JP2021105670A - Fixing device and image forming apparatus - Google Patents

Abstract

To prevent, with a simpler configuration, temperature unevenness of a fixing belt that occurs when a resistance heating element has a plurality of heating areas in a longitudinal direction and corresponds to the boundary parts between the heating areas.SOLUTION: An image forming apparatus (100) comprises: a plate-like heater (82) that extends in a longitudinal direction; a holder (83) that supports the heater (82); a fixing belt (81) that rotates while sliding its inner peripheral surface on a surface of the heater (82); and a pressure roller that is in pressure contact with the surface of the heater (82) with the fixing belt (81) therebetween to form a fixing nip. A resistance heating element (82B) provided on the heater (82) has a first heating area (R1) and a second heating area (R2) that is arranged adjacent to the first heating area (R1) in the longitudinal direction. A support surface (83A) of the holder (83) supporting the heater (82) is provided with concave parts (83D) for accommodating heat insulating material at positions corresponding to the boundary parts between the first heating area (R1) and the second heating area (R2) in the longitudinal direction.SELECTED DRAWING: Figure 6

Description

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

As one type of fixing device used in an electrophotographic image forming apparatus, there is a type in which a fixing belt having a low heat capacity and a thin wall is heated by an elongated plate-shaped heater provided with a resistance heating element on a base material. The heater is supported by the holder so as to cover the back surface, and is arranged inside the fixing belt. The fixing belt rotates while sliding the inner peripheral surface on the surface of the heater. On the outside of the fixing belt, a pressurizing body that presses against the surface of the heater via the fixing belt to form a fixing nip is arranged. The pressurizing body often has a rotating function, and rotates the fixing belt while sliding it on the surface of the heater. By passing the recording material to which the developer image is transferred through the fixing nip, the developer image is fixed on the recording material.

In such a type of fixing device, when a recording material having a width smaller than the maximum size recording material that can be passed is passed, the temperature of the non-passing portion of the heater rises compared to the temperature of the passing portion. .. This is because, in many cases, the temperature of the heater is controlled based on the temperature of the paper-passing part, and the temperature of the non-paper-passing part where the recording material does not take heat is higher than that of the paper-passing part. ..

An increase in the temperature of the non-paper-passing portion causes deterioration or damage of parts such as a heater and a pressurizing body. Further, if a large-sized recording material is passed while the temperature of the non-passing portion is greatly increased, a high temperature offset may occur at the end of the recording material that has passed through the non-passing portion.

In Patent Document 1, in order to prevent such a temperature rise of a non-passing portion, a resistance heating element of a heating element (corresponding to a heater) is made of a material having a negative resistance temperature characteristic, and further, this resistance A configuration is disclosed in which a heating element is divided into three or more portions in the longitudinal direction. The resistance heating element is divided into a plurality of blocks corresponding to a plurality of heat generating regions, and there is a gap between the blocks. Each block is supplied with a current so as to flow in the transport direction of the recording material, and each block is electrically connected in series. In such a configuration, the calorific value of the block corresponding to the non-passing paper portion where the temperature has increased becomes smaller than the calorific value of the block corresponding to the non-passing paper portion whose temperature has decreased due to the heat removal of the recording material. , It is possible to prevent the temperature rise of the non-passing paper part.

Further, Patent Document 1 also discloses a configuration in which the resistance of the resistance heating element in the vicinity of the gap portion is increased in order to compensate for the decrease in the calorific value of the gap portion between the blocks. This is because the temperature of the fixing belt may drop at the portion sliding in the gap portion where the resistance heating element does not exist, and the fixing property may be worse than the other portions.

Japanese Unexamined Patent Publication No. 2007-25474

In the configuration disclosed in Patent Document 1, in a configuration in which the resistance heating element has a plurality of heat generation regions, the resistance of the resistance heating element in the vicinity of the gap portion between the blocks is increased to compensate for the decrease in the heat generation amount in the gap portion. ing. However, in order to partially increase the resistance of the resistance heating element, it is necessary to make the sheet resistance higher than the other parts or to reduce the thickness of the resistance heating element. Therefore, the configuration is complicated as compared with a configuration having a resistance heating element having a uniform sheet resistance or a resistance heating element having a uniform thickness.

Further, although there is no gap portion, even when the heat generation amount of the resistance heating element is different in the longitudinal direction to have a plurality of heat generation regions, the temperature of the fixing belt is at the boundary portion between the heat generation regions when the fixing device is started up. Depression occurs. This is because heat is transferred from a region having a high calorific value to a region having a low calorific value. At the boundary portion of the high calorific value region, the temperature drops as compared with the other portion of the high calorific value region.

As described above, when the resistance heating element has a plurality of heat generating regions regardless of the presence or absence of the gap portion, the temperature of the fixing belt drops corresponding to the boundary portion between the heat generating regions. When the heat generating regions are lined up in the longitudinal direction, the temperature of the fixing belt may be uneven in the longitudinal direction due to such a drop, and may appear as streaky fixing unevenness along the conveying direction, which may be conspicuous. ..

One aspect of the present invention is a fixing device having a simpler configuration and capable of suppressing temperature unevenness of a fixing belt corresponding to a boundary portion between heat generating regions, which occurs when the resistance heating element has a plurality of heat generating regions in the longitudinal direction. The purpose is to provide.

In order to solve the above-mentioned problems, in the fixing device according to one aspect of the present invention, a plate-shaped heater having a resistance heating element on a base material and extending in the longitudinal direction, supporting the heater, and the heater. A holder that covers the back surface, a fixing belt that rotates while sliding an inner peripheral surface on the surface of the heater, and a pressurizing body that presses against the surface of the heater via the fixing belt to form a fixing nip. The resistance heating element has a first heating region and a second heating region arranged adjacent to the first heating region in the longitudinal direction, and the holder faces the back surface of the heater. The support surface has a support surface for supporting the heater, and the support surface is provided with a recess for accommodating a heat insulating material at a position corresponding to a boundary portion between the first heat generation region and the second heat generation region in the longitudinal direction. It is characterized by being.

According to the above configuration, the resistance heating element has a first heat generating region and a second heat generating region arranged adjacent to the first heat generating region in the longitudinal direction. That is, the resistance heating element has a plurality of heat generating regions in the longitudinal direction. When the resistance heating element has a plurality of heat generating regions in the longitudinal direction, the temperature unevenness of the fixing belt corresponding to the boundary portion of the heat generating region becomes remarkable, such as when the fixing device is started up, and the streaky fixing along the conveying direction. It may become uneven and stand out.

However, according to the above configuration, a recess for accommodating the heat insulating material is provided at a position corresponding to the boundary portion between the first heat generating region and the second heat generating region on the support surface of the holder. By providing such a recess, the heat insulating effect of the holder in the portion corresponding to the boundary portion can be enhanced as compared with the other portions. As a result, the temperature drop of the fixing belt corresponding to the boundary portion between the heat generating regions that appears prominently when the fixing device is started up is suppressed, and the fixing property can be improved.

Moreover, in the above configuration, it is possible to suppress the temperature drop of the fixing belt corresponding to the boundary portion between the heat generating regions only by processing the holder side. Therefore, the configuration can be simplified as compared with the configuration in which the sheet resistance of the resistance heating element is partially increased or the thickness of the resistance heating element is partially reduced.

Therefore, it is possible to provide a fixing device capable of suppressing temperature unevenness of the fixing belt corresponding to the boundary portion between the heat generating regions, which occurs when the resistance heating element has a plurality of heat generating regions in the longitudinal direction with a simpler configuration. Can be done.

In the fixing device according to one aspect of the present invention, the first heat generation region and the second heat generation region are further arranged at intervals in the longitudinal direction, and the recess is the first heat generation region. The configuration may be provided at a position corresponding to the gap portion between the second heat generating regions.

With the above configuration, when there is a gap between the first heat generation region and the second heat generation region, the temperature drop of the fixing belt due to the gap portion is suppressed by the recess provided at the position corresponding to the gap portion. be able to.

In the fixing device according to one aspect of the present invention, the heat generation amount of the second heat generation region is smaller than the heat generation amount of the first heat generation region, and the recess is the first heat generation region in the second heat generation region. Can also be configured to extend in the longitudinal direction to the position of the end on the side opposite to the adjacent side.

According to the above configuration, the heat generation amount in the second heat generation region is smaller than the heat generation amount in the first heat generation region. If there is such a difference in the amount of heat generated, the temperature rise of the fixing belt at the time of starting up the fixing device will be delayed in the portion corresponding to the second heat generating region where the calorific value is small compared to the portion corresponding to the first heat generating region. , Temperature unevenness occurs.

However, according to the above configuration, the recess extends in the longitudinal direction to the position of the end portion of the second heat generation region on the side opposite to the side adjacent to the first heat generation region. By extending the recess so as to cover the second heat generation region in this way, the heat insulating effect of the holder in the portion corresponding to the second heat generation region can be enhanced as compared with the other portions. As a result, temperature unevenness at startup can also be suppressed.

In the recess, after the temperature of the fixing belt in the portion corresponding to the second heat generation region catches up with the temperature in the portion corresponding to the first heat generation region, the temperature rise in the corresponding portion in the second heat generation region where the calorific value is small. Contribute to.

The fixing device according to one aspect of the present invention may further have a structure in which the base material is made of metal.

Further, the fixing device according to one aspect of the present invention is configured such that the pressurizing body is a pressurizing roller having a core metal extending in the longitudinal direction and an elastic layer provided on the core metal. You can also do it.

In order to solve the above-mentioned problems, the image forming apparatus according to one aspect of the present invention includes the fixing device according to one aspect of the present invention, and the developer image transferred to the recording material by the image forming unit is displayed. It is passed through the fixing nip of the fixing device and fixed to the recording material.

According to one aspect of the present invention, with a simpler configuration, it is possible to suppress temperature unevenness of the fixing belt corresponding to the boundary portion between the heat generating regions, which occurs when the resistance heating element has a plurality of heat generating regions in the longitudinal direction. A fixing device can be provided.

It is sectional drawing which shows the structure of the image forming apparatus which concerns on one Embodiment of this invention. It is a perspective view of the fixing device mounted on the image forming apparatus shown in FIG. It is sectional drawing of the fixing device shown in FIG. It is an exploded view of the heater part arranged inside the fixing belt in the fixing device shown in FIG. It is the bottom view of the holder and the bottom view of the heater in the heater part shown in FIG. It is sectional drawing of the main part of the fixing device shown in FIG. It is the bottom view of the holder and the bottom view of the heater in the heater part of the fixing device mounted on the image forming apparatus which concerns on another embodiment of this invention. FIG. 7 is a schematic cross-sectional view of a main part of the fixing device shown in FIG. 7. It is the bottom view of the holder and the bottom view of the heater in the heater part of the fixing device mounted on the image forming apparatus which concerns on still another Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

1. 1. Overall Configuration of Image Forming Device The configuration of the electrophotographic image forming apparatus 100 will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is a monochrome printer having only one set of image forming units described later, but the present invention is not limited to a monochrome printer, and is also applied to a color printer. be.

As shown in FIG. 1, the image forming apparatus 100 includes a photoconductor 1, a charging apparatus 2, an exposure apparatus 3, a developing apparatus 4, a transfer apparatus 5, a cleaning apparatus 6, a pickup roller 71, and a plurality of transport roller pairs 72 to 75. It includes a fixing device 8, a paper feed tray 9, and a paper output tray 10.

The photoconductor 1 has a raw tube made of a conductive metal such as aluminum, and a photosensitive layer provided on the outer peripheral surface of the raw tube. The photoconductor 1 is an organic photoconductor (OPC), and is a photosensitive drum having a positively charged photosensitive layer having a positive polarity of an image forming potential. The photosensitive layer of the photoconductor 1 is charged by the charging device 2 while rotating, and is exposed by the laser beam from the exposure device 3, to form an electrostatic latent image on the surface. The photosensitive member 1 may be a photosensitive belt in which a photosensitive layer is provided on the outer peripheral surface of a metal annular belt.

The charging device 2 is a device that charges the surface of the photoconductor 1, for example, a charging roller that charges the photoconductor 1 in contact with the photoconductor 1, a scorotron charger that charges the photoconductor 1 in a non-contact manner, and the like. The exposure apparatus 3 is an apparatus for exposing the charged surface of the photoconductor 1. The exposure apparatus 3 has, for example, a plurality of light emitting elements arranged in a line along the direction of the rotation axis of the photoconductor 1, and emits light according to print data to cause static electricity on the surface of the photoconductor 1. Form a latent image.

The developing device 4 is a device that supplies a developing agent to an electrostatic latent image formed on the surface of the photoconductor 1, and includes, for example, a developing roller and a developing container containing the developing agent. The transfer device 5 is a device that transfers the developer image formed on the surface of the photoconductor 1 to the recording material 15, for example, a transfer roller. The recording material includes recording paper, OHP, envelopes, thick paper, and the like. The cleaning device 6 is a device for removing the developer remaining on the photoconductor 1 and the paper dust adhering to the photoconductor 1 from the photoconductor 1, for example, a cleaning roller.

The photoconductor 1, charging device 2, exposure device 3, developing device 4, transfer device 5, and cleaning device 6 constitute an image forming unit that forms a developer image according to print data and transfers it to a recording material. Will be done.

The fixing device 8 is a device that fixes the developer image transferred to the recording material 15 to the recording material 15 by heat and pressure. Details of the fixing device 8 will be described later. The paper feed tray 9 is a tray on which the recording material 15 before printing is placed, and the paper ejection tray 10 is a tray on which the recording material 15 after printing is discharged and placed.

The pickup roller 71 is a roller that feeds the recording material 15 one by one from the paper feed tray 9. Each of the plurality of transport roller pairs 72, 73, 74, and 75 is a roller pair that transports the recording material 15 fed by the pickup roller 71 to the paper output tray 10 along the transport path 16. The transport path 16 passes between the photoconductor 1 and the transfer device 5 and through the fixing nip N (see FIG. 3) of the fixing device 8 which will be described later.

Although not shown, the image forming apparatus 100 includes a control unit including an ASIC (Application Specific Integrated Circuit) or the like. The control unit controls the operation of each of the above-mentioned parts in the image forming apparatus 100.

2. Explanation of Operation of Image Forming Device A series of image forming processes by the image forming apparatus 100 configured as described above will be briefly described with reference to FIG. The image forming apparatus 100 starts the printing process when the print data is received from an information terminal device such as a personal computer or an image reading device for reading a document. As a result, the surface of the photoconductor 1 is uniformly positively charged by the charging device 2 as it rotates. Then, the laser beam is irradiated from the exposure apparatus 3 toward the photoconductor 1. As a result, a predetermined electrostatic latent image corresponding to the print data is formed on the surface of the photoconductor 1. That is, on the surface of the uniformly positively charged photoconductor 1, the potential of the portion irradiated with the laser beam is lowered.

Next, the rotation of the developing roller of the developing device 4 supplies the developer supported on the developing roller and positively charged to the electrostatic latent image formed on the surface of the photoconductor 1. As a result, the electrostatic latent image of the photoconductor 1 is developed, and the developer image by reverse development is supported on the surface of the photoconductor 1.

Further, in parallel with the process for forming the developer image described above, a process for transporting the recording material 15 is performed. That is, the rotation of the pickup roller 71 causes the recording materials 15 to be sent out one by one from the paper feed tray 9 to the transport path 16. The recording material 15 sent out to the transfer path 16 is transported by the transfer roller pairs 72 and 73 to the transfer position where the photoconductor 1 and the transfer device 5 come into contact with each other.

Then, when passing through the transfer position, the developer image supported on the surface of the photoconductor 1 is transferred to the surface of the recording material 15 by the transfer bias applied to the transfer device 5. The transferred developer image is thermally fixed to the recording material 15 when passing through the fixing nip N (see FIG. 3) of the fixing device 8 located on the downstream side of the transfer path 16 from the transfer position. After that, the recording material 15 is discharged onto the paper discharge tray 10 by the transport roller pairs 74 and 75.

3. 3. Configuration of Fixing Device Next, the configuration of the fixing device 8 will be described with reference to FIGS. 2 to 6.

FIG. 2 is a perspective view of the fixing device 8 mounted on the image forming apparatus 100 shown in FIG. 1, and FIG. 3 is a cross-sectional view of the fixing device 8. FIG. 4 is an exploded view of a heater portion arranged inside the fixing belt in the fixing device. FIG. 5 is a bottom view of the holder 83 and a bottom view of the heater 82 in the heater section. FIG. 6 is a schematic cross-sectional view of a main part of the fixing device 8.

As shown in FIGS. 2 and 3, the fixing device 8 includes a fixing belt 81, a heater 82, a holder 83, a pressure roller 84, and a stay 85. The fixing belt 81 is a thin-walled, low-heat capacity cylindrical member. The fixing belt 81 is made of a single-layer or composite-layer film having heat resistance, releasability, strength, durability, and the like.

The heater 82 is a heat source for fixing, and as shown in FIG. 4, has a plate shape extending in the longitudinal direction. The heater 82 includes an elongated plate-shaped base material 82A and a resistance heating element 82B provided on the base material 82A along the longitudinal direction. The longitudinal direction is a direction parallel to the rotation axis of the pressure roller 84 and a direction orthogonal to the transport direction of the recording material 15 in the fixing nip N described later. In other words, the longitudinal direction is the width direction of the recording material 15 passing through the fixing nip N.

As shown in FIGS. 4 and 5, the resistance heating element 82B has a plurality of heat generating regions in the longitudinal direction. Specifically, the resistance heating element 82B has a first heat generation region R1 and two second heat generation regions R2 and R2 arranged adjacent to the first heat generation region R1 in the longitudinal direction. The first heat generation region R1 corresponds to the passage region of the small-sized recording material 15 including the center in the longitudinal direction in the base material 82A. The second heat generation region R2 corresponds to the passage regions on both sides of the first heat generation region R1 on the end side of the recording material 15 having the maximum size that allows paper to pass. The maximum size recording material 15 passes through the first heat generation region R1 and the two second heat generation regions R2 and R2 on both sides thereof.

The heat generation amount of the second heat generation region R2 is set to be smaller than the heat generation amount of the first heat generation region R1. As a result, it is possible to reduce the amount of heat generated on the end side of the fixing belt 81, which the recording material 15 passes through only when the recording material 15 has a large size and the temperature tends to rise too much. As a result, deterioration or damage of parts such as the heater 82 and the pressure roller 84 can be prevented or reduced. In addition, a high temperature offset that occurs at the end of the large-sized recording material 15 can be avoided.

The image forming apparatus 100 of the present embodiment is a so-called center-based image forming apparatus that conveys the recording material 15 with the center in the longitudinal direction as a conveying reference. Therefore, the second heat generation region R2 is arranged on both sides of the first heat generation region R1. In the case of a so-called side-based image forming apparatus that transports the recording material 15 using one end in the longitudinal direction as a transport reference, the first heat generation region R1 and the second heat generation region R2 are arranged in this order from the transport reference end. Will be done.

Further, in the present embodiment, the first heat generation region R1 and the second heat generation region R2 are arranged at intervals in the longitudinal direction, and the first heat generation region R1 and the second heat generation region R2 are located between the first heat generation region R1 and the second heat generation region R2. There is a gap G. Although not shown, wiring and terminals for supplying power to the first heat generating region R1 and wiring and terminals for supplying power to the two second heat generating regions R2 and R2 are provided on the base material 82A. .. The terminal for supplying power to the first heat generation region R1 and the terminal for supplying power to the second heat generation regions R2 and R2 may be arranged together at one end of the base material 82A in the longitudinal direction. preferable. As a result, power can be supplied to the two circuits by connecting the harness to one end in the longitudinal direction.

Further, in the present embodiment, a metal base material, more specifically a steel base material, is used as the base material 82A. That is, the heater 82 of this embodiment is a steel heater. The heater 82 may be a ceramic heater or the like in which ceramic is used for the base material 82A.

Such a heater 82 is supported by the holder 83. The holder 83 is a member that supports the heater 82 and holds the rotation of the fixing belt 81, and is made of a resin material having heat resistance and insulating properties. In this embodiment, the holder 83 has a shallow gutter shape and has a support surface 83A on the bottom surface that supports the heater 82. The support surface 83A supports the heater 82 facing the back surface of the heater 82, that is, the surface of the base material 82A opposite to the resistance heating element 82B. The heater 82 is arranged with the surface on which the resistance heating element 82B is provided facing the outer periphery.

As shown in FIGS. 3 and 4, a plurality of upstream guide ribs 83B and a plurality of downstream guide ribs 83C for guiding the rotation of the fixing belt 81 are provided in the longitudinal direction on both sides of the support surface 83A of the holder 83 in the lateral direction. It is provided along. The lateral direction is a direction orthogonal to the longitudinal direction and the thickness direction of the heater 82. The lateral direction can also be said to be the paper transport direction at the fixing nip N. The upstream guide ribs 83B of the plurality of upstream guide ribs 83B are arranged so as to be spaced apart from each other in the longitudinal direction. Similarly, the downstream guide ribs 83C of the plurality of downstream guide ribs 83C are arranged so as to be spaced apart from each other in the longitudinal direction. The plurality of upstream guide ribs 83B are located on the upstream side of the fixing belt 81 in the rotational direction with respect to the support surface 83A.

The outer cross-sectional shape of the plurality of upstream guide ribs 83B and the plurality of downstream guide ribs 83C forms a substantially semicircular arc, and the inner peripheral surface of the fixing belt 81 slides on the outer portion. By providing a plurality of upstream guide ribs 83B and a plurality of downstream guide ribs 83C, it is possible to reduce the contact area between the holder 83 and the inner peripheral surface of the fixing belt 81, reduce friction, and improve the rotational stability of the fixing belt 81. can.

Further, the holder 83 is provided with a recess 83D for accommodating the heat insulating material at a position corresponding to the boundary portion between the first heat generating region R1 and the second heat generating region R2 in the resistance heating element 82B, that is, at the position of the gap G. .. The recess 83D is provided to suppress a drop in the temperature of the fixing belt 81 at the boundary between the first heat generation region R1 and the second heat generation region R2. This will be described later.

The stay 85 is a member for increasing the rigidity of the holder 83, and is arranged on the surface of the holder 83 opposite to the support surface 83A. If the rigidity of the holder 83 itself is high, the stay 85 may be omitted. In the present embodiment, the stay 85 is handled integrally with the holder 83 by being attached to the holder 83. Hereinafter, the holder 83, the heater 82 supported by the holder 83, the stay 85 attached to the holder 83, and the stay 85 are collectively referred to as a heater unit 86.

Such a heater portion 86 is arranged inside the fixing belt 81. In other words, the fixing belt 81 is externally fitted to the heater portion 86 with a margin in the peripheral length. The fixing belt 81 rotates while sliding the inner peripheral surface on the surfaces of the plurality of guide ribs 83B and 83C provided on the holder 83 and the heater 82.

The pressurizing roller 84 is an example of a pressurizing body, and forms a fixing nip N by pressure contacting the surface of the heater 82 via the fixing belt 81. More specifically, both ends of the pressure roller 84 are supported by a pair of side frames via bearings. Further, both ends of the stay 85 in the longitudinal direction are urged toward the pressure roller 84 by a spring. As a result, the heater 82 is pressed toward the pressure roller 84 substantially uniformly in the longitudinal direction via the stay 85, and a fixing nip N is formed between the fixing belt 81 and the pressure roller 84.

The pressure roller 84 has an elastic layer 84B made of a rubber material or the like around the core metal portion 84A. The pressure roller 84 is rotationally driven by a motor included in the image forming apparatus 100, and the fixing belt 81 is driven to rotate as the pressure roller 84 rotates.

The pressurizing body is not limited to the pressurizing roller 84, and may be composed of, for example, a pressurizing belt and a nip forming member. That is, an elastic pad, a resin-made or metal-made pressure plate, or the like is arranged as a nip-forming member in the space surrounded by the pressure belt. The nip forming member press-contacts the surface of the heater 82 via the fixing belt 81 and the pressure belt to form the fixing nip N.

4. Operation of the fixing device The pressure roller 84 is rotationally driven, and the fixing belt 81 is driven to rotate accordingly. The heater 82 is energized, the temperature of the heater 82 rises to a predetermined temperature, and the temperature is adjusted. In such a state, the recording material 15 carrying an unfixed developer image is introduced between the fixing belt 81 of the fixing nip N and the pressure roller 84. In the fixing nip N, the developer image supporting surface side of the recording material 15 is in close contact with the outer surface of the fixing belt 81, and the fixing nip N is sandwiched and conveyed together with the fixing belt 81.

In this sandwiching and transporting process, the heat of the heater 82 is applied to the recording material 15 via the fixing belt 81, and the developer image on the recording material 15 is heated and pressurized on the recording material 15 to be melt-fixed. The recording material 15 that has passed through the fixing nip N is discharged from the fixing device 8.

5. Recessed portion of holder As described above, in the present embodiment, the resistance heating element 82B of the heater 82 has a first heating region R1 located at the center in the longitudinal direction and two adjacent to the first heating region R1 in the longitudinal direction. It is provided with a second heat generation region R2. The heat generation amount of the second heat generation region R2 is set to be smaller than the heat generation amount of the first heat generation region R1. As a result, as described above, the amount of heat generated on the end side of the fixing belt 81 is reduced to prevent or reduce deterioration and damage of parts, and the high temperature offset generated at the end of the large-sized recording material 15 is avoided. can.

However. Since the portion of the gap G, which is the boundary portion between the first heat generation region R1 and the second heat generation region R2, does not generate heat, the temperature of the fixing belt 81 causes a temperature drop corresponding to the gap G. Such a drop in temperature occurs remarkably when the fixing device 8 is started up. Then, such a drop in temperature causes streaky fixing unevenness along the paper transport direction when forming an image on the large-sized recording material 15.

Therefore, in the present embodiment, in order to suppress the temperature drop of the fixing belt 81 corresponding to such a gap G, as shown in FIGS. 5 and 6, the gap G on the support surface 83A of the holder 83 is supported. A recess 83D for accommodating the heat insulating material is provided at the position. In the present embodiment, since the gaps G exist at two places in the longitudinal direction, the recesses 83D are also provided at two places in the longitudinal direction.

Air is housed in the recess 83D as a heat insulating material. Further, the recess 83D extends along the lateral direction, and is formed from one end to the other end of the support surface 83A in the lateral direction. The heat insulating material may be a material having a lower thermal conductivity than the holder 83. For example, it may be composed of artificial mineral fibers such as heat-resistant glass wool, rock wool, alkaline earth silicate wool (AES), refractory ceramic fiber (RCF), and alumina fiber. By providing such a recess 83D, the heat insulating effect of the holder 83 in the portion corresponding to the gap G of the resistance heating element 82B can be enhanced as compared with the other portions.

As a result, it is possible to prevent the temperature of the fixing belt 81 from dropping at the portion corresponding to the gap G of the resistance heating element 82B, and it is possible to suppress or prevent the fixing unevenness caused by the temperature unevenness of the fixing belt 81.

Moreover, in the above configuration, processing such as changing the line width and thickness of the resistance heating element 82B of the heater 82 is not performed, so that the configuration can be simplified.

Further, in the present embodiment, the recess 83D is composed of recesses formed on the support surface 83A, and a plurality of recesses 83D are realized by a simple configuration using air as a heat insulating material.

Further, in the present embodiment, as shown in FIG. 6, the width of the recess 83D in the longitudinal direction is set to be larger than the width of the gap G of the resistance heating element 82B in the longitudinal direction. Therefore, the recess 83D overlaps with each end of the first heat generating region R1 and the second heat generating region R2 facing each other with the gap G interposed therebetween. As a result, it is possible to more reliably suppress the temperature drop of the portion corresponding to the gap G of the resistance heating element 82B.

[Embodiment 2]
Other embodiments of the present invention will be described below. For convenience of explanation, the same reference numerals will be added to the members having the same functions as the members described in the above embodiment, and the description will not be repeated.

FIG. 7 is a bottom view of the holder 183 and a bottom view of the heater 82 in the fixing device 18 mounted on the image forming apparatus of the present embodiment. FIG. 8 is a schematic cross-sectional view of a main part of the fixing device 18. The difference between the fixing device 18 and the fixing device 8 described above is the difference between the holder 83 and the holder 183. More specifically, the recess 183D provided on the support surface 83A is different. Other configurations are the same as those of the fixing device 8.

As described above, the heat generation amount of the second heat generation region R2 is set to be smaller than the heat generation amount of the first heat generation region R1. Therefore, in the case of the fixing device 8, the temperature rise of the fixing belt 81 at the time of starting up the fixing device 8 is slower in the portion corresponding to the second heat generation region R2 having a small heat generation amount than in the portion corresponding to the first heat generation region R1. .. In such a state, when an image is formed on the large-sized recording material 15 passing through the second heat generation region R2, the fixing belt of the portion corresponding to the first heat generation region R1 and the portion corresponding to the second heat generation region R2 is formed. Fixing unevenness may occur due to the difference in temperature of 81.

Therefore, in the present embodiment, as shown in FIGS. 7 and 8, the recess 183D in the holder 183 is adjacent to the first heat generation region R1 in the second heat generation region R2 from the position corresponding to the gap G in the resistance heating element 82B. It extends in the longitudinal direction to the position of the end on the opposite side to the side to be used. That is, the recess 183D is formed to have a length that covers the entire area of the second heat generating region R2 in the longitudinal direction.

With such a configuration, the heat insulating effect of the holder 83 of the portion corresponding to the second heat generation region R2 as well as the portion corresponding to the gap G can be enhanced as compared with the other portions. As a result, it is possible to suppress temperature unevenness between the portion corresponding to the first heat generation region R1 and the portion corresponding to the second heat generation region R2 when the fixing device 18 is started up. As a result, even if an image is formed on the large-sized recording material 15 passing through the second heat generation region R2 when the fixing device 18 is started up, a good image without fixing unevenness can be obtained.

In the portion of the recess 183D that overlaps the second heat generation region R2, after the temperature of the fixing belt 81 in the portion corresponding to the second heat generation region R2 catches up with the temperature of the fixing belt 81 in the portion corresponding to the first heat generation region R1 It contributes to raising the temperature of the corresponding portion of the second heat generation region R2.

The effect of eliminating the fixing unevenness due to the delay in temperature rise of the second heat generation region R2 can be achieved by providing a recess only in the portion of the support surface 83A corresponding to the second heat generation region R2.

[Embodiment 3]
Other embodiments of the present invention will be described below. For convenience of explanation, the same reference numerals will be added to the members having the same functions as the members described in the above embodiment, and the description will not be repeated.

In the above-described first and second embodiments, as a configuration in which the resistance heating element 82B of the heater 82 has a plurality of heat generation regions, a configuration in which a gap G exists between the first heat generation region R1 and the second heat generation region R2 is exemplified. did. However, as described above, the amount of heat generated can be partially changed without providing the gap G by making the sheet resistance of the resistance heating element higher than that of other parts or by reducing the thickness of the resistance heating element. Can be done.

As shown in FIG. 9, in the present embodiment, in the fixing device 19, the resistance heating element 182B of the heater 182 has a sheet resistance higher than that of other parts, or the thickness of the resistance heating element is reduced. A first heating region R1 and two second heating regions R2 are provided. In FIG. 9, the first heat generation region R1 is hatched, and the two second heat generation regions R2 are cross-dot hatched.

Although not shown, wiring and terminals for supplying power to the resistance heating element 182B are provided on the base material 82A. In the configuration in which the heat generation region is divided by providing the gap G of the first and second embodiments, it is necessary to divide the circuit into the first heat generation region R1 and the two second heat generation regions R2 and R2. In such a resistance heating element 182B, one circuit for supplying power to the resistance heating element 182B may be provided.

In such a configuration, since there is no gap G between the first heat generation region R1 and the two second heat generation regions R2, the temperature of the fixing belt 81 does not drop in temperature corresponding to the gap G. However, as described above, heat transfer occurs from the first heat generation region R1 having a high heat generation amount to the second heat generation region R2 having a low heat generation amount. Therefore, at the boundary portion between the first heat generation region R1 having a high heat generation amount and the second heat generation region R2, the temperature of the fixing belt 81 drops as compared with the other parts of the first heat generation region R1.

Therefore, in the present embodiment, as shown in FIG. 9, a recess 83D for accommodating the heat insulating material is provided at a position corresponding to the boundary portion between the first heat generating region R1 and the second heat generating region R2. Since the temperature drop occurs at the boundary portion of the first heat generation region R1 with the second heat generation region R2, at least the recess 83D needs to be provided so as to overlap with the first heat generation region R1 at the boundary portion. More preferably, the recess 83D is provided so as to straddle the boundary portion between the first heat generation region R1 and the second heat generation region R2.

It is also possible to combine a configuration in which the first heat generation region R1 and the second heat generation region R2 are provided by partially changing the amount of heat generated, and the recess 183D described in the second embodiment.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

1 Photoreceptor (image forming part)
2 Charging device (image forming unit)
3 Exposure device (image forming unit)
4 Developing device (image forming unit)
5 Transfer device (image forming unit)
6 Cleaning device (image forming part)
8, 18, 19 Fixing device 9 Paper feed tray 10 Paper output tray 15 Recording material 16 Transport path 71 Pickup roller 72, 73, 74, 75 Transport roller pair 81 Fixing belt 82,182 Heater 82A Base material 82B, 182B Resistor heating element 83,183 Holder 83A Support surface 83B Upstream guide rib (guide rib)
83C Downstream guide rib 83D, 183D Recess 84 Pressurized roller (pressurizing body)
85 Stay 86 Heater 100 Image forming device

Claims (6)

A plate-shaped heater with a resistance heating element on the base material that extends in the longitudinal direction,
A holder that supports the heater and covers the back surface of the heater.
A fixing belt that rotates while sliding the inner peripheral surface on the surface of the heater,
A pressurizing body that presses against the surface of the heater via the fixing belt to form a fixing nip, is provided.
The resistance heating element has a first heat generation region and a second heat generation region arranged adjacent to the first heat generation region in the longitudinal direction.
The holder has a support surface that faces the back surface of the heater and supports the heater.
The fixing device is characterized in that the support surface is provided with a recess for accommodating a heat insulating material at a position corresponding to a boundary portion between the first heat generation region and the second heat generation region in the longitudinal direction. The first heat generation region and the second heat generation region are arranged so as to be spaced apart from each other in the longitudinal direction.
The fixing device according to claim 1, wherein the recess is provided at a position corresponding to a gap portion between the first heat generation region and the second heat generation region. The calorific value of the second heat generation region is smaller than the calorific value of the first heat generation region.
The recess according to claim 1 or 2, wherein the recess extends in the longitudinal direction to a position of an end portion of the second heat generating region on the side opposite to the adjacent side. Fixing device. The fixing device according to any one of claims 1 to 3, wherein the base material is made of metal. According to any one of claims 1 to 4, the pressurizing body is a pressurizing roller having a core metal extending in the longitudinal direction and an elastic layer provided on the core metal. The fixing device described. The fixing device according to any one of claims 1 to 5 is provided, and a developer image transferred to a recording material by an image forming unit is passed through the fixing nip of the fixing device and fixed to the recording material. An image forming apparatus characterized in that the image is formed.

Images