JP2011059387A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device that can uniformize the heating temperature in a fixing belt and effectively uses heat energy, and to provide an image forming apparatus that includes the fixing device. <P>SOLUTION: The fixing device includes: a fixing belt 21; a thermal conductive member 22 disposed inside the fixing belt 21; a heater 25 disposed in the thermal conducting member 22 and used to heat the thermal conductive member 22; a nip forming member 23 disposed opposite a pressure roller 31 via the fixing belt 21 and forming a fixing nip N between the fixing belt 21 and the pressure roller 31; a reinforcing member 24 disposed in the thermal conducting member 22 and supporting the nip forming member 23; and a heat uniformizing member 26 disposed in contact with the internal surface of the thermal conducting member 22, in an area different from the area where the heater 25 is disposed, in the area where the inside of the thermal conducting member 22 is separated by the reinforming member 24. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes a formed image on a recording medium by heating and pressing the recording medium at a nip portion between the fixing member and the pressure member, and an image forming apparatus including the fixing device.

  In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, a copy or a recorded material is obtained by heat-fixing an unfixed image transferred onto a recording sheet as a recording medium.

  At the time of fixing, the recording paper carrying the unfixed image is heated and pressed against the unfixed image while being conveyed, so that the developer contained in the unfixed image, in particular, the toner is melted and softened, and the recording medium is used. The toner is fixed onto the recording paper by allowing the recording paper to penetrate.

  There are various types of fixing devices, and the film heating type fixing device described in Patent Document 1 has a heat resistance between a ceramic heater as a heating element and a pressure roller as a pressure member. A fixing nip is formed by sandwiching a film (fixing film), a recording medium on which an unfixed toner image to be fixed is formed is introduced into the fixing nip, and the recording medium is conveyed together with the fixing film. In the fixing nip, the heat of the ceramic heater is applied to the recording medium through the fixing film and is pressed to fix the unfixed toner image on the recording medium surface by heat and pressure.

  According to the film heating type fixing device, an on-demand type device can be configured by using a low-heat capacity member as a ceramic heater and a fixing film. Therefore, ceramic as a heat source only when image forming of the image forming device is performed. It is only necessary to energize the heater so that it generates heat at a predetermined fixing temperature. The waiting time from power-on of the image forming apparatus to an image forming executable state is short (quick start property), and power consumption during standby is also low. There are advantages such as significantly smaller (power saving).

  Further, in Patent Document 2, a pipe-like metal heat conduction member is installed so as to face the inner peripheral surface of an endless fixing member such as a fixing belt or a fixing film, and the metal heat conduction member is directly or A configuration has been proposed in which the entire fixing member is heated sufficiently and uniformly by indirectly heating. According to this configuration, the warm-up time can be shortened by thinning the fixing member and the metal heat conduction member.

  However, in the prior art, since a thin fixing member such as a fixing film is used, the thermal conductivity in the width direction (axial direction) of the fixing member is deteriorated.

  That is, when a small-size paper such as an envelope is passed, the temperature of the non-sheet passing portion rises and enters the toner offset region, and a recording material having a width wider than that of the envelope immediately after the continuous envelope feeding passes. When the unfixed toner image is fixed, the toner corresponding to the non-sheet passing portion at the time of envelope feeding is offset to the fixing member.

  Further, the temperature of the non-sheet passing portion of the fixing member excessively increases, which may damage the fixing member itself. Conventionally, in order to avoid an excessive temperature rise of the non-sheet passing portion, The throughput had to be reduced.

  Therefore, in Patent Document 3, in order to solve the heating problem, the fixing member has a higher thermal conductivity than the fixing member for the purpose of uniformizing the heating temperature in the width direction (thermal equalization). A configuration for abutting the heat conducting member has been proposed.

  However, in the prior art, as described above, since the fixing member is thinned, the heat capacity is small, and the temperature is greatly lowered by contact with the good heat conducting member. This is unavoidable when the temperature difference between the good heat conducting member and the fixing member is large.

  For this reason, it is necessary to keep the temperature of the good heat conducting member high to some extent. In particular, in the standby state, the user expects to be able to print immediately, and the good heat conducting member needs to be at a high temperature.

  However, disposing the good heat conduction member at a position where it can be heated by the heat source causes a part of the heat supply amount to be transmitted to the good heat conduction member, thereby reducing the heat supply amount to the fixing member during warm-up. . For this reason, it is necessary to significantly increase the warm-up time for the fixing member.

  Accordingly, the present invention provides a fixing device that solves the above-described problems of the prior art and makes it possible to make the heating temperature uniform in the fixing belt and effectively use heat energy, and an image forming apparatus including the fixing device. For the purpose.

  In order to achieve the above object, the invention described in claim 1 is directed to a fixing member, a heat conducting member provided inside the fixing member, and heating for heating the heat conducting member provided inside the heat conducting member. A member, a nip forming member disposed opposite to the pressure member via the fixing member to form a fixing nip between the fixing member and the pressure member, and the nip forming member provided inside the heat conducting member The heat provided in contact with the inner surface of the heat conducting member in a region different from the region where the heating member is disposed in the region divided by the supporting member inside the heat conducting member and the supporting member And an equalizing member.

  According to the fixing device according to the present invention, it is possible to make the heating temperature uniform in the fixing belt and to effectively use the heat energy.

  In addition, according to the image forming apparatus equipped with the fixing device according to the present invention, high-quality image formation by a good fixing process is realized.

Schematic configuration diagram of the entire image forming apparatus for explaining the embodiment FIG. 3 is a front cross-sectional view showing a main part of the fixing device according to the first embodiment of the present invention. The side view which shows the support structure in Embodiment 1 of the fixing device of this invention. Explanatory drawing which shows temperature distribution of the longitudinal direction of a fixing belt at the time of continuously passing an envelope in Embodiment 1. FIG. 6 is a diagram illustrating a change in time after the warm-up of the fixing device is finished and a transition is made to a standby state and a temperature of the heat leveling member in the first embodiment. Front sectional drawing which shows the principal part in Embodiment 2 of the fixing device of this invention. Explanatory drawing which shows the longitudinal direction temperature distribution of the fixing belt at the time of passing an envelope continuously in Embodiment 2. Front sectional drawing which shows the principal part in Embodiment 3 of the fixing device of this invention. Explanatory drawing of the problem in the holding member in Embodiment 3 shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an entire image forming apparatus for explaining an embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes an apparatus body of an electrophotographic copying machine as an image forming apparatus, 2 an original reading unit that optically reads image information of an original D, and 3 an image information read by the original reading unit 2. An exposure unit that irradiates the exposed exposure light L onto the photosensitive drum 5 to form a latent image, 4 a developing unit that develops a toner image on the photosensitive drum 5 and visualizes it, and 7 an image on the photosensitive drum 5. A transfer unit that transfers the toner image formed on the recording medium P to the recording medium P, a document conveying unit that conveys the document D loaded on the document setting table 11 to the document reading unit 2, and 12 to 14 recording media such as transfer paper P is a paper storage unit in which P is stored.

  Reference numeral 20 denotes a fixing device for fixing an unfixed toner image on the recording medium P, 21 denotes a fixing belt as a fixing member provided in the fixing device 20, and 31 denotes a pressure member provided in the fixing device 20. It is a pressure roller.

  Next, an operation during normal image formation in the image forming apparatus having the above configuration will be described.

  First, the document D is conveyed from the document setting table 11 in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 10 and passes over the document reading unit 2. At this time, the image information of the document D passing above is optically read by the document reading unit 2.

  The optical image information read by the document reading unit 2 is transmitted to the exposure unit 3 after being converted into an electrical signal. The exposure unit 3 emits laser exposure light L, which is modulated based on the image information of the transmitted electrical signal, toward the photosensitive drum 5, thereby forming a latent image on the surface of the photosensitive drum 5.

  The photosensitive drum 5 rotates in the clockwise direction in the figure, and the latent image on the surface is developed in the developing unit 4 and is visualized as a toner image. Thereafter, the toner image on the photosensitive drum 5 is transferred onto the recording medium P conveyed by the registration roller 9 at a timing in the transfer unit 7.

  A conveying operation for the recording medium P will be described. First, one of the plurality of paper feeding units 12, 13, and 14 of the apparatus main body 1 is automatically or manually selected.

  For example, if the paper feed unit 12 is selected, the uppermost sheet of the recording medium P stored in the paper feed unit 12 is transported toward the transport path K by the transport roller. When the transported recording medium P passes through the transport path K and reaches the position of the registration roller 9, the recording medium P is aligned with the image formed on the photosensitive drum 5 by the registration roller 9. Once stopped, the sheet is conveyed toward the transfer unit 7 at the same timing.

  The recording medium P after the toner image has been transferred passes through the transfer unit 7 and is then sent to the fixing device 20. The recording medium P that has reached the fixing device 20 is sent to the fixing nip N between the fixing belt 21 and the pressure roller 31, and in the fixing nip N, heat received from the fixing belt 21 having a heating member therein, and fixing. The toner image is fixed by being heated and pressurized by the pressure received from the belt 21 and the pressure roller 31.

  The recording medium P that has undergone the fixing process is sent out from the fixing nip N and then discharged from the apparatus main body 1.

  In this way, a series of image forming processes is completed.

  Next, the configuration and operation of Embodiment 1 of the fixing device installed in the image forming apparatus according to the present invention will be described in detail.

  FIG. 2 is a front cross-sectional view showing the main part of the first embodiment of the fixing device, and FIG. 3 is a side view showing the support structure in the first embodiment of the fixing device.

  As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a heat conducting member 22, a nip forming member 23, a reinforcing member 24 that also serves as a heat shielding member, and a heater 25 that is a heating member. The heat leveling member 26, a pressure roller 31 as a pressure member, guide plates 35 and 37 of the recording medium P, a temperature sensor 40, and the like.

  The fixing belt 21 is a thin and flexible endless belt, and rotates and moves in an arrow direction (clockwise direction) in FIG. The fixing belt 21 is formed by sequentially laminating an elastic layer and a release layer on a base material, and the entire thickness thereof is set to 1 mm or less.

  The base material of the fixing belt 21 has a layer thickness of 30 to 50 μm, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide resin.

  The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing this elastic layer, minute irregularities on the surface of the fixing belt 21 in the fixing nip N are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, so that the generation of a so-called crushed skin image is suppressed. Is done.

  The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and is a resin such as PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. Made of material. By providing this release layer, the releasability (peelability) for the toner (toner image T) on the recording medium P is secured.

  Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm, and in the first embodiment, the diameter of the fixing belt 21 is set to 30 mm. Inside the fixing belt 21 (inner peripheral surface side), a heat conducting member 22, a nip forming member 23, a reinforcing member 24, and a heater 25 are installed.

  The nip forming member 23 is provided so as to be in contact with the inner peripheral surface side of the fixing belt 21 and forms a fixing nip N by contacting the pressure roller 31 via the fixing belt 21. As shown in FIG. 3, the both ends of the nip forming member 23 in the width direction (longitudinal direction) are fixedly supported by a side plate 43 constituting the fixing device 20 via a support member 41.

  As shown in FIG. 2, the nip forming member 23 is formed such that the curvature of the surface facing the pressure roller 31 follows the curvature of the pressure roller 31. Thereby, since the recording medium P is sent out from the fixing nip N so as to follow the curvature of the pressure roller 31, the problem that the recording medium P after the fixing process is attracted to the fixing belt 21 and does not separate is suppressed. Can do.

  Note that it is preferable to form the sliding contact surface of the nip forming portion 23 with a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the nip forming member 23 and the fixing belt 21 are in sliding contact.

  The reinforcing member 24 functions as a supporting member that reinforces the strength of the nip forming member 23 by supporting the nip forming member 23 in the fixing nip N, and a function as a heat shielding member that absorbs and shields the heat of the heater 25. And the end is in contact with the nip forming member 23 and extends to the inner central portion of the fixing belt 21.

  As shown in FIG. 3, the reinforcing member 24 is formed to have substantially the same length in the width direction as the nip forming member 23, and both ends in the width direction are attached to the side plate 43 of the fixing device 20 via the support member 41. Fixedly supported.

  The reinforcing member 24 abuts on the pressure roller 31 via the nip forming member 23 and the fixing belt 21, so that the nip forming member 23 is deformed by the pressure applied by the pressure roller 31 in the fixing nip N ( To bend).

  The reinforcing member 24 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the above-described function. Furthermore, the mechanical strength of the reinforcing member 24 can be increased by increasing the section modulus by forming the reinforcing member 24 so as to have a horizontally long cross section along the pressing direction by the pressure roller 31. it can.

  The heater 25 is composed of a halogen heater or a carbon heater, and both ends thereof are fixed to the side plate 43 of the fixing device 20.

  Then, the heat conducting member 22 is heated by the radiant heat of the heater 25 whose output is controlled by the power supply unit installed in the apparatus main body 1. The fixing belt 21 is entirely heated by the heat conducting member 22, and heat is applied to the toner image T on the recording medium P from the surface of the heated fixing belt 21 in the fixing nip N.

  The output control of the heater 25 is performed based on the detection result of the belt surface temperature by the temperature sensor 40 such as a thermistor facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25.

  In this example, the heat conducting member 22 is installed so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the fixing nip N, and is heated by the radiant heat of the heater 25 to heat (heat transfer) the fixing belt 21. . As a material of the metal heat conductor 22, a metal pipe material having heat conductivity such as aluminum, iron, stainless steel or the like can be used. As shown in FIG. 3, both ends of the heat conducting member 22 in the width direction are fixedly supported on the side plates 43 of the fixing device 20 via the supporting members 41.

  Even if the apparatus is speeded up because the fixing belt 21 is heated over a wide range in the circumferential direction without locally heating only a part of the fixing belt 21 by the heat conducting member 22. The fixing belt 21 is sufficiently heated, and the occurrence of fixing failure can be suppressed.

  Further, in order to improve the heating efficiency of the fixing belt 21, even when the heat conducting member 22 is thinned, the heat conducting member 22 is provided separately from the nip forming member 23 that receives pressure from the pressure roller 31. Therefore, problems such as the heat conduction member 22 bending and the inner peripheral surface of the fixing belt 21 rubbed strongly, and problems such as the heat conduction member 22 bending and the driving torque of the fixing belt 21 increasing are suppressed. Is done.

  As described above, according to the fixing device 20 of the first embodiment, the fixing belt 21 is heated over a wide area on the inner periphery. Therefore, even when the speed of the device is increased, the fixing belt 21 is sufficiently heated and fixed. The occurrence of defects can be suppressed. Therefore, since the fixing belt 21 can be efficiently heated with a relatively simple configuration, the warm-up time and the first print time are shortened, and the size of the apparatus is reduced.

  The difference in outer diameter between the fixing belt 21 and the heat conducting member 22 is preferably within 1 mm. As a result, the area in which the heat conducting member 22 and the fixing belt 21 are in sliding contact with each other is increased, thereby preventing a problem that the wear of the fixing belt 21 increases, and the heat conducting member 22 and the fixing belt 21 are separated too much. A problem that the heating efficiency of the fixing belt 21 is reduced can be suppressed.

  Furthermore, since the heat conducting member 22 is disposed in the vicinity of the fixing belt 21 so that the circular posture of the flexible fixing belt 21 is maintained to some extent, deterioration / breakage due to deformation of the fixing belt 21 is reduced. can do.

  It is also conceivable that the sliding surface of the heat conducting member 22 is made of a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the heat conducting member 22 and the fixing belt 21 are in sliding contact. .

  The pressure roller 31 has a diameter of 30 mm in this example, and presses against the fixing belt 21 to form a desired fixing nip N between the pressure roller 31 and the fixing belt 21.

  The pressure roller 31 has a configuration in which an elastic layer 33 is formed on a hollow cored bar 32. The elastic layer 33 of the pressure roller 31 is made of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. A thin release layer made of a resin material such as PFA or PTFE may be provided on the surface layer of the elastic layer 33.

  Further, when the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the fixing nip N can be reduced, and thus the heat conduction member 22 is generated. The bending can be further reduced.

  As shown in FIG. 3, both ends of the pressure roller 31 are rotatably supported on the side plate 43 of the fixing device 20 via bearings 42, and a drive (not shown) is provided at the end of the pressure roller 31. A gear 45 that meshes with the drive gear of the mechanism is provided, and is driven to rotate in the direction of the arrow (counterclockwise) in FIG.

  Further, a heat source such as a halogen heater can be provided inside the pressure roller 31.

  In the first embodiment, the diameter of the fixing belt 21 is made equal to the diameter of the pressure roller 31. However, the diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 31. . In that case, since the curvature of the fixing belt 21 in the fixing nip N is smaller than the curvature of the pressure roller 31, the recording medium P sent out from the fixing nip N is easily separated from the fixing belt 21.

  The heat leveling member 26 is installed on the inner peripheral surface of the heat conducting member 22 and at a position facing the heater 25 with the reinforcing member 24 interposed therebetween, and as shown in FIG. 20 side plates 43 are fixed.

  In the first embodiment, a heat pipe capable of rapidly transporting a large amount of heat energy using a latent heat of evaporation / condensation despite a slight temperature difference is used as the thermal leveling member 26. The heat pipe is a heat conduction element in which a working fluid is sealed in a pipe, and is a good heat conductor having a heat conductivity several hundred times that of copper having a high heat conductivity.

  The shape of the surface on which the heat leveling member 26 is installed opposite to the heat conducting member 22 is a shape along the side surface of the heat conducting member 22, and the contact area between the heat conducting member 22 and the heat leveling member 26 is increased. By doing so, good thermal conductivity is obtained.

  In FIG. 2, guide plates 35 and 37 are provided on the upstream side and the downstream side of the fixing nip N in the recording medium conveyance direction. A guide plate 35 (entrance guide plate) for guiding the recording medium P conveyed toward the fixing nip N is disposed on the upstream side, and the recording medium P sent out from the fixing nip N is guided on the downstream side. A guide plate 37 (exit guide plate) is provided. Both guide plates 35 and 37 are fixed to the side plate 43 of the fixing device 20.

  Next, the operation of the fixing device having the above configuration will be described.

  When the power switch of the apparatus main body 1 is turned on, electric power is supplied to the heater 25, and rotation driving of the pressure roller 31 in the direction of the arrow in FIG. As a result, the fixing belt 21 is driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31.

  Thereafter, as described above, the recording medium P is fed from the paper feeding units 12 to 14, and the toner image is developed on the recording medium P by the developing unit 4. The recording medium P on which the toner image T is formed is guided by the guide plate 35 and conveyed in the direction of the arrow Y10 in FIG. 2, and is sent to the fixing nip N between the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. Is done.

  At the fixing nip N, the surface of the recording medium P is heated by the fixing belt 21 heated by the heat conducting member 22 and the pressure of the nip forming member 23 supported and reinforced by the reinforcing member 24 and the pressure roller 31. The toner image T is fixed. Thereafter, the recording medium P is sent out from the fixing nip N and conveyed in the direction of the arrow Y11.

  In the conventional fixing device, the temperature at the non-sheet passing portion of the fixing belt 21 when the recording medium is continuously fed as the recording medium, particularly in the case of an envelope or A4 portrait and letter portrait size, during the above-described fixing operation. Rises excessively, and the toner image T on the recording medium P is offset to the fixing belt 21, so that a good fixed image cannot be obtained. Furthermore, if the non-sheet passing portion temperature of the fixing belt 21 rises excessively, a large temperature gradient is locally generated in the temperature distribution of the fixing belt 21, causing a problem that the fixing belt 21 is damaged. It was necessary to reduce the throughput of the fixing device.

  Therefore, in the first embodiment, in order to solve the above-described problem, for the purpose of suppressing an excessive increase in the temperature of the non-sheet passing portion of the fixing belt 21 when continuously passing a small-size recording material as a recording medium, As shown in FIG. 2, the heat leveling member 26 is disposed opposite to the heat conducting member 22.

  FIG. 4 is an explanatory diagram showing the temperature distribution in the longitudinal direction (axial direction) of the fixing belt when the envelope is continuously fed in the first embodiment.

  In FIG. 4, when the heat leveling member 26 for assisting heat conduction is not provided, the temperature distribution of the fixing belt 21 is as shown by the curve A in FIG. 4, and the temperature of the non-sheet passing portion is increased. When an unfixed toner image on a recording material having a width wider than that of the envelope, for example, A3 size or letter size paper, is fixed immediately after the envelope is continuously passed, The toner corresponding to the non-sheet passing portion is offset to the fixing belt 21.

  Further, the temperature of the non-sheet passing portion of the fixing belt 21 may rise excessively, and the fixing belt 21 itself may be damaged.

  For this reason, in the conventional fixing device, in order to avoid an excessive temperature rise in the non-sheet passing portion, it is necessary to reduce the throughput of the fixing device.

  On the other hand, when the thermal leveling member 26 is disposed opposite to the inner surface of the heat conducting member 22 as in the fixing device of the present embodiment, the temperature of the non-sheet passing portion of the fixing belt 21 increases due to the continuous sheet passing of the envelope. Even if it starts, the heat | fever by the temperature rise of a non-sheet passing part can be transferred to the sheet passing area by the heat leveling member 26, so that the temperature distribution shown in the curve B of FIG. It is possible to prevent the temperature from reaching the toner offset region.

  For this reason, even if a large size paper such as A3 size or letter size is passed immediately after continuous envelope feeding, toner offset does not occur, and at the same time, damage to the fixing device due to excessive temperature rise can be prevented.

  By the way, when the heat leveling member 26 is at a low temperature, heat is taken away from the fixing belt 21 through the heat conducting member 22, so that the temperature rise of the fixing belt 21 is delayed. For this reason, in the image forming apparatus, even when it is necessary to perform image formation (printing) promptly from the standby state, when the temperature of the heat leveling member 26 is low, the temperature of the fixing belt 21 decreases. As a result, an image defect or a waiting time until the temperature of the fixing belt 21 rises occurs.

  Here, the standby state (standby state) means a state in which the fixing device is partially warmed and held so that the user can print quickly.

  In general, if the fixing belt 21 in the standby state is kept rotating, the life of the fixing belt 21 is greatly impaired, so that the fixing belt 21 is held in a rotation stopped state. Therefore, it is necessary to keep the thermal leveling member 26 at a high temperature even in the standby state, that is, the state where the fixing belt 21 is not rotated.

  As shown in FIG. 2, the heat leveling member 26 is installed so as to face and contact the inner peripheral surface of the heat conducting member 22, and there is no gap or another member between the heat conducting member 22, so that the heat resistance The temperature of the heat leveling member 26 rises due to heat conduction from the heat conducting member 22.

  Further, since the reinforcing member 24 absorbs the heat of the heater 25 and the temperature rises, the temperature of the thermal leveling member 26 is also affected by radiant heat from the reinforcing member 24 and convective heat transfer of air heated by the reinforcing member 24. To rise.

  Further, since the heat conducting member 22 is installed inside the fixing belt 21 with a small gap, and the convection of the air sandwiched between the heat conducting member 22 and the fixing belt 21 is limited, The heat radiation amount on the outer peripheral surface of the conductive member 22 is kept small. Therefore, the temperature of the entire circumference of the heat conducting member 22 can be kept high. As described above, the temperature of the heat leveling member 26 can be kept high even in the standby state.

  Here, when the heat leveling member 26 is installed on the inner peripheral surface of the heat conducting member 22 and at a position where it is directly heated from the heater 25, the warm-up time is significantly increased. That is, since the heat generated from the heater 25 is used as it is for increasing the temperature of the heat leveling member 26, the temperature rise of the heated surface of the heat conducting member 22 is delayed.

  Therefore, in order to minimize the delay of the warm-up time due to the installation of the heat leveling member 26, the heat leveling member 26 is located on the inner peripheral surface of the heat conducting member 22 and at a position not directly heated from the heater 25. Need to be installed. Even at a position where the heater 25 is not directly heated, the temperature rises slowly during the standby state due to heat conduction from the heat conduction member 22, radiation heat from the reinforcing member 24, and convection heat transfer as described above.

  Further, as described above, the fixing belt 21 needs to form an elastic layer in order to uniformly transmit heat to the toner image T on the recording medium P and suppress the generation of a scum skin image. This elastic layer is formed of a rubber material, and its thermal conductivity is significantly worse than that of metal. On the other hand, if the thickness is increased in order to increase the thermal conductivity, the heat capacity of the fixing belt 21 increases and the warm-up time becomes longer. Furthermore, the outer peripheral surface of the fixing belt 21 has a large amount of heat released to the air, and the temperature greatly decreases as the distance from the heating source increases. Therefore, the effect of warming the thermal leveling member 26 by heat conduction from the fixing belt 21 cannot be expected in the standby state.

  FIG. 5 shows a change in time after the warm-up of the fixing device is completed and a transition to the standby state and a temperature of the heat leveling member.

  When the thermal leveling member 26 is brought into contact with the fixing belt 21, the temperature of the thermal leveling member 26 decreases with time after the transition to the standby state, as shown by a curve A in FIG. . When the heat leveling member 26 is fixed to the inner peripheral surface of the heat conducting member 22, the temperature of the heat leveling member 26 increases with time after shifting to the standby state, as shown by a curve B in FIG. Can be maintained at a temperature necessary to prevent the temperature of the fixing belt 21 from decreasing.

  As described above, it is possible to perform printing in a state in which a good fixing can be promptly performed even from the standby state (standby state) while the thermal leveling member 26 is provided.

  In the first embodiment, since the reinforcing member 24 is formed of a metal heat conductor such as stainless steel or iron, the reinforcing member 24 stores heat from the heater 25 during a printing operation. Thereby, even when the printing operation is completed and the heater 25 is turned off, the heat conducting member 22 and the heat leveling member 26 receive the heat stored in the reinforcing member 24 and receive the heat conducting member 22 and the heat leveling. Since the temperature drop of the member 26 slows down, the warm-up time when the printing operation is resumed can be shortened.

  More specifically, in this embodiment, the reinforcing member 24 that shields the heat from the heater 25 and has directivity in the heating direction of the heater 25 inside the heat conducting member 22, and is not directly heated from the heater 25. By providing the thermal leveling member 26 made of a material having a higher thermal conductivity than the thermal conductive member 22 provided in the region, the thermal leveling member 26 is provided in the region that is not directly heated from the heater 25, The heat leveling member 26 can prevent the heat from the heater 25 from being excessively deprived, the heat leveling member 26 can be uniformly heated by the heat leveling member 26, and the warm-up time is short. In addition, the fixing process from the standby state can be executed quickly.

  FIG. 6 is a front cross-sectional view illustrating a main part of the fixing device according to the second exemplary embodiment.

  In the following description, members corresponding to those in the first embodiment described with reference to FIG.

  The fixing device according to the second embodiment is different from the configuration according to the first embodiment in that a composite of a sheet-like member 27 and a hard magnetic member 28 is used as the thermal leveling member 26.

  In this example, a graphite sheet is used as the sheet-like member 27. The graphite sheet is obtained by processing graphite into a sheet shape, and has a very high in-plane thermal conductivity, a low specific gravity and a small heat capacity, and is therefore suitable as a heat leveling member. Furthermore, since it is flexible, it can be attached along the inner peripheral surface of the heat conducting member 22 and the contact area can be increased.

  Further, as the hard magnetic member 28, an inexpensive and easy-to-mold ferrite magnet is used, and nickel, which is a soft magnetic material, is used as the base material of the fixing belt 21 facing the hard magnetic member 28.

  As shown in FIG. 6, the magnetic force generated from the hard magnetic material 28 acts on the soft magnetic material constituting the fixing belt 21, so that the fixing belt 21 is attracted toward the heat conducting member 22. Therefore, a state in which the fixing belt 21 and the heat conducting member 22 are always in stable contact is obtained, and the heat of the fixing belt 21 is easily transmitted to the sheet-like member 27 through the heat conducting member 22, thereby enhancing the effect of heat leveling. Can do.

  FIG. 7 is an explanatory diagram showing the temperature distribution in the longitudinal direction of the fixing belt when the envelope is continuously fed in the second embodiment.

  When the hard magnetic material 28 according to the second exemplary embodiment is not provided, the temperature distribution of the fixing belt 21 becomes a curve A shown in FIG. 7, and the temperature of the non-sheet passing portion rises and enters the toner offset region. .

  On the other hand, when the hard magnetic material 28 is provided, the effect of thermal leveling by the sheet-like member 27 is enhanced, and the temperature of the non-sheet passing portion reaches the toner offset region as shown by a curve B shown in FIG. Can be prevented.

  FIG. 8 is a front cross-sectional view showing the main part of the fixing device according to the third embodiment.

  In the fixing device according to the third embodiment, the heat conduction member 22 in the fixing nip N portion is formed with a concave portion 22a that is recessed inward, and the nip forming member 23 is installed in the concave portion 22a via a heat insulating member 29, and the reinforcement is performed. The configuration of the first embodiment is different from that of the first embodiment in that the end portion of the member 24 is installed so as to press the nip forming member 23 through the recess 22a and the heat insulating member 29 and to extend to the inner central portion of the fixing belt 21.

  Also in the fixing device having the configuration of the third embodiment, the same operation and effect can be obtained by installing the thermal leveling member 26 of the above-described embodiment.

  In the third embodiment, the heat conducting member 22 that contacts or faces the inner peripheral surface of the fixing belt 21 and holds and heats the fixing belt 21 is formed by bending a thin metal plate into a pipe shape. Yes. As a result, the manufacturing cost is relatively low, the heating efficiency of the fixing belt 21 is increased, the warm-up time and the first print time are short, and even when the apparatus is speeded up, fixing failure or the like occurs. Can be deterred.

  However, in the heat conducting member 22, as shown in FIG. 8, if the side end portion 22b of the recessed portion 22a after bending is left open, a springback occurs as shown in FIG. The side end portion 22b tends to open, causing uneven contact and uneven contact pressure with the fixing belt 21.

  Therefore, for the side end portion 22b of the heat conducting member 22, it is necessary to make at least a part of the width direction (axial direction) of the heat conducting member 22 into a joined state so that the side end portion 22b is not opened by the springback. There is. For example, it can be considered that the side end portion 22b is joined by welding.

  Further, in the heat conducting member 22 shown in FIG. 8, when the corner 22c and the vicinity thereof in the recess 22a come into contact with the pressure roller 31 via the fixing belt 21, the heat conducting member 22 is deformed (particularly, the pressure roller). The contact unevenness between the fixing belt 21 and the heat conducting member 22 is likely to occur.

  Therefore, in this example, the heat conducting member 22 is configured not to contact the pressure roller 31 via the fixing belt 21 including the corner portion 22c. Specifically, the corner portion 22c of the heat conducting member 22 is set to be located away from the vicinity of the nip portion N with respect to the pressure roller 31.

  In the present embodiment, the present invention is applied to a fixing device using the pressure roller 31 as a pressure member. However, the present invention is also applied to a fixing device using a pressure belt or a pressure pad as the pressure member. The present invention can be applied. In this case, the same effect as that of the present embodiment can be obtained.

  In the present embodiment, the heat conducting member 22 is formed so that the cross-sectional shape thereof is substantially circular. However, the heat conducting member 22 may be formed so that the cross-sectional shape thereof is polygonal, or the heat conducting member 22. It is also possible to provide a slit on the peripheral surface.

  In this embodiment, the fixing belt 21 having a multilayer structure is used as the fixing member. However, an endless fixing film made of polyimide resin, polyamide resin, fluorine resin, metal, or the like can be used as the fixing member. In this case, the same effect as that of the present embodiment can be obtained.

  The present invention can be applied to a fixing device for fixing a toner image, and a fixing unit in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine including the fixing device.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 20 Fixing apparatus 21 Fixing belt (fixing member)
22 heat conduction member 23 nip forming member 24 reinforcing member (supporting member)
25 Heater (heating member)
26 Thermal equalization member 31 Pressure roller (Pressure member)
N fixing nip

JP-A-4-44075 JP 2008-154822 A JP 2001-66933 A

Claims (10)

A fixing member;
A heat conducting member provided inside the fixing member;
A heating member that is provided inside the heat conducting member and heats the heat conducting member;
A nip forming member that is installed opposite to the pressure member via the fixing member and forms a fixing nip between the fixing member and the pressure member;
A support member provided inside the heat conducting member and supporting the nip forming member;
A thermal leveling member provided in contact with an inner surface of the heat conducting member in a region different from a region where the heating member is disposed among regions divided by the support member in the heat conducting member;
A fixing device comprising:   The fixing device according to claim 1, wherein the thermal leveling member is a member made of a material having a thermal conductivity larger than that of the thermal conductive member.   The fixing device according to claim 1, wherein the support member is a member that blocks heat from the heating member and has directivity in a heating direction of the heating member.   The fixing device according to claim 1, wherein the heat conducting member is made of a metal pipe material.   The curvature of the side facing the said heat conductive member in the said heat | fever equalization member is set substantially equal to the curvature of the internal peripheral surface of the said heat conductive member, The any one of Claims 1-4 characterized by the above-mentioned. Fixing device.   The fixing device according to claim 1, wherein the heat leveling member is formed of a member including a hard magnetic material, and the fixing member is formed of a member including a soft magnetic material.   The fixing device according to claim 1, wherein the heat leveling member includes a member including a heat pipe.   The fixing device according to claim 1, wherein the thermal leveling member is formed of a member including a graphite sheet.   The fixing device according to claim 1, wherein the fixing member is an endless belt-like member having flexibility.   An image forming apparatus comprising: an image forming unit that forms an image on a recording medium; and a fixing unit that performs a fixing process on a recording medium on which an image is formed by the image forming unit. An image forming apparatus comprising the fixing device according to any one of Items 1 to 9.

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