JP2012145912A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of suppressing image defect.SOLUTION: A fixing device comprises: a fixing belt; an induction current generating part; and a temperature-sensitive magnetic body. The fixing belt is a cylindrical belt including a conductive layer. The induction current generating part generates an induction current in the conductive layer. The temperature-sensitive magnetic body is disposed to oppose the induction current generating part with the fixing belt disposed therebetween. At a temperature higher than Curie temperature, a temperature range of the temperature-sensitive magnetic body in a temperature region where relative permeability of the temperature-sensitive magnetic body is lowered to be substantially zero in accordance with temperature increase of the temperature-sensitive magnetic body is not smaller than a difference between a temperature of the temperature-sensitive magnetic body in a steady state attained after a plurality of recording media with a smaller width than the fixing belt have passed through the fixing belt and a temperature of the fixing belt.

Description

  Embodiments described herein relate generally to a fixing device and an image forming apparatus.

  As a conventional fixing device, a device for heating a fixing belt to a predetermined temperature by an electromagnetic induction heating (IH) method is known. The fixing device includes an IH coil in the vicinity of the fixing belt and a temperature-sensitive magnetic body inside the fixing belt. When a sheet having a size smaller than the width of the fixing belt passes through the fixing device, the entire fixing belt is heated in order to keep the region through which the sheet has passed at the fixing temperature. Accordingly, the region where the sheet does not pass is excessively heated, and accordingly, the temperature of the temperature-sensitive magnetic body rises and exceeds the Curie temperature. At this time, the relative magnetic permeability of the temperature-sensitive magnetic body suddenly decreases and becomes substantially zero, that is, the temperature-sensitive magnetic body suddenly loses its magnetism, so that the temperature-sensitive magnetic body indirectly increases the temperature of the fixing belt. You will not be able to get. Accordingly, the temperature of the fixing belt is lower than the fixing temperature. When the temperature of the fixing belt is lowered, in order to keep the temperature of the fixing belt at the fixing temperature, it is necessary to control the current flowing in the IH coil so as to increase significantly and quickly.

  However, it is difficult to control the current flowing through the IH coil so as to follow a sudden change in magnetism of the temperature-sensitive magnetic body.

JP 2011-118389 A

  An object of the embodiments is to provide a fixing device and an image forming apparatus capable of suppressing image defects.

  The fixing device according to the embodiment includes a fixing belt, an induced current generation unit, and a temperature-sensitive magnetic body. The fixing belt has a cylindrical shape including a conductive layer. The induced current generator generates an induced current in the conductive layer. The temperature-sensitive magnetic body is disposed so as to face the induction current generating unit via the fixing belt. At a temperature higher than the Curie temperature, the temperature range of the temperature-sensitive magnetic body in a temperature region where the relative permeability of the temperature-sensitive magnetic body decreases to substantially zero as the temperature of the temperature-sensitive magnetic body rises is It is equal to or greater than the difference between the temperature in the steady state of the thermosensitive magnetic body after a plurality of recording media having a width smaller than the width of the belt has passed through the fixing belt and the temperature of the fixing belt.

1 is a schematic configuration diagram illustrating an image forming apparatus equipped with a fixing device according to an embodiment. 1 is a schematic configuration diagram illustrating a fixing device according to an embodiment. It is a perspective view which shows the external appearance of a temperature-sensitive magnetic body. FIG. 6 is an equal magnetic flux density diagram when a temperature-sensitive magnetic body is disposed inside a fixing coil and a magnetic flux is generated by an IH portion. It is a graph which shows the relationship between the temperature of a thermosensitive magnetic body, and a relative magnetic permeability. FIG. 10 is a diagram for explaining temperature changes of the fixing belt and the temperature-sensitive magnetic body when a sheet having a short width is supplied to the fixing device, and FIG. FIGS. 4B, 4C, and 4D are diagrams showing temperature changes of the fixing belt and the temperature-sensitive magnetic body after the sheet has passed through the fixing belt. It is. Similarly, FIG. 7 is a diagram for explaining temperature changes of the fixing belt and the temperature-sensitive magnetic body when a sheet having a short width is supplied to the fixing device. FIG. (B), (c), and (d) show the temperature change of the fixing belt and the temperature-sensitive magnetic body after the sheet passes through the fixing belt. FIG.

  Hereinafter, the fixing device and the image forming apparatus according to the embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus 10 equipped with a fixing device according to an embodiment. The image forming apparatus 10 is, for example, a color MFP (Multi Functional Peripheral) which is a tandem image forming apparatus. The image forming apparatus 10 includes a scanner unit 11, an image forming unit 12, and a paper feeding unit 13.

  The scanner unit 11 reads a document image and forms image data based on the read image.

  The image forming unit 12 forms a duplicate image on a sheet P as a recording medium supplied from the paper supply unit 13 based on the image data formed by the scanner unit 11.

  The image forming unit 12 includes four sets of image forming stations 14Y, 14M, 14C, and 14K of Y (yellow), M (magenta), C (cyan), and K (black). These are arranged in parallel along the intermediate transfer belt 15.

  The image forming station 14Y includes a photosensitive drum 16Y that rotates in the direction of arrow a. The image forming station 14Y includes a charger 17Y, a developing device 18Y, and a photoreceptor cleaner 19Y around the photoreceptor drum 16Y.

  Similarly, the other image forming stations 14M, 14C, and 14K include photoconductor drums 16M, 16C, and 16K that rotate in the same direction as the photoconductor drum 16Y, and each of these photoconductor drums 16M, 16C, and 16K. In the periphery, chargers 17M, 17C, and 17K, developing devices 18M, 18C, and 18K, and photoconductor cleaners 19M, 19C, and 19K are provided.

  The image forming unit 12 includes a laser exposure device 20 on the image forming stations 14Y, 14M, 14C, and 14K. The laser exposure apparatus 20 irradiates the photosensitive drums 16Y, 16M, 16C, and 16K with laser beams 21Y, 21M, 21C, and 21K corresponding to the respective colors, and statically irradiates the photosensitive drums 16Y, 16M, 16C, and 16K. An electrostatic latent image is formed.

  In the image forming unit 12, the surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K are uniformly charged by the chargers 17Y, 17M, 17C, and 17K, respectively. When the laser exposure device 20 irradiates the charged surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K with laser beams 21Y, 21M, 21C, and 21K based on the image data formed by the scanner unit 11, Electrostatic latent images are formed on the surfaces of the body drums 16Y, 16M, 16C, and 16K. When each of the developing devices 18Y, 18M, 18C, and 18K supplies toner charged so as to be attracted to the electrostatic latent image to the electrostatic latent image, each surface of the photosensitive drums 16Y, 16M, 16C, and 16K A toner image of each color is formed.

  The image forming unit 12 includes a backup roller 22 and a driven roller 23 that support the intermediate transfer belt 15. As the rollers 22 and 23 rotate, the intermediate transfer belt 15 travels in the direction of arrow b.

  The image forming unit 12 includes primary transfer rollers 24Y, 24M, 24C, and 24K at positions facing the respective photosensitive drums 16Y, 16M, 16C, and 16K through the intermediate transfer belt 15. The primary transfer rollers 24Y, 24M, 24C, and 24K primarily transfer the toner images of the respective colors formed on the photosensitive drums 16Y, 16M, 16C, and 16K to the intermediate transfer belt 15 so as to overlap each other. . As a result, a toner image is formed on the intermediate transfer belt 15. Each photoreceptor cleaner 19Y, 19M, 19C, 19K removes toner remaining on each photoreceptor drum 16Y, 16M, 16C, 16K after the primary transfer.

  The image forming unit 12 includes a secondary transfer roller 25 at a position facing the backup roller 22 via the intermediate transfer belt 15. The secondary transfer roller 25 rotates in the direction of arrow c following the intermediate transfer belt 15.

  The image forming unit 12 takes out the sheet P from the sheet feeding unit 13 by the pickup roller 26 and feeds the sheet P to the secondary transfer roller 25 along the conveyance path 27. The sheet P is fed to the secondary transfer roller 25 in accordance with the timing at which the toner image formed on the intermediate transfer belt 15 reaches the position of the secondary transfer roller 25. The toner image formed on the intermediate transfer belt 15 is secondarily transferred to the sheet P fed to the secondary transfer roller 25.

  The image forming apparatus 10 includes a fixing device 28, a paper discharge roller pair 29, and a paper discharge unit 30. The fixing device 28 fixes the toner image secondarily transferred to the sheet P to the sheet P. As a result, a duplicate image of the original image read by the scanner unit 11 is formed on the sheet P. The paper discharge roller pair 29 discharges the sheet P on which the duplicate image is formed. The paper discharge unit 30 places the sheet P discharged by the paper discharge roller pair 29.

  Although the image forming apparatus 10 according to the embodiment is a tandem image forming apparatus, the image forming apparatus is not limited to the tandem system, and the number of developing devices is not limited. The image forming apparatus may transfer the toner image directly from the photosensitive drum to the sheet.

  Next, the fixing device 28 will be described. FIG. 2 is a diagram schematically illustrating the fixing device 28 according to the embodiment. The fixing device 28 includes a fixing belt 31, a pressure pad 32, a pressure roller 33, an electromagnetic induction heating (IH) unit 34, a temperature sensitive magnetic body 35, a magnetic flux shielding member 36, and a temperature sensor 37.

  The fixing belt 31 is a cylindrical endless belt and has a multilayer structure including a heat generating layer which is a conductive layer. The fixing belt 31 has a configuration in which, for example, a heat generating layer, an elastic layer, and a release layer are stacked in this order from the inner peripheral side to the outer peripheral side. The fixing belt 31 rotates in the direction of arrow d following or independently of the pressure roller 33.

  The heat generating layer is a layer in which eddy current is generated by the magnetic flux generated from the IH unit 34. The heat generating layer is heated by the Joule heat of the eddy current generated in the heat generating layer. The metal constituting the heat generating layer is, for example, Ni, Fe, Cu, Au, Ag, Al or the like. These metals may be used alone, or two or more kinds of alloys may be used. The heat generating layer is composed of, for example, three layers of Ni—Cu—Ni.

  The elastic layer is made of an elastic body such as silicone rubber, and the release layer is made of a fluororesin, for example. Here, the release layer is a layer for suppressing the toner forming the toner image on the sheet P from adhering to the fixing belt 31.

  The fixing belt 31 is thinned and has a low heat capacity in order to shorten the time required for warming up. That is, the thickness of each of the heat generation layer, the elastic layer, and the release layer is thinned in order to shorten the time required for warming up.

  The pressure pad 32 is provided with a release layer made of, for example, a fluororesin on the surface of an elastic body such as a heat-resistant silicon sponge or silicon rubber. The pressure pad 32 is provided inside the fixing belt 31 and presses the fixing belt 31 from the inside of the fixing belt 31 toward the pressure roller 33.

  The pressure roller 33 includes, for example, an elastic layer 33b made of heat-resistant silicon sponge or silicon rubber around the core metal 33a, and a release layer 33c made of fluorine resin such as PFA resin on the surface. The pressure roller 33 is provided so that the longitudinal direction thereof is parallel to the longitudinal direction of the fixing belt 31. The pressure roller 33 rotates in the direction of arrow e as a gear (not shown) provided at the end of the core bar 33a is rotated by a motor (not shown).

  The IH unit 34 generates an eddy current that is an induced current in the heat generating layer of the fixing belt 31. The IH unit 34 includes an electromagnetic induction heating (IH) coil 34a and a ferrite core 34b. The ferrite core 34b is provided outside the fixing belt 31 on the opposite side of the pressure roller 33 so as to be close to the fixing belt 31, and is formed in an arc shape along the outer peripheral surface of the fixing belt 31. It is. The ferrite core 34 b includes an IH coil 34 a on the surface facing the fixing belt 31.

  The IH coil 34 a is an induced current generator that generates an eddy current that is an induced current in the heat generation layer of the fixing belt 31. The IH coil 34a is, for example, a litz wire obtained by bundling a plurality of copper wires coated with a heat-resistant polyamideimide that is an insulating material. When a high frequency current of about 20 kHz to 100 kHz, for example, is applied from the excitation circuit 38 to the IH coil 34a, the IH coil 34a generates a magnetic flux. This magnetic flux generates an eddy current in the heat generating layer of the fixing belt 31.

  Note that the magnitude of the high-frequency current output from the excitation circuit 38 is controlled by the control circuit 39 in accordance with the temperature of the fixing belt 31 detected by the temperature sensor 37.

  The temperature-sensitive magnetic body 35 assists in raising the temperature of the fixing belt 31. That is, the temperature-sensitive magnetic body 35 indirectly increases the temperature of the fixing belt 31 based on the magnetic flux generated from the IH unit 34. The temperature-sensitive magnetic body 35 is formed in an arc shape along the inner peripheral surface of the fixing belt 31, and is located at a position facing the IH coil 34 a of the IH portion 34 through the fixing belt 31. And spaced apart.

  FIG. 3 is a perspective view schematically showing the temperature-sensitive magnetic body 35. As shown in FIG. 3, the temperature-sensitive magnetic body 35 has a plurality of slits 35 a that are orthogonal to the direction in which the eddy current I induced by the IH unit 34 (dotted line I in the drawing) flows. These slits 35a divide the eddy current I. As a result, only a small eddy current is generated between the slits 35a. Therefore, when the slit 35a is provided, it is possible to suppress an excessive increase in the temperature of the temperature-sensitive magnetic body 35 as compared with the case where the slit 35a is not provided.

  These slits 35a are preferably formed at equal intervals. By forming the slits 35a at equal intervals, it is possible to suppress temperature unevenness in the temperature-sensitive magnetic body 35.

  The temperature-sensitive magnetic body 35 preferably has the same temperature as that of the fixing belt 31, but actually the temperature of the temperature-sensitive magnetic body 35 also increases due to the magnetic flux generated from the IH unit 34. The slit 35a is provided in order to prevent the temperature of the temperature-sensitive magnetic body 35 from rising due to the magnetic flux emitted from the IH unit 34. The slit 35a can suppress heat generation of the temperature-sensitive magnetic body 35 as these intervals are narrowed. However, a predetermined interval (for example, 4 to 6 mm) is provided for the convenience of manufacturing and the strength of the temperature-sensitive magnetic body 35. ) It is difficult to make it narrower.

  FIG. 4 is an equal magnetic flux density diagram when the temperature-sensitive magnetic body 35 is disposed inside the fixing coil 31 and a magnetic flux is generated by the IH unit 34. When a magnetic flux is generated by the IH unit 34, the magnetic flux generates heat in the periphery of the temperature-sensitive magnetic body 35 as shown in FIG. The magnetic flux generated around the temperature-sensitive magnetic body 35 further causes the fixing coil 31 to generate heat. Further, the temperature of the temperature-sensitive magnetic body 35 is increased by Joule heat of a small eddy current generated in the temperature-sensitive magnetic body 35, and this temperature further increases the temperature of the fixing coil 31. As a result, the temperature-sensitive magnetic body 35 indirectly increases the temperature of the fixing belt 31.

  The temperature-sensitive magnetic body 35 is composed of a member whose relative permeability varies with temperature. FIG. 5 is a graph showing the relationship between the temperature of the temperature-sensitive magnetic body 35 and the relative magnetic permeability. As shown in FIG. 5, the temperature-sensitive magnetic body 35 has the following relative magnetic permeability characteristics. That is, the relative magnetic permeability of the temperature-sensitive magnetic body 35 increases with an increase in temperature in a low temperature region. However, when it exceeds a certain temperature (Curie temperature Tc described later), it is substantially zero so as to be proportional to the increase in temperature. To fall.

  Note that the relative permeability is substantially zero means a relative permeability that does not increase the temperature of the fixing belt 31 even when a magnetic flux is generated around the temperature-sensitive magnetic body 35.

In the following description, the temperature region below the Curie temperature Tc is the low temperature region T _L , and the temperature region above the Curie temperature Tc and the relative permeability is reduced to substantially zero is the first high temperature region T _H1 , high temperature region T _H1 above temperature region, i.e. relative permeability substantially the temperature range of zero second high temperature region T _H2, and referred.

  Here, as shown in FIG. 5, the temperature-sensitive magnetic body 35 provided in the fixing device 28 according to the present embodiment has physical properties such that the relative dielectric constant is substantially highest at the fixing temperature T <b> 1 of the fixing device 28. A temperature-sensitive magnetic body 35 is applied. This is because the indirect temperature rise effect of the fixing belt 31 by the temperature-sensitive magnetic body 35 is efficiently obtained.

Further, as shown in FIG. 5, a straight line indicating a change in relative permeability in the low temperature region T _L is L1, and a straight line indicating a change in relative permeability in the low temperature region of the first high temperature region T _H1 is L2, of the first high temperature region T _H1, the straight line indicating the change in the relative magnetic permeability in the high temperature region L3, and L4 of the straight line indicating the change in the relative magnetic permeability in the second high temperature region T _H2. The temperature at the intersection of the straight line L1 and the straight line L2 is defined as the Curie temperature Tc, and the temperature difference between the Curie temperature Tc and the temperature T34 at the intersection of the straight line L3 and the straight line L4 is defined as ΔTtrans. At this time, as the temperature-sensitive magnetic substance 35 provided in the fixing device 28 according to this embodiment, the temperature-sensitive magnetic substance 35 in which the temperature difference between the first high temperature region T _H1 ΔTtrans has 20 ° C. or more physical properties is applied. That is, the temperature-sensitive magnetic body 35 provided in the fixing device 28 according to the present embodiment has a feeling that the relative permeability does not become substantially zero even when this temperature is 20 ° C. or more higher than the Curie temperature Tc. This is a warm magnetic body 35. Such a temperature-sensitive magnetic body 35 is a magnetic shunt alloy made of an alloy of iron and nickel, for example. In this embodiment, the reason why the temperature difference between the first high temperature region T _H1 ΔTtrans to apply temperature-sensitive magnetic substance 35 having a 20 ° C. or more physical properties described below.

As described above, the temperature-sensitive magnetic body 35 provided in the fixing device 28 according to the present embodiment has substantially the highest relative dielectric constant at the fixing temperature T1 of the fixing device 28 (a temperature slightly lower than the Curie temperature Tc). It has a relative magnetic permeability characteristics made, and the temperature difference ΔTtrans the first high temperature region T _H1 is one that has a relative permeability characteristics over 20 ° C..

  Refer to FIG. 2 again. The magnetic flux shielding member 36 of the fixing device 28 is made of, for example, aluminum. The magnetic flux shielding member 36 is provided in the fixing belt 31 at a position where the temperature-sensitive magnetic body 35 is interposed between the magnetic flux shielding member 36 and the fixing belt 31. The magnetic flux shielding member 36 suppresses generation of noise based on the magnetic flux generated by the IH unit 34 in the sensor 40 provided in the fixing belt 31.

  The temperature sensor 37 is a sensor for detecting the temperature of the fixing belt 31. As shown in FIG. 2, the temperature sensor 37 may be a non-contact type provided at a position separated from the fixing belt 31, or may be a contact type that contacts the fixing belt 31, although illustration is omitted. Good.

  In such a fixing device 28, as shown in FIG. 2, when the pressure pad 32 presses the fixing belt 31, the surface of the pressure pad 32 and the fixing belt 31 are curved corresponding to the surface shape of the pressure roller 33. Thus, the nip portion 41 is formed. While the fixing belt 31 has reached the fixing temperature T1 (however, the fixing temperature T1 <the Curie temperature Tc of the temperature-sensitive magnetic body 35) by the IH unit 34, the pressure roller 33 rotates in the direction of arrow e, and the fixing belt 31 When the sheet P is guided to the nip portion 41 and the toner image formed on the sheet P is heated in the nip portion 41, the toner image is pressurized at the same time. This heat and pressure stabilize the toner image on the sheet P. The toner image on the sheet P that has passed through the nip portion 41 is cooled to be fixed on the sheet P, and a duplicate image is formed on the sheet P.

  A case where a sheet P having a width shorter than the length of the fixing belt 31 in the longitudinal direction is supplied to the fixing device 28 will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram for explaining temperature changes of the fixing belt 31 and the temperature-sensitive magnetic body 35 when a sheet P having a short width is supplied to the fixing device 28. FIG. 4 is a diagram illustrating a positional relationship between the belt 31 and the temperature-sensitive magnetic body 35 and the supplied sheet P. FIGS. 5B, 5C, and 5D are diagrams after the sheet P passes through the fixing belt 31. FIG. FIG. 6 is a diagram showing temperature changes of the fixing belt 31 and the temperature sensitive magnetic body 35. Similarly, FIG. 7 is a diagram for explaining temperature changes of the fixing belt 31 and the temperature-sensitive magnetic body 35 when the sheet P having a short width is supplied to the fixing device 28. ) Is a diagram showing the positional relationship between the fixing belt 31 and the temperature-sensitive magnetic body 35 and the supplied sheet P. FIGS. 5B, 5C, and 5D show the positional relationship between the fixing belt 31 and the sheet P. FIG. 6 is a diagram showing temperature changes of the fixing belt 31 and the temperature-sensitive magnetic body 35 after passing.

  As shown in FIG. 6A, when a sheet P having a width Ws shorter than the longitudinal length Wb of the fixing belt 31 is supplied to the fixing device 28, the sheet through which the sheet P passes in the fixing belt 31. The temperature of the passage area 31a (hereinafter referred to as the paper passing area 31a) is lower than the fixing temperature T1 (FIG. 6B). At this time, the temperature of the temperature-sensitive magnetic body 35 is slightly higher than that of the fixing belt 31 because the temperature-sensitive magnetic body 35 itself is also heated by the magnetic flux emitted from the IH unit 34.

  The lowered temperature of the fixing belt 31 is detected by the temperature sensor 37 (FIG. 2). The control circuit 39 (FIG. 2) controls the excitation circuit 38 (FIG. 2) based on the detected temperature to increase the current flowing through the IH coil 34a of the IH unit 34. As a result, the temperature of the fixing belt 31 rises due to the direct and indirect temperature rise effect by the IH unit 34, and the temperature of the paper passing area 31a becomes the fixing temperature T1 (FIG. 6C).

  When the sheet P having a short width Ws is supplied to the fixing device 28 a plurality of times, the entire fixing belt 31 is heated to control the temperature of the paper passing area 31a at the fixing temperature T1 each time. The temperature of the 31 sheet non-passing area 31b (hereinafter referred to as the non-sheet passing area 31b) increases, and accordingly, the temperature of the end portion 35b of the thermosensitive magnetic body 35 corresponding to the portion 31b also increases. As a result, the temperature of the end 35b of the temperature-sensitive magnetic body 35 exceeds the Curie temperature Tc (FIG. 6 (d)).

  When the temperature of the end portion 35b of the temperature-sensitive magnetic body 35 exceeds the Curie temperature Tc, the relative permeability of this portion decreases. Accordingly, since the effect of indirectly increasing the temperature of the fixing belt 31 at the end portion 35b of the temperature-sensitive magnetic body 35 is reduced, the temperature of the non-sheet passing region 31b of the fixing belt 31 is reduced. On the other hand, the temperature of the end portion 35b of the temperature-sensitive magnetic body 35 remains above the Curie temperature Tc (FIG. 7B).

  If this state continues for a certain time, the temperature of the end portion 35b of the temperature-sensitive magnetic body 35 further rises, but at the same time, the heat of the end portion 35b moves toward the center. Therefore, the temperature of the temperature-sensitive magnetic body 35 is made substantially uniform regardless of the location, and the temperature exceeds the Curie temperature Tc (FIG. 7C). As described above, after the plurality of sheets P smaller than the width Wb in the longitudinal direction of the fixing belt 31 pass through the fixing device 28, the temperature of the temperature-sensitive magnetic body 35 is substantially uniform regardless of the place. Is defined as the steady state of the temperature-sensitive magnetic body 35, the temperature of the temperature-sensitive magnetic body 35 in the steady state is about 20 ° C. higher than the temperature of the fixing belt 31.

  When the temperature of the temperature-sensitive magnetic body 35 in the steady state exceeds the Curie temperature Tc, the relative magnetic permeability of the entire temperature-sensitive magnetic body 35 is reduced, and the indirect fixing belt 31 of the indirect fixing belt 31 due to magnetic flux generated around the temperature-sensitive magnetic body 35 is reduced. Since the temperature increase effect decreases, the temperature of the fixing belt 31 decreases (FIG. 7D).

Here, as in the present embodiment, as the temperature-sensitive magnetic substance 35, by applying the temperature-sensitive magnetic substance 35 in which the temperature difference between the first high temperature region T _H1 ΔTtrans has a relative magnetic permeability characteristics of the above 20 ° C., sensitive Even if the temperature of the temperature magnetic body 35 is about 20 ° C. higher than the temperature of the fixing belt 31 and the temperature of the entire temperature sensitive magnetic body 35 exceeds the Curie temperature Tc, the relative magnetic permeability does not become zero. Therefore, although the effect of indirectly increasing the temperature of the fixing belt 31 due to the magnetic flux generated around the temperature-sensitive magnetic body 35 is reduced, it does not become zero. Therefore, the temperature of the fixing belt 31 is only slightly decreased (solid line in FIG. 7D).

In contrast, as in the prior art, as temperature-sensitive magnetic substance, by applying the temperature-sensitive magnetic substance temperature difference between the first high temperature region T _H1 ΔTtrans has a 20 ° C. less than the relative magnetic permeability characteristics, the temperature-sensitive magnetic When the temperature of the body becomes about 20 ° C. higher than the temperature of the fixing belt 31 and the temperature of the entire temperature-sensitive magnetic body exceeds the Curie temperature Tc, the relative permeability rapidly decreases and becomes substantially zero. Accordingly, the effect of indirectly increasing the temperature of the fixing belt 31 due to the magnetic flux generated around the temperature-sensitive magnetic body is substantially zero. Accordingly, the temperature of the fixing belt 31 is significantly reduced (the chain line in FIG. 7D).

  As shown in FIG. 7D, when the temperature of the fixing belt 31 decreases, the temperature sensor 37 (FIG. 2) detects this temperature, and the control circuit 39 (FIG. 2) detects the excitation circuit 38 (FIG. 2). By controlling the above, the temperature of the fixing belt 31 is raised to the fixing temperature T1.

As described above, according to the fixing device 28 and the image forming apparatus 10 according to the present embodiment, since the first temperature difference ΔTtrans is 20 ° C. or more temperature-sensitive magnetic substance 35 in the high temperature region T _H1 is applied Even when the temperature of the fixing belt 31 is decreased due to the temperature of the entire temperature-sensitive magnetic body 35 exceeding the Curie temperature Tc, the amount of decrease in the temperature of the fixing belt 31 can be suppressed. As a result, in order to set the temperature of the fixing belt 31 to the fixing temperature T1, it is not necessary to increase the current flowing through the IH coil 34a significantly and quickly, and the IH coil 34a is made to follow the magnetic change of the temperature-sensitive magnetic body 35. The flowing current can be easily controlled. Accordingly, the temperature of the fixing belt 31 is excessively increased, so that the duplicate image becomes a high temperature offset image, or the temperature of the fixing belt 31 is insufficient, so that the duplicate image becomes a low temperature offset image. Therefore, it is possible to suppress image defects that occur in the duplicate image.

Furthermore, according to the fixing device 28 and the image forming apparatus 10 according to the present embodiment, since the first temperature difference ΔTtrans is 20 ° C. or more temperature-sensitive magnetic substance 35 in the high temperature region T _H1 is applied, the fixing belt 31 Even if there is temperature unevenness, the relative permeability of the temperature-sensitive magnetic body 35 is suppressed from changing greatly according to this, and the temperature of the fixing belt 31 is suppressed from changing greatly. Accordingly, it is possible to suppress image defects that occur in the duplicate image based on the temperature unevenness of the fixing belt 31.

  Although the embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

For example, the temperature-sensitive magnetic substance 35 in the present embodiment, the temperature difference between the first high temperature region T _H1 ΔTtrans has had a relative magnetic permeability characteristics of the above 20 ° C., sensitive, such as shown in FIG. 7 (c) If the temperature and the difference between the temperature and the temperature-sensitive magnetic substance 35 of the fixing belt 31 in the steady state of temperature magnetic body becomes T ° C., as the temperature-sensitive magnetic substance 35, the temperature difference between the first high temperature region T _H1 DerutaTtrans is T If a temperature-sensitive magnetic body having a relative magnetic permeability characteristic of at least ° C. is applied, the same effects as those of the fixing device 28 and the image forming apparatus 10 according to the present embodiment can be obtained. That is, the temperature-sensitive magnetic substance, the temperature difference between the first high temperature region T _H1 ΔTtrans is, by applying the temperature-sensitive magnetic substance having a temperature difference or more relative permeability characteristics of the temperature and the temperature-sensitive magnetic substance of the fixing belt 31 For example, the same effects as those of the fixing device 28 and the image forming apparatus 10 according to the present embodiment can be obtained.

28... Fixing device 31... Fixing belt 31 a... Sheet passing area (sheet passing area)
31b ... Sheet non-passing area (non-sheet passing area)
34 ... Electromagnetic induction heating (IH) section 34a ... Electromagnetic induction heating (IH) coil 34b ... Ferrite core 35 ... Temperature-sensitive magnetic body 35a ... Slit

Claims (7)

A cylindrical fixing belt including a conductive layer;
An induced current generator for generating an induced current in the conductive layer;
A temperature-sensitive magnetic body disposed to face the induced current generating unit via the fixing belt;
Comprising
At a temperature higher than the Curie temperature, the temperature range of the temperature-sensitive magnetic body in a temperature region where the relative permeability of the temperature-sensitive magnetic body decreases to substantially zero as the temperature of the temperature-sensitive magnetic body rises is Fixing, wherein a plurality of recording media having a width smaller than the width of the belt is equal to or greater than a difference between a temperature in a steady state of the temperature-sensitive magnetic body after passing through the fixing belt and a temperature of the fixing belt. apparatus. A cylindrical fixing belt including a conductive layer;
An induced current generator for generating an induced current in the conductive layer;
The temperature range of the temperature region, which is arranged to face the induction current generating unit via the fixing belt and has a relative magnetic permeability substantially reduced to zero with its own temperature rise at a temperature higher than the Curie temperature, is 20 A temperature-sensitive magnetic material having a temperature of ℃ or higher,
A fixing device.   The fixing device according to claim 1, wherein the temperature-sensitive magnetic body has a plurality of slits.   The fixing device according to claim 3, wherein the plurality of slits are formed at equal intervals.   The fixing device according to claim 1, wherein the temperature-sensitive magnetic body is made of a magnetic shunt alloy. An image forming unit for forming a toner image on a recording medium;
A cylindrical fixing belt including a conductive layer disposed so as to contact the toner image;
An induced current generator for generating an induced current in the conductive layer;
The temperature range of the temperature region, which is arranged to face the induction current generating unit via the fixing belt and has a relative magnetic permeability substantially reduced to zero with its own temperature rise at a temperature higher than the Curie temperature, is 20 A temperature-sensitive magnetic material that is at or above ° C
An image forming apparatus comprising:   The image forming apparatus according to claim 6, wherein the temperature-sensitive magnetic body has a plurality of slits.

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