JP2007079131A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic induction heating type fixing device and image forming apparatus in which a rising time is short without reducing heating efficiency even when a heating member with temperature self-controllability is used, and excessive temperature elevation is surely suppressed even if small-sized recording media are continuously fixed or device driving is stopped suddenly. <P>SOLUTION: There are provided a magnetic flux generating means 25 to which an AC is applied to generate magnetic flux and a heating member 23 which generates heat by the magnetic flux. The heating member 23 comprises a first heating layer 23a which is formed so that the Curie point becomes lower than or equal to 300°C, and a second heating layer 23b of which volume resistivity is lower than that of the first heating layer 23a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein, and more particularly to an electromagnetic induction heating type fixing device and an image forming apparatus. .

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an apparatus using an electromagnetic induction heating type fixing device is often used for the purpose of reducing the start-up time of the apparatus and saving energy (for example, , See Patent Document 1).

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device includes a support roller (heat generation roller) as a heat generating member, a fixing auxiliary roller (fixing roller), a fixing belt stretched between the support roller and the fixing auxiliary roller, and a support. An induction heating unit facing the roller via the fixing belt, a pressure roller facing 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 unit 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 the toner image on the recording medium 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.
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 small energy consumption and a short start-up time.

  On the other hand, 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.

  Further, Patent Document 3 and the like disclose a fixing device that uses an electromagnetic induction heating method and adjusts the Curie point of the core portion (magnetic core) of the induction heating portion in the width direction. 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-size recording medium is passed.

Japanese Patent Application Laid-Open No. H10-228561 and the like describe a fixing device using an electromagnetic induction heating method, and for the purpose of preventing the shaft core of the fixing roller (heating roller) from being heated and deteriorating the bearing. A technique is disclosed in which the heat generating layer is composed of a first heat generating layer made of a magnetic material and a second heat generating layer made of a nonmagnetic material.
Specifically, the first heat generating layer is formed such that its specific resistance is higher than that of the second heat generating layer and its thickness is thicker than that of the second heat generating layer. In this technique, the second heat generating layer made of a nonmagnetic material is used as a main heat generating layer, and the first heat generating layer made of a magnetic material is provided so that the magnetic flux generated from the magnetic flux generating means does not reach the axis of the fixing roller. To do.

JP 2002-82549 A JP 2000-214703 A JP 2000-162912 A Reissue WO2003 / 43379

  In the conventional fixing device described above, when a small-sized 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 member overheats. was there.

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), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  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 size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (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.

In order to solve such a problem, it is conceivable to form a support roller as a heat generating member with a material having a Curie point (a material capable of self-temperature control). That is, by setting the Curie point of the heat generating member near the temperature at which hot offset does not occur (for example, 250 ° C.), an effect of limiting the excessive temperature rise of the heat generating member and suppressing the occurrence of hot offset is expected. it can.
However, in this case, since the temperature rise of the heat generating member slows down near the Curie point, the magnetic material whose Curie point is much higher than the target fixing temperature (for example, 180 ° C.) ( For example, the rise time until reaching the target fixing temperature is longer than that of a heat generating member using soft iron having a Curie point of 790 ° C.).

  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. .

  In addition, in the technique of Patent Document 4 or the like, in order to prevent the shaft core of the fixing roller from being heated, the heat generating layer of the fixing roller is divided into a first heat generating layer made of a magnetic material and a second heat generating layer made of a nonmagnetic material. The effect of preventing excessive temperature rise at both ends in the width direction of the heat generating member (fixing roller) cannot be expected.

  The present invention has been made to solve the above-described problems. Even when a heat-generating member having self-temperature controllability is used, the start-up time is short without reducing the heat-generating efficiency, and the To provide an electromagnetic induction heating type fixing device and an image forming apparatus in which excessive temperature rise is reliably suppressed even when a recording medium of a size is continuously fixed or when the apparatus is suddenly stopped. It is in.

The inventor of the present application has come to know the following matters as a result of repeated studies to solve the above-mentioned problems.
That is, in addition to the first heat generating layer having a Curie point of 300 ° C. or lower, the heat generating member includes only the first heat generating layer by providing the heat generating member with the second heat generating layer having a volume resistivity lower than that of the first heat generating layer. As compared with the case of configuring the above, it is possible to maintain a high self-temperature control capability (self-temperature controllability) without reducing the heat generation efficiency of the heat generating member. In particular, when the coil part is disposed so as to sandwich the front and back surfaces of the heat generating member, the heat generation efficiency and self-temperature controllability are compared to when the coil part is disposed facing only one side of the heat generating member. Is increased. Furthermore, by providing the first heat generating layer and the second heat generating layer on the heat generating member, the power supply unit that supplies the alternating current to the magnetic flux generating means is stabilized.

  The present invention is based on the above-described matters. That is, the fixing device according to the first aspect of the present invention is a fixing device for fixing a toner image on a recording medium, to which an alternating current is applied. A heat generating member for generating magnetic flux; and a heat generating member for generating heat by the magnetic flux, wherein the heat generating member includes a first heat generating layer formed to have a Curie point of 300 ° C. or less, and the first heat generating layer. And a second heat generating layer having a volume resistivity lower than the volume resistivity.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the second heat generating layer is made of a nonmagnetic material.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the thickness of the second heat generating layer is greater than a penetration depth corresponding to the frequency of the alternating current. Is also formed to be thin.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the second heat generating layer is made of copper or nickel.

  The 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 heat generating member is closer to the magnetic flux generating means than the second heat generating layer. Are provided with a nickel layer.

  The 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 first heat generating layer is made of an alloy of nickel, iron, and chromium. .

  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 magnetic flux generating means is disposed so as to sandwich the front and back surfaces of the heat generating member. It is a coil part.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to the seventh aspect, wherein the heat generating member has the second heat generating layer on the front and back sides with respect to the first heat generating layer. It is equipped.

  According to a ninth aspect of the present invention, in the fixing device according to the seventh or eighth aspect, the first heat generating layer has the alternating current when the temperature is lower than the Curie point. The penetration depth is 3 times or more and 17 times or less the penetration depth corresponding to the frequency.

  According to a tenth aspect of the present invention, in the fixing device according to any one of the seventh to ninth aspects, the coil portion sandwiches the front and back surfaces of the heat generating member once or a plurality of times. Thus, they are wound apart.

  According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, the magnetic flux generating means is arranged so as to face only one side of the heat generating member. It was established.

  A fixing device according to a twelfth aspect of the present invention is the fixing device according to the eleventh aspect, wherein the first heat generating layer and the second heat generating layer are spaced apart from each other.

  According to a thirteenth aspect of the present invention, in the fixing device according to the twelfth aspect of the present invention, a nonmagnetic conductive layer is provided on the side of the first heat generation layer that does not face the second heat generation layer. It is.

  According to a fifteenth aspect of the present invention, in the fixing device according to the thirteenth aspect, the volume resistivity of the nonmagnetic conductive layer is lower than the volume resistivity of the first heat generating layer. It is formed.

  A fixing device according to a fifteenth aspect of the present invention is the fixing device according to the thirteenth or fourteenth aspect, wherein the nonmagnetic conductive layer is a cored bar made of aluminum.

  According to a sixteenth aspect of the present invention, in the fixing device according to any one of the thirteenth to fifteenth aspects, the thickness of the nonmagnetic conductive layer corresponds to the frequency of the alternating current. It is formed to be thicker than the penetration depth.

  According to a seventeenth aspect of the present invention, in the fixing device according to any one of the twelfth to sixteenth aspects, an electrical insulating property is provided between the first heat generating layer and the second heat generating layer. It is provided with the elastic layer which has.

  Further, in the fixing device according to claim 18, in the invention according to any one of claims 12 to 17, the first heat generating layer has a Curie point of 100 ° C or higher and 250 ° C or lower. It is formed as follows.

  According to a nineteenth aspect of the present invention, in the fixing device according to any one of the twelfth to eighteenth aspects, the thickness of the first heat generating layer corresponds to the frequency of the alternating current. It is formed so as to be equivalent to the penetration depth.

  A fixing device according to a twentieth aspect of the present invention is the fixing device according to any one of the first to nineteenth aspects, wherein the heating member is a heating member that heats a fixing member that melts a toner image. Is.

  According to a twenty-first aspect of the present invention, in the fixing device according to the twentieth aspect, the fixing member is a fixing belt, and the heating member stretches the fixing belt together with a fixing auxiliary roller. The supporting auxiliary roller is disposed so as to come into contact with the pressure roller that presses the conveyed recording medium via the fixing belt.

  A fixing device according to a twenty-second aspect of the present invention is the fixing device according to any one of the first to nineteenth aspects, wherein the heat generating member is a fixing member that melts a toner image.

  The fixing device according to a twenty-third aspect of the present invention is the fixing device according to the twenty-second aspect, wherein the fixing member is a fixing belt stretched between a support roller and a fixing auxiliary roller. The roller is disposed so as to come into contact with the pressure roller that presses the conveyed recording medium via the fixing belt.

  A fixing device according to a twenty-fourth aspect of the invention is the fixing device according to the twenty-second aspect, wherein the fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed. .

  An image forming apparatus according to a twenty-fifth aspect of the present invention includes the fixing device according to any one of the first to twenty-fourth aspects.

  According to the present invention, in the electromagnetic induction heating type fixing device, in addition to the first heat generating layer having a Curie point of 300 ° C. or less, the heat generating member is provided with a second heat generating layer having a volume resistivity lower than that of the first heat generating layer. ing. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even in such a case, it is possible to provide a fixing device and an image forming apparatus in which excessive temperature rise is reliably suppressed and the power supply unit is stabilized.

  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.

Embodiment 1 FIG.
A first 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;

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 in the image forming apparatus main body 1 will be described in detail.
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. Is done.

  Here, 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. The elastic layer of the fixing auxiliary roller 21 has a thickness of 3 to 10 mm and an Asker hardness of 10 to 50 degrees. The fixing auxiliary roller 21 is rotationally driven counterclockwise in FIG. 2 by a driving unit (not shown).

  The support roller 23 as a heating member (heat generating member) is formed in a cylindrical shape having a diameter of 20 mm. The support roller 23 includes a first heat generating layer 23a made of a magnetic conductive material and a second heat generating layer 23b made of a conductive material. Specifically, as shown in FIG. 4, the second heat generating layer 23b is provided on each of the front and back surfaces (the inner peripheral surface side and the outer peripheral surface side) with respect to the first heat generating layer 23a.

Here, the first heat generating layer 23a of the support roller 23 is formed of a material having a Curie point of 300 ° C. or lower. As a material for the first heat generating layer 23a, a magnetic conductive material such as nickel, iron, chromium, or an alloy thereof can be used. In the first embodiment, a magnetic shunt alloy having a Curie point that is higher than the fixable temperature and lower than or equal to 300 ° C. is used as the material of the first heat generating layer 23a. Specifically, it is an alloy of nickel, iron, and chromium, and the curie point is set to 250 ° C. by adjusting the addition amount of each material and the processing conditions.
As described above, the support roller 23 is heated without being excessively heated by electromagnetic induction by providing the support roller 23 with the first heat generating layer 23a made of a magnetic shunt alloy having a Curie point near the fixing temperature of the fixing belt 22. Will be.

The thickness (layer thickness) D1 of the first heat generating layer 23a is the penetration depth (the volume resistivity and the relative magnetic permeability of the first heat generating layer, and the temperature when the temperature of the first heat generating layer 23a is equal to or lower than the Curie point. The frequency of the alternating current applied to the coil portion 25 is determined by δ1.
3 × δ1 ≦ D1 ≦ 17 × δ1 Formula (1)
Is set to hold. As a result, the heat generation efficiency and the self-temperature controllability of the support roller 23 are improved.

On the other hand, the second heat generating layer 23b of the support roller 23 is formed of a conductive material having a volume resistivity lower than that of the first heat generating layer 23a. Since the volume resistivity of the first heat generating layer 23a is 8.0 × 10 ⁻⁷ Ω · m, the second heat generating layer 23b is made of a material having a volume resistivity lower than 8.0 × 10 ⁻⁷ Ω · m. Is formed. Specifically, it is preferable to use copper, aluminum, gold, silver, or the like having a volume resistivity of 3.0 × 10 ⁻⁸ Ω · m or less as the second heat generating layer 23b. In the first embodiment, the non-magnetic material copper is used as the material of the second heat generating layer 23b.

The thickness (layer thickness) D2 of the second heat generation layer 23b is determined by the penetration depth of the second heat generation layer 23b (the volume resistivity and relative permeability of the second heat generation layer and the alternating current applied to the coil portion 25). ) Is defined as δ2.
D2 ≦ δ2 Formula (2)
Is set to hold. As a result, the heat generation efficiency and the self-temperature controllability of the support roller 23 are improved.

The support roller 23 configured in this manner rotates counterclockwise in FIG. The coil part 25 is arrange | positioned so as to oppose the front and back (it is an outer peripheral surface and an inner peripheral surface) of the support roller 23 (refer FIG. 3). The first heat-generating layer 23a is electromagnetically heated as a main heat-generating layer (heat-generating main layer) by the magnetic flux generated from the coil unit 25 as magnetic flux generating means, and the heat-generating layer (heat-generating auxiliary layer) followed by the second heat-generating layer 23b. Will be heated by electromagnetic induction.
In the first embodiment, the support roller 23 includes the first heat generation layer 23a and the second heat generation layer 23b. However, a reinforcing layer, an elastic layer, a heat insulation layer, and the like are provided on the heat generation layers 23a and 23b of the support roller 23. It can also be provided.

Hereinafter, the fixing belt 22 will be described in detail.
Referring to FIG. 2, a fixing belt 22 as a fixing member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21.
The fixing belt 22 is a multi-layered endless belt in which an elastic layer and a release layer are sequentially formed on a base material (disposed on the inner peripheral surface side). The base material 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 is 30 to 200 μm from the viewpoint of heat capacity and strength.

  The elastic layer 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 of the fixing belt 22 includes tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer (FEP). Or the like, a mixture of these resins, or a dispersion of these resins in a heat resistant resin. The release layer has a thickness of 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 can be provided between the layers of the fixing belt 22.

Referring to FIGS. 2 and 3, the induction heating unit 24 as a magnetic flux generation unit includes a coil unit 25 formed in a loop shape.
Here, the coil portion 25 is an exciting coil disposed so as to sandwich the front and back surfaces (the inner peripheral surface and the outer peripheral surface) of the fixing belt 22 and the support roller 23. A part of the fixing belt 22 and the support roller 23 is sandwiched in the loop of the loop-shaped coil portion 25.
Specifically, as shown in FIG. 3, the coil portion is wound apart so as to sandwich the front and back surfaces of the fixing belt 22 and the support roller 23 (heating member) once. The coil portion 25 extends in parallel with 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.

  Here, the high frequency power supply unit 40 applies an alternating current having a frequency in the range of 10 k to 1 MHz (preferably 10 k to 300 kHz) to the coil unit 25. However, as the frequency of the alternating current applied from the high frequency power supply unit 40 increases, the heat generation efficiency of the support roller 23 increases, but the high frequency power supply unit 40 increases in size and cost. In consideration of this point, in the first embodiment, an alternating current having a frequency of 30 kHz is mainly applied to the coil unit 25 with the use frequency band in the high-frequency power supply unit 40 in the range of 20 k to 40 kHz.

  In the first embodiment, the coil portion 25 is a single loop-shaped excitation coil, but a plurality of loop-shaped coil portions may be used. In other words, the coil portion can be wound apart so as to sandwich the front and back surfaces of the fixing belt 22 and the support roller 23 (heat generating member) a plurality of times.

  Referring to FIG. 2, the pressure roller 30 is formed by forming an elastic layer such as fluororubber or silicone rubber on a cylindrical member made of aluminum, copper or the like. The elastic layer of the pressure roller 30 has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees. The pressure roller 30 is in pressure contact with the auxiliary fixing roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides the conveyance of the recording medium P and promotes the separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30. Yes.

  On the outer peripheral surface of the fixing belt 22 and on the upstream side of the fixing nip portion, a thermistor 38 as a temperature sensitive element having high thermal response is in contact. The thermistor 38 detects the surface temperature (fixing temperature) on the fixing belt 22 and adjusts the output of the induction heating unit 24.

The fixing device 20 configured as described above operates as follows.
By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the support roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the direction of the arrow. The fixing belt 22 is heated by the support roller 23.

  Specifically, the magnetic field lines are alternately switched in both directions in the loop of the coil unit 25 by causing the high-frequency alternating current having the above-described frequency to flow from the high-frequency power source unit 40 to the coil unit 25. By forming the alternating magnetic field in this way, when the temperature of the support roller 23 is equal to or lower than the Curie point, eddy currents are generated on the front and back surfaces of the support roller 23, and Joule heat is generated by the electrical resistance of the support roller 23. This occurs and the support roller 23 is heated. The fixing belt 22 is heated by receiving heat from the support roller 23 that has generated heat.

Thereafter, the surface of the heated fixing belt 22 passes through the position of the thermistor 38 and reaches a contact portion with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

  The surface of the fixing belt 22 that has passed through the position of the pressure roller 30 then reaches the position facing the coil portion 25 again. Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

In such a fixing process, if the temperature of the support roller 23 exceeds its own Curie point, heat generation of the support roller 23 is limited.
That is, when the temperature of the support roller 23 (first heat generation layer 23a) induction-heated by the induction heating unit 24 exceeds the Curie point, the support roller 23 (first heat generation layer 23a) loses magnetism, Heat generation of the support roller 23 (first heat generating layer 23a) is limited. Thereby, the generation amount of Joule heat in the support roller 23 is reduced, and excessive temperature rise is suppressed.

  Such self-temperature control capability (self-temperature controllability) is obtained when the coil portion 25 is arranged in a loop with respect to the heat generating member 23 as in the first embodiment (for example, on the outer periphery). It is particularly high compared to the case where the coil portion 25 is disposed so as to face only on the surface side.

Hereinafter, the self-temperature control capability will be described in detail.
4 is a cross-sectional view showing the support roller 23 and the coil portion 25. FIGS. 5 and 6 are cross-sectional views of the support roller 23 and the coil portion 25 as viewed in the width direction. The broken line arrows in FIGS. 5 and 6 indicate the lines of magnetic force generated when an alternating current flows through the coil portion 25.
As shown in FIG. 4, the coil portion 25 is disposed so as to sandwich the front and back surfaces of the support roller 23. As a result, as shown in FIG. 5, coil currents H in opposite directions always flow through the coil portion 25 facing the outer peripheral surface of the support roller 23 and the coil portion 25 facing the inner peripheral surface of the support roller 23. Become. Therefore, the magnetic lines of force B1 and B2 generated by the two coil portions 25 sandwiching the support roller 23 also rotate in opposite directions. Then, reverse eddy currents A1 and A2 flow on the front and back surfaces of the support roller 23 as a heat generating member, and heat is generated due to Joule loss on both the front and back surfaces.

Here, the eddy current induced in the heat generating layer (metal) by the alternating magnetic flux generated by the alternating current increases as it approaches the surface of the heat generating layer, and decreases exponentially as the distance from the surface increases. When the heat generating layer is a magnetic material, the induced eddy current is further concentrated on the surface of the heat generating layer.
The depth from the surface at the position where the eddy current is reduced to 0.368 times the current density at the surface is referred to as the current penetration depth δ. The penetration depth δ is obtained by the following equation.
δ (m) = 503 · [ρ / (μf)] ^1/2 Formula (3)
In the above equation (3), ρ is the volume resistivity (Ω · m) of the heat generating layer, μ is the relative permeability of the heat generating layer, and f is the frequency (Hz) of the alternating current that excites the heat generating layer. .
Eddy currents that flow farther from the surface of the heat generating layer than the penetration depth are very small compared to those near the surface of the heat generating layer and have little effect on induction heating. If the thickness of the heat generating layer is equal to or greater than the penetration depth, the magnetic flux that has entered from the surface of the heat generating layer loses energy in the heat generating layer, and can hardly pass through the heat generating layer.

  In the first embodiment, a magnetic shunt alloy is used as the material of the first heat generating layer 23 a of the support roller 23. When the temperature of the magnetic shunt alloy (the first heat generating layer 23a) is equal to or lower than the Curie point and the frequency of the alternating current is 30 kHz, as shown in FIG. The support rollers 23 are inductively heated without being interfered with each other by concentrating at positions close to the front and back surfaces.

  On the other hand, when the temperature of the magnetic shunt alloy is equal to or higher than the Curie point (the relative permeability is 1) and the frequency of the alternating current is 30 kHz, the coil portion 25 and the support roller facing the outer peripheral surface of the support roller 23 The alternating magnetic flux generated by the coil portion 25 facing the inner peripheral surface of the 23 interferes with the magnetic shunt alloy (the first heat generating layer 23a). Therefore, the eddy currents A1 and A2 flowing through the magnetic shunt alloy are canceled out, and the heat generation amount of the support roller 23 is significantly reduced.

As described above, by arranging the coil portion 25 so as to sandwich the front and back surfaces of the support roller 23 (heat generating member), it is possible to obtain a very high self-temperature control capability and heat generation efficiency.
At that time, the thickness of the first heat generating layer 23a disposed so that the front and back surfaces are sandwiched between the coil portions 25 satisfies the relationship of the formula (1), so that the above-described effect is ensured.

Specifically, as the thickness of the first heat generating layer 23a is reduced, when the same voltage is applied to the coil portion 25, the first heat generating layer 23a when the temperature of the first heat generating layer 23a is equal to or lower than the Curie point. The amount of heat generated decreases. This decrease in the amount of heat generation increases rapidly when the thickness of the first heat generation layer 23a becomes thinner than a predetermined value, and the heat generation efficiency of the support roller 23 decreases. As a result of repeated research, the inventor of the present application has found that the thickness (D ≧ 3 ×) is three times or more the penetration depth corresponding to the frequency of the alternating current when the temperature of the first heat generating layer 23a is equal to or lower than the Curie point. It has been found that by forming the first heat generating layer 23a so as to be δ), it is possible to maintain good heat generation efficiency and self-temperature controllability in the support roller 23.
Further, as the thickness of the first heat generating layer 23a is increased, the amount of heat generated when the temperature of the first heat generating layer 23 becomes higher than the Curie point increases. The rate of decrease in the amount of heat generated with respect to the amount of heat generated when the temperature is equal to or lower than the Curie point is lowered, and the self-temperature controllability of the first heat generating layer 23a is decreased. As a result of repeated research, the inventor of the present application has a thickness of 17 times or less (D ≦ 17 ×) with respect to the penetration depth corresponding to the frequency of the alternating current when the temperature of the first heat generating layer 23a is equal to or lower than the Curie point. It was found that the high self-temperature controllability of the support roller 23 can be maintained by forming the first heat generating layer 23a so as to satisfy δ).

  The self-temperature control capability described above is manifested even when the support roller 23 is configured by only the first heat generating layer 23a. However, when the support roller 23 is configured only by the first heat generation layer 23a, the heat generation efficiency of the support roller 23 is reduced. On the other hand, by providing the second heat generating layer 23b on the support roller 23 in addition to the first heat generating layer 23a as in the first embodiment, the heat generation efficiency in the support roller 23 is not lowered, and the high self The temperature control capability can be maintained.

Hereinafter, a detailed description will be given based on experimental results and simulation results.
FIG. 7 shows a case where the support roller 23 is formed of only a magnetic shunt alloy having a Curie point of 250 ° C. (in the graph Q1) in the fixing device 20 of the first embodiment, and the support roller 23 is made of magnetic stainless steel (SUS430). This is an experimental result comparing the temperature rise characteristic (start-up characteristic) of the fixing device with the case of forming only by the graph (the graph is Q0). Specifically, for each fixing device, the support roller 23 was rotated simultaneously with the application of power to raise the temperature of the fixing belt 22, and the change in the surface temperature of the fixing belt 22 with time was measured. The input power at the initial stage of heating was adjusted to be equal to each other.
Here, the temperature rise characteristic is the length of time for raising the temperature to the temperature required for fixing belt 22 to fix the toner (180 ° C. in the first embodiment). The shorter the device, the easier it is for the user.

From the graph Q0 in FIG. 7, when the support roller 23 is formed only of SUS430, since there is no self-temperature controllability, the temperature of the fixing belt 22 exceeds the fixable temperature (180 ° C.) when power is continuously applied. However, the temperature continues to rise. Therefore, temperature control using a temperature sensor or the like is necessary to prevent excessive temperature rise.
It can be seen from the graph Q0 that the rate of temperature increase gradually decreases with time. This is due to the fact that the volume resistivity of SUS430 increases as the temperature increases. This is because the increase in the volume resistivity increases the impedance of the entire fixing device and reduces the power used for heat generation.

  From the graph Q1 in FIG. 7, when the support roller 23 is made of only a magnetic shunt alloy, the temperature does not increase any more when the support roller is heated to the Curie point (250 ° C.). For this reason, the temperature of the fixing belt 22 stops at a temperature (about 230 ° C.) at which the reduced amount of heat generated from the magnetic shunt alloy and the amount of heat released from the fixing belt 22 are balanced. Due to the self-temperature control capability of the magnetic shunt alloy, it is possible to prevent an excessive temperature rise of the support roller 22 (or the fixing belt 22) without a temperature sensor or the like.

However, when the support roller 23 is formed of only a magnetic shunt alloy, the temperature rise characteristic (start-up time) is lower than when the support roller 23 is formed of only SUS430. This is due to the change in permeability over time in the magnetic shunt alloy.
A magnetic shunt alloy is an alloy that becomes nonmagnetic due to a sharp decrease in magnetic permeability when its temperature rises above the Curie point, but does not become nonmagnetic at the moment when the temperature reaches the Curie point. Even at a temperature below the Curie point, if the temperature is in the vicinity of the Curie point, the magnetism gradually weakens as the temperature rises. Therefore, not only does the volume resistivity increase as in SUS430, but also the phenomenon in which the magnetic permeability decreases, the rate of decrease in temperature rise rate due to temperature increase becomes greater than that of SUS430. As a result, the temperature rise time to the fixing possible temperature becomes longer than SUS430.
In order to solve this problem, a measure can be considered in which the Curie point of the magnetic shunt alloy is set high so that the magnetic permeability does not decrease at a temperature near the fixable temperature. However, in that case, the self-temperature control ability by the magnetic shunt alloy is reduced, and temperature control using a temperature sensor or the like is necessary to prevent overheating.

As a result of diligent study, the inventor of the present application divides the support roller 23, which is a heat generating member, into a first heat generating layer 23a made of a magnetic shunt alloy and a second material made of a conductive material having a lower volume resistivity than the first heat generating layer 23a. It has been found that the above-described problem can be solved by forming the heat generating layer 23b.
In order to increase the heat generation efficiency of electromagnetic induction heating, it is desirable to increase the amount of magnetic flux to be crossed and increase the conductivity of the heat generating member. By configuring the support roller 23 as described above, the conductivity of the support roller 23 is increased, and the heat generation efficiency and the self-temperature controllability are improved.

Specifically, referring to FIG. 4, the thickness of the first heat generating layer 23a made of a magnetic shunt alloy is set to 0.3 mm. Each of the copper-plated second heat generating layers 23b formed on both sides of the first heat generating layer 23a has a thickness of 5 μm (the total layer thickness is 10 μm).
As described above, by providing the second heat generating layer 23b on both sides of the first heat generating layer 23a, the magnetic flux generated from both the coil portions 25 sandwiching the support roller 23 can be linked to both the second heat generating layers 23b. Therefore, the heat generation efficiency of the support roller 23 is improved.

In the first embodiment, the second heat generating layer 23b is provided on both sides of the first heat generating layer 23a. However, the second heat generating layer 23a is provided only on one side (the inner peripheral surface side or the outer peripheral surface side) of the first heat generating layer 23a. Two heat generating layers 23b can also be provided. Even in this case, it is possible to prevent excessive temperature rise of the support roller 23 while maintaining high self-temperature controllability while reducing the decrease in the heat generation efficiency of the support roller 23.
Moreover, the construction method of the second heat generating layer 23b is not limited to the plating construction method, and other construction methods such as vapor deposition, welding, adhesion of metal foil, etc. can be used.

FIG. 8 shows a case where the support roller 23 is formed of only a magnetic shunt alloy having a Curie point of 250 ° C. and a thickness of 0.3 mm (graph Q1), and the support roller 23 is composed of the first heat generating layer 23a and the second heat generating layer 23a. This is a result of comparing the temperature rise characteristics (start-up characteristics) of the fixing device with the case where the heat generation layer 23b is used (the configuration of the first embodiment and the graph S1).
From FIG. 8, it can be seen that when the support roller 23 is formed of the first heat generating layer 23a and the second heat generating layer 23b, the temperature rise characteristic is remarkably improved. Specifically, the time for the surface temperature of the fixing belt 22 to rise to the fixable temperature (180 ° C.) was 30 seconds for the graph Q1 compared to 50 seconds for the graph Q1.
It can also be seen that when the support roller 23 is formed of the first heat generating layer 23a and the second heat generating layer 23b, the self-temperature control capability is also improved. Specifically, the temperature at which the surface temperature of the fixing belt 22 is controlled and maintained is 230 ° C. in the graph Q1 and 220 ° C. in the graph S1.

  FIG. 9 is a result of comparing the heat generation amount of the support roller 23 calculated by the alternating magnetic field analysis simulation between the first embodiment and the conventional one. FIG. 9 shows that when the heat generation amount of the support roller 23 is 100 when the support roller 23 is made of only a magnetic shunt alloy having a Curie point of 250 ° C. and a thickness of 0.3 mm, the first heat generation is performed on the support roller 23. The ratio of the amount of heat generated by the support roller 23 when the layer 23a and the second heat generation layer 23b are formed (the configuration of the first embodiment) is displayed. In both fixing devices, the magnitudes of the voltages input to the coil unit 25 are the same.

From FIG. 9, when the support roller 23 is formed of the first heat generation layer 23a and the second heat generation layer 23b, the heat generation amount is improved to 164% compared to the case where the support roller 23 is formed of only the magnetic shunt alloy. You can see that This result is consistent with the result of the temperature rise efficiency improving in FIG.
The reason why the calorific value is improved also from the calculation result is that the conductivity of the support roller 23 (heat generating member) is improved by applying copper plating to the magnetic shunt alloy. Specifically, when the inductance of the support roller 23 decreases and the effective resistance increases, the effective power obtained when the same voltage is applied to the coil portion 25 is increased, and the magnetic coupling is also improved to increase the power. The heat conversion efficiency is improved.

  FIG. 10 is also a result of comparing the heat generation amount of the support roller 23 calculated by the alternating magnetic field analysis simulation between the first embodiment and the conventional one. In FIG. 10A, when the support roller 23 is formed of the first heat generation layer 23a and the second heat generation layer 23b (this is the configuration of the first embodiment), the temperature of the support roller 23 is equal to or lower than the Curie point. The ratio of the heat generation amount when the temperature of the support roller 23 is equal to or higher than the Curie point when the heat generation amount at that time is 100 is displayed. FIG. 10B shows that when the support roller 23 is made of only a magnetic shunt alloy, the temperature of the support roller 23 when the temperature of the support roller 23 is equal to or lower than the Curie point is 100, the Curie point. The ratio of the calorific value when it is above is displayed.

  From FIG. 10, it can be seen that when the temperature of the support roller 23 is changed from the Curie point or lower to the Curie point or higher, the magnetism of the magnetic shunt alloy is lost and the heat generation amount is reduced. It can be seen that when the support roller 23 is formed of the first heat generating layer 23a and the second heat generating layer 23b, the rate of decrease in the amount of heat generation is increased. Specifically, the rate of decrease in the amount of heat generation when the temperature falls below the Curie point to above the Curie point is 32% when the support roller 23 is made of only a magnetic shunt alloy, whereas the support roller 23 Was 12% when formed with a magnetic shunt alloy (first heat generating layer 23a) and copper plating (second heat generating layer 23b). That is, it can be confirmed that the configuration of the first embodiment improves the self-temperature control capability of the fixing device.

This is because the copper used as the material of the second heat generating layer 23b is a nonmagnetic and low resistance metal. That is, a non-magnetic and low-resistance metal tends to cause eddy currents to flow. However, since the effective resistance is low, Joule heat is not generated so much and a reaction magnetic field with respect to the magnetic field from the coil portion 25 is generated. Therefore, when the temperature of the support roller 23 is equal to or lower than the Curie point, eddy current easily flows through the support roller 23 due to copper plating, and the amount of heat generated by the magnetic shunt alloy increases. On the other hand, when the temperature of the support roller 23 is equal to or higher than the Curie point, the magnetic shunt alloy becomes a material that is not easily induction-heated, and the magnetic flux from the coil portion 25 is weakened by the effect of generating a reaction magnetic field of copper, thereby generating heat. The amount is very small.
Thus, the support roller 23 is constituted by the first heat generating layer 23a made of a magnetic shunt alloy and the second heat generating layer 23b made of a conductive material having a volume resistivity lower than that of the first heat generating layer 23a. In addition, it is possible to provide a fixing device having good heat generation efficiency and high self-temperature control capability.

  FIG. 11 shows the result of calculation of the ratio of heat generation of the first heat generating layer 23a and the second heat generating layer 23b in the support roller 23 of the first embodiment by an alternating magnetic field analysis simulation. As shown in FIG. 11, the heat generation amount N1 of the magnetic shunt alloy (first heat generation layer 23a) is 78% of the heat generation amount of the entire support roller 23, and the heat generation amount N2 of copper (second heat generation layer 23b) is the whole. Of 22%. From FIG. 11, the magnetic shunt alloy (first heat generating layer 23a) functions as a main heat generating layer, and copper (second heat generating layer 23b) increases the conductivity of the entire support roller 23 and functions as a subordinate heat generating layer. I understand that. When the temperature of the support roller 23 is equal to or higher than the Curie point, the copper (second heat generation layer 23b) does not generate heat and improves the self-temperature control function.

  FIG. 12 shows the first heat generation when the thickness of the second heat generation layer 23b (copper) is changed in the configuration of the support roller 23 of the first embodiment including the first heat generation layer 23a and the second heat generation layer 23b. It is the result of having calculated the ratio of the heat_generation | fever of the layer 23a and the 2nd heat-generating layer 23b by alternating current magnetic field analysis simulation. FIG. 13 shows the support roller 23 when the thickness of the second heat generation layer 23b (copper) is changed in the configuration of the support roller 23 of the first embodiment including the first heat generation layer 23a and the second heat generation layer 23b. It is the result of having calculated the change of the total calorific value of this by the alternating current magnetic field analysis simulation. Note that the alternating magnetic field analysis simulation in FIGS. 12 and 13 uses a support roller in which copper plating is applied only to the outer periphery of the magnetic shunt alloy as a calculation model.

  From FIG. 12 and FIG. 13, as the thickness of copper (second heat generation layer 23b) increases, the heat generation rate N1 of the magnetic shunt alloy (first heat generation layer 23a) increases and the heat generation rate N2 of copper decreases. It can be seen that the amount of heat generated by the entire support roller 23 increases. This is because the conductivity of the entire support roller 23 is increased by increasing the thickness of copper. Accordingly, the thickness of the copper (second heat generating layer 23b) is preferably as long as the thickness is less than the penetration depth (380 μm) when the frequency of the alternating current applied to the coil portion 25 is 30 kHz. Become. If the thickness of the copper (second heat generating layer 23b) becomes thicker than the penetration depth (380 μm), the magnetic flux of the coil portion 25 will not reach the magnetic shunt alloy, so The technical significance of the first heat generating layer 23a and the second heat generating layer 23b is lost.

  Further, FIG. 13 shows that when the thickness of the copper plating becomes larger than a predetermined value, the rate of increase in the amount of heat generated by the entire support roller 23 decreases. In order to quickly raise the temperature of the support roller 23, it is necessary to increase the heat generation amount and decrease the heat capacity. Therefore, the thickness of the copper (second heat generation layer 23b) to be actually used should be 10 to 60 μm. preferable. This value indicates the optimum thickness of the copper plating applied to one side of the magnetic shunt alloy (first heat generating layer 23a). Therefore, when the second heat generating layer 23b is provided on both sides of the magnetic shunt alloy (first heat generating layer 23a) as shown in FIG. 4, the thickness of the second heat generating layer 23b on both sides should be 10 to 60 μm. become.

In the first embodiment, the second heat generating layer 23b is formed of copper. However, the second heat generating layer 23b can be formed of nickel.
FIG. 14 shows the result of comparison of the heat generation amount of the support roller 23 calculated by the alternating magnetic field analysis simulation with that of the conventional one, and corresponds to FIG. 9 described above. FIG. 14 shows that the first heat generation of the support roller 23 when the heat generation amount of the support roller 23 is 100 when the support roller 23 is made of only a magnetic shunt alloy having a Curie point of 250 ° C. and a thickness of 0.3 mm. The ratio of the amount of heat generated by the support roller 23 when the layer 23a (magnetic shunt alloy) and the second heat generating layer 23b (nickel) are formed is displayed. The layer thicknesses of the first heat generating layer 23a and the second heat generating layer 23b and the frequency of the alternating current are the same as those in the first embodiment.

From FIG. 14, when the support roller 23 is formed of the first heat generation layer 23 a and the second heat generation layer 23 b (nickel), the heat generation amount is 125% as compared with the case where the support roller 23 is formed of only the magnetic shunt alloy. It can be seen that there is an improvement. This is because the volume resistivity of the second heat generating layer 23b (nickel) is 7.24 × 10 ⁻⁸ Ω · m, and the volume resistivity (8.0 × 10 6) of the first heat generating layer 23a (magnetic shunt alloy). ^-7 Ω · m). As described above, even when nickel, which is a magnetic material, is used for the second heat generating layer 23b, the conductive material having a volume resistivity lower than that of the first heat generating layer 23a is almost the same as that of the first embodiment. The same effect can be obtained.

Further, since the thickness of the second heat generating layer 23b (nickel) is less than the penetration depth when the frequency of the alternating current applied to the coil portion 25 is 30 kHz, the self-temperature control function is sufficiently exhibited. 10 to 30 μm is preferable.
By using nickel plating as the second heat generating layer 23b in this manner, although the effect of improving the heat generation amount is reduced as compared with copper plating, the rust prevention and wear resistance of the support roller 23 are improved and the long life is achieved. Can be provided.

Further, the fixing device according to the first embodiment can obtain an effect of stabilizing the high frequency power supply unit 40 that applies an alternating current to the coil unit 25.
15 and 16 show changes in the surface temperature of the fixing belt 22 when the Curie point of the magnetic shunt alloy used for the first heat generating layer 23a is set to 220 ° C. lower than 250 ° C. in the fixing device according to the first embodiment. It is the experimental result which confirmed (the temperature rising characteristic of the support roller 23) and the power consumption characteristic of the power supply part 40. FIG. When the surface of the fixing belt 22 is controlled to 180 ° C., there is a loss due to heat transfer from the support roller 23 to the peripheral members constituting the fixing device via the fixing belt 22. Must have the above Curie points.

  FIG. 15 shows experimental results in which the change in surface temperature of the fixing belt 22 and the power consumption characteristics of the power supply unit 40 are confirmed when the support roller 23 is composed of only the magnetic shunt alloy. FIG. 16 shows the change in surface temperature of the fixing belt 22 and the power consumption of the power supply unit 40 when the support roller 23 is composed of the magnetic shunt alloy (first heat generating layer 23a) and copper (second heat generating layer 23b). It is the experimental result which confirmed the characteristic. Note that the thickness and arrangement of the first heat generating layer 23a and the second heat generating layer 23b according to FIG. 16 are the same as those in the first embodiment. Further, the same high-frequency power supply unit 40 for supplying an alternating current to the fixing device shown in FIGS. 15 and 16 was used, and the power consumption was controlled to 1200 W.

As shown in FIG. 15, when the support roller 23 is composed of only a magnetic shunt alloy, the allowable current / voltage of the power supply unit 40 is exceeded before the surface temperature of the fixing belt 22 reaches 180 ° C. The part 40 has made an emergency stop.
On the other hand, as shown in FIG. 16, when the support roller 23 is composed of a magnetic shunt alloy (first heat generating layer 23a) and copper (second heat generating layer 23b), the surface temperature of the fixing belt 22 is increased. It was heated to the fixing temperature, and further, the temperature increase of the fixing belt 22 was suppressed to about 200 ° C. as desired. Moreover, it was confirmed that there was no emergency stop of the power supply part 40 and the power supply part 40 was operating stably.

Hereinafter, an emergency stop of the power supply unit 40 will be described.
When the surface of the fixing belt 22 is heated to 180 ° C., the support roller 23 generates heat up to the vicinity of the Curie point. At this time, since the magnetism of the first heat generating layer 23a is lowered, the electrical characteristics when combined with the coil portion 25 change. Specifically, since the inductance and resistance are reduced and the impedance is reduced, when viewed from the power supply unit 40 (inverter power supply), it becomes easy to supply current and voltage to the coil unit. At this time, if the same voltage as that before the magnetism of the first heat generating layer 23a is reduced is applied to the coil portion 25, the current that can be supplied from the power supply portion 40 is exceeded, so that an overcurrent of the circuit is prevented in advance. The safety device equipped to do this works and an emergency stop occurs. In other words, since the difference between the Curie point of the magnetic shunt alloy and the control temperature becomes small, the change in electrical characteristics when the support roller 23 is heated to near the control temperature becomes large. The margin for the voltage is reduced.

When the second heat generating layer 23b is added to the magnetic shunt alloy (first heat generating layer 23a), the emergency stop of the power supply unit 40 does not occur because the non-magnetic material (or the Curie point is the control temperature) as the second heat generating layer 23b. By using a sufficiently higher magnetic material), the electrical characteristics of the second heat generating layer 23b do not change even if the electrical characteristics of the first heat generating layer 23a change in the vicinity of the Curie point of the first heat generating layer 23a. by. Therefore, changes in the electrical characteristics of the entire support roller 23 (the first heat generating layer 23a and the second heat generating layer 23b) are suppressed.
As described above, in the fixing device 20 according to the first embodiment, in addition to the improvement of the temperature rise characteristic and the self-temperature control capability of the support roller 23, the margin for the allowable current / voltage of the power supply unit 40 is improved. A stabilization of 40 is achieved.

  As described above, in the first embodiment, in the electromagnetic induction heating type fixing device 20, in addition to the first heat generating layer 23a having a Curie point of 300 ° C. or lower, the volume resistance is higher than that of the first heat generating layer 23a. The second heat generating layer 23b having a low rate is provided on the support roller 23 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also the power supply part 40 can be stabilized.

  In the first embodiment, the support roller 23 having the first heat generating layer 23a and the second heat generating layer 23b is used as a heat generating member. On the other hand, the fixing belt 22 may be provided with a first heat generating layer and a second heat generating layer, and the fixing belt may be used as a heat generating member instead of the support roller. Further, the fixing belt 22 and the support roller 23 can be used as a heat generating member. In this case, the same effect as in the first embodiment can be obtained by providing the first heat generating layer and the second heat generating layer similar to those in the first embodiment on the member used as the heat generating member.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 17 is a cross-sectional view illustrating the support roller and the coil portion of the fixing device according to the second embodiment, and corresponds to FIG. 4 according to the first embodiment. The fixing device according to the second embodiment is different from that according to the first embodiment in that the support roller 23 includes a nickel layer on the coil portion 25 side with respect to the second heat generating layer 23b.

As shown in FIG. 17, the support roller 23 as the heat generating member in the second embodiment includes a first heat generating layer 23a and second heat generating layers 23b disposed on both sides of the first heat generating layer 23a. And nickel layers 23c respectively formed on the second heat generating layer 23b.
The first heat generating layer 23a is made of a magnetic shunt alloy similar to that of the first embodiment, and is formed to have a thickness of 0.3 mm. The second heat generating layer 23b is a copper plating layer, and is formed to have a thickness of 7.5 μm (total thickness is 15 μm). The nickel layer 23c is a nickel plating layer, and is formed to have a thickness of 0.5 μm (total thickness is 1 μm).

  In the fixing device according to the second embodiment, the coil portion 25 is disposed so as to sandwich the front and back surfaces of the support roller 23 as in the first embodiment. The support roller 23 is electromagnetically heated by the magnetic flux generated from the coil portion 25.

  FIG. 18 shows a result of comparing the heat generation amount of the support roller 23 calculated by the alternating magnetic field analysis simulation between the first embodiment and the second embodiment. FIG. 18 shows the heat generation of the support roller 23 in the second embodiment when the heat generation amount of the support roller 23 is 100 when the thickness of the second heat generation layer in the first embodiment is 7.5 μm. The amount ratio is displayed. The calculation conditions by the alternating magnetic field analysis simulation are the same as those in FIGS. 9 and 14 described above.

From FIG. 18, when the support roller 23 is formed of the first heat generation layer 23a, the second heat generation layer 23b, and the nickel layer 23c, the heat generation amount is that the support roller 23 is formed of the first heat generation layer 23a and the second heat generation layer 23b. It is 99% of the calorific value in the case, and it can be seen that there is almost no difference between the two.
In the second embodiment, since the nickel layer 23c is provided on the copper plating layer (second heat generating layer 23b) that is relatively susceptible to rust and wear, the support roller 23 has the rust prevention and wear resistance. As a result, the life of the fixing device can be extended. Further, it can be seen from the result of FIG. 18 that the heat generation efficiency of the support roller 23 is hardly lowered by providing the nickel layer 23c.

FIG. 19 shows the ratio of the heat generation amount when the temperature of the support roller 23 is equal to or higher than the Curie point in the support roller 23 according to the second embodiment, where the heat generation amount when the temperature is equal to or lower than the Curie point is 100. It is the calculation result which showed.
From FIG. 19, when the temperature of the support roller 23 is equal to or higher than the Curie point, the amount of heat generation is reduced to 24% when the temperature is equal to or lower than the Curie point, and the self-temperature controllability of the support roller 23 is sufficiently ensured. Recognize.

  From these results, as shown in FIG. 17, the support roller 23 is formed of the first heat generation layer 23a, the second heat generation layer 23b, and the nickel layer 23c, so that the heat generation efficiency and the self-temperature controllability are high and the life is extended. An improved fixing device can be provided. In this case, the nickel layer 23c needs to have a thickness that does not affect induction heating. Specifically, the thickness of the nickel layer 23c is desirably 10 μm or less on one side.

As described above, in the second embodiment, as in the first embodiment, in the electromagnetic induction heating type fixing device 20, in addition to the first heat generating layer 23a having a Curie point of 300 ° C. or lower, A second heat generating layer 23b having a volume resistivity lower than that of the first heat generating layer 23a is provided on the support roller 23 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also the power supply part 40 can be stabilized.
Furthermore, in the second embodiment, since the nickel layer 23c is provided on the coil portion 25 side with respect to the second heat generating layer 23b, it is possible to reduce the occurrence of rust and wear on the support roller 23.

Embodiment 3 FIG.
The third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 20 is a cross-sectional view illustrating a main part of the image forming apparatus according to the third embodiment. The image forming apparatus of the third embodiment is mainly the tandem type color image forming apparatus, and the point that the fixing roller 31 is used as the heat generating member and the fixing member is the same as that of the first embodiment. Is different.

  The image forming apparatus according to the third embodiment is a tandem color image forming apparatus. As shown in FIG. 20, a plurality of photosensitive drums 18BK, 18Y, 18M, and 18C are arranged in parallel on the transfer belt 8 in the image forming unit. Although not shown, a charging unit, an exposure unit, a developing unit, a cleaning unit, and a charge eliminating unit are disposed on the outer periphery of the plurality of photosensitive drums 18BK, 18Y, 18M, and 18C (process cartridge 4 in FIG. 1). Can be referred to.) Then, a toner image of each color (black, yellow, magenta, cyan) is formed on each photosensitive drum 18BK, 18Y, 18M, 18C.

The transfer unit 7 includes a transfer belt 8 that transports the recording medium P, a bias roller 9 that faces each of the photosensitive drums 18BK, 18Y, 18M, and 18C via the transfer belt 8, and a cleaning roller that cleans the surface of the transfer belt 8. 14, etc.
The transfer belt 8 sequentially conveys the recording medium P conveyed from the direction of the arrow to a position facing each of the photosensitive drums 18Y, 18M, 18C, and 18BK. At this time, the toner images of the respective colors are transferred onto the recording medium P by the transfer bias applied to the bias roller 9. Thus, a full-color toner image is formed on the recording medium P. Thereafter, the recording medium P on which a full-color toner image is formed is separated from the transfer belt 8 and conveyed toward the fixing device 20.

On the other hand, the fixing device 20 according to the third embodiment mainly includes a fixing roller 31 (fixing member) as a heat generating member, a pressure roller 30, an induction heating unit 24, and the like.
The fixing roller 31 includes a first heat generating layer 31a made of a magnetic shunt alloy, a second heat generating layer 31b made of copper, an elastic layer made of silicone rubber, a release layer made of a fluorine compound, and the like. As in the first embodiment, the first heat generating layer 31a of the fixing roller 31 is formed of a magnetic shunt alloy having a Curie point that is higher than the fixable temperature and lower than or equal to 300 ° C., and has a thickness of the above formula. It is formed so as to satisfy the relationship (1). The second heat generating layer 31b of the fixing roller 31 is formed of a conductive material having a volume resistivity lower than the volume resistivity of the first heat generating layer 31a, and the thickness thereof is the same as in the first embodiment. It is formed so as to satisfy the relationship of the above formula (2).

Moreover, the induction heating part 24 is comprised by the coil part 25 formed in loop shape similarly to the said Embodiment 1. FIG. That is, the coil portion 25 is disposed so as to sandwich the front and back surfaces (the inner peripheral surface and the outer peripheral surface) of the fixing roller 31.
When an alternating current having a desired frequency is supplied to the coil unit 25, magnetic lines of force are formed in the loop of the coil unit 25, and the heat generating layers 31a and 31b of the fixing roller 31 are heated by electromagnetic induction. The entire fixing roller 31 is heated by the heat generated by the heat generating layers 31a and 31b. In this way, the heated fixing roller 31 heats and melts the toner image on the recording medium P conveyed from the direction of the arrow and fixes the toner image on the recording medium P.

  Also in the third embodiment, when the temperature of the first heat generating layer 31a of the fixing roller 31 exceeds the Curie point, the heat generation of the heat generating member (the fixing roller 31) is efficiently performed as in the first embodiment. Will be limited.

  As described above, in the third embodiment, in the electromagnetic induction heating type fixing device 20, in addition to the first heat generating layer 31a having a Curie point of 300 ° C. or lower, the volume resistance is higher than that of the first heat generating layer 31a. A second heat generating layer 31b having a low rate is provided on the fixing roller 31 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also a power supply part can be stabilized.

  In the third embodiment, the fixing roller 31 is used as the fixing member facing the induction heating unit 24. However, a cylindrical fixing belt (fixing film) may be used as the fixing member facing the induction heating unit 24. it can. In this case, the holding member that holds the fixing belt in a cylindrical shape is brought into contact with a part of the inner peripheral surface of the fixing belt. Further, in order to form an appropriate fixing nip between the fixing belt and the pressure roller 30, the pressure member is brought into contact with a position on the inner peripheral surface of the fixing belt facing the pressure roller 30. Also for such a fixing device 20, the coil portion 25 is disposed so as to sandwich the front and back surfaces of the heat generating layer in the fixing belt as a heat generating member, and the first heat generating layer and the second heat generating layer are provided on the fixing belt. Thus, the same effect as in the third embodiment can be obtained.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 21 is a cross-sectional view showing the fixing device according to the fourth embodiment, and corresponds to FIG. 2 of the first embodiment. In the fixing device of the fourth embodiment, the position of the induction heating unit 24 is different from that of the first embodiment.

The fixing device 20 according to the fourth embodiment mainly includes a fixing belt 22 as a fixing member, a heat generating plate 28 as a heat generating member, an induction heating unit 24, a support roller 23, a pressure roller 30, and the like.
The heat generating plate 28 includes a first heat generating layer 28a made of a magnetic shunt alloy having a Curie point higher than the fixable temperature and lower than 300 ° C., and a second heat generating layer 28b having a volume resistivity lower than that of the first heat generating layer 28a. And is composed of. The heat generating plate 28 is in contact with the inner peripheral surface of the fixing belt 22 with a predetermined pressure.

  As shown in FIG. 21, the induction heating unit 24 according to the fourth embodiment is disposed at a position facing the outer peripheral surface and inner peripheral surface of the fixing belt 22 and the heat generating plate 28 from the support roller 23 to the auxiliary fixing roller 21. This is a looped coil portion 25. That is, the coil portion 25 is disposed so as to sandwich the fixing belt 22 and the heat generating plate 28.

In the fixing device 20 configured as described above, a line of magnetic force is formed between the fixing belt 22 and the coil portion 25 sandwiching the heat generating plate 28 by supplying an alternating current having a desired frequency to the loop-shaped coil portion 25. Thus, the heating plate 28 is induction heated by electromagnetic induction. The fixing belt 22 is heated by the heat generated by the heat generating plate 28.
Also in the fourth embodiment, when the temperature of the first heat generating layer 28a in the heat generating plate 28 exceeds the Curie point, the heat generation of the heat generating member (heat generating plate 28) is efficiently performed as in the first embodiment. Will be limited.

  As described above, in the fourth embodiment, in the electromagnetic induction heating type fixing device 20, in addition to the first heat generating layer 28a having a Curie point of 300 ° C. or lower, the volume resistance is higher than that of the first heat generating layer 28a. The second heat generating layer 28b having a low rate is provided on the heat generating plate 28 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also a power supply part can be stabilized.

Embodiment 5. FIG.
A fifth embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 22 is a cross-sectional view showing fixing device 20 in the fifth embodiment. FIG. 23 is a schematic diagram illustrating a state of magnetic flux acting on the support roller when the temperature of the first heat generating layer is equal to or lower than the Curie point. FIG. 24 illustrates a case where the temperature of the first heat generating layer is equal to or higher than the Curie point. It is the schematic which shows the state of the magnetic flux which acts on a support roller.
In the fixing device according to the fifth embodiment, the induction heating unit 24 as the magnetic flux generation unit is arranged such that the induction heating unit 24 as the magnetic flux generation unit faces only the outer peripheral surface side of the fixing roller 31. Is different from that of the third embodiment, which is disposed so as to face the front and back surfaces of the fixing roller 31.

  As shown in FIG. 22, the induction heating unit 24 as a magnetic flux generation unit is disposed so as to face only the outer peripheral surface side of the fixing roller 31. The induction heating unit 24 includes a coil unit 25, a core unit 26, a coil guide 27, and the like. The coil portion 25 is wound in the width direction (in the direction perpendicular to the paper surface of FIG. 22) by winding a litz wire bundled with thin wires on a coil guide 27 disposed so as to cover a part of the outer periphery of the fixing roller 31. It is an extension. The coil guide 27 is made of a resin material having high heat resistance and holds the coil portion 25. The core portion 26 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and the center core 26a and the side cores 26b are formed in order to form an efficient magnetic flux toward the heat generating layers 31a and 31b. Is provided. The core part 26 is installed so as to face the coil part 25 extending in the width direction.

In the fixing roller 31, an elastic layer 31c, a first heat generating layer 31a, a second heat generating layer 31b, and a release layer (not shown) are sequentially laminated on a core metal 31d made of aluminum having a thickness of 1 mm. It is a thing.
The elastic layer 31c is made of an elastic material such as silicone rubber and has a thickness of 50 to 500 μm. Thereby, the heat capacity is not so large, and a good fixed image can be obtained.

The first heat generating layer 31a is made of a magnetic shunt alloy having a Curie point of 300 ° C. or less, and has a thickness of 50 μm.
The second heat generating layer 31b is made of copper having a volume resistivity lower than that of the first heat generating layer 31a, and the thickness thereof is 15 μm.
The release layer is formed of a fluorine compound such as PFA and has a thickness of 30 μm. The release layer is for improving the toner release property on the surface of the fixing roller 20 with which the toner image (toner) T is in direct contact.
In the fifth embodiment, the second heat generating layer 31b is disposed on the outer peripheral surface side of the first heat generating layer 31a. However, the second heat generating layer 31b is disposed on the inner peripheral surface side or both sides of the first heat generating layer 31a. It can also be set up.

The fixing device 20 configured as described above operates as follows.
When the fixing roller 31 is driven to rotate clockwise in FIG. 22 by a drive motor (not shown), the pressure roller 30 also rotates counterclockwise. The fixing roller 31 as a fixing member is heated by the magnetic flux generated from the induction heating unit 24 at a position facing the induction heating unit 24.

  Specifically, by supplying a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) to the coil unit 25, the magnetic field lines are alternately bidirectional in the vicinity of the heat generating layers 31 a and 31 b. It is formed to switch to By forming an alternating magnetic field in this way, eddy currents are generated in the heat generating layers 31a and 31b of the fixing roller 20, and the heat generating layers 31a and 31b are inductively heated by generating Joule heat due to their electrical resistance. Thus, the fixing roller 20 is heated by induction heating of the heat generating layers 31a and 31b.

Thereafter, the surface of the fixing roller 31 heated by the induction heating unit 24 reaches a contact portion with the pressure roller 30. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted. The surface of the fixing roller 31 that has passed through the fixing position then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

FIG. 23 shows the state of the magnetic flux generated from the coil portion 25 when the temperature of the first heat generating layer 31a made of the magnetic shunt alloy is equal to or lower than the Curie point by a broken line arrow.
When the temperature of the first heat generating layer 31a is equal to or lower than the Curie point, the magnetic flux generated from the coil part 25 passes through the core part 26 as a path, passes through the second heat generating layer 31b and the first heat generating layer 31a, and returns to the core part 26 again. . This is because the first heat generating layer 31a made of a magnetic shunt alloy becomes a magnetic body and the penetration depth becomes very shallow. Therefore, the magnetic flux forms a magnetic circuit that does not pass through the first heat generating layer 31a. Then, an induced current flows through the fixing roller 31 to generate heat due to Joule heat.
Also in the fifth embodiment, since the second heat generating layer 31b is provided on the first heat generating layer 31a, good heat generation efficiency can be obtained.

FIG. 24 shows the state of the magnetic flux generated from the coil portion 25 when the temperature of the first heat generating layer 31a made of the magnetic shunt alloy is equal to or higher than the Curie point by a broken line arrow.
When the temperature of the first heat generating layer 31a is equal to or higher than the Curie point, the magnetic flux generated from the coil part 25 passes through the core part 26 through the second heat generating layer 31b and the first heat generating layer 31a and passes to the cored bar 31d. After reaching, it returns to the core part 26 again. This is because the first heat generating layer 31a made of a magnetic shunt alloy becomes a nonmagnetic material and the penetration depth becomes very deep. Therefore, the magnetic flux forms a magnetic circuit including the second heat generating layer 31b, the first heat generating layer 31a, and the cored bar 31d.

Here, since the cored bar 31d is formed of nonmagnetic and low resistance aluminum, a large amount of a reaction magnetic field with respect to the magnetic field from the coil portion is generated, and the inductance of the entire fixing roller 31 is increased. Since the effective resistance is small, heat generation due to Joule heat becomes very small. That is, in the fifth embodiment, the cored bar 31d has a function of shielding the magnetic flux in addition to the function of maintaining the rigidity of the fixing roller 31. As the material of the cored bar 31d, in addition to aluminum, a nonmagnetic / low resistance material such as gold, silver, copper, magnesium, or an alloy thereof can be used.
Thus, due to the difference in magnetic flux between FIGS. 23 and 24, when the magnetic shunt alloy (first heat generating layer 31a) is heated to a temperature above the Curie point, the amount of heat generation becomes very small and self-temperature control works. . Also in the fifth embodiment, since the second heat generating layer 31b is provided on the first heat generating layer 31a, good self-temperature controllability can be obtained.

Hereinafter, simulation results showing the effects in the fifth embodiment will be described.
FIG. 25 is a result of comparing the heat generation amount of the fixing roller 31 calculated by the alternating magnetic field analysis simulation between the conventional one and the fifth embodiment. FIG. 25 shows the fixing roller 31 according to the fifth embodiment when the heat generation amount of the fixing roller 31 when the first heat generating layer according to the fifth embodiment is not provided (conventional configuration) is 100. The ratio of the calorific value of is displayed. As a calculation condition by the alternating magnetic field analysis simulation, an alternating voltage having the same size and a frequency of 30 kHz was applied to the coil.

  From FIG. 25, the heat generation amount when the first heat generation layer 31 a and the second heat generation layer 31 b are formed as the heat generation layer of the fixing roller 31 is the heat generation amount when only the second heat generation layer 31 b is formed as the heat generation layer of the fixing roller 31. It is about 120% of the amount, and it can be seen that the heating efficiency is improved.

FIG. 26 shows the ratio of the heat generation amount when the temperature of the fixing roller 31 is equal to or higher than the Curie point in the fixing roller 31 of the fifth embodiment, where the heat generation amount when the temperature is equal to or lower than the Curie point is set to 100. It is the calculation result which showed.
26, since the temperature of the fixing roller 31 (first heat generating layer 31a) becomes equal to or higher than the Curie point, the magnetism of the first heat generating layer 31a is lost and the cored bar 31d made of aluminum shields the magnetic flux. It can be seen that the calorific value is reduced to 16% below the Curie point, and the self-temperature controllability of the fixing roller 31 is sufficiently secured. When the first heat generating layer 31a is not provided on the fixing roller 31 (which is a conventional configuration), such self-temperature controllability is not ensured.

  As described above, in the fifth embodiment, in the electromagnetic induction heating-type fixing device 20, in addition to the first heat generating layer 31a having a Curie point of 300 ° C. or lower, the volume resistance compared to the first heat generating layer 31a. A second heat generating layer 31b having a low rate is provided on the fixing roller 31 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also a power supply part can be stabilized.

  In the fifth embodiment, the fixing roller 31 is used as the fixing member. However, even when the fixing belt 22 is used as the fixing member, the same effect as in the fifth embodiment can be obtained. In that case, in the fixing device, the induction heating unit 24 is disposed on one side (for example, the outer peripheral side) of the fixing belt 22.

Embodiment 6 FIG.
27, the sixth embodiment of the present invention will be described in detail.
FIG. 27 is a cross-sectional view showing fixing device 20 in the sixth embodiment, and corresponds to FIG. 22 in the fifth embodiment. In the fixing device according to the sixth embodiment, the induction heating unit 24 as the magnetic flux generation unit is arranged such that the induction heating unit 24 as the magnetic flux generation unit faces the inner peripheral surface of the fixing roller 31. This is different from that of the fifth embodiment which is disposed so as to face the outer peripheral surface of the fixing roller 31.

As shown in FIG. 27, in the fixing device 20 according to the sixth embodiment, an induction heating unit 24 is installed inside the fixing roller 31. The induction heating unit 25 includes a coil unit 25, a core unit 26, and the like.
A magnetic flux shielding member 50 is installed so as to face the outer peripheral surface of the fixing roller 31. The magnetic flux shielding member 50 is made of a nonmagnetic and low resistance material such as aluminum, gold, silver, copper, magnesium, or an alloy thereof. By installing the magnetic flux shielding member 50 so as to face the induction heating unit 24 via the fixing roller 31, the temperature rise efficiency and the self-temperature controllability of the fixing roller 31 are improved.

  Here, the fixing roller 31 according to the sixth embodiment includes an elastic layer 31c, a second heat generating layer 31b, a first heat generating layer 31a, a release layer (not shown) on a cored bar 31d made of nonmagnetic stainless steel (SUS304). Are sequentially stacked. The material, configuration, and the like of each layer in the fixing roller 31 are substantially the same as those in the fifth embodiment except that the stacking order of the second heat generating layer 31b and the first heat generating layer 31a is different.

  As described above, in the sixth embodiment, in the same manner as in the fifth embodiment, in the electromagnetic induction heating type fixing device 20, in addition to the first heat generating layer 31a having a Curie point of 300 ° C. or lower, A second heat generating layer 31b having a volume resistivity lower than that of the first heat generating layer 31a is provided on the fixing roller 31 as a heat generating member. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also a power supply part can be stabilized.

Embodiment 7 FIG.
A seventh embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 28 is a cross-sectional view showing fixing device 20 in the seventh embodiment, and corresponds to FIG. 22 in the fifth embodiment. In the fixing device according to the seventh embodiment, the first heat generating layer 31a and the second heat generating layer 31b are adjacent to each other in that the first heat generating layer 31a and the second heat generating layer 31b are spaced apart from each other. This is different from that of the fifth embodiment.

As shown in FIG. 28, the fixing device 20 according to the seventh embodiment is also arranged so that the induction heating unit 24 faces only the outer peripheral surface side of the fixing roller 31 as in the fifth embodiment. ing.
In the fixing device 20 according to the seventh embodiment, the fixing roller 31 includes a first heat generation layer 31a, an elastic layer 31c, a second heat generation layer 31b, and a metal core 31d (nonmagnetic conductive layer) made of aluminum. A release layer (not shown) is sequentially laminated. In other words, the first heat generating layer 31a made of a magnetic shunt alloy and the second heat generating layer 31b made of copper are disposed apart from each other with the elastic layer 31c having electrical insulation therebetween.

In the seventh embodiment, the cored bar 31d as the nonmagnetic conductive layer is disposed on the side (the inner peripheral surface side) that does not face the second heat generating layer 31b with respect to the first heat generating layer 31a. . The cored bar 31d is made of aluminum and has a thickness of 0.5 mm or more. Specifically, the cored bar 31d is formed so that its volume resistivity is lower than the volume resistivity of the first heat generating layer 31a, and its thickness permeates corresponding to the frequency of the alternating current applied to the coil portion 25. It is formed to be thicker than the depth.
Thereby, the effect of shielding the magnetic flux can be obtained while suppressing the heat generation of the cored bar 31d itself. In the seventh embodiment, the thickness of the cored bar 31d is 1 mm. In the seventh embodiment, aluminum is used as the material of the cored bar 31d, but copper, silver, magnesium, or an alloy thereof can also be used.

The first heat generating layer 31a is made of a magnetic shunt alloy having a Curie point of 100 to 250 ° C. As a result, the fixing roller 31 is heated without being excessively heated by electromagnetic induction. In the seventh embodiment, the Curie point of the first heat generating layer 31a is set to 150 ° C.
The first heat generating layer 31 a is formed so that its thickness is substantially equal to the penetration depth corresponding to the frequency of the alternating current applied to the coil portion 25. Thereby, the energy by electromagnetic induction heating can be concentrated on the 2nd heat generating layer 31b. In the seventh embodiment, the thickness of the first heat generating layer 31a is 50 μm.

  The elastic layer 31c is made of an elastic material such as foamed silicone rubber having electrical insulation, and has a thickness of 3 mm. Thereby, the temperature rise efficiency is improved without the heat of the second heat generating layer 31 b arranged on the surface side of the fixing roller 31 flowing into the fixing roller 31.

  The second heat generating layer 31b is made of copper as a good conductive material having a lower volume resistivity than the first heat generating layer 31a, and has a thickness of 15 μm. The release layer is made of a fluorine compound such as PFA, PTFE, or FEP, and has a thickness of 5 to 50 μm (preferably 10 to 30 μm).

  As a metal suitable for electromagnetic induction heating, a metal having magnetism and high resistance is generally known. On the other hand, in the seventh embodiment, by thinning the highly conductive material, the substantial resistance of the second heat generating layer 31b can be arbitrarily set, and the heat generation amount can be improved. . In addition to copper, silver, aluminum, and magnesium can be used as the material of the second heat generating layer 31b, or nickel that is a magnetically conductive material can be used.

In the seventh embodiment, although not shown, the second heat generating layer 31b is formed by plating on a base material made of an insulating heat-resistant resin material. As the substrate, polyimide, polyamideimide, PEEK, PES, PPS, fluororesin, or the like can be used. The layer thickness of the base material is 30 to 200 μm from the viewpoint of heat capacity and strength.
Furthermore, a high-resistance nonmagnetic metal material that does not significantly affect induction heating, such as nonmagnetic stainless steel (SUS304), can also be used as the base material. By using SUS304 as a base material, the heat capacity can be reduced and the energy of electromagnetic induction heating can be concentrated on the second heat generating layer 31b. In this case, the thinner the SUS 304 is, the better (for example, 50 μm or less), and it is desirable that the thickness is at least a penetration depth corresponding to the frequency of the alternating current to be applied. Thereby, the energy of electromagnetic induction heating can be concentrated on the second heat generating layer 31b. The method for forming the second heat generating layer 31b is not limited to the plating method, and other methods such as vapor deposition, welding, and adhesion of metal foil can be used.

As described above, in the configuration in which the first heat generating layer 31a and the second heat generating layer 31b are arranged apart from each other, the second heat generating layer 31b is electromagnetically heated as a main heat generating layer by the magnetic flux generated from the coil portion 25. The By adopting a configuration in which a portion mainly heated by electromagnetic induction heating is limited to the second heat generating layer 31b, even when the surface of the fixing roller 31 is heated to 180 ° C. by heating the second heat generating layer 31b at the time of startup, Due to the presence of the elastic layer 31c, the temperature of the first heat generating layer 31a remains below the Curie point. Therefore, even if the magnetic shunt alloy is used, it is possible to prevent the rise speed from slowing down.
Further, when a small-sized recording medium is continuously fixed or when the apparatus suddenly stops driving, the heat on the surface of the fixing roller 31 is transferred to the first heat generating layer 31a through the elastic layer 31c. When the temperature of the first heat generation layer 31a exceeds the Curie point, the magnetism is lost, and the heat generation amount of the fixing roller 31 is reduced.

FIG. 29 shows the state of the magnetic flux generated from the coil portion 25 when the temperature of the first heat generating layer 31a made of the magnetic shunt alloy is equal to or lower than the Curie point by a broken line arrow.
When the temperature of the first heat generating layer 31a is equal to or lower than the Curie point, the magnetic flux generated from the coil part 25 passes through the core part 26 as a path, passes through the second heat generating layer 31b and the first heat generating layer 31a, and returns to the core part 26 again. . This is because the first heat generating layer 31a made of a magnetic shunt alloy becomes a magnetic body and the penetration depth becomes very shallow. Therefore, the magnetic flux forms a magnetic circuit that does not pass through the cored bar 31d. At this time, the eddy current does not flow to the first heat generating layer 31a formed to a thickness substantially equal to the penetration depth, but flows almost to the second heat generating layer 31b having a low volume resistivity. Thereby, the 2nd heat generating layer 31b is heated intensively.

FIG. 30 shows the state of the magnetic flux generated from the coil portion 25 when the temperature of the first heat generating layer 31a made of the magnetic shunt alloy is equal to or higher than the Curie point by a broken line arrow.
When the temperature of the first heat generating layer 31a is equal to or higher than the Curie point, the magnetic flux generated from the coil part 25 passes through the core part 26 through the second heat generating layer 31b and the first heat generating layer 31a and passes to the cored bar 31d. After reaching, it returns to the core part 26 again. This is because the first heat generating layer 31a made of a magnetic shunt alloy becomes a nonmagnetic material and the penetration depth becomes very deep. Therefore, the magnetic flux forms a magnetic circuit including the second heat generating layer 31b, the first heat generating layer 31a, and the cored bar 31d.

Here, since the cored bar 31d is formed of nonmagnetic and low resistance aluminum, a large amount of a reaction magnetic field with respect to the magnetic field from the coil portion is generated, and the inductance of the entire fixing roller 31 is increased. Since the effective resistance is small, heat generation due to Joule heat becomes very small.
Thus, due to the difference in magnetic flux in FIGS. 29 and 30, when the magnetic shunt alloy (first heat generating layer 31a) is heated to a Curie point or higher, the amount of heat generation becomes very small and self-temperature control works. . Here, the magnetic shunt alloy (first heat generating layer 31a) in the seventh embodiment has almost no function as a heat generating layer, and forms a magnetic circuit up to the cored bar 31d when the temperature becomes equal to or higher than the Curie point. It has a function for.

Hereinafter, experimental results and simulation results showing the effects of the seventh embodiment will be described.
FIG. 31 shows a case where the heat generating layer of the fixing roller 31 is formed of only a magnetic shunt alloy having a Curie point of 250 ° C. and a thickness of 0.4 mm (graph Q10), and the first heat generating layer 31a on the fixing roller 31. In addition, the temperature rise characteristics (start-up characteristics) of the fixing device are compared with the case where the second heat generating layer 31b is provided (the configuration of the seventh embodiment is the graph S10).
From FIG. 31, it can be seen that when the first heat generating layer 23a and the second heat generating layer 23b are formed on the fixing roller 31, the temperature rise characteristic is remarkably improved. Specifically, the time for the surface temperature of the fixing roller 31 to rise to the fixable temperature (180 ° C.) was 30 seconds for the graph Q10 and 10 seconds for the graph S10.

  Thus, the rise time of the fixing roller 31 has been shortened for two reasons. The first reason is that by forming the first heat generating layer 31a with a magnetic shunt alloy, only the roller surface is rapidly heated by the second heat generating layer 31b at the time of start-up, and the temperature of the first heat generating layer 31a becomes the Curie point. (In the seventh embodiment, the temperature is set to 150 ° C.) The rise is completed before the temperature rises. Therefore, the rise speed does not slow down due to a decrease in the magnetic permeability of the magnetic shunt alloy. The second reason is that the heat capacity of the second heat generating layer 31b becomes very small by using very thin copper as the second heat generating layer 31b.

  From FIG. 31, it can be seen that the self-temperature control ability is acting by forming the first heat generating layer 31a with a magnetic shunt alloy and optimizing its Curie point. Specifically, the temperature at which the surface temperature of the fixing roller 31 is controlled and maintained is 230 ° C. in the graph Q10 and 260 ° C. in the graph S10. Before the fixing roller 31 rises to a temperature at which fixing failure or thermal breakage occurs, the temperature of the first heat generating layer 31a becomes a temperature higher than the Curie point due to heat transfer from the surface side, and the amount of heat generation decreases.

FIG. 32 shows the ratio of the heat generation amount when the temperature of the fixing roller 31 is equal to or higher than the Curie point in the fixing roller 31 of the seventh embodiment, where the heat generation amount when the temperature is equal to or lower than the Curie point is 100. It is the calculation result which showed.
From FIG. 32, since the temperature of the fixing roller 31 (first heat generating layer 31a) becomes equal to or higher than the Curie point, the magnetism of the first heat generating layer 31a is lost. It can be seen that the self-temperature controllability of the fixing roller 31 is sufficiently secured.

  FIG. 33 is a result of calculating the ratio of heat generation of the first heat generating layer 31a, the second heat generating layer 31b, and the cored bar 31d in the fixing roller 31 of the seventh embodiment by an alternating magnetic field analysis simulation. As shown in FIG. 33, the heat generation amount N2 of copper (second heat generation layer 31b) is 98.27% of the heat generation amount of the entire fixing roller 31, and the heat generation amount N1 of the magnetic shunt alloy (first heat generation layer 31a). Was 1.7% of the total calorific value, and the calorific value of aluminum (core metal 23d) was 0.03% of the total calorific value. Therefore, it can be seen that copper (second heat generating layer 31b) functions as a main heat generating layer. From the above results, it can be seen that the rise time (temperature rise time) is shortened and the self-temperature controllability acts.

  FIG. 34 shows a case where the thickness of the core metal 23d (aluminum) is changed in the configuration of the fixing roller 31 according to the seventh embodiment, and the temperature of the first heat generating layer 31a (magnetic shunt alloy) is equal to or higher than the Curie point. This is the result of calculating the fluctuation of the heat generation amount of the fixing roller 31 by the AC magnetic field analysis simulation. In the graph, the calorific value of the fixing roller when the thickness of the cored bar 31d is 0.1 mm is 100. In addition, as a calculation condition by the alternating magnetic field analysis simulation, an alternating voltage having the same size and a frequency of 30 kHz was applied to the coil.

  FIG. 34 shows that the heat generation amount of the fixing roller 31 decreases as the thickness of the cored bar 31d increases from 0.1 mm. Since the penetration depth of aluminum (core metal 31d) with respect to an alternating current of 30 kHz is about 0.5 mm, when the thickness of the core metal 31d is thinner than the penetration depth, the effect of the core metal 31d as a magnetic flux shielding member is obtained. It turns out that it is not enough. Specifically, when the thickness of the cored bar 31d is equal to or smaller than the penetration depth, the amount of heat generated when the temperature of the magnetic shunt alloy is equal to or higher than the Curie point increases as the thickness decreases, and the self-temperature control capability increases. It turns out that it falls. On the other hand, when the thickness of the cored bar 31d is equal to or greater than the penetration depth (0.5 mm), the heat generation amount increases as the thickness increases, but the increase rate of the heat generation amount does not increase so much. Then, when the thickness of the cored bar 31d exceeds 1.0 mm, the heat generation amount becomes substantially constant. From these facts, it can be seen that the thickness of the cored bar 31d is desirably equal to or greater than the penetration depth.

  As described above, in the seventh embodiment, in the electromagnetic induction heating type fixing device 20, the first heat generating layer 31a having a Curie point of 300 ° C. or lower (100 ° C. or higher and 250 ° C. or lower), and the first heating layer 31a. The second heat generating layer 31b having a volume resistivity lower than that of the first heat generating layer 31a is provided on the fixing roller 31 so as to be separated from each other. As a result, the start-up time is short without reducing the heat generation efficiency, maintaining high self-temperature controllability, and fixing a small size recording medium continuously, or when the device suddenly stops driving, etc. Even if it exists, excessive temperature rise is suppressed reliably, and also a power supply part can be stabilized.

  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 embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view illustrating a fixing device in the image forming apparatus of FIG. 1. FIG. 3 is a perspective view showing the vicinity of a coil portion in the fixing device of FIG. 2. It is sectional drawing which shows a support roller and a coil part. It is the schematic which shows the state of the eddy current which arises in a support roller when temperature is below a Curie point. It is the schematic which shows the state of the eddy current which arises in a support roller when temperature is more than a Curie point. It is a graph which shows the temperature rising characteristic in the conventional fixing device. 3 is a graph illustrating a temperature rise characteristic of the fixing device according to the first embodiment. It is a graph which shows the emitted-heat amount of a support roller. It is a graph which shows the calorific value change of a support roller when temperature changes from the Curie point or less to the Curie point or more. It is a graph which shows the heat generation efficiency of the 1st heat generating layer and the 2nd heat generating layer in a support roller. It is a graph which shows the relationship between the thickness of a 2nd heat generating layer, and the heat generation efficiency of a support roller. It is a graph which shows the relationship between the thickness of a 2nd heat generating layer, and the emitted-heat amount. It is a graph which shows the emitted-heat amount of a support roller at the time of forming a 2nd heat generating layer with nickel. 6 is a graph showing power consumption characteristics in a conventional fixing device. 6 is a graph showing power consumption characteristics of the fixing device according to the first embodiment. It is sectional drawing which shows the support roller and coil part of the fixing device in Embodiment 2 of this invention. It is a graph which shows the emitted-heat amount in the support roller of FIG. 18 is a graph showing a change in heat generation when the temperature changes from the Curie point or lower to the Curie point or higher in the support roller of FIG. It is a block diagram which shows the principal part of the image forming apparatus in Embodiment 3 of this invention. It is sectional drawing which shows the fixing device in Embodiment 4 of this invention. It is sectional drawing which shows the fixing device in Embodiment 5 of this invention. FIG. 6 is a schematic diagram showing a state of magnetic flux acting on the fixing roller when the temperature of the first heat generating layer is equal to or lower than the Curie point. FIG. 6 is a schematic diagram showing a state of magnetic flux acting on the fixing roller when the temperature of the first heat generating layer is equal to or higher than the Curie point. It is a graph which shows the emitted-heat amount of the fixing roller of FIG. FIG. 23 is a graph showing a change in heat generation when the temperature changes from the Curie point or lower to the Curie point or higher in the fixing roller of FIG. 22. It is sectional drawing which shows the fixing device in Embodiment 6 of this invention. It is sectional drawing which shows the fixing device in Embodiment 7 of this invention. FIG. 6 is a schematic diagram showing a state of magnetic flux acting on the fixing roller when the temperature of the first heat generating layer is equal to or lower than the Curie point. FIG. 6 is a schematic diagram showing a state of magnetic flux acting on the fixing roller when the temperature of the first heat generating layer is equal to or higher than the Curie point. 10 is a graph showing a temperature rise characteristic of a fixing device according to a seventh embodiment. FIG. 29 is a graph showing changes in heat generation when the temperature changes from the Curie point or lower to the Curie point or higher in the fixing roller of FIG. 28. 3 is a graph showing the heat generation efficiency of a first heat generation layer and a second heat generation layer in a fixing roller. 3 is a graph showing the relationship between the thickness of a core metal and the amount of heat generated by a fixing roller.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device, 21 fixing auxiliary roller,
22 fixing belt (fixing member),
23 Support roller (heating member, heating member),
23a first heat generating layer, 23b second heat generating layer, 23c nickel layer,
24 induction heating part (magnetic flux generating means),
25 coil section, 26 core section,
26a center core, 26b side core, 27 coil guide,
28 heating plate (heating member, heating member),
28a first heat generating layer, 28b second heat generating layer,
30 pressure roller,
31 fixing roller (heating member, fixing member),
31a first heat generating layer, 31b second heat generating layer,
31c elastic layer, 31d cored bar,
40 High frequency power supply.

Claims (25)

A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating a magnetic flux when an alternating current is applied;
A heating member that generates heat by the magnetic flux,
The heat generating member includes a first heat generating layer formed to have a Curie point of 300 ° C. or less, and a second heat generating layer having a volume resistivity lower than the volume resistivity of the first heat generating layer. A fixing device. The fixing device according to claim 1, wherein the second heat generating layer is made of a nonmagnetic material. The fixing device according to claim 1, wherein the second heat generating layer is formed so that a thickness thereof is thinner than a penetration depth corresponding to the frequency of the alternating current. The fixing device according to claim 1, wherein the second heat generating layer is made of copper or nickel. 5. The fixing device according to claim 1, wherein the heat generating member includes a nickel layer on a side of the magnetic flux generating unit with respect to the second heat generating layer. The fixing device according to claim 1, wherein the first heat generating layer is made of an alloy of nickel, iron, and chromium. The fixing device according to claim 1, wherein the magnetic flux generation unit is a coil portion disposed so as to sandwich the front and back surfaces of the heat generating member. The fixing device according to claim 7, wherein the heat generating member includes the second heat generating layer on each of the front and back surfaces with respect to the first heat generating layer. The first heat generating layer is formed to have a thickness of 3 times or more and 17 times or less with respect to a penetration depth corresponding to the frequency of the alternating current when the temperature is lower than the Curie point. The fixing device according to claim 7, wherein the fixing device is a magnetic head. The fixing device according to claim 7, wherein the coil portion is wound apart so as to sandwich the front and back surfaces of the heat generating member once or a plurality of times. The fixing device according to claim 1, wherein the magnetic flux generation unit is disposed so as to face only one side of the heat generating member. The fixing device according to claim 11, wherein the first heat generating layer and the second heat generating layer are disposed to be separated from each other. The fixing device according to claim 12, further comprising a nonmagnetic conductive layer on a side of the first heat generating layer that does not face the second heat generating layer. The fixing device according to claim 13, wherein the nonmagnetic conductive layer is formed so that a volume resistivity thereof is lower than a volume resistivity of the first heat generating layer. The fixing device according to claim 13, wherein the nonmagnetic conductive layer is a cored bar made of aluminum. The fixing device according to claim 13, wherein the nonmagnetic conductive layer is formed to have a thickness greater than a penetration depth corresponding to the frequency of the alternating current. . The fixing device according to claim 12, further comprising an elastic layer having electrical insulation between the first heat generation layer and the second heat generation layer. The fixing device according to claim 12, wherein the first heat generating layer is formed so that a Curie point thereof is 100 ° C. or more and 250 ° C. or less. 19. The fixing device according to claim 12, wherein the first heat generating layer is formed to have a thickness equal to a penetration depth corresponding to a frequency of the alternating current. . The fixing device according to claim 1, wherein the heat generating member is a heating member that heats a fixing member that melts a toner image. The fixing member is a fixing belt,
The heating member is a support roller that stretches the fixing belt together with a fixing auxiliary roller,
21. The fixing device according to claim 20, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image. The fixing member is a fixing belt stretched between a support roller and a fixing auxiliary roller,
23. The fixing device according to claim 22, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. 23. The fixing device according to claim 22, wherein the fixing member is a fixing roller that abuts on a pressure roller that presses a recording medium to be conveyed. An image forming apparatus comprising the fixing device according to any one of claims 1 to 24.

Images