JP7419811B2 - Fixing device and image forming device - Google Patents

Description

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

One type of fixing device used in an electrophotographic image forming apparatus is a type in which a thin fixing belt with a low heat capacity is heated by a long and narrow plate-shaped heater having a resistance heating element provided on a base material. The heater is supported by a holder so that its back surface is covered, and is disposed inside the fixing belt. The fixing belt rotates while sliding its inner peripheral surface on the surface of the heater. A pressure body is disposed on the outside of the fixing belt and presses against the surface of the heater via the fixing belt to form a fixing nip. In many cases, the pressure body has a rotating function, and rotates the fixing belt while sliding it on the surface of the heater. The developer image is fixed on the recording material by passing the recording material onto which the developer image has been transferred through a fixing nip.

In this type of fixing device, when a recording material with a width smaller than the maximum size of recording material that can be passed through is passed, the temperature of the non-paper passing section of the heater rises compared to the temperature of the paper passing section. . This is because the temperature of the heater is often controlled based on the temperature of the paper passing section, and the temperature of the non-paper passing section, where heat is not absorbed by the recording material, rises compared to the paper passing section. .

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

Patent Document 1 discloses that in order to prevent such a temperature rise in the non-paper passing area, a resistance heating element of a heating element (corresponding to a heater) is made of a material having a negative resistance temperature characteristic, and furthermore, this resistance A configuration is disclosed in which the heating element is divided into three or more parts in the longitudinal direction. The resistance heating element is divided into a plurality of blocks corresponding to a plurality of heat generating areas, and gaps exist between each block. Each block is supplied with power so that a current flows in the recording material conveyance direction, and each block is electrically connected in series. In such a configuration, the amount of heat generated by the block corresponding to the non-paper passing area whose temperature has increased is smaller than the amount of heat generated by the block corresponding to the non-paper passing area whose temperature has decreased due to heat removal from the recording material. , it is possible to prevent a rise in temperature in the non-sheet passing area.

Further, Patent Document 1 also discloses a configuration in which the resistance of a resistance heating element near the gap is increased in order to compensate for a decrease in the amount of heat generated in the gap between the blocks. This is because the temperature of the fixing belt drops in the part where it slides in the gap where no resistance heating element is present, and the fixing performance may be worse than in other parts.

Japanese Patent Application 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 areas, the resistance of the resistance heating element near the gap between each block is increased to compensate for the decrease in the amount of heat generated in the gap. ing. However, in order to increase the resistance of a part of the resistance heating element, it is necessary to make the sheet resistance higher than other parts or to reduce the thickness of the resistance heating element. Therefore, the structure becomes more complicated than a structure having a resistance heating element with a uniform sheet resistance or a resistance heating element with a uniform thickness.

In addition, even though there is no gap, if the heat generation amount of the resistance heating element is varied in the longitudinal direction to provide multiple heat generation areas, the temperature of the fixing belt will rise at the boundary between the heat generation areas when the fixing device is started up. A decline occurs. This is because heat moves from an area with a high calorific value to an area with a low calorific value. At the boundary portion of the region with a high calorific value, the temperature drops compared to other parts of the region with a high calorific value.

As described above, when the resistance heating element has a plurality of heat generating regions regardless of the presence or absence of a gap portion, a drop in the temperature of the fixing belt occurs corresponding to the boundary portion between the heat generating regions. When the heat generating areas are arranged in the longitudinal direction, such a drop may cause temperature unevenness in the fixing belt along the longitudinal direction, which may appear as streak-like fixing unevenness along the conveyance direction and become noticeable. .

One aspect of the present invention is a fixing device that has a simpler configuration and can suppress temperature unevenness of a fixing belt corresponding to a boundary between heat generating regions that occurs when a 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 problems, a fixing device according to one aspect of the present invention includes a plate-shaped heater that includes a resistance heating element on a base material and extends in the longitudinal direction, supports the heater, and supports the heater. a holder that covers a back surface; a fixing belt that rotates while sliding its inner peripheral surface on the surface of the heater; and a pressure 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 area and a second heating area disposed adjacent to the first heating area in the longitudinal direction, and the holder faces a back surface of the heater. , a support surface that supports the heater, and the support surface is provided with a recess that accommodates a heat insulating material at a position corresponding to a boundary between the first heat generation region and the second heat generation region in the longitudinal direction. It is characterized by

According to the above configuration, the resistance heating element has the first heat generation region and the second heat generation region disposed adjacent to the first heat generation 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 multiple heat generating areas in the longitudinal direction, temperature unevenness of the fixing belt corresponding to the boundary between the heat generating areas becomes noticeable, such as when starting up the fixing device, and streak-like fixing occurs along the conveyance direction. There is a risk that it will become uneven and noticeable.

However, according to the above configuration, the recess for accommodating the heat insulating material is provided at a position corresponding to the boundary between the first heat generating area and the second heat generating area on the support surface of the holder. By providing such a recessed portion, the heat insulation effect of the holder in the portion corresponding to the boundary portion can be increased more than in other portions. This suppresses a drop in the temperature of the fixing belt corresponding to the boundary between the heat-generating regions, which occurs noticeably when the fixing device is started up, and improves fixing performance.

Furthermore, with the above configuration, it is possible to suppress a drop in the temperature of the fixing belt corresponding to the boundary portion between the heat generating regions only by processing on the holder side. Therefore, the structure can be simpler than a structure 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 an object of the present invention to provide a fixing device that has a simpler configuration and can suppress temperature unevenness of a fixing belt corresponding to a boundary between heat generating regions, which occurs when a resistance heating element has a plurality of heat generating regions in the longitudinal direction. I can do it.

In the fixing device according to one aspect of the present invention, the first heat generating region and the second heat generating region are arranged with a distance from each other in the longitudinal direction, and the recess is arranged between the first heat generating region and the second heat generating region. It may also be configured such that it is provided at a position corresponding to the gap between the second heat generating regions.

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

In the fixing device according to one aspect of the present invention, the amount of heat generated in the second heat generation region is smaller than the amount of heat generated in the first heat generation region, and the recessed portion is formed in the first heat generation region in the second heat generation region. may extend in the longitudinal direction to the position of the end on the opposite side to the adjacent side.

According to the above configuration, the amount of heat generated in the second heat generation region is smaller than the amount of heat generated in the first heat generation region. If there is such a difference in the amount of heat generated, when the fixing device is started up, the temperature of the fixing belt will rise later in the part corresponding to the second heat generating area, which has a smaller amount of heat, than in the part corresponding to the first heat generating area. , temperature unevenness occurs.

However, according to the above configuration, the recess extends in the longitudinal direction to the position of the end of the second heat generating region on the opposite side to the side adjacent to the first heat generating region. In this way, by extending the concave portion so as to cover the second heat generating region, the heat insulation effect of the holder in the portion corresponding to the second heat generating region can also be increased more than in other portions. Thereby, temperature unevenness at startup can also be suppressed.

Note that, after the temperature of the fixing belt in the part corresponding to the second heat generation area catches up with the temperature in the part corresponding to the first heat generation area, the temperature of the part corresponding to the second heat generation area, which has a small amount of heat generation, increases. Contribute to

In the fixing device according to one aspect of the present invention, the base material may be made of metal.

The fixing device according to one aspect of the present invention is further configured such that the pressure body is a pressure roller having a core bar extending in the longitudinal direction and an elastic layer provided on the core bar. You can also do that.

In order to solve the above problems, an image forming apparatus according to one aspect of the present invention includes a fixing device according to one aspect of the present invention, and the image forming apparatus according to one aspect of the present invention is configured to transfer a developer image transferred to a recording material in an image forming section to The recording material is passed through the fixing nip of the fixing device to be fixed on 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 areas, which occurs when the resistance heating element has a plurality of heat generating areas in the longitudinal direction. A fusing device can be provided.

1 is a cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a perspective view of a fixing device installed in the image forming apparatus shown in FIG. 1. FIG. 3 is a sectional view of the fixing device shown in FIG. 2. FIG. 3 is an exploded view of a heater section disposed inside a fixing belt in the fixing device shown in FIG. 2. FIG. FIG. 5 is a bottom view of a holder and a bottom view of a heater in the heater section shown in FIG. 4. FIG. FIG. 3 is a schematic cross-sectional view of essential parts of the fixing device shown in FIG. 2; FIG. 7 is a bottom view of a holder and a bottom view of a heater in a heater section of a fixing device installed in an image forming apparatus according to another embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of essential parts of the fixing device shown in FIG. 7; FIG. 7 is a bottom view of a holder and a bottom view of a heater in a heater section of a fixing device installed in an image forming apparatus according to still another embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

1. Overall Configuration of Image Forming Apparatus The configuration of an electrophotographic image forming apparatus 100 will be described based on FIG. 1. FIG. 1 is a cross-sectional view showing the configuration of an image forming apparatus 100 according to an embodiment of the present invention. Although the image forming apparatus 100 is a monochrome printer having only one set of image forming units, which will be described later, the scope of application of the present invention is not limited to monochrome printers, but can also be applied to color printers. be.

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

The photoreceptor 1 includes a blank tube made of a conductive metal such as aluminum, and a photosensitive layer provided on the outer peripheral surface of the blank tube. The photoconductor 1 is an organic photoconductor (OPC), and is a photoconductor drum having a positively chargeable photoconductor layer in which the polarity of the image forming potential is positive. The photosensitive layer of the photoreceptor 1 is charged by a charging device 2 while rotating, and is exposed to laser light from an exposure device 3 to form an electrostatic latent image on the surface. Note that the photoreceptor 1 may be a photoreceptor belt in which a photoreceptor 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 photoreceptor 1, and is, for example, a charging roller that charges the photoreceptor 1 by contacting it, or a scorotron charger that charges the photoreceptor 1 without contact. The exposure device 3 is a device that exposes the charged surface of the photoreceptor 1 to light. The exposure device 3 has, for example, a plurality of light emitting elements arranged in a line along the direction of the rotation axis of the photoreceptor 1, and generates electrostatic charge on the surface of the photoreceptor 1 by emitting light according to print data. Form a latent image.

The developing device 4 is a device that supplies developer to the electrostatic latent image formed on the surface of the photoreceptor 1, and includes, for example, a developing roller and a developing container containing the developer. The transfer device 5 is a device that transfers the developer image formed on the surface of the photoreceptor 1 onto the recording material 15, and is, for example, a transfer roller. Note that recording materials include recording paper, OHP, envelopes, cardboard, and the like. The cleaning device 6 is a device that removes developer remaining on the photoconductor 1 and paper powder adhering to the photoconductor 1 from the photoconductor 1, and is, for example, a cleaning roller.

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

The fixing device 8 is a device that fixes the developer image transferred to the recording material 15 onto the recording material 15 using 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 discharge 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 sheet at a time from the paper feed tray 9. Each of the plurality of conveyance roller pairs 72 , 73 , 74 , and 75 is a roller pair that conveys the recording material 15 fed by the pickup roller 71 to the paper discharge tray 10 along the conveyance path 16 . The conveyance path 16 passes between the photoreceptor 1 and the transfer device 5 and through a fixing nip N (see FIG. 3) of the fixing device 8, which will be described later.

Further, although not shown, the image forming apparatus 100 includes a control unit configured from an ASIC (Application Specific Integrated Circuit) or the like. The control section controls the operations of each of the above-mentioned parts of the image forming apparatus 100.

2. Description of Operation of Image Forming Apparatus A series of image forming processes performed by the image forming apparatus 100 configured as described above will be briefly described with reference to FIG. 1. When the image forming apparatus 100 receives print data from an information terminal device such as a personal computer or an image reading device that reads a document, it starts printing processing. As a result, the surface of the photoreceptor 1 is uniformly positively charged by the charging device 2 as the photoreceptor 1 rotates. Laser light is then irradiated from the exposure device 3 toward the photoreceptor 1, respectively. As a result, a predetermined electrostatic latent image is formed on the surface of the photoreceptor 1 according to the print data. That is, of the uniformly positively charged surface of the photoreceptor 1, the potential of the portion irradiated with the laser beam decreases.

Next, as the developing roller of the developing device 4 rotates, the positively charged developer carried on the developing roller is supplied to the electrostatic latent image formed on the surface of the photoreceptor 1 . As a result, the electrostatic latent image on the photoreceptor 1 is developed, and a developer image is carried on the surface of the photoreceptor 1 by reversal development.

Further, in parallel with the process for forming the developer image described above, a process for conveying the recording material 15 is performed. That is, by the rotation of the pickup roller 71, the recording materials 15 are sent out one by one from the paper feed tray 9 to the conveyance path 16. The recording material 15 sent out to the conveyance path 16 is conveyed by a pair of conveyance rollers 72 and 73 to a transfer position where the photoreceptor 1 and the transfer device 5 come into contact.

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

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

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

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 cylindrical member that is thin and has a low heat capacity. The fixing belt 81 is made of a single layer or composite layer film having heat resistance, mold 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 a base material 82A having an elongated plate shape, and a resistance heating element 82B provided thereon along the longitudinal direction. Note that the longitudinal direction is a direction parallel to the rotation axis of the pressure roller 84 and perpendicular to the conveyance direction of the recording material 15 in the fixing nip N, which will be 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 generating region R1 and two second heat generating regions R2, R2 arranged adjacent to the first heat generating region R1 in the longitudinal direction. The first heat generating region R1 corresponds to a passage region of the small-sized recording material 15 including the longitudinal center of the base material 82A. The second heat generating region R2 corresponds to the end-side passage region of the recording material 15 of the largest size that can be passed, on both sides of the first heat generating region R1. The largest size recording material 15 passes through the first heat generating region R1 and the two second heat generating regions R2, R2 on both sides thereof.

The amount of heat generated in the second heat generation region R2 is set smaller than the amount of heat generated in the first heat generation region R1. As a result, the recording material 15 passes only when the recording material 15 is large in size, and the amount of heat generated at the end of the fixing belt 81, where the temperature tends to rise too much, can be reduced. As a result, deterioration and damage to components such as the heater 82 and the pressure roller 84 can be prevented or reduced. Furthermore, high temperature offset occurring at the edge of the large-sized recording material 15 can also be avoided.

The image forming apparatus 100 of this embodiment is a so-called center-based image forming apparatus that transports the recording material 15 with the longitudinal center as the transport reference. Therefore, the second heat generating region R2 is arranged on both sides of the first heat generating 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 generating region R1 and the second heat generating region R2 are arranged in this order from the end serving as the transport reference. be done.

Further, in the present embodiment, the first heat generating region R1 and the second heat generating region R2 are spaced apart from each other in the longitudinal direction, and between the first heat generating region R1 and the second heat generating region R2, A gap G exists. Although not shown, wiring and terminals that feed power to the first heat generating region R1 and wires and terminals that feed power to the two second heat generating regions R2, R2 are provided on the base material 82A. . Note that the terminal for feeding power to the first heat generating region R1 and the terminal for feeding power to the second heat generating regions R2, R2 may be arranged together at one end in the longitudinal direction of the base material 82A. preferable. Thereby, power can be supplied to two circuits by connecting a harness to one end in the longitudinal direction.

Further, in this 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. Note that the heater 82 may be a ceramic heater in which the base material 82A is made of ceramic.

Such a heater 82 is supported by a holder 83. The holder 83 is a member that supports the heater 82 and holds the fixing belt 81 in rotation, and is made of a heat-resistant and insulating resin material. In this embodiment, the holder 83 has a shallow gutter shape and has a support surface 83A that supports the heater 82 on the bottom surface. The support surface 83A supports the heater 82 while facing the back surface of the heater 82, that is, the surface of the base material 82A on the opposite side from 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, which guide the rotation of the fixing belt 81, are provided on both sides of the support surface 83A in the lateral direction of the holder 83 in the longitudinal direction. It is located along. Note that the lateral direction is a direction perpendicular to the longitudinal direction and the thickness direction of the heater 82. The lateral direction can also be said to be the conveyance direction of the paper in the fixing nip N. The upstream guide ribs 83B of the plurality of upstream guide ribs 83B are spaced apart from each other in the longitudinal direction. Similarly, the downstream guide ribs 83C of the plurality of downstream guide ribs 83C are spaced apart from each other in the longitudinal direction. The plurality of upstream guide ribs 83B are located upstream in the rotational direction of the fixing belt 81 with respect to the support surface 83A.

The plurality of upstream guide ribs 83B and the plurality of downstream guide ribs 83C have a substantially semicircular outer cross-sectional shape, and the inner circumferential surface of the fixing belt 81 slides on this outer portion. By providing the plurality of upstream guide ribs 83B and the 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 a heat insulating material at a position corresponding to the boundary 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 generating region R1 and the second heat generating region R2. This will be discussed later.

The stay 85 is a member for increasing the rigidity of the holder 83, and is arranged on the opposite side of the support surface 83A of the holder 83. If the holder 83 itself has high rigidity, the stay 85 can be omitted. In this embodiment, the stay 85 is attached to the holder 83 and is treated as one with the holder 83. Hereinafter, the holder 83, the heater 82 supported by the holder 83, and the stay 85 attached to the holder 83 will be collectively referred to as a heater section 86.

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

The pressure roller 84 is an example of a pressure body, and is pressed against the surface of the heater 82 via the fixing belt 81 to form a fixing nip N. More specifically, both ends of the pressure roller 84 are supported by a pair of side frames via bearings. Further, both longitudinal ends of the stay 85 are biased toward the pressure roller 84 by springs. As a result, the heater 82 is pressed almost uniformly in the longitudinal direction toward the pressure roller 84 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 part 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.

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

4. Operation of Fixing Device The pressure roller 84 is rotationally driven, and the fixing belt 81 is driven to rotate accordingly. The heater 82 is energized, and the temperature of the heater 82 is raised to a predetermined temperature, thereby controlling the temperature. In this state, the recording material 15 carrying an unfixed developer image is introduced between the fixing belt 81 and the pressure roller 84 in the fixing nip N. At the fixing nip N, the developer image bearing surface side of the recording material 15 is in close contact with the outer surface of the fixing belt 81, and the recording material 15 is conveyed through the fixing nip N together with the fixing belt 81.

During this nipping and conveying process, heat from 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 onto the recording material 15 to be melted and fixed. The recording material 15 that has passed through the fixing nip N is discharged from the fixing device 8.

5. Concave Portion of Holder As described above, in this embodiment, the resistance heating element 82B of the heater 82 has a first heat generating region R1 located at the center in the longitudinal direction, and two regions adjacent to the first heat generating region R1 in the longitudinal direction. and a second heat generating region R2. The amount of heat generated in the second heat generation region R2 is set smaller than the amount of heat generated in the first heat generation region R1. As described above, this reduces the amount of heat generated at the end of the fixing belt 81, prevents or reduces component deterioration and damage, and avoids high-temperature offset that occurs at the end of the large-sized recording material 15. can.

however. Since the portion of the gap G that is the boundary between the first heat generating region R1 and the second heat generating region R2 does not generate heat, a temperature drop corresponding to the gap G occurs in the temperature of the fixing belt 81. Such a drop in temperature occurs noticeably when the fixing device 8 is started up. Such a drop in temperature causes streak-like fixing unevenness along the paper conveyance direction when an image is formed on the large-sized recording material 15.

Therefore, in this embodiment, in order to suppress the drop in temperature of the fixing belt 81 corresponding to such a gap G, as shown in FIGS. A recess 83D for accommodating a heat insulating material is provided at the position. In this embodiment, since the gap G exists at two locations in the longitudinal direction, the recesses 83D are also provided at two locations in the longitudinal direction.

Air is accommodated in the recess 83D as a heat insulating material. Moreover, the recessed part 83D extends along the lateral direction, and is formed from one end of the support surface 83A to the other end in the lateral direction. Note that the heat insulating material may be made of a material having a lower thermal conductivity than the holder 83. For example, it may be made of heat-resistant glass wool, rock wool, alkaline earth silicate wool (AES), refractory ceramic fiber (RCF), or artificial mineral fiber such as alumina fiber. By providing such a recess 83D, the heat insulation effect of the portion of the holder 83 corresponding to the gap G of the resistance heating element 82B can be increased more than that of the other portion.

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

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

Further, in this embodiment, the recesses 83D are formed by recesses formed in the support surface 83A, and the plurality of recesses 83D are realized with a simple structure using air as a heat insulating material.

Furthermore, in this embodiment, as shown in FIG. 6, the width of the recess 83D in the longitudinal direction is set 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, which face each other with the gap G interposed therebetween. Thereby, it is possible to more reliably suppress the drop in temperature of the portion of the resistance heating element 82B corresponding to the gap G.

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

FIG. 7 is a bottom view of the holder 183 and the heater 82 in the fixing device 18 installed in the image forming apparatus of this embodiment. FIG. 8 is a schematic cross-sectional view of the main parts 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 in the support surface 83A is different. The other configurations are the same as those of the fixing device 8.

As described above, the amount of heat generated in the second heat generation region R2 is set to be smaller than the amount of heat generated in the first heat generation region R1. Therefore, in the case of the fixing device 8, when the fixing device 8 is started up, the temperature of the fixing belt 81 rises more slowly in the portion corresponding to the second heat generating region R2 with a small amount of heat generation than in the portion corresponding to the first heat generating region R1. . In such a state, when an image is formed on the large-sized recording material 15 passing through the second heat generating area R2, the fixing belt between the part corresponding to the first heat generating area R1 and the part corresponding to the second heat generating area R2 is formed. There is a possibility that uneven fixing may occur due to the difference in temperature of 81.

Therefore, in this embodiment, as shown in FIGS. 7 and 8, the first heat generating region R1 in the second heat generating region R2 is adjacent to the recess 183D in the holder 183 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 from the side where it is attached. That is, the recess 183D is formed to have a length that covers the entire second heat generating region R2 in the longitudinal direction.

With such a configuration, the heat insulation effect of the portion of the holder 83 corresponding to the second heat generating region R2 as well as the portion corresponding to the gap G can be increased more than that of the other portions. Thereby, it is also possible to suppress temperature unevenness between the portion corresponding to the first heat generating region R1 and the portion corresponding to the second heat generating 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 generating region R2 when the fixing device 18 is started up, a good image without fixing unevenness can be obtained.

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

Note that the effect of eliminating fixing unevenness due to a delay in temperature rise of the second heat generating region R2 can be achieved by providing a recessed portion only in the portion of the support surface 83A that corresponds to the second heat generating region R2.

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

In the first and second embodiments described above, 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 mentioned above, by making the sheet resistance of the resistance heating element higher than other parts or by reducing the thickness of the resistance heating element, it is possible to partially change the amount of heat generated without providing the gap G. I can do it.

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 by making the resistance heating element thinner. A first heat generating region R1 and two second heat generating regions R2 are provided. In FIG. 9, the first heat generating region R1 is hatched, and the two second heat generating regions R2 are cross-dot hatched.

Although not shown, wiring and terminals for feeding power to the resistance heating element 182B are provided on the base material 82A. In the configuration of Embodiments 1 and 2 in which the heat generation areas are divided by providing the gap G, it was necessary to divide the circuit into one for the first heat generation area R1 and one for the two second heat generation areas R2, R2. In such a resistance heating element 182B, it is sufficient to provide one circuit for feeding power to the resistance heating element 182B.

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

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

Note that the configuration in which the first heat generating region R1 and the second heat generating region R2 are provided by partially changing the amount of heat generated can be combined with the recessed portion 183D described in the second embodiment.

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

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

Claims (5)

a plate-shaped heater having a resistance heating element on a base material and extending in the longitudinal direction;
a holder that supports the heater and covers the back side of the heater;
a fixing belt that rotates while sliding its inner peripheral surface on the surface of the heater;
a pressure 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 heat generation region and a second heat generation region disposed 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 supporting surface is provided with a recess for accommodating a heat insulating material at a position corresponding to a boundary between the first heat generating region and the second heat generating region in the longitudinal direction ,
The first heat generating region and the second heat generating region are spaced apart from each other in the longitudinal direction.
and
The recess is provided at a position corresponding to a gap between the first heat generating area and the second heat generating area.
is,
A fixing device characterized in that the length of the recess in the longitudinal direction is greater than the length of the gap portion in the longitudinal direction. a plate-shaped heater having a resistance heating element on a base material and extending in the longitudinal direction;
a holder that supports the heater and covers the back side of the heater;
a fixing belt that rotates while sliding its inner peripheral surface on the surface of the heater;
a pressure body that presses against the surface of the heater via the fixing belt to form a fixing nip;
Equipped with
The resistance heating element has a first heat generation region and a second heat generation region disposed 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 supporting surface includes a boundary between the first heat generating area and the second heat generating area in the longitudinal direction.
A recess for accommodating a heat insulating material is provided at a position corresponding to the
The first heat generating region and the second heat generating region are spaced apart from each other in the longitudinal direction.
and
The recess is provided at a position corresponding to a gap between the first heat generating area and the second heat generating area.
is,
The amount of heat generated in the second heat generation region is smaller than the amount of heat generated in the first heat generation region,
The fixing device is characterized in that the concave portion extends in the longitudinal direction to a position of an end of the second heat generating region on a side opposite to the side adjacent to the first heat generating region in the second heat generating region. Device . The fixing device according to claim 1 or 2 , wherein the base material is made of metal. 4. The pressure roller according to claim 1 , wherein the pressure body is a pressure roller having a core bar extending in the longitudinal direction and an elastic layer provided on the core bar. The fixing device described. The fixing device according to any one of claims 1 to 4 is provided, and the developer image transferred to the recording material in the image forming section is passed through the fixing nip of the fixing device to be fixed on the recording material. An image forming apparatus characterized in that:

Images