁻⁴ mm or less. A fixing device is provided.

  According to a second aspect of the present invention, in the configuration according to the first aspect, the cooling unit includes a plurality of cooling members that cool the fixing belt in contact with the fixing belt, and the cooling member includes: The temperature is low in order from the cooling member on the heating member side.

  According to a third aspect of the present invention, in the configuration according to the second aspect of the present invention, the plurality of cooling members have a smaller heat capacity in order from the cooling member on the heating member side.

  According to a fourth aspect of the present invention, in the configuration according to the first aspect, the cooling unit includes a cooling member that contacts the fixing belt and cools the fixing belt, and the cooling member includes the heating member. The cooling capacity is increased from the member side toward the peeling member side.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: the fixing device according to any one of the first to fourth aspects; and an image forming unit that forms the image on a recording medium according to image information representing the image. provide.

  According to the first or fifth aspect of the present invention, it is possible to prevent the occurrence of uneven glossiness in the image after being heated and pressurized as compared with the case where the shrinkage amount of the fixing belt is not controlled.

  According to the second aspect of the present invention, the cooling temperature can be set by each cooling member, and the fixing belt can be cooled stepwise.

  According to the third aspect of the present invention, the temperature can be rapidly increased in order from the cooling member on the heating member side by the temperature increase of the heating member.

  According to the fourth aspect of the present invention, it is easier to control the temperature of the fixing belt while in contact with the cooling member, compared to the case where the cooling member not having this configuration is used.

  Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a diagram schematically illustrating the overall configuration of the image forming apparatus according to the present embodiment. This image forming apparatus can be roughly classified as follows: an image formed with a color material is transferred onto a recording medium, and the transferred image is fixed on the recording medium. The image forming unit 1 fixes the image onto the recording medium. A secondary fixing unit 2 that reheats and represses the formed image to make the image on the recording medium glossy.

(Configuration of image forming unit 1)
First, the image forming unit 1 will be described. As shown in FIG. 2, the control unit 17 includes a CPU (Central Processing Unit) 17A, a ROM (Read Only Memory) 17B storing a control program, a RAM (Random Access Memory) 17C, and a storage unit 17D storing various information. A communication interface 17E that functions as a communication interface with an external computer device, a control interface 17F that is connected to each part of the image forming apparatus and mediates transmission and reception of signals and information between each part and the CPU 17A, and an image represented by the image information An image processing unit 17G that performs image processing and an operation unit 17H that includes various keys for operating the image forming apparatus are provided. Each unit of the control unit 17 is connected by a bus 171, and various information and various signals are exchanged between the units via the bus 171.

  When the control program stored in the ROM 17B is executed by the CPU 17A, each unit of the image forming apparatus is controlled by the control unit 17, and a function of forming an image on a recording medium is realized in the image forming apparatus. Then, when receiving image information representing a color image from the external device via the communication interface 17E, the control unit 17 supplies the received image information to the image processing unit 17G. Upon receiving the image information, the image processing unit 17G performs image processing such as gradation correction and screen processing on the image represented by the image information. Then, image information of each color image of Y (Yellow), M (Magenta), C (Cyan), and K (black) is generated from the image that has been subjected to image processing, and the generated image information is output to the exposure device 12. .

  The control unit 17 controls each unit of the secondary fixing unit 2 in accordance with the operation performed on the operation unit 17H. Specifically, when the user performs an operation for instructing reheating and repressing of the image on the recording medium in the operation unit 17H, the control unit 17 controls the secondary fixing unit 2 to perform recording. The image fixed on the medium is again heated and pressed. When the user performs an operation on the operation unit 17H to instruct not to reheat and repress the image on the recording medium, the control unit 17 controls the secondary fixing unit 2 to control the recording medium. The image fixed above is prevented from being heated and repressed again.

  The photoconductor 10 having a cylindrical shape has a photoconductive layer made of OPC (Organic Photo Conductor) as a charge acceptor formed on the surface thereof, and an arrow A in FIG. Rotate in the direction. The charging device 11 is a corotron, for example, and charges the surface of the photoreceptor 10 by corona discharge. The exposure device 12 includes a light source that outputs light, and irradiates the surface of the photoconductor 10 with light according to image information of each color Y, M, C, and K supplied from the control unit 17. The exposure device 12 changes the potential of the irradiated region by irradiating the photosensitive member 10 with light, and for each image information of each color of Y, M, C, K, an electrostatic latent image corresponding to an image represented by the image information Form.

  The developing device 13 is a rotary developing device, a developing roll 13Y that holds Y (Yellow) toner, a developing roll 13M that holds M (Magenta) toner, and a developing roll that holds C (Cyan) toner. 13C and a developing roll 13K that holds K (black) toner. The developing device 13 causes the developing roll to face the photoconductor 10 under the control of the control unit 17. Specifically, for example, when an electrostatic latent image corresponding to a Y image is formed on the photoconductor 10 by the exposure device 12, the developing device 13 rotates to cause the developing roll 13 </ b> Y to face the photoconductor 10. When the developing roll 13Y faces the photoreceptor 10, the Y toner held on the developing roll 13Y adheres to the electrostatic latent image on the photoreceptor 10, and a toner image corresponding to the Y image is formed on the surface of the photoreceptor 10. It is formed. Similarly, when an electrostatic latent image corresponding to each color is formed for other colors (M, C, K), the developing roll of the color corresponding to the electrostatic latent image faces the photoconductor 10. A toner image of each color is formed on the surface of the photoreceptor 10.

  The cleaning device 16 is a device that removes toner remaining on the surface of the photoconductor 10 without being transferred onto the sheet. The cleaning device 16 scrapes off the toner remaining on the photoreceptor 10 and holds the scraped toner.

  The intermediate transfer belt 20 is an endless belt and is stretched around a drive roll 21, support rolls 22 and 23, and a backup roll 24. The drive roll 21 is a roll for moving the intermediate transfer belt 20 around. The drive roll 21 is rotated by a motor (not shown) to move the intermediate transfer belt 20 in the direction of arrow B in FIG. The support rolls 22 and 23 are rolls that support the intermediate transfer belt 20 and rotate with the movement of the intermediate transfer belt 20.

  The primary transfer roll 15 is a roll that transfers the toner image formed on the surface of the photoconductor 10 to the intermediate transfer belt 20, and faces the photoconductor 10 with the intermediate transfer belt 20 interposed therebetween. The primary transfer roll 15 is connected to a power source (not shown), and a voltage is applied from this power source. Since a voltage is applied to the primary transfer roll 15, a potential difference is generated between the photosensitive member 10 and an electric field is formed. When the toner image formed on the photoreceptor 10 moves to a position facing the primary transfer roll 15, the toner image on the photoreceptor 10 is transferred onto the intermediate transfer belt 20 by the formed electric field.

  The recording medium storage unit 30 stores a sheet-like recording medium (for example, a sheet of paper or plastic), and can store a plurality of recording media. The pick-up roll 31 is rotated by a motor (not shown), and feeds the recording medium stored in the recording medium storage unit 30 one by one to the transport path S. Regarding the conveyance path S, in the following description, the recording medium storage unit 30 side is referred to as upstream, and the discharge roll 37 side is referred to as downstream. The conveyance roll pairs 32, 33, and 34 are rotated by a motor (not shown), and convey the recording medium in the conveyance path S between the intermediate transfer belt 20 and the secondary transfer roll 25.

  The backup roll 24 and the secondary transfer roll 25 are rolls that transfer the toner image transferred to the intermediate transfer belt 20 onto a recording medium. The secondary transfer roll 25 moves to the backup roll 24 immediately before the recording medium is conveyed between the backup roll 24 and the secondary transfer roll 25, contacts the intermediate transfer belt 20, and backs up the intermediate transfer belt 20. Press against the roll 24. The backup roll 24 is connected to a power source (not shown) and is applied with a voltage. When the secondary transfer roll 25 presses the intermediate transfer belt 20 against the backup roll 24, a potential difference is generated between the backup roll 24 and the secondary transfer roll 25, and an electric field corresponding to the voltage applied to the backup roll 24 is formed. Is done. When the recording medium is conveyed between the toner image on the intermediate transfer belt 20 and the secondary transfer roll 25, the toner image on the intermediate transfer belt 20 is transferred onto the recording medium by the formed electric field. . The secondary transfer roll 25 moves in the opposite direction to the backup roll 24 when the transfer of the toner image is completed. As a result, the intermediate transfer belt 20 is separated from the backup roll 24.

  The belt cleaner 25 is a device that removes toner remaining on the intermediate transfer belt 20 without being transferred to the recording medium. The belt cleaner 25 scrapes off the toner remaining on the intermediate transfer belt 20 and holds the scraped toner.

  The conveyance belt 35 is a belt that conveys the recording medium on which the toner image is transferred. The conveyance belt 35 is an endless belt, and moves in the direction of arrow C in FIG. 1 to convey the recording medium conveyed on the belt to the guide member 36. The guide member 36 is a plate-like rectangular member, and is disposed on the upstream side of the conveyance path S when viewed from the heating roll 41 and the pressure roll 42. The guide member 36 guides the recording medium transported by the transport belt 35 between the heating roll 41 and the pressure roll 42.

  The heating roll 41 and the pressure roll 42 are rolls that fix the toner image transferred onto the recording medium to the recording medium. The heating roll 41 has, for example, a halogen lamp as a heat source therein, and is heated to a predetermined temperature under the control of the control unit 17 to increase the temperature of the heating roll 41. Further, the heating roll 41 rotates in the direction of arrow D in FIG. The pressure roll 42 is opposed to the heating roll 41 with the conveyance path S interposed therebetween, and is pressed against the heating roll 41. When the recording medium on which the toner image is transferred is conveyed between the heating roll 41 and the pressure roll 42, the recording medium moves in the direction of the discharge roll 37. Here, the toner image on the recording medium is fixed to the recording medium by heat and pressure from the heating roll 41 and the pressure roll 42.

  The discharge roll pair 37 is a roll for transporting the recording medium on which the toner image is fixed to the secondary fixing unit 2. The discharge roll pair 37 is disposed on the downstream side of the conveyance path S when viewed from the heating roll 41 and the pressure roll 42, and the secondary fixing unit 2 transfers the recording medium on which the image is fixed by the heating roll 41 and the pressure roll 42. To send.

(Configuration of secondary fixing unit 2)
Next, the secondary fixing unit 2 will be described. The path changing member 50 changes the conveyance direction of the recording medium in the secondary fixing unit 2. The path changing member 50 guides the recording medium conveyed by the discharge roll pair 37 in the direction of either the discharge roll pair 51 or the conveyance roll pair 52 under the control of the control unit 17. The discharge roll pair 51 is a roll that discharges the recording medium to the outside of the secondary fixing unit 2, and discharges the recording medium guided by the path changing member 50 to the outside of the secondary fixing unit 2. The conveyance roll pairs 52 and 55 are rolls that convey the recording medium, and convey the recording medium guided by the path changing member 50 to the secondary fixing device 7. The discharge roll pair 56 is a roll for discharging the recording medium to the outside of the secondary fixing unit 2, and discharges the recording medium that has passed through the secondary fixing device 7 to the outside of the secondary fixing unit 2.

(Configuration of secondary fixing device 7)
The secondary fixing device 7 is a device that performs a fixing process again on the toner image fixed on the recording medium by the image forming unit 1. As shown in FIG. 3, the secondary fixing device 7 includes a fixing belt 70, a heating roll 71, a pressure roll 75, a peeling roll 72, a steering roll 73, a cooling having a first cooling member 81 and a second cooling member 82. Part 80 and blowers 100 </ b> A and 100 </ b> B. The fixing belt 70 heated by the heating roll 71 is cooled by the cooling part 80.

  In this embodiment, the heating roll 71 includes a core 71A, a release layer 71B, and a heating halogen lamp 71C. For example, the core 71A is made of metal and has a cylindrical shape. In this embodiment, a release layer 71B made of a tetrafluoroethylene resin such as polytetrafluoroethylene is formed on the peripheral surface. The heating halogen lamp 71 </ b> C is disposed inside the core 71 </ b> A, and its temperature is controlled by the controller 17. The temperature of the peripheral surface of the heating roll 71 becomes a predetermined temperature by the heat generated by the heating halogen lamp.

  The pressure roll 75 includes a core 75A, an elastic body layer 75B, and a release layer 75C. The core 75A is made of metal and has a cylindrical shape. In this embodiment, an elastic body layer 75B made of silicone rubber having a rubber hardness (JIS-A) of about 40 ° is formed on the peripheral surface. . In the present embodiment, a release layer 75C made of a tetrafluoroethylene resin such as polytetrafluoroethylene is formed on the surface of the elastic layer 75B. The pressure roll 75 is rotated in the direction of arrow E in FIG. 3 by a motor (not shown). The pressure roll 75 is moved in the direction of the heating roll 71 or the direction opposite to the heating roll 71 by a moving mechanism (not shown) under the control of the control unit 17.

  The steering roll 73 is a roll that supports the fixing belt 70 and rotates as the fixing belt 70 moves. Further, the steering roll 73 changes the angle with respect to the moving direction of the fixing belt 70 to prevent the fixing belt 70 from moving in the rotation axis direction of the steering roll 73.

  The peeling roll 72 has a cylindrical shape, and rotates with the circumferential movement of the fixing belt 70. When the recording medium conveyed in close contact with the fixing belt 70 moves to the position of the peeling roll 72, it is peeled off from the fixing belt 70 due to the rigidity of the recording medium.

  The fixing belt 70 is stretched around a heating roll 71, a peeling roll 72, and a steering roll 73, and moves around in the direction of arrow F in FIG. 3 as the heating roll 71 rotates. FIG. 4 is a view showing a cross section of the fixing belt 70. As shown in FIG. 4, it has the base material layer 70A and the surface layer 70B. The surface layer 70B is made of, for example, silicone rubber. The base material layer 70A is formed of a metal such as nickel, aluminum, or stainless steel. The thickness of the base layer 70A is preferably in the range of 30 μm to 200 μm, more preferably in the range of 40 μm to 150 μm, and still more preferably in the range of 50 μm to 130 μm. When the thickness of the base material layer 70A is less than 30 μm, the dimensional change when heated or cooled is large and the strength is insufficient. On the other hand, when the thickness of the base material layer 70A exceeds 200 μm, the fixing belt 70 is increased. This is because the heat capacity of the battery becomes larger and it becomes difficult to transfer heat. In the present embodiment, the fixing belt has a diameter of 168 [φmm], a width of 320 [mm], and a thickness of 30 [μm] on a stainless steel base layer 70A having a thickness of 50 [μm]. A surface layer 70B of silicone rubber is formed.

  In the present embodiment, the base material layer 70A is formed of metal, but the base material layer 70A may be formed of a synthetic resin such as polybutylene terephthalate, polyimide, or polyimide amide. Further, when the base layer 70A is formed of a synthetic resin, charging is performed by adding a powder having characteristics of conducting electricity such as carbon powder (carbon black) to the base layer 70A to reduce the volume resistivity. You may make it suppress adhesion of dust by.

  The blower 100 </ b> A sends air to the first cooling member 81, and the blower 100 </ b> B sends air to the second cooling member 82. Each blower sends air to each cooling member to dissipate the heat of the cooling member into the air.

  The cooling unit 80 cools the fixing belt 70 heated by the heating roll 71, and includes a first cooling member 81 and a second cooling member 82. The first cooling member 81 is disposed on the downstream side of the transport path S when viewed from the heating roll 71 and the pressure roll 75 and is in contact with the fixing belt 70. Further, the second cooling member 82 is disposed on the downstream side of the transport path S as viewed from the first cooling member 81 and is in contact with the fixing belt 70.

  The first cooling member 81 and the second cooling member 82 are heat sinks formed of a metal having high thermal conductivity (for example, aluminum or copper), and each cooling unit has a large surface area to increase heat dissipation. A large number of plate-like protrusions (fins) 90 are provided. In addition, when the space | interval between each plate-shaped protrusion 90 is narrowed and the number of the plate-shaped protrusion 90 is increased, the surface area of each cooling member will become large, but when the space | interval of the plate-shaped protrusion 90 is too narrow, between each plate-shaped protrusion 90. Since the air flow deteriorates, an interval at which cooling can be efficiently performed is determined and set by experiment.

  The secondary fixing device 7 reheats and represses the recording medium conveyed with the toner image on the heating roll 71 side between the heating roll 71 and the pressure roll 75, and heats and softens the toner image. It is brought into close contact with the fixing belt 70. By the way, the fixing belt 70 is cooled by the cooling member and contracts. However, in the toner image that is in close contact with the fixing belt 70, a part that peels off from the fixing belt 70 before being cooled and solidified occurs. In the image after peeling off, gloss unevenness may occur.

In order to confirm under which conditions gloss unevenness occurs, the present inventor has a temperature between the temperature of the fixing belt 70 before contacting the cooling member and the temperature of the fixing belt 70 when contacting the cooling member. An experiment was conducted to adjust the difference and examine the conditions for occurrence of uneven gloss. In the experiment, the diameter of the base material layer 70A of the fixing belt 70 is 168 [φmm], the thickness is 50 [μm], the width is 320 [mm], and the moving speed of the fixing belt is 52 [mm / sec]. did. Further, a fixing belt 70 in which a polyimide having a linear expansion coefficient of 54 × 10 ⁻⁶ [1 / ° C.] is a base material layer and SUS304 (linear expansion coefficient of 17.3 × 10 ⁻⁶ [1 / ° C.]) The fixing belt having a base material layer of 18% chromium and 8% nickel stainless steel) was examined for conditions of occurrence of gloss unevenness. The temperature of the fixing belt before coming into contact with the cooling member is 1 cm upstream from the upstream end in the conveying path S of the cooling member, and the temperature of the fixing belt when in contact with the cooling member is the conveying path S of the cooling member. It measured in the position of 1 cm downstream from the upstream edge part.

FIG. 5 shows a temperature difference (horizontal axis) between the temperature of the fixing belt before contacting the cooling member and the temperature of the fixing belt 70 when contacting the cooling member, and 1 [mm] in the circumferential direction of the fixing belt 70. ] Is a graph showing the relationship with the amount of contraction (vertical axis). As a result of the experiment, in the case of the belt using polyimide as the base material layer, gloss unevenness did not occur when the temperature difference was 9 ° C. or less. Further, in the case of a belt using SUS304 as a base material layer, gloss unevenness did not occur when the temperature difference was 28 ° C. or less. The amount of expansion and contraction of the belt when the temperature difference is 9 ° C. in the belt using polyimide as the base layer and the amount of contraction of the belt when the temperature difference is 28 ° C. and the belt using SUS 304 as the base layer are both It is 5 × 10 ⁻⁴ [mm] per 1 mm. That is, it can be said that the occurrence of uneven gloss can be suppressed by cooling the belt while suppressing the expansion / contraction amount to 5 × 10 ⁻⁴ [mm] or less per 1 mm.
In this experiment, a fixing belt using polyimide and SUS as a base material layer was used. However, the relationship between the amount of expansion and contraction of the belt and gloss unevenness is not limited to the belt using these as base materials. When the shrinkage amount of the fixing belt 70 is large, a portion of the toner image that is in close contact with the fixing belt 70 is peeled off from the fixing belt 70 before being cooled and solidified, and the image after peeling off from the fixing belt 70 is generated. The phenomenon that gloss unevenness occurs does not depend on the belt base material.

  When the recording medium reaches the position of the peeling roll 72, the recording medium does not peel from the fixing belt 70 unless the toner image on the recording medium is solidified. The temperature at which the recording medium is peeled off from the fixing belt 70 varies depending on the component of the toner or the resin component for glossing the surface of the recording medium. It is desirable that the temperature be 60 ° C. to 80 ° C., which is lower than the temperature at which softening occurs (hereinafter referred to as the peeling temperature). In the present embodiment, the size of the second cooling member 82, the amount of air blown by the blower 100B, and the like are obtained through experiments and set so that the temperature of the second cooling member 82 is 70 ° C.

FIG. 6 schematically shows a graph representing a temperature drop in the moving direction of the fixing belt using the fixing belt and the cooling member used in the above experiment. When the temperature of the heating roll 71 is controlled to 120 ° C., the first cooling member 81 is cooled to 95 ° C., and the temperature of the second cooling member 82 is cooled to 70 ° C., the fixing belt 70 heated by the heating roll 71. The temperature is lowered to 95 ° C. by the first cooling member 81. Thereafter, the area where the recording medium is in close contact moves to the position of the second cooling member 82 by the circumferential movement of the fixing belt 70, and is cooled to 70 ° C. by the second cooling member 82 (line L1 in FIG. 6). ).
A line L2 in FIG. 6 is a graph showing a temperature decrease of the fixing belt when the first cooling member 81 is not used and the second cooling member is used for cooling. When the first cooling member 81 and the second cooling member 82 are used (line L1), a rapid temperature drop of the fixing belt is observed as in the case where only the second cooling member 82 is used (line L2). In addition, it is cooled to the peeling temperature while suppressing the shrinkage amount of the fixing belt to such an extent that uneven gloss does not occur.

(Operation of the embodiment)
Next, the operation of this embodiment will be described. First, the recording medium on which the toner image is fixed in the image forming unit 1 is sent to the secondary fixing unit 2 by the discharge roll pair 37. If the user inputs an instruction not to reheat and repress the image on the recording medium by operating the operation unit 17H before the toner image is formed on the recording medium. The path changing member 50 is controlled by the control unit 17 and the recording medium is guided toward the discharge roll pair 51. Since the recording medium guided to the discharge roll pair 51 is discharged out of the secondary fixing unit 2 by the discharge roll 51, the recording medium is not reheated and repressurized.

  On the other hand, if the user inputs an instruction to reheat and repress the image on the recording medium before operating the operation unit 17H before the toner image is formed on the recording medium, the control unit 17 Then, the path changing member 50 is controlled, and the recording medium is guided toward the conveying roll pair 52. The recording medium guided toward the transport roll pair 52 is transported to the secondary fixing device 7 by the transport roll pair 52 and the transport roll pair 55.

  The recording medium conveyed to the secondary fixing device 7 is conveyed between the heating roll 71 and the pressure roll 75 in a state where the toner image is on the heating roll 71 side. In a state where the pressure roll 75 is pressed against the heating roll 71, when the recording medium is conveyed between the pressure roll 75 and the heating roll 71, the recording medium is brought into close contact with the fixing belt 70, and the heating roll 71 And the pressure roll 75 are heated and pressurized. The color material on the recording medium is melted by heating and is in close contact with the surface of the endless belt. Here, the fixing belt 70 expands when heated.

  Now, since the fixing belt 70 moves around with the rotation of the heating roll 71, the recording medium that is heated and pressurized and is in close contact with the fixing belt 70 moves to the downstream side of the conveyance path S together with the fixing belt 70. . When the region where the recording medium is in close contact with the fixing belt 70 moves to the position of the first cooling member 81, the portion of the recording medium and the fixing belt 70 where the recording medium is in close contact is cooled by the first cooling member 81. The Thereafter, the area where the recording medium is in close contact is moved to the position of the second cooling member 82 by the circumferential movement of the fixing belt 70, and is cooled by the second cooling member 82.

  The region cooled by the second cooling member 82 moves to the position of the peeling roll 72 by the circumferential movement of the fixing belt 70. When the recording medium reaches the position of the peeling roll 72, the recording medium is peeled off from the fixing belt 70 by its own rigidity and sent to the discharge roll pair 56. The recording medium sent to the discharge roll pair 56 is discharged out of the secondary fixing device 7 by the discharge roll pair 56.

[Modification]
As mentioned above, although embodiment of this invention was described, embodiment mentioned above is an example of embodiment which concerns on this invention, This invention is not limited to embodiment mentioned above, It can implement with other various forms. It is. For example, the present invention may be implemented by modifying the above-described embodiment as follows.
In the embodiment described above, a cylindrical roll is used for both the pressure member and the peeling member. However, the roll is not limited to the roll shape, and any member can be used as long as the fixed fixing belt can move around.

  In the above-described secondary fixing device 7, a heat source that heats the pressure roll 75 may be provided in the pressure roll 75. Further, in the above-described embodiment, if the temperature of each cooling member of the cooling unit 80 is maintained at a predetermined temperature, it is not necessary to provide a blower that sends air to the cooling unit 80.

  In the above-described embodiment, the first cooling member 81 and the second cooling member 82 are heat sinks, but a metal member is brought into contact with the belt, and this member is cooled by liquid to cool the fixing belt 70. You may do it.

  In the embodiment described above, the number of cooling members of the cooling unit 80 is not two, but the third cooling member 83 may be provided as shown in FIG. 7, and the number of cooling members may be three. Further, the number of cooling members may be four or more. In the above-described embodiment, the material and size of the cooling member on the upstream side in the conveyance direction of the recording medium and the cooling member on the downstream side are different, and the heat capacity of the cooling member in the upstream direction is on the downstream side. It may be smaller than the heat capacity of the cooling member.

  A temperature sensor may be arranged in each cooling member included in the cooling unit 80, and control may be performed so that the temperature of the cooling member falls within a predetermined temperature range. When there are a plurality of cooling members, the size of each cooling member, the number of protruding members, and the material of the cooling member may be the same. In this case, the temperature of the cooling member arranged on the downstream side of the transport path S is lowered by controlling the amount of air sent by each blower.

  In the above-described embodiment, the cooling member 84 may be designed to have a higher cooling capacity as the downstream side of the transport path S is reached. Here, the cooling capacity refers to an amount of decrease in the temperature of the fixing belt 70 in the moving direction of the fixing belt 70. For example, as shown in FIG. 8, in the cooling member 84, the interval between the plate-like protrusions 90 (fins) may become narrower from the upstream side to the downstream side of the transport path S. Further, as shown in FIG. 9, the height of the cooling member 84 may be gradually increased from the upstream side of the conveyance path S toward the downstream side. According to these configurations, the cooling capacity of the cooling member 84 increases as it becomes downstream of the transport path S. For this reason, as shown in FIG. 10, the temperature decrease of the fixing belt 70 is smaller toward the upstream side of the conveyance path S and increases toward the downstream side. For example, when a cooling member as shown in FIGS. 8 and 9 is used, if the cooling capacity is designed so that the temperature of the fixing belt 70 at the position where the recording material is peeled is cooled to the peeling temperature, the cooling is performed. It is not necessary to provide a plurality of members.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 3 is a block diagram illustrating a hardware configuration of a control unit 17. FIG. 3 is a schematic diagram showing a configuration of a secondary fixing device 7. FIG. 3 is a view showing a cross section of the fixing belt 70. FIG. Relationship between the temperature difference between the temperature of the fixing belt before contacting the cooling member and the temperature of the fixing belt 70 when contacting the cooling member, and the amount of expansion / contraction per 1 mm in the circumferential direction of the fixing belt 70 It is the graph which showed. 6 is a graph showing a temperature change of the fixing belt 70. FIG. 6 is a diagram illustrating a secondary fixing device 7 according to a modified example of the invention. FIG. 6 is a diagram illustrating a secondary fixing device 7 according to a modified example of the invention. FIG. 6 is a diagram illustrating a secondary fixing device 7 according to a modified example of the invention. 6 is a graph showing a temperature change of the fixing belt 70.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image formation part, 2 ... Secondary fixing part, 7 ... Secondary fixing device, 17 ... Control part, 70 ... Fixing belt, 71 ... Heating roll, 72 ... * Peeling roll, 73 ... steering roll, 75 ... pressure roll, 80 ... cooling part, 81 ... first cooling member, 82 ... second cooling member, 83 ... third Cooling member, 84 ... cooling member, 90 ... plate-like protrusion, 100A, 100B ... blower

Claims (5)

A heating member for heating the recording medium on which the image of the color material is transferred;
A pressure member disposed opposite the heating member and pressed against the heating member;
An endless fixing belt that conveys the recording medium supplied between the heating member and the pressure member in the direction of the circular movement by being circulated around the heating member.
A peeling member that spans the fixing belt and peels the recording medium conveyed by the fixing belt from the fixing belt;
The fixing belt is disposed between the peeling member and the heating member so as to come into contact with the fixing belt, and the shrinkage amount of the fixing belt per mm in the moving direction of the fixing belt is 5 × 10 ⁻⁴ mm or less. And a cooling unit that cools the fixing belt.   The cooling unit includes a plurality of cooling members that contact the fixing belt to cool the fixing belt, and the cooling member has a lower temperature in order from the cooling member on the heating member side. Item 4. The fixing device according to Item 1.   The fixing device according to claim 2, wherein the plurality of cooling members have a heat capacity that decreases in order from the cooling member on the heating member side.   The cooling section has a cooling member that contacts the fixing belt and cools the fixing belt, and the cooling member has a cooling capacity that increases from the heating member side toward the peeling member side. The fixing device according to claim 1.   An image forming apparatus comprising: the fixing device according to claim 1; and an image forming unit that forms the image on a recording medium in accordance with image information representing the image.

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