JP6269790B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a belt fixing mechanism using a belt as a fixing member.

As is well known, an electrophotographic image forming apparatus outputs a copy image through the following steps.
In other words, the electrostatic latent image formed on the photosensitive member, which is a latent image carrier, is subjected to visible image processing with toner, and the toner image is transferred to a recording medium such as recording paper and then fixed, thereby copying the image. Is output.

Examples of the fixing method used in the image forming apparatus include a heat roller fixing method, a belt fixing method, a film fixing method, and an electromagnetic induction heating fixing method.
In the heat fixing roller system, a fixing roller and a pressure roller that are in contact with each other with a recording paper conveyance path interposed therebetween are used. In this system, the toner image is melted and penetrated into the recording paper by the action of the heat from the heat source provided in the fixing roller and the pressure corresponding to the pressure applied from the pressure roller. The phenomenon that the toner image melts and penetrates the recording paper is the same in the fixing system having the following configuration.
In the belt fixing method, a fixing belt serving as a good heat conductor, a pressure roller, a roller equipped with the belt, and a heating source for the belt are used instead of the fixing roller (for example, Patent Document 1).
In the film fixing method, a fixing belt serving as a good heat conductor, a pressure roller, a roller equipped with the belt, and a heating source for the belt are used instead of the fixing roller (for example, Patent Document 2).
In the electromagnetic induction heating and fixing method, a configuration in which an electromagnetic induction coil for improving heat generation efficiency is provided on a heating member is used (for example, Patent Document 1).

The fixing system has the following required issues.
Shorten the warm-up time (time required from normal temperature to the printable temperature (reload temperature) such as when the power is turned on), and also the first print time (after receiving a print request, printing through print preparations) The time required for the operation to complete the paper discharge is shortened.
In the fixing device, fixing failure may occur for the following reason.
The image forming apparatus is an apparatus that can perform high-speed processing. When the number of fixed sheets per unit time, that is, the number of sheets passing through the fixing device is increased by high-speed processing, the amount of heat supplied to the recording sheet moving at high speed must be increased. This is because the amount of heat necessary for fixing is given to the recording paper as the time for the recording paper to pass through the fixing device becomes shorter.
However, if the amount of heat required at the beginning of continuous printing is not secured, the temperature will drop greatly, and if the paper is passed without reaching the required amount of heat during high-speed continuous printing, there is a possibility that fixing failure will occur. .
In addition, as the speed of image forming apparatuses increases, the number of sheets passed per unit time increases and the required heat quantity increases, so the so-called temperature drop, which is a shortage of heat quantity especially at the beginning of continuous printing, may be a problem. There is a problem that fixing failure occurs when the speed is increased.

On the other hand, in addition to the above-described fixing methods, there is a fixing method called a surf fixing method using a ceramic heater.
The surf fixing method uses a configuration in which only the nip portion is locally heated and the other portions are not heated. In this fixing method, since the heat capacity and the size can be reduced as compared with the belt-type fixing device, it is possible to rise to a predetermined temperature and shorten the first print time, but there are the following problems.
In other words, the surf fixing method has a problem that fixing is liable to occur because the belt is in the coldest state at the entrance of the nip sheet or the like because it is not heated in any part other than the local part. In particular, in a high-speed machine, there is a problem in that fixing failure is more likely to occur because the belt rotates fast and the heat radiation of the belt outside the nip increases.

  Therefore, in order to cope with such a problem, a fixing device has been proposed in which a good fixability can be obtained even when mounted on a high-production image forming apparatus in a configuration using an endless belt ( For example, Patent Document 3).

The fixing device disclosed in Patent Document 3 uses the configuration shown in FIG.
Endless belt 100, pipe-like metal heat conductor 200 disposed inside endless belt 100, heat source 300 disposed in metal heat conductor 200, and metal heat conductor 200 via endless belt 100 A pressure roller 400 is provided that forms a nip portion N that can contact and convey the recording paper.
The endless belt 100 is rotated by the rotation of the pressure roller 400. At this time, the metal heat conductor 200 guides the movement of the endless belt 100. Further, the endless belt 100 is heated by the heat source 300 in the metal heat conductor 200 via the metal heat conductor 200, so that the entire endless belt 100 can be heated. This makes it possible to shorten the first print time from the heating standby time and to solve the shortage of heat during high-speed rotation.

  However, it is necessary to further improve the thermal efficiency in order to further save energy and improve the first print time. Therefore, a configuration in which the endless belt is not heated indirectly via a metal heat conductor (a member denoted by reference numeral 200 in FIG. 9) but directly heated (without a metal heat conductor). It has been proposed (for example, Patent Document 4).

The configuration of the fixing device disclosed in Patent Document 4 is shown in FIG.
In FIG. 10, the fixing device removes the pipe-shaped metal heat conductor from the inside of the endless belt 100, and instead, a plate-shaped nip forming member 500 is provided at a position facing the pressure roller 400.
In the case of this configuration, the endless belt 100 can be directly heated by the heat source 300 at a place other than the place where the nip forming member 500 is disposed, so that the heat transfer efficiency is greatly improved and the power consumption is reduced.
As a result, it is possible to further shorten the first print time from the heating standby time. Moreover, the cost reduction by not providing a metal heat conductor can also be anticipated. In this fixing device, the nip forming member 500 is supported by a support member 600 such as stainless steel, and the strength of the nip forming member 500 against the pressure applied by the pressure roller 400 is increased.

However, in the fixing device shown in FIG. 10, a small-diameter belt having a diameter of about 30 mm is used for the endless belt 100 for the purpose of further improving the thermal efficiency by reducing the heat radiation area.
In such a configuration, the size of the support member 600 disposed in the endless belt 100 tends to be small. As a result, sufficient strength of the nip forming member 500 cannot be obtained, and when the nip forming member 500 is bent due to the pressure applied by the pressure roller 400, the surface pressure distribution and the nip width of the nip portion N vary, thereby fixing. There is a risk that defects will occur.

  Accordingly, an object of the present invention is to provide a fixing device having a configuration capable of improving the strength of a support member that supports a nip forming member and preventing the nip forming member from bending, in view of the problems in the conventional fixing device. And an image forming apparatus including the fixing device.

To achieve this object, the present invention comprises a rotatable endless fixing belt, a nip forming member disposed inside the fixing belt, and abutting the nip forming member via the fixing belt. And a counter rotating body that forms a nip portion with the fixing belt, a heating source that directly heats the fixing belt at a location other than the nip portion, and a support member that supports the nip forming member. In the fixing device for transporting a recording medium carrying an unfixed image to the nip portion between the fixing belt and the counter rotating body, and fixing the unfixed image on the recording medium, the support member is A first part extending in a pressure direction of the counter rotating body, a second part extending from the bent part of the first part and supporting the nip forming member, and the second part separated from the first part. Opposing third part And, and defining a section modulus to 200 mm ³ or more, the heat source is a radiant heat source, wherein the nip forming member is characterized in that the not heated directly by the heating source.

According to the present invention, the first part extending in the pressurizing direction of the counter-rotating body, the second part extending from the first bent part and supporting the nip forming member, and the second part separated, the first part By having the third part facing each other and setting the section modulus of the support member to a predetermined value, for example, 200 (mm ³ ) or more, it becomes possible to select a sectional shape having a large section modulus even if the sectional area is the same. .
As a result, each member can be laid out efficiently by using a member whose strength is ensured within the diameter of the fixing belt having a reduced diameter, and the support member is prevented from being bent and deformed. Deflection of the nip forming member due to contact can be prevented, and the nip width can be formed uniformly in the axial direction of the opposing rotating body, so that a good image can be obtained.

1 is a diagram for describing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram for explaining a schematic configuration of a fixing device mounted on the image forming apparatus. FIG. 3 is a diagram for explaining a configuration of a nip forming member used in the fixing device shown in FIG. 2. It is a figure for demonstrating the structure of a reflective surface. 2A and 2B are diagrams illustrating a configuration of an end portion of the fixing belt, in which FIG. 3A is a perspective view, FIG. 3B is a plan view, and FIG. 3C is a side view as viewed from the rotation axis direction of the fixing belt. FIG. 3 is a diagram for explaining a configuration of a stay used in the fixing device shown in FIG. 2. It is a figure which shows the modification of a stay. It is a figure for demonstrating schematic structure of the fixing device which concerns on other embodiment. It is a schematic block diagram of the conventional fixing device. It is a schematic block diagram of another conventional fixing device.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, and a cleaning device. A backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to the bottle container 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. Here, the recording medium includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet and the like in addition to plain paper. Although not shown, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

The basic operation of the image forming apparatus having the above configuration is as follows.
When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the transport path R is timed by the registration roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the transfer electric field formed in the secondary transfer nip causes a transfer on the intermediate transfer belt 30. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

Next, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 that is used as a rotatable fixing rotating body, a pressure roller 22 that is used as an opposing rotating body that can be rotated in opposition to the fixing belt 21, and the fixing belt 21. A halogen heater 23 used as a heating source for heating, a nip forming member 24 disposed inside the fixing belt 21, a stay 25 used as a support member for supporting the nip forming member 24, and light emitted from the halogen heater 23 A reflecting member 26 that reflects to the fixing belt 21, a temperature sensor 27 that is used as temperature detecting means for detecting the temperature of the fixing belt 21, a separation member 28 that can separate the paper from the fixing belt 21, and a pressure roller 22 are fixed. A pressurizing unit (not shown) used for pressurizing the belt 21 is provided.

The fixing belt 21 is a thin and flexible endless belt member (including a film).
The fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), or polytetra And a release layer on the outer peripheral side made of fluoroethylene (PTFE) or the like. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

The pressure roller 22 includes a cored bar 22a, an elastic layer 22b using foamable silicone rubber, silicone rubber, or fluorine rubber disposed on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Or it is comprised by the mold release layer 22c in which PTFE etc. are used. The pressure roller 22 is in contact with the nip forming member 24 through the fixing belt 21 by being pressed toward the fixing belt 21 by a pressing unit (not shown).
At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width.

  The pressure roller 22 is rotationally driven by a drive source (not shown) such as a motor provided in the printer body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. Further, when there is no elastic layer, the heat capacity is reduced and the fixability is improved. However, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, which may cause uneven gloss in the solid portion of the image. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more.

  By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. Further, the fixing rotator and the counter rotator are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  Each halogen heater 23 is fixed to a side plate (not shown) of the fixing device 20 at both ends. Each halogen heater 23 generates heat by being output controlled by a power supply unit disposed in the printer body. The output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be maintained at a desired temperature. In addition to the halogen heater, an IH (electromagnetic induction), a resistance heating element, a carbon heater, or the like may be used as a heating source for heating the fixing belt 21.

The nip forming member 24 is shown in FIG.
The nip forming member 24 includes a base pad 241 and a sliding sheet (low friction sheet) 240 around which the base pad 241 is wound.
The base pad 241 is a member that determines the shape of the nip portion N in response to the pressure applied by the pressure roller 22. For this reason, it is arranged in parallel with the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22 and is fixedly supported by a stay 25 used as a support member of the nip forming member 24. As will be described later, the base pad 241 is made of a resin such as liquid crystal polymer (LCP), or a material such as metal or ceramic.
Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in parallel with the axial direction of the pressure roller 22. The stay 25 is preferably made of a metal material having high mechanical strength such as stainless steel (SUS) or iron in order to satisfy the function of preventing the nip forming member 24 from bending, but the stay 25 is made of resin. It is also possible.

The base pad 241 is made of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. Accordingly, it is possible to prevent the base pad 241 from being deformed by heat in the toner fixing temperature range and to ensure a stable state of the nip portion N. As a result, the output image quality can be stabilized.
For the base pad 241, general materials such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone (PEEK), etc. It is possible to use a heat resistant resin.

A sliding sheet (low friction sheet) 240 having a low friction coefficient is disposed on at least the surface of the base pad 241 facing the fixing belt 21.
The sliding sheet (low friction sheet) 240 slides the surface of the fixing belt 21 when the fixing belt 21 rotates. The sliding sheet (low friction sheet) 240 is used to reduce the driving torque generated in the sliding fixing belt 21 and reduce the load caused by the frictional force on the fixing belt 21. As a material of the sliding sheet (low friction sheet) 240, for example, PTFE or the like is used.

  The base pad 241 has a function of determining the shape of the nip portion N formed by the pressure roller 22 that is opposed to the sliding sheet (low friction sheet) 240 therebetween. Therefore, the surface facing the nip portion N is substantially flat, in other words, has a straight shape, and a material that is hard to some extent is used as a material for maintaining this shape. Specifically, a crystalline thermoplastic used for liquid crystal polymer (LCP) or the like, for example, a molded product such as an aramid fiber is used. Further, in place of the resin, a material capable of maintaining the shape such as metal or ceramics may be used.

  The reflecting member 26 is disposed between the stay 25 and the halogen heater 23 using aluminum, stainless steel (SUS), or the like whose surface can be used as a reflecting surface. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Moreover, since the reflecting member 26 is directly heated by the halogen heater 23, it is desirable that the reflecting member 26 be formed of a high melting point metal material or the like. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved.

  Further, the reflective surface may be formed by subjecting the surface of the stay 25 on the side of the halogen heater 23 to mirror processing such as polishing or painting without providing the reflective member 26 as in the present embodiment. In addition, the reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is desirably 90% or more.

  However, the shape and material of the stay 25 cannot be freely selected in order to ensure its strength. For this reason, if the reflecting member 26 is separately provided as in the present embodiment, the degree of freedom in selecting the shape and material is increased, and the reflecting member 26 and the stay 25 can be specialized in their functions. Further, since the reflecting member 26 is provided between the halogen heater 23 and the stay 25, the position of the reflecting member 26 with respect to the halogen heater 23 becomes close, so that the fixing belt 21 can be efficiently heated.

Further, in order to further improve the heating efficiency of the fixing belt 21 by light reflection, it is necessary to examine the direction of the reflecting surface of the reflecting member 26 or the stay 25.
For example, as shown in FIG. 4A, when the reflecting surfaces 70 are arranged concentrically with the halogen heater 23 as the center, the light is reflected toward the halogen heater 23. Efficiency will decrease.
On the other hand, as shown in FIG. 4B, when a part or all of the reflecting surface 70 is disposed in the direction other than the halogen heater 23 to reflect the light toward the fixing belt, the halogen heater 23 is used. Since the amount of light reflected in the direction is reduced, the heating efficiency by reflected light can be improved.

The fixing device 20 according to the present embodiment has various contrivances in the configuration in order to further improve energy saving and first print time.
Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method).
In this embodiment, in FIG. 2, nothing is interposed between the left portion of the fixing belt 21 and the halogen heater 23 facing this position. As a result, radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 at a position where the halogen heater 23 and the fixing belt 21 face each other.

In order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small diameter.
Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are in the range of 20 to 50 μm, 100 to 300 μm, and 5 to 50 μm, and the total thickness is 1 mm. It is set as follows. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are made equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  FIG. 5 is a diagram illustrating the configuration of the end portion in the width direction (axial direction) of the fixing belt. In the figure, (A) is a perspective view, (B) is a plan view, and (C) is a side view as seen from the rotation axis direction of the fixing belt. 5 (A) to (C), only the configuration of one end is shown, but the opposite end also has the same configuration. Only the configuration of the end will be described.

  As shown in FIG. 5A or 5B, a belt holding member 40 is inserted into the end portion of the fixing belt 21 in the width direction. An end in the width direction of the fixing belt 21 is rotatably held by a belt holding member 40. Here, the belt holding member 40 includes a belt detent guide portion 40a and a belt rotation guide portion 40b. The belt detent guide portion 40a functions as a guide for detent in the axial direction (thrust direction) of the fixing belt 21, and the belt rotation guide portion 40b functions as a guide in the rotation direction of the belt. As shown in FIG. 5C, the belt holding member 40 is formed in a C-shape that opens at the position of the nip portion (position where the nip forming member 24 is disposed). The end of the stay 25 is fixed to the belt holding member 40 and positioned.

As shown in FIG. 5A or 5B, protection for protecting the end portion in the width direction of the fixing belt 21 between the end surface of the fixing belt 21 and the opposing surface of the belt detent guide portion 40a facing the fixing belt 21. A slip ring 41 as a member is provided.
Since the belt detent guide portion 40a does not rotate, wear occurs with contact with the end of the fixing belt 21 and rotation. Therefore, the slip ring 41 that can rotate with the rotation of the fixing belt 21 is attached to the fixing belt 21. And the belt detent guide portion 40a, the wear of the belt detent guide portion 40a can be reduced.
As a result, when the fixing belt 21 is shifted in the width direction (axial direction), it is possible to prevent the end portion of the fixing belt 21 from coming into direct contact with the belt detent guide portion 40a and wear the end portion. And can prevent damage.

  Further, the slip ring 41 is fitted to the belt holding member 40 with a margin with respect to the outer periphery. For this reason, when the end of the fixing belt 21 comes into contact with the slip ring 41, the slip ring 41 can be rotated with the fixing belt 21, but the slip ring 41 does not rotate and is stationary. I do not care. As a material of the slip ring 41, it is preferable to apply a so-called super engineering plastic excellent in heat resistance, for example, PEEK, PPS, PAI, PTFE and the like.

  Although not shown in the drawings, shielding members that shield heat from the halogen heater 23 are disposed between the fixing belt 21 and the halogen heater 23 at both ends in the axial direction of the fixing belt 21. Thereby, in particular, an excessive temperature rise in the non-sheet passing region of the fixing belt during continuous sheet feeding can be suppressed, and deterioration and damage of the fixing belt due to heat can be prevented. In this embodiment, the only members that contact the inner peripheral surface of the fixing belt 21 are the belt holding member 40 and the nip forming member 24 at both ends. In addition to these members, the members contact the inner peripheral surface of the fixing belt 21. There is no belt guide that guides rotation.

Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG.
When the power switch of the printer main body is turned on, power is supplied to the halogen heater 23, and the pressure roller 22 is started to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the sheet P carrying the unfixed toner image T in the image forming process described above is conveyed in the direction of arrow F1 in FIG. 2 while being guided by a guide plate (not shown), It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The sheet P on which the toner image T is fixed is carried out from the nip portion N in the direction of arrow F2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of the separation member 28. Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller 13 (see FIG. 1) and stocked on the paper discharge tray 14 (see FIG. 1) as described above.

Hereinafter, the structure of the stay will be described in more detail.
As shown in FIG. 6, the stay 25 is in contact with the nip forming member 24 and extends in the paper conveyance direction (vertical direction in the figure), and upstream and downstream sides of the base 25a in the paper conveyance direction. And a rising portion 25b extending in the contact direction of the pressure roller 22 (left side in the figure). The leading end of each rising portion 25b is disposed so as to be close to the inner peripheral surface of the fixing belt 21 in the contact direction of the pressure roller 22.

A distance d between the leading end of the rising portion 25 b and the inner peripheral surface of the fixing belt 21, that is, a distance d between the leading end of the rising portion 25 b and the inner surface of the fixing belt 21 along the contact direction with the pressure roller 22. Is set based on the following conditions.
For example, if the fixing belt 21 is rigid and has little vibration during running (does not flutter), the distance d is set to about 0.02 mm where the stay 25 and the fixing belt 21 do not contact each other. Yes. The dimension of 0.02 mm set as the distance d is a value considering the processing accuracy of the fixing belt 21.
On the other hand, in the case where the fixing belt 21 is thin like a film and does not have sufficient rigidity, the distance d is also considered not to come into contact with the stay 25 in consideration of the fact that the fluttering during traveling increases. Is set to 3.0 mm or less.
When the reflecting member 26 is attached to the tip of the rising portion 25b as in this embodiment, the distance d needs to be set so that the reflecting member 26 does not contact the fixing belt 21. .

  Thus, by arranging the tip of the rising portion 25 b so as to be close to the inner peripheral surface of the fixing belt 21, the rising portion 25 b can be lengthened in the contact direction of the pressure roller 22. That is, since the rising portion 25b has a horizontally long cross section extending in the pressing direction of the pressure roller 22, the section coefficient is increased, and the stay 25 that receives pressure from the pressure roller 22 is bent in the longitudinal direction. By suppressing the occurrence, the mechanical strength can be improved.

Here, the section modulus is a coefficient calculated from the shape of the section as a reference for calculating the magnitude of the bending stress generated in the structural material. When a lateral load is applied to the stay 25, the stay 25 is bent and deformed. The stress generated in the stay 25 by this bending action is tensioned on the convex side and compressed on the concave side with a neutral surface that is not subjected to tension or compression as a boundary. This bending stress in a cross section of the stay 25 is proportional to the distance from the neutral axis (a straight line passing through the centroid of the cross section at the intersection of the neutral plane and the cross section), and is maximum at a point farthest from the neutral axis. The section modulus is obtained by dividing the moment of inertia of the section by the distance from the neutral axis to this point, and is a constant determined by the shape of the section and the position of the neutral axis. Even if the cross-sectional areas are the same, the maximum bending stress generated in the stay 25 can be reduced by using a cross-sectional shape having a large section modulus.
The second moment of area (second moment of area) is the amount that indicates the difficulty of deformation of the object with respect to the bending moment. Like the moment of inertia, “I (Large Eye)”. It is represented by When the cross section of the object is changed, the value of the moment of inertia of the cross section is also changed, so that it is used as a design index for improving the durability of the structure. The unit is expressed in cm ⁴ .

The necessary surface pressure for preventing slip or the like from being rotationally driven at the nip portion N is 0.6 (Kgf / cm ² ) or more. If the section modulus of the stay 25 is 200 (mm ³ ) or more, the pressure roller 22 is rotationally driven at the nip portion N, and the bending deformation of the stay 25 is prevented when the driving force is transmitted to the fixing belt 21. . In addition, by selecting a cross-sectional shape having a large cross-sectional modulus even if the cross-sectional area is the same, each member can be efficiently laid out within the diameter of the fixing belt 21 having a reduced diameter.

In the present embodiment, the nip forming member 24 is compactly formed in order to arrange the stay 25 as large as possible in the fixing belt 21.
Specifically, the width of the nip forming member 24 in the sheet conveyance direction is formed smaller than the width of the stay 25 in the sheet conveyance direction.
In FIG. 6, the heights of the nip forming member 24 at the upstream end 24a and the downstream end 24b in the sheet conveyance direction with respect to the nip portion N or the virtual extension line E are h1 and h2, respectively. When the maximum height with respect to the nip portion N or its virtual extension line E in the portion of the nip forming member 24 other than the end portion 24a and the downstream end portion 24b is h3, h1 ≦ h3 and h2 ≦ h3 are configured. Yes.

  By having such a relationship, the upstream end 24a and the downstream end 24b of the nip forming member 24 in the sheet conveying direction are connected to the respective bent portions of the stay 25 on the upstream and downstream sides in the sheet conveying direction and the fixing belt 21. Therefore, the bent portions can be arranged close to the inner peripheral surface of the fixing belt 21. Thereby, the stay 25 can be arranged as large as possible in a limited space in the fixing belt 21, and the strength of the stay 25 can be ensured.

  Further, in the present embodiment, the fixing belt 21 is guided only by the nip forming member 24 at portions other than the end portion (at the end portion, the fixing belt 21 is also guided by the belt holding member 40). That is, since no guide member other than the nip forming member 24 is provided between the fixing belt 21 and the stay 25, the stay 25 can be disposed closer to the fixing belt 21, and the strength of the stay can be improved. I can plan.

  In the present embodiment, the halogen heater 23 is arranged inside the both rising portions 25b or inside the inner surface extension line L of both the rising portions 25b. By arranging the halogen heater 23 in this way, the halogen heater 23 and the stay 25 can be accommodated in the fixing belt 21 in a compact manner.

Further, as in this embodiment, a part (or all) of the halogen heater 23 is accommodated inside the stay 25, so that the light irradiation range from the halogen heater 23 to the fixing belt 21 is limited to a predetermined range. Will be.
Generally, in the circumferential direction of the fixing belt 21, the heating temperature is high at a portion near the halogen heater 23, and conversely, the heating temperature is low at a portion far from the halogen heater 23. Therefore, as in this embodiment, the halogen heater 23 is accommodated inside the stay 25, and the irradiation range of the light to the fixing belt 21 is narrowed down to a range in which the distance variation is relatively small. Therefore, it is possible to improve image quality.

7A and 7B, a modified example of the stay will be described.
The stay 25 shown in FIGS. 2 and 6 is arranged so that both rising portions 25b are substantially orthogonal to the base portion 25a. In FIG. 7A, the stay indicated by reference numeral 250 is provided. Then, both the rising parts 250b are inclined (opened state indicated by the symbol θ) with respect to the base part 250a. Further, as shown in FIG. 7 (B), the rising portion 250b may be one.
Also in these modified examples, the leading end of the rising portion 250b is brought close to the contact surface of the pressure roller 22 with respect to the inner peripheral surface of the fixing belt 21, and the section coefficient of the stay 250 is set to 200 (mm ³ ) or more. Thus, the strength of the stay 25 can be ensured.
If the section modulus is 200 (mm ³ ) or more, the stay 250 can be formed in other shapes.

  The halogen heater 23 shown in FIG. 7B includes a downstream inner surface extension line S in the fixing belt rotation direction at the rising portion 250b and an upstream inner surface extension line S ′ in the fixing belt rotation direction at the base portion 250a of the stay 250. Since the amount of heat radiation from the heating of the fixing belt 21 to the arrival of the nip portion N can be minimized, the energy saving performance can be further improved.

Next, another embodiment of the fixing device to which the present invention is applied will be described with reference to FIG.
The fixing device 20 shown in FIG. 8 includes three halogen heaters 23 as heating sources. In this case, the fixing belt 21 can be heated in a range corresponding to various widths of the paper by changing the heat generation area for each halogen heater 23. Other configurations are basically the same as those of the embodiment shown in FIG.

That is, also in this embodiment, as shown in FIG. 8, the stay 25 has a section modulus of 200 (mm ³ ) or more, and the rising portion 25 b is a pressure roller with respect to the inner peripheral surface of the fixing belt 21. It is made to approach in 22 contact direction.
In FIG. 8, h1, h2, and h3 are heights in the nip forming member 24 similar to those shown in FIG. 6, and in this embodiment, the stay 25 is made as large as possible in the fixing belt 21. In order to arrange, h1 ≦ h3 and h2 ≦ h3.

  In the configuration shown in FIG. 8, unlike the configuration shown in FIG. 2, the nip forming member 24 is made of a sheet metal member having pieces 2400a and 2400a ′ capable of gripping upper and lower surfaces of the nip forming member 24. The low friction sheet 50 is provided on the surface that is held by the holding member 2400 and faces the nip portion N of the nip forming member 24 as in the configuration shown in FIG.

As described above, according to the present invention, the stay 25 has a section modulus of 200 (mm ³ ) or more, so that the mechanical strength of the stay 25 can be secured, and the nip forming member 24 by the pressure roller 22 can be secured. Can be prevented. As a result, the nip width can be formed uniformly in the axial direction of the pressure roller 22, and a good image can be obtained.

  In particular, in the configuration in which the diameter of the fixing belt 21 is reduced as in the above-described embodiment, the space for arranging the stays 25 and 250 is also reduced. However, by applying the configuration of the present invention, the section coefficient is the same even if the cross-sectional area is the same. It is possible to select a cross-sectional shape having a large diameter, and it is possible to efficiently lay out each member within the diameter of the fixing belt 21 having a reduced diameter and to secure the strength of the stays 25 and 250.

  Further, in each of the embodiments of the present invention, the nip forming member 24 is compactly formed, and further, no separate guide member is provided between the fixing belt 21 and the stay 25. It is possible to secure a large space necessary for arranging the stays 25 and 250. For this reason, in the said embodiment, the stays 25 and 250 can be formed compactly and sufficient intensity | strength, and it becomes possible to prevent the bending of the nip formation member 24 by the pressure roller 22 more reliably.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. In addition, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, and can be mounted on a monochrome image forming apparatus, other printers, copiers, facsimiles, or complex machines thereof. .

20 Fixing device 21 Fixing belt 22 Pressure roller (opposite rotating body)
23 Halogen heater (heating source)
24 Nip forming member 25, 250 Stay (support member)
25a, 250a Base portion 25b, 250b Rising portion 70 Reflecting surface d Distance between the leading end of the rising portion and the inner peripheral surface of the fixing belt L Internal extension line of the rising portion N Nip portion P Paper (recording medium)

JP 2004-286922 A JP 2010-79309 A JP 2007-334205 A Japanese Patent Laid-Open No. 2007-233011

Claims (18)

A rotatable endless fixing belt;
A nip forming member disposed inside the fixing belt;
An opposing rotating body that forms a nip portion with the fixing belt by contacting the nip forming member via the fixing belt;
A heating source for directly heating the fixing belt at a place other than the nip portion;
A support member for supporting the nip forming member,
In a fixing device that conveys a recording medium carrying an unfixed image to the nip portion between the rotating fixing belt and the counter rotating body, and fixes the unfixed image on the recording medium.
The support member includes a first portion extending in a pressing direction of the counter rotating body;
A second part extending from the first bent part and supporting the nip forming member;
Having a third part facing the first part across the second part;
And the section modulus is defined as 200 mm ³ or more ,
The fixing device according to claim 1, wherein the heating source is a radiant heat source, and the nip forming member is not directly heated by the heating source . The nip forming member has a protrusion protruding toward the support member;
The fixing device according to claim 1, wherein the second portion is in contact with the protruding portion . A rotatable endless fixing belt;
A nip forming member disposed inside the fixing belt;
An opposing rotating body that forms a nip portion with the fixing belt by contacting the nip forming member via the fixing belt;
A heating source for directly heating the fixing belt at a place other than the nip portion;
A support member for supporting the nip forming member,
In a fixing device that conveys a recording medium carrying an unfixed image to the nip portion between the rotating fixing belt and the counter rotating body, and fixes the unfixed image on the recording medium.
The support member includes a first portion extending in a pressing direction of the counter rotating body;
A second part extending from the first bent part and supporting the nip forming member;
Having a third part facing the first part across the second part;
And the section modulus is defined as 200 mm ³ or more,
The nip forming member has a protrusion protruding toward the support member;
The fixing device, wherein the second portion is in contact with the protruding portion . The fixing belt is rotatably held at the end of the fixing belt by a belt holding member,
4. The fixing device according to claim 1 , further comprising a fixing belt end protection member disposed between the belt holding member and an end surface of the fixing belt . 5. A rotatable endless fixing belt;
A nip forming member disposed inside the fixing belt;
An opposing rotating body that forms a nip portion with the fixing belt by contacting the nip forming member via the fixing belt;
A heating source for directly heating the fixing belt at a place other than the nip portion;
A support member for supporting the nip forming member,
In a fixing device that conveys a recording medium carrying an unfixed image to the nip portion between the rotating fixing belt and the counter rotating body, and fixes the unfixed image on the recording medium.
The support member includes a first portion extending in a pressing direction of the counter rotating body;
A second part extending from the first bent part and supporting the nip forming member;
Having a third part facing the first part across the second part;
And the section modulus is defined as 200 mm ³ or more,
The fixing belt is rotatably held at the end of the fixing belt by a belt holding member,
A fixing device comprising a fixing belt end protecting member disposed between the belt holding member and an end surface of the fixing belt . The support member, the fixing device according to any one of claims 1 to 5, characterized in that a reflecting surface for reflecting light emitted from the heating source. A rotatable endless fixing belt;
A nip forming member disposed inside the fixing belt;
An opposing rotating body that forms a nip portion with the fixing belt by contacting the nip forming member via the fixing belt;
A heating source for directly heating the fixing belt at a place other than the nip portion;
A support member for supporting the nip forming member,
In a fixing device that conveys a recording medium carrying an unfixed image to the nip portion between the rotating fixing belt and the counter rotating body, and fixes the unfixed image on the recording medium.
The support member includes a first portion extending in a pressing direction of the counter rotating body;
A second part extending from the first bent part and supporting the nip forming member;
Having a third part facing the first part across the second part;
And the section modulus is defined as 200 mm ³ or more,
A fixing device , wherein the support member is provided with a reflecting surface that reflects light emitted from the heating source . The fixing device according to claim 6, wherein a reflectance of the reflecting surface is 90% or more . 9. The apparatus according to claim 6 , wherein a part or all of the reflective surface is disposed in a direction in which light is reflected toward the fixing belt in a direction other than the heating source . Fixing device. The fixing device according to claim 1 , wherein the heating source is not in contact with the fixing belt . 11. The apparatus according to claim 1 , wherein the first member and the third member are respectively provided at the upstream and downstream ends of the support member in the recording medium conveyance direction. Fixing device. The heating source is arranged inside the first part and the third part formed at each end part, or inside an inner surface extension line of the first part and the third part. The fixing device according to claim 11 . Fixing equipment according to any one of claims 1 to 12, characterized in that the diameter of the fixing belt is set at 20 to 40 mm. The fixing device according to claim 1, wherein the nip portion has a straight shape. The fixing device according to claim 1, wherein the nip forming member is made of resin, metal, or plastic. The said 1st part and said 3rd part are arrange | positioned outside the width | variety of the conveyance direction of the said fixing belt of the said nip formation member, The any one of Claims 1 thru | or 15 characterized by the above-mentioned. Fixing device. The fixing device according to claim 1, wherein the heating source is a radiant heat source, and the nip forming member is not directly heated by the heating source.   An image forming apparatus comprising the fixing device according to claim 1.

Images