JP5071019B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus. More specifically, the present invention relates to an electromagnetic induction heating type fixing device.

  An electrophotographic image forming apparatus generally has a fixing device for fixing a toner image transferred onto a recording material such as paper by heating and pressing. As this fixing device, for example, there is one using an electromagnetic induction heating method as described in Patent Document 1. In the device of this document, a coil assembly that generates a high-frequency magnetic field is disposed opposite to a metal sleeve that is rotatably provided. This is to heat the metal sleeve by inducing an induced eddy current in the metal sleeve by a high frequency magnetic field. In this document, it is said that this method can provide a fixing device with good heat conversion efficiency and less wear and deformation.

In the apparatus of the above-mentioned literature, the metal sleeve is sandwiched between an internal pressure member that abuts on the inner surface and an external pressure member that faces the internal pressure member, and is rotated in a driven manner. Therefore, the distance between the outer surface of the metal sleeve and the coil assembly is not necessarily stable. On the other hand, there is a belt in which a fixing belt including an induction heating layer in which eddy current is induced is bonded to a fixing roller disposed on the inner periphery thereof. Alternatively, a fixing roller is inserted into the fixing belt so as not to sag at least when used (see, for example, Patent Document 2). In this way, the fixing belt is stably rotated by rotationally driving the fixing roller.
JP 10-740007 A JP-A-2005-351928

  However, in the fixing device described in Patent Document 2, the fixing belt and the fixing roller are in contact with each other. As a result, the heat generated in the induction heating layer of the fixing belt escapes to the fixing roller. Some fixing rollers are provided with a sponge layer serving as a heat insulating layer as the outermost layer. Even if such a fixing roller was used, the escape of heat could not be completely prevented. On the other hand, there was a demand to prevent the escape of heat and improve the temperature rise. This is because the preheating time can be shortened and the power consumption in the fixing device can be reduced.

  The present invention has been made to solve the problems of the conventional fixing device described above. That is, an object of the present invention is to provide a fixing device capable of preventing the heat generated in the dielectric heating layer of the fixing belt from escaping to the fixing roller and raising the temperature in a short time.

  In order to solve this problem, the fixing device of the present invention includes an endless fixing belt having an electromagnetic induction heating layer, a fixing roller disposed inside the fixing belt, and a nip portion formed with the fixing belt and the fixing roller. And a fixing device that includes a pressure roller that generates a magnetic flux to be applied to an electromagnetic induction heating layer of a fixing belt, and passes a sheet carrying a toner image through a nip portion to fix the toner image to the sheet However, the outer diameter of the fixing roller is smaller than the inner diameter of the fixing belt, and the outer surface of the fixing roller and the inner surface of the fixing belt are in contact with each other at the nip portion and not at other portions. The generator is located on the opposite side of the pressure roller across the fixing belt, and the surface of the magnetic flux generator facing the fixing belt has two or more locations in the axial direction of the fixing roller. Where, and ribs are provided in contact with the fixing belt, a portion other than the rib in the magnetic flux generating unit is one that is not in contact with the fixing belt.

  According to the fixing device of the present invention, the outer diameter of the fixing roller is smaller than the inner diameter of the outer fixing belt. In other words, the outer peripheral length of the fixing roller is smaller than the inner peripheral length of the fixing belt, and if properly arranged, they can be prevented from contacting each other. The outer surface of the fixing roller and the inner surface of the fixing belt can be in contact with each other at the nip portion and not at other portions. Therefore, an air layer is formed between the fixing roller and the fixing belt. This layer of air can provide thermal insulation. Furthermore, a rib is provided in the magnetic flux generation part arranged on the opposite side of the nip part. Accordingly, the fixing belt in a portion not in contact with the fixing roller is stably disposed by the rib. Thereby, the air layer is stably formed. Therefore, the fixing device can prevent the heat generated in the dielectric heating layer of the fixing belt from escaping to the fixing roller and can raise the temperature in a short time.

Further, in the present invention, the ribs, that provided from the image forming region in the roller axis direction on both sides of the outside.
Therefore, the rib does not become an obstacle to image formation.

Further, in the present invention, the fixing belt has an elastic layer and a release layer on the outer surface side of the electromagnetic induction heating layer, and the electromagnetic induction heating layer is fixed outside the image forming area in the roller axial direction of the fixing belt. An exposed portion is formed on the outer surface side of the belt, and the rib contacts the exposed portion .
Therefore, the rib contacts the electromagnetic induction heating layer. This electromagnetic induction heat generating layer is made of metal, and no abrasion powder is generated even if it slides. Therefore, it is possible to form an image with good image quality.

Further, in another aspect of the present invention, the fixing belt has an elastic layer and a release layer on the outer surface side of the electromagnetic induction heat generating layer, and the elastic layer is disposed outside the image forming area in the roller axial direction of the fixing belt. There is the sliding layer in place of the release layer is provided region, in which the ribs are in contact with the sliding layer.
Therefore, the rib contacts the sliding layer. Therefore, good slidability can be obtained.

Furthermore, in the present invention, it is desirable that the rib be made of a fluororesin.
If this is the case, the rib itself is excellent in slidability.

Further, in the present invention, it is desirable to have lid members having a diameter larger than the inner diameter of the fixing belt at both ends of the fixing roller in the roller axial direction.
In this case, an air layer formed between the outer surface of the fixing roller and the inner surface of the fixing belt is confined by the lid members at both end portions in the axial direction. Therefore, good heat insulation can be maintained.

  According to the fixing device of the present invention, the heat generated in the dielectric heating layer of the fixing belt can be prevented from escaping to the fixing roller, and the temperature can be raised in a short time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an induction heating type fixing device.

  As shown in FIG. 1, the fixing device 1 of the present embodiment includes a heating roller 11, a pressure roller 12, and a magnetic flux generator 13. The heating roller 11 and the pressure roller 12 are arranged in parallel to each other, and both are rotatably supported. The pressure roller 12 is urged toward the heating roller 11 in a direction perpendicular to the axis. As a result, as shown, the heating roller 11 is more deformed, and a nip is formed between the heating roller 11 and the pressure roller 12. During the fixing process, the sheet is passed through the nip between the heating roller 11 and the pressure roller 12 from the bottom to the top in the figure. A separation claw 14 for separating the paper from the heating roller 11 is provided near the exit of the nip. Further, the magnetic flux generator 13 is provided with a thermostat 15 for preventing overheating.

  As shown in FIG. 2, the heating roller 11 has a five-layer configuration including a cored bar 21, a heat insulating layer 22, a heating element layer 23, an elastic layer 24, and a release layer 25 from the inside. Among these, the core metal 21 and the heat insulating layer 22 are bonded to each other and are collectively referred to as a fixing roller 27. The heating element layer 23, the elastic layer 24, and the release layer 25 are bonded to each other, and are collectively referred to as a fixing belt 28. The fixing roller 27 and the fixing belt 28 are not bonded. A fixing roller 27 is inserted into an endless fixing belt 28. The roller hardness of the heating roller 11 as a whole is preferably about 30 to 90 degrees in terms of Asker C hardness.

  In this embodiment, as shown in FIG. 1, the inner peripheral diameter of the fixing belt 28 is formed larger than the outer peripheral diameter of the fixing roller 27. Therefore, there is a space S between the fixing roller 27 and the fixing belt 28 except for the nip portion with the pressure roller 12. The difference between the inner peripheral diameter of the fixing belt 28 and the outer peripheral diameter of the fixing roller 27 is that the space S does not disappear even when the fixing device 1 is heated for the fixing operation and the fixing roller 27 is thermally expanded. Is set to about. Thereby, the fixing roller 27 and the fixing belt 28 are thermally insulated by the air in the space S even during the fixing operation. Accordingly, the heat generated in the fixing belt 28 is considerably prevented from escaping to the fixing roller 27.

  The cored bar 21 is a support that supports the entire heating roller 11 and needs to have sufficient heat resistance and strength. For example, an aluminum pipe having a wall thickness of about 4 mm and a diameter of 15 to 25 mmφ may be used. Alternatively, a heat-resistant molded pipe such as PPS (polyphenylene sulfide), an iron pipe, or the like can be used. If possible, non-magnetic materials that are less susceptible to electromagnetic induction are preferred.

  The heat insulating layer 22 is for preventing the heat generated by the heating element layer 23 from escaping to the cored bar 21. Therefore, a sponge material (heat insulation structure) made of a rubber material or a resin material having low thermal conductivity, heat resistance and elasticity is preferable. If it does in this way, between the metal core 21 and the heat generating body layer 23 can be heat-insulated and hold | maintained. Further, the deflection of the fixing belt 28 is allowed, and the nip width can be kept large. In addition, the hardness of the heating roller 11 as a whole can be reduced to facilitate deformation. Thereby, it is possible to improve paper discharge performance and paper separation performance.

  For example, when a silicon sponge material is used as the heat insulating layer 22, a layer having a thickness of 2 to 15 mm, more preferably 3 to 10 mm is used. The heat insulation layer 22 has an Asker C hardness of 20 to 60 degrees, more preferably 30 to 50 degrees. Alternatively, the heat insulating layer 22 may have a two-layer structure of a rubber material and a resin material.

  The heating element layer 23 is a layer that receives the magnetic flux generated by the magnetic flux generator 13 and induces an induced current, thereby generating heat. For example, it is formed of an endless nickel electroformed belt. In this case, it is desirable to use one having a thickness of 10 to 100 μm, more preferably 20 to 50 μm.

  Or as a material of the heat generating body layer 23, the following may be sufficient. For example, other magnetic materials (magnetic metal) such as magnetic stainless steel may be used. Any material having a relatively high magnetic permeability μ and a resistivity ρ within an appropriate range can be used. Moreover, even if it is a nonmagnetic material, if it is electroconductive materials, such as a metal, it can be used by devising a thin film. Further, a resin in which exothermic particles such as metal particles are dispersed may be used. Further, if a resin-based material is used for the heating element layer 23, the paper separation property can be improved.

  The elastic layer 24 is for improving the adhesion between the surface of the heating roller 11 and the paper. This is a layer of rubber material or resin material having heat resistance and elasticity. As the material, for example, heat-resistant elastomers such as silicon rubber and fluorine rubber that can withstand use at the fixing temperature are suitable. Further, the above materials may be mixed with various fillers for the purpose of thermal conductivity and reinforcement. Examples of the particles filled for improving the thermal conductivity include diamond, silver, copper, aluminum, marble, and glass. Practically, silica, alumina, magnesium oxide, boron nitride, beryllium oxide and the like are preferable.

  The elastic layer 24 has a thickness of 10 to 800 μm, more preferably 100 to 300 μm. If the thickness of the elastic layer 24 is less than 10 μm, it is difficult to obtain sufficient elasticity in the thickness direction. On the other hand, when the thickness exceeds 800 μm, it is difficult to cause the heat generated in the heating element layer 23 to reach the outer peripheral surface of the heating roller 11, and the thermal efficiency is deteriorated, which is not preferable.

  The elastic layer 24 has a JIS hardness of 1 to 80 degrees, more preferably 5 to 30 degrees. If the hardness is within this range, stable fixing properties can be secured while preventing a decrease in strength and adhesion of the elastic layer 24. Examples of silicon rubber having a hardness within this range include, for example, one-component, two-component, or three-component or more silicone rubber, LTV (Low Temperature Vulcanizable) type, RTV (Room Temperature Vulcanizable) Sulfur) type, HTV (High Temperature Vulcanizable) type silicon rubber, condensation type or addition type silicon rubber, or the like can be used. Here, silicon rubber having a JIS hardness of 10 degrees and a thickness of 200 μm is used.

  The release layer 25 is the outermost layer of the heating roller 11 and is for improving the release property between the heating roller 11 and the paper. As the release layer 25, a layer that can withstand use at a fixing temperature and has excellent release properties with respect to toner is used. For example, silicon rubber, fluorine rubber, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP Fluorine resins such as (tetrafluoroethylene / hexafluoropropylene copolymer) are preferred. The thickness of the release layer 25 is 5 to 100 μm, more preferably 10 to 50 μm. Further, in order to improve the adhesive force between the release layer 25 and the elastic layer 24, an adhesion treatment with a primer or the like may be performed. Moreover, you may add a electrically conductive material, an abrasion-resistant material, and a heat conductive material as a filler in the mold release layer 25 as needed.

  Next, the pressure roller 12 will be described. As shown in FIG. 3, the pressure roller 12 includes a cored bar 31, a heat insulating layer 32, and a release layer 33. The cored bar 31 is an aluminum pipe having a wall thickness of 3 mm. If the strength can be secured, a heat-resistant molded pipe such as PPS or an iron pipe can be used as the core metal 3. However, the material of the cored bar 31 is more preferably a non-magnetic material that is hardly affected by electromagnetic induction, like the cored bar 21 of the heating roller 11.

  A heat insulating layer 32 is provided on the outer periphery of the cored bar 31. The heat insulation layer 32 is a silicon sponge rubber layer having a thickness in the range of 3 to 10 mm. Instead of the one heat insulating layer 32, a two-layer structure of silicon rubber and silicon sponge may be used.

  The release layer 33 on the outermost periphery of the pressure roller 12 is for improving the release property of the roller surface with respect to the paper, like the release layer 25 of the heating roller 11. The release layer 33 is a layer made of a fluororesin such as PTFE or PFA and having a thickness of 5 to 100 μm, more preferably 10 to 50 μm. In this embodiment, the pressure roller 12 is pressed against the heating roller 11 with a load of 300 to 500 N, and the nip width is about 5 to 15 mm. When it is desired to change the nip width, the load may be set to a different size.

  Next, the magnetic flux generator 13 will be described. The magnetic flux generator 13 faces the outer periphery of the heating roller 11 and is disposed in parallel to the heating roller 11 along the longitudinal direction of the heating roller 11. As shown in FIG. 1, the magnetic flux generator 13 includes an exciting coil 41 and a magnetic core 42 covered with a coil bobbin 43.

  The exciting coil 41 is a coil wound along the longitudinal direction of the heating roller 11. The cross section (see FIG. 1) has a slightly curved shape following the outer periphery of the heating roller 11. A high frequency inverter 44 is connected to the excitation coil 41, and high frequency power of 10 to 100 kHz and 100 to 2000 W is supplied. Therefore, in this embodiment, the winding of the exciting coil 41 is a litz wire formed by bundling several tens to several hundreds of thin wires. Furthermore, assuming that heat is transferred to the winding, in this embodiment, the winding is coated with a heat resistant resin.

  The exciting coil 41 has a main coil 51 and a demagnetizing coil 52. The main coil 51 is provided in the axial direction of the heating roller 11 with a length that is at least the maximum width capable of image formation. On the other hand, the degaussing coil 52 is a short coil provided at both longitudinal ends of the main coil 51. Accordingly, when forming an image on a wide sheet, only the main coil 51 is used to heat the wide range of the heating roller 11. In the case of forming an image on a narrow paper, only the narrow range of the central portion of the heating roller 11 is heated by canceling the magnetic flux generated by the main coil 51 at both ends by the demagnetizing coil 52.

  The magnetic core 42 is for increasing the efficiency of the magnetic circuit and for magnetic shielding. The magnetic core 42 has a main core 53, an end core 54, and a bottom core 55. The main core 53 has a curved shape as shown in FIG. 1, and is disposed so as to cover the exciting coil 41. A hem core 55 is disposed at both hems of the main core 53. End cores 54 are disposed at both ends of the main core 53 in the axial direction. As the main core 53, a core having a substantially “E” cross section and having a central portion protruding toward the heating roller 11 may be used. In this way, the heat generation efficiency can be further increased.

  Each of the magnetic cores 42 is made of a material with high magnetic permeability and low loss. Since this embodiment uses high frequency, cores made of alloys such as permalloy tend to have large eddy current losses in the core. Therefore, when such a material is used, it is desirable to use a laminated core. In addition, when the magnetic shielding of the magnetic circuit part by the exciting coil 41 and the magnetic core 42 can be sufficiently performed by other means, the core may not be provided (air core). Furthermore, as the magnetic core 42, a resin material in which magnetic powder is dispersed can be used. Although this material has a slightly low magnetic permeability, it has the advantage that the shape can be set freely.

  The coil bobbin 43 includes a bobbin main body 56 that covers the entire magnetic core 42 and the exciting coil 41, and a rib 57 provided outside the bobbin main body 56. The ribs 57 are substantially arc-shaped convex portions provided at both axial ends of the bobbin main body 56. The rib 57 is formed integrally with the bobbin main body 56. When assembled as the fixing device 1, the ribs 57 are provided at positions in contact with ranges 58 (see FIG. 4) outside the sheet passing area at both ends in the axial direction of the fixing belt 28. The fixing belt 28 is in contact with the rib 57 so that a stable arrangement is maintained even during rotation. Accordingly, the space S between the fixing belt 28 and the fixing roller 27 is also stably maintained. Therefore, the rib 57 enables positioning of the fixing belt 28 having excellent accuracy and durability.

  In this embodiment, as shown in FIG. 4, there is a range 58 where the elastic layer 24 and the release layer 25 are not provided outside the paper passing area at both ends in the axial direction of the fixing belt 28. That is, in this range 58, the heating element layer 23 is exposed. And the rib 57 is provided in the position which contacts this range 58, respectively. That is, the rib 57 is in direct contact with the heating element layer 23. Unlike the release layer 25 and the elastic layer 24, the heating element layer 23 is a metal and not a resin. Therefore, even if the rib 57 continues to slide with respect to the heating element layer 23, wear is unlikely to occur. If the rib 57 is in direct contact with the release layer 25, wear powder or the like due to wear of the resin may occur, which may cause image quality deterioration. In the present embodiment, this is not the case because the rib 57 is in contact with the range 58.

  The rib 57 may be made of a material such as a fluororesin having excellent heat resistance and slidability. In this case, it may be formed separately from the bobbin main body 56 and attached by fitting or the like. By doing so, the slidability between the rib 57 and the fixing belt 28 is further improved. In this case, the rib 57 can be exchanged as necessary. Furthermore, as shown in FIG. 5, a sliding layer 59 such as a fluororesin may be provided also in a range 58 of the fixing belt 28 with which the rib 57 contacts. By doing so, the slidability between the rib 57 and the fixing belt 28 is further improved.

  Further, sealing plates 61 are provided at both axial ends of the heating roller 11 as shown in FIGS. The sealing plate 61 is a disk-like member provided with a through hole 62 for passing the rotating shaft (core metal 21) of the heating roller 11 in the center thereof. The outer diameter of the sealing plate 61 is larger than the outer diameter of the heating roller 11. Therefore, the air in the space S between the fixing roller 27 and the fixing belt 28 is sealed to some extent by the sealing plates 61 on both ends. That is, the air in this space S does not change much with the outside. Thereby, since the airtightness of the air layer of the space S can be maintained to some extent, the heat insulating effect by this air layer is improved.

  Further, since the sealing plate 61 covers both ends of the heating roller 11, only the fixing belt 28 of the heating roller 11 is prevented from being shifted from the fixing roller 27 in the axial direction to be moved to one side. . That is, the sealing plate 61 also has a function of preventing the belt from shifting. 6 and 7 show the heating roller 11 in a state where it is not subjected to pressure by the pressure roller 12. The pressure roller 12 is in pressure contact with the heating roller 11 only on the inner side in the axial direction from the sealing plates 61 on both sides. The sealing plate 61 is formed in such a size as to cover both ends of the space S even in the heating roller 11 in a state where a part thereof is pressed by the pressure roller. The belt slip prevention function is performed by another member, and instead of the sealing plate 61, a sealing plate only for air sealing may be provided.

  Next, the operation of the fixing device 1 of this embodiment will be described. In the fixing device 1 of the present embodiment, as shown in FIG. 1, the pressure roller 12 is pressed against the heating roller 11, and a nip is formed between them. Further, the pressure roller 12 is driven to rotate in the clockwise direction in the drawing. As a result, the heating roller 11 is driven to rotate counterclockwise in the figure by the frictional force with the pressure roller 12. Note that the relationship between the driving and the driven may be reversed.

  In the magnetic flux generator 13, high frequency power is supplied to the exciting coil 41 by the high frequency inverter 44. The magnetic flux induced thereby passes through the inside of the magnetic core 42 without leaking to the outside. Then, the magnetic flux exits between the protrusions of the magnetic core 42 and penetrates the heating element layer 23 of the heating roller 11. Thereby, an eddy current flows through the heating element layer 23 and the heating element layer 23 generates Joule heat. And the high frequency inverter 44 is controlled so that it may become suitable fixing temperature (for example, about 100-200 degreeC). For this purpose, a thermistor should be provided separately.

  The generated heat is transmitted to the surface of the heating roller 11 through the elastic layer 24 bonded to the heating element layer 23. The sheet carrying the toner image is inserted into the nip between the heating roller 11 and the pressure roller 12 with the surface on which the toner image is placed facing the heating roller 11 side. Then, while passing through the nip between the heating roller 11 and the pressure roller 12, the toner is melted and fixed on the paper. The sheet that has passed through the nip is separated from the heating roller 11 and conveyed to the subsequent stage. If the sheet remains stuck to the heating roller 11 after passing through the nip, it is forcibly separated from the heating roller 11 by the separation claw 14. This prevents the paper from jamming in the fixing device 1. Note that the tip of the separation claw 14 may or may not be in contact with the surface of the heating roller 11.

  In the fixing device 1 of this embodiment, there is a space S between the inner peripheral surface of the heating element layer 23 of the fixing belt 28 and the heat insulating layer 22 on the outer periphery of the fixing roller 27. The fixing belt 28 and the fixing roller 27 are in contact only at the nip portion with the pressure roller 12. Therefore, the space between the heating element layer 23 and the fixing roller 27 is thermally insulated by the air layer in the space S.

  Thereby, as shown in FIG. 8, the fixing belt 28 can be heated in a short time. In this figure, the temperature rise characteristic by the fixing device 1 of the present embodiment is indicated by a solid line, and the temperature rise characteristic by a conventional fixing device having no space between the fixing belt and the fixing roller is indicated by a broken line. In either case, the transition of the temperature of the surface of the heating roller when the same constant power is supplied to the magnetic flux generator 13 is graphed. As can be seen from this figure, according to the embodiment of the present embodiment, the time to reach the target value of 185 ° C. can be shortened by about 30% compared to the conventional one.

  In addition, the fixing device 1 of the present embodiment also has an effect of improving the separation performance. In the heating roller 11, when the pressure is applied by the pressure roller 12, the outer periphery of the fixing roller 27 is deformed so as to be slightly crushed. Therefore, the larger the difference between the inner diameter of the fixing belt 28 and the outer diameter of the fixing roller 27, the larger the angle formed by the fixing belt 28 before and after the nip exit. For example, as shown in FIG. 9, when the outer diameter of the fixing roller 27 is smaller than the inner diameter of the fixing belt 28, the angle α formed by the fixing belt 28 at the nip outlet is large. On the other hand, in the conventional heating roller having no space between the fixing belt 28 and the fixing roller 27 ', the angle β formed by the fixing belt 28 at the nip exit is slightly small. In this embodiment, since the angle α formed by the fixing belt 28 is large, the sheet can be easily separated at the exit of the nip.

  This separation performance was tested using three types of fixing devices in which the same fixing belt and three types of fixing rollers having different diameters were combined. Here, the fixing belt 28 having an inner diameter of about 40 mmφ was used. The fixing roller of this embodiment has an outer diameter of 34 mmφ and a sufficient space S. As comparative examples, two types of fixing rollers 27 having an outer diameter of 38, 40 mmφ were tested. In Comparative Example 2 in which the outer diameter of the fixing roller is 40 mmφ, there is almost no gap between the fixing roller and the fixing belt.

Furthermore, in this test, a relatively thin sheet, which is prone to separation failure, was used, and an almost full-color image was formed with a slight margin at the tip. The evaluation criteria for separability were as follows.
○ when there is no uneven gloss
△ when slight gloss unevenness occurs due to poor separation
This test was conducted in a normal environment with an air temperature of 23 ° C. and a humidity of 65%.

  The test results are shown in Table 1. In the examples, no gloss unevenness occurred in any image. In an image having a tip margin of 1.5 mm, gloss unevenness occurred in both Comparative Examples 1 and 2. In an image having a tip margin of 3 mm, gloss unevenness occurred in Comparative Example 2. From this result, it was found that the sheet separation performance was improved in the present embodiment in which the outer diameter of the fixing roller is small and the difference from the inner diameter of the fixing belt is large.

  As described above in detail, according to the fixing device 1 of the present embodiment, the outer diameter of the fixing roller 27 of the heating roller 11 is made considerably smaller than the inner diameter of the fixing belt 28. Accordingly, a space S is formed between the fixing roller 27 and the fixing belt 28. Since the air inside the space S functions as a heat insulating layer, the heat generated by the fixing belt 28 is difficult to escape to the fixing roller 27. Thus, the present embodiment is a fixing device 1 that can raise the temperature in a short time.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the shape of the bobbin of the magnetic flux generation unit 13 and the arrangement of the core are examples, and are not limited thereto. The ribs only need to be in contact with the fixing belt 28 and held at an appropriate position, and the shape and arrangement thereof are not limited to the above-described embodiments. In addition, this embodiment can be applied to color or monochrome image forming apparatuses such as printers, FAX machines, and copiers.

2 is a cross-sectional view illustrating a fixing device according to the present embodiment. FIG. It is explanatory drawing which shows the layer structure of a heating roller. It is explanatory drawing which shows the layer structure of a pressure roller. FIG. 6 is an explanatory diagram showing a relationship between the arrangement of ribs and the layer configuration of the fixing belt. FIG. 6 is an explanatory diagram showing a relationship between the arrangement of ribs and the layer configuration of the fixing belt. It is explanatory drawing which shows a sealing plate. It is explanatory drawing which shows a sealing plate. It is a graph which shows the temperature rising characteristic by the fixing device of this form. It is explanatory drawing which shows the shape of the fixing belt in a nip exit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 12 Pressure roller 13 Magnetic flux generation part 27 Fixing roller 28 Fixing belt 57 Rib 59 Sliding layer 61 Sealing plate

Claims (4)

An endless fixing belt having an electromagnetic induction heat generating layer, a fixing roller disposed inside the fixing belt, a pressure roller forming a nip portion with the fixing belt and the fixing roller, and an electromagnetic induction heat generating layer of the fixing belt A fixing device for fixing a toner image on a sheet by passing a sheet carrying a toner image through the nip portion,
An outer diameter of the fixing roller is smaller than an inner diameter of the fixing belt;
The outer surface of the fixing roller and the inner surface of the fixing belt are in contact with each other at the nip portion and are not in contact with other portions.
The magnetic flux generation part is located on the opposite side of the pressure roller with the fixing belt in between, and the surface of the magnetic flux generation part facing the fixing belt has an axial direction of the fixing roller (hereinafter, “ Ribs that contact the fixing belt are provided on both sides outside the image forming area in the “roller axial direction”,
Portions other than the ribs in the magnetic flux generating portion are not in contact with the fixing belt,
The fixing belt has an elastic layer and a release layer on the outer surface side of the electromagnetic induction heating layer;
An exposed portion is formed outside the image forming area in the roller axial direction of the fixing belt, and the electromagnetic induction heating layer is exposed to the outer surface side of the fixing belt,
The fixing device according to claim 1, wherein the rib contacts the exposed portion. An endless fixing belt having an electromagnetic induction heat generating layer, a fixing roller disposed inside the fixing belt, a pressure roller forming a nip portion with the fixing belt and the fixing roller, and an electromagnetic induction heat generating layer of the fixing belt A fixing device for fixing a toner image on a sheet by passing a sheet carrying a toner image through the nip portion,
An outer diameter of the fixing roller is smaller than an inner diameter of the fixing belt;
The outer surface of the fixing roller and the inner surface of the fixing belt are in contact with each other at the nip portion and are not in contact with other portions.
The magnetic flux generation part is located on the opposite side of the pressure roller with the fixing belt in between, and the surface of the magnetic flux generation part facing the fixing belt has an axial direction of the fixing roller (hereinafter, “ Ribs that contact the fixing belt are provided on both sides outside the image forming area in the “roller axial direction”,
Portions other than the ribs in the magnetic flux generating portion are not in contact with the fixing belt,
The fixing belt has an elastic layer and a release layer on the outer surface side of the electromagnetic induction heating layer;
Outside the image forming area in the roller axial direction of the fixing belt, there is an area where a sliding layer is provided instead of the elastic layer and the release layer,
The fixing device according to claim 1, wherein the rib contacts the sliding layer. The fixing device according to claim 1 or 2,
The fixing device according to claim 1, wherein the rib is made of a fluororesin. In the fixing device according to any one of claims 1 to 3,
A fixing device having a lid member having a diameter larger than the inner diameter of the fixing belt at both ends of the fixing roller in the roller axial direction.

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