JP6607055B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

Various sizes of paper are used in image forming apparatuses such as copying machines and printers. A wide range of paper compatibility is required, and conventionally, a fixing method that adjusts a heating range by controlling energization to a plurality of halogen heaters having different heating regions has been widely adopted as a low-cost method.
Although the usage frequency for the whole is very low, compatibility with large size (special size) paper larger than A3 size such as A3 Nobi and 13 inches is also required.

At the same time as paper compatibility, due to the recent increase in demand for energy saving, maintaining the heating source of the fixing device at a temperature at a level where it can immediately shift to the fixing operation and bringing it into a preheating state causes an increase in power consumption. It is no longer done.
As an adverse effect, it cannot be used immediately when the user wants to use it, leading to an increase in the return time from the so-called energy saving mode, and the convenience is impaired.
For this reason, in recent years, various techniques for shortening the recovery time have been proposed, and as a directionality, the basic technique is to reduce the heat capacity of the fixing member, that is, to reduce the thickness.

In Patent Document 1, a nip forming member is provided inside a thin and flexible endless belt member that quickly rises to a fixing temperature, and the nip forming member and the pressure roller are interposed between the belt member and the pressure roller. A fixing device that forms a nip by contact pressure with a pressure roller is disclosed.
A plurality of halogen heaters having different light distributions are provided in a portion different from the nip inside the cylindrical belt member.
At both ends in the axial direction of the belt member, an end heat source (planar shape) that can be used for a large size paper such as A3 Nobi by using it with a halogen heater at a position upstream of the nip in the rotation direction of the belt member. Heater) is provided. The end heat source is provided so as to contact the inner surface or the outer surface of the belt member.
By adopting a configuration in which an end heat source is provided separately from the halogen heater, the length of the halogen heater corresponding to a large size paper is not increased to widen the heating range, and a large size paper such as A3 Novi Without adding a special halogen heater, it is possible to handle large-size paper with a simple configuration.

If a configuration in which a halogen heater and a planar heater are used separately as in Patent Document 1, paper compatibility can be improved without hindering downsizing, and energy saving can be realized.
However, due to the thinning of the fixing member, the amount of heat transfer per unit time in the axial direction of the fixing member also decreases. During paper passing, the non-sheet passing portion of the fixing member will not be deprived of heat by the paper, so the temperature will rise excessively. The temperature in the axial direction cannot be kept uniform.
For this reason, there is a concern that an abnormal image may occur due to temperature unevenness of the fixing member.

  The present invention has been made in view of such a current situation, and provides a fixing device capable of achieving both improvement in paper compatibility and energy saving, and suppressing occurrence of abnormal images due to temperature unevenness of the fixing member. With a purpose.

  In order to achieve the above object, a fixing device of the present invention is provided with an endless fixing member having flexibility, a facing member disposed to face the fixing member, and an inner side of the fixing member. A nip forming member for forming a nip for nipping and conveying a recording medium between the fixing member and the opposing member; a first heating source for heating the fixing member at a position different from the nip; A planar second heating source that heats the fixing member at the nip portion, and the nip forming member is positioned on the nip side of the first nip forming member and the first nip forming member. The second nip forming member is laminated, and the second heating source is between the first nip forming member and the second nip forming member and in the axial direction of the fixing member. Both ends of the portion corresponding to the heating region of the first heating source The heat transfer from the fixing member to the nip forming member side in the portion corresponding to the heating area by the first heating source of the nip is arranged in the heating area by the second heating source. The heat transferability from the nip forming member to the fixing member side in the corresponding part is configured to be smaller.

  According to the present invention, it is possible to provide a fixing device that can achieve both improved paper compatibility and energy saving, and can suppress the occurrence of abnormal images due to temperature unevenness of the fixing member.

1 is a schematic configuration diagram of a color printer as an image forming apparatus according to a first embodiment of the present invention. It is a schematic sectional drawing of a nip site | part. It is a schematic sectional drawing of the nip site | part which shows nip width | variety. FIG. 3 is a perspective view of a main part showing a support configuration of a fixing belt. It is a disassembled perspective view of a nip forming unit. It is a figure which shows the heating area | region by a halogen heater and a planar heater. It is sectional drawing for demonstrating the heat transfer characteristic in a nip. It is a figure which shows a planar heater, (a) is a top view, (b) is a side view. FIG. 3A is a cross-sectional view of a nip, FIG. 3A is a cross-sectional view in a direction parallel to the paper transport direction, and FIG. FIG. 6 is a cross-sectional view of a nip in a direction orthogonal to the paper transport direction. FIG. 10 is a cross-sectional view of a nip in a direction orthogonal to a paper conveyance direction in the second embodiment. It is a figure of the site | part of a nip, (a) is a side view, (b) is a fragmentary sectional view of the integral structure of a soaking | uniform-heating member and a low heat conductivity member. 9A and 9B are cross-sectional views of a nip according to a fifth embodiment. FIG. 10A is a cross-sectional view in a direction parallel to the paper transport direction, and FIG. It is a figure explaining the positional relationship of the planar heater and fixing belt used for each embodiment. It is a figure which shows the nip formation unit used for the modification of each embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
1 to 10 show a first embodiment.
First, the outline of the configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.
The image forming apparatus 100 is a tandem color printer in which image forming units that form a plurality of color images are juxtaposed along the moving direction of the intermediate transfer belt.

  The image forming apparatus 100 includes a photosensitive drum 20Y as an image carrier that can form images corresponding to colors separated into yellow (Y), cyan (C), magenta (M), and black (Bk). , 20C, 20M, 20Bk.

The visible toner images formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk are superimposed on the intermediate transfer belt 11 as an intermediate transfer member that can move in the direction of the arrow A1 while facing the photosensitive drums. In addition, primary transfer is performed.
Thereafter, the sheet S as a recording medium is collectively transferred by the secondary transfer process.
Around each photosensitive drum 20, an apparatus for image forming processing is arranged according to the rotation of the photosensitive drum.

An apparatus for image forming processing will be described on behalf of the photosensitive drum 20Bk that forms a black image.
Around the photosensitive drum 20Bk, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk that perform image forming processing are sequentially arranged along the rotation direction of the photosensitive drum 20Bk.
After charging by the charging device 30Bk, optical writing based on image information is performed on the surface of the photosensitive drum 20Bk by the optical writing device 8 to form an electrostatic latent image.
The electrostatic latent image is visualized as a toner image by the developing device 40Bk.

The toner image formed on each photosensitive drum 20 is transferred to the same position on the intermediate transfer belt 11 while the intermediate transfer belt 11 moves in the A1 direction.
The primary transfer is performed by shifting the timing from the upstream side in the A1 direction to the downstream side by applying a voltage from the primary transfer roller 12 disposed opposite to the photosensitive drums with the intermediate transfer belt 11 interposed therebetween. Is called.
The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this color order from the upstream side in the moving direction of the intermediate transfer belt 11.
Each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is provided in an image station for forming yellow, cyan, magenta, and black images, respectively.

The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color and above each photosensitive drum 20, and includes an intermediate transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, And an intermediate transfer belt unit 10 having 12 Bk.
Further, the image forming apparatus 100 includes a secondary transfer roller 5 as a secondary transfer unit that is disposed to face the intermediate transfer belt 11 and rotates along with the intermediate transfer belt 11.
Further, the image forming apparatus 100 includes an intermediate transfer belt cleaning device 13 that is disposed to face the intermediate transfer belt 11 and cleans the upper surface of the intermediate transfer belt 11.
The optical writing device 8 is arranged below the four image stations so as to face them.

The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygon mirror as a deflecting means, and the like.
The optical writing device 8 emits writing light Lb corresponding to each color to each photosensitive drum 20 to form an electrostatic latent image on each photosensitive drum 20.
In FIG. 1, for the sake of convenience, the writing light is labeled Lb for only the black image station, but the same applies to other image stations.

Below the image forming apparatus 100, a sheet feeding device 61 is provided as a sheet feeding cassette on which sheets S transported between the photosensitive drums 20 and the intermediate transfer belt 11 are stacked.
The sheet S conveyed from the sheet feeding device 61 is transferred between the intermediate transfer belt 11 and the secondary transfer roller 5 by the registration roller pair 4 at a predetermined timing in accordance with the toner image formation timing by the image station. It is fed out toward the secondary transfer part.
The sensor detects that the leading edge of the sheet S has reached the registration roller pair 4.

The sheet S on which the toner image has been transferred is sent to the fixing device 150 where heat and pressure are applied to fix the toner image.
The fixed sheet S is discharged onto the upper surface of the main body of the image forming apparatus as a discharge tray by the discharge roller pair 7.
Below the upper surface of the main body of the image forming apparatus, toner bottles 9Y, 9C, 9M, and 9Bk filled with toners of yellow, cyan, magenta, and black are provided.

The intermediate transfer belt unit 10 includes a driving roller 72 and a driven roller 73 around which the intermediate transfer belt 11 is wound, in addition to the intermediate transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, and 12Bk.
The driven roller 73 also has a function as a tension urging unit for the intermediate transfer belt 11. For this reason, the driven roller 73 is provided with an urging unit using a spring or the like.
The intermediate transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the intermediate transfer belt cleaning device 13 constitute a transfer device 71.
The sheet feeding device 61 includes a feeding roller 3 that abuts on the upper surface of the uppermost sheet S. When the feeding roller 3 is driven to rotate counterclockwise, the uppermost sheet S is removed. The sheet is fed toward the registration roller pair 4.

The intermediate transfer belt cleaning device 13 provided in the transfer device 71 includes a cleaning brush and a cleaning blade disposed so as to face and contact the intermediate transfer belt 11.
The intermediate transfer belt cleaning device 13 scrapes and removes foreign matters such as residual toner on the intermediate transfer belt 11 with a cleaning brush and a cleaning blade.
The intermediate transfer belt cleaning device 13 also has discharge means for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

The configuration of the fixing device 150 will be described in detail below.
As shown in FIG. 2, the fixing device 150 includes a fixing belt 14 that is a thin and flexible endless fixing member, and an opposing member that is disposed outside the fixing belt 14 so as to face the fixing belt 14. Pressure roller 16. The fixing belt 14 is formed in a cylindrical shape (cylindrical shape).
Inside the fixing belt 14, a nip forming unit 18 for forming a nip N that conveys the sheet S while being sandwiched between the fixing belt 14 and the pressure roller 16 is provided.
The nip forming unit 18 includes a nip forming member 22 that is disposed inside the fixing belt 14 so as to face the pressure roller 16, and a stay member that holds the nip forming member 22 against the pressure applied from the pressure roller 16. 26.

The nip forming member 22 includes a base member 23 as a first nip forming member and a heat equalizing member 25 as a second nip forming member positioned on the nip side of the base member 23 in the thickness direction of the fixing belt 14 in the nip. It has the structure laminated | stacked on.
A planar heater 24 as a second heating source is provided between the base member 23 and the soaking member 25.
Each of the base member 23, the heat equalizing member 25, and the stay member 26 has a length that extends in the axial direction of the fixing belt 14 (hereinafter also referred to as “longitudinal direction”) (see FIG. 5).

The heat equalizing member 25 is provided to prevent the heat of the planar heater 24 from staying locally and to actively move the heat in the longitudinal direction of the fixing belt 14 to reduce the temperature non-uniformity in the longitudinal direction. It has been.
For this reason, it is desirable that the soaking member 25 be a material that can transfer heat in a short time, and it is desirable that the soaking member 25 be a member having high thermal conductivity such as copper, aluminum, or silver. In consideration of cost, availability, thermal conductivity characteristics, and workability, it is most desirable to use copper.
In the present embodiment, the heat equalizing member 25 is formed by bending a copper plate having a thickness of about 0.5 mm into a concave shape. The thickness of the soaking member 25 is exaggerated in FIG.

The soaking member 25 slides on the inner surface of the fixing belt 14 via a low friction sheet as a sliding sheet. The sliding torque can be reduced by applying a lubricant such as fluorine grease or silicone oil to the sliding sheet.
The heat equalizing member 25 may be in direct contact with the inner surface of the fixing belt 14.
The stay member 26 has a box shape with an opening opposite to the nip side, and two halogen heaters 28a and 28b as first heating sources are disposed therein.
The fixing belt 14 is directly heated by radiant heat from the inner surface side by the halogen heaters 28a and 28b at the opening side of the stay member 26, in other words, at a position different from the nip.

In order to increase the heating efficiency of the halogen heaters 28 a and 28 b, a plate-like reflection member 31 that reflects light emitted from the halogen heaters 28 a and 28 b to the fixing belt 14 is provided on the inner surface of the stay member 26.
The reflecting member 31 is provided to suppress wasteful energy consumption due to the stay member 26 being heated by radiation heat from the halogen heaters 28a and 28b.
The same effect can be obtained by performing heat insulation or mirror treatment on the inner surface of the stay member 26 instead of providing the reflecting member 31.

As shown in FIG. 3, the pressure roller 16 has a configuration in which a silicone rubber layer 16b is provided on a hollow metal roller 16a (not shown in other figures).
In order to obtain releasability, a release layer having a layer thickness of 5 to 50 μm made of PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene) is provided on the surface of the rubber layer 16b.
The pressure roller 16 is rotated by a driving force transmitted through a gear from a driving source such as a motor provided in the image forming apparatus.
The pressure roller 16 is pressed against the fixing belt 14 by a spring or the like, and the rubber layer 16b of the pressure roller 16 is crushed and deformed to form a predetermined nip width Nw in the sheet conveyance direction. The

The pressure roller 16 may be a solid roller, but a hollow roller may have a smaller heat capacity. The pressure roller 16 may have a heating source such as a halogen heater inside.
The rubber layer 16b may be solid rubber, but if there is no heater inside the pressure roller, sponge rubber may be used.
Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt 14 to lose heat.

The fixing belt 14 is an endless belt or a film using a metal material such as nickel or SUS having a layer thickness of 30 to 50 μm, or a resin material such as polyimide.
The surface layer of the belt has a release layer such as a PFA or PTFE layer, and has a release property so that toner does not adhere.
There may be an elastic layer formed of a silicone rubber layer or the like between the belt substrate and the PFA or PTFE layer.
When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, the subtle irregularities on the belt surface are transferred to the image and the fixing unevenness included in the solid portion of the image There is a problem that (uneven gloss) remains.

In order to improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed and fixing unevenness is improved.
The fixing belt 14 rotates with contact friction by the rotation of the pressure roller 16.
The fixing belt 14 is sandwiched and rotated at the nip portion, but both end portions are held in a cylindrical shape except for the nip portion, and the cross-sectional shape of the fixing belt 14 is stably maintained in a circular shape.
As illustrated in FIG. 2, a separation member 32 that separates the sheet S from the fixing belt 14 is provided on the downstream side of the nip N in the sheet conveyance direction.

In this embodiment, as shown in FIGS. 2 and 3, the shape of the nip N is flat. However, the shape of the nip N may be convex toward the fixing belt 14 as viewed from the pressure roller 16 or other shapes. May be.
In the nip shape where the fixing belt 14 is recessed, the discharge direction of the front end of the sheet is closer to the pressure roller 16 and the separation is improved, so that the occurrence of jam is suppressed. If the nip shape is straight, the envelope can be adjusted as appropriate, such as good paper passage.
The surface of the base member 23 facing the pressure roller 16 may be concave, and the heat equalizing member 25 may be made to follow this.

The stay member 26 prevents the nip forming member 22 that receives pressure from the pressure roller 16 from being bent, and a uniform nip width is obtained in the longitudinal direction.
In this embodiment, the pressure roller 16 is pressed toward the fixing belt 14 to form a nip. However, the nip forming unit 18 may be pressed toward the pressure roller 16 to form a nip.
The stay member 26 has a sufficient bending strength to support the nip forming member 22. As the material, a metal material such as stainless steel or iron, or a metal oxide such as ceramics is used.

As shown in FIG. 4, the fixing belt 14 is rotatably supported at both ends in the axial direction by flanges 36 serving as support members protruding in the axial direction from the side plates 34. Although FIG. 4 shows a support configuration on one side in the axial direction of the fixing belt 14, the other side also has the same configuration.
The flange 36 that guides both ends of the fixing belt 14 has an outer diameter substantially equal to the inner diameter of the fixing belt 14, and has a length of 5 to 10 mm inward from both ends of the fixing belt 14.
The fixing belt 14 is guided by the flange 36 so that the cross-sectional shape is maintained in a circular shape even during traveling (during rotation).

A portion corresponding to the nip N of the flange 36 is opened to place the nip forming unit 18 at a predetermined position.
The stay member 26 has a length extending over the entire axial direction of the fixing belt 14, and both sides are fixed to the side plate 34 and supported in a positioned state.

As shown in FIG. 5, two protrusions 26 b and 26 c extending in the longitudinal direction of the fixing belt 14 are formed on the side surface 26 a on the pressure roller 16 side of the stay member 26.
On the surface 23a of the base member 23 facing the pressure roller 16, recesses 23b are formed at both ends in the longitudinal direction, and the sheet heaters 24 are respectively accommodated in the recesses 23b and fixed by means such as adhesion. Yes.
The heat equalizing member 25 is fitted so as to cover the surface facing the pressure roller 16 in the integrated configuration of the base member 23 and the planar heater 24, that is, the surface 23a side, and is integrated by means such as adhesion, and integrated. The formed base member 23 and the soaking member 25 are accommodated and positioned between the protrusions 26b and 26c, and fixed to the side surface 26a by means such as adhesion. With this configuration, the surface 25a forms a nip forming surface.

  A surface 25a facing the pressure roller 16 of the heat equalizing member 25 supported by the base member 23 is a surface that directly contacts the fixing belt 14, and is a substantial nip forming surface. Since the heat equalizing member 25 is supported by the base member 23 supported by the stay member 26, it becomes a rigid body against the pressure applied by the pressure roller 16.

FIG. 6 shows the positional relationship between the heating ranges of the halogen heaters 28 a and 28 b and the planar heater 24.
The planar heater 24 is disposed at a position to heat the outside of both ends of the heating area of the halogen heater 28 b in the axial direction of the fixing belt 14.
In recent years, there has been a need to pass papers of various thicknesses and sizes while improving paper compatibility.
Especially for small size papers such as postcards and envelopes with a width of around 100 mm, papers with a size of around 300 mm such as A3 size and A4 horizontal size widely distributed in the market, and papers larger than A3 size such as A3 Nobi and 13 inches Sex is required.

The difference between the width of A3 vertical size (A3T) or A4 horizontal size (A4Y) and A3 novi (AN; 329 mm) and 13 inches (13IN; 330 mm) is 32 to 33 mm.
Therefore, if the heating is performed on both sides in the axial direction, the sheet-corresponding width can be expanded from the A3 size to a size such as 13 inches if the sheet heater 24 can heat the half of the width of 16 to 16.5 mm. The planar heater 24 may be a small heater having an axial length of about 20 mm.

When passing a large size sheet such as A3 Nobi or 13 inches, the halogen heaters 28a and 28b and the sheet heater 24 are energized.
When passing a sheet of A3 size or smaller, only the halogen heaters 28a and 28b or the halogen heater 28a are energized, and the sheet heater 24 is not energized.

In order to meet the demand for improved paper compatibility and energy saving, it is necessary to reduce the thickness of the heated member such as the fixing belt, but the axial temperature inside the fixing belt cannot be kept uniform due to the reduction in thickness. Further, an excessive temperature rise in the non-sheet passing portion is more likely to be caused.
For this reason, conventionally, the production rate must be reduced to reduce the input energy of the heating source to prevent the temperature from rising, and the user's request could not be satisfied.
Furthermore, with regard to compatibility with large-size paper such as A3 Nobi, in the heating method using a halogen heater, for example, in the case of a popular machine, a plurality of heaters corresponding to small-size paper are provided inside a fixing roller having a diameter of about 30 mm. The number of heaters cannot be increased easily.

For this reason, it is necessary to use a halogen heater having a heat generation length that matches the paper width larger than the A3 size. Speaking from the usage frequency of the paper size, there are overwhelmingly many papers of about 300 mm width. In order to cope with a large size, it is necessary to heat up to the vicinity of 330 mm width, and energy consumption of the difference is wasted when passing a frequently used paper of about 300 mm.
Furthermore, the temperature rises in the vicinity of the end in the longitudinal direction when passing A3 size paper in the vertical direction or A4 size paper in the horizontal direction. It was necessary to provide.
Although the structure which provides a reflecting plate is also known, the malfunction that the temperature of the heater end part abnormally rose has also occurred.

  Conventionally, some fixing members are directly cooled by a cooling fan or the like when a temperature rise occurs in a non-sheet passing portion, but the effect is small. There is also known an induction heating method that uses a magnetic shunt alloy whose magnetism changes depending on the temperature to be heated, and controls the heat generation width by controlling the magnetic flux.

  According to the configuration of the present embodiment, the above problem can be solved by adding a simple configuration in which the planar heaters 24 are added in the vicinity of both ends of the fixing belt 14 in the longitudinal direction.

In the configuration of Patent Document 1, if an attempt is made to increase the heat transfer efficiency from the end heat source to the belt member, the frictional force between the end heat source and the belt member increases, resulting in poor running of the belt member.
If the contact pressure of the end heat source with respect to the belt member is reduced in order to eliminate the running failure of the belt member, the contact tends to become unstable, resulting in poor heat transfer to the belt member and poor heating efficiency.
There were also problems such as overheating of the end heat source and belt damage due to poor heat transfer. Further, there has been a problem that the residual toner that has not been fixed on the conveyed paper is remelted on the belt member at the end heat source and remains as fixed toner.

In the present embodiment, the planar heater 24 is arranged between the base member 23 and the heat equalizing member 25 in the nip forming surface.
As a result, the planar heater 24 can be arranged without providing an extra space inside the fixing belt 14, and the various problems described in Patent Document 1 can be solved.
That is, since the sheet heater 24 does not directly contact the fixing belt 14, the problem of contact pressure between the sheet heater 24 and the fixing belt 14 does not occur.

When the sheet heater 24 for heating the vicinity of both ends of the fixing belt 14 is used, the halogen heaters 28a and 28b corresponding to other normal size papers are controlled to be heated in accordance with the temperature rise at the ends.
As a result, when the amount of heat generated by the planar heater 24 that heats the end portion is low, only the heating range corresponding to the halogen heaters 28a and 28b is heated first, thereby preventing energy from being consumed more than necessary. Can do.
The transport speed when transporting a sheet of a size that uses the planar heater 24 is made slower than the transport speed of a sheet of any other size. By reducing the productivity of large-size paper that is used less frequently in this way, the planar heaters 24 at both ends can be simplified (reduced in cost) and become efficient.
Although FIG. 6 shows a configuration in which the first heating source has two halogen heaters, the present invention is not limited to this, and a configuration having three or more halogen heaters for small-size paper may be used. .

The gist of the present invention will be described with reference to FIG.
FIG. 7 is a cross-sectional view of the vicinity of the sheet heater 24 as seen from the sheet conveying direction. The fixing belt 14 heated by the halogen heaters 28a and 28b not only applies heat to the paper and toner at the nip portion, but also transfers heat to the heat equalizing member 25 and is deprived of heat as indicated by an arrow A.
In particular, when the temperature is raised from room temperature, the temperature of the soaking member 25 is low, so the amount of heat flowing from the fixing belt 14 is large, and the temperature raising time (return time) is delayed. Therefore, it is desirable to insulate from the fixing belt 14 toward the heat equalizing member 25 so that the recovery time is short.

On the other hand, since the planar heater 24 is provided to heat the fixing belt 14 at the nip portion, as indicated by an arrow B, the thermal conductivity from the planar heater 24 to the heat equalizing member 25 is higher. Since heat can be transferred to the fixing belt 14 earlier, the temperature raising time can be shortened.
Furthermore, a uniform temperature distribution in the plane direction of the nip can be obtained by the good heat transfer property by the heat equalizing member 25. For this reason, the occurrence of abnormal images caused by the temperature unevenness of the surface of the fixing belt 14 can be suppressed without the temperature unevenness at the portion of the planar heater 24 being transferred to the fixing belt 14.

By optimizing the thermal conductivity of the nip portion according to the position of the heating area of each of the first heating source and the second heating source, the recovery time is shortened, energy saving performance is improved, and abnormal images are generated. Prevention becomes possible.
In the present embodiment, in order to realize this, the heat transfer from the fixing belt 14 to the nip forming member 22 side in the portion corresponding to the heating region by the halogen heaters 28 a and 28 b of the nip corresponds to the heating region by the planar heater 24. The heat transferability from the nip forming member 22 to the fixing belt 14 side in the portion to be reduced is configured to be smaller.

Here, the base member 23 that is the first nip forming member and the heat equalizing member 25 that is the second nip forming member will be described from the viewpoint of heat transfer.
The base member 23 is a member supported by transmitting a load from the pressure roller 16 by a biasing means such as a spring to the stay member 26.
The base member 23 is made of a heat-resistant resin such as liquid crystal polymer, polyimide, polyamideimide, PPS (poniphenylene sulfide), and PET (polyethylene terephthalate). The reason why the base member 23 is made of resin is to make it difficult to remove heat from the fixing belt 14 as much as possible, and to realize low thermal conductivity and low heat capacity.

If a high thermal conductivity and high heat capacity member such as a metal is used for the base member 23, the heat from the fixing belt 14 is excessively removed, and the temperature of the fixing belt 14 is difficult to rise at the time of warm-up or return, and the return time is delayed. Will lead to.
The base member 23 does not support all the urging load from the pressure roller 16, but receives the full load by the stay member 26, so that the base member 23 only needs to have a strength that does not cause compressive deformation.

As shown in FIG. 8, the planar heater 24 has a configuration in which a resistance heating element 38 is patterned on a ceramic substrate 37 having an outer shape of about 10 mm × 20 mm, and an insulating layer 39 made of a thin glass layer is laminated. . A terminal 45 connected to the power source and the switch element is provided at the end of the planar heater 24.
The resistance heating element 38 is not provided up to the outer peripheral portion of the ceramic substrate 37. For this reason, the calorific value of the outer peripheral part of the planar heater 24 is lower than that of the central part.
As shown in FIG. 9, a space 23 c is formed on the bottom surface of the recess 23 b of the base member 23 that supports the planar heater 24, and the upper surface of the space 23 c has a heater seat surface 23 d having a width of about 1 to 2 mm. It has become. The outer peripheral portion of the planar heater 24 having a low calorific value is in contact with and supported by the heater seat surface 23d.
FIG. 7 shows an example in which the recess 23b of the base member 23 is formed so as not to open at the axial end of the base member 23 and to be surrounded on all four sides in the axial direction.

Due to the support structure of the planar heater 24, the contact area between the planar heater 24 and the soaking member 25 is larger than the contact area between the planar heater 24 and the base member 23, and the soaking member 25 side from the planar heater 24. That is, the heat transfer to the fixing belt 14 side is improved. In other words, the heat flow from the planar heater 24 to the base member 23 side is suppressed as much as possible.
The contact surface of the planar heater 24 with respect to the soaking member 25 may be on the ceramic base 37 side or the insulating layer 39 side. However, when the surface heater 24 is brought into contact with the insulating layer side composed of a thin film glass layer, the heating rate is fast and efficient. .

As described above, the sheet heater 24 has the resistance heating element 38 on one surface side, and one surface side having the resistance heating element 38 mainly generates heat, and the other surface side has too much heat. It is configured not to reach.
The planar heater 24 used in the present embodiment has a resistance heating element 38 on the side in contact with the recess 23a, and a terminal 45 is provided on the surface side.
As shown in FIG. 14, the sheet heater 24 is provided with a resistance heating element 38 on the side not in contact with the fixing belt 14, so that the supplied power reaches the fixing belt 14 even if the insulating layer 39 is damaged. It is configured not to. In particular, when the fixing belt 14 is made of metal as described above, other parts in the image forming apparatus, for example, a known contact thermistor for the fixing belt may be adversely affected through the metal in the fixing belt. Rise. Therefore, the above-described configuration is more suitable for securing a creepage distance between the fixing belt 14 and the resistance heating element 38.

The heat equalizing member 25 is a thin-walled heat conducting member disposed on the contact surface side of the base member 23 with the fixing belt 14. As the soaking member 25, it is preferable to use a copper plate or an aluminum plate having high thermal conductivity. In the present embodiment, the heat equalizing member 25 has a shape bent into a concave shape. As a result, the edge (corner) of the metal material hits the fixing belt 14 to prevent excessive wear.
The thickness of the heat equalizing member 25 is desirably about 0.3 mm to 0.5 mm, and is configured to be easily deformed by a load from the pressure roller 16 without having rigidity and to closely adhere to the surface shape of the base member 23. To do.

The thickness of the heat equalizing member 25 also affects the amount of heat transfer, and the greater the thickness, the greater the amount of heat transfer in the plane direction. Therefore, the temperature rise of the fixing belt 14 due to the above-described sheet passing portion and non-sheet passing portion is not uniform. It is easy to cancel sex. However, since the heat capacity increases, the warm-up time and the recovery time are delayed.
Conversely, the smaller the thickness of the soaking member 25, the faster the warm-up time and the return time, but the temperature uniformity performance decreases. According to the experiments and studies by the present inventors, it is desirable to use a copper plate having a thickness of about 0.3 mm to 0.5 mm for the soaking member 25.

Based on FIG. 7, the heat flow when the fixing belt 14 is heated from room temperature will be described.
When a print signal is input, the vicinity of the center in the axial direction of the fixing belt 14 is heated by the halogen heaters 28a and 28b almost simultaneously. Since the fixing belt 14 rotates at the time of heating, temperature unevenness occurs at the initial stage of heating in the circumferential direction and the axial direction, and the temperature is balanced by heat conduction in the fixing belt 14 with time.
On the other hand, the sheet heater 24 is energized almost simultaneously with the printing signal, and the sheet heater 24 generates heat. When the sheet heater 24 generates heat, the heat is transferred to the base member 23 and the soaking member 25.
At this time, if the heat conductivity of the base member 23 is high, heat flows out to the side opposite to the nip, so that the rate of temperature increase on the nip side decreases.

In order to solve this problem, in the present embodiment, as shown in FIG. 10, the soaking member 25 has the thermal conductivity of the portion 25 </ b> A corresponding to the heating area by the halogen heaters 28 a and 28 b by the planar heater 24. It is smaller than the thermal conductivity of the portion 25B corresponding to the heating region.
In other words, the thermal conductivity of the heat equalizing member 25 is different between both end portions and the center side in the longitudinal direction of the fixing belt 14. In this case, both end portions and the center side of the heat equalizing member 25 may be configured as separate members, or the heat equalizing member 25 made of the same material may be subjected to a process of changing the thermal conductivity.
In addition to the difference in thermal conductivity, in the present embodiment, as described above, the contact area between the planar heater 24 and the heat equalizing member 25 is made larger than the contact area between the planar heater 24 and the base member 23. Therefore, heat can be efficiently transmitted to the nip side.

As a result, heat can be efficiently transferred to the nip side in the portion of the planar heater 24, and in the portion corresponding to the region heated by the halogen heaters 28a and 28b, the heat equalizing member 25 at the time of return or at the beginning of paper feeding. Even in the case where is cooled, it does not absorb more heat than necessary.
On the other hand, the end temperature rise and the non-uniform temperature in the nip that occur when the paper is continuously fed are the same as those in the vicinity of the planar heater 24 because the temperature rises over a certain period of time. Thermal conductivity is not required on the center side of the heat equalizing member 25.
Heat from the sheet heater 24 is transferred to the heat equalizing member 25, and heat from the halogen heaters 28 a and 28 b is transferred from the fixing belt 14 to the heat equalizing member 25.
At the time of warm-up, there is no or little influence of heat transfer due to the passage of paper immediately after returning, so it is better to suppress the heat transfer to the heat equalizing member 25 in the portion corresponding to the area heated by the halogen heaters 28a and 28b. Desirably, it is desirable to promote heat transfer to the heat equalizing member 25 in the region heated by the planar heater 24.

11 and 12 show a second embodiment. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and the description on the structure and function already described will be omitted as appropriate.
As shown in FIG. 11, in the present embodiment, a low thermal conductivity member 27 as a third nip forming member is provided on the nip side surface of the heat equalizing member 25.
The third nip forming member has a structure associated with the heat equalizing member 25, and a material that becomes thermal resistance is provided separately on the nip side of the heat equalizing member 25. As shown in FIG. 12B, the low thermal conductivity member 27 may be integrally formed on the surface of the soaking member 25 in a film shape.

Since the heat equalizing member 25 is in direct contact with the fixing belt 14, heat resistance, slidability (low friction coefficient), and wear resistance are required, and a fluorine-based resin is desirable.
If the low thermal conductivity member 27 is made of a fluorine-based resin as a sliding material, the thermal conductivity is lower than that of the material of the soaking member 25 such as copper or aluminum, and it also serves as a heat resistance material.
As shown in FIG. 11, the thickness of the low thermal conductivity member 27 is set to be large at the center in the longitudinal direction and small near the planar heater 24. Thereby, the heat transfer characteristic similar to 1st Embodiment can be acquired.
As the sliding material, polyacetal or polyamide may be used.

The thickness of the low thermal conductivity member 27 may be constant in the longitudinal direction, and the surface roughness may be rougher on the center side than in the vicinity of the planar heater 24 (third embodiment).
In the portion corresponding to the region heated by the halogen heaters 28a and 28b, the contact point between the low thermal conductivity member 27 and the fixing belt 14 is reduced, so that the same effect as described above can be obtained by inhibiting heat transfer. it can.

The heat conductivity of the base member 23 may be made smaller than the heat conductivity of the soaking member 25 to reduce the heat transfer property in the direction of arrow A in FIG. 7 (fourth embodiment).
An elastic body, preferably an elastic body having high thermal conductivity, is interposed between the heat equalizing member 25 and the planar heater 24 so that the heat of the planar heater 24 can be efficiently transferred to the heat equalizing member 25. .

FIG. 13 shows a fifth embodiment.
In the present embodiment, the planar heater 24 protrudes toward the heat equalizing member 25 by the dimension c with respect to the surface 23a facing the pressure roller 16 of the base member 23.
In other words, the surface of the planar heater 24 that overlaps the heat equalizing member 25 protrudes from the surface 23 a of the base member 23 facing the pressure roller 16 to the heat equalizing member 25.
By doing in this way, the soaking | uniform-heating member 25 and the planar heater 24 can be made to contact reliably, and the heat conductivity of the arrow B direction of FIG. 7 can be improved.
If the planar heater 24 and the surface 23a of the base member 23 are on the same plane, the planar heater 24 may be further away from the nip than the surface 23a of the base member 23 due to design tolerances.

When the surface of the planar heater 24 is separated from the nip, a sufficient contact area with the heat equalizing member 25 cannot be ensured, resulting in poor heat transfer, and not only a delay in temperature rise time but also the temperature of the planar heater 24 itself. There is a possibility that the temperature rises excessively and melts beyond the heat resistance temperature of the base member 23.
In the present embodiment, the planar heater 24 is protruded so that the heat of the planar heater 24 can be reliably transferred to the heat equalizing member 25 even if there is a manufacturing error.

FIG. 15 shows a modification of the nip forming unit. The nip forming unit 63 includes a nip forming member 22, a planar heater 24, and a stay member 64 that holds the nip forming member 22 against the pressure applied from the pressure roller 16.
The stay member 64 integrally includes a receiving portion 64a configured similarly to the stay member 26 to receive the nip forming member 22, and a leg portion 64b having a substantially triangular cross-sectional shape. Between the leg portion 64b and the fixing belt 14, halogen heaters 28a and 28b are arranged as first heating sources for directly heating the fixing belt 14 from the inner surface side by radiant heat.
In order to increase the heating efficiency of the halogen heaters 28a and 28b, a reflecting member 65 made of an arc-shaped plate that reflects the light emitted from the halogen heaters 28a and 28b to the fixing belt 14 includes a leg portion 64b and halogen heaters 28a and 28b. It is provided between.

Even if the nip forming unit 63 described above is used in place of the nip forming unit 18, the same effects as those of the above-described embodiments can be obtained.
Instead of providing the reflecting member 65, the outer surface of the leg portion 64b may be heat-insulated or mirror-finished. In this case, the heating efficiency is slightly reduced as compared with the case where the reflecting member 65 is provided.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to such specific embodiments, and unless specifically limited by the above description, the present invention described in the claims is not limited. Various modifications and changes are possible within the scope of the gist.
The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 14 Fixing belt as fixing member 16 Pressure roller as opposing member 22 Nip forming member 23 Base member as first nip forming member 24 Planar heater as second heat source 25 Leveling as second nip forming member Thermal member 27 Low thermal conductivity member 28a, 28b as third nip forming member Halogen heater as first heating source 150 Fixing device S Paper as recording medium

JP 2014-178370 A

Claims (9)

An endless fixing member having flexibility;
A facing member disposed to face the fixing member;
A nip forming member provided inside the fixing member for forming a nip for nipping and conveying a recording medium between the fixing member and the facing member;
A first heating source for heating the fixing member at a position different from the nip;
A planar second heating source for heating the fixing member at the nip portion;
With
The nip forming member has a configuration in which a first nip forming member and a second nip forming member positioned on the nip side of the first nip forming member are stacked,
The second heating source is between the first nip forming member and the second nip forming member, and at both ends of the portion corresponding to the heating region of the first heating source in the axial direction of the fixing member. Placed in the position to heat the outside,
The heat transfer from the fixing member to the nip forming member side in the portion corresponding to the heating region by the first heating source of the nip is from the nip forming member in the portion corresponding to the heating region by the second heating source. A fixing device configured to be smaller than heat conductivity to the fixing member side. The fixing device according to claim 1,
The second nip forming member is a fixing device in which the thermal conductivity of the portion corresponding to the heating region by the first heating source is smaller than the thermal conductivity of the portion corresponding to the heating region by the second heating source. The fixing device according to claim 1,
A second nip forming member is formed of a metal material, and a third nip forming member having a lower thermal conductivity than the second nip forming member is provided on a surface side of the second nip forming member that contacts the fixing member. The fixing device is provided, and the third nip forming member has a thickness of a portion corresponding to the heating region by the first heating source larger than a thickness of a portion corresponding to the heating region by the second heating source. The fixing device according to claim 1,
A second nip forming member is formed of a metal material, and a third nip forming member having a lower thermal conductivity than the second nip forming member is provided on a surface side of the second nip forming member that contacts the fixing member. The fixing device is provided, and the third nip forming member has a surface roughness of a portion corresponding to the heating region by the first heating source larger than a surface roughness of a portion corresponding to the heating region by the second heating source. The fixing device according to claim 4.
A fixing device in which the third nip forming member is formed of a sliding material. In the fixing device according to any one of claims 1 to 5,
A fixing device in which a contact area of the second heating source with respect to the second nip forming member is larger than a contact area with respect to the first nip forming member. The fixing device according to any one of claims 1 to 6,
The fixing device in which the first nip forming member has a lower thermal conductivity than the second nip forming member. The fixing device according to any one of claims 1 to 7,
The second heating source is accommodated in the recess of the first nip forming member, and the second heating source has a surface on the side overlapping the second nip forming member on the second nip forming member rather than the first nip forming member. Fixing device protruding to the side.   An image forming apparatus comprising the fixing device according to claim 1.

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