JP2007108392A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can reduce power consumption even when a fixing belt is employed and can shorten a warm-up time, and to provide an image forming apparatus. <P>SOLUTION: The fixing device includes the fixing belt 71 which is heated by a heat source and turned, a pressurization member 73 which forms a nip area in contact with the fixing belt 71, and a backup member 72 which is opposite to the pressurization member 73 via the fixing belt 71. The backup member 72 has an elastic layer 732 around a metal core and on the outside of the metal core. The fixing belt 71 is brought into contact with only the backup member 72 in the internal circumferential face of the fixing belt 71. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes a toner image on a recording material and an image forming apparatus such as a copying machine, a printer, and a facsimile machine that includes the fixing device and forms an image.

  An electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine transfers a toner image from a surface of an image carrier such as a photosensitive member or an intermediate transfer member onto a recording material, and fixes the transferred toner image. An image is formed on the recording material.

  Current image forming apparatuses are required to reduce power consumption and shorten warm-up time. In this respect, power consumption is high, and it is important to improve the fixing device most related to warm-up time. In consideration of this point, a fixing device that uses a fixing belt having a small heat capacity and rapidly heats to shorten the warm-up time has been proposed (see Patent Documents 1 and 2).

Since fixing belts are generally several hundred microns thick and have low rigidity, many conventional fixing devices support a fixing belt by contacting a plurality of metal rollers on the inner peripheral surface of the fixing belt. .
JP 2004-29360 A JP 2005-77834 A

  However, even if a fixing belt with a small heat capacity is used to shorten the warm-up time, etc., if a plurality of metal rollers are brought into contact with the inner peripheral surface of the fixing belt, the heat of the fixing belt is taken away by the metal rollers. End up. As a result, even if the fixing belt is set to the reference temperature, power is consumed as much heat is taken away by the metal roller or the like, and extra warm-up time is required. This phenomenon becomes more prominent as the number of metal rollers etc. in contact with the fixing belt increases.

  Therefore, an object of the present invention is to provide a fixing device and an image forming apparatus that can reduce power consumption and warm-up time even when a fixing belt is employed.

  In order to achieve the above object, in the present invention, the configuration of the fixing belt and the backup member contacting the fixing belt is improved.

That is, in the fixing device of the present invention,
A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
The fixing belt is in contact with only the backup member on a part of the inner peripheral surface of the fixing belt.

In the fixing device of the present invention,
A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
The fixing belt itself has a perfect circular shape.

In the fixing device of the present invention,
A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
The fixing belt is a belt having a flatness ratio of 50 or more.

In the image forming apparatus of the present invention,
An image forming apparatus for forming an image on a recording material by fixing a toner image transferred from an image carrier,
A fixing device according to any one of claims 1 to 10 is provided.

  The fixing device and the image forming apparatus according to the present invention can reduce power consumption and warm-up time even when a fixing belt is employed.

  FIG. 1 is an explanatory diagram showing the overall configuration of the image forming apparatus.

  The image forming apparatus shown in FIG. 1 includes a double-sided document automatic feeder RADF and an image forming apparatus main body A.

  The double-sided document automatic feeder RADF is located at the upper part of the image forming apparatus main body A and can be opened and closed. The document on the document feed tray a is transported by a feed roller b, a separation roller c, a registration roller d, and a transport drum e.

  The image forming apparatus main body A includes an image reading unit 1, a control unit 2, an image writing unit 3, an image forming unit 4, a recording material storage unit 5, a conveying unit 6, a fixing device 7, a paper discharging unit 8, and a reconveying unit 9. Etc.

  The optical system of the image reading means 1 includes an exposure unit 14 having a light source and a first mirror, a V mirror unit 15 having a second mirror and a third mirror, a lens 16, and a CCD image sensor 17. The reading operation for the document conveyed by the double-sided document automatic feeder RADF is performed in a state where the exposure unit 14 is positioned below the slit exposure glass 13. The reading operation for the document placed on the platen glass 11 is performed by moving the exposure unit 14 and the V mirror unit 15.

  The document image read by the image reading means 1 is subjected to image processing by the control means 2, converted into a signal as image data, and stored in a memory.

  Next, a process for forming an image on the recording material P will be described.

  The photosensitive member 21 is driven by a main motor (not shown), the surface of the photosensitive member 21 is supplied with a voltage by a power source (not shown), and is negatively charged by the discharge of the charger 22 (in this embodiment − 750V). Next, the image writing unit 3 performs optical writing according to the image information, and an electrostatic latent image is formed on the photoreceptor 21. When the formed electrostatic latent image passes through the developing device 23, the toner charged negatively in the developing device 23 adheres to the portion of the latent image by application of the negative developing bias, and the toner is deposited on the photoreceptor 21. An image is formed. The formed toner image is transferred from the photoreceptor 21 to the recording material P by the transfer device 24A, and the recording material P is separated by the separator 24B. The toner on the photoreceptor 21 remaining after the transfer is cleaned by the cleaning means 25. The separated recording material P is sent to a fixing device 7 including a fixing belt, a pressure member, and the like. As a result, the toner image is fixed to the recording material P, and the recording material P on which the image has been formed is discharged by the paper discharge means 8 to the paper discharge tray 81 outside the apparatus.

  In the case of double-sided printing, the recording material P on which the image is formed on the first surface is sent to the re-conveying means 9 by the conveying path switching plate 82, reversed, and image formation is again performed on the second surface by the image forming means 4. Thereafter, the paper is discharged by a paper discharge means 8 to a paper discharge tray 81 outside the apparatus.

  In the case of reverse paper discharge, the recording material P branched from the normal paper discharge path by the transport path switching plate 82 is switched back and upside down in the reverse paper discharge section 83, and then is discharged from the apparatus by the paper discharge means 8. The paper is discharged to the paper discharge tray 81.

  Currently, image forming apparatuses are required to reduce power consumption and warm-up time. As described above, there are fixing apparatuses that employ a fixing belt with a small heat capacity to shorten the warm-up time. To do. However, if a plurality of metal rollers or the like are brought into contact with the inner peripheral surface of the fixing belt, the heat of the fixing belt is taken away by the metal rollers or the like. Electricity is consumed as much as it is deprived of, and warm-up time is also increased. Accordingly, a fixing device as shown in FIGS. 2 and 3 has been found. The fixing device will be described in detail below.

  FIG. 2 is a front view of the fixing device 7, and FIG. 3 is a perspective view of the main part of the fixing device 7.

  The fixing device 7 passes the recording material through a nip region formed by the fixing belt 71 and a pressure roller 73 that is a pressure member, and fixes the toner image on the recording material.

  The fixing belt 71 is heated by a heater 74 that is a heat source, and melts the toner image on the recording material that has entered the nip region. The fixing belt 71 is, for example, PI (polyimide amide 100 μm) coated with PFA (perfluoroalkoxy) (30 μm), or Ni (100 μm) coated with PFA. As shown in FIGS. 2 and 3, the fixing belt 71 has a substantially perfect circle shape. The circumference of the fixing belt 71 is 40π (π: circumference ratio) mm, and as shown in FIG. 2, it is rotated clockwise at a peripheral speed of 350 to 410 (mm / s).

  The pressure roller 73 that is in contact with the fixing belt 71 to form a nip region is centered on, for example, a hollow aluminum cored bar 731 (thickness 2 mm), and an elastic layer 732 (for example, sponge and silicon rubber) Φ40 mm roller having a two-layer structure.

  A backup roller (backup member) 72 is provided inside the fixing belt 71 (area A in the figure) so as to face the pressure roller 73 with the fixing belt 71 interposed therebetween. The backup roller 72 holds the fixing belt 71 together with the pressure roller 72. The configuration of the backup roller 72 is such that an elastic layer 722 such as silicon rubber is provided outside the cored bar 721 with the cored bar 721 as the center. By providing the elastic layer 722, the heat of the fixing belt 71 can be prevented from decreasing. Although the backup roller 72 has the same diameter in the longitudinal direction, the diameter of the central portion in the longitudinal direction may be a crown shape that is larger than the diameters of both ends in consideration of preventing the fixing belt 71 from shifting.

  The pressure roller 73 is pressed against the fixing belt 71 by a biasing member (not shown) such as a spring at a linear pressure of 29.4 N / cm, and the backup roller 72 and the pressure roller 73 are elastically deformed to form a nip region. is doing. Therefore, both rollers need to have an elastic layer. The length in the short direction of the nip region at this time is about 10.5 mm, although it varies depending on the linear pressure and the hardness of the roller surface.

  On the inner peripheral surface of the fixing belt 71, the fixing belt 71 and the backup roller 72 are in contact with each other. The contacted portion is the back portion of the nip region, and a good nip region can be formed by making contact at this portion. Since the fixing belt 71 is in contact only with the backup roller 72, the heat of the fixing belt 71 can be prevented from lowering compared to a conventional fixing belt in which a plurality of metal rollers or the like are in contact with each other. It is possible to shorten the warm-up time. The fixing belt 71 literally needs to be in contact only with the backup roller 72. For example, in order to stabilize the rotation of the fixing belt 71, when the fixing belt 71 rotates and swings greatly, the fixing belt 71 is guided by the guide plate. Even if the fixing belt 71 is temporarily in contact with a member other than the backup roller 72 for some reason, such as being in contact with (not shown), the fixing belt 71 is substantially in contact with the backup roller 72 only. If the heat of the fixing belt 71 can be prevented from being lowered, it can be said that such a mode is also within the scope of the present invention.

  The fixing belt 71 is a perfect circle belt. By using the fixing belt 71 having such a shape, the fixing belt 71 can be fixed only by being supported by one backup roller 72, and further, it is not necessary to support the fixing belt 71 by a plurality of rollers or the like. It is possible to reduce power consumption and warm-up time.

  The fixing belt 71 is a belt having a flatness ratio of 50 or more. The flatness referred to here is the measurement of the diameter of the fixing belt 71 with the fixing belt 71 in a horizontal plane so that the rotation center axis of the fixing belt 71 is parallel to the horizontal plane. The value is b / a × 100 where b is the small diameter. When the flatness of the fixing belt 71 is low, the behavior of the fixing belt 71 becomes unstable when the fixing belt 71 rotates, and the paper entering the nip area and the fixing belt 71 come into contact with each other outside the nip area, and image distortion occurs. Arise. Therefore, in order to stably rotate the fixing belt 71 having a low aspect ratio, it is necessary to support the fixing belt 71 with a plurality of rollers or the like, and thus it is not possible to reduce power consumption and warm-up time. Therefore, the fixing belt 71 needs to be a belt having an aspect ratio of 50 or more. With such a flat belt, the fixing belt 71 can be stably fixed only by being supported by one backup roller 72, and further, it is not necessary to support the fixing belt 71 by a plurality of rollers or the like. Can be reduced and the warm-up time can be shortened. The fixing belt 71 is more preferably a belt having a flatness ratio of 95 or more. If the distance between the fixing belt 71 and the heater 74 varies, the fixing belt 71 is not heated properly, or the fixing belt 71 contacts the heater 74 and is damaged. Therefore, the flatness of the fixing belt 71 is desirably 95 or more so that the distance between the fixing belt 71 and the heater 74 does not fluctuate.

  The fixing belt 71 is positioned by being sandwiched between the backup member 72 and the pressure roller 73. As a specific configuration of the fixing belt 71, the following can be considered.

  If the circumferential length L of the fixing belt is too long, the shape of the fixing belt 71 becomes unstable, and the distance from the heater 74 cannot be properly secured. On the other hand, if it is too short, a sufficient nip area cannot be secured and a good image cannot be formed. Considering these points, it is desirable to set the circumferential length L of the fixing belt in a range of 10π mm ≦ L ≦ 60π mm (π: circumferential ratio).

  If the thickness T of the fixing belt is too thin, the shape of the fixing belt 71 becomes unstable. On the other hand, if it is too thick, the fixing belt 71 does not have a flat shape in the nip region due to the rigidity of the fixing belt 71 and curls the recording material. Considering these points, it is desirable to set the thickness T of the fixing belt in a range of 100 μm ≦ T ≦ 500 μm.

  A heater 74 as a heat source heats the fixing belt 71 from the outer peripheral surface of the fixing belt 71. Although heating from the inside of the fixing belt 71 may be considered, there is not enough space inside the fixing belt 71 and the backup roller 72 inside the fixing belt 71 is deteriorated by heat. It is desirable to heat from the surface.

  Further, if the heater 74 and the fixing belt 71 are brought into contact with each other, the outer peripheral surface of the fixing belt 71 is deteriorated. Therefore, it is desirable that the heater 74 and the fixing belt 71 are not in contact with each other.

  As the heater 74 for heating the fixing belt 71 in a non-contact manner, a dielectric heating type can be considered, which is a desirable form from the viewpoint of thermal efficiency. The induction heating method is a method in which the fixing belt 71 is induction-heated by passing an alternating current through an exciting coil included therein. The exciting coil is formed using a litz wire in which thin wires are bundled, and a core material made of a high relative magnetic constant such as a ferrite core or permalloy is provided at the center and part of the back surface of the exciting coil. An excitation current of 20 kHz to 50 kHz is applied to the excitation coil from the excitation circuit and is heated by electromagnetic induction.

  As shown in FIG. 2 and FIG. 3, the configuration of the fixing belt 71, the backup roller 72, and the like was found, but how much reduction in power consumption and warm-up time can be achieved was studied using an image forming apparatus together with a comparative example. .

  First, a comparative example will be described.

  FIG. 4 is a diagram showing the form of two types of fixing rollers as a comparative example.

  FIG. 4A is a diagram showing one form of a comparative example. A fixing roller 75 having a halogen heater 751 therein is used as a pressure roller instead of the fixing belt 71, the backup roller 72, and the heater 74 shown in FIG. 73. In this method, a halogen heater 751 is provided inside a hollow core metal 752 (thickness 0.6 mm, diameter 35 to 40 mm) and heated from the inside. FIG. 4B is a diagram showing another embodiment, in which a fixing roller 76 having an elastic layer 762 outside the cored bar 761 is added instead of the fixing belt 71 and the backup roller 72 shown in FIG. This is opposed to the pressure roller 73. The configuration of the fixing roller 76 will be described in detail. An elastic layer 762 such as a sponge is provided around the cored bar 761, and a Ni coating layer 763 (100 to 200 μm) is provided around the core layer 761. The diameter of the fixing roller 76 is the fixing roller 76. Like 75, it is about 35-40 mm. The fixing roller 76 is heated by a heater 74 located outside.

  FIG. 5 is a view showing the form of two types of fixing belts and the like which are embodiments of the present invention.

  FIG. 5A is a diagram showing one form of the embodiment, and has the same configuration as FIG. The configuration of the fixing belt 71 and the like is as described above, and a description thereof is omitted here. FIG. 5B is a diagram showing another embodiment. A difference from FIG. 5A is that a plurality of elastic layers having different thermal conductivities are provided. An elastic layer 722 and an elastic layer 723 are provided on the outer side of the cored bar 721. In order to prevent the heat of the fixing belt 71 from decreasing, the elastic layer 722 closer to the cored bar 721 is more elastic than the elastic layer 723 located on the outer side. It has a low thermal conductivity. For example, a sponge can be used as the elastic layer 722 and a solid rubber can be used as the elastic layer 723.

  The warm-up time and the like are examined using the image forming apparatus based on the above four forms, and the experimental results are shown in FIGS.

  6-8, the fixing roller 75 shown in FIG. 4A is the roller A, the fixing roller 76 shown in FIG. 4B is the roller B, the fixing belt 71 shown in FIG. The fixing belt 71 indicated by 5 (b) is referred to as a belt B. 6 to 8 are graphs showing changes in the surface temperature of the fixing roller or the fixing belt. In FIGS. 6 to 8, the horizontal axis indicates the elapsed time (sec), and the vertical axis indicates the surface of the fixing roller or the fixing belt. Indicates temperature (° C.). 7 is an enlarged view of the elapsed time 0 to 80 sec in FIG. 6, FIG. 8 is an enlarged view of the elapsed time 140 to 200 sec in FIG. 6, and FIG. 9 is an enlarged view of the elapsed time 380 to 420 sec in FIG. . As an experimental condition, first, the warm-up of the image forming apparatus is started (A area in FIG. 6), and image formation is continuously performed immediately after the warm-up is completed (B area in FIG. 6). A state is set (region C in FIG. 6). After the idling state is set for a while, the idling state is restored (D area in FIG. 6), a large amount of image is formed (E area in FIG. 6), and after the image formation is completed, the idling state is again set (in FIG. 6). F region). The idling state is set, and then the idling state is restored (region G in FIG. 6), and continuous image formation is performed immediately after the restoration (region H in FIG. 6). It was examined how the surface temperature of the fixing roller or the fixing belt changed through the state change of the image forming apparatus as described above.

  First, the temperature change of the fixing roller or the like between 0 and 80 sec will be examined based on FIG.

  When the warming-up is started, the temperature of the roller B, the belt A, and the belt B increases in the same manner, and reaches about 200 ° C. in about 15 seconds. However, the roller A finally reaches around 200 ° C. in about 23 sec, and the warm-up time is longer than that of the roller B or the like. This is presumably because the fixing roller 75 is heated from the inside and the heat conductivity is poor, and it takes time until the surface of the fixing roller 75 reaches a predetermined temperature. The surface temperature of the fixing roller and the like temporarily decreases during the time (from about 30 to about 38 seconds) from the completion of warming up to the start of image formation. In this state, the surface temperature of the roller A and the roller B rapidly decreases, whereas the surface temperature of the belt A and the belt B does not decrease so much. Therefore, the belt A and the belt B do not take so much time to reach an appropriate surface temperature of 190 ° C. for image formation. This is because the fixing belt 71 is in contact with only the backup roller 73 on the inner peripheral surface of the fixing belt 71, so heat of the fixing belt 71 is not lost.

  As described above, when the temperature change of the fixing roller or the like between 0 and 80 seconds is examined, the belts A and B are superior to the rollers A and B from the viewpoint of the warming up time and the temperature decrease from the completion of the warming up.

  Next, the temperature change of the fixing roller or the like during the elapsed time 140 to 200 sec is examined based on FIG.

  Looking at the time of returning from the idling state, the recovery time of the roller B, the belt A, and the belt B is slightly shorter than that of the roller A although it is slightly. This is also because the heat conductivity is poor because the fixing roller 75 is heated from the inside, and it takes time for the surface of the fixing roller 75 to reach a predetermined temperature. In addition, the surface temperature of the fixing roller or the like temporarily decreases during the time (from about 146 to about 152 seconds) until the image formation starts after returning from the idling state. In this state, as in FIG. 7, the surface temperatures of the rollers A and B rapidly decrease, whereas the surface temperatures of the belts A and B do not decrease so much.

  As described above, when the temperature change of the fixing roller or the like between 140 and 200 seconds is examined, the belts A and B are superior to the rollers A and B from the viewpoint of the return from the idling state and the temperature decrease after the return. ing.

  Next, the temperature change of the fixing roller or the like during the elapsed time of 380 to 420 seconds will be examined based on FIG.

  Looking at the time of return from the idling state, the return time of the roller B, belt A, and belt B is shorter than that of the roller A, though slightly. This is also because the heat conductivity is poor because the fixing roller 75 is heated from the inside, and it takes time for the surface of the fixing roller 75 to reach a predetermined temperature. Further, the surface temperature of the fixing roller or the like temporarily decreases during the time (from about 385 to about 392 sec) until the image formation is started after returning from the idling state. In this state, the rate of decrease in the surface temperature increases in the order of belt B, belt A, roller B, and roller A. Further, when comparing the belt A and the belt B, there is no difference between the belt A and the belt B in FIG. 8, but the surface temperature of the belt B does not decrease when returning from the idling state after forming a large amount of images. This is because the backup roller is provided with a plurality of elastic layers having different thermal conductivities and the outer elastic layer having a high thermal conductivity is provided, so that it is difficult to transfer the heat of the fixing belt once warmed to the backup roller 73. it can. Therefore, a better result was obtained by providing a plurality of elastic layers having different thermal conductivities. Even in this case, the surface temperature of the belt A does not drop more than that of the rollers A and B.

  As described above, when the temperature change of the fixing roller or the like between 380 and 420 seconds is examined, the belts A and B are more preferable in terms of return from the idling state after a large amount of image formation and temperature decrease after the return. It is superior to roller A and roller B, and belt B is superior to belt A.

  As judged from the above experimental results, the belt A and belt B, which are examples, are superior to the roller A and roller B, which are comparative examples, and can reduce power consumption and warm-up time.

  It should be noted that the present invention is not limited to the above-described embodiment, and may be in other forms as long as it is within the scope of the present invention.

1 is a cross-sectional configuration diagram of an image forming apparatus showing an example of an embodiment of the present invention. FIG. 3 is a front view of the fixing device. FIG. 3 is a perspective view of a main part of the fixing device. It is a figure showing the form of two types of fixing rollers which are comparative examples. FIG. 2 is a diagram illustrating the form of two types of fixing belts and the like according to an embodiment of the present invention. It is a figure showing the result of having examined change of surface temperature, such as a fixing belt. It is an enlarged view showing the result of examining the change in the surface temperature of the fixing belt or the like. It is an enlarged view showing the result of examining changes in the surface temperature of a fixing belt or the like. It is an enlarged view showing the result of examining changes in the surface temperature of a fixing belt or the like.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 7 Fixing apparatus 71 Fixing belt 72 Backup roller (backup member)
721 Core 723, 723 Elastic layer 73 Pressure roller (pressure member)
74 Heater 731 Core Bar 732 Elastic Layer

Claims (11)

A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
The fixing device according to claim 1, wherein the fixing belt is in contact with only the backup member on a part of an inner peripheral surface of the fixing belt. A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
A fixing device, wherein the fixing belt itself has a perfect circle shape. A fixing belt that is heated and rotated by a heat source;
A pressure member that contacts the fixing belt to form a nip region;
A backup member facing the pressure member via the fixing belt;
A fixing device comprising:
The backup member has an elastic layer around the cored bar around the cored bar,
The fixing device is a fixing device having a flatness ratio of 50 or more. The fixing device according to claim 1, wherein the portion where the fixing belt and the backup member are in contact is a back surface portion of the nip region. 5. The fixing device according to claim 1, wherein a circumferential length L of the fixing belt and a thickness T of the fixing belt satisfy the following relational expression.
10πmm ≦ L ≦ 60πmm (π: Pi ratio)
100 μm ≦ T ≦ 500 μm The fixing device according to claim 1, wherein the backup member includes a plurality of elastic layers having different thermal conductivities. The fixing device according to claim 6, wherein the elastic layer closer to the core of the backup member has a lower thermal conductivity than the elastic layer positioned outside. The fixing device according to claim 1, wherein the heat source heats the fixing belt from an outer peripheral surface of the fixing belt. The fixing device according to claim 1, wherein the heat source and the fixing belt are not in contact with each other. The fixing device according to claim 1, wherein the heat source is an induction heating method. An image forming apparatus for forming an image on a recording material by fixing a toner image transferred from an image carrier,
An image forming apparatus comprising the fixing device according to claim 1.

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