JP5550244B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that heats and pressurizes a recording medium to fix an image on the recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art An electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these includes a fixing device that fixes a toner image on a recording medium such as paper or OHP. In general, a fixing device provided in an image forming apparatus widely employs a method in which heat and pressure are applied to a recording medium, and toner melted by the heat is attached to the recording medium with pressure to perform fixing. This type of fixing device includes a fixing member that is heated by a heating unit such as a halogen heater, and a pressure member that contacts the fixing member with a predetermined pressure. When image fixing processing is performed, first, a warm-up operation is performed in which the fixing member is heated to a preset temperature threshold (hereinafter referred to as a fixing temperature) by a heating unit. After the warm-up operation is completed, the recording medium is passed through a fixing nip formed between the heating unit and the pressure member, so that the image is fixed by heating and pressing the recording medium.

  However, the heat fixing type fixing device as described above cannot start printing during the warm-up operation and causes the user to wait, so that it is required to shorten the warm-up time. In addition, as a measure for energy saving in recent years, many image forming apparatuses have been developed that reduce power consumption by shutting off the energization of the fixing device during standby. In particular, in such an energy-saving image forming apparatus, the warm-up operation when returning from the standby state to the usable state increases, and therefore there is an increasing demand for shortening the warm-up time. For example, Patent Document 1 below proposes a fixing device using a resistance heating element having higher heat conversion efficiency than a halogen lamp in order to shorten the warm-up time.

  FIG. 11 shows a schematic configuration of a fixing device using the resistance heating element. The fixing device includes a rotating body 100, a heating body 200, a fixing belt 300 stretched over the rotating body 100 and the heating body 200, and a pressure member 400 pressed against the fixing belt 300. The heating element 200 is configured by sequentially laminating a resistance heating element 210, an electrical insulating layer 220, and a low friction layer 230, and the low friction layer 230 is in contact with the inner peripheral surface of the fixing belt 300.

  The operation of the fixing device shown in FIG. 11 will be briefly described below. The resistance heating element 210 is heated by supplying power to the resistance heating element 210 from a power supply unit (not shown). Further, by rotating the rotating body 100 in the direction of the arrow X in the figure, the fixing belt 300 runs around in the direction of the arrow Y in the figure. Then, in the state where the fixing belt 300 is heated to a predetermined fixing temperature by the heat generated by the resistance heating element 210, an unfixed image T is formed in the fixing nip N formed by the pressure member 400 and the fixing belt 300 being pressed against each other. Is passed through the recording medium P, and the recording medium P is heated and pressurized to fix the image.

  However, in the fixing device shown in FIG. 11, the resistance heating element 210, the insulating layer 220, and the low friction layer 230 that constitute the heating body 200 are formed to be curved, so that these members are brought into complete contact with each other. It was difficult to fix. Then, if these members are not sufficiently fixed to each other and a gap is generated, there is a problem that the heat of the resistance heating element 210 is not easily transmitted to the fixing belt 300 and the warm-up time becomes long.

  On the other hand, as shown in FIG. 12A, when the heating element 200 is formed in a flat plate shape, the resistance heating element 210, the insulating layer 220, and the low friction layer 230 are easily brought into contact with each other. It is possible to prevent a decrease in thermal conductivity due to. However, in this case, as shown in FIG. 12B, when the fixing belt 300 is run, the contact between the heating body 200 and the fixing belt 300 becomes unstable, so that the heating of the fixing belt 300 is effective. Can't be done efficiently, and the warm-up time becomes long. Further, if the tension of the fixing belt 300 is increased in order to ensure stable contact between the heating body 200 and the fixing belt 300, a local load on the fixing belt 300 increases at the edge portion of the heating body 200, and the fixing belt. 300 may be damaged.

  Therefore, in view of such circumstances, the present invention provides a fixing device capable of shortening the warm-up time by effectively heating the fixing belt, and an image forming apparatus including the fixing device. To do.

The invention of claim 1 is a heating member in which only a flat plate-like heating element is provided as a heating element, an endless fixing belt stretched over the heating member and at least one support member, and the fixing belt. A pressure member that is in pressure contact with the recording medium, and passing the recording medium through a fixing nip formed by pressure contact between the pressure member and the fixing belt, thereby fixing an unfixed image on the recording medium. In the fixing device, the heating member includes a plurality of curved plate portions formed with curved portions that contact the inner peripheral surface of the fixing belt, and the flat plate-like heating element is interposed between the curved plate portions. The arranged flat portions are connected to each other, and the flat plate-like heating element is arranged in contact with only the flat portion.

  In the fixing device of the present invention, since the heating element is arranged on the flat surface of the heating member, the heating element can be arranged in contact with the heating member with certainty. As a result, a decrease in thermal conductivity due to poor contact between the heating element and the heating member can be prevented, and the fixing belt can be effectively heated. The fixing device of the present invention is in contact with the fixing belt by the curved surface portion of the heating member. For this reason, when the fixing belt is run, the contact state between the heating member and the fixing belt can be stabilized, and the occurrence of a gap between the heating member and the fixing belt can be suppressed. . As a result, good contact between the heating member and the fixing belt can be ensured, and the fixing belt can be effectively heated. Further, since the curved surface portion of the heating member is in contact with the fixing belt, it is possible to prevent a local load from being generated on the fixing belt. As a result, it is possible to suppress the wear and damage of the fixing belt and to prolong the service life.

  In the fixing device of the present invention, the heating member is disposed in contact with the inner peripheral surface of the fixing belt without contacting the outer peripheral surface of the fixing belt. When the heating member is brought into contact with the outer peripheral surface of the fixing belt, the adhesion matter such as toner adhering to the outer peripheral surface of the fixing belt is sandwiched between the fixing belt and the heating member, thereby causing poor contact. There is a possibility that the belt cannot be heated sufficiently. On the other hand, when the heating member is disposed in contact with the inner peripheral surface of the fixing belt as in the fixing device of the present invention, no deposits are caught between the fixing belt and the heating member. There is no risk of insufficient heating.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the curved surface portion and the flat surface portion are integrally formed.

  By integrally forming the curved surface portion and the flat surface portion, the heat of the heating element is easily transmitted to the fixing belt.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the heating member includes a plurality of curved plate portions in which the curved surface portion is formed, the flat portion, and the curved plate portion. It has a flat plate part connected via a bending part between them.

  The bending rigidity of the heating member can be improved by connecting the flat plate portion between the curved plate portions via the bent portion. Therefore, the heating member can be prevented from being bent or deformed, and the fixing belt can be stably supported and run by the heating member.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the surface of the heating member that faces the fixing belt in a non-contact state is made of a heat radiation material. It is.

  By configuring the surface of the heating member that faces the fixing belt in a non-contact state with a heat radiating material, it is possible to heat the fixing belt with radiant heat emitted from the surface composed of the heat radiating material. . As a result, the fixing belt can be heated more effectively.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the heating member has electrical insulation and thermal conductivity formed by blending a thermally conductive inorganic particulate filler. It is comprised by the resin which has.

  Since the resin constituting the heating member has thermal conductivity, the heating member can efficiently transfer the heat of the heating element to the fixing belt. In addition, since the resin constituting the heating member has electrical insulation, the heating element can be disposed on the heating member without using the insulating member, and the thermal conductivity is reduced by interposing the insulating member separately. Can be prevented.

According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the fixing device performs a fixing process by passing a recording medium having at least two types of sizes through the fixing nip. The heating member has a plurality of the plane portions, and the plurality of plane portions include a plane portion in which the flat plate-like heating element is disposed so as to correspond to a small size recording medium passage region, and a small size recording. Ri consists a medium passage region outside the a and a large size recording medium penetration plane portion in which the plate-like heating element is disposed in correspondence with the region, each plate-like heating element, each of the planar portion It is arranged in contact with only .

  When a small-size recording medium is continuously passed through the fixing nip, the heating element disposed corresponding to the small-size recording medium passage area generates a large amount of heat so that the temperature in the small-size recording medium passage area is increased. While recovering to a predetermined temperature, it is possible to suppress an excessive temperature rise in other regions. In addition, when a large-sized recording medium is continuously passed through the fixing nip, the temperature in the large-sized recording medium passage region can be recovered to a predetermined temperature by causing all the heating elements to generate heat equally. .

  A seventh aspect of the present invention is an image forming apparatus including the fixing device according to any one of the first to sixth aspects.

  The fixing device of the present invention can be mounted on an image forming apparatus.

  According to the present invention, the heating member includes the flat surface portion on which the heating element is disposed and the curved surface portion that contacts the inner peripheral surface of the fixing belt, so that the contact between the heating member and the heating element, and the heating member Both the contact with the fixing belt can be ensured satisfactorily. As a result, the fixing belt can be heated efficiently, and the warm-up time can be shortened.

1 is a schematic diagram illustrating an overall configuration of a color image forming apparatus of the present invention. 1 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating a main part of another fixing device according to the first exemplary embodiment of the present invention. FIG. 6 is a diagram illustrating a main part of a fixing device according to a second embodiment of the invention. FIG. 10 is a diagram illustrating an embodiment in which the configuration according to the second embodiment is applied to a fixing device that transports a sheet based on a center. FIG. 10 is a diagram illustrating an embodiment in which the configuration according to the second embodiment is applied to a fixing device that conveys a sheet with reference to an end portion. FIG. 6 is a diagram illustrating a main part of a fixing device according to a third embodiment of the present invention. FIG. 10 is a diagram illustrating a main part of another fixing device according to Embodiment 3 of the present invention. FIG. 10 is a diagram illustrating a main part of a fixing device according to a fourth embodiment of the present invention. FIG. 10 is a diagram illustrating a main part of another fixing device according to Embodiment 4 of the present invention. It is a schematic block diagram of the conventional fixing device. (A) is a schematic block diagram of a fixing device of a comparative example, (B) is a diagram showing the main part of (A).

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. The image forming apparatus according to the present invention shown in FIG. 1 includes four process units 1Y, 1C, 1M, and 1Bk that are detachably attached to the image forming apparatus main body 50. The process units 1Y, 1C, 1M, and 1Bk have the same configuration except that they contain toners of different colors of yellow, cyan, magenta, and black corresponding to the color separation components of the color image. Therefore, the configuration of one process unit 1Y will be described as an example.

  The process unit 1Y includes a photosensitive member 2 as an electrostatic latent image carrier, a charging roller 3 as a charging unit that charges the surface of the photosensitive member 2, and a developing unit that forms a toner image on the surface of the photosensitive member 2. A developing device 4 and a cleaning blade 5 as a cleaning means for cleaning the surface of the photoreceptor 2 are provided.

  Above each of the process units 1Y, 1C, 1M, and 1Bk, an exposure device 7 is disposed as an exposure unit that exposes the surface of the photoreceptor 2. On the other hand, an intermediate transfer unit 6 is disposed below each process unit 1Y, 1C, 1M, 1Bk. The intermediate transfer unit 6 has an endless intermediate transfer belt 10. The intermediate transfer belt 10 is stretched around a plurality of rollers 21 to 24 and is configured to be able to run around in the direction of the arrow in the figure.

  Four primary transfer rollers 11 as primary transfer means are disposed on the inner peripheral surface of the intermediate transfer belt 10. The photoconductor 2 included in each process unit 1Y, 1C, 1M, and 1Bk is pressed against the outer peripheral surface of the intermediate transfer belt 10 at a position facing the four primary transfer rollers 11 to form a primary transfer nip. A secondary transfer roller 12 as a secondary transfer unit is disposed at a position facing one roller 24 that stretches the intermediate transfer belt 10. The secondary transfer roller 12 is pressed against the outer peripheral surface of the intermediate transfer belt 10 to form a secondary transfer nip.

  Below the image forming apparatus main body 50, a plurality of paper feed cassettes 13 containing paper P as a recording medium are disposed. Each paper feed cassette 13 is provided with a paper feed roller 14 and the like for carrying out the paper P. A conveyance path R for guiding the paper P is disposed in the image forming apparatus main body 50. In the transport path R, a pair of registration rollers 15 are disposed upstream of the secondary transfer roller 12 in the paper transport direction. Further, a fixing device 8 for fixing an image on the paper P is disposed downstream of the secondary transfer roller 12 in the paper transport direction. Further, a pair of paper discharge rollers 16 are disposed at the end (downstream end) of the transport path R, and a stock unit 20 for stocking the paper P discharged outside the apparatus is provided in the vicinity of the paper discharge rollers 16. It is provided.

The basic operation of the image forming apparatus will be described below with reference to FIG.
When the image forming operation is started, the photoconductors 2 of the process units 1Y, 1C, 1M, and 1Bk are driven to rotate counterclockwise by a driving device (not shown), and the surface of each photoconductor 2 is driven by the charging roller 3. It is uniformly charged to a predetermined polarity. The surface of each charged photoconductor 2 is irradiated with laser light from the exposure device 7, and an electrostatic latent image is formed on the surface of each photoconductor 2. At this time, the image information to be exposed on each photoconductor 2 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. The electrostatic latent image formed on the photoreceptor 2 in this way is supplied with toner by each developing device 4, whereby the electrostatic latent image is visualized as a toner image.

  Further, a constant voltage or a constant current controlled voltage having a polarity opposite to the toner charging polarity is applied to each primary transfer roller 11. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 11 and each photoconductor 2. Then, the intermediate transfer belt 10 in which the toner images of the respective colors formed on the photoreceptors 2 of the process units 1Y, 1C, 1M, and 1Bk travel in the direction of the arrow in the drawing by the transfer electric field formed in the primary transfer nip. The images are superimposed and transferred sequentially. Thus, the intermediate transfer belt 10 carries a full-color toner image on its surface.

  Residual toner adhering to the surface of each photoconductor 2 after the toner image is transferred is removed from the surface of the photoconductor 2 by each cleaning blade 5, and then the surface is subjected to static elimination action by a static eliminator (not shown). Then, the surface potential is initialized to prepare for the next image formation.

  As the paper feed roller 14 rotates, the paper P is sent from one of the plurality of paper feed cassettes 13 to the transport path R. The sheet P sent to the transport path R is timed by the registration roller 15 and is sent to the secondary transfer nip between the secondary transfer roller 12 and the roller 24 facing it. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 10 is applied to the secondary transfer roller 12, and a transfer electric field is formed in the secondary transfer nip. Then, the toner images on the intermediate transfer belt 10 are collectively transferred onto the paper P by the transfer electric field formed in the secondary transfer nip. The paper P on which the toner image has been transferred is conveyed to the fixing device 8, and the toner image is fixed by applying heat and pressure to the paper P. The paper P on which the toner image is fixed is discharged to the stock unit 20 by the paper discharge roller 16.

  The above description is an image forming operation when a full-color image is formed on the recording medium S. A single color image can be formed using any one of the four process units 1Y, 1C, 1M, and 1Bk. Two or three process units may be used to form a two or three color image.

  Next, the configuration of the fixing device, which is a characteristic part of the present invention, will be described with reference to FIGS. 2-10, the same code | symbol shows the same member or part.

  FIG. 2 is a schematic configuration diagram of the fixing device according to the first exemplary embodiment of the present invention. The fixing device 8 includes a fixing roller 30, a fixing belt 31, a pressure roller 32, and a heating member 33. The fixing belt 31 is stretched around the fixing roller 30 and the heating member 33. The pressure roller 32 is pressed against the fixing belt 31 at a position facing the fixing roller 30, and a fixing nip N is formed at the pressed position. The fixing roller 30 is configured to be rotationally driven in the direction of the arrow in the figure by a driving source (not shown), and the fixing belt 31 and the pressure roller 32 circulate in the direction of the arrow in the figure by the rotational driving of the fixing roller 30. It is designed to run or rotate.

  The fixing roller 30 is configured by disposing an elastic layer made of silicon rubber or the like around a metal core made of aluminum, iron, or the like. The fixing belt 31 is provided with an elastic layer such as silicon rubber on an endless belt base material formed of a flexible resin such as polyimide or a metal such as nickel, and the surface of the elastic layer. In addition, a release layer formed of a fluororesin layer or the like is provided in order to secure the release property of the toner. The pressure roller 32 is provided with an elastic layer made of silicon rubber or the like around a hollow metal core made of aluminum, iron, or the like. The formed release layer is arranged.

  The heating member 33 includes a semi-cylindrical curved plate portion 34 and a flat plate portion 35 formed integrally with the end portion of the curved plate portion 34. The curved plate portion 34 has a curved surface portion 34 a formed in a convex arc shape that contacts the inner peripheral surface of the fixing belt 31. The flat plate part 35 has a flat part 35a, and a heating element 36 such as a resistance heating element is disposed on the flat part 35a.

  As a material of the heating member 33, metal or resin can be applied. In general, when a metal material is applied as the material of the heating member 33, the heating member 33 can easily transmit the heat of the heating element 36 to the fixing belt 31, so that the warm-up time can be shortened. On the other hand, when the heating member 33 is formed of a resin material, there is an advantage that the heating member 33 can be easily formed into a complicated shape and the degree of freedom in design is increased. In order to increase the thermal conductivity of the heating member 33, for example, a metal material such as copper or aluminum is suitable. Further, as the material of the heating member 33, a resin having thermal conductivity and electrical insulation may be applied. As such a resin, for example, a resin formed by highly blending (for example, 85% by weight or more) a thermally conductive inorganic particulate filler with a matrix resin can be applied. Thereby, the heating member 33 can have a thermal conductivity (2 to 18 W / m · k) comparable to that of stainless steel. In addition, since the heating member 33 has electrical insulation, the heating element 36 can be disposed on the heating member 33 without using an insulating member, and a decrease in thermal conductivity due to the presence of the insulating member is prevented. It is possible.

  Further, in order to improve the heating efficiency of the heating member 33, a heat insulating material such as felt is disposed on the surface of the heating member 33 opposite to the surface in contact with the fixing belt 31, so that the heating member 33 is wasted. It is preferable to suppress heat dissipation. The curved surface portion 34a of the heating member 33 that comes into contact with the fixing belt 31 is preferably made of a material having a heat resistance and a small friction coefficient, such as a fluororesin or diamond-like carbon. In particular, when the fixing belt 31 is made of a belt base material made of polyimide resin, it is desirable that the curved surface portion 34a of the heating member 33 is made of fluororesin. As a result, when the fixing belt 31 travels around, an attracting force due to frictional charging is generated between the polyimide resin and the fluororesin, and the contact between the fixing belt 31 and the heating member 33 becomes more stable. It is possible to improve heat conduction.

  As shown in FIG. 3, the curved plate portion 34 and the flat plate portion 35 of the heating member 33 are not necessarily formed integrally, and may be formed separately. However, it is easier to transfer the heat of the heating element 36 to the fixing belt 31 when the curved plate portion 34 and the flat plate portion 35 are formed integrally than when they are formed separately.

  FIG. 4 shows a main part of the fixing device according to the second embodiment of the present invention. As shown in FIG. 4, the heating member 33 of the second embodiment has two flat plate portions 35, unlike the first embodiment, and a heating element 36 is disposed on the flat portion 35 a of each flat plate portion 35. Yes. FIG. 5 shows the heating member 33 as viewed from the back side. As shown in FIG. 5, a heating element 36 is disposed at the center in the longitudinal direction of the upper one plane portion 35a, and heat is generated at both ends in the longitudinal direction of the lower plane portion 35a. A body 36 is disposed. The fixing device according to the second embodiment can perform fixing processing by passing at least two types of paper sheets through the fixing nip. The paper sheets of each size are based on the center of the fixing belt 31 in the width direction. (Center reference). In FIG. 5, a symbol W1 indicates a preset small size paper passage region (recording medium passage region), and a symbol W2 indicates a preset large size paper passage region (recording medium passage region). Here, the heating element 36 disposed in the central portion of the upper flat portion 35a is disposed in correspondence with the small-size paper passage area W1. On the other hand, the two heating elements 36 disposed at both ends of the lower flat portion 35a are outside the small-size paper passage area W1 and within the large-size paper passage area W2 (area indicated by reference numeral W3). It is arranged corresponding to.

  FIG. 6 shows a fixing device that conveys sheets of a plurality of sizes with reference to one end portion in the width direction of the fixing belt 31 (in this case, the left end portion in the figure). That is, the edge reference fixing device shown in FIG. 6 is different from the center reference fixing device shown in FIG. 5 in the setting region of the small-size paper passage region W1. In this case, as shown in FIG. 6, the heating element 36 is disposed from the left end portion in the longitudinal direction of the upper plane portion 35a to the center portion of the two plane portions 35a, and the length of the lower plane portion 35a is set. Another heating element 36 is disposed at the right end of the direction. As a result, a position corresponding to the small size paper passage area W1 and a position outside the small size paper passage area W1 and corresponding to the large size paper passage area W2 (area indicated by reference numeral W3), respectively. A heating element 36 is provided.

  4 to 6, the configuration of the fixing device according to the second embodiment of the present invention has been described. However, since the configuration other than the above-described configuration is the same as that of the fixing device according to the first embodiment of the present invention, the description thereof is omitted. To do. In addition, in the said Example 2, although the heating member 33 has the two flat plate parts 35 (plane part 35a), it is good also considering the number of the flat plate parts 35 (plane part 35a) as three or more.

  FIG. 7 shows a main part of the fixing device according to the third embodiment of the present invention. As shown in FIG. 7, the heating member 33 according to the third embodiment has two curved plate portions 34, and the flat plate portion 35 is connected between the curved plate portions 34 via bent portions 37. FIG. 8 shows a main part of another fixing device according to the third embodiment of the present invention. As shown in FIG. 8, the heating member 33 provided in the fixing device has a plurality of flat plate portions 35 disposed between the curved plate portions 34. In this case, the curved plate portions 34 and the flat plate portions 35 are connected via the bent portions 37, and the flat plate portions 35 are also connected via the bent portions 37. In addition, the number of each of the curved plate part 34 and the flat plate part 35 is not limited to the number shown in FIG.7 and FIG.8, You may provide 3 or more, respectively. Further, in the fixing device according to the third embodiment of the present invention shown in FIG. 7 and FIG. 8, the other configurations are the same as those of the fixing device according to the first embodiment of the present invention, so that the description thereof is omitted.

  9 and 10 show the main part of a fixing device according to Embodiment 4 of the present invention. In the heating member 33 of the fourth embodiment, the flat plate portion 35 is connected between the curved plate portions 34 similarly to the heating member 33 of the third embodiment shown in FIGS. 7 and 8. Further, the surface of the heating member 33 according to the fourth embodiment shown in FIGS. 9 and 10 that is opposed to the fixing belt 31 in a non-contact state is formed of a heat radiation material 38. Specifically, a heat-resistant black paint as a heat radiation material 38 is applied to the surface of the flat plate portion 35 facing the fixing belt 31. Thereby, the heat radiation property of the surface of the heating member 33 coated with the black paint is improved as compared with the surface on the opposite side. Further, in the fixing device according to the fourth embodiment of the present invention shown in FIG. 9 and FIG. 10, the other configurations are the same as those of the fixing device according to the first embodiment of the present invention, so that the description thereof is omitted.

The operation of the fixing device according to each of the embodiments of the present invention will be described below.
First, operations common to the embodiments of the present invention will be described with reference to FIG. By supplying power to the heating element 36 from a power supply unit (not shown), the heating element 36 is caused to generate heat. Further, the fixing roller 30 is rotationally driven in the direction of the arrow in the figure, and the fixing belt 31 and the pressure roller 32 are run around or rotated in the direction of the arrow in the figure. Then, in a state where the fixing belt 31 is heated to a predetermined fixing temperature due to heat generated by the heating element 36, the recording medium P on which the unfixed image T is formed is passed through the fixing nip N, and the recording medium P is heated and heated. The image is fixed by pressing.

  Unlike the conventional fixing device shown in FIG. 11, the fixing device according to each embodiment of the present invention has a heating element 36 disposed on the flat portion 35 a of the heating member 33. For this reason, it is possible to arrange the heating element 36 in contact with the heating member 33 with certainty. As a result, a decrease in thermal conductivity due to poor contact between the heating element 36 and the heating member 33 can be prevented, and the fixing belt 31 can be effectively heated. Further, the fixing device of the present invention is in contact with the fixing belt 31 by the curved surface portion 34a of the heating member 33, unlike the fixing device shown in FIG. For this reason, the fixing device of the present invention can stabilize the contact state between the heating member 33 and the fixing belt 31 when the fixing belt 31 is run, and the like. It is possible to suppress the generation of a gap. Also by this, the fixing belt 31 can be effectively heated. As described above, in the present invention, both the contact between the heating member 33 and the heating element 36 and the contact between the heating member 33 and the fixing belt 31 are obtained by forming the flat surface portion 35 a and the curved plate portion 34 on the heating member 33. Ensure good. As a result, the fixing belt 31 can be heated efficiently, and the warm-up time can be shortened. Further, when the curved surface portion 34 a of the heating member 33 comes into contact with the fixing belt 31, it is possible to prevent a local load from being generated on the fixing belt 31. As a result, the wear of the fixing belt 31 can be suppressed and the life can be extended.

  In the fixing device of the present invention, the heating member 33 is disposed in contact with the inner peripheral surface of the fixing belt 31 without contacting the outer peripheral surface of the fixing belt 31. When the heating member 33 is brought into contact with the outer peripheral surface of the fixing belt 31, a deposit such as toner adhering to the outer peripheral surface of the fixing belt 31 is caught between the fixing belt 31 and the heating member 33, resulting in poor contact. As a result, the fixing belt 31 may not be heated sufficiently. On the other hand, when the heating member 33 is disposed in contact with the inner peripheral surface of the fixing belt 31 as in the fixing device of the present invention, no deposits are caught between the fixing belt 31 and the heating member 33. There is no possibility that the heating of the fixing belt 31 becomes insufficient.

  By the way, in a fixing device that conveys paper of different sizes with the central portion in the width direction of the fixing belt 31 as a reference, when fixing processing is performed by continuously passing small-size paper, fixing through which the small-size paper passes is performed. The amount of heat on the center side of the belt 31 is lost. On the other hand, the amount of heat is hardly lost on the end side of the fixing belt 31 through which the small-size sheet of the fixing belt 31 does not pass. In this case, if the heating is performed uniformly over the entire width direction of the fixing belt 31, the temperature rises excessively on both ends. Therefore, in the fixing device according to the second embodiment of the present invention illustrated in FIGS. 4 and 5, the heating element 36 is located at a position corresponding to the inside of the small size paper passage area W1 and outside the small size paper passage area W1. Are arranged separately at positions corresponding to the large-size paper passage area W2. When continuously passing small-size paper, a large amount of heat is generated by the heating element 36 disposed on the center side, thereby recovering the temperature in the small-size paper passage area W1 to a predetermined fixing temperature. It is possible to suppress an excessive temperature rise in the other region. In addition, when passing large-size paper, all the heating elements 36 on the center side and both ends are heated equally to restore the temperature in the large-size paper passage area W2 to a predetermined fixing temperature. Can be made.

  Although the operation and effect of the second embodiment has been described by taking the center reference fixing device shown in FIG. 5 as an example, the end reference fixing device shown in FIG. By controlling the heat generation, it is possible to suppress the occurrence of a partial high temperature state of the fixing belt 31.

  When the flat plate portion 35 is connected between the curved plate portions 34 via the bent portion 37 as in the fixing device according to the third embodiment of the present invention shown in FIG. 7 or FIG. 8, for example, the bent portion shown in FIG. Compared to the case where the portion 37 is not provided, the bending rigidity of the heating member 33 in the longitudinal direction can be improved. For this reason, the bending and deformation of the heating member 33 in the longitudinal direction can be suppressed, and the fixing belt 31 can be stably supported and run by the heating member 33.

  Further, as in the fixing device according to the fourth embodiment of the present invention illustrated in FIG. 9 or FIG. 10, the surface of the heating member 33 that faces the fixing belt 31 in a non-contact state is configured with the heat radiation material 38. The fixing belt 31 can also be heated by the radiant heat emitted from the surface formed of the heat radiation material 38. Thereby, the fixing belt 31 can be heated more effectively, and the warm-up time can be shortened.

  As mentioned above, although the Example of this invention was described, this invention is not limited to the above-mentioned Example, Of course, a various change can be added in the range which does not deviate from the summary of this invention. For example, in FIG. 2, the fixing roller 30 is applied as one of the supporting members that support the fixing belt 31, but the fixing belt 31 is supported by a non-rotating fixing pad or the like other than a rotating body such as the fixing roller 30. It may be configured to. In addition to the pressure roller 32, a pressure belt or the like can be used as a pressure member that is pressed against the fixing belt 31 to form a fixing nip. Further, the fixing device of the present invention can be mounted not only on the color image forming apparatus shown in FIG. 1 but also on a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

DESCRIPTION OF SYMBOLS 8 Fixing device 30 Fixing roller 31 Fixing belt 32 Pressure roller 33 Heating member 34 Curved plate part 34a Curved part 35 Flat part 35a Plane part 36 Heating element 37 Bending part 38 Thermal radiation material N Fixing nip P Paper W1 Small size paper passage Area W2 Large size paper passage area

Japanese Patent No. 3998955

Claims (7)

As a heating element, a heating member in which only a flat heating element is disposed , an endless fixing belt stretched over the heating member and at least one support member, and a pressure member in pressure contact with the fixing belt A fixing device that performs a fixing process of an unfixed image on the recording medium by passing the recording medium through a fixing nip formed by press-contacting the pressure member and the fixing belt.
The heating member has a plurality of curved plate portions formed with curved portions that contact the inner peripheral surface of the fixing belt, and the flat plate-like heating element is disposed between the curved plate portions. It is formed by connecting flat parts,
The fixing device according to claim 1, wherein the flat heating element is disposed in contact with only the flat portion.   The fixing device according to claim 1, wherein the curved surface portion and the flat surface portion are integrally formed.   The heating member includes a plurality of curved plate portions in which the curved surface portion is formed, and a flat plate portion in which the flat surface portion is formed and connected between the curved plate portions via a bent portion. The fixing device according to 1 or 2.   4. The fixing device according to claim 1, wherein a surface of the heating member that faces the fixing belt in a non-contact state is formed of a heat radiation material. 5.   The fixing device according to any one of claims 1 to 4, wherein the heating member is made of a resin having electrical insulation and thermal conductivity formed by blending a thermally conductive inorganic particulate filler. A fixing device that performs fixing processing by passing recording media of at least two types of sizes through a fixing nip,
The heating member includes a plurality of the flat portions, and the plurality of flat portions include a flat portion in which the flat plate-like heating element is disposed so as to correspond to a small-sized recording medium passage region, and a small size. A flat portion on which the flat plate-like heating element is disposed outside the recording medium passage area and corresponding to the large-size recording medium passage area,
6. The fixing device according to claim 1, wherein each of the plate-shaped heating elements is disposed in contact with only each of the planar portions.   An image forming apparatus comprising the fixing device according to claim 1.

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