JP5839258B2 - Fixing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device that heat-fixes an unfixed image on a recording material using a fixing member heated by an induction heating method, and a copying machine, a printer, a facsimile machine, a printing machine, and the like provided with the fixing device. The present invention relates to an image forming apparatus such as a composite apparatus.

  This type of image forming apparatus generally undergoes a fixing process in which a toner image formed on a latent image carrier is transferred to a recording material (hereinafter referred to as “paper”) and then the toner image is heated and fixed on the paper. , Output an image. In this fixing process, the toner image is fixed on the paper by melting the toner by heat and pressure and penetrating the toner into the paper. In recent years, an induction heating method has attracted attention as a heating method employed in fixing processing. In the induction heating method, an induction magnetic flux generated by a high-frequency magnetic field generated by a magnetic field generating member such as an exciting coil penetrates a heat generating layer having magnetism provided on a fixing belt to generate an eddy current in the heat generating layer, thereby generating heat. In this method, the fixing belt is heated by generating heat in the layer.

  Patent Document 1 discloses an induction heating type fixing device in which an exciting coil that generates a magnetic flux and induction-heats a heat generation layer of a fixing sleeve (endless sheet member) by the magnetic flux is arranged to face the outer peripheral surface of the fixing sleeve. Has been. The fixing sleeve of this fixing device has a magnetic shunt alloy layer on the inner peripheral surface side of the heat generating layer. The magnetic shunt alloy exhibits magnetism until reaching the Curie temperature, but has a function of losing magnetism when the Curie temperature is exceeded. By providing such a magnetic shunt alloy layer on the fixing sleeve, the induction magnetic flux generated by the exciting coil does not reach the inner peripheral surface side of the fixing sleeve until the temperature of the magnetic shunt alloy reaches the Curie temperature. When the heat of the heat generating layer that is induction-heated propagates and the temperature of the magnetic shunt alloy becomes equal to or higher than the Curie temperature, it is transmitted to the inner peripheral surface of the fixing sleeve.

  In the fixing device described in Patent Document 1, a demagnetizing member is provided on the inner peripheral surface side of the fixing sleeve. The demagnetizing member generates a magnetic flux that cancels the induced magnetic flux when the induced magnetic flux acting on the demagnetizing member fluctuates. Therefore, according to the fixing device described in Patent Document 1, when the induction magnetic flux is generated by the exciting coil, the heating layer is rapidly heated by induction heating until the magnetic shunt alloy reaches the Curie temperature. When the alloy reaches the Curie temperature or higher, the induced magnetic flux of the exciting coil acts on the demagnetizing member, and the magnetic flux penetrating the heat generating layer decreases. Accordingly, the temperature of the fixing sleeve can be stabilized near the Curie temperature of the magnetic shunt alloy without performing electronic temperature control. Such a function is called a self-temperature control function.

  However, in the fixing device that realizes the self-temperature control function using the demagnetizing member, when the temperature of the magnetic shunt alloy becomes equal to or higher than the Curie temperature, the demagnetizing effect by the demagnetizing member sufficiently reaches the heating layer of the fixing belt. It is necessary to install a demagnetizing member at a position close to the exciting coil and the magnetic shunt alloy. At this time, since the heat generating layer is interposed between the exciting coil and the magnetic shunt alloy, the degaussing member has to be disposed close to the heat generating layer. Even if the magnetic shunt alloy and the demagnetizing member are disposed in a non-contact state, if they are disposed close to each other, heat is transferred from the magnetic shunt alloy that has reached a high temperature to the demagnetizing member by convection heat transfer or radiation. For this reason, the warm-up time required to raise the temperature of the fixing belt to the target temperature increases by the heat capacity of the demagnetizing member. As the distance between the magnetic shunt alloy and the degaussing member is shorter, the amount of heat transfer from the magnetic shunt alloy to the degaussing member increases, so the warm-up time tends to increase. In particular, when the magnetic shunt alloy and the degaussing member are in contact with each other, the amount of heat transfer from the magnetic shunt alloy to the degaussing member is increased, so that the warm-up time is likely to further increase.

  On the other hand, the fixing device described in Patent Document 1 includes a drive mechanism that displaces the degaussing member with respect to the excitation coil, and moves the demagnetization member to a position retracted from the position facing the excitation coil during warm-up. Thus, at the time of warm-up, even if the magnetic shunt alloy becomes equal to or higher than the Curie temperature, the demagnetizing effect by the demagnetizing member does not work, and the fixing sleeve can be raised to a temperature equal to or higher than the Curie temperature of the magnetic shunt alloy. According to this fixing device, the temperature increase rate of the fixing sleeve does not decrease even near the Curie temperature of the magnetic shunt alloy as compared with the configuration in which the degaussing member is always arranged to face the exciting coil. It can be shortened.

  However, this fixing device requires a drive mechanism for moving the position of the demagnetizing member, and there is a problem that the size of the device is increased and the cost is increased. Therefore, in a fixing device that realizes a self-temperature control function using a demagnetizing member, a new configuration that can shorten the warm-up time without providing such a drive mechanism is desired.

  The present invention has been made in view of the above background, and an object of the present invention is to shorten the warm-up time without providing a drive mechanism when realizing a self-temperature control function using a demagnetizing member. It is an object of the present invention to provide a fixing device that can be used and an image forming apparatus including the fixing device.

In order to achieve the above object, the present invention provides a fixing member comprising an endless sheet member that has a heat generating layer and heat-fixes an unfixed image on a recording material by heat generated in the heat generating layer, and the fixing member. And a magnetic field generating member that generates a magnetic field for inductively heating the heat generating layer of the fixing member, and is disposed opposite to the magnetic field generating member across the heat generating layer. A magnetic shunt member disposed integrally with or separately from the fixing member, and disposed on the opposite side of the magnetic field generating member across the magnetic shunt member, and a portion facing the magnetic field generating member is located on the fixing side A demagnetizing member having a shape along the surface of the member, and when the temperature of the magnetic shunt member becomes equal to or higher than the Curie temperature by the heat of the heat generating layer of the fixing member, the magnetic field of the magnetic field generating member is applied to the demagnetizing member. Acting to strike this with the degaussing member In the fixing device having a self-temperature control function that suppresses excessive heating of the heat generating layer due to the generation of a magnetic field to be erased and the magnitude of the magnetic field acting on the heat generating layer by the magnetic field being weakened, the demagnetizing member includes: , the inner portion of the fixing member circumferentially in opposite portion between the magnetic field generating member, an opening of the order magnetic flux generated by the magnetic field the magnetic field generating member have been generated by omission of the relatively small small magnetic flux portion It is characterized by comprising a single member .
The present invention also includes a fixing member having an exothermic layer, an endless sheet member that heat-fixes an unfixed image on a recording material by heat generated in the exothermic layer, and an inner peripheral surface or outer periphery of the fixing member. A magnetic field generating member disposed opposite to a part of the surface in the circumferential direction and generating a magnetic field for inductively heating the heat generating layer of the fixing member; and the fixing member disposed on the opposite side of the magnetic field generating member across the heat generating layer. The magnetic shunt member provided integrally or separately with the magnetic shunt member, and the magnetic field generating member is disposed on the opposite side of the magnetic shunt member, and a portion facing the magnetic field generating member extends along the surface of the fixing member. A demagnetizing member having a shape, and when the temperature of the magnetic shunt member becomes equal to or higher than the Curie temperature by the heat of the heat generation layer of the fixing member, the magnetic field of the magnetic field generating member acts on the demagnetizing member. A magnetic field that counteracts this is generated, In the fixing device having a self-temperature control function that suppresses excessive heating of the heat generation layer due to the magnitude of the magnetic field acting on the heat generation layer by the magnetic field, the degaussing member is connected to the magnetic field generation member. A location where the distance between the heat generation layer and the small magnetic flux portion where the amount of magnetic flux generated by the magnetic field generated by the magnetic field generating member is relatively small is the longest in the facing portion in the inner portion of the facing portion in the circumferential direction of the fixing member It is comprised by the single member provided with.

  In the present invention, the demagnetizing member is disposed so as to face the magnetic field generating member disposed facing the circumferential portion of the inner circumferential surface or the outer circumferential surface of the fixing member. Since this demagnetizing member has a shape that faces the magnetic field generating member along the surface of the fixing member, the facing portion is possible with respect to the magnetic field generating member disposed on the opposite side across the fixing member. It is possible to arrange them as close as possible. Accordingly, since a large amount of the induced magnetic flux generated by the magnetic field generating member reaches the close-facing portion of the demagnetizing member, a large amount of repulsive magnetic flux that reduces the induced magnetic flux is generated. Further, the demagnetizing member arranged in this way is arranged as close as possible to the heat generating layer of the fixing member. Therefore, the induced magnetic flux penetrating the heat generating layer can be effectively reduced by the large amount of repulsive magnetic flux generated in the degaussing member.

  Here, the amount of magnetic flux that passes through the portion of the degaussing member facing the magnetic field generating member at a certain moment is not uniform, and there are portions with a large amount of magnetic flux and portions with a small amount of magnetic flux depending on the positional relationship with the magnetic field generating member. To do. And even if the part (small magnetic flux part) with a relatively small amount of magnetic flux among the demagnetizing members is disposed close to the heat generating layer, the demagnetizing effect on the heat generating layer is low. Therefore, in the present invention, the small magnetic flux portion of the demagnetizing member is omitted or formed so that the distance from the heat generating layer is the longest in the facing portion of the demagnetizing member. As a result, the amount of heat transferred from the heat generation layer to the demagnetization member can be reduced compared to a configuration in which the facing portion of the demagnetization member is disposed uniformly close to the heat generation layer, and the warm-up caused by the demagnetization member An increase in time can be suppressed.

  That is, according to the present invention, among the portions of the demagnetizing member facing the magnetic field generating member, the portion that greatly affects the demagnetizing effect of the heat generating layer is disposed close to the heat generating layer to ensure a sufficient self-temperature control function. At the same time, a small magnetic flux portion that has a small influence on the demagnetizing effect of the heat generating layer is separated from the heat generating layer to reduce the amount of heat transfer from the heat generating layer to the demagnetizing member, thereby shortening the warm-up time.

  According to the present invention, when the self-temperature control function is realized using the demagnetizing member, an excellent effect that the warm-up time can be shortened without providing a drive mechanism is obtained.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a schematic diagram when a fixing device employed in the printer is viewed from a pressure roller rotation axis direction. FIG. 3 is a schematic diagram when the fixing device is viewed from an entrance side in a sheet conveyance direction. FIG. 3 is a perspective view illustrating an appearance of a magnetic flux generation unit in the fixing device. It is explanatory drawing which shows the structure of the exciting coil in the magnetic flux generation part. FIG. 3 is a cross-sectional view in the thickness direction of a fixing sleeve in the fixing device. (A) is explanatory drawing which represented typically the mode of the magnetic field when the temperature of the magnetic shunt alloy in an identification attachment apparatus is less than Curie temperature. (B) is explanatory drawing which represented typically the mode of the magnetic field when the temperature of the magnetic shunt alloy is more than Curie temperature. FIG. 6 is a schematic diagram illustrating a configuration of a fixing device according to a comparative example. It is a schematic diagram which shows the structure of the fixing device which concerns on another comparative example. FIG. 10 is a schematic diagram illustrating a configuration of a fixing device according to another comparative example. FIG. 10 is a schematic diagram when the fixing device of Modification 1 is viewed from the pressure roller rotation axis direction. It is a perspective view of the demagnetizing member of the modification 2. FIG. 10 is a schematic diagram when the fixing device of Modification 3 is viewed from the direction of the pressure roller rotation axis.

Hereinafter, an embodiment in which the present invention is applied to a laser printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment.
This printer has a photosensitive drum 1 as a latent image carrier. The surface of the photosensitive drum 1 is uniformly charged by a charging roller 50 as charging means that contacts the photosensitive drum 1 while being driven to rotate in the direction of arrow A in the figure. Thereafter, scanning exposure is performed based on image information by an optical writing unit 51 as a latent image forming unit, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. As the charging unit and the latent image forming unit, those different from the charging roller 50 and the optical writing unit 51 can be used. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 2 to form a toner image on the photosensitive drum 1. The toner image formed on the photosensitive drum 1 is used as a recording material conveyed from a paper feed cassette 54 through a paper feed roller 55 and a resist roller pair 56 by a transfer unit as a transfer means having a transfer roller 53. Transferred onto the paper 52. With the above configuration, the toner image forming means in the present embodiment is realized.

  After the transfer, the paper 52 is fixed with a toner image by the fixing device 10 as a fixing unit, and is discharged outside the apparatus. Specifically, the paper is discharged onto a paper discharge tray 61 that stores the paper 52 discharged from the fixing device 10 after fixing. Untransferred toner remaining on the photosensitive drum 1 without being transferred is removed from the surface of the photosensitive drum 1 by a cleaning unit 58 as a cleaning unit. Further, the residual charge on the photosensitive drum 1 is removed by a static elimination lamp 59 as a static elimination means.

Next, the fixing device 10 that is a characteristic part of the printer of this embodiment will be described in detail.
FIG. 2 is a schematic view of the fixing device 10 employed in the printer according to the present embodiment as viewed from the direction of the pressure roller rotation axis.
The fixing device 10 includes a fixing sleeve 11 as a fixing member made of an endless sheet member having a heat generating layer. The fixing sleeve 11 is installed so as to have a substantially cylindrical shape, and rotates in the direction of the arrow in the drawing. The fixing sleeve 11 is in pressure contact with the pressure roller 12 by a nip forming member 13 and a pressure support member 14 that supports the fixing sleeve 11 so that the fixing nip can be formed by contacting the pressure roller 12.

  In addition, a magnetic flux generator 15 is disposed in the vicinity of the outer peripheral surface of the fixing sleeve 11. The magnetic flux generator 15 is fixed to the fixing device main body. Further, a demagnetizing member 16 is disposed in the vicinity of the inner peripheral surface of the fixing sleeve 11 so as to face the magnetic flux generator 15. This demagnetizing member 16 is also fixed to the fixing device body. The demagnetizing member 16 is made of aluminum, for example.

FIG. 3 is a schematic diagram when the fixing device is viewed from the entrance side in the sheet conveyance direction.
The fixing sleeve 11 is supported by flange members 17 at both ends in the rotation axis direction. Further, the pressure support member 14 and the demagnetizing member 16 are also supported by the flange member 17. In this embodiment, the pressure roller 12 receives a driving force from a driving motor (not shown) and is rotationally driven in the direction of the arrow in the figure, and the fixing sleeve 11 receives a driving force from the pressure roller 12 at the fixing nip. Followed rotation. High friction regions 12 a are provided at both ends of the outer peripheral surface of the pressure roller 12, and the fixing sleeve 11 is prevented from slipping with respect to the pressure roller 12.

FIG. 4 is a perspective view showing the appearance of the magnetic flux generator 15.
The magnetic flux generator 15 includes an exciting coil 15 a as a magnetic field generating member that generates a magnetic field for inductively heating the heat generating layer of the fixing sleeve 11. In addition, the magnetic flux generator 15 includes five arch-shaped cores (arch cores) 15 b that are curved in accordance with the curvature of the outer peripheral surface of the fixing sleeve 11 in parallel with the rotation axis direction of the fixing sleeve 11. As shown in FIG. 4, the exciting coil 15 a is a flat coil (planar coil) positioned between the arch core 15 b and the fixing sleeve 11, and its coil axis substantially coincides with the normal direction of the outer peripheral surface of the fixing sleeve 11. Thus, the fixing sleeve 11 is disposed so as to face the outer peripheral surface.

FIG. 5 is an explanatory diagram showing the configuration of the exciting coil 15a.
The fixing device 10 of the present embodiment generates a high-frequency magnetic field (magnetic flux) around the excitation coil 15a by driving the excitation coil 15a of the magnetic flux generator 15 with high frequency by an inverter 15c that is a power supply source. Most of the magnetic flux generated thereby is guided toward the fixing sleeve 11 from both ends 15d of the arch core 15b through the inside of the arch core 15b. Due to this high-frequency magnetic field, an eddy current is generated in the heat generating layer of the fixing sleeve 11, whereby the heat generating layer is inductively heated, and the temperature of the fixing sleeve 11 rises.

FIG. 6 is a cross-sectional view of the fixing sleeve 11 in the thickness direction.
The fixing sleeve 11 has a diameter of, for example, 40 mm, and in order from the inner peripheral surface side, the magnetic shunt alloy 11a that is a magnetic shunt member, the first antioxidant layer 11b, the heat generating layer 11c, the second antioxidant layer 11d, the elastic layer 11e, It has a layered structure in which a release layer 11f which is a surface layer is laminated. A known and appropriate magnetic shunt alloy can be used for the magnetic shunt alloy 11a, and the thickness is, for example, 50 μm. Further, for example, nickel strike plating can be used for the antioxidant layers 11b and 11d, and the thickness is set to 1 μm or less, for example. For example, copper plating can be used for the heat generating layer 11c, and the thickness is set to 15 μm, for example. For example, silicone rubber can be used for the elastic layer 11e, and the thickness thereof is, for example, 150 μm. For the release layer 11f, for example, PFA can be used, and the thickness is, for example, 30 μm. The thickness of the fixing sleeve 11 of the present embodiment is, for example, in the range of 200 μm to 250 μm. However, these are all examples, and the layer configuration, material, thickness, and the like of the fixing sleeve 11 are appropriately set.

  The magnetic shunt alloy 11a of the present embodiment is made of a magnetic body (for example, a magnetic shunt alloy material containing iron or nickel) formed so that the Curie temperature is, for example, 100 ° C. or higher and 300 ° C. or lower. Since the fixing sleeve 11 is provided over the entire inner peripheral surface of the fixing sleeve 11, the exciting coil 15 a disposed to face the outer peripheral surface of the fixing sleeve 11 and the demagnetizing member 16 disposed to face the inner peripheral surface of the fixing sleeve 11. It is configured to always intervene.

Fig.7 (a) is explanatory drawing which represented typically the mode of the magnetic field when the temperature of the magnetic shunt alloy 11a is less than Curie temperature.
When the temperature of the magnetic shunt alloy 11a is lower than the Curie temperature, the magnetic shunt alloy 11a remains magnetic. Therefore, the induced magnetic flux from the exciting coil 15a does not pass through the magnetic shunt alloy 11a as shown in FIG. Since the magnetic shunt alloy 11a is located between the exciting coil 15a and the demagnetizing member 16, when the temperature of the magnetic shunt alloy 11a is lower than the Curie temperature, the induced magnetic flux from the exciting coil 15a is applied to the demagnetizing member 16. Not reach. Therefore, the demagnetizing member 16 does not generate a magnetic field that reduces the induced magnetic flux from the exciting coil 15a. As a result, the heat generating layer 11c of the fixing sleeve 11 is induction-heated by the induction magnetic flux from the exciting coil 15a without being demagnetized by the demagnetizing member 16, and rapidly heated.

FIG. 7B is an explanatory view schematically showing the state of the magnetic field when the temperature of the magnetic shunt alloy 11a is equal to or higher than the Curie temperature.
When the heating layer 11c of the fixing sleeve 11 is heated by induction, the heat is transferred to the magnetic shunt alloy 11a and the magnetic shunt alloy 11a also rises in temperature. When the temperature of the magnetic shunt alloy 11a becomes equal to or higher than the Curie temperature, the magnetic shunt alloy 11a loses its magnetism, so that the induced magnetic flux from the exciting coil 15a passes through the magnetic shunt alloy 11a as shown in FIG. Reaches the demagnetizing member 16. This induced magnetic flux changes with time. Therefore, when such induced magnetic flux passes through the degaussing member 16 that is a conductor, an induced current (eddy current) flows through the demagnetizing member 16, and this induced eddy current acts in a direction to cancel the induced magnetic flux. A repulsive magnetic flux that cancels the induced magnetic flux is induced. When a repulsive magnetic flux is generated in the demagnetizing member 16 in this way, the repellent magnetic flux reduces the induced magnetic flux from the exciting coil 15a (demagnetizing effect). As a result, the induced magnetic flux acting on the heat generating layer 11c decreases, heat generation of the heat generating layer 11c is suppressed, and the temperature T of the magnetic shunt alloy layer decreases.

  When the induction magnetic flux acting on the heat generating layer 11c is reduced, the heat generation efficiency of the heat generating layer 11c is lowered, so that the temperature of the heat generating layer 11c is lowered and the temperature of the magnetic shunt alloy 11a is also lowered. Thereafter, when the temperature of the heat generating layer 11c decreases and the temperature of the magnetic shunt alloy 11a falls below the Curie temperature, the induced magnetic flux from the exciting coil 15a cannot pass through the magnetic shunt alloy 11a again. Thereby, the degaussing effect by the degaussing member 16 is lost, and the temperature of the heat generating layer 11c rises again.

  With such a self-temperature control function, according to the fixing device 10 of the present embodiment, the temperature rises almost instantaneously until the magnetic shunt alloy 11a reaches the Curie temperature, but increases when the magnetic shunt alloy 11a reaches the Curie temperature. It keeps constant temperature without being heated. Therefore, the magnetic material is made of a magnetic material made of such a material that the Curie temperature of the material forming the magnetic shunt alloy 11a falls within the range of 100 ° C. to 300 ° C., which is the target fixing temperature required for the printer according to the present embodiment. If the magnetic alloy 11a is formed, the temperature of the fixing sleeve 11 can be maintained at approximately the target fixing temperature without excessively increasing the temperature of the fixing sleeve 11. Therefore, high releasability and heat resistance on the surface of the fixing sleeve 11 can be ensured without using electronic temperature control.

  Here, as shown in FIG. 8, if the demagnetizing member 16A is formed of a flat plate member and the demagnetizing member 16A is entirely separated from the exciting coil 15a, the demagnetizing member 16A and the exciting coil 15a Since the distance is long, the induced magnetic flux that passes through the magnetic shunt alloy 11a and reaches the demagnetizing member 16A is small. Thus, the repulsive magnetic flux generated by the demagnetizing member 16A is small, and a sufficient demagnetizing effect cannot be exerted on the heat generating layer 11c. For this reason, the heat generation layer 11c may be excessively heated, and a sufficient self-temperature control function cannot be obtained.

  On the other hand, if the demagnetizing member 16B is a curved plate-like member that is curved in accordance with the inner peripheral surface of the fixing sleeve 11, as shown in FIG. 9, the entire demagnetizing member 16B is the inner peripheral surface of the fixing sleeve 11. Can be placed close to each other. According to this configuration, since the distance between the demagnetizing member 16B and the exciting coil 15a disposed opposite to the outer peripheral surface of the fixing sleeve 11 is short, the induced magnetic flux that passes through the magnetic shunt alloy 11a and reaches the demagnetizing member 16B increases. A sufficient demagnetizing effect can be exerted on the heat generating layer 11c. However, in this configuration, since the distance between the demagnetizing member 16B and the heat generating layer 11c of the fixing sleeve 11 is also close, the heat of the heat generating layer 11c easily propagates from the magnetic shunt alloy 11a to the demagnetizing member 16B by convective heat transfer and radiation. Become. As a result, the heating rate of the heat generating layer 11c is slowed, and the warm-up time is lengthened. That is, when the degaussing member 16B is brought close to the exciting coil 15a in order to obtain a sufficient self-temperature control function, the distance between the demagnetizing member 16B and the heat generating layer 11c also becomes close, leading to a longer warm-up time.

  Here, as shown in FIG. 9, in the configuration in which the entire demagnetizing member 16B is curved and brought closer to the inner peripheral surface of the fixing sleeve 11, the core facing portion 16b facing the core portion of the exciting coil 15a is used. However, a larger amount of the induced magnetic flux from the exciting coil 15a passes through the winding facing portion 16a facing the winding portion of the exciting coil 15a. Therefore, since the repulsive magnetic flux generated in the winding facing portion 16a is larger than that in the core facing portion 16b, the winding facing portion 16a has a larger influence on the demagnetizing effect of the heat generating layer 11c than the core facing portion 16b.

  Therefore, in the demagnetizing member 16 of the present embodiment, as shown in FIG. 2, the winding facing portion 16a is curved in accordance with the inner peripheral surface of the fixing sleeve 11, and the core facing portion 16b is formed to be flat. Has been. As a result, the entire winding facing portion 16a can be disposed close to the inner peripheral surface of the fixing sleeve 11, and the distance from the exciting coil 15a disposed facing the outer peripheral surface of the fixing sleeve 11 is as short as possible. It can be. On the other hand, as for the core facing portion 16b, the distance from the inner peripheral surface of the fixing sleeve 11 is longer than that in the configuration shown in FIG. 9, so that the heat of the heat generating layer 11c is difficult to propagate to the demagnetizing member 16. . As a result, the warm-up time can be shortened compared to the configuration shown in FIG.

  According to the present embodiment, the demagnetizing effect due to the repulsive magnetic flux generated by the core facing portion 16b is smaller than that in the configuration shown in FIG. However, since the demagnetizing effect of the core facing portion 16b is originally smaller than the demagnetizing effect of the winding facing portion 16a, even if the demagnetizing effect of the core facing portion 16b is reduced, the exciting coil 15a A sufficient demagnetizing effect can be obtained by the winding facing portions 16a arranged in proximity, and a sufficient self-temperature control function can be exhibited.

  In this embodiment, the gap between the winding facing portion 16a of the demagnetizing member 16 and the inner peripheral surface of the fixing sleeve 11 is set to 3 mm ± 0.5 mm, but this value can be set as appropriate. Further, according to the present embodiment, it was confirmed that the warm-up time can be shortened by about 2 seconds as compared with the configuration shown in FIG.

  In the present embodiment, the demagnetizing member 16 is an example of a single member. However, as shown in FIG. 10, the demagnetizing member is divided into, for example, two parts, and each demagnetizing member 16C is wound on the exciting coil 15a. You may comprise so that it may oppose. In this case, since the area facing the inner peripheral surface of the fixing sleeve 11 is reduced, the amount of heat transferred from the heat generating layer 11c to the degaussing member can be further reduced as compared with the above embodiment. However, if the demagnetizing member is divided in this way, an induced current (eddy current) generated when the induced magnetic flux that has passed through the magnetic shunt alloy 11a penetrates the demagnetizing member 16C is less likely to be generated. It may be necessary to ensure that magnetic flux is generated. Therefore, when it is difficult to ensure that a sufficient repulsive magnetic flux is generated by another method, it is desirable that the demagnetizing member is constituted by a single member.

[Modification 1]
Next, a modified example of the fixing device in the above embodiment (hereinafter, this modified example is referred to as “modified example 1”) will be described.
FIG. 11 is a schematic diagram of the fixing device of Modification 1 when viewed from the direction of the pressure roller rotation axis.
In the demagnetizing member 26 according to the first modification, the shape of the core facing portion 26b is not a planar shape but a shape protruding in a direction away from the inner peripheral surface of the fixing sleeve 11. With such a demagnetizing member 26, since the distance between the core facing portion 26b and the heat generating layer 11c is larger than that in the above embodiment, the heat of the heat generating layer 11c is more difficult to propagate to the demagnetizing member 26, and the warm It is possible to further shorten the up time.

[Modification 2]
Next, another modified example of the fixing device in the above embodiment (hereinafter, this modified example is referred to as “Modified Example 2”) will be described.
FIG. 12 is a perspective view of a demagnetizing member according to the second modification.
As shown in FIG. 12, the degaussing member 36 of the second modification is formed by opening a portion 36c by removing a part of the core facing portion 36b. With such a demagnetizing member 26, the heat of the heat generating layer 11c is less likely to propagate to the demagnetizing member 36 than in the above-described embodiment and Modification 1, and the warm-up time can be further shortened. Can do.

  In the second modification, the circumferential length of the fixing sleeve in the fixing sleeve is adjusted so that the opening 36c faces the core (air) of the exciting coil 15a. Further, it is desirable that the fixing sleeve shaft length of the opening 36c be equal to or smaller than the minimum paper width size. In this printer, the minimum paper width size is the short side of the postcard size, and accordingly, the fixing sleeve shaft length of the opening 36c is set to 105 mm.

[Modification 3]
Next, still another modified example (hereinafter, this modified example will be referred to as “modified example 34”) of the fixing device in the above embodiment will be described.
FIG. 13 is a schematic diagram when the fixing device of the third modification is viewed from the direction of the pressure roller rotation axis.
In the fixing device according to the third modification, the magnetic shunt alloy is separated from the fixing sleeve 11, and the fixing sleeve 11 and the magnetic shunt alloy 41 are configured separately. The magnetic shunt alloy 41 is fixed to the fixing device main body so as to be in contact with or not in contact with the fixing sleeve 11. Further, the magnetic shunt alloy 41 of the third modification is configured to face only a part of the fixing sleeve 11 in the circumferential direction. As a result, the heat capacity of the magnetic shunt alloy 41 can be reduced compared to the case where the magnetic shunt alloy 11a is provided over the entire circumference of the fixing sleeve 11 as in the above-described embodiment and the first and second modifications, and warm-up is performed. Time can be shortened.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A fixing member such as an endless sheet member having an exothermic layer 11c, which heat-fixes an unfixed image on a sheet 52 as a recording material by heat generated in the exothermic layer 11c; A magnetic field generating member such as an excitation coil 15a, which is disposed opposite to a circumferential surface or a part of the outer circumferential surface in the circumferential direction and generates a magnetic field for induction heating the heat generating layer 11c of the fixing member, and the magnetic field generating member sandwiching the heat generating layer 11c. Is disposed on the opposite side of the fixing member, and is disposed on the opposite side of the magnetic field generating member with the magnetic shunt member sandwiched between the magnetic shunt members such as the magnetic shunt alloys 11a and 41 provided separately or separately from the fixing member. And the demagnetizing members 16, 26, and 36 having a shape along the surface of the fixing member at a portion facing the magnetic field generating member, and the temperature of the magnetic shunt member by the heat of the heat generating layer 11c of the fixing member. Is Curie When the temperature becomes higher than the temperature, the magnetic field of the magnetic field generating member acts on the demagnetizing members 16, 26, and 36 to generate a magnetic field that counteracts the demagnetizing members 16, 26, and 36, and the magnetic field causes the heat generating layer 11c. In the fixing device having a self-temperature control function that suppresses excessive heating of the heat generating layer 11c due to weakening of the acting magnetic field, the demagnetizing members 16, 26, and 36 are connected to the magnetic field generating member. It has an opening part 36c that is a part of the opposed part and has a small magnetic flux part that is relatively small in the amount of magnetic flux generated by the magnetic field generated by the magnetic field generating member, or the core facing parts 16b, 26b, 36b. The distance between the small magnetic flux portion such as the heat generating layer 11c is the longest.
According to this, as described above, among the demagnetizing members facing the magnetic field generating member, the facing portions 16a, 26a, and 36a that greatly affect the demagnetizing effect of the heat generating layer are arranged close to the heat generating layer. The small magnetic flux portions 16b, 26b, 36b, and 36c, which ensure a sufficient self-temperature control function and have a small influence on the demagnetizing effect of the heat generating layer, are arranged away from the heat generating layer so that the heat generating layer is demagnetized. The amount of heat transfer can be reduced and the warm-up time can be shortened.

(Aspect B)
In the aspect A, the demagnetizing member is a single member.
According to this, compared to the configuration in which the demagnetizing member is divided, an induced current (eddy current) generated when the induced magnetic flux that has passed through the magnetic shunt member passes through the demagnetizing member is likely to be generated. Thus, a repulsive magnetic flux can be generated and a more sufficient self-temperature control function can be obtained.

(Aspect C)
In the above aspect A or B, the magnetic field generating member is a planar coil such as an exciting coil 15a that is substantially parallel to the inner peripheral surface or the outer peripheral surface of the fixing member facing the magnetic member, and the demagnetizing members 16, 26, and 36 The small magnetic flux portions 16b, 26b, 36b, and 36c are portions facing the core of the coil.
According to this, as described above, it is possible to achieve both a sufficient self-temperature control function and a shortened warm-up time with a simple configuration.

(Aspect D)
In any one of the above aspects A to C, the fixing member is installed so as to have a substantially cylindrical shape, and the magnetic field generating member is curved on the inner peripheral surface or the outer peripheral surface of the fixing member facing the fixing member. It is arranged according to.
According to this, the magnetic field generating member can be disposed closer to the heat generating layer 11c of the fixing member and the demagnetizing members 16, 26, 36, and the heat generation efficiency by induction heating of the heat generating layer 11c is improved and the demagnetization is performed. A high demagnetization effect by the member can be realized, and a stable self-temperature control function can be realized.

(Aspect E)
In any one of the above aspects A to D, the magnetic field generating member is disposed to face the outer peripheral surface of the fixing member, and the magnetic shunt member is on the inner peripheral surface side of the fixing member with respect to the heat generating layer 11c. And provided integrally with the fixing member.
According to this, the configuration of the fixing device can be simplified and the cost can be reduced as in the embodiment and the first and second modifications.

(Aspect F)
In any one of the above aspects A to E, the magnetic shunt member is provided separately from the fixing member, and is configured to face a part in the circumferential direction of the fixing member.
According to this, as described in Modification 3 above, the magnetic shunting member is formed more than in the case where the magnetic shunting member is provided over the entire circumference of the fixing member as in the above embodiment and Modifications 1 and 2. The heat capacity can be reduced and the warm-up time can be shortened.

DESCRIPTION OF SYMBOLS 10 Fixing device 11 Fixing sleeve 11a, 41 Magnetic shunt alloy 11b, 11d Antioxidation layer 11c Heat generation layer 11e Elastic layer 11f Release layer 12 Pressure roller 13 Nip forming member 14 Pressure support member 15 Magnetic flux generation part 15a Excitation coil 15b Arch core 16, 26, 36 Demagnetizing member 16a, 26a, 36a Winding facing portion 16b, 26b, 36b Core facing portion 36c Opening portion

JP 2009-58829 A

Claims (7)

A fixing member comprising an endless sheet member that has a heat generating layer and heat-fixes an unfixed image on the recording material by heat generated in the heat generating layer;
A magnetic field generating member disposed opposite to a part of the inner circumferential surface or the outer circumferential surface of the fixing member to generate a magnetic field for inductively heating the heat generating layer of the fixing member;
A magnetic shunt member disposed on the opposite side of the magnetic field generating member across the heat generating layer and provided integrally with or separately from the fixing member;
A demagnetizing member disposed on the opposite side of the magnetic field generating member with the magnetic shunt member interposed therebetween, and a portion facing the magnetic field generating member having a shape along the surface of the fixing member,
When the temperature of the magnetic shunt member becomes equal to or higher than the Curie temperature due to the heat of the heat generating layer of the fixing member, the magnetic field of the magnetic field generating member acts on the demagnetizing member, and a magnetic field is generated that counteracts the demagnetizing member, In a fixing device having a self-temperature control function that suppresses excessive heating of the heat generating layer due to weakening of the magnitude of the magnetic field acting on the heat generating layer by the magnetic field.
The degaussing member, the inner portion of the fixing member circumferentially in opposite portion between the magnetic field generating member, the order amount of magnetic flux generated by the magnetic field the magnetic field generating member have been generated by omission of the relatively small small magnetic flux portion A fixing device comprising a single member having an opening . A fixing member comprising an endless sheet member that has a heat generating layer and heat-fixes an unfixed image on the recording material by heat generated in the heat generating layer;
A magnetic field generating member disposed opposite to a part of the inner circumferential surface or the outer circumferential surface of the fixing member to generate a magnetic field for inductively heating the heat generating layer of the fixing member;
A magnetic shunt member disposed on the opposite side of the magnetic field generating member across the heat generating layer and provided integrally with or separately from the fixing member;
A demagnetizing member disposed on the opposite side of the magnetic field generating member with the magnetic shunt member interposed therebetween, and a portion facing the magnetic field generating member having a shape along the surface of the fixing member,
When the temperature of the magnetic shunt member becomes equal to or higher than the Curie temperature due to the heat of the heat generating layer of the fixing member, the magnetic field of the magnetic field generating member acts on the demagnetizing member, and a magnetic field is generated that counteracts the demagnetizing member, In a fixing device having a self-temperature control function that suppresses excessive heating of the heat generating layer due to weakening of the magnitude of the magnetic field acting on the heat generating layer by the magnetic field .
The demagnetizing member includes a small magnetic flux portion that generates a relatively small amount of magnetic flux generated by the magnetic field generated by the magnetic field generating member and an inner portion of the fixing member circumferential direction in a portion facing the magnetic field generating member, and the heat generating layer. A fixing device comprising a single member having a longest distance among the opposed portions . The fixing device according to claim 1 or 2,
The magnetic field generating member is a planar coil substantially parallel to the inner circumferential surface or outer circumferential surface of the fixing member facing the magnetic field generating member,
The fixing device according to claim 1, wherein the small magnetic flux portion of the demagnetizing member is a portion facing the core of the coil. The fixing device according to any one of claims 1 to 3,
The fixing member is installed so as to have a substantially cylindrical shape,
The fixing device according to claim 1, wherein the magnetic field generating member is arranged in accordance with a curvature of an inner peripheral surface or an outer peripheral surface of the fixing member facing the magnetic field generating member. The fixing device according to any one of claims 1 to 4,
The magnetic field generating member is disposed opposite to the outer peripheral surface of the fixing member,
The fixing device, wherein the magnetic shunt member is provided integrally with the fixing member on an inner peripheral surface side of the fixing member with respect to the heat generating layer. The fixing device according to any one of claims 1 to 5,
The fixing device, wherein the magnetic shunt member is provided separately from the fixing member, and is configured to face a part of the fixing member in the circumferential direction. An image forming apparatus comprising: a toner image forming unit that forms a toner image on a recording material; and a heat fixing unit that heat-fixes the toner image formed on the recording material to the recording material.
An image forming apparatus using the fixing device according to claim 1 as the heat fixing unit.

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