JP2007163929A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which an excessive temperature rising is securely suppressed and a rise time is reduced even when small-sized recording mediums are consecutively fixed or when the drive of the device suddenly stops, for example, in a fixing process of an electromagnetic induction heat system, , and to provide an image forming apparatus. <P>SOLUTION: The fixing device 20 fixes a toner image T on the recording medium P. The fixing device 20 includes coils 25 that generate magnetic fluxes, and two fixing rollers 31, serving as heat generating members, that generate heat by the magnetic fluxes generated by the coils 25. The coils 25 are disposed so that an unfixed image formed on the recording medium P is held between the fixing rollers 31 (heat generating members) disposed opposite to each other, especially between contact parts (nip parts), in order to apply heat/pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof.

  2. Description of the Related Art Conventionally, for example, an image forming apparatus such as an electrophotographic system, such as a copying machine, a printer, or a facsimile, usually has a rotating photosensitive drum, and the photosensitive layer of the photosensitive drum is uniformly charged. After that, an electrostatic latent image is formed by exposure with a laser beam from a laser scanning unit. Furthermore, after the electrostatic latent image is developed with toner, it is transferred onto a transfer paper as a recording material, and further, a mechanism is provided for passing the transfer paper through a heat fixing device and heat fixing the toner onto the transfer paper. .

  An example of such a fixing device is disclosed in Japanese Patent Application Laid-Open No. 2002-82549 (Patent Document 1). This patent document 1 is an electromagnetic induction heating type fixing device, which includes a support roller (heat generating roller), a fixing auxiliary roller (fixing roller), a fixing belt stretched between the supporting roller and the fixing auxiliary roller, and a supporting roller. An induction heating unit that faces the fixing belt via a fixing belt, a pressure roller that faces the fixing auxiliary roller via the fixing belt, and the like. The induction heating unit includes a coil unit (excitation coil) extending in the width direction (a direction orthogonal to the conveyance direction of the recording medium), a core facing the coil unit, and the like.

  The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes a toner image on a recording medium (for example, recording paper) conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, by applying a high-frequency alternating current to the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated in the vicinity of the support roller surface. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.

  In addition, such an electromagnetic induction heating type fixing device is known as being capable of raising the surface temperature (fixing temperature) of the fixing belt to a desired temperature with a short start-up time with low energy consumption.

  On the other hand, Japanese Patent Application Laid-Open No. 2000-214703 (Patent Document 2) and the like disclose a fixing device using an electromagnetic induction heating method in which a core portion is formed so as to sandwich a fixing belt. That is, the core portion of the induction heating unit is disposed so as to face the outer peripheral surface and the inner peripheral surface of the fixing belt. This technique aims to improve the heat generation efficiency of the fixing belt.

Japanese Patent Application Laid-Open No. 2000-162912 (Patent Document 3) discloses a fixing device using an electromagnetic induction heating method, in which the Curie point of the core portion (magnetic core) of the induction heating portion is adjusted in the width direction. Techniques to do this are disclosed. Specifically, the curie point of the core part at both ends in the width direction is formed to be smaller than the curie point at the center part in the width direction. This technique is intended to suppress the temperature rise that occurs at both ends in the width direction of the fixing belt when a small-sized recording medium is passed.
JP 2002-82549 A JP 2000-214703 A JP 2000-162912 A

  However, in the conventional fixing device described above, when a small size recording medium is continuously fixed, or when the device suddenly stops driving due to a paper jam or the like, a part or all of the fixing belt overheats. There was something to do. Details are as follows.

  A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include recording media of irregular sizes in addition to recording media of various regular sizes in the A and B rows of JIS dimensions. Even in the case of recording media of the same size (for example, A4 size), when the longitudinal direction is the transport direction and when the short direction (the direction orthogonal to the longitudinal direction) is the transport direction, the width direction size Are dealing with different recording media.

  When fixing such a recording medium having a different size in the width direction with the fixing device, the heat distribution in the width direction of the fixing belt fluctuates according to the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small width direction size, a lot of heat is taken away at the position of the fixing belt (paper passing area) corresponding to the width direction size of the recording medium, and the other positions. The fixing temperature is lower than (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature in the center portion in the width direction of the fixing belt, the fixing temperature in the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will rise (overheated). As described above, when a large recording medium in the width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Furthermore, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, it is considered that the fixing belt is thermally damaged.

  On the other hand, if it is attempted to control the fixing temperature in the entire width direction of the fixing belt based on the fixing temperature at both ends in the width direction of the fixing belt, the fixing temperature at both ends in the width direction of the fixing belt can be controlled to a desired temperature. However, the fixing temperature at the center in the width direction is lowered. As described above, when the recording medium is fixed in a state where the fixing temperature at the center portion in the width direction of the fixing belt is lowered, a cold offset occurs on the recording medium corresponding to the temperature lowered position.

  Further, when a paper jam (jam) occurs in the conveyance path in the image forming apparatus, the driving of the fixing device is suddenly stopped. In such a case, the portion of the fixing belt facing the induction heating unit instantaneously overheats in a short time until the energization to the induction heating unit is cut off. As a result, it is also conceivable that thermal damage occurs to components such as the fixing belt and the coil portion of the induction heating unit.

  On the other hand, the technology disclosed in Patent Document 2 described above improves the heat generation efficiency of the fixing belt by optimizing the shape of the core portion disposed so as to sandwich the fixing belt. Therefore, the effect of suppressing the excessive temperature increase of the fixing belt cannot be expected.

  Moreover, the above-mentioned techniques such as Patent Document 3 adjust the Curie point of the core portion of the induction heating unit in the width direction. However, since the overheating of the fixing member heated by the induction heating unit occurs before the overheating of the core portion occurs, the effect of directly suppressing the overheating of the fixing belt cannot be expected. .

  Further, in the above-described fixing device, only the fixing member is heated, and the pressure member on the pressure side facing the heating member is not heated. For this reason, the pressure member absorbs the heat of the surface of the fixing member heated, which is one of the factors that hinder the temperature rise of the fixing member. As a result, the time (rise time) until the fixing member secures the necessary amount of heat is increased. This necessary amount of heat is the amount of heat necessary to fix the toner on the transfer paper.

  In addition, there is a method in which a halogen lamp is inserted into a hollow pressure roller as a pressure member to perform auxiliary heating, but the efficiency is low, and the heat generation mechanism must be equipped with two types of electromagnetic induction and halogen methods. Therefore, the control mechanism is complicated and the cost is increased.

  The present invention has been made in view of the above circumstances, and by simultaneously heating the opposing pressure members, the temperature of the fixing member is prevented from being lowered due to the temperature outflow to the pressure members. The problem is to reduce the rise time.

  In addition, a material having a Curie point (a material capable of self-temperature control) is used for the heat generating member, and a coil portion that generates a magnetic flux is opposed to the main surface of the heat generating member so that the toner transferred to the recording medium (transfer paper) By arranging the coil part so as to sandwich the front and back surfaces of the heat generating members facing each other at the same time, the ability of the heat generating member to control the self-temperature is improved, and when a small-sized recording medium is continuously fixed or To provide a fixing device and an image forming apparatus capable of reliably suppressing excessive temperature rise even when the drive is suddenly stopped, and realizing high-efficiency heating, simplification of a control mechanism, and cost reduction. Let it be an issue.

  According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, comprising: a coil unit that generates a magnetic flux; and a heat generating member that generates heat by the magnetic flux. Further, the present invention is characterized in that the unfixed image formed on the recording medium is disposed so as to sandwich the front and back surfaces of the heat-generating members disposed so as to be heated and pressed.

  A fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the heat generating member includes a conductive heat generating layer having a Curie point near a target value of the fixing temperature, and the conductive The heat generating layer is characterized in that it has a volume resistivity of 7.0 × 10 −6 Ωcm or less.

  A fixing device according to a third aspect of the present invention is the fixing device according to the first or second aspect, wherein the heat generating member includes a heat generating layer, and the heat generating layer is made of a magnetic shunt alloy. .

  A fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein an alternating current is applied to the coil portion.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the coil portion is formed in a loop shape, and the heating member is formed of the coil portion. It is characterized by being inserted into a loop.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the two heating members arranged to face each other are simultaneously heated.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein the coil portion is formed in a loop shape, and two heating members are the coil portion. It is characterized by being inserted into the same loop.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to any one of the first to seventh aspects, wherein a contact portion (nip portion) of two heat generating members arranged opposite to each other is preferentially provided. It is characterized by heating.

  A fixing device according to a ninth aspect of the present invention is the fixing device according to any one of the first to eighth aspects, wherein the heat generating member is a fixing member that melts a toner image. To do.

  An image forming apparatus according to a tenth aspect of the present invention includes the fixing device according to any one of the first to ninth aspects.

  According to the first aspect of the present invention, in the fixing device for fixing the toner image to the recording medium, temperature outflow to the pressure member for pressing the unfixed image formed on the recording medium can be reduced, and the rise time can be reduced. .

  According to the second to fourth aspects of the invention, in addition to the effect of the first aspect, the self-temperature control of the fixing member can be performed.

  According to the invention of claim 5, in addition to the effects of claims 1 to 4, when the coil portion is arranged in a loop shape with respect to the heat generating member using the magnetic shunt alloy, the main surface side of the heat generating member (for example, The self-temperature control capability is higher than when the coil portion is disposed on the outer peripheral surface side. Further, by interposing the heat generating member, the heat generation efficiency (rise) of the heat generating member is also improved, and the above effect can be obtained without providing a conductive layer on the heat generating member. Simplified. Accordingly, it is possible to provide a fixing device using a heat generating member that is inexpensive and does not have a problem caused by providing a conductive layer such as delamination.

  According to the sixth aspect of the invention, in addition to the effects of the first to fifth aspects, the rise time can be further reduced by simultaneously controlling the two heat generating members.

  According to the invention of claim 7, in addition to the effects of claims 1 to 6, the heat generation efficiency can be improved by reducing useless leakage of the magnetic field.

According to the invention of claim 8, in addition to the effects of claims 1 to 7, by specializing portion having a high magnetic flux density at the contact portion (nip portion), raised reduction and further the rise time, the efficiency be able to.

  According to the ninth aspect of the present invention, in addition to the effects of the first to eighth aspects, it is possible to provide a fixing device that has high safety and realizes low cost by reducing the number of parts.

  According to the tenth aspect of the present invention, it is possible to obtain an image forming apparatus that contributes to the satisfaction of the user with a quick operation by the fixing device having a short rise time. In addition, high safety and efficient fixing are possible, and as a result, it is possible to contribute to reduction in environmental load by reducing power consumption and reduction in cost by reducing the number of parts.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

  The embodiment of the present invention will be described in detail with reference to FIGS. First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG. In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit containing a recording medium P such as paper, 13 a registration roller for conveying the recording medium P to the transfer unit 7, 15 a manual paper feeding unit, 18 a photosensitive drum as an image carrier, and 20 a recording 1 shows a fixing device that fixes an unfixed image on a medium P; The fixing device 20 is an application of a fixing device of an embodiment described later. However, the fixing device shown in FIG. 2 used in a comparative example described later is also applied.

  With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described. First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the drawing, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined electrophotographic process (charging process, exposure process, development process). Is done. Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

  On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows. First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

  After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10. Thus, a series of image forming processes is completed.

  Next, the configuration and operation of the fixing device 20 of the comparative example in the image forming apparatus main body 1 will be described in detail with reference to FIG. As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22, a support roller 23, an induction heating unit 24, a pressure roller 30, a thermistor 38, a guide plate 35, a separation plate 36, and the like. Composed.

  The support roller 23 as a heating member (heat generating member) includes a heat generating layer (cylindrical portion) made of a magnetic conductive material. The cylindrical portion of the support roller 23 is formed so that its thickness (layer thickness) is about 0.6 mm. The support roller 23 rotates counterclockwise in FIG. The induction heating unit 24 includes a pair of coil portions 25 and 25, and the coil portions 25 and 25 are disposed so as to face the front and back surfaces (the outer peripheral surface and the inner peripheral surface) of the support roller 23. (See FIG. 3). As shown in FIG. 3, the coil portion 25 extends in parallel to the width direction of the fixing belt 22 and the support roller 23. One end in the width direction of the coil portion 25 is a folded portion that connects the inner peripheral surface side and the outer peripheral surface side, and the high-frequency power source portion 40 is connected to the other end. Then, an alternating current of 10 k to 1 MHz (preferably 10 k to 300 kHz) is applied to the coil unit 25 from the high frequency power supply unit 40.

  Here, as a material of the support roller 23 as a heat generating member, a magnetic conductive material such as nickel, iron, chromium, or an alloy thereof can be used. Specifically, it is an alloy of nickel, iron, and chromium, and a desired Curie point can be obtained by adjusting the amount of each material added and the processing conditions. Thus, by forming the support roller 23rf with a magnetic conductive material having a Curie point near the fixing temperature of the fixing belt 22, the support roller 23 is heated without being overheated by electromagnetic induction. Become.

  The action of suppressing this excessive temperature rise is as follows. When the temperature of the support roller 23 and the heat generating layer 22b exceeds the Curie point, heat generation of the support roller 23 and the heat generating layer 22b is limited. That is, when the temperature of the support roller 23 and the heat generating layer 22b heated by the induction heating unit 24 exceeds the Curie point, the support roller 23 and the heat generating layer 22b lose their magnetism, so that overcurrent near the surface is increased. Occurrence is limited. Thereby, both generation | occurrence | production of the Joule heat in the support roller 23 and the heat generating layer 22b falls, and an excessive temperature rise is suppressed.

  Here, the fixing auxiliary roller 21 is rotationally driven in a counterclockwise direction in FIG. 2 by a driving unit (not shown). The fixing auxiliary roller 21 is formed by forming an elastic layer such as silicone rubber on the surface of a cored bar made of stainless steel or the like. In general, the elastic layer of the auxiliary fixing roller 21 is formed to have a thickness of 3 to 10 mm and an Asker hardness of 10 to 50 degrees. You can have it. In the present embodiment, the support roller 23 has only the heat generating layer. However, a reinforcing layer, an elastic layer, a heat insulating layer, or the like may be provided on the heat generating layer of the support roller 23. For example, a 30 μm PFA tube may be coated on the surface layer. Hereinafter, the fixing belt 22 will be described in detail.

  Referring to FIG. 2, a fixing belt 22 (fixing member) as a heat generating member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21. As shown in FIG. 4A, the fixing belt 22 is a multi-layered endless belt in which a heat generating layer 22b, an elastic layer 22c, and a release layer 22d are sequentially formed on a base material 22a. The base material 22a is made of an insulating heat-resistant resin material, and for example, polyimide, polyamideimide, PEEK, PES, PPS, fluorine resin, or the like can be used. The layer thickness of the base material 22a is formed to be 30 to 200 μm from the viewpoint of heat capacity and strength. The heat generating layer 22b of the fixing belt 22 is made of a magnetic conductive material and has a layer thickness of 1 to 20 μm. The heat generating layer 22b is formed on the base material 22a by plating, sputtering, vacuum deposition or the like.

  Here, a magnetic conductive material such as nickel or stainless steel can be used as the material of the heat generating layer 22b. In the present embodiment, a magnetic shunt alloy whose Curie point is higher than the fixable temperature and lower than 300 ° C. is used as the material of the heat generating layer 22b. Specifically, it is an alloy of nickel, iron, and chromium, and a desired Curie point can be obtained by adjusting the amount of each material added and the processing conditions. Thus, by forming the heat generating layer 22b with a magnetic conductive material having a Curie point near the fixing temperature of the fixing belt 22, the heat generating layer 22b is heated without being overheated by electromagnetic induction. Become.

  The elastic layer 22c of the fixing belt 22 is made of silicone rubber, fluorosilicone rubber, or the like, and is formed to have a layer thickness of 50 to 500 μm and an Asker hardness of 5 to 50 degrees. Thereby, a uniform image quality without gloss unevenness can be obtained in the output image.

The release layer 22d of the fixing belt 22 is made of tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP). ), A mixture of these resins, or a dispersion of these resins in a heat resistant resin. The layer thickness of the release layer 22d is 5 to 50 μm (preferably 10 to 30 μm). Thereby, the toner releasability on the fixing belt 22 is ensured and the flexibility of the fixing belt 22 is ensured.
A primer layer or the like may be provided between the layers 22 a to 22 d of the fixing belt 22.

  In the present embodiment, the fixing belt 22 as the heat generating member has a four-layer structure (the structure shown in FIG. 4A), but other multilayer structures shown in FIGS. 4B to 4D. It can also be. The fixing belt 22 in FIG. 4B includes a heat generating layer 22b, an elastic layer 22c, and a release layer 22d. Here, the heat generating layer 22b may be made of a resin material such as polyimide, polyamideimide, PEEK, PES, PPS, or fluororesin in which magnetic conductive particles are dispersed. In that case, magnetic conductive particles are added within a range of 20 to 90% by weight with respect to the resin material. Specifically, the magnetic conductive particles are dispersed in a resin material in a varnish state using a dispersing device such as a roll mill, a sand mill, or a centrifugal defoaming device. This is adjusted to an appropriate viscosity with a solvent and formed into a desired layer thickness with a mold.

  In the fixing belt 22 of FIG. 4C, a plurality of heat generating layers 22b are provided in a base material 22a, and an elastic layer 22c and a release layer 22d are sequentially formed thereon. In the fixing belt 22 of FIG. 4D, an elastic layer 22c having a plurality of heat generating layers 22b is formed on a base material 22a, and a release layer 22d is further formed as a surface layer. Also in these cases, the same effect as in the present embodiment can be obtained by configuring the heat generating layer 22b in the same configuration as in the present embodiment.

  Specific examples are shown below.

  In Example 1, a magnetic shunt alloy having a Curie point not lower than the fixable temperature and not higher than 300 degrees was used as the base material of the fixing roller 31 that is the heat generating member and the fixing member shown in FIG. The primer layer was dried on the base material as a base, and then silicone (Toray: DY39-2083) was coated with 200 μm as an elastic layer and vulcanized, and then a primer was further coated and PFA was coated with 20 μm as a release layer. The fixing roller 31 was used. PFA is powdered fluororesin: MP102 (Co., Ltd .: Mitsui DuPont Fluoro Chemical Co., Ltd.), powder coating is performed, baked at 340 ° C for 30 minutes, taken out from the furnace, allowed to cool, and then subjected to secondary processing. I did it. As the release layer, FEP, PTFE, PFA, or a mixture of them at a certain ratio can be used. Preferably, PFA can be used from strength and smoothness. Moreover, as a formation method of a mold release layer, a baking process can also be performed after powder coating. Furthermore, wet spray coating, a method of covering the elastic layer with a tube shape, or the like can also be used.

  As shown in FIG. 5, coil portions 25, 25 are arranged on the fixing rollers 31, 31 serving as the heat generating member and the fixing member, with the nip portion (contact portion) of the fixing rollers 31, 31 being sandwiched therebetween, and fixing. The apparatus 20 is configured. The driving method of the coil portions 25, 25 is the same as that shown in FIG. The fixing device 20 is used as the fixing device 20 in FIG. The coil portion 25 is disposed so as to be concentrated particularly at the nip portion, and heats and presses the unfixed image on the recording medium P by causing the fixing rollers 31 and 31 themselves to generate heat. The rise time until the fixing rollers 31 and 31 reached 180 ° C. and the toner adhesion at the end when 1K sheets were passed were evaluated by the image forming apparatus 1 assembled with the fixing device 20 described above.

  FIG. 6 shows a form of the second embodiment. One fixing roller 31 in FIG. 5 is constituted by a fixing belt 22 stretched by a stretch roller 26. The fixing belt 22 is configured as shown in FIG. 4B, and has a heat generating layer, an elastic layer, and a release layer. More specifically, the fixing belt 22 is an annular polyimide material in which a heat generating layer having a layer thickness of 100 μm is provided on the inner peripheral portion of the fixing belt 22 and magnetic conductive particles having a diameter of 60 mm when dispersed are dispersed. As in Example 1, the outer surface of the heat generating layer was dried using the primer layer as a base, and then coated with 200 μm of silicone (Toray: DY39-2083) and vulcanized as an elastic layer, and then applied with a primer. Then, 20 μm of PFA was applied as a release layer. Further, the fixed pad 28 is pressed as a pressure member so that a sufficient nip pressure can be obtained. The coil portions 25 and 25 are arranged so as to be concentrated particularly on the nip portion between the fixing roller 31 and the fixing belt 22 (and the fixed pad 28), and the fixed pad 28 is also formed of a magnetic shunt alloy capable of induction heat generation and is in contact with the fixing belt. The surface is coated with the raw resin PFA used in Example 1 in order to improve the slipperiness. In order to improve lubricity, grease or the like may be applied to the inner surface of the belt. Instead of FIG. 6, a configuration in which one tension roller 26 is provided as shown in FIG. 7 may be adopted.

(Comparative Example 1) The fixing device 20 was configured as shown in FIG.

(Comparative Example 2) The base material constituting the heat generating member and the fixing member (corresponding to the fixing roller 31) in Example 1 was changed from a magnetic shunt alloy to SUS430, and the same evaluation as in Example 1 was performed. A table comparing time is shown.

  From the evaluation results in Table 1, the effects described in the above embodiments can be confirmed. That is, the heat generation efficiency is increased at the nip portion of the heat generating member and the fixing member (fixing roller 31), thereby shortening the rise time. Even in the belt shape, the effect of shortening the rise time is recognized. Further, by using the magnetic shunt alloy in combination, the self-temperature control function is exhibited, and toner adhesion at the end is reduced.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating a fixing device used in a comparative example of the embodiment. FIG. 3 is a perspective view showing the vicinity of a coil portion of the fixing device of FIG. 2. FIG. 3 is a cross-sectional view illustrating a fixing member in the fixing device of the embodiment. FIG. 3 is a cross-sectional view illustrating the fixing device according to the first exemplary embodiment. It is sectional drawing which shows the fixing device of Example 2 in embodiment. FIG. 10 is a cross-sectional view illustrating another example of the fixing device according to the second exemplary embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing apparatus 21 Fixing auxiliary roller 22 Fixing belt (heating member)
22b Heat generation layer 22a Base material 22c Elastic layer 22d Release layer 23 Support roller 24 Induction heating unit 25 Coil unit 26 Stretching roller 28 Fixed pad (heat generation member)
30 Pressure roller 31 Fixing roller (heating member, fixing member)
35 Guide plate 36 Separator plate 38 Thermistor 40 High frequency power supply P Recording medium

Claims (10)

A fixing device for fixing a toner image on a recording medium, comprising: a coil unit that generates magnetic flux; and a heat generating member that generates heat by the magnetic flux,
The fixing device according to claim 1, wherein the coil portion is disposed so as to sandwich the front and back surfaces of a heat generating member disposed to face each other to heat and press the unfixed image formed on the recording medium.   The heat generating member includes a conductive heat generating layer having a Curie point in the vicinity of a fixing temperature target value, and the conductive heat generating layer is formed so as to have a volume resistivity of 7.0 × 10 −6 Ωcm or less. The fixing device according to claim 1, wherein the fixing device is provided.   The fixing device according to claim 1, wherein the heat generating member includes a heat generating layer, and the heat generating layer is made of a magnetic shunt alloy.   The fixing device according to claim 1, wherein an alternating current is applied to the coil portion.   The fixing device according to claim 1, wherein the coil portion is formed in a loop shape, and the heat generating member is sandwiched in the loop of the coil portion.   6. The fixing device according to claim 1, wherein two fixing members disposed opposite to each other are heated at the same time.   The fixing device according to claim 1, wherein the coil portion is formed in a loop shape, and two heat generating members are sandwiched in the same loop of the coil portion.   The fixing device according to claim 1, wherein the fixing device preferentially heats a contact portion between two heating members arranged to face each other.   The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image.   An image forming apparatus comprising the fixing device according to claim 1.

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