JP7456256B2 - Heating device and image forming device - Google Patents

Description

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

In an electrophotographic fixing device, the nip forming member is made of a metal material with good thermal conductivity, and the support member that receives the part is made of a highly insulating resin in order to suppress temperature unevenness in the axial direction during paper feeding. There is a technology that has a similar configuration (for example, Patent Document 1).
Conventional nip forming members that cover the entire nip surface are made of metal, so they have a large heat capacity and have a problem in that they take a long time to rise. Further, since the nip shape formed by the nip forming member affects paper separation performance, the exit portion may be required to have a complicated shape. However, if all the nip forming members are made of metal, it is difficult to form the desired shape, such as a small curved shape (R shape), resulting in large variations in separation performance, and furthermore, the heat capacity becomes larger than necessary. There was a problem that it took a long time to start up.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heating device that has a simple configuration, has less temperature unevenness in the axial direction of a fixing member, has a small heat capacity, and has a short start-up time.

In order to solve the above-mentioned problems, the present invention provides a heating device including a rotatable fixing member, a heat source for heating the fixing member, a pressure member in contact with an outer peripheral surface of the fixing member, and a nip forming member located inside the fixing member and in contact with the pressure member via the fixing member to form a nip portion between the fixing member and the pressure member,
The nip forming member is composed of a resin nip forming member and a metal nip forming member,
the metal nip forming member has a flat surface that contacts the fixing member to form the nip portion, and a bent portion at an end portion of the flat surface on a downstream side of the nip that is bent toward the resin nip forming member,
the resin nip forming member is provided with a recess for receiving the bent portion ,
The bent portion has a convex shape at at least one location of the end portion,
The recess has a shape that fits into the protrusion,
the metal nip forming member has a length along an axial direction of the fixing member that corresponds to a plurality of different sizes of recording media,
The bent portion is characterized in that the convex shape is provided in an unused area that is not used by at least one size .

According to the present invention, it is possible to provide a heating device that has a simple configuration, has little temperature unevenness in the axial direction of the fixing member, has a small heat capacity, and has a short start-up time.

1 is a schematic cross-sectional view showing an example of an image forming apparatus that is a color printer provided with a fixing device having a heating device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration example of a fixing device according to an embodiment. FIG. 3 is a schematic cross-sectional view illustrating a configuration example of a nip forming member included in a fixing device according to an embodiment. It is a schematic sectional view explaining the example of composition of the nip formation member of a comparative example. 4 is a diagram illustrating an example of the shape of a heat equalizing member included in the nip forming member of FIG. 3. FIG. FIG. 7 is a diagram illustrating another configuration example of a nip forming member included in the fixing device of one embodiment. It is a figure explaining the other example of the shape of a heat equalizing member.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments shown below, and may be modified within the scope of those skilled in the art, such as other embodiments, additions, modifications, deletions, etc. These are also included within the scope of the present invention as long as they exhibit the functions and effects of the present invention. Further, in each drawing, components and corresponding parts having the same configuration or function are denoted by the same reference numerals, and the explanation thereof will be omitted.

A heating device in one embodiment includes a rotatable fixing member, a heat source that heats the fixing member, a pressure member that contacts the outer peripheral surface of the fixing member, and a pressure member that is located inside the fixing member and applies pressure via the fixing member. The image forming apparatus includes at least a nip forming member that comes into contact with the pressure member to form a nip between the fixing member and the pressure member. The nip forming member (for example, the nip forming member 80 in FIG. 3) is composed of a resin nip forming member (for example, the base member 80a in FIG. 3) and a metal nip forming member (for example, the heat equalizing member 80b in FIG. 3). The nip forming member has a flat surface that contacts the fixing member to form a nip portion (for example, the flat surface 80b2 in FIG. 3), and a bent portion that bends the downstream end of the flat surface toward the resin nip forming member (for example, the flat surface 80b2 in FIG. The resin nip forming member is characterized by having a recess (for example, the recess 80a1 in FIG. 3) for accommodating the bend.

In this way, the metal nip forming member is simply bent once downstream of the nip, and the bent end is shaped to fit into the recess of the resin nip forming member, thereby reducing the edge of the metal nip forming member. There is no contact between the fixing member and the resin nip member, and the resin nip member can be molded into a shape that ensures separation performance at the nip exit, allowing for a highly precise configuration with a high degree of freedom. Furthermore, by freely changing the bending length of the metal nip forming member, it is possible to change the heat uniformity in the width direction of the metal nip forming member and improve the heat uniformity only in the necessary areas (outside the paper passing area). Therefore, with a simple configuration, it is possible to provide a heating device that can achieve both quick start-up and decrease in productivity due to excessive temperature rise outside the paper passing area of the fixing member, and also has stable separation performance.

First, an example of an image forming apparatus using a fixing device having a heating device of the present invention will be described. In the following embodiments, a fixing device using a heating device according to an embodiment of the present invention is also referred to as a "fixing device of an embodiment" as appropriate.
FIG. 1 is a schematic cross-sectional view showing an example of an image forming apparatus, which is a color printer, provided with a fixing device according to an embodiment of the present invention.
The image forming apparatus 10 includes an electrophotographic image forming section and a fixing device 50 (described later with reference to FIG. 2). The image forming section is provided with a plurality of image forming means 1a, 1b, 1c and 1d.

The plurality of image forming means 1a, 1b, 1c, and 1d each have the same configuration, and only the corresponding toner colors differ. For example, a black toner image, a magenta toner image, a cyan toner image, and a yellow toner image are formed in the plurality of image forming means 1a, 1b, 1c, and 1d, respectively. Although four image forming means are shown in FIG. 1, this is just an example, and the present invention is not limited to this.
Note that the plurality of image forming means 1a, 1b, 1c, and 1d have the same configuration except for the difference in developer (toner) color, so in the following description, reference numerals a, b, c, and d will be Explanation will be given with subscripts omitted as appropriate. Furthermore, the subscripts will be omitted as appropriate for the photoreceptor 2, charging member 3, developing device 4, cleaning means 5, and primary transfer roller 8, which will be explained later.

The image forming means 1 includes a drum-shaped photoreceptor 2, which is an electrostatic latent image carrier, and around the photoreceptor 2, a charging member 3, a developing device 4, and a cleaning means 5 are provided. .
The photoreceptor 2 can be rotated clockwise, and a charging member 3 is pressed against the surface of the photoreceptor 2 .
The charging member 3 is driven to rotate as the photoreceptor 2 is rotated. Further, a predetermined bias voltage is applied to the charging member 3 by a high-voltage power source (not shown), so that the surface of the photoreceptor 2 that is rotationally driven can be uniformly charged.
Note that the illustrated charging member 3 employs a roller-like member that contacts the photoreceptor 2, but it is also possible to employ a non-contact type that utilizes corona discharge or the like.

Further, in the image forming apparatus 10 shown in FIG. 1, an exposure device 6 is provided diagonally below in parallel to the four image forming means.
The exposure device 6 has appropriate components such as a light source, a polygon mirror, an f-theta lens, and a reflecting mirror. The exposure device 6 exposes each charged photoreceptor 2 to light based on image information formed according to image data of each color toner, and creates an electrostatic latent image on each photoreceptor 2.

The electrostatic latent image formed on the photoconductor 2 using the exposure device 6 is developed and visualized by applying toner of each color as the photoconductor 2 rotates and passes through the development device 4. .
Note that toner bottles 20a, 20b, 20c, and 20d filled with toner of each color of black, magenta, cyan, and yellow are arranged above inside the image forming apparatus 10. A predetermined amount of each color toner is supplied from toner bottles 20a, 20b, 20c, and 20d to each color developing device 4a, 4b, 4c, and 4d via a transport path (not shown), respectively.

Further, an endless intermediate transfer belt 7 configured as an intermediate transfer body is disposed opposite the photoconductor 2 of each image forming means 1 .
1 is configured by being wound around a plurality of support rollers (e.g., support rollers 15a, 15b, etc.). The support roller 15a is connected to a drive motor (not shown) as a drive source. By driving the drive motor, the intermediate transfer belt 7 rotates counterclockwise in the figure, and the support roller 15b, which can be rotated by the intermediate transfer belt 7, is also rotated.
The photoconductors 2 are in contact with the surface of the intermediate transfer belt 7 .
A primary transfer roller 8 is disposed on the back surface of the intermediate transfer belt 7 so as to face the photoconductor 2 with the belt therebetween.

A primary transfer bias is applied to the primary transfer roller 8 from a high voltage power source (not shown), and the toner image on the photoreceptor 2 developed by the developing device 4 is primarily transferred onto the intermediate transfer belt 7 .
Note that the primary transfer residual toner remaining on the photoconductor 2 without being primarily transferred is removed by the intermediate transfer belt cleaning means 19 in preparation for the next image forming operation by the photoconductor 2, and the toner on the photoconductor 2 is removed. is completely removed.

Furthermore, in the image forming apparatus 10, a secondary transfer roller 18 serving as a secondary transfer device is provided downstream of the primary transfer roller 8 in the driving direction of the intermediate transfer belt 7.
The secondary transfer roller 18 faces the support roller 15b across the intermediate transfer belt 7. The secondary transfer roller 18 and the support roller 15b form a secondary transfer nip portion with the intermediate transfer belt 7 interposed therebetween.
The image forming apparatus 10 further includes a paper feed cassette 30 as a recording medium stacking unit, a feed roller 31, a registration roller pair (alignment roller pair) 35, etc. As viewed from the secondary transfer roller 18, a fixing device 50 and a paper discharge roller pair 36 are provided downstream in the conveying direction of the recording medium P.

Next, the image forming operation (image forming process) will be explained.
First, the photoreceptor 2 described above is rotationally driven in a clockwise direction by a drive source (not shown), and at this time, the surface of the photoreceptor is irradiated with light from a static eliminator (not shown) to initialize the surface potential.
The surface of the photoreceptor 2 whose surface potential has been initialized is then uniformly charged to a predetermined polarity by the charging member 3.
The charged photoconductor surface is irradiated with laser light from the exposure device 6, thereby forming an electrostatic latent image on the photoconductor surface.
At this time, the image information exposed on each photoreceptor 2 is monochrome image information obtained by separating a desired full-color image into toner color information of yellow, cyan, magenta, and black.
The electrostatic latent image formed on the photoreceptor in this way is applied with each color toner (developer) from the developing device 4 when passing through the developing device 4, and is visualized as a developed toner image. .

Further, the intermediate transfer belt 7 is driven to run counterclockwise in the figure. A primary transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor is applied to the primary transfer roller 8 . As a result, a transfer electric field is formed between the photoreceptor 2 and the intermediate transfer belt 7. Then, the toner image on the photoreceptor 2 is electrostatically primarily transferred onto an intermediate transfer belt 7 that is rotationally driven in synchronization with the photoreceptor 2.
In this manner, the primary transferred toner images of each color are sequentially superimposed on the intermediate transfer belt 7 at the same timing from the upstream side in the conveyance direction of the intermediate transfer belt 7, thereby forming a desired full-color image.

On the other hand, the recording medium on which the image is to be formed is separated one by one from the recording medium stack loaded in the paper feed cassette 30 to the pair of registration rollers 35 by the action of an appropriate conveyance member such as the feed roller 31. and then delivered. At this time, the leading edge of the conveyed recording medium hits the nip portion of the pair of registration rollers 35 that have not yet started rotating, forming a so-called loop, thereby performing registration of the recording medium.

Thereafter, the pair of registration rollers 35 start to rotate in synchronization with the full-color toner image carried on the intermediate transfer belt 7. Then, the recording medium is sent toward a secondary transfer nip portion that is composed of a support roller 15b and a secondary transfer roller 18 that faces the support roller 15b with the intermediate transfer belt 7 interposed therebetween.
In this embodiment, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the surface of the intermediate transfer belt is applied to the secondary transfer roller 18. As a result, the full-color toner image formed on the surface of the intermediate transfer belt 7 is transferred onto the recording medium all at once.

The recording medium onto which the toner image has been transferred is further conveyed to a fixing device 50, and as it passes through the fixing device 50, heat and pressure are applied to the recording medium to fix the toner image on the recording medium as a permanent image.
The image-formed recording medium on which the image has been fixed is discharged to a recording medium discharge section such as the discharge tray 29 via the paper discharge roller pair 36, thereby completing the image forming operation.
Note that residual toner remaining on the intermediate transfer belt 7 without being transferred at the secondary transfer nip portion where the secondary transfer roller 18 is disposed is removed and collected by the intermediate transfer belt cleaning means 19.

Next, the configuration of the fixing device 50 will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view illustrating a configuration example of a fixing device according to an embodiment.
The fixing device 50 includes a fixing belt 60 as a rotatable fixing member, a holder 51 as a fixing belt holding member that holds the fixing belt 60 at both ends, and a rotatable rotatable member that contacts the outer peripheral surface of the fixing belt 60. A pressure roller 70 is provided as a pressure member.
The fixing device 50 also includes a halogen heater 61 as a heat source for heating the fixing belt 60, a nip forming member 80 disposed to face the pressure roller 70, and a nip forming member 80 inside the fixing belt 60. It includes a supporting member 90 for supporting, and a reflecting plate 54 for reflecting radiant heat from the halogen heater 61. The reflection plate 54 is arranged between the heater and the support member 90 and is fixed to the support member 90 with screws (not shown).
Further, the fixing device 50 includes a side plate (not shown) that fixes the holder 51 and the support member 90, a temperature sensor (not shown) as a temperature detection means for detecting the temperature of the fixing belt 60, and a pressure roller 70. The fixing belt 60 is provided with a biasing means (not shown) that biases the fixing belt 60 to form a nip N.

The fixing belt 60 is composed of a thin, flexible, endless belt member (including a film). Specifically, the fixing belt 60 includes an inner base material made of a metal material such as nickel or SUS, or a resin material such as polyimide (PI).
Furthermore, it is constituted by a release layer on the outer peripheral side formed of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like.
Furthermore, an elastic layer made of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base material and the release layer.

The pressure roller 70 includes a core bar 72, an elastic layer 71 made of foamable silicone rubber, silicone rubber, fluororubber, etc. provided on the surface of the core bar 72, and PFA or PTFE provided on the surface of the elastic layer 71. It is composed of a release layer (not shown) consisting of, etc.
The pressure roller 70 is urged toward the fixing belt 60 by an unillustrated urging means, and is brought into contact with the nip forming member 80 via the fixing belt 60.
At the location where the pressure roller 70 and the fixing belt 60 come into pressure contact, the elastic layer 71 of the pressure roller 70 is crushed, so that a nip (nip portion) N of a predetermined width in the width direction of the nip forming member 80 is formed. It is formed.

The nip N is continuously formed in the longitudinal direction of the nip forming member 80 (the axial direction of the fixing belt 60). Further, the pressure roller 70 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer body. When the pressure roller 70 is driven to rotate, the driving force is transmitted to the fixing belt 60 through the nip N, and the fixing belt 60 is driven to rotate.

In order to satisfy the function of preventing the nip forming member 80 from deflecting, the support member 90 is desirably made of a metal material with high mechanical strength such as stainless steel or iron. By integrating the parts by caulking, the support member 90 is made inexpensive and highly rigid.

Two halogen heaters 61, a central heater 61a and an end heater 61b, are used in parallel. In the following description, when the central heater 61a and the end heater 61b are collectively referred to as the halogen heater 61.
The central heater 61a and the end heater 61b have different heat generation ranges. The halogen heater 61 can heat the fixing belt 60 according to the size of the paper that is passed through the fixing device 50 . Specifically, the fixing device 50 of the present embodiment includes a central heater 61a that heats a position corresponding to the central region of the fixing belt 60 in the axial direction (hereinafter also referred to as the "longitudinal direction"); It is provided with two end heaters 61b and an end heater 61b that heats a position corresponding to the end region in the longitudinal direction. When passing a wide paper (recording medium) such as A3 portrait, both the center heater 61a and the end heater 61b are turned on. When passing narrow paper such as A4 portrait paper, only the central heater 61a is turned on. Thereby, power consumption used to heat the fixing belt 60 can be suppressed.

Next, the basic operation of the fixing device 50 according to this embodiment will be explained.
When a power switch (not shown) of the main body of the image forming apparatus 10 is turned on, power is supplied to the halogen heater 61 and the pressure roller 70 starts rotating clockwise. As a result, the fixing belt 60 is driven to rotate counterclockwise due to the frictional force with the pressure roller 70 .

Thereafter, the recording medium P, which is an image carrier carrying an unfixed toner image T in the above-described image forming process, is conveyed in the direction of arrow M while being guided by a guide plate (not shown), and is fixed in a pressed state. It is fed into the nip N between the belt 60 and the pressure roller 70.
Then, the toner image T is fixed on the surface of the recording medium P by the heat generated by the fixing belt 60 heated by the halogen heater 61 and the pressing force between the fixing belt 60 and the pressure roller 70 .

The recording medium P with the toner image T fixed thereon is carried out from the nip N. At this time, the leading edge of the recording medium P comes into contact with the leading edge of the separating member 75 supported by a side plate (not shown), so that the recording medium P is separated from the fixing belt 60 . Thereafter, as described above, the separated recording medium P is discharged from the machine by the paper discharge roller and is stocked on the paper discharge tray.

Next, the nip forming member 80 will be explained.
The nip forming member 80 is formed from a base member 80a made of resin as a resin nip forming member, and a heat equalizing member 80b provided on the surface of the base member 80a as a metal nip forming member. When viewed in cross section, the base member 80a is configured to come into contact with the support member 90 at two upper and lower legs.

In this configuration, the role of the resin base member 80a is to provide heat insulation. When the heat equalizing member 80b is placed directly on the surface of the support member 90 to form the nip N, the heat of the fixing belt 60 is absorbed by the support member 90, preventing deterioration of the form uptime and TEC (Typical Electricity Consumption) value. Since heat resistance is required in addition to heat insulation, it is recommended to use LCP (liquid crystal polymer) or PAI (polyamideimide) as the resin material for the base member 80a.

On the other hand, when the nip forming member is made of only a resin member, although it has a high heat insulation effect, it is weak against temperature rise outside the paper passing area during continuous paper passing. In order to solve this problem, the nip forming member 80 is provided with a heat equalizing member 80b, which actively moves heat in the longitudinal direction and suppresses temperature rise at the end during continuous paper feeding, thereby reducing temperature non-uniformity in the longitudinal direction. Reduce.
Therefore, the heat equalizing member 80b is preferably made of a material that can transfer heat in a short time, and is preferably made of a material with high thermal conductivity such as copper, aluminum, or silver. Considering cost, availability, thermal conductivity characteristics, and processability, it is most desirable to use copper.
Hereinafter, details of the nip forming member included in the fixing device of one embodiment will be described.

Embodiment 1.
FIG. 3 is a schematic cross-sectional view illustrating a configuration example of a nip forming member included in a fixing device according to an embodiment, in which (A) is a diagram schematically showing the nip forming member, and (B) is a diagram showing a broken line shown in (A). This is an enlarged view of the part surrounded by . FIG. 4 is a schematic cross-sectional view illustrating a configuration example of a nip forming member of a comparative example, in which (A) is a diagram showing comparative example 1, and (B) is a diagram showing comparative example 2.

The heat equalizing member 80b is made of a metal material and has a large heat capacity. For this reason, when the heat equalizing member 91b is configured to cover the entire surface of the base member 91a like the nip forming member 91 of Comparative Example 1 in FIG. The problem is that the paper becomes long, and complicated bending is required to ensure paper separation performance, resulting in large variations in shape and differences in separation performance from machine to machine. In addition, when the end of the metal material of the heat equalizing member 92b exists in the middle of the nip N, as in the nip forming member 92 of Comparative Example 2 in FIG. There has been a problem in that the fixing belt 60 is easily scratched due to the end portion of the metal material coming into contact with the fixing belt 60.

Therefore, one embodiment is configured as shown in FIG. 3(A).
The base member 80a is provided with a recess 80a1, such as a groove, a recess, or a step, on the downstream side of the nip in contact with the heat equalizing member 80b.
The heat equalizing member 80b has a bent portion 80b1 formed by bending the end downstream of the nip toward the base member 80a, and is inserted into the recessed portion 80a1. Further, the heat equalizing member 80b has a flat surface 80b2 that is in contact with the fixing belt 60 and forms a nip N. The bent portion 80b1 is formed by bending the end of the plane 80b2 on the downstream side of the nip toward the base member 80a.
Here, the downstream side of the nip is defined as the portion downstream from the center of the nip N along the conveyance direction M of the recording medium P of the fixing device 50 (hereinafter also referred to as "conveyance direction M" as appropriate). Further, the width direction (also referred to as the “axial direction”) is a direction perpendicular to the conveying direction M, and is a direction along the axial direction of the fixing belt 60.

The heat-uniforming member 80b will be explained using the nip length L1 and the length L2 shown in FIG. In addition, the bent portion 80b1 is accommodated in the recessed portion 80a1 provided on the downstream side of the nip. In this way, as shown in FIG. 3, the end portion (sheet metal edge portion) of the heat equalizing member 80b can be inserted into the recess 80a1 and prevented from coming into contact with the fixing belt 60. Furthermore, the curved shape of the bent portion 80b1 is brought into contact with the fixing belt 60.
Here, the nip length L1 is a length at which the nip forming member 80 comes into contact with the pressure roller 70 via the fixing belt 60 to form a nip N along the conveyance direction M.
The length L2 is the length from the nip N to the bent portion 80b1, and is set to a length that provides a margin for the plane 80b2 so that the formation of the nip N is not hindered. Therefore, it is preferable that L2 has a minimum length.
Further, the recessed portion 80a1 has a shape that can accommodate the bent portion 80b1.
Although L2 is provided in the embodiment, the effects of the present invention can of course be obtained even without L2. In other words, the effects of the present invention can be obtained not only at a flat location where the heat equalizing member is located, but also when the nip N includes the protruding shape 80a2 of the base member.

In this way, the portion of the nip forming member 80 that is in main contact with the fixing belt 60 is constructed of a heat equalizing member 80b made of a metal material with good thermal conductivity, and the contact between the fixing belt 60 and the flat surface 80b2 reduces the rise in end temperature when small-sized paper is passed through due to the axial heat equalizing effect.
Furthermore, by using the base member 80a made of a resin material for the other parts, the low thermal conductivity of the resin material prevents heat from being dissipated to areas other than the nip N, and the warm-up time can be shortened.

Furthermore, by providing the bent portion 80b1 downstream of the nip, contact between the end portion (edge portion) of the heat equalizing member 80b made of a metal member and the fixing belt 60 can be avoided, and the bent shape of the bent portion 80b1 (the flat surface 80b2 Abrasion of the fixing belt 60 can be reduced by contacting the fixing belt 60 at the bent portion (which separates the fixing belt 60 from the bent portion 80b1).
In addition, the heat equalizing member 80b has a bent portion 80b1 downstream of the nip portion, and is arranged outside the range (nip width) where the pressure roller 70 contacts. In this way, by making the flat surface 80b2 of the heat equalizing member 80b larger than the length of the nip N (for example, the nip length L1 in FIG. 2), it is possible to eliminate a step in the nip range where sliding resistance is high.

The base member 80a has an overhanging shape 80a2 that overhangs in the direction of the fixing belt 60 from a position one step lower than the plane 80b2 (a position away from the fixing belt 60 and the plane 80b2) on the downstream side of the nip from the recess 80a1. In FIG. 3(B), the base member 80a is provided with a projecting shape 80a2 from a position that is lower than the plane 80b2 by the length X of the heat equalizing member 80b. In this way, the fixing belt 60 does not come into contact with the edge portion of the base member 0a, and high durability and separability can be ensured.

Furthermore, the overhanging shape 80a2 improves paper separation (recording medium separation) by making the edge of the recess 80a1 of the base member 80a protrude toward the downstream side of the nip from a position lower than the heat equalizing member 80b. can be secured. In addition, since the edge of the recessed portion 80a1 does not come into contact with the fixing belt 60, the fixing device has stable separation performance while reducing wear on the fixing belt 60. Furthermore, since the shape of the base member 80a made of resin can be produced using a mold, there is little variation in the target shape, and it is possible to secure the desired shape.

This embodiment has a simple configuration, little temperature unevenness in the axial direction of the fixing member, ample separation capacity, and a small heat capacity that shortens the warm-up time.

Embodiment 2.
In Embodiment 2, the shape of the bent portion provided in the heat equalizing member 80b shown in FIG. 3 will be described.
5A and 5B are diagrams illustrating an example of the shape of the heat equalizing member included in the nip formation member shown in FIG. is a diagram illustrating an example of the shape of the heat equalizing member 80b, (C) is a sectional view taken along line AA shown in (A), and (D) is a sectional view taken along line BB shown in (A). , (E) is a sectional view taken along the line CC shown in (A). Note that the AA' line shown in (E) indicates the position corresponding to the AA line shown in (A), and the BB' line also corresponds to the BB line shown in (A). This indicates the position corresponding to .

The end of the bent portion 80b1 may be a straight line with no change in length from the curved shape that changes from the flat surface 80b2 to the bent portion 80b1, but as shown in FIG. 5(B), the end of the bent portion 80b1 The convex shape 80b3 may be provided by changing the length from the bent shape to the end (hereinafter also referred to as "length of the bent portion" as appropriate) depending on the position in the width direction. For example, the length of the bent portion of line AA (FIG. 6(C)) is length L3, and the length of the bent portion of line BB (FIG. 6(D)) is length L4. , the length of the bent portion of line BB is longer than that of line AA (L3<L4).

Further, in the nip forming member 80, it is preferable that the convex shape 80b3 of the bent portion 80b1 engages with the concave portion 80a1. Specifically, it is preferable that the heat equalizing member 80b is changed in at least one part in the width direction to have a convex shape 80b3, and that the base member 80a is provided with a recessed portion 80a1 that fits into the convex shape 80b3. In this way, when the bent portion 80b1 is inserted into the recessed portion 80a1, the position in the width direction (thrust direction) is also restricted (for example, the position of the arrow S in FIG. 5(E) is restricted), and the positioning becomes easier. This makes it possible to accurately maintain the positions of the base member 80a and the heat equalizing member 80b with a simple configuration.
The convex shape 80b3 may be configured to pass through as shown in FIG. 3(D) and come into contact with a metal support member during pressurization, thereby releasing heat to the support member. Alternatively, the length of the bent portion including the convex shape is smaller than the depth of the concave portion of the nip forming member, so that the length of the bent portion including the convex shape is smaller than the depth of the concave portion of the nip forming member. The contact portion between the heat equalizing member and the nip forming member during pressing is a flat surface, and the pressing member can be stably supported by the flat contact.

It is preferable that the convex shape 80b3 is provided outside the paper passing area corresponding to at least the main paper width, and the length of the bent portion 80b1 is increased. In this way, excessive temperature rise outside the main paper passing area can be prevented. The area outside the paper passing area corresponding to the main paper width is, for example, A4 vertical size (approximately 210 mm). Further, outside the paper passing area corresponding to the main paper width, at least one size is not used, for example, when the length along the axial direction of the heat equalizing member 80b corresponds to a plurality of recording media of different sizes. It may be an unused area (an area excluding the paper passing area of all sizes).
In FIG. 5(B), the width W1 is greater than or equal to the width W2 of the A4 portrait size, which is the main size of the recording medium P, and an example is shown in which a convex shape 80b3 is provided at the end of the bent portion 80b1 on the outside of the width W1. . In the range of the width W1, the bent portion 80b1 has a length L3, a convex shape 80b3 is provided outside the width W1, and the bent portion 80b1 has a length L4.

Embodiment 3.
In Embodiment 3, another configuration example of the nip forming member will be described.
FIG. 6 is a schematic cross-sectional view illustrating another example of the configuration of the nip forming member included in the fixing device of one embodiment.
As shown in FIG. 6(A), the nip forming member 81 may accommodate a bent portion 81b1, which is formed by bending and overlapping the ends of the heat equalizing member 81b, in the recess 81a1. At this time, the recess 81a1 is preferably formed to have a step that can accommodate the folded and overlapped bent portion 81b1 so that the surface of the heat equalizing member 81b in contact with the fixing belt 60 is flat.
In this way, the bent portion of the heat equalizing member on the downstream side of the nip may be bent into a hemming shape instead of being bent into an L-shape.

Further, the surface of the heat equalizing member 80b that faces the inner surface of the fixing belt 60 is a surface that directly contacts the fixing belt 60, and serves as a nip forming surface. Therefore, in order to further enhance the heat-uniforming effect, the heat-uniforming member 80b is coated with a coating having excellent sliding performance on its surface.Furthermore, in order to lower the contact resistance with the fixing belt 60, the coated surface is further coated. It is preferable to apply grease. In this way, the contact resistance between the heat equalizing member 80b and the fixing belt 60 can be reduced, and the fixing belt 60 can be prevented from being worn out.

For example, instead of a configuration in which the heat equalizing member is in direct contact with the belt as in FIG. 6(B), in order to reduce the sliding resistance of the nip N, a nip forming member may be configured by wrapping a sliding sheet 82c made of PTFE thread impregnated with a lubricant such as silicone oil around the sliding sheet 82c.
In addition, the nip forming member 82 in Figure 6 (B) shows an example of a configuration in which a sliding sheet 82c is wrapped around the nip forming member 80 shown in Figure 3, but a sliding sheet may also be wrapped around the nip forming member 81 shown in Figure 6 (A).

Embodiment 4.
In Embodiment 4, another example of the shape of the heat equalizing member will be described.
FIG. 7 is a diagram illustrating another example of the shape of the heat equalizing member included in the nip forming member of one embodiment.
The convex shape provided on the bent portion 80b1 is placed outside the paper passing area of the main paper width (for example, A4 portrait size) and outside of the area corresponding to the second paper width (for example, A3 portrait size) that is larger than the main paper width. It is preferable that the bending length of the inner side is longer than that of the inner side. FIG. 7(A) shows that the length from the bent shape of the bent portion 83b1 to the end of the heat equalizing member 83b is divided into three levels L3, L4, and L5 (L3<L4<L5) at the center in the width direction. A convex shape 83b3 that is elongated outward (from the center) is shown.

Further, the convex shape provided on the bent portion 80b1 may be formed such that the length of the outer bent portion in the width direction becomes longer in stages. FIG. 7(B) shows a convex shape 84b3 in which the length from the bent shape of the bent portion 84b1 to the end of the heat equalizing member 84b is increased in multiple steps outward from the center in the width direction. ing.
In the heat equalizing members shown in FIGS. 5, 8(A), and 8(B), the curved portion may have a convex shape with a corner or a corner of the step being curved (smooth step). Furthermore, in the heat equalizing members of FIGS. 5, 8(A), and 8(B), the length of the bent portion in the width direction gradually changes such that the length of the bent portion in the width direction becomes longer toward the outside, at least within the maximum paper passing area. (change gradually or smoothly).

Additionally, it is preferable that the central portion of the heat equalizing member is formed to have a convex shape, and the convex portion abuts on the resin nip forming member or the support member.
The heat equalizing member 85b in FIG. 7C shows an example in which a smooth convex shape 85b4 is provided in the center of the curved portion 85b1.
In a nip forming member having a heat equalizing member with a flat nip N, the pressing force at the central portion is weakened due to the bending of the pressure roller 70 and the fixing belt 60. The heat equalizing member 85b is provided with a convex shape at the center in the width direction, thereby preventing a decrease in the pressing force due to bending. Although FIG. 7C shows an example in which a smooth convex shape 85b4 is formed, the present invention is not limited to this, and a convex shape may be formed in a part of the central portion.

As described in the above embodiments, one embodiment of the present invention has the following features regarding the nip component of the electrophotographic fixing device.
Among the nip forming members, the base member is made of a resin material with high heat insulation properties, and the heat equalizing plate portion that contacts the pressure member is made of a heat equalizing member having good thermal conductivity (for example, made of metal). The nip forming member may be made of two or more types of materials.
Further, the heat equalizing member has a cross-sectional shape, and by eliminating the bent portion of the heat equalizing member that contacts the pressure member, the shape forming the nip portion becomes a flat plate, which can be easily produced. Furthermore, since the volume (heat capacity) of the entire heat equalizing member is reduced, the rise time is also shortened, and by using a material with good thermal conductivity, it is possible to improve heat uniformity in the axial direction.

Furthermore, since the plane forming the nip portion of the heat equalizing member is a flat plate, it is easy to change the shape, and by changing the axial area at the center and the ends, the drop in end temperature immediately after start-up can be improved.
In addition, the heat equalizing member that contacts the pressure member and the base member made of heat insulating resin form a continuous nip plane. If an irregular shape is required at the nip exit to improve separation performance with the shape of the belt, the resin base member can be molded, allowing for a large degree of freedom in shape. Therefore, there is no need for complex processing of the heat equalizing member.
In this way, the nip forming members form a continuous surface made of different materials (good and bad thermal conductivity).

50 Fixing device 60 Fixing belt (fixing member)
70 Pressure roller (pressure member)
80 Nip forming members 80a to 85a Base member (resin nip forming member)
80a1, 81a1 Recesses 80b to 85b Heat equalizing member (metal nip forming member)
80b1 to 80b1 Bend portions 80b2, 83b2 to 85b2 Plane 82c Sliding sheet

Japanese Patent Application Publication No. 2016-173559

Claims (10)

a rotatable fuser member;
a heat source for heating the fixing member;
a pressure member that contacts an outer peripheral surface of the fixing member;
a nip forming member that is located inside the fixing member and abuts against the pressure member via the fixing member to form a nip portion between the fixing member and the pressure member,
The nip forming member is composed of a resin nip forming member and a metal nip forming member,
the metal nip forming member has a flat surface that contacts the fixing member to form the nip portion, and a bent portion at an end portion of the flat surface on a downstream side of the nip that is bent toward the resin nip forming member,
the resin nip forming member is provided with a recess for receiving the bent portion ,
The bent portion has a convex shape at at least one location of the end portion,
The recess has a shape that fits into the protrusion,
the metal nip forming member has a length along an axial direction of the fixing member that corresponds to a plurality of different sizes of recording media,
The bent portion has the convex shape provided in an unused area that is not used by at least one size.
A heating device characterized by: 2. The resin nip forming member has an overhanging shape that extends toward the fixing member from a position downstream of the nip from the recess and a distance from the fixing member that is longer than the plane . Heating device as described. 3. The heating device according to claim 1 , wherein the metal nip forming member has the flat surface bent at a position downstream of the nip portion to form the bent portion. The heating device according to any one of claims 1 to 3 , wherein the metal nip forming member has a fluororesin coating layer on its surface. The unused area exists on both sides of the central part in the axial direction,
The heating device according to claim 1 , wherein the bent portion has the convex shape provided in the unused area on both sides. The unused area exists on both sides of the central part in the axial direction,
The bent portion is provided with the convex shape in the unused area on both sides,
2. The heating device according to claim 1 , wherein the convex shape has at least one step in which a length away from the center is longer than a length near the center. 7. The heating device according to claim 6 , wherein the convex shape has a curved corner or a corner of the step. The heating device according to any one of claims 1 and 5 , wherein the convex shape has a shape in which the outer side is gradually longer than the center part along the axial direction. . 9. The heating device according to claim 1 , wherein the metal nip forming member is thicker at a central portion in the axial direction than at the other portion . An image forming apparatus comprising the heating device according to claim 1 .