JP2010002656A - Fixing belt used for fixing device, fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing belt which is used for an induction heat generation system fixing device and is enhanced in durability. <P>SOLUTION: The fixing belt 56 has conductive layers (such as a heat generation conductive layer 514) and generates heat by electromagnetic induction. The Vickers hardness of the conductive layers are adjusted to ≤Hv200 and ≥Hv130. The conductive layers are Permalloy and their thickness is ≥30 μm and ≤130 μm. The fixing belt 56 is a seamless belt manufactured through one or multiple times of plastic workings. The Vickers hardness of the conductive layers is adjusted by performing annealing processing after at least the last plastic working. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a belt having a metal layer heated by an induction heating method, a fixing device using the belt, and an image forming apparatus including the fixing device, and more particularly to a technique for improving durability of the belt.

In recent years, among the fixing devices provided in electrophotographic and electrostatic recording image forming apparatuses, those using a heat source with a relatively high heat conversion efficiency and a compact induction heat generation method have emerged, and energy saving, space efficiency, and warm-up time have appeared. It is attracting attention from the viewpoint of shortening of
In particular, the heat capacity of the heat generating part can be designed to be considerably small by adopting a configuration in which the magnetic flux generated by flowing an alternating current through the exciting coil is guided to the conductive heat generating layer using a core material such as a ferrite core. Therefore, the warm-up time can be greatly shortened.

  However, since the heat does not easily move when the heat capacity of the heat generating portion becomes small, a portion where the recording sheet does not pass (hereinafter referred to as “non-sheet passing portion”) outside the fixing member in the width direction when a small-sized recording sheet having a small width is continuously used. )) Abnormally rises, causing thermal destruction and deterioration of peripheral members, and if a wide recording sheet subsequently passes, high temperature offset occurs only on the outer side in the width direction, gloss unevenness, etc. There is a problem that occurs.

Therefore, in the fixing device, as a method of suppressing the temperature rise of the non-sheet passing portion, a technique for shielding only the magnetic flux to the non-sheet passing portion by moving the conductive member according to the sheet width, or a non-sheet passing by a demagnetizing coil. A technique for canceling only the magnetic flux to the part is known.
In the above fixing device, a magnetic shunt alloy having a Curie point slightly higher than the fixing temperature is used for the heat generating portion, so that when the temperature of the non-sheet passing portion rises to some extent, the non-sheet passing portion automatically There is a technique for suppressing an excessive temperature rise in the non-sheet passing portion by providing a self-temperature control function in which only the heat generating portion at the position loses magnetic rectification and the amount of heat generation is reduced.

On the other hand, the method using a fixing belt as a fixing member can be designed to have a considerably small heat capacity of the fixing belt, so that the warm-up time can be greatly shortened.
In order to heat such a fixing belt by an induction heating method while providing a self-temperature control function, a magnetic shunt alloy is used for another member that comes into contact with the fixing belt, such as a roller or a regulation plate, to generate heat. Thus, a method of indirectly heating the heat of another member by heat conduction, a method of directly heating by providing a magnetic shunt alloy layer in the fixing belt, and the like can be considered.

For example, Patent Document 1 discloses a fixing device using a magnetic layer (magnetic shunt alloy) having a Curie temperature of 100 to 300 ° C. and a cylindrical or belt-shaped rotating body made of an induction heating layer (copper). In addition, an elastic layer (Si rubber) and a release layer (PFA) are formed on the induction heating layer, an excitation part is provided outside the rotating body, and a nonmagnetic material having a lower electrical resistivity than the rotating body is provided inside the rotating body. In the part where the temperature is raised above the Curie temperature, the rotating body becomes a non-magnetic body, and the induced current flows through the non-magnetic material having a low electrical resistivity, so that the amount of heat generated in that part is reduced. Yes.
JP 2007-279672 A

However, when a conductive layer that generates heat by electromagnetic induction, such as a magnetic shunt alloy layer, is provided in the fixing belt, the layer structure becomes more complex than in the past, and fatigue due to internal stress due to deformation such as bending occurs. Since it is easy to accumulate and eventually leads to local destruction, there is a problem that the life is shortened.
SUMMARY OF THE INVENTION The present invention provides a fixing belt having a conductive layer, a fixing layer having a conductive layer, a fixing device having the fixing belt, and an image forming apparatus having the fixing device, which are used in an induction heating type fixing device. Objective.

In order to achieve the above object, a fixing belt according to the present invention is provided with a conductive layer and generates heat by electromagnetic induction, and the conductive layer is adjusted to have a Vickers hardness of Hv200 or less and Hv130 or more. It is characterized by being.
In order to achieve the above object, a fixing device according to the present invention is a fixing device including the fixing belt.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus including the fixing device.

With the configuration described in the means for solving the problem, the hardness of the conductive layer is adjusted, and as a result, a fixing belt having improved durability can be provided.
Here, in the fixing belt, the fixing device, and the image forming apparatus, the conductive layer may be permalloy.
As a result, it is possible to solve the problem that the fixing belt using the permalloy used in the fixing device having the self-temperature control function is easily damaged.

Here, in the fixing belt, the fixing device, and the image forming apparatus, the conductive layer may have a layer thickness of 30 μm or more and 130 μm or less.
Thereby, the layer thickness is further adjusted, and as a result, it is possible to provide a fixing belt having further improved durability.
Here, in the fixing belt, the fixing device, and the image forming apparatus, the fixing belt is a seamless belt manufactured through one or a plurality of plastic workings, and is subjected to an annealing process at least after the last plastic working. Thus, the Vickers hardness of the conductive layer can be adjusted.

  As a result, the Vickers altitude of the conductive layer was adjusted by darely performing annealing after plastic processing, which was previously thought to reduce hardness and decrease durability. A fixing belt that exhibits stable fixing performance and improved durability can be provided.

[Embodiment 1]
<Overview>
Embodiment 1 is an image forming apparatus including a fixing device that melts and fixes an unfixed image on a recording sheet using an induction heat source heat source, and the fixing belt is subjected to plastic processing once or a plurality of times. Thus, the fixing belt is extended in life by adjusting the Vickers hardness Hv to 200 or less and 130 or more by performing annealing treatment after at least the last plastic working.

<Configuration>
1. Overall Configuration of Image Forming Apparatus FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to the first embodiment.
As shown in FIG. 1, an image forming apparatus 1 according to the present embodiment is a tandem color digital printer, and includes an image processing unit 3, a feeding unit 4, a fixing device 5, and a control unit 6, and a network (for example, in-house) When a print execution instruction is received from an in-house terminal device, a color image is formed on a recording sheet and output in accordance with the instruction.

  The image processing unit 3 is a part mainly responsible for image formation, and forms image images for forming yellow, magenta, cyan, and black toner images along the intermediate transfer belt 11 circulating in the direction indicated by the arrow A. Units 3Y, 3M, 3C, and 3K are sequentially arranged, and an optical unit 10 including a light emitting element such as a laser diode is disposed below each image forming unit. In the image processing section 3, an image forming unit mainly composed of components having “Y” after the reference number generates an image of yellow toner, and similarly, “M” is added after the reference number. An image forming unit mainly composed of the constituent elements is a magenta toner image, and an image forming unit mainly composed of the constituent elements having “C” after the reference number is a cyan toner image. An image forming unit mainly composed of components having “K” after the reference number generates an image using black toner.

The image forming unit 3Y includes a photosensitive drum 31Y, and a charger 32Y, a developing device 33Y, a primary transfer roller 34Y, and a cleaner 35Y disposed around the photosensitive drum 31Y.
In generating an image using yellow toner, the charger 32Y uniformly charges the photosensitive drum 31Y, and the control unit 6 controls the laser beam L to the photosensitive drum 31Y uniformly charged by the optical unit 10. The electrostatic latent image is emitted to form an electrostatic latent image, and the developing device 33Y develops the formed electrostatic latent image with yellow toner, and the developed toner image is primarily transferred to the intermediate transfer belt 11 and primary transferred. Thereafter, the toner remaining on the photosensitive drum 31Y is removed by the cleaner 35Y.

The image forming units 3M, 3C, and 3K also have the same configuration as that of the image forming unit 3Y (the reference numerals are omitted in the drawing), and similarly generate images with toner of each color.
Each time the toner image primarily transferred to the intermediate transfer belt 11 passes through each of the image forming units, the respective colors are superimposed, and finally a full-color toner image is generated.
On the other hand, the feeding unit 4 is a part mainly responsible for transporting the recording sheet, and a paper feeding cassette 41 for storing the recording sheet S and a feeding roller 42 for feeding the stored recording sheet S one by one to the transporting path 43. And a timing roller pair 44 for timing to send out the fed recording sheet S and a secondary transfer roller 45, and the recording sheet S is conveyed to the secondary transfer position 46 and is generated on the intermediate transfer belt 11. The toner image is secondarily transferred to the recording sheet S at the secondary transfer position 46.

The fixing device 5 heats and pressurizes the recording sheet S on which the toner image is secondarily transferred, and fixes the toner image on the recording sheet S. The fixing device 5 will be described in detail below.
The recording sheet S after fixing is discharged to a discharge tray 72 by driving a discharge roller 71 and the like.
The control unit 6 is a controller that collectively controls the overall operation, temperature control, and the like of the image forming apparatus 1, and for each light-emitting element of the optical unit 10 for each image forming unit based on image data to be formed. A drive signal is generated, and the timing is adjusted so that the toner images of the respective colors are accurately superimposed in the primary transfer, or the toner images are accurately transferred to the recording sheet S in the secondary transfer.
2. Details of Fixing Device FIG. 2 is a diagram schematically showing the configuration of the fixing device 5.

As shown in FIG. 2, the fixing device 5 includes a heating roller 51, a pressure roller 52, and a magnetic flux generator 53. FIG. 2 is an enlarged view of the fixing device 5 in the fixing device 1 of FIG. 1 rotated 90 degrees clockwise so that the right side is downward.
The heating roller 51 and the pressure roller 52 are arranged in parallel to each other, and both are rotatably supported. The pressure roller 52 is urged toward the heating roller 51 in a direction perpendicular to the axis, A nip is formed between the heating roller 51 and the pressure roller 52. A separation claw 54 for separating the recording sheet after fixing from the heating roller 51 is provided in the vicinity of the exit of the nip (right side in the figure).
3. Details of Heating Roller FIG. 3 is a diagram showing an outline of the layer structure from the center to the surface of the heating roller 51.

  As shown in FIG. 3, the heating roller 51 includes, in order from the center, a metal core 511, a heat insulating layer 512, an auxiliary heat generation control layer 513, a heat generation control layer 514, a main heat generating body layer 515, an antioxidant layer 516, an elastic layer 517, And a release layer 518 having an eight-layer structure. Here, the metal core 511 and the heat insulating layer 512 are bonded to form a roller-shaped fixing roller 55. Further, the heat generation control layer 514, the main heat generating layer 515, the antioxidant layer 516, the elastic layer 517, and the release layer 518 are bonded to each other to form an endless belt-like fixing belt 56. Further, the auxiliary heat generation control layer 513 alone forms a plate-like sliding contact member 57. The fixing roller 55 and the sliding contact member 57 are inserted into the fixing belt 56 and are not bonded to each other. Further, the sliding contact member 57 and the fixing belt 56 are in contact with each other, and the sliding contact member 57 and the fixing roller 55 are not in contact with each other.

  As shown in FIG. 2, the fixing roller 55 is pressed against the pressure roller 52 with the fixing belt 56 interposed therebetween, and the outer diameter of the fixing roller 55 is formed to be considerably smaller than the inner diameter of the fixing belt 56. There is a space SP between the fixing belt 56 and the upper portion of the fixing belt 56. The sliding contact member 57 is fixed and arranged in the space SP. Further, as shown in FIG. 2, the sliding contact member 57 has a circular cross section along the rotation direction of the fixing belt 56, and has a length substantially equal to that of the heating roller 51 in the depth direction. The fixing belt 56 is stretched between the fixing roller 55 and the sliding contact member 57.

In the present embodiment, the surface of the sliding contact member 57 that contacts the fixing belt 56 is a curved surface that is curved along the inner peripheral side of the fixing belt 56. Therefore, the auxiliary heat generation control layer 513 of the sliding contact member 57 and the heat generation control layer 514 located on the inner peripheral side of the fixing belt 56 are always in contact.
With the above-described structure, the fixing device 5 has a small contact area between the fixing belt 56 and the fixing roller 55, so that the amount of heat that escapes from the fixing belt 56 to the fixing roller 55 is small and the thermal efficiency is good. Further, since the auxiliary heat generation control layer 513 is not provided in the fixing belt 56, the heat capacity of the fixing belt 56 can be reduced accordingly. Therefore, the warm-up time can be shortened.
(A) Core Bar The core bar 511 is a support body that supports the entire heating roller 51 and needs to have sufficient heat resistance and strength.

As a specific example of the cored bar 511, a copper pipe having a wall thickness of about 4 mm and an outer diameter of 15 to 25 mmφ, or a material such as stainless steel (SUS) or aluminum can be used.
(B) Heat Insulating Layer The heat insulating layer 512 prevents heat generated in the fixing belt 56 from escaping to the cored bar 511 and allows the fixing belt 56 to bend to keep the nip width large and obtain good print quality. Layer. Therefore, the material of the heat insulating layer 512 is preferably a sponge body (heat insulating structure) made of a rubber material or a resin material having low thermal conductivity and heat resistance and elasticity, and a two-layer structure of a solid body and a sponge body. May be used.

  As a specific example of the heat-insulating layer 512, when a silicon sponge material is used, the thickness is preferably in the range of 1 to 10 mm, and more preferably in the range of 2 to 7 mm. The hardness of the heat insulating layer 512 is preferably 20 to 60 degrees in terms of Asker C hardness, and more preferably 30 to 50 degrees in practical use. The roller hardness of the heating roller 51 as a whole is preferably about 30 to 90 degrees in terms of Asker C hardness.

In this specification, the features of the present application are described using a color digital printer as an example. However, the present invention can also be applied to, for example, a single-color printer having only one color image forming unit. Can obtain good print quality even without the heat insulating layer 512.
(C) Auxiliary heat generation control layer The auxiliary heat generation control layer 513 is a layer that cancels the original magnetic flux by generating a reverse magnetic field when the heat generation control layer 514 loses magnetism at a high temperature. Therefore, it is preferable to use a nonmagnetic material having a low electrical resistivity that is lower than that of the heat generation control layer 514 at a high temperature. Therefore, the relative magnetic permeability of the auxiliary heat generation control layer 513 is preferably in the range of 0.99 to 2.0, and more practically in the range of 0.99 to 1.1. Further, the volume resistivity of the auxiliary heat generation control layer 513 is preferably in the range of 1.0 to 10.0 × 10 ⁻⁸ Ωm, and more practically in the range of 1.0 to 2.0 × 10 ⁻⁸ Ωm.

As a specific example of the auxiliary heat generation control layer 513, it is made of copper having a film thickness of about 0.2 to 1.0 mm, or is made of a material such as SUS or aluminum as long as it is within the above ranges of relative permeability and volume resistivity. Can also be used.
Here, “high temperature” in the present specification indicates a temperature range in an overheated state, and more specifically means a temperature exceeding the Curie temperature of the heat generation control layer 514.
(D) Heat generation control layer The heat generation control layer 514 is a magnetic layer having a volume resistivity that is moderately larger than that of the auxiliary heat generation control layer 513 at room temperature, and uses a material having a Curie temperature comparable to the fixing temperature. . For example, the relative permeability of the heat generation control layer 514 is desirably in the range of 50 to 2000, and more practically in the range of 100 to 1000. Further, the volume resistivity of the heat generation control layer 514 in the temperature range lower than the Curie temperature is preferably in the range of 2 to 200 × 10 ⁻⁸ Ωm, and more preferably in the range of 5 to 100 × 10 ⁻⁸ Ωm. . The thickness of the heat generation control layer 514 is preferably in the range of 20 to 200 μm, and more practically in the range of 40 to 100 μm. Furthermore, when the target fixing temperature is about 180 ° C. (170 to 190 ° C.), the Curie temperature is preferably in the range of 150 to 220 ° C., ideally in the range of 180 to 200 ° C. Is more desirable.

In this embodiment, permalloy having a Curie temperature of 190 ° C. is used for the heat generation control layer 514. Since permalloy having a higher Curie temperature can be obtained as the nickel ratio is higher, the Curie temperature of the heat generation control layer 514 is adjusted by the component ratio of permalloy. Further, the Curie temperature can be adjusted by using an alloy containing chromium, baltic, molybdenum and the like and adjusting the ratio of these.
(E) Main Heating Element Layer The main heating element layer 515 is a layer that receives the magnetic flux generated by the magnetic flux generator 53 and induces an induced current to generate heat. In the present embodiment, a non-magnetic material is used for the main heating element layer 515, and a magnetic material is used even if the relative permeability is low by using a thin film of copper, silver or the like having particularly good conductivity. The heat generation efficiency is higher than when it is used. Further, the relative magnetic permeability of the main heating element layer 515 is desirably in the range of 1.0 to 2.0. In order to obtain good exothermic properties, the thickness of the main heating element layer 515 is desirably in the range of 5 to 40 μm. The volume resistivity of the main heating element layer 515 is smaller than the volume resistivity of the heat generation control layer 514 at a high temperature. Further, the volume resistivity of the main heating element layer 515 at high temperature is preferably substantially the same as that of the cored bar 511, specifically, it is preferably in the range of 1.0 to 10.0 × 10 ⁻⁸ Ωm, and 1.0 to 2.0 × 10. ^-8 range of Ωm is more desirable.

As a specific example of the main heating element layer 515, when copper is used, a thickness of about 10 μm is desirable. When a magnetic material such as nickel is used, even if the thickness is increased to about 40-100 μm, good heat generation is achieved. It may be obtained by dispersing particles of conductive material such as copper or silver in a resin material, or by coating these conductive materials on a resin material. Here, when the main heating element layer 515 based on a resin material is used, the flexibility of the fixing belt 56 tends to increase, and the separation of the recording sheet can be improved.
(F) Antioxidation layer Antioxidation layer 516 is a layer for preventing oxidation of main heating element layer 515, respectively. Each anti-oxidation layer cuts off the contact between each anti-oxidation layer and the outside air (air), can suppress corrosion of the main heating element layer 515, and maintains good adhesion with the elastic layer 517 over a long period of time. Is done. In particular, when the main heating element layer 515 is copper, the growth of the oxide film on copper is intense, and the strength of the oxide film itself is very weak. Therefore, if the antioxidant layer 516 is not present, peeling occurs in the oxide film layer. Because it is easy, it is more effective.

  The material of the anti-oxidation layer 516 is preferably a metal material that is at least more resistant to corrosion than copper and has no temper. Further, in order to reduce the influence on heat generation performance, it is preferably non-magnetic and low resistance. It is good to form thin with the material of. For example, nickel, chromium, and silver are particularly suitable because they are relatively easy to form, have little effect on heat generation performance, and have good adhesion to the elastic layer. Further, when the thickness of the antioxidant layer 516 is less than 0.5 μm, the sealing performance deteriorates due to pinholes, and when the thickness exceeds 40 μm, the heat generation performance is affected and the effect of preventing overheating is adversely affected. Therefore, the range of 0.5 to 40 μm is desirable.

Note that a polyimide resin may be used as the material of the antioxidant layer 516. Since the polyimide resin is an insulator, it has no influence on the heat generation performance. However, since the polyimide resin has a slight air permeability compared to the metal material, if the thickness is less than 3 μm, the sealing performance becomes insufficient and an oxide film grows. If the thickness exceeds 70 μm, the main heating element layer Since it is difficult to cause the heat generated in 515 to reach the outer peripheral surface of the heating roller 51 and the thermal efficiency is deteriorated, the thickness is preferably in the range of 3 to 70 μm.
(G) Elastic Layer The elastic layer 517 is a layer for transmitting heat uniformly and flexibly to the toner image and preventing image noise from being generated due to the toner image being crushed or non-uniformly melted. Therefore, the material of the elastic layer 517 is preferably a rubber material or a resin material having heat resistance and elasticity.

  As a specific example of the elastic layer 517, for example, a heat-resistant elastomer such as silicone rubber or fluororubber that can withstand use at a fixing temperature is suitable. In addition, you may mix the various fillers for the purpose of thermal conductivity, reinforcement, etc. in said material. For example, the particles filled for improving thermal conductivity include diamond, silver, copper, aluminum, marble, glass, etc., and practically silica, alumina, magnesium oxide, boron nitride, beryllium oxide. Etc. are preferred.

If the thickness of the elastic layer 517 is less than 10 μm, it is difficult to obtain sufficient elasticity in the thickness direction. If the thickness exceeds 800 μm, the heat generated in the main heating element layer 515 is difficult. Is difficult to reach the outer peripheral surface of the heating roller 51, and the thermal efficiency is deteriorated. Therefore, the thickness is preferably in the range of 10 to 800 μm, and more preferably in the range of 100 to 300 μm.
The hardness of the elastic layer 517 is preferably in the range of 1 to 80 degrees as JIS hardness, and more preferably in the range of 5 to 30 degrees. If the hardness is within this range, it is possible to ensure stable fixing properties while preventing the strength of the elastic layer 517 from decreasing and the adhesiveness from decreasing.

Examples of silicone rubbers whose hardness falls within this range include silicone rubbers of one, two, three or more components, LTV (Low Temperature Vulcanizable) type, RTV (Room Temperature Vulcanizable: Room temperature vulcanization type), HTV (High Temperature Vulcanizable) type, condensation type and addition type silicone rubber can be used. In the present embodiment, silicone rubber having a JIS hardness of 10 degrees and a thickness of 200 μm is used.
(H) Release Layer The release layer 518 is the outermost layer of the heating roller 51 and is a layer for improving the release property from the recording sheet. Therefore, the material of the release layer 518 can withstand use at the fixing temperature and has excellent release properties with respect to the toner, for example, silicone rubber, fluororubber, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer). ), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP (tetrafluoroethylene / hexafluoropropylene copolymer), and the like, and a mixture thereof Is preferred.

Further, the thickness of the release layer 518 is desirably in the range of 5 to 100 μm, and more desirably in the range of 10 to 50 μm.
In order to improve the adhesive force between the release layer 518 and the elastic layer 517, an adhesion treatment with a primer or the like may be performed. Moreover, you may add a electrically conductive material, an abrasion-resistant material, a good heat conductive material etc. as a filler in the mold release layer 519 as needed.
(I) Example of Manufacturing Method of Sliding Member The copper plates that will later become the auxiliary heat generation control layer 513 are each rolled and subjected to pressing to form the sliding member 57.
(J) Example of Manufacturing Method of Fixing Belt First, a permalloy plate that later becomes the heat generation control layer 514, a copper plate that later becomes the main heating element layer 515, and a nickel plate that later becomes the antioxidant layer 516 are each rolled. Are layered in order and clad, and then subjected to plastic processing such as drawing, spinning, and DI (drawing / ironing) to form an endless belt. Subsequently, the belt is annealed in an oven at 800 ° C. for about 1 to 2 hours, and the Vickers hardness of Permalloy increased to about Hv250 by plastic working is returned to about Hv130. Subsequently, a silicone rubber sheet serving as the elastic layer 517 and a fluororubber sheet serving as the release layer 518 are bonded to the outer peripheral surface of the annealed belt with an adhesive, whereby the fixing belt 56 is completed. Here, when bonding with an adhesive, for example, “Primer C” manufactured by Toray Dow Corning is effective.

In the endless belt, since the main heating element layer 515 and the antioxidant layer 516 are very thin layers, only the permalloy plate that will later become the heat generation control layer 514 is rolled, and this is subjected to drawing, spinning, and DI processing. After performing plastic working such as (drawing and ironing) and forming it into an endless belt, this is annealed, and further, copper that becomes the main heating element layer 515 and nickel that becomes the antioxidant layer 516, It may be formed by plating or a coating film.
4). Details of Pressure Roller As shown in FIG. 2, the pressure roller 52 has a three-layer configuration including a cored bar 521, a heat insulating layer 522, and a release layer 523 in order from the center.
(A) Core Bar The core bar 521 is a support body that supports the entire pressure roller 52 and needs to have sufficient heat resistance and strength.

As a concrete example of the cored bar 521, an aluminum pipe having a wall thickness of about 3 mm and an outer diameter of 15 to 25 mmφ, or a molded pipe made of a material having excellent heat resistance such as polyphenylene sulfide resin (PPS) is used. May be. It is not impossible to use an iron pipe, but a non-magnetic material that is not easily affected by electromagnetic induction is more preferable.
(B) Heat insulation layer The heat insulation layer 522 is a layer provided on the outer periphery of the cored bar 521 so as not to let the heat of the nip escape to the cored bar 521. Therefore, the material of the heat insulating layer 522 needs to have low thermal conductivity and heat resistance.

A specific example of the heat insulating layer 522 is a silicone sponge rubber layer having a thickness in the range of 3 to 10 mm, and a two-layer structure of silicone rubber and silicone sponge may be used.
(C) Release Layer The release layer 523 is the outermost layer of the pressure roller 52 and is a layer for improving the release property from the recording sheet, like the release layer 518 of the heating roller 51. Therefore, the material of the release layer 523 is the same as that of the release layer 518.

The thickness of the release layer 523 is preferably in the range of 10 to 50 μm.
5). Details of Magnetic Flux Generation Unit The magnetic flux generation unit 53 faces the outer periphery of the heating roller 51 and is disposed in parallel with the heating roller 51 along the rotation axis direction of the heating roller 51, toward the fixing belt 56 and the fixing roller 55. To generate magnetic flux.

As shown in FIG. 2, the magnetic flux generator 53 includes an exciting coil 531, a high frequency inverter 532, a magnetic core 533, a coil bobbin 534, a thermistor 535, and a controller 536.
(A) Excitation coil The excitation coil 531 is a coil wound along the longitudinal direction of the heating roller 51, and its cross section (see FIG. 2) has a slightly curved shape following the outer periphery of the heating roller 51. ing. The excitation coil 531 is connected to a high frequency inverter 532 and supplied with high frequency power.

In the present embodiment, the winding of the exciting coil 531 is a litz wire formed by bundling dozens to hundreds of thin strands. Further, since the exciting coil 531 self-heats when energized, the winding is coated with a heat-resistant resin so as to maintain insulation even at high temperatures. Further, the exciting coil 631 may be air-cooled by, for example, a fan. In addition, the exciting coil 531 of this Embodiment is connected in the longitudinal direction, and is not divided into a plurality.
(B) High frequency inverter The high frequency inverter 532 supplies high frequency power of 20 to 40 kHz and 100 to 2000 W to the exciting coil 531.

In this embodiment, since the output frequency of the high-frequency inverter 532 is set to 20 to 40 kHz, the heat generation efficiency is high and a sufficiently high fixing temperature can be obtained. Here, if the output frequency is less than 20 kHz, the heat generation efficiency is greatly reduced. Conversely, if the output frequency is greater than 40 kHz, the power supply is insufficient during continuous paper feeding and the necessary fixing temperature can be obtained. This is not preferable because a fixing failure may occur.
(C) Magnetic body core The magnetic body core 533 increases the efficiency of the magnetic circuit and shields the magnetism, and includes a main core 533a, an end core 533b, and a bottom core 533c. The main core 533a has an arch shape as shown in FIG. In the present embodiment, 13 core pieces having a length of about 10 mm are arranged in the axial direction of the heating roller 51. In addition, as the main core 533a, a cross section having a portion protruding toward the heating roller 51 at the center can be used. The cross section having a substantially “E” shape can be used. The rate can be increased. In addition, the end core 533 b is obtained by arranging core pieces having a square cross section and a length of 5 to 10 mm at both ends of the heating roller 51. Further, the hem core 533c has a rectangular cross section and is rapidly arranged in a range substantially corresponding to the longitudinal dimension of the heating roller 51.

  The magnetic core 533 is formed of a material having high magnetic permeability and low eddy current loss. The Curie temperature of the magnetic core 533 of this embodiment is desirably in the range of 140 to 220 ° C, and more desirably in the range of 160 to 200 ° C. In this embodiment, high frequency is used, so that the loss of eddy current in the core tends to be large, and furthermore, the core made of a high permeability alloy such as permalloy tends to have large loss of eddy current. It is desirable to have a laminated structure.

In addition, when the magnetic shielding of the magnetic circuit portion by the exciting coil 531 and the magnetic core 533 is sufficiently performed by other means, the core may be omitted. Further, as the magnetic core 533, a resin material in which magnetic powder is dispersed can be used. The magnetic permeability is slightly low, but there is an advantage that the shape can be freely set.
(D) Coil bobbin The coil bobbin 534 is an air core for forming an exciting coil 531 by winding an electric wire.
(E) Thermistor The thermistor 535 is disposed in contact with the surface of the heating roller 51 and detects the surface temperature of the heating roller 51 before fixing.

The arrangement position of the heating roller 51 is a portion through which the recording sheet passes regardless of the size of the recording sheet in the roller axis direction. For example, the heating roller 51 is left-justified with respect to the heating roller 51. If it is, it is arranged near the left end of the heating roller 51. Further, the rotation direction of the heating roller 51 is arranged slightly upstream from the entrance of the fixing nip.
The surface temperature of the heating roller 51 before fixing is not limited to the thermistor, and may be detected by other non-contact temperature sensors.
(F) Control Unit The control unit 536 controls the high-frequency inverter 532 based on the detection result of the thermistor 535 during the fixing process so that the surface temperature before fixing of the heating roller 51 falls within the appropriate fixing temperature range. To do.

Here, an appropriate fixing temperature is set in advance according to the type of toner and the like, and is about 100 to 200 ° C., for example.
<Operation>
During the fixing process, as shown by the arrow in FIG. 2, the pressure roller 52 is driven to rotate clockwise in the drawing. Thereby, the heating roller 51 is driven and rotated counterclockwise in the figure by the frictional force with the pressure roller 52. Note that the relationship between the driving and the driven may be reversed.

The high frequency inverter 532 supplies high frequency power to the excitation coil 531 based on control by the control unit 536. As a result, the exciting coil 531 generates a magnetic flux, which passes through the inside of the magnetic core 533, exits between the protrusions of the magnetic core 533, and reaches the heating roller 51.
At this time, if the heat generation control layer 514 is lower than the Curie temperature, the heat generation control layer 514 has a high magnetic permeability, so that the magnetic flux hardly leaks to the inner peripheral side of the heating roller 51 due to the shielding effect. Therefore, if the temperature is lower than the Curie temperature of the heat generation control layer 514, most of the magnetic flux generated by the exciting coil 531 passes through the thickness of the main heating element layer 515 and the heat generation control layer 514 in the circumferential direction of the heating roller 51. Then, the magnetic flux density is very high in these layers. For example, since this state is during warm-up, both the main heating element layer 515 and the heat generation control layer 514 generate heat. Furthermore, in this embodiment, since the heat capacity of the layers contributing to heat generation (the main heating element layer 515 and the heat generation control layer 514) is small and the fixing belt 56 is thermally insulated by the heat insulation layer 522, the temperature rises in a shorter time. Can be warmed.

Further, in the present embodiment, the main heating element layer 515 is a non-magnetic material, but since it is a very thin layer, the amount of heat generated by the main heating element layer 515 is large. This can be explained as follows. In general, when a high-frequency alternating electric field is applied, eddy currents induced in the conductive layer concentrate on the surface layer due to the so-called skin effect, and do not flow very much inside.
The degree of the skin effect is expressed by the following formula 1.

δ = √ (ρ / (π · f · μ)) (Equation 1)
Where δ is the penetration depth (depth at which the current density becomes 1 / e of the surface), f is the frequency of the alternating voltage, μ is the magnetic permeability, and ρ is the volume resistivity. Here, the resistance per penetration depth δ is expressed by the skin resistance R shown in the following formula 2. Using this R, the heat generation amount P of the conductive layer is expressed by the following formula 3.
R = ρ / δ (Formula 2)
P = R · I ² (Formula 3)
However, I is an eddy current.

  In the heat generation layer of the magnetic material, the range in which the eddy current flows is limited by the skin effect regardless of the thickness of the layer itself, so that the current density is large and the heat generation amount is large. The lifting of the non-magnetic material has a small skin effect and eddy current flows through the entire layer. Since the main heating element layer 515 of this embodiment is a very thin layer of a non-magnetic material, even if an eddy current flows through the entire layer, the current density is large and a sufficient calorific value can be obtained. In addition, the leakage of magnetic flux toward the cored bar 511 is further prevented by the low resistance main heating element layer 515.

  The heat thus generated is transmitted to the surface of the heating roller 51 through the antioxidant layer 516 and the elastic layer 517 bonded to the main heating element layer 515. Further, the high frequency inverter 532 is controlled by the control unit 536 so that the surface temperature of the heating roller 51 becomes an appropriate fixing temperature. The recording sheet S carrying the toner image is inserted into the nip between the heating roller 51 and the pressure roller 52 with the surface on which the toner image is placed facing the heating roller 51, and the left side in FIG. From the direction to the right, while the recording sheet S passes through the nip, the toner is melted and fixed.

  The recording sheet S that has passed through the nip is separated from the heating roller 51 and conveyed to the subsequent stage. Here, even after the recording sheet S passes through the nip, the recording sheet S is forcibly separated from the heating roller 51 by the separation claw 54 even if it remains attached to the heating roller 51, so that jamming of the recording sheet S is prevented. . Note that the tip of the separation claw 54 may or may not be in contact with the surface of the heating roller 51.

  Since the heat is removed from the surface of the heating roller 51 by the recording sheet S and the toner by the fixing process, the surface temperature of the heating roller 51 decreases in the range in which the recording sheet S passes in the axial direction of the roller. In the range where no paper is passed, the surface temperature of the heating roller 51 hardly decreases. On the other hand, the thermistor 535 detects the temperature at the location where the recording sheet S is passed. Therefore, the control unit 536 receives the detection result of the thermistor 535 and controls the high-frequency inverter 532 so that the temperature of the portion through which the recording sheet S is passed becomes the fixing temperature.

  When the recording sheet S having a relatively small sheet width is continuously fixed, the temperature particularly increases in a range where the recording sheet S is not passed, and the temperature of the heat generation control layer 514 in this range exceeds the Curie temperature. Then, the magnetic permeability of the heat generation control layer 514 in this range is greatly reduced and the shielding effect is weakened, so that most of the magnetic flux passes through the main heating element layer 515 and the heat generation control layer 514 and further leaks to the inner peripheral side. . Therefore, the amount of heat generated by the main heating element layer 515 and the heat generation control layer 514 in this range is also greatly reduced.

  Further, in the present embodiment, in the range where the temperature of the heat generation control layer 514 exceeds the Curie temperature, the magnetic flux that has penetrated through the main heat generation layer 515 and the heat generation control layer 514 and further leaked to the inner peripheral side is the auxiliary heat generation control. Layer 513 is reached. Here, since the auxiliary heat generation control layer 513 is made of, for example, copper and has a low resistance, an eddy current easily flows. Therefore, most of the eddy current due to the magnetic flux reaching the auxiliary heat generation control layer 513 is within the auxiliary heat generation control layer 513. It occurs but hardly generates heat. Further, a counter electromotive force is generated by the eddy current generated in the auxiliary heat generation control layer 513, and the magnetic flux generated thereby acts in a direction to cancel the original magnetic flux. Therefore, the density of magnetic flux acting on the main heating element layer 515 and the heat generation control layer 514 is further reduced, and the amount of heat generation is further reduced. Therefore, in a range where the temperature of the heat generation control layer 514 exceeds the Curie temperature, almost no heat is generated at any location in the radial direction of the heating roller 51.

  Therefore, at a location where the temperature has risen excessively, the amount of heat generation is greatly reduced as the magnetic permeability of the heat generation control layer 514 changes. On the other hand, the heat generation amount does not decrease in the sheet passing range. This is because in the sheet passing range, the magnetic permeability of the heat generation control layer 514 does not decrease and the distribution of magnetic flux density does not change. Further, the function of the auxiliary heat generation control layer 513 can further reduce the amount of heat generated when the magnetic permeability of the heat generation control layer 514 changes. Further, in this embodiment, since the thickness of the auxiliary heat generation control layer 513 is larger than that of the other layers, the heat generation amount of the auxiliary heat generation control layer 513 can be effectively suppressed, and the fixing device as a whole has high thermal efficiency. It has become.

  In this embodiment, since the main heating element layer 515 and the heat generation control layer 514 are laminated, a change in surface temperature is quickly transmitted to the heat generation control layer 514. Accordingly, as soon as the surface temperature of a part of the heating roller 51 becomes higher than the temperature suitable for fixing, the amount of heat generated in that part is greatly reduced, so that the excessive temperature rise state does not continue. However, the Curie temperature of the heat generation control layer 514 is selected so as to obtain such an effect. In addition, the auxiliary heat generation control layer may be laminated in the fixing belt. In this case, the sliding contact member 57 may be omitted, but in this embodiment, the auxiliary heat generation control layer 513 is fixedly disposed. Therefore, the heat capacity of the fixing belt is small as compared with the case where the auxiliary heat generation control layer is laminated in the fixing belt. Accordingly, the warm-up time can be further shortened.

Further, in the present embodiment, a non-magnetic main heating element layer 515 is provided. Particularly, since the main heating element layer 515 is very thin, the total heat generation amount is large. Therefore, the controllable range of input power is wide. In addition, since the heat capacity of the main heating element layer 515 is small, the warm-up time is short.
<Verification>
(A) First Experiment First, the characteristic that the conductive layer of the fixing belt cured by plastic working is reduced in hardness by annealing treatment was examined.

Here, the conductive layer is a layer in which at least one of the antioxidant layer, the main heating element layer, the heat generation control layer, and the heat generation control layer, or two or more of these layers are clad. .
In this experiment, permalloy alone was used as the conductive layer of the fixing belt, and the annealing temperature was 800 ° C.
FIG. 4 is a diagram showing the relationship between the annealing time and the hardness when the permalloy work-hardened by plastic working is annealed.

Permalloy's hardness before plastic working was Hv130 in Vickers hardness, and Vickers hardness increased to Hv250 by plastic working.
As shown in FIG. 4, the permalloy having a Vickers hardness of Hv250 after plastic working decreases in hardness with the lapse of annealing time, and is approximately equal to the Vickers hardness Hv130 before plastic working around 1 hour after the start of annealing. Return.

Here, as the Vickers hardness tester, a micro Vickers hardness tester was used.
(B) Second Experiment Next, the relationship between the hardness and thickness of the conductive layer of the fixing belt and each quality was examined.
FIG. 5 is a diagram showing the quality of each fixing belt with different hardness and thickness of the conductive layer.

This experiment includes permalloy as the conductive layer of the fixing belt, and the thickness of the permalloy is 8 types in increments of 20 μm from 10 μm to 150 μm. For each of these thicknesses, Hv250 which is not annealed after plastic processing, after plastic processing A total of 24 types of samples were evaluated, each including three types of Hv200 that had undergone some annealing treatment A and Hv130 that had undergone sufficient annealing treatment B after plastic working.
The quality items evaluated here are nip width, image noise, and durability. Evaluate whether nip width is 500 N or less and a nip of 10 mm or more can be secured. Whether or not image noise was generated was evaluated, and durability was evaluated for whether the fixing belt was damaged after printing 300,000 sheets.

As shown in FIG. 5, the Hv250 fixing belt cannot be used due to any quality problem at all thicknesses, and the Hv200 fixing belt has any thickness from 30 μm to 130 μm. The Hv130 fixing belt can be used without causing any quality problems at a thickness of 50 μm to 130 μm.
<Summary>
As described above, according to the first embodiment, the Vickers hardness of the conductive layer can be adjusted to Hv200 or less and Hv130 or more by performing an annealing process after at least the last plastic working, and for a long time. A fixing belt exhibiting stable fixing performance and improved durability can be provided.

Conventionally, it has been considered that when annealing is performed after plastic working, the hardness decreases and the durability decreases. However, by deliberately applying this, it is possible to provide a fixing belt that adjusts the Vickers altitude of the conductive layer, exhibits a stable fixing performance over a long period of time, and has improved durability.
Further, by providing the heating roller 51 with the main heating element layer 515, the heat generation control layer 514, and the auxiliary heat generation control layer 513, in the fixing belt 56, the portion where the surface temperature exceeds the Curie temperature of the heat generation control layer 514 is transmitted. Since the magnetic susceptibility is greatly reduced, the magnetic flux density is greatly reduced, and the amount of heat generation is reduced only at that point. Therefore, even when a small size recording sheet is continuously fed, a partial excessive temperature rise does not occur and stable fixing performance can be exhibited.

In the first embodiment, permalloy is used as an example of the conductive layer of the fixing belt, and a technique for improving the quality of the fixing belt by performing an annealing process after plastic working has been described. However, the conductive layer is not limited to permalloy. The technique can be applied to other metal layers as well.
In addition, the shape, method, and the like of the fixing device in the first embodiment are merely examples, and other shapes, methods, and the like can be used as long as the fixing belt includes a metal layer that is heated by an induction heat generation method. Even so, the technology is equally applicable.

The present invention can be widely applied to the technical field of an image forming apparatus including a fixing device.
According to the present invention, it is possible to manufacture a fixing belt with improved durability used in an induction heating type fixing device, and thus its industrial utility value is extremely high.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to Embodiment 1. FIG. 2 is a diagram schematically illustrating a configuration of a fixing device 5. FIG. FIG. 2 is a diagram showing an outline of a layer structure from the center to the surface of a heating roller 51. It is a figure which shows the relationship between annealing time and hardness at the time of annealing the permalloy work-hardened by plastic working. It is a figure which shows the propriety of each quality for every fixing belt from which the hardness and thickness of an electroconductive layer differ.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Image process part 4 Feeding part 5 Fixing part 6 Control part 10 Optical part 11 Intermediate transfer belt 3Y, 3M, 3C, 3K Image forming unit 31Y, 31M, 31C, 31K Photosensitive drum 32Y, 32M, 32C , 32K Charger 33Y, 33M, 33C, 33K Developer 34Y, 34M, 34C, 34K Primary transfer roller 35Y, 35M, 35C, 35K Cleaner 41 Paper feed cassette 42 Feeding roller 43 Conveyance path 44 Timing roller pair 45 Secondary transfer Roller 46 Secondary transfer position 51 Heating roller 52 Pressure roller 53 Magnetic flux generation part 54 Separation claw 55 Fixing roller 56 Fixing belt 57 Sliding member 71 Paper discharge roller 72 Paper discharge tray 511 Core metal 512 Heat insulation layer 513 Auxiliary heat generation control layer 514 Heat generation control layer 515 Main heating element layer 516 Antioxidation Stop layer 517 Elastic layer 518 Release layer 519 Release layer 521 Core metal 522 Heat insulation layer 523 Release layer 531 Excitation coil 532 High frequency inverter 533 Magnetic core 533a Main core 533b End core 533c Bottom core 534 Coil bobbin 535 Thermistor control unit 535 Thermistor control unit 631 Excitation coil

Claims (6)

A fixing belt having a conductive layer and generating heat by electromagnetic induction,
The conductive layer is
A fixing belt having a Vickers hardness adjusted to Hv200 or lower and Hv130 or higher. The fixing belt according to claim 1, wherein the conductive layer is permalloy. The conductive layer is
The fixing belt according to claim 2, wherein the layer thickness is 30 μm or more and 130 μm or less. The fixing belt is
It is a seamless belt manufactured through one or more plastic workings,
The fixing belt according to claim 1, wherein the Vickers hardness of the conductive layer is adjusted by performing an annealing process at least after the last plastic working.   A fixing device comprising the fixing belt according to claim 1.   An image forming apparatus comprising the fixing device according to claim 5.

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